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US20130171674A1 - Method for quantifying the amount of cholesterol in high-density lipoprotein 3 - Google Patents

Method for quantifying the amount of cholesterol in high-density lipoprotein 3 Download PDF

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US20130171674A1
US20130171674A1 US13/811,562 US201113811562A US2013171674A1 US 20130171674 A1 US20130171674 A1 US 20130171674A1 US 201113811562 A US201113811562 A US 201113811562A US 2013171674 A1 US2013171674 A1 US 2013171674A1
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surfactant
polyoxyethylene
cholesterol
hdl3
ether
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Maiko Higuchi
Yasuki Itoh
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Denka Co Ltd
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Denka Seiken Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/92—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving lipids, e.g. cholesterol, lipoproteins, or their receptors
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/34—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase
    • C12Q1/42—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase involving phosphatase
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/34—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase
    • C12Q1/44—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase involving esterase
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/60—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving cholesterol
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
    • G01N2333/90—Enzymes; Proenzymes
    • G01N2333/914—Hydrolases (3)
    • G01N2333/916—Hydrolases (3) acting on ester bonds (3.1), e.g. phosphatases (3.1.3), phospholipases C or phospholipases D (3.1.4)
    • G01N2333/918—Carboxylic ester hydrolases (3.1.1)
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2405/00—Assays, e.g. immunoassays or enzyme assays, involving lipids
    • G01N2405/04—Phospholipids, i.e. phosphoglycerides
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2405/00—Assays, e.g. immunoassays or enzyme assays, involving lipids
    • G01N2405/08—Sphingolipids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2800/00—Detection or diagnosis of diseases
    • G01N2800/32—Cardiovascular disorders
    • G01N2800/323—Arteriosclerosis, Stenosis

Definitions

  • the present invention relates to a method for quantifying cholesterol in high-density lipoprotein 3 (which may be hereinafter referred to as “HDL3”) (cholesterol in HDL3 may be hereinafter referred to as “HDL3 cholesterol”).
  • HDL3 high-density lipoprotein 3
  • HDL3 cholesterol cholesterol in HDL3
  • HDL high-density lipoprotein
  • a predetermined lower limit is regarded as an indication of dislipidemia, and the value is known to be useful as an index of arteriosclerosis.
  • HDL is constituted by apoprotein, phospholipid, cholesterol and triglyceride.
  • HDL can be divided into subfractions based on the difference in the content of apolipoprotein E among apoproteins in HDL, and HDLs having higher contents of apoE are defined as apoE-rich HDL.
  • HDL has been conventionally studied as a whole, but each of the subfractions HDL2 and HDL3 is now known to have unique functions. It is clinically known that CETP deficiency prevents cholesterol transport from HDL to LDL and IDL, leading to an increase in the HDL cholesterol level.
  • the HDL increased by CETP deficiency is HDL2.
  • HDL2 is said to have an antiarteriosclerotic action. It is also said that CETP deficiency causes an increase in apoE-rich HDL, and that, since apoE-rich HDL has a strong cholesterol-drawing ability and antiplatelet action, it is a good HDL.
  • a decrease in the hepatic lipase activity prevents conversion of HDL3 to HDL2, resulting in an increase in HDL3. It is suggested that increased HDL3 leads to increased incidence rates of coronary artery diseases. In view of such tendencies, it is expected that measurement of each HDL subfraction may contribute to judgment of whether or not a patient is suffering from an arteriosclerotic disease and of the cause of the disease. Further, at present, in view of these functions of HDL subfractions, manufacturers are developing therapeutic agents that inhibit the function of CETP, decrease the LDL cholesterol level, and increase the HDL cholesterol level.
  • HDL subfractions examples include ultracentrifugation, high-performance liquid chromatography (HPLC), HDL3 precipitation (Patent Document 1) and NMR.
  • HDL3 precipitation is a method wherein a reagent containing a divalent metal ion and dextran sulfate is used to aggregate lipoproteins other than HDL3, and HDL3 in the supernatant portion is recovered by centrifugation and measured using an automatic analyzer.
  • NMR which is a method wherein the number of particles of lipoprotein is measured by magnetic resonance, is not commonly employed since the method requires special equipment.
  • Patent Document 2 There is another method for analyzing an HDL subfraction (Patent Document 2). Although this method enables measurement with a general purpose automatic analyzer, the method employs a method wherein a surfactant is used to prevent an enzyme from acting on lipoproteins other than HDL3. Therefore, since the HDL3 reaction is allowed to proceed in the presence of the lipoproteins other than the lipoprotein of interest, the measurement might be influenced by such lipoproteins or, in cases where the prevention is not sufficient, the lipoproteins other than HDL3 might be undesirably measured together.
  • An object of the present invention is to provide a method that enables quantification of HDL3 in a test sample without requiring a laborious operation.
  • the present inventors intensively studied to discover that phospholipase and sphingomyelinase act on lipoprotein but hardly act on HDL3.
  • the present inventors then inferred that HDL3 cholesterol in a test sample can be quantified by allowing phospholipase or sphingomyelinase to act on the test sample to eliminate cholesterol and then quantifying cholesterol in the remaining HDL3.
  • the present inventors then experimentally confirmed that this is possible, thereby completing the present invention.
  • the present invention provides a method for quantifying cholesterol in high-density lipoprotein 3, the method comprising:
  • Step 1 wherein phospholipase and/or sphingomyelinase is/are allowed to act on a test sample to transfer cholesterol to the outside of the reaction system;
  • Step 2 wherein cholesterol remaining in the reaction system is quantified.
  • HDL3 cholesterol in a test sample can be specifically quantified with an automatic analyzer without requirement of a laborious operation such as ultracentrifugation or pretreatment. Further, quantification of the HDL2 cholesterol level can also be carried out by subtracting the HDL3 cholesterol level from the total HDL cholesterol level obtained by a conventional method for quantifying the total HDL cholesterol in a test sample.
  • FIG. 1 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent D in Step 2.
  • FIG. 2 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent G in Step 2.
  • FIG. 3 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent H in Step 2.
  • FIG. 4 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent I in Step 2.
  • FIG. 5 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent K in Step 2.
  • FIG. 6 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent L in Step 2.
  • test sample to be subjected to the method of the present invention is not restricted as long as HDL3 cholesterol in the sample can be quantified, and the test sample is preferably serum or blood plasma, or a dilution thereof. Serum or a dilution thereof is especially preferred.
  • phospholipase and/or sphingomyelinase (these may be hereinafter referred to as the “phospholipase and/or the like”) is/are allowed to act on a test sample.
  • the phospholipase is not restricted as long as it acts on phosphatidyl choline.
  • Phospholipase A, phospholipase C and phospholipase D are preferred, and phospholipase C and phospholipase D are especially preferred. Since the phospholipase and the like are commercially available, commercially available products may be preferably used.
  • Each of the phospholipase and/or the like may be used alone, or two or more types of the phospholipase and/or the like may be used in combination.
  • the final concentration of the phospholipase and/or the like is preferably about 0.1 to about 100 U/mL, more preferably about 0.2 to about 50 U/mL.
  • HDL3 is hardly affected, while lipoproteins other than HDL3 are affected, resulting in transfer of cholesterol of the lipoproteins to the outside of the reaction system.
  • Step 1 of the method of the present invention cholesterol is transferred to the outside of the reaction system by the action(s) of the phospholipase and/or the like.
  • the term “transferred to the outside of the reaction system” herein means that cholesterol and esters thereof are eliminated or protected such that the cholesterol and esters thereof are not involved in the later steps.
  • the term “elimination” herein means that cholesterol of lipoprotein in a test sample is degraded such that the cholesterol does not affect the reaction for measurement of cholesterol in a later step.
  • Examples of the method for eliminating lipoprotein cholesterol include a method wherein cholesterol esterase and cholesterol oxidase are allowed to act on the cholesterol, followed by decomposition of the produced hydrogen peroxide into water and oxygen using catalase. Alternatively, a hydrogen donor may be reacted with the produced hydrogen peroxide using peroxidase to convert the hydrogen peroxide to a colorless quinone.
  • the method for eliminating lipoprotein cholesterol is not restricted to these. The method of elimination of cholesterol per se is known in the art, and is also described concretely in Examples below.
  • protection means to protect lipoprotein in a test sample such that the lipoprotein does not react upon cholesterol measurement in a later step.
  • examples of the method of protection of lipoprotein include, but are not limited to, a method wherein a surfactant is used to specifically protect each lipoprotein such that cholesterol esterase and cholesterol oxidase do not act on the lipoprotein.
  • Step 1 by preliminarily adding an enzyme system and a surfactant for transferring cholesterol to the outside of the reaction system at the same time, both steps can be carried out at the same time as a single step.
  • the concentration (the concentration means the final concentration unless otherwise specified in the present specification) of cholesterol esterase is preferably about 0.1 to about 10.0 U/mL, more preferably about 0.2 to about 2.0 U/mL.
  • the concentration of cholesterol oxidase is preferably about 0.05 to about 10.0 U/mL, more preferably about 0.1 to about 1.0 U/mL.
  • the cholesterol esterase is not restricted as long as it acts on ester-type cholesterol, and examples of the cholesterol esterase which may be used include commercially available products such as cholesterol esterase (CEBP, CEN) manufactured by Asahi Kasei Corporation and cholesterol esterase (COE-311, COE-312) manufactured by Toyobo Co., Ltd. Further, the cholesterol oxidase is not restricted as long as it acts on free cholesterol, and examples of the cholesterol oxidase which may be used include commercially available products such as cholesterol oxidase (CONII) manufactured by Asahi Kasei Corporation and cholesterol oxidase (COO-311, COO-321, COO-331) manufactured by Toyobo Co., Ltd.
  • CONII cholesterol oxidase
  • COO-321, COO-331 cholesterol oxidase
  • the concentration of peroxidase is preferably about 2.0 to about 5.0 U/mL, more preferably about 3.0 to about 4.0 U/mL. In cases where a compound for conversion into a colorless quinone is used, the concentration of the compound is preferably about 0.4 to about 0.8 mmol/L.
  • the solution is preferably Good's, Tris, phosphate or glycine buffer solution, and is preferably a Good's buffer such as bis(2-hydroxyethyl)iminotris(hydroxyethyl)methane (Bis-Tris), piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES), piperazine-1,4-bis(2-ethanesulfonic acid) sesqui sodium salt monohydrate (PIPES 1.5Na), 3-morpholinopropanesulfonic acid (MOPSO), N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) or piperazine-1,4-bis(2-hydroxy-3-propa
  • Bis-Tris bis(2-hydroxyethyl)iminotris(hydroxyethyl)methane
  • PPES
  • the reaction temperature in Step 1 is preferably about 25 to about 40° C., more preferably 35 to 38° C., most preferably 37° C.
  • the reaction time is not restricted, and is usually about 2 to about 10 minutes.
  • Step 1 can be carried out in the absence of a surfactant, Step 1 is preferably carried out in the coexistence of a surfactant that reacts with lipoproteins other than HDL or HDL3 in view of accurate quantification of HDL3 cholesterol.
  • the term “react” when used for a surfactant in the present invention, the term means that the surfactant leads lipoprotein to the outside of the reaction system, making an enzyme act easily, or means to protect lipoprotein such that an enzyme cannot act on the lipoprotein.
  • surfactant that reacts with lipoproteins other than HDL include, but are not limited to, anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, polyoxyethylene alkyl ether sodium sulfate amide nonion, polyoxyethylene nonylphenyl ether and amide nonion; and nonionic surfactants such as polyoxyethylene polycyclic phenyl ether having an HLB value of 14 to 17.
  • anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, polyoxyethylene alkyl ether sodium sulfate amide nonion, polyoxyethylene nonylphenyl ether and amide nonion
  • nonionic surfactants such as polyoxyethylene polycyclic phenyl ether having an HLB value of 14 to 17.
  • surfactant examples include Pluronic, Pluronic P123 (ADEKA Corporation), Pluronic F88 (ADEKA Corporation), Levenol WX (Kao Corporation), Nonion HS-220 (NOF Corporation), Nymid MT-215 (NOF Corporation), Newcol-723 (NOF Corporation), Newcol-2614 (Nippon Nyukazai Co, Ltd.) and Newcol-714 (Nippon Nyukazai Co, Ltd.).
  • surfactant that reacts with lipoproteins other than HDL3 include, but are not limited to, nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether; anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, amide ether sulfate and polyoxyethylene-stearylamine; amphoteric surfactants such as coconut oil fatty acid-amidopropyldimethyl-aminoacetic acid betaine, alkyl dimethyl-aminoacetic acid betaine and lauryl betaine; and cationic surfactants such as lauryl trimethyl ammonium chloride.
  • nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether
  • anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, amide ether sulfate and polyoxyethylene-stearylamine
  • amphoteric surfactants such as coconut oil fatty acid-amid
  • examples of the nonionic surfactants include polyoxyethylene distyrene-modified phenyl ether Emulgen A500 (trade name; manufactured by Kao Corporation; company names hereinafter represent names of manufacturers, and all names described together with company names hereinafter represent trade names);
  • examples of the anionic surfactants include polyoxyethylene-polyoxypropylene condensates Pluronic F127 (ADEKA Corporation), Pluronic F68 (ADEKA Corporation) and Pluronic P103 (ADEKA Corporation), amide ether sulfate Sunamide CF-10 (NOF Corporation) and polyoxyethylene-stearylamine Nymeen S210 (NOF Corporation);
  • examples of the amphoteric surfactants include a coconut oil fatty acid-amidopropyldimethyl-aminoacetic acid betaine Nissan Anon BDF-SF (NOF Corporation), alkyl dimethyl-aminoacetic acid betaine Nissan Anon BF (NOF Corporation) and lauryl betaine Amphitol 24B (Kao Corporation);
  • the concentration of the surfactant that reacts with lipoproteins other than HDL3 is preferably 0.01 to 5.0% by weight, more preferably about 0.03 to about 3.0% by weight.
  • reaction conditions reaction temperature, time, buffer and the like are as described above.
  • Step 2 cholesterol remaining in the reaction system is quantified.
  • the “surfactant that reacts with at least HDL3” includes a surfactant that specifically reacts with HDL3, surfactant that specifically reacts with HDL (that is, reacts with HDL2 and HDL3) and surfactant that reacts with all lipoproteins.
  • examples of the surfactant that specifically reacts with HDL3 include nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether Emulgen A90 (Kao Corporation), polyoxyethylene lauryl ether Emulgen 120 (Kao Corporation) and p-isooctyl polyoxyethylene phenol formaldehyde polymer Triton-WR-1339 (Nacalai Tesque); amphoteric surfactants such as lauryl dimethyl-aminoacetic acid betaine Nissan Anon BL-SF (NOF Corporation) and polyoxyethylene lauryl ether Persoft NK-100 (NOF Corporation); and cationic surfactants such as fatty acid series phosphoric acid ester ADEKA COL PS-440E (ADEKA Corporation).
  • nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether Emulgen A90 (Kao Corporation), polyoxyethylene lauryl ether Emulgen 120 (Kao Corporation) and
  • Examples of the surfactant that specifically reacts with HDL include nonionic surfactants having an HLB of 11 to 14 such as polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether and polyoxyethylene cumyl phenyl ether; and imidazoline-type amphoteric surfactants.
  • Emulgen A60 Kerat Corporation
  • Emulgen B66 Keratin B66
  • Emulgen LS110 Keratin CMP-11
  • Newcol-710 Nippon Nyukazai Co, Ltd.
  • Newcol-610 Nippon Nyukazai Co, Ltd.
  • Newcol-2609 Nippon Nyukazai Co, Ltd.
  • Nissan Anon GLM-R-LV NOF Corporation
  • surfactant that specifically reacts with all lipoproteins examples include nonionic surfactants such as polyoxyethylene lauryl ether, polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether.
  • Anionic surfactants such as lauryl alcohol alkoxylate and sodium polyoxyethylene-alkyl phenyl ether sulfate may also be used.
  • Emulgen 707 Keratin 707
  • Emulgen 909 Keratin 909
  • Emulgen 108 Keratin 108
  • Nymeen L207 NOF Corporation
  • Adekatol LB83 ADKA Corporation
  • Adekatol LB103 ADKA Corporation
  • Newcol-707 Neippon Nyukazai Co, Ltd.
  • the concentration of the surfactant is preferably 0.01 to 5.0% (w/v), more preferably 0.05 to 2.0% (w/v).
  • Step 2 cholesterol is quantified by the reaction of such surfactants.
  • the surfactant used is different between Step 1 and Step 2.
  • Methods of quantification per se of cholesterol are well known, and any of the well known methods may be used. A concrete description is also given in Examples below. For example, ester-type cholesterol in lipoprotein is hydrolyzed with cholesterol esterase to produce free cholesterol and a fatty acid, and the produced free cholesterol and free cholesterol inherently existing in lipoprotein are converted using cholesterol oxidase to generate cholestenone and hydrogen peroxide. A quinone pigment is then formed in the presence of peroxidase, and quantified.
  • Examples of compounds that generate a quinone pigment include HDAOS (N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline), DAOS (N-ethyl-N(-2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline sodium salt) or TOOS (N-ethyl-N(-2-hydroxy-3-sulfopropyl)-3-methylaniline sodium salt dihydrate) and 4-aminoantipyrine, but the compounds are not restricted as long as the combination allows generation of a quinone pigment.
  • the cholesterol esterase and cholesterol oxidase used in Step 1 may be used as they are in Step 2 without further addition.
  • the concentration of the compound for generation of a quinone pigment is preferably about 0.5 to about 2.0 mmol/L in the case of HDAOS, or 0.1 to 2.0 mmol/L in the case of 4-aminoantipyrine.
  • the concentration of peroxidase is preferably 0.4 to 5.0 U/mL.
  • a catalase inhibitor sodium azide is used by addition to the reaction liquid in Step 2.
  • the concentration of sodium azide in this case is usually about 0.1 g/L to about 1.0 g/L.
  • reaction temperature, time, buffer, pH and the like may be the same as the reaction conditions for Step 1 described above.
  • the HDL2 cholesterol level in the test sample by subtracting the HDL3 cholesterol level obtained by Step 1 and Step 2 from the HDL cholesterol level in the test sample. Since methods for determining the HDL cholesterol level in a test sample are well known (e.g., JP 2001-103998 A) and kits for such methods are commercially available, the quantification can be easily carried out using these.
  • Reagent A and Reagent B having the compositions described below were prepared, and reagents were prepared by adding various surfactants to Reagent A to a concentration of 0.1% (w/v) or 1.0% (w/v).
  • Reagent A containing the various surfactants described below was mixed with Reagent B at a ratio of 1:3. Cholesterol in each of the HDL2 fraction and the HDL3 fraction was reacted with the resulting mixture, and the final absorbances at a main wavelength of 700 nm and a sub-wavelength of 600 nm were measured and compared.
  • HDL2 fraction Fractionation was carried out to obtain the HDL2 fraction and the HDL3 fraction as follows.
  • a test sample containing HDL that is, serum was subjected to ultracentrifugation using a solution with sodium chloride and sodium bromide such that separation occurs at a density at the border between HDL2 and HDL3 (1.125), and each resulting fraction was collected.
  • Table 1 below shows surfactants with which the ratio of HDL2/HDL3 was not more than 0.75 and the ratios of CM-IDL/HDL3 and LDL/HDL3 were not more than 0.75. These surfactants were determined to be surfactants that react with HDL3.
  • Table 2 shows surfactants with which the ratio of HDL2/HDL3 was not less than 1.25 and the ratios of CM-IDL/HDL2 and LDL/HDL2 were not less than 1.25. These surfactants were determined to be surfactants that react with lipoproteins other than HDL3.
  • Table 3 shows surfactants with which the ratio of HDL2/HDL3 was between 0.75 and 1.25 and the ratios of CM-IDL/HDL2, LDL/HDL2, CM-IDL/HDL3 and LDL/HDL3 were not more than 0.75. These surfactants were determined to be surfactants that react with HDL.
  • Table 4 shows surfactants with which the ratio of HDL2/HDL3 was between 0.75 and 1.25 and the ratios of CM-IDL/HDL2, LDL/HDL2, CM-IDL/HDL3 and LDL/HDL3 were not less than 0.75. These surfactants were determined to be surfactants that react with all lipoproteins.
  • Table 5 shows surfactants that could not be grouped into any of the above categories. These surfactants were determined to be surfactants that react with lipoproteins other than HDL.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL
  • Emulgen A90, Emulgen 120, Nissan Anon BL-SF, Triton WR-1339, Persoft NK-100 and ADEKA COL PS-440E were surfactants that specifically react with HDL3.
  • Emulgen A500, Nissan Anon BDF-SF, Nissan Anon BF, Nymeen S210, Pluronic P103, Kohtamin 24P, Sunamide CF-10, Amphitol 24B, Pluronic F68 and Pluronic F127 were surfactants that specifically react with lipoproteins other than HDL3.
  • Emulgen B66, Emulgen A60, Emulgen LS110, Nowol 610, Newcol 2609, Newcol-CMP-11, Nissan Anon GLM-RLV and Newcol-710 were surfactants that specifically react with HDL.
  • Emulgen 108, Emulgen 707, Newcol 707, Adekatol LB83, Adekatol LB103 and Emulgen 909 were surfactants that specifically react with all lipoproteins.
  • Newcol-714, Newcol-723, Newcol-2614, Nymeen S215, Pluronic P123, Levenol WX, Nymid MT-215, Nonion HS220 and Pluronic F88 were surfactants that specifically react with lipoproteins other than HDL.
  • CM-LDL fraction Fractionation by ultracentrifugation was carried out to obtain the CM-LDL fraction, HDL2 fraction and HDL3 fraction, and each fraction was reacted with Reagent E prepared by adding phospholipase D (PLDP) to Reagent A used in Reference Example 1.
  • Reagent D described below was further added to the reaction solution to perform measurement.
  • 150 ⁇ L of Reagent E was added to 2 ⁇ L of serum, and the reaction was allowed to proceed for 5 minutes with warming, followed by addition of Reagent D to the reaction solution and additional 5 minutes of reaction with warming
  • the absorbances at a main wavelength of 700 nm and a sub-wavelength of 600 nm were measured.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Phospholipase D 5.0 U/mL
  • FIG. 1 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent D. Specific reaction with HDL3 can be seen.
  • Reagent F was prepared by adding a surfactant and sphingomyelinase to Reagent A used in Reference Example 1, and Reagent G was prepared for the step of measuring HDL3 in the product obtained by reaction with Reagent F.
  • the compositions of these reagents were as shown below. Fractionation was carried out by ultracentrifugation to obtain the fraction from CM to IDL, LDL fraction, HDL2 fraction and HDL3 fraction, and the obtained fractions were subjected to measurement. The procedure for measurement with the reagents was the same as in Example 1. The absorbance was measured at each measurement time.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Pluronic F68 0.03 w/v % Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Sphingomyelinase 0.5 U/mL
  • FIG. 2 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent G. Specific reaction with HDL3 can be seen.
  • the absorbance was measured in the same manner as in Example 2 using Reagent H which was prepared with the same composition as that of Reagent E used in Example 1 except that phospholipase C was used as the phospholipase and a surfactant was added.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Pluronic F68 0.03 w/v % Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Phospholipase C 5.0 U/mL
  • FIG. 3 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent H. Specific reaction with HDL3 can be seen.
  • the absorbance was measured in the same manner as in Example 2 using Reagent I which was prepared with the same composition as that of Reagent H used in Example 3 except that phospholipase D (PLDP) was used as the phospholipase and a surfactant was added.
  • PLDP phospholipase D
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Pluronic F68 0.03 w/v % Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Phospholipase D 5.0 U/mL
  • FIG. 4 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent I. Specific reaction with HDL3 can be seen.
  • the absorbance was measured in the same manner as in Example 2 except that Reagent J and Reagent K having the compositions described below were used.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Pluronic P103 0.03 w/v % Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Phospholipase D 5.0 U/mL
  • FIG. 5 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent K. Specific reaction with HDL3 can be seen.
  • the absorbance was measured in the same manner as in Example 2 except that Reagent J used in Example 5 and Reagent L having the composition described below were used.
  • FIG. 6 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent L. Specific reaction with HDL3 can be seen.
  • Reagent M was prepared and used in combination with Reagent D to measure HDL-C (C represents cholesterol; the same applies hereinafter) in the test sample. From this value, the value obtained by measuring HDL3-C using Reagent I and Reagent D in Example 4 was subtracted, to calculate HDL2-C. The values of HDL-C, HDL3-C and HDL2-C in each sample were as shown in Table 6.
  • BES buffer (pH 7.0) 100 mmol/L HDAOS 0.7 mmol/L Pluronic P88 0.1 w/v % Catalase 600 U/L Cholesterol oxidase 1.4 U/mL Cholesterol esterase 0.8 U/mL Phospholipase D 5.0 U/mL

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Abstract

A method that enables quantification of cholesterol in high-density lipoprotein 3 (HDL3) in a test sample without requiring a laborious operation is disclosed. The method for quantifying cholesterol in HDL3 comprises: Step 1 wherein phospholipase and/or sphingomyelinase is/are allowed to act on a test sample to transfer cholesterol to the outside of the reaction system; and Step 2 wherein cholesterol remaining in the reaction system is quantified. The method enables specific quantification of HDL3 cholesterol in a test sample using an automatic analyzer without requirement of a laborious operation such as ultracentrifugation or pretreatment. Further, quantification of the HDL2 cholesterol level can also be carried out by subtracting the HDL3 cholesterol level from the total HDL cholesterol level obtained by a conventional method for quantifying the total HDL cholesterol in a test sample.

Description

    TECHNICAL FIELD
  • The present invention relates to a method for quantifying cholesterol in high-density lipoprotein 3 (which may be hereinafter referred to as “HDL3”) (cholesterol in HDL3 may be hereinafter referred to as “HDL3 cholesterol”).
    • BACKGROUND ART
  • Since high-density lipoprotein (HDL) receives cholesterol from various tissues including walls of blood vessels with arteriosclerosis, it is involved in the action of removal of cholesterol accumulated in cells. Therefore, HDL cholesterol is also called the reverse cholesterol transport system. High-density lipoprotein is known to have a negative correlation with arteriosclerotic diseases such as coronary arteriosclerosis. Accordingly, an HDL value lower than a predetermined lower limit is regarded as an indication of dislipidemia, and the value is known to be useful as an index of arteriosclerosis.
  • HDL is constituted by apoprotein, phospholipid, cholesterol and triglyceride. HDL has a density of d=1.063 to 1.210 g/mL, and can be divided into two fractions, that is, HDL2 wherein d=1.063 to 1.125 g/mL and HDL3 wherein d=1.125 to 1.210 g/mL. A notch is found at the portion of d=1.125 in the distribution curve of lipoprotein, and the part having higher densities in the curve corresponds to HDL3. Alternatively, HDL can be divided into subfractions based on the difference in the content of apolipoprotein E among apoproteins in HDL, and HDLs having higher contents of apoE are defined as apoE-rich HDL.
  • In terms of the functions, HDL has been conventionally studied as a whole, but each of the subfractions HDL2 and HDL3 is now known to have unique functions. It is clinically known that CETP deficiency prevents cholesterol transport from HDL to LDL and IDL, leading to an increase in the HDL cholesterol level. The HDL increased by CETP deficiency is HDL2. HDL2 is said to have an antiarteriosclerotic action. It is also said that CETP deficiency causes an increase in apoE-rich HDL, and that, since apoE-rich HDL has a strong cholesterol-drawing ability and antiplatelet action, it is a good HDL. Further, a decrease in the hepatic lipase activity prevents conversion of HDL3 to HDL2, resulting in an increase in HDL3. It is suggested that increased HDL3 leads to increased incidence rates of coronary artery diseases. In view of such tendencies, it is expected that measurement of each HDL subfraction may contribute to judgment of whether or not a patient is suffering from an arteriosclerotic disease and of the cause of the disease. Further, at present, in view of these functions of HDL subfractions, manufacturers are developing therapeutic agents that inhibit the function of CETP, decrease the LDL cholesterol level, and increase the HDL cholesterol level.
  • Establishment of a simple method for measuring the HDL subfractions may lead to detailed elucidation of their functions, and to their therapeutic effects in the future.
  • Examples of methods for measuring HDL subfractions which have been known so far include ultracentrifugation, high-performance liquid chromatography (HPLC), HDL3 precipitation (Patent Document 1) and NMR.
  • In ultracentrifugation, fractionation is carried out utilizing the difference in the density of lipoprotein. This method has drawbacks in that the operation requires a skill; the method takes many days; and the cost is high. In the method by Okazaki et al. wherein HPLC is used for separating HDL2 and HDL3, the operation takes a long time, and special equipment is required. HDL3 precipitation is a method wherein a reagent containing a divalent metal ion and dextran sulfate is used to aggregate lipoproteins other than HDL3, and HDL3 in the supernatant portion is recovered by centrifugation and measured using an automatic analyzer. This method is not widely used since the method has drawbacks in that the operation of this method also requires a skill; the method is a manual method; the method requires an operation of sample pretreatment; and a certain length of time is required before measurement. Further, NMR, which is a method wherein the number of particles of lipoprotein is measured by magnetic resonance, is not commonly employed since the method requires special equipment.
  • There is another method for analyzing an HDL subfraction (Patent Document 2). Although this method enables measurement with a general purpose automatic analyzer, the method employs a method wherein a surfactant is used to prevent an enzyme from acting on lipoproteins other than HDL3. Therefore, since the HDL3 reaction is allowed to proceed in the presence of the lipoproteins other than the lipoprotein of interest, the measurement might be influenced by such lipoproteins or, in cases where the prevention is not sufficient, the lipoproteins other than HDL3 might be undesirably measured together.
  • Thus, as an alternative to the above methods, a reagent which enables simple and more selective quantification of the cholesterol level needs to be invented.
    • PRIOR ART DOCUMENTS Patent Documents
  • [Patent Document 1] JP 2009-207463 A
  • [Patent Document 2] JP 2001-346598 A
    • SUMMARY OF THE INVENTION Problems to be Solved by the Invention
  • An object of the present invention is to provide a method that enables quantification of HDL3 in a test sample without requiring a laborious operation.
    • Means for Solving the Problems
  • The present inventors intensively studied to discover that phospholipase and sphingomyelinase act on lipoprotein but hardly act on HDL3. The present inventors then inferred that HDL3 cholesterol in a test sample can be quantified by allowing phospholipase or sphingomyelinase to act on the test sample to eliminate cholesterol and then quantifying cholesterol in the remaining HDL3. The present inventors then experimentally confirmed that this is possible, thereby completing the present invention.
  • That is, the present invention provides a method for quantifying cholesterol in high-density lipoprotein 3, the method comprising:
  • Step 1 wherein phospholipase and/or sphingomyelinase is/are allowed to act on a test sample to transfer cholesterol to the outside of the reaction system; and
  • Step 2 wherein cholesterol remaining in the reaction system is quantified.
    • Effect of the Invention
  • By the present invention, HDL3 cholesterol in a test sample can be specifically quantified with an automatic analyzer without requirement of a laborious operation such as ultracentrifugation or pretreatment. Further, quantification of the HDL2 cholesterol level can also be carried out by subtracting the HDL3 cholesterol level from the total HDL cholesterol level obtained by a conventional method for quantifying the total HDL cholesterol in a test sample.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent D in Step 2.
  • FIG. 2 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent G in Step 2.
  • FIG. 3 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent H in Step 2.
  • FIG. 4 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent I in Step 2.
  • FIG. 5 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent K in Step 2.
  • FIG. 6 shows a diagram illustrating a result of Examples of the present invention in terms of changes in the absorbance of each fraction after addition of Reagent L in Step 2.
    •  BEST MODE FOR CARRYING OUT THE INVENTION
  • The test sample to be subjected to the method of the present invention is not restricted as long as HDL3 cholesterol in the sample can be quantified, and the test sample is preferably serum or blood plasma, or a dilution thereof. Serum or a dilution thereof is especially preferred.
  • In Step 1 of the present invention, phospholipase and/or sphingomyelinase (these may be hereinafter referred to as the “phospholipase and/or the like”) is/are allowed to act on a test sample. The phospholipase is not restricted as long as it acts on phosphatidyl choline. Phospholipase A, phospholipase C and phospholipase D are preferred, and phospholipase C and phospholipase D are especially preferred. Since the phospholipase and the like are commercially available, commercially available products may be preferably used. Each of the phospholipase and/or the like may be used alone, or two or more types of the phospholipase and/or the like may be used in combination.
  • The final concentration of the phospholipase and/or the like (total concentration, in cases where two or more types of the phospholipase and/or the like are used—the same applies hereinafter) is preferably about 0.1 to about 100 U/mL, more preferably about 0.2 to about 50 U/mL.
  • When the phospholipase and/or the like is/are allowed to act on a test sample, HDL3 is hardly affected, while lipoproteins other than HDL3 are affected, resulting in transfer of cholesterol of the lipoproteins to the outside of the reaction system.
  • In Step 1 of the method of the present invention, cholesterol is transferred to the outside of the reaction system by the action(s) of the phospholipase and/or the like. The term “transferred to the outside of the reaction system” herein means that cholesterol and esters thereof are eliminated or protected such that the cholesterol and esters thereof are not involved in the later steps.
  • The term “elimination” herein means that cholesterol of lipoprotein in a test sample is degraded such that the cholesterol does not affect the reaction for measurement of cholesterol in a later step. Examples of the method for eliminating lipoprotein cholesterol include a method wherein cholesterol esterase and cholesterol oxidase are allowed to act on the cholesterol, followed by decomposition of the produced hydrogen peroxide into water and oxygen using catalase. Alternatively, a hydrogen donor may be reacted with the produced hydrogen peroxide using peroxidase to convert the hydrogen peroxide to a colorless quinone. The method for eliminating lipoprotein cholesterol is not restricted to these. The method of elimination of cholesterol per se is known in the art, and is also described concretely in Examples below.
  • The term “protection” means to protect lipoprotein in a test sample such that the lipoprotein does not react upon cholesterol measurement in a later step. Examples of the method of protection of lipoprotein include, but are not limited to, a method wherein a surfactant is used to specifically protect each lipoprotein such that cholesterol esterase and cholesterol oxidase do not act on the lipoprotein.
  • In Step 1, by preliminarily adding an enzyme system and a surfactant for transferring cholesterol to the outside of the reaction system at the same time, both steps can be carried out at the same time as a single step.
  • In Step 1, in cases where cholesterol esterase and cholesterol oxidase are used, the concentration (the concentration means the final concentration unless otherwise specified in the present specification) of cholesterol esterase is preferably about 0.1 to about 10.0 U/mL, more preferably about 0.2 to about 2.0 U/mL. The concentration of cholesterol oxidase is preferably about 0.05 to about 10.0 U/mL, more preferably about 0.1 to about 1.0 U/mL. The cholesterol esterase is not restricted as long as it acts on ester-type cholesterol, and examples of the cholesterol esterase which may be used include commercially available products such as cholesterol esterase (CEBP, CEN) manufactured by Asahi Kasei Corporation and cholesterol esterase (COE-311, COE-312) manufactured by Toyobo Co., Ltd. Further, the cholesterol oxidase is not restricted as long as it acts on free cholesterol, and examples of the cholesterol oxidase which may be used include commercially available products such as cholesterol oxidase (CONII) manufactured by Asahi Kasei Corporation and cholesterol oxidase (COO-311, COO-321, COO-331) manufactured by Toyobo Co., Ltd.
  • In Step 1, in cases where peroxidase is used, the concentration of peroxidase is preferably about 2.0 to about 5.0 U/mL, more preferably about 3.0 to about 4.0 U/mL. In cases where a compound for conversion into a colorless quinone is used, the concentration of the compound is preferably about 0.4 to about 0.8 mmol/L.
  • As the reaction liquid to be used in Step 1, various buffers used in normal biochemical reactions may be used, and the pH of the reaction liquid is preferably between 5 and 8. The solution is preferably Good's, Tris, phosphate or glycine buffer solution, and is preferably a Good's buffer such as bis(2-hydroxyethyl)iminotris(hydroxyethyl)methane (Bis-Tris), piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES), piperazine-1,4-bis(2-ethanesulfonic acid) sesqui sodium salt monohydrate (PIPES 1.5Na), 3-morpholinopropanesulfonic acid (MOPSO), N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) or piperazine-1,4-bis(2-hydroxy-3-propanesulfonic acid) (POPSO).
  • The reaction temperature in Step 1 is preferably about 25 to about 40° C., more preferably 35 to 38° C., most preferably 37° C. The reaction time is not restricted, and is usually about 2 to about 10 minutes.
  • The present inventors further discovered surfactants that react with lipoproteins other than HDL3. Although Step 1 can be carried out in the absence of a surfactant, Step 1 is preferably carried out in the coexistence of a surfactant that reacts with lipoproteins other than HDL or HDL3 in view of accurate quantification of HDL3 cholesterol.
  • When the term “react” is used for a surfactant in the present invention, the term means that the surfactant leads lipoprotein to the outside of the reaction system, making an enzyme act easily, or means to protect lipoprotein such that an enzyme cannot act on the lipoprotein.
  • Examples of the surfactant that reacts with lipoproteins other than HDL include, but are not limited to, anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, polyoxyethylene alkyl ether sodium sulfate amide nonion, polyoxyethylene nonylphenyl ether and amide nonion; and nonionic surfactants such as polyoxyethylene polycyclic phenyl ether having an HLB value of 14 to 17. More specific examples of the surfactant include Pluronic, Pluronic P123 (ADEKA Corporation), Pluronic F88 (ADEKA Corporation), Levenol WX (Kao Corporation), Nonion HS-220 (NOF Corporation), Nymid MT-215 (NOF Corporation), Newcol-723 (NOF Corporation), Newcol-2614 (Nippon Nyukazai Co, Ltd.) and Newcol-714 (Nippon Nyukazai Co, Ltd.).
  • Examples of the surfactant that reacts with lipoproteins other than HDL3 include, but are not limited to, nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether; anionic surfactants such as polyoxyethylene-polyoxypropylene condensates, amide ether sulfate and polyoxyethylene-stearylamine; amphoteric surfactants such as coconut oil fatty acid-amidopropyldimethyl-aminoacetic acid betaine, alkyl dimethyl-aminoacetic acid betaine and lauryl betaine; and cationic surfactants such as lauryl trimethyl ammonium chloride. More specifically, examples of the nonionic surfactants include polyoxyethylene distyrene-modified phenyl ether Emulgen A500 (trade name; manufactured by Kao Corporation; company names hereinafter represent names of manufacturers, and all names described together with company names hereinafter represent trade names); examples of the anionic surfactants include polyoxyethylene-polyoxypropylene condensates Pluronic F127 (ADEKA Corporation), Pluronic F68 (ADEKA Corporation) and Pluronic P103 (ADEKA Corporation), amide ether sulfate Sunamide CF-10 (NOF Corporation) and polyoxyethylene-stearylamine Nymeen S210 (NOF Corporation); examples of the amphoteric surfactants include a coconut oil fatty acid-amidopropyldimethyl-aminoacetic acid betaine Nissan Anon BDF-SF (NOF Corporation), alkyl dimethyl-aminoacetic acid betaine Nissan Anon BF (NOF Corporation) and lauryl betaine Amphitol 24B (Kao Corporation); and the cationic surfactants include lauryl trimethyl ammonium chloride Kohtamin 24P (Kao Corporation). Each of these may be used alone, or two or more types of these may be used in combination.
  • The concentration of the surfactant that reacts with lipoproteins other than HDL3 is preferably 0.01 to 5.0% by weight, more preferably about 0.03 to about 3.0% by weight.
  • Also in cases where Step 1 is carried out in the coexistence of a surfactant, the reaction conditions (reaction temperature, time, buffer and the like) are as described above.
  • Thereafter, in Step 2, cholesterol remaining in the reaction system is quantified. This can be carried out by allowing reaction with a surfactant that reacts with at least HDL3, to quantify cholesterol. The “surfactant that reacts with at least HDL3” includes a surfactant that specifically reacts with HDL3, surfactant that specifically reacts with HDL (that is, reacts with HDL2 and HDL3) and surfactant that reacts with all lipoproteins.
  • Examples of the surfactant which may be used in Step 2 include nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene lauryl ether and p-isooctyl polyoxyethylene phenol formaldehyde polymers; amphoteric surfactants such as lauryl dimethyl-aminoacetic acid betaine and polyoxyethylene lauryl ether; cationic surfactants such as fatty acid series phosphoric acid ester; nonionic surfactants having an HLB of 11 to 14 such as polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether and polyoxyethylene cumyl phenyl ether; imidazoline-type amphoteric surfactants; nonionic surfactants such as polyoxyethylene lauryl ether, polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether; and anionic surfactants such as lauryl alcohol alkoxylate and sodium polyoxyethylene-alkyl phenyl ether sulfate. Each of these may be used alone, or two or more types of these may be used in combination.
  • More specifically, examples of the surfactant that specifically reacts with HDL3 include nonionic surfactants such as polyoxyethylene distyrene-modified phenyl ether Emulgen A90 (Kao Corporation), polyoxyethylene lauryl ether Emulgen 120 (Kao Corporation) and p-isooctyl polyoxyethylene phenol formaldehyde polymer Triton-WR-1339 (Nacalai Tesque); amphoteric surfactants such as lauryl dimethyl-aminoacetic acid betaine Nissan Anon BL-SF (NOF Corporation) and polyoxyethylene lauryl ether Persoft NK-100 (NOF Corporation); and cationic surfactants such as fatty acid series phosphoric acid ester ADEKA COL PS-440E (ADEKA Corporation).
  • Examples of the surfactant that specifically reacts with HDL, which may be used, include nonionic surfactants having an HLB of 11 to 14 such as polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether and polyoxyethylene cumyl phenyl ether; and imidazoline-type amphoteric surfactants. Specific examples of the surfactant that specifically reacts with HDL, which may be used, include Emulgen A60 (Kao Corporation), Emulgen B66 (Kao Corporation), Emulgen LS110 (Kao Corporation), Newcol-CMP-11 (Nippon Nyukazai Co, Ltd.), Newcol-710 (Nippon Nyukazai Co, Ltd.), Newcol-610 (Nippon Nyukazai Co, Ltd.), Newcol-2609 (Nippon Nyukazai Co, Ltd.) and Nissan Anon GLM-R-LV (NOF Corporation).
  • Examples of the surfactant that specifically reacts with all lipoproteins, which may be used, include nonionic surfactants such as polyoxyethylene lauryl ether, polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether. Anionic surfactants such as lauryl alcohol alkoxylate and sodium polyoxyethylene-alkyl phenyl ether sulfate may also be used. Specific examples of the surfactant that specifically reacts with all lipoproteins, which may be used, include Emulgen 707 (Kao Corporation), Emulgen 909 (Kao Corporation), Emulgen 108 (Kao Corporation), Nymeen L207 (NOF Corporation), Adekatol LB83 (ADEKA Corporation), Adekatol LB103 (ADEKA Corporation) and Newcol-707 (Nippon Nyukazai Co, Ltd.).
  • In Step 2, the concentration of the surfactant is preferably 0.01 to 5.0% (w/v), more preferably 0.05 to 2.0% (w/v).
  • In Step 2, cholesterol is quantified by the reaction of such surfactants. It should be noted that the surfactant used is different between Step 1 and Step 2. Methods of quantification per se of cholesterol are well known, and any of the well known methods may be used. A concrete description is also given in Examples below. For example, ester-type cholesterol in lipoprotein is hydrolyzed with cholesterol esterase to produce free cholesterol and a fatty acid, and the produced free cholesterol and free cholesterol inherently existing in lipoprotein are converted using cholesterol oxidase to generate cholestenone and hydrogen peroxide. A quinone pigment is then formed in the presence of peroxidase, and quantified. Examples of compounds that generate a quinone pigment include HDAOS (N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline), DAOS (N-ethyl-N(-2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline sodium salt) or TOOS (N-ethyl-N(-2-hydroxy-3-sulfopropyl)-3-methylaniline sodium salt dihydrate) and 4-aminoantipyrine, but the compounds are not restricted as long as the combination allows generation of a quinone pigment. In cases where cholesterol esterase and cholesterol oxidase are used in Step 1, the cholesterol esterase and cholesterol oxidase used in Step 1 may be used as they are in Step 2 without further addition.
  • The concentration of the compound for generation of a quinone pigment is preferably about 0.5 to about 2.0 mmol/L in the case of HDAOS, or 0.1 to 2.0 mmol/L in the case of 4-aminoantipyrine. The concentration of peroxidase is preferably 0.4 to 5.0 U/mL. In a process wherein hydrogen peroxide produced in Step 1 is decomposed using catalase, a catalase inhibitor sodium azide is used by addition to the reaction liquid in Step 2. The concentration of sodium azide in this case is usually about 0.1 g/L to about 1.0 g/L.
  • The other reaction conditions for Step 2 (reaction temperature, time, buffer, pH and the like) may be the same as the reaction conditions for Step 1 described above.
  • Further, it is also possible to calculate the HDL2 cholesterol level in the test sample by subtracting the HDL3 cholesterol level obtained by Step 1 and Step 2 from the HDL cholesterol level in the test sample. Since methods for determining the HDL cholesterol level in a test sample are well known (e.g., JP 2001-103998 A) and kits for such methods are commercially available, the quantification can be easily carried out using these.
  • The present invention will now be described more concretely by way of Examples below. However, the present invention is not limited to the Examples below.
    • EXAMPLES Reference Example 1
  • Reagent A and Reagent B having the compositions described below were prepared, and reagents were prepared by adding various surfactants to Reagent A to a concentration of 0.1% (w/v) or 1.0% (w/v). Immediately before the measurement, Reagent A containing the various surfactants described below was mixed with Reagent B at a ratio of 1:3. Cholesterol in each of the HDL2 fraction and the HDL3 fraction was reacted with the resulting mixture, and the final absorbances at a main wavelength of 700 nm and a sub-wavelength of 600 nm were measured and compared.
  • Fractionation was carried out to obtain the HDL2 fraction and the HDL3 fraction as follows. A test sample containing HDL, that is, serum was subjected to ultracentrifugation using a solution with sodium chloride and sodium bromide such that separation occurs at a density at the border between HDL2 and HDL3 (1.125), and each resulting fraction was collected.
  • Table 1 below shows surfactants with which the ratio of HDL2/HDL3 was not more than 0.75 and the ratios of CM-IDL/HDL3 and LDL/HDL3 were not more than 0.75. These surfactants were determined to be surfactants that react with HDL3. Table 2 shows surfactants with which the ratio of HDL2/HDL3 was not less than 1.25 and the ratios of CM-IDL/HDL2 and LDL/HDL2 were not less than 1.25. These surfactants were determined to be surfactants that react with lipoproteins other than HDL3. Table 3 shows surfactants with which the ratio of HDL2/HDL3 was between 0.75 and 1.25 and the ratios of CM-IDL/HDL2, LDL/HDL2, CM-IDL/HDL3 and LDL/HDL3 were not more than 0.75. These surfactants were determined to be surfactants that react with HDL. Table 4 shows surfactants with which the ratio of HDL2/HDL3 was between 0.75 and 1.25 and the ratios of CM-IDL/HDL2, LDL/HDL2, CM-IDL/HDL3 and LDL/HDL3 were not less than 0.75. These surfactants were determined to be surfactants that react with all lipoproteins. Table 5 shows surfactants that could not be grouped into any of the above categories. These surfactants were determined to be surfactants that react with lipoproteins other than HDL.
    • Reagent A
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    • Reagent B
  • BES buffer (pH 6.6) 100 mmol/L
    Sodium azide 0.1%
    4-Aminoantipyrine 4.0 mmol/L
    Peroxidase 2.4 U/mL
  • TABLE 1
    HDL2/ CM-IDL/ CM-IDL/ LDL/ LDL/
    Concentration CM-IDL LDL HDL2 HDL3 HDL3 HDL2 HDL3 HDL2 HDL3
    Emulgen A90  1% 219 161 339 448 0.76 0.65 0.49 0.47 0.36
    0.1% 198 119 306 519 0.59 0.65 0.38 0.39 0.23
    Emulgen 120  1% 560 564 806 1267 0.64 0.69 0.44 0.70 0.45
    0.1% 494 465 499 793 0.63 0.99 0.62 0.93 0.59
    Nissan Anon  1% 441 941 721 1244 0.58 0.61 0.35 1.31 0.76
    BL-SF 0.1% 396 290 321 294 1.09 1.23 1.35 0.90 0.99
    Triton  1% 317 216 560 972 0.58 0.57 0.33 0.39 0.22
    WR-1339 0.1% 203 117 385 582 0.66 0.53 0.35 0.30 0.20
    Persoft  1% 687 603 1036 1569 0.66 0.66 0.44 0.58 0.38
    NK-100 0.1% 503 421 648 785 0.83 0.78 0.64 0.65 0.54
    ADEKA  1% 771 1099 1124 1633 0.69 0.69 0.47 0.98 0.67
    COL PS-440E 0.1% 1019 1410 1555 1715 0.91 0.66 0.59 0.91 0.82
    (Unit: Abs × 10000)
  • Emulgen A90, Emulgen 120, Nissan Anon BL-SF, Triton WR-1339, Persoft NK-100 and ADEKA COL PS-440E were surfactants that specifically react with HDL3.
  • TABLE 2
    HDL2/ CM-IDL/ CM-IDL/ LDL/ LDL/
    Concentration CM-IDL LDL HDL2 HDL3 HDL3 HDL2 HDL3 HDL2 HDL3
    Emulgen A500  1% 27 77 105 86 1.22 0.26 0.31 0.73 0.90
    0.1% 105 44 36 20 1.80 2.92 5.25 1.22 2.20
    Nissan Anon  1% 304 226 328 242 1.36 0.93 1.26 0.69 0.93
    BDF-SF 0.1% 272 91 82 42 1.95 3.32 6.48 1.11 2.17
    Nissan Anon  1% 512 461 581 571 1.02 0.88 0.90 0.79 0.81
    BF 0.1% 687 127 394 280 1.41 1.74 2.45 0.32 0.45
    Nymeen  1% 485 252 290 222 1.31 1.67 2.18 0.87 1.14
    S210 0.1% 514 278 271 199 1.36 1.90 2.58 1.03 1.40
    Pluronic  1% 87 72 102 81 1.26 0.85 1.07 0.71 0.89
    P103 0.1% 63 46 36 25 1.44 1.75 2.52 1.28 1.84
    Kohtamin  1% 495 185 359 288 1.25 1.38 1.72 0.52 0.64
    24P 0.1% 580 323 307 177 1.73 1.89 3.28 1.05 1.82
    Sunamide  1% 427 322 339 251 1.35 1.26 1.70 0.95 1.28
    CF-10 0.1% 479 321 308 184 1.67 1.56 2.60 1.04 1.74
    Amphitol  1% 471 392 509 481 1.06 0.93 0.98 0.77 0.81
    24B 0.1% 596 558 384 283 1.36 1.55 2.11 1.45 1.97
    Pluronic F68  1% 127 47 45 62 0.73 2.82 2.05 1.04 0.76
    0.1% 1328 275 175 129 1.36 7.59 10.29 1.57 2.13
    Pluronic  1% 523 260 138 109 1.27 3.79 4.80 1.88 2.39
    F127 0.1% 137 78 59 60 0.98 2.32 2.28 1.32 1.30
    (Unit: Abs × 10000)
  • Emulgen A500, Nissan Anon BDF-SF, Nissan Anon BF, Nymeen S210, Pluronic P103, Kohtamin 24P, Sunamide CF-10, Amphitol 24B, Pluronic F68 and Pluronic F127 were surfactants that specifically react with lipoproteins other than HDL3.
  • TABLE 3
    HDL2/ CM-IDL/ CM-IDL/ LDL/ LDL/
    CM-IDL LDL HDL2 HDL3 HDL3 HDL2 HDL3 HDL2 HDL3
    Emulgen B66  1% 375 281 1434 1473 0.97 0.26 0.25 0.20 0.19
    0.1% 361 185 1396 1441 0.97 0.26 0.25 0.13 0.13
    Emulgen A60  1% 375 281 1434 1473 0.97 0.26 0.25 0.20 0.19
    0.1% 361 185 1396 1441 0.97 0.26 0.25 0.13 0.13
    Emulgen LS110  1% 851 1267 1454 1463 0.99 0.59 0.58 0.87 0.87
    0.1% 744 1034 1518 1529 0.99 0.49 0.49 0.68 0.68
    Newcol-610  1% 500 447 1386 1470 0.94 0.36 0.34 0.32 0.30
    0.1% 439 320 1431 1472 0.97 0.31 0.30 0.22 0.22
    Newcol-2609  1% 636 553 1509 1556 0.97 0.42 0.41 0.37 0.36
    0.1% 547 543 1512 1502 1.01 0.36 0.36 0.36 0.36
    Newcol-CMP-11  1% 681 519 1498 1551 0.97 0.45 0.44 0.35 0.33
    0.1% 542 371 1435 1529 0.94 0.38 0.35 0.26 0.24
    Nissan Anon  1% 593 841 1219 1214 1.00 0.49 0.49 0.69 0.69
    GLM-R-LV 0.1% 92 112 68 59 1.15 1.35 1.56 1.65 1.90
    Newcol-710  1% 506 491 1303 1597 0.82 0.39 0.32 0.38 0.31
    0.1% 400 297 1344 1476 0.91 0.30 0.27 0.22 0.20
    (Unit: Abs × 10000)
  • Emulgen B66, Emulgen A60, Emulgen LS110, Nowol 610, Newcol 2609, Newcol-CMP-11, Nissan Anon GLM-RLV and Newcol-710 were surfactants that specifically react with HDL.
  • TABLE 4
    HDL2/ CM-IDL/ CM-IDL/ LDL/ LDL/
    CM-IDL LDL HDL2 HDL3 HDL3 HDL2 HDL3 HDL2 HDL3
    Emulgen 108  1% 2284 2390 2197 2202 1.00 1.04 1.04 1.09 1.09
    0.1% 1609 1815 1585 1548 1.02 1.02 1.04 1.15 1.17
    Emulgen 707  1% 3169 3021 2928 3048 0.96 1.08 1.04 1.03 0.99
    0.1% 1186 1546 1443 1375 1.05 0.82 0.86 1.07 1.12
    Newcol-707  1% 2349 2700 2783 2703 1.03 0.84 0.87 0.97 1.00
    0.1% 4106 4766 4850 4910 0.99 0.85 0.84 0.98 0.97
    Adekatol LB83  1% 1592 1611 1523 1509 1.01 1.05 1.06 1.06 1.07
    0.1% 1661 1680 1611 1598 1.01 1.03 1.04 1.04 1.05
    Adekatol LB103  1% 1418 1556 1533 1492 1.03 0.92 0.95 1.02 1.04
    0.1% 1228 1579 1582 1540 1.03 0.78 0.80 1.00 1.03
    Emulgen 909  1% 4248 3432 3488 3407 1.02 1.22 1.25 0.98 1.01
    0.1% 2467 2607 2704 2633 1.03 0.91 0.94 0.96 0.99
    (Unit: Abs × 10000)
  • Emulgen 108, Emulgen 707, Newcol 707, Adekatol LB83, Adekatol LB103 and Emulgen 909 were surfactants that specifically react with all lipoproteins.
  • TABLE 5
    HDL2/ CM-IDL/ CM-IDL/ LDL/ LDL/
    CM-IDL LDL HDL2 HDL3 HDL3 HDL2 HDL3 HDL2 HDL3
    Newcol-714  1% 178 139 260 218 1.19 0.68 0.82 0.53 0.64
    0.1% 203 116 220 203 1.08 0.92 1.00 0.53 0.57
    Newcol-723  1% 127 96 178 135 1.32 0.71 0.94 0.54 0.71
    0.1% 28 64 78 63 1.24 0.36 0.44 0.82 1.02
    Newcol-2614  1% 137 111 211 177 1.19 0.65 0.77 0.53 0.63
    0.1% 142 84 143 103 1.39 0.99 1.38 0.59 0.82
    Nymeen S215  1% 207 169 226 170 1.33 0.92 1.22 0.75 0.99
    0.1% 183 166 213 165 1.29 0.86 1.11 0.78 1.01
    Pluronic P123  1% 187 142 222 169 1.31 0.84 1.11 0.64 0.84
    0.1% 79 68 108 97 1.11 0.73 0.81 0.63 0.70
    Levenol WX  1% 122 120 163 134 1.22 0.75 0.91 0.74 0.90
    0.1% 80 75 67 27 2.48 1.19 2.96 1.12 2.78
    Mymid MT-215  1% 31 250 272 203 1.34 0.11 0.15 0.92 1.23
    0.1% 27 228 263 195 1.35 0.10 0.14 0.87 1.17
    Nonion HS220  1% 329 268 322 253 1.27 1.02 1.30 0.83 1.06
    0.1% 223 182 280 224 1.25 0.80 1.00 0.65 0.81
    Pluronic F88  1% 54 45 33 46 0.72 1.64 1.17 1.36 0.98
    0.1% 45 51 31 49 0.63 1.45 0.92 1.65 1.04
    (Unit: Abs × 10000)
  • Newcol-714, Newcol-723, Newcol-2614, Nymeen S215, Pluronic P123, Levenol WX, Nymid MT-215, Nonion HS220 and Pluronic F88 were surfactants that specifically react with lipoproteins other than HDL.
    • Example 1
  • Fractionation by ultracentrifugation was carried out to obtain the CM-LDL fraction, HDL2 fraction and HDL3 fraction, and each fraction was reacted with Reagent E prepared by adding phospholipase D (PLDP) to Reagent A used in Reference Example 1. Reagent D described below was further added to the reaction solution to perform measurement. In the measurement, 150 μL of Reagent E was added to 2 μL of serum, and the reaction was allowed to proceed for 5 minutes with warming, followed by addition of Reagent D to the reaction solution and additional 5 minutes of reaction with warming The absorbances at a main wavelength of 700 nm and a sub-wavelength of 600 nm were measured.
    • Reagent E
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Phospholipase D 5.0 U/mL
    • Reagent D
  • BES buffer (pH 6.6) 100 mmol/L
    Sodium azide 0.1%
    Emulgen B66 1.5%
    4-Aminoantipyrine 4.0 mmol/L
    Peroxidase 2.4 U/mL
  • FIG. 1 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent D. Specific reaction with HDL3 can be seen.
    • Example 2
  • Reagent F was prepared by adding a surfactant and sphingomyelinase to Reagent A used in Reference Example 1, and Reagent G was prepared for the step of measuring HDL3 in the product obtained by reaction with Reagent F. The compositions of these reagents were as shown below. Fractionation was carried out by ultracentrifugation to obtain the fraction from CM to IDL, LDL fraction, HDL2 fraction and HDL3 fraction, and the obtained fractions were subjected to measurement. The procedure for measurement with the reagents was the same as in Example 1. The absorbance was measured at each measurement time.
    • Reagent F
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Pluronic F68 0.03 w/v %
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Sphingomyelinase 0.5 U/mL
    • Reagent G
  • BES buffer (pH 6.6) 100 mmol/L
    Sodium azide 0.1%
    Emulgen A90 2.0%
    4-Aminoantipyrine 4.0 mmol/L
    Peroxidase 2.4 U/mL
  • FIG. 2 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent G. Specific reaction with HDL3 can be seen.
    • Example 3
  • The absorbance was measured in the same manner as in Example 2 using Reagent H which was prepared with the same composition as that of Reagent E used in Example 1 except that phospholipase C was used as the phospholipase and a surfactant was added.
    • Reagent H
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Pluronic F68 0.03 w/v %
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Phospholipase C 5.0 U/mL
  • FIG. 3 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent H. Specific reaction with HDL3 can be seen.
    • Example 4
  • The absorbance was measured in the same manner as in Example 2 using Reagent I which was prepared with the same composition as that of Reagent H used in Example 3 except that phospholipase D (PLDP) was used as the phospholipase and a surfactant was added.
    • Reagent I
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Pluronic F68 0.03 w/v %
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Phospholipase D 5.0 U/mL
  • FIG. 4 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent I. Specific reaction with HDL3 can be seen.
    • Example 5
  • The absorbance was measured in the same manner as in Example 2 except that Reagent J and Reagent K having the compositions described below were used.
    • Reagent J
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Pluronic P103 0.03 w/v %
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Phospholipase D 5.0 U/mL
    • Reagent K
  • BES buffer (pH 6.6) 100 mmol/L
    Sodium azide 0.1%
    Emulgen 120 1.0%
    4-Aminoantipyrine 4.0 mmol/L
    Peroxidase 2.4 U/mL
  • FIG. 5 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent K. Specific reaction with HDL3 can be seen.
    • Example 6
  • The absorbance was measured in the same manner as in Example 2 except that Reagent J used in Example 5 and Reagent L having the composition described below were used.
    • Reagent L
  • BES buffer (pH 6.6) 100 mmol/L
    Sodium azide 0.1%
    Emulgen 909 1.0%
    4-Aminoantipyrine 4.0 mmol/L
    Peroxidase 2.4 U/mL
  • FIG. 6 shows the result in terms of changes in the absorbance with time of each fraction after addition of Reagent L. Specific reaction with HDL3 can be seen.
    • Example 7
  • Reagent M was prepared and used in combination with Reagent D to measure HDL-C (C represents cholesterol; the same applies hereinafter) in the test sample. From this value, the value obtained by measuring HDL3-C using Reagent I and Reagent D in Example 4 was subtracted, to calculate HDL2-C. The values of HDL-C, HDL3-C and HDL2-C in each sample were as shown in Table 6.
    • Reagent M
  • BES buffer (pH 7.0) 100 mmol/L
    HDAOS 0.7 mmol/L
    Pluronic P88 0.1 w/v %
    Catalase 600 U/L
    Cholesterol oxidase 1.4 U/mL
    Cholesterol esterase 0.8 U/mL
    Phospholipase D 5.0 U/mL
  • TABLE 6
    HDL-C HDL3-C HDL2-C
    84.5 50.0 34.5
    85.1 49.9 35.2
    99.0 57.1 41.9
    88.2 45.2 43.0
    86.6 49.9 36.7
    (Unit: mAbs)

Claims (15)

1. A method for quantifying cholesterol in high-density lipoprotein 3, said method comprising:
Step 1 wherein phospholipase and/or sphingomyelinase is/are allowed to act on a test sample to transfer cholesterol to the outside of the reaction system; and
Step 2 wherein cholesterol remaining in the reaction system is quantified.
2. The method according to claim 1, wherein said phospholipase is phospholipase C and/or phospholipase D.
3. The method according to claim 1 or 2, wherein said Step 1 is carried out in the presence of a surfactant(s) that react(s) with lipoprotein other than high-density lipoprotein 3.
4. The method according to claim 3, wherein said surfactant is at least one nonionic surfactant which is polyoxyethylene distyrene-modified phenyl ether.
5. The method according to claim 3, wherein said surfactant is at least one anionic surfactant selected from the group consisting of polyoxyethylene-polyoxypropylene condensates, amide ether sulfate and polyoxyethylene-stearylamine.
6. The method according to claim 3, wherein said surfactant is at least one amphoteric surfactant selected from the group consisting of coconut oil fatty acid-amidopropyldimethyl-aminoacetic acid betaine, alkyl dimethyl-aminoacetic acid betaine and lauryl betaine.
7. The method according to claim 3, wherein said surfactant is a cationic surfactant which is lauryl trimethyl ammonium chloride.
8. The method according to claim 1, wherein said Step 2 is carried out in the presence of a surfactant(s) that react(s) at least with high-density lipoprotein 3.
9. The method according to claim 8, wherein said surfactant used in Step 2 is at least one nonionic surfactant selected from the group consisting of polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene lauryl ether and p-isooctyl polyoxyethylene phenol formaldehyde polymers.
10. The method according to claim 8, wherein said surfactant used in Step 2 is at least one amphoteric surfactant selected from the group consisting of lauryl dimethyl-aminoacetic acid betaine and polyoxyethylene lauryl ether.
11. The method according to claim 8, wherein said surfactant used in Step 2 is at least one cationic surfactant which is fatty acid series phosphoric acid ester.
12. The method according to claim 8, wherein said surfactant used in Step 2 is at least one nonionic surfactant having an HLB of 11 to 14, selected from the group consisting of polyoxyethylene distyrene-modified phenyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether and polyoxyethylene cumyl phenyl ether.
13. The method according to claim 8, wherein said surfactant used in Step 2 is at least one imidazoline-type amphoteric surfactant.
14. The method according to claim 8, wherein said surfactant used in Step 2 is at least one nonionic surfactant selected from the group consisting of polyoxyethylene lauryl ether, polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether.
15. The method according to claim 8, wherein said surfactant used in Step 2 is at least one anionic surfactant selected from the group consisting of lauryl alcohol alkoxylate and sodium polyoxyethylene-alkyl phenyl ether sulfate.
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