High-performance liquid chromatographic determination of alpha-keto acids in plasma with fluorometric detection

Separation and quantification of 2-keto-3-deoxy-gluconate (KDG) a major metabolite in pectin and alginate degradation pathways

A rapid and sensitive High Performance Liquid Chromatography (HPLC) method with photometric and fluorescence detection is developed for routine analysis of 2-Keto-3-deoxy-gluconate (KDG), a catabolite product of pectin and alginate. These polysaccharides are primary-based compounds for biofuel production and for generation of high-value-added products. HPLC is performed, after derivatization of the 2-oxo-acid groups of the metabolite with o-phenylenediamine (oPD), using a linear gradient of trifluoroacetic acid and acetonitrile. Quantification is accomplished with an internal standard method. The gradient is optimized to distinguish KDG from its close structural analogues such as 5-keto-4-deoxyuronate (DKI) and 2,5-diketo-3-deoxygluconate (DKII). The proposed method is simple, highly sensitive and accurate for time course analysis of pectin or alginate degradation.

Determination of α-ketoglutaric and pyruvic acids in urine as potential biomarkers for diabetic II and liver cancer

Background: A simple and sensitive hollow fiber-liquid phase microextraction with in situ derivatization method was developed for the determination of α-ketoglutaric (α-KG) and pyruvic acids (PA) in small-volume urine samples. 2,4,6-trichloro phenyl hydrazine was used as derivatization agent. Results: Under the optimum extraction conditions, enrichment factors of 742 and 400 for α-KG and PA, respectively, were achieved. Calibration curves were linear over the range 1 to 1000 ng/ml (r2 ≥ 0.998). Detection and quantitation limits were 0.03 and 0.02, and 0.10 and 0.05 ng/ml for α-KG and PA, respectively. Conclusion: The concentrations in diabetic II and liver cancer samples were significantly lower than those from healthy people, showing their potential as biomarkers for these diseases.

Quantification of branched-chain keto acids in tissue by ultra fast liquid chromatography-mass spectrometry

Branched-chain keto acids (BCKAs) are associated with increased susceptibility to several degenerative diseases. However, BCKA concentrations in tissues or the amounts of tissue available are frequently at the limit of detection for standard plasma methods. To accurately and quickly determine tissue BCKAs, we have developed a sensitive ultra fast liquid chromatography-mass spectrometry (UFLC-MS) method. BCKAs from deproteinized tissue extractions were o-phenylenediamine (OPD) derivatized, ethyl acetate extracted, lyophilized in a vacuum centrifuge, and reconstituted in 200 mM ammonium acetate. Samples were injected onto a Shimadzu UFLC system coupled to an AB-Sciex 5600 Triple TOF mass spectrometer instrument that detected masses of the OPD BCKA products using a multiple reaction monitoring method. An OPD-derivatized (13)C-labeled keto acid was used as an internal standard. Application of the method for C57BL/6J (wild-type) and PP2Cm knockout mouse tissues, including kidney, adipose tissue, liver, gastrocnemius, and hypothalamus, is shown. The lowest tissue concentration measured by this method was 20 nM, with the standard curve covering a wide range (7.8-32,000 nM). Liquid chromatography-mass spectrometry run times for this assay were less than 5 min, facilitating high throughput, and the OPD derivatives were found to be stable over several days.

A new strategy for the selective determination of d-amino acids: Enzymatic and chemical modifications for pre-column derivatization

A new strategy for the selective determination of D-amino acids (DAAs) employing a pre-column derivatization was designed with concepts based on both enzymatic and chemical modifications. Selective determination of DAAs was accomplished by following: DAA was enzymatically modified with D-amino acid oxidase (DAAO: EC 1.4.3.3) to form an alpha-keto acid. Subsequently, resulting alpha-keto acid was detected by high-performance liquid chromatography (HPLC) after chemical modification with o-phenylenediamine (PDA) in the presence of 2-mercaptoethanol (2ME) to give the corresponding quinoxalinol derivative (PDA-alpha-keto acid derivative). After optimizing the pre-column derivatization and HPLC separation, five peaks corresponding to DAAs (D-alanine, D-leucine, D-methionine, D-phenylalanine, D-valine (as the standard mixture of DAAs in this paper) were separately eluted and monitored by means of a conventional HPLC system with a gradient elution on octadecyl silica gel (ODS) column and a fluorescence detector (Ex.: 341 nm, Em.: 413 nm), respectively. It was confirmed that the present method was incapable of detecting L-amino acids (LAA) when a sample solution consisting of both LAAs and DAAs was examined. The linearity of the peak-area responses to their concentration range of DAAs from 10 to 500 microM is 0.994-1.000, and their detection limits were 0.2-1 microM (signal/noise = 3). When this method was applied to a methanolic extract of short-necked clams, Ruditapes philippinarum (in Japanese, Asari), a big peak, corresponding to D-alanine was detected, corresponding to 2.9 mg/g D-alanine. In this paper, we present an example of pre-column derivatization method that was newly configured to take into account both the biological and chemical properties of the substances in question.

Quantitative determination of free intracellular alpha-keto acids in neutrophils

For the first time, a procedure is described for the quantitative analysis of free alpha-keto acid content in human neutrophils (PMNs) relative to single cell number by reversed-phase fluorescence high-performance liquid chromatography. The procedure is minimally invasive and is unsurpassed in the quality of PMN separation, ease of sample preparation as well as sample stability. This method can satisfy the rigorous demands for an ultra-sensitive, comprehensive and rapid intracellular alpha-keto acid analysis in particularly for the surveillance of severe diseases as well as cellular or organ dysfunction.

Branched-Chain Keto-Acids and Pyruvate in Blood: Measurement by HPLC with Fluorimetric Detection and Changes in Older Subjects

Background: Measurement of keto-acids is important in various clinical situations. The aim of the present work was to develop a rapid HPLC method for the determination of keto-acids in human serum and to assess the concentrations of these acids in young adults and institutionalized elderly adults. This method was applied to the determination of blood keto-acid concentrations of young adults and institutionalized elderly people, divided into age groups

Methods: Four keto-acids (α-ketoisocaproate, α-ketoisovalerate, α-keto-β-methylvalerate, and pyruvate) were derivatized with o-phenylenediamine to give fluorescent derivatives. After the sample preparation step (75 min to prepare 20 samples), the derivatives were separated chromatographically on a reversed-phase column using a binary gradient.

Results: The fluorometric detection of the four keto-acids was rapid, <12 min. The method is repeatable and reproducible: the CVs were <6% and <11%, respectively, for each of the keto-acids. We found no significant difference between males and females. Concentrations of the branched-chain keto-acids decreased after age 60 years, especially α-ketoisocaproate, which decreased ∼40%.

Conclusions: The proposed method allows rapid and reliable measurement of keto-acids. The data demonstrate that changes in branched-chain keto-acids concentrations in serum occur with age.

Aminopyrazine analogues as chemiluminescence derivatization reagents for pyruvic acid

Aminopyrazine analogues were studied as sensitive and selective chemiluminescence derivatization reagents for pyruvic acid. These analogues reacted with pyruvic acid under acidic conditions at 100 degrees C to produce Cypridina luciferin derivatives, which exhibit chemiluminescence by reaction with hydrogen peroxide in the presence of potassium t-butoxide in dimethylformamide. Of the four aminopyrazine analogues (2-amino-5-phenylpyrazine, 2-amino-5-(4-hydroxyphenyl)pyrazine, 2-amino-5-(3,4, 5-trimethoxyphenyl)pyrazine, and 2-aminoquinoxaline), in the present test 2-amino-5-(3,4,5-trimethoxyphenyl) pyrazine was the most sensitive for pyruvic acid, and the chemiluminescence intensity was about four times higher than that obtained with aminopyrazine.

High-performance liquid chromatography-fluorescence assay of pyruvic acid to determine cysteine conjugate beta-lyase activity: application to S-1,2-dichlorovinyl-L-cysteine and S-2-benzothiazolyl-L-cysteine

An HPLC-fluorescence assay has been developed for the determination of the activity of rat renal cytosolic cysteine conjugate beta-lyase. The method is based on isocratic HPLC separation and fluorescence detection of pyruvic acid, derivatized with o-phenylenediamine (OPD), and is shown to be rapid, specific, and very sensitive. The assay has been evaluated with two model substrates for rat renal cytosolic beta-lyase, notably S-1,2-dichorovinyl-L-cysteine (DCVC) and S-2-benzothiazolyl-L-cysteine (BTC). Equimolar formation of pyruvic acid and 2-mercaptobenzothiazole, a chromophoric thiol, indicated that pyruvic acid formation actually reflects the beta-elimination activity of beta-lyase during the beta-elimination of BTC. From this it follows that the pyruvic acid assay can be applied to the measurement of the beta-elimination activity of this enzyme, independent of the presence of chromophoric groups or radiolabels in substrates. Due to the large linear range and the very high sensitivity of the present HPLC-fluorescence assay (detection limit, 7.5 pmol of pyruvic acid), both good and poor substrates of beta-lyase can be measured. Enzyme kinetic data are presented for the model substrates BTC and DCVC and for four structurally related S-2,2-difluoroethyl-L-cysteine conjugates.

High-performance liquid chromatographic determination of D-amino acid oxidase activity

A new procedure for the assay of D-amino acid oxidase activity has been developed. alpha-Ketoisovaleric acid, derived from D-valine, was estimated by high-performance liquid chromatography after reaction with o-phenylenediamine to give the corresponding quinoxalinol derivative. alpha-Ketovaleric acid was used as an internal standard to ensure the reproducibility of the method. As an example of application, kidney cortex homogenates were analyzed for their D-amino acid oxidase activity. The advantages of the presented procedure for the determination of the enzymatic activity in biological samples compared with previously reported procedures are discussed.

Determination of alpha-keto acids including phenylpyruvic acid in human plasma by high-performance liquid chromatography with chemiluminescence detection

A highly sensitive method for the determination of alpha-keto acids including phenylpyruvic acid in human plasma is investigated. The method employs high-performance liquid chromatography with chemiluminescence detection. The acids and alpha-ketocaproic acid (internal standard) in human plasma are isolated by anion-exchange chromatography on a Toyopak DEAE cartridge, and then converted into the corresponding chemiluminescent derivatives with 4,5-diaminophthalhydrazide dihydrochloride, a chemiluminescence derivatization reagent for alpha-keto acids. The derivatives are separated within 50 min on a reversed-phase column, TSKgel ODS-120T, with isocratic elution, followed by chemiluminescence detection; the chemiluminescence is produced by the reaction of the derivatives with hydrogen peroxide in the presence of potassium hexacyanoferrate(III). The detection limits for the acids are in the range 9-92 pmol/ml in plasma (signal-to-noise ratio = 3). This sensitivity permits precise determination of several alpha-keto acids including phenylpyruvic acid, which cannot be determined by other HPLC methods, in 10 microliters of normal human plasma. The chemiluminescent product from phenylpyruvic acid was characterized as 3-benzyl-7,8-dihydropyridazino[4,5-g]quinoxaline-2,6,9(1H)-trione.

High-performance liquid chromatographic analysis of alpha-keto acids produced from amino acid metabolism in oral Bacteroides

Profiles of metabolic alpha-keto acids were determined by a high-performance liquid chromatographic method and applied to characterization of oral black-pigmented Bacteroides. Each bacterial strain was incubated with amino acids in a chemically defined medium. After production alpha-keto acids were purified by hydrazide gel column treatment and converted to u.v.-absorbing derivatives. They were analysed by reversed-phase ion-pair chromatography. Black-pigmented Bacteroides species were differentiated into two groups according to production of aromatic alpha-keto acids. Bacteroides gingivalis, B. endodontalis and B. loescheii produced both p-hydroxyphenylpyruvic and phenylpyruvic acids. However, no such alpha-keto acids were produced by B. levii, B. intermedius and B. denticola. In addition, production profiles of several aliphatic alpha-keto acids (alpha-ketoglutaric, pyruvic, alpha-ketobutyric, alpha-ketoisovaleric, alpha-ketoisocaproic, and alpha-keto-beta-methylvaleric acids) separated each individual species in such groups. The present study offers useful chemotaxonomic information on amino acid metabolic activity of oral black-pigmented Bacteroides species.

A sensitive chromatographic method for the detection of pyruvyl groups in microbial polymers from sediments

A method was developed for the quantitation of pyruvyl groups in microbial polymers using mild acid hydrolysis, o-phenylenediamine labeling, reversed-phase high-performance liquid chromatography (RP-HPLC), and fluorescence detection. The method was used to determine the pyruvate content of various microbial exopolysaccharides and to estimate the abundance of polymeric pyruvate in freshwater sediments. The results of this method were compared with those of several other pyruvate assays. The detection limit of the method was 1.6 nmol pyruvate. As little as 3.7μg of the bacterial polysaccharide xanthan gum, or from 5 to 22 mg of sediment (depending on polymeric pyruvate content), were needed for detection and quantitation of polymeric pyruvate. The results should be useful in determining the contribution of polymeric pyruvate to total metal-binding ligands in sediments.

A convenient enzymatic method for the determination of 4-methyl-2-oxopentanoate in plasma: comparison with high performance liquid chromatographic analysis

A simple and rapid spectrophotometric method for the estimation of 4-methyl-2-oxopentanoate in plasma samples by use of NAD+-dependent D-2-hydroxyisocaproate dehydrogenase from Lactobacillus casei ssp. pseudoplantarum is described. It is based on the kinetic measurement of the decrease of NADH absorbance at 334 nm. Applicability is demonstrated by comparative measurement of 4-methyl-2-oxopentanoate content in plasma of patients with maple syrup urine disease by the enzymatic and a reversed phase high performance liquid chromatographic method.

High-performance liquid chromatographic methods with fluorescence detection for the determination of branched-chain amino acids and their alpha-keto analogues in plasma samples of healthy subjects and uraemic patients

High-performance liquid chromatographic (HPLC) methods have been developed for the quantification of branched-chain amino acids (BCAA) and their keto analogues (BCKA). Amino acids and their keto analogues were derivatized with o-phthalaldehyde, 2-mercaptoethanol and o-phenylenediamine sulphate prior to HPLC. Both separations were performed on a reversed-phase column, using a multi-step gradient system with two solvents and a fluorescence detector. These methods are simple and sensitive and give highly reproducible results. By using an automatic system, the instability problem is avoided and the reaction kinetics are controlled. The use of a simple clean-up procedure with preparative cation-exchange chromatography before BCKA analysis concentrates the dilute plasma sample. The methods were applied to the determination of BCAA and BCKA in plasma samples of healthy volunteers and patients with chronic renal disorders. The relationship between the concentrations of BCAA and BCKA in plasma for these two groups is shown.

Determination of alpha-keto acids in serum and urine by high-performance liquid chromatography with fluorescence detection

A simple, rapid and highly sensitive high-performance liquid chromatographic method for the determination of alpha-keto acids in serum and urine is described. In dilute hydrochloric acid, alpha-keto acids are converted by 1,2-diamino-4,5-dimethoxybenzene into highly fluorescent quinoxalinone derivatives. The derivatives are isocratically separated simultaneously within 14 min by reversed-phase chromatography on a Radial-Pak cartridge C18 and detected fluorimetrically. The limits of detection are 10-300 fmol in an injection volume of 10 microliters (40-1200 pmol/ml of serum or urine). This sensitivity permits precise determination of several alpha-keto acids in 5 microliter of serum or urine from healthy persons, and also the determination of phenylpyruvic acid in normal urine which cannot be simultaneously determined by other methods.

Measurement of alpha-keto acids in plasma using an amino acid analyzer

A method for measuring keto acid concentrations in physiological fluids using an amino acid analyzer was developed. After preliminary deproteinization and removal of amino acids, reduction with sodium cyanoborohydride at 105 degrees C resulted in efficient conversion of the keto acids to their corresponding amino acids. In applying the technique to plasma samples, the use of MeOH for deproteinization was necessary to avoid the large losses of keto acids that occurred during precipitation of proteins with perchloric acid. The method was used to follow plasma ketoisocaproate concentrations in rat plasma after administration of leucine, and was sufficiently sensitive to detect concomitant changes in other branched-chain keto acid concentrations.