Liquid chromatography-mass spectrometry for the qualitative analyses of iminodipeptides in the urine of patients with prolidase deficiency

Prolidase activity assays. A survey of the reported literature methodologies

Prolidase (EC.3.4.13.9) is a dipeptidase known nowadays to play a pivotal role in several physiological and pathological processes. More in particular, this enzyme is involved in the cleavage of proline- and hydroxyproline-containing dipeptides (imidodipeptides), thus finely regulating the homeostasis of free proline and hydroxyproline. Abnormally high or low levels of prolidase have been found in numerous acute and chronic syndromes affecting humans (chronic liver fibrosis, viral and acute hepatitis, cancer, neurological disorders, inflammation, skin diseases, intellectual disability, respiratory infection, and others) for which the content of proline is well recognized as a clinical marker. As a consequence, the accurate analytical determination of prolidase activity is of greatly significant importance in clinical diagnosis and therapy. Apart from the Chinard's assay, some other more sensitive and well validated methodologies have been published. These include colorimetric and spectrophotometric determinations of free proline produced by enzymatic reactions, capillary electrophoresis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, electrochemoluminescence, thin layer chromatography, and HPLC. The aim of this comprehensive review is to make a detailed survey of the in so far reported analytical techniques, highlighting their general features, as well as their advantages and possible drawbacks, providing in the meantime suggestions to stimulate further research in this intriguing field.

Improved prolidase activity assay allowed enzyme kinetic characterization and faster prolidase deficiency diagnosis

BACKGROUND

Prolidase is a metallo-exopeptidase hydrolyzing X-Pro and X-Hyp dipeptides. Its absence or reduced level is typical in prolidase deficiency (PD) patients, and altered prolidase activity was reported in various diseases. Therefore, standardized and accurate measurement of prolidase activity is essential for PD diagnosis, as well as to elucidate the pathophysiology of other disorders.

METHODS

Human recombinant prolidase was used to optimize a spectrophotometric enzyme activity assay. Kinetic parameters and Mn(2+) affinity were evaluated. The method was validated on blood and fibroblasts from PD patients.

RESULTS

An activation step consisting in prolidase incubation with 1 mmol/l MnCl(2) and 0.75 mmol/l reduced glutathione at 50°C for 20 min was necessary to obtain the maximum activity and to accurately determine, for the recombinant enzyme, V(max) (489 U/mg), K(m) (5.4 mM) and Mn(2+) affinity (54 mM(-1)). The method applied to PD diagnosis revealed an intra-assay CV=8% for blood and 9% for fibroblasts lysates. The inter-assay CV was 21% for blood and 20% for cell lysates.

CONCLUSION

We optimized a faster spectrophotometric method to measure the activity when the enzyme is fully activated, this is crucial to allow a reliable evaluation of prolidase activity from different sources.

The role of emerging techniques in the investigation of prolidase deficiency: From diagnosis to the development of a possible therapeutical approach

The aim of the present article is to review the efforts performed in the past two decades by numerous research groups for the development of methods that allow a correct diagnosis of prolidase deficiency (PD), a rare autosomal recessive disorder and for the rationalization of a possible therapeutic intervention on these patients. In particular, the interest of the reader is focused on the application of capillary electrophoresis (i) for the detection of biological markers that reflect the pathological feature of the disease and (ii) for the determination of the efficiency of a carrier system in delivering prolidase inside cells in a possible therapy based on enzyme replacement.

Optimization of a capillary electrophoretic method to detect and quantify the Gly-Pro dipeptide in complex matrices from long term cultured prolidase deficiency fibroblasts

A capillary electrophoresis (CE) method has been developed and optimized for the detection of Gly-Pro dipeptide in complex biological samples: medium, cell layer and matrix obtained from long term cultured human fibroblasts of control and prolidase deficiency patients. The influence of different detergents in the sample preparation and electrophoretic conditions were investigated. The method was validated for cellular extracts with respect to limits of detection and quantitation, precision, linearity, accuracy and robustness. The optimized method was applied to real samples and revealed a significant increase of intracellular Gly-Pro dipeptide in prolidase deficiency fibroblasts with respect to the control.

Corticosteroid treatment of prolidase deficiency skin lesions by inhibiting iminodipeptide-primed neutrophil superoxide generation

We studied the pathogenetic role of iminodipeptides, and the effects of corticosteroids on the skin lesions of two adult female siblings with prolidase deficiency. The elder sister had had severe skin ulcers and mental retardation since childhood, while the younger sister had shown milder clinical manifestations since late adolescence. The ulcers showed vascular wall thickening and neutrophil infiltration. Oral prednisolone at moderate doses was not effective, but corticosteroid pulse therapy followed by a moderate dose of prednisolone improved the preulcerative indurated lesions and ulcers. A 2-year follow-up of the younger patient indicated that N-formyl methionyl leucyl phenylalanine-induced neutrophil superoxide generation was elevated, in parallel with an increase in the serum iminodipeptide level, when the skin ulcers and preulcerative indurated lesions were most active. Corticosteroid pulse therapy downregulated the superoxide generation by neutrophils. The serum iminodipeptide level, however, did not decrease during 25 days after pulse therapy. These findings suggest that iminodipeptides may play an important part in aggravating the skin lesions by priming neutrophil superoxide generation, and that high-dose corticosteroids improve the skin lesions, probably by inhibiting the infiltration, and superoxide generation by, neutrophils. Neutrophil superoxide generation was more prominent in the elder sister, suggesting that clinical severity may depend on the response of neutrophils to the iminodipeptides. Chronic stimulation by superoxide may cause thickening of cerebral blood vessels and eventual mental retardation.

Simultaneous determination of gamma-aminobutyric acid and glutamic acid in the brain of 3-mercaptopropionic acid-treated rats using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

The measurement of gamma-aminobutyric acid (GABA) and glutamic acid (Glu) in the whole brain and in various regions of the brain in 3-mercaptopropionic acid (3-MPA)-treated rats has been developed using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The recoveries of these compounds were 94.90+/-4.18% for GABA, 95.60+/-2.86% for Glu after ion-exchange treatment. The detection limits for GABA and Glu were 2.5+/-0.3 microg/ml and 5.0+/-0.8 microg/ml, respectively, when 20 microl sample were injected. GABA concentration in the whole brain decreased gradually to 5 min and reached 63% of normal value after administration of 3-MPA, and the concentration increased gradually thereafter until 60 min. Conversely, the concentration of Glu in the whole brain increased gradually to 10 min and reached 154% of normal value, and after that decreased gradually and reached almost normal level at 60 min after administration of 3-MPA. GABA concentration in various regions of brain decreased to 5 min in all regions after administration of 3-MPA, and reached normal levels at 60 min as in the whole brain. This method was found to be useful for studies of metabolism of GABA and Glu in biological samples.

Highly sensitive determination of N-terminal prolyl dipeptides, proline and hydroxyproline in urine by high-performance liquid chromatography using a new fluorescent labelling reagent, 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride

A highly sensitive pre-column HPLC method for simultaneous determination of prolyl dipeptides, Pro and Hyp in urine was developed. The analytes were labelled with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride at 70 degrees C for 20 min. The derivatives separated on tandem reversed-phase columns by a gradient elution and were monitored with fluorescence detection at 318 nm (excitation) and 392 nm (emission). The detection limits for prolyl dipeptides, Pro and Hyp were 1-5 fmol/injection (S/N = 3). Urine samples were treated with o-phthalaldehyde, followed by purification on a Bond Elut C18 column before conducting the labelling reaction. Pro-Hyp, Pro-Gly and Pro-Pro were identified as prolyl dipeptides in urine. The within-day and between-day relative standard deviations were 1.5-4.8 and 1.7-5.8%, respectively. The concentrations of Pro-Hyp, Pro-Gly, Pro-Pro, Pro and Hyp in normal human urine were 97.6 +/- 28.2, 2.74 +/- 1.48, 2.08 +/- 1.13, 6.71 +/- 3.34 and 2.30 +/- 1.59 nmol/mg creatinine, respectively.

Hypotaurine disproportionation reaction: identification of products

Hypotaurine, concentrated under reduced pressure in HCl solution, partially (30-40%) degrades into taurine (about 30%), 2-aminoethyl-2-aminoethanethiolsulfonate (about 10%) and ethanolamine. The degradation products were identified using LC/APCI-MS, NMR, amino acid analysis and various chromatographies. The identities were confirmed by comparing the HPLS, MS and NMR characteristics of authentic compounds. One of the degradation processes during concentration of HCl solution of hypotaurine is therefore a disproportionation reaction which can interfere with the experimental results, when studying hypotaurine in biological systems.

Metabolism of cystathionine, N-monoacetylcystathionine, perhydro-1,4-thiazepine-3,5-dicarboxylic acid, and cystathionine ketimine in the liver and kidney of D,L-propargylglycine-treated rats

Experimental cystathioninuria was induced by injection of D,L-propargylglycine in rats. The novel cystathionine metabolites, N-monoacetylcystathionine (NAc-cysta), perhydro-1,4-thiazepine-3,5-dicarboxylic acid (PHTZDC), and cystathionine ketimine (CK), were identified previously in the urine of patients with cystathioninuria and D,L-propargylglycine-treated rats. In this study, we identified these compounds in the liver and kidney of D,L-propargylglycine-treated rats using liquid chromatography-mass spectrometry with an atmospheric pressure chemical ionization interface system (LC/APCI-MS) and an amino acid analyzer. The metabolism of these compounds in the liver and kidney of D,L-propargylglycine-treated rats was also studied. PHTZDC, NAc-cysta, and CK were accumulated in the rat tissues in proportion to the content of cystathionine after D,L-propargylglycine administration. The concentrations of these compounds in the liver were higher than those in the kidney, and these compounds reached maxima earlier in the liver than in the kidney.

The effects of serum iminodipeptides and prednisolone on superoxide generation and tyrosyl phosphorylation of proteins in neutrophils from a patient with prolidase deficiency

The aim of this study was to examine the effects of serum iminodipeptides and prednisolone on superoxide generation and tyrosyl phosphorylation of proteins in neutrophils from a patient with prolidase deficiency, and also to find the causative effects of superoxide on inflammatory skin lesions. When the neutrophils from a patient with prolidase deficiency (PDPPMN) were preincubated with prolyl-proline (Pro-Pro), which is one of the iminodipeptides found at high concentration in the serum of patients with prolidase deficiency, the N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide generation was enhanced in a concentration-dependent manner, although the extent of enhancing effect was lower than that in neutrophils from healthy humans (HPPMN). Pro-Pro also enhanced superoxide generation induced by opsonized zymosan (OZ) in PDPPMN but not that induced by arachidonic acid or phorbol 12-myristate 13-acetate. Herbimycin A and genistein decreased the fMLP- and OZ-induced superoxide generations after priming by Pro-Pro. 1-(5-isoquinoline-sulfonyl)-2-methyl-piperazine (H-7) and staurosporine did not decrease, but rather enhanced, the superoxide generation in a low concentration range. When PDPPMN were prepared, tyrosyl phosphorylation of 45 kDa protein in PDPPMN had already occurred. The phosphorylation was scarcely increased by incubation of the cells with Pro-Pro, in contrast to that in HPPMN. Genistein decreased the phosphorylation of 45 kDa protein in both PDPPMN and HPPMN. These results suggest that the priming effect of iminodipeptides on superoxide generation in PDPPMN is coupled with phosphorylation of 45 kDa protein by protein tyrosine kinase. Protein tyrosine kinase may play a critical role(s) in the regulatory mechanism of priming by iminodipeptides and activation of NADPH oxidase in the patient's neutrophils. In prolidase deficiency, the characteristic skin manifestations are inflammatory indurations and chronic leg ulcers. Prednisolone improves the ulcers, and this compound decreased the fMLP- and OZ-induced superoxide generation and tyrosyl phosphorylation of 45 kDa protein in the patient's neutrophils after priming by Pro-Pro. When inflammatory skin lesions were present, the levels of iminodipeptides in the patient's serum were elevated and the superoxide generation by neutrophils was up-regulated. When skin lesions were healing or absent, the levels of iminodipeptides in the patient's serum and superoxide generation by neutrophils were higher than those of healthy controls but lower than those in the inflammatory stages. Thus, the enhancement of superoxide generation by neutrophils via serum iminodipeptides would be one of the inducers of inflammatory skin lesions. Corticosteroid administration might be a therapeutic modality of choice for skin lesions.

Simultaneous determination of creatinine, creatine, and guanidinoacetic acid in human serum and urine using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A rapid and direct method for simultaneous determination of creatinine, creatine, and guanidinoacetic acid in biological samples has been developed by using column liquid chromatography-mass spectrometry (LC/APCI-MS). The determinations of creatinine, creatine, and guanidinoacetic acid in the samples of human urine and serum were carried out by scanning the [M + H]+ ions of each compound. The recoveries of authentic compounds were 93.87 +/- 6.00% (n = 5) for creatinine, 94.80 +/- 8.93% (n = 5) for creatine, and 90. 92 +/- 7.96% (n = 5) for guanidinoacetic acid after ion-exchange resin treatment. The content of creatinine in human urine and serum was also measured by the Jaffé method, a common method of determination of creatinine currently used in hospitals. The contents of creatinine, creatine, and guanidinoacetic acid obtained using LC/APCI-MS coincided well with those reported in previous papers.

Use of capillary zone electrophoresis for analysis of imidodipeptides in urine of prolidase-deficient patients

Prolidase deficiency (PD) is characterized by massive urinary excretion of imidodipeptides X-Pro and X-Hyp. We report the applicability of capillary zone electrophoresis to urinary imidodipeptide determination. The protocol is fast, simple, reliable, only small amounts of sample are required and there is minimal sample preparation. Electropherograms of urine samples from control subjects and four patients with prolidase deficiency were compared. The presence of imidodipeptides normally absent in urine was evident in patients' urine. Further analysis of urine samples enabled identification of excreted imidodipeptides and the pattern of excretion appeared to be heterogeneous for different patients. This method appears to be useful for identification of imidodipeptides in biological samples, as an efficient aid in diagnosis of PD, and as a method for providing more information about this disease.

Identification of N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine in the urine of a patient with cystathioninuria using LC/APCI-MS

A new cystathionine metabolite has been identified in the urine of a patient with cystathioninuria using liquid chromatography-mass spectrometry with an atmospheric pressure chemical ionization interface system (LC/APCI-MS). By this method a very intense quasi-molecular ion was observed as a base peak of synthetic N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine (NAc-OCPC). The quasimolecular ion [M + H]+ of NAc-OCPC observed in the urine of a patient with cystathioninuria was the same as that of the authentic compound (m/z 264). The retention time and Rf value on paper chromatography of the synthetic compound were the same as those of the urinary compound from the patient with cystathioninuria. From these results, this new cystathionine metabolite was identified as N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine.

Determination of D,L-propargylglycine and N-acetylpropargylglycine in urine and several tissues of D,L-propargylglycine-treated rats using liquid chromatography-mass spectrometry

An experimental animal model with cystathioninuria was obtained by the injection of D,L-propargylglycine into rats. The concentrations of D,L-propargylglycine in urine, several tissues and serum at different times after the injection were measured by liquid chromatography-mass spectrometry. The propargylglycine accumulated rapidly in several tissues and serum of the rats, and reached its maximum level at about 2 h after the injection. Approximately 21.2% of the administered propargylglycine was excreted in urine. N-Acetylpropargylglycine was identified as a new metabolite of propargylglycine in urine. The concentration of propargylglycine was 100 times that of N-acetylpropargylglycine in urine.

Liquid chromatographic-mass spectrometric analysis of N-acetylamino acids in human urine

Liquid chromatography-atmospheric pressure chemical-ionization mass spectrometry (LC-APCI-MS) was used for the analysis of N-acetylamino acids that could not be determined with an amino acid analyzer. LC-APCI-MS could directly detect the protonated molecular ions of various synthetic N-acetylamino acids, distinguishing N-acetylserine from O-acetylserine and N(alpha)-acetyllysine from N(epsilon)- acetyllysine. Furthermore, N-acetylasparagine, N-acetylaspartic acid, N-acetylglutamine and N-acetylglutamic acid were identified in normal human urine. The assay data for N-acetylaspartic acid agree with a previous report using gas chromatography-mass spectrometry. These results demonstrate the usefulness of the apparatus described above for the analysis of N-acetylamino acids in biological samples.

Measurement of iminodipeptides in the serum of patients with prolidase deficiency using liquid chromatography-mass spectrometry

Iminodipeptides containing C-terminal proline or hydroxyproline were determined in sera from patients with prolidase deficiency, in their mother's serum, and in the sera of unrelated controls, using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The separation was carried out on a reversed phase column using 1 g/l aqueous trifluoroacetic acid-methanol (75 + 25, by vol.). The quasi-molecular ions ([M + H])+ of various iminodipeptides containing C-terminal proline and hydroxyproline were observed in the sera of patients with prolidase deficiency, using selected ion monitoring. The quasi-molecular ions ([M + H])+ of iminodipeptides containing C-terminal proline were not observed in the sera of normal subjects or the patients' mother, but the latter did contain various iminodipeptides with C-terminal hydroxyproline. This method proved useful for the determination of iminodipeptides in the sera of patients with prolidase deficiency.

Sensitive determination of N-terminal prolyl peptides by high-performance liquid chromatography with laser-induced fluorescence detection

Short-chain peptides with an N-terminal proline (Pro-Gly, Pro-Ile, Pro-Gly-Gly, Pro-Leu-Gly-NH2, and Pro-Thr-Pro-Ser-NH2, etc.) were determined by HPLC with laser-induced fluorescence (LIF) detection. The peptides were quantitatively labelled with 4-(N,N-dimethylaminosulphonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) at 50 degrees C after 1 h in a 0.1 M borax (pH 9.3)-acetonitrile mixture. The rate of reaction decreases inversely with the molecular weight of the peptides. The mean value of fluorescent emission of the resulting DBD-peptides and DBD-peptide amides was 573 nm (excitation, 453 nm). The proline peptides, including bioactive peptides such as Pro-Leu-Gly-NH2 (release inhibitor of melanocyte-stimulating hormone), Pro-Thr-Pro-Ser-NH2 (IgA1 proteinase inhibitor) and Pro-Asp-Val-Asp-His-Val- Phe-Leu-Arg-Phe-NH2 [FMRF amide-like (Phe-Met-Arg-Phe-NH2) neuropeptide], were well separated by reversed-phase HPLC with water-acetonitrile containing 0.1% trifluoroacetic acid (TFA). The acetonitrile concentration in the mobile phase had a profound effect upon the retention times, and the capacity factors (k') were dependent on the hydrophobicity of the peptides. The structure of DBD-Pro-Leu-Gly-NH2 was identified by LC-atmospheric pressure chemical ionization MS. The chromatographic detection limits (S/N = 2) of the peptides with a 15-mW argon-ion laser at 488 nm were in the 6-28 fmol range. The detection limits were improved to 2-5 fmol with a microbore column. The detectability was two orders of magnitude higher than with a conventional fluorescence detector using xenon arc lamp.

Analysis of urinary organic acids by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

We developed a new method for the rapid determination of urinary organic acids using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. Mass spectra of authentic organic acids obtained in the negative-ion mode showed intense [M-H]- ions with some fragment ions. Urine samples of patients with methylmalonic aciduria, ornithine transcarbamylase deficiency, and phenylketonuria were extracted using anion-exchange columns. The mass chromatograms of the extracts showed some dominant peaks of abnormal metabolites characteristic of each disorder. This is a useful method for the analysis of urinary organic acids for the diagnosis of organic aciduria, because the sample preparation is simple.

Determination of pilocarpine in aqueous humour by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A new method has been developed for rapid analysis and determination of pilocarpine in aqueous humour using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. The chromatography was carried out on a reversed-phase phenyl column with 0.1% acetic acid-acetonitrile (95:5, v/v). Pilocarpine and its analogues, isopilocarpine, pilocarpic acid and isopilocarpic acid, were separated. An aqueous humour sample was deproteinized with methanol. After evaporation, the residue was dissolved in the mobile phase. The method was applied to the analysis of the metabolite in aqueous humour after the topical application of 2% pilocarpine (w/v) eye-drops. The main metabolite, pilocarpic acid, was easily identified. The protonated molecular ion of pilocarpine was used for the determination. The calibration curve had a good linearity within the concentration range investigated (2 ng to 10 micrograms/ml). The limit of determination was estimated to be an aqueous humour concentration of ca. 2 ng/ml. The method was applied to the determination of unchanged pilocarpine after the topical application of 2% pilocarpine (w/v) eye-drops.

The use of liquid chromatography-mass spectrometry for the identification and quantification of urinary iminodipeptides in prolidase deficiency

It has been reported that the urine of patients with prolidase deficiency contains various iminodipeptides with a carboxyl-terminal proline (hydroxyproline). These iminodipeptides have hitherto been detected indirectly by acid hydrolysis or enzymatic digestion, followed by amino acid analysis. In the present study, it was shown that X-Pro could be distinguished from Pro-X when the iminodipeptides were analysed directly by liquid chromatography coupled with atmospheric pressure ionization mass spectrometry (LC/API-MS), with scanning of the protonated molecule ions ([M+H]+). The same procedure also successfully quantified urinary iminodipeptides from patients with prolidase deficiency. A quantitative investigation of two siblings with prolidase deficiency revealed that the patient with severe clinical symptoms excreted more iminodipeptides than the other who did not have serious symptoms. LC/API-MS also revealed iminodipeptides (Gly-Hyp and Pro-Hyp) in the urine of the mother of the patients and in normal volunteers. Patients excreted much more Pro-Hyp than normal volunteers, whereas no quantitative differences were found between the mother and controls. In patients, the excretion of large quantities of X-Pro is due to their very low prolidase activity towards this type of substrate. In the erythrocytes of patients, prolidase activity towards X-Hyp was extremely low; even in the mother and normal volunteers, it was remarkably low in comparison with the activity against X-Pro.

Identification of N-acetyl-alpha-aminoadipic acid in the urine of a patient with alpha-aminoadipic and alpha-ketoadipic aciduria

A 3.5-year-old Japanese boy with a mild speech disturbance excreted a large amount of alpha-aminoadipic acid into the urine. The amino acid analysis using an amino acid analyser confirmed the presence of alpha-aminoadipic acid in both urine and plasma. We detected alpha-aminoadipic acid in the hydrolysate of the effluent and washwater fraction through cation exchange resin. This suggested the presence of acetylated derivatives and we identified N-acetyl-alpha-aminoadipic acid using liquid chromatography-atmospheric pressure ionization mass spectrometry (LC-API-MS). The concentrations of alpha-aminoadipic acid and N-acetyl-alpha-aminoadipic acid in the urine of a patient with alpha-aminoadipic aciduria were 376.9 nmol/mg creatinine and 18.1 nmol/mg creatinine, respectively. We also detected alpha-ketoadipic acid in the urine of this patient using LC-API-MS.

Determination of cystathionine and perhydro-1,4-thiazepine-3,5-dicarboxylic acid in the urine of a patient with cystathioninuria using column liquid chromatography-mass spectrometry

A method for the measurement of cystathionine and perhydro-1,4-thiazepine-3,5-dicarboxylic acid in the urine of a patient with cystathioninuria has been developed, using column liquid chromatography-mass spectrometry. Cystathionine and perhydro-1,4-thiazepine-3,5-dicarboxylic acid were determined by scanning the [M + H]+ ions of each compound. The recoveries were 80-92.4% for cystathionine and 80-100% for perhydro-1,4-thiazepine-3,5-dicarboxylic acid after ion-exchange treatment. The results agreed well with those obtained using an amino acid analyser. The concentrations found for cystathionine and perhydro-1,4-thiazepine-3,5-dicarboxylic acid were 1.289 +/- 0.099 mg/ml and 0.310 +/- 0.0067 mg/ml, respectively.

Identification of NAc-HCPC and NAc-beta-CEC, and qualitative analyses of sulphur amino acids in the urine of a patient with cystathioninuria using liquid chromatography/atmospheric pressure ionization mass spectrometry

Standard sulphur amino acids and various cystathionine metabolites in the urine of a patient with cystathioninuria were analysed using liquid chromatography/mass spectrometry with an atmospheric pressure ionization interface system. Very intense quasi-molecular ions ([M + H]+) of synthetic cystathionine, N-monoacetylcystathionine, perhydro-1,4-thiazepine-3,5-dicarboxylic acid, S-(3-hydroxy-3-carboxy-n-propyl)cysteine, S-(2-carboxyethyl) cysteine, S-(2-hydroxy-2-carboxyethyl)homocysteine, S-(carboxymethyl)homocysteine, N-acetyl-S-(3-hydroxy-3-carboxy-n-propyl)cysteine and N-acetyl-S-(2-carboxyethyl)cysteine were observed by this method. Quasi-molecular ions ([M + H]+) of these sulphur amino acids were observed in the urine sample of the patient with cystathioninuria, and N-acetyl-HCPC and N-acetyl-beta-CEC as N-substituted sulphur amino acids were also identified in the urine of the same patient.

Liquid chromatographic-mass spectrometric analysis for screening of patients with cystinuria, and identification of cystine stone

Analyses of amino acids in the urine of a normal human and of patients with heterozygous and homozygous cystinuria have been carried out, using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. A kidney cystine stone was also analysed by this system. Very intense quasi-molecular ions ([M + H]+) of standard cystine, arginine, lysine and ornithine were observed on mass chromatograms as base peaks. Mass chromatograms of the urine samples from a normal human and from patients with heterozygous and homozygous cystinuria were easily distinguishable. The retention times in the mass chromatogram and mass spectrum of kidney stone cystine was almost the same as that of authentic cystine.

Liquid chromatography-mass spectrometry for simultaneous analyses of iminodipeptides containing an N-terminal or a C-terminal proline

Simultaneous analyses of synthetic iminodipeptides containing an N-terminal proline or a C-terminal proline have been demonstrated using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The separation of iminodipeptides was carried out on a reversed-phase high-performance liquid chromatographic column using 0.1% aqueous trifluoroacetic acid-methanol (75:25, v/v, pH 2.0) as mobile phase. Very intense protonated molecular ions [M + H]+ of various synthetic iminodipeptides, Pro-Gly, Gly-Pro, Pro-Ala, Ala-Pro, Pro-Val, Val-Pro, Pro-Leu and Leu-Pro, were observed. Pro-Gly (Pro-X) and Gly-Pro (X-Pro) have the same protonated molecular ion (m/z 173), but the peaks of these compounds on the mass chromatograms were clearly distinguished by the differences of the retention times and mass spectra. The synthetic iminodipeptides containing an N-terminal proline added to urine samples from a patient with prolidase deficiency were also distinguished from iminodipeptides containing a C-terminal proline in urine samples from a patient with prolidase deficiency by scanning the [M + H]+ ion of each iminodipeptide. We established the method to measure simultaneously the various iminodipeptides containing an N-terminal or a C-terminal proline in biological samples.