Simultaneous determination of several amino acids, including homocysteine, cysteine and glutamic acid, in human plasma by isocratic reversed-phase high-performance liquid chromatography with fluorimetric detection

A method for the simultaneous measurement of two biologically important thiol compounds cysteine and homocysteine and five amino acids including neurotransmitters aspartate and glutamate is reported. This method utilized derivatization of compounds with o-phthalaldehyde in the presence of 2-mercaptoethanol following alkylation of the free sulfydryl group with iodoacetic acid followed by separation using reversed-phase high-performance liquid chromatography. These o-phthalaldehyde-2-mercaptoethanol-labeled compounds were separated within 30 min on a Spherisorb ODS-2 column with isocratic elution using 17% methanol, 0.04 M sodium phosphate buffer (pH 7.0), 0.002 M Na2EDTA and detected fluorimetrically (excitation 340 nm, emission 450 nm). Using this method, the concentrations of homocysteine, cysteine, glutamic acid. aspartic acid, asparagine, serine and glutamine in human plasma were determined.

Do different dialytic techniques have different atherosclerotic and antioxidant activities?

To compare the chronic effect of several dialytic techniques (bicarbonate dialysis, BHD; acetate free biofiltration, AFB; hemodiafiltration, HDF; paired filtration dialysis, PFD) on atherosclerosis and antioxidant activity, three different indices were created. The first (atherosclerotic index = AI) is formed using the sum of three plasma substances: MDA, Hcy, and Cys (malondialdehyde, homocysteine, cysteine). The second (antioxidant activity index = AOAI) is the sum of five erythrocyte (E) parameters: E-GSH, GPx, CAT, SOD, GR (E-glutathione, E-glutathione peroxidase, E-catalase, E-superoxide dismutase, E-glutathione reductase). The third (defense index = DI) is derived from the previous two: (AOAI - AI). The indices were so expressed as AI in mmol/L, AOAI in U/g hemoglobin (Hb), and DI in arbitrary units. These indices were calculated in 20 controls and 51 chronic HD patients (26 female, 25 male) before, during, and after the first session of the week. HD patients were divided according to their dialytic technique: BHD, n = 35; AFB, n = 5 patients; HDF, n = 7 patients; or PFD = 4 patients. All patients had been treated with a given technique for at least 12 months, before entering the study. As expected, HD patients had AI values higher than controls, both before and after the session, with a mean value of 541 (before) and 331 (after), whereas controls had a mean value of 205. The AOAI was lower than controls, both before and after the session, the mean value being 1,122 (before) and 1,582 (after), that of controls being 2,424. In all cases, PFD gave the best "acute" results; at the end of a PFD session, near normal values of AI, AOAI, and DI (defensive index = AOAI - AI) were obtained.

Equine dysautonomia (grass sickness) is associated with altered plasma amino acid levels and depletion of plasma sulphur amino acids

To determine whether equine dysautonomia (ED) is associated with alterations in plasma amino acid metabolism, plasma amino acid profiles were determined for horses with acute (n = 10), subacute (n = 6) and chronic (n = 7) ED and for healthy cograzing horses (n = 6) and control horses (n = 10). Horses with acute ED had perturbations in plasma amino acid profiles resembling those of severe protein malnutrition. In addition, horses with ED and cograzing healthy horses had depletion of the plasma sulphur amino acids cyst(e)ine and methionine. As similar plasma amino acid perturbations occur in subacute/chronic cyanide toxicity, the role of cyanogenic glycosides in the aetiology of ED warrants further study. Unfortunately, amino acid analysis cannot be used as a definitive premortem diagnostic test for ED, since there was overlap in the individual amino acid levels of control, cograzing and ED horses.

Late confirmation of acute methyl bromide poisoning using S-methylcysteine adduct testing

Methyl bromide poisoning is difficult to confirm because routine laboratory testing has not been reliable. Measurable levels of the parent agent are rapidly reduced, probably as a result of direct tissue chemical reaction. Serum bromide levels have been used as an indirect measure of exposure and/or toxicity but are inconsistent. Recently special testing has shown that protein adducts formed after exposure to methyl bromide may be a better measure of significant exposure. The S-methylcysteine adduct was used to confirm acute methyl bromide toxicity 10 weeks after an exposure. Additionally, genotyping of the glutathione-S-transferase TI enzyme in erthyrocytes from this case characterized a predisposition to the neurotoxic effects of methyl bromide.

The relation between plasma cysteine, plasma homocysteine and coronary atherosclerosis

Several studies have reported that elevated plasma levels of total homocysteine (tHcy) are related to an increased risk of cardiovascular disease. Only a few studies have looked at the effect of cysteine, another amino thiol, on cardiovascular disease risk. Therefore, in the present case-control study we compared plasma total cysteine (tCys) levels and plasma tHcy levels among subjects with severe coronary atherosclerosis (cases, n=131), subjects without severe coronary atherosclerosis (coronary controls, n=88) and healthy subjects (population-based controls, n=101). Cases were defined as those having > or =90% occlusion in one and > or =40% occlusion in a second coronary artery, while coronary controls had a maximum of 50% occlusion in only one coronary artery. Both males and females, aged 26--64 years were studied. We have previously reported that plasma tHcy is an independent risk factor for coronary atherosclerosis in this study population. In the present analysis, we found that cases had statistically significant higher mean plasma tCys levels than coronary controls and population-based controls (295.8+/-40.2, 279.0+/-35.5 and 282.6+/-32.4 micromol/l, respectively). The odds ratio (OR) of coronary atherosclerosis for the upper tertile of tCys compared with the bottom tertile was 2.5 (95% confidence interval (CI), 1.4--4.3). However, the association between tCys and coronary atherosclerosis was confounded to a great extent by risk factors (OR, 1.0; 95% CI, 0.5--2.0). The multivariate adjusted OR of coronary atherosclerosis per 1 S.D. increase in plasma tCys was 1.0 (95% CI, 0.8--1.3). The corresponding OR per 1 S.D. increase in plasma tHcy was 1.4 (95% CI, 1.1--1.8). We conclude that plasma tCys, unlike plasma tHcy, is not an independent risk factor for atherosclerosis.

Investigation of relationship between reduced, oxidized, and protein-bound homocysteine and vascular endothelial function in healthy human subjects

Previous studies investigating homocysteine and vascular disease have relied on total plasma homocysteine as the sole index of homocysteine status. We examined the dynamic relationship between vascular endothelial function and concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine to identify the homocysteine form associated with endothelial dysfunction in humans. We investigated 14 healthy volunteers (10 men, 4 women). Brachial artery flow-mediated dilatation was measured at baseline and at 30, 60, 120, 240, and 360 minutes after oral (1) L-methionine (50 mg/kg), (2) L-homocysteine (5 mg/kg), and (3) placebo. Plasma concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine were measured at each time point, and nitroglycerin-induced dilatation at was assessed at 0, 120, and 360 minutes. Flow-mediated dilatation fell, and concentrations of total, protein-bound oxidized, free oxidized, and reduced homocysteine increased after oral homocysteine and oral methionine (all P<0.05 for difference in time course compared with placebo). Flow-mediated dilatation showed a reciprocal relationship with reduced homocysteine during both homocysteine and methionine loading. In both loading studies, peak reduction in flow-mediated dilatation coincided with maximal reduced homocysteine concentrations. In contrast, there was no consistent relationship between flow-mediated dilatation and free oxidized homocysteine, protein-bound oxidized homocysteine, or related species. Nitroglycerin-induced dilatation was unchanged by oral homocysteine and oral methionine (P>0.10 compared with placebo). Reduced homocysteine is closely associated with endothelial dysfunction during oral methionine and oral homocysteine loading. Our observations support the hypothesis that reduced homocysteine is the deleterious form of homocysteine for vascular function in vivo and suggest a less important role for other homocysteine species.

Pre-column derivatization high-performance liquid chromatographic method for determination of cysteine, cysteinyl-glycine, homocysteine and glutathione in plasma and cell extracts

A sensitive high-performance liquid chromatographic method for quantification of sulphydryl and disulfide amino acids in human plasma using ultra violet spectrophotometric detection was developed. Precolumn derivatization with 5,5'-dithio-bis-nitrobenzoic acid (DTNB) and an optional pre-derivatization reaction with dithiothreitol allowed both quantitative reduction of disulfides for measurement of total amino acid levels and the measurement of the reduced forms. A dynamic range of 500 nmol/l-750 micromol/l allowed the major analytes of interest to be quantified in plasma without sample dilution. The assay is a sensitive and precise method for the determination of sulphydryl and disulfide amino acids in plasma and cell extracts.

Homocysteine metabolism in children with Down syndrome: in vitro modulation

The gene for cystathionine beta-synthase (CBS) is located on chromosome 21 and is overexpressed in children with Down syndrome (DS), or trisomy 21. The dual purpose of the present study was to evaluate the impact of overexpression of the CBS gene on homocysteine metabolism in children with DS and to determine whether the supplementation of trisomy 21 lymphoblasts in vitro with selected nutrients would shift the genetically induced metabolic imbalance. Plasma samples were obtained from 42 children with karyotypically confirmed full trisomy 21 and from 36 normal siblings (mean age 7.4 years). Metabolites involved in homocysteine metabolism were measured and compared to those of normal siblings used as controls. Lymphocyte DNA methylation status was determined as a functional endpoint. The results indicated that plasma levels of homocysteine, methionine, S-adenosylhomocysteine, and S-adenosylmethionine were all significantly decreased in children with DS and that their lymphocyte DNA was hypermethylated relative to that in normal siblings. Plasma levels of cystathionine and cysteine were significantly increased, consistent with an increase in CBS activity. Plasma glutathione levels were significantly reduced in the children with DS and may reflect an increase in oxidative stress due to the overexpression of the superoxide dismutase gene, also located on chromosome 21. The addition of methionine, folinic acid, methyl-B(12), thymidine, or dimethylglycine to the cultured trisomy 21 lymphoblastoid cells improved the metabolic profile in vitro. The increased activity of CBS in children with DS significantly alters homocysteine metabolism such that the folate-dependent resynthesis of methionine is compromised. The decreased availability of homocysteine promotes the well-established "folate trap," creating a functional folate deficiency that may contribute to the metabolic pathology of this complex genetic disorder.

The role of cysteine and homocysteine in venous and arterial thrombotic disease

Hyperhomocysteinemia is a risk factor for arterial and venous thrombosis, whereas few data are available on the total cysteine (tCy) levels in thrombophilic patients. We studied 82 patients with a previous myocardial infarction (MI; group 1), 68 patients with a previous deep venous thrombosis (group 2), and 100 control subjects (group 3). We assayed total homocysteine (tHcy) and tCy levels by high-performance liquid chromatography with fluorimetric detection. The odds ratios (ORs) for high levels of tCy and tHcy in venous thrombosis and MI were markedly increased in group 1 (fasting tCy: OR, 3.6; 95% confidence interval [CI], 1.6-11.2; postmethionine tCy: OR, 0.97; CI, 0.3-4.0; fasting tHcy: OR, 8.3; CI, 3.9-18.6; postmethionine tHcy: OR, 12.5; CI, 6.8-27.2) and in group 2 (fasting tCy: OR, 2.9; CI, 1.1-7.8; postmethionine tCy: OR, 0.86; CI 0.2-2.6; fasting tHcy: OR, 8.0; CI 3.6-18.0; postmethionine tHcy: OR, 11.0; CI, 6.0-22.1). Our data suggest that plasma tCy levels are a risk factor for venous thrombosis and MI independently of tHcy levels and that it may be appropriate to study both variables simultaneously to thoroughly study the methionine metabolism.

Reduction of Cr (VI) by cysteine: significance in human lymphocytes and formation of DNA damage in reactions with variable reduction rates

The induction of genotoxicity by Cr (VI) is dependent on its reductive activation inside the cell. Our recent studies have found that reduction of Cr (VI) by cysteine resulted in the formation of mutagenic Cr (III)-DNA adducts in the absence of oxidative DNA damage. In this work, we examined the formation of oxidative and Cr (III)-dependent types of DNA damage under a broader range of Cr (VI) and cysteine concentrations and investigated a potential role of this reducer in intracellular metabolism of Cr (VI). Peripheral lymphocytes from unexposed humans had 7.8-fold excess of glutathione over cysteine, whereas lymphocytes from stainless steel welders contained only 3 times higher amount of glutathione (p = 0.0009) which was entirely caused by the decrease in the concentration of glutathione. A strong correlation (r = 0.72) between the levels of both thiols was found in lymphocytes from controls. The number of DNA-protein crosslinks in lymphocytes from welders was 4.1 times higher than among controls, indicating the presence of Cr (VI)-dependent DNA damage. The average rate of Cr (VI) reduction by cysteine was approximately 5 times faster than that by glutathione. Higher reduction rate combined with the decrease in the intracellular concentration of glutathione should make cysteine a predominant Cr (VI)-reducing thiol in lymphocytes of welders. Analysis of the initial rates of Cr (VI) reduction by different concentrations of cysteine suggested the presence of one- and two-electron pathways, with one-electron mechanism dominating in the physiological range of concentrations. There was no detectable formation of DNA breaks or abasic sites under a broad range of Cr (VI) and cysteine concentrations, resulting in up to 68-fold differences in the rates of reduction and the production of as many as 3 Cr (III)-DNA adducts per 10 bp. The reactions with slow reduction rates (low concentrations of cysteine) led to the most extensive formation of Cr (III)-DNA adducts. In summary, these results further establish Cr (III)-DNA adducts as the major form of DNA damage resulting from Cr (VI) metabolism by cysteine. The role of cysteine in reduction of Cr (VI) becomes more significant under conditions of occupational exposure to Cr (VI)-containing welding fumes.

Novel approach for the determination of the redox status of homocysteine and other aminothiols in plasma from healthy subjects and patients with ischemic stroke

BACKGROUND

Plasma "redox" status can be assessed by measurements of reduced (r)-, free (f)-, oxidized (ox)-, and protein-bound (b)-homocysteine (Hcy) plus the related aminothiols cysteine, cysteinylglycine (CysGly), and glutathione (GSH), but sample collection has been complex. The redox status has not been determined in ischemic stroke patients and may provide increased understanding of its role in pathogenesis. We wished to examine the feasibility of this measurement in samples collected in readily available acidic sodium citrate.

METHODS

We measured aminothiols and their stability in stabilized protein-free filtrate using acidic sodium citrate (BioPool Stabilyte, pH 4.3) vs EDTA whole blood. Before analysis, plasma samples were also ultrafiltered to obtain a protein-free filtrate. The concentrations of total Hcy (tHcy), fHcy, and rHcy and their related aminothiols, cysteine, cysteinylglycine, and glutathione were simultaneously determined on acidic sodium-citrated blood using reversed-phase HPLC with fluorescence detection. Bound and oxidized aminothiols were calculated by difference using the concentrations of the total, free, and reduced fractions. Using this approach, we compared the redox status in newly diagnosed ischemic stroke patients (n = 20) and healthy age- and sex-matched subjects (n = 20).

RESULTS

tHcy, tCys, tCysGly, and tGSH concentrations in whole blood with Stabilyte were stable for 8 h; the reduced fraction of each aminothiol was stable for 4 h. Recovery in the protein-free filtrate was 90-100% for all reduced thiols in acidified sodium-citrated blood. Patients with ischemic stroke had higher plasma tHcy, fHcy, bHcy, rHcy, and oxHcy (P <0.0005) and higher plasma t-, f-, r-, and oxCys (P <0.05). t-, b-, and rCysGly concentrations were lower in the stroke patients (P <0.05), as were t-, b-, and oxGSH (P <0.005).

CONCLUSIONS

Collection of blood in acidic sodium citrate (BioPool Stabilyte) permits the determination of the redox status of Hcy and its related aminothiols, which may add to the understanding of their relationship to the etiology of cerebrovascular disease.

Blood glutathione and cysteine concentrations in twin children

Glutathione and cysteine are major antioxidants in blood that are associated with health and longevity. To ensure their measurement, careful attention to avoid auto-oxidation is necessary to stabilize the samples. Since no report of these compounds has been reported in children, our goal was to determine their levels of reduced and oxidized glutathione (GSH and GSSG) and cysteine (Cys and CSSC), To this end, 140 healthy children, ages 2 to 9 years from the Louisville Twin Study were studied. Blood samples were collected and analyzed for GSH, GSSG, Cys, and CSSC by our HPLC dual electrochemical method. The results showed that GSH and total GSH (GSH + GSSG) levels for monozygotic (MZ) twins were significantly higher (P < 0.001) than levels for dizygotic (DZ) twins. However, the opposite occurred for Cys and total Cys (Cys + CSSC) in that the levels were significantly higher for DZ twins than for MZ twins. (P < 0.005-0.013). In spite of this marked difference in zygosity, the within-pair correlations for twin pairs used for estimating heritability suggested that there was a major environmental influence for total GSH and total Cys. Finally. GSH levels were significantly lower for young (2-9 years) children than adults (P < 0.001).

Plasma total cysteine as a risk factor for vascular disease: The European Concerted Action Project

BACKGROUND

Elevated plasma total homocysteine (tHcy) is a risk factor for cardiovascular disease. Although cysteine is structurally similar and metabolically linked to tHcy, its relation to the risk of cardiovascular disease has received little attention. We studied the relation between plasma total cysteine (tCys) levels and the risk of vascular disease in the coronary, cerebral, and peripheral vessels.

METHODS AND RESULTS

This case-control study included 750 patients with vascular disease and 800 age- and sex-matched control subjects recruited from 19 centers in 9 European countries. Conventional risk factors for cardiovascular disease were recorded. In addition, plasma levels of tCys, tHcy, folate, B(6), B(12), and creatinine were measured. Overall, a U-shaped relationship was observed between tCys and risk of vascular disease. With the middle range of 250 to 275 micromol/L tCys used as the reference category, the adjusted risk of vascular disease at low (</=225 micromol/L) tCys levels was 2.1 (95% CI 1.2 to 3.6), and the risk at high (>300 micromol/L) tCys levels was 1.6 (95% CI 1.1 to 2.3). Different shapes of the dose-response relationship were seen for the 3 vascular disease categories. The relation with peripheral vascular and cerebrovascular disease was U-shaped, whereas a weak positive relation was observed with coronary heart disease.

CONCLUSIONS

Our data show a significant U-shaped relationship between tCys and cardiovascular disease after adjustment for tHcy, creatinine, and other cardiovascular disease risk factors.

Effect of long-term depletion of plasma methionine on the growth and survival of human brain tumor xenografts in athymic mice

Depletion of plasma methionine is expected to inhibit or reverse growth of methionine-dependent tumors; however, modulation of methionine and other sulfur amino acids is not a trivial task in experimental animals. L-Methioninase from Pseudomonas putida at 1,000 U/kg causes acute reduction of plasma methionine by 80% in mice, but recovery occurs within 14 hours. Restriction of dietary choline and replacement of dietary methionine with homocystine results in 50% chronic reduction of plasma methionine. A > 70% reduction can be accomplished with a diet deficient in methionine, homocystine, and choline, but ultimately this diet is lethal. Plasma methionine can be lowered to a steady state of < 5 microM in mice with a combination of dietary restriction of methionine, homocysteine, and choline and synchronous treatments with intraperitoneal injections of 1,000 U/kg L-methioninase and 25-50 mg/kg homocystine, each administered at 12-hour intervals. Modulation of plasma methionine by this means causes no weight loss or pathologies in liver or pancreas, and it does not markedly alter levels of cysteine, homocysteine, or glutathione in plasma or in hepatic tissue. When this procedure is applied to athymic mice bearing human medulloblastoma (Daoy) tumors subcutaneously, tumor growth is inhibited. Methionine deprivation arrests mitosis by blocking the cell cycle in G2 and induces apoptosis. Tumor stasis was achieved in 100% of treated animals within 4 days of treatment, and regression was seen in one-third of animals after a 10-day period. These data strongly support the use of methionine-depleting regimens for tumor treatments.

High cysteine levels in renal transplant recipients: relationship with hyperhomocysteinemia and 5,10-MTHFR polymorphism

BACKGROUND

Long-term survival of renal transplant recipients seems to be influenced by the occurrence of thromboembolic complications and cardiovascular disease. Preliminary data available in the literature found high levels of cysteine (Cy) as a risk factor for deep venous thrombosis independently of high homocysteine (tHcy) levels, but no data are available about Cy levels in renal transplant recipients.

METHODS

To investigate Cy, tHcy, and plasminogen activator inhibitor-1 (PAI-1) levels and the prevalence of 5,10-methylenetetrahydrofolate reductase (MTHFR) in renal transplantation, we studied 70 stable renal transplant recipients and 66 age- and sex-matched normal subjects as controls.

RESULTS

Cy, tHcy, and PAI-1 levels were significantly higher in renal transplant recipients with respect to controls (Cy: 254 micromol/L [117-466] vs. 198 micromol/L [99-331], P<0.001; tHcy: 17.0 micromol/L [4.0-68] vs. 8.1 micromol/L [2.0-24.0], P<0.00001; PAI-1: 16.8 IU/ml [5.1-45.5] vs. 7.9 IU/ml [4.0-18.0], P<0.00001). High Cy levels were detected in 35.8% of patients. Hyperhomocysteinemia, both in the fasting state and postmethionine loading test, was diagnosed in 90% of cases. The odds ratios for Cy and tHcy levels within the fourth quartile with respect to the other quartiles were markedly increased in renal transplant recipients even after adjustment for prevalent cardiovascular risk factors, glomerular filtration rate, tHcy and, Cy, respectively (Cy: 29.0 micromol/L [95% CI 7.0-111]; tHcy: 29.9 micromol/L [95% CI 7.5-118.1]). Fasting tHcy levels correlated well with PAI-1 (r=0.65; P<0.0001) but not with Cy levels (r=0.10; P=0.4). The prevalence of the MTHFR 677TT genotype in renal transplant recipients was not significantly higher in patients than in controls (mutant allele frequency: 0.48 in patients and 0.47 in controls) and was associated with significantly higher fasting and postmethionine tHcy levels both in controls and patients. After 2 months of vitamin supplementation, tHcy (Pre: 17.0 micromol/L [4.0-68]; Post: 7.5 micromol/L [2.3-21.9]; P<0.0001) and PAI-1 levels (Pre: 16.8 IU/ml [5.1-45.5]; Post: 10 IU/ml [2.0-25]; P<0.001) were significantly decreased, whereas Cy levels showed a small decrease that did not reach statistical significance (Pre: 254 micromol/L [117-466]; Post: 209 micromol/L [168-300]; P=0.3). Patients with the MTHFR 677TT genotype had the major percentage of decrease of tHcy levels with respect to the other genotypes.

CONCLUSION

In conclusion, this study demonstrates the presence of elevated Cy plasma levels in renal transplant recipients. Vitamin supplementation reduces tHcy but not Cy levels, and the amount of decrease seems to be influenced by the MTHFR genotype.

Determination of reduced, protein-unbound, and total concentrations of N-acetyl-L-cysteine and L-cysteine in rat plasma by postcolumn ligand substitution high-performance liquid chromatography

A high-performance liquid chromatographic assay was developed for the quantitative determination of the sulfur-containing amino acids N-acetyl-L-cysteine (NAC) and L-cysteine (Cys) in rat plasma. The thiols were separated by reverse-phase ion-pair chromatography, and the column eluent was continuously mixed with an iodoplatinate-containing solution. The substitution of sulfur of the thiol compound with iodide was quantitatively determined by measuring changes in the absorption at 500 nm. The low-molecular-weight disulfides and mixed disulfide conjugates of thiols with proteins were entirely reduced to the original reduced compounds by dithiothreitol. By reducing these two types of disulfides separately during sample pretreatment, the reduced, protein-unbound, and total thiol concentrations could also be determined. Validation testing was performed, and no problems were encountered. The limit of detection was approximately 20 pmol of thiol on the column. The present method was used to measure the plasma concentrations of NAC and Cys in the rat after a bolus intravenous administration of NAC, focusing on disulfide formation. The binding of NAC to protein through mixed disulfide formation proceeds in a time-dependent and reversible manner. Moreover, this "stable" covalent binding might limit total drug elimination, while the unbound NAC is rapidly eliminated. Consequently, the analytical method described in this study is very useful for the determination of plasma NAC and Cys, including disulfide conjugates derived from them.

Determination of allicin, S-allylcysteine and volatile metabolites of garlic in breath, plasma or simulated gastric fluids

Various components of garlic and aged garlic extract, including allicin, S-allylcysteine (SAC) and volatile metabolites of allicin were determined in breath, plasma and simulated gastric fluids by HPLC, gas chromatography (GC) or HPLC- and GC-mass spectrometry (MS). Data indicate that allicin decomposes in stomach acid to release allyl sulfides, disulfides and other volatiles that are postulated to be metabolized by glutathione and/or S-adenosylmethionine to form allyl methyl sulfide. SAC can be absorbed by the body and can be determined in plasma by HPLC or HPLC-MS using atmospheric pressure chemical ionization (APCI)-MS.

Parenteral vitamin B12 reduces hyperhomocysteinemia in end-stage renal disease

OBJECTIVE

The authors found considerably lower plasma total homocysteine (tHcy) concentrations in patients with end-stage renal disease (ESRD) on maintenance hemodialysis, who routinely received high-dose parenteral vitamin B12, than in comparable patients receiving much higher doses of folic acid but only replacement-dose oral vitamin B12. They therefore sought prospective evidence that high-dose parenterally administered vitamin B12 may partially ameliorate renal failure-associated hyperhomocysteinemia.

DESIGN

Open phase 2 clinical trial.

SETTING

Outpatient hemodialysis unit.

PATIENTS

Fourteen clinically stable patients on maintenance hemodialysis with normal baseline serum vitamin B12 concentrations.

INTERVENTION

Three parenteral injections of 1 mg vitamin B12 given at 4-week intervals.

OUTCOME MEASURES

Plasma tHcy and serum vitamin B12 concentrations were measured before, during and 7 months after the termination of vitamin B12 therapy.

RESULTS

The mean (and standard error) baseline plasma tHcy was 26.5 (1.8) micromol/L. The plasma tHcy value fell successively after each vitamin injection to reach a value of 23.6 (1.6) micromol/L 1 month after the final injection (p < 0.05), while the serum vitamin B12 concentration increased from 471 (42) pmol/L to 890 (74) pmol/L (p < 0.05). Seven months after the final injection, the serum B12 concentration had fallen and tHcy had risen to near their original values.

CONCLUSIONS

Three monthly vitamin B12 injections modestly but distinctly reduced tHcy concentrations in hemodialysis patients whose prior vitamin B12 status was normal. Randomized placebo-controlled clinical trials of longer duration and using larger or more frequent parenteral doses are indicated to determine whether administration of this safe and inexpensive vitamin can improve hyperhomocysteinemia in ESRD.

Homocysteine and lipid lowering agents. A comparison between atorvastatin and fenofibrate in patients with mixed hyperlipidemia

BACKGROUND

Hyperhomocysteinemia is a risk factor for cardiovascular disease. Elevation in homocysteine levels has recently been demonstrated during lipid lowering treatment with fibrates. We compared the effect of a statin and a fibrate (atorvastatin and fenofibrate) on plasma levels of homocysteine and other thiol compounds in hyperlipidemic patients.

METHOD AND RESULTS

The study was of open randomized, parallel design with a preliminary screening phase, and a 6 week placebo period. After the placebo period, patients were allocated randomly to atorvastatin or fenofibrate for a 6 month period. Plasma thiols were assayed by high pressure liquid chromatography with fluorescence detection. There were 29 patients in the fenofibrate group and 24 in the atorvastatin group. Fenofibrate induced a significant increase in both homocysteine and cysteine plasma levels (+35.8 and +18%, respectively, P<0.0001); by contrast, cysteinylglycine remained stable. There were no significant changes in any thiol compounds in the atorvastatin group. Both treatments induced a significant decrease in uric acid, although fenofibrate was noticeably more effective than atorvastatin (-22.8 and -6.4%, respectively). Fenofibrate induced a non-significant increase in creatinine (12%) while atorvastatin reduced it (4.7%, NS).

CONCLUSION

Our study confirms that the induction of elevations in plasma homocysteine and cysteine levels are a distinct feature of the pleiotropic effects of fibrates. Further studies are needed not only to investigate the potential deleterious effects of this modification, but also to define the specific mechanism which underlies such fibrate-mediated action.

Various forms of plasma cysteine and its metabolites in patients undergoing hemodialysis

The thiol tripeptide glutathione (GSH) is particularly important as an antioxidative protector in the cells. GSH is also a form of storage and transport of cysteine. Under physiological conditions, the kidney plays an essential role in GSH biodegradation to free cysteine via gamma-glutamyl cycle and subsequently in further metabolism of this sulfur amino acid. Our aim was to assess to what degree renal insufficiency affects the level of various cysteine forms and its metabolites (sulfates and sulfane sulfur compounds) in the plasma, and whole blood GSH levels. The concentrations of all the above mentioned sulfur compounds were measured in plasma of patients with end stage renal failure (ESRF) before and after dialysis and in a group of healthy controls. In plasma of patients with ESRF before dialysis tendency towards significant elevation of cystine, protein-bound cysteine and sulfates levels was evident. Simultaneously, a decrease of plasma level of sulfane sulfur compounds, products of anaerobic sulfur metabolism, and whole blood GSH concentration was found. As a consequence, the ratio between the reduced cysteine and the total cysteine concentration was markedly decreased. The dialysis session restore this ratio to the value observed in plasma of control individuals. These findings indicate disturbances in the thiol-disulfide equilibrium and show a higher oxidation status in plasma of patients with ESRF than in healthy controls.