Excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients

Hyperhomocysteinemia and assessment of its associated factors in renal transplant recipients: a single-center study in northern Iran

INTRODUCTION

Hyperhomocysteinemia (hyperHcy) is an important risk factor for atherosclerosis, which is currently a major cause of death in renal transplant patients (RTRs). The aim of this study was to determine the associated factors of hyperHcy in RTRs in northern Iran.

METHODS

In 148 stable RTRs, total serum homocysteine (tHcy) level, folate, serum albumin and creatinine, creatinine clearance, lipid status, body mass index (BMI), and blood cyclosporine levels (C0 and C2) were determined. The mean doses of cyclosporine A (mg/kg/day) were recorded.

RESULTS

In this analytic cross-sectional study the prevalence of hyperHcy was 70.3%. Hyperhomocysteinemia was defined as total serum homocysteine of 12 μmol/L or greater. The comparison of the group of 44 patients with tHcy level less than 12 and the group of 104 patients with tHcy level of 12 μmol/L or greater revealed that those subjects with hyperHcy were mostly younger, male, with lower BMI, history of glomerulonephritis, higher serum level of uric acid, and blood cyclosporine trough level (C0) and used higher doses of cyclosporine A. Significant correlation was found between tHcy level and recipients age, serum creatinine, BUN, folate concentrations, and creatinine clearance. However, multivariate analysis indicated that serum folate (P=0.01), vitamin B12 (P=0.05), creatinine (P=0.03), and BUN (P=0.05), and blood cyclosporine trough level (C0, P=0.005) were independently associated with tHcy levels.

CONCLUSION

HyperHcy persists after successful kidney transplantation in the majority of RTRs. Serum creatinine, BUN, folate and vitamin B12, and blood cyclosporine trough level (C0) are independently associated with tHcy levels.

Chronic treatment with cyclosporine affects systemic purinergic parameters, homocysteine levels and vascular disturbances in rats

Vascular disease is a major cause of morbidity and mortality among transplanted recipients and cyclosporine (CsA) treatment has been consistently implicated in this event. In this study we assessed total blood homocysteine levels (tHcy), ecto-nucleotidase activities and adenine nucleotide/nucleoside levels searching for parameters related to the mechanisms of vascular damage induced by chronic CsA treatment in non-transplanted rats. Thirty male Wistar rats were divided in three groups: control group treated with corn oil, CsA 5mg/kg and CsA 15 mg/kg, administered by daily gastric gavage during 8 weeks. CsA 15 mg/kg treatment increased blood levels of tHcy. Both CsA treatments (5mg/kg and 15 mg/kg) decreased adenine nucleotides hydrolysis by ecto-nucleotidases in serum, which negatively correlated with tHcy levels (r: -0.74, r: -0.63 and r: -0.63, p<0.004, for ATP, ADP and AMP, respectively). CsA 15mg/kg induced a statistically significant increase in ADP and decrease in adenosine (ADO) plasma levels compared to control group. THcy levels were positively correlated with plasma ADP levels and negatively correlated with ADO levels (r: 0.84, p<0.0001 and r: -0.68, p<0.0001, respectively). Rats under CsA 15 mg/kg treatment presented cell injury and inflammatory responses in the endothelium and intima layer of the aorta artery. In conclusion, blood ecto-nucleotidases activity, tHcy, and ADP and ADO levels may be implicated in vascular injury induced by CsA treatment.

Relationship between serum homocysteine and other parameters in renal transplant patients

INTRODUCTION

Hyperhomocysteinemia frequently occurs after renal transplantation. We therefore assessed whether serum homocysteine (Hcy) concentrations were correlated with clinical, paraclinical, and arterial Doppler parameters among renal transplant patients.

METHODS

A cross-sectional study was performed on 47 patients (30 males, 17 females) who received unrelated living donor renal transplants.

RESULTS

The mean serum Hcy concentration was 21.7 +/- 8.4 micromol/L (range = 5.8-48 micromol/L); 37 patients (79%) showed hyperhomocysteinemia (Hcy >or= 15 micromol/L). Serum Hcy was strongly related to body mass index (BMI; r = .43, P = .002), cyclosporine trough level (r = .44, P = .005), and serum creatinine concentration (r = .32, P = .028), but not to age, transplant duration, or sex. Multivariate analysis showed that only BMI (P = .003) and cyclosporine trough level (P = .0037) were independent predictors of serum Hcy concentrations. Hyperhomocysteinemia was more prevalent among patients taking mycophenolate mofetil (MMF) than azathioprine (86% vs 50%; P = 0.017). The hyperhomocysteinemia and normohomocysteinemia groups did not differ significantly in mean carotid intima-media thickness (IMT; 0.78 +/- 0.348 vs 0.77 +/- 0.419 mm, P = .97) or mean intrarenal resistive index (RI) (0.7 +/- 0.06 vs 0.7 +/- 0.06, P = .85). The two groups also did not differ in sex prevalence, diabetes, C-reactive protein >or= 5 mg/L, or mean low-density lipoprotein, high-density lipoprotein, and mean arterial pressure (MAP) values.

CONCLUSION

Serum Hcy correlated with higher cyclosporine trough levels and obesity. Hyperhomocysteinemia was more common among patients taking MMF than azathioprine, but had no effect on intrarenal RI or carotid IMT.

Homocysteine in Renal Transplant Recipients: Association with Transplant Duration and Renal Function

BACKGROUND

Hyperhomocystinemia is an established risk factor for cardiovascular events and has been identified as an important cause of morbidity and mortality in renal transplant recipients. This investigation was aimed to determine the effect of age and transplant duration on serum total homocysteine (tHcy) levels in renal transplant recipients.

METHODS

We analyzed serum levels of tHcy, albumin, alkaline phosphatase, alanine transferase, bilirubin, calcium, corrected calcium, cholesterol, creatinine, folate, phosphate, potassium, sodium, triglycerides, urea and vitamin B12 in 88 transplant patients (ages, 14-67 years; transplant duration, 1-252 months) and 60 control subjects.

RESULTS

Our results showed significant hyperhomocystinemia in transplant patients (19.92 +/- 0.72) as compared to controls (9.28 +/- 0.25), while male subjects in both groups had significantly higher tHcy than females. There was no correlation between patients' age and serum tHcy, whereas the time after transplantation was significantly correlated with tHcy (r=0.318, P<0.01). A significant correlation was observed between tHcy and serum urea, creatinine, vitamin B12 and potassium in renal transplant patients.

CONCLUSION

This study clearly demonstrated significant hyperhomocystinemia and renal impairment in transplant recipients. A time-course increase in serum tHcy during posttransplant duration warrants long-term monitoring of patients for effective clinical management.

Cardiovascular complications after renal transplantation and their prevention

By the time of renal transplantation, end-stage renal disease patients have a huge burden of cardiovascular disease (CVD) and are heavily saturated with atherosclerotic risk factors. Worsening of preexisting risk factors or new CVD risk factors may develop in the posttransplant period consequent in part to the diabetogenic and atherogenic potential of immunosuppressive drugs. The annual risk of a fatal or non-fatal CVD event of 3.5 to 5% in kidney transplant recipients is 50-fold higher than the general population. Renal allograft dysfunction, proteinuria, anemia, moderate hyperhomocysteinemia and elevated serum C-reactive protein concentrations, each dependently confer greater risk of CVD morbidity and mortality in the posttransplant period. Long-term care of renal transplant recipients should programmatically incorporate the recommendations of the National Kidney Foundation Working Groups and European Best Practice Guidelines Expert Group on Renal Transplantations into the management of hypertension, dyslipidemia, smoking, and posttransplant diabetes mellitus. Timely utilization of coronary revascularization procedures should be undertaken as these treatments are equally effective in the kidney transplant population.

Reviews: Altered Laboratory Findings Associated with End-Stage Renal Disease

Several laboratory parameters can be altered in advanced renal failure. Results may be difficult to interpret and may become misleading and unreliable in such a context. On the other hand, some of the alterations may reflect real abnormalities. Thus sufficient knowledge and careful judgment are required by the clinician. We reviewed different publications related to biochemical anomalies in renal failure and report some of the main findings. The sections are divided as follows: cardiovascular risk factors and markers, inflammation markers, pancreatic and liver function tests, hormones, bone turnover indices and parathyroid hormone assays, tumor markers, carbohydrate metabolism indicators, and others. The information provided should be useful to clinicians involved in the care of renal failure patients.

Effect of cyclosporine A on total homocysteine level in a rabbit model

BACKGROUND

Moderate hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Cyclosporine (CsA) has been suggested to interfere with folate-assisted remethylation of homocysteine, thus causing hyperhomocysteinemia. But, this issue is controversial. In this experimental study, we attempted to determine the association between CsA administration and total homocysteine levels. Working with rabbits that have normal creatinine levels, we obviated the misleading effects of renal functional variations, which are the most important confounding factors affecting total homocysteine level.

METHODS

Male New Zealand rabbits fed a standard quantity of diet received 10 days of subcutaneous injections of 10 mg/kg per day CsA. After these loading doses, CsA (20 mg/kg) was administered subcutaneously three times a week for 20 days. After first 30 days, the rabbits were followed for another 30 days without CsA therapy. Plasma creatinine, BUN, and total homocysteine levels were measured on days 0, 10, 30, and 60.

RESULTS

There were no significant changes in BUN results on days 0, 10, 30, and 60 (P > .05). There was a slight, but significant, increase in mean creatinine levels during CsA administration (P < .01). However, the mean creatinine levels remained in the normal ranges during the 60 days of study. No significant changes were observed in total homocysteine levels (P > .05) compared to baseline, 10-, 30-, and 60-day values.

CONCLUSION

Our experimental research minimized confounding factors. It showed that CsA does not increase total homocysteine levels, confirming clinical studies that reported no association between CsA and total homocysteine.

L-folic acid supplementation in healthy postmenopausal women: effect on homocysteine and glycolipid metabolism

CONTEXT

Hyperhomocysteinemia as well as alterations of glycemic and lipidic metabolism are recognized as risk factors for cardiovascular diseases.

OBJECTIVE

The aim of this study was to examine the effect of L-folic acid supplementation on homocysteine (Hcy) and related thiols, such as cysteine (Cys) and Cys-glycine (Cys-Glyc) pathways and their relationship to glucose, insulin, and lipidic metabolism in normoinsulinemic postmenopausal women.

DESIGN

This study was a randomized placebo, not double-blind, trial.

SETTING

The study was performed in an academic research center.

PATIENTS OR OTHER PARTICIPANTS

Twenty healthy postmenopausal women were selected. No patient was taking drugs known to affect lipid or glucose metabolism.

INTERVENTION(S)

Patients underwent two hospitalizations before and after 8 wk of L-acid folic (7.5 mg/d) or placebo administration. The glycemic metabolism was studied by an oral glucose tolerance test and a hyperinsulinemic euglycemic clamp. Hcy metabolism was studied by a standardized oral methionine-loading test.

MAIN OUTCOME MEASURE(S)

Hcy, Cys, and Cys-Glyc, basally and after a methionine loading test, were measured. Basal insulin, glucose, and peptide C levels as well as area under the curve for insulin, area under the curve for peptide, hepatic insulin extraction, and metabolic index were assayed. The total cholesterol, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol levels and the cholesterol/HDL and LDL/HDL ratios were also measured.

RESULTS

The total basal Hcy concentration and the plasma postmethionine loading Hcy values were significantly decreased (P < 0.01) in L-folic acid-treated patients, whereas postmethionine loading Cys-Glyc levels were markedly increased (P < 0.02). Furthermore, L-folic acid intake induced a significant improvement in carbohydrate metabolism through an increase in fractional hepatic insulin extraction (P < 0.05) and peripheral insulin sensitivity (P < 0.02) in normoinsulinemic women. HDL levels considerably increased, inducing an improvement in other atherosclerotic indexes, such as cholesterol/HDL and LDL/HDL ratios (P < 0.03).

CONCLUSIONS

These results show that folic acid supplementation lowers plasma Hcy levels and improves insulin and lipid metabolism, reducing the risk of cardiovascular disease.

Impact of Homocysteinemia on Long-Term Renal Transplant Survival

AIM

We prospectively followed a cohort of 202 renal transplant recipients for 5 years to examine the impact of fasting homocysteinemia on long-term patient and renal allograft survival.

METHODS

Cox proportional hazards regression analysis was used to identify independent predictors of all-cause mortality and graft loss.

RESULTS

Hyperhomocysteinemia (tHcy >15 micromol/L) was present in 48.7% of the 202 patients, predominantly among men (55.8%) as opposed to women (37.1%). At the end of the follow-up period, 13 (6.4%) patients had died including 10 from cardiovascular disease, and 23 had (11.4%) had lost their grafts. Patient death with a functioning allograft was the most prevalent cause of graft loss (13 recipients). Levels of tHcy were higher among patients who died than among survivors (median 23.9 vs 14.3 micromol/L; P = .005). Median tHcy concentration was also higher among the patients who had lost their allografts than those who did not (median 19.0 vs 14.1 micromol/L; P = .001). In a Cox regression model including gender, serum creatinine concentration, transplant duration, traditional cardiovascular risk factors, and associated conditions, such as past cardiovascular disease, only tHcy concentration (ln) (HR = 5.50; 95% CI, 1.56 to 19.36; P = .008) and age at transplantation (HR = 1.07; 95% CI, 1.02 to 1.13; P = .01) were independent predictors of patient survival. After censoring data for patient death, tHcy concentration was not a risk factor for graft loss.

CONCLUSIONS

This prospective study shows that tHcy concentration is a significant predictor of mortality, but not of graft loss, after censoring data for patient death.

Hyperhomocysteinemia and MTHFR C677T and A1298C polymorphisms are associated with chronic allograft nephropathy in renal transplant recipients

Hyperhomocysteine has been reported to be an important risk factor for the development of atherosclerosis. Identification of risk factors, such as hyperhomocysteinemia, is crucial for a better understanding of the events that lead to degenerative processes in the vascular system and for a correct understanding of the potential role of methylene-tetrahydrofolate reductase enzymes (MTHFR) to help in the treatment of vascular disease observed in chronic allograft nephropathy (CAN). In this study we analyzed the plasma homocysteine concentrations and MTHFR C677T and A1298C polymorphism frequencies among 110 renal transplant recipients (53 with CAN and 57 with normal renal function). All recipients had undergone renal transplantation at least 12 months prior to this investigation to establish a possible correlation with the posttransplant outcome. Plasma homocysteine concentrations were measured by liquid chromatography-tandem mass spectrometry and MTHFR polymorphisms were investigated by the PCR-RFLP technique. The results demonstrated that in renal transplant recipients, hyperhomocysteinemia in addition to the presence of the allelic variants for both MTHFR polymorphisms (677T/1298C) might play a role as an additional risk factor for CAN. We understand that analysis of these polymorphisms might have a role in the CAN process. Therefore, studies to evaluate their presence in renal transplant patients may be extremely useful to individualize immunosuppressive protocols to inhibit or retard the progression of CAN.

Idiopathic intracranial hypertension in cystinosis

OBJECTIVES

To report a high frequency of idiopathic intracranial hypertension (IIH) in patients with cystinosis and to speculate on the relationship between these two disorders.

STUDY DESIGN

Retrospective case series and review of the literature regarding risk factors for the development of IIH in cystinosis.

RESULTS

Eight patients with cystinosis had documented papilledema, normal neuroimaging of the brain, cerebrospinal fluid (CSF) opening pressure greater than 200 mm of H2O, and normal CSF composition. No common medication, condition, or disease except cystinosis was found in these persons. Six of the patients had received prednisone, growth hormone, cyclosporine, oral contraceptives, vitamin D, or levothyroxine at the time of onset of IIH. Five patients had previous renal transplants.

CONCLUSION

No single risk factor for the development of IIH linked IIH to cystinosis in our patients. However, thrombosis susceptibility as a result of renal disease or impaired CSF reabsorption in the arachnoid villi as a result of cystine deposition might lead to the development of IIH in cystinosis.

Plasma homocysteine levels in living kidney donors before and after uninephrectomy

An increased prevalence of hyperhomocysteinemia has been observed among patients with end-stage renal disease, and numerous studies have demonstrated that kidney function is one of the most important determinants of plasma total homocysteine (tHcy) concentration. In an effort to understand the mechanism of hyperhomocysteinemia in renal disease, we chose, as our model, living kidney donors who had undergone uninephrectomy. We studied 10 living kidney donors and measured fasting plasma tHcy, plasma creatinine, folate, vitamins B(12) and B(6), and high-sensitivity C-reactive protein (hsCRP) 24 hours before nephrectomy and 2 days, 6 weeks, and 6 months after nephrectomy compared to the values 24 hours before nephrectomy. Mean fasting tHcy and creatinine concentrations were significantly higher in donors 2 days, 6 weeks and 6 months after nephrectomy they were 24 hours before nephrectomy. Both the increases in tHcy levels 2 days after nephrectomy and subsequent decreases 6 weeks and 6 months after are paralleled by the changes in plasma creatinine values, although neither returned to its presurgery value. Decreases in tHcy are significantly correlated with decreases in creatinine values. The B vitamins were unchanged, and the hsCRP level was increased 2 days after surgery but had returned to the baseline level after 6 weeks. We conclude that tHcy and creatinine levels parallel each other after uninephrectomy and that the gradual decrease in tHcy is accounted for by hypertrophy of the remaining kidney. Our results, the first to be obtained from living kidney donors, support the hypothesis that renal metabolism of tHcy is the mechanism responsible for the correlation between renal function and plasma tHcy level.

Hyperhomocysteinemia in patients with Behçet’s disease: is it due to inflammation or therapy?

Considerable discrepancies exist in the literature with respect to plasma total homocysteine (tHcy) levels in Behçet's disease (BD). The aim of this study was to evaluate tHcy concentrations in these patients. Thirty-two patients with BD and 20 age- and body mass index-matched healthy volunteers were enrolled. Plasma tHcy concentrations were significantly higher, while vitamin B12 and folate levels were significantly lower in patients with thrombosis and eye involvement than those without. C-reactive protein levels also correlated significantly in a negative manner with vitamin B12 and folate but positively with tHcy. In conclusion, increased use or accelerated catabolism of folate and vitamin B12 due to chronic inflammation and moderately increased tHcy concentrations related with deficiency of these cofactors, and immunosuppressive drug administration might be potential threats of vascular disease in BD.

Strategies for ensuring effective surveillance in post-transplant patients: practical organization and clinical evaluation

Results of renal transplantation have improved steadily over the years. This article reviews the current status of patient and graft survival and discusses major causes of mortality and renal allograft failure. Review of recent literature demonstrates that the traditional enemies of transplantation, acute rejection and opportunistic infections are no longer major problems facing transplantation. Chronic graft nephropathy and death with functioning graft due to cardiovascular disease are the main challenges in the current era. An impact of an early graft thrombosis, recurrent renal disease and post-transplant malignancies are also reviewed. Chronic graft nephropathy is examined in a context of differences between two calcineurin inhibitors, cyclosporin microemulsion and tacrolimus. Strategies of post-transplant surveillance are suggested.

Meta-analysis of plasma homocysteine, serum folate, serum vitamin B12, and thermolabile MTHFR genotype as risk factors for retinal vascular occlusive disease

PURPOSE

To assess the role of plasma total homocysteine (tHcy) levels, serum folate and vitamin B(12)levels, and homozygosity for the thermolabile methylenetetrahydrofolate reductase genotype (TT) as risk factors for retinal vascular occlusive disease.

DESIGN

Meta-analysis of literature.

METHODS

A MEDLINE search was performed to identify all published case-control studies of plasma tHcy levels, serum folate and vitamin B(12) levels, and TT genotype in persons with retinal vascular occlusive disease. Main outcome measures included calculation of plasma tHcy, serum folate, and serum vitamin B(12) standard differences and odds ratios (OR) of TT genotype between cases and controls.

RESULTS

In total, 614 patients with all types of retinal vein occlusion had higher plasma tHcy levels than 762 control subjects (standard difference, 0.867; 95% confidence interval [CI] = 0.735, 0.999; P <.001). Plasma tHcy levels were also higher in 154 patients with retinal artery occlusion compared with 358 control subjects (standard difference 1.174; 95% CI = 0.947, 1.402; P <.001). Serum folates, but not vitamin B(12) levels, were lower in 287 patients with retinal vascular occlusion than in the same number of control subjects (standard difference, 0.508; 95% CI = 0.340, 0.675; P <.001; and -0.060; 95% CI = -0.024, 0.104; P =.474, respectively). Similar proportions of 690 patients with retinal vein occlusion and 2754 control subjects demonstrated the TT genotype (OR = 1.332; 95% CI = 0.995, 1.783; P =.054) as did 152 patients with retinal artery occlusions and 435 control subjects (OR = 1.716; 95% CI = 0.977, 3.014; P =.060).

CONCLUSIONS

Retinal vascular occlusion is associated with elevated plasma tHcy levels and low serum folate levels, but not serum vitamin B(12) levels and TT genotype. Until a prospective multicenter trial is undertaken, plasma tHcy levels and serum folate levels should be determined in patients with retinal vascular occlusions, and dietary supplementation with low doses of folate and vitamin B(12) should be considered for affected persons.

Homocysteine and cardiovascular disease in renal disease. Review Article

Elevated homocysteine (hyperhomocysteinaemia) in renal patients is a major concern for physicians. Although cause and effect between homocysteine and cardiovascular disease (CVD) has not been established in either the general population or renal patients, there is much evidence that this relationship does exist. Purported mechanisms that may explain this effect include increases in endothelial injury, smooth muscle cell proliferation, low-density lipoprotein oxidation and changes in haemostatic balance. Renal patients have a much greater incidence of hyperhomocysteinaemia and this may be explained by decreases in either the renal or extrarenal metabolism of the compound. We conclude that data from long-term placebo-controlled trials are urgently required to determine whether hyperhomocysteinaemia in renal patients is a cause of CVD events and requires therapeutic targeting.

Vitamin supplementation reduces the progression of atherosclerosis in hyperhomocysteinemic renal-transplant recipients

BACKGROUND

We previously demonstrated among renal-transplant recipients (RTRs) a high prevalence of hyperhomocysteinemia, which might account for their elevated cardiovascular risk. The purpose of our study was to document, in hyperhomocysteinemic RTRs, the effect of vitamin supplementation on carotid intima-media thickness (cIMT), which is an early sign of atherosclerosis.

METHODS

A total of 56 stable hyperhomocysteinemic RTRs were randomly assigned to vitamin supplementation (folic acid 5 mg/day; vitamin B(6) 50 mg/day; vitamin B(12) 400 microg) (group A) or placebo treatment (group B) for 6 months. All subjects underwent cardiovascular risk-factor assessment, including fasting homocysteine (Hcy) levels assay, and high resolution B-mode ultrasound to measure the intima-media thickness of common carotid arteries, at time of enrollment and after 6 months.

RESULTS

Fasting Hcy levels markedly decreased in group A after treatment (21.8 [15.5-76.6] micromol/L vs. 9.3 [5.8-13] micromol/L; P<0.0001), whereas no significant changes were observed in group B (20.5 [17-37.6] micromol/L vs. 20.7 [15-34] micromol/L; P=not significant). In group A, cIMT significantly decreased after treatment (0.95+/-0.20 mm vs. 0.64+/-0.17 mm; P<0.0001). All except one patient showed a reduction of cIMT and the mean percentage of cIMT decrease was -32.2+/-12.9%. Patients with methylenetetrahydrofolate reductase (MTHFR) C677T +/+ genotype, with higher Hcy levels, had the major percentage of decrease of Hcy with respect to the other genotypes (mean decrease: MTHFR +/+ 74.8+/-5.7%; MTHFR +/- 58.1+/-10%; MTHFR -/- 56.3+/-8.6%). In hyperhomocysteinemic patients without vitamin supplementation (group B) we documented a significant increase in cIMT after 6 months (0.71+/-0.16 mm vs. 0.87+/-0.19 mm; P<0.05). In 19 of 28 subjects we observed an increase in cIMT, and in 9 of 28 the cIMT was unmodified. The mean percentage of cIMT increase was + 23.3+/-21.1%.

CONCLUSIONS

Our results demonstrate a beneficial effect of the treatment of hyperhomocysteinemia by vitamin supplementation on cIMT in a group of RTRs.

Variability of post-methionine load plasma homocysteine assays

BACKGROUND

Numerous variations of the methionine load test are frequently used as dynamic function tests to assess homocysteine metabolism. Lack of standardization impedes inter-laboratory comparisons. Criteria based on biological variation are suggested to standardize the methionine load test.

METHODS

Weekly methionine load tests (n=5) with blood sampling at 0, 4, 6 and 8 h were performed on 15 young men. For both basal and post-methionine load homocysteine measurements, total variance (sigma(S)(2)), within-subject variance (sigma(I)(2)), between-subject variance (sigma(G)(2)) and analytical variance (sigma(A)(2)) were calculated from an appropriate analysis of variance (ANOVA).

RESULTS

Plasma homocysteine concentrations measured 6 h after methionine loading had analytical, within-subject and between-subject coefficients of variation of 5.2%, 17.5% and 9.7%, respectively. Measurements at 4 h had a higher within-subject coefficient of variation. Adjustment of post-methionine load homocysteine concentrations for basal levels resulted in considerable increases of all the measures of variation.

CONCLUSIONS

Adjustment of post-methionine load plasma homocysteine concentrations for basal levels does not improve the interpretation of changes in serial results due to the higher analytical and biological variance of adjusted concentrations. It is suggested that the methionine load test is standardized to a single, unadjusted homocysteine measurement at 6 h.

Emergent cardiovascular risk factor: homocysteine

Homocysteine is an independent, modifiable risk factor for cardiovascular disease. It is an intermediate amino acid formed during the metabolism of methionine. Plasma homocysteine is normally < or = 12 micromol/L, but when elevated has many deleterious cardiovascular effects. This review explains homocysteine metabolism, the effects of elevated homocysteine, factors contributing to high homocysteine, and its measurement. Risk factors for elevated homocysteine and intervention with B vitamins are discussed. Cardiovascular nurses are encouraged to facilitate homocysteine awareness through a variety of educational means.

Influence of mycophenolic acid and tacrolimus on homocysteine metabolism

BACKGROUND

The effect of mycophenolate mofetil (MMF) on homocysteine (Hcy) metabolism is unknown.

METHODS

This in vitro study examined whether mycophenolic acid or tacrolimus influences the formation of Hcy as determined by measuring the total Hcy (tHcy) concentrations in supernatants of human renal proximal tubule epithelial cells. Cells were incubated with and without vitamins (folate, vitamin B6 and B12) in the presence of low or high methionine concentrations at different mycophenolic acid (0, or 5, or 20 microg/mL) or tacrolimus (0, or 10, or 25 ng/mL) concentrations for 24, 48 or 72 hours. The concentration of tHcy in culture supernatants was measured by a fluorescence polarization immunoassay. The effect of MMF on tHcy plasma levels was also examined in 454 kidney graft recipients.

RESULTS

Comparisons of tHcy levels in culture supernatants over time by four way ANOVA showed that methionine concentration (P < 0.00001), time (P < 0.00001), vitamins (P = 0.002728), and mycophenolic acid concentration (P = 0.000095) were all significant predictors of tHcy concentrations. This was due to significantly lower tHcy levels with using mycophenolic acid at a high concentration versus control at the 48- and 72-hour time points. By contrast, tacrolimus showed no effect in vitro. Among the kidney graft recipients, male patients on MMF therapy showed lower plasma tHcy concentrations as compared to those on azathioprine (P = 0.03).

CONCLUSION

Our study suggests a tHcy lowering effect of MMF in male transplant recipients, which improves the cardiovascular disease risk profile, whereas tacrolimus showed no effect.

Hyperhomocysteinemia in renal transplant recipients

Renal transplantation is a commonly performed curative procedure for end-stage renal disease. With the increase in renal allograft half-lives, attention is now being focused on cardiovascular morbidity and death in the renal transplant recipient (RTR) population. Among the more novel cardiovascular disease (CVD) risk factors for which this group is at risk is hyperhomocysteinemia. Hyperhomocysteinemia has been associated with an increased risk of CVD, although prospective randomized trials designed to prove causality are still ongoing. Since plasma total homocysteine levels are inversely related to renal function, RTRs have a greatly increased prevalence of hyperhomocysteinemia. Other determinants of homocysteine include B-vitamins, albumin, age, and genetic polymorphisms. Although RTRs are resistant to the typical B-vitamin doses used to correct hyperhomocysteinemia in the general population, they do respond to supraphysiologic dose therapy. In terms of prevalence, etiology, and treatment of hyperhomocysteinemia, RTRs are very similar to the much larger chronic renal insufficiency population. For this reason, RTRs have been chosen as an ideal study population in investigating the effect of reducing hyperhomocysteinemia on CVD outcomes.

Treatment of hyperhomocysteinemia with folic acid reduces oxidative stress in renal transplant recipients

BACKGROUND

We conducted a prospective, uncontrolled, open study to assess the relationship between homocysteine (tHcy) and oxidative stress in chronic, stable, renal transplant recipients (RTR).

METHODS

Included in the study were 17 chronic, stable RTR. All the patients received folic acid (5 mg/day). tHcy and total antioxidant capacity (TAOC) were measured before and at the end of the study period.

RESULTS

Mean tHcy concentration was 26+/-10 micromol/L. tHcy significantly decreased during the study period (26+/-10 vs. 18+/-7 micromol/L; P<0.001). There was a significant inverse relationship between TAOC and tHcy (r= -0.33; P=0.01). TAOC significantly increased during the study period (1.49+/-0.23-1.78+/-0.6; P<0.001). There was an inverse relationship between the variation in tHcy and the variation in TAOC (r= -0.44; P=0.01).

CONCLUSION

Our results demonstrate that hyperhomocysteinemia contributed to increased oxidative stress in RTR. tHcy-lowering treatment with folic acid may lower oxidative stress.

Folate status among patients with non-small cell lung cancer: a case-control study

BACKGROUND AND OBJECTIVES

This case control study explored the purported inverse relationship between folate status and lung cancer development.

METHODS

Folate status of 46 postoperative non-small cell lung cancer (NSCLC) patients was compared to that of 44 non-cancer patients. Cancer patients had completed treatment > 3 months prior and had no evidence of cancer. Ineligibility criteria for all patients included (1) > 2 alcoholic drinks/day (2) ongoing tobacco use, or (3) folate supplementation > 400 microg/day.

RESULTS

No differences were found between groups in serum and RBC folate after adjustment for age and use of folate-interfering medications: geometric means (GM) x /geometric standard error (GSE): 7.9 ng/ml x /1.1 vs. 7.8 ng/ml x /1.1, respectively (P = 0.91) for serum folate; 264 ng/ml x /1.1 vs. 263 ng/ml x /1.1, respectively (P = 0.97) for RBC folate. Age- and creatinine-adjusted homocysteine was no different between groups: GM x /GSE: 9.4 micromol/L x /1.0 vs. 8.6 micromol/L x /1.0, respectively (P = 0.17). No difference were seen in folate intake. Frequencies of the homozygous genotype for the MTHFR polymorphism, an enzyme important in folate metabolism and associated with a reduced risk of other cancers, were no different.

CONCLUSIONS

This case control study does not support the hypothesis that low folate is an independent risk factor for NSCLC.

Serum cystatin C is an independent predictor of total homocysteine levels in stable Korean renal transplant recipients with normal serum creatinine

OBJECTIVES

To examine the determinants of fasting plasma total homocysteine (tHcy) levels such as cystatin C, serum creatinine (SCr), estimated glomerular filtration rate (GFR) from Cockroft-Gault equation, albumin, plasma folate, vitamin B12, and pyridoxal-5'-phosphate (PLP) among Korean renal transplant recipients (RTR) with normal SCr levels (< or =1.4 mg/dL).

DESIGN

Cross-sectional study.

SETTING

Nephrology and Transplant Service, Catholic University Kangnam St. Mary's Hospital, Seoul, Korea.

PARTICIPANTS

Fifty-one chronic stable Korean RTR with normal SCr levels (< or =1.4 mg/dL) 6 months or more following transplantation.

MEASURES

Medical record review, anthropometric measurements, and overnight (10 to 14 hours) fasting blood samples for measurement of plasma tHcy, folate, vitamin B12, PLP, SCr, albumin, and cystatin C.

RESULTS

General linear regression model including age, gender, vitamin status, and measurements of renal function showed that cystatin C and folate were independent predictors of tHcy levels. The partial regression coefficient for folate was -0.444 (P <.01) and for cystatin C, it was +0.334 (P <.05). SCr, estimated GFR, vitamin B12, PLP, age, and gender were not independent predictors of tHcy levels in this model.

CONCLUSION

Both cystatin C and folate status were major independent determinants of fasting tHcy levels in the subgroup of Korean RTR with normal SCr.

Cystatin C Is an Independent Predictor of Fasting and Post-Methionine Load Total Homocysteine Concentrations among Stable Renal Transplant Recipients

Background: An increased prevalence of hyperhomocysteinemia with an increased incidence of cardiovascular disease events has been reported among stable renal transplant recipients (RTRs). Preliminary studies in a small number of these individuals have shown that serum creatinine and cystatin C, both markers of kidney function and glomerular filtration rate, are independent determinants of fasting tHcy concentrations; however, determinants of tHcy concentrations after a methionine load have not been studied.

Methods: We determined the prevalence of both fasting and 4-h post-methionine load (PML) tHcy concentrations in 78 stable RTRs and compared the role of cystatin C with the role of serum creatinine as determinants of fasting and PML tHcy.

Results: Of the 78 RTRs, 21 (26.9%) had fasting and PML tHcy within the respective reference intervals, and 57 (73.1%) had increased plasma tHcy. Of these 57 RTRs, 22 had fasting hyperhomocysteinemia, 9 had PML hyperhomocysteinemia, and 26 had combined hyperhomocysteinemia (both fasting and PML). Unadjusted Pearson correlations showed that fasting plasma tHcy correlated with both cystatin C (r = 0.564; P &lt;0.001) and creatinine (r = 0.519; P &lt;0.001) and that increases in PML tHcy modestly correlated with cystatin (r = 0.205; P = 0.072), but not creatinine (r = 0.057; P = 0.624). General linear regression modeling with stepwise analysis of covariance showed that both cystatin C (partial R = 0.554; P &lt;0.001) and creatinine (partial R = 0.535; P &lt;0.001) were independent predictors of fasting tHcy, but of the two, only cystatin C (partial R = 0.242; P = 0.035) was an independent predictor of increased PML tHcy.

Conclusions: Clinically stable RTRs have an excess prevalence of moderate hyperhomocysteinemia, and additional cases can be detected by methionine loading. Both creatinine and cystatin C are independent predictors of fasting tHcy in these individuals; however, only cystatin C is a determinant of tHcy concentration after a methionine load, probably because cystatin C is a more sensitive marker of glomerular filtration rate than serum creatinine.

Impaired homocysteine metabolism and atherothrombotic disease

Based on recent retrospective, prospective, and experimental studies, mild to moderate elevation of fasting or postmethionine-load plasma homocysteine is accepted as an independent risk factor for cardiovascular disease and thrombosis in both men and women. Hyperhomocysteinemia results from an inhibition of the remethylation pathway or from an inhibition or a saturation of the transsulfuration pathway of homocysteine metabolism. The involvement of a high dietary intake of methionine-rich animal proteins has not yet been investigated and cannot be ruled out. However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia. Recent experimental studies have suggested that moderately elevated homocysteine levels are a causal risk factor for atherothrombotic disease because they affect both the vascular wall structure and the blood coagulation system. The oxidant stress that results from impaired homocysteine metabolism, which modifies the intracellular redox status, might play a central role in the molecular mechanisms underlying moderate hyperhomocysteinemia-mediated vascular disorders. Because folate supplementation can efficiently reduce plasma homocysteine levels, both in the fasting state and after methionine loading, results from further prospective cohort studies and from on-going interventional trials will determine whether homocysteine-lowering therapies can contribute to the prevention and reduction of cardiovascular risk. Additionally, these studies will provide unequivocal arguments for the independent and causal relationship between hyperhomocysteinemia and atherothrombotic disease.

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.

Recommendations for the outpatient surveillance of renal transplant recipients. American Society of Transplantation

Many complications after renal transplantation can be prevented if they are detected early. Guidelines have been developed for the prevention of diseases in the general population, but there are no comprehensive guidelines for the prevention of diseases and complications after renal transplantation. Therefore, the Clinical Practice Guidelines Committee of the American Society of Transplantation developed these guidelines to help physicians and other health care workers provide optimal care for renal transplant recipients. The guidelines are also intended to indirectly help patients receive the access to care that they need to ensure long-term allograft survival, by attempting to systematically define what that care encompasses. The guidelines are applicable to all adult and pediatric renal transplant recipients, and they cover the outpatient screening for and prevention of diseases and complications that commonly occur after renal transplantation. They do not cover the diagnosis and treatment of diseases and complications after they become manifest, and they do not cover the pretransplant evaluation of renal transplant candidates. The guidelines are comprehensive, but they do not pretend to cover every aspect of care. As much as possible, the guidelines are evidence-based, and each recommendation has been given a subjective grade to indicate the strength of evidence that supports the recommendation. It is hoped that these guidelines will provide a framework for additional discussion and research that will improve the care of renal transplant recipients.

The folate cycle and disease in humans

The prevalence of hyperhomocysteinemia in renal disease patients, its treatment by folate administration, and its aggravation by the 677 C-->T mutation of methylene-tetrahydrofolate (methylene-THF) reductase has established the folate cycle as an important factor in the pathogenesis and management of renal disease. Proper function of the folate cycle depends on normal function of involved enzymes adequate of the vitamin and its correct disposition within the body. Vital processes in folate disposition include conversion of dietary folylpolyglutamates to monoglutamates, intestinal absorption, receptor and carrier-mediated transport across cell membranes, and cellular export. Folate coenzymes are responsible for the one-carbon unit transfer in intermediary metabolism and are required for several reactions in key metabolic processes, for example of purine, pyrimidine and methionine synthesis, and glycine and serine metabolism. Methionine synthase and its recently discovered reducing protein as well as methylene tetrahydrofolate reductase are key folate enzymes in homocysteine metabolism. Deficiencies of these enzymes are important causes of severe disease in the rare remethylation defects causing homocystinuria. Knowledge of their catalytic and molecular properties is important in understanding possible causes of moderate hyperhomocysteinemia, as for example, the well-known 677 C-->T transition of methylene tetrahydrofolate reductase.

Homocysteine metabolism in renal failure

Of the many amino acid abnormalities that are present in chronic renal failure, hyperhomocysteinemia has drawn increasing attention because of its proposed role in the development and/or progression of atherothrombotic disease. Renal function is a major determinant of fasting plasma homocysteine level, and the inverse relationship between the glomerular filtration rate (GFR) and plasma homocysteine level is present throughout the whole range of renal function. Although this suggests an active renal homocysteine metabolism, no important urinary excretion or active homocysteine extraction has been demonstrated in the human kidney. Analysis of plasma concentrations of the various cofactors and substrates of homocysteine metabolism, and the effects of different therapies indicate that an abnormal folate metabolism may be the cause of hyperhomocysteinemia in uremia. This is further supported by the finding that homocysteine remethylation, as assessed by stable isotope techniques, is impaired in dialysis patients. It is unclear whether decreased remethylation is also responsible for other abnormalities of homocysteine metabolism in renal failure such as the exaggerated rise and the impaired decline of plasma homocysteine concentration after methionine or homocysteine loading. More studies are necessary to pinpoint the precise mechanisms that lead to hyperhomocysteinemia in renal failure. This should lead to optimal treatment and, ultimately, to the prevention of cardiovascular complications in this vulnerable patient group.

Is there a role of cyclosporine A on total homocysteine export from human renal proximal tubular epithelial cells?

BACKGROUND

Immunosuppressive therapy may influence homocysteine metabolism in allograft recipients. We examined whether cyclosporine A influences the in vitro formation of homocysteine as determined by the measurement of total homocysteine (tHcy) concentrations in supernatants of human renal proximal tubule epithelial cells (hRPTEC), an important site of homocysteine metabolism.

METHODS

Cells were incubated with and without vitamins in the presence of low or high methionine concentrations at different cyclosporine A concentrations for 24, 48 and 72 hours (N = 7 for each experiment). The concentration of tHcy in culture supernatants was measured by a fluorescence polarization immunoassay. Data were analyzed by four-way ANOVA, three-way ANOVA and t tests.

RESULTS

The Hcy export from hRPTEC (tHcy in the culture supernatant) was 2.69 micromol/L during standard cell culture conditions at time point 24 hours and increased by 28.3% at 48 hours and by 44.6% at 72 hours. Comparisons of tHcy levels in culture supernatants over time by four way ANOVA showed that cyclosporine A at 200 or 800 ng/mL had no influence on tHcy export from hRPTEC (P = 0.67991). In contrast, the presence of vitamins in the medium (P = 0.000001), in vitro methionine loading (P < 0.000001), and prolonged incubation time (P < 0.000001) were associated with an increase of tHcy export from hRPTEC. Significant interactions in this analysis were "vitamins x methionine" (P = 0.001804), "vitamins x time" (P = 0.001478), "methionine x time" (P < 0.000001), and "vitamins x methionine x time" (P = 0.018128), pointing to a combined effect of vitamins in the presence of high methionine concentrations at the later time points.

CONCLUSION

Our study shows that hRPTEC export Hcy into the cell culture medium, an effect that is enhanced by in vitro methionine loading and modulated by the presence of vitamins. Cyclosporine A had no major influence on Hcy export from tubule cells. Therefore, our findings do not support the assumption that cyclosporine A elevates total homocysteine plasma levels in organ transplant patients.

Homocysteine, its metabolites, and B-group vitamins in renal transplant patients

BACKGROUND

Increased plasma total homocysteine (tHcy) levels are an independent risk factor for cardiovascular morbidity in patients with normal and impaired renal function, including stable renal transplant recipients (RTRs). Plasma concentrations of the metabolites of Hcy, such as cystathionine (Cys), methylmalonic acid (MMA), 2-methylcitric acid (MC), and its diastereomers MCI and MCII have been reported in only a few articles. We therefore looked for the serum concentration of these metabolites and their relationship to renal function, cardiovascular diseases, the immunosuppressive treatment, and serum concentrations of cobalamin and folate.

METHODS

Fifty RTRs (mean age 50.4 +/- 11.8 years, 35.9 +/- 44.4 months after kidney transplantation) and 35 controls (NP; mean age 43.5 +/- 14.4 years) were studied. Total Hcy and its metabolites were measured by gas chromatography-mass spectrometry (GC-MS).

RESULTS

Total Hcy, MMA, Cys, and MC were elevated twofold to sixfold as compared with NP, with a significant interrelationship between these compounds. With the exception of Cys, they were significantly correlated with serum creatinine. Serum folate levels were inversely correlated with tHcy, Cys and cobalamin with MMA and the ratio of MCI/MCII. There was no correlation between tHcy concentration and its metabolites with immunosuppressive treatment (CsA vs. FK506), clinical history, or current findings of cardiovascular complications and blood pressure profile.

CONCLUSION

Prospective studies are needed to find out whether the lowering or normalization of serum concentrations of tHcy and its metabolites due to treatment with B vitamins should be achieved to reduce the cardiovascular risk and improve the long-term outcome of allografts and of patients.

Effect of MTHFR genotypes and hyperhomocysteinemia on patient and graft survival in kidney transplant recipients

BACKGROUND

The total homocysteine (tHcy) plasma level, which is partly determined by the MTHFR 677C-->T genotype, may be associated with vascular disease. We prospectively examined the influence of MTHFR genotypes (677C-->T, 1298A-->C) and tHcy plasma concentration on all cause mortality and graft outcomes of renal transplant recipients.

METHODS

Baseline tHcy plasma levels of 189 patients (three groups with either the MTHFR 677CC, CT or TT genotype, including 63 patients in each group, were matched for age, gender, body mass index and creatinine clearance at baseline), were obtained between September 1996 and May 1997. Follow-up data (time until return to dialysis therapy, time and cause of death) were collected from April to June 1999. Kaplan-Meier survival estimations were calculated and plotted, the groups (three MTHFR 677C-->T genotype groups, or three MTHFR 1298A-->C genotype groups, or two groups with tHcy plasma levels above/below 15 micromol/L) were compared by log-rank test. Age, gender, body mass index (BMI), time since transplantation, serum creatinine, creatinine clearance, combined MTHFR 677C-->T/1298A-->C genotypes, tHcy, folate and vitamin B12 plasma levels were evaluated with regard to graft and patient survival in a multivariate Cox-proportional hazard regression model.

RESULTS

During the follow-up period of 2.26 +/- 0.66 years, 9 patients died (5 in the TT, 2 in the CT and 2 in the CC genotype group; P = 0.34) and 22 returned to dialysis treatment (7 in the TT, 9 in the CT and 6 in the CC genotype group; P = 0.65). There was also no influence of MTHFR 1298A-->C genotypes (AA genotype, 114 patients; AC genotype, 64 patients; CC genotype, 11 patients) on patient or graft survival (P = 0.7087 and P = 0.1633, respectively). Two of 93 patients with a tHcy plasma level < or = 15 micromol/L died, in contrast to 7 of 96 patients in the tHcy > 15 micromol/L group, P = 0.0778. Two patients in the low tHcy group had to return to dialysis, in contrast to 20 patients in the high tHcy group (P = 0.0001). In the multivariate model there was no significant predictor of patient survival, and the serum creatinine was the only predictor of graft survival (P < 0.0001).

CONCLUSIONS

In summary, our study shows that neither MTHFR 677C-->T/1298A-->C genotypes nor hyperhomocysteinemia are independently associated with patient or graft survival following kidney transplantation.

Effects of methionine loading on plasma and erythrocyte sulphur amino acids and sulph-hydryls before and after co-factor supplementation in haemodialysis patients

BACKGROUND

Hyperhomocysteinaemia, which is potentially atherogenic, is common in chronic haemodialysis (HD) patients but the reason for this is not yet known. The methionine (Met) loading test (MLT) is used to test the capacity of homocysteine (Hcy) disposal by the trans-sulphuration pathway and thus may provide information on the metabolism of sulphur amino acids. The availability of vitamin B(6) and folic acid, as co-factors for Hcy metabolism may affect the response to MLT. In the present study, we compared the effect of Met loading on plasma and erythrocyte (RBC) sulphur amino acids and sulph-hydryls before and after co-factor supplementation in healthy subjects and HD patients.

METHODS

In 10 HD patients and 10 healthy subjects the effect of Met loading, 0.1 g/kg BW, on plasma and RBC methionine metabolites was studied over 7 h, before and after 4 weeks supplementation with high daily doses of vitamin B(6) (200 mg) and folic acid (15 mg).

RESULTS

MLT before vitamin supplementation in HD patients, compared to the healthy subjects, caused significantly greater increases in plasma Hcy levels (43+/-12 vs 15+/-5 micromol/l), cysteinesulphinic acid (CSA) (1.34 vs 0.36 micromol/l) and gamma-glutamylcysteine (0.98+/-0.83 vs -01+/-0.42 micromol/l) and no decline in plasma cysteine (Cys) (0.5+/-33.9 vs -31+/-26 micromol/l), but no significant differences in plasma taurine, cysteinylglycine, and glutathione concentrations. In RBCs there was a small increase in Hcy levels and a more marked increase in Tau levels, with no difference between the healthy subjects and HD patients. Vitamin supplementation in pharmacological doses failed to correct the abnormal responses to MLT in the HD patients.

CONCLUSIONS

Oral methionine loading in HD patients leads to higher accumulation of Hcy and other Met metabolites in plasma and RBCs than in healthy subjects, indicating impaired metabolism of sulphur amino acids via the trans-sulphuration pathway. Supplementation with high doses of vitamin B(6) and folic acid does not correct this impairment, suggesting that it most probably is not due to lack of these co-factors.

Influence of 699C-->T and 1080C-->T polymorphisms of the cystathionine beta-synthase gene on plasma homocysteine levels

The association of moderately elevated total homocysteine (tHcy) levels with coronary artery disease is increasingly being recognized. However, the role of genetic influence on plasma tHcy levels is not completely understood. We studied 1,055 individuals with respect to the effect of two silent polymorphisms, the 699C--> T and the 1080C-->T, of the cystathionine beta-synthase (CBS) gene on plasma tHcy levels. Individuals who were heterozygous or homozygous for the T699 allele had lower post-methionine load (PML) tHcy levels when compared to individuals with the C/C genotype. This association was statistically significant (p = 0.005) for the T/T genotype compared to the C/C genotype and became even more significant (p = 0.000002) when individuals carrying the 68-bp insertion (844ins68) and the T1080 allele were excluded from the analysis. With regard to the 1080C-->T polymorphism, the T1080 allele was associated with significantly lower PML tHcy levels only when individuals carrying the 844ins68 and T699 allele were excluded from the study (p = 0.01 for 1080T/T genotype compared to 1080C/C genotype). We speculate that the 699C-->T and 1080C-->T polymorphisms may be in linkage disequilibrium with regulatory elements that upregulate CBS gene transcription.

Effect of MTHFR 1298A-->C and MTHFR 677C-->T genotypes on total homocysteine, folate, and vitamin B(12) plasma concentrations in kdiney graft recipients

The effect of 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298A-->C on total homocysteine (tHcy), folate and vitamin B(12) levels was investigated in 733 kidney graft recipients. The six major genotype combinations were used as grouping variables, and age, gender, BMI, serum creatinine, and creatinine clearance and ln-folate, ln-vitamin B(12), or logarithmus naturalis tHcy (ln-tHcy) were used as covariates in three ANCOVA and multiple stepwise linear regression models. Hyperhomocysteinemia was present in 49.7% of the patients. The allele frequency of MTHFR 677T and 1298C was 0.319 and 0.326. MTHFR genotype and all other variables were significant predictors of ln-tHcy (higher tHcy plasma levels for MTHFR 677TT/1298AA versus all other five genotype groups: P < 0. 05). BMI, creatinine clearance, ln-tHcy, and MTHFR genotype influenced ln-folate (lower folate levels for MTHFR 677TT/1298AA versus all other genotype groups: P < 0.05). Creatinine clearance and ln-tHcy were the only predictors of ln-vitamin B(12) levels. In a prespecified subgroup analysis (n = 496), the MTHFR genotype also influenced tHcy levels and compound heterozygous patients had significantly lower folate levels as compared with MTHFR 677CC/1298AA and 677CC/1298CC. This study shows that the MTHFR 677TT/1298AA and 677CT/1298AC genotypes are significant predictors of tHcy and folate plasma levels.

Hyperhomocysteinemia in hemodialysis patients: effects of 12-month supplementation with hydrosoluble vitamins

BACKGROUND

High-efficiency hemodialysis may induce a deficiency in hydrosoluble vitamins. Supplementation with B-complex vitamins has been shown to lower serum homocysteine concentrations in several groups, but relatively few studies have concerned hemodialysis patients. Our objectives were to determine the status in B-complex vitamins in a large cohort of unsupplemented hemodialysis patients and to assess the effects of supplementation with hydrosoluble vitamins on serum homocysteine over one year.

METHODS

Serum total homocysteine (tHcy), vitamin B12, folate, pyridoxal-5'-phosphate (P-5'-P; the active moiety of vitamin B6), as well as red blood cell folate concentrations, were measured in 168 chronic dialysis patients on three times weekly high-efficiency hemodialysis and not supplemented with hydrosoluble vitamins. Their methylenetetrahydrofolate reductase C677T (MTHFR) genotypes were also determined (homozygotes TT, heterozygotes CT, without mutation CC). All involved patients were then supplemented with hydrosoluble vitamins (once daily by mouth, DiaVite; R&D Laboratories, Minneapolis, MN, USA), and half of them were randomized to receive in addition 10 mg intravenously of folic acid posthemodialysis (30 mg intravenously per week). Serum tHcy was monitored after 6 and 12 months of supplementation in the 140 and 128 patients available for follow-up.

RESULTS

At baseline, serum and red blood cell folate concentrations were within normal limits in all patients except for two with borderline serum folate (mean values of 21 +/- 8 and 1195 +/- 454 nmol/L), whereas serum vitamin B12 and P-5'-P were below normal in 11 and 65 patients, respectively (mean values of 327 +/- 215 pmol/L and 19 +/- 16 nmol/L for the 168 patients). Initial tHcy levels were increased in all patients (mean 33.3 +/- 16.6 for a normal below 11.8 +/- 1.5 micromol/L); tHcy significantly decreased to 23.5 +/- 7.6 micromol/L after six months (P < 0.0001 vs. baseline) and to 21.7 +/- 6.1 micromol/L after 12 months (P < 0.0001 vs. baseline) for the entire group, but was normalized in only four patients at 12 months. After six months, the mean reduction in tHcy was slightly but significantly greater for patients receiving intravenous folic acid (12.2 +/- 18.5 micromol/L) compared with patients not receiving it (8.3 +/- 9.8 micromol/L, P < 0.05). However, at 12 months, no difference between both subgroups persisted. When considering the different genotypes, tHcy at baseline tended to be higher for TT than CT and CC (39.8 +/- 30.9 vs. 31.4 +/- 10.5 vs. 31.6 +/- 11.8 micromol/L) and decreased to respective values of 21.1 +/- 6.9 versus 21.4 +/- 6.1 versus 22.2 +/- 5.9 micromol/L at 12 months. The impact of the addition of folic acid to DiaVite appeared particularly significant in TT patients at six months.

CONCLUSIONS

(1) Hyperhomocysteinemia was present in 100% of our hemodialysis patients. (2) Nearly 40% of our unsupplemented hemodialysis patients were deficient in vitamin B6. (3) Supplementation with DiaVite(R) has resulted in significant tHcy reductions for all three genotypes. (4) The impact of the proposed supplementation protocol was found after six months and was maintained, but did not increase further after 12 months of the same regimen. (5) The addition of intravenous folic acid has been associated with a more pronounced decrease in tHcy in TT patients.

Effects of a high-fat-sucrose diet on enzymes in homocysteine metabolism in the rat

Hyperhomocysteinemia (HH) and hyperinsulinemia are both risk factors for cardiovascular disease. To examine the effects of hyperinsulinemia on homocysteine metabolism, we fed rats a high-fat-sucrose (HFS) diet and then measured the hepatic mRNA and activity of 2 key enzymes involved in this metabolic pathway: 5,10-methylenetetrahydrofolate reductase (MTHFR) and cystathionine-beta-synthase (CbetaS). Fischer rats made insulin-resistant by a HFS diet were examined at 6 months and 2 years of age and compared with control rats fed a low-fat, complex-carbohydrate (LFCC) diet. At the end of 6 months, the HFS rats were heavier than the LFCC rats (214 +/- 3.4 v 188 +/- 1.4 g, P < .01). There were no differences in blood glucose between HFS and LFCC rats; however, plasma insulin and homocysteine concentrations were elevated in HFS rats (insulin, 56 +/- 12 v 14.5 +/- 2.9 microU/mL; homocysteine, 10.77 +/- 0.9 v 6.89 +/- 0.34 micromol/L, P < .01). Hepatic CbetaS enzyme activity was significantly lower in HFS compared with LFCC rats (0.45 v 0.64 U/mg, P = .0001), and this decrease was reflected in a decrease of the CbetaS mRNA concentration. In contrast, hepatic MTHFR enzyme activity and mRNA concentration were significantly elevated in the HFS group compared with controls (HFS and LFCC, 8.62 and 4.8 nmol/h/mg protein, respectively, P = .0001). These changes in plasma homocysteine, CbetaS, and MTHFR were significantly correlated with the degree of obesity and hyperinsulinemia. Fasting plasma insulin correlated significantly and positively with plasma homocysteine (r = .51, P < .01) and MTHFR activity (r = .48, P < .01) and negatively with CbetaS activity (r = -.54, P < .001). CbetaS and MTHFR activities were inversely correlated with each other (r = -.58, P < .001). In conclusion, rats fed a HFS diet are hyperinsulinemic, and the hyperinsulinemia is associated with an elevated homocysteine concentration and changes in 2 key enzymes in homocysteine metabolism.

Plasma homocysteine levels in renal transplanted patients on cyclosporine or tacrolimus therapy: effect of treatment with folic acid

Hyperhomocysteinemia, an independent risk cardiovascular factor, has been reported in renal transplanted patients (RTP). The aim of the present study was to evaluate homocysteine levels in RTP treated with cyclosporine or tacrolimus, and the changes observed in the two groups of patients after treatment with folic acid. Forty-two RTP with stable function (21 treated with cyclosporine and 21 with tacrolimus, matched by gender and age) were studied. Forty healthy control subjects were matched by age and gender with the patients. In RTP, homocysteine was increased compared with the controls (16.4 +/-5.2 vs 8.0 +/- 1.8 micromol/L; p < 0.001), but there was no difference in vitamin B12 and folic acid levels. Thirty-three patients and one control showed hyperhomocysteinemia (78.5 vs 2.5%; p < 0.001). Homocysteine correlated negatively with creatinine clearance in the patients (p = 0.04), but no correlation was found with vitamin B12, folic acid and lipoproteins. By univariate analysis, patients treated with cyclosporine had higher homocysteine than those treated with tacrolimus (p = 0.03), but multivariate analysis did not confirm these results. In 21 patients with hyperhomocysteinemia and folate levels similar to those of the controls, folic acid (5 mg/d for 3 months) was administered. Homocysteine decreased significantly (19.1 +/- 4.8 vs 13.2 +/- 3.4 micromol/L; p < 0.001), with a median reduction of 31% and with no differences observed in patients treated with either cyclosporine or tacrolimus. We concluded that hyperhomocysteinemia is very frequent in RTP, but homocysteine levels are not different in patients treated with cyclosporine or tacrolimus. Folic acid therapy produces a significant decrease in homocysteine concentrations, in the absence of clear folate deficiency, without differences in relation to immunosuppressant therapy.

Hyperhomocysteinemia in organ transplantation

An elevated total homocysteine plasma concentration is associated with an increased morbidity and mortality due to cardiovascular disease in the general population, in patients with renal failure and in recipients of kidney or heart transplants. The fasting or post-methionine loading plasma concentration of total homocysteine is elevated in 50-60% of renal transplant recipients with stable graft function and in the majority of heart transplant recipients. Fasting and post-methionine loading hyperhomocysteinemia can be normalized in virtually all renal transplant patients by a combination of folic acid (5 mg/d), vitamin B6 (50 mg/d) and vitamin B12 (0.4 mg/d). In individuals without renal failure much lower doses of folate and vitamin B12 are able to correct hyperhomocysteinemia. Currently, prospective studies are under way to clarify whether folate and vitamin therapy improves cardiovascular disease morbidity and mortality in the general population and in organ transplant recipients. While population wide screening for and treatment of hyperhomocysteinemia is generally not recommended, treatment of high risk patients, including renal failure patients and kidney and heart transplant recipients, can be considered but still represents an experimental therapy.