Hyperhomocysteinemia confers an independent increased risk of atherosclerosis in end-stage renal disease and is closely linked to plasma folate and pyridoxine concentrations

Dialysis Outcomes and Practice Patterns Study (DOPPS) data on medications in hemodialysis patients

BACKGROUND

Medications affect many measures of hemodialysis patients' well-being.

METHODS

The Dialysis Outcomes and Practice Patterns Study (DOPPS) has evaluated the use of hydroxymethyl glutaryl coenzyme A reductase inhibitors (statins), analgesics, antidepressants, and multivitamins. Additionally, DOPPS has reported on the associations between vascular access outcomes and related medications.

RESULTS

Prescription of statins varied widely across countries, with the highest use in the United States. Patients prescribed statins had lower risk of cardiac and noncardiac causes of mortality than those who were not prescribed statins. DOPPS data also show that statins are underprescribed relative to recent Kidney Disease Outcomes Quality Initiative guidelines. No guidelines have been established for analgesic use, but high pain levels self-reported by hemodialysis patients suggest opportunities for improved pain management strategies. Guidelines for analgesic use in dialysis patients may help balance improved quality of life against potential side effects of analgesics. Medical and patient questionnaires show that depression in hemodialysis patients is common, frequently underdiagnosed, usually untreated, and associated with increased rates of mortality and hospitalization. Calcium channel blockers were associated with improved primary graft patency, aspirin with improved secondary graft patency, and angiotensin-converting enzyme inhibitors with improved secondary fistula patency. All 3 medications were associated with significantly decreased relative risk for access failure. There is large country variation in multivitamin use, with significantly higher use in the United States compared with Europe and Japan. Patients taking multivitamins had lower mortality risk than patients not taking multivitamins.

CONCLUSION

DOPPS findings on medications indicate that prospective trials are needed before guidelines can be developed for appropriate medication use in these different therapeutic categories.

Homocysteine clearance and methylation flux rates in health and end-stage renal disease: association withS-adenosylhomocysteine

Hyperhomocysteinemia is a risk factor for cardiovascular disease and occurs frequently in end-stage renal disease (ESRD), but its pathogenesis is poorly understood. We aimed to evaluate one-carbon flux rates of methionine and homocysteine (Hcy) in ESRD patients and healthy controls. Transmethylation (TM), remethylation (RM), and transsulfuration (TS), as well as Hcy clearance by TS (i.e., TS/plasma total Hcy concentration) and by RM (i.e., RM/plasma total Hcy concentration) were evaluated in relation to body composition, vitamins, and S-adenosylhomocysteine (AdoHcy) and S-adenosylmethionine (AdoMet) levels. After a fixed protein diet for 3 days, primed-continuous infusion of [2H3-methyl-1-13C]methionine was performed in the postabsorptive state in 12 hemodialysis patients and 16 healthy volunteers. Hcy clearance by TS (−80%, P < 0.001) and by RM (−77%, P < 0.001) in ESRD patients was decreased compared with healthy controls. The absolute flux rates of TM (−27%, P < 0.01) and RM (−28%, P = 0.02) were lower in the ESRD patients. After adjustment for age, TS was not significantly reduced. Whole blood AdoHcy was significantly elevated in ESRD and was a significant determinant of TM (standardized β = −1.24, P = 0.01) and RM (standardized β = −1.43, P = 0.03). In conclusion, patients with ESRD have impaired Hcy clearance by TS and RM. Elevated whole blood AdoHcy levels are associated with impaired RM and TM flux rates in these patients, and AdoHcy may be a key regulatory compound in one-carbon flux.

International variation in vitamin prescription and association with mortality in the dialysis outcomes and practice patterns study (DOPPS)

BACKGROUND

The prevalence of water-soluble vitamin use among hemodialysis (HD) patients and whether mortality and hospitalization are associated with water-soluble vitamin use by HD patients have not previously been reported. The present study investigates patterns of water-soluble vitamin use among HD patients in the Dialysis Outcomes and Practice Patterns Study (DOPPS) I and evaluates outcomes associated with vitamin use.

METHODS

The study sample came from the DOPPS I, a prospective observational study of adult HD patients (N = 16,345) randomly selected from 308 representative dialysis facilities in France, Germany, Italy, Japan, Spain, the United Kingdom, and the United States. Time-dependent Cox regression models were used to assess relative risk (RR) for mortality and hospitalization for patients administered water-soluble vitamins versus those not administered water-soluble vitamins.

RESULTS

There was large variation by region in the percentage of patients administered water-soluble vitamins: Europe ranged from a low of 3.7% in the United Kingdom to a high of 37.9% in Spain; 5.6% in Japan; and 71.9% in the United States. Patient use of water-soluble vitamins was associated with a substantially and significantly lower risk for mortality (RR, 0.84; P = 0.001). Lower RR for facility-level mortality also was associated with greater water-soluble vitamin use (RR, 0.98; P = 0.05 per 10% more patients administered water-soluble vitamins at the facility).

CONCLUSION

Although only a randomized trial could prove that water-soluble vitamins improve outcomes, use of water-soluble vitamins is a minimal-risk practice pattern associated with improved outcomes in this prospective observational study.

Atherosclerosis and folic acid supplementation trial in chronic renal failure: Baseline results

BACKGROUND

Atherosclerosis and Folic Acid Supplementation Trial (ASFAST) is a randomized placebo controlled trial assessing whether high-dose folic acid can reduce cardiovascular events and atherosclerosis progression in patients with chronic renal failure (CRF). Here we report the baseline results and compare indices of arterial structure (carotid intima-medial thickness (IMT)) and function (systemic arterial compliance (SAC)), pressure augmentation index (AI(x)) and pulse wave velocity (PWV a-f and PWV f-d)) to age- and sex-matched controls.

METHODS

Three hundred and fifteen subjects with CRF (serum creatinine > or = 0.40 mmol/L) aged 24-79 years (mean +/- SD: 56.6 +/- 13.6 years) and 213 healthy controls (58.2 +/- 10.2 years) were studied. Fasting blood samples were assayed for lipids (both groups), total homocysteine (tHcy), red cell folate, cobalamin and fibrinogen (CRF group). Ultrasound B mode measurements were used to determine mean carotid IMT and applanation tonometry techniques to determine SAC, AI(x), PWV (a-f), PWV (f-d) and central pressures.

RESULTS

Ninety-six per cent of the CRF group had at least one of: hypertension, hypercholesterolaemia, diabetes or smoking; 35% had established cardiovascular disease. The mean IMT was greater in CRF patients than in controls (0.86 +/- 0.19 vs 0.68 +/- 0.11 mm, P < 0.001). The SAC was significantly lower, and PWV (a-f) and AI(x) significantly higher. The tHcy was increased in 97% of the CRF group (27.3 +/- 2.9 micromol/L (normal < 13)). Total homocysteine did not correlate with IMT or any other measure of arterial function. However, those in the upper quantile of tHcy (> or =25 micromol/L) did have higher PWV (a-f) and lower SAC than those in the lower quantile.

CONCLUSIONS

Compared to normals, patients with CRF exhibited a 10-15-year shift to the right in age-related increases in carotid IMT and PWV (a-f), and significantly increased central pressure augmentation. This 5-year study is examining the impact of high-dose folic acid therapy on cardiovascular end-points, IMT progression and arterial function in CRF.

Translational upregulation of folate receptors is mediated by homocysteine via RNA-heterogeneous nuclear ribonucleoprotein E1 interactions

Cellular acquisition of folate is mediated by folate receptors (FRs) in many malignant and normal human cells. Although FRs are upregulated in folate deficiency and downregulated following folate repletion, the mechanistic basis for this relationship is unclear. Previously we demonstrated that interaction of an 18-base cis-element in the 5'-untranslated region of FR mRNA and a cystolic trans-factor (heterogeneous nuclear ribonucleoprotein E1 [hnRNP E1]) is critical for FR synthesis. However, the molecular mechanisms controlling this interaction, especially within the context of FR regulation and folate status, have remained obscure. Human cervical carcinoma cells exhibited progressively increasing upregulation of FRs after shifting of folate-replete cells to low-folate media, without a proportionate rise in FR mRNA or rise in hnRNP E1. Translational FR upregulation was accompanied by a progressive accumulation of the metabolite homocysteine within cultured cells, which stimulated interaction of the FR mRNA cis-element and hnRNP E1 as well as FR biosynthesis in a dose-dependent manner. Abrupt reversal of folate deficiency also led to a rapid parallel reduction in homocysteine and FR biosynthesis to levels observed in folate-replete cells. Collectively, these results suggest that homocysteine is the key modulator of translational upregulation of FRs and establishes the linkage between perturbed folate metabolism and coordinated upregulation of FRs.

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.

In Vitro and in Vivo Interactions of Homocysteine with Human Plasma Transthyretin

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease and an emerging risk factor for cognitive dysfunction and Alzheimer's disease. Greater than 70% of the homocysteine in plasma is disulfide-bonded to protein cysteine residues. The identity and functional consequences of protein homocysteinylation are just now emerging. The amyloidogenic protein transthyretin (prealbumin), as we now report, undergoes homocysteinylation at its single cysteine residue (Cys10) both in vitro and in vivo. Thus, when human plasma or highly purified transthyretin was incubated with 35S-L-homocysteine followed by SDS-PAGE and PhosphorImaging, two bands corresponding to transthyretin dimer and tetramer were observed. Treatment of the labeled samples with beta-mercaptoethanol prior to SDS-PAGE removed the disulfide-bound homocysteine. Transthyretin-Cys10-S-S-homocysteine was then identified in vivo in plasma from normal donors, patients with end-stage renal disease, and homocystinurics by immunoprecipitation and high performance liquid chromatography/electrospray mass spectrometry. The ratios of transthyretin-Cys10-S-S-homocysteine and transthyretin-Cys10-S-S-sulfonate to that of unmodified transthyretin increased with increasing homocysteine plasma concentrations, whereas the ratio of transthyretin-Cys10-S-S-cysteine to that of unmodified transthyretin decreased. The hyperhomocysteinemic burden is thus reflected in the plasma levels of transthyretin-Cys10-S-S-homocysteine, which in turn may contribute to the pathological consequences of amyloid disease.

Randomized, placebo-controlled trial of intramuscular vitamin B12for the treatment of hyperhomocysteinaemia in dialysis patients

BACKGROUND

Plasma homocysteine is elevated in patients with end-stage renal disease (ESRD) and is a risk factor for cardiovascular disease. Folic acid has been shown to partially reduce homocysteine levels in dialysis patients. It is not known whether vitamin B12 reduces homocysteine independent of folic acid in patients who are not vitamin B12 deficient.

AIM

To determine whether 1 mg vitamin B12 lowers homocysteine in stable, chronic, haemodialysis patients independent of folic acid.

METHODS

Twenty-eight haemodialysis patients were randomized to receive three doses of 1 mg vitamin B12 or 1 mL saline placebo in a double-blind fashion at 1-month intervals. Fasting plasma total homocysteine, folic acid, red-cell folate, vitamin B12 and haemoglobin levels were determined prior to each dose and 4 weeks after the final injection. The study was powered to detect a 30% reduction in homocysteine over the 3 months.

RESULTS

Both the two groups were well matched with respect to total homocysteine levels, folic acid, red-cell folate and vitamin B12 levels. Serum vitamin B12 levels were significantly higher in the treatment group compared to placebo (217.7 pmol/L; 95% confidence interval (CI) 103.0-332.5; P < 0.001) at the end of the trial but homocysteine levels were not significantly different (3.08 micromol/L; 95% CI -4.44-10.61; P= 0.406).

CONCLUSIONS

The administration of intramuscular vitamin B12 over a 3-month period does not result in any reduction of plasma homocysteine levels in haemo-dialysis patients independent of folate status, however reductions of <30% cannot be excluded by the present study. High-dose folic acid remains the treatment of choice in reducing homocysteine, but whether this results in a reduction in cardiovascular events remains to be determined.

Plasma total homocysteine in Mexican rural and urban women fed typical model diets

OBJECTIVE

The purpose of the present work was to determine the fasting plasma total homocysteine (tHcy) levels and the time-course response of tHcy concentrations after the consumption of urban and rural Mexican model diets in two groups of Mexican women from urban and rural areas.

METHODS

Thirty-three adult women (age range = 18-49 y) were studied. Fifteen women were from a rural community in the state of Mexico. The other 18 were from cities and consumed diets that regularly included an important amount of animal foods. The study was designed as a two-period crossover study in which subjects consumed the model urban or rural diet in a 2-wk interval. Seven milliliters of venous blood was drawn before ingestion of experimental diets (basal) to measure total cholesterol, high-density lipoprotein cholesterol, triacylglycerol, tHcy, folate, vitamin B12, and methionine. Blood samples were then obtained 30, 60, 90, 180, and 240 min after the beginning of meal consumption.

RESULTS

The rural and urban groups showed similar concentrations of tHcy 4 h after meal consumption and after fasting. However, the urban and rural groups had higher methionine plasma concentrations after the urban diet than after the rural diet. In contrast, there was no significant difference in methionine plasma levels between the rural and urban groups with each diet. Those women with low tHcy concentrations maintained those values over the study period, and those with high tHcy concentrations maintained those values. There was no significant difference in tHcy concentrations due to consumption of the two diets (P = 0.31) or the interaction between population and diet (P = 0.84). However, there was a significant difference in the concentration of tHcy between the rural (8.73 +/- 0.17 microM/L) and the urban (9.27 +/- 0.13 microM/L) populations (P = 0.01). In both groups, average tHcy concentration was in the normal range. In both populations, the nutrition status for folate and vitamin B12 was adequate, although plasma folate concentration was significantly lower in the rural population than in the urban population (P < 0.01). Plasma vitamin B12 concentrations were similar in both groups. No subject had low plasma vitamin B12.

CONCLUSIONS

Plasma tHcy concentrations in rural and urban Mexican women were within the range considered adequate; however, urban women showed significant higher concentrations than did rural women independently of the consumed diet and the plasma methionine concentration. These results indicated that there is no short-term variation in plasma tHcy due to the consumption of rural or urban diets.

Variations in the lipid profile of patients with chronic renal failure treated with pyridoxine

Background

Hyperhomocysteinemia and lipid abnormalities are commonly found in patients with chronic renal failure; both are recognized as risk factors for atherosclerosis. The homocysteine-lowering effect of pyridoxine is controversial. This study was performed to determine the effect of a high dose of pyridoxine (300 mg i.v. three times a week) on plasma and red blood cell lipid profile and plasma homocysteine concentration in twelve chronic renal failure patients on regular hemodialysis. Fasting blood samples were taken at the beginning of the study (basal 1), after 30 and 60 days of treatment and 4 months after withdrawal (basal 2).

Results

Pyridoxine supplementation induced a significant decrease in total plasma homocysteine level and also a lowering effect in plasma total cholesterol and triglycerides. These biochemical data increased when the samples were taken at basal 2, reaching the levels obtained at the beginning of the experiment. LDL cholesterol increased whereas HDL cholesterol was reduced during the treatment. In erythrocyte membranes vitamin B6 therapy enhanced the cholesterol/phospholipid ratio as well as the fluorescence anisotropy of diphenyl-hexatriene.

Conclusions

We conclude that high doses of pyridoxine represent an effective strategy to ameliorate both plasma homocysteine levels and lipid profiles in chronic renal failure patients, protecting them from atherosclerosis. Further research using a long-term treatment would be necessary in an attempt to restore the fatty acid pattern and the fluidity of red cell membranes.

Understanding the transition from alternative medicine to mainstream science: the homocysteine theory of heart disease and the crucial role of effective mentoring

A deficiency of effective 'mentoring' may contribute to the relatively low quality of alternative medicine research and to the medical/scientific community's reluctance to consider even its most promising theories. This hypothesis derives from a case-study of the homocysteine theory of heart disease (HTSD), one of only a few recent theories to have made the transition from 'alternative' to 'mainstream'.

Is there additional effect of MTHFR C677T mutation on lipid abnormalities in renal allograft recipients?

BACKGROUND

The MTHFR C677T mutation and elevated atherogenic lipoprotein levels are known as cardiovascular risk factors in patients with renal transplantation treated with cyclosporine (CsA). The aim of the present study was to eveluate the contribution of MTHFR C677T mutation to the risk of dyslipidemia in renal transplant recipients. We also studied the effect of the MTHFR-C677 T genotype on transplant survival.

METHODS

The study included 29 nondiabetic renal transplant recipients and 27 healthy controls. MTHFR C677T genotypes were determined by PCR and RFLP techniques. Biochemical parameters were measured in a computerized autoanalyzer.

RESULTS

In the patient group, the distribution of the CC, CT, and TT genotypes was 44.8% (n = 13), 37.9% (n = 11), and 17.2% (n = 5), respectively. The frequencies of the C and T alleles were 0.64 and 0.36, respectively. Subjects with the T allele had the highest levels of TC (P <.05) and LDL-C (P <.05); subjects with the CC genotype had the lowest.

CONCLUSIONS

We observed that the MTHFR T allele has an unfavorable effect on serum lipid profile, leading to a rise in the total and LDL cholesterol concentrations. Thus, we believe that MTHFR C allele has a protective effect and MTHFR T allele has a detrimental effect on the serum lipid profile.

Folate treatment and unbalanced methylation and changes of allelic expression induced by hyperhomocysteinaemia in patients with uraemia

BACKGROUND

Hyperhomocysteinaemia occurs in several genetically determined and acquired disorders and is highly prevalent in patients with uraemia. In these disorders, homocysteine precursor S-adenosylhomocysteine, a powerful competitive inhibitor of S-adenosylmethionine-dependent methyltransferases, is increased, suggesting unbalanced methylation. We aimed to investigate whether DNA hypomethylation is present in patients with uraemia who also have hyperhomocysteinaemia and whether regulation of specific classes of genes, dependent on DNA methylation, is compromised.

METHODS

We selected men with hyperhomocysteinaemia and uraemia who were having standard haemodialysis treatment, and compared them with healthy male controls. We measured the homocysteine concentration from plasma samples and obtained DNA and RNA samples from peripheral mononuclear cells. DNA methylation was assessed by cytosine extension assay and by Southern blotting. Allelic expression of pseudoautosomal and imprinted genes was investigated by analysis of suitable restriction fragment length polymorphisms.

FINDINGS

Total DNA hypomethylation was higher in patients than in controls (z score -4.593, p=0.0006) and allelic expression was changed in both sex-linked and imprinted genes. The shift from monoallelic to biallelic expression was dependent on homocysteine concentrations. Folate therapy, a common method to reduce hyperhomocysteinaemia, restored DNA methylation to normal levels and corrected the patterns of gene expression.

INTERPRETATION

Our results suggest that hyperhomocysteinaemia affects epigenetic control of gene expression, which can be reverted by folate treatment. Our data support the hypothesis that the toxic action of homocysteine can be mediated by macromolecule hypomethylation.

Hyperhomocysteinemia and end-stage renal disease: determinants and association with cardiovascular disease in Tunisian patients

The study reports on plasma total homocysteine (tHcy) levels in Tunisian patients with chronic renal failure (CRF) and those treated with hemodialysis (HD) and renal transplant (RT). The aims of the study were to identify the determinants of tHcy concentration and to test the association between hyperhomocysteinemia and atherothrombotic disease in end-stage renal disease (ESRD). A total of 35 CRF patients on conservative treatment, 50 HD patients, and 30 RT recipients, and 31 age- and sex-matched healthy subjects were included. Plasma tHcy was assessed by a fluorescent-polarizing immunoassay method. Multivariate analysis was applied to identify the main determinants of tHcy concentration and to assess the relationship between hyperhomocysteinemia and cardiovascular disease. Plasma mean tHcy concentration was significantly increased (p < 0.001) in CRF patients (mean +/- SD) (28.9 +/- 9.8 micromol/l), in HD patients (29.4 +/- 11.1 micromol/l), and in RT (19.3 +/- 6.3 micromol/l) patients compared to controls (11.9 +/- 4.1 micromol/l). Multivariate analysis using GLM ANOVA modeling demonstrated that tHcy was significantly higher in males (p = 0.02), and was related to age (p = 0.008), albumin (p = 0.005), vitamin B12 (p = 0.002), folate (p = 0.00001), and creatinine clearance (p = 0.0008). However, tHcy was not associated with C-reactive protein and did not significantly differ between CRF, HD, or RT patients. The upper quartile of tHcy concentration was significantly associated with atherothrombotic cardiovascular disease (unadjusted odds ratio (OR) = 3.09; 95% CI, 1.11-8.61; p = 0.01). This association remained significant after adjusting for sex, age, hypertension, and smoking (multi-adjusted OR = 4.78; 95% CI, 1.92-11.9; p = 0.0008). The mean tHcy concentration was 2 to 3 times higher in ESRD patients than in subjects with normal renal function. This increase could be related to glomerular filtration rate reduction and functional B vitamins deficiency, but was not associated with inflammation. The upper quartile of tHcy concentrations confers 4.78-fold increased independent risk for atherothrombotic events in ESRD patients.

Potential strategies to normalize the levels of homocysteine in chronic renal failure patients

Recently published evidence suggests that, either than folate therapy, the enhancement of homocysteine remethylation in tissues by correcting the multiple abnormalities of the remethylation pathway in chronic renal failure that extend beyond folate-related disturbances, or else the improved removal of uremic toxins and/or Hcy through intensified dialysis procedures may represent two strategies to normalize total homocysteine in uremic patients.

Cardiovascular risk factors in predialysis patients: baseline data from the Chronic Renal Impairment in Birmingham (CRIB) study

BACKGROUND

Patients with end-stage kidney failure have a greatly increased risk of developing premature cardiac and vascular disease. However, little is known about the evolution of cardiovascular diseases in individuals with less severely impaired kidney function.

METHODS

The prevalence of cardiovascular diseases and of suspected cardiovascular risk factors was studied in a group of 369 individuals (median age, 63 years, 67% male) with various degrees of impaired kidney function (calculated creatinine clearances 6 to 105 mL/min), in 103 patients with angiographically proven coronary artery disease, and in 103 apparently healthy individuals. These patients are being followed prospectively.

RESULTS

Of those patients with kidney disease, 34% had a history of vascular disease and 21% had left ventricular hypertrophy on electrocardiogram at baseline. Traditional risk factors were prevalent, with a history of hypertension in 76% of kidney disease patients, diabetes in 15%, and dyslipidemia with reduced low-density lipoprotein (LDL) cholesterol, elevated serum triglycerides, and decreased high-density lipoprotein (HDL) levels. Other possible cardiovascular risk factors include elevated concentrations of plasma homocysteine, as well as low serum albumin and hemoglobin levels. Patients with more severely impaired renal function had lower diastolic blood pressures, lower LDL and HDL cholesterol levels, were more anemic, and had higher plasma homocysteine concentrations.

CONCLUSIONS

Vascular disease and left ventricular hypertrophy are prevalent among patients with chronic kidney disease not requiring dialysis. In addition to traditional risk factors, other features of the uremic syndrome such as anemia, hyperhomocysteinemia, and inflammation (suggested by hypoalbuminemia) may contribute.

Genetic approaches in the clinical investigation of complex disorders: malnutrition, inflammation, and atherosclerosis (MIA) as a prototype

Despite major research efforts and improvements in dialysis technology, patients with end-stage renal disease (ESRD) experience an extremely high mortality, which seems to be increasingly related to cardiovascular disease. Cardiovascular disease has been linked to the presence of systemic inflammation and malnutrition (MIA syndrome), in addition to the high prevalence of traditional risk factors observed in ESRD patients. Since the mechanisms underlying the development of these complications of ESRD are largely unknown, new strategies for identification of risk factors, pathophysiologic pathways, and targets for intervention are warranted. Although the combined impact of MIA complications seems to determine the extremely poor clinical outcome in the ESRD patients, there are significant unexplained individual differences in the development of the MIA syndrome, implying that genetic differences might play a role. The vast information generated by the advances in molecular genetics offers a great opportunity to analyze the causes of differences not only in our susceptibility to (or protection from) various diseases, but also in the age of onset, severity of illness, and in the way our bodies respond to treatment. In this review, we summarize an integrated approach in the investigation of complex disorders, requiring the interactive collaboration between laboratory, clinical, and epidemiologic resources using the MIA syndrome as a prototype. We focus on the application of common genetic variations (single nucleotide polymorphisms [SNPs]) in association with studies to generate potential risk profiling using data from multiple vulnerability genes. The appropriate application of this approach may be essential in the early identification of high-risk individuals and groups of patients for whom specific therapeutic interventions are indicated, thus creating a tailor-made clinical management for the future.

[Atherosclerosis and uremia: signifance of non-traditional risk factors]

Arteriosclerosis, atherosclerosis and vascular calcification are causally related to the high morbidity and mortality of patients with chronic renal failure. Oxidative stress and carbonyl stress of uremia, dialysis procedure and/or intravenous iron therapy result in AGE (advanced glycation end-product), ALE (advanced lipoxidation end-product) and AOPP (advanced oxidation protein product) formation, favouring together with elevated CRP (C-reactive protein) levels the development of cardiovascular and cerebrovascular complications. Enhanced plasma levels of homocysteine and ADMA (asymmetric dimethylarginine) contribute to this process. In addition, in chronic renal insufficiency hyperphosphatemia and an enhanced calcium x phosphorus ion product are associated with the morbidity and mortality of the patients, particularly in the presence of fetuin deficiency. Phosphorus, AGEs and AOPPs, beside other factors, catalyze the conversion of vascular smooth muscle cells to osteoblast--like cells (particularly in the presence of monocytes/macrophages), resulting in bone matrix protein formation. Other risk factors, such as age, male sex, smoking, hypertension, diabetes, chronic inflammation, insulin resistance or dyslipidemia (enhanced non-HDL-cholesterol) also contribute to the atherosclerotic risk profile of the patient with chronic renal insufficiency. While there is growing understanding of the mechanisms involved in arteriosclerosis, atherosclerosis and vascular calcification in uremia, we are still missing effective therapeutic maneuvers for reduction of excess mortality in uremic patients.

Diagnosis and therapy of coronary artery disease in renal failure, end-stage renal disease, and renal transplant populations

Even though cardiovascular disease is the leading cause of death in patients with CRF and end-stage renal disease (ESRD), ill-conceived notions have led to therapeutic nihilism as the predominant strategy in the management of cardiovascular disease in these populations. The recent data clearly support the application of proven interventions in the general population, such as angiotensin-converting enzyme inhibitors and statins to patients with CRF and ESRD. The advances in coronary stents and intracoronary irradiation have decreased the restenosis rates in renal failure patients. Coronary artery bypass with internal mammary graft might be the procedure of choice for coronary revascularization in these patients. The role of screening for asymptomatic coronary disease is established as a pretransplant procedure, but it is unclear whether this will be applicable to all patients with ESRD. Future studies need to focus on unraveling the mechanisms by which uremia leads to increased cardiovascular events to design optimal therapies targeted toward these mechanisms and improve cardiovascular outcomes.

Hyperhomocysteinemia induces renal hemodynamic dysfunction: is nitric oxide involved?

Hyperhomocysteinemia is associated with endothelial dysfunction, although the underlying mechanism is unknown. Previous studies have shown that nitric oxide (NO) plays an important role in the regulation of systemic and renal hemodynamics. This study investigated whether hyperhomocysteinemia induces renal oxidative stress and promotes renal dysfunction involving disturbances of the NO-pathway in Wistar rats. During 8 wk, control (C) and hyperhomocysteinemic (HYC) groups had free access to tap water and homocysteine-thiolactone (HTL, 50 mg/kg per d), respectively. At 8 wk, plasma homocysteine concentration, renal superoxide anion (O(2)), nitrotyrosine, and nitrite+nitrate levels, and renal function were measured. To assess NO involvement, the responses to L-Arginine (L-Arg, 300 mg/kg) and N(G)-nitro-L-arginine-methyl-ester (L-NAME, 20 microg/kg per min for 60 min) were analyzed. The HYC group showed higher homocysteine concentration (7.6 +/- 1.7 versus 4.9 +/- 1.0 micromol/L; P < 0.001), (O(2) production (157.92 +/- 74.46 versus 91.17 +/- 29.03 cpm. 10(3)/mg protein), and nitrite+nitrate levels (33.4 +/- 5.1 versus 11.7 +/- 4.3 micro mol/mg protein; P < 0.001) than the control group. Western blot analyses showed a nitrotyrosine mass 46% higher in the HYC group than in the controls. Furthermore, the HYC group showed lower GFR, renal plasma flow (RPF), and higher renal vascular resistance (RVR) than the controls. After L-Arg administration, the responses of GFR, RPF, and RVR were attenuated by 36%, 40%, and 50%, respectively; after L-NAME, the responses of RPF and RVR were exaggerated by 79% and 112%, respectively. This suggests a reduced NO bioavailability to produce vasodilation and an enhanced sensitivity to NO inhibition. In conclusion, hyperhomocysteinemia induces oxidative stress, NO inactivation, and renal dysfunction involving disturbances on the NO-pathway.

Hyperhomocysteinemia and its relationship to cardiovascular disease in ESRD: influence of hypoalbuminemia, malnutrition, inflammation, and diabetes mellitus

BACKGROUND

In the general population, a mildly elevated plasma total homocysteine (tHcy) level is an independent and graded risk factor for cardiovascular disease (CVD). In patients with end-stage renal disease (ESRD), CVD is highly prevalent and a major cause of premature mortality, and plasma tHcy levels are as much as three to four times greater than in the general population. Several other risk factors, such as diabetes mellitus (DM), inflammation, and malnutrition, also are prevalent and contribute to CVD in patients with ESRD, and there are strong associations between inflammation, malnutrition, and hypoalbuminemia in these patients. Several investigations in patients with ESRD have shown the important role of vitamin status for plasma tHcy, but little attention has been given to the influence of nutritional status. However, it is obvious that hypoalbuminemia is of interest because a substantial fraction of tHcy (>70%) is protein bound, mainly to albumin.

RESULTS

In studies of patients with ESRD in whom the prevalence of hyperhomocysteinemia was very high (>90%), tHcy level was strongly related to serum albumin level, and patients with malnutrition had lower levels of both tHcy and serum albumin than those with normal nutritional status. Furthermore, inflammation, DM, and CVD are associated with hypoalbuminemia and therefore a lower degree of hyperhomocysteinemia. In our studies, in different groups of patients with ESRD, we showed that greater tHcy levels were associated with lower CVD mortality. However, this apparently paradoxical association between lower CVD mortality and lower plasma tHcy levels (although still abnormally high) does not refute the concept that hyperhomocysteinemia is a risk factor for CVD because almost all patients may have had long-standing elevated plasma tHcy levels within a range that makes them prone to develop atherosclerosis. Instead, a potentially detrimental effect of hyperhomocysteinemia on CVD in patients with ESRD may be obscured by the influence of hypoalbuminemia, whatever the cause, because hypoalbuminemia and its causes are strong predictors of mortality.

CONCLUSION

Our findings imply that nutritional status and serum albumin level, as well as the presence of inflammation and DM, should be taken into consideration when evaluating tHcy as a risk factor for CVD in patients with ESRD.

Free cysteine is increased in plasma from hemodialysis patients

BACKGROUND

Although only the total thiol concentration, which includes bound and free forms, has been determined in most previous clinical studies, the free form may be a better predictor of cardiovascular risk.

METHODS

We measured the apparent concentration of free homocysteine (Hcy) and cysteine (Cys) in filtered and acid-soluble fractions of plasma in healthy control subjects and in patients with chronic renal failure just before and after a hemodialysis session.

RESULTS

In control, filtered Hcy and acid-soluble Hcy were similar, while filtered Cys was much smaller than in acid-soluble Cys. In prehemodialysis samples, filtered Cys was more than 60 times as abundant (259.2 +/- 26.2 micromol/L) as in control samples (4.1 +/- 0.7 micromol/L ). Free-to-total ratios for filtered Cys were 1.6 +/- 0.3% in controls, but 40.9 +/- 2.7% in prehemodialysis patients.

CONCLUSIONS

The filtered fraction of thiols can be used to estimate solute transport across the dialysis membrane. In addition, the possible involvement of cysteine in the pathogenesis of atherosclerosis in hemodialysis patients should be reexamined.

Reverse epidemiology of cardiovascular risk factors in maintenance dialysis patients

Conventional risk factors of cardiovascular disease and mortality in the general population such as body mass, serum cholesterol, and blood pressure are also found to relate to outcome in maintenance dialysis patients, but often in an opposite direction. Obesity, hypercholesterolemia, and hypertension appear to be protective features that are associated with a greater survival among dialysis patients. A similar protective role has been described for high serum creatinine and possibly homocysteine levels in end-stage renal disease (ESRD) patients. These findings are in contrast to the well-known association between over-nutrition and poor outcome in the general population. The association between under-nutrition and adverse cardiovascular outcome in dialysis patients, which stands in contrast to that seen in non-ESRD individuals, has been referred to as "reverse epidemiology." Publication bias may have handicapped or delayed additional reports with such paradoxical findings in ESRD patients. The etiology of this inverse association between conventional risk factors and clinical outcome in dialysis patients is not clear. Several possible causes are hypothesized. First, survival bias may play a role since only a small number of patients with chronic kidney disease (CKD) survive long enough to reach ESRD. Hence, the dialysis patients are probably a distinctively selected population out of CKD patients and may not represent the risk factor constellations of their CKD predecessors. Second, the time discrepancy between competitive risk factors may play a role. For example, the survival disadvantages of under-nutrition, which is frequently present in dialysis patients, may have a major impact on mortality in a shorter period of time, and this overwhelms the long-term negative effects of over-nutrition on survival. Third, the presence of the "malnutrition-inflammation complex syndrome" (MICS) in dialysis patients may also explain the existence of reverse epidemiology in dialysis patients. Both protein-energy malnutrition and inflammation or the combination of the two are much more common in dialysis patients than in the general population and many elements of MICS, such as low weight-for-height, hypocholesterolemia, or hypocreatininemia, are known risk factors of poor outcome in dialysis patients. The existence of reverse epidemiology may have a bearing on the management of dialysis patients. It is possible that new standards or goals for such traditional risk factors as body mass, serum cholesterol, and blood pressure should be considered for these individuals.

Mortality differences by dialysis modality among incident ESRD patients with and without coronary artery disease

It is unclear whether peritoneal dialysis (PD) compared with hemodialysis (HD) confers a survival advantage in end-stage renal disease (ESRD) patients with coronary artery disease (CAD). This hypothesis was tested in a national cohort of 107,922 patients starting dialysis therapy between May 1, 1995, and July 31, 1997. Data on patient characteristics were obtained from the Center for Medicare and Medicaid Services Medical Evidence Form (CMS) and linked to mortality data from the United States Renal Data System (USRDS). Patients were classified on the basis of CAD presence and followed until death or the end of 2 yr. Nonproportional Cox regression models estimated the relative risk (RR) of death for patients with and without CAD by dialysis modality using primarily the intent-to-treat but also the as-treated approach. Diabetic patients (DM) and nondiabetic patients (non-DM) were analyzed separately. Among DM, patients with CAD treated with PD had a 23% higher RR (95% CI, 1.12 to 1.34) compared with similar HD patients, whereas patients without CAD receiving PD had a 17% higher RR (CI, 1.08 to 1.26) compared with HD. Among non-DM, patients with CAD treated with PD had a 20% higher RR (CI. 1.10 to 1.32) compared with HD patients, whereas patients without CAD had similar survival on PD or HD (RR = 0.99; CI, 0.93 to 1.05). The mortality risk for new ESRD patients with CAD differed by treatment modality. In both DM and non-DM, patients with CAD treated with PD had significantly poorer survival compared with HD. Whether differences in solute clearance and/or cardiac risk profiles between PD and HD may explain these findings deserves further investigation.

S-adenosylhomocysteine and the ratio of S-adenosylmethionine to S-adenosylhomocysteine are not related to folate, cobalamin and vitamin B6 concentrations

BACKGROUND

It is unclear whether homocysteine itself is causal in the pathogenesis of cardiovascular disease. Alternatively or additionally, the association between homocysteine and cardiovascular disease may be because of its metabolic precursor, S-adenosylhomocysteine, or of the ratio of S-adenosylmethionine to S-adenosylhomocysteine. Therefore, it is relevant to know how these moieties are interrelated, and whether, as is the case for homocysteine, they are influenced by blood levels of folate, cobalamin or vitamin B6.

DESIGN

We cross-sectionally studied a population-based cohort of 97 Caucasian subjects aged 60-85 years. Concentrations of homocysteine, S-adenosylhomocysteine, S-adenosylmethionine, folate, cobalamin and vitamin B6 were measured in fasting blood samples.

RESULTS

In multiple regression analysis, homocysteine was associated with vitamin B12 (per 50 pmol L-1 increase of cobalamin, change in homocysteine, -0.70 mmol L-1; 95% CI, -1.30 to -0.10 mmol L-1) and folate (per 100 nmol L-1 increase in erythrocyte folate, change in homocysteine, -0.68 mmol L-1; 95% CI -1.28 to -0.08 mmol L-1). S-adenosylhomocysteine, S-adenosylmethionine and the ratio of S-adenosylmethionine to S-adenosylhomocysteine were not associated with serum folate, cobalamin or vitamin B6, nor with erythrocyte folate. Furthermore, plasma homocysteine showed a negative correlation with the ratio of S-adenosylmethionine to S-adenosylhomocysteine in plasma (r = -0.27; P < 0.01) but not in erythrocytes.

CONCLUSIONS

In contrast to homocysteine, the plasma concentrations of S-adenosylhomocysteine and the ratio of S-adenosylmethionine to S-adenosylhomocysteine were not associated with the folate, cobalamin and vitamin B6 concentrations in the present study. If these precursors in part explain why homocysteine is associated with cardiovascular disease, homocysteine-lowering treatment with B vitamins may be less effective than currently expected, at least in an elderly population.

Update on Cobalamin, Folate, and Homocysteine

Three topics affecting cobalamin, folate, and homocysteine that have generated interest, activity, and advances in recent years are discussed. These are: (I) the application of an expanded variety of tools to the diagnosis of cobalamin deficiency, and how these affect and are affected by our current understanding of deficiency; (II) the nature of the interaction between homocysteine and vascular disease, and how the relationship is affected by vitamins; and (III) the improved understanding of relevant genetic disorders and common genetic polymorphisms, and how these interact with environmental influences.

The diagnostic approach to cobalamin deficiency now allows better diagnosis of difficult and atypical cases and more confident rejection of the diagnosis when deficiency does not exist. However, the process has also become a complex and sometimes vexing undertaking. Part of the difficulty derives from the lack of a diagnostic gold standard among the many available tests, part from the overwhelming numerical preponderance of patients with subclinical deficiency (in which isolated biochemical findings exist without clinical signs or symptoms) among the cobalamin deficiency states, and part from the decreased availability of reliable tests to identify the causes of a patient’s cobalamin deficiency and thus a growing deemphasis of that important part of the diagnostic process. In Section I, Dr. Carmel discusses the tests, the diagnostic issues, and possible approaches to the clinical evaluation. It is suggested no single algorithm fits all cases, some of which require more biochemical proof than others, and that differentiating between subclinical and clinical deficiency, despite their overlap, may be a helpful and practical point of departure in the evaluation of patients encountered in clinical practice. The arguments for and against a suggested expansion of the cobalamin reference range are also weighed.

The epidemiologic data suggest that homocysteine elevation is a risk factor for vascular and thrombotic disease. In Section II, Dr. Green notes that the interactions of metabolism and clinical risk are not well understood and a causative relationship remains unproven despite new reports that lowering homocysteine levels may reduce vascular complications. Genetic and acquired influences may interact in important ways that are still being sorted out. The use of vitamins, especially folate, often reduces homocysteine levels but also carries potential disadvantages and even risks. Folate fortification of the diet and supplement use have also markedly reduced the frequency of folate deficiency, and cobalamin deficiency is now the more common deficiency state, especially among the elderly.

Although genetic disorders are rare, they illuminate important metabolic mechanisms and pose diagnostic challenges, especially when clinical presentation occurs later in life. In Section III, Drs. Rosenblatt and Watkins use selected disorders to illustrate the subject. Imerslund-Gräsbeck syndrome, a hereditary disorder of cobalamin absorption at the ileal level, demonstrates genetic heterogeneity. Finnish patients show mutation of the gene for cubilin, the multiligand receptor for intrinsic factor. Surprisingly, Norwegian and other patients have been found recently to have mutations of the AMN (amnionless) gene, mutations that are lethal in mice at the embryonic stage. Two disorders of cobalamin metabolism, cblG and cblE, are now known to arise from mutations of the methionine synthase and methionine synthase reductase genes, respectively. These disorders feature megaloblastic anemia and neurologic manifestations. The folate disorder selected for illustration, methylenetetrahydrofolate reductase (MTHFR) deficiency, paradoxically causes neurological problems but no megaloblastic anemia. This rare deficiency is the most common inborn error of folate metabolism. It is distinct from the very common MTHFR gene polymorphisms, mutations that cause mild to moderate reductions in MTHFR activity but no direct clinical manifestations. The MTHFR polymorphisms, especially the 677C→T mutation, may contribute to vascular and birth defect risks, while reducing the risk of certain malignancies, such as colon cancer. These polymorphisms and those of genes for other enzymes and proteins related to cobalamin, folate, and homocysteine metabolism may be important role players in frequent interactions between genes and the environment.

Plasmatic homocysteine concentration and its relationship with complications associated to diabetes mellitus

BACKGROUND AND METHODS

In the search for new factors of cardiovascular risk associated to diabetes mellitus (DM), special attention has been paid in recent years to hyperhomocysteinaemia. Therefore, we have established the concentration of homocysteine (Hcy) and other biochemical parameters in the plasma of a group of 57 type 1 and 32 type 2 diabetic patients and 54 control subjects and studied whether plasmatic homocysteinaemia was related to macroangiopathy, nephropathy, retinopathy and neuropathy. Because of significant differences for plasma Hcy values between men and women in the control group, we distinguished between both groups throughout the study.

RESULTS

Patients with DM had higher Hcy than control subjects (11.7+/-5.4 vs. 10.1+/-2.4 micromol/l, p<0.05). Fasting hyperhomocysteinaemia was considered as the mean of the plasma Hcy for control subjects+2 SD (14.9 micromol/l in total group, 15.6 micromol/l in males and 13.9 micromol/l in females). In the studied groups with complications, we found significant differences between normohomocysteinaemic type 1 diabetic patients and those considered hyperhomocysteinaemic by us. On the other hand, patients having type 1 DM and complications had higher plasmatic Hcy concentration than those with no complications.

CONCLUSIONS

We have found a relationship between high Hcy levels and prevalence of macroangiopathy, retinopathy and nephropathy in the type 1 diabetic patients, which was not been observed in the type 2 diabetic patients of our study. As a result, we consider plasmatic Hcy a complication-risk indicator in type 1 DM, and we recommend its use together with already established biochemical parameters in the control of the evolution of the disease.

Association between serum aspartate transaminase and homocysteine levels in hemodialysis patients

BACKGROUND

Hyperhomocysteinemia is a common metabolic abnormality in patients undergoing hemodialysis (HD). An impairment of remethylation of homocysteine (Hcy) is seen in these patients but cannot account completely for hyperhomocysteinemia. Homocysteine is derived from transmethylation of methionine that can be metabolized through transamination pathway alternatively. However, the significance of transamination in the metabolism of Hcy in HD patients is not studied.

METHODS

A total of 145 patients undergoing HD for more than 3 months were enrolled in the study. Vitamins B were not prescribed routinely to these patients. Among them, 49 patients had positive test results for hepatitis B surface antigen or antihepatitis C virus antibody. Serum Hcy, folic acid, vitamin B12, pyridoxal 5' -phosphate, methionine, and transaminase were measured, and parameters of dialysis adequacy were calculated. Multiple linear regression model was used to analyze the factors determining Hcy levels.

RESULTS

All patients had higher Hcy levels (40.3 +/- 28.3 micromol/L) than the upper limit of reference range 15 micromole/L. The levels of vitamin B(12) were all higher than 160 pg/mL (118 pmol/L). Only 9 patients had serum folic acid lower than 3 ng/mL (6.8 nmol/L). The predialysis Hcy levels were correlated with age, HD duration, folic acid, vitamin B12, and aspartate transaminase (AST) levels among all patients or the subgroup of hepatitis noncarriers with linear multiple regression analysis. In hepatitis carriers, AST levels were not associated with Hcy. A cutoff value of AST less than 14 U/L predicted a predialysis Hcy level higher than 27 micromol/L in noncarriers, with a sensitivity of 83.9% and a specificity of 50.2%.

CONCLUSION

In addition to vitamin B12 and folic acid, the serum AST levels correlated inversely with predialytic Hcy levels independently in hepatitis noncarrier HD patients. The results suggest that transamination may play an important role in the development of hyperhomocysteinemia when impaired transmethylation is encountered in uremic patients.

Pharmacotherapy of hyperhomocysteinaemia in patients with thrombophilia

Hyperhomocysteinaemia is often the result of inherited abnormalities of the enzymes involved in homocysteine metabolism or vitamin deficiencies (vitamins B12, B6 or folate) and is present in approximately 5% of the general population. High homocysteine levels in these individuals are associated with a significant increase in relative risk for both arterial and venous thromboembolic disease. Consequently, effective homocysteine-lowering therapeutic strategies have been extensively investigated. Folic acid represents the cornerstone of treatment. In daily doses of at least 0.4 mg, it effectively reduces homocysteine levels, even in non-folate-deficient patients. The addition of vitamins B12 and/or B6, to folic acid supplementation may provide a small further reduction in homocysteine levels in certain groups of patients. Renal impairment is an important cause of hyperhomocysteinaemia. Individuals with hyperhomocysteinaemia secondary to renal disease commonly require significantly higher doses of folic acid (5-40 mg) to achieve maximal therapeutic effect. The important question of whether effective homocysteine-lowering therapy translates into a reduction in vascular disease remains unknown but is being addressed in a series of ongoing prospective trials.

Relationship of renal function to homocysteine and lipoprotein(a) levels: the frequency of the combination of both risk factors in chronic renal impairment

BACKGROUND

Total homocysteine (tHcy) and lipoprotein(a) [Lp(a)] levels have been recognized as risk factors for vascular disease. The combination of elevated tHcy and Lp(a) levels may be particularly atherogenic, although no study has examined the prevalence of the combination of both risk factors in patients with chronic renal impairment.

METHODS

One hundred ninety-seven patients with renal impairment were studied. Patients had glomerular filtration rate (GFR) measured by clearance of chromium 51-labeled EDTA. Blood was obtained for the determination of tHcy, Lp(a), and apolipoprotein(a) [apo(a)] isoform levels.

RESULTS

Patients were divided into five groups according to GFR. Mean tHcy levels in the five groups were as follows: GFR less than 10 mL/min, 30.2 +/- 9.8 (SD) micromol/L; GFR of 10 to 20 mL/min, 26.6 +/- 10.5 micromol/L; GFR of 20 to 30 mL/min, 23.9 +/- 8.6 micromol/L; GFR of 30 to 45 mL/min, 22.2 +/- 8.6 micromol/L; and GFR of 45 to 75 mL/min, 18.2 +/- 9.1 micromol/L compared with control levels of 12.7 +/- 4.6 micromol/L. There was a progressive increase in median Lp(a) levels with declining renal function: median Lp(a) levels for those with a GFR less than 10 mL/min were 37.1 mg/dL (range, 0.6 to 156.0 mg/dL); GFR of 10 to 20 mL/min, 30.3 mg/dL (range, 2.6 to 163.7 mg/dL); GFR of 20 to 30 mL/min, 26.1 mg/dL (range, 0.0 to 164.0 mg/dL); GFR of 30 to 45 mL/min, 20.9 mg/dL (range, 0.0 to 99.8 mg/dL), and GFR of 45 to 75 mL/min, 16.8 mg/dL (range, 2.1 to 81.0 mg/dL) compared with control values of 12.5 mg/dL (range, 0.0 to 88.7 mg/dL).

CONCLUSION

Defining hyperhomocysteinemia as tHcy levels greater than the 90th percentile of controls and elevated Lp(a) level as greater than 30 mg/dL, the frequency of the combination increased with declining renal function. Fifty-eight percent of patients with a GFR less than 10 mL/min had both hyperhomocysteinemia and elevated Lp(a) levels, and even in patients with mild renal impairment, 20% of patients had both risk factors present.

Homocysteine and cystatin C level changes in haemodialysed patients and connection with cerebro- and cardiovascular complications

Plasma homocysteine and Cystatin C levels of 360 chronic haemodialysed patients were measured in fasting (191 men, mean age: 55.5 years; and 169 women, mean: 62.9 years). The patients were divided into subgroups: diabetes mellitus (34 men and 38 women 7 vs 8 IDDM). obliterative arteriosclerosis (68 men and 61 women), cardiovascular complications (75 men and 84 women) and stroke (16 men and 12 women), and after renal transplantation in chronic rejection (15 men and 5 female). Homocysteine was determined by IMx analyser from Abbott by FPIA method. Immunoturbidimetric method was used for quantification of Cystatin C (PETIA). The lowest Cystatin C concentration was found in diabetic patients (4.35 +/- 0.15 mg/l in men and 3.18 +/- 1.77 mg/l in women) and the highest one occurred in anuric and bilateral nephrectomised and transplanted chronic rejected patients (6.075 mg/l in men and 6.35 mg/l in women: p<0.001). The homocysteine levels (24.98 +/- 2.94 micromol/l in men and 23.88 +/- 1.76 micromol/l in women) exceeded the upper limit of reference range (<15.0 micromol/l). There was a significant difference in favour of subgroup of cardiovascular (27.25 micromol/l in men and 26.87 micromol/l in women) and stroke patients (27.16 micromol/l in men and 30.76 micromol/l in women p<0.001). Elevated levels were found in chronic rejected patients with accelerated arteriosclerotic events (25.94 micromol/l in men and 27.43 micromol/l in women). Good positive linear correlation was found between serum homocysteine and Cystatin C levels (r=0.2393 and 0.2252). The authors demonstrated hyperhomocysteinaemia associated with high Cystatin C concentration in four subgroups of haemodialysed patients (obliterative and accelerated arteriosclerosis, cardiovascular disease, and cerebrovascular complications and stroke).

Hyperhomocysteinemia and thrombosis

Homocysteine (Hcy) is a sulfhydryl amino acid derived from the metabolic conversion of methionine, which is dependent on vitamins (folic acid, B12, and B6) as cofactors or cosubstrates. In 1969, McCully first reported the presence of severe atherosclerotic lesions in patients with severe hyperhomocysteinemia and hypothesized the existence of a pathogenic link between hyperhomocysteinemia and atherogenesis. Several case-control and cross-sectional studies were consistent with the initial hypothesis of McCully, showing that moderate hyperhomocysteinemia is also associated with heightened risk of occlusive arterial disease. Less consistent results have been reported by prospective cohort studies of subjects who were healthy at the time of their enrollment, whereas prospective cohort studies of patients with overt coronary artery disease or other conditions at risk consistently confirmed the association between moderate hyperhomocysteinemia and cardiovascular morbidity and mortality. More recently, an association between moderate hyperhomocysteinemia and heightened risk of venous thromboembolism has been documented, suggesting that hyperhomocysteinemia might be involved not only in atherogenesis, but also in thrombogenesis. The mechanisms by which hyperhomocysteinemia might contribute to atherogenesis and thrombogenesis are incompletely understood. The mainstay of treatment of hyperhomocysteinemia is folic acid, alone or in combination with vitamin B12 and vitamin B6. Although it is quite clear that vitamins effectively reduce the plasma levels of total homocysteine (tHcy), we do not yet know whether they will decrease the risk of vascular disease. The results of ongoing randomized, placebo-controlled, double-blind trials of the effects of vitamins on the thrombotic risk will help in defining whether the relationship between hyperhomocysteinemia and thrombosis is causal, and will potentially have a dramatic effect in the prevention of thromboembolic events.

Homocysteine and arterial disease. Experimental mechanisms

Hyperhomocysteinemia (hH(e)) in the general population is associated with incidence and progression of arterial occlusive disease, although the underlying mechanisms are not well defined. Current research supports a role for homocysteine (H(e))-mediated endothelial damage and endothelial dysfunction. This mechanism appears to be a key factor in subsequent impaired endothelial-dependent vasoreactivity and decreased endothelium thromboresistance. These consequences may predispose hyperhomocysteinemic vessels to the development of increased atherogenesis. Additional mechanisms of H(e)-mediated vascular pathology, including protein homocysteinylation and vascular smooth muscle cell proliferation may also play a role. Continued investigation into the mechanisms contributing to H(e) toxicity will provide further insight into the processes by which hH(e) may increase atherosclerosis.

Is folate a promising agent in the prevention and treatment of cardiovascular disease in patients with renal failure?

Management of the conventional cardiovascular risk factors is insufficient to prevent the dramatic increase in atherosclerotic cardiovascular morbidity and mortality in patients with renal failure. Folate recently received attention as a potential alternative treatment option to decrease the excess cardiovascular risk in the uremic population. Folate administration is the principal treatment modality for hyperhomocysteinemia. Hyperhomocysteinemia is prevalent in more than 85% of patients with end-stage renal disease (ESRD) and is independently associated with increased odds for atherosclerotic cardiovascular disease. Several attempts have been made to normalize homocysteine levels in uremic patients with folate-based vitamin regimens. Although supraphysiologic doses of folic acid afford greater reductions in homocysteine levels than standard doses, the response to treatment is generally only partial and the large majority of ESRD patients have residual hyperhomocysteinemia. Several defects in folate metabolism have been described in uremia, which may explain the relative folate resistance in patients with renal failure, but their clinical relevance remains uncertain. It appears unlikely that the hyperhomocysteinemia in ESRD can be cured solely with folic acid supplements, since folate does not affect the prolonged plasma elimination of homocysteine, which is the primary defect in homocysteine metabolism in uremia. Folate restores endothelial dysfunction, associated with hyperlipidemia, diabetes and hyperhomocysteinemia. The beneficial effect appears to be independent of its homocysteine-lowering capacity and is possibly related to an improved bioavailability of nitric oxide. However, folate has failed to improve endothelial dysfunction in uremic patients. In the ESRD population, multiple metabolic and hemodynamic abnormalities adversely affect endothelial function. In addition, irreversible structural vascular disease already may be present. Folate should, therefore, probably be an integral part of an "endothelial protective regimen," consisting of lipid-lowering agents, antihypertensives and antioxidant vitamins and started very early in patients with renal failure. Before large-scale folate administration can be recommended, effects on hard endpoints of cardiovascular disease need to be demonstrated in randomized trials. Such trials are currently underway in patients with normal renal function at high risk for cardiovascular disease, and one trial has recently been initiated in stable renal transplant recipients.

Association between plasma homocysteine and vascular atherosclerotic disease in older persons

Plasma homocysteine is a risk factor for coronary artery disease, stroke, extracranial carotid arterial disease, peripheral arterial disease, and aortic atherosclerosis in older persons. Randomized trials are in progress investigating whether multivitamin therapy to decrease plasma homocysteine levels will reduce the risk for cardiovascular disease. (c) 2000 by CHF, Inc.

Plasma aminothiol oxidation in chronic hemodialysis patients

BACKGROUND

Plasma aminothiols, including homocysteine, cysteine, and glutathione, function as an important extracellular redox system. We examined the plasma aminothiol concentration and redox status in ten chronic hemodialysis patients compared to ten age-matched healthy subjects.

METHODS

Plasma levels of reduced, free oxidized, and protein-bound homocysteine, cysteine, cysteinylglycine, and glutathione were determined using high-pressure liquid chromatography (HPLC).

RESULTS

Total plasma homocysteine, cysteine, and cysteinylglycine levels were significantly elevated in hemodialysis patients before dialysis compared to healthy subjects. Total plasma concentration of cysteine and homocysteine significantly decreased after hemodialysis. The ratio of free oxidized to free reduced homocysteine, cysteine, cysteinylglycine, and glutathione were each significantly elevated before dialysis compared to healthy subjects, and decreased significantly by the end of dialysis. The free oxidized to reduced ratio of cysteine and homocysteine were also significantly correlated with total plasma concentrations.

CONCLUSIONS

Plasma aminothiols are excessively oxidized in uremia, while the hemodialysis procedure is restorative of redox status. Oxidized aminothiols are candidate uremic toxins.

Apolipoprotein A-IV serum concentrations are elevated in patients with mild and moderate renal failure

Cell culture studies and investigations in mice that overexpress either human or mouse apolipoprotein A-IV (apoA-IV) revealed anti-atherogenic properties of apoA-IV. An association between low apoA-IV concentrations and coronary artery disease in humans was demonstrated; therefore, apoA-IV may also play an antiatherogenic role in humans. Because apoA-IV is markedly elevated in dialysis patients, patients with the earliest and modest stages of renal impairment were studied to assess the association of apoA-IV with GFR and atherosclerotic complications. GFR was measured by the use of iohexol in 227 non-nephrotic patients with different degrees of renal impairment. ApoA-IV increased significantly with decreasing GFR and was already elevated in earliest stages of renal disease (GFR > 90 ml/min per 1.73 m2). Multiple linear regression analysis identified renal function parameters (GFR, creatinine, and urea) as the most important determinants of apoA-IV levels in serum of these patients. Twenty-six patients had already experienced 36 atherosclerotic events. Logistic regression analysis identified three variables associated with atherosclerotic complications: age, apoA-IV, and gender. Each 1 mg/dl increase of apoA-IV decreased the odds ratio for an atherosclerotic complication by 8% (P = 0.011). The data clearly show that the anti-atherogenic apoA-IV starts to increase during the earliest phases of renal insufficiency, which makes apoA-IV an early marker of renal impairment.

Hyperhomocysteinemia predicts cardiovascular outcomes in hemodialysis patients

BACKGROUND

We prospectively tested the prediction power of homocysteinemia for all-cause and cardiovascular outcomes in a cohort of 175 hemodialysis patients followed for 29 +/- 12 months.

METHODS

Survival analysis was performed by the Cox's proportional hazard model and data were expressed as hazard ratio and 95% confidence interval (CI).

RESULTS

During the follow-up period 51 patients died, 31 of them (61%) of cardiovascular causes and 16 patients developed non-fatal atherothrombotic complications. Plasma total homocysteine was an independent predictor of cardiovascular mortality (P=0.01). Combined analysis of fatal and non-fatal atherothrombotic events showed that homocysteine was a strong and independent predictor of these outcomes because the risk of these events was 8.2 times higher (95% CI 1.9 to 32.2) in patients in the third homocysteine tertile than in those in the first tertile (P=0.005).

CONCLUSIONS

There is a clear association between hyperhomocysteinemia and incident cardiovascular mortality and atherothrombotic events in hemodialysis patients. Intervention studies are needed to determine whether the accumulation of this substance has a causal role in the pathogenesis of cardiovascular damage in patients undergoing hemodialysis.

Elevated plasma 4-pyridoxic acid in renal insufficiency

BACKGROUND

Renal insufficiency is associated with altered vitamin B-6 metabolism. We have observed high concentrations of 4-pyridoxic acid, the major catabolite of vitamin B-6 metabolism, in plasma during renal insufficiency.

OBJECTIVE

The objective was to evaluate the renal handling of 4-pyridoxic acid and the effects of renal dysfunction on vitamin B-6 metabolism.

DESIGN

We measured the renal clearance of 4-pyridoxic acid and creatinine in 17 nonpregnant, 17 pregnant, and 16 lactating women. We then examined the influence of vitamin B-6 or alkaline phosphatase activity on the ratio of 4-pyridoxic acid to pyridoxal (PA:PL) in plasma in 10 men receiving a low (0.4 mg pyridoxine.HCl/d) or high (200 mg pyridoxine.HCl/d) vitamin B-6 intake for 6 wk, in 10 healthy subjects during a 21-d fast, in 1235 plasma samples from 799 people screened for hypophosphatasia, and in 67 subjects with a range of serum creatinine concentrations.

RESULTS

Renal clearance of 4-pyridoxic acid was 232 +/- 94 mL/min in nonpregnant women, 337 +/- 140 mL/min in pregnant women, and 215 +/- 103 mL/min in lactating healthy women. These values were approximately twice the creatinine clearance, indicating that 4-pyridoxic acid is at least partially eliminated by tubular secretion. Elevated plasma creatinine concentrations were associated with marked elevations in 4-pyridoxic acid and PA:PL. PA:PL was not affected by wide variations in vitamin B-6 intake or by the wide range of pyridoxal-P concentrations encountered while screening for hypophosphatasia.

CONCLUSIONS

Plasma 4-pyridoxic acid concentrations are markedly elevated in renal insufficiency. Plasma PA:PL can distinguish between increases in 4-pyridoxic acid concentrations due to increased dietary intake and those due to renal insufficiency.

Homocysteine and cardiovascular disease in diabetes mellitus

BACKGROUND

Patients with diabetes mellitus (DM) have 2- to 6-fold increase in the prevalence of cardiovascular disease (CVD) compared to non-DM subjects. Epidemiological data show that DM is synergic with other conventional risk factors. Total plasma homocysteine (tHcy) is an emerging CVD risk factor. We reviewed the literature to explore the relation between tHcy and CVD in patients with DM.

METHODS

We searched the MEDLINE database for articles on homocysteine, DM and CVD published from January 1991 to October 2000.

RESULTS

The mean plasma tHcy level is usually low or normal in DM patients, except when nephropathy is present. Levels in that case tend to be higher than in non-DM patients. An independent association with tHcy and CVD was shown in retrospective studies, for DM patients. Prospective studies showed an association between elevated tHcy and all cause mortality in DM patients. In general, the association between elevated levels of tHcy and the outcome was stronger than in non-DM individuals, for all types of study.

DISCUSSION

To date, there are no prospective work that specifically examined the relationship between levels of tHcy and the presence of CVD in the DM population. Nor are there studies to show that treating elevated tHcy results in a reduction of CVD events. Such studies are ongoing. Nevertheless, since hyperhomocysteinemia is potentially reversible with vitamin therapy, interaction of DM with high levels tHcy on the risk of CVD may have consequences with regard to management of primary and secondary prevention in DM patients who are at particularly high risk of CVD events.

Association of endothelial dysfunction with sulfur amino acid metabolism in chronic renal failure

Moderate hyperhomocysteinemia and endothelial dysfunction are consistent findings in uremic patients. Although an exceedingly high incidence of cardiovascular disease and stroke has been shown in dialysis patients, several traditional risk factors are relatively limited predictors. Hyperhomocysteinemia could be a principal candidate for endothelial dysfunction. Recent findings suggest that hyperhomocysteinemia may impair endothelial function by the generation of oxygen species and decreased nitric oxide (NO) bioavailability. However, the precise mechanisms underlying the link between hyperhomocysteinemia and impaired endothelial function in chronic renal failure remain unclear. Endothelial function was evaluated by the response to reactive hyperemia and donor of NO. We observed impairment in both endothelium-dependent and endothelium-independent vasodilation in dialysis patients. These data suggest that patients with chronic renal failure may have defective NO-mediated function in the endothelium and smooth muscle of vessels. Most reports have shown only impairment of endothelium-dependent vasodilation, whereas another report observed impaired smooth muscle function and intact endothelial function. Only a few previous observations included a full set of vascular function data, such as baseline vessel diameter, reactive hyperemia, and responses of endothelium to hyperemia and NO donor, although all these observations could be essential for comparison with other reports. Treatment with folic acid was reported to reduce plasma homocysteine levels, but not to normal levels, and failed to improve impaired endothelial function in patients in a predialysis phase and on maintenance dialysis therapy. Another investigation, directed at reducing homocysteine levels in earlier stages of renal failure, may be necessary to clarify the link between hyperhomocysteinemia and endothelial function.

An MTHFR variant, homocysteine, and cardiovascular comorbidity in renal disease

BACKGROUND

It is unclear whether total serum homocysteine (tHcy) and the C677T mutation of methylenetetrahydrofolate reductase (MTHFR) are associated with cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD).

METHODS

A cross-sectional sample of 459 patients with ESRD on chronic dialysis was assessed to determine whether tHcy and the C677T mutation are associated with CVD prevalence in multiple logistic regression. As CVD mortality is high, we examined the relationship between homozygosity and duration of dialysis.

RESULTS

Mean tHcy was higher in patients without a history of CVD (35.2 micromol/L vs. 30.4 micromol/L, P = 0.02). In multivariate models, CVD was negatively associated with tHcy and positively associated with TT genotype, male gender, and body mass index. Mean tHcy levels were higher among those with the TT genotype compared with those with the CC genotype when adjusted for age, folate, creatinine, and albumin (37.9 micromol/L vs. 31.9 micromol/L, P = 0.005). Among whites, the prevalence of the TT genotype was higher in those having undergone less than one year of dialysis (P = 0.002).

CONCLUSIONS

The C677T genotype of MTHFR is associated with CVD in ESRD and may be a more meaningful marker than tHcy for abnormal homocysteine metabolism in ESRD. Prospective data from ongoing clinical trials are needed to improve our understanding of these findings. Screening for this polymorphism may help guide prevention measures.

Total plasma homocysteine and related amino acids in end-stage renal disease (ESRD) patients measured by gas chromatography-mass spectrometry--comparison with the Abbott IMx homocysteine assay and the HPLC method

Increased concentrations of homocysteine probably contribute to the high cardiovascular morbidity and mortality in hemodialysed end-stage renal disease (ESRD) patients and are determined by a variety of factors such as age, residual renal function, and vitamin status. Fasting plasma concentrations of total homocysteine, methionine, cysteine, and cystathionine were determined by gas chromatography-mass spectrometry (GC-MS) in 131 ESRD patients receiving daily oral folate (160-320 microg) and vitamin B6 (10-20 mg) supplements. Concentrations of homocysteine determined by GC-MS were compared with those measured by high-performance liquid chromatography (HPLC) and an immunofluorescence method (IMx analyzer) using Passing-Bablok regression analysis. Mean plasma concentration of total homocysteine determined by GC-MS (28.7+/-11.9 micromol/l [mean+/-SD]) was significantly lower than that determined by HPLC (34.0+/-14.5 micromol/l; p<0.001) or IMx (32.4+/-13.9 micromol/l; p<0.001). A close correlation existed between GC-MS and HPLC (r=0.931; y=1.203 x+0.279) and GC-MS and IMx (r=0.896; y=1.105 x+0.766). Linear regression analysis showed positive correlations between plasma concentrations of homocysteine and cysteine (r=0.434; p<0.001) and homocysteine and cystathionine (r=0.187; p=0.032). Plasma concentrations of homocysteine correlated negatively with folate (r=-0.281; p=0.001) and vitamin B12 (r=-0.229; p=0.009). GC-MS proved to be a sensitive and reliable method for the determination of total plasma homocysteine and related amino acids. Despite vitamin supplementation, ESRD patients requiring chronic maintenance hemodialysis, have high plasma concentrations of homocyst(e)ine which seems to be metabolized mainly within the transsulfuration pathway, while remethylation to methionine seems to be disturbed.

Hyperhomocysteinemia in chronic renal failure patients: relation to nutritional status and cardiovascular disease

A moderate increase in plasma total homocysteine (tHcy) is considered to be an independent risk factor for cardiovascular disease (CVD) in the general population. Almost all chronic renal failure (CRF) patients have plasma concentration of tHcy that is elevated 3 to 4 times above normal. The prevalence of CVD, diabetes mellitus, malnutrition and hypoalbuminemia is high in CRF patients. Previous investigations have focused on the role of vitamin status on plasma tHcy in CRF patients, but little information exists on the influence of nutritional status and hypoalbuminemia on plasma tHcy in CRF, although a substantial fraction of tHcy (>70%) is protein-bound, mainly to albumin. Our study in patients with end-stage renal disease showed that more than 90% of the patients had elevated plasma tHcy levels, which were higher in patients with normal nutritional status than in malnourished patients. Moreover, plasma tHcy was inversely correlated with subjective global nutritional assessment (high values denote malnutrition) and positively correlated with serum albumin and protein intake. Hence, it seems likely that serum-albumin is a strong determinant of plasma tHcy in CRF patients and this may contribute to the lower tHcy levels in malnourished patients. Patients with diabetes mellitus had lower serum-albumin and plasma tHcy than non-diabetic patients, irrespective whether they were malnourished or not. Patients with CVD had lower (although still elevated) plasma tHcy levels than those without CVD. An explanation may be that the prevalence of diabetes mellitus, malnutrition and hypoalbuminema, i.e. factors that decrease tHcy, was higher in patients with CVD, which may explain why they had less elevated values. Assuming that hyperhomocysteinemia carries an independent risk of CVD, this implies that almost all CRF patients are exposed to this risk. CRF patients with CVD had a higher prevalence of malnutrition, hypoalbuminemia and diabetes mellitus, which was associated with a lower plasma Hcy level. This may explain why plasma tHcy was lower (although still abnormally high) in patients with CVD than in patients without CVD. The lower tHcy levels in CVD patients do not contradict the assumption that hyperhomocysteinemia is a risk factor for CVD since almost all patients are exposed to this risk, and other factors might be present that confound the relationship between the absolute tHcy levels and CVD. Our findings imply that nutritional status and serum albumin, as well as the presence of diabetes mellitus, should be taken into consideration when evaluating tHcy as a risk factor for CVD in CRF patients.