Riboflavin is a determinant of total homocysteine plasma concentrations in end-stage renal disease patients

Vitamin Supplement Use in Patients With CKD: Worth the Pill Burden?

All vitamins play essential roles in various aspects of body function and systems. Patients with chronic kidney disease (CKD), including those receiving dialysis, may be at increased risk of developing vitamin deficiencies due to anorexia, poor dietary intake, protein energy wasting, restricted diet, dialysis loss, or inadequate sun exposure for vitamin D. However, clinical manifestations of most vitamin deficiencies are usually subtle or undetected in this population. Testing for circulating levels is not undertaken for most vitamins except folate, B12, and 25-hydroxyvitamin D because assays may not be available or may be costly to perform and do not always correlate with body stores. The last systematic review through 2016 was performed for the Kidney Disease Outcome Quality Initiative (KDOQI) 2020 Nutrition Guideline update, so this article summarizes the more recent evidence. We review the use of vitamins supplementation in the CKD population. To date there have been no randomized trials to support the benefits of any vitamin supplementation for kidney, cardiovascular, or patient-centered outcomes. The decision to supplement water-soluble vitamins should be individualized, taking account the patient's dietary intake, nutritional status, risk of vitamins deficiency/insufficiency, CKD stage, comorbid status, and dialysis loss. Nutritional vitamin D deficiency should be corrected, but the supplementation dose and formulation need to be personalized, taking into consideration the degree of 25-hydroxyvitamin D deficiency, parathyroid hormone levels, CKD stage, and local formulation. Routine supplementation of vitamins A and E is not supported due to potential toxicity. Although more trial data are required to elucidate the roles of vitamin supplementation, all patients with CKD should undergo periodic assessment of dietary intake and aim to receive various vitamins through natural food sources and a healthy eating pattern that includes vitamin-dense foods.

Dietary Micronutrients and Risk of Chronic Kidney Disease: A Cohort Study with 12 Year Follow-Up

We investigated the association between dietary micronutrient intakes and the risk of chronic kidney disease (CKD) in the Ansan-Ansung study of the Korean Genome and Epidemiologic Study (KoGES), a population-based prospective cohort study. Of 9079 cohort participants with a baseline estimate glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² and a urine albumin to creatinine ratio (UACR) <300 mg/g and who were not diagnosed with CKD, we ascertained 1392 new CKD cases over 12 year follow-up periods. The risk of CKD according to dietary micronutrient intakes was presented using hazard ratios (HRs) and 95% confidence intervals (95% CIs) in a full multivariable Cox proportional hazard models, adjusted for multiple micronutrients and important clinico-epidemiological risk factors. Low dietary intakes of phosphorus (<400 mg/day), vitamin B2 (<0.7 mg/day) and high dietary intake of vitamin B6 (≥1.6 mg/day) and C (≥100 mg/day) were associated with an increased risk of CKD stage 3B and over, compared with the intake at recommended levels (HR = 6.78 [95%CI = 2.18–21.11]; HR = 2.90 [95%CI = 1.01–8.33]; HR = 2.71 [95%CI = 1.26–5.81]; HR = 1.83 [95%CI = 1.00–3.33], respectively). In the restricted population, excluding new CKD cases defined within 2 years, an additional association with low folate levels (<100 µg/day) in higher risk of CKD stage 3B and over was observed (HR = 6.72 [95%CI = 1.40–32.16]). None of the micronutrients showed a significant association with the risk of developing CKD stage 3A. Adequate intake of micronutrients may lower the risk of CKD stage 3B and over, suggesting that dietary guidelines are needed in the general population to prevent CKD.

Inverse Association Between Riboflavin Intake and New-Onset Hypertension

The prospective relation of dietary riboflavin intake with hypertension remains uncertain. We aimed to investigate the relationship of dietary riboflavin intake with new-onset hypertension and examine possible effect modifiers in general population. A total of 12 245 participants who were free of hypertension at baseline from China Health and Nutrition Survey were included. Dietary intake was measured by 3 consecutive 24-hour dietary recalls combined with a household food inventory. The study outcome was new-onset hypertension, defined as systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg or diagnosed by physician or under antihypertensive treatment during the follow-up. A total of 4303 (35.1%) subjects developed hypertension during 95 573 person-years of follow-up. Overall, there was a nonlinear, inverse association between total, plant-based, or animal-based riboflavin intake and new-onset hypertension (allPfor nonlinearity, <0.001). The risk of new-onset hypertension was increased only in participants with relatively lower riboflavin intake. Accordingly, a significantly lower risk of new-onset hypertension was found in participants in quartiles 2 to 4 of total riboflavin intake (hazard ratio, 0.74 [95% CI, 0.68–0.80]), plant-derived riboflavin intake (hazard ratio, 0.77 [95% CI, 0.71–0.84]), or animal-derived riboflavin intake (hazard ratio, 0.70 [95% CI, 0.65–0.77]), compared with those in quartile 1. In addition, the association between total riboflavin intake and new-onset hypertension was particularly evident in those with lower dietary sodium/potassium intake ratio (Pinteraction, <0.001). In summary, there was an inverse association between riboflavin intake and new-onset hypertension in general Chinese adults. Our results emphasized the importance of maintaining relatively higher riboflavin intake levels for the prevention of hypertension.

Assessment of Serum Folic Acid and Homocysteine in Thalassemia Major Patients Before and After Folic Acid Supplement Cessation

BACKGROUND

Thalassemic patients have ineffective erythropoiesis. In recent treatment protocols, there are little data on folic acid supplementation for patients with thalassemia because it is supposed that regular blood transfusions prevent bone marrow hyperfunctioning.

OBJECTIVE

Investigators aimed to assess serum folic acid and homocysteine (Hcy) in thalassemia major patients before and after folic acid supplement cessation.

PATIENTS AND METHODS

This study was a before-after controlled clinical trial conducted in 17th Shahrivar Hospital, Rasht, North of Iran, during May to October 2016. The patients enrolled in this study had thalassemia major on regular blood transfusion and older than 2 years of age. They had at least a 6-month history of folic acid supplement consumption before enrollment in the study (1 mg/daily). Complete blood count, serum folic acid, and serum Hcy were measured before discontinuation of folic acid supplement. Then, patients did not receive folic acid for a month and after 1 month of folic acid cessation, the measurements were repeated. All data were entered in SPSS version 20.0 and analyzed.

RESULTS

Among the 40 patients in this study, 25 (62.5%) were female. The mean age of the participants was 21.39±11.17 years old. The mean of body mass index was 21.38±3.32 kg/m. Most of the participants had used folic acid supplement >5 years (29, 72.5%). The serum Hcy level was significantly increased (5.24±2.35 vs. 5.93±2.56; P=0.008) and serum folic acid level was decreased significantly (14.74±4.20 vs. 8.80±4.16; P<0.0001) from baseline.

CONCLUSIONS

Cessation of folic acid supplementations in beta thalassemia major patients can lead to a significant decrease in serum folic acid and increase in Hcy levels. According to our findings and efficacy of folic acid in patients with beta thalassemia major, it is recommended to use the supplementation in all patients.

Water soluble vitamins and peritoneal dialysis - State of the art

This review presents the results of a systematic literature search concerning water soluble vitamins and peritoneal dialysis modality. We provide an overview of the data available on vitamin requirements, dietary intake, dialysis related losses, metabolism and the benefits of supplementation. We also summarise the current recommendations concerning the supplementation of vitamins in peritoneal dialysis and discuss the safety of an administration of vitamins in pharmacological doses.

Water-soluble vitamins in people with low glomerular filtration rate or on dialysis: a review

People with low glomerular filtration rate and people on dialysis are spontaneously at risk for vitamin deficiency because of the potential for problems with decreased appetite and decreased sense of smell and taste, leading to decreased intake, and because decreased energy or decreased cognitive ability results in difficulties in shopping and cooking. Imposed dietary restrictions because of their renal dysfunction and because of comorbidities such as hypertension and diabetes exacerbate this problem. Finally, particularly for water-soluble vitamins, loss may occur into the dialysate. We did not identify any randomized trials of administering daily doses close to the recommended daily allowances of these vitamins. In people who are eating at all, deficiencies of B5 and B7 seem unlikely. It is unclear whether supplements of B2 and B3 are necessary. Because of dialyzability and documented evidence of insufficiency in dialysis patients, B1 supplementation is likely to be helpful. B6, B9, and B12 are implicated in the hyperhomocysteinemia observed in patients on dialysis. These vitamins have been studied in combinations, in high doses, with the hope of reducing cardiovascular outcomes. No reductions in patient-important outcomes were seen in adequately powered randomized trials. Because of their involvement in the homocysteine pathway, however, supplementation with lower doses, close to the recommended daily allowances, may be helpful. Vitamin C deficiency is common in patients on dialysis who are not taking supplements: low-dose supplements are warranted. Vitamins for dialysis patients contain most or all of the B vitamins and low-dose vitamin C. We are not aware of any medical reasons to choose one over another.

Association between plasma homocysteine and riboflavin status in Acute Lymphoblastic Leukemia in children

Remethylation of homocysteine to methionine is dependent on an adequate supply of one or more of the B vitamins like folate, vitamin B(12) and vitamin B(6). Plasma total homocysteine (tHcy) is also influenced by genetic factors such as polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene. MTHFR is a flavo enzyme and a key player in folate metabolism and changes in its activity could modify the susceptibility to Acute Lymphoblastic Leukemia (ALL). In this case - control study we have examined the effect of riboflavin status as measured by erythrocyte glutathione reductase activation coefficient (EGRAC) on homocysteine levels along with vitamin B(12) and folate in pediatric ALL. Folate and B(12) levels were significantly lower among cases as compared to controls while EGRAC and tHcy did not differ significantly among the groups. The multivariate regression analysis revealed that in the ALL group EGRAC significantly influences tHcy levels suggesting that riboflavin availability may be a predictor of tHcy levels in patients with ALL. This finding may have implications for tHcy lowering therapy.

Dietary intakes and biochemical status of B vitamins in a group of children receiving dialysis

OBJECTIVE

We investigated the dietary intake and biochemical status of B vitamins (thiamin, riboflavin, vitamin B6, and vitamin B12) in a group of mainly unsupplemented children with endstage renal disease receiving dialysis, to determine if B vitamin supplementation is indicated.

DESIGN

This was a cross-sectional, observational clinical trial.

SETTING

Children with endstage renal disease were receiving dialysis, under the care of Renal Services, at Starship Children's Health (Grafton, Auckland, New Zealand).

PATIENTS

We studied 12 children (including 7 girls, and 8 children receiving peritoneal dialysis) mean age 7.8 +/- 5.3 years (SD).

INTERVENTION

Three-day diet records were collected and analyzed with FoodWorks software. Blood was collected for vitamin assay testing.

MAIN OUTCOME MEASURE

Dietary intake of B vitamins was measured as a percentage of recommended dietary intake (RDI) or adequate intakes (AIs) for age. Biochemical status was measured as the concentration of each B vitamin compared with reference ranges.

RESULTS

Mean intakes from diet alone comprised <100% of the RDI or AI for each B vitamin. Mean intakes, with nutritional support, reached >100% of the RDI or AI for each B vitamin. All children achieved >100% RDI or AI for thiamin, riboflavin, and vitamin B12. Two children who were not receiving nutritional support received <100% of the RDI for vitamin B6. Blood levels of B vitamins were normal to high, compared with reference ranges, for each B vitamin in all children, indicating adequate status.

CONCLUSIONS

Intakes were adequate in the majority of children. Status was adequate in all children. In this group of children undergoing dialysis, B-vitamin supplementation was not indicated.

Role of thrombotic risk factors in end-stage renal disease

INTRODUCTION

Genetic polymorphisms that are found among factors of the coagulation cascade are factor V leiden mutation (FVL), prothrombin (PT), and methylenetetrahydrofolate reductase (MTHFR), reported for thrombotic complications. We have investigated the associations of these gene polymorphisms in patients with end-stage renal disease (ESRD).

METHODS

We genotyped 258 patients for FV G1691A, PT G20210A, and MTHFR (C677T, A1298C) gene by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and were compared with 569 healthy controls. Serum folate, total homocysteine (tHcys), and vitamin B(12) were measured in both patients with ESRD and controls.

RESULTS

No homozygous individuals for the mutant AA genotype of FVL G1691A were observed in this study. The frequency of the heterozygous genotypes was (11.2%), which was nearly 3 times higher than that observed in controls (3.2%), with a odds ratio of 3.87 (P = .0001, 95% CI = 2.11-7.11). PT G20210A mutation was missing in both patients and the controls. At MTHFR locus, TT genotype of C677T was present in 9.6% among ESRD, while CC genotype of A1298C was present in 11.7% of the ESRD. In control group, it was significantly low that is, 4.2% and 3.2%, respectively (P = .0034; OR = 2.44, 95% CI = 1.36-4.36 and P < .0001; OR = 4.03; 95% CI = 2.2-7.37). The combined analysis of the 2 genotypes showed further increased risk in ESRD ~15 folds. Further, the carrier of TT and CC genotypes of C677T and A1298C had significantly higher total homocysteine (tHcys) level than those with CC and AA genotypes (P < .001).

CONCLUSION

The carrier of FVL, TT genotype of C677T, and CC genotype of A1298C polymorphisms may act as risk factors for ESRD.

Riboflavin supplementation and biomarkers of cardiovascular disease in the elderly

BACKGROUND

High levels of total plasma homocysteine are potentially harmful in the elderly.

OBJECTIVE

To investigated the effects of oral riboflavin supplementation on plasma total homocysteine, ferritin, uric acid and C-reactive protein concentration in elderly people with a low riboflavin status. We performed a four-week randomized, placebo-controlled, double-blind trial of riboflavin supplementation in seven Portuguese day social centers.

DESIGN

Eighty-eight individuals (66.7% female), aged between 60 and 94 years, volunteered to participate in the study following interview. Forty-two subjects, with an erythrocyte glutathione reductase activation coefficient (EGRAC) >or= 1.2, were included in the intervention trial. All subjects gave informed consent. Study subjects were administered 10 mg riboflavin (n=21) or placebo (n=21) each day for 28 days.

RESULTS

Riboflavin supplementation significantly decreased plasma tHcy (P=0.005) and EGRAC (P=0.014), but not plasma ferritin, uric acid or C-reactive protein.

CONCLUSIONS

In this elderly group, we found that 10 mg/day oral riboflavin supplementation lowered plasma homocysteine concentrations in subjects with low riboflavin status.

Effect of B vitamin supplementation on plasma homocysteine levels in celiac disease

AIM: To investigate the effect of vitamin supplements on homocysteine levels in patients with celiac disease.

METHODS: Vitamin B6, folate, vitamin B12, and fasting plasma homocysteine levels were measured in 51 consecutive adults with celiac disease [median (range) age 56 (18-63) years; 40% men, 26 (51%) had villous atrophy, and 25 (49%) used B-vitamin supplements] and 50 healthy control individuals matched for age and sex. Finally, the C677T polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR) was evaluated in 46 patients with celiac disease and all control individuals.

RESULTS: Patients with celiac disease and using vitamin supplements had higher serum vitamin B6 (P = 0.003), folate (P < 0.001), and vitamin B12 (P = 0.012) levels than patients who did not or healthy controls (P = 0.035, P < 0.001, P = 0.007, for vitamin B6, folate, and vitamin B12, respectively). Lower plasma homocysteine levels were found in patients using vitamin supplements than in patients who did not (P = 0.001) or healthy controls (P = 0.003). However, vitamin B6 and folate, not vitamin B12, were significantly and independently associated with homocysteine levels. Twenty-four (48%) of 50 controls and 23 (50%) of 46 patients with celiac disease carried the MTHFR thermolabile variant T-allele (P = 0.89).

CONCLUSION: Homocysteine levels are dependent on Marsh classification and the regular use of B-vitamin supplements is effective in reduction of homocysteine levels in patients with celiac disease and should be considered in disease management.

Plasma protein homocysteinylation in uremia

Protein homocysteinylation is proposed as one of the mechanisms of homocysteine toxicity. It occurs through various means, such as the post-biosynthetic acylation of free amino groups (protein-N-homocysteinylation, mediated by homocysteine thiolactone) and the formation of a covalent -S-S- bond found primarily with cysteine residues (protein-S-homocysteinylation). Both protein modifications are a cause of protein functional derangements. Hemodialysis patients in the majority of cases are hyperhomocysteinemic, if not malnourished. Protein-N-homocysteinylation and protein-S-homocysteinylation are significantly increased in hemodialysis patients compared to controls. Oral folate treatment normalizes protein-N-homocysteinylation levels, while protein-S-homocysteinylation is significantly reduced. Albumin binding experiments after in vitro homocysteinylation show that homocysteinylated albumin is significantly altered at the diazepam, but not at the warfarin and salicilic acid binding sites.

Clin Chem Lab Med 2007;45:1678–82.

Effects of riboflavin and folic acid supplementation on plasma homocysteine levels in healthy subjects

BACKGROUND

Observational studies have shown an inverse relationship between vitamin B2 status and total homocysteine levels, a risk factor for cardiovascular disease. We hypothesize that intervention with riboflavin will lower total homocysteine levels. The total homocysteine lowering by the three genotypes (CC, CT, TT) of methylenetetrahydrofolate reductase polymorphism (677C-->T) was also studied.

METHODS

The decrease in total homocysteine levels after supplementation with riboflavin (10 mg/d) or folic acid (1 mg/d) for 3 weeks was compared in two groups of healthy subjects (17 per group, matched by age and gender) (Phase 1). Then, both groups received supplementation with folic acid and riboflavin for an additional 3 weeks (Phase 2).

RESULTS

During Phase 1, total homocysteine levels were lowered by 2% or 4% after supplementation with riboflavin or folic [corrected] acid, respectively, although neither decrease was statistically significant (P=0.50 and 0.19). Compared to subjects of CC genotype, total homocysteine lowering in subjects of CT genotype was approaching significance (P=0.059) for the folic acid group, but not for the riboflavin group. After Phase 2, total homocysteine levels were not lowered significantly in either the folic acid (1%) or the riboflavin (2%) group. However, in the folic acid-riboflavin combined group, total homocysteine lowering in subjects of TT type was larger when compared to subjects of CC and CT types (P=0.007).

CONCLUSIONS

Riboflavin supplementation did not lower total homocysteine levels in healthy subjects with CC type of C677T polymorphism. However, supplementation with folic acid or with both folic acid and riboflavin may be important for CT and TT subjects in optimizing their homocysteine metabolism. These findings are relevant in characterizing the factors controlling the high total homocysteine levels for subjects of CT and TT genotypes.

Effects of short-term folic acid and/or riboflavin supplementation on serum folate and plasma total homocysteine concentrations in young Japanese male subjects

OBJECTIVE

To investigate the effects of short-term folic acid and/or riboflavin supplementation on serum folate and plasma plasma total homocysteine (tHcy) concentrations in young Japanese male subjects.

DESIGN

In a double blind, randomized controlled trial.

INTERVENTION

Subjects were randomly assigned to one of four groups and received a placebo (control group), 800 microg/day folic acid (FA group), 8.4 mg/day riboflavin (R group), or both (FAR group) for 2 weeks.

SETTING

Tokyo, Japan.

SUBJECTS

In total, 32 healthy male volunteers aged 20-29 years.

RESULTS

At the end of the 2 week supplementation period, the tHcy concentration decreased significantly in the FA group. Serum folate concentrations had increased between 2.7 and 2.0-fold in the FA and FAR groups, respectively, but the mean within-group changes in serum folate and plasma tHcy concentrations did not differ between these two groups. At the end of the study, alanine amino transferase was decreased in the R and FAR groups, while alanine amino transferase was increased in the FA group.

CONCLUSION

Supplementation with folic acid, 800 microg/day, for 2 weeks, increased the serum and red blood cell folate concentrations and decreased the plasma tHcy concentrations in healthy young male subjects. Riboflavin supplementation may have blunted the effect of folic acid, which resulted in a diminished reduction of tHcy in our subjects.

Homocysteine metabolism in renal failure

PURPOSE OF REVIEW

This review focuses on recent findings (June 2002-July 2003) on the topic of homocysteine, a sulfur amino acid associated with cardiovascular disease, and its metabolism in renal failure, a condition with a high prevalence of both hyperhomocysteinemia and cardiovascular disease.

RECENT FINDINGS

A large meta-analysis of prospective studies in the general population established that hyperhomocysteinemia is a risk factor for cardiovascular disease. The results of intervention trials, once available, will also have to be tested in a meta-analysis, because of predicted problems with their statistical power. In kidney patients, intervention trials, still in the recruiting stage, target transplant patients, because of their unique characteristics related to folate responsiveness. As for the cause of hyperhomocysteinemia, new findings show that in humans, renal metabolic extraction depends on renal plasma flow in the post-absorptive state. Folate absorption or interconversion seems not to be affected. Riboflavin is a determinant of plasma homocysteine levels in uraemia. The consequences of hyperhomocysteinemia in uraemia are DNA hypomethylation and altered gene expression.

SUMMARY

The causes of hyperhomocysteinemia in renal failure are still not clear. However, the possibilities include defective renal or extrarenal metabolism as a result of uraemic toxicity. Renal plasma flow is important in homocysteine renal metabolism. Among the consequences of hyperhomocysteinemia in renal failure are impaired protein and DNA methylation, with an alteration in the allelic expression of genes regulated through methylation. Intervention trials are under way to test whether hyperhomocysteinemia is causally related to cardiovascular disease in this patient population.

Effect of TCN2 776C>G on vitamin B12 cellular availability in end-stage renal disease patients

BACKGROUND

Transcobalamin II is a serum protein that transports vitamin B12 from the intestine to the tissues. This complex, holo-transcobalamin II, may reflect vitamin B12 availability in the body. Conflicting data exist with regard to the effect of a polymorphism in the gene coding for transcobalamin II, TCN2 776C>G, on transcobalamin II levels in the general population, which in turn may affect holo-transcobalamin II, vitamin B12, as well as total homocysteine (tHcy) plasma levels. The effect of TCN2 776C>G on vitamin B12 cellular availability in dialysis patients is unknown.

METHODS

We examined the effect of TCN2 776C>G on holo-transcobalamin II, vitamin B12, and tHcy plasma concentrations in 120 dialysis patients.

RESULTS

Holo-transcobalamin II levels were normal or supranormal in all patients and showed a linear association with albumin (r = 0.205, P = 0.025) and with vitamin B12 (r = 0.778, P = 0.001), but not with age, creatinine, body mass index, tHcy, ln-tHcy, vitamin B6, plasma folate, and red blood cell folate concentration. TCN2 776C>G showed no effect on holo-transcobalamin II, vitamin B12, and tHcy concentration [one-way analysis of variance (ANOVA), post-hoc Scheffe test]. Multiple linear regression analyses showed that albumin and B12 are independently associated with holo-transcobalamin II, whereas TCN2 776C>G and MTHFR 677C>T had no effect. Independent predictors of ln-tHcy included creatinine, red blood cell folate, and the MTHFR 677TT genotype. There was also an effect of the TCN2 776CC genotype on ln-tHcy levels in this multivariate analysis, however, that deserves cautious interpretation because there was no effect of TCN2 genotypes by ANOVA and Scheffe test [median ln-tHcy concentrations according to TCN2 genotypes (micromol/L): CC, 3.22; CG, 3.30; GG, 3.23].

CONCLUSION

TCN2 776C>G does not influence holo-transcobalamin II or vitamin B12 levels, and has no major effect on tHcy concentrations of end-stage renal disease patients.

Effect of glutamate carboxypeptidase II and reduced folate carrier polymorphisms on folate and total homocysteine concentrations in dialysis patients

This study was designed to examine the effect of two single nucleotide polymorphisms in the reduced folate carrier 1 (RFC1 80G>A) and the glutamate carboxypeptidase 2 (GCP2 1561C>T) gene on total homocysteine (tHcy) plasma level and folate status in 120 chronic dialysis patients. Red blood cell folate concentration was higher in patients with the GCP2 CT or TT genotype (ANOVA, P = 0.04). Among patient groups with different RFC1 genotypes, red blood cell folate level was not significantly different. A multivariate analysis confirmed that the GCP2 1561C>T genotype (P = 0.011) had a significant influence on the red blood cell folate concentration. Overall, serum folate, creatinine, and the GCP2 polymorphism explained nearly 50% of the variance of red blood cell folate. A linear multivariate regression analysis showed that red blood cell folate (P < 0.001), creatinine (P < 0.001), and the 5,10-methylenetetrahydrofolate reductase (MTHFR) 677T allele (P = 0.013) are independent predictors of tHcy plasma level explaining 49% of the variance of tHcy plasma concentration. GCP2 1561C>T and RFC1 80G>A showed no effect on tHcy and folate plasma level. In conclusion, GCP2 1561C>T, but not RFC1 80G>A, is a predictor of red blood cell folate level in chronic dialysis patients. Both polymorphisms have no major effect on tHcy plasma concentration in end-stage renal disease patients.

Genetic determinants of the homocysteine level

Elevated total homocysteine (tHcy) plasma concentrations indicate folate and/or vitamin B12 deficiency and are associated with cardiovascular disease and neural tube defects. Evidence has accumulated that folate-, vitamin B12-, and Hcy-metabolism are under genetic control. Because Hcy metabolism is impaired in renal failure, MTHFR 677 C>T, GCP2 1561C>T, RFC1 80G>A, and TCN2 776G>C may further aggravate hyperhomocysteinemia in these patients. The most consistent effect on tHcy plasma concentrations is observed for 677C>T of MTHFR, whereas GCP2, RFC1, and TCN2 polymorphisms show no major effect on tHcy concentrations. Much is yet to be learned about the impact of genetic variants on tHcy levels, human diseases, the genetic-nutrient interactions, as well as the pharmacogenetic consequences in Hcy and vitamin metabolism.

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.

[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.

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.