Influence of 5,10-methylenetetrahydrofolate reductase gene polymorphism on plasma homocysteine concentration in patients with end-stage renal disease

Homocysteine exchange across skeletal muscle in patients with chronic kidney disease

Sites and mechanisms regulating the supply of homocysteine (Hcy) to the circulation are unexplored in humans. We studied the exchange of Hcy across the forearm in CKD patients (n = 17, eGFR 20 ± 2 ml/min), in hemodialysis (HD)-treated patients (n = 14) and controls (n = 9). Arterial Hcy was ~ 2.5 folds increased in CKD and HD patients (p < 0.05-0.03 vs. controls). Both in controls and in patients Hcy levels in the deep forearm vein were consistently greater (+~7%, p < 0.05-0.01) than the corresponding arterial levels, indicating the occurrence of Hcy release from muscle. The release of Hcy from the forearm was similar among groups. In all groups arterial Hcy varied with its release from muscle (p < 0.03-0.02), suggesting that muscle plays an important role on plasma Hcy levels. Forearm Hcy release was inversely related to folate plasma level in all study groups but neither to vitamin B12 and IL-6 levels nor to muscle protein net balance. These data indicate that the release of Hcy from peripheral tissue metabolism plays a major role in influencing its Hcy plasma levels in humans and patients with CKD, and that folate is a major determinant of Hcy release.

Decisive evidence corroborates a null relationship between MTHFR C677T and chronic kidney disease: A case-control study and a meta-analysis

BACKGROUND

Previous meta-analyses have explored the association between the C677T polymorphism of methyltetrahydrofolate reductase (MTHFR) and chronic kidney disease (CKD) but there were no studies with a decisive conclusion. Furthermore, the high heterogeneity among different populations is not yet interpreted.

OBJECTIVES

This study used trial sequential analysis (TSA) to evaluate whether the nowadays conclusion supported by current cumulative samples. We also applied case-weighted meta-regression to explore the potential gene-environment interactions.

METHODS

For the first stage of this study we conducted a case-control study involving 847 dialysis patients from 7 hemodialysis centers in Taipei during 2015 to 2018 and 755 normal controls from a health center in the Tri-Service General Hospital. The second stage combined the results from the first stage with previous studies. The previous studies were collected from PubMed, EMBASE, and Web of Science databases before January 2018.

RESULTS

From the case-control study, the T allele of MTHFR C677T appeared to have a protective effect on end-stage renal disease compared with the C allele [odds ratio (OR): 0.80, 95% CI (confidence interval) = 0.69-0.93]. However, the meta-analysis contradicted the results in Asian (OR = 1.12, 95% CI = 0.96-1.30). The same analysis was also applied in Caucasian and presented similar results from Asian (OR = 1.18, 95% CI = 0.98-1.42). The TSA showed our case-control study to be the decisive sample leading to a null association among Asian population. The high heterogeneity (I = 75%) could explain the contradictory results between the case-control study and the meta-analysis. However, further case-weighted meta-regression did not find any significant interaction between measured factors and MTHFR C677T on CKD.

CONCLUSIONS

High heterogeneities were found in both Caucasian and Asian, which caused the null relationship in meta-analysis while there were significant effects in individual studies. Future studies should further explore the high heterogeneity that might be hidden in unmeasured gene-environment interactions, to explain the diverse findings among different populations.

Thrombophilic risk factors in hemodialysis: Association with early vascular access occlusion and patient survival in long-term follow-up

Objective

Thrombophilic risk factors (TRFs) occur rather frequently in hemodialysis (HD) patients. However, little is known about their significance in HD patients, besides their potential impact on arteriovenous (AV) access failure, with varying results. We examined the effects of a wide variety of TRFs on both early AV fistula occlusion and survival among HD patients in long-term follow-up.

Methods

In this single-center, observational study, 70 consecutive HD patients from our dialysis center were examined with respect to shunt occlusion within the first 2 years after fistula creation and patient survival in a long-term follow-up (at least 16 years). We examined the presence of factor V, prothrombin, and MTHFR mutations using real-time fluorescence polymerase chain reaction. Furthermore, antithrombin (AT), protein C, protein S, and antiphospholipid antibodies (APL-Abs) were assessed.

Results

Among the 70 patients, 32 had MTHFR mutations, 10 had heterozygous factor V Leiden mutations, 4 had prothrombin mutations, 4 had protein S deficiency, 2 had protein C deficiency, 9 had AT deficiency, and 14 had APL-Abs. 40 patients had shunt occlusion. TRFs were associated with a significantly increased risk for shunt thrombosis (P<0.02). Kaplan–Meier analysis with a log-rank test revealed significantly shorter survival in HD patients with TRFs (P<0.02). Cox regression analysis showed that the presence of TRFs (P<0.05; hazard ratio, 1.94; 95% CI: 1.07–3.56), but not early shunt occlusion, was associated with short patient survival.

Conclusions

TRFs in hemodialysis patients have a strong impact on patient survival and early AV fistula failure; however, patient survival is not significantly affected by early shunt occlusion.

Is there any genetic predisposition of MMP-9 gene C1562T and MTHFR gene C677T polymorphisms with essential hypertension?

The current study was conducted to determine whether there is a relation between hypertension and two different polymorphisms, including C1562T of the Matrix metalloproteinase-9 (MMP-9) gene and C677T of the methylenetetrahydrofolate reductase (MTHFR) gene. Genomic DNA obtained from 224 persons (125 patients with hypertension and 99 healthy controls) were used in the study. Polymorphisms were determined by using polymerase chain reaction-restriction fragment length polymorphism and electrophoresis. The results were statistically analyzed and were found to be statistically significant. The frequencies of the C1562T genotypes were found to be, in controls CC 75.8 % and CT 24.2 % and in patients CC 71.2 %, and CT 28.8 %. The frequencies of C677T genotype were found to be, in controls CC 56.6 %, CT 38.4 and TT 5.1 % in controls and in patients CC 52 %, CT 30.4 % and TT 17.6 %. In conclusion, we may suggest that there is no relation between the essential hypertension and C1562T polymorphism of MMP-9 gene; on the other hand C677T polymorphism (genotype TT) of MTHFR gene can be regarded as a genetic indicator for the development of essential hypertension.

Uremia-related metabolic cardiac risk factors in chronic kidney disease

Growing evidence has been gathered over the last 15 years regarding the role of nontraditional or uremia-related risk factors in the pathogenesis of atherosclerosis in subjects with renal failure. Among those factors, dyslipidemia, inflammation, hyperhomocysteinemia, and oxidant stress have been extensively studied. However, the clinical significance of many of these factors remains controversial in light of reported studies. In this article, the existing evidence regarding the role of uremia-related risk factors in the pathogenesis of atherosclerosis is reviewed, with special emphasis on prevalence, cardiac risk, and management in patients with chronic kidney disease (CKD). Consensus treatment recommendations are provided for risk factors for which there is evidence to support preventive or therapeutic interventions.

Vitamin B12 decreases, but does not normalize, homocysteine and methylmalonic acid in end-stage renal disease: a link with glycine metabolism and possible explanation of hyperhomocysteinemia in end-stage renal disease

The genetic and environmental factors influencing catabolism of homocysteine in end-stage renal disease (ESRD) patients remain poorly understood. This study investigated how genetic and nutritional influences affect the response to high-dose vitamin B(12) and folate treatment in ESRD patients with hyperhomocysteinemia. We studied 81 hemodialysis patients with hyperhomocysteinemia (> 16 micromol/L) on varied doses of a multivitamin containing 1 mg of folic acid per day. After screening blood work, all patients were switched to daily multivitamin therapy including 1 mg of folic acid for 4 weeks. Vitamin B(12), 1 mg/d, was added for an additional 4 weeks. Patients were then randomized to receive folic acid or placebo. The influence of the 3 methylenetetrahydrofolate reductase (MTHFR) 677 C-->T genotypes on the efficacy of vitamin therapy was assessed. In addition, we investigated how the metabolic complications of ESRD, including the relationship between methylmalonic acid (MMA) and circulating glycine, may contribute to hyperhomocysteinemia. There was no significant difference in total homocysteine (tHcy) levels between the MTHFR 677 C-->T genotypes during the screening phase of the trial. Treatment with a daily multivitamin containing 1 mg folate significantly lowered tHcy levels in all patients by 19.2%. Further supplementation with 1 mg vitamin B(12) resulted in greater tHcy reduction among subjects with the MTHFR 677 T/T genotype (P<.01, T/T v C/C or C/T) while lowering MMA equally in all MTHFR genotypes. There was a significant positive correlation between plasma glycine levels and MMA (P <.05). High-dose vitamin therapy significantly lowers, but does not normalize, MMA and tHcy levels. The MTHFR genotype, while influencing homocysteine levels, was not responsible for the majority of the elevation in plasma tHcy.

Hyperhomocysteinemia is related to residual glomerular filtration and folate, but not to methylenetetrahydrofolate-reductase and methionine synthase polymorphisms, in supplemented end-stage renal disease patients undergoing hemodialysis

Glomerular filtration is one of the major determinants of plasma total homocysteine (tHcy). To evaluate the respective roles of residual glomerular filtration (by measuring a specific protein marker, cystatin C), genetic polymorphisms and nutritional status in tHcy blood levels in end-stage renal disease patients (ESRD) under hemodialysis and supplemented with folate, we measured tHcy, folate, vitamin B12 (B12), creatinine, cystatin C, albumin and C-reactive protein and determined the polymorphism of methylenetetrahydrofolate reductase (MTHFR) (C677T and A1289C) and of methionine synthase (MS) (A2756G) in 114 ESRD patients before hemodialysis and 76 control subjects. All patients received a folate supplementation of 700 microg/day. Hyperhomocysteinemia was observed in all patients and exceeded the upper normal limit by 2-fold in 52.4% of the patients. Serum folate was significantly increased and the B12 level was not different from controls. Folate, Cystatin C and creatinine were significantly correlated to tHcy, while no correlation was found between tHcy, albumin and C-reactive protein. No difference in genotype frequency between ESRD patients and controls was found for MTHFR A1289C and MS A2756G. The MTHFR 677TT genotype was less frequent and was associated with a significantly higher tHcy level in patients. Folate and residual glomerular filtration estimated by cystatin C and creatinine levels were two independent determinants of tHcy in ESRD patients. These data suggest that hyperhomocysteinemia is a consequence as well as a complicating factor of renal failure.

MTHFR gene polymorphism, homocysteine and cardiovascular disease

Homocysteine is an emerging new risk factor for cardiovascular disease. It is a thiol compound derived from methionine and involved in two main metabolic pathways: the cycle of activated methyl groups, requiring folate and vitamin B12 as cofactors, and the transsulfuration pathway to cystathionine and cysteine requiring vitamin B6 as cofactor. The homocysteine metabolism represents an interesting model of gene-environment interaction. Elevations in homocysteine may be caused by genetic defects in enzymes involved in its metabolism or by deficiencies in cofactor levels. A common polymorphism in the gene coding for the 5,10-methylene tetrahydrofolate reductase (MTHFR) (C677T, Ala --> Val) is associated with a decreased activity of the enzyme due to thermolability. In case of homozygosity for the Val allele, a relative deficiency in the remethylation process of homocysteine into methionine leads to a mild-to-moderate hyperhomocysteinemia, a condition recognized as an independent risk factor for atherosclerosis. The genetic influence of the MTHFR polymorphism on homocysteine levels is attenuated in females in premenopausal age and is not significant in subjects who exhibit serum levels of folate and/or vitamin B12 above the 50th percentile of distribution in the general population. The prevalence of the Val/Val genotype varies among different ethnic groups. It is very low in African populations, whereas in Europe and North America it ranges between 5% and 15%. In Italy an even higher prevalence has been reported in some regions. The question whether the MTHFR polymorphism might be per se an independent contributor to cardiovascular risk is debated. The interaction between this or other genetic factors and environmental/nutritional conditions (i.e. intake of vitamins such as folate) is a key determinant for homocysteine concentrations in healthy conditions as well as in some disease (i.e. in renal disorders). Another example of gene/environment interaction in the field of atherosclerosis is given by the apolipoprotein E polymorphism and its influence in response to diet. The presence of a high prevalence of risk-related allelic variants of such candidate genes within a certain population could serve to locally reinforce the recommendations concerning nutrient intake.

Recent insights into the molecular genetics of the homocysteine metabolism

The homocysteine plasma level is determined by non-genetic and genetic factors. In recent years evidence has accumulated that the total homocysteine plasma level of patients under different forms of renal replacement therapy is influenced by a common mutation at nucleotide position 677 of the gene coding for 5,10-methylenetetrahydrofolate reductase (MTHFR 677C-->T). Furthermore, compound heterozygosity for the 677T allele and a novel A-->C polymorphism at nucleotide position 1298 of MTHFR is suggested to correlate with a decrease of folate plasma concentrations. Because polymorphisms of genes coding for proteins involved in the metabolism of homocysteine may contribute to elevated total homocysteine plasma concentrations, molecular genetic analyses of the homocysteine pathways experienced a drift towards screening for candidate genes with a putative relationship to total homocysteine plasma levels. One example is the cloning of the FOLR1 gene coding for the folate-binding protein (Folbp1), which has recently been inactivated in mice, thus representing an elegant model to investigate the consequence on the homocysteine metabolism. Furthermore, the recent characterization of the CUBN gene encoding the intrinsic factor-vitamin B12 receptor (cubilin) provides a basis to identify the causative mutations in patients suffering from a hereditary syndrome of hyperhomocysteinemia that presents with megaloblastic anemia and proteinuria. This review focuses on recent insights into the molecular genetics of MTHFR, FOLR1, and CUBN, and their relationships to the metabolism of the amino acid homocysteine.

C-reactive protein, oxidative stress, homocysteine, and troponin as inflammatory and metabolic predictors of atherosclerosis in ESRD

Mortality in patients with end-stage renal disease remains high, with cardiovascular disease accounting for half of these deaths. Novel risk factors such as inflammation, oxidative stress, hyperhomocysteinemia, and high troponin levels are associated with cardiovascular risk in the general population. While there are substantial epidemiologic data confirming that these novel risk factors are associated with cardiovascular risk in end-stage renal disease patients, a causal relationship has not been established. Inflammation is readily identified by the presence of high levels of C-reactive protein, while studies of oxidative stress are hampered by the lack of a standardized test. The cause of both is unknown. Hyperhomocysteinemia results from decreased remethylation to methionine, although vitamin supplementation only partially corrects the defect, suggesting that uremic inhibition of the enzymatic process may be important. The most promising strategies for correcting oxidative stress and hyperhomocysteinemia are vitamin E and folinic acid therapy, respectively. Troponin I appears to be a more specific marker of myocardial injury than Troponin T, but troponin T retains its ability to predict cardiovascular mortality as well as all-cause mortality. Sorting out the role of each of these risk factors may be difficult since the factors may influence each other, may increase oxidative stress, and may mediate atherosclerosis through oxidative modification of lipids.