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

Interventions for lowering plasma homocysteine levels in dialysis patients

BACKGROUND

People with end-stage kidney disease (ESKD) have high rates of cardiovascular events. Randomised controlled trials (RCTs) of homocysteine-lowering therapies have not shown reductions in cardiovascular event rates in the general population. However, people with kidney disease have higher levels of homocysteine and may have different mechanisms of cardiovascular disease. We performed a systematic review of the effect of homocysteine-lowering therapies in people with ESKD.

OBJECTIVES

To evaluate the benefits and harms of established homocysteine lowering therapy (folic acid, vitamin B6, vitamin B12) on all-cause mortality and cardiovascular event rates in patients with ESKD.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register to 25 January 2016 through contact with the Information Specialist using search terms relevant to this review.

SELECTION CRITERIA

Studies conducted in people with ESKD that reported at least 100 patient-years of follow-up and assessed the effect of therapies that are known to have homocysteine-lowering properties were included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data using a standardised form. The primary outcome was cardiovascular mortality. Secondary outcomes included all-cause mortality, incident cardiovascular disease (fatal and nonfatal myocardial infarction and coronary revascularisation), cerebrovascular disease (stroke and cerebrovascular revascularisation), peripheral vascular disease (lower limb amputation), venous thromboembolic disease (deep vein thrombosis and pulmonary embolism), thrombosis of dialysis access, and adverse events. The effects of homocysteine-lowering therapies on outcomes were assessed with meta-analyses using random-effects models. Prespecified subgroup and sensitivity analyses were conducted.

MAIN RESULTS

We included six studies that reported data on 2452 participants with ESKD. Interventions investigated were folic acid with or without other vitamins (vitamin B6, vitamin B12). Participants' mean age was 48 to 65 years, and proportions of male participants ranged from 50% to 98%.Homocysteine-lowering therapy probably leads to little or no effect on cardiovascular mortality (4 studies, 1186 participants: RR 0.93, 95% CI 0.70 to 1.22). There was no evidence of heterogeneity among the included studies (I² = 0%). Homocysteine-lowering therapy had little or no effect on all-cause mortality or any other of this review's secondary outcomes. All prespecified subgroup and sensitivity analyses demonstrated little or no difference. Reported adverse events were mild and there was no increase in the incidence of adverse events from homocysteine-lowering therapies (3 studies, 1248 participants: RR 1.12, 95% CI 0.51 to 2.47; I(2) = 0%). Overall, studies were assessed as being at low risk of bias and there was no evidence of publication bias.

AUTHORS' CONCLUSIONS

Homocysteine-lowering therapies were not found to reduce mortality (cardiovascular and all-cause) or cardiovascular events among people with ESKD.

Vitamin B and its derivatives for diabetic kidney disease

BACKGROUND

Diabetes is a leading cause of end-stage kidney disease (ESKD) mainly due to development and progression of diabetic kidney disease (DKD). In absence of definitive treatments of DKD, small studies showed that vitamin B may help in delaying progression of DKD by inhibiting vascular inflammation and endothelial cell damage. Hence, it could be beneficial as a treatment option for DKD.

OBJECTIVES

To assess the benefits and harms of vitamin B and its derivatives in patients with DKD.

SEARCH METHODS

We searched the Cochrane Renal Group's Specialised Register to 29 October 2012 through contact with the Trials' Search Co-ordinator using search terms relevant to this review.

SELECTION CRITERIA

We included randomised controlled trials comparing vitamin B or its derivatives, or both with placebo, no treatment or active treatment in patients with DKD. We excluded studies comparing vitamin B or its derivatives, or both among patients with pre-existing ESKD.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study eligibility, risk of bias and extracted data. Results were reported as risk ratio (RR) or risk differences (RD) with 95% confidence intervals (CI) for dichotomous outcomes and mean difference (MD) with 95% CI for continuous outcomes. Statistical analyses were performed using the random-effects model.

MAIN RESULTS

Nine studies compared 1354 participants randomised to either vitamin B or its derivatives with placebo or active control were identified. A total of 1102 participants were randomised to single vitamin B derivatives, placebo or active control in eight studies, and 252 participants randomised to multiple vitamin B derivatives or placebo. Monotherapy included different dose of pyridoxamine (four studies), benfotiamine (1), folic acid (1), thiamine (1), and vitamin B12 (1) while combination therapy included folic acid, vitamin B6, and vitamin B12 in one study. Treatment duration ranged from two to 36 months. Selection bias was unclear in three studies and low in the remaining six studies. Two studies reported blinding of patient, caregiver and observer and were at low risk of performance and detection bias, two studies were at high risk bias, and five studies were unclear. Attrition bias was high in one study, unclear in one study and low in seven studies. Reporting bias was high in one study, unclear in one study, and low in the remaining seven studies. Four studies funded by pharmaceutical companies were judged to be at high risk bias, three were at low risk of bias, and two were unclear.Only a single study reported a reduction in albuminuria with thiamine compared to placebo, while second study reported reduction in glomerular filtration rate (GFR) following use of combination therapy. No significant difference in the risk of all-cause mortality with pyridoxamine or combination therapy was reported. None of the vitamin B derivatives used either alone or in combination improved kidney function: increased in creatinine clearance, improved the GFR; neither were effective in controlling blood pressure significantly compared to placebo or active control. One study reported a significant median reduction in urinary albumin excretion with thiamine treatment compared to placebo. No significant difference was found between vitamin B combination therapy and control group for serious adverse events, or one or more adverse event per patient. Vitamin B therapy was reported to well-tolerated with mild side effects in studies with treatment duration of more than six months. Studies of less than six months duration did not explicitly report adverse events; they reported that the drugs were well-tolerated without any serious drug related adverse events. None of the included studies reported cardiovascular death, progression from macroalbuminuria to ESKD, progression from microalbuminuria to macroalbuminuria, regression from microalbuminuria to normoalbuminuria, doubling of SCr, and quality of life. We were not able to perform subgroup or sensitivity analyses or assess publication bias due to insufficient data.

AUTHORS' CONCLUSIONS

There is an absence of evidence to recommend the use of vitamin B therapy alone or combination for delaying progression of DKD. Thiamine was found to be beneficial for reduction in albuminuria in a single study; however, there was lack of any improvement in kidney function or blood pressure following the use of vitamin B preparations used alone or in combination. These findings require further confirmation given the limitations of the small number and poor quality of the available studies.

Utility and limitations of biochemical markers of vitamin B12 deficiency

BACKGROUND

There is an urgent need for proper utilization of laboratory markers to diagnose vitamin B12 deficiency that should reduce false negative cases. We worked out a diagnostic algorithm that provides a two-step detection of vitamin B12 deficiency using holotranscobalamin as a first line marker and methylmalonic acid (MMA) as a second line marker.

MATERIALS AND METHODS

We tested 1359 serum samples sent to our laboratory for total vitamin B12 assay. Serum samples were used for the determination of holotranscobalamin, MMA and creatinine.

RESULTS

Compared with total B12, holotranscobalamin showed a higher area under the receiver operating characteristic curve for detecting MMA levels > 300 nM. However, the distribution of holotranscobalamin in individuals with elevated creatinine irrespective of MMA and in individuals with elevated MMA irrespective of creatinine was shifted into the higher ranges. In the grey zone of holotranscobalamin between 23 and 75 pM (the range extending from the 90% diagnostic sensitivity to the 90% diagnostic specificity), MMA testing as a second line marker would help detecting 18% of deficient cases. Lowering MMA after vitamin B12 treatment may help setting the diagnosis of B12 deficiency in individuals with elevated creatinine.

DISCUSSION

Testing for vitamin B12 deficiency should start with holotranscobalamin measurement. Holotranscobalamin between 23 and 75 pM should be followed by MMA testing that can filter substantial number of deficient cases in the grey range in individuals with normal renal function. This diagnostic strategy may significantly improve assessing vitamin B12 deficiency.

Folic acid supplementation and cardiac and stroke mortality among hemodialysis patients

OBJECTIVE

We sought to assess whether the use of folic acid vitamin supplements reduced cardiac and stroke mortality in hemodialysis patients. Further, we examined whether the consumption of folic acid from vitamin supplements >1000 microg compared with the standard 1000 microg, and 1000 microg compared with either a lower dose or no consumption, were associated with reduced cardiac and stroke mortality risk.

DESIGN

We performed a secondary analysis of data from the Hemodialysis Study, a randomized clinical trial examining dialysis treatment regimens over a 3-year follow-up.

PARTICIPANTS

Participants included 1846 hemodialysis patients previously participating in the Hemodialysis Study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Cardiac and stroke mortality were our main outcome measures.

RESULTS

Based on time-dependent Cox proportional hazard regression models, folic acid consumption from vitamin supplements, above or below the standard 1000-microg dose, was not associated with a decrease or increase in cardiac mortality (P = .53, above vs. standard dose; P = .46, below vs. standard dose). There was also no association between folic acid consumption and mortality from stroke (P = .27, above vs. standard dose; P = .64, below vs. standard dose).

CONCLUSION

The consumption of higher than the standard 1000-microg prescribed dose of folic acid was not beneficial in reducing cardiac or stroke mortality in hemodialysis patients. Similarly, the consumption of less than the standard dose was not associated with an increase in either cardiac or stroke mortality.

Prevalence of methylenetetrahydrofolate gene (MTHFR) C677T polymorphism among chronic hemodialysis patients and its association with cardiovascular disease: a cross-sectional analysis

INTRODUCTION

Cardiovascular disease (CVD) remains the main cause of morbidity and mortality in end stage renal disease (ESDR) patients. A common C-T mutation at nucleotide position 677 (C677T) has been identified in the gene coding for methylenetetrahydrofolate reductase (MTHFR), which is involved in the remethylation of homocysteine (Hcy). The C677T mutation decreases MTHFR activity, tends to increase Hcy concentrations in individuals who are homozygous for the T/T genotype, and may predispose to CVD. Recent reports suggested that the T/T genotype may predispose type 2 diabetic and hypertensive patients to the development of progressive renal insufficiency. The aim of this cross-sectional study is to analyze the prevalence of the MTHFR C677T gene polymorphism among a group of chronic dialysis patients in comparison to age- and gender-matched controls. We also examined the possible association between CVD and MTHFR gene mutation in this group of patients.

PATIENTS AND METHODS

Fifty chronic hemodialysis patients were included in the study. They were 29 males and 21 females with a mean age of 41.57 +/- 11.76 years. Three patients (6%) were diabetic (type 2). Mean duration of dialysis was 6.4 +/- 3.2 years (range 1-15 years). CVD was defined as being present if there was a medical history of coronary artery disease, cerebrovascular stroke or transient ischemic attacks. MTHFR C677T gene polymorphism was analyzed by PCR in order to discriminate between homozygous (C/C and T/T) and heterozygous (C/T) genotypes. We also measured serum vitamin B(12), folate, total plasma Hcy (tHcy), lipid profile and serum albumin concentrations in the study group. Thirty healthy subjects (16 males and 14 females with mean age of 37.42 +/- 7.63 years) served as healthy controls.

RESULTS

Thirteen patients (26%) experienced at least one cardiovascular event: two (4%) had a history of ischemic cerebrovascular disease, 13 (26%) had coronary artery disease, and one patient (2%) had myocardial infarction. The C677T mutation of MTHFR was not found to be different in hemodialysis patients and healthy controls. Thirty dialysis patients (60%) and 19 healthy subjects (63.33%) had only the wild-type allele (C/C), 16 dialysis patients (32%) and nine healthy controls (30%) had one T allele (C/T), and four dialysis patients (8%) and two healthy controls (6.67%) had two copies (T/T) of the T allele. There were no differences between patients with the three different MTHFR genotypes (C/C, C/T, T/T) regarding cardiovascular events or cardiovascular risk factors. Age, gender, percentages of diabetic and hypertensive patients, serum folate, vitamin B(12), lipid profile, and tHcy levels were not significantly different between the three groups (P > 0.05). Hemodialysis patients with CVD were significantly older compared to those without CVD (P = 0.02). Diabetes status was significantly associated with cardiovascular events (P = 0.01).

CONCLUSIONS

In the dialysis population that we studied, MTHFR C677T gene polymorphism occurred in a pattern similar to that seen for age- and gender-matched healthy controls. No significant association was detected between the T/T genotype and CVD in dialysis patients. Plasma total homocysteine levels were not affected by mutation of the gene coding for MTHFR, and this may be explained by the normal serum folate and vitamin B(12) levels found in the study group.

Application of metabolomic principles to disorders of nucleotide metabolism reveals new metabolic perturbations

A metabolomic analysis of plasma amino acids and acylcarnitines was applied to four disorders of nucleotide metabolism. Multivariate analysis gave score plots that show segregation of hypoxanthine phosphoribosyltransferase and adenine phosphoribosyltransferase deficient plasma from controls with equivocal results for adenosine deaminase and dihydropyrimidine dehydrogenase deficiencies. Loadings plots revealed the principal metabolites responsible for the discrimination between these classes. There were increases for HPRT in C4-, C6-, and C3-DC (malonyl)-carnitines, and decreased serine. For APRT there were increases in C4- to C10- and C3-DC to C6-DC-carnitines, urea, 1-methylhistidine, 3-methylhistidine, and decreased tryptophan. For ADA deficiency there were increases in C4- and C6-carnitines, taurine, and isoleucine.

A pharmacogenomic evaluation of migraine therapy

Migraine is a common idiopathic primary headache disorder with significant mental, physical and social health implications. Accompanying an intense unilateral pulsating head pain other characteristic migraine symptoms include nausea, emesis, phonophobia, photophobia and in approximately 20-30% of migraine cases, neurologic disturbances associated with the aura phase. Although selective serotonin (5-HT) receptor agonists (i.e., 5-HT(1B/1D)) are successful in alleviating migrainous symptoms in < or = 70% of known sufferers, for the remaining 30%, additional migraine abortive medications remain unsuccessful, not tested or yet to be identified. Genetic characterization of the migrainous disorder is making steady progress with an increasing number of genomic susceptibility loci now identified on chromosomes 1q, 4q, 5q, 6p, 11q, 14q, 15q, 17p, 18q, 19p and Xq. The 4q, 5q, 17p and 18q loci involve endophenotypic susceptibility regions for various migrainous symptoms. In an effort to develop individualized pharmacotherapeutics, the identification of these migraine endophenotypic loci may well be the catalyst needed to aid in this goal. In this review the authors discuss the present treatment of migraine, known genomic susceptibility regions and results from migraine (genetic) association studies. The authors also discuss pharmacogenomic considerations for more individualized migraine prophylactic treatments.

Renal transplantation in a 14-year-old girl with vitamin B12-responsive cblA-type methylmalonic acidaemia

Renal tubular dysfunction and chronic renal failure are well recognised complications of methylmalonic acidaemia (MMA) and can occur even in the context of optimal medical metabolic management. Organ transplantation, such as renal and combined liver and renal transplants, have been utilised in the past for children whose disease cannot be managed by conservative medical practices and those with end stage renal disease. Our patient was diagnosed with B(12)-responsive MMA (subsequently proven to be cblA-type MMA) in the postoperative period following renal transplantation for idiopathic chronic renal failure. She remains well, with excellent graft function and metabolic control 4 years after transplantation. This patient highlights the importance of testing for the inborn errors of metabolism in patients presenting with recurrent acidosis and progressive renal impairment.

Cobalamin (vitamin B12) in subacute combined degeneration and beyond: traditional interpretations and novel theories

Subacute combined degeneration (SCD) is a neuropathy due to cobalamin (Cbl) (vitamin B(12)) deficiency acquired in adult age. Hitherto, the theories advanced to explain the pathogenesis of SCD have postulated a causal relationship between SCD lesions and the impairment of either or both of two Cbl-dependent reactions. We have identified a new experimental model, the totally gastrectomized rat, to reproduce the key morphological features of the disease [spongy vacuolation, intramyelinic and interstitial edema of the white matter of the central nervous system (CNS), and astrogliosis], and found new mechanisms responsible for the pathogenesis of SCD: the neuropathological lesions in TGX rats are not only due to mere vitamin withdrawal but also to the overproduction of the myelinolytic tumor necrosis factor (TNF)-alpha and the reduced synthesis of the two neurotrophic agents, epidermal growth factor (EGF) and interleukin-6. This deregulation of the balance between TNF-alpha and EGF synthesis induced by Cbl deficiency has been verified in the sera of patients with pernicious anemia (but not in those with iron-deficient anemia), and in the cerebrospinal fluid (CSF) of SCD patients. These new functions are not linked to the coenzyme functions of the vitamin, but it is still unknown whether they involve genetic or epigenetic mechanisms. Low Cbl levels have also been repeatedly observed in the sera and/or CSF of patients with Alzheimer's disease or multiple sclerosis, but whether Cbl deficit plays a role in the pathogenesis of these diseases is still unclear.

Response of Homocysteine, Cystathionine, and Methylmalonic Acid to Vitamin Treatment in Dialysis Patients

Background: Hyperhomocysteinemia is observed in &gt;80% of hemodialysis patients and is considered a risk factor for cardiovascular disease. Vitamin treatment lowers total homocysteine (tHcy) concentrations in plasma and may therefore reduce the associated risk. Current treatment strategies have not achieved normalization of tHcy in the majority of dialysis patients.

Methods: We administered folic acid (5 mg) plus vitamin B6 (50 mg) and B12 (0.7 mg) intravenously to 38 hyperhomocysteinemic patients (tHcy &gt;18 μmol/L) after each dialysis treatment. The treatment phase lasted 1 month, and serum concentrations of tHcy, methylmalonic acid (MMA), and cystathionine were measured at weeks 0, 2, 4, 6, 8, and 24.

Results: The median serum tHcy concentration decreased significantly, from 26.1 μmol/L at baseline to 13.2 μmol/L at week 4. The median change in tHcy after 4 weeks was 13.4 μmol/L (−51%) compared with baseline. Serum MMA and cystathionine concentrations were reduced by 28% and 26%, respectively, but neither was normalized at 4 weeks. Backward-elimination stepwise regression analysis revealed that higher concentrations of tHcy, MMA, and cystathionine and lower folate at baseline predict changes of tHcy after treatment. Twenty weeks after vitamin withdrawal, tHcy concentrations returned to values comparable to baseline (median, 24.8 μmol/L).

Conclusions: The combination of folic acid, vitamin B12, and vitamin B6 used in this study normalized serum concentrations of tHcy in almost all of our hyperhomocysteinemic dialysis patients. This regimen may be used to investigate the effects of homocysteine normalization on cardiovascular outcomes in hemodialysis patients.

Rat transcobalamin: cloning and regulation of mRNA expression

Transcobalamin (TC) has been cloned and used for studying its gene expression in the rat. TC mRNA is distributed widely in adult rat tissues, but at different levels (kidney > liver > lung > yolk sac > intestine > heart > brain > spleen > muscle). TC mRNA levels were 4-fold higher in the jejunum and ileum compared to its levels in the duodenum. During postnatal development, TC mRNA levels in the ileum declined 4-fold from day 4 to day 12, but increased by 5-fold between days 12 and 24. In contrast, TC mRNA levels increased by 2.5-fold in the kidney from day 4 to day 12 and then declined by 2-fold by day 24. Adrenalectomy of adult rats resulted in a 4-fold decline in ileal levels of TC mRNA and a 50% decline in the ileal mucosal formation of the TC-[(57)Co] cobalamin (Cbl) complex following oral administration of [(57)Co]Cbl complexed to gastric intrinsic factor (IF). Cortisone treatment reversed these changes noted in the ileum. In contrast to ileum, kidney TC mRNA levels were not altered significantly in adrenalectomized rats before and after cortisone treatment. Taken together, this study has provided evidence for the regulation of TC gene expression in the rat kidney and intestine during their postnatal development, and cortisone selectively regulates ileal but not kidney TC mRNA levels.