Homocysteine and risk in end-stage renal disease: a matter of context

What is the meaning of homocysteine in patients on dialysis?

OBJECTIVE

To evaluate the determinants of total plasma homocysteine levels and their relations with nutritional parameters, inflammatory status, and traditional risk factors for cardiovascular disease in renal failure patients on dialysis treatment.

DESIGN

The study was conducted on 70 clinically stable patients, 50 of them on hemodialysis (70% men; 55.3 ± 14.5 years) and 20 on peritoneal dialysis (50% men; 62 ± 13.7 years). Patients were analyzed in terms of biochemical parameters (serum lipids, creatinine, homocysteine [Hcy], creatine-kinase [Ck], folic acid, and vitamin B(12)), anthropometric data, markers of inflammatory status (tumor necrosis factor-alpha, C-reactive protein, interleukin-6), and adapted subjective global assessment.

RESULTS

The total prevalence of hyperhomocysteinemia (>15 μmol/L) was 85.7%. Plasma folic acid and plasma vitamin B(12) were within the normal range. Multiple regression analysis (r(2) = 0.20) revealed that the determinants of total Hcy were type of dialysis, creatinine, Ck, folic acid, and total cholesterol. Hcy was positively correlated with albumin and creatinine and negatively correlated with total cholesterol, high density lipoprotein cholesterol, folic acid, and vitamin B(12).

CONCLUSIONS

The determinants of total Hcy in the study sample were type of dialysis, creatinine, Ck, folic acid, and total cholesterol. Evidently, the small sample size might have had an effect on the statistical analyses and further studies are needed. However, Hcy in patients on dialysis treatment may not have the same effect as observed in the general population. In this respect, the association between malnutrition and inflammation may be a confounding factor in the determination of the true relationship between Hcy, nutritional status, and cardiovascular risk factors in this group.

Is homocysteine toxic in uremia?

High levels of homocysteine have been implicated as a cardiovascular risk factor in the general population and in patients with chronic renal failure, and particularly patients on hemodialysis. To classify a risk factor as causally related to a certain disease, both strong epidemiologic data and sound basic-science studies establishing a mechanism are needed. Among the latter, the hypomethylation of proteins and DNA, and protein homocysteinylation, have been investigated in uremia, providing for an array of toxic effects in this disease.

Effects of folic acid and vitamin B complex on serum C-reactive protein and albumin levels in stable hemodialysis patients

OBJECTIVE

Folic acid and vitamin B complex administration in uremic patients has been reported to lower plasma total homocysteine (tHcy) levels, but whether or not this has a beneficial effect on the inflammatory state is not clear.

METHODS

We conducted a randomized open labeled study to determine the effects of folic acid (5 mg daily) and vitamin B complex administration on plasma tHcy levels as well as inflammatory (serum high-sensitivity C reactive protein, hs-CRP) and nutritional (serum albumin) markers in patients on maintenance hemodialysis. Treatment was given for 3 consecutive months to 61 patients on maintenance hemodialysis. Another 60 patients, all age-, sex-, hemodialysis duration-matched served as control group.

MAIN OUTCOME MEASURES

Plasma tHcy, serum hs-CRP, albumin, creatinine (Cr), post-dialysis body weight (BW), and normalized protein catabolism rate (nPCR).

RESULTS

After 3 months, levels of plasma tHcy and serum hs-CRP, Cr, and nPCR were significantly decreased while levels of serum albumin, vitamin B(12), folate, and BW were significantly increased. The dialytic dose (KT/V) and dietary intake remained unchanged. However, correlations between the magnitude of reduction of tHcy & hs-CRP, tHcy & Cr, and Cr & nPCR were statistically significant.

CONCLUSIONS

Folic acid and vitamin B complex co-administration effectively lowers tHcy and hs-CRP levels and increases albumin levels in stable hemodialysis subjects, underscoring their potential benefit to attenuate the state of inflammation and possibly improve the nutritional status in patients on hemodialysis.

Impact of inflammation on epigenetic DNA methylation - a novel risk factor for cardiovascular disease?

OBJECTIVE

The lifespan of dialysis patients is as short as in patients with metastatic cancer disease, mainly due to cardiovascular disease (CVD). DNA methylation is an important cellular mechanism modulating gene expression associated with ageing, inflammation and atherosclerotic processes.

DESIGN

DNA methylation was analysed in peripheral blood leucocytes from three different groups of chronic kidney disease (CKD) populations (37 CKD stages 3 and 4 patients, 98 CKD stage 5 patients and 20 prevalent haemodialysis patients). Thirty-six healthy subjects served as controls. Clinical characteristics (diabetes mellitus, nutritional status and presence of clinical CVD), inflammation and oxidative stress biomarkers, homocysteine and global DNA methylation in peripheral blood leucocytes (defined as HpaII/MspI ratio by the Luminometric Methylation Assay method) were evaluated. CKD stage 5 patients (n=98) starting dialysis treatment were followed for a period of 36 +/- 2 months.

RESULTS

Inflamed patients had lower ratios of HpaII/MspI, indicating global DNA hypermethylation. Analysis by the Cox regression model demonstrated that DNA hypermethylation (HpaII/MspI ratio <median) was significantly associated with both all-cause (RR 5.0; 95% CI: 1.7-14.8; P<0.01) and cardiovascular (RR 13.9; 95% CI: 1.8-109.3; P<0.05) mortality, even following the adjustment for age, CVD, diabetes mellitus and inflammation.

CONCLUSION

The present study demonstrates that global DNA hypermethylation is associated with inflammation and increased mortality in CKD.

Folic acid therapy reduces plasma homocysteine levels and improves plasma antioxidant capacity in hemodialysis patients

OBJECTIVE

We evaluated the effects of folic acid on homocysteine levels and oxidative stress in 46 stable patients on hemodialysis.

METHODS

This double-blind, placebo-controlled, randomized trial assessed the effects of 6 mo of 10 mg of folic acid (26 patients) or placebo (20 patients) given three times weekly after each dialysis under nurse supervision on homocysteine levels, total plasma antioxidant capacity, and hydroperoxide plasma levels.

RESULTS

Folic acid treatment normalized plasma homocysteine levels in most patients, significantly increased total plasma antioxidant capacity levels, but had no significant effect on hydroperoxide levels. Placebo treatment had no statistically significant effect on the three parameters.

CONCLUSION

The folic acid therapy protocol effectively lowered plasma homocysteine levels and improved the total plasma antioxidant capacity in hemodialysis patients. Further studies are required to assess the usefulness of folic acid for decreasing cardiovascular mortality in patients with chronic kidney disease.