Vitamin B6 metabolism and homocysteine in end-stage renal disease and chronic renal insufficiency

Homocysteine (tHcy) is a risk factor for atherosclerosis inpatients with end-stage renal disease and chronic renal insufficiency (CRI). Vitamin B-6 deficiency may result in high tHcy levels, especially after a methionine load (PML). Therefore, we evaluated vitamin B-6 metabolism and tHcy (fasting and PML) levels in patients with CRI and those on hemodialysis (HD) therapy before and during high-dose sequential vitamin B-6 and folic acid supplementation in mate patients (27 patients, HD, 17 patients, CRI) and 19 age-matched healthy controls. Vitamin B-6 doses were 100 mg/d in patients with CRI and 200 mg/d in HD patients, plus folic acid (5 mg/d), for more than 3 months in each period. We analyzed vitamin B-6 metabolites by high-performance liquid chromatography In plasma and red blood cells (RBCs) and fasting tHcy in all cases and PML in subgroups of 11 HD patients and 14 patients with CRI. We found vitamin 136 deficiency and high tHcy (fasting and PML) levels in all patients. Plasma and RBC levels of pyridoxal and pyridoxal phosphate were abnormally low, whereas levels of pyridoxic acid (PA), an end product of vitamin B-6 metabolism, were extremely high in both groups. Fasting and PML tHcy levels were partially resistant to vitamin B-6 supplements, with different response patterns In HD patients and those with CRI. Thus, the PML defect was more responsive to folic acid in HD patients, whereas vitamin B-6 partially reduced PML tHcy levels in patients with CRI. Resistance of tHcy to vitamin B6 treatment in patients with CRI and HD patients Is not caused by poor absorption or low tissue stores. Rather, nonvitamin factors or potentially toxic PA levels may be implicated in abnormal vitamin B-6 and/or tHcy metabolism during renal insufficiency. (C) 2002 by the National Kidney Foundation, Inc.