Elevated serum S-adenosylhomocysteine in cobalamin-deficient elderly and response to treatment

Abstract

Background: S-Adenosylmethionine (SAM)-dependent methylation reactions produce S-adenosylhomocysteine (SAH), the precursor of homocysteine, which has been associated with adverse events when it is elevated. Objective: We studied a cohort of elderly with a high prevalence of cobalamin deficiency to determine whether SAH, SAM, or their ratio was abnormal; whether they correlated with other markers of vitamin deficiency; and whether they changed with cobalamin therapy. Design: A convenience sample of elderly attending nutrition centers was enrolled for baseline demographic, biochemical, and nutritional assessments. Methylmalonic acid (MMA), total homocysteine, and other metabolites were measured by using gas chromatography-mass spectrometry. Serum SAM and SAH were measured by using stable-isotope-dilution liquid chromatography-mass spectrometry. Subjects found to have elevated serum MMA were treated with oral cyanocobalamin tablets (1000 μg/d) for 3 mo. Subjects with normal MMA were randomly assigned to 1 of 3 dosage groups: 0, 25, or 100 μg cyanocobalamin/d. Results: The 149 elderly subjects had a mean age of 76.3 y; 81% were female, and 30% were African American. Serum MMA concentrations were elevated in 30% and SAH concentrations were elevated in 64% of the cohort. Those with elevated MMA concentrations had higher SAH and SAM concentrations. High-dose oral cobalamin lowered SAH, MMA, and total homocysteine concentrations significantly, although subjects with creatinine concentrations >109 umol/L had higher posttreatment SAH than did those with lower creatinine. Conclusions: Elevated serum SAH concentrations are common in elderly and are strongly influenced by both renal status and cobalamin deficiency. These elevated concentrations can be lowered with high-dose oral cobalamin therapy. © 2006 American Society for Nutrition.