Adequate or elevated dietary folate does not ameliorate the reduced antioxidant capacity induced by vitamin B12 deficiency in aged rats.

Folate could have an antioxidant role but also may be detrimental under vitamin B₁₂ deficiency. The aim was to investigate the effect of different dietary folic acid (FA) levels, on oxidative stress in B₁₂ induced deficient aged rats. Thirty-five male aged Sprague-Dawley rats, were fed either a vitamin B₁₂ deficient (n = 27) or a control diet (n = 8) during eight weeks. Then, animals were divided into four groups: B₁₂ and FA deficient diet (DBDF), B₁₂ deficient diet and FA control diet (DBCF), B₁₂ deficient diet and FA supplemented diet (DBSF), and control diet (CBCF) for a 30 days period. Methionine metabolism and antioxidant status were evaluated. Both vitamins deficiencies elevated serum homocysteine (Hcy) (7.7 vs. 4.3 μmol/L, p < 0.05) and reduced S-adenosylmethionine hepatic content (283.7 vs. 581.9 μg/g protein, p < 0.05), the total antioxidant capacity (155.7 vs. 189.3 μmol/L, p < 0.05), glutathione (GSH) (120.5 vs. 419.9 μg/mg protein, p < 0.05) and oxidized glutathione (0.9 vs. 2.6 μg/mg protein, p < 0.05) compared to control. Activities of glutathione peroxidase and glutathione reductase enzymes or damage to macromolecules were unaffected. Adequate or elevated dietary FA in B₁₂ deficiency rats decreased Hcy (5.7 and 6.3 μmol/L, respectively) and increased total antioxidant capacity (189.8 and 192.6 μmol/L, respectively) to values similar to control group, whereas GSH concentration was significantly lower than control (209.1 and 208.0 μg/mg protein respectively, p < 0.05). In conclusion, in a vitamin B₁₂ deficiency status, adequate or elevated FA prevented impairment in one-carbon metabolism, but does not fully reverse the decrease in antioxidant capacity.