Vitamin B12 reduces ribavirin-induced genotoxicity in phytohemaglutinin-stimulated human lymphocytes.

Ribavirin, an N-glycosyl nucleoside (1-beta-D-ribofuranosyl-1, 2, 4-triazole-3 carboxamide), is a synthetic purine nucleoside analogue with a broad spectrum of antiviral activity, however, its high toxicity poses a major disadvantage of its use as a therapeutic. Various studies have shown that vitamin B12 plays a significant role in maintaining the stability of the human genome. We therefore investigated the potential beneficial effect of vitamin B12 in reducing ribavirin-induced genotoxicity. To test this, we used the cytokinesis-block micronucleus (CBMN) assay. Human blood cells were treated in vitro with increasing doses of ribavirin (0.05, 0.17, 0.32, 0.47 and 0.65 micromol/ml) for three different periods of time (2, 4 and 17 hrs). Duplicate cultures were supplemented with 50 mul of vitamin B12 during the drug treatment (final concentration of 13.5 microg/ml). Micronuclei formation and cell proliferation potential were then scored in both sets of samples and the corresponding controls. The results showed that supplementation with vitamin B12 lowered the frequency of micronuclei (Z = 2.02, p < 0.04) and recovered the proliferation potential of the treated cells for each treatment period, except for the conditions with the highest concentration of ribavirin and the shortest time. These observations underscore the unique beneficial effects of vitamin B12 in reducing genotoxicity, particularly by recovering the proliferation potential of treated cells, as demonstrated by the decrease in mononucleated cells and enhancement of binucleated and polynucleated cells. The mechanism by which vitamin B12 reduces ribavirin-induced genotoxicity is related to de novo synthesis of nucleotides, and is worthy of further investigation.