Objective is to speculate on the
ribavirin induced
anemia by inhibiting
S-adenosylhomocysteine (
SAH)-hydrolase activity. The major toxicity associated with the use of
ribavirin is
hemolytic anemia. This adverse effect has been ascribed to the accumulation of
ribavirin triphosphate in the erythrocyte, which interferes with erythrocyte function.
Ribavirin has been found to inhibit
SAH-hydrolase activity in erythrocyte. SAH is further hydrolyzed to
adenosine and
homocysteine by
SAH-hydrolase. The formation of
S-adenosylmethionine (SAM) is then demethylated to SAH. SAH, the metabolite of SAM, on the other hand is a powerful inhibitor of
methyltransferase enzymes, competing for the SAM binding site. A concurrent decrease in SAM and an increase in SAH levels would inhibit methylation of many tissue components including
proteins,
DNA,
RNA,
phospholipids and other small molecules. The
enzyme protein carboxyl
methyltransferase type II has been recently shown to play a crucial role in the repair of damaged
proteins. SAM is the methyl donor of the reaction, and its demethylated product, SAH is the natural inhibitor of this reaction, as well as of most SAM-dependent methylations. The
biological function of this transmethylation reaction is related to the repair or degradation of age-damaged
proteins. Methyl
ester formation in erythrocyte membrane
proteins has been used as a marker reaction to tag these abnormal residues and to monitor their increase associated with erythrocyte ageing diseases.
Liver disease is complicated by
cholesterol deposition in hepatic and extrahepatic membranes. Erythrocyte membrane fluidity has been improved with the administration of SAM and correlated with the
cholesterol/
phospholipid ratio of the membranes. The levels of
SAH-hydrolase activity were also found to undergo a sharp decrease with red cell ageing. The similarity of these alterations with certain morphofunctional characteristics of erythrocyte in some conditions as
chronic renal failure,
liver disease and
hereditary spherocytosis makes it possible to hypothesize that the inhibition of
SAH-hydrolase could constitute at least a part of
ribavirin induced
hemolytic anemia.