High-dose clevudine decreased the mitochondrial activities in INS-1E cells. (A) Clevudine reduced the MTT signal, which reflects total mitochondrial activity within each well. (B) Clevudine decreased the enzymatic activity of cytochrome c oxidase (COX). Data are presented as means ± SEM. The number of experiments is shown in parenthesis. * and ** denote p < 0.05 and p < 0.01, respectively.