Retrospective study of possible alpha-2 mu-globulin nephropathy and associated cell proliferation in male Fischer 344 rats dosed with t-butyl alcohol.

Tert-butyl alcohol, an important commodity chemical, additive to unleaded gasoline, and contaminant of drinking water, was evaluated for toxicity and was found to enhance nephropathy in male Fischer 344 rats. Because male rats treated with t-butyl alcohol for 2 years had a low incidence of renal cortical tumors, additional renal sections for the 90-day toxicity study were examined for the presence of hyaline droplet accumulation, nephropathy, and evidence of replicative DNA synthesis (S-phase nuclei) to indirectly and retrospectively investigate a possible role of alpha-2 mu-globulin in the pathogenesis of the nephropathy. Dose levels for t-butyl alcohol were 0, 0.25, 0.5, 1, 2, and 4% (w/v) administered in drinking water. Significant body weight gain depressions were observed in all treated males, and there was an absolute weight loss in the 4% male group, none of which survived to the end of the study. Except for the 4% dose group, there was a treatment-related increase in hyaline droplet accumulation in the renal proximal tubules with crystalline, rectangular, and rhomboid forms of the protein evident. The severity of nephropathy was enhanced in treated rats, except for the 4% dose group. Replicative DNA synthesis, as measured by immunohistochemical staining for proliferating cell nuclear antigen, was increased in proximal tubules of rats dosed with 2% t-butyl alcohol. It is concluded that t-butyl alcohol exacerbated nephropathy in male Fischer 344 rats and increased renal accumulation of hyaline protein material consistent with alpha-2 mu-globulin deposition.