Evaluation of the in vivo interaction of methyl tert-butyl ether with alpha 2u-globulin in male F-344 rats

Methyl tert-butyl ether(MTBE), a fuel additive blended into unleaded gasoli ne, decreases emissions of selected air pollutants, Exposure to MTBE causes a low incidence of renal tumors in male, but not female, F-344 rats. A num ber of chemicals that cause male rat-specific renal tumors also cause a syn drome unique to male rats referred to as alpha 2u-globulin (alpha 2u) nephr opathy (alpha 2u-N). Previous investigations have demonstrated that MTBE ex posure induces a mild accumulation of alpha 2u in male F-344 rats. The obje ctive of the present study was to determine if MTBE, or a metabolite of MTB E, interacts with alpha 2u in male rats administered MTBE orally. Eleven-we ek-old male and female F-344 rats were administered 750 mg [C-14]MTBE/kg bo dy wt or an equivalent volume of 10% emulphor orally for 4 consecutive days . Although [C-14]MTBE-treated male rats exhibited a statistically significa nt increase in renal alpha 2u concentration, the total radioactivity recove red was similar in kidney samples from [C-14]MTBE-treated male and female r ats. Further analysis of kidney cytosol prepared from [C-14]MTBE-treated ra ts revealed that a slightly greater percentage of radioactivity coeluted on a G-25 gel filtration column with the total protein fraction from male rat s than from female rats. Gel filtration (Sephadex G-75 column) and anion ex change chromatography, however, did not demonstrate any coelution of MTBE-d erived radioactivity with the low-molecular-weight protein fraction or alph a 2u fraction, respectively, in kidney cytosol prepared from [C-14]MTBE-tre ated male or female rats. Further experimentation using a sealed vial equil ibration system demonstrated that d-limonene oxide, a chemical with a high affinity for alpha 2u, displaced MTBE in male, but not female, rat kidney s amples following administration of MTBE. These findings provide indirect ev idence that MTBE interacts with a male-specific protein such as alpha 2u in male F-344 rats. Since the pathogenesis of alpha 2u-N is dependent on the formation of a reversibly bound chemical-alpha 2u complex, demonstration of an in vivo interaction of MTBE or one of its metabolites with alpha 2u sup ports the alpha 2u mechanism as a cause of MTBE-induced protein droplet nep hropathy in male rats. (C) 1999 Academic Press.