Evaluation of the in vivo interaction of methyl tert-butyl ether with alpha2u-globulin in male F-344 rats.

Methyl tert-butyl ether (MTBE), a fuel additive blended into unleaded gasoline, 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 number of chemicals that cause male rat-specific renal tumors also cause a syndrome unique to male rats referred to as alpha2u-globulin (alpha2u) nephropathy (alpha2u-N). Previous investigations have demonstrated that MTBE exposure induces a mild accumulation of alpha2u in male F-344 rats. The objective of the present study was to determine if MTBE, or a metabolite of MTBE, interacts with alpha2u in male rats administered MTBE orally. Eleven-week-old male and female F-344 rats were administered 750 mg [14C]MTBE/kg body wt or an equivalent volume of 10% emulphor orally for 4 consecutive days. Although [14C]MTBE-treated male rats exhibited a statistically significant increase in renal alpha2u concentration, the total radioactivity recovered was similar in kidney samples from [14C]MTBE-treated male and female rats. Further analysis of kidney cytosol prepared from [14C]MTBE-treated rats revealed that a slightly greater percentage of radioactivity coeluted on a G-25 gel filtration column with the total protein fraction from male rats than from female rats. Gel filtration (Sephadex G-75 column) and anion exchange chromatography, however, did not demonstrate any coelution of MTBE-derived radioactivity with the low-molecular-weight protein fraction or alpha2u fraction, respectively, in kidney cytosol prepared from [14C]MTBE-treated male or female rats. Further experimentation using a sealed vial equilibration system demonstrated that d-limonene oxide, a chemical with a high affinity for alpha2u, displaced MTBE in male, but not female, rat kidney samples following administration of MTBE. These findings provide indirect evidence that MTBE interacts with a male-specific protein such as alpha2u in male F-344 rats. Since the pathogenesis of alpha2u-N is dependent on the formation of a reversibly bound chemical-alpha2u complex, demonstration of an in vivo interaction of MTBE or one of its metabolites with alpha2u supports the alpha2u mechanism as a cause of MTBE-induced protein droplet nephropathy in male rats.