Toxicological Sciences 53, 24-32 (2000)
Copyright © 2000 by the Society of Toxicology
Biotransformation and Male Rat-Specific Renal Toxicity of Diethyl Ethyl- and Dimethyl Methylphosphonate
Department of Toxicology, University of Würzburg, Versbacherstrasse 9, 97078 Würzburg, Germany; and * Clariant GmbH, Brüningstrasse 50, 65926 Frankfurt am Main, Germany
Dimethyl methylphosphonate (DMMP) is a widely used chemical. Diethyl ethylphosphonate (DEEP) has been proposed as a replacement for DMMP in several applications. A long-term carcinogenesis study with DMMP in rats and mice showed a significant increase in the incidence of kidney tumors after 2 years of exposure in male but not in female rats and both sexes of mice. DMMP is not genotoxic. Due to these findings, a role of 
2u-globulin accumulation in organ-specific tumorigenicity may be possible. 2u-Globulin is a low-molecular-weight protein synthesized in male rats under androgen control. Several male rat specific renal carcinogens have been shown to bind to 2u-globulin and to impair the renal degradation of this protein. This impairment results in 2u-globulin accumulation in the kidney, lysosomal overload, cell death, cell proliferation, and finally, renal tumor induction. To further characterize the toxicology of DMMP and DEEP, we investigated the biotransformation of these compounds and their ability to induce 2u-globulin accumulation in kidney. Biotransformation of both DMMP and DEEP were studied in male and female rats after single oral doses of 50 and 100 mg/kg. 31P-NMR and GC/MS showed that unchanged DMMP was excreted with urine; methyl phosphonate was identified as the only metabolite in urine. Unchanged DEEP was also excreted with urine; in addition, ethyl ethylphosphonate and ethylphosphonate were urinary metabolites. The majority of the applied dose of both compounds was recovered in urine within 24 h indicating rapid absorption and excretion. No sex-differences in rates of formation or excretion of metabolites were seen. To investigate 2u-globulin accumulation in the kidney after DMMP and DEEP, male and female Fischer-344 rats were administered DMMP or DEEP daily for five consecutive days by gavage. DMMP doses were 500- and 1000-mg/kg body weight (bw); due to marked toxicity, daily DEEP dose of 50 and 100 mg/kg had to be used. Control rats received corn oil only and positive controls received five doses of 500-mg/kg bw trimethylpentane (TMP). Relative kidney weights were increased in male rats dosed with DMMP, DEEP, and TMP. 2u-Globulin in kidney cytosol was separated and quantified by capillary electrophoresis and by SDS-PAGE and Western blotting. In DMMP-, DEEP-, and TMP-treated rats, dose-dependent increases in the 2u-globulin content were observed by both methods in male, but not female rats. The increase of 2u-globulin accumulation was accompanied by the formation of protein droplets in the proximal tubules of male rats. These data demonstrate that the sex specific increase in kidney tumors by DMMP in male rats may be due to 2u-globulin accumulation and that similar toxic effects are to be expected from DEEP.
Key Words: dimethyl methylphosphonate (DMMP); diethyl ethylphosphonate (DEEP); trimethylpentane (TMP); 2|gu-globulin nephropathy; protein droplets.