Testosterone contributes sex differences of urinary biomarkers for nephrotoxicity in rats

Urinary biomarkers have been used widely in non-clinical toxicity studies to detect kidney dysfunction/injury caused by drugs under development. Although their usefulness to evaluate nephrotoxicity has been well studied, knowledge about sex differences in the urinary excretion levels of these biomarkers remains inadequate. We previously demonstrated the existence of sex differences in the excretion levels of urinary biomarkers and that these differences were associated with the endogenous testosterone levels. In this study, testosterone was repeatedly administered subcutaneously to female rats for 4 weeks along with male rats as a comparison control, to investigate how the blood levels of testosterone contribute to the sex differences in the urinary biomarker and renal cortical protein levels. The results showed that the urinary excretion of leucine aminopeptidase (LAP), gamma-glutamyltransferase (γ-GTP), cystatin C (Cys-C), liver-type fatty acid binding protein (L-FABP), and beta2-microglobulin (β2MG) were increased, and the urinary excretion of kidney injury molecule 1 (Kim-1) was decreased. The protein level of megalin, an endocytic receptor, in the renal cortex, was higher in female rats than in male rats, and testosterone treatment led to decrease in the level in the female rats. Our results suggest that the blood testosterone level might be responsible for the sex differences in the urinary excretion levels of low-molecular-weight proteins via regulating the expression level of megalin in the renal cortex.