Hyaline droplet nephropathy resulting from exposure to 3,5,5-trimethylhexanoyloxybenzene sulfonate

Abstract

Acute oral dosing of 3,5,5-trimethylhexanoyloxybenzene sulfonate (THBS) to adult male and female rats causes a male rat-specific nephrotoxicity manifested as exacerbation of hyaline droplet formation. This chemical is structurally distinct from the volatile hydrocarbons known to cause male rat-specific kidney lesions. Therefore, to classify THBS as a hyaline droplet-inducing agent, experiments were conducted to determine whether [ 14C]THBS equivalents bound to α2u-globulin and caused the protein to accumulate in male rat kidney cortex. Two-dimensional gel electrophoretic separation of male rat kidney proteins indicated that α2u-globulin levels in kidney increased 24 hr after a single oral dose of THBS (500 mg/kg). Furthermore, a sex-dependent retention of THBS was noted as there was approximately 10 times more THBS equivalent in male rat kidney than in female rat kidney. Equilibrium dialysis experiments indicated that 40% of THBS equivalents bound reversibly to male rat kidney proteins, whereas no interaction between THBS and female rat kidney proteins was detected. Specific binding of THBS to α2u-globulin was determined by anion-exchange HPLC after which metabolites in the α2u-globulin fraction were identified by gas chromatography with parallel radioactivity-mass spectrometry and mass spectrometry-matrix isolation Fourier-transform infrared analysis. Four metabolites of THBS were found in this protein fraction, and the major component (approximately 70%) was identified as the cis ggg-lactone of 3,5,5-trimethylhexanoic acid. Experiments were also conducted in mice to determine whether THBS bound to any mouse kidney proteins, particularly mouse urinary protein. The results indicated that there was no interaction between THBS and mouse urinary protein, a protein which shares siggificant homology with α2u-globulin. These results indicate that THBS treatment exacerbates hyaline droplet formation in male rat kidneys by binding to α2u-globulin, thereby causing the protein to accumulate in the renal cortex. The interaction between THBS and α2u-globulin appears to be unique to this male rat-specific protein as THBS does not interact with a very similar protein found in mice.