The Inhibin B Response to Testicular Toxicants Ethylene Glycol Monomethyl Ether or Dibromoacetic Acid in Male Rats


Correspondence to: Katharine Whitney, Department of Pathology, Preclinical Safety, AbbVie, R469 AP13A, 1 North Waukegan Road, North Chicago, IL 60064.




This study was conducted as part of an ILSI-HESIconsortium effort to assess the utility of circulating inhibin B as an early biomarker of testicular toxicity in rats.


Two known testicular toxicants were selected for use in this study: ethylene glycol monomethyl ether (EGME) and dibromoacetic acid (DBAA). EGME (200 mg/kg/day), DBAA (250 mg/kg/day), or vehicle control (0.2% hydroxypropyl methylcellulose [HPMC]) was administered orally to male rats for 3, 6, or 14 consecutive days. On study days 4, 7, and 15, serum was collected for evaluation of inhibin B levels from all surviving animals and a subset of animals was necropsied from each of the control, EGME, and DBAAgroups.


Administration of EGMEresulted in spermatocyte degeneration in late stage tubules and spermatocyte depletion to stage III on day 4, progressing to loss of spermatocytes and round spermatids to stage VI by day 7 and continued germ cell loss and degeneration of elongating spermatids by day 15. Inhibin B levels among EGME-treated animals progressively decreased relative to their respective controls at all time points. Administration of DBAA was associated with spermatid retention at all three time points and abnormal residual bodies at days 7 and 15. Inhibin B levels among DBAA-treated animals decreased progressively relative to their respective controls on days 7 and 15.


Serum inhibin B levels in rats provided a signal of testicular toxicity for each of these known testicular toxicants administered at high levels; however, histopathology provided the earliest evidence of toxic effects.