3-Methylcholanthrene Induces Chylous Ascites in TCDD-Inducible Poly-ADP-Ribose Polymerase (Tiparp) Knockout Mice.

TCDD-inducible poly-ADP-ribose polymerase (TIPARP) is an aryl hydrocarbon receptor (AHR) target gene that functions as part of a negative feedback loop to repress AHR activity. Tiparp^-/- mice exhibit increased sensitivity to the toxicological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), including lethal wasting syndrome. However, it is not known whether Tiparp^-/- mice also exhibit increased sensitivity to other AHR ligands. In this study, we treated male Tiparp^-/- or wild type (WT) mice with a single injection of 100 mg/kg 3-methylcholanthrene (3MC). Consistent with TIPARP's role as a repressor of AHR signaling, 3MC-treated Tiparp^-/- mice exhibited increased hepatic Cyp1a1 and Cyp1b1 levels compared with WT mice. No 3MC-treated Tiparp^-/- mice survived beyond day 16 and the mice exhibited chylous ascites characterized by an accumulation of fluid in the peritoneal cavity. All WT mice survived the 30-day treatment and showed no signs of fluid accumulation. Treated Tiparp^-/- mice also exhibited a transient and mild hepatotoxicity with inflammation. 3MC-treated WT, but not Tiparp^-/- mice, developed mild hepatic steatosis. Lipid deposits accumulated on the surface of the liver and other abdominal organs in the 3MC-Tiparp^-/- mice. Our study reveals that Tiparp^-/- mice have increased sensitivity to 3MC-induced liver toxicity, but unlike with TCDD, lethality is due to chylous ascites rather than wasting syndrome.