The present study investigated the potential role for activation of PPARα and CAR/PXR by potassium PFOS (K⁺ PFOS) with respect to the etiology of hepatic hypertrophy and hepatocellular adenoma in rats. Male Sprague-Dawley rats were fed K⁺ PFOS (20 or 100 ppm) for either 1, 7, or 28 days. Wyeth 14,643 (Wy 14,643, 50 ppm) and phenobarbital (PB, 500 ppm) were the controls for PPARα and CAR/PXR activation, respectively. Measurements included: plasma ALT, AST, cholesterol, triglycerides, and glucose; liver protein and DNA content; liver activities of palmitoyl CoA oxidase (ACOX), Cyp4A, CYP2B, and CYP3A; induction of liver CYP4A1, CYP2E1, CYP2B1/2, and CYP3A1 proteins (SDS-PAGE and Western blots); liver and thyroid microscopic histopathology, apoptotic index, and cell proliferation index. Terminal body weight was decreased by K⁺ PFOS (100 ppm) and Wy 14,643. All test-compound treatments increased liver weight. Plasma lipids were decreased by both PFOS and Wy 14,643. After treatment for 1 day, K⁺ PFOS (100 ppm), PB, and Wy 14,643 increased mean hepatic DNA concentration and total hepatic DNA, and total DNA remained elevated after treatment for 7 days and 28 days (PB and Wy 14,643 only). Hepatic P450 concentration was elevated after 7 and 28 days by K⁺ PFOS and by PB. K⁺ PFOS and Wy 14,643 increased liver activities of ACOX and CYP4A as well as increased liver CYP4A1 protein. By 28 days of treatment, K⁺ PFOS and PB increased liver activities of CYP2B and CYP3A as well as increased liver CYP2B1/2 and CYP3A1 proteins, and Wy 14,643 increased CYP2B enzyme activity to a slight extent. All test compounds increased the liver cell proliferative index and decreased the liver apoptotic index. No histological changes of the thyroid were noted; however, PB and WY increased thyroid follicular cell proliferation index (seven-day treatment only), while K⁺ PFOS did not. The thyroid follicular cell apoptotic index did not differ between groups. The hepatomegaly and hepatocellular adenoma observed after dietary exposure of Sprague-Dawley rats to K⁺ PFOS likely are due to the increased expression of xenosensor nuclear receptors PPARα and CAR/PXR. Given the markedly lower or absent response of human hepatocytes to the proliferative stimulus from activation of PPARα and CAR/PXR, the hepatocellular proliferative response from activation of these receptors by PFOS observed in rats is not expected to be of human relevance.
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