Modulation of ammonium perfluorooctanoate-induced hepatic damage by genetically different PPARα in mice

Abstract

Perfluorooctanoic acid is a ligand for peroxisome proliferator-activated receptor (PPARα). Ammonium perfluorooctanoate (APFO) at 0.1 and 0.3 mg/kg doses activated mouse PPARα, but not human PPARα. This study aimed to clarify whether milligram-order APFO can activate human PPARα, and the receptor is involved in APFO-induced chronic hepatic damage. Male Sv/129 wild-type (mPPARα), Pparα-null, and humanized PPARα (hPPARα) mice (8 weeks old) were divided into three groups. The first was treated with water and the other two with 1.0 and 5.0 mg/kg APFO for 6 weeks, orally, respectively. Both doses activated mouse and human PPARα to a similar or lower degree in the latter. APFO dose dependently increased hepatic triglyceride levels in Pparα-null and hPPARα mice, but conversely decreased those in mPPARα ones. APFO-induced hepatic damage differed markedly among the three genotyped groups: single-cell necrosis was observed in all genotyped mice; inflammatory cells and macrovesicular steatosis only in Pparα-null mice; and microvesicular steatosis and hydropic degenerations in hPPARα and Pparα-null mice. The molecular mechanism underlying these differences may be attributable to those of gene expressions involved in lipid homeostasis (PPARα, β- and ω-oxidation enzymes, and diacylglycerol acyltransferases) and uncoupling protein 2. Thus, milligram-order APFO activated both mouse and human PPARα in a different manner, which may reflect histopathologically different types of hepatic damage.

Fig. 1

Liver histopathological findings after APFO treatment. Liver section photomicrograph taken from mPPARα (a), Pparα-null (b) and hPPPARα (c) mice treated with 0 mg/kg of APFO. Liver from mPPARα (d), Pparα-null (e) and hPPARα (f) mice treated with 1.0 mg/kg of APFO. Liver from mPPARα (g), Pparα-null (h), hPPARα (i) mice treated with 5.0 mg/kg of APFO. PV, portal vein; CV, central vein; original magnification ×400. Arrowheads (j) and arrows (k) indicate hypertrophied and hydropic hepatocytes with eosinophilic cytoplasm in mPPARα and Pparα-null mice treated with 5.0 mg/kg APFO, respectively

Fig. 2

mRNA expressions of PPARα and the related genes in livers from mPPARα, Pparα-null and hPPARα mice treated with APFO. Values represent means ± SD for 8–10 mice per group. *Significantly different from respective control (0 mg/kg) group (P < 0.05). #Significantly different from respective low-dose (1.0 mg/kg) group (P < 0.05). ^†Significantly different from control of mPPARα (P < 0.05). ^§Significantly different from control of Pparα-null mice (P < 0.05)

Fig. 3

Protein expressions of PPARα and the related genes in livers from mPPARα, Pparα-null and hPPARα mice treated with APFO. a Representative Western blot analyses. As an internal standard, GAPDH was stained. b Each band was quantified by densitometric analysis. Histogram presents means ± SD for 8–10 mice per group, and the mean from each control group in mPPARα mice was assigned a value of 1.0. *Significantly different from respective control (0 mg/kg) group (P < 0.05). #Significantly different from respective low-dose (1.0 mg/kg) group (P < 0.05). ^†Significantly different from control of mPPARα (P < 0.05). ^§Significantly different from control of Pparα-null mice (P < 0.05)

Fig. 3

Protein expressions of PPARα and the related genes in livers from mPPARα, Pparα-null and hPPARα mice treated with APFO. a Representative Western blot analyses. As an internal standard, GAPDH was stained. b Each band was quantified by densitometric analysis. Histogram presents means ± SD for 8–10 mice per group, and the mean from each control group in mPPARα mice was assigned a value of 1.0. *Significantly different from respective control (0 mg/kg) group (P < 0.05). #Significantly different from respective low-dose (1.0 mg/kg) group (P < 0.05). ^†Significantly different from control of mPPARα (P < 0.05). ^§Significantly different from control of Pparα-null mice (P < 0.05)