Interaction among peroxisome proliferators-activated receptor alpha, cytochrome P450 oxysterol 7α-hydroxylase and estrogen receptor and its association with intrahepatic cholestasis in pregnant rats

Objective To investigate the relationship between interaction of peroxisome proliferators-activated receptor alpha (PPARα), cytochrome P450 oxysterol 7α-hydroxylase (CYP7B1) and estrogen receptor (ER) and intrahepatic cholestasis in pregnant rats. Methods Eighty clean SD pregnant rats were selected and divided into four groups randomly with 20 in each. Since the 13th day of pregnancy,rats in the control group was injected subcutaneously with refined vegetable oil 2.0 ml · kg-1 · d -1 , those in the low-dose, moderate-dose and high-dose groups received 17-α-ethynylestradiol (EE) 1.0 mg · kg-1 · d-1,1.25 mg · kg-1 · d-1 and 1.5 mg · kg-1 · d-1, respectively. All rats were sacrificed at the 21at day of pregnancy and maternal hepatic tissues were collected. The serum levels of alanine aminotransferase(ALT), aspartate transaminase (AST), total bile acid (TBA) and bilirubin (BIL) were determined by enzyme linked immunosorbent assay (ELISA). The mRNA expressions of PPARα, CYP7B1, Erα and Erβ in maternal rat livers were examined by real-time PCR. Results (1) Biochemical indicators: the serum levels of ALT,AST, TBA and BIL were significantly lower in the control group than in the rest 3 groups,respectively control group: (41.1 ± 2.8 ) U/L, (44.4 ± 3.6) U/L, (26.4 ± 5.6 ) μmol/L and( 2.8 ± 0.2)U/L;low-dose group: (48.2 ±3.4) U/L,(47.9 ±3.7) U/L,(36.4 ±4.2) μmol/L and (4.2 ±0.2) U/L;moderate-dose group: (70.4 ± 5.3 ) U/L, (68.4 ± 5.6) U/L, (64.3 ± 3.8 ) μmol/L and ( 6.2 ± 1.2)U/L; high-dose group: (72.4 ±7.6) U/L, (70.2 ±3.8) U/L, (72.4 ±7.8) μmol/L and (8.2 ±2.2)U/L, P<0.05], and those in the moderate or high-dose groups were higher than in the low-dose group (P<0.05). (2) mRNA expression of Erα and Erβ: the mRNA expression of Erα in pregnant rat livers increased in a dose-dependent manner, which were all significantly higher than that in the control group,respectively ( low-dose group: 0.76 ± 0.02 ); moderate -dose group: ( 0.99 ± 0.04; high-dose group:1.21 ±0.01 ;control group:0.65 ±0.01, P <0.05), but no difference was found among the 4 groups in the mRNA expression of Erβ ( P > 0.05 ). (3) mRNA expression of CYP7B1 and PPARα: the mRNA expression of CYP7B1 in pregnant rat livers increased from the low-dose group to the high-dose group, and were all higher than that of the control group ( low-dose group: 0.93 ± 0.01; moderate-dose group: 0.99 ±0.06; high-dose group: 1.22 ± 0.04; control group: 0.75 ± 0.02, P < 0.05 ). However, the mRNA expression of PPARα decreased from the low-dose group to the high-dose group, and were all lower than that of the control group (low-dose group: 0.83 ± 0.05; moderate-dose group: 0.71 ± 0.02; high-dose group:0.64 ± 0.03; control group: 1.35 ± 0. 05; P < 0.05 ) . Conclusions The down regulated mRNA expression of PPARα, caused by higher dose of estrogen, may increase the expression of CYP7B1 due to the ineffectiveness of the inhibition of PPARα on CYP7B1, which may further stimulate the Erα activity and then induce intrahepatic cholestasis. Abnormal expression of PPARα, CYP7B1 and ER may play a role in the pathogenesis of estrogen-induced intrahepatic cholestasis.