Induction of P-glycoprotein expression and activity by prolactin in female rat liver.

AIM: P-glycoprotein (P-gp) plays a critical role in the excretion of xenobiotics into bile. Previous studies have demonstrated that prolactin (PRL) regulates biotransformation and bile salt transport. Here we investigate whether the capability of the liver to transport xenobiotics into bile is altered in hyperprolactinemic states studying the modulation of hepatic P-gp by PRL. METHODS: We used lactating post-partum rats (PP), as a model of physiological hyperprolactinemia (15 and 21 days after delivery: PP15 and PP21, respectively), and ovariectomized rats treated with PRL (300 µg/day, 7 days, via osmotic minipumps, OVX + PRL). Hepatic P-gp expression and activity were evaluated by western blotting and using rhodamine 123 as substrate in vivo, respectively. Since P-gp is encoded by Mdr1a and Mdr1b in rodents, we quantified their expression by qPCR in primary hepatocyte cultures exposed to 0.1 µg/ml of PRL after 12 h. To further study the mechanism of hepatic P-gp modulation by PRL, hepatocytes were pretreated with actinomycin D and then exposed to PRL (0.1 µg/ml) for 12 h. KEY FINDINGS: We found increased hepatic P-gp protein expression and activity in PP15 and OVX + PRL. Also, a significant increase in Mdr1a and Mdr1b mRNA levels was observed in primary hepatocyte cultures exposed to PRL, pointing out the hormone direct action. Actinomycin D prevented these increases, confirming a transcriptional up-regulation of P-gp by PRL. SIGNIFICANCE: These findings suggest the possibility of an increased biliary excretion of xenobiotics substrates of P-gp, including therapeutic agents, affecting their pharmaco/toxicokinetics in hyperprolactinemic situations.

Protective effect of genistein pre-treatment on paraquat hepatotoxicity in rats.

Paraquat (PQ), an herbicide widely used in agriculture, is considered a highly toxic compound. In hepatocytes, P-glycoprotein (P-gp/Abcb1) is a canalicular transporter involved in PQ extrusion from the cell. Previously, we demonstrated that genistein (GNT) induces P-gp in rat liver. In this study, the protective role of GNT pretreatment towards hepatic damage in a model of acute intoxication with PQ in rats, was investigated. Wistar rats were randomized in 4 groups: Control, GNT (5 mg/kg/day sc, 4 days), PQ (50 mg/kg/day ip, last day) and GNT+ PQ. Hepatic lipoperoxidation (LPO) was evaluated by the thiobarbituric acid reactive substances method. Hepatic levels of 4-hydroxynonenal protein adducts (4-HNEp-add) and glutathione-S-transferase alpha (GSTα) protein expression were evaluated by Western blotting. Hepatic glutathione levels and plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST) were also measured. Biliary excretion of PQ was studied in vivo and in isolated perfused liver. PQ was quantified by HPLC. PQ significantly increased AST and ALT activities, malondialdehyde and 4-HNEp-add levels, whereby pretreatment with GNT ameliorated this effect. PQ biliary excretion remained unchanged after treatments in both experimental models. Hepatic GSTα expression was augmented in GNT group. GNT pretreatment increased hepatic glutathione levels in PQ + GNT group. These results agree with the lower content of 4-HNEp-adds in GNT + PQ group respect to PQ group. Unexpectedly, increased activity of P-gp did not enhance PQ biliary excretion. Thus, GNT protective mechanism is likely through the induction of GSTα which results in increased 4-HNE metabolism before formation of protein adducts.

ABC Transporters: Regulation and Association with Multidrug Resistance in Hepatocellular Carcinoma and Colorectal Carcinoma.

For most cancers, the treatment of choice is still chemotherapy despite its severe adverse effects, systemic toxicity and limited efficacy due to the development of multidrug resistance (MDR). MDR leads to chemotherapy failure generally associated with a decrease in drug concentration inside cancer cells, frequently due to the overexpression of ABC transporters such as P-glycoprotein (P-gp/MDR1/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2), which limits the efficacy of chemotherapeutic drugs. The aim of this review is to compile information about transcriptional and post-transcriptional regulation of ABC transporters and discuss their role in mediating MDR in cancer cells. This review also focuses on drug resistance by ABC efflux transporters in cancer cells, particularly hepatocellular carcinoma (HCC) and colorectal carcinoma (CRC) cells. Some aspects of the chemotherapy failure and future directions to overcome this problem are also discussed.