ABSTRACT
BACKGROUND: Metformin, as a first-line treatment for diabetes, interacts with many protein kinases and transcription factors which affect the expression of downstream target genes governing drug metabolism. Sulfotransferase, SULT2A1, one phase II metabolic enzyme, sulfonates both xenobiotic and endobiotic compounds to accelerate drug excretion. Herein, we designed experiments to investigate the effects and mechanisms of metformin on SULT2A1 expression in vitro. METHODS: The hepatocellular carcinoma cell line, HepaRG, was cultured with different concentrations of metformin. The cell viability was measured using CCK8 kit. HepaRG was used to evaluate the protein expression of pregnane X receptor (PXR), the constitutive androstane receptor (CAR), SULT2A1, AMP-activated protein kinase (AMPK), and phosphorylation of AMPK (p-AMPK), respectively, at different concentrations of metformin with or without rifampin (human PXR activator) and CITCO (human CAR activator). The coregulators with CAR on SULT2A1 promoter response elements have also been characterized. RESULTS: We showed that metformin did not affect the basic expression of SULT2A1 but could suppress the expression of SULT2A1 induced by the activator of human CAR. Investigations revealed that metformin which could block CAR nuclear translocation further suppress SULT2A1. In addition, we found that the prevented CAR transfer into the nucleus by metformin was partially an AMPK-dependent event. CONCLUSION: The present study indicated that the activation of AMPK-CAR pathway mediated the suppression of SULT2A1 by metformin. Metformin may affect the metabolism and clearance of drugs which are SULT2A1 substrates. The results that emerged from this work provide substantial insights into an appropriate medication in the treatment of diabetes patients.
ABSTRACT
BACKGROUND: Type 2 diabetes has become one of the most common diseases worldwide, causing a serious social burden. As a first-line treatment for diabetes, metformin can effectively improve insulin resistance. It has been reported that 12α-hydroxylated BA (mainly CA) is associated with insulin resistance. The purpose of this study was to analyze the changes in CA and possible signaling mechanisms in diabetic rats after metformin intervention. METHODS: HepG2 cells were cultured after adding different concentrations of metformin. The cell viability was measured using CCK8 kit, and the expression of FXR, MAFG, and CYP8B1 in cells was detected by WB. The rat models of type 2 diabetes were induced by low-dose streptozotocin by feeding a high-fat diet, and the control rats (CON) were fed on normal food; the diabetic rats (DM) were given a high-fat diet without supplementation with metformin, while the metformin-treated diabetic rats (DM + MET) were given a high-fat diet and supplemented with metformin. Biochemical parameters were detected at the end of the test. Expression levels of FXR, CYP8B1, and MAFG were assessed by WB. Serum CA were measured using an enzyme-linked immunosorbent assay (ELISA). RESULTS: In HepG2 cells, metformin dose-dependently enhanced the transcriptional activity of FXR and MAFG and inhibited the expression of CYP8B1. Metformin-treated DM rats showed improved glucose and bile acid metabolism. In addition, significantly increased FXR and MAFG and decreased CYP8B1 were observed in DM + MET rats. At the same time, the CA content of metformin-treated rats was lower than that of diabetic rats. CONCLUSION: Changes in CA synthesis after metformin treatment may be associated with inhibition of CYP8B1. These results may play an important role in improving insulin sensitivity after metformin treatment.
