Berberine metabolites exhibit triglyceride-lowering effects via activation of AMP-activated protein kinase in Hep G2 cells

Abstract

Ethnopharmacological relevance: Rhizoma coptidis (Huanglian in Chinese) is commonly used in Chinese folk medicine to treat diarrhea, diabetes, hypertension, hyperlipidemia and tumors. This herb has increasingly gained attention because of its use as a hypolipidemic herb. Berberine (BBR) is the most important constituent of R. coptidis that contribute to the pharmacological efficacy of the herb.

Aim of the study: Pharmacokinetic studies have indicated that BBR has poor oral bioavailability. Interestingly, several reports show that absorbed BBR is extensively metabolized in rats and humans. We speculate that the BBR metabolites might be responsible for the pharmacological effects. The aim of this study is to examine BBR metabolites for their triglyceride (TG)-lowering activities and the molecular mechanism to clarify BBR genuine effective forms in vivo.

Materials and methods: Four BBR metabolites were examined their TG-lowering effects with a commercial triglyceride assay kit. Real-time PCR and Western blotting were used to confirm genes and proteins of interest, respectively.

Results: Among those BBR metabolites, M2 exhibited the more potential effects on TG-lowering and AMP-activated protein kinase (AMPK) activation in Hep G2 cells as compared with BBR. Moreover, BBR and M2 inhibited gene expressions of acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), glycerol-3-phosphate acyltransferase (GPAT) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), but motivated gene expression of medium chain acyl-CoA dehydrogenase (mCAD) significantly.

Conclusions: The results suggested that the TG-lowering effects of BBR and M2 might be partially mediated by the up-regulation of lipolysis gene expressions and down-regulation of lipogenesis gene expressions through activation of the AMPK signaling pathway. BBR and its metabolites might be in vivo active forms of oral doses of BBR, and M2 might be a promising drug candidate against hyperlipidemia.

Keywords: AMPK; Berberine; Hyperlipidemia; Metabolites; Triglyceride.