A study of the lipoprotein lipase inhibitory mechanism ofPoncirus trifoliatawater extracts

Abstract

Purpose: Poncirus trifoliata has been reported to have anti-inflammatory, antioxidant, and immune activities. However, its anti-obesity activity and the mechanism by which the water extract of dried, immature fruit of Poncirus trifoliata (PF-W) acts are not clear. This study suggests a potential mechanism associated with the anti-obesity activity of PF-W. Methods: We measured the effect of PF-W on lipoprotein lipase (LPL) regulation using enzyme-linked immunosorbent assay (ELISA) and an activity assay. The LPL regulation mechanism was examined by reverse transcription polymerase chain reaction (RTPCR) to measure the mRNA expression of biomarkers related to protein transport and by western blot for analysis of the protein expression of the transcription factor CCAAT-enhancer-binding protein (C/EBPβ). Results: The total polyphenol and flavonoid content of PF-W was 52.15 ± 4.02 and 6.56 ± 0.47 mg/g, respectively. PF-W treatment decreased LPL content in media to 58 ± 5% of that in control adipocyte media, and increased LPL content to 117 ± 3.5% of that in control adipocytes, but did not affect the mRNA expression of LPL. PF-W also increased the mRNA expression of sortilin-related receptor (SorLA), a receptor that induces endocytosis and intracellular trafficking of LPL, in a concentration- and timedependent manner. Finally, cell fractionation revealed that PF-W treatment induced the expression of C/EBPβ, a SorLA transcription factor, in the nuclei of 3T3-L1 adipocytes. Conclusion: The LPL secretion and activity assay showed PF-W to be an LPL secretion inhibitor, and these results suggest the potential mechanism of PF-W involving inhibition of LPL secretion through C/EBPβ-mediated induction of SorLA expression.