In vitro effects of active components of Polygonum Multiflorum Radix on enzymes involved in the lipid metabolism.

BACKGROUND

Raw and processed Polygoni Multiflori Radix (PMR and PMRP) are used in the prevention and treatment of non-alcoholic fatty liver disease (NAFLD), hyperlipidemia or related diseases. In our previous research, 2, 3, 5, 4'-tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG) displayed the most important role in the total cholesterol (TC) lowering effect among all the chemical constituents of Polygonum multiflorum. Emodin and physcion displayed more favorable triglyceride (TG) reducing effects than TSG. However, there are few researches focus on the approach and mechanism of how do Polygonum multiflorum exhibit good lipid regulation activity. The targeted sites of active substances of Polygonum multiflorum are still not clearly elucidated. This research pays close attention to how major chemical components of Polygonum multiflorum affect the TC and TG contents in liver cells.

METHODS

In this research, a sensitive, accurate and rapid in vitro model, steatosis hepatic L02 cell, was used to explore target sites of active chemical substances of Polygonum multiflorum for 48h. Steatosis hepatic L02 cell was exposed to emodin, physcion and TSG, respectively. The contents of four key enzymes in the pathway of synthesis and decomposition of TC and TG were investigated after exposure. Meanwhile, the contents of lipid transfer protein were also tested. The diacylgycerol acyltransferase 1 (DGAT1) controlled the biosynthesis of TG from free fatty acids while 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase) limited the biosynthesis of TC. Hepatic triglyceride lipase (HTGL) and cholesterol 7α-hydroxylase (CYP7A) played the key role in the lipolysis procedure of TG and TC.

RESULTS

The synthesis of TC and TG in steatosis L02 cells were apparently increased in the model group compared to the control group. Intracellular contents of HMG-CoA reductase and DGAT1 increased 32.33% and 56.52%, while contents of CYP7A and HTGL decreased 21.61% and 47.37%. Emodin, physcion and TSG all showed down-regulation effects on HMG-CoA reductase, while up-regulation effects on CYP7A. The most remarkable effect on HMG-CoA reductase was found on emodin. Emodin could reduce the DGAT1 content from 438.44 ± 4.51 pg/mL in model group to 192.55 ± 9.85 pg/mL (100 μm). The content of HTGL in 300 μm physcion group was 3.15 ± 0.15 U/mL, which was more significantly effective than the control, lovastatin and fenofibrate group.

CONCLUSIONS

TSG could raise the content of CYP7A and then promote the lipolysis of cholesterol. Moreover, TSG also showed the best LDL-reducing effect. Emodin could inhibit HMG-CoA reductase and DGAT1, which were key enzymes in the synthesis of TC and TG. Physcion increased the content of HTGL, and then could boost the lipolysis of triglyceride. At the same time, physcion showed the best VLDL-reducing effect. In view of the above conclusions, we contributed the lipid regulation activity to an overall synergy of TSG, emodin and physcion.