The Effects Of Caffeine On PGE₂ Synthesis In Hbx（+） Liver Cells

Objective: Coffee is a common drink. Various biological activities of caffeine, the main constituent of coffee, have been widely studied. In the prevention and treatment of diseases, caffeine has a positive effect. Some studies have shown drinking coffee could reduce the risk of liver cancer. PGE2 is one of the important products with the most biological activities synthesized by cyclooxygenase. Studies have shown that PGE2 is significantly increased in malignant tumor tissue, and could promote the growth of tumor cells. Therefore, inhibition of PGE2 has become one of the valuable research directions against inflammation to cancer. Currently, many drugs or compounds that could inhibit cells to produce PGE2 have been found. These drugs could destroy various enzymes in the generation process of PGE2 or affect their expression to achieve the goal. In this work, we investigated the mechanism of caffeine in influencing HBx(+) hepatocytes to synthesize PGE2. Methods: The effects of caffeine on hepatocytes, including the cell proliferation, the PGE2 secretion, the related proteins expression of PPARγ-EGR1-m PGES-1 axis and the promoter activity of COX-2 and m PGES-1, were detected by MTT test, ELISA, Western-blotting and Dual-Luciferase Reporter Assay, respectively. Results: Different contents of caffeine were used to act on four strains of hepatocyte(HL7702, HL7702-HBx, Hep G2, and Hep G2-HBx) to investigate their effects on cell proliferation. The results showed that the proliferation inhibition of caffeine on the four strains of hepatocyte increased with increasing concentration of the drug, and is more significant in 800 μM concentration(P<0.05). The inhibition activity of caffeine on the four strains of hepatocyte started to be observed on the fourth day(P<0.05) in a concentration-dependent and time-dependent manner. Meanwhile, the inhibition of caffeine on HL7702-HBx and Hep G2-HBx cells was most significant at the concentration of 800 μM and on the seventh day, which was significantly higher than HL7702 and Hep G2 cells(P<0.05). the impact of caffeine on COX-2 and m PGES-1 protein expression, 800 μM caffeine was used to act on HL7702, HL7702-HBx, Hep G2, and Hep G2-HBx cells. After 7days, the cell protein was extracted. The test result showed that caffeine had insignificant impact on COX-2 protein expression of the four strains(P>0.05). The m PGES-1 protein expression with the addition of caffeine was significantly lower that without drug(P<0.05). The m PGES-1 protein expression of HL7702-HBx and Hep G2-HBx cells with the addition of caffeine was significantly lower than that of HL7702 and Hep G2 cells. The inhibition of caffeine on HBx(+) hepatocytes was most significant at the concentration of 800 μM and on the seventh day. Meanwhile, the PGE2 secretion and the expression of m PGES-1 and EGR1 were down-regulated, while PPARγ expression was up-regulated. The m PGES-1 promoter activity of HBx(+) hepatocytes decreased more significantly than that of HBx(-) hepatocytes. Moreover, The expression of EGR1 and PPARγ changed more significantly in HBx(+) hepatocytes cultured for 12 to 24 hours in the presence of 5m M caffeine. The limited success may be due to caffeine releasing the binding of HBx and PPARγ and furthmore affecting the m PGES-1 expression via EGR1 in HBx(+) hepatocytes. Conclusion: These results may provide an experimental basis and rationalization proposal for the preventive strategy of HBV-infected patients from HCC.