Green and black tea extracts inhibit HMG-CoA reductase and activate AMP kinase to decrease cholesterol synthesis in...

Area of Science:

• Biochemistry
• Cell Biology
• Nutritional Science

Background:

• Green and black tea consumption is linked to reduced serum cholesterol in humans and animals.
• Suppression of hepatic cholesterol synthesis is a proposed mechanism for tea's cholesterol-lowering effects.

Purpose of the Study:

• To investigate the impact of green and black tea extracts on cholesterol synthesis in cultured rat hepatoma cells.
• To elucidate the molecular mechanisms by which tea extracts affect cholesterol biosynthesis, focusing on HMG-CoA reductase activity.

Main Methods:

• Cultured rat hepatoma cells were treated with green and black tea extracts.
• Cholesterol synthesis was measured using radiolabeled acetate and mevalonate incorporation.
• HMG-CoA reductase activity and the phosphorylation status of HMG-CoA reductase and AMP kinase were assessed.

Main Results:

• Green and black tea extracts inhibited cholesterol synthesis by up to 55% and 78%, respectively.
• Inhibition appeared to occur at or above HMG-CoA reductase, with direct inhibition observed in microsomal preparations.
• Both tea extracts increased the phosphorylation of AMP kinase and HMG-CoA reductase, indicating enzyme inactivation, with distinct time courses for green and black tea.

Conclusions:

• Green and black tea decrease cholesterol synthesis in liver cells through dual mechanisms.
• These mechanisms involve direct inhibition of HMG-CoA reductase and enhanced inactivation of the enzyme via AMP kinase-mediated phosphorylation.
• The findings support the role of tea consumption in managing cholesterol levels through modulation of hepatic cholesterol synthesis.