Inhibition of human LDL lipid peroxidation by black pepper extracts and piperine

Atherosclerosis, a chronic inflammatory and progressive disease, is a major cause of coronary heart disease resulted from the accumulation of plague inside the arteries [1]. The oxidized low-density lipoprotein is strongly implicated to play an important role in the generation and progression of the atherosclerotic plaque. Black pepper (Piper nigrum) has been reported as the anti-inflammatory and antioxidant agent. This study aimed at investigating the black pepper extracts and its major alkaloid, piperine, as antioxidants in preventing LDL oxidation. Black pepper extracts were prepared by maceration technique with water, methanol, dichloromethane, hexane and diethyl ether. LDL was isolated by ultracentrifugation and dialysed before subjected to copper-induced oxidation. Using two different approaches, conjugated diene formation during lipid peroxidation was monitored continually by UV-spectrophotometer, and changes in the relative electrophoretic mobility (REM) of lipoprotein were monitored by agarose gel electrophoresis. Suppression of copper-induced LDL oxidation was measured by change in 234nm absorbance in the presence and absence of either black pepper extracts or piperine. Using each compound at 10µg/ml, diethyl ether, dichloromethane extracts and piperine significantly inhibited in vitro oxidation, and extracts from methanol and hexane had stronger inhibitory activity against LDL oxidation than water. Cotreatment of LDL with copper and one of these extracts -methanol (100µg/ml), dichloromethane and diethyl ether (25–100µg/ml)- significantly decreased REM, indicating the inhibition of LDL oxidation. In conclusion, this study shows that particular black pepper extracts and piperine could reduce in vitro LDL oxidation, suggesting their role in lowering the atherosclerosis risk.

Reference: [1] Ross, R. (1999) N. Engl. J. Med. 340:115–126.