Effects of capsaicinoids and curcumin on copper-induced oxidation of human serum

Introduction: Oxidation of low density lipoprotein (LDL) cholesterol is believed to be the first step in the development and progression of atherosclerosis. The active ingredients of spices such as chilli and turmeric (capsaicin and curcumin, respectively) have been shown to reduce the susceptibility of LDL to oxidation. One of the techniques used to study the oxidation of LDL is to isolate and subject LDL to metal-induced (copper or iron) oxidation. However, whole serum may represent a closer situation to in vivo than isolated LDL. Methods: We investigated the effects of different concentrations of capsaicin, dihydrocapsaicin and curcumin on copper-induced oxidation of serum. Serum samples, collected from six fasting healthy individuals (3 men and 3 women, mean age 34 +/- 10 years) was diluted 50-fold in phosphate-buffered saline (pH 7.4), incubated with increasing concentrations (0.1, 0.5, 0.7, 1, 2 and 3uM) of capsaicin, dihydrocapsaicin and curcumin, and subjected to copper (100uM) induced oxidation. Oxidation kinetics were determined for each serum sample in duplicate by measuring absorbance at 245nm at 37 degree Celsius using a multi-position spectroscope (Cintra 10E UV-VIS , GBC scientific equipments, Victoria, Australia) every 10 min for 300 min. Lag time (before initiation of oxidation) and rate of oxidation (slope of propagation phase) were calculated from the oxidation curves. Results: Lag time increased and rate of oxidation decreased (p<0.05) with the increasing concentrations of the antioxidants. A 50% increase in lag time (from control) was observed at concentrations between 0.5 to 0.7uMfor capsaicin, dihydrocapsaicin and curcumin. Although the rate of oxidation decreased with increasing concentrations of the tested antioxidants, the total oxidation was lower with capsaicin and dihydrocapsaicin compared to curcumin. Conclusion: This study shows that oxidation of serum lipids is reduced by capsaicinoids and curcumin in a concentration-dependent manner.