Garlic's ability to prevent in vitro Cu2+-induced lipoprotein oxidation in human serum is preserved in heated garlic: effect unrelated to Cu2+-chelation

Cu2+-induced lipoprotein oxidation in human serum was followed by the formation of conjugated dienes at 234 nm and 37°C by 240 min in a phosphate buffer 20 mM, pH 7.4. Blood serum and CuSO4 were added to a final concentration of 0.67% and 0.0125 mM, respectively. The lag time and the area under the curve from the oxidation curves were obtained. The Cu2+-chelating properties of garlic extracts were assessed using an approach based upon restoring the activity of xanthine oxidase inhibited in the presence of 0.050 mM Cu2+. The activity of xanthine oxidase was assessed by monitoring the production of superoxide anion at 560 nm and the formation of uric acid at 295 nm. Data were compared by parametric or non-parametric analysis of variance followed by a post hoc test.Extracts from garlic powder and raw garlic inhibited in a dose-dependent way Cu2+-induced lipoprotein oxidation. The heating of garlic extracts or garlic cloves was unable to alter significantly the increase in lag time and the decrease in the area under the curve observed with the unheated garlic extracts or raw garlic. In addition, it was found that the garlic extracts were unable to chelate Cu2+.(a) the heating of aqueous extracts of raw garlic or garlic powder or the heating of garlic cloves by boiling, microwave or pickling do not affect garlic's ability to inhibit Cu2+-induced lipoprotein oxidation in human serum, and (b) this ability is not secondary to Cu2+-chelation.Garlic (Allium sativum) has been cultivated since ancient times and used as a spice and condiment for many centuries [1]. During the past years, there has been a growing awareness of the potential medicinal uses of garlic [2-5]. The antioxidant properties of garlic are well documented [6-8]. In particular, aqueous garlic extract [9] and aged garlic extract [10-12] are able to prevent Cu2+-induced low density lipoprotein (LDL) oxidation. In addition, Ide et al. [10] and Ho et al. [13] have shown that some garlic compounds such as S-allylc