The spice principles curcumin (from turmeric) and eugenol (from cloves) are good inhibitors of lipid peroxidation. Lipid peroxidation is known to be initiated by reactive oxygen species. The effect of curcumin and eugenol on the generation of reactive oxygen species in model systems were investigated. Both curcumin and eugenol inhibited superoxide anion generation in xanthine-xanthine oxidase system to an extent of 40% and 50% at concentrations of 75 microM and 250 microM respectively. Curcumin and eugenol also inhibited the generation of hydroxyl radicals (.OH) to an extent of 76% and 70% as measured by deoxyribose degradation. The .OH-radical formation measured by the hydroxylation of salicylate to 2,3-dihydroxy benzoate was inhibited to an extent of 66% and 46%, respectively, by curcumin and eugenol at 50 microM and 250 microM. These spice principles also prevented the oxidation of Fe2+ in Fentons reaction which generates .OH radicals.

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Polyunsaturated fatty acids (PUFA) are vulnerable to peroxidative attack. Protecting PUFA from peroxidation is essential to utilize their beneficial effects in health and in preventing disease. The antioxidants vitamin E, t-butylhydroxy toluene (BHT) and t-butylhydroxy anisole (BHA) inhibited ascorbate/Fe(2+)-induced lipid peroxidation in rat liver microsomes. In addition, a number of spice principles, for example, curcumin (5-50 microM) from turmeric, eugenol (25-150 microM) from cloves and capsaicin (25-150 microM) from red chillies inhibited lipid peroxidation in a dose-dependent manner. Zingerone from ginger inhibited lipid peroxidation at high concentrations (greater than 150 microM) whereas linalool (coriander), piperine (black pepper) and cuminaldehyde (cumin) had only marginal inhibitory effects even at high concentrations (600 microM). The inhibition of lipid peroxidation by curcumin and eugenol was reversed by adding high concentrations of Fe2+.

The antioxidant spice principles curcumin and eugenol when given by gavage lowered the carrageenan-induced edema in the foot pads of rats. This lowering effect was dependent on the concentration, the time gap between the administration of spice principles and the induction of inflammation by carrageenan. Dietary lipids also influenced the extent of inflammation. Animals fed 10% cod liver oil [containing n-3 polyunsaturated fatty acids (PUFA)] for 10 weeks showed a significantly lower inflammation compared to that observed in animals fed diets supplemented with 10% groundnut oil (rich in n-6 PUFA) or 10% coconut oil (rich in medium-chain saturated fatty acids). Supplementation of diets with 1 weight% of curcumin did not affect the inflammatory responses of animals to carrageenan injection. However, supplementation of diets with 0.17 weight% eugenol further lowered inflammation by 16, 32 and 30% in animals fed coconut oil, groundnut oil and cod liver oil, respectively. Therefore, combinations of dietary lipids with spice principles like eugenol can help in lowering inflammation.

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