Combination chemoprevention of experimental gastric carcinogenesis by S-allylcysteine and lycopene:: Modulatory effects on glutathione redox cycle antioxidants

Combination chemoprevention by diet-derived agents is a promising strategy for protection against gastric cancer. We therefore evaluated the combined chemopreventive effect of S-allylcysteine (SAC), an organosulfur constituent of garlic, and lycopene, a major carotenoid present in tomatoes, against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and saturated sodium chloride (S-NaCl)-induced gastric carcinogenesis in Wistar rats. The animals were divided into eight groups of six animals each. Rats in group 1 were given MNNG by intragastric intubation on days 0 and 14 as well as S-NaCl every 3 days during weeks 0-3. Animals in groups 2-4, administered MNNG and S-NaCl as in group 1, received in addition SAC and lycopene alone and in combination, respectively, three times per week starting on the day following the first exposure to MNNG. Groups 5-7 were given the chemopreventive agents alone, whereas group 8 served as controls. The animals were sacrificed after an experimental period of 21 weeks. Measurement of lipid peroxidation and antioxidants of the glutathione redox cycle in the stomach, liver, and erythrocytes was used to monitor the chemopreventive potential of SAC and lycopene. In the tumor tissue, diminished lipid peroxidation was accompanied by an increase in reduced glutathione (GSH) and GSH-dependent enzymes, whereas in the liver and erythrocytes, enhanced lipid peroxidation was associated with antioxidant depletion. Although SAC and lycopene alone significantly suppressed the development of gastric cancer, administration of SAC and lycopene in combination was more effective in inhibiting MNNG-induced stomach tumors and modulating the redox status in the tumor and host tissues. The results of the present study validate the hypothesis that diet-derived chemopreventive agents such as SAC and lycopene in combination may interact synergistically with high efficacy and lessened toxicity against gastric cancer.