Modulation of antioxidant enzymes and apoptosis in mice by dietary lipids and treadmill exercise

The current experiments were designed to study the effect of dietary n-6 and n-3 polyunsaturated fatty acids on antioxidant enzyme activity and dexamethasone (DEX)-induced apoptosis in spleen cells of sedentary (Sed) and treadmill-exercised (Ex) ICR male mice. Two-month-old mice maintained on AIN 76 formula diet, supplemented with either 5% corn oil (CO) or 5% fish oil (FO) diets, were trained on a treadmill to run from 45 to 50 min 1 km/day, 6 days a week for 12 weeks. After 12 weeks of exercise, both Sed and Ex groups were sacrificed. Blood and various tissues, including spleen, were collected asceptically. Increased serum and spleen homogenate peroxide [malondialdehyde (MDA)] levels were observed in mice fed FO (n-3 PUFA) diets, compared to mice fed CO (n-6 PUFA). However, exercise did not alter MDA levels in either CO- or FO-fed mice. Feeding n-3 PUFA significantly increased superoxide dismutase (SOD), catalase, and glutathione peroxidase activity of spleen homogenates. Exercise also significantly increased SOD and peroxidase in CO-fed animals, whereas catalase, glutathione peroxidase, and glutathione transferase were higher in FO-fed mice, compared to the Sed group. Apoptosis and necrosis were quantitated in splenocytes incubated with or without 1 microM Dex in RPMI medium for 8 and 24 hr. Cells were stained with Annexin V and propidium iodide (PI) for apoptotic and necrotic cells. FO-fed mice showed higher apoptosis (64 vs 50%) and necrosis (40 vs 22%) in spleen cells than CO-fed mice. Cells from FO-fed mice, incubated in medium alone, showed increased apoptosis (112%) 24 hr after incubation, and necrosis (37 and 70%) at 8 and 24 hr of incubation, compared to CO-fed mice. In Ex group, apoptosis was increased in both CO- and FO-fed mice only at 24 hr after incubation. In summary, these results indicate that FO (n-3 PUFA-enriched) diets increase apoptosis and antioxidant enzyme activity in spleen cells, probably due to elevated lipid peroxides.