Effect of dietary vitamin E on apoptosis and proliferation of murine splenocytes

Abstract

Vitamin E (Vit E) is one of the most potent natural lipophilic antioxidants shown to inhibit proliferation of cancer cells and influence apoptosis in in-vitro systems. In the present investigation, we studied the effect of dietary Vit E on splenocyte proliferation, apoptosis, and necrosis. Two-month old male ICR mice were fed an AIN tm 76 formula diet for three months with 10% (W/W) corn oil, supplemented with Vit E at normal (75 IU/kg) or higher (500 IU/kg) levels, or without Vit E as zero Vit E group. In vivo analysis revealed both serum lipid peroxides (MDA) and splenocyte peroxides (dichlorofluorescein staining) were found to be reduced with increased dietary Vit E levels in a dose-dependent manner; whereas, serum Vit E levels were found to be augmented with increased levels of dietary Vit E. Also, apoptosis and necrosis were measured in splenocytes incubated with and without 1 μM dexamethasone (DEX) in RPMI media for eight and 21 hours. Cells were stained with Annexin V and Propidium Iodide (PI), and both apoptotic and necrotic cells were analyzed simultaneously by a FACScan desktop flow cytometer using the Cell Quest Program. High and normal levels of Vit E increased necrosis by 29 and 18% in the cells placed in media, and 67 and 34% in cells incubated with DEX for eight hours, respectively, in comparison to that in the zero Vit E-fed group. However, in splenocytes from the high Vit E group apoptosis was decreased by 32 and 49.5% in cells incubated for eight hours in media alone or with DEX, respectively. Furthermore, in the high Vit E group necrosis was increased by 25% and apoptosis was decreased by 17% in cells incubated for 21 hr in media alone, compared to that of the zero Vit E group. In addition, proliferation of splenocytes, either stimulated or unstimulated with mitogens, was also found to be decreased with increasing levels of dietary Vit E. In conclusion, our results indicate that dietary Vit E appears to alter both cell proliferation and programmed cell death (apoptosis vs. necrosis), by lowering lipid peroxides.