Inhibition of T-cell activation and induction of apoptosis by areca nut extract

• Main Authors: Chia-Chi Wang, 王家琪
• Other Authors: Ton-Rong Jan
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/45811774801992146750

碩士 === 國立臺灣大學 === 獸醫學研究所 === 93 === Betel quid chewing is an etiologic factor for oral squamous cell carcinoma (OSCC). Experimental evidence suggests that impaired immune reactivity was associated with the occurrence of OSCC. The objective of the present studies was to investigate the effect of areca nut extract (ANE) on T-cell function and cytokine expression. Pretreatment of splenocytes with ANE suppressed the production of IL-2 and the T-helper 1 (TH1) cytokine IFN-γ induced by PMA/Io. ANE suppression of IL-2 secretion was also demonstrated in EL4 cells. In contrast, the steady state mRNA expression of IL-2 and IFN-γ in splenocytes was not significantly inhibited by ANE. Moreover, ANE treatment produced a marked inhibition on the proliferation of splenocytes and EL4 cells as measured by a MTT assay. A 24-hr exposure of EL4 cells to ANE resulted in a marked reduction in cell viability and growth rate. Treatment of splenocytes and EL4 cells with ANE also increased the percentage of apoptotic cells, as evidenced by annexin V/ propidium iodide flow cytometry and DNA laddering. For mechanistic studies, the expression of various caspase mRNA in EL4 cells was simultaneously determined by a RNase protection assay. The steady state mRNA expression of caspase-2 was enhanced at 4 hr after ANE treatment. Depolarization of mitochondrial membrane potential in T cells was demonstrated by a decrease in rhodamine123 fluorescence after ANE treatment. The role of reactive oxygen species (ROS) in ANE-mediated effects on cytokine production was further investigated. Pretreatment of splenocytes with anti-oxidants, including N-acetyl-cysteine, superoxide dismutase and glutathione, partially attenuated the effect of ANE on T cell metabolic activity and IL-2 production, whereas ANE-induced suppression of IFN-γ production was almost completely reversed by pretreatment with anti-oxidants. Taken together, results from the present studies demonstrated that ANE markedly suppressed the activity and cytokine production by T cells, which was associated with the induction of apoptosis in T cells. In addition, the mechanistic studies suggested that the inhibitory effect of ANE on T cell activity and cytokine production was mediated, at least in part, via the induction of ROS in T cells by ANE.