Pujari Geetanjali, Berni Andrea, Palitti Fabrizio, Chatterjee A
Molecular Genetics Laboratory, Department of Biotechnology and Bioinformatics, North-Eastern Hill University, Shillong, India.
Mutat Res. 2009 Apr 30;675(1-2):23-8. doi: 10.1016/j.mrgentox.2009.02.001. Epub 2009 Feb 10.
Endogenous thiols, especially the tripeptide-reduced glutathione (GSH), are known to play an important role in cellular defense against radiation. However, there are evidences that suggest that GSH may not be an efficient protector of DNA. The present study will determine whether modulation of endogenous GSH levels protects or potentiates the amount of chromosomal damage induced by ionizing radiation (IR). Human lymphocytes were isolated and then treated with GSH (for 1h) or buthionine sulfoximine (BSO; GSH-depleting agent for 5 h) before X-irradiation. DNA damage was analyzed by scoring chromosome aberrations (CAs) and by comet assay. The level of endogenous GSH was measured in lymphocytes treated with GSH, BSO or X-rays. A roughly 20% increase in endogenous GSH level was observed after a 3-h treatment with exogenous GSH and this reduced the frequency of all types of CA and aberrant metaphase chromosomes induced by 1 and 2 Gy of X-rays and also decreased the tail moment as determined by comet assay, suggesting radiation protection. Such uniform protection by GSH pretreatment was not visible while cells were exposed to 3 Gy or higher. Interestingly, in GSH-depleted lymphocytes, the frequency of radiation-induced CA was increased in a non-uniform manner. Therefore, an increase in the level of endogenous GSH in lymphocytes was unable to reduce chromosomal damage induced by 3 Gy or above, whereas decrease in the level of GSH enhanced the frequency of CA at all radiation doses in a non-uniform manner. It seems that GSH did not act as a radioprotector against DNA damage induced by higher dose X-rays rather it acts as a modulator of DNA repair activity.
内源性硫醇，尤其是三肽还原型谷胱甘肽（GSH），已知在细胞抵御辐射方面发挥重要作用。然而，有证据表明GSH可能并非DNA的有效保护剂。本研究将确定内源性GSH水平的调节是否能保护或增强电离辐射（IR）诱导的染色体损伤量。分离出人淋巴细胞，然后在X射线照射前用GSH（处理1小时）或丁硫氨酸亚砜胺（BSO；GSH消耗剂，处理5小时）进行处理。通过对染色体畸变（CA）进行评分和彗星试验分析DNA损伤。在经GSH、BSO或X射线处理的淋巴细胞中测量内源性GSH水平。用外源性GSH处理3小时后，观察到内源性GSH水平大约增加了20%，这降低了由1 Gy和2 Gy X射线诱导的所有类型CA和异常中期染色体的频率，并且也降低了彗星试验测定的尾矩，表明具有辐射防护作用。当细胞暴露于3 Gy或更高剂量时，GSH预处理的这种均匀保护作用不明显。有趣的是，在GSH耗竭的淋巴细胞中，辐射诱导的CA频率以非均匀方式增加。因此，淋巴细胞内源性GSH水平的增加无法减少3 Gy及以上剂量诱导的染色体损伤，而GSH水平的降低则以非均匀方式在所有辐射剂量下增加了CA的频率。似乎GSH并非针对高剂量X射线诱导的DNA损伤的辐射防护剂，而是作为DNA修复活性的调节剂。
