Influence of glutathione levels on radiation-induced chromosomal DNA damage and repair in human peripheral lymphocytes.

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.