Abstract
The protective effect of cysteine was studied in muntjac and human lymphocytes in vitro scoring chromosomal aberrations in harlequin stained first cycle metaphases, induced by X-irradiation at G 0. Its protective efficiency was also studied against the radiomimetic clastogen, bleomycin, in muntjac cells. 30 μg and 1 mg/ml of cysteine were given prior to 2, 3, and 4 Gy, and 2 mg/ml prior to only 4 Gy. 30 μg cysteine protected only against deletions in 4 Gy-treated cells while 1 mg protected against deletions by all three doses of X-rays. However, rearrangements were not reduced significantly in any of these, probably due to their low frequency. But when cysteine was increased to 2 mg, both types of aberrations were reduced significantly. This shows that a sufficient number of aberrations and an optimum concentration of the protector are essential for eliciting the best protective effect. This conclusion is further supported by the results of 2 mg cysteine treatment in human lymphocytes which yielded higher frequencies of rearrangements with 2 and 3 Gy X-rays than 4 Gy in muntjac, but had a relatively lower frequency of deletions. Thus the most abundant categories of aberration, i.e., deletions in muntjac and exchanges in humans, were reduced significantly by 2 mg cysteine, associated with a prominent reduction in the frequency of aberrant metaphases. Therefore, the differential protection observed with a low concentration of the protector and an insufficient yield of aberrations induced only indicates protection provided to the most frequent type of aberration by a protector when present in lower concentration. Cysteine pretreatment yielded weak protection against the effects of bleomycin, but posttreatment caused a mild potentiation of the clastogenic effect of BLM without altering the cell cycle kinetics. In this context, an action of cysteine as a reducing agent on BLM is suggested. Although cysteine alone caused severe retardation of the cell cycle, when given prior to X-irradiation, not only its delaying effect was not observed, but also it reduced the X-ray induced cell cycle delay. This might be due to the oxidation of cysteine by its radical scavenging action.
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More From: Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
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