title: Protective effect of cysteine against X-ray- and bleomycin-induced chromosomal aberrations and cell cycle delay.
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 G0. Its protective efficiency was also studied against the radiomimetic clastogen, bleomycin, in muntjac cells. 30 micrograms 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 micrograms 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.
authors.affiliation: Cytogenetics Laboratory, Banaras Hindu University, Varanasi, India.
authors.forename: A
authors.initials: A
authors.lastname: Chatterjee
authors.forename: M J
authors.initials: MJ
authors.lastname: Raman
mesh_terms: D000818:Animals; D016587:Antimutagenic Agents / Q000494:pharmacology*; D001761:Bleomycin / Q000633:toxicity; D002453:Cell Cycle / Q000187:drug effects* / Q000528:radiation effects*; D002478:Cells, Cultured; D016009:Chi-Square Distribution; D002869:Chromosome Aberrations; D003545:Cysteine / Q000378:metabolism / Q000494:pharmacology*; D003670:Deer; D016166:Free Radical Scavengers; D017353:Gene Deletion; D006801:Humans; D008214:Lymphocytes; D008297:Male; D009153:Mutagens / Q000633:toxicity; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D016587:Antimutagenic Agents; D016166:Free Radical Scavengers; D009153:Mutagens; D011837:Radiation-Protective Agents; D001761:Bleomycin; D003545:Cysteine