Evaluation of sister chromatid exchange and cytotoxicity in murine tissues in vivo and lymphocytes in vitro following methyl isocyanate exposure.

Abstract

The purpose of this study was to assess sister chromatid exchange (SCE) levels and cell cycle kinetics in various murine tissues following MIC exposure. Following exposure of mice to MIC, these parameters were measured in bone marrow and alveolar macrophages labeled with BrdUrd in vivo and in peripheral blood and spleen lymphocytes cultured in the presence of BrdUrd in vitro. Target concentrations of MIC were 2, 15, and 30 ppm (3 hr).Neither elevated SCE frequencies nor inhibition of cell cycling were evident in lipopolysaccharide (LPS)-or concanavalin A (ConA)-stimulated spleen lymphocytes, or in LPS-stimulated peripheral blood lymphocyte (PBL) cultures from mice exposed for 3 hr to MIC concentrations as high as 30.5 ppm. Inhibition of cell cycling and poor culture success rates were apparent in ConA-stimulated PBLs following MIC exposures as low as 2.3 ± 0.4 ppm for 3 hr.At the lowest MIC dose employed, the cycling characteristics of bone marrow and alveolar macrophages were not altered, and SCE frequencies were at control levels. However, severe cell cycle inhibition was observed in these tissues at MIC concentrations of 15 ppm or greater. A marker of cytotoxicity at this dose was a high frequency (approximately 33-90%) of occurrence of first division cells containing a latereplicating Y chromosome.Despite its apparent cellular toxicity, MIC is not genotoxic as measured by SCE analysis in the tissues examined in this study.

Genotoxic and Carcinogenic Effects of Methyl Isocyanate (MIC) Reviewed on Exposed Bhopal Population and Future Perspectives for Assessment of Long-Term MIC-Effect

“…However, elevated SCEs were reported by Goswami [27] and Mason et al [31]. Depression of mitotic (MI) and replicative indices (RI) in Ghosh et al [26] study was not consistent with MIC-exposure in Bhopal population, which was consistent with Conner et al [32] in murine alveolar macrophages. However, delayed cell cycle was reported by Deo et al [28] in peripheral lymphocytes of the MIC-exposed people, and also in experimental animals [33].…”

In silico docking of methyl isocyanate (MIC) and its hydrolytic product (1, 3-dimethylurea) shows significant interaction with DNA Methyltransferase 1 suggests cancer risk in Bhopal-Gas-Tragedy survivors

“…Besides, the immunotoxic (Karol et al, 1987), genotoxic (Conner et al, 1987;Tice et al, 1987), reproductive and developmental toxic effects (Schwetz et al, 1987) are well-documented in humans and animals. However, the etiology of MIC in carcinogenesis is far from completely understood (Senthilkumar et al, 2012;Senthilkumar, 2012).…”

A retrospective review of cytogenetic studies on methyl isocyanate with special reference to the Bhopal gas tragedy: Is the next generation also at risk?

“…Although a number of biomarkers are available to assess transient and permanent genotoxic responses, biomonitoring studies on human populations should essentially focus on more definitive cytogenetic end-points. New developments in the post-genomics era have provided tools for the assessment of environmental and occupational exposure to Peripheral blood and spleen lymphocytes cultured in the presence of BrdU in vitro [40] Mononuclear leucocyte counts and mitotic indices [43] MIC was assayed both in the presence and absence of Aroclor-1254-induced S9, using 5 tester strains of Salmonella typhimurium, TA97a, TA98, TA100, TA102 and TA104 [44] Ames Salmonella/microsome mutagenicity test [45] Studied genotoxic response of MIC-modified DNA in E. coli [46] Chromosome aberrations in root cells, and growth retardation and chlorophyll mutation of seedlings, the frequencies of which varied from one locality to another in seeds of Solanum surattense Burm…”

“…Striking findings of resistance were documented in plants like Artocarpus integrifolia, Casuarina equisetifolia, Ficus bengalensis and Mangifera indica [8] Genotoxic potential of MIC in exposed animal subjects MIC has a significant potential for inducing cancer in rodents [47] Sister chromatid exchanges (SCEs) and cell cycle kinetics in murine tissues [40] Chromosomal aberrations and sister chromatid exchanges in bone marrow metaphase cells, induction of micronuclei in polychromatic erythrocytes and the inhibition of bone marrow cellular proliferation and erythropoiesis in mice [48] In vivo micronucleus test, chromosomal aberrations, sister chromatid exchanges in bone marrow cells of rodent somatic cells [49] In vivo micronucleus test and chromosomal analysis of bone marrow cells in mice [50] Mutagenic and cytotoxic effects in mouse micronucleus test [51] Genotoxic potential of MIC in exposed human subjects…”

“…The population-based cancer register of the ICMR revealed higher incidence rates (crude and Cytogenetic studies in cell lines and small animals with reference to MIC The genotoxic potential of MIC in cultured cells after in vitro exposure to MIC has been evaluated in several studies (Table 1). Conner et al [40] assessed sister chromatid exchange (SCE) levels and cell cycle kinetics in various murine tissues following MIC exposure, and discovered that despite its apparent cellular toxicity, MIC was not genotoxic as measured by SCE analysis. However, MIC was found to induce SCEs and chromosomal aberrations in CHO cells [41].…”