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MN & CA: Biomarkers for Genotoxicity

Furquan Ahmad Ansari, Iqbal Ahmad, Mohd. Yunus and Qamar Rahman

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Across the Globe, it is known from ancient time, mineral fibres having great deal of importance for its use in the manufacturing of different kind of mineral based-products. Asbestos is one of the fibrous mineral silicates, which accounts more than 3,000 of its uses all over the World (Ramanathan and Subramanian, 2001). In India, there are about 13 large and 673 small-scale asbestos based industrial units. Along with this, it is also estimated that asbestos industry directly gives employment to 6,000 workers, and another 1,00,000 peoples indirectly dependent on its usages. The epidemiological and biochemical changes induced by asbestos in relation to their occupational health hazards have been well documented (Mossman et al., 1990). Asbestos has been known for its carcinogenic and co-carcinogenic property (Mossman et al., 1990). Asbestos related diseases take a long latency period of 10 to 40 years before appearance of the obvious symptoms. The risks of carcinogenic and co-carcinogenic effects from asbestos continue owing to the persistence of the fibres from mining, milling, manufacturing and its use in building materials and other products and it is well known that the human population is exposed to complexes of mixture of different pollutants via occupationally, domestically and or, environmentally.

For this reason, epidemiological and mechanistic research on the toxic effects of asbestos and minerals fibres is still needed.

Exposure to asbestos causes various lesions ranging from simple non-malignant inflammatory reactions, pleural thickening and asbestosis to malignant mesothelioma and bronchiogenic carcinoma (Mossman et al., 1990). As mentioned earlier, asbestos fibres are well known environmental carcinogen, however, the underlying mechanisms of their action have still not clearly been identified. To determine the genotoxic risk associated to environmental and occupational exposure of asbestos; micronuclei (MN) and Chromosomal aberrations (CA) analysis techniques are being used.

Micronuclei (MN) and Chromosomal aberration (CA) analysis techniques across the Globe are being emerging tool as a biomarker for the genotoxic risk to asbestos as earlier mentioned. Studies conducted In Vitro and experimental animals have shown that asbestos is a genotoxic carcinogen, causing chromosomal breaks and deletions (Okayasu et al., 1999). Previous studies done in our laboratory has reported that the induction of MN and CA in lymphocytes of workers occupationally exposed to asbestos (Rahman et al., 2000).

The studies of DNA damage at the chromosome level is an essential part of genetic toxicology because chromosomal mutation is an important event in carcinogenesis and these techniques have been emerged as one of the preferred methods for assessing chromosome damage.

Studies in lymphocytes culture system are a valuable tool by which toxicant potential of xenobiotic can be assessed at genetic level. Blood is the most frequently used tissue specimen for cytogenetic diagnosis for a variety of clinical cases because peripheral blood can be easily obtains from subjects of all age groups. For chromosomal aberration and micronuclei analysis methods of Moorhead et al., 1960 and Fenech, 1993 are being used.

Accordingly, lymphocytes from the peripheral blood are stimulated by the Mitogen, phytohaemagglutinin (PHA) to divide in culture and a large no. of metaphases can be seen 72 hours after setting up of culture. The culture medium contains 5 ml RPMI-1640, 15% fetal/ borne calf serum, 1% L-glutamine, 1% Sod. Heparin (100 units/ml), 1% penicillin streptomycin containing 10,000 units/ml penicillin, 10000 mcg/ml speptomycin, 2% PHA. Incubation continues for 72 hours. Colchicine (10 mcg/ml) is added 1 hr prior to harvest cells at metaphase stage. The cell suspension is kept in prewarmed hypotonic (0.075 M KCl) solution to swell the metaphase then the cells are fixed with Carnoy’s fixative to prepare slides for microscopic observation of chromosomal aberrations.

Lucknow-226 001 E-mail: [email protected] Mohd. Yunus - Dean, Department of Environmental Science, Babasaheb Bhimrao Ambedkar University (A Central University)

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