Genotoxic Hazard and Oxidative Stress Induced by Wastewater Irrigated Soil With Special Reference to Pesticides and Heavy Metal Pollution

Enhancement of industrial growth and urbanization, soil contamination is increasingly prominent. Therefore, it’s important to examine possible adverse effects of industrial waste. Samples were found to be polluted with several heavy-metals and pesticides. Gas chromatographic results showed occurrence of high-level of organochlorine and organophosphate pesticides. Genotoxicity of soil extracts was assessed using environmental-risk assessment models. Soil samples were extracted in hexane and dichloromethane solvents and were evaluated for genotoxic potential by prokaryotic (Ames test, plasmid nicking assay and E. coli K-12 DNA repair defective mutants) and eukaryotic (Allium cepa root chromosomal aberration and Vigna radiata seed-germination test) bioassays. Strain TA98 was found most susceptible among soil extracts. Hexane soil extract of wastewater irrigation was determined more mutagenic than DCM samples in terms of mutagenic index, mutagenic potential and induction factor for Ames strains. The damage in DNA repair defective mutants of hexane extracts were found higher compared to DCM extracts at dose of 20 μl/ml of culture. Survival in polA, lexA and recA mutants were 39%, 47% and 55% while treated with hexane extract. Allium cepa test, mitotic index was decreased in dose-dependent way and various kinds of chromosomal aberrations were found. Vigna radiata seeds germination and other parameters were also affected when treated with contaminated soil. Oxidative stress in V. radiata roots were also showed under CLS microscope. Genotoxicity of contaminated soil extract was also confirmed by plasmid nicking test. Our study provides possible explanation for the assessment of potential health and environmental hazards of the industrial region.

Inhibition of transcription factor assembly and structural stability on mitoxantrone binding with DNA

MTX (mitoxantrone) is perhaps the most promising drug used in the treatment of various malignancies. Comprehensive literature on the therapeutics has indicated it to be the least toxic in its class, although its mechanism of action is still not well defined. In the present study, we have evaluated the associated binding interactions of MTX with naked DNA. The mechanism of MTX binding with DNA was elucidated by steady-state fluorescence and a static-type quenching mechanism is suggested for this interaction. Thermodynamic parameters from van 't Hoff plots showed that the interaction of these drugs with DNA is an entropically driven phenomenon. The binding mode was expounded by attenuance measurements and competitive binding of a known intercalator. Sequence specificity of these drug–DNA complexes was analysed by FTIR (Fourier-transform infrared) spectroscopy and molecular modelling studies. CD spectroscopy and the plasmid nicking assay showed that the binding of this drug with DNA results in structural and conformational perturbations. EMSA (electrophoretic mobility-shift assay) results showed that these drug–DNA complexes prevent the binding of octamer TF (transcription factor) to DNA. In summary, the study implicates MTX-induced conformational instability and transcription inhibition on DNA binding.

The acid deoxyribonuclease of neutrophils: a possible participant in apoptosis-associated genome destruction

Human neutrophils are terminally differentiated cells that spontaneously undergo apoptosis in tissue culture. Apoptosis in these cells can be delayed by culture in the presence of granulocyte colony- stimulating factor or other inflammatory mediators. Neutrophils were found to contain an acid endonuclease that appeared to be responsible for the internucleosomal DNA cleavage that accompanies apoptosis. As measured by a plasmid nicking assay, this endonuclease had a molecular weight (M(r)) of 35,000, a pH optimum of 5.5, and a threshold for activity of pH 6.6 to 6.8. It was weakly inhibited by divalent cations (Ca2+, Mg2+, and Zn2+) and more strongly inhibited by aurintricarboxylic acid and N-bromosuccinimide. DNA from neutrophils treated with nigericin in buffers of defined pH displayed nucleosomal ladders whose prominence varied with pH in a manner that paralleled the pH dependence of the plasmid cleavage assays, consistent with internucleosomal DNA cleavage by the acid endonuclease. We have previously shown that neutrophils undergo acidification to a pH value as low as 6.0 during apoptosis; we suggest that this endonuclease may be responsible for the DNA cleavage seen in apoptotic neutrophils.