Implication of DNA repair genes in prostate tumourigenesis in Indian males.

Background & objectives: Prostate cancer (CaP) is the fifth most common cancer among Indian men. Tumour protein p53 (TP53) gene increases the fidelity of DNA replication and homologous recombination by transcriptional transactivation of mismatch repair (MMR) genes. DNA repair thus has a potential role in molecular carcinogenesis of CaP. The aim of the present study was to identify mutations, and polymorphisms in TP53 gene and MMR protein expression in CaP in Indian male population. Methods: TP53 codon 72 polymorphism was analysed in 105 CaP, 120 benign prostatic hyperplasia (BPH) cases and 106 normal controls. Mutational analysis of TP53 was done in DNA extracted from formalin fixed paraffin embedded tissue of 80 CaP and 24 BPH cases. Expression of MMR proteins viz. hMLH1, hMSH2, hPMS1 and hPMS2 was studied in 80 CaP, 15 prostatic intraepithelial neoplasia (PIN) and 15 BPH cases. Results: A somatic C/A variation at the intronic boundary of exon 7 in TP53 gene was observed in one each biopsy samples from CaP and BPH. A significant association of codon 72 TP53 Pro/Pro genotype was observed with the risk of CaP (OR, 2.59, P=0.02) and BPH (OR, 6.27, P<0.001). Immunohistochemical analysis of MMR proteins showed maximum loss of hPMS1 expression in cases of CaP and PIN while no loss in expression of MMR proteins was observed in BPH cases. The study also identified a significant loss of hPMS2 protein in poorly differentiated tumours (Gleason score >7) than in well differentiated tumours (Gleason score 3-6) (P<0.05). Interpretation & conclusions: The results of the present study demonstrate that TP53 codon 72 polymorphism plays significant role in the pathogenesis and susceptibility to CaP and BPH. Also, an aberrant MMR protein expression could be involved in progression of prostate cancer through PIN, early CaP to aggressive CaP. The loss of hPMS2 protein expression may serve as a marker for progression of CaP.

Pathological studies on Bovine papilloma virus-fern interaction in hamsters.

Early pathological changes of Bovine papilloma virus (BPV-2)-fern (Pteridium aquilinum and Onychium contiguum fern) interaction in hamsters were studied. In bracken-exposed cattle, BPV induces malignancy in gastrointestinal and urinary bladder mucosa. Cutaneous warts were transmitted successfully in hamsters approximately after 3 months post inoculation while urinary bladder tumour of enzootic bovine haematuria cases were not transmitted. Histologically, tumour was diagnosed as fibroma. Onychium produced more pronounced effects than bracken fern which was characterized by significant reduction in body weight and testicular atrophy. BPV-fern interaction was not appreciable during early period of tumour induction and requires long-term studies for 12 to 18 months.

Appropriate models and an understanding of carcinogenic mechanisms--requirements for hazard risk assessment.

Given the immense variety of compounds developed for introduction into the human environment, appropriate carcinogen risk assessment is essential. One of the responsible international bodies recognized as providing a lead in this endeavour is the International Agency for Research on Cancer (IARC), primarily through the Monographs on the Evaluation of Carcinogenic Risks to Humans. However, serious allegations have recently been made that industry now has undue influence on the decisions of the IARC Workshops as to category assignment, especially concerning down-grading of risk. The contention is that too much stress is placed on mechanistic considerations which have not been sufficiently validated. Since avoidance of carcinogens in our environment is clearly of prime importance to cancer prevention, open discussion of how they should be identified is of essential significance to the APOCP. Clearly, decisions should be based solely on scientific evidence and there should be no place for politics or polemic. We have therefore looked, in what we hope is a dispassionate fashion, at the arguments offered in the recent literature, while admitting to a bias towards taking into account all the available knowledge on mechanisms of action of carcinogens and modulating agents. As scientists, generation of an understanding of this area is one of the main reasons why we receive our salaries. To blindly argue that carcinogenicity, for example at high dose in one strain of experimental animal, necessarily implies human risk at normal levels of exposure is obviously untenable. At the same time, precipitous conclusions regarding species-specific mechanisms must naturally be avoided. Both academic and industrial researchers need to apply a balanced judgement and to simply imply that any association with industrial concerns is likely to lead to irresponsible behaviour to the detriment of public health is not tenable. With regard to regulatory decision making, we should be concentrating more attention on mechanisms, rather than less, especially in light of recent findings pointing to hormesis at low doses of carcinogens, which will inevitably generate heated discussion and the charge of bias in favour of industry. The onus is on all members of the scientific community to impartially view all the epidemiological and experimental data which are available in decision-making.

Use of yeast respiratory adaptation test system to detect chemical mutagens/carcinogens in mammals.

An approach to follow distribution of injected DNA-acting chemicals (mutagens/carcinogens) in animal tissues has been described. This is based on the use of respiratory adaptation (mitochondrial biogenesis) process in Saccharomyces cerevisiae during transition from anaerobic to aerobic state. By virtue of specific interaction of such chemicals with mitochondrial DNA associated with promitochondrial structures this process is extremely sensitive to DNA-acting chemicals. Solutions of berylium sulphate, aflatoxin G1, aflatoxin B1, and carbaryl (all known DNA-acting agents) were injected to rats at low concentrations and, after 24 hr, distribution of these chemicals or their metabolites was studied by determining the inhibitory action of appropriately diluted urine and tissue homogenates on respiratory adaptation in S.cerevisiae. Detectable amounts of the chemicals and their DNA-acting metabolites could be analyzed in urine, liver, lungs, kidney and spleen.

transplacental carcinogenic promoting activity of chloroacetonitrile the role of L-ornithine and its relation to glutathione content in embryonic tissue

The possible transplacental carcinogenic promoting activity of chloroacetonitrile [CAN, a by-product of drinking water chlorination process] in timed pregnant mice was studied. The activity was investigated through the assessment of the embryonic ornithine-decarboxylase [ODS] activity in relation to the embryonic glutathione [GSH] content after maternal administration of CAN. CAN was administered orally in a single dose of 25, 50, 70, 100 and 150 mg/kg diluted in 0.2 ml corn oil to the pregnant mice [GD 11.5]. All mice were killed 2 hours after treatment and the embryonic tissue was prepared for analysis. Also, a time course study protocol was studied, CAN was given in a single oral dose of 25 or 75 mg/kg to the pregnant mice and they were killed at 2, 6, 12, 24 and 48 hours post-treatment at GD 11.5. Maternal administration of CAN in doses of 25, 50, 75 mg/kg produced a marked increase in ODC activity expressed as pmole 14CO2/mg protein/30 min., associated with a significant reduction in GSH content. However, treatment with CAN either in a dose of 100 or 150 mg/kg showed significant reductions in ODC activity and GSH content. Concerning time-course study protocol, maternal administration of CAN either in 25 or 75 mg/kg produced a significant increase in the embryonic ODC activity accompanied with a remarkable decrease in GSH content measured at 2, 6, 12, 24 and 48 hours post-maternal treatment. The increase in the embryonic carcinogenic marker ODC which was associated with GSH depletion after administration of non-cytotoxic doses of CAN reflected an indication towards the mechanistic pathway of the transplacental carcinogenic promoting potential of CAN

Rapid technique for the detection of carcinogens using mice liver microsomes.

Mice liver microsomes were prepared at low g (10,000 g) force by Ca(2+)-aggregation method and were used for the detection of carcinogens by degranulation technique. RNA/protein ratio of these microsomes was 0.177 which was comparable to rat liver microsomes. Per cent degranulation with two carcinogens (O-dianisidine and benzidine) at 20 micrograms concentration was 21 per cent on the basis of RNA/protein ratio basis with both the carcinogens. At 40 micrograms concentration the per cent degranulation was observed to be almost double. Both the carcinogens required NADPH for their activation.