N.K. Mehrotra

Micronucleus induction by diuron in mouse bone marrow

Diuron, a widely used substituted urea herbicide, induced the formation of micronuclei in bone marrow cells of Swiss mice. A single i.p. dose of 340 mg/kg b.w. diuron which is maximum tolerated dose (MTD) increased significantly the number of micronuclei at 30 h and 48 h time period. The dose of 170 mg/kg b.w. also induced the micronuclei formation in the above time period. However, a dose of 85 mg/kg b.w. was ineffective at the time periods studied. No induction of micronuclei was observed at 72 h time period after all the doses of diuron studied as compared to the solvent control. The diuron-induced frequency of micronucleated erythrocytes was independent of the sex of the test animals.

Carcinogenic activity of a carbamate fungicide, mancozeb on mouse skin

Mancozeb, a polymeric complex of ethylene bis (dithiocarbamate) manganese with zinc salt is a protective fungicide. In the present study complete carcinogenic activity of mancozeb, has been observed following topical application on dorsal mouse skin. Female Swiss albino mice were exposed to mancozeb at a dose of 100 mg/kg body weight dissolved in 100 microliters dimethyl sulfoxide 3 times per week. Development of tumours was observed after 31 weeks (217 days) of mancozeb application. A high rate of mortality was observed after 54 weeks (378 days) of mancozeb application due to its toxicity and the study was terminated after 60 weeks. On histological examination, these tumours were found mostly to be benign in nature, e.g., squamous cell papillomas and keratoacanthomas.

Tumour initiating activity of mancozeb — A carbamate fungicide in mouse skin

Mancozeb is a protectant fungicide and is a polymeric complex of ethylene bis(dithiocarbamate)manganese (i.e. Maneb) with zinc salt. In this study, the tumour initiating ability of mancozeb has been observed by a 2-stage initiation-promotion protocol in mouse skin.

Assessment of mutagenic potential of thiram

Thiram is a widely used dithiocarbamate fungicide. In this study, the mutagenicity of thiram was investigated using the micronucleus and dominant lethal tests in Swiss albino mice. A single ip injection of 100 mg thiram/kg body weight, which is the maximum tolerated dose (MTD), significantly induced micronucleus formation in bone marrow cells after 30 and 48 hr of exposure; 50% and 25% of the MTD also induced micronucleus formation after the above time periods. A significant number of dead implants were induced when thiram was given to male mice in the diet at 10% of the oral LD50 during the whole spermatogenesis cycle (8 wk); this post-implantation loss indicates a dominant lethal mutation.

Assessment of mutagenic potential of propoxur and its modulation by indole-3-carbinol.

Propoxur is a widely used dithiocarbamate pesticide. In the present set of investigations, mutagenicity of propoxur (in formulation) was studied using the micronucleus assay in bone marrow of Swiss mice. Single intraperitoneal (i.p.) administration of 25 mg/kg body weight dose of propoxur, which is a maximum tolerated dose (MTD), significantly induced the micronucleus formation in bone marrow cells after a 24- and 48-hr exposure. A half and a quarter of the MTD (12.5 and 6.25 mg/kg) were found ineffective to induce the micronuclei formation after 24- and 48-hr time periods by the i.p. route. However, the PCE:NCE ratio was inhibited significantly with all the dose levels at both time periods. Oral administration of propoxur at different dose levels also induced micronuclei formation. A single application of 50 and 25 mg/kg dose levels of propoxur, which are MTD and 50% of MTD, also significantly induced micronuclei formation after 24- and 48-hr time periods in bone marrow cells of Swiss mice as compared with solvent control group, whereas a 12.5 mg/kg dose of propoxur was ineffective in inducing micronuclei formation. Single application of indole-3-carbinol (I3C), a glucobrassicin derivative present in cruciferous vegetables, significantly inhibited the propoxur-induced micronuclei formation when it was given at the dose level of 500 mg/kg body weight 48 hr before the single application of propoxur. Therefore, it seems that propoxur is mutagenic in the above test systems and I3C inhibited the mutagenicity of propoxur significantly.

Antitumour activity of protein A in a mouse skin model of two-stage carcinogenesis

Protein A (PA) is an immunostimulating glycoprotein (mol. wt. 43,000 kDa) obtained from Staphylococcus aureus cowan I. The antitumour property of PA is well documented in the literature in various transplantable tumours of rats and mice. In the present set of investigations, the antitumour property of PA was tested in Swiss albino mice in a two-stage initiation-promotion mouse skin carcinogenesis model. The animals were initiated topically with a single subcarcinogenic dose (52 microgram) of 7,12-dimethylbenzanthracene (DMBA). PA was administered intraperitoneally (1 microgram/animal), twice weekly for 2 weeks. Promotion was performed by twice weekly applications of 12-O- tetradecanoyl phorbol-13-acetate (TPA) at a dose of 5 microgram/animal for 32 weeks. The result showed that the treatment schedule can effectively check the onset of tumorigenesis, the cumulative number of tumours and the average number of tumours per mouse. In the PA administered group, 30% of the animals remained tumour free until the termination of the experiments (i.e. 32 weeks of promotion). Thus the present study proves that protein A can effectively inhibit DMBA initiated and TPA promoted mouse skin carcinogenesis.

Protection against 7,12-dimethylbenzanthracene-induced tumour initiation by protein A in mouse skin

Protein A is an immunostimulating glycoprotein obtained from Staphylococcus aureus Cowan I. Its antitumour activity is proven in various tumour models. Its ability to provide protection against tumour initiation by the chemical carcinogen 7,12-dimethylbenzanthracene (DMBA) has been investigated in the present study using a mouse skin model of two-stage carcinogenesis. Protein A was administered intraperitoneally (1 microgram/animal 20 g body wt.) twice a week for 2 weeks, prior to initiation by DMBA. The promotion was performed by twice weekly applications of 12-O-tetradecanoyl phorbol-13-acetate (TPA) (3 or 5 micrograms/animal in 100 microliters acetone). Protein A provided significant protection to animals from DMBA-induced tumour initiation as was observed by the decrease in cumulative number of tumours, percent of animals developing tumours, number of tumours per animal and rate of tumour growth. Our data indicate that protein A has anticarcinogenic properties.

Carcinogenicity and co-carcinogenicity studies on propoxur in mouse skin

Propoxur (2-isopropoxyphenyl methylcarbamate) is a widely used broad spectrum carbamate insecticide mainly used to control household pests. Propoxur exposure is reported to inhibit cholinesterase activity in rodents. Apart from other toxic effects, propoxur was found to possess tumorigenic activity in rats after oral administration. Propoxur does not produce tumours in mice or hamsters, or bladder hyperplasia in dogs and monkeys following oral feeding. In this set of investigations the complete carcinogenic, tumour initiating and promoting potential of propoxur was evaluated in male and female Swiss albino mice, since no information was available following dermal exposure of propoxur. The animals were exposed to propoxur through topical painting on the interscapular region at a dose of 100 mg/kg body weight. The results revealed that propoxur has tumour promoting potential on mouse skin following a two-stage initiation-promotion protocol, but it failed to induce the tumour(s) at a significant level, when tested for tumour initiating and complete carcinogenic property.

Carcinogenic and cocarcinogenic studies with carbaryl following topical exposure in mice

Carbaryl (1-naphthyl methyl carbamate: C12H11NO2) CAS Reg. No. 63-25-2) is a widely used broad spectrum carbamate insecticide known to exert various toxic effects on experimental animals. Along with various other toxicological effects carbaryl is reported to increase the incidence of neoplasm in various tissues in rats after oral or intraperitoneal administration. No study has so far been reported in rodents to assess its carcinogenic/cocarcinogenic potential after topical exposure. In this set of investigations, the complete carcinogenic, tumour initiating and tumour promoting property of carbaryl was tested on the skin of female Swiss albino mice. The animals were exposed to carbaryl through topical painting on the interscapular region at a dose of 100 mg/kg body wt. The results revealed that carbaryl has tumour initiating potential, at the test dose, on mouse skin following two stage, initiation-promotion protocol, but, it failed to induce the tumour(s) when tested for complete carcinogenic and tumour promoting properties.

Tumour initiatory activity of a herbicide diuron on mouse skin

In the present investigation, the tumour initiating activity of a herbicide diuron 3-(3,4 dichlorophenyl)-1,1 dimethyl urea has been observed following multiple topical applications at a dose of 250 mg/kg body weight in a standard two-stage initiation-promotion protocol on mouse skin for carcinogenicity testing. It was found that 9 applications of the herbicide given on the interscapular region in a thrice weekly schedule up to 3 weeks and followed, after 1 week, by the repeated 3 times per week application of a known skin tumour promoter 12-O-tetradecanoyl phorbol 13-acetate (TPA), 5 micrograms dissolved in 100 microliters of acetone in the same initiated area, led to the development of benign skin tumours. However, a single dose of diuron, used for each application as above and followed by repeated TPA applications, with the same dose and painting schedule as in the case of multiple applications, failed to initiate tumour development.