Promotion of hepatocarcinogenesis by hexachlorobenzene in energy-restricted rats

Diuron Lacks Promoting Potential in a Rat Liver Bioassay

The promoting activity of the herbicide Diuron was evaluated in a medium-term rat liver carcinogenesis bioassay that uses as endpoint immunohistochemically identified glutathione S-transferase positive (GST-P+) foci. Male Wistar rats were allocated to the following groups: G1 to G6 were initiated for liver carcinogenesis by a single dose of diethylnitrosamine (DEN, 200 mg/kg) while groups G7 and G8 received only 0.9% NaCl (DEN vehicle). From the 2nd week animals were fed a basal diet (G1 and G7) or a diet added with Diuron at 125, 500, 1250, 2500 and 2500 ppm (G2 to G5 and G8, respectively) or 200 ppm Hexaclorobenzene (HCB; G6). The animals were submitted to 70% partial hepatectomy at the 3rd week and sacrificed at the 8th week. The herbicide did not alter ALT or creatinine serum levels. No conspicuous GST-P+ foci development was registered in non-initiated rats fed Diuron at 2500 ppm. While DEN-initiated animals fed Diuron at 1250 or 2500 ppm developed mild centrilobular hypertrophy, DEN-initiated HCB-fed animals showed severe liver centrilobular hypertrophy and significant GST-P+ foci development. These findings indicate that the medium-term assay adopted in this study does not reveal any liver carcinogenesis initiating or promoting potential of Diuron in the rat.

Seasonal variations of DNA-adduct patterns in open field farmers handling pesticides

Seasonal variations of DNA-adduct levels in peripheral blood cells were evaluated in open field farmers (n=26) by use of the 32P-postlabelling assay. Samples were collected before (sample S0) and during (sample S4) the period of intensive pesticide use. A similar sampling procedure was applied to a referent group (n=29). Exposure to pesticides was estimated via a detailed questionnaire. For the group of farmers, an increase in mean adduct level was observed during the season (mean RALS0=3.9+/-3.4 x 10(-10), mean RALS4=13.3+/-15.7 x 10(-10); p=0.008; RAL=relative adduct level). The mean adduct levels were significantly different between farmers and referents only in the S4 samples, with higher levels for farmers (p=0.02). The number of different adducts per individual was higher for farmers at S4 when compared with S0 (p=0.02) and compared with the referents at S4 (p=0.03). However, the increase of the adduct level in farmers did not seem to be attributable to the occurrence of specific new adducts in S4 as compared with S0, but was supposedly due to intensification of pre-existing spots and/or appearance of new unspecific ones. This would be in agreement with indirect genotoxic (epigenetic) effects known for several pesticides, even though a direct mechanism cannot be ruled out definitively. The implication of the pesticides used by the farmers in the modulation of DNA-adduct patterns was explored by analysis of exposure data obtained from the questionnaire.

Does toxoplasmosis cause DNA damage? An evaluation in isogenic mice under normal diet or dietary restriction

Toxoplasmosis is an anthropozoonotic widespread disease, caused by the coccidian protozoan parasite Toxoplasma gondii. Since there are no data regarding the genotoxicity of the parasite in vivo, this study was designed to evaluate the genotoxic potential of the toxoplasmosis on isogenic mice with normal diet or under dietary restriction and submitted to a treatment with sulfonamide (375 microg/kg per day). DNA damage was assessed in peripheral blood, liver and brain cells using the comet assay (tail moment). The results for leucocytes showed increases in the mean tail moment in mice under dietary restriction; in infected mice under normal diet; in infected, sulfonamide-treated mice under normal diet; in infected mice under dietary restriction and in infected sulfonamide-treated mice under dietary restriction. In liver and brain cells, no statistically significant difference was observed for the tail moment. These results indicated that dietary restriction and T. gondii were able to induce DNA damage in peripheral blood cells, as detected by the comet assay.

Effects of fasting and intermittent fasting on rat hepatocarcinogenesis induced by diethylnitrosamine

The influences of fasting on DEN-initiation and of intermittent fasting (IF) on the rat liver chemical carcinogenesis process were evaluated in a 52-week long assay. Three groups of adult male Wistar rats were used: Groups 1 to 3 were treated with a single i.p. injection of 200 mg/kg of diethylnitrosamine (DEN). Group 2 was submitted to 48 h fasting prior to DEN treatment. After the 4th week, Group 3 was submitted to IF, established as 48 h weekly fasting during 48 weeks, while Groups 1 and 2 were fed ad libitum until the 52nd week. All animals were submitted to 70% partial hepatectomy and sacrificed at the 3rd and 52nd weeks, respectively. Fasting prior to DEN-initiation did not influence the development of altered foci of hepatocytes (AFHs) and of hepatic nodules (Group 2 vs. Group G1). IF inhibited the development of preneoplastic lesions, since this dietary regimen decreased the number and the size of glutathione S-transferase (GST-P) positive foci and the number and size of liver nodules (Group G3 vs. Group G1). The inhibitory effect of IF was also reflected in the development of clear and basophilic cell foci. These results indicate that long-term IF regimen exerts an anti-promoting effect on rat hepatocarcinogenesis induced by DEN.

Factors affecting the storage and excretion of toxic lipophilic xenobiotics

Lipophilic toxins have been introduced into the environment both as functional compounds, such as pesticides, and as industrial waste from incineration or the manufacture of electrical transformer components. Among these substances are compounds that are carcinogenic and that affect the endocrine system. Accidental high exposures of humans to some lipophilic toxins have produced overt disease symptoms including chloracne and altered liver function. These toxic materials have been the recent focus of international effort to reduce or eliminate classes of halogenated hydrocarbons from the environment. Evidence of the widespread distribution of lipophilic toxins in the biosphere has been obtained by analyses of human tissues and human milk. The principal route of entry of lipophilic toxins into humans is through the food chain, and most of them are stored in adipose tissue. A common route of excretion is in bile, but there is also evidence of nonbiliary excretion into the intestine. Enterohepatic circulation of many of these compounds slows their removal from the body. Substances that interrupt the enterohepatic circulation of compounds that enter the intestine by the biliary and nonbiliary routes increase the rate of their removal from the body and reduce their storage half-lives. Reduction in body fat, along with these dietary substances that interrupt enterohepatic circulation, further enhances the excretion rate. Areas for further research include optimizing regimens for body burden reductions, understanding the nature of nonbiliary excretion, and following the effects of tissue redistribution during loss of body fat.