Potentiation of 2,6-dinitrotoluene genotoxicity in Fischer-344 rats by pretreatment with Aroclor 1254.

Pretreatment of Fischer 344 rats for 5 weeks with Aroclor 1254, a commercial mixture of polychlorinated biphenyls, potentiated the genotoxicity of 2,6-dinitrotoluene (DNT), a component of an industrial chemical used in the production of polyurethane foams. This interaction resulted from Aroclor 1254-mediated bioactivation of DNT to markedly greater levels of the genotoxic metabolites, that were excreted in urine and formed DNA adducts in the liver. A significant increase in the excretion of mutagenic urinary DNT metabolites was observed after the first week of Aroclor 1254 treatment, peaked at week 2 and then declined by nearly 25% at week 4. Nevertheless, by week 5, there was almost a 4-fold increase in the formation of hepatic DNA adducts. Significantly elevated hepatic metabolism and increased beta-glucuronidase in the small intestine and cecum, at 4 weeks, may account for the increased adducts and decreased urinary mutagens. Altered nitroreductase activity, reduced pH, and changes in the microfloral population may also play a role in the effect of Aroclor 1254 on the bioactivation of DNT. Such chemical interactions could be important to predictive risk assessment because the overall cancer risk of the mixture would exceed that determined by the current guidelines for chemical mixtures.

Clostridium difficile infection in hamsters fed an atherogenic diet.

Diarrhea and unexpected death were encountered in a group of young Syrian hamsters (Mesocricetus auratus) used for hyperlipoproteinemia and atherosclerosis research. The animals were fed an atherogenic diet containing 18% saturated fat and 0.366% cholesterol. Mortality began 45 days after hamsters were placed on this atherogenic diet. The atherogenic studies were aborted at 74 days because of high mortality. Toxigenic Clostridium difficile was isolated from animals found dead or euthanatized because of illness. Signs observed were unexpected death and acute liquid diarrhea. Characteristic pathologic changes were necrosis and hemorrhage of the intestinal mucosa with acute inflammation. Hepatic lipidosis was a consistent finding presumed to be associated with the consumption of the atherogenic diet. The study was repeated by placing 23 hamsters on the atherogenic diet and 10 hamsters on the control diet. In animals fed the atherogenic diet, the average time to mortality differed between studies, but clinical signs, gross and histologic lesions, culture findings, and toxin results in both atherogenic diet groups were similar. C. difficile was not isolated from the feeds. No antibiotics were found in the atherogenic diet. The results from these studies suggest that hamsters fed an atherogenic diet have increased susceptibility to disease caused by C. difficile as compared with hamsters fed a normal fat and cholesterol diet.

Burn injury induces a biphasic immunoglobulin M response to bacterial antigen.

We studied 75 BALB/c mice to examine the role of impaired immunoglobulin M (IgM) synthesis in the increased risk of bacterial infection after burn injury by investigating the kinetics of IgM synthesis to peptidoglycan polysaccharide (PGPS), a ubiquitous bacterial antigen. Splenocytes were isolated 1, 5, and 8 days postburn (PBD) and cultured with lipopolysaccharide for 5 days. Culture supernatant was collected and anti-PGPS IgM and total IgM levels were measured by ELISA. Total IgM-secreting cells were measured by ELISPOT assay. Total IgM and anti-PGPS IgM per IgM-secreting cell were calculated. On PBD 1, anti-PGPS IgM synthesis but not total IgM synthesis is increased in burned animals. By PBD 5, total IgM and anti-PGPS IgM synthesis in the burn group start to fall and by PBD 8, both are significantly decreased. The early increase in anti-PGPS IgM synthesis represents a positive response to bacterial challenge. However, the late nonspecific decrease in total IgM and anti-PGPS IgM synthesis suggests a potential mechanism for increased susceptibility to bacterial infection 5 to 10 days after burn injury.

Microbial succession and intestinal enzyme activities in the developing rat.

The succession of gut bacteria and selected intestinal enzyme activities in developing 7-35-d-old rats was studied. Aerobes and anaerobes were identified as members of four broad major bacterial groups, i.e. Gram-positive rods, Gram-positive cocci, Gram-negative rods and obligate anaerobes. The enzyme activities of nitro and azo reductases, beta-glucuronidase, dechlorinase and dehydrochlorinase were determined by anaerobic incubation of intestinal homogenates with 3,4-dichloronitrobenzene, methyl orange, p-nitrophenyl-beta-D-glucuronide, and p,p'-DDT respectively. Nitroreductase and azo reductase activities increased significantly with the appearance of anaerobes in the large intestine. No increase in either nitroreductase or azo reductase activities in the small intestine was found. The early and high level of beta-glucuronidase activity in the small and large intestines coincided with high numbers of coliforms recovered in 7 and 14 d animals. Dehydrochlorinase activity appeared early but was undetectable at both 21 and 28 d. Its activity increased at 35 d. Dechlorinase activity was variable in development. The rapid changes in the microbial flora and intestinal enzyme activities may influence the susceptibility of pre-pubescent rats to a variety of toxicants. Therefore, age-dependent toxicity may be important in the risk assessment of some environmental chemicals.

Potentiation of 2,6-dinitrotoluene genotoxicity in Fischer 344 rats by pretreatment with coal tar creosote.

Pretreatment of male Fischer 344 rats for 5 wk with coal tar creosote, a coal distillation product that is widely used as a wood preservative, potentiated the excretion of urinary mutagens in 2,6-dinitrotoluene (DNT) treated rats. Creosote increased the bioactivation of DNT to significantly greater levels of urinary genotoxic metabolites and/or formed DNA adducts in the liver. A significant increase in the excretion of mutagenic DNT metabolites was observed after the first week of creosote treatment, peaked at wk 3, and then decreased by 33% after 5 wk of treatment. Nevertheless, there was a significant increase (66%) in the formation of DNT-derived DNA adducts in the livers of rats treated with DNT plus creosote at wk 5. Increased cecal beta-glucuronidase activity and reduced small intestinal nitroreductase activity may play roles in the bioactivation of DNT. The excretion of mutagenic DNT metabolites supplies useful information about the bioactivation of DNT; it does not provide a useful index of DNT-derived hepatic DNA adduct formation. Such interactions could be important to predictive risk assessment because the overall cancer risk of such chemical mixtures may exceed the sum of the component risks.