The large bowel carcinogenic effects of hydrazines and related compounds occurring in nature and in the environment

The work environment impact assessment: a methodologic framework for evaluating health-based interventions

BACKGROUND

A new conceptual framework is needed to evaluate health-based interventions based on the premise that like the environment, workplaces are complex ecologies. The proposed Work Environment Impact Assessment (WEIA) is analogous to Environmental Impact Assessment (EIA), a concept and method developed 30 years ago in the environmental policy arena to evaluate potential consequences of human activity for the natural environment. WEIA entails identifying and evaluating both intended and unintended consequences, or outcomes, associated with a particular intervention. Because the workplace is a complex ecology, changes in one aspect may lead to changes in other aspects. WEIA calls for a systematic and comprehensive approach to the total work environment.

METHODS

To illustrate the utility of WEIA we use this approach to evaluate an intervention to reduce the public's exposure to the pesticide Alar, which had been used on apples until it was withdrawn from the market in 1989.

RESULTS

While this intervention did indeed reduce the public's exposure to Alar, it also led to other unintended consequences, namely new ergonomic hazards for apple pickers, increased stress levels in the orchards for both pickers and growers, as well as new worker, and perhaps public, exposure to potent neurotoxins.

CONCLUSIONS

The goal of using WEIA is not to engage in a risk-risk debate that stalls worthwhile interventions. Rather, we propose that by conducting a Work Environment Impact Assessment, all possible positive and negative "ripple" effects stemming from an intervention can be considered, so that the intervention can be designed to achieve maximum benefit.

Lack of tumorigenic activity of 1,1-dimethylhydrazine in Syrian golden hamsters treated by subcutaneous injection

Syrian golden hamsters were treated throughout their lifespan by weekly subcutaneous injections of 1,1-dimethylhydrazine (1,1-DMH) at doses of 0, 8, 17 and 35 mg/kg body weight. In contrast to our previous study using European hamsters, no treatment-related tumors occurred in this study.

Dietary protein and chronic toxicity of 1,2-dimethylhydrazine fed to mice

1,2-Dimethylhydrazine-HCl (DMH-2HCl) is derived from the natural toxin cycasin, and is extensively used to induce cancers in experiments with rodents. We examined the toxicity of DMH-2HCl, incorporated into purified diets varying in protein, to determine concentrations compatible with long-term survival in B6C3H1 mice. Initial studies showed single-dose oral LD50 values (95% confidence intervals) of 26 (18-32) mg DMH-2HCl/kg body weight for males, and 60 (53-65) for females. A 6-wk study was performed with diets containing 10 or 40% soybean protein with doses of 0, 11.25, 22.5, 45, 90, and 180 mg DMH-2HCl/kg diet. All mice fed the highest dose were removed from the study due to severe toxicity. Declines in food consumption and body weight occurred in both sexes, accelerated with increasing log(DMH) dose, and were substantially more severe in groups fed 10% protein. A 5-mo study was subsequently performed with male mice fed 10 or 40% protein diets containing doses of 0, 15, 30, or 45 mg DMH-2HCl/kg diet. In this longer study, dose-related declines of food intake and body weight were also more pronounced with 10% protein. Histopathologic examination of samples from 29 organs/tissues revealed hepatic changes most commonly, and these were more severe at higher DMH levels. Lesions ranged from focal centrilobular hepatocellular necrosis to severe toxic hepatitis, associated with lobular disorganization and hepatocellular hypertrophy. Frequent dose-dependent lesions were also found in kidneys, adrenals, and heart. Renal changes included focal subcapsular fibrosis with atrophy, and hyperplasia of the tubular epithelium. Adrenal cortical hypertrophy was noted at the two highest DMH doses. Focal cardiac myocytolysis was also noted at high DMH doses. Renal damage occurred only rarely in the absence of liver pathology, and adrenal hypertrophy only rarely without renal damage. Cardiac myocytolysis was found in 14% of mice without hepatic, renal, or adrenal damage, but in 62% of those with lesions in each of those organs. No evidence of gastrointestinal toxicity was observed. Hepatic, renal, and adrenal lesions were more frequent and severe in mice fed the low-protein diet. The protective effect of high protein was DMH-dose dependent. The lower doses in these studies could be used to investigate effects of diet, cocarcinogens, or chemopreventative agents on carcinogenesis resulting from chronic, low-level dietary exposure to DMH.

Cytochrome P450 activity and distribution in the human colon mucosa

Enzymatic activity associated with the mixed-function oxidase system was determined in microsomes prepared from the mucosal cells extracted from normal human colons. A high activity toward nitrogen oxidation reactions was observed. 1,2-Dimethylhydrazine, a colon-specific carcinogen, was metabolized at a higher rate in vitro by human colon microsomes as compared with the rat, and exhibited a km ten-fold lower, 1.03 mmol/l versus 9.68 mmol/l, respectively. This activity was inhibited by classic cytochrome P450 inhibitors; 70% inhibition was achieved using 70 mmol/l metyrapone (2-methyl-1,2-di-3-pyridyl-1-propanone), 20 mmol/l; SKF-525A (diethylaminoethyl-2,-2-diphenylvalerate HCl), or 350 mumol/l n-octylamine. These data suggest the presence of a stable, active mixed-function oxidase system in the human colon mucosa which has a preferential activity toward nitrogenous compounds and provides a mechanism for the activation of carcinogens. Its distribution in the colon appears to parallel the reported incidence of human colonic carcinomas.

Free radical activation of monomethyl and dimethyl hydrazines in isolated hepatocytes and liver microsomes

Isolated hepatocytes and liver microsomes incubated with monomethyl-1,1 dimethyl- and 1,2 dimethyl-hydrazines produced free radical intermediates which were detected by ESR spectroscopy by using 4-pyridyl-1-oxide-t-butyl nitrone (4-POBN) as spin trapping agent. The spectral features of the spin adducts derived from all three hydrazine derivatives corresponded to the values reported for the methyl free radical adduct of 4-POBN. In the microsomal preparations inhibitors of the mixed function oxidase system and the destruction of cytochrome P450 by pretreating the rats with CoCl2 all decreased the free radical formation. Methimazole, an inhibitor of FAD-containing monoxygenase system, similarly decreased the activation of 1,1 dimethyl-hydrazine, but not that of monomethyl- and 1,2 dimethyl-hydrazines. The addition to liver microsomes of physiological concentrations of glutathione (GSH) lowered by approx. 80% the intensities of the ESR signals. Consistently, incubation of isolated hepatocytes with methyl-hydrazines decreased the intracellular GSH content, suggesting that GSH can effectively scavenge the methyl free radicals. The results obtained suggest that methyl free radicals could be the alkylating species responsible for the toxic and/or carcinogenic effect of methyl-hydrazines.

Induction of malignant peripheral nerve sheath tumors in European hamsters with 1,1-dimethylhydrazine (UDMH)

A rate of up to 43% of malignant peripheral nerve sheath tumors (PNST) was induced in European hamsters (EH) after weekly s.c. administration of 1,1-dimethylhydrazine (UDMH). The overall neoplastic response in the treated EH was also elevated as compared to the untreated controls. Histologically, the malignant PNST were neurofibrosarcomas and melanotic as well as unpigmented schwannomas. The occurrence of melanotic schwannomas is briefly discussed with regard to the histogenesis of this rare tumor type.

The effect of diets high in fat and/or fiber on colonic absorption of DMH in the rat

The possibility that long-term feeding of diets high in fat or fiber could alter the colonic mucosa and subsequent colonic absorption of 1,2-dimethylhydrazine (DMH) in situ was examined in the rat model. Male Sprague-Dawley rats were fed one of four experimental diets for six weeks prior to studies of DMH absorption and bile acid excretion; dietary treatments consisted of two levels of fat (12 and 47% of calories from corn oil) fed at each of two levels of fiber (plus or minus 15% wheat bran). Two sets of DMH absorption studies (Studies 1 and 2) were performed; the first used a 10- and the second a 20-minute test period. In Study 1, DMH absorption was greater in those animals that had been fed the high level of corn oil when additional fiber was not present in the diet. When a longer absorption period was used (Study 2), this effect of diet on DMH absorption was not apparent. The level of fiber, not the fat intake, altered bile acid excretion. Bile acid concentration (mg/g dry wt) decreased with added fiber, whereas total bile acid excretion (mg/day) increased. These results indicate that high levels of dietary fat may result in small increases in DMH absorption which are unrelated to changes in bile acid concentration.

Mutagenicity and toxicity of carcinogenic and other hydrazine derivatives: correlation between toxic potency in animals and toxic potency in Salmonella typhimurium TA1538

Eleven hydrazine derivatives and an aromatic amine were examined for mutagenicity and toxicity to Salmonella typhimurium. Phenylhydrazine, 2-nitrophenylhydrazine, 4-nitrophenylhydrazine, 2,4-dinitrophenylhydrazine, p-tolylhydrazine, and 4-nitroaniline were found to be frameshift mutagens (strain TA1538). Benzylhydrazine, m-hydroxybenzylhydrazine, p-hydrazinobenzoic acid, L-tyrosine hydrazide, p-aminobenzoyl hydrazide, and isoniazid were not mutagenic. All chemicals were toxic to strain TA1538. A qualitative correlation was found between the pK of the compounds and their mutagenicity. Relative toxicities of hydrazines to bacteria were found to be closely correlated with the relative toxicities of the same compounds in animals. Described herein is a methodology for the rapid prescreening of chemicals which may be used as drugs for those with a high benefit/risk ratio.

Considerations on the carcinogenicity of the mushroom poison gyromitrin and its metabolites

Monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH), but not N-methyl-N-formylhydrazine (MFH), a mushroom poison, can be oxidized by the weak oxidant 2,6-dichlorophenolindophenol. Hydrogen peroxide is formed by this oxidation, and has been found to cause decay of DNA in aqueous solution as measured by the decreased viscosity of a DNA solution in the presence of the hydrazines. Furthermore, MMH and UDMH but not MFH inhibit the incorporation of [3H]thymidine and [3H]uridine into DNA and RNA of Ehrlich ascites carcinoma (EAC) cells. These experiments show that MFH is an inactive compound in contrast to MMH and UDMH. Since the hydrolysis rate of MFH, to produce MMH, is low, it is concluded that MFH must be activated in vivo into toxic metabolites which are ultimately responsible for the known high carcinogenicity of MFH.

Nitrosamines and nitrosamides in the etiology of gastrointestinal cancer

It has been amply demonstrated that N-nitroso compounds are formed by interaction of nitrite with secondary and tertiary amino compounds, and that this reaction can occur in vivo as well as in food processed with nitrite. The favored site of reaction in vivo is the stomach. It is likely that N-nitroso compounds formed in this way, especially nitrosamides, could reach the colon and contribute to the induction of colon tumors.