On the question of the carcinogenic action of hydrazine--evaluation on the basis of new experimental results

Exploring the molecular and functional cellular response to hydrazine via transcriptomics and DNA repair mutant cell lines

Hydrazine is a rodent carcinogen and is classified as a probable human carcinogen by IARC. Though hydrazine is positive in both in vitro and in vivo DNA strand break (comet) assays, hydrazine was reported to be negative in an in vitro mutation Muta Mouse lung epithelial cell (FE1) test, as well as in a regulatory-compliant, in vivo Big Blue mouse mutation test. In this article, mechanistic studies explored the cellular response to hydrazine. When tested in a regulatory-compliant mouse lymphoma assay, hydrazine yielded unusual, weakly positive results. This prompted an investigation into the transcriptional response to hydrazine in FE1 cells via RNA sequencing. Amongst the changes identified was a dose-dependent increase in G2/M DNA damage checkpoint activation associated genes. Flow cytometric experiments in FE1 cells revealed that hydrazine exposure led to S-phase cell cycle arrest. Clonogenic assays in a variety of cell lines harboring key DNA repair protein deficiencies indicated that hydrazine could sensitize cells lacking homology dependent repair proteins (Brca2 and Fancg). Lastly, hprt assays with hydrazine were conducted to determine whether a lack of DNA repair could lead to mutagenicity. However, no robust, dose-dependent induction of mutations was noted. The transcriptional and cell cycle response to hydrazine, coupled with functional investigations of DNA repair-deficient cell lines support the inconsistencies noted in the genetic toxicology regulatory battery. In summary, while hydrazine may be genotoxic, transcriptional and functional processes involved in cell cycle regulation and DNA repair appear to play a nuanced role in mediating the mutagenic potential.

In vitro and in vivo mammalian mutation assays support a nonmutagenic mechanism of carcinogenicity for hydrazine

Hydrazine has been described as a mutagenic, probable human carcinogen. It is mutagenic in in vitro systems such as bacterial reverse mutation (Ames) tests and some yeast systems, as well as in in vivo systems with drosophila. It was shown to cause chromosome damage both in vitro and in vivo but was negative in some well-validated mammalian mutation systems such as CHO HPRT assays. Importantly, there is only one in vivo gene mutation test reported, which was negative. Our objective was to determine if hydrazine is mutagenic in mammalian test systems. Thus, we conducted an in vitro gene mutation test in Muta™Mouse lung epithelial cells (FE1 cell assay) and a regulatory-compliant in vivo Big Blue® mouse test. Consistent with previous reports, an additional six-well Ames assay showed that hydrazine was mutagenic to bacteria. The FE1 cell assay was negative in conditions with and without metabolic activation when tested to cytotoxicity limits. In the Big Blue® mouse study, female mice received dosages of hydrazine up to 10.9 mg/kg via drinking water for 28 days. This dose is comparable to a dose used in a carcinogenicity study where female mice had significant increases in hepatocellular adenoma at 11.5 mg/kg. There were no increases in mutant frequency in liver and lung, two tissues sensitive to the carcinogenic effects of hydrazine in mice. Our research shows that hydrazine is not mutagenic in mammalian cells either in vitro or in vivo, indicating mutagenicity may not play a role in the carcinogenicity of hydrazine.

Studies on the Disposition and Metabolism of Hydrazine in Rats in vivo

1 Rats were given various doses of hydrazine orally and their plasma and liver hydrazine levels were determined (at various times up to 270 min after dosing) by gas chromatography/ mass spectrometry.

2 The increase in the peak plasma level and in the area under the plasma concentration-time curve (AUC) were not directly proportional to the dose.

3 The ratio of plasma to liver hydrazine varied with dose suggesting saturation of an uptake mechanism might be occurring.

4 In a separate experiment hydrazine was still detectable in the plasma and liver 24 h after dosing with hydrazine i.p.

5 Rats were given the same doses of hydrazine and urine was collected for 24 h after dosing and assayed for hydrazine and acetylhydrazine. The proportion of hydrazine and acetylhydrazine excreted declined with dose.

6 Liver samples were taken for histopathological examination 96 h after dosing. Only after the highest dose (81 mg kg-1) was there evidence of fatty liver, 96 h after a single dose, and a reduction in both liver and body weight.

Carcinogenicity and chronic toxicity of hydrazine monohydrate in rats and mice by two-year drinking water treatment

The carcinogenicity and chronic toxicity of hydrazine monohydrate was examined by administrating hydrazine monohydrate in drinking water to groups of 50 F344/DuCrj rats and 50 Crj:BDF1 mice of both sexes for two years. The drinking water concentration of hydrazine monohydrate was 0, 20, 40 or 80 ppm (wt/wt) for male and female rats and male mice; and 0, 40, 80 or 160 ppm for female mice. Survival rates of each group of males and females rats and mice were similar to the respective controls, except female rats administered 80 ppm. Two-year administration of hydrazine monohydrate produced an increase in the incidences of hepatocellular adenomas and carcinomas in rats of both sexes along with hepatic foci. In mice, the incidences of hepatocellular adenomas and carcinomas were increased in females, and significantly increased incidences of hepatocellular adenomas in females administered 160 ppm were observed. Thus, hydrazine monohydrate is carcinogenic in two species, rats and mice. Additionally, non-neoplastic renal lesions in rats and mice and non-neoplastic nasal lesions in mice were observed.

Development of a biosensor test system with GFP reporter protein for detection of DNA damages

A sensitive biosensor test system was developed for evaluation of premutation effects of propellants on the cell genome.

Human health perspective on environmental exposure to hydrazines: a review

Hydrazines are colorless liquid compounds that have been found at various Department of Defense hazardous waste sites. They are designated as environmental contaminants causing adverse effects to public health and have been identified at many National Priorities List (NPL) hazardous waste sites and federal facilities sites in the United States. Three chemically similar hydrazines-hydrazine, 1,1-dimethylhydrazine, and 1,2-dimethylhydrazine--occur in the environment and cause adverse health effects to persons living near hazardous waste sites. Humans are exposed to hydrazines by drinking contaminated, water, by inhaling contaminated air, or by swallowing or touching contaminated dust. Human occupational data and studies in laboratory animals suggest that people exposed to hydrazines may develop adverse systemic health effects or cancer. Hydrazines have caused cancer in animals following acute- or intermediate- duration exposure by the oral and inhalation routes. The U.S. Environmental Protection Agency, the U.S. Department of Health and Human Services, the International Agency for Research on Cancer, and the World Health Organization have classified hydrazines as possible cancer-causing environmental contaminants.

DNA damage in the nasal passageway: a literature review

The purpose of this review is to provide a compilation of work examining DNA damage in the nasal cavity. There are numerous methods to identify and quantify damage to DNA and the diversity of methods and toxicologic endpoints is illustrated by the range of studies presented here. There are a large number of independent studies measuring endpoints in the upper respiratory tract; however, with regard to toxicant induced DNA damage in the nasal passageway, the effects of two compounds, 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and formaldehyde (HCHO), appear to have been extensively characterized. The body of work on NNK and formaldehyde have provided insights into molecular mechanisms of DNA damage and repair and induced cell replication and its relationship to nasal cancer. With new technologies and molecular techniques, the sensitivity to enable evaluations of the minute quantities of nasal tissue available in test species and human biopsy impact the study of the nasal-toxicant interactions. As methods used to characterize DNA damage increase in sensitivity, the importance of both exogenous and endogenous sources of DNA damage, steady-state levels of cellular damage, repair, and resulting mutations, low-dose exposure assessments and inter-species extrapolation will become increasingly complex. Additional studies of DNA damage in the nasal passage will undoubtedly challenge future estimations of risk and impact what are perceived to be acceptable levels of exposure to known and predicted carcinogens. The aim of this paper is to provide to the interested scientist literature relevant to the effects of agents on nasal DNA, so that areas of insufficient information can be identified and used to further develop and expand the knowledge base for nasal DNA toxicant interactions.

In vitro microsomal metabolism of hydrazine

1. It has been demonstrated that hydrazine is metabolized by rat liver enzymes located in the microsomal fraction. This metabolism was reduced in the absence of oxygen or NADPH and was increased by NADH in the presence of NADPH. 2. Microsomal enzyme inhibitors, piperonyl butoxide and metyrapone, significantly inhibited hydrazine metabolism but glutathione had no affect and was not depleted. 3. In addition to P450, flavin monooxygenase may also be involved in catalysing the microsomal metabolism of hydrazine. 4. Liver microsomes prepared from either beta-naphthoflavone, acetone or the isoniazid-pretreated rat did not show a significant increase in hydrazine metabolism compared with microsomes from the control rat. However, although phenobarbitone pretreatment increased overall microsomal hydrazine metabolism this was not increased relative to P450 content. 5. Hydrazine metabolism was 20-70% lower in human microsomes prepared from three individuals compared with the control rat. 6. Hydrazine is also metabolized by rat liver mitochondria but the monoamine oxidase inhibitors clorgyline and pargyline do not significantly decrease this.

Influence of inducers and inhibitors of cytochrome P450 on the hepatotoxicity of hydrazine in vivo

Hydrazine hepatotoxicity in vivo, as manifested by triglyceride accumulation, depletion of ATP and reduced glutathione (GSH) was shown to be dose related. The effect of pretreatment of rats with various inhibitors and inducers of cytochrome P450 on these dose-response relationships was investigated. Pretreatment with the inhibitor piperonyl butoxide increased triglyceride accumulation whereas pretreatment with the inducers phenobarbital and beta-naphthoflavone (BNF) resulted in reduced triglyceride accumulation. Pretreatment with the inducers acetone and isoniazid also enhanced triglyceride accumulation. Only phenobarbital pretreatment also significantly reduced GSH and ATP depletion. A linear correlation was found between hepatic glutathione and ATP levels in non-pretreated animals given various doses of hydrazine. However, exponential relationships were found between hepatic triglycerides and both hepatic ATP and glutathione. The results suggest that i) the hepatotoxicity of hydrazine can be modulated by inducing or inhibiting particular isoenzymes of cytochrome P450, ii) ATP and GSH depletion may not be directly involved in the development of fatty liver.

Effect of acute and repeated exposure to low doses of hydrazine on hepatic microsomal enzymes and biochemical parameters in vivo

A single dose of hydrazine (3 mg.kg-1 i.p.) caused hepatic accumulation of triglycerides and depletion of ATP in rats after 9 h. Repeated exposure of rats to hydrazine (approximately equal to 2.5 mg.kg-1 per day) for 10 days resulted in depletion of hepatic reduced glutathione (GSH) and triglycerides. Repeated exposure to hydrazine also caused a significant (time dependent) induction of p-nitrophenol hydroxylase (NPH) activity together with changes in other hepatic microsomal enzymes. These included 7-pentoxyresorufin O-deethylase (PROD) and 7-ethoxyresorufin O-de ethylase (EROD) activity, total cytochrome P450, cytochrome b5 and cytochrome P450 reductase activity. Repeated exposure to lower levels of hydrazine (approximately equal to 0.250 mg.kg-1 per day) caused no significant hepatic biochemical or microsomal changes after 5 or 10 days except for an increase in NPH activity (17%) and liver ATP (15%) after 5 days.