Grantee Research Project Results
1999 Progress Report: Development of Biomarkers for haloacetonitriles-induced cell injury in Peripheral Blood
EPA Grant Number: R825955Title: Development of Biomarkers for haloacetonitriles-induced cell injury in Peripheral Blood
Investigators: Ahmed, Ahmed Elsayed
Institution: The University of Texas Medical Branch - Galveston
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1997 through September 30, 2000 (Extended to November 10, 2002)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $485,147
RFA: Drinking Water (1997) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
Drinking waters are contaminated with a mixture of halogenated hydrocarbons that are disinfection byproducts. Among those are a number of toxic and carcinogenic halogenated acetonitriles (HAN) that are known to stimulate a variety of acute and chronic adverse effects in man and in laboratory animals. Dichloroacetonitrile (DCAN), chloroacetonitrile (CAN), dibromoacetonitrile (DBAN), and bromoacetonitrile (BAN) are aliphatic nitriles that generally are known as HANs. These byproducts are formed when residual chlorine react with natural organic substances in the biologic system, and they also are found in the environment. Animal studies indicated the teratogenic and carcinogenic potential of HANs. The goal is to develop unique biomarkers, in a readily accessible compartment such as blood, for HAN exposure and HAN-induced cell injury. We also plan to evaluate some of the responses to HAN in human peripheral blood cells in vitro and develop an animal model for dermal and inhalation exposure to HAN using female rats and mice.Progress Summary:
To evaluate the mechanism of HAN-induced DNA damage, the effect of DCAN on the conversion of native super coiled plasmid DNA to circular or linear forms was quantified electrophoretically. The results indicated that DCAN-induced oxidative DNA damage in vitro, and that H2O2 mediation of DCAN-induced DNA damage is a possible mechanism of DCAN genotoxicity. Further studies were conducted to examine DCAN-induced DNA damage as influenced by addition of iron (Fe II) to incubation mixtures. Such conditions are more prevalent in mammalian systems, where iron is a common component in cells. The results of these studies established a role for iron in the mechanism of HAN-induced genotoxicity and substantiated the hypothesis that oxidation of DCAN to reactive intermediates by reactive oxygen species is a possible mechanism for HAN-induced DNA damage.To develop unique biomarkers, in peripheral blood, for exposure and HAN-induced cellular injury that result from HAN-induced alkylative or oxidative damage to cellular molecules, we investigated the interaction of HAN with macrophages in culture. The data indicated the dose dependent DCAN-induced apoptosis or necrosis in macrophages is due to the disturbance in redox balance (GSH/GSSG ratio) and initiation of reactive oxygen species mediated oxidative damage mechanisms.
We further examined the mechanism of DBAN toxicity in mouse fibroblasts (Mb16tsA), as these cells are widely distributed and participate in several repair processes in vivo. The data indicated that DBAN causes oxidative stress leading to membrane and nuclear damage in this cell type. To evaluate the dynamics of HAN-induced DNA damage and repair, base excision repair (BER) was used as a marker of hormesis in mouse fibroblasts exposed to DBAN. The data indicated that there is a 2.5-fold and 2-fold increase in the up-regulation of BER at 0.1 µM and 2.5 µM of DBAN, respectively. At 10 µM and 20 µM of DBAN, a down regulation (1.2- and 3.2-fold, respectively) was indicated.
In vivo experiments revealed that gastrointestinal tissues are potential target sites of acute and chronic toxicity of HAN. To examine the mechanism of CAN target organ toxicity, we studied its effect on glutathione (GSH) homeostasis and its impact on oxidative DNA damage in gastric mucosal cells of rats. These data indicate that a mechanism for CAN induced toxicity may be mediated by depletion of glutathione, release of cyanide, interruption of the energy metabolism, and induction of oxidative stress, which leads to oxidative damage to gastric DNA. These effects were further verified in cultured rat gastric epithelial cells (GECs) in vitro. The results suggest that CAN has a potential cytotoxic effect in rat GECs, and thiol group-donors, antioxidants, and iron chelators play a critical role against CAN-induced cellular damage.
Future Activities:
The previous studies collectively indicate that oxidative damage to macromolecules, cells, and tissues is a major feature of the mechanism for HAN-induced toxicity. Therefore, we will focus on the characterization and quantitative determination of oxidative and alkylative damages to cellular macromolecules (DNA and hemoglobin adducts) following inhalation exposure of rats to HAN. The significance of this research is that our studies should provide basis for the development of regulatory guidelines and policies governing the tolerance levels for chronic human exposure to HAN.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 23 publications | 7 publications in selected types | All 7 journal articles |
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Ahmed AE, Jacob S, Nouraldeen AM. Chloroacetonitrile (CAN) induces glutathione depletion and 8-hydroxylation of guanine bases in rat gastric mucosa. Journal of Biochemical and Molecular Toxicology 1999;13(3-4):119-126. |
R825955 (1999) R825955 (Final) |
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Supplemental Keywords:
drinking water disinfection, disinfection byproducts, haloacetonitriles, biomarkers of exposure, peripheral blood, DNA adducts, hemoglobin adducts, cyanomethyl guanine, cyanomethyl valine., RFA, Scientific Discipline, Water, Environmental Chemistry, Health Risk Assessment, Biochemistry, Drinking Water, dermal exposure, halogenated disinfection by-products, public water systems, biomarkers, haloacetonitriles, human health effects, exposure and effects, animal model, chemical byproducts, disinfection byproducts (DPBs), dose response, exposure, community water system, carcinogenicity, inhalation, toxicity, treatment, cell injury, halogenated hydrocarbons, drinking water contaminants, peripheral blood, DBP exposureProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.