Mechanisms of monohalogenated acetic acid induced genomic DNA damage

Disinfection of drinking water stands among the greatest public health achievements in human history. Killing or inactivation of pathogenic microbes by chemical oxidants such as chlorine, chloramine, or ozone have greatly reduced incidence of waterborne diseases. However, the disinfectant also reacts with organic and inorganic matter in the source water and generates a mixture of toxic disinfection byproducts (DBPs) as an unintended consequence. Since they were first discovered in 1974, over 600 individual DBPs have been detected in disinfected water. Exposure to DBPs is associated with increased risks for developing cancers of the colon, rectum, and bladder, and also for adverse pregnancy outcomes including small for gestational age and congenital malformations. While individual DBPs are teratogenic or carcinogenic, because they are formed at low concentrations during disinfection, it is unlikely that any one DBP can account for these increased risks. While genotoxicity and oxidative stress have been suggested, the mechanisms connecting DBP exposures to adverse health and pregnancy outcomes remain unknown. Investigating mechanisms of toxicity for individual, or classes of DBPs will provide a better understanding of how multiple DBPs interact to generate adverse health and pregnancy outcomes. Monohalogenated acetic acids (monoHAAs) iodoacetic acid (IAA), bromoacetic acid (BAA), and chloroacetic acid (CAA) are genotoxic and mutagenic with the consistent rank order of toxicity of IAA > BAA > CAA. The comparative toxicity of these compounds was highly correlated with their SN2 reactivity. The working hypothesis that monoHAAs were directly alkylating DNA was tested and rejected when no damage accumulated in acellular DNA. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was investigated as a possible molecular target for the monoHAAs; each of the monoHAAs inhibited GAPDH with variable efficacy. The ability to inhibit GAPDH correlated strongly with multiple toxicological endpoints measured for the monoHAAs. Inhibition of GAPDH was known to disrupt cellular Ca2+ homeostasis and generate reactive oxygen species (ROS). The roles Ca2+ and ROS played in mode of genotoxic action for the monoHAAs were investigated. Each of the monoHAAs generated biomarkers of oxidative stress, measured both with toxicogenomic analysis and with the production of an antioxidant response element driven reporter gene. The antioxidant butylated hydroxyanisole and the intracellular Ca2+ chelator BAPTA-AM reduced genomic DNA damage induced by each of the monoHAAs, supporting the hypothesis that monoHAAs induced genotoxicty by a cascade of events initiated by inhibition of GAPDH. Disruption of Ca2+ homeostasis was a common event in genotoxicity induced by bromacetonitrile (BAN) and bromoacetamide (BAM). Although the BAN and BAM act through depletion of glutathione and BAA acts by inhibiting GAPDH, when BAN or BAM was combined with BAA in a defined component, binary mixture the genotoxicity was additive. These data suggested that the collective action of multiple DBPs acting through different pathways could converge to disrupt Ca2+ homeostasis, generate ROS, and cause genomic DNA damage.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Pals, Justin

Contributors dc:contributor

• Plewa, Michael J.
• Mariñas, Benito J.
• Rayburn, A.L.
• Miller, Brian K.

• Drinking water
• Disinfection Byproducts (DBPs)
• Haloacetic acids
• Toxicity
• Genotoxicity
• Oxidative stress
• Toxicogenomics

Statement dc:rights

• Copyright 2014 Justin Pals

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/50530

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/50530