Nitrogenous disinfection by-products and their metabolic impact on human gut microbiota

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PROJECT SUMMARY Nitrogenous disinfection by-products (N-DBPs) are ubiquitous contaminants in tap water, and form when chlorine reacts with natural organic matter in tap water. Chronic exposure to these contaminants is linked with adverse health outcomes, including bladder cancer, miscarriages, and low birthweight. Yet, N-DBPs are unregulated. Comparative toxicity assessments have suggested that N-DBPs are genotoxic and cytotoxic. Nevertheless, standard toxicity assessments are limiting because animal studies and in vitro assays do not always recapitulate human biology. The human gastrointestinal tract microbiome plays an important role in human health and disease progression. Studies have demonstrated that the gut microbiome can degrade xenobiotic compounds into biotransformation products with various toxic effects. Furthermore, xenobiotic exposure has the potential to change microbiome composition and gene expression, which can play a role in adverse health outcomes in humans. In an effort to understand the health effects of N-DBP exposure, this project investigates the interactions between N-DBPs and the human gastrointestinal tract microbiome. The central hypothesis of this study is that microbiome and N-DBP interactions play a role in adverse health effects after exposure. The long-term objective of this project is to investigate the chemical and biological interactions between N-DBPs and the human gut microbiome to elucidate potential mechanisms of adverse effects. The specific aims will test the hypotheses that (1) gut microbiota degrade N-DBPs into biotransformation products with various toxic effects, and (2) environmentally-relevant N-DBP exposure can perturb gut community structures and functional activities. Aim 1 will identify N-DBP biotransformation products in the presence of gut microbiota. We will measure N-DBP degradation and biotransformation products using liquid chromatography (LC) – mass spectrometry (MS). Using a computational toxicology approach, we will predict biotransformation product toxicities based on chemical structure to determine if gut microbiota change N-DBP toxic effects. Aim 2 will determine microbial community gene expression changes in the gut following N-DBP exposure. For this work, we will perform metatranscriptomics to determine differential gene expression changes after N-DBP exposure. We will identify a subset of statistically-significant upregulated or downregulated genes that are relevant to biotransformation or cell stress. To ensure successful completion of this project, state-of-the-art resources, mentorship and training at the University of Michigan will be readily available. These aims will provide a key first step in the long-term goal of defining the relationship between N-DBP exposure, the gut microbiome, and human health risks. Overall, this interdisciplinary study will have a significant impact on understanding N-DBP toxicity mechanisms post-ingestion, and implications of N-DBP exposure on health.