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Chronic arsenic exposure from drinking water is a global public health issue, which is associated with numerous human diseases and influences millions of people worldwide. The effects of arsenic exposure to the metabolic networks remain elusive. Here, we exposed female C57BL/6J mice to 1 ppm inorganic arsenic in drinking water for 3 months to investigate how arsenic exposure perturbs serum and fecal metabolic profiles. We found decreased levels of serum compounds with antioxidative activities in arsenic-treated mice, in accordance with elevated oxidative stress indicated by higher urinary 8-oxo-2'-deoxyguanosine (8-oxo-dG) levels. Moreover, the levels of multiple lysophosphatidylcholines (lysoPCs) were significantly increased in the sera of arsenic-exposed mice, including lysoPC (O-18:0), lysoPC (20:3), lysoPC (18:1), and lysoPC (22:6). Arsenic exposure perturbed the levels of several key polyunsaturated fatty acids (PUFAs) in the fecal samples in concert with alterations in related microbial pathways. Additionally, changes in the abundances of many functional metabolites, together with decreased levels of amino acids, were found in the fecal samples of arsenic-treated mice. By delineating the impact of arsenic exposure on the metabolic profiles, the findings may provide new biomarkers and mechanistic insights into arsenic-associated diseases.

As the primary active substance in tobacco, nicotine affects the activity of the central nervous system, and its effects are sex-dependent. There are complex interactions between the gut and brain, and the gut microbiome can influence neuronal activity and host behavior, with diverse chemical signaling being involved. However, it is unclear whether nicotine can affect the normal gut microbiome and associated chemical signaling of the gut-brain axis. Sex is an important factor that shapes the gut microbiome, but the role of sex in the interaction among nicotine, gut bacteria, and related metabolites remains unknown. In this study, we applied high-throughput sequencing and gas chromatography-mass spectrometry (GC-MS) to explore how nicotine exposure affects the gut microbiome and its metabolism in female and male C57BL/6J mice, with a focus on the chemical signaling involved in gut-brain interactions. 16S sequencing results indicated that the community composition of the gut microbiome was differentially perturbed by nicotine in females and males. Differential alterations of bacterial carbohydrate metabolic pathways are consistent with lower body weight gain in nicotine-treated males. Oxidative stress response and DNA repair genes were also specifically enriched in the nicotine-treated male gut microbiome. The fecal metabolome indicated that multiple neurotransmitters, such as glutamate, gamma-aminobutyric acid (GABA), and glycine, were differentially altered in female and male mice. Some neuroactive metabolites, including leucine and uric acid, were also changed. This study demonstrates a sex-dependent effect of nicotine on gut microbiome community composition, functional bacterial genes, and the fecal metabolome.

Lead exposure remains a global public health issue, and the recent Flint water crisis has renewed public concern about lead toxicity. The toxicity of lead has been well established in a variety of systems and organs. The gut microbiome has been shown to be highly involved in many critical physiological processes, including food digestion, immune system development, and metabolic homeostasis. However, despite the key role of the gut microbiome in human health, the functional impact of lead exposure on the gut microbiome has not been studied. The aim of this study is to define gut microbiome toxicity induced by lead exposure in C57BL/6 mice using multiomics approaches, including 16S rRNA sequencing, whole genome metagenomics sequencing, and gas chromatography-mass spectrometry (GC-MS) metabolomics. 16S rRNA sequencing revealed that lead exposure altered the gut microbiome trajectory and phylogenetic diversity. Metagenomics sequencing and metabolomics profiling showed that numerous metabolic pathways, including vitamin E, bile acids, nitrogen metabolism, energy metabolism, oxidative stress, and the defense/detoxification mechanism, were significantly disturbed by lead exposure. These perturbed molecules and pathways may have important implications for lead toxicity in the host. Taken together, these results demonstrated that lead exposure not only altered the gut microbiome community structures/diversity but also greatly affected metabolic functions, leading to gut microbiome toxicity.

The gut microbiome is deeply involved in numerous aspects of human health; however, it can be readily perturbed by environmental toxicants, such as arsenic. Meanwhile, the interaction among host, gut microbiome, and xenobiotics is a very complex dynamic process. Previously, we have demonstrated that gut microbiome phenotypes driven by host genetics and bacterial infection affect the responses to arsenic exposure. The role of host sex in shaping the gut microbiome raises the question whether sex plays a role in exposure-induced microbiome responses. To examine this, we used 16S rRNA sequencing and metagenomics sequencing to analyze the changes of the gut microbiome and its associated functional metagenome in both female and male C57/BL6 mice. Our results clearly demonstrated that arsenic exposure perturbed the trajectory and function of the gut microbiome in a sex-specific manner.

Large individual differences in susceptibility to arsenic-induced diseases are well-documented and frequently associated with different patterns of arsenic metabolism. In this context, the role of the gut microbiome in directly metabolizing arsenic and triggering systemic responses in diverse organs raises the possibility that gut microbiome phenotypes affect the spectrum of metabolized arsenic species. However, it remains unclear how host genetics and the gut microbiome interact to affect the biotransformation of arsenic. Using an integrated approach combining 16S rRNA gene sequencing and HPLC-ICP-MS arsenic speciation, we demonstrate that IL-10 gene knockout leads to a significant taxonomic change of the gut microbiome, which in turn substantially affects arsenic metabolism.

Exposure to arsenic affects large human populations worldwide and has been associated with a long list of human diseases, including skin, bladder, lung, and liver cancers, diabetes, and cardiovascular disorders. In addition, there are large individual differences in susceptibility to arsenic-induced diseases, which are frequently associated with different patterns of arsenic metabolism. Several underlying mechanisms, such as genetic polymorphisms and epigenetics, have been proposed, as these factors closely impact the individuals' capacity to metabolize arsenic. In this context, the role of the gut microbiome in directly metabolizing arsenic and triggering systemic responses in diverse organs raises the possibility that perturbations of the gut microbial communities affect the spectrum of metabolized arsenic species and subsequent toxicological effects. In this study, we used an animal model with an altered gut microbiome induced by bacterial infection, 16S rRNA gene sequencing, and inductively coupled plasma mass spectrometry-based arsenic speciation to examine the effect of gut microbiome perturbations on the biotransformation of arsenic. Metagenomics sequencing revealed that bacterial infection significantly perturbed the gut microbiome composition in C57BL/6 mice, which in turn resulted in altered spectra of arsenic metabolites in urine, with inorganic arsenic species and methylated and thiolated arsenic being perturbed. These data clearly illustrated that gut microbiome phenotypes significantly affected arsenic metabolic reactions, including reduction, methylation, and thiolation. These findings improve our understanding of how infectious diseases and environmental exposure interact and may also provide novel insight regarding the gut microbiome composition as a new risk factor of individual susceptibility to environmental chemicals.