The impacts of glutathione on Clostridioides difficile infection

About This Grant

PROJECT SUMMARY/ABSTRACT Clostridioides difficile is a diarrheal pathogen that causes significant human morbidity and mortality. The status quo as it pertains to treating C. difficile infections (CDIs) is antibiotic use and, in recurrent cases, microbiome restoration therapy (MRT). Antibiotics contribute to antibiotic resistance and recurrent CDIs. Although MRTs (e.g., defined consortia of microbes or fecal transplant) are increasingly accessible, the long-term sustainability and accessibility of these treatments remain to be determined. These limitations highlight the need for new and more precise strategies for coping with CDI. One framework for developing such strategies is to better understand key metabolic processes of C. difficile and use this understanding to develop ways to reduce its fitness and pathogenesis in the gastrointestinal (GI) tract. C. difficile is a cysteine auxotroph and the GI tract contains low levels of cysteine, highlighting gaps in our understanding of how C. difficile acquires this amino acid during infection. One possible source of cysteine for C. difficile during infection is glutathione (GSH). GSH is the most abundant low molecular weight thiol within mammalian cells, where it serves as an antioxidant. GSH is also produced, consumed, and sensed by phylogenetically diverse bacteria, where it can be used as a source of amino acids, nutritional sulfur, and as a signaling molecule to modulate gene expression. Our data indicate that C. difficile consumes GSH as a source of cysteine in vitro. Our data also suggest that GSH levels increase in the GI tracts of mice with CDI relative to uninfected mice and relative to mice colonized with avirulent C. difficile. Despite these observations, detailed knowledge of the C. difficile-, microbiome-, and host-based determinants of GSH levels in the GI tract under homeostasis and during CDI remain unclear. In the proposed work, we will use a mouse model of CDI to define how C. difficile-mediated inflammation impacts GSH concentrations in the distal GI tract. In addition, we will generate targeted mutations in C. difficile to disable its ability to metabolize GSH. These mutants will allow us to determine how C. difficile GSH utilization impacts CDI in mice. Upon successful completion of the proposed work, we will have generated foundational data on how C. difficile acquires and metabolizes GSH during murine CDI. This will build the foundation for future R01-funded work, which will provide deeper mechanistic insights into GSH acquisition and utilization by C. difficile during CDI. We anticipate that these insights will allow for the development of drugs to disable C. difficile GSH metabolism, probiotics that impact C. difficile's ability to acquire GSH, or diet-based strategies to alter available cysteine and GSH in the distal GI. The proposed work will therefore be an important foundation for developing new approaches to target C. difficile metabolism and to mitigate CDI in at-risk human populations.