Inhibition of Bacterial and Host-Derived H2S Production for the Therapeutic Enhancement of Anti-Bacterial Host Defense

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Abstract. According to the CDC, at least 2 million people per year in the U.S. develop illness arising from antibiotic-resistant bacteria, and there are at least 23,000 resultant deaths annually. Certain patient populations, such as surgery and trauma patients, are especially susceptible to infections with opportunistic microorganisms and receive aggressive antibiotic therapy. The development of new antibacterial therapies - to be used either in combination with current antibiotics or as an alternative to antibiotics - would reduce complications associated with a wide range of diseases and infections. This project will explore a novel approach to antibacterial therapy through inhibition of hydrogen sulfide (H2S) production. Over the last decade, H2S emerged as an endogenous gasotransmitter produced by mammalian cells. Recent work shows that H2S is also produced by bacteria. Importantly, bacterial H2S has been identified as a novel mechanism that protects the bacteria against antibiotic induced, oxidant-mediated killing in vitro. Whether or not bacteria produce H2S as a defense against the immune system is not known. Our preliminary data show that inhibition of either host or bacterial H2S improves bacterial clearance in vivo. Therefore, H2S-producing enzymes may be novel targets for antibacterial therapy. Since H2S also has multiple physiological roles, it is critical to understand the regulation and relevance of specific host and bacterial H2S-synthesizing enzymes during host- pathogen interactions. This project will address these questions through the following Specific Aims: Aim 1. To identify the contributions of specific H2S-synthesizing enzymes to the production of H2S that mediates bacterial and host responses during infection. Tissue H2S levels, expression and activity of the various H2S-synthesizing enzymes will be measured before and during infection. Mice deficient in H2S-synthesizing enzymes will be compared to wild type mice. Infections with wild type versus H2S-deficient strains of bacteria will elucidate the relative contributions of bacterial- versus host-derived H2S. Patterns and potential enzymatic regulators of constitutive and infection-associated H2S levels will be identified. Aim 2. To determine the roles of H2S in host susceptibility to infection and bacterial resistance to antibiotic therapy. The functional relevance of specific enzymes to infection responses will be determined in two models of infection: S. aureus pneumonia and E. coli abdominal sepsis. H2S-deficient knockout mice will be infected and survival, bacterial clearance, local and systemic inflammation, organ dysfunction, and immune cell activation will be measured and compared to that in WT mice. The same outcomes will be measured after infection with H2S-deficient strains of bacteria. Resistance of H2S-deficient and wild type bacteria to oxidative killing by the host will be examined. Finally, the efficacy of antibiotic treatment in combination with host or bacterial H2S-deficiency will be evaluated. This project will identify specific sources of bacterial or host-derived H2S to be pharmacologically targeted in the future as a fundamentally novel approach to treat bacterial infection.