| Summary: | Intense research on carbon monoxide (CO) over recent years has demonstrated the increasing relevance of this gaseous signalling molecule in biology and medicine. A wide array of protective effects has been attributed to CO, including vasodilation, antiinflammation and anti-apoptosis. The advent of carbon monoxide-releasing molecules (CO-RMs) has revolutionised this field, providing a means by which the interaction between transition metals and carbonyls can be exploited to allow more controlled endogenous delivery of this noxious gas. It is via such compounds that the bactericidal activity of CO against a number of bacterial species has been most effectively explored. The best established CO-RM is the novel, water-soluble Ru(CO)3Cl(glycinate) (CORM- 3). In this thesis, CORM-3 is shown to inhibit respiration of diverse bacteria as well as Candida albicans and, interestingly, stimulates respiration of intact cells of Escherichia coli prior to inhibition. Proton translocation measurements (H+/O quotients, i.e. proton extrusion on pulsing anaerobic cells with O2, and the subsequent backflow of protons to the cytoplasm) show that respiratory stimulation cannot be attributed to dissipation of the protonmotive force, i.e. true uncoupling. Additionally, the bactericidal activity of CORM-3 is augmented in the absence of haem proteins and transcriptomic profiling of anaerobically-grown haem-deficient E. coli following exposure to CORM-3, and to a lesser extent inactivated CORM-3, reveals a multifaceted response. Of particular note is the up-regulation of iron-starvation response genes. Together, these data suggest that CORM-3 has targets additional to respiratory oxidases and that haem may act as a 'COsink', thereby providing protection against CO. Furthermore, CORM-3 is shown to be without effect on human macrophage functionality in a model of Neisseria meningitidis infection. This is the most complete study to date on the anti-microbial effects of a CO-RM and it highlights the multifaceted and complex action of these compounds. Importantly, control molecules depleted of CO reveal that CORM-3 toxicity is due to CO release; however, its potent anti-bacterial activity is not mimicked by CO gas. It is therefore becoming increasingly evident that there are several unidentified mechanisms underlying the effectiveness of CO-RMs in tackling microbial sepsis and pathogenesis.
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