Anti-inflammatory actions of a novel hemin-induced electrophile in Sickle Cell Disease

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Sickle Cell Disease (SCD) is the most prevalent genetic blood disorder in the US affecting an estimated 1 in 365 African Americans and 1 in 16,300 Hispanic Americans. SCD is associated with decreased life expectancy and significant physical and psychological morbidity due to complications arising from recurrent vaso-occlusion and hemolytic anemia. The activation of TLR4 by hemoglobin-derived products is a central component of a pernicious inflammatory cascade that involves endothelial activation, formation of multicellular platelet/neutrophil/erythrocyte aggregates and oxidative stress. The effects of SCD on kynurenine metabolism and in particular, on the generation of a novel bioactive kynurenine-derived metabolite were hitherto unappreciated. The bioactive kynurenine-derived mediator discovered herein activates Nrf2-dependent expression of antioxidant enzymes and inhibits NF-κB regulated inflammatory signaling as well as abrogates NLRP3 inflammasome activity. Formation of the bioactive kynurenine metabolite is upregulated in steady state in both mouse models and human SCD patients, and preliminary data suggests that levels are further increased by hemin, a critical mediator of vaso-occlusive crises (VOC) and organ injury. By inhibiting NF-κB- dependent responses and downregulating the NLRP3 inflammasome, this novel kynurenine-derived compound has the potential to act as an endogenous anti-inflammatory mediator capable of regulating endothelial, platelet and immune cell activation to attenuate VOC. Furthermore, Nrf2 activation is known to be protective in SCD via inhibition of pro-inflammatory signaling, upregulation of the heme-catabolizing enzyme HO-1, and by increasing endogenous antioxidant defenses that scavenge reactive species. By utilizing relevant primary cell culture systems derived from animals bearing key pathway deletions, a clinically relevant SCD transgenic mouse model, highly specific LC-MS/MS strategies and state-of-the-art quantitative fluorescence intravital lung microscopy, the research plan will establish the mechanisms behind the anti-inflammatory actions of the bioactive kynurenine metabolite and its potential to attenuate vaso-occlusion in vivo. The present application is built on solid biochemical foundations, and applies critical biological and analytical tools to successfully transition from in vitro chemistry to translational science with the ultimate objective of positively impacting human health. The knowledge gained from this research plan will be of pivotal importance for generating solid preliminary for future R01 applications aimed at better defining the pathophysiological role of the kynurenine- derived bioactive metabolite in SCD as well as in other hematological and non-hematological conditions in which chronic inflammation, oxidative stress and ischemic organ injury are involved.