Pharmacological application of carbon monoxide ameliorates islet-directed autoimmunity in mice via anti-inflammatory and anti-apoptotic effects.

AIMS/HYPOTHESIS: Recent studies have identified carbon monoxide (CO) as a potential therapeutic molecule for the treatment of autoimmune diseases owing to its anti-inflammatory and anti-apoptotic properties. We explored the efficacy and the mechanisms of action of the CO-releasing molecule (CORM)-A1 in preclinical models of type 1 diabetes. METHODS: The impact of CORM-A1 on diabetes development was evaluated in models of spontaneous diabetes in NOD mice and in diabetes induced in C57BL/6 mice by multiple low-dose streptozotocin (MLDS). Ex vivo analysis was performed to determine the impact of CORM-A1 both on T helper (Th) cell and macrophage differentiation and on their production of soluble mediators in peripheral tissues and in infiltrates of pancreatic islets. The potential effect of CORM-A1 on cytokine-induced apoptosis in pancreatic islets or beta cells was evaluated in vitro. RESULTS: CORM-A1 conferred protection from diabetes in MLDS-induced mice and reduced diabetes incidence in NOD mice as confirmed by preserved insulin secretion and improved histological signs of the disease. In MLDS-challenged mice, CORM-A1 attenuated Th1, Th17, and M1 macrophage response and facilitated Th2 cell differentiation. In addition, CORM-A1 treatment in NOD mice upregulated the regulatory arm of the immune response (M2 macrophages and FoxP3+ regulatory T cells). Importantly, CORM-A1 interfered with in vitro cytokine-induced beta cell apoptosis through the reduction of cytochrome c and caspase 3 levels. CONCLUSIONS/INTERPRETATION: The ability of CORM-A1 to protect mice from developing type 1 diabetes provides a valuable proof of concept for the potential exploitation of controlled CO delivery in clinical settings for the treatment of autoimmune diabetes.