The acute inflammatory response is essential for host defense and requires active resolution to return to homeostasis. Failed resolution plays a major role in the development of chronic inflammation and the etiology of multiple diseases such as arthritis, periodontitis, thrombosis, fibrosis, and cancer. The resolution of inflammation is an active process driven by specialized pro-resolving lipid mediators (SPM) that arise from polyunsaturated fatty acids such as arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, and docosapentaenoic acid. SPMs counter-regulate pro-inflammatory mediators, increase uptake of bacteria, cellular debris, and apoptotic neutrophils, and decrease the influx of infiltrating leukocytes. Granuloma formation occurs during inflammation when the immune system is unable to eliminate bacteria, fungi, or a foreign body and instead forms an enclosure. Chronic granuloma formation leads to necrotic lesions, loss of tissue regeneration, loss of tissue/organ function, and potentially death. The role of specialized pro-resolving lipid mediators in granuloma formation and subsequent loss of tissue regeneration and organ function is not known. Here we identified a novel peptide-conjugated pro- resolving lipid mediator, 4,5-Resolvin Conjugate in Tissue Regeneration-1, that significantly decreases granuloma formation as well as increases the amount of tissue regenerated and accelerates the time required for tissue regeneration.
Chronic granuloma formation leads to necrotic lesions, loss of tissue regeneration, loss of tissue/organ function, and potentially death. The role of specialized pro-resolving lipid mediators (SPMs) in granuloma formation and subsequent loss of tissue regeneration and organ function are of interest. Here we further defined the Resolvin D3 and Resolvin D4 pathway, identified a novel glutathione-conjugated specialized pro-resolving lipid mediator in this pathway, and examined its role in the formation of granulomas and during tissue regeneration. We report that glutathione is enzymatically conjugated to the intermediate 4S,5S-epoxy-resolvin (prepared via total organic synthesis) by glutathione S-transferases in human macrophages to a novel 4,5- Resolvin Conjugate in Tissue Regeneration-1 (4,5-RCTR1). In a model of granuloma formation in vitro, 4,5-RCTR1 significantly reduced (p<0.05) advancement of granuloma severity by human blood mononuclear cells. Expression of the leukocyte adhesion molecule, integrin �2 (CD18), was decreased on monocytes and macrophages in the granuloma system in the presence of 4,5- RCTR1. Finally, this newly identified cysteinyl-SPM significantly increased the amount of tissue regenerated (p<0.05) and accelerated the speed of regeneration by ~ 24h in Planarian regeneration. Together, these results provide evidence for a 4(5) epoxide resolvin pathway in the biosynthesis of novel 4,5 cysteinyl-SPMs that reduce granuloma.
