Acute inflammation resolves by mechanisms that are not fully understood. Persistence of the inflammatory response (chronic inflammation) can lead to scarring and loss of organ function. An actively coordinated program of resolution initiates in the first few hours after an inflammatory response is triggered by tissue injury. Resolution of inflammation is enabled if granulocytes are eliminated via efferocytosis and the tissue mononuclear cell population (macrophages, m[fcy]) returns to baseline count and phenotypes. We observed that compared to non- diabetic animals, dead cell clearance activity (efferocytosis) was markedly impaired in wound macrophages harvested from diabetic mice. Oxidants produced by NADPH oxidase are directly involved in the oxidation and externalization of phosphatidyl serine (PS), a process that is critical for dead cell recognition. Compromised NADPH oxidase activity was observed in macrophages harvested from diabetic wounds. Milk fat globule EGF factor 8 (MFG-E8; also known as lactadehrin) is secreted by activated m[fcy]. MFG-E8 acts as a bridging molecule that is capable of binding to phosphatidyl serine on apoptotic cells as well as avb3 or avb5 integrin receptors on m[fcy].The presence of arginine residues renders this protein susceptible to glycation. Using ELISA and Biacor assays we demonstrate that glyoxal, a product of glucose oxidation, can glycate MFG-E8. Once glycated the affinity of MFG-E8 for binding with PS markedly diminished. Diabetic wound tissue showed presence of glycated MFG-E8. These data suggest compromised NADPH oxidase activity in diabetic wound cells result in diminished phosphatidylserine oxidation impairing the process of dead cell recognition by m[fcy]. Glycation of MFG-E8 diabetic macrophages represents another major mechanism that impairs dead cell recognition and clearance in diabetic wounds. Such dysfunction in macrophage activity is in direct conflict with resolution of inflammation resulting in chronic inflammation noted in diabetic wounds.

Supported by RO1 DK 076566 to SR.