The surface of the eye actively suppresses inflammation while maintaining a remarkable capacity for epithelial wound repair. Our understanding of mechanisms that balance inflammatory/reparative responses to provide effective host defense while preserving tissue function is limited, in particular, in the cornea. Lipoxin A 4 (LXA 4 ) and docosahexaenoic acid-derived neuroprotectin D1 (NPD1) are lipid autacoids formed by 12/15-lipoxygenase (LOX) pathways that exhibit anti-inflammatory and neuroprotective properties. Here, we demonstrate that mouse corneas generate endogenous LXA 4 and NPD1. 12/15-LOX (Alox15) and LXA 4 receptor mRNA expression as well as LXA 4 formation were abrogated by epithelial removal and restored during wound healing. Amplification of these pathways by topical treatment with LXA 4 or NPD1 (1 g) increased the rate of re-epithelialization (65-90%, n ‫؍‬ 6 -10, p < 0.03) and attenuated the sequelae of thermal injury. In contrast, the proinflammatory eicosanoids, LTB 4 and 12R-hydroxyeicosatrienoic acid, had no impact on corneal re-epithelialization. Epithelial removal induced a temporally defined influx of neutrophils into the stroma as well as formation of the proinflammatory chemokine KC. Topical treatment with LXA 4 and NPD1 significantly increased PMNs in the cornea while abrogating KC formation by 60%. More importantly, Alox15-deficient mice exhibited a defect in both corneal re-epithelialization and neutrophil recruitment that correlated with a 43% reduction in endogenous LXA 4 formation. Collectively, these results identify a novel action for the mouse 12/15-LOX (Alox15) and its products, LXA 4 and NPD1, in wound healing that is distinct from their well established anti-inflammatory properties.

Exacerbated inflammation plays an important role in the pathogenesis of ischemic renal injury (IRI), which is the major cause of intrinsic acute renal failure. Clinical studies suggest that long-term treatment with ω-3 polyunsaturated fatty acids (PUFA) improves renal function and lowers the risk of death or end-stage renal disease. Docosahexaenoic acid, a principle ω-3 PUFA of fish oils, is of particular interest as it is found in most human tissues and is converted to protectin D1 (PD1), which exhibits antiinflammatory and proresolving bioactions. We set out to investigate the impact of acute dietary modulation of ω-3 or ω-6 PUFA on IRI and renal lipid autacoid circuits, using an established mouse model and liquid chromatography-mass spectroscopy/mass spectroscopy-based lipidomics. Thirty minutes of renal ischemia significantly elevated serum creatinine in the ω-6 diet group while renal function remained normal in the matched ω-3 diet group. Notably, extending ischemia to 45 min caused 100% mortality in the ω-6 group, in sharp contrast to 0% mortality in the ω-3 group. Protection against IRI in the ω-3 group correlated with decreased polymorphonuclear leukocyte recruitment, chemokine and cytokine levels, abrogated formation of lipoxygenase- and cyclooxygenase-derived eicosanoids, and increased renal levels of PD1. Systemic treatment with PD1 reduced kidney polymorphonuclear leukocyte influx and, more importantly, amplified renoprotective heme-oxygenase-1 protein and mRNA expression in injured and uninjured kidneys. These findings suggest therapeutic or dietary amplification of PD1 circuits restrains acute renal injury and that short-term changes in dietary ω-3 and ω-6 PUFA dramatically impacts renal lipid autacoid formation and outcome of IRI.

In the immune-privileged cornea, epithelial wounds heal rapidly with almost no scarring and, unlike in most other tissues, acute inflammation in the absence of infection is beneficial to healing. Molecular mechanisms, which account for this striking property, remain to be clearly defined, but they likely include autacoids that control leukocyte activation. Two prominent enzymes, 12/15-lipoxygenase (LOX), which generates antiinflammatory lipid autacoids, and heme-oxygenase (HO), which generates antioxidants and carbon monoxide, are highly expressed in human and mouse corneas. LXA4, an endogenous 12/15-LOX product, proved to be a potent inhibitor of exacerbated inflammation and significantly increased re-epithelialization in corneal wounds. In vivo deletion of 12/15-LOX correlated with exacerbated inflammation and impaired wound healing in 12/15-LOX(-/-) mice, a phenotype that was rescued by treatment with LXA4. More importantly, 12/15-LOX(-/-) mice demonstrated impaired induction of HO-1 in both acute and exacerbated inflammation. Topical LXA4 restored HO-1 expression in 12/15-LOX(-/-) mice and amplified HO-1 gene expression in human corneal epithelial cells. HO-2(-/-) mice, which fail to induce HO-1, also demonstrated exacerbated inflammation in response to injury, a phenotype that, notably, correlated with a 50% reduction in endogenous LXA4 formation. Collectively, results demonstrate a critical role for LXA4 in inflammatory/reparative responses and provide the first evidence that 12/15-LOX and HO systems function in concert to control inflammation.

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