Molecular Mechanisms of Topical Anti-Inflammatory Effects of Lipoxin A₄in Endotoxin-Induced Uveitis

Abstract

Lipoxin A 4 (LXA 4 ) is a lipid mediator that plays an important role in inflammation resolution. We assessed the anti-inflammatory effect of LXA 4 on endotoxin-induced uveitis (EIU) in rats. The inflammatory cell number and levels of tumor necrosis factor-␣ (TNF-␣), interleukin-1␤ (IL-1␤), prostaglandin E 2 (PGE 2 ), and protein, as well as expression of cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF), in the anterior chamber of the eye were determined 24 h after lipopolysaccharide (LPS; 200 g/paw) intradermal injection. The immunohistochemical reactivities of nuclear factor-B (NF-B) and c-Jun were also examined. Topical LXA 4 (1-10 ng/eye) pretreatment decreased the number of inflammatory cells and the protein leakage into the aqueous humor (AqH). In addition, topical LXA 4 (10 ng/eye) inhibited the LPS-induced production of IL-1␤, TNF-␣, and PGE 2 , and expression of COX-2 and VEGF. A decreased activation of NF-B and c-Jun was also found in LXA 4 -treated eyes. It is very interesting that an anti-inflammatory effect was achieved even when LXA 4 (10 ng/eye) was applied topically after LPS challenge, as indicated by the reduction in the cellular and protein extravasations into the AqH. Moreover, topical treatment of corticosteroid prednisolone (200 g/eye) beginning before or after LPS injection reduced all of the molecular and biochemical alterations promoted on EIU rats in an efficacy similar to that of LXA 4 . Together, the present results provide clear evidence that pharmacological activation of LXA 4 signaling pathway potently reduces the EIU in rats. Therefore, LXA 4 stable analogs could represent promising agents for the management of ocular inflammatory diseases.

Anti-Inflammatory Mechanisms of the Annexin A1 Protein and Its Mimetic Peptide Ac2-26 in Models of Ocular Inflammation In Vivo and In Vitro

“…Because the increased expression of inflammatory mediators, especially IL-1b, IL-6, TNF-a, and NO, contributes to the development of uveitis (9,10,14), their levels were analyzed in supernatants of the ocular tissues obtained after maceration. In contrast, the cytokines IL-6 and IL-8 are the chemical mediators released in larger quantities by ARPE-19 cells after LPS activation for 24 h (2); therefore, they were analyzed in cell supernatants under all experimental conditions.…”

“…In this model, LPS binds to TLR4 on eye cells (10)(11)(12) and stimulates the synthesis and release of proinflammatory chemical mediators, such as NO, platelet-activating factor, TNFa, IL-1b, and other cytokines (9,10). The most commonly activated pathway in this model is that of NF-kB, which is followed by its translocation from the cytoplasm to the nucleus (9,13).…”

“…The most commonly activated pathway in this model is that of NF-kB, which is followed by its translocation from the cytoplasm to the nucleus (9,13). The subsequently increased expression of inflammatory mediators exacerbates the development of uveitis by breaking down the blood-ocular barrier, which leads to edema formation and contributes to leukocyte influx (9,13,14).…”

“…The animal model of endotoxin-induced uveitis (EIU) (8) has been used by several researchers to understand the pathogenesis of uveitis (4,9). In this model, LPS binds to TLR4 on eye cells (10)(11)(12) and stimulates the synthesis and release of proinflammatory chemical mediators, such as NO, platelet-activating factor, TNFa, IL-1b, and other cytokines (9,10).…”

“…In this model, LPS binds to TLR4 on eye cells (10)(11)(12) and stimulates the synthesis and release of proinflammatory chemical mediators, such as NO, platelet-activating factor, TNFa, IL-1b, and other cytokines (9,10). The most commonly activated pathway in this model is that of NF-kB, which is followed by its translocation from the cytoplasm to the nucleus (9,13). The subsequently increased expression of inflammatory mediators exacerbates the development of uveitis by breaking down the blood-ocular barrier, which leads to edema formation and contributes to leukocyte influx (9,13,14).…”