The fungus-derived retinoprotectant theissenolactone C improves glaucoma-like injury mediated by MMP-9 inhibition

Background: Elevated intraocular pressure (IOP) is a major risk factor for glaucoma that has been found to induce matrix metalloproteinase-9 (MMP-9) activation and result in eventual retinal dysfunction. Proinflammatory cytokines such as monocyte chemoattractant protein-1 (MCP-1) and interleukin-1 beta (IL-1 beta) were also found to be involved in disease progression by mediating MMP-9 production. We previously reported that fungal derivative theissenolactone C (LC53) could exert ocular protective effects by suppressing neuro inflammation in experimental uveitis. Purpose: The aim of this study was to investigate the retinoprotective effects of natural compound LC53 on the high IOP-induced ischemia/reperfusion (I/R)-injury model of glaucoma and its cellular mechanisms. Methods: A high IOP-induced I/R-injury model was manipulated by normal saline injection into the anterior chamber of the rat eye. MCP-1-stimulated monocytes and IL-1 beta-activated primary astrocytes were used to investigate the cellular mechanisms of LC53. Retinal function was evaluated with the scotopic threshold response (STR) and combined rod-cone response by electroretinography (ERG). As a positive control, rats were treated with memantine. MMP-9 gelatinolysis, mRNA expression and protein expression were analyzed by gelatin zymography, RT-PCR, and Western Blot, respectively. The phosphorylation levels of MAPKs and NF-kappa B p65 were tested by Western Blot. Additionally, the levels of inflammatory MCP-1 and IL-1 beta were determined by ELISA. Results: The present study revealed that LC53 preserved the retina functional deficiency assessed by scotopic threshold response (STR) and combined rod-cone response of ERG after high IOP-induced I/R injury. These retinal protective effects of LC53 were positively correlated with inhibitory activities in I/R injury-elicited ocular MMP-9 activation and expression. The increased level of MCP-1 was not affected, and the enhanced IL-1 beta production was partially reduced by LC53 in the retina after I/R injury. According to cellular studies, LC53 significantly and concentration-dependently abrogated MMP-9 activation and expression in MCP-1-stimulated THP-1 monocytes. We found the inhibitory activities of LC53 were through the ERK- and NF-kappa B-dependent pathways. In addition, LC53 dramatically suppressed IL-1 beta-induced MMP-9 activation and expression in primary astrocytes. The phosphorylation of 65-kD protein (p65) of NF-kappa B was substantially blocked by LC53 in IL-1 beta-stimulated primary astrocytes. Conclusion: LC53 exerted a retinal protective effect through NF-kappa B inhibition and was highly potent against MMP-9 activities after high IOP-induced I/R injury, suggesting that LC53 would be a promising drug lead for glaucoma or related medical conditions attributed to retinal ischemia.