Melatonin exerts anti-angiogenic and anti-inflammatory effects in alkali-burned corneas

BACKGROUND: Corneal neovascularization (CNV) caused by alkali burn injury is tightly associated with an inflammatory reaction and can lead to vision loss. Melatonin is involved in anti-inflammation and anti-angiogenesis, but its role in CNV has not yet been investigated. METHODS: We induced CNV using sodium hydroxide (NaOH) and compared the reactions of vehicle control and melatonin-treated male C57BL/6 mice at 7 and 14 days following the corneal burn. The infiltration of inflammatory cells and the expression of proangiogenic factors, chemokines, and inflammation-related molecules were quantified via immunohistochemical (IHC) analysis and quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), respectively. Murine peritoneal macrophages were used in vitro to further verify the effect of melatonin in inflammatory CNV. RESULTS: Compared with the vehicle control mice, the melatonin-treated mice showed significant inhibition of angiogenesis and reduction of corneal epithelial defects in alkali-burned corneas. Concomitantly, the infiltration of inflammatory cells and F4/80(+) cells were dramatically reduced after melatonin treatment. The messenger RNA (mRNA) expression of proangiogenic factors [vascular endothelial growth factors (VEGF) and matrix metalloproteinase-9 (MMP-9)], monocyte chemotactic protein-1 (MCP-1), nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3), and pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) and IL-6] were down-regulated in the melatonin-treated mice. Moreover, melatonin inhibited the expression of these factors in murine peritoneal macrophages. CONCLUSIONS: Melatonin inhibits the neovascular and inflammatory responses in corneal alkali burn injury, suggesting that it may be a potential therapy for CNV.