Tetramethylpyrazine inhibits keratitis and neovascularization induced by corneal alkali burn by suppressing the TLR4/NF-κB pathway activation and NLRP1/NLRP3 inflammasomes in rats

Abstract

The role and related mechanisms of tetramethylpyrazine (TMP) in corneal alkali burn in rats were expected to be explored in this article. After construction of corneal alkali burn rat models, TMP eye drops were given four times daily for consecutive 7 days. H&E staining was utilized for observing the histopathological changes of corneas on the 3rd and 7th days of treatment; immunohistochemistry for detecting the Nestin protein expression changes; qRT-PCR for determining the expression changes of genes correlated with neovascularization [C-X-C Motif Chemokine Ligand 1 (CXCL-1), vascular endothelial growth factor A (VEGFA) and CD31] and inflammation-related factors [monocyte chemoattractant protein-1 (MCP-1), interleukin-1β (IL-1β), tumour necrosis factor α (TNF-α), and IL-6]; Western blot for testing NLR Family Pyrin Domain Containing 1 (NLRP1)/NLRP3 inflammasomes and toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) pathway-related protein expression changes. All above trials were completed based on rat corneal tissue. TMP ameliorated the pathological damage in alkali-burned rat corneal tissue. Specifically, TMP treatment decreased Nestin-positive cell expression and the CXCL-1, VEGFA and CD31 mRNA expression in alkali-burned rat corneal tissue dose-dependently. TMP also down-regulated the IL-1β, TNF-α, MCP-1 and IL-6 mRNA expression and inhibited the NLRP1, caspase-1, NLRP3, pro-IL-1β and mature IL-1β protein expression in the alkali-burned rat corneal tissue. In addition, TMP treatment down-regulated the myeloid differentiation factor 88 (MyD88) and TLR4 protein expression and decreased the p–NF–κB p65/NF-κB p65 ratio in the alkali-burned rat corneal tissue. The mechanism of TMP relieving the inflammatory response and inhibiting neovascularization caused by corneal alkali burn in rats might have a correlation with the suppression of acitivation of TLR4/NF-κB pathway and NLRP1/NLRP3 inflammasomes in rats.