Reduced NF-κB/NLRP3/IL-18 signaling increases the protective effect of L-glutamine against LPS-induced retinal inflammation in mice: Utilization of network pharmacology and experimental validation

Abstract

Regarding retinal inflammation, NF-κB activation has been demonstrated to stimulate the NLRP3 inflammasome, which subsequently promotes IL-18 production, resulting in heightened inflammatory damage. Concurrently, GLP-1 has shown a role in reducing the likelihood of retinal inflammation. Nonetheless, the exact mechanism by which GLP-1 can reduce inflammation in the retina by modulating NF-κB/NLRP3/IL-18 axis remains unknown. Therefore, it may be worthwhile investigating the effects of L-glutamine (L-glu), a GLP-1 inducer, on LPS-induced retinal inflammation in rats, considering the involvement of NF-κB/NLRP3/IL-18 signaling. This study utilized the strategy of network pharmacology with subsequent experimental validation to predict the targets and associated pathways related to L-glu and retinal inflammation. To authenticate the in vivo pharmacological efficacy of L-glu, 60 mice were divided into 4 groups. The expression and level of GLP-1, in addition to IGF-2 and IL-18 levels were assayed. Gene expression of PPARγ and XO, as well as protein expression of p-TLR4, SIRT1, NLRP3, and caspase-1 were determined. The Nrf2/HO-1, MDA, and TAC were also detected. Retinal histopathology and immunostaining were lastly done. Network analysis identified 251 overlapping targets and 462 pathways between L-glu and retinal inflammation. Experimentally, L-glu enhanced the IGF-2-dependent PPARγ expression by boosting GLP-1 secretion. PPARγ then restricted TLR4 phosphorylation and XO expression to activate SIRT1/Nrf2 and alleviate oxidative stress. SIRT1 simultaneously inhibited the NF-κB-driven secretion of TNF-α and IL-6, as well as the ensuing activation of NLRP3/caspase-1/IL-18. These findings suggested that L-glu may confer protection against LPS-induced retinal inflammation in a GLP-1-dependent manner via prohibiting NF-κB/NLRP3/IL-18 pathway.

Keywords: IGF-2; L-glutamine; Lipopolysaccharide; NF-κB/NLRP3/IL-18 axis; Retinal inflammation.