Increased succinate receptor GPR91 involved in the pathogenesis of Mooren's ulcer

AIM： To investigate the expression of succinate receptor GPR91 and its pathogenic roles in Mooren＇s ulcer（MU）.METHODS： Biopsy specimens were obtained from 7 patients with MU and 6 healthy donors. The expression of GPR91 in MU tissues was evaluated using quantitative realtime reverse transcription polymerase chain reaction（qRTPCR） and immunohistochemistry（IHC）. Succinate was used to activate GPR91 signaling, and the effect of GPR91 on the expression of interleukin-1β（IL-1β）, NLRP3, vascular endothelial growth factor（VEGF） and matrix metalloproteinase-13（MMP-13） in human peripheral blood mononuclear cells（PBMCs） was determined. The influence of GPR91 on the nuclear factor-κB（NF-κB） signaling in PBMCs was investigated by detecting the phosphorylation of p65. Moreover, the expression of IL-1β, VEGF, MMP-13 and phosphorylated p65（p-p65） in the tissues of MU was examined by qRT-PCR or IHC.RESULTS： GPR91 mRNA expression showed a higher level in the MU group than in the healthy control group. IHC analysis also revealed that the expression of GPR91 was elevated in patients with MU compared with healthy controls. Moreover, ligation of GPR91 with succinate promoted the lipopolysaccharide-induced production of NLRP3, IL-1β, VEGF and MMP-13 in PBMCs through increased phosphorylation of p65. Pharmacological inhibition of the NF-κB signaling reversed GPR91 induced production of NLRP3, IL-1β, VEGF and MMP-13. These findings, coupled with the elevated amounts of IL-1β, VEGF, MMP-13 and p-p65 observed in the MU biopsies, constituted a rational basis for the involvement of GPR91 in the pathogenesis of MU.CONCLUSION： This study indicates the increased succinate receptor GPR91 in conjunctival or corneal tissues is involved in the pathogenesis of MU through elevated NF-κB activity, which may provide a new therapeutic target for MU.

Interventions of natural and synthetic agents in inflammatory bowel disease, modulation of nitric oxide pathways

Inflammatory bowel disease(IBD)refers to a group of disorders characterized by chronic inflammation of the gastrointestinal(GI)tract.The elevated levels of nitric oxide(NO)in serum and affected tissues;mainly synthesized by the inducible nitric oxide synthase(iNOS)enzyme;can exacerbate GI inflammation and is one of the major biomarkers of GI inflammation.Various natural and synthetic agents are able to ameliorate GI inflammation and decrease iNOS expression to the extent comparable with some IBD drugs.Thereby,the purpose of this study was to gather a list of natural or synthetic mediators capable of modulating IBD through the NO pathway.Electronic databases including Google Scholar and PubMed were searched from 1980 to May 2018.We found that polyphenols and particularly flavonoids are able to markedly attenuate NO production and iNOS expression through the nuclear factorκB(NF-κB)and JAK/STAT signaling pathways.Prebiotics and probiotics can also alter the GI microbiota and reduce NO expression in IBD models through a broad array of mechanisms.A number of synthetic molecules have been found to suppress NO expression either dependent on the NF-κB signaling pathway(i.e.,dexamethasone,pioglitazone,tropisetron)or independent from this pathway(i.e.,nicotine,prednisolone,celecoxib,β-adrenoceptor antagonists).Co-administration of natural and synthetic agents can affect the tissue level of NO and may improve IBD symptoms mainly by modulating the Toll like receptor-4 and NF-κB signaling pathways.