Antagonism of G protein-coupled receptor 55 prevents lipopolysaccharide-induced damages in human dental pulp cells

Pulpitis is a common oral inflammatory disease in dental pulp commonly associated with bacterial infection. G protein-coupled receptor 55 (GPR55) is a member of the G protein‐coupled receptors family that has been found to regulate inflammatory response. However, its roles in dental pulp inflammation have not been investigated. In this study, we used lipopolysaccharide (LPS) to induce inflammation in human dental pulp cells (hDPCs) to simulate an in vitro model of pulpitis. We found that LPS markedly induced the GPR55 expression in hDPCs. Treatment with the GPR55 antagonist ML-193 ameliorated the LPS-caused decrease in cell viability and increase in lactate dehydrogenase release. The upregulated inflammatory cytokines, interleukin-6 (IL-6) and tumour necrosis factor α, in LPS-challenged hDPCs were also attenuated by ML-193. Treatment with ML-193 ameliorated LPS-induced production of the inflammatory mediators cyclooxygenase-2/prostaglandin E2 (COX-2/PGE2), and inducible nitric oxide synthase/nitric oxide (iNOS/NO) in hDPCs. ML-193 also inhibited the activation of Toll-like receptor 4-myeloid differentiation primary response 88-nuclear factor-κB (TLR4-Myd88-NF-κB) signaling in LPS-induced hDPCs via decreased expressions of TLR4, Myd88, and p-NF-κB 65. Our study provides evidence that the GPR55 antagonist ML-193 exhibited anti-inflammatory activity in LPS-stimulated hDPCs through inhibiting TLR4-Myd88-NF-κB signaling. The results imply that ML-193 might be a novel agent for pulpitis.