Effect of neuropeptides on human dental pulp cells; mRNA expression of proinflammatory cytokines

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An investigation of the interactions between neuropeptides and dental pulp cells is critical in elucidating the cellular mechanism of pulpitis. We investigated the effect of neuropeptide stimulation on the mRNA expressions of proinflammatory cytokines in human dental pulp cells. Human dental pulp cells (HDPC) were collected from first premolars extracted for orthodontic reasons. The HDPC were cultured in 10% FBS-containing Dulbecco's Modified Eagle's Medium (DMEM) to subconfluence. Third-passage cells were used for the experiment. Substance P (SP) and calcitonin gene-related peptide (CGRP) were used as neuropeptides. The mRNA expression of the proinflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α were quantified at 6 and 24 hours. In HDPC, the neuropeptides increased the mRNA expression of only IL-8 among the proinflammatory cytokines. At six hours after stimulation, the IL-8 mRNA expression of the SP 10^<-5>M, SP 10^<-4>M, and CGRP 10^<-6>M groups were significantly different from that of the negative control (p<0.05). The IL-8 mRNA expression of the SP 10^<-4>M+CGRP 10^<-6>M group was significantly increased (p<0.05). However, no synergistic effect was noted. Regarding the effect of neuropeptides on the dental pulp, the IL-8 mRNA expression induced localized neutrophil infiltration.