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Mechanisms of Stem Cell-mediated Antinociception

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      Management of post-endodontic pain with NSAIDs and opioids are associated with serious side effects. Stem cells participate in wound healing; however, their role in regulation of nociception presents a gap in knowledge. This study sought to evaluate mechanisms of Stem Cells of Apical Papilla (SCAP)-mediated reversal of apical periodontitis (AP)-induced mechanical allodynia (MA). Using a mouse model of AP, we first established a model of orofacial MA using von Frey filaments. Post-baseline thresholds, pre-labeled SCAP were injected intravenously in one-half of AP animals once/week for 3 weeks; Sham animals served as controls; MA was measured 24 hours post injections. Immunohistochemistry of periapical lesions and medullary dorsal horn (MDH) was performed for expression of SCAP and nociceptive marker, c-fos. Teeth with AP were extracted at 3 weeks and co-cultured with or without SCAP. Conditioned Media (CM) was collected and applied to mouse cultured trigeminal neurons (TGs) followed by application of capsaicin (15nM; CAP) to evaluate TG nociceptor activity using calcium-imaging. Statistics: 2-way ANOVA with Tukey's post-hoc test. MA peaked at day 21 in AP mice. This effect was fully reversed by SCAP injections. Immunohistochemistry demonstrated SCAP homing into periapical lesions with no expression in the MDH. AP mice showed robust expression of c-fos in the MDH, which was drastically reduced after SCAP injections. Lastly, CM from Teeth alone sensitized CAP-evoked calcium accumulation. However, CM from Teeth co-cultured with SCAP significantly reduced CAP sensitization. Collectively, this study, for the first time establishes a model of MA in mice with AP, which is reversed by SCAP. This appears to be a peripheral effect as SCAP homed to periapical lesions and data from calcium-imaging suggest that SCAP release soluble factors in the periphery that inhibit TG activity. These findings provide significant insight into mechanisms of stem cell-mediated analgesia. Start-up funds (PID 156778).
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