ENDOGENOUS PERIPHERAL PAIN REGULATORY SYSTEMS IN OROFACIAL PAIN PATIENTS

The prevalence of endodontic pain ranges from 32-60% for irreversible pulpitis and ~60% for cases with apicalperiodontitis. Importantly, sex-related differences have been reported in these patients. Moreover, differencesalso exist in the clinical presentation with ~40% of patients with apical periodontitis experience no pain(asymptomatic patients) despite similar radiographic presentation of bone resorption as symptomatic patients.This is an important finding as the incidence of persistent pain at 1-6 years after endodontic treatment is ashigh as 10-12% of all patients, particularly given recent concerns about non-steroidal anti-inflammatory drug(NSAIDs) toxicity and opioid dependence and NIH calls for development of ?personalized medicine?. Therefore,mechanisms mediating inhibition of nociception in asymptomatic patients may reveal novel factors or pathwaysthat can be activated and therefore therapeutic in symptomatic patients. We developed a clinically translational model wherein surgical biopsies collected from patientsundergoing endodontic microsurgeries undergo biochemical and functional analyses. Our preliminary datademonstrates that 1) CM from symptomatic patients (with pain) evoked significant increases in [Ca2+]i incultured TG neurons while CM from asymptomatic patients (no-pain) did not. Moreover, CM fromasymptomatic patients also desensitized CAP-evoked [Ca2+]i ; and 2) significantly greater levels of ?-endorphinwas detected in asymptomatic periapical lesions compared to symptomatic periapical lesions. Based on citedliterature and our preliminary data, our central hypothesis is that soluble factors released from symptomaticand asymptomatic inflamed human apical tissues differentially regulate mouse TG nociceptor activities. Totest this, we propose the following aims:Specific Aim #1 will determine the functional role of CM from asymptomatic patients on regulation ofTG neuronal activity. We will test the hypothesis that factors released from periapical lesions fromasymptomatic patients inhibit TG neuronal activity. After surgical biopsy collection, we will perform thefollowing: 1) apply CM from asymptomatic patients to mouse TG neurons to measure in vitro calcitonin gene-related peptide (CGRP) release and [Ca2+]i under basal and stimulated conditions; 2) inject CM fromasymptomatic patients in mouse vibrissal pad to evaluate in vivo spontaneous pain and mechanical allodynia;3) determine if a non-opioid inhibitory system is also present by using naloxone; 4) if evidence for a non-opioidinhibitor/s is found, determine if it is a lipid or a peptide; and 5) conduct secondary analyses to identify potentialgender-differences.Specific Aim #2 will determine the functional role of CM from symptomatic on regulation of TGneuronal activity. We will test the hypothesis that factors released from periapical lesions from symptomaticpatients will activate or sensitize TG neuronal activity. After surgical biopsy collection, we will perform thefollowing: 1) apply CM from symptomatic patients to mouse TG neurons to measure in vitro CGRP release and[Ca2+]I under basal and stimulated conditions; 2) inject CM from symptomatic patients in mouse vibrissal pad toevaluate in vivo spontaneous pain and mechanical allodynia; 3) determine if the painful soluble factor/s is alipid or a peptide; 4) conduct secondary analyses to evaluate the effect of gender-differences. Overall, we believe this application has considerable significance: 1) There is a striking variation in painresponses in endodontic patients (Nixdorf et al. 2016; Polycarpou et al. 2005); 2) Development of a clinicallytranslational model to understand differences in pain states and possible sex differences would provide afoundation for a future R01 on translational mechanisms of nociceptor regulation; 3) This knowledge base mayextend to other non-painful inflammatory conditions (e.g., asymptomatic inflammatory prostatitis, asymptomaticinflammatory bowel disease, asymptomatic pelvic inflammatory diseases), increasing its medical significance.