Lily, P See
| Lily, P See |
Lily, P See1, Su-Min Lee1, Steven Wang2, Bekir Karabucak1, Claire, H Mitchell3
1Endodontics / Basic & Translational Sciences, University of Pennsylvania; 2Oral and Maxillofacial Surgery/Pharmacology, University of Pennsylvania, School of Dental Medicine; 3Basic & Translational Sciences, University of Pennsylvania
Introduction
Dental pain remains one of the most prevalent pain conditions, and is usually associated with pulpal injury or strain. Both mechanisms are found to trigger ATP release through Pannexin-1 channels in other tissues of the body, while extracellular ATP stimulating P2X3 receptors contributes to nociception in small sensory neurons, similar to those innervating pulp. This study probed the potential involvement of purinergic nociception in human dental pain by comparing distributions of P2X3 and Pannexin-1 proteins in symptomatic and asymptomatic pulpitis.
Methods
Patients were screened for extractions of sound teeth and teeth with moderate-to-severe caries with/without pain. A pain history and clinical examination was performed prior to extraction. Twenty-seven patients were consented, thirty teeth collected and divided into 3 groups (n=10/group) based on clinical diagnosis: normal pulp (NP), asymptomatic irreversible pulpitis (AIP), symptomatic irreversible pulpitis (SIP). Immunofluorescence staining was performed for P2X3, Pannexin-1, and neuronal marker PGP9.5. Entire pulps were imaged using confocal microscopy, with ImageJ analysis calculating mean staining intensity and percent area stained. Hematoxyin-and-eosin staining was performed to determine the histological diagnosis. Parametric data was analyzed by ANOVA, nonparametric data analyzed by a Kruskall-Wallis test. Appropriate post-hoc tests followed (p<0.05).
Results
Both P2X3 and Pannexin-1 immunoreactivity were observed as bundles and branches throughout the pulpal tissue. P2X3 was exclusively found on nerves fibers; whereas Pannexin-1 was found accompanying nerve fibers, blood vessels, and other structures throughout the pulp. With inflammation, P2X3, Pannexin-1, and PGP9.5 clustered in larger bundles. Analysis of staining intensity and area demonstrated higher expression of all antibodies in SIP, with reduced expression of P2X3 and PGP9.5 in AIP. PGP9.5 and P2X3 stained a significantly greater area in SIP samples compared to control (p<0.05), and AIP samples (p<0.01). P2X3 staining intensity was significantly increased in SIP samples compared to AIP samples (p<0.01). Histological analysis revealed that in asymptomatic teeth Pannexin-1 was only elevated in later stages of inflammation, characterized by a limited area of necrosis and dense infiltration of chronic inflammatory cells.
Conclusion
Preliminary evaluation of human pulpal samples suggests a trend towards increased expression of P2X3, Pannexin-1, and PGP9.5 in symptomatic teeth, and decreased expression of P2X3 and PGP9.5 in asymptomatic teeth. Pannexin-1 expression seems dependent on severity of inflammation.