Variability in Capsaicin-stimulated Calcitonin Gene-related Peptide Release from Human Dental Pulp

Abstract

Introduction: The unique innervation and anatomic features of dental pulp contribute to the remarkable finding that any physical stimulation of pulpal tissue is painful. Furthermore, when pathological processes such as caries affect teeth and produce inflammation of the pulp, the pain experienced can be quite intense and debilitating. To better understand these underlying neurobiological mechanisms and identify novel analgesic targets for pulpally derived pain, we have developed a powerful ex vivo model using human tooth slices.

Methods: Noncarious, freshly extracted teeth were collected and sectioned longitudinally into 1-mm-thick slices containing both dental pulp and the surrounding mineralized tissues. Tooth slices from 36 patients were exposed to 60 μmol/L capsaicin to stimulate the release of calcitonin gene-related peptide (CGRP) from nerve terminals in the pulp. Patient factors were analyzed for their effects on capsaicin-stimulated CGRP release using a mixed model analysis of variance.

Results: Approximately one third of the variability observed in capsaicin-evoked CGRP release was attributable to differences between individuals. In terms of individual factors, there was no effect of anesthesia type, sex, or age on capsaicin-stimulated CGRP release. Using a within-subject study design, a significant effect of capsaicin on CGRP release was observed.

Conclusions: Capsaicin-stimulated CGRP release from dental pulp is highly variable between individuals. A within-subject study design improves the variability and maximizes the potential of this powerful translational model to test the efficacy of novel pharmacotherapeutic agents on human peripheral nociceptors.

Keywords: Calcitonin gene-related peptide; TRPV1; capsaicin; dental pulp; human tissue; pain; primary afferent; tooth slice; transient receptor potential cation channel V1; translational research.

Figure 1

Heterogeneity in capsaicin-induced CGRP release from human tooth slices. Each data point on this figure shows the mean amount of CGRP released in response to 60 uM capsaicin from individual tooth slices obtained from each subject. Some subjects only contributed a single slice, so only a single data point is shown. Release is presented as the % of total CGRP content, mean ± SEM.

Figure 2

Effect of patient factors on capsaicin-induced CGRP release from human tooth slices. The analyzed patient factors did not influence the amount of capsaicin-stimulated CGRP release from tooth slices. (A) Sex. 42 teeth were collected from 23 female patients, yielding 88 tooth slices. 16 teeth were collected from 13 male patients, yielding 29 tooth slices. (B) Anesthesia type. 26 teeth were collected from 10 patients receiving I.V. anesthesia, yielding a total of 59 tooth slices. 32 teeth were collected from 26 patients receiving only local anesthetic, yielding 58 tooth slices. (C) Dental arch. 35 maxillary molars were collected, yielding 69 tooth slices. 23 mandibular molars were collected, yielding 48 tooth slices.

Figure 3

Evaluation of CGRP release using a within-subject experimental design. Release was measured for 11 subjects. Difference in amount of CGRP released from subject matched tooth slices treated with either capsaicin (60 uM) (CAP) or vehicle (VEH). CGRP levels were normalized to total CGRP content. The slices treated with capsaicin released more CGRP than those treated with vehicle (paired two-tailed t-test, p<0.01, n=11).