Opiorphin Response to Capsaicin Is Altered in Temporomandibular Disorder Patients
Objectives: Human opiorphin is an endogenous anti-nociceptive modulator of opioid-dependent pathways whose function might be altered in chronic pain. The aim of the study was to compare the differences in salivary opiorphin response to burning sensations caused by tongue-applied capsaicin between patients with chronic temporomandibular disorders (TMD) and healthy controls.
Methods: A total of 32 volunteers participated, 16 in each group (TMD, control). To generate the burning sensation, a series of capsaicin-soaked paper discs were applied to the tongue every 30 seconds for 5 minutes. Saliva samples for opiorphin quantification were collected three times: before, right after (end of 5th minute) and 20 min after capsaicin application. The intensity of burning sensations was recorded using a numerical pain rating scale (NPRS) over a 25-minute period. Opiorphin levels were measured using HPLC-MS/MS.
Results: Patients in both groups didn’t differ in age, hypervigilance, or somatosensory amplification (p>0.05). Significant differences in opiorphin levels were present in all 3 measuring points between TMD and the control group with significantly higher levels in the TMD group (p<0.001). Subjective reporting of experimental burning sensation intensity (NPRS) didn’t differ between the groups (p>0.05); however, the increase in opiorphin levels following the capsaicin stimulation was observed only in the TMD group while in the control group levels didn’t change.
Conclusions: Higher opiorphin levels and an additional increase of opiorphin levels after capsaicin stimulation in TMD patients indicate the potential involvement of endogenous opioids in chronic pain mechanism and, therefore, the initiation and perpetuation of TMD.