Tear Opiorphin Levels in Ocular Pain Caused by Corneal Foreign Body

Abstract

Purpose: Opiorphin is an endogenous inhibitor of enkephalin-degrading enzymes. It has a strong analgesic effect in chemical and mechanical pain models. We aimed to evaluate the tear opiorphin levels in ocular pain caused by corneal foreign bodies and demonstrate whether there is any correlation with pain levels obtained from the Visual Analog Scale (VAS) score and tear opiorphin level. Methods: Thirty-two healthy individuals and 34 individuals diagnosed with corneal foreign bodies were included in this study. Tear opiorphin levels were measured by the ELISA method using a commercially available kit. The difference in tear opiorphin levels between the patient and control groups were evaluated using the Mann–Whitney U test. The correlation between VAS scores and tear opiorphin levels was evaluated using the Spearman rank correlation coefficient. Results: The median values of tear opiorphin levels of the patient and control groups were 134 pg/mL (86.86–296.25) and 109.80 pg/mL (66.15–191.49), respectively. The Mann–Whitney U test showed a statistically significant difference in tear opiorphin levels between patient and control groups (P < 0.05). No ocular pain was reported in the control group. The median VAS score of the patient group was 6 points (1–9). No correlation was found between VAS scores and tear opiorphin levels in the patient group. Conclusions: The cornea is the most densely innervated tissue, and the highest opiorphin concentrations have been observed in tear. It is, therefore, expected that the stimulation or damage to the nerve endings in cornea would cause an increase in opiorphin secretion as a pain relief mechanism.

New Perspectives in the Pathophysiology and Treatment of Pain in Patients with Dry Eye Disease

“…Salaric et al reported an increase in salivary opiorphin in patients with burning mouth syndrome [ 33 ], while, more recently, Ozdogan et al described an increase in salivary opiorphin in patients with dental pain caused by pulp inflammation [ 34 ]. Opiorphin levels were reported to be increased in the tears of patients with ocular pain caused by a corneal foreign body [ 35 ]. This suggests that opiorphin may play a role in the modulation of orofacial and eye pain [ 8 , 35 ].…”

“…Opiorphin levels were reported to be increased in the tears of patients with ocular pain caused by a corneal foreign body [ 35 ]. This suggests that opiorphin may play a role in the modulation of orofacial and eye pain [ 8 , 35 ]. Opiorphin reduces pain caused by different origins in a manner comparable, if not greater, to morphine in terms of both efficacy and potency [ 30 , 36 ].…”

GlicoPro, Novel Standardized and Sterile Snail Mucus Extract for Multi-Modulative Ocular Formulations: New Perspective in Dry Eye Disease Management

“…Inflammation of the ocular surface can result in damage to the corneal sub-basal nerve plexus, which detects mechanical, thermal, and chemical stimuli, and generates output perceivable as pain or a range of dysesthesias [34]. Our results indicated the presence of opiorphin in the protein supply of GlicoPro at the same concentration that is normally present in tears [12]. This peptide, which acts as a natural potent non-opioid endogenous analgesic, may have therapeutic effects on the neurosensory abnormalities responsible for DED symptoms such as NP.…”

“…Opiorphin is also secreted in tears, where it prevents the degradation of encephalins, and thus inhibits pain perception [10,11]. Ozdogan et al reported that opiorphin levels are increased in patients diagnosed with corneal foreign objects compared with healthy individuals, suggesting that opiorphin secretion increases in response to pain [12].…”

Topical Therapeutic Options in Corneal Neuropathic Pain

“…Enkephalins are associated with an analgesic effect, but their action is relatively short-lived due to the presence of enzymes that rapidly degrade these neuropeptides. Endogenous inhibitors of enkephalin enzymes do exist and are present in foreign body models of ocular pain (Ozdogan et al, 2020;Lasagni Vitar et al, 2021). Thus, pharmacologic inhibition of such enzymes may be a therapeutic target.…”