The opioid peptide biphalin modulates human corneal epithelial wound healing in vitro

Purpose: Analgesic drugs, including nonselective opioids and non-steroidal anti-inflammatory drugs, should be used with great precautions to relieve pain after trauma to the corneal epithelium because of their unfavorable effects on wound healing. Biphalin is a synthetic opioid peptide that has been demonstrated to possess a strong analgesic effect on rodents. The purpose of this study is to investigate the effects of biphalin on human corneal epithelial wound healing. Methods: An immortalized human corneal epithelial cell (HCEC) culture was used to analyze the effects of biphalin on wound healing. The toxicity of biphalin at various concentrations was measured by the MTT assay. The effects of 1 μM and 10 μM biphalin on wound closure, cell migration and proliferation were tested in an in vitro scratch assay of HCECs. Naloxone, a non-selective competitive opioid receptor antagonist, was also used to inhibit the effects of biphalin in all experiments. Results: Biphalin did not cause any toxic effect on HCECs at concentrations lower than 100 μM at various incubation time points. Biphalin significantly increased wound healing at 1 μM concentration in an in vitro scratch assay of HCECs (P < 0.05). It also significantly increased migration of HCECs (P < 0.01). There was no significant difference between the biphalin and control groups of HCECs in the Ki67 proliferation assay. Conclusion: Biphalin, which is a synthetic opioid peptide, promotes corneal epithelial wound healing by increasing cell migration. This role should be evaluated in further in vivo and clinical studies.