Reversal of Diabetic Dry Eye by Topical Opioid Receptor Blockade Follows Dual Pathways

PURPOSE. To determine pathways in the trigeminal ganglion and corneal epithelium that are targeted by topical naltrexone (NTX) treatment for dry eye. METHODS. NTX drops were administered topically daily for 15 days to the corneal surface of male and female adult type 1 diabetic rats. Schirmer scores and corneal sensitivity were measured at baseline, 5, 10, and 15 days. Trigeminal ganglion and corneal epithelium were processed for immunohistochemistry to detect expression of opioid growth factor receptor (OGFr), Ki67, nerve growth factor, insulin-like growth factor-1, calcitonin gene-related peptide, substance P, and TNF-α. A proteomic study determined protein changes in the cornea. RESULTS. Corneal sensitivity and tear production in diabetic rats were restored to normal levels within 5 days after topical NTX. Assessment of corneal tissue after 15 days of treatment revealed that defects in OGFr expression, epithelial cell number, and Ki67⁺ expression were restored to normal by NTX. Inflammation markers (e.g., TNF-α) were reduced in tissue from diabetic rats treated with NTX. Proteomic data suggest diabetes causes dysregulation in inflammatory biological processes. The percentages of calcitonin gene-related peptide–positive neurons, but not substance P–positive neurons, in the trigeminal ganglion were increased after NTX treatment. Diabetic male and female rats responded to NTX in a comparable manner. CONCLUSIONS. Type 1 diabetes results in decreased tear production and altered corneal surface sensitivity. These complications coincide with dysregulated OGFr that maintains ocular homeostasis. Reversal of dry eye and restoration of corneal sensitivity in diabetic male and female rats after 15 days of topical treatment with NTX occur following dual pathways of increased cellular proliferation and reduction of inflammation.