Insulin-regulated aminopeptidase inhibitor C9 restores cellular activity in methadone-damaged primary cell cultures.

Insulin-regulated aminopeptidase (IRAP) is emerging as a pharmaceutical target for treatment of neurotoxic- and neurodegenerative symptoms commonly seen in cognitive impairments. Ligands of IRAP, such as Angiotensin IV and similar analogues, bind to the active site of IRAP and causes an inhibition of its enzymatic activity, which is suggested to improve cognitive functions. Opioids are widely used in the clinic to treat for example pain and opioid use disorder, however opioid use have been associated with cognitive impairments, impaired neuronal development, and neuronal damage. To evaluate the potential of the macrocyclic IRAP inhibitor compound 9 (C9), the present study examined the restorative effects of C9 after opioid-induced cell toxicity. The toxic impact of the commonly used opioids methadone and buprenorphine was determined in rat primary hippocampal and cortical cells, along with the effects on various viability markers after subsequent treatment with C9. The metabolism of tetrazolium bromide salt (MTT) was measured to assess mitochondrial activity, and the level of membrane damage was assessed by measuring lactate dehydrogenase (LDH) in the cell media. Fluorescent calcein dye was used to evaluate intracellular esterase activity. In conclusion, this study demonstrate that methadone and buprenorphine induce toxic effects in primary hippocampal and cortical cell cultures and that IRAP inhibitor C9 has a restorative effect on intracellular esterase activity in methadone-damaged cells.