Shekher Mohan*, Tanner Robinson, Noah Allen, Lance Armstrong and Sarah Stevens
Study background: Heme and its catabolized form, hemin, are cytotoxic due to their ability to contribute to the production of reactive oxygen species, increase intracellular calcium levels and stimulate glutamate mediatedexcitotoxicity. Previous work has shown that activation of the opioid receptors (i.e., mu, kappa and delta) is neuroprotective against ischemia-induced neuronal death and neurotoxicity induced by A β oligomers in vitro. However, the role of these opioid receptor in hemin toxicity remains unclear. Activation of the Mu-receptor results in decreased 3, 5’-cyclic adenosine monophosphate (cAMP) and adenylyl cyclase activity, which then results in reduced cAMP-dependent Ca2+ influx. Therefore, we hypothesized that the activation of the opioid receptors by morphine may decrease hemin toxicity.
Methods: The human neuroblastoma SK-N-SH and human astroglia A172 cells were treated with hemin (3.125, 6.25, 12.5, 25, 50 and 75 μM) for 18 h. In separate experiments, both cells types were pre- and co-treated with opioid receptor agonist morphine (10 μM) and hemin (75 μM) or naltrexone (10 μM) alone and pre- and cotreatment with hemin (75 μM) for 18 h. Cell viability was assessed using two assays, LDH and the number of live cells measured using the Calcein-AM.
Results: In both SK-N-SH and A172 cells, hemin-dose dependently induced significant cell death compared to the vehicle control. When pre-treated and co-treated with morphine, hemin toxicity in both cell types was significantly attenuated. The protection mediated by morphine from hemin was blocked by opioid antagonist, naltrexone.
Conclusion: Together, the results suggest that activation of the opioid receptors my morphine is protective against hemin toxicity in vitro and these findings suggest that cytoprotection may occur through the cAMP-AC pathway. Therefore, activation of for example the Mu-receptor could be used to minimize neuronal and glial damage following exposure to supraphysiological levels of hemin.
