ABSTRACT
BACKGROUND: The effect of opioids on nitric oxide (NO)- and peroxynitrite-induced neuronal cell death is largely unknown. In the present study, we examined the effect of morphine on NO- and peroxynitrite-induced cell death using a human neuroblastoma SH-SY5Y cell line, which abundantly expresses micro, delta, kappa-opioid receptors. METHODS: The cultured cells were pretreated with morphine and exposed to 3-morpholinosydnonimine (SIN-1) that simultaneously generates NO and superoxide, thus possibly forming peroxynitrite. The cell damage was assessed by using MTT assay and crystal violet staining. Morphological nuclear changes and enzymatic evidences of apoptosis of the cells after exposure to SIN-1 for 24 hours were evaluated by using 4', 6-diamidino-2-phenylindole (DAPI) staining and the measurement of pro-apoptotic protease (caspase-3) activity, respectively. Levels of reduced glutathion (GSH) were measured by monochloronimane (MCB) assay. RESULTS: Pretreatment of SH-SY5Y with morphine significantly inhibited the apoptotic cell death. Morphine also inhibited SIN-1-induced caspase-3 (pro-apoptotic protease) activity in a dose-dependent manner. However, naloxone (20 microM) could not antagonize completely the effect of morphine in SIN- 1-induced cell death. Pre-administered GSH and N-acetylcysteine (NAC) have been found to protect SIN-induced apoptosis, and the neuroblastoma cells treated with morphine had significantly elevated the levels of GSH. CONCLUSIONS: The present study shows that morphine protects the human neuroblastoma cell line SH- SY5Y from peroxynitrite-induced apoptotic cell death through elevated GSH levels. The protective actionof morphine seems to be associated with inhibition of the apoptotic pathway. However, it is suggested that morphine protects the cells possibly via other unknown mechanisms in addition to the activation of opioid receptors.