Purpose: The expression pattern of the opioid receptor (MOR) in pituitary neuroendocrine tumors (PitNET) and the possible effect of morphine and naloxone on GH3 cell growth and apoptosis were evaluated.
Methods: The 114 pituitary tissues including non-functioning, GH-producing and ACTH-producing PitNET and healthy cadaver pituitary tissues were included. The expression level of the MOR gene and protein was assessed using real-time PCR and Western blot. The association with patient demographic characteristics was assessed. Morphine and naloxone were applied to assess their possible pharmacological role in GH3 pituitary adenoma cell death. The cytotoxic effect, the apoptosis rate, the cell cycle distribution, the content of reactive oxygen species and the caspase 3 activity were measured.
Results: MOR gene levels increased significantly in pituitary neuroendocrine tumors (PitNET) compared to the healthy pituitary samples. The increased level of MOR gene expression was prominent in invasive functional and non-functional pituitary tumors. A consistent expression pattern was demonstrated for MOR protein levels in PitNET samples. A dose- and time-dependent reduction in the rate of GH3 pituitary cells was observed after morphine treatment with an IC50 of 483 µM after 24 h of incubation. Morphine induced early apoptosis, accumulation of cells in sub-G1 phase, increase in cellular ROS levels and caspase-3 activity. The observed effects of morphine were reversed after MOR blockade using 10 and 25 µM naloxone.
Conclusion: The possible contributing role of the MOR in pituitary tumor cell growth and the putative pharmaceutical effect of morphine in pituitary neuroendocrine tumor cell death (PitNET) is illustrated.
Keywords: Apoptosis; GH3 cells; Morphine; Naloxone; Pituitary adenoma; μ opioid receptor.
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