BACKGROUND: In previous studies, we have attributed opiate alkaloid selectivityto a subtype of the neuronal mu receptor known as mu3, expressed on human blood cells. Opiate alkaloidactivation of this receptor subtype leads to the release of constitutively derived nitric oxide. In thisreport, we show by real-time RT-PCR that the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) initiatesthe down regulation of mu receptor gene expression in human mononuclear cells after 30 minutes. Superoxidedismutase, a free radical scavenger, blocks the effect of SNAP. MATERIAL AND METHODS: Human mononuclearcells isolated from whole blood were treated with SNAP (100 microM), and also with SNAP plus superoxidedismutase (100 U/ml) at different time points. Real-time RT-PCR with total RNA extracted from the cellswas used to analyze expression of the mu opiate receptor. RESULTS: Mu opiate receptor gene expressionwas significantly down regulated in cells treated with SNAP at 30 min, and superoxide dismutase blockedthe effect of SNAP. At 2 and 6 hours, a rebound effect was observed as noted by an increase in mu receptorexpression, and at 24 hours mu receptor expression returned to control levels in the SNAP-treated cells.CONCLUSIONS: This study confirms that human mononuclear cells express the mu opiate receptor transcriptand demonstrates that nitric oxide is involved in regulation of its expression.

Keywords: Poly(ethylene glycol), liposome, Drug Delivery, protein adsorption, dysopsonization