Opioid receptor gene expression in human neuroblastoma SH-SY5Y cells following tapentadol exposure.

Recent studies showed that combination of mu opioid receptor (MOP) agonism and monoamine reuptake inhibition may improve the therapeutic effect of opioids by reducing requirement for MOP activation. Tapentadol, showing such a combined mechanism of action, exhibits delayed analgesic tolerance development compared to pure MOP agonists. Here we investigated how opioid receptors are regulated following different schedules (two ranges of concentrations for 24 and 48 h) of tapentadol exposure in vitro in SH-SY5Y cells. MOP and nociceptin/orphaninFQ (NOP) receptor gene expressions were quantified using qReal-Time PCR. Moreover, studies were performed in U2 cells to assess tapentadol effect on MOP internalization compared with morphine and DAMGO. Ten and 100 nM tapentadol for 48 h induced a significant increase of MOP gene expression; cells exposed to 100 μM tapentadol for 24 and 48 h showed a significant increase of MOP mRNA levels. NOP gene expression showed a significant decrease following tapentadol at all low concentrations used after 24 h and at high concentrations (45 and 60 μM) after 24 h and (60 μM) after 48 h. Differently from DAMGO, tapentadol or morphine showed no effects on MOP internalization. This study suggests that tapentadol affects MOP and NOP gene expression and MOP internalization showing a pattern distinct from classical MOP agonists. Whether these differences can explain the improved therapeutic profile of tapentadol remains to be investigated.