Abstract
Background: Morphine dependence and the subsequent withdrawal syndrome restrict its clinical use in management of chronic pain. The precise mechanism for the development of dependence is still elusive. Thalidomide is a glutamic acid derivative, recently has been reconsidered for its clinical use due to elucidation of different clinical effects. Phosphoinositide 3-kinase (PI3K) is an intracellular transducer enzyme, which activates Akt that in turns increases the level of nitric oxide. It is well established that elevated levels of nitric oxide has a pivotal role in the development of morphine dependence. In the present study, we aimed to explore the effect of thalidomide on the development of morphine dependence targeting PI3K/Akt (PKB) and nitric oxide (NO) pathways.
Methods: Male NMRI mice and human glioblastoma T98G cell line were used to study the effect of thalidomide on morphine dependence. In both models, the consequent effect of thalidomide on PI3K/Akt and/or NO signaling in morphine dependence was determined using behavioral tests, cell toxicity, metabolite measurement, quantitative real time reverse transcription-PCR, and western blot analysis. Statistical differences between various groups were analyzed using one-way ANOVA followed by Tukey's post-hoc test. P<0.05 was considered statistically significant in all experiments.
Results: Thalidomide alone or in combination with PI3K inhibitor, Akt inhibitor, or nitric oxide synthase (NOS) inhibitors significantly reduced naloxone induced withdrawal signs in morphine dependent mice (P<0.05). Also, the levels of nitrite in hippocampus of morphine dependent mice were significantly reduced by thalidomide in compared to vehicle treated morphine dependent mice (P<0.05). In T98G human glioblastoma cells, thalidomide alone or in combination with PI3K and Akt inhibitors significantly reduced iNOS expression in comparison to the morphine treated cells. Also, morphine-induced p-Akt was suppressed when T98G cells were pretreated with thalidomide.
Conclusions: Our results suggest that morphine induces Akt, which has a crucial role in the induction of NOS activity, leading to morphine dependence. Moreover, these data indicate that thalidomide attenuates the development of morphine dependence in vivo and in vitro by inhibition of PI3K/Akt and nitric oxide signaling pathways.
