ABSTRACT
Morphine is the most common drug of choice in clinical pain management; however, morphine tolerance presents a significant clinical challenge. The pathogenesis of morphine tolerance is known to be closely associated with angiotensin II receptor type 1 (AT1R) in microglia. As an AT1R antagonist, candesartan may serve an important role in regulating morphine tolerance. Therefore, the present study aimed to investigate the role of candesartan in morphine tolerance, and to explore the underlying mechanism. To meet this aim, BV2 microglial cells were treated with morphine or candesartan alone, or as a combination, and the expression levels of AT1R in BV2 cells were detected by reverse transcriptionquantitative PCR (RTqPCR) and western blotting. The levels of the inflammatory cytokines tumor necrosis factorα, interleukin (IL)1ß and IL6 were subsequently detected by ELISA and western blotting. In addition, immunofluorescence analysis, western blotting and RTqPCR were used to detect the expression levels of the BV2 cell activation marker, ionized calciumbinding adaptor molecule 1 (IBA1). Western blotting was also used to detect the expression levels of peroxisome proliferatoractivated receptorγ/AMPactivated protein kinase (PPARγ/AMPK) signaling pathwayassociated proteins. Finally, the cells were treated with the PPARγ antagonist GW9662 and the AMPK inhibitor compound C to further explore the mechanism underlying the effects of candesartan on improving morphine tolerance. The expression levels of AT1R were revealed to be significantly increased following morphine induction; however, candesartan treatment inhibited the expression levels of AT1R, the levels of inflammatory cytokines and the protein expression levels of IBA1 in morphineinduced BV2 cells in a dosedependent manner. These processes may be associated with activation of the PPARγ/AMPK signaling pathway. Taken together, the present study revealed that treatment with candesartan reduced morphineinduced inflammatory response and cellular activation of BV2 cells via PPARγ/AMPK signaling.