Angiotensin II receptor type 1 blocker candesartan improves morphine tolerance by reducing morphine-induced inflammatory response and cellular activation of BV2 cells via the PPAR?/AMPK signaling pathway

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 transcription-quantitative PCR (RT-qPCR) and western blotting. The levels of the inflammatory cytokines tumor necrosis factor-alpha, interleukin (IL)-1 beta and IL-6 were subsequently detected by ELISA and western blotting. In addition, immunofluorescence analysis, western blotting and RT-qPCR were used to detect the expression levels of the BV2 cell activation marker, ionized calcium-binding adaptor molecule 1 (IBA-1). Western blotting was also used to detect the expression levels of peroxisome proliferator-activated receptor-gamma/AMP-activated protein kinase (PPAR gamma/AMPK) signaling pathway-associated proteins. Finally, the cells were treated with the PPAR gamma 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 IBA-1 in morphine-induced BV2 cells in a dose-dependent manner. These processes may be associated with activation of the PPAR gamma/AMPK signaling pathway. Taken together, the present study revealed that treatment with candesartan reduced morphine-induced inflammatory response and cellular activation of BV2 cells via PPAR gamma/AMPK signaling.