PMID- 27855689 OWN - NLM STAT- MEDLINE DCOM- 20171006 LR - 20220410 IS - 1742-2094 (Electronic) IS - 1742-2094 (Linking) VI - 13 IP - 1 DP - 2016 Nov 17 TI - Metformin reduces morphine tolerance by inhibiting microglial-mediated neuroinflammation. PG - 294 LID - 294 AB - BACKGROUND: Tolerance seriously impedes the application of morphine in clinical medicine. Thus, it is necessary to investigate the exact mechanisms and efficient treatment. Microglial activation and neuroinflammation in the spinal cord are thought to play pivotal roles on the genesis and maintaining of morphine tolerance. Activation of adenosine monophosphate-activated kinase (AMPK) has been associated with the inhibition of inflammatory nociception. Metformin, a biguanide class of antidiabetic drugs and activator of AMPK, has a potential anti-inflammatory effect. The present study evaluated the effects and potential mechanisms of metformin in inhibiting microglial activation and alleviating the antinociceptive tolerance of morphine. METHODS: The microglial cell line BV-2 cells and mouse brain-derived endothelial cell line bEnd3 cells were used. Cytokine expression was measured using quantitative polymerase chain reaction. Cell signaling was assayed by western blot and immunohistochemistry. The antinociception and morphine tolerance were assessed in CD-1 mice using tail-flick tests. RESULTS: We found that morphine-activated BV-2 cells, including the upregulation of p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation, pro-inflammatory cytokines, and Toll-like receptor-4 (TLR-4) mRNA expression, which was inhibited by metformin. Metformin suppressed morphine-induced BV-2 cells activation through increasing AMPK phosphorylation, which was reversed by the AMPK inhibitor compound C. Additionally, in BV-2 cells, morphine did not affect the cell viability and the mRNA expression of anti-inflammatory cytokines. In bEnd3 cells, morphine did not affect the mRNA expression of interleukin-1beta (IL-1beta), but increased IL-6 and tumor necrosis factor-alpha (TNF-alpha) mRNA expression; the effect was inhibited by metformin. Morphine also did not affect the mRNA expression of TLR-4 and chemokine ligand 2 (CCL2). Furthermore, systemic administration of metformin significantly blocked morphine-induced microglial activation in the spinal cord and then attenuated the development of chronic morphine tolerance in mice. CONCLUSIONS: Metformin significantly attenuated morphine antinociceptive tolerance by suppressing morphine-induced microglial activation through increasing AMPK phosphorylation. FAU - Pan, Yinbing AU - Pan Y AD - Department of Anesthesiology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Sun, Xiaodi AU - Sun X AD - Department of Anesthesiology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Jiang, Lai AU - Jiang L AD - Department of Pharmacology, Jiangsu Key Laboratory of Neurodegeneration, Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Hu, Liang AU - Hu L AD - Department of Pharmacology, Jiangsu Key Laboratory of Neurodegeneration, Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Kong, Hong AU - Kong H AD - Department of Pharmacology, Jiangsu Key Laboratory of Neurodegeneration, Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Han, Yuan AU - Han Y AD - Jiangsu Province Key Laboratory of Anesthesiology, School of Anesthesiology, Xuzhou Medical College, Xuzhou, Jiangsu, 221004, People's Republic of China. FAU - Qian, Cheng AU - Qian C AD - Department of Pharmacology, Jiangsu Key Laboratory of Neurodegeneration, Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Song, Chao AU - Song C AD - Department of Oncology, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People's Republic of China. FAU - Qian, Yanning AU - Qian Y AD - Department of Anesthesiology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. FAU - Liu, Wentao AU - Liu W AD - Department of Pharmacology, Jiangsu Key Laboratory of Neurodegeneration, Nanjing Medical University, Nanjing, Jiangsu, 210029, People's Republic of China. painresearch@njmu.edu.cn. LA - eng PT - Journal Article PT - Research Support, Non-U.S. Gov't DEP - 20161117 PL - England TA - J Neuroinflammation JT - Journal of neuroinflammation JID - 101222974 RN - 0 (Aif1 protein, mouse) RN - 0 (Analgesics, Opioid) RN - 0 (Calcium-Binding Proteins) RN - 0 (Cytokines) RN - 0 (Hypoglycemic Agents) RN - 0 (Microfilament Proteins) RN - 0 (NR1 NMDA receptor) RN - 0 (Receptors, N-Methyl-D-Aspartate) RN - 76I7G6D29C (Morphine) RN - 9100L32L2N (Metformin) RN - EC 2.7.11.13 (Protein Kinase C) RN - EC 2.7.11.31 (AMP-Activated Protein Kinases) SB - IM MH - AMP-Activated Protein Kinases/metabolism MH - Analgesics, Opioid/*pharmacology MH - Animals MH - Calcium-Binding Proteins/metabolism MH - Cell Line, Transformed MH - Cytokines/metabolism MH - Dose-Response Relationship, Drug MH - *Drug Tolerance MH - Hypoglycemic Agents/*pharmacology MH - Inflammation/*drug therapy/pathology MH - Macrophage Activation/drug effects MH - Metformin/*pharmacology MH - Mice MH - Microfilament Proteins/metabolism MH - Microglia/*drug effects MH - Morphine/*pharmacology MH - Phosphorylation/drug effects MH - Protein Kinase C/metabolism MH - Receptors, N-Methyl-D-Aspartate/metabolism MH - Signal Transduction/drug effects MH - Spinal Cord/cytology PMC - PMC5114746 OTO - NOTNLM OT - AMPK OT - Cytokines OT - Glia activation OT - MAPK OT - Morphine tolerance EDAT- 2016/11/20 06:00 MHDA- 2017/10/07 06:00 PMCR- 2016/11/17 CRDT- 2016/11/19 06:00 PHST- 2016/06/15 00:00 [received] PHST- 2016/10/31 00:00 [accepted] PHST- 2016/11/19 06:00 [entrez] PHST- 2016/11/20 06:00 [pubmed] PHST- 2017/10/07 06:00 [medline] PHST- 2016/11/17 00:00 [pmc-release] AID - 10.1186/s12974-016-0754-9 [pii] AID - 754 [pii] AID - 10.1186/s12974-016-0754-9 [doi] PST - epublish SO - J Neuroinflammation. 2016 Nov 17;13(1):294. doi: 10.1186/s12974-016-0754-9.