• Hui Fan, Teng-Fei Li, Nian Gong, and Yong-Xiang Wang.
• King's Lab, Shanghai Jiao Tong University School of Pharmacy, 800 Dongchuan Road, Shanghai, 200240, China.
• Neuropharmacology. 2016 Feb 1; 101: 98-109.

AbstractLamiophlomis rotata (L. rotata, Duyiwei) is an orally available Tibetan analgesic herb widely prescribed in China. Shanzhiside methylester (SM) is a principle effective iridoid glycoside of L. rotata and serves as a small molecule glucagon-like peptide-1 (GLP-1) receptor agonist. This study aims to evaluate the signal mechanisms underlying SM anti-allodynia, determine the ability of SM to induce anti-allodynic tolerance, and illustrate the interactions between SM and morphine, or SM and β-endorphin, in anti-allodynia and anti-allodynic tolerance. Intrathecal SM exerted dose-dependent and long-lasting (>4 h) anti-allodynic effects in spinal nerve injury-induced neuropathic rats, with a maximal inhibition of 49% and a projected ED50 of 40.4 μg. SM and the peptidic GLP-1 receptor agonist exenatide treatments over 7 days did not induce self-tolerance to anti-allodynia or cross-tolerance to morphine or β-endorphin. In contrast, morphine and β-endorphin induced self-tolerance and cross-tolerance to SM and exenatide. In the spinal dorsal horn and primary microglia, SM significantly evoked β-endorphin expression, which was completely prevented by the microglial inhibitor minocycline and p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. SM anti-allodynia was totally inhibited by the GLP-1 receptor antagonist exendin(9-39), minocycline, β-endorphin antiserum, μ-opioid receptor antagonist CTAP, and SB203580. SM and exenatide specifically activated spinal p38 MAPK phosphorylation. These results indicate that SM reduces neuropathic pain by activating spinal GLP-1 receptors and subsequently stimulating microglial β-endorphin expression via the p38 MAPK signaling. Stimulation of the endogenous β-endorphin expression may be a novel and effective strategy for the discovery and development of analgesics for the long-term treatment of chronic pain.Copyright © 2015 Elsevier Ltd. All rights reserved.

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