Lemairamin, isolated from the Zanthoxylum plants, alleviates pain hypersensitivity via spinal α7 nicotinic acetylcholine receptors

Lemairamin (also known as wgx-50), is isolated from the pericarps of the Zanthoxylum plants. As an agonist of alpha 7 nicotinic acetylcholine receptors (alpha 7nAChRs), it can reduce neuroinflammation in Alzheimer's disease. This study evaluated its antinociceptive effects in pain hypersensitivity and explored the underlying mechanisms. The data showed that subcutaneous lemairamin injection dose-dependently inhibited formalin-induced tonic pain but not acute nociception in mice and rats, while intrathecal lemairamin injection also dose-dependently produced mechanical antiallodynia in the ipsilateral hindpaws of neuropathic and bone cancer pain rats without affecting mechanical thresholds in the contralateral hindpaws. Multiple bi-daily lemairamin injections for 7 days did not induce mechanical antiallodynic tolerance in neuropathic rats. Moreover, the antinociceptive effects of lemairamin in formalin-induced tonic pain and mechanical antiallodynia in neuropathic pain were suppressed by the alpha 7nAChR antagonist methyllycaconitine. In an alpha 7nAChR antagonist-reversible manner, intrathecal lemairamin also stimulated spinal expression of IL-10 and beta-endorphin, while lemairamin treatment induced IL-10 and beta-endorphin expression in primary spinal microglial cells. In addition, intrathecal injection of a microglial activation inhibitor minocycline, anti-IL-10 antibody, anti-b-endorphin antiserum or m-opioid receptor-preferred antagonist naloxone was all able to block lemairamin-induced mechanical antiallodynia in neuropathic pain. These data demonstrated that lemairamin could produce antinociception in pain hypersensitivity through the spinal IL-10/beta-endorphin pathway following alpha 7nAChR activation. (C) 2020 Elsevier Inc. All rights reserved.