The non‐peptide GLP‐1 receptor agonist WB4‐24 blocks inflammatory nociception by stimulating β‐endorphin release from spinal microglia

Abstract

BACKGROUND AND PURPOSETwo peptide agonists of the glucagon-like peptide-1 (GLP-1) receptor, exenatide and GLP-1 itself, exert anti-hypersensitive effects in neuropathic, cancer and diabetic pain. In this study, we have assessed the anti-allodynic and anti-hyperalgesic effects of the non-peptide agonist WB4-24 in inflammatory nociception and the possible involvement of microglial β-endorphin and pro-inflammatory cytokines. EXPERIMENTAL APPROACHWe used rat models of inflammatory nociception induced by formalin, carrageenan or complete Freund's adjuvant (CFA), to test mechanical allodynia and thermal hyperalgesia. Expression of β-endorphin and pro-inflammatory cytokines was measured using real-time quantitative PCR and fluorescent immunoassays. KEY RESULTSWB4-24 displaced the specific binding of exendin (9-39) in microglia. Single intrathecal injection of WB4-24 (0.3, 1, 3, 10, 30 and 100 μg) exerted dose-dependent, specific, anti-hypersensitive effects in acute and chronic inflammatory nociception induced by formalin, carrageenan and CFA, with a maximal inhibition of 60-80%. Spinal WB4-24 was not effective in altering nociceptive pain. Subcutaneous injection of WB4-24 was also antinociceptive in CFA-treated rats. WB4-24 evoked β-endorphin release but did not inhibit expression of pro-inflammatory cytokines in either the spinal cord of CFA-treated rats or cultured microglia stimulated by LPS. WB4-24 anti-allodynia was prevented by a microglial inhibitor, β-endorphin antiserum and a μ-opioid receptor antagonist. CONCLUSIONS AND IMPLICATIONSOur results suggest that WB4-24 inhibits inflammatory nociception by releasing analgesic β-endorphin rather than inhibiting the expression of proalgesic pro-inflammatory cytokines in spinal microglia, and that the spinal GLP-1 receptor is a potential target molecule for the treatment of pain hypersensitivity including inflammatory nociception.

Morroniside, a secoiridoid glycoside from Cornus officinalis, attenuates neuropathic pain by activation of spinal glucagon‐like peptide‐1 receptors

“…We previously showed the presence and absence of human GLP‐1 receptors on HEK293 cells and HEK293T cells using immunofluorescence staining, and the protective effect of exenatide against loss of cell viability induced by hydrogen peroxide in HEK293 cells but not in HEK293T cells (Fan et al ., ). Morroniside was further employed to test whether it could activate GLP‐1 receptors in HEK293 cells.…”

“…Beside its clinical utility against diabetes mellitus, activation of GLP‐1 receptors also exhibits neuroprotection in several animal models of neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, peripheral neuropathy, multiple sclerosis, ischaemia and stroke (Kim et al ., ; Harkavyi and Whitton, ; Holscher, ; Hansen et al ., ; Jia et al ., ). Moreover, activation of spinal GLP‐1 receptors by the peptide agonists GLP‐1(7‐37) and exenatide and the non‐peptide agonist WB4‐24 was shown to produce antinociception in a variety of rodent models of pain hypersensitivity, including neuropathic pain, inflammatory pain, bone cancer pain and diabetic neuropathic pain, through spinal β‐endorphin expression and secretion (Zhu et al ., ; Gong et al ., ; Gong et al ., ; Fan et al ., ; Fan et al ., ).…”

Bullatine A stimulates spinal microglial dynorphin A expression to produce anti-hypersensitivity in a variety of rat pain models

“…The concentration of minocycline was based on the previous references [26–29]. The second treatment was administered 1 h after the first treatment, and the microglia were collected 6 h later.…”

Neuropeptides and Microglial Activation in Inflammation, Pain, and Neurodegenerative Diseases

“…Of the opioid receptors so far identified, microglia express μ - and κ -receptors, but not δ -receptors, and an additional opioid receptor-independent pathway may also exist for endogenous opioid receptor ligands [17, 55–57]. However, activation of the GLP-1 receptor/ β -END pathway does not inhibit proinflammatory cytokine production in cultured microglia stimulated by LPS [94]. On the contrary, β -END has been shown to directly enhance basal and GP-120-induced TNF- α , IL-1 β , and IL-6 release in brain perivascular microglia, where it also enhances replication of the human immunodeficiency virus (HIV), effects that are blocked by an opioid receptor antagonist [95].…”