Abstract
Background: People worldwide suffer from neuropathic pain, and indicated medications are often either not effective or induce tolerance and abuse. Therefore, there is an urgent need to identify additional therapeutic options to treat this form of pain. Nicotinic acetylcholine receptors (nAChRs), particularly α7-nAChRs, have been implicated in pain signaling. Therefore, this study was designed to investigate the extent to which the selective positive allosteric modulator (PAM) of α7 AChRs, PAM-2, modulates neuropathic pain. The working hypothesis, that PAM-2 inhibits inflammatory signaling and neuropathic pain, was tested using animal and cellular models.
Methods: The anti-neuropathic pain activity of PAM-2 was assessed in two independent murine models of neuropathic pain. Briefly, neuropathic pain was induced in adult, male CD-1 mice (n=10/condition) via i.p. administration of either streptozotocin (STZ) or oxaliplatin (OXA). After 14 days, when neuropathic pain was present, mice were administrated with PAM-2 (1.0 or 3.0 mg/kg, p.o.) or vehicle. The pain threshold was subsequently determined by the cold plate test before and 15, 30, 45, and 60 min after treatment. In addition, C20 human microglial cells were exposed to interleukin (IL)-1β (20 ng/ml) or vehicle alone, and in combination with nicotine (3 μM), PAM-2 (1-100 μM), or nicotine + PAM-2 for 24 h. After 24 h, cytokine/chemokine levels in the culture media were measured by ELISA.
Results: A single dose of PAM-2 (3.0 mg/kg) decreased both STZ- and OXA-induced neuropathic pain in mice. Repeated treatment with an inactive dose (1.0 mg/kg) of PAM-2 showed anti-pain activity in OXA-treated mice after 14, but not 7, days of treatment. Additionally, methyllycaconitine blocked the anti-pain effects elicited by PAM-2, supporting the view that a7 AChRs are instrumental in the anti-pain actions of PAM-2. Cellular experiments revealed that nicotine minimally inhibited IL-1B-induced IL-6 and interferon-gamma-induced chemotactic protein 10 expression in C20 human microglial cells, and that this inhibition was potentiated by PAM-2 (100 uM). However, we cannot rule out the possibility that PAM- 2 was cytotoxic in this cell culture model.
Conclusions: These findings indicate that a7 AChRs are involved in neuropathic pain signaling and that a7-PAMs may potentially be used therapeutically. The extent to which these protective effects involve reduced neuroinflammation remains to be determined.
Methods: The anti-neuropathic pain activity of PAM-2 was assessed in two independent murine models of neuropathic pain. Briefly, neuropathic pain was induced in adult, male CD-1 mice (n=10/condition) via i.p. administration of either streptozotocin (STZ) or oxaliplatin (OXA). After 14 days, when neuropathic pain was present, mice were administrated with PAM-2 (1.0 or 3.0 mg/kg, p.o.) or vehicle. The pain threshold was subsequently determined by the cold plate test before and 15, 30, 45, and 60 min after treatment. In addition, C20 human microglial cells were exposed to interleukin (IL)-1β (20 ng/ml) or vehicle alone, and in combination with nicotine (3 μM), PAM-2 (1-100 μM), or nicotine + PAM-2 for 24 h. After 24 h, cytokine/chemokine levels in the culture media were measured by ELISA.
Results: A single dose of PAM-2 (3.0 mg/kg) decreased both STZ- and OXA-induced neuropathic pain in mice. Repeated treatment with an inactive dose (1.0 mg/kg) of PAM-2 showed anti-pain activity in OXA-treated mice after 14, but not 7, days of treatment. Additionally, methyllycaconitine blocked the anti-pain effects elicited by PAM-2, supporting the view that a7 AChRs are instrumental in the anti-pain actions of PAM-2. Cellular experiments revealed that nicotine minimally inhibited IL-1B-induced IL-6 and interferon-gamma-induced chemotactic protein 10 expression in C20 human microglial cells, and that this inhibition was potentiated by PAM-2 (100 uM). However, we cannot rule out the possibility that PAM- 2 was cytotoxic in this cell culture model.
Conclusions: These findings indicate that a7 AChRs are involved in neuropathic pain signaling and that a7-PAMs may potentially be used therapeutically. The extent to which these protective effects involve reduced neuroinflammation remains to be determined.
| Original language | American English |
|---|---|
| State | Published - 4 Sep 2020 |
| Event | Oklahoma State University Center for Health Sciences Research Day 2020 - Oklahoma State University Center for Health Sciences College of Osteopathic Medicine, Tulsa, United States Duration: 27 Feb 2020 → 28 Feb 2020 |
Conference
| Conference | Oklahoma State University Center for Health Sciences Research Day 2020 |
|---|---|
| Country/Territory | United States |
| City | Tulsa |
| Period | 27/02/20 → 28/02/20 |