Little Joshua W, Ford Amanda, Symons-Liguori Ashley M, Chen Zhoumou, Janes Kali, Doyle Timothy, Xie Jennifer, Luongo Livio, Tosh Dillip K, Maione Sabatino, Bannister Kirsty, Dickenson Anthony H, Vanderah Todd W, Porreca Frank, Jacobson Kenneth A, Salvemini Daniela
1 Saint Louis University School of Medicine, Saint Louis, MO USA.
2 University of Arizona, Department of Pharmacology and Anesthesiology, Tucson, AZ USA.
Brain. 2015 Jan;138(Pt 1):28-35. doi: 10.1093/brain/awu330. Epub 2014 Nov 19.
Chronic pain is a global burden that promotes disability and unnecessary suffering. To date, efficacious treatment of chronic pain has not been achieved. Thus, new therapeutic targets are needed. Here, we demonstrate that increasing endogenous adenosine levels through selective adenosine kinase inhibition produces powerful analgesic effects in rodent models of experimental neuropathic pain through the A3 adenosine receptor (A3AR, now known as ADORA3) signalling pathway. Similar results were obtained by the administration of a novel and highly selective A3AR agonist. These effects were prevented by blockade of spinal and supraspinal A3AR, lost in A3AR knock-out mice, and independent of opioid and endocannabinoid mechanisms. A3AR activation also relieved non-evoked spontaneous pain behaviours without promoting analgesic tolerance or inherent reward. Further examination revealed that A3AR activation reduced spinal cord pain processing by decreasing the excitability of spinal wide dynamic range neurons and producing supraspinal inhibition of spinal nociception through activation of serotonergic and noradrenergic bulbospinal circuits. Critically, engaging the A3AR mechanism did not alter nociceptive thresholds in non-neuropathy animals and therefore produced selective alleviation of persistent neuropathic pain states. These studies reveal A3AR activation by adenosine as an endogenous anti-nociceptive pathway and support the development of A3AR agonists as novel therapeutics to treat chronic pain.
慢性疼痛是一种全球性负担,会导致残疾和不必要的痛苦。迄今为止,尚未实现对慢性疼痛的有效治疗。因此,需要新的治疗靶点。在此,我们证明通过选择性抑制腺苷激酶来提高内源性腺苷水平,可在实验性神经病理性疼痛的啮齿动物模型中通过A3腺苷受体(A3AR,现称为ADORA3)信号通路产生强大的镇痛作用。给予一种新型且高度选择性的A3AR激动剂也获得了类似的结果。这些作用可通过阻断脊髓和脊髓上的A3AR来预防,在A3AR基因敲除小鼠中消失,且独立于阿片类和内源性大麻素机制。A3AR激活还可缓解非诱发的自发疼痛行为,而不会促进镇痛耐受性或产生内在奖赏。进一步研究表明,A3AR激活通过降低脊髓广动力范围神经元的兴奋性,并通过激活血清素能和去甲肾上腺素能延髓脊髓回路对脊髓伤害性感受产生脊髓上抑制,从而减少脊髓疼痛处理。至关重要的是,激活A3AR机制不会改变非神经病变动物的伤害性感受阈值,因此可选择性缓解持续性神经病理性疼痛状态。这些研究揭示了腺苷激活A3AR作为一种内源性抗伤害感受途径,并支持将A3AR激动剂开发为治疗慢性疼痛的新型疗法。