Intrathecal injection of adenosine 2A receptor agonists reversed neuropathic allodynia through protein kinase (PK)A/PKC signaling

Abstract

A single intrathecal dose of adenosine 2A receptor (A2AR) agonist was previously reported to produce a multi-week reversal of allodynia in a chronic constriction injury (CCI) model of neuropathic pain. We aimed to determine if this long-term reversal was induced by A2AR agonism versus more generalized across adenosine receptor subtypes, and begin to explore the intracellular signaling cascades involved. In addition, we sought to identify whether the enduring effect could be extended to other models of neuropathic pain. We tested an A1R and A2BR agonist in CCI and found the same long duration effect with A2BR but not A1R agonism. An A2AR agonist (ATL313) produced a significant long-duration reversal of mechanical allodynia induced by long established CCI (administered 6 wk after surgery), spinal nerve ligation and sciatic inflammatory neuropathy. To determine if ATL313 had a direct effect on glia, ATL313 was coadministered with lipopolysaccharide to neonatal microglia and astrocytes in vitro. ATL313 significantly attenuated TNFα production in both microglia and astrocytes but had no effect on LPS induced IL-10. Protein kinase C significantly reversed the ATL313 effects on TNF in vitro in microglia and astrocytes, while a protein kinase A inhibitor only effected microglia. Both intrathecal PKA and PKC inhibitors significantly reversed the effect of the A2AR agonist on neuropathic allodynia. Therefore, A2AR agonists administered IT remain an exciting novel target for the treatment of neuropathic pain.

Pathological pain and the neuroimmune interface

“…The factors driving the recruitment and differentiation of such anti-inflammatory phenotypes are not well understood. Nociceptive hypersensitivity associated with spinal gliosis is attenuated by intrathecal administration of IL-1Ra, elevation of spinal IL-10 levels, and by systemic administration of glatiramer acetate, which increases expression of IL-4 + and IL-10 + T cells in the spinal dorsal horn 8,26,114,115 . Aside from the effects of IL-1Ra on excitatory postsynaptic current (EPSC) frequency and NR1 subunit phosphorylation, it remains to be shown whether other anti-inflammatory cytokines directly regulate central sensitization 96,101 .…”

“…The adenosine GPCRs A 2A and A 2B are expressed by peripheral immune cells and glia, and pharmacologically targeting these receptors with a single intrathecal injection of specific agonists reverses established peripheral nerve injury-nociceptive hypersensitivity for more than 4 weeks 114,115 . This therapeutic effect is dependent on the activation of protein kinase A (PKA) and protein kinase C (PKC), leading to elevated IL-10 and decreased TNF levels.…”

The therapeutic potential of interleukin-10 in neuroimmune diseases

“…Interestingly, the A2AR is upregulated on macrophages and microglia following inflammatory signals such as LPS, CpG, lipoteichoic acid, or TNF, and on lymphocytes from MS and ALS patients, providing a unique pharmacological target for immune cells and glia exclusively activated by prior proinflammatory signals (Grinberg et al, 2009; Gyoneva et al, 2009; Vincenzi et al, 2013a, 2013b). As with IL-10-based gene therapies, a single administration of A2AR agonist after the onset of CCI-induced allodynia or collagen-induced arthritis resulted in sustained suppression of disease symptoms (Loram et al, 2009, 2013; Mazzon et al, 2011). A2AR agonist effects on allodynia appear to furthermore be dependent on sustained IL-10 release, although the mechanisms underlying this effect are not fully understood (Loram et al, 2009, 2013).…”

“…As with IL-10-based gene therapies, a single administration of A2AR agonist after the onset of CCI-induced allodynia or collagen-induced arthritis resulted in sustained suppression of disease symptoms (Loram et al, 2009, 2013; Mazzon et al, 2011). A2AR agonist effects on allodynia appear to furthermore be dependent on sustained IL-10 release, although the mechanisms underlying this effect are not fully understood (Loram et al, 2009, 2013). Genetic inactivation of the A2AR has also been shown to exacerbate brain damage in the experimental autoimmune encephalomyelitis (EAE) model of MS, providing further evidence for a protective effect of A2ARs in neuroimmune diseases (Yao et al, 2012).…”

Modulating the delicate glial–neuronal interactions in neuropathic pain: Promises and potential caveats

“…ATL313 is an adenosine 2A agonist that suppresses proinflammatory cytokines while enhancing the anti-inflammatory cytokine IL-10. One intrathecal injection has been shown to reverse neuropathic pain for 4 to 6 weeks in animal models of chronic constriction nerve injury, peripheral neuropathy, spinal cord injury, and central neuropathic pain (Loram et al, 2009, 2013). Orr et al (2009) suggested that microglial motility can switch between chemoattraction and repulsion based on changes in cell surface receptor signaling.…”