Kali Janes

Controlling murine and rat chronic pain through A3 adenosine receptor activation

Clinical management of chronic neuropathic pain is limited by marginal effectiveness and unacceptable side effects of current drugs. We demonstrate A3 adenosine receptor (A3AR) agonism as a new target‐based therapeutic strategy. The development of mechanoallodynia in a well‐characterized mouse model of neuropathic pain following chronic constriction injury of the sciatic nerve was rapidly and dose‐depend‐ently reversed by the A3AR agonists: IB‐MECA, its 2‐chlorinated analog (Cl‐IB‐MECA), and the structurally distinct MRS1898. These effects were naloxone insensitive and thus are not opioid receptor mediated. IB‐MECA was ≥1.6‐fold more efficacious than morphine and >5‐fold more potent. In addition, IB‐MECA was equally efficacious as gabapentin (Neurontin) or amitriptyline, but respectively >350‐ and >75‐fold more potent. Besides its potent standalone ability to reverse established mechanoallodynia, IB‐MECA significantly increased the antiallodynic effects of all 3 analgesics. Moreover, neuropathic pain development in rats caused by widely used chemotherapeutics in the taxane (paclitaxel), platinum‐complex (oxaliplatin), and proteasome‐inhibitor (bortezomib) classes was blocked by IB‐MECA without antagonizing their antitumor effect. A3AR agonist effects were blocked with A3AR antagonist MRS1523, but not with A1AR (DPCPX) or A2AAR (SCH‐442416) antagonists. Our findings provide the scientific rationale and pharmacological basis for therapeutic development of A3AR agonists for chronic pain.—Chen, Z., Janes, K., Chen, C., Doyle, T., Bryant, L., Tosh, D.K., Jacobson, K.A., Salvemini, D. Controlling murine and rat chronic pain through A3 adenosine receptor activation. FASEB J. 26, 1855‐1865 (2012). www.fasebj.org

Bioenergetic deficits in peripheral nerve sensory axons during chemotherapy-induced neuropathic pain resulting from peroxynitrite-mediated post-translational nitration of mitochondrial superoxide dismutase

Summary Peroxynitrite contributes to chemotherapy‐induced neuropathic pain via post‐translational nitration and inactivation of mitochondrial superoxide dismutase ultimately leading to ATP depletion within peripheral sensory nerve axons. Abstract Many of the widely used anticancer drugs induce dose‐limiting peripheral neuropathies that undermine their therapeutic efficacy. Animal models of chemotherapy‐induced painful peripheral neuropathy (CIPN) evoked by a variety of drug classes, including taxanes, vinca alkaloids, platinum‐complexes, and proteasome‐inhibitors, suggest that the common underlying mechanism in the development of these neuropathies is mitotoxicity in primary nerve sensory axons (PNSAs) arising from reduced mitochondrial bioenergetics [eg adenosine triphosphate (ATP) production deficits due to compromised respiratory complex I and II activity]. The causative mechanisms of this mitotoxicity remain poorly defined. However, peroxynitrite, an important pro‐nociceptive agent, has been linked to mitotoxicity in several disease states and may also drive the mitotoxicity associated with CIPN. Our findings reveal that the development of mechano‐hypersensitivity induced by paclitaxel, oxaliplatin, and bortezomib was prevented by administration of the peroxynitrite decomposition catalyst Mn(III) 5,10,15,20‐tetrakis(N‐n‐hexylpyridinium‐2‐yl)porphyrin (MnTE‐2‐PyP5+) without interfering with their anti‐tumor effects. Peak CIPN was associated with the nitration and inactivation of superoxide dismutase in the mitochondria, but not in the cytosol, as well as a significant decrease in ATP production within the PNSAs; all of these events were attenuated by MnTE‐2‐PyP5+. Our results provide continued support for the role of mitotoxicity in the development of CIPN across chemotherapeutic drug classes, and identify peroxynitrite as a key mediator in these processes, thereby providing the rationale towards development of “peroxynitrite‐targeted” therapeutics for CIPN.

Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states

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.

The Development and Maintenance of Paclitaxel-induced Neuropathic Pain Require Activation of the Sphingosine 1-Phosphate Receptor Subtype 1

Background: Chemotherapy-induced peripheral neuropathy (CIPN) is a critical dose-limiting side effect of many chemotherapeutic agents, including paclitaxel. Results: Spinal activation of the S1P-to-S1PR1 axis contributes to the development and maintenance of paclitaxel-induced neuropathic pain through enhanced neuroinflammatory processes. Conclusion: Inhibition of S1PR1 blocks and reverses paclitaxel-induced neuropathic pain without interfering with anticancer effects. Significance: Targeting the S1PR1 signaling pathway could be an effective approach for the treatment of CIPN. The ceramide-sphingosine 1-phosphate (S1P) rheostat is important in regulating cell fate. Several chemotherapeutic agents, including paclitaxel (Taxol), involve pro-apoptotic ceramide in their anticancer effects. The ceramide-to-S1P pathway is also implicated in the development of pain, raising the intriguing possibility that these sphingolipids may contribute to chemotherapy-induced painful peripheral neuropathy, which can be a critical dose-limiting side effect of many widely used chemotherapeutic agents. We demonstrate that the development of paclitaxel-induced neuropathic pain was associated with ceramide and S1P formation in the spinal dorsal horn that corresponded with the engagement of S1P receptor subtype 1 (S1PR1)-dependent neuroinflammatory processes as follows: activation of redox-sensitive transcription factors (NFκB) and MAPKs (ERK and p38) as well as enhanced formation of pro-inflammatory and neuroexcitatory cytokines (TNF-α and IL-1β). Intrathecal delivery of the S1PR1 antagonist W146 reduced these neuroinflammatory processes but increased IL-10 and IL-4, potent anti-inflammatory/neuroprotective cytokines. Additionally, spinal W146 reversed established neuropathic pain. Noteworthy, systemic administration of the S1PR1 modulator FTY720 (Food and Drug Administration-approved for multiple sclerosis) attenuated the activation of these neuroinflammatory processes and abrogated neuropathic pain without altering anticancer properties of paclitaxel and with beneficial effects extended to oxaliplatin. Similar effects were observed with other structurally and chemically unrelated S1PR1 modulators (ponesimod and CYM-5442) and S1PR1 antagonists (NIBR-14/15) but not S1PR1 agonists (SEW2871). Our findings identify for the first time the S1P/S1PR1 axis as a promising molecular and therapeutic target in chemotherapy-induced painful peripheral neuropathy, establish a mechanistic insight into the biomolecular signaling pathways, and provide the rationale for the clinical evaluation of FTY720 in chronic pain patients.

Spinal neuroimmune activation is independent of T-cell infiltration and attenuated by A3 adenosine receptor agonists in a model of oxaliplatin-induced peripheral neuropathy

Many commonly used chemotherapeutics including oxaliplatin are associated with the development of a painful chemotherapy-induced peripheral neuropathy (CIPN). This dose-limiting complication can appear long after the completion of therapy causing a significant reduction in quality-of-life and impeding cancer treatment. We recently reported that activation of the Gi/Gq-coupled A3 adenosine receptor (A3AR) with selective A3AR agonists (i.e., IB-MECA) blocked the development of chemotherapy induced-neuropathic pain in models evoked by distinct agents including oxaliplatin without interfering with their anticancer activities. The mechanism(s) of action underlying these beneficial effects has yet to be explored. Our results herein demonstrate that the development of oxaliplatin-induced mechano-hypersensitivity (allodynia and hyperalgesia) in rats is associated with the hyperactivation of astrocytes, but not microglial cells, increased production of pro-inflammatory and neuroexcitatory cytokines (TNF, IL-1β), and reductions in the levels of anti-inflammatory/neuroprotective cytokines (IL-10, IL-4) in the dorsal horn of the spinal cord. These events did not require lymphocytic mobilization since oxaliplatin did not induce CD45(+)/CD3(+) T-cell infiltration into the spinal cord. A3AR agonists blocked the development of neuropathic pain with beneficial effects strongly associated with the modulation of spinal neuroinflammatory processes: attenuation of astrocytic hyperactivation, inhibition of TNF and IL-1β production, and an increase in IL-10 and IL-4. These results suggest that inhibition of an astrocyte-associated neuroinflammatory response contributes to the protective actions of A3AR signaling and continues to support the pharmacological basis for selective A3AR agonists as adjuncts to chemotherapeutic agents for the management of chronic pain.

A3 adenosine receptor agonist prevents the development of paclitaxel-induced neuropathic pain by modulating spinal glial-restricted redox-dependent signaling pathways.

Summary A3AR agonists prevent paclitaxel‐induced neuropathic pain via modulating spinal redox‐dependent signaling pathways (restoring glutamatergic homeostasis, attenuating proinflammatory pathways). ABSTRACT Chemotherapy‐induced peripheral neuropathy accompanied by chronic neuropathic pain is the major dose‐limiting toxicity of several anticancer agents including the taxane paclitaxel (Taxol). A critical mechanism underlying paclitaxel‐induced neuropathic pain is the increased production of peroxynitrite in spinal cord generated in response to activation of the superoxide‐generating enzyme, NADPH oxidase. Peroxynitrite in turn contributes to the development of neuropathic pain by modulating several redox‐dependent events in spinal cord. We recently reported that activation of the Gi/Gq‐coupled A3 adenosine receptor (A3AR) with selective A3AR agonists (ie, IB‐MECA) blocked the development of chemotherapy induced‐neuropathic pain evoked by distinct agents, including paclitaxel, without interfering with anticancer effects. The mechanism or mechanisms of action underlying these beneficial effects has yet to be explored. We now demonstrate that IB‐MECA attenuates the development of paclitaxel‐induced neuropathic pain by inhibiting the activation of spinal NADPH oxidase and two downstream redox‐dependent systems. The first relies on inhibition of the redox‐sensitive transcription factor (NF&kgr;B) and mitogen activated protein kinases (ERK and p38) resulting in decreased production of neuroexcitatory/proinflammatory cytokines (TNF‐&agr;, IL‐1&bgr;) and increased formation of the neuroprotective/anti‐inflammatory IL‐10. The second involves inhibition of redox‐mediated posttranslational tyrosine nitration and modification (inactivation) of glia‐restricted proteins known to play key roles in regulating synaptic glutamate homeostasis: the glutamate transporter GLT‐1 and glutamine synthetase. Our results unravel a mechanistic link into biomolecular signaling pathways employed by A3AR activation in neuropathic pain while providing the foundation to consider use of A3AR agonists as therapeutic agents in patients with chemotherapy‐induced peripheral neuropathy.

Anti-superoxide and anti-peroxynitrite strategies in pain suppression.

Superoxide (SO, O(2)·(-)) and its reaction product peroxynitrite (PN, ONOO(-)) have been shown to be important in the development of pain of several etiologies. While significant progress has been made in teasing out the relative contribution of SO and PN peripherally, spinally, and supraspinally during the development and maintenance of central sensitization and pain, there is still a considerable void in our understanding. Further research is required in order to develop improved therapeutic strategies for selectively eliminating SO and/or PN. Furthermore, it may be that PN is a more attractive target, in that unlike SO it has no currently known beneficial role. Our group has been at the forefront of research concerning the role of SO and PN in pain, and our current findings have led to the development of two new classes of orally active catalysts which are selective for PN decomposition while sparing SO. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Identification of A3 adenosine receptor agonists as novel non-narcotic analgesics.

Chronic pain negatively impacts the quality of life in a variety of patient populations. The current therapeutic repertoire is inadequate in managing patient pain and warrants the development of new therapeutics. Adenosine and its four cognate receptors (A1, A2A, A2B and A3) have important roles in physiological and pathophysiological states, including chronic pain. Preclinical and clinical studies have revealed that while adenosine and agonists of the A1 and A2A receptors have antinociceptive properties, their therapeutic utility is limited by adverse cardiovascular side effects. In contrast, our understanding of the A3 receptor is only in its infancy, but exciting preclinical observations of A3 receptor antinociception, which have been bolstered by clinical trials of A3 receptor agonists in other disease states, suggest pain relief without cardiovascular side effects and with sufficient tolerability. Our goal herein is to briefly discuss adenosine and its receptors in the context of pathological pain and to consider the current data regarding A3 receptor‐mediated antinociception. We will highlight recent findings regarding the impact of the A3 receptor on pain pathways and examine the current state of selective A3 receptor agonists used for these studies. The adenosine‐to‐A3 receptor pathway represents an important endogenous system that can be targeted to provide safe, effective pain relief from chronic pain.

Chemotherapy-induced pain is promoted by enhanced spinal adenosine kinase levels through astrocyte-dependent mechanisms

Abstract Development of chemotherapy-induced neuropathic pain (CINP) compromises the use of chemotherapy and greatly impacts thousands of lives. Unfortunately, there are no Food and Drug Administration–approved drugs to prevent or treat CINP. Neuropathological changes within CNS, including neuroinflammation and increased neuronal excitability, are driven by alterations in neuro-glia communication; but, the molecular signaling pathways remain largely unexplored. Adenosine is a potent neuroprotective purine nucleoside released to counteract the consequences of these neuropathological changes. Adenosine signaling at its adenosine receptors (ARs) is dictated by adenosine kinase (ADK) in astrocytes, which provides a cellular sink for the removal of extracellular adenosine. We now demonstrate that chemotherapy (oxaliplatin) in rodents caused ADK overexpression in reactive astrocytes and reduced adenosine signaling at the A3AR subtype (A3AR) within the spinal cord. Dysregulation of ADK and A3AR signaling was associated with increased proinflammatory and neuroexcitatory interleukin-1&bgr; expression and activation of nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome, but not putative oxaliplatin-associated GSK3&bgr; transcriptional regulation. Intrathecal administration of the highly selective A3AR agonist MRS5698 attenuated IL-1&bgr; production and increased the expression of potent anti-inflammatory and neuroprotective IL-10. The effects of MRS5698 were blocked by attenuating IL-10 signaling in rats with intrathecal neutralizing IL-10 antibody and in IL-10−/− knockout mice. These findings provide new molecular insights implicating astrocyte-based ADK-adenosine axis and nucleotide-binding oligomerization domain-like receptor protein 3 in the development of CINP and IL-10 in the mechanism of action of A3AR agonists. These findings strengthen the pharmacological rationale for clinical evaluation of A3AR agonists already in advanced clinical trials as anticancer agents as an adjunct to chemotherapy.

The Contribution of Nitroxidative Stress to Pathophysiological Pain and Opioid Analgesic Failure

Chronic pain affects nearly 10 % of the population worldwide and poses a tremendous socioeconomic burden. Current therapeutic strategies, which range from nonsteroidal anti-inflammatory drugs (NSAIDs) to powerful opioids like morphine and fentanyl, do not effectively manage chronic pain in the majority of patients. A better understanding of pathophysiological nociception and the therapeutic targets therein is necessary. The generation of nitroxidative (nitrative and oxidative) stress—that is, the formation of superoxide and nitric oxide in tandem, their subsequent reaction to afford peroxynitrite, and the reaction of peroxynitrite and its decomposition products with biological molecules—is clearly involved in various types of persistent pain. In this chapter, we will catalogue the mechanistic pharmacological studies that support the contribution of nitroxidative stress to chronic pain, identify the cellular and enzymatic sources of nitroxidative species involved in this pathology, and delineate the mechanisms by which nitroxidative stress impacts nociceptive processing to produce persistent pain. Specifically, we will highlight the contribution of peroxynitrite (e.g., through nitration chemistry) to enhanced pro-nociceptive neurotransmission (modifications of glutamatergic, vanilloid, and prostaglandin signaling), suppressed inhibitory neurotransmission (modifications of GABAergic and catecholamine signaling), and to changes in transcriptional regulation that underpin chronic pain. Our overall goal is to refine the current generalized understanding of roles of reactive oxygen and nitrogen species in persistent pain by defining nitroxidative stress as a specific, targetable pro-nociceptive mechanism for the ultimate treatment of chronic pain.