Novel promising pharmacological targets and drugs for the treatment of neuropathic pain: focusing on prokineticin system and selective A3 adenosine receptor (A3AR) agonists in an animal model

Chronic neuropathic pain represents a huge unmet medical need affecting millions of individuals worldwide. Opioids have been regarded for millennia as among the most effective drugs for the treatment of acute and persistent pain. However, chronic opioid exposure give rise to a well-known plethora of side effects such as nausea, constipation, tolerance and addiction and cognitive impairment. For these reason novel non-narcotic analgesics are needed. In the last decade both adenosine pathway through A3 receptor and prokineticin system have emerged as promising therapeutic targets for the management of neuropathic pain. Using the well characterized chronic constriction injury (CCI) model in mice, the work of this PhD thesis was aimed at the: I) Investigation of A3AR agonists’ mechanism of action in alleviating neuropathic pain A3AR highly selective agonists are able to block and reverse neuropathic pain, but molecular mechanisms underlying their beneficial effects remained unknown. Wild type (WT), Rag1-/-, A3AR-/- and IL-10-/- mice were used: following CCI mice were reconstituted with an intravenous injection of T cells isolated from WT or different transgenic donors. Onset and development of mechano-allodynia was followed up using Von Frey filaments before and after A3AR agonists systemic and intrathecal administration. We were able to demonstrate that selective A3AR agonists are able to reverse CCI-induced neuropathic pain by directly activate A3AR expressed on CD4+ T cells, inducing the release of IL-10. II) Investigation of the modulation of prokineticin system following CCI in PKR1 and PKR2 knock out mice Prokineticin system activation is strongly involved in the onset and progression of neuropathic pain, but relative contribution of PKR1 and PKR2 signalling remain unknown. WT, PKR1-/- and PKR2-/- male mice underwent CCI surgery. Onset and development of mechano-allodynia and thermal hyperalgesia were followed up using Von Frey filaments and Plantar test, respectively. Lumbar region of spinal cord was harvested for immunofluorescence assay. We demonstrate that PKR1 is crucial for the development of a correct sensitivity to pain after injury, since its absence gave rise to a “contralateral neuropathy”. We hypothesize that PKR1 signalling is also involved in the regulation of the expression of alternative spliced forms of PKR2, essential for a correct nociception.