Differential expression of P2X7 receptor and IL-1β in nociceptive and neuropathic pain

Background: Despite substantial progress, pathogenesis and therapy of chronic pain are still the focus of many investigations. The ATP-gated P2X7 receptor (P2X7R) has previously been shown to play a central role in animal models of nociceptive inflammatory and neuropathic pain. Recently, we found that the adaptive immune system is involved in the pathophysiology of chronic nociceptive and neuropathic pain in humans. So far, data regarding P2X7R expression patterns on cells of the adaptive immune system of pain patients are scarce. We therefore analyzed the P2X7R expression on peripheral blood lymphocytes and monocytes, as well as serum levels of IL-1 beta in patients suffering from chronic nociceptive and neuropathic pain in comparison to healthy volunteers in order to identify individuals who might benefit from a P2X7R modulating therapy. Methods: P2X7R messenger RNA (mRNA) and protein expression were determined in patients with either chronic nociceptive low back pain (CLBP) or neuropathic pain (NeP), and in healthy volunteers by quantitative real-time PCR (qPCR) and by fluorescence-assisted cell-sorting (FACS), respectively. IL-1 beta serum levels were measured with a multiplex cytokine assay. Results: Compared to healthy volunteers, P2X7R mRNA (1.6-fold, p = 0.038) and protein levels were significantly increased on monocytes (NeP: 24.6 +/- 6.2, healthy volunteers: 17.0 +/- 5.4; p = 0.002) and lymphocytes (NeP: 21.8 +/- 6.5, healthy volunteers: 15.6 +/- 5.2; p = 0.009) of patients with NeP, but not in patients with CLBP. Similarly, IL-1 beta serum concentrations were significantly elevated only in NeP patients (1.4-fold, p = 0.04). Conclusions: A significant upregulation of P2X7R and increased IL-1 beta release seems to be a particular phenomenon in patients with NeP. P2X7R inhibitors may therefore represent a potential option for the treatment of this frequently intractable type of pain.