Kenichiro Nagata

Behavioral phenotypes of mice lacking purinergic P2X4 receptors in acute and chronic pain assays

A growing body of evidence indicates that P2X receptors (P2XRs), a family of ligand-gated cation channels activated by extracellular ATP, play an important role in pain signaling. In contrast to the role of the P2X3R subtype that has been extensively studied, the precise roles of others among the seven P2XR subtypes (P2X1R-P2X7R) remain to be determined because of a lack of sufficiently powerful tools to specifically block P2XR signaling in vivo. In the present study, we investigated the behavioral phenotypes of a line of mice in which the p2rx4 gene was disrupted in a series of acute and chronic pain assays. While p2rx4-/- mice showed no major defects in pain responses evoked by acute noxious stimuli and local tissue damage or in motor function as compared with wild-type mice, these mice displayed reduced pain responses in two models of chronic pain (inflammatory and neuropathic pain). In a model of chronic inflammatory pain developed by intraplantar injection of complete Freunds adjuvant (CFA), p2rx4-/- mice exhibited attenuations of pain hypersensitivity to innocuous mechanical stimuli (tactile allodynia) and also of the CFA-induced swelling of the hindpaw. A most striking phenotype was observed in a test of neuropathic pain: tactile allodynia caused by an injury to spinal nerve was markedly blunted in p2rx4-/- mice. By contrast, pain hypersensitivity to a cold stimulus (cold allodynia) after the injury was comparable in wild-type and p2rx4-/- mice. Together, these findings reveal a predominant contribution of P2X4R to nerve injury-induced tactile allodynia and, to the lesser extent, peripheral inflammation. Loss of P2X4R produced no defects in acute physiological pain or tissue damaged-induced pain, highlighting the possibility of a therapeutic benefit of blocking P2X4R in the treatment of chronic pain, especially tactile allodynia after nerve injury.

Antidepressants inhibit P2X4 receptor function: a possible involvement in neuropathic pain relief

BackgroundNeuropathic pain is characterized by pain hypersensitivity to innocuous stimuli (tactile allodynia) that is nearly always resistant to known treatments such as non-steroidal anti-inflammatory drugs or even opioids. It has been reported that some antidepressants are effective for treating neuropathic pain. However, the underlying molecular mechanisms are not well understood. We have recently demonstrated that blocking P2X4 receptors in the spinal cord reverses tactile allodynia after peripheral nerve injury in rats, implying that P2X4 receptors are a key molecule in neuropathic pain. We investigated a possible role of antidepressants as inhibitors of P2X4 receptors and analysed their analgesic mechanism using an animal model of neuropathic pain.ResultsAntidepressants strongly inhibited ATP-mediated Ca2+ responses in P2X4 receptor-expressing 1321N1 cells, which are known to have no endogenous ATP receptors. Paroxetine exhibited the most powerful inhibition of calcium influx via rat and human P2X4 receptors, with IC50 values of 2.45 μM and 1.87 μM, respectively. Intrathecal administration of paroxetine produced a striking antiallodynic effect in an animal model of neuropathic pain. Co-administration of WAY100635, ketanserin or ondansetron with paroxetine induced no significant change in the antiallodynic effect of paroxetine. Furthermore, the antiallodynic effect of paroxetine was observed even in rats that had received intrathecal pretreatment with 5,7-dihydroxytryptamine, which dramatically depletes spinal 5-hydroxytryptamine.ConclusionThese results suggest that paroxetine acts as a potent analgesic in the spinal cord via a mechanism independent of its inhibitory effect on serotonin transporters. Powerful inhibition on P2X4 receptors may underlie the analgesic effect of paroxetine, and it is possible that some antidepressants clinically used in patients with neuropathic pain show antiallodynic effects, at least in part via their inhibitory effects on P2X4 receptors.

Reduced pain behaviors and extracellular signal-related protein kinase activation in primary sensory neurons by peripheral tissue injury in mice lacking platelet-activating factor receptor.

Peripheral tissue injury causes the release of various mediators from damaged and inflammatory cells, which in turn activates and sensitizes primary sensory neurons and thereby produces persistent pain. The present study investigated the role of platelet‐activating factor (PAF), a phospholipid mediator, in pain signaling using mice lacking PAF receptor (pafr−/− mice). Here we show that pafr−/− mice displayed almost normal responses to thermal and mechanical stimuli but exhibit attenuated persistent pain behaviors resulting from tissue injury by locally injecting formalin at the periphery as well as capsaicin pain and visceral inflammatory pain without any alteration in cytoarchitectural or neurochemical properties in dorsal root ganglion (DRG) neurons and a defect in motor function. However, pafr−/− mice showed no alterations in spinal pain behaviors caused by intrathecally administering agonists for N‐methyl‐d‐aspartate (NMDA) and neurokinin1 receptors. A PAFR agonist evoked an intracellular Ca2+ response predominantly in capsaicin‐sensitive DRG neurons, an effect was not observed in pafr−/− mice. By contrast, the PAFR agonist did not affect C‐ or Aδ‐evoked excitatory post‐synaptic currents in substantia gelatinosa neurons in the dorsal horn. Interestingly, mice lacking PAFR showed reduced phosphorylation of extracellular signal‐related protein kinase (ERK), an important kinase for the sensitization of primary sensory neurons, in their DRG neurons after formalin injection. Furthermore, U0126, a specific inhibitor of the ERK pathway suppressed the persistent pain by formalin. Thus, PAFR may play an important role in both persistent pain and the sensitization of primary sensory neurons after tissue injury.

Involvement of the chemokine CCL3 and the purinoceptor P2X7 in the spinal cord in paclitaxel-induced mechanical allodynia

BackgroundPaclitaxel is an effective chemotherapeutic agent widely used for the treatment of solid tumors. The major dose-limiting toxicity of paclitaxel is peripheral neuropathy. The mechanisms underlying the development and maintenance of paclitaxel-induced peripheral neuropathy are still unclear, and there are no currently established effective treatments. Accumulating evidence in models of neuropathic pain in which peripheral nerves are lesioned has implicated spinal microglia and chemokines in pain hypersensitivity, but little is know about their roles in chemotherapy-induced peripheral neuropathy. In the present study, we investigated the role of CC-chemokine ligand 3 (CCL3) in the spinal cord in the development and maintenance of mechanical allodynia using a rat model of paclitaxel-induced neuropathy.FindingsRepeated intravenous administration of paclitaxel induced a marked decrease in paw withdrawal threshold in response to mechanical stimulation (mechanical allodynia). In these rats, the number of microglia in the spinal dorsal horn (SDH) was significantly increased. Paclitaxel-treated rats showed a significant increase in the expression of mRNAs for CCL3 and its receptor CCR5 in the SDH. Intrathecal administration of a CCL3-neutralizing antibody not only attenuated the development of paclitaxel-induced mechanical allodynia but also reversed its maintenance. Paclitaxel also upregulated expression of purinoceptor P2X7 receptors (P2X7Rs), which have been implicated in the release of CCL3 from microglia, in the SDH. The selective P2X7R antagonist A438079 had preventive and reversal effects on paclitaxel-induced allodynia.ConclusionsOur findings suggest a contribution of CCL3 and P2X7Rs in the SDH to paclitaxel-induced allodynia and may provide new therapeutic targets for paclitaxel-induced painful neuropathy.

Change of formulation decreases venous irritation in breast cancer patients receiving epirubicin

PurposeEpirubicin is an antitumor drug, particularly used in the treatment of the breast cancer. The peripheral intravenous infusion of epirubicin frequently causes venous irritation such as, erythema, injection site pain, and phlebitis. The purpose of the present study was to investigate the risk factor associated with the epirubicin-induced venous irritation and to establish a suitable administration method of epirubicin.MethodsThe phlebitis scores (Visual Infusion Phlebitis score) were evaluated retrospectively using the collected nursing record. We analyzed the risk factor associated with venous irritation in 97 patients administered with epirubicin from December 2004 to September 2008. We subsequently changed the regimen of epirubicin and examined the incidence of venous irritation in 26 patients administered with epirubicin from August 2009 to March 2010.ResultsThe phlebitis scores were significantly higher in the patients treated with ready-to-use solution compared with lyophilized powder (P = 0.04). Based on this result, we switched the formulation of epirubicin to lyophilized powder. After the intervention, the phlebitis scores were significantly decreased (P = 0.003). An ordinal logistic regression analysis revealed that use of ready-to-use solution was a significant predictor for venous irritation (odds ratio = 3.70; 95%, confidence intervals, 1.29–11.45; P = 0.02).ConclusionsThe use of ready-to-use solution was a risk factor for epirubicin-induced venous irritation. The change of formulation by pharmacist intervention decreased the risk of venous irritation.

Risk factors for predicting severe neutropenia induced by amrubicin in patients with advanced lung cancer

Background: Neutropenia is one of the most frequent and dose-limiting toxicities in amrubicin (AMR) therapy. However, the predictive factors for the development of severe neutropenia in AMR therapy remain unknown. Methods: The subjects were 61 advanced lung cancer patients treated with AMR monotherapy. All data were retrospectively collected from the electronic medical record system. A stepwise logistic regression analysis was performed to identify risk factors for grade 3–4 neutropenia. Results: Of a total 61 patients, 50 were male and 11 were female. The median dose of AMR was 35.0 mg/m2. The incidence of grade 3–4 neutropenia during the first course was 62%. In multivariate analysis, female gender (OR = 6.68; 95% CI 1.01–134.15; p = 0.049), higher AMR doses (40 mg/m2 or more) (OR = 5.98; 95% CI 1.77–23.74; p = 0.003), and lower hematocrit values (OR = 2.04 per 5% decrease; 95% CI 1.04–4.38; p = 0.036) were significantly associated with severe neutropenia induced by AMR. Conclusion: The present results suggest that female gender, higher doses of AMR, and lower baseline hematocrit values are predictive factors associated with severe neutropenia induced by AMR in patients with advanced lung cancer. Patients who have these predictive factors should be monitored carefully and considered for early granulocyte colony-stimulating factor support.

Efficacy and safety of aprepitant in allogeneic hematopoietic stem cell transplantation.

To evaluate the efficacy and safety of aprepitant added to standard antiemetic regimens used in high‐dose chemotherapy for allogeneic hematopoietic stem cell transplantation (allo‐HSCT).

Efficacy and safety of an increased-dose of dexamethasone in patients receiving fosaprepitant chemotherapy in Japan

BACKGROUND Antiemetic triplet therapy including dexamethasone (DEX) is widely used for patients receiving highly emetogenic chemotherapy (HEC). In Japan, the appropriate dose of DEX has not been established for this combination. MATERIALS AND METHODS To assess the efficacy and safety of increased-dose DEX, we retrospectively examined patients receiving HEC with antiemetic triplet therapy. RESULTS Twenty-four patients (fosaprepitant group) were given an increased-dose of DEX (average total dose: 45.8mg), fosaprepitant, and 5-HT3 antagonist. A lower-dose of DEX (33.6mg), oral aprepitant, and 5-HT3 antagonist were administered to the other 48 patients (aprepitant group). The vomiting control rates in the fosaprepitant and aprepitant groups were 100% and 85.4% in the acute phase, and were 75.0% and 64.6% in the delayed phase. The incidences of toxicity were similar comparing the two groups. CONCLUSIONS Triplet therapy using an increased-dose of DEX is suggested to be safe and effective for patients receiving HEC.