Comparative analgesic efficacy of pregabalin administered according to either a prevention protocol or an intervention protocol in rats with cisplatin‐induced peripheral neuropathy

Chemotherapy‐induced peripheral neuropathy (CIPN) is a type of peripheral neuropathic pain that may be dose‐limiting in patients administered potentially curative cancer chemotherapy dosing regimens. In cancer survivors, persistent CIPN adversely affects patient quality of life and so adjuvant drugs (anticonvulsants eg pregabalin or antidepressants eg amitriptyline) are recommended for the relief of CIPN. However, most studies in rodent models of CIPN involve administration of single bolus doses of adjuvant drugs to assess pain‐relieving efficacy. Hence this study was designed to assess the efficacy of pregabalin administered to CIPN‐rats according to either a prevention or an intervention protocol. Groups of male Sprague‐Dawley rats received four single intraperitoneal bolus doses of cisplatin at 3 mg/kg at once‐weekly intervals to induce CIPN. For the prevention protocol, oral pregabalin (or vehicle) was administered to CIPN‐rats once‐daily for 21 consecutive days from day 0 to day 20 inclusive. For the intervention protocol, oral pregabalin was administered once‐daily for 21 consecutive days from day 28 to day 48, inclusive. Mechanical allodynia and mechanical hyperalgesia in the bilateral hindpaws were assessed just prior to each dose of cisplatin and at least once weekly until study completion (day 27, prevention protocol; or day 48, intervention protocol). Mechanical allodynia and mechanical hyperalgesia were also determined at the time of peak effect at about 2 hours post pregabalin/vehicle administration, once weekly until study completion. For the prevention protocol in CIPN‐rats, pregabalin alleviated mechanical hyperalgesia but not mechanical allodynia. For the intervention protocol, pregabalin alleviated both mechanical allodynia and mechanical hyperalgesia in the hindpaws.     

脊髓神经元凋亡在鞘内注射血小板活化因子诱发大鼠痛敏中的作用

目的：探讨脊髓神经元凋亡在鞘内注射血小板活化因子（PAF）诱发大鼠痛敏中的作用。方法鞘内置管成功的雄性 Sprague-Dawley 大鼠60只,随机分为2组：对照组,30只,鞘内注射人工脑脊液（arti-ficial cerebral spinal fluid,ACSF）10μl;PAF 组,30只,鞘内注射 PAF 10μg,溶解于10μl 人工脑脊液;分别于鞘内给药前1 d、给药后1、3、5、7、14 d 分别测定机械痛阈（PWMT）和热痛阈（PWTL）。取 L4-6脊髓,采用TUNEL 法观察脊髓神经元凋亡。结果鞘内注射血小板活化因子（PAF）可诱发出大鼠机械性触诱发痛和热痛觉过敏。PAF 组术后1 d 脊髓中开始有少量凋亡神经元出现,凋亡指数于术后3 d 开始迅速增加,术后5 d 达峰值,与对照组比较,有显著性差异（P 〈0.01）。结论鞘内注射 PAF 诱发大鼠触觉异常痛敏和热痛敏,脊髓神经元凋亡可能参与了鞘内注射 PAF 大鼠痛敏的形成。     

Repetitive Treatment with Diluted Bee Venom Attenuates the Induction of Below-Level Neuropathic Pain Behaviors in a Rat Spinal Cord Injury Model

The administration of diluted bee venom (DBV) into an acupuncture point has been utilized traditionally in Eastern medicine to treat chronic pain. We demonstrated previously that DBV has a potent anti-nociceptive efficacy in several rodent pain models. The present study was designed to examine the potential anti-nociceptive effect of repetitive DBV treatment in the development of below-level neuropathic pain in spinal cord injury (SCI) rats. DBV was applied into the Joksamli acupoint during the induction and maintenance phase following thoracic 13 (T13) spinal hemisection. We examined the effect of repetitive DBV stimulation on SCI-induced bilateral pain behaviors, glia expression and motor function recovery. Repetitive DBV stimulation during the induction period, but not the maintenance, suppressed pain behavior in the ipsilateral hind paw. Moreover, SCI-induced increase in spinal glia expression was also suppressed by repetitive DBV treatment in the ipsilateral dorsal spinal cord. Finally, DBV injection facilitated motor function recovery as indicated by the Basso–Beattie–Bresnahan rating score. These results indicate that the repetitive application of DBV during the induction phase not only decreased neuropathic pain behavior and glia expression, but also enhanced locomotor functional recovery after SCI. This study suggests that DBV acupuncture can be a potential clinical therapy for SCI management.     

Enhancement of antinociceptive effect of morphine by antidepressants in diabetic neuropathic pain model

BackgroundRecent studies have shown that influence of antidepressants on analgesic action of opioids is heterogeneous. The aim of this study was to investigate the effect of acute and repeated (21 days) antidepressant (amitriptyline, moclobemide and reboxetine) treatment on the antinociceptive action of morphine, an opioid agonist, in streptozotocin (STZ)-induced neuropathic pain model.MethodsThe studies were performed on the male Wistar rats. The changes in nociceptive thresholds were determined by using mechanical stimuli (the Randall–Selitto and the von Frey tests). Diabetes was induced by intramuscular administration of STZ.ResultsIn this work we report that acute as well as repeated per os administration of antidepressants (amitriptyline, moclobemide and reboxetine) significantly potentiated the antihyperalgesic effect of morphine in STZ-induced neuropathic pain model.ConclusionCombination therapy, such as classical antidepressants (amitriptyline, moclobemide) with opioids, or agents with noradrenaline reuptake inhibition and μ-opioid receptor activation could be a new target for research into treatment of painful diabetic neuropathy.     

Effect of S-methylisothiourea,an inducible nitric oxide synthase inhibitor,in joint pain and pathology in surgically induced model of osteoarthritis

The aim of the present study was to evaluate in vivo modulatory effect of S-methylisothiourea (SMT), a preferential inhibitor of inducible nitric oxide synthase (iNOS) on pain and pathology in the surgical model of osteoarthritis (OA) in rats. The OA was produced by the anterior cruciate ligament transection (ACLT) and medial meniscectomy (MMx) of right knee. SMT was administered 1 day prior to the production of OA and continued up to day 42 postoperation. Mechanical hyperalgesia, thermal hyperalgesia, tail flick latency after repeated flexion and extension of OA knee and knee diameter of right knee were determined at weekly intervals. Serum levels of IL-1β, TNF-α and nitrite concentration were determined at the end of the experiment. Glycosaminoglycan (GAG) content, collagen content and histopathological evaluation of articular cartilage were also determined at the end of the experiment. SMT reduced mechanical hyperalgesia and the serum levels of IL-1β, TNF-α and nitrite. Further, SMT reduced the loss of GAG from articular cartilage. Microscopically, SMT reduced the severity of the cartilage lesion. The results indicate the effectiveness of SMT in attenuating the pain and pathology of experimental OA phase by reducing the production of nitric oxide and interleukin-1β and tumor necrosis factor-α, which are known to play a major role in the pathophysiology of OA.     

Expression and effect of sodium-potassium-chloride cotransporter on dorsal root ganglion neurons in a rat model of chronic constriction injury

Sodium-potassium-chloride cotransporter 1 (NKCC1) and potassium-chloride cotransporter 2 (KCC2) are associated with the transmission of peripheral pain.We investigated whether the increase of NKCC1 and KCC2 is associated with peripheral pain transmission in dorsal root ganglion neurons.To this aim,rats with persistent hyperalgesia were randomly divided into four groups.Rats in the control group received no treatment,and the rat sciatic nerve was only exposed in the sham group.Rats in the chronic constriction injury group were established into chronic constriction injury models by ligating sciatic nerve and rats were given bumetanide,an inhibitor of NKCC1,based on chronic constriction injury modeling in the chronic constriction injury + bumetanide group.In the experiment measuring thermal withdrawal latency,bumetanide (15 mg/kg) was intravenously administered.In the patch clamp experiment,bumetanide (10 μg/μL) and acutely isolated dorsal root ganglion neurons (on day 14) were incubated for 1 hour,or bumetanide (5 μg/μL) was intrathecally injected.The Hargreaves test was conducted to detect changes in thermal hyperalgesia in rats.We found that the thermal withdrawal latency of rats was significantly decreased on days 7,14,and 21 after model establishment.After intravenous injection of bumetanide,the reduction in thermal retraction latency caused by model establishment was significantly inhibited.Immunohistochemistry and western blot assay results revealed that the immune response and protein expression of NKCC1 in dorsal root ganglion neurons of the chronic constriction injury group increased significantly on days 7,14,and 21 after model establishment.No immune response or protein expression of KCC2 was observed in dorsal root ganglion neurons before and after model establishment.The Cl^– (chloride ion) fluorescent probe technique was used to evaluate the change of Cl^– concentration in dorsal root ganglion neurons of chronic constriction injury model rats.We found that the relative optical density of N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (a Cl^– fluorescent probe whose fluorescence Cenintensity decreases as Cl– concentration increases) in the dorsal root ganglion neurons of the chronic constriction injury group was significantly decreased on days 7 and 14 after model establishment.The whole-cell patch clamp technique revealed that the resting potential and action potential frequency of dorsal root ganglion neurons increased,and the threshold and rheobase of action potentials decreased in the chronic constriction injury group on day 14 after model establishment.After bumetanide administration,the above indicators were significantly suppressed.These results confirm that CCI can induce abnormal overexpression of NKCC1,thereby increasing the Cl^– concentration in dorsal root ganglion neurons;this then enhances the excitability of dorsal root ganglion neurons and ultimately promotes hyperalgesia and allodynia.In addition,bumetanide can achieve analgesic effects.All experiments were approved by the Institutional Ethics Review Board at the First Affiliated Hospital,College of Medicine,Shihezi University,China on February 22,2017 (approval No.A2017-169-01).     

Challenging the challenge: A randomized controlled trial evaluating the inflammatory response and pain perception of healthy volunteers after single-dose LPS administration,as a potential model for inflammatory pain in early-phase drug development

Background and aimsFollowing an infection, cytokines not only regulate the acute immune response, but also contribute to symptoms such as inflammatory hyperalgesia. We aimed to characterize the acute inflammatory response induced by a human endotoxemia model, and its effect on pain perception using evoked pain tests in two different dose levels. We also attempted to determine whether combining a human endotoxemia challenge with measurement of pain thresholds in healthy subjects could serve as a model to study drug effects on inflammatory pain.Methods and resultsThis was a placebo-controlled, randomized, cross-over study in 24 healthy males. Twelve subjects were administered a bolus of 1 ng/kg LPS intravenously, and twelve 2 ng/kg LPS. Before days of placebo/LPS administration, subjects completed a full study day without study drug administration, but with identical pain threshold testing. Blood sampling and evoked pain tests (electrical burst and -stair, heat, pressure, and cold pressor test) were performed pre-dose and at frequent intervals up to 10hr post-dose. Data were analysed with a repeated-measures ANCOVA. For both dose levels, LPS induced an evident acute inflammatory response, but did not significantly affect any of the pain modalities. In a post-hoc analysis, lowering of pain thresholds was observed in the first 3 h after dosing, corresponding with the peak of the acute inflammatory response around 1–3 h post-dose.ConclusionMild acute systemic inflammation, as induced by 1 ng/kg and 2 ng/kg LPS intravenous administration, did not significantly change pain thresholds in this study. The endotoxemia model in combination with evoked pain tests is not suitable to study acute inflammatory hyperalgesia in healthy males.     

不同选择性环氧合酶抑制剂对瑞芬太尼麻醉后痛觉过敏的影响

目的探讨不同选择性环氧合酶抑制剂对瑞芬太尼麻醉后痛觉过敏的影响。方法选择瑞芬太尼维持的全麻下行全子宫切除术的患者60例,根据麻醉诱导前15 min用药不同分为2组,A组30例给予帕瑞昔布钠40mg,B组30例给予酮咯酸氨丁三醇30 mg,观察术后15、30 min的疼痛评分和术后4、8、12、24 h的疼痛评分,病人自控镇痛(PCA)按压次数、镇痛药物消耗量。结果 A组在术后15 min疼痛评分小于B组(P<0.05);术后4 h内A组的镇痛药物消耗量和PCA按压次数均少于B组(P<0.05)。结论麻醉诱导前给予帕瑞昔布钠相比酮咯酸氨丁三醇能更有效地抑制瑞芬太尼所致的痛觉过敏。