Role of Neurotrophins in Neuropathic Pain

Neurotrophins (NTs) belong to a family of structurally and functionally related proteins, they are the subsets of neurotrophic factors. Neurotrophins are responsible for diverse actions in the developing peripheral and central nervous systems. They are important regulators of neuronal function, affecting neuronal survival and growth. They are able to regulate cell death and survival in development as well as in pathophysiologic states. NTs and their receptors are expressed in areas of the brain that undergo plasticity, indicating that they are able to modulate synaptic plasticity.Recently, neurotrophins have been shown to play significant roles in the development and transmission of neuropathic pain. Neuropathic pain is initiated by a primary lesion or dysfunction in the nervous system. It has a huge impact on the quality of life. It is debilitating and often has an associated degree of depression that contributes to decreasing human well being. Neuropathic pain ranks at the first place for sanitary costs.Neuropathic pain treatment is extremely difficult. Several molecular pathways are involved, making it a very complex disease. Excitatory or inhibitory pathways controlling neuropathic pain development show altered gene expression, caused by peripheral nerve injury. At present there are no valid treatments over time and neuropathic pain can be classified as an incurable disease.Nowadays, pain research is directing towards new molecular methods. By targeting neurotrophin molecules it may be possible to provide better pain control than currently available.     

Introduction: chronic pain studies of the lidocaine patch 5% using the Neuropathic Pain Scale

The manifestation of pain in any individual patient may result from a variety of underlying mechanisms that also may vary from one disease state to another. Global measures of pain intensity and relief are inadequate for characterizing specific pain qualities or identifying the unique effects of pain treatments on different pain qualities. The Neuropathic Pain Scale (NPS) is a recently developed measure designed to assess distinct pain qualities and may allow differentiation of therapeutic effects, even in cases where global pain response may be similar. Three studies are presented that provide preliminary evidence for the utility of the NPS for characterizing distinct pain qualities and changes in pain qualities in patients treated with the lidocaine patch 5% for a variety of neuropathic and non-neuropathic chronic pain conditions, including low-back pain, osteoarthritis, post-herpetic neuralgia, and painful diabetic neuropathy.     

Multidimensional Effectiveness of Botulinum Toxin in Neuropathic Pain: A Systematic Review of Randomized Clinical Trials

Although botulinum toxin (BoNT) has been suggested as a treatment to counter neuropathic pain, no previous systematic reviews investigated the multidimensional effects of BoNT on pain relief and Health-Related Quality of Life (HR-QoL). The aim of this systematic review is to summarize the current evidence on the effectiveness of BoNT treatment for neuropathic pain, and to characterize its multidimensional effectiveness in order to guide physicians in clinical practice. Five databases were systematically searched up to 4 April 2022, to identify randomized controlled trials satisfying the following criteria: adults suffering from neuropathic pain, BoNT administration, any comparator, multidimensional assessment of pain as primary outcome, HR-QoL, physical function, anxiety and depression, and sleep quality as secondary outcomes. Twelve studies were included. The multidimensional pain scales used were short-form McGill Pain Questionnaire, Neuropathic pain scale, Neuropathic Pain Symptom Inventory, International SCI Pain Basic Data Set, West Haven-Yale Multidimensional Pain Inventory, Brief Pain Inventory, and Douleur Neuropathique 4. These scales highlighted the positive effects of BoNT administration. According to the Jadad scale, all the RCTs included were high-quality studies. BoNT administration might be effectively introduced in the comprehensive management of neuropathic pain. Further research should focus on optimal and cost-effective therapeutic protocols.     

Neurotrophic factors as novel therapeutics for neuropathic pain

Neuropathic pain is a chronic condition that is caused by injury to the nervous system. Unlike acute pain, which is protective, neuropathic pain persists and serves no useful purpose, and severely affects quality of life. However, present therapies have modest efficacy in most patients, are palliative rather than curative, and their side effects represent significant limitations. Tremendous progress has been made over the past decade in our understanding of the biology of pain sensory neurons. The recent discovery that neurotrophic factors play an important role in neuropathic pain indicates that these pathways could serve as novel intervention points for therapy. Moreover, neurotrophic factors have the potential to address the underlying pathophysiology of neuropathic pain, thereby halting or reversing the disease process.     

Pharmacological management of neuropathic pain following spinal cord injury

Spinal cord injury (SCI) has a number of severe and disabling consequences, including chronic pain, and around 40% of patients develop persistent neuropathic pain. Pain following SCI has a detrimental impact on the patient's quality of life and is a major specific healthcare problem in its own right. Thus far, there is no cure for the pain and oral pharmaceutical intervention is often inadequate, commonly resulting in a reduction of only 20-30% in pain intensity. Neuropathic pain sensations are characterized by spontaneous persistent pain and a range of abnormally evoked responses, e.g. allodynia (pain evoked by normally non-noxious stimuli) and hyperalgesia (an increased response to noxious stimuli). Neuropathic pain following SCI may be present at or below the level of injury. Oral pharmacological agents used in the treatment of neuropathic pain act either by depressing neuronal activity, by blocking sodium channels or inhibiting calcium channels, by increasing inhibition via GABA agonists, by serotonergic and noradrenergic reuptake inhibition, or by decreasing activation via glutamate receptor inhibition, especially by blocking the NMDA receptor. At present, only ten randomized, double-blind, controlled trials have been performed on oral drug treatment of pain after SCI, the results of most of which were negative. The studies included antidepressants (amitriptyline and trazodone), antiepileptics (gabapentin, pregabalin, lamotrigine and valproate) and mexiletine. Gabapentin, pregabalin and amitriptyline showed a significant reduction in neuropathic pain following SCI. Cannabinoids have been found to relieve other types of central pain, and serotonin noradrenaline reuptake inhibitors as well as opioids relieve peripheral neuropathic pain and may be used to treat patients with SCI pain.     

Emerging therapies for neuropathic pain

Neuropathic pain develops as a result of damage to either the peripheral or central nervous system. It is characterised by spontaneous burning pain and/or ongoing pain with accompanying hyperalgesia and allodynia. Neuropathic pain is difficult to treat as it is often refractory to conventional analgesic treatments, with most patients obtaining only partial relief. At present, there are four major medication categories that are considered first-line treatment for neuropathic pain: antidepressants, anticonvulsants, local anaesthetic/topical agents and opioids. The efficacy of these treatments in neuropathic pain, excepting opioids, has been discovered serendipitously. However, responder rates and overall efficacy is poor with these agents and tolerability or side effects are often limiting. This update will review existing treatment options for neuropathic pain, and highlight more recent advances in the development of novel analgesics to treat this chronic disorder.     

Emerging therapies for neuropathic pain

Neuropathic pain develops as a result of damage to either the peripheral or central nervous system. It is characterised by spontaneous burning pain and/or ongoing pain with accompanying hyperalgesia and allodynia. Neuropathic pain is difficult to treat as it is often refractory to conventional analgesic treatments, with most patients obtaining only partial relief. At present, there are four major medication categories that are considered first-line treatment for neuropathic pain: antidepressants, anticonvulsants, local anaesthetic/topical agents and opioids. The efficacy of these treatments in neuropathic pain, excepting opioids, has been discovered serendipitously. However, responder rates and overall efficacy is poor with these agents and tolerability or side effects are often limiting. This update will review existing treatment options for neuropathic pain, and highlight more recent advances in the development of novel analgesics to treat this chronic disorder.     

Depression-like behavior and mechanical allodynia are reduced by bis selenide treatment in mice with chronic constriction injury: a comparison with fluoxetine, amitriptyline, and bupropion

Rationale

Neuropathic pain is associated with significant co-morbidities, including depression, which impact considerably on the overall patient experience. Pain co-morbidity symptoms are rarely assessed in animal models of neuropathic pain. Neuropathic pain is characterized by hyperexcitability within nociceptive pathways and remains difficult to treat with standard analgesics.

Objectives

The present study determined the effect of bis selenide and conventional antidepressants (fluoxetine, amitriptyline, and bupropion) on neuropathic pain using mechanical allodynic and on depressive-like behavior.

Methods

Male mice were subjected to chronic constriction injury (CCI) or sham surgery and were assessed on day 14 after operation. Mice received oral treatment with bis selenide (1–5 mg/kg), fluoxetine, amitriptyline, or bupropion (10–30 mg/kg). The response frequency to mechanical allodynia in mice was measured with von Frey hairs. Mice were evaluated in the forced swimming test (FST) test for depression-like behavior.

Results

The CCI procedure produced mechanical allodynia and increased depressive-like behavior in the FST. All of the drugs produced antiallodynic effects in CCI mice and produced antidepressant effects in control mice without altering locomotor activity. In CCI animals, however, only the amitriptyline and bis selenide treatments significantly reduced immobility in the FST.

Conclusion

These data demonstrate an important dissociation between the antiallodynic and antidepressant effects in mice when tested in a model of neuropathic pain. Depressive behavior in CCI mice was reversed by bis selenide and amitriptyline but not by the conventional antidepressants fluoxetine and buproprion. Bis selenide was more potent than the other drugs tested for antidepressant-like and antiallodynic effects in mice.     

Neuropathic pain: is the end of suffering starting in the gene therapy?

Neuropathic pain is defined as pain initiated or caused by a primary lesion or dysfunction in the nervous system. It is a devastating and difficult to manage consequence of peripheral nerve injury and has a variety of clinical symptoms. Neuropathic pain is a major health problem. It has been estimated that 70% of patients with advanced cancer and inflammatory pathologies are afflicted by chronic pain. About 95% of patients with spinal cord injuries have neuropathic pain problems. Chronic pain is debilitating and cause of depression and decreasing quality of life. Pharmacological treatment for the symptoms of painful neuropathy is difficult, because there has been limited understanding of the underlying causes and systemic levels that an effective dose can have on multiple side effects. The use of molecular methods, such as gene therapy, stem cell therapy and viral vector for delivery of biologic antinociceptive molecules, has led to a better understanding of the underlying mechanisms of the induction of intractable neuropathic pain.     

神经病理性疼痛的受体机制研究进展

神经病理性疼痛是一类治疗难度非常大的慢性疼痛,由于其发病机制尚未完全阐明,目前尚缺乏理想的治疗药物。以往研究显示,神经病理性疼痛与阿片受体、NMDA受体等有关,现阶段又发现多种受体参与了神经病理性疼痛的病理生理过程。该文综述了嘌呤与嘧啶受体、GABA受体、PAF受体等在神经病理性疼痛发病机制中的作用。     

基于炎症信号通路的生物碱治疗神经病理性疼痛的研究进展

神经病理性疼痛是由神经系统原发性损害和功能障碍所激发或引起的疼痛,炎症作为神经病理性疼痛发展的重要病机之一,是生物体对组织损伤做出的一种正常生理反应。炎症介导的神经病理性疼痛发展机制与外周神经敏化、中枢神经敏化息息相关,包括神经炎症反应、氧化应激反应、离子通道改变、胶质细胞的活化。常见的中药成分马钱子碱、小檗碱、去氢紫堇鳞茎碱、川芎嗪、氧化苦参碱、青藤碱均可缓解神经病理性疼痛。生物碱可通过多条途径影响神经病理性疼痛,其发挥的抗炎作用影响着外周神经敏化和中枢神经敏化,是治疗神经病理性疼痛的重要机制之一。因此生物碱介导的炎症反应具有良好的抗神经元损伤作用,对神经病理性疼痛产生一定的治疗作用。总结了炎症参与神经病理性疼痛和生物碱抗炎镇痛的机制,拟从分子层面阐释生物碱发挥抗神经病理性疼痛的作用机制。     

Conclusions: chronic pain studies of lidocaine patch 5% using the Neuropathic Pain Scale

Many chronic pain patients have multiple etiologies for their pain, and accurate characterization of pain qualities and pain relief is essential for managing their pain. The ability to utilize a validated tool for assessing pain qualities and for identifying unique analgesic therapy effects on different pain qualities may assist clinicians in devising an appropriate treatment regimen. The Neuropathic Pain Scale (NPS) is a novel pain metric for characterizing pain in 10 dimensions. The ability to differentiate among pain qualities for each patient may result in a more refined and effective choice of therapy. The three research articles in this Supplement demonstrate the utility of the NPS in chronic pain patients treated with the lidocaine patch 5%, a peripherally acting medication that is not associated with systemic accumulation of the active drug. Significant reduction in the intensity of commonly reported pain qualities in patients with neuropathic and non-neuropathic chronic pain due to low-back pain, osteoarthritis, post-herpetic neuralgia, and painful diabetic neuropathy were achieved. The NPS offers clinicians a reliable means to accurately identify pain qualities associated with each individual patient and to target and assess the efficacy of various therapeutic options on those pain components. Utilizing the NPS, the lidocaine patch 5% was effective in treating chronic pain of both neuropathic and non-neuropathic origins suggesting that a given treatment's effect on various pain qualities may be consistent across pain types.     

NMDAR/PSD-95/nNOS复合物在神经病理性疼痛中的研究进展

神经病理性疼痛是一种常见的慢性疼痛疾病,发病机制复杂且临床治疗效果欠佳。最近研究表明, N-甲基-D-天冬氨酸受体/突触后致密蛋白95/神经元型一氧化氮合酶（NMDAR/PSD-95/nNOS）复合物在神经病理性疼痛中发挥重要作用。研究发现,如果不直接抑制NMDAR或nNOS,选择性阻断NMDAR/PSD-95或者nNOS/PSD-95的相互作用,可以在不影响NMDAR和nNOS生理功能的前提下抑制神经病理性疼痛中NO的病理性释放,可能获得没有明显副作用的安全有效的神经病理性疼痛的治疗药物。故本文对NMDAR/PSD-95/nNOS复合物在神经病理性疼痛中的研究进展进行综述。     

电压门控性钠通道亚型和神经病理性疼痛

神经病理性疼痛是神经系统损伤引起的一种慢性疼痛。感觉神经元上的电压门控性钠通道在多种由外周神经损伤引起的神经病理性疼痛中具有重要的作用。近年来,随着对钠通道亚型在神经病理性疼痛发病机制中作用的阐明,发展特异性的钠通道亚型阻断药物将成为治疗神经病理性疼痛的重要研究方向。     

Pain mechanisms in patients with chronic pain

The mechanisms involved in the development of chronic pain are varied and complex. Pain processes are plastic and unrelieved pain may lead to changes in the neural structure involved in pain generation. Nociceptive pain announces the presence of a potentially damaging stimulus that occurs when noxious stimuli activate primary afferent neurons. Neuropathic pain is initiated or caused by a primary lesion or dysfunction in the nervous system resulting from trauma, infection, ischaemia, cancer or other causes such as chemotherapy. The exact mechanisms involved in the pathophysiology of chronic pain are not well understood, but rapid and long-term changes are thought to occur in parts of the central nervous system that are involved in the transmission and modulation of pain following injury. Peripheral and central sensitization of sensory nerve fibres are the primary reasons for hypersensitivity to pain after injury, and mainly occur in inflammatory and neuropathic pain. During these processes the sensation of pain is enhanced as a result of changes in the environment, the nerve fibres and modifications of the functional properties and the genetic programme of primary and secondary afferent neurons. Non-steroidal anti-inflammatory drugs and opioid analgesics are two of the most common classes of drugs used for the treatment of pain. Response to drug treatment shows significant interindividual variability and can lead to side effects. The neurobiological mechanisms that cause pain may account for the different types of pain observed. Identification of these mechanisms may allow us to move from an empirical therapeutic approach to one that it is specifically targeted at the particular mechanisms of the type of pain experienced by an individual patient.     

P2X4受体结构及其参与神经病理性痛机制的研究进展

神经病理性痛是神经系统炎症或损伤后引发的一种慢性疼痛,其发病机制复杂,目前仍缺乏有效的治疗药物。近年来针对P2X4受体的蛋白结构及配体结合相关的重要部位开展了大量研究,发现表达于脊髓背角小胶质细胞的P2X4受体在神经病理性痛的发生和发展过程中具有重要的作用,提示其可能参与了神经病理性痛的发病。本文就P2X4受体的结构及其参与神经病理性痛的可能机制作一综述,试图为靶向P2X4受体研发新型抗神经病理性痛药物提供新的线索。     

Cannabinoids for the treatment of neuropathic pain: clinical evidence

Neuropathic pain is a worldwide epidemic that occurs in 3 to 8% of individuals in industrialized countries and is often refractory to existing treatments. Drugs currently available to target neuropathic pain are, at best, moderately effective and include antidepressants, gabapentin, NMDA receptor antagonists, as well as other anticonvulsants, all of which are limited by their adverse-effect profiles. Cannabinoid drugs are emerging as a promising class of drugs to treat neuropathic pain and have been tested for analgesic effects in a range of chronic pain conditions. Data show that cannabinoids are often effective in individuals with refractory pain receiving concomitant analgesic drugs. Clinical studies on cannabinoids for the treatment of neuropathic pain are reviewed, focusing on clinical trials published within the last five years. Data from large, well-controlled studies show that cannabinoids are moderately effective in reducing chronic pain and that side effects are comparable to existing treatments, suggesting that cannabinoids can play a useful role in the management of chronic pain. Like other drugs for neuropathic pain, cannabinoids have a dose titration that is limited by psychoactive side effects. The development of cannabinoid drugs to target neuropathic pain with improved therapeutic ratios will depend upon the development of cannabinoid treatments with reduced psychoactivity.     

The clinical picture of neuropathic pain.

Neuropathic pains refer to a heterogeneous group of pain conditions characterised by lesion or dysfunction of the normal sensory pathways. Clinical characteristics include: delayed onset of pain after nervous system lesion, pain in area of sensory loss, spontaneous and different evoked types of pains. It has so far only been possible to classify these pains on basis of underlying cause or on anatomical location. The mechanisms underlying neuropathic pain are not yet clear, but neuronal hyperexcitability in those neurons that have lost their normal patterned input seems to be a common denominator for many, if not all types, of neuropathic pains. Along these lines, a mechanism-based classification has recently been proposed, which is an attractive approach because it provides a frame for a rationally based therapy of neuropathic pains. The clinical manifestations of neuronal hyperexcitability due to nervous system lesions is described.     

Ziconotide infusion for severe chronic pain: case series of patients with neuropathic pain

Ziconotide intrathecal infusion was recently approved by the United States Food and Drug Administration for the treatment of intractable severe chronic pain. Patients with neuropathic pain make up a significant population among those who experience chronic pain for which there are less than optimal pharmacotherapeutic options. Published clinical trials provide a global view of ziconotide efficacy and safety. A subset of patients in clinical trials obtained complete pain relief, a remarkable finding given the history of drug treatment for neuropathic pain. To provide more information regarding those who respond to ziconotide therapy, we discuss three patients with neuropathic pain who received ziconotide infusion. Two patients with longstanding neuropathic pain, one with complex regional pain syndrome (formerly known as reflex sympathetic dystrophy) of the leg and one with lumbar radiculitis, achieved temporary but complete pain relief from single 5- and 10-microg epidural test doses. In the third case, a patient with longstanding bilateral leg and foot neuropathic pain from acquired immunodeficiency syndrome and antiretroviral drug therapy achieved considerable pain relief from a long-term continuous intrathecal infusion. The patients who received a single dose had mild central nervous system adverse effects such as sedation, somnolence, nausea, headache, and lightheadedness. The patient who received the intrathecal infusion experienced mild-to-severe adverse effects depending on the rate of infusion; these effects included sedation, confusion, memory impairment, slurred speech, and double vision. This patient could sense impending adverse effects and made rate adjustments or suspended infusion to avert untoward symptoms. In all three cases, patients achieved considerable pain relief that was long-lasting and persisted well after dose administration or suspension of infusion.