Antidepressants and gabapentinoids in neuropathic pain: Mechanistic insights

Discovery and Profiling of New Multimodal Phenylglycinamide Derivatives as Potent Antiseizure and Antinociceptive Drug Candidates

We developed a focused series of original phenyl-glycinamide derivatives which showed potent activity across in vivo mouse seizure models, namely, maximal electroshock (MES) and 6 Hz (using both 32 and 44 mA current intensities) seizure models. Following intraperitoneal (i.p.) administration, compound (R)-32, which was identified as a lead molecule, demonstrated potent protection against all seizure models with ED50 values of 73.9 mg/kg (MES test), 18.8 mg/kg (6 Hz, 32 mA test), and 26.5 mg/kg (6 Hz, 44 mA test). Furthermore, (R)-32 demonstrated efficacy in both the PTZ-induced kindling paradigm and the ivPTZ seizure threshold test. The expression of neurotrophic factors, such as mature brain-derived neurotrophic factor (mBDNF) and nerve growth factor (NGF), in the hippocampus and/or cortex of mice, and the levels of glutamate and GABA were normalized after PTZ-induced kindling by (R)-32. Importantly, besides antiseizure activity, (R)-32 demonstrated potent antinociceptive efficacy in formalin-induced pain, capsaicin-induced pain, as well as oxaliplatin- and streptozotocin-induced peripheral neuropathy in mice (i.p.). No influence on muscular strength and body temperature in mice was observed. Pharmacokinetic studies and in vitro ADME-Tox data (i.e., high metabolic stability in human liver microsomes, a weak influence on CYPs, no hepatotoxicity, satisfactory passive transport, etc.) proved favorable drug-like properties of (R)-32. Thermal stability of (R)-32 shown in thermogravimetry and differential scanning calorimetry gives the opportunity to develop innovative oral solid dosage forms loaded with this compound. The in vitro binding and functional assays indicated its multimodal mechanism of action. (R)-32, beyond TRPV1 antagonism, inhibited calcium and sodium currents at a concentration of 10 μM. Therefore, the data obtained in the current studies justify a more detailed preclinical development of (R)-32 for epilepsy and pain indications.

Quantitative analysis of nortriptyline's analgesic properties: a comparative systematic review and meta-analysis

OBJECTIVES

This study aims to quantitatively analyse nortriptyline's analgesic potency, safety and tolerability.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

The systematic search was conducted in Scopus, Web of Science and PubMed in February 2023.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Clinical trials evaluating the efficacy of nortriptyline in reducing pain scores (open-label studies and comparisons of nortriptyline with placebo or other analgesics) in different pain types were included.

DATA EXTRACTION AND SYNTHESIS

The data extraction procedure and the screening phases were carried out based on predetermined eligibility criteria. To pool the data, the standardised mean difference (SMD) and standardised mean change (SMC) methods, along with random-effect and fixed-effect meta-analysis, were used. The risk of bias was assessed using the Cochrane Collaboration method, and the Grading of Recommendations Assessment, Development and Evaluation criteria were used to measure the certainty of the results.

RESULTS

14 of the initial 648 studies were eventually imported. Nortriptyline was reported to significantly reduce pain severity in chronic low back pain, painful symptoms in major depressive disorder, neuropathy, chronic pelvic pain and neuropathic corneal pain. However, it was not superior to placebo in fibromyalgia and knee osteoarthritis. In comparison to placebo and various alternative analgesics, the pooled SMD for lowering pain scores was 0.43 (0.23-0.64) and -0.18 (-0.39 to 0.03), respectively. In the pretreatment and post-treatment analyses, the pooled SMC was -1.20 (-1.48 to -0.93). Although constipation and xerostomia were the most commonly reported side effects, all references indicated that the adverse events were well tolerated at the administered dosages.

CONCLUSION

While nortriptyline is effective in some chronic pains, such as neuropathies, it lacks efficacy in some other chronic pains, such as fibromyalgia and osteoarthritis. Nortriptyline is well tolerated when administered in doses intended for its analgesic effects. Moreover, several studies suggested that the analgesic effects of nortriptyline are comparable to those of amitriptyline and gabapentin.

Integrating mechanistic-based and classification-based concepts into perioperative pain management: an educational guide for acute pain physicians

Chronic pain begins with acute pain. Physicians tend to classify pain by duration (acute vs chronic) and mechanism (nociceptive, neuropathic and nociplastic). Although this taxonomy may facilitate diagnosis and documentation, such categories are to some degree arbitrary constructs, with significant overlap in terms of mechanisms and treatments. In clinical practice, there are myriad different definitions for chronic pain and a substantial portion of chronic pain involves mixed phenotypes. Classification of pain based on acuity and mechanisms informs management at all levels and constitutes a critical part of guidelines and treatment for chronic pain care. Yet specialty care is often siloed, with advances in understanding lagging years behind in some areas in which these developments should be at the forefront of clinical practice. For example, in perioperative pain management, enhanced recovery protocols are not standardized and tend to drive treatment without consideration of mechanisms, which in many cases may be incongruent with personalized medicine and mechanism-based treatment. In this educational document, we discuss mechanisms and classification of pain as it pertains to commonly performed surgical procedures. Our goal is to provide a clinical reference for the acute pain physician to facilitate pain management decision-making (both diagnosis and therapy) in the perioperative period.

Postoperative Multimodal Analgesia Strategy for Enhanced Recovery After Surgery in Elderly Colorectal Cancer Patients

Enhanced Recovery After Surgery (ERAS) protocols have substantially proven their merit in diminishing recuperation durations and mitigating postoperative adverse events in geriatric populations undergoing colorectal cancer procedures. Despite this, the pivotal aspect of postoperative pain control has not garnered the commensurate attention it deserves. Typically, employing a multimodal analgesia regimen that weaves together nonsteroidal anti-inflammatory drugs, opioids, local anesthetics, and nerve blocks stands paramount in curtailing surgical complications and facilitating reduced convalescence within hospital confines. Nevertheless, this integrative pain strategy is not devoid of pitfalls; the specter of organ dysfunction looms over the geriatric cohort, rooted in the abuse of analgesics or the complex interplay of polypharmacy. Revolutionary research is delving into alternative delivery and release modalities, seeking to allay the inadvertent consequences of analgesia and thereby potentially elevating postoperative outcomes for the elderly post-colorectal cancer surgery populace. This review examines the dual aspects of multimodal analgesia regimens by comparing their established benefits with potential limitations and offers insight into the evolving strategies of drug administration and release.

Patterns of gabapentinoid use among long-term opioid users

OBJECTIVE

Understanding the clinical and demographic profile of patients on gabapentinoids can highlight areas of prescribing disparities, inform clinical practice, and guide future research to optimize effectiveness and safety of gabapentinoids for pain management. We used a national sample of Medicare beneficiaries to examine trends, patterns, and patient-level predictors of gabapentinoid use among long-term opioid users.

METHODS

Using a national Medicare sample between 2014 and 2020, we examined factors associated with gabapentinoid use among long-term opioid users. We included Medicare eligible long-term opioid users with no prior gabapentinoid use. The primary outcome was gabapentinoid use after the long-term opioid use episode. Logistic regression was used to test the association with gabapentinoid use for year, age, sex, race/ethnicity, region, Medicare entitlement, low-income status, frailty, pain locations, anxiety, depression, opioid use disorder, and opioid morphine milligrams equivalent.

RESULTS

Gabapentinoid use among long-term opioid users increased from 12.6% in 2014 to 16.8% in 2019 (p < .0001). Factors associated with increased gabapentinoid use were Hispanic ethnicity, back pain, nerve pain, and moderate or high opioid usage. Factors associated with decreased gabapentinoid use were older age and Medicare entitlement due to old age.

CONCLUSIONS

Variation of gabapentinoid use by socio-demographics and insurance status indicates opportunities to improve pain management and a need for shared therapeutic decision making informed by discussion between pain patients and providers regarding safety and effectiveness of pain therapies. Our findings underscore the need for future research into the comparative effectiveness and safety of gabapentinoids for non-cancer chronic pain in various subpopulations.

Corneal neuropathic pain: a review to inform clinical practice

Corneal neuropathic pain (CNP) is a poorly defined disease entity characterised by an aberrant pain response to normally non-painful stimuli and categorised into having peripheral and central mechanisms, with the former responding to instillation of topical anaesthetic. CNP is a challenging condition to diagnose due to numerous aetiologies, an absence of clinical signs and ancillary tests (in vivo confocal microscopy and esthesiometry), lacking the ability to confirm the diagnosis and having limited availability. Symptomatology maybe mirrored by severe and chronic forms of dry eye disease (DED), often leading to misdiagnosis and inadequate treatment. In practice, patients with suspected CNP can be assessed with questionnaires to elicit symptoms. A thorough ocular assessment is also performed to exclude any co-existent ocular conditions. A medical and mental health history should be sought due to associations with autoimmune disease, chronic pain syndromes, anxiety and depression. Management begins with communicating to the patient the nature of their condition. Ophthalmologists can prescribe topical therapies such as autologous serum eyedrops to optimise the ocular surface and promote neural regeneration. However, a multi-disciplinary treatment approach is often required, including mental health support, particularly when there are central mechanisms. General practitioners, pain specialists, neurologists and psychologists may be needed to assist with oral and behavioural therapies. Less data is available to support the safety and efficacy of adjuvant and surgical therapies and the long-term natural history remains to be determined. Hence clinical trials and registry studies are urgently needed to fill these data gaps with the aim to improve patient care.

Effect of Gabapentin on Tendon-to-Bone Healing in a Rat Model of Rotator Cuff Repair

BACKGROUND

Gabapentin is often used as an analgesic after rotator cuff repair surgery and is recommended as an additional analgesic for arthroscopic rotator cuff repairs. However, evidence of its effects on biological healing mechanisms is lacking. The objective of this study was to investigate the potential of gabapentin in improving tendon-to-bone healing after rotator cuff repair using a rat model.

MATERIALS AND METHODS

A total of 20 male rats were randomly allocated to one of two groups: group 1 (repair only, n=10) or group 2 (gabapentin injection, n=10). The rats in the experimental group (group 2) were administered 80 mg/kg of gabapentin subcutaneously 30 minutes before surgery, followed by 80 mg/kg subcutaneously every 24 hours for 48 hours. We used the left shoulder of every rat, while for biomechanical analysis, we used the right shoulder.

RESULTS

There was no significant difference in the load to failure, ultimate stress, or elongation between the groups. Collagen continuity, orientation, and density were better in group 2 than group 1.

CONCLUSION

In a rat model of rotator cuff repair, gabapentin had a positive impact on the quality of collagen organization at the junction between the tendon and bone, while preserving the biomechanical properties. We propose the use of gabapentin as a supplementary analgesic agent for postoperative pain relief after arthroscopic rotator cuff repair; however, further studies of the effect of gabapentin on biological healing mechanisms are required. [Orthopedics. 202x;4x(x):xx-xx.].

The Impact of Gabapentinoids on Pain-Related Outcomes after Knee and Hip Surgery: A Systematic Review with Meta-Analysis of Randomized Controlled Trials

Background: Postoperative pain remains a significant challenge after knee and hip surgeries, two of the most frequently performed procedures, preventing patients from seeking timely surgical help. Gabapentinoids, gabapentin, and pregabalin, have been gaining attention in postoperative pain management. Methods: We conducted a meta-analysis to evaluate the efficacy of gabapentinoids in pain management after knee and hip surgery. PubMed, Scopus, and Cochrane Library were searched for relevant randomized controlled trials (RCTs) published before January 2023. Results: Fifteen articles reporting 1320 patients were analyzed. Cumulative pain intensity at rest and on movement was lower in the experimental group with the mean difference (MD) = -0.30 [-0.55,-0.05], p-value = 0.02, and MD = -0.41 [-0.68,-0.13], p-value = 0.004, respectively. However, the difference was not clinically meaningful and lacked statistical significance at each time period. The gabapentinoid group required less opioid consumption in morphine equivalents (MD = -6.42 [-9.07, -3.78] mg, p-value < 0.001). There was a lower incidence of postoperative nausea in the experimental group with a risk ratio (RR) of 0.69 [0.55, 0.86], p-value < 0.001. A subgroup analysis showed that gabapentinoids reduced pain on movement on postoperative day two after total knee arthroplasty but not hip arthroplasty. There was insufficient data to examine the efficacy of gabapentinoids in the reduction of chronic postoperative pain in knee/hip surgery. Conclusions: Thus, gabapentinoids were associated with a reduction in postoperative pain intensity at rest and on movement, morphine consumption, and the incidence of postoperative nausea in the early postoperative period following knee and hip surgeries. However, pain reduction was not clinically relevant. Sedation has not been evaluated in this work and, if performed, this may have influenced the conclusions. An important limitation of this study is that different gabapentinoids, their administration times and dosages, as well as varying intraoperative management protocols, were pooled together.

Mirogabalin inhibits scratching behavior of spontaneous model mouse of atopic dermatitis

Introduction: Atopic dermatitis (AD) is one of the most prevalent intractable chronic itch diseases worldwide. In recent years, new molecular-targeted drugs have emerged, but side effects and economic challenges remain. Therefore, since it is important for AD patients to have a wider range of treatment options, it is important to explore new therapeutic agents. Gabapentinoids, gabapentin and pregabalin, have been shown to be effective for the clinical treatment of several chronic itch. Recently, mirogabalin (MGB) was developed as a novel gabapentinoid. MGB is a drug for neuropathic pain and has a margin of safety between its side effects and the analgesic effect for animal experiments. Herein, we showed that MGB exhibited an antipruritic effect in a mouse model of AD using NC/Nga mice. Methods and results: The oral administration of MGB (10 mg/kg) inhibited spontaneous scratching behavior in AD mice and its effect was dose dependently. Then, when MGB (10 mg/kg) was orally administrated to healthy mice, it did not affect motor function, including locomotor activity, wheel activity, and coordinated movement. Moreover, gabapentin (100 mg/kg) and pregabalin (30 mg/kg), inhibited spontaneous scratching behavior in AD mice and decreased motor function in healthy mice. Furthermore, intracisternal injection of MGB (10 μg/site) significantly suppressed spontaneous scratching behavior in AD mice. Discussion: In summary, our results suggest that MGB exerts an antipruritic effect via the spinal dorsal horn using NC/Nga mice. We hope that MGB is a candidate for a novel therapeutic agent for AD with relatively few side effects.

Repetitive transcranial magnetic stimulation in central post-stroke pain: a meta-analysis and systematic review of randomized controlled trials

Background

The rehabilitation of central post-stroke pain (CPSP) is a complex clinical challenge, and repetitive transcranial magnetic stimulation (rTMS) has been widely applied in the research of neurofunctional recovery following stroke. However, there is currently no reliable evidence-based medicine supporting the efficacy of rTMS in central post-stroke pain. This review aims to evaluate the effects of rTMS on central post-stroke pain.

Methods

Following the PRISMA guidelines, we conducted searches on PubMed, Cochrane Library, Embase, Web of Science, CNKI, and Wan Fang Data Knowledge Service Platform. We searched for randomized controlled trials (RCTs) investigating the use of rTMS in treating central post-stroke pain, and conducted screening based on inclusion and exclusion criteria. Characteristics of the included RCTs were extracted. The heterogeneity of the trials was assessed using the I2 statistic. Meta-analysis was performed using Stata 17 software. Bias risk and methodological quality were evaluated using the Cochrane RoB 2 tool and the Pedro scale.

Results

A total of six randomized controlled trials involving 288 patients met our inclusion criteria. In our analysis, rTMS was more effective in treating patients with CPSP compared to the placebo group (SMD=-1.15, 95% CI: -1.69, -0.61, P < 0.001). Furthermore, results from subgroup analysis indicated no statistically significant difference in the improvement of pain for durations exceeding 6 months when comparing rTMS to conventional treatment (SMD=-0.80, 95% CI: -1.63, 0.03, P = 0.059).

Conclusion

TMS can alleviate pain in CPSP patients and improve their motor function, but its effects on depression, anxiety, and MEP-latency are not significant.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, CRD42024497530.

Electroacupuncture attenuates neuropathic pain via suppressing BIP-IRE-1α-mediated endoplasmic reticulum stress in the anterior cingulate cortex

Studies have suggested that endoplasmic reticulum stress (ERS) is involved in neurological dysfunction and that electroacupuncture (EA) attenuates neuropathic pain (NP) via undefined pathways. However, the role of ERS in the anterior cingulate cortex (ACC) in NP and the effect of EA on ERS in the ACC have not yet been investigated. In this study, an NP model was established by chronic constriction injury (CCI) of the left sciatic nerve in rats, and mechanical and cold tests were used to evaluate behavioral hyperalgesia. The protein expression and distribution were evaluated using western blotting and immunofluorescence. The results showed that glucose-regulated protein 78 (BIP) and inositol-requiring enzyme 1α (IRE-1α) were co-localized in neurons in the ACC. After CCI, BIP, IRE-1α, and phosphorylation of IRE-1α were upregulated in the ACC. Intra-ACC administration of 4-PBA and Kira-6 attenuated pain hypersensitivity and downregulated phosphorylation of IRE-1α, while intraperitoneal injection of 4-PBA attenuated hyperalgesia and inhibited the activation of P38 and JNK in ACC. In contrast, ERS activation by intraperitoneal injection of tunicamycin induced behavioral hyperalgesia in naive rats. Furthermore, EA attenuated pain hypersensitivity and inhibited the CCI-induced overexpression of BIP and pIRE-1α. Taken together, these results demonstrate that EA attenuates NP by suppressing BIP- and IRE-1α-mediated ERS in the ACC. Our study presents novel evidence that ERS in the ACC is implicated in the development of NP and provides insights into the molecular mechanisms involved in the analgesic effect of EA.

Mechanisms and treatment of opioid-induced pruritus: Peripheral and central pathways

BACKGROUND AND OBJECTIVE

Pruritus (also known as itch) is defined as an unpleasant and irritating sensation of the skin that provokes an urge to scratch or rub. It is well known that opioid administration can cause pruritus, which is paradoxical as itch and pain share overlapping sensory pathways. Because opioids inhibit pain but can cause itching. Significant progress has been made to improve our understanding of the fundamental neurobiology of itch; however, much remains unknown about the mechanisms of opioid-induced pruritus. The prevention and treatment of opioid-induced pruritus remains a challenge in the field of pain management. The objective of this narrative review is to present and discuss the current body of literature and summarize the current understanding of the mechanisms underlying opioid-induced pruritus, and its relationship to analgesia, and possible treatment options.

RESULTS

The incidence of opioid-induced pruritus differs with different opioids and routes of administration, and the various mechanisms can be broadly divided into peripheral and central. Especially central mechanisms are intricate, even at the level of the spinal dorsal horn. There is evidence that opioid receptor antagonists and mixed agonist and antagonists, especially μ-opioid antagonists and κ-opioid agonists, are effective in relieving opioid-induced pruritus. Various treatments have been used for opioid-induced pruritus; however, most of them are controversial and have conflicting results.

CONCLUSION

The use of a multimodal analgesic treatment regimen combined with a mixed antagonist and κ agonists, especially μ-opioid antagonists, and κ-opioid agonists, seems to be the current best treatment modality for the management of opioid-induced pruritus and pain.

SIGNIFICANCE

Opioids remain the gold standard for the treatment of moderate to severe acute pain as well as cancer pain. It is well known that opioid-induced pruritus often does not respond to regular antipruritic treatment, thereby posing a challenge to clinicians in the field of pain management. We believe that our review makes a significant contribution to the literature, as studies on the mechanisms of opioid-induced pruritus and effective management strategies are crucial for the management of these patients.

Neurophysiology of corneal neuropathic pain and emerging pharmacotherapeutics

The altered activity generated by corneal neuronal injury can result in morphological and physiological changes in the architecture of synaptic connections in the nervous system. These changes can alter the sensitivity of neurons (both second-order and higher-order projection) projecting pain signals. A complex process involving different cell types, molecules, nerves, dendritic cells, neurokines, neuropeptides, and axon guidance molecules causes a high level of sensory rearrangement, which is germane to all the phases in the pathomechanism of corneal neuropathic pain. Immune cells migrating to the region of nerve injury assist in pain generation by secreting neurokines that ensure nerve depolarization. Furthermore, excitability in the central pain pathway is perpetuated by local activation of microglia in the trigeminal ganglion and alterations of the descending inhibitory modulation for corneal pain arriving from central nervous system. Corneal neuropathic pain may be facilitated by dysfunctional structures in the central somatosensory nervous system due to a lesion, altered synaptogenesis, or genetic abnormality. Understanding these important pathways will provide novel therapeutic insight.

Desipramine induces anti-inflammatory dorsal root ganglion transcriptional signatures in the murine spared nerve injury model

Monoamine-targeting antidepressants serve as frontline medications for chronic pain and associated comorbidities. While persistent anti-allodynic properties of antidepressants generally require weeks of treatment, several groups have demonstrated acute analgesic effects within hours of administration, suggesting a role in non-mesocorticolimbic pain processing regions such as the peripheral nervous system. To further explore this possibility, after four weeks of spared nerve injury or sham surgeries, we systemically administered desipramine or saline for an additional three weeks and performed whole transcriptome RNA sequencing on L3-6 dorsal root ganglia. Along with alterations in molecular pathways associated with neuronal activity, we observed a robust immunomodulatory transcriptional signature in the desipramine treated group. Cell subtype deconvolution predicted that these changes were associated with A- and C-fibers. Of note, differentially expressed genes from the dorsal root ganglia of DMI-treated, injured mice were largely unique compared to those from the nucleus accumbens of the same animals. These observations suggest that, under peripheral nerve injury conditions, desipramine induces specific gene expression changes across various regions of the nociceptive circuitry.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Combination Drug Therapy for the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (NP) is an increasingly prevalent disease and leading cause of disability which is challenging to treat. Several distinct classes of drugs are currently used for the treatment of chronic NP, but each drug targets only narrow components of the underlying pathophysiological mechanisms, bears limited efficacy, and comes with dose-limiting side effects. Multimodal therapies have been increasingly proposed as potential therapeutic approaches to target the multiple mechanisms underlying nociceptive transmission and modulation. However, while preclinical studies with combination therapies showed promise to improve efficacy over monotherapy, clinical trial data on their efficacy in specific populations are lacking and increased risk for adverse effects should be carefully considered. Drug-drug co-crystallization has emerged as an innovative pharmacological approach which can combine two or more different active pharmaceutical ingredients in a single crystal, optimizing pharmacokinetic and physicochemical characteristics of the native molecules, thus potentially capitalizing on the synergistic efficacy between classes of drugs while simplifying adherence and minimizing the risk of side effects by reducing the doses. In this work, we review the current pharmacological options for the treatment of chronic NP, focusing on combination therapies and their ongoing developing programs and highlighting the potential of co-crystals as novel approaches to chronic NP management.

Mechanisms and treatments of chronic pain after traumatic brain injury

While pain after trauma generally resolves, some trauma patients experience pain for months to years after injury. An example, relevant to both combat and civilian settings, is chronic pain after traumatic brain injury (TBI). Headache as well as pain in the back and extremities are common locations for TBI-related chronic pain to be experienced. TBI-related pain can exist alone or can exacerbate pain from other injuries long after healing has occurred. Consequences of chronic pain in these settings include increased suffering, higher levels of disability, serious emotional problems, and worsened cognitive deficits. The current review will examine recent evidence regarding dysfunction of endogenous pain modulatory mechanisms, neuroplastic changes in the trigeminal circuitry and alterations in spinal nociceptive processing as contributors to TBI-related chronic pain. Key pain modulatory centers including the locus coeruleus, periaqueductal grey matter, and rostroventromedial medulla are vulnerable to TBI. Both the rationales and existing evidence for the use of monoamine reuptake inhibitors, CGRP antagonists, CXCR2 chemokine receptor antagonists, and interventional therapies will be presented. While consensus guidelines for the management of chronic post-traumatic TBI-related pain are lacking, several approaches to this clinically challenging situation deserve focused evaluation and may prove to be viable therapeutic options.

Neuropathic pain: From actual pharmacological treatments to new therapeutic horizons

Neuropathic pain, caused by a lesion or disease affecting the somatosensory system, affects between 3 and 17% of the general population. The treatment of neuropathic pain is challenging due to its heterogeneous etiologies, lack of objective diagnostic tools and resistance to classical analgesic drugs. First-line treatments recommended by the Special Interest Group on Neuropathic Pain (NeuPSIG) and European Federation of Neurological Societies (EFNS) include gabapentinoids, tricyclic antidepressants (TCAs) and selective serotonin noradrenaline reuptake inhibitors (SNRIs). Nevertheless these treatments have modest efficacy or dose limiting side effects. There is therefore a growing number of preclinical and clinical studies aim at developing new treatment strategies to treat neuropathic pain with better efficacy, selectivity, and less side effects. In this review, after a brief description of the mechanisms of action, efficacy, and limitations of current therapeutic drugs, we reviewed new preclinical and clinical targets currently under investigation, as well as promising non-pharmacological alternatives and their potential co-use with pharmacological treatments.

Antidepressant-like Effects of Representative Types of Food and Their Possible Mechanisms

Depression is a mental disorder characterized by low mood, lack of motivation, negative cognitive outlook, and sleep problems. Suicide may occur in severe cases, although suicidal thoughts are not seen in all cases. Globally, an estimated 350 million individuals grapple with depression, as reported by the World Health Organization. At present, drug and psychological treatments are the main treatments, but they produce insufficient responses in many patients and fail to work at all in many others. Consequently, treating depression has long been an important topic in society. Given the escalating prevalence of depression, a comprehensive strategy for managing its symptoms and impacts has garnered significant attention. In this context, nutritional psychiatry emerges as a promising avenue. Extensive research has underscored the potential benefits of a well-rounded diet rich in fruits, vegetables, fish, and meat in alleviating depressive symptoms. However, the intricate mechanisms linking dietary interventions to brain function alterations remain largely unexplored. This review delves into the intricate relationship between dietary patterns and depression, while exploring the plausible mechanisms underlying the impact of dietary interventions on depression management. As we endeavor to unveil the pathways through which nutrition influences mental well-being, a holistic perspective that encompasses multidisciplinary strategies gains prominence, potentially reshaping how we approach and address depression.

Adjuvants for balanced anesthesia in ambulatory surgery

Balanced anesthesia relies on the simultaneous administration of different drugs to attain an anesthetic state. The classic triad of anesthesia is a combination of a hypnotic, an analgesic, and a neuromuscular blocker. It is predominantly the analgesic pillar of this triad that became more and more supported by adjuvant therapy. The aim of this approach is to evolve into an opioid-sparing technique to cope with undesirable side effects of the opioids and is fueled by the opioid epidemic. The optimal strategy for balanced general anesthesia in ambulatory surgery must aim for a transition to a multimodal analgesic regimen dealing with acute postoperative pain and ideally reduce the most common adverse effects patients are faced with at home; sore throat, delayed awakening, memory disturbances, headache, nausea and vomiting, and negative behavioral changes. Over the years, this continuum of "multimodal general anesthesia" adopted many drugs with different modes of action. This review focuses on the most recent evidence on the different adjuvants that entered clinical practice and gives an overview of the different mechanisms of action, the potential as opioid-sparing or hypnotic-sparing drugs, and the applicability specifically in ambulatory surgery.

Novel Drug Targets and Emerging Pharmacotherapies in Neuropathic Pain

Neuropathic pain is a debilitating condition characterized by abnormal signaling within the nervous system, resulting in persistent and often intense sensations of pain. It can arise from various causes, including traumatic nerve injury, neuropathy, and certain diseases. We present an overview of current and emerging pharmacotherapies for neuropathic pain, focusing on novel drug targets and potential therapeutic agents. Current pharmacotherapies, including tricyclic antidepressants, gabapentinoids, and serotonin norepinephrine re-uptake inhibitors, are discussed, as are emerging treatments, such as ambroxol, cannabidiol, and N-acetyl-L-cysteine. Additionally, the article highlights the need for further research in this field to identify new targets and develop more effective and targeted therapies for neuropathic pain management.

Pregabalin as an effective treatment for acute postoperative pain following spinal surgery without major side effects: protocol for a prospective, randomized controlled, double-blinded trial

BACKGROUND

Patients experience considerable postoperative pain after spinal surgery. As the spine is located at the centre of the body and supports body weight, severe postoperative pain hinders upper body elevation and gait which can lead to various complications, including pulmonary deterioration and pressure sores. It is important to effectively control postoperative pain to prevent such complications. Gabapentinoids are widely used as preemptive multimodal analgesia, but their effects and side effects are dose-dependent. This study was designed to examine the efficacy and side effects of varying doses of postoperative pregabalin for the treatment of postoperative pain after spinal surgery.

METHODS

This is a prospective, randomized controlled, double-blind study. A total of 132 participants will be randomly assigned to the placebo (n = 33) group or to the pregabalin 25 mg (n = 33), 50 mg (n = 33), or 75 mg (n = 33) groups. Each participant will be administered placebo or pregabalin once prior to surgery and every 12 h after surgery for 72 h. The primary outcome will be the visual analogue scale pain score, total dose of administered intravenous patient-controlled analgesia, and frequency of rescue analgesic administered for 72 h from arrival to the general ward after surgery, subdivided into four periods: 1-6 h, 6-24 h, 24-48 h, and 48-72 h. The secondary outcomes will be the incidence and frequency of nausea and vomiting due to intravenous patient-controlled analgesia. Safety will be assessed by monitoring the occurrence of side effects such as sedation, dizziness, headache, visual disturbance, and swelling.

DISCUSSION

Pregabalin is already widely used as preemptive analgesia and, unlike nonsteroidal anti-inflammatory drugs, is not associated with a risk of nonunion after spinal surgery. A recent meta-analysis demonstrated the analgesic efficacy and opioid-sparing effect of gabapentinoids with significantly decreased risks of nausea, vomiting, and pruritus. This study will provide evidence for the optimal dosage of pregabalin for the treatment of postoperative pain after spinal surgery.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05478382. Registered on 26 July 2022.

Chronic pain, chronic stress and substance use: overlapping mechanisms and implications

Chronic pain is among the most common reasons adults in the U.S. seek medical care. Despite chronic pain's substantial impact on individuals' physical, emotional, and financial wellness, the biologic underpinnings of chronic pain remain incompletely understood. Such deleterious impact on an individuals' wellness is also manifested in the substantial co-occurrence of chronic stress with chronic pain. However, whether chronic stress and adversity and related alcohol and substance misuse increases risk of developing chronic pain, and, if so, what the overlapping psychobiological processes are, is not well understood. Individuals suffering with chronic pain find alleviation through prescription opioids as well as non-prescribed cannabis, alcohol, and other drugs to control pain, and use of these substances have grown significantly. Substance misuse also increases experience of chronic stress. Thus, given the evidence showing a strong correlation between chronic stress and chronic pain, we aim to review and identify overlapping factors and processes. We first explore the predisposing factors and psychologic features common to both conditions. This is followed by examining the overlapping neural circuitry of pain and stress in order to trace a common pathophysiologic processes for the development of chronic pain and its link to substance use. Based on the previous literature and our own findings, we propose a critical role for ventromedial prefrontal cortex dysfunction, an overlapping brain area associated with the regulation of both pain and stress that is also affected by substance use, as key in the risk of developing chronic pain. Finally, we identify the need for future research in exploring the role of medial prefrontal circuits in chronic pain pathology. Critically, in order to alleviate the enormous burden of chronic pain without exacerbating the co-occurring substance misuse crisis, we emphasize the need to find better approaches to treat and prevent chronic pain.

Neuropathic Pain and Spinal Cord Injury: Management, Phenotypes, and Biomarkers

Chronic neuropathic pain after a spinal cord injury (SCI) continues to be a complex condition that is difficult to manage due to multiple underlying pathophysiological mechanisms and the association with psychosocial factors. Determining the individual contribution of each of these factors is currently not a realistic goal; however, focusing on the primary mechanisms may be more feasible. One approach used to uncover underlying mechanisms includes phenotyping using pain symptoms and somatosensory function. However, this approach does not consider cognitive and psychosocial mechanisms that may also significantly contribute to the pain experience and impact treatment outcomes. Indeed, clinical experience supports that a combination of self-management, non-pharmacological, and pharmacological approaches is needed to optimally manage pain in this population. This article will provide a broad updated summary integrating the clinical aspects of SCI-related neuropathic pain, potential pain mechanisms, evidence-based treatment recommendations, neuropathic pain phenotypes and brain biomarkers, psychosocial factors, and progress regarding how defining neuropathic pain phenotypes and other surrogate measures in the neuropathic pain field may lead to targeted treatments for neuropathic pain after SCI.

A Review of Recent Pharmacological Advances in the Management of Diabetes-Associated Peripheral Neuropathy

Diabetic peripheral neuropathy is a common complication of longstanding diabetes mellitus. These neuropathies can present in various forms, and with the increasing prevalence of diabetes mellitus, a subsequent increase in peripheral neuropathy cases has been noted. Peripheral neuropathy has a significant societal and economic burden, with patients requiring concomitant medication and often experiencing a decline in their quality of life. There is currently a wide variety of pharmacological interventions, including serotonin norepinephrine reuptake inhibitors, gapentanoids, sodium channel blockers, and tricyclic antidepressants. These medications will be discussed, as well as their respective efficacies. Recent advances in the treatment of diabetes mellitus with incretin system-modulating drugs, specifically glucagon-like peptide-1 agonists, have been promising, and their potential implication in the treatment of peripheral diabetic neuropathy is discussed in this review.

Therapeutic potential of opioid receptor heteromers in chronic pain and associated comorbidities

Chronic pain affects 20% to 45% of the global population and is often associated with the development of anxio-depressive disorders. Treatment of this debilitating condition remains particularly challenging with opioids prescribed to alleviate moderate to severe pain. However, despite strong antinociceptive properties, numerous adverse effects limit opioid use in the clinic. Moreover, opioid misuse and abuse have become a major health concern worldwide. This prompted efforts to design original strategies that would efficiently and safely relieve pain. Targeting of opioid receptor heteromers is one of these. This review summarizes our current knowledge on the role of heteromers involving opioid receptors in the context of chronic pain and anxio-depressive comorbidities. It also examines how heteromerization in native tissue affects ligand binding, receptor signalling and trafficking properties. Finally, the therapeutic potential of ligands designed to specifically target opioid receptor heteromers is considered. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Activation of β2-Adrenergic Receptors in Microglia Alleviates Neuropathic Hypersensitivity in Mice

Drugs enhancing the availability of noradrenaline are gaining prominence in the therapy of chronic neuropathic pain. However, underlying mechanisms are not well understood, and research has thus far focused on α2-adrenergic receptors and neuronal excitability. Adrenergic receptors are also expressed on glial cells, but their roles toward antinociception are not well deciphered. This study addresses the contribution of β2-adrenergic receptors (β2-ARs) to the therapeutic modulation of neuropathic pain in mice. We report that selective activation of β2-ARs with Formoterol inhibits pro-inflammatory signaling in microglia ex vivo and nerve injury-induced structural remodeling and functional activation of microglia in vivo. Systemic delivery of Formoterol inhibits behaviors related to neuropathic pain, such as mechanical hypersensitivity, cold allodynia as well as the aversive component of pain, and reverses chronically established neuropathic pain. Using conditional gene targeting for microglia-specific deletion of β2-ARs, we demonstrate that the anti-allodynic effects of Formoterol are primarily mediated by microglia. Although Formoterol also reduces astrogliosis at late stages of neuropathic pain, these functions are unrelated to β2-AR signaling in microglia. Our results underline the value of developing microglial β2-AR agonists for relief from neuropathic pain and clarify mechanistic underpinnings.

Pregabalin attenuates long-lasting post-inflammatory nociplastic mechanical sensitization in mice

Nociplastic pain, the most recently proposed mechanistic descriptor of chronic pain, is the pain resulting from an altered nociceptive system and network without clear evidence of nociceptor activation, injury or disease in the somatosensory system. As the pain-associated symptoms in many patients suffering from undiagnosed pain would result from the nociplastic mechanisms, it is an urgent issue to develop pharmaceutical therapies that would mitigate the aberrant nociception in nociplastic pain. We have recently reported that a single injection of formalin to the upper lip shows sustained sensitization lasting for more than 12 days at the bilateral hindpaws, where there is no injury or neuropathy in rats. Using the equivalent model in mice, we show that pregabalin (PGB), a drug used for treating neuropathic pain, significantly attenuates this formalin-induced widespread sensitization at the bilateral hindpaws, even on the 6 day after the initial single orofacial injection of formalin. On the 10th day after formalin injection, the hindlimb sensitization before PGB injection was no more significant in mice receiving daily PGB injections, unlike those receiving daily vehicle injections. This result suggests that PGB would act on the central pain mechanisms that undergo nociplastic changes triggered by initial inflammation and mitigate widespread sensitization resulting from the established changes.

Potential novel therapeutic strategies for neuropathic pain

Purpose

To explore the potential therapeutic strategies of different types of neuropathic pain (NP) and to summarize the cutting-edge novel approaches for NP treatment based on the clinical trials registered on ClinicalTrials.gov.

Methods

The relevant clinical trials were searched using ClinicalTrials.gov Dec 08, 2022. NP is defined as a painful condition caused by neurological lesions or diseases. All data were obtained and reviewed by the investigators to confirm whether they were related to the current topic.

Results

A total of 914 trials were included in this study. They were divided into painful diabetic neuropathy (PDN), postherpetic neuralgia (PHN), sciatica (SC), peripheral nerve injury-related NP (PNI), trigeminal neuralgia (TN), chemotherapy-induced NP (CINP), general peripheral NP (GPNP) and spinal cord injury NP (SCI-NP). Potential novel therapeutic strategies, such as novel drug targets and physical means, were discussed for each type of NP.

Conclusion

NP treatment is mainly dominated by drug therapy, and physical means have become increasingly popular. It is worth noting that novel drug targets, new implications of conventional medicine, and novel physical means can serve as promising strategies for the treatment of NP. However, more attention needs to be paid to the challenges of translating research findings into clinical practice.

Palliative care for cancer patients in veterinary medicine

Neoplasms account for approximately half of the deaths of dogs over ten years of age. This finding, associated with the fact that canine cancer patients will often suffer from the consequences of the systemic spread of the tumour and paraneoplastic syndromes, shows the importance of understanding palliative care by veterinarians and owners. In view of this, this review aims to address palliative care that can be used in veterinary medicine to promote the patient's well-being and quality of life.

Development of a PET radioligand for α2δ-1 subunit of calcium channels for imaging neuropathic pain

Neuropathic pain affects 7-10% of the adult population. Being able to accurately monitor biological changes underlying neuropathic pain will improve our understanding of neuropathic pain mechanisms and facilitate the development of novel therapeutics. Positron emission tomography (PET) is a noninvasive molecular imaging technique that can provide quantitative information of biochemical changes at the whole-body level by using radiolabeled ligands. One important biological change underlying the development of neuropathic pain is the overexpression of α2δ-1 subunit of voltage-dependent calcium channels (the target of gabapentin). Thus, we hypothesized that a radiolabeled form of gabapentin may allow imaging changes in α2δ-1 for monitoring the underlying pathophysiology of neuropathic pain. Here, we report the development of two 18F-labeled derivatives of gabapentin (trans-4-[18F]fluorogabapentin and cis-4-[18F]fluorogabapentin) and their evaluation in healthy rats and a rat model of neuropathic pain (spinal nerve ligation model). Both isomers were found to selectively bind to the α2δ-1 receptor with trans-4-[18F]fluorogabapentin having higher affinity. Both tracers displayed around 1.5- to 2-fold increased uptake in injured nerves over the contralateral uninjured nerves when measured by gamma counting ex vivo. Although the small size of the nerves and the signal from surrounding muscle prevented visualizing these changes using PET, this work demonstrates that fluorinated derivatives of gabapentin retain binding to α2δ-1 and that their radiolabeled forms can be used to detect pathological changes in vitro and ex vivo. Furthermore, this work confirms that α2δ-1 is a promising target for imaging specific features of neuropathic pain.

PSD-95 in the anterior cingulate cortex contributes to neuropathic pain by interdependent activation with NR2B

Studies suggest that the scaffolding protein, postsynaptic density protein-95 (PSD-95), is involved in multiple neurological dysfunctions. However, the role of PSD-95 in the anterior cingulate cortex (ACC) in neuropathic pain (NP) has not been investigated. The current study addressed the role of PSD-95 in the ACC in NP and its modulating profile with NMDA receptor subunit 2B (NR2B). The NP model was established by chronic constriction injury (CCI) of the sciatic nerve, and mechanical and thermal tests were used to evaluate behavioral hyperalgesia. Protein expression and distribution were evaluated using immunohistochemistry and western blotting. The results showed that PSD-95 and NR2B were co-localized in neurons in the ACC. After CCI, both PSD-95 and NR2B were upregulated in the ACC. Inhibiting NR2B with Ro 25-6981 attenuated pain hypersensitivity and decreased the over-expression of PSD-95 induced by CCI. Furthermore, intra-ACC administration of PSD-95 antisense oligonucleotide not only attenuated pain hypersensitivity but also downregulated the NR2B level and the phosphorylation of cyclic AMP response element-binding protein. These results demonstrated that PSD-95 in the ACC contributes to NP by interdependent activation of NR2B.

The Effect of Neuromodulatory Drugs on the Intensity of Chronic Pelvic Pain in Women: A Systematic Review

OBJECTIVE

 To evaluate the effect of neuromodulatory drugs on the intensity of chronic pelvic pain (CPP) in women.

DATA SOURCES

 Searches were carried out in the PubMed, Cochrane Central, Embase, Lilacs, OpenGrey, and Clinical Trials databases.

SELECTION OF STUDIES

 The searches were carried out by two of the authors, not delimiting publication date or original language. The following descriptors were used: chronic pelvic pain in women OR endometriosis, associated with MESH/ENTREE/DeCS: gabapentinoids, gabapentin, amitriptyline, antidepressant, pregabalin, anticonvulsant, sertraline, duloxetine, nortriptyline, citalopram, imipramine, venlafaxine, neuromodulation drugs, acyclic pelvic pain, serotonin, noradrenaline reuptake inhibitors, and tricyclic antidepressants, with the Boolean operator OR. Case reports and systematic reviews were excluded.

DATA COLLECTION

 The following data were extracted: author, year of publication, setting, type of study, sample size, intervention details, follow-up time, and results.

DATA SYNTHESIS

 A total of 218 articles were found, with 79 being excluded because they were repeated, leaving 139 articles for analysis: 90 were excluded in the analysis of the titles, 37 after reading the abstract, and 4 after reading the articles in full, and 1 could not be found, therefore, leaving 7 articles that were included in the review.

CONCLUSION

 Most of the studies analyzed have shown pain improvement with the help of neuromodulators for chronic pain. However, no improvement was found in the study with the highest statistical power. There is still not enough evidence that neuromodulatory drugs reduce the intensity of pain in women with CPP.

Switch of serotonergic descending inhibition into facilitation by a spinal chloride imbalance in neuropathic pain

Descending control from the brain to the spinal cord shapes our pain experience, ranging from powerful analgesia to extreme sensitivity. Increasing evidence from both preclinical and clinical studies points to an imbalance toward descending facilitation as a substrate of pathological pain, but the underlying mechanisms remain unknown. We used an optogenetic approach to manipulate serotonin (5-HT) neurons of the nucleus raphe magnus that project to the dorsal horn of the spinal cord. We found that 5-HT neurons exert an analgesic action in naïve mice that becomes proalgesic in an experimental model of neuropathic pain. We show that spinal KCC2 hypofunction turns this descending inhibitory control into paradoxical facilitation; KCC2 enhancers restored 5-HT-mediated descending inhibition and analgesia. Last, combining selective serotonin reuptake inhibitors (SSRIs) with a KCC2 enhancer yields effective analgesia against nerve injury-induced pain hypersensitivity. This uncovers a previously unidentified therapeutic path for SSRIs against neuropathic pain.

Association between gabapentinoids and oedema treated with loop-diuretics: a pooled sequence symmetry analysis from the United States and Denmark

AIMS

To assess the gabapentinoid-oedema-loop diuretic prescribing cascade in adults using large administrative health care databases from the US and Denmark.

METHODS

This study used a sequence symmetry analysis to assess loop diuretic initiation before and after the initiation of gabapentinoids among patients aged 20 years or older without heart failure or chronic kidney disease. Data from MarketScan Commercial and Medicare Supplemental Claims databases (2005 to 2019) and Danish National Prescription Register (2005 to 2018) were analyzed. Use of loop diuretics associated with initiation of selective norepinephrine reuptake inhibitors (SNRI) was used as a negative control. We assessed the pooled temporality of loop diuretic initiation relative to gabapentinoid or SNRI initiation across the two countries. Secular trend-adjusted sequence ratios (aSRs) with 95% Cis were calculated using data from 90 days before and after initiation of gabapentinoids. Pooled ratio of aSRs were calculated by comparing gabapentinoids to SNRIs.

RESULTS

Among the 1,511,493 gabapentinoid initiators (Denmark [n=338,941]; United States [n=1,172,552]), 20,139 patients had a new loop diuretic prescription 90 days before or after gabapentinoid initiation, resulting in a pooled aSR of 1.33 (95% CI 1.06-1.67). The pooled aSR for the negative control (i.e., SNRI) was 0.84 (95% CI 0.75-0.94), which resulted in a pooled ratio of aSRs of 1.58 (95% CI 1.23-2.04). Pooled estimated incidence of the gabapentinoid-loop diuretic prescribing cascade was 8.14 (95% CI, 1.92-34.49) events per 1000 patient years.

CONCLUSION

We identified evidence of the gabapentinoid-oedema-loop diuretic prescribing cascade in two countries.

Computational approach to decode the mechanism of curcuminoids against neuropathic pain

BACKGROUND

Curcumin (CUR), demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) are the main components of turmeric that commonly used to treat neuropathic pain (NP). However, the mechanism of the therapy is not sufficiently clarified. Herein, network pharmacology, molecular docking and molecular dynamics (MD) approaches were used to investigate the mechanism of curcuminoids for NP treatment.

METHODS

Active targets of curcuminoids were obtained from the Swiss Target database, and NP-related targets were retrieved from GeneCards, OMIM, Drugbank and TTD databases. A protein-protein interaction (PPI) network was built to screen the core targets. Furthermore, DAVID was used for GO and KEGG pathway enrichment analyses. Interactions between potential targets and curcuminoids were assessed by molecular docking and the MD simulations were run for 100ns to validate the docking results on the top six complexes.

RESULTS

CUR, DMC, and BDMC had 100, 99 and 100 targets respectively. After overlapping with NP there were 33, 33 and 31 targets respectively. PPI network analysis of TOP 10 core targets, TNF, GSK3β were common targets of curcuminoids. Molecular docking and MD results indicated that curcuminoids bind strongly with the core targets. The GO and KEGG showed that curcuminoids regulated nitrogen metabolism, the serotonergic synapse and ErbB signaling pathway to alleviate NP. Furthermore, specific targets in these three compounds were also analysed at the same time.

CONCLUSIONS

This study systematically explored and compared the anti-NP mechanism of curcuminoids, providing a novel perspective for their utilization.

Symptom-based pharmacotherapy for neuropathic pain related to spinal disorders: results from a patient-based assessment

Existing guidelines advocate an updated therapeutic algorithm for chronic neuropathic pain (NeP), but pharmacotherapeutic management should be individualized to pain phenotypes to achieve higher efficacy. This study was aimed to evaluate the efficacy of medications, based on NeP phenotypes, and to propose symptom-based pharmacotherapy. This retrospective study was enrolled 265 outpatients with chronic NeP related to spinal disorders. The patients were classified into three groups: spinal cord-related pain, radicular pain, and cauda equina syndrome. Data were obtained from patient-based questionnaires using Neuropathic Pain Symptom Inventory (NPSI) and the Brief Scale for Psychiatric Problems in Orthopaedic Patients, and from clinical information. The proportions of patients with ≥ 30% and ≥ 50% reduction in NPSI score for each pain subtype (spontaneous pain, paroxysmal pain, evoked pain, and paresthesia/dysesthesia) and drugs were evaluated. The pain reduction rate was significantly lower in patients with spinal cord-related pain, especially for paresthesia/dysesthesia. For spinal cord-related pain, duloxetine and neurotropin had insufficient analgesic effects, whereas mirogabalin was the most effective. Pregabalin or mirogabalin for radicular pain and duloxetine for cauda equina syndrome are recommended in cases of insufficient analgesic effects with neurotropin. The findings could contribute to better strategies for symptom-based pharmacotherapeutic management.

Nerve injury induces transient locus coeruleus activation over time: role of the locus coeruleus-dorsal reticular nucleus pathway

ABSTRACT

The transition from acute to chronic pain results in maladaptive brain remodeling, as characterized by sensorial hypersensitivity and the ensuing appearance of emotional disorders. Using the chronic constriction injury of the sciatic nerve as a model of neuropathic pain in male Sprague-Dawley rats, we identified time-dependent plasticity of locus coeruleus (LC) neurons related to the site of injury, ipsilateral (LCipsi) or contralateral (LCcontra) to the lesion, hypothesizing that the LC→dorsal reticular nucleus (DRt) pathway is involved in the pathological nociception associated with chronic pain. LCipsi inactivation with lidocaine increased cold allodynia 2 days after nerve injury but not later. However, similar blockade of LCcontra reduced cold allodynia 7 and 30 days after inducing neuropathy but not earlier. Furthermore, lidocaine blockade of the LCipsi or LCcontra reversed pain-induced depression 30 days after neuropathy. Long-term pain enhances phosphorylated cAMP-response element binding protein expression in the DRtcontra but not in the DRtipsi. Moreover, inactivation of the LCcontra→DRtcontra pathway using dual viral-mediated gene transfer of designer receptor exclusively activated by designer drugs produced consistent analgesia in evoked and spontaneous pain 30 days postinjury. This analgesia was similar to that produced by spinal activation of α2-adrenoreceptors. Furthermore, chemogenetic inactivation of the LCcontra→DRtcontra pathway induced depressive-like behaviour in naïve animals, but it did not modify long-term pain-induced depression. Overall, nerve damage activates the LCipsi, which temporally dampens the neuropathic phenotype. However, the ensuing activation of a LCcontra→DRtcontra facilitatory pain projection contributes to chronic pain, whereas global bilateral LC activation contributes to associated depressive-like phenotype.

Systematic Review of Voltage-Gated Calcium Channel α2δ Subunit Ligands for the Treatment of Chronic Neuropathic Pain and Insight into Structure-Activity Relationship (SAR) by Pharmacophore Modeling

BACKGROUND

Neuropathic pain (NP) is a complex symptom related to the nerve damage. The discovery of new drugs for treating chronic NP has been continuing for several decades, while more progress is still needed to be made because of the unsatisfactory efficacy and the side effects of the currently available drugs. Among all the approved drugs for chronic NP, voltage-gated calcium channel (VGCC) α2δ subunit ligands, also known as gabapentinoids, are among the first-line treatment and represent a class of efficacious and relatively safe therapeutic agents. However, new strategies are still needed to be explored due to the unsatisfied response rate.

OBJECTIVES

To review the latest status of the discovery and development of gabapentinoids for the treatment of chronic NP by covering both the marketed and the preclinical/clinical ones. To analyze the structure-activity relationship (SAR) of gabapentinoids to facilitate the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

METHODS

We searched PubMed Central, Embase, Cochrane Library, Web of Science, Scopus and Espacenet for the literature and patents of diabetic peripheral neuropathic pain, postherpetic neuralgia, fibromyalgia, voltage-gated calcium channel α2δ subunit and related therapeutic agents from incipient to June 10, 2021. The SAR of gabapentinoids were analyzed by pharmacophore modeling using Phase module in Schrödinger suite.

RESULTS

A variety of gabapentinoids were identified as VGCC α2δ ligands that have ever been under development for the treatment of chronic NP. Among them, four gabapentinoids are marketed, one is at the active late clinical trials, and eight have been discontinued. Pharmacophore models were generated by using Phase module in Schrödinger suite, and common pharmacophores were predicted based on pharmacophoric features and analyzed.

CONCLUSION

The latest progress of the discovery and development of gabapentinoids for the treatment of chronic NP was reviewed. Moreover, the structure-activity relationship (SAR) of gabapentinoids is analyzed by pharmacophore modeling, which will be valuable for the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

Cannabinoid drugs against chemotherapy-induced adverse effects: focus on nausea/vomiting, peripheral neuropathy and chemofog in animal models

Although new drugs are being developed for cancer treatment, classical chemotherapeutic agents are still front-line therapies, despite their frequent association with severe side effects that can hamper their use. Cannabinoids may prevent or palliate some of these side effects. The aim of the present study is to review the basic research which has been conducted evaluating the effects of cannabinoid drugs in the treatment of three important side effects induced by classical chemotherapeutic agents: nausea and vomiting, neuropathic pain and cognitive impairment. Several published studies have demonstrated that cannabinoids are useful in preventing and reducing the nausea, vomits and neuropathy induced by different chemotherapy regimens, though other side effects can occur, such as a reduction of gastrointestinal motility, along with psychotropic effects when using centrally-acting cannabinoids. Thus, peripherally-acting cannabinoids and new pharmacological options are being investigated, such as allosteric or biased agonists. Additionally, due to the increase in the survival of cancer patients, there are emerging data that demonstrate an important cognitive deterioration due to chemotherapy, and because the cannabinoid drugs have a neuroprotective effect, they could be useful in preventing chemotherapy-induced cognitive impairment (as demonstrated through studies in other neurological disorders), but this has not yet been tested. Thus, although cannabinoids seem a promising therapeutic approach in the treatment of different side effects induced by chemotherapeutic agents, future research will be necessary to find pharmacological options with a safer profile. Moreover, a new line of research awaits to be opened to elucidate their possible usefulness in preventing cognitive impairment.

Title: Novel Analgesic Potential of ß2-Agonists for Neuropathic Pain via ß2-Agonist Action

PURPOSE OF REVIEW

Multimodal therapies are often employed to treat chronic pain, and ß2-agonists are a potential drug class that shows promise. The primary aim of this paper is to discuss the role of ß2-agonists as an adjunctive therapy for chronic pain based on the current literature.

RECENT FINDINGS

Recent studies in mouse models have shown that the ß2-adrenergic system plays an essential role in the analgesic properties of antidepressant drugs used to treat neuropathic pain and that the adrenergic relies on an intact endogenous opioid system to be effective. Studies also show that ß2-agonism alone is adequate to exert anti-allodynic effects in a mouse model. This paper summarized the basic physiology and pharmacology of the sympathetic nervous system and specifically the ß2-adrenergic system and summarized current literature in its involvement in the treatment of chronic neuropathic pain.

Gabapentinoid Use in Perioperative Care and Current Controversies

PURPOSE OF REVIEW

This review summarizes the risks and benefits of gabapentinoids (gabapentin and pregabalin) for perioperative pain control and the controversies surrounding their use in a variety of settings. We review current literature with the goal of providing patient-centric and procedure-specific recommendations for the use of these medications.

RECENT FINDINGS

Gabapentinoids are among the most prescribed medications in the USA, and typically for off-label indications such as postoperative pain. In the perioperative setting, multimodal analgesic or "opioid-sparing" regimens have become the standard of care-and some clinical protocols include gabapentinoids. At the same time, guidelines regarding the perioperative use of gabapentinoids are conflicting and evidence supporting their broad use is lacking. Gabapentinoids administered perioperatively reduce opioid requirements and pain scores for a variety of surgeries. The extent of opioid and pain reduction, however, is not always clinically significant. These medications reduce postoperative nausea and vomiting as well as pruritis, likely as a feature of reducing opioid intake, but are associated with side effects such as dizziness, ataxia, and cognitive dysfunction. Gabapentinoids also increase the risk of respiratory depression, in particular when paired with opioids. There is thus evidence suggesting that the routine use of these medications for perioperative pain management is not recommended. An individualized, patient- and surgery-specific approach should be used, although research is still needed to determine risks and benefits during perioperative use.

A narrative review of molecular mechanism and therapeutic effect of Cannabidiol (CBD)

Cannabidiol (CBD) is an abundant non-psychoactive phytocannabinoid in Cannabis extracts which has high affinity on a series of receptors, including type 1 cannabinoid receptor (CB1), type 2 cannabinoid receptor (CB2), GPR55, transient receptor potential vanilloid (TRPV), and peroxisome proliferator-activated receptor gamma (PPARγ). By modulating the activities of these receptors, CBD exhibits multiple therapeutic effects, including neuroprotective, antiepileptic, anxiolytic, antipsychotic, anti-inflammatory, analgesic and anti-cancer properties. CBD could also be applied to treat or prevent COVID-19 and its complications. Here, we provide a narrative review of CBD's applications in human diseases: from mechanism of action to clinical trials.

Association of co-prescribing of opioid and benzodiazepine substitutes with incident falls and fractures among older adults: a cohort study

OBJECTIVE

Examine the association between the co-prescribing of opioids, benzodiazepines, gabapentinoids (pregabalin and gabapentin) and selective serotonin reuptake inhibitors/serotonin and norepinephrine reuptake inhibitors (SSRI/SNRIs) in different combinations and the risk of falls and fractures.

DESIGN

Retrospective cohort study from 2015 to 2018.

SETTING

Medicare enrolment and claims data.

PARTICIPANTS

Medicare beneficiaries with both chronic pain and anxiety disorders in 2016 with continuous enrolments in Parts A and B from 2015 to 2016 who were prescribed any combination of opioid, benzodiazepine, gabapentinoid and SSRI/SNRI in 2017 for ≥7 days, as documented in their Medicare Part D coverage.

INTERVENTIONS

Any combination of use of seven drug regimens (benzodiazepine +opioid; benzodiazepine +gabapentinoid; benzodiazepine +SSRI/SNRI; opioid +gabapentinoid; opioid +SSRI/SNRI; gabapentinoid +SSRI/SNRI; ≥3 drug classes).

MAIN OUTCOMES

First event of fall and the first event of fracture after the index date, which was the first day of combination drug use that lasted ≥7 days in 2017.

RESULTS

A total of 47 964 patients (mean [SD] age, 75.9 [7.1]; 78.0% woman) with diagnoses of both chronic pain and anxiety were studied. The median (Q1-Q3) duration of drug combination use was 26 (14-30) days. After adjusting for demographic characteristics, chronic conditions and history of hospitalisation and fall or fracture, the co-prescribing of ≥3 drugs (adjusted HR [aHR], 1.38; 95% CI 1.14 to 1.67) and opioid plus gabapentinoid (aHR, 1.18; 95% CI 1.02 to 1.37) were associated with a high fall risk, compared with benzodiazepineplus opioid co-prescribing, findings consistent with the secondary analysis using inverse probability of treatment weighting with propensity scores. The co-prescribing of benzodiazepine plus gabapentinoid (aHR, 0.76; 95% CI 0.59 to 0.98) was associated with lower fracture risk compared with the co-prescribing of benzodiazepine plus opioid, though this finding was not robust.

CONCLUSIONS

Our findings add to comparative toxicity research on different combinations of gabapentinoids and serotonergic agents commonly prescribed with or as substitutes for opioids and benzodiazepines in patients with co-occurring chronic pain and anxiety.

Antiallodynic action of phosphodiesterase inhibitors in a mouse model of peripheral nerve injury

Neuropathic pain arises as a consequence of a lesion or disease affecting the somatosensory nervous system. It is accompanied by neuronal and non-neuronal alterations, including alterations in intracellular second messenger pathways. Cellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) are regulated by phosphodiesterase (PDE) enzymes. Here, we studied the impact of PDE inhibitors (PDEi) in a mouse model of peripheral nerve injury induced by placing a cuff around the main branch of the sciatic nerve. Mechanical hypersensitivity, evaluated using von Frey filaments, was relieved by sustained treatment with the non-selective PDEi theophylline and ibudilast (AV-411), with PDE4i rolipram, etazolate and YM-976, and with PDE5i sildenafil, zaprinast and MY-5445, but not by treatments with PDE1i vinpocetine, PDE2i EHNA or PDE3i milrinone. Using pharmacological and knock-out approaches, we show a preferential implication of delta opioid receptors in the action of the PDE4i rolipram and of both mu and delta opioid receptors in the action of the PDE5i sildenafil. Calcium imaging highlighted a preferential action of rolipram on dorsal root ganglia non-neuronal cells, through PDE4B and PDE4D inhibition. Rolipram had anti-neuroimmune action, as shown by its impact on levels of the pro-inflammatory cytokine tumor necrosis factor-α (TNFα) in the dorsal root ganglia of mice with peripheral nerve injury, as well as in human peripheral blood mononuclear cells (PBMCs) stimulated with lipopolysaccharides. This study suggests that PDEs, especially PDE4 and 5, may be targets of interest in the treatment of neuropathic pain.