Neuropathic Pain and Pharmacological Treatment

Gabapentinoid prescriptions for neuropathic and musculoskeletal pain in Lebanon

Aim: The purpose of this study is to analyze the different characteristics of gabapentinoids prescription by Lebanese orthopedics surgeons. Methods: This is an observational, cross-sectional study using a survey which was carried out in collaboration with the Lebanese Orthopedic Society over a 3-month period. Results: Forty-two orthopedic surgeons responded, most of them prescribing gabapentinoids in their daily practice with only half of the patients feeling relief after taking them. Furthermore, most of the surgeons prescribed these drugs for patients above 18 years old and for both acute and chronic pain. Conclusion: Even though almost half of the patients do not experience relief after taking gabapentinoids, these drugs are becoming more and more prescribed.

An update to pain management after spinal cord injury: from pharmacology to circRNAs

Neuropathic pain (NP) following a spinal cord injury (SCI) is often hard to control and therapies should be focused on the physical, psychological, behavioral, social, and environmental factors that may contribute to chronic sensory symptoms. Novel therapeutic treatments for NP management should be based on the combination of pharmacological and nonpharmacological options. Some of them are addressed in this review with a focus on mechanisms and novel treatments. Several reports demonstrated an aberrant expression of non-coding RNAs (ncRNAs) that may represent key regulatory factors with a crucial role in the pathophysiology of NP and as potential diagnostic biomarkers. This review analyses the latest evidence for cellular and molecular mechanisms associated with the role of circular RNAs (circRNAs) in the management of pain after SCI. Advantages in the use of circRNA are their stability (up to 48 h), and specificity as sponges of different miRNAs related to SCI and nerve injury. The present review discusses novel data about deregulated circRNAs (up or downregulated) that sponge miRNAs, and promote cellular and molecular interactions with mRNAs and proteins. This data support the concept that circRNAs could be considered as novel potential therapeutic targets for NP management especially after spinal cord injuries.

Role of peripheral nerve stimulation in treating chronic neuropathic pain: an international focused survey of pain medicine experts

Interventional pain management (IPM) options for refractory neuropathic pain (NP) have recently increased with availability of peripheral nerve stimulation (PNS) equipment and expertise. Given a lack of high-quality evidence and guidelines on this topic, we sought to understand the perception of physicians with expertise in treating NP regarding IPM and the role of PNS. We emailed a survey in March 2022 to international NP experts including pain medicine physicians, researchers, and leaders of 11 professional pain societies. No representatives from vendors of PNS systems were included in the design of the survey nor as respondents. Among 24 respondents (67% of those contacted), the distal common peroneal, tibial, and sural nerves were most frequently targeted (60%) with PNS. Persistent postsurgical pain of more than 3 months was the most common indication for PNS (84%). The aggregate NP treatment algorithm in order of median rank was non-opioid medications as first line, IPM including epidural/perineural steroid injections tied with transcutaneous electrical nerve stimulation as second line, pulsed radiofrequency (RF) tied with RF ablation/denervation as third line, temporary then permanent PNS as fourth line, followed by spinal cord stimulation, opioids, cryoablation, botulinum, peripheral nerve field stimulation, intrathecal targeted drug delivery, and others. Before offering PNS, 12 respondents (50%) indicated their preference for trialing non-neuromodulation treatments for 1-3 months. Twenty-two respondents (92%) agreed PNS should be offered early in the treatment of neuropathic pain. The most common barriers to PNS use were cost, lack of high-quality evidence in support of its use, lack of exposure to PNS in training programs, and lack of familiarity with the use of ultrasound guidance. PNS appears to have an increasing role in the treatment of NP but more research is needed on the outcomes of PNS to elucidate its role.

Neuropeptide Y in the amygdala contributes to neuropathic pain-like behaviors in rats via the neuropeptide Y receptor type 2/mitogen-activated protein kinase axis

Neuropeptide Y (NPY) is a highly conserved endogenous peptide in the central and peripheral nervous systems, which has been implicated in nociceptive signaling in neuropathic pain. However, downstream mechanistic actions remain uncharacterized. In this study, we sought to investigate the mechanism of NPY and its receptor NPY2R in the amygdala in rats with neuropathic pain-like behaviors induced by chronic constriction injury (CCI) of the sciatic nerve. The expression of NPY and NPY2R was found to be aberrantly up-regulated in neuropathic pain-related microarray dataset. Further, NPY was found to act on NPY2R in the basolateral amygdala (BLA). As reflected by the decrease in mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) as well as the increase of NPY expression in the amygdala of rats with neuropathic pain-like behaviors, NPY was closely related to the effect of amygdala nerve activity in neuropathic pain. Subsequently, mechanistic investigations indicated that NPY2R activated the MAPK signaling pathway in the amygdala. NPY2R-induced decrease of MWT and TWL were also restored in the presence of MAPK signaling pathway antagonist. Moreover, it was revealed that NPY2R overexpression promoted the viability while inhibiting the apoptosis of microglia. Taken together, NPY in the amygdala interacts with NPY2R to activate the MAPK signaling pathway, thereby promoting the occurrence of neuropathic pain.

Clinical Epidemiology and Management of Hidradenitis Suppurativa

Hidradenitis suppurativa is a chronic immune-mediated inflammatory skin disease with a prevalence of 0.1-1%, characterized by nodules and abscesses in the axillae, groin, and inframammary areas, sometimes developing into tunnels (or fistulas) and scars. Because hidradenitis suppurativa is more common in women and in those aged 18-40 years, obstetrician-gynecologists (ob-gyns) have the opportunity to diagnose, educate, initiate treatment, and coordinate care with ancillary health care professionals. The recently published North American treatment guidelines, along with management information for patients with hidradenitis suppurativa who are pregnant or breastfeeding, are summarized. By diagnosing and optimizing hidradenitis suppurativa treatment early in the disease course, ob-gyns can reduce morbidity, with the potential to favorably alter disease trajectory.

Pain management in hidradenitis suppurativa and a proposed treatment algorithm

Pain contributes substantially to reduced quality of life in individuals living with hidradenitis suppurativa (HS). Although improved understanding of HS pathogenesis and treatment has resulted in improved evidence-based HS management guidelines, comprehensive pain management guidelines have yet to be developed. Few HS-specific data exist to guide pharmacologic analgesia; however, recognizing HS pain as either acute or chronic and predominantly nociceptive (aching and gnawing pain due to tissue damage) versus neuropathic (burning-type pain due to somatosensory nervous system dysfunction) provides a conceptual framework for applying outside pain management practices to HS management. This article incorporates the best available evidence from the HS and pain literature to propose an HS pain algorithm that integrates psychological, pharmacologic, and complementary and alternative treatment modalities.

Effects of miR-150 on neuropathic pain process via targeting AKT3

MicroRNAs (miRNA) are reported to be a vital regulator of neuropathic pain. Even so, the molecular mechanisms of miRNA function on neuropathic pain development are known little. Our research was designed to investigate the role of miRNA in neuropathic pain development in rat modle set up by chronic sciatic nerve injury (CCI). Increasing miR-150 expression could significantly alleviate neuropathic pain in CCI rats. For farther researching the regulation mechanism of miR-150 on neuropathic pain, we screened AKT3 as a possible target of miR-150 by bioinformatic mechods and predicted a possible target of miR-150 in 3'-untranslated region (UTR) of AKT3 who serves as an oncogene. In rat model, the expression both of AKT3 mRNA and protein were significantly upregulated. The overexpressed miR-150 importantly repressed the level of AKT3 and simultaneously alleviate mechanical and thermal hyperalgesia in rat model. These suppressant impacts of miR-150 on neuropathic pain process can be reversed by the overexpression of AKT3. Considering all above results, our research declared that miR-150 can restrain neuropathic pain process though targeting AKT3 in vivo, suggesting that miR-150 could be the therapeutic target for neuropathic pain therapy by regulating AKT3.

Economic Impact of Adherence to Pain Treatment Guidelines in Chronic Pain Patients

Objectives

This research compared health care resource use (HCRU) and costs for pharmacotherapy prescribing that was adherent vs nonadherent to published pain management guidelines. Conditions included osteoarthritis (OA) and gout (GT) for nociceptive/inflammatory pain, painful diabetic peripheral neuropathy (pDPN) and post-herpetic neuralgia (PHN) for neuropathic pain, and fibromyalgia (FM) for sensory hypersensitivity pain.

Methods

This retrospective cohort study used claims from MarketScan Commercial and Medicare Databases identifying adults newly diagnosed with OA, GT, pDPN, PHN, or FM during July 1, 2006, to June 30, 2013, with 12-month continuous coverage before and after initial (index) diagnosis. Patients were grouped according to their pharmacotherapy pattern as adherent, nonadherent, or “unsure” according to published pain management guidelines using a claims-based algorithm. Adherent and nonadherent populations were compared descriptively and using multivariate statistical analyses for controlling bias.

Results

Final cohort sizes were 441,465 OA, 76,361 GT, 10,645 pDPN, 4,010 PHN, and 150,321 FM, with adherence to guidelines found in 51.1% of OA, 25% of GT, 59.5% of pDPN, 54.9% of PHN, and 33.5% of FM. Adherent cohorts had significantly (P < 0.05) fewer emergency department (ED) visits and lower proportions with hospitalizations or ED visits. Mean health care costs increased following diagnosis across all conditions; however, adherent cohorts had significantly lower increases in adjusted costs pre-index to postindex (OA $5,286 vs $9,532; GT $3,631 vs $7,873; pDPN $9,578 vs $16,337; PHN $2,975 vs $5,146; FM $2,911 vs $3,708; all P < 0.001; adherent vs nonadherent, respectively).

Conclusions

Adherence to pain management guidelines was associated with significantly lower HCRU and costs compared with nonadherence to guidelines.

Development of a novel algorithm to determine adherence to chronic pain treatment guidelines using administrative claims

Objective

To develop a claims-based algorithm for identifying patients who are adherent versus nonadherent to published guidelines for chronic pain management.

Methods

Using medical and pharmacy health care claims from the MarketScan® Commercial and Medicare Supplemental Databases, patients were selected during July 1, 2010, to June 30, 2012, with the following chronic pain conditions: osteoarthritis (OA), gout (GT), painful diabetic peripheral neuropathy (pDPN), post-herpetic neuralgia (PHN), and fibromyalgia (FM). Patients newly diagnosed with 12 months of continuous medical and pharmacy benefits both before and after initial diagnosis (index date) were categorized as adherent, nonadherent, or unsure according to the guidelines-based algorithm using disease-specific pain medication classes grouped as first-line, later-line, or not recommended. Descriptive and multivariate analyses compared patient outcomes with algorithm-derived categorization endpoints.

Results

A total of 441,465 OA patients, 76,361 GT patients, 10,645 pDPN, 4,010 PHN patients, and 150,321 FM patients were included in the development of the algorithm. Patients found adherent to guidelines included 51.1% for OA, 25% for GT, 59.5% for pDPN, 54.9% for PHN, and 33.5% for FM. The majority (~90%) of patients adherent to the guidelines initiated therapy with prescriptions for first-line pain medications written for a minimum of 30 days. Patients found nonadherent to guidelines included 30.7% for OA, 6.8% for GT, 34.9% for pDPN, 23.1% for PHN, and 34.7% for FM.

Conclusion

This novel algorithm used real-world pharmacotherapy treatment patterns to evaluate adherence to pain management guidelines in five chronic pain conditions. Findings suggest that one-third to one-half of patients are managed according to guidelines. This method may have valuable applications for health care payers and providers analyzing treatment guideline adherence.

Continuous neuropathic pain secondary to endoscopic procedures: report of two cases and review of the literature

Neuropathic pain encompasses a spectrum of conditions that can arise from a lesion or dysfunction of the central or the peripheral nervous system, and it may develop at variable intervals after nerve injury or inflammation. Nerve injuries arising from surgical procedures commonly occur secondary to the surgical trauma, and in rare instances they are a complication of intubation during general anesthesia or endoscopic procedures. A series of 2 cases of bilateral glossopharyngeal neuropathic pain subsequent to endoscopic procedures is presented with a review of the literature concerning the mechanisms of development of neuropathic pain after these procedures. The purpose of these case reports is to make dentists aware of the occurrence, the mechanisms of nerve injuries, and the treatment of neuropathic pain after endoscopic procedures. In the first case, the patient had relief of pain with a combination therapy of clonazepam 1.0 mg in divided doses twice daily and gabapentin 300 mg in divided doses 3 times daily. In the second case, the patient had significant relief of pain with a monotherapy of gabapentin 1200 mg in divided doses 3 times daily.

Gram Scale Syntheses of (-)-Incarvillateine and Its Analogs. Discovery of Potent Analgesics for Neuropathic Pain

(-)-Incarvillateine (INCA) is the major antinociceptive component of Incarvillea sinensis, which has been used to treat rheumatism and relieve pain in traditional Chinese medicine. We have developed a concise and general synthetic approach for INCA, which enabled gram-scale asymmetric syntheses of (-)-INCA, (-)-incarvilline, (-)-isoincarvilline, and six other INCA analogues. The synthesis of isoincarvilline was reported for the first time. Three structurally simplified analogues of INCA were also synthesized. In vivo screening found that INCA and two structurally optimized analogues were efficacious in preventing the acetic acid-induced writhing response. Moreover, their analgesic efficacy was demonstrated in formalin induced pain model. More importantly, administration of 20 or 40 mg/kg INCA and two structurally optimized analogues showed strong analgesic effects in spared nerve injury (SNI) model, and their effective doses were lower than the current gold standard, gabapentin (100 mg/kg in this model).

Discontinued neuropathic pain therapy between 2009-2015

INTRODUCTION

Studies have shown that neuropathic pain remains imprecisely responsive to conventional therapies, therefore posing an ongoing, vexing clinical conundrum for healthcare resource utilization. This manuscript reflects the stark reality of the limited pharmacological choices available to clinicians and is a reflective of an ongoing need for more extensive neuropathic pain clinical research.

AREAS COVERED

The authors review a total of 33 potential drugs for neuropathic pain which were discontinued in the period between 01/01/2009 and 12/31/2014. Eleven drugs were terminated in the first phase of clinical trials; nineteen were discontinued in the second phase, while only three drugs reached the third phase.

EXPERT OPINION

Since only 40-60% of patients obtain partial pain relief from current neuropathic pain treatment options, assuring that they receive new medications for this complex disorder is imperative. However, the authors believe that future studies should not only focus on the discovery of new compounds. Efforts should also be devoted to developing a better understanding of the therapeutic challenges of neuropathic pain, as well as to designing and carrying out clinical trials in collaboration between pharmaceutical companies, physicians and scientists. Furthermore, the authors believe that other outcome measures besides pain intensity, such as functionality and quality of life, should receive more attention.

Inhibition of voltage-gated sodium channels by sumatriptan bioisosteres

Voltage-gated sodium channels are known to play a pivotal role in perception and transmission of pain sensations. Gain-of-function mutations in the genes encoding the peripheral neuronal sodium channels, hNav1.7–1.9, cause human painful diseases. Thus while treatment of chronic pain remains an unmet clinical need, sodium channel blockers are considered as promising druggable targets. In a previous study, we evaluated the analgesic activity of sumatriptan, an agonist of serotonin 5HT_1B/D receptors, and some new chiral bioisosteres, using the hot plate test in the mouse. Interestingly, we observed that the analgesic effectiveness was not necessarily correlated to serotonin agonism. In this study, we evaluated whether sumatriptan and its congeners may inhibit heterologously expressed hNav1.7 sodium channels using the patch-clamp method. We show that sumatriptan blocks hNav1.7 channels only at very high, supratherapeutic concentrations. In contrast, its three analogs, namely 20b, (R)-31b, and (S)-22b, exert a dose and use-dependent sodium channel block. At 0.1 and 10 Hz stimulation frequencies, the most potent compound, (S)-22b, was 4.4 and 1.7 fold more potent than the well-known sodium channel blocker mexiletine. The compound induces a negative shift of voltage dependence of fast inactivation, suggesting higher affinity to the inactivated channel. Accordingly, we show that (S)-22b likely binds the conserved local anesthetic receptor within voltage-gated sodium channels. Combining these results with the previous ones, we hypothesize that use-dependent sodium channel blockade contributes to the analgesic activity of (R)-31b and (S)-22b. These later compounds represent promising lead compounds for the development of efficient analgesics, the mechanism of action of which may include a dual action on sodium channels and 5HT_1D receptors.

Sigma-1 receptors and animal studies centered on pain and analgesia

INTRODUCTION

Neuropathic pain is difficult to relieve with standard analgesics and tends to be resistant to opioid therapy. Sigma-1 receptors activated during neuropathic injury may sustain pain. Neuropathic injury activates sigma-1 receptors, which results in activation of various kinases, modulates the activity of multiple ion channels, ligand activated ion channels and voltage-gated ion channels; alters monoamine neurotransmission and dampens opioid receptors G-protein activation. Activation of sigma-1 receptors tonically inhibits opioid receptor G-protein activation and thus dampens analgesic responses. Therefore, sigma-1 receptor antagonists are potential analgesics for neuropathic and adjuvants to opioid therapy.

AREAS COVERED

This article reviews the importance of sigma-1 receptors as pain generators in multiple animal models in order to illustrate both the importance of these unique receptors in pathologic pain and the potential benefits to sigma-1 receptor antagonists as analgesics.

EXPERT OPINION

Sigma-1 receptor antagonists have a great potential as analgesics for acute neuropathic injury (herpes zoster, acute postoperative pain and chemotherapy induced neuropathy) and may, as an additional benefit, prevent the development of chronic neuropathic pain. Antagonists are potentially effective as adjuvants to opioid therapy when used early to prevent analgesic tolerance. Drug development is complicated by the complexity of sigma-1 receptor pharmacodynamics and its multiple targets, the lack of a specific sigma-1 receptor antagonist, and potential side effects due to on-target toxicities (cognitive impairment, depression).

Synthesis and biological evaluation of novel sigma-1 receptor antagonists based on pyrimidine scaffold as agents for treating neuropathic pain

The discovery and synthesis of a new series of pyrimidines as potent sigma-1 receptor (σ1R) antagonists, associated with pharmacological antineuropathic pain activity, are the focus of this article. The new compounds were evaluated in vitro in σ-1 and σ-2 receptor binding assays. The nature of the pyrimidine scaffold was crucial for activity, and a basic amine was shown to be necessary according to the known pharmacophoric model. The most promising derivative was 5-chloro-2-(4-chlorophenyl)-4-methyl-6-(3-(piperidin-1-yl)propoxy)pyrimidine (137), which exhibited a high binding affinity to σ1R receptor (Ki σ1 = 1.06 nM) and good σ-1/2 selectivity (1344-fold). In in vivo tests, compound 137 exerted dose-dependent antinociceptive effects in mice formalin model and rats CCI models of neuropathic pain. In addition, no motor impairments were found in rotarod tests; acceptable pharmacokinetic properties were also noted. These data suggest compound 137 may constitute a novel class of drugs for the treatment of neuropathic pain.