Neuropathic Pain Treatment: Still a Challenge

Traditional uses, phytochemistry, pharmacology, applications, and quality control of Gastrodia elata Blume: A comprehensive review

ETHNOPHARMACOLOGICAL RELEVANCE

Gastrodia elata Blume (G. elata) has a long historical application in Asian countries and its tubers, seeds, and stalks are capable of being utilized for medicine, food, or health care products.

AIM OF THE REVIEW

This study aimed to offer a systematic and up-to-date analysis of the current review of the G. elata research advances in traditional uses, phytochemistry, pharmacology, applications, and quality control, as well as a scientific reference for the development and utilization of this plant.

MATERIALS AND METHODS

Electronic databases including PubMed, Web of Science, Google Scholar, ScienceDirect, SciFinder, and CNKI were used for the collection of publications on G. elata. The following keywords of G. elata were used truncated with other relevant topic terms, such as phenolic compounds, polysaccharides, glycosides, neuroprotection, learning and memory improvement effects, cardioprotection, applications, and quality control.

RESULTS AND CONCLUSIONS

Approximately 134 chemical components mainly categorizing as phenolic compounds, polysaccharides, glycosides, organic acids, and sterols were reported from this plant. Moreover, preclinical studies indicated that G. elata performs several functions, including neuroprotection, learning and memory improvement effects, cardioprotection, vaso-modulatory effect, anti-depression, anti-cancer, and other effects. Currently, G. elata has been widely applied to clinics and foods. The available literature shows that the quality of G. elata might be affected by factors such as origin, fungus, and harvest time, which will have an impact on the drug efficacy. According to past research, G. elata is a potential medicinal and edible plant with several active components and pharmacological activity that has a high application value in medicine and the food business. Nevertheless, few studies have concentrated on characterization of polysaccharides structure and study of non-medicinal parts, implying that further comprehensive research on its polysaccharides structure and non-medicinal parts is critical for full utilization of resources of G. elata.

Research Hotspots and Trends on Acupuncture for Neuropathic Pain: A Bibliometric Analysis from 2002 to 2021

Purpose

In this study, we aimed to systematically determine the trend, research hotspots, and directions of the future development of acupuncture for neuropathic pain (NP) by bibliometric analysis.

Methods

Based on the relevant literature on acupuncture for NP in the databases of Web of Science from January 2002 to December 2021, Citespace software and VOSviewer were used to determine the use of acupuncture for the treatment of NP. The annual publications, countries, authors, research institutions, keywords, co-cited references, and journals were analyzed to explore the research hotspot and development trends in this field.

Results

A total of 1462 records of acupuncture for NP from 2002 to 2021 were obtained. Chingliang Hsieh (20) is the most effective author and Han JS (585 co-citations) is the most influential author. The most productive institutions and countries are Kyung Hee UNIV (88) and China, respectively (480). UNIV Maryland of the USA has the highest centrality (0.12). Evidence-based complementary and alternative medicine (89) is the most prolific journal, and Pain is the most influential journal (4200 co-citations). Ji-sheng Han (2003) is the most frequently cited article (158 co-citations). Electroacupuncture, bee-venom acupuncture, and percutaneous electrical stimulation are the most commonly studied acupuncture types. The analgesic mechanism of acupuncture and acupuncture-neuroimaging was a research hotspot over the years. The clinical evidence of acupuncture for NP should be further studied in the future.

Conclusion

The study using bibliometric analysis methods to investigate the publications on acupuncture for NP so as to provide potential research directions in the future.

Cellular and Molecular Machinery of Neuropathic Pain: an Emerging Insight

Purpose of Review

Neuropathic pain (NP) has been ubiquitously characterized by lesion and its linked somatosensory system either the central nervous system (CNS) or peripheral nervous system (PNS) This PNS episode is the most prevalent site of NP origin and is found to be associated with afferent nerve fibers carrying pain signals from injured/trauma site to the CNS including the brain. Several kinds of pharmacotherapeutic drugs shuch as analgesics, anti-convulsants, and anti-depressants are being employed for the its possible interventions. The NP has been a great interest to follow different pathophysiological mechanisms which are often considered to correlate with the metabolic pathways and its mediated disease. There is paucity of knowledge to make such mechanism via NP.

Recent Finding

Most notably, recent pandemic outbreak of COVID-19 has also been reported in chronic pain mediated diabetes, inflammatory disorders, and cancers. There is an increasing incidence of NP and its complex mechanism has now led to identify the possible investigations of responsible genes and proteins via bioinformatics tools. The analysis might be more instrumental as collecting the genes from pain genetic database, analyzing the variants through differential gene expression (DEG) and constructing the protein–protein interaction (PPI) networks and thereby determining their upregulating and downregulating pathways.

Summary

This review sheds a bright light towards several mechanisms at both cellular and molecular level, correlation of NP-mediated disease mechanism and possible cell surface biomarkers (receptors), and identified genes could be more promising for their pharmacological targets.

Pain in the Cancer Survivor

Recent decades have demonstrated significant strides in cancer screening, diagnostics and therapeutics. As such there have been dramatic changes in survival following a diagnosis of cancer.

Gastrodia elata Blume Polysaccharides Attenuate Vincristine-Evoked Neuropathic Pain through the Inhibition of Neuroinflammation

Vincristine (Vin) is a well-known antitumor agent that frequently evokes neuropathic pain and decreases the quality of life of patients. Polysaccharides (GBP) extracted from Gastrodia elata Blume have been demonstrated to possess anti-inflammatory and neuroprotective effects in vivo; however, the effects of GBP on Vin-induced neuropathic pain remain unknown. The present study is aimed at exploring the alleviative potential of GBP against chemotherapy-evoked peripheral neuropathy to better understand and extend its pharmacological application. Vin was administered intraperitoneally to evoke neuropathic pain. GBP was orally administered for 21 days. The mechanical allodynia and thermal hyperalgesia were assessed using the Von Frey test and hot-plate test. Histopathological changes were assessed by hematoxylin and eosin staining. ELISA kits were used to measure the levels of inflammatory cytokines in the sciatic nerve, spinal cord, and dorsal root ganglion (DRG). qRT-PCR was employed to examine the expression of inflammatory cytokines and Sirtuin1 (SIRT1) in the sciatic nerve, spinal cord, and DRG. Our findings revealed that GBP treatment enhanced the paw withdrawal latency and paw withdrawal threshold and restored Vin-induced sciatic nerve damage in rats. GBP also attenuated the Vin-induced increase of proinflammatory cytokine levels, including IL-6, IL-8, TNF-α, IL-1β, and NF-κB. On the molecular level, treatment with GBP downregulated the mRNA levels of IL-6, IL-8, TNF-α, and IL-1β in the sciatic nerve, spinal cord, and DRG. Meanwhile, GBP increased SIRT1 activity and mRNA expression levels. Our data indicated that GBP exerted a potential protective effect against chemotherapy-induced neuropathic pain which might be mediated via the inhibition of neuroinflammation.

Effectiveness of Intravenous Immunoglobulin for Management of Neuropathic Pain: A Narrative Review

Administrations of intravenous immunoglobulin (IVIG), an immune-modulating blood-derived product, may be beneficial for managing neuropathic pain. Here, we review previous studies to investigate the effectiveness of IVIG in managing neuropathic pain due to various neurological disorders. The electronic databases PubMed, Scopus, Embase, and the Cochrane Library were searched for studies published up to February 2020. Two reviewers independently assessed the studies using strict inclusion criteria. Ten studies were included and qualitatively analyzed. The review included patients with pain due to complex regional pain syndrome (CRPS), diabetic polyneuropathy, and others, such as postherpetic neuralgia and trigeminal neuralgia. We found that IVIG may be one of the beneficial options for managing neuropathic pain from various neurological disorders. In the four articles reviewed, no major adverse effects were reported, and the trend was toward a positive pain-reducing effect in eight articles. However, to confirm the benefits of IVIG on reducing neuropathic pain, more high-quality studies are required.

Association between clinical characteristics and pain relief in patients with axial spondyloarthritis treated with non-steroidal anti-inflammatory drugs

Objectives

The aim of this study was to evaluate pain relief in axial spondyloarthritis (axSpA) patients treated with non-steroidal anti-inflammatory drugs (NSAIDs) and to investigate the relation of the demographic, clinical, and psychological characteristics with pain relief.

Patients and methods

Between February 2017 and December 2019, a total of 94 patients (61 males, 33 females; mean age: 28.3±8.1 years; range, 14 to 54 years) who were diagnosed with axSpA and treated with NSAIDs were included. The patients were assessed at baseline and at three months. A reduction of 30% in the Numeric Rating Scale (NRS) indicates a clinically meaningful improvement. The patients were divided into the relief group (≥30% improvement in NRS) and non-relief group (<30% improvement). Potential influential factors for pain relief such as neuropathic pain (NP), disease activity, function, pain catastrophizing, and pain self-efficacy were assessed. The relationship between patients’ characteristics and pain relief was analyzed.

Results

Seventy-two (76.6%) patients achieved pain relief. These patients had significantly higher baseline erythrocyte sedimentation rate, C-reactive protein, and lower percentage of NP. There was no significant difference between the two groups in function, pain catastrophizing, and pain self-efficacy. Multiple logistic regression analysis revealed that patients with NP were less likely to achieve pain relief (odds ratio [OR]: 3.531, 95% confidence interval [CI]: 1.155-10.789; p=0.027).

Conclusion

Pain relief is still insufficient in some axSpA patients, despite the administration of NSAIDs. The presence of NP is significantly associated with poor pain relief. Alternative medications instead of NSAIDs are needed to achieve optimal pain relief, when NP is diagnosed.

Optogenetics: Therapeutic spark in neuropathic pain

Optogenetics is an emerging field, which uses light and molecular genetics to manipulate the activity of live cells by expressing light-sensitive proteins. With the discovery of bacteriorhodopsin, a light-sensitive bacterial protein, in 1971 Oesterhelt and Stoeckenius laid the pavement of optogenetics. However, the cross-integration of different disciplines is a little more than a decade old. The toolbox contains fluorescent sensors and optogenetic actuators that enable visualization of signaling events and manipulation of cellular activities, respectively. Neuropathic pain is pain caused either by damage or disease that affects the somatosensory system. The exact mechanism for neuropathic pain is not known, however proposed mechanisms include immune reactions, ion channel expressions, and inflammation. Current regimen for the disease provides about 50% relief for only 40-60% of patients. Recent in vivo and in vitro studies demonstrate the potential therapeutic applications of optogenetics by manipulating the activity of neurons. This review summarizes the basic concept, therapeutic applications for neuropathy, and potential of optogenetics to reach from bench to bedside in the near future.

Normalizing JMJD6 Expression in Rat Spinal Dorsal Horn Alleviates Hyperalgesia Following Chronic Constriction Injury

Jumonji domain-containing protein 6 (JMJD6) is a homolog of hypoxia-inducible factor (HIF) asparaginyl hydroxylase, an inhibitor of HIF. HIF-1α is known to participate in neuropathic pain (NPP) during chronic constriction injury (CCI); however, the roles of JMJD6 in NPP have not been systematically investigated. In this study, we examined the temporal distribution and cellular location of JMJD6 in the spinal cord during CCI. In addition, we assessed behavioral changes representative of NPP in rats. Following CCI, lentiviral vectors (LV-JMJD6) were intrathecally administered to observe the changes in the expression of JMJD6, HIF-1α, and its downstream factor caspase-3. Co-immunoprecipitation was used to detect potential interactions between JMJD6 and HIF-1α. We found that JMJD6 was decreased in rats following CCI, which was accompanied by significant NPP–associated behavioral changes. JMJD6 was mainly expressed in neurons. Intrathecal injection of LV-JMJD6 following CCI alleviated the thermal and mechanical hyperalgesia, normalized JMJD6 protein expression, and decreased HIF-1α protein expression with a corresponding reduction in caspase-3 protein expression. Furthermore, the co-immunoprecipitation analyses showed that JMJD6 and HIF-1α protein immunoprecipitated with each other, indicating an interaction between these two proteins. Taken together, the results suggest that JMJD6 may serve as a sensor in neurons of the adult rat spinal cord during the CCI state. Furthermore, JMJD6 may exert its function in NPP by regulating HIF-1α in rats exposed to CCI.

Hydrogen-Rich Saline Activated Autophagy via HIF-1α Pathways in Neuropathic Pain Model

Background

Neuropathic pain is a chronic and intractable pain, with very few effective analgesics. It involves an impaired cell autophagy process. Hydrogen-rich saline (HRS) reportedly reduces allodynia and hyperalgesia in a neuropathic pain model; however, it is unknown whether these effects involve autophagy induction.

Methods

We investigated the relationship between HRS and cell autophagy in a neuropathic pain model generated by chronic constriction injury (CCI) in Sprague–Dawley rats. Rats received an intraperitoneal injection of HRS (10 mL/kg daily, from 1 day before until 14 days after CCI), 3MA (autophagy inhibitor), 2ME2 (HIF-1α inhibitor), or EDHB (HIF-1α agonist). The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were tested 1 day before and 1, 3, 7, 10, and 14 days after the operation. HIF-1α and cell autophagy markers in the spinal cord were evaluated by western blotting and real-time PCR assays at 14 days after CCI. Autophagosomes with double membranes were identified by transmission electron microscopy.

Results

CCI caused behavioral hypersensitivity to mechanical and thermal stimulation in the hind-paw of the injured side. HRS improved MWT and TWL, activated autophagy, and increased autophagosomes and autolysosomes in CCI rats. 3-MA aggravated hyperalgesia and allodynia and suppressed autophagy, while EDHB attenuated hyperalgesia and activated the autophagy procedure and the HIF-1α downstream target gene BNIP3. HIF-1α inhibitors reversed the regulatory effects of HRS on autophagy in CCI rats at 14 days after spinal cord injury.

Conclusion

HRS reduced mechanical hyperalgesia and activation of cell autophagy in neuropathic pain through a HIF1-dependent pathway.

Antinociceptive effects of HUF-101, a fluorinated cannabidiol derivative

Cannabidiol (CBD) is a phytocannabinoid with multiple pharmacological effects and several potential therapeutic properties. Its low oral bioavailability, however, can limit its clinical use. Preliminary results indicate that fluorination of the CBD molecule increases its pharmacological potency. Here, we investigated whether HUF-101 (3, 10, and 30mg/kg), a fluorinated CBD analogue, would induce antinociceptive effects. HUF-101 effects were compared to those induced by CBD (10, 30, and 90mg/kg) and the cannabinoid CB_1/2 receptor agonist WIN55,212-2 (1, 3, and 5mg/kg). These drugs were tested in male Swiss mice submitted to the following models predictive to antinociceptive drugs: hot plate, acetic acid-induced writhing, and carrageenan-induced inflammatory hyperalgesia. To evaluate the involvement of CB₁ and CB₂ receptors in HUF-101 and CBD effects, mice received the CB₁ receptor antagonist AM251 (1 or 3mg/kg) or the CB₂ receptor antagonist AM630 (1 or 3mg/kg) 30min before HUF-101, CBD, or WIN55,212-2. In the hot plate test, HUF-101 (30mg/kg) and WIN55,212-2 (5mg/kg) induced antinociceptive effects, which were attenuated by the pretreatment with AM251 and AM630. In the abdominal writhing test, CBD (30 and 90mg/kg), HUF-101 (30mg/kg), and WIN55,212-2 (3 and 5mg/kg) induced antinociceptive effects indicated by a reduction in the number of writhing. Whereas the pretreatment with AM630 did not mitigate the effects induced by any drug in this test, the pretreatment with AM251 attenuated the effect caused by WIN55,212-2. In the carrageenan-induced hyperalgesia test, CBD (30 and 90mg/kg), HUF-101 (3, 10 and 30mg/kg) and WIN55,212-2 (1mg/kg) decreased the intensity of mechanical hyperalgesia measured by the electronic von Frey method. The effects of all compounds were attenuated by the pretreatment with AM251 and AM630. Additionally, we evaluated whether HUF-101 would induce the classic cannabinoid CB₁ receptor-mediated tetrad (hypolocomotion, catalepsy, hypothermia, and antinociception). Unlike WIN55,212-2, CBD and HUF-101 did not induce the cannabinoid tetrad. These findings show that HUF-101 produced antinociceptive effects at lower doses than CBD, indicating that the addition of fluoride improved its pharmacological profile. Furthermore, some of the antinociceptive effects of CBD and HUF-101 effects seem to involve the activation of CB₁ and CB₂ receptors.

Low doses of amitriptyline, pregabalin, and gabapentin are preferred for management of neuropathic pain in India: is there a need for revisiting dosing recommendations?

Background

Current therapy for the treatment of neuropathic pain is often unsatisfactory. Considerable variation in treatment pattern still exists in spite of availability of sufficient literature from various guidelines. Recent Indian market data suggested that the utilization (sale) of drugs such as amitriptyline, pregabalin, and gabapentin was more for low-dose unit packs than that of the high-dose unit packs, raising the belief that these drugs are prescribed at a lower dose than is actually recommended in the guidelines. To test this hypothesis, a survey was conducted across speciality throughout the country to observe the prescription pattern of these drugs amongst the health care providers in India.

Methods

Three hundred fifty survey forms were distributed of which 281 forms were included for analysis.

Results

It was observed that the commonly used initiation and maintenance dose for amitriptyline, pregabalin, and gabapentin was 5–10 mg/day, 50–75 mg/day, and 100–300 mg/day, respectively. The reason to select the lower dosages was to have a balancing effect to achieve good efficacy with minimum side effects. Care-givers reported no side effects/not many side effects as a reason in 22.2%, 16.88%, and 23.86% patients with amitriptyline, pregabalin, and gabapentin, respectively. Sedation and giddiness were commonly reported with all three drugs.

Conclusions

Commonly prescribed drugs for management of neuropathic pain, such as amitriptyline, pregabalin, and gabapentin are preferred at lower doses in Indian clinical settings. Acceptable efficacy and low tolerance to the standard dosage is believed to be the reason behind the prescribed dose.