Topical gabapentin gel alleviates allodynia and hyperalgesia in the chronic sciatic nerve constriction injury neuropathic pain model

6-Methoxyflavone antagonizes chronic constriction injury and diabetes associated neuropathic nociception expression

Neuropathy is a disturbance of function or a pathological change in nerves causing poor health and quality of life. A proportion of chronic pain patients in the community suffer persistent neuropathic pain symptoms because current drug therapies may be suboptimal so there is a need for new therapeutic modalities. This study investigated the neuroprotective flavonoid, 6-methoxyflavone (6MF), as a potential therapeutic agent and gabapentin as the standard comparator, against neuropathic models. Thus, neuropathic-like states were induced in Sprague-Dawley rats using sciatic nerve chronic constriction injury (CCI) mononeuropathy and systemic administration of streptozotocin (STZ) to induce polyneuropathy. Subsequent behaviors reflecting allodynia, hyperalgesia, and vulvodynia were assessed and any possible motoric side-effects were evaluated including locomotor activity, as well as rotarod discoordination and gait disruption. 6MF (25-75 mg/kg) antagonized neuropathic-like nociceptive behaviors including static- (pressure) and dynamic- (light brushing) hindpaw allodynia plus heat/cold and pressure hyperalgesia in the CCI and STZ models. 6MF also reduced static and dynamic components of vulvodynia in the STZ induced polyneuropathy model. Additionally, 6MF reversed CCI and STZ suppression of locomotor activity and rotarod discoordination, suggesting a beneficial activity on motor side effects, in contrast to gabapentin. Hence, 6MF possesses anti-neuropathic-like activity not only against different nociceptive modalities but also impairment of motoric side effects.

Efficacy assessment of novel methanimine derivatives in chronic constriction injury-induced neuropathic model: An in-vivo, ex-vivo and In-Silico approach

The multicomponent etiology, complex clinical implications, dose-based side effect and degree of pain mitigation associated with the current pharmacological therapy is incapable in complete resolution of chronic neuropathic pain patients which necessitates the perpetual requirement of novel medication therapy. Therefore, this study explored the ameliorative aptitude of two novel methanimine imitative like (E)-N-(4-nitrobenzylidene)-4‑chloro-2-iodobenzamine (KB 09) and (E)-N-(4-methylbenzylidene)-4‑chloro-2-iodobenzamine (KB 10) in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in rat model. Standard behavioral tests like dynamic and static allodynia, cold, thermal and mechanical hyperalgesia along with rotarod activity were performed at various experimental days like 0, 3, 7, 14 and 21. Enzyme linked immunosorbent assay (ELISA) on spinal tissue and antioxidant assays on sciatic nerve were executed accompanied by molecular docking and simulation studies. Prolonged ligation of sciatic nerve expressively induced hyperalgesia as well as allodynia in rats. KB 09 and KB 10 substantially attenuated the CCI elicited hyperalgesia and allodynia. They significantly reduced the biomarkers of pain and inflammation like Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in ELISA and while enhanced the GSH, SOD and CAT and diminished the MDA levels during antioxidant assays. KB 09 displayed -9.62 kcal/mol with TNF-α and -7.68 kcal/mol binding energy with IL-6 whereas KB 10 exhibited binding energy of -8.20 kcal/mol with IL-6 while -11.68 kcal/mol with TNF-α and hence both trial compounds ensured stable interaction with IL-6 and TNF-α during computational analysis. The results advocated that both methanimine derivatives might be novel candidates for attenuation of CCI-induced neuropathic pain prospects via anti-nociceptive, anti-inflammatory and antioxidant mechanisms.

Selective enhancement of fear extinction by inhibiting neuronal adenylyl cyclase 1 (AC1) in aged mice

Adenylyl cyclase 1 (AC1) is a selective subtype of ACs, which is selectively expressed in neurons. The activation of AC1 is activity-dependent, and AC1 plays an important role in cortical excitation that contributes to chronic pain and related emotional disorders. Previous studies have reported that human-used NB001 (hNB001, a selective AC1 inhibitor) produced analgesic effects in different animal models of chronic pain. However, the potential effects of hNB001 on learning and memory have been less investigated. In the present study, we found that hNB001 affected neither the induction nor the expression of trace fear, but selectively enhanced the relearning ability during the extinction in aged mice. By contrast, the same application of hNB001 did not affect recent, remote auditory fear memory, or remote fear extinction in either adult or aged mice. Furthermore, a single or consecutive 30-day oral administration of hNB001 did not affect acute nociceptive response, motor function, or anxiety-like behavior in either adult or aged mice. Our results are consistent with previous findings that inhibition of AC1 did not affect general sensory, emotional, and motor functions in adult mice, and provide strong evidence that inhibiting the activity of AC1 may be beneficial for certain forms of learning and memory in aged mice.

Topical gabapentin solution for the management of burning mouth syndrome: A retrospective study

OBJECTIVE

The aim of this retrospective study was to evaluate the effectiveness and safety of topical gabapentin solution (250 mg/mL) for the management of burning mouth syndrome (BMS).

STUDY DESIGN

A retrospective chart review was conducted of all patients diagnosed with BMS and managed with gabapentin 250 mg/mL solution (swish and spit) between January 2021 and October 2022. Patient-reported outcomes included changes in burning score ranked on a 10-point numeric rating scale (NRS) and reported adverse drug reactions (ADR). Wilcoxon signed-rank test was used to assess differences in the oral burning score ranked on a NRS (0-10) between the baseline visit and the second visit.

RESULTS

A total of 19 patients (68.4% females) with BMS were included and evaluated for follow-up at a median of 86 days (range: 29-195). Overall, patients reported a median 2-point burning decrease on a 0-10 NRS between the baseline visit and the second visit (p < 0.01). ADRs were reported by 3 patients (15.8%).

CONCLUSION

Although this was a small retrospective study, BMS management with topical gabapentin (250 mg/mL) appears to be effective and well-tolerated. Future randomized prospective studies are needed to verify these preliminary findings.

Effectiveness of topical gabapentin in the treatment of vulvodynia: a narrative synthesis

Vulvodynia is a leading cause of dyspareunia in premenopausal women, causing considerable morbidity and sexual dysfunction. A multimodal approach is used to treat vulvodynia. Alongside psychosocial interventions and physiotherapy, pharmacological treatment such as oral gabapentin are used in the treatment of vulvodynia. Topical formulations of gabapentin have shown promise in animal models and case reports investigating its use in other pain conditions. The topical route also avoids the systemic complications of gabapentin such as somnolence, dizziness, and peripheral edema. This study aimed to perform a narrative synthesis of studies investigating the use of topical gabapentin in the treatment of vulvodynia. The primary outcome was a change in pain score following treatment with topical gabapentin. A broad literature search was performed, which identified four studies for inclusion. The included studies reported improved pain measures following treatment; however, conclusions cannot be made due to methodological heterogeneity and inherent limitations. These include lack of control arms, small sample sizes, lack of patient randomization, and use of combination treatments. Due to the paucity of evidence, this review supports the future implementation of double-blind randomized controlled trials to further investigate the efficacy of topical gabapentin in the treatment of vulvodynia.

Taselisib moderates neuropathic pain through PI3K/AKT signaling pathway in a rat model of chronic constriction injury

BACKGROUND

Neuropathic pain is a chronic condition commonly caused by inflammation-induced disturbances or lesions of somatosensory functions in the nervous system. The aim of this study was to investigate the effects and mechanisms of Taselisib on chronic constriction injury (CCI)-induced neuropathic pain in rats.

METHODS

The rats were divided into four groups: sham group, sham + Taselisib (10mg/kg orally once a day) group, CCI group, and CCI + Taselisib (10mg/kg orally once a day) group. Pain behavioral tests, recorded by measuring paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL), were conducted on days 0, 3, 7, 14, and 21 after surgery. After testing, the animals were euthanized and spinal dorsal horns were collected. Pro-inflammatory cytokines were quantified using ELISA and qRT-PCR. PI3K/pAKT signaling was assessed using Western blot and immunofluorescence.

RESULTS

PWT and TWL were significantly reduced after CCI surgery, but were successfully increased by Taselisib treatment. Taselisib treatment notably suppressed the upregulation of pro-inflammatory cytokines, including IL-6, IL-1β, and TNF-⍺. Taselisib treatment significantly reduced the elevated phosphorylation of AKT and PI3K induced by CCI.

CONCLUSION

Taselisib can alleviate neuropathic pain by inhibiting the pro-inflammatory response, potentially through the PI3K/AKT signaling pathway.

Recent Progress in Gels for Neuropathic Pain

Neuropathic pain is a complex and debilitating condition that affects millions of people worldwide. While several treatment options are available, they often have limited efficacy and are associated with adverse effects. In recent years, gels have emerged as a promising option for the treatment of neuropathic pain. Inclusion of various nanocarriers, such as cubosomes and niosomes, into gels results in pharmaceutical forms with higher drug stability and increased drug penetration into tissues compared to products currently marketed for the treatment of neuropathic pain. Furthermore, these compounds usually provide sustained drug release and are biocompatible and biodegradable, which makes them a safe option for drug delivery. The purpose of this narrative review was to provide a comprehensive analysis of the current state of the field and identify potential directions for future research in the development of effective and safe gels for the treatment of neuropathic pain, ultimately improving the quality of life for patients suffering from neuropathic pain.

Efficacy of 2-Hydroxyflavanone in Rodent Models of Pain and Inflammation: Involvement of Opioidergic and GABAergic Anti-Nociceptive Mechanisms

The current work examined the pharmacological potential of a selected flavanone derivative 2-hydroxyflavanone as a promising remedy for the treatment and management of pain. The selected flavanone derivative (2-HF) was evaluated for its analgesic and anti-inflammatory potentials following standard pharmacological protocols including hot plate, acetic acid-induced writhing and tail immersion tests. Naloxone and pentylenetetrazol were used to evaluate the potential implication of GABAergic and opioidergic mechanisms. The anti-inflammatory potential of 2-HF was confirmed using carrageenan-, serotonin- and histamine-induced paw edema models as well as a xylene-induced ear edema model. Furthermore, the anti-neuropathic potential of 2-HF was tested using a cisplatin-induced neuropathic pain model. Our sample, at the tested concentrations of 15, 30 and 45 mg kg−1, showed considerable analgesic, anti-inflammatory effects, as well as efficacy against neuropathic pain. Naloxone and pentylenetetrazol at 1 and 15 mg kg−1 antagonized the anti-nociceptive activities of 2-hydroxyflavanone indicating the involvement of opioidergic and GABAergic mechanisms. In the static allodynia model, combination of gabapentin 75 mg kg−1 with 2-HF at 15, 30, 45 mg kg−1 doses exhibited considerable efficacy. In cold allodynia, 2-hydroxyflavanone, at doses of 15, 30 and 45 mg kg−1 and in combination with gabapentin (75 mg kg−1), demonstrated prominent anti-allodynic effects. The paw withdrawal latency was considerably increased in gabapentin + cisplatin treated groups. Moreover, cisplatin + 2-hydroxyflavanone 15, 30, 45 mg kg−1 showed increases in paw withdrawal latency. Likewise, considerable efficacy was observed for 2-hydroxyflavanone in thermal hyperalgesia and dynamic allodynia models. Our findings suggest that 2-hydroxyflavanone is a potential remedy for pain syndrome, possibly mediated through opioidergic and GABAergic mechanisms.

Co-Combination of Pregabalin and Withaniacoagulans-Extract-Loaded Topical Gel Alleviates Allodynia and Hyperalgesia in the Chronic Sciatic Nerve Constriction Injury for Neuropathic Pain in Animal Model

The current study reports the fabrication of co-combination gel using Pregabalin and Withania coagulans fruit extract to validate its effectiveness for neuropathic pain in chronic constriction injury (CCI) rat models. Three topical gels were prepared using Carbopol 934 through a pseudo-ternary phase diagram incorporating the Pregabalin (2.5%), Withania coagulans extract (2%), and co-combination of both Pregabalin (2.5%) and Withania coagulans extract (2%). Gels were characterized. FTIR showed a successful polymeric network of the gel without any interaction. The drug distribution at the molecular level was confirmed by XRD. The AFM images topographically indicated the rough surface of gels with a size range from 0.25 to 330 nm. DSC showed the disappearance of sharp peaks of the drug and extract, showing successful incorporation into the polymeric network of gels. The in vitro drug release of co-combination gel was 73% over 48 h. The mechanism of drug release by combination gel was Higuchi+ fickian with values of n (0.282) and R2 (0.947). An in vivo study for pain assessment via four methods: (i) heat hyperalgesia, (ii) cold allodynia, (iii) mechano-hyperalgesia, and (iv) dynamic mechano-allodynia, confirmed that topical treatment with co-combination gel reduced the pain significantly as indicated by the p value: R1 (p < 0.001), R2 (p < 0.001), R3 (p < 0.015), and R4 (p < 0.0344). The significance order was R2 (****) > R1 (***) > R3 (**) > R4 (*) > R5 (ns).

The 7-Hydroxyflavone attenuates chemotherapy-induced neuropathic pain by targeting inflammatory pathway

Vincristine and paclitaxel are widely used chemotherapeutic drugs for the treatment of brain tumors, breast cancer, leukemia, lymphomas, and malignant solid tumors. Though, these drugs are associated with some severe adverse effects including peripheral neuropathic pain. The anti-nociceptive and anti-inflammatory properties of the 7-Hydroxyflavone (7HF) were evaluated in the mice using thermally- and chemically-induced nociception, naloxone antagonistic test, and carrageenan-induced paw edema models. Initially, the in-vitro cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitory assays were carried out. Peripheral neuropathic pain was induced in the Sprague Dawley (SD) rats by administration of paclitaxel (4 mg/kg) and vincristine (200 µg/kg) on days 1, 3, 5, 7, and 9, respectively. The protective effect of 7HF was assessed against the chemotherapy-induced peripheral neuropathy in the rats. Moreover, the expression of the inflammatory mediators in the spinal cord was investigated through RT-PCR. In addition, a computational study was performed to find the potential therapeutic targets and the binding mechanism of 7HF. The 7HF caused concentration-dependent inhibition of COX-2 and 5-LOX, it attenuated the nociceptive pain, carrageenan-induced paw edema, and the development of mechanical and cold allodynia, and hyperalgesia dose-dependently without causing motor coordination deficit. Likewise, the 7HF decreased the vincristine-induced increased expression of different inflammatory mediators including COX-2, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), and nuclear factor-kappa B (NF-κB). The computational study showed the effective interactions of 7HF with the binding sites of NF-κB, COX-2, and 5-LOX, exert its inhibitory activities. These findings reveal that the 7HF has anti-nociceptive, anti-inflammatory, and anti-neuropathic potentials.

Pharmacological evaluation of the gabapentin salicylaldehyde derivative, gabapentsal, against tonic and phasic pain models, inflammation, and pyrexia

Gabapentinoids are effective drugs in most animal models of pain and inflammation with variable effects in humans. The current study evaluated the pharmacological activity of gabapentin (GBP) and its salicylaldehyde derivative (gabapentsal; [2-(1-(((2-hydroxybenzylidene) amino) methyl) cyclohexyl) acetic acid]; GPS) in well-established mouse models of nociceptive pain, inflammatory edema, and pyrexia at doses of 25-100 mg/kg. GPS allayed tonic visceral pain as reflected by acetic acid-induced nociception and it also diminished thermally induced nociception as a mimic of phasic thermal pain. Antagonism of GPS-induced antinociceptive activities by naloxone (NLX, 1.0 mg/kg, subcutaneously, s.c), beta-funaltrexamine (β-FNT, 5.0 mg/kg, s.c), naltrindole (NT, 1.0 mg/kg, s.c), and nor-binaltorphimine (NOR-BNI, 5.0 mg/kg, s.c), and pentylenetetrazole (PTZ-15 mg/kg, intraperitoneally, i.p) implicated an involvement of both opioidergic and GABAergic mechanisms. Tail immersion test was conducted in order to delineate the mechanistic insights of antinociceptive response. Inflammatory edema induced by carrageenan, histamine, or serotonin was also effectively reversed by GPS in a fashion analogous to aspirin (150 mg/kg, i.p), chlorpheniramine (1.0 mg/kg, i.p), and mianserin (1.0 mg/kg, i.p), respectively. Additionally, yeast-induced pyrexia was decreased by GPS in a comparable manner to acetaminophen (50 mg/kg, i.p). These observations suggest that GPS possesses ameliorative properties in tonic, phasic, and tail immersion tests of nociception via opioidergic and GABAergic mechanisms, curbs inflammatory edema, and is antipyretic in nature.

Mechanistic evaluation of a novel cyclohexenone derivative's functionality against nociception and inflammation: An in-vitro, in-vivo and in-silico approach

The synthesis of a novel cyclohexanone derivative (CHD; Ethyl 6-(4-metohxyphenyl)-2-oxo-4-phenylcyclohexe-3-enecarboxylate) was described and the subsequent aim was to perform an in vitro, in vivo and in silico pharmacological evaluation as a putative anti-nociceptive and anti-inflammatory agent in mice. Initial in vitro studies revealed that CHD inhibited both cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) enzymes and it also reduced mRNA expression of COX-2 and the pro-inflammatory cytokines TNF-α and IL-1β. It was then shown that CHD dose dependently inhibited chemically induced tonic nociception in the abdominal constriction assay and also phasic thermal nociception (i.e. anti-nociception) in the hot plate and tail immersion tests in comparison with aspirin and tramadol respectively. The thermal test outcomes indicated a possible moderate centrally mediated anti-nociception which, in the case of the hot plate test, was pentylenetetrazole (PTZ) and naloxone reversible, implicating GABAergic and opioidergic mechanisms. CHD was also effective against both the neurogenic and inflammatory mediator phases induced in the formalin test and it also disclosed anti-inflammatory activity against the phlogistic agents, carrageenan, serotonin, histamine and xylene compared with standard drugs in edema volume tests. In silico studies indicated that CHD possessed preferential affinity for GABAA, opioid and COX-2 target sites and this was supported by molecular dynamic simulations where computation of free energy of binding also favored the formation of stable complexes with these sites. These findings suggest that CHD has prospective anti-nociceptive and anti-inflammatory properties, probably mediated through GABAergic and opioidergic interactions supplemented by COX-2 and 5-LOX enzyme inhibition in addition to reducing pro-inflammatory cytokine expression. CHD may therefore possess potentially beneficial therapeutic effectiveness in the management of inflammation and pain.

The antioxidant N-(2-mercaptopropionyl)-glycine (tiopronin) attenuates expression of neuropathic allodynia and hyperalgesia

The current pharmacotherapy of neuropathic pain is inadequate as neuropathic pain involves varied clinical manifestations with multifactorial etiology, modulated by a cascade of physical and molecular events leading to different clinical presentations of pain. There is an accumulating evidence of the involvement of oxidative stress in neuropathy, and antioxidants have shown promise in mitigating neuropathic pain syndromes. To explore the evidence supporting this beneficial proclivity of antioxidants, this study investigated the antinociceptive effectiveness of N-(2-mercaptopropionyl)glycine or tiopronin, a well-recognized aminothiol antioxidant, in a refined chronic constriction injury (CCI) rat model of neuropathic pain. Tiopronin (10, 30, and 90 mg/kg, i.p.) and pregabalin (30 mg/kg, i.p.) were administered daily after CCI surgery. The neuropathic paradigms of mechanical/cold allodynia and mechanical/heat hyperalgesia were assessed on days 3, 7, 14, and 21 post-nerve ligation. At the end of study, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels were estimated in the sciatic nerve, dorsal root ganglion, and spinal cord for assessing the extent of oxidative stress. The expression of neuropathic nociception was attenuated by tiopronin which was observed as a significant attenuation of CCI-induced allodynia and hyperalgesia. Tiopronin reversed the neuronal oxidative stress by significantly reducing MDA, and increasing SOD, CAT, and GSH levels. Pregabalin also showed similar beneficial propensity on CCI-induced neuropathic aberrations. These findings suggest prospective neuropathic pain attenuating efficacy of tiopronin and further corroborated the notion that antioxidants are effective in mitigating the development and expression of neuropathic pain and underlying neuronal oxidative stress.

Topical Treatments and Their Molecular/Cellular Mechanisms in Patients with Peripheral Neuropathic Pain-Narrative Review

Neuropathic pain in humans results from an injury or disease of the somatosensory nervous system at the peripheral or central level. Despite the considerable progress in pain management methods made to date, peripheral neuropathic pain significantly impacts patients' quality of life, as pharmacological and non-pharmacological methods often fail or induce side effects. Topical treatments are gaining popularity in the management of peripheral neuropathic pain, due to excellent safety profiles and preferences. Moreover, topical treatments applied locally may target the underlying mechanisms of peripheral sensitization and pain. Recent studies showed that peripheral sensitization results from interactions between neuronal and non-neuronal cells, with numerous signaling molecules and molecular/cellular targets involved. This narrative review discusses the molecular/cellular mechanisms of drugs available in topical formulations utilized in clinical practice and their effectiveness in clinical studies in patients with peripheral neuropathic pain. We searched PubMed for papers published from 1 January 1995 to 30 November 2020. The key search phrases for identifying potentially relevant articles were "topical AND pain", "topical AND neuropathic", "topical AND treatment", "topical AND mechanism", "peripheral neuropathic", and "mechanism". The result of our search was 23 randomized controlled trials (RCT), 9 open-label studies, 16 retrospective studies, 20 case (series) reports, 8 systematic reviews, 66 narrative reviews, and 140 experimental studies. The data from preclinical studies revealed that active compounds of topical treatments exert multiple mechanisms of action, directly or indirectly modulating ion channels, receptors, proteins, and enzymes expressed by neuronal and non-neuronal cells, and thus contributing to antinociception. However, which mechanisms and the extent to which the mechanisms contribute to pain relief observed in humans remain unclear. The evidence from RCTs and reviews supports 5% lidocaine patches, 8% capsaicin patches, and botulinum toxin A injections as effective treatments in patients with peripheral neuropathic pain. In turn, single RCTs support evidence of doxepin, funapide, diclofenac, baclofen, clonidine, loperamide, and cannabidiol in neuropathic pain states. Topical administration of phenytoin, ambroxol, and prazosin is supported by observational clinical studies. For topical amitriptyline, menthol, and gabapentin, evidence comes from case reports and case series. For topical ketamine and baclofen, data supporting their effectiveness are provided by both single RCTs and case series. The discussed data from clinical studies and observations support the usefulness of topical treatments in neuropathic pain management. This review may help clinicians in making decisions regarding whether and which topical treatment may be a beneficial option, particularly in frail patients not tolerating systemic pharmacotherapy.

A novel gabapentin analogue assuages neuropathic pain response in chronic sciatic nerve constriction model in rats

Gabapentin (GBP) is an established drug that has been used in the management of symptoms of neuropathy but it is associated with unwanted side effects such as sedation and motor incoordination. The goal of the study was to find out a drug with greater efficacy and safety for the treatment of neuropathic pain. Our previously synthesized GABA analogue (Gabapentsal, GPS) was tested (25-100 mg/kg, i.p) in chronic constriction injury (CCI) induced nociceptive model of static allodynia, dynamic allodynia, thermal hyperalgesia, mechanical hyperalgesia and cold allodynia in rats (Sprague Dawley). Open field and rotarod tests were performed to assess the impact of GPS on the motor performance of the animals. GBP (100 mg/kg, i.p) was used as a standard for comparison. GPS dose dependently reduced static (P <0.001) and dynamic allodynia (P <0.001), thermal hyperalgesia (P <0.001), mechanical hyperalgesia (P < 0.001) and cold allodynia (P < 0.001). In comparison to GBP, GPS failed to alter any significantly the motor performance of rats in both the open field and rotarod assays. These results suggest that GPS is effective in alleviating nociception in CCI neuropathic pain model but free from the side effect of motor discoordination seen in the treatment with GBP. In conclusion, GPS may prove to be a prospectively more effective and safer option in the management of neuropathic syndromes.

Attenuation of nociceptive and paclitaxel-induced neuropathic pain by targeting inflammatory, CGRP and substance P signaling using 3-Hydroxyflavone

Paclitaxel is an anti-microtubule agent, most widely used chemotherapeutic agent for the treatment of malignant solid tumors. However, it is associated with some severe side effects including painful neurotoxicity with reporting of neuropathic pain and sensory abnormalities by patients during and after paclitaxel therapy. Peripheral neuropathy was induced by the administration of paclitaxel (4 mg/kg on days 1, 3, 5, and 7). In this study, the anti-nociceptive and anti-inflammatory propensity of 3-Hydroxyflavone (3HF) in mice and the preventive effect of 3HF against paclitaxel-induced peripheral neuropathy in Sprague Dawley (SD) rats were investigated. Moreover, tactile and cold allodynia, thermal and tail immersion hyperalgesia, and effects on motor-coordination were also evaluated. Furthermore, the expression of proinflammatory cytokines i.e. Calcitonin gene-related peptide (CGRP), and Substance P from the spinal cord was examined through RT-PCR. Additionally, a computational structural biology approach was applied to search the potential therapeutic targets and to predict the binding mechanism of 3HF. Treatment of 3HF alleviated the nociceptive pain, paw edema, development of tactile and cold allodynia, and hyperalgesia. Similarly, treatment with 3HF suppressed the paclitaxel-induced increase in mRNA expression of several inflammatory cytokines including tumor necrosis factor -α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6), CGRP, and Substance P. However, the daily treatment of 3HF did not affect the motor behaviors of rats. The inhibitory mechanism of 3HF in neuropathic pain is predicted with extensive computational bioinformatics approach which indicates that the 3HF effectively interacts with the binding domains of Nuclear factor-kappa B (NF-κB), CGRP receptor and the receptor of Substance P to exert its inhibitory activities. However, the computationally predicted binding affinities revealed that the potential of binding of the compound with Substance P receptor (Neurokinin 1 receptor) is higher than the other receptors; there NK1R could be the most possible binding target of 3HF. These findings indicate that 3HF has anti-nociceptive, anti-inflammatory, and anti-neuropathic pain effects against paclitaxel-induced neuropathic pain.

Comprehensive Review of Topical Analgesics for Chronic Pain

PURPOSE OF REVIEW

Topical analgesics are a non-opioid option for the treatment of chronic pain conditions including neuropathic pain, musculoskeletal pain, and osteoarthritis. There are many topical medications available; however their efficacy is variable. This article reviews the various topical analgesics, their mechanisms of action, and their efficacy.

RECENT FINDINGS

Studies have found topical NSAIDs are useful in treating acute musculoskeletal pain syndromes (strains and sprains) and show some efficacy in treating hand and knee osteoarthritis (Derry et al. Cochrane Database Syst Rev 5:CD008609, 2017). Topical capsaicin 8% has been shown to be efficacious in the treatment of postherpetic neuralgia, painful diabetic peripheral neuropathy, and HIV-neuropathy (Derry et al. Cochrane Database Syst Rev 1:CD007393, 2017). Topical lidocaine has been widely studied and found to reduce pain in patients with postherpetic neuralgia (Knezevic et al. Pain Manag 7:537-58, 2017). Although many other topical analgesics are available, there is limited data to support the efficacy of other agents. Topical analgesics are a relatively benign treatment for chronic pain conditions including neuropathic pain, musculoskeletal, and myofascial pain. There is evidence to support the use of topical NSAIDs, high concentration topical capsaicin, and topical lidocaine for various painful conditions.

7β-(3-Ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z Notonipetranone Attenuates Neuropathic Pain by Suppressing Oxidative Stress, Inflammatory and Pro-Apoptotic Protein Expressions

7β-(3-Ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z-notonipetranone (ECN), a sesquiterpenoid obtained from a natural source has proved to be effective in minimizing various side effects associated with opioids and nonsteroidal anti-inflammatory drugs. The current study focused on investigating the effects of ECN on neuropathic pain induced by partial sciatic nerve ligation (PSNL) by mainly focusing on oxidative stress, inflammatory and apoptotic proteins expression in mice. ECN (1 and 10 mg/kg, i.p.), was administered once daily for 11 days, starting from the third day after surgery. ECN post-treatment was found to reduce hyperalgesia and allodynia in a dose-dependent manner. ECN remarkably reversed the histopathological abnormalities associated with oxidative stress, apoptosis and inflammation. Furthermore, ECN prevented the suppression of antioxidants (glutathione, glutathione-S-transferase, catalase, superoxide dismutase, NF-E2-related factor-2 (Nrf2), hemeoxygenase-1 and NAD(P)H: quinone oxidoreductase) by PSNL. Moreover, pro-inflammatory cytokines (tumor necrotic factor-alpha, interleukin 1 beta, interleukin 6, cyclooxygenase-2 and inducible nitric oxide synthase) expression was reduced by ECN administration. Treatment with ECN was successful in reducing the caspase-3 level consistent with the observed modulation of pro-apoptotic proteins. Additionally, ECN showed a protective effect on the lipid content of myelin sheath as evident from FTIR spectroscopy which showed the shift of lipid component bands to higher values. Thus, the anti-neuropathic potential of ECN might be due to the inhibition of oxidative stress, inflammatory mediators and pro-apoptotic proteins.

Topical agents: a thoughtful choice for multimodal analgesia

For over a thousand years, various substances have been applied to the skin to treat pain. Some of these substances have active ingredients that we still use today. However, some have been discontinued due to their harmful effect, while others have been long forgotten. Recent concerns regarding the cardiovascular and renal risk from nonsteroidal anti-inflammatory drugs, and issues with opioids, have resulted in increasing demand and attention to non-systemic topical alternatives. There is increasing evidence of the efficacy and safety of topical agents in pain control. Topical analgesics are great alternatives for pain management and are an essential part of multimodal analgesia. This review aims to describe essential aspects of topical drugs that physicians should consider in their practice as part of multimodal analgesia. This review describes the mechanism of popular topical analgesics and also introduces the most recently released and experimental topical medications.

Percutaneous delivery of levetiracetam as an alternative to topical nonsteroidal anti-inflammatory drugs: formulation development, in vitro and in vivo characterization

The study focused on formulation of carmellose sodium hydrogels and nonionic microemulsions with 5% and 10% of levetiracetam and investigation of drug concentration influence on their physicochemical characteristics and in-use stability as well as influence of drug concentration and carrier type on in vitro drug release and in vivo antihyperalgesic/antiedematous activity in a rat model of localized (intraplantar) carrageenan-induced inflammation. Hydrogels were pseudoplastic semisolids with thixotropy and pH 7.37-7.58. Microemulsions were low viscous Newtonian nanodispersions of oil droplets (13.11-15.11 nm) in water, with pH 4.01-4.64. Physical stability of the investigated systems was preserved over the 3-month storage under ambient conditions. Levetiracetam release followed zero order and Korsmeyer-Peppas models (R² ≥ 0.99) reflecting the combined effects of drug concentration and carrier viscosity. All levetiracetam-loaded formulations produced significant reduction of hyperalgesia and paw swelling induced by carrageenan (p < 0.001). Their efficacy in exerting antihyperalgesic activity was significantly higher than that observed with the reference 5% ibuprofen hydrogel preparation (up to 6 h) (p < 0.001), while antiedematous activity was comparable with the reference product. No erythema and visible blood vessels were observed in a rat ear test. The study demonstrated percutaneous delivery of levetiracetam as useful and safe therapeutic option for localized inflammatory pain with potential to overcome the insufficient efficacy of topically applied nonsteroidal anti-inflammatory drugs in the form of a hydrogel. Graphical abstract.

Efficacy of a topical gabapentin gel in a cisplatin paradigm of chemotherapy-induced peripheral neuropathy

BACKGROUND

Chemotherapy induced peripheral neuropathy (CIPN) has been attributed to chemotherapeutic agents such as cisplatin which adversely affect disease outcome leading to increased cancer related morbidity. The clinical efficacy of systemic gabapentin in neuropathic pain management is limited by central side-effects in addition to a scarceness of conclusive evidence of its efficacy in CIPN management. The topical route therefore may provide a relatively safe alternative for neuropathic pain treatment in general and CIPN in particular.

METHODS

Cisplatin induced neuropathic nociception was established in rats after a single weekly cisplatin injection (3.0 mg/kg, intraperitoneally) for 4 weeks. The evoked neuropathic sensation of allodynia was assessed by plantar application of von Frey monofilaments as the paw withdrawal threshold (PWT), whereas the expression of heat-hypoalgesia was determined on a hot-plate as paw withdrawal latency (PWL). Gabapentin gel (10% w/w) was applied three-times daily on the hind paws while in a concurrent systemic study, gabapentin was administered daily (75 mg/kg, intraperitoneally) for 4 weeks. To assess any evidence of neurological adverse symptoms of cisplatin and the central side-effect propensity of systemic or topical gabapentin, evaluation of motor coordination (rotarod test) and gait (footprint analysis) were performed.

RESULTS

Cisplatin invoked a progressive development of neuropathic hind paw allodynia (decreased PWT, days 7-28) and heat hypoalgesia (increased PWL, days 21-28). Topical gabapentin significantly delayed the expression of both allodynia on protocol days 21 and 28 and heat-hypoalgesia (day 28). Systemic gabapentin displayed a comparative anti-neuropathic predisposition through a sustained suppression of tactile allodynia on days 14 and 21-28 as well as thermal hypoalgesia (days 21 and 28). Systemic gabapentin also impaired motor coordination and gait thus affirming its clinically documented central side effects, but these outcomes were not evident after topical treatment.

CONCLUSIONS

Both topical and systemic gabapentin exhibit a propensity to attenuate CIPN in a cisplatin paradigm. Gabapentin applied topically may therefore provide an adjunctive or alternative route for CIPN management upon cessation of systemic medications due to intolerable side-effects.

IL-35 alleviates inflammation progression in a rat model of diabetic neuropathic pain via inhibition of JNK signaling

Background

Emerging evidence has demonstrated that inflammation is involved in the occurrence and development of diabetic neuropathic pain (DNP). The anti-inflammatory property of interleukin (IL)-35 makes it a promising candidate to block the pain perception. The present study was undertaken to investigate whether IL-35 could attenuate DNP in streptozotocin (STZ)-induced rat model and its potential mechanism.

Methods

The rat model of DNP was established by a single STZ injection followed by measurements of fasting blood glucose and insulin. Fourteen days after STZ injection, DNP rats were intrathecally injected with IL-35, c-Jun N-terminal kinase (JNK) inhibitor or activator or dimethylsulfoxide (DMSO) as vehicle control, respectively. The mechanical allodynia was assayed to evaluate the therapeutic effect of IL-35. In mechanism study, the serum and protein levels of inflammatory cytokines using ELISA and western blotting and the activation of JNK signaling were further evaluated by quantitative reverse transcription PCR (qRT-PCR). Histopathologic changes were evaluated by Nissl staining. Apoptosis was examined using TUNEL staining.

Results

DNP rats exhibited increased fasting blood glucose and insulin levels and reduced insulin sensitivity index (ISI). Intrathecal injection of IL-35 reduced accumulation of pro-inflammatory cytokines in the spinal cord of DNP rats. Furthermore, IL-35 displayed anti-inflammatory and anti-apoptotic effects via inhibition of JNK pathway.

Conclusion

IL-35 treatment mitigated DNP via downregulating JNK signaling pathway.

Pain management in neurocritical care; an update

PURPOSE OF REVIEW

Pain management in neurocritical care is a subject often avoided because of concerns over the side-effects of analgesics and the potential to cause additional neurological injury with treatment. The sedation and hypercapnia caused by opioids have been feared to mask the neurological examination and contribute to elevations in intracranial pressure. Nevertheless, increasing attention to patient satisfaction has sparked a resurgence in pain management. As opioids have remained at the core of analgesic therapy, the increasing attention to pain has contributed to a growing epidemic of opioid dependence. In this review, we summarize the most recent literature regarding opioids and their alternatives in the treatment of acute pain in patients receiving neurocritical care.

RECENT FINDINGS

Studies on pain management in neurocritical care continue to explore nonopioid analgesics as part of a multimodal strategy aimed at decreasing overall opioid consumption. Agents including local anesthetics, acetaminophen, ketamine, gabapentinoids, and dexmedetomidine continue to demonstrate efficacy. In addition, the prolonged longitudinal course of many recent trials has also revealed more about the transition from acute to chronic pain following hospitalization.

SUMMARY

In an era of increasing attention to patient satisfaction mitigated by growing concerns over the harms imposed by opioids, alternative analgesic therapies are being investigated with promising results.

Management of chronic neuropathic pain with single and compounded topical analgesics

The goal of our review was to emphasize important aspects that physicians should take into consideration when prescribing topical analgesics as part of chronic neuropathic pain treatment. We discuss the dermatopharmacokinetics and microstructural components of the skin, differences between topical and transdermal drug delivery, and topical medication effects on peripheral neuropathy and central sensitization. Even though the US FDA approved topical analgesics are 8%-capsaicin and 5%-lidocaine patches for treating postherpetic neuralgia, there are many other studies conducted on the efficacy of topical ketamine cream, clonidine gel, topical gabapentin, topical baclofen and topical phenytoin for peripheral neuropathic pain, either alone or in combination with other formulations. Furthermore, we discuss new compounded topical analgesics that are becoming more popular and that are showing promising results in the management of chronic peripheral neuropathies. However, more studies are needed for elucidation of the role of topical analgesics and their effects, especially when combined with other treatments.

A bacosides containing Bacopa monnieri extract alleviates allodynia and hyperalgesia in the chronic constriction injury model of neuropathic pain in rats

BACKGROUND

The current therapy of neuropathic pain is inadequate and is limited by the extent of pain relief and the occurrence of dose dependant side effects. Insufficient control of pain with conventional medications prompts the use of complementary and alternative medicine therapies by patients with neuropathic pain. This study therefore investigated a standardized methanolic extract of Bacopa monnieri, a widely reputed nootropic plant, for prospective antinociceptive effect in the chronic constriction injury (CCI) model of neuropathic pain.

METHODS

Placement of four loose ligatures around the sciatic nerve produced partial denervation of the hindpaw in rats. Bacopa monnieri (40 and 80 mg/kg, p.o) and the positive control, gabapentin (75 mg/kg, i.p), were administered daily after CCI or sham surgery and the behavioral paradigms of static- and dynamic-allodynia (paw withdrawal threshold to von Frey filament stimulation [PWT] and paw withdrawal latency to light-brushing [PWL]), cold-allodynia (paw withdrawal duration [PWD] to acetone), heat- (PWL to heat-stimulus) and punctate-hyperalgesia (PWD to pin-prick) were assessed on days 3, 7, 14 and 21.

RESULTS

CCI consistently generated static- (days 3-21), dynamic- (days 14-21) and cold-allodynia (days 3-21) plus heat- and mechano-hyperalgesia (days 3-21). The tested doses of Bacopa monnieri significantly attenuated the CCI-induced allodynia and hyperalgesia, exemplified by increased PWT (days 7-21), PWL to light brushing (days 14-21) and heat (days 7-21) as well as decreased PWD to pin prick and cold stimuli (days 3-21). The extract also counterbalanced the CCI-induced aberrations in the nociceptive behaviors by increasing the pain threshold to that of pre-surgery baseline. Gabapentin also afforded analogous beneficial behavioral profile but of higher magnitude.

CONCLUSIONS

Our findings suggest that Bacopa monnieri can be used as adjuvant therapy for neuropathic pain conditions afflicted with allodynia and hyperalgesia.

Pregabalin can decrease acute pain and morphine consumption in laparoscopic cholecystectomy patients: A meta-analysis of randomized controlled trials

BACKGROUND

Pregabalin has been used as an adjunct for the management of acute pain in laparoscopic cholecystectomy. This meta-analysis aimed to illustrate the efficacy and safety of pregabalin for pain management following laparoscopic cholecystectomy.

METHODS

In March 2017, a systematic computer-based search was conducted in PubMed, EMBASE, Web of Science, Cochrane Database of Systematic Reviews, and Google databases. Data on patients prepared for laparoscopic cholecystectomy in studies that compared pregabalin versus placebo were retrieved. The primary endpoints were the visual analog scale (VAS) score with rest or mobilization at 6, 12, and 24 hours and total morphine consumption. The secondary outcomes were the morphine-related complications (i.e., nausea, vomiting, dizziness, somnolence, headache, pruritus, urine retention, respiratory depression, and blurred vision). Continuous outcomes were expressed as the weighted mean difference (WMD) with a corresponding 95% confidence interval (CI), and discontinuous outcomes were expressed as a risk ratio (RR) with a corresponding 95% CI.

RESULTS

Twelve clinical studies with 938 patients (gabapentin group = 536, control group = 402) were ultimately included in the meta-analysis. Pregabalin was associated with reduced pain scores with rest at 6, 12, and 24 hours, which corresponded to a reduction of 11.27 points at 6 hours, 9.46 points at 12 hours, and 3.99 points at 24 hours on a 100-point VAS. Moreover, pregabalin was associated with reduced pain scores with mobilization at 6, 12, and 24 hours, which corresponded to a reduction of 8.74 points, 5.80 points and 6.37 points at 6, 12, and 24 hours, respectively, on a 110-point VAS. Furthermore, pregabalin reduced the occurrence of nausea and vomiting. There were no significant differences in the occurrence of respiratory depression, pruritus, dizziness, blurred vision, and headache.

CONCLUSIONS

Pregabalin was efficacious in the reduction of postoperative pain, total morphine consumption, and morphine-related complications following laparoscopic cholecystectomy. In addition, a high dose of pregabalin was more effective than a low dose. The dose of pregabalin differed across the studies, and the heterogeneity was large. More studies are needed to verify the optimal dose of pregabalin in laparoscopic cholecystectomy patients.

Gabapentin can decrease acute pain and morphine consumption in spinal surgery patients: A meta-analysis of randomized controlled trials

BACKGROUND

Approximately 80% of patients who underwent spinal surgeries experience moderate to extreme postoperative pain. Gabapentin was used as an adjunct for the management of acute pain in approximately half of enhanced recovery programs. This meta-analysis aimed to illustrate the efficacy and safety of gabapentin for pain management following spinal surgery.

METHODS

In January 2017, a systematic computer-based search was conducted in PubMed, EMBASE, Web of Science, Cochrane Database of Systematic Reviews, and Google database. Data on patients prepared for spine surgery in studies that compared gabapentin versus placebo were retrieved. The primary endpoint was the visual analog scale (VAS) at 12 hours and 24 hours and total morphine consumption. The secondary outcomes were complications that included nausea, dizziness, somnolence, headache, pruritus, urine retention, and vomiting. After testing for publication bias and heterogeneity between studies, data were aggregated for random-effects models when necessary.

RESULTS

Seven clinical studies with 581 patients (gabapentin group=383, control group=198) were ultimately included in the meta-analysis. Gabapentin was associated with reduced pain scores at 12 hours and 24 hours, corresponding to a reduction of 11.18 points (95% CI, -13.85 to -8.52 points) at 12 hours and 9.94 points (95% CI, -13.99 to -5.89 points) at 24 hours on a 100-point VAS. Similarly, gabapentin was associated with a reduction in total morphine consumption (-2.04, 95% CI -2.71, -1.37). Furthermore, gabapentin can reduce the occurrence of vomiting (risk ratio [RR] 0.46, 95% CI 0.27, 0.78, P = 0.004), urine retention (RR = 0.57, 95% CI 0.34, 0.98, P = 0.041, NNT = 11.9) and pruritus (RR = 0.38, 95% CI 0.22, 0.66, P = 0.001, NNT = 5.6) and the number needed to treat (NNT = 20.1). There were no significant differences in the occurrence of nausea, dizziness, somnolence, or headache.

CONCLUSIONS

Gabapentin was efficacious in the reduction of postoperative pain, total morphine consumption, and morphine-related complications following spine surgery. In addition, a high dose (≥900 mg/d) of gabapentin is more effective than a low dose (<900 mg/d). The number of included studies is limited, and more studies are needed to verify the effects of gabapentin in spinal surgery patients.