Analgesic activity of a novel use-dependent sodium channel blocker, crobenetine, in mono-arthritic rats

Small molecule targeting Na V 1.7 via inhibition of CRMP2-Ubc9 interaction reduces pain-related outcomes in a rodent osteoarthritic model

ABSTRACT

Osteoarthritis (OA) is a highly prevalent and disabling joint disease, characterized by pathological progressive joint deformation and clinical symptoms of pain. Disease-modifying treatments remain unavailable, and pain-mitigation is often suboptimal, but recent studies suggest beneficial effects by inhibition of the voltage-gated sodium channel Na V 1.7. We previously identified compound 194 as an indirect inhibitor of Na V 1.7 by preventing SUMOylation of the Na V 1.7-trafficking protein, collapsin response mediator protein 2. Compound 194 reduces the functional activity of Na V 1.7 channels and produces effective analgesia in a variety of acute and neuropathic pain models. However, its effectiveness has not yet been evaluated in models of OA. Here, we explore the effects of 194 on pain-related outcomes in the OA-like monoiodoacetate model using behavioral assessment, biochemistry, novel in vivo fiber photometry, and patch clamp electrophysiology. We found that the monoiodoacetate model induced (1) increased pain-like behaviors and calcium responses of glutamatergic neurons in the parabrachial nucleus after evoked cold and mechanical stimuli, (2) conditioned place aversion to mechanical stimulation, (3) functional weight bearing asymmetry, (4) increased sodium currents in dorsal root ganglia neurons, and (5) increased calcitonin gene-related peptide-release in the spinal cord. Crucially, administration of 194 improved all these pain-related outcomes. Collectively, these findings support indirect inhibition of Na V 1.7 as an effective treatment of OA-related pain through the inhibition of collapsin response mediator protein 2-SUMOylation via compound 194.

Design, optimization, and evaluation of topical gel of Cardiospermum halicacabum and Ricinus communis L. leaves extract for the treatment of rheumatoid arthritis

This research aims to develop and assess the anti-arthritic properties of a topically herbal gel including leaf extracts from Cardiospermum halicacabum and Ricinus communis L. in rats. Utilizing gelling agents carbopol 940 (2.5, 5, 7.5 g), nine herbal gel compositions were created. Prepared formulations were then assessed for physical appearance, spreadability, viscosity, net content, pH, extrudability, in vitro diffusion profile, and main skin irritant tests. According to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) recommendations, the stability research for the topical herbal gel composition was completed, and Freund's Complete Adjuvant (FCA) induced arthritis technique was used to assess the anti-arthritic efficacy. Additional procedures included measuring the body weight, paw volume, biochemical and hematological variables, histological analysis, and in vitro serum biomarker detection. The prepared gels followed the instructions and were uniform and stable. F5 performed better than the other compositions in terms of release kinetics (97.20%). The gel proved safe and non-toxic since no erythema or edema was seen during the skin irritation test. Comparing the herbal gel F5 comprising carbopol 940 to rats with arthritis, the topical treatment showed considerable (p < .001) anti-arthritic effect. The anti-arthritic action of the gel formulations was confirmed by decreased paw volume, absence of agglutination in reacting protein and rheumatic factor, a decline in TNFα level, restoration to baseline biochemical and hematological characteristics, decrease in thymus and spleen weight, and histopathological study.

Pharmacological Dissection of the Crosstalk between NaV and CaV Channels in GH3b6 Cells

Thanks to the crosstalk between Na⁺ and Ca²⁺ channels, Na⁺ and Ca²⁺ homeostasis interplay in so-called excitable cells enables the generation of action potential in response to electrical stimulation. Here, we investigated the impact of persistent activation of voltage-gated Na⁺ (Na_V) channels by neurotoxins, such as veratridine (VTD), on intracellular Ca²⁺ concentration ([Ca²⁺]_i) in a model of excitable cells, the rat pituitary GH3b6 cells, in order to identify the molecular actors involved in Na⁺-Ca²⁺ homeostasis crosstalk. By combining RT-qPCR, immunoblotting, immunocytochemistry, and patch-clamp techniques, we showed that GH3b6 cells predominantly express the Na_V1.3 channel subtype, which likely endorses their voltage-activated Na⁺ currents. Notably, these Na⁺ currents were blocked by ICA-121431 and activated by the β-scorpion toxin Tf2, two selective Na_V1.3 channel ligands. Using Fura-2, we showed that VTD induced a [Ca²⁺]_i increase. This effect was suppressed by the selective Na_V channel blocker tetrodotoxin, as well by the selective L-type Ca_V channel (LTCC) blocker nifedipine. We also evidenced that crobenetine, a Na_V channel blocker, abolished VTD-induced [Ca²⁺]_i elevation, while it had no effects on LTCC. Altogether, our findings highlight a crosstalk between Na_V and LTCC in GH3b6 cells, providing a new insight into the mode of action of neurotoxins.

Benzomorphan skeleton, a versatile scaffold for different targets: A comprehensive review

Despite the fact that the benzomorphan skeleton has mainly been employed in medicinal chemistry for the development of opioid analgesics, it is a versatile structure. Its stereochemistry, as well as opportune modifications at the phenolic hydroxyl group and at the basic nitrogen, play a pivotal role addressing the benzomorphan-based compounds to a specific target. In this review, we describe the structure activity-relationships (SARs) of benzomorphan-based compounds acting at sigma 1 receptor (σ1R), sigma 2 receptor (σ2R), voltage-dependent sodium channel, N-Methyl-d-Aspartate (NMDA) receptor-channel complex and other targets. Collectively, the SARs data have highlighted that the benzomorphan nucleus could be regarded as a useful template for the synthesis of drug candidates for different targets.

Benzomorphan scaffold for opioid analgesics and pharmacological tools development: A comprehensive review

Benzomorphan, derived by morphine skeleton simplification, has been the subject of exploration in medicinal chemistry for the development of new drugs and pharmacological tools to explore opioid pharmacology in vitro and in vivo. Building upon these evidences, the design and synthesis of benzomorphan-based compounds, appropriately modified at the basic nitrogen and/or the phenolic hydroxyl (8-OH) group, represent a valid and versatile strategy to obtain analgesics. In this review, to improve the body of information in this field, we report structure activity-relationships (SARs) of benzomorphan-based compounds analysing data literature of last 25 years. Collectively, SARs data highlighted that the benzomorphan nucleus represents a template in the achievement of a specific functional profile, by modifying N-substituent or 8-OH group.

Evaluation of N-substituent structural variations in opioid receptor profile of LP1

The benzomorphan scaffold has great potential as lead structure and the nature of the N-substituent is able to influence affinity, potency, and efficacy at all three opioid receptors. Building upon these considerations, we synthesized a new series of LP1 analogues by introducing naphthyl or heteroaromatic rings in propanamide side chain of its N-substituent (9-15). In vitro competition-binding assays in HEK293 cells stably expressing MOR, DOR or KOR showed that in compound 9 the 1-naphthyl ring led to the retention of MOR affinity (Ki(MOR)=38±4nM) displaying good selectivity versus DOR and KOR. In the electrically stimulated GPI, compound 9 was inactive as agonist but produced an antagonist potency value (pA2) of 8.6 in presence of MOR agonist DAMGO. Moreover, subcutaneously administered it antagonized the antinociceptive effects of morphine with an AD50=2.0mg/kg in mouse-tail flick test. Modeling studies on MOR revealed that compound 9 fit very well in the binding pocket but in a different way in respect to the agonist LP1. Probably the replacement of its N-substituent on the III, IV and V TM domains reflects an antagonist behavior. Therefore, compound 9 could represent a potential lead to further develop antagonists as valid therapeutic agents and useful pharmacological tools to study opioid receptor function.

Anti-inflammatory and antiarthritic activity of anthraquinone derivatives in rodents

Aloe emodin is isolated compound of aloe vera which is used traditionally as an anti-inflammatory agent. In vitro pharmacokinetic data suggest that glucuronosyl or sulfated forms of aloe emodin may provide some limitations in its absorption capacity. Aloe emodin was reported to have in vitro anti-inflammatory activity due to inhibition of inducible nitric oxide (iNO) and prostaglandin E2, via its action on murine macrophages. However, present work evidenced that molecular docking of aloe emodin modulates the anti-inflammatory activity, as well as expression of COX-2 (cyclooxygenase-2) in rodent. The AEC (4,5-dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2 carboxylic acid) was synthesized using aloe emodin as starting material. The study was planned for evaluation of possible anti-inflammatory and antiarthritic activity in carrageenan rat induced paw oedema and complete Freund's adjuvant induced arthritis in rats. The AE (aloe emodin) and AEC significantly (P < 0.001) reduced carrageenan induced paw edema at 50 and 75 mg/kg. Complete Freund's adjuvant induced arthritis model showed significant (P < 0.001) decrease in injected and noninjected paw volume, arthritic score. AE and AEC showed significant effect on various biochemical, antioxidant, and hematological parameters. Diclofenac sodium 10 mg/kg showed significant (P < 0.001) inhibition in inflammation and arthritis.

Pain treatment for patients with osteoarthritis and central sensitization

Osteoarthritis is one of the most frequent, disabling, and costly pathologies of modern society. Among the main aims of osteoarthritis management are pain control and functional ability improvement. The exact cause of osteoarthritis pain remains unclear. In addition to the pathological changes in articular structures, changes in central pain processing or central sensitization appear to be involved in osteoarthritis pain. The latter calls for a broader approach to the management of patients with osteoarthritis. Yet, the scientific literature offers scant information addressing the treatment of central sensitization, specifically in patients with osteoarthritis. Interventions such as cognitive-behavioral therapy and neuroscience education potentially target cognitive-emotional sensitization (and descending facilitation), and centrally acting drugs and exercise therapy can improve endogenous analgesia (descending inhibition) in patients with osteoarthritis. Future studies should assess these new treatment avenues.

A novel model of combined neuropathic and inflammatory pain displaying long-lasting allodynia and spontaneous pain-like behaviour

Many clinical cases of chronic pain exhibit both neuropathic and inflammatory components. In contrast, most animal models of chronic pain focus on one type of injury alone. Here we present a novel combined model of both neuropathic and inflammatory pain and characterise its distinctive properties. This combined model of chronic constriction injury (CCI) and intraplantar Complete Freund's Adjuvant (CFA) injection results in enhanced mechanical allodynia, thermal hyperalgesia, a static weight bearing deficit, and notably pronounced spontaneous foot lifting (SFL) behaviour (which under our conditions was not seen in either individual model and may reflect ongoing/spontaneous pain). Dorsal root ganglion (DRG) expression of Activating Transcription Factor-3 (ATF-3), a marker of axonal injury, was no greater in the combined model than CCI alone. Initial pharmacological characterisation of the new model showed that the SFL was reversed by gabapentin or diclofenac, typical analgesics for neuropathic or inflammatory pain respectively, but not by mexiletine, a Na(+) channel blocker effective in both neuropathic and inflammatory pain models. Static weight bearing deficit was moderately reduced by gabapentin, whereas only diclofenac reversed mechanical allodynia. This novel animal model of chronic pain may prove a useful test-bed for further analysing the pharmacological susceptibility of complicated clinical pain states.

Topical pain management with the 5% lidocaine medicated plaster--a review

BACKGROUND

The topical 5% lidocaine medicated plaster is recommended as first-line treatment for localized peripheral neuropathic pain.

SCOPE

In order to provide an overview of the efficacy and safety of the lidocaine plaster in the treatment of different neuropathic pain conditions, all efficacy and safety studies (randomized, controlled, or open-label with well described methodology), case reports, and pharmacological studies on the lidocaine plaster retrieved from a PubMed literature research (1960-March 2012) plus additional references identified from retrieved articles were included.

FINDINGS

The lidocaine plaster is efficacious in the treatment of neuropathic pain symptoms associated with previous herpes zoster infection. Results from a large open-label controlled study suggest that the lidocaine plaster could be at least as effective as systemic pregabalin in the treatment of postherpetic neuralgia and painful diabetic polyneuropathy. Open-label studies indicate efficacy in the treatment of other localized neuropathic pain conditions, such as painful idiopathic sensory polyneuropathy, complex regional pain syndrome, carpal tunnel syndrome sequelae, postsurgical and posttraumatic pain. Quality of life markedly improved in a variety of neuropathic pain conditions and long-term treatment provided sustained relief in patients with neuropathic pain who are responsive to lidocaine plaster. The lidocaine plaster is usually well tolerated. The risk of systemic adverse events and pharmacokinetic interactions with concomitant medication is minimal owing to low systemic exposure.

CONCLUSIONS

Treatment of several, primarily neuropathic and mixed-pain conditions with the 5% lidocaine medicated plaster was found efficacious and safe. Further controlled studies, in particular where only small open-label studies or case reports are available, should be considered.

Modulation of arthritis in rats by Toxicodendron pubescens and its homeopathic dilutions

BACKGROUND

Toxicodendron pubescens P. Mill (Anacardiaceae) known in homeopathy as Rhus toxicodendron (Rhus tox) is used as an anti-inflammatory medicine in homeopathic practice. In this study, Rhus tox in its crude form and homeopathic dilutions (3cH, 6cH, 30cH, 200cH) was evaluated for effects on Complete Freund's Adjuvant (CFA) induced arthritis in rats.

METHOD

We assessed the severity of arthritis through observations including inflammatory lesions, body and organ weight and hematological parameters including C-reactive protein (CRP). Blinded radiological analysis of the affected joints and pain intensity determination was also carried out.

RESULTS

Rhus tox protected rats from CFA-induced inflammatory lesions, body weight changes and hematological alterations. Rhus tox protected against radiological joint alterations due to arthritis. Arthritic pain scores were also favorably affected by Rhus tox. All the dilutions of Rhus tox including crude form showed anti-arthritic activity. The maximum protective effect was evident in the crude form at 10mg/kg/day, by mouth.

CONCLUSION

This study supports claims in the homeopathic literature on the role of Rhus tox and its ultra dilutions in the treatment of arthritis and associated pain. Further study is needed to explain this anti-arthritic effect of Rhus tox.

Anti-Arthritic Activity of Bartogenic Acid Isolated from Fruits of Barringtonia racemosa Roxb. (Lecythidaceae)

The fruits of Barringtonia racemosa are prescribed in the ayurvedic literature for the treatment of pain, inflammation and rheumatic conditions. In present investigation, activity guided isolation of bartogenic acid (BA) and its evaluation in the Complete Freund's Adjuvant (CFA)-induced arthritis in rats is reported. Among the various extracts and fractions investigated preliminarily for carrageenan-induced acute inflammation in rats, the ethyl acetate fraction displayed potent anti-inflammatory activity. Large-scale isolation and characterization using chromatography and spectral study confirmed that the constituent responsible for the observed pharmacological effects was BA. Subsequently the BA was evaluated for effectiveness against CFA-induced arthritis in rats. The results indicate that at doses of 2, 5, and 10 mg kg⁻¹ day⁻¹, p.o., BA protects rats against the primary and secondary arthritic lesions, body weight changes and haematological perturbations induced by CFA. The serum markers of inflammation and arthritis, such as C-reactive protein and rheumatoid factor, were also reduced in the BA-treated arthritic rats. The overall severity of arthritis as determined by radiological analysis and pain scores indicated that BA exerts a potent protective effect against adjuvant-induced arthritis in rats. In conclusion, the present study validates the ethnomedicinal use of fruits of B. racemosa in the treatment of pain and inflammatory conditions. It further establishes the potent anti-arthritic effects of BA. However, additional clinical investigations are needed to prove the efficacy of BA in the treatment of various immuno-inflammatory disorders.

Brain activity for chronic knee osteoarthritis: dissociating evoked pain from spontaneous pain

Chronic pain is a hallmark of osteoarthritis (OA), yet little is known about its properties and representation in the brain. Here we use fMRI combined with psychophysics to study knee pain in fourteen OA patients and nine healthy controls. Mechanical painful pressure stimuli were applied to the knee in both groups and ratings of evoked pain and related brain activity examined. We observe that psychophysical properties and brain activation patterns of evoked pain are essentially the same between OA patients and healthy subjects, and between worse and better OA knees. In OA patients, stimulus-related brain activity could be distinguished from brain activity associated with spontaneous pain. The former activated brain regions commonly observed for acute painful stimuli in healthy subjects, while the spontaneous pain of OA engaged prefrontal-limbic regions closely corresponding to areas observed for spontaneous pain in other chronic pain conditions, such as chronic back pain and post-herpetic neuralgia. Arthritis-related clinical characteristics of knee OA also mapped to prefrontal-limbic regions. In a subgroup of patients (n=6) we examined brain activity changes for a 2-week, repeat measure, cyclooxygenase-2 inhibitor (valdecoxib) therapy. Treatment decreased spontaneous pain for the worse knee and clinical characteristics of OA, and increased blood and csf levels of the drug which correlated positively with prefrontal-limbic brain activity. These findings indicate dissociation between mechanically induced and spontaneous OA knee pain, the latter engaging brain regions involved in emotional assessment of the self, and challenge the standard clinical view regarding the nature of OA pain.

Therapy of trigeminal neuralgia secondary to multiple sclerosis

Trigeminal neuralgia occurs in approximately 1-2% of patients suffering from multiple sclerosis. Its pathophysiology is common to idiopathic forms and resides in altered properties of the sensory axonal membrane at the root entry zone into the pons, leading to parossistic firing. Antiepileptic drugs of the sodium channel blocker type, such as carbamazepine, lamotrigine, and phenytoin are highly effective in controlling pain. However, side effects on the CNS may, at higher doses, severely worsen the already impaired neurologic conditions in multiple sclerosis patients. Baclofen, a presynaptic muscle relaxant is also beneficial in trigeminal pain. Whatever the drug, habituation and loss of efficacy are likely to occur sooner or later. Symptomatic, neurolesive surgery is indicated in cases resistant or intolerant to medical therapy. Radiofrequency thermorhizotomy, either monitored by trigeminal evoked potentials or not, is the recommended procedure, as it may be considered the most reliable as far as localization and degree of lesion are concerned.

Experience with oral mexiletine in primary erythromelalgia in children

Primary erythromelalgia is characterized by burning pain, redness, and warmth in the extremities. We present two cases of primary erythromelalgia both of whom presented with a history of several months of severe burning pain in both hands and feet. Both patients had received multiple pain medications with no improvement in symptoms. Pain was relieved by putting affected parts in ice cold water, which resulted in immersion injury of the affected parts. Both patients stopped taking part in school and social activities. We tried oral mexiletine, a class Ib antiarrythmic agent, in view of its reported role in various chronic painful conditions. Dramatic improvement was observed with its use. Both patients improved after several weeks of use, and there were fewer soaking episodes. We observed no adverse effects with mexilitine therapy.

Comparison of the effectiveness and tolerability of lidocaine patch 5% versus celecoxib for osteoarthritis-related knee pain: post hoc analysis of a 12 week, prospective, randomized, active-controlled, open-label, parallel-group trial in adults

BACKGROUND

Cyclooxygenase-2 (COX-2) selective inhibitors and nonselective NSAIDs are commonly used to treat osteoarthritis (OA) of the knee.

OBJECTIVE

The aim of this study was to compare the effectiveness of the lidocaine patch 5% with that of celecoxib 200 mg/d in the treatment of OA-related knee pain; however, the study was terminated prematurely by the sponsor because of tolerability concerns regarding the class of COX-2 selective inhibitors. A post hoc analysis of the available data is presented here.

METHODS

This multicenter, randomized, open-label, active-controlled, parallel-group study included patients >or=18 years of age with unilateral or bilateral moderate to severe OA of the knee. Patients were randomized to receive treatment with either the lidocaine patch 5% or celecoxib 200 mg/d. The primary efficacy end point was change from baseline to 12 weeks in the Western Ontario and McMaster Universities (WOMAC) OA Index pain subscale. Secondary end points included additional WOMAC subscales and Brief Pain Inventory (BPI) measures. Because this trial was prematurely terminated, a post hoc analysis was performed using a random pattern-mixture model of all observed cases of the intent-to-treat population.

RESULTS

A total of 143 patients were randomized to treatment (lidocaine patch 5%, 69 patients; mean [SD] age, 60.2 [11.4] years; 65.2% female; 66.7% white; weight, 94.1 [23.3] kg) or celecoxib 200 mg/d (74 patients; age, 58.2 [12.1] years; 63.5% female; 68.9% white; weight, 94.3 [22.5] kg). Baseline pain WOMAC OA subscale scores (lidocaine patch 5%, 12.087; celecoxib 200 mg/d, 12.514) and mean rates of change over time (baseline to week 2, -1.5916 vs -1.6513 per week; weeks 2-6, -0.0168 vs -0.119 per week; weeks 6-12, -0.1818 vs -0.1579 per week) were not significantly different between the 2 groups. Improvement in additional WOMAC subscales and in several BPI measures were not significantly different between the 2 groups. Treatment-related adverse events were reported in 8 patients in each treatment group (11.6% in the lidocaine patch 5% group and 10.8% in the celecoxib 200-mg/d group) and were considered mild or moderate in severity.

CONCLUSION

Statistically significant differences in effectiveness and tolerability were not found between these 2 treatments in these patients with OA knee pain.

A preliminary fMRI study of analgesic treatment in chronic back pain and knee osteoarthritis

The effects of an analgesic treatment (lidocaine patches) on brain activity in chronic low back pain (CBP) and in knee osteoarthritis (OA) were investigated using serial fMRI (contrasting fMRI between before and after two weeks of treatment). Prior to treatment brain activity was distinct between the two groups: CBP spontaneous pain was associated mainly with activity in medial prefrontal cortex, while OA painful mechanical knee stimulation was associated with bilateral activity in the thalamus, secondary somatosensory, insular, and cingulate cortices, and unilateral activity in the putamen and amygdala. After 5% lidocaine patches were applied to the painful body part for two weeks, CBP patients exhibited a significant decrease in clinical pain measures, while in OA clinical questionnaire based outcomes showed no treatment effect but stimulus evoked pain showed a borderline decrease. The lidocaine treatment resulted in significantly decreased brain activity in both patient groups with distinct brain regions responding in each group, and sub-regions within these areas were correlated with pain ratings specifically for each group (medial prefrontal cortex in CBP and thalamus in OA). We conclude that the two chronic pain conditions involve distinct brain regions, with OA pain engaging many brain regions commonly observed in acute pain. Moreover, lidocaine patch treatment modulates distinct brain circuitry in each condition, yet in OA we observe divergent results with fMRI and with questionnaire based instruments.

Pain Controlling and Cytokine-regulating Effects of Lyprinol, a Lipid Extract of Perna Canaliculus, in a Rat Adjuvant-induced Arthritis Model

Using an adjuvant-induced arthritis rat model, we investigated the effects of a lipid extract of Perna canaliculus (Lyprinol®) on pain. Radiological examinations, as well as levels of pro- and anti-inflammatory (AI) cytokines, were measured aiming to provide independent objective data to the pain controlling investigation. We confirmed the ability of Lyprinol® to control pain at the initial phase of its administration; with similar efficacy to that observed with Naproxen. The pain scores slowly increased again in the group of rats treated with Lyprinol® after day 9–14. The Naproxen-treated rats remained pain-free while treated. Both Naproxen and Lyprinol® decreased the levels of the pro-inflammatory cytokines TNF-α and IFN-γ, and increased that of IL-10. Extra-virgin olive oil was ineffective on cytokine secretion. Rats treated with Lyprinol® were apparently cured after 1 year. This study confirms the AI efficacy of this lipid extract of P. canaliculus, its initial analgesic effect, its perfect tolerance and its long-term healing properties.

Arthritis and pain. Neurogenic origin of joint pain

Arthritis pain affects millions of people worldwide yet we still have only a limited understanding of what makes our joints ache. This review examines the sensory innervation of diarthroidal joints and discusses the neurophysiological processes that lead to the generation of painful sensation. During inflammation, joint nerves become sensitized to mechanical stimuli through the actions of neuropeptides, eicosanoids, proteinase-activated receptors and ion channel ligands. The contribution of immunocytes to arthritis pain is also reviewed. Finally, the existence of an endogenous analgesic system in joints is considered and the reasons for its inability to control pain are postulated.

Pharmacology of 2-[4-(4-Chloro-2-fluorophenoxy)phenyl]-pyrimidine-4-carboxamide: A Potent, Broad-Spectrum State-Dependent Sodium Channel Blocker for Treating Pain States

Voltage-gated Na(+) channels may play important roles in establishing pathological neuronal hyperexcitability associated with chronic pain in humans. Na(+) channel blockers, such as carbamazepine (CBZ) and lamotrigine (LTG), are efficacious in treating neuropathic pain; however, their therapeutic utility is compromised by central nervous system side effects. We reasoned that it may be possible to gain superior control over pain states and, in particular, a better therapeutic index, by designing broad-spectrum Na(+) channel blockers with higher potency, faster onset kinetics, and greater levels of state dependence than existing drugs. 2-[4-(4-Chloro-2-fluorophenoxy)phenyl]-pyrimidine-4-carboxamide (PPPA) is a novel structural analog of the state-dependent Na(+) channel blocker V102862 [4-(4-fluorophenoxy)benzaldehyde semicarbazone]. Tested on recombinant rat Na(v)1.2 channels and native Na(+) currents in cultured rat dorsal root ganglion neurons, PPPA was approximately 1000 times more potent, had 2000-fold faster binding kinetics, and > or =10-fold higher levels of state dependence than CBZ and LTG. Tested in rat pain models against mechanical endpoints, PPPA had minimal effective doses of 1 to 3 mg/kg p.o. in partial sciatic nerve ligation, Freund's complete adjuvant, and postincisional pain. In all cases, efficacy was similar to clinically relevant comparators. Importantly, PPPA did not produce motor deficits in the accelerating Rotarod assay of ataxia at doses up to 30 mg/kg p.o., indicating a therapeutic index >10, which was superior to CBZ and LTG. Our experiments suggest that high-potency, broad-spectrum, state-dependent Na(+) channel blockers will have clinical utility for treating neuropathic, inflammatory, and postsurgical pain. Optimizing the biophysical parameters of broad-spectrum voltage-gated Na(+) channel blockers may lead to improved pain therapeutics.

The Role of Sodium Channels in Chronic Inflammatory and Neuropathic Pain

Clinical and experimental data indicate that changes in the expression of voltage-gated sodium channels play a key role in the pathogenesis of neuropathic pain and that drugs that block these channels are potentially therapeutic. Clinical and experimental data also suggest that changes in voltage-gated sodium channels may play a role in inflammatory pain, and here too sodium-channel blockers may have therapeutic potential. The sodium-channel blockers of interest include local anesthetics, used at doses far below those that block nerve impulse propagation, and tricyclic antidepressants, whose analgesic effects may at least partly be due to blockade of sodium channels. Recent data show that local anesthetics may have pain-relieving actions via targets other than sodium channels, including neuronal G protein-coupled receptors and binding sites on immune cells. Some of these actions occur with nanomolar drug concentrations, and some are detected only with relatively long-term drug exposure. There are 9 isoforms of the voltage-gated sodium channel alpha-subunit, and several of the isoforms that are implicated in neuropathic and inflammatory pain states are expressed by somatosensory primary afferent neurons but not by skeletal or cardiovascular muscle. This restricted expression raises the possibility that isoform-specific drugs might be analgesic and lacking the cardiotoxicity and neurotoxicity that limit the use of current sodium-channel blockers.

PERSPECTIVE

Changes in the expression of neuronal voltage-gated sodium channels may play a key role in the pathogenesis of both chronic neuropathic and chronic inflammatory pain conditions. Drugs that block these channels may have therapeutic efficacy with doses that are far below those that impair nerve impulse propagation or cardiovascular function.

Lidocaine iontophoresis mediates analgesia in lateral epicondylalgia treatment

BACKGROUND AND PURPOSE

Iontophoresis transcutaneously delivers anti-inflammatory and analgesic drugs for the treatment of musculoskeletal dysfunction. Lidocaine is a local anaesthetic with analgesic but no anti-inflammatory properties. The purpose of this investigation was to examine the clinical use of lidocaine iontophoresis-mediated analgesia in a larger treatment algorithm for five patients with lateral humeral epicondylalgia.

METHOD

The investigation was a case series design of five subjects, aged 52 (+/- 6) years, with epicondylalgia of 12-393 days' duration. At each treatment session, the patients received cryotherapy, cross-fibre massage and passive stretch. Between sessions analgesia was provided by an 80 mA-min low-current, long-duration lidocaine iontophoresis (LI) over a 24-hour period. Patients were treated on an every-other-day basis for a total of three treatment sessions. Clinical improvements were determined by triplicate measurements of dolorimetric force over the affected epicondyle prior to treatment 1 (baseline), prior to sessions 2 and 3, and one week following the last session.

RESULTS

Patients demonstrated an increasing tolerance to dolorimetric force application prior to the next session. The force values prior to session 2 (3.1 (+/- 1.1) Newton (N)) and one week following the third session (3.4 (+/- 0.5) N) were significantly improved from the baseline values (2.1 (+/- 0.9) N).

CONCLUSIONS

Pain associated with lateral epicondylalgia decreased, and function improved in all patients at the final measurement. One patient returned during the 90-day follow-up period to seek additional medical attention. This investigation documents the potential for analgesia provided by LI in the rehabilitation process of musculoskeletal dysfunction.

Analysis of human Nav1.8 expressed in SH-SY5Y neuroblastoma cells

The tetrodotoxin-resistant voltage-gated sodium channel alpha-subunit Nav1.8 is expressed in nociceptors and has been implicated in chronic pain. Difficulties of heterologous expression have so far precluded analysis of the pharmacological properties of human Nav1.8. To address this we have introduced human Nav1.8 in neuroblastoma SH-SY5Y cells. Voltage-clamp analysis showed that human Nav1.8 generated an inward tetrodotoxin-resistant sodium current with an activating threshold around -50 mV, half maximal activation at -11+/-3 mV and a reversal potential of 67+/-4 mV. These properties closely match those of the endogenous rat tetrodotoxin-resistant sodium current in dorsal root ganglia suggesting that the expressed human channel is in a near physiological conformation. Human Nav1.8 was resistant to tetrodotoxin and activated by the pyrethroid toxin deltamethrin. Both voltage-activated and deltamethrin-activated human Nav1.8 were inhibited by the sodium channel blockers BIII 890 CL, NW-1029, and mexiletine. Inhibition of Nav1.8 by these compounds may underlie their known analgesic effects in animal models.

Topical lidocaine patch 5% may target a novel underlying pain mechanism in osteoarthritis

Recent literature and animal research has provided insight to potentially new analgesic targets for managing osteoarthritis (OA) pain. Primary afferent neurons located in affected joints express excessive amounts of abnormally functioning sodium (Na) channels on their surface in response to the inflammatory process. These Na channels may play an integral role in production of pain and hyperalgesia. Hence, the authors set out to conduct a 2-week, open-label, multicenter proof-of-concept study to evaluate the effectiveness and safety of lidocaine patch 5% monotherapy in adults with OA pain of the knee (n = 20). Patients with OA of one or both knees who were experiencing inadequate pain relief (defined as an average daily pain intensity of > 4 on a 0 to 10 pain scale) with their current analgesic regimen (i.e. APAP, NSAIDs, COX-2 inhibitors, tramadol) were enrolled and had all analgesic medications discontinued. Treatment with the lidocaine patch 5% resulted in significant improvements in the Western Ontario and McMaster Universities OA Index (WOMAC) pain, stiffness, physical function subscales and composite index (48.4, 41.1, 47.0, and 46.8% improvements respectively, p < 0.01). In addition, significant improvement was noted for pain intensity, pain relief, and pain interference with quality of life as measured by the Brief Pain Inventory (p < 0.05). The lidocaine patch 5% was generally well tolerated and no patients discontinued due to treatment-related adverse events. Given the open-label design, lack of a control group, and small sample size, the findings from our pilot study need to be confirmed by larger randomized controlled trials. Topical lidocaine patch 5% may provide clinicians with a novel, non-systemic therapy for OA pain with a unique mechanism of action.

Use of the lidocaine patch 5% in reducing intensity of various pain qualities reported by patients with low-back pain

OBJECTIVE

To determine the impact of the lidocaine patch 5% on pain qualities associated with low-back pain (LBP) through use of the Neuropathic Pain Scale (NPS).

PATIENTS AND METHODS

Patients were enrolled in an open-label, non-randomized, prospective, 6-week study involving 8 clinical trial sites in the United States. Eligible patients had non-radicular LBP and reported moderate-to-severe pain on the NPS at study enrollment. Patients were stratified to 3 groups based on the duration of their LBP, defined as acute/sub-acute (< 3 months), short-term chronic (3-12 months), or long-term chronic LBP (> 12 months). The lidocaine patch 5% was applied to the area of maximal pain, using no more than a total of 4 patches changed every 24 h. Effectiveness was measured by change from baseline to Week 2 and Week 6 in 4 composite measures of the NPS: NPS-10, NPS-4, NPS-8, and NPS-non-allodynia. Safety was assessed by adverse events (AEs), dermal assessment of application site(s), and skin sensory testing.

RESULTS

In the combined patient population (n = 71), 6 weeks of treatment with lidocaine patch 5% significantly improved all 4 NPS composite measures at both Week 2 and Week 6 (p < 0.001). Separate analyses by subgroups revealed differential improvements in the 4 composite measures. Eleven patients (15.5%) experienced treatment-related AEs that were primarily mild-to-moderate and dermal in nature.

CONCLUSIONS

In patients with moderate-to-severe LBP, 2 weeks and 6 weeks of treatment with the lidocaine patch 5% significantly reduces the intensity of pain qualities as measured by all 4 NPS composite measures. Lidocaine patch 5% is well tolerated with few systemic AEs and may provide beneficial pain relief for patients receiving multidisciplinary treatment without increasing risks for adverse drug interactions. Pain scales such as the NPS offer the ability to measure various pain qualities experienced by LBP patients and may allow clinicians to assess the treatment impact of different medications.

Lidocaine patch 5% and its positive impact on pain qualities in osteoarthritis: results of a pilot 2-week, open-label study using the Neuropathic Pain Scale

OBJECTIVE

To determine the impact of the lidocaine patch 5% on distinct pain qualities associated with osteoarthritis (OA) through use of the Neuropathic Pain Scale (NPS), an assessment tool designed to assess intensity of various pain qualities (i.e.sharp, dull).

PATIENTS AND METHODS

Patients were enrolled in a prospective, open-label, non-randomized, parallel-group, 2-week study involving 8 clinical trial sites in the United States. Eligible patients had radiographic evidence of OA involving one or both knees and reported moderate-to-severe pain (despite prn or stable doses of analgesics) on the NPS at study enrollment. Patients on prn analgesics were discontinued from all analgesic regimens prior to study entry and received lidocaine patch 5% as monotherapy. Those on stable doses of analgesics were continued on their other analgesic regimens with no additions or dose alterations allowed other than the lidocaine patch 5% as add-on therapy. The lidocaine patch 5% was applied to the area of maximal pain, using no more than a total of 4 patches changed every 24 h. Effectiveness was measured by change from baseline to Week 2 in 4 composite measures of the NPS: NPS-10, NPS-4, NPS-8, and NPS-nonallodynia. Safety was assessed by adverse events (AEs), dermal assessment of application site(s), and skin sensory testing.

RESULTS

In the combined patient population (n = 100), 2 weeks of treatment with lidocaine patch 5% significantly improved all 4 NPS composite measures (p < 0.001). Separate analyses by subgroups revealed significant improvements in all 4 composite measures for both the monotherapy group (n = 12; p < 0.01) and add-on therapy group (n = 88; p < 0.001). No treatment-related AEs were reported for the monotherapy group. In the add-on therapy group, 5 patients experienced mild-to-moderate treatment-related AEs.

CONCLUSIONS

In patients with moderate-to-severe OA of the knee, 2 weeks of treatment with the lidocaine patch 5% significantly reduces the intensity of pain qualities as measured by all 4 NPS composite measures. Our results coincide with previously reported improvements in pain and physical function in the same patient population, as measured by the Western Ontario and McMaster Universities OA Index. Measuring the various qualities of pain appears to be a valid approach for assessing clinical outcomes in the treatment of OA pain. Pain measures such as the NPS can capture the multi-dimensional properties of a patient's pain experience and may offer clinicians the possibility to identify differential effects of analgesic treatments on various pain qualities associated with OA.

Effectiveness of the lidocaine patch 5% on pain qualities in three chronic pain states: assessment with the Neuropathic Pain Scale

OBJECTIVE

To determine the impact of the lidocaine patch 5% on pain qualities associated with chronic pain from postherpetic neuralgia (PHN), painful diabetic neuropathy (DN), and low-back pain (LBP), using the Neuropathic Pain Scale (NPS).

PATIENTS AND METHODS

Patients with PHN, painful DN, and LBP were enrolled if they had partial response to gabapentin-containing analgesic regimens and if they reported moderate-to-severe pain on the NPS at study enrollment. Eligible patients were included in an open-label, non-randomized, prospective, 2-week study across 7 clinical trial sites in the United States. The lidocaine patch 5% was applied to the area of maximal pain, using no more than a total of 4 patches changed every 24 h. Patients were maintained on their other analgesic regimens with no dose adjustment or additions allowed. Treatment effect was measured by change from baseline to Week 2 in 4 composite measures of the NPS: NPS-10, NPS-4, NPS-8, and NPS-non-allodynia. Safety was assessed by adverse events (AEs), dermal assessment of application site(s), and skin sensory testing.

RESULTS

In the combined patient population (n = 77), 2 weeks of treatment with the lidocaine patch 5% significantly improved all 4 composite measures (p < 0.01). In the subgroup analyses, the lidocaine patch 5% demonstrated numerical advantage for all 4 NPS composite measures for the PHN patients (n = 8), and significantly improved all 4 composite measures for the painful DN patients (n = 41; p < 0.001) and LBP patients (n = 28; p < or = 0.005). Overall, 8 patients (10%) experienced mild-to-moderate treatment-related AEs.

CONCLUSIONS

The lidocaine patch 5% effectively reduces the intensity of all common pain qualities in patients with moderate-to-severe chronic pain resulting from PHN, painful DN, or LBP. Treatment is well tolerated in combination with other analgesic regimens, with no reports of serious AEs or adverse drug interactions. Assessment scales such as the NPS may offer the possibility to differentiate between various pain states and to assess treatment outcomes for various pain qualities associated with a given pain state.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.

A comparison of the anti-nociceptive effects of voltage-activated Na+ channel blockers in the formalin test

We have used the rat formalin test to compare the anti-nociceptive properties of several voltage-activated Na(+) channel blockers. The antiarrhthymic mexiletine (37.5 and 50 mg/kg, i.p.) attenuated flinching behaviour in both first and second phases of the test compared with vehicle (P<0.05). The anti-convulsants lamotrigine (15 and 30 mg/kg, i.p.) and carbamazepine (20 mg/kg, i.p.) also inhibited second phase flinching behaviour compared with vehicle (P<0.05), although phenytoin (up to 40 mg/kg, i.p.) was without effect. Riluzole (5 mg/kg, i.p.), in contrast to lubeluzole (up to 10 mg/kg, i.p.) also inhibited second phase flinching behaviour compared with vehicle (P<0.05). When tested against an acute thermal nociceptive stimulus mexiletine, lubeluzole and riluzole exhibited anti-nociceptive effects. The anti-nociceptive doses used in the formalin test produced no motor impairment in the rotarod test. Thus, voltage-activated Na(+) channel blockers can attenuate nociceptive behaviour in the formalin test, and a specific mechanism of action on Na(+) channel function may be required for this to occur.