The antiallodynic and antihyperalgesic effects of neurotropin in mice with spinal nerve ligation

Combined antiallodynic effects of Neurotropin®-tramadol and Neurotropin®-mirogabalin in rats with L5-spinal nerve ligation

We aimed to examine the efficacy of combination therapies of Neurotropin® with tramadol and Neurotropin with mirogabalin for neuropathic pain management. A neuropathic pain model (L5 spinal nerve ligation model: L5-SNL) using male Wistar rats was generated through tight ligation of the left fifth lumbar nerve using silk sutures. Mechanical allodynia was assessed using the 50% paw withdrawal threshold. The combined antiallodynic effects were evaluated using isobolographic analyses. Small intestinal transit was evaluated using the charcoal meal test, and motor coordination using the rota-rod test. Neurotropin (50-200 NU/kg, p.o.), tramadol (7.5-60 mg/kg, p.o.), and mirogabalin (3-30 mg/kg, p.o.) showed a dose-dependent antiallodynic effect in L5-SNL rats. The combined antiallodynic effects of Neurotropin and tramadol were additive or synergistic, whereas those of Neurotropin and mirogabalin were additive. Neurotropin (100-400 NU/kg, p.o.) did not affect the small intestinal transit, whereas tramadol (30-100 mg/kg, p.o.) significantly inhibited it. Neurotropin (100-400 NU/kg, p.o.) did not affect the walking time, whereas mirogabalin (10-100 mg/kg, p.o.) significantly decreased it. Neurotropin dose-dependently ameliorated mechanical allodynia in rats, and combination therapy with Neurotropin-tramadol or Neurotropin-mirogabalin may alleviate neuropathic pain without aggravating the adverse effects of tramadol and mirogabalin.

Combined effect of Neurotropin® and methylcobalamin on postherpetic neuralgia in mice infected with herpes simplex virus type-1

BACKGROUND

Postherpetic pain (PHP) is difficult to control. Although Neurotropin® (NTP) and methylcobalamin (MCB) are often prescribed to treat the pain, the efficacy of combined treatment for PHP remains imcompletely understood.

OBJECTIVE

In this study, we investigate the combined effects of NTP and MCB on PHP in mice.

METHODS

NTP and MCB were administered from day 10-29 after herpes simplex virus type-1 (HSV-1) infection. The pain-related responses were evaluated using a paint brush. The expression of neuropathy-related factor (ATF3) and nerve repair factors (GAP-43 and SPRR1A) in the dorsal root ganglion (DRG) and neurons in the skin were evaluated by immunohistochemical staining. Nerve growth factor (NGF) and neurotrophin-3 (NT3) mRNA expression levels were evaluated using real-time PCR.

RESULTS

Repeated treatment with NTP and MCB after the acute phase inhibited PHP. Combined treatment with these drugs inhibited PHP at an earlier stage than either treatment alone. In the DRG of HSV-1-infected mice, MCB, but not NTP, decreased the number of cells expressing ATF3 and increased the number of cells expressing GAP-43- and SPRR1A. In addition, MCB, but not NTP, also increased and recovered non-myelinated neurons decreased in the lesional skin. NTP increased the mRNA levels of NTF3 in keratinocytes, while MCB increased that of NGF in Schwann cells.

CONCLUSION

These results suggest that combined treatment with NTP and MCB is useful for the treatment of PHP. The combined effect may be attributed to the different analgesic mechanisms of these drugs.

Neurotropin® accelerates peripheral nerve regeneration in a rat sciatic nerve crush injury model

BACKGROUND

Peripheral nerve injuries are common and serious conditions. The effect of Neurotropin® (NTP), a nonprotein extract derived from the inflamed skin of rabbits inoculated with vaccinia virus, on peripheral nerve regeneration has not been fully elucidated. However, it has analgesic properties via the activation of descending pain inhibitory systems. Therefore, the current study aimed to determine the effects of NTP on peripheral nerve regeneration.

METHODS

We examined axonal outgrowth of dorsal root ganglion (DRG) neurons using immunocytochemistry in vitro. In addition, nerve regeneration was evaluated functionally, electrophysiologically, and histologically in a rat sciatic nerve crush injury model in vivo. Furthermore, gene expression of neurotrophic factors in the injured sciatic nerves and DRGs was evaluated.

RESULTS

In the dorsal root ganglion neurons in vitro, NTP promoted axonal outgrowth at a concentration of 10 mNU/mL. Moreover, the systemic administration of NTP contributed to the recovery of motor and sensory function at 2 weeks, and of sensory function, nerve conduction velocity, terminal latency, and axon-remyelination 4 weeks after sciatic nerve injury. In the gene expression assessment, insulin-like growth factor 1 and vascular endothelial growth factor expressions were increased in the injured sciatic nerve 2 days postoperatively.

CONCLUSIONS

Therefore, NTP might be effective in not only treating chronic pain but also promoting peripheral nerve regeneration after injury.

Neurotropin® ameliorates chronic pain associated with scar formation in a mouse model: A gene expression analysis of the inflammatory response

Background: Scar formation after trauma and surgery involves an inflammatory response and can lead to the development of chronic pain. Neurotropin® (NTP) is a nonprotein extract of inflamed skin of rabbits inoculated with vaccinia virus. It has been widely used for the treatment of chronic pain. However, the in vivo effects of NTP on painful scar formation have not been determined. To investigate the molecular mechanisms underlying the effects of NTP on the inflammatory response, we evaluated gene expression in the scar tissues and dorsal root ganglions (DRGs) of mice administered NTP and control mice. Methods and results: Mice injected with saline or NTP were used as controls; other mice were subjected to surgery on the left hind paw to induce painful scar formation, and then injected with saline or NTP. Hind paw pain was evaluated by measuring the threshold for mechanical stimulation using the von Frey test. The paw withdrawal threshold gradually returned to pre-operative levels over 4 weeks post-operation; NTP-treated mice showed a significantly shortened recovery time of approximately 3 weeks, suggesting that NTP exerted an analgesic effect in this mouse model. Total RNA was extracted from the scarred hind paw tissues and DRGs were collected 1 week post-operation for a microarray analysis. Gene set enrichment analysis revealed that the expression of some gene sets related to inflammatory responses was activated or inhibited following surgery and NTP administration. Quantitative real-time reverse transcription-polymerase chain reaction analysis results for several genes were consistent with the microarray results. Conclusion: The administration of NTP to the hind paws of mice with painful scar formation following surgery diminished nociceptive pain and reduced the inflammatory response. NTP inhibited the expression of some genes involved in the response to surgery-induced inflammation. Therefore, NTP is a potential therapeutic option for painful scar associated with chronic pain.

Clinical Efficacy of Neurotropin for Lumbar Spinal Stenosis with Low Back Pain

PURPOSE

We compared the clinical effects of Neurotropin, limaprost alfadex, and a combination of both drugs for lumbar spinal stenosis (LSS) with low back pain (LBP).

METHODS

We conducted a multicenter, randomized, active-controlled, open-label trial from March 2021 to May 2022. Participants were patients diagnosed with LSS by MRI and were randomly assigned to three groups: Neurotropin/limaprost combination (NL group), Neurotropin (N group), and limaprost group (L group). Participants received the drugs administered orally for 12 weeks, and each examination and observation was performed before any drug administration and every 2 weeks thereafter. We recorded age, sex, height, weight, duration of symptoms, intermittent claudication distance, level of stenosis in MRI, and concomitant analgesics as examination items in the trial period. Items measured during the trial were visual analog scale (VAS) score (mm) for LBP, leg pain and numbness, walking activity (walking speed, stride length), standing balance (3 m Timed Up-and-Go (TUG) Test results, Five Times Sit-to-Stand Test (FTSST) results), LBP/Quality of Life (QOL)-related scores (Oswestry Disability Index (ODI), Euro QOL 5-Dimensions 5-Level (EQ-5D-5L), Roland-Morris Disability Questionnaire (RDQ)), psychological factors (Pain catastrophizing scale (PCS) and Pain Self-Efficacy Questionnaire (PSEQ) scores), and adverse events. Each item was evaluated using changes at each visit (weeks 2-12) from baseline value before drug administration (week 0), and changes were considered significant when p < 0.05.

RESULTS

We included results from 64 patients in the present study; 24 were assigned to the NL group (mean age 71.2 years), 20 to the N group (mean age 76.2 years), and 20 to the L group (mean age 74.4 years). There were no significant differences between the three groups in patient characteristics, concomitant analgesics, or baseline VAS score, gait balance, or QOL-related scores (p ≥ 0.05). The VAS and leg pain scores were significantly improved in Group L, and LBP was improved significantly in Group N. QOL and ODI scores improved significantly in the NL and L groups, EQ-5D score improved significantly in the L group, and RDQ score improved significantly in all groups (p < 0.05). Psychological factor and PCS scores improved significantly in the NL and L groups (p < 0.05). Walking speed and stride length were improved significantly in the NL and N groups (p < 0.05). TUG/FTSST scores were improved significantly in all groups (p < 0.05). Leg pain VAS score was improved significantly (p < 0.05) in the L group compared with the NL group after 6 and 12 weeks of administration, and LBP VAS was improved significantly in the N group after 6 weeks compared with the NL group (p < 0.05). Walking speed was significantly improved in the NL group after 2 weeks compared with the N group and improved significantly in the NL group after 6 weeks (p < 0.05) compared with the L group. RDQ was decreased significantly in the L group compared with the NL group after 8 weeks (p < 0.05).

CONCLUSIONS

Combined use of Neurotropin and limaprost showed an additional effect on walking speed compared with single drug administration. Neurotropin may contribute to the improvement of low back pain, walking speed/stride length, and standing balance.

TRIAL REGISTRATION

Japan Registry of Clinical Trials (jRCTs031200282).

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

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

Post-Event Application of Neurotropin Protects against Ischemic Insult toward Better Outcomes in a Murine Model of Subarachnoid Hemorrhage

Early brain injury (EBI) is closely linked to the development of delayed cerebral ischemia and poor outcomes after aneurysmal subarachnoid hemorrhage (SAH). This study aimed to evaluate the neuroprotective effect of neurotropin on EBI in a murine model of SAH. Twenty-four C57BL/6N mice were treated with intraperitoneal injections of either saline or 2.4 units of neurotropin at 1 h after SAH induction and for 3 days consecutively. SAH was created by an endovascular perforation method. In addition to the assessment of cerebral infarction and survival rate, motor and neurocognitive functions were also measured after SAH. Compared to the saline control group, the neurotropin group showed better recovery from locomotive and neurological declines after SAH. The neurotropin group also showed lower rates of post-SAH acute cerebral infarction and better memory and route-learning scores (p < 0.05). Meanwhile, there was no significant between-group differences in the overall mortality, hemodynamic parameters, or body weights. In conclusion, post-event treatment with neurotropin could be protective against EBI, lowering the incidence of ischemia and improving some motor and neurocognitive functions after SAH.

Cytokine expressions of spinal cord injury treated by neurotropin and nafamostat mesylate

Background

Spinal cord injury (SCI) leads to severe physical disability and sensory dysfunction. Neurotropin (NTP) has been used clinically to alleviate neuropathic pain, while nafamostat mesylate (NM) used clinical on pancreatitis patients through inhibiting synthetic serine protease. Our previous studies showed that NTP and NM were able to repair SCI. However, the underlying mechanism has not been fully explored after treatment with these 2 different drugs.

Methods

The drugs NTP and NM were administered on a contusion SCI Wistar rat model. Cytokine array analysis was performed to describe the changes of 67 proteins after acute SCI. Hierarchical clustering and volcano plot analysis were conducted to clarify protein change profiles. The differently expressed proteins related to biological processes were analyzed by functional protein association networks, Gene Ontology and pathway analysis. Flow cytometric analysis was detected to reflect the activation of immune system after drug intervention, while withdrawal threshold and BBB score were detected to evaluated the mechanical allodynia and functional recovery after SCI.

Results

HGF, β-NGF, and activin were the 3 most upregulated proteins, while the receptor for RAGE, IL-1α, and TNF-α were the 3 most downregulated proteins after NTP treatment. Adiponectin, decorin and CTACK were the 3 most upregulated proteins, while RAGE, IL-1α, and IL-1β were the 3 most downregulated proteins in the NM group. Number of lymphocytes was decreased while BBB score was increased both in NTP and NM group. But only NTP could improve mechanical pain threshold after SCI.

Conclusions

The PI3K-Akt, Jak-STAT signaling pathway and apoptosis might participate in SCI restoration by NTP, while the MAPK and NOD-like receptor signaling pathway may participated in repairing SCI with NM. We concluded that NTP regulated the microenvironment via a neuroprotective effect and inhibition of inflammation to repair SCI, while NM healed SCI through an anti-inflammatory effect. Both NTP and NM could down-regulate the activation of immune system and improve the functional recovery while only NTP could improve the pathological neuralgia after SCI. Elucidating the molecular mechanisms of these 2 clinical drugs indicates that they their expected to be effective clinical treatment for SCI.

Intramuscularly injected neurotropin reduced muscular mechanical hyperalgesia induced by repeated cold stress in rats

An extract of rabbit skin inflamed by inoculation with the vaccinia virus, neurotropin [by intravenous, oral, and intramuscular (i.m.) administration], has been used in China and Japan for the treatment of chronic pain. In this study, we investigated the analgesic mechanism of i.m. neurotropin. Rats were exposed to repeated cold stress, and muscular mechanical hyperalgesia was evaluated by measuring the withdrawal threshold of the gastrocnemius muscle using Randall-Selitto apparatus. I.m. but not subcutaneous, neurotropin dose dependently reduced the repeated cold stress-induced muscular mechanical hyperalgesia for 3 h, but it had no effect in normal rats. Injections of neurotropin into the right gastrocnemius, quadriceps femoris, biceps brachii, and trapezius muscles reduced the muscular mechanical hyperalgesia of the gastrocnemius muscle bilaterally. Intrathecal administration of antagonists to GABAergic, serotonergic, and cholinergic receptors, but not α2-adrenergic receptors, and intraperitoneal administration of opioid receptor antagonist inhibited the analgesic effect of neurotropin. These results indicated that an i.m. injection of neurotropin induced long-lasting wide-spread bilateral muscular analgesia by activating spinal serotonergic and GABAergic receptors. As distinct from analgesia by systemic administration, spinal cholinergic and opioidergic, but not adrenergic receptors, are also involved. The present study supports the effectiveness of neurotropin treatment for muscular mechanical hyperalgesia.

Neuroprotective effects of neurotropin in a mouse model of hypoxic-ischemic brain injury

PURPOSE

Ischemic-hypoxic insult leads to detrimental effects on multiple organs. The brain is especially vulnerable, and it is hard to regenerate once damaged. Currently, therapeutic options are very limited. Previous studies have reported neuroprotective effects of neurotropin, a non-protein extract derived from the inflamed skin of rabbits inoculated with vaccinia virus, using a murine model of peripheral nerve injury and cultured cell lines. However, whether neurotropin might have protective effects against brain injuries remains unclear. We, therefore, investigated the neuroprotective effect of neurotropin and possible underlying mechanisms, using a mouse model of hypoxic-ischemic brain injury.

METHODS

Hypoxic-ischemic brain injury was induced via a combination of the left common carotid artery occlusion and exposure to hypoxic environment (8% oxygen) in adult male C57BL/6 mice. Immediately following induction of hypoxia-ischemia, mice received either saline or 2.4 units of neurotropin. The survival rate, neurological function, infarct volume, and expression of inflammatory cytokines were evaluated.

RESULTS

Compared to the control group, the neurotropin group exhibited a significantly higher survival rate (100% vs. 62.5%, p < 0.05) and lower neurological deficit scores (1; 0-2 vs. 3; 0-5, median; range, p < 0.05) after the hypoxic-ischemic insult. The administration of neurotropin also reduced infarct volume (18.3 ± 5.1% vs. 38.3 ± 7.2%, p < 0.05) and mRNA expression of pro-inflammatory cytokines.

CONCLUSIONS

The post-treatment with neurotropin improved survival and neurological outcomes after hypoxic-ischemic insult. Our results indicate that neurotropin has neuroprotective effects against hypoxic-ischemic brain injury by suppressing pro-inflammatory cytokines.

Fisetin exerts antihyperalgesic effect in a mouse model of neuropathic pain: engagement of spinal serotonergic system

Fisetin, a natural flavonoid, has been shown in our previous studies to exert antidepressant-like effect. As antidepressant drugs are clinically used to treat chronic neuropathic pain, this work aimed to investigate the potential antinociceptive efficacies of fisetin against neuropathic pain and explore mechanism(s). We subjected mice to chronic constriction injury (CCI) by loosely ligating the sciatic nerves, and Hargreaves test or von Frey test was used to assess thermal hyperalgesia or mechanical allodynia, respectively. Chronic fisetin treatment (5, 15 or 45 mg/kg, p.o.) ameliorated thermal hyperalgesia (but not mechanical allodynia) in CCI mice, concomitant with escalated levels of spinal monoamines and suppressed monoamine oxidase (MAO)-A activity. The antihyperalgesic action of fisetin was abolished by chemical depletion of spinal serotonin (5-HT) but potentiated by co-treatment with 5-HTP, a precursor of 5-HT. Moreover, intraperitoneal (i.p.) or intrathecal (i.t.) co-treatment with 5-HT₇ receptor antagonist SB-258719 completely abrogated fisetin's antihyperalgesia. These findings confirm that chronic fisetin treatment exerts antinociceptive effect on thermal hyperalgesia in neuropathic mice, with spinal serotonergic system (coupled with 5-HT₇) being critically involved. Of special benefit, fisetin attenuated co-morbidly behavioral symptoms of depression and anxiety (evaluated in forced swim test, novelty suppressed feeding test and light-dark test) evoked by neuropathic pain.

Neurotropin suppresses inflammatory cytokine expression and cell death through suppression of NF-κB and JNK in hepatocytes

Inflammatory response and cell death in hepatocytes are hallmarks of chronic liver disease, and, therefore, can be effective therapeutic targets. Neurotropin® (NTP) is a drug widely used in Japan and China to treat chronic pain. Although NTP has been demonstrated to suppress chronic pain through the descending pain inhibitory system, the action mechanism of NTP remains elusive. We hypothesize that NTP functions to suppress inflammatory pathways, thereby attenuating disease progression. In the present study, we investigated whether NTP suppresses inflammatory signaling and cell death pathways induced by interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) in hepatocytes. NTP suppressed nuclear factor-κB (NF-κB) activation induced by IL-1β and TNFα assessed by using hepatocytes isolated from NF-κB-green fluorescent protein (GFP) reporter mice and an NF-κB-luciferase reporter system. The expression of NF-κB target genes, Il6, Nos2, Cxcl1, ccl5 and Cxcl2 induced by IL-1β and TNFα was suppressed after NTP treatment. We also found that NTP suppressed the JNK phosphorylation induced by IL-1β and TNFα. Because JNK activation contributes to hepatocyte death, we determined that NTP treatment suppressed hepatocyte death induced by IL-1β and TNFα in combination with actinomycin D. Taken together, our data demonstrate that NTP attenuates IL-1β and TNFα-mediated inflammatory cytokine expression and cell death in hepatocytes through the suppression of NF-κB and JNK. The results from the present study suggest that NTP may become a preventive or therapeutic strategy for alcoholic and non-alcoholic fatty liver disease in which NF-κB and JNK are thought to take part.

Chronic resveratrol treatment exerts antihyperalgesic effect and corrects co-morbid depressive like behaviors in mice with mononeuropathy: involvement of serotonergic system

Patients suffering from chronic neuropathic pain are at high risk of co-morbid depression, which burdens healthcare. This work aimed to investigate the effects of resveratrol, a phenolic monomer enriched in red wine and grapes, on pain-related and depressive-like behaviors in mice with mononeuropathy, and explored the mechanism(s). Mice received chronic constriction injury (CCI) of sciatic nerves, and sequentially developed pain-related and depressive-like behaviors, as evidenced by sensory hypersensitivity (thermal hyperalgesia in Hargreaves test and mechanical allodynia in von Frey test) and behavioral despair (prolonged immobility time in forced swim test). Chronic treatment of neuropathic mice with resveratrol (30 mg/kg, p.o., twice per day for three weeks) normalized their thermal hyperalgesia (but not mechanical allodynia) and depressive-like behaviors, and these actions were abolished by chemical depletion of central serotonin (5-HT) but potentiated by co-treatment with 5-HTP, a precursor of 5-HT. The anti-hyperalgesia and anti-depression exerted by resveratrol may be pharmacologically segregated, since intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of methysergide, a non-selective 5-HT receptor antagonist, separately abrogated the two actions. Furthermore, the antihyperalgesic action of resveratrol was preferentially counteracted by co-administration of the 5-HT7 receptor antagonist SB-258719, while the anti-depression was abrogated by 5-HT1A receptor antagonist WAY-100635. These results confirm that chronic resveratrol administration exerts curative-like effects on thermal hyperalgesia and co-morbid depressive-like behaviors in mice with mononeuropathy. Spinal and supraspinal serotonergic systems (coupled with 5-HT7 and 5-HT1A receptors, respectively) are differentially responsible for the antihyperalgesic and antidepressant-like properties of resveratrol.

Chronic curcumin treatment normalizes depression-like behaviors in mice with mononeuropathy: involvement of supraspinal serotonergic system and GABAA receptor

RATIONALE

Comorbid depression is commonly observed in individuals who suffer from neuropathic pain, which necessitates improved treatment. Curcumin, a phenolic compound derived from Curcuma longa, possesses both antinociceptive and antidepressant-like activities in animal studies, suggesting its possible usefulness in treating this comorbidity.

OBJECTIVE

We investigated the effect of curcumin on depressive-like behaviors in mice with mononeuropathy, and explored the mechanism(s).

METHODS

Chronic constriction injury (CCI) was produced by loosely ligating the sciatic nerves in mice. The nociceptive behaviors were examined using Hargreaves test, and the depressive-like behaviors were determined by forced swim test (FST) and tail suspension test (TST).

RESULTS

After CCI injury, the neuropathic mice developed nociceptive and depressive-like behaviors, as shown by thermal hyperalgesia in Hargreaves test and protracted immobility time in FST and TST. Chronic treatment of neuropathic mice with curcumin (45 mg/kg, p.o., twice per day for 3 weeks) corrected their exacerbated nociceptive and depressive-like behaviors, which was abolished by chemical depletion of brain serotonin rather than noradrenaline. The paralleled antinociceptive and antidepressant-like actions of curcumin seem to be pharmacologically segregated, since intrathecal and intracerebroventricular injection of methysergide, a nonselective 5-HT receptor antagonist, separately counteracted the two actions of curcumin. Further, this antidepression was abrogated by repeated co-treatment with 5-HT1A receptor antagonist WAY-100635 and greatly attenuated by acute co-treatment with GABAA receptor antagonist bicuculline.

CONCLUSION

Curcumin can normalize the depressive-like behaviors of neuropathic mice, which may be independent of the concurrent analgesic action and possibly mediated via the supraspinal serotonergic system and downstream GABAA receptor.

Spinal noradrenergic modulation and the role of the alpha-2 receptor in the antinociceptive effect of intrathecal nefopam in the formalin test

BACKGROUND

Nefopam has shown an analgesic effect on acute pain including postoperative pain. The reuptake of monoamines including serotonin and noradrenaline has been proposed as the mechanism of the analgesic action of nefopam, but it remains unclear. Although alpha-adrenergic agents are being widely used in the perioperative period, the role of noradrenergic modulation in the analgesic effect of nefopam has not been fully addressed.

METHODS

Changes in the antinociceptive effect of intrathecal (i.t.) nefopam against formalin-elicited flinching responses were explored in Sprague-Dawley rats pretreated with i.t. 6-hydroxydopamine (6-OHDA), which depletes spinal noradrenaline. In addition, antagonism to the effect of nefopam by prazosin and yohimbine was evaluated to further elucidate the antinociceptive mechanism of i.t. nefopam.

RESULTS

Pretreatment with i.t. 6-OHDA alone did not alter the flinching responses in either phase of the formalin test, while it attenuated the antinociceptive effect of i.t. nefopam significantly during phase 1, but not phase 2. The antagonist of the alpha-2 receptor, but not the alpha-1 receptor, reduced partially, but significantly, the antinociceptive effect of i.t. nefopam during phase 1, but not during phase 2.

CONCLUSIONS

This study demonstrates that spinal noradrenergic modulation plays an important role in the antinociceptive effect of i.t. nefopam against formalin-elicited acute initial pain, but not facilitated pain, and this action involves the spinal alpha-2 but not the alpha-1 receptor.

Combined antiallodynic effect of Neurotropin® and pregabalin in rats with L5-spinal nerve ligation

AIMS

In this study, we investigated the combined effect of Neurotropin® and pregabalin for L5-spinal nerve ligation (L5-SNL) model in rats and thiopental-induced sleep in mice.

MAIN METHODS

The left fifth lumbar nerve of rats was tightly ligated with silk sutures under pentobarbital anesthesia. The hindpaw withdrawal threshold was measured by application of von Frey filaments. Thiopental sodium was intravenously administered in mice and sleeping time was measured. In L5-SNL rats, an isobolographic analysis was performed to clarify the combined antiallodynic effect of Neurotropin and pregabalin 14 days after ligation in rats. In isobolographic analysis and thiopental-induced sleep test, Neurotropin and pregabalin were orally administered to coincide with the timing of the peak effect of each drug.

KEY FINDINGS

Neurotropin (50-200 NU/kg) and pregabalin (2.5-10mg/kg) showed a dose-dependent antiallodynic action in L5-SNL rats. The antiallodynic effect of pregabalin was reversed by intrathecal injection of yohimbine or ondansetron. Isobolographic analysis suggested that the combined antiallodynic effect of Neurotropin and pregabalin in L5-SNL rats may have been more than a mere additive effect. Neurotropin (50-400 NU/kg) had no effect on thiopental-induced sleeping time whereas pregabalin (30-100mg/kg) significantly prolonged it. When the dose of pregabalin was 30 mg/kg, Neurotropin (50-400 NU/kg) did not further exacerbate the prolongation effect of pregabalin on thiopental-induced sleep.

SIGNIFICANCE

It was suggested that when Neurotropin was administered in combination with pregabalin, it might provide more effective pain relief than that obtained with each agent alone in neuropathic pain without aggravating adverse effects of pregabalin.

Antinociceptive effects of neurotropin in a rat model of central neuropathic pain: DSP-4 induced noradrenergic lesion

Neurotropin is a nonprotein extract isolated from inflamed skin of rabbits inoculated with vaccinia virus, and used for treatment of neuropathic pain. In the present study, we have determined whether neurotropin could exert antinociceptive action using the central neuropathic pain model that we recently established. Rats were randomly allocated to 3 groups: Sham group (n=20), DSP-4 [N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine] group (50mg/kg ip, n=18), and DSP-4+5,7-DHT [5,7-dihydroxytryptamine] group (ip DSP-4 50mg/kg+icv 5,7-DHT 200μg, n=18). In Sham, DSP-4 and DSP-4+5,7-DHT groups, the effects of ip neurotropin (100NU/Kg) on hot-plate latency in rats with no lesion, noradrenergic neuron depletion and both noradrenergic and serotonergic neuronal depletion were studied, respectively. Rats in each group were subdivided equally to 2 subgroups: saline and neurotropin. After completion of the hot-plate tests, each rat was decapitated, the cerebral cortex was dissected from its internal structure for measurement of norepinephrine contents. Hot-plate latency significantly decreased by ∼40% 10 days after ip DSP-4 or after ip DSP-4 and 5,7-DHT. Norepinephrine contents in DSP-4 treated rats (55.6±6.3ng/ng tissue) and DSP-4+5,7-DHT treated rats (35.3±6.3ng/ng tissue) were significantly lower than those in intact rats (131.6±5.7ng/ng tissue, p<0.01). Neurotropin significantly increased the area under the curve (AUC) of the hot-plate latency in the DSP-4 and DSP-4+5,7-DHT groups but not in the Sham group. There was a significant correlation between AUC and norepinephrine contents in saline subgroup (p<0.01, r=0.597) but not in neurotropin subgroup in DSP-4 group. Neurotropin exerted an antinociceptive effect in DSP-4 induced central neuropathic pain. The present data suggest neuronal pathways other than descending inhibitory noradrenergic and serotonergic systems may be involved in neurotropin mediated antinociception.

Ion channel blockers for the treatment of neuropathic pain

Neuropathic pain, a severe chronic pain condition characterized by a complex pathophysiology, is a largely unmet medical need. Ion channels, which underlie cell excitability, are heavily implicated in the biological mechanisms that generate and sustain neuropathic pain. This review highlights the biological evidence supporting the involvement of voltage-, proton- and ligand-gated ion channels in the neuropathic pain setting. Ion channel modulators at different research or development stages are reviewed and referenced. Ion channel modulation is one of the main avenues to achieve novel, improved neuropathic pain treatments. Voltage-gated sodium and calcium channel and glutamate receptor modulators are likely to produce new, improved agents in the future. Rationally targeting subtypes of known ion channels, tackling recently discovered ion channel targets or combining drugs with different mechanism of action will be primary sources of new drugs in the longer term.