山本 昇平

We have recently found that the synthetic curcumin derivative CNB-001 suppresses lipopolysaccharide (LPS)-induced nitric oxide (NO) production in cultured microglia, demonstrating that it exerts anti-neuroinflammatory effects by regulating microglial activation. To explore the molecular mechanisms underlying the anti-inflammatory effect of CNB-001, the present study investigated whether CNB-001 is also effective for microglial NO production induced by other stimulants than LPS. Treatment of primary cultured rat microglia with thrombin, a serine protease that has been proposed as a mediator of cerebrovascular injuries, caused the expression of inducible NO synthase (iNOS) and the production of NO. The thrombin-induced NO production was completely blocked by the presence of SCH-79797, a selective protease-activated receptor 1 (PAR-1) antagonist, suggesting that the effect of thrombin is mediated by PAR-1. CNB-001 (1-10 µM) attenuated the thrombin-induced iNOS expression and NO production without affecting the PAR-1 expression. In addition, thrombin treatment caused rapid phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). The changes in ERK and p38 MAPK were significantly suppressed by the presence of CNB-001. These results demonstrate that CNB-001 suppresses thrombin-stimulated microglial activation by inhibiting the ERK and p38 MAPK pathways.

Cilnidipine is a dihydropyridine derivative that inhibits N-type and L-type voltage-gated Ca2+ channels (VDCCs). We recently reported that a selective N-type VDCC blocker attenuated the spinal long-term potentiation (LTP) of C-fiber-evoked field potentials recorded in the spinal dorsal horn of rats, which served as a model for examining synaptic function during central pain sensitization. In this study, we investigated the effects of cilnidipine on the changes related to neuropathic pain induced by nerve injury. Mechanical allodynia and hyperalgesia were evaluated by von Frey test and pin prick test, respectively. Spinal LTP of C-fiber-evoked field potentials were evaluated by in vivo electrophysiology. Intrathecally administrated cilnidipine attenuated mechanical allodynia and hyperalgesia in the spared nerve injury mouse model. Using in vivo electrophysiology in rats, cilnidipine (10 mu m) administered spinally inhibited the induction and maintenance of high-frequency stimulation-induced LTP of C-fiber-evoked field potentials, while basal C-fiber-evoked field potentials in naive rats were unaffected. The basal C-fiber-evoked field potentials in nerve-injured rats were strongly inhibited by cilnidipine. Treatment with a specific N-type VDCC blocker, omega o-conotoxin GVIA, which reportedly attenuates C-fiber-evoked field potentials both before and after the induction of LTP, attenuated mechanical allodynia and hyperalgesia in nerve-injured mice. By contrast, an L-type VDCC blocker, nicardipine attenuated only mechanical hyperalgesia, but not mechanical allodynia in nerve-injured mice, and also attenuated the established LTP of C-fiber-evoked field potentials in rats. These results suggested that N-type and L-type VDCC blockers may effectively alleviate the hyperalgesia and allodynia associated with neuropathic pain without affecting normal pain perception.

Oxaliplatin (L-OHP) is a platinum-based chemotherapy drug, used in standard treatment of colorectal cancer. L-OHP frequently causes acute peripheral neuropathies. These adverse effects limit cancer therapy with L-OHP. The present study was designed to reveal the changes in sensory nerve function in L-OHP-injected rats. Mechanical static allodynia, dynamic allodynia, and cold allodynia were evaluated using the von Frey test, brush test, and acetone test, respectively. Sensory nerve fiber responsiveness was measured using a Neurometer. The fifth lumbar ventral root was sectioned to record multi-unit efferent discharges. Single intraperitoneal administration of L-OHP induced mechanical static allodynia, dynamic allodynia, and cold allodynia in Wistar/ST rats. The thresholds for paw withdrawal induced by 2000 Hz (A beta-fiber) and 5 Hz (C-fiber), but not 250 Hz (A delta-fiber) sine-wave electrical stimulation were reduced in L-OHP-treated rats. Multi-unit efferent discharges were increased by mechanical stimulation using a von Frey filament applied to the plantar surface of the hindpaw. The discharges during and after stimulation were increased in the L-OHP-treated rats. Cold stimulation, but not brush stimulation, increased the discharges in L-OHP-treated rats. These results suggest that sensitization of A beta- and C-fibers, but not A delta-fibers, contributes to the development of L-OHP-induced mechanical and cold allodynia. (C) 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of Japanese Pharmacological Society. This is an open access article under the CC BY-NC-ND license.

Oseltamivir, an anti-influenza virus drug, induces marked hypothermia in normal mice. We have proposed that the hypothermic effect arises from inhibition of the nicotinic acetylcholine receptor function of sympathetic ganglion neurons which innervate the brown adipose tissue (a heat generator). It has been reported that local anesthetics inhibit nicotinic acetylcholine receptor function by acting on its ionic channels, and that bupropion, a nicotinic antagonist, induces hypothermia. In this study, we compared the effects of oseltamivir, procaine and bupropion on body temperature, cardiovascular function and neuromuscular transmission Intraperitoneal administration of oseltamivir (100 mg/kg), procaine (86.6 mg/kg) and bupropion (86.7 mg/kg) lowered the core body temperature of normal mice. At lower doses (10-30 mg/kg oseltamivir, 8.7-26 mg/kg procaine and bupropion), when administered subcutaneously, the three drugs antagonized the hypothermia induced by intraperitoneal injection of nicotine (1 mg/kg). In anesthetized rats, intravenous oseltamivir (30-100 mg/kg), procaine (10 mg/kg) and bupropion (10 mg/kg) induced hypotension and bradycardia. Oseltamivir alone (100 mg/kg) did not inhibit neuromuscular twitch contraction of rats, but at 3-30 mg/kg it augmented the muscle-relaxing effect of d-tubocurarine. Similar effects were observed when lower doses of procaine (10-30 mg/kg) and bupropion (3-10 mg/kg) were administered, suggesting that systemic administration of oseltamivir inhibits muscular nicotinic acetylcholine receptors. These results support the idea that the hypothermic effect of oseltamivir is due to its effects on sympathetic ganglia which innervate the brown adipose tissue, and suggest that oseltamivir may exert non-selective ion channel blocking effects like those of ester-type local anesthetics. (C) 2015 Elsevier B.V. All rights reserved.

Oxaliplatin, a platinum-based chemotherapy drug, frequently causes acute and chronic peripheral neuropathies including mechanical hyperalgesia. These adverse effects hinder anticancer therapy with the drug. In this study, we examined several drugs that might prevent oxaliplatin-induced peripheral neuropathy. Single intraperitoneal (i.p.) injection of oxaliplatin (10 mg/kg) induced cold allodynia (acetone test) and mechanical hyperalgesia (von Frey test). Gabapentin, but not simvastatin and atorvastatin, prevented oxaliplatin-induced mechanical hyperalgesia without affecting cold allodynia. Moreover, oxaliplatin caused phosphorylation of cofilin protein in the spinal cord, which has been shown to be involved in the neuropathic hyperalgesia. This increased phosphorylation of cofilin was also attenuated by gabapentin treatment. These results suggest that gabapentin is useful for relieving oxaliplatin-induced mechanical hyperalgesia and that the pathogenic mechanisms of cold allodynia and mechanical hyperalgesia differ.

Isoprenylation is crucial step for activating many intracellular signaling. The present study examined whether inhibition of the protein isoprenylation could affect neuropathic pain in partial sciatic nerve-ligated mice. Intrathecal treatment with a geranylgeranyl transferase I inhibitor GGTI-2133, but not with a farnesyl transferase inhibitor FTI-277, dose-dependently blocked the thermal hyperalgesia in partial sciatic nerve-ligated mice. Intrathecal treatment with GGTI-2133 also attenuated the mechanical allodynia in partial sciatic nerve-ligated mice. Phosphorylated MARCKS expression was increased in the ipsilateral side of the spinal cord dorsal horn in partial sciatic nerve-ligated mice, and this increase was attenuated by GGTI-2133 but not by FTI-277. These results suggest that protein isoprenylation by geranylgeranyl transferase I is involved in the neuropathic pain. (C) 2014 Published by Elsevier Ireland Ltd.

Lysophosphatidic acid (LPA) has been considered one of the molecular culprits for neuropathic pain. Understanding how LPA changes the function of primary afferent fibers might be an essential step for clarifying the pathogenesis of neuropathic pain. The present study was designed to identify the primary afferent fibers (A beta, A delta, or C) participating in LPA-induced allodynia in ddY mice. Mechanical allodynia and thermal hyperalgesia were evaluated by the von Frey filament test and thermal paw withdrawal test, respectively. Sensory nerve fiber responsiveness was measured using a Neurometer. Daily repeated intrathecal treatment with LPA led to a decrease in the mechanical, but not thermal nociceptive threshold, and a reduction in the threshold for paw withdrawal induced by 2000-Hz (A beta fiber) and 250-Hz (A delta fiber), but not 5-Hz (C fiber) sine-wave electrical stimulation. When the transient receptor potential cation channel subfamily V member 1 (TRPV1) receptor agonist resiniferatoxin (RTX) was administered subcutaneously before the start of LPA treatment, LPA-induced mechanical allodynia and A beta and A delta fiber hypersensitivity demonstrated by neurometry were not affected, indicating that TRPV1-expressing nerve fibers (possibly C fibers) might not be essential for LPA-induced allodynia. LPA-induced allodynia was reversed by treatment with RTX at 7 days after the start of LPA treatment. Expression of TRPV1 on myelinated nerve fibers after repeated intrathecal LPA treatment was observed in the dorsal root ganglion. These results suggest that sensitization of A beta and A delta fibers, but not C fibers, contributes to the development of intrathecally administered LPA-induced mechanical allodynia. Moreover, increased or newly expressed TRPV1 receptors in A beta and A delta fibers are considered to be involved in the maintenance of LPA-induced allodynia. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved.

Oseltamivir, an anti-influenza virus drug, has strong antipyretic effects in mice (Biological and Pharmaceutical Bulletin, 31, 2008, 638) and patients with influenza. In addition, hypothermia has been reported as an adverse event. The prodrug oseltamivir is converted to oseltamivir carboxylate (OC), an active metabolite of influenza virus neuraminidase. In this study, core body temperature was measured in mice, and oseltamivir and OC were administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p). Low i.c.v. doses of oseltamivir and OC dose-dependently produced hypothermia. Zanamivir (i.c.v.), another neuraminidase inhibitor, did not produce hypothermia. These results suggested that the hypothermic effects of oseltamivir (i.p. and i.c.v.) and OC (i.c.v.) are not due to neuraminidase inhibition. OC (i.p.) did not lower body temperature. Although mecamylamine (i.c.v.) blocked the hypothermic effect of nicotine-administered i.c.v., the hypothermic effects of oseltamivir and OC (i.c.v.) were not blocked by mecamylamine (i.c.v.). The effect of oseltamivir (i.p.) was markedly increased by s.c.-pre-administered mecamylamine and also hexamethonium, a peripherally acting ganglionic blocker, suggesting their potentiating interaction at peripheral sites. The hypothermic effect of nicotine (i.c.v.) was decreased by lower doses of oseltamivir (i.c.v.), suggesting the anti-nicotinic action of oseltamivir. These results suggest that oseltamivir (i.p.) causes hypothermia through depression of sympathetic temperature regulatory mechanisms via inhibition of nicotinic receptor function and through unknown central mechanisms. © 2013 Nordic Pharmacological Society. Published by John Wiley &amp Sons Ltd.

Neuropathic pain induces allodynia and hyperalgesia. In the spared nerve injury (SNI) model, marked mechanical hyperalgesia is manifested as prolongation of the duration of paw withdrawal after pin stimulation. We have previously reported that spinal ventral root discharges (after-discharges) after cessation of noxious mechanical stimulation applied to the corresponding hindpaw were prolonged in anesthetized spinalized rats. Since these after-discharges occurred through transient receptor potential (TRP) V1-positive fibers, these fibers could contribute to mechanical hyperalgesia. Therefore, we examined whether selective deletion of TRPV1-positive fibers by resiniferatoxin, an ultrapotent TRPV1 agonist, would affect the behavioral changes and ventral root discharges in SNI rats. Mechanical allodynia in the von Frey test, mechanical hyperalgesia after pin stimulation, and enhancement of ventral root discharges, but not thermal hyperalgesia in the plantar test, appeared in Wistar rats with SNI. Mechanical hyperalgesia was abolished by treatment with resiniferatoxin, whereas mechanical allodynia was not affected. Moreover, resiniferatoxin eliminated after-discharges completely. These results show that TRPV1-positive fibers do not participate in the mechanical allodynia caused by sensitization of A beta-fibers, but contribute to the enhancement of after-discharges and mechanical hyperalgesia following SNI. It is suggested that the mechanisms responsible for generating mechanical allodynia differ from those for prolongation of mechanical hyperalgesia.

It has been reported that one of the serious adverse events after the treatment of oseltamivir phosphate (OP) for influenza patients is sudden death resulting from cardiorespiratory arrest. To investigate the aetiology of such an adverse consequence, we examined effects of OP (expressed as free base) on blood pressure and ventilation in anaesthetized rats with vagotomy. Intravenous OP (30200 mg/kg) caused dose-dependent hypotension and bradycardia in spontaneously breathing animals. Concomitantly with changes in blood pressure, the tracheal airflow increased. The ventilatory rate hastened during the injection and then transiently slowed around 1 min. after the administration (transient hypopnea). Thereafter, it gradually returned to control. The hypopnea increased with increasing dose and ventilatory arrest occurred at 200 mg/kg. Intraduodenal OP (5001000 mg/kg) provoked cardioventilatory arrest 72218 min. after the injection. Oseltamivir carboxylate (100200 mg/kg, i.v.), an active metabolite of OP, had no significant effect on ventilation and blood pressure. In artificially ventilated animals, intravenous OP caused slowing of the respiratory rate around 1 min. after the injection in a dose-dependent manner. This effect of OP waned in 5 min. after the administration. The amplitude of phrenic nerve discharge was not changed at lower doses (30100 mg/kg). The phrenic nerve stopped to discharge immediately after higher doses (150200 mg/kg). We demonstrated that OP causes central suppression of the respiratory function in rats and suggest a relationship between the OP-induced cardiorespiratory arrest and sudden death observed in influenza patients after taking OP.

Voltage-dependent Ca2+ channels (VDCCs) play a crucial role in the spinal pain transduction. We previously reported that nociceptive mechanical stimuli to the rat hindpaw evoked two types of ventral root discharges that increased during stimulation (during-discharges) and after cessation of stimulation (after-discharges). To explore the involvement of VDCCs in these ventral root discharges, several VDCC blockers were applied directly to the surface of the spinal cord. Spinalized rats were laminectomized. The fifth lumbar ventral root was sectioned and used for multi-unit efferent discharges recording. An agar pool was constructed on the first lumbar vertebra for drug application. Ethosuximide (a T-type VDCC blocker) had no effect on ventral root discharges. omega-Conotoxin GVIA (an N-type VDCC blocker) preferentially suppressed after-discharges. omega-Agatoxin IVA (a P/Q-type VDCC blocker), diltiazem, and verapamil (L-type VDCC blockers) nonselectively depressed both during- and after-discharges. The more selective L-type VDCC blocker nicardipine depressed only after-discharges and the depression was exhibited when nicardipine was microinjected into the dorsal horn, but not into the ventral horn. These findings suggested that N- and L-type VDCCs in the dorsal horn were involved in the generation of after-discharges and these blockers might be useful for treatment of persistent pain that involves the spinal pathway.

Clinical and experimental observations indicated that 3-hydroxy-3-methylglutaryl CoA reductase inhibitor statins have pleiotropic effects. The present study determined the antinociceptive property of centrally administered simvastatin on the forrnalin-induced nociception in the mouse. Intrathecal administration of simvastatin at doses of 0.5 - 50 nmol dose-dependently attenuated the second, but not the first, phase of the formalin-induced nociception, which was partially reversed by mevalonate (5 mu mol). Intracerebroventricular injection of simvastatin (50 nmol) did not affect the formalin-induced nociception. These results suggest that simvastatin-induced antinociception is mediated by attenuation of the sensitization of spinal nociceptive transmission.

Carnosine is a biologically active dipeptide that is found in fish and chicken muscle. Recent studies have revealed that carnosine has neuroprotective activity in zinc-induced neural cell apoptosis and ischemic stroke. In the present study, we examined the expression of carnosine in the spinal cord, and the antinociceptive potency of carnosine in a mouse model of inflammation-induced nociceptive pain. Immunohistochemical studies with antiserum against carnosine showed an abundance of carnosine-immunoreactivity in the dorsal horn of the mouse spinal cord. Double-immunostaining techniques revealed that carnosine was expressed in the neurons and astrocytes in the spinal cord. Oral administration of carnosine attenuated the number of writhing behaviors induced by the intraperitoneal administration of 0.6% acetic acid. Treatment with carnosine also attenuated the second phase, but not the first phase, of the nociceptive response to formalin. Moreover, intrathecal, but not intraplanter, administration of carnosine attenuated the second phase of the nociceptive response to formalin. Our immunohistochemical and behavioral data suggest that carnosine has antinociceptive effects toward inflammatory pain, which may be mediated by the attenuation of nociceptive sensitization in the spinal cord. (C) 2012 Elsevier B.V. All rights reserved.

Oseltamivir phosphate (Tamiflu), an anti-influenza virus drug, is hydrolyzed by carboxylesterase to an active metabolite. The metabolite inhibits the influenza virus-specific neuraminidase. In this study, the effects of oseltamivir on normal core body temperature were studied in mice. Oseltamivir (30-300 mg/kg, intraperitoneally (i.p.) and 100-1000 mg/kg, orally (p.o.)) dose-dependently lowered the body temperature. The effects of oseltamivir (p.o.) continued longer than those of oseltamivir (i.p.), and approximately triple doses of oral oseltamivir were needed to produce the same peak effects as intraperitoneal oseltamivir. The non-steroidal anti-inflammatory drug diclofenac (1-30 mg/kg, i.p.) did not affect body temperature, and (at 30 and 60 mg/kg, s.c.) did not interact with the hypothermic effects of oseltamivir (100 mg/kg, i.p.). Zanamivir, which also inhibits neuraminidase, did not produce hypothermia at doses of 100 and 300 mg/kg, i.p. Clopidogrel (100, 300 mg/kg, i.p.), which is metabolized by the same carboxylesterase, tended to decrease the hypothermic effects of oseltamivir (100 mg/kg, i.p.). These results suggest that the hypothermic effects of oseltamivir are due to its hydrolytic metabolite, and that the hypothermia observed in mice has some relationship to the antipyretic effects and severe hypothermia (adverse event) observed in influenza patients after taking oseltamivir. © 2008 Pharmaceutical Society of Japan.