Pharmacological evaluation of novel (6-aminopyridin-3-yl)(4-(pyridin-2-yl)piperazin-1-yl) methanone derivatives as TRPV4 antagonists for the treatment of pain.

A novel series of (6-aminopyridin-3-yl)(4-(pyridin-2-yl)piperazin-1-yl) methanone derivatives were identified as selective transient receptor potential vanilloid 4 (TRPV4) channel antagonist and showed analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig and rat. Modification of right part based on the compound 16d which was disclosed in our previous communication led to the identification of compound 26i as a flagship compound. In this paper, we described the details about design, synthesis and structure-activity relationship (SAR) analysis at right and left part of these derivatives (Fig. 1).

Suppression of the acute upregulation of phosphorylated-extracellular regulated kinase in ventral tegmental area by a µ-opioid receptor agonist is related to resistance to rewarding effects in a mouse model of bone cancer.

We investigated the mechanisms underlying the suppression of the rewarding effects of opioids using the femur bone cancer (FBC) mouse model. The rewarding and antinociceptive effects of subcutaneously administered morphine and oxycodone in the FBC model mice were assessed using the conditioned place preference test and the von-Frey test. In FBC mice, antinociceptive doses of morphine (30 mg/kg) and oxycodone (5 mg/kg) did not produce the rewarding effects but excessive doses of morphine (300 mg/kg) and oxycodone (100 mg/kg) did. Western blot analyses revealed a transient and significant increase in phosphorylated-extracellular regulated kinase (p-ERK) levels in ventral tegmental area (VTA) 5 min after the administration of morphine in sham-group. Interestingly, in FBC group, a regular dose of morphine did not increase p-ERK levels but a high dose of morphine caused an increase in p-ERK level 5 min after administration. The rewarding effects of a regular dose of and a high dose of morphine in the sham-operation and FBC model, respectively, were significantly inhibited by the MEK inhibitor. The suppression of p-ERK might result in resistance to these rewarding effects under the conditions of bone cancer.

Discovery of novel 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives as orally bioavailable TRPV4 antagonists for the treatment of pain: Part 2.

A series of 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives have been identified as selective TRPV4 antagonists that display inhibition potencies against 4α-phorbol 12,13-didecanoate (4αPDD), well known as a TRPV4 selective agonist and/or a hypotonicity. In particular, 9-(6-((2',4'-dimethyl-[4,5'-bithiazol]-2-yl)amino)nicotinoyl)-3-oxa-9-azabicyclo[3.3.1]nonan-7-one showed an analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig (reported in Part 1). However, there are some concerns such as species differences and the need for higher plasma exposure to achieve target efficacy for evaluation by an in vivo pain model. In this Letter, we report the resolution of some of the problems by further optimizing the chemical scaffold.

Discovery of novel 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives as orally bioavailable TRPV4 antagonists for the treatment of pain: Part 1.

A novel series of 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives were found by high throughput screening of the TRPV4 receptor, at which these compounds showed competitive antagonist potential against 4α-phorbol 12,13-didecanoate (4αPDD) as the selective TRPV4 agonist and showed excellent selectivity for TRPV1, N-type and L-type calcium ion channels, but poor ADME profile. In our SAR strategy, we found that the lead molecule 1 also having the unique 3-oxa-9-azabicyclo [3.3.1] nonan-7-one on the right part showed potent TRPV4 antagonist activity, good solubility at pH 6.8, good microsomal stability for human and better ADME profile including oral bioavailability. Moreover, compound 1 had an analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig. In this letter, we report a lead optimization process to identify the lead compound 1 (Fig. 1).

Heterogeneous effects of antiepileptic drugs in an in vitro epilepsy model--a functional multineuron calcium imaging study.

Epilepsy is a chronic brain disease characterised by recurrent seizures. Many studies of this disease have focused on local neuronal activity, such as local field potentials in the brain. In addition, several recent studies have elucidated the collective behavior of individual neurons in a neuronal network that emits epileptic activity. However, little is known about the effects of antiepileptic drugs on neuronal networks during seizure-like events (SLEs) at single-cell resolution. Using functional multineuron Ca(2+) imaging (fMCI), we monitored the activities of multiple neurons in the rat hippocampal CA1 region on treatment with the proconvulsant bicuculline under Mg(2+) -free conditions. Bicuculline induced recurrent synchronous Ca(2+) influx, and the events were correlated with SLEs. Other proconvulsants, such as 4-aminopyridine, pentetrazol, and pilocarpine, also induced synchronous Ca(2+) influx. We found that the antiepileptic drugs phenytoin, flupirtine, and ethosuximide, which have different mechanisms of action, exerted heterogeneous effects on bicuculline-induced synchronous Ca(2+) influx. Phenytoin and flupirtine significantly decreased the peak, the amount of Ca(2+) influx and the duration of synchronous events in parallel with the duration of SLEs, whereas they did not abolish the synchronous events themselves. Ethosuximide increased the duration of synchronous Ca(2+) influx and SLEs. Furthermore, the magnitude of the inhibitory effect of phenytoin on the peak synchronous Ca(2+) influx level differed according to the peak amplitude of the synchronous event in each individual cell. Evaluation of the collective behavior of individual neurons by fMCI seems to be a powerful tool for elucidating the profiles of antiepileptic drugs.

Topological organization of CA3-to-CA1 excitation.

The CA1-projecting axons of CA3 pyramidal cells, called Schaffer collaterals, constitute one of the major information flow routes in the hippocampal formation. Recent anatomical studies have revealed the non-random structural connectivity between CA3 and CA1, but little is known regarding the functional connectivity (i.e. how CA3 network activity is functionally transmitted downstream to the CA1 network). Using functional multi-neuron calcium imaging of rat hippocampal slices, we monitored the spatiotemporal patterns of spontaneous CA3 and CA1 burst activity under pharmacological GABAergic blockade. We found that spatially clustered CA3 activity patterns were transformed into layered CA1 activity sequences. Specifically, synchronized bursts initiated from multiple hot spots in CA3 ensembles, and CA1 neurons located deeper in the pyramidal cell layer were recruited during earlier phases of the burst events. The order of these sequential activations was maintained across the bursts, but the sequence velocity varied depending on the inter-burst intervals. Thus, CA3 axons innervate CA1 neurons in a highly topographical fashion.

Effect of the norepinephrine transporter (NET) inhibition on µ-opioid receptor (MOR)-induced anti-nociception in a bone cancer pain model.

Although norepinephrine transporter (NET) inhibition has an additional effect on µ-opioid receptor (MOR)-mediated anti-nociception in inflammatory and neuropathic pain, its effect on cancer pain is not well characterized. We investigated the additional effect of NET inhibition on MOR activation using a mouse femur bone cancer (FBC) pain model by comparing the anti-nociceptive effect of the dual-acting opioids tramadol and tapentadol and the clinically used MOR-targeted opioids oxycodone and morphine. The anti-nociceptive effects of subcutaneously administered opioids were assessed using the von-Frey filament test. Oxycodone (1 - 10 mg/kg) and morphine (5 - 50 mg/kg) dose-dependently exhibited potent anti-nociceptive effects, whereas tramadol (10 - 56 mg/kg) and tapentadol (10 - 30 mg/kg) exhibited partial effects. Rota-rod analyses of tapentadol at a higher dose (> 30 mg/kg) showed a significant decrease in motor coordination, which was partially recovered by pretreatment with MOR or α(1)-adrenoceptor antagonists. The partial anti-nociceptive effect of tapentadol (30 mg/kg) was completely suppressed by a MOR antagonist, but not by α(1)- or α(2)-adrenoceptor antagonists, suggesting that neither α(1)-adrenoceptor- nor α(2)-adrenoceptor-mediated pathways are involved in anti-nociception in the FBC model. We conclude that addition of NET inhibition does not contribute to MOR-mediated anti-nociception in bone cancer pain.

The contribution of Gi/o protein to opioid antinociception in an oxaliplatin-induced neuropathy rat model.

Oxaliplatin is a chemotherapeutic agent that induces chronic refractory neuropathy. To determine whether opioids effectively relieve this chronic neuropathy, we investigated the efficacies of morphine, oxycodone, and fentanyl, and the mechanisms underlying opioid antinociception, in oxaliplatin-induced neuropathy in rats. Rats exhibited significant mechanical allodynia following 2 weeks of chronic oxaliplatin administration. Within the range of doses that did not induce sedation and/or muscle rigidity, morphine (3 mg/kg, subcutaneously, s.c.) and oxycodone (0.3-0.56 mg/kg, s.c.) completely reversed oxaliplatin-induced mechanical allodynia, whereas fentanyl (0.017-0.03 mg/kg, s.c.) showed partial antinociception. The antinociception of the optimal doses of morphine and oxycodone were completely inhibited by pertussis toxin (PTX; 0.5 µg/rat, i.c.v.), a Gi/o protein inhibitor, while the partial effect of fentanyl was not affected in the oxaliplatin model. In the [(35)S]-GTPγS binding assay, activation of µ-opioid receptor by fentanyl, but not by morphine or oxycodone, in the mediodorsal thalamus was significantly reduced in oxaliplatin-treated rats. These results indicate that the lower antinociceptive potency of fentanyl in the oxaliplatin model might in part result from the loss of PTX-sensitive Gi/o protein activation, and the degree of Gi/o protein activation might be related to the potency of antinociception by opioids in this model.

Establishment of opioid-induced rewarding effects under oxaliplatin- and Paclitaxel-induced neuropathy in rats.

The rewarding effects of µ-receptor agonists can be suppressed under several pain conditions. We recently showed that clinically used µ-receptor agonists possess efficacies for relieving the neuropathic pain induced by chemotherapeutic drug in rats; however, it is possible that the use of µ-receptor agonists may trigger the rewarding effects even under chemotherapeutic drug-induced neuropathic pain. Nevertheless, no information is available regarding whether µ-receptor agonists produce psychological dependence under chemotherapeutic drug-induced neuropathic pain. Therefore, we examined the effects of neuropathy induced by chemotherapeutic drugs on the rewarding effects of morphine, oxycodone, and fentanyl in rats. Repeated treatment with oxaliplatin or paclitaxel produced neuropathy as measured by the von Frey test. Rewarding effects produced by antinociceptive doses of µ-receptor agonists were not suppressed under oxaliplatin- or paclitaxel-induced neuropathy. Furthermore, the morphine-induced increase in the release of dopamine from the nucleus accumbens, which is a critical step in the rewarding effects of µ-receptor agonists, was not altered in paclitaxel-treated rats. These results suggest that the rewarding effects of µ-receptor agonists can still be established under oxaliplatin- or paclitaxel-induced neuropathic pain. Therefore, patients should be carefully monitored for psychological dependence on µ-receptor agonists when they are used to control chemotherapeutic drug-induced neuropathic pain.

Enhanced antitumor effects of an engineered measles virus Edmonston strain expressing the wild-type N, P, L genes on human renal cell carcinoma.

Measles virus Edmonston strain (MV-Edm) is thought to have remarkable oncolytic activity that selectively destroys human tumor cells. The P/V/C protein of wild-type MV was shown to resist the antiviral effects of interferon (IFN)-alpha. Here, we engineered new MVs by arming MV-Edm tag strain (a V-defective vaccine-lineage strain, MV-Etag) with the P or N, P, and L genes of wild-type MV (MV-P and MV-NPL, respectively). The oncolytic activities of the MVs were determined in human renal cell carcinoma (RCC) cell lines and primary human RCC cells by the MTT assay. The antitumor efficacy of the MVs was evaluated in A-498 xenografts in nude mice. IFN-alpha effectively inhibited the replication of MV-Etag and MV-P, but not MV-NPL. MV-NPL more efficiently induced cytopathic effects (CPEs) in OS-RC-2 cells, even in the presence of human IFN-alpha. MV-NPL replicated more rapidly than MV-P and MV-Etag in A-498 cells. Apoptosis was induced earlier in A-498 cells by MV-NPL than MV-Etag and MV-P. MV-NPL showed more significant antitumoral effects and had prolonged replication compared to MV-Etag and MV-P. In this study, we demonstrated that the newly engineered MV-NPL has more effective oncolytic activity and may help establish an innovative cancer therapy.

Discovery of Atabecestat (JNJ-54861911): A Thiazine-Based ß-Amyloid Precursor Protein Cleaving Enzyme 1 Inhibitor Advanced to the Phase 2b/3 EARLY Clinical Trial.

Accumulation of amyloid ß peptides (Aß) is thought to be one of the causal factors of Alzheimer's disease (AD). The aspartyl protease ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the rate-limiting protease for Aß production, and therefore, BACE1 inhibition is a promising therapeutic approach for the treatment of AD. Starting with a dihydro-1,3-thiazine-based lead, Compound J, we discovered atabecestat 1 (JNJ-54861911) as a centrally efficacious BACE1 inhibitor that was advanced into the EARLY Phase 2b/3 clinical trial for the treatment of preclinical AD patients. Compound 1 demonstrated robust and dose-dependent Aß reduction and showed sufficient safety margins in preclinical models. The potential of reactive metabolite formation was evaluated in a covalent binding study to assess its irreversible binding to human hepatocytes. Unfortunately, the EARLY trial was discontinued due to significant elevation of liver enzymes, and subsequent analysis of the clinical outcomes showed dose-related cognitive worsening.

Destruxin E decreases Beta-amyloid generation by reducing colocalization of beta-amyloid-cleaving enzyme 1 and beta-amyloid protein precursor.

Alzheimer-disease-associated beta-amyloid (Abeta) is produced by sequential endoproteolysis of beta-amyloid protein precursor (betaAPP): the extracellular portion is shed by cleavage in the juxtamembrane region by beta-amyloid-cleaving enzyme (BACE)/beta-secretase, after which it is cleaved by presenilin (PS)/gamma-secretase near the middle of the transmembrane domain. Thus, inhibition of either of the secretases reduces Abeta generation and is a fundamental strategy for the development of drugs to prevent Alzheimer disease. However, it is not clear how small compounds reduce Abeta production without inhibition of the secretases. Such compounds are expected to avoid some of the side effects of secretase inhibitors. Here, we report that destruxin E (Dx-E), a natural cyclic hexadepsipeptide, reduces Abeta generation without affecting BACE or PS/gamma-secretase activity. In agreement with this, Dx-E did not inhibit Notch signaling. We found that Dx-E decreases colocalization of BACE1 and betaAPP, which reduces beta-cleavage of betaAPP. Therefore, the data demonstrate that Dx-E represents a novel Abeta-reducing process which could have fewer side effects than secretase inhibitors.

Post-stroke pain caused by peripheral sensory hypersensitization after transient focal cerebral ischemia in rats.

The mechanisms underlying central post-stroke pain are not well understood and there is no satisfactory treatment. Here, in a rat model of stroke, we measured nociceptive threshold using current stimulation of primary afferent neurons in both hind paws. Male Wistar rats underwent middle cerebral artery occlusion (MCAO) for 50 min. Nociceptive thresholds for Aß, Aδ and C fiber stimulation (at 2000, 250, and 5 Hz, respectively, using a Neurometer), and neurological deficits, were measured for 23 days after MCAO. Sensory thresholds in both hind paws were significantly lower in MCAO model rats than in control rats for 23 days after MCAO, with the greatest difference seen in Aδ fibers and the smallest in C fibers. Brain infarct area was measured histologically, and the correlation between neurological deficit and infarct size was examined. Neurological deficits were worse in animals with larger infarcts. Furthermore, correlations were observed between infarct size, neurological deficit, and sensory threshold of Aδ fibers 1 day after MCAO. These findings indicate that rats develop hyperalgesia after MCAO and that sensory abnormalities in Aδ fibers after cerebral ischemia may play an important role in post-stroke pain.

Mice deficient in protein tyrosine phosphatase receptor type Z (PTPRZ) show reduced responsivity to methamphetamine despite an enhanced response to novelty.

Methamphetamine (METH), a commonly abused drug, elevates extracellular dopamine (DA) levels by inducing DA efflux through the DA transporter (DAT). Emerging evidence in rodent models suggests that locomotor responses to a novel inescapable open field may predict behavioral responses to abused drugs; METH produces more potent stimulant effects in high responders to novelty than in low responders. We herein found that mice deficient in protein tyrosine phosphatase receptor type Z (Ptprz-KO) exhibited an enhanced behavioral response to novelty; however, METH-induced hyperlocomotion was significantly lower in Ptprz-KO than in wild-type mice when METH was administered at a non-toxic dose of 1 mg per kg body weight (bdw). Single-cell RT-PCR revealed that the majority of midbrain DA neurons expressed PTPRZ. No histological alterations were observed in the mesolimbic or nigrostriatal dopaminergic pathways in Ptprz-KO brains; however, a significant decrease was noted in brain DA turnover, suggesting functional alterations. In vivo microdialysis experiments revealed that METH-evoked DA release in the nucleus accumbens was significantly lower in Ptprz-KO mice than in wild-type mice. Consistent with this result, Ptprz-KO mice showed significantly fewer cell surface DAT as well as weaker DA uptake activity in striatal synaptosomes prepared 1 hr after the administration of METH than wild-type mice, while no significant differences were observed in the two groups treated with saline. These results indicate that the high response phenotype of Ptprz-KO mice to novelty may not be simply attributed to hyper-dopaminergic activity, and that deficits in PTPRZ reduce the effects of METH by reducing DAT activity.

Trifluoromethyl Dihydrothiazine-Based ß-Secretase (BACE1) Inhibitors with Robust Central ß-Amyloid Reduction and Minimal Covalent Binding Burden.

The ß-site amyloid precursor protein cleaving enzyme 1 (BACE1, also known as ß-secretase) is a promising target for the treatment of Alzheimer's disease. A pKa lowering approach over the initial leads was adopted to mitigate hERG inhibition and P-gp efflux, leading to the design of 6-CF3 dihydrothiazine 8 (N-(3-((4S,6S)-2-amino-4-methyl-6-(trifluoromethyl)-5,6-dihydro-4H-1,3-thiazin-4-yl)-4-fluorophenyl)-5-cyanopicolinamide). Optimization of 8 led to the discovery of 15 (N-(3-((4S,6S)-2-amino-4-methyl-6-(trifluoromethyl)-5,6-dihydro-4H-1,3-thiazin-4-yl)-4-fluorophenyl)-5-(fluoromethoxy)pyrazine-2-carboxamide) with an excellent balance of potency, hERG inhibition, P-gp efflux, and metabolic stability. Oral administration of 8 elicited robust Aß reduction in dog even at 0.16 mg/kg. Reflecting the reduced hERG inhibitory activity, no QTc prolongation was observed at high doses. The potential for reactive metabolite formation of 15 was realized in a nucleophile trapping assay using [14 C]-KCN in human liver microsomes. Utilizing covalent binding (CVB) in human hepatocytes and the maximum projected human dosage, the daily CVB burden of 15 was calculated to be at an acceptable value of below 1 mg/day. However, hepatotoxicity was observed when 15 was subjected to a two-week tolerance study in dog, which prevented further evaluation of this compound.

Discovery of an Extremely Potent Thiazine-Based ß-Secretase Inhibitor with Reduced Cardiovascular and Liver Toxicity at a Low Projected Human Dose.

Genetic evidence points to deposition of amyloid-ß (Aß) as a causal factor for Alzheimer's disease. Aß generation is initiated when ß-secretase (BACE1) cleaves the amyloid precursor protein. Starting with an oxazine lead 1, we describe the discovery of a thiazine-based BACE1 inhibitor 5 with robust Aß reduction in vivo at low concentrations, leading to a low projected human dose of 14 mg/day where 5 achieved sustained Aß reduction of 80% at trough level.

Reduced retinal function in amyloid precursor protein-over-expressing transgenic mice via attenuating glutamate-N-methyl-d-aspartate receptor signaling.

Here, we examined whether amyloid-beta (Abeta) protein participates in cell death and retinal function using three types of transgenic (Tg) mice in vivo [human mutant amyloid precursor protein (APP) Tg (Tg 2576) mice, mutant presenilin-1 (PS-1) knock-in mice, and APP/PS-1 double Tg mice]. ELISA revealed that the insoluble form of Abeta(1-40) was markedly accumulated in the retinas of APP and APP/PS-1, but not PS-1 Tg, mice (vs. wild-type mice). In APP Tg and APP/PS-1 Tg mice, immunostaining revealed accumulations of intracellular Abeta(1-42) in retinal ganglion cells and in the inner and outer nuclear layers. APP Tg and APP/PS-1 Tg, but not PS-1 Tg, mice had less NMDA-induced retinal damage than wild-type mice, and the reduced damage in APP/PS-1 Tg mice was diminished by the pre-treatment of N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester, a gamma-secretase inhibitor. Furthermore, the number of TUNEL-positive cells was significantly less in ganglion cell layer of APP/PS-1 Tg mice than PS-1 Tg mice 24 h after NMDA injection. The phosphorylated form of calcium/calmodulin-dependent protein kinase IIalpha (CaMKIIalpha), but not total CaMKIIalpha or total NMDA receptor 1 (NR1) subunit, in total retinal extracts was decreased in non-treated retinas of APP/PS-1 Tg mice (vs. wild-type mice). CaMKIIalpha and NR2B proteins, but not NR1, in retinal membrane fraction were significantly decreased in APP/PS-1 Tg mice as compared with wild-type mice. The NMDA-induced increase in p-CaMKIIalpha in the retina was also lower in APP/PS-1 Tg mice than in wild-type mice. In electroretinogram and visual-evoked potential recordings, the implicit time to each peak from a light stimulus was prolonged in APP/PS-1 mice versus wild-type mice. Hence, Abeta may impair retinal function by reducing activation of NMDA-receptor signaling pathways.

Interleukin-1 beta up-regulates TACE to enhance alpha-cleavage of APP in neurons: resulting decrease in Abeta production.

The proinflammatory cytokine interleukin (IL)-1beta is up-regulated in microglial cells surrounding amyloid plaques, leading to the hypothesis that IL-1beta is a risk factor for Alzheimer's disease. However, we unexpectedly found that IL-1beta significantly enhanced alpha-cleavage, indicated by increases in sAPPalpha and C83, but reduced beta-cleavage, indicated by decreases in sAPPbeta and Abeta40/42, in human neuroblastoma SK-N-SH cells. IL-1beta did not significantly alter the mRNA levels of BACE1, ADAM-9, and ADAM-10, but up-regulated that of TACE by threefold. The proform and mature form of TACE protein were also significantly up-regulated. A TACE inhibitor (TAPI-2) concomitantly reversed the IL-1beta-dependent increase in sAPPalpha and decrease in sAPPbeta, suggesting that APP consumption in the alpha-cleavage pathway reduced its consumption in the beta-cleavage pathway. IL-1Ra, a physiological antagonist for the IL-1 receptor, reversed the effects of IL-1beta, suggesting that the IL-1beta-dependent up-regulation of alpha-cleavage is mediated by the IL-1 receptor. IL-1beta also induced this concomitant increase in alpha-cleavage and decrease in beta-cleavage in mouse primary cultured neurons. Taken together we conclude that IL-1beta is an anti-amyloidogenic factor, and that enhancement of its signaling or inhibition of IL-1Ra activity could represent potential therapeutic strategies against Alzheimer's disease.

Ibudilast produces anti-allodynic effects at the persistent phase of peripheral or central neuropathic pain in rats: Different inhibitory mechanism on spinal microglia from minocycline and propentofylline.

Microglia exhibit various activation phenotypes in the spinal cord after peripheral nerve injury, and promote neuropathic pain. Ibudilast is a phosphodiesterase inhibitor with anti-inflammatory activity, but its effect on activated microglia in chronic neuropathic pain is poorly understood. We investigated whether ibudilast was effective on established allodynia associated with activated microglial phenotypes in two rat models of peripheral and central neuropathic pain. A single intrathecal injection of ibudilast (25 µg) inhibited established allodynia on days 7-21 after sciatic nerve injury in rats. Repeated injections of ibudilast (25 µg/day) reduced the numbers of phosphorylated p38-positive cells without changing hypertrophic microglia, whereas minocycline (100 µg/day) decreased the numbers of hypertrophic microglia associated with phosphorylated p38 levels in the spinal cord. Gene analysis revealed that minocycline, but not ibudilast, increased the expression of anti-inflammatory cytokine genes Il10 and Tgfß1 in the spinal cord. Propentofylline (100 µg/day) was less effective on microglial phenotypes and established allodynia. Ibudilast inhibited persistent allodynia after the recovery of motor deficits in experimental autoimmune encephalomyelitis rats. Therefore, ibudilast might be effective for chronic neuropathic pain after peripheral and central nerve damage. Ibudilast mediated these effects on activated microglia using a different mechanism compared with minocycline and propentofylline.

Sensitization of transient receptor potential vanilloid 4 and increasing its endogenous ligand 5,6-epoxyeicosatrienoic acid in rats with monoiodoacetate-induced osteoarthritis.

Transient receptor potential vanilloid 4 (TRPV4) receptor modulates pain, and this has been noted in several animal models. However, the involvement of TRPV4 in osteoarthritic (OA) pain remains poorly understood. This study assessed the functional changes in TRPV4 and the expression of its endogenous ligand 5,6-epoxyeicosatrienoic acid (5,6-EET) in a rat monoiodoacetate (MIA)-induced OA pain model (MIA rats). Monoiodoacetate-treated rats showed reduced grip strength as compared to sham-treated rats, and this loss in function could be recovered by the intraarticular administration of a TRPV4 antagonist (HC067047 or GSK2193874). By contrast, the intraarticular administration of the TRPV4 agonist, GSK1016790A, increased the pain-related behaviors in MIA rats but not in sham rats. TRPV4 expression was not increased in knee joints of MIA rats; however, the levels of phosphorylated TRPV4 at Ser824 were increased in dorsal root ganglion neurons. In addition, 5,6-EET was increased in lavage fluids from the knee joints of MIA rats and in meniscectomy-induced OA pain model rats. 5,6-EET and its metabolite were also detected in synovial fluids from patients with OA. In conclusion, TRPV4 was sensitized in the knee joints of MIA rats through phosphorylation in dorsal root ganglion neurons, along with an increase in the levels of its endogenous ligand 5,6-EET. The analgesic effects of the TRPV4 antagonist in the OA pain model rats suggest that TRPV4 may be a potent target for OA pain relief.