Analgesic Effects of Sokeikakketsuto on Chemotherapy-Induced Mechanical Allodynia and Cold Hyperalgesia in Rats.

The anticancer agents including oxaliplatin, paclitaxel, and bortezomib cause severe peripheral neuropathy. The Kampo medicine Sokeikakketsuto (SOKT) has been widely used to treat several types of pain. In this study, the analgesic effects of SOKT on oxaliplatin-, paclitaxel-, and bortezomib-induced peripheral neuropathy were investigated in rat models. Rats were treated with oxaliplatin (4 mg/kg, intraperitoneally (i.p.), twice a week for four weeks), paclitaxel (4 mg/kg, i.p., twice a week for two weeks), or bortezomib (0.2 mg/kg, i.p., twice a week for two weeks). SOKT (0.3 or 1.0 g/kg) or duloxetine hydrochloride (30 mg/kg, as a positive control) was administered orally after neuropathy developed. Mechanical allodynia and cold hyperalgesia were assessed using the von Frey test and the acetone test, respectively. These tests were performed immediately before and 30, 60, 90, and 120 min after the administration of the drugs. Repeated treatment of oxaliplatin induced mechanical allodynia and cold hyperalgesia. A single administration of SOKT (1 g/kg, per os (p.o.)), as well as duloxetine, temporarily reversed both the mechanical allodynia and the cold hyperalgesia. Repeated administration of paclitaxel and bortezomib also induced the mechanical allodynia. SOKT and duloxetine reversed the mechanical allodynia caused by bortezomib, but not by paclitaxel. SOKT might have the potential to become a new drug to relieve the symptom of oxaliplatin- or bortezomib-induced peripheral neuropathy.

Loss of diffuse noxious inhibitory control after traumatic brain injury in rats: A chronic issue.

Chronic pain is one of the most challenging and debilitating symptoms to manage after traumatic brain injury (TBI), yet the underlying mechanisms remain elusive. The disruption of normal endogenous pain control mechanisms has been linked to several forms of chronic pain and may play a role in pain after TBI. We hypothesized therefore that dysfunctional descending noradrenergic and serotonergic pain control circuits may contribute to the loss of diffuse noxious inhibitory control (DNIC), a critical endogenous pain control mechanism, weeks to months after TBI. For these studies, the rat lateral fluid percussion model of mild TBI was used along with a DNIC paradigm involving a capsaicin-conditioning stimulus. We observed sustained failure of the DNIC response up to 180-days post injury. We confirmed, that descending α2 adrenoceptor-mediated noradrenergic signaling was critical for endogenous pain inhibition in uninjured rats. However, augmenting descending noradrenergic signaling using reboxetine, a selective noradrenaline reuptake inhibitor, failed to restore DNIC after TBI. Furthermore, blocking serotonin-mediated descending signaling using selective spinal serotonergic fiber depletion with 5, 7-dihydroxytryptamine was also unsuccessful at restoring endogenous pain modulation after TBI. Unexpectedly, increasing descending serotonergic signaling using the selective serotonin reuptake inhibitor escitalopram and the serotonin-norepinephrine reuptake inhibitor duloxetine restored the DNIC response in TBI rats at both 49- and 180- days post injury. Consistent with these observations, spinal serotonergic fiber depletion with 5, 7-dihydroxytryptamine eliminated the effects of escitalopram. Intact α2 adrenoceptor signaling, however, was not required for the serotonin-mediated restoration of DNIC after TBI. These results suggest that TBI causes maladaptation of descending nociceptive signaling mechanisms and changes in the function of both adrenergic and serotonergic circuits. Such changes could predispose those with TBI to chronic pain.

Duloxetine ameliorates the impairment of diffuse noxious inhibitory control in rat models of peripheral neuropathic pain and knee osteoarthritis pain.

Diffuse noxious inhibitory control (DNIC) is a phenomenon to reflect descending pain modulation in animals. Conditioned pain modulation (CPM) is the human counterpart of DNIC and is reduced in patients with several chronic pain conditions. Duloxetine is a serotonin and noradrenaline reuptake inhibitor that ameliorates CPM impairment in patients with diabetic neuropathy. Although some studies have reported the effects of different pharmacological agents on CPM, few studies have compared the effects of some analgesics in both humans and rodents. Therefore, we established a stable evaluation method for DNIC in rats and determined whether duloxetine and other specific analgesics affect DNIC impairment in rat models of peripheral neuropathic pain and osteoarthritis pain, two types of chronic pain. As a conditioning stimulus, capsaicin was injected into the forepaw of rats. The paw withdrawal threshold (PWT) in response to mechanical pressure was measured for the hindpaw. Peripheral neuropathic pain and osteoarthritis pain models were developed by partial sciatic nerve ligation (PSNL) and the intra-articular injection of 2 mg monoiodoacetate (MIA), respectively. Capsaicin (30-100 µg/site) increased the PWT, in a dose-dependent manner, in naive rats. The threshold significantly increased at 30 µg and reached its maximal level at 100 µg. The change in PWT following capsaicin injection was significantly reduced in PSNL-treated rats, but the threshold was increased by the subcutaneous administration of duloxetine (10 mg/kg). The oral administrations of pregabalin (10 mg/kg) and celecoxib (3 mg/kg) did not affect the PWT in PSNL-treated rats. Similarly, MIA-injected rats also showed a reduced change in PWT following capsaicin injection. Duloxetine, but not pregabalin and celecoxib, significantly increased the PWT in MIA-injected rats. These results suggested that duloxetine can directly ameliorate DNIC impairment in rat models of chronic pain. Duloxetine may be useful for modulating chronic pain by restoring function to the endogenous, descending, inhibitory pathway.

Analgesic Effect of Duloxetine on an Animal Model of Monosodium Iodoacetate-Induced Hip Osteoarthritis.

We investigated the efficacy of duloxetine on hyperalgesia, histopathological and radiographic findings, pain-related sensory innervation of dorsal-root ganglia (DRG), and spinal changes in a rat model of induced hip osteoarthritis (OA). The right hip joints of male Sprague-Dawley rats (n = 6 rats/group) in the Sham group were injected with 25 µl of sterile saline and 25 µl of sterile saline with 2 mg of monosodium iodoacetate (MIA) were injected to the MIA + Vehicle and MIA + Duloxetine groups. We injected duloxetine 20 mg/kg intraperitoneally in the MIA + Duloxetine group 28 days after injection, whereas rats in the MIA + Vehicle group were injected with 0.5 ml of 20% dimethyl sulfoxide. We assessed hyperalgesia, histopathological changes, immunoreactive (-ir) neurons for calcitonin gene-related peptide and activating transcription factor 3 in DRG, and immunoreactive neurons for ionized-calcium-binding adaptor molecule 1 (Iba1) in the dorsal horn of the spinal cord. MIA administration into the hip joint let to mechanical hyperalgesia of the ipsilateral hind paw (p < 0.05). A single injection of duloxetine significantly attenuated it in induced hip OA (p < 0.05) and suppressed the number of Iba1-ir microglia of the ipsilateral dorsal horn (p < 0.05). These results suggest that a single injection of duloxetine suppressed mechanical hyperalgesia and may influence the expression of Iba1 in the microglia of the ipsilateral dorsal horn in the MIA-induced hip OA. This finding implies the inhibitory effects of duloxetine against neuropathic pain, which may lead to a change of microglial activities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:422-430, 2020.

Anticonvulsive activity of duloxetine: A new choice for the epileptic patients with depression.

The aim of this study was to investigate the antiepileptic effects of duloxetine in the maximal electroshock test and convulsions induced by four compounds: Pentylenetetrazole, 3-mercaptopropionic acid, thiosemicarbazide, and bicuculline. Duloxetine exhibited moderate anticonvulsive activity with an ED50 (median effective dose) of 48.21 mg/kg in the maximal electroshock test in mice. The anticonvulsive action of duloxetine was also confirmed in chemical-induced seizure tests, where this drug decreased tonic convulsions. Single administration of duloxetine (6.25-25 mg/kg) significantly increased the anticonvulsant effects of valproate, carbamazepine, and oxcarbazepine in the maximal electroshock test. Furthermore, pretreatment with thiosemicarbazide (an inhibitor of GABA synthesis enzyme) significantly increased the ED50 of duloxetine, suggesting the GABAergic system may contribute to the anticonvulsive action of duloxetine. These results support the use of duloxetine in the treatment of coexisting depression and epilepsy.

Pharmacological sensitivity of reflexive and nonreflexive outcomes as a correlate of the sensory and affective responses to visceral pain in mice.

Pain encompasses both sensory and affective dimensions which can be differentially modulated by drugs. Here, we compare the pharmacological sensitivity of the sensory and affective responses using acetic acid-induced abdominal writhings (sensory-reflexive outcome) and acetic acid-induced depression of reward seeking behaviour (RSB, affective-nonreflexive outcome) to a highly palatable food in mice. We found that the expression of RSB critically depends on factors such as sex and previous knowledge and type of the food stimulus. Intraperitoneal administration of acetic acid (iAA) produced a long-lasting (beyond the resolution of writhing behaviour) and concentration-dependent decrease on both appetitive-approach and consummatory dimensions of RSB. Ibuprofen and diclofenac were much more potent in reversing AA-induced changes in RSB: latency to eat (ED50 = 2 and 0.005 mg/kg, intraperinoneally, respectively) and amount consumed (ED50 = 11 and 0.1 mg/kg) than in AA-induced writhing (ED50 = 123 and 60 mg/kg). Morphine and duloxetine inhibited the writhing response (ED50 = 0.8 and 6 mg/kg, respectively) but not the AA-induced changes in RSB. Caffeine was ineffective in both AA-induced writhing and RSB changes. Overall, this study characterized a preclinical mouse model of hedonic deficits induced by pain that can be used to assess affective responses as well as complementary classic reflexive approaches in the evaluation of candidate analgesics.

Spinal Disinhibition in Experimental and Clinical Painful Diabetic Neuropathy.

Impaired rate-dependent depression (RDD) of the Hoffman reflex is associated with reduced dorsal spinal cord potassium chloride cotransporter expression and impaired spinal γ-aminobutyric acid type A receptor function, indicative of spinal inhibitory dysfunction. We have investigated the pathogenesis of impaired RDD in diabetic rodents exhibiting features of painful neuropathy and the translational potential of this marker of spinal inhibitory dysfunction in human painful diabetic neuropathy. Impaired RDD and allodynia were present in type 1 and type 2 diabetic rats but not in rats with type 1 diabetes receiving insulin supplementation that did not restore normoglycemia. Impaired RDD in diabetic rats was rapidly normalized by spinal delivery of duloxetine acting via 5-hydroxytryptamine type 2A receptors and temporally coincident with the alleviation of allodynia. Deficits in RDD and corneal nerve density were demonstrated in patients with painful diabetic neuropathy compared with healthy control subjects and patients with painless diabetic neuropathy. Spinal inhibitory dysfunction and peripheral small fiber pathology may contribute to the clinical phenotype in painful diabetic neuropathy. Deficits in RDD may help identify patients with spinally mediated painful diabetic neuropathy who may respond optimally to therapies such as duloxetine.

Pretreated duloxetine protects hippocampal CA1 pyramidal neurons from ischemia-reperfusion injury through decreases of glial activation and oxidative stress.

Duloxetine (DXT), a serotonin/norepinephrine reuptake inhibitor, is widely used for the treatment of major depressive disorders. In the present study, we investigated the neuroprotective effect of pre-treated DXT in the hippocampal CA1 region following transient global cerebral ischemia. Pre-treatment with 40mg/kg DXT protected pyramidal neurons in the CA1 region from ischemia-reperfusion injury. In addition, pre-treatment with DXT reduced ischemia-induced activations of microglia and astrocytes in the ischemic CA1 region. On the other hand, we found that pre-treatment with DXT did not increase 4-hydroxy-2-noneal (a marker for lipid peroxidation) and significantly increased the expression of Cu, Zn-superoxide dismutase, an antioxidant, in the CA1 pyramidal neurons compared with non-treated those after ischemia-reperfusion. These results indicate that pre-treated DXT has neuroprotective effect against transient global cerebral ischemia and suggest that the neuroprotective effect of DXT may be due to the attenuation of ischemia-induced glial activation as well as the decrease of oxidative stress.

Antidepressant drugs in convulsive seizures: Pre-clinical evaluation of duloxetine in mice.

Convulsive seizures (CS) are deleterious consequences of acute cerebral insults and prejudicial events in epilepsy, affecting more than 50 million people worldwide. Molecular mechanisms of depression and epilepsy include an imbalance between excitatory and inhibitory neurotransmission provoking oxidative stress (OS). OS is intimately linked to the origin and evolution of CS and is modulated by antidepressant and anticonvulsant drugs. Although newer antidepressants have exhibited a possible protective role in CS, studies analyzing serotonin and norepinephrine reuptake inhibitors merit to be further investigated. Thus, this study challenged the traditional model of pentylenetetrazol-induced CS, with only one administration of duloxetine. Male Swiss mice were treated with duloxetine (dose corresponding to the therapeutic range for human depression or greater, by allometric calculation; 10, 20 or 40 mg/kg), 30 min before pentylenetetrazol. Behavioral and electroencephalographic alterations were monitored. Lipid peroxidation, nitrites and catalase and superoxidase activities were measured in cortex. Behavioral and electroencephalographic results suggested a possible biphasic effect of duloxetine on CS, with anticonvulsant actions at therapeutic doses and a proconvulsant effect at higher doses. Duloxetine (20 mg/kg) also prevented lipid peroxidation and decreased catalase and superoxide dismutase activities in the cerebral cortex, with no influence on nitrites levels. These data demonstrated an anticonvulsant effect of duloxetine in CS for the first time. This extra anticonvulsant effect may allow the doses of anticonvulsants to be reduced, causing fewer side effects and possibly decreasing morbidity and mortality due to drug interactions in polytherapy.

The effect of serotonin-noradrenaline reuptake inhibitor duloxetine on the intervertebral disk-related radiculopathy in rats.

INTRODUCTION: Neuropathic pain, commonly related to intervertebral disk (IVD) degeneration, responds poorly to standard pain treatments. Serotonin-noradrenaline reuptake inhibitors (SNRIs) have been reported to reduce neuropathic pain; however their effect on radiculopathy induced by lumbar disk herniation remains unclear. The aim of this study was to investigate the effect of SNRI duloxetine in rat model of IVD-related neuropathic pain. MATERIALS AND METHODS: Effects of SNRI duloxetine were tested in Sprague-Dawley rats (n = 135). Neuropathic pain was induced by applying autologous nucleus pulposus (NP) on the left L5 dorsal root ganglion (DRG). Duloxetine in concentrations 0.4 mg/kg (low dose) and 1.2 mg/kg (high dose) or saline were administered orally for 10 days. Von Frey test was carried out on post-operative days 2, 7, 14, 21, and 28 to test pain sensitivity. Immunohistochemistry of L5 DRG and L5 segment of spinal cord (SC) was performed on days 7 and 21 to examine expressions of tumor necrosis factor alpha (TNF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and ionized calcium-binding adapter molecule 1 (Iba1). On days 14, 21, and 28, expressions of TNF in DRG as well as NGF and BDNF in SC were tested by immunoblotting. Sham-operated rats and naive rats were used as controls. RESULTS: Duloxetine in both concentrations significantly improved pain threshold from postoperative day 21 onward, compared to the NP + saline group (p < 0.05). High-dose duloxetine significantly inhibited the expression of TNF in DRG (day 28, p < 0.05). Both duloxetine concentrations reduced the expression of NGF in SC (day 21, p < 0.05), but the expression of BDNF remained unchanged. CONCLUSION: SNRI duloxetine inhibited neuropathic pain in rats possibly via down-regulating TNF, NGF, and microglia activation. We conclude that duloxetine, and most likely other SNRIs, may be used for the management of lumbar neuropathic pain.

Effect of Duloxetine on Urethral Resting Pressure and on Sphincter Contractility in Response to Coughing and Magnetic Stimulation in Healthy Women.

OBJECTIVES: As a proof-of-mechanism (POM) study of drugs developed to treat stress urinary incontinence (SUI) has not been conducted, this urodynamic study in healthy women was performed to determine an appropriate method to confirm POM, and to evaluate the effect of duloxetine, a serotonin and noradrenaline reuptake inhibitor, on urethral resting pressure and on sphincter contractility in response to coughing and magnetic stimulation. METHODS: The urethral pressure profiles at rest, during coughing and during sacral root magnetic stimulation (SMS), and the motor threshold (MT) for urethral sphincter contraction in response to transcranial magnetic stimulation (TMS) were measured before and 6 h after the administration of 40 mg duloxetine in 10 healthy female subjects. RESULTS: Oral administration of duloxetine significantly increased the mean and maximal urethral closure pressures at rest over the proximal and middle third of the urethra. During coughing, duloxetine marginally significantly increased the mean distal urethral pressure and significantly reduced the mean delay in the distal urethral pressure peak relative to the vesical peak. Although duloxetine did not change amplitudes of pressure spikes in response to SMS, this drug significantly lowered the MT in response to TMS. CONCLUSION: The proposed method for measuring the urethral resistance in healthy women can be used in POM studies of new drugs developed to treat SUI. CLINICAL TRIAL REGISTRATION NUMBER: UMIN000009096.

Complete Freund's adjuvant-induced reduction of exploratory activity in a novel environment as an objective nociceptive endpoint for sub-acute inflammatory pain model in rats.

BACKGROUND: Hind paw injection of complete Freund's adjuvant (CFA) is a commonly used sub-acute inflammatory pain model in rodents with typical subjective endpoint measurements of paw withdrawal to thermal or mechanical stimuli. METHODS: Here, we assessed CFA-induced reduction of exploratory activity in a novel environment (CRANE) as an objective nociceptive endpoint in rats. CFA (50%) was subcutaneously injected into the plantar aspect of the hind paw either unilaterally or bilaterally (150 µL/paw). Exploratory activity was recorded using an automated locomotor activity system. RESULTS: Bilateral CFA injection reduced exploratory activity 4-48 h following injection, compared to sham controls. Unilateral CFA injection produced less reduction of exploratory activity, compared to bilateral injection. Effects of orally dosed standard analgesics on CRANE were examined 48 h following bilateral CFA injection. Diclofenac treatment produced dose-related reversal of CRANE at 0.03-1.0 mg/kg with a plateau effect observed at higher doses (up to 30 mg/kg). Ibuprofen also produced dose-related reversal CRANE at 0.3-3.0 mg/kg with a plateau effect at higher doses (up to 60 mg/kg). Similarly, celecoxib produced dose-related reversal CRANE at 3-10 mg/kg, but not 30 mg/kg. Gabapentin (up to 100 mg/kg) and duloxetine (up to 30 mg/kg) produced no reversal of CRANE. CONCLUSIONS: The results presented here demonstrate that CRANE provides an objective assessment of pain behaviours for sub-acute inflammatory pain in rats. The pharmacological profile of standard analgesics supports that CRANE model may potentially be used to identify novel analgesic agents for the treatment of sub-acute inflammatory pain.