Efficacy of Duloxetine, a Potent and Balanced Serotonergic and Noradrenergic Reuptake Inhibitor, in Inflammatory and Acute Pain Models in Rodents

Schwann cell TRPA1 elicits reserpine-induced fibromyalgia pain in mice

BACKGROUND AND PURPOSE

Fibromyalgia is a complex clinical disorder with an unknown aetiology, characterized by generalized pain and co-morbid symptoms such as anxiety and depression. An imbalance of oxidants and antioxidants is proposed to play a pivotal role in the pathogenesis of fibromyalgia symptoms. However, the precise mechanisms by which oxidative stress contributes to fibromyalgia-induced pain remain unclear. The transient receptor potential ankyrin 1 (TRPA1) channel, known as both a pain sensor and an oxidative stress sensor, has been implicated in various painful conditions.

EXPERIMENTAL APPROACH

The feed-forward mechanism that implicates reactive oxygen species (ROS) driven by TRPA1 was investigated in a reserpine-induced fibromyalgia model in C57BL/6J mice employing pharmacological interventions and genetic approaches.

KEY RESULTS

Reserpine-treated mice developed pain-like behaviours (mechanical/cold hypersensitivity) and early anxiety-depressive-like disorders, accompanied by increased levels of oxidative stress markers in the sciatic nerve tissues. These effects were not observed upon pharmacological blockade or global genetic deletion of the TRPA1 channel and macrophage depletion. Furthermore, we demonstrated that selective silencing of TRPA1 in Schwann cells reduced reserpine-induced neuroinflammation (NADPH oxidase 1-dependent ROS generation and macrophage increase in the sciatic nerve) and attenuated fibromyalgia-like behaviours.

CONCLUSION AND IMPLICATIONS

Activated Schwann cells expressing TRPA1 promote an intracellular pathway culminating in the release of ROS and recruitment of macrophages in the mouse sciatic nerve. These cellular and molecular events sustain mechanical and cold hypersensitivity in the reserpine-evoked fibromyalgia model. Targeting TRPA1 channels on Schwann cells could offer a novel therapeutic approach for managing fibromyalgia-related behaviours.

Ayahuasca and its major component harmine promote antinociceptive effects in mouse models of acute and chronic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Ayahuasca (AYA) is a psychedelic brew used in religious ceremonies. It is broadly used as a sacred medicine for treating several ailments, including pain of various origins.

AIM OF THE STUDY

To investigate the antinociceptive effects of AYA and its mechanisms in preclinical models of acute and chronic pain in mice, in particular during experimental neuropathy.

MATERIALS AND METHODS

The antinociceptive effects of AYA administered orally were assessed in the following models of pain: formalin test, Complete Freund's Adjuvant (CFA)-induced inflammation, tail flick test, and partial sciatic nerve ligation model of neuropathic pain. Antagonism assays and Fos immunohistochemistry in the brain were performed. AYA-induced toxicity was investigated. AYA was chemically characterized. The antinociceptive effect of harmine, the major component present in AYA, was investigated.

RESULTS

AYA (24-3000 μL/kg) dose-dependently reduced formalin-induced pain-like behaviors and CFA-induced mechanical allodynia but did not affect CFA-induced paw edema or tail flick latency. During experimental neuropathy, single treatments with AYA (24-3000 μL/kg) reduced mechanical allodynia; daily treatments once or twice a day for 14 days promoted consistent and sustained antinociception. The antinociceptive effect of AYA (600 μL/kg) was reverted by bicuculline (1 mg/kg) and methysergide (5 mg/kg), but not by naloxone (5 mg/kg), phaclofen (2 mg/kg), and rimonabant (10 mg/kg), suggesting the roles of GABAA and serotonergic receptors. AYA increased Fos expression in the ventrolateral periaqueductal gray and nucleus raphe magnus after 1 h, but not after 6 h or 14 days of daily treatments. AYA (600 μL/kg) twice a day for 14 days did not alter mice's motor function, spontaneous locomotion, body weight, food and water intake, hematological, biochemical, and histopathological parameters. Harmine (3.5 mg/kg) promoted consistent antinociception during experimental neuropathy.

CONCLUSIONS

AYA promotes consistent antinociceptive effects in different mouse models of pain without inducing detectable toxic effects. Harmine is at least partially accountable for the antinociceptive properties of AYA.

The effect of duloxetine on postoperative pain and opium consumption in spine surgery: A systematic review

Background

Postoperative pain after spinal surgery is a major problem that can impact patients' quality of life. Duloxetine is a serotonin and norepinephrine reuptake inhibitor (SNRI) with analgesic effect in different pain disorders. In this study, we aim to evaluate the safety and analgesic effect of duloxetine on acute and chronic pain following spine surgery.

Methods

A systematic search was completed on MEDLINE, PsycINFO, and Embase through OVID from inception to April 2023 to find relevant articles. We used Cochrane methodology to evaluate the bias of included studies. Investigated outcomes included postoperative pain, opioid consumption, and adverse events.

Results

Seven articles involving 487 participants were included in our systematic review. Out of 7 papers, 5 were randomized clinical trials, 1 was a pilot trial and 1 was a retrospective observational study. The results of these studies indicated the analgesic effect of duloxetine on postoperative pain, which was measured using numeric rating scale, verbal numeric scale, brief pain inventory, and visual analogue scale. Duloxetine was generally safe without serious adverse events. The most common reported adverse events included headache, nausea, vomiting, itching, dizziness, and drowsiness.

Conclusions

Duloxetine may be an effective treatment option for postoperative pain following spine surgery, but further rigorously designed and well-controlled randomized trials are required.

Prediction of duloxetine efficacy in addition to self-management in painful temporomandibular disorders: A randomised, placebo-controlled clinical trial

BACKGROUND

Conditioned pain modulation (CPM) is a potential predictor of treatment response that has not been studied in temporomandibular disorders (TMD).

OBJECTIVES

We conducted a randomised, double-blind, placebo-controlled trial (RCT) of duloxetine in addition to self-management (SM) strategies to investigate its efficacy to reduce pain intensity in painful TMD patients. Moreover, we investigated whether baseline CPM would predict the duloxetine efficacy to reduce TMD pain intensity.

METHODS

Eighty participants were randomised to duloxetine 60 mg or placebo for 12 weeks. The primary outcomes were the change in the pain intensity from baseline to week-12 and CPM-sequential paradigm at baseline. Safety, physical and emotional functioning outcomes were also evaluated.

RESULTS

Of 80 participants randomised, 78 were included in intention-to-treat analysis. Pain intensity decreased for SM-duloxetine and SM-placebo but did not differ between groups (p = .82). A more efficient CPM was associated with a greater pain intensity reduction regardless of the treatment group (p = .035). Physical and emotional functioning did not differ between groups, but adverse events (p = .014), sleep impairment (p = .003) and catastrophizing symptoms (p = .001) were more prevalent in SM-duloxetine group.

CONCLUSION

This study failed to provide evidence of a beneficial effect of adding duloxetine to SM strategies for treatment of painful TMD. Nonetheless, this RCT has shown the feasibility of applying pain modulation assessment to predict short-term treatment response in painful TMD patients, which confirms previous finds that CPM evaluation may serve a step forward in individualising pain treatment.

Efficacy of Duloxetine on electrodiagnostic findings of Paclitaxel-induced peripheral neuropathy, does it have a prophylactic effect? A randomized clinical trial

This study aimed to evaluate the efficacy of Duloxetine on electrodiagnostic findings of Paclitaxel-induced peripheral neuropathy in patients with breast cancer. This randomized, double-blind clinical trial was conducted on 40 patients with breast cancer who received Paclitaxel as their first chemotherapy session. All the patients were randomly allocated into two groups, intervention (20 subjects) and placebo (20 subjects). The intervention group received 30 mg duloxetine/day in the first week, followed by 60 mg (twice daily) until 8 weeks. The patient neurotoxicity questionnaire (PNQ) was used to evaluate the severity of neuropathy. Nerve conduction study was also performed. The evaluations were performed at the baseline and 8 weeks after the treatment. Out of 20 subjects in the placebo group, 10 (50%) patients had neurotoxicity (two milds, three moderate, four severe, and one incapacitated), according to PNQ. However, in the duloxetine group, two patients had mild neurotoxicity ( P = 0.03). Significant differences between groups related to the mean of Median Sensory Latency ( P <0.001), Median Motor Latency ( P < 0.001), and Median Motor velocity ( P = 0.001) were reported. However, the relative risk of polyneuropathy between the two groups (relative risk: 1) was not significant. Regarding the results, duloxetine could be an effective treatment for preventing paclitaxel-induced peripheral neuropathy in patients with breast cancer, and an electrodiagnostic study confirmed this effect.

Between guidelines and clinical trials: evidence-based advice on the pharmacological management of non-specific chronic low back pain

The pharmacological management of nonspecific chronic low back pain (NCLBP) aims to restore patients' daily activities and improve their quality of life. The management of NCLBP is not well codified and extremely heterogeneous, and residual symptoms are common. Pharmacological management should be considered as co-adjuvant to non-pharmacological therapy, and should be guided by the symptoms reported by the patients. Depending on the individual severity of NCLPB, pharmacological management may range from nonopioid to opioid analgesics. It is important to identify patients with generalized sensory hypersensitivity, who may benefit from dedicated therapy. This article provides an evidence-based overview of the principles of pharmacological management of NCLPB.

Treatment of Pain in Rats, Mice, and Prairie Dogs

Recent myomorph and scuiromorph rodent analgesia studies are reviewed and evaluated for potential clinical application. Differences between laboratory animal studies and clinical use in diseased animals are discussed. Analgesia classes reviewed include local anesthetics, nonsteroidal anti-inflammatories, acetaminophen, opioids, and adjuvants such as anticonvulsants. Routes of administration including sustained-release mechanisms are discussed, as are reversal agents. Drug interactions are reviewed in the context of beneficial multimodal analgesia as well as potential adverse effects. Dosage recommendations for clinical patients are explored.

Advances in the management of fibromyalgia: what is the state of the art?

INTRODUCTION

Fibromyalgia (FM) is a chronic pain syndrome associated with fatigue, insomnia, dyscognition, and emotional distress. Critical illness mechanisms include central sensitization to nociceptive and non-nociceptive stimuli often resulting in hypersensitivity to all sensory input.

AREAS COVERED

The clinical presentation of FM can vary widely and therefore requires therapies tailored to each patient's set of symptoms. This manuscript examines currently prescribed therapeutic approaches supported by empirical evidence as well as promising novel treatments. Although pharmacological therapy until now has been only moderately effective for FM symptoms, it represents a critical component of every treatment plan.

EXPERT OPINION

Currently approved pharmacological therapies for FM symptoms have limited but proven effectiveness. Novel therapies with cannabinoids and naltrexone appear promising. Recent functional imaging studies of FM have discovered multiple brain network abnormalities that may provide novel targets for mechanism-based therapies. Future treatment approaches, however, need to improve more than clinical pain but also other FM domains like fatigue, insomnia, and distress.

Anti-Inflammatory Medicinal Plants of Bangladesh—A Pharmacological Evaluation

Inflammatory diseases are considered major threats to human health worldwide. In Bangladesh, a number of medicinal plants have been used in traditional medicine from time immemorial in the treatment of diverse diseases, including inflammatory disorders. This assignment aims at providing the status of the medicinal plants of Bangladesh which are traditionally used in the management of inflammatory disorders and are investigated for their anti-inflammatory prospects using different preclinical studies and future research directions. The information of medicinal plants assembled in this review was obtained from a literature search of electronic databases such as Google Scholar, PubMed, Scopus, Web of Science and ScienceDirect up to December, 2020 from publications on plants investigated for their anti-inflammatory activities, in which the place of plant sample collection was identified as Bangladesh. Keywords for primary searches were “anti-inflammatory,” “Bangladeshi,” and “medicinal plants.” Criteria followed to include plant species were plants that showed significant anti-inflammatory activities in 1) two or more sets of experiments in a single report, 2) same or different sets of experiments in two or more reports, and, 3) plants which are traditionally used in the treatment of inflammation and inflammatory disorders. In this study, 48 species of medicinal plants have been reviewed which have been used in traditional healing practices to manage inflammatory disorders in Bangladesh. The mechanistic pathways of the in vivo and in vitro study models used for the evaluation of anti-inflammatory properties of plant samples have been discussed. Selected plants were described in further detail for their habitat, anti-inflammatory studies conducted in countries other than Bangladesh, and anti-inflammatory active constituents isolated from these plants if any. Medicinal plants of Bangladesh have immense significance for anti-inflammatory activity and have potential to contribute toward the discovery and development of novel therapeutic approaches to combat diseases associated with inflammation. However, the plants reviewed in this article had chiefly undergone preliminary screening and require substantial investigations including identification of active molecules, understanding the mechanism of action, and evaluation for safety and efficacy to be followed by the formulation of safe and effective drug products.

Efficacy of duloxetine compared with opioid for postoperative pain control following total knee arthroplasty

Background

The purpose of this study was to assess the efficacy of duloxetine as an alternative to opioid treatment for postoperative pain management following total knee arthroplasty (TKA).

Methods

Among 944 patients, 290 (30.7%) of patients received opioid or duloxetine for pain control for 6 weeks when the pain Visual Analogue Scale (VAS) score was greater than 4 out of 10 at the time of discharge. 121 patients in the Opioid group and 118 in the Duloxetine group were followed up for more than one year. Preoperative and postoperative patient reported outcome measures (pain VAS score, Western Ontario and McMaster Universities OA Index (WOMAC) score were compared. The rate of further drug prescription (opioid or duloxetine) after 6 weeks of first prescription, 30-day readmission rate, and side effects were also investigated.

Results

There was no significant difference in pain VAS score, WOMAC Pain and Function score, at each time point between before and after surgery (all p>0.05). Fifteen (9.8%) patients in the opioid group and six (4.4%) patients in the duloxetine group were prescribed additional medication after first 6 weeks, showing no significant (p>0.05) difference in proportion. The 30-day readmission rate and the incidence of side effects were also similar (all p>0.05). There was no difference in the incidence of side effects between the two groups (p>0.05).

Conclusion

Duloxetine and opioid did not show any difference in pain control, function, and side effects for up to one year after TKA. Although large-scale randomized controlled trials are still required to further confirm the side effects of duloxetine, it can be considered as an alternative to opioid for postoperative pain control following TKA.

Evaluation of an herbal therapy to alleviate acute pain and stress of disbudded dairy calves under organic management

The objective of this experiment was to evaluate a herbal therapy used in place of standard synthetic analgesia to mitigate disbudding pain of dairy calves. For this experiment, 54 calves were randomly assigned to one of three treatments: 1) local anesthetic lidocaine given as a cornual nerve block before cautery disbudding (AD); 2) sham disbudding (SD); or 3) herbal tincture (Dull It, Dr. Paul's Lab, Mazomanie, WI) composed of white willow (Salix alba L.) bark, St. John's wort (Hypericum perforatum L.), chamomile (Matricaria recutita L.), arnica (Arnica montana L.), and fennel (Foeniculum vulgare Mill.) administered orally before and after cautery disbudding (TD). Behaviors were assessed during disbudding, and behaviors and blood plasma cortisol concentrations were assessed following disbudding. Tail wag, head movement, forcing ahead, and kick rates recorded during disbudding were similar among treatments. When averaged across the 360-min observation period following disbudding, injury-directed behavioral rates of head jerks, head shakes, horn bud scratches, and head rubs were greater (P ≤ 0.03) for calves in the AD group than calves in the SD group, calves in the TD group had greater (P < 0.01) horn bud scratch and head rub rates compared to calves in the SD group, and calves in the AD group had a greater (P < 0.01) horn bud scratch rate than calves in the TD group. Calves in the AD group took 1.6 [95% confidence interval (CI) = 1.0 to 2.4, P = 0.03] times longer to lie down after disbudding compared to calves in the TD group. Serum cortisol concentrations were greater (P ≤ 0.01) for calves in the TD group compared to calves in the SD group at 10, 30, and 90 min after disbudding. At 30 min after disbudding, calves in the AD group had 5.8 ng/mL (95% CI = -1.1 to 12.7 ng/mL, P = 0.02) greater serum cortisol compared to calves in the SD group, while calves in the TD group had 14.3 ng/mL (95% CI = 1.5 to 27.1 ng/mL, P < 0.01) greater serum cortisol than calves in the AD group. In conclusion, neither the local anesthetic lidocaine nor the orally administered herbal tincture attenuated both acute injury-directed behaviors and blood plasma cortisol concentrations in disbudded calves, and the tincture was clearly less effective at mitigating cortisol; therefore, additional analgesic may be required to properly manage disbudding pain effectively.

Long-lasting analgesia via targeted in situ repression of NaV1.7 in mice

Current treatments for chronic pain rely largely on opioids despite their substantial side effects and risk of addiction. Genetic studies have identified in humans key targets pivotal to nociceptive processing. In particular, a hereditary loss-of-function mutation in NaV1.7, a sodium channel protein associated with signaling in nociceptive sensory afferents, leads to insensitivity to pain without other neurodevelopmental alterations. However, the high sequence and structural similarity between NaV subtypes has frustrated efforts to develop selective inhibitors. Here, we investigated targeted epigenetic repression of NaV1.7 in primary afferents via epigenome engineering approaches based on clustered regularly interspaced short palindromic repeats (CRISPR)-dCas9 and zinc finger proteins at the spinal level as a potential treatment for chronic pain. Toward this end, we first optimized the efficiency of NaV1.7 repression in vitro in Neuro2A cells and then, by the lumbar intrathecal route, delivered both epigenome engineering platforms via adeno-associated viruses (AAVs) to assess their effects in three mouse models of pain: carrageenan-induced inflammatory pain, paclitaxel-induced neuropathic pain, and BzATP-induced pain. Our results show effective repression of NaV1.7 in lumbar dorsal root ganglia, reduced thermal hyperalgesia in the inflammatory state, decreased tactile allodynia in the neuropathic state, and no changes in normal motor function in mice. We anticipate that this long-lasting analgesia via targeted in vivo epigenetic repression of NaV1.7 methodology we dub pain LATER, might have therapeutic potential in management of persistent pain states.

Wide-Range Measurement of Thermal Preference-A Novel Method for Detecting Analgesics Reducing Thermally-Evoked Pain in Mice

Background: Wide use of oxaliplatin as an antitumor drug is limited by severe neuropathy with pharmacoresistant cold hypersensitivity as the main symptom. Novel analgesics to attenuate cold hyperalgesia and new methods to detect drug candidates are needed. Methods: We developed a method to study thermal preference of oxaliplatin-treated mice and assessed analgesic activity of intraperitoneal duloxetine and pregabalin used at 30 mg/kg. A prototype analgesiameter and a broad range of temperatures (0–45 °C) were used. Advanced methods of image analysis (deep learning and machine learning) enabled us to determine the effectiveness of analgesics. The loss or reversal of thermal preference of oxaliplatin-treated mice was a measure of analgesia. Results: Duloxetine selectively attenuated cold-induced pain at temperatures between 0 and 10 °C. Pregabalin-treated mice showed preference towards a colder plate of the two used at temperatures between 0 and 45 °C. Conclusion: Unlike duloxetine, pregabalin was not selective for temperatures below thermal preferendum. It influenced pain sensation at a much wider range of temperatures applied. Therefore, for the attenuation of cold hypersensitivity duloxetine seems to be a better than pregabalin therapeutic option. We propose wide-range measurements of thermal preference as a novel method for the assessment of analgesic activity in mice.

Effectiveness of duloxetine on severity of pain and quality of life in chronic low back pain in patients who had posterior spinal fixation

Background:

In this study, we want to search the effectiveness of Duloxetine on the severity of pain and quality of life in patients with chronic low back pain who had posterior spinal fixation.

Methods:

In this randomized, placebo-controlled trial done in 6 months 50 patients who had CLBP and were candidates for PSF surgery selected and divided into two groups (drug and placebo). They filled the VAS, SF-36, and Hamilton questionnaires before surgery and after 6 weeks from using 30 mg of duloxetine or placebo.

Results:

Significant differences were evidenced among groups for the Visual Analogue Scale (P = 0.005) and Verbal Analogue Scale (p = 0.003). Patients in the Duloxetine group have more visual and verbal pain scores than the placebo group. In the quality of life, there was a significant difference between the two groups before the intervention. Also, significant differences were evidenced among groups for the Hamilton Anxiety Rating Scale (p = 0.17). After the intervention, only the Hamilton Anxiety Rating Scale (p = 0.001) and ‘bodily pain’ and ‘general health’ subscales of quality of life (p = 0.008, 0.004, respectively) have a significant difference between the two groups. There was a significant difference between pre and post-intervention in the Hamilton Anxiety Rating Scale only in the duloxetine group. Also, in terms of quality of life, the subscales of ‘physical role’, ‘emotional role’, ‘physical pain’ and ‘total score of quality of life’ in the duloxetine and placebo groups were significantly different between pre and post-intervention. However, the subscales of ‘physical function’ and ‘general health’ were significantly different only in the duloxetine group between pre and post-intervention.

Conclusion:

The results suggest that the use of duloxetine in patients who had spinal surgery can help to better control back pain, on the other hand, it can cause a better psychological condition that affects the quality of life.

Magnetic resonance imaging for chronic pain: diagnosis, manipulation, and biomarkers

Pain is a multidimensional subjective experience with biological, psychological, and social factors. Whereas acute pain can be a warning signal for the body to avoid excessive injury, long-term and ongoing pain may be developed as chronic pain. There are more than 100 million people in China living with chronic pain, which has raised a huge socioeconomic burden. Studying the mechanisms of pain and developing effective analgesia approaches are important for basic and clinical research. Recently, with the development of brain imaging and data analytical approaches, the neural mechanisms of chronic pain have been widely studied. In the first part of this review, we briefly introduced the magnetic resonance imaging and conventional analytical approaches for brain imaging data. Then, we reviewed brain alterations caused by several chronic pain disorders, including localized and widespread primary pain, primary headaches and orofacial pain, musculoskeletal pain, and neuropathic pain, and present meta-analytical results to show brain regions associated with the pathophysiology of chronic pain. Next, we reviewed brain changes induced by pain interventions, such as pharmacotherapy, neuromodulation, and acupuncture. Lastly, we reviewed emerging studies that combined advanced machine learning and neuroimaging techniques to identify diagnostic, prognostic, and predictive biomarkers in chronic pain patients.

The pharmacological management of chronic lower back pain

INTRODUCTION

Treating chronic low back pain (LBP) can be challenging, and the most effective pharmacological therapy is controversial. The present systematic review investigated the efficacy of various pharmacological compounds to achieve pain relief and improve disability in chronic LBP patients. The present study focused on acetaminophen, amoxicillin, flupirtine, baclofen, tryciclic antidepressants (TCAs), duloxetine, topiramate, gabapentinoids, non-steroid anti-inflammatory drugs (NSAIDs) and opioids.

AREAS COVERED

All randomized clinical trials comparing two or more drug treatments for chronic low back pain were accessed. Studies reporting outcomes concerning patients with neurologic or mechanic, specific or aspecific low back pain with or without radiculopathy were included. LBP was considered chronic if pain had lasted more than 6 weeks. Data from 47 articles (9007 patients: mean age: 52.62 ± 7.0 years; mean BMI: 28.26 ± 2.8; mean follow-up: 3.23 ± 3.2 months) were obtained.

EXPERT OPINION

According to published level I evidence, only baclofen, duloxetine, NSAIDs, and opiates showed to improve pain and disability levels in patients with LBP. However, the patients' demographics are heterogeneous, and the results must be interpreted with caution and in the light of possible adverse events connected to the use of these drugs.

The potential efficacy of serotonin noradrenaline reuptake inhibitor duloxetine in dropped head syndrome: A case report and review of the literature

A 78 year-old female presented with dropped head syndrome (DHS). Three months before her initial visit to our hospital, the patient noticed a pronounced flexion of her head and neck with subsequent deterioration of symptoms, which included neck pain, difficulty with forward gaze, and gait disturbance. Cervical radiographs demonstrated scoliotic and kyphotic changes, and her symptom deteriorated over time, especially in the standing position. Duloxetine was administered for her low back pain because nonsteroidal anti-inflammatory drugs deemed ineffective. The patient demonstrated marked improvements in both radiographic and clinical appearances after 4 months. Her neck pain decreased from 8 to 2 out of 10 in the Numeric Rating Scale, and her symptoms such as difficulty with forward gaze and gait disturbance had also resolved. Duloxetine is a serotonin noradrenaline reuptake inhibitor that is usually used for chronic musculoskeletal pain, neuropathic pain, or depression. In this report, we present another potential application of duloxetine in the treatment of DHS. The following possibilities were considered for the improved outcomes: (1) pain relief may have helped the patient feel comfortable enough to move her neck, and (2) we suppose that serotonin and noradrenaline reuptake may contribute to the improvement of DHS, because there might be a potential disequilibrium of neurotransmitters such as serotonin, dopamine and noradrenaline in DHS patients. Although further investigation is needed to clarify the mechanism, duloxetine should be considered as one of the optional treatments for DHS.

Apical periodontitis-induced mechanical allodynia: A mouse model to study infection-induced chronic pain conditions

Infection-induced chronic pain is an under-studied pain condition. One example is apical periodontitis, which evokes considerable mechanical allodynia that persists after treatment in 7% to 12% of patients. Available analgesics often provide incomplete relief. However, a preclinical model to study pain mechanisms associated with apical periodontitis is not available. Here, we report a mouse model of apical periodontitis to facilitate studies determining mechanisms mediating persistent infection-induced pain. Mice were anesthetized and the left first molar was exposed to the oral environment for six weeks. Bone resorption, as an indicator of apical periodontitis, was quantified using microcomputed tomography. Mechanical allodynia was determined using extraoral von-Frey filaments in both male and female mice. The expression of c-fos in the medullary dorsal horn was assessed using immunohistochemistry. Mice with apical periodontitis developed significant mechanical allodynia by day 7 that was maintained for 42 days. Mechanical thresholds were significantly lower in females compared to males. Administration of ibuprofen, morphine, or MK-801 reversed mechanical allodynia. Finally, apical periodontitis triggered an upregulation of c-fos in the medullary dorsal horn. Collectively, this model simulates signs of clinical pain experienced by patients with apical periodontitis, detects sex differences in allodynia, and permits the study of peripheral and central trigeminal pain mechanisms.

An Open-Label, 52-Week, Phase III Trial of Duloxetine in Japanese Patients with Chronic Low Back Pain

Objective

To evaluate the safety and efficacy of duloxetine treatment for 52 weeks.

Design

Multicenter, open-label, phase III clinical study.

Setting

Forty-one medical institutions in Japan.

Subjects

Japanese patients with chronic low back pain (CLBP).

Methods

Duloxetine 60 mg once-daily was administered for 52 weeks. Safety was evaluated based on adverse events (AEs), vital signs, laboratory test values, electrocardiogram, Columbia-Suicide Severity Rating Scale, and occurrence of falls. The efficacy outcome measures were the Brief Pain Inventory (BPI; average pain, worst pain, least pain, and pain right now), BPI Interference, Patient’s Global Impression of Improvement (PGI-I), Clinical Global Impressions of Severity (CGI-S), Roland-Morris Disability Questionnaire–24 (RDQ-24), 36-Item Short-Form Health Survey (SF-36), and European Quality of Life-5 Dimensions Questionnaire (EQ-5D).

Results

In total, 151 patients (83 who completed a 14-week placebo-controlled superiority trial and 68 newly registered patients) were enrolled. The incidence rates of AEs and adverse drug reactions (ADRs) were 86.1% and 50.3%, respectively. ADRs with an incidence of ≥5% were somnolence, constipation, nausea, and dry mouth. Treatment discontinuation for AEs occurred in 16 patients. A significant reduction in the BPI average pain score (mean ± SD) was observed at all assessment time points from week 2 (−1.02 ± 1.37) to week 50 (−2.26 ± 1.63), compared with baseline. BPI pain severity (worst pain, least pain, and pain right now), BPI Interference, PGI-I, CGI-S, RDQ-24, SF-36, and EQ-5D showed significant improvement.

Conclusion

Japanese patients with CLBP had significant pain reduction over 52 weeks without new safety concerns.

Duloxetine by Modulating the Akt/GSK3 Signaling Pathways Has Neuroprotective Effects against Methamphetamine-Induced Neurodegeneration and Cognition Impairment in Rats

BACKGROUND

The neuroprotective effects of duloxetine, as an antidepressant agent, and the neurodegenerative effects of methamphetamine have been shown in previous studies. Nonetheless, their exact neurochemical and behavioral effects are still unclear. In the current study, we sought to clarify the molecular mechanisms involved in the protective effects of duloxetine against methamphetamine-induced neurodegeneration.

METHODS

Forty adult male rats were divided randomly into 5 groups. Group 1 was the negative control and received normal saline, Group 2 was the positive control and received methamphetamine, and Groups 3, 4, and 5 were concurrently treated with methamphetamine (10 mg/kg) and duloxetine (5, 10, and 15 mg/kg, respectively). All the treatments were continued for 21 days. Between days 17 and 21, the Morris Water Maze (MWM) was used to assess learning and memory in the treated groups. On day 22, the hippocampus was isolated from each rat and oxidative, antioxidant, and inflammatory factors were measured. Additionally, the expression levels of the total and phosphorylated forms of the Akt and GSK3 proteins were evaluated via the ELISA method.

RESULTS

Duloxetine in all the administered doses ameliorated the effects of the methamphetamine-induced cognition impairment in the MWM. The chronic abuse of methamphetamine increased malondialdehyde, tumor necrosis factor-α, and interleukin-1β, while it decreased superoxide dismutase, glutathione peroxidase, and glutathione reductase activities. Duloxetine not only prevented these malicious effects of methamphetamine but also activated the expression of Akt (both forms) and inhibited the expression of GSK3 (both forms) in the methamphetamine-treated rats.

CONCLUSION

We conclude that the Akt/GSK3 signaling pathways might have a critical role in the protective effects of duloxetine against methamphetamine-induced neurodegeneration and cognition impairment.

Disabling the Gβγ-SNARE interaction disrupts GPCR-mediated presynaptic inhibition, leading to physiological and behavioral phenotypes

G protein-coupled receptors (GPCRs) that couple to G_i/o proteins modulate neurotransmission presynaptically by inhibiting exocytosis. Release of Gβγ subunits from activated G proteins decreases the activity of voltage-gated Ca²⁺ channels (VGCCs), decreasing excitability. A less understood Gβγ-mediated mechanism downstream of Ca²⁺ entry is the binding of Gβγ to SNARE complexes, which facilitate the fusion of vesicles with the cell plasma membrane in exocytosis. Here, we generated mice expressing a form of the SNARE protein SNAP25 with premature truncation of the C terminus and that were therefore partially deficient in this interaction. SNAP25Δ3 homozygote mice exhibited normal presynaptic inhibition by GABA_B receptors, which inhibit VGCCs, but defective presynaptic inhibition by receptors that work directly on the SNARE complex, such as 5-hydroxytryptamine (serotonin) 5-HT_1b receptors and adrenergic α_2a receptors. Simultaneously stimulating receptors that act through both mechanisms showed synergistic inhibitory effects. SNAP25Δ3 homozygote mice had various behavioral phenotypes, including increased stress-induced hyperthermia, defective spatial learning, impaired gait, and supraspinal nociception. These data suggest that the inhibition of exocytosis by G_i/o-coupled GPCRs through the Gβγ-SNARE interaction is a crucial component of numerous physiological and behavioral processes.

Tumor growth activity of duloxetine in Ehrlich carcinoma in mice

Objective

The objective of this study was to analyze whether duloxetine influences tumor growth in Ehrlich carcinoma. The mice were administered 5 or 30 mg/kg of duloxetine or saline solution. All animals were inoculated with tumor cells. The tumor progression was evaluated by body weight, abdominal circumference, ascites volume and tumor cell count. The effect of duloxetine on immune response was evaluated by lymphoid cells, nitric oxide (NO) production, arginase and superoxide dismutase (SOD) activity and the spleen immunophenotyping.

Results

There was no difference between the groups regarding weight, abdominal circumference, ascites volume and number of tumor cells. Duloxetine increased the cells of the inguinal lymph node. There was no difference in the number of cells in the bone marrow and spleen. Ascites SOD activity was greater in Duloxetine groups. There were no differences in the levels of NO, nitrite, and arginase. The number of antibody for CD3 (CD3+), CD4+, CD8+ and CD28+ cells was lower in the duloxetine groups. In conclusion, duloxetine has no direct effect on tumor growth and does not alter immunity. The drug increased the SOD that fights free radicals and led the migration of lymphocytes, suggesting that duloxetine could be used in tumor-bearing individuals.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3655-4) contains supplementary material, which is available to authorized users.

Antiepileptic drugs as analgesics/adjuvants in inflammatory pain: current preclinical evidence

Inflammatory pain is the most common type of pain that is treated clinically. The use of currently available treatments (classic analgesics - NSAIDs, paracetamol and opioids) is limited by insufficient efficacy and/or side effects/tolerance development. Antiepileptic drugs (AEDs) are widely used in neuropathic pain treatment, but there is substantial preclinical evidence on their efficacy against inflammatory pain, too. In this review we focus on gabapentinoids (gabapentin and pregabalin) and dibenzazepine AEDs (carbamazepine, oxcarbazepine, and recently introduced eslicarbazepine acetate) and their potential for relieving inflammatory pain. In models of somatic, visceral and trigeminal inflammatory pain, that have a translational value for inflammatory conditions in locomotor system, viscera and head/face, AEDs have demonstrated analgesic activity. This activity was mostly consistent, dependent on the dose and largely independent on the site of inflammation and method of its induction, nociceptive stimuli, species, specific drug used, its route of administration and dosing schedule. AEDs exerted comparable efficacy with classic analgesics. Effective doses of AEDs are lower than toxic doses in animals and, when expressed as equivalent human doses, they are largely overlapping with AEDs doses already used in humans for treating epilepsy/neuropathic pain. The main mechanism of antinociceptive/antihyperalgesic action of gabapentinoids in inflammatory pain models seems to be α₂δ-dependent suppression of voltage-gated calcium channels in primary sensory neurons that leads to reduced release of neurotransmitters in the spinal/medullar dorsal horn. The suppression of NMDA receptors via co-agonist binding site primarily at spinal sites, activation of various types of K⁺ channels at spinal and peripheral sites, and activation of noradrenergic and serotonergic descending pain modulatory pathways may also contribute. Inhibition of voltage-gated sodium channels along the pain pathway is probably the main mechanism of antinociceptive/antihyperalgesic effects of dibenzazepines. The recruitment of peripheral adrenergic and purinergic mechanisms and central GABAergic mechanisms may also contribute. When co-administered with classic/other alternative analgesics, AEDs exerted synergistic/additive interactions. Reviewed data could serve as a basis for clinical studies on the efficacy/safety of AEDs as analgesics/adjuvants in patients with inflammatory pain, and contribute to the improvement of the treatment of various inflammatory pain states.

Neuroprotective effect of duloxetine in a mouse model of diabetic neuropathy: Role of glia suppressing mechanisms

AIMS

Painful diabetic neuropathy (PDN) is one of the most frequent complications of diabetes and the current therapies have limited efficacy. This study aimed to study the neuroprotective effect of duloxetine, a serotonin noradrenaline reuptake inhibitor (SNRI), in a mouse model of diabetic neuropathy.

MAIN METHODS

Nine weeks after developing of PDN, mice were treated with either saline or duloxetine (15 or 30 mg/kg) for four weeks. The effect of duloxetine was assessed in terms of pain responses, histopathology of sciatic nerve and spinal cord, sciatic nerve growth factor (NGF) gene expression and on the spinal expression of astrocytes (glial fibrillary acidic protein, GFAP) and microglia (CD₁₁b).

KEY FINDINGS

The present results highlighted that duloxetine (30 mg/kg) increased the withdrawal threshold in von-Frey test. In addition, both doses of duloxetine prolonged the licking time and latency to jump in the hot-plate test. Moreover, duloxetine administration downregulated the spinal expression of both CD₁₁b and GFAP associated with enhancement in sciatic mRNA expression of NGF.

SIGNIFICANCE

The current results highlighted that duloxetine provided peripheral and central neuroprotective effects in neuropathic pain is, at least in part, related to its downregulation in spinal astrocytes and microglia. Further, this neuroprotective effect was accompanied by upregulation of sciatic expression of NGF.

Effects of pregabalin and duloxetine on neurotransmitters in the dorsal horn of the spinal cord in a rat model of fibromyalgia

Dysfunction of the monoamine systems in the nervous system is associated with the clinical symptoms of fibromyalgia. Reserpine-induced myalgia (RIM) rats are a putative model of fibromyalgia in which muscle pressure thresholds and monoamine content is reduced in the brain and spinal cord. We examined the effects of pregabalin and duloxetine, drugs approved for fibromyalgia treatment, on the levels of extracellular neurotransmitters in the dorsal horn of the spinal cord in RIM rats using microdialysis. Male SD rats were used for all experiments. To generate RIM rats, reserpine was injected at 1 mg/kg subcutaneously once daily for three consecutive days. The pressure threshold of the mid-gastrocnemius muscle was measured using a Randall-Selitto apparatus. Norepinephrine, dopamine, and serotonin were detected using high-performance liquid chromatography with electrochemical detection, and glutamate and γ-aminobutyric acid (GABA) were detected using liquid chromatography-mass spectrometry. The muscle pressure threshold in RIM rats was significantly lower than that in normal rats. While the levels of monoamines and glutamate were lower in the spinal cord of RIM rats than in normal rats, levels of GABA did not markedly differ. Duloxetine increased the levels of all three monoamines in normal and RIM rats in a dose-dependent manner. In contrast, pregabalin only increased norepinephrine levels in RIM rats. These results indicate that while both pregabalin and duloxetine ameliorate muscle pressure thresholds in RIM rats, their effects on the levels of extracellular neurotransmitters in the spinal cord differ considerably.

Perioperative Duloxetine and Etoricoxibto improve postoperative pain after lumbar Laminectomy: a randomized, double-blind, controlled study

BACKGROUND

Duloxetine, Etoricoxib and opioid are of the commonly administered drugs in Lumbar laminectomy. The aim of this study is to assess the effect of perioperative use of Duloxetine in combination with Etoricoxib on postoperative pain and opioid requirements.

METHODS

One hundred twenty patients with ASA physical status were enrolled with age between 18 and 70 years. Patients were divided randomly into four groups of 30 patients: group P received placebo, group E received etoricoxib 120 mg, group D received duloxetine 60 mg and group D/E received duloxetine 60 mg capsules and etoricoxib 120 mg; 1 h before surgery and 24 h after.

RESULTS

Neither Duloxetine nor etoricoxib individually had effect on pain with movement, while their combination revealed a significant reduction in pain scores over the entire postoperative period at rest and on movement. Etoricoxib showed a significant decrease in pain at all times at rest when compared with group P, while it showed significant pain decrease only at 0, 2 and 4 h when compared with group D. On the other hand duloxetine alone showed significant decrease in pain at rest at 24 h and 48 h when compared with group P. ConcerningMorphine requirement after 24 h.; it wassignificantly lower in the D/E group in comparison with groups P, E and D. It should be noted also that there was a significant decrease morphine requirement in both groups E and D.

CONCLUSION

The perioperative administration of the combination of etoricoxib and duloxetine improved analgesia and reduced opioid consumption without significant side effects.

TRIAL REGISTRATION

ISRCTN48329522 . 17 June 2017.

Chronic Treatment with Fluoxetine Induces Sex-Dependent Analgesic Effects and Modulates HDAC2 and mGlu2 Expression in Female Mice

Gender and sex differences in pain recognition and drug responses have been reported in clinical trials and experimental models of pain. Among antidepressants, contradictory results have been observed in patients treated with selective serotonin reuptake inhibitors (SSRIs). This study evaluated sex differences in response to the SSRI fluoxetine after chronic administration in the mouse formalin test. Adult male and female CD1 mice were intraperitoneally injected with fluoxetine (10 mg/kg) for 21 days and subjected to pain assessment. Fluoxetine treatment reduced the second phase of the formalin test only in female mice without producing behavioral changes in males. We also observed that fluoxetine was able to specifically increase the expression of metabotropic glutamate receptor type-2 (mGlu2) in females. Also a reduced expression of the epigenetic modifying enzyme, histone deacetylase 2 (HDAC2), in dorsal root ganglia (DRG) and dorsal horn (DH) together with an increase histone 3 acetylation (H3) level was observed in females but not in males. With this study we provide evidence that fluoxetine induces sex specific changes in HDAC2 and mGlu2 expression in the DH of the spinal cord and in DRGs and suggests a molecular explanation for the analgesic effects in female mice.

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.

Wu-tou decoction attenuates neuropathic pain via suppressing spinal astrocytic IL-1R1/TRAF6/JNK signaling

Neuropathic pain (NP) caused by nerve injuries continues to be an intractable challenge due to inadequate therapeutic strategies. Recent study demonstrated glia-induced neuro-inflammation in the spinal cord, especially the activation of astrocytes, plays an essential role in the development of NP, which opens new avenues for NP treatment. In this study, we explored the anti-hyperalgesia properties of Wu-tou decoction (WTD) and showed that WTD potently attenuates mechanical allodynia and heat hyperalgesia in lumbar 5 (L5) spinal nerve ligation (SNL)-induced NP without noticeable side effect or affecting basal pain perception of mice. Mechanistically, initial targets screening tests indicated WTD's analgesic action may be centrally mediated within the spinal cord, which further verified by its inhibitory actions on glia-releasing factors of IL-1β, CCL2 and CXCL1. Meanwhile, WTD significantly reduced spinal IL-1R1, TRAF6 expressions, p-JNK levels, and number of GFAP/IL-1R1, GFAP/TRAF6, GFAP/p-JNK positive astrocytes in the superficial lamina of spinal cord. Additionally, co-administration of IL-1Ra increased the anti-hyperalgesia effects of WTD and further decreased CCL2 and CXCL1 expressions, while no synergistic effects were detected when TRAF6 or JNK inhibitors were co-administrated with WTD. Thus, our data suggested that the effective inhibition of spinal astrocytic IL-1R1/TRAF6/JNK signaling (especially IL-1R1) contributes, at least in part, to WTD's anti-hyperalgesia action. It also indicates that WTD might be a promising candidate for the treatments of chronic pain, especially under NP-related neurological disorders.

Assessment of direct analgesic effect of duloxetine for chronic low back pain: post hoc path analysis of double-blind, placebo-controlled studies

Background

Comorbid depression and depressive symptoms are common in patients with chronic low back pain (CLBP). Duloxetine is clinically effective in major depressive disorder and several chronic pain states, including CLBP. The objective of this post hoc meta-analysis was to assess direct and indirect analgesic efficacy of duloxetine for patients with CLBP in previous clinical trials.

Methods

Post hoc path analyses were conducted of 3 randomized, double-blind, clinical studies of patients receiving duloxetine or placebo for CLBP. The primary outcome measure for pain was the Brief Pain Inventory, average pain score. A secondary outcome measure, the Beck Depression Inventory-II, was used for depressive symptoms. The changes in score from baseline to endpoint were determined for each index. Path analyses were employed to calculate the proportion of analgesia that may be attributed to a direct effect of duloxetine on pain.

Results

A total of 851 patients (400 duloxetine and 451 placebo) were included in this analysis. Duloxetine significantly improved pain scores compared with placebo (p<0.001). It also significantly improved depressive scores compared with placebo (p=0.015). Path analyses showed that 91.1% of the analgesic effect of duloxetine could be attributed to a direct analgesic effect, and 8.9% to its antidepressant effect. Similar results were obtained when data were evaluated at weeks 4 and 7, and when patients were randomized to subgroups based on baseline pain scores, baseline depressive symptoms scores, and gender.

Conclusion

Duloxetine significantly improved pain in patients with CLBP. Path analyses results suggest that duloxetine produced analgesia mainly through mechanisms directly impacting pain modulation rather than lifting depressive symptoms. This effect was consistent across all subgroups tested.

Pharmacokinetic profiles contribute to the differences in behavioral pharmacology of 071031B enantiomers as novel serotonin and norepinephrine reuptake inhibitors

Our previous study indicated that a chiral compound 071031B was a novel serotonin and noradrenaline reuptake inhibitor with superior antidepressant activity compared to duloxetine. The present study aimed to investigate chiral pharmacology differences of 071031B enantiomers, S-071031B and R-071031B, and disclose mechanisms underlying the behavioral differences based on target profiles and pharmacokinetic profiles. In vivo behavioral tests indicated that S-071031B was more potent than R-071031B in two depression models (the forced swimming test in mice and rats) and two pain models (the acetic acid-induced writhing and formalin tests in mice). In vitro assays revealed that both S-071031B and R-071031B showed high affinity for human serotonin transporters and norepinephrine transporters with equal potency, and showed consistently equipotent inhibitory effects on serotonin and norepinephrine uptake. Pharmacokinetic studies demonstrated that oral availability and hepatic metabolism, rather than pH stability, intestinal transport, and plasma binding, contributed to enantiomers' behavioral differences. Based on these findings, it is suggested that S-071031B is a more active enantiomer, and the differential pharmacokinetic profiles, but not target affinity, contribute to differences of S-071031B and R-071031B in behavioral pharmacology. Moreover, current PK-PD study may provide positive exploration for chiral antidepressants development.

Influence of tramadol on acute thermal and mechanical cutaneous nociception in dogs

OBJECTIVE

The aim of the study was to evaluate the influence of tramadol on acute nociception in dogs.

STUDY DESIGN

Experimental, blinded, randomized, crossover study.

ANIMALS

Six healthy laboratory Beagle dogs.

METHODS

Dogs received three treatments intravenously (IV): isotonic saline placebo (P), tramadol 1 mg kg^-1 (T1) and tramadol 4 mg kg^-1 (T4). Thermal thresholds were determined by ramped contact heat stimulation (0.6 °C second^-1) at the lateral thoracic wall. Mechanical thresholds (MT) were measured using a probe containing three blunted pins which were constantly advanced over the radial bone, using a rate of force increase of 0.8 N second^-1. Stimulation end points were defined responses (e.g. skin twitch, head turn, repositioning, vocalization) or pre-set cut-out values (55 °C, 20 N). Thresholds were determined before treatment and at predetermined time points up to 24 hours after treatment. At each measurement point, blood was collected for determination of O-desmethyltramadol concentrations. The degree of sedation and behavioural side effects were recorded. Data were analysed by one-way anova and two-way anova for repeated measurements.

RESULTS

Thermal nociception was not influenced by drug treatment. Mechanical nociception was significantly increased between P and T1 at 120 and 240 minutes, and between P and T4 at 30, 60, 240 and 420 minutes. T1 and T4 did not differ. O-desmethyltramadol (M1) maximum plasma concentrations (C_max) were 4.2±0.8 ng mL^-1 and 14.3±2.8 ng mL^-1 for T1 and T4, respectively. Times to reach maximum plasma concentrations (T_max) were 27.6±6.3 minutes for T1 and 32.1±7.8 minutes for T4. No sedation occurred. There were signs of nausea and mild to moderate salivation in both groups.

CONCLUSION AND CLINICAL RELEVANCE

Tramadol was metabolized marginally to O-desmethyltramadol and failed to produce clinically relevant acute antinociception. Therefore, the use of tramadol for acute nociceptive pain is questionable in dogs.

Centrally Targeted Pharmacotherapy for Chronic Abdominal Pain: Understanding and Management

Chronic abdominal pain has a widespread impact on the individual and the society. Identifying and explaining mechanisms of importance for the pain experience within a biopsychosocial context are central in order to select treatment that has a chance for symptom reduction. With current knowledge of brain-gut interactions, chronic abdominal pain, which mostly appears in functional gastrointestinal disorders, to a large extent involves pain mechanisms residing within the brain. As such, the use of centrally targeted pharmacotherapy as an effective treatment option is obvious in a selected number of patients. The antidepressants are most common, but also other classes of medications can be used, either alone or in combination. The latter option refers to when there is insufficient effect of one drug alone or side effects limiting dosage, and when combined in lower doses, certain drugs give rise to augmentation effects. This chapter outlines basic mechanisms of importance for the understanding of chronic abdominal pain and the pharmacologic treatment options.

Randomized, Double-blind, Placebo-controlled Phase III Trial of Duloxetine Monotherapy in Japanese Patients With Chronic Low Back Pain

STUDY DESIGN

A 14-week, randomized, double-blind, multicenter, placebo-controlled study of Japanese patients with chronic low back pain (CLBP) who were randomized to either duloxetine 60 mg once daily or placebo.

OBJECTIVE

This study aimed to assess the efficacy and safety of duloxetine monotherapy in Japanese patients with CLBP.

SUMMARY OF BACKGROUND DATA

In Japan, duloxetine is approved for the treatment of depression, diabetic neuropathic pain, and pain associated with fibromyalgia; however, no clinical study of duloxetine has been conducted for CLBP.

METHODS

The primary efficacy measure was the change in the Brief Pain Inventory (BPI) average pain score from baseline to Week 14. Secondary efficacy measures included BPI pain (worst pain, least pain, pain right now), Patient's Global Impression of Improvement, Clinical Global Impressions of Severity, and Roland-Morris Disability Questionnaire, among other measures, and safety and tolerability.

RESULTS

In total, 458 patients were randomized to receive either duloxetine (n = 232) or placebo (n = 226). The BPI average pain score improved significantly in the duloxetine group compared with that in the placebo group at Week 14 [-2.43 ± 0.11 vs. -1.96 ± 0.11, respectively; between-group difference (95% confidence interval), - 0.46 [-0.77 to-0.16]; P = 0.0026]. The duloxetine group showed significant improvement in many secondary measures compared with the placebo group, including BPI pain (least pain, pain right now) (between-group difference: -1.69 ± 0.10, P = 0.0009; -2.42 ± 0.12, P P = 0.0230, respectively), Patient's Global Impression of Improvement (2.46 ± 0.07, P = 0.0026), Clinical Global Impressions of Severity (-1.46 ± 0.06, P = 0.0019), and Roland-Morris Disability Questionnaire (-3.86 ± 0.22, P = 0.0439). Adverse events occurring at a significantly higher incidence in the duloxetine group were somnolence, constipation, nausea, dizziness, and dry mouth, most of which were mild or moderate in severity and were resolved or improved.

CONCLUSION

Duloxetine 60 mg was effective and well tolerated in Japanese CLBP patients.

LEVEL OF EVIDENCE

2.

Drug combinations in diabetic neuropathic pain: an experimental validation

BACKGROUND

Diabetic neuropathy is the most common complication of diabetes mellitus, and the different drug combinations available do not provide effective pain relief. The present study was performed to observe the effect of amitripyline, duloxetine, sitagliptin, and pregabalin, and their combinations on streptozotocin (STZ)-induced diabetic neuropathy.

METHODS

Diabetic neuropathy was induced by STZ, and the tail-flick test was used to assess thermal hyperalgesia before and after (at 30, 60, and 120 min) drug administration. One week after STZ administration, the blood glucose level was observed to be in the diabetic range.

RESULTS

Administration of all the drugs except sitagliptin increased the tail-flick latency significantly as compared to control. Further, the drugs amitriptyline, duloxetine, and pregabalin showed significant pain-relieving effect, when either two of them were administered in combination, although the different combinations had varied degree of pain relief. However, sitagliptin was observed to have no effect when administered alone or in combination with the other three drugs.

CONCLUSIONS

Therefore, the study provides new insights concerning combined therapy of pain, which further needs clinical exploration.

Effects of subthalamic deep brain stimulation with duloxetine on mechanical and thermal thresholds in 6OHDA lesioned rats

Chronic pain is the most common non-motor symptom of Parkinson's disease (PD) and is often overlooked. Unilateral 6-hydroxydopamine (6-OHDA) medial forebrain bundle lesioned rats used as models for PD exhibit decreased sensory thresholds in the left hindpaw. Subthalamic deep brain stimulation (STN DBS) increases mechanical thresholds and offers improvements with chronic pain in PD patients. However, individual responses to STN high frequency stimulation (HFS) in parkinsonian rats vary with 58% showing over 100% improvement, 25% showing 30-55% improvement, and 17% showing no improvement. Here we augment STN DBS by supplementing with a serotonin-norepinephrine reuptake inhibitor commonly prescribed for pain, duloxetine. Duloxetine was administered intraperitoneally (30mg/kg) in 15 parkinsonian rats unilaterally implanted with STN stimulating electrodes in the lesioned right hemisphere. Sensory thresholds were tested using von Frey, Randall-Selitto and hot-plate tests with or without duloxetine, and stimulation to the STN at HFS (150Hz), low frequency (LFS, 50Hz), or off stimulation. With HFS or LFS alone (left paw; p=0.016; p=0.024, respectively), animals exhibited a higher mechanical thresholds stable in the three days of testing, but not with duloxetine alone (left paw; p=0.183). Interestingly, the combination of duloxetine and HFS produced significantly higher mechanical thresholds than duloxetine alone (left paw, p=0.002), HFS alone (left paw, p=0.028), or baseline levels (left paw; p<0.001). These findings show that duloxetine paired with STN HFS increases mechanical thresholds in 6-OHDA-lesioned animals more than either treatment alone. It is possible that duloxetine augments STN DBS with a central and peripheral additive effect, though a synergistic mechanism has not been excluded.

Supraspinal Projection of Serotonergic and Noradrenergic Pathways Modulates Nociceptive Transmission in the Lower Urinary Tract of Rats

OBJECTIVES

To investigate the effect of descending serotonergic and noradrenergic pathways on nociception in the lower urinary tract (LUT).

METHODS

Female Sprague-Dawley rats were used. Following intraperitoneal administration of Vehicle or Milnacipran (30 mg/kg), which is one of serotonin-noradrenaline reuptake inhibitors (SNRI), 0.1% AA was infused into the bladder in normal (n = 4, each) and spinal cord injury (SCI) (n = 4, each) rats for 2 h on consciousness, and c-Fos, 5-HT and DβH were stained using immunohistochemistry at the L6 spinal cord as spinal areas associated with LUT.

RESULTS

In SCI rats, 5-HT or DβH-positive fibers were not observed at the L6 spinal cord, while there were many 5-HT and DβH-positive fibers in normal rats. The total number of c-Fos-positive cells was significantly increased in SCI rats compared to Normal rats (209.4 ± 7.1 in Normal, 336.4 ± 28.9 in SCI, P < 0.05), which indicated that interruption of supraspinal modulation enhances nocieptive transmission in the LUT. Regarding the effect of Milnacipran administration, the number of c-Fos-positive cells was significantly decreased at all region of the L6 spinal cord in normal rats (P < 0.05), while this reduction was not observed in SCI rats. This result demonstrated that administration of SNRI attenuates nocieptive transmission in the LUT, indicating that 5-HT and noradrenaline work as mediators of endogenous analgesic mechanisms through the supraspinal descending pain pathways.

CONCLUSIONS

Supraspinal projections of descending serotonergic and noradrenergic pathways to the lower lumbar spinal cord modulate nocieptive transmission in the LUT. Administration of SNRI attenuates nocieptive transmission in the LUT, which could result from enhancement of modulating descending serotonergic and noradrenergic pathways.

Prior stress exposure increases pain behaviors in a rat model of full thickness thermal injury

Thermal burns among individuals working in highly stressful environments, such as firefighters and military Service Members, are common. Evidence suggests that pre-injury stress may exaggerate pain following thermal injury; however current animal models of burn have not evaluated the potential influence of pre-burn stress. This sham-controlled study evaluated the influence of prior stress exposure on post-burn thermal and mechanical sensitivity in male Sprague-Dawley rats. Rats were exposed to 20 min of inescapable swim stress or sham stress once per day for three days. Exposure to inescapable swim stress (1) increased the intensity and duration of thermal hyperalgesia after subsequent burn and (2) accelerated the onset of thermal hyperalgesia and mechanical allodynia after subsequent burn. This stress-induced exacerbation of pain sensitivity was reversed by pretreatment and concurrent treatment with the serotonin-norepinephrine reuptake inhibitor (SNRI) duloxetine. These data suggest a better understanding of mechanisms by which prior stress augments pain after thermal burn may lead to improved pain treatments for burn survivors.