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Persistent use of prescription opioids beyond the period of surgical recovery is a large part of a public health problem linked to the current opioid crisis in the United States. However, few studies have been conducted to examine whether morphine reward is influenced by acute pain and injury.
Metabotropic glutamate receptor 5 (mGlu5) has been shown to modulate nociception in animals, but no mGlu5 antagonists have been developed commercially as analgesics. The mGlu5 antagonist fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea] was originally evaluated for development as a non-benzodiazepine anxiolytic. Fenobam is analgesic in numerous mouse pain models, acting exclusively via mGlu5 blockade. Furthermore, fenobam showed no signs of analgesic tolerance with up to two weeks of daily dosing in mice. Analgesic effects of fenobam in humans have not been reported. The purpose of this investigation was to evaluate fenobam pharmacokinetics and analgesic effects in humans. We first evaluated single-dose oral fenobam disposition in a parallel-group dose-escalation study in healthy volunteers. A second investigation tested the analgesic effects of fenobam in an established experimental human pain model of cutaneous sensitization utilizing capsaicin cream and heat, in a double-blind placebo-controlled study. The primary outcome measure was the area of hyperalgesia and allodynia around the area applied with heat/capsaicin. Secondary outcome measures included nociception, measured as pain rating on a visual analog scale, heat-pain detection threshold, and effects on cognition and mood. Fenobam plasma exposures showed considerable inter-individual variability, and were not linear with dose. Fenobam reduced sensitization vs placebo at a single time-point (peak plasma concentration); we found no other difference between fenobam and placebo. Our results suggest highly variable fenobam disposition, and minimal analgesic effects at the dose tested. We suggest that future studies testing analgesic effects of mGlu5 blockade are warranted, but such studies should employ molecules with improved pharmacokinetic profiles.
Advanced analyses of electroencephalography (EEG) are rapidly becoming an important tool in understanding the brain's processing of pain. To date, it appears that none have been explored as a way of distinguishing between migraine patients with aura (MWA) vs. those without aura (MWoA). In this work, we apply a mixture of predictive, e.g., classification methods and attribute-selection techniques, and traditional explanatory, e.g., statistical, analyses on functional connectivity measures extracted from EEG signal acquired from at-rest participants (N = 52) during their interictal period and tested them against the distinction between MWA and MWoA. We show that a functional connectivity metric of EEG data obtained during resting state can serve as a sole biomarker to differentiate between MWA and MWoA. Using the proposed analysis, we not only have been able to present high classification results (average classification of 84.62%) but also to discuss the underlying neurophysiological mechanisms upon which our technique is based. Additionally, a more traditional statistical analysis on the selected features reveals that MWoA patients show higher than average connectivity in the Theta band (p = 0.03) at rest than MWAs. We propose that our data-driven analysis pipeline can be used for resting-EEG analysis in any clinical context.
Early detection of patients with chronic diseases at risk of developing persistent pain is clinically desirable for timely initiation of multimodal therapies. Quality follow-up registries may provide the necessary clinical data; however, their design is not focused on a specific research aim, which poses challenges on the data-analysis strategy. Here, machine-learning was used to identify early parameters that provide information about a future development of persistent pain in rheumatoid arthritis (RA). Data of 288 patients were queried from a registry based on the Swedish Epidemiological Investigation of RA (EIRA). Unsupervised machine-learning identified three distinct patient subgroups (low, median and high) persistent pain intensities. Next, supervised machine learning, implemented as random forests followed by computed ABC analysis-based item categorization, was used to select predictive parameters among 21 different demographic, patient rated and objective clinical factors. The selected parameters were used to train machine-learned algorithms to assign patients pain-related subgroups (1,000 random resamplings, 2/3 training, 1/3 test data). Algorithms trained with three-month data of patient global assessment and health assessment questionnaire provided pain group assignment at a balanced accuracy of 70 %. When restricting the predictors to objective clinical parameters of disease severity, swollen joint count and tender joint count acquired at three months provided a balanced accuracy of rheumatoid arthritis of 59 %. Results indicate that machine-learning is suited to extract knowledge from data queried from pain and disease related registries. Early functional parameters of RA are informative for the development and degree of persistent pain.
Experimental and clinical studies have shown that Tonic Spinal Cord Stimulation (SCS) releases GABA in the spinal dorsal horn. Recently, it was suggested that Burst SCS does not act via spinal GABAergic mechanisms. Therefore, we studied spinal GABA-release during Burst and Tonic SCS, both anatomically and pharmacologically, in a well-established chronic neuropathic pain model.
Altered expression of circular RNA (circRNA) is recognized as a contributor to malignant pain where microRNA (miRNA) exerts an essential effect. We generated a murine model for bone malignancy pain in which 2472 osteolytic sarcoma cells were injected into the femurs of mice. CircRNA microarray and quantitative PCR (qPCR) and revealed that circ9119 expression was repressed in the spinal cord of bone malignancy pain model mice, which is the first relay site involved in the transmission of nociceptive information to the cerebrum of mice that receive spinal analgesics for malignancy pain. Overexpression of circ9119 by plasmid injection in the model mice reduced progressive thermal hyperalgesia and mechanical hyperalgesia. Bioinformatics prediction and dual-luciferase reporter assay showed that circ9119 functions as a sponge of miR-26a, which targets the TLR3 3'-untranslated region. Furthermore, expression of miR-26a was elevated and TLR3 level was repressed in bone malignancy pain model mice, which were counteracted by circ9119 in the spinal cord of tumor-bearing mice. Moreover, excessive expression of miR-26a was involved in the recovery of mice from progressive thermal hyperalgesia and mechanical hyperalgesia triggered via circ9119. TLR3 knockdown in bone malignancy pain model mice thoroughly impaired pain in the initial stages and reduced the effects of circ9119 on hyperalgesia. Our research findings indicate that targeting the circ9119-miR-26a-TLR3 axis may be a promising analgesic strategy to manage malignancy pain.
Synovitis is one of the possible pain generators in osteoarthritis (OA) and is associated with upregulation of proinflammatory cytokines, which can lead to worsening of the postoperative pain. This exploratory study aimed to investigate the association between perioperative synovitis and self-reported pain 12 months after total knee arthroplasty (TKA) in patients with OA.
N-Acetylaspartylglutamate (NAAG) is the third most prevalent neurotransmitter in the mammalian nervous system, yet its therapeutic potential is only now being fully recognized. Drugs that inhibit the inactivation of NAAG by glutamate carboxypeptidase II (GCPII) increase its extracellular concentration and its activation of its receptor, mGluR3. These drugs warrant attention, as they are effective in animal models of several clinical disorders including stroke, traumatic brain injury and schizophrenia. In inflammatory and neuropathic pain studies, GCPII inhibitors moderated both the primary and secondary pain responses when given systemically, locally or in brain regions associated with the pain perception pathway. The finding that GCPII inhibition also moderated the motor and cognitive effects of ethanol intoxication led to the discovery of their procognitive efficacy in long-term memory tests in control mice and in short-term memory in a mouse model of Alzheimer's disease. NAAG and GCPII inhibitors respectively reduce cocaine self-administration and the rewarding effects of a synthetic stimulant. Most recently, GCPII inhibition also has been reported to be efficacious in a model of inflammatory bowel disease. GCPII was first discovered as a protein expressed by and released from metastatic prostate cells where it is known as prostate specific membrane antigen (PSMA). GCPII inhibitors with high affinity for this protein have been developed as prostate imaging and radiochemical therapies for prostate cancer. Taken together, these data militate in favor of the development and application of GCPII inhibitors in more advanced preclinical research as a prelude to clinical trials.
Vixotrigine is a voltage- and use-dependent Nav1.7 channel blocker under investigation for the treatment of peripheral neuropathic pain conditions, including trigeminal neuralgia. Vixotrigine is metabolized primarily via uridine diphosphate-glucuronosyltransferases (UGTs). Carbamazepine, a UGT and cytochrome P450 3A4 inducer, is a first-line treatment for trigeminal neuralgia. We conducted a double-blind, randomized, placebo-controlled, parallel-group, single-center phase 1 study to investigate the impact of coadministering vixotrigine and carbamazepine on their respective pharmacokinetics (PK) in healthy volunteers, the safety and tolerability of combined treatment, and PK recovery of vixotrigine following carbamazepine discontinuation. Randomly assigned treatments were carbamazepine (100 mg twice a day, days 1-3 and 200 mg twice a day, days 4-21) or placebo on days 1 to 21. All volunteers received vixotrigine 150 mg 3 times a day on days 16 to 28. At prespecified times, whole-blood samples were collected for PK assessment. Statistical analyses were performed on the log-transformed PK parameters area under the concentration-time curve within a dosing interval (AUC ) and maximum observed concentration (C ) for vixotrigine, carbamazepine, and metabolites. Vixotrigine AUC and C were reduced by 31.6% and 26.3%, respectively, when coadministered with carbamazepine compared with placebo. Seven days after carbamazepine discontinuation, vixotrigine AUC and C remained 24.5% and 21.4% lower compared with placebo. Carbamazepine AUC and C were <10% lower when coadministered with vixotrigine compared on days 15 and 21. Vixotrigine/carbamazepine coadministration was well tolerated. These results suggest that vixotrigine does not have an effect on carbamazepine PK, and although carbamazepine has an effect on the exposure of vixotrigine, the effect is not considered clinically relevant.
To compare the prevalence and characteristics of chronic postsurgical pain (CPSP) between laparoscopic hysterectomy (LH) and abdominal hysterectomy (AH) groups 3, 6, and 12 months after surgery, and to assess the impact of pain on the activities of daily living (ADL) of patients.