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Neuropathic pain is a refractory condition that involves de novo protein synthesis in the nociceptive pathway. The mechanistic target of rapamycin (mTOR) is a master regulator of protein translation; however, mechanisms underlying its role in neuropathic pain remain elusive. Using the spared nerve injury-induced neuropathic pain model, we found that mTOR was preferentially activated in large-diameter dorsal root ganglion (DRG) neurons and spinal microglia. However, selective ablation of mTOR in DRG neurons, rather than microglia, alleviated acute neuropathic pain in mice. We showed that injury-induced mTOR activation promoted the transcriptional induction of Npy likely via signal transducer and activator of transcription 3 (STAT3) phosphorylation. NPY further acted primarily on Y2 receptors (Y2R) to enhance neuronal excitability. Peripheral replenishment of NPY reversed pain alleviation upon mTOR removal, whereas Y2R antagonists prevented pain restoration. Our findings reveal an unexpected link between mTOR and NPY/Y2R in promoting nociceptor sensitization and neuropathic pain.
Learn More >Chronic regional pain syndrome (CRPS) is a debilitating, painful condition of limbs that often arises after an injury and is associated with significant morbidity. The Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument, used to assess the quality of clinical practice guidelines (CPGs), was used to evaluate seven CRPS management guideline. Out of the seven CPGs evaluated using the AGREE II instrument, only one from Royal College of Physicians was found to have high-quality consensus guidelines for diagnosis and management of CRPS. Future CPGs should be backed by systematic literature searches, focus on guidelines clinical translation into clinical practice and applicability to the desired patient population.
Learn More >Persistent or recurrent neck pain is associated with perturbations in the autonomic nervous system balance, and nociceptive stimulation has been seen to influence this balance. However, very few prospective studies have addressed the extent to which changes in pain associate with changes in autonomic cardiac regulation. Therefore, we investigated if changes in pain vary with changes in heart rate variability in a cohort of patients treated for persistent or recurrent neck pain.
Learn More >The Kv3.4 channel regulates action potential (AP) repolarization in nociceptors and excitatory synaptic transmission in the spinal cord. We hypothesize that this is a tunable role governed by protein kinase-C-dependent phosphorylation of the Kv3.4 cytoplasmic N-terminal inactivation domain (NTID) at four nonequivalent sites. However, there is a paucity of causation evidence linking the phosphorylation status of Kv3.4 to the properties of the AP. To establish this link, we used adeno-associated viral vectors to specifically manipulate the expression and the effective phosphorylation status of Kv3.4 in cultured dorsal root ganglion (DRG) neurons from mixed-sex rat embryos at embryonic day 18. These vectors encoded GFP (background control), wild-type (WT) Kv3.4, phosphonull (PN) Kv3.4 mutant (PN = S[8,9,15,21]A), phosphomimic (PM) Kv3.4 mutant (PM = S[8,9,15,21]D), and a Kv3.4 nonconducting dominant-negative (DN) pore mutant (DN = W429F). Following viral infection of the DRG neurons, we evaluated transduction efficiency and Kv3.4 expression and function via fluorescence microscopy and patch clamping. All functional Kv3.4 constructs induced current overexpression with similar voltage dependence of activation. However, whereas Kv3.4-WT and Kv3.4-PN induced fast transient currents, the Kv3.4-PM induced currents exhibiting impaired inactivation. In contrast, the Kv3.4-DN abolished the endogenous Kv3.4 current. Consequently, Kv3.4-DN and Kv3.4-PM produced APs with the longest and shortest durations, respectively, whereas Kv3.4-WT and Kv3.4-PN produced intermediate results. Moreover, the AP widths and maximum rates of AP repolarization from these groups are negatively correlated. We conclude that the expression and effective phosphorylation status of the Kv3.4 NTID confer a tunable mechanism of AP repolarization, which may provide exquisite regulation of pain signaling in DRG neurons.The AP is an all-or-none millisecond-long electrical impulse that encodes information in the frequency and patterns of repetitive firing. However, signaling may also depend on the plasticity and diversity of the AP waveform. For instance, the shape and duration of the AP may regulate nociceptive synaptic transmission between a primary sensory afferent to a secondary neuron in the spinal cord. Here, we used mutants of the Kv3.4 voltage-gated potassium channel to manipulate its expression and effective phosphorylation status in dorsal root ganglion neurons and directly show how the expression and malleable inactivation properties of Kv3.4 govern the AP duration and repolarization rate. These results elucidate a mechanism of neural AP plasticity that may regulate pain signaling.
Learn More >Chronic pain is a major burden for the society and remains more prevalent and severe in females. The presence of chronic pain is linked to persistent alterations in the peripheral and the central nervous system. One of the main types of peripheral pain transducers are the transient receptor potential channels (TRP), also known as thermoTRP channels, which intervene in the perception of hot and cold external stimuli. These channels, and especially TRPV1, TRPA1 and TRPM8, have been subjected to profound investigation because of their role as thermosensors and also because of their implication in acute and chronic pain. Surprisingly, their sensitivity to endogenous signaling has been far less studied. Cumulative evidence suggests that the function of these channels may be differently modulated in males and females, in part through sexual hormones, and this could constitute a significant contributor to the sex differences in chronic pain. Here, we review the exciting advances in thermoTRP pharmacology for males and females in two paradigmatic types of chronic pain with a strong peripheral component: chronic migraine and chemotherapy-induced peripheral neuropathy (CIPN). The possibilities of peripheral druggability offered by these channels and the differential exploitation for men and women represent a development opportunity that will lead to a significant increment of the armamentarium of analgesic medicines for personalized chronic pain treatment.
Learn More >Prescription opioids are a primary driver of opioid-related deaths. Although craving is a substantial component of OUD, the degree to which craving leads to misuse among chronic pain patients on long-term prescription opioids is unknown. A clear understanding of the factors that lead to misuse in this vulnerable population is needed for the development of safe and effective practices for opioid taper. This narrative review summarizes the relevant literature on the role of craving in addiction and chronic pain through epidemiological and behavioral studies. The first part of this review examines the role of craving in predicting opioid use/misuse in individuals with chronic pain with and without OUD. The second part covers methods on how craving is evaluated experimentally using both subjective and objective measures and provides related findings. The overall goal of this review is to facilitate the development of a population-specific description of craving in those who use opioids to control chronic pain and to describe how it may be mechanistically linked to patterns of opioid (mis)use.
Learn More >Fabry disease (FD) is a rare, progressive, X-linked inherited disorder of glycosphingolipid metabolism. It is a monogenic disease due to α-galactosidase A (α-GAL) enzyme deficiency, leading to the accumulation of globotriaosylceramide (GL3) within lysosomes beginning in utero. Multiple systems are involved, most notably the vascular, renal, cardiac, and nervous systems. Early clinical manifestations include neuropathic pain, angiokeratomas, anhidrosis, cornea verticillata, and gastrointestinal symptoms. In the later stages, FD manifests with transient ischemic attacks, strokes, hearing loss, and life-threatening complications involving the kidneys and heart. Cardiac involvement in Fabry disease is typically characterized by increased left ventricular wall thickness/mass, functional abnormalities, valvular heart disease, arrhythmias, and heart failure. The life expectancy of the patient with untreated Fabry disease falls significantly once cardiac or renal manifestations develop. This review will focus on the cardiac manifestations of FD and the role of multimodality imaging in diagnosis and follow-up.
Learn More >People living with chronic pain may use wearable health technology (WHT) in conjunction with an expert-directed pain management program for up to one year. WHT use may be associated with improvements in key patient outcomes.
Learn More >Aceclofenac controlled-release (CR) is a once-a-day tablet with 200 mg of aceclofenac, and is bioequivalent to conventional aceclofenac. However, its safety in humans has not been well studied in Korea. Therefore, we aimed to evaluate the overall incidence and patterns of adverse events (AEs), the effectiveness of aceclofenac CR, and the differences in incidence rates of the AEs based on each patient's baseline charateristics. This study was conducted on patients receiving aceclofenac CR in clinical practice at each investigational institution to treat musculoskeletal pain and inflammation. The subjects were administered one tablet of aceclofenac CR (200 mg once-a-day) and were observed for 4 weeks post-administration. Factors affecting the occurrence of AEs were evaluated, and the Visual Analogue Scale (VAS) was used to measure the pain intensity. Among 14,543 subjects, the incidence rate of AEs was 0.86%, and that of adverse drug reactions was 0.74%. No serious AEs and unexpected adverse drug reactions were monitored. The incidence rates of AEs were significantly higher in females, inpatient treatment, individuals with concurrent disorders, and those receiving concomitant medications, respectively (all P < 0.05). Four weeks post-using aceclofenac CR, the mean changes in VAS was significantly decreased compared to prior administration. The overall clinical efficacy rate was 91.63%. This study confirmed that no severe adverse reactions were observed for aceclofenac CR exceeding those previously reported for safety results of conventional formulation of this drug in routine clinical practice settings. The use of aceclofenac CR might not violate the previously reported information on the safety and effectiveness of aceclofenac.
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