Central Sensitization, N-methyl-D-aspartate Receptors, and Human Experimental Pain Models: Bridging the Gap between Target Discovery and Drug Development

Adult zymosan re-exposure exacerbates the molecular alterations in the brainstem rostral ventromedial medulla of rats with early life zymosan-induced cystitis

Recent evidence suggests that the descending modulatory pathways from the brainstem rostral ventromedial medulla (RVM) are important for bladder inflammatory pain. This study aimed to identify the long-term molecular changes in RVM neurons due to early life cystitis during neuronal development and the effect of reexposure later in adulthood. RVM tissues from two treatment protocols were used: (1) neonatal zymosan exposures with acute adult rechallenge (RC) and (2) only neonatal zymosan exposures (NRC). RNAseq analysis showed upregulation of several genes associated with synaptic plasticity (Grin1, Grip2, Notch1, Arc, and Scn2b) in the cystitis groups compared to controls in both protocols. The RC protocol exhibited a stronger treatment effect with significantly higher fold differences between the groups compared to the NRC protocol (p < 0.001, fold differences RC vs NRC). In microarrays, miR-34a-5p showed cystitis-induced downregulation in both protocols. Bioinformatics analysis identified multiple 3'UTRs complementary binding sites for miR-34a-5p on Grin2b, Notch1, Grip2, Scn2b, and Arc genes. The enhanced response in the RC protocol indicates a possible priming effect of early life cystitis on rechallenge in adulthood. These long-term molecular alterations may play a critical role in the development of chronic bladder pain conditions as seen in patients with Interstitial Cystitis/Bladder pain syndrome.

Adding Ketamine to Epidural Morphine Does Not Prolong Postoperative Analgesia After Lumbar Laminectomy or Discectomy

BACKGROUND

Epidural opioids provide effective postoperative analgesia after lumbar spine surgery. Ketamine has been shown to reduce opioid-induced central sensitization and hyperalgesia. We hypothesized that adding ketamine to epidural opioids would prolong the duration of analgesia and enhance analgesic efficacy after lumbar spine surgery.

METHODS

American Society of Anesthesiologists physical status class I to II patients aged between 18 and 70 years with normal renal function undergoing lumbar laminectomy were recruited into this single-center randomized trial. Patients were randomized to receive either single-dose epidural morphine (group A) or epidural morphine and ketamine (group B) for postoperative analgesia. The primary objective was to compare the duration of analgesia as measured by time to the first postoperative analgesic request. Secondary objectives were the comparison of pain scores at rest and movement, systemic hemodynamics, and the incidence of side effects during the first 24 hours after surgery.

RESULTS

Fifty patients were recruited (25 in each group), of which data from 48 were available for analysis. The mean±SD duration of analgesia was 20±6 and 23±3 hours in group A and group B, respectively ( P =0.07). There were 12/24 (50%) patients in group A and 17/24 (71%) patients in group B who did not receive rescue analgesia during the first 24-hour postoperative period ( P =0.07). Pain scores at rest and movement, systemic hemodynamics, and postoperative complications were comparable between the groups.

CONCLUSIONS

The addition of ketamine to epidural morphine did not prolong the duration of analgesia after lumbar laminectomy.

Perioperative methadone for posterior spinal fusion in adolescents: Results from a double-blind randomized-controlled trial

BACKGROUND

Posterior spinal fusion is the most common surgical procedure performed for correction of adolescent idiopathic scoliosis in the United States. Intraoperative methadone has been shown to improve pain control in adult patients undergoing complex spine surgery, and current pediatric studies show encouraging results; however, prospective randomized-controlled trials are lacking in the pediatric literature.

AIMS

We conducted a single-center double-blind randomized-controlled trial to compare intraoperative use of methadone to morphine in pediatric patients undergoing posterior spinal fusion.

METHODS

A total of 47 adolescents undergoing posterior spinal fusion were randomized (stratified by sex) to either a methadone (n = 25) or morphine (n = 22) group. The primary outcome was postoperative opioid consumption. Secondary outcomes included postoperative pain severity, opioid-related side effects, and ratio of patient-controlled analgesia injections: attempts as a behavioral index of uncontrolled pain.

RESULTS

Patients in the methadone group consumed less total opioid postoperatively (median [interquartile range], 0.3 mg/kg [0.1, 0.5]) than patients in the morphine group (0.3 mg/kg [0.2, 0.6]), median difference [95% confidence interval] -0.07 [-0.2 to 0.02]; (p = .026). Despite the lower amount of opioid used postoperatively, pain scores for the methadone group (3.5 [3.0, 4.3]) were not significantly different from those in the morphine group (4.0 [3.2, 5.0]; p = .250). Groups did not differ on opioid-related side effects.

CONCLUSIONS

A two-dose intraoperative methadone regimen resulted in decreased opioid consumption compared to morphine. Although the clinical significance of these results may be limited, the analgesic equipoise without increased opioid-related side effects and potential for a lower incidence of chronic pain may tip the balance in favor of routine methadone use for adolescents undergoing posterior spinal fusion.

Altered pain processing and sensitization in sickle cell disease: a scoping review of quantitative sensory testing findings

OBJECTIVES

Over 50% of adults living with sickle cell disease (SCD) have chronic pain, but the underlying mechanisms of chronic pain in this population remain unclear. Quantitative sensory testing is an important measurement tool for understanding pain and sensory processing. This scoping review summarizes quantitative sensory testing methodologies used in sickle cell studies and the evidence for central sensitization in this population.

METHODS

We conducted a systematic search of PubMed, Embase, and CINAHL to identify studies using quantitative sensory testing in individuals living with sickle cell disease. Search strategies were based on variations of the terms "sickle cell disease," and "quantitative sensory testing." Eligible studies were observational or experimental studies in human participants living with SCD that reported findings and detailed methodology for at least 1 quantitative sensory testing modality.

RESULTS

Our search yielded a total of 274 records; 27 of which are included in this scoping review. Of the 27 studies, 17 were original studies (with combined total of 516 adult and 298 pediatric participants), and 10 were secondary or subgroup analyses of these prior studies. Significant variation existed in quantitative sensory testing methodologies across studies, including testing locations, type and intensity of stimuli, and interpretation of findings. Of the identified studies, 22% (2/9 studies) reported sensory abnormalities in mechanical sensitivity and thresholds, 22% (2/9 studies) reported abnormal pressure pain thresholds, 46% (6/13 studies) reported sensory abnormalities in thermal pain thresholds and tolerance (cold and warm), and 50% (2/4 studies) reported abnormalities in temporal summation.

CONCLUSION

Future studies should use standardized quantitative sensory testing protocols with consistent and operationalized definitions of sensitization to provide clear insight about pain processing and central sensitization in sickle cell disease.

Precision, integrative medicine for pain management in sickle cell disease

Sickle cell disease (SCD) is a prevalent and complex inherited pain disorder that can manifest as acute vaso-occlusive crises (VOC) and/or chronic pain. Despite their known risks, opioids are often prescribed routinely and indiscriminately in managing SCD pain, because it is so often severe and debilitating. Integrative medicine strategies, particularly non-opioid therapies, hold promise in safe and effective management of SCD pain. However, the lack of evidence-based methods for managing SCD pain hinders the widespread implementation of non-opioid therapies. In this review, we acknowledge that implementing personalized pain treatment strategies in SCD, which is a guideline-recommended strategy, is currently fraught with limitations. The full implementation of pharmacological and biobehavioral pain approaches targeting mechanistic pain pathways faces challenges due to limited knowledge and limited financial and personnel support. We recommend personalized medicine, pharmacogenomics, and integrative medicine as aspirational strategies for improving pain care in SCD. As an organizing model that is a comprehensive framework for classifying pain subphenotypes and mechanisms in SCD, and for guiding selection of specific strategies, we present evidence updating pain research pioneer Richard Melzack's neuromatrix theory of pain. We advocate for using the updated neuromatrix model to subphenotype individuals with SCD, to better select personalized multimodal treatment strategies, and to identify research gaps fruitful for exploration. We present a fairly complete list of currently used pharmacologic and non-pharmacologic SCD pain therapies, classified by their mechanism of action and by their hypothesized targets in the updated neuromatrix model.

Betaine Attenuates Chronic Constriction Injury-Induced Neuropathic Pain in Rats by Inhibiting KIF17-Mediated Nociception

Kinesin superfamily proteins transport a diverse range of cargo, including excitatory receptors to the dendrite and axon of a neuron via retrograde and anterograde fashions along microtubules, causing central sensitization and neuropathic pain. In this study, we have performed in silico molecular dynamics simulation to delineate the dynamic interaction of betaine with KIF17, a kinesin protein, known to be involved in neuropathic pain. The results from the molecular dynamics study suggest that the betaine-KIF17 complex is stabilized through hydrogen bonding, polar interactions, and water bridges. Findings from in vivo studies suggest a significant increase in pain hypersensitivity, oxido-nitrosative stress, and KIF17 overexpression in the sciatic nerve, dorsal root ganglion (DRG), and spinal cord of nerve-injured rats, which was significantly attenuated on treatment with betaine. Betaine treatment also restored the increased NR2B expressions and levels of proinflammatory cytokines and neuropeptides in the DRG and spinal cord of nerve-injured rats. Findings from the current study suggest that betaine attenuates neuropathic pain in rats by inhibiting KIF17-NR2B-mediated neuroinflammatory signaling.

Novel uses of ketamine in the emergency department

INTRODUCTION

: Ketamine is gaining renewed interest among healthcare providers due to its novel clinical applications in the emergency department (ED) setting.

AREAS COVERED

: This article provides a comprehensive discussion of ketamine's pharmacological properties, including safety profile and adverse effects, in addition to an overview of current evidence for ketamine (racemic formulation) in the management of ED patients with acute agitation, pain, and depression/suicide ideation.

EXPERT OPINION

: Ketamine is an effective adjunct to opioids, providing greater pain relief than morphine alone. As an analgesic agent, administration of ketamine (0.1-0.3 mg/kg IV) alone can provide analgesia similar to that of morphine in patients with acute visceral and musculoskeletal pain. Moreover, ketamine provides equal analgesic efficacy to morphine in a variety of chronic painful conditions including pain associated with cancer, vaso-occlusive pain crisis associated with sickle cell disease, and in patients with high opioid tolerance and/or opioid dependency. Available literature shows that ketamine (1-2mg/kg IV or 4-5 mg/kg IM) is a safe, rapid (<5 minutes) and effective tranquilization agent for ED patients with acute agitation. Finally, there is growing evidence that suggests ketamine may have a potential utility in the management of patients with self-harm ideation or acute depressive episodes. Intravenous infusion of ketamine (0.5 mg/kg over 40 mins) has been shown to produce an antidepressant effect and decrease in suicidal ideation within 4 hours with effects lasting up to one week.

Moving Toward a Multimodal Analgesic Regimen for Acute Sickle Cell Pain with Non-Opioid Analgesic Adjuncts: A Narrative Review

Purpose of Review

Sickle cell disease (SCD) is an inherited hemoglobinopathy with potential life-threatening complications that affect millions of people worldwide. Severe and disabling acute pain, referred to as a vaso-occlusive crisis (VOC), is a fundamental symptom of the disease and the primary driver for acute care visits and hospitalizations. Despite the publication of guidelines for VOC management over the past decade, management of VOCs remains unsatisfactory for patients and providers.

Recent Findings

Acute SCD pain includes pain secondary to VOCs and other forms of acute pain. Distinguishing VOC from non-VOC pain may be challenging for both patients and clinicians. Further, although opioids have been the gold-standard for VOC pain management for decades, the current highest standard of care for all acute pain is a multimodal approach that is less dependent on opioids, and, instead incorporates analgesics and adjuvants from different mechanistic pathways. In this narrative review, we focus on a multimodal pharmacologic approach for acute SCD pain management and explore the evidence for existing non-opioid pharmacological adjuncts. Moreover, we present an explanatory model of pain, which is not only novel in its application to SCD pain but also captures the multidimensional nature of the SCD pain experience and supports the need for such a multimodal approach. This model also highlights opportunities for new investigative and therapeutic targets - both pharmacological and non-pharmacological.

Summary

Multimodal pain regimens that are less dependent on opioids are urgently needed to improve acute pain outcomes for individuals with SCD. The proposed explanatory model for SCD pain offers novel opportunities to improve acute pain management for SCD patients.

Beta 2-adrenergic receptor mediates noradrenergic action to induce cyclic adenosine monophosphate response element-binding protein phosphorylation in satellite glial cells of dorsal root ganglia to regulate visceral hypersensitivity

ABSTRACT

Sympathoneuronal outflow into dorsal root ganglia (DRG) is suggested to be involved in sympathetically maintained chronic pain, which is mediated by norepinephrine (NE) action on DRG cells. This study combined in vitro and in vivo approaches to identify the cell types of DRG that received NE action and examined cell type-specific expression of adrenergic receptors (ARs) in DRG. Using DRG explants, we identified that NE acted on satellite glial cells (SGCs) to induce the phosphorylation of cAMP response element-binding protein (CREB). Using primarily cultured SGCs, we identified that beta (β)2-adrenergic receptor but not alpha (α)adrenergic receptor nor other βAR isoforms mediated NE-induced CREB phosphorylation and CRE-promoted luciferase transcriptional activity. Using fluorescence in situ hybridization and affinity purification of mRNA from specific cell types, we identified that β2AR was expressed by SGCs but not DRG neurons. We further examined β2AR expression and CREB phosphorylation in vivo in a model of colitis in which sympathetic nerve sprouting in DRG was observed. We found that β2AR expression and CREB phosphorylation were increased in SGCs of thoracolumbar DRG on day 7 after colitis induction. Inhibition but not augmentation of β2AR reduced colitis-induced calcitonin gene-related peptide release into the spinal cord dorsal horn and colonic pain responses to colorectal distention. Prolonged activation of β2AR in naive DRG increased calcitonin gene-related peptide expression in DRG neurons. These findings provide molecular basis of sympathetic modulation of sensory activity and chronic pain that involves β2AR-mediated signaling in SGCs of DRG.

Enhanced Recovery After Cesarean: Current and Emerging Trends

Purpose of Review

What are the latest enhanced recovery elements for cesarean delivery?

Recent Findings

Enhanced recovery after cesarean delivery (ERAC) provides an evidenced-based system to improve maternal outcomes, functional recovery, maternal-infant bonding, and patient experience. Postsurgical recovery has evolved from a one-dimensional pain score to a holistic multidimensional approach emphasizing faster functional recovery. ERAC involves multidisciplinary efforts of the anesthesiologist, obstetrician, nursing, hospital, and patient. Components of ERAC include preoperative patient education, limited fasting, carbohydrate load, limiting opioids intra- and postoperatively, using scheduled non-opioid analgesics and supplementing with advanced therapies for women at higher risk for pain. ERAC protocols reduce opioid consumption, reduce length of stay, and improve maternal and neonatal outcomes.

Summary

Implementing ERAC standardized care will likely be the most important change you can make in your practice to improve outcomes, improve quality care, help address racial disparities, and minimize opioid exposure and potential for addiction.

Pioglitazone Attenuates Experimental Colitis-Associated Hyperalgesia through Improving the Intestinal Barrier Dysfunction

Impaired intestinal mucosal integrity during colitis involves the peroxisome proliferator-activated receptor-γ (PPARγ), an important anti-inflammatory factor in intestinal mucosa homoeostasis, which is a potential target in colitis. Recurrent chronic pain is a vital pathogenetic feature of colitis. Nevertheless, potential functions of PPARγ in the colitis-associated hyperalgesia remain unclear. This study aimed to investigate biological roles of pioglitazone in relieving colitis-associated pain hypersensitivity by a PPARγ tight junction protein-dependent mechanism during the course of dextran sodium sulfate (DSS)-induced intestinal inflammation. The DSS-induced colitis model was generated in C57BL/6 mice. Changes in colitis induced the injury of intestinal mucosal barrier and hyperalgesia after a 6-day treatment of pioglitazone (25 mg/kg, IP injection) were assessed through immunofluorescent, hematoxylin and eosin (H&E) staining, western blot analysis, and determination of paw withdrawal mechanical threshold. A significant reduction of paw withdrawal mechanical threshold occurred after DSS treatment. Follow-up data showed that systematic administration of PPARγ agonist pioglitazone ameliorated the DSS-induced colitis and the development of colitis-associated hyperalgesia by repairing the intestinal mucosal barrier. The tight junction proteins ZO-1 and Claudin-5 were upregulated by PPARγ signaling, which in turn promoted the improvement of intestinal barrier function. Moreover, pioglitazone inhibited phosphorylation of ERK and NF-κB in the colon and decreased the levels of inflammatory cytokines in both colon spine tissues. Furthermore, systemically pioglitazone treatment inhibited the activation of microglia and astrocytes, as well as DSS-induced phosphorylation of NR2B subunit in spinal cord, which was correspondingly consistent with the pain behavior. Pioglitazone ameliorates DSS-induced colitis and attenuates colitis-associated mechanical hyperalgesia, with improving integrity of the intestinal mucosal barrier by directly upregulating tight junction proteins. The PPARγ-tight junction protein signaling might be a potential therapeutic target for the treatment of colitis-associated chronic pain.

Oral pharmacotherapeutics for the management of peripheral neuropathic pain conditions - a review of clinical trials

INTRODUCTION

Epidemiological studies have shown that 6.9-10% of people suffer from neuropathic pain, a complex painful condition which is often undertreated. Data regarding the effectiveness of treatment options for patients with neuropathic pain is inconsistent, and there is no single treatment option that shows cost-effectiveness across studies.

AREAS COVERED

In this narrative review, the authors present the results of different prospective, randomized controlled trials, systematic reviews and meta-analyses assessing the effects of different oral medications in the management of various peripheral neuropathic pain conditions. The authors discuss the effectiveness of commonly used oral medications such as voltage-gated calcium channels antagonists, voltage-gated sodium channel antagonists, serotonin-norepinephrine reuptake inhibitors, NMDA antagonists, and medications with other mechanisms of action.

EXPERT OPINION

Most of the presented medications were more effective than placebo; however, when compared to each other, none of them were significantly superior. The heterogeneity of the studies looking into different oral neuropathic conditions has been the major issue that prevents us from making stronger recommendations. There are multiple reasons including high placebo responsiveness, improperly treated underlying comorbidities (particularly anxiety and depression), and inter-patient variability. Different sensory phenotypes should also be taken into consideration when designing future clinical trials for neuropathic pain.