Pharmacological profiles of alpha 2 adrenergic receptor agonists identified using genetically altered mice and isobolographic analysis

Dexmedetomidine reduced the severity of emergence delirium and respiratory complications, but increased intraoperative hypotension in children underwent tonsillectomy: a retrospective analysis

BACKGROUND

Intraoperative dexmedetomidine can be useful for its sedative and analgesic sparing effects, and for the prevention of emergence delirium. Conversely, it can cause hypotension and bradycardia. The aim of this study was to assess the safety and efficacy of dexmedetomidine in pediatric anesthesia.

METHODS

This is a retrospective cohort study in children who received intravenous dexmedetomidine (Dex group) or opioids (No-Dex group) during general anesthesia for tonsillectomy, between November 2014 and November 2016. From the medical records, data on the intraoperative phase (hemodynamic adverse events, respiratory failure at the emergence, awakening and extubation times, emergence delirium), recovery room (pain, hemodynamic parameters, and desaturation), and ward stay (pain, and nausea and vomiting) were investigated. Time of hospital discharge was calculated.

RESULTS

Three hundred twenty-eight (Dex group 183; No-Dex group 145) children ranging from 1.5 to 10 years were included. The percentage of intraoperative hypotension was significantly higher in the Dex group (P=0.01). The extubation times were significantly higher in No-Dex group (P=0.0001), although the awakening times were significantly longer with dexmedetomidine (P=0.0001). Desaturation episodes were higher in the Dex group (P=0.0001). The incidence of emergence delirium was similar in the two groups, but of greater intensity in the No-Dex group. While in the immediate postoperative period there was no difference in pain, after 24 hours, the incidence of pain and vomiting was significantly higher (P=0.003; P=0.0001) in the No-Dex group.

CONCLUSIONS

Although several outcome parameters showed important advantages of dexmedetomidine over opioid-based regimens in terms of safety and efficacy, issues such as the increased intraoperative hypotension, indicated that it is not possible to draw any definitive conclusions.

Centralizing the Knowledge and Interpretation of Pain in Chemotherapy-Induced Peripheral Neuropathy: A Paradigm Shift towards Brain-Centric Approaches

Chemotherapy-induced peripheral neuropathy (CIPN) is a side effect of cancer treatment, often linked with pain complaints. Patients report mechanical and thermal hypersensitivity that may emerge during chemotherapy treatment and may persist after cancer remission. Whereas the latter situation disturbs the quality of life, life itself may be endangered by the appearance of CIPN during cancer treatment. The causes of CIPN have almost entirely been ascribed to the neurotoxicity of chemotherapeutic drugs in the peripheral nervous system. However, the central consequences of peripheral neuropathy are starting to be unraveled, namely in the supraspinal pain modulatory system. Based on our interests and experience in the field, we undertook a review of the brain-centered alterations that may underpin pain in CIPN. The changes in the descending pain modulation in CIPN models along with the functional and connectivity abnormalities in the brain of CIPN patients are analyzed. A translational analysis of preclinical findings about descending pain regulation during CIPN is reviewed considering the main neurochemical systems (serotoninergic and noradrenergic) targeted in CIPN management in patients, namely by antidepressants. In conclusion, this review highlights the importance of studying supraspinal areas involved in descending pain modulation to understand the pathophysiology of CIPN, which will probably allow a more personalized and effective CIPN treatment in the future.

Dexmedetomidine Prolongs Lidocaine Intravenous Regional Anesthesia in Rats by Blocking the Hyperpolarization-Activated Cation Current

Purpose

Intravenous regional anesthesia (IVRA) using lidocaine provides effective localized analgesia but its duration is limited. The mechanism by which dexmedetomidine enhances lidocaine IVRA is unclear but may involve modulation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

Materials and Methods

Lidocaine IVRA with varying dexmedetomidine concentrations was performed in the tails of Sprague-Dawley rats. Tail-flick and tail-clamping tests assessed IVRA analgesia and anesthesia efficacy and duration. Contributions of α2 adrenergic receptors and HCN channels were evaluated by incorporating an α adrenergic receptor antagonist, the HCN channel inhibitor ZD7288, and the HCN channel agonist forskolin. Furthermore, whole-cell patch clamp electrophysiology quantified the effects of dexmedetomidine on HCN channels mediating hyperpolarization-activated cation current (Ih) in isolated dorsal root ganglion neurons.

Results

Dexmedetomidine dose-dependently extended lidocaine IVRA duration and analgesia, unaffected by α2 receptor blockade. The HCN channel inhibitor ZD7288 also prolonged lidocaine IVRA effects, while the HCN channel activator forskolin shortened effects. In dorsal root ganglion neurons, dexmedetomidine concentration-dependently inhibited Ih amplitude and shifted the voltage-dependence of HCN channel activation.

Conclusion

Dexmedetomidine prolongs lidocaine IVRA duration by directly inhibiting HCN channel activity, independent of α2 adrenergic receptor activation. This HCN channel inhibition represents a novel mechanism underlying the anesthetic and analgesic adjuvant effects of dexmedetomidine in IVRA.

Antinociceptive Agents as General Anesthetic Adjuncts: Supra-additive and Infra-additive Interactions

The hypothesis "General anesthesia consists of producing both loss of consciousness and the inhibition of noxious stimuli reaching the brain and causing arousal" was used as a basis for the review of published data on general anesthetic interactions with antinociceptive agents: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. This review is focused on a specific type of anesthetic interaction-the transformation of antinociceptive agents into general anesthetic adjuncts. The primary aim is to answer 2 questions. First, how does an antinociceptive agent transform the effect of an anesthetic in providing a certain component of anesthesia-hypnosis, immobility, or hemodynamic response to noxious stimulation? Second, does a combination of an anesthetic with an adjunct result in a simple summation of their respective effects or in a supra-additive or infra-additive interaction? The Medline database was searched for data describing the interactions of antinociceptive agents and general anesthetics. The following classes of antinociceptive agents were considered: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. Drugs used in combination with antinociceptive agents were general anesthetics and benzodiazepines. The following terms related to drug interactions were used: anesthetic interactions, synergy, antagonism, isobolographic analysis, response surface analysis, and fractional analysis. The interactions of antinociceptive agents with general anesthetics result in a decrease of general anesthetic requirements, which differ for each of the components of general anesthesia: hypnosis, immobility, and hemodynamic response to noxious stimulation. Most studies of the nature of anesthetic interactions are related to opioid-general anesthetic combinations, and their conclusions usually confirm supra-additivity.

Measuring neuron-regulated immune cell physiology via the alpha-2 adrenergic receptor in an ex vivo murine spleen model

The communication between the nervous and immune systems plays a crucial role in regulating immune cell function and inflammatory responses. Sympathetic neurons, which innervate the spleen, have been implicated in modulating immune cell activity. The neurotransmitter norepinephrine (NE), released by sympathetic neurons, influences immune cell responses by binding to adrenergic receptors on their surface. The alpha-2 adrenergic receptor (α2AR), expressed predominantly on sympathetic neurons, has received attention due to its autoreceptor function and ability to modulate NE release. In this study, we used fast-scan cyclic voltammetry (FSCV) to provide the first subsecond measurements of NE released in the white pulp region of the spleen and validated it with yohimbine, a known antagonist of α2AR. For further application of FSCV in neuroimmunology, we investigated the extent to which subsecond NE from sympathetic neurons is important for immune cell physiology and cytokine production, focusing on tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), and interleukin-6 (IL-6). Our findings provide insights into the regulatory mechanisms underlying sympathetic-immune interactions and show the significance of using FSCV, a traditional neurochemistry technique, to study these neuroimmune mechanisms.

THE effect of general anesthetics on genetic absence epilepsy in WAG/Rij rats

AIM

To establish safe and straightforward anesthesia used in experiments, we examined the effect of ketamine, ketamine/xylazine, urethane, chloral hydrate, pentobarbital, isoflurane, dexmedetomidine, and dexmedetomidine/ketamine on epileptiform activity in genetic absence epilepsy (WAG\Rij) rats.

MATERIALS AND METHOD

Sixty-three male WAG/Rij rats weighing (170-190 g) were used. Tripolar electrodes were inserted into the skull. After ECoG activities were recorded for each animal for 2 hours as controls, , the anesthetic substances were administered and the recording continued for another 2 hours. All the anesthetic substances were administered intraperitoneally except isoflurane, which was administered by inhalation.The PowerLab system was used for electrophysiological activity recording and analysis.

RESULTS

The administration of ketamine (90 mg/kg), ketamine/xylazine (90/10 mg/kg), urethane (1.25 g/kg), chloral hydrate (175 mg/kg), pentobarbital (50-90 mg/kg), isoflurane (induction 5%, maintaining 3-4%), dexmedetomidine (0.5-1 mg/kg), and dexmedetomidine/ketamine (50/90 mg/kg), significantly decreased the total number of SWD, the total number of spikes, and the SWD duration (p < 0,05). The mean duration of SWD was not affected in pentobarbital (50-90 mg/kg), isoflurane (induction 5%, maintaining 3-4%), dexmedetomidine (0.5-1 mg/kg), and Dexmedetomidine/ketamine (50/90 mg/kg) groups (p > 0.05). Time scale showed a significant decrease in the total number of SWD in the first 20 minutes (P < 0.001) for all groups except dexmedetomidine (0.5-1 mg/kg), and dexmedetomidine/ketamine (50/90 mg/kg) groups (p > 0.05).

CONCLUSION

The anesthetics we used significantly reduced the epileptiform activity immediately after the administration, except dexmedetomidine and dexmedetomidine/ketamine groups, so we recommend using dexmedetomidine and Dexmedetomidine/ketamine in electrophysiological studies accompanied by anesthetics.

Discovery, Structure-Activity Relationships, and In Vivo Evaluation of Novel Aryl Amides as Brain Penetrant Adaptor Protein 2-Associated Kinase 1 (AAK1) Inhibitors for the Treatment of Neuropathic Pain

Effective treatment of chronic pain, in particular neuropathic pain, without the side effects that often accompany currently available treatment options is an area of significant unmet medical need. A phenotypic screen of mouse gene knockouts led to the discovery that adaptor protein 2-associated kinase 1 (AAK1) is a potential therapeutic target for neuropathic pain. The synthesis and optimization of structure-activity relationships of a series of aryl amide-based AAK1 inhibitors led to the identification of 59, a brain penetrant, AAK1-selective inhibitor that proved to be a valuable tool compound. Compound 59 was evaluated in mice for the inhibition of μ2 phosphorylation. Studies conducted with 59 in pain models demonstrated that this compound was efficacious in the phase II formalin model for persistent pain and the chronic-constriction-injury-induced model for neuropathic pain in rats. These results suggest that AAK1 inhibition is a promising approach for the treatment of neuropathic pain.

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

Role of α2-Adrenoceptor Subtypes in Suppression of L-Type Ca2+ Current in Mouse Cardiac Myocytes

Sarcolemmal α2 adrenoceptors (α2-AR), represented by α2A, α2B and α2C isoforms, can safeguard cardiac muscle under sympathoadrenergic surge by governing Ca²⁺ handling and contractility of cardiomyocytes. Cardiomyocyte-specific targeting of α2-AR would provide cardiac muscle-delimited stress control and enhance the efficacy of cardiac malfunction treatments. However, little is known about the specific contribution of the α2-AR subtypes in modulating cardiomyocyte functions. Herein, we analyzed the expression profile of α2A, α2B and α2C subtypes in mouse ventricle and conducted electrophysiological antagonist assay evaluating the contribution of these isoforms to the suppression of L-type Ca²⁺ current (I_CaL). Patch-clamp electro-pharmacological studies revealed that the α2-agonist-induced suppression of I_CaL involves mainly the α2C, to a lesser extent the α2B, and not the α2A isoforms. RT-qPCR evaluation revealed the presence of adra2b and adra2c (α2B and α2C isoform genes, respectively), but was unable to identify the expression of adra2a (α2A isoform gene) in the mouse left ventricle. Immunoblotting confirmed the presence only of the α2B and the α2C proteins in this tissue. The identified α2-AR isoform-linked regulation of I_CaL in the mouse ventricle provides an important molecular substrate for the cardioprotective targeting.

Rapid Recovery and Short Duration Anesthesia after Low Dose Ketamine and High Dose Dexmedetomidine in Rhesus Macaques (Macaca mulatta)

Anesthesia in rhesus macaques is required for many procedures. Although ketamine is the backbone of most anesthetic protocols, tolerance to the drug can develop, resulting in the need for higher doses to provide sufficient restraint. Combination with other drugs, such as α-agonists, can be ketamine-sparing, providing for sufficient restraint at lower ketamine doses. In addition, because α-agonists are reversible, recovery from anesthesia has the potential to be much shorter. We hypothesized that use of a low dose of ketamine with a high dose of dexmedetomidine, an α2 receptor selective agonist, in male and female rhesus macaques less than 15 y of age would provide adequate anesthesia for short procedures and that recovery would be faster than in macaques given a higher dose of ketamine (10 mg/kg) alone. We found that the combination, in conjunction with atipamezole for reversal, provided smooth induction of anesthesia and significantly shorter recovery time than did ketamine alone, with no significant effects of sex. The combination of low dose ketamine and high dose dexmedetomidine also provided a 30-min window of anesthesia with analgesia sufficient for mild to moderately painful procedures.

Tiletamine/zolazepam and dexmedetomidine with tramadol provide effective general anesthesia in rats

Background

Tiletamine/zolazepam is a dissociative anesthetic combination commonly used in small animals but information is limited in rats. The alpha-2 agonist, dexmedetomidine, has gained popularity in laboratory animal anesthesia. Tramadol is a weak opioid mu agonist. The aim of this study was to assess whether the tiletamine/zolazepam/dexmedetomidine (ZD) combination effectively provides a surgical anesthesia plane comparable to tiletamine/zolazepam/dexmedetomidine with tramadol (ZDT) in a minor procedure in rats.

Methods

Rats were induced with ZD or ZDT. After the loss of paw withdrawal, a small incision was made on the rats' left thighs as a surgical stimulus. Rats were maintained under a surgical anesthesia plane by assessing the loss of the paw withdrawal reflex for 45 minutes, then atipamezole was administered. Monitored anesthesia parameters included: (a) physiological parameters - pulse rate (PR), respiratory rate (RR), tissue oxygen saturation (%SpO2), and body temperature; (b) duration parameters - induction time, onset and duration of surgical anesthesia plane, onset of recovery, and recovery time.

Results

PR was significantly lower at 10 minutes in ZD and 5 minutes in ZDT groups. No difference was observed for RR, %SpO2, and body temperature. Likewise, there were no differences for duration parameters: induction time was less than 3 minutes; onset and duration of surgical anesthesia plane were approximately 5 and 45 minutes, respectively; onset of recovery (time to move) was 51 minutes; and recovery time was 52 minutes, respectively.

Conclusion

These data suggest the ZD combination provides a surgical anesthesia plane comparable to ZDT in a rat incisional pain model.

Emerging benefits and drawbacks of α2 -adrenoceptor agonists in the management of sepsis and critical illness

Agonists of α₂ -adrenoceptors are increasingly being used for the provision of comfort, sedation and the management of delirium in critically ill patients, with and without sepsis. In this context, increased sympathetic and inflammatory activity are common pathophysiological features linked to multi-organ dysfunction, particularly in patients with sepsis or those undergoing cardiac surgery requiring cardiopulmonary bypass. Experimental and clinical studies support the notion that the α₂ -adrenoceptor agonists, dexmedetomidine and clonidine, mitigate sympathetic and inflammatory overactivity in sepsis and cardiac surgery requiring cardiopulmonary bypass. These effects can protect vital organs, including the cardiovascular system, kidneys, heart and brain. We review the pharmacodynamic mechanisms by which α₂ -adrenoceptor agonists might mitigate multi-organ dysfunction arising from pathophysiological conditions associated with excessive inflammatory and adrenergic stress in experimental studies. We also outline recent clinical trials that have examined the use of dexmedetomidine in critically ill patients with and without sepsis and in patients undergoing cardiac surgery.

Adrenergic signalling in osteoarthritis

Adrenoceptors (ARs) mediate the effects of the sympathetic neurotransmitters norepinephrine (NE) and epinephrine (E) in the human body and play a central role in physiologic and pathologic processes. Therefore, ARs have long been recognized as targets for therapeutic agents, especially in the field of cardiovascular medicine. During the past decades, the contribution of the sympathetic nervous system (SNS) and particularly of its major peripheral catecholamine NE to the pathogenesis of osteoarthritis (OA) attracted growing interest. OA is the most common degenerative joint disorder worldwide and a disease of the whole joint. It is characterized by progressive degradation of articular cartilage, synovial inflammation, osteophyte formation, and subchondral bone sclerosis mostly resulting in chronic pain. The subchondral bone marrow, the periosteum, the synovium, the vascular meniscus and numerous tendons and ligaments are innervated by tyrosine hydroxylase-positive (TH+) sympathetic nerve fibers that release NE into the synovial fluid and cells of all abovementioned joint tissues express at least one out of nine AR subtypes. During the past decades, several in vitro studies explored the AR-mediated effects of NE on different cell types in the joint. So far, only a few studies used animal OA models to investigate the contribution of distinct AR subtypes to OA pathogenesis in vivo. This narrative review shortly summarizes the current background knowledge about ARs and their signalling pathways at first. In the second part, we focus on recent findings in the field of NE-induced AR-mediated signalling in different joint tissues during OA pathogenesis and at the end, we will delineate the potential of targeting the adrenergic signalling for OA prevention or treatment. We used the PubMed bibliographic database to search for keywords such as 'joint' or 'cartilage' or 'synovium' or 'bone' and 'osteoarthritis' and/or 'trauma' and 'sympathetic nerve fibers' and/or 'norepinephrine' and 'adrenergic receptors / adrenoceptors' as well as 'adrenergic therapy'.

Clinically relevant concentrations of dexmedetomidine may reduce oxytocin-induced myometrium contractions in pregnant rats

BACKGROUND

Recently, there have been some trials to use dexmedetomidine in the obstetric field but concerns regarding the drug include changes in uterine contractions after labor. We aimed to evaluate the effects of dexmedetomidine on the myometrial contractions of pregnant rats.

METHODS

In a pilot study, the contraction of the myometrial strips of pregnant Sprague-Dawley rats in an organ bath with oxytocin at 1 mU/ml was assessed by adding dexmedetomidine from 10-6 to 10-2 M accumulatively every 20 min, and active tension and the number of contractions were evaluated. Then, changes in myometrial contractions were evaluated from high doses of dexmedetomidine (1.0 × 10-4 to 1.2 × 10-3 M). The effective concentrations (EC) for changes in uterine contractions were calculated using a probit model.

RESULTS

Active tension and the number of contractions were significantly decreased at 10-3 M and 10-4 M dexmedetomidine, respectively (P < 0.05). A complete loss of contractions was seen at 10-2 M. Dexmedetomidine (1.0 × 10-4 to 1.2 × 10-3 M) decreased active tension and the number of contractions in a concentration-dependent manner. The EC95 of dexmedetomidine for inhibiting active tension and the number of contractions was 5.16 × 10-2 M and 2.55 × 10-5 M, respectively.

CONCLUSIONS

Active tension of the myometrium showed a significant decrease at concentrations of dexmedetomidine higher than 10-3 M. Thus, clinical concentrations of dexmedetomidine may inhibit uterine contractions. Further research is needed for the safe use of dexmedetomidine in the obstetrics field.

Upregulation of μ-Opioid Receptor in the Rat Spinal Cord Contributes to the α2-Adrenoceptor Agonist Dexmedetomidine-Induced Attenuation of Chronic Morphine Tolerance in Cancer Pain

Background

Sustained morphine treatment for cancer pain has been limited due to analgesic tolerance. Opioid receptor internalization and desensitization mediated by downregulation of mu-opioid receptor (MOR) expression have been confirmed as one of the mechanisms of chronic morphine tolerance. In addition to the opiate system, the α2-adrenergic system is involved in the development of morphine tolerance. Several studies reported that co-administration of α2-adrenoceptor agonist dexmedetomidine inhibits morphine tolerance in normal or neuropathic pain animals. However, the effect of dexmedetomidine on morphine tolerance has not been studied in cancer pain. Therefore, we investigated the effect of intrathecal injection of dexmedetomidine on the development of morphine tolerance in cancer pain and on the expression of MOR in the spinal cord of morphine-tolerant cancer pain rats.

Methods

The model was established using a rat’s right hind paw injection of Walker 256 cancer cells. Subcutaneous morphine (10mg/kg) was administrated twice daily for 7 days; meanwhile, the rats received intrathecal α2-adrenoceptor agonist dexmedetomidine (10μ/kg) or antagonist MK-467 (0.25mg/kg) in test groups. Rats receiving drug vehicle served as the control group. Antinociception was detected by von Frey filaments and hot-plate tests. The expression of MOR in the spinal cord was examined through real-time reverse transcription polymerase chain reaction and Western blotting. The data were analyzed via analysis of variance followed by Student t-test with Bonferroni correction.

Results

Seven-day chronic morphine administration elicited notable analgesic tolerance in the rats with cancer pain. Co-administration of α2-adrenoceptor agonist dexmedetomidine enhanced morphine analgesia and attenuated morphine tolerance, which could be blocked by α2-adrenoceptor antagonist MK-467. Furthermore, pre-treatment of dexmedetomidine significantly upregulated MOR protein expression without a notable change in MOR mRNA expression in the spinal cord.

Conclusion

Our findings suggest that intrathecal injection of dexmedetomidine enhanced morphine analgesia and attenuated morphine tolerance in cancer pain, potentially by upregulating MOR expression in the spinal cord. The α2-adrenoceptor agonist may provide a more versatile analgesia option for morphine treatment for cancer pain.

Regulators of G protein signalling as pharmacological targets for the treatment of neuropathic pain

Neuropathic pain, a specific type of chronic pain resulting from persistent nervous tissue lesions, is a debilitating condition that affects about 7% of the population. This condition remains particularly difficult to treat because of the poor understanding of its underlying mechanisms. Drugs currently used to alleviate this chronic pain syndrome are of limited benefit due to their lack of efficacy and the elevated risk of side effects, especially after a prolonged period of treatment. Although drugs targeting G protein-coupled receptors (GPCR) also have several limitations, such as progressive loss of efficacy due to receptor desensitization or unavoidable side effects due to wide receptor distribution, the identification of several molecular partners that contribute to the fine-tuning of receptor activity has raised new opportunities for the development of alternative therapeutic approaches. Regulators of G protein signalling (RGS) act intracellularly by influencing the coupling process and activity of G proteins, and are amongst the best-characterized physiological modulators of GPCR. Changes in RGS expression have been documented in a range of models of neuropathic pain, or after prolonged treatment with diverse analgesics, and could participate in altered pain processing as well as impaired physiological or pharmacological control of nociceptive signals. The present review summarizes the experimental data that implicates RGS in the development of pain with focus on the pathological mechanisms of neuropathic pain, including the impact of neuropathic lesions on RGS expression and, reciprocally, the influence of modifying RGS on GPCRs involved in the modulation of nociception as well as on the outcome of pain. In this context, we address the question of the relevance of RGS as promising targets in the treatment of neuropathic pain.

Insight into Pain Modulation: Nociceptors Sensitization and Therapeutic Targets

Pain is a complex multidimensional concept that facilitates the initiation of the signaling cascade in response to any noxious stimuli. Action potential generation in the peripheral nociceptor terminal and its transmission through various types of nociceptors corresponding to mechanical, chemical or thermal stimuli lead to the activation of receptors and further neuronal processing produces the sensation of pain. Numerous types of receptors are activated in pain sensation which vary in their signaling pathway. These signaling pathways can be regarded as a site for modulation of pain by targeting the pain transduction molecules to produce analgesia. On the basis of their anatomic location, transient receptor potential ion channels (TRPV1, TRPV2 and TRPM8), Piezo 2, acid-sensing ion channels (ASICs), purinergic (P2X and P2Y), bradykinin (B1 and B2), α-amino-3-hydroxy-5- methylisoxazole-4-propionate (AMPA), N-methyl-D-aspartate (NMDA), metabotropic glutamate (mGlu), neurokinin 1 (NK1) and calcitonin gene-related peptide (CGRP) receptors are activated during pain sensitization. Various inhibitors of TRPV1, TRPV2, TRPM8, Piezo 2, ASICs, P2X, P2Y, B1, B2, AMPA, NMDA, mGlu, NK1 and CGRP receptors have shown high therapeutic value in experimental models of pain. Similarly, local inhibitory regulation by the activation of opioid, adrenergic, serotonergic and cannabinoid receptors has shown analgesic properties by modulating the central and peripheral perception of painful stimuli. This review mainly focused on various classes of nociceptors involved in pain transduction, transmission and modulation, site of action of the nociceptors in modulating pain transmission pathways and the drugs (both clinical and preclinical data, relevant to targets) alleviating the painful stimuli by exploiting nociceptor-specific channels and receptors.

A genome-wide cross-phenotype meta-analysis of the association of blood pressure with migraine

Blood pressure (BP) was inconsistently associated with migraine and the mechanisms of BP-lowering medications in migraine prophylaxis are unknown. Leveraging large-scale summary statistics for migraine (N_cases/N_controls = 59,674/316,078) and BP (N = 757,601), we find positive genetic correlations of migraine with diastolic BP (DBP, r_g = 0.11, P = 3.56 × 10⁻⁰⁶) and systolic BP (SBP, r_g = 0.06, P = 0.01), but not pulse pressure (PP, r_g = −0.01, P = 0.75). Cross-trait meta-analysis reveals 14 shared loci (P ≤ 5 × 10⁻⁰⁸), nine of which replicate (P < 0.05) in the UK Biobank. Five shared loci (ITGB5, SMG6, ADRA2B, ANKDD1B, and KIAA0040) are reinforced in gene-level analysis and highlight potential mechanisms involving vascular development, endothelial function and calcium homeostasis. Mendelian randomization reveals stronger instrumental estimates of DBP (OR [95% CI] = 1.20 [1.15–1.25]/10 mmHg; P = 5.57 × 10⁻²⁵) on migraine than SBP (1.05 [1.03–1.07]/10 mmHg; P = 2.60 × 10⁻⁰⁷) and a corresponding opposite effect for PP (0.92 [0.88–0.95]/10 mmHg; P = 3.65 × 10⁻⁰⁷). These findings support a critical role of DBP in migraine susceptibility and shared biology underlying BP and migraine.

The association between blood pressure (BP) and migraine is poorly understood. Here, the authors explore this relationship using summary-level GWAS data for BP and migraine. Cross-trait meta-analysis reveals shared loci between BP and migraine, while Mendelian randomization suggests that diastolic BP specifically plays a key role in migraine susceptibility.

Dexmedetomidine promotes breast cancer cell migration through Rab11-mediated secretion of exosomal TMPRSS2

Background

Dexmedetomidine (DEX), a highly selective α2-adrenergic receptor agonist, has been reported to increase the malignancy of breast cancer cells in vitro and stimulate tumor growth in mice. Transmembrane protease serine 2 (TMPRSS2) demonstrates proteolytic activity, resulting in degradation of the extracellular matrix (ECM). This study investigated whether and how TMPRSS2 regulates migration of DEX-treated breast cancer cells.

Methods

Breast cancer cell lines MCF-7 and MDA-MB-231 were treated with DEX and scratch assay was performed. Expressions of TMPRSS2, α2-adrenergic receptor, phospho-STAT3^Tyr705, Rab11, and ECM components were assessed using real-time polymerase chain reaction (real-time PCR), Western blotting, and immunofluorescence staining. ELISA and ultracentrifugation were used to quantify secreted exosomal proteins. Knockdown assay was used to inhibit the expression of TMPRSS2 and Rab11.

Results

DEX significantly increased the migration of MCF-7 and MDA-MB-231, which was accompanied by the upregulation and colocalization of TMPRSS2 and α2-adrenergic receptor. Nuclear phospho-STAT3^Tyr705 was increased dramatically following DEX treatment, and TMPRSS2 upregulation was significantly suppressed by the STAT3 inhibitor WP1066. Meanwhile, TMPRSS2 knockdown decreased DEX-induced cellular migration. TMPRSS2 and Rab11 were significantly detected in the media and the isolated exosomes from DEX-treated cells, and their colocalization was also revealed. Rab11 knockdown prevented exosomal TMPRSS2 from increasing in DEX-treated cells. In normal cultured MDA-MB-231, migration was increased by Rab11-positive exosomes isolated from DEX-treated MCF-7. Moreover, transmission electron microscopy showed that Rab11-positive exosomes enriched more components than Rab11-negative exosomes. Additionally, a reduction in ECM components fibronectin, collagen IV, matrix metallopeptidase 16, and Tenascin C was detected after DEX treatment, but was prohibited when TMPRSS2 or Rab11 were knocked down.

Conclusions

This study provides evidence that DEX upregulates TMPRSS2 expression via the activation of α2-adrenergic receptor/STAT3 signaling and promotes TMPRSS2 secretion in exosomes through Rab11, thus resulting in degradation of the ECM, which is responsible for DEX-induced migration of breast cancer cells.

The Results of Preoperative Topical Brimonidine Usage in Pterygium Surgery

Purpose: To evaluate the reduction of conjunctival and episcleral hyperemia and bleeding in pterygium surgery following the use of topical brimonidine preoperatively. Methods: In this study, 45 patients who had undergone pterygium surgery under topical anesthesia were enrolled. Brominidine tartrate 0.15% eye drops were applied topically to 25 eyes of 25 patients at the sixth and third minutes preoperatively, and no drops were applied to 20 eyes of 20 patients for vasoconstriction. Preoperative and postoperative photographs and video images were taken. Results: Vasoconstriction effects of topical brimonidine tartrate on surface vessels were observed. The surface area of blood vessels was reduced 60% within 5 min; this effect was observed with the help of Photoshop and ImageJ programs and it lasted for ∼20 min. The surgery lasts for 7 min, on average, so the conjunctival whitening formed by brimonidine tartrate provides a safe and comfortable operative area throughout the surgery. Conclusion: We recommend applying brimonidine tartrate before pterygium surgery due to its conjunctival whitening effect to provide a safe and comfortable operative area throughout the surgery.

Spinal α2 -adrenoceptors and neuropathic pain modulation; therapeutic target

Neuropathic pain can arise from disease or damage to the nervous system. The most common symptoms of neuropathic pain include spontaneous pain, allodynia, and hyperalgesia. There is still limited knowledge about the factors that initiate and maintain neuropathic pain. However, ample evidence has proved the antinociceptive role of spinal α-adrenoceptors following nerve injury. It is well-documented that noradrenergic descending pathways from supraspinal loci exert an inhibitory influence on the spinal cord nociceptive neurons, mostly through the activation of spinal α₂ -adrenoceptors. This, in turn, suppresses transmission of pain input and the hyperexcitability of spinal dorsal horn neurons. There is considerable evidence demonstrating that spinal application of α₂ -adrenoceptor agonists leads to analgesic effects in animal models of neuropathic pain. Today, despite the recent rapid development of neuroscience and drug discovery, effective drugs with clear basic mechanisms have remained a mystery. Here, we give an overview of the cellular mechanisms through which brainstem adrenergic descending inhibitory processing can alter spinal pain transmission to the higher centres, and how these pathways change in neuropathic pain conditions focusing on the role of spinal α₂ -adrenoceptors in the spinal dorsal horn. We then suggest that α₂ -adrenoceptor agonist may be useful to treat neuropathic pain. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Antinociceptive Effects of the Antidepressant Phenelzine are Mediated by Context-Dependent Inhibition of Neuronal Responses in the Dorsal Horn

The putative strong anti-nociceptive properties of the antidepressant phenelzine (PLZ) have not been widely explored as a treatment for pain. Antinociceptive effects of PLZ were identified in the formalin model of tonic pain (Mifflin et al., 2016) and in allodynia associated with experimental autoimmune encephalomyelitis, (EAE) a mouse model of multiple sclerosis (Potter et al., 2016). Here, we further clarify the specific types of stimuli and contexts in which PLZ modulates nociceptive sensitivity. Our findings indicate that PLZ selectively inhibits ongoing inflammatory pain while sparing transient reflexive and acute nociception. We also investigated the cellular mechanisms of action of PLZ in the dorsal horn, and as expected of a monoamine-oxidase inhibitor, PLZ increased serotonin (5HT) immunoreactivity. We next used two approaches to test the hypothesis that PLZ inhibits the activation of spinal nociresponsive neurons. First, we evaluated the formalin-evoked protein expression of the immediate early gene, c-fos. PLZ reduced Fos expression in the superficial dorsal horn. Second, we evaluated the effects of PLZ on intracellular calcium responses to superfusion of glutamate (0.3-1.0 mM) in an ex vivo lumbar spinal cord slice preparation. Superfusion with PLZ (100-300 μM) reduced 1 mM glutamate-evoked calcium responses. This was blocked by pretreatment with the 5HT1A-receptor antagonist WAY-100,635, but not the alpha-2 adrenergic antagonist idazoxan. We conclude that PLZ exerts antinociceptive effects through a 5-HT/5HT1AR-dependent inhibition of neuronal responses within nociceptive circuits of the dorsal horn.

Synergistic Interaction Between Dexmedetomidine and Ulinastatin Against Vincristine-Induced Neuropathic Pain in Rats

Antimicrotubulin chemotherapeutic agents such as vincristine (VCR), often induce peripheral neuropathic pain. It is usually permanent and seriously harmful to cancer patients' quality of life and can result in the hampering of clinical treatments. Currently, there is no definitive therapy, and many of the drugs approved for the treatment of other neuropathic pain have shown little or no analgesic effect. It is therefore vital to find new and novel therapeutic strategies for patients suffering from chemotherapeutic agent-induced neuropathic pain to improve patients' quality of life. This study shows that intrathecal injections of dexmedetomidine (DEX), or intraperitoneally administered ulinastatin (UTI) significantly reduces Sprague Dawley rats' mechanical allodynia induced by VCR via upregulation of interleukin-10 expression and activating the α2-adrenergic receptor in dorsal root ganglion (DRG). Moreover, when combined there is a synergistic interaction between DEX and UTI, which acts against VCR-induced neuropathic pain. This synergistic interaction between DEX and UTI may be partly attributed to a common analgesic pathway in which the upregulation of interleukin -10 plays an important role via activating α2-adrenergic receptor in rat dorsal root ganglion. The combined use of DEX and UTI does not affect the rat's blood pressure, heart rate, sedation, motor score, spatial learning, or memory function. All of these show that the combined use of DEX and UTI is an effective method in relieving VCR-induced neuropathic pain in rats.

PERSPECTIVE

This article documents the synergistic interaction between 2 widely used drugs, DEX and UTI, against VCR-induced neuropathic pain. The results provide a potential target and novel drug administrated method for the clinical treatment of chemotherapy-induced peripheral neuropathic pain.

The Sedative Effect of Propranolol on Critically Ill Patients: A Case Series

INTRODUCTION

Recent studies have examined the effectiveness of alpha-2 adrenergic agonists for controlling delirium and agitation. Propranolol, a non-selective beta-adrenergic antagonist with good penetration of the blood-brain barrier, has not been investigated for this purpose.

MATERIALS AND METHODS

We retrospectively reviewed the medical records of all patients who were prescribed propranolol in our Medical Surgical ICU from January 1, 2010, to December 31, 2013. We recorded the sedation level and daily dose of sedatives, analgesics, and antipsychotics administered each day for 6 days after starting propranolol, and compared them to the day before starting propranolol.

RESULTS

Sixty-four patients met inclusion criteria. Thirty-eight episodes met exclusion criteria, leaving 27 patients (31 episodes). The administration of propranolol was associated with significant reductions in fentanyl equivalents (65%, p = 0.009), midazolam equivalents (57%, p = 0.048), propofol (16%, p = 0.009), and haloperidol (44%, p = 0.024) on day 2 after starting propranolol compared with baseline. A stratified analysis showed that these decreases were seen regardless of clinical improvement or deterioration.

CONCLUSION

The use of propranolol was associated with a significant reduction in doses of sedatives and analgesia. Further studies are needed to determine whether propranolol may be a useful adjuvant for managing delirium and agitation in the ICU.

Neuroprotection and neurotoxicity in the developing brain: an update on the effects of dexmedetomidine and xenon

Growing and consistent preclinical evidence, combined with early clinical epidemiological observations, suggest potentially neurotoxic effects of commonly used anesthetic agents in the developing brain. This has prompted the FDA to issue a safety warning for all sedatives and anesthetics approved for use in children under three years of age. Recent studies have identified dexmedetomidine, the potent α2-adrenoceptor agonist, and xenon, the noble gas, as effective anesthetic adjuvants that are both less neurotoxic to the developing brain, and also possess neuroprotective properties in neonatal and other settings of acute ongoing neurologic injury. Dexmedetomidine and xenon are effective anesthetic adjuvants that appear to be less neurotoxic than other existing agents and have the potential to be neuroprotective in the neonatal and pediatric settings. Although results from recent clinical trials and case reports have indicated the neuroprotective potential of xenon and dexmedetomidine, additional randomized clinical trials corroborating these studies are necessary. By reviewing both the existing preclinical and clinical evidence on the neuroprotective effects of dexmedetomidine and xenon, we hope to provide insight into the potential clinical efficacy of these agents in the management of pediatric surgical patients.

A Comparative Study of Intravenous Dexmedetomidine and Intravenous Clonidine for Postspinal Shivering in Patients Undergoing Lower Limb Orthopedic Surgeries

Background:

Dexmedetomidine and clonidine have been used for the prevention and treatment of shivering following spinal blockade. A prospective randomized, double-blinded study was conducted to compare the efficacy and safety of dexmedetomidine and clonidine in controlling postspinal shivering.

Methods:

A total of sixty participants of equal sex, aged between 18 and 60 years of American Society of Anesthesiologists (ASA) I/II Class, who underwent orthopedic lower limb surgeries under spinal anesthesia with ≥Grade III shivering were randomly divided into two groups, Group D (n = 30) received injection dexmedetomidine 0.5 μg/kg and Group C (n = 30) received injection clonidine 1 μg/kg when they experienced shivering. Time taken to control shivering, response rate, recurrence rate, and side effects such as nausea, vomiting, dry mouth, respiratory depression, and deep sedation were observed.

Results:

The demographic profile, ASA Class, duration of surgery, duration of anesthesia, temperature, onset and grade of shivering were all comparable between the two groups. Time taken to control shivering and recurrence rate were significantly lower in Group D when compared with Group C. Level of sedation was adequate with Group D, and the incidence of hypotension and bradycardia were significantly higher in Group C. The other side effects profiles were comparable between the two groups.

Conclusion:

Dexmedetomidine 0.5 μg/kg is more efficient than clonidine 1 μg/kg in controlling postspinal blockade shivering. Dexmedetomidine has early onset of effect, high response rate, and less recurrence rate with added advantage of good sedation and stable cardiorespiratory parameters.

Combined Interactions with I1-, I2-Imidazoline Binding Sites and α2-Adrenoceptors To Manage Opioid Addiction

Tolerance and dependence associated with chronic opioid exposure result from molecular, cellular, and neural network adaptations. Such adaptations concern opioid and nonopioid systems, including α2-adrenoceptors (α2-ARs) and I1- and I2-imidazoline binding sites (IBS). Agmatine, one of the hypothesized endogenous ligands of IBS, targeting several systems including α2-ARs and IBS, proved to be able to regulate opioid-induced analgesia and to attenuate the development of tolerance and dependence. Interested in the complex pharmacological profile of agmatine and considering the nature of its targets, we evaluated two series of imidazolines, rationally designed to simultaneously interact with I1-/I2-IBS or I1-/I2-IBS/α2-ARs. The compounds showing the highest affinities for I1-/I2-IBS or I1-/I2-IBS/α2-ARs have been selected for their in vivo evaluation on opiate withdrawal syndrome. Interestingly, 9, displaying I1-/I2-IBS/α2-ARs interaction profile, appears more effective in reducing expression and acquisition of morphine dependence and, therefore, might be considered a promising tool in managing opioid addiction.

Inhibition of AAK1 Kinase as a Novel Therapeutic Approach to Treat Neuropathic Pain

To identify novel targets for neuropathic pain, 3097 mouse knockout lines were tested in acute and persistent pain behavior assays. One of the lines from this screen, which contained a null allele of the adapter protein-2 associated kinase 1 (AAK1) gene, had a normal response in acute pain assays (hot plate, phase I formalin), but a markedly reduced response to persistent pain in phase II formalin. AAK1 knockout mice also failed to develop tactile allodynia following the Chung procedure of spinal nerve ligation (SNL). Based on these findings, potent, small-molecule inhibitors of AAK1 were identified. Studies in mice showed that one such inhibitor, LP-935509, caused a reduced pain response in phase II formalin and reversed fully established pain behavior following the SNL procedure. Further studies showed that the inhibitor also reduced evoked pain responses in the rat chronic constriction injury (CCI) model and the rat streptozotocin model of diabetic peripheral neuropathy. Using a nonbrain-penetrant AAK1 inhibitor and local administration of an AAK1 inhibitor, the relevant pool of AAK1 for antineuropathic action was found to be in the spinal cord. Consistent with these results, AAK1 inhibitors dose-dependently reduced the increased spontaneous neural activity in the spinal cord caused by CCI and blocked the development of windup induced by repeated electrical stimulation of the paw. The mechanism of AAK1 antinociception was further investigated with inhibitors of α2 adrenergic and opioid receptors. These studies showed that α2 adrenergic receptor inhibitors, but not opioid receptor inhibitors, not only prevented AAK1 inhibitor antineuropathic action in behavioral assays, but also blocked the AAK1 inhibitor-induced reduction in spinal neural activity in the rat CCI model. Hence, AAK1 inhibitors are a novel therapeutic approach to neuropathic pain with activity in animal models that is mechanistically linked (behaviorally and electrophysiologically) to α2 adrenergic signaling, a pathway known to be antinociceptive in humans.

Alpha-2A Adrenoceptor Agonist Guanfacine Restores Diuretic Efficiency in Experimental Cirrhotic Ascites: Comparison with Clonidine

BACKGROUND

In human cirrhosis, adrenergic hyperfunction causes proximal tubular fluid retention and contributes to diuretic-resistant ascites, and clonidine, a sympatholytic drug, improves natriuresis in difficult-to-treat ascites.

AIM

To compare clonidine (aspecific α2-adrenoceptor agonist) to SSP-002021R (prodrug of guanfacine, specific α2A-receptor agonist), both associated with diuretics, in experimental cirrhotic ascites.

METHODS AND RESULTS

Six groups of 12 rats were studied: controls (G1); controls receiving furosemide and potassium canrenoate (G2); rats with ascitic cirrhosis due to 14-week CCl4 treatment (G3); cirrhotic rats treated (over the 11th-14th CCl4 weeks) with furosemide and canrenoate (G4), furosemide, canrenoate and clonidine (G5), or diuretics and SSP002021R (G6). Three rats of each group had their hormonal status and renal function assessed at the end of 11th, 12th, 13th, and 14th weeks of respective treatments.Cirrhotic rats in G3 and G4 gained weight over the 12th-14th CCl4 weeks. In G4, brief increase in sodium excretion over the 11th-12th weeks preceded worsening of inulin clearance and natriuresis (diuretic resistance). In comparison with G4, the addition of clonidine (G5) or guanfacine (G6) to diuretics improved, respectively, sodium excretion over the 11th-12th CCl4 weeks, or GFR and electrolytes excretion over the 13th-14th CCl4 weeks. Natriuretic responses in G5 and G6 were accompanied by reduced catecholamine serum levels.

CONCLUSIONS

α2A-receptor agonists restore glomerular filtration rate and natriuresis, and delay diuretic-resistant ascites in experimental advanced cirrhosis. Clonidine ameliorates diuretic-dependent natriuresis just for a short time.

The adrenergic α2-receptor, sexual incentive motivation and copulatory behavior in the male rat

Adrenergic α2 antagonists are known to enhance sexual incentive motivation and modify copulatory behavior while agonists are consistently inhibitory. However, many of the drugs employed in earlier studies were of modest specificity for the α2 receptor, and the importance of the different subtypes of this receptor remains completely unknown. In the present series of experiments we determined the effects on sexual incentive motivation and copulatory behavior of additional, highly specific compounds, as well as of agonists selective for each of the three subtypes of the α2 receptor. Sexual incentive motivation and copulatory behavior were evaluated in male rats in well established procedures. Among the α2 antagonists, RX 821002 reliably enhanced sexual incentive motivation while fluparoxan only had a modest effect. In large doses both drugs reduced copulatory behavior. The agonist S 18616 reduced both incentive motivation and copulation. None of the subtype selective agonists (BRL 44408, ARC 239, JP 1302) had any consistent effect. A peripheral α2 antagonist, L 659,066 was also ineffective. Even though there are some differences between α2 antagonists with regard to their effects on sexual incentive motivation and copulatory behavior it seems safe to conclude that antagonism of the adrenergic α2 receptor enhances motivation without any concomitant stimulation of copulatory behavior. It appears that antagonism of a single receptor subtype is insufficient for having this effect. Perhaps non-selective α2 antagonists could be used for the treatment of male sexual dysfunction.

Noradrenaline-mediated facilitation of inhibitory synaptic transmission in the dorsal horn of the rat spinal cord involves interlaminar communications

In the dorsal horn of the spinal cord (DH), noradrenaline (NA) is released by axons originating from the locus coeruleus and induces spinal analgesia, the mechanisms of which are poorly understood. Here, the effects of NA on synaptic transmission in the deep laminae (III-V) of the DH were characterized. It was shown that exogenously applied, as well as endogenously released, NA facilitated inhibitory [γ-aminobutyric acid (GABA)ergic and glycinergic] synaptic transmission in laminae III-IV of the DH by activating α1-, α2- and β-adrenoceptors (ARs). In contrast, NA had no effect on excitatory (glutamatergic) synaptic transmission. Physical interruption of communications between deep and more superficial laminae (by a mechanical transection between laminae IV and V) totally blocked the effects of α2-AR agonists and strongly reduced the effects of α1-AR agonists on inhibitory synaptic transmission in laminae III-IV without directly impairing synaptic release of GABA or glycine from neurons. Short-term pretreatment of intact spinal cord slices with the glial cell metabolism inhibitor fluorocitrate or pharmacological blockade of ionotropic glutamate and ATP receptors mimicked the consequences of a mechanical transection between laminae IV and V. Taken together, the current results indicate that the facilitation of inhibitory synaptic transmission in laminae III-IV of the DH by NA requires functional interlaminar connections between deep and more superficial laminae, and might strongly depend on glia to neuron interactions. These interlaminar connections and glia to neuron interactions could represent interesting targets for analgesic strategies.

Dual allosteric modulation of opioid antinociceptive potency by α2A-adrenoceptors

Opioid and α2-adrenoceptor (AR) agonists are analgesic when administered in the spinal cord and show a clinically beneficial synergistic interaction when co-administered. However, α2-AR antagonists can also inhibit opioid antinociception, suggesting a complex interaction between the two systems. The α2A-AR subtype is necessary for spinal adrenergic analgesia and synergy with opioids for most agonist combinations. Therefore, we investigated whether spinal opioid antinociception and opioid-adrenergic synergy were under allosteric control of the α2A-AR. Drugs were administered intrathecally in wild type (WT) and α2A-knock-out (KO) mice and antinociception was measured using the hot water tail immersion or substance P behavioral assays. The α2A-AR agonist clonidine was less effective in α2A-KO mice in both assays. The absence of the α2A-AR resulted in 10-70-fold increases in the antinociceptive potency of the opioid agonists morphine and DeltII. In contrast, neither morphine nor DeltII synergized with clonidine in α2A-KO mice, indicating that the α2AAR has both positive and negative modulatory effects on opioid antinociception. Depletion of descending adrenergic terminals with 6-OHDA resulted in a significant decrease in morphine efficacy in WT but not in α2A-KO mice, suggesting that endogenous norepinephrine acts through the α2A-AR to facilitate morphine antinociception. Based on these findings, we propose a model whereby ligand-occupied versus ligand-free α2A-AR produce distinct patterns of modulation of opioid receptor activation. In this model, agonist-occupied α2A-ARs potentiate opioid analgesia, while non-occupied α2A-ARs inhibit opioid analgesia. Exploiting such interactions between the two receptors could lead to the development of better pharmacological treatments for pain management.

Investigation of allyphenyline efficacy in the treatment of alcohol withdrawal symptoms

We have recently demonstrated that allyphenyline, behaving as α2C-adrenoceptor/serotonin 5-HT1A receptor agonist and α2A-adrenoceptor antagonist, in mice enhanced morphine analgesia, attenuated morphine withdrawal symptoms, showed significant antidepressant-like activity and was devoid of sedative side effects. Opioid and alcohol withdrawal shares several common neurobiological and molecular mechanisms. Therefore, in this study we expanded our analysis of the pharmacological properties of allyphenyline by investigating its ability to prevent the expression of somatic withdrawal signs, anxiety-like behavior and hyperlocomotion associated with chronic ethanol intoxication. Rats were subjected to induction of ethanol dependence via repeated daily intragastric ethanol (20%) administration for 4 consecutive days. Twelve hours after the last alcohol administration, somatic alcohol withdrawal signs were scored. Results revealed a significant expression of physical withdrawal signs that were not affected by intraperitoneal (i.p.) administration of allyphenyline at the doses of 0.05, 0.275 and 0.5 mg/kg. In contrast, allyphenyline (0.05 and 0.275 mg/kg i.p.) significantly reduced hyperanxiety-like behavior observed 6 days after alcohol intoxication as measured using the defensive burying test. Allyphenyline also reduced open field hyperlocomotor activity associated with alcohol withdrawal. Notably, the anxiolytic effect of the compound, as well as the already reported antidepressant action, was observed at very low doses, suggesting the involvement of its α2C-adrenoceptor/serotonin 5-HT1A receptor agonism. Therefore, the present investigation suggests that allyphenyline might represent an interesting pharmacological tool to investigate the potential of compounds exhibiting α2C-adrenoceptor/serotonin 5-HT1A receptor agonism and α2A-adrenoceptor antagonism in the treatment of hyperanxiety and hyperlocomotion occurring during alcohol withdrawal in dependent subjects.

Antagonism/Agonism modulation to build novel antihypertensives selectively triggering i1-imidazoline receptor activation

Pharmacological studies have suggested that I1-imidazoline receptors are involved in the regulation of cardiovascular function and that selective I1-agonists, devoid of the side effects associated with the common hypotensive α2-adrenoreceptor agonists, might be considered as a second generation of centrally acting antihypertensives. Therefore, in the present study, inspired by the antihypertensive behavior of our selective I1-agonist 4, we designed, prepared, and studied the novel analogues 5-9. A selective I1-profile, associated with significant hemodinamic effects, was displayed by 5, 8, and 9. Interestingly, the highest potency and longest lasting activity displayed by 8 (carbomethyline) suggested that van der Waals interactions, promoted by the ortho methyl decoration of its aromatic moiety, are particularly advantageous. In addition, in analogy to what was noted for (S)-(+)-4, the observation that only (S)-(+)-8 displayed significant hemodynamic effects unequivocally confirmed the stereospecific nature of the I1 proteins.

Current role of dexmedetomidine in clinical anesthesia and intensive care

Dexmedetomidine is a new generation highly selective α2-adrenergic receptor (α2-AR) agonist that is associated with sedative and analgesic sparing effects, reduced delirium and agitation, perioperative sympatholysis, cardiovascular stabilizing effects, and preservation of respiratory function. The aim of this review is to present the most recent topics regarding the advantages in using dexmedetomidine in clinical anesthesia and intensive care, while discussing the controversial issues of its harmful effects.

Effectiveness of dexmedetomidine for emergence agitation in infants undergoing palatoplasty: a randomized controlled trial

OBJECTIVES

In infants, there is a high incidence of emergence agitation (EA) after sevoflurane (Sev) anesthesia. This study aimed to test the hypothesis that dexmedetomidine (Dex) administration would reduce the incidence and severity of EA after Sev-based anesthesia in infants undergoing palatoplasty.

METHODS

A prospective randomized clinical trial was conducted with 70 patients undergoing palatoplasty, aged 10-14 months. Infants were randomly allocated into two groups: Dex (n=35) and saline (n=35). In the Dex group, Dex (6 μg/kg/h) was administered approximately 10 min before the end of the surgery for 10 min, followed by 0.4 μg/kg/h until 5 min after extubation. In the saline group, an equivalent amount of saline was administered in a similar manner. After the surgery, patients were transferred to the postanesthetic care unit (PACU). The infant's behavior and pain were assessed with scoring system for EA (5-point rating scale) and pain scale (PS; 10-point rating scale), respectively. EA and PS were estimated at six time points (after extubation, leaving the operating room, 0, 30, 60, and 120 min after arrival in PACU).

RESULTS

EA and PS scores were significantly lower in the Dex group than in the saline group from extubation to 120 min after arrival in PACU.

CONCLUSIONS

Dex administration has the advantage of a reduced EA and PS without any adverse effects. Dex provided satisfactory recovery in infants undergoing palatoplasty.

Neurobiological studies of chronic pain and analgesia: Rationale and refinements

Chronic pain is a complex condition for which the need for specialized research and therapies has been recognized internationally. This review summarizes the context for the international call for expansion of pain research to improve our understanding of the mechanisms underlying pain in order to achieve improvements in pain management. The methods for conducting sensory assessment in animal models are discussed and the development of animal models of chronic pain is specifically reviewed, with an emphasis on ongoing refinements to more closely mimic a variety of human pain conditions. Pharmacological correspondences between pre-clinical pain models and the human clinical experience are noted. A discussion of the 3Rs Framework (Replacement, Reduction, Refinement) and how each may be considered in pain research is featured. Finally, suggestions are provided for engaging principal investigators, IACUC reviewers, and institutions in the development of strong partnerships to simultaneously expand our knowledge of the mechanisms underlying pain and analgesia while ensuring the humane use of animals in research.

Analgesia, enhancement of spinal morphine antinociception, and inhibition of tolerance by ultra-low dose of the α2A-adrenoceptor selective antagonist BRL44408

Ultra-low doses of non-selective α2-adrenoceptor antagonists augment acute spinal morphine antinociception and block morphine tolerance; however, the receptor involved in mediating these effects is currently unknown. Here, we used tail flick and paw pressure tests on the rat to investigate the acute analgesic and tolerance-inducing effects of spinal morphine and norepinephrine alone or in combination with an ultra-low dose of the α2A-adrenoceptor antagonist, BRL44408. We also assessed the potential antinociceptive effects of BRL44408 alone following spinal administration. A spinal dose of BRL44408, over 1000-fold lower than that required to inhibit clonidine-induced antinociception (1.65ng/10µL), significantly prolonged morphine and norepinephrine action in both nociception tests. Following repeated morphine or norepinephrine injections, 1.65ng BRL44408 attenuated both the decline of antinociceptive effect and increase in morphine ED50 values, responses indicative of acute morphine tolerance. BRL44408 administered alone produced a delayed antinociceptive effect unrelated to repeated nociceptive testing. This response was partially reduced by the α2-adrenoceptor antagonist atipamezole (10µg). Ultra-low dose BRL44408 was able to inhibit the loss of morphine- and norepinephrine-induced antinociceptive response, and prevent the loss of drug potency due to repeated agonist exposure. This implicates the spinal α2A-adrenoceptor subtype in the action of ultra-low dose α2-adrenoceptor antagonists on morphine and norepinephrine tolerance. The BRL44408-induced analgesia is partially dependent on its interaction with the α2-adrenoceptors. Thus, this agent class may be useful in pain therapy.

Does dexmedetomidine as a neuraxial adjuvant facilitate better anesthesia and analgesia? A systematic review and meta-analysis

Background

Neuraxial application of dexmedetomidine (DEX) as adjuvant analgesic has been invetigated in some randomized controlled trials (RCTs) but not been approved because of the inconsistency of efficacy and safety in these RCTs. We performed this meta-analysis to access the efficacy and safety of neuraxial DEX as local anaesthetic (LA) adjuvant.

Methods

We searched PubMed, PsycINFO, Scopus, EMBASE, and CENTRAL databases from inception to June 2013 for RCTs that investigated the analgesia efficacy and safety for neuraxial application DEX as LA adjuvant. Effects were summarized using standardized mean differences (SMDs), weighed mean differences (WMDs) or odds ratio (OR) with suitable effect model. The primary outcomes were postoperative pain intensity and analgesic duration, bradycardia and hypotension.

Results

Sixteen RCTs involving 1092 participants were included. Neuraxial DEX significantly decreased postoperative pain intensity (SMD, −1.29; 95% confidence interval (CI), −1.70 to −0.89; P<0.00001), prolonged analgesic duration (WMD, 6.93 hours; 95% CI, 5.23 to 8.62; P<0.00001) and increased the risk of bradycardia (OR, 2.68; 95% CI, 1.18 to 6.10; P = 0.02). No evidence showed that neuraxial DEX increased the risk of other adverse events, such as hypotension (OR, 1.54; 95% CI, 0.83 to 2.85; P = 0.17). Additionally, neuraxial DEX was associated with beneficial alterations in postoperative sedation scores and number of analgesic requirements, sensory and motor block characteristics, and intro-operative hemodynamics.

Conclusion

Neuraxial DEX is a favorable LA adjuvant with better and longer analgesia. The greatest concern is bradycardia. Further large sample trials with strict design and focusing on long-term outcomes are needed.

Activation of a Gq-coupled membrane estrogen receptor rapidly attenuates α2-adrenoceptor-induced antinociception via an ERK I/II-dependent, non-genomic mechanism in the female rat

Though sex differences in pain and analgesia are known, underlying mechanisms remain elusive. This study addresses the selective contribution of membrane estrogen receptors (mERs) and mER-initiated non-genomic signaling mechanisms in our previously reported estrogen-induced attenuation of α2-adrenoceptor-mediated antinociception. By selectively targeting spinal mERs in ovariectomized female rats using β-estradiol 6-(O-carboxy-methyl)oxime bovine serum albumin (E2BSA) (membrane impermeant estradiol analog), and ERα selective agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), ERβ selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), G-protein-coupled estrogen receptor 30 (GPR30) agonist G1 and Gq-coupled mER (Gq-mER) agonist STX, we provide strong evidence that Gq-mER activation may solely contribute to suppressing clonidine (an α2-adrenoceptor agonist)-induced antinociception, using the nociceptive tail-flick test. Increased tail-flick latencies (TFLs) by intrathecal (i.t.) clonidine were not significantly altered by i.t. PPT, DPN, or G1. In contrast, E2BSA or STX rapidly and dose-dependently attenuated clonidine-induced increase in TFL. ICI 182,780, the ER antagonist, blocked this effect. Consistent with findings with the lack of effect of ERα and ERβ agonists that modulate receptor-regulated transcription, inhibition of de novo protein synthesis using anisomycin also failed to alter the effect of E2BSA or STX, arguing against a contribution of genomic mechanisms. Immunoblotting of spinal tissue revealed that mER activation increased levels of phosphorylated extracellular signal-regulated kinase (ERK) but not of protein kinase A (PKA) or C (PKC). In vivo inhibition of ERK with U0126 blocked the effect of STX and restored clonidine antinociception. Although estrogen-induced delayed genomic mechanisms may still exist, data presented here indicate that Gq-mER may solely mediate estradiol-induced attenuation of clonidine antinociception via a rapid, reversible, and ERK-dependent, non-genomic mechanism, suggesting that Gq-mER blockade might provide improved analgesia in females.

New therapeutic uses for an alpha2 adrenergic receptor agonist--dexmedetomidine in pain management

Dexmedetomidine was initially approved for clinical use as a sedative. Its development in pain management has been limited. Dexmedetomidine has analgesic effects and analgesic-sparing properties, especially for patients with obstructed airways. Mixing dexmedetomidine with local anesthetics is a promising new avenue to enhance local anesthetics' effectiveness. Peripheral, spinal and supraspinal α(2A)-ARs are responsible for the analgesic function of dexmedetomidine. Animal studies have shown that antinociceptive synergism results from co-application of dexmedetomidine and opioids or local anesthetics. Dexmedetomidine has potential adverse effects such as hypotension and bradycardia. Therefore, dexmedetomidine is contraindicated for patients suffering from bradycardia or using β-adrenergic antagonists. Clinical trials of dexmedetomidine in chronic pain or hyperalgesia are lack.

Dexmedetomidine: an adjuvant making large inroads into clinical practice

The introduction of newer more selective α(-2) adrenergic agonist, dexmedetomidine has made a revolution in the field of anesthesia owing to its varied application. The aim of the current review is to highlight the various clinical and pharmacological aspects of dexmedetomidine in daily routine practice of anesthesiology and intensive care besides its potential role in other clinical specialties. This review of dexmedetomidine was carried out after searching the medical literature in Pubmed, Science direct, Scopus, Google scholar and various text books and journal articles using keywords anesthesia, dexmedetomidine, neurosurgery, pediatric surgery, regional dexmedetomidine, anesthesia, regional, neurosurgery, and pediatric surgery. Dexmedetomidine has made its application from a novel sedating agent in the intensive care unit to its use as an adjuvant in various regional anesthetic techniques because of its "cooperative sedation" without any respiratory depression. It has a favorable pharmacokinetic profile suitable to be used in the perioperative period to reduce the requirements of opioids and anesthetic drugs. There are few side-effects of dexmedetomidine, which should always be kept in mind before choosing the patients for its use. The various side-effects associated with dexmedetomidine include, but are not limited to hypotension, bradycardia, worsening of heart block, dry mouth, and nausea. However, large scale randomized controlled trials are still needed to establish various effects of dexmedetomidine and to clearly define its safety profile.

Exploring multitarget interactions to reduce opiate withdrawal syndrome and psychiatric comorbidity

Opioid addiction is often characterized as a chronic relapsing condition due to the severe somatic and behavioral signs, associated with depressive disorders, triggered by opiate withdrawal. Since prolonged abstinence remains a major challenge, our interest has been addressed to such objective. Exploring multitarget interactions, the present investigation suggests that 3 or its (S)-enantiomer and 4, endowed with effective α2C-AR agonism/α2A-AR antagonism/5-HT1A-R agonism, or 7 and 9-11 producing efficacious α2C-AR agonism/α2A-AR antagonism/I2-IBS interaction might represent novel multifunctional tools potentially useful for reducing withdrawal syndrome and associated depression. Such agents, lacking in sedative side effects due to their α2A-AR antagonism, might afford an improvement over current therapies with clonidine-like drugs.