LC-derived excitatory synaptic transmission to dorsal raphe serotonin neurons is inhibited by activation of alpha2-adrenergic receptors.

In the central nervous system, noradrenaline transmission controls the degree to which we are awake, alert, and attentive. Aberrant noradrenaline transmission is associated with pathological forms of hyper- and hypo-arousal that present in numerous neuropsychiatric disorders often associated with dysfunction in serotonin transmission. In vivo, noradrenaline regulates the release of serotonin because noradrenergic input drives the serotonin neurons to fire action potentials via activation of excitatory α1-adrenergic receptors (α1-AR). Despite the critical influence of noradrenaline on the activity of dorsal raphe serotonin neurons, the source of noradrenergic afferents has not been resolved and the presynaptic mechanisms that regulate noradrenaline-dependent synaptic transmission have not been described. Using an acute brain slice preparation from male and female mice and electrophysiological recordings from dorsal raphe serotonin neurons, we found that selective optogenetic activation of locus coeruleus terminals in the dorsal raphe was sufficient to produce an α1-AR-mediated excitatory postsynaptic current (α1-AR-EPSC). Activation of inhibitory α2-adrenergic receptors (α2-AR) with UK-14,304 eliminated the α1-AR-EPSC via presynaptic inhibition of noradrenaline release, likely via inhibition of voltage-gated calcium channels. In a subset of serotonin neurons, activation of postsynaptic α2-AR produced an outward current through activation of GIRK potassium conductance. Further, in vivo activation of α2-AR by systemic administration of clonidine reduced the expression of c-fos in the dorsal raphe serotonin neurons, indicating reduced neural activity. Thus, α2-AR are critical regulators of serotonin neuron excitability.

The effects of dexmedetomidine on intraoperative neurophysiologic monitoring modalities during corrective scoliosis surgery in pediatric patients: A systematic review.

BACKGROUND: During scoliosis surgery, motor evoked potentials (MEP), and somatosensory evoked potentials (SSEP) have been reported to be affected by the use of higher doses of anesthetic agents. Dexmedetomidine, a sympatholytic agent, an alpha-2 receptor agonist, has been used as an adjunctive agent to lower anesthetic dose. However, there is conflicting evidence regarding the effects of dexmedetomidine on the intraoperative neurophysiological monitoring of MEP and SSEP during surgery, particularly among pediatric patients. OBJECTIVES: This systematic review aimed to determine whether, during spinal fusion surgery in pediatric patients with scoliosis, dexmedetomidine alters MEP amplitude or SSEP latency and amplitude and, if so, whether different doses of dexmedetomidine display different effects (PROSPERO registration number CRD42022300562). METHODS: We searched PubMed, Scopus, and Cochrane Library on January 1, 2022 and included randomized controlled trials, observational cohort and case-control studies and case series investigating dexmedetomidine in the population of interest and comparing against a standardized anesthesia regimen without dexmedetomidine or comparing multiple doses of dexmedetomidine. Animal and in vitro studies and conference abstracts were excluded. RESULTS: We found substantial heterogeneity in the risk of bias (per Cochrane-preferred tools) of the included articles (n = 5); results are summarized without meta-analysis. Articles with the lowest risk of bias indicated that dexmedetomidine was associated with MEP loss and that higher doses of dexmedetomidine increased risk. In contrast, articles reporting no association between dexmedetomidine and MEP loss suffered from higher risk of bias, including suspected or confirmed problems with confounding, outcome measurement, participant selection, results reporting, and lack of statistical transparency and power. CONCLUSION: Given the limitations of the studies available in the literature, it would be advisable to conduct rigorous randomized controlled trials with larger sample sizes to assess the effects of dexmedetomidine use of in scoliosis surgery in pediatric patients.

Effect of constant rate infusion of detomidine with and without vatinoxan on blood glucose and insulin concentrations in horses.

OBJECTIVE: To assess the effects of an α2-adrenoceptor agonist (detomidine) constant rate infusion (CRI) with and without an α2-adrenoceptor antagonist (vatinoxan) CRI on blood insulin and glucose concentrations, heart rate, intestinal borborygmi, and sedation during and after infusion in horses. STUDY DESIGN: Randomized, blinded, crossover, experimental study. ANIMALS: A total of nine healthy, adult Finnhorse mares. METHODS: Horses were treated with an intravenous (IV) detomidine loading dose (0.01 mg kg-1), followed by CRI (0.015 mg kg-1 hour-1), and the same doses of detomidine combined with an IV vatinoxan loading dose (0.15 mg kg-1), followed by CRI (detomidine and vatinoxan; 0.05 mg kg-1 hour-1) with an 18 day washout period. Infusion time was 60 minutes and horses were monitored for 240 minutes after the infusion. Heart rate, borborygmi score and sedation were assessed, and blood glucose, insulin and triglyceride concentrations were measured. Data were analyzed using repeated measures ancova and Wilcoxon signed-rank tests. Values of p < 0.05 were considered statistically significant. RESULTS: Insulin concentration decreased during (median nadir 1.7, range 0.0-2.9 µIU mL-1 at 60 minutes, p < 0.0001) and increased after detomidine CRI (median 36.6, range 11.7-78.4 µIU mL-1 at 180 minutes, p = 0.0001) significantly compared with detomidine and vatinoxan CRI. A significant elevation of blood glucose (peak 11.5 ± 1.6 mmol L-1 at 60 minutes, p < 0.0001) was detected during detomidine CRI. Vatinoxan alleviated the insulin changes and abolished the significant increase in blood glucose. Vatinoxan alleviated the decrease in heart rate (p = 0.0001) during detomidine infusion. No significant differences were detected in sedation scores between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Vatinoxan attenuated the negative adverse effects of detomidine CRI and thus is potentially beneficial when used in combination with an α2-adrenoceptor agonist CRI in horses.

Dexmedetomidine modulates neuronal activity of horizontal limbs of diagonal band via α2 adrenergic receptor in mice.

BACKGROUND AND OBJECTIVES: Dexmedetomidine (DEX) is widely used in clinical sedation which has little effect on cardiopulmonary inhibition, however the mechanism remains to be elucidated. The basal forebrain (BF) is a key nucleus that controls sleep-wake cycle. The horizontal limbs of diagonal bundle (HDB) is one subregions of the BF. The purpose of this study was to examine whether the possible mechanism of DEX is through the α2 adrenergic receptor of BF (HDB). METHODS: In this study, we investigated the effects of DEX on the BF (HDB) by using whole cell patch clamp recordings. The threshold stimulus intensity, the inter-spike-intervals (ISIs) and the frequency of action potential firing in the BF (HDB) neurons were recorded by application of DEX (2 µM) and co-application of a α2 adrenergic receptor antagonist phentolamine (PHEN) (10 µM). RESULTS: DEX (2 µM) increased the threshold stimulus intensity, inhibited the frequency of action potential firing and enlarged the inter-spike-interval (ISI) in the BF (HDB) neurons. These effects were reversed by co-application of PHEN (10 µM). CONCLUSION: Taken together, our findings revealed DEX decreased the discharge activity of BF (HDB) neuron via α2 adrenergic receptors.

Effects of Intravenous Dexmedetomidine on Hemodynamic Responses to Pneumoperitoneum During Laparoscopic Cholecystectomy.

BACKGROUND: Dexmedetomidine is a potent α_2 agonist which has been used for blunting the stress responses during critical events such as laryngoscopy, endotracheal intubation, pneumoperitoneum creation, and extubation. The purpose of this study was to see the efficacy of intravenously administered dexmedetomidine at a dose of 0.5 mcg/kg in attenuating the hemodynamic responses due to pneumoperitoneum during laparoscopic cholecystectomy under general anesthesia. METHODS: Sixty patients, ASA-PS class I (American Society of Anesthesiologist physical status class I), aged between 18 and 60 years, of either sex with weight ranging from 50 to 80 kg, scheduled for laparoscopic cholecystectomy were randomized into two groups (groups A and B) in a double-blinded fashion. Both groups were pre-medicated with an injection glycopyrrolate. Group A received 100 mL normal saline (NS) over 10 minutes while group B received dexmedetomidine 0.5 mcg/kg diluted in 100 mL NS over 10 minutes before induction of general anesthesia. Heart rate, systolic, diastolic, and mean arterial pressures were noted. RESULTS: Following pneumoperitoneum, there was no statistically significant difference in the hemodynamic parameters between the two groups (P > 0.05). CONCLUSION: Administration of dexmedetomidine at a dose of 0.5 mcg/kg before induction did not blunt the hemodynamic responses to pneumoperitoneum during laparoscopic cholecystectomy.

Dexmedetomidine attenuates sleep deprivation-induced inhibition of hippocampal neurogenesis via VEGF-VEGFR2 signaling and inhibits neuroinflammation.

Long periods of sleep deprivation (SD) have serious effects on health. While the α2 adrenoceptor agonist dexmedetomidine (DEX) can improve sleep quality for patients who have insomnia, the effect of DEX on cognition and mechanisms after SD remains elusive. C57BL/6 mice were subjected to 20 h SD daily for seven days. DEX (100 µg/kg) was administered intravenously twice daily (at 1:00 p.m. and 3:00 p.m.) during seven days of SD. We found that systemic administration of DEX attenuated cognitive deficits by performing the Y maze and novel object recognition tests and increased DCX+, SOX2+, Ki67+, and BrdU+NeuN+/NeuN+ cell numbers in the dentate gyrus (DG) region of SD mice by using immunofluorescence, western blotting, and BrdU staining. DEX did not reverse the decrease in DCX+, SOX2+, or Ki67+ cell numbers in SD mice after administration of the α2A-adrenoceptor antagonist BRL-44408. Furthermore, the vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (VEGFR2) expression was upregulated in SD+DEX mice compared with SD mice. Luminex analysis showed that the neurogenic effects of DEX were possibly related to the inhibition of neuroinflammation, including IL-1α, IL-2, CCL5, and CXCL1. Our results suggested that DEX alleviated the impaired learning and memory of SD mice potentially by inducing hippocampal neurogenesis via the VEGF-VEGFR2 signaling pathway and by suppressing neuroinflammation, and α2A adrenoceptors are required for the neurogenic effects of DEX after SD. This novel mechanism may add to our knowledge of DEX in the clinical treatment of impaired memory caused by SD.

Tumour immune rejection triggered by activation of α2-adrenergic receptors.

Immunotherapy based on immunecheckpoint blockade (ICB) using antibodies induces rejection of tumours and brings clinical benefit in patients with various cancer types1. However, tumours often resist immune rejection. Ongoing efforts trying to increase tumour response rates are based on combinations of ICB with compounds that aim to reduce immunosuppression in the tumour microenvironment but usually have little effect when used as monotherapies2,3. Here we show that agonists of α2-adrenergic receptors (α2-AR) have very strong anti-tumour activity when used as monotherapies in multiple immunocompetent tumour models, including ICB-resistant models, but not in immunodeficient models. We also observed marked effects in human tumour xenografts implanted in mice reconstituted with human lymphocytes. The anti-tumour effects of α2-AR agonists were reverted by α2-AR antagonists, and were absent in Adra2a-knockout (encoding α2a-AR) mice, demonstrating on-target action exerted on host cells, not tumour cells. Tumours from treated mice contained increased infiltrating T lymphocytes and reduced myeloid suppressor cells, which were more apoptotic. Single-cell RNA-sequencing analysis revealed upregulation of innate and adaptive immune response pathways in macrophages and T cells. To exert their anti-tumour effects, α2-AR agonists required CD4+ T lymphocytes, CD8+ T lymphocytes and macrophages. Reconstitution studies in Adra2a-knockout mice indicated that the agonists acted directly on macrophages, increasing their ability to stimulate T lymphocytes. Our results indicate that α2-AR agonists, some of which are available clinically, could substantially improve the clinical efficacy of cancer immunotherapy.

Dexmedetomidine alleviates oxidative stress and mitochondrial dysfunction in diabetic peripheral neuropathy via the microRNA-34a/SIRT2/S1PR1 axis.

OBJECTIVE: Dexmedetomidine (Dex) is a highly selective α2-adrenoceptor agonist with sedative, analgesic, sympatholytic, and hemodynamic-stabilizing properties, which plays a neuroprotective role in diabetic peripheral neuropathy (DPN) and diabetes-induced nerve damage. However, the related molecular mechanisms are not fully understood. Therefore, our study explored the mechanism of Dex in DPN using rat and RSC96 cell models. METHODS: Sciatic nerve sections were observed under an optical microscope and the ultrastructure of the sciatic nerves was observed under a transmission electron microscope. Oxidative stress was assessed by detecting MDA, SOD, GSH-Px, and ROS levels. The motor nerve conduction velocity (MNCV), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) of rats were measured. Cell viability, apoptosis, and the changes in the expression of related genes and proteins were examined. Furthermore, the relationship between microRNA (miR)-34a and SIRT2 or SIRT2 and S1PR1 was analyzed. RESULTS: Dex reversed DPN-induced decreases in MNCV, MWT, and TWL. Dex alleviated oxidative stress, mitochondrial damage, and apoptosis in both the rat and RSC96 cell models of DPN. Mechanistically, miR-34a negatively targeted SIRT2, and SIRT2 inhibited S1PR1 transcription. The overexpression of miR-34a or S1PR1 or the inhibition of SIRT2 counteracted the neuroprotective effects of Dex in DPN in vivo and in vitro. CONCLUSION: Dex alleviates oxidative stress and mitochondrial dysfunction associated with DPN by downregulating miR-34a to regulate the SIRT2/S1PR1 axis.

Radioprotective effects of α2-adrenergic receptor agonist dexmedetomidine on X-ray irradiation-induced pancreatic islet cell damage.

Comprehensive epidemiological analyses conducted in the last 30 years have revealed a link between radiation and DM. We aimed to determine the effects of dexmedetomidine pretreatment on radiation-induced pancreatic islet cell damage. Twenty-four rats were divided into three groups: group 1 (control group), group 2 (only X-ray irradiation group), and group 3 (X-ray irradiation + dexmedetomidine). We observed necrotic cells with vacuoles accompanying loss of cytoplasm in the islets of Langerhans, extensive edematous areas, and vascular congestions in group 2. In group 3, we observed a decrease in necrotic cells in the islets of Langerhans, and edematous areas and vascular congestion was also reduced. We determined a decrease in ß-cells, α-cells, and D-cells in the islets of Langerhans in group 2 compared to the control group. In group 3, ß-cells, α-cells, and D-cells were elevated compared to group 2. Ionizing radiation may induce DM. Dexmedetomidine appears to exert a radioprotective effect.

Rapid emergence from dexmedetomidine sedation in Sprague Dawley rats by repurposing an α2-adrenergic receptor competitive antagonist in combination with caffeine.

BACKGROUND: The α2 adrenergic receptor agonist dexmedetomidine is an important intravenous sedative with analgesic properties. Currently available dexmedetomidine reversal agents, like the α2-receptor antagonist atipamezole, cause serious adverse effects at the large dosages required for effective reversal; they are not used clinically. Without reversal agents, emergence times from dexmedetomidine sedation are slow. In this study we tested the ability of low-dose atipamezole, in combination with caffeine, to reverse dexmedetomidine sedation. The low dose of atipamezole employed should not be associated with unwanted effects. METHODS: Two different sedation protocols were employed. In the first protocol, a bolus of dexmedetomidine was rapidly applied and the drug was allowed to equilibrate for 10 min before rats received either saline (as control) or low-dose atipamezole with caffeine. Following this procedure, rats were placed on their backs. Emergence from sedation was the time for rats to recover their righting reflex and stand with 4 paws on the floor. A second sedation protocol simulated a pediatric magnetic resonance imaging (MRI) scan. Adult rats were sedated with dexmedetomidine for one hour followed by 30 min with both dexmedetomidine and propofol. At the end of 90 min, rats received either saline (control) or a combination of low-dose atipamezole, and caffeine. Recovery of the righting reflex was used as a proxy for emergence from sedation. RESULTS: Emergence from sedation, the time for rats to recover their righting reflex, decreased by ~ 90% when using an atipamezole dose ~ 20 fold lower than manufacturer's recommendation, supplemented with caffeine. Using an atipamezole dose ~ tenfold lower than recommended, with caffeine, emergence times decreased by ~ 97%. A different stimulant, forskolin, when tested, was as effective as caffeine. For the MRI simulation, emergence times were decreased by ~ 93% by low-dose atipamezole with caffeine. CONCLUSIONS: Low dose atipamezole with caffeine was effective at reversing dexmedetomidine sedation. Emergence was rapid and the rats regained not only their righting reflex but also their balance and their ability to carry out complex behaviors. These findings suggest that the combination of low dose atipamezole with caffeine may permit rapid clinical reversal of dexmedetomidine without unwanted effects.

Electrophysiological and Clinical Predictors of Methylphenidate, Guanfacine, and Combined Treatment Outcomes in Children With Attention-Deficit/Hyperactivity Disorder.

OBJECTIVE: The combination of d-methylphenidate and guanfacine (an α-2A agonist) has emerged as a potential alternative to either monotherapy in children with attention-deficit/hyperactivity disorder (ADHD), but it is unclear what predicts response to these treatments. This study is the first to investigate pretreatment clinical and electroencephalography (EEG) profiles as predictors of treatment outcome in children randomized to these different medications. METHOD: A total of 181 children with ADHD (aged 7-14 years; 123 boys) completed an 8-week randomized, double-blind, comparative study with d-methylphenidate, guanfacine, or combined treatments. Pretreatment assessments included ratings on ADHD, anxiety, and oppositional behavior. EEG activity from cortical sources localized within midfrontal and midoccipital regions was measured during a spatial working memory task with encoding, maintenance, and retrieval phases. Analyses tested whether pretreatment clinical and EEG measures predicted treatment-related change in ADHD severity. RESULTS: Higher pretreatment hyperactivity-impulsivity and oppositional symptoms and lower anxiety predicted greater ADHD improvements across all medication groups. Pretreatment event-related midfrontal beta power predicted treatment outcome with combined and monotherapy treatments, albeit in different directions. Weaker beta modulations predicted improvements with combined treatment, whereas stronger modulation during encoding and retrieval predicted improvements with d-methylphenidate and guanfacine, respectively. A multivariate model including EEG and clinical measures explained twice as much variance in ADHD improvement with guanfacine and combined treatment (R2= 0.34-0.41) as clinical measures alone (R2 = 0.14-.21). CONCLUSION: We identified treatment-specific and shared predictors of response to different pharmacotherapies in children with ADHD. If replicated, these findings would suggest that aggregating information from clinical and brain measures may aid personalized treatment decisions in ADHD. CLINICAL TRIAL REGISTRATION INFORMATION: Single Versus Combination Medication Treatment for Children With Attention Deficit Hyperactivity Disorder; https://clinicaltrials.gov; NCT00429273.

Effects of dexmedetomidine on oxygenation and inflammatory factors in patients undergoing uvulopalatopharyngoplasty: a prospective, randomized, placebo-controlled trial.

PURPOSE: Uvulopalatopharyngoplasty (UPPP) can aggravate lung inflammatory reactions in patients with obstructive sleep apnoea syndrome (OSAS). Dexmedetomidine (Dex) is a selective α-2 adrenoreceptor agonist that can alleviate lung injury. This study was designed to investigate the effects of Dex on oxygenation and inflammatory factors in patients undergoing UPPP in the early perioperative period. METHODS: Patients with OSAS undergoing UPPP were randomly allocated to the Dex Group or Control Group. Arterial blood gas analyses were performed, and the respiratory index (RI) and oxygenation index (OI) were calculated upon entering the operating room (T0) and immediately after surgery (T3). The inflammatory factors tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-10 (IL-10) were measured at T0 and T3. RESULTS: A total of 44 patients with OSAS were randomized. There was no significant difference in basic patient characteristics between the two groups. The preoperative RI and OI were not significantly different between the two groups, but they were altered immediately after surgery relative to the corresponding preoperative value (p < 0.05). Compared with the Control Group, the RI was significantly lower at T3 in the Dex Group (p < 0.001). However, there was no significant difference in the OI between the two groups (p = 0.128). The inflammatory factors TNF-α (p < 0.001) and IL-6 (p = 0.018) were lower, while IL-10 was higher in the Dex Group than in the Control Group (p < 0.001). CONCLUSION: Dexmedetomidine can improve the oxygenation and inhibit the inflammatory response in patients undergoing UPPP in the early perioperative period. TRIAL REGISTRATION: The present clinical study has been registered at Clinical Trials under number NCT03612440.

Dexmedetomidine Alters the Inflammatory Profile of Rat Microglia In Vitro.

BACKGROUND: Microglia are a primary mediator of the neuroinflammatory response to neurologic injury, such as that in traumatic brain injury. Their response includes changes to their cytokine expression, metabolic profile, and immunophenotype. Dexmedetomidine (DEX) is an α2 adrenergic agonist used as a sedative in critically ill patients, such as those with traumatic brain injury. Given its pharmacologic properties, DEX may alter the phenotype of inflammatory microglia. METHODS: Primary microglia were isolated from Sprague-Dawley rats and cultured. Microglia were activated using multiple mediators: lipopolysaccharide (LPS), polyinosinic-polycytidylic acid (Poly I:C), and traumatic brain injury damage-associated molecular patterns (DAMP) from a rat that sustained a prior controlled cortical impact injury. After activation, cultures were treated with DEX. At the 24-h interval, the cell supernatant and cells were collected for the following studies: cytokine expression (tumor necrosis factor-α [TNFα], interleukin-10 [IL-10]) via enzyme-linked immunosorbent assay, 6-phosphofructokinase enzyme activity assay, and immunophenotype profiling with flow cytometry. Cytokine expression and metabolic enzyme activity data were analyzed using two-way analysis of variance. Cell surface marker expression was analyzed using FlowJo software. RESULTS: In LPS-treated cultures, DEX treatment decreased the expression of TNFα from microglia (mean difference = 121.5 ± 15.96 pg/mL; p < 0.0001). Overall, DEX-treated cultures had a lower expression of IL-10 than nontreated cultures (mean difference = 39.33 ± 14.50 pg/mL, p < 0.0001). DEX decreased IL-10 expression in LPS-stimulated microglia (mean difference = 74.93 ± 12.50 pg/mL, p = 0.0039) and Poly I:C-stimulated microglia (mean difference = 23.27 ± 6.405 pg/mL, p = 0.0221). In DAMP-stimulated microglia, DEX decreased the activity of 6-phosphofructokinase (mean difference = 18.79 ± 6.508 units/mL; p = 0.0421). The microglial immunophenotype was altered to varying degrees with different inflammatory stimuli and DEX treatment. CONCLUSIONS: DEX may alter the neuroinflammatory response of microglia. By altering the microglial profile, DEX may affect the progression of neurologic injury.

Dexmedetomidine in Psychiatry: Repurposing of its Fast-Acting Anxiolytic, Analgesic and Sleep Modulating Properties.

Drug repurposing is a strategy to identify new indications for already approved drugs. A recent successful example in psychiatry is ketamine, an anesthetic drug developed in the 1960s, now approved and clinically used as a fast-acting antidepressant. Here, we describe the potential of dexmedetomidine as a psychopharmacological repurposing candidate. This α2-adrenoceptor agonist is approved in the US and Europe for procedural sedation in intensive care. It has shown fast-acting inhibitory effects on perioperative stress-related pathologies, including psychomotor agitation, hyperalgesia, and neuroinflammatory overdrive, proving potentially useful in clinical psychiatry. We offer an overview of the pharmacological profile and effects of dexmedetomidine with potential utility for the treatment of neuropsychiatric symptoms. Dexmedetomidine exerts fast-acting and robust sedation, anxiolytic, analgesic, sleep-modulating, and anti-inflammatory effects. Moreover, the drug prevents postoperative agitation and delirium, possibly via neuroprotective mechanisms. While evidence in animals and humans supports these properties, larger controlled trials in clinical samples are generally scarce, and systematic studies with psychiatric patients do not exist. In conclusion, dexmedetomidine is a promising candidate for an experimental treatment targeting stress-related pathologies common in neuropsychiatric disorders such as depression, anxiety disorders, and posttraumatic stress disorder. First small proof-of-concept studies and then larger controlled clinical trials are warranted in psychiatric populations to test the feasibility and efficacy of dexmedetomidine in these conditions.

Features of α2-Adrenergic Regulation of Isolated Rat Heart after Hypokinesia.

We studied the effect of the α2-adrenergic receptor agonist clonidine hydrochloride (10-9-10-6 M) on the isolated heart of adult rats after 30-day restriction of motor activity. In hypokinetic rats, in comparison with control animals, clonidine caused a positive inotropic effect; the dynamics of coronary flow was changed after stimulation of α2-adrenergic receptors by clonidine in the minimum and maximum concentrations. Moreover, clonidine in concentrations of 10-8 and 10-7 M reduced coronary flow both in the control group and against the background of hypokinesia. Clonidine (10-8-10-6 M) had a negative chronotropic effect in control and hypokinetic animals, while the dynamics of HR was multidirectional, i.e. either an increase or decrease in the effects was observed depending of the agonist concentration. Overall, the data obtained indicate the participation of α2-adrenergic receptors in adaptive processes after motor activity limitation.

Dexmedetomidine Promotes Angiogenesis and Vasculogenic Mimicry in Human Hepatocellular Carcinoma through α 2-AR/HIF-1α/VEGFA Pathway.

Objective: Dexmedetomidine (DEX), the most specific α 2-adrenergic receptor agonist widely used for its sedative and analgesic properties, has been reported to upregulate HIF-1α expression to protect hypoxic and ischemic tissues. However, it is largely unclear whether DEX can also upregulate Hypoxia-inducible factor-1 alpha (HIF-1α) expression and its downstream vascular endothelial growth factor-A (VEGFA) in cancer tissues with oxygen-deficient tumor microenvironment. Methods: We used SMMC-7721 cells, MHCC97-H cells, and a mouse model of orthotopic hepatic carcinoma to explore the effect of DEX on angiogenesis and vasculogenic mimicry (VM) and its mechanism. Under normoxic (20% O 2) and hypoxic (1% O 2) conditions, DEX was used to intervene cells, and yohimbine was used to rescue them. Results: The results showed that DEX promoted angiogenesis and VM in human liver cancer cells within a certain dose range, and the addition of yohimbine inhibited this effect. DEX could activate HIF-1α/VEGFA pathway, which was further verified by silencing HIF-1α. Consistently, in vivo results also showed that DEX can up-regulate HIF-1α/VEGFA expression, and enhance the number of VM channels and microvessel density (MVD). Conclusion: We believe that HIF-1α/VEGFA might be an important signaling pathway by which DEX promotes angiogenesis and VM formation in human hepatocellular carcinoma, whereas α 2-adrenergic receptor mediation might be the critical mechanisms.

DEXMEDETOMIDINE PREVENTS PDIA3 DECREASE BY ACTIVATING α2-ADRENERGIC RECEPTOR TO ALLEVIATE INTESTINAL I/R IN MICE.

ABSTRACT: Background: Dexmedetomidine (DEX) attenuates intestinal I/R injury, but its mechanism of action remains to be further elucidated. Protein disulfide isomerase A3 (PDIA3) has been reported as a therapeutic protein for the prevention and treatment of intestinal I/R injury. This study was to investigate whether PDIA3 is involved in intestinal protection of DEX and explore the underlying mechanisms. Methods: The potential involvement of PDIA3 in DEX attenuation of intestinal I/R injury was tested in PDIA3 Flox/Flox mice and PDIA3 conditional knockout (cKO) in intestinal epithelium mice subjected to 45 min of superior mesenteric artery occlusion followed by 4 h of reperfusion. Furthermore, the α2-adrenergic receptor (α2-AR) antagonist, yohimbine, was administered in wild-type C57BL/6N mice intestinal I/R model to investigate the role of α2-AR in the intestinal protection conferred by DEX. Results: In the present study, we identified intestinal I/R-induced obvious inflammation, endoplasmic reticulum (ER) stress-dependent apoptosis, and oxidative stress, and all the aforementioned changes were improved by the administration of DEX. PDIA3 cKO in the intestinal epithelium have reversed the protective effects of DEX. Moreover, yohimbine also reversed the intestinal protection of DEX and downregulated the messenger RNA and protein levels of PDIA3. Conclusion: DEX prevents PDIA3 decrease by activating α2-AR to inhibit intestinal I/R-induced inflammation, ER stress-dependent apoptosis, and oxidative stress in mice.

Structure-based discovery of nonopioid analgesics acting through the α2A-adrenergic receptor.

Because nonopioid analgesics are much sought after, we computationally docked more than 301 million virtual molecules against a validated pain target, the α2A-adrenergic receptor (α2AAR), seeking new α2AAR agonists chemotypes that lack the sedation conferred by known α2AAR drugs, such as dexmedetomidine. We identified 17 ligands with potencies as low as 12 nanomolar, many with partial agonism and preferential Gi and Go signaling. Experimental structures of α2AAR complexed with two of these agonists confirmed the docking predictions and templated further optimization. Several compounds, including the initial docking hit '9087 [mean effective concentration (EC50) of 52 nanomolar] and two analogs, '7075 and PS75 (EC50 4.1 and 4.8 nanomolar), exerted on-target analgesic activity in multiple in vivo pain models without sedation. These newly discovered agonists are interesting as therapeutic leads that lack the liabilities of opioids and the sedation of dexmedetomidine.

[Dexmedetomidine improves alcohol withdrawal symptom via activating α2 adrenergic receptor in rat hippocampus].

The purpose of this study was to investigate the effects of α2 adrenergic receptor agonist dexmedetomidine on withdrawal symptoms in alcohol-dependent rats and the underlying mechanism, so as to provide a scientific basis for the treatment of alcohol withdrawal syndrome (AWS). Adult Sprague-Dawley (SD) male rats were orally administered with 6% aqueous alcohol continuously for 28 d to establish alcohol drinking model, and then stopped drinking to induce AWS. Enzyme-linked immunosorbent assay (ELISA) was used to determine the content of norepinephrine (NE) in the locus coeruleus and hippocampus of rats. Dexmedetomidine (5, 10, and 20 µg/kg) was intraperitoneally injected respectively when the rats showed significant AWS. In some rats, α2 adrenergic receptor antagonist yohimbine was injected into hippocampus in advance. The results showed that, compared with the control group, the 6 h withdrawal group exhibited significantly increased AWS score and amount of repeat drinking. The NE contents in hippocampus and locus coeruleus of the last drinking and the 6 h withdrawal groups were significantly increased compared with those of the control group. Dexmedetomidine intervention significantly decreased AWS score and hippocampus NE content in the 6 h withdrawal group, while yohimbine could reverse these effects of dexmedetomidine. These results suggest that dexmedetomidine might improve the withdrawal symptoms in alcohol-dependent rats via activating α2 adrenergic receptor.

The Role of Dexmedetomidine in Tumor-Progressive Factors in the Perioperative Period and Cancer Recurrence: A Narrative Review.

Dexmedetomidine, a specific α2 adrenergic receptor agonist, is highly frequently used in the perioperatively for its favorable pharmacology, such as mitigating postoperative cognitive dysfunction. Increasing attention has been recently focused on the effect of whether dexmedetomidine influences cancer recurrence, which urges the discussion of the role of dexmedetomidine in tumor-progressive factors. The pharmacologic characteristics of dexmedetomidine, the tumor-progressive factors in the perioperative period, and the relationships between dexmedetomidine and tumor-progressive factors were described in this review. Available evidence suggests that dexmedetomidine could reduce the degree of immune function suppression, such as keeping the number of CD3+ cells, NK cells, CD4+/CD8+ ratio, and Th1/Th2 ratio stable and decreasing the level of proinflammatory cytokine (interleukin 6 and tumor necrosis factor-alpha) during cancer operations. However, dexmedetomidine exhibits different roles in cell biological behavior depending on cancer cell types. The conclusions on whether dexmedetomidine would influence cancer recurrence could not be currently drawn for the lack of strong clinical evidence. Therefore, this is still a new area that needs further exploration.