Involvement of protein kinase B/Akt in analgesic effect of dexmedetomidine on neuropathic pain

An Investigation of the Molecular Mechanisms Underlying the Analgesic Effect of Jakyak-Gamcho Decoction: A Network Pharmacology Study

Herbal drugs have drawn substantial interest as effective analgesic agents; however, their therapeutic mechanisms remain to be fully understood. To address this question, we performed a network pharmacology study to explore the system-level mechanisms that underlie the analgesic activity of Jakyak-Gamcho decoction (JGd; Shaoyao-Gancao-Tang in Chinese and Shakuyaku-Kanzo-To in Japanese), an herbal prescription consisting of Paeonia lactiflora Pallas and Glycyrrhiza uralensis Fischer. Based on comprehensive information regarding the pharmacological and chemical properties of the herbal constituents of JGd, we identified 57 active chemical compounds and their 70 pain-associated targets. The JGd targets were determined to be involved in the regulation of diverse biological activities as follows: calcium- and cytokine-mediated signalings, calcium ion concentration and homeostasis, cellular behaviors of muscle and neuronal cells, inflammatory response, and response to chemical, cytokine, drug, and oxidative stress. The targets were further enriched in various pain-associated signalings, including the PI3K-Akt, estrogen, ErbB, neurotrophin, neuroactive ligand-receptor interaction, HIF-1, serotonergic synapse, JAK-STAT, and cAMP pathways. Thus, these data provide a systematic basis to understand the molecular mechanisms underlying the analgesic activity of herbal drugs.

Role of Spinal Cord Akt-mTOR Signaling Pathways in Postoperative Hyperalgesia Induced by Plantar Incision in Mice

Poor postoperative pain (POP) control increases perioperative morbidity, prolongs hospitalization days, and causes chronic pain. However, the specific mechanism(s) underlying POP is unclear and the identification of optimal perioperative treatment remains elusive. Akt and mammalian target of rapamycin (mTOR) are expressed in the spinal cord, dorsal root ganglion, and sensory axons. In this study, we explored the role of Akt and mTOR in pain-related behaviors induced by plantar incision in mice. Plantar incision activated spinal Akt and mTOR in a dose-dependent manner. Pre-treatment with Akt inhibitors intrathecally prevented the activation of mTOR dose-dependently. In addition, blocking the Akt-mTOR signaling cascade attenuated pain-related behaviors and spinal Fos protein expression induced by plantar incision. Our observations demonstrate that Akt-mTOR might be a potential therapeutic target for the treatment of POP.

Effects of Caudal Epidural Dexmedetomidine on Pain, Erythrocyte Sedimentation Rate and Quality of Life in Patients with Failed Back Surgery Syndrome; A Randomized Clinical Trial

Objective

To evaluate the effects of dexmedetomidine in caudal epidural on controlling pain, erythrocyte sedimentation rate (ESR) and quality of life in patients with failed back surgery syndrome (FBSS).

Methods

The study was a single-blind clinical trial. From the total of 70 patients suffering from low back pain caused by a failed back surgery syndrome were referred to Akhtar and Imam Hossein Hospitals between the ages of 25 to 75 years with a history of back pain more than 12 weeks and a visual analogue scale (VAS) score of higher than 3, and 50 people were randomly selected and divided into two groups of dexmedetomidine and control. The control group received an epidural dose of 10 cc containing triamcinolone and bupivacaine, and the dexmedetomidine group received an epidural dose of 10 cc, containing dexmedetomidine, triamcinolones and bupivacaine with diluted normal saline. Epidural caudal injections were performed in the abdomen in a laid down position. Before starting the study and at the end of the fourth week, the two test groups were measured for visual analogue scale (VAS) and ESR and were asked to complete the quality of life questionnaire.

Results

Overall, 50 patients with FBSS were enrolled. The mean age was 53.88 ± 8.9 years (range 25-75); 54% (27/50) were men. The results showed that the injection of dexmedetomidine in epidural caudal was associated with decreased pain (p=0.001) and improved quality of life (p=0.022), while showed no significant effect on ESR (p=0.110).

Conclusion

Administration of dexmedetomidine in the epidural caudal is effective in controlling pain and quality of life in patients with failed back surgery syndrome.

Dexmedetomidine Attenuates Neuropathic Pain by Inhibiting P2X7R Expression and ERK Phosphorylation in Rats

α2-Adrenoceptor agonists attenuate hypersensitivity under neuropathic conditions. However, the mechanisms underlying this attenuation remain largely unknown. In the present study, we explored the potential roles of purinergic receptor 7 (P2X7R)/extracellular signal-regulated kinase (ERK) signaling in the anti-nociceptive effect of dexmedetomidine in a rat model of neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve. An animal model of CCI was adopted to mimic the clinical neuropathic pain state. Behavioral hypersensitivity to mechanical and thermal stimuli was determined by von Frey filament and Hargreaves' tests, and the spinal P2X7R expression level and ERK phosphorylation were analyzed using western blot analysis and immunohistochemistry. In parallel with the development of mechanical and thermal hyperalgesia, a significant increase in P2X7R expression was noted in the ipsilateral spinal cord on day 7 after CCI. Intrathecal administration of dexmedetomidine (2.5 µg) for 3 days not only attenuated neuropathic pain but also inhibited the CCI-induced P2X7R upregulation and ERK phosphorylation. Intrathecal dexmedetomidine administration did not produce obvious effects on locomotor function. The present study demonstrated that dexmedetomidine attenuates the neuropathic pain induced by CCI of the sciatic nerve in rats by inhibiting spinal P2X7R expression and ERK phosphorylation, indicating the potential therapeutic implications of dexmedetomidine administration for the treatment of neuropathic pain.

The Effect of Dexmedetomidine on Lumbar Epidural Injection for Failed Back Surgery Syndrome

Purpose. Failed back surgery syndrome is a chronic pain condition requiring rapid, effective, and efficient management. This study evaluates the effect of adding dexmedetomidine to lumbar epidural steroids in patients with failed back surgery syndrome. Methods. Fifty patients suffering from failed back surgery syndrome were randomly assigned to one of two groups, receiving an epidural injection of 20 mL of either a mixture of betamethasone (14 mg) and bupivacaine 0.5 mg (group C) or a mixture of betamethasone (14 mg), bupivacaine 0.5 mg, and dexmedetomidine (0.5 μg/kg) (group D) adjusted to the volume with normal saline. The effect was evaluated using visual analogue scale (VAS), analgesic requirement, and Oswestry disability index 2 weeks, 4 weeks, 8 weeks, and 12 weeks after injection. Results. VAS and ibuprofen consumption showed a significant reduction in group D. The Oswestry disability index was significantly improved in group D. There were no records of hypotension, bradycardia, sedation, or hypoxemia in both groups. Conclusion. The present study demonstrated potential safe and effective usage of adding dexmedetomidine to epidural steroid to control pain in patients with failed back surgery syndrome.

Inhibiting spinal neuron-astrocytic activation correlates with synergistic analgesia of dexmedetomidine and ropivacaine

Background

This study aims to identify that intrathecal (i.t.) injection of dexmedetomidine (Dex) and ropivacaine (Ropi) induces synergistic analgesia on chronic inflammatory pain and is accompanied with corresponding “neuron-astrocytic” alterations.

Methods

Male, adult Sprague-Dawley rats were randomly divided into sham, control and i.t. medication groups. The analgesia profiles of i.t. Dex, Ropi, and their combination detected by Hargreaves heat test were investigated on the subcutaneous (s.c.) injection of complete Freund adjuvant (CFA) induced chronic pain in rat and their synergistic analgesia was confirmed by using isobolographic analysis. During consecutive daily administration, pain behavior was daily recorded, and immunohistochemical staining was applied to investigate the number of Fos-immunoreactive (Fos-ir) neurons on hour 2 and day 1, 3 and 7, and the expression of glial fibrillary acidic protein (GFAP) within the spinal dorsal horn (SDH) on day 1, 3, 5 and 7 after s.c. injection of CFA, respectively, and then Western blot to examine spinal GFAP and β-actin levels on day 3 and 7.

Results

i.t. Dex or Ropi displayed a short-term analgesia in a dose-dependent manner, and consecutive daily administrations of their combination showed synergistic analgesia and remarkably down-regulated neuronal and astrocytic activations indicated by decreases in the number of Fos-ir neurons and the GFAP expression within the SDH, respectively.

Conclusion

i.t. co-delivery of Dex and Ropi shows synergistic analgesia on the chronic inflammatory pain, in which spinal “neuron-astrocytic activation” mechanism may play an important role.

Effects of intravenous and intrathecal dexmedetomidine in spinal anesthesia: a meta-analysis

PURPOSE

To assess the effects of dexmedetomidine on the duration of sensory and motor block, postoperative analgesia, hypotension, bradycardia, and side effects in patients undergoing spinal anesthesia.

METHODS

Two researchers searched MEDLINE, EMBASE, and the Cochrane controlled trial register independently for randomized controlled trials comparing dexmedetomidine with a placebo without any language restrictions.

RESULTS

A total of 412 patients from eight trials were included in this study. The results revealed that dexmedetomidine was statistically significant in prolonging the duration of sensory block (mean difference, MD = 73.55; 95% CI, [55.69, 91.40] P < 0.00001, I(2)  = 89%) and motor block (MD = 59.11; 95% CI, [29.58, 88.65] P < 0.00001, I(2)  = 91%) and the time to first request for postoperative analgesia (MD = 245.77, 95% CI, [143.53, 348.00] P < 0.00001, I(2)  = 98%). The occurrence of hypotension (OR = 0.60, 95% CI, [0.3-1.23], P = 0.40, I(2)  = 3%) and side effects (OR = 0.9, 95% CI, [0.36-2.22], P = 0.88, I(2)  = 0%) was not significantly different between dexmedetomidine and placebo. However, dexmedetomidine was associated with more frequent bradycardia requiring atropine (OR = 7.55; 95% CI, [2.76-20.63], P = 0.63, I(2)  = 0%).

CONCLUSIONS

This meta-analysis has shown that dexmedetomidine prolonged the duration of spinal anesthesia and improved postoperative analgesia and did not increase the incidence of hypotension and adverse events, but needs more atropine to reverse bradycardia.