Effect of dexmedetomidine on brain edema and neurological outcomes in surgical brain injury in rats

Protective effect of dexmedetomidine against delayed bone healing caused by morphine via PI3K/Akt mediated Nrf2 antioxidant defense system

Background

As a class of analgesics, opioids are frequently used to treat both acute and chronic moderate to severe pain. Patients frequently receive opioid painkillers after orthopedic accidents or surgeries. Evidence suggests that opioid drug users have a 55.1% higher risk of fracture and poor bone repair than non-users of opioid drugs. The key pathogenic alterations in the incidence and progression of poor bone repair are over apoptosis and aging of osteoblasts due to the stress caused by oxidation. Dexmedetomidine (Dex) has been proven to protect against a variety of degenerative illnesses by reducing oxidative stress. However, nothing is known about how it affects bone repair.

Methods

PI3K/Akt/Nrf2 pathway was detected by immunofluorescence and Western blot. SOD, CAT, JC-1, dihydroethidium and mitosox were used in the Oxidative Stress. Micro-CT, H&E and Masson's staining, immunohistochemically were performed to evaluate the therapeutic effects of DEX on calvarial defects in the morphine-induced rat model.

Results

We found that morphine-induced an imbalance in the metabolism and catabolism of primary rat Osteoblasts. However, these conditions could be inhibited by DEX treatment. In the meantime, DEX induced the expression of Nrf2-regulated antioxidant enzymes such as NQO1, HO-1, GCLm, GCLc, and TrxR1. DEX-mediated Nrf2 activation is linked to the PI3K/Akt signaling system. Furthermore, it has been established that intravenous DEX enhanced the growth of bone healing in a model of a surgically produced rat cranial lesion.

Conclusion

This is the first description of the unique DEX mechanism acting as a Nrf2 activator against morphine-mediated oxidative harm, raising the possibility that the substance may be used to prevent bone defects.

Dexmedetomidine Ameliorated Cognitive Dysfunction Induced by Intestinal Ischemia Reperfusion in Mice with Possible Relation to the Anti-inflammatory Effect Through the Locus Coeruleus Norepinephrine System

Cognitive impairment is a common central nervous system complication that occurs following surgery or organs damage outside the nervous system. Neuroinflammation plays a key role in the molecular mechanisms of cognitive impairment. Dexmedetomidine alleviates neuroinflammation and reduces cognitive dysfunction incidence; however, the mechanism by which dexmedetomidine alleviates cognitive dysfunction remains unclear. This study evaluated the effect of dexmedetomidine on attenuation of early cognitive impairment induced by intestinal ischemia–reperfusion in mice and examined whether the locus coeruleus norepinephrine (LCNE) system participates in the anti-inflammatory effect of dexmedetomidine. The superior mesenteric artery was clamped for 45 min to induce intestinal ischemia reperfusion injury. Dexmedetomidine alone or combined with DSP-4, a selective locus coeruleus noradrenergic neurotoxin, was used for pretreatment. Postoperative cognition was assessed using the Morris water maze. Serum and hippocampal levels of IL-1β, TNF-α, norepinephrine (NE), and malondialdehyde (MDA) were assessed by enzyme-linked immunosorbent assay. Immunofluorescence, immunohistochemistry, and hematoxylin and eosin staining were used to evaluate the expression of tyrosine hydroxylase (TH) in the locus coeruleus, hippocampal microglia, and intestinal injury. Pretreatment with dexmedetomidine alleviated intestinal injury and decreased the serum and hippocampal levels of NE, IL-1β, TNF-α, and MDA at 24 h after intestinal ischemia reperfusion, decreased TH-positive neurons in the locus coeruleus, and ameliorated cognitive impairment. Similarly, DSP-4 pre-treatment alleviated neuroinflammation and improved cognitive function. Furthermore, α2-adrenergic receptor antagonist atipamezole or yohimbine administration diminished the neuroprotective effects and improved cognitive function with dexmedetomidine. Therefore, dexmedetomidine attenuated early cognitive dysfunction induced by intestinal ischemia–reperfusion injury in mice, which may be related to its anti-inflammatory effects through the LCNE system.

The glymphatic system and subarachnoid hemorrhage: disruption and recovery

The glymphatic system, or glial-lymphatic system, is a waste clearance system composed of perivascular channels formed by astrocytes that mediate the clearance of proteins and metabolites from the brain. These channels facilitate the movement of cerebrospinal fluid throughout brain parenchyma and are critical for homeostasis. Disruption of the glymphatic system leads to an accumulation of these waste products as well as increased interstitial fluid in the brain. These phenomena are also seen during and after subarachnoid hemorrhages (SAH), contributing to the brain damage seen after rupture of a major blood vessel. Herein this review provides an overview of the glymphatic system, its disruption during SAH, and its function in recovery following SAH. The review also outlines drugs which target the glymphatic system and may have therapeutic applications following SAH.

MiR-665 Participates in the Protective Effect of Dexmedetomidine in Ischemic Stroke by ROCK2/NF-κB Axis

Ischemic stroke is a grievous intimidation to the healthiness of sufferers. Previous studies have reported that dexmedetomidine (DEX) has a protective effect on a variety of organs. This paper aimed to explore the regulatory mechanism of DEX in ischemic stroke through miR-665/ROCK2 axis. The mice model of ischemic stroke was constructed by middle cerebral artery occlusion (MCAO). The cell model of ischemic stroke was constructed by oxygen-glucose deprivation (OGD). Cell viability and apoptosis were assessed by CCK-8 assay and flow cytometry. The expression of cytokines was detected by ELISA. Lactate dehydrogenase (LDH) concentration was evaluated by LDH kit. The cerebral infarct volume of MCAO mice was detected by TTC staining, and the apoptosis of brain cells was detected by TUNEL staining. The target relationship between ROCK2 and miR-665 was analyzed by dual-luciferase reporter assay. DEX contributed cell viability from 42 to 66% (1 μM) and restrained cell apoptosis from 26 to 18% in HT22 cells treated with OGD (P < 0.01). Meanwhile, DEX decreased the expression of cytokines and LDH concentration from 184 to 126% (P < 0.001). Moreover, the expression of miR-665 enhanced 2.9 times (P < 0.05) and the expression of ROCK2 (P < 0.05) and NF-κB p65 (P < 0.01) reduced 1.8 times and 2.2 times after DEX treatment in OGD induced HT22. And miR-665 knockdown attenuated the effect of DEX on inflammation damage (the levels of TNF-α, IL-1β and IL-6 increased 1.36 times, 1.31 times, 1.43 time, respectively, and IL-10 decreased 1.68 times) and apoptosis from 17 to 25% (P < 0.01). MiR-665 directly targeted ROCK2 and regulated ROCK2 and NF-κB p65 expression (P < 0.01). Furthermore, ROCK2 overexpression inhibited the protective effect of DEX in HT22 induced by OGD (P < 0.001), while miR-665 overexpression reversed the regulatory of ROCK2 (P < 0.01). In vivo, DEX decreased cerebral infarction volume and inhibited apoptosis of brain cell (P < 0.001). DEX has a protective effect in ischemic stroke by promoting miR-665 expression to downregulate ROCK2/NF-κB axis, suggesting DEX has a beneficial effect on ischemic stroke and miR-665 is a conceivable target for the therapeutics and diagnosis of ischemic stroke.

Dexmedetomidine attenuates haemorrhage-induced thalamic pain by inhibiting the TLR4/NF-κB/ERK1/2 pathway in mice

BACKGROUND

Thalamic pain, a neuropathic pain syndrome, frequently occurs after stroke. This research aimed to investigate the effect of dexmedetomidine (DEX) on thalamic pain.

METHODS

The cellular localization of the TLR4 protein was determined by immunostaining. The expression of Iba1, GFAP and protein associated with the TLR4/NF-κB/ERK1/2 pathway was measured by Western blotting. Continuous pain hypersensitivity was evaluated by behavioural tests. The results were analysed by one-way ANOVA, two-way ANOVA and Tukey's post hoc test.

RESULTS

The results demonstrated that DEX obviously alleviated thalamic pain induced by haemorrhage on the ipsilateral side and delayed the development of pain hypersensitivity. Furthermore, the expression levels of Iba1, GFAP and proteins associated with the TLR4/NF-κB/ERK1/2 signalling pathway were greatly increased in mice with thalamic pain, but these effects were reversed by DEX.

CONCLUSION

Our findings suggest that DEX alleviates the inflammatory response during thalamic pain through the TLR4/NF-κB/ERK1/2 signalling pathway and might be a potential therapeutic agent for thalamic pain.

Dexmedetomidine Inhibits Acute Lung Injury by Upregulating miR-144 Expression in Mice

The understanding of lung injury’s mechanisms at the molecular level is not fully completed. MicroR-NAs (miRNAs), which are part of different pathophysiological processes, are essential biological regulators that operate by suppressing target genes. A mouse model of acute lung injury (ALI), which is triggered by lipopolysaccharide (LPS), was used to analyze miR-144 level in the ALI mice with or without dexmedetomidine treatment. Inflammation was investigated by the ratio of wet weight’s value to dry weight (W/D) of the lung, the release of cytokines TNF-α, cytokines IL-6, and cytokines IL-1β, and MPO activity. To validate the effect of dexmedetomidine on miR-144, overex-pression and knockdown of miR-144 were applied to treat antagomir144 and agomir144. The result suggested that LPS-triggered ALI was alleviated by dexmedetomidine. miR-144 was downregulated in ALI mice. The knockdown of miR-144 attenuated the protection of dexmedetomidine to acute lung injury. Overexpression of miR-144 attenuated the ALI, which was induced by LPS.

Dexmedetomidine Post-Conditioning Alleviates Cerebral Ischemia-Reperfusion Injury in Rats by Inhibiting High Mobility Group Protein B1 Group (HMGB1)/Toll-Like Receptor 4 (TLR4)/Nuclear Factor kappa B (NF-κB) Signaling Pathway

BACKGROUND Cerebral ischemia-reperfusion injury is a pivotal cause of deaths due to cerebrovascular accident. Increased research efforts are needed to reveal the mechanism underlying its aggravation or alleviation. In this study, the effects of dexmedetomidine post-conditioning on the HMGB1/TLR4/NF-kappaB signaling pathway in cerebral ischemia-reperfusion rats was explored. MATERIAL AND METHODS Ninety rats were randomly divided into 5 groups - a sham group (Sham), a model group (I/R), a dexmedetomidine post-conditioning group (Dex), a recombinant high mobility group protein B1 group (rHMGB1), and a recombinant HMGB1+dexmedetomidine post-conditioning group (rHMGB1+Dex) - with 18 rats in each group. Longa grading, wet-dry weighing, TTC staining, HE staining, and immunohistochemical staining were used to assess brain damage. ELISA, RT-PCR, and Western blot analyses were performed to assess expression of IL-1ß, TNF-alpha, IL-6, IL-8, HMGB1, TLR4, and NF-kappaB. RESULTS Compared with the I/R group, the neurological function score, brain water content, infarction area, and the number of COX-2- and IBA-1-positive cells in the Dex group were significantly lower, accompanied by downregulated expression of the HMGB1/TLR4/NF-kappaB pathway, alleviated inflammation, and oxidative stress injury in brain tissue. These trends were mostly reversed in the rHMGB1 group and rHMGB1+Dex group, but not in the Dex group. Furthermore, when compared to the Dex group, there were significant increases of H₂O₂, MDA, NO, IL-1ß, TNF-alpha, IL-6, IL-8, HMGB1, TLR4, and p-P65 in the rHMGB1 group and rHMGB1+Dex group, in which a significant decrease of T-AOC, SOD, and p-IkappaBalpha was also detected. CONCLUSIONS Dexmedetomidine post-conditioning can alleviate cerebral ischemia-reperfusion injury in rats by inhibiting the HMGB1/TLR4/NF-kappaB signaling pathway.

Surgically-induced brain injury: where are we now?

Neurosurgical procedures cause inevitable brain damage from the multitude of surgical manipulations utilized. Incisions, retraction, thermal damage from electrocautery, and intraoperative hemorrhage cause immediate and long-term brain injuries that are directly linked to neurosurgical operations, and these types of injuries, collectively, have been termed surgical brain injury (SBI). For the past decade, a model developed to study the underlying brain pathologies resulting from SBI has provided insight on cellular mechanisms and potential therapeutic targets. This model, as seen in a rat, mouse, and rabbit, mimics a neurosurgical operation and causes commonly encountered post-operative complications such as brain edema, neuroinflammation, and hemorrhage. In this review, we elaborate on SBI and its clinical impact, the SBI animal models and their clinical relevance, the importance of applying therapeutics before neurosurgical procedures (i.e., preconditioning), and the new direction of applying venom-derived proteins to attenuate SBI.

Differential effects of propofol and dexmedetomidine on neuroinflammation induced by systemic endotoxin lipopolysaccharides in adult mice

Propofol and dexmedetomidine are commonly used in clinical situations where neuroinflammation may be imminent or even established but comparative data on their effects on neuroinflammatory and cognitive parameters are lacking. Using a murine model of neuroinflammation induced by systemic lipopolysaccharide (LPS), this study compared the effects of these two agents on cognitive function, neuroinflammatory parameters, oxidative stress and neurotransmission. Male adult C57BL/6 N mice were anaesthetised with propofol or dexmedetomidine prior to intraperitoneal injection of LPS. Cognitive and motor function were assessed by the Y-maze and Rotarod tests respectively. Inflammatory responses were evaluated by relative levels of cytokine mRNA and immunoreactivity of glia cells. LPS caused a marked elevation in IL-1β and TNF-α levels both peripherally and in the brain, together with microglia activation (p <  0.05) and cognitive impairment. These changes were accompanied by an increase in 8-hydroxy-2'-deoxyguanosine (8-OHdG) (p <  0.05). Dexmedetomidine attenuated microglia activation (p <  0.05) and the elevation in 8-OHdG level (p <  0.05). Propofol did not affect cognition. However, both drugs lowered the number of vesicular glutamate transporter 1 (VGLUT 1), but was associated with higher levels of apoptosis and 8-OHdG (p <  0.05). Data from this study suggest dexmedetomidine and propofol have different anti-neuroinflammatory and neuroprotective profiles. However, neither drug can fully attenuate the effects of LPS induced cognitive impairment.

Thrombin Preconditioning in Surgical Brain Injury in Rats

The surgical brain injury model replicates neurosurgical brain parenchymal damage. Postsurgical brain edema correlates with postoperative neurological dysfunction. Intranasal administration is a proven method of delivering therapies to brain tissue. Thrombin preconditioning decreased brain edema and improved neurological outcomes in models of ischemic brain injury. We hypothesized thrombin preconditioning in surgical brain injury may improve postoperative brain edema and neurological outcomes. Adult male Sprague-Dawley rats (n = 78) weighing 285-355 g were randomly assigned to sham or pre-injury treatment: one-time pretreatment 1 day prior, one-time pretreatment 5 days prior, and daily preconditioning for 5 days prior. Treatment arms were divided into vehicle or thrombin therapies, and subdivided into intranasal (thrombin 5 units/50 μL 0.9 % saline) or intracerebral ventricular (thrombin 0.1 unit/10 μL 0.9 % saline) administration. Blinded observers performed neurological testing 24 h after brain injury followed immediately by measurement of brain water content. There was a significant difference in ipsilateral brain water content and neurological outcomes between all treatment groups and the sham group. However, there was no change in brain water content or neurological outcomes between thrombin- and vehicle-treated animals. Thrombin preconditioning did not significantly improve brain edema or neurological function in surgical brain injury in rats.

Neuroprotective effects of dexmedetomidine conditioning strategies: Evidences from an in vitro model of cerebral ischemia

AIMS

Dexmedetomidine is a selective agonist of α2-adrenergic receptors with clinical anesthetic and analgesic properties that has also shown neuroprotective effects on several models of brain injury. Because perioperative stroke and brain damage are frequent causes of death in critical care units, we aimed to investigate neuroprotective properties of dexmedetomidine using an in vitro model of cerebral ischemia.

MAIN METHODS

Primary mixed rat brain cortical cultures were subjected to oxygen and glucose deprivation and treated with different doses of dexmedetomidine in order to analyze three conditioning strategies: preconditioning, intraconditioning and postconditioning.

KEY FINDINGS

All dexmedetomidine pre-, intra- and postconditioning treatments showed neuroprotective effects reducing brain cell necrosis, although only preconditioning showed antiapoptotic effects. Dexmedetomidine treatments also reduced IL-6 and TNF-α levels, especially in the preconditioning groups. Oxidative stress was attenuated with all dexmedetomidine preconditioning treatments, but only with the higher dose in the intraconditioning group, and no effects were observed in the postconditioning. All conditioning strategies increased BDNF levels.

SIGNIFICANCE

Dexmedetomidine-mediated neuroprotective effects in an in vitro model of cerebral ischemia involve the attenuation of inflammation and oxidative stress and the increment of BDNF expression.

Dexmedetomidine Modulates Histamine-induced Ca(2+) Signaling and Pro-inflammatory Cytokine Expression

Dexmedetomidine is a sedative and analgesic agent that exerts its effects by selectively agonizing α2 adrenoceptor. Histamine is a pathophysiological amine that activates G protein-coupled receptors, to induce Ca(2+) release and subsequent mediate or progress inflammation. Dexmedetomidine has been reported to exert inhibitory effect on inflammation both in vitro and in vivo studies. However, it is unclear that dexmedetomidine modulates histamine-induced signaling and pro-inflammatory cytokine expression. This study was carried out to assess how dexmedetomidine modulates histamine-induced Ca(2+) signaling and regulates the expression of pro-inflammatory cytokine genes encoding interleukin (IL)-6 and -8. To elucidate the regulatory role of dexmedetomidine on histamine signaling, HeLa cells and human salivary gland cells which are endogenously expressed histamine 1 receptor were used. Dexmedetomidine itself did not trigger Ca(2+) peak or increase in the presence or absence of external Ca(2+). When cells were stimulated with histamine after pretreatment with various concentrations of dexmedetomidine, we observed inhibited histamine-induced [Ca(2+)]i signal in both cell types. Histamine stimulated IL-6 mRNA expression not IL-8 mRNA within 2 hrs, however this effect was attenuated by dexmedetomidine. Collectively, these findings suggest that dexmedetomidine modulates histamine-induced Ca(2+) signaling and IL-6 expression and will be useful for understanding the antagonistic properties of dexmedetomidine on histamine-induced signaling beyond its sedative effect.

Molecular targets and mechanism of action of dexmedetomidine in treatment of ischemia/reperfusion injury

Dexmedetomidine (DEX), a highly specific α2-adrenergic agonist, which exhibits anaesthetic-sparing, analgesia and sympatholytic properties. DEX modulates gene expression, channel activation, transmitter release, inflammatory processes and apoptotic and necrotic cell death. It has also been demonstrated to have protective effects in a variety of animal models of ischemia/reperfusion (I/R) injury, including the intestine, myocardial, renal, lung, cerebral and liver. The broad spectrum of biological activities associated with DEX continues to expand, and its diverse effects suggest that it may offer a novel therapeutic approach for the treatment of human diseases with I/R involvement.