Effects of intracisternal and intravenous dexmedetomidine on ischemia-induced brain injury in rat: a comparative study

The neuroprotective effect of dexmedetomidine and its mechanism

Dexmedetomidine (DEX) is a highly selective α2 receptor agonist that is routinely used in the clinic for sedation and anesthesia. Recently, an increasing number of studies have shown that DEX has a protective effect against brain injury caused by traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), cerebral ischemia and ischemia–reperfusion (I/R), suggesting its potential as a neuroprotective agent. Here, we summarized the neuroprotective effects of DEX in several models of neurological damage and examined its mechanism based on the current literature. Ultimately, we found that the neuroprotective effect of DEX mainly involved inhibition of inflammatory reactions, reduction of apoptosis and autophagy, and protection of the blood–brain barrier and enhancement of stable cell structures in five way. Therefore, DEX can provide a crucial advantage in neurological recovery for patients with brain injury. The purpose of this study was to further clarify the neuroprotective mechanisms of DEX therefore suggesting its potential in the clinical management of the neurological injuries.

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.

Neuroprotective role of dexmedetomidine pretreatment in cerebral ischemia injury via ADRA2A-mediated phosphorylation of ERK1/2 in adult rats

Neuroprotective effects of dexmedetomidine (Dex) have been reported in various models of brain injury. However, to our knowledge, the neuroprotective mechanism of Dex pretreatment in rats remains unknown. The aim of the present study was to detect the expression of the α2A adrenergic receptor (ADRA2A) in focal ischemic brain tissues and to investigate the protective role and corresponding mechanism of Dex pretreatment in cerebral ischemia in rats. A hypoxia/reoxygenation (H/R) cell model in primary cultured astrocytes and a focal cerebral ischemia/reperfusion (I/R) model in adult rats were used. The expression of ADRA2A and extracellular signal-regulated kinases 1 and 2 (ERK1/2) in the primary cultured astrocytes and rat brain ischemic tissues was detected in the different conditions prior to and following Dex pretreatment using western blotting. The H/R model of primary cultured astrocytes and the focal cerebral I/R model in adult rats were successfully constructed. Under the normal oxygen conditions, 500 ng/ml Dex pretreatment increased the expression of ADRA2A and phosphorylated (p)-ERK1/2 in the astrocytes compared with in the control group. Hypoxic culture for 6 h and then reoxygenation for 24 h decreased the levels of p-ERK1/2 in the astrocytes compared with those in control group. This decrease was prevented by Dex pretreatment for 3 h. The hypoxic culture and then reoxygenation increased the expression of ADRA2A. Similarly, compared with those prior to Dex treatment, the levels of ADRA2A and p-ERK1/2 in the brain ischemic tissues following Dex treatment were increased. The levels of ADRA2A and p-ERK1/2 were 0.72±0.23 and 0.66±0.25 following Dex treatment, compared with 0.76±0.22 and 0.31±0.18, respectively, prior to Dex treatment. The effect of Dex pretreatment increasing p-ERK1/2 expression was attenuated by AG1478 pretreatment. In summary, Dex appeared to promote phosphorylation of ERK1/2 in astrocytes under H/R. As a specific agonist of ADRA2A, Dex may activate phosphorylation of ERK1/2 via ADRA2A in astrocytes. Thus, the neuroprotective role of Dex pretreatment against cerebral ischemic injury may function via ADRA2A-mediated phosphorylation of ERK1/2.

Dexmedetomidine Regulates 6-hydroxydopamine-Induced Microglial Polarization

Microglia have undergone extensive characterization and have been shown to present distinct phenotypes, such as the M1 or M2 phenotypes, depending on their stimuli. As a highly specific neurotoxin, 6-hydroxydopamine (6-OHDA) can be used to further our understanding of the immune response in Parkinson's disease (PD). Dexmedetomidine (DEX), a centrally selective α2-adrenoceptor agonist, performs very well as an anti-anxiety medication, sedative and analgesic. In the present study, we investigated the effects of DEX on 6-OHDA-induced microglial polarization. Our results indicate that treatment with 6-OHDA promotes microglial polarization toward the M1 state in BV2 microglia cells by increasing the release of interleukin (IL)-6, IL-1β, or tumor necrosis factor-α, which can be prevented by pretreatment with DEX. In addition, we found that 6-OHDA blocked IL-4-mediated microglial M2 polarization by suppressing expression of the microglial M2 markers arginase-1 (Arg-1), resistin-like α (Retnla/Fizz1), and chitinase 3-like 3 (Chi3l3/Ym1), which could be ameliorated by pretreatment with DEX. Notably, the inhibitory effects of 6-OHDA on IL-4-mediated induction of the anti-inflammatory marker genes IL-10, IL-13, and transforming growth factor-β2 could be significantly alleviated by pretreatment with DEX in a dose-dependent manner (P < 0.01). Mechanistically, alternations in the activation of signal transducer and activator of transcription 6 were involved in this process. These findings suggest that administration of DEX has the potential to interrupt the process of microgliosis in PD.

The neuroprotective action of dexmedetomidine on apoptosis, calcium entry and oxidative stress in cerebral ischemia-induced rats: Contribution of TRPM2 and TRPV1 channels

Dexmedetomidine (DEX) may act as an antioxidant through regulation of TRPM2 and TRPV1 channel activations in the neurons by reducing cerebral ischemia-induced oxidative stress and apoptosis. The neuroprotective roles of DEX were tested on cerebral ischemia (ISC) in the cultures of rat primary hippocampal and DRG neurons. Fifty-six rats were divided into five groups. A placebo was given to control, sham control, and ISC groups, respectively. In the third group, ISC was induced. The DEX and ISC+DEX groups received intraperitoneal DEX (40 μg/kg) 3, 24, and 48 hours after ISC induction. DEX effectively reversed capsaicin and cumene hydroperoxide/ADP-ribose-induced TRPV1 and TRPM2 densities and cytosolic calcium ion accumulation in the neurons, respectively. In addition, DEX completely reduced ISC-induced oxidative toxicity and apoptosis through intracellular reactive oxygen species production and depolarization of mitochondrial membrane. The DEX and ISC+DEX treatments also decreased the expression levels of caspase 3, caspase 9, and poly (ADP-ribose) polymerase in the hippocampus and DRG. In conclusion, the current results are the first to demonstrate the molecular level effects of DEX on TRPM2 and TRPV1 activation. Therefore, DEX can have remarkable neuroprotective impairment effects in the hippocampus and DRG of ISC-induced rats.