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

Dexmedetomidine Attenuates Neuroinflammation-Mediated Hippocampal Neurogenesis Impairment in Sepsis-Associated Encephalopathy Mice through Central α2A-Adrenoceptor

Sepsis-associated encephalopathy (SAE), one of the common complications of sepsis, is associated with higher ICU mortality, prolonged hospitalization, and long-term cognitive decline. Sepsis can induce neuroinflammation, which negatively affects hippocampal neurogenesis. Dexmedetomidine has been shown to protect against SAE. However, the potential mechanism remains unclear. In this study, we added lipopolysaccharide (LPS)-stimulated astrocytes-conditioned media (LPS-CM) to neural stem cells (NSCs) culture, which were pretreated with dexmedetomidine in the presence or absence of the α2-adrenoceptor antagonist yohimbine or the α2A-adrenoceptor antagonist BRL-44408. LPS-CM impaired the neurogenesis of NSCs, characterized by decreased proliferation, enhanced gliogenesis, and declined viability. Dexmedetomidine alleviated LPS-CM-induced impairment of neurogenesis in a dose-dependent manner. Yohimbine, as well as BRL-44408, reversed the effects of dexmedetomidine. We established a mouse model of SAE via cecal ligation and perforation (CLP). CLP-induced astrocyte-related neuroinflammation and hippocampal neurogenesis deficits, accompanied by learning and memory decline, which were reversed by dexmedetomidine. The effect of dexmedetomidine was blocked by BRL-44408. Collectively, our findings support the conclusion that dexmedetomidine can protect against SAE, likely mediated by the combination of inhibiting neuroinflammation via the astrocytic α2A-adrenoceptor with attenuating neuroinflammation-induced hippocampal neurogenesis deficits via NSCs α2A-adrenoceptor.

Neuroprotective actions of norepinephrine in neurological diseases

Precise control of norepinephrine (NE) levels and NE-receptor interaction is crucial for proper function of the brain. Much evidence for this view comes from experimental studies that indicate an important role for NE in the pathophysiology and treatment of various conditions, including cognitive dysfunction, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and sleep disorders. NE provides neuroprotection against several types of insults in multiple ways. It abrogates oxidative stress, attenuates neuroinflammatory responses in neurons and glial cells, reduces neuronal and glial cell activity, promotes autophagy, and ameliorates apoptotic responses to a variety of insults. It is beneficial for the treatment of neurodegenerative diseases because it improves the generation of neurotrophic factors, promotes neuronal survival, and plays an important role in the regulation of adult neurogenesis. This review aims to present the evidence supporting a principal role for NE in neuroprotection, and molecular mechanisms of neuroprotection.

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.

Aloperine protects against cerebral ischemia/reperfusion injury via activating the PI3K/AKT signaling pathway in rats

Cerebral ischemia is among the leading causes of death and long-term disability worldwide. The aim of the present study was to investigate the effects of aloperine (ALO) on cerebral ischemia/reperfusion (I/R) injury in rats and elucidate the possible underlying mechanisms. Therefore, a rat model of reversible middle cerebral artery occlusion (MCAO) was established to induce cerebral I/R injury. Following pretreatment with different doses of ALO, the histopathological changes in the brain tissue were evaluated by hematoxylin and eosin staining. The degree of cerebral infarction was determined using by 2,3,5-triphenyltetrazolium chloride staining. Additionally, the levels of oxidative stress- and inflammation-related factors were measured using commercially available kits. Cell apoptosis was assessed by TUNEL staining, while the expression levels of apoptosis- and PI3K/AKT signaling pathway-related proteins were determined by western blot analysis. The results demonstrated that ALO alleviated histopathological injury in the brain tissue and the area of cerebral infarction in a dose-dependent manner. Furthermore, significantly reduced levels of reactive oxygen species and malondialdehyde were observed in the ALO-treated rats post-MCAO/reperfusion, accompanied by increased levels of superoxide dismutase, catalase and glutathione. Consistently, treatment with ALO notably decreased the concentration of inflammatory factors, including TNF-α, IL-1β and IL-6, in a dose-dependent manner. In addition, ALO attenuated neuronal cell apoptosis, downregulated the expression of Bax and upregulated that of Bcl-2. I/R markedly reduced the expression levels of phosphorylated (p-)PI3K and p-AKT, which were dose-dependently restored by ALO intervention. Collectively, the aforementioned findings indicated that ALO could improve cerebral I/R injury and alleviate oxidative stress, inflammation and cell apoptosis via activating the PI3K/AKT signaling pathway, thus supporting the therapeutic potential of ALO against cerebral I/R injury in ischemic stroke.

Dexmedetomidine reduces ventilator-induced lung injury via ERK1/2 pathway activation

Mechanical ventilation (MV) can contribute to ventilator-induced lung injury (VILI); dexmedetomidine (Dex) treatment attenuates MV-related pulmonary inflammation, but the mechanisms remain unclear. Therefore, the present study aimed to explore the protective effect and the possible molecular mechanisms of Dex in a VILI rodent model. Adult male Sprague-Dawley rats were randomly assigned to one of seven groups (n=24 rats/group). Rats were euthanized after 4 h of continuous MV, and pathological changes, lung wet/dry (W/D) weight ratio, the levels of inflammatory cytokines (IL-1β, TNF-α and IL-6) in the bronchoalveolar lavage fluid (BALF), and the expression levels of Bcl-2 homologous antagonist/killer (Bak), Bcl-2, pro-caspase-3, cleaved caspase-3 and the phosphorylation of ERK1/2 in the lung tissues were measured. Propidium iodide uptake and TUNEL staining were used to detect epithelial cell death. The Dex pretreatment group exhibited fewer pathological changes, lower W/D ratios and lower expression levels of inflammatory cytokines in BALF compared with the VILI group. Dex significantly attenuated the ratio of Bak/Bcl-2, cleaved caspase-3 expression levels and epithelial cell death, and increased the expression of phosphorylated ERK1/2. The protective effects of Dex could be partially reversed by PD98059, which is a mitogen-activated protein kinase (upstream of ERK1/2) inhibitor. Overall, dexmedetomidine was found to reduce the inflammatory response and epithelial cell death caused by VILI, via the activation of the ERK1/2 signaling pathway.

Mechanisms of Dexmedetomidine in Neuropathic Pain

Dexmedetomidin is a new-generation, highly selective α2 adrenergic receptor agonist with a large number of advantages, including its sedative and analgesic properties, its ability to inhibit sympathetic nerves, its reduced anesthetic dosage, its hemodynamic stability, its mild respiratory depression abilities, and its ability to improve postoperative recognition. Its safety and effectiveness, as well as its ability to provide a certain degree of comfort to patients, make it a useful anesthetic adjuvant for a wide range of clinical applications. For example, dexmedetomidine is commonly used in patients undergoing general anesthesia, and it also exerts sedative effects during tracheal intubation or mechanical ventilation in intensive care unit patients. In recent years, with the deepening of clinical research on dexmedetomidine, the drug is still applied in the treatment of spastic pain, myofascial pain, neuropathic pain, complex pain syndrome, and chronic headache, as well as for multimodal analgesia. However, we must note that the appropriateness of patient and dose selection should be given attention when using this drug; furthermore, patients should be observed for adverse reactions such as hypotension and bradycardia. Therefore, the safety and effectiveness of this drug for long-term use remain to be studied. In addition, basic experimental studies have also found that dexmedetomidine can protect important organs, such as the brain, heart, kidney, liver, and lung, through various mechanisms, such as antisympathetic effects, the inhibition of apoptosis and oxidative stress, and a reduction in the inflammatory response. Moreover, the neuroprotective properties of dexmedetomidine have received the most attention from scholars. Hence, in this review, we mainly focus on the characteristics and clinical applications of dexmedetomidine, especially the role of dexmedetomidine in the nervous system and the use of dexmedetomidine in the relief of neuropathic pain.