The Protective Effect And Mechanisms Of Dexmedetomidine On Brain Damage Of Septic Mice

Objective: Sepsis-associated encephalopathy (SAE) is a frequent and nasty complication of sepsis, which brings patients with increased risk of death and long-term brain dysfunctions. Patients with SAE are characterized by changes in mental status and usually need sedation in clinical. Dexmedetomidine (Dex), as an anesthetic adjuvant, has been widely used in clinical and has been suggested for short-term sedation in intensive care unit (ICU), but its influences on sepsis-induced brain damage are rarely known. So in our study, we aimed to explore the effect of Dex on the development of SAE, and its potential mechanisms.Methods: Lipopolysaccharide (LPS, 10 mg/kg) was intraperitoneally injected to male BALB/c mice inducing sepsis. Dex (25 μg/kg) was given intraperitoneally immediately after LPS injection. Evens blue (EB) was injected through tail veins at 8 h after LPS injection,and 2 h later,brain tissues of each group were took out to detect the concentration of EB in brain tissues. Levels of TNF-α, IL-1β, malondialdehyde(MDA) and reactive oxygen species (ROS) were detected in the tissues of mice brain eight hours later after drug administration. Hematoxylin and eosin (HE) staining was used to detect brain pathologic change. We also detected apoptosis using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and Bcl-2, Bax, Cleaved caspase-3, iNOS expressions of hippocampus and cortex by western blot.Results:1. The results of EB detection (ng/mg): The average concentration of group LPS is(1.17±0.26), which are more than group Control (0.52±0.22) (P < 0.01). The average concentration of group LPS+Dex is (0.81±0.12),which are more than group LPS(1.17±0.26) (P< 0.05).2. The results of HE and TUNEL stainings:① HE stainings: The brain sections of group Control showed that the cytomorphology of neurons and the architectures of cortex and hippocampus are normal. While, it showed that LPS administration induced the changes of cytomorphology of neurons in the cerebral cortex and hippocampus 8 h later, which is characterized by condensed and hyperchromatic nuclei, retracted and smaller cell bodies accompanied by irregular shapes and a wide perineuronal vacuolations around the degenerative neurons. Interestingly,after treatment with Dex,the morphological abnormalities were ameliorated,and the amount of abnormal neurons was decreased both in the hippocampus and cortex.②TUNEL stainings: The brain sections of group LPS showed increased numbers of TUNEL-positives cells in cortex and hippocampal CA1 and CA1 regions than group Control, while TUNEL-positives cells were decreased in group LPS+Dex compared to group LPS.3. The results of TNF-α, IL-1β, ROS and MDA①TNF-a (pg/mg): The average of group LPS is (847.70± 120.01),which are more than group Control (428.71±47.01) (P < 0.01). The average concentration of group LPS+Dex is (348.59±158.42), which are more than group LPS (847.70±120.01)(P<0.01).②IL-1β (pg/mg): The average concentration of group LPS is (224.08±61.32),which are more than group Control (128.56±41.52) (P < 0.05). The average concentration of group LPS+Dex is (197.06±46.13), which are more than group LPS(128.56±41.52)(P<0.05).③The results of ROS: The average concentration of group LPS is higher than group Control (P < 0.01). The average concentration of group LPS+Dex is lower than group LPS (P < 0.05).④MDA (nmol/mg): The average concentration of group LPS is (11.96±1.58),which are more than group Control (8.29±1.02) (P < 0.01). The average concentration of group LPS+Dex is (8.700±0.92), which are more than group LPS (11.96±1.58) (P <0.01).4. The results of Western blot:①iNOS: The relative expression levels of group LPS in cortex and hippocampus are higher than group Control (P < 0.01), while relative expression levels of group LPS+Dex in cortex and hippocampus are lower than group LPS (cortex: P < 0.01;hippocampus: P < 0.05).②Bax/Bcl-2 : The relative expression levels of group LPS in cortex and hippocampus are higher than group Control (P < 0.01), while relative expression levels of group LPS+Dex in cortex and hippocampus are lower than group LPS(cortex: P < 0.01; hippocampus: P < 0.05).③Cleaved caspase-3: The relative expression levels of group LPS in cortex and hippocampus are higher than group Control (P < 0.01), while relative expression levels of group LPS+Dex in cortex and hippocampus are lower than group LPS (P <0.01).Conclusions: Our results indicated that Dex could reverse LPS administration-induced abnormal changes of cytomorphology and increased neuroapoptosis in mice brain. Further, we found that the protective effects of Dex may be associated with inhibiting brain inflammation and oxidative stress, regulating the relative expressions levels of Bcl-2/Bax, and reducing the level of Cleaved caspase-3.