Attenuation of neuroinflammation by dexmedetomidine is associated with activation of a cholinergic anti-inflammatory pathway in a rat tibial fracture model

Intestinal microbiota impact sepsis associated encephalopathy via the vagus nerve

OBJECTIVE

The pathogenesis of sepsis associated encephalopathy (SAE) remains poorly understood. Vagus nerve plays an important role in gut-microbiota-brain axis. This study aimed to investigate whether vague nerve is a key mediator of the impact of intestinal microbiota on SAE.

METHODS

Male rats were randomly divided into four groups (n=20): SHAM (SH) group, lipopolysaccharide (LPS) group, fecal microbiota transplantation (FMT) +LPS group, and vagotomy (VGX)+LPS+FMT group. The left cervical vagotomy was performed 30min before LPS administration in LPS+FMT+VGX group. LPS+ FMT and LPS+FMT+VGX groups received nasogastric infusion of feces from healthy donor three times a day. Fecal samples were collected every two days to monitor changes in microbiota composition by 16S rDNA analysis. Brain function was evaluated by behavioral tests and EEG. The levels of tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6, IL-10 in brain cortex were detected by ELISA. The expression of Iba-1 in brain cortex was assessed by immunohistochemistry and Western blot analysis.

RESULTS

Significant modification of microbiota composition, characterized by a profound increase of commensals in the Firmicutes phylum and depletion of opportunistic organisms in the Proteobacteria phylum, was observed in FMT groups compared to LPS group. Furthermore, we identified a reconstituted bacterial community enriched in Firmicutes and depleted of Proteobacteria. In both FMT groups the diversity of the fecal microbiota and the microbiota composition were similar to SH group. LPS mice treated with FMT demonstrated a better spatial memory and less EEG abnormalities, significantly attenuated levels of IL-1β, IL-6, TNF-α, and decreased number of Iba-1 positive microglia in the cortex, but these beneficial effects of FMT were reversed by VGX.

CONCLUSIONS

FMT can change intestinal microbiota in sepsis patients, and vagus nerve is a key mediator between intestinal microbiota and SAE. These findings suggest that FMT and vagus nerve are potential therapy targets for treating SAE.

Dexmedetomidine reduces the neuronal apoptosis related to cardiopulmonary bypass by inhibiting activation of the JAK2-STAT3 pathway

Cardiopulmonary bypass (CPB) constitutes one of the primary methodologies pertaining to cardiac surgery. However, this form of surgery can cause damage to the body. Many studies have reported that dexmedetomidine confers cerebral protection. In this study, we aimed to investigate the effect and mechanism of dexmedetomidine on neuronal apoptosis caused by CPB. Here, rats were treated with different doses of dexmedetomidine by intravenous infusion 2 hours after CPB. We observed that dexmedetomidine treatment to rats reduces the S100β, NSE levels in plasma, and neuronal apoptosis following CPB in a dose-dependent manner. Furthermore, we observed that the beneficial effect of dexmedetomidine treatment following CPB was associated with a reduction in IL6, an inflammatory cytokine in plasma and cortex. Our results suggest that dexmedetomidine provides neuroprotective effects by inhibiting inflammation and reducing neuronal apoptosis. There was a correlation between the protective effect on the brain and the dose of dexmedetomidine. In addition, dexmedetomidine administration inhibits phosphorylation of JAK2 and STAT3 proteins in the hippocampus of rats 2 hours after CPB. Therefore, we speculate that the JAK2–STAT3 pathway plays an important role in the neuroprotective effects of dexmedetomidine following brain injury induced by CPB.

Dexmedetomidine Prevents Lipopolysaccharide-Induced MicroRNA Expression in the Adult Rat Brain

During surgery or infection, peripheral inflammation can lead to neuroinflammation, which is associated with cognitive impairment, neurodegeneration, and several neurodegenerative diseases. Dexmedetomidine, an α-2-adrenoceptor agonist, is known to exert anti-inflammatory and neuroprotective properties and reduces the incidence of postoperative cognitive impairments. However, on the whole the molecular mechanisms are poorly understood. This study aims to explore whether dexmedetomidine influences microRNAs (miRNAs) in a rat model of lipopolysaccharide (LPS)-induced neuroinflammation. Adult Wistar rats were injected with 1 mg/kg LPS intraperitoneal (i.p.) in the presence or absence of 5 µg/kg dexmedetomidine. After 6 h, 24 h, and 7 days, gene expressions of interleukin 1-β (IL1-β), tumor necrosis factor-α (TNF-α), and microRNA expressions of miR 124, 132, 134, and 155 were measured in the hippocampus, cortex, and plasma. Dexmedetomidine decreased the LPS-induced neuroinflammation in the hippocampus and cortex via significant reduction of the IL1-β and TNF-α gene expressions after 24 h. Moreover, the LPS-mediated increased expressions of miR 124, 132, 134, and 155 were significantly decreased after dexmedetomidine treatment in both brain regions. In plasma, dexmedetomidine significantly reduced LPS-induced miR 155 after 6 h. Furthermore, there is evidence that miR 132 and 134 may be suitable as potential biomarkers for the detection of neuroinflammation.

Dexmedetomidine preconditioning plays a neuroprotective role and suppresses TLR4/NF-κB pathways model of cerebral ischemia reperfusion

BACKGROUND

Dexmedetomidine has been reported to play an efficient role on multi-organ protection. Our study aims to investigate the neuroprotective of dexmedetomidine preconditioning on cerebral ischemic reperfusion (I/R) injury and investigate the underlining signaling mechanisms.

METHODS

Cerebral I/R models were established with SD rats through middle cerebral artery occlusion (MCAO). After 2h of ischemia followed by 7days of reperfusion, the degree of cerebral tissue injury was detected by HE, Nissl and TUNEL staining. Glial fibrillary acidic protein (GFAP) positive and TNF-α positive cells were stained by immunohistochemistry and counted under microscope. TLR4, NF-κB and TIR-domain containing adapter-inducing interferon-β (TRIF) expression were detected by real time PCR and western blot.

RESULTS

Dexmedetomidine preconditioning markedly prevented the ischemia-induced cellular damage observed from HE and Nissl staining in hippocampus and cortex. Dexmedetomidine observably decreased the number of apoptotic cells in TUNEL staining. Besides, yohimbine could specifically suppress the protective effect of dexmedetomidine. GFAP expression was distinctly inhibited by dexmedetomidine preconditioning (10μg/kg, 20μg/kg) in cerebral ischemia area. Dexmedetomidine preconditioning inhibited the expression of TLR4 and NF-κB and increased that of TRIF.

CONCLUSION

The results of this study suggest that dexmedetomidine preconditioning plays a neuroprotective role against I/R injury. Dexmedetomidine might suppress TLR4/NF-??B pathway and drive TLR4/TRIF signaling pathway to reduce the inflammatory injury.

Assessment of different loading doses of dexmedetomidine hydrochloride in preventing adverse reaction after combined spinal-epidural anesthesia

We conducted the present study to investigate the effects of the different loading doses of dexmedetomidine hydrochloride in the prevention of adverse reactions after combined spinal-epidural anesthesia. A total of 200 patients that were admitted to the Department of Obstetrics at the Second Affiliated Hospital of Xi'an Jiaotong University hospital and treated with cesarean section through the use of combined spinal-epidural anesthesia from December, 2014 to June, 2016, were randomly divided into 4 groups. The therapeutic regimens of patients were shown as follows: group A was administered an intravenous pump of 10 ml/l physiological saline in surgery until the end of the delivery. group B was administered 0.2 µg/kg dexmedetomidine. group C was administered 0.4 µg/kg dexmedetomidine. group D was administered 0.6 µg/kg dexmedetomidine. The anesthesia plane was adjusted to the level below the T10 plane. After the onset of anesthesia, participants of each group were treated with an intravenous pump of dexmedetomidine at loading dose. After intravenous pumping for 10 min in each group during the surgery, patients were administered with an intraoperative maintenance dose of 0.2 µg/kg/h until the end of the delivery. The heart rate (HR), mean arterial pressure (MAP), Narcotrend index (NI), Ramsay sedation score and the incidence of adverse reactions at each time-point of the start of drug administration (T0), 10 min (T2), 30 min (T3), 60 min (T4), 90 min (T5) and the end of surgery (T6) were recorded. Within 24 h post-delivery, the degree of amnesia from using dexmedetomidine until the end of the delivery were followed up. Compared to group A and T0, the HRs of participants at T3-6 in groups B and C were decreased. The MAP at T1 in group D was increased. In groups B and C, the NIs were significantly decreased at T2-6, the Ramsay scores were increased at T3-6, and the differences were statistically significant (P<0.05). The follow-up within 24 h after delivery showed that the degree of anterograde amnesia from groups B to D was significantly higher than group A, with statistically significant difference (P<0.05). A combined spinal-epidural anesthesia with 0.6 µg/kg loading dose of dexmedetomidine, by intravenous pumping within 10 min before cesarean section, can achieve a satisfied sedative effect at 30 min after administration. It maintains the characteristics of intraoperative hemodynamic stability and less adverse reactions. Therefore, it is of great significance to improve the quality of cesarean section delivery.

Microglia mediate postoperative hippocampal inflammation and cognitive decline in mice

Surgery can induce cognitive decline, a risk that increases with advancing age. In rodents, postoperative cognitive decline (POCD) is associated with the inflammatory activation of hippocampal microglia. To examine the role of microglia in POCD, we inhibited the colony-stimulating factor 1 receptor (CSF1R) in adult mice, effectively depleting CNS microglia. Surgical trauma (tibial fracture) reduced the ability of mice to remember a conditioned response learned preoperatively, a deficit more pronounced and persistent in mice with diet-induced obesity (DIO). Whereas microglial depletion by itself did not affect learning or memory, perioperative microglial depletion remarkably protected mice, including those with DIO, from POCD. This protection was associated with reduced hippocampal levels of inflammatory mediators, abrogation of hippocampal recruitment of CCR2⁺ leukocytes, and higher levels of circulating inflammation-resolving factors. Targeting microglia may thus be a viable strategy to mitigate the development of POCD, particularly in those with increased vulnerability.

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.