Dexmedetomidine alleviates airway hyperresponsiveness and allergic airway inflammation through the TLR4/NF‑κB signaling pathway in mice

Effects of dexmedetomidine on dynamic lung compliance in general anesthesia with desflurane: A randomized controlled study

Objective

The aim of this study was to evaluate the effect of dexmedetomidine on lung compliance in patients under general anesthesia with desflurane.

Methods

This prospective, randomized, double-blind, controlled trial included 51 patients who received general anesthesia undergoing lower limb fracture surgery. Participants were assigned to either the experimental (loading dose of 0.25 μg/kg dexmedetomidine over 10 min, followed by a maintenance dose of 0.3 μg/kg/h until the end of the surgery) or control (0.9% saline) group. Anesthesia was maintained with desflurane, analgesics and muscle relaxants. The two groups were compared for hemodynamic parameters, dynamic lung compliance, oxygenation index, and postoperative complications.

Results

While dynamic lung compliance showed no significant difference between the two groups at T1 (P = 0.321), it was significantly higher in the experimental group at all other time points (all P < 0.001). In the control group, Cdyn at T4, T5, T6, and T7 were lower than that at T1 (P = 0.032, 0.043, 0.032 and 0.018, respectively). There were no significant between-group differences in the mean arterial pressure and heart rate. Compared to the control group, the experimental group had a higher oxygenation index at T1 (P < 0.001), T2 (P < 0.001), T3 (P < 0.001), T4 (P = 0.02), and T5 (P = 0.016) and significantly lower peak airway pressure at all time points (all P < 0.001). Both groups had comparable postoperative outcomes.

Conclusions

Dexmedetomidine infusion at a loading dose of 0.25 μg/kg and maintenance dose of 0.3 μg/kg/h improved dynamic lung compliance in patients receiving desflurane during general anesthesia.

Advances in respiratory physiology in mouse models of experimental asthma

Recent advances in mouse models of experimental asthma coupled with vast improvements in systems that assess respiratory physiology have considerably increased the accuracy and human relevance of the outputs from these studies. In fact, these models have become important pre-clinical testing platforms with proven value and their capacity to be rapidly adapted to interrogate emerging clinical concepts, including the recent discovery of different asthma phenotypes and endotypes, has accelerated the discovery of disease-causing mechanisms and increased our understanding of asthma pathogenesis and the associated effects on lung physiology. In this review, we discuss key distinctions in respiratory physiology between asthma and severe asthma, including the magnitude of airway hyperresponsiveness and recently discovered disease drivers that underpin this phenomenon such as structural changes, airway remodeling, airway smooth muscle hypertrophy, altered airway smooth muscle calcium signaling, and inflammation. We also explore state-of-the-art mouse lung function measurement techniques that accurately recapitulate the human scenario as well as recent advances in precision cut lung slices and cell culture systems. Furthermore, we consider how these techniques have been applied to recently developed mouse models of asthma, severe asthma, and asthma-chronic obstructive pulmonary disease overlap, to examine the effects of clinically relevant exposures (including ovalbumin, house dust mite antigen in the absence or presence of cigarette smoke, cockroach allergen, pollen, and respiratory microbes) and to increase our understanding of lung physiology in these diseases and identify new therapeutic targets. Lastly, we focus on recent studies that examine the effects of diet on asthma outcomes, including high fat diet and asthma, low iron diet during pregnancy and predisposition to asthma development in offspring, and environmental exposures on asthma outcomes. We conclude our review with a discussion of new clinical concepts in asthma and severe asthma that warrant investigation and how we could utilize mouse models and advanced lung physiology measurement systems to identify factors and mechanisms with potential for therapeutic targeting.

Dexmedetomidine Protects against Airway Inflammation and Airway Remodeling in a Murine Model of Chronic Asthma through TLR4/NF-κB Signaling Pathway

Asthma is a common respiratory disease characterized by chronic airway inflammation. Dexmedetomidine (DEX), a highly selective α2 adrenergic receptor agonist, has been shown to participate in regulating inflammatory states and thus exert organ protective actions. However, the potential of DEX in asthma is still unknown. This study is aimed at investigating the role of DEX in a mouse model of house dust mite- (HDM-) induced asthma and exploring its underlying mechanism. Here, we found that DEX treatment significantly ameliorated airway hyperresponsiveness, airway inflammation, and airway remodeling in the asthmatic mice, which were similar to the efficacy of the reference anti-inflammatory drug dexamethasone. In addition, DEX reversed the increased expression of toll-like receptor 4 (TLR4) and its downstream signaling adaptor molecule nuclear factor-κB (NF-κB) in the lung tissue of asthmatic mice. Furthermore, these protective effects of DEX were abolished by yohimbine, an α2 adrenergic receptor antagonist. These results indicate that DEX is capable of ameliorating airway inflammation and remodeling in asthmatic mice, and this protective effect is associated with the inhibition of the TLR4/NF-κB signaling pathway.

Ketamine Attenuates Airway Inflammation via Inducing Inflammatory Cells Apoptosis and Activating Nrf2 Pathway in a Mixed-Granulocytic Murine Asthma Model

Purpose

The use of ketamine, an anesthetic, as a treatment for asthma has been investigated in numerous studies. However, how ketamine affects asthma is unclear. The present study examined the effects of ketamine on a murine model of mixed-granulocytic asthma, and the role of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway.

Methods

The murine model of mixed-granulocytic asthma was established using ovalbumin (OVA) for sensitization and the combination of OVA and lipopolysaccharides (LPS) for challenge. The main characteristics of asthma, oxidative stress biomarkers, and the expression of the Nrf2 pathway were examined. ML385 was administered to verify the role of the Nrf2 pathway.

Results

Mice in the OVA +LPS group developed asthmatic characteristics, including airway hyperresponsiveness, mixed-granulocytic airway inflammation, mucus overproduction, as well as increased levels of oxidative stress and impaired apoptosis of inflammatory cells. Among the three concentrations, ketamine at 75mg/kg effectively attenuated these asthmatic symptoms, activated the Nrf2 pathway, decreased oxidative stress, and induced apoptosis of eosinophils and neutrophils in bronchoalveolar lavage fluid (BALF) with a reducing level of myeloid cell leukemia 1(Mcl-1). ML385 (an Nrf2 inhibitor) eliminated the protective effects of ketamine on the mixed-granulocytic asthma model.

Conclusion

The study concluded that ketamine reduced oxidative stress and attenuated asthmatic symptoms (neutrophilic airway inflammation) by activating the Nrf2-Keap1 pathway, with 75 mg/kg ketamine showing the best results. Ketamine administration also increased neutrophil and eosinophil apoptosis in BALF, which may contribute to the resolution of inflammation. The use of ketamine as a treatment for asthma may therefore be beneficial.

Dexmedetomidine attenuates airway inflammation and oxidative stress in asthma via the Nrf2 signaling pathway

Allergic asthma is a chronic inflammatory disease in which oxidative stress serves a pivotal role. In clinical practice, dexmedetomidine (DEX), an α‑2‑adrenergic receptor agonist, is used as a sedative. DEX exhibits antioxidative and organ‑protective properties. In a murine model of asthma, DEX has a therapeutic effect via the toll like receptor 4/NF‑кB signaling pathway; however, whether DEX can exert an antioxidative effect on asthma has yet to be elucidated. In the present study, a T helper (Th)2‑dominant murine asthma model was established. DEX treatment significantly reduced eosinophilic airway inflammation, mucus overproduction and airway hyperresponsiveness, as well as the concentrations of Th2 cytokines. The lung tissues of mice with asthma were characterized by redox imbalance (increased oxidative stress and impaired antioxidant capacity). DEX treatment alleviated this imbalance by decreasing the levels of malondialdehyde and reactive oxygen species, and increasing the levels of glutathione. Furthermore, the nuclear factor erythroid 2‑related factor 2 (Nrf2) signaling pathway was inhibited in the lung tissues of asthmatic mice; these effects were noted in its downstream genes, heme oxygenase 1 and glutathione peroxidase 4. In mice with asthma, DEX treatment induced the expression of these antioxidant genes and the activation of Nrf2, whereas ML385 (an inhibitor of Nrf2) partially abrogated the antioxidative and therapeutic effects of DEX. To the best of our knowledge, the present study is the first to demonstrate the protective effect of DEX on Th2‑dominant asthma through the activation of the Nrf2 signaling pathway. The results suggested that the antioxidative properties of DEX could be beneficial in clinical application of DEX for the relief of asthmatic symptoms.

Dexmedetomidine reduces IL-4 and IgE expression through downregulation of theTLR4/NF-κB signaling pathway to alleviate airway hyperresponsiveness in OVA mice

BACKGROUND

Airway hyperresponsiveness (AHR) is a clinical manifestation of airflow limitation due to abnormal tracheal and bronchial sensitivity and is the main basis for the diagnosis of asthma. Patients with AHR are at high risk of perioperative tracheal and bronchospasm, which can lead to hypoxaemia and haemodynamic instability and, in severe cases, to a life-threatening 'silent lung'. It is therefore important to reduce the incidence or intensity of AHR episodes in the perioperative period. The inflammatory response is key to the development and progression of AHR.

HYPOTHESIS/PURPOSE

Based on the modulatory role of dexmedetomidine (DEX) in the inflammatory response, we hypothesised that dexmedetomidine (DEX) attenuates inflammatory properties by inhibiting the toll-like receptor 4 (TLR4)/nuclear factor (NF-κB) signalling pathway and can reduce the respiratory parameters of mechanical ventilation in ovalbumin-induced allergic airway hyperresponsiveness.

STUDY DESIGN

BABL/C mice were divided into control and OVA groups (ovalbumin-induced allergy. Ten mice in all OVA models were randomly selected for in vivo invasive lung function monitoring to analyse airway resistance parameters and demonstrate successful model establishment. The remaining OVA mice were treated with dexmedetomidine 25 μg/kg for 5 days (OVA + DEX group) or dexmedetomidine 25 μg/kg + yohimbine 1 mg/kg for 5 days (OVA + DEX + yohimbine). After treatment, bronchoalveolar lavage fluid (BAL) and peripheral blood (ELISA) and lung tissue (H&E and PAS) were collected for analysis of inflammatory factors, and lung tissue was verified by PCR for genes and proteins that do correlate with inflammatory mediators.

RESULTS

All airway resistance parameters were increased in OVA mice by invasive lung function monitoring. Proximal airway resistance (parameter Rn) and total respiratory resistance (parameter Rrs) were attenuated after dexmedetomidine intervention treatment. Dexmedetomidine reduced total inflammatory cell count and inflammatory infiltration of lung tissue in BALF and down-regulated IL-4 and IgE levels in BALF and peripheral blood, as shown by Giemsa, H&E, PAS staining and ELISA; this mechanism of action was found to be related to the TLR4/NFκB pathway, but not to TLR4/NFκB, as measured by PCR.

CONCLUSION

Dexmedetomidine reduces hyperresponsiveness and airway inflammatory responses. This mechanism of action may be related to the TLR4/NFκB signalling pathway. Overall conclusions are presented in.