Effect of continuous local dexamethasone on tissue biomechanics and histology after inhalational burn in a preclinical model

Burn inhalation injury and intubation with dexamethasone-eluting endotracheal tubes modulate local microbiome and alter airway inflammation

Background

Inhalation injuries, caused by exposure to extreme heat and chemical irritants, lead to complications with speaking, swallowing, and breathing. This study investigates the effects of thermal injury and endotracheal tube (ETT) placement on the airway microbiome and inflammatory response. A secondary aim is to assess the impact of localized dexamethasone delivery via a drug-eluting ETT to reduce laryngeal scarring.

Methods

Inhalation injury was developed in swine by administering heated air (150°C-160°C) under endoscopic visualization. Following injury, segments of regular or dexamethasone-loaded endotracheal tubes (ETTs) were placed in the injured airways for 3 or 7 days. Computed tomography (CT) scans were used to assess airway narrowing post-injury. Biofilm formation on the ETTs was investigated using micro-CT and microscopy. The airway microbiome was analyzed via 16S rRNA sequencing. Inflammatory markers were quantified using an immunoassay and macrophage populations in laryngeal tissue were assessed with CD86 and CD206 staining. Tracheal tissues were also histologically examined for epithelial thickness, collagen area, and mucin production.

Results

CT scans confirmed airway narrowing post-injury, particularly around ETT sites. Biofilm formation was more extensive on dexamethasone-coated ETTs at later timepoints. Beta diversity analysis revealed significant shifts in microbial composition related to ETT type (R2 = 0.04, p < 0.05) and duration of placement (R2 = 0.22, p < 0.05). Differential abundance analysis demonstrated significant positive log fold changes in genera such as Bergeriella, Peptostreptococcus, and Bacteriodes with thermal injury over time. Inflammatory markers IFN-γ, IL-4, and IL-1β were elevated in dexamethasone-ETT groups at 3 days, then decreased by 7 days. Macrophage markers CD86 and CD206 were significantly greater in dexamethasone groups compared to regular ETT groups at 7 days (p = 0.002 and p = 0.0213, respectively). Epithelial thickness was significantly greater with regular ETT placement compared to dexamethasone ETT placement in the burn-injured airway at 3 days (p = 0.027).

Conclusion

Thermal inhalation injury and ETT placement significantly impact airway inflammation, structural integrity, and microbiome composition. Dexamethasone-eluting ETTs, intended to reduce inflammation, increased biofilm formation and elevated cytokine levels, suggesting complex interactions between the drug coating and the host immune response. The airway microbiome shifted significantly with specific taxa thriving in the inflamed environment.

Localized delivery of therapeutics impact laryngeal mechanics, local inflammatory response, and respiratory microbiome following upper airway intubation injury in swine

BACKGROUND

Laryngeal injury associated with traumatic or prolonged intubation may lead to voice, swallow, and airway complications. The interplay between inflammation and microbial population shifts induced by intubation may relate to clinical outcomes. The objective of this study was to investigate laryngeal mechanics, tissue inflammatory response, and local microbiome changes with laryngotracheal injury and localized delivery of therapeutics via drug-eluting endotracheal tube.

METHODS

A simulated traumatic intubation injury was created in Yorkshire crossbreed swine under direct laryngoscopy. Endotracheal tubes electrospun with roxadustat or valacyclovir- loaded polycaprolactone (PCL) fibers were placed in the injured airway for 3, 7, or 14 days (n = 3 per group/time and ETT type). Vocal fold stiffness was then evaluated with normal indentation and laryngeal tissue sections were histologically examined. Immunohistochemistry and inflammatory marker profiling were conducted to evaluate the inflammatory response associated with injury and ETT placement. Additionally, ETT biofilm formation was visualized using scanning electron microscopy and micro-computed tomography, while changes in the airway microbiome were profiled through 16S rRNA sequencing.

RESULTS

Laryngeal tissue with roxadustat ETT placement had increasing localized stiffness outcomes over time and histological assessment indicated minimal epithelial ulceration and fibrosis, while inflammation remained severe across all timepoints. In contrast, vocal fold tissue with valacyclovir ETT placement showed no significant changes in stiffness over time; histological analysis presented a reduction in epithelial ulceration and inflammation scores along with increased fibrosis observed at 14 days. Immunohistochemistry revealed a decline in M1 and M2 macrophage markers over time for both ETT types. Among the cytokines, IL-8 levels differed significantly between the roxadustat and valacyclovir ETT groups, while no other cytokines showed statistically significant differences. Additionally, increased biofilm formation was observed in the coated ETTs with notable alterations in microbiota distinctive to each ETT type and across time.

CONCLUSION

The injured and intubated airway resulted in increased laryngeal stiffness. Local inflammation and the type of therapeutic administered impacted the bacterial composition within the upper respiratory microbiome, which in turn mediated local tissue healing and recovery.

Electrospun composite-coated endotracheal tubes with controlled siRNA and drug delivery to lubricate and minimize upper airway injury

Endotracheal Tubes (ETTs) maintain and secure a patent airway; however, prolonged intubation often results in unintended injury to the mucosal epithelium and inflammatory sequelae which complicate recovery. ETT design and materials used have yet to adapt to address intubation associated complications. In this study, a composite coating of electrospun polycaprolactone (PCL) fibers embedded in a four-arm polyethylene glycol acrylate matrix (4APEGA) is developed to transform the ETT from a mechanical device to a dual-purpose device capable of delivering multiple therapeutics while preserving coating integrity. Further, the composite coating system (PCL-4APEGA) is capable of sustained delivery of dexamethasone from the PCL phase and small interfering RNA (siRNA) containing polyplexes from the 4APEGA phase. The siRNA is released rapidly and targets smad3 for immediate reduction in pro-fibrotic transforming growth factor-beta 1 (TGFϐ1) signaling in the upper airway mucosa as well as suppressing long-term sequelae in inflammation from prolonged intubation. A bioreactor was used to study mucosal adhesion to the composite PCL-4APEGA coated ETTs and investigate continued mucus secretory function in ex vivo epithelial samples. The addition of the 4APEGA coating and siRNA delivery to the dexamethasone delivery was then evaluated in a swine model of intubation injury and observed to restore mechanical function of the vocal folds and maintain epithelial thickness when observed over 14 days of intubation. This study demonstrated that increase in surface lubrication paired with surface stiffness reduction significantly decreased fibrotic behavior while reducing epithelial adhesion and abrasion.

Endotracheal tubes with dexamethasone eluting electrospun coating improve tissue mechanical function after upper airway injury

Corticosteroid-eluting endotracheal tubes (ETTs) were developed and employed in a swine laryngotracheal injury model to maintain airway patency and provide localized drug delivery to inhibit fibrotic scarring. Polycaprolactone (PCL) fibers with or without dexamethasone were electrospun onto the ETT surface PCL-only coated ETTs and placed in native airways of 18 Yorkshire swine. Regular and dexamethasone-PCL coated ETTs were placed in airways of another 18 swine injured by inner laryngeal mucosal abrasion. All groups were evaluated after 3, 7 and 14 days (n = 3/treatment/time). Larynges were bisected and localized stiffness determined by normal indentation, then sequentially matched with histological assessment. In the native airway, tissue stiffness with PCL-only ETT placement increased significantly from 3 to 7 days (p = 0.0016) and 3 to 14 days (p < 0.0001) while dexamethasone-PCL ETT placement resulted in stiffness decreasing from 7 to 14 days (p = 0.031). In the injured airway, localized stiffness at 14 days was significantly greater after regular ETT placement (23.1 ± 0.725 N/m) versus dexamethasone-PCL ETTs (17.10 ± 0.930 N/m, p < 0.0001). Dexamethasone-loaded ETTs were found to reduce laryngotracheal tissue stiffening after simulated intubation injury compared to regular ETTs, supported by a trend of reduced collagen in the basement membrane in injured swine over time. Findings suggest localized corticosteroid delivery allows for tissue stiffness control and potential use as an approach for prevention and treatment of scarring caused by intubation injury.