A CONSORT-guided, randomized controlled clinical trial of nebulized administration of dexamethasone and saline on lower airway cytokine mRNA expression in horses with moderate asthma.

Overview

• This clinical trial investigated how nebulized dexamethasone affects inflammatory cytokine mRNA expression in the lower airways of horses with moderate asthma compared to saline treatment.
• The study found that nebulized dexamethasone increased the expression of several inflammatory cytokines but did not improve airway inflammation.

Study Objective and Background

• The research aimed to explore the impact of nebulized dexamethasone on cytokine mRNA regulation in horses with moderate asthma, an area that had not been studied before.
• Dexamethasone is a corticosteroid commonly used as an anti-inflammatory treatment, and understanding its effects via nebulization could guide better therapeutic approaches.
• Moderate equine asthma involves airway inflammation where cytokines play key roles in disease progression and control.

Study Design and Methodology

• Design: Prospective, randomized, controlled, blinded clinical trial following CONSORT guidelines to ensure scientific rigor.
• Subjects: 16 horses with naturally occurring moderate asthma and 4 healthy control horses, all housed in a dusty environment to maintain consistent exposure to an asthma trigger.
• Treatment Groups: Horses were randomly assigned to two groups using Microsoft Excel’s randomization function:
  • One group received nebulized dexamethasone (15 mg once daily).
  • The other group received nebulized saline (0.9%, 3 mL) as a placebo control.
• Sampling: Samples were collected before treatment (Day 0) and after 13 days of treatment (Day 14):
  • Blood samples were taken to monitor endogenous cortisol levels.
  • Tracheal mucus and bronchoalveolar lavage (BAL) fluid samples were collected to analyze airway inflammation.
• Measures:
  • qPCR was applied to BAL fluid to quantify mRNA expression of a panel of inflammatory cytokines including IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-17, IL-23, interferon-gamma (IFN-γ), Eotaxin-2, and tumor necrosis factor-alpha (TNF-α).
  • The relative expression software tool was used to analyze the quantitative PCR data and compare changes between Day 0 and Day 14.

Key Findings

• Horses treated with nebulized dexamethasone showed significant increases in the relative mRNA expression of:
  • IL-5 by 1.70-fold
  • IL-6 by 1.71-fold
  • IL-17 by 3.25-fold
  • IL-12 by 1.66-fold
  • TNF-α by 1.94-fold
• There was a significant decrease in the expression of IL-23 by 1.76-fold (P = 0.04) in the dexamethasone group.
• The saline-treated group showed no significant changes in any cytokine mRNA expression.
• Despite these molecular changes, neither dexamethasone nor saline treatment resulted in improvement of inflammatory cell profiles in airway cytology.

Interpretation and Conclusions

• The unexpected increase in several pro-inflammatory cytokine mRNAs suggests that nebulized dexamethasone might modulate cytokine gene expression in a complex manner rather than uniformly suppressing inflammation.
• The decrease in IL-23, which is involved in promoting certain inflammatory pathways, might indicate some nuanced immunomodulatory effects.
• The lack of improvement in airway cell inflammation despite altered cytokine expression highlights a potential disconnect between mRNA changes and clinical inflammatory response under these treatment conditions.
• This finding suggests that nebulized dexamethasone at the tested dose and duration may not be effective for controlling airway inflammation in moderate equine asthma.
• Additional studies might be needed to:
  • Clarify the role of individual cytokines in equine asthma when treated with corticosteroids.
  • Determine if different dosages, treatment durations, or administration methods improve outcome.
  • Investigate the translation of mRNA changes to protein levels and clinical signs.

Significance

• This study contributes important clinical evidence regarding the molecular effects of nebulized corticosteroids in equine asthma.
• It challenges assumptions about the anti-inflammatory efficacy of inhaled dexamethasone, suggesting a need for cautious interpretation and further research.
• The results guide veterinarians considering nebulized steroid therapies for asthma management in horses and emphasize a tailored approach based on molecular as well as clinical parameters.