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Updated: Aug 17, 2026
Murine Oropharyngeal Aspiration Model of Ventilator-associated and Hospital-acquired Bacterial Pneumonia
Published on: June 28, 2018
[Study of rat beta-defensin-2 gene and protein expression in ventilator-associated pneumonia]
Qing-ping Wu1, Shang-long Yao, Xiang-ming Fang
1Department of Anesthesiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, Hubei, China.
Objective:
To study the changes in the expression of rat beta-defensin-2 (RBD-2) gene in the lung tissue with P. aeruginosa (PA) pneumonia following tracheal mechanical ventilation (MV), and to evaluate the pathogenesis of ventilator-associated pneumonia (VAP).
Methods:
A total of 58 normal healthy Sprague-Dawley rats, weighing between 280 and 320 g, were randomly divided into the control group and the conventional MV group (CMV). A tracheal catheter was inserted via mouth in every rat under urethane anesthesia. PA (1 MIC, 0.2 ml) was instilled into the tracheal in the control group. Rats of CMV group received MV (V(T)=12 ml/kg) through tracheal tube for 24 hours, and then were challenged intra-tracheally with PA (1 MIC, 0.2 ml). Fluid loss was replenished through intravenous infusion. The arterial catheter was used for hemodynamics, parameters were monitored, and arterial blood gases were determined. Samples of lung were harvested at 0 hours, 15 hours, 3 hours, 6 hours, 12 hours, 1 day, 3 days and 5 days, respectively, after bacterial challenge. The mRNA of RBD-2 was detected by reverse transcription-polymerase chain reaction (RT-PCR), and the protein levels were analyzed by Western blotting.
Results:
Expression of RBD-2 mRNA and protein was lower in CMV group compared with the control 3 hours before instillation of bacteria. RBD-2 mRNA increased 3 hours after bacteria instillation, reaching the peak at 12-24 hours. No significant difference in RBD-2 expression between the control group and the CMV group within 3 hours, but it was significantly higher at 3 hours, 6 hours, 12 hours, 1 day, 3 days and 5 days in the control group than in the CMV group. The number of inflammatory cells infiltrating the bronchial submucous layer was significantly higher in the control group than in the CMV group (P<0.05). There was milder interstitial pulmonary edema and less red blood cells in the alveoli in the control group than in the CMV group. The mortality rate of the CMV group was 60%, which was significantly higher than that of the control group (20%, P<0.05). The positive rates of blood culture and bronchoalveolar lavage fluid (BALF) bacterial culture were also higher in the CMV group (P<0.05). The survival rate in CMV group (40%) was lower than that of the control group (P<0.05).
Conclusion:
The lowering of BD-2 gene and protein expression in the CMV group 3 hours after bacteria challenge might be one of the contributory factors in causing VAP.
Insights
Mechanical ventilation (MV) in rats with pneumonia led to decreased rat beta-defensin-2 (RBD-2) expression, contributing to ventilator-associated pneumonia (VAP). Lower RBD-2 levels correlated with increased inflammation and mortality, suggesting a role in VAP pathogenesis.
Area of Science:
- Pulmonary Medicine
- Immunology
- Microbiology
Context:
- Ventilator-associated pneumonia (VAP) is a significant complication in mechanically ventilated patients.
- The role of antimicrobial peptides like rat beta-defensin-2 (RBD-2) in VAP pathogenesis is not fully understood.
Purpose:
- To investigate the expression of RBD-2 in lung tissue during P. aeruginosa (PA) pneumonia in rats undergoing mechanical ventilation (MV).
- To elucidate the potential contribution of altered RBD-2 expression to the development of VAP.
Summary:
- RBD-2 mRNA and protein expression were significantly lower in rats subjected to conventional mechanical ventilation (CMV) compared to controls, particularly after PA challenge.
- While initial RBD-2 expression showed no difference within 3 hours, it was markedly elevated in controls versus CMV groups at later time points.
- CMV group exhibited increased inflammatory cell infiltration, pulmonary edema, and higher mortality rates, alongside increased bacterial load.
Impact:
- Reduced RBD-2 expression during MV may be a key factor in VAP development.
- Findings highlight the importance of innate immune responses, specifically defensins, in combating VAP.
- This study provides insights into the mechanisms underlying VAP and suggests potential therapeutic targets.
