J. A. Kanter1, H. Sun2, M. M. DeCamp1, P. Sporn2, J. I. Sznajder2, A. Bharat1 1Northwestern University,Division Of Thoracic Surgery, Feinberg School Of Medicine,Chicago, IL, USA 2Northwestern University,Division Of Pulmonary And Critical Care Medicine, Feinberg School Of Medicine,Chicago, IL, USA
Introduction: Poor healing after lung surgery is manifested by prolonged air leaks (PAL). PAL can affect over 50% of patients with emphysema and 25% of those with normal lungs. Although PAL remains the predominant cause of morbidity and mortality following lung surgery, its pathogenesis remains unknown. Here we determined whether high carbon dioxide levels (hypercapnia) in the pleural cavity leads to poor lung healing and PAL.
Methods: Human data was collected from an IRB-approved prospective clinical trial on patients undergoing lung resection. Intrapleural gas analysis was performed on the air leaking into the chest drainage tube using spectroscopy. Cultures were performed in chambers with adjustable CO2 levels. Cell migration was determined by scratch wound and transwell migration assays using serum-depleted medium to limit cell proliferation. Western blot and gene/RNA arrays were performed to analyze the chemokine CXCL12 and the GTPase protein Rac1.
Results:
Human: Intrapleural CO2 levels showed a strong correlation with duration of air leaks in patients undergoing lung resection (n=120, r=0.07, p<0.001). Patients with PAL had a three-fold higher level of intrapleural CO2 compared to those without (p<0.001). Intrapleural hypercapnia was associated with a 2.5-fold decreased pleural CXCL12 levels (p<0.001). Decreasing intrapleural CO2 concentration using supplemental oxygen and extrapleural suction resulted in a two-fold reduction of the duration of air leaks (n=20, p=0.001).
Laboratory: Hypercapnia (15-20%) impaired cell migration and wound healing of primary human and murine alveolar epithelial cells as well as cell lines A549 (human) and MLE12 (murine), independent of cell proliferation. Although total intracellular Rac1 was preserved, both CXCL12 and activated Rac1 were significantly reduced in hypercapnia. Exogenous CXCL12 restored intracellular activated Rac1 levels and reversed the inhibition of cell migration in hypercapnia. CXCL12 antagonist AMD-3100 or CXCL12-antibodies blocked the effects of exogenous CXCL12 in hypercapnia and suppressed cell migration in normocapnia.
Conclusion: Intrapleural hypercapnia suppresses migration of alveolar epithelial cells that are crucial for repair following lung injury. This is likely due to suppression of intracellular Rac1 activation, which is known to trigger cell migration. Further, levels of CXCL12 that can activate Rac1 are suppressed by intrapleural hypercapnia. Hence, modulation of intrapleural CO2 levels and/or CXCL12 might promote lung healing following surgery.