Elevated levels of the receptor for advanced glycation end products, a marker of alveolar epithelial type I cell injury, predict impaired alveolar fluid clearance in isolated perfused human lungs

Abstract

Background: Although alveolar epithelial injury is a major determinant of outcome in patients with acute lung injury, there is no reliable biological marker of alveolar epithelial injury. The primary objective was to determine whether elevated levels of the receptor for advanced glycation end products (RAGE), a marker of alveolar epithelial injury, reflect impaired alveolar fluid clearance (AFC) in an ex vivo perfused human lung preparation. A second objective was to determine whether levels of a marker of endothelial injury, von Willebrand factor antigen (vWF:Ag), are associated with impaired AFC.

Methods: Human lungs (N = 30) declined for transplantation by the California Transplant Donor Network were perfused at a constant pulmonary artery pressure of 12 mm Hg. Following rewarming to 36 degrees C, the lungs were inflated with a continuous positive airway pressure of 10 cm H(2)O. RAGE and vWF:Ag levels and AFC rates were then measured.

Results: The rate of AFC was inversely correlated with RAGE levels in the alveolar fluid (p < 0.005). Similarly, the concentration of RAGE in the alveolar fluid was significantly higher in lungs with submaximal AFC, defined in a prespecified analysis as <or= 14%/h, when compared with lungs with preserved AFC (median 0.82 vs 0.43 microg/mL; p < 0.05). In contrast, vWF:Ag levels did not correlate with the rate of AFC.

Conclusions: RAGE may be a useful biological marker of alveolar epithelial injury and impaired AFC in donor lungs prior to transplant and perhaps in patients with acute lung injury.

Figure 1

Alveolar fluid levels of RAGE according to the reason for lung rejection: The median is shown by the horizontal line within the box. The values between the lower and upper quartiles (25th to 75th centiles) are within the box. The whiskers represent the limits of the 90th and 10th centile values. Outliers are shown as filled circles (p < 0.005; Kruskal-Wallis test).

Figure 2

RAGE levels and AFC. RAGE levels in alveolar fluid were significantly higher in lungs with submaximal AFC (≤ 14%/h, n = 14) than in lungs with preserved fluid clearance (> 14%/h, n = 16). The distinction between groups in terms of AFC rates was previously described in patients with hydrostatic pulmonary edema and in patients with ALI. RAGE levels in the alveolar fluid are expressed as median and centiles. The median is shown by the horizontal line within the box. The values between the lower and upper quartiles (25th to 75th centiles) are within the box. The whiskers represent the limits of the 90th and 10th centile values. Outliers are shown as filled circles (p < 0.05; Mann-Whitney U test).

Figure 3

AFC and RAGE levels. The rate of AFC was inversely correlated with the level of RAGE in alveolar fluid (left, A) [p < 0.05; R = -0.55] but not with perfusate RAGE levels (right, B).

Figure 4

Correlation of alveolar fluid and perfusate levels of RAGE. Data have been log-transformed (natural logarithm). For every one-log increase in alveolar fluid RAGE, the perfusate level of RAGE increased by 0.5 log (p < 0.005); expressed differently, for every doubling in alveolar fluid RAGE, the concentration of RAGE in perfusate increased by 40%.

Figure 5

Effect of cold ischemia time on AFC and RAGE levels. The duration of cold ischemia (the time from procurement to experiment) was inversely correlated with the rate of AFC (R = -0.50; p < 0.05) [left, A] and positively correlated with the airspace levels of RAGE (R = 0.56; p < 0.01) [right, B].