Measurement of ceruloplasmin in the lungs of patients with acute respiratory distress syndrome: is plasma or local production the major source?
BACKGROUND
Oxidant-induced tissue damage is thought to contribute to the lung injury seen in patients with acute respiratory distress syndrome (ARDS). Ceruloplasmin (CP) is a major circulating antioxidant, increased levels of which have been measured in bronchoalveolar lavage fluid (BALF) taken from such patients. Traditionally, CP detected in these circumstances was thought to be plasma-derived, moving into the alveolar spaces as a consequence of the increased alveolar-capillary permeability that characterises ARDS. However, recent studies in murine models suggest that CP may be synthesised in the airways and even alveoli under physiological conditions.


OBJECTIVE
The aims of this investigation were therefore to identify the source of any increased levels of CP detectable in BALF taken from patients with established ARDS.


METHODS
Matched BALF and plasma samples taken from patients with ARDS (n = 46) and from controls without lung disease (n = 11) were analysed for CP (132 kD) and plasma specific albumin (ALB, 68 kD) and (alpha(2)-macroglobulin (alpha(2)-M, 820 kD).


RESULTS
All three proteins were increased in BALF taken from patients with ARDS compared to controls (p < 0.01, ALB and CP; p < 0.001, alpha(2)-M). When protein levels were expressed as the ratios of BALF: plasma (designated Q), Q(CP) and Q(alpha2)-M increased in parallel to Q(ALB) (p < 0.001), indicating that all increases were primarily plasma-derived. Their relative coefficients of excretion (RCE: Q(CP)/Q(ALB) and Q(alpha2)-M/Q(ALB)) demonstrated that the larger molecular weight protein, alpha(2)-M, gave the best discrimination between patients with ARDS and normal controls (0.85 vs. 0.04; p < 0. 01), indicating that this was the most sensitive marker of alveolar-capillary permeability.


CONCLUSIONS
Increased levels of CP in BALF from patients with ARDS are mainly attributable to plasma exudation.
Baker
C S
CS
Cell Biology Unit, National Heart and Lung Institute, Imperial College School of Medicine, London, UK. c.s.baker@mds.qmw.ac.uk
Evans
T W
TW
Haslam
P L
PL
D000328:Adult; D000368:Aged; D001798:Blood Proteins / Q000032:analysis*; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry* / Q000166:cytology; D016022:Case-Control Studies; D002452:Cell Count; D002570:Ceruloplasmin / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D005260:Female; D006801:Humans; D008168:Lung / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D012128:Respiratory Distress Syndrome / Q000378:metabolism*; D012307:Risk Factors
D001798:Blood Proteins; D002570:Ceruloplasmin