Pulmonary capillary endothelial dysfunction in early systemic sclerosis.

OBJECTIVE: Pulmonary capillary endothelium-bound angiotensin-converting enzyme (PCEB-ACE) activity is a sensitive and quantifiable index of endothelial function in vivo. Systemic sclerosis (SSc) is characterized by endothelial damage and excess collagen formation, causing mainly pulmonary hypertension (PH) in the limited cutaneous SSc (lcSSc) subset and interstitial lung disease with pulmonary interstitial fibrosis (PIF) in the diffuse cutaneous SSc (dcSSc) subset. This study was undertaken to investigate the hypothesis that PCEB-ACE activity is reduced early in SSc, in the absence of PH or PIF. METHODS: Applying indicator-dilution techniques, we measured single-pass transpulmonary hydrolysis and percent metabolism (%M) of a synthetic ACE substrate and calculated functional capillary surface area (FCSA) in 25 SSc patients and 11 controls. Substrate hydrolysis and %M reflect ACE activity per capillary; FCSA reflects ACE activity per vascular bed. RESULTS: PCEB-ACE activity was decreased in both SSc subsets. Among patients without PH, substrate hydrolysis and %M were decreased in patients with lcSSc and more profoundly in those with dcSSc; loss of FCSA normalized to body surface area (FCSA/BSA) was observed in dcSSc, but not in lcSSc. High-resolution computed tomography of the lung, performed in all SSc patients, revealed no correlation between substrate %M, hydrolysis, or FCSA/BSA and the degree of PIF; 5 dcSSc and 5 lcSSc patients with no detectable PIF exhibited decreases in hydrolysis and %M, while FCSA/BSA was decreased only in dcSSc. CONCLUSION: Depression of PCEB-ACE activity, indicating pulmonary endothelial dysfunction, occurs early in SSc, in the absence of PH or PIF, and is more pronounced, at this early pulmonary disease stage, in dcSSc than in lcSSc.

Pulmonary capillary endothelium-bound angiotensin-converting enzyme activity in acute lung injury.

BACKGROUND: Pulmonary capillary endothelium-bound (PCEB) angiotensin-converting ectoenzyme (ACE) activity alteration is an early, sensitive, and quantifiable lung injury index in animal models. We hypothesized that (1) PCEB-ACE alterations can be found in patients with acute lung injury (ALI) and (2) PCEB-ACE activity correlates with the severity of lung injury and may be used as a quantifiable marker of the underlying pulmonary capillary endothelial dysfunction. METHODS AND RESULTS: Applying indicator-dilution techniques, we measured single-pass transpulmonary hydrolysis of the synthetic ACE substrate (3)H-benzoyl-Phe-Ala-Pro (BPAP) in 33 mechanically ventilated, critically ill patients with a lung injury score (LIS) ranging from 0 (no lung injury) to 3.7 (severe lung injury) and calculated the kinetic parameter A(max)/K(m). Both parameters decreased early during the ALI continuum and were inversely related to APACHE II score and LIS. Hydrolysis decreased with increasing cardiac output (CO), whereas 2 different patterns were observed between CO and A(max)/K(m). CONCLUSIONS: PCEB-ACE activity decreases early during ALI, correlates with the clinical severity of both the lung injury and the underlying disease, and may be used as a quantifiable marker of underlying pulmonary capillary endothelial dysfunction.