Expression of neutral endopeptidase activity during clinical and experimental acute lung injury.
BACKGROUND
Neutral endopeptidase (NEP), an enzyme that cleaves inflammatory bioactive peptides, may play a protective role in the pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, its low extracellular activity hinders the precise measurement of changes that take place during ALI/ARDS. The main objective of this study was to clarify the regulation of NEP activity and its expression during ALI/ARDS.


METHODS
In a clinical study, we measured plasma NEP activity in patients who developed postoperative ALI/ARDS, using a HPLC fluorometric system. In an experimental study, we induced ALI by intratracheal instillation of hydrochloric acid (HCl) or lipopolysaccharide (LPS) in mice, and similarly measured NEP activity in plasma, lung tissue, and broncho-alveolar lavage fluid (BALF). We also studied the distribution and measured the amounts of NEP protein, using immuno-histochemical and immunoblot analyses, and measured the levels of NEP mRNA, using real-time reverse transcription-polymerase chain reaction, in the lungs of mice with ALI.


RESULTS
The plasma NEP activity was significantly lower in patients presenting with ALI/ARDS than in controls. Similarly, the NEP activity in plasma and lung tissue was markedly lower, and lung injuries more severe in LPS- than in HCl-treated mice. In contrast, the activity of NEP in the BALF of LPS-treated mice was increased. The intratracheal instillation of LPS decreased the gene expression of NEP in the lung. Immuno-histochemical and Western immunoblot studies in mice confirmed a) the presence of NEP in the alveolar wall, a critical target in ALI/ARDS, and b) a decrease in its expression in HCl- and LPS-induced ALI.


CONCLUSIONS
In this experimental and clinical study of ALI/ARDS, the activity of NEP was significantly decreased in plasma and increased in the alveolar air space.
Department of Anesthesiology and Intensive Care, Kyoto Prefectural University of Medicine, Kyoto, Japan. soshi@koto.kpu-m.ac.jp
Soshi
S
Hashimoto
Fumimasa
F
Amaya
Kentaro
K
Oh-Hashi
Kazutoshi
K
Kiuchi
Satoru
S
Hashimoto
D055371:Acute Lung Injury / Q000097:blood* / Q000201:enzymology*; D000368:Aged; D000818:Animals; D004195:Disease Models, Animal; D015870:Gene Expression; D006801:Humans; D008168:Lung / Q000201:enzymology*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008875:Middle Aged; D015260:Neprilysin / Q000097:blood*; D014018:Tissue Distribution
D015260:Neprilysin