Antiproteases modulate bronchial epithelial cell responses to endotoxin.

Escherichia coli endotoxin (0.1 to 1000 micrograms/ml) stimulated the release of neutrophil chemotactic activity (P < 0.001) and induced bronchial epithelial cell (BEC) cytotoxicity assessed by lactate dehydrogenase release (P < 0.001). Endotoxin (100 micrograms/ml) inhibited BEC accumulation (P < 0.001). In the present study, we investigated the role of proteolytic activity of BECs per se in response to endotoxin. Several structurally and functionally different antiproteases, alpha 1 protease inhibitor, soybean trypsin inhibitor, two chloromethyl ketone derivatives (N-tosyl-L-lysine chloromethyl ketone and methoxysuccinyl-Ala-Ala-Pro-Val chloromethyl ketone), and L-658,758, a neutrophil elastase inhibitor, attenuated the release of neutrophil chemotactic activity and lactate dehydrogenase (P < 0.01). alpha 1-Protease inhibitor and N-tosyl-L-lysine chloromethyl ketone attenuated the inhibition of BEC accumulation by endotoxin (P < 0.001). The proteolytic enzyme activity measured by synthetic substrates revealed that endotoxin significantly augmented the serine proteolytic activity in the cell layers. Culture supernatant fluids and cell lysates of BECs in the presence of endotoxin solubilized 14C-labeled casein. These data suggest that responses of BECs to endotoxin may involve activation of cellular proteolytic activity.