Neutral endopeptidase of a human airway epithelial cell line recovers after hypochlorous acid exposure: dexamethasone accelerates this by stimulating neutral endopeptidase mRNA synthesis.

Hypocholorous acid (HOCl) exposure of Calu-1 cells in situ leads to a relatively rapid and substantial decrease in whole cell neutral endopeptidase (NEP) activity that may result from the internalization of NEP from plasma membrane surfaces. To confirm this, and to assess the time course of changes in cell NEP after oxidant exposure and the potential influence of corticosteroid treatment on these, we evaluated Calu-1 NEP activity by high performance liquid chromatography and NEP-specific mRNA over the ensuing 48 h after HOCl in the presence or absence of 1 microM dexamethasone. Cells, grown to confluency in Dulbecco's modified Eagle's medium with 10% fetal bovine serum, were exposed for 5 min to 100 microM HOCl and then maintained in culture for 48 h thereafter. Before exposure, some cell plates were cooled to 4 degrees C and/or incubated for 5 min in 1 mM sodium azide. In some experiments, post-HOCl changes in NEP-specific mRNA in the presence or absence of dexamethasone were also evaluated using Northern blot analysis. We found that sodium azide at 4 degrees C totally blocked the effect of HOCl on Calu-1 NEP (n = 6). In the absence of sodium azide, NEP activity spontaneously recovered to preexposure levels within 24 h. This recovery occurred 6 h earlier in the presence of 1 microM dexamethasone. Furthermore, dexamethasone increased NEP activity at 24 and 48 h after HOCl. Northern blot analysis indicated that NEP-specific mRNA did not change during spontaneous recovery, but was increased by dexamethasone 24 h after HOCl.(ABSTRACT TRUNCATED AT 250 WORDS)