Compromised inhibition of human lung lavage cell elastases

Pilot Study of the Effects of ONO-5046 in Patients with Acute Respiratory Distress Syndrome

Evidence has linked neutrophil elastase to acute respiratory distress syndrome (ARDS), suggesting that inhibiting the activity of this enzyme could prevent the development and progression of ARDS. However, few clinical trials have examined this notion. We therefore examined the effects of ONO-5046 (sivelestat, a specific inhibitor of neutrophil elastase; sodium N-[2-[4-(2,2-dimethylpropionyloxy) phenylsulfonylaminobenzoyl]amino-acetate tetrahydrate]) in a randomized, double-blinded trial in patients with ARDS. We randomly assigned 24 patients with ARDS to groups that received conventional therapy without or with sivelestat (0.2 mg. kg(-1). h(-1)) for 14 days. The variables of interest associated with clinical outcome were the duration of mechanical ventilation; changes in oxygenation from baseline; changes in cytokine levels from baseline; number of patients alive at 30 days who did not need mechanical ventilation; and mortality rate. The length of intensive care unit stay, number of ventilation days, and mortality rates did not statistically differ between groups. ARDS was more persistent in the control than in the sivelestat group (control, 19.5 +/- 7.4 days; sivelestat, 13.5 +/- 5.9 days; P = 0.039). Neutrophil elastase activity significantly differed between groups at 72 h after treatment. Levels of interleukin-6 were lower in the sivelestat group than in the controls at 24, 48, and 72 h after treatment. ONO-5046 apparently did not affect survival or the duration of mechanical ventilation.

Proteases and lung injury

OBJECTIVE

Acute respiratory distress syndrome (ARDS) represents an inflammatory process that is initiated by diverse systemic and/or pulmonary insults, resulting in a clinical syndrome of severe respiratory distress and refractory hypoxemia. Neutrophils and their cytotoxic products, including oxidants and proteases, such as elastase, have been implicated as playing a key role in the pathophysiology of ARDS. This article reviews some of the physiologic actions of proteases, specifically elastase, the evidence for neutrophil elastase involvement in ARDS, and the potential therapeutic use of neutrophil elastase inhibitors in lung injury.

DATA SOURCE

A review of published literature (original articles and reviews) in English from 1965 to 2002.

CONCLUSION

Although the data support a key role for neutrophil elastase in the pathogenesis of ARDS, further study is needed to fully define the actions of neutrophil elastase, and how these actions affect host functions, before we can exploit this knowledge for therapeutic benefit.

Macrophages and the pathogenesis of COPD

Macrophages are long-lived effector cells within the lung. They are reactive, responding to endogenous and exogenous stimuli, as well as proactive, producing mediators that modulate the behavior of surrounding cells. In addition, they play a critical role in the clearance of apoptotic neutrophils. Their role in COPD probably reflects a number of functional properties. However, if the link between increased proteinase burden and tissue destruction and injury in patients with COPD is correct, then macrophages must be very significant. Even though other cells, including epithelial cells and fibroblasts, have been shown to express higher matrix metalloproteinase (MMP) levels in lung tissue from subjects with COPD and emphysema, the numbers of resident cells do not appear to increase by the same factor as that of sequestered macrophages. The combination of a 5- to 10-fold increase in macrophage numbers, the up-regulation of MMPs, and their co-release with other classes of stored proteinases must be highly significant in terms of an increase in proteinase potential in the small airways and respiratory units. This may account for increased tissue destruction and inflammatory mediator activation leading to the pathology that occurs during COPD. Since only about 15% of smokers develop clinically significant disease, it seems likely, in smokers without COPD, that these processes either are strictly controlled or that lung repair mechanisms are more effective.