Chronic Obstructive Pulmonary Disease: Role of Alpha-1-antitrypsin
Abstract: The only proven genetic risk factor for Chronic Obstructive Pulmonary Disease (COPD) is an inherited Z (Glu342¡úLys) deficiency of alpha-1-antitrypsin (AAT), a major inhibitor of neutrophil elastase. In vivo, AAT is found in both native (inhibitory) and modified (non-inhibitory) forms. There is now increasing evidence that the different forms of AAT may exhibit biological activities independent of protease inhibition. The aim of my studies was to validate polymerized (non inhibitory) form of AAT as a potential COPD biomarker and to investigate its biological effects in vitro. We have discovered that a mouse monoclonal antibody, ATZ11, raised against the mutant Z AAT, does not detect the mutation per se, but recognizes a conformation-dependent epitope in polymerized and elastase-complexed AAT. By using this antibody we show that in Z deficiency subjects a predominant fraction of plasma AAT is in a polymerized form. In addition, a positive staining of endothelial cells with ATZ11 is detected in both wild-type M and deficiency Z individuals. The levels of total and polymerized serum AAT and inflammatory biomarkers in M and Z COPD patients and controls were correlated. Hypothetically, by using factor analysis, we were able to segregate the variables measured into two independent components: the first containing MMP9, MCP-1, IL-8 and VEGF and the second ¨C total and polymerized AAT, sE-selectin and ICAM-1. We demonstrate that 95% of originally grouped individuals can be correctly classified on the basis of the measured variables. This suggests that the combinations of biomarkers may provide useful diagnostic tools. We next investigated the release of pro-inflammatory molecules by monocytes isolated from blood of COPD patients and controls with and without Z AAT deficiency under basal conditions and after stimulation with endotoxin. Dependent on disease state and AAT genotype the different profiles of pro-inflammatory molecules are released by monocytes. The development of COPD may also be ascribed to acquired AAT deficiency, which results from the post-translational modifications of the protein. We have tested whether native and modified (polymerized) forms of AAT differ in their effects on primary human monocytes in vitro. Both native and polymerized AAT exhibit similar pro-inflammatory effects at lower, but not at physiological, concentrations. These properties of AAT appear to be dependent on protein concentration, but not on molecular form. Our studies support a central role of AAT in inflammation and serve as a basis for the future research in identifying new biological role(s) of AAT in vivo.
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