Alpha-1 antitrypsin genotypes and associated inhibitory activity towards neutrophil serine proteinases, in vitro

Native PI*M α-1 antitrypsin (AAT) inhibits neutrophil serine proteases (NSPs): human neutrophil elastase (HNE), proteinase 3 (PR3) and cathepsin G (CG) involved in the lung tissue destruction. AAT favors HNE, thus PR3 and CG might play more important role in COPD development. PI*F and PI*Z AAT alleles have lower inhibitory activity towards HNE but reliable data regarding their activity towards PR3 and CG are lacking. Methods: AAT protein was isolated using affinity chromatography from serum of clinically asymptomatic and respiratory subjects carrying PI*MM,MZ,ZZ and FM AAT genotypes. Anti-HNE, -PR3 and -CG activity of AAT preparations was assessed by innovative fluorescence resonance energy transfer (FRET) method. Results: The trend towards decreasing anti-HNE, -PR3 and -CG activity of MMu003eMZu003eZZ AAT proteins was found in both healthy and respiratory groups by regression analysis (R2u003e0.8). A significant difference in % HNE, PR3 and CG inhibition (p=0.000, p=0.000 and p=0.046 respectively) was noted between AAT proteins isolated from ZZ COPD (39±22; 51±1; 32±17 %) vs. MM healthy (100±0; 100±9; 100±28 %) as well as between ZZ COPD vs. MM COPD (95±6, 94±5 and 101±22) with p= 0.002, p=0.000 and p=0.036 accordingly. Conclusions: PI*Z AAT variant have diminished inhibitory activity towards HNE but also towards PR3 and CG. AAT inhibitory activity towards NSPs corresponded in vitro with AAT phenotype and clinical status of patients.