Alpha1-antitrypsin (A1AT, SERPINA1), a major circulating inhibitor of neutrophil elastase (NE) and proteinase-3 (PR3), has been proposed to reduce the processing and release of IL-1β. Since the anti-inflammatory properties of A1AT are influenced by the presence of polyunsaturated fatty acids, we compared effects of fatty acid-free (A1AT-0) and α-linoleic acid bound (A1AT-LA) forms of A1AT on lipopolysaccharide (LPS)-induced synthesis of IL-1β precursor and the release of IL-1β from human blood neutrophils. The presence of A1AT-LA or A1AT-0 significantly reduced LPS induced release of mature IL-1β. However, only A1AT-LA reduced both steady state mRNA levels of IL-1β and the secretion of mature IL-1β. In LPS-stimulated neutrophils, mRNA levels of TLR2/4, NFKBIA, P2RX7, NLRP3, and CASP1 decreased significantly in the presence of A1AT-LA but not A1AT-0. A1AT-0 and A1AT-LA did not inhibit the direct enzymatic activity of caspase-1, but we observed complexes of either form of A1AT with NE and PR3. Consistent with the effect on TLR and IL-1β gene expression, only A1AT-LA inhibited LPS-induced gene expression of NE and PR3. Increased gene expression of PPAR-γ was observed in A1AT-LA treated neutrophils without of LPS stimulation, and the selective PPAR-γ antagonist (GW9662) prevented the reduction in IL-1β by A1AT-LA. We conclude from our data, that the ability of A1AT to reduce TLR and IL-1β gene expression depends on its association with LA. Moreover, the anti-inflammatory properties of A1AT-LA are likely to be mediated by the activation of PPAR-γ.
Keywords: LPS; SERPINA1; alpha1 antitrypsin; fatty acids; human neutrophils; inflammasome; α-linoleic acid.