α-Linoleic Acid Enhances the Capacity of α1-Antitrypsin to Inhibit Lipopolysaccharide-Induced IL-1β in Human Blood Neutrophils

Alphal-antitrypsin (A1AT, SERPINA1), a major circulating inhibitor of neutrophil elastase (NE) and protelnase-3 (PR3), has been proposed to reduce the processing and release of IL-1β. Since the antiinflammatory properties of A1AT are influenced by the presence of polyunsaturated fatty acids, we compared the effects of fatty acid-free (A1AT-0) and α-linoleic acid (LA)-bound (A1AT-LA) forms of A1AT) on lipopolysaccharide (LPS)-induced synthesis of the 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 peroxisome proliferator-activated receptor (PPAR)-γ was observed in A1AT-LA-treated neutrophils without LPS stimulation, and the selective PPAR-γ antagonist (GW9662) prevented a 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 antiinflammatory properties of A1AT-LA are likely to be mediated by activation of PPARγ.