10: Recombinant alpha-1 antitrypsin-Fc (AAT-Fc) inhibits candida-induced IL 1β secretion from human CD14 monocytes: comparison to plasma-derived AAT and caspase 1 inhibition

Abstract

Although often studied for its ability to inhibit neutrophil elastase, alpha-1 antitrypsin (AAT) has broad anti-inflammatory properties not related to its anti-protease activity. For example, monotherapy of mice with human plasma-derived AAT prevents pancreatic islet beta cell allograft rejection, the incidence of diabetes in the NOD mouse, DSS colitis, ischemia–reperfusion injury in the heart and graft versus host disease. Clinical trials are being conducted using AAT to treat late onset diabetes mellitus and graft versus host disease. However, AAT is purified from pooled human plasma and since the treatment dose is 60 mg/kg (or higher), plasma-derived AAT dosing requires intravenous infusion. In addition, human plasma carries the risk of infection with unknown viruses. Therefore, we produced recombinant human AAT as an Fc fusion protein and studied its properties in various animal models of systemic and local inflammation. We compared AAT-Fc with plasma-derived AAT. Plasma-derived or AAT-Fc reduced monosodium urate crystal acute knee joint arthritis; however, AAT-Fc at 2 mg/kg intraperitoneally was as effective as 80 mg/kg of plasma AAT (40-fold less). We next studied the ability of AAT to reduce IL1 β secretion from human blood monocytes stimulated with heat-killed Candida albicans in vitro. Although plasma-derived AAT reduced Candida-induced IL1b secretion at 500–1000 μg/mL by 50%, AAT-Fc was as effective at μg/mL. At 25 μg/mL, AAT-Fc reduced IL1 β secretion by 55% compared to 44% using 10 μM of a specific caspase1 inhibitor. The intracellular levels of IL1 β following Candida stimulation were also reduced by AAT- Fc, for example, 51% inhibition at 12 mg/mL, suggesting that AAT-Fc reduces IL-1 β synthesis as well as secretion. In contrast to reducing IL1 β , AAT-Fc at 12 mg/mL induces the release of the IL-1receptor antagonist from monocytes. Without being derived from human plasma, recombinant AAT-Fc is safe and due to its high specific activity, may be administered subcutaneously.