Novel anti-inflammatory effects of alpha-1-antitrypsin on lung microvascular endothelial cells

The acute phase protein alpha-1-antitrypsin (AAT) is released into the circulation at high concentrations (1.3–2mg/ml). The knowledge that an inherited AAT-deficiency increases susceptibility to chronic inflammatory conditions and that AAT is one of the major inhibitors of neutrophil proteases, suggests an important role for AAT in controlling acute phase inflammation and preventing development of chronic inflammation and tissue damage. Recent studies have also shown that exogenous AAT can be internalized by endothelial cells and suppresses cell apoptosis by inhibiting caspases-1 and 3. To further investigate the effects of AAT on endothelial cells, we first examined its influence on release of pro-inflammatory cytokine, TNFα. Primary lung microvascular endothelial cells were stimulated for 4 to 8h with TNFα in the presence or absence of human plasma derived preparation of AAT (Prolastin®, 2mg/ml). Under these experimental conditions, AAT clearly reduced TNFα concentrations in cell supernatants (61±11%) as compared to cells stimulated with TNFα alone. We next focused on the intracellular calcium-dependent calpains which are known to enhance leukocyte-endothelium interactions and endothelial dysfunction. Pre-incubation of endothelial cells for 1 hour with AAT (2mg/ml), efficiently reduced calpain activity (up to 53±8% of basal levels).

Thus, our results give further evidence for anti-inflammatory activities of AAT and reveal a previously unknown function for AAT, namely to inhibit calpains in endothelial cells. Calpain activity is implicated in numerous pathological conditions including Alzheimer's disease, demyelination events of multiple sclerosis, neuronal damage after spinal cord injury and hypoxic/ischaemic injury to brain, kidney and heart organs. Therefore, the property of AAT to regulate calpain activity may be important in a wide array of pathological states.