Abstract Body: Introduction: Inflammation drives atherosclerosis, with recent clinical trials targeting atherogenic cytokines released by immune cells. However, inflammation also triggers these same cells to release proteases. This elevated proteolytic activity may accelerate plaque development but is not being explored clinically. Neutrophil elastase (NE) is a serine protease secreted by neutrophils and macrophages. NE is enriched in atheromatous plaques and plasma levels can rise up to ten-fold in inflammation. In vitro, NE modifies the protein components of low-density lipoprotein (LDL) and high-density lipoprotein (HDL), and these modified lipoproteins are rapidly internalized by macrophages. These data suggest a proatherogenic role of NE, but it is unknown how these modified lipoproteins are metabolized in plasma or how they affect plaque development in vivo.

Objectives: Alpha-1-antitrypsin (AAT) is the endogenous inhibitor of NE. Here, we aim to determine the effects of elastolytic activity on lipoprotein metabolism and atherosclerosis using a two-pronged approach: (1) administration of elastase to lipoproteins and (2) use of an AAT-deficient (Serpina1^-/-) mouse as a model for chronically elevated elastase activity.

Results: Western blotting revealed NE degradation of apolipoproteins in plasma from wild type and Serpina1^-/- mice ex vivo. ApoB degradation was also observed when NE was injected in vivo into Serpina1^-/- mice. Interestingly, modified particles were rapidly cleared from circulation. In human plasma, elastase treatment resulted in an HDL shift towards larger fractions, suggesting elastase may cause HDL aggregation. Lipoprotein profile analysis revealed that Serpina1^-/- mice on chow diet have increased HDL-cholesterol. To understand the effect of this deficiency on early-stage atherosclerotic lesions, we conducted an 8-week atherosclerosis study in male mice with Western diet feeding and Ldlr-ASO injections. Plasma elastase levels were notably higher at study termination in both genotypes. En face analysis showed that Serpina1^-/- mice had ~45% higher aortic arch lesion area compared to wild type mice.

Conclusions: NE modifies lipoproteins ex vivo and in vivo which may affect their metabolism relevant to atherosclerosis pathophysiology. AAT-deficient (Serpina1^-/-) mice have increased plasma cholesterol and increased early-stage atherosclerotic plaque burden. Studies are underway to determine the effect of AAT-deficiency on more developed lesions.