Background
High-density lipoproteins (HDL) are a complex mixture of lipids and proteins with vasculoprotective properties. However, HDL components could suffer post-translational modifications (PTMs) under pathological conditions, leading to dysfunctional HDL. We studied whether HDL are modified in abdominal aortic aneurysm (AAA) and the effect on HDL functionality.
Methods
HDL were isolated by ultracentrifugation from AAA tissue (HDL-T) and from plasma of healthy volunteers and then incubated with AAA tissue-conditioned medium (HDL-AAA CM). PTMs from these particles were characterized using Comet-PTM. The ability of HDL-AAA CM for promoting cholesterol efflux was determined ex vivo and in vivo by using J774A.1 [3H]cholesterol-labeled mouse macrophages and after injecting [3H]cholesterol-labeled mouse macrophages and HDL into the peritoneal cavity of wild-type C57BL/6 mice, respectively. Trp50 and Trp108 oxidized forms of APOA1 in HDL incubated with conditioned-medium of activated neutrophils and in plasma of AAA patients and controls were measured by targeted parallel reaction monitoring. Findings: Oxidation was the most prevalent PTM in apolipoproteins, particularly in APOA1. Trp50 and Trp108 in APOA1 were the residues most clearly affected by oxidation in HDL-T and in HDL-AAA CM, when compared to their controls. In addition, cholesterol efflux was decreased in macrophages incubated with HDL-AAA CM in vitro and a decreased macrophage-to-serum reverse cholesterol transport was also observed in mice injected with HDL-AAA CM. Finally, both oxidized Trp50 and Trp108 forms of APOA1 were increased in HDL incubated with conditioned-medium of activated neutrophils and in plasma of AAA patients in relation to controls. Interpretation: Oxidative modifications of HDL present in AAA tissue and plasma were closely associated with the loss of vasculoprotective properties of HDL in AAA. FUND: MINECO, ISCiii-FEDER, CIBERDEM, CIBERCV and LA CAIXA.