The most well-studied of these is the incorporation of acute phase proteins such as SAA, symmetric dimethylarginine (SDMA), lipopolysaccharide binding protein (LBP), alpha-1-antitrypsin (A1AT), or fibrinogen into HDLs protein cargo . protein cargo. The most studied of these enzymes is the antioxidant enzyme paraoxonase-1 (PON-1), although roles for other enzymes such as lipoprotein-associated phospholipid A2 (Lp-PLA2)  and LCAT  have also been demonstrated. The presence of PON-1 has been shown to protect both HDL and LDL from oxidation in vitro [33, 37], while its absence (using PON-1 knockout mice) has been demonstrated to have the opposite effect . Interactions with ApoA-I appear to be crucial for its activity, as demonstrated by the significantly increased capacity for PON-1 to prevent LDL oxidation and promote RCT in HDL particles containing ApoA-I as Rabbit Polyclonal to E-cadherin opposed to those containing ApoA-II or IV . Additional antioxidant effects of ApoA-I also likely contribute to HDLs antioxidant properties via its ability to directly bind and remove oxidised lipids MBP146-78 from LDL particles within the vascular wall, as treatment of arterial cell walls with ApoA-I or an Apo-AI mimetic peptide in vitro prevents MBP146-78 the oxidation of LDL, as does injection of ApoA-I into both mice and humans [40, 41]. HDL has also been shown in a number of studies to reduce superoxide production in endothelial cells treated with tumour necrosis factor alpha (TNF-) [42C44], possibly through inhibitory effects on nicotinamide adenine dinucleotide phosphate (NADPH)-oxidases mediated through HDL-associated lysosphingolipids MBP146-78 and their interaction with S1P3 and SR-BI receptors . Both this pathway and others have also been shown to have downstream effects on the production of numerous inflammatory-mediated adhesion molecules such as vascular and intercellular adhesion molecules (VCAM-1 and ICAM-1) , E-selectin , and monocyte chemoattractant protein-1 (MCP-1) [45, 47], reducing their expression and limiting monocyte transmigration across the vascular wall. Furthermore, ABCA1-mediated cholesterol efflux to ApoA-I may also provide additional suppression through the activation of anti-inflammatory signalling molecules during reverse MBP146-78 cholesterol transport . HDL Structure and Dysfunction in Chronic Inflammation: When Good Cholesterol Turns Bad Inflammation Alters HDL Structure The concept that individuals with chronic disease may have structurally modified and potentially dysfunctional HDL was initially suggested in the mid-1990s, where evidence was produced for the first time showing the replacement of ApoA-I and paraoxonase-1 (PON-1) during an acute inflammatory response with acute phase proteins such as ceruloplasmin and serum-amyloid A (SAA) . In this seminal study, the authors further noted that the antioxidant and anti-inflammatory vasoprotective properties of these modified HDL particles were also lostor in certain caseseven completely reversed, suggesting that conformational changes in the HDL particle may have negatively affected its function. Since then, wide-ranging structural changes have been reported in a variety of inflammatory disease states, many of which have been implicated in the generation of a dysfunctional phenotype which may act to increase atherosclerotic risk. The most well-studied of these is the incorporation of acute phase proteins such as SAA, symmetric dimethylarginine (SDMA), lipopolysaccharide binding protein (LBP), alpha-1-antitrypsin (A1AT), or fibrinogen into HDLs protein cargo . These changes in turn result in reciprocal and detrimental reductions in ApoA-I, a decrease in the activity of HDL-associated antioxidant enzymes such as PON-1 and Lp-PLA2, and an increased presence of inflammatory enzymes and lipid peroxidation products such as myeloperoxidase (MPO) and malondialdehyde (MDA) . Furthermore, compositional changes in.