Abstract
Cardiovascular disease risk depends on high-density lipoprotein (HDL) function, not HDL-cholesterol. Isolevuglandins (IsoLGs) are lipid dicarbonyls that react with lysine residues of proteins and phosphatidylethanolamine. IsoLG adducts are elevated in atherosclerosis. The consequences of IsoLG modification of HDL have not been studied. We hypothesized that IsoLG modification of apoA-I deleteriously alters HDL function. We determined the effect of IsoLG on HDL structure-function and whether pentylpyridoxamine (PPM), a dicarbonyl scavenger, can preserve HDL function. IsoLG adducts in HDL derived from patients with familial hypercholesterolemia (n = 10, 233.4 ± 158.3 ng/mg) were found to be significantly higher than in healthy controls (n = 7, 90.1 ± 33.4 pg/mg protein). Further, HDL exposed to myeloperoxidase had elevated IsoLG-lysine adducts (5.7 ng/mg protein) compared with unexposed HDL (0.5 ng/mg protein). Preincubation with PPM reduced IsoLG-lysine adducts by 67%, whereas its inactive analogue pentylpyridoxine did not. The addition of IsoLG produced apoA-I and apoA-II cross-links beginning at 0.3 molar eq of IsoLG/mol of apoA-I (0.3 eq), whereas succinylaldehyde and 4-hydroxynonenal required 10 and 30 eq. IsoLG increased HDL size, generating a subpopulation of 16-23 nm. 1 eq of IsoLG decreased HDL-mediated [3H]cholesterol efflux from macrophages via ABCA1, which corresponded to a decrease in HDL-apoA-I exchange from 47.4% to only 24.8%. This suggests that IsoLG inhibits apoA-I from disassociating from HDL to interact with ABCA1. The addition of 0.3 eq of IsoLG ablated HDL's ability to inhibit LPS-stimulated cytokine expression by macrophages and increased IL-1β expression by 3.5-fold. The structural-functional effects were partially rescued with PPM scavenging.
Highlights
Cardiovascular disease risk depends on high-density lipoprotein (HDL) function, not HDL-cholesterol
Whereas IsoLG-protein adducts were previously found in oxidized LDL, in human atherosclerotic lesions [16], and ϳ80% of all IsoLG-protein adducts in plasma were not associated with apoB-containing lipoproteins [17], we sought to determine the levels of IsoLG-protein adducts in HDL isolated from patients with hypercholesterolemia and atherosclerosis
We found that IsoLG-protein adducts were significantly higher (p Ͻ 0.05) in familial hypercholesterolemic (FH) (233.4 Ϯ 158.3 pg/mg protein) than in controls (90.1 Ϯ 33.4 pg/mg protein) (Fig. 2B)
Summary
4-hydroxyl-2(E)-nonenal (HNE) [14] and malondialdehyde [15]. Lipid peroxidation has long been postulated to play a critical role in the pathogenesis of atherosclerosis due to oxidative modification of LDL. Once HDL is modified, it loses important protective functions and acquires pro-atherosclerotic properties. Another important pathway of oxidative modification involves reactive intermediates produced by phagocytic white blood cells, the cellular hallmark of inflammation. Because IsoLG is extremely reactive and cross-links proteins, we hypothesize that modification of HDL proteins ( cross-linking of its structural proteins apoA-I and apoA-II) by IsoLG generated under oxidative conditions of atherosclerosis would cause deleterious consequences to HDL particle structure and function. We examine the consequences of IsoLG in cross-linking HDL proteins, particle morphology, and various HDL functions, including apoA-I exchange, cholesterol efflux, and protection against inflammation. We test the ability of PPM to preserve HDL and protect against dysfunction
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