Reactive Dicarbonyl Scavenging Effectively Reduces MPO-Mediated Oxidation of HDL and Restores PON1 Activity

Abstract

Atheroprotective functions of high-density lipoproteins (HDL) are related to the activity of HDL-associated enzymes such as paraoxonase 1 (PON1). We examined the impact of inhibition of myeloperoxidase (MPO)-mediated HDL oxidation by PON1 on HDL malondialdehyde (MDA) content and HDL function. In the presence of PON1, crosslinking of apoAI in response to MPO-mediated oxidation of HDL was abolished, and MDA-HDL adduct levels were decreased. PON1 prevented the impaired cholesterol efflux capacity of MPO-oxidized HDL from Apoe−/− macrophages. Direct modification of HDL with MDA increased apoAI crosslinking and reduced the cholesterol efflux capacity. MDA modification of HDL reduced its anti-inflammatory function compared to native HDL. MDA-HDL also had impaired ability to increase PON1 activity. Importantly, HDL from subjects with familial hypercholesterolemia (FH-HDL) versus controls had increased MDA-apoAI adducts, and PON1 activity was also impaired in FH. Consistently, FH-HDL induced a pro-inflammatory response in Apoe−/− macrophages and had an impaired ability to promote cholesterol efflux. Interestingly, reactive dicarbonyl scavengers, including 2-hydroxybenzylamine (2-HOBA) and pentyl-pyridoxamine (PPM), effectively abolished MPO-mediated apoAI crosslinking, MDA adduct formation, and improved cholesterol efflux capacity. Treatment of hypercholesterolemic mice with reactive dicarbonyl scavengers reduced MDA-HDL adduct formation and increased HDL cholesterol efflux capacity, supporting the therapeutic potential of reactive carbonyl scavenging for improving HDL function.

Myeloperoxidase-induced modification of HDL by isolevuglandins inhibits paraoxonase-1 activity

“…Individuals with atherosclerotic cardiovascular disease consistently show reduced circulating PON1 activity ( 11 , 12 , 13 , 38 , 39 ). Association of MPO with HDL has previously been shown to reduce the PON1 activity of HDL ( 21 , 26 ) and to correlate with increased atherosclerosis ( 40 ). Our studies demonstrate that association of MPO with HDL in vitro generates IsoLG that directly modifies the lysine residues of PON1 and that direct modification of PON1 is the primary mechanism by which IsoLG reduces PON1 activity.…”

“…MPO bound to HDL can be detected in circulation and atherosclerotic plaques ( 41 , 42 , 43 ). MPO associates with HDL through interactions with apoA-I and PON1 ( 21 ), and association of MPO with HDL in vitro reduces PON1 activity ( 21 , 26 ).…”

“…Mpo −/− mice have lower levels of IsoLG–protein adducts than WT mice ( 27 ). In vitro incubation of MPO with HDL increases HDL modification by both MDA and IsoLGs ( 26 , 28 ). HDL modification by IsoLGs is increased in patients with familial hypercholesterolemia (FH) ( 28 ), a group with highly enhanced risk for cardiovascular disease.…”

“…Dicarbonyl scavengers such as 2-hydroxylbenzylamine and 5-O′-pentyl-pyridoxamine block the modification of lysines by IsoLGs, ONE, SCA, and MDA, with these scavengers having greater reactivity for IsoLG than MDA ( 29 , 30 ). We have shown that treatment of Ldlr−/− mice with these scavengers not only reduces their HDL modification by both IsoLG and MDA ( 31 ) but also enhances their PON1 activity ( 26 ) and reduces their atherosclerosis ( 31 ). We therefore used in vitro studies to test the hypothesis that IsoLG or other 4-ketoaldehyde modification of PON1 contributed to MPO-mediated inactivation of PON1.…”

Lipid Peroxidation as a Link between Unhealthy Diets and the Metabolic Syndrome

“…For example, malondialdehyde was found to dose-dependently reduce the insulin content in the pancreas and to contribute to beta cell death [82]. HDL prevents beta cell apoptosis and diabetes by promoting cholesterol efflux from these cells, but acrolein-or MDA-modified HDL loses this protective property [83][84][85]. oxLDL impairs insulin gene expression and causes death of pancreatic beta cells, through induction of oxidative stress and ER stress [86].…”