Role of PON2 in innate immune response in an acute infection model.

N-(3-oxododecanoyl)-l-homoserine lactone (3OC(12)-HSL) is a quorum-sensing molecule produced by gram-negative microbial pathogens such as Pseudomonas aeruginosa (PAO1). 3OC(12)-HSL is involved in the regulation of bacterial virulence factors and also alters the function of the host immune cells. Others and we have previously shown that paraoxonase 2 (PON2), a member of the paraoxonase gene family expressed in immune cells, hydrolyzes 3OC(12)-HSL. In this study, we examined i) whether macrophage PON2 participates in 3OC(12)-HSL hydrolysis, ii) the effect of PON2 deficiency in acute PAO1 infection in mice and iii) the effect of 3OC(12)-HSL on PON2 deficient (PON2-def) macrophages. When compared to wild type macrophages, both intact cells and membrane-enriched protein lysates obtained from PON2-def macrophages show a marked impairment in their ability to hydrolyze 3OC(12)-HSL. PON2 expression (message and protein) is not altered in response to 3OC(12)-HSL in macrophages. 3OC(12)-HSL treated PON2-def macrophages showed i) an increase in ER stress and oxidative stress, ii) defective phosphatidylinositol 3-kinase (PI3 kinase)/AKT activation, and iii) reduced phagocytosis function. Moreover, the nitration to phosphorylation ratio of Tyr458 in p85 protein, the regulatory subunit of PI3-kinase that has been correlated with the phagocytosis function of macrophages, was increased in PON2-def macrophages. Antioxidant treatment reversed the effects of PON2 deficiency in macrophage phagocytosis function. Furthermore, following administration of 1.6 × 10(7) CFU of PAO1, bacterial clearance was significantly reduced in the lungs (5.7 fold), liver (2.5 fold), and spleen (14.8 fold) of PON2-def mice when compared to wild type mice. Our results suggest that PON2 plays an important role in innate immune defense against PAO1 infection.

Macrophage paraoxonase 2 regulates calcium homeostasis and cell survival under endoplasmic reticulum stress conditions and is sufficient to prevent the development of aggravated atherosclerosis in paraoxonase 2 deficiency/apoE-/- mice on a Western diet.

Paraoxonase 2 deficiency (PON2-def) alters mitochondrial function and exacerbates the development of atherosclerosis in mice. PON2 overexpression protects against ER stress in cell culture. In this paper, we examined the role of PON2 in the unexplored link between ER stress and mitochondrial dysfunction and tested whether restoration of PON2 in macrophages is sufficient to reduce aggravated atherosclerosis in PON2-def/apoE(-/-) mice on a Western diet. ER stress response genes, intracellular calcium levels, and apoptotic nuclei were significantly elevated in PON2-def/apoE(-/-) macrophages compared to apoE(-/-) macrophages in response to ER stressors, but not at the basal level. In contrast, PON2-def/apoE(-/-) macrophages exhibited greater mitochondrial stress at the basal level, which was further worsened in response to ER stressors. There was no difference in ER stress response genes and apoptotic nuclei between apoE(-/-) and PON2-def/apoE(-/-) macrophages when pretreated with xestospongin (which blocks the release of calcium from ER) suggesting that PON2 modulates cell survival and ER stress by maintaining calcium homeostasis. Treatment with a mitochondrial calcium uptake inhibitor, RU360, attenuated ER stressor mediated mitochondrial dysfunction in PON2-def/apoE(-/-) macrophages. CHOP expression (ER stress marker) and apoptotic nuclei were significantly higher in aortic lesions of PON2-def/apoE(-/-) mice compared to apoE(-/-) mice fed a Western diet. Restoration of PON2 in macrophages reduced ER stress, mitochondrial dysfunction and apoptosis in response to ER stressors. Furthermore, restoration of PON2 in macrophages reduced lesional apoptosis and atherosclerosis in PON2-def/apoE(-/-) mice on a Western diet. Our data suggest that macrophage PON2 modulates mechanisms that link ER stress, mitochondrial dysfunction and the development of atherosclerosis.

Adenovirus-mediated expression of human paraoxonase 3 protects against the progression of atherosclerosis in apolipoprotein E-deficient mice.

OBJECTIVE: We have previously reported that human paraoxonase 3 (PON3) is an HDL-associated protein capable of preventing LDL oxidation in vitro. The objective of the present study was to determine whether elevated levels of human PON3 in mice could protect against the progression of atherosclerosis in vivo. METHODS AND RESULTS: Twenty-six week-old apolipoprotein E-deficient mice were injected with 3x10(11) particles of adenovirus expressing either GFP alone (AdGFP) or together with human PON3 (AdPON3). Three weeks after injection, lesion area was significantly lower in AdPON3-treated mice compared with AdGFP controls. Serum from AdPON3 mice contained significantly lower levels of lipid hydroperoxides and exhibited an enhanced potential to efflux cholesterol from cholesterol-loaded macrophages. In addition, LDL was less susceptible to oxidation, whereas HDL was more capable of protecting against LDL oxidation. Exogenous human PON3 was not detected in the serum or HDL and more surprisingly we demonstrate that endogenous mouse PON3 is not associated with HDL, suggesting that the antioxidant function of PON3 is at the cellular level in mice. CONCLUSIONS: This study demonstrates for the first time that PON3 enhances the antiatherogenic capacity of serum and protects against the progression of atherosclerosis in vivo.

Oral small peptides render HDL antiinflammatory in mice and monkeys and reduce atherosclerosis in ApoE null mice.

A peptide containing only 4 amino acid residues (KRES) that is too small to form an amphipathic helix, reduced lipoprotein lipid hydroperoxides (LOOH), increased paraoxonase activity, increased plasma HDL-cholesterol levels, rendered HDL antiinflammatory, and reduced atherosclerosis in apoE null mice. KRES was orally effective when synthesized from either L or D-amino acids suggesting that peptide-protein interactions were not required. Remarkably, changing the order of 2 amino acids (from KRES to KERS) resulted in the loss of all biologic activity. Solubility in ethyl acetate and interaction with lipids, as determined by differential scanning calorimetry, indicated significant differences between KRES and KERS. Negative stain electron microscopy showed that KRES formed organized peptide-lipid structures whereas KERS did not. Another tetrapeptide FREL shared many of the physical-chemical properties of KRES and was biologically active in mice and monkeys when synthesized from either L- or D-amino acids. After oral administration KRES and FREL were found associated with HDL whereas KERS was not. We conclude that the ability of peptides to interact with lipids, remove LOOH and activate antioxidant enzymes associated with HDL determines their antiinflammatory and antiatherogenic properties regardless of their ability to form amphipathic helixes.

Apolipoprotein A-I mimetic peptides.

Despite identical amino acid composition, differences in class A amphipathic helical peptides caused by differences in the order of amino acids on the hydrophobic face results in substantial differences in antiinflammatory properties. One of these peptides is an apolipoprotein A-I (apoA-I) mimetic, D-4F. When given orally to mice and monkeys, D-4F caused the formation of pre-beta high-density lipoprotein (HDL), improved HDL-mediated cholesterol efflux, reduced lipoprotein lipid hydroperoxides, increased paraoxonase activity, and converted HDL from pro-inflammatory to antiinflammatory. In apolipoprotein E (apoE)-null mice, D-4F increased reverse cholesterol transport from macrophages. Oral D-4F reduced atherosclerosis in apoE-null and low-density lipoprotein (LDL) receptor-null mice. In vitro when added to human plasma at nanomolar concentrations, D-4F caused the formation of pre-beta HDL, reduced lipoprotein lipid hydroperoxides, increased paraoxonase activity, and converted HDL from pro-inflammatory to antiinflammatory. Physical-chemical properties and the ability of various class A amphipathic helical peptides to activate lecithin cholesterol acyltransferase (LCAT) in vitro did not predict biologic activity in vivo. In contrast, the use of cultured human artery wall cells in evaluating these peptides was more predictive of their efficacy in vivo. We conclude that the antiinflammatory properties of different class A amphipathic helical peptides depends on subtle differences in the configuration of the hydrophobic face of the peptides, which determines the ability of the peptides to sequester inflammatory lipids. These differences appear to be too subtle to predict efficacy based on physical-chemical properties alone. However, understanding these physical-chemical properties provides an explanation for the mechanism of action of the active peptides.

Oral D-4F causes formation of pre-beta high-density lipoprotein and improves high-density lipoprotein-mediated cholesterol efflux and reverse cholesterol transport from macrophages in apolipoprotein E-null mice.

BACKGROUND: These studies were designed to determine the mechanism of action of an oral apolipoprotein (apo) A-I mimetic peptide, D-4F, which previously was shown to dramatically reduce atherosclerosis in mice. METHODS AND RESULTS: Twenty minutes after 500 microg of D-4F was given orally to apoE-null mice, small cholesterol-containing particles (CCPs) of 7 to 8 nm with pre-beta mobility and enriched in apoA-I and paraoxonase activity were found in plasma. Before D-4F, both mature HDL and the fast protein liquid chromatography fractions containing the CCPs were proinflammatory. Twenty minutes after oral D-4F, HDL and CCPs became antiinflammatory, and there was an increase in HDL-mediated cholesterol efflux from macrophages in vitro. Oral D-4F also promoted reverse cholesterol transport from intraperitoneally injected cholesterol-loaded macrophages in vivo. In addition, oral D-4F significantly reduced lipoprotein lipid hydroperoxides (LOOH), except for pre-beta HDL fractions, in which LOOH increased. CONCLUSIONS: The mechanism of action of oral D-4F in apoE-null mice involves rapid formation of CCPs, with pre-beta mobility enriched in apoA-I and paraoxonase activity. As a result, lipoprotein LOOH are reduced, HDL becomes antiinflammatory, and HDL-mediated cholesterol efflux and reverse cholesterol transport from macrophages are stimulated.

Paraoxonase 2 deficiency alters mitochondrial function and exacerbates the development of atherosclerosis.

Increased production of reactive oxygen species (ROS) as a result of decreased activities of mitochondrial electron transport chain (ETC) complexes plays a role in the development of many inflammatory diseases, including atherosclerosis. Our previous studies established that paraoxonase 2 (PON2) possesses antiatherogenic properties and is associated with lower ROS levels. The aim of the present study was to determine the mechanism by which PON2 modulates ROS production. In this report, we demonstrate that PON2-def mice on the hyperlipidemic apolipoprotein E(-/-) background (PON2-def/apolipoprotein E(-/-)) develop exacerbated atherosclerotic lesions with enhanced mitochondrial oxidative stress. We show that PON2 protein is localized to the inner mitochondrial membrane, where it is found associated with respiratory complex III. Employing surface-plasmon-resonance, we demonstrate that PON2 binds with high affinity to coenzyme Q(10), an important component of the ETC. Enhanced mitochondrial oxidative stress in PON2-def mice was accompanied by significantly reduced ETC complex I + III activities, oxygen consumption, and adenosine triphosphate levels in PON2-def mice. In contrast, overexpression of PON2 effectively protected mitochondria from antimycin- or oligomycin-mediated mitochondrial dysfunction. Our results illustrate that the antiatherogenic effects of PON2 are, in part, mediated by the role of PON2 in mitochondrial function.

The double jeopardy of HDL.

The ability of high-density lipoprotein (HDL) to promote cholesterol efflux is thought to be important in its protection against cardiovascular disease. Anti-inflammatory properties of HDL have emerged as additional properties that may also be important. HDL appears to have evolved as part of the innate immune system functioning to inhibit inflammation in the absence of an acute phase response (APR) but functioning to increase inflammation in the presence of an APR. Inbred strains of mice that are genetically susceptible to atherosclerosis have pro-inflammatory HDL, while inbred strains that are resistant to atherosclerosis have anti-inflammatory HDL. In one small study, humans with coronary heart disease (CHD) or CHD equivalents had pro-inflammatory HDL prior to statin therapy and about half continued to have pro-inflammatory HDL after statin therapy despite a profound decrease in plasma lipids. Pro-inflammatory HDL was relatively weak in its ability to promote cholesterol efflux while anti-inflammatory HDL was better in promoting cholesterol efflux. In other studies, oxidative alterations of the major protein of HDL, apolipoprotein A-I (apoA-I), impaired the ability of the apoA-I to promote cholesterol efflux. Thus, HDL structure and function may be more important than HDL-cholesterol levels in predicting risk for cardiovascular disease.