Macrophage paraoxonase 1 (PON1) binding sites

Paraoxonase 1 (PON1), an HDL-associated esterase, is known to possess anti-oxidant and anti-atherogenic properties. PON1 was shown to protect macrophages from oxidative stress, to inhibit macrophage cholesterol biosynthesis, and to stimulate HDL-mediated cholesterol efflux from the cells. The aim of the present study was to characterize macrophage PON1 binding sites which could be responsible for the above anti-atherogenic activities.Incubation of FITC-labeled recombinant PON1 with J774 A.1 macrophage-like cell line at 37 °C, resulted in cellular binding and internalization of PON1, leading to PON1 localization in the cell’s cytoplasm compartment. In order to determine whether PON1 uptake is mediated via a specific binding to the macrophage, FITC-labeled recombinant PON1 was incubated with macrophages at 4 °C, followed by cell membranes separation. Macrophage membrane fluorescence was shown to be directly and dose-dependently related to the labeled PON1 concentration. Furthermore, binding assays performed at 4 and at 37 °C, using labeled and non-labeled recombinant PON1 (for competitive inhibition), demonstrated a dose-dependent significant 30% decrement in labeled PON1 binding to the macrophages, by the non-labeled PON1. Similarly, binding assays, using labeled PON1 and non-labeled HDL (the natural carrier of PON1 in the circulation) indicated that HDL decreased the binding of labeled PON1 to macrophages by 25%. Unlike HDL, LDL had no effect on labeled PON1 binding to macrophages. Finally, HDL were pre incubated without or with PON1 or apolipoprotein AI (apoAI) antibodies, in order to block PON1 or apoAI ability to bind to the cells. HDL incubation with antibody to PON1 or to apoAI significantly decreased HDL ability to inhibit macrophages-mediated LDL oxidation (by 32% or by 25%, respectively). A similar trend was also observed for HDL-mediated cholesterol efflux from macrophages, with an inhibitory effect of 35% or 19%, respectively. These results suggest that blocking HDL binding to macrophages through its apo A-I, and more so, via its PON1, results in the attenuation of HDL-PON1 biological activities.In conclusion, PON1 specifically binds to macrophage binding sites, leading to anti-atherogenic effects. Macrophage PON1 binding sites may thus be a target for future cardio protection therapy.     

S-Glutathionylation regulates HDL-associated paraoxonase 1 (PON1) activity

HDL-associated paraoxonase 1 (PON1) undergoes inactivation under oxidative stress and is preserved by dietary antioxidants. PON1 cysteines can affect PON1 enzymatic activities. S-Glutathionylation, a redox regulatory mechanism characterized by the formation of a mixed disulfide between a protein thiol and oxidized glutathione (GSSG), was shown to preserve some enzymes from irreversible inactivation under pathological conditions. We questioned whether PON1 activity is regulated by S-glutathionylation. Incubation of PON1 or HDL with GSSG indeed resulted in a dose-dependent inactivation of PON1 activities, including its physiological activity to increase HDL-mediated macrophage cholesterol efflux. This PON1 inactivation was associated with the formation of a mixed disulfide bond between GSSG and PON1's cysteine residue(s), as detected by immunoblotting with anti-glutathione IgG. PON1 activity was recovered following the addition of a reducing agent, DL-Dithiothreitol (DTT), to the PON1-SSG complex. We thus conclude that HDL-associated serum PON1 can undergo S-glutathionylation under oxidative stress with a consequent reversible inactivation.     

PON1 paraoxonase activity is reduced during HDL oxidation and is an indicator of HDL antioxidant capacity

The aim of this study was to investigate the effect of HDL oxidation on PON1 paraoxonase activity. Also, we were interested in investigating the mechanism by which PON1 could be inactivated and the correlation between its enzymatic activity and the antioxidant properties of HDL. Three different oxidation systems were used for the HDL oxidation: (1) oxidation induced by THP1 cells, (2) oxidation induced by copper ions at a concentration 10 microM, and (3) oxidation induced by *OH and O2.- oxygen free radicals produced by gamma-radiolysis. HDL oxidation was followed by the measurement of lipid peroxide formation, and PON1 activity was determined by measuring the rate of paraoxon hydrolysis. Our results show that HDL oxidation is accompanied by a reduction in the PON1 paraoxonase activity. The extent of PON1 inactivation depends both on the extent of HDL oxidation and on the oxidation system used. The rates of HDL oxidation and PON1 inactivation were significantly correlated (r = 0.93, p < 0.0054). Our results show that oxidized HDL loses its protective effect toward LDL oxidation. The antioxidant action of HDL towards LDL oxidation and the degradation of PON1 paraoxonase activity were significantly correlated (r = 0.95, p < 0.04).     

Paraoxonase (PON1) deficiency is associated with increased macrophage oxidative stress: studies in PON1-knockout mice

Human serum paraoxonase (PON1), an HDL-associated esterase, protects lipoproteins against oxidation, probably by hydrolyzing specific lipid peroxides. As arterial macrophages play a key role in oxidative stress in early atherogenesis, the aim of the present study was to examine the effect of PON1 on macrophage oxidative stress. For this purpose we used mouse arterial and peritoneal macrophages (MPM) that were harvested from two populations of PON1 knockout (KO) mice: one on the genetic background of C57BL/6J (PON1(0)) and the other one on the genetic background of apolipoproteinE KO (PON1(0)/E(0)). Serum and LDL, but not HDL, lipids peroxidation was increased in PON1(0), compared to C57BL/6J mice, by 84% and by 220%, respectively. Increased oxidative stress was shown in peritoneal and in arterial macrophages derived from either PON1(0) or PON1(0)/E(0) mice, compared to their appropriate controls. Macrophage oxidative stress was expressed by increased lipid peroxides content in MPM from PON1(0) and from PON1(0)/E(0) mice by 48% and by 80%, respectively, and by decreased reduced glutathione (GSH) content, compared to the appropriate controls. Furthermore, increased capacity of MPM from PON1(0) and PON1(0)/E(0) mice to oxidize LDL (by 40% and by 19%, respectively) and to release superoxide anions was observed. In accordance with these results, PON1(0) mice MPM exhibited 130% increased translocation of the cytosolic p47phox component of NADPH-oxidase to the macrophage plasma membrane, suggesting increased activation of macrophage NADPH-oxidase in PON1(0) mice, compared to control mice MPM. The increase in oxidative stress in PON1-deficient mice was observed despite the presence of the two other members of the PON gene family. PON2 and PON3 activities and mRNA expression were both found to be present in PON1-deficient mice MPM. Upon incubation of PON1(0)/E(0) derived macrophages with human PON1 (7.5 arylesterase units/ml), cellular peroxides content was decreased by 18%, macrophage superoxide anion release was decreased by 33%, and macrophage-mediated oxidation of LDL was reduced by 22%. Finally, a 42% increase in the atherosclerotic lesion area was observed in PON1(0)/E(0) mice, in comparison to E(0) mice under regular chow diet. We thus concluded that PON1 can directly reduce oxidative stress in macrophages and in serum, and that PON1-deficiency results in increased oxidative stress not only in serum, but also in macrophages, a phenomenon that can contribute to the accelerated atherosclerosis shown in PON1-deficient mice.     

Oligomeric states of the detergent-solubilized human serum paraoxonase (PON1)

Human plasma paraoxonase (HuPON1) is a high density lipoprotein (HDL)-bound enzyme exhibiting antiatherogenic properties. The molecular basis for the binding specificity of HuPON1 to HDL has not been established. Isolation of HuPON1 from HDL requires the use of detergents. We have determined the activity, dispersity, and oligomeric states of HuPON1 in solutions containing mild detergents using nondenaturing electrophoresis, size exclusion chromatography, and cross-linking. HuPON1 was active whatever its oligomeric state. In nonmicellar solutions, HuPON1 was polydisperse. In contrast, HuPON1 exhibited apparent homogeneity in micellar solutions, except with CHAPS. The enzyme apparent hydrodynamic radius varied with the type of detergent and protein concentration. In C(12)E(8) micellar solutions, from sedimentation velocity, equilibrium analytical ultracentrifugation, and radioactive detergent binding, HuPON1 was described as monomers and dimers in equilibrium. A decrease of the detergent concentration shifted this equilibrium toward the formation of dimers. About 100 detergent molecules were associated per monomer and dimer. The assembly of amphiphilic molecules, phospholipids in vivo, in sufficiently large aggregates could be a prerequisite for anchoring of HuPON1 and then allowing stabilization of the enzyme activity. Changes of HDL size and shape could strongly affect the binding affinity and stability of HuPON1 and result in reduced antioxidative capacity of the lipoprotein.     

Oxidative inactivation of lactonase activity of purified human paraoxonase 1 (PON1)

Paraoxonase1 (PON1), one of HDL-associated antioxidant proteins, is known to lose its activity in vivo systems under oxidative stress. Here, we examined the effect of various oxidants on lactonase activity of PON1, and tried to protect the lactonase activity from oxidative inactivation. Among the oxidative systems tested, the ascorbate/Cu²⁺ system was the most potent in inactivating the lactonase activity of purified PON1; in contrast to a limited role of Fe²⁺, Cu²⁺ (0.05–1.0 µM) remarkably enhanced the inactivation of PON1 in the presence of ascorbate (0.02–0.1 mM). Moreover, Cu²⁺ alone inhibited the lactonase activity at concentrations as low as 1 µM. The ascorbate/Cu²⁺-mediated inactivation of PON1 lactonase activity was prevented by catalase, but not general hydroxyl radical scavengers, suggesting the implication of Cu²⁺-bound hydroxyl radicals in the oxidative inactivation. Compared to arylesterase activity, lactonase activity appears to be more sensitive to Cu²⁺-catalyzed oxidation. Separately, ascorbate/Cu²⁺-mediated inactivation of lactonase activity was prevented by oleic acid as well as phoshatidylcholine. Taken together, our data demonstrate that Cu²⁺-catalyzed oxidation may be a primary factor to cause the decrease of PON1 lactonase activity under oxidative stress and that lactonase activity of PON1 is most susceptible to ascorbate/Cu²⁺ among PON1 activities. In addition, we have showed that radical-induced inactivation of lactonase activity is prevented by some lipids.     

Estradiol enhances cell-associated paraoxonase 1 (PON1) activity in vitro without altering PON1 expression

PON1 is a high density lipoprotein-associated enzyme that plays an important role in organophosphate detoxification and prevention of atherosclerosis. In vivo animal and human studies have indicated that estradiol (E2) supplementation enhances serum PON1 activity. In this study, we sought to determine if E2 directly up-regulates cell-associated PON1 activity in vitro and to characterize the mechanism of regulation. In vitro E2 treatment of both the human hepatoma cell line Huh7 and normal rat hepatocytes resulted in a 2- to 3-fold increase in cell-associated PON1 catalytic activity. E2 potently induced PON1 activity with average EC₅₀ values of 15 nM for normal hepatocytes and 68 nM for Huh7. The enhancement of PON1 activity by E2 was blocked by the estrogen receptor (ER) antagonist ICI 182,780 indicating that E2 was acting through the ER. The up-regulation of PON1 activity by E2 did not involve enhancement of PON1 mRNA or protein levels and did not promote secretion of PON1. Thus, E2 can enhance cell-associated PON1 activity in vitro without altering PON1 gene expression or protein level. Our data suggest that E2 may regulate the specific activity and/or stability of cell surface PON1.     

Arylesterase activity of paraoxonase 1 (PON1) on HDL3 and HDL2: Relationship with Q192R,C-108T,and L55M polymorphisms

BackgroundControversy exists regarding the role of the subfractions of high-density lipoproteins (HDL₂ and HDL₃) in cardiovascular disease. The functionality of these particles, and their protective role, is due in part to the paraoxonase 1 (PON1) presence in them. The polymorphisms rs662 (Q192R, A/G), rs854560 (L55 M, T/A), and rs705379 (C-108T) of the PON1 gene have been related to enzyme activity and, with the anti-oxidative capacity of the HDL. The objective was to determine the arylesterase PON1 activity in HDL₃ and HDL₂ and its relationship with the polymorphisms mentioned, in a young population.MethodsThe polymorphisms were determined through mini-sequencing (SnaPshot). The HDL subpopulations were separated via ionic precipitation, cholesterol was measured with enzymatic methods, and PON1 activity was measured through spectrophotometry.ResultsThe results show that the PON1 polymorphisms do not influence the cholesterol in the HDL. A variation between 40.02 and 43.9 mg/dL was in all the polymorphisms without significant differences. Additionally, PON1 activity in the HDL₃ subfractions was greater (62.83 ± 20 kU/L) than with HDL₂ (35.8 ± 20.8 kU/L) in the whole population and in all the polymorphisms (p < 0.001), and it was independent of the polymorphism and differential arylesterase activity in the Q192R polymorphism (QQ > QR > RR). Thus, 115.90 ± 30.7, 88.78 ± 21.3, 65.29 ± 10.2, respectively, for total HDL, with identical behavior for HDL₃ and HDL₂.ConclusionsPON1 polymorphisms do not influence the HDL_-c, and the PON activity is greater in the HDL₃ than in the HDL₂, independent of the polymorphism, but it is necessary to delve into the functionality of these findings in different populations.     

High affinity, stability, and lactonase activity of serum paraoxonase PON1 anchored on HDL with ApoA-I

Serum paraoxonase (PON1) is a high-density lipoprotein (HDL)-associated enzyme exhibiting antiatherogenic properties. This study examined the interaction of recombinant PON1 with reconstituted HDL comprised of PC, cholesterol, and various apolipoproteins (apoA-I, -II, and -IV). The affinity, stability, and lactonase activity were strongly correlated, with apoA-I exhibiting the strongest effects, apoA-IV exhibiting weaker yet significant effects, and apoA-II having a negative effect relative to protein-free particles. We found that PON1 binds apoA-I HDL with sub-nanomolar affinities (K(d) < 10(-)(9) M) and slow dissociation rates (t(1/2) > 80 min), while binding affinity for other particles was dramatically lower. A truncated form of PON1 lacking the N-terminal helix maintains considerable binding to apoA-I HDL (K(d) = 1.2 x 10(-)(7) M), validating the structural model which indicates additional parts of the enzyme involved in HDL binding. Kinetic inactivation assays revealed the existence of an equilibrium between two forms of PON1 differing in their stability by a factor of 100. Various lipoproteins and detergent preparations shift this equilibrium toward the more stable conformation. Consistent with its highest affinity, only apoA-I HDL is capable of totally shifting the equilibrium toward the stable form. The paraoxonase and arylesterase activities were stimulated by HDL by 2-5-fold as previously reported, almost independently of the apoliporotein content. In contrast, only apoA-I is capable of stimulating the lactonase activity by 相似文献   

Activity of paraoxonase 1 (PON1) and its relationship to markers of lipoprotein oxidation in healthy Slovaks

Low-density lipoproteins (LDLs), when modified by free radicals derived from artery wall cells, induce atherosclerosis. In contrast to oxidized LDL (ox-LDL), high-density lipoproteins (HDLs) are able to prevent atherosclerosis through a protein with antioxidant properties, paraoxonase 1 (PON1). The purpose of this study was to explore the association between the activity of HDL-associated PON1 and circulating ox-LDL as well as to investigate the relationship between ox-LDL and parameters of lipid profile in thirty Slovaks aged 21-73 years because recent studies have presented controversial results concerning PON1 and its role in LDL oxidation. For determination of circulating ox-LDL sandwich ELISA was used and other lipid parameters were determined by routine laboratory analyses. PON1 activities were assayed by two synthetic substrates - paraoxon and phenyl acetate. Lipid peroxides were determined spectrophotometrically. Of the lipid parameters examined, ox-LDL level correlated positively with total (P < 0.0001) and LDL-cholesterol (P < 0.001). Triacylglycerols (TAG) (P < 0.001), lipid peroxides (P < 0.01) and atherogenic index (AI = total cholesterol/HDL) (P < 0.0001) were also strongly correlated with ox-LDL. No inverse relationships were observed between ox-LDL and HDL-cholesterol or arylesterase/paraoxonase activities of PON1. Furthermore, it was found that ox-LDL (P < 0.01) and lipid peroxides (P < 0.05) were significantly higher in men than in women. PON1 arylesterase activity was marginally affected by sex. The results of this study suggest that the anti-atherogenic properties of HDLs are not directly related to their total concentration and that PON1 activity determined towards synthetic compounds (paraoxon and phenyl acetate) reflects no association with markers of oxidative stress. Furthermore, it follows from our results that men are more susceptible to developing atherosclerosis compared to women.     

Structure-activity relationship on human serum paraoxonase (PON1) using substrate analogues and inhibitors

Substrate analogues based on the parent compounds paraoxon and phenyl acetate were tested on human serum paraoxonase (PON1) to explore the active site of the enzyme. Replacement of the nitro group of paraoxon with an amine or hydrogen, as well as electronic changes to the parent compound, converted these analogues into inhibitors. Introduction of either electron-withdrawing or donating groups onto phenyl acetate resulted in reduction in their rate of hydrolysis by PON1.     

Identification of residues essential for human paraoxonase (PON1) arylesterase/organophosphatase activities

Human serum paraoxonase (PON1) is a calcium-dependent organophosphatase. To identify residues essential for PON1 activity, we adopted complementary approaches based on chemical modification and site-directed mutagenesis. To detect 45Ca2+ binding to native and chemically modified PON1, we performed nondenaturating gel electrophoresis. The environment of calcium-binding sites was probed using the Ca2+ analogue, terbium. Tb3+ binds to calcium-binding sites as shown by displacement of 45Ca2+ by Tb3+. Binding of Tb3+ is accompanied by a complete loss of enzyme activity. PON1 chemical modification with the Trp-selective reagent, N-bromosuccinimide, and the Asp/Glu-selective, dicyclohexylcarbodiimide, established that Trp and Asp/Glu residues are components of the PON1 active center and calcium-binding sites. Additional evidence for the presence of a Trp residue in the PON1 calcium-binding sites was a characteristic fluorescence emission at 545 nm from the PON1-Tb3+ complex and abolishment of that fluorescence upon modification by N-bromosuccinimide. The importance of aromatic/hydrophobic character of the residue 280 was demonstrated by site-directed mutagenesis: the W280F mutant was fully active while the W280A and W280L mutants had markedly reduced activity. Twelve amino acids among conserved His and Asp/Glu residues were found essential for PON1 arylesterase and organophosphatase activities: H114, H133, H154, H242, H284, D53, D168, D182, D268, D278, E52, and E194. Finally, the cysteines constituting the PON1 disulfide bond (C41 and C352) were essential, but the glycan chains linked to Asn 252 and 323 were not essential for PON1 secretion and activity.     

Human carotid lesion linoleic acid hydroperoxide inhibits paraoxonase 1 (PON1) activity via reaction with PON1 free sulfhydryl cysteine 284

Paraoxonase 1 (PON1) is an HDL-associated lactonase with antiatherogenic properties. These include dampening the oxidation properties of human carotid lesion lipid extract (LLE), which in turn inactivates the enzyme. The aims of this study were to identify the PON1 inhibitor in LLE and explore the mechanism of inhibition. LLE inhibited both recombinant PON1 and HDL-PON1 lactonase activity in a dose- and time-dependent manner. Addition of antioxidants or electrophiles to LLE did not prevent PON1 inhibition. LLE was unable to inhibit a PON1 mutant lacking Cys284, whereas it did inhibit all other PON1 mutants tested. The inhibitor in the LLE was identified as linoleic acid hydroperoxide (LA-OOH) and inhibition was specific to this hydroperoxide. During its inhibition, PON1 acted like a peroxidase enzyme, reducing LA-OOH to LA-hydroxide via its Cys284. A similar reaction occurred with external thiols, such as DDT or cysteine, which also prevented PON1 inhibition and restored enzyme activity after inhibition. Thus, the antiatherogenic properties of HDL could be, at least in part, related to the sulfhydryl-reducing characteristics of its associated PON1, which are further protected and recycled by the sulfhydryl amino acid cysteine.     

Species- and substrate-specific stimulation of human plasma paraoxonase 1 (PON1) activity by high chloride concentration

Paraoxonase 1 (PON1), contained in plasma high-density lipoproteins, plays an important role in the protection of plasma lipoproteins and cell membranes from oxidative damage. Previous studies indicate that human PON1 is stimulated by high NaCl concentrations. The aim of this study was to characterize in more detail the effect of salts on serum PON1. Paraoxon-hydrolyzing activity of human serum was stimulated by 81.6% following the addition of 1 M NaCl. The effect of NaCl was dose-dependent between 0.5 and 2 M. PON1 activity toward phenyl acetate was reduced by 1 M NaCl by 55.2%. Both the paraoxon- and phenyl acetate-hydrolysing activity was slightly lower in heparinized plasma than in serum, but NaCl had similar stimulatory and inhibitory effects on these activities, respectively. In rat, rabbit, and mouse, NaCl reduced PON1 activity. KCl had a similar effect on human PON1 as NaCl. Sodium nitrite also stimulated human PON1 but much less effectively than chloride salts. In contrast, sucrose, sodium acetate and sodium lactate had no significant effect. NaBr was a less effective PON1 activator than NaCl, whereas the effect of NaJ was non-significant. The activity of human PON1 toward homogentisic acid lactone and gamma-decanolactone was unaltered by NaCl. These data indicate that: 1) high concentrations of chlorides stimulate human PON1 activity toward paraoxon but not other substrates, 2) PON1 is inhibited by Cl(-) in other mammalian species, 3) the potency of human PON1 activation by halogene salts increases with decreasing atomic mass of the halide anion.     

In vitro efficacy of some cattle drugs on bovine serum paraoxonase 1 (PON1) activity

Serum paraoxonase 1 (EC 3.1.8.1, PON1), a calcium-associated enzyme, has an ability to hydrolyze organophosphate compounds. Related to this property, PON1 has a critical role in antioxidant mechanisms. It is well-known that the enzyme protects LDL from oxidation. In this study we investigated the in vitro inhibitory effects of some drugs. These drugs are oxytocin, dexamethasone, atropine sulphate, gentamicin sulphate, sulfadoxine-trimethoprim, furosemid, metamizole sodium and toldimfos sodium. The IC₅₀ values obtained varied markedly from 0.014 to 507.72?mg/mL. According to our findings, most potent and significant inhibition was displayed by dexamethasone, atropine sulphate and furosemid.     

In vitro efficacy of some cattle drugs on bovine serum paraoxonase 1 (PON1) activity

Serum paraoxonase 1 (EC 3.1.8.1, PON1), a calcium-associated enzyme, has an ability to hydrolyze organophosphate compounds. Related to this property, PON1 has a critical role in antioxidant mechanisms. It is well-known that the enzyme protects LDL from oxidation. In this study we investigated the in vitro inhibitory effects of some drugs. These drugs are oxytocin, dexamethasone, atropine sulphate, gentamicin sulphate, sulfadoxine-trimethoprim, furosemid, metamizole sodium and toldimfos sodium. The IC(50) values obtained varied markedly from 0.014 to 507.72 mg/mL. According to our findings, most potent and significant inhibition was displayed by dexamethasone, atropine sulphate and furosemid.     

VLDL triglycerides inhibit HDL-associated paraoxonase 1 (PON1) activity: in vitro and in vivo studies

We analyzed, for the first time, both in vitro and in vivo, the effect of very low density lipoprotein (VLDL), or of pure triglycerides, on high-density lipoprotein (HDL)-associated paraoxonase1 (PON1) catalytic activities. Incubation of serum or HDL from healthy subjects with VLDL (0-330 μg protein/mL) significantly decreased serum PON1 lactonase or arylesterase activities by up to 11% or 24%, and HDL-associated PON1 lactonase or arylesterase activities by up to 32% or 46%, respectively, in a VLDL dose-dependent manner. VLDL (0-660μg protein/mL) also inhibited recombinant PON1 (rePON1) lactonase or arylesterase activities by up to 20% or 42%, respectively. Similar inhibitory effect was noted upon rePON1 incubation with pure triglyceride emulsion. Bezafibrate therapy to three hypertriglyceridemic patients (400 mg/day, for one month) significantly decreased serum triglyceride concentration by 67%, and increased serum HDL cholesterol levels by 48%. PON1 arylesterase or paraoxonase activities in the patients' HDL fractions after drug therapy were significantly increased by 86-88%, as compared to PON1 activities before treatment. Similarly, HDL-PON1 protein levels significantly increased after bezafibrate therapy. Finally, bezafibrate therapy improved HDL biological activity, as HDL obtained after drug therapy showed increased ability to induce cholesterol efflux from J774A.1 macrophages, by 19%, as compared to HDL derived before therapy. We thus conclude that VLDL triglycerides inhibit PON1 catalytic activities, and bezafibrate therapy significantly improved HDL-PON1 catalytic and biological activities. ? 2012 International Union of Biochemistry and Molecular Biology, Inc.     

In vitro inhibition effect of some coumarin compounds on purified human serum paraoxonase 1 (PON1)

Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro effect of some hydroxy and dihydroxy ionic coumarin derivatives (1–20) on purified PON1 activity was investigated. Among these compounds, derivatives 11–20 are water soluble. In investigated compounds, compounds 6 and 13 were found the most active (IC₅₀?=?35 and 34?µM) for PON1, respectively. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.     

DNA polymorphisms in two paraoxonase genes (PON1 and PON2) are associated with the risk of coronary heart disease.

A common polymorphism at codon 192 in the human paraoxonase (PON) 1 gene has been shown to be associated with increased risk for coronary heart disease (CHD) in Caucasian populations. However, these findings have not been reported consistently in all Caucasian and non-Caucasian populations, suggesting that this is not a functional mutation but may mark a functional mutation present in either PON1 or a nearby gene. Recently, two other PON-like genes, designated "PON2" and "PON3," have been identified, and they are linked with the known PON1 gene on chromosome 7. Identification of additional polymorphisms in the PON-gene cluster may help to locate the functional polymorphism. In this report, we describe the existence of a common polymorphism at codon 311 (Cys-->Ser; PON2*S) in the PON2 gene, as well as its association with CHD alone and in combination with the PON1 codon 192 polymorphism in Asian Indians. The frequency of the PON2*S allele was significantly higher in cases than in controls (.71 vs. .61; P=.016). The age- and sex-adjusted odds ratio (OR) was 2.5 (95% confidence interval &sqbl0;95% CI&sqbr0;=1.8-3.1; P=.0090) for the PON2*S allele carriers. Further stratification of the PON2*S association, on the basis of the presence or absence of the PON1*B allele, showed that the CHD risk associated with the PON2*S allele was confined to PON1*B-allele carriers. Likewise, the PON1*B-allele risk was present only among PON2*S carriers. Age- and sex-adjusted ORs for the PON2*S and PON1*B were 3.6 (95% CI=2.6-4.6; P=.011) and 2.9 (95% CI=2.4-3.5; P=.0002) among the PON1*B and PON2*S carriers, respectively. Our data indicate that both polymorphisms synergistically contribute to the CHD risk in this sample and that this genetic risk is independent of the conventional plasma lipid profile.     

Differential effects of paraoxonase 1 (PON1) polymorphisms on cancer risk: evidence from 25 published studies

Paraoxonase is an HDL-associated enzyme that plays a preventive role against oxidative stress, which is thought to contribute to cancer development. PON1 activity varies widely among individuals, which is in part related to two common nonsynonymous polymorphisms in the PON1 gene (Q192R and L55M). The polymorphisms in PON1 have been implicated in cancer risk. However, results from the studies to date have been conflicting. To clarify the association, a meta-analysis was performed for 7,073 cases and 9,520 controls from 25 published case–control studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association. Significant associations between PON1-L55M but not Q192R polymorphism and total cancer were observed from all the comparisons. In stratified analyses, PON1-55M allele was a risk factor for breast cancer. Similarly, increased risk was observed for prostate cancer (OR = 1.18, 95% CI: 1.01–1.36, P _{heterogeneity} = 0.260) and Caucasian population (OR = 1.18, 95% CI: 1.02–1.38, P _{heterogeneity} = 0.1) of the LM genotype, compared with the LL genotype. For PON1-Q192R polymorphism, PON1-192R allele was a decreased risk factor for cancer in the Asian group (RR vs QQ: OR = 0.61, 95% CI: 0.38–0.98, P _{heterogeneity} = 0.268; QR vs QQ: OR = 0.71, 95% CI: 0.52–0.96, P _{heterogeneity} = 0.130; RR + QR vs QQ: OR = 0.71, 95% CI: 0.53–0.95, P _{heterogeneity} = 0.135). Although some modest bias could not be eliminated, this meta-analysis suggests that the PON1-55M allele is a risk factor for the development of cancer, in particular for breast cancer. Future studies with larger sample sizes are warranted to further evaluate these associations.