Studies on human serum paraoxonase/arylesterase

Enhancement in the production of recombinant human paraoxonase 1 in Escherichia coli: A comprehensive approach of cellular engineering and optimization of protein folding process in vitro

Human paraoxonase 1(hPON1) belongs to the paraoxonase (PON) family. It is a calcium-dependent enzyme with a size of ∼43 kDa and is composed of 6 bladed beta-barrel structures with two calcium ions in its active site. In humans, it is synthesized in the liver and remains bound with the high-density lipoproteins (HDL) within the blood. It has immense potential to tackle the poisoning associated with the use of organophosphates (OPs) and their derivatives, such as nerve agents, due to role in their degradation. Therefore, hPON1 serves as a potential bio-scavenger that can be used as an antidote or as a surface decontaminating agent in OPs poisoning. However, present systems prove insufficient to produce it in sufficient quantity to make it industrially relevant. Here, our efforts involve producing it recombinantly in an E. coli system with enhanced expression levels by altering cellular and environmental conditions. This has been further improved by the development of in-vitro refolding process for the denatured recombinant hPON1 (rhPON1) protein. This methodology resulted in approximately 200 mg of the enzymatically functional protein from 1 l of E. coli culture. Proper refolding of rhPON1 was confirmed by comparing its enzymatic activity and conformation with serum purified hPON1.

Decreased serum PON1 arylesterase activity in familial hypercholesterolemia patients with a mutated LDLR gene

Paraoxonase 1 (PON1) is a serum enzyme associated with high density lipoprotein (HDL) regulation through its paraoxonase and arylesterase activity. PON1 inhibits the oxidation of HDL and low density lipoprotein (LDL), and is involved in the pathogenesis of a variety of diseases including atherosclerosis. Conversely, mutations in the low density lipoprotein receptor (LDLR) result in failure of receptor mediated endocytosis of LDL leading to its elevated plasma levels and onset of familial hypercholesterolemia (FH). In the current study we investigated the role of PON1 polymorphisms rs662; c.575A > G (p.Gln192Arg) and rs854560; c.163T > A (p.Leu55Met) in a large family having FH patients harboring a functional mutation in LDLR. Genotypes were revealed by RFLP, followed by confirmation through Sanger sequencing. PON1 activity was measure by spectrophotometry. Our results show significantly reduced serum paraoxonase and arylesterase activities in FH patients compared with the healthy individuals of the family (p < 0.05). PON1 QQ192 genotype showed a significantly higher association with FH (p=0.0002). PON1 Q192 isoform was associated with reduced serum paraoxonase activity by in silico analysis and PON1 R192 exhibited higher serum paraoxonase and arylesterase activity than the other polymorphs. Our results highlight that the combination of LDLR mutations and PON1 MMQQ genotypes may lead to severe cardiac events.

Increased levels of lipid hydroperoxides in plasma of patients with multiple sclerosis: a relationship with paraoxonase activity

Paraoxonase, an enzyme associated with high density lipoproteins (HDL), plays an important role in the anti-oxidant and anti-inflammatory properties exerted by HDL. Increasing evidence supports a role of free radicals and oxidative stress in the inflammatory processes and in the pathogenesis of multiple sclerosis (MS). The aim of this study was to further investigate the relationship between oxidative damage and MS; therefore we compared the paraoxonase activity and levels of cholesteryl ester hydroperoxides (CE-OOH), as marker of lipid peroxidation, in plasma isolated from healthy subjects (n=89) and from MS patients (n=24) in the early stage disability (EDSSB<3.5). Our results demonstrated for the first time that the activity of paraoxonase in the plasma of MS subjects was significantly lower with respect to controls (p<0.001). Moreover, our results showed a significant increase in the levels of CE-OOH in plasma from MS subjects (p<0.001). CE-OOH are biologically active substances derived from the oxidation of cholesteryl ester localized in the hydrophobic core of plasma lipoproteins (HDL, LDL). Therefore, our study demonstrates alterations of lipoprotein peroxidation in MS and provides further evidence that oxidative stress and impairment of the anti-oxidant system may play a role in MS.

Toward Understanding the Catalytic Mechanism of Human Paraoxonase 1: Site-Specific Mutagenesis at Position 192

Human paraoxonase 1 (h-PON1) is a serum enzyme that can hydrolyze a variety of substrates. The enzyme exhibits anti-inflammatory, anti-oxidative, anti-atherogenic, anti-diabetic, anti-microbial and organophosphate-hydrolyzing activities. Thus, h-PON1 is a strong candidate for the development of therapeutic intervention against a variety conditions in human. However, the crystal structure of h-PON1 is not solved and the molecular details of how the enzyme hydrolyzes different substrates are not clear yet. Understanding the catalytic mechanism(s) of h-PON1 is important in developing the enzyme for therapeutic use. Literature suggests that R/Q polymorphism at position 192 in h-PON1 dramatically modulates the substrate specificity of the enzyme. In order to understand the role of the amino acid residue at position 192 of h-PON1 in its various hydrolytic activities, site-specific mutagenesis at position 192 was done in this study. The mutant enzymes were produced using Escherichia coli expression system and their hydrolytic activities were compared against a panel of substrates. Molecular dynamics simulation studies were employed on selected recombinant h-PON1 (rh-PON1) mutants to understand the effect of amino acid substitutions at position 192 on the structural features of the active site of the enzyme. Our results suggest that, depending on the type of substrate, presence of a particular amino acid residue at position 192 differentially alters the micro-environment of the active site of the enzyme resulting in the engagement of different subsets of amino acid residues in the binding and the processing of substrates. The result advances our understanding of the catalytic mechanism of h-PON1.

Human paraoxonase 1 as a pharmacologic agent: limitations and perspectives

Human PON1 (h-PON1) is a multifaceted enzyme and can hydrolyze (and inactivate) a wide range of substrates. The enzyme shows anti-inflammatory, antioxidative, antiatherogenic, ant-diabetic, antimicrobial, and organophosphate (OP)-detoxifying properties. However, there are certain limitations regarding large-scale production and use of h-PON1 as a therapeutic candidate. These include difficulties in producing recombinant h-PON1 (rh-PON1) using microbial expression system, low hydrolytic activity of wild-type h-PON1 towards certain substrates, and low storage stability of the purified enzyme. This review summarizes the work done in our laboratory to address these limitations. Our results show that (a) optimized polynucleotide sequence encoding rh-PON1 can express the protein in an active form in E. coli and can be used to generate variant of the enzyme having enhanced hydrolytic activity, (b) in vitro refolding of rh-PON1 enzyme can dramatically increase the yield of an active enzyme, (c) common excipients can be used to stabilize purified rh-PON1 enzyme when stored under different storage conditions, and (d) variants of rh-PON1 enzyme impart significant protection against OP-poisoning in human blood (ex vivo) and mouse (in vivo) model of OP-poisoning. The rh-PON1 variants and their process of production discussed here will help to develop h-PON1 as a therapeutic candidate.

Paraoxonase 1 polymorphisms within a Mississippi USA population as possible biomarkers of enzyme activities associated with disease susceptibility

Paraoxonase (PON1) hydrolyzes paraoxon (PO) and diazoxon (DZO), active metabolites of insecticides parathion and diazinon. The PON1 gene has single nucleotide polymorphisms (SNPs) including a codon 192 arginine (R) to glutamine (Q) and methionine (M) to leucine (L) at codon 55. Hydrolysis of PO (POase), DZO (DZOase), dihydrocoumarin (lactonase), and phenyl acetate (arylesterase) were evaluated for associations with race, gender, age, and PON1 55/192 SNP genotypes. Variables were analyzed both individually and in combination. QQ individuals had higher lactonase (p < 0.001) than RR individuals. This might partially explain why predominantly RR African Americans have higher rates of coronary disease than predominantly QQ Caucasians. Significant (p < 0.001) differences in arylesterase were seen among genotypes with QQ and MM lowest whereas RR and LL were highest. This opposes the prevailing belief that arylesterase is unaffected by genotype and suggests that this activity cannot be used to quantify PON1 protein.

Characterization of human paraoxonase 1 variants suggest that His residues at 115 and 134 positions are not always needed for the lactonase/arylesterase activities of the enzyme

Human paraoxonase 1 (h-PON1) hydrolyzes variety of substrates and the hydrolytic activities of enzyme can be broadly grouped into three categories; arylesterase, phosphotriesterase, and lactonase. Current models of the catalytic mechanism of h-PON1 suggest that catalytic residues H115 and H134 mediate the lactonase and arylesterase activities of the enzyme. H-PON1 is a strong candidate for the development of catalytic bioscavenger for organophosphate poisoning in humans. Recently, Gupta et al. (Nat. Chem. Biol. 2011. 7, 120) identified amino acid substitutions that significantly increased the activity of chimeric-PON1 variant (4E9) against some organophosphate nerve agents. In this study we have examined the effect of these (L69G/S111T/H115W/H134R/R192K/F222S/T332S) and other substitutions (H115W/H134R and H115W/H134R/R192K) on the hydrolytic activities of recombinant h-PON1 (rh-PON1) variants. Our results show that the substitutions resulted in a significant increase in the organophosphatase activity of all the three variants of rh-PON1 enzyme while had a variable effect on the lactonase/arylesterase activities. The results suggest that H residues at positions 115 and 134 are not always needed for the lactonase/arylesterase activities of h-PON1 and force a reconsideration of the current model(s) of the catalytic mechanism of h-PON1.

Paraoxonase 1 gene polymorphism does not affect clopidogrel response variability but is associated with clinical outcome after PCI

Background

Paraoxonase (PON) is a high-density-lipoprotein (HDL) associated enzyme with antioxidative and anti-atherogenic property. Its function is associated with coronary artery disease and its activity genetically controlled. We evaluated whether genetic variation of PON-1 is associated with clinical outcome in a large cohort of Korean patients with drug-eluting stents implantation.

Methods

A total of 1676 patients with drug-eluting stent implantation were enrolled in the prospective CROSS-VERIFY cohort from June 2006 to June 2010. We genotyped the PON1-Q192R gene, measured clopidogrel on-treatment platelet reactivity (OPR), and analyzed lipid profiles. The primary endpoint was the composite of cardiac death, myocardial infarction, and stent thrombosis at 12 months.

Results

PON-1 genotyping data were available in 1336 patients. Since the Q-allele is associated with decreased PON-activity, we analyzed the outcome between patients with QQ/QR (815 patients, 61%) and those with RR-genotype (521 patients, 39%). After adjustment for common cardiac risk factors, the QQ/QR-genotype was an independent predictor of the primary thrombotic endpoint with an 11-fold increased risk (HR 11.6, 95% CI: 1.55–87.0), but not repeat revascularization (HR 1.12, 95% CI: 0.78–1.61). The QQ/QR-genotype was not associated with OPR (QQ/QR: 231±86 PRU vs. RR 236±82 PRU, p = 0.342) but higher small-dense LDL levels (1.20±0.12 mg/dL vs. 0.76±0.15 mg/dL, p = 0.027). The increased risk of thrombotic outcomes was more profound in acute coronary syndrome (ACS) patients compared with non-ACS patients.

Conclusion

PON1 Q-allele is an independent predictor of worse cardiovascular outcome independent of platelet function and is associated with significantly higher levels of small dense LDL-C.

The concentration of thiobarbituric acid reactive substances (TBARS) and paraoxonase activity in blood of patients with osteoarthrosis after endoprosthesis implantation

Background

The aim of this study was to evaluate the concentration of malondialdehyde (MDA) in erythrocytes and in blood plasma and the activity of blood paraoxonase (PON1) of patients with osteoarthrosis (OA) submitted to endoprosthesis implantation for evaluating oxidative stress.

Material/Methods

Study was conducted on 55 patients with OA and on 54 total movement-efficient volunteers. The material for the study was venous blood plasma, serum and erythrocytes.

Results

Increased concentration of MDAe before surgery was observed in the group of men and in patients with a degenerative process affecting hip joints. After an implantation of endoprosthesis, MDAe decreased to the level observed in the control groups. In the study group MDA concentration in plasma was slightly lower before surgery, and after an operation it reached the value of the parameter of the reference groups. Regardless of sex or age, paraoxonase activity was almost twice as high in almost all subgroups as in the reference group. A positive correlation between PON 1 activity and MDAe concentration was demonstrated both before and after surgery in the group of men.

Conclusions

The increase of PON1 activity in patients’ serum in relation to the control groups indicates a probable pathogenic role of the increased formation of reactive oxygen species in the course of OA and may suggest acute inflammation of the synovial joint. The high level of PON 1 activity after endoprosthesis implantation indicates that surgical treatment may additionally stimulate ROS generation. MDAe concentration indicate more intensive process of lipid peroxidation in the elderly.

Paraoxonase-1 and ischemia-modified albumin in patients with end-stage renal disease

End-stage renal disease (ESRD) with and/or without treatment by hemodialysis (HD) is associated with accelerated atherosclerosis, leading to cardiovascular disease (CVD) including acute coronary syndromes. Therefore, the regulation of CVD is a crucial issue for ESRD patients. Given the recent reports that paraoxonase-1 (PON-1) and ischemia-modified albumin (IMA) could predict CVD-related mortality in ESRD, the two recent biomarkers may be useful for preventive strategies for CVD. This review paper presents current data on the relationships between PON-1, IMA, and ESRD. Many studies have shown that circulating PON-1 activity is lower in ESRD patients, and we have shown that its levels increase after HD. Although circulating IMA levels can increase before HD in ESRD patients, there remains to be little data. Our pilot study has shown a significant inverse correlation between PON-1 and IMA in ESRD patients. Although the pathogenic link between PON-1 and IMA remains speculative, considering both biomarkers may provide new insights into the prevention of CVD in ESRD patients.

Serum paraoxonase activity is associated with variants in the PON gene cluster and risk of Alzheimer disease

Previous studies have shown association of single nucleotide polymorphisms (SNPs) in 3 contiguous genes (PON1, PON2, and PON3) encoding paraoxonase with risk of Alzheimer disease (AD). We evaluated the association of serum paraoxonase activity measured by phenyl acetate (PA) and thiobutyl butyrolactone (TBBL) with risk of AD and with 26 SNPs spanning the PON gene cluster in 266 AD cases and 306 sibling controls from the MIRAGE study. The odds of AD (adjusted for age, gender, and ethnicity) increased 20% for each standard deviation decrease in PA or TBBL activity. There were association signals with activity in all 3 genes. Haplotypes including SNPs spanning the PON genes were generally more significant than haplotypes comprising SNPs from 1 gene. Significant interactions were observed between SNP pairs located across the PON cluster with either serum activity measure as the outcome, and between several PON SNPs and PA activity with AD status as the outcome. Our results suggest that low serum paraoxonase activity is a risk factor for AD. Furthermore, multiple variants in PON influence serum paraoxonase activity and their effects may be synergistic.

The role of chronic inflammation and Leu55Met PON1 polymorphism in the pathogenesis of polycystic ovary syndrome

INTRODUCTION

Polycystic ovary syndrome (PCOS) is an endocrine disorder with a complex pathogenesis in which hormonal disturbances, metabolic disorders and chronic inflammation have been considered. Relationships among the paraoxonase 1 (PON1) gene, hyperandrogenism and insulin resistance in women with PCOS have been reported.

AIM

The aim of this study was to evaluate patients with PCOS for the existence of chronic inflammation and to assess the relationship between PON1 polymorphism and hormonal, metabolic and inflammatory parameters in these women.

MATERIAL AND METHODS

One hundred thirty women with PCOS and 70 healthy women were studied. Anthropometric, hormonal (total testosterone, androstenedione, DHEA-S, LH, FSH), metabolic (fasting glucose and insulin, oral glucose tolerance test, insulin sensitivity and resistance indices, lipids) and inflammatory parameters (hsCRP, fibrinogen, WBC) were assessed and analysis of PON1 Leu55Met polymorphism was carried out in all subjects.

RESULTS

WBC, fibrinogen and hsCRP levels did not differ significantly between the PCOS and control groups. The genotype frequencies of the Leu55Met PON1 polymorphism were similar in both groups. There were no relationships between PON1 genotypes and metabolic parameters.

CONCLUSIONS

As chronic low-grade inflammation was not observed in the women with PCOS, there is no direct link between inflammation and PCOS markers per se. None of the variants of the Leu55Met PON1 polymorphism was associated with more frequent occurrence of PCOS or metabolic disorders, including insulin resistance.

Benefits and difficulties in measuring HDL subfractions and human paraoxonase-1 activity during statin treatment

Dyslipidaemia including decreased high density lipoprotein cholesterol concentration is one of several factors that have been implicated in increased cardiovascular risk. Since their introduction in the 1980s, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have emerged as the one of the best-selling class of medications to date, with numerous trials demonstrating powerful efficacy in preventing cardiovascular diseases. Although statins have been shown to modestly raise or not alter HDL-cholesterol, their effect on HDL subfractions and on HDL-associated enzymes including human paraoxonase-1 (PON1) has not yet been fully explored. This review summarizes the currently available data on the effect of statins on HDL subfractions and on PON1 activity with a particular emphasis on the clinical relevance of these effects. Moreover, methodological problems of HDL subfraction and PON1 activity determinations are also discussed.

Human paraoxonase-1 activity in childhood obesity and its relation to leptin and adiponectin levels

Childhood obesity is a predisposing factor for adult cardiovascular diseases. Human serum paraoxonase (PON1) may protect against atherosclerosis by hydrolyzing lipid peroxides in oxidized LDL. Alterations and potential correlations of PON1 activities, leptin and adiponectin levels in childhood obesity were studied. We measured PON1 paraoxonase and arylesterase activities, anthropometric parameters, leptin and adiponectin levels in 59 white, obese (obese group-OB: BMI corrected for age: 95.1 +/- 3.5 percentile, age: 11.9 +/- 1.6 y) and 51 normal-weight children (control group-C: BMI corrected for age: 64.1 +/- 8.4 percentile, age: 12.0 +/- 3.9 y). Obese children had significantly lower PON1 paraoxonase (OB: 84.80 (64.33/144.74) U/L versus. C: 99.42 (83.33/152.05) U/L; p < 0.05) and arylesterase activities (OB: 94.40 (82.20/108.70) U/L versus. C: 115.20 (93.70/126.00) U/L; p < 0.01), higher leptin (OB: 37.05 (24.33/53.87) ng/mL versus. C: 4.62 (2.52/17.6) ng/mL; p < 0.0001) and lower adiponectin levels (OB: 7.56 (5.69/12.06) microg/mL versus. C: 11.51 (8.84/14.49) microg/mL; p < 0.001) compared with the normal-weight group. PON1 arylesterase activity showed inverse univariate correlation with leptin (r = -0.29; p < 0.05) and positive correlation with adiponectin levels (r = 0.39; p < 0.01). In multiple regression analysis adiponectin was strongly associated with PON1 arylesterase activity in obese children (beta = 0.45, p < 0.02). Our results emphasize the importance of the investigated metabolic alterations which may have further effects on cardiovascular morbidity and mortality in later adulthood. Altered levels of leptin, adiponectin and PON1 activities may be useful markers beside the general risk factors in childhood obesity.

Paraoxonase 1 interactions with HDL, antioxidants and macrophages regulate atherogenesis - a protective role for HDL phospholipids

Macrophage cholesterol accumulation and foam cell formation is the hallmark of early atherogenesis. In addition to macrophages, at least three more major players regulate atherosclerosis development; paraoxonase 1 (PON1), antioxidants, and HDL. PON1 is an HDL-associated lactonase which posses antioxidant and anti-atherogenic properties. PON1 protects against macrophage-mediated LDL oxidation, and increases HDL binding to macrophages which, in turn, stimulates HDL's ability to promote cholesterol efflux. These two major anti-atherogenic properties of HDL (and of PON1) require, at least in part, macrophage binding sites for HDL-associated PON1. Indeed, PON1, as well as HDL-associated PON1, specifically binds to macrophages, leading to anti-atherogenic effects. Macrophage PON1 binding sites may thus be a target for future cardioprotection therapy. Studying the interactions among PON1, antioxidants, and macrophages can thus assist in achieving appropriate treatment and prevention of atherosclerosis.

Lipid-lowering effects of polydatin from Polygonum cuspidatum in hyperlipidemic hamsters

Hyperlipidaemias are common in obese people, and they increase the risk of cardiovascular diseases such as coronary heart disease (CHD) and atherosclerosis (AS). Previous studies have shown that several drugs can depress serum cholesterol. However, they could cause serious side effects in various clinical settings. The objective of the present study was to evaluate the lipid-lowering effects of polydatin in high-fat/cholesterol (HFC)-fed hamsters. The levels of lipids in hamsters were measured enzymatically before and after the administration of polydatin. Significant differences between HFC and HFC+polydatin were detected for those concentrations. Decreased levels of serum TC, TG and LDL-C and the concentrations of hepatic TG were found. Experimental results also showed that polydatin elevated LDL-C/HDL-C and TC/HDL-C ratios. In concert with other effects, serum cholesterol-lowering effect in hamsters may contribute to the regulation properties attributed to polydatin.

Atorvastatin effect on the distribution of high-density lipoprotein subfractions and human paraoxonase activity

Human serum paraoxonase-1 (PON1) protects lipoproteins against oxidation by hydrolyzing lipid peroxides in oxidized low-density lipoprotein (LDL); therefore, it may protect against atherosclerosis. Changes in the ratio of high-density lipoprotein (HDL) subfractions may alter the stability and the antioxidant capacity of PON1. The aim of the study was to examine the effect of atorvastatin treatment on the distribution of HDL subfractions, LDL size, cholesteryl ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT), and PON1 activity. In all, 33 patients with type IIa and IIb hypercholesterolemia were involved in the study. LDL sizes and HDL subfractions were determined by gradient gel electrophoresis. CETP, LCAT, and PON1 activities were measured spectrophotometrically. Three months of treatment with atorvastatin 20 mg daily significantly increased the HDL3 (+8.13%) and decreased the HDL2a and HDL2b subfractions (-1.57% and -6.55%, respectively). The mean LDL size was significantly increased (+3.29%). The level of oxidized LDL was significantly decreased (-46.0%). The PON1 activity was augmented by the atorvastatin treatment (+5.0%). The CETP activity positively correlated with the HDL2b level and negatively correlated with the HDL3 and HDL2a levels. Atorvastatin alters the HDL subfractions, which may improve its antiatherogenic effect via enhancement of the PON1 activity.

The human paraoxonase-1 phenotype modifies the effect of statins on paraoxonase activity and lipid parameters

AIMS

Human serum paraoxonase-1 (PON1) protects lipoproteins against oxidation by hydrolysing lipid peroxides in oxidized low-density lipoprotein, therefore it may protect against atherosclerosis. One of the two common PON1 gene polymorphisms within the PON1 gene is the Q192R, whose prevalence can be estimated by phenotype distribution analysis. The goal of this study was to clarify the role of PON1 phenotypes on the effect of three different statins on paraoxonase activity and lipid parameters.

METHODS

One hundred and sixty-four patients with type IIb hypercholesterolaemia were involved in the study. We examined the effect of 10 mg day(-1) atorvastatin, 10/20 mg day(-1) simvastatin and 80 mg day(-1) extended-release fluvastatin treatment on lipid levels and paraoxonase activity in patients with different PON1 phenotypes. The phenotype distribution of PON1 was determined by the dual substrate method.

RESULTS

Three months of statin treatment significantly increased paraoxonase activity in every statin-treated group. In patients with AB+BB phenotype, statin treatment was significantly more effective on paraoxonase activity than in the AA group. Statin treatment more effectively decreased triglyceride levels in the AB+BB group compared with the AA group in the whole study population and in the simvastatin-treated group. Atorvastatin treatment was significantly more effective on apolipoprotein B levels in patients with AB+BB phenotype than in the AA phenotype group.

CONCLUSIONS

The PON1 phenotype may be a novel predictive factor for the effectiveness of statin treatment on PON1 activity and serum lipid levels; however, different types of statins may exert different effects on these parameters.

Effect of acylethanolamides on lipid peroxidation and paraoxonase activity

N-acylethanolamides (NAEs) are hydrophobic molecules synthesized in many tissues. An increase in the plasma levels of NAEs has been observed in human diseases. Previous studies have suggested that NAEs could exert a protective effect against oxidative stress. Aim of the study was to investigate whether NAEs (oleoylethanolamide, palmitoylethanolamide and anandamide), differing for acyl chain length and unsaturation, exert a protective role against plasma lipid peroxidation triggered by incubation with Cu2+2 or AAPH (2,2'-azobis(2-amidinopropane) dihydrochloride). Moreover, we investigated the effect of NAEs on the activity of HDL-associated paraoxonase (PON1), an enzyme involved in the antioxidant end anti-inflammatory role of human high density lipoproteins (HDL). The results demonstrated that the NAEs protect plasma lipids and PON1 activity against AAPH and/or copper-induced oxidation.

Paraoxonase (PON)1 192R allele carriage is associated with reduced risk of inflammatory bowel disease

The paraoxonase (PON) genes family maps to chromosome 7q21-q22, within a loci that also showed evidence of susceptibility genes for both Crohn's disease (CD) and ulcerative colitis (UC). In this case-control study we investigated the possible relationship between PON1 and PON2 polymorphisms and the risk of inflammatory bowel disease (IBD). PON1 192Q/R, PON1 55L/M, and PON2 311S/C polymorphisms were investigated by RFLP analysis in DNA samples from 224 patients with CD, 58 patients with UC, and 311 healthy controls. The PON1 192R allele was significantly less common among IBD Ashkenazi patients (allelic OR = 0.61, P = 0.004, 95% CI = 0.44-0.85). In agreement with the individual SNP analysis, Ashkenazi IBD patients had a higher frequency of haplotype PON1 192Q/PON1 55L/PON2 311S (26.3% vs 17.3%; P=0.003) and a lower frequency of haplotype PON1 192R/PON1 55L/PON2 311S (18.9% vs 27.7%; P=0.008). Our results suggest that in this Ashkenazi Jewish population, carriage of PON1 R192 allele may confer protection against the development of IBD.

Paraoxonases are associated with intestinal inflammatory diseases and intracellularly localized to the endoplasmic reticulum

We demonstrated previously that the paraoxonase (PON1/2/3) genes and proteins are expressed in human intestinal biopsies and in Caco-2 cells. The current study aims were to explore whether PON1/2/3 expression is different in inflammatory bowel diseases (IBD) or celiac disease compared to healthy controls, and to explore the intracellular localization of PON1/2/3. Our results showed that significantly fewer biopsies expressed PON1 and PON3 in the duodenum of celiac patients (PON1, P<0.0001; PON3, P=0.03), in the terminal ileum of Crohn's patients (PON1, P=0.001; PON3, P=0.008), and in the colon of UC patients (PON1, P=0.02; PON3, P=0.06) compared to controls. Since all three disorders share markedly elevated inflammatory mediators we explored the PON1/2/3 mRNA expression on cytokine stimulation. No changes were observed in Caco-2 and HT29 cells. Immunofluorescence experiments localized PON1/2/3 exclusively to the endoplasmic reticulum (ER) in both CaCo-2 and HT29 cells. These results demonstrate for the first time a novel relationship between PON1 and PON3 expression and several inflammatory gastrointestinal disorders. Together with the localization of PON1/2/3 enzymes to the ER, it may be suggested that PON1/2/3 may have extracellular functions as part of the host response in IBD and celiac disease.

Oxidation–reduction potential and paraoxonase–arylesterase activity in trauma patients

The amount of oxidative stress in severely traumatized patients is usually based on various individual parameters such as total antioxidants and lipid peroxidation. Serial measurements of plasma oxidation-reduction potential (ORP) in severely traumatized patients as a simple mean of assessing overall oxidative stress is described. Serial whole blood samples were obtained from multi-trauma patients (N=39) and healthy individuals (N=10). Plasma ORP in multi-trauma patients increased during the first few days of hospitalization and approached normal ORP levels upon discharge. On the ORP maxima day (5.8 days+/-0.5 SEM), a statistically significant decrease (p<0.05) was observed for negative acute phase reactants such as plasma paraoxonase-arylesterase (PON-AE) activity and total plasma protein in comparison with admission plasma levels. Monitoring ORP could be a useful tool for assessing the degree of oxidative stress, inflammation, severity of injury, and potential efficacy of treatment.

Differential effect of lysophospholipids on activities of human plasma paraoxonase1, either soluble or lipid-bound

Interaction of paraoxonase1 (PON1) with lysophospholipids was examined with respect to activity regulation and binding property. Paraoxonase activity of purified PON1 was partially inhibited by palmitoyl-lysophosphatidyl-glycerol (palmitoyl-lysoPG) and lysophosphatidylinositol (lysoPI), which had a stimulatory effect on arylesterase and diazoxonase activities. The selective inhibition of paraoxonase activity by palmitoyl-lysoPG, characterized by noncompetitiveness and charge interaction, was also observed with HDL- or dimyristoylphosphatidylcholine (DMPC)-bound PON1. Meanwhile, lysophosphatidylcholine (lysoPC) stimulated all three activities of purified PON1, although it stimulated DMPC-bound or HDL-bound PON1 to a lesser extent. The stimulatory action of lysophospholipids was observed around their CMC, suggesting that micelle formation of lysophospholpids might be involved in the stimulation of PON1 activity. Presumably in support of this, the tryptophan fluorescence intensity of PON1 was increased by lysophospholipids at concentrations required for the stimulation of PON1 activity. Separately, lysoPC stimulation was less remarkable for DMPC-bound PON1 than for either dimyristoylphosphatidylserine (DMPS)- or dimyristoylphosphatidylglycerol-bound PON1, suggesting a tight association between PON1 and DMPC. In support of this, the stimulatory role of apolipoprotein A-I was less prominent for DMPC-bound PON1 than for DMPS-bound PON1. Taken together, these data suggest that the inhibition of paraoxonase activity by lysoPG or lysoPI may be due to binding to a site distinct from the active center, whereas the stimulation by lysophospholipid may be ascribed to the micelle formation around the lipid-associable region of PON1.

Serum paraoxonase 1 activity and malondialdehyde levels in patients with ulcerative colitis

This study was designed to evaluate the oxidative and antioxidative status in patients with ulcerative colitis by detecting antioxidant enzyme paraoxonase 1 activity together with the level of a well-known marker of oxidative stress, malondialdehyde. Serum paraoxonase 1 activity and malondialdehyde levels were analysed in 30 patients with ulcerative colitis and 30 controls using a spectrophotometric method; correlation analysis was made between these variables. Serum malondialdehyde levels were higher in the ulcerative colitis group (median: 2.5, range: 0.5-9.4 nmol ml(-1)) than among the controls (median:1.1, range: 0.5-2.3 nmol ml(-1); p < 0.001) whereas paraoxonase 1 activities were lower in the ulcerative colitis group (median: 158.4, range: 61.6-264.1 U l(-1)) than in the control group (median: 233.3, range: 114.4-431.0 U l(-1); p < 0.001). There was no correlation between serum malondialdehyde level, paraoxonase 1 activity and disease activity. (1) Increased reactive oxygen metabolites levels in ulcerative colitis may result in a pro-oxidation environment, which in turn could result in decreased antioxidant paraoxonase 1 activity and increased malondialdehyde levels, (2) increased cytokines may be a possible cause of decreased paraoxonase 1 activity and (3) decreased serum paraoxonase 1 activity may be a part of an inflammatory response.

Preferable stimulation of PON1 arylesterase activity by phosphatidylcholines with unsaturated acyl chains or oxidized acyl chains at sn-2 position

To examine the effect of phospholipids on PON1 activities, purified PON1 was exposed to phospholipids prior to the determination of arylesterase and paraoxonase activities. Phosphatidylcholines with saturated acyl chains (C10-C16) showed a stimulation of both activities, chain length-dependent, with a greater stimulation of arylesterase activity, suggesting the implication of lipid bilayer in the stimulatory action. Such a preferable stimulation of arylesterase activity was more remarkable with phosphatidylcholines with polyunsaturated acyl chains or oxidized chains at sn-2 position, implying that the packing degree of acyl chain may be also important for the preferable stimulation of arylesterase activity. Separately, 1-palmitoyl-lysoPC also stimulated arylesterase activity preferably, indicating that the micellar formation of lipids around PON1 also contributes to the stimulatory action. Additionally, phosphatidylglycerols slightly enhanced arylesterase activity, but not paraoxonase activity. In contrast, phosphatidylserine and phosphatidic acid (> or =0.1 mM) inhibited both activities Further, such a preferable stimulation of arylesterase activity by phosphatidylcholines was also reproduced with VLDL-bound PON1, although to a less extent. These data indicate that phosphatidylcholines with polyunsaturated acyl chains or oxidized chain, or lysophosphatidylcholine cause a preferable stimulation of arylesterase activity, thereby contributing to the decrease in the ratio of paraoxonase activity to arylesterase activity.

Serum paraoxonase 1 activity and lipid peroxidation levels in patients with age-related macular degeneration

Our objective was to investigate antioxidant paraoxonase 1 (PON1) activity together with malondialdehyde (MDA) levels to evaluate oxidative stress in patients with age-related macular degeneration (AMD), an important cause of blindness in the elderly population. Serum PON1 activity and MDA levels were analyzed in 37 patients with AMD and compared with 29 healthy controls using a spectrophotometric method. Serum MDA levels were significantly higher in the patient group (2.76 +/- 1.28 nmol/ml) than controls (1.00 +/- 0.36 nmol/ml; p < 0.001), whereas PON1 activity was lower in the patient group (132.27 +/- 63.39 U/l) than controls (312.13 +/- 136.23 U/l; p < 0.001). There was a negative correlation between MDA and PON1 levels (r = -0.470, p < 0.001). We conclude that the observed increase in MDA levels may be related to decreased PON1 activity; the present data also demonstrated that an obvious negative correlation between PON1 activity and MDA levels exists in patients with AMD. PON1 is also an antioxidant agent, therefore effective antioxidant therapy to inhibit lipid peroxidation is necessary and agents to increase PON1 activity may be a therapeutic option in AMD.

Effects of caloric restriction and gender on rat serum paraoxonase 1 activity

Paraoxonase 1 (PON1) associates to specific high-density lipoproteins (HDLs)--those containing apolipoprotein A-I (apoA-I) and apolipoprotein J (apoJ)--and is largely responsible for their antiatherogenic properties. Caloric restriction (CR) has been shown to reduce major atherosclerotic risk factors. The aims of this work were to study PON1 activity response to CR (40% over 14 weeks) and to elucidate whether there are adaptive differences related to gender. Serum and liver paraoxonase and arylesterase activities, serum triglyceride, total and HDL cholesterol concentrations, serum PON1, apoA-I and apoJ contents and liver PON1 mRNA levels were measured. No effects of CR or gender were observed in triglyceride, total cholesterol concentration and PON1 mRNA levels. HDL cholesterol was higher in female rats than in male rats and increased with CR only in the latter animals. Serum PON1 activities tended to be higher in female rats and dropped with CR, with females showing the biggest decrease. Serum PON1 content was higher in female rats and decreased in both genders with CR, whereas apoA-I and apoJ contents, which were higher in female rats too, decreased only in the former animals, accounting for the high PON1 activity decrease observed in these animals. In conclusion, the short-term CR-associated reduction of serum PON1 activity and PON1, apoA-I and apoJ levels points toward a reduced stability of HDL-PON1 complexes and/or HDL particle levels responsible for PON1 transport and function in the blood. Moreover, the variations in PON1 activity and apolipoprotein levels show gender-related differences that are indicative of a different adaptive strategy of male and female rats when faced with a period of food restriction.

Assessment of paraoxonase 1 activity and malondialdehyde levels in patients with rheumatoid arthritis

OBJECTIVES

We aimed to evaluate antioxidant paraoxonase 1 activity together with malondialdehyde (MDA) (an oxidative stress parameter) levels in patients with rheumatoid arthritis.

DESIGN AND METHODS

Fifty-seven rheumatoid arthritis patients were included in the study and subgrouped according to disease activity (active, n = 31; inactive, n = 26) and compared with healthy controls (n = 25). Serum paraoxonase 1 activity and MDA levels were measured according to an enzymatic spectrophotometric method.

RESULTS

Serum MDA level was higher (P = 0.001) whereas paraoxonase 1 activity was lower (P = 0.001) in the patient group than the controls. When active and inactive subgroups were compared with the control group, there was a statistically significant difference between each parameter. Serum MDA levels were significantly higher, while paraoxonase 1 activity was lower in the active and inactive rheumatoid arthritis groups than the control group. But there was not any difference between active and inactive patients with RA. There was a negative correlation between MDA levels and paraoxonase 1 activity.

CONCLUSIONS

Increased reactive oxygen species levels in rheumatoid arthritis may result in a pro-oxidation environment, which in turn could result in decreased antioxidant paraoxonase 1 activity and increased MDA levels.

High-level expression of recombinant human paraoxonase 1 Q in silkworm larvae (Bombyx mori)

Human serum paraoxonase 1 (hPON1) belongs to a family of enzymes that catalyze the hydrolysis of a broad range of esters and lactones. Although the very first identification of hPON1 might have been as a calcium-dependent paraoxonase/arylesterase, PON1 is in fact a lactonase associated with high-density lipoprotein and strongly stimulated by apoA-I. PON1 hydrolyzes various organophosphates, including insecticides and nerve gases. PON1 also plays a key role in prevention of atherosclerosis. Mediation of cholesterol efflux from macrophage is a key in vivo function of PON1. In present study, the hPON1 Q gene was cloned into baculovirus transfer vector pVL1392 and expressed in silkworm expression system. The rhPON1 Q presented two bands with every near molecular weight of about 40 and 43 kDa according to sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blotting analysis. The expression level was up to 1,256 mg/L in haemolymph, about 50 times as high as that from BmN cells (24.8 mg/L). After purified by two chromatography steps (DEAE-Sepharose and HiTrap Chelating HP), the purity of rhPON1 Q was up to 90%, and the enzymatic properties are similar to serum hPON1.

Polymorphisms in the PON gene cluster are associated with Alzheimer disease

Paraoxonase is an arylesterase enzyme that is expressed in the liver and found in the circulation in association with apoA1 and the high-density lipoprotein, and prevents the accumulation of oxidized lipids in low-density lipoproteins in vitro. Common polymorphisms in genes encoding paraoxonase are established risk factors in a variety of vascular disorders including coronary artery disease and carotid artery stenosis, but their association with Alzheimer disease (AD) is controversial. We tested the association of 29 SNPs in PON1, PON2 and PON3 with AD in 730 Caucasian and 467 African American participants of the MIRAGE Study, an ongoing multi-center family-based genetic epidemiology study of AD. Eight SNPs were associated with AD in the African American families (0.0001< or =P< or =0.04) and two SNPs were associated with AD in Caucasian families (0.01< or =P< or =0.04). Of note, the pattern of association for the PON1 promoter SNP -161[C/T] was the same in both ethnic groups (P=0.006). Haplotype analysis using sliding windows revealed 11 contiguous SNP combinations spanning the three PON genes with significant global test scores (0.006< or =P< or =0.04) in the two ethnic groups combined. The most significantly associated haplotype comprised SNPs in the region spanning the -161[C/T] SNP (P=0.00009). Our results demonstrate association between AD and variants in the PON gene cluster in Caucasians and African Americans.

Bile acids decrease hepatic paraoxonase 1 expression and plasma high-density lipoprotein levels via FXR-mediated signaling of FGFR4

OBJECTIVE

The purpose of this research was to determine how dietary bile acids repress hepatic expression of paraoxonase 1 (PON1).

METHODS AND RESULTS

C57BL/6 mice and C3H/HeJ mice, having different susceptibilities to atherosclerosis, were fed a chow diet and an atherogenic diet containing taurocholate. Compared with the more atherosclerosis-susceptible C57BL/6 mice, C3H/HeJ mice display resistance to dietary bile acid repression of hepatic PON1 mRNA and decreased high-density lipoprotein cholesterol. Whereas knockout of toll receptor 4 did not affect response to taurocholate, deletion of either FXR or FGFR4 blocked taurocholate repression of PON1 and CYP7A1. FGF19, an activator of FGFR4 expressed in human ileum, decreased expression of both PON1 and CYP7A1 expression by human hepatoma cells. In all of the mice studied, dietary taurocholate increased ileal expression of FGF15, a FXR-inducible murine homologue of human FGF19.

CONCLUSIONS

Hepatic PON1 and CYP7A1 mRNA expression is repressed by bile acids via FXR-mediated induction of FGF15. Thus, the inability of C3H/HeJ mice to display taurocholate repression of PON1 and CYP7A1 mRNAs was not because of a lack of induction of FGF15 but rather signaling events distal to FGF15-FGFR4 association.

Facilitated replacement of Kupffer cells expressing a paraoxonase-1 transgene is essential for ameliorating atherosclerosis in mice

Resident macrophages (i.e., Kupffer cells) are derived from hematopoietic stem cells (HSCs) and are primarily responsible for the removal from plasma of oxidized forms of low-density lipoprotein (LDL). The therapeutic potential of Kupffer cell expression of a transgene encoding paraoxonase-1 (PON1), whose plasma activity correlates with the protection from atherosclerosis, was examined in mice rendered atherosclerosis-susceptible through genetic deletion of the LDL receptor. Mice having their bone marrow engrafted with HSCs expressing the PON1 transgene (PON1-Tg) driven by a macrophage-specific promoter were injected i.v. with saline (vehicle only) or with gadolinium chloride (GdCl(3)), an agent that rapidly causes Kupffer cell apoptosis. One month later, GdCl(3)-facilitated Kupffer cell apoptosis increased the hepatic expression of transgenic PON1 mRNA by 9-fold. After 12 weeks of being fed a cholesterol-enriched atherogenic diet, mice injected with GdCl(3) exhibited 50% reductions in both aortic sinus atherosclerotic lesions (P < 0.0097) and surface lesions of the abdominal aorta (P < 0.006). In contrast, mice receiving HSCs expressing the PON1-Tg but not treated with GdCl(3) showed no protection from atherosclerosis. In addition, mice engrafted with HSCs not expressing the PON1-Tg but injected with GdCl(3) also showed no protection from atherosclerosis. These findings, showing that GdCl(3)-enhanced hepatic expression of the PON1-Tg is essential for reducing atherosclerosis, indicate that Kupffer cells play an important role in atherogenesis. GdCl(3)-facilated replacement of Kupffer cells may enhance the efficacy of other HSC-based gene therapies.

Paraoxonase 1 (PON1) is present in postprandial chylomicrons

Paraoxonase 1 (PON1) is an esterase, associated in serum with high density lipoprotein (HDL). As diet affects serum PON1 activity, we questioned whether PON1 is also carried by postprandial chylomicrons. Chylomicrons were isolated by ultracentrifugation from plasma of 10 healthy men, 3h after the consumption of a high fat, high carbohydrate meal, and were analyzed for the presence of PON1 arylesterase activity and protein. The present study shows for the first time that, in addition to the presence of PON1 mainly on HDL, postprandial chylomicrons also contain minor, but significant amount of PON1. PON1 was also present in chylomicrons derived from fasted patients with hyperchylomicronemia. In addition, PON1 was detected in very low density lipoprotein (VLDL), but not in LDL. The origin of chylomicron PON1 could be partly attributed to its transfer from HDL. Finally, this study demonstrates that postprandial chylomicrons inhibit copper ion-induced LDL oxidation, secondary to hydrolysis of lipid peroxides, a phenomenon which could be related, at least in part, to the chylomicron PON1 content. We conclude that postprandial chylomicrons contain PON1, which may function in the removal of atherogenic oxidized lipids.

Dietary antioxidants and paraoxonases against LDL oxidation and atherosclerosis development

Oxidative modification of low-density lipoprotein (LDL) in the arterial wall plays a key role in the pathogenesis of atherosclerosis. Under oxidative stress LDL is exposed to oxidative modifications by arterial wall cells including macrophages. Oxidative stress also induces cellular-lipid peroxidation, resulting in the formation of 'oxidized macrophages', which demonstrate increased capacity to oxidize LDL and increased uptake of oxidized LDL. Macrophage-mediated oxidation of LDL depends on the balance between pro-oxidants and antioxidants in the lipoprotein and in the cells. LDL is protected from oxidation by antioxidants, as well as by a second line of defense--paraoxonase 1 (PON1), which is a high-density lipoprotein-associated esterase that can hydrolyze and reduce lipid peroxides in lipoproteins and in arterial cells. Cellular paraoxonases (PON2 and PON3) may also play an important protective role against oxidative stress at the cellular level. Many epidemiological studies have indicated a protective role for a diet rich in fruits and vegetables against the development and progression of cardiovascular disease. A large number of studies provide data suggesting that consumption of dietary antioxidants is associated with reduced risk for cardiovascular diseases. Basic research provides plausible mechanisms by which dietary antioxidants might reduce the development of atherosclerosis. These mechanisms include inhibition of LDL oxidation, inhibition of cellular lipid peroxidation and consequently attenuation of cell-mediated oxidation of LDL. An additional possible mechanism is preservation/increment of paraoxonases activity by dietary antioxidants. This review chapter presents recent data on the anti-atherosclerotic effects and mechanism of action of three major groups of dietary antioxidants-vitamin E, carotenoids and polyphenolic flavonoids.

Preferential inhibition of paraoxonase activity of human paraoxonase 1 by negatively charged lipids

To determine the causes responsible for a preferential decrease of paraoxonase activity, which has been observed in the serum of patients with cardiovascular diseases, the inactivation or inhibition of paraoxonase 1 (PON1) by various endogenous factors was examined using paraoxon or phenyl acetate as a substrate. When purified PON1 was incubated with various endogenous oxidants or aldehydes, they failed to cause a preferential reduction of paraoxonase activity, suggesting no participation of the inactivation mechanism in the preferential loss of paraoxonase activity. Next, when we examined the inhibition of PON1 activity by endogenous lipids, monoenoic acids such as palmitoleic acid or oleic acid inhibited paraoxonase activity preferentially, in contrast to a parallel inhibition of both activities by polyunsaturated or saturated acids. Noteworthy, oleoylglycine inhibited paraoxonase activity, but not arylesterase activity, complying with the selective inhibition of paraoxonase activity. Moreover, such a selective inhibition of paraoxonase activity was also expressed by lysophosphatidylglycerol or lysophosphatidylinositol, but not by lysophosphatidylserine or lysophosphatidylcholine, indicating the importance of the type of head group. Furthermore, such a preferential or selective inhibition of paraoxonase activity was also observed with PON1 associated with HDL or plasma. These data suggest that some negatively charged lipids may correspond to factors causing the preferential inhibition of paraoxonase activity of PON1.