Quantification of human serum paraoxonase by enzyme-linked immunoassay: population differences in protein concentrations

Quantifying PON1 on HDL with nanoparticle-gated electrokinetic membrane sensor for accurate cardiovascular risk assessment

Cardiovascular disease-related deaths (one-third of global deaths) can be reduced with a simple screening test for better biomarkers than the current lipid and lipoprotein profiles. We propose using a highly atheroprotective subset of HDL with colocalized PON1 (PON1-HDL) for superior cardiovascular risk assessment. However, direct quantification of HDL proteomic subclasses are complicated by the peroxides/antioxidants associated with HDL interfering with redox reactions in enzymatic calorimetric and electrochemical immunoassays. Hence, we developed an enzyme-free Nanoparticle-Gated Electrokinetic Membrane Sensor (NGEMS) platform for quantification of PON1-HDL in plasma within 60 min, with a sub-picomolar limit of detection, 3-4 log dynamic range and without needing sample pretreatment or individual-sample calibration. Using NGEMS, we report our study on human plasma PON1-HDL as a cardiovascular risk marker with AUC~0.99 significantly outperforming others (AUC~0.6-0.8), including cholesterol/triglycerides tests. Validation for a larger cohort can establish PON1-HDL as a biomarker that can potentially reshape cardiovascular landscape.

A PON for All Seasons: Comparing Paraoxonase Enzyme Substrates, Activity and Action including the Role of PON3 in Health and Disease

Paraoxonases (PONs) are a family of hydrolytic enzymes consisting of three members, PON1, PON2, and PON3, located on human chromosome 7. Identifying the physiological substrates of these enzymes is necessary for the elucidation of their biological roles and to establish their applications in the biomedical field. PON substrates are classified as organophosphates, aryl esters, and lactones based on their structure. While the established native physiological activity of PONs is its lactonase activity, the enzymes’ exact physiological substrates continue to be elucidated. All three PONs have antioxidant potential and play an important anti-atherosclerotic role in several diseases including cardiovascular diseases. PON3 is the last member of the family to be discovered and is also the least studied of the three genes. Unlike the other isoforms that have been reviewed extensively, there is a paucity of knowledge regarding PON3. Thus, the current review focuses on PON3 and summarizes the PON substrates, specific activities, kinetic parameters, and their association with cardiovascular as well as other diseases such as HIV and cancer.

Circulating Lactonase Activity but Not Protein Level of PON-1 Predicts Adverse Outcomes in Subjects with Chronic Kidney Disease

The burden of cardiovascular disease and death in chronic kidney disease (CKD) outpaces that of the other diseases and is not adequately described by traditional risk factors alone. Diminished activity of paraoxonase (PON)-1 is associated with increased oxidant stress, a common feature underlying the pathogenesis of CKD. We aimed to assess the prognostic value of circulating PON-1 protein and PON lactonase activity on adverse clinical outcomes across various stages and etiologies of CKD. Circulating PON-1 protein levels and PON lactonase activity were measured simultaneously in patients with CKD as well as a cohort of apparently healthy non-CKD subjects. Both circulating PON-1 protein levels and PON lactonase activity were significantly lower in CKD patients compared to the non-CKD subjects. Similarly, across all stages of CKD, circulating PON-1 protein and PON lactonase activity were significantly lower in patients with CKD compared to the non-CKD controls. Circulating PON lactonase activity, but not protein levels, predicted future adverse clinical outcomes, even after adjustment for traditional risk factors. The combination of lower circulating protein levels and higher activity within the CKD subjects were associated with the best survival outcomes. These findings demonstrate that diminished circulating PON lactonase activity, but not protein levels, predicts higher risk of future adverse clinical outcomes in patients with CKD.

The most effective polymorphisms of paraoxonase-1 gene on enzyme activity and concentration of paraoxonase-1 protein in type 2 diabetes mellitus patients and non-diabetic individuals: A systematic review and meta-analysis

INTRODUCTION

Many studies have evaluated the association of paraoxonase-1 (PON1) gene polymorphisms with enzyme activity and concentration in type 2 diabetes mellitus (T2DM). However, the exact impact of these polymorphisms is not still obvious. Hence, we conducted a systematic review and meta-analysis to clarify the association of PON1 polymorphisms with its enzyme characteristics in T2DM patients and non-diabetic individuals.

METHODS

We searched electronic databases including PubMed, Web of Science, Embase and Scopus for publications by April 2018. The pooled response ratio (rr) for the association and their corresponding 95% confidence intervals (CIs) were calculated using a fixed-effect model.

RESULTS

Fifteen relevant studies fulfilled our inclusion criteria. The results showed a 1.25-fold increase in total PON1 activity in non-diabetic group against T2DM patients (p-value = 0.024). Also, only Q192R and L55M polymorphisms had sufficient studies to be included in the meta-analysis. All three genotypes of Q192R polymorphism showed significantly different activities between the study groups with the highest pooled effect size for RR genotype (rr_QQ < rr_QR < rr_RR) while this difference was seen only in LL genotype of L55M polymorphism. Therefore, Q192R polymorphism was more correlated with type 2 diabetes mellitus. In case of concentration, there was no significant differences between two groups (p-value = 0.897).

CONCLUSION

Current meta-analysis suggested that the observed difference of total PON1 activity was due to the different activity of various genotypes of PON1 enzyme in case of L55M and Q192R polymorphisms so that LL and RR genotypes had the most important role in the establishment of mentioned difference.

Effects of Short-Term Hypothyroidism on the Lipid Transfer to High-Density Lipoprotein and Other Parameters Related to Lipoprotein Metabolism in Patients Submitted to Thyroidectomy for Thyroid Cancer

BACKGROUND

Elevation of low-density lipoprotein (LDL) cholesterol is the hallmark of the dyslipidemia observed in hypothyroidism, but alterations on high-density lipoprotein (HDL) plasma levels and metabolism are less understood. The aim of this study was to explore aspects of HDL metabolism and enzymes that act on HDL after a short period of overt hypothyroidism.

METHODS

Eighteen women (age 44 ± 11 years; body mass index 27.9 ± 5.2 kg/m²) were studied before total thyroidectomy for thyroid cancer, when they were euthyroid, and after thyroidectomy, in overt hypothyroidism for three weeks, following levothyroxine withdrawal for performance of a whole-body scan.

RESULTS

Thyrotropin and free thyroxine confirmed hypothyroidism; low thyroglobulin and radioiodine uptake indicated near absence of thyroid tissue. LDL cholesterol (125 ± 35 vs. 167 ± 40 mg/dL; p = 0.0002), HDL cholesterol (HDL-C; 39 ± 8 vs. 46 ± 10 mg/dL; p = 0.0025), non-HDL-C (149 ± 38 vs. 201 ± 46 mg/dL; p < 0.0001), unesterified cholesterol (53 ± 10 vs. 70 ± 16 mg/dL; p = 0.0003), apolipoprotein (apo) A-I (1.32 ± 0.19 vs. 1.44 ± 0.22 g/L; p < 0.04), and apo B (0.97 ± 0.25 vs. 1.31 ± 0.28 g/L; p < 0.0001) plasma concentrations were all higher in hypothyroidism compared to values in the euthyroid state, but triglycerides and Lp(a) were unchanged. There were no changes in HDL particle size and lipid composition, cholesteryl ester transfer protein and lecithin cholesterol acyltransferase concentrations and in paraoxonase-1 activity. Regarding the in vitro assay to estimate lipid transfer to HDL, there were no changes when comparing the euthyroid to the hypothyroid state, but when adjusted for HDL-C, the unesterified cholesterol (0.14 ± 0.03 vs. 0.11 ± 0.02; p < 0.0001), triglycerides (0.11 ± 0.02 vs. 0.09 ± 0.02; p < 0.0001), phospholipids (0.44 ± 0.09 vs. 0.40 ± 0.07; p = 0.0205), and esterified cholesterol (0.14 ± 0.03 vs. 0.13 ± 0.03; p = 0.0043) transfer to HDL were all diminished in hypothyroidism.

CONCLUSIONS

In short-term hypothyroidism, HDL-C increased, but this did not increase the capacity of the HDL fraction to receive lipids or the activity of paraoxonase-1, the anti-oxidation enzyme associated to HDL.

Incident type 2 diabetes is associated with HDL, but not with its anti-oxidant constituent - paraoxonase-1: The prospective cohort PREVEND study

OBJECTIVE

High-density lipoprotein cholesterol (HDL-C) is an established risk marker for cardiovascular disease and consistently associated with type 2 diabetes risk. Serum paraoxonase-1 (PON-1) - an anti-oxidant constituent of HDL - is inversely associated with cardiovascular disease risk, but its relationship with incident type 2 diabetes is uncertain. We aimed to investigate the prospective association between PON-1 and type 2 diabetes risk.

METHODS

PON-1 was measured as its arylesterase activity at baseline in the Prevention of Renal and Vascular End-stage Disease (PREVEND) prospective study of 5947 predominantly Caucasian participants aged 28-75years with no pre-existing diabetes, that recorded 500 type 2 diabetes cases during a median follow-up of 11.2years.

RESULTS

Serum PON-1 was positively correlated with HDL-C (r=0.17; P<0.001). In analyses adjusted for conventional diabetes risk factors, the hazard ratio (95% CI) for type 2 diabetes per 1 standard deviation increase in PON-1 was 1.07 (0.98 to 1.18; P=0.13), which remained non-significant (1.02 (0.93 to 1.12) P=0.65) after additional adjustment for potential confounders. The association was unchanged on further adjustment for HDL-C (1.05 (0.96 to 1.15; P=0.29). However, in subsidiary analyses in the same set of participants, serum HDL-C concentration was inversely and independently associated with risk of type 2 diabetes.

CONCLUSIONS

Incident type 2 diabetes is associated with HDL cholesterol but not with its anti-oxidant constituent - PON-1 - in a large cohort of apparently healthy men and women. The current data question the importance of PON-1 activity for the development of diabetes.

Paraoxonase 1 (Q192R) gene polymorphism, coronary heart disease and the risk of a new acute coronary event

INTRODUCTION

Paraoxonase 1 (PON1) plays a major role in the oxidation of low density lipoprotein and in the prevention of coronary atherogenesis. In this context, coding region polymorphisms of PON1 gene, responsible for the enzyme activity, has become of interest as a marker for atherogenesis.

METHODS

A study and follow-up was conducted on 529 patients with an acute coronary event in order to assess the association between the PON1 Q192R (rs662;A/G) polymorphism, the type of acute coronary syndrome, cardiovascular risk factors (arterial hypertension, diabetes mellitus, dyslipidaemia, and smoking), the extent and severity of coronary atherosclerosis, and the medium-term clinical follow-up.

RESULTS

The QQ genotype was found in 245 (46.3%) patients, with 218 (41.2%) patients showing the QR genotype, and 66 (14.5%) patients had the RR genotype. No significant differences were found between the QQ and QR/RR genotypes as regards the clinical characteristics, the analytical data, and the angiographic variables. Similarly, Kaplan-Meier survival analysis showed no significant differences in presenting with a new acute coronary event (p=0.598), cardiac mortality (p=0.701), stent thrombosis (p=0.508), or stent re-stenosis (p=0.598) between QQ and QR/RR genotypes during the follow-up period (3.3±2.2 years).

CONCLUSIONS

In patients with an acute coronary syndrome, the PON1 Q192R genotypes did not influence the risk of suffering a new acute coronary event during the medium-term follow-up.

Proteomic and lipidomic analyses of paraoxonase defined high density lipoprotein particles: Association of paraoxonase with the anti-coagulant, protein S

PURPOSE

Characterizing high density lipoprotein (HDL) particles and their relevance to HDL function is a major research objective. One aim is to identify functionally distinct particles. To try to limit both functional and compositional heterogeneity the present study focused on paraoxonase-1 (PON1) as a target for isolation of a minor HDL subfraction.

EXPERIMENTAL DESIGN

Immunoaffinity techniques were applied to isolate PON1-containing HDL (P-HDL) and total HDL (T-HDL), which were subsequently characterized and compared.

RESULTS

Analyses of the lipidomes showed significant differences between the fractions in the relative concentrations of individual lipid subspecies, notably reduced levels of unsaturated lysophosphatidylcholine (p < 0.05) in P-HDL (reflected in a significantly reduced total lysophosphatidylcholine polyunsaturated fatty acid content, p < 0.004). Significant differences were also observed for the proteomes. P-HDL was highly enriched in the anti-coagulant, vitamin K activated protein S (prot S) (p < 0.0001), and alpha2 macroglobulin (p < 0.01), compared to T-HDL. Conversely, procoagulant proteins kininogen 1 and histidine-rich glycoprotein were largely excluded from P-HDL. Immunoabsorption of PON1 from plasma significantly reduced prot S anti-coagulant activity.

CONCLUSIONS AND CLINICAL RELEVANCE

The P-HDL lipidome and proteome showed significant differences from T-HDL. Enrichment in anti-coagulation proteins indicates complementary functionalities within P-HDL particles and underlines their anti-atherosclerotic potential.

High Density Lipoprotein: Assembly, Structure, Cargo, and Functions

Cardiovascular disease (CVD) is the leading cause of death globally. For close to four decades, we have known that high density lipoprotein (HDL) levels are inversely correlated with the risk of CVD. HDL is a complex particle that consists of proteins, phospholipids, and cholesterol and has the ability to carry micro-RNAs. HDL is constantly undergoing remodelling throughout its life-span and carries out many functions. This review summarizes many of the different aspects of HDL from its assembly, the receptors it interacts with, along with the functions it performs and how it can be altered in disease. While HDL is a key cholesterol efflux particle, this review highlights the many other important functions of HDL in the innate immune system and details the potential therapeutic uses of HDL outside of CVD.

The paraoxonase-1 pathway is not a major bioactivation pathway of clopidogrel in vitro

BACKGROUND AND PURPOSE

Clopidogrel is a prodrug bioactivated by cytochrome P450s (CYPs). More recently, paraoxonase-1 (PON1) has been proposed as a major contributor to clopidogrel metabolism. The purpose of this study was to assess the relative contribution of CYPs and PON1 to clopidogrel metabolism in vitro.

EXPERIMENTAL APPROACH

Clopidogrel metabolism was studied in human serum, recombinant PON1 enzyme (rePON1), pooled human liver microsomes (HLMs), HLMs with the CYP2C19*1/*1 genotype and HLMs with the CYP2C19*2/*2 genotype. Inhibition studies were also performed using specific CYP inhibitors and antibodies. Clopidogrel and its metabolites were measured using LC/MS/MS method.

KEY RESULTS

PON1 activity was highest in the human serum and there was no difference in PON1 activity between any of the HLM groups. The production of clopidogrel's active metabolite (clopidogrel-AM) from 2-oxo-clopidogrel in pooled HLMs was approximately 500 times that in serum. When 2-oxo-clopidogrel was incubated with rePON1, clopidogrel-AM was not detected. Clopidogrel-AM production from 2-oxo-clopidogrel was lower in CYP2C19*2/*2 HLMs compared with CYP2C19*1/*1 HLMs, while PON1 activity in HLMs with both genotypes was similar. Moreover, incubation with inhibitors of CYP3A, CYP2B6 and CYP2C19 significantly reduced clopidogrel bioactivation while a PON1 inhibitor, EDTA, had only a weak inhibitory effect.

CONCLUSION AND IMPLICATIONS

This in vitro study shows that the contribution of PON1 to clopidogrel metabolism is limited at clinically relevant concentrations. Moreover, CYP2C19, CYP2B6 and CYP3A play important roles in the bioactivation of clopidogrel.

Investigation of ovarian cancer associated sialylation changes in N-linked glycopeptides by quantitative proteomics

Background

In approximately 80% of patients, ovarian cancer is diagnosed when the patient is already in the advanced stages of the disease. CA125 is currently used as the marker for ovarian cancer; however, it lacks specificity and sensitivity for detecting early stage disease. There is a critical unmet need for sensitive and specific routine screening tests for early diagnosis that can reduce ovarian cancer lethality by reliably detecting the disease at its earliest and treatable stages.

Results

In this study, we investigated the N-linked sialylated glycopeptides in serum samples from healthy and ovarian cancer patients using Lectin-directed Tandem Labeling (LTL) and iTRAQ quantitative proteomics methods. We identified 45 N-linked sialylated glycopeptides containing 46 glycosylation sites. Among those, ten sialylated glycopeptides were significantly up-regulated in ovarian cancer patients’ serum samples. LC-MS/MS analysis of the non-glycosylated peptides from the same samples, western blot data using lectin enriched glycoproteins of various ovarian cancer type samples, and PNGase F (+/−) treatment confirmed the sialylation changes in the ovarian cancer samples.

Conclusion

Herein, we demonstrated that several proteins are aberrantly sialylated in N-linked glycopeptides in ovarian cancer and detection of glycopeptides with abnormal sialylation changes may have the potential to serve as biomarkers for ovarian cancer.

Paraoxonase 1 (PON1) polymorphisms, haplotypes and activity in predicting cad risk in North-West Indian Punjabis

BACKGROUND

Human serum paraoxonase-1 (PON1) prevents oxidation of low density lipoprotein cholesterol (LDL-C) and hydrolyzes the oxidized form, therefore preventing the development of atherosclerosis. The polymorphisms of PON1 gene are known to affect the PON1 activity and thereby coronary artery disease (CAD) risk. As studies are lacking in North-West Indian Punjabi's, a distinct ethnic group with high incidence of CAD, we determined PON1 activity, genotypes and haplotypes in this population and correlated them with the risk of CAD.

METHODOLOGY/PRINCIPAL FINDINGS

350 angiographically proven (≥ 70% stenosis) CAD patients and 300 healthy controls were investigated. PON1 activity was determined towards paraoxon (Paraoxonase; PONase) and phenylacetate (Arylesterase; AREase) substrates. In addition, genotyping was carried out by using multiplex PCR, allele specific oligonucleotide -PCR and PCR-RFLP methods and haplotyping was determined by PHASE software. The serum PONase and AREase activities were significantly lower in CAD patients as compared to the controls. All studied polymorphisms except L55M had significant effect on PONase activity. However AREase activity was not affected by them. In a logistic regression model, after adjustment for the conventional risk factors for CAD, QR (OR: 2.73 (1.57-4.72)) and RR (OR, 16.24 (6.41-41.14)) genotypes of Q192R polymorphism and GG (OR: 2.07 (1.02-4.21)) genotype of -162A/G polymorphism had significantly higher CAD risk. Haplotypes L-T-G-Q-C (OR: 3.25 (1.72-6.16)) and L-T-G-R-G (OR: 2.82 (1.01-7.80)) were also significantly associated with CAD.

CONCLUSIONS

In conclusion this study shows that CAD patients had lower PONase and AREase activities as compared to the controls. The coding Q192R polymorphism, promoter -162A/G polymorphism and L-T-G-Q-C and L-T-G-R-G haplotypes are all independently associated with CAD.

Determination of paraoxonase 1 status and genotypes at specific polymorphic sites

The procedures for determining paraoxonase (PON1) status and for determining PON1 genotypes for polymorphisms in coding and important regulatory regions are described. PON1 status is determined by a functional two-substrate analysis of plasma PON1 activities. Differences in catalytic efficiency of the PON1₁₉₂Q and PON1₁₉₂R alloforms result in the clear separation of all three phenotypes at position 192 (Q/Q, Q/R, R/R) and at the same time, the two-substrate analysis indicates activity levels of PON1. Because the enzyme activity levels are as important as the polymorphic genotypes, this two-substrate analysis of PON1 status provides the most relevant information for investigating the association of PON1 genetics with susceptibilities to disease, organophosphorus insecticide sensitivity, and pharmacokinetic status of drug metabolism. Genotyping of polymorphic sites alone fails to provide this important information but can be useful for gene frequency determination and forensic analysis. Analytical procedures for determining PON1 status and genotypes are described.

Smoking is associated with reduced serum paraoxonase, antioxidants and increased oxidative stress in normolipidaemic acute myocardial infarct patients

BACKGROUND

Paraoxonase is a high-density lipoprotein (HDL)-associated enzyme that protects lipoproteins from oxidative modifications and from becoming atherogenic in nature. Smoking is a well-known major cardiovascular risk factor that promotes lipid peroxidation (LP). The present study examined the hypothesis that smoking modulates the activity of paraoxonase and depletes antioxidants.

AIM

The present study evaluated paraoxonase activity, antioxidant status and LP in smoking and non-smoking normolipidaemic acute myocardial infarct (AMI) patients, and results were compared with controls.

SETTINGS AND DESIGN

The serum paraoxonase activities, antioxidants and LP were determined in 86 normolipidaemic patients diagnosed of AMI, and 86 age-sex-matched healthy volunteers served as control.

MATERIAL AND METHODS

Serum paraoxonase activities were measured by enzymatic kit. The glutathione peroxidase, superoxide dismutase and catalase activity was determined by standard methods. Malondialdehyde was measured by the thiobarbituric acid reaction, and conjugated diene levels by the Recknagel and Glende method. Serum uric acid, total bilirubin, serum albumin and lipid profiles were analysed by standard methods.

STATISTICS

The values were expressed as mean±SD, and data from the patients and control were compared using the Student t test.

RESULTS AND CONCLUSION

The total cholesterol/HDL cholesterol ratio, triglycerides, low-density lipoprotein cholesterol, low-density lipoprotein/HDL cholesterol ratio and triglyceride/HDL cholesterol ratio were significantly higher, and HDL cholesterol significantly lower in smokers compared with non-smoking AMI patients. Superoxide dismutase, glutathione peroxidase and catalase were significantly higher in non-smokers compared with smokers. Serum albumin, uric acid and bilirubin were higher in the control compared with smoking AMI patients. The malondialdehyde and conjugated dienes were significantly higher, and paraoxonase activities were significantly lower in smokers compared with non-smokers.

Investigation of sialylation aberration in N-linked glycopeptides by lectin and tandem labeling (LTL) quantitative proteomics

The accuracy in quantitative analysis of N-linked glycopeptides and glycosylation site mapping in cancer is critical to the fundamental question of whether the aberration is due to changes in the total concentration of glycoproteins or variations in the type of glycosylation of proteins. Toward this goal, we developed a lectin-directed tandem labeling (LTL) quantitative proteomics strategy in which we enriched sialylated glycopeptides by SNA, labeled them at the N-terminus by acetic anhydride ((1)H(6)/(2)D(6)) reagents, enzymatically deglycosylated the differentially labeled peptides in the presence of heavy water (H(2)(18)O), and performed LC/MS/MS analysis to identify glycopeptides. We successfully used fetuin as a model protein to test the feasibility of this LTL strategy not only to find true positive glycosylation sites but also to obtain accurate quantitative results on the glycosylation changes. Further, we implemented this method to investigate the sialylation changes in prostate cancer serum samples as compared to healthy controls. Herein, we report a total of 45 sialylated glycopeptides and an increase of sialylation in most of the glycoproteins identified in prostate cancer serum samples. Further quantitation of nonglycosylated peptides revealed that sialylation is increased in most of the glycoproteins, whereas the protein concentrations remain unchanged. Thus, LTL quantitative technique is potentially an useful method for obtaining simultaneous unambiguous identification and reliable quantification of N-linked glycopeptides.

Myeloperoxidase and paraoxonase-1 in type 2 diabetic patients

BACKGROUND AND AIMS

Reduced high density lipoproteins (HDL) and increased oxidative stress are features of type 2 diabetes. Myeloperoxidase is an oxidative enzyme partly associated with HDL and causing HDL dysfunction. It is an independent risk factor for cardiovascular disease. Paraoxonase-1 is an HDL-associated enzyme that protects against cardiovascular disease and is reduced in diabetes. The present study examined if serum myeloperoxidase was (i) increased in type 2 diabetes, (ii) correlated with paraoxonase-1 activity.

METHODS AND RESULTS

The study was based on cross-sectional analyses of serum myeloperoxidase and paraoxonase-1 in type 2 diabetic patients and non-diabetic participants, with and without cardiovascular disease. Serum myeloperoxidase concentrations were not increased in type 2 diabetic patients without cardiovascular disease compared to non-diabetic controls. They were significantly higher in type 2 patients and non-diabetic patients with angiographically confirmed coronary disease. HDL-associated myeloperoxidase was correlated with serum myeloperoxidase (r=0.80, p<0.001) but not HDL-cholesterol (r=0.08) or apolipoprotein AI (r=0.08). Multivariate analyses showed serum myeloperoxidase to be an independent determinant of paraoxonase activities (arylesterase, p=0.024; paraoxonase, p=0.026).

CONCLUSIONS

Myeloperoxidase is an independent, negative determinant of paraoxonase-1 activity, which may be one mechanism by which it promotes HDL dysfunction and increases cardiovascular risk. Increased serum myeloperoxidase is not a feature of type 2 diabetes in the absence of overt cardiovascular disease. The level of HDL-associated myeloperoxidase is determined by the serum concentration of the enzyme suggesting that, in the context of reduced HDL concentrations in diabetic patients, myeloperoxidase may have a greater impact on HDL function.

PON1 is a longevity gene: results of a meta-analysis

Paraoxonase 1 (PON1) is one of the most studied genes regarding cardiovascular risk, oxidative stress and inflammation. Several lines of evidence suggests that PON1 promotes an atheroprotective effect. Patients carrying PON1 codon 192 QQ genotype display a higher risk of cardiovascular events, the major cause of mortality in the elderly: it can be predicted that gene variants increasing the risk of mortality will be under-represented in long-living individuals. We first reported that PON1 R allele (R+) carriers are significantly more represented in Italian centenarians; subsequently this topic has been addressed by many other groups, and here we report a meta-analysis on 11 studies in different populations selected by a review of the literature available in PubMed and testing the effect of the Q192R polymorphism on human ageing. QUORUM guidelines for meta-analysis have been followed, and a total number of 5962 subjects have been included: 2795 young controls (<65 years of age) and 3167 old subjects (>65 years of age). The Mantel-Haenszel weighting for pooling in presence of a fixed effects model has been applied. The meta-analysis of R carriers showed a significant result with an overall OR of 1.16 (1.04-1.30, 95% CI, p=0.006). The meta-analysis of QR genotype also showed a significant result, with an overall OR of 1.14 (1.02-1.27, 95% CI, p=0.016). The results show that PON1 gene variants at codon 192 impact on the probability of attaining longevity, and that subjects carrying RR and QR genotypes (R+ carriers) are favoured in reaching extreme ages. These results likely represent the counterpart of the effects observed on cardiovascular diseases (CVD), as centenarians and nonagenarians escaped or delayed the onset of the major age-related diseases, including CVD.

Both paraoxonase-1 genotype and activity do not predict the risk of future coronary artery disease; the EPIC-Norfolk Prospective Population Study

BACKGROUND

Paraoxonase-1 (PON1) is an antioxidant enzyme, that resides on high-density lipoprotein (HDL). PON1-activity, is heavily influenced by the PON1-Q192R polymorphism. PON1 is considered to protect against atherosclerosis, but it is unclear whether this relation is independent of its carrier, HDL. In order to evaluate the atheroprotective potential of PON1, we assessed the relationships among PON1-genotype, PON1-activity and risk of future coronary artery disease (CAD), in a large prospective case-control study.

METHODOLOGY/PRINCIPAL FINDINGS

Cases (n = 1138) were apparently healthy men and women aged 45-79 years who developed fatal or nonfatal CAD during a mean follow-up of 6 years. Controls (n = 2237) were matched by age, sex and enrollment time. PON1-activity was similar in cases and controls (60.7+/-45.3 versus 62.6+/-45.8 U/L, p = 0.3) and correlated with HDL-cholesterol levels (r = 0.16, p<0.0001). The PON1-Q192R polymorphism had a profound impact on PON1-activity, but did not predict CAD risk (Odds Ratio [OR] per R allele 0.98[0.84-1.15], p = 0.8). Using conditional logistic regression, quartiles of PON1-activity showed a modest inverse relation with CAD risk (OR for the highest versus the lowest quartile 0.77[0.63-0.95], p = 0.01; p-trend = 0.06). PON1-activity adjusted for Q192R polymorphism correlated better with HDL-cholesterol (r = 0.26, p<0.0001) and more linearly predicted CAD risk (0.79[0.64-0.98], p = 0.03; p-trend = 0.008). However, these relationships were abolished after adjustment for HDL (particles-cholesterol-size) and apolipoproteinA-I (0.94[0.74-1.18], p-trend = 0.3).

CONCLUSIONS/SIGNIFICANCE

This study, shows that PON1-activity inversely relates to CAD risk, but not independent of HDL, due to its close association with the HDL-particle. These data strongly suggest that a low PON1-activity is not a causal factor in atherogenesis.

The paraoxonases: role in human diseases and methodological difficulties in measurement

Research into the paraoxonase (PON) gene family has flourished over the past few years. In the 1970s and 1980s, only PON1 was known, and the investigations were conducted, essentially, by toxicologists focusing on protection against organophosphate poisoning. Since then, two new members of the family, PON2 and PON3, have been identified, both being shown to play antioxidant and anti-inflammatory roles. Evidence exists indicating that the PON family is central to a wide variety of human illnesses such as cardiovascular disease, diabetes mellitus, metabolic syndrome, obesity, non-alcoholic steatohepatitis, and several mental disorders. However, research is hampered considerably by the methods currently available to measure the activity of these enzymes. In this review, we summarize the state of knowledge on PON biochemistry and function, the influence of genetic variations, and the involvement of PON in several diseases. The problems associated with PON measurement, such as sample acquisition, lack of reference methods, and variety of substrates, will be presented. Also, we cover some of the present lines of research and propose some others for future progress in this field.

Anti-(apolipoprotein A-1) IgGs are associated with high levels of oxidized low-density lipoprotein in acute coronary syndrome

ApoA-1 (apolipoprotein A-1) is the main component of HDL (high-density lipoprotein) and stabilizes PON-1 (paraoxonase-1), which prevents lipid peroxidation and oxLDL (oxidized low-density lipoprotein) formation. Autoantibodies against apoA-1 [anti-(apoA-1) IgG] have been found in antiphospholipid syndrome and systemic lupus erythematosous, two diseases with an increased risk of thrombotic events, as well as in ACS (acute coronary syndrome). OxLDL levels are also elevated in these diseases. Whether anti-(apoA-1) IgGs exist in other prothrombotic conditions, such as APE (acute pulmonary embolism) and stroke, has not been studied and their potential association with oxLDL and PON-1 activity is not known. In the present study, we determined prospectively the prevalence of anti-(apoA-1) IgG in patients with ACS (n=127), APE (n=58) and stroke (n=34), and, when present, we tested their association with oxLDL levels. The prevalance of anti-(apoA-1) IgG was 11% in the ACS group, 2% in the control group and 0% in the APE and stroke groups. The ACS group had significantly higher median anti-(apoA-1) IgG titres than the other groups of patients. Patients with ACS positive for anti-(apoA-1) IgG had significantly higher median oxLDL values than those who tested negative (226.5 compared with 47.7 units/l; P<0.00001) and controls. The Spearman ranked test revealed a significant correlation between anti-(apoA-1) IgG titres and serum oxLDL levels (r=0.28, P<0.05). No association was found between PON-1 activity and oxLDL or anti-(apoA-1) IgG levels. In conclusion, anti-(apoA-1) IgG levels are positive in ACS, but not in stroke or APE. In ACS, their presence is associated with higher levels of oxLDL and is directly proportional to the serum concentration of oxLDL. These results emphasize the role of humoral autoimmunity as a mediator of inflammation and coronary atherogenesis.

Determinants of variation in human serum paraoxonase activity

Paraoxonase-1 (PON1) is associated with high-density lipoprotein (HDL) particles and is believed to contribute to antiatherogenic properties of HDLs. We assessed the determinants of PON1 activity variation using different substrates of the enzyme. PON1 activity in serum samples from 922 participants in the San Antonio Family Heart Study was assayed using a reliable microplate format with three substrates: paraoxon, phenyl acetate and the lactone dihydrocoumarin. There were major differences among results from the three substrates in degree of effect by various environmental and genetic factors, suggesting that knowledge of one substrate activity alone may not provide a complete sense of PON1 metabolism. Three significant demographic covariates (age, smoking status and contraceptive usage) together explained 1-6% of phenotypic variance, whereas four metabolic covariates representing lipoprotein metabolism (apoAII, apoAI, triglycerides and non-HDL cholesterol) explained 4-19%. Genes explained 65-92% of phenotypic variance and the dominant genetic effect was exerted by a locus mapping at or near the protein structural locus (PON1) on chromosome 7. Additional genes influencing PON1 activity were localized to chromosomes 3 and 14. Our study identified environmental and genetic determinants of PON1 activity that accounted for 88-97% of total phenotypic variance, suggesting that few, if any, major biological determinants are unrepresented in the models.

Physicochemical and Biological Data for the Development of Predictive Organophosphorus Pesticide QSARs and PBPK/PD Models for Human Risk Assessment

A search of the scientific literature was carried out for physiochemical and biological data [i.e., IC50, LD50, Kp (cm/h) for percutaneous absorption, skin/water and tissue/blood partition coefficients, inhibition ki values, and metabolic parameters such as Vmax and Km] on 31 organophosphorus pesticides (OPs) to support the development of predictive quantitative structure-activity relationship (QSAR) and physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models for human risk assessment. Except for work on parathion, chlorpyrifos, and isofenphos, very few modeling data were found on the 31 OPs of interest. The available percutaneous absorption, partition coefficients and metabolic parameters were insufficient in number to develop predictive QSAR models. Metabolic kinetic parameters (Vmax, Km) varied according to enzyme source and the manner in which the enzymes were characterized. The metabolic activity of microsomes should be based on the kinetic activity of purified or cDNA-expressed cytochrome P450s (CYPs) and the specific content of each active CYP in tissue microsomes. Similar requirements are needed to assess the activity of tissue A- and B-esterases metabolizing OPs. A limited amount of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CaE) inhibition and recovery data were found in the literature on the 31 OPs. A program is needed to require the development of physicochemical and biological data to support risk assessment methodologies involving QSAR and PBPK/PD models.

High-density lipoprotein cholesterol and paraoxonase 1 (PON1) genetics and serum PON1 activity in prepubertal children in Spain

BACKGROUND

Oxidative stress plays an important role in atherosclerosis. Paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated enzyme that inhibits low-density lipoprotein (LDL) oxidation and may play a protective role against coronary heart disease. The aim of this study was to analyze the relationship between HDL-cholesterol (HDL-C) and PON1 in a Spanish prepubertal population with high plasma HDL-C levels.

METHODS

The study population included 1,266 children between the ages of 6 and 8 years. Serum PON1 activity was measured by the hydrolysis of paraoxon. PON1 192Q/R and PON1 55L/M polymorphisms were analyzed by PCR and restriction analysis.

RESULTS

The prevalence of the less common PON1 192R and PON 55M alleles in this population was 30% and 38%, respectively. No significant correlations between serum PON1 activity and lipid profile were observed. Multiple linear regression analysis showed that the PON1 192Q/R polymorphism accounts for 69% of PON1 activity in the children in the study, with the PON1 55L/M polymorphism accounting for an additional 5% of this variation in boys, and for an additional 3% together with HDL-C concentration in girls.

CONCLUSIONS

PON1 192Q/R polymorphism is the main determinant of PON1 activity in the prepubertal population in this study, accounting for around 70% of serum PON1 activity. HDL-C concentration has a small contribution to serum PON1 activity in girls.

Genetic polymorphisms in the Paraoxonase 1 gene and risk of ovarian epithelial carcinoma

Oxidative stress during successive ovulations increases the opportunity for DNA damage to ovarian epithelial cells and the potential for malignant transformation. Paraoxonase 1 (PON1) is an endogenous free radical scavenger that reduces oxidative stress. The association of two common functional single nucleotide polymorphisms (SNP), rs854560 T>A and rs662 A>G, with the risk of epithelial ovarian cancer was examined in a population-based case-control study in Hawaii. A personal interview and blood specimens were collected from 274 women with histologically confirmed, primary ovarian cancer and 452 controls frequency matched on age and ethnicity. Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by unconditional logistic regression. Both PON1 SNPs were significantly associated with ovarian cancer risk. The ORs were 0.53 (95% CI, 0.35-0.79; P for allele-dose effect = 0.01) for women carrying the rs854560 T allele compared with women with the AA genotype and 0.65 (95% CI, 0.44-0.95; P for allele-dose effect = 0.03) for women carrying the rs662 A allele compared with women with the GG genotype. The association of the rs854560 T genotype with risk was stronger among smokers (OR, 0.33; 95% CI, 0.17-0.64; P for allele-dose effect = 0.0007) than among nonsmokers (OR, 0.68; 95% CI, 0.40-1.18; P for allele-dose effect = 0.53). The decreased risk associated with the rs854560 T allele was also stronger among obese women (OR, 0.19; 95% CI, 0.06-0.55; P for allele-dose effect = 0.007) than among nonobese women (OR, 0.62; 95% CI, 0.40-0.98; P for allele-dose effect = 0.16). Our study provides evidence for an association of two PON1 SNPs with the risk of epithelial ovarian cancer. Possible effect modification of these associations by tobacco smoking and obesity needs confirmation in other studies.

Paraoxonases (PON1, PON2, PON3) analyses in vitro and in vivo in relation to cardiovascular diseases

Mammalian paraoxonases (PON1, PON2, PON3) are a unique family of calcium-dependent hydrolases, with enzymatic activities toward a broad range of substrates (lactones, thiolactones, carbonates, esters, phosphotriesters). Although PONs physiological substrates were not yet identified, some studies suggest that they could be some lactones, or some specific oxidized phospholipids, or products of both enzymatic and nonenzymatic oxidation of arachidonic and docosahexaenoic acid, as well as N-acyl-homoserine lactones (which are quorum-sensing signals of pathogenic bacteria). Since no endogenous substrates for PONs activity determination are available yet, synthetic substrates such as paraoxon, phenyl acetate, and several lactones are used for PONs activity assays. All three members of the PON family (PON 1/2/3) were shown to protect from atherosclerosis development. Their anti-atherogenic biological activities were studied in vitro using serum or cell cultures, and also in vivo, using PON 1/2/3 knockout or transgenic mice, as well as humans - healthy volunteers and atherosclerotic patients (diabetics, hypercholesterolemics, and hypertensives).

Development of an immunoblot assay with infrared fluorescence to quantify paraoxonase 1 in serum and plasma

Paraoxonase 1 (PON1) requires calcium for activity and is inactivated in the presence of EDTA. Because of this, studies to date have used serum or heparinized plasma for both activity and mass assays of PON1. Whole serum and EDTA plasma were analyzed by SDS-electrophoresis and Western blot using anti-PON1 monoclonal antibody 4C10. Because PON1 has one disulfide and one free cysteine residue, the samples were reduced with dithiothreitol before electrophoresis. Western blot identified a major PON1 band with a molecular mass of approximately 45 kDa and two minor bands of approximately 40 and 35 kDa in both serum and EDTA plasma. This established that PON1 is inactive, but structurally intact, in EDTA plasma and suggested that a mass assay could be developed based on SDS-electrophoresis and Western blot. Linearity was established for plasma and for a PON1 standard. Quantification was based on the major PON1 band at 45 kDa. The correlation between serum and plasma PON1 mass was 0.9553. The between-run variation was determined with a serum pool to be 7.8%. The mass of PON1 in serum was significantly correlated with arylesterase activity (r = 0.85). Thus, we have demonstrated the feasibility of measuring PON1 mass in either serum or EDTA plasma.

The development of human sera tests for HDL-bound serum PON1 and its lipolactonase activity

Serum paraoxonase (PON1) is a lipolactonase that associates with HDL-apolipoprotein A-I (HDL-apoA-I) and thereby plays a role in the prevention of atherosclerosis. Current sera tests make use of promiscuous substrates and provide no indications regarding HDL-PON1 complex formation. We developed new enzymatic tests that detect total PON1 levels, irrespective of HDL status and R/Q polymorphism, as well as the degree of catalytic stimulation and increased stability that follow PON1's tight binding to HDL-apoA-I. The tests are based on measuring total PON1 levels with a fluorogenic phosphotriester, measuring the lipolactonase activity with a chromogenic lactone, and assaying the enzyme's chelator-mediated inactivation rate. The latter two are affected by tight HDL binding and thereby derive the levels of the serum PON1-HDL complex. We demonstrate these new tests with a group of healthy individuals (n=54) and show that the levels of PON1-HDL vary by a factor of 12. Whereas the traditionally applied paraoxonase and arylesterase tests weakly reflect PON1-HDL levels (R=0.64), the lipolactonase test provides better correlation (R=0.80). These new tests indicate the levels and activity of PON1 in a physiologically relevant context as well as the levels and quality of the HDL particles with which the enzyme is associated.

HDL oxidation compromises its influence on paraoxonase-1 secretion and its capacity to modulate enzyme activity

OBJECTIVE

The purpose of this study was to analyze the consequences of HDL oxidation for paraoxonase-1 metabolism and function.

METHODS AND RESULTS

HDL was oxidized with AAPH, copper ions, and hypochlorite. Secretion studies were performed using human paraoxonase-1-transfected cells lines and primary rat hepatocytes. Stability studies were performed with recombinant paraoxonase. Conditioned medium had significantly reduced paraoxonase-1 when Cu or AAPH-oxidized HDL was the acceptor complex (P<0.01); reduction was dose-dependent on the degree of oxidation. Oxidized HDL had a reduced capacity to stabilize/improve activity of secreted paraoxonase-1. Reduced secretion could not be attributed to enzyme inactivation by lipoperoxides, reduced binding affinity of HDL, or oxidation of the lipid component alone. Hypochlorite oxidation of HDL did not modify HDL-mediated paraoxonase-1 release, but activity of HDL-associated paraoxonase-1 was particularly sensitive to such treatment.

CONCLUSIONS

AAPH and copper, but not hypochlorite, oxidation of HDL compromises its ability to promote release of paraoxonase-1 and stabilize enzyme activity. HDL-associated paraoxonase-1 is highly sensitive to hypochlorite. Reducing paraoxonase-1 renders HDL susceptible to oxidation, which may compromise HDL function. It provides a novel example at the HDL level of the detrimental effects of oxidative stress, and underlines the need for further evaluation of the consequences of HDL oxidation.

Postprandial modulation of serum paraoxonase activity and concentration in diabetic and non-diabetic subjects

OBJECTIVES

To analyse the HDL associated anti-oxidant enzyme paraoxonase-1, during postprandial hyperlipaemia.

METHODS AND RESULTS

Type 2 diabetic patients (n=72), glucose intolerant patients (n=10) and controls (n=38) consumed a high fat:high carbohydrate meal. Blood samples were collected up to 4h and analysed for lipids and paraoxonase-1. In vitro studies examined HDL function with respect to the enzyme. There were significant postprandial increases in serum triglycerides. Paraoxonase-1 activity decreased significantly throughout the postprandial phase. Concentrations of the enzyme initially decreased significantly, but returned to fasting concentrations at 4h. Specific activities were significantly lower at 4h, compared to fasting. The decrease in specific activity was linked to the dynamic phase of postprandial lipoprotein metabolism. Apo AI limited loss of paraoxonase-1. HDL isolated after being subjected to postprandial conditions in vitro had reduced capacity to associate with and stabilise PON1.

CONCLUSIONS

Postprandial hyperlipaemia was associated with changes to serum paraoxonase-1, consistent with a reduced anti-oxidant potential of HDL. No differences were observed between diabetic and non-diabetic patients, suggesting that the effect was linked to postprandial hyperlipaemia. Modifications to paraoxonase-1 could contribute to increased risk of vascular disease associated with postprandial lipaemia, particularly in diabetic patients, who are already deficient in serum paraoxonase-1.

PON1 status of farmworker mothers and children as a predictor of organophosphate sensitivity

The objective was to determine PON1 status as a predictor for organophosphorus insecticide sensitivity in a cohort of Latina mothers and newborns from the Salinas Valley, California, an area with high levels of organophosphorus insecticide use. PON1 status was established for 130 pregnant Latina women and their newborns using a high-throughput two substrate activity/analysis method which plots rates of diazoxon (DZO) hydrolysis against rates of paraoxon (PO) hydrolysis. Arylesterase activity (AREase) was determined using phenylacetate as a substrate, allowing comparison of PON1 levels across PON1192 genotypes in mothers and children. Phenylacetate hydrolysis is not affected by the Q192R polymorphism. Among newborns, levels of PON1 (AREase) varied by 26-fold (4.3-110.7 U/ml) and among mothers by 14-fold (19.8-281.4 U/ml). On average, children's PON1 levels were four-fold lower than the mothers' PON1 levels (P<0.001). Average PON1 levels in newborns were comparable with reported hPON1 levels in transgenic mice expressing human PON1Q192 or PON1R192, allowing for prediction of relative sensitivity to chlorpyrifos oxon (CPO) and DZO. The predicted range of variability in sensitivity of mothers and children in the same Latino cohort was 65-fold for DZO and 131 to 164-fold for CPO. Overall, these findings indicate that many of the newborns and some of the mothers in this cohort would be more susceptible to the adverse effects of specific organophosphorus pesticide exposure due to their PON1 status. Of particular concern are exposures of pregnant mothers and newborns with low PON1 status.

Paraoxonase polymorphisms, haplotypes, and enzyme activity in Latino mothers and newborns

Recent studies have demonstrated widespread pesticide exposures in pregnant women and in children. Plasma paraoxonase 1 (PON1) plays an important role in detoxification of various organophosphates. The goals of this study were to examine in the Center for Health Assessment of Mothers and Children of Salinas (CHAMACOS) birth cohort of Latina mothers and their newborns living in the Salinas Valley, California, the frequencies of five PON1 polymorphisms in the coding region (192QR and 55LM) and the promoter region (-162AG, -909CG, and -108CT) and to determine their associations with PON1 plasma levels [phenylacetate arylesterase (AREase) ] and enzyme activities of paraoxonase (POase) and chlorpyrifos oxonase (CPOase) . Additionally, we report results of PON1 linkage analysis and estimate the predictive value of haplotypes for PON1 plasma levels. We found that PON1-909, PON1-108, and PON1(192) had an equal frequency (0.5) of both alleles, whereas PON1-162 and PON1(55) had lower variant allele frequencies (0.2) . Nearly complete linkage disequilibrium was observed among coding and promoter polymorphisms (p < 0.001) , except PON1(192) and PON1-162 (p > 0.4) . Children's PON1 plasma levels (AREase ranged from 4.3 to 110.7 U/mL) were 4-fold lower than their mothers' (19.8 to 281.4 U/mL) . POase and CPOase activities were approximately 3-fold lower in newborns than in mothers. The genetic contribution to PON1 enzyme variability was higher in newborns (R2 = 25.1% by genotype and 26.3% by haplotype) than in mothers (R2 = 8.1 and 8.8%, respectively) . However, haplotypes and genotypes were comparable in predicting PON1 plasma levels in mothers and newborns. Most of the newborn children and some pregnant women in this Latino cohort may have elevated susceptibility to organophosphate toxicity because of their PON1192 genotype and low PON1 plasma levels.

Paraoxonase Activity and Genotype Predispose to Successful Aging

The paraoxonase 1 codon 192 R allele has been previously reported to have a role in successful aging. The relationship between PON1 genotypes, enzymatic activity, and mass concentration was evaluated in a group of 229 participants from 22 to 104 years of age, focusing our attention on nonagenarian/centenarian participants. We found a genetic control for paraoxonase activity that is maintained throughout life, also in the nonagenarians/centenarians. This activity decreases significantly during aging and shows different mean values among R and M carriers, where R+ and M- carriers have the significant highest paraoxonase activity. Results from the multinomial regression logistic model show that paraoxonase activity as well as R+ and M- carriers contribute significantly to the explanation of the longevity phenotype. In conclusion, we show that genetic variability at the PON1 locus is related to paraoxonase activity throughout life, and suggest that both parameters affect survival at extreme advanced age.

Association of Paraoxonase-1 Activity and Concentration With Angiographic Severity and Extent of Coronary Artery Disease

OBJECTIVES

The goal of this study was to examine the association between paraoxonase-1 (PON1) activity and concentration and the severity and extent of coronary artery disease (CAD).

BACKGROUND

Paraoxonase-1, a high-density lipoprotein-associated enzyme, is proposed to have an antiatherogenic effect by protecting low-density lipoproteins against oxidation.

METHODS

We studied PON1 activity and concentration in 107 patients with known or suspected CAD referred for cardiac catheterization. Based on visual estimation of coronary angiograms, subjects were classified as having no or mild CAD (<50% stenosis) and significant CAD (> or =50% stenosis). Quantitative coronary angiography (QCA) was used to estimate the indexes of severity, extent, and overall atheroma burden of CAD.

RESULTS

We found lower values of PON1 activity and concentration (p = 0.003 and p = 0.016, respectively) in the group with significant CAD as compared with the group with no or mild CAD. The PON1 activity was significantly inversely correlated with CAD severity (r = -0.364, p < 0.001), extent (r = -0.221, p = 0.022), and atheroma burden (r = -0.277, p = 0.004). Similarly, PON1 concentration correlated with CAD severity (r = -0.306, p = 0.001) and atheroma burden (r = -0.229, p = 0.017). In multiple regression analysis, gender and PON1 activity were significant determinants of the severity of CAD independently of age, hypertension, smoking, abnormal glucose regulation, and high-density lipoprotein cholesterol.

CONCLUSIONS

Our results indicate that PON1 activity and concentration are lower in subjects with significant CAD, and that there is a significant relationship between PON1 activity and concentration and CAD assessed by QCA.

Tandem purification of two HDL-associated partner proteins in human plasma, paraoxonase (PON1) and phosphate binding protein (HPBP) using hydroxyapatite chromatography

Human plasma paraoxonase (PON1) is calcium-dependent enzyme that hydrolyses esters, including organophosphates and lactones, and exhibits anti-atherogenic properties. Human phosphate binding protein (HPBP) was discovered as contaminant during crystallization trials of PON1. This observation and uncertainties for the real activities of PON1 led us to re-evaluate the purity of PON1 preparations. We developed a hydroxyapatite chromatography for the separation of both HDL-associated proteins. We confirmed that: (1) HPBP is strongly associated to PON1 in HDL, and generally both proteins are co-purified; (2) standard purification protocols of PON1 lead to impure enzyme; (3) hydroxyapatite chromatography allows the simultaneous purification of PON1 and HPBP.

Paraoxonase-1 and serum concentrations of HDL-cholesterol and apoA-I

Paraoxonase-1 (PON1) and HDL are tightly associated in plasma, and this is generally assumed to reflect the need for the enzyme to associate with a hydrophobic complex. The association has been examined in coronary cases and age-matched controls. Highly significant (P < 0.0001), positive associations were observed between PON1 activities and concentrations and HDL-cholesterol and apolipoprotein A-I (apoA-I) concentrations in cases and controls. Corrected slopes were significantly different in cases (cases vs. controls: arylesterase, r = 0.19 vs. 0.38, P < 0.02 for apoA-I and r = 0.15 vs. 0.34, P < 0.02 for HDL-cholesterol) such that if PON1 should influence serum HDL, it would be less effective in coronary cases. When examined as a function of the PON1 gene promoter polymorphism C-107 T, highly significant differences (P < 0.001) in HDL-cholesterol and apoA-I were observed between genotypes for controls, with high expresser alleles having the highest HDL concentrations. This relationship was lost in cases with coronary disease. The coding region polymorphisms Q192R and L55M of the PON1 gene showed no association with HDL. The promoter polymorphism was an independent determinant of HDL concentrations in multivariate analyses. These data are consistent with an impact of PON1 on plasma concentrations of HDL, with detrimental modifications to the relationship in coronary cases.

Paraoxonase-1 promoter polymorphism C--107T and serum apolipoprotein AI interact to modulate serum paraoxonase-1 status

OBJECTIVES

The objective was to examine the hypothesis that modifications to paraoxonase-1 specific activity (SP, activity per unit mass peptide) could contribute to serum paraoxonase-1 status, a determinant of the clinical efficacy of the enzyme.

METHODS

Enzyme activities and concentrations were determined in a large population (n=912) of patients and controls. SP were subsequently examined as a function of paraoxonase-1 gene polymorphisms, plasma lipids and lipoproteins, and physiological and pathophysiological parameters.

RESULTS

Pathophysiological parameters (diabetes, metabolic syndrome, smoking, aging) did not promote variations in paraoxonase-1 SP, whilst coronary disease lowered SP (P<0.003). No serum lipid, apolipoprotein or lipoprotein component had an impact on specific activity, with the exception of apolipoprotein AI (P<0.005, both substrates). The paraoxonase-1 promoter C--107T and Q192R polymorphisms influenced SP and, together with apolipoprotein AI, were highly significant, independent determinants in regression models. There was an interaction between apolipoprotein AI and the C--107T polymorphism, which significantly modulated SP and serum paraoxonase-1 status.

CONCLUSIONS

Enzyme inactivation giving rise to modulated activity per unit mass of peptide is not a major contributor to pathological effects of disease on serum paraoxonase-1 status. The C--107T polymorphism and serum apolipoprotein AI have major impacts individually on SP and also provide an example of gene-environment interaction to modulate such activities. These effects accentuate the differences between--107C and--107T allele carriers in terms of serum paraoxonase-1 status. The data underline the complexity of the factors that determine serum paraoxonase-1 status and suggest that the latter would benefit from therapeutic modulation of serum high density lipoproteins.

The effect of statin therapy on plasma high-density lipoprotein cholesterol levels is modified by paraoxonase-1 in patients with familial hypercholesterolaemia

OBJECTIVES

Statins reduce low-density lipoprotein cholesterol (LDL-C) and can raise high-density lipoprotein cholesterol (HDL-C). HDL-bound paraoxonase-1 (PON1) is associated with variations in plasma HDL-C, and may, therefore, contribute to changes of HDL-C during statin therapy.

DESIGN

The effects of baseline PON1 status to HDL-C changes because of statin therapy were investigated. PON1 status was determined with (i) PON1 -107C>T and 192Q>R genotype, (ii) PON1 levels and (iii) PON1 paraoxonase, diazoxonase and arylesterase activity.

SETTING

Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands.

SUBJECTS

A total of 134 familial hypercholesterolaemia (FH) patients undergoing atorvastatin or simvastatin therapy.

RESULTS

PON1 levels and activities significantly modified the HDL-C increment (P=0.002 for PON1 levels and arylesterase activity and P=0.001 for diazoxonase activity). The effects were even more evident amongst subgroup classifications based on PON1 status and baseline HDL-C concentrations: the HDL-C increment was more pronounced in subgroups of -107CT/TT or 192QR/RR genotype combined with low baseline HDL-C (+13.9%, P<0.001, respectively+15.4%, P<0.001). In contrast, the -107CC or 192QQ genotype in combination with high baseline HDL-C, did not show a significant increase of HDL-C.

CONCLUSIONS

PON1 status in conjunction with baseline HDL-C levels predicts HDL-C increment during statin therapy in FH patients.

Butyrylcholinesterase, paraoxonase, and albumin esterase, but not carboxylesterase, are present in human plasma

The goal of this work was to identify the esterases in human plasma and to clarify common misconceptions. The method for identifying esterases was nondenaturing gradient gel electrophoresis stained for esterase activity. We report that human plasma contains four esterases: butyrylcholinesterase (EC 3.1.1.8), paraoxonase (EC 3.1.8.1), acetylcholinesterase (EC 3.1.1.7), and albumin. Butyrylcholinesterase (BChE), paraoxonase (PON1), and albumin are in high enough concentrations to contribute significantly to ester hydrolysis. However, only trace amounts of acetylcholinesterase (AChE) are present. Monomeric AChE is seen in wild-type as well as in silent BChE plasma. Albumin has esterase activity with alpha- and beta-naphthylacetate as well as with p-nitrophenyl acetate. Misconception #1 is that human plasma contains carboxylesterase. We demonstrate that human plasma contains no carboxylesterase (EC 3.1.1.1), in contrast to mouse, rat, rabbit, horse, cat, and tiger that have high amounts of plasma carboxylesterase. Misconception #2 is that lab animals have BChE but no AChE in their plasma. We demonstrate that mice, unlike humans, have substantial amounts of soluble AChE as well as BChE in their plasma. Plasma from AChE and BChE knockout mice allowed identification of AChE and BChE bands without the use of inhibitors. Human BChE is irreversibly inhibited by diisopropylfluorophosphate, echothiophate, and paraoxon, but mouse BChE spontaneously reactivates. Since human plasma contains no carboxylesterase, only BChE, PON1, and albumin esterases need to be considered when evaluating hydrolysis of an ester drug in human plasma.

Small, dense lipoprotein particles and reduced paraoxonase-1 in patients with the metabolic syndrome

The presence of the metabolic syndrome (World Health Organization definition) and its association with lipoprotein abnormalities suggestive of greater susceptibility to oxidative stress have been analyzed in patients with angiographically defined coronary artery disease. The odds ratio for the presence of the metabolic syndrome was significantly higher in coronary artery disease-positive patients (P < 0.001). The metabolic syndrome was also associated with more severe coronary disease (P < 0.01). Patients with the metabolic syndrome had significantly decreased low-density lipoprotein-cholesterol/apolipoprotein B and high-density lipoprotein-cholesterol/apolipoprotein AI ratios, indicative of the presence of small, dense lipoprotein particles. The syndrome was also associated with reduced concentrations and activities of the antioxidant enzyme, paraoxonase-1. The metabolic syndrome is characterized by smaller, denser lipoprotein particles that increase their susceptibility to oxidative modifications and diminished serum paraoxonase-1, which is a major determinant of the antioxidant capacity of high-density lipoproteins. These may be contributory factors to the increased presence and severity of coronary disease in such patients.

Very low density lipoproteins provide a vector for secretion of paraoxonase-1 from cells

Paraoxonase-1 (PON1) requires a suitable acceptor complex for its secretion from producing cells. The serum lipoprotein, high-density lipoprotein (HDL) has been shown to accomplish this function, whereas low-density lipoproteins are ineffective. The present study examined the influence of the third serum lipoprotein subclass, very low density lipoproteins (VLDL), on PON1 secretion. VLDL were shown to promote secretion of PON1 from a transfected Chinese hamster ovary model and from transfected hepatocytes in a high-affinity, saturable manner. The effects of HDL and VLDL were not additive, suggesting that they may employ a common secretion pathway. VLDL was able to stabilise secreted PON1 enzyme activity, but less effectively than stabilisation by HDL. Following co-incubation of VLDL and HDL, the majority of PON1 accumulated in HDL even if HDL was added after initial association of the enzyme with VLDL. VLDL to HDL transfer of PON1 was rapid and did not require lipolysis of VLDL. Low levels of active PON1 were associated with VLDL in human serum, and VLDL-associated enzyme activity was proportional to serum triglyceride concentrations. Serum triglycerides were positively associated with whole serum PON1 mass but negatively associated with specific activity. PON1-enriched VLDL was more resistant to oxidation in vitro. The present study suggests that the triglyceride transport vector, VLDL, can modulate PON1 metabolism and activity. This is due, in part, to an influence of the lipoprotein on PON1 secretion. PON1 was associated with VLDL in human serum, where triglycerides correlated independently with variations in serum mass and activity of the enzyme. VLDL-associated PON1 exerted an anti-oxidative effect, which may be of physiological benefit.

Indications that paraoxonase-1 contributes to plasma high density lipoprotein levels in familial hypercholesterolemia

HDL-associated paraoxonase type 1 (PON1) can protect LDL and HDL against oxidative modification in vitro and therefore may protect against cardiovascular disease. We investigated the effects of PON1 levels, activity, and genetic variation on high density lipoprotein-cholesterol (HDL-C) levels, circulating oxidized LDL (OxLDL), subclinical inflammation [high-sensitive C-reactive protein (Hs-CRP)], and carotid atherosclerosis. PON1 genotypes (L55M, Q192R, -107C/T, -162A/G, -824G/A, and -907G/C) were determined in 302 patients with familial hypercholesterolemia. PON1 activity was monitored by the hydrolysis rate of paraoxon, diazoxon, and phenyl acetate. PON1 levels, OxLDL, and Hs-CRP were determined using an immunoassay. The genetic variants of PON1 that were associated with high levels and activity of the enzyme were associated with higher HDL-C levels (P values for trend: 0.008, 0.020, 0.042, and 0.037 for L55M, Q192R, -107C/T, and -907G/C, respectively). In addition to the PON1 genotype, there was also a positive correlation between PON1 levels and activity and HDL-C (PON1 levels: r = 0.37, P < 0.001; paraoxonase activity: r = 0.23, P = 0.01; diazoxonase activity: r = 0.29, P < 0.001; arylesterase activity: r = 0.19, P = 0.03). Our observations support the hypothesis that both PON1 levels and activity preserve HDL-C in plasma.