The separation of sheep and human serum "A"-esterase activity into the lipoprotein fraction by ultracentrifugation

Do PON1-Q192R and PON1-L55M polymorphisms modify the effects of hypoxic training on paraoxonase and arylesterase activity?

BACKGROUND

Low levels of antioxidant paraoxonase 1 (PON1) enzyme activity, PON1-Q192R polymorphism (a glutamine (Q) to arginine (R) substitution at position 192), PON1-L55M polymorphism (a leucine (L) to methionine (M) substitution at position 55), and oxidized low-density lipoprotein (oxLDL) are risk factors for coronary heart disease. Aerobic exercise improves PON1 activity, but the effects of hypoxic exercise are yet unclear. The aim of this study was to determine the effects of hypoxic underwater rugby training on PON1 activity and oxLDL levels and the role of the mentioned polymorphisms.

METHODS

Serum PON1 and arylesterase activities (ARE), PON1, PON3, and oxLDL protein levels (by using the enzyme-linked immunosorbent assays) were determined in an athletic group (42 trained male underwater rugby players; age = 21.7 ± 4.2 years, mean ± SD) and a control group (43 sedentary men; age = 23.9 ± 3.2 years). The polymorphisms were determined from genomic DNA samples.

RESULTS

PON1 activity (25.1%, p = 0.052), PON3 (p < 0.001), and oxLDL (p < 0.001) of the athletic group, including most genotype groups, were higher than those of the control group. In comparison to the controls, PON1 activity levels (p = 0.005) of the PON1-Q192R homozygote QQ genotype group and PON1 activity levels (30%, p = 0.116) of the PON1-L55M homozygote LL genotype group were higher, whereas ARE activity values of athletic R allele carrier (Rc = QR + RR) (p = 0.005) and LL group (p = 0.002) were lower than the control genotype groups related to their polymorphisms.

CONCLUSION

Hypoxic training can cause (1) significant oxidative stress, including oxLDL, and an antioxidant response (increase in PON1 activity and PON3), (2) differences in the activity of PON1 and ARE, which are modified by PON1-Q192R and PON1-L55M polymorphisms, respectively, and (3) improvements in PON1 activity of QQ and LL groups. However, hypoxic training can cause a disadvantage of LL and Rc groups for ARE.

Paraoxonase 1 and atherosclerosis

Paraoxonase 1 (PON1), residing almost exclusively on HDL, was discovered because of its hydrolytic activity towards organophosphates. Subsequently, it was also found to hydrolyse a wide range of substrates, including lactones and lipid hydroperoxides. PON1 is critical for the capacity of HDL to protect LDL and outer cell membranes against harmful oxidative modification, but this activity depends on its location within the hydrophobic lipid domains of HDL. It does not prevent conjugated diene formation, but directs lipid peroxidation products derived from these to become harmless carboxylic acids rather than aldehydes which might adduct to apolipoprotein B. Serum PON1 is inversely related to the incidence of new atherosclerotic cardiovascular disease (ASCVD) events, particularly in diabetes and established ASCVD. Its serum activity is frequently discordant with that of HDL cholesterol. PON1 activity is diminished in dyslipidaemia, diabetes, and inflammatory disease. Polymorphisms, most notably Q192R, can affect activity towards some substrates, but not towards phenyl acetate. Gene ablation or over-expression of human PON1 in rodent models is associated with increased and decreased atherosclerosis susceptibility respectively. PON1 antioxidant activity is enhanced by apolipoprotein AI and lecithin:cholesterol acyl transferase and diminished by apolipoprotein AII, serum amyloid A, and myeloperoxidase. PON1 loses this activity when separated from its lipid environment. Information about its structure has been obtained from water soluble mutants created by directed evolution. Such recombinant PON1 may, however, lose the capacity to hydrolyse non-polar substrates. Whilst nutrition and pre-existing lipid modifying drugs can influence PON1 activity there is a cogent need for more specific PON1-raising medication to be developed.

Association of PON-1 polymorphism with susceptibility to and severity of ischemic stroke in the Chinese population

Aim: The authors aimed to investigate whether polymorphisms of PON-1 were associated with the susceptibility to and severity of ischemic stroke (IS). Methods: In this study, 302 IS patients and 303 healthy controls were enrolled. Polymorphisms rs854560 and rs854572 of PON-1 were detected using SNaPshot single-nucleotide polymorphism typing technology. Results: The rs854572 polymorphism of the PON-1 gene showed a significant correlation with IS, and its GG genotype reduced the risk of IS (recessive model, p = 0.001). The GG genotype was also associated with mild stroke (p = 0.032). No association was observed between rs854560 and IS. Conclusion: PON-1 rs854572 polymorphism was related to the risk of IS and could be a biomarker to access the severity of IS.

In vitro age-related differences in rats to organophosphates

The mechanism of toxic action for organophosphates (OPs) is the persistent inhibition of acetylcholinesterase (AChE) resulting in accumulation of acetylcholine and subsequent hyperstimulation of the nervous system. Organophosphates display a wide range of acute toxicities. Differences in the OP's chemistries results in differences in the compound's metabolism and toxicity. Acute toxicities of OPs appear to be principally dependent on compound specific efficiencies of detoxication, and less dependent upon efficiencies of bioactivation and sensitivity of AChE. Serine esterases, such as carboxylesterase (CaE) and butyrylcholinesterase (BChE), play a prominent role in OP detoxication. Organophosphates can stoichiometrically inhibit these enzymes, removing OPs from circulation thus providing protection for the target enzyme, AChE. This in vitro study investigated age-related sensitivity of AChE, BChE and CaE to twelve structurally different OPs in rat tissues. Sensitivity of esterases to these OPs was assessed by inhibitory concentration 50s (IC50s). The OPs displayed a wide range of inhibitory potency toward AChE with IC50s in the low nM-μM range with no differences among ages; however, the CaE IC50s generally increased with age reflecting greater protection in adults. These results suggest age-related differences in acute toxicities of OPs in mammals are primarily a result of their detoxication capacities.

Synthesis, characterization, and in vitro effect of the Cu(II) complex with niflumic acid and 3-picoline on paraoxanase-I

Niflumic acid is used to treat inflammatory rheumatoid diseases, pain, and fever. The present study reports the experimental, spectroscopic, thermal, structural analyses, and biological activities of this complex. The nonsteroidal anti-inflammatory drug niflumic acid, 3-picoline, and copper(II) chloride were utilized to synthesize a new complex: [Cu₂ Cl ₂ (nif) ₂ (3-pic) ₄ ]. The crystal structure of [Cu ₂ Cl ₂ (nif) ₂ (3-pic) ₄ ] was determined by X-ray crystallography. The complex crystallizes in the triclinic space group P-1 and each Cu(II) center displayed six-coordinated distorted octahedral geometry. Two Cu(II) centers are connected by a chloro-bridge to form the binuclear metal core. Finally, the in vitro effects of the synthesized new complex and free niflumic acid were evaluated on the human serum paraoxonase 1 enzyme. At low doses, both the new complex and free niflumic acid showed very good inhibition activity with different inhibition mechanisms. In addition, the results showed that the new complex has more inhibition activity than free niflumic acid.

Paraoxonase-1 and arylesterase levels in patients with ulcerative colitis

BACKGROUND AND STUDY AIMS

The role of oxidative stress in inflammatory bowel disease is increasingly recognised as an important factor. It is assumed that reduced levels of paraoxonase-1 (PON-1) and arylesterase (ARE) may lead to increased inflammation due to increased oxidative stress. This study aimed to investigate the relationship between ARE and PON-1 levels in ulcerative colitis (UC) patients and the difference in these levels in UC patients in comparison to the control group.

PATIENTS AND METHODS

The study population consisted of 66 (73.3%) UC patients and 24 (26.7%) healthy individuals as the control group. The UC patients and the control group were compared in terms of PON-1 and ARE levels as oxidative stress markers. The UC patients were also grouped according to Mayo UC activity scores, and the differences in their PON-1 and ARE levels were assessed.

RESULTS

The ARE values were statistically higher in the control group in comparison to the UC patients. Concentrations of PON-1 were not statistically different in the UC and control groups. The ARE value was found to be significantly lower in the UC patients with a haemoglobin level below 10 mg/dl. There was a correlation between the ARE and PON-1 values in the UC patients, but there was no difference between the ARE and PON-1 values, based on the UC patients' Mayo disease severity scores.

CONCLUSION

This study found that the ARE values of UC patients were lower than those of healthy subjects. The same results could not be determined for PON-1. The data suggest that the antioxidative capacity of UC patients may be reduced.

Functional implications of single nucleotide polymorphisms rs662 and rs854860 on the antioxidative activity of paraoxonase1 (PON1) in patients with rheumatoid arthritis

BACKGROUND

Atherosclerosis leading to cardiovascular disease (CVD) is the main cause of mortality and morbidity in patients with rheumatoid arthritis (RA). Paraoxonase1 (PON1) is the best understood member of plasma paraoxonases with anti-atherogenic properties.

PATIENTS AND METHODS

Spanish RA (n = 549) consecutively recruited from 1 single center and 477 ethnically matched healthy controls were included in a case-control study. The concentration of PON1 was evaluated by means of an enzyme-linked immunosorbent sssay (ELISA). An arylesterase/paraoxonase assay kit was used to evaluate PON1 activity. Sample genotyping was performed by using TaqMan assays-on-demand. All results were expressed as medians ± interquartile range. One-way ANOVA comparisons were done using a nonparametric Kruskall-Wallis test. P values under 0.05 were considered to be significant.

RESULTS

The concentration of PON1 in the RA group was higher than in control group (p = 0.0003), although the differences were not significant when PON1 activities were compared between both groups. No significant differences were found related to distributions of rs662 genotypes in RA patients compared to healthy controls. Among rs854860 polymorphisms, overall genotype was widely distributed between RA patients and controls. Overall PON1 concentration in plasma was not significantly different between individuals carrying any of rs662 (p = 0.8501) or rs854860 (p = 0.2741) polymorphisms. Although PON1 levels were not associated with any of the SNPs in the study, differences appear when enzyme activities are compared for each SNP separately. CVD in RA patients correlate with increased PON1 levels and lower PON1 activity.

CONCLUSIONS

Although protective role of PON1 against oxidative damage in vivo could be related to other activities, in our study arylesterase activity was useful to identify phenotypic differences with emphasis placed on two SNPs coding for nonconservative amino acid changes in the functional protein.

Asymmetrical flow field-flow fractionation for improved characterization of human plasma lipoproteins

High- and low-density lipoproteins (HDL and LDL) are attractive targets for biomarker discovery. However, ultracentrifugation (UC), the current methodology of choice for isolating HDL and LDL, is tedious, requires large sample volume, results in sample loss, and does not readily provide information on particle size. In this work, human plasma HDL and LDL are separated and collected using semi-preparative asymmetrical flow field-flow fractionation (SP-AF4) and UC. The SP-AF4 and UC separation conditions, sample throughput, and liquid chromatography/mass spectrometry (LC/MS) lipidomic results are compared. Over 600 μg of total proteins is recovered in a single SP-AF4 run, and Western blot results confirm apoA1 pure and apoB100 pure fractions, consistent with HDL and LDL, respectively. The SP-AF4 separation requires ~ 60 min per sample, thus providing a marked improvement over UC which can span hours to days. Lipidome analysis of SP-AF4-prepared HDL and LDL fractions is compared to UC-prepared HDL and LDL samples. Over 270 lipids in positive MS mode and over 140 lipids in negative MS mode are identified by both sample preparation techniques with over 98% overlap between the lipidome. Additionally, lipoprotein size distributions are determined using analytical scale AF4 coupled with multiangle light scattering (MALS) and dynamic light scattering (DLS) detectors. These developments position SP-AF4 as a sample preparation method of choice for lipoprotein biomarker characterization and identification. Graphical abstract ᅟ.

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.

Targeted Proteomics Identifies Paraoxonase/Arylesterase 1 (PON1) and Apolipoprotein Cs as Potential Risk Factors for Hypoalphalipoproteinemia in Diabetic Subjects Treated with Fenofibrate and Rosiglitazone

Low levels of high-density lipoprotein cholesterol (HDL-C) and high triglyceride levels contribute to the excess rate of cardiovascular events seen in subjects with type 2 diabetes. Fenofibrate treatment partially reverses dyslipidemia in these subjects. However, a paradoxical marked reduction in HDL-C and HDL's major protein, apolipoprotein A-I, is a complication of fenofibrate in combination with rosiglitazone, an insulin-sensitizing agent. Risk factors for this condition, termed hypoalphalipoproteinemia, have yet to be identified. Using a case-control study design with subjects enrolled in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, we tested the hypothesis that alterations in HDL's protein cargo predispose diabetic subjects to fenofibrate/rosiglitazone-induced hypoalphalipoproteinemia. HDL was isolated from blood obtained from controls (no decreases or increase in HDL-C while receiving fenofibrate/rosiglitazone therapy) and cases (developed hypoalphalipoproteinemia after fenofibrate/rosiglitazone treatment) participating in the ACCORD study before they began fenofibrate/rosiglitazone treatment. HDL proteins were quantified by targeted parallel reaction monitoring (PRM) and selected reaction monitoring (SRM) with isotope dilution. This approach demonstrated marked increases in the relative concentrations of paraoxonase/arylesterase 1 (PON1), apolipoprotein C-II (APOC2), apolipoprotein C-I, and apolipoprotein H in the HDL of subjects who developed hypoalphalipoproteinemia. The case and control subjects did not differ significantly in baseline HDL-C levels or other traditional lipid risk factors. We used orthogonal biochemical techniques to confirm increased levels of PON1 and APOC2. Our observations suggest that an imbalance in HDL proteins predisposes diabetic subjects to develop hypoalphalipoproteinemia on fenofibrate/rosiglitazone therapy.

Implications of serum paraoxonase activity in obesity, diabetes mellitus, and dyslipidemia

Human serum paraoxonase 1 (PON1) is an enzyme with esterase activity, and is physically bound to high-density lipoproteins (HDL). It plays a key role in the action of HDL toward protection of lipoprotein and biological membrane against oxidative damage. It may have a protective role against atherosclerosis by virtue of its action on hydrolyzing lipid peroxides and preventing accumulation of phospholipids in oxidized low-density lipoprotein (LDL). PON1 is hypothesized to be an indicator of the risk of atherosclerosis and coronary artery disease development. Numerous studies have implicated PON1 activity in relation to various endocrine disorders. The current article reviews the clinical perspectives of PON1 activity with regards to obesity, diabetes mellitus with its complications, and dyslipidemia.

The Past and Present of Paraoxonase Enzyme: Its Role in the Cardiovascular System and Some Diseases

Although paraoxonase is synthesized in many tissues including the heart, colon, kidneys, lungs, small intestines and brain, its major locus of synthesis is the liver. PON1 is in close association with apolipoproteins and protects LDL against oxidation. It was reported that PON1 quantities dropped to 40 times lower than normal in cardiovascular diseases and diseases like diabetes, ulcerative colitis, Crohn's disease, chronic renal failure, SLE, Behcet's disease, cancer, hepatitis B, obesity, metabolic syndrome, Alzheimer's and dementia. It is speculated that the concerning decline in serum PON1 amount results from single nucleotide polymorphism in the coding (Q192R, L55M) and promoter (T-108C) sites of the PON1 gene. Additionally, circulating amounts of PON1 are affected by vitamins, antioxidants, fatty acids, dietary factors, drugs, age and lifestyle. This collection attempts to review and examine the past and present studies of paraoxonase and its relation with the cardiovascular system and some relevant diseases.

Low high-density lipoprotein cholesterol is not responsible for decreased paraoxonase activity in chronic renal failure

BACKGROUND/AIMS

Human paraoxonase-1 (PON1) is responsible for the antioxidant effect of high-density lipoprotein (HDL) by inhibiting low-density lipoprotein oxidation. Previous studies discovered dyslipidemia (DL) and decreased PON1 activity in chronic renal failure (CRF). We aimed to determine PON and arylesterase activity, phenotypic distribution of the PON1 enzyme, and lipid profile in low and normal HDL cholesterol (HDL-C) patients with CRF, and renal transplant (TX), compared to primary DL.

METHODS

116 CRF (low or normal HDL-C), 52 TX (low or normal HDL-C), and 62 DL patients (low or normal HDL-C) were included. PON and arylesterase activities were measured spectrophotometrically. Phenotype was determined using the dual substrate method.

RESULTS

Aryl/HDL-C was significantly higher in low HDL-C patients. Patients with CRF had significantly lower arylesterase activity compared to DL, independent of HDL-C. PON activity and PON/HDL-C did not differ significantly in CRF compared to TX and DL. Phenotypic distribution was similar in patient groups. Low HDL-C CRF patients had significantly lower cholesterol and triglyceride than DL.

CONCLUSION

Decreased arylesterase activity, correlating with PON1 enzyme protein quantity, is not explicable by decreased HDL-C in CRF. Low HDL-C CRF patients' increased cardiovascular morbidity is not attributable to changes in PON1 activity, or phenotypic distribution.

Paraoxonase: Its antiatherogenic role in chronic renal failure

Paraoxonase (PON) is an aryldialkylphosphatase, which reversibly binds and hydrolyzes organophosphates. The PON family has three members (PON1, PON2 and PON3); they share structural properties and enzymatic activities. PON1 is shown to reside over high density lipoprotein (HDL) and has both antioxidant and antiatherogenic functions. Function of PON2 and PON3 are speculative and still under research. Several methodologies were developed over the years to determine the activity and mass of PON1, of which spectrophotometer-based methods using certain chemicals as substrate predominate. Several studies have shown decreased levels of PON1 in chronic renal failure (CRF) patients, particularly those on hemodialysis. The role of PON1 in development of cardiovascular disease has drawn considerable attention in recent years. Several authors have shown decreased levels of HDL and PON1 activity in CRF patients on hemodialysis and reported this to be a risk factor in the development of CVD. Enhancement or maintenance of the PON1 activity may prevent development of CVDs and its consequences in patients on hemodialysis.

Paraoxonase 1 polymorphism Q192R affects the pro-inflammatory cytokine TNF-alpha in healthy males

Background

Human paraoxonase 1 (PON1) is an HDL-associated enzyme with anti-oxidant/anti-inflammatory properties that has been suggested to play an important protective role against coronary heart diseases and underlying atherogenesis. The common PON1 Q192R polymorphism (rs662, A>G), a glutamine to arginine substitution at amino acid residue 192, has been analyzed in numerous association studies as a genetic marker for coronary heart diseases, however, with controversial results.

Findings

To get a better understanding about the pathophysiological function of PON1, we analyzed the relationships between the Q192R polymorphism, serum paraoxonase activity and serum biomarkers important for atherogenesis. Genotyping a cohort of 49 healthy German males for the Q192R polymorphism revealed an allele distribution of 0.74 and 0.26 for the Q and R allele, respectively, typical for Caucasian populations. Presence of the R192 allele was found to be associated with a significantly increased paraoxonase enzyme activity of 187.8 ± 11.4 U/l in comparison to the QQ192 genotype with 60.5 ± 4.9 U/l. No significant differences among the genotypes were found for blood pressure, asymmetric dimethylarginine, LDL, HDL, triglycerides, and cholesterol. As expected, MIP-2 alpha a cytokine rather not related to atherosclerosis is not affected by the PON1 polymorphism. In contrast to that, the pro-inflammatory cytokine TNF-alpha is enhanced in R192 carriers (163.8 ± 24.7 pg/ml vs 94.7 ± 3.2 pg/ml in QQ192 carriers).

Conclusions

Our findings support the hypothesis that the common PON1 R192 allele may be a genetic risk factor for atherogenesis by inducing chronic low-grade inflammation.

Ghrelin, paraoxonase and arylesterase levels in depressive patients before and after citalopram treatment

OBJECTIVES

The purpose of this study was to examine alterations in lipid profiles and in the serum concentrations of acylated and desacylated ghrelin, paraoxonase and arylesterase in psychiatric patients before and after treatment with 40 mg citalopram daily for 3 months.

DESIGN AND METHODS

Samples were collected from 22 healthy controls and 24 psychiatric patients before and after citalopram treatment. Blood levels of acylated and desacylated ghrelin were measured by radioimmunoassay. Paraoxonase and arylesterase activities were determined spectrophotometrically. Lipid parameters were measured on the OLYMPUS-AU400.

RESULTS

It was found that the levels of acylated, desacylated ghrelin, paraoxonase arylesterase, total cholesterol and triglyceride were lower in depressive patients before citalopram treatment than in the control group. Those parameters were not restored after citalopram treatment except for the arylesterase level.

CONCLUSION

Decreased PON1 and ghrelin levels as well as fluctuations in lipid profiles may be involved in the etiology of depressive disorders.

Comparative expression analysis reveals differences in the regulation of intestinal paraoxonase family members

The paraoxonase (PON) gene cluster contains three members (PON1, PON2, and PON3), located on chromosome 7q21.3-22.1. Until now there has been little insight into their regulation in human intestine. This study was designed to determine the regulation of PONs by oxidative stress and inflammatory factors. Differentiated Caco-2/15 cells, cultured on polycarbonate Transwell filter inserts, exhibited transcripts of the 3 PONs whereas Western blot revealed the protein expression of PON2 and PON3 only. Iron-ascorbate-mediated lipid peroxidation, lipopolysaccharides (LPS), tumor necrosis factor-alpha and interferon-gamma induced differential effects on the gene expression and protein mass of PONs. In particular, LPS down-regulated PON2 protein expression, which was accompanied with decreased levels of IkappaBalpha, the inhibitor of the proinflammatory transcription factor nuclear factor-kappa B (NF-kappaB). Selective inactivation of NF-kappaB by the action of caffeic acid phenethyl ester (CAPE) partially attenuated but did not abolish LPS-triggered decline of PON2. However, the combination of CAPE and antioxidants completely abrogated the negative impact of LPS on PON2. Therefore, our data indicate that oxidative stress and proinflammatory agents selectively affect the expression of PONs. Our findings also suggest that both NF-kappaB pathway and lipid peroxidation are implicated in LPS-dependent diminution of PON2.

Association of oxidative stress and paraoxonase status with PROCAM risk score

OBJECTIVES

Oxidative stress and paraoxonase activity play a significant role in the pathogenesis of cardiovascular disease (CVD). The Prospective Cardiovascular Münster (PROCAM) study evaluated the prevalence of CVD risk factors and postulated the prediction of future CVD events. We therefore investigated the association between plasma markers of oxidative stress and paraoxonase status with PROCAM risk score.

DESIGN AND METHODS

Oxidative stress status parameters [lipid peroxidation measured as thiobarbituric acid-reacting substances (TBARS), superoxide anion (O(2)(-)), superoxide dismutase (SOD) activity, total sulphydryl group content] and paraoxonase (PON1) status were assessed in 211 participants. The predicted 10-year risk was calculated according to the PROCAM algorithm.

RESULTS

As expected subjects with high PROCAM risk score (high CVD risk) had significantly higher concentrations of oxidative stress parameters (TBARS and O(2)(-)P<0.001 and P<0.05, respectively). The PON1(192) phenotype distribution among CVD risk groups was not significantly different. Logistic regression analyses revealed significant associations of all the examined oxidative stress status parameters with calculated CVD risk score. The potential of the parameters for CVD risk prediction was tested via multivariate analysis. Only the O(2)(-) level retained a strong association with high CVD risk.

CONCLUSIONS

Our study demonstrated that high PROCAM risk score is associated with increased oxidative stress, indicating for the first time that elevated O(2)(-) is independently associated with high CVD risk.

Bovine Paraoxonase 1 Activities in Serum and Distribution in Lipoproteins

Paraoxonase 1 (PON1) is an enzyme associated with high-density lipoprotein (HDL) and has a protective effect against oxidation of lipoproteins in mammals. We investigated PON1 enzyme activities in bovine serum and its distribution among bovine serum lipoproteins. Paraoxonase activity and arylesterase activity in serum (152 Holstein cows and 42 Japanese Blacks) were 275 +/- 55 U/ml and 130 +/- 27 U/ml (mean +/- SD), respectively. There was a high correlation (r=0.962) between the two enzyme activities, and the activity ratio of paraoxonase/arylesterase did not exhibit individual variation. More than 85% of both paraoxonase and arylesterase activities were detected in the HDL fraction separated by ultracentrifugation. The 43-kDa protein in the HDL fraction was identified as bovine PON1 by N-terminal amino acid sequence analysis. Bovine PON1 was purified by ultracentrifugation and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an anti-bovine PON1 antiserum was developed. The concentration of PON1 protein determined by immunoblotting was closely correlated (r=0.976) with paraoxonase activity in serum. Bovine HDL was further fractionated into subpopulations, and the distribution of PON1 was examined. Paraoxonase activity and PON1 protein increased with decreasing HDL size and approximately 60% of total paraoxonase activity was distributed in the heavy HDL fraction. The different distributions of PON1 among HDL subpopulations might be concerned to the function and metabolism of bovine HDL.

A fluorogenic substrate for detection of organophosphatase activity

A new fluorogenic substrate for the specific detection of organophosphatase (OPase) activity has been designed and evaluated. Our results indicate that 7-diethylphospho-6,8-difluor-4-methylumbelliferyl (DEPFMU) is hydrolyzed specifically by the OPases, mammalian serum paraoxonase and bacterial organophosphorus hydrolase (OPH). The apparent K(m) of DEPFMU is 29 microM for OPH and 91 and 200 microM for the PON1 L(55)R(192) and PON1 L(55)Q(192) isoforms of human paraoxonase, respectively. DEPFMU-based assay systems are 10-100 times more sensitive for OPH and mammalian paraoxonase detection than existing methods. Importantly, DEPFMU is poorly hydrolyzed by both serum and cellular phosphatases and, therefore, may be used as part of a robust and sensitive assay for detecting not only purified, but also highly impure, preparations of OPase such as blood samples. The superior sensitivity of DEPFMU makes it potentially useful in the search for new enzymes that may hydrolyze nerve poisons such as sarin, soman, and VX, monitoring the decontamination of organophosphates (OPs) by OPH and determining serum paraoxonase activity which appears to be important for protection against atherosclerosis, sepsis, and OP toxicity.

Enzymes involved in the detoxification of organophosphorus, carbamate and pyrethroid insecticides through hydrolysis

The most employed insecticides for indoor and agriculture purposes belong to carbamates, pyrethroid or organophosphates. The chemical structures of these three groups correspond to carbamic, carboxylic and triphosphoric esters. Technical monographs suggest that the hydrolysis of ester bonds of carbamates and pyrethroids plays an important role in the detoxification of these compounds. However, detailed studies about enzymes hydrolysing carbamates and pyrethroids in vertebrates are not available. Certain carbamate hydrolysing activities are associated to serum albumin. Phosphotriesterases, being of an unknown physiological role, hydrolyse (in some cases stereospecifically) organophosphorus insecticides (OP). Phosphotriesterases have been found in a multitude of species, from mammals to bacteria. A phosphotriesterase activity, EDTA-resistant, has been detected in serum albumin. Phosphotriesterases in serum of mammals display polymorphisms. Phosphotriesterases offer applications in therapy of organophosphorus poisonings, in biodegradation and bioremedation of organophosphates. Similar studies should be developed with enzymes hydrolysing pyrethroids and carbamate insecticides. Such studies will improve the knowledge of the detoxification routes in non-target species and will help to design specific and safer carbamate and pyrethroid insecticides.

Effects of 5' regulatory-region polymorphisms on paraoxonase-gene (PON1) expression

Human HDL-associated paraoxonase (PON1) hydrolyzes a number of toxic organophosphorous compounds and reduces oxidation of LDLs and HDLs. These properties of PON1 account for its ability to protect against pesticide poisonings and atherosclerosis. PON1 also hydrolyzes a number of lactone and cyclic-carbonate drugs. Among individuals in a population, PON1 levels vary widely. We previously identified three polymorphisms in the PON1 regulatory region that affect expression levels in cultured human hepatocytes. In this study, we determined the genotypes of three regulatory-region polymorphisms for 376 white individuals and examined their effect on plasma-PON1 levels, determined by rates of phenylacetate hydrolysis. The -108 polymorphism had a significant effect on PON1-activity level, whereas the -162 polymorphism had a lesser effect. The -909 polymorphism, which is in linkage disequilibrium with the other sites, appears to have little or no independent effect on PON1-activity level in vivo. Other studies have found that the L55M polymorphism in the PON1-coding region is associated with differences in both PON1-mRNA and PON1-activity levels. The results presented here indicate that the L55M effect of lowered activity is not due to the amino acid change but is, rather, largely due to linkage disequilibrium with the -108 regulatory-region polymorphism. The codon 55 polymorphism marginally appeared to account for 15.3% of the variance in PON1 activity, but this dropped to 5% after adjustments for the effects of the -108 and Q192R polymorphisms were made. The -108C/T polymorphism accounted for 22.8% of the observed variability in PON1-expression levels, which was much greater than that attributable to the other PON1 polymorphisms. We also identified four sequence differences in the 3' UTR of the PON1 mRNA.

The serum paraoxonase activity in patients with chronic renal failure and hyperlipidemia

Human serum paraoxonase is physically associated with an apolipoprotein (Apo-A1) and clusterin-containing high-density lipoprotein (HDL) and prevents low-density lipoprotein from lipid peroxidation. The aim of our study was to determine whether paraoxonase activity or phenotype is altered in patients with chronic renal failure and in hyperlipidemic subjects without renal insufficiency and to compare the values with those of healthy controls. We investigated the serum paraoxonase activity and polymorphism in 119 hemodialyzed uremic patients, 107 patients with primary hyperlipoproteinemia, and in 110 healthy control subjects. The serum paraoxonase activity was significantly decreased both in hyperlipidemic (p < 0.01) and uremic patients (p < 0.001) as compared with controls. On comparison, the serum paraoxonase activity was significantly lower (p < 0.001) in uremic than in hyperlipoproteinemic patients. The HDL and Apo-A1 levels were as follows: uremic < hyperlipidemic < control. To assess whether the observed reduction in paraoxonase activity was due to HDL and Apo-A1 level decreases, we standardized the enzyme activity for HDL and Apo-A1 concentrations. We found that the standardized paraoxonase activity (paraoxonase/HDL ratio) was also lower in the uremic patients (103.3 +/- 69.5) as compared with hyperlipidemic patients (137.64 +/- 81.0) and controls (194.45 +/- 94.45). The standardized values for Apo-A1 showed a similar tendency: paraoxonase/Apo-A1 ratio in uremic patients 89.64 +/- 47.8, in hyperlipidemic patients 128.12 +/- 69.83, and in controls 161.40 +/- 47.35. The phenotypic distribution of paraoxonase (AA, AB, BB) did not change significantly in the patient groups. These results suggest that HDL concentration and phenotypic distribution of paraoxonase may not be the only determining factors, but that other as yet undetermined factors could be involved in the enzyme activity changes.

Paraoxonase activity in the serum and hepatic mRNA levels decrease during the acute phase response

Numerous epidemiological studies have suggested an association between the acute phase response and atherosclerosis. Paraoxonase (PON) is an HDL associated enzyme that protects LDL from oxidative stress. Here we demonstrate that serum PON activity decreases following endotoxin (LPS) administration in Syrian hamsters. This decrease is seen within 24 h following LPS treatment and doses as low as 100 ng/100 g body weight of LPS elicit a reduction in serum PON activity. LPS also induces a marked decrease in PON1 mRNA in the liver (80% decrease). The decrease in mRNA levels is observed as early as 4 h and is sustained for at least 48 h after a single LPS treatment. Moreover, TNF and IL-1, cytokines which mediate the acute phase response, also decrease serum PON activity and PON mRNA levels in the liver. Additionally, TNF and IL-1 treatment of HepG2 cells results in a decrease in PON mRNA levels indicating that these cytokines are capable of directly affecting liver cells. Along with other changes in lipid metabolism that occur during the acute phase response, the decrease in PON could be another factor linking the acute phase response with increased atherogenesis.

Modulated serum activities and concentrations of paraoxonase in high density lipoprotein deficiency states

Paraoxonase is a high density lipoprotein (HDL) associated enzyme with a hypothesised role in the protection of low density lipoproteins (LDL) from oxidative stress. The present study examined paraoxonase in several genetically distinct HDL deficiency states. Despite reduction or even absence of detectable HDL, enzyme activity was present in sera from A-I-Pisa, A-I-Helsinki, A-I-Milano and Tangier patients. Both enzyme activities and peptide concentrations were modulated (reduced) but specific activities were broadly similar to controls, suggesting an impact on peptide concentration rather than an inhibition of enzyme activity. Despite the absence of HDL in A-I-Pisa and Tangier subjects, there was no association of paraoxonase with very low density lipoproteins or LDL. Paraoxonase function is maintained in HDL deficient states. It implies that certain HDL-associated anti-atherogenic processes may not be entirely compromised by HDL deficiency. This has important implications for the cardiovascular risk associated with modulated HDL concentrations.

Purification and characterization of paraoxon hydrolase from rat liver

Paraoxonase (paraoxon hydrolase), an enzyme that hydrolyses paraoxon (O,O-diethyl O-p-nitrophenyl phosphate), is located in mammals primarily in the serum and liver. Although considerable information is available regarding serum paraoxonase, little is known about the hepatic form of this enzyme. The present work represents the first study on the purification of rat liver paraoxonase. This enzyme has been purified 415-fold to apparent homogeneity with a final specific activity of 1370 units/mg using a protocol consisting of five steps: solubilization of the microsomal fraction, hydroxyapatite adsorption, chromatography on DEAE-Sepharose CL-6B, non-specific affinity chromatography on Cibacron Blue 3GA and anion exchange on Mono Q HR 5/5. The presence of Ca2+ and Triton X-100 in the buffers throughout the purification procedure was essential for maintaining enzyme activity. SDS/PAGE of the final preparation indicated a single protein-staining band with an apparent Mr of 45 000. N-terminal and internal amino acid sequences were determined and compared with those of paraoxonases from human and rabbit serum and mouse liver, showing a high similarity. The pH profile showed optimum activity at pH 8.5. The pH stability and heat inactivation of the enzyme were also studied. The Km for liver paraoxonase was 1.69 mM.

Paraoxonase genotypes, lipoprotein lipase activity, and HDL

Paraxonase, an enzyme associated with the high density lipoprotein (HDL) particle, hydrolyzes paraoxon, the active metabolite of the insecticide parathion. Several studies have shown that paraxonase levels in humans have a distribution characteristic of two alleles, one with low activity and the other with high activity. Paraoxonase also has arylesterase activity, which does not exhibit activity polymorphism and can therefore serve as an estimate of enzyme protein. Although the ability of paraoxon to irreversibly inhibit lipoprotein lipase (LPL) has been exploited experimentally for many years, the role of plasma paraoxonase in lipoprotein metabolism is unknown. Seventy-two normal individuals were examined for paraoxonase genotypes, plasma paraoxonase and arylesterase activities, postheparin LPL and hepatic lipase (HL) activities, and lipoprotein levels to determine whether (1) paraoxonase activity or genotype determines lipoprotein levels via an effect on LPL or HL activity or (2) variation in LPL and HL activities determines HDL levels and indirectly affects paraoxonase activity and protein levels in plasma. In the entire group, paraoxonase activity was related to arylesterase activity and genotype. Whereas arylesterase activity was correlated with HDL cholesterol (HDL-C) and apolipoproteinA-I (apoA-I) levels, neither arylesterase nor paraoxonase was correlated with LPL or HL activity. Furthermore, LPL activity was positively correlated and HL inversely correlated with HDL cholesterol and apoA-I levels, whereas LPL was inversely correlated with triglyceride levels. The paraoxonase genotypes of the study group were 30 individuals homozygous for the low-activity allele, 38 heterozygotes, and 4 individuals homozygous for the high-activity allele. Paraoxonase genotype accounted for approximately .75 of the variation in paraoxonase activity. Paraoxonase activity was linearly related to arylesterase activity within each subgroup. No difference in either LPL or HL activity was seen as a function of paraoxonase genotype, nor were differences seen in plasma triglyceride or HDL-C by genotype by ANOVA. The relation between LPL and HL and components of HDL in the paraoxonase genotypic subgroups in general reflected the associations seen in the group as a whole. Multivariate analysis showed that LPL, HL, and arylesterase, a measure of paraoxonase mass, were independent predictors of HDL cholesterol, while paraoxonase genotype or activity was not. Thus, variation in LPL and HL appears to be significantly related to HDL cholesterol and apoA-I levels. The levels of HDL are a major correlate of paraoxonase protein levels, while paraoxonase genotype is the major predictor of plasma paraoxonase activity.

Serum paraoxonase activity, concentration, and phenotype distribution in diabetes mellitus and its relationship to serum lipids and lipoproteins

Human serum paraoxonase is physically associated with HDL and has been implicated in the detoxification of organophosphates and possibly in the prevention of LDL lipid peroxidation. We investigated the serum activity and concentration of paraoxonase in 78 patients with type 1 diabetes mellitus, 92 with type 2 diabetes, and 82 nondiabetic control subjects. Paraoxonase activity was generally lower in diabetics than in control subjects. This decrease was unrelated to differences in paraoxonase phenotype distribution or its serum concentration. Rather, the difference in paraoxonase activity was explained by its specific activity, which was lower in diabetics, indicating either the presence of a circulating inhibitor or disturbance of the interaction of paraoxonase with HDL affecting its activity. Paraoxonase specific activity was lowest in patients with peripheral neuropathy, suggesting an association of paraoxonase with neuropathy. In control subjects but not patients with diabetes, paraoxonase correlated with HDL cholesterol and apolipoprotein A-1. Our results indicate that the low paraoxonase activity in diabetes is due to decreased specific activity. In other studies low serum paraoxonase activity has been associated with increased susceptibility to atherosclerosis, and the present results also suggest an association with peripheral neuropathy, which could be due to reduced capacity to detoxify lipid peroxides in diabetes.

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

Paraoxonase is a serum protein bound to high-density lipoproteins (HDLs). The physiological function of the enzyme is unknown, but a role in lipid metabolism has been postulated. To date, studies of the protein have had to rely on measurements of enzyme activity with various substrates. We have developed a highly specific, competitive e.l.i.s.a. using a previously characterized monoclonal antibody. The assay can detect 20 ng of paraoxonase with a working range of 75-600 ng. Intra- and interassay coefficients of variation were 6.5 and 7.9% respectively. Serum concentrations of paraoxonase in healthy subjects from Geneva and Manchester ranged from 25 to 118 micrograms/ml. There were significant differences in mean concentrations between the two groups (Geneva, 79.3 +/- 18.7 micrograms/ml; Manchester, 59.9 +/- 24.1 micrograms/ml: P < 0.001), differences also apparent when subjects were compared according to paraoxonase phenotype. These appeared to be largely a consequence of differences in apolipoprotein A-I concentrations between the two populations, suggesting that HDL particle number may be important in determining serum levels of paraoxonase. Paraoxonase specific activities were also significantly different between the two groups of subjects (Geneva, 2.08 +/- 0.96 units/mg; Manchester, 3.08 +/- 1.73 units/mg: P < 0.001), which may reflect differences in HDL particle composition. The e.l.i.s.a. should furnish the necessary complement to studies of paraoxonase enzymic activity and has already provided evidence for differences with respect to serum levels of the protein both between populations and between phenotypes within populations.

Multiple forms of sheep serum A-esterase activity associated with the high-density lipoprotein

Five lipoproteins of sheep serum expressing A-esterase activity, but with differing activities towards four organophosphate substrates, were separated by a combination of gel filtration and ion-exchange chromatography. Each had an Mr of approx. 360,000 and contained a major peptide of Mr 28,000-30,000 that appeared to be present as several isoforms on urea/agarose isoelectric focusing. In every case this peptide split into a number of bands on urea/agarose isoelectric focusing. The bands appear to represent isoforms of the peptide, and four lipoproteins yielded characteristic patterns of bands. This peptide resembles the apolipoprotein A-I of human serum, and available evidence suggests that this is the protein that expresses A-esterase activity. Evidence is presented for the existence of different species of high-density lipoprotein HDL2 particles containing different complements of peptide isoforms and expressing contrasting substrate specificities towards organophosphates.