Paraoxonase activity is reduced by a pro-atherosclerotic diet in rabbits

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.

Excesive consumption of unsaturated fatty acids leads to oxidative and inflammatory instability in Wistar rats

Lifestyle modifications such as increase in high-fat food consumption importantly increases the risks for cardiovascular disease. The principal objective of this study is to analyze effects of different high fat diet (HFD) sources on haemodynamic parameters, lipid and oxidative profile, myeloperoxidase activity, and markers of inflammation (IL-6/pentraxin-3). HFD containing 20% of fat, provided by lard (saturated) or soybean oil (unsaturated), as well as control diet were administering to three groups (L, SO and C). Food efficiency ratio and plasma lipids were significantly elevated in both HFD groups. However, only SO group showed an increase in systolic arterial pressure, oxidative stress index, myeloperoxidase activity, liver lipids as well as markers of inflammation: IL-6 and pentraxin-3 (PTX3). In summary, these results indicate inflammogenic potential of excessive soybean oil consumption in triggering liver damage.

Relationship between rs854560 PON1 Gene Polymorphism and Tobacco Smoking with Coronary Artery Disease

Paraoxonase-1 (PON1) is the antioxidant marker of high-density lipoproteins protecting against atherosclerosis and coronary artery disease (CAD) phenotype. The purpose of the present study was to determine whether the PON1 gene rs854560 polymorphism (163T>A) is associated with CAD in Polish population. rs854560 was genotyped in 494 subjects: 248 patients with premature CAD and 246 blood donors as a control. We found that the risk of CAD was significantly higher in TT homozygotes than in A allele carriers (OR = 1.87, p = 0.041). The synergistic effect between the TT genotype and cigarette smoking was observed (SIM = 9.81; SI = 14.70). The relative increase in risk from interaction between factors was over 37 (RERI = 36.13). The PON1 polymorphism did not modulate the risk of CAD in response to exposure to other traditional risk factors. In conclusion, the rs854560 polymorphism may modulate the risk of CAD in response to cigarette smoking in Polish population. Carriers of TT genotype seem to be particularly at risk of CAD, when exposed to cigarette smoking.

The role of cholesterol-enriched diet and paraoxonase 1 inhibition in atherosclerosis progression

Introduction: Atherosclerosis could be deemed as a chronic, progressive, and inflammatory disease. It has been well-documented that high-density lipoprotein (HDL) can reduce the risk of the atherosclerosis occurrence through exerting some anti-atherogenic mechanisms. In recent years, the strong evidence has suggested that paraoxonase 1 (PON1) may contribute to antioxidant properties of HDL. In the present study, the impact of a diet enriched with cholesterol and also the PON1 inhibition on atheroma formation and lipid profile has been investigated.

Methods: In this study, 24 New Zealand rabbits were randomly assigned to three groups receiving standard diet, atherogenic diet, and atherogenic diet plus once daily intramuscular injection of nandrolone decanoate as the PON1 inhibitor. Triglyceride, cholesterol, HDL, and low-density lipoprotein (LDL) were determined and both cholesterol accumulation in aorta and fatty streak formation were evaluated.

Results: The comparison of the results in three groups reveals that cholesterol level in the group received cholesterol-enriched diet plus once daily injection of PON1 inhibitor was higher than the groups received standard diet or atherogenic diet without PON1 inhibitor (P < 0.05). Furthermore, the percentage of atheroma with type-I lesions was equal to 75% compared with the group received atherogenic diet plus nandrolone at 30%. Additionally, the differences in fatty streak formation in aorta, as well as the right and left coronary arteries in three groups given show that the difference between groups receiving atherogenic diet and standard diet was significantly lower (P < 0.05) than the difference between groups receiving atherogenic diet plus PON1 inhibitor and standard diet.

Conclusion: It can be concluded that lack of paraoxanase1 or even reduced the activity of this enzyme could accelerate the progression of fatty streak lesions toward advanced atherosclerotic lesions.

Paraoxonase 1 gene polymorphisms and enzyme activities in coronary artery disease and its relationship to serum lipids and glycemia

OBJECTIVES

Oxidative stress and inflammation are important processes in development of atherosclerosis. Paraoxonase 1 (PON1) is a bioscavenger enzyme associated with inflammation and oxidative stress. We evaluate the association of two single nucleotide polymorphisms in PON1 gene, and enzyme activities with lipid profile and glycemia.

METHODS

This case-control study consisted of 126 patients with coronary artery disease (CAD) and 203 healthy controls. PON Q192R and L55M polymorphisms were detected by real-time PCR. Paraoxonase and arylesterase activities were determined spectrophotometrically. Blood glucose, cholesterol, triglycerides, HDL, and LDL were measured.

RESULTS

PON1 QR192 polymorphism had a major effect on paraoxonase but no effect on arylesterase serum activities. Paraoxonase activity was higher in RR genotype and lowest in QQ genotype. Paraoxonase and arylesterase activities were higher in LL and lower in MM genotypes of PON1 LM55 polymorphism. RQ and LM variants showed intermediate activities between respective homozygous. Elevated concentrations of triglycerides in cases correlate with QQ variant or the presence of M allele. Glucose levels were elevated in cases with QQ variant or with the presence of M allele. Cholesterol and LDL did not show variations in control and cases with any variant of both polymorphisms. HDL is lower in cases with respect to controls independently of genotypes. All differences were significant with p<0.05.

CONCLUSIONS

Our results confirm the relationship between variations in PON1 activities and lipid metabolism, and showed that genetically programmed low PON1 activities would have certain responsibility in the increase in glycemia and concomitantly the aggravation of atherosclerotic disease.

How HDL protects LDL against atherogenic modification: paraoxonase 1 and other dramatis personae

PURPOSE OF REVIEW

To summarize the current evidence about how HDL impedes the oxidative and glycative atherogenic modification of LDL.

RECENT FINDINGS

Paraoxonase 1 (PON1) is located on HDL. Meta-analysis of clinical epidemiological investigations reveals a substantial association of low serum PON1 activity with coronary heart disease incidence independent of other risk factors including HDL cholesterol and apolipoprotein AI (apoAI). Transgenic animal models also indicate an antiatherosclerotic role for PON1. However, highly purified and recombinant PON1 do not retain their antioxidant properties.

SUMMARY

The therapeutic potential of PON1 should be recognized in preventing atherosclerosis and combating infection and organophosphate toxicity. In unleashing this potential, it is important to consider that both highly purified and recombinant PON1 are dissociated from the lipid phase and other components of HDL, such as apoAI and apoM, all of which may be required for HDL (through its PON1 component) to hydrolyze more lipophilic substrates.

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Proteomics investigations of HDL: challenges and promise

High density lipoprotein (HDL) is recognized as the major negative risk factor of cardiovascular disease and number of anti-atherogenic functions has been ascribed to HDL. HDL is an assembly of a neutral lipid core and an outer shell consisting of polar lipids and proteins. It has been defined many different ways based on various distinct properties including density flotation, protein composition, molecular size, and electrophoretic migration. Overall the studies characterizing HDL clearly demonstrate that it is a complex heterogeneous mixture of particles. Furthermore several studies convincingly demonstrated that certain populations of HDL particles have a distinct functionality suggesting that HDL may serve as a platform for assembly of protein complexes with very specific biological functions. Indeed recent proteomics studies described over 100 proteins associated with HDL. Here we review approaches to isolation and proteomic analysis of HDL and discuss potential problems associated with isolation methods which may confound our understanding of the relation of the HDL composition and its biological function.

Astaxanthin prevents changes in the activities of thioredoxin reductase and paraoxonase in hypercholesterolemic rabbits

This study explored the effects of the antioxidant astaxanthin on paraoxonase and thioredoxin reductase activities as well as on other oxidative stress parameters and on the lipid profile in hypercholesterolemic rabbits. Rabbits were fed a standard or a hypercholesterolemic diet alone or supplemented with 50, 100 and 500 mg/100 g of astaxanthin for 60 days. Antioxidant enzymes activities, lipid profile and oxidative stress markers were evaluated in the serum. The hypercholesterolemic diet increased lipids, including unsaturated fatty acids level, whereas it decreased saturated fatty acids level. These changes were accompanied by increased levels of oxidized low-density lipoprotein and oxidized low-density lipoprotein antibodies, as well as lipid and protein oxidation. Astaxanthin (100 and 500 mg/100 g) prevented hypercholesterolemia-induced protein oxidation, whereas 500 mg/100 g of astaxanthin decreased protein oxidation per se. The activities of superoxide dismutase and thioredoxin reductase were enhanced, whereas paraoxonase activity was inhibited in hypercholesterolemic rabbits. All astaxanthin doses prevented changes in thioredoxin reductase and paraoxonase activities. This effect was not related to a direct effect of astaxanthin on these enzymes, because in vitro astaxanthin enhanced thioredoxin reductase and had no effect on paraoxonase activity. Astaxanthin could be helpful in cardiovascular diseases by restoring thioredoxin reductase and paraoxonase activities.

Effect of dietary lipids on paraoxonase-1 activity and gene expression

AIMS

Aim of the paper was to summarize the literature about the effect of dietary lipids on activity of paraoxonase-1 (PON1), a multifunctional enzyme associated with high density lipoprotein (HDL). PON1 exerts a protective effect against oxidative damage of cells and lipoproteins and modulates the susceptibility of HDL and LDL to atherogenic modifications such as homocysteinylation.

DATA SYNTHESIS

The present review shows evidence that the amount and the composition of dietary lipids are key factors in the modulation of PON1. The effect of dietary lipids is also modulated by PON1 polymorphisms. The molecular mechanisms involved include an effect on PON1 hepatic synthesis or secretion and/or modification of PON1 interactions with HDL. Changes of PON1 activity could also be related to dietary intake of oxidized lipids that behave as PON1 inhibitors.

CONCLUSION

Dietary fatty acids by the modulation of PON1 gene expression and activity could constitute an useful approach for the prevention of human diseases associated with oxidative damage.

Serum paraoxonase-3 concentration in HIV-infected patients. Evidence for a protective role against oxidation

We investigated the influence of the HIV infection on serum paraoxonase-3 (PON3) concentration and assessed the relationships with lipoprotein-associated abnormalities, immunological response, and accelerated atherosclerosis. We studied 207 HIV-infected patients and 385 healthy volunteers. Serum PON3 was determined by in-house ELISA, and PON3 distribution in lipoproteins was investigated by fast-performance liquid chromatography (FPLC). Polymorphisms of the PON3 promoter were analyzed by the Iplex Gold MassArray(TM) method. PON3 concentrations were increased (about three times) in HIV-infected patients with respect to controls (P < 0.001) and were inversely correlated with oxidized LDL levels (P = 0.038). Long-term use of nonnucleoside reverse transcriptase inhibitor (NNRTI)-based antiretroviral therapy was associated with a decrease of PON3 concentrations. In a multivariate linear regression analysis, these relationships were still strong when the main confounding covariates were considered. PON3 was mainly found in HDL in HIV-infected patients, but a substantial amount of the protein was detected in LDL particles. This study reports for the first time an important increase in serum PON3 concentrations in HIV-infected patients that is associated with their oxidative status and their treatment with NNRTI. Long-term, prospective studies are needed to confirm the possible influence of this enzyme on the course of this disease and its possible utility as an analytical biomarker.

Immunobiochemical analysis of Paraoxonase1 (anti-oxidant), xanthine oxidase (oxidant) enzymes and lipid profile of cardiac disease patients in Lahore Metropolitan, Pakistan

Cardiac diseases are the major cause of death. Paraoxonase1 (PON1) is known as free radicals scavenger/anti-atherosclerosis, whereas xanthine oxidase (XO) is a free radicals generator. This study was undertaken to determine and compare the Paraoxonase and arylesterase activities of PON1 enzyme and activity of XO enzyme. The concentration of XO and PON1 enzymes along with lipid profile, lipid peroxides, and thiol level in plasma of cardiac patients (n=200) and healthy persons (n=200) of Lahore metropolitan, Pakistan was also determined. Anti-PON1 and anti-XO antibodies were developed, purified, and used to measure the concentration of PON1 and XO by competitive ELISA. It is observed that low paraoxonase (P=0.0073)/arylesterase activity (P=0.0038) of PON1 enzyme and its low concentration (P=0.0049) were observed in cardiac patients, whereas elevated level of XO activity (P=0.0129) and its concentration (P=0.0097) was observed in cardiac patients as compared with healthy persons. Low levels of HDL (P=0.0013), thiol (P=0.0014) and high level of cholesterol (P=0.0025), triglycerides (P=0.0018), LPO (P=0.0014), and LDL level (P=0.05) were observed in cardiac patients admitted in intensive care unit as compared with hypertensive patients and control subjects. It is concluded that overall low PON1 and high XO activities do cause imbalance of free radical system which ultimately leads to or enhance the cardiac pathological conditions.

Single intravenous injection of plasmid DNA encoding human paraoxonase-1 inhibits hyperlipidemia in rats

Paraoxonase-1 (PON1, EC 3.1.8.1) is a high-density lipoprotein (HDL)-associated antioxidant enzyme, and its activity correlates negatively with the level of plasma low-density lipoprotein cholesterol (LDL-C) and triglyceridemia (TG). In this study, we examined the therapeutic effect of plasmid DNA containing the human PON1 gene (pcDNA/PON1) in hyperlipidemic model rats. The rats were fed a high-fat and high-cholesterol diet for 25 days to produce a hyperlipidemic animal model. Single intravenous injection of pcDNA/PON1 into model rats prevented dyslipidemia and hepatic lipid accumulation. The mechanisms of pcDNA/PON1 in treating hyperlipidemia were associated with increases of serum antioxidant PON1 and SOD activities, and with reduction of the levels of total cholesterol (TC), LDL-C and TG. The results suggest the potential therapeutic effect of pcDNA/PON1 on hyperlipidemia.

Actions of ferulic acid and vitamin E on prevention of hypercholesterolemia and atherogenic lesion formation in apolipoprotein E-deficient mice

This study was carried out to investigate whether dietary vitamin E and ferulic acid (FA) can exert possible interactions on preventions of hypercholesterolemia and atherogenic lesion formation in C57BL/65 apolipoprotein E-deficient (apo E(-/-)) mice. Four-week-old male apo E(-/-) mice were randomly divided into three groups and given one of three types of Western diets with various amounts of vitamin E (0.02%, 0%, or 0.2%) for 15 weeks. FA was added to vitamin E-free Western diet and vitamin E-rich Western diet at the 0.02% level. The plasma total cholesterol concentration was significantly lowered when FA was added to the vitamin E-free and vitamin E-rich Western diet as compared to the normal vitamin E Western diet (0.02% vitamin E), and this was accompanied with a decreased hepatic acyl-coenzyme A:cholesterol acyltransferase activity. The hepatic and erythrocyte thiobarbituric acid-reactive substances levels were significantly lowered when FA was added to the vitamin E-rich Western diet, which was attributable to increased activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) and paraoxonase. Accordingly, vitamin E and/or FA are beneficial for prevention of hypercholesterolemia and atherogenesis in apo E(-/-) mice. In particular, dietary FA exhibited an anti-atherosclerotic property, and this effect was synergistically enhanced with the vitamin E supplement.

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

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

Variation in paraoxonase-1 activity and atherosclerosis

PURPOSE OF REVIEW

Paraoxonase-1 (PON1) is an HDL-associated protein of 354 amino acids with a molecular mass of 43 000 Da. It is synthesized in the liver, and in serum it is almost exclusively associated with HDL. PON1 has been reported to be an important contributor to the antioxidant and anti-inflammatory activities of HDL. PON1 impedes oxidative modification of LDL. PON1 serum activity is related to systemic lipid peroxidation stress and prospective cardiovascular risk. In this review, we discuss the relationship between PON1 activity and atherosclerotic diseases and various factors modulating PON1 activity including genes, age, lifestyle factors and medical conditions. Finally, evidence that pharmacological agents may affect PON1 activity is summarized.

RECENT FINDINGS

There is increasing evidence from both animal and human studies linking low PON1 activity to an increased likelihood of cardiovascular diseases. Two prospective studies reported a significantly lower incidence of major cardiovascular events in participants with the highest systemic PON1 activity, compared with those with the lowest activity.

SUMMARY

PON1 is a potentially antiatherogenic HDL-associated enzyme that protects LDL from oxidative modification. Enhancing PON1 activity could be an important target for future pharmacological agents aimed at decreasing cardiovascular risk.

Genetic polymorphism in paraoxonase 1 (PON1): Population distribution of PON1 activity

Paraoxonase-1 (PON1) is a serum esterase that hydrolyzes the activated oxon form of several organophosphates. The central role of PON1 in detoxification of organophosphate (OP) pesticides was demonstrated in knockout mouse studies, suggesting that human variability in PON1 needs to be considered in health risk assessments involving exposure to these pesticides. The current analysis focused on two genetic loci in which polymorphisms demonstrated to affect PON1 activity. Detailed kinetic studies and population studies found that the *192Q (wild type) allele is more active toward some substrates (such as sarin, soman, and diazoxon) and less active toward others (such as paraoxon or chlorpyrifos) relative to the variant *192R allele. Another allele that affects activity is *55M; PON1 enzyme quantity, rather than specific activity or substrate preference, is altered. The *192R variant occurs commonly with a frequency of 25-64% across the populations analyzed. The *55M allele is less common, occurring in 5-40% of individuals depending upon the ethnic group studied. These activity and allele frequency data were incorporated into Monte Carlo simulations in which the frequency of both variant alleles was simultaneously modeled in Caucasian, African American, and Japanese populations. The resulting Monte Carlo activity distributions were bimodal for the substrate paraoxon with approximately fourfold differences between low- and high-activity modal medians. Differences in activity between total population median and 1st percentile were five- to sixfold. When sarin metabolic variability was simulated, the population distributions were unimodal. However, there was an even greater degree of interindividual variability (median to 1st percentile difference >20-fold). These results show that the combined effects of two PON1 allelic variants yielded a population distribution that is associated with a considerable degree of interindividual variability in enzyme activity. This indicates that assessments involving PON1 substrates need to evaluate polymorphism-related variability in enzyme activity to display the distribution of internal doses and adverse responses. This may best be achieved via physiologically based pharmacokinetic (PBPK) models that input PON1 activity distributions, such as those generated in this analysis, to simulate the range of oxon internal doses possible across the population.

Beneficial effects of curcumin on hyperlipidemia and insulin resistance in high-fat-fed hamsters

This study investigated the effect of curcumin (0.05-g/100-g diet) supplementation on a high-fat diet (10% coconut oil, 0.2% cholesterol, wt/wt) fed to hamsters, one of the rodent species that are most closely related to humans in lipid metabolism. Curcumin significantly lowered the levels of free fatty acid, total cholesterol, triglyceride, and leptin and the homeostasis model assessment of insulin resistance index, whereas it elevated the levels of high-density lipoprotein cholesterol and apolipoprotein (apo) A-I and paraoxonase activity in plasma, compared with the control group. The levels of hepatic cholesterol and triglyceride were also lower in the curcumin group than in the control group. In the liver, fatty acid beta-oxidation activity was significantly higher in the curcumin group than in the control group, whereas fatty acid synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and acyl coenzyme A:cholesterol acyltransferase activities were significantly lower. Curcumin significantly lowered the lipid peroxide levels in the erythrocyte and liver compared with the control group. These results indicate that curcumin exhibits an obvious hypolipidemic effect by increasing plasma paraoxonase activity, ratios of high-density lipoprotein cholesterol to total cholesterol and of apo A-I to apo B, and hepatic fatty acid oxidation activity with simultaneous inhibition of hepatic fatty acid and cholesterol biosynthesis in high-fat-fed hamsters.

Paraoxonase 1 response to a high-fat diet: gender differences in the factors involved

Diets consumed in industrialized countries are rich in fat and increase the incidence of atherosclerosis, a process reported to be influenced by gender. Considering the anti-atherogenic role attributed to serum Paraoxonase 1 (PON1) activity, and given the pro-atherogenic effects described for saturated fatty acids (SFA), as opposed to the beneficial ones conferred to monounsaturated fatty acids (MUFA), the aim of this study was to investigate the response of male and female rat serum PON1 activity and its related factors to a high-fat (HF), hypercaloric diet (fat representing 55.2% of the energy) containing similar amounts of SFA and MUFA. The HF diet feeding did not alter total body weight, but increased adiposity. Nevertheless, and in spite of the increased adiposity, the HF diet did not entail a more pro-inflammatory serum adipokine or lipid profile or increased lipid peroxidation. Paraoxonase activity was reduced in both male and female HF fed rats, due to a reduction of PON1 mRNA levels in males and to a reduced stability and/or number of HDL particles responsible for PON1 transport in females. Both the maintenance of body weight and the MUFA content in the diet would be among the factors responsible for the attenuation of the negative effects usually related to excessive fat intake and for the reduction in PON activity, whose antioxidant activity would be less necessary in this situation.

Effect of Walnut-Enriched Restructured Meat in the Antioxidant Status of Overweight/Obese Senior Subjects with at Least One Extra CHD-Risk Factor

BACKGROUND

A number of recent studies indicate that antioxidants reduce the oxidative stress associated with the development of coronary heart diseases (CHD).

OBJECTIVE

(i) To investigate whether the erythrocyte catalase (CAT), superoxide dismutase (SOD), total glutathione, reduced glutathione (GSH), oxidized glutathione (GSSG), and lipid peroxidation (LPO), and serum uric acid and paraoxonase-1 (PON1) are modified at increased CHD-risk individuals consuming walnut-enriched meat (WM), (ii) to evaluate whether these changes were influenced by basal serum cholesterol, body mass index or smoking habit.

DESIGN

The study was a non blinded, cross-over, placebo-controlled trial in which 22 volunteers (60% overweight and 40% obese) with increased CHD-risk were randomly assigned to receive WM or control meat (CM) during two different periods of 5 weeks.

RESULTS

A significant interaction time*treatment (p < 0.05) was observed in all enzymes and substrates tested except HDL-C, uric acid and LPO. The treatment significantly increased CAT activity, total glutathione and GSSG (p < 0.05). Significant gender*time*treatment interaction (p = 0.043) for total glutathione was found increasing at the end of the WM period in male but not changing in female. Total glutathione and GSH/GSSG ratio (p < 0.05) were lower in smokers. Hypercholesterolemics presented higher uric acid (p < 0.05) but no enzyme activities or substrate concentrations were different from those of normocholesterolemics.

CONCLUSIONS

The WM tested appears to be a functional food as it improved the antioxidant status of increased CHD-risk volunteers. Despite its high energy content, it also appears adequate for overweight and obese people because did not exert negative effect upon body weight.

Sex-specific QTL effects on variation in paraoxonase 1 (PON1) activity in Mexican Americans

Paraoxonase 1 (PON1), a high-density lipoprotein-associated enzyme known to protect against cellular damage from toxic agents, may also have antioxidant properties. PON1 activity levels have been reported to differ by sex in human and animal studies with females exhibiting higher basal levels. We measured PON1 activity frozen serum for 1,406 individuals in over 40 extended pedigrees from the San Antonio Family Heart Study (SAFHS). We used a maximum likelihood-based, variance decomposition approach implemented in SOLAR to test for genotype-by-sex (G x S) interaction on variation in PON1 activity and to determine if any of the four PON1 quantitative trait loci (QTL) previously reported by us for this population might account for sex differences in PON1 activity levels. The residual additive genetic correlation (rho(G) = 0.82) between males and females is significantly different from 1 (P = 0.009), suggesting that some of the genes that influence PON1 activity act differently in females and males or, possibly, that a different combination of genes influences this trait in each sex. In addition to the QTL at or near the PON structural locus on 7q21-22, three other potential QTLs were evaluated for sex-specific effects: one each on chromosomes 12, 17 and 19. The QTL on chromosome 17 (LOD = 2.32, P = 0.0003; flanked by microsatellite marker loci D17S974 and D17S969) shows a significant (P = 0.005) sex-specific effect on PON1 activity; accounting for 6% of the additive genetic variance in males and 20% in females. This study represents the first formal statistical genetic test for G x S interactions on normal quantitative variation in PON1 activity in humans.

The strange case of Dr HDL and Mr HDL: Does a NO’s story illuminate the mystery of HDL’s dark side uncovered by Dr HDL’s drug targeting CETP?

Recently, the first large-scale morbidity and mortality trial (ILLUMINATE) to evaluate the cardiovascular end points of a CETP inhibitor (torcetrapib) has been prematurely stopped because the mortality was significantly increased in the treated group. Why torcetrapib caused excess death is not known. Based on the fact that HDL interacts with endothelial nitric oxyde synthase (eNOS) and nitric oxide (NO) secretion, which partly controlled blood pressure and than torcetrapib could increase blood pressure among some patients, we hypothesize that CETP inhibition could have significantly inhibit eNOS. CETP inhibition would have enlarged HDL size resulting in a deficit in the interaction between HDL and the Scavenger Receptor class B type I (SR-BI), which is an important link between HDL and eNOS activation. We suggest than the deficit in NO secretion would have been sufficient among all patients to induce a destabilization of the plaques of atheroma, but could have induced a pathogenic increase in blood pressure only in patients whose eNOS activity was naturally weak due to genetic polymorphisms of this enzyme. We also hypothesize that the increase in HDL levels, induced by CETP inhibition, coupled with the capacity of HDL to induce endothelin-1 secretion would have aggravated the cardiovascular risks under this CETP inhibitor treatment.

Time-dependent modulation of rat serum paraoxonase 1 activity by fasting

High-density lipoprotein-associated paraoxonase 1 (PON1) protects the endothelium from the pro-oxidant activity of oxidised low-density lipoprotein. Whereas fasting has been related to increased oxidative stress, intermittent fasting and caloric restriction are associated to increased resistance to oxidative injury. Taking into consideration that serum PON1 activity is modulated by a restriction of caloric intake and because there is no evidence regarding PON1 response to total food deprivation, we investigated whether PON1 activity is involved in the response aimed to counteract the greater oxidative stress associated to fasting and whether serum PON1 activity is altered by the length of food deprivation. Male Wistar rats were randomly divided into five groups: fed and 6-, 12-, 24- or 48-h fasted rats. Serum PON1 activity increases within the first hours of fasting, representing a prompt adaptation designed to attenuate blood lipid peroxidation that cannot be sustained when fasting is prolonged. This PON1 response to early fasting could be part of the mechanisms triggered by periodically repeated short periods of food deprivation - intermittent fasting - which result in increased resistance to stress by stimulating antioxidant defences.

Association between paraoxonase activity and lipid levels in patients with premature coronary artery disease

BACKGROUND

South Asians, especially Indians show increased risk for atherosclerosis and have the higher mortality rates due to coronary artery disease. The increasing incidence of coronary artery disease in young patients is possibly due to industrialization, stress of life, less exercise and increasing incidence of smoking and other factors. We attempted to determine an independent association of paraoxonase with coronary artery disease in young patients.

METHOD

The lipid profile and serum paraoxonase were investigated in 120 angiographically-proven premature coronary artery disease patients (99 males and 21 females, all <45 years) with diabetes mellitus, smoking, hyperlipidemia, obesity, hypertension along with 50 (41 male and 9 female) normal subjects and compared.

RESULTS

A significant increase was observed in the concentrations of total cholesterol, triglycerides and LDL cholesterol in premature coronary artery disease patients. The activities of paraoxonase and HDL cholesterol concentrations decreased in coronary artery disease patients compared to control subjects.

CONCLUSION

A paraoxonase was an independent (p<0.001, OR 14.9 and 95% CI 5.6-35.9) risk factor for premature coronary artery disease patients along with lipid profiles. Paraoxonase activity should be evaluated in all coronary artery disease patients in the absence of traditional risk factors.

Probucol up-regulates paraoxonase 1 expression in hepatocytes of hypercholesterolemic rabbits

Paraoxonase 1 (PON1), an HDL-associated enzyme, has anti-oxidative property. Probucol, a hydrophobic antioxidant drug, inhibits progression of atherosclerosis and post-angioplasty restenosis. However, the mechanism by which probucol affects atherosclerosis is not completely understood. Sixteen rabbits fed with high cholesterol diet for 8 weeks were randomly divided into two groups: (1) starch group (n = 8): maintained high cholesterol diet plus starch (500 mg/kg/d) for 6 weeks; (2) probucol group (n = 8): the same cholesterol diet plus probucol (500 mg/kg/d) for 6 weeks. Control group (n = 8) was fed with normal diet for 14 weeks. The classic in-situ two-step perfusion of the liver with collagenase IV was used to isolate the parenchymal hepatocytes. The total activity of superoxide dismutase (SOD) and malondialdehyde (MDA) and PON1 concentrations in serum were measured after 0, 8, and 14 weeks of feeding. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the mRNA expression of PON1. Compared with control group, rabbits fed with high cholesterol diet showed higher levels of serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C), all of which were significantly reduced by probucol. Probucol significantly decreased the MDA concentration but was ineffective on SOD activity. High cholesterol diet decreased serum PON1 concentration and down-regulated PON1 mRNA expression in hepatocytes. Probucol significantly increased serum PON1 level and up-regulated the mRNA expression of PON1 as compared with starch group (0.65 +/- 0.06 versus 0.46 +/- 0.05, P = 0.001). The PON1 concentration is negatively associated with MDA concentration (r = -0.86, P = 0.003) but not with the level of HDL-C. In conclusion, probucol decreased MDA concentration, and increased PON1 serum level as well as mRNA expression in hepatocytes, which may help us to understand its antioxidant and anti-atherogenic effects.

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

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

Paraoxonase 1 Q192R (PON1-192) polymorphism is associated with reduced lipid peroxidation in healthy young men on a low-carotenoid diet supplemented with tomato juice

The HDL-bound enzyme paraoxonase (PON) protects LDL from oxidation and may therefore attenuate the development of atherosclerosis. We examined the effect of tomato and carrot juice consumption on PON1 activity and lipid peroxidation in healthy young volunteers with different PON1-192 genotypes (Q/R substitution at position 192). In this randomized cross-over study twenty-two healthy, non-smoking men on a low-carotenoid diet received 330 ml/d tomato juice (37.0 mg lycopene, 1.6 mg beta-carotene) or carrot juice (27.1 mg beta-carotene, 13.1 mg alpha-carotene) for 2 weeks. Intervention periods were preceded by 2-week low-carotenoid intake. We determined the PON1-192 genotype by restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) and measured ex vivo LDL oxidation (lag time), plasma malondialdehyde and PON1 activity at the beginning and end of each intervention period. At baseline, lag time was higher (P<0.05) in QQ (111 (sd 9) min) than in QR/RR subjects (101 (sd 8) min). Neither tomato nor carrot juice consumption had significant effects on PON1 activity. However, tomato juice consumption reduced (P<0.05) plasma malondialdehyde in QR/RR (Delta: -0.073 (sd 0.11) micromol/l) as compared to QQ subjects (Delta:+0.047 (sd 0.13) micromol/l). Carrot juice had no significant effect on malondialdehyde irrespective of the PON1-192 genotype. Male volunteers with the QR/RR genotype showed an increased lipid peroxidation at baseline. Although tomato and carrot juice fail to affect PON1 activity, tomato juice intake reduced lipid peroxidation in healthy volunteers carrying the R-allele of the PON1-192 genotype and could thus contribute to CVD risk reduction in these individuals.

Paraoxonase 1 (PON1) is present in postprandial chylomicrons

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

Modulation of paraoxonase (PON1) activity

Paraoxonase 1 (PON1) is a serum enzyme closely associated with high density lipoprotein (HDL). PON1 hydrolyzes several organophosphorus compounds used as insecticides, as well as nerve agents; it metabolizes toxic oxidized lipids associated with both low density lipoprotein (LDL) and HDL; and it can hydrolyze a number of lactone-containing pharmaceutical compounds, inactivating some, while activating others. Serum PON1 activity in a given population can vary by 40-fold. Though most of this variation can be explained by polymorphisms in the coding region (Q192R) and the 5' regulatory region (T-108C), modulation of PON1 by a variety of other factors should be taken into account, including other polymorphisms recently discovered but not yet characterized. This paper examines the major factors (environmental chemicals, drugs, smoking, alcohol, diet, age, disease conditions) that have been shown to modulate PON1 activity in either direction. As PON1 plays a protective role in organophosphate toxicity, and, because of its antioxidant capacity, in cardiovascular disease, a better understanding of how PON1 can be modulated by environmental factors has potential toxicological and clinical consequences.

Dietary antioxidants and paraoxonases against LDL oxidation and atherosclerosis development

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

Genetic and environmental factors modulating serum concentrations and activities of the antioxidant enzyme paraoxonase-1

PON1 (paraoxonase-1) is an HDL (high-density lipoprotein)-associated enzyme capable of hydrolysing diverse substrates from OP (organophosphate) toxins to oxidized phospholipids. As such, it has been linked with both the prevention of OP poisoning and inhibition of atherosclerosis initiated by oxidatively modified LDL (low-density lipoprotein). Mice deficient in PON1 are more susceptible to OP poisoning and oxidative stress and more prone to develop atherosclerosis than their wild-type siblings. There are a number of polymorphisms in the PON1 gene which affect serum PON1 activity and concentration. Many (but not all) studies in human populations have suggested that these polymorphisms may be a risk factor for atherosclerosis. The serum concentration of PON1 across the general population is highly variable and there is some debate as to whether genotype or phenotype (i.e. the quantity or quality of the enzyme) is most accurately associated with risk of disease development. What is clear is that factors influencing serum levels of PON1, be they genetic or environmental, will, in turn, affect the capacity of HDL to protect LDL from oxidation and, consequently, may be linked to atherosclerosis. This review will focus on mechanisms which determine the serum concentration of PON1, including gene expression and genetic polymorphisms, protein secretion and association with HDL, pharmacological and environmental factors.

Paraoxonase 1 and atherosclerosis: is the gene or the protein more important?

The oxidation of low-density lipoprotein (LDL) is centrally involved in the initiation and progression of atherosclerosis. High-density lipoprotein (HDL) paraoxonase 1 (PON1) retards the oxidation of LDL and is a major antiatherosclerotic component of HDL. The PON1 gene contains a number of functional polymorphisms in both the coding and the promoter regions, which affect either the level or the substrate specificity of PON1. Genetic case-control and prospective studies conducted to date have produced confusing results. Meta-analysis of these studies indicates no simple relationship between the PON1 polymorphisms and the presence of coronary heart disease (CHD). However, at the present moment in time, it seems that PON1 status, i.e., activity and/or concentration, is more closely related to CHD, and indeed, PON1 has shown to be an independent risk factor for CHD in a prospective study, compared to the genetic polymorphisms. PON1 levels can also be modulated by environmental\lifestyle and possibly pharmaceutical factors. Larger, better designed, preferably prospective studies are needed to determine further the association of PON1 genetic polymorphisms and status with CHD.

Paraoxonases 1, 2, and 3, oxidative stress, and macrophage foam cell formation during atherosclerosis development

Paraoxonases PON1 and PON3, which are both associated in serum with HDL, protect the serum lipids from oxidation, probably as a result of their ability to hydrolyze specific oxidized lipids. The activity of HDL-associated PON1 seems to involve an activity (phospholipase A2-like activity, peroxidase-like activity, lactonase activity) which produces LPC. To study the possible role of PON1 in macrophage foam cell formation and atherogenesis we used macrophages from control mice, from PON1 knockout mice, and from PON1 transgenic mice. Furthermore, we analyzed PON1-treated macrophages and PON1-transfected cells to demonstrate the contribution of PON1 to the attenuation of macrophage cholesterol and oxidized lipid accumulation and foam cell formation. PON1 was shown to inhibit cholesterol influx [by reducing the formation of oxidized LDL (Ox-LDL), increasing the breakdown of specific oxidized lipids in Ox-LDL, and decreasing macrophage uptake of Ox-LDL]. PON1 also inhibits cholesterol biosynthesis and stimulates HDL-mediated cholesterol efflux from macrophages. PON2 and PON3 protect against oxidative stress, with PON2 acting mainly at the cellular level. Whereas serum PON1 and PON3 were inactivated under oxidative stress, macrophage PON2 expression and activity were increased under oxidative stress, probably as a compensatory mechanism against oxidative stress. Intervention to increase the paraoxonases (cellular and humoral) by dietary or pharmacological means can reduce macrophage foam cell formation and attenuate atherosclerosis development.

The role of paraoxonase 1 activity in cardiovascular disease: potential for therapeutic intervention

The antioxidant activity of high density lipoprotein (HDL) is largely due to the paraoxonase (PON) 1 located on it. Experiments with transgenic PON1 knockout mice indicate the potential for PON1 to protect against atherogenesis. This effect of HDL in decreasing low density lipoprotein (LDL) lipid peroxidation is maintained for longer than that of antioxidant vitamins and could therefore be more protective. Several important advances in the field of PON research have occurred recently, not least the discovery that two other members of the PON gene family -PON2 and PON3 - may also have important antioxidant properties. Significant advances have been made in understanding the basic biochemical function of PON1 and the discovery of possible modulators of its activity. Case-control studies of PON1 activity and coronary heart disease (CHD) have shown a clear association between CHD and low serum PON1 activity. This relationship has been further strengthened by the publication of the first prospective study showing low serum PON1 activity to be an independent predictor of new CHD events. Furthermore, decreased CHD risk has been revealed by meta-analysis to be associated with the polymorphisms of PON1, which are most active in lipid peroxide hydrolysis. Although this is likely to be an underestimate of the true contribution of PON1 to CHD (because these polymorphisms explain only a small component of the variation in PON1 activity), it is important because genetic influences are unlikely to be confounded by other factors linked with both CHD and diminished PON1 activity. PON1 is being extensively researched and it is hoped that therapeutic approaches will emerge to increase its activity. Clinical trials of these, if successful, will not only provide a novel means of preventing atherosclerosis, but also provide a more satisfactory means of testing the oxidant hypothesis of atherosclerosis than antioxidant vitamin supplementation has proved to be.

Polygonatum Rhizoma Affects Antioxidant Defense Systems Without Changing mRNA Expression in Diet-Induced Hypercholesterolemic Rabbits

This study was conducted to determine the antioxidant effects of a Polygonatum extract compared with the major antioxidant, vitamin E, in rabbits fed a high-cholesterol diet. Rabbits were given a high-cholesterol (0.5%, wt/wt) diet with vitamin E (0.03%, wt/wt) or a Polygonatum extract (0.05%, wt/wt) for 8 weeks. The body weight gain (g/week) was only significantly increased only in the high-cholesterol-fed control group, yet the relative liver weight was significantly lower in the Polygonatum group compared with the other groups. The supplementation of vitamin E and Polygonatum extract led to an increase in the hepatic catalase (CAT) activity without any change in superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities. Hepatic total glutathione content was significantly higher in the Polygonatum group than in the other groups. The level of hepatic mitochondrial H(2)O(2) was significantly lower in the two supplemented groups compared with the control group, whereas the level of cytosolic H(2)O(2) was only significantly lower in the Polygonatum group than in the control group. The level of plasma thiobarbituric acid-reactive substances (TBARS) was only significantly lower in the vitamin E group, whereas the level of hepatic TBARS was slightly lower in the Polygonatum group than in the other groups. In the case of the high-density lipoprotein-related antioxidant enzyme, vitamin E supplementation produced the highest plasma paraoxonase (PON) activity compared with the other groups, although there was no difference in the hepatic PON activity among the groups. Meanwhile, the plasma vitamin E concentration was significantly higher in the vitamin E and Polygonatum groups than in the control group; however, plasma vitamin A concentration did not differ significantly between the groups. As regards the mRNA expressions of hepatic antioxidant enzymes, the vitamin E and Polygonatum extract supplementation had no effect on the SOD, CAT, GSH-Px, and PON mRNA expression. Accordingly, these results indicate that the Polygonatum extract had a positive effect on the antioxidant defense system based on decreasing the content of hepatic TBARS and hydrogen peroxide, increasing the CAT activity and total glutathione level in the liver, and sparing the plasma vitamin E. Thus, further studies on the functional components in Polygonatum extract and their biological efficacies are needed.

The effects of lipid-lowering therapy on paraoxonase activities and their relationships with the oxidant???antioxidant system in patients with dyslipidemia

BACKGROUND

Atorvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, which is used for lipid-lowering therapy, is an effective statin modulating process involved in atherosclerosis. Paraoxonase (PON) associated with high-density lipoprotein (HDL) has been postulated to have a role in protecting low-density lipoprotein (LDL) against oxidative modification. Oxidation of serum LDL is an important early step in the development of atherosclerosis and auto-antibodies against oxidized LDL (AuAb-oxLDL) reflect in-vivo LDL oxidation.

DESIGN AND METHODS

To examine the effect of atorvastatin (10 mg/day) therapy on PON activity in serum and HDL, the study group included 40 patients with dyslipidemia (19 women and 21 men), 25 of whom had hypercholesterolemia and of 15 of whom had mixed-type hyperlipidemia. By taking blood samples from the patients, levels of serum lipids, lipid peroxidation product as malondialdehyde (MDA), total antioxidant status (TAS) and AuAb-oxLDL and the activities of PON in serum and isolated HDL were determined.

RESULTS

The mean levels of total cholesterol, triglyceride, LDL-cholesterol, MDA and AuAb-oxLDL were decreased while HDL-cholesterol and TAS were increased significantly after lipid-lowering therapy in patients with dyslipidemia. On the other hand, PON activities in serum and HDL were increased significantly. The percentage increase in serum PON activity was associated significantly with the percentage decrease in serum AuAb-oxLDL (r=-0.32, P=0.047) and that of HDL PON activity was associated with the percentage increase in HDL-cholesterol level after atorvastatin therapy (r=0.52, P=0.001). The therapy was more effective in increasing PON activity in patients with HDL levels above 35 mg/dl.

CONCLUSION

It was concluded that atorvastatin therapy in dyslipidemic patients decreases the level of oxidative stress and increases PON activity, especially in patients with HDL levels above 35mg/dl.

High density lipoprotein can modulate the inhibitory effect of oxLDL on prostacyclin generation by rat aorta in vitro

To examine the effect of oxidized low density lipoprotein (oxLDL) on prostacyclin (PGI2) generation by rat aorta in vitro and whether high density lipoprotein (HDL) has any protective effect against the inhibition of PGI2 generation induced by oxLDL is the objective of this study. Preincubation of aortas with oxLDL resulted in significant inhibition of PGI2 generation compared to preincubation with normal low density lipoprotein (nLDL) or buffer only. The inhibitory effect of oxLDL resided in its lipid moiety while the lipid fraction of nLDL showed no effect. Aortas preincubated with 10 microg/ml of lyso phosphatidycholine (lyso PC) also showed 30% inhibition of PGI2 generation, indicating that lyso PC was among the lipid components of oxLDL which inhibited PGI2 generation. Preincubation of aortas with a mixture of HDL and oxLDL at a ratio of 10:1 showed a significant recovery of PGI2 generation compared to aortas preincubated with only oxLDL, indicating a protective role for HDL. When HDL was incubated with oxLDL the transfer of lyso PC from oxLDL to HDL suggested that HDL trapped lyso PC from oxLDL thus preventing it from acting on the aorta. However, when a mixture of HDL and oxLDL at a ratio of 3:1 was preincubated with aortas, no protective effect of HDL was observed. Preincubation of aortas with a mixture of HDL plus oxLDL at a ratio of 8:1, which was incubated for 1 h at 37 degrees C, produced significantly less PGI2 than aortas preincubated only with oxLDL, indicating that HDL under these conditions was not protective but even enhanced the inhibitory effect of oxLDL. Similarly, aortas preincubated with HDL plus whole oxLDL (at a ratio of 10:1); containing all the small molecular weight oxidation products and characterized by high levels of thiobarbituric acid reactive substance (TBARS) and lipid hydroperoxides; produced significantly less PGI2 than aortas preincubated with whole oxLDL. These results were evaluated in light of possible modification of HDL by oxLDL and its lipid oxidation products such as aldehydes and lipid peroxides. The modified HDL can add more lipid peroxides and increase the effectiveness of lipid peroxides originally present in oxLDL.

The transgenic rabbit as model for human diseases and as a source of biologically active recombinant proteins

Until recently, transgenic rabbits were produced exclusively by pronuclear microinjection which results in additive random insertional transgenesis; however, progress in somatic cell cloning based on nuclear transfer will soon make it possible to produce rabbits with modifications to specific genes by the combination of homologous recombination and subsequent prescreening of nuclear donor cells. Transgenic rabbits have been found to be excellent animal models for inherited and acquired human diseases including hypertrophic cardiomyopathy, perturbed lipoprotein metabolism and atherosclerosis. Transgenic rabbits have also proved to be suitable bioreactors for the production of recombinant protein both on an experimental and a commercial scale. This review summarizes recent research based on the transgenic rabbit model.

[Paraoxonase, something more than an enzyme?]

Coronary heart disease is one of the major causes of death in developed countries. The hypothesis that peroxidation of low density lipoproteins (LDL) may be the initial step of the atherosclerotic process has promoted numerous studies aimed at investigating the mechanisms by which the body protects itself from such oxidative phenomena. Among these mechanisms we find the paraoxanase (PON) enzyme, which is quite thriving the last decades. This enzyme is principally associated with high density lipoproteins (HDL) but it also seems to help LDL to recover their antioxidant status. This paper reviews different aspects concerning the mechanisms implicated in the induction and activity of this enzyme, as well as its production, attachment to HDL, and modifications of its activity due to external factors. The use of genetic techniques, the study of the polimorphisms of the PON enzyme and the possibility of increasing paraoxonase activity by means of pharmacotherapy and/or dietary therapy open new perspectives with regard to coronary heart disease treatment and prevention.

Two cinnamate derivatives produce similar alteration in mRNA expression and activity of antioxidant enzymes in rats

Cinnamate is a widespread secondary metabolite of phenolic compound synthesized by plants for defensive purposes. The current study was designed to investigate the effect of two structurally related cinnamate derivatives, 4-hydroxycinnamate and 3-(4-hydroxyphenyl)propionic acid (HPP), on the mRNA expression and activity of antioxidant enzymes in high-cholesterol-fed rats. Male rats were fed a 1 g/100 g high-cholesterol diet with supplements of either 4-hydroxycinnamate or HPP (0.135 mmol/100 g diet) for 6 weeks. The plasma paraoxonase activity was found to be higher in the cinnamate-derivative-supplemented groups than in the control group. The erythrocyte superoxide dismutase (SOD) and catalase (CAT) activities, plus glutathione (GSH) level, were all significantly higher in the 4-hydroxycinnamate- and HPP-supplemented groups than in the control group. However, both 4-hydroxycinnamate and HPP supplementation significantly lowered the hepatic activities and mRNA expression of CAT and glutathione peroxidase (GSH-Px) compared to the control group. The hepatic mRNA expression and activity of SOD did not differ between the groups. The hepatic thiobarbituric acid reactive substances (TBARS) level was significantly lowered by the 4-hydroxycinnamate and HPP supplementation. Accordingly, these results indicate that supplementation by 4-hydroxycinnamate and HPP would seem to enhance the antioxidative defense of erythrocyte. Both HPP and 4-hydroxycinnamate would appear to be beneficial in improving the function of antioxidative enzymes on a molecular level in high-cholesterol-fed rats.

Transgenic rabbits as therapeutic protein bioreactors and human disease models

Genetically modified laboratory animals provide a powerful approach for studying gene expression and regulation and allow one to directly examine structure-function and cause-and-effect relationships in pathophysiological processes. Today, transgenic mice are available as a research tool in almost every research institution. On the other hand, the development of a relatively large mammalian transgenic model, transgenic rabbits, has provided unprecedented opportunities for investigators to study the mechanisms of human diseases and has also provided an alternative way to produce therapeutic proteins to treat human diseases. Transgenic rabbits expressing human genes have been used as a model for cardiovascular disease, AIDS, and cancer research. The recombinant proteins can be produced from the milk of transgenic rabbits not only at lower cost but also on a relatively large scale. One of the most promising and attractive recombinant proteins derived from transgenic rabbit milk, human alpha-glucosidase, has been successfully used to treat the patients who are genetically deficient in this enzyme. Although the pronuclear microinjection is still the major and most popular method for the creation of transgenic rabbits, recent progress in gene targeting and animal cloning has opened new avenues that should make it possible to produce transgenic rabbits by somatic cell nuclear transfer in the future. Based on a computer-assisted search of the studies of transgenic rabbits published in the English literature here, we introduce to the reader the achievements made thus far with transgenic rabbits, with emphasis on the application of these rabbits as human disease models and live bioreactors for producing human therapeutic proteins and on the recent progress in cloned rabbits.

Atheroprotective effects of high-density lipoproteins

Observational studies provide overwhelming evidence that a low high-density lipoprotein (HDL)-cholesterol level increases the risk of coronary events, both in healthy subjects and in patients with coronary heart disease. Based on in vitro experiments, several mechanistic explanations for the atheroprotective function of HDL have been suggested. However, few of these were verified in vivo in humans or in experiments with transgenic animals. The HDL functions currently most widely held to account for the antiatherogenic effect include participation in reverse cholesterol transport, protection against endothelial dysfunction, and inhibition of oxidative stress. This review summarizes current views on the molecular mechanism underlying these atheroprotective effects of HDL.

Serum paraoxonase: effect of the apolipoprotein composition of HDL and the acute phase response

Genetic variations of paraoxonase (PON) correlate with HDL cholesterol and apolipoprotein A-I (apoA-I), suggesting antiatherogenic properties. Atherosclerosis occurs naturally in humans and rabbits but not in mice. We compared variations of PON arylesterase activity (PON AEase, phenylacetate substrate) in humans, rabbits, and mice. In humans and rabbits, >95% of PON AEase is HDL associated. In mice, about 30% of PON AEase is lipid poor. In the absence of apoA-I in mice, total PON AEase is reduced and >60% is lipid poor. PON AEase level and distribution is restored in apoA-I-/- mice injected with adenoviruses encoding human apoA-I and in transgenic mice expressing human apoA-I at a steady-state level. Thus, while apoA-I is not required for the HDL association of PON AEase, induced variations in apoA-I correlate with changes in HDL-associated, but not lipid-poor, PON AEase. PON AEase associates only with apoA-I- or apoE-containing HDL but not VLDL. In the absence of both apoA-I and apoE, PON AEase is all-lipid-poor. PON AEase is displaced from HDL by ultracentrifugation and following incubation with serum amyloid A. Variations in the PON distribution between HDL and lipid-poor fractions may have important consequences in its antioxidant activity and in atherogenesis.