Paraoxonase gene polymorphism in Japanese subjects with coronary heart disease

High expressor paraoxonase PON1 gene promoter polymorphisms are associated with reduced risk of vascular disease in younger coronary patients

Human paraoxonase-1 is hypothesised to protect serum lipoproteins from oxidative stress. Decreased serum activity of paraoxonase-1 in animal models is associated with an increased risk of vascular disease and has been linked to the anti-oxidant capacity of the enzyme. Promoter polymorphisms of the human paraoxonase-1 gene strongly influence serum concentrations of the enzyme. The present study examined the hypothesis that promoter polymorphisms may be genetic risk factors for vascular disease in man. Genotypes arising from the promoter C(-907)G polymorphism were analysed in the ECTIM2 population. The global odds ratio for myocardial infarction, comparing the high expressor GG genotype to other genotypes, was 0.77 (0.61-0.97) (P=0.024). The association with the promoter genotype was more pronounced in the youngest age group (odds ratio 0.52 (0.31-0.87), P=0.012) and was progressively lost with age (respectively 50 years to <60 years, P=0.26; >60 years, P=0.45). There was no association between the promoter genotypes and serum lipids. The data are consistent with the high expressor promoter genotype being linked to reduced risk of myocardial infarction. The influence of the genotype may be compromised in older patients.

The Paraoxonase-1 Codon192 Polymorphism Is Associated with Fasting Total Cholesterol and LDL-Cholesterol Concentrations only in Postmenopausal Women.The REGICOR Study

Paraoxonase-1 (PON1) is a high-density lipoprotein (HDL)-linked enzyme which appears to protect low-density lipoproteins (LDL) from oxidation. PON1 activity is associated with variation at the PON1 gene locus, specifically the common amino acid polymorphism at codon 192, for which the Q192 allele specifies low activity and the R192 allele specifies high activity. We investigated the association between the PON1 codon 192 polymorphism and fasting concentrations of glucose, lipids, lipoproteins and PON1 activity in 1380 subjects (724 men and 656 women). Several anthropometric and environmental factors were assessed in the present study. The PON1 Q192 allele frequency was 0.70 and 0.68 in men and women, respectively. In women, but not in men, significant associations were found between the PON1 codon 192 genotype and both total and LDL-cholesterol (p=0.004 and p=0.008, respectively), and subgroup analysis indicated that this relationship was predominant in postmenopausal women. Specifically, the Q192 allele was associated with increased total and LDL-cholesterol concentrations. Furthermore, these lipoprotein variables were higher among postmenopausal women with Q192/Q192 and Q192/R192 genotypes than in premenopausal women with the same genotypes (p<0.001). The findings suggest a gender-specific lipoprotein-genotype association with PON1 codon 192 genotypes in this study sample.

Polymorphic metabolizing genes and susceptibility to atherosclerosis among cigarette smokers

Atherosclerosis (AR) is the leading cause of morbidity and mortality in the US and cigarette smoking is a major contributing factor to the disease. Like cigarette smoking in lung cancer, genetic susceptibility may be an important factor in determining who is more likely to develop AR. However, the current emphasis has been on susceptibility based on altered cardiovascular homeostasis. In this investigation, we studied 120 AR patients and 90 matched controls to elucidate the association between polymorphisms in some metabolizing genes (GSTM1, GSTT1, CYP2E1, mEH, PON1, and MPO) and susceptibility to AR. We found that the GSTT1 null allele and the fast allele of mEH(*) (exon 4) are associated with risk for AR. Furthermore, the combined genotypes GSTM1 null/ CYP2E1(*)5B, GSTM1 null/mEH YY, and GSTT1 null/mEH YY are significantly associated with susceptibility to AR (OR = 15.42, 95% CI = 1.33-77.93, P = 0.021; OR = 3.48, 95% CI = 1.63-8.04, P = 0.0008; OR = 3.4; 95% CI = 0.99-17.38, P = 0.05; respectively). We have also conducted cytogenetic analysis to elucidate if induction of chromosome aberrations (CAs) is a biomarker of AR susceptibility. We found that among cigarette smokers (AR patients and smoker controls), individuals having the GSTM1 null allele had a significantly higher frequency of CAs compared to those with the normal allele (P < 0.05). This association was not found among nonsmokers. In addition, individuals who had inherited the CYP2E1(*)5B allele exhibited a significantly higher CA frequency (8.0 +/- 0.82) compared to those with the CYP2E1 wild-type genotype (4.31 +/- 0.35). Since the analysis of genetic susceptibility factors is still in its infancy, our study may stimulate additional investigations to understand the roles of genetic susceptibility and cigarette smoking in AR.

Paraoxonase-2 is a ubiquitously expressed protein with antioxidant properties and is capable of preventing cell-mediated oxidative modification of low density lipoprotein

The oxidation of apolipoprotein B-containing lipoproteins and cell membrane lipids is believed to play an integral role in the development of fatty streak lesions, an initial step in atherogenesis. We have previously shown that two antioxidant-like enzymes, paraoxonase (PON)-1 and PON3, are high density lipoprotein-associated proteins capable of preventing the oxidative modification of low density lipoprotein (LDL) (Reddy, S. T., Wadleigh, D. J., Grijalva, V., Ng, C., Hama, S., Gangopadhyay, A., Shih, D. M., Lusis, A. J., Navab, M., and Fogelman, A. M. (2001) Arterioscler. Thromb. Vasc. Biol. 21, 542-547). In the present study, we demonstrate that PON2 (i) is not associated with high density lipoprotein; (ii) has antioxidant properties; and (iii) prevents LDL lipid peroxidation, reverses the oxidation of mildly oxidized LDL (MM-LDL), and inhibits the ability of MM-LDL to induce monocyte chemotaxis. The PON2 protein was overexpressed in HeLa cells using the tetracycline-inducible ("Tet-On") system, and its antioxidant capacity was measured in a fluorometric assay. Cells that overexpressed PON2 showed significantly less intracellular oxidative stress following treatment with hydrogen peroxide or oxidized phospholipid. Moreover, cells that overexpressed PON2 were also less effective in oxidizing and modifying LDL and, in fact, were able to reverse the effects of preformed MM-LDL. Our results suggest that PON2 possesses antioxidant properties similar to those of PON1 and PON3. However, in contrast to PON1 and PON3, PON2 may exert its antioxidant functions at the cellular level, joining the host of intracellular antioxidant enzymes that protect cells from oxidative stress.

Paraoxonase genotype modifies the effect of pravastatin on high-density lipoprotein cholesterol

Paraoxonase (PON) is an enzyme carried by high-density lipoprotein cholesterol (HDL-C). Two gene polymorphisms leading to amino acid substitutions of methionine for leucine at position 55 (M/L55) and arginine for glutamine at position 192 (R/Q192) modulate the activity of the enzyme and possibly also lipid and apolipoprotein concentrations. Our purpose was to examine the effect of the PON genotype on HDL-C and apolipoprotein AI (apo AI) responses to pravastatin treatment. Fifty-one mildly hypercholesterolemic male subjects (mean age 35 +/- 4 years) were enrolled by this prospective, randomized, double-blind study. Lipid concentrations were measured at baseline and after 6 months of pravastatin (n = 25) or placebo (n = 26) therapy. Low active (MM, ML or QQ) and high active (LL or RQ, RR) PON genotype groups were related to lipid and apolipoprotein concentration changes. Pravastatin increased the apo AI concentration 12% (P = 0.017, RANOVA) and tended to increase the HDL-C concentration (P = 0.095, RANOVA) in R allele carriers but not in QQ homozygotes. Significant predictors of the change in apo AI concentration during pravastatin treatment were R/Q192 genotype (P = 0.002), apo AI concentration at baseline (P = 0.002) and M/L55 genotype (P = 0.042). Correspondingly, R/Q192 (P = 0.009) and M/L55 (P = 0.050) genotypes were the statistically significant determinants of HDL-C concentration change. The PON genotype thus modifies the effect of pravastatin on serum HDL-C and apo AI concentrations. This could partly explain the contradictory results obtained from previous studies on the effects of statins on the serum HDL-C concentration.

Serum paraoxonase and arylesterase activities in hemodialysis patients

Cardiac death from atherosclerosis is common in hemodialysis patients. Human serum paraoxonase (PON1), an esterase, is associated with high-density lipoprotein and inhibits the susceptibility to oxidization of low-density lipoprotein (LDL). The PON1 genetic polymorphisms of 192 Gln/Arg and 55 Leu/Met in the amino acid sequence are partly involved in the PON1 enzyme activity. We investigated the PON1 enzyme activities for paraoxon (paraoxonase) and phenylacetate (arylesterase), and the two polymorphisms in 96 patients undergoing hemodialysis and in 136 normal controls. Both activities were significantly lower in the hemodialysis patients than in the controls (97+/-43 vs 155+/-57 micromol/min/l for paraoxonase, and 71+/-20 vs 92+/-22 mmol/min/l for arylesterase, respectively). There was no difference in the distribution of the two polymorphisms between patients and controls, and in every subgroup classified by the polymorphisms, both paraoxonase and arylesterase activities were lower in patients than in controls. This suggested that the enzyme activities of PON1 decreased in hemodialysis patients, independent of the genetic polymorphism. The decrease in PON1 enzyme activity in hemodialysis patients may modify a susceptibility to oxidization of LDL, which contributes to an acceleration of atherosclerosis.

Genetic variations of the paraoxonase gene in patients with coronary artery disease

OBJECTIVES

Paraoxonase (PON) plays an important role in preventing low density lipoprotein (LDL) oxidation and thus may be involved in protection against atherosclerosis. Several studies have suggested that genetic variations of the PON gene are associated with plasma HDL levels and coronary artery disease (CAD). This study was conducted to elucidate the association between three polymorphisms of the PON1 and PON2 genes and Korean patients with CAD.

DESIGN AND METHODS

One hundred ninety-one patients with CAD and 113 age-matched normal controls were examined by polymerase chain reaction (PCR). The PCR products were analyzed for PON polymorphisms by restriction enzyme digestion.

RESULTS

There was linkage disequilibria between each polymorphism pair in the CAD and control groups. The Hsp92II polymorphism at codon 54 of the PON1 gene was positively associated with HDL-cholesterol levels in the control group (p = 0.02). An association between the AlwI polymorphism and HDL-cholesterol level appeared statistically significant in women of the normal group (p = 0.04). In addition, the DdeI and AlwI polymorphisms were positively associated with HDL (p = 0.02) and LDL (p = 0.03) levels in men of the CAD group, respectively.

CONCLUSIONS

Our study suggested a gene-gene interaction between the PON1 and PON2 polymorphisms for CAD risk. However, we could not exclude the possibility that these polymorphisms may have linkage disequilibrium with a tightly linked PON3 locus or significant atherosclerotic alleles of nearby genes. Family studies may, therefore, help to confirm the role of the PON polymorphism for CAD risk.

Paraoxonase status in coronary heart disease: are activity and concentration more important than genotype?

Human serum paraoxonase (PON1) hydrolyzes oxidized lipids in low density lipoprotein (LDL) and could therefore retard the development of atherosclerosis. In keeping with this hypothesis, several case-control studies have shown a relationship between the presence of coronary heart disease (CHD) and polymorphisms at amino acid positions 55 and 192 of PON1, which we associated with a decreased capacity of PON1 to protect LDL against the accumulation of lipid peroxides, but some other studies have not. However, the PON1 polymorphisms are only 1 factor in determining the activity and concentration of the enzyme. Only 3 of the previous 18 studies directly determined PON1 activity and concentration. Therefore, we studied PON1 activity, concentration, and gene distribution in 417 subjects with angiographically proven CHD and in 282 control subjects. We found that PON1 activity and concentration were significantly lower in subjects with CHD than in control subjects (activity to paraoxon 122.8 [3.3 to 802.8] versus 214.6 [26.3 to 620.8] nmol. min(-1). mL(-1), P<0.001; concentration 71.6 [11.4 to 489.3] versus 89.1 [16.8 to 527.4] microg/mL, P<0.001). There were no differences in the PON1-55 and -192 polymorphisms or clusterin concentration between patients with CHD and control subjects. These results indicate that lower PON1 activity and concentration and, therefore, the reduced ability to prevent LDL lipid peroxidation may be more important in determining the presence of CHD than paraoxonase genetic polymorphisms.

Paraoxonase gene polymorphisms and plasma oxidized low-density lipoprotein level as possible risk factors for exudative age-related macular degeneration

PURPOSE

Paraoxonase (E.C.3.1.1.2) is a polymorphic protein shown to prevent low-density lipoprotein oxidation. Our purpose is to evaluate the hypothesis that paraoxonase gene polymorphisms and plasma oxidized low-density lipoprotein level play a role in the occurrence of exudative age-related macular degeneration.

METHODS

We analyzed paraoxonase genotypes (A/B, Gln-Arg192 and L/M, Leu-Met54) and plasma oxidized low-density lipoprotein levels in 72 unrelated Japanese patients with exudative age-related macular degeneration and compared the results with those of 140 age-matched and sex-matched control subjects.

RESULTS

The distribution of paraoxonase 192 and paraoxonase 54 polymorphisms was significantly different between the patients with age-related macular degeneration and control subjects (chi-square = 6.226, P =.0445, and chi-square = 6.863, P =.0323, respectively). The high frequency of the BB genotype at position 192 was observed in the exudative age-related macular degeneration group compared with control subjects (52.8% vs 35.0%, respectively; P =.0127). The high frequency of the LL genotype at position 54 was observed in the patients more than the controls (91.7% vs 77.1%, respectively; P =.0090). The mean (+/- SE) oxidized low-density lipoprotein levels in the patients was significantly higher than in the controls (19.1 +/- 1.0 vs 16.2 +/- 0.6 U/ml, P <.01).

CONCLUSION

These results indicate that the paraoxonase gene polymorphisms may represent a possible genetic risk factor for age-related macular degeneration and that increased plasma oxidized low-density lipoprotein may be involved in the pathogenesis of age-related macular degeneration.

Paraoxonase producing PON1 gene M/L55 polymorphism is related to autopsy-verified artery-wall atherosclerosis

Paraoxonase (PON) is an antioxidative enzyme, which eliminates lipid peroxides. PON has two common polymorphisms (M/L55 and R/Q192) that influence PON concentration and activity. We studied whether the M/L55 or R/Q192 genotype relates with the severity of atherosclerosis of the abdominal aorta, and the mesenteric and common iliac arteries in 123 consecutive autopsy cases (90 males and 33 females, aged 18-93 years). The severity of atherosclerosis in the arteries was evaluated, and the percentage of stenosis was measured. The intimal thickness in the internal elastic lamina (IEL) of the coeliac (CA), superior mesenteric (SMA) and inferior mesenteric (IMA) arteries were measured by light-microscopy. The LL homozygous men had more atherosclerotic plaques and complicated lesions in the common iliac arteries (56.8%) than the M allele carriers (28.3%, P=0.007). In logistic regression analysis, age (P<0.001) and the PON M/L55 genotype (P=0.015) were associated significantly with the severity of atherosclerosis in the common iliac arteries independent of smoking status, R/Q192 genotype, hypertension, diabetes mellitus, BMI and sex. The mean intima of the IMA was significantly thicker (P=0.035) and the number of stenotic lesions in SMAs significantly higher (P=0.008) in the LL homozygous men than M allele carriers. In turn, the R/Q192 genotype was not statistically significantly associated with plaque type, intimal thickness in the IEL or with the number of stenotic lesions. This study demonstrates that PON L55 homozygosity is an independent risk factor for autopsy-verified atherosclerosis in Finns.

Relationship of age-related myocardial infarction risk and Gln/Arg 192 variants of the human paraoxonase1 gene: the REGICOR study

Paraoxonase1 (PON1) seems to exert a major antioxidant effect by removing lipid-peroxidation products. A common polymorphism of the PON1 gene, the PON1-192 genetic polymorphism, modulates PON1 activity and has been related in some studies to coronary heart disease. Oxidized LDL is believed to play a crucial role in the pathogenesis of atherosclerosis and there are studies providing support for the oxidative stress theory of aging. We have conducted a case-control study to determine whether PON1 activity and PON1-192 genetic variants have a different impact on myocardial infarction (MI) risk among individuals stratified by tertiles of age distribution. PON1-192 genotypes and PON1 activity were determined in 280 consecutive MI patients and 396 control subjects. Serum PON1 activity levels were significantly higher in controls than in MI patients [226 U/l (159-351) vs. 216 U/l (146-298), median (interquartile range), P=0.005]. A decline of PON1 activity levels with advancing age in subjects carrying the low-activity QQ genotype was observed, particularly in MI patients. PON1 activity and age negatively correlated in MI patients but not in controls. In the entire population, middle-aged and older subjects showed MI risks of 1.89 (P=0.012) and 2.69 (P<0.001) respectively, compared with young subjects. These risks increased to 2.41 (P=0.016) and 4.39 (P<0.001), respectively, in QQ homozygotes in comparison with younger QQ homozygotes, decreased to 1.53 (P=0.314) and 2.08 (P=0.112), respectively, in QR heterozygotes, and also lowered to 1.95 (P=0.410) and 0.51 (P=0.508) in RR homozygotes who were middle-aged and older, respectively, compared with younger RR carriers. The effect of PON1-192 genotypes on the association of the older age-category and MI risk was gene-dosage related. PON1 activity decreases as a function of age in subjects homozygous for the Q allele. Age may also act on MI risk as a function of PON1-192 alleles. The risk of MI increases with advancing age, principally among subjects carrying the low-activity QQ genotype.

Paraoxonase and atherosclerosis

There is considerable evidence that the antioxidant activity of high density lipoprotein (HDL) is largely due to the paraoxonase-1 (PON1) located on it. Experiments with transgenic PON1 knockout mice indicate the potential for PON1 to protect against atherogenesis. This protective effect of HDL against low density lipoprotein (LDL) lipid peroxidation is maintained longer than is the protective effect of antioxidant vitamins and could thus be more important. There is evidence that the genetic polymorphisms of PON1 least able to protect LDL against lipid peroxidation are overrepresented in coronary heart disease, particularly in association with diabetes. However, these polymorphisms explain only part of the variation in serum PON1 activity; thus, a more critical test of the hypothesis is likely to be whether low serum PON1 activity is associated with coronary heart disease. Preliminary case-control evidence suggests that this is indeed the case and, thus, that the quest for dietary and pharmacological means of modifying serum PON1 activity may allow the oxidant model of atherosclerosis to be tested in clinical trials.

Human paraoxonase-3 is an HDL-associated enzyme with biological activity similar to paraoxonase-1 protein but is not regulated by oxidized lipids

Paraoxonase-1 (PON1) is a secreted protein associated primarily with high density lipoprotein (HDL) and participates in the prevention of low density lipoprotein (LDL) oxidation. Two other paraoxonase (PON) family members, namely, PON2 and PON3, have been identified. In this study, we report the cloning and characterization of the human PON3 gene from HepG2 cells. Tissue Northern analysis identifies an approximately 1.3-kb transcript for PON3 primarily in the liver. PON3-specific peptide antibodies detect an approximately 40-kDa protein associated with HDL and absent from LDL. Pretreatment of cultured human aortic endothelial cells with supernatants from HeLa Tet On cell lines overexpressing PON3 prevents the formation of mildly oxidized LDL and inactivates preformed mildly oxidized LDL. In contrast to PON1, PON3 is not active against the synthetic substrates paraoxon and phenylacetate. Furthermore, PON3 expression is not regulated in HepG2 cells by oxidized phospholipids and is not regulated in the livers of mice fed a high-fat atherogenic diet.

Serum paraoxonase is reduced in type 1 diabetic patients compared to non-diabetic, first degree relatives; influence on the ability of HDL to protect LDL from oxidation

Paraoxonase is a serum enzyme with an anti-oxidant function, protecting low density lipoproteins (LDL) from oxidative modifications. Diabetic patients are suggested to be at greater risk of oxidative stress, which may contribute to the significantly higher incidence of vascular disease in this population. Less efficient protection mechanisms may be one feature of the greater susceptibility to oxidation in diabetes. In this context, the present study examined the hypothesis that serum paraoxonase is reduced in type 1 (insulin-dependent) diabetic patients and that the reduction can affect the anti-oxidant capacity of HDL. Serum paraoxonase concentrations and activities were compared in type 1 patients and first degree, non-diabetic relatives with particular attention paid to the confounding effects of paraoxonase gene polymorphisms. In addition, the ability of HDL-paraoxonase to protect low density lipoproteins from oxidation was analysed in an in vitro system. Serum concentrations and enzyme activities of paraoxonase were significantly lower in type 1 patients compared to non-diabetic, first degree relatives. The differences were independent of promoter and coding region polymorphisms, which influence serum concentrations and activities of the enzyme. Overall, paraoxonase concentrations were a mean 13.3+/-4.5% lower (P<0.02) in type 1 patients. Specific activities did not differ between diabetic and non-diabetic groups. The concentration ratios of LDL cholesterol:paraoxonase (1.37+/-0.51 vs. 1.18+/-0.37, P=0.003) and apolipoprotein B:paraoxonase (0.84+/-0.33 vs. 0.71+/-0.40; P=0.012) were significantly higher in diabetic patients, consistent with a reduced capacity to protect LDL from oxidation. In vitro oxidation studies showed that a significantly higher level of lipid hydroperoxides was generated in LDL in the presence of HDL, containing paraoxonase levels equivalent to those of type 1 patients, compared to HDL containing paraoxonase levels equivalent to those of control subjects (mean difference 8.1%, P<0.05). The study demonstrates that serum concentrations of the antioxidant enzyme paraoxonase are significantly lower in type 1 (insulin-dependent) diabetic patients compared to non-diabetic, first-degree relatives, independently of known gene polymorphisms. Concentrations are reduced to an extent that can affect its anti-oxidant capacity. The results are consistent with the contention that modifications to serum paraoxonase in type 1 patients can increase risk of lipoprotein oxidation and, consequently, risk of vascular disease.

Paraoxonase1-192 polymorphism modulates the nonfatal myocardial infarction risk associated with decreased HDLs

Serum paraoxonase1 (PON1), a high density lipoprotein (HDL)-linked enzyme, appears to have a role in the protection of low density lipoproteins from oxidative stress. PON1 enzyme activity for paraoxon as a substrate is modulated, along with others at the PON1 locus, by the PON1-192 polymorphism, which contains low paraoxon-activity and high paraoxon-activity alleles (Q and R, respectively). The association of PON1 with HDL suggests that impaired serum concentrations of the lipoprotein could have consequences for the susceptibility to oxidative stress. Because PON1-192 polymorphism strongly influences PON1 activity toward paraoxon, we tested the hypothesis that this polymorphism may modulate the myocardial infarction (MI) risk associated with low HDL cholesterol concentrations. Two hundred eighty consecutive MI patients and 396 control subjects were studied. When considered as a whole, PON1-192 genetic polymorphism was not associated with higher MI risk. In the entire population, decreased HDL cholesterol concentration (<0.90 mmol/L in men and <1.11 mmol/L in women) conferred an MI risk of 2.56 (P=0.0001) compared with normal HDL levels. The risk increased to 4.51 (P<0.0001) in QQ homozygous HDL-deficient subjects relative to QQ homozygotes with normal HDL levels, decreased to 1.83 (P=0.1046) in QR heterozygote HDL-deficient subjects, and also decreased (to 1.41, P=0.6243) in RR homozygote HDL-deficient individuals compared with RR carriers with normal HDL cholesterol concentration. The effect of PON1-192 genotypes on the association of low HDL cholesterol levels and MI was related to gene dosage. A significantly decreased enzyme activity was found in HDL-deficient MI patients compared with HDL-deficient control subjects (median 208 U/L [interquartile range 136 to 298 U/L] versus median 235 U/L [interquartile range 163 to 350 U/L], respectively; P=0.025]. QQ homozygous MI patients showed the greatest difference of PON1 activity levels between normal and HDL-deficiency state groups (14.9%, P=0.002). Our observations raise the question of whether the decrease in PON1 activity and the MI risk associated with HDL deficiency are more evident in the low paraoxon-activity QQ genotype. It can be argued that the low paraoxon-activity QQ genotype, which may be adequate to prevent lipid peroxidation in normolipidemic subjects, may be insufficient when an HDL-deficiency state and low PON1 activity reflecting oxidative stress coexist. The risk of nonfatal MI is increased in HDL-deficiency states, principally among subjects carrying the low paraoxon-activity QQ genotype.

A prospective study of paraoxonase gene Q/R192 polymorphism and severity, progression and regression of coronary atherosclerosis, plasma lipid levels, clinical events and response to fluvastatin

Human serum paraoxonase (PON1) is a high-density lipoprotein (HDL)-associated enzyme that is responsible for the protective effect of HDL against oxidation of low-density lipoprotein (LDL). PON1 has a Glu to Arg polymorphism at codon 192 (CGA-->CAA) which is designated R/Q192. The R/Q192 polymorphism has been associated with coronary artery disease (CAD) in several, but not all, case-control studies. We prospectively studied the association of the Q/R192 genotypes with the severity, progression and regression of CAD, plasma lipid levels, clinical events and response to treatment with fluvastatin in a well-characterized cohort. Genotypes were determined by polymerase chain reaction (PCR) and restriction mapping with AlwI enzyme in 356 subjects in the Lipoprotein and Coronary Atherosclerosis Study (LCAS). Fasting plasma lipids were measured and quantitative coronary angiograms were obtained at baseline and 2.5 years following randomization to fluvastatin or placebo. A total of 177 (50%), 142 (40%) and 37 (10%) subjects had Q/Q, Q/R and R/R genotypes, respectively. Baseline and final plasma levels of HDL, LDL, triglyceride and other lipoproteins, lesion-specific minimum lumen diameters (MLD), mean MLD, number of coronary lesions and total occlusions at baseline and follow-up and clinical event rates were not significantly different among the genotypes. There was no genotype-treatment interaction with respect to plasma lipid levels and angiographic indices of CAD. The Q/R192 variants of PON1 are not associated with severity, progression or regression of coronary atherosclerosis, plasma lipid levels, clinical events, or response to treatment with fluvastatin. Thus, the Q/R192 polymorphism is not a major risk factor in susceptibility to CAD in the LCAS population.

Serum arylesterase/diazoxonase activity and genetic polymorphisms in patients with type 2 diabetes

Human serum paraoxonase (PON1) is associated with high-density lipoprotein (HDL) and inhibits the oxidation of low-density lipoprotein (LDL) in vitro, suggesting that PON1 protects against atherosclerosis. We detected 3 polymorphisms of the PON1 gene and investigated PON1 enzyme activities as paraoxonase (PON), arylesterase (ARYL) and diazoxonase (DIAZ), and serum PON1 concentration in 106 patients with type 2 diabetes and 161 control subjects. All 3 enzyme activities and specific activities of PON1 in diabetic patients were significantly lower than those in controls, while there was no difference in serum PON1 concentration between the patient and control groups. The specific activities of PON, ARYL, and DIAZ in patients were 6.82 +/- 3.14 nmol x min(-1) x U(-1) (mean +/- SD, U; unit for serum PON1 concentration), 4.77 +/- 0.17 micromol x min(-1) x U(-1), and 193 +/- 92 nmol x min(-1) x U(-1), respectively, whereas those in controls were 9.33 +/- 3.92 nmol x min(-1) x U(-1), 5.36 +/- 0.14 micromol x min(-1) x U(-1), and 242 +/- 103 nmol x min(-1) x U(-1), respectively. There was no significant difference in the allelic frequencies of -108C/T, 55L/M, or 192Q/R between the patient and control groups. When each enzyme activity was compared between the patient and control groups in each genotype subgroup, all activities were lower in the patient group. The PON and ARYL activities were lower in patients with retinopathy or nephropathy than in those without such complications, and the ARYL activity was also lower in patients with neuropathy. In conclusion, all specific enzyme activities of PON1 were lower in patients with type 2 diabetes independent of the -108C/T, 55L/M, or 192Q/R polymorphism, and this impaired PON1 function may be involved in development of diabetic microangiopathy.

Paraoxonase (PON1) phenotype is a better predictor of vascular disease than is PON1(192) or PON1(55) genotype

The paraoxonase (PON1) PON1-Q192R and PON1-L55M polymorphisms have been inconsistently associated with vascular disease. Plasma PON1 activity phenotypes vary markedly within genotypes and were, therefore, expected to add to the informativeness of genotype for predicting vascular disease. The case-control sample included 212 age- and race-matched men (mean age 66.4 years). The 106 carotid artery disease (CAAD) cases had >80% carotid stenosis, and the 106 controls had <15%. Two PON1 substrate hydrolysis rates (paraoxon [POase] and diazoxon [DZOase]) were significantly lower in cases than in controls and were significant predictors of CAAD by use of logistic regression (POase, P=0.005; DZOase, P=0.019). DZOase predicted vascular disease independently of lipoprotein profile, high density lipoprotein subfractions, apolipoprotein A-I, and smoking. PON1-192 and PON1-55 genotypes or haplotypes did not predict case-control status unless the activity phenotype was also included as a predictor by use of logistic regression. When phenotype was included as a predictor, PON1-192 and PON1-55 genotypes or combined haplotypes were significant predictors (P<0.05). In conclusion, examining PON1-192 and/or PON1-55 genotypes alone may mistakenly lead to the conclusion that there is no role of PON1 in CAAD. These results support the benefit of a "level crossing" approach that includes intervening phenotypes in the study of complexly inherited disease.

The paraoxonase Leu-Met54 and Gln-Arg191 gene polymorphisms are not associated with the risk of coronary heart disease

BACKGROUND

Evidence has been presented that gene polymorphisms (PON54 L/M, PON191 Q/R) of paraoxonase are risk factors of coronary heart disease.

RESULTS

We determined both PON genotypes in 535 male individuals who were free of vascular disease and in 2249 male subjects who underwent coronary angiography, and analysed the relation of both gene variations to CAD and MI. Both gene polymorphisms were in linkage disequilibrium (P<0.0001). Coronary artery disease: the PON54 gene polymorphism was not associated with an increased risk of CAD. In the total sample and also in younger subjects, an association of the PON191 gene variation with the risk of CAD was not detected when the control group of individuals without coronary heart disease was compared with patients with at least one diseased vessel (verified by coronary angiography). In individuals younger than 62 years, a moderate increase in the relative risk of CAD associated with the PON191 R allele (1.45 (1. 08-1.95); P=0.015) were found, when subjects without vessel disease (verified by coronary angiography) were compared with CAD patients. Myocardial infarction: an association of the PON54 gene variation with MI was not detected when the control group of individuals without coronary heart disease were compared with patients with at least one MI. A marginal increase in the risk of MI associated with the PON54 LL genotype (OR 1.27 (1.05-1.51); P=0.011) were detected when patients without MI but with coronary angiography were compared with MI positive patients. Subgroup analyses of low- and high-risk populations did not reveal any association of both PON gene polymorphisms with CAD or MI.

CONCLUSION

The present findings do not strengthen the hypothesis that the paraoxonase gene polymorphisms are independently associated with coronary heart disease indicating that these gene variations are of little usefulness as genetic markers of cardiovascular disease.

Tobacco smoking modifies association between Gln-Arg192 polymorphism of human paraoxonase gene and risk of myocardial infarction

Paraoxonase, a high density lipoprotein-associated human serum enzyme, plays a role in atherosclerosis by protecting against lipid peroxidation. Its activity is modulated by 2 common amino acid polymorphisms at positions 192 (Gln-->Arg) and 55 (Met-->Leu) in the paraoxonase gene (P:ON1). We studied the association of P:ON1 polymorphisms and myocardial infarction (MI) in a population-based study consisting of 492 cases and 518 controls matched for age, sex, and area of residence, all living in Costa Rica. The allele frequency of P:ON1(192Arg) was higher in cases (0.27) than in controls (0.24, P:=0.008), whereas that of P:ON1(55Leu) was identical (0.26). Compared with P:ON1(192Gln-Gln), the P:ON1(192Arg) allele was associated with an increased risk of MI (odds ratio [OR] 1.36, CI 1.06 to 1.75), and this association was independent of the P:ON1(55) polymorphism, which was not associated with MI (OR 1.10, CI 0.82 to 1.48). Adjustment for lipid and nonlipid risk factors strengthened the association between P:ON1(192Arg) and the risk of MI (OR 1.51, CI 1.13 to 2.03). Interestingly, this association was evident only among nonsmokers (OR 1.90, CI 1.29 to 2.79): there was no evidence of an association in smokers (OR 0.95, CI 0.57 to 1.79). The interaction between P:ON1(192) and smoking status was statistically significant (P:=0.04). Thus, the PON1(192) but not the PON1(55) gene polymorphism is associated with an increased risk of MI. This association is not evident among smokers.

Analysis of paraoxonase (PON1) L55M status requires both genotype and phenotype

Paraoxonase (PON1) is tightly associated with high-density lipoprotein particles and is believed to contribute to the prevention of atherosclerosis by metabolizing oxidized lipids. PON1 also hydrolyses the bioactive oxon forms of organophosphorus pesticides such as parathion, diazinon and chlorpyrifos. Two common polymorphisms have been identified in the coding sequence of human PON1: L55M and R192Q. Several previous studies have found that the presence of the PON1R192 allele raises the risk of cardiovascular disease while others found no correlation. The studies, however, have focused on the genotype of PON1 and not the expression level of the protein. We found that the PON1 expression level in plasma, as determined by the rates of paraoxon and diazoxon hydrolysis, varies widely among individuals and within a genotype. Previous studies found that individuals having Met at PON155 have lower levels of both PON1 mRNA and activity. In this study, we determined the plasma activity levels of PON1 and examined the relationships between PON155 genotype and PON1 level. As with PON1192, we found considerable overlap in activity among the PON155 genotypes. Of the 317 individuals whose PON1 status was determined in this study, 48.9% were PON1Q192 homozygotes. Analysis of the PON1QQ192 population showed that while the average PON1 activity (diazoxon hydrolysis) was 12266 U/L for PON1LL55 and 7777 U/L for PON1MM55, a given PONMM55 individual could have more than twice the activity of a PON1LL55 individual. PON1 status, which includes PON1 level as well as PON1192 genotype, may be a better predictor for cardiovascular disease or organophosphate susceptibility than PON1 genotype alone.

The human paraoxonase Gln-Argl92 (Q/R) polymorphism in turkish patients with coronary artery disease

It has been suggested that a Q/R (Glnl92Arg) polymorphism of paraoxonase (PON) might be associated with the predisposition to coronary artery disease (CAD). Therefore, we studied the human paraoxonase gene (PON1) polymorphism in Turkish patients with CAD by polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP). This polymorphism was determined in 96 CAD patients and in 105 control subjects. The frequencies of the QQ, QR, and RR genotypes were found as 36.5, 52.0, and 11.5% in CAD patients and 48.6, 41.0, and 10.4% in control subjects, respectively. The QR genotype was the most common in the patient group, whereas the QQ genotype was more frequent in individuals without CAD. Frequency of the R allele was higher among CAD patients compared to controls (38.5% versus 31%). However, neither the genotype nor the allele distribution of the Gln92Arg polymorphism of PON1 was statistically significantly different between the two groups (P>0.05). Although both systolic and diastolic blood pressure levels were slightly higher in patients with the QQ genotype, there was no differences in regard to age, sex, serum triglyceride, total cholesterol or high-density lipoprotein cholesterol among CAD patients with different PONI Gln192Arg genotypes. In summary, our results suggest that no association exists between the Gln192Arg polymorphism of paraoxonase and CAD in Turkish patients.

Evidence for association between paraoxonase gene polymorphisms and atherosclerotic diseases

Paraoxonase 1 (PON1) is proposed to have an anti-atherogenic action. Two polymorphisms at the PON1 (M/L55 and Q/R192) have been shown to be associated with coronary artery disease (CAD). This conclusion is not drawn universally, however, and specific ethnic characteristics may be important determinants in this association. Recently two homologues of PON1 - PON2 and PON3 - were identified and Sanghera et al. demonstrated C/S311 polymorphism at PON2 was associated with the risk of CAD. Within that context, we investigated the association between the aforementioned three polymorphisms and CAD and ischemic stroke in a Japanese population. The study population included 431 control subjects, 210 CAD patients, and 235 ischemic stroke patients. Genotype distributions and allele frequencies of M/L55 and C/S311 were similar among the control and patient groups, whereas the R192 allele frequency was significantly higher (P<0.001) in CAD (75%) and ischemic stroke (76%) patients than in control subjects (65%). When confounding influences of other risk factors were controlled for by multivariate analysis, R192 remained an independent risk determinant (additive model: OR (95% CI), P value CAD: 2.01 (1.45-2.79), 0.0001; ischemic stroke: 1.84 (1.34-2.52), 0.0002 (three genotypes into calculation)). Taken together, our data indicate that the Q/R192 is principally associated with both CAD and ischemic stroke in Japanese.

Effect of physical activity on lipid levels in a population-based sample of men with and without the Arg192 variant of the human paraoxonase gene

The prevalence of cardiovascular risk factors in Gerona, Spain, is high for the low myocardial infarction incidence and mortality rates in the province. Physical activity is a protective factor against coronary heart disease. We investigated whether the genetic variants Q and R of the paraoxonase Gln-Arg 192 polymorphism were involved in different responses of lipids to physical activity. Serum triglycerides, HDL-cholesterol concentrations, and the paraoxonase Gln-Arg 192 polymorphism were determined in 262 men randomly selected from a representative population sample in a cross-sectional study conducted in Gerona, Spain. The Minnesota Leisure Time Physical Activity Questionnaire was used to assess energy expenditure in leisure time physical activity. No differences were found in lipid levels among tertiles of physical activity distribution in subjects with the QQ genotype. However, R carriers showed a significant decreasing trend in triglyceride levels and in log-triglyceride-to-HDL-cholesterol ratio and a significant increasing trend in HDL-cholesterol concentration with the amount of physical activity. R carriers included in the low tertile of physical activity distribution had HDL-cholesterol levels significantly lower than those of QQ homozygous men in the same physical activity category (1.04 mmol/L vs. 1.22 mmol/L, P = 0.024). R carriers of the higher tertile of physical activity distribution showed the most favorable lipid profile in this genetic group. A statistically-significant interaction between paraoxonase genotypes and physical activity was observed for log triglycerides (P = 0.018), HDL-cholesterol concentration (P = 0.017), and log triglyceride-to-HDL-cholesterol ratio (P = 0.008). The beneficial association of the amount of physical activity and lipid traits found in men with the R allele suggests that this population subgroup needs to be physically active to achieve a favorable lipoprotein phenotype similar to that observed in QQ homozygous men.

Paraoxonase activity in two healthy populations with differing rates of coronary heart disease

BACKGROUND

The rate of coronary heart disease is over three-fold greater in Belfast than in Toulouse and the excess risk cannot be totally explained by 'classical' risk factors such as total cholesterol, LDL-cholesterol, smoking, etc.

DESIGN

The effect of the human serum paraoxonase (PON1) 192-genetic polymorphism on plasma lipid and lipoprotein concentrations and on PON1 activity and concentration was investigated in 186 randomly selected healthy subjects from Toulouse and 165 from Belfast.

RESULTS

The frequency of the R allele of PON1, which has been related to the risk of coronary heart disease, was significantly higher in Belfast (0.33) than in Toulouse (0.24; chi2 = 7.229, P = 0.0072). Subjects from Belfast also had significantly higher serum cholesterol, triglycerides, LDL-cholesterol, and apolipoprotein B, and significantly lower HDL-cholesterol and apolipoprotein A1, but these lipoprotein parameters were independent of the PON1 192-polymorphisms. PON1 activity towards paraoxon was significantly higher in the Belfast population than in Toulouse (median values: 179.7 vs. 129.4 nmol min-1 mL-1 serum, respectively; P < 0.05), which is consistent with our finding of a greater prevalence of the R allele. The median serum concentration of PON1 was 56.3 microgram mL-1 in Belfast, which was significantly lower (P < 0.005) than the level of 71 microgram mL-1 in Toulouse.

CONCLUSIONS

Our results thus provide further support for the hypothesis that populations at increased CHD risk have diminished serum PON1 concentration and an increased prevalence of the R allele of PON1. They are also consistent with reports that the ability of PON1 to hydrolyse paraoxon is inversely related to its capacity to hydrolyse lipid-peroxides, and thus to its antiatherogenic action.

Catalase and paraoxonase in hypertensive type 2 diabetes mellitus: correlation with glycemic control

OBJECTIVES

Type 2 diabetes mellitus (DM) is well recognized as being associated with increased prevalence of hypertension. Experimental and epidemiologic studies have shown that oxygen-free radicals are elevated because antioxidant enzyme activities are altered both in uncontrolled essential hypertension and DM itself. Recently paraoxonase (PON) has been recognized as an antioxidant enzyme that hydrolyzes lipid peroxides. The aim of this study is to evaluate simultaneously PON activities and antioxidant status in hypertensive type 2 DM cases and to establish any possible relationship between these parameters and duration of hypertension or diabetes, hemoglobin (Hb) A1c levels, and lipid parameters.

DESIGN AND METHODS

Nineteen normotensive subjects with type 2 DM, 37 hypertensive (diastolic blood pressure 90 mm Hg or more) subjects with type 2 DM, and 25 normotensive control subjects with normal glucose tolerance were selected for this study. Superoxide dismutase (SOD), catalase, and basal-stimulated PON activities were measured by the methods of Sun et al.; Goth; and Eckerson, Wyte, and La Du, respectively; other lipid parameters were determined using an autoanalyzer.

RESULTS

Catalase activities of either hypertensive patients with type 2 DM or type 2 DM patients without complication were found to be higher than controls (p<0.01), although no significant difference in SOD and basal-stimulated PON activities was observed between these groups. A significant elevation in catalase activity (p = 0.004) of patients with high HbA1c levels (>7.0%) (n = 37) compared with patients with low HbA1c levels (<7.0%) (n = 19) was detected. There was also a positive correlation between the catalase activities and fasting glucose levels and HbA1c concentrations in hypertensive patients with type 2 DM (r = 0.4567, p<0.05 and r = 0.3686, p<0.05, respectively). An increase in catalase activity of patients with B and/or AB phenotype compared with patients with A phenotype was also noted.

CONCLUSION

Poor glycemic control in diabetes is strongly associated with an increase in free radicals and consequent diabetic complications. Uncontrolled glucose metabolism may also be the cause of alterations in antioxidant enzymes. Among these, catalase correlates best with poor glycemic control. The current data reveal that B allele carriers of PON are more susceptible to oxidant stress.

Paraoxonase polymorphisms are not associated with cardiovascular risk in renal transplant recipients

BACKGROUND

Paraoxonase (PON1) gene variants have been identified as risk factors for cardiovascular disease (CVD). There are two common PON1 polymorphisms at position 55 (Leu-Met change) and 192 (Gln-Arg change) of the amino acid chain. Leucine at position 55 and arginine at position 192 have been associated with increased cardiovascular risk. The increased prevalence of CVD in renal transplant recipients can be only partly explained by the increased prevalence of conventional risk factors.

METHODS

We therefore investigated PON1 polymorphisms in renal transplant recipients (N = 491) with (N = 103) and without CVD (N = 388) using polymerase chain reaction-restriction fragment length analysis. PON1 polymorphisms and their associated PON1/arylesterase activities were also assessed in a subgroup of patients (N = 165).

RESULTS

The genotype distribution and allele frequencies for both polymorphisms were similar in both groups. The frequencies for LL, LM, and MM genotypes for the 55 position in patients with CVD were 0.39, 0.51, and 0.10, respectively, compared with 0.43, 0.43, and 0.14 in patients without CVD (P = 0.31). The distribution for the QQ, QR, and RR genotypes at the 192 position were 0.48, 0.43, and 0.09, respectively, in patients with CVD compared with 0.46, 0.46, and 0.08 in patients without CVD (P = 0.8). There were highly significant differences in serum activities of PON1/arylesterase between genotypes defined by 55 and 192 polymorphisms. Leucine at position 55 and arginine at position 192 were associated with higher activities.

CONCLUSION

These data indicate that there is no association between the PON1 gene variants, conferring higher enzyme activity, and the increased cardiovascular risk in renal transplant recipients.

Paraoxonase 1 mutations in a Turkish population

Human serum paraoxonase 1 (PON1) catalyzes the hydrolysis of certain organophosphate pesticides and nerve gases and so may alter significantly an individual's susceptibility to the toxicity of these chemicals. Moreover, PON1 hydrolyzes lipid peroxides complexed to low density lipoproteins (LDL) and therefore it was suggested that PON1 may be one of the genes that is involved in the pathogenesis of cardiovascular diseases. Its activity shows interindividual and interethnic variability. At least two mutation sites, namely Gln192Arg (Q/R) and Leu55Met (L/M) were reported responsible for the variations in enzyme activity. The aim of the present study was to determine the frequency of these mutations in Turks and compare the results with other European and Oriental populations. A total of 381 unrelated Turkish individuals were genotyped for Gln192Arg and Leu55Met polymorphisms by PCR-RFLP using AlwI and NlaIII, respectively. Genotype distribution was QQ = 0.49, QR = 0.40, RR = 0.11, and LL = 0.52, LM = 0.39, MM = 0.09. Thus frequencies of high activity alleles R (Arg) and L (Leu) were found as 0.31 and 0.72, respectively. The frequency of these alleles was slightly higher in Turkish subjects than other Caucasian populations but much lower compared to Oriental populations.

Paraoxonase genes and disease

The paraoxonase gene family contains at least three members, including PON1, PON2 and PON3, which are located on chromosome 7q21.3-22.1. Until recently, there has been little insight into the role of the respective gene products in human physiology and pathology. However, emerging evidence from biochemical and genetic experiments is providing clues about the role(s) of the products of these genes. For example, the PON1 gene product is serum paraoxonase, which is expressed mainly in the liver and which hydrolyzes organophosphates. Serum paraoxonase circulates on a subfraction of high-density lipoproteins and appears to use phospholipids on both low and high-density lipoprotein particles as a physiological substrate. This functional relationship could explain the reported associations between common variation in the PON1 gene and phenotypes related to atherosclerosis and lipoprotein metabolism. In contrast, the PON2 mRNA is expressed ubiquitously, and to date there are no mechanistic experiments that yield insights into its physiological role. However, there have been reports of association between common variation in PON2 and some metabolic quantitative phenotypes, such as plasma lipoproteins, plasma glucose, birthweight and atherosclerosis. Such genetic associations could point to the possible physiological role(s) of PON2. At present, the role of the PON3 gene product is very poorly understood. Complementary lines of research should soon clarify whether there might be merit in clinical testing for genetic variation in the paraoxonase gene family or whether the gene products might be good candidates for therapeutic interventions.

Low serum paraoxonase: a risk factor for atherosclerotic disease?

Serum paraoxonase (PON1) hydrolyses organophosphate (OP) insecticides and nerve gases and is responsible for determining the selective toxicity of these compounds in mammals. PON1 has two genetic polymorphisms giving rise to amino acid substitutions at position 55 and 192. The 192 polymorphism is the major determinant of the PON1 activity polymorphism towards organophosphates. However, the 55 polymorphism also modulates activity. PON1 also may be a determinant of resistance to the development of atherosclerosis by protecting lipoproteins against oxidative modification perhaps by hydrolysing phospholipid-hydroperoxides. The PON1 polymorphisms are important in determining the capacity of high-density lipoprotein (HDL) to protect low-density lipoprotein (LDL) against oxidative modification in vitro and this may explain the relationship between the PON1 alleles and coronary heart disease in case-control studies.

The role of paraoxonase (PON1) in the detoxication of organophosphates and its human polymorphism

In human populations, serum paraoxonase (PON1) exhibits a substrate dependent polymorphism. The Arg192 isoform hydrolyzes paraoxon rapidly but diazoxon, soman and especially sarin slowly. On the other hand, the Gln192 isoform hydrolyzes paraoxon slowly, but diazoxon, soman and sarin more rapidly than the Arg192 isoform. Our experiments with a mouse model system have convincingly shown that PON1 plays a major role in the detoxication of organophosphate (OP) compounds processed through the P450/PON1 pathway. Recent studies have also shown that PON1 plays an important role in the metabolism of oxidized lipid compounds. Currently, there is an effort underway to identify genes and polymorphisms that play an important role in 'environmental susceptibility'. The PON1 polymorphism has been cited as a prime example of such a genetic polymorphism. The advent of the polymerase chain reaction (PCR) for DNA amplification with improvements, modifications and automation has provided a very convenient way to do individual genotyping. It is tempting to set up large scale PCR analyses of populations to determine individuals at risk for environmental exposures affected by the PON1 polymorphism. In fact, a number of such studies have already been carried out in examining the relationship of the PON1 polymorphism to vascular disease. We advocate the use of a high throughput two-dimensional enzyme assay that provides both PON1 genotype and phenotype (PON1 status). The high level of variation of gene expression within each genetic class in humans, together with our animal model studies indicate that it is very important to determine PON status as opposed to PON1 genotype alone. Experiments in rats and mice have shown that injection of PON1 purified from rabbit serum by the i.v., i.p. or i.m. route, significantly increases PON1 activities in rodents' plasma. Under these conditions, the acute toxicity (assessed by the degree of acetylcholinesterase inhibition) of paraoxon and chlorpyrifos oxon is significantly decreased, compared to control animals. Protection is maximal when PON1 is administered before the OPs, but still occurs when PON1 is utilized as a post-exposure treatment. Furthermore, protection by PON1 is also provided toward the parent compound chlorpyrifos. Pon1-knockout mice display a much greater sensitivity to chlorpyrifos oxon toxicity than wild mice. However, the acute toxicity of guthion, which is not a substrate for PON1, does not differ between knockout and wild mice. These observations underline the importance of considering both genetic variability of enzyme isoform as well as enzyme level (PON1 status) and the developmental time course of appearance of PON1 in developing risk assessment models.

Serum paraoxonase activity and phenotype distribution in Turkish subjects with coronary heart disease and its relationship to serum lipids and lipoproteins

Recently, biochemical studies of paraoxonase in the serum of humans have shown that much of this enzymes' activity is associated with high-density lipoprotein (HDL) and paraoxonase may play a role in lipid metabolism preventing the accumulation of the lipoperoxides. In this study, a possible relationship between coronary heart disease (CHD) and paraoxonase activity were investigated. Serum triglycerides, total cholesterol, HDL-cholesterol and paraoxonase activity were measured in unrelated healthy donors and CHD patients. It was found that paraoxonase activity was trimodally distributed in both groups but no statistically significant difference was found between phenotype distributions of controls and CHD patients (gene frequencies; 0.632 and 0.382 of controls, 0.702 and 0.298 of patients for the A and B alleles, respectively). However, in CHD group, a high possibility was found to be phenotype A compared with the control group. A relative risk of 1.48 (95% confidence intervals (CI), 0.986-2.227) was found for the relation between CHD and the paraoxonase activity. Patients' HDL-cholesterol values were lower and triglycerides were higher than controls (P<0.001). It may be concluded from the present study that although no statistically significant difference was found between paraoxonase phenotype distributions of controls and CHD patients, a decrease in paraoxonase activity could become a risk factor for this disease.

Human serum paraoxonase (PON 1) is inactivated by oxidized low density lipoprotein and preserved by antioxidants

Human serum paraoxonase (PON1) can protect low density lipoprotein (LDL) from oxidation induced by either copper ion or by the free radical generator azo bis amidinopropane hydrochloride (AAPH). During LDL oxidation in both of these systems, a time-dependent inactivation of PON arylesterase activity was observed. Oxidized LDL (Ox-LDL) produced by lipoprotein incubation with either copper ion or with AAPH, indeed inactivated PON arylesterase activity by up to 47% or 58%, respectively. Three possible mechanisms for PON inactivation during LDL oxidation were considered and investigated: copper ion binding to PON, free radical attack on PON, and/or the effect of lipoprotein-associated peroxides on the enzyme. As both residual copper ion and AAPH are present in the Ox-LDL preparations and could independently inactivate the enzyme, the effect of minimally oxidized (Ox-LDL produced by LDL storage in the air) on PON activity was also examined. Oxidized LDL, as well as oxidized palmitoyl arachidonoyl phosphatidylcholine (PAPC), lysophosphatidylcholine (LPC, which is produced during LDL oxidation by phospholipase A2-like activity), and oxidized cholesteryl arachidonate (Ox-CA), were all potent inactivators of PON arylesterase activity (PON activity was inhibited by 35%-61%). PON treatment with Ox-LDL (but not with native LDL), or with oxidized lipids, inhibited its arylesterase activity and also reduced the ability of the enzyme to protect LDL against oxidation. PON Arylesterase activity however was not inhibited when PON was pretreated with the sulfhydryl blocking agent, p-hydroxymercurybenzoate (PHMB). Similarly, on using recombinant PON in which the enzyme's only free sulfhydryl group at the position of cysteine-284 was mutated, no inactivation of the enzyme arylesterase activity by Ox-LDL could be shown. These results suggest that Ox-LDL inactivation of PON involves the interaction of oxidized lipids in Ox-LDL with the PON's free sulfhydryl group. Antioxidants such as the flavonoids glabridin or quercetin, when present during LDL oxidation in the presence of PON, reduced the amount of lipoprotein-associated lipid peroxides and preserved PON activities, including its ability to hydrolyze Ox-LDL cholesteryl linoleate hydroperoxides. We conclude that PON's ability to protect LDL against oxidation is accompanied by inactivation of the enzyme. PON inactivation results from an interaction between the enzyme free sulfhydryl group and oxidized lipids such as oxidized phospholipids, oxidized cholesteryl ester or lysophosphatidylcholine, which are formed during LDL oxidation. The action of antioxidants and PON on LDL during its oxidation can be of special benefit against atherosclerosis since these agents reduce the accumulation of Ox-LDL by a dual effect: i.e. prevention of its formation, and removal of Ox-LDL associated oxidized lipids which are generated during LDL oxidation.

The Gln-Arg 191 polymorphism of the human paraoxonase gene is not associated with the risk of coronary artery disease among Chinese in Taiwan

Paraoxonase (PON1) is a high density lipoprotein-associated enzyme capable of hydrolyzing lipid peroxides, and thus, might protect lipoproteins from oxidation. A common polymorphism due to an amino acid substitution (Gln-Arg) at codon 191 is considered to be a major determinant of variation in serum PON1 activity. Recent studies have suggested that the PON1-191 polymorphism is an independent risk factor for coronary atherosclerosis in patients with or without diabetes mellitus. The association of PON1-191 polymorphism genotypes and coronary artery disease (CAD) among Chinese subjects in Taiwan was examined. The genotype of 218 angiographically documented CAD patients and the same number of age- and sex-matched control subjects was determined. Genotypes AA, AB and BB were present in 25 (11%), 102 (47%) and 91 (42%) of control subjects, respectively, and in 30 (14%), 96 (44%) and 92 (42%) of CAD patients, respectively (chi2 = 0.57, P = 0.75 between groups). The frequency of the A allele was 0.36 for the control group and 0.35 for CAD patients (P = 0.94). No significant differences in the PON1-191 genotype frequencies could be found between groups when multivariate logistic regression analysis was performed, or different subgroups of age, sex or risk factors were analyzed. Among control subjects, there was also no significant difference between genotypes of the PON1-191 polymorphism and various clinical and lipid variables. In conclusion, our data suggest that there is no association between the Gln-Arg 191 polymorphism of the human PON1 gene and CAD among Chinese subjects in Taiwan.

High density associated enzymes: their role in vascular biology

Enzymes associated with circulating HDL include lecithin: cholesterol acyl transferase, phospholipid transfer protein, cholesterol ester transfer protein, paraoxonase 1 and platelet activating factor acetylhydrolase. Together with lipoprotein lipase and hepatic lipase these enzymes produce important lipoprotein remodeling and modulate their structure and function and therefore their role in artery wall metabolism.

Paraoxonase active site required for protection against LDL oxidation involves its free sulfhydryl group and is different from that required for its arylesterase/paraoxonase activities: selective action of human paraoxonase allozymes Q and R

Human serum paraoxonase (PON 1) exists in 2 major polymorphic forms (Q and R), which differ in the amino acid at position 191 (glutamine and arginine, respectively). These PON allozymes hydrolyze organophosphates and aromatic esters, and both also protect LDL from copper ion-induced oxidation. We have compared purified serum PONs of both forms and evaluated their effects on LDL oxidation, in respect to their arylesterase/paraoxonase activities. Copper ion-induced LDL oxidation, measured by the production of peroxides and aldehydes after 4 hours of incubation, were reduced up to 61% and 58%, respectively, by PON Q, but only up to 46% and 38%, respectively, by an equivalent concentration of PON R. These phenomena were PON-concentration dependent. Recombinant PON Q and PON R demonstrated similar patterns to that shown for the purified serum allozymes. PON Q and PON R differences in protection of LDL against oxidation were further evaluated in the presence of glutathione peroxidase (GPx). GPx (0.1 U/mL) alone reduced copper ion-induced LDL oxidation by 20% after 4 hours of incubation. The addition of PON R to the above system resulted in an additive inhibitory effect on LDL oxidation, whereas PON Q had no such additive effect. The 2 PON allozymes also differed by their ability to inhibit initiation, as well as propagation, of LDL oxidation. PON Q was more efficient in blocking LDL oxidation if added when oxidation was initiated, whereas PON R was more potent when added 1 hour after the initiation of LDL oxidation. These data suggest that the 2 allozymes act on different substrates. Both PON allozymes were also able to reduce the oxidation of phospholipids and cholesteryl ester. PON Q arylesterase activity was reduced after 4 hours of LDL oxidation by only 28%, whereas the arylesterase activity of PON R was reduced by up to 55%. Inactivation of the calcium-dependent PON arylesterase activity by using the metal chelator EDTA, or by calcium ion removal on a Chelex column, did not alter PON's ability to inhibit LDL oxidation. However, blockage of the PON free sulfhydryl group at position 283 with p-hydroxymercuribenzoate inhibited both its arylesterase activity and its protection of LDL from oxidation. Recombinant PON mutants in which the PON free sulfhydryl group was replaced by either alanine or serine were no longer able to protect against LDL oxidation, even though they retained paraoxonase and arylesterase activities. Overall, these studies demonstrate that PON's arylesterase/paraoxonase activities and the protection against LDL oxidation do not involve the active site on the enzyme in exactly the same way, and PON's ability to protect LDL from oxidation requires the cysteine residue at position 283.

Paraoxonase gene polymorphism and coronary artery disease in Indian subjects

The human serum HDL-linked paraoxonase enzyme limits the LDL peroxidation by preventing transformation of LDL into biologically active atherogenic particles. Paraoxonase serum activity varies among individuals due to an Gln/Arg polymorphism with low (A phenotype) and high activity (B phenotype). The present study correlates the paraoxonase enzyme activity and the paraoxonase gene polymorphism among 200 Indians with or without coronary artery disease (CAD). We analyzed the PON enzyme activity and have identified A and B phenotypes by Alwl restriction mapping. In 120 CAD patients, the genotypes A and B constituted 75 and 25%, where as in 80 control subjects, the genotypes A and B constituted 25 and 17%, respectively. The frequency of AB genotype is higher in CAD subjects with or without diabetes, than in controls. Arg allele frequency was higher (0.45) in CAD subjects than in controls (0.17). The conventional risk factors and the family history of CAD did not affect the genotype frequency distribution among Indians. In conclusion, paraoxonase polymorphism may have been involved in the predisposition to CAD through a mechanism other than lipid oxidation.

Genetic polymorphism of paraoxonase 1 (PON1) and susceptibility to Parkinson's disease

Toxicologists have thought that the paraoxonase (PON) enzyme polymorphism might contribute to effects of pollutants and other environmental chemicals on susceptibility to cancer, birth defects and Parkinson's disease (PD). We studied a biallelic PON1 polymorphism at codon 192 (A and B alleles) in 166 patients with sporadic idiopathic PD. The frequency of the B (Arg) allele of PON1 was significantly increased in patients with PD than in healthy controls (chi2=8.75, df=1, P<0.005). The relative risk of PD in homozygotes for the B allele was 1.60 fold higher than individuals with the A (Gln) allele (chi2=7.38, df=1, P<0.01). Our data suggest that environmental neurotoxins metabolized by PON1 might be responsible for neurodegeneration with aging and that the B (Arg) allele form might have genetic susceptibility to PD.

Human serum paraoxonase

1. Human serum paraoxonase (PON1) is a Ca2+-dependent 45-kDa glycoprotein that is associated with high density lipoprotein (HDL). 2. PON1 hydrolyzes organophosphate (OP) insecticides and nerve gases and is responsible for determining the selective toxicity of these compounds in mammals. 3. PON1 has two genetic polymorphisms giving rise to amino acid substitutions at positions 55 and 192. The position-192 polymorphism is the major determinant of the PON1 activity polymorphism. However, the position-55 polymorphism also modulates activity. 4. Genotyping individuals for both PON1 polymorphisms may provide a method for identifying those most at risk of OP poisoning. The effect of the PON1 polymorphisms on activity may explain why some Gulf War veterans have developed Gulf War syndrome and some have not, despite similar OP exposure. 5. PON1 may also be a determinant of resistance to the development of atherosclerosis by protecting lipoproteins against oxidative modification, perhaps by hydrolyzing phospholipid hydroperoxides. 6. The PON 1 polymorphisms are important in determining the capacity of HDL to protect low density lipoprotein against oxidative modification in vitro, which may explain the relation between the PON1 alleles and coronary heart disease in case-control studies.

Paraoxonase and coronary heart disease

Paraoxonase (PON1) hydrolyses organophosphate insecticides and nerve gases and is responsible for determining the selective toxicity of these compounds in mammals. Human PON1 has two genetic polymorphisms giving rise to amino-acid substitutions at positions 55 and 192. The 192 polymorphism is the major determinant of the PON1 activity polymorphism towards organophosphates. However, the 55 polymorphism also modulates activity. Ex vivo, the PON1 polymorphisms are important in determining the capacity of HDL to protect LDL against oxidative modification in vitro and this may explain the relationship between the PON1 alleles and coronary heart disease in case-control studies. In recent case-control studies serum PON1 concentration and activity were also found to be decreased in coronary heart disease (CHD) independent of the PON1 polymorphism, and in diabetes serum PON1 specific activity decrease is also independent of the PON1 genetic polymorphism. HDL from transgenic mice lacking PON1 fails to protect LDL against oxidative modification. Thus PON1 may be a determinant of resistance to the development of atherosclerosis by protecting lipoproteins against oxidative modification, perhaps by hydrolysing phospholipid and cholesteryl-ester hydroperoxides.

Lack of association between carotid intima-media thickness and paraoxonase gene polymorphism in non-insulin dependent diabetes mellitus

Paraoxonase (PON) is an HDL-bound enzyme capable of hydrolyzing lipid peroxides and believed to be in part responsible for the protective effect of HDL against LDL oxidation. Its activity is mainly determined by a gene polymorphism of the PON 1 gene (Glu-Arg 192). Low activity has been related to an elevated incidence of myocardial infarction. In several case-control studies, however, the high activity B allele is paradoxically more prevalent in patients. We have re-investigated this relationship, using carotid intima-media thickness (IMT) as a surrogate continuous variable for macroangiopathy. Genotypes were determined in 197 non insulin-dependent diabetic patients (HbAlc 8.8+/-0.15%, BMI 28.3+/-0.36). IMT, measured by high resolution mode B ultrasound, was the same for all genotypes (AA: 0.83+/-.013, AB 0.82+/-.017 and BB: 0.81+/-.034 mm). Bearers of the B allele displayed higher Lp(a) concentration (AA: 197+/-28, AB: 221+/-26, BB: 225+/-45 mg/l, P=0.024) with a significant linear trend (P < 0.005). Multiple regression showed age and systolic blood pressure, but not Lp(a), to be the main determinants of IMT variability without the contribution of the PON genotype. No consistent differences could be found between genotypes in the peroxidizability of LDL (lag-time, rate of diene production and maximal concentration). Our data support the view that there is no association between the early changes of atherosclerosis as defined by carotid IMT and variation in codon 192 of PON 1.

Paraoxonase as a risk marker for cardiovascular disease: facts and hypotheses

Paraoxonase (PON1) is a Ca2+-dependent enzyme whose mechanism of action is incompletely elucidated. PON1 was originally found to be responsible for the hydrolysis of paraoxon, a catabolite of the insecticide parathion, but this enzyme is equally able to hydrolyze other substrates such as phenyl acetate. PON1 exhibits two sequence polymorphisms, Arg-->Gln 192 and Met-->Leu 55, respectively, of which the former is responsible for the distinct catalytic activity of the two corresponding allozymes against paraoxon. The PON1 gene is a member of a family of at least three related genes. Although the physiologic substrate of PON1 is unknown, a protective role against the oxidative degradation of serum lipoproteins has been attributed to this enzyme. Indeed, PON1 is a component of a spectrum of circulating high density lipoprotein particles and can hydrolyze oxidized phospholipids and cholesteryl ester hydroperoxides. Studies have been conducted to evaluate the possible "protective" role of PON, and especially the influence of the Arg-->Gln 192 polymorphism, in coronary artery disease. Results from these investigations are conflicting, and recent data suggest a complex pattern with influences from other polymorphisms in either the PON1 and/or the PON2 and PON3 genes, or even another region of the gene cluster. A number of related factors, which include the heterogeneity of the high density lipoprotein particles incorporating PON(s), the metabolism of associated apolipoproteins such as apoJ/clusterin, the respective roles of PON(s) and other high density lipoprotein-associated enzymes such as platelet-activating-factor acetyl-hydrolase and lecithin-cholesterol acyltransferase, modifications of high density lipoprotein composition and activity under acute-phase conditions, the dietary and environmental regulation of PON(s), and the actual in situ availability of PON in the atherosclerotic artery wall, must equally be taken into account.

Serum paraoxonase activity and its relationship to diabetic complications in patients with non-insulin-dependent diabetes mellitus

Paraoxonase (PON) is an esterase associated with high-density lipoprotein (HDL). Serum PON activity is affected by PON gene polymorphism (L/M, Leu-Met54, and Q/R, Gln-Arg191). We investigated PON activity and polymorphism in 108 patients (53 men and 55 women) with non-insulin-dependent diabetes mellitus (NIDDM) and 161 control subjects (82 men and 79 women) matched to the patients by age and gender. Serum PON activity was determined using paraoxon as a substrate. PON gene polymorphisms were detected by the restriction fragment length polymorphism method after a polymerase chain reaction. The mean PON activity in the patients was significantly lower than in the controls (116+/-55 and 162+/-57 U/L, respectively, P < .001). The distribution of each genotype showed no difference between the patient and control groups, and PON activity increased in the order of the QQ < OR < RR genotype and MM < LM < LL genotype in both groups. However, among each genotype subgroup, the activity was lower in patients than in controls. Forty-one patients with retinopathy had lower PON activity than those without the complication (94+/-36 and 129+/-61 U/L, respectively, P < .002). There was also a significant difference in PON activity between patients with and without overt proteinuria (93+/-38 and 122+/-58 U/L, respectively, P < .05). Logistic analysis showed that serum PON activity was one of the significant factors for retinopathy. These results suggest that decreased PON activity in patients with NIDDM is involved in diabetic vascular complications.