Plasma Paraoxonase Research Articles

Genistein as a potential inducer of the anti‐atherogenic enzyme paraoxonase‐1: studies in cultured hepatocytes in vitro and in rat liver in vivo

A number of cardioprotective effects, including the reduced oxidation of the low-density lipoprotein (LDL) particles, have been attributed to dietary soy isoflavones. Paraoxonase 1 (PON1), an enzyme mainly synthesized in the liver, may exhibit anti-atherogenic activity by protecting LDL from oxidation. Thus, dietary and pharmacological inducers of PON1 may decrease cardiovascular disease risk. Using a luciferase reporter gene assay we screened different flavonoids for their ability to induce PON1 in Huh7 hepatocytes in culture. Genistein was the most potent flavonoid with regard to its PON1-inducing activity, followed by daidzein, luteolin, isorhamnetin and quercetin. Other flavonoids such as naringenin, cyanidin, malvidin and catechin showed only little or no PON1-inducing activity. Genistein-mediated PON1 transactivation was partly inhibited by the oestrogen-receptor antagonist fulvestrant as well as by the aryl hydrocarbon receptor antagonist 7-ketocholesterol. In contrast to genistein, the conjugated genistein metabolites genistein-7-glucuronide, genistein-7-sulfate and genistein-7,4′-disulfate were only weak inducers of PON1 transactivation. Accordingly, dietary genistein supplementation (2 g/kg diet over three weeks) in growing rats did not increase hepatic PON1 mRNA and protein levels as well as plasma PON1 activity. Thus, genistein may be a PON1 inducer in cultured hepatocytes in vitro, but not in rats in vivo.

In vitro effects of three antidepressant drugs on plasma paraoxonase activity

Paraoxonase 1 (PON1) is important in organophosphates and xenobiotic metabolism and as an antioxidant bio-scavenger. PON1 activity was shown to significantly decrease in depressed patients after antidepressant treatment instauration. Our aim was to investigate the in vitro inhibitory effects of three antidepressants (imipramine, amitriptyline and fluoxetine) on PON1 activity. Plasma from healthy volunteers was spiked with antidepressant drugs. The working solutions were then diluted with plasma to obtain concentrations that covered the therapeutic margin. PON1 was tested by a kinetic method in triplicate after incubation at 37°C for 2 h. Tricyclic antidepressants significantly inhibited PON1. Fluoxetine had no effect. The inhibition percentage for imipramine was 15.6% at 100 μg/L after incubation for 1 h (131±1 vs. 155±2 IU/L; p<0.01). At 350 μg/L, the inhibition percentage for imipramine 19.2% after 1 h and 20.2% after 2 h. Amitriptyline was a stronger inhibitor: 26% after 30 min at 125 μg/L. At 250 μg/L, the inhibition percentage for amitriptyline was 36.5% after 30 min (100±4 vs. 159±2 IU/L; p<0.01). The tested tricyclic antidepressants significantly inhibit PON1 activity in a concentration-dependent manner. Amitriptyline had a higher inhibition potency than imipramine.

Maternal plasma prolidase, matrix metalloproteinases 1 and 13, and oxidative stress levels in pregnancies complicated by preterm premature rupture of the membranes and chorioamnionitis

This study aimed to investigate the role of various biochemical markers in preterm premature rupture of membranes (PPROM) and in prediction of chorioamnionitis in patients with PPROM. This case-control study included a total of 100 pregnant women at 26-34 gestational weeks. Of these women, 50 were healthy and 50 had PPROM. The biochemical markers in the maternal plasma including prolidase, matrix metalloproteinase (MMP) 1 and 13, total oxidative status (TOS), total antioxidant capacity (TAC), glutathione peroxidase (GPx), catalase (CAT), paraoxonase-1 (PON-1), tumor necrosis factor alpha (TNF-α), and high sensitive C-reactive protein (hs-CRP) were assayed. These levels were compared between the PPROM and control groups and between women with or without chorioamnionitis in the PPROM group. Compared to the control group, the levels of prolidase, MMP-13, and TOS were significantly higher (p values <0.001, 0.020, and 0.035, respectively) and those of TAC and PON-1 were significantly lower in the maternal plasma of the PPROM group (p values=0.012 and <0.001, respectively). The plasma prolidase and TOS levels were significantly higher (p values=0.033 and 0.005, respectively) and the plasma TAC and PON-1 levels were significantly lower in women with chorioamnionitis as compared with the corresponding values in women without chorioamnionitis in the PPROM group (p values =0.041 and 0.048, respectively). The multivariate logistic regression analysis observed that prolidase, TAC, and PON-1 were important markers for the presence of PPROM and prolidase and TOS were important markers for predicting chorioamnionitis. This study suggested that maternal plasma prolidase, TAC, and PON-1 may be useful for the diagnosis of PPROM, and prolidase and TOS may be used to predict chorioamnionitis in patients with PPROM.

Human Plasma Paraoxonase 1 (PON1) Arylesterase Activity During Aging: Correlation with Susceptibility of LDL Oxidation

The role of free radicals has long been proposed as a cause for the aging process. Oxidative stress is considered a major factor for altering many physiological processes and enzymatic activities during aging and is also known to play a major role in the development of several age-dependent diseases. Paraoxonase 1 (PON1) is an anti-atherosclerotic enzyme that mainly prevents accumulation of lipoperoxides and inhibits the lipid oxidation in low-density lipoproteins (LDL). This study was undertaken to investigate the antioxidant behavior of PON1 by measuring its arylesterase activity. The susceptibility of LDL for oxidation and the radical scavenging activity of plasma were also measured during aging in humans. Arylesterase activity of PON1 was measured in plasma of human subjects between 20 and 81 years of age of both genders. The susceptibility of LDL for oxidation and radical scavenging activity were measured in plasma. Decrease in plasma arylesterase activity of PON1, increase in susceptibility of LDL for oxidation and decrease in plasma radical scavenging activity were observed as a function of human age. The study provides evidence of a relationship between PON1 activity, LDL oxidation and free radical scavenging activity of plasma. The present results emphasize the dependency of PON1 activity to prevailing oxidative stress during human aging. Our findings assume significance in view of the possible categorization of PON1 as a longevity gene.

Altered expression of apoA-I, apoA-IV and PON-1 activity in CBS deficient homocystinuria in the presence and absence of treatment: Possible implications for cardiovascular outcomes

Classical homocystinuria (HCU) is caused by mutations in cystathionine beta-synthase (CBS) which, if untreated, typically results in cognitive impairment, thromboembolic complications and connective tissue disturbances. Paraoxonase-1 (PON1) and apolipoprotein apoA-I are both synthesized in the liver and contribute to much of the cardioprotective effects of high density lipoprotein. Additionally, apoA-I exerts significant neuro-protective effects that act to preserve cognition. Previous work in a Cbs null mouse model that incurs significant liver injury, reported that HCU dramatically decreases PON1 expression. Conflicting reports exist in the literature concerning the relative influence of homocysteine and cysteine upon apoA-I expression. We investigated expression of PON1 and apoA-I in the presence and absence of homocysteine lowering therapy, in both the HO mouse model of HCU and human subjects with this disorder. We observed no significant change in plasma PON1 paraoxonase activity in either mice or humans with HCU indicating that this enzyme is unlikely to contribute to the cardiovascular sequelae of HCU. Plasma levels of apoA-I were unchanged in mice with mildly elevated homocysteine due to CBS deficiency but were significantly diminished in both mice and humans with HCU. Subsequent experiments revealed that HCU acts to dramatically decrease apoA-I levels in the brain. Cysteine supplementation in HO mice had no discernible effect on plasma levels of apoA-I while treatment to lower homocysteine normalized plasma levels of this lipoprotein in both HO mice and humans with HCU. Our results indicate that plasma apoA-I levels in HCU are inversely related to homocysteine and are consistent with a plausible role for decreased expression of apoA-I as a contributory factor for both cardiovascular disease and cognitive impairment in HCU.

Aronia melanocarpa (chokeberry) polyphenol rich extract reduces plasma cholesterol and improves antioxidant function in Apolipoprotien E knockout mice

The objective of this work was to evaluate the effect of polyphenol‐rich chokeberry extract (CBE) on lipid metabolism and antioxidant function in a mouse model for atherosclerosis. Male apoE−/− mice were fed a high fat/high cholesterol diet (15% fat, 0.2% cholesterol by wt) supplemented with 0.005% or 0.05% of CBE by wt for 4 weeks (n = 10/group). The 0.05% CBE diet provided daily doses of 0.19 mg anthocyanins, 0.17 mg phenolic acids, 0.06 mg proanthocyanidins, and 0.02 mg flavonoids. Mice consuming 0.05% CBE had ~20% lower plasma total cholesterol concentrations compared with control, without altering triglyceride levels. Despite the hypercholesterolemic effect of CBE, mRNA levels of low‐density lipoprotein receptor and HMG‐CoA reductase in CBE‐fed mice were not significantly different from controls. Dietary CBE did not alter hepatic lipids or expression of genes involved in lipogenesis and fatty acid β‐oxidation. Dietary 0.05% CBE increased plasma paraoxonase‐1 (PON1) activity 39%, but did not affect glutathione peroxidase and superoxide dismutase activities. Thus, dietary CBE improves antioxidant function and its cholesterol‐lowering effect may be independent of hepatic cholesterol metabolism. Supported by College of Agriculture and Natural Resources and Research Foundation at the University of Connecticut.

Clarifying the importance of CYP2C19 and PON1 in the mechanism of clopidogrel bioactivation and in vivo antiplatelet response

It is thought that clopidogrel bioactivation and antiplatelet response are related to cytochrome P450 2C19 (CYP2C19). However, a recent study challenged this notion by proposing CYP2C19 as wholly irrelevant, while identifying paraoxonase-1 (PON1) and its Q192R polymorphism as the major driver of clopidogrel bioactivation and efficacy. The aim of this study was to systematically elucidate the mechanism and relative contribution of PON1 in comparison to CYP2C19 to clopidogrel bioactivation and antiplatelet response. First, the influence of CYP2C19 and PON1 polymorphisms and plasma paraoxonase activity on clopidogrel active metabolite (H4) levels and antiplatelet response was assessed in a cohort of healthy subjects (n = 21) after administration of a single 75 mg dose of clopidogrel. There was a remarkably good correlation between H4 AUC (0-8 h) and antiplatelet response (r2 = 0.78). Furthermore, CYP2C19 but not PON1 genotype was predictive of H4 levels and antiplatelet response. There was no correlation between plasma paraoxonase activity and H4 levels. Secondly, metabolic profiling of clopidogrel in vitro confirmed the role of CYP2C19 in bioactivating clopidogrel to H4. However, heterologous expression of PON1 in cell-based systems revealed that PON1 cannot generate H4, but mediates the formation of another thiol metabolite, termed Endo. Importantly, Endo plasma levels in humans are nearly 20-fold lower than H4 and was not associated with any antiplatelet response. Our results demonstrate that PON1 does not mediate clopidogrel active metabolite formation or antiplatelet action, while CYP2C19 activity and genotype remains a predictor of clopidogrel pharmacokinetics and antiplatelet response.

Paraoxonase activity in healthy, diabetic, and hemodialysis patients

Paraoxonase 1 (PON1) is mainly complexed to HDL and is responsible, at least in part, for their antioxidant properties. The aims of our study were to determine the phenotype distribution and enzymatic activities of PON1 and the oxidative stress status of healthy subjects and diabetic and hemodialysis patients. PON1 paraoxonase and arylesterase activities and oxidative stress markers [malondialdehyde (MDA) and vitamin E levels] were measured in 300 individuals as a function of health status. The prevalence of the PON1 phenotypes in the study population was 74.51%, 18.15% and 7.34% for QQ, QR and RR, respectively. The phenotype distribution did not change significantly as a function of health status (healthy, diabetes, hemodialysis). However, the hemodialysis patients had lower PON1 paraoxonase and arylesterase activities than the diabetic patients and healthy subjects, while there were no significant differences between the diabetic patients and the healthy subjects. Oxidative stress markers (MDA levels and vitamin E/cholesterol ratio) were significantly higher in the diabetic and hemodialysis patients than in the healthy subjects. The lower plasma PON1 enzymatic activities in the hemodialysis patients was not associated with a difference in the phenotype distribution of PON1. Oxidative stress conditions were significantly higher in these patients, which may increase the risk of atherosclerosis in this population.

Urinary 8-hydroxy-2′-deoxyguanosine level and plasma paraoxonase 1 activity with Alzheimer’s disease

Alzheimer's disease (AD) is the most frequent cause of dementia and age is the most important risk factor for AD. Aging is associated with increased free radical production and oxidative stress plays an important role in the pathogenesis of AD. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a biomarker indicating oxidative DNA damage. Paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated antioxidant enzyme and prevents especially oxidation of low-density lipoproteins. The aim of this study is to measure urinary 8-OHdG levels and serum PON1 activity in patients with AD. A total of 21 elderly patients diagnosed with moderate AD (10 men and 11 women, aged 76 ± 7.8 years) were included in the study. A total of 20 healthy elderly volunteers (11 men and nine women, aged 81 ± 7.2 years) were enrolled as a control group. Levels of urinary 8-OHdG, serum PON1 activity and lipid profile were determined in patients and controls. Urinary 8-OHdG levels were significantly increased, but serum PON1 activity was significantly decreased in patients compared to controls. Lipid profile did not show a difference between the groups. There was a negative correlation between 8-OHdG levels and PON1 activity only in the patient group (r=-0.536). Analytical performance characteristics of the methods used were satisfactory. In this study, evidence of increased oxidative DNA damage was determined in AD patients as well as decreased serum PON1 activity. Oxidant stress and oxidative DNA damage are important pathological processes in AD. The biomarkers, urinary 8-OHdG level and serum PON1 activity can be used to determine and monitor the status of patients with AD.

Longitudinal changes in PON1 activities, PON1 phenotype distribution and oxidative status throughout normal pregnancy

The purpose of the present study was to determine changes in plasma paraoxonase-1 activity (an indicator of paraoxonase phenotype) throughout normal pregnancy and its relationship with maternal oxidative stress status. The frequencies of the paraoxonase-1 phenotype in the studied population were determined using a two-substrate (paraoxon/diazoxon) activity method. As a parameter of oxidative stress status we measured the redox balance. Paraoxonase-1 activity significantly decreased at gestational week 32. In addition, the lipid profile was more atherogenic. Redox balance was significantly increased across gestational weeks. There were independent direct associations between maternal smoking habits before pregnancy, glucose concentrations and redox balance with PON1 activity in the third trimester. This study shows that pregnancy is followed by a decrease in PON1 activity and increased risk for development of cardiovascular diseases. We conclude that changes in paraoxonase-1 status during pregnancy are associated with maternal oxidative stress status and smoking habits.

The Role of Combined Assessment of Defense Against Oxidative Stress and Inflammation in the Evaluation of Peripheral Arterial Disease

Atherosclerosis in symptomatic peripheral arterial disease affects wide portions of numerous arteries in lower extremities. The resulting active inflammation in a considerable amount of arterial tissue facilitates systemic detection via measurement of inflammation-related variables. We reasoned that the combined assessment of defense against oxidative stress, in the form of paraoxonase-1 (PON1), and monocyte migration measured as circulating (C-C motif) ligand 2 (CCL2), may play a role in the evaluation of these patients. Plasma CCL2 and serum PON1-related variables, assessed by their interaction with functional genetic variants, were measured in a cross-sectional study in patients with symptomatic PAD. We found that PON1 activity and concentration were significantly lower and CCL2 concentration higher in PAD patients compared to controls, that the combination of plasma CCL2 and PON1- related values, especially PON1 concentration differentiated, almost perfectly, controls from patients and that the expression of CCL2 and PON1 generally co-localized in the atherosclerotic lesion. Since no association with genetic variants was found, such a relationship is probably the result of the disease. Our data suggest a coordinated role between CCL2 and PON1 that may be detected in blood with simple measurements and may represent an indicator of the extent of atherosclerosis.

Plasma Paraoxonase-1, Oxidized Low-Density Lipoprotein and Lipid Peroxidation Levels in Gout Patients

Gout patients have a high incidence of atherosclerotic coronary heart disease. Low serum paraoxonase (PON) activity is considered a risk factor for atherosclerosis. The relationships among paraoxonase-1 (PON1) activity, oxidative stress parameters, and atherosclerosis in gout is not known. Therefore, we determined the plasma levels of malondialdehyde (MDA), oxidized low-density lipoprotein (Ox-LDL), and activities of PON1/superoxide dismutase (SOD) activities in 49 gout patients (mean age 44.2 ± 7.0 years) and 42 healthy, age-matched controls (mean age 45.0 ± 9.3 years). PON1 was measured spectrophotometrically, MDA by thiobarbituric acid method, SOD by Griess reaction, and Ox-LDL by sandwich ELISA. Lipid and other biochemical parameters were determined by routine laboratory methods. In gout patients, PON1/SOD activities and MDA/Ox-LDL levels were 131.3 ± 25.3/75.3 ± 28.9 kU l(-1) and 6.12 ± 1.67 nmol ml(-1)/690.1 ± 180.2 μg l(-1), respectively. In controls, these were 172.5 ± 27.8/94.0 ± 26.3 kU l(-1) and 4.10 ± 1.25 nmol ml(-1)/452.3 ± 152.1 μg l(-1), respectively. Thus, in gout patients, there was a significant decrease in PON1 (P < 0.01) and SOD (P < 0.05) activities, and an increase in MDA (P < 0.01) and Ox-LDL (P < 0.01) levels compared with controls. PON1 activity correlated positively with SOD (P < 0.05), and negatively with MDA (P < 0.01) and Ox-LDL (P < 0.01). These results suggest that gout patients were in a state of oxidative stress and the protective effects of HDL against atherosclerosis maybe dependent on PON1 activity. These findings may explain in part the reported increase in cardiovascular mortality in gout patients.

Relation between Methylmercury Exposure and Plasma Paraoxonase Activity in Inuit Adults from Nunavik

Background: Methylmercury (MeHg) exposure has been linked to an increased risk of coronary heart disease (CHD). Paraoxonase 1 (PON1), an enzyme located in the high-density–lipoprotein (HDL) fraction of blood lipids, may protect against CHD by metabolizing toxic oxidized lipids associated with low-density liproprotein and HDL. MeHg has been shown to inhibit PON1 activity in vitro, but this effect has not been studied in human populations.Objectives: This study was conducted to determine whether blood mercury levels are linked to decreased plasma PON1 activities in Inuit people who are highly exposed to MeHg through their seafood-based diet.Methods: We measured plasma PON1 activity using a fluorogenic substrate and blood concentrations of mercury and selenium by inductively coupled plasma mass spectrometry in 896 Inuit adults. Sociodemographic, anthropometric, clinical, dietary, and lifestyle variables as well as PON1 gene variants (rs705379, rs662, rs854560) were considered as possible confounders or modifiers of the mercury–PON1 relation in multivariate analyses.Results: In a multiple regression model adjusted for age, HDL cholesterol levels, omega-3 fatty acid content of erythrocyte membranes, and PON1 variants, blood mercury concentrations were inversely associated with PON1 activities [β-coefficient = –0.063; 95% confidence interval (CI), –0.091 to –0.035; p < 0.001], whereas blood selenium concentrations were positively associated with PON1 activities (β-coefficient = 0.067; 95% CI, 0.045–0.088; p < 0.001). We found no interaction between blood mercury levels and PON1 genotypes.Conclusions: Our results suggest that MeHg exposure exerts an inhibitory effect on PON1 activity, which seems to be offset by selenium intake.

Development of an automated method for the determination of human paraoxonase1 activity

Abstract Background: Human plasma paraoxonase1 (PON1) is an esterase catalyzing the hydrolysis of organophosphorus pesticides and other xenobiotics. The aims of this study were to develop a rapid method to determinate PON1 activity, evaluate some interference, and study the influence of storage temperature on PON1 activity assay. Methods: Measurement of PON1 activity was performed for 369 samples by measuring the hydrolysis of paraoxon using a spectrophotometric method adapted on konelab 30 ⃞. Results: The developed method facilitates the determination of PON1 activity at the rate of more than 200 samples per hour, and it is linear between 2 and 900 IU/L. Intra and inter-assay imprecision coefficients of variation were 2% and 5% respectively. PON1 activity in serum was correlated with those in heparinized plasma (r = 0.994, p &lt; 0.001) and in plasma/EDTA (r = 0.962, p &lt; 0.001). The mean inhibition of the PON1 activity was, by EDTA/K3, 41 ± 10 %. There was not significant PON1 activity variation after 40 days of storage at -20°C or at +4 ⃞ C. There were no substantial interferences from haemoglobin, jaundice and hyperlipidemia. Conclusion: The developed method is reliable, reproducible, and suitable. It can also be performed on heparinized plasma for the determination of PON1 activity. Hence, it may be useful for assaying PON1 activity in several intoxications such as organophosphorus, sarin, and soman nerve agents.

Pondering the Significance of PON1

Another strong pharmacogenetic variant for clopidogrel response emerges.

Raspberry juice consumption, oxidative stress and reduction of atherosclerosis risk factors in hypercholesterolemic golden Syrian hamsters

The effects of raspberries on early atherosclerosis in Syrian hamsters were investigated using three juices prepared from var. Cardinal, Glen Ample and Tulameen berries. The hamsters received an atherogenic diet for 12 weeks and at the same time a juice at a daily dose corresponding to the consumption of 275 ml by a 70 kg human. A control group received the same diet with water instead juice. The principal polyphenolic compounds in the juices were anthocyanins and ellagitannins, which were present at concentrations of 218-305 μg mL(-1) and 45-72 μg mL(-1), respectively. The three juices had similar but not identical effects. They all inhibited cardiac and aortic production of superoxide anion and increased hepatic glutathione peroxidase activity although only Tulameen juice brought about a significant increase in superoxide dismutase activity. Glen Ample was the only juice to significantly increase plasma paraoxonase activity. All the juices lowered plasma triglyceride level while consumption of Tulameen and Cardinal, but not Glen Ample, significantly lowered plasma total cholesterol and LDL-cholesterol. Cardinal was the sole juice to significantly increase HDL-cholesterol and likewise it also significantly reduced body weight. These findings suggest that moderate consumption of raspberry juices can help to prevent the development of early atherosclerosis, with the underlying mechanisms related to improved antioxidant status and serum lipid profiles.

Surgery-induced changes in red blood cell and plasma lipid peroxidation, enzymatic and non-enzymatic antioxidants, and blood hematology of female rats: protective role of methylene blue and vitamin E

Objective The aim was to determine the effects on red blood cell (RBC) and plasma lipid peroxidation, antioxidants and blood hematology of intraperitoneally administered vitamin E (VE) and 1% methylene blue (MB) solutions for prevention of adhesions in rats. Study design Thirty-seven female Sprague–Dawley rats were randomized into four groups. An adhesion model was constituted on the left uterine horn in three of the groups. They were then given intraperitoneally 0.9% saline (C group), 10 mg VE (VE group) and 1% MB (MB group) solutions, respectively. A sham group (Sh group), on which laparotomy was performed, received 2 ml of 0.9% saline solution. Results In the C group, the adhesion scores were significantly higher than in the VE ( p < 0.01), MB ( p < 0.01) and Sh groups ( p < 0.005). Results showed that adhesion formation significantly induced nitric oxide (NO) ( p < 0.01) and malondialdehyde (MDA) in plasma ( p < 0.01). The levels of RBC glutathione (GSH) ( p < 0.05) and plasma VE ( p < 0.01) significantly increased after VE administration, whereas the levels of MDA (RBC and plasma) ( p < 0.01), plasma NO ( p < 0.01), blood lymphocyte count ( p < 0.05) and blood white blood cell (WBC) counts ( p < 0.01) decreased. Treatment with MB caused a significant increase in plasma VE ( p < 0.01). On the other hand, results showed that MB significantly decreased blood WBC counts ( p < 0.01), plasma paraoxonase (PON1) ( p < 0.001) and NO ( p < 0.01), and RBC glutathione peroxidase (GPx) activity ( p < 0.05) and MDA levels ( p < 0.01). Conclusion Intraperitoneal administration of MB and VE is significantly effective in preventing intraabdominal adhesion formation in a rat model. Further investigations are necessary, however, to better understand the underlying biochemical mechanisms on lipid peroxidation and antioxidants of MB.

Continuous Reduction of Plasma Paraoxonase Activity With Increasing Dialysis Vintage in Hemodialysis Patients

Plasma paraoxonase (PON) is an enzyme that hydrolyzes organic phosphate and aromatic carboxylic acid esters. Reduced activity is associated with early events of atherogenesis. The relevance of PON phenotypes is not well characterized in hemodialysis patients. In a cross-sectional study we measured PON activity in 377 hemodialysis patients photometrically using the substrates 4-nitrophenylacetate and phenylacetate. The PON ratio was calculated from 4-nitrophenylacetate-derived activity divided by phenylacetate-derived activity. Frequency distribution of the PON ratio showed three different PON phenotypes. 74% of hemodialysis patients showed PON phenotype 1, 21% PON phenotype 2, and 5% PON phenotype 3. Compared to hemodialysis patients with PON 1, patients with PON 2 or 3 showed higher conversion rates for 4-nitrophenylacetate. We observed a significant reduction of PON ratio with increasing dialysis vintage (P<0.001 by ANOVA and post test for linear trend). In patients on hemodialysis treatment for less than 12 months, the PON ratio was 1.16 ± 0.08 (n=64). In patients on hemodialysis treatment for more than 60 months the PON ratio was 1.00 ± 0.04 (n=130; P=0.05). This reduction of PON activity was due to reduced 4-nitrophenylacetate-derived PON activity with increasing dialysis vintage. In conclusion, plasma PON ratio significantly declines with increasing dialysis vintage.

Effects of high sucrose diet, gemfibrozil, and their combination on plasma paraoxonase 1 activity and lipid levels in rats.

We investigated the influence of high sucrose diet (HSD) after 3 or 5 weeks of administration on paraoxonase 1 (PON1) activity in plasma of normolipidemic rats and the relationship between serum PON1 activity, triacylglycerides (TGs), HDL and total cholesterol vs. the control group of rats fed normal, control diet (CD). Because the data about the influence of gemfibrozil (GEM) on PON1 activity are controversial, we also investigated its effects (administration in the 4th and 5th week in rats on HSD and CD) on plasma PON1 activity and lipid levels in normolipidemic rats, and in rats with hypertriglyceridemia caused by HSD. Our results obtained in rats on HSD show a significant increase of plasma TGs levels by 47% (P<0.05) after 5 weeks of treatment, and PON1 activity by 32% and 23% (P<0.05) after 3 and 5 weeks, but without change in lipid levels vs. rats on CD. In the rats on CD and HSD, GEM caused a significant decrease of PON1 activity by 44% and 33%, while a significant decrease of TGs level by 38% (P<0.05) was measured only in rats on CD. The effects of GEM on total cholesterol, HDL and LDL in both groups of rats were typical for its action on lipoprotein metabolism. Because GEM in the rat liver stimulates proliferation of peroxisomes, β oxidation, and production of H₂O₂, it is possible that the oxidative stress induced by GEM damages hepatocytes and lowers the synthesis of PON1.

The differentiating effect of glimepiride and glibenclamide on paraoxonase 1 and platelet-activating factor acetylohydrolase activity

Aims The present study was designed to examine the effect of sulphonylureas, glimepiride (GM) and glibenclamide (GB), on paraoxonase 1 (PON1) and platelet activating factor acetylohydrolase (PAF-AH) activity in normal and streptozotocin(STZ)-induced (50 mg/kg) diabetic rats. Main methods In treated groups, glimepiride (0.1 mg/kg) or glibenclamide (2 mg/kg) was given orally for 4 weeks. A PON1 and PAF-AH activity were estimated by spectrophotometric method. Key findings Hyperglycemia was accompanied by a significant decrease in plasma PON1 activity toward paraoxon (P < 0.001) and phenyl acetate (P < 0.01) and increase in plasma PAF-AH activity (P < 0.01). In STZ-induced diabetic rats the administration of both GM and GB had no effect on plasma PON1 activity but reversed elevated plasma PAF-AH activity (GM: P < 0.05, GB: P < 0.01). In non-diabetic rats after either GM or GB administration the decreased PON1 activity in the plasma was observed (GM: P < 0.001, GB: P < 0.05), but plasma PAF-AH activity remained unchanged. Both GM and GB had no effect on total plasma antioxidant capacity in diabetic and control treated groups. Additionally, both drugs increased PON1 activity toward phenyl acetate in the liver, in diabetic rats (GM: P < 0.05, GB:ns) as well as in non-diabetic rats (GM: P < 0.001, GB: P < 0.001), and reduced lipid peroxidation in the liver. Significance These results demonstrate that in streptozotocin-induced diabetic rats as well as in normal rats glimepiride and glibenclamide have no beneficial effects on circulating PON1 and PAF-AH activities, but both drugs increase PON1 activity in the liver.