Paraoxonase 1 Arylesterase Activity Research Articles

A study of paraoxonase1 (PON1) activities, HDL cholesterol and its association with vascular complication in type 2 diabetes mellitus

The aim of this study is to find out the clinical relevance of estimating serum paraoxonase1 (PON1) arylesterase and PON1 lactonase activity in type 2 diabetes mellitus patients in relation to the development of vascular complications. We have investigated the fasting blood glucose level, HDL cholesterol levels, PON1 arylesterase and PON1 lactonase activities in 80 type 2 diabetes mellitus (DM) patients (DM without complication n = 40, DM with vascular complication n = 40) and compared with 40 healthy age- and sex-matched controls. PON1 arylesterase (ARE) and lactonase (LACT) activities in DM patients with complications (ARE = 60.615 ± 15.510 KU/L, LACT = 18.056 ± 4.215 U/L) are decreased significantly than in DM without complications (ARE = 93.507 ± 21.813 KU/L, LACT = 32.387 ± 8.918 U/L) which are also decreased significantly as compared to controls (ARE = 159.94 ± 45.87 KU/L, LACT = 50.625 ± 6.973 U/L). Logistic regression analysis is applied for assessing predictive utility for diabetic complications demonstrated a significant contribution of PON1 lactonase (Naglekerke’s R2 = 0.625, AUC = 0.907) and arylesterase (Naglekerke’s R2 = 0.427, AUC = 0.853) activities. Decreased PON1 lactonase and arylesterase activities may be considered as an additional risk factor for the development of vascular complications in type 2 DM.

Postprandial Paraoxonase 1 Activity Following Consumption of Recommended Amounts of Mixed Meals in Healthy Males.

Postprandial lipid level increases induce oxidative stress, which is involved in atherogenesis. The antioxidant properties of paraoxonase 1 (PON1) have attracted attention. However, changes in postprandial PON1 levels differ across prior studies, and changes in PON1 lactonase activity, potentially relevant to PON1 physiology, after the consumption of ordinary meals are unknown. Herein we evaluated postprandial serum lipid levels and PON1 changes following mixed-meal consumption of the amounts recommended for ordinary meals. Nine healthy male volunteers consumed three different meals in a randomized cross-over design. The test meals were as follows: S, white rice; SMF, S with fat-containing protein-rich main dishes; and SMFV: SMF with vegetable dishes. The serum lipid concentrations and PON1 lactonase and arylesterase activities were determined during a three-hour period after the consumption of these meals. The postprandial triglyceride levels were higher after consuming the SMF and SMFV meals than after consuming the S meal. Despite postprandial high-density lipoprotein cholesterol being unchanged, PON1 lactonase activity was decreased, while PON1 arylesterase activity was increased in the postprandial state after all test meals. Postprandial changes in lactonase and arylesterase activities did not differ among the test meals. Inverse changes in PON1 lactonase and arylesterase activities were observed after consuming recommended ordinary meals. This observation provides useful information for choosing PON1 species as postprandial markers.

Distribution of Paraoxonase-1 Enzyme Activity in Some Sheep Organs

PON-1 (aryldialkylphosphatase) is an esterase enzyme synthesized by the liver and released into the serum where it is associated with HDL lipoprotein. This study aimed to detect the distribution of PON1 in ram liver, kidney and rumen in addition to GPx and SOD. PON1 paraoxonase activity was detected in liver (1.74�0.10), kidney (1.42�0.04), while it was not detected in rumen. PON1 arylesterase activity was detected in liver (0.26�0.01), kidney (0.25�0.02), while it was not detected in rumen. GPx activity was detected in liver (135.9�2.52), kidney (11.2�0.42), SOD activity was detected in liver (693.39�7.58), kidney (676.72�4.86), while it was not detected in rumen. PON1 is positively correlated to GPx and SOD, while it is negatively correlated to MDA.

Serum Paraoxonase Activity and Malondialdehyde Serum Concentrations Remain Unaffected in Response to Hydroxyurea Therapy in β-Thalassemia Patients.

β-Thalassemia is the most common hereditary disorder characterized by reduced production of β-globin chains of hemoglobin A (HbA). In recent years, hydroxyurea (HU) has shown promising therapeutic benefits in patients with β-thalassemia by fetal hemoglobin augmentation. We have analyzed effects of hydroxyurea treatment on oxidative stress in β-thalassemia patients by assessing activities of paraoxonase (PON) and arylesterase along with malondialdehyde (MDA) and total reactive oxygen species (ROS) concentrations. Blood samples from 159 individuals including 56 HU-treated and 58 untreated β-thalassemia patients and 45 healthy controls were analyzed. PON activity was found to be highest in healthy individuals (177.76 ± 4.44 U/mL) as compared to treated (52.67 ± 3.65 U/mL) and untreated (55.11 ± 3.26 U/mL) patients. A similar trend was observed in the case of arylesterase activity in normal, β-thalassemia-treated, and untreated (210.0 ± 11.25 U/mL, 163.03 ± 9.04 U/mL, 139.77 ± 10.10 U/mL) subjects. Serum MDA concentrations (2.59 ± 0.09 nmol/mL, 2.45 ± 0.08 nmol/mL, and 1.15 ± 0.05 nmol/mL) and total ROS concentrations (3.73 ± 0.20 nmol/mL, 3.54 ± 0.23 nmol/mL, and 2.45 ± 0.14 nmol/mL) were significantly elevated in both groups (untreated and treated) as compared to healthy individuals (P < .01). Oxidative stress was found to be markedly elevated in β-thalassemia patients as compared to healthy controls. Insignificant differences were, however, observed in mean concentrations of PON1 paraoxonase and arylesterase activities, serum MDA concentration and total ROS concentrations between HU-treated and untreated patients. We propose that HU therapy alone seems to be ineffective in managing oxidative stress and is likely to offer a better clinical outcome when supplemented with efficient iron chelation therapy and antioxidants.

Paraoxonase-1 activity is positively related to phospholipid transfer protein activity in type 2 diabetes mellitus: Role of large HDL particles

ObjectivesHigh density lipoprotein (HDL)-associated paraoxonase-1 (PON-1) exerts anti-oxidative properties, whereas phospholipid transfer protein (PLTP) is able to convert mature HDL into larger and smaller HDL particles. Here we tested associations of PON-1 with PLTP in type 2 diabetes mellitus (T2DM), a condition characterized by lower PON-1 activity and higher PLTP activity. Design and methodsSerum PON-1 (arylesterase activity), plasma PLTP activity (liposome-vesicle HDL system), and (apo)lipoproteins were measured in 81 T2DM subjects (mean age 59±9years; 31 women; no insulin treatment). In 48 participants, HDL subfractions were measured by nuclear magnetic resonance spectroscopy. ResultsIn univariate correlation analysis, PON-1 activity was positively related to PLTP activity (r=0.348, p=0.001). PLTP activity was positively related to blood pressure, body mass index and triglycerides, whereas PON-1 activity was positively to HDL cholesterol and apoA-I (p<0.05 to <0.01 for each). Both PLTP activity and PON-I activity were positively related to large HDL particles (r=0.379, p=0.008 and r=0.411, p=0.004, respectively). In multivariable linear regression analysis, PON-1 activity was associated with PLTP activity independent of clinical covariates and HDL cholesterol or apoA-I (β=0.340, p=0.001 and β=0.320, p=0.003, respectively). The association of PON-1 activity with PLTP activity was lost in analysis which included large HDL particles (large HDL: β=0.411, p=0.004). ConclusionsPON-1 activity is positively related to PLTP activity in T2DM, raising the possibility that PLTP could act to maintain PON-1. This association may in part be attributable to a common relationship of PON-1 and PLTP with large HDL particles.

Nevirapine modulation of paraoxonase-1 in the liver: An in vitro three-model approach

IntroductionNevirapine is associated with severe hepatotoxicity, through the formation of reactive metabolites. Paraoxonase-1 (PON-1) is a promiscuous enzyme involved in the metabolism of xeno- and endobiotics and proposed as a biomarker of hepatotoxicity. The aim of this work was to explore the effects of nevirapine and its phase I metabolites, 2-hydroxy-nevirapine and 12-hydroxy-nevirapine, on PON-1 activities. Material and methods2D and 3D primary cultures of rat hepatocytes, and also HepG2 2D cell cultures, were exposed to nevirapine, 2-hydroxy-nevirapine, and 12-hydroxy-nevirapine. The paraoxonase (POase), arylesterase (AREase) and lactonase (LACase) activities of PON-1 were quantified. ResultsEffects of nevirapine and its metabolites were only observed in the 3D cell model. Both nevirapine and 12-hydroxy-nevirapine increased POase (p<0.05, p<0.01) and LACase activities (p<0.05, p<0.001). The AREase activity was increased only upon 12-hydroxy-nevirapine exposure (p<0.01). These modulatory effects were observed at 300μM concentrations of nevirapine and 12-hydroxy-nevirapine. ConclusionsThe formation of 12-hydroxy-nevirapine seems to be the main factor responsible for the increase of PON-1 activities induced by nevirapine exposure. This effect was only observed in the 3D model, suggesting that an in vivo-like system is necessary for this modulation to occur. The present data suggest that the 3D model is a more suitable in vitro model than the conventional ones to explore drug effects on PON-1.

Serum paraoxonase and arylesterase activities in patients with chronic otitis media

Objectives: Paraoxonase-1 (PON1) prevents oxidative stress by inhibiting the oxidation of cell membrane lipids by the reactive oxygen species that form during acute and chronic inflammation. The aim of this study was to investigate serum PON1 activity and oxidative stress in patients with chronic otitis media (COM).Methods: Fifty consecutive patients with COM and 55 controls were enrolled in the present study. The patients were divided into two groups according to the presence of cholesteatoma. The serum PON1 arylesterase activities and lipid hydroperoxide (LOOH) levels were determined.Results: Serum paraoxonase and arylesterase activities were significantly lower in the COM patients than in the controls (P < 0.001 for all comparisons), whereas the LOOH levels were significantly higher (P < 0.001).Discussion: These results indicated that a lower level of PON1 activity was associated with an oxidant–antioxidant imbalance. In addition, decreased PON1 activity may play an important role in the pathophysiology of COM.

The Paraoxonase 1 Arylesterase Activity, Total Oxidative Stress, Nitric Oxide and Vitamin C Levels in Maternal Serum, and Their Relation to Birth Weight of Newborn.

Aim of this study is to find out clinical relevance of estimating PON1 arylesterase activity, total oxidative stress (TOS), nitric oxide (NO), and vitamin C levels in maternal serum for prediction of birth weight of newborn. We have investigated the PON1 arylesterase activity, TOS, NO, vitamin C, total protein, and albumin levels in 56 postnatal clinic patients having newborn weighing <2500gm (low birth weight) and compared with 56 postnatal clinic patients having newborn weighing >2500gm. Samples were collected immediately after delivery. PON1 arylesterase activity levels show significant decrease in cases as compared to controls (93.27±13.76kU/l vs. 112.77±9.42kU/l). Nitric oxide (nitrate+nitrite) levels are also found to be significantly decreased in cases with respect to controls (22.89±2.65 umol/l vs. 24.73±3.80 umol/l). Total oxidative stress is significantly increased in cases than in control subjects (23.34±2.64μmol H2O2 equiv./l vs.±21.43±2.47μmol H2O2 equiv/l). Vitamin C levels are also significantly decreased in cases as compared to controls (1.23±0.25mg/dl vs. 1.34±0.28mg/dl). Positive correlation between neonatal birth weight and maternal serum PON1 arylesterase activity (r=0.682, p<0.05) while negative correlation is obtained between neonatal birth weight and maternal serum oxidative stress (r=-0.478, p<0.05). Logistic regression analysis is applied for assessing predictive utility which demonstrated a significant association of birth weight with PON1 arylesterase activity (AUC=0.960, Naglekerke's R (2)=0.793, p<0.05). Decreased arylesterase activity and antioxidant vitamin C levels with increased total oxidative stress in maternal serum may be considered as the additional risk factors for the development of low birth weight newborn.

Higher Levels of Oxidized Low Density Lipoproteins in Alzheimer's Disease Patients: Roles for Platelet Activating Factor Acetyl Hydrolase and Paraoxonase-1.

Alzheimer's disease (AD) is associated with oxidative damage of low density lipoproteins (ox-LDL). In order to investigate whether higher levels of ox-LDL are related to alterations of the activity of enzymes involved in lipid metabolism, we studied the activity of paraoxonase-1 (PON1) and platelet activating factor acetylhydrolase (PAF-AH) in AD patients and the relationship between biochemical markers and severity of the disease. Levels of ox-LDL, PON1 (paraoxonase, arylesterase, and lactonase activities), and PAF-AH activity were evaluated in plasma from 49 patients affected by AD and from 34 control subjects matched for gender and age. Our results demonstrated alterations in the activities of PON1 and PAF-AH in AD patients compared to controls and showed, for the first time, a relationship between the activities of these enzymes, ox-LDL levels, and severity of the disease. A significant negative correlation was observed between the ratio PON1/PAF-AH and ox-LDL. Whatever the causes that contribute to a systemic oxidative stress in AD, our results have shown that AD patients exhibit higher PAF-AH activity than control subjects and higher ox-LDL. This phenomenon, in combination with diminished PON1 in these patients and, consequently, the relatively lower ratio PON1/PAF-AH activity, could contribute to inflammation and oxidative stress of plasma lipoproteins.

PON1 polymorphisms are associated with polycystic ovary syndrome susceptibility, related traits, and PON1 activity in Indian women with the syndrome

To investigate the association of paraoxonase 1 (PON1) polymorphisms (L55M and Q192R) with polycystic ovary syndrome (PCOS) susceptibility and its related traits in Indian women. Case-control study. Academic research institute, infertility, and endocrinology clinics. Controls (n = 326), women with PCOS (n = 482). None. Genotypic and allelic frequency distribution, genotype-phenotype association, different PON1 activities (lactonase, arylesterase, and paraoxonase). The genotypic and allelic frequency distributions of the L55M polymorphism were significantly different between lean controls and lean women with PCOS, and this polymorphism reduced the risk of PCOS development in lean but not in obese Indian women. Furthermore, this polymorphism was significantly associated with decreased 2-hour glucose, apolipoprotein B, free and bioavailable T, and free androgen index concurrent with increased sex hormone-binding globulin (SHBG) and FSH levels only in lean women with PCOS. However, Q192R polymorphism showed comparable genotypic frequency distribution between controls and women with PCOS. PON1 lactonase and arylesterase activities were significantly decreased in women with PCOS compared with controls. PON1 polymorphisms were shown to influence its activities. Our study showed that L55M, but not Q192R, polymorphism is significantly associated with reduced PCOS susceptibility only in lean women and also impacts glucose metabolism, lipid parameters, and hyperandrogenemia in them. Our study therefore suggests the possibility of differential genetic pathophysiology of PCOS between lean and obese women.

Low protective PON1 lactonase activity in an Arab population with high rates of coronary heart disease and diabetes

BackgroundRecent studies showing that high density lipoproteins (HDL) can effect plaque regression indicate that recent trial failures do not exclude an atheroprotective role of HDL. Instead, they highlight differences between HDL function and measured HDL-cholesterol (HDL-C). PON1 is one key functional activity of HDL. Urban Palestinians have lower HDL-C and a higher incidence and mortality of coronary heart disease than those of Israelis. We hypothesized that the cardioprotective PON1 lactonase and arylesterase activities and PON1 functional genotype may differ between Palestinians and Israelis. MethodsWe measured PON1 activities in a cross-sectional population-based study of Palestinian (n=960) and Israeli (n=694) residents in Jerusalem, 1654 participants in all. ResultsPalestinians had high prevalences of obesity and diabetes and low mean concentrations of HDL-cholesterol (0.97mmol/l in men and 1.19mmol/l in women). Lactonase and arylesterase activities were lower by 10.8% (p=1.2∗10−14) and 2.7% (p<0.0005), respectively, in Palestinians as compared to Israelis. The functional genotype distribution, demonstrated by plotting paraoxonase vs lactonase activities, showed a modest between-group difference (p=0.024), with 12.1% RR in Palestinian Arabs vs 8.4% in Israeli Jews, but no overall difference in allele frequencies. Lactonase correlated inversely with age (Spearman's rho=−.156), weakly with BMI (−.059), positively with HDL-C (.173) and non-HDL-C (.103), but was not associated with triglycerides or fasting glucose. Palestinians showed consistently lower lactonase activity in logistic regression models adjusted for multiple covariates and for functional genotype (odds ratios of 1.81 and 1.98, respectively, for the lower fifth vs the upper 4 fifths of lactonase activity p<0.0001). ConclusionWe showed a lower physiologically-significant lactonase PON1 activity in an Arab population, a finding consistent with the high cardiovascular and diabetes risk of Palestinians.

Altered lipid subfraction profile and impaired antioxidant defense of high-density lipoprotein in Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is a rare disease caused by biallelic mutation in the 7-dehydrocholesterol (7DHC) reductase gene. High oxidizability of 7DHC and the appearance of small-sized low-density lipoprotein (LDL) subfractions indicate increased endogenous oxidative stress that is counterbalanced by natural antioxidant defense mechanisms including the high-density lipoprotein (HDL)-associated paraoxonase-1 (PON1) enzyme. PON1 prevents lipoproteins from oxidative modifications; however, PON1 activity and the distribution of lipoprotein subfractions have not been studied in SLOS. 7DHC levels and PON1 arylesterase activities were measured spectrophotometrically in 11 SLOS patients and 10 healthy children. Lipoprotein subfractions were detected by polyacrylamide gel electrophoresis. Compared to controls, there was a shift towards the small-dense LDL subfraction and the large HDL subfraction in SLOS. PON1 arylesterase activity was significantly decreased in SLOS patients and correlated negatively with the proportion of small-dense LDL subfraction and the proportion of large HDL subfraction. Significant positive correlations were detected between PON1 arylesterase activity and the ratios of intermediate and small HDL subfractions. Decreased PON1 activity and the deleterious shift in the distribution of lipoprotein subfractions may contribute to the impaired antioxidant status observed in SLOS. Monitoring of serum PON1 arylesterase activity may be a complementary biomarker in SLOS.

Role of Curcumin in Modulating Plasma PON1 Arylesterase Activity and Susceptibility to LDL Oxidation in Oxidatively Challenged Wistar Rats

Curcumin (β-diketones diferuloylmethane), a biphenolic compound of Curcuma longa is reported to elicit a plethora of health protective effects. The present study was carried out to investigate the in vivo protective effect of curcumin (340 mg/kg b.w., oral) against HgCl2 induced oxidative stress in wistar rats. PON1 arylesterase activity, -SH value, and LDL oxidation susceptibility were determined in plasma of control, control+ curcumin, control+ HgCl2, HgCl2+ curcumin treated rats. Oxidative stress down-regulated PON1 activity, decreased -SH value and increased LDL oxidation susceptibility in plasma. Curcumin treatment significantly (p<0.05) increased PON1 activity, -SH value and reduced LDL oxidation susceptibility in healthy and HgCl2 treated rats. We show that curcumin protects PON1 activity, -SH value and LDL oxidation, and hypothesize that its supplementation may lower the incidence of those diseases where reduced PON1 activity and higher LDL oxidation is reported. Keywords: Curcumin, LDL oxidation, oxidative stress, plasma, PON1, thiol (-SH).

Sleepiness, inflammation and oxidative stress markers in middle-aged males with obstructive sleep apnea without metabolic syndrome: a cross-sectional study.

BackgroundThe simultaneous occurrence of metabolic syndrome and excessive daytime sleepiness are very common in obstructive sleep apnea (OSA) patients. Both conditions, if present in OSA, have been reported to be associated with inflammation and disruption of oxidative stress balance that impair the cardiovascular system. To verify the impact of daytime sleepiness on inflammatory and oxidative stress markers, we evaluated OSA patients without significant metabolic disturbance.MethodsThirty-five male subjects without diagnostic criteria for metabolic syndrome (Adult Treatment Panel III) were distributed into a control group (n = 10) (43 ± 10.56 years, apnea-hypopnea index - AHI 2.71 ± 1.48/hour), a non-sleepy OSA group (n = 11) (42.36 ± 9.48 years, AHI 29.48 ± 22.83/hour) and a sleepy OSA group (n = 14) (45.43 ± 10.06 years, AHI 38.20 ± 25.54/hour). Excessive daytime sleepiness was considered when Epworth sleepiness scale score was ≥ 10. Levels of high-sensitivity C-reactive protein, homocysteine and cysteine, and paraoxonase-1 activity and arylesterase activity of paraoxonase-1 were evaluated.ResultsPatients with OSA and excessive daytime sleepiness presented increased high-sensitivity C-reactive protein levels even after controlling for confounders. No significant differences were found among the groups in paraoxonase-1 activity nor arylesterase activity of paraoxonase-1. AHI was independently associated and excessive daytime sleepiness tended to have an association with high-sensitivity C-reactive protein.ConclusionsIn the absence of metabolic syndrome, increased inflammatory response was associated with AHI and daytime sleepiness, while OSA was not associated with abnormalities in oxidative stress markers.

Alteration of HDL functionality and PON1 activities in acute coronary syndrome patients

ObjectiveThe functionality of HDL has been suggested as an important factor in the prevention of cardiovascular and coronary artery diseases. The objective of the present study was to investigate the functionality of HDL and the factors that may affect the anti-atherogenic properties of HDL in ACS patients. Methods and resultsOne hundred healthy subjects and 205 ACS patients were recruited. HDL functionality was evaluated by measuring their capacity to mediate cholesterol efflux from J774 macrophages. Oxidative stress status was determined by measuring plasma malondialdehyde (MDA), protein carbonyl, and vitamin E levels by HPLC. The PON1 Q192R polymorphism status and PON1 paraoxonase and arylesterase activities of the healthy subjects and ACS patients were also determined. The HDL of ACS patients displayed a limited capacity to mediate cholesterol efflux, especially via the ABCA1-pathway. MDA (7.06±0.29μM) and protein carbonyl (9.29±0.26μM) levels were significantly higher in ACS patients than in healthy subjects (2.29±0.21μM and 3.07±0.17μM, respectively, p<0.0001), while α- and γ-tocopherol (vitamin E) levels in ACS patients were 8-fold (p<0.001) and 2-fold (p<0.05) lower than in healthy subjects. Paraoxonase, arylesterase and HDL-corrected PON1 activities (PON1 activity/HDL ratio) were significantly lower in ACS patients. Logistic regression analyses showed that high PON1 paraoxonase and arylesterase activities had a significant protective effect (OR=0.413, CI 0.289–0.590, p<0.001; OR=0.232 CI 0.107–0.499, p<0.001, respectively) even when adjusted for HDL level, age, BMI, and PON1 polymorphism. ConclusionThe results of the present study showed that the functionality of HDL is impaired in ACS patients and that the impairment may be due to oxidative stress and an alteration of PON1 activities.

HDL3 stimulates paraoxonase 1 antiatherogenic catalytic and biological activities in a macrophage model system: in vivo and in vitro studies.

We analyzed in-vivo and in-vitro high density lipoprotein (HDL) effects on paraoxonase 1 (PON1) antiatherogenic properties in serum and in macrophages. Intraperitoneal injection to C57BL/6 mice of recombinant PON1 (rePON1) + HDL, in comparison to HDL or to rePON1 alone, significantly increased serum PON1 arylesterase activity (by 20%), and serum-mediated cholesterol efflux from J774A.1 macrophages (by 18%). Similarly, in peritoneal macrophages (MPM) harvested from mice injected with HDL + rePON1 versus rePON1 alone, we observed reduction in oxidative stress (by 11%), increase in cellular PON1 activity (by 14%) and in HDL-mediated cholesterol efflux (by 38%). Incubation of serum or HDL with rePON1, substantially increased PON1 arylesterase activity, two-fold more than the expected additive values. HDL2 and HDL3 increased PON1 activity by 199% or 274%, respectively. Macrophage (J774A.1) cholesterol efflux rate significantly increased by HDL3 + rePON1 versus HDL3 alone (by 19%), but not by HDL2 + rePON1 versus HDL2 alone. Oxidation of HDL3 reduced its ability to induce macrophage cholesterol efflux, and abolished HDL3 stimulatory effects on rePON1. Addition of exogenous polyphenol quercetin (60 µM), but not phosphatidylcholine or apolipoprotein A1, to HDL + rePON1 increased PON1 activity (by 404%), increased the ability to reduce oxidative stress in J774A.1 macrophages (by 53%) and to stimulate macrophage cholesterol efflux (by 14%). Upon adding the hypocholesterolemic drug simvastatin (15 µg/mL) to HDL + rePON1, PON1 activity and the ability to induce macrophage cholesterol efflux increased, in comparison to HDL + rePON1. We thus concluded that HDL (mostly HDL3), stimulates PON1 antiatherogenic activities in macrophages, and these PON1 activities were further stimulated by quercetin, or by simvastatin.

Exploring the aryl esterase catalysis of paraoxonase-1 through solvent kinetic isotope effects and phosphonate-based isosteric analogues of the tetrahedral reaction intermediate

Although a recent study of Debord etal. in Biochimie (2014; 97:72-77) described the thermodynamics of the catalysed hydrolysis of phenyl acetate by human paraoxonase-1, the mechanistic details along the reaction route of this enzyme remain unclear. Therefore, we briefly present the solvent kinetic isotope effects on the phenyl acetate esterase activity of paraoxonase-1 and its inhibition with the phenyl methylphosphonate anion, which is a stable isosteric analogue that mimics the high-energy tetrahedral intermediate on the hydroxide-promoted hydrolysis pathway. The data show normal isotope effects, while proton inventory analysis indicates that two protons contribute to the kinetic isotope effect. Coherently, moderate competitive inhibition with the phenyl methylphosphonate anion reveals that the rate-limiting transition state suboptimally resembles the tetrahedral intermediate. The implications of these findings can be attributed to two possible reaction mechanisms that might occur during the paraoxonase-1-catalysed hydrolysis of phenyl acetate.

Paraoxonase 1 Activity in Patients with Chronic Obstructive Pulmonary Disease

Introduction: Paraoxonase 1 (PON1) is an antioxidative enzyme manly associated with high density lipoproteins (HDL) in the peripheral blood. The aim of this study was to determine the PON1 paraoxonase and arylesterase activities in patients with chronic obstructive pulmonary disease (COPD). We also aimed to determine the concentration of reduced thiol groups as a marker of protein oxidation. Materials and methods: The study included 105 patients with stable COPD and 44 healthy controls. PON1 activities and thiols concentration were assayed in sera by spectrophotometry. Results: PON1 basal (POX) and salt-stimulated paraoxonase activity (POX1) as well as arylesterase activity (ARE) were significantly reduced in COPD patients. In addition, concentration of reduced thiol groups was significantly decreased in COPD group. PON1 activities were similar in patients with different disease severity (GOLD stages). However, a significant reduction in POX, POX1 and ARE was observed already in GOLD II stage when compared to controls. POX and POX1 showed modest while ARE yielded very good power for discrimination between healthy subjects and COPD patients. Univariate and multivariate logistic regression analysis indicated that ARE is a good COPD predictor. Conclusion: Reduction of PON1 activity observed in COPD patients could be partly caused by oxidative environment. Lower concentrations of reduced thiol groups in COPD patients suggest that a decrease in PON1 activity could reflect oxidative changes of enzyme free cysteine residues. Furthermore, decreased PON1 arylesterase activity might indicate a down-regulation of PON1 concentration. Our results suggest that ARE could be considered as potential biomarker for COPD diagnosis.

Serum paraoxonase-1 activity is more closely related to HDL particle concentration and large HDL particles than to HDL cholesterol in Type 2 diabetic and non-diabetic subjects

ObjectivesWe determined relationships of the anti-oxidative enzyme, paraoxonase-1 (PON-1), with high density lipoprotein (HDL) subfractions, and tested whether these relationships are stronger than those with HDL cholesterol and apolipoprotein A-I (apoA-I) in subjects with and without type 2 diabetes mellitus (T2DM). Design and methodsSerum PON-1 (arylesterase activity) and HDL subfractions (nuclear magnetic resonance spectroscopy) were determined in 67 T2DM patients and in 56 non-diabetic subjects. ResultsPON-1 activity, HDL cholesterol and apoA-I were decreased in T2DM (all p<0.05). The HDL particle concentration was unaltered, but large HDL particles, medium HDL particles and HDL particle size were decreased, whereas small HDL particles were increased in T2DM (all p<0.05). PON-1 was more closely related to HDL cholesterol than to apoA-I (p=0.001). In turn, the positive relationship of PON-1 with the HDL particle concentration and with large HDL particles was stronger than that with HDL cholesterol (both p<0.01). The inverse relationship of PON-1 with T2DM was only modestly attenuated by HDL cholesterol or HDL particle characteristics. ConclusionsPON-1 activity is more closely related to the HDL particle concentration or large HDL particles than to HDL cholesterol. Impaired PON-1 activity in T2DM is not to a considerable extent explained by altered HDL subfraction levels.

0169 Paraoxonase 1 activity, in the fructose-fed rats, in the presence and in the absence of an antioxidant treatment with alpha-lipoic acid

Paraoxonase 1 (PON1) is an esterase synthesized by the liver and secreted into the plasma, where it is associated with high density lipoproteins (HDL). Its role is to protect LDL and HDL from oxidation, thus preventing atherosclerosis. A decreased level of plasma PON1 activities has been found in diabetes mellitus, cardiovascular disorders and chronic liver diseases; but, it can also be influenced by diet and life-style. The purpose of this study was to assess the PON1 activities in the insulin-resistant rats fed with a fructose-enriched diet, in the presence and in the absence of an antioxidant treatment with alpha-lipoic acid (AL). 48 male Sprague-Dawley rats were randomized into two series: rats fed for 3 months with standard chow (Control) or with standard chow supplemented with fructose (60%). In each series, a group of rats was treated intraperitoneally during 14 days/month with NaCl 0.9% and another group with 50 mg/kg/day AL. At the end of the 3 months, we assessed: 1) peripheral tissue resistance to insulin (HOMA-IR) and plasma lipid profile, 2) paraoxonase, arylesterase and lactonase activities of PON1, 3) plasma homocysteine (Hcy) level and 4) hepatic transaminase activities: aspartate-aminotransferase and alanine-aminotransferase. The fructose intake increased peripheral tissue resistance to insulin (HOMA-IR) and plasma lipoprotein level, less the HDL. Also, transaminase and PON1 activities, especially arylesterase and lactonase activities, and the plasma Hcy level were significantly (p>0.05) enhanced in the fructose group. The AL discontinuous treatment associated with the fructose-enriched diet improved the tissue sensitivity to insulin and decreased the plasma lipoprotein levels. Moreover, the AL treatment restored PON1 and transaminase activities, without influencing the Hcy concentration. A decrease in plasma transaminase activities was noted even when AL was associated with standard diet. In our experimental conditions, the fructose intake induced an increase in plasma transaminase and PON1 activities in association with a Hyperhomocysteinemia. The AL treatment restored the enzymes’ activities and had a hepatoprotective effect, but without influence on Hcy level.