Intestinally implanted Nippostrongylus brasiliensis adult worms decrease serum paraoxonase-1 activity in rats

We have previously reported a significant decrease in serum PON1 activity after Nippostrongylus brasiliensis infection in Wistar rats in association with the inflammatory response mounted against the parasite in the migratory phase of infection. However, the roles of intestinal phase and the associated oxidative stress during N. brasiliensis infection on PON1 activity have not yet been elucidated. In the present study, we observed a significant reduction in serum paraoxonase and arylesterase activity on days 6 and 9 post-implantation with N. brasiliensis adult worms in the absence of a significant increase in various serum pro-inflammatory cytokines. In addition, provision of the antioxidant butylated hydroxyanisole (BHA) to adult worm-implanted rats did not ameliorate the reduction in PON1 activity. Due to the prolonged intestinal phase of gastrointestinal nematode infections, alterations in PON1 activity during this phase need to be further examined to elucidate the mechanism of alteration in PON1 activity.     

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

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

Gender related differences in paraoxonase 1 response to high-fat diet-induced oxidative stress

Objective: To evaluate the influence of the pro‐oxidant and proinflammatory state related to dietary obesity on serum paraoxonase 1 (PON1) activity in male and female rats. Methods and Procedures: Adult Wistar rats of both genders were fed on a high‐fat diet to induce weight gain or standard diet for 14 weeks. Body weight was assessed weekly and food intake fortnightly throughout the dietary treatment. Biometrical parameters and serum lipid profile, glucose, insulin, and adipokine levels were measured. To assess the effect of dietary obesity on oxidative stress, levels of liver and serum thiobarbituric acid reactive substances, liver protein carbonyl groups, liver antioxidant enzymes activities, and serum PON1 activities were measured. Results: High‐fat diet feeding induced a significant body weight gain in both male and female rats, as well as a reduction of liver antioxidant protection. High‐fat diet increased serum lipid peroxides in male rats and reduced serum PON1 activities and serum apolipoprotein A‐I (apoA‐I) levels in females, although did not alter serum PON1 or apolipoprotein J (apoJ) levels. Discussion: Our results reveal a gender dimorphism in the high‐fat diet‐induced reduction of serum PON1 activity, which is likely to be related to the greater obese and proinflammatory state achieved in female rats. We suggest that the enhanced oxidative stress caused by dietary increased body weight, on leading to high‐density lipoprotein (HDL), apoA‐I or PON1 oxidation could entail the destabilization of the PON1 association to HDL or a direct inactivation of PON1 enzymatic activity, thus accounting for the decreased serum PON1 activities observed in female rats.     

Paraoxonase 1 (PON1) attenuates diabetes development in mice through its antioxidative properties

Paraoxonase 1 (PON1) is a lipo-lactonase which is associated with HDL and possesses antioxidative properties. Diabetes is characterized by increased oxidative stress and by decreased PON1 activity. We aimed to analyze whether oxidative status and PON1 levels in mouse sera and macrophages could affect streptozotocin (STZ)-induced diabetes development. We have used two models of mice under low oxidative stress: STZ-injected apolipoprotein E-deficient mice supplemented with the antioxidant vitamin E, and P47(phox) knockout mice. In both mice models the decreased serum basal oxidative stress, was associated with a decreased rate of diabetes development, compared with control STZ-injected apolipoprotein E-deficient mice or with C57BL mice respectively. These data suggest that oxidative stress accelerates diabetes development. Next, we analyzed the effect of PON1 on macrophage oxidative stress and on diabetes development in STZ-injected C57BL mice, PON1 knockout mice, and PON1 transgenic mice. PON1 overexpression was associated with decreased diabetes-induced macrophage oxidative stress, decreased diabetes development, and decreased mortality, in comparison to C57BL mice, and even more so when compared to PON1KO mice. We thus concluded that on increasing PON1 expression in mice, diabetes development is attenuated, a phenomenon which could be attributed to the antioxidative properties of PON1, as decrement of oxidative stress significantly attenuated STZ-induced diabetes development.     

Paraoxonase, a cardioprotective enzyme: continuing issues

PURPOSE OF REVIEW: The paraoxonase family consists of three members (PON1, PON2 and PON3) that share structural properties and enzymatic activities, among which is the ability to hydrolyze oxidized lipids in LDL. The exact function of the different family members is not clear although the conservation among the individual family members across species suggests a strong evolutionary pressure to preserve these functional differences. The purpose of this review is to highlight several problems with respect to the mechanism of action of paraoxonase and differences between the family members that merit further study. RECENT FINDINGS: PON1 transgenic mice are at lower risk for atherosclerosis, which is consistent with PON1 gene knockout studies in mice and human genetic polymorphism studies. The exact mechanism by which paraoxonase is cardioprotective is not clear, although it is likely to be related to its antioxidant properties especially on LDL. PON1 levels are influenced by a variety of environmental factors, including statins and cytokines. The preferential association of PON1 with HDL is mediated in part by its signal peptide and by desorption from the plasma membrane of expressing cells by HDL or phospholipid. Apolipoprotein A-I is not necessary for PON1 association with HDL, but its activity is stabilized in the presence of the apolipoprotein. Only in the absence of both lecithin cholesterol acyltransferase and apolipoprotein E is paraoxonase associated with non-HDL lipoproteins. The displacement of paraoxonase by serum amyloid A may explain in part the proinflammatory nature of HDL in the acute phase. The mechanism by which PON3 associates with HDL has not been studied. In addition to the ability to hydrolyze oxidized lipids in LDL, paraoxonase also alters the oxidative state of macrophages. Exogenous PON1 is able to reverse the oxidative stress in macrophages in aged apolipoprotein E deficient and PON1 deficient mice. The increase in oxidative stress in macrophages from PON1 deficient mice occurs despite the expression of PON2 and PON3 in macrophages. PON1 has recently been shown to contain phospholipase A2 activity, with the subsequent release of lysophosphatidylcholine that influences macrophage cholesterol biosynthesis. SUMMARY: PON1 mass and activity in the plasma significantly influence the risk of developing cardiovascular disease. This is likely mediated by its antioxidation properties on LDL and/or macrophages. The precise mechanism by which this HDL associated protein prevents or attenuates oxidation of LDL and the oxidative stress of macrophages remains to be clarified. The role of PON2 and PON3 in atherosclerosis and their antioxidant properties with respect to LDL and macrophages also merit further investigation.     

PON1 55/192 polymorphism, oxidative stress, type, prognosis and severity of stroke

We investigated the association of PON1 55/192 polymorphisms with type, severity and prognosis of stroke and oxidative markers. Paraoxonase1 (PON1), Glutathione Reductase (GSH-Rd) and Malondialdehyde (MDA) levels were measured at day 1 and at day 5 following the onset of stroke. Genotypes were determined by polymerase chain reaction and restriction digestion. The frequencies of QQ and MM genotypes of PON1 192 and PON1 55, respectively, were significantly higher in controls than in patients. However, the allele frequencies of PON1 192 R and PON1 55 L were significantly more frequent in patients compared to controls. The frequency of combined genotype of RR/LL was significantly higher in cardioembolic group than in atherothrombotic group. PON1 activities were significantly diminished in stroke patients compared to controls. In contrast, serum MDA levels were significantly greater in patients than the values in controls. GSH-Rd activity was higher in patients with small lesion and good prognosis than those with large and poor prognosis. Low density lipoprotein (LDL) levels in patients with large lesions were higher than those with small lesions. PON1 55/192 polymorphisms influence activity of the enzyme. PON1 55/192 genotypes have been associated with MDA levels. In conclusion, PON1 genetic variations are associated with risk factors, severity, type and prognosis of stroke and oxidative stress.     

S-Glutathionylation regulates HDL-associated paraoxonase 1 (PON1) activity

HDL-associated paraoxonase 1 (PON1) undergoes inactivation under oxidative stress and is preserved by dietary antioxidants. PON1 cysteines can affect PON1 enzymatic activities. S-Glutathionylation, a redox regulatory mechanism characterized by the formation of a mixed disulfide between a protein thiol and oxidized glutathione (GSSG), was shown to preserve some enzymes from irreversible inactivation under pathological conditions. We questioned whether PON1 activity is regulated by S-glutathionylation. Incubation of PON1 or HDL with GSSG indeed resulted in a dose-dependent inactivation of PON1 activities, including its physiological activity to increase HDL-mediated macrophage cholesterol efflux. This PON1 inactivation was associated with the formation of a mixed disulfide bond between GSSG and PON1's cysteine residue(s), as detected by immunoblotting with anti-glutathione IgG. PON1 activity was recovered following the addition of a reducing agent, DL-Dithiothreitol (DTT), to the PON1-SSG complex. We thus conclude that HDL-associated serum PON1 can undergo S-glutathionylation under oxidative stress with a consequent reversible inactivation.     

The age-related paraoxonase 1 response is altered by long-term caloric restriction in male and female rats

Caloric restriction (CR) has been shown to attenuate age-related oxidative damage and to improve major atherosclerotic risk factors. Paraoxonase 1 (PON1), an enzyme specifically associated with HDL containing apolipoproteins A-I and J, has been reported to prevent the proatherosclerotic effects of oxidized LDL. The aim of this study was to evaluate whether modulation of PON1 activity is part of the underlying CR mechanisms that attenuate the age-associated negative effects. Experimental groups were 1 year old rats of both genders subjected to 40% CR for 1 year and two ad libitum-fed groups, also including rats of both genders, euthanized at 6 months or 2 years. Aging impaired the serum lipid profile and increased lipid peroxidation, PON1 activities, and the content of both PON1 and apolipoprotein J in HDL, which suggests an HDL subfraction redistribution to protect LDL more effectively from oxidation. The CR-associated improved lipid profile and the decreased lipid peroxide levels would lead to the decreased arylesterase activity seen in old CR animals, suggesting that PON1 modulation is not an integral part of the main antioxidant mechanisms of CR but rather that CR would determine a more youthful and less oxidative situation in which the protection of LDL would be less necessary.     

Serum lipid profile paraoxonase and arylesterase activities in psoriasis

Psoriasis is a common chronic and recurrent inflammatory skin disease with unknown etiology that has been associated with abnormal plasma lipid metabolism and oxidative stress. There are controversial results in the previous studies investigating oxidant/antioxidant systems in psoriasis. The aim of this work was to evaluate dyslipidemia, oxidative stress, total antioxidant capacity and serum paraoxonase (PON1) and arylesterase (ARE) activities in psoriasis, and to look for a correlation between these parameters and lesion percentage in psoriasis. Thirty psoriatic patients and twenty three sex‐ and agematched healthy volunteers were included in the study. From blood samples, lipid profile, malondialdehyde (MDA) levels, total antioxidant capacity (TAO), serum PON1 and ARE activities were determined. No significant differences between the patients and controls were found in terms of total cholesterol, triacylglycerol (TAG), HDL‐cholesterol, LDL‐cholesterol, VLDL‐cholesterol, MDA and TAO levels. Serum PON1 and sodium‐stimulated PON1 activities (p < 0.05) and ARE activity (p < 0.01) were found significantly higher in the patients than in the controls. There was not any significant correlation between lesion percentage and the parameters studied. Copyright © 2009 John Wiley & Sons, Ltd.     

Iron-ascorbic acid-induced oxidant stress and its quenching by paraoxonase 1 in HDL and the liver: comparison between humans and rats

Paraoxonase 1 (PON1) is a serum enzyme closely associated with high-density lipoprotein (HDL), which may protect against atherosclerosis by hydrolyzing lipid peroxides and several organophosphorus compounds. The purpose of the present study was to test the hypothesis that lipid peroxidation modifies the activity and protein mass of PON1 in humans and rats. Our findings revealed that the bulk of the activity monitored by the hydrolysis of paraoxon and phenyl acetate was confined to liver intracellular endoplasmic reticulum-derived microsomes and was mostly recovered in circulating HDL3. Confirmation was obtained by the determination of PON1 expression by Western blot. It is noteworthy that PON1 levels were consistently decreased in human sera, HDL, and liver microsomes compared with rat counterparts. Concomitant with iron-ascorbate-mediated lipid peroxidation, there was a decline in PON1 activity and protein in both HDL3 and microsomes, which was attenuated by butylated hydroxytoluene antioxidant treatment. The current data indicate that PON1 localization in microsomes and HDL3 could represent a selective cellular and lipoprotein response to oxidative stress. This was tested by the iron-ascorbate oxygen-radical generating system. It is also proposed that the increased PON1 level may have a function related to the well-known atherosclerosis resistance of rats.     

Activity of paraoxonase 1 and lipid profile in healthy children

Paraoxonase 1 (PON1) seems to have a relevant role in detoxifying processes and in atherosclerosis. The aim of this study was to determine PON1 activity, the total antioxidant capacity, as well as entire lipid profile in children for screening of possible risk of atherosclerosis development. Serum PON1 arylesterase/paraoxonase activities were determined spectrophotometrically. The total antioxidant capacity of the serum was measured by TEAC method. Parameters of lipid profile were analyzed by routine laboratory methods. It has been shown that PON1 arylesterase/ paraoxonase activities were very similar to values found in adults. In children, no significant correlation between PON1 arylesterase activity and HDL was observed. PON1 paraoxonase activity correlated only with atherogenic index. PON1 arylesterase activity was significantly higher in girls than in boys. The antioxidant capacity was inversely related to the body mass index. In this study, PON1 activity was determined in healthy children aged 11 to 12 years and we found a similarity in PON1 activities of children and adults. Moreover, the results of our study support the hypothesis that higher body weight of children may contribute to a greater risk for development of atherosclerosis in which oxidative stress plays a role.     

Trends of reproductive hormones in male rats during psychosocial stress: role of glucocorticoid metabolism in behavioral dominance

Stress in socially subordinate male rats, associated with aggressive attacks by dominant males, was studied in a group-housing context called the visible burrow system (VBS). It has been established that subordinate males have reduced serum testosterone (T) and higher corticosterone (CORT) relative to dominant and singly housed control males. The relationship of the decreased circulating T levels in subordinate males to changes in serum LH concentrations has not been evaluated previously. Since decreases in LH during stress may cause reductions in Leydig cell steroidogenic activity, the present study defined the temporal profiles of serum LH, T, and CORT in dominant and subordinate males on Days 4, 7, and 14 of a 14-day housing period in the VBS. The same parameters were followed in serum samples from single-housed control males. Leydig cells express glucocorticoid receptors and may also be targeted for direct inhibition of steroidogenesis by glucocorticoid. We hypothesize that Leydig cells are protected from inhibition by CORT at basal concentrations through oxidative inactivation of glucocorticoid by 11beta-hydroxysteroid dehydrogenase (11betaHSD). However, Leydig cell steroidogenesis is inhibited when 11betaHSD metabolizing capacity is exceeded. Therefore, 11betaHSD enzyme activity levels were measured in Leydig cells of VBS-housed males at the same time points. Significant increases in LH and T relative to control were observed in the dominant animals on Day 4, which were associated with the overt establishment of behavioral dominance as evidenced by victorious agonistic encounters. Serum LH and T were lower in subordinate males on Day 7, but T alone was lower on Day 14, suggesting that lowered LH secretion in subordinates may gradually be reversed by declines in androgen-negative feedback. Serum CORT levels were higher in subordinate males compared to control at all three time points. In contrast, oxidative 11betaHSD activity in Leydig cells of dominant males was higher relative to control and unchanged in subordinates. These results suggest the following: 1) failure of Leydig cells of subordinate males to compensate for increased glucocorticoid action during stress, by increasing 11betaHSD oxidative activity, potentiates stress-mediated reductions in T secretion; and 2) an inhibition of the reproductive axis in subordinate males at the level of the pituitary.     

A biphasic U-shape effect of cellular oxidative stress on the macrophage anti-oxidant paraoxonase 2 (PON2) enzymatic activity

Expression of macrophage paraoxonase 2 (PON2), a cellular lactonase with anti-oxidant and anti-atherogenic properties, was shown to be upregulated under high oxidative stress. The aim of the present study was to analyze the relationship between the extent of cellular oxidative stress in J774A.1 macrophage and PON2 lactonase activity under various levels of oxidation, obtained by cell incubation with either anti-oxidants or oxidants. PON2 activity exhibited a U-shape response curve. In the oxidative stress range below that of control untreated cells, PON2 activity decreased upon increasing macrophage oxidative state, whereas in the range over that of control untreated cells, PON2 activity increased. The biphasic effect of oxidative stress on macrophage PON2 activity could be related to PON2 inactivation (decreased enzymatic activity) under oxidative stress induction at its low range, whereas at high range of oxidative stress, macrophage anti-oxidant compensatory mechanism up-regulates PON2 (increased protein expression), in order to cope with oxidative burden.     

The effect of peroxisome proliferator-activated receptors alpha (PPARalpha) agonist, fenofibrate, on lipid peroxidation, total antioxidant capacity, and plasma paraoxonase 1 (PON 1) activity.

The aim of this study was to investigate the effect of peroxisome proliferator activated receptors alpha agonist, fenofibrate, on the level of oxidative stress, total antioxidant capacity, and plasma paraoxonase 1 (PON 1) activity in the rat. The adult male Wistar rats received fenofibrate for 7 days. The drug was added to food at concentrations 0.005%, 0.05% and 0.5%, which corresponded to doses of 3, 30 and 300 mg/kg/day, respectively. Fenofibrate treatment dose-dependently reduced plasma concentration of malonyldialdehyde and 4-hydroxydialkenals. The level of these lipid peroxidation products in animals treated with 0.005%, 0.05% and 0.5% fenofibrate was lower than in control group by 52.8%, 62.7% and 87.1%, respectively. Lipid hydroperoxides in plasma decreased by 29.7%, 23.4% and 27.5% in these groups, respectively. The drug had no significant effect on total antioxidant capacity measured as ferric reducing ability of plasma (FRAP). Paraoxon-hydrolyzing activity (PON) of plasma paraoxonase was 81.5% lower in animals receiving 0.05% fenofibrate and 69.2% lower in rats treated with 0.5% fenofibrate than in control. Phenyl acetate hydrolyzing activity (arylesterase, AE) was reduced by 15.2%, 49.6% and 55.8% in rats receiving 0.005%, 0.05% and 0.5% fenofibrate, respectively. PON/AE ratio decreased following 0.05% and 0.5% fenofibrate by 64.9% and 30.4%, respectively. The drug had no significant effect on total plasma triglycerides and cholesterol concentrations. The results indicate that fenofibrate treatment favourably modulates oxidant-antioxidant balance and unfavourably affects plasma PON 1 activity in normolipidemic rats. These effects can contribute to the influence of PPARalpha agonists on pathological processes involved in atherogenesis.     

Paraoxonases and cardiovascular diseases: pharmacological and nutritional influences

PURPOSE OF REVIEW: To summarize the new articles published in the last year on paraoxonases, including their expression in cardiovascular diseases, and regulation by pharmacological and nutritional means. RECENT FINDINGS: The elucidation of the crystal structure of the paraoxonase 1 (PON1) gene, obtained by directed evolution, shows that it consists of a six-bladed beta-propeller with a unique active site. PON1 is present in HDL but also in lipoprotein-deficient serum, in VLDL and in chylomicrons. PON1 protects lipids in lipoproteins, in macrophages and in erythrocytes from oxidation. Cellular PON2 and PON3 were also shown to reduce oxidative stress. Beyond its antioxidative properties, PON1 possesses additional antiatherogenic properties against macrophage foam cell formation: attenuation of cholesterol and oxidized lipids influx, inhibition of macrophage cholesterol biosynthesis and stimulation of macrophage cholesterol efflux. The PON1 gene is regulated by Sp1 and protein kinase C, whereas the PON2 gene in macrophages is regulated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. PON1 activity and mass are both reduced in cardiovascular diseases and the hypocholesterolemic drugs, statins, increase serum PON1 activity (by reducing oxidative stress, or by upregulating hepatic PON1 expression). Expression of cellular PON2, like PON1, was upregulated by statins. Nutritional antioxidants, such as polyphenols, increase PON1 mRNA expression and activity, by an aryl hydrocarbon receptor-dependent mechanism. SUMMARY: The elucidation of PON1 structure and its active center has enabled a better understanding of its mechanism of action, including its physio-pathological substrate(s). Some drugs and nutrients including dietary antioxidants and polyphenols considerably increase the activities of paraoxonases which, in turn, can reduce oxidative stress and atherosclerosis development.     

Investigation of the common paraoxonase 1 variants with paraoxonase activity on bone fragility in Turkish patients

There is increasing evidence of a biochemical link between oxidative stress and bone metabolism. Oxidative stress has been shown to be involved in bone resorption as it causes loss of bone mineral density (BMD). Paraoxonase 1 (PON1), can prevent these effects of the oxidative stress on bone formation. It has been suggested that the PON1 gene as possibly implicated in reduced BMD in bone fragility cases. It has been hypothesized that PON1 gene polymorphisms may influence both the risk of osteoporosis and osteopenia occurrence and prognosis. The aim of our study is to evaluate the relationship between PON1 polymorphisms and bone fragility development. Seventy-four osteoporotic, 121 osteopenic and 79 nonosteoporotic postmenopausal women were recruited. For detection of the polymorphisms, polymerase chain reaction-restriction fragment length polymorphism techniques have been used. BMD was measured at the lumbar spine and hip by dual-energy X-ray absorptiometry. Distributions of PON1 (PON 192 and PON 55) polymorphisms in study groups were not significantly different. But, there was medium strength connection between in the osteopenic with control groups regarding PON1 55–PON1 192 haplotypes and we found a power strength connection between in the osteoporosis with control groups regarding PON1 55–PON1 192 haplotypes. Furthermore, subjects with PON1 192RR and PON1 55LL genotypes had lower PON activity values of osteoporotic subject compared to healthy control and this difference was statistically significant (p < 0.05). This result suggest that PON1 genotypes could be higher risk for osteoporosis, as determined by reduced BMD.     

Serum Paraoxonase and Arylesterase Activities and Oxidative Stress Levels in Patients with SSRI Intoxication

Oxidative stress is a critical route of damage in various psychological stress-induced disorders, such as depression. Paraoxonase-1 (PON1) plays an important role as an endogenous free-radical scavenging molecule. The aim of this study was to evaluate the influence of serum PON1 activity and oxidative stress in patients with selective serotonin reuptake inhibitor (SSRI) intoxication. A total of 11 patients with SSRI intoxication and 20 healthy controls were enrolled. The serum total antioxidant capacity (TAC) and malondialdehyde (MDA) levels, as well as the paraoxonase and arylesterase activities, were measured spectrophotometrically. The serum TAC levels and the paraoxonase and arylesterase activities were significantly lower (for all, p < 0.001), whereas the serum MDA levels were significantly higher in the patients with SSRI intoxication than in the controls (p < 0.001). These results indicated that decreased PON1 activity and increased oxidative stress represent alternative mechanisms in SSRI toxicity. More studies are needed to elucidate the role of PON1 activity in the etiology of SSRI intoxication.     

HDL-associated paraoxonase-1 can redistribute to cell membranes and influence sensitivity to oxidative stress

Paraoxonase-1 (PON1) is a high-density lipoprotein (HDL)-associated serum enzyme thought to make a major contribution to the antioxidant capacity of the lipoprotein. In previous studies, we proposed that HDL promoted PON1 secretion by transfer of the enzyme from its plasma membrane location to HDL transiently anchored to the hepatocyte. This study examined whether PON1 can be transferred into cell membranes and retain its enzymatic activities and functions. Using Chinese hamster ovary and human endothelial cells, we found that recombinant PON1 as well as PON1 associated with purified human HDL was freely exchanged between the external medium and the cell membranes. Transferred PON1 was located in the external face of the plasma membrane of the cells in an enzymatically active form. The transfer of PON1 led to a gain of function by the target cells, as revealed by significantly reduced susceptibility to oxidative stress and significantly increased ability to neutralize the bacterial virulence agent 3-oxo-C₁₂-homoserine lactone. The data demonstrate that PON1 is not a fixed component of HDL and suggest that the enzyme could also exert its protective functions outside the lipoprotein environment. The observations may be of relevance to tissues exposed to oxidative stress and/or bacterial infection.     

Paraoxonases (PONs) 1, 2, and 3 are expressed in human and mouse gastrointestinal tract and in Caco-2 cell line: selective secretion of PON1 and PON2

The paraoxonase (PON) family contains three genes (PON1/2/3) that are believed to be involved in the protection against oxidative stress. PON1 and PON3 are circulating in serum attached to high-density lipoprotein fraction (HDL), whereas PON2 is ubiquitously expressed. The intestine is the second major organ that synthesizes lipoproteins; therefore, we examined PON mRNA expression and protein levels in gastrointestinal biopsies from humans, from C57BL6 mice, and from Caco-2 cells, a colon carcinoma-derived cell line that exhibits properties of intestinal epithelium at differentiation. PON 1/2/3 mRNA and proteins were present in human biopsies with variable expression among different gastrointestinal segments. Only PON2 and PON3 were present in mice. All PON mRNA, proteins, and enzymatic activities were present in Caco-2 cells. Oxidation of CaCo-2 cells with ferrum ascorbate had no significant effect on PON mRNA expression, but it increased paraoxonase and lactonase activity, whereas statinase activity was decreased. We showed polarized secretion of PON1 (basolateral) and PON2 (apical) into Caco-2 culture medium, raising the possibility that intestine is capable of producing and releasing PON1 and PON3 to the circulation, whereas PON2 is released at the brush-border membrane to intestinal lumen where it may perform another yet unclear function.     

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.