Identification of paraoxonase 3 in rat liver microsomes: purification and biochemical properties

A PON for All Seasons: Comparing Paraoxonase Enzyme Substrates, Activity and Action including the Role of PON3 in Health and Disease

Paraoxonases (PONs) are a family of hydrolytic enzymes consisting of three members, PON1, PON2, and PON3, located on human chromosome 7. Identifying the physiological substrates of these enzymes is necessary for the elucidation of their biological roles and to establish their applications in the biomedical field. PON substrates are classified as organophosphates, aryl esters, and lactones based on their structure. While the established native physiological activity of PONs is its lactonase activity, the enzymes’ exact physiological substrates continue to be elucidated. All three PONs have antioxidant potential and play an important anti-atherosclerotic role in several diseases including cardiovascular diseases. PON3 is the last member of the family to be discovered and is also the least studied of the three genes. Unlike the other isoforms that have been reviewed extensively, there is a paucity of knowledge regarding PON3. Thus, the current review focuses on PON3 and summarizes the PON substrates, specific activities, kinetic parameters, and their association with cardiovascular as well as other diseases such as HIV and cancer.

The Structure and Function of Paraoxonase-1 and Its Comparison to Paraoxonase-2 and -3

Serum paraoxonase-1 (PON1) is the most studied member of the group of paraoxonases (PONs). This enzyme possesses three enzymatic activities: lactonase, arylesterase, and paraoxonase activity. PON1 and its isoforms play an important role in drug metabolism as well as in the prevention of cardiovascular and neurodegenerative diseases. Although all three members of the PON family have the same origin and very similar amino acid sequences, they have different functions and are found in different locations. PONs exhibit substrate promiscuity, and their true physiological substrates are still not known. However, possible substrates include homocysteine thiolactone, an analogue of natural quorum-sensing molecules, and the recently discovered derivatives of arachidonic acid—bioactive δ-lactones. Directed evolution, site-directed mutagenesis, and kinetic studies provide comprehensive insights into the active site and catalytic mechanism of PON1. However, there is still a whole world of mystery waiting to be discovered, which would elucidate the substrate promiscuity of a group of enzymes that are so similar in their evolution and sequence yet so distinct in their function.

Paraoxonase 3: Structure and Its Role in Pathophysiology of Coronary Artery Disease

Spanning three decades in research, Paraoxonases (PON1) carried potential of dealing with neurotoxicity of organophosphates entering the circulation and preventing cholinergic crisis. In the past few years, the Paraoxonase multigene family (PON1, PON2, PON3) has been shown to play an important role in pathogenesis of cardiovascular disorders including coronary artery disease (CAD). The PON genes are clustered in tandem on the long arm of human chromosome 7 (q21, 22). All of them have been shown to act as antioxidants. Of them, PON3 is the least studied member as its exact physiological substrate is still not clear. This has further led to limitation in our understanding of its role in pathogenesis of CAD and development of the potential therapeutic agents which might modulate its activity, expression in circulation and tissues. In the present review, we discuss the structure and activity of human PON3 enzyme and its Single nucleotide variants that could potentially lead to new clinical strategies in prevention and treatment of CAD.

In vitro inhibitory effects of palonosetron hydrochloride, bevacizumab and cyclophosphamide on purified paraoxonase-I (hPON1) from human serum

In this study, we investigated the effects of the drugs, palonosetron hydrochloride, bevacizumab and cyclophosphamide, on human serum paraoxonase-I (hPON1) enzyme activity in in vitro conditions. The enzyme was purified ∼231-fold with 34.2% yield by using ammonium sulphate precipitation, DEAE-Sephadex A-50 ion-exchange chromatography and Sephadex G-200 gel-filtration chromatography from human serum. hPON1 exhibited a single protein band on the SDS polyacrylamide gel electrophoresis. The inhibition studies were performed on paraoxonase activity of palonosetron hydrochloride, bevacizumab and cyclophosphamide. Ki constants were found as 0.033±0.001, 0.054±0.003 mM and 3.419±0.518 mM, respectively. Compared to the inhibition rates of the drugs, palonosetron hydrochloride has the maximum inhibition rate. However, inhibition mechanisms of the drugs were determined as noncompetitive by Lineweaver-Burk curves.

An alternative purification method for human serum paraoxonase 1 and its interactions with anabolic compounds

In this study, an alternative purification method for human paraoxonase 1 (hPON1) enzyme was developed using two-step procedures, namely, ammonium sulfate precipitation and Sepharose-4B-L-tyrosine-3-aminophenantrene hydrophobic interaction chromatography. SDS-polyacrylamide gel electrophoresis of the enzyme indicates a single band with an apparent M(W) of 43 kDa. The enzyme was purified 219-fold with a final specific activity of 4,408,400 U/mg and a yield of 10%. Furthermore, we examined the in vitro effects of some anabolic compounds, such as zeranol, 17 β-estradiol, diethylstilbestrol, oxytocin, and trenbolone on the enzyme activity to understand the better inhibitory properties of these molecules. The five anabolic compounds dose dependently decreased the activity of hPON1 with inhibition constants in the millimolar-micromolar range. The results show that these compounds exhibit inhibitory effects on hPON1 at low concentrations with IC50 values ranging from 0.064 to 16.900 µM.

Impact of antibacterial drugs on human serum paraoxonase-1 (hPON1) activity: an in vitro study

OBJECTIVE

To investigate the in vitro effects of the antibacterial drugs, meropenem trihydrate, piperacillin sodium, and cefoperazone sodium, on the activity of human serum paraoxonase (hPON1).

METHODS

hPON1 was purified from human serum using simple chromatographic methods, including DEAE-Sephadex anion exchange and Sephadex G-200 gel filtration chromatography.

RESULTS

The three antibacterial drugs decreased in vitro hPON1 activity. Inhibition mechanisms meropenem trihydrate was noncompetitive while piperacillin sodium and cefoperazone sodium were competitive.

CONCLUSIONS

Our results showed that antibacterial drugs significantly inhibit hPON1 activity, both in vitro, with rank order meropenem trihydrate piperacillin sodium cefoperazone sodium in vitro.

Purification and characterization of paraoxonase 1 (PON1) from Swiss Black, Holstein, and Montofon bovines

Paraoxonase 1 (PON1: EC 3.1.8.1) is a calcium-dependent enzyme associated with high-density lipoproteins (HDLs) and has a protective effect against oxidation of low-density lipoproteins (LDLs) in mammals. PON1 is the best-studied member of a family of enzymes called serum paraoxonases, or PONs, identified in mammals and other vertebrates as well as in invertebrates. PONs exhibit a range of important activities, including drug metabolism and detoxification of organophosphates such as nerve agents. This study reports, for the first time, purification and biochemical characterization of serum PON1 from different bovine breeds namely Swiss Black, Holstein, and Montofon. Bovine serum PON1s were purified using ammonium sulfate precipitation followed by Sepharose-4B-L-tyrosine-1-naphthylamine hydrophobic interaction chromatography. SDS-polyacrylamide gel electrophoresis of the purified enzymes indicates a single band with an apparent MW of 43 kDa. The purified enzymes had a specific activity of 10.78, 27.00, and 22.38 U/mg for Swiss Black, Holstein, and Montofon bovines, respectively. The overall purification rates of our method were 262.47-, 2,476.90-, and 538.06-fold for Swiss Black, Holstein, and Montofon bovines, respectively. Furthermore, using phenyl acetate as a substrate, we determined the K M and V max values of the purified enzymes, as 0.80 mM, 1428.5 U/ml for Swiss Black; 0.40 mM, 714.3 U/ml for Holstein; and 0.50 mM, 1,111.1 U/ml for Montofon bovine. The present study has revealed that there is no substantial difference in PON1 activities among the studied bovine breeds.

The Past and Present of Paraoxonase Enzyme: Its Role in the Cardiovascular System and Some Diseases

Although paraoxonase is synthesized in many tissues including the heart, colon, kidneys, lungs, small intestines and brain, its major locus of synthesis is the liver. PON1 is in close association with apolipoproteins and protects LDL against oxidation. It was reported that PON1 quantities dropped to 40 times lower than normal in cardiovascular diseases and diseases like diabetes, ulcerative colitis, Crohn's disease, chronic renal failure, SLE, Behcet's disease, cancer, hepatitis B, obesity, metabolic syndrome, Alzheimer's and dementia. It is speculated that the concerning decline in serum PON1 amount results from single nucleotide polymorphism in the coding (Q192R, L55M) and promoter (T-108C) sites of the PON1 gene. Additionally, circulating amounts of PON1 are affected by vitamins, antioxidants, fatty acids, dietary factors, drugs, age and lifestyle. This collection attempts to review and examine the past and present studies of paraoxonase and its relation with the cardiovascular system and some relevant diseases.

The human paraoxonase gene cluster as a target in the treatment of atherosclerosis

The paraoxonase (PON) gene cluster contains three adjacent gene members, PON1, PON2, and PON3. Originating from the same fungus lactonase precursor, all of the three PON genes share high sequence identity and a similar β propeller protein structure. PON1 and PON3 are primarily expressed in the liver and secreted into the serum upon expression, whereas PON2 is ubiquitously expressed and remains inside the cell. Each PON member has high catalytic activity toward corresponding artificial organophosphate, and all exhibit activities to lactones. Therefore, all three members of the family are regarded as lactonases. Under physiological conditions, they act to degrade metabolites of polyunsaturated fatty acids and homocysteine (Hcy) thiolactone, among other compounds. By detoxifying both oxidized low-density lipoprotein and Hcy thiolactone, PONs protect against atherosclerosis and coronary artery diseases, as has been illustrated by many types of in vitro and in vivo experimental evidence. Clinical observations focusing on gene polymorphisms also indicate that PON1, PON2, and PON3 are protective against coronary artery disease. Many other conditions, such as diabetes, metabolic syndrome, and aging, have been shown to relate to PONs. The abundance and/or activity of PONs can be regulated by lipoproteins and their metabolites, biological macromolecules, pharmacological treatments, dietary factors, and lifestyle. In conclusion, both previous results and ongoing studies provide evidence, making the PON cluster a prospective target for the treatment of atherosclerosis.

Molecular fractionation and characterization of a Candida albicans fraction that increases tumor cell adhesion to hepatic endothelium

Systemic candidiasis remains a major complication among patients suffering from hematological malignancies and favors the development of hepatic metastasis. To contribute to the understanding of the underlying mechanisms, the aim of this study was to identify molecules that may increase tumor cell adhesion to hepatic endothelial cells. To this end, a well-established in vitro model was used to determine the enhancement of tumor cell adhesion induced by Candida albicans and its fractions. Different fractions were obtained according to their molecular weight (M(r)) (five) or to their isoelectric point (pI) (four), using preparative electrophoresis and preparative isoelectric focusing, respectively, followed by affinity chromatography. The fraction that most enhanced melanoma cell adhesion to endothelium had an M(r) range from 45 to 66 kDa. It was characterized using two-dimensional electrophoresis, and 14 proteins were identified by peptide mass fingerprinting: Dor14p, Fba1p, Pdi1p, Pgk1p, Idh2p, Mpg1p, Sfa1p, Ape3p, Ilv5p, Tuf1p, Act1p, Eno1p, Qcr2p, and Adh1p. Of these, several are related to the immunogenic response, and the latter seven belonged to the most reactive fraction according to their pI range, from 5 to 5.6. These findings could represent a step forward in the search for new targets, to suppress the pro-metastatic effect of C. albicans.

Purification and kinetic properties of rabbit liver paraoxonase 1

Paraoxonase 1 (PON1) is synthesized in the liver and secreted into the blood, where it is associated exclusively with HDL. In this study, rabbit liver PON1 enzyme was purified to homogeneity using a new purification approach, and the kinetic properties of the enzyme were investigated using phenyl acetate and homocysteine thiolactone as substrates. Rabbit liver PON1 was purified through the preparation of liver microsomal fraction, Sephacryl S300 HR gel filtration chromatography, DEAE Trisacryl M ion-exchange chromatography and hydroxyapatite chromatography steps. Using this method, rabbit liver PON1 was purified 576 times with a specific activity of 2726 U/mg protein. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed the obtained enzyme as a single protein band close to 40 kDa. The Km of the this enzyme was found as 0.55+/-0.024 mM for phenyl acetate and 17.31+/-1.2 mM for homocysteine thiolactone. In this study, a new approach was used to purify PON1 enzyme from rabbit liver and for the first time in the literature, its kinetics was studied with homocysteine thiolactone as substrate.

Improving the ex vivo stability of drug ester compounds in rat and dog serum: inhibition of the specific esterases and implications on their identity

In drug development, it has been noticed that some drug compounds, especially esters, are unstable in serum samples ex vivo. This can lead to a substantial underestimation of the actual drug concentration. The rat and the dog, representing a rodent and non-rodent species, respectively, are widely used in preclinical studies. We studied the degradation of three structurally different drug esters in rat and dog serum. Moreover, the efficiency of selected enzyme inhibitors to prevent these degradations was investigated. Furthermore, we found indications of the identity of the drug-specific esterases by means of their inhibitor sensitivity as well as by protein purification and identification. The studied drugs were sagopilone, drospirenone, and methylprednisolone aceponate (MPA) all of which are used in (pre-)clinical drug development. The sagopilone-cleaving esterases in rat serum were inhibited by serine hydrolase inhibitors. We partly purified these esterases resulting in an activity yield of 5% and a purification factor of 472. Using matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF)-mass spectrometry (MS), the rat carboxylesterase isoenzyme ES-1 was identified in these fractions, thus pointing to its involvement in sagopilone cleavage. Drospirenone cleavage in rat serum was effected by butyrylcholinesterase (BChE) and paraoxonase 1 (PON1) as we deduced from the high efficacy of certain serine hydrolase and metallohydrolase inhibitors, respectively. Likewise, some inhibition characteristics implied that MPA was cleaved in rat serum by BChE and serine proteases. Partial purification of the MPA-specific esterases resulted in activity yields of 1-2%, exhibiting up to 10,000-fold purification. In dog serum, we found that sagopilone was not degraded which was in contrast to MPA and drospirenone. MPA degradation was mainly prevented by serine hydrolase inhibitors. We used a three-step purification to isolate the esterases cleaving MPA. This procedure resulted in an activity yield of 12% and 645-fold purification. By protein identification using liquid chromatography (LC)-electrospray ionization (ESI)-MS, we identified alpha(2)-macroglobulin (alpha(2)M) in the active fractions. We therefore assumed that serine hydrolases, probably butyrylcholinesterase, known to form esteratically active complexes with alpha(2)M, were responsible for MPA cleavage. In contrast, PON1 was assumed to be involved in drospirenone cleavage due to the high efficiency of metallohydrolase inhibitors. This indication was supported by the presence of PON1 in drospirenone-cleaving fractions as we found by affinity chromatography and Western immunoblotting for isolation and detection of PON1, respectively. The identity of the assumed cleaving enzymes remains, however, to be further studied. The inhibitors we found can serve as a tool for stabilizing drug ester compounds in biological samples ex vivo.

Modulation of paraoxonase 1 and 3 expression after moderate exercise training in the rat

Paraoxonases (PONs) are a small family of antioxidant enzymes whose antiatherogenic activity is well known. The aim of the present study was the evaluation of the effects of moderate aerobic training on their expression using a rat model. In order to discriminate between PON1 and PON3 enzymatic activity, we took advantage of some differences in their substrate preferences. PON1 and PON3 enzymatic activities and their protein levels were analyzed in plasma and in liver microsomes, and their mRNA levels in the liver. Exercise training did not affect PON1 expression or enzymatic activity but increased PON3 mRNA, protein levels, and enzymatic activity. Training also induced variations in plasma membrane composition, including an increase in polyunsaturated and a decrease in mono- and di-unsaturated fatty acids. On the other hand, acute exercise inhibited PON activities while increasing PON3 protein content in liver microsomes and reversing the relative composition in mono-, di-, and poly-unsaturated fatty acids, suggesting that physical stress, by altering membrane composition, may impair PON release from liver membranes. In conclusion, we documented, for the first time, the presence of PON3 in rat serum and, notably, found that the upregulation of PON3, rather than PON1, appears to be associated with physical training.

Purification human PON1Q192 and PON1R192 isoenzymes by hydrophobic interaction chromatography and investigation of the inhibition by metals

In this study, a new purification strategy for human PON1 enzyme was developed using two-step procedures, namely ammonium sulfate precipitation and sepharose-4B-L-tyrosine-9-aminophenantrene hydrophobic interaction chromatography. SDS polyacrylamide gel electrophoresis of the enzyme indicates a single band with an apparent MW of 43kDa. Overall purification rate of our method was found 901-fold for R isoenzyme and 453-fold for Q isoenzyme. The V(max) and K(M) of the purified enzyme were determined for Q isoenzyme 55 EU and 0.599 mM and for R isoenzyme 50 EU and 0.492 mM, respectively. The in vitro effects of some heavy metals (Hg, Cd, Cu, Mn and Ni) were investigated on the purified human serum PON1Q and R isoenzyme, using paraoxon as substrate. Metals were more effective inhibitors on purified human serum PON1(R192) activity than PON1(Q192) activity. The kinetics of interaction of metals with the purified human serum PON1(R192) and PON1(Q192) indicated a different inhibition pattern. Kinetic constants K(M), V(max), and inhibition type were determined.

Effect of pre-germinated brown rice intake on diabetic neuropathy in streptozotocin-induced diabetic rats

BACKGROUND

To study the effects of a pre-germinated brown rice diet (PR) on diabetic neuropathy in streptozotocin (STZ)-induced diabetic rats.

METHODS

The effects of a PR diet on diabetic neuropathy in STZ-induced diabetic rats were evaluated and compared with those fed brown rice (BR) or white rice (WR) diets with respect to the following parameters: blood-glucose level, motor-nerve conduction velocity (NCV), sciatic-nerve Na+/K+-ATPase activity, and serum homocysteine-thiolactonase (HTase) activity.

RESULTS

Compared with diabetic rats fed BR or WR diets, those fed a PR diet demonstrated significantly lower blood-glucose levels (p < 0.001), improved NCV (1.2- and 1.3-fold higher, respectively), and increased Na+/K+-ATPase activity (1.6- and 1.7-fold higher, respectively). The PR diet was also able to normalize decreased serum homocysteine levels normally seen in diabetic rats. The increased Na+/K+-ATPase activity observed in rats fed PR diets was associated with elevations in HTase activity (r = 0.913, p < 0.001). The in vitro effect of the total lipid extract from PR bran (TLp) on the Na+/K+-ATPase and HTase activity was also examined. Incubation of homocysteine thiolactone (HT) with low-density lipoprotein (LDL) in vitro resulted in generation of HT-modified LDL, which possessed high potency to inhibit Na+/K+-ATPase activity in the sciatic nerve membrane. The inhibitory effect of HT-modified LDL on Na+/K+-ATPase activity disappeared when TLp was added to the incubation mixture. Furthermore, TLp directly activated the HTase associated with high-density lipoprotein (HDL).

CONCLUSION

PR treatment shows efficacy for protecting diabetic deterioration and for improving physiological parameters of diabetic neuropathy in rats, as compared with a BR or WR diet. This effect may be induced by a mechanism whereby PR intake mitigates diabetic neuropathy by one or more factors in the total lipid fraction. The active lipid fraction is able to protect the Na+/K+-ATPase of the sciatic-nerve membrane from the toxicity of HT-modified LDL and to directly activate the HTase of HDL.

Stability of highly purified human paraoxonase (PON1): Association with human phosphate binding protein (HPBP) is essential for preserving its active conformation(s)

The biological role of human paraoxonase (PON1) remains unclear, whilst there is a consensus that the enzyme has a protective influence. A toxicological role, protecting from environmental poisoning by organophosphate derivatives drove earlier works, and more recently, clinical interest has focused on a protective role in vascular disease. PON1 resides essentially on HDL particles, a complex and dynamic molecular environment. Our recent discovery of the human phosphate binding protein (HPBP), displaying a firm propensity to associate with PON1, has steered new directions for characterizing PON1 functional state. Here, we report investigations on the effect of HPBP on oligomerization, storage and thermal stability of PON1. We found that purified PON1 is as a mixture of at least two states, and that the absence of HPBP favors homo-oligomerization of PON1 into state(s) of higher molecular size. We showed that HPBP allows stabilizing active conformation(s) of PON1 disencumbered of its natural environment. We also showed that PON1 exhibits intrinsically a remarkable thermal stability, and that the association of HPBP strongly contributes to slow the denaturation rate. A hybrid recombinant PON1 was shown more thermostable than the human enzyme, and its stability was unaffected by the presence of HPBP. Altogether, the results strongly encourage further study of the human enzyme.

Comparative hydrolysis of O-hexyl O-2,5-dichlorophenyl phosphoramidate and paraoxon in different tissues of vertebrates

The Ca(2+)-dependent and EDTA-resistant hydrolysis of O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) and paraoxon was studied in serum and subcellular fractions of liver, kidney and brain of hen, rat and rabbit. HDCP was the best substrate among all the tissues studied, except that of rabbit serum which showed the highest Ca(2+)-dependent paraoxon hydrolysing activity (paraoxonase). High HDCP hydrolysing activity (HDCPase) was detected in the brain tissue of the three species studied, whereas low or no paraoxonase was found. The HDCPase/paraoxonase ratio of Ca(2+)-dependent hydrolysing activities ranged from 0.5 to 83 for tissues of the same species. EDTA-resistant HDCPase activity was more than 50% of the total activities in hen tissues, with an almost undetectable Ca(2+)-dependent paraoxonase activity in most organs. The same response was observed in rat tissues, except for serum where the Ca(2+)-dependent HDCPase and paraoxonase activities were higher (70 and 25% of total activities, respectively). EDTA-resistant HDCPase and paraoxonase activities represented less than 25% of all activities in rabbit tissues. Paraoxon has traditionally been the substrate for measuring organophosphorus hydrolysing activities. However, HDCP could be a good substrate in addition to paraoxon for monitoring other phosphotriesterases in biological tissues.

Effect of metal ions and calcium on purified PON1 and PON3 from rat liver

The effect of several metal ions and calcium on purified paraoxonases (PON1 and PON3) from rat liver was studied. PON1 and PON3 were also inhibited by EDTA and both enzyme activities were restored by the addition of free calcium. The reactivation by calcium was a time-dependent effect for PON1; however, this was not the case for PON3. We also studied the response of PON1 and PON3 to several inhibitors: Co, Cu, Mn, Hg and p-hydroxymercurybenzoate (pOHMB), and determined the type of inhibition and the inhibition constants. Among all the compounds tested, mercurials (Hg and pOHMB) were the most potent inhibitors of PON1. For PON3 mercurials and copper showed the highest inhibitory potency. Purified PON3 also showed different inhibition patterns as compared to PON1. A comparison of PON1 and PON3 shows qualitative and quantitative differences in the sensitivity against the inhibitors tested, showing major differences in the case of cobalt, copper and pOHMB, which may be related to structural differences of both PONs. These results increase our knowledge of the biochemical properties of PON1 and PON3 and may help in the understanding of their physiological role as a potential detoxification mechanism against environmental metal ions.

Effects of some antibiotics on paraoxonase from human serum in vitro and from mouse serum and liver in vivo

Paraoxonase (PON1, EC 3.1.8.1) is an esterase protein which plays multifunctional role in metabolism. Therefore, in this study the effects of commonly used antibiotics, namely sodium ampicillin, ciprofloxacin, rifamycin SV and clindamycin phosphate, on human PON1 were investigated in vitro and in vivo. Human serum paraoxonase (PON1) was separately purified by ammonium sulfate precipitation and hydrophobic interaction chromatography. The in vitro effects of the antibiotics in purifying human serum paraoxonase was determined using paraoxon as a substrate, and the IC50 values of these drugs exhibiting inhibition effects were found from graphs of hydratase activity % by plotting the concentration of the drugs. It was determined that sodium ampicillin, ciprofloxacin, and clindamycin phosphate were effective inhibitors on human serum PON1, and the inhibition kinetics of interaction of sodium ampicillin, ciprofloxacin, and clindamycin phosphate with the human serum PON1 was also determined, with the Ki of sodium ampicillin, ciprofloxacin, and clindamycin phosphate being 0.00714+/-0.00068, 6.5x10(-6)+/-4.59x10(-7), 0.0291+/-0.0077 mM, respectively. The in vivo effects of the antibiotics on paraoxonase enzyme activity in mouse serum and liver PON1 were also investigated. Mouse liver PON1 activity showed a statistically significant change at 2, 4 and 6 h of drug application in vivo. Sodium ampicillin and clindamycin phosphate exhibited about 80% mouse liver PON1 at 2 or 4 h (p: 0.034, 0.003 and 0.021, respectively). In addition, ciprofloxacin and rifamycin SV only showed inhibition at 4 h incubation. Sodium ampicillin (17.12 mg/kg) lead to a significant decrease in mouse serum PON1 after 4 h drug administration. Ciprofloxacin (3.2 mg/kg), rifamycin SV (3.56 mg/kg) and clindamycin phosphate (2.143 mg/kg) did not exhibit any inhibition effect for the mouse serum PON1, in vivo.

Tandem purification of two HDL-associated partner proteins in human plasma, paraoxonase (PON1) and phosphate binding protein (HPBP) using hydroxyapatite chromatography

Human plasma paraoxonase (PON1) is calcium-dependent enzyme that hydrolyses esters, including organophosphates and lactones, and exhibits anti-atherogenic properties. Human phosphate binding protein (HPBP) was discovered as contaminant during crystallization trials of PON1. This observation and uncertainties for the real activities of PON1 led us to re-evaluate the purity of PON1 preparations. We developed a hydroxyapatite chromatography for the separation of both HDL-associated proteins. We confirmed that: (1) HPBP is strongly associated to PON1 in HDL, and generally both proteins are co-purified; (2) standard purification protocols of PON1 lead to impure enzyme; (3) hydroxyapatite chromatography allows the simultaneous purification of PON1 and HPBP.

Differential effect of antioxidant treatment on plasma and tissue paraoxonase activity in hyperleptinemic rats

Recent studies suggest that adipose tissue hormone, leptin, is involved in atherogenesis, especially in obese subjects. Previously, we have demonstrated that experimentally induced hyperleptinemia decreases plasma paraoxonase 1 (PON1) activity. The aim of this study was to investigate whether treatment with synthetic antioxidant, Tempol, modulates the effect of leptin on plasma and tissue PON1 in the rat. Leptin was administered at a dose of 0.25 mgkg-1 s.c. twice daily for 7 days and Tempol was added to the drinking water at a concentration of 2 mM. Leptin reduced plasma PON1 activity toward paraoxon, phenyl acetate and gamma-decanolactone to 71.1, 72.3 and 57.1% of control, respectively. In addition, leptin decreased PON1 activity toward paraoxon in aorta, renal cortex and medulla to 78.6, 49.2 and 48.0% of control, respectively, but had no effect on PON1 in heart, lung and liver. PON1 activity toward phenyl acetate was lower following leptin treatment only in aorta. Leptin increased plasma concentration and urinary excretion of isoprostanes as well as malonyldialdehyde + 4-hydroxyalkenals level in aorta, renal cortex and renal medulla. Coadministration of Tempol prevented leptin-induced oxidative stress and normalized PON1 activity in aorta and kidney. However, Tempol had no effect on plasma PON1 in leptin-treated rats. These data indicate that hyperleptinemia decreases tissue PON1 activity through oxidative stress-dependent mechanism. In contrast, leptin-induced downregulation of plasma PON1 is not mediated by oxidative stress.

Amphenicol and macrolide derived antibiotics inhibit paraoxonase enzyme activity in human serum and human hepatoma cells (HepG2) in vitro

Human serum paraoxonase (hPON1) was separately purified by ammonium sulfate precipitation and hydrophobic interaction chromatography. The in vitro effects of commonly used antibiotics, namely clarithromycin and chloramphenicol, on purified human serum paraoxonase enzyme activity (serum hPON1) and human hepatoma (HepG2) cell paraoxonase enzyme activity (liver hPON1) were determined. Serum hPON1 and liver hPON1 were determined using paraoxon as a substrate and IC(50) values of these drugs exhibiting inhibition effects were found from graphs of hydratase activity (%) by plotting concentration of the drugs. We determined that chloramphenicol and clarithromycin were effective inhibitors of serum hPON1.

Cloning, purification, and refolding of human paraoxonase-3 expressed in Escherichia coli and its characterization

Human paraoxonase (hPON3) is a high density lipoprotein-related glycoprotein with multi-enzymatic properties and antioxidant activity which is proposed to participate in the prevention of low density lipoprotein (LDL) oxidation. In this study, hPON3 gene was amplified from Human Fetal Liver Marathon-Ready cDNA and expressed in Escherichia coli. A majority of the expressed protein existed as inclusion bodies. The inclusion bodies were solubilized with Triton X-100 and refolded in vitro. The refolded rhPON3 was purified by DEAE-Sepharose Fast Flow and its purity was up to 90%. The Km and Vmax values of refolded rhPON3, in respect to phenylacetate hydrolysis were 7.47 +/- 2.14 mM and 66 +/- 17 U/min/mg (n = 3). The Km and Vmax values of refolded rhPON3, in respect to dihydrocoumarin hydrolysis were 0.83 +/- 0.21 mM and 621 +/- 66 U/min/mg (n = 3). The refolded rhPON3 exhibited similar antioxidant activity to that of rhPON3 purified from the soluble fraction of cell lysate and could effectively protect LDL from Cu2+ induced oxidation.

Human paraoxonases (PON1, PON2, and PON3) are lactonases with overlapping and distinct substrate specificities

The paraoxonase (PON) gene family in humans has three members, PON1, PON2, and PON3. Their physiological role(s) and natural substrates are uncertain. We developed a baculovirus-mediated expression system, suitable for all three human PONs, and optimized procedures for their purification. The recombinant PONs are glycosylated with high-mannose-type sugars, which are important for protein stability but are not essential for their enzymatic activities. Enzymatic characterization of the purified PONs has revealed them to be lactonases/lactonizing enzymes, with some overlapping substrates (e.g., aromatic lactones), but also to have distinctive substrate specificities. All three PONs metabolized very efficiently 5-hydroxy-eicosatetraenoic acid 1,5-lactone and 4-hydroxy-docosahexaenoic acid, which are products of both enzymatic and nonenzymatic oxidation of arachidonic acid and docosahexaenoic acid, respectively, and may represent the PONs' endogenous substrates. Organophosphates are hydrolyzed almost exclusively by PON1, whereas bulky drug substrates such as lovastatin and spironolactone are hydrolyzed only by PON3. Of special interest is the ability of the human PONs, especially PON2, to hydrolyze and thereby inactivate N-acyl-homoserine lactones, which are quorum-sensing signals of pathogenic bacteria. None of the recombinant PONs protected low density lipoprotein against copper-induced oxidation in vitro.

Pharmacogenetics of paraoxonases: a brief review

The human paraoxonase (PON) gene family consists of three members, PON1, PON2, and PON3, aligned next to each other on chromosome 7. By far the most-studied member of the family is the serum paraoxonase 1 (PON1), a high-density lipoprotein-associated esterase/lactonase. Early research focused on its capability to hydrolyze toxic organophosphates, and its name derives from one of its most commonly used in vitro substrates, paraoxon. Studies in the last 2 decades have demonstrated PON1's ability to protect against atherosclerosis by hydrolyzing specific derivatives of oxidized cholesterol and/or phospholipids in oxidized low-density lipoprotein and in atherosclerotic lesions. Levels and genetic variability of PON1 influence sensitivity to specific insecticides and nerve agents, as well as the risk of cardiovascular disease. More recently, the other two members of the PON family, PON2 and PON3, have also been shown to have antioxidant properties. A major goal in present research on the paraoxonases is to identify their natural substrates and to elucidate the mechanism(s) of their catalytic activities.