Purification of PON1 from human serum and assessment of enzyme kinetics against metal toxicity

Molecular Structure of Paraoxonase-1 and Its Modifications in Relation to Enzyme Activity and Biological Functions-A Comprehensive Review

PON1 is a Ca2+-dependent enzyme that indicates a hydrolytic activity towards a broad spectrum of substrates. The mechanism of hydrolysis catalyzed by this enzyme is poorly understood. It was shown that the active site of PON1 is highly dynamic. The catalytic center of this enzyme consists of side chains of amino acids binding two calcium ions, from which the first one performs a structural function and the other one is responsible for the catalytic properties of PON1. This review summarizes available information on the structure of PONs, the role of amino acids located in the active site in specificity, and multiple substrate affinity of enzymes for understanding and explaining the basis of the physiological function of PONs. Moreover, in this paper, we described the changes in the structure of PONs induced by environmental and genetic factors and their association with diseases. The detoxification efficiency depends on the polymorphism of the PON1 gene, especially Q192R. However, data on the association between single-nucleotide polymorphisms (SNPs) in the PON1 gene and cardiovascular or neurodegenerative diseases are insufficient. The reviewed papers may confirm that PON1 is a very promising tool for diagnostics, but further studies are required.

Highly Sensitive and Rapid Screening Technique for the Detection of Organophosphate Pesticides and Copper Compounds Using Bifunctional Recombinant TrxA-PvCarE1

Enabling the detection of organophosphate pesticide (OP) residues through enzyme inhibition-based technology is crucial for ensuring food safety and human health. However, the use of acetylcholinesterase, the primary target enzyme for OPs, isolated from animals in practical production poses challenges in terms of sensitivity and batch stability. To address this issue, we identified a highly sensitive and reproducible biorecognition element, TrxA-PvCarE1, derived from red kidney beans and successfully overexpressed it in Escherichia coli. The resulting recombinant TrxA-PvCarE1 exhibited remarkable sensitivity toward 10 OPs, surpassing that of commercial acetylcholinesterase. Additionally, this approach demonstrated the capability to simultaneously detect copper compounds with high sensitivity, expanding the range of pesticides detectable using the traditional enzyme inhibition method. Spiking recovery tests conducted on cowpea and carrot samples verified the suitability of the TrxA-PvCarE1-based technique for real-life sample analysis. In summary, this study highlights a promising comprehensive candidate for the rapid detection of pesticide residues.

The Increase in Paraoxonase 1 Is Associated With Decrease in Left Ventricular Volume in Kidney Transplant Recipients

Background: Patients on dialysis have impaired cardiac function, in part due to increased fluid volume and ventricular stress. Restored kidney function through transplantation reduces left ventricular volume in both systole and diastole. We previously reported that the decrease in NT-proB-type natriuretic peptide (NT-proBNP) was associated with a decrease in adiponectin. Paraoxonase 1 (PON1) has been inversely associated with cardiovascular outcomes. We now report the association of changes in PON1 with changes in left ventricular volume and left ventricular mass after kidney transplantation.

Design: Patients on dialysis were assessed at baseline and 12 months after kidney transplantation (n = 38). A comparison group of patients on dialysis who were not expected to receive a transplant in the next 24 months were studied (n = 43) to determine if the change of PON1 with kidney transplantation achieved a significance greater than that due to biologic variation. Left ventricular volume and mass were determined by cardiac magnetic resonance imaging. PON1 was measured by arylesterase activity and by mass.

Results: PON1 mass and activity were not different between the groups at baseline. Both PON1 mass and activity were increased post-kidney transplantation (p < 0.0001 for change). The change in PON1 mass (p = 0.0062) and PON1 arylesterase activity (p = 0.0254) were inversely correlated with the change in NT-proBNP for patients receiving a kidney transplant. However, only the change in the PON1 mass, and not the change in PON1 arylesterase, was inversely correlated with the change in left ventricular volume (ml/m2.7) (p = 0.0146 and 0.0114 for diastolic and systolic, respectively) and with the change in hemoglobin (p = 0.0042).

Conclusion: Both PON1 mass and arylesterase activity are increased by kidney transplantation. The increase in PON1 mass is consistent with a novel relationship to the increase in hemoglobin and decrease in left ventricular volume and NT-proBNP seen when kidney function is restored.

Metabolic status of the coral Mussismilia harttii in field conditions and the effects of copper exposure in vitro

It is widely known that metals can alter enzyme functioning, however, little is known about the mechanisms of metal toxicity in energy metabolism enzymes of corals. Thus, the present study had two objectives: firstly, we evaluated the activity of eight metabolic enzymes of the coral Mussismilia harttii to clarify metabolic functioning under field conditions. After that, we investigated the in vitro effect of copper (Cu) exposure in the activity of an enzyme representative of each metabolism stage. We evaluated enzymes involved in glycolysis (hexokinase, HK; phosphofructokinase, PFK; pyruvate kinase, PK and lactate dehydrogenase, LDH), Krebs cycle (citrate synthase, CS and isocitrate dehydrogenase, IDH), electron transport chain (electron transport system activity, ETS) and pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH). The in vitro tests were performed through contamination of the reaction medium using Cu concentrations of 0, 1.4, 3.7 and 14.2 μg L^-1. The results showed that M. harttii has elevated activity of HK, PK and CS in field conditions compared to the activity of other energy metabolism enzymes evaluated. Moreover, lower activities of LDH and ETS in exposed samples were observed. In conclusion, in field conditions this species has elevated aerobic metabolism and glucose may be an important energetic fuel. Also, exposure to Cu in vitro caused inhibition of LDH and ETS by direct binding.

Benzenesulfonamide derivatives containing imine and amine groups: Inhibition on human paraoxonase and molecular docking studies

Sulfonamides known as inhibitors of many metabolic enzymes have been widely used as antimicrobial drugs for a long time. In the present study, we investigated in vitro inhibitory activities of benzenesulfonamide derivatives on human paraoxonase-I (hPON1). For this aim, PON1 was purified from human serum with a specific activity of 2603.57 EU/mg and 8.34% yield using simple chromatographic methods. The various concentrations of early-synthesized sixteen sulfonamide derivatives were tested on the paraoxonase activity. Ki values of compounds were found in the range of 0.28-357.70 µM. Compound H4 had the highest inhibitory activity on hPON1 as competitive. Estimated structure-activity relationship (SAR) for compounds was done based on different substituents and their positions in the compounds. Besides, the molecular docking analysis of compound H4 was performed to understand the binding interactions on the active site of the enzyme. According to these experimental results, compound H4 was a potential inhibitor of PON1.

Evaluation of the paraoxonase-1 kinetic parameters of the lactonase activity by nonlinear fit of progress curves

Although paraoxonase-1 (PON1) activity has been demonstrated to be a reliable biomarker of various diseases, clinical studies have been based only on relative comparison of specific enzyme activities, which capture differences mainly due to (usually unknown) PON1 concentration. Hence, the aim of this report is to present for the first time the simple evaluation method for determining autonomous kinetic parameter of PON1 that could be also associated with polymorphic forms and diseases; i.e. the Michaelis constant which is enzyme concentration independent quantity. This alternative approach significantly reduces the number of experiments needed, and it yields the results with great accuracy.

Purification and characterization of the carbonic anhydrase enzyme from horse mackerel (Trachurus trachurus) muscle and the impact of some metal ions and pesticides on enzyme activity

In this paper, the total carbonic anhydrase (CA) enzyme was purified from horse mackerel (Trachurus trachurus) muscle with a specific activity of 23,063.93 EU/mg, purification fold of 551.08, total activity of 1522.22 EU/mL and a yield of 18.50% using sulfanilamide affinity column chromatography. For obtaining the subunit molecular mass and enzyme purity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for this part was performed and a single band was clearly recorded. The molecular mass of this enzyme was found approximately 35 kDa. The optimum temperature and pH values were obtained from Arrhenius plot. In addition, the inhibitory effects of different heavy metal ions (Fe²⁺, Cu²⁺, Co²⁺, Pb²⁺ Hg²⁺ and As³⁺) and some pesticides (thiram, clofentezine, propineb, deltamethrin, azoxystrobin and thiophanate) on horse mackerel (Trachurus trachurus) muscle tissue CA enzyme activities were investigated by utilizing esterase assay activity. The used metal ions and pesticides had IC₅₀ values in the range of 0.21-13.84 mM and 3.78-70.58 mM, respectively.

Paraoxonases: metabolic role and pharmacological projection

Atherosclerosis is one of the leading causes of death in Western countries, with high-density lipoproteins (HDL) playing an important protective role due to their ability to inhibit oxidation of low-density lipoproteins (LDL), thus relieving vascular subendothelial damage. One of the proteins constituting HDL particles is paraoxonase-1 (PON1), an enzyme able to hydrolyze aryl esters, lactones, and organophosphates. Other closely related paraoxonases are designated as PON2, which is a protein localized inside many different kinds of cells, and PON3, not only present in HDL but also in mitochondria and endoplasmic reticulum, as well. Given that the amount and the activity of PON1 in human serum are significantly lower in people suffering from cardiovascular diseases, enhancing both parameters might contribute to their treatment and prevention. One of the physiologically interesting substrates for the abovementioned hydrolytic cleavage is homocysteine thiolactone (HTL), an atherothrombotic active form of homocysteine. Although it was therefore postulated that PON1 would participate in preventing the HTL-mediated lipid peroxidation, some attention is recently paid to other enzymes, like biphenyl hydrolase-like protein, that seem to more selectively involved in lowering this risk factor. The aim of this paper is to elucidate the role of paraoxonases, especially PON1, by reviewing the latest studies in order to understand both its physiological role and modulation by drugs, nutrients, and plant extracts.

Metals and Paraoxonases

The paraoxonases (PONs) are a three-gene family which includes PON1, PON2, and PON3. PON1 and PON3 are synthesized primarily in the liver and a portion is secreted in the plasma, where they are associated with high-density lipoproteins (HDLs), while PON2 is an intracellular enzyme, expressed in most tissues and organs, including the brain. PON1 received its name from its ability to hydrolyze paraoxon, the active metabolite of the organophosphorus (OP) insecticide parathion, and also more efficiently hydrolyzes the active metabolites of several other OPs. PON2 and PON3 do not have OP-esterase activity, but all PONs are lactonases and are capable of hydrolyzing a variety of lactones, including certain drugs, endogenous compounds, and quorum-sensing signals of pathogenic bacteria. In addition, all PONs exert potent antioxidant effects. PONs play important roles in cardiovascular diseases and other oxidative stress-related diseases, modulate susceptibility to infection, and may provide neuroprotection (PON2). Hence, significant attention has been devoted to their modulation by a variety of dietary, pharmacological, lifestyle, or environmental factors. A number of metals have been shown in in vitro, animal, and human studies to mostly negatively modulate expression of PONs, particularly PON1, the most studied in this regard. In addition, different levels of expression of PONs may affect susceptibility to toxicity and neurotoxicity of metals due to their aforementioned antioxidant properties.

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.

Inhibitory effects of some phenolic compounds on the activities of carbonic anhydrase: from in vivo to ex vivo

Carbonic anhydrase (CA) inhibitors have been used for more than 60 years for therapeutic purposes in many diseases table such as in medications against antiglaucoma and as diuretics. Phenolic compounds are a new class of CA inhibitor. In our study, we tested the effects of arachidonoyl dopamine, 2,4,6-trihydroxybenzaldehyde and 3,4-dihydroxy-5-methoxybenzoic acid on esterase and the CO2-hydratase activities of CA I and II isozymes purified from in vivo to ex vivo. The Ki values of arachidonoyl dopamine, 2,4,6-trihydroxybenzaldehyde and 3,4-dihydroxy-5-methoxybenzoic acid were 203.80, 1170.00 and 910.00 μM, respectively for hCA I and 75.25, 354.00 and 1510.00 μM, respectively for hCA II. Additionally, IC50 values from in vivo studies were found to be in the range of 173.25-1360.0 μM for CA I and II, respectively, using CO2-hydratase activity methods. These results demonstrated that phenolic compounds used in in vivo studies could be used in different biomedical applications to inhibit approximately 30% of the CO2-hydratase activity of the total CA enzyme of rat erythrocytes.

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.

Pharmacogenetics of paraoxonase activity: elucidating the role of high-density lipoprotein in disease

PON1 is a key component of high-density lipoproteins (HDLs) and is at least partially responsible for HDL's antioxidant/atheroprotective properties. PON1 is also associated with numerous human diseases, including cardiovascular disease, Parkinson's disease and cancer. In addition, PON1 metabolizes a broad variety of substrates, including toxic organophosphorous compounds, statin adducts, glucocorticoids, the likely atherogenic L-homocysteine thiolactone and the quorum-sensing factor of Pseudomonas aeruginosa. Numerous cardiovascular and antidiabetic pharmacologic agents, dietary macronutrients, lifestyle factors and antioxidant supplements affect PON1 expression and enzyme activity levels. Owing to the importance of PON1 to HDL function and its individual association with diverse human diseases, pharmacogenomic interactions between PON1 and the various factors that alter its expression and activity may represent an important therapeutic target for future investigation.

Purification of Holstein bull semen paraoxonase 1 (PON1) by hydrophobic interaction chromatography and investigation of its inhibition kinetics by heavy metals

In this study, paraoxonase 1 (PON1; EC 3.1.8.1) was purified from bull semen, and some characteristics of the enzyme were investigated. In vitro inhibition effect of some heavy metals, including Cu(2+), Mn(2+), Cd(2+), Zn(2+), Ni(2+), and Pb(2+), on the activity of the purified enzyme was also investigated. The purification of bull semen PON1 procedure was composed of two steps: ammonium sulfate precipitation and Sepharose-4B-L-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The enzyme, having a specific activity of 288 EU/mg proteins, was purified 22.67-fold with a yield of 89 %. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the purified enzyme showed the presence of a single band with an apparent MW of 66 kDa. The V max and K M values for the paraoxon substrate were determined as 100 EU and 8.0 × 10(-5) M, respectively. The inhibitory effects of different heavy metals on PON1 activity were determined by using the paraoxon as a substrate. The results showed that all the metals, except for Cd(2+), inhibited the PON1 enzyme activity in a concentration-dependent fashion. IC50 values of Cu(2+), Mn(2+), Zn(2+), Ni(2+), and Pb(2+) were found as 2.59 × 10(-3), 1.17 × 10(-3), 42.74 × 10(-3), 99.10 × 10(-3), 48.80 × 10(-3) mM, respectively. Conversely, Cd(2+) increased the bull semen PON1 enzyme activity. The present study has demonstrated that Cu(2+), Mn(2+), Zn(2+), Ni(2+), and Pb(2+) are serious toxic metals, which are able to increase the risk of oxidative stress development and a subsequent decrease of semen quality.

Characterization of carbonic anhydrase from Turkish native "Gerze" chicken and influences of metal ions on enzyme activity

Abstract Carbonic anhydrase was purified and characterized from erythrocytes of the Turkish native chicken, Gerze, for the first time. The enzyme was purified 57.65-fold with a yield of 52%, and a specific activity of 954.08 U/mg proteins having optimum pH at 8.0; optimum temperature at 30 °C; optimum ionic strength at 10 mM and stable pH at 8.0. The purified enzyme had apparent KM and Vmax values of 0.73 mM and 0.236 μmol × min(-1), respectively. Al(+3), Hg(+2), Cu(+2), Pb(+2), and Cd(+2) showed inhibitory effects on the enzyme. Pb(+2) exhibited the strongest inhibitory action. Cd(+2) and Hg(+2) were moderate inhibitor, whereas Al(+3) and Cu(+2) showed weaker actions. All tested metals inhibited the enzyme in competitive manner. Our findings indicate that these metals inhibit the chicken enzyme in a similar manner to other α-CAs from mammals investigated earlier, but susceptibility to various metals differ between the native chicken and other mammalian enzymes.

Goose fat, a promising nutrient for fish feeding, activates antioxidant enzymes in rainbow trout, Oncorhynchus mykiss

The objective of this experiment was to test effects of different dietary lipids in rainbow trout feeding on the activity and expression of antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST). Four iso-nitrogenous and iso-lipidic casein-gelatin based experimental diets were formulated. The sources of dietary lipids were cod liver oil (CO, rich in polyunsaturated fatty acids), goose fat (GF, rich in saturated fatty acids and monounsaturated fatty acids), soybean oil (SO, rich in linoleic acid), and a blend of CO, GF and SO. Dietary treatments had no significant effect on growth performance and survival was not affected. SOD, GPx and GST enzymes had the maximum activity in GF diet. However qPCR data showed that SOD and GPx mRNA levels were minimum in GF group. Overall data showed that rainbow trout liver enzymes were activated upon GF diet probably activating the enzyme structure itself without stimulating gene expression.

Carbonic anhydrase activity from the gilthead sea bream (Sparus aurata) liver: the toxicological effects of heavy metals

Many studies have shown that metal ions may lead to oxidative stress in biological systems. Accordingly, DNA damage, protein modification, enzyme inhibition and activation, lipid peroxidation and many other effects may occur in living organisms. Many different formations of metal ions may enter human cells along with water, air, and various foods, and humans are negatively affected by these conditions, either directly or indirectly. These effects may cause irreversible damage to human metabolism. In this study, the toxicological effects of heavy metals on carbonic anhydrase enzyme activity from the gilthead sea bream liver were investigated. The carbonic anhydrase enzyme was purified via affinity chromatography and had a specific activity of 6775.5EUmg(-1). The kinetics and characteristic properties, such as optimum pH, stable pH, optimum temperature, activation energy (Ea), activation enthalpy (ΔH), Q10, Km, and Vmax, were determined for the purified enzyme SDS-polyacrylamide gel electrophoresis showed a single band and molecular weight of the subunit was approximately 25kDa. Cd(II), Cu(II), Ni(II) and Ag(I) inhibited the enzyme activity in vitro. The type of inhibition and Ki values for these metals were calculated from Lineweaver-Burk plots as 17.74mM, 36.20mM, 12.85mM and 0.025mM for Cd(II), Cu(II), Ni(II) and Ag(I), respectively. All the metals were noncompetitive inhibitors.

Synthesis and biological evaluation of novel bromophenol derivatives as carbonic anhydrase inhibitors

Here, we provide an alternative synthesis of the natural bromophenol 3,4-dibromo-5-(2,3-dibromo-4,5-dihydroxybenzyl)-6-(ethoxymethyl)benzene-1,2-diol (3) and the first synthesis of (4,5-dihydroxy-2-methylphenyl)(3,4-dihydroxyphenyl)methanone (18) and its brominated derivatives 19-21. The compounds were characterized and tested against the two most studied members of the pH regulatory enzyme family, carbonic anhydrase (CA). The inhibitory potencies of the novel compounds and two natural bromophenols 2, 3 were analyzed at the human isoforms hCA I and hCA II as targets and the KI values were calculated. The KI values of the novel compounds were measured in the range of 13.7-32.7 mM for the hCA I isozyme and 0.65-1.26 mM for the hCA II isozyme. The structurally related compound 14 was also tested in order to understand the structure–activity relationship, and the clinically used sulfonamide acetazolamide (AZA)was tested for comparison reasons. All of the compounds exhibited competitive inhibition with 4-nitrophenylacetate as substrate. The compounds showed strong inhibitory activity against hCA I, being more effective as compared to the clinically used AZA (KI: 36.2 mM), but rather less activity against hCA II.

Effects of some anti-neoplastic drugs on sheep liver sorbitol dehydrogenase

Stress is an important factor for many diseases in living metabolisms. The mini pathway named as polyol is a critical junction for stress factors. This pathway has two enzymes: aldose reductase (AR) and sorbitol dehydrogenase (SDH). It is linked with some diseases such as diabetes mellitus and some cancer types. In particular, SDH is very sensitive and unstable in in vitro conditions. In this study, SDH was purified by using simple and rapid chromatographic methods such as DEAE-Sephadex and CM-Sephadex C-50 columns. Subunit and active form molecular weights were found as 39.8 kDa and 150 kDa, respectively. The in vitro effects of some antineoplastic drugs were investigated. IC(50) values were 0.025, 0.081, 0.291, 1.62, 4.86, 6.54 mM for dacarbazine, methotrexate, epirubicin hydrochloride, calcium folinate, gemcitabine hydrochloride, oxaliplatin, respectively. From these results, dacarbazine was lowest IC(50) value and it is the strongest inhibitor for liver SDH enzyme activity compared to the other drugs.

Dietary cholesterol increases paraoxonase 1 enzyme activity

HDL-associated paraoxonase 1 (PON1) activity has been consistently associated with cardiovascular and other diseases. Vitamins C and E intake have previously been positively associated with PON1 in a subset of the Carotid Lesion Epidemiology and Risk (CLEAR) cohort. The goal of this study was to replicate these findings and determine whether other nutrient intake affected PON1 activity. To predict nutrient and mineral intake values, 1,402 subjects completed a standardized food frequency survey of their dietary habits over the past year. Stepwise regression was used to evaluate dietary and covariate effects on PON1 arylesterase activity. Five dietary components, cholesterol (P < 2.0 × 10(-16)), alcohol (P = 8.51 × 10(-8)), vitamin C (P = 7.97 × 10(-5)), iron (P = 0.0026), and folic acid (0.037) were independently predictive of PON1 activity. Dietary cholesterol was positively associated and predicted 5.5% of PON1 activity, second in variance explained. This study presents a novel finding of dietary cholesterol, iron, and folic acid predicting PON1 activity in humans and confirms prior reported associations, including that with vitamin C. Identifying and understanding environmental factors that affect PON1 activity is necessary to understand its role and that of HDL in human disease.

Crossroads in the evaluation of paraoxonase 1 for protection against nerve agent and organophosphate toxicity

Human paraoxonase 1 (PON1), a 45kDa arylesterase associated with circulating high density lipoproteins (HDL), has been described as an anti-atherogenic element in cardiovascular disorders. The efficacy of PON1 as a catalytic bioscavenger against OP and CWNA toxicity has been on debate for the last few decades. Hydrolysis of various organophosphates (OPs) and chemical warfare nerve agents (CWNAs) by PON1 has been demonstrated in both in vitro and in vivo experiments. Recently, we established the protective efficacy of human and rabbit serum purified PON1 as well as human recombinant PON1 expressed in Trichoplusia ni larvae against nerve agent toxicity in guinea pigs. Exogenous administration of purified PON1 was effective in protecting against 1.2 X LCt(50) of sarin and soman administered endotracheally with microinstillation technology. However, the short half-life of exogenously administered PON1, probably due to poor association with circulating HDL, warrant alternative approaches for successful utility of PON1 in the treatment of OP/CWNA toxicity. In this mini review, we address the pros and cons of current PON1 prophylaxis and propose potential solutions for successful development of PON1 as an effective catalytic bioscavenger.

Lead inhibits paraoxonase 2 but not paraoxonase 1 activity in human hepatoma HepG2 cells

Lead is an environmental toxicant of great concern for humans and animals. Lead-induced liver damage and malfunction are partly due to a disturbance of the cellular antioxidant balance. Paraoxonase 1 (PON1) and PON2 are highly expressed in the liver and have been proposed as antioxidative enzymes. In this study, the effects of lead on PON1 and PON2 activities were investigated in human hepatoma HepG2 cells by exposing the cells to various concentrations of lead acetate for 24, 48, or 72 h. The results show that a significant increase in reactive oxygen species was observed even at the lowest concentration of lead treatment. However, only the highest concentration of lead significantly influenced cell viability. Lead had no influence on cell-associated PON1 activity, but it significantly decreased cytoplasmic PON2 activity in a concentration- and time-dependent manner. This reduction was rescued by the addition of calcium. A significant increase of PON2 transcript was observed by real-time polymerase chain reaction, while PON2 protein expression did not change in the western blot analysis. Taken together, these results indicate that lead reduces PON2, but not PON1, activity and that this reduction is reversed by calcium. Lead-induced oxidative stress and decreased PON2 activity lead to the upregulation of PON2 transcript.

Investigation of heavy metal effects on immobilized paraoxanase by glutaraldehyde

Serum paraoxonase 1 (PON1) was purified from bovine serum using hydrophobic interaction chromotography on Sepharose 4B-coupled l-tyrosine 1-naphthylamine gel, and monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Paraoxonase enzyme was immobilized using different ratios of glutaraldehyde and the maximum activity was observed with 7% glutaraldehyde. The effects of inhibition by Mn(+2), Co(+2) and Cu(+2) heavy metals on the immobilized and free enzyme activities were studied. At the optimum pH and temperature, the K(m) and V(max) kinetic values for bovine serum paraoxonase and immobilized paraoxonase towards paraoxon substrate were determined as 0.296 × 10(-3) M & 37.04 EU vs. 0.727-10(-3) M & 36.36 EU, respectively.

Influence of cobalt and zinc exposure on mRNA expression profiles of metallothionein and cytocrome P450 in rainbow trout

The present research aims to evaluate the effects of cobalt and zinc exposure of rainbow trout (Oncorhynchus mykiss) on metallothioneins and cytocrome P450. Mature rainbow trouts were exposed to 10 mg/L CoCl(2).6H(2)O and 1 mg/L ZnSO(4).7H(2)O. After 6, 12, 24, and 48 h of treatment, expressions of muscle MT-A, MT-B, and CYP P4501A1 mRNAs were measured by means of quantitative real-time polymerase chain reaction. During the exposure experiments, no mortalities occurred. We observed that expression levels of all genes increased with exposure time. Since the organism has not learned how to completely dispose of heavy metals and tends to bioaccumulate them, our results indicate that cobalt and zinc exposure may result in accumulation of the non-eliminated metals which may lead to fish death.

In vitro enzymatic response of Turkish native chicken "Gerze" to heavy metal exposure

Glucose-6-phosphate dehydrogenase (G6PD) was purified and characterized from the Turkish native chicken, Gerze, erythrocytes for the first time, and some characteristics were investigated. Purification procedure consisted of ammonium sulphate fractionation and affinity chromatography on 29, 59-ADP Sepharose-4B. The enzyme was purified 1063.22-fold with a yield of 43.27% and specific activity of 93.5 EU/mg proteins. Kinetic parameters of the enzyme were determined with glucose-6-phosphate (G6P) as substrate and purified enzyme had an apparent K(M) and V(max) values of 0.222 mM and 0.097 U/ml, respectively. The same parameters were determined with NADP(+) and the K(M) and V(max) values were 0.0603 mM and 0.153 U/ml, respectively. The following metals, Cd(+2), Pb(+2), Hg(+2), Cu(+2), Zn(+2) and Fe(+3) showed inhibitory effects on the enzyme. Cd(+2) and Pb(+2) exhibited the strongest inhibitory action. Hg(+2) and Cu(+2) were moderate inhibitors, whereas Zn(+2) and Fe(+3) showed weaker actions. All tested metals inhibited the enzyme in competitive manner.

The impact of heavy metals on the activity of carbonic anhydrase from rainbow trout (Oncorhynchus mykiss) kidney

Many environmental and health problems have become a consequence of contamination of soil and water by toxic heavy metals and organic pollutants in the present age of technology. Heavy metals play vital roles in enzyme activities and other metabolic events with their bioaccumulative and nonbiodegradable properties among aquatic pollutants. Metal toxicity causes irregular metallothioneins protein synthesis, renal damage, and disruption of bone structure in humans and wildlife. In this study, we investigated in vitro effects of some metals on chemical-targeted carbonic anhydrase (CA) enzyme from rainbow trout kidney. The enzyme was purified with a specific activity of 17,285 EU × mg(-1) and 31.7% yield and approximately 1800-fold using simple affinity purification method. Molecular weights of the subunit and native enzyme were estimated as 28.7 kDa and 26.9 kDa via sodium dodecyl sulfate polyacrylamide gel electrophoresis and Sephadex-G 200 column, respectively. Other kinetic properties of the enzyme were determined. Apparent K(m) , V (max) and k (cat) values were 0.40 mM, 0.097 µmol min(-1) and 15.2 s(-1) for p-nitrophenylacetate substrate, respectively. Inhibitory effects of cobalt, zinc, copper, cadmium and silver on CA activity were determined using the esterase method under in vitro conditions. IC(50) and K(i) values were calculated for metals. K(i) values for Co(2+), Zn(2+), Cu(2+), Cd(2+) and Ag(+) were 0.035, 1.2, 34.8, 103 and 257 from Lineweaver-Burk graphs, respectively. Consequently, in vitro inhibition rank order was determined as Co(2+) > Zn(2+) > Cu(2+) > Cd(2+) > Ag(+). The potential inhibitor for CA was found as Co(2+) from these results.

Synthesis and carbonic anhydrase inhibitory properties of novel bromophenols including natural products

(2-Bromo-3,4-dimethoxyphenyl) (3,4-dimethoxyphenyl)methanone (10) and its derivatives with Br, one dibromide and isomeric three tribromides, were synthesized. Demethylation of these compounds afforded a series of new bromophenols. Inhibition of human cytosolic carbonic anhydrase II (hCA II) isozyme by these new bromophenols and naturally occurring 3,4,6-tribromo-5-(2,5-dibromo-3,4-dihydroxybenzyl)benzene-1,2-diol (3), and 5,5'-methylenebis(3,4,6-tribromo-benzene-1,2-diol) (4) was investigated. The synthesized compounds showed carbonic anhydrase inhibitory capacities with IC(50) values in the range of 0.7-372 μM against hCA II. Some bromophenols investigated here showed effective hCA II inhibitory activity and might be used as leads for generating novel carbonic anhydrase inhibitors which are valuable drug candidates for the treatment of glaucoma, epilepsy, gastric and duodenal ulcers, neurological disorders, or osteoporosis.

In vitro inhibition of α-carbonic anhydrase isozymes by some phenolic compounds

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, gastric and duodenal ulcers, neurological disorders or osteoporosis. We report here the inhibitory capacities of some phenolic compounds against three human CA isozymes (hCA I, hCA II, and hCA VI) and the gill carbonic anhydrase of the teleost fish Dicentrarchus labrax (European seabass) (dCA). The isozymes showed quite diverse inhibition profiles with these compounds. These data may lead to design novel CAIs with a diverse inhibition mechanism compared to sulfonamide/sulfamate inhibitors.

IGF and GH mRNA levels are suppressed upon exposure to micromolar concentrations of cobalt and zinc in rainbow trout white muscle

The objective of this study was to assess the effects of cobalt and zinc exposure of rainbow trout (Oncorhynchus mykiss) on insulin like growth factors (IGF) and growth hormone (GH). Mature rainbow trouts were exposed to 0.42, 2.1, 4.2, 21 and 42μmol/L Co(2+) (added as CoCl(2)·6H(2)O) and 0.34, 1.7, 3.4, 17 and 34μmol/L Zn(2+) (added as ZnSO(4)i·7H(2)O). After 6, 12, 24 and 48h of treatment, expressions of white muscle IGF-I, IGF-II and GH mRNAs were measured by means of quantitative Real Time PCR. During the exposure experiments, no mortalities occurred. The most effective metal concentrations, which caused significant alterations, were determined to be 42μmol/L Co(2+) (10mg CoCl(2)·6H(2)O/L) and 3.4μmol/L Zn(+2) (1mg ZnSO(4)·7H(2)O/L). The following results were obtained for these concentrations. Expression of IGF-I did not change at 6h in zinc treatment while the decrease (p<0.05) was observed at 12h and 24h, and this decrease became stronger at 48h. Cobalt exposure caused a decrease in IGF-I mRNA level at 6h, 12h, 24h and 48h (p<0.05). Both zinc and cobalt exposure resulted in significant decreases in GH expression at 6h. Exposure of trout to Zn resulted in a decrease in expression of IGF-II starting from 6h whereas the significant decrease started at 6h in cobalt exposure and this decrease elevated at 24h. The results indicate that micromolar cobalt and zinc exposure causes significant attenuation in the expressions of these three genes' time dependently. Our findings show that IGF-I is the most resistant and GH is the most sensitive component against cobalt and zinc exposure. We conclude that IGF/GH axis might be strongly affected by the short term exposure to low micromolar concentrations of zinc and cobalt due to alterations of these genes.

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.