The human serum paraoxonase/arylesterase polymorphism.

The heterozygous human serum paraoxonase phenotype can be clearly distinguished from both homozygous phenotypes on the basis of its distinctive ratio of paraoxonase to arylesterase activities. A trimodal distribution of the ratio values was found with 348 individual serum samples, measuring the ratio of paraoxonase activity (with 1 M NaCl in the assay) to arylesterase activity, using phenylacetate. The three modes corresponded to the three paraoxonase phenotypes, A, AB, and B (individual genotypes), and the expected Mendelian segregation of the trait was observed within families. The paraoxonase/arylesterase activity ratio showed codominant inheritance. We have defined the genetic locus determining the aromatic esterase (arylesterase) responsible for the polymorphic paraoxonase activity as esterase-A (ESA) and have designated the two common alleles at this locus by the symbols ESA*A and ESA*B. The frequency of the ESA*A allele was estimated to be .685, and that of the ESA*B allele, 0.315, in a sample population of unrelated Caucasians from the United States. We postulate that a single serum enzyme, with both paraoxonase and arylesterase activity, exists in two different isozymic forms with qualitatively different properties, and that paraoxon is a "discriminating" substrate (having a polymorphic distribution of activity) and phenylacetate is a "nondiscriminating" substrate for the two isozymes. Biochemical evidence for this interpretation includes the cosegregation of the degree of stimulation of paraoxonase activity by salt and paraoxonase/arylesterase activity ratio characteristics; the very high correlation between both the basal (non-salt stimulated) and salt-stimulated paraoxonase activities with arylesterase activity; and the finding that phenylacetate is an inhibitor for paraoxonase activities in both A and B types of enzyme.     

Molecular basis for the polymorphic forms of human serum paraoxonase/arylesterase: glutamine or arginine at position 191, for the respective A or B allozymes.

The paraoxonase/arylesterase gene is located close to the cystic fibrosis gene on chromosome 7. Human serum contains two paraoxonase/arylesterase allozymes, A and B, which differ in their substrate specificities and kinetic properties. Purified A, AB, and B esterases were digested with trypsin, and the resultant peptides were compared by high-performance liquid chromatography. The elution profiles were very similar for all three samples, except for (1) one peptide (i.e., peptide A) seen only in the A and AB profiles and (2) another peptide (i.e., peptide B) seen only in the B and AB profiles. Sequencing revealed that peptide A had glutamine at amino acid position 191, whereas peptide B was generated by cleavage on the carboxy side of position 191, presumably because there was a basic (trypsin-specific) amino acid at that position. Working independently, our laboratory and one other laboratory have sequenced the coding region for paraoxonase from human liver cDNA libraries and have identified two polymorphic sites: Arg/Gln at position 191 and Leu/Met at position 54. Using PCR amplification and direct sequencing of nucleotides in both polymorphic regions with genomic DNA, we have estimated the allelic frequencies and have determined their concordance with the serum paraoxonase allozyme phenotypes in 27 unrelated adults and in 16 members of a three-generation pedigree. Among unrelated individuals, the Met/Leu polymorphism at position 54 did not correlate with the serum esterase phenotype. In contrast, the particular amino acid at position 191 correlated perfectly with serum phenotypes: A-type individuals had Gln at position 191, and B-type individuals had Arg at position 191; AB-type serum was found only with the heterozygous (Arg/Gln) combination. Pedigree analysis showed both polymorphisms to be inherited in the expected Mendelian manner and confirmed that only the 191 polymorphism showed concordance with the serum paraoxonase/arylesterase phenotypes.     

Paraoxon hydrolysis in human serum mediated by a genetically variable arylesterase and albumin.

Gel filtration chromatography resolves human serum paraoxonase into two fractions: (1) a high molecular weight fraction that is completely inhibited by EDTA and coelutes with arylesterase (E.C.3.1.1.2); and (2) a second fraction that is closely associated with albumin, is only partially inhibited by EDTA, and has relatively little arylesterase activity under the assay conditions used. The activity of the high molecular weight fraction is stimulated by NaCl, whereas the albumin associated activity is partially inhibited by NaCl and is not present in serum derived from an analbuminemic individual. Our data suggest that albumin itself, rather than a protein bound to or cofractionating with albumin, mediates paraoxonase activity. The variation in levels of the activity of the nonalbumin, high molecular weight enzyme is responsible for the observed polymorphism of paraoxonase activity in human serum or plasma. An optimal assay of polymorphic paraoxonase activity should be based on activity measurements of the nonalbumin fraction. It is considered likely that only the nonalbumin fraction is responsible for in vivo hydrolysis of paraoxon.     

A sandwich enzyme-linked immunosorbent assay for human serum paraoxonase concentration

Serum paraoxonase (PON) is associated with plasma high density lipoproteins, and prevents the oxidative modification of low density lipoproteins. We have developed a sensitive sandwich enzyme-linked immunosorbent assay (ELISA), using two monoclonal antibodies against PON, to measure serum PON concentration. The concentration of PON in healthy Japanese subjects was 59.3 +/- 1.3 microgram/mL (mean +/- SEM; n = 87). Serum PON concentrations in relation to the PON 192 genetic polymorphism were: 69.5 +/- 2.9 microgram/mL in the QQ genotype; 63.0 +/- 1.9 microgram/mL in the QR genotype; and 52.8 +/- 1.7 microgram/mL in the RR genotype. Concentrations were significantly lower in the RR than in the QQ genotype (P < 0.01). Serum paraoxonase specific activity was higher in RR than in QQ subjects (18.6 +/- 0.40 vs. 2. 56 +/- 0.05 nmol/min/microgram, P < 0.01), but arylesterase specific activity was unrelated to genotype. PON concentration was positively associated (P < 0.001) with both serum arylesterase activity and, after adjusting for the effect of the position 192 polymorphism, with serum paraoxonase activity. Subjects with angiographically verified coronary heart disease had significantly lower PON concentrations than the healthy controls (52.0 +/- 2.3 microgram/mL; n = 35, P < 0.01). This association was independent of the position 192 genotype. Our new ELISA should be of value for epidemiologic and clinical studies of serum PON concentration. immunosorbent assay for human serum paraoxonase concentration.     

Paraoxonase 55 and 192 polymorphism and its relationship to serum paraoxonase activity and serum lipids in Turkish patients with non-insulin dependent diabetes mellitus

We investigated the effect of PON 55 and PON 192 polymorphisms on serum PON1 activity and lipid profiles in 213 non-insulin dependent diabetes mellitus (NIDDM) individuals and 116 non-diabetic controls among Turkish subjects. The distribution of PON 55/192 gene polymorphism was determined by polymerase chain reaction-based restriction fragment length polymorphism. Serum lipid levels were measured enzymically. PON activity was measured by spectrophotometric assay of p-nitrophenol production following addition of paraoxon. We found that PON 55 and 192 genotype distribution was similar in patients and controls and paraoxonase activity was generally lower in diabetics than in control subjects. We showed that PON 55 and 192 genotypes have a major effect on serum PON activity. PON 192 BB homozygotes had significantly higher PON activity than AA and AB genotypes among the control and NIDDM populations (p<0.001). PON 55 MM homozygotes had significantly lower PON activity than did LL and LM genotypes in control and NIDDM populations (p<0.05). The PON1 55 and 192 polymorphisms did not consistently influence the serum lipid profiles in either population. In conclusion, our results suggest that the paraoxonase activities are affected by PON1 genetic variability in Turkish NIDDM patients and controls.     

Spectrophotometric assays for the enzymatic hydrolysis of the active metabolites of chlorpyrifos and parathion by plasma paraoxonase/arylesterase

Human serum plasma paraoxonase/arylesterase exhibits a genetic polymorphism for the hydrolysis of paraoxon. One allelic form of the enzyme hydrolyzes paraoxon slowly with a low turnover number and the other(s) hydrolyzes paraoxon rapidly with a high turnover number. Chlorpyrifos-oxon, the active metabolite of the insecticide chlorpyrifos (Dursban), is also hydrolyzed by plasma arylesterase/paraoxonase. A specific assay for measuring hydrolysis of this compound is described. This assay is not subject to interference by the esterase activity of serum albumin. The Km for chlorpyrifos-oxon hydrolysis was 75 microM. Hydrolysis was inhibited by phenyl acetate, EDTA, and organic solvents. Enzyme activity required calcium ions and was stimulated by sodium chloride. Hydrolysis was optimized by using methanol instead of acetone to dissolve substrate. Unlike the multimodal distribution of paraoxonase, the distribution of chlorpyrifos-oxonase activity failed to show clear multimodality. An improvement in the assay for hydrolysis of paraoxon by plasma arylesterase/paraoxonase was achieved by elimination of organic solvents. Plotting chlorpyrifos-oxonase activity vs paraoxonase activity for a human population using the new assay conditions provided an excellent resolution of low activity homozygotes from heterozygotes for this allele. A greater than 40-fold difference in rates of chlorpyrifosoxon hydrolysis observed between rat (low activity) and rabbit sera (high activity) correlated well with the reported large differences in LD50 values for chlorpyrifos in these two animals, consistent with an important role of serum paraoxonase in detoxification of organophosphorus pesticides in vivo.     

Distribution profile of paraoxonase phenotypes among the Gujaratis

BACKGROUND:

Paraoxonase (PON1) can hydrolyze organophosphate pesticides (OP) and has a key role in the susceptibility of human in OP toxicity. The human-enzyme shows polymorphism and variations in the distribution profile of its phenotypes among different ethnic groups have been observed.

AIMS:

To see the distribution pattern of total PON1 activity in 45 healthy attendants of poisoning cases; 121 healthy unrelated farm-labours and 59 normal subjects of trauma.

MATERIALS AND METHODS:

The PON1 activities from serum/plasma samples of these healthy normal individuals were estimated with/without addition of 1M NaCl in order to determine salt-stimulated and basal activity. The PON 1 phenotypes were determined on the basis of percent activation of enzyme activity.

RESULTS:

Tri-modal distribution of basal PON1 activity was observed among all these individuals. 52.0% of the individuals belonged to Phenotype A, 46.6% to phenotype AB while 1.4% to Phenotype B with gene frequency of allele-A and allele-B being 0.753 and 0.247 respectively in excellent agreement with Hardy-Weinberg equilibrium.

CONCLUSION:

Maximum number of individuals belonged to phenotype-A (low PON1 activity) showing potential vulnerability towards Op-poisoning.     

A study of the polymorphism and ethnic distribution differences of human serum paraoxonase

The enzyme serum paraoxonase shows a polymorphism in Europeans which is governed by two alleles. The first allele has a gene frequency p_low of 0.716–0.777, and is manifested as a low activity group in homozygotes. More than 50% of all European test subjects can be included in this group. A second allele with a gene frequency q_high of 0.223–0.284 was found in typical European distributions and is manifested in both the form of a second heterozygotic and a third homozygotic group with high activities. The Hardy-Weinberg rule for a two-allele model is valid for the distribution. The gene frequency p_low of the first allele decreases as one moves from Europe in the direction of Africa and Asia. In typical Mongoloid and Negroid collectives, less than 10% of the population can be included in the low-activity group, a group which is not even demonstrable in the Aborigines of Australia. The serum paraoxonase of the Aborigine population shows unimodal distribution. The validity of the Hardy-Weinberg rule for a three-allele model must be rejected in all examined collectives. Human serum paraoxonase shows neither age-related changes in activity nor sex-dependent activity differences.     

Serum paraoxonase polymorphism in three populations of southeast Asia.

Serum paraoxonase hydrolyzes paraoxon, the principal metabolite of the insecticide parathion. Serum paraoxonase is polymorphic and controlled by two codominant alleles - PON*A and PON*B representing low and high activity, respectively. Three populations of southeast Asia comprising 194 Chinese, 159 Filipinos and 73 Dravidian Indians were investigated for serum paraoxonase polymorphism. The frequency of PON*B was found to be 0.14 in the Chinese, 0.04 in the Filipinos and 0.18 in Dravidian Indians. The distribution of the PON phenotypes was at Hardy-Weinberg equilibrium in all the three populations studied.     

Plasma paraoxonase polymorphism: a new enzyme assay, population, family, biochemical, and linkage studies.

Plasma paraoxonase hydrolyzes paraoxon, the principal metabolite of the insecticide parathione. A genetic polymorphism for enzyme activity has been previously demonstrated. We describe a new assay based on the differential inhibition by EDTA of plasma paraoxonase from persons with the high-activity allele (PX*H) that suggests a trimodality of activity levels in population studies. The gene frequency of the low activity allele (PX*L) in 531 Seattle blood donors of European origin was .7207. Family studies were consistent with codominant autosomal inheritance of two alleles, PX*L (low) and PX*H (high), coding for products with different activity levels. Biochemical measurements of sera from presumed homozygotes for the two different alleles revealed minor physicochemical differences suggestive of a structural difference between the allelic products. No evidence for linkage of the paraoxonase locus with any of 19 polymorphic markers would be detected.     

Levels of paraoxonase and arylesterase activities and malondialdehyde in workers exposed to ionizing radiation

We examined levels of malondialdehyde (MDA) (an end-product of lipid peroxidation) and paraoxonase (PON1) (an antioxidant enzyme) activity and PON1 phenotypes in people who were exposed to ionizing radiation for different time periods and doses. A total of 78 individuals (mean age 34 +/- 7 years) were included in the study. Fifty-one of them were radiology workers whereas the control group was composed of 27 healthy volunteers who had never worked in a radiology-related job. Paraoxon was used as substrate for measurement of PON1 activity levels (basal and NaCl-stimulated). Phenylacetate was used as substrate for measurement of arylesterase activity levels. Cumulative levels of serum NaCl-stimulated PON1/arylesterase activities were utilized for phenotypic differentiation. In radiology workers, three different phenotypes were determined based on paraoxonase/arylesterase ratio. The ratios were 1.09 +/- 0.30 for AA (homozygote low activity); 2.91 +/- 1.07 for AB (heterozygote activity) and 4.97 +/- 1.21 for BB (homozygote high activity). There was a statistically meaningful negative correlation between serum MDA levels and PON1 activity levels in all phenotypes (p < 0.05). PON1 activity levels were found to be 25-35% lower in people who were exposed to long-term ( > 5 years) radiation compared to controls. There was no statistically significant correlation between serum arylesterase activity and MDA levels in these subjects (r = -0.185, p > 0.05). PON1 activity levels were decreased whereas serum MDA levels were increased in individuals exposed to radiation for a long period. PON phenotypes of people employed in jobs which expose them to radiation should be determined and based on these findings they should be advised to avoid risk factors inducing oxidative stress, such as smoking, and to consume foods rich in vitamins and trace elements to increase their antioxidant capacity.     

Role of genetic polymorphism of human plasma paraoxonase/arylesterase in hydrolysis of the insecticide metabolites chlorpyrifos oxon and paraoxon

Plasma paraoxonase is a polymorphic enzyme that hydrolyzes paraoxon, the neurotoxic, active metabolite of the insecticide parathion. This enzyme is specified by at least two alleles with frequencies of about .7 and .3 among Caucasoid populations. A specific assay was developed that measured the activity of human plasma paraoxonase without interference from serum albumin which contributes significantly to the hydrolytic breakdown of paraoxon at the high pH values used in many previous assays. There was an 11-fold variation in paraoxonase activities, and the population distribution was at least bimodal. However, this specific assay did not improve the discrimination between the three genetic classes: (1) homozygotes for the low-activity allele, (2) heterozygotes, and (3) homozygotes for the high-activity allele. Chlorpyrifos oxon--the neurotoxic metabolite of the organophosphorus insecticide chlorpyrifos (Dursban)--was hydrolyzed by the same plasma fraction that hydrolyzed paraoxon. There was only four- to fivefold variability in enzyme activity, and the population distribution was unimodal. Homozygotes for low paraoxonase activity ranged over almost the entire spectrum of chlorpyrifos oxonase activity. Possible differences in susceptibility to chlorpyrifos toxicity therefore are unlikely to be predicted by the paraoxonase genotype alone. The ratio of paraoxonase over that of chlorpyrifos oxonase provided an excellent method for genetic typing of the paraoxonase polymorphism, as did the substitution of phenylacetate for chlorpyrifos as the substrate.     

Serum paraoxonase activity and phenotype distribution in Turkish subjects with coronary heart disease and its relationship to serum lipids and lipoproteins.

Recently, biochemical studies of paraoxonase in the serum of humans have shown that much of this enzymes' activity is associated with high-density lipoprotein (HDL) and paraoxonase may play a role in lipid metabolism preventing the accumulation of the lipoperoxides. In this study, a possible relationship between coronary heart disease (CHD) and paraoxonase activity were investigated. Serum triglycerides, total cholesterol, HDL-cholesterol and paraoxonase activity were measured in unrelated healthy donors and CHD patients. It was found that paraoxonase activity was trimodally distributed in both groups but no statistically significant difference was found between phenotype distributions of controls and CHD patients (gene frequencies; 0.632 and 0.382 of controls, 0.702 and 0.298 of patients for the A and B alleles, respectively). However, in CHD group, a high possibility was found to be phenotype A compared with the control group. A relative risk of 1.48 (95% confidence intervals (CI), 0.986-2.227) was found for the relation between CHD and the paraoxonase activity. Patients' HDL-cholesterol values were lower and triglycerides were higher than controls (P<0.001). It may be concluded from the present study that although no statistically significant difference was found between paraoxonase phenotype distributions of controls and CHD patients, a decrease in paraoxonase activity could become a risk factor for this disease.     

Paraoxonase 1 (PON1) and its relationship to lipid variables, age and gender in healthy volunteers

Recent studies implied that low-density lipoprotein (LDL) modified predominantly by oxidation or glycation, significantly contributes to the formation of atherosclerotic lesions. In contrast to oxidized LDL (ox-LDL), high-density lipoprotein (HDL) is able to prevent accumulation of ox-LDL in arterial walls. This antiatherogenic property of HDL is attributed in part to several enzymes associated with the lipoprotein, including HDL-associated paraoxonase 1 (PON1). In this study we analyzed PON1 arylesterase/paraoxonase activities in relation to serum lipid profile, gender and age in thirty clinically healthy Slovak volunteers. Our results showed that PON1 arylesterase and paraoxonase activities were lower in citrated plasma than in serum by 16.6% and 27.3%, respectively. Among serum lipoproteins, only HDL-cholesterol level showed significant positive correlation with PON1 arylesterase activity (p = 0.042). Likewise, we found a significant relationship between atherogenic index (AI = total cholesterol/HDL-cholesterol) and PON1 arylesterase activity (p = 0.023). No significant correlation could be demonstrated between PON1 paraoxonase activity and serum lipid profile, age or gender. Furthermore, it was found that PON1 paraoxonase/arylesterase activities were higher in women compared with both investigated activities in men, but these differences were not statistically significant. These results confirmed a positive correlation between HDL-cholesterol and PON1 arylesterase activity. Moreover, it was found out that PON1 paraoxonase activity is not influenced either by gender or by age. PON1 arylesterase activity was however affected by gender to a limited extent.     

Effects of 5' regulatory-region polymorphisms on paraoxonase-gene (PON1) expression

Human HDL-associated paraoxonase (PON1) hydrolyzes a number of toxic organophosphorous compounds and reduces oxidation of LDLs and HDLs. These properties of PON1 account for its ability to protect against pesticide poisonings and atherosclerosis. PON1 also hydrolyzes a number of lactone and cyclic-carbonate drugs. Among individuals in a population, PON1 levels vary widely. We previously identified three polymorphisms in the PON1 regulatory region that affect expression levels in cultured human hepatocytes. In this study, we determined the genotypes of three regulatory-region polymorphisms for 376 white individuals and examined their effect on plasma-PON1 levels, determined by rates of phenylacetate hydrolysis. The -108 polymorphism had a significant effect on PON1-activity level, whereas the -162 polymorphism had a lesser effect. The -909 polymorphism, which is in linkage disequilibrium with the other sites, appears to have little or no independent effect on PON1-activity level in vivo. Other studies have found that the L55M polymorphism in the PON1-coding region is associated with differences in both PON1-mRNA and PON1-activity levels. The results presented here indicate that the L55M effect of lowered activity is not due to the amino acid change but is, rather, largely due to linkage disequilibrium with the -108 regulatory-region polymorphism. The codon 55 polymorphism marginally appeared to account for 15.3% of the variance in PON1 activity, but this dropped to 5% after adjustments for the effects of the -108 and Q192R polymorphisms were made. The -108C/T polymorphism accounted for 22.8% of the observed variability in PON1-expression levels, which was much greater than that attributable to the other PON1 polymorphisms. We also identified four sequence differences in the 3' UTR of the PON1 mRNA.     

New data on the world distribution of paraoxonase (PON1 Gln 192 --> Arg) gene frequencies

The physiological role of human paraoxonase (PON), a serum enzyme that hydrolyzes organophosphate insecticides and nerve agents, is not clear. Of the three genes in the paraoxonase gene family, PON1 shows a polymorphism, Gln 192 --> Arg, governed by two common alleles named *Q and *R. These determine two different isoforms associated, respectively, with lower and higher activity towards paraoxon, a toxic metabolic product of the insecticide parathion. The *R allele has often been found associated with an increased risk of coronary heart disease. As human populations tend towards greater exposure to environmental changes, including changes in dietary habits and contact with insecticides or other toxic substances, health risks will change as well. In studying the prevention of these newly emerging risks, it could be important to know the distribution of the two alleles in the various world populations. In this paper we report on the genotype and allele frequencies of this polymorphism in different populations, most of which have never been examined for this polymorphism. Samples were taken from mainland Italy, Sardinia, Ethiopia, Benin, and Ecuador. The *R allele frequencies for the samples were: 0.313, 0.248, 0.408, 0.612, and 0.789, respectively. The data show a large variability in allele frequencies, and, in particular, that PON1 allele distribution depends on membership to different geographic populations.     

The development of human sera tests for HDL-bound serum PON1 and its lipolactonase activity

Serum paraoxonase (PON1) is a lipolactonase that associates with HDL-apolipoprotein A-I (HDL-apoA-I) and thereby plays a role in the prevention of atherosclerosis. Current sera tests make use of promiscuous substrates and provide no indications regarding HDL-PON1 complex formation. We developed new enzymatic tests that detect total PON1 levels, irrespective of HDL status and R/Q polymorphism, as well as the degree of catalytic stimulation and increased stability that follow PON1's tight binding to HDL-apoA-I. The tests are based on measuring total PON1 levels with a fluorogenic phosphotriester, measuring the lipolactonase activity with a chromogenic lactone, and assaying the enzyme's chelator-mediated inactivation rate. The latter two are affected by tight HDL binding and thereby derive the levels of the serum PON1-HDL complex. We demonstrate these new tests with a group of healthy individuals (n=54) and show that the levels of PON1-HDL vary by a factor of 12. Whereas the traditionally applied paraoxonase and arylesterase tests weakly reflect PON1-HDL levels (R=0.64), the lipolactonase test provides better correlation (R=0.80). These new tests indicate the levels and activity of PON1 in a physiologically relevant context as well as the levels and quality of the HDL particles with which the enzyme is associated.     

Decreased stability of the M54 isoform of paraoxonase as a contributory factor to variations in human serum paraoxonase concentrations

There are considerable variations in serum concentrations of the high density lipoprotein (HDL)-associated enzyme, paraoxonase (PON), which is an important determinant of the antioxidant capacity of HDL. The present study examined the hypothesis that differences in the stability of isoforms arising from the coding region L54M polymorphism could contribute to such variations. A model system was developed using transfected Chinese hamster ovary cells to secrete recombinant PON corresponding to human L or M isoforms. The recombinant peptides exhibited the molecular properties of human serum PON. They formed complexes with lipoproteins in culture medium, notably binding to apolipoprotein A-I-containing particles. The enzymatic properties of the recombinant isoforms were comparable to those of human serum PON. The recombinant M isoform lost activity more rapidly and to a greater extent than the recombinant L isoform [26.0 +/- 3.0% vs. 14.0 +/- 1.0% (phenylacetate substrate) and 36.1 +/- 2.0% vs. 19.3 +/- 2.0% (paraoxon substrate) over 96 h (P < 0.01)] in medium containing fetal calf serum or PON-free human serum. Addition of a protease inhibitor resulted in retention of activity by both isoforms. Parallel results were obtained in incubation studies of human serum from donors homozygous LL or MM for the L54M polymorphism. Enzyme activity was lost more rapidly and to a greater extent from MM than LL sera (P < 0.01). A parallel loss of PON peptide mass was also observed, with a significantly greater loss from MM homozygotes (P < 0.001). It corresponded to the appearance of a smaller molecular mass band on SDS-PAGE analysis. Direct analysis of the proteolytic effect using HDL isolated from homozygotes and incubated with purified kallikrein confirmed the greater loss of activity from MM homozygotes and the protective effect of proteolysis inhibitor. The results provide evidence for lesser stability of the M54 isoform of PON, apparently involving greater susceptibility to proteolysis. It provides one mechanism to explain variations in serum levels of PON and has implications for the antioxidant capacity of HDL.     

Paraoxonase 192 gene polymorphism and serum paraoxonase activity in high grade gliomas and meningiomas

The purpose of this study was to demonstrate the relationship between serum PON1 activity and PON 192 polymorphism in brain tumours. The distribution of PON 192 polymorphism in 42 high grade gliomas and 42 meningiomas were determined by polymerase chain reaction--based restriction fragment length polymorphism analysis and compared with 50 healthy control subjects. Serum paraoxonase1 activities were also measured and compared in the same population. We found that in both tumour groups serum PON1 activity was significantly lower than the control group (p < 0.001), but did not differ between meningiomas and high grade gliomas. There was no significant difference either in distribution of the AA, AB and BB genotypes or in the allelic frequencies, between the patient group and control subjects (p > 0.05). Our results suggest that serum PON1 as a part of the lipid peroxidation scavenging systems might be involved in the tumourigenesis of brain tumours.     

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.