Characterization of cDNA clones encoding rabbit and human serum paraoxonase: the mature protein retains its signal sequence

Role of paraoxonase 1 in organophosphate G-series nerve agent poisoning and future therapeutic strategies

Chemical warfare nerve agents (CWNA) are neurotoxic chemicals unethically used as agents of mass destruction by terrorist outfits and during war. The available antidote against CWNA-mediated toxicity is not sufficiently effective and possesses several limitations. As a countermeasure, paraoxonase 1 (PON1), a catalytic bioscavenger, is being developed as a prophylactic treatment. However, the catalytic activity and substrate specificity of human PON1 are insufficient to be used as a potential antidote. Several laboratories have made different approaches to enhance the CWNA hydrolytic activity against various nerve agents. This review explores the holistic view of PON1 as a potential prophylactic agent against G-series CWNA poisoning, from its initial development to recent advancements and limitations. Apart from this, the review also provides an overview of all available PON1 variants that could be used as a potential prophylactic agent and discusses several possible ways to counteract immunogenicity.

Enhancement in the production of recombinant human paraoxonase 1 in Escherichia coli: A comprehensive approach of cellular engineering and optimization of protein folding process in vitro

Human paraoxonase 1(hPON1) belongs to the paraoxonase (PON) family. It is a calcium-dependent enzyme with a size of ∼43 kDa and is composed of 6 bladed beta-barrel structures with two calcium ions in its active site. In humans, it is synthesized in the liver and remains bound with the high-density lipoproteins (HDL) within the blood. It has immense potential to tackle the poisoning associated with the use of organophosphates (OPs) and their derivatives, such as nerve agents, due to role in their degradation. Therefore, hPON1 serves as a potential bio-scavenger that can be used as an antidote or as a surface decontaminating agent in OPs poisoning. However, present systems prove insufficient to produce it in sufficient quantity to make it industrially relevant. Here, our efforts involve producing it recombinantly in an E. coli system with enhanced expression levels by altering cellular and environmental conditions. This has been further improved by the development of in-vitro refolding process for the denatured recombinant hPON1 (rhPON1) protein. This methodology resulted in approximately 200 mg of the enzymatically functional protein from 1 l of E. coli culture. Proper refolding of rhPON1 was confirmed by comparing its enzymatic activity and conformation with serum purified hPON1.

The Relationship between Cancer and Paraoxonase 1

Extensive research has been carried out to understand and elucidate the mechanisms of paraoxonase 1 (PON1) in the development of diseases including cancer, cardiovascular diseases, neurological diseases, and inflammatory diseases. This review focuses on the relationship between PON1 and cancer. The data suggest that PON1, oxidative stress, chronic inflammation, and cancer are closely linked. Certainly, the gene expression of PON1 will remain challenging to study. Therefore, targeting PON1, redox-sensitive pathways, and transcription factors promise prevention and therapy in the development of several diseases, including cancer.

The Role of Nutritional Habits and Moderate Red Wine Consumption in PON1 Status in Healthy Population

Paraoxonase 1 (PON1) plays a role as antioxidant on HDL. Including in diet additionally ingest of polyphenolic compounds can stimulate PON1 transcription and increase its activity. The aim of this study was to evaluate the effect of dietary intake, red wine consumption, and PON1 genotypes (Q192R, L55M and C-108T) on the specific activity of PON1 in a healthy population. A descriptive and analytical pilot study was conducted in Mexican volunteers clinically healthy (n = 45) aged from 21–59 years. Over 6 weeks, the study participants ingested 120 mL of red wine per day. PON1 concentration, PON1 activities, genetic polymorphisms and dietary intake were evaluated. The preliminary fingerprinting of the wine was determined to corroborate the presence of phenolic compounds such as tannins and gallotannins. Neither dietary intake nor PON1 genotypes showed an effect on the specific activity of PON1. However, a significant increase in specific AREase activity after red wine consumption period was observed in the study participants. Our data suggest that the moderate consumption of red wine has a beneficial effect on PON1 specific AREase activity in this healthy Mexican population.

The association between PON1 gene polymorphisms (Q192R and L55M) and nephrotic syndrome in Iraqi children

Background: The role of paraoxonase 1 enzyme (PON1) and its single nucleotide polymorphisms (SNPs) in children with nephrotic syndrome (NS) has been reported previously in different ethnic and racial groups with divergent results. The human PON1 gene contains two coding region polymorphisms leading to two different PON1 isoforms. Objectives: The aim of the present study was to find out the association between the PON1 (Q192R and L55M) polymorphisms and their relation with serum PON1 activity as well as lipid profile tests (total cholesterol, TC; triglycerides, TG; high-density lipoprotein cholesterol, HDL-c; and low-density lipoprotein cholesterol, LDL-c) in children with NS. Methods: This study included a total of 80 participants (40 with NS in the age group of 2-14 years and 40 age and sex-matched healthy controls). The PON1 enzyme activity and lipid profile tests were measured in serum samples of all included participants. The PON1 genotype was determined by PCR-restriction enzyme fragment length polymorphism (PCR-RFLP) for both PON1 alleles (192 and 55) SNPs. Results: Our findings showed that the mean levels of lipid profile tests (TC, TG, LDL-c) were significantly increased in patients when compared with healthy controls (p<0.05), while the HDL-c concentration was significantly decreased in patients than that of controls. Also, the patients had significantly lower concentrations of PON1 when compared with the controls regardless of the genotype Q192R and L55M polymorphisms. Moreover, the homozygous RR genotype for PON1 SNP 192 and MM homozygous genotype for PON1 SNP 55 were significantly frequent in patients when compared with the controls. Conclusions: Our results support that the presence of the homozygous RR genotype for PON1 SNP 192 and MM homozygous genotype for PON1 SNP 55 were significantly higher in patients compared with the controls.

Paraoxonase-1 (PON1) Status Analysis Using Non-Organophosphate Substrates

Human paraoxonase-1 (PON1) is a high-density lipoprotein-associated enzyme with antioxidant, anti-inflammatory, and antiapoptotic roles. The ability of PON1 to hydrolyze specific organophosphate (OP) compounds and prevent accumulation of oxidized lipids in lipoproteins has prompted a large number of studies investigating PON1's role in modulating toxicity and disease. Most of these studies, however, have only focused on PON1 single nucleotide polymorphism analyses and have ignored PON1 activity levels, arguably the most important parameter in determining protection against exposure and disease. We developed a two-substrate activity assay termed "PON1 status" that reveals both the functional PON1₁₉₂ genotype and plasma PON1 activity levels. While our previous studies with PON1 status demonstrated that both PON1₁₉₂ functional genotype and enzymatic activity levels obtained exclusively by determining PON1 status are required for a proper evaluation of PON1's role in modulating OP exposures and risk of disease, the original PON1 status assay requires the use of highly toxic OP metabolites. As many laboratories are not prepared to handle such toxic compounds and the associated waste generated, determination of PON1 status has been limited to rather few studies. Here, we describe a PON1 status protocol that uses non-OP substrates with a resolution equivalent to that of the original PON1 status approach. We have also included useful suggestions to ensure the assays can easily be carried out in any laboratory. The protocols described here will enable a proper examination of the risk of exposure or susceptibility to disease in PON1 epidemiological studies without the need to handle highly toxic substrates. © 2021 Wiley Periodicals LLC. Basic Protocol: Determining PON1 status using non-organophosphate substrates Support Protocol 1: Experimental pathlength determination Support Protocol 2: PON1 DNA genotyping for the Q192R (rs662) polymorphism.

Paraoxonase-1 and -3 Protein Expression in the Brain of the Tg2576 Mouse Model of Alzheimer's Disease

BACKGROUND

Brain oxidative lipid damage and inflammation are common in neurodegenerative diseases such as Alzheimer's disease (AD). Paraoxonase-1 and -3 (PON1 and PON3) protein expression was demonstrated in tissue with no PON1 or PON3 gene expression. In the present study, we examine differences in PON1 and PON3 protein expression in the brain of a mouse model of AD.

METHODS

we used peroxidase- and fluorescence-based immunohistochemistry in five brain regions (olfactory bulb, forebrain, posterior midbrain, hindbrain and cerebellum) of transgenic (Tg2576) mice with the Swedish mutation (KM670/671NL) responsible for a familial form of AD and corresponding wild-type mice.

RESULTS

We found intense PON1 and PON3-positive staining in star-shaped cells surrounding Aβ plaques in all the studied Tg2576 mouse-brain regions. Although we could not colocalize PON1 and PON3 with astrocytes (star-shaped cells in the brain), we found some PON3 colocalization with microglia.

CONCLUSIONS

These results suggest that (1) PON1 and PON3 cross the blood-brain barrier in discoidal high-density lipoproteins (HDLs) and are transferred to specific brain-cell types; and (2) PON1 and PON3 play an important role in preventing oxidative stress and lipid peroxidation in particular brain-cell types (likely to be glial cells) in AD pathology and potentially in other neurodegenerative diseases as well.

The Relevance of Noncoding DNA Variations of Paraoxonase Gene Cluster in Atherosclerosis-Related Diseases

The human paraoxonase (PON) gene cluster is comprised of three contiguous genes (PON1, PON2 and PON3) of presumably common origin coding three lactonases of highly similar structure and substrate specificity. The catalytic activity of PON proteins is directed toward artificial organophosphates and in physiological conditions toward thiolactones and oxidized phospholipids. Consequently, PON enzymes are regarded as an effective defense against oxidative stress and, as a result, against atherosclerosis development. Additionally, both PON's serum activity and its concentration are influenced by several polymorphic variations in coding and noncoding DNA regions of the PON gene cluster remaining in linkage disequilibrium. Hence, the genetic polymorphism of the PON gene cluster may contribute to atherosclerotic process progression or deceleration. In this review the authors analyzed the relevance of noncoding DNA polymorphic variations of PON genes in atherosclerosis-related diseases involving coronary and peripheral artery disease, stroke, diabetes mellitus, dementia and renal disease and concluded that the effect of PON gene cluster' polymorphism has a considerable impact on the course and outcome in these conditions. The following PON genetic variations may serve as additional predictors of the risk of atherosclerosis in selected populations and individuals.

HDL Proteome and Alzheimer's Disease: Evidence of a Link

Several lines of epidemiological evidence link increased levels of high-density lipoprotein-cholesterol (HDL-C) with lower risk of Alzheimer's disease (AD). This observed relationship might reflect the beneficial effects of HDL on the cardiovascular system, likely due to the implication of vascular dysregulation in AD development. The atheroprotective properties of this lipoprotein are mostly due to its proteome. In particular, apolipoprotein (Apo) A-I, E, and J and the antioxidant accessory protein paraoxonase 1 (PON1), are the main determinants of the biological function of HDL. Intriguingly, these HDL constituent proteins are also present in the brain, either from in situ expression, or derived from the periphery. Growing preclinical evidence suggests that these HDL proteins may prevent the aberrant changes in the brain that characterize AD pathogenesis. In the present review, we summarize and critically examine the current state of knowledge on the role of these atheroprotective HDL-associated proteins in AD pathogenesis and physiopathology.

Association between serum paraoxonase 1 activity and its polymorphisms with multiple sclerosis: a systematic review

BACKGROUND

Human serum paraoxonase (PON) is an enzyme that is synthesized by the liver and enters the bloodstream, and it is transmitted by high-density lipoproteins (HDL). Paraoxonase 1 (PON1) is a hydrolytic enzyme with a wide range of substrates and the ability to protect against lipid oxidation. In this study, due to the activity of PON1 in the brain and its antioxidant effects on the reduction of neurological disorders in the central nervous system, the role of PON1 and its polymorphisms related to multiple sclerosis has been examined to enhance treatment methods.

METHODS

This article is a systematic review. In this study, the role of PON1 and its polymorphisms in multiple sclerosis (MS) has been investigated. Articles published in Persian and international databases of SID, Google Scholar, ISI (WoS), Magiran, PubMed, Scopus, IranDoc, Science Direct, and Iran Medix were examined, using the search keywords of Paraoxonase 1, polymorphism, multiple sclerosis, and PON1.

RESULTS

PON1 is undoubtedly a potential factor in the pathogenesis of multiple sclerosis, and it plays an important role in protecting antioxidants in the blood. Oxidative stress and lipid peroxidation are factors in the pathogenesis of MS. Both inflammatory cytokines and oxidative stress have a detrimental effect on PON1. However, reducing the activity of PON1 may help to restore the pathogenesis of the disease.

CONCLUSION

Decreased PON1 activity and PON1 polymorphism are associated with several neurological diseases, including ischemic stroke, white matter lesions (WMLs), amyotrophic lateral sclerosis (ALS), dementia, and Parkinson's disease. PON1-55M alleles in Italians and PON1-192Q alleles in Poles were associated with a high risk of MS. Moreover, PON1-55 and PON1-192 polymorphisms were not associated with MS onset age, nor its evolutionary type.

Genetic associations and serum paraoxonase levels with atherosclerosis in western Iranian patients

The oxidative modification of low-density lipoprotein (LDL) in the arterial wall plays a pivotal role in the initiation and progression of atherosclerosis which is a complex and progressive disorder. Paraoxonase1 (PON1), which is required for lipid metabolism, is believed to protect LDL from oxidation. The relationship between PON1 gene Leusin55Methionin (L55M) and Glutamine192Arginine (Q192R) polymorphisms in western Iranians with atherosclerosis and its association with enzyme activity and oxidized low-density lipoprotein (oxLDL) were examined in the present study. In this study, blood specimens were collected from 145 healthy individuals and 154 patients with atherosclerosis proven by angiography referred to Shahid Madani Hospital, Khorramabad, Iran. Genomic deoxy ribonucleic acid (DNA) was extracted from whole blood. For all the subjects, restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) was carried out for the detection of L55M and Q192R polymorphisms. PON1 enzyme activity and the level of oxLDL were also evaluated. There was a 3.114-fold increase in the risk of developing atherosclerosis in the subjects presenting the PON1L55M, MM genotype compared to those with the LL genotype (OR 3.114; 95% CI 1.412-6.870). PON1Q192R polymorphism in the PON1 gene was not associated with atherosclerosis. Patients with atherosclerosis had significantly higher oxLDL and reduced PON1 enzyme activity (P < 0.05) compared to the controls. There was no association between the type of genotype, enzyme activity, and oxLDL level. It has been concluded that PON1L55M polymorphism and MM genotype are associated with an increased risk of coronary artery disease (CAD) in Iranian patients with atherosclerosis. We did not find any relationship between PON1Q192R polymorphism and atherosclerosis.

Prenatal exposure to organophosphate pesticides, maternal paraoxonase 1 genotype, and childhood neurodevelopment at 24 months of age in Shandong, China

Prenatal organophosphate pesticide (OP) exposure was reported to negatively affect childhood neurodevelopment. Paraoxonase 1 (PON1) is a key enzyme in the metabolism of OPs and may affect an individual's susceptibility to OP exposure. However, little is known about its role in the associations of prenatal OP exposure and childhood neurodevelopment. We measured dimethylphosphate (DM), diethylphosphate (DE), and total dialkylphosphate (DAP) metabolites in maternal urine (n = 436) as well as PON1_-108C/T and PON1₁₉₂Q/R genotypes in maternal blood (n = 244). We assessed the modifying effects of maternal PON1_-108C/T and PON1₁₉₂Q/R genotypes on relationships between prenatal OP exposure and developmental quotients (DQs) in 24-month-old children in Shandong, China (n = 172). Among children of mothers carrying PON1_-108CC, a tenfold increase in prenatal DMs was associated with a 5.72-point decrease in social domain DQ scores. Among children of mothers carrying PON1₁₉₂QQ, a tenfold increase in prenatal DMs and DAPs were associated with a 7.68- and 7.67-point decrease in gross motor domain DQ scores, respectively. Among children of mothers carrying PON1₁₉₂QQ, a tenfold increase in prenatal DMs, DEs, and DAPs were associated with a 7.52-, 9.07-, and 9.60-point decrease in social domain DQ scores, respectively. Maternal PON1 genotype might modify the associations between prenatal OP exposure and children's neurodevelopment at 24 months of age.

PON-1 carbamylation is enhanced in HDL of uremia patients

High-density lipoprotein (HDL) carbamylation has been known in uremia patients. Paraoxonase-1 (PON-1) is an important HDL protein responsible for HDL anti-oxidant, arylesterase and lactonase activities. PON-1 carbamylation in uremic HDL has never been explored. We isolated HDL from uremia patients and control healthy subjects for study. Sandwich ELISA was used to estimate carbamylated PON-1 protein expression in HDL, and nanoflow liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) was applied to identify the amino acid in PON-1 carbamylated. PON-1 enzyme activities were estimated by substrates conversion method. HDL anti-oxidant activity was gauged by fluorescence changes of indicator dye in the presence of H₂O₂. Our study results proved that the degree of PON-1 carbamylation was higher in uremic HDL than in control HDL. Sandwich ELISA study showed that carbamylated PON-1 concentration in uremic HDL was 1.49 ± 0.08 fold higher than that in HDL from controls (p < 0.05). The nanoLC-MS/MS showed that the carbamylation of lysine 290 (K290) of PON-1, a residue adjacent to PON-1 activity determining site, was detected in uremic HDL but not detected in control HDL. K290 carbamylation leads to local conformation changes that reduce accessible solvent accessibility. The HDL paraoxonase, arylesterase, and lactonase activities were all significantly lower in uremia patients than in control subjects. Additionally, HDL anti-antioxidant ability was also lower in uremia patients. Carbamylation of PON-1 in uremia patients could be one of the factors in impairing PON-1 enzyme activities and HDL anti-oxidation function.

Serum paraoxonase 1 activity is paradoxically maintained in nonalcoholic fatty liver disease despite low HDL cholesterol

Nonalcoholic fatty liver disease (NAFLD) is characterized by low HDL cholesterol, but the activity of the HDL-associated antioxidative enzyme paraoxonase-1 (PON-1) remains unclear. To determine the association of PON-1 with suspected NAFLD, we measured serum enzyme activity in 7,622 participants of the Prevention of Renal and Vascular End-Stage Disease cohort. A fatty liver index (FLI) ≥60, a proxy of NAFLD, was present in 2,083 participants (27.3%) and coincided with increased prevalence of T2D, metabolic syndrome (MetS), (central) obesity, elevated triglycerides, and low HDL cholesterol (all P < 0.001). In men and women combined, serum PON-1 activity did not vary according to elevated FLI (P = 0.98), whereas in men with elevated FLI PON-1 activity was increased (P = 0.016). In multivariable linear regression analyses (adjusted for age, sex, T2D, MetS, alcohol use, and smoking), PON-1 activity was unexpectedly associated with elevated FLI (β = 0.083; P < 0.001). In a sensitivity analysis (n = 5,126) that excluded subjects with positive cardiovascular history, impaired estimated glomerular filtration rate, elevated urinary albumin excretion, and drug use, PON-1 activity was also independently associated with elevated FLI (β = 0.045; P = 0.017). These results indicate that PON-1 is paradoxically maintained and may even be increased in NAFLD despite inverse associations with metabolic disorders and low HDL cholesterol.

Effects of Paraoxonase-1 variants on course of severity and mortality of Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever (CCHF) is an acute viral hemorrhagic fever caused by Crimean Congo hemorrhagic fever virus (CCHFV). Paraoxonase-1 (PON1) is a high density lipoprotein (HDL)-binding protein which defense the body against oxidative stress. To investigate the role of the PON1 gene in CCHF, we screened the genotypes of two single nucleotide polymorphisms (Q192R [rs662] and L55M [rs854560]) in CCHF patients stratified according to course of severity and mortality by using PCR-based RFLP assay. Overall, 132 patients diagnosed as CCHF were enrolled in this study. The frequencies of the three genotypes and two alleles of Q192R and L55M polymorphisms didn't show any statistically significant differences in terms of mortality and disease severity (p > 0.05). Any statistically significant differences were not found between severe and mild and fatal and non-fatal CCHF patients according to seven composite genotypes (p > 0.05). When we analyzed the clinical characteristics of CCHF patients stratified according to PON1gene polymorphisms, any statistically significant differences were not also observed (p > 0.05). Our study showed no possible association between genotypes of PON1 gene Q192R and L55M polymorphisms and CCHF.

Paraoxonase-1 and Early-Life Environmental Exposures

Acute and chronic exposures to widely used organophosphorus (OP) insecticides are common. Children's detoxification mechanisms are not well developed until several years after birth. The increased cases of neurodevelopmental disorders in children, together with their increased susceptibility to OP neurotoxicity cannot be explained by genetic factors alone but could be related to gene-environment interactions. Paraoxonase-1 (PON1) is an enzyme that can detoxify OPs but its catalytic efficiency for hydrolysis to certain OPs is modulated by the Q192R polymorphism. Studies with animals have provided important information on the role of PON1 in protecting against gestational and postnatal toxicity to OPs. The PON1Q192 allele is less efficient in hydrolyzing certain OPs than the PON1R192 allele. Maternal PON1 status (PON1 activity levels, the most important measurement, and functional Q192R phenotype) modulates the detrimental effects of exposure to the OP chlorpyrifos oxon on fetal brain gene expression and biomarkers of exposure. Epidemiologic studies suggest that children from mothers with lower PON1 status who were in contact with OPs during pregnancy tend to show smaller head circumference at birth and adverse effects in cognitive function during childhood. Infants and children are vulnerable to OP toxicity. The detrimental consequences of OPs on neurodevelopment can lead to future generations with permanent cognitive problems and susceptibility to develop neurodegenerative diseases. Improved methods using mass spectrometry to monitor OP-adducted biomarker proteins are needed and will be extremely helpful in early life biomonitoring, while measurement of PON1 status as a biomarker of susceptibility will help identify mothers and children highly sensitive to OPs. The use of adductomics instead of enzymatic activity assays for biomonitoring OP exposures have proved to provide several advantages, including the use of dried blood spots, which would facilitate monitoring newborn babies and children.

Valproic acid inhibits glioblastoma multiforme cell growth via paraoxonase 2 expression

We studied the potential mechanisms of valproic acid (VPA) in the treatment of glioblastoma multiforme (GBM). Using the human U87, GBM8401, and DBTRG-05MG GBM-derived cell lines, VPA at concentrations of 5 to 20 mM induced G2/M cell cycle arrest and increased the production of reactive oxygen species (ROS). Stress-related molecules such as paraoxonase 2 (PON2), cyclin B1, cdc2, and Bcl-xL were downregulated, but p27, p21 and Bim were upregulated by VPA treatment. VPA response element on the PON2 promoter was localized at position -400/−1. PON2 protein expression was increased in GBM cells compared with normal brain tissue and there was a negative correlation between the expression of PON2 and Bim. These findings were confirmed by the public Bredel GBM microarray (Gene Expression Omnibus accession: GSE2223) and the Cancer Genome Atlas GBM microarray datasets. Overexpression of PON2 in GBM cells significantly decreased intracellular ROS levels, and PON2 expression was decreased after VPA stimulation compared with controls. Bim expression was significantly induced by VPA in GBM cells with PON2 silencing. These observations were further shown in the subcutaneous GBM8401 cell xenograft of BALB/c nude mice. Our results suggest that VPA reduces PON2 expression in GBM cells, which in turn increases ROS production and induces Bim production that inhibits cancer progression via the PON2–Bim cascade.

Serum Albumin Binding and Esterase Activity: Mechanistic Interactions with Organophosphates

The albumin molecule, in contrast to many other plasma proteins, is not covered with a carbohydrate moiety and can bind and transport various molecules of endogenous and exogenous origin. The enzymatic activity of albumin, the existence of which many scientists perceive skeptically, is much less studied. In toxicology, understanding the mechanistic interactions of organophosphates with albumin is a special problem, and its solution could help in the development of new types of antidotes. In the present work, the history of the issue is briefly examined, then our in silico data on the interaction of human serum albumin with soman, as well as comparative in silico data of human and bovine serum albumin activities in relation to paraoxon, are presented. Information is given on the substrate specificity of albumin and we consider the possibility of its affiliation to certain classes in the nomenclature of enzymes.

An alternative purification method for human serum paraoxonase 1 and its interaction with methidathion

In this study, an alternative purification method for human Paraoxonase 1 (hPON1) enzyme was developed using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-L-tyrosine-1-aminoanthracene hydrophobic interaction chromatography. SDS-polyacrylamide gel electrophoresis of the enzyme indicates a single band with an apparent MW of 43 kDa. The enzyme was purified 674-fold with a yield of 16%. Furthermore, we examined the in vitro effect of methidathion on the enzyme activity to understand the better inhibitory properties of the compound. Methidathion is a highly toxic insecticide used to control a broad spectrum of agricultural insect and mite pests. IC₅₀ value was found to be 0.130 mM for the pesticide. Methidathion showed a competitive inhibition with Ki of 0.119 mM for paraoxon.

Paraoxonases-1, -2 and -3: What are their functions?

Paraoxonase-1 (PON1), an esterase/lactonase primarily associated with plasma high-density lipoprotein (HDL), was the first member of this family of enzymes to be characterized. Its name was derived from its ability to hydrolyze paraoxon, the toxic metabolite of the insecticide parathion. Related enzymes PON2 and PON3 were named from their evolutionary relationship with PON1. Mice with each PON gene knocked out were generated at UCLA and have been key for elucidating their roles in organophosphorus (OP) metabolism, cardiovascular disease, innate immunity, obesity, and cancer. PON1 status, determined with two-substrate analyses, reveals an individual's functional Q192R genotype and activity levels. The three-dimensional structure for a chimeric PON1 has been useful for understanding the structural properties of PON1 and for engineering PON1 as a catalytic scavenger of OP compounds. All three PONs hydrolyze microbial N-acyl homoserine lactone quorum sensing factors, quenching Pseudomonas aeruginosa's pathogenesis. All three PONs modulate oxidative stress and inflammation. PON2 is localized in the mitochondria and endoplasmic reticulum. PON2 has potent antioxidant properties and is found at 3- to 4-fold higher levels in females than males, providing increased protection against oxidative stress, as observed in primary cultures of neurons and astrocytes from female mice compared with male mice. The higher levels of PON2 in females may explain the lower frequency of neurological and cardiovascular diseases in females and the ability to identify males but not females with Parkinson's disease using a special PON1 status assay. Less is known about PON3; however, recent experiments with PON3 knockout mice show them to be susceptible to obesity, gallstone formation and atherosclerosis. Like PONs 1 and 2, PON3 also appears to modulate oxidative stress. It is localized in the endoplasmic reticulum, mitochondria and on HDL. Both PON2 and PON3 are upregulated in cancer, favoring tumor progression through mitochondrial protection against oxidative stress and apoptosis.

Impacts on Sirtuin Function and Bioavailability of the Dietary Bioactive Compound Dihydrocoumarin

The plant secondary metabolite and common food additive dihydrocoumarin (DHC) is an inhibitor of the Sirtuin family of NAD+-dependent deacetylases. Sirtuins are key regulators of epigenetic processes that maintain silent chromatin in yeast and have been linked to gene expression, metabolism, apoptosis, tumorogenesis and age-related processes in multiple organisms, including humans. Here we report that exposure to the polyphenol DHC led to defects in several Sirtuin-regulated processes in budding yeast including the establishment and maintenance of Sir2p-dependent silencing by causing disassembly of silent chromatin, Hst1p-dependent repression of meiotic-specific genes during the mitotic cell cycle. As both transient and prolonged exposure to environmental and dietary factors have the potential to lead to heritable alterations in epigenetic states and to modulate additional Sirtuin-dependent phenotypes, we examined the bioavailability and digestive stability of DHC using an in vivo rat model and in vitro digestive simulator. Our analyses revealed that DHC was unstable during digestion and could be converted to melilotic acid (MA), which also caused epigenetic defects, albeit less efficiently. Upon ingestion, DHC was observed primarily in intestinal tissues, but did not accumulate over time and was readily cleared from the animals. MA displayed a wider tissue distribution and, in contrast to DHC, was also detected in the blood plasma, interstitial fluid, and urine, implying that the conversion of DHC to the less bioactive compound, MA, occurred efficiently in vivo.

Paraoxnase1 Gene Polymorphism in Childhood Idiopathic Nephrotic Syndrome

BACKGROUND

Paraoxonase1 (PON1) is a serum enzyme bound to high-density lipoproteins with antioxidant properties. Molecular studies of PON1 revealed 2 polymorphic sites at amino acids 55 and 192 resulting in 2 different allozymes, the L and M-genotype at residue 55 and A and B at site 192, respectively. We have studied the association between PON1 gene polymorphisms and the minimal change nephrotic syndrome/focal segmental glomerulosclerosis (MCNS/FSGS) types of idiopathic nephrotic syndrome (INS) in Kuwaiti Arab children.

METHODS

The PON1 gene, 55 and 192 polymorphisms were analyzed in 50 children with INS (32 MSCN, 18 FSGS) and compared to 50 controls. Serum creatinine, albumin and lipids were measured in all subjects.

RESULTS

The LL genotype was detected in 50% of the INS patients compared to 48% of controls (p = 0.84). The heterozygous LM genotype was detected in 42% of INS patients compared 36% of controls (p = 0.68). The MM-genotype was detected in 8% of INS patients and 16% of controls (p = 0.35). The L-allele frequency in its homozygous and heterozygous forms was found in 71% of INS patients compared to 66% controls (p = 0.54). The L-allele frequency (LM and LL) was significantly higher in FSGS compared to MCNS patients (p = 0.0001) and when compared to controls (p = 0.0007). All patients and controls had the AA form of the 192 PON1 gene polymorphism.

CONCLUSION

Our data demonstrate a strong association between the L-allele of PON1 gene 55 polymorphism with FSGS in Kuwaiti Arab children with INS. PON1 genotyping can help in the early prediction of FSGS, which might guide clinicians to a better therapeutic approach.

[On the Enzymatic Activity of Albumin]

Albumin molecule, unlike molecules of many other plasma proteins, is not covered with carbohydrate shell. It plays a crucial role in maintaining of colloid osmotic pressure of the blood, and is able to bind and transport various endogenous and exogenous molecules. The enzymatic activity of albumin, the existence and the role of which most researchers are still skeptical to accept, is of the main interest to us. In this review, a history of the issue is traced, with particular attention to the esterase activity of albumin. The kinetic and thermodynamic characteristics of the interaction of albumin with some substrates are adduced, and possibility of albumin being attributed to certain groups of Enzyme Nomenclature is considered.

PON1 polymorphisms are predictors of ability to attain HDL-C goals in statin-treated patients

OBJECTIVES

PON1 plays an important role in inhibiting LDL-C oxidation, which reduces atherosclerosis and cardiovascular disease. Elevated PON1 activity or levels may contribute to increased HDL-C levels, but controversy exists over the hypothesis that genetic variation in the PON1 gene locus modulates HDL-C levels and responses to statin treatment. Therefore, the objective of this study was to investigate the association between two polymorphisms in the PON1 gene and statin responses in a south Brazilian population.

DESIGN AND METHODS

The study population included 433 dyslipidemic patients who were prescribed statins. Total cholesterol, triglyceride, HDL-C and LDL-C levels were measured in these patients both before and after approximately 6months of treatment with simvastatin/atorvastatin. Genotypes were assessed by real-time PCR for two PON1 polymorphisms, Q192R (rs662) and L55M (rs854560).

RESULTS

Baseline lipid levels were not associated with Q192R or L55M polymorphisms. For the Q192R (rs662) polymorphism, we observed that HDL-C goals were attained less often in patients with RR homozygosity than in Q allele carriers (χ(2) P=0.009, adjusted residual analysis P=0.003). For the L55M (rs854560) polymorphism, LL homozygotes were underrepresented among subjects that achieved the HDL-C goal (χ(2) P=0.026, adjusted residual analysis P=0.008). Analysis by univariate logistic regression confirmed that QQ/QR and MM/ML carriers had an increased chance of attaining HDL-C goals (OR=2.41, CI95%=1.32-4.40, P=0.004 and OR=1.68, CI95%=1.15-2.45, P=0.008). In a multivariate logistic analysis used to assess predictors of attaining an HDL-C goal>1.55mmol/L, we observed that gender (OR=1.71, CI95%=1.04-2.83, P=0.036), baseline HDL-C levels (OR=1.13, CI95%=1.10-1.16, P<0.001) and the QQ/QR+MM/ML genotypes increased the chance of achieving HDL-C goals (OR=2.81, CI95%=1.35-5.85, P=0.006).

CONCLUSIONS

The results of this study show that the Q192R (rs662) and L55M (rs854560) polymorphisms may play a role in interindividual variation in achievement of HDL-C goals in response to statins.

Allele frequencies of PON1 Q192R polymorphism in four populations of India

The allelic distribution at Paraoxonase 1 (PON1) Q192R polymorphism determines differential sensitivity towards certain organophosphate pesticides. The alleles Q (Glutamine) and R (Arginine) at amino acid position 192 are responsible for the lower and higher activity of the enzyme towards paraoxon respectively, making knowledge of this distribution in different populations vital. This study reports the genotype and allele frequencies of the Gln192Arg polymorphism of PON1 in four populations of India, comprising two caste and two tribal groups hitherto unexamined for this polymorphism. The R allele frequencies in Jat, Meo, Santhal and Zeliangrong populations were found to be 0.47, 0.45, 0.54 and 0.51 respectively. The gene diversity analyses show a high genetic differentiation at this locus indicative of the role of populations' history and other evolutionary forces. A comparison with allele frequencies among 106 populations from different continents showed a concordance with their geographic distribution which will have repercussions in policies targeting pesticide usage.

PON3 knockout mice are susceptible to obesity, gallstone formation, and atherosclerosis

We report the engineering and characterization of paraoxonase-3 knockout mice (Pon3KO). The mice were generally healthy but exhibited quantitative alterations in bile acid metabolism and a 37% increased body weight compared to the wild-type mice on a high fat diet. PON3 was enriched in the mitochondria-associated membrane fraction of hepatocytes. PON3 deficiency resulted in impaired mitochondrial respiration, increased mitochondrial superoxide levels, and increased hepatic expression of inflammatory genes. PON3 deficiency did not influence atherosclerosis development on an apolipoprotein E null hyperlipidemic background, but it did lead to a significant 60% increase in atherosclerotic lesion size in Pon3KO mice on the C57BL/6J background when fed a cholate-cholesterol diet. On the diet, the Pon3KO had significantly increased plasma intermediate-density lipoprotein/LDL cholesterol and bile acid levels. They also exhibited significantly elevated levels of hepatotoxicity markers in circulation, a 58% increase in gallstone weight, a 40% increase in hepatic cholesterol level, and increased mortality. Furthermore, Pon3KO mice exhibited decreased hepatic bile acid synthesis and decreased bile acid levels in the small intestine compared with wild-type mice. Our study suggests a role for PON3 in the metabolism of lipid and bile acid as well as protection against atherosclerosis, gallstone disease, and obesity.

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.

Human paraoxonase 1 as a pharmacologic agent: limitations and perspectives

Human PON1 (h-PON1) is a multifaceted enzyme and can hydrolyze (and inactivate) a wide range of substrates. The enzyme shows anti-inflammatory, antioxidative, antiatherogenic, ant-diabetic, antimicrobial, and organophosphate (OP)-detoxifying properties. However, there are certain limitations regarding large-scale production and use of h-PON1 as a therapeutic candidate. These include difficulties in producing recombinant h-PON1 (rh-PON1) using microbial expression system, low hydrolytic activity of wild-type h-PON1 towards certain substrates, and low storage stability of the purified enzyme. This review summarizes the work done in our laboratory to address these limitations. Our results show that (a) optimized polynucleotide sequence encoding rh-PON1 can express the protein in an active form in E. coli and can be used to generate variant of the enzyme having enhanced hydrolytic activity, (b) in vitro refolding of rh-PON1 enzyme can dramatically increase the yield of an active enzyme, (c) common excipients can be used to stabilize purified rh-PON1 enzyme when stored under different storage conditions, and (d) variants of rh-PON1 enzyme impart significant protection against OP-poisoning in human blood (ex vivo) and mouse (in vivo) model of OP-poisoning. The rh-PON1 variants and their process of production discussed here will help to develop h-PON1 as a therapeutic candidate.

Dietary squalene increases high density lipoprotein-cholesterol and paraoxonase 1 and decreases oxidative stress in mice

BACKGROUND AND PURPOSE

Squalene, the main hydrocarbon in the unsaponifiable fraction of virgin olive oil, is involved in cholesterol synthesis and it has been reported to own antiatherosclerotic and antiesteatosic effects. However, the squalene's role on lipid plasma parameters and the influence of genotype on this effect need to be addressed.

EXPERIMENTAL APPROACHES

Three male mouse models (wild-type, Apoa1- and Apoe- deficient) were fed chow semisynthetic diets enriched in squalene to provide a dose of 1 g/kg during 11 weeks. After this period, their plasma parameters and lipoprotein profiles were analyzed.

KEY RESULTS

Squalene administration at a dose of 1 g/kg showed decreased reactive oxygen species in lipoprotein fractions independently of the animal background and caused an specific increase in high density lipoprotein (HDL)-cholesterol levels, accompanied by an increase in phosphatidylcholine and paraoxonase 1 and no changes in apolipoproteins A1 and A4 in wild-type mice. In these mice, the cholesterol increase was due to its esterified form and associated with an increased hepatic expression of Lcat. These effects were not observed in absence of apolipoprotein A1. The increases in HDL- paraoxonase 1 were translated into decreased plasma malondialdehyde levels depending on the presence of Apolipoprotein A1.

CONCLUSIONS AND IMPLICATIONS

Dietary squalene promotes changes in HDL- cholesterol and paraoxonase 1 and decreases reactive oxygen species in lipoproteins and plasma malondialdehyde levels, providing new benefits of its intake that might contribute to explain the properties of virgin olive oil, although the phenotype related to apolipoproteins A1 and E may be particularly relevant.

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.

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 bovine serum paraoxonase and its immobilization on Eupergit C 250 L by covalent attachment

Serum paraoxonase (PON1) is a high-density lipoprotein (HDL)-associated enzyme that protects lipoproteins, both low-density lipoprotein (LDL) and HDL, against oxidation, and is considered as an antioxidative/anti-inflammatory component of HDL. In this study, PON1 was purified from bovine serum by ammonium sulfate precipitation and hydrophobic interaction chromatography on sepharose-4B-l-tyrosine-1-napthylamine. It was then immobilized on an unmodified Eupergit® C 250 L support. The immobilized PON1 retained a high catalytic activity and showed increased thermal stability compared to the native enzyme.

Dietary fatty acid intake is associated with paraoxonase 1 activity in a cohort-based analysis of 1,548 subjects

BACKGROUND

Paraoxonase 1 (PON1) is a cardioprotective, HDL-associated glycoprotein enzyme with broad substrate specificity. Our previous work found associations between dietary cholesterol and vitamin C with PON1 activity. The goal of this study was to determine the effect of specific dietary fatty acid (DFA) intake on PON1 activity.

METHODS

1,548 participants with paraoxonase activity measures completed the Harvard Standardized Food Frequency Questionnaire to determine their daily nutrient intake over the past year. Eight saturated, 3 monounsaturated, and 6 polyunsaturated DFAs were measured by the questionnaire. To reduce the number of observations tested, only specific fatty acids that were not highly correlated (r < 0.8) with other DFAs or that were representative of other DFAs through high correlation within each respective group (saturated, monounsaturated, or polyunsaturated) were retained for analysis. Six specific DFA intakes - myristic acid (14 carbon atoms, no double bonds - 14:0), oleic acid (18:1), gadoleic acid (20:1), α-linolenic acid (18:3), arachidonic acid (20:4), and eicosapentaenoic acid (20:5) - were carried forward to stepwise linear regression, which evaluated the effect of each specific DFA on covariate-adjusted PON1 enzyme activity.

RESULTS

Four of the 6 tested DFA intakes - myristic acid (p = 0.038), gadoleic acid (p = 6.68 × 10(-7)), arachidonic acid (p = 0.0007), and eicosapentaenoic acid (p = 0.013) - were independently associated with covariate-adjusted PON1 enzyme activity. Myristic acid, a saturated fat, and gadoleic acid, a monounsaturated fat, were both positively associated with PON1 activity. Both of the tested polyunsaturated fats, arachidonic acid and eicosapentaenoic acid, were negatively associated with PON1 activity.

CONCLUSIONS

This study presents the largest cohort-based analysis of the relationship between dietary lipids and PON1 enzyme activity. Further research is necessary to elucidate and understand the specific biological mechanisms, whether direct or regulatory, through which DFAs affect PON1 activity.

Paraoxonases: ancient substrate hunters and their evolving role in ischemic heart disease

Interest in the role of paraoxonases (PON) in cardiovascular research has increased substantially over the past two decades. These multifaceted and pleiotropic enzymes are encoded by three highly conserved genes (PON1, PON2, and PON3) located on chromosome 7q21.3-22.1. Phylogenetic analysis suggests that PON2 is the ancient gene from which PON1 and PON3 arose via gene duplication. Although PON are primarily lactonases with overlapping, but distinct specificities, their physiologic substrates remain poorly characterized. The most interesting characteristic of PON, however, is their multifunctional roles in various biochemical pathways. These include protection against oxidative damage and lipid peroxidation, contribution to innate immunity, detoxification of reactive molecules, bioactivation of drugs, modulation of endoplasmic reticulum stress, and regulation of cell proliferation/apoptosis. In general, PON appear as "hunters" of old and new substrates often involved in athero- and thrombogenesis. Although reduced PON activity appears associated with increased cardiovascular risk, the correlation between PON genotype and ischemic heart disease remains controversial. In this review, we examine the biochemical pathways impacted by these unique enzymes and investigate the potential use of PON as diagnostic tools and their impact on development of future therapeutic strategies.

Antioxidant and anti-inflammatory role of paraoxonase 1: implication in arteriosclerosis diseases

Paraoxonase 1 (PON1) is a hydrolytic enzyme with wide range of substrates, and capability to protect against lipid oxidation. Despite of the large number of compounds that can be hydrolyzed by paraoxonase, the biologically relevant substrates are still not clearly determined. There is a massive in vitro and in vivo data to demonstrate the beneficial effects of PON1 in several atherosclerosis-related processes. The enzyme is primarily expressed in liver; however, it is also localized in other tissues. PON1 attracted significant interest as a protein that is responsible for the most of antioxidant properties of high-density lipoprotein (HDL). Several bioactive molecules such as dietary polyphenols, aspirin and its hydrolysis product salicylate, are known to stimulate PON1 transcription activation in mouse liver and HepG2 cell line. Studies on the activity, function, and genetic makeup have revealed a protective role of PON1. Some striking data were obtained in PON1 gene knockout and PON1 transgenic mouse models and in human studies. The goal of this review is to assess the current understanding of PON1 expression, enzymatic and antioxidant activity, and its atheroprotective effects. Results from in vivo and in vitro basic studies; and from human studies on the association of PON1 with coronary artery disease (CAD) and ischemic stroke will be discussed.

Ontogeny of mammalian metabolizing enzymes in humans and animals used in toxicological studies

It is well recognized that expression of enzymes varies during development and growth. However, an in-depth review of this acquired knowledge is needed to translate the understanding of enzyme expression and activity into the prediction of change in effects (e.g. kinetics and toxicity) of xenobiotics with age. Age-related changes in metabolic capacity are critical for understanding and predicting the potential differences resulting from exposure. Such information may be especially useful in the evaluation of the risk of exposure to very low (µg/kg/day or ng/kg/day) levels of environmental chemicals. This review is to better understand the ontogeny of metabolizing enzymes in converting chemicals to either less-toxic metabolite(s) or more toxic products (e.g. reactive intermediate[s]) during stages before birth and during early development (neonate/infant/child). In this review, we evaluated the ontogeny of major "phase I" and "phase II" metabolizing enzymes in humans and commonly used experimental animals (e.g. mouse, rat, and others) in order to fill the information gap.

Paraoxonase 1 (PON1) as a genetic determinant of susceptibility to organophosphate toxicity

Paraoxonase (PON1) is an A-esterase capable of hydrolyzing the active metabolites (oxons) of a number of organophosphorus (OP) insecticides such as parathion, diazinon and chlorpyrifos. PON1 activity is highest in liver and in plasma. Human PON1 displays two polymorphisms in the coding region (Q192R and L55M) and several polymorphisms in the promoter and the 3'-UTR regions. The Q192R polymorphism imparts differential catalytic activity toward some OP substrates, while the polymorphism at position -108 (C/T) is the major contributor of differences in the levels of PON1 expression. Both contribute to determining an individual's PON1 "status". Animal studies have shown that PON1 is an important determinant of OP toxicity. Administration of exogenous PON1 to rats or mice protects them from the toxicity of specific OPs. PON1 knockout mice display a high sensitivity to the toxicity of diazoxon and chlorpyrifos oxon, but not of paraoxon. In vitro catalytic efficiencies of purified PON192 alloforms for hydrolysis of specific oxon substrates accurately predict the degree of in vivo protection afforded by each isoform. Evidence is slowly emerging that a low PON1 status may increase susceptibility to OP toxicity in humans. Low PON1 activity may also contribute to the developmental toxicity and neurotoxicity of OPs, as shown by animal and human studies.

Stabilization of organophosphorus hydrolase by entrapment in silk fibroin: formation of a robust enzymatic material suitable for surface coatings

Organophosphates are some of the most acutely toxic compounds synthesized on an industrial scale, and organophosphorus hydrolase (OPH) has the ability to hydrolyze and inactivate a number of these chemicals. However, OPH activity is vulnerable to harsh environmental conditions that would accompany its practical utility in the field; a limitation that can also be extended to conditions required for incorporation of OPH into useful materials. Here we present evidence that entrapment of OPH in silk fibroin leads to stabilization of OPH activity under a variety of conditions that would otherwise reduce free enzyme activity, such as elevated temperature, UV light exposure and the presence of detergent. Silk fibroin entrapment of OPH also allowed for its dispersal into a polyurethane-based coating that retained organophosphate hydrolysis activity after formulation, application and drying. Together, the data presented here demonstrate the utility of silk fibroin entrapment for the protection of OPH activity under a variety of environmental conditions.

Solubilization and humanization of paraoxonase-1

Paraoxonase-1 (PON1) is a serum protein, the activity of which is related to susceptibility to cardiovascular disease and intoxication by organophosphorus (OP) compounds. It may also be involved in innate immunity, and it is a possible lead molecule in the development of a catalytic bioscavenger of OP pesticides and nerve agents. Human PON1 expressed in E. coli is mostly found in the insoluble fraction, which motivated the engineering of soluble variants, such as G2E6, with more than 50 mutations from huPON1. We examined the effect on the solubility, activity, and stability of three sets of mutations designed to solubilize huPON1 with fewer overall changes: deletion of the N-terminal leader, polar mutations in the putative HDL binding site, and selection of the subset of residues that became more polar in going from huPON1 to G2E6. All three sets of mutations increase the solubility of huPON1; the HDL-binding mutant has the largest effect on solubility, but it also decreases the activity and stability the most. Based on the G2E6 polar mutations, we “humanized” an engineered variant of PON1 with high activity against cyclosarin (GF) and found that it was still very active against GF with much greater similarity to the human sequence.

Paraoxonase 1 and homocysteine metabolism

Paraoxonase 1 (PON1), a component of high-density lipoprotein (HDL), is a calcium-dependent multifunctional enzyme that connects metabolisms of lipoproteins and homocysteine (Hcy). Both PON1 and Hcy have been implicated in human diseases, including atherosclerosis and neurodegeneration. The involvement of Hcy in disease could be mediated through its interactions with PON1. Due to its ability to reduce oxidative stress, PON1 contributes to atheroprotective functions of HDL in mice and humans. Although PON1 has the ability to hydrolyze a variety of substrates, only one of them-Hcy-thiolactone-is known to occur naturally. In humans and mice, Hcy-thiolactonase activity of PON1 protects against N-homocysteinylation, which is detrimental to protein structure and function. PON1 also protects against neurotoxicity associated with hyperhomocysteinemia in mouse models. The links between PON1 and Hcy in relation to pathological states such as coronary artery disease, stroke, diabetic mellitus, kidney failure and Alzheimer's disease that emerge from recent studies are the topics of this review.

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.