Proinflammatory cytokines but not acute phase serum amyloid A or C-reactive protein, downregulate paraoxonase 1 (PON1) expression by HepG2 cells

Dyslipidemia in rheumatoid arthritis: the possible mechanisms

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease, of which the leading cause of death is cardiovascular disease (CVD). The levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), and high-density lipoprotein cholesterol (HDL-c) in RA decrease especially under hyperinflammatory conditions. It is conflictive with the increased risk of CVD in RA, which is called "lipid paradox". The systemic inflammation may explain this apparent contradiction. The increased systemic proinflammatory cytokines in RA mainly include interleukin-6(IL-6)、interleukin-1(IL-1)and tumor necrosis factor alpha(TNF-α). The inflammation of RA cause changes in the subcomponents and structure of HDL particles, leading to a weakened anti-atherosclerosis function and promoting LDL oxidation and plaque formation. Dysfunctional HDL can further worsen the abnormalities of LDL metabolism, increasing the risk of cardiovascular disease. However, the specific mechanisms underlying lipid changes in RA and increased CVD risk remain unclear. Therefore, this article comprehensively integrates the latest existing literature to describe the unique lipid profile of RA, explore the mechanisms of lipid changes, and investigate the impact of lipid changes on cardiovascular disease.

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 PON1 Variants in Disease Susceptibility in a Turkish Population

Paraoxonase 1 (PON1) enzyme plays a major role in antioxidant defense and protects the cells against reactive species. The most common PON1 Q192R and L55M polymorphisms are responsible for a wide variation of PON1 activity, which showed an up to 13-fold interindividual variation among the same genotype. PON1 genotypes were evaluated with the development of pancreatitis, colorectal cancer, and hypothyroidism in a hospital-based, case-control study. Individuals with rs662 G allele had a two-fold risk of developing hypothyroidism. A weak association was found between rs854560 T allele and pancreatitis. The results were preliminary. Further studies with a larger number and detailed biochemical parameters are needed.

Oxidative Stress Biomarkers and Peripheral Endothelial Dysfunction in Rheumatoid Arthritis: A Monocentric Cross-Sectional Case-Control Study

Previous studies have suggested that oxidative stress may heighten atherosclerotic burden in rheumatoid arthritis (RA), but direct evidence is lacking.

OBJECTIVE

To evaluate the relationship between established plasma oxidative stress biomarkers and peripheral endothelial dysfunction (ED), a marker of early atherosclerosis, in RA.

METHODS

Paroxonase-1 (PON-1), protein-SH (PSH), and malondialdehyde (MDA) were measured in 164 RA patient s and 100 age- and sex-matched healthy controls without previous cardiovascular events. Peripheral ED, evaluated by flow-mediated pulse amplitude tonometry, was defined by log-transformed reactive hyperemia index (Ln-RHI) values < 0.51.

RESULTS

PON-1 activity and PSH concentrations were significantly reduced in RA patients compared to controls. In regression analysis, increased plasma MDA levels were significantly associated with reduced Ln-RHI [B coefficient (95% CI) = -0.003 (-0.005 to -0.0008), p = 0.008] and the presence of peripheral ED (OR (95% CI) = 1.75 (1.06-2.88), p = 0.028). Contrary to our expectations, increased PON-1 activity was significantly associated, albeit weakly, with the presence of ED (OR (95% CI) = 1.00 (1.00-1.01), p = 0.017).

CONCLUSIONS

In this first evidence of a link between oxidative stress and markers of atherosclerosis, MDA and PON-1 showed opposite associations with peripheral vasodilatory capacity and the presence of ED in RA. Further studies are needed to determine whether this association predicts atherosclerotic events in the RA population.

Decreases in Paraoxonase-1 Activities Promote a Pro-inflammatory Effect of Lipids Peroxidation Products in Non-smoking and Smoking Patients with Acute Pancreatitis

Aim: The study investigated the extent to which tobacco smoke exposure causes changes in lipids biochemistry through measurement blood concentrations of: paraoxonase-1 (PON-1) activities as lipid-bound enzyme into cell membrane, concentration of malonyldialdehyde (MDA), protein adducts of 4-hydroxynonenal (HNE-adducts), oxidized low density lipoproteins (oxLDL), total cholesterol (CH) and high-density lipoprotein cholesterol (HDL). Additionally, the activity of P isoform of glutathione S-transferase (GST-π) was measured. Methods: Investigations were performed in the blood of patients with acute pancreatitis (AP) on the 1st, 3rd and 7th day of hospitalization and in healthy volunteers. The activities of PON-1 forms, GST-π were determined spectrophotometrically. Concentrations of PON-1, MDA, HNE-adducts, oxLDL, HDL, CH were measured using commercial tests. Results: Near 2-fold higher concentrations of MDA, HNE-adducts, oxLDL, correlating with inflammatory markers in AP patients compared to healthy subjects were demonstrated, which were accompanied by gradually increasing CH/HDL ratio during hospitalization. During hospital treatment, decreased activities of all PON-1 subtypes were observed in AP patients compared to healthy subjects, more pronounced in tobacco smokers. A decreased PON-1 phosphotriesterase activity in non-AP control group smokers compared to non-smokers was noted. In non-smoking AP patients GST-π activity normalized during hospitalization in contrast to smokers. Conclusions: GST-π and PON-1 phosphotriesterase activities seem to be a sensitive marker of pro/antioxidative imbalance in smokers. Lipids peroxidation products generated during AP can intensify preexisting inflammation. Increasing stay in the hospital was associated with worsening of lipids peroxidation markers and the parameters of lipid profile, in both non-smoking and smoking AP patients, what can indicate that the oxidative-inflammatory process are not extinguished.

Serum paraoxonase-1 activity is inversely related to free thyroxine in euthyroid subjects: The PREVEND Cohort Study

BACKGROUND

Low-normal thyroid function within the euthyroid range has been suggested to enhance atherosclerosis susceptibility. Paraoxonase-1 (PON-1) may protect against atherosclerotic cardiovascular disease development by attenuating oxidative stress. We evaluated relationships of PON-1 with thyroid stimulating hormone (TSH), free T₄ , free T₃ , lipids and apolipoprotein (apo)A-I in euthyroid subjects, and assessed whether such relationships are modified in the context of the metabolic syndrome (MetS).

MATERIALS AND METHODS

Serum PON-1 activity (arylesterase activity), TSH, free T₄ , free T₃ , lipids and apoA-I was measured in 2206 euthyroid subjects (aged 28-75 years; 1138 men (age 49 ± 13 years) and 1068 women (age 46 ± 12 years), recruited from the general population (PREVEND cohort).

RESULTS

In age- and sex-adjusted analysis, PON-1 activity (divided into tertiles) was positively related to TSH (β = -0.045, P = .036) and inversely to free T₄ (β = -0.042, P = .050) but not to free T₃ (β = -0.027, P = .20). PON-1 activity was positively related to total cholesterol, non-HDL cholesterol and triglycerides, as well as to HDL cholesterol and apoA-I (P < .01 to <.001). The inverse relationship of PON-1 activity with free T₄ remained present after adjustment for lipids and other potential confounders (β = -0.066, P = .002), but the positive relationship with TSH lost significance (β = 0.034, P = .11). The inverse relationship of PON-1 activity with free T₄ was not different in subjects with vs without MetS (P = .94), nor modified by the presence of its individual components (P ≥ .22 for each).

CONCLUSIONS

Serum PON-1 activity is inversely associated with free T₄ in euthyroid subjects, suggesting that low-normal thyroid function may affect PON-1 regulation.

Downregulation of human paraoxonase 1 (PON1) by organophosphate pesticides in HepG2 cells

Paraoxonase 1 (PON1) is a calcium-dependent esterase synthesized primarily in the liver and secreted into the plasma where it is associated with high-density lipoproteins (HDL). PON1 hydrolyzes and detoxifies some toxic metabolites of organophosphorus compounds (OPs) such as methyl parathion and chlorpyrifos. Thus, PON1 activity and expression levels are important for determining susceptibility against OPs poisoning. Some studies have demonstrated that OPs can modulate gene expression through interactions with nuclear receptors. In this study, we evaluated the effects of methyl parathion and chlorpyrifos on the modulation of PON1 in Human Hepatocellular Carcinoma (HepG2) cells by real-time PCR, PON1 activity assay, and western blot. The results showed that the treatments with methyl parathion and chlorpyrifos decreased PON1 mRNA and immunoreactive protein and increased inflammatory cytokines in HepG2 cells. The effects of methyl parathion and chlorpyrifos on the downregulation of PON1 gene expression in HepG2 cells may provide evidence of OPs cytotoxicity related to oxidative stress and an inflammatory response. A decrease in the expression of the PON1 gene may increase the susceptibility to OPs intoxication and the risk of diseases related to inflammation and oxidative stress. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 490-500, 2017.

A retrospective controlled study of thiol disulfide homeostasis as a novel marker in Crimean Congo hemorrhagic fever

OBJECTIVES

Crimean Congo hemorrhagic fever (CCHF) is the second most common hemorrhagic fever worldwide. This study aimed to evaluate the oxidant-antioxidant balance of patients with CCHF by detecting dynamic thiol disulfide homeostasis (TDH), which is a novel oxidative stress marker, and other molecules, including paraoxonase (PON), arylesterase (ARES), ceruloplasmin (CLP), myeloperoxidase (MPO), and catalase.

METHODS

This retrospective, cross-sectional, controlled study, which involved patients with CCHF and healthy volunteers, measured dynamic TDH using a novel automated method developed by Erel.

RESULTS

We recruited 69 adult patients with CCHF (31 females, 38 males, median age 46 years). The case fatality rate was 1.49% (1/69). Increased disulfide/native thiol and disulfide/total thiol ratios, decreased total antioxidant status (TAS), and increased total oxidant status (TOS) were found in patients with CCHF. TAS, PON, and ARES values were found to be positively correlated with both native and total thiol levels, whereas TOS and CLP were negatively correlated with both, at a significant level. MPO activity was similar in both groups.

DISCUSSION

This is the first study in the literature to evaluate dynamic TDH in CCHF. TDH shifts to the oxidative side in patients with CCHF, leading to an increase in TOS.

Can ecological history influence response to pollutants? Transcriptomic analysis of Manila clam collected in different Venice lagoon areas and exposed to heavy metal

Chronic exposure to environmental pollutants can exert strong selective pressures on natural populations, favoring the transmission over generations of traits that enable individuals to survive and thrive in highly impacted environments. The lagoon of Venice is an ecosystem subject to heavy anthropogenic impact, mainly due to the industrial activities of Porto Marghera (PM), which led to a severe chemical contamination of soil, groundwater, and sediments. Gene expression analysis on wild Manila clams collected in different Venice lagoon areas enabled to identify differences in gene expression profiles between clams collected in PM and those sampled in clean areas, and the definition of molecular signatures of chemical stress. However, it remains largely unexplored to which extent modifications of gene expression patterns persists after removing the source of contamination. It is also relatively unknown whether chronic exposure to xenobiotics affects the response to other chemical pollutants. To start exploring such issues, in the present study a common-garden experiment was coupled with transcriptomic analysis, to compare gene expression profiles of PM clams with those of clams collected in the less impacted area of Chioggia (CH) during a period under the same control conditions. Part of the two experimental groups were also exposed to copper for seven days to assess whether different "ecological history" does influence response to such pollutant. The results obtained suggest that the chronic exposure to chemical pollution generated a response at the transcriptional level that persists after removal for the contaminated site. These transcriptional changes are centered on key biological processes, such as defense against either oxidative stress or tissue/protein damage, and detoxification, suggesting an adaptive strategy for surviving in the deeply impacted environment of Porto Marghera. On the other hand, CH clams appeared to respond more effectively to copper exposure than PM animals, proposing that chronic exposure to chemical toxicants either lowers the sensitivity to additional toxicants or blunts the capacity to respond to novel chemical challenges in PM clams.

The role of serum amyloid A and sphingosine-1-phosphate on high-density lipoprotein functionality

The high-density lipoprotein (HDL) is one of the most important endogenous cardiovascular protective markers. HDL is an attractive target in the search for new pharmaceutical therapies and in the prevention of cardiovascular events. Some of HDL's anti-atherogenic properties are related to the signaling molecule sphingosine-1-phosphate (S1P), which plays an important role in vascular homeostasis. However, for different patient populations it seems more complicated. Significant changes in HDL's protective potency are reduced under pathologic conditions and HDL might even serve as a proatherogenic particle. Under uremic conditions especially there is a change in the compounds associated with HDL. S1P is reduced and acute phase proteins such as serum amyloid A (SAA) are found to be elevated in HDL. The conversion of HDL in inflammation changes the functional properties of HDL. High amounts of SAA are associated with the occurrence of cardiovascular diseases such as atherosclerosis. SAA has potent pro-atherogenic properties, which may have impact on HDL's biological functions, including cholesterol efflux capacity, antioxidative and anti-inflammatory activities. This review focuses on two molecules that affect the functionality of HDL. The balance between functional and dysfunctional HDL is disturbed after the loss of the protective sphingolipid molecule S1P and the accumulation of the acute-phase protein SAA. This review also summarizes the biological activities of lipid-free and lipid-bound SAA and its impact on HDL function.

Regulatory effects of dioxin-like and non-dioxin-like PCBs and other AhR ligands on the antioxidant enzymes paraoxonase 1/2/3

Paraoxonase 1 (PON1), an antioxidant enzyme, is believed to play a critical role in many diseases, including cancer. PCBs are widespread environmental contaminants known to induce oxidative stress and cancer and to produce changes in gene expression of various pro-oxidant and antioxidant enzymes. Thus, it appeared of interest to explore whether PCBs may modulate the activity and/or gene expression of PON1 as well. In this study, we compared the effects of dioxin-like and non-dioxin-like PCBs and of various aryl hydrocarbon receptor (AhR) ligands on PON1 regulation and activity in male and female Sprague-Dawley rats. Our results demonstrate that (i) the non-dioxin-like PCB154, PCB155, and PCB184 significantly reduced liver and serum PON1 activities, but only in male rats; (ii) the non-dioxin-like PCB153, the most abundant PCB in many matrices, did not affect PON1 messenger RNA (mRNA) level in the liver but significantly decreased serum PON1 activity in male rats; (iii) PCB126, an AhR ligand and dioxin-like PCB, increased both PON1 activities and gene expression; and (iv) even though three tested AhR ligands induced CYP1A in several tissues to a similar extent, they displayed differential effects on the three PONs and AhR, i.e., PCB126 was an efficacious inducer of PON1, PON2, PON3, and AhR in the liver, while 3-methylcholantrene induced liver AhR and lung PON3, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent AhR agonist, increased only PON3 in the lung, at the doses and exposure times used in these studies. These results show that PCBs may have an effect on the antioxidant protection by paraoxonases in exposed populations and that regulation of gene expression through AhR is highly diverse.

Paired measurement of serum amyloid A (SAA) and paraoxonase 1 (PON1) as useful markers in breast cancer recurrence

OBJECTIVES

Paraoxonase 1 (PON1) and serum amyloid A (SAA) are carried by HDL. In case of inflammation, SAA and PON1 tend to change in opposite direction. In this study we determined if inflammation leads to altered PON1 activity using three different substrate hydrolysis rates, paraoxonase (PON), arylesterase (ARE) and lactonase (LAC) in breast cancer recurrence.

DESIGN AND METHODS

49 patients with a recurrence of breast cancer were analyzed for SAA, CRP, lipids, oxidized LDL, PON, ARE and LAC. Distribution of PON1 activities across the quartiles of CRP and SAA were compared by the Kruskal Wallis test. Non-parametric estimates of the survivor function were computed with Kaplan-Meier method. The association of SAA and ARE with short term death was assessed by logistic regression models.

RESULTS

HDL and ARE decrease significantly across the quartiles of CRP. No significant differences were observed across SAA quartiles. The survival time was significantly related to the level of SAA (log rank: p<0.001) as well as the level of ARE (log rank: p=0.039). SAA and ARE were independently related to survival time below one year.

CONCLUSIONS

PON1 does not seem to be directly affected by SAA, for any of the tested substrates, PON, ARE and LAC. The combined measurement of SAA and ARE could be a useful tool in this clinical situation, since they are independently related to short term death.

Oxidized low density lipoprotein and inflammation in gout patients

To analyze the levels of oxidized low density lipoprotein (ox-LDL) and inflammatory cytokines in the plasma of gout patients. The levels of ox-LDL, hypersensitive C-reactive protein (hs-CRP), interleukin-1β, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were measured in the plasma of 41 gout patients [28 in acute phase episode, 13 in intermittent phase (IP)], and in 40 healthy controls. The relationship between ox-LDL and inflammation was also explored by measuring the levels of several pro-inflammatory cytokines in the plasma. The plasma levels of ox-LDL, hs-CRP, IL-6 and TNF-α were significantly increased in patients with gout in the acute phase compared to those in the IP group and healthy controls (P < 0.05), but the levels of TGF-β were significantly lower in the acute phase group than in the IP group and healthy controls (P < 0.01). The levels of ox-LDL in the gout patients in the IP were significantly higher than those in healthy controls (P < 0.05). Correlation analysis indicated that the levels of ox-LDL were positively correlated with hs-CRP, IL-6 and TNF-α (r = 0.343, r = 0.386, r = 0.659, P < 0.01, respectively), but negatively correlated with TGF-β levels in patients in the acute phase (r = -0.240, P < 0.05). The levels of ox-LDL in gout patients were significantly higher than those in healthy controls. The changes in ox-LDL levels may be associated with enhanced inflammation in gout patients.

Indices of paraoxonase and oxidative status do not enhance the prediction of subclinical cardiovascular disease in mixed-ancestry South Africans

We evaluated the association of indices of paraoxonase (PON1) and oxidative status with subclinical cardiovascular disease (CVD) in mixed-ancestry South Africans. Participants were 491 adults (126 men) who were stratified by diabetes status and body mass index (BMI). Carotid intima-media thickness (CIMT) was used as a measure of subclinical CVD. Indices of PON1 and oxidative status were determined by measuring levels and activities (paraoxonase and arylesterase) of PON1, antioxidant activity (ferric reducing antioxidant power and trolox equivalent antioxidant capacity), and lipid peroxidation markers (malondialdehyde and oxidized LDL). Diabetic subjects (28.9%) displayed a significant decrease in PON1 status and antioxidant activity as well as increase in oxidized LDL and malondialdehyde. A similar profile was apparent across increasing BMI categories. CIMT was higher in diabetic than nondiabetic subjects (P < 0.0001) but showed no variation across BMI categories. Overall, CIMT correlated negatively with indices of antioxidant activity and positively with measures of lipid oxidation. Sex, age, BMI, and diabetes altogether explained 29.2% of CIMT, with no further improvement from adding PON1 and/or antioxidant status indices. Though indices of PON1 and oxidative status correlate with CIMT, their measurements may not be useful for identifying subjects at high CVD risk in this population.

Epigenetic patterns of two gene promoters (TNF-α and PON) in stroke considering obesity condition and dietary intake

Some causal bases of stroke remain unclear, but the nutritional effects on the epigenetic regulation of different genes may be involved. The aim was to assess the impact of epigenetic processes of human tumor necrosis factor (TNF-α) and paraoxonase (PON) promoters in the susceptibility to stroke when considering body composition and dietary intake. Twenty-four patients (12 non-stroke/12 stroke) were matched by sex (12 male/12 female), age (mean 70 ± 12 years old), and BMI (12 normal-weight/12 obese; mean 28.1 ± 6.7 kg/m(2)). Blood cell DNA was isolated and DNA methylation levels of TNF-α (-186 to +349 bp) and PON (-231 to +250 bp) promoters were analyzed by the Sequenom EpiTYPER approach. Histone modifications (H3K9ac and H3K4me3) were analyzed also by chromatin immunoprecipitation in a region of TNF-α (-297 to -185). Total TNF-α promoter methylation was lower in stroke patients (p < 0.001) and showed no interaction with body composition (p = 0.807). TNF-α and PON total methylation levels correlated each other (r = 0.44; p = 0.031), especially in stroke patients (r = 0.72; p = 0.008). The +309 CpG methylation site from TNF-α promoter was related to body weight (p = 0.027) and the region containing three CpGs (from -170 to -162 bp) to the percentage of lipid intake and dietary indexes (p < 0.05) in non-stroke patients. The methylation of PON +15 and +241 CpGs was related to body weight (p = 0.021), waist circumference (p = 0.020), and energy intake (p = 0.018), whereas +214 was associated to the quality of the diet (p < 0.05) in non-stroke patients. When comparing stroke vs non-stroke patients regarding the histone modifications analyzed at TNF-α promoter, no changes were found, although a significant association was identified between circulating TNF-α level and H3K9ac with H3K4me3. TNF-α and PON promoter methylation levels could be involved in the susceptibility to stroke and obesity outcome, respectively. The dietary intake and body composition may influence this epigenetic regulation in non-stroke patients.

Serum paraoxonase 1 activity and oxidative stress in pediatric patients with pulmonary tuberculosis

OBJECTIVES

The aim of this study was to determine the oxidative stress and paraoxonase 1 (PON1) levels in children with pulmonary tuberculosis (TB) compared to healthy controls, and to examine the association of demographical with oxidative stress.

SUBJECTS AND METHODS

Forty children diagnosed with pulmonary TB and 40 age- and gender-matched healthy controls were enrolled in the study. Serum total antioxidant status (TAS), total oxidant status (TOS) and PON1 levels were measured. The oxidative stress index (OSI) was calculated to indicate the degree of oxidative stress.

RESULTS

The TAS levels were lower (1.73 ± 0.5 vs. 2.54 ± 1.2 μmol Trolox Eq/l) while TOS levels were significantly higher (26.9 ± 14.4 vs. 13.4 ± 7.7 μmol H2O2 Eq/l) in the TB group than in the controls (p < 0.001). The OSI was significantly higher in the TB group than in the controls (21.2 ± 5.1 vs. 6.5 ± 4.9 units, p = 0.006). Serum PON1 levels were significantly lower in the TB group than in the controls (14.2 ± 13.2 vs. 28.4 ± 17.3 U/l, p < 0.001). The lower PON1 levels correlated with TAS and OSI levels but not with anthropometric parameters (r = 0.264, p = 0.018 and r = -0.255, p = 0.023, respectively).

CONCLUSION

The TOS and OSI levels were higher and the TAS and PON1 levels were lower in pediatric patients with pulmonary TB when compared to healthy controls. This indicates greater oxidative stress in the patients.

The regulation of hepatic Pon1 by a maternal high-fat diet is gender specific and may occur through promoter histone modifications in neonatal rats

The antioxidant (AOX) defense system is critical for combating whole-body oxidative stress, and the present study aimed to determine the consequences of a maternal high-fat (HF) diet on neonatal hepatic lipid accumulation, oxidative stress, the expression of AOX genes, as well as epigenetic histone modifications within Pon1, an AOX enzyme. Hepatic thiobarbituric acid reactive substances were significantly increased and nonesterified fatty acids decreased in offspring of HF-fed dams, while triglycerides increased in male but not female HF offspring when compared to controls (C). Pon1, Pon2, Pon3 and Sod2 were significantly increased in offspring of HF-fed dams when compared to C. However, the increase in Pon1 and Pon3 was only significant in male but not female offspring. When compared to C, the hepatic Pon1 promoter of male and female HF offspring had significantly more acetylated histone H4 as well as dimethylated histone H3 at lysine residue 4, which are both involved in transcriptional activation. Trimethylation of histone H3 at lysine residue 9, which is involved in transcriptional repression, was only associated with genes in females. Results from the present study reveal that a maternal HF diet affects hepatic metabolism in the neonate in a gender-specific manner, and these differences, in association with epigenetic modification of histones, may contribute to the known gender differences in oxidative balance.

Paired measurements of paraoxonase 1 and serum amyloid A as useful disease markers

Paraoxonase 1 (PON1) and serum amyloid A (SAA) are proteins carried by high-density lipoprotein (HDL) particles. Among the HDL-associated protein molecules, SAA, an inflammation-related marker, and PON1, an antioxidant marker, tend to change in relatively clear opposite directions in physiological situations. In clinical chemistry, paired measurements of both markers may provide useful information to understand dysfunctional HDL in diseases with inflammation and oxidative stress conditions. Actually, limited clinical studies have suggested that the combined use of PON1 and SAA may be a tool for observing the pathophysiology of some disease entities. From the findings of experimental studies, PON1 appears to be cooperatively regulated by inflammation- and oxidative stress-related molecules linked with SAA regulation in humans. More studies remain to be performed to ascertain the value of paired measurements of both promising markers in clinical practice.

Interleukin-6 upregulates paraoxonase 1 gene expression via an AKT/NF-κB-dependent pathway

The aim of this study is to investigate the relationship between paraoxonase 1 (PON1) and atherosclerosis-related inflammation. In this study, human hepatoma HepG2 cell line was used as a hepatocyte model to examine the effects of the pro-inflammatory cytokines on PON1 expression. The results showed that IL-6, but not TNF-α and IL-1β, significantly increased both the function and protein level of PON1; data from real-time RT-PCR analysis revealed that the IL-6-induced PON1 expression occurred at the transcriptional level. Increase of IκB kinase activity and IκB phosphorylation, and reduction of IκB protein level were also observed in IL-6-treated HepG2 cells compared with untreated culture. This event was accompanied by increase of NF-κB-p50 and -p65 nuclear translocation. Moreover, treatment with IL-6 augmented the DNA binding activity of NF-κB. Furthermore, pharmacological inhibition of NF-κB activation by PDTC and BAY 11-7082, markedly suppressed the IL-6-mediated PON1 expression. In addition, IL-6 increased the levels of phosphorylated protein kinase B (PKB, AKT). An AKT inhibitor LY294002 effectively suppressed IKK/IκB/NF-κB signaling and PON1 gene expression induced by IL-6. Our findings demonstrate that IL-6 upregulates PON1 gene expression through an AKT/NF-κB signaling axis in human hepatocyte-derived HepG2 cell line.

Paraoxonase-1 status in patients with hereditary hemochromatosis

Hereditary hemochromatosis (HH) is characterized by accumulation of iron, oxidative stress, inflammation, and fibrogenesis in liver tissue. In this setting, research on the protection afforded by intracellular antioxidants is of clinical relevance. Paraoxonase-1 (PON1) is an enzyme that degrades lipid peroxides. This study investigates the alterations in serum PON1 status, PON1 gene polymorphisms, and PON1 hepatic expression in patients with HH. We performed a case-control study in 77 patients with HH (80.5% men, 22-70 years of age) and 408 healthy individuals (43.1% men, 26-74 years of age). Serum PON1 activities against different substrates and PON1192 and PON155 polymorphisms were analyzed. PON1 protein expression was investigated in 20 liver biopsies. HH patients had significantly lower serum PON1 activity, which was inversely correlated with ferritin (marker of iron stores) and serum 8-isoprostane concentrations (index of oxidative stress). PON1 protein expression in liver tissue was higher in patients and showed stronger staining in hepatocytes surrounding the areas of inflammation. Our study provides preliminary evidence that PON1 may play a role in protecting against iron-induced oxidative stress in hereditary hemochromatosis.

Soy protein, genistein, and daidzein improve serum paraoxonase activity and lipid profiles in rheumatoid arthritis in rats

In this study, we investigated the effects of genistein, daidzein, and soy protein on paraoxonase and arylesterase activity, malondialdehyde (MDA) levels, and lipid profiles of arthritic rats in vivo and the results were compared with that of dexamethasone. Seventy-two female Sprague-Dawley rats were divided into six groups: healthy control, animals with collagen-induced arthritis (CIA), CIA-soy protein (7 g/kg)-treated rats, CIA-genistein (20 mg/kg)-treated animals, CIA-daidzein (20 mg/kg)-treated rats, and CIA-dexamethasone (1 mg/kg)-treated rats. Rheumatoid arthritis was induced using collagen type II and the treatments were carried out by daily gavages feedings for 50 days. The paraoxonase activity in serum was measured spectrophotometrically using paraoxon and phenylacetate as substrates. Serum MDA and lipids levels were determined using enzymatic colorimetric methods. Arthritis-induced decreases in paraoxonase and arylesterase activity was restored after treatment with soy protein and isoflavones (P<.05). MDA concentrations were lower after treatment with all tested compounds. However, only soy protein could partially improve the lipid profile.

Hormonal and chemical regulation of paraoxonases in mice

In humans and rodents, paraoxonase (PON/Pon) 1 expression and activity in livers and serum are higher in females than in males, and some drugs increase paraoxonase's expression. However, the underlining mechanisms of gender-divergent expression and chemical regulation of Pon1 remain largely unknown. The present study determined the regulatory mechanisms contributing to gender-divergent and chemically altered Pon expression in mouse livers. Pon1 mRNA was much more abundant in the livers of mice than other tissues, with higher levels in female livers than male livers at mRNA and protein levels. Pon2 mRNA was ubiquitously expressed in mouse tissues, but minimally in mouse liver. Pon3 mRNA was most abundant in mouse lung and liver and less abundant in other tissues. Pon1 mRNA was lowest in fetal liver, markedly increased at parturition, and remained relatively constant thereafter. Pon2 and Pon3 mRNA are highly expressed in fetal liver and decreased after birth. Male-pattern growth hormone (GH) administration in hypophysectomized and lit/lit mice decreased Pon1 expression. Sex hormones and female-pattern GH administration had no effect on Pon1 expression, indicating the importance of male-pattern GH in regulating Pon1. Aryl hydrocarbon receptor, pregnane X receptor, and NF-E2-related factor activators had no effect on Pon1 mRNA. A constitutive androstane receptor (CAR) activator decreased Pon1 expression in wild-type but not CAR-null mice. In conclusion, Pon1 mRNA was most abundant in adult mouse livers, whereas Pon2 and Pon3 mRNAs were most abundant in fetal mouse livers. Female-predominant Pon1 expression in mouse livers is caused by the inhibitory effects of male-pattern GH secretion, and CAR activation decreases Pon1 expression.

Paraoxonase activity and expression is modulated by therapeutics in experimental rat nonalcoholic Fatty liver disease

Objective. The objective of the present study is to investigate the effect of rosiglitazone, metformin, ezetimibe, and valsartan (alone or in combinations) on paraoxonase (PON) activity and PON-mRNA expression in nonalcoholic fatty liver disease (NAFLD). Methods. 54 Male Sprague-Dawley rats were divided to 9 groups: chow diet group (15 weeks); methionine-choline-deficient diet (MCDD) group (15 weeks); MCDD-treated groups for the last 6 weeks with either metformin (M), rosiglitazone (R), metformin plus rosiglitazone (M+R), ezetimibe (E), valsartan (V), or a combination of R+M+V or of R+M+V+E for a total period of 15 weeks. Results. PON activities in serum and liver were decreased in MCDD rats. PON activity in serum increased significantly in all treatment groups. PON activity in liver was also increased significantly, except only in groups R, E, V, R+M+V, and R+M+V+E. Liver PON3 mRNA expression increased significantly in groups R+M, E, V, R+M+V, and R+M+V+E whereas liver PON2 mRNA expression increased significantly in MCDD, R+M, E, V, R+M+V, and R+M+V+E. Conclusions. PON activities in serum and liver were decreased in NAFLD. Treatment with insulin sensitizers, ezetimibe, and valsartan increased PON activity and reduced oxidative stress both in serum and liver.

The three-gene paraoxonase family: physiologic roles, actions and regulation

The paraoxonase (PON) gene family is composed of three members (PON1, PON2, PON3) that share considerable structural homology and are located adjacently on chromosome 7 in humans. By far the most-studied member is PON1, a high-density lipoprotein-associated esterase/lactonase, also endowed with the capacity to hydrolyze organophosphates, but all the three proteins prevent oxidative stress and fight inflammation. They therefore seem central to a wide variety of human illnesses, including atherosclerosis, diabetes mellitus, mental disorders and inflammatory bowel disease. The major goal of this review is to highlight the regulation of each of the paraoxonase components by diverse nutritional molecules and pharmacological agents as well as a number of pathophysiological events, such as oxidative stress and inflammation. Considerable and detailed cell-based studies and animal model experiments have been provided to allow a thorough scrutiny of PON modulation, which will increase our understanding and ability to target these genes in order to efficiently increase their transcriptional activity and decrease the risks of developing different disorders.

A homogeneous cell-based assay for measurement of endogenous paraoxonase 1 activity

Paraoxonase 1 (PON1) is a high-density lipoprotein-associated enzyme that plays an important role in organophosphate detoxification and prevention of atherosclerosis. Thus, there is significant interest in identifying nutritional and pharmacological enhancers of PON1 activity. To identify such compounds, we developed a rapid homogeneous assay to detect endogenous cell-associated PON1 activity. PON1 activity was measured by the simple addition of fluorigenic PON1 substrate DEPFMU to live Huh7 cells in medium and monitoring change in fluorescence. A specific PON1 inhibitor, 2-hydroxyquinoline, was used to confirm that the observed activity was due to PON1. The assay was optimized and characterized with regard to time course, substrate and sodium chloride concentration, number of cells, and tolerance to dimethyl sulfoxide and serum. Aspirin, quercetin, and simvastatin are compounds reported to increase PON1 expression. Consistent with the literature and Western blot data, these compounds enhanced PON1 activity in this assay with comparable efficacies and potencies. A known toxic compound did not increase assay signal. This assay method also detected PON1 activity in normal hepatocytes. Thus, a novel homogeneous assay for detection of endogenous PON1 expression has been developed and is amenable to high-throughput screening for the identification of small molecules that enhance PON1 expression.

Paraoxonase: a multifaceted biomolecule

BACKGROUND

Paraoxonase enzyme was first identified as a protective barrier against organophosphorus poisoning. After painstaking research spanning the last three decades, the knowledge about this enzyme has increased immensely. The present review attempts to elaborate the role of paraoxonase enzyme in normal physiology as well as provide an overview of the various disorders in which the enzyme may have a role in etiopathogenesis.

METHODS

The literature was searched from the websites of the National Library of Medicine (http://www.ncbi.nlm.nih.gov/) and Pub Med Central, the U.S. National Library of Medicine's digital archive of life sciences journal literature.

RESULTS

Paraoxonase acts as an important antioxidant enzyme against oxidative stress. The enzyme has been implicated in the pathogenesis of a number of disorders including cardiovascular disorders, cancers etc.

CONCLUSIONS

A better understanding of the molecular mechanism of the enzyme along with the regulatory circuits will help us to utilize agonists to potentiate the anti oxidant actions of the enzyme.

Effect of N-acetylcysteine on the murine model of colitis induced by dextran sodium sulfate through up-regulating PON1 activity

Reactive oxygen species (ROS) are increased in inflammatory bowel disease (IBD) and have been implicated as mediators of intestinal inflammation. We investigated the hypothesis that N-acetylcysteine (NAC) as a glutathione (GSH) precursor attenuates disease progression in a murine dextran sodium sulfate (DSS)-induced colitis model. A colitis model was induced by adding 5% DSS into the drinking water for 7 days. BALB/c mice were injiciatur enema with saline, 5-ASA, N-acetylcysteine, respectively, and free drinking water as control group. DSS-treated mice developed severe colitis as shown by bloody diarrhea, weight loss, and pathologic involvement. Colon lengths were significantly decreased in DSS-treated mice with decreased GSH activity too (P < 0.01). ROS in the colon, the level of interleukin 1 beta (IL-1 beta) in colonic mucosa, serum tumor necrosis factor a (TNF-alpha), MPO, and MDA were significantly increased in DSS-treated animals (P < 0.01), with decreased PON1 activity (P < 0.01). However, NAC significantly decreased colonic MPO activity, ROS, TNF-alpha and IL-1 beta levels and increased PON1 activity and GSH concentration. Moreover, NAC attenuated the macroscopic colonic damage and the histopathologic changes-induced by DSS while similar to 5-ASA group. These results suggest that NAC may be effective in the treatment of colitis through its up-regulating PON1 and scavenging oxygen-derived free radicals.

Non-alcoholic fatty liver disease and the metabolic syndrome: An update

Sedentary lifestyle and poor dietary choices are leading to a weight gain epidemic in westernized countries, subsequently increasing the risk for developing the metabolic syndrome and nonalcoholic fatty liver disease (NAFLD). NAFLD is estimated to affect approximate 30% of the general US population and is considered the hepatic manifestation of the metabolic syndrome. Recent findings linking the components of the metabolic syndrome with NAFLD and the progression to nonalcoholic steatohepatitis (NASH) will be reviewed; in particular, the role of visceral adipose tissue, insulin resistance, and adipocytokines in the exacerbation of these conditions. While no therapy has been proven effective for treating NAFLD/NASH, common recommendations will be discussed.

Paraoxonases are associated with intestinal inflammatory diseases and intracellularly localized to the endoplasmic reticulum

We demonstrated previously that the paraoxonase (PON1/2/3) genes and proteins are expressed in human intestinal biopsies and in Caco-2 cells. The current study aims were to explore whether PON1/2/3 expression is different in inflammatory bowel diseases (IBD) or celiac disease compared to healthy controls, and to explore the intracellular localization of PON1/2/3. Our results showed that significantly fewer biopsies expressed PON1 and PON3 in the duodenum of celiac patients (PON1, P<0.0001; PON3, P=0.03), in the terminal ileum of Crohn's patients (PON1, P=0.001; PON3, P=0.008), and in the colon of UC patients (PON1, P=0.02; PON3, P=0.06) compared to controls. Since all three disorders share markedly elevated inflammatory mediators we explored the PON1/2/3 mRNA expression on cytokine stimulation. No changes were observed in Caco-2 and HT29 cells. Immunofluorescence experiments localized PON1/2/3 exclusively to the endoplasmic reticulum (ER) in both CaCo-2 and HT29 cells. These results demonstrate for the first time a novel relationship between PON1 and PON3 expression and several inflammatory gastrointestinal disorders. Together with the localization of PON1/2/3 enzymes to the ER, it may be suggested that PON1/2/3 may have extracellular functions as part of the host response in IBD and celiac disease.

Monounsaturated fat decreases hepatic lipid content in non-alcoholic fatty liver disease in rats

AIM: To evaluate the effects of different types of dietary fats on the hepatic lipid content and oxidative stress parameters in rat liver with experimental non-alcoholic fatty liver disease (NAFLD).

METHODS: A total of 32 Sprague-Dawley rats were randomly divided into five groups. The rats in the control group (n = 8) were on chow diet (Group 1), rats (n = 6) on methionine choline-deficient diet (MCDD) (Group 2), rats (n = 6) on MCDD enriched with olive oil (Group 3), rats (n = 6) on MCDD with fish oil (Group 4) and rats (n = 6) on MCDD with butter fat (Group 5). After 2 mo, blood and liver sections were examined for lipids composition and oxidative stress parameters.

RESULTS: The liver weight/rat weight ratio increased in all treatment groups as compared with the control group. Severe fatty liver was seen in MCDD + fish oil and in MCDD + butter fat groups, but not in MCDD and MCDD + olive oil groups. The increase in hepatic triglycerides (TG) levels was blunted by 30% in MCDD + olive oil group (0.59 ± 0.09) compared with MCDD group (0.85 ± 0.04, p < 0.004), by 37% compared with MCDD + fish oil group (0.95 ± 0.07, p < 0.001), and by 33% compared with MCDD + butter group (0.09 ± 0.1, p < 0.01). The increase in serum TG was lowered by 10% in MCDD + olive oil group (0.9 ± 0.07) compared with MCDD group (1.05 ± 0.06). Hepatic cholesterol increased by 15-fold in MCDD group [(0.08 ± 0.02, this increment was blunted by 21% in MCDD + fish oil group (0.09 ± 0.02)]. In comparison with the control group, ratio of long-chain polyunsaturated fatty acids omega-6/omega-3 increased in MCDD + olive oil, MCDD + fish oil and MCDD + butter fat groups by 345-, 30- and 397-fold, respectively. In comparison to MCDD group (1.58 ± 0.08), hepatic MDA contents in MCDD + olive oil (3.3 ± 0.6), MCDD + fish oil (3.0 ± 0.4), and MCDD + butter group (2.9 ± 0.36) were increased by 108%, 91% and 87%, respectively (p < 0.004). Hepatic paraoxonase activity decreased significantly in all treatment groups, mostly with MCDD + olive oil group (-68%).

CONCLUSION: Olive oil decreases the accumulation of triglyceride in the liver of rats with NAFLD, but does not provide the greatest antioxidant activity.

Serum paraoxonase 1 activity and malondialdehyde levels in patients with ulcerative colitis

This study was designed to evaluate the oxidative and antioxidative status in patients with ulcerative colitis by detecting antioxidant enzyme paraoxonase 1 activity together with the level of a well-known marker of oxidative stress, malondialdehyde. Serum paraoxonase 1 activity and malondialdehyde levels were analysed in 30 patients with ulcerative colitis and 30 controls using a spectrophotometric method; correlation analysis was made between these variables. Serum malondialdehyde levels were higher in the ulcerative colitis group (median: 2.5, range: 0.5-9.4 nmol ml(-1)) than among the controls (median:1.1, range: 0.5-2.3 nmol ml(-1); p < 0.001) whereas paraoxonase 1 activities were lower in the ulcerative colitis group (median: 158.4, range: 61.6-264.1 U l(-1)) than in the control group (median: 233.3, range: 114.4-431.0 U l(-1); p < 0.001). There was no correlation between serum malondialdehyde level, paraoxonase 1 activity and disease activity. (1) Increased reactive oxygen metabolites levels in ulcerative colitis may result in a pro-oxidation environment, which in turn could result in decreased antioxidant paraoxonase 1 activity and increased malondialdehyde levels, (2) increased cytokines may be a possible cause of decreased paraoxonase 1 activity and (3) decreased serum paraoxonase 1 activity may be a part of an inflammatory response.

Paraoxonase and arylesterase levels in rheumatoid arthritis

It was reported that lipid peroxidation (LPO) products increase in rheumatoid arthritis (RA) patients and increased LPO products reduce many antioxidants. Lipid hydroperoxides (LOOHs) are byproduct of LPO. Paraoxonase (PON), arylesterase (ARE), free sulfhydryl (SH) groups, and ceruloplasmin (CP) are enzymes or proteins with antioxidant characteristics. This study aims to determine the levels of LOOHs and SH, and the activities of PON1, ARE, and CP in RA patients. The study included 47 active RA cases and 23 healthy volunteers. The levels of LOOHs and SH, and the activities of PON1, ARE, and CP were determined using appropriate methods. Student's t test and Spearman's correlation analysis methods were employed in the statistical evaluation. The level of LOOHs was found to be higher (p<0.001), while the level of SH and the activities of PON1, ARE, and CP were found to be lower (p<0.001, <0.001, <0.01, and <0.01, respectively) in the RA patient group when compared with the control group. There was a negative correlation between the level of LOOHs and the activity of PON1 in the patient group (r= -0.420 and p<0.01). The results of our study indicate increased oxidant and decreased antioxidant presence in RA patients. PON1 and ARE are known to have antiatherosclerotic effects in addition to their antioxidant characteristics. As the decrease in these antioxidants, resulting from increased oxidative stress in RA patients, development of atherosclerosis besides tissue injury seems inevitable.

Assessment of paraoxonase 1 activity and malondialdehyde levels in patients with rheumatoid arthritis

OBJECTIVES

We aimed to evaluate antioxidant paraoxonase 1 activity together with malondialdehyde (MDA) (an oxidative stress parameter) levels in patients with rheumatoid arthritis.

DESIGN AND METHODS

Fifty-seven rheumatoid arthritis patients were included in the study and subgrouped according to disease activity (active, n = 31; inactive, n = 26) and compared with healthy controls (n = 25). Serum paraoxonase 1 activity and MDA levels were measured according to an enzymatic spectrophotometric method.

RESULTS

Serum MDA level was higher (P = 0.001) whereas paraoxonase 1 activity was lower (P = 0.001) in the patient group than the controls. When active and inactive subgroups were compared with the control group, there was a statistically significant difference between each parameter. Serum MDA levels were significantly higher, while paraoxonase 1 activity was lower in the active and inactive rheumatoid arthritis groups than the control group. But there was not any difference between active and inactive patients with RA. There was a negative correlation between MDA levels and paraoxonase 1 activity.

CONCLUSIONS

Increased reactive oxygen species levels in rheumatoid arthritis may result in a pro-oxidation environment, which in turn could result in decreased antioxidant paraoxonase 1 activity and increased MDA levels.

Relationship of serum paraoxonase 1 activity and paraoxonase 1 genotype to risk of systemic lupus erythematosus

OBJECTIVE

Low serum paraoxonase 1 (PON1) activity determined with paraoxon as substrate has been found to be associated with coronary artery disease. This study was undertaken to examine the relationship of PON1 activity and genotype to risk of systemic lupus erythematosus (SLE).

METHODS

The impact of 7 PON1 single-nucleotide polymorphisms (SNPs) was analyzed in relation to PON1 activity, SLE risk, lupus nephritis, antiphospholipid antibody (aPL) positivity, and carotid vascular disease in 380 SLE patients (334 white, 46 black) and 497 controls (455 white, 42 black).

RESULTS

Compared with findings in controls, PON1 activity with paraoxon substrate was reduced both in white lupus patients (mean +/- SEM 618.9 +/- 24.0 units/liter versus 719.6 +/- 24.6 units/liter; P = 0.007) and in black lupus patients (991.1 +/- 82.7 units/liter versus 1,164.3 +/- 101.4 units/liter; P = 0.2711). Low PON1 activity in SLE was not associated with the occurrence of aPL, carotid vascular disease, or the use of immunosuppressive drugs. In multiple regression analyses, the Q192R SNP was found to be independently associated with PON1 activity and explained 28% and 41% of the variation in PON1 activity in white patients and black patients, respectively. Stratification of the lupus sample by presence (n = 81) or absence (n = 247) of renal disease revealed significant associations with 3 promoter SNPs, with odds ratios of 3.82 (95% confidence interval [95% CI] 1.49-9.82, P = 0.005), 3.41 (95% CI 1.35-8.61, P = 0.009), and 2.17 (95% CI 1.01-4.68, P = 0.049).

CONCLUSION

To our knowledge, this is the first study to assess the role of PON1 activity in SLE risk in a large biracial sample from the US. Our data indicate that low PON1 activity determined with paraoxon substrate is independently associated with SLE and that certain PON1 SNPs are associated with lupus nephritis.

A role for FXR and human FGF-19 in the repression of paraoxonase-1 gene expression by bile acids

Paraoxonase-1 (PON1), an enzyme that metabolizes organophosphate insecticides, is secreted by the liver and transported in the blood complexed to HDL. In humans and mice, low plasma levels of PON1 have also been linked to the development of atherosclerosis. We previously reported that hepatic Pon1 expression was decreased when C57BL/6J mice were fed a high-fat, high-cholesterol diet supplemented with cholic acid (CA). In the current study, we used wild-type and farnesoid X receptor (FXR) null mice to demonstrate that this repression is dependent upon CA and FXR. PON1 mRNA levels were also repressed when HepG2 cells, derived from a human hepatoma, were incubated with natural or highly specific synthetic FXR agonists. In contrast, fibroblast growth factor-19 (FGF-19) mRNA levels were greatly induced by these same FXR agonists. Furthermore, treatment of HepG2 cells with recombinant human FGF-19 significantly decreased PON1 mRNA levels. Finally, deletion studies revealed that the proximal -230 to -96 bp region of the PON1 promoter contains regulatory element(s) necessary for promoter activity and bile acid repression. These data demonstrate that human PON1 expression is repressed by bile acids through the actions of FXR and FGF-19.

Genetic and environmental factors modulating serum concentrations and activities of the antioxidant enzyme paraoxonase-1

PON1 (paraoxonase-1) is an HDL (high-density lipoprotein)-associated enzyme capable of hydrolysing diverse substrates from OP (organophosphate) toxins to oxidized phospholipids. As such, it has been linked with both the prevention of OP poisoning and inhibition of atherosclerosis initiated by oxidatively modified LDL (low-density lipoprotein). Mice deficient in PON1 are more susceptible to OP poisoning and oxidative stress and more prone to develop atherosclerosis than their wild-type siblings. There are a number of polymorphisms in the PON1 gene which affect serum PON1 activity and concentration. Many (but not all) studies in human populations have suggested that these polymorphisms may be a risk factor for atherosclerosis. The serum concentration of PON1 across the general population is highly variable and there is some debate as to whether genotype or phenotype (i.e. the quantity or quality of the enzyme) is most accurately associated with risk of disease development. What is clear is that factors influencing serum levels of PON1, be they genetic or environmental, will, in turn, affect the capacity of HDL to protect LDL from oxidation and, consequently, may be linked to atherosclerosis. This review will focus on mechanisms which determine the serum concentration of PON1, including gene expression and genetic polymorphisms, protein secretion and association with HDL, pharmacological and environmental factors.

Paraoxonase 1 and atherosclerosis: is the gene or the protein more important?

The oxidation of low-density lipoprotein (LDL) is centrally involved in the initiation and progression of atherosclerosis. High-density lipoprotein (HDL) paraoxonase 1 (PON1) retards the oxidation of LDL and is a major antiatherosclerotic component of HDL. The PON1 gene contains a number of functional polymorphisms in both the coding and the promoter regions, which affect either the level or the substrate specificity of PON1. Genetic case-control and prospective studies conducted to date have produced confusing results. Meta-analysis of these studies indicates no simple relationship between the PON1 polymorphisms and the presence of coronary heart disease (CHD). However, at the present moment in time, it seems that PON1 status, i.e., activity and/or concentration, is more closely related to CHD, and indeed, PON1 has shown to be an independent risk factor for CHD in a prospective study, compared to the genetic polymorphisms. PON1 levels can also be modulated by environmental\lifestyle and possibly pharmaceutical factors. Larger, better designed, preferably prospective studies are needed to determine further the association of PON1 genetic polymorphisms and status with CHD.

Pharmacogenetics of paraoxonases: a brief review

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

Human paraoxonase-1 gene expression by HepG2 cells is downregulated by interleukin-1beta and tumor necrosis factor-alpha, but is upregulated by interleukin-6

Recent studies have demonstrated that human paraoxonase-1 (PON1) associated with HDL, plays a role for anti-atherosclerotic effects of HDL, however, the relationships between PON1 and inflammatory cytokines remain unclear. To clarify this point, we evaluated the transcriptional regulation of PON1 gene by IL-1beta, IL-6 and TNF-alpha in HepG2 cells using luciferase reporter gene assay. We determined the nucleotide sequence of upstream of PON1 gene, and constructed plasmids containing various lengths of upstream region. In the plasmid constructs of U39 (PON1 upstream -1232/-6), U682 (-589/-6), U797 (-472/-6) and U953 (-318/-6), U953 showed a stepwise upregulation in basal promoter activity. The relative promoter activities using U682 plasmid were generally downregulated by IL-1beta and TNF-alpha, but were upregulated by IL-6. By the combination of IL-1beta, IL-6 and/or TNF-alpha, the promoter activities were proportionally regulated. The result of PON1 transcriptional regulation by cytokines in HepG2 cells was confirmed to be concordant with that of regulation of PON1 mRNA expression by cytokines. These results suggest that PON1 mRNA expression by hepatocytes is regulated by proinflammatory cytokines and that proinflammatory cytokines secreted in a disease state, may play a role in the development of atherosclerotic lesion via modification of PON1 mRNA expression affecting on the anti-oxidative property of HDL.

Serum paraoxonase activity decreases in rheumatoid arthritis

OBJECTIVE

To estimate the alterations of paraoxonase 1 (PON1) and high-density lipoprotein (HDL) in rheumatoid arthritis (RA).

DESIGN AND METHODS

We investigated the serum enzyme activity and concentration of PON1 and their relationship with serum lipids, high-density lipoprotein (HDL) parameters, and acute phase reactants of serum amyloid A (SAA) and C-reactive protein (CRP) in patients with RA.

RESULTS

Serum paraoxonase (PON) activity was significantly decreased in RA patients (n = 64, 131 +/- 53 micro mol/min/L) compared with healthy subjects (n = 155, 164 +/- 59) despite the absence of any difference in serum lipid levels between the two groups. This decrease of serum PON activity in RA patients was found in every genotype (Q/Q, Q/R, R/R) of PON1 at 192 Q/R. There was a different distribution in PON1 Q/R genotypes between RA patients and healthy subjects, and RA patients exhibited less (44%) positive PON1-Q than did the healthy subjects (66%). In a further investigation of age- and gender-matched subgroups of RA (n = 25) and healthy subjects (n = 25), not only serum PON activity, but also lecithin-cholesterol acyltransferase (LCAT) was found to be significantly decreased in RA patients (125 +/- 61 micro mol/min/L, 63.2 +/- 17.2 nmol/ml/hr/37 degrees C) than in healthy subjects (169 +/- 67, 74.7 +/- 19.5), respectively. PON1 and LCAT as well as HDL constituent apolipoprotein (apo) AI and apo AII, were altered significantly in RA patients.

CONCLUSIONS

Acute-phase HDL, which is remodeled structurally and functionally in RA, might be less anti-atherogenic due to the impairment of original HDL function. These alterations of HDL in RA patients may explain in part the reported increase in cardiovascular mortality in patients with RA.