Human serum paraoxonase concentration predicts cardiovascular mortality in hemodialysis patients

Effect of Dialyzer Reuse on the Activity of Paraoxonase 1 in Patients on Hemodialysis

Background

Cardiovascular disease is the major cause of mortality in patients undergoing chronic hemodialysis treatment. The oxidative modification of low-density lipoprotein is a crucial step in the pathogenesis of atherosclerosis. Paraoxonase 1 (PON1) is the protein responsible for most of the antioxidant activity of high-density lipoprotein, and its reduced levels are associated with more cardiovascular events in several populations. In hemodialysis patients, reduced PON1 activity has been shown to be associated with increased cardiovascular mortality. Studies have shown that after the hemodialysis session, the activity of PON1 increases. The influence of dialyzer reuse on the activity of PON1 is unknown. We aimed to evaluate the effect of the reuse of two types of dialyzers (polynephron and polyethersulfone) on the PON1 activity of hemodialysis patients.

Subjects and Methods

A total of 30 patients on hemodialysis were included. Pre- and post-dialysis blood samples were collected to analyze the activity of PON1 in thefirst use of the dialyzer and in the hemodialysis session of its sixth reuse. This process was carried out with polynephron (bisphenol-free) and polyethersulfone dialyzers.

Results

We found that post-dialysis PON1 activity was significantly higher than pre-dialysis activity in both thefirst use and sixth reuse (P < 0.001).

Conclusion

The practice of reusing the dialyzer did not interfere with the improvement of PON1 activity after the hemodialysis session.

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.

Altered HDL Proteome Predicts Incident CVD in Chronic Kidney Disease Patients

Patients with chronic kidney disease (CKD) are at high risk for CVD. However, traditional lipid risk factors, including low HDL levels, cannot completely explain the increased risk. Altered HDL proteome is linked with both CVD and CKD, but the role of HDL proteins in incident CVD events in patients with CKD is unknown. In this prospective case-control study, we used targeted proteomics to quantify 31 HDL proteins in 92 subjects (46 incident new CVD and 46 one-to-one matched controls) at various stages of CKD. We tested associations of HDL proteins with incident CVD using matched logistic regression analysis. In the model fully adjusted for clinical confounders, lipid levels, C-reactive protein, and proteinuria, no significant associations were found for HDL-C, but we observed inverse associations between levels of HDL proteins paraoxonase/arylesterase 1 (PON1), paraoxonase/arylesterase 3 (PON3), and LCAT and incident CVD. Odds ratios (per 1 SD) were 0.38 (0.18–0.97, P = 0.042), 0.42 (0.20–0.92, P = 0.031), and 0.30 (0.11–0.83, P = 0.020) for PON1, PON3, and LCAT, respectively. Apolipoprotein A-IV remained associated with incident CVD in CKD patients in models adjusted for clinical confounders and lipid levels but lost significance with the addition of C-reactive protein and proteinuria to the model. In conclusion, levels of four HDL proteins, PON1, PON3, LCAT, and apolipoprotein A-IV, were found to be inversely associated with incident CVD events in CKD patients. Our observations indicate that HDLs' protein cargo, but not HDL-C levels, can serve as a marker—and perhaps mediator—for elevated CVD risk in CKD patients.

Paraoxonase 1 gene variants concerning cardiovascular mortality in conventional cigarette smokers and non-smokers treated with hemodialysis

Cigarette smoking effects might correspond with paraoxonase 1 gene (PON1) single nucleotide variants (SNVs). We investigated the association of PON1 rs705379, rs854560, and rs662 with cardiovascular mortality in hemodialysis (HD) patients concerning conventional cigarette smoking. Cardiovascular, cardiac, coronary heart disease (CHD)- and non-CHD-related deaths were analyzed in 206 HD cigarette smokers and 659 HD non-smokers. P-values were adjusted for sex, age, and high-density lipoprotein cholesterol. Among all smokers, the rs705379 TT genotype was associated with cardiovascular (P = 0.028), cardiac (P = 0.046), and cardiac non-CHD-related (P = 0.001) mortality. Non-diabetic smokers showed similar qualitative significance to all smokers concerning mentioned death rates (P-values 0.011, 0.044, and 0.009, respectively). In diabetic non-smokers, the rs705379 T allele correlated with CHD-related deaths (P = 0.020). The rs854560 T allele was associated with lower cardiovascular mortality in non-diabetic smokers (P = 0.008). The rs854560 TT genotype showed a negative non-significant correlation with non-CHD-related cardiac death in all non-smokers (P = 0.079). In diabetic smokers, the rs662 G allele was associated with higher cardiac mortality (P = 0.005). In all non-smokers and non-diabetic non-smokers, the rs662 G correlated with cardiovascular deaths (P = 0.020 and P = 0.018, respectively). Genotyping PON1 SNVs may help argue HD smokers harboring the rs705379 TT genotype or T allele and non-smokers possessing the rs662 G allele for prevention against cardiovascular diseases. These groups are more burdened genetically for cardiovascular mortality.

Paraoxonase 1 concerning dyslipidaemia, cardiovascular diseases, and mortality in haemodialysis patients

Paraoxonase 1 (PON1) is known for preventing atherosclerosis through lipid-modifying features, antioxidant activity, anti-inflammatory, anti-apoptosis, anti-thrombosis, and anti-adhesion properties. Uremic patients requiring haemodialysis (HD) are especially prone to atherosclerosis and its complications. We analysed the PON1 gene (PON1) polymorphisms and serum PON1 (paraoxonase) activity concerning dyslipidaemia and related cardiovascular diseases and mortality to show how they associate under uremic conditions modified by maintenance HD treatment. The rs662 AA + AG (OR 1.76, 95%CI 1.10-2.80, P = 0.018), rs854560 TT (OR 1.48, 95%CI 1.04-2.11, P = 0.031), and rs854560 AT + TT (OR 1.28, 95%CI 1.01-1.63, P = 0.040) contributed to the prevalence of atherogenic dyslipidaemia diagnosed by the triglyceride (TG)/HDL-cholesterol ratio ≥ 3.8. The normalized serum PON1 activity positively correlated with atherogenic dyslipidaemia (ẞ 0.67 ± 0.25, P = 0.008). The PON1 rs854560 allele T was involved in the higher prevalence of ischemic cerebral stroke (OR 1.38, 1.02-1.85, P = 0.034). The PON1 rs705379 TT genotype contributed to cardiovascular (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac (HR 1.34, 95% CI 1.05-1.71, P = 0.018) mortality. All P-values were obtained in multiple regression analyses, including clinical variables. Multifaceted associations of PON1 with dyslipidaemia, ischemic cerebral stroke, and cardiovascular mortality in HD patients provide arguments for the consideration of PON1 and its protein product as therapeutic targets in the prevention of atherosclerosis and its complications in uremic patients.

PON1 lactonase activity and its association with cardiovascular disease

BACKGROUND

Paraoxonase 1 (PON1) is important in the development of atherosclerosis, and it has become the subject of intensive research. Our aim was to evaluate the association of serum PON1 activity and polymorphisms with cardiovascular disease (CVD) using four different substrates.

MATERIALS AND METHODS

Activity of PON1-related to arylesterase (AREase and 4-CMPAse), paraoxonase (PONase), and lactonase (LACase), and polymorphisms (A-162G, T-108C, L55M, and Q192R) were evaluated in subjects with CVD, cardiovascular risk factor (CFR), and controls. An ordered logistic-regression analysis of PON1 phenotypes was performed in the CVD group with respect to the control group.

RESULTS AND CONCLUSIONS

Logistic-regression analysis showed that CC-108 genotype was associated with CRF and CVD. The CVD group had the lowest activities of PON1. The LACase might be a better biomarker for CVD (OR, 0.52; 95% CI, 0.44-0.61) followed by CMPAse (OR, 0.82; 95% CI, 0.77-0.86), AREase (OR, 0.98; 95% CI, 0.97-0.99) and PONase (OR, 0.99, 95% CI, 0.99-0.99). Logistic regression of PON1 phenotypes by haplotypes showed that LACase activity was not influenced by the polymorphisms and that it could be a new potential biomarker in the development of CVD. Larger scale longitudinal studies are required.

Circulating Lactonase Activity but Not Protein Level of PON-1 Predicts Adverse Outcomes in Subjects with Chronic Kidney Disease

The burden of cardiovascular disease and death in chronic kidney disease (CKD) outpaces that of the other diseases and is not adequately described by traditional risk factors alone. Diminished activity of paraoxonase (PON)-1 is associated with increased oxidant stress, a common feature underlying the pathogenesis of CKD. We aimed to assess the prognostic value of circulating PON-1 protein and PON lactonase activity on adverse clinical outcomes across various stages and etiologies of CKD. Circulating PON-1 protein levels and PON lactonase activity were measured simultaneously in patients with CKD as well as a cohort of apparently healthy non-CKD subjects. Both circulating PON-1 protein levels and PON lactonase activity were significantly lower in CKD patients compared to the non-CKD subjects. Similarly, across all stages of CKD, circulating PON-1 protein and PON lactonase activity were significantly lower in patients with CKD compared to the non-CKD controls. Circulating PON lactonase activity, but not protein levels, predicted future adverse clinical outcomes, even after adjustment for traditional risk factors. The combination of lower circulating protein levels and higher activity within the CKD subjects were associated with the best survival outcomes. These findings demonstrate that diminished circulating PON lactonase activity, but not protein levels, predicts higher risk of future adverse clinical outcomes in patients with CKD.

PON1 concentration and high-density lipoprotein characteristics as cardiovascular biomarkers

Introduction

Serum paraoxonase 1 (PON1) is now known to be related to cardiovascular diseases (CVD). The aim of this study was to determine the relationship between PON1 concentration and high-density lipoprotein (HDL) subclasses in patients with proven CVD, cardiovascular risk factors but no CVD (CRF), and in healthy controls (control group).

Material and methods

A case-control study was carried out with 69 volunteers from the Mexican Institute of Social Security, Mexico. Clinical parameters, lipid profile, PON1 concentration, PON1 activities (AREase and CMPAase), and HDL subclasses were evaluated.

Results

Patients with CVD had significantly higher glucose and lower total cholesterol than the control group had (p < 0.01). AREase activity was not different between the control (122.57 ±30.72 U/ml), CRF (115.81 ±32.81 U/ml), and CVD (109.34 ±29.60 U/ml) groups. PON1 concentration was significantly lower in CVD patients than in CRF and control patients (p < 0.001); a positive correlation was observed between AREase activity and PON1 concentration in the CVD group (Rho = 0.58; p < 0.01). Logistic regression analysis showed that the decrease in PON1 level was associated with the CVD group (RRR = 0.20; 95% CI: 0.09–0.45) but not with the CRF group (RRR = 1.29; 95% CI: 0.89–1.90). Significant differences were observed in HDL 2a and HDL 3a concentrations between the control group and CRF and CVD groups (p < 0.05), but not between the CRF and CVD groups.

Conclusions

Our data suggest that PON1 status and HDL characteristics could be early biomarkers that predict the potential for developing CVD.

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 Endocan Levels are Associated With Paraoxonase 1 Concentration in Patients With Chronic Kidney Disease

Endocan is a soluble proteoglycan released by the vascular endothelium. The increase of its serum levels is associated with inflammation, endothelial dysfunction and cardiovascular events in patients with chronic kidney disease (CKD). We studied the association of serum endocan with the lipid profile of 105 CKD patients with dyslipidemia, divided in two groups, non-dialyzed (CKD, N = 57) and hemodialysis (HD, N = 48) in comparison with 30 normal controls (NC). We also analyzed endocan in relation with the concentration of two serum HDL-linked members of the paraoxonase (PON) family, PON1 and PON3, which have been previously found to have antiatherogenic properties. The results showed that endocan levels were significantly higher in HD patients than in CKD patients (P < 0.001) and NC (P < 0.001). PON1 was significantly decreased only in HD patients compared to NC (P < 0.001), whereas PON3 was significantly increased in both patient groups (P < 0.001). Endocan levels were significantly and positively correlated with total cholesterol and LDL-C in CKD and additionally were negatively correlated with HDL-C in HD group. PON1 levels were significantly correlated with endocan in both groups, while no correlation was observed for PON3 in either group. Multiple regression analysis between endocan and the above lipid parameters in the total of patients revealed that endocan was independently associated only with PON1 (β = -0.513, P = 0.002). It is concluded that the increase of serum endocan levels in patients with CKD may be associated with the decrease of PON1 concentration, irrespective of lipid alterations produced by atherosclerosis development.

Chronic Kidney Disease and Disproportionally Increased Cardiovascular Damage: Does Oxidative Stress Explain the Burden?

Chronic kidney disease (CKD) patients are among the groups at the highest risk for cardiovascular disease and significantly shortened remaining lifespan. CKD enhances oxidative stress in the organism with ensuing cardiovascular damage. Oxidative stress in uremia is the consequence of higher reactive oxygen species (ROS) production, whereas attenuated clearance of pro-oxidant substances and impaired antioxidant defenses play a complementary role. The pathophysiological mechanism underlying the increased ROS production in CKD is at least partly mediated by upregulation of the intrarenal angiotensin system. Enhanced oxidative stress in the setting of the uremic milieu promotes enzymatic modification of circulating lipids and lipoproteins, protein carbamylation, endothelial dysfunction via disruption of nitric oxide (NO) pathways, and activation of inflammation, thus accelerating atherosclerosis. Left ventricular hypertrophy (LVH) and heart failure are hallmarks of CKD. NADPH oxidase activation, xanthine oxidase, mitochondrial dysfunction, and NO-ROS are the main oxidative pathways leading to LVH and the cardiorenal syndrome. Finally, a subset of antioxidant enzymes, the paraoxonases (PON), deserves special attention due to abundant clinical evidence accumulated regarding reduced serum PON1 activity in CKD as a contributor to the increased burden of cardiovascular disease. Future, meticulously designed studies are needed to assess the effects of antioxidant therapy on patients with CKD.

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.

Sudden cardiac death and chronic kidney disease: From pathophysiology to treatment strategies

Chronic kidney disease (CKD) patients demonstrate higher rates of cardiovascular mortality and morbidity; and increased incidence of sudden cardiac death (SCD) with declining kidney failure. Coronary artery disease (CAD) associated risk factors are the major determinants of SCD in the general population. However, current evidence suggests that in CKD patients, traditional cardiovascular risk factors may play a lesser role. Complex relationships between CKD-specific risk factors, structural heart disease, and ventricular arrhythmias (VA) contribute to the high risk of SCD. In dialysis patients, the occurrence of VA and SCD could be exacerbated by electrolyte shifts, divalent ion abnormalities, sympathetic overactivity, inflammation and iron toxicity. As outcomes in CKD patients after cardiac arrest are poor, primary and secondary prevention of SCD and cardiac arrest could reduce cardiovascular mortality in patients with CKD.

Human paraoxonase-1 (PON1): Gene structure and expression, promiscuous activities and multiple physiological roles

Human PON1 is a HDL-associated lipolactonase capable of preventing LDL and cell membrane oxidation and is therefore considered to be atheroprotective. PON1 contributes to the antioxidative function of HDL and reductions in HDL-PON1 activity, prevalent in a wide variety of diseases with an inflammatory component, are believed to lead to dysfunctional HDL which can promote inflammation and atherosclerosis. However, PON1 is multifunctional and may contribute to other HDL functions such as in innate immunity, preventing infection by quorum sensing gram negative bacteria by destroying acyl lactone mediators of quorum sensing, and putative new roles in cancer development and the promotion of healthy ageing. In this review we explore the physiological roles of PON1 in disease development, as well as PON1 gene and protein structure, promiscuous activities and the roles of SNPs and ethnicity in determining PON1 activity.

Potential cardiovascular risk protection of bilirubin in end-stage renal disease patients under hemodialysis

We evaluated the potential cardiovascular risk protection of bilirubin in hemodialysis (HD) patients. An enlarged set of studies were evaluated in 191 HD patients, including hematological study, lipid profile, iron metabolism, nutritional, inflammatory markers, and dialysis adequacy. The TA duplication screening in the UDP-glucuronosyltransferase 1 A1 (UGT1A1) promoter region was also performed. The UGT1A1 genotype frequencies in HD patients were 49.2%, 42.4%, and 8.4% for 6/6, 6/7, and 7/7 genotypes, respectively. Although no difference was found in UGT1A1 genotype distribution between the three tertiles of bilirubin, significant differences were found with increasing bilirubin levels, namely, a decrease in platelet, leukocyte, and lymphocyte counts, transferrin, oxidized low-density lipoprotein (ox-LDL), ox-LDL/low-density lipoprotein cholesterol ratio, apolipoprotein (Apo) A, Apo B, and interleukin-6 serum levels and a significant increased concentration of hemoglobin, hematocrit, erythrocyte count, iron, transferrin saturation, Apo A/Apo B ratio, adiponectin, and paraoxonase 1 serum levels. After adjustment for age these results remained significant. Our data suggest that higher bilirubin levels are associated with beneficial effects in HD patients, by improving lipid profile and reducing the inflammatory grade, which might contribute to increase in iron availability. These results suggest a potential cardiovascular risk protection of bilirubin in HD patients.

Paraoxonase-1 (PON1) promoter region polymorphisms, serum PON1 status and coronary heart disease

INTRODUCTION

Serum paraoxonase-1 (PON1) retards the oxidation of low-density lipoprotein and cell membranes and is atheroprotective. Polymorphisms in the promoter region of the PON1 gene have been shown to affect serum PON1 levels and have been related to the presence of coronary heart disease (CHD) in some studies. However, contradictory results have been reported with regard to promoter region polymorphisms and CHD presence; therefore we have re-examined the effects of the C-108T and G-909C promoter polymorphisms on PON1 levels and the presence of CHD in a large case-control study.

MATERIAL AND METHODS

Paraoxonase-1 activity, concentration and the C-108T and G-909C polymorphisms were measured in 417 people with CHD and 282 healthy controls, in a case control study.

RESULTS

Paraoxonase-1 activity and concentration were significantly lower in the CHD population compared to controls regardless of their C-108T and G-909C genotype (p < 0.001). Paraoxonase-1 activity was significantly different in the C-108T genotypes in both the control and CHD groups in the order TT < TC < CC (p < 0.01). Paraoxonase-1 concentration was significantly different in the CHD group only in the G-909C genotype in the order GG > GC > CC (p < 0.01). Haplotype analysis revealed no consistent patterns of PON1 activity in the CHD population; however, in the controls PON1 activity differed between haplotypes GGCC > GGTC > GGTT (p < 0.05) and GCCC > GCTC > GCTT (p < 0.02). Neither promoter polymorphism was associated with CHD presence.

CONCLUSIONS

Paraoxonase-1 status was significantly lower in people with CHD and was affected by the promoter region polymorphisms.

Paraoxonase 1 Phenotype and Mass in South Asian versus Caucasian Renal Transplant Recipients

South Asian renal transplant recipients have a higher incidence of cardiovascular disease compared with Caucasian renal transplant recipients. We carried out a study to determine whether paraoxonase 1, a novel biomarker for cardiovascular risk, was decreased in South Asian compared with Caucasian renal transplant recipients. Subjects were matched two to one on the basis of age and sex for a total of 129 subjects. Paraoxonase 1 was measured by mass, arylesterase activity, and two-substrate phenotype assay. Comparisons were made by using a matched design. The frequency of PON1 QQ, QR and RR phenotype was 56%, 37%, and 7% for Caucasian subjects versus 35%, 44%, and 21% for South Asian subjects (χ(2) = 7.72, P = 0.02). PON1 mass and arylesterase activity were not significantly different between South Asian and Caucasian subjects. PON1 mass was significantly associated with PON1 phenotype (P = 0.0001), HDL cholesterol (P = 0.009), LDL cholesterol (P = 0.02), and diabetes status (P < 0.05). Arylesterase activity was only associated with HDL cholesterol (P = 0.003). Thus the frequency of the PON1 RR phenotype was higher and that of the QQ phenotype was lower in South Asian versus Caucasian renal transplant recipients. However, ethnicity was not a significant factor as a determinant of PON1 mass or arylesterase activity, with or without analysis including PON1 phenotype. The two-substrate method for determining PON1 phenotype may be of value for future studies of cardiovascular complications in renal transplant recipients.

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.

Paraoxonase 1 in chronic kidney failure

In this review we summarize the findings from the literature and our own laboratory on the decreased PON1 activity in renal failure, the mechanisms proposed and the effect of interventions. In addition to profound alterations in lipoproteins, reduced serum PON1 activity has been clearly established in the past decade and could contribute to accelerated development of atherosclerosis in ESRD and in HD. PON1 lactonase activity is lower in ESRD patients. Hemodialysis partially restores PON1 lactonase and the other activities. PON1 activity recovery after dialysis suggests that uremic toxins may play a mechanistic role in PON1 inactivation. Lower PON1 activity in CRF patients is associated with low thiol concentration, high CRP, and is beneficially enhanced with vitamin C and flavonoids. Changes in HDL subclasses, namely lower HDL₃ in these patients may also play a role in PON1 lower activity. Future research should focus on: (1) mechanistic studies on causes for low PON1 activity and mass; (2) prospective studies focusing on whether there is an added predictive value in measuring PON1 activity (and PON1 activity in HDL₃) in this patient population; (3) intervention studies attempting to increase PON1 activity.

Paraoxonase-1 and ischemia-modified albumin in patients with end-stage renal disease

End-stage renal disease (ESRD) with and/or without treatment by hemodialysis (HD) is associated with accelerated atherosclerosis, leading to cardiovascular disease (CVD) including acute coronary syndromes. Therefore, the regulation of CVD is a crucial issue for ESRD patients. Given the recent reports that paraoxonase-1 (PON-1) and ischemia-modified albumin (IMA) could predict CVD-related mortality in ESRD, the two recent biomarkers may be useful for preventive strategies for CVD. This review paper presents current data on the relationships between PON-1, IMA, and ESRD. Many studies have shown that circulating PON-1 activity is lower in ESRD patients, and we have shown that its levels increase after HD. Although circulating IMA levels can increase before HD in ESRD patients, there remains to be little data. Our pilot study has shown a significant inverse correlation between PON-1 and IMA in ESRD patients. Although the pathogenic link between PON-1 and IMA remains speculative, considering both biomarkers may provide new insights into the prevention of CVD in ESRD patients.

Comparative modeling of PON2 and analysis of its substrate binding interactions using computational methods

Paraoxonase (PON) constitutes a family of calcium-dependent mammalian enzymes comprising of PON1, PON2, and PON3. PON family shares ~60% sequence homology. These enzymes exhibit multiple activities like paraoxonase, arylesterase, and lactonase in a substrate dependent manner. Decreased PON activity has been reported in diseases like cardiovascular disease, atherosclerosis, and diabetes. Even though, PON2 is the oldest member of the family, PON1 is the only member studied in silico. In this study, the structure of PON2 was modeled using MODELLER 9v7 and its interactions with relevant ligands and it's physiological substrate homocysteine thiolactone was performed using AutoDock 4.0. The results reveal that PON1 and PON2 share common ligand binding patterns for arylesterase and lactonase activity, whereas in case of paraoxon binding, the residues involved in the interactions were different. Interestingly, the substrate HCTL was found to have the lowest free energy of binding (ΔG) and highest affinity for PON2 than PON1.

Assessment of low-density lipoprotein oxidation, paraoxonase activity, and arterial distensibility in epileptic children who were treated with anti-epileptic drugs

OBJECTIVE

Studies show that anti-epileptic drugs increase oxidative stress. Thus, low-density lipoprotein oxidation increases and atherogenesis is induced. Paraoxonase-associated high-density lipoprotein protects low-density lipoprotein and high-density lipoprotein oxidation. The effects of anti-epileptic drugs on paraoxonase activity has not been investigated yet. The aim of this study is to investigate the effect of anti-epileptic drugs on paraoxonase activity, lipid profiles, folat, vitamin B12, homocysteine, thyroid hormones, apolipoprotein A-1, total anti-oxidant capacity, malondialdehyd, nitric oxide, and oxidised low-density lipoprotein. The association with carotid-femoral pulse wave velocity and current biochemical parameters had been searched for assessing the effects of anti-epileptic drugs on the vascular system.

PATIENTS AND METHODS

We recruited 59 epileptic patients treated with anti-epileptic drugs and 23 controls (group IV) at least 6 months ago. The epileptic group was divided into three groups by receiving anti-epileptic drugs as follows: group I: carbamazepine, group II: valproic acid, and group III: carbamazepine and valproic acid. Arterial distensibility was assessed with the Complior device.

RESULTS

There was no difference between the current biochemical parameters in epileptic children. Serum-free T4 was decreased, when compared with group IV. Thyroid-stimulating hormone was increased in group II, compared with group IV. The carotid-femoral pulse wave velocity was increased in group III, compared with group IV. The carotid-femoral pulse wave velocity was correlated with thyroid-stimulating hormone and valproic acid levels.

CONCLUSIONS

Anti-epileptic drugs may induce atherogenesis by affecting the thyroid hormones. According to the current data, the effects of thyroid hormones on vascular system may be independent of other biochemical markers. Epileptic patients using anti-epileptic drugs must be followed closely for arterial stiffness, and also for the development and progression of atherosclerosis.

Role of protein kinase C in pitavastatin-induced human paraoxonase I expression in Huh7 cells

We have demonstrated that pitavastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, enhanced human serum paraoxonase (PON1) gene promoter activity and that protein kinase C (PKC) activated PON1 expression through Sp1 in cultured HepG2 cells. We investigated whether PKC was involved in pitavastatin-induced PON1 expression. PON1 gene promoter activity was assessed by a reporter gene assay using cultured Huh7 cells. PON1 protein expression and PKC activation were measured by Western blotting. The binding activity of Sp1 to the PON1 gene upstream was analyzed by electrophoretic mobility shift assay. Both PON1 gene promoter activity and PON1 protein expression were elevated by pitavastatin stimulation. The effects of pitavastatin on PON1 promoter activity and PON1 protein expression were attenuated by both bisindolylmaleimide IX (Ro-31-8220) and bisindolylmaleimide I. Electrophoretic mobility shift assay showed that pitavastatin increased the Sp1-PON1 DNA binding, and this effect was attenuated by Ro-31-8220. Pitavastatin activated atypical PKC, but never conventional or novel PKC. Myristoylated pseudosubstrate peptide inhibitor of PKCzeta abolished the pitavastatin-increased PON1 promoter activity; however, calphostin C and Gö6976 (PKC inhibitors except for PKCzeta) did not influence the promoter activity. In addition, an overexpression of dominant negative form of PKCzeta expression vector obviously decreased pitavastatin-induced PON1 promoter activation. These observations suggest that pitavastatin activates PKC, especially PKCzeta isoform, which increases the binding intensity of Sp1 to PON1 DNA promoter responsible for enhanced transcription of PON1 gene and increased PON1 protein expression in Huh7 cells.

Association of the novel cardiovascular risk factors paraoxonase 1 and cystatin C in type 2 diabetes

Paraoxonase 1 (PON1) has been reported to be associated with proteinuria in subjects with type 2 diabetes mellitus (T2DM). Plasma cystatin C is more accurate than creatinine for identifying stage 3 kidney disease in T2DM. We tested the hypothesis that PON1 and cystatin C would be associated in T2DM subjects from an Aboriginal Canadian community, who are at high risk for the development of nephropathy. PON1 A(-162)G and PON2 Ala148Gly genotypes, cystatin C, HbA1c, high density lipoprotein cholesterol (HDLC), waist circumference (waist), and duration of diabetes were included in the regression analysis with log(e) (ln) of PON1 mass as the dependent variable. A regression model including PON2 Ala148Gly genotype, HDLC, and ln cystatin C explained 25.8% of the variance in PON1 mass. Conversely, waist, age, ln HbA1c, ln duration of diabetes, and ln PON1 mass, but not PON2 genotype, explained 38% of the variance in cystatin C. Subjects with cystatin C estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m(2) (stage 3 kidney disease) had significantly lower PON1 mass compared with subjects with cystatin C-eGFR >60 ml/min per 1.73 m(2). The lower mass of PON1, an anti-inflammatory HDL-associated enzyme, in T2DM with cystatin C-eGFR <60 ml/min per 1.73 m(2) may contribute to their increased risk for cardiovascular disease.

Lipid peroxidation in hemodialysis patients: effect of vitamin C supplementation

OBJECTIVES

Renal failure is associated with several metabolic disturbances and increasing evidences support a role of oxidative stress and impaired antioxidant defence in the pathologic mechanisms that may contribute to accelerated atherogenesis in these patients. Aim of the study was to further investigate the relationship between oxidative stress and chronic renal failure.

DESIGN AND METHODS

We compared the paraoxonase (PON1) activity, the levels of lipid hydroperoxides and AGE adducts in plasma of hemodialysis patients before and after intravenous administration of vitamin C.

RESULTS

An increase in lipid hydroperoxides, AGE adducts and a decrease in the activity of PON1 were observed in patients with respect to controls. The comparison before and after supplementation with vitamin C showed an increase of PON1 activity and a decrease of AGE and lipid hydroperoxides levels.

CONCLUSIONS

The results provide further evidence that lipid peroxidation and impairment of antioxidant system in plasma of patients may play a role in renal disease and suggest that evaluation of PON1 activity could represents an useful approach to monitor antioxidant treatment and new dialysis therapies.

Development of an immunoblot assay with infrared fluorescence to quantify paraoxonase 1 in serum and plasma

Paraoxonase 1 (PON1) requires calcium for activity and is inactivated in the presence of EDTA. Because of this, studies to date have used serum or heparinized plasma for both activity and mass assays of PON1. Whole serum and EDTA plasma were analyzed by SDS-electrophoresis and Western blot using anti-PON1 monoclonal antibody 4C10. Because PON1 has one disulfide and one free cysteine residue, the samples were reduced with dithiothreitol before electrophoresis. Western blot identified a major PON1 band with a molecular mass of approximately 45 kDa and two minor bands of approximately 40 and 35 kDa in both serum and EDTA plasma. This established that PON1 is inactive, but structurally intact, in EDTA plasma and suggested that a mass assay could be developed based on SDS-electrophoresis and Western blot. Linearity was established for plasma and for a PON1 standard. Quantification was based on the major PON1 band at 45 kDa. The correlation between serum and plasma PON1 mass was 0.9553. The between-run variation was determined with a serum pool to be 7.8%. The mass of PON1 in serum was significantly correlated with arylesterase activity (r = 0.85). Thus, we have demonstrated the feasibility of measuring PON1 mass in either serum or EDTA plasma.