Validation of PON1 enzyme activity assays for longitudinal studies

The importance of paraoxonase 1 activity in chronic kidney disease

Paraoxonase 1 (PON1) is one of the most significant antioxidative enzymes associated with high-density lipoprotein (HDL). It has been proved that is involved in the pathogenesis of many diseases including chronic kidney disease (CKD). The association between PON1 and CKD seems to be mutual, such that the disease produces a significant decrease in PON1 activity levels, while the genetics of PON1 may affect the risk of susceptibility to CKD. Recent studies reveal that the decrease in serum PON1 activity observed in non-dialyzed and dialyzed CKD patients as well as in renal transplant (RT) patients is linked to an increased vulnerability to atherosclerosis. We intend to summarize current literature concerning PON1 activity in CKD, highlighting on the main determinants of PON1 activity, its association with oxidative stress, the impact of its genetic polymorphism on the disease development, the effect of drugs and nutritional state. Furthermore, evidence supporting the implication of reduced PON1 activity in the incident of cardiovascular disease in CKD patients, is also examined. It appears that despite the lack of standardization of PON1 activity measurement, PON1 remains a valuable biomarker for the researchers through the last decades, which contributes to the assessment of the antioxidant status having prognostic benefit on adverse clinical outcomes at various stages and etiologies of kidney disease.

PON1 enzyme activity assays for serum and heparinized plasma in horses and stability evaluation of the enzyme activity over different freeze-thaw cycles and mimic transportation

Consistent information and standardization procedures regarding the time of storage for frozen samples and the effects of storage time on enzyme activity are still missing in the literature. Thus, we evaluated the effects of different storage temperatures (-20 °C and - 80 °C), three repetitive freeze/thaw cycles, and 24-h mimic transportation on the activities of PON1 (paraoxonase and arylesterase), enzymes involved in the protection and detoxification processes of reactive molecules. PON1 enzymes' activity was validated on serum and heparinized plasma in horses. The results revealed that conditions and time of storage of blood samples for PON1 analyses altered the activities of both enzymes in both sample types, evidencing that these conditions can lead to protein degradation or general alteration. Specifically, paraoxonase and arylesterase activities significantly decreased among storage temperatures, with major effects detected at -20 °C. The repeated freeze/thaw cycles at -20 °C and 24-h mimic transport conditions also generated an expected degradation of the arylesterase in both serum and heparinized plasma while freeze/thaw cycles at -80 °C caused an increase of both arylesterase and paraoxonase activities on both sample types. In general, similar enzyme responses were detected between serum and heparinized plasma.

Blood and liver telomere length, mitochondrial DNA copy number, and hepatic gene expression of mitochondrial dynamics in mid-lactation cows supplemented with l-carnitine under systemic inflammation

The current study was conducted to examine the effect of l-carnitine (LC) supplementation on telomere length and mitochondrial DNA copy number (mtDNAcn) per cell in mid-lactation cows challenged by lipopolysaccharide (LPS) in blood and liver. The mRNA abundance of 31 genes related to inflammation, oxidative stress, and the corresponding stress response mechanisms, the mitochondrial quality control and the protein import system, as well as the phosphatidylinositol 3-kinase/protein kinase B pathway, were assessed using microfluidics integrated fluidic circuit chips (96.96 dynamic arrays). In addition to comparing the responses in cows with or without LC, our objectives were to characterize the oxidative and inflammatory status by assessing the circulating concentration of lactoferrin (Lf), haptoglobin (Hp), fibrinogen, derivates of reactive oxygen metabolites (dROM), and arylesterase activity (AEA), and to extend the measurement of Lf and Hp to milk. Pluriparous Holstein cows were assigned to either a control group (CON, n = 26) or an LC-supplemented group (CAR; 25 g LC/cow per day; d 42 ante partum to d 126 postpartum (PP), n = 27). On d 111 PP, each cow was injected intravenously with LPS (Escherichia coli O111:B4, 0.5 µg/kg). The mRNA abundance was examined in liver biopsies of d -11 and +1 relative to LPS administration. Plasma and milk samples were frequently collected before and after the challenge. After LPS administration, circulating plasma fibrinogen and serum dROM concentrations increased, whereas AEA decreased. Moreover, serum P4 initially increased by 3 h after LPS administration and declined thereafter irrespective of grouping. The Lf concentrations increased in both groups after LPS administration, with the CAR group showing greater concentrations in serum and milk than the CON group. After LPS administration, telomere length in blood increased, whereas mtDNAcn per cell decreased; however, both remained unaffected in liver. For mitochondrial protein import genes, the hepatic mRNA abundance of the translocase of the mitochondrial inner membrane (TIM)-17B was increased in CAR cows. Moreover, TIM23 increased in both groups after LPS administration. Regarding the mRNA abundance of genes related to stress response mechanisms, 7 out of 14 genes showed group × time interactions, indicating a (local) protective effect due to the dietary LC supplementation against oxidative stress in mid-lactating dairy cows. For mtDNAcn and telomere length, the effects of the LPS-induced inflammation were more pronounced than the dietary supplementation of LC. Dietary LC supplementation affected the response to LPS primarily by altering mitochondrial dynamics. Regarding mRNA abundance of genes related to the mitochondrial protein import system, the inner mitochondrial membrane translocase (TIM complex) seemed to be more sensitive to dietary LC than the outer mitochondrial membrane translocase (TOM complex).

Paraoxonase 1 and atrial fibrillation: Is there a relationship?

Atrial fibrillation (AF) is associated with oxidative stress and inflammation. Paraoxonase-1 (PON1), circulates in blood bound to high-density lipoproteins and reduces systemic oxidative stress. The aim of this study was to evaluate PON1 serum concentration and PON1 arylesterase activity (AREase) in patients with AF. We studied a group of 67 patients with symptomatic paroxysmal or persistent AF admitted for cardioversion and a control group of 59 patients without AF. Clinical parameters, lipid profile, PON1 concentration and AREase were evaluated. A significant difference in serum PON1 concentration and in AREase was found among the two groups. In a multivariate linear regression model, the presence of AF was associated with low PON1 concentration (P = .022). The body mass index was also independently associated with PON1 values (P < .001). Only the high-density lipoproteins-cholesterol level was independently associated with AREase (P = .002). PON1 serum concentrations and AREase were diminished in patients with AF, and the presence of AF was independently associated with low PON1 values.

Paraoxonase 1 (PON1) L55M and Q192R polymorphisms are not associated with chronic kidney disease in Thai individuals with type 2 diabetes

BACKGROUND

Decreased paraoxonase 1 (PON1) activity and PON1 polymorphisms have been found to be associated with chronic kidney disease (CKD) in type 2 diabetes mellitus (T2DM).

OBJECTIVE

This study aimed to investigate the association of the PON1 L55M and Q192R polymorphisms with CKD in T2DM, as well as their relationship with PON1 activity.

METHODS

A total of 166 T2DM patients, including 83 CKD patients and 83 non-CKD patients, were recruited. Biochemical parameters and paraoxonase (PONase) and arylesterase (AREase) activities were measured. The PON1 L55M and Q192R polymorphisms were analysed by a polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. Data were analysed using the chi-square test, Student's t-test and logistic regression analysis.

RESULTS

Total cholesterol, TGs, LDL-C and Cr were significantly higher in CKD patients than in non-CKD patients. In contrast, the estimated glomerular filtration rate (eGFR) and AREase activity were significantly lower in CKD patients than in non-CKD patients (P < .05). The genotype and allele frequencies of the PON1 L55M and Q192R polymorphisms were not significantly different between CKD and non-CKD patients. Multivariate logistic regression analysis showed no association between the PON1 L55M and Q192R polymorphisms and CKD in T2DM. In addition, among all patients, patients with the PON1 LM genotype had significantly lower PONase activity than those with the LL genotype (P < .05). Among all patients, CKD patients and non-CKD patients, those with the PON1 RR genotype had significantly higher PONase activity but lower AREase activity than patients with the QR and QQ genotypes (P < .05).

CONCLUSIONS

PON1 activity was influenced by the PON1 L55M and Q192R polymorphisms. However, the PON1 L55M and Q192R polymorphisms may not be considered genetic biomarkers for CKD in T2DM.

Association between inflammatory markers and serum paraoxonase and arylesterase activities in the general population: a cross-sectional study

Background

Recent studies focused on modulating factors of paraoxonase-1 (PON1) activity. In some studies the association between pro-inflammatory markers and PON1 activity was examined, but so far no population-based investigations on this issue have been conducted. The present study investigated the relationships between the pro-inflammatory markers tumor necrosis factor (TNF)-α, leptin, interleukin (IL)-6, and high-sensitive C-reactive protein (hs-CRP) and paraoxonase and arylesterase, two hydrolytic activities of PON1, in the population-based Bavarian Food Consumption Survey II.

Methods

Based on 504 participants (217 men, 287 women), the relationship between the pro-inflammatory markers and the outcomes paraoxonase and arylesterase activities were investigated using multivariable linear models.

Results

Circulating plasma levels of leptin (P-value < 0.0001), hs-CRP (P-value = 0.031) and IL-6 (P-value = 0.045) were significantly non-linearly associated with arylesterase activity. Leptin levels were also significantly associated with paraoxonase activity (P-value = 0.024) independently from confounding factors, including high-density lipoprotein (HDL) cholesterol. With increasing levels of these inflammatory parameters, arylesterase and paraoxonase activities increased; however, at higher levels (> 75th percentile) the activities reached a plateau or even decreased somewhat. After Bonferroni-Holm correction, only leptin remained non-linearly but significantly associated with arylesterase activity (adjusted overall P-value < 0.0001). Neither age nor sex nor obesity modified the associations. No association was found between TNF-α and paraoxonase or arylesterase activity.

Conclusions

The present findings suggest that in persons with very high levels of inflammation, PON1 activity may be impaired, a fact that might subsequently be accompanied by a higher risk for cardiometabolic diseases. Whether or not the measurement of PON1 activity in combination with a lipid profile and certain inflammatory markers could improve the prediction of cardiometabolic diseases in middle-aged individuals from the general population should be evaluated in clinical studies.

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

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

Kiwifruit Supplementation Increases the Activity of the Paraoxonase Enzyme and decreases Oxidized Low-Density Lipoprotein in High-Fat Diet Fed Hamsters

Background: It is shown that kiwifruit elevates serum high-density lipoprotein cholesterol (HDL-C) levels and exhibits beneficial effects on human health due to its antioxidant potential. Objectives: This study aimed to investigate the impact of kiwifruit on the activity of the paraoxonase 1 (PON1) enzyme, as a main antioxidant enzyme in HDL functionality, in a high-fat diet (HFD). Methods: To this end, 42 male Syrian hamsters were divided into 6 groups including hamsters receiving a normal diet (the control normal group), a regular diet supplemented with kiwifruit at two concentrations (i.e., 1.86 g/kg and 3.73 g/kg), a HFD comprised of 15% butterfat + 0.05% cholesterol (the control high-fat group), and a HFD supplemented with kiwifruit at two concentrations (i.e., 1.86 and 3.73 g/kg) for 8 weeks. Results: The results showed that supplementation of kiwifruit to the HFD increased the levels of HDL-C and remarkably reduced the concentrations of oxidized low-density lipoprotein (ox-LDL) and malondialdehyde (MDA) compared with the control-HF group. In addition, the paraoxonase activity of PON1 significantly increased in HFD supplemented with kiwifruit (1.86 g/kg), and finally, arylesterase (ARE) activity increased in all treated groups when compared with untreated groups. Conclusion: Our findings suggested that kiwifruit can improve the lipid profile and prevent oxidative stress-induced by lipid peroxidation in hamsters receiving HFD, thus increasing the ARE and paraoxonase activities of PON1.

Association between rs662 (A > G) and rs854560 (A > T) polymorphisms in PON1 gene and the susceptibility for psoriasis in mestizo population of Western Mexico

Psoriasis is a chronic, autoimmune skin disease. In psoriasis, PON1 activity is diminished and peroxidation biomarkers are elevated. The most studied PON1 polymorphisms are rs662 (A > G) and rs854560 (A > T), which have been associated with the antioxidant activity of PON1, risk of cardiovascular diseases and psoriasis development. The aim of this study, was to determine the association of rs662 (A > G) and rs854560 (A > T) PON1 polymorphisms with psoriasis susceptibility in Western Mexico population. In this case-control study, we included 104 psoriasis patients and 124 control subjects. The genotyping of polymorphisms rs662 (A > G) and rs854560 (A > T) of PON1 was carried out by PCR-RFLPs. The lipid profiles were quantified by enzymatic colorimetric method, and PON1 activity was determined by spectrophotometry. The lipid profile levels, except HDL-C and atherogenic index, were higher in patients vs. controls. Patients presented lower paraoxonase and arylesterase activity. The G allele of rs662 (A > G) is associated with risk for psoriasis, while the T allele of rs854560 (A > T) is associated with low susceptibility to psoriasis. The AG haplotype was more frequent within the patient group (p < 0.05). The AA and AG genotypes of rs662 (A > G) and TT and AA genotypes of rs854560 (A > T) are associated with lower PONase and ARE activity in patients vs. controls. Patients with the G allele of rs662 (G > A) and T alleles of rs854560 (A > T) show significant differences in the lipid levels in comparison to controls. These results suggest that carriers of G allele of rs662 (A > G) present a greater susceptibility to psoriasis.

Serum paraoxonase 1 activity in cats: analytical validation, reference intervals, and correlation with serum amyloid A and alpha-1-acid glycoprotein

Paraoxonase 1 (PON1) is an inflammation marker associated with lipid oxidation and is used as a diagnostic marker in people. There is no information about the suitable substrate and analytic performance in cats, or its biological behavior compared with other inflammation markers. Our aims were to validate a paraoxon-based method to measure PON1 activity in feline serum, to assess stability of PON1 under different storage conditions and the impact of interfering elements, to determine a reference interval (RI) for healthy cats, and to correlate PON1 activity with 2 major acute-phase proteins. Intra- and inter-assay precision, accuracy, and RI were assessed using fresh serum. The same specimens were stored at room temperature, refrigerated, or frozen, and retested at defined intervals. Hemolysis, lipemia, and icterus were simulated to study interferences. PON1 results were compared to serum amyloid A (SAA) and alpha-1-acid glycoprotein (AGP) results. Analytical validation yielded precise and accurate results. PON1 activity is stable for up to 24 h at room temperature and up to 48 h at 4°C. Freezing at -20°C results in an increase after 72 h, with return to baseline values after 1 wk, that again increases after 6 mo. Only hyperlipemia interfered with PON1 activity. The RI based on 71 healthy cats was 58-154 U/L. PON1 activity was negatively correlated with AGP, but not with SAA. Serum PON1 activity can be measured accurately in cats, and it acts as a negative acute-phase protein.

Arylesterase activity but not PCSK9 levels is associated with chronic kidney disease in type 2 diabetes

PURPOSE

Oxidative stress and dyslipidemia have been found to be associated with the progression of chronic kidney disease (CKD) in type 2 diabetes mellitus (T2DM) patients. Paraoxonase 1 (PON-1) activity, and proprotein convertase subtilisin kexin type 9 (PCSK9) levels play an important role regarding anti-oxidants, and lipid metabolism, respectively. The aim of this study was to investigate the association of PON-1 activity, and PCSK9 levels with CKD in T2DM.

METHODS

A total of 180 T2DM (87 CKD, and 93 non-CKD) with age-, and gender-matched subjects were recruited in this study. PON-1 activity was measured with two kinds of substrate: paraoxon for paraoxonase (PONase) activity and phenylacetate for arylesterase (AREase) activity. PCSK9 levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

AREase activity was significantly lower in CKD compared with non-CKD (225.53 ± 108.73 vs. 257.45 ± 106.12 kU/L, p = 0.044) in T2DM, whereas there was no significant difference in PONase activity and PCSK9 levels between CKD and non-CKD groups. In addition, multivariate logistic regression analysis showed that the lowest tertile of AREase increased the risk for CKD in T2DM (OR 3.251; 95% CI 1.333-7.926, p = 0.010), whereas PONase activity and PCSK9 levels were not associated with CKD in T2DM.

CONCLUSION

Reduced AREase activity can increase the risk for CKD in T2DM patients. AREase activity, but not PONase activity and PCSK9 levels, may be used as the biomarker for predicting the progression of CKD in T2DM.

Conventional and innovative methods to assess oxidative stress biomarkers in the clinical cardiovascular setting

Oxidative stress has a pivotal and widely described role in the onset and progression of atherosclerotic plaque and cardiovascular disease. Many oxidative stress-related biomarkers can be measured in biological samples; however, there are still many aspects that limit the adoption of oxidative stress assessment in clinical laboratory practice. Here, we report an overview of the different sources and main common oxidative stress biomarkers relevant for cardiovascular physiopathology, describing in detail a recently proposed lipidomic assay for ceramide assessment, as a promising future development in oxidative stress evaluation among the many available redox-related tests.

Crosstalk Between Adipokines and Paraoxonase 1: A New Potential Axis Linking Oxidative Stress and Inflammation

Paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated protein that endows its carrier with (lipo-)lactonase-dependent antioxidative features. Low levels of PON1 activity have been observed in association with obesity, a major risk factor for cardiovascular disease (CVD). Considering the well-recognized atheroprotective role of PON1, exogenous/endogenous factors that might modulate its levels/activity are raising great interest. Since adipokines represent a molecular link between obesity and CVD, we here explored the possible impact of these substances on PON1 activity/expression. The levels of interleukin (IL)-6, IL-8, tumor necrosis factor alpha, monocyte chemoattractant protein-1, hepatocyte growth factor, resistin, leptin, and adiponectin were measured along with arylesterase, paraoxonase, and lactonase activities of PON1 in 107 postmenopausal women. Moreover, the direct effect of resistin on PON1 expression was evaluated in vitro. Multivariate analysis revealed that only resistin was significantly and inversely correlated with PON1-lactonase activities (r = −0.346, p < 0.001) regardless of confounding factors such as age or HDL-cholesterol. It is worth noting that no statistical link was found between adipokine and arylesterase or paraoxonase, the two promiscuous activities of PON1. Notably, resistin down-regulated PON1 expression occurred in hepatocellular carcinoma cultures. Our study suggests that resistin might be a negative modulator of PON1 expression and anti-oxidative activity.

The epigenetic regulation of paraoxonase 1 (PON1) as an important enzyme in HDL function: The missing link between environmental and genetic regulation

BACKGROUND

Paraoxonase 1 (PON1) is an important antiatherogenic and antioxidant enzyme in the circulation that has been associated with adverse health outcomes particularly cardiovascular disease (CVD) and other metabolic disorders. PON1 is a highly promiscuous enzyme and can hydrolyse a large variety of substrates, however, detailed structure/function studies have concluded that the natural substrates for PON1 are lipophilic lactones. The interindividual variability in PON1 activity has been mainly attributed to genetic determinants; however, it appears that the contribution of epigenetics has been ignored as a result of the lack of adequate research.

CONTENT

Epigenetic processes, including the histone modifications in the PON1 gene, the methylation of CpG sites in the promoter region of the PON1 gene and the microRNA modulation of PON1 expression can be responsible for the under researched gap between the environmental and genetic regulation of PON1. Environmental factors, including diet, pollution and lifestyle-related factors widely differ between individuals and populations and can cause large differences in the distribution of PON1 and it is important to note that their effects may be exerted through the epigenetic processes. This review discusses and emphasizes the importance of the epigenetic regulation of PON1 as a less-studied subject to highlight future research landscapes.

SUMMARY

Epigenetic regulation is known as an important contributor to the pathogenesis of human diseases, particularly multifactorial diseases such as CVD, which is life-threatening. Due to the importance of PON1 in the functionality of high-density lipoprotein (HDL) and its association with CVD, further explorations of its epigenetic regulation using advanced methods such as Methyl-Seq may lead to the identification of new epigenetic contributors that in turn may lead to targeted therapies.

Sex difference: an important issue to consider in epidemiological and clinical studies dealing with serum paraoxonase-1

The aim of this study was to evaluate the influence of sex on serum paraoxonase-1 (PON1) activities and on its relationship with cardiovascular disease risk factors such as overall and central obesity. Arylesterase and lactonase activities of PON1 were assessed in 374 women and 92 men. Both arylesterase and lactonase activities were significantly higher in women compared to men (p<0.001), irrespectively of confounders such as high density lipoprotein-cholesterol, age, smoking and body mass index or waist circumference. Sex also strongly influenced the interplay between PON1 and both fat measures, with only the arylesterase showing a significant and independent inverse correlation with the former parameter (r = -0.248, p<0.001) and the risk of overall obesity (odds ratio: 0.559, 95% confidence interval: 0.340-0.919) in women, but not in men; conversely, neither of the two activities remained associated with waist circumference in men or women after full adjustment. Noteworthy, the association between arylesterase and BMI in the female subsample was significant among women younger than forty-five years (r = -0.453, p<0.001, R ² = 0.207). In conclusion, our study suggests that sex might chiefly influence PON1 activity and its contribution to cardiovascular disease risk. Further studies are needed to confirm and clarify our preliminary findings.

Paraoxonase-1 activities in individuals with different HDL circulating levels: Implication in reverse cholesterol transport and early vascular damage

BACKGROUND AND AIMS

Epidemiological data showing that high-density lipoprotein cholesterol (HDL-C) is inversely associated with cardiovascular disease have led to the idea that cholesterol contained in this lipoprotein may be protective. Against, recent evidence suggests that the athero-protection from HDLs may result from other functions, unrelated to the carried cholesterol. HDL accessory proteins, such as paraoxonase 1 (PON1), have been suggested to endows HDL with antioxidant and anti-inflammatory properties and to contribute to the athero-protective function of the lipoprotein. We aimed to evaluate whether extreme fluctuation in HDL-C levels correlates with PON1 activity.

METHODS

Levels of PON1-related arylesterase and lactonase were assessed in subjects with primary hyperalphalipoproteinemia (HAL, HDL-C>90th percentile), hypoalphalipoproteinemia (HA, HDL-C<10th percentile) and controls. Cholesterol efflux capacity (CEC) through several pathways and other metabolic parameters and markers of vascular disease were also determined.

RESULTS

Despite the marked change in HDL-C and Apoliprotein A1 (APO A1) (p < 0.001 for all comparisons), arylesterase and lactonase were only slightly increased in HAL compared with HA subjects (p < 0.05), but not vs. controls. This change in PON1 activities was no longer significant after adjustment for either HDL-C or APO A1. Both enzymatic activities were positively associated only with aqueous diffusion CEC (r = 0.318, p < 0.05 and r = 0.355, p < 0.05, respectively) and negatively with the presence of plaques (p < 0.05).

CONCLUSIONS

We showed that extreme high/low HDL-C levels are not associated with equal increase/decrease in PON1 activities. This enzyme appears to contribute to the HDL role in reverse cholesterol transport and anti-atherosclerosis processes. Further investigation is required to corroborate our findings.

Dysfunctional high density lipoprotein failed to rescue the function of oxidized low density lipoprotein-treated endothelial progenitor cells: a novel index for the prediction of HDL functionality

Lipid metabolic disorders play critical roles in atherogenesis. Traditionally, it has been suggested that reduced high density lipoprotein (HDL) levels might be an important morbidity indicator for cardiovascular diseases. Therefore, it has been argued that therapeutically raising HDL levels may reduce atherogenesis in patients with dyslipidemia. However, recent clinical trials to elevate serum HDL levels by pharmacologic approaches failed to demonstrate clinical efficacy. Thus, to investigate the functionality of HDL and to explore the possible clinical relevance as well as to define an effective indicator that can represent HDL function may provide another key and reference to disclose the clinical treatment of dyslipidemia. We analyzed the association between the data of dichlorofluorescein assay (assay the functionality of HDL), the effect of HDL on oxidized low density lipoprotein (oxLDL)-stimulated endothelial progenitor cells (EPCs) in vitro, levels of circulating EPCs, and ex vitro EPC colony forming units of each case, we defined the indicator (relative HDL index (RHDL index) = dichlorofluorescein assay result of each subject/dichlorofluorescein assay reading of our young healthy controls) that may represent functionality of HDL. HDL from healthy adults protected oxLDL-treated EPCs by modulating p38 mitogen-activated protein kinase and Rho activation and by promoting nitric oxide production. HDL from subject with RHDL index ≧2 also failed to restore the functionality of oxLDL-treated EPCs via cell-signaling pathways in vitro. The RHDL index significantly correlated with patients' circulating EPC number or EPC colony forming units ex vivo. In conclusions, we explored the RHDL index as a score to predict a patient's EPC functions in vivo and ex vitro.

Sex difference: an important issue to consider in epidemiological and clinical studies dealing with serum paraoxonase-1

The aim of this study was to evaluate the influence of sex on serum paraoxonase-1 (PON1) activities and on its relationship with cardiovascular disease risk factors such as overall and central obesity. Arylesterase and lactonase activities of PON1 were assessed in 374 women and 92 men. Both arylesterase and lactonase activities were significantly higher in women compared to men (p<0.001), irrespectively of confounders such as high density lipoprotein-cholesterol, age, smoking and body mass index or waist circumference. Sex also strongly influenced the interplay between PON1 and both fat measures, with only the arylesterase showing a significant and independent inverse correlation with the former parameter (r = −0.248, p<0.001) and the risk of overall obesity (odds ratio: 0.559, 95% confidence interval: 0.340–0.919) in women, but not in men; conversely, neither of the two activities remained associated with waist circumference in men or women after full adjustment. Noteworthy, the association between arylesterase and BMI in the female subsample was significant among women younger than forty-five years (r = −0.453, p<0.001, R² = 0.207). In conclusion, our study suggests that sex might chiefly influence PON1 activity and its contribution to cardiovascular disease risk. Further studies are needed to confirm and clarify our preliminary findings.

PON1 DNA methylation and neurobehavior in Mexican-American children with prenatal organophosphate exposure

PON1 is a multifunctional enzyme involved in oxidative stress and detoxification of some organophosphate (OP) pesticides. It has been associated with nervous system diseases like Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and autism. We previously found that PON1 susceptible genotypes were associated with lower IQ scores in children. Epigenetic marks, such as DNA methylation, can regulate gene expression. Yet, data on whether DNA methylation may influence the relationship between PON1 levels and neurobehavior are limited. In this study, we used Illumina 450K and EPIC BeadChip arrays to assess PON1 DNA methylation in blood specimens collected from children (n = 238) at birth (cord blood) and age 7 years and examined their relationship with cognitive outcomes. The Wechsler Intelligence Scale for Children was used to assess Full Scale IQ and four composite measures (Verbal Comprehension, Perceptual Reasoning, Working Memory, and Processing Speed Indexes) in 7-year-old children. We observed a consistent yet nonsignificant inverse relationship of methylation at several CpG sites close to the PON1 transcription start site with Full Scale IQ and other composite measures of cognition. We also found an inverse relationship between cord blood methylation at cg15887283 with working memory and a positive association of 7-year-old methylation at cg22798737 with processing speed, independent of OP exposure. However, none of the associations remained significant after accounting for multiple comparisons. This study provides some evidence of the role DNA methylation may play in the known relationship between PON1 and neurobehavior in children, however it appears to be only suggestive and warrants additional research.

Distribution of Paraoxonase-1 (PON-1) and Lipoprotein Phospholipase A2 (Lp-PLA2) across Lipoprotein Subclasses in Subjects with Type 2 Diabetes

Paraoxonase-1 (PON1) and lipoprotein phospholipase A2 (Lp-PLA2) may exert an important protective role by preventing the oxidative transformation of high- and low-density lipoproteins (HDL and LDL, respectively). The activity of both enzymes is influenced by lipidome and proteome of the lipoprotein carriers. T2DM typically presents significant changes in the molecular composition of the lipoprotein subclasses. Thus, it becomes relevant to understand the interaction of PON1 and Lp-PLA2 with the subspecies of HDL, LDL, and other lipoproteins in T2DM. Serum levels of PON1-arylesterase and PON1-lactonase and Lp-PLA2 activities and lipoprotein subclasses were measured in 202 nondiabetic subjects (controls) and 92 T2DM outpatients. Arylesterase, but not lactonase or Lp-PLA2 activities, was inversely associated with TD2M after adjusting for potential confounding factors such as age, sex, smoking, body mass index, hypertension, and lipoprotein subclasses (odds ratio = 3.389, 95% confidence interval 1.069–14.756). Marked difference between controls and T2DM subjects emerged from the analyses of the associations of the three enzyme activities and lipoprotein subclasses. Arylesterase was independently related with large HDL-C and small intermediate-density lipoprotein cholesterol (IDL-C) in controls while, along with lactonase, it was related with small low-density lipoprotein cholesterol LDL-C, all IDL-C subspecies, and very low-density lipoprotein cholesterol (VLDL-C) in T2DM (p < 0.05 for all). Concerning Lp-PLA2, there were significant relationships with small LDL-C, large IDL-C, and VLDL-C only among T2DM subjects. Our study showed that T2DM subjects have lower levels of PON1-arylesterase compared to controls and that T2DM occurrence may coincide with a shift of PON1 and Lp-PLA2 towards the more proatherogenic lipoprotein subclasses. The possibility of a link between the two observed phenomena requires further investigations.

Evaluating the link between Paraoxonase-1 levels and Alzheimer's disease development

At present, the etiopathogenesis of Alzheimer's disease (AD), the most common form of dementia, remains far to be fully deciphered. In the recent years, also the centrality of amyloid-β peptide in the pathogenesis of the neurodegenerative disease has been questioned and other hypotheses have been advanced. Notably, a common denominator of many of these theoretical models is represented by oxidative stress, which is widely proposed to play a role in the disease initiation and/or progression. Paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated enzyme that endows its carrier with multiple biological functions, including the ability to contrast oxidative damage to lipid components of lipoproteins and cells and protect from toxicity of specific organophosphorus pesticides. The peculiar multi-functionality nature of PON1 might be the key for explaining the vast epidemiological data showing a close association between low serum PON1 activity and risk of several diseases, including cardiovascular and neurodegenerative diseases, in particular AD. In this review, we discuss the possible link between PON1 with AD pathogenesis and we hypothesize eventual mechanistic pathways that could account from epidemiological observations. We also highlight the methodological issue limitation in PON1 studies that still impede to give a definitive and certain picture of its effective biological impact on human health including AD.

Effect of Repeated Freeze-Thaw on Serum Biomarkers Associated with Eye Disease

Background

Serum biomarkers are associated with eye diseases, which results in the need for cryopreservation of serum samples. However, the effect on serum biomarker levels of repeatedly freezing and thawing remains poorly understood. The aim of this study was to evaluate the effects of repeated freeze-thaw on the serum levels of the protein, complement C3c (C3c), the micromolecule, uric acid (UA), and the enzyme, angiotensin-converting enzyme (ACE).

Material/Methods

Serum samples were obtained from 50 patients who attended an ophthalmic outpatient department. Following baseline measurements, the serum samples from each subject were divided into aliquots and stored at −80°C for further analysis, following between one to six freeze-thaw cycles. The serum levels of C3c, UA, and ACE were measured immediately after the stored serum samples were thawed.

Results

The serum level of C3c was significantly changed after the first freeze-thaw cycle (p<0.05), and a significant alteration in serum ACE levels occurred after the third freeze-thaw cycle (p<0.05). The serum UA level remained unchanged after all freeze-thaw cycles. Repeated freeze-thaw cycles significantly increased the serum levels of C3c and decreased the serum levels of ACE. The serum levels of C3c, UA, and ACE, respectively were significantly correlated (p<0.001), while the correlation coefficient for C3c and UA were improved when compared with ACE.

Conclusions

Repeated freeze-thaw can have variable effects on the serum levels of biomarkers, C3c, UA and ACE, which supports the need for quality control of cryopreserved serum for biomarker evaluation.

Paraoxonase-1 and Early-Life Environmental Exposures

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

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

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.

Lactonase Activity and Lipoprotein-Phospholipase A2 as Possible Novel Serum Biomarkers for the Differential Diagnosis of Autism Spectrum Disorders and Rett Syndrome: Results from a Pilot Study

Rett syndrome (RTT) and autism spectrum disorders (ASDs) are not merely expression of brain dysfunction but also reflect the perturbation of physiological/metabolic homeostasis. Accordingly, both disorders appear to be associated with increased vulnerability to toxicants produced by redox imbalance, inflammation, and pollution, and impairment of systemic-detoxifying agents could play a role in the exacerbation of these detrimental processes. To check this hypothesis, the activities of two mechanistically related blood-based enzymes, paraoxonase-1 (arylesterase, paraoxonase, and lactonase), and lipoprotein-associated phospholipase A₂ (Lp-PLA₂) were measured in the serum of 79 ASD and 95 RTT patients, and 77 controls. Lactonase and Lp-PLA₂ showed a similar trend characterized by significantly lower levels of both activities in ASD compared to controls and RTT (p < 0.001 for all pairwise comparisons). Noteworthy, receiving operator curve (ROC) analysis revealed that lactonase and, mostly, Lp-PLA₂ were able to discriminate between ASD and controls (lactonase: area under curve, AUC = 0.660; Lp-PLA₂, AUC = 0.780), and, considering only females, between ASD and RTT (lactonase, AUC = 0.714; Lp-PLA₂, AUC = 0.881). These results suggest that lactonase and, especially, Lp-PLA₂ activities might represent novel candidate biomarkers for ASD.

Paraoxonase, arylesterase and lactonase activities of paraoxonase-1 (PON1) in obese and severely obese women

Obesity is independently associated with disturbances in lipid and lipoprotein metabolism, oxidative stress, and is a well-established independent risk factor for cardiovascular diseases (CVD). Human paraoxonase 1 (PON1) is a pleotropic high-density lipoprotein (HDL)-associated enzyme with antioxidant and anti-inflammatory proprieties that have been suggested to contribute to the athero-protective function of the lipoprotein. The aim of this study was to investigate whether obesity is associated with PON1 activity and whether this association is influenced by oxidative stress, inflammation and HDL cholesterol (HDL-C) concentration. The promiscuous activities, arylesterase and paraoxonase, and the putative physiological activity, lactonase, of PON1 were assessed in the serum of 214 obese and severely obese, 101 overweight and 129 normal-weight women. Levels of high-sensitivity C-reactive protein (hs-CRP), hydroperoxides (by-products of lipid oxidative damage) and lipid profiles were also evaluated. Arylesterase activity was the only activity that significantly differed across the groups (ANOVA, p < .01), with the greatest decrease observed in individuals with body mass index (BMI) > 40 kg/m² compared to controls (p < .001). This activity was also inversely, although weakly (r = -0.160, p < .001) correlated with the BMI, and the association was independent of age and levels of oxidative stress and inflammation, but not of HDL-C concentration. In conclusion, our results suggest that the apparent obesity-associated decrement of PON1 activity might simply reflect the decrease in concentration of its plasmatic carrier.

The inverse association of HDL-cholesterol with future risk of hypertension is not modified by its antioxidant constituent, paraoxonase-1: The PREVEND prospective cohort study

BACKGROUND AND AIMS

High-density lipoprotein cholesterol (HDL-C), an established risk marker for atherosclerotic cardiovascular disease (CVD), has been shown to be inversely and independently associated with incident hypertension. Paraoxonase-1 (PON-1) is an HDL-bound esterase enzyme associated with CVD, but its relationship with incident hypertension has not been previously investigated. We aimed at evaluating the prospective association between PON-1 and hypertension risk.

METHODS

PON-1 arylesterase activity was measured in serum at baseline in 3988 participants without pre-existing hypertension in the Prevention of Renal and Vascular End-stage Disease (PREVEND) prospective population-based study. During a median follow-up of 10.7 years, 1206 participants developed hypertension.

RESULTS

In age- and sex-adjusted analysis, the hazard ratio (95% CI) for incident hypertension per 1 standard deviation increase in PON-1 was 1.01 (0.96-1.07; p = 0.656), which remained non-significant after adjustment for several established hypertension risk factors and other potential confounders (0.99, 0.93 to 1.05; p = 0.764). The association was also non-existent on further adjustment for HDL-C (1.00 (0.94-1.06; p = 0.936)) and did not importantly vary across several clinical subgroups. In analyses in the same set of participants, HDL-C was continuously inversely and independently associated with hypertension risk; the association persisted after further adjustment for PON-1 activity and was not modified by PON-1 activity.

CONCLUSIONS

In this Caucasian cohort of men and women, HDL-C, but not its anti-oxidant constituent - PON-1, is inversely, continuously and independently associated with future risk of hypertension. The association is independent of and not modified by PON-1.

Effects of the SGLT2 inhibitor dapagliflozin on HDL cholesterol, particle size, and cholesterol efflux capacity in patients with type 2 diabetes: a randomized placebo-controlled trial

BACKGROUND

Sodium-glucose co-transporter-2 inhibitors (SGLT2i) reduce glucose levels, body weight, and blood pressure, possibly resulting in cardiovascular protection. In phase III trials, SGLT2i were shown to increase HDL cholesterol. We aimed to evaluate whether the SGLT2i dapagliflozin affects HDL function in a randomized placebo-controlled trial.

METHODS

Thirty-three type 2 diabetic patients were randomized to receive dapagliflozin 10 mg or placebo for 12 weeks on top of their glucose lowering medications. The primary end-point was the change in cholesterol efflux capacity (CEC) from macrophages at study end versus baseline. Secondary endpoints were changes in: distribution of HDL subfractions, lipid profile, activity of enzymes that mediate HDL antioxidant properties (PON1 and ARE) and cholesterol metabolism (CETP), HbA1c, body weight and composition.

RESULTS

Thirty-one patients completed the study, n = 16 in the placebo group and n = 15 in the dapagliflozin group. Patients randomized to dapagliflozin were older and had lower adiposity indexes, although these differences disappeared after correction for multiple testing. Therapy with dapagliflozin reduced HbA1c by 0.9% and body weight by 3.1 kg, mainly attributable to reduction of body water and lean mass. As compared to placebo, dapagliflozin reduced CEC (-6.7 ± 2.4 versus 0.3 ± 1.8%; p = 0.043), but this effect was no longer significant after adjusting for age and BMI. No change was detected in HDL cholesterol, HDL subfractions, activity of PON1, ARE, and CETP.

CONCLUSIONS

Despite improvements in glucose control and reduction in body weight, therapy with dapagliflozin exerted no significant effect on HDL cholesterol levels and HDL functionality. Trial registration EudraCT 2014-004270-42; NCT02327039.

Development of an automated method for the determination of human paraoxonase1 activity

Background: Human plasma paraoxonase1 (PON1) is an esterase catalyzing the hydrolysis of organophosphorus pesticides and other xenobiotics. The aims of this study were to develop a rapid method to determinate PON1 activity, evaluate some interference, and study the influence of storage temperature on PON1 activity assay.

Methods: Measurement of PON1 activity was performed for 369 samples by measuring the hydrolysis of paraoxon using a spectrophotometric method adapted on konelab 30 ⃞.

Results: The developed method facilitates the determination of PON1 activity at the rate of more than 200 samples per hour, and it is linear between 2 and 900 IU/L. Intra and inter-assay imprecision coefficients of variation were 2% and 5% respectively. PON1 activity in serum was correlated with those in heparinized plasma (r = 0.994, p < 0.001) and in plasma/EDTA (r = 0.962, p < 0.001). The mean inhibition of the PON1 activity was, by EDTA/K3, 41 ± 10 %. There was not significant PON1 activity variation after 40 days of storage at -20°C or at +4 ⃞ C. There were no substantial interferences from haemoglobin, jaundice and hyperlipidemia.

Conclusion: The developed method is reliable, reproducible, and suitable. It can also be performed on heparinized plasma for the determination of PON1 activity. Hence, it may be useful for assaying PON1 activity in several intoxications such as organophosphorus, sarin, and soman nerve agents.

Paraoxonase 1 Activity and Survival in Sepsis Patients

BACKGROUND

Sepsis is a state of augmented oxidative stress and diminished antioxidant capacity. High density lipoprotein (HDL) particles were shown to possess antioxidant and anti-inflammatory properties, as well as Paraoxonase 1 (PON1), which is an enzyme that is also protective against HDL oxidation. Previous studies suggested a possible role of decreased PON1 activity or HDL levels in sepsis patients.

AIMS

The present study was designed to test a hypothesis that higher PON1 activity and HDL-cholesterol levels could predict a better survival in sepsis patients.

STUDY DESIGN

Observational study.

METHODS

Venous blood samples were collected from sepsis patients for HDL-cholesterol levels, PON1 activity and cytokine assays (TNF-α and IL-6) and Acute Physiologic and Chronic Health Evaluation II (APACHE II) scores were calculated in order to weight patients' disease severity on the day of sepsis diagnosis. Patients were followed-up until the 28(th) day for any cause intra-hospital mortality. Data were statistically analyzed for effects of study parameters on patients' survival.

RESULTS

In total, 85 patients with sepsis were included in the study. The mean age was 65.2±17.9 years and 48 were male; at the end of the 28-day follow-up period, 46 survived. TNF-α (86.9±10.5 vs 118.6±16.4) and IL-6 levels (906.7±82.7 vs 1323.1±54.3) were significantly higher in non-survivors, while PON1 activity (140.7±42.3 vs 66.7±46.6) and HDL-cholesterol levels (43.6±8.1 vs 34.5±8.9) were significantly higher in survivors (p<0.001 for all). TNF-α (r=-0.763) and IL-6 levels (r=-0.947) showed strong negative correlations, PON1 activity (r=0.644) and HDL-cholesterol levels (r=0.477) showed positive correlations with patient survival (p<0.001 for all). Survival estimates significantly favored TNF-α (Log Rank 59.5, p<0.001) and IL-6 levels (Log Rank 53.2, p<0.001) according to PON1 activity (Log Rank 5.4, p<0.03) and HDL-cholesterol levels (Log Rank 8.3, p<0.005). Regression analyses for relative contributions of parameters to survival showed that higher IL-6 levels (t: -16.489, p<0.001) were the most significant negative factor for survival, and TNF-α levels (t: -4.417, p<0.001), whereas PON1 activity had a positive effect (t:3.210, p<0.003).

CONCLUSION

The present study showed that although low PON1 activity and HDL-cholesterol levels were related to mortality, higher levels were not found to be as predictive as cytokine levels for survival.

Paraoxonase-1 enzyme activity assay for clinical samples: validation and correlation studies

BACKGROUND

Paraoxonase-1 (PON1) enzyme is reported in various types of tissues and linked to numerous pathophysiological disorders. It is a potential biomarker in many pathological conditions such as cardiovascular diseases.

MATERIAL AND METHODS

We conducted several small-scale studies to evaluate PON1 performance as affected by sample types, storage, and interferences. We also carried out short-term studies to compare the performance of the widely used PON1 assay to the similar commercially available PON1 kit assay method; sample size for the method comparison was N=40, and the number varied for other validation experiments.

RESULTS

Our studies using various types of anticoagulants show that samples collected in tubes with NaF, citrate, EDTA, clot activator, and sodium heparin have increased PON1 levels that are 49%, 24.5%, 19.8%, 11.4%, and 8%, respectively, higher compared to serum samples collected in plain tubes. However, samples collected in lithium heparin tubes demonstrated 10.4% lower PON1 levels compared to serum collected in plain tubes. Biological interference such as hemolysis has little effect on PON1 levels; however, samples spiked with lipids have shown 13% lower PON 1 levels. Our studies comparing the PON1 method commonly available for PON1 assay and a similar non-ELISA commercially available PON1 kit method showed a weak Spearman correlation coefficient of R2=0.40 for the range of 104.9-245.6 U/L.

CONCLUSIONS

The current study provides new validation data on enzyme PON1 performance. While no appreciable change was seen with storage, samples type affects the enzyme performance. Our results should encourage additional clinical studies to investigate other aspects of factors known to affect PON1 enzyme function and performance.

Interaction effects between Paraoxonase 1 variants and cigarette smoking on risk of coronary heart disease in a Singaporean Chinese population

OBJECTIVE

Paraoxonase 1 (PON1) plays an important role in reducing the risk of coronary heart disease (CHD). Smoking is known to reduce PON1 activity. We aimed to investigate the effects of interactions between PON1 variants and smoking on CHD in the Singaporean Chinese population.

METHODS

In a case-control study nested within Singapore Chinese Health Study (N=1914), subjects with and without CHD were classified into never-smokers and ever-smokers (ever smoked at least one cigarette a day for 1 year or longer). Associations at four independent SNPs at the PON1 locus (rs3735590, rs3917550, rs662, rs3917481) with CHD were evaluated using logistic regression, before/after stratification on smoking status. Interactions between smoking and PON1 variants were analyzed with likelihood ratio tests, by including the SNP*smoking interaction term in regression analyses.

RESULTS

The T allele at the coding SNP, rs662, was associated with higher risk of CHD in ever-smokers only (OR=1.35, 95% CI 1.08-1.68; adjusted P=0.036). At the miR-SNP, rs3735590, carrying at least one copy of minor allele T was associated with increased risk of CHD in a dominant manner in never-smokers only (OR=1.53, 95% CI 1.11-2.11; adjusted P=0.036). Significant interactions between two PON1 SNPs and smoking in relation to CHD risk were identified (adjusted P=0.012 for rs662; adjusted P=0.044 for rs3735590). These associations remained significant after adjustment for known CHD risk factors and upon correction for multiple tests.

CONCLUSIONS

Two PON1 SNPs, rs662 and rs3735590, were found to significantly interact with cigarette smoking to modulate the risk of CHD in the Singaporean Chinese population.

PON1 as a model for integration of genetic, epigenetic, and expression data on candidate susceptibility genes

Recent genome- and epigenome-wide studies demonstrate that the DNA methylation is controlled in part by genetics, highlighting the importance of integrating genetic and epigenetic data. To better understand molecular mechanisms affecting gene expression, we used the candidate susceptibility gene paraoxonase 1 (PON1) as a model to assess associations of PON1 genetic polymorphisms with DNA methylation and arylesterase activity, a marker of PON1 expression. PON1 has been associated with susceptibility to obesity, cardiovascular disease, and pesticide exposure. In this study, we assessed DNA methylation in 18 CpG sites located along PON1 shores, shelves, and its CpG island in blood specimens collected from newborns and 9-year-old children participating (n = 449) in the CHAMACOS birth cohort study. The promoter polymorphism, PON1_-108 , was strongly associated with methylation, particularly for CpG sites located near the CpG island (P << 0.0005). Among newborns, these relationships were even more pronounced after adjusting for blood cell composition. We also observed significant decreases in arylesterase activity with increased methylation at the same nine CpG sites at both ages. Using causal mediation analysis, we found statistically significant indirect effects of methylation (β(95% confidence interval): 6.9(1.5, 12.4)) providing evidence that DNA methylation mediates the relationship between PON1_-108 genotype and PON1 expression. Our findings show that integration of genetic, epigenetic, and expression data can shed light on the functional mechanisms involving genetic and epigenetic regulation of candidate susceptibility genes like PON1.

Organophosphate pesticide exposure, PON1, and neurodevelopment in school-age children from the CHAMACOS study

INTRODUCTION

Organophosphate (OP) pesticides remain widely used in agriculture. Previously, we reported that PON1 genotype was directly associated with neurodevelopment at age two, and that PON1 genotype may increase susceptibility to OP exposure.

OBJECTIVES

We examined the relationships of maternal and child PON1 genotype and enzyme activity levels and neurodevelopment at school age and examined their interaction with maternal dialkyl phosphate (DAP) metabolite levels to investigate differential susceptibility to OP-related neurotoxicity.

METHODS

Participants were from the CHAMACOS longitudinal birth cohort of Latino families in an agricultural region of California. We measured DAP metabolites of OP pesticides in maternal and child urine samples, and analyzed PON1192 and PON1-108 genotypes and enzyme activity [arylesterase (ARYase), paraoxonase (POase)] in maternal and child blood. We examined their association with children׳s performance on the Conners׳ Kiddie Continuous Performance Test (K-CPT) at 5 years (n=296) and the Wechsler Intelligence Scale for Children (WISC-IV) at 7 years (n=327).

RESULTS

Maternal and child PON1 genotype was not related to performance on K-CPT or WISC, although WISC scores tended to be lowest in children and children of mothers who carried the PON-108TT genotype. Pregnancy ARYase levels were positively associated with all WISC subscales (e.g., 4.0 point increase in Full Scale IQ per standard deviation increase in ARYase, 95% CI=1.6, 6.4), while pregnancy POase levels were positively associated with WISC Processing Speed only. Maternal PON1-108 weakly modified the relationship of maternal DAPS and K-CPT scores (pinteraction=0.21) and WISC verbal IQ (pinteraction=0.71). The association between DAPs and Full-Scale IQ was strongest for children of mothers with lowest-tertile ARYase levels (pinteraction=0.27). This relationship held for both diethyl and dimethyl DAPs and for all subscales of the WISC.

CONCLUSIONS

We extend our previous findings that PON1 genotype and enzyme levels may be directly related to performance on certain domains of neurodevelopment in school-age children. Lower maternal PON1 enzyme levels during pregnancy may also increase susceptibility of children to neurotoxicity from OP pesticide exposure.

Serum paraoxonase 1 (PON1) measurement: an update

Paraoxonase 1 (PON1) is a widely studied enzyme based on its protective role against poisoning by organophosphate (OP) metabolites of specific OP insecticides and in vascular disease, as well as its use as biomarker of diseases involving oxidative stress, inflammation and liver diseases.

This review provides an update about the current knowledge in the field of the analytical procedures that are used for PON1 measurements. It will be specially focused on: (a) characteristics of the different substrates used for measuring PON1, with emphasis in four aspects: toxicity, polymorphism influence, rate of hydrolysis and diagnostic performance. And (b) the technical aspects of PON1 assays, in which the reagents and reaction conditions, sources of variation, quality control systems, equipment and interferences with other esterases will be discussed.

The information provided in this review can contribute to a more accurate and safe measurements of PON1 in laboratories and encourage researchers to explore the wide areas of PON1 in veterinary medicine that are still unknown.

Plasma paraoxonase and arylesterase activities in smokers and smokeless tobacco users as Maraş powder

CONTEXT

Maraş powder (MP), a different type of smokeless tobacco (ST) prepared from a tobacco called Nicotiana rustica Linn, is widely used in the Southern Turkey. Smoking and ST cause oxidative stress (OS) in the human body. Paraoxonase (PON) and arylesterase (ARE) are antioxidant enzymes.

OBJECTIVE

To investigate the effects of MP on activities of PON, ARE, and malondialdehyde (MDA) levels in plasma and to compare these parameters in smokers and MP users (MPU).

MATERIALS AND METHODS

The study consisted of smokers, MPU, and control group (CG) neither smoking nor using MP healthy subjects. PON and ARE activities were measured spectrophotometrically using paraoxon and phenylacetate substrates, respectively.

RESULTS

PON and ARE activities were decreased whereas MDA levels were increased in tobacco groups compared to the CG. The differences of ARE and MDA values between the tobacco groups and CG were found statistically significant (p < 0.01). But no significant differences were detected between the groups in the activity of PON (p > 0.05). However, the lowest activities of the enzymes were obtained in MPU.

CONCLUSION

Our results can help to evaluate harmful effects of cigarette and ST as MP. These effects can be attributed to increased OS. Increased plasma MDA levels and decreased ARE activities may be important in assessing oxidant/antioxidant imbalance in MPU as well as smokers. Also, using of MP has harmful effects at least cigarette smoking.

Associations of PON1 and genetic ancestry with obesity in early childhood

Obesity in children has become an epidemic in the U.S. and is particularly prominent in minority populations such as Mexican-Americans. In addition to physical activity and diet, genetics also plays a role in obesity etiology. A few studies in adults and adolescents suggest a link between obesity and paraoxonase 1 (PON1), a multifunctional enzyme that can metabolize organophosphate pesticides and also has antioxidant properties. We determined PON1₁₉₂ genotype and arylesterase levels (ARYase, measure of PON1 enzyme quantity), to characterize the relationship between PON1 and obesity in young Mexican-American children (n = 373) living in an agricultural community in California. Since PON1 polymorphisms and obesity both vary between ethnic groups, we estimated proportional genetic ancestry using 106 ancestral informative markers (AIMs). Among children, PON1₁₉₂ allele frequencies were 0.5 for both alleles, and the prevalence of obesity was high (15% and 33% at ages two and five, respectively). The average proportion of European, African, and Native American ancestry was 0.40, 0.09, and 0.51, yet there was wide inter-individual variation. We found a significantly higher odds of obesity (9.3 and 2.5- fold) in PON1_192QQ children compared to PON1_192RR children at ages two and five, respectively. Similar relationships were seen with BMI Z-scores at age two and waist circumference at age five. After adjusting for genetic ancestry in models of PON1 and BMI Z-score, effect estimates for PON1₁₉₂ genotype changed 15% and 9% among two and five year old children, respectively, providing evidence of genetic confounding by population stratification. However even after adjustment for genetic ancestry, the trend of increased BMI Z-scores with increased number of PON1₁₉₂ Q alleles remained. Our findings suggest that PON1 may play a role in obesity independent of genetic ancestry and that studies of PON1 and health outcomes, especially in admixed populations, should account for differences due to population stratification.

Cholinesterase and paraoxonase (PON1) enzyme activities in Mexican-American mothers and children from an agricultural community

Exposure to organophosphate and carbamate pesticides can lead to neurotoxic effects through inhibition of cholinesterase enzymes. The paraoxonase (PON1) enzyme can detoxify oxon derivatives of some organophosphates. Lower PON1, acetylcholinesterase, and butyrylcholinesterase activities have been reported in newborns relative to adults, suggesting increased susceptibility to organophosphate exposure in young children. We determined PON1, acetylcholinesterase, and butyrylcholinesterase activities in Mexican-American mothers and their 9-year-old children (n=202 pairs) living in an agricultural community. We used Wilcoxon signed-rank tests to compare enzymatic activities among mothers and their children, and analysis of variance to identify factors associated with enzyme activities. Substrate-specific PON1 activities were slightly lower in children than their mothers; however, these differences were only statistically significant for the paraoxon substrate. We observed significantly lower acetylcholinesterase but higher butyrylcholinesterase levels in children compared with their mothers. Mean butyrylcholinesterase levels were strongly associated with child obesity status (body mass index Z scores >95%). We observed highly significant correlations among mother-child pairs for each of the enzymatic activities analyzed; however, PON1 activities did not correlate with acetylcholinesterase or butyrylcholinesterase activities. Our findings suggest that by age 9 years, PON1 activities approach adult levels, and host factors including sex and obesity may affect key enzymes involved in pesticide metabolism.

R-carrying genotypes of serum paraoxonase (PON1) 192 polymorphism and higher activity ratio are related to susceptibility against ischemic stroke

The polymorphic gene of serum paraoxonase (PON1) and its activity involved in atherosclerosis. The purpose of the study was to analyze PON1 192 Q/R polymorphism and the enzyme activities in ischemic stroke. The polymorphism as the most common polymorphism in PON1 gene coding sequence is associated with variation in the enzyme activity and vascular disease. The study included 85 stroke patients and 71 control subjects. PON1 192 polymorphism was genotyped using PCR protocol. Paraoxonase activity (Para) and arylesterase activity (Aryl) were determined spectrophotometrically using paraoxon and phenylacetate as the substrates. The QR and RR genotypes were more frequent in stroke population compared to controls, resulting in a higher frequency of the R allele in patients (0.24 vs 0.18, OR = 1.41). Patients had significantly higher Para/Aryl ratio than that of controls (P = 0.016). In stroke patients, Para/Aryl and Para/HDL ratios increased with this order: QQ < QR < RR. Hypertension significantly increased the risk of ischemic stroke by 15-fold among R-containing people, while this was significantly increased 4-fold for QQ homozygotes. Smoking increased the risk of having ischemic stroke in both QQ homozygote and QR + RR group (OR = 2.84 and OR = 2.33, respectively). In conclusion, these data highlight the importance of PON1 192 R allele and high Para/Aryl ratio in susceptibility to ischemic stroke in the population. The presence of the 192 R allele potentiates the risk of stroke especially in hypertensive people. Decreased Aryl and increased Para/Aryl, Para/HDL and Aryl/HDL ratios may be markers indicated the increased susceptibility to ischemic stroke in the population.