Can HDL cholesterol be replaced by paraoxonase 1 activity in the prediction of severe coronary artery disease in patients with type 2 diabetes?

BACKGROUND AND AIMS: Novel biomarkers are required to improve cardiovascular disease prediction in patients with type 2 diabetes (T2D) as a high-risk population. This study was conducted to examine whether coronary artery disease (CAD) risk assessment can be improved by substituting high-density lipoprotein (HDL)-bound paraoxonase 1 (PON1) activity for HDL cholesterol (HDL-C) concentration in patients with T2D. METHODS AND RESULTS: In this study, we studied 139 patients with T2D (mean age 64.12 ± 8.17 years) who underwent coronary angiographic examination. The initial rate of substrate hydrolysis was spectrophotometrically assayed in kinetic mode for measuring PON1 activity. Receiver operating characteristic (ROC) graphs are created by plotting true positivity versus false positivity. In patients with HbA1c ≥ 7%, PON1 (AUC = 0.7, p = 0.029) and nonHDL-C/PON1 (AUC = 0.75, p = 0.013) were significantly more capable of differentiating patients with CAD from those without CAD compared to HDL-C and nonHDL-C/HDL-C. Also, the predictive power of PON1 (AUC = 0.64, p = 0.029) and nonHDL-C/PON1 (AUC = 0.71, p = 0.004) were significantly higher in comparison with HDL-C and nonHDL-C/HDL-C for CAD characterization in patients aged ≥50 years. Moreover, PON1 and nonHDL-C/PON1 are associated with the incidence of CAD with an AUC of 0.7 (p = 0.026) and AUC of 0.64 (p = 0.087), respectively, among subjects with low HDL-C. CONCLUSION: PON1 and the ratio of nonHDL-C/PON1 significantly improve the prediction of severe CAD in T2D patients and in patients with HbA1c ≥ 7%, age ≥50 years, or low HDL-C. PON1 activity and lipid ratios using this enzyme may be valuable as substitutes of HDL-C for increasing clinical efficacies in cardiovascular risk assessment.

Paraoxonase-1 (PON-1) Arylesterase Activity Levels in Patients with Coronary Artery Disease: A Meta-Analysis.

Aim: To review and compare the PON-1 arylesterase activity between coronary artery disease (CAD) and non-CAD patients. Methods: Data were obtained by searching MEDLINE and Scopus for all investigations published between January 1, 2000 and March 1, 2021 comparing PON-1 arylesterase activity between CAD and controls. Results: Twenty studies, based on 5417 patients, met the inclusion criteria and were included in the analysis. A random effect model revealed that PON-1 arylesterase activity was significantly lower in the CAD group compared to controls (SMD = -0.587, 95%CI = -0.776 to -0.339, p < 0.0001, I 2 = 92.3%). In CAD patients, the PON-1 arylesterase activity was significantly higher among CAD patients without diabetes mellitus (DM) compared to those with diabetes (SMD: 0.235, 95% CI: 0.014 to 0.456, p = 0.03, I 2 = 0%). Conclusions: PON-1 activity is significantly lower in CAD patients, and those without DM presented a significantly higher PON-1 arylesterase activity.

Epigenetics of paraoxonases.

PURPOSE OF REVIEW: Studies have shown the three-member paraoxonase (PON) multigene family to be involved in the development of a large variety of diseases with an inflammatory component. Environmental factors such as lifestyle-related factors differ widely between populations and it is important to consider that their impacts may be exerted through the epigenetic mechanisms, which connect genes, the environment and disease development and are a potential therapeutic avenue. RECENT FINDINGS: In the review period, very little was published on epigenetics of PON2 or PON3, mostly on their diagnostic value in cancer by measuring methylation levels of these genes. However, the picture is more promising with PON1. Here, several studies have linked the epigenetic regulation of PON1 to various metabolic processes and particularly to the development of several diseases, including stroke, heart disease, aortic valve stenosis and chronic obstructive pulmonary disease. SUMMARY: Studies into the epigenetic regulation of the PON family are in their infancy. However, recent studies linking epigenetic regulation of PON1 to disease development will encourage further research and open up the possibility for new potential therapeutic interventions.

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.

Phenotypes and concentration of PON1 in cardiovascular disease: The role of nutrient intake.

BACKGROUND AND AIMS: Paraoxonase 1 (PON1) is considered to play a crucial role as an anti-atherosclerotic factor. The PON1 activity is affected by genetic polymorphisms, environmental factors, age, sex, lifestyle, pharmaceutical drugs, and dietary factors. The aim of this study was to evaluate the association between macro- and micronutrients as well as PON1 concentration and activities in patients with cardiovascular diseases (CVD), cardiovascular risk factors but no CVD (CRF), and in healthy controls (control group). METHODS AND RESULTS: A case-control study was carried out with 356 volunteers from the Mexican Institute of Social Security, Mexico. Clinical parameters, lipid profile, PON1 activities (AREase, LACase, CMPAase and PONase), and PON1 concentration were evaluated. There was a differential intake of macro- and micronutrients among the study groups. The intake of proteins and carbohydrates was higher in the CVD group than in the CFR and control groups (p < 0.05). AREase, LACase, and CMPAase activities and PON1 concentration were lowest in the CVD group. CONCLUSION: LACase and CMPAase activities, as well as PON1 concentration, could be included in the battery of CVD predictive biomarkers in the Mexican population.

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.

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.

Unexpectedly higher diazoxon hydrolysis by serum paraoxonase-1 in coronary heart disease.

OBJECTIVES: Low serum PON1 activities (paraoxon, phenyl-acetate or lactone substrates) are associated with coronary heart disease (CHD). We investigated the rate of diazoxon hydrolysis by PON1 in a population with CHD. DESIGN & METHODS: Case- control study of 410 subjects with CHD and 274 controls. PON1 activity towards paraoxon and diazoxon, PON1 serum concentration and the PON1-55 and 192 polymorphisms were determined. RESULTS: There were no differences in the distribution of the PON1-55 or PON1-192 genotypes between the CHD and controls, however, PON1 activity towards diazoxon (DIAZ) was significantly (+160%) higher in CHD. In the control population, DIAZ was significantly different between the PON1-192 genotypes in the order QQ > QR > RR (P < .001). However, in CHD the order was QQ > QR = RR. In CHD DIAZ was significantly higher in all the PON1-192 and 55 genotypes compared to controls. In both populations DIAZ was significantly different between the PON1-55 genotypes in the order LL > LM > MM (P < .001). CONCLUSION: If this result can be replicated in other studies and/or with other PON1 substrates, there may be major diagnostic and mechanistic implications for the relationship of PON1 and CHD.

Transcriptional regulation of human Paraoxonase 1 by nuclear receptors.

Paraoxonase 1 (PON1) is a calcium-dependent lactonase synthesized primarily in the liver and secreted into the plasma, where it is associates with high density lipoproteins (HDL). PON1 acts as antioxidant preventing low-density lipoprotein (LDL) oxidation, a process considered critical in the initiation and progression of atherosclerosis. Additionally, PON1 hydrolyzes and detoxifies some toxic metabolites of organophosphorus compounds (OPs). Thus, PON1 activity and expression levels are important for determining susceptibility to OPs intoxication and risk of developing diseases related to inflammation and oxidative stress. Increasing evidence has demonstrated the modulation of PON1 expression by many factors is due to interaction with nuclear receptors (NRs). Here, we briefly review the studies in this area and discuss the role of nuclear receptors in the regulation of PON1 expression, as well as how understanding these mechanisms may allow us to manipulate PON1 levels to improve drug efficacy and treat disease.

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.

Targeting paraoxonase-1 in atherosclerosis.

INTRODUCTION: Paraoxonase-1 (PON1) is a Ca(2+) dependent, high-density lipoprotein-associated lactonase which is capable of retarding/inhibiting low-density lipoprotein (LDL) oxidation. LDL oxidation is believed to be central to the initiation and progression of atherosclerosis, therefore, PON1 is considered to be atheroprotective. AREAS COVERED: Relevant literature on PON1 was identified in PubMed. Here, we discuss the background to research on PON1 in atherosclerosis, the evidence for and against PON1 being atheroprotective, potential mechanisms of this atheroprotection and current knowledge on human PON1 regulation. EXPERT OPINION: Although current knowledge on PON1 indicates it to be atheroprotective, further clinical and basic studies are warranted to show that PON1 is causally linked to atherosclerosis, how it is atheroprotective and how it is regulated in vivo in humans.

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 is not associated with coronary artery calcification in type 2 diabetes: results from the PREDICT study.

OBJECTIVES: To determine any association between serum paraoxonase-1 (PON1) activity, protein and coding region genetic polymorphisms and coronary artery calcification (CACS) and to determine factors which modulate serum PON1 in type 2 diabetes (T2DM). METHODS AND RESULTS: 589 patients (419 Caucasian, 120 South Asian, 50 other) from the PREDICT Study were investigated. All patients were asymptomatic for coronary disease and had established T2DM. CACS, lipids, lipoproteins, inflammatory markers, insulin resistance and PON1 activity, concentration and Q192R and L55M genotypes were measured. Independent associations were: 1) PON1 activity negatively with insulin resistance, triglycerides and PON1-55 genotype and positively with PON1-192 genotype; 2) PON1 concentration negatively with Caucasian ethnicity, duration of diabetes and statin use and positively with plasma creatinine and PON1-192 genotype. There was no association between CACS and any of the PON1 activity, concentration or genotype and this finding was not different in the various ethnic groups within the PREDICT study. CONCLUSION: PON1 is modulated by a number of factors, some of which are reported here for the first time, including ethnicity and insulin resistance in subjects with T2DM. No association between CACS and PON1 was found.

Coincubation of PON1, APO A1, and LCAT increases the time HDL is able to prevent LDL oxidation.

The inhibition of low-density lipoprotein (LDL) oxidation by high-density lipoprotein (HDL) is a major antiatherogenic property of this lipoprotein. This activity is due, in part, to HDL associated proteins. However, whether these proteins interact in the antioxidant activity of HDL is unknown. LDL was incubated with apolipoprotein A1 (apo A1), lecithin:cholesterol acyltransferase (LCAT), and paraoxonase-1 (PON1) alone or in combination, in the presence or absence of HDL under oxidizing conditions. LDL lipid peroxide concentrations were determined. Apo A1, LCAT, and PON1 all inhibit LDL oxidation in the absence of HDL and enhance the ability of HDL to inhibit LDL oxidation. Their effect was additive rather than synergistic; the combination of these proteins significantly enhanced the length of time LDL was protected from oxidation. This seemed to be due to the ability of PON1 to prevent the oxidative inactivation of LCAT. Apo A1, LCAT, and PON1 can all contribute to the antioxidant activity of HDL in vitro. The combination of apo A1, LCAT, and PON1 prolongs the time that HDL can prevent LDL oxidation, due, at least in part, to the prevention LCAT inactivation.

Effect of dilution on high-density lipoprotein associated paraoxonase-1 activity.

OBJECTIVES: To investigate the effects of dilution on high-density lipoprotein (HDL) associated paraoxonase-1 (PON1) activity. DESIGN AND METHODS: HDL was prepared by ultracentrifugation, diluted with TRIS buffer pH 8.2 (0-128 fold) and assayed spectrophotometrically for PON1 activity using paraoxon and phenyl acetate. RESULTS: HDL-PON1 activity increased progressively with dilution to over 200% of the undiluted activity by 128 fold dilution (P<0.001). Conversely HDL size decreased. CONCLUSION: These results indicate the urgent need to standardise conditions for measuring PON1 activity.

Cholesteryl-ester transfer protein enhances the ability of high-density lipoprotein to inhibit low-density lipoprotein oxidation.

Therapeutic strategies to increase high-density lipoprotein (HDL) to treat or prevent vascular disease include the use of cholesteryl-ester transfer protein (CETP) inhibitors. Here, we show, to the best of our knowledge for the first time, that addition of CETP to HDL enhances the ability of HDL to inhibit low-density lipoprotein oxidation by ∼ 30% for total HDL and HDL(2) (both P < 0.05) and 75% for HDL(3) (P < 0.01). Therefore, CETP inhibition may be detrimental to the antiatherosclerotic properties of HDL, and these findings may partly explain the failure of the CETP inhibitor, torcetrapib, treatment to retard vascular disease despite large increases in HDL, in addition to its "off target" toxicity, a property which appears not to be shared by other members of this class of CETP inhibitor currently under clinical trial. Further, detailed studies are urgently required.

Immunohistochemical analysis of paraoxonases-1 and 3 in human atheromatous plaques.

BACKGROUND: The paraoxonase (PON) enzyme family comprising PON1, PON2 and PON3 are antioxidant enzymes that degrade bioactive oxidised lipids and are thus antiatherogenic. MATERIALS AND METHODS: We investigated the localisation of the PON proteins during the development of atherosclerosis by immunohistochemical analysis. RESULTS: In normal aortas, PON1 and PON3 were localised to smooth muscle cells (SMC) and endothelial cells. PON3 staining was stronger than that of PON1. During atherosclerosis development, SMC staining for PON1 and PON3 was greatly reduced, while macrophage staining for both proteins increased with PON1 predominating. Macrophage staining for PON1 and PON3 was significantly and positively related to the amount of aortic inflammation (both P<0·001). CONCLUSIONS: Our data add support to the growing body of evidence for a cellular protective effect of PON1 and PON3 against the proinflammatory/proatherosclerotic effects of lipid peroxidation.

Human tissue distribution of paraoxonases 1 and 2 mRNA.

We have studied the distribution of mRNA for paraoxonases (PON) 1 and 2 in 24 human tissues using Gene Expression Panels. PON1 mRNA was restricted to adult kidney, liver, and colon as well as fetal liver, whereas PON2 mRNA was more widely distributed in adult human brain, heart, kidney, spleen, liver, colon, lung, small intestine, muscle, stomach, testis, placenta, salivary, thyroid and adrenal glands, pancreas, skin, and bone marrow, as well as fetal brain and liver. PON2 mRNA was not found in ovary, uterus, or plasma leukocytes using the panels. However, using real time PCR, we found PON2 mRNA expression in human plasma leukocytes. There were differences between the tissue distribution of mRNAs found in this study and the immunohistochemical localization of the PON1 and PON2 proteins reported previously. In particular, PON1 protein is much more widely distributed than its mRNA, possibly indicating the delivery of PON1 to various tissues by HDL. In addition, differences between PON2 mRNA and protein distributions could be due to missence mutations in the PON2 gene, causing nontranslation of mRNA to protein in some tissues.