Human PON3, Effects Beyond the HDL

Pleiotropic functions and clinical importance of circulating HDL-PON1 complex

High density lipoprotein (HDL) functions are mostly mediated through a complex proteome, particularly its enzymes. HDL can provide a scaffold for the assembly of several proteins that affect each other's function. HDL particles, particularly small, dense HDL3, are rich in paraoxonase 1 (PON1), which is an important enzyme in the functionality of HDL, so the antioxidant and antiatherogenic properties of HDL are largely attributed to this enzyme. There is an increasing need to represent a valid, reproducible, and reliable method to assay HDL function in routine clinical laboratories. In this context, HDL-associated proteins may be key players; notably PON1 activity (its arylesterase activity) may be a proper candidate because its decreased activity can be considered an important risk factor for HDL dysfunctionality. Of note, automated methods have been developed for the measurement of serum PON1 activity that facilitates its assay in large sample numbers. Arylesterase activity is proposed as a preferred activity among the different activities of PON1 for its assay in epidemiological studies. The binding of PON1 to HDL is critical for the maintenance of its activity and it appears apolipoprotein A-I plays an important role in HDL-PON1 interaction as well as in the biochemical and enzymatic properties of PON1. The interrelationships between HDL, PON1, and HDL's other components are complex and incompletely understood. The purpose of this review is to discuss biochemical and clinical evidence considering the interactions of PON1 with HDL and the role of this enzyme as an appropriate biomarker for HDL function as well as a potential therapeutic target.

Paraoxonase 3: Structure and Its Role in Pathophysiology of Coronary Artery Disease

Spanning three decades in research, Paraoxonases (PON1) carried potential of dealing with neurotoxicity of organophosphates entering the circulation and preventing cholinergic crisis. In the past few years, the Paraoxonase multigene family (PON1, PON2, PON3) has been shown to play an important role in pathogenesis of cardiovascular disorders including coronary artery disease (CAD). The PON genes are clustered in tandem on the long arm of human chromosome 7 (q21, 22). All of them have been shown to act as antioxidants. Of them, PON3 is the least studied member as its exact physiological substrate is still not clear. This has further led to limitation in our understanding of its role in pathogenesis of CAD and development of the potential therapeutic agents which might modulate its activity, expression in circulation and tissues. In the present review, we discuss the structure and activity of human PON3 enzyme and its Single nucleotide variants that could potentially lead to new clinical strategies in prevention and treatment of CAD.

Paraoxonase 3 inhibits cell proliferation and serves as a prognostic predictor in hepatocellular carcinoma

Paraoxonase 3 (PON3) exerts prominent anti-inflammation and anti-oxidation properties mainly at the cellular level, and is primarily expressed in the liver. However, its role in HCC remains unexplored. Here, we investigated the expression pattern, clinical significance, and function of PON3 in HCC. PON3 mRNA and protein levels were respectively determined in two large cohorts using quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC) of tissue microarray. We found that PON3 was downregulated in most HCCs. Kaplan-Meier and log-rank test showed that PON3 downregulation predicted shorter recurrence-free survival (RFS) and overall survival (OS) time in all HCC patients, especially early-stage HCC patients. Cox regression analysis revealed that the PON3 downregulation was an independent risk factor for RFS and OS. Gain- and loss-of-function experiments revealed that PON3 suppressed cell proliferation in vivo and in vitro, which was attributed to its cell-cycle arrest effect. In addition, microarray analysis showed that some pro-proliferative genes were elevated when PON3 was knockdown, and these genes possibly involved in the underlying mechanisms. In conclusion, our studies reveal the cell proliferation inhibitory function of PON3 and offer a potential prognostic predictor and therapeutic target for HCC.

Paraoxonase activities in human follicular fluid: role in follicular maturation

The paraoxonases (PONs) are antioxidant enzymes associated with beneficial effects against several diseases and some exposures. Little is known, however, about the role of PONs in human reproduction. This work was conducted to investigate whether any association existed between the activities of the PON enzymes (1, 2, and 3) with the follicular size and fertility parameters in assisted reproduction. The study included 100 subfertile women (patients) and 55 proven fertile women (oocyte donors), all undergoing an ovarian stimulation cycle. Follicular fluid from small (diameter <12 mm) and large (diameter ≥18 mm) follicles was collected from each woman. The PONs were quantified in follicular fluid by immunoblotting. PON1 arylesterase and paraoxonase, PON2 methyl paraoxonase and PON3 simvastatinase activities from both donors and patients were significantly higher (P < 0.001) in follicular fluid from large follicles compared with small ones. In large follicles, PON3 activity was significantly higher (P < 0.01) in donors compared with patients. Follicular fluid PON1 arylesterase and paraoxonase activity was positively correlated with the number of retrieved oocytes in donors. This study shows an increase in the activities of PONs with follicle size, thus providing indirect evidence for the role of PONs in follicle maturation.

A long-term high-fat, high-sucrose diet in Bama minipigs promotes lipid deposition and amyotrophy by up-regulating the myostatin pathway

Skeletal muscle is as an important regulator of blood glucose and glycolipid metabolism and is closely related to motor ability. The underlying mechanisms by which dietary ectopic lipids in skeletal muscle prevents muscle growth remain elusive. We utilized miniature Bama swine as a model to mimic human obesity using prolonged dietary induction. After 23 months on a high-fat, high-sucrose diet, metabolic disorders were induced in the animals, which exhibited increased body weight, extensive lipid deposition in the skeletal muscle and amyotrophy. Microarray profiles demonstrated the up-regulation of genes related to fat deposition and muscle growth inhibition. We outline a clear potential pathway that in combination with increased 11β-hydroxysteroid dehydrogenase type 1, promotes expression of a major inhibitor, myostatin, by converting corticosterone to cortisol, which leads to the growth inhibition of skeletal muscle. This research provides new insights into the treatment of muscle diseases induced by obesity.

Paraoxonase activity as a marker of exposure to xenobiotics in tobacco smoke

The paraoxonase (PON) family is composed of 3 proteins (PON1, PON2, and PON3), each of which plays a crucial role in the body, displaying antioxidant, anti-inflammatory, and antiatherosclerotic properties. The activities and properties of PON proteins can be modulated by a number of environmental factors, including cigarette smoke. In the present article, a review of existing literature is employed to analyze both the direct and the indirect impact of cigarette smoking on the activity of members of the PON family. Cigarette smoking leads to direct inhibition of the hydrolytic activity of PON enzymes by modification of thiol groups, by the reactions of free radicals, or by inhibiting enzyme-active regions with heavy metals. It has been shown that cigarette smoking correlates with a decrease in high-density lipoprotein (HDL) concentration as well as with an increase in other components of the lipid profile (low-density lipoprotein (LDL), triglycerides, and total cholesterol). By decreasing HDL levels, cigarette smoking likely acts indirectly to induce a decline in PON1 activity. Inhibition of PON1 activity by smoking is a reversible process after cessation of exposure to the xenobiotics in tobacco smoke.

Association between paraoxonases gene expression and oxidative stress in hepatotoxicity induced by CCl4

Objectives. The purpose of the study is to evaluate the hepatoprotective effect of rutin in carbon tetrachloride- (CCl₄-) induced liver injuries in rat model. Methods. Forty male Wistar albino rats were divided into four groups. Group I was the control group and received dimethyl sulphoxide (DMSO) and olive oil. Group II received rutin. Groups III was treated with CCl₄. Group IV was administered rutin after 48 h of CCl₄ treatment. Liver enzymes level, lipid profile, lipid peroxidation, and hydrogen peroxide were measured. The genes expression levels were monitored by real time RT-PCR and western blot techniques. Results. CCl₄ group showed significant increase in alanine aminotransferase (ALT), aspartate aminotransferase (AST), thiobarbituric acid reactive substances (TBAR), hydrogen peroxide (H₂O₂), and lipid profile and a significant decrease in glutathione peroxidase (GPx), glutathione S transferase (GST), catalase (CAT), paraoxonase-1 (PON-1), paraoxonase-3 (PON-3), peroxisome proliferator activated receptor delta (PPAR-δ), and ATP-binding cassette transporter 1 (ABAC1) genes expression levels. Interestingly, rutin supplementation completely reversed the biochemical and gene expression levels induced by CCl₄ to control values. Conclusion. CCl₄ administration causes aberration of genes expression levels in oxidative stress pathway resulting in DNA damage and hepatotoxicity. Rutin causes hepatoprotective effect through enhancing the antioxidant genes.

Modulation of paraoxonases during infectious diseases and its potential impact on atherosclerosis

The paraoxonase (PON) gene family includes three members, PON1, PON2 and PON3, aligned in tandem on chromosome 7 in humans and on chromosome 6 in mice. All PON proteins share considerable structural homology and have the capacity to protect cells from oxidative stress; therefore, they have been implicated in the pathogenesis of several inflammatory diseases, particularly atherosclerosis. The major goal of this review is to highlight the modulation of each of the PONs by infective (bacterial, viral and parasitic) agents, which may shed a light on the interaction between infectious diseases and PONs activities in order to effectively reduce the risk of developing atherosclerosis.

Protectors or Traitors: The Roles of PON2 and PON3 in Atherosclerosis and Cancer

Cancer and atherosclerosis are major causes of death in western societies. Deregulated cell death is common to both diseases, with significant contribution of inflammatory processes and oxidative stress. These two form a vicious cycle and regulate cell death pathways in either direction. This raises interest in antioxidative systems. The human enzymes paraoxonase-2 (PON2) and PON3 are intracellular enzymes with established antioxidative effects and protective functions against atherosclerosis. Underlying molecular mechanisms, however, remained elusive until recently. Novel findings revealed that both enzymes locate to mitochondrial membranes where they interact with coenzyme Q10 and diminish oxidative stress. As a result, ROS-triggered mitochondrial apoptosis and cell death are reduced. From a cardiovascular standpoint, this is beneficial given that enhanced loss of vascular cells and macrophage death forms the basis for atherosclerotic plaque development. However, the same function has now been shown to raise chemotherapeutic resistance in several cancer cells. Intriguingly, PON2 as well as PON3 are frequently found upregulated in tumor samples. Here we review studies reporting PON2/PON3 deregulations in cancer, summarize most recent findings on their anti-oxidative and antiapoptotic mechanisms, and discuss how this could be used in putative future therapies to target atherosclerosis and cancer.

Studies on protective effects of human paraoxonases 1 and 3 on atherosclerosis in apolipoprotein E knockout mice

Paraoxonase (PON) possesses antiatherogenic potentials, but the distinct functions of PON members in alleviating atherosclerosis are not yet clear. This study aimed to evaluate the protective effects of hPON1 and hPON3 against atherosclerosis, and thereby exploring their synergistic mechanism in atherosclerosis development. We generated the recombinant adenovirus AdPON1 and AdPON3, which were capable of expressing hPON1 and hPON3. After AdPON1 and AdPON3 were injected intravenously into 5-week-old apolipoprotein E knockout mice, abundant hPON1 and hPON3 mRNA expression levels were detected. However, increase in serum lactonase activity was detected only in AdPON1-treated mice. Serum antioxidation and anti-inflammation capabilities in AdPON1-treated mice, reflected by malondialdehyde, total antioxidant capability and tumor necrosis factor-alpha levels, were greatly enhanced, whereas those in AdPON3-treated mice were not significantly affected. Nevertheless, histological analysis revealed that adenovirus-mediated expression of hPON1, hPON3 or both of them reduced atherosclerotic plaque area to a similar extent. Although no synergistic mechanism was detected in reducing arterial lesion size, hPON1 and hPON3 showed synergistic effects on promoting macrophage cholesterol efflux. In conclusion, hPON1 and hPON3 exhibited similar potentials in reducing arterial lesion size, but they exerted antiatherogenic effects in distinct ways.

High-density lipoprotein metabolism and the human embryo

BACKGROUND

High-density lipoprotein (HDL) appears to be the dominant lipoprotein particle in human follicular fluid (FF). The reported anti-atherogenic properties of HDL have been attributed in part to reverse cholesterol transport. The discoveries of the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette A1 lipid (ABCA1) transporter have generated studies aimed at unraveling the pathways of HDL biogenesis, remodeling and catabolism. The production of SR-BI and ABCA1 knockout mice as well as other lipoprotein metabolism-associated mutants has resulted in reduced or absent fertility, leading us to postulate the existence of a human hepatic-ovarian HDL-associated axis of fertility. Here, we review an evolving literature on the role of HDL metabolism on mammalian fertility and oocyte development.

METHODS

An extensive online search was conducted of published articles relevant to the section topics discussed. All relevant English language articles contained in Pubmed/Medline, with no specific time frame for publication, were considered for this narrative review. Cardiovascular literature was highly cited due to the wealth of relevant knowledge on HDL metabolism, and the dearth thereof in the reproductive field.

RESULTS

Various vertebrate models demonstrate a role for HDL in embryo development and fertility. In our clinical studies, FF levels of HDL cholesterol and apolipoprotein AI levels were negatively associated with embryo fragmentation, but not with embryo cell cleavage rate. However, the HDL component, paraoxonase 1 arylesterase activity, was positively associated with embryo cell cleavage rate.

CONCLUSIONS

HDL contributes to intra-follicular cholesterol homeostasis which appears to be important for successful oocyte and embryo development.

Modulation of paraoxonase 1 and 3 expression after moderate exercise training in the rat

Paraoxonases (PONs) are a small family of antioxidant enzymes whose antiatherogenic activity is well known. The aim of the present study was the evaluation of the effects of moderate aerobic training on their expression using a rat model. In order to discriminate between PON1 and PON3 enzymatic activity, we took advantage of some differences in their substrate preferences. PON1 and PON3 enzymatic activities and their protein levels were analyzed in plasma and in liver microsomes, and their mRNA levels in the liver. Exercise training did not affect PON1 expression or enzymatic activity but increased PON3 mRNA, protein levels, and enzymatic activity. Training also induced variations in plasma membrane composition, including an increase in polyunsaturated and a decrease in mono- and di-unsaturated fatty acids. On the other hand, acute exercise inhibited PON activities while increasing PON3 protein content in liver microsomes and reversing the relative composition in mono-, di-, and poly-unsaturated fatty acids, suggesting that physical stress, by altering membrane composition, may impair PON release from liver membranes. In conclusion, we documented, for the first time, the presence of PON3 in rat serum and, notably, found that the upregulation of PON3, rather than PON1, appears to be associated with physical training.

Determinants of variation in human serum paraoxonase activity

Paraoxonase-1 (PON1) is associated with high-density lipoprotein (HDL) particles and is believed to contribute to antiatherogenic properties of HDLs. We assessed the determinants of PON1 activity variation using different substrates of the enzyme. PON1 activity in serum samples from 922 participants in the San Antonio Family Heart Study was assayed using a reliable microplate format with three substrates: paraoxon, phenyl acetate and the lactone dihydrocoumarin. There were major differences among results from the three substrates in degree of effect by various environmental and genetic factors, suggesting that knowledge of one substrate activity alone may not provide a complete sense of PON1 metabolism. Three significant demographic covariates (age, smoking status and contraceptive usage) together explained 1-6% of phenotypic variance, whereas four metabolic covariates representing lipoprotein metabolism (apoAII, apoAI, triglycerides and non-HDL cholesterol) explained 4-19%. Genes explained 65-92% of phenotypic variance and the dominant genetic effect was exerted by a locus mapping at or near the protein structural locus (PON1) on chromosome 7. Additional genes influencing PON1 activity were localized to chromosomes 3 and 14. Our study identified environmental and genetic determinants of PON1 activity that accounted for 88-97% of total phenotypic variance, suggesting that few, if any, major biological determinants are unrepresented in the models.