Probucol up-regulates paraoxonase 1 expression in hepatocytes of hypercholesterolemic rabbits

HDL and Cholesterol Ester Transfer Protein (CETP)

Cholesterol ester transfer protein (CETP) is important clinically and is one of the major targets in cardiovascular disease studies. With high conformational flexibility, its tunnel structure allows unforced movement of high-density lipoproteins (HDLs), VLDLs, and LDLs. Research in reverse cholesterol transports (RCT) reveals that the regulation of CETP activity can change the concentration of cholesteryl esters (CE) in HDLs, VLDLs, and LDLs. These molecular insights demonstrate the mechanisms of CETP activities and manifest the correlation between CETP and HDL. However, animal and cell experiments focused on CETP give controversial results. Inhibiting CETP is found to be beneficial to anti-atherosclerosis in terms of increasing plasma HDL-C, while it is also claimed that CETP weakens atherosclerosis formation by promoting RCT. Currently, the CETP-related drugs are still immature. Research on CETP inhibitors is targeted at improving efficacy and minimizing adverse reactions. As for CETP agonists, research has proved that they also can be used to resist atherosclerosis.

Systematic Review of Metabolic Syndrome Biomarkers: A Panel for Early Detection, Management, and Risk Stratification in the West Virginian Population

INTRODUCTION

Metabolic syndrome represents a cluster of related metabolic abnormalities, including central obesity, hypertension, dyslipidemia, hyperglycemia, and insulin resistance, with central obesity and insulin resistance in particular recognized as causative factors. These metabolic derangements present significant risk factors for cardiovascular disease, which is commonly recognized as the primary clinical outcome, although other outcomes are possible. Metabolic syndrome is a progressive condition that encompasses a wide array of disorders with specific metabolic abnormalities presenting at different times. These abnormalities can be detected and monitored via serum biomarkers. This review will compile a list of promising biomarkers that are associated with metabolic syndrome and this panel can aid in early detection and management of metabolic syndrome in high risk populations, such as in West Virginia.

METHODS

A literature review was conducted using PubMed, Science Direct, and Google Scholar to search for markers related to metabolic syndrome. Biomarkers searched included adipokines (leptin, adiponectin), neuropeptides (ghrelin), pro-inflammatory cytokines (IL-6, TNF-α), anti-inflammatory cytokines (IL-10), markers of antioxidant status (OxLDL, PON-1, uric acid), and prothrombic factors (PAI-1).

RESULTS

According to the literature, the concentrations of pro-inflammatory cytokines (IL-6, TNF-α), markers of pro-oxidant status (OxLDL, uric acid), and prothrombic factors (PAI-1) were elevated in metabolic syndrome. Additionally, leptin concentrations were found to be elevated in metabolic syndrome as well, likely due to leptin resistance. In contrast, concentrations of anti-inflammatory cytokines (IL-10), ghrelin, adiponectin, and antioxidant factors (PON-1) were decreased in metabolic syndrome, and these decreases also correlated with specific disorders within the cluster.

CONCLUSION

Based on the evidence presented within the literature, the aforementioned biomarkers correlate significantly with metabolic syndrome and could provide a minimally-invasive means for early detection and specific treatment of these disorders. Further research is encouraged to determine the efficacy of applying these biomarkers to diagnosis and treatment in a clinical setting.

Did we abandon probucol too soon?

PURPOSE OF REVIEW

Probucol is a potent antioxidative drug that has been used for prevention and treatment of atherosclerotic cardiovascular diseases and xanthoma. Probucol has been used as a lipid-lowering drug for a long time especially in Japan, although Western countries quitted its use because of the reduction in serum HDL-cholesterol (HDL-C). This review highlights both basic and clinical studies that provide new insights into the pleiotropic effects of probucol.

RECENT FINDINGS

Recently, the mechanisms for the pharmacologic actions of probucol have been elucidated at the molecular level with a special focus on HDL metabolism and its functions. Probucol enhances plasma cholesteryl ester transfer protein activity and hepatic scavenger receptor class B type I, causing a decrease in HDL-C. It also accelerates the antioxidative function of HDL via increase in paraoxonase 1 activity. Recent retrospective analyses of probucol-treated patients with heterozygous familial hypercholesterolemia and those after coronary revascularization demonstrated a strong beneficial effect of probucol on secondary prevention of cardiovascular events and mortality.

SUMMARY

Probucol has pleiotropic and beneficial therapeutic effects on cardiovascular system. Although statins are effective for lowering LDL-cholesterol (LDL-C) and reducing coronary heart disease risk, probucol should be considered as an option in case statins are not effective.

Antioxidant and lipid-regulating effects of probucol combined with atorvastatin in patients with acute coronary syndrome

OBJECTIVE

To investigate the effects of probucol combined with atorvastatin on the serum oxidation index and lipid levels in patients diagnosed with acute coronary syndrome (ACS).

METHODS

We randomly assigned 126 ACS patients (77 males and 49 females) to the control group (atorvastatin 20 mg/day, n=62) or the treatment group (atorvastatin 20 mg/day and probucol 750 mg/day, n=64). All the patients were followed up for 12 weeks. As oxidization indices, we measured the serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), oxidized LDL (ox-LDL), and paraoxonase-1 (PON1) before and after treatment. We also monitored the adverse effects of the drugs during the treatment.

RESULTS

At baseline, there were no obvious differences (P>0.05) between the two groups (including age, gender, etc.). After 12 weeks of treatment, the ox-LDL levels in the treatment group were significantly lower while PON1 levels were significantly higher than those in the control group. There were no statistically significant difference between the two groups with respect to the side effects (P<0.05).

CONCLUSIONS

The combined use of atorvastatin and probucol in ACS patients could reduce ox-LDL expression and increase PON1 expression more effectively than use atorvastatin alone.

Pharmacogenetics of paraoxonase activity: elucidating the role of high-density lipoprotein in disease

PON1 is a key component of high-density lipoproteins (HDLs) and is at least partially responsible for HDL's antioxidant/atheroprotective properties. PON1 is also associated with numerous human diseases, including cardiovascular disease, Parkinson's disease and cancer. In addition, PON1 metabolizes a broad variety of substrates, including toxic organophosphorous compounds, statin adducts, glucocorticoids, the likely atherogenic L-homocysteine thiolactone and the quorum-sensing factor of Pseudomonas aeruginosa. Numerous cardiovascular and antidiabetic pharmacologic agents, dietary macronutrients, lifestyle factors and antioxidant supplements affect PON1 expression and enzyme activity levels. Owing to the importance of PON1 to HDL function and its individual association with diverse human diseases, pharmacogenomic interactions between PON1 and the various factors that alter its expression and activity may represent an important therapeutic target for future investigation.

Serum lipid peroxidation markers are correlated with those in brain samples in different stress models

OBJECTIVE

Stress can stimulate increased production of oxygen radicals. We investigated the correlations between serum levels of lipid peroxidation markers and those in brain samples in different stress models.

METHODS

Animals (n = 96) were divided equally into eight groups: a control group and groups treated with vitamin E (Vit E); exposed to immobilisation stress; exposed to immobilisation stress and treated with Vit E; exposed to cold stress; exposed to cold stress and treated with Vit E; exposed to both immobilisation and cold stress; and a final group exposed to both immobilisation and cold stress and treated with Vit E. Thiobarbituric acid-reactive substance (TBARS) in brain samples and levels of TBARS, corticosterone, conjugated dienes (CD), lipids, and paraoxonase-1 (PON1) activity in serum were analysed.

RESULTS

Serum corticosterone (p < 0.001), CD (p < 0.05), lipid (p < 0.05) levels, and brain TBARS (p < 0.05) levels were significantly higher in all stress groups than in controls, and the elevated levels were reversed in the Vit E-treated stress groups (p < 0.05). Serum PON1 activity was not different among the groups (p > 0.05). Serum TBARS levels increased significantly in all stress groups (p < 0.05), but this elevation was only reversed in the group exposed to both immobilisation and cold stress and treated with Vit E (p < 0.001).

CONCLUSION

These results suggest that serum levels of lipid peroxidation markers can be determined readily and may be useful as indicators to evaluate the effects of oxidative stress in the brain.

Inhibition of suicidal erythrocyte death by probucol

Probucol, an antioxidant and anti-inflammatory agent counteracting atherosclerosis and restenosis, is partially effective by influencing suicidal cell death or apoptosis. In analogy to apoptosis of nucleated cells, suicidal death of erythrocytes or eryptosis is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptosis is stimulated by increase in cytosolic Ca(2+) activity, for example, after energy depletion or oxidative stress. The present study explored whether probucol influences eryptosis. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter (FSC), and cytosolic Ca(2+) concentration from fluo-3 fluorescence in flow cytometry. As a result, energy depletion (48-hour glucose removal) increased annexin-V-binding, decreased FSC, and increased fluo-3 fluorescence. Probucol (≤30 μM) did not significantly modify annexin-V-binding, FSC, or fluo-3 fluorescence in the presence of glucose but (at ≥5 μM) blunted the effect of glucose depletion on annexin-V-binding. Probucol (≥20 μM) only slightly blunted the effects of glucose depletion on FSC and fluo-3 fluorescence. Ca(2+) ionophore ionomycin (1 μM) and oxidative stress (30-minute exposure to 0.3 mM of tert-butylhydroperoxide) increased annexin-V-binding, effects again blunted by 30 μM of probucol. In conclusion, probucol blunts cell membrane scrambling after energy depletion and oxidative stress, effects primarily because of interference with the scrambling effects of increased cytosolic Ca(2+) concentration.

Hormonal and chemical regulation of paraoxonases in mice

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

Regulation of hepatic paraoxonase-1 expression

Serum paraoxonase-1 (PON1) is a member of the paraoxonases family (PON1, PON2, and PON3). PON1 is synthesized and secreted by the liver, and in circulation it is associated with HDL. PON1 has antioxidative properties, which are associated with the enzyme's capability to decrease oxidative stress in atherosclerotic lesions and to attenuate atherosclerosis development. Epidemiological evidence demonstrates that low PON1 activity is associated with increased risk of cardiovascular events and cardiovascular disease and is an independent risk factor for coronary artery disease. Therefore, pharmacological modulation of PON1 activity or PON1 gene expression could constitute a useful approach for preventing atherosclerosis. A primary determinant of serum PON1 levels is the availability of the enzyme for release by the liver, the principal site of PON1 production. Together with the enzyme secretion rate, enzymatic turnover, and protein stability, the level of PON1 gene expression is a major determinant of PON1 status. This paper summarizes recent progress in understanding the regulation of PON1 expression in hepatocytes.

The human paraoxonase gene cluster as a target in the treatment of atherosclerosis

The paraoxonase (PON) gene cluster contains three adjacent gene members, PON1, PON2, and PON3. Originating from the same fungus lactonase precursor, all of the three PON genes share high sequence identity and a similar β propeller protein structure. PON1 and PON3 are primarily expressed in the liver and secreted into the serum upon expression, whereas PON2 is ubiquitously expressed and remains inside the cell. Each PON member has high catalytic activity toward corresponding artificial organophosphate, and all exhibit activities to lactones. Therefore, all three members of the family are regarded as lactonases. Under physiological conditions, they act to degrade metabolites of polyunsaturated fatty acids and homocysteine (Hcy) thiolactone, among other compounds. By detoxifying both oxidized low-density lipoprotein and Hcy thiolactone, PONs protect against atherosclerosis and coronary artery diseases, as has been illustrated by many types of in vitro and in vivo experimental evidence. Clinical observations focusing on gene polymorphisms also indicate that PON1, PON2, and PON3 are protective against coronary artery disease. Many other conditions, such as diabetes, metabolic syndrome, and aging, have been shown to relate to PONs. The abundance and/or activity of PONs can be regulated by lipoproteins and their metabolites, biological macromolecules, pharmacological treatments, dietary factors, and lifestyle. In conclusion, both previous results and ongoing studies provide evidence, making the PON cluster a prospective target for the treatment of atherosclerosis.

Pharmacological and dietary modulators of paraoxonase 1 (PON1) activity and expression: the hunt goes on

Paraoxonase 1 (PON1) is a high density lipoprotein (HDL)-associated enzyme displaying esterase and lactonase activity. PON1 hydrolyzes several organophosphorus (OP) insecticides and nerve agents, a number of exogenous and endogenous lactones, and metabolizes toxic oxidized lipids of low density lipoproteins (LDL) and HDL. As such, PON1 plays a relevant role in determining susceptibility to OP toxicity, cardiovascular diseases and several other diseases. Serum PON1 activity in a given population can vary by at least 40-fold. Most of this variation can be accounted for by genetic polymorphisms in the coding region (Q192R, L55M) and in the promoter region (T-108C). However, exogenous factors may also modulate PON1 activity and/or level of expression. This paper examines various factors that have been found to positively modulate PON1. Certain drugs (e.g. hypolipemic and anti-diabetic compounds), dietary factors (antioxidants, polyphenols), and life-style factors (moderate alcohol consumption) appear to increase PON1 activity. Given the relevance of PON1 in protecting from certain environmental exposure and from cardiovascular and other diseases, there is a need for further mechanistic, animal, and clinical research in this area, and for consideration of possible alternative strategies for increasing the levels and activity of PON1.

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

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

The differentiating effect of glimepiride and glibenclamide on paraoxonase 1 and platelet-activating factor acetylohydrolase activity

AIMS

The present study was designed to examine the effect of sulphonylureas, glimepiride (GM) and glibenclamide (GB), on paraoxonase 1 (PON1) and platelet activating factor acetylohydrolase (PAF-AH) activity in normal and streptozotocin (STZ)-induced (50 mg/kg) diabetic rats.

MAIN METHODS

In treated groups, glimepiride (0.1 mg/kg) or glibenclamide (2 mg/kg) was given orally for 4 weeks. A PON1 and PAF-AH activity were estimated by spectrophotometric method.

KEY FINDINGS

Hyperglycemia was accompanied by a significant decrease in plasma PON1 activity toward paraoxon (P < 0.001) and phenyl acetate (P < 0.01) and increase in plasma PAF-AH activity (P < 0.01). In STZ-induced diabetic rats the administration of both GM and GB had no effect on plasma PON1 activity but reversed elevated plasma PAF-AH activity (GM: P < 0.05, GB: P < 0.01). In non-diabetic rats after either GM or GB administration the decreased PON1 activity in the plasma was observed (GM: P < 0.001, GB: P < 0.05), but plasma PAF-AH activity remained unchanged. Both GM and GB had no effect on total plasma antioxidant capacity in diabetic and control treated groups. Additionally, both drugs increased PON1 activity toward phenyl acetate in the liver, in diabetic rats (GM: P < 0.05, GB:ns) as well as in non-diabetic rats (GM: P < 0.001, GB: P < 0.001), and reduced lipid peroxidation in the liver.

SIGNIFICANCE

These results demonstrate that in streptozotocin-induced diabetic rats as well as in normal rats glimepiride and glibenclamide have no beneficial effects on circulating PON1 and PAF-AH activities, but both drugs increase PON1 activity in the liver.

Assessment of lipoprotein profiles study (ALPS) and antioxidant activity in healthy subjects treated with AGI-1067

BACKGROUND

AGI-1067 (succinobucol) is a phenolic derivative of probucol that inhibits the vascular oxidative-inflammatory cascade and is intended to have an improved clinical profile.

OBJECTIVE

The Assessment of Lipoprotein Profiles (ALPS) study evaluated the effects of AGI-1067 on lipid, antioxidant, antiinflammatory and safety profiles in healthy subjects.

METHODS

This was a double-blind, placebo-controlled, 12-week, multicenter trial. Eligible subjects, aged 18 to 65 years, had low-density lipoprotein cholesterol (LDL-C) ≤ 190 mg/dL, triglyceride (TG) ≤ 600 mg/dL and Framingham risk <10%. Subjects were randomized 1:1 to oral 300 mg AGI-1067 (n = 127) or matching placebo (n = 127) once daily.

RESULTS

AGI-1067 and placebo treatment had small changes (mean) in: LDL-C (+2.98 vs -1.52 mg/dL, respectively; P = 0.057), apolipoprotein B (+1.48 vs -1.91 mg/dL; P = 0.267), high-density lipoprotein cholesterol (HDL-C) [-3.69 vs -0.29 mg/dL; P < 0.001], and apolipoprotein (Apo) A-I (-10.43 vs -6.14 mg/dL; P = 0.021). Subjects with baseline LDL-C > 130 mg/dL showed the largest decreases in HDL-C and ApoA-I, while subjects with LDL-C ≤130 mg/dL had insignificant changes in both parameters. Changes in cholesteryl ester transfer protein mass were significantly correlated (P < 0.0001) with LDL-C changes, but not HDL-C. Paraoxonase activity increased with AGI-1067 vs little change in placebo (+1.78 vs +0.15 U/L, respectively; P = 0.077). HDL particles isolated from AGI-1067 treated subjects showed significant antioxidant potency vs HDL particles from placebo subjects (thiobarbituric acid reactive substances in a LDL oxidation assay decreased -25.88% vs +7.88, respectively; P = 0.011).

CONCLUSION

The ALPS study demonstrated that AGI-1067 had minor effects on LDL and HDL cholesterol. More dramatic effects were observed for HDL-associated paraoxonase and thiobarbituric acid reactive substances activity, suggesting that the antiatherosclerotic properties of AGI-1067 may involve an HDL antioxidant mechanism consistent with inhibition of the oxidative-inflammatory cascade, rather than involving a lipid regulating pathway.

Effects of atorvastatin therapy on hypercholesterolemic rabbits with respect to oxidative stress, nitric oxide pathway and homocysteine

Hypercholesterolemia is characterized with changes in lipid profile, nitric oxide pathway and oxidative stress markers. This study is designed to evaluate the effects of hypercholesterolemic diet and atorvastatin therapy on oxidative stress, lipid peroxide and thiobarbituric acid reactive substances (TBARS), NO pathway markers, nitric oxide(NO) and asymmetric dimethylarginine (ADMA), homocysteine, and paraoxonase activity (PON1) in rabbits. Twenty rabbits fed with high-cholesterol diet for 8 weeks were randomly divided into 2 groups on the fourth week of the hypercholesterolemic diet. First group was fed with high-cholesterol diet alone, whereas the second group with the same cholesterol diet plus atorvastatin (0.3 mg/kg/day) for 4 weeks. High-cholesterol diet increased total cholesterol, low density lipoprotein (LDL-C), high density lipoprotein (HDL-C), ADMA, TBARS and lipid peroxide levels and reduced PON1 activity and NO levels in rabbits. Four weeks of atorvastatin therapy significantly increased HDL-C, PON1 activity and reduced LDL-C, TBARS and lipid peroxide concentrations. Atorvastatin therapy is beneficial in decreasing oxidative stress related with hypercholesterolemia, mainly affecting lipid profile and PON1 activity.

Effect of the anti-oxidant probucol on soluble thrombomodulin (sTM) in hypercholesterolemic rabbits

INTRODUCTION

Thrombomodulin is an integral endothelial cell membrane protein, exists not only on the surface of endothelial cells but also as soluble fragments circulating in plasma. Probucol has anti-oxidant properties as well as cholesterol-lowering effects and may affect soluble thrombomodulin (sTM).

METHODS

Sixteen rabbits fed with high-cholesterol diet for 8 weeks were randomly divided into two groups: (1) high-cholesterol group (n=8): maintained high-cholesterol diet; (2) probucol group (n=8): the same diet plus probucol for 6 weeks. Control group (n=8) was fed with normal diet for 14 weeks. The levels of sTM and oxidized low-density lipoprotein (OX-LDL) were measured using ELISA.

RESULTS

There were atherosclerotic lesions in aortas and intimal thickness significantly increased in high-cholesterol group. Probucol significantly reduced the lesion area (56.4%+/-9.8% vs 82.5%+/-10.5%) and decreased the intimal thickness (44.65+/-7.25 mum vs 72.21+/-8.32) as compared with high-cholesterol group, all P<0.01. Probucol decreased the level of OX-LDL and sTM as compared with high-cholesterol group, all P<0.05.

CONCLUSIONS

Probucol retarded the plaques formation may relate to decrease plasma OX-LDL and sTM concentration, which may improve endothelial function in hypercholesterolemic rabbit.