Anti-atherogenicity of nutritional antioxidants

Epidemiological studies have indicated that fruit- and vegetable-rich diets play a protective role against cardiovascular disease. An explanation for this protection lies in the presence of antioxidant vitamins in fruits and vegetables. A large number of studies have provided data suggesting that consumption of dietary antioxidants is associated with reduced risk for cardiovascular disease. Plausible mechanisms by which these antioxidants may reduce the development of atherosclerosis include inhibition of low-density lipoprotein (LDL) oxidation, cellular lipid peroxidation and cell-mediated oxidation of LDL, and reduction in blood cholesterol levels. This review reports on the recent data of the anti-atherosclerotic effects and mechanistical aspects of three major groups of dietary antioxidants: vitamin E, carotenoids and flavonoids.     

Role of antioxidants in atherosclerosis: epidemiological and clinical update

Low density lipoprotein (LDL) oxidative modification in the vascular wall seems to be a key factor in atherosclerosis development. Oxidised LDLs might recruit monocytes and favour their transformation into foam cells through a receptor-mediated intake (scavenger pathway). Moreover oxidised LDLs show cytotoxic potential which is probably responsible for endothelial cell damage and macrophage degeneration in the atherosclerotic human plaque. Following the oxidation hypothesis of atherosclerosis the role of natural antioxidants, i.e. Vitamin C, Vitamin E and carotenoids, has been investigated in a large number of epidemiological, clinical and experimental studies. Animal studies indicate that dietary antioxidants may reduce atherosclerosis progression, and observational data in humans suggest that antioxidant vitamin ingestion is associated with reduced cardiovascular disease, but the results of randomised controlled trials are mainly disappointing. It has been suggested that natural antioxidants may be effective only in selected subgroups of patients with high levels of oxidative stress or depletion of natural antioxidant defence systems. The favourable effects shown by some studies relating antioxidant dietary intake and cardiovascular disease, may have been exerted by other chemicals present in foods. Flavonoids are the ideal candidates, since they are plentiful in foods containing antioxidant vitamins (i.e. fruits and vegetables) and are potent antioxidants. Tea and wine, rich in flavonoids, seem to have beneficial effects on multiple mechanisms involved in atherosclerosis. Future studies should probably select patients in a context of high-oxidative stress / low-antioxidant defence, to verify if antioxidants may really prove useful as therapeutic anti-atherosclerotic agents.     

Inhibition of lipoprotein lipid oxidation

According to the oxidative modification hypothesis, antioxidants that inhibit the oxidation of low-density lipoprotein (LDL) are expected to attenuate atherosclerosis, yet not all antioxidants that inhibit LDL oxidation in vitro inhibit disease in animal models of atherosclerosis. As with animal studies, a benefit with dietary supplements of antioxidants in general and vitamin E in particular was anticipated in humans, yet the overall outcome of large, randomized controlled studies has been disappointing. However, in recent years it has become clear that the role of vitamin E in LDL oxidation and the relationship between in vitro and in vivo inhibition of LDL oxidation are more complex than previously appreciated, and that oxidative events in addition to LDL oxidation in the extracellular space need to be considered in the context of an antioxidant as a therapeutic drug against atherosclerosis. This review focuses on some of these complexities, proposes a novel method to assess in vitro 'oxidizability' of lipoprotein lipids, and summarizes the present situation of development of antioxidant compounds as drugs against atherosclerosis and related cardiovascular disorders.     

Pomegranate juice flavonoids inhibit low-density lipoprotein oxidation and cardiovascular diseases: studies in atherosclerotic mice and in humans

The beneficial health effects attributed to the consumption of fruit and vegetables are related, at least in part, to their antioxidant activity. Of special interest is the inverse relationship between the intake of dietary nutrients rich in polyphenols and cardiovascular diseases. This effect is attributed to polyphenols' ability to inhibit low-density lipoprotein (LDL) oxidation, macrophage foam cell formation and atherosclerosis. Pomegranate polyphenols can protect LDL against cell-mediated oxidation via two pathways, including either direct interaction of the polyphenols with the lipoprotein and/or an indirect effect through accumulation of polyphenols in arterial macrophages. Pomegranate polyphenols were shown to reduce the capacity of macrophages to oxidatively modify LDL, due to their interaction with LDL to inhibit its oxidation by scavenging reactive oxygen species and reactive nitrogen species and also due to accumulation of polyphenols in arterial macrophages; hence, the inhibition of macrophage lipid peroxidation and the formation of lipid peroxide-rich macrophages. Furthermore, pomegranate polyphenols increase serum paraoxonase activity, resulting in the hydrolysis of lipid peroxides in oxidized lipoproteins and in atherosclerotic lesions. These antioxidative and antiatherogenic effects of pomegranate polyphenols were demonstrated in vitro, as well as in vivo in humans and in atherosclerotic apolipoprotein E deficient mice. Dietary supplementation of polyphenol-rich pomegranate juice to atherosclerotic mice significantly inhibited the development of atherosclerotic lesions and this may be attributed to the protection of LDL against oxidation.     

Green tea polyphenols as an anti-oxidant and anti-inflammatory agent for cardiovascular protection

Our review aims to examine the cellular and molecular mechanisms of cardiovascular protection of green tea polyphenols, particularly epigallocatechin gallate (EGCG), which focuses on the anti-oxidative and anti-inflammatory effects. EGCG is the major and the most active component in green tea. Studies have shown that EGCG protects cellular damage by inhibiting DNA damage and oxidation of LDL. One of the protective properties of EGCG is its ability to scavenge free radicals. EGCG can also reduce the inflammatory response associated with local tissue injuries such as the hepatocellular necrosis in acute liver injury induced by carbon tetrachloride. The protective effect of EGCG is due to its ability to decrease lipid peroxidation, oxidative stress and the production of nitric oxide (NO) radicals by inhibiting the expression of iNOS. EGCG also ameliorates the overproduction of pro-inflammatory cytokines and mediators, reduces the activity of NF-kappaB and AP-1 and the subsequent formation of peroxynitrite with NO and reactive oxygen species. Thus, EGCG effectively mitigates cellular damage by lowering the inflammatory reaction and reducing the lipid peroxidation and NO generated radicals leading to the oxidative stress. Green tea is proposed to be a dietary supplement in the prevention of cardiovascular diseases in which oxidative stress and proinflammation are the principal causes.     

Effect of eplerenone,a selective aldosterone blocker,on blood pressure,serum and macrophage oxidative stress,and atherosclerosis in apolipoprotein E-deficient mice

Oxidative stress is involved in the pathogenesis of atherosclerosis, and angiotensin II (AT-II) induces oxidative stress and enhances atherogenesis. Aldosterone, which has an important role in the pathology of heart failure, has recently been implicated as a mediator of AT-II biologic activities. In this study, we analyzed whether administration of the selective aldosterone blocker eplerenone to atherosclerotic apolipoprotein E-deficient (E0) mice would affect their oxidative status and atherogenesis. Apolipoprotein E-deficient mice were administered chow containing eplerenone (200 mg/kg/day) for 3 months. Blood pressure, serum and macrophage oxidative status, and aortic atherosclerotic lesion area were evaluated in mice treated with eplerenone compared with untreated mice. Eplerenone administration significantly decreased systolic and diastolic blood pressure by 12% and 11%, respectively, compared with untreated mice. Serum susceptibility to lipid peroxidation decreased by as much as 26%, and serum paraoxonase activity increased by 28% in eplerenone-treated mice compared with untreated mice. Peritoneal macrophages from eplerenone-treated mice contained reduced levels of lipid peroxides, and their macrophage oxidation of low-density lipoprotein (LDL) and superoxide ion release were significantly reduced (by 17% and 43%, respectively), compared to untreated mice. Daily injections of AT-II (0.1 mL, 10(-)7M) during the final 3 weeks of the study in eplerenone-treated mice substantially attenuated the eplerenone-mediated reduction in macrophage superoxide release and LDL oxidation. Finally, the atherosclerotic lesion area in aortas of eplerenone-treated mice was significantly reduced (by 35%) versus untreated mice, and this effect was reversed by AT-II. Administration of the selective aldosterone blocker eplerenone significantly reduced oxidative stress and atherosclerosis progression in E0 mice. These data suggest that aldosterone could have a significant pro-oxidative role in the pathogenesis of atherosclerosis.     

Postprandial effects of wine consumption on lipids and oxidative stress biomarkers

Postprandial lipemia has been recognized as a risk factor for atherosclerosis development. Consuming meals with suitable sources of antioxidants such as red wine reduces postprandial oxidative stress. However, information about the postprandial effects of wine ingestion outside meals on lipids and on in vivo low-density lipoprotein (LDL) oxidation in humans is scarce. The aim of this study was to investigate postprandial changes in lipids and in vivo LDL oxidation after moderate (250 ml) red wine ingestion, before and after sustained wine consumption of 250 ml/day for 4 days. After 4 days of sustained wine consumption a decrease in the LDL/high-density lipoprotein cholesterol ratio was observed after wine ingestion (p = 0.026). On day 4, a decrease in oxidized LDL levels and an increase in the antioxidant enzyme glutathione peroxidase activity (p = 0.025) were observed after wine ingestion. Our results show that consumption of red wine at moderate doses outside meals does not promote oxidative stress. Daily consumption of moderate doses of red wine can improve postprandial lipid profile and oxidative status when wine is ingested outside meals.     

The role of statins in oxidative stress and cardiovascular disease

Statins have emerged as a highly efficacious class of drugs in the prevention of cardiovascular events. The primary mechanism of its cardioprotective effect is likely through its effectiveness in lowering serum lipids, particularly the low density lipoprotein (LDL) fractions. Recent studies suggest that statins also confer direct beneficial effects on the vascular cells in the attenuation of the atherogenic process through a variety of mechanisms. It remains the current dogma that oxidative modification of the LDL particles in the vessel wall plays a critical role for these lipoprotein particles to initiate the atherogenic cascade. The current failure of a number of antioxidants, which includes vitamin E, to favorably impact on the cardiovascular outcome in large scale clinical trials attests to the complexity of the oxidation processes in biological systems. In this review, we will highlight the current advances in a number of endogenous pro-oxidative and anti-oxidative systems in how they contribute to the net oxidative stress and how statin drugs may modulate this complex array of pro- and anti-oxidative processes.     

Atorvastatin effect on high-density lipoprotein-associated paraoxonase activity and oxidative DNA damage

Objective High-density lipoprotein (HDL)-associated antioxidant paraoxonase (PON) may reduce low-density lipoprotein (LDL) oxidation and prevent atherosclerosis. The aim of this present study was to investigate the effect of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor atorvastatin on hydrogen-peroxide-induced DNA damage by comet assay and the correlation between oxidative DNA damage and antioxidant PON activity. Methods Thirteen type-II/a hyperlipidemic patients were enrolled in the study. We examined the effect of 10 mg/day atorvastatin treatment on lipid levels and the degree of DNA damage in lymphocytes separated from hyperlipidemic patients, nitric oxide (NO), thiobarbituric acid-reactive substances (TBARS), PON levels and activity. Results After 6 months, atorvastatin treatment significantly decreased serum cholesterol and LDL-cholesterol levels. The triglyceride level did not change, and there was no significant change in the HDL cholesterol level. The visual score characteristic to the degree of DNA damage in comet assay was significantly decreased, as well as the TBARS level, while the level of NO was non-significantly increased. PON activity and the PON/HDL ratio were significantly increased after atorvastatin treatment. There was a negative correlation between DNA damage and PON activity, as well as between DNA damage and the PON/HDL ratio before and after atorvastatin treatment. Conclusion These findings show that atorvastatin treatment favorably affected the lipid profile, increasing the activity of HDL-associated PON and decreasing the cytotoxic effect of oxidative stress.     

Induction of lipid peroxidation in biomembranes by dietary oil components.

Prooxidant formation and resulting lipid peroxidation are supposed to be involved in the pathogenesis of various diseases including cancer. Cancer risk is possibly influenced by the composition of diet with high intake of fat and red meat being harmful and high consumption of fruits and vegetables being protective. Since dietary oils may contain potential prooxidants, the aim of the present study was to prove (i) whether oxidative stress in biomembranes may be induced by dietary oils and if, (ii) which impact it has on the viability and proliferation of cultured colon (carcinoma) cells. Lipid hydroperoxide content in dietary oils increased after heating. Linoleic acid hydroperoxide (LOOH) and/or oils with different hydroperoxide contents induced lipid peroxidation in liposomes, erythrocyte ghosts and colon cells. Upon incubation with liposomes, both LOOH and heated oil induced lipid peroxidation only in the presence of iron and ascorbate. LOOH was sufficient to start lipid peroxidation of erythrocyte ghosts. LOOH incorporates into the lipid bilayer decreasing membrane fluidity and initiating lipid peroxidation in the lipid phase. When cultured cells (IEC18 intestinal epithelial cells, SW480 and HT29/HI1 colon carcinoma cells) were exposed to LOOH, they responded by cell death both via apoptosis and necrosis. Cells with higher degree of membrane unsaturation were more susceptible and antioxidants (vitamin E and selenite) were protective indicating the involvement of oxidative stress. Thus, peroxidation of biomembranes can be initiated by lipid hydroperoxides from heated oils. Dietary consumption of heated oils may lead to oxidative damage and to cell death in the colon. This may contribute to the enhanced risk of colon cancer due to regenerative cell proliferation.     

Oxidative stress and atherosclerosis

Oxidative stress is a continuous level of oxidative damage in animal cells, which is caused by an overabundance of reactive oxygen species or a decline in antioxidant ability against them. Oxidative stress increases with individual risk factors of atherosclerosis such as obesity, hypertension, hyperlipidemia, diabetes and smoking. Thus, oxidative stress is considered to play a key role in the pathogenesis of atherosclerosis. This review discusses the relationship between oxidative stress and atherosclerosis based on findings from our research group. We have found that atherosclerotic lesions are formed in the aorta of mice fed a high-cholesterol and high-linoleic diet, in parallel with elevated serum lipid peroxide levels. This model is useful for primary screening of antiatherosclerotic agents with antioxidative activity. One notable factor in the development of atherosclerosis is oxidized low-density lipoprotein (OxLDL). In order to examine OxLDL levels in blood, we have developed anion-exchange HPLC methods using stepwise elution. Using these methods, we have found that OxLDL markedly increases in a rat model of metabolic syndrome, in animals exposed to cigarette smoke and in smokers in parallel with other oxidative stress markers. These oxidative stress markers have been attenuated by administration of several antioxidants. In addition, we have found that smoking accelerates atherogenesis in the aorta of apoE-deficient mice and this acceleration can be ameliorated by administration of vitamin E. These observations suggest that antioxidant supplementation may be an effective therapeutic strategy for metabolic syndrome and smoking-induced diseases in which elevated oxidative stress plays a pivotal role.     

S-nitrosothiols do not induce oxidative stress, contrary to other nitric oxide donors, in cultures of vascular endothelial or smooth muscle cells.

Nitric oxide (NO) has been described to exert various anti-atherogenic actions. However, NO, in some cases, has been shown to stimulate the oxidation of low-density lipoprotein (LDL), which constitute an important triggering event in atherosclerosis. Thus, some NO donors, despite their advantages, might also induce oxidative stress. Therefore, the purpose of this study is to examine the effect of three different NO donors on LDL oxidation, in acellular system as well as in cultures of normal endothelial cells or smooth muscle cells, which constitute the two major cellular components of the arterial wall. Sodium nitroprusside oxidized strongly LDL in medium alone as well as in endothelial or smooth muscle cell cultures. Sydnonimine-1 (SIN-1) oxidized LDL already in the absence of cells and enhanced clearly the LDL oxidation in the cultures. S-nitroso-N-acetylpenicillamine was unable to oxidize LDL in synthetic medium alone as well as in the presence of cells, showing that the amount of superoxide and other reactive oxygen species released by these cells did not suffice, contrary to those liberated by macrophages, to combine to NO providing oxidant activity.     

Correlation between oxidation of low density lipoproteins and prostacyclin synthesis in cultured smooth muscle cells

The effect of antioxidants on the oxidation of low density lipoproteins in relation to prostacyclin synthesis was investigated in the prescence of rabbit smooth muscle cells (SMC) and Fe-containing culture medium. The lipid peroxidation of low density lipoproteins (LDL) assayed as thiobarbituric acid reactive substances was increased from 0.5 to 1.4 nmol malondialdehyde/mL by the presence of smooth muscle cells. Two potent antioxidants, nordihydroguairetic acid (NDGA) and butylated hydroxytoluene (BHT), inhibited lipoprotein oxidation by IC50 values of 0.2 and 0.8 microM, respectively. Inhibition of lipoprotein oxidation was associated with an increased prostacyclin synthesis by the SMC, the effect being more pronounced with nordihydroguairetic acid than with butylated hydroxytoluene. The stable metabolite of the lipid hydroperoxide, 15-hydroxyeicosatetraenoic acid (15-HETE), formed in the 15-lipoxygenase pathway was measured following antioxidant treatment and found to be eliminated or greatly reduced by both antioxidants. The results presented show that lipid hydroperoxides, formed as a consequence of lipoprotein oxidation and promoted by the smooth muscle cells through a lipoxygenase reaction, may regulate prostacyclin synthase, a process which may be influenced by the addition of antioxidants.     

Effect of atorvastatin on paraoxonase1 (PON1) and oxidative status

It has been proposed that paraoxonase1 (PON1), a high density lipoprotein (HDL)-associated esterase/lactonase, has antiatherosclerotic properties. The activity of PON1 is influenced by PON1 polymorphisms. However, the influence of PON1 polymorphisms on PON1 activity and oxidative stress in response to lipid-lowering drugs remains poorly understood. The objective of the present study was to investigate the effects of atorvastatin on PON1 activity and oxidative status. The influence of PON1 polymorphisms on PON1 activity and oxidative status in response to atorvastatin treatment was also evaluated. In total, 22 hypercholesterolemic patients were treated with atorvastatin at a dose of 10 mg/day for 3 months. Lipid profile, lipid oxidation markers (malondialdehyde (MDA), conjugated diene (CD), total peroxides (TP)), total antioxidant substance (TAS), oxidative stress index (OSI), and paraoxonase1 activity were determined before and after treatment. L55M, Q192R, and T(-107)C PON1 polymorphisms were also determined. Atorvastatin treatment significantly reduced the levels of total cholesterol (24.5%), low density lipoprotein (LDL) cholesterol (25.4%), triglycerides (24.4%), CD (4.4%), MDA (15.2%), TP (13.0%) and OSI (24.0%), and significantly increased the levels of TAS (27.3%), and PON1 activity (14.0%). Interestingly, the increase in PON1 activity and the reduction in oxidative stress in response to atorvastatin were influenced only by the PON1 T-107C polymorphism. Atorvastatin treatment improved the lipid profile, lipid oxidation, and oxidative/antioxidative status markers including the activity of PON1 towards paraoxon. These beneficial effects may be attributed to the antioxidant properties of statins and the increase in PON1 activity. The increase in PON1 activity was enhanced by the PON1 T-107C polymorphism.     

Role of oxidatively modified low density lipoproteins and anti-oxidants in atherothrombosis

Retrospective studies have demonstrated an association between coronary artery disease (CAD) and increased plasma levels of oxidised low density lipoproteins (LDL). A very recent prospective study in heart transplant patients has demonstrated that oxidised LDL is an independent risk factor for transplant CAD, thus further supporting the hypothesis that oxidised LDL is actively involved in the development of CAD. The increase of circulating oxidised LDL is most probably caused by back-diffusion from the atherosclerotic arterial wall in the blood, independent of plaque rupture. Indeed, plasma levels of oxidised LDL were very similar in patients with stable CAD and in patients with acute coronary syndromes. These were, however, associated with increased release of malondialdehyde (MDA)-modified LDL. Oxidised LDL may be generated by radical-mediated or by lipoxygenase or phospholipase catalysed lipid oxidation, and by myeloperoxidase catalysed protein and lipid oxidation. Prostaglandin synthesis by endothelial cells under oxidative stress and platelet activation are associated with the release of aldehydes; these induce the oxidative modification of the apolipoprotein B-100 moiety of LDL in the absence of lipid peroxidation, and thus generate MDA-modified LDL. Efficient prevention of in vivo oxidation may involve efficient cholesterol lowering, improving the anti-oxidative status of LDL by increasing the anti-oxidant content and increasing the oleate content of LDL, and by shifting the LDL away from phenotype B (characterised by small dense LDL particles). Anti-oxidative and anti-inflammatory enzymes associated with HDL may inhibit the oxidation of LDL or reverse the atherothrombotic effects of LDL.     

Role of oxidatively modified low density lipoproteins and anti-oxidants in atherothrombosis

Retrospective studies have demonstrated an association between coronary artery disease (CAD) and increased plasma levels of oxidised low density lipoproteins (LDL). A very recent prospective study in heart transplant patients has demonstrated that oxidised LDL is an independent risk factor for transplant CAD, thus further supporting the hypothesis that oxidised LDL is actively involved in the development of CAD. The increase of circulating oxidised LDL is most probably caused by back-diffusion from the atherosclerotic arterial wall in the blood, independent of plaque rupture. Indeed, plasma levels of oxidised LDL were very similar in patients with stable CAD and in patients with acute coronary syndromes. These were, however, associated with increased release of malondialdehyde (MDA)-modified LDL. Oxidised LDL may be generated by radical-mediated or by lipoxygenase or phospholipase catalysed lipid oxidation, and by myeloperoxidase catalysed protein and lipid oxidation. Prostaglandin synthesis by endothelial cells under oxidative stress and platelet activation are associated with the release of aldehydes; these induce the oxidative modification of the apolipoprotein B-100 moiety of LDL in the absence of lipid peroxidation, and thus generate MDA-modified LDL. Efficient prevention of in vivo oxidation may involve efficient cholesterol lowering, improving the anti-oxidative status of LDL by increasing the anti-oxidant content and increasing the oleate content of LDL, and by shifting the LDL away from phenotype B (characterised by small dense LDL particles). Anti-oxidative and anti-inflammatory enzymes associated with HDL may inhibit the oxidation of LDL or reverse the atherothrombotic effects of LDL.     

The Role of Paraoxonase 1 Activity in Cardiovascular Disease

The antioxidant activity of high density lipoprotein (HDL) is largely due to the paraoxonase (PON) 1 located on it. Experiments with transgenic PON1 knockout mice indicate the potential for PON1 to protect against atherogenesis. This effect of HDL in decreasing low density lipoprotein (LDL) lipid peroxidation is maintained for longer than that of antioxidant vitamins and could therefore be more protective. Several important advances in the field of PON research have occurred recently, not least the discovery that two other members of the PON gene family -PON2 and PON3 - may also have important antioxidant properties. Significant advances have been made in understanding the basic biochemical function of PON1 and the discovery of possible modulators of its activity. Case-control studies of PON1 activity and coronary heart disease (CHD) have shown a clear association between CHD and low serum PON1 activity. This relationship has been further strengthened by the publication of the first prospective study showing low serum PON1 activity to be an independent predictor of new CHD events. Furthermore, decreased CHD risk has been revealed by meta-analysis to be associated with the polymorphisms of PON1, which are most active in lipid peroxide hydrolysis. Although this is likely to be an underestimate of the true contribution of PON1 to CHD (because these polymorphisms explain only a small component of the variation in PON1 activity), it is important because genetic influences are unlikely to be confounded by other factors linked with both CHD and diminished PON1 activity. PON1 is being extensively researched and it is hoped that therapeutic approaches will emerge to increase its activity. Clinical trials of these, if successful, will not only provide a novel means of preventing atherosclerosis, but also provide a more satisfactory means of testing the oxidant hypothesis of atherosclerosis than antioxidant vitamin supplementation has proved to be.     

Hesperidin a flavanoglycone protects against gamma-irradiation induced hepatocellular damage and oxidative stress in Sprague-Dawley rats

Oxidative stress plays a pivotal role in the pathogenesis and progression of gamma-irradiation induced cellular damage and the administration of dietary antioxidants has been suggested to protect against the subsequent tissue damage. Here, we present the data to explore the hepatoprotective and antioxidant effect of hesperidin, a naturally occurring citrus flavanoglycone, against gamma-irradiation induced oxidative damage in the liver of rats. Healthy male Sprague-Dawley rats were exposed to gamma-irradiation (1 Gy, 3 Gy and 5 Gy) and were administered hesperidin (50 mg/kg and 100 mg/kg, b.w, orally) for 7 days post irradiation. The changes in body weight, liver weight, spleen index, serum and liver aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), gamma-glutamyl transpeptidase (gamma-GT) and serum ceruloplasmin levels were determined along with differences in the liver histopathology. Liver thiobarbuturic acid reactive substance as an index for lipid peroxidation and the levels of enzymatic antioxidants like superoxide dismutase, catalase, glutathione peroxidase and the status of non-enzymatic antioxidants as an index for oxidative stress were also determined. Exposure to gamma-irradiation resulted in hepatocellular damage in a dose-dependent manner, featuring a significantly decreased body weight and liver weight and higher levels of serum AST, ALT, ALP, LDH and gamma-GT levels and a simultaneous decrease in their levels in the liver tissue. Oxidative stress was evidenced by elevated levels of lipid peroxidation and a decrease in the levels of key enzymatic and non-enzymatic antioxidants in the liver. However, the gamma-irradiation induced toxic effects were dramatically and dose-dependently inhibited by hesperidin treatment as observed by the restoration in the altered levels of the marker enzymes, lipid peroxidation, enzymatic and non-enzymatic antioxidants. The results of the biochemical observations were supported by the histopathological findings. Thus, oral administration of hesperidin was found to offer protection against gamma-irradiation induced hepatocellular damage and oxidative stress in rats, probably by exerting a protective effect against hepatocellular necrosis via its free radical scavenging and membrane stabilizing ability.     

Clinical study on the effect of simvastatin on paraoxonase activity

Human paraoxonase (PON1) is a serum high-density lipoprotein-associated phosphotriesterase. High-density lipoprotein (HDL) plays the role of a carrier and the site of action of this enzyme. According to a majority of authors, PON1 acts as an antioxidant, preventing low-density lipoprotein (LDL) peroxidation. However, due to the fact that in vivo serum PON1 is predominantly associated with HDL, its major physiological role might be to protect HDL, rather than LDL, from oxidation. Nevertheless, the physiological substrate of PON1 still remains to be discovered. The objective of this study was to determine changes in PON1 activity during treatment with simvastatin (CAS 79902-63-9, Lipex) in patients with type IIa and/or IIb hyperlipoproteinemia. PON1 activity was assessed in 32 patients with hyperlipoproteinemia type IIa or IIb with an LDL cholesterol concentration higher than 4.2 mmol/l. Patients received simvastatin in a daily dose of 20 mg. The lipid status and PON1 activity were assessed at baseline, as well as 3 and 6 months after the beginning of treatment. The study demonstrated a statistically significant lipid lowering effect of simvastatin on total and LDL cholesterol, and an increase in PON1 activity in patients with both types of hyperlipoproteinemia. No statistically significant correlation was observed either between changes in PON1 activity and HDL, HDL2, HDL3 and LDL cholesterol and triglyceride levels, or between their first differences in patients with both type IIa and IIb hyperlipoproteinemia. The obtained results suggest that the antioxidant properties of simvastatin might be caused by a mechanism independent of apoAI-containing lipoprotein concentration. The antioxidant properties of simvastatin, which play an important role in HDL protection from oxidation, could be the mechanism inducing the increase in PON1 activity.     

Regulation of paraoxonase 1 (PON1) in PCB 126-exposed male Sprague Dawley rats

3,3′,4,4′,5-Pentachlorobiphenyl (PCB 126), an aryl hydrocarbon receptor (AhR) agonist and most potent dioxin-like PCB congener, significantly alters gene expression, lipid metabolism, and oxidative stress in the liver. PON1, an antioxidant and anti-atherogenic enzyme, is produced in the liver and secreted into the blood where it is incorporated into high density lipoprotein (HDL) and protects LDL and cellular membranes against lipid peroxidation. To explore the regulation of PON1, male Sprague-Dawley rats were treated with ip injections of corn oil or 1 μmol/kg or 5 μmol/kg PCB 126 and euthanized up to two weeks afterwards. Serum total and HDL-cholesterol were increased by low dose and decreased by high dose exposure, while LDL-cholesterol was unchanged. PCB 126 significantly increased hepatic PON1 gene expression and liver and serum PON1 activities. Liver and serum thiobarbituric acid reactive substances levels were not elevated except for high dose and long exposure times. Serum antioxidant capacity was unchanged across all exposure doses and time points. This study, the first describing the regulation of gene expression of PON1 by a PCB congener, raises interesting questions whether elevated PON1 is able to ameliorate PCB 126-induced lipid peroxidation and whether serum PON1 levels may serve as a new biomarker of exposure to dioxin-like compounds.