Seasonal variation in copper-mediated low-density lipoprotein oxidation in vitro is related to varying plasma concentration of oxidised lipids in summer and winter

Dual signaling evoked by oxidized LDLs in vascular cells

The oxidative theory of atherosclerosis relies on the modification of low density lipoproteins (LDLs) in the vascular wall by reactive oxygen species. Modified LDLs, such as oxidized LDLs, are thought to participate in the formation of early atherosclerotic lesions (accumulation of foam cells and fatty streaks), whereas their role in advanced lesions and atherothrombotic events is more debated, because antioxidant supplementation failed to prevent coronary disease events and mortality in intervention randomized trials. As oxidized LDLs and oxidized lipids are present in atherosclerotic lesions and are able to trigger cell signaling on cultured vascular cells and macrophages, it has been proposed that they could play a role in atherogenesis and atherosclerotic vascular remodeling. Oxidized LDLs exhibit dual biological effects, which are dependent on extent of lipid peroxidation, nature of oxidized lipids (oxidized phospholipids, oxysterols, malondialdehyde, α,β-unsaturated hydroxyalkenals), concentration of oxidized LDLs and uptake by scavenger receptors (e.g. CD36, LOX-1, SRA) that signal through different transduction pathways. Moderate concentrations of mildly oxidized LDLs are proinflammatory and trigger cell migration and proliferation, whereas higher concentrations induce cell growth arrest and apoptosis. The balance between survival and apoptotic responses evoked by oxidized LDLs depends on cellular systems that regulate the cell fate, such as ceramide/sphingosine-1-phosphate rheostat, endoplasmic reticulum stress, autophagy and expression of pro/antiapoptotic proteins. In vivo, the intimal concentration of oxidized LDLs depends on the influx (hypercholesterolemia, endothelial permeability), residence time and lipid composition of LDLs, oxidative stress intensity, induction of defense mechanisms (antioxidant systems, heat shock proteins). As a consequence, the local cellular responses to oxidized LDLs may stimulate inflammatory or anti-inflammatory pathways, angiogenic or antiangiogenic responses, survival or apoptosis, thereby contributing to plaque growth, instability, complication (intraplaque hemorrhage, proteolysis, calcification, apoptosis) and rupture. Finally, these dual properties suggest that oxLDLs could be implicated at each step of atherosclerosis development, from early fatty streaks to advanced lesions, depending on the nature and concentration of their oxidized lipid content.

FRP inhibits ox-LDL-induced endothelial cell apoptosis through an Akt-NF-{kappa}B-Bcl-2 pathway and inhibits endothelial cell apoptosis in an apoE-knockout mouse model

Atherosclerosis is the most common cause of cardiovascular diseases in the world. Although the development of atherosclerosis appears to be the result of multiple maladaptive pathways, a particularly important factor in the pathogenesis of atherosclerosis is oxidized low-density lipoprotein (ox-LDL), which contributes to endothelial damage. Data from our laboratory and others show that follistatin-related protein (FRP), which is expressed in the vasculature, has cardioprotective effects, suggesting that loss of FRP protection might play a role in the development of atherosclerosis. In the present study, we determined whether FRP overexpression protects against endothelial cell (EC) damage, an intermediate end point for atherosclerosis. We bred apoE-knockout (apoE(-/-)) mice that were FRP(+) transgenic (they overexpressed FRP). We compared them with control mice (their littermates). Human umbilical vein endothelial cells (HUVECs) were isolated and treated with ox-LDL and recombinant FRP. FRP-induced signal transduction and Bcl-2 mRNA and protein stability were analyzed. After 16 wk, apoE(-/-) FRP(+) mice had significantly fewer apoptotic ECs than controls. In vitro experiments showed that the effect of FRP on EC apoptosis was mediated by upregulation of expression of the antiapoptotic protein Bcl-2. In HUVECs, FRP upregulated Bcl-2 transcription via a PI3K-Akt-NF-kappaB pathway. We conclude that FRP overexpression maintains EC viability by preventing apoptosis via Bcl-2 upregulation. FRP may be a novel therapeutic target for the prevention and treatment of vascular EC injury and of atherosclerosis.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

The regular supplementation with an antioxidant mixture decreases oxidative stress in healthy humans. Gender effect

BACKGROUND

Antioxidant consumption is claimed to be associated with improved antioxidant defenses and with the prevention of free radical-associated diseases. We evaluated if the regular supplementation with an antioxidant mixture modified oxidative stress parameters in healthy humans.

METHODS

Malondialdehyde (MDA), vitamin E (alpha-tocopherol), beta-carotene, and ubiquinol-10 were determined in plasma by HPLC; plasma 2-thiobarbituric acid reactive substances (TBARS) were evaluated fluorometrically. The supplement contained 106 IU vitamin E, 10 mg beta-carotene, 60 mg coenzyme Q-10, and 40 microg selenium.

RESULTS

After a 10-day wash out period, 16 healthy, free-living adults (31-48 years old; 9 women, 7 men) consumed the supplement daily during 30 days. At day 20, plasma concentration of vitamin E (alpha-tocopherol), beta-carotene, and ubiquinol-10 increased 45%, 66%, and 104%, respectively, over baseline values. Plasma MDA concentrations were reduced at days 20 (25%) and 30 (32%). Plasma TBARS concentrations decreased steadily during the treatment, reaching at day 30 an 11% decrease compared to baseline. Segregating by gender, both MDA and TBARS plasma concentrations were higher in men than in women at baseline. However, such differences disappeared after 30 days of supplementation.

CONCLUSION

The observed modifications in variables associated with oxidative stress are indicative of an effective antioxidant action of the used mixture of lipid soluble compounds, and gender differences suggest that men should optimize their antioxidants defenses earlier in life than women.