Lipoproteins protection from oxidation

However, peroxidation can also occur in extracellular lipid transport proteins, such as low-density lipoprotein (LDL), that are protected from oxidation only by antioxidants present in the lipoprotein itself or the exttacellular environment of the artery wall. It appeats that these antioxidants are not always adequate to protect LDL from oxidation in vivo, and extensive lipid peroxidation can occur in the artery wall and contribute to the pathogenesis of atherosclerosis (Palinski et al., 1989 Ester-bauer et al., 1990, 1993 Yla-Herttuala et al., 1990 Salonen et al., 1992). Once initiation occurs the formation of the peroxyl radical results in a chain reaction, which, in effect, greatly amplifies the severity of the initial oxidative insult. In this situation it is likely that the peroxidation reaction can proceed unchecked resulting in the formation of toxic lipid decomposition products such as aldehydes and the F2 isoprostanes (Esterbauer et al., 1991 Morrow et al., 1990). In support of this hypothesis, cytotoxic aldehydes such as 4-... 

Dipyridamole has also been shown to have antioxidant effects (19). Antioxidants act to remove harmful reactive-oxygen species and protect low-density lipoproteins (LDL) from oxidation oxidized LDL plays a key role in the development and propagation of atherosclerosis. The antioxidant effects of dipyridamole may be both direct (by scavenging oxygen and hydroxyl radicals, inhibiting lipid peroxidation and oxidative modification of LDL) (20-22) and indirect (via adenosine, which reduces superoxide anion generation). Dipyridamole has been shown to be a more effective anioxidant than ascorbic acid, alpha-tocopherol, or probucol (22). 

Consumption of products rich in phenolic acids, such as wine and the Mediterranean diet, correlates with a reduced risk of cardiovascular disease. Since phenolic acids may exhibit antioxidant properties, a role in protecting low-density lipoprotein (LDL) from oxidative modification has been proposed [47, 99]. 

Because the carotenoids favour hydrophobic domains they are generally localised in the membranes and lipoproteins of animal cells. In this location they can influence the oxidation of membrane lipids and prevent the passage of free radicals from one cellular compartment to another. Thus, DNA in the nucleus is protected from intracellularly generated ROS by (at least) the nuclear membrane and from extracellular ROS by a number of membranes. Should ROS reach the nucleus, base oxidation can occur. The base most susceptible to oxidation is guanine, although all other bases can also be affected. The cell has the ability to detect damaged bases, excise them. 

Limited studies have focused on dietary intake of astaxanthin by humans. In a study reported by Miki, an astaxanthin-containing drink was used to protect low-density lipoprotein from oxidation (astaxanthin was administered at doses of 3.6 to 14.4 mg/day over a 2-week period). Progressive slowing of LDL oxidation with increasing doses of astaxanthin was observed and no ill effects were reported. 

McAnlis, G.T., McEneny, J., Pearce, J., and Young, I.S., Black tea consumption does not protect low density lipoprotein from oxidative modification, Eur. J. Clin. Nutr., 52, 202, 1998. 

Schroeter, H. et al., Flavonoids protect neurons from oxidized low-density-lipoprotein-induced apoptosis involving c-Jun N-terminal kinase (INK), c-Jun and caspase-3, Biochem. J., 358, 547, 2001. 

Spin trapping has also been applied to the investigation of lipid peroxidation catalysed by myoglobin in linoleate emulsions,204 as well as the oxidation of phospholipids in low-density lipoproteins (18.1) by HOC1.205 Hiramoto et al. have shown that, by quenching the attacking radicals, linoleic acid can protect DNA from oxidation.206 Lipid peroxidation has also been monitored by spin labelling.207... 

Phenolic compounds also have important antioxidant properties, protecting food from oxidation [9]. The antioxidant properties of phenolic compounds can have an impact on human health and they are regarded as having a protective effect against low-density lipoprotein (LDL) oxidation and cardiovascular diseases [3], Recently phenolic compounds have been widely used in cosmetic preparations to delay aging [10]. 

Brown, J.E. and Rice-Evans, C.A. 1998. Luteolin rich artichoke extract protects low density lipoprotein from oxidation in vitro. Free Radio. Res. 29, 247-255. 

Atherosclerosis is a chronic inflammation of the arterial vessel wall resulting in plaque formation that eventually may cause cardiovascular events, such as myocardial infarction or cerebral vascular accidents. The presence of autoimmune components in atherosclerosis is well established. Autoantibodies to heat-shock proteins and oxidized low-density lipoproteins (oxLDL) are prevalent in the circulation of patients with atherosclerosis, but the role of these autoantibodies is debated. While anti-oxLDL IgG antibodies may facilitate uptake of oxLDL by foam cells in the lesions, natural IgM antibodies directed to oxLDL may even protect from atherosclerosis. Atherosclerotic plaques also contain some T cells that are considered to be autoreactive, although the respective autoantigens have not yet been identified. These T cells are probably not involved in the plaque formation as such, but they may cause plaque instability, rupture, and subsequent clinical events. 

Oleuropein appears to interfere with some biological processes such as lipoprotein oxidation, platelet aggregation, platelet and leukocyte eicosanoid production and cardiovascular control too. As previously described, oleuropein and hydroxy-tyrosol are characterised by a catechol moiety that appears to be needed for their scavenger and antioxidant activities. In fact, it was demonstrated that these compounds prevent thermally initiated autoxidation of methyl linoleate in homogenous solutions [56], protect LDL from oxidation [57] and inhibit production of... 

The mature erythrocyte cannot synthesize new membrane proteins or lipids. However, membrane lipids can be freely exchanged with circulating lipoprotein lipids. The glutathione system protects the proteins and lipids from oxidative damage. 

Visioli, F. and Galli, C. (1994) Oleuropein protects low density lipoprotein from oxidation. Life Sciences, 55, 1965-71. 

High density lipoproteins (HDL). Smaller lipoproteins with buoyant density 1.063 1.21 g/mL that carry cholesterol as well as a wide variety of peptides involved in oxidant defence and regulation of inflammation. High HDL levels generally confer protection from atherosclerosis. 

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