The artifactual nature of lipid peroxides detected in extracts of human aorta

Dicarbonyl-Dependent Modification of LDL as a Key Factor of Endothelial Dysfunction and Atherosclerotic Vascular Wall Damage

The review presents evidence that the main damage to the vascular wall occurs not from the action of “oxidized” LDL, which contain hydroperoxy acyls in the phospholipids located in their outer layer, but from the action of LDL particles whose apoprotein B-100 is chemically modified with low molecular weight dicarbonyls, such as malondialdehyde, glyoxal, and methylglyoxal. It has been argued that dicarbonyl-modified LDL, which have the highest cholesterol content, are particularly “atherogenic”. High levels of dicarbonyl-modified LDL have been found to be characteristic of some mutations of apoprotein B-100. Based on the reviewed data, we hypothesized a common molecular mechanism underlying vascular wall damage in atherosclerosis and diabetes mellitus. The important role of oxidatively modified LDL in endothelial dysfunction is discussed in detail. In particular, the role of the interaction of the endothelial receptor LOX-1 with oxidatively modified LDL, which leads to the expression of NADPH oxidase, which in turn generates superoxide anion radical, is discussed. Such hyperproduction of ROS can cause destruction of the glycocalyx, a protective layer of endotheliocytes, and stimulation of apoptosis in these cells. On the whole, the accumulated evidence suggests that carbonyl modification of apoprotein B-100 of LDL is a key factor responsible for vascular wall damage leading to atherogenesis and endothelial dysfunction. Possible ways of pharmacological correction of free radical processes in atherogenesis and diabetogenesis are also discussed.

Vitamin E and stress. 6. Iron overloading and the metabolism of D-alpha-tocopherol in the rat

1. The effects of iron overloading and unsaturation of dietary lipid on the metabolism of α-tocopherol in the rat were studies.

2. Young adult male vitamin E-deficient rats were given 1000 i.u. of vitamin A and 100 μg of [14C-5-Me]D-α-tocopherol and then given diets containing 5% methyl oleate or 5% cod-liver oil fatty-acid methyl esters. Rats from each group were given intramuscular injections of iron-dextran (50 mg Fe/kg rat) at 48 h intervals for 15 days, and compared with controls given dextran. After this time, liver, kidney and the remainder of the carcass were analysed for [14C]α-tocopherol, and liver and kidney were also analysed for vitamin A.

3. There was no evidence that Fe overloading caused any increase in the destruction of either tocopherol or vitamin A in vivo, whether or not the diet contained polyunsaturated fatty acids. Indeed, treatment with Fe significantly decreased the metabolism of the radioactive tocopherol dose in all three tissues studied.

4. These experiments show that the stress effect of Fe in the vitamin E-deficient animal is unrelated to an increase in oxidative reactions. They provide further evidence that ‘lipid peroxidation’ is not causally concerned in ‘anti-vitamin E’ stress conditions and that α-tocopherol does not function, in vivo, as an antioxidant.

Autoxidation of tissue lipids. I. Incorporation of dietary fatty acids and formation of monocarbonyl compounds in adipose tissue lipids of the vitamin E-deficient rat

Male weanling rats were fed vitamin E-deficient and vitamin E-supplemented diets containing 5% corn oil or cod-liver oil for 16 weeks, after which their adipose tissue lipids were extracted and analyzed in a nitrogen atmosphere for carbonyl compounds and fatty acids.The vitamin E-deficient cod-liver oil-fed rats, exhibiting incisor depigmentation and darkened adipose tissue, yielded lipids which had a lower iodine value, contained less polyunsaturated fatty acids, and contained more carbonyl compounds, particularly alkanals and alk-2-enals, than the lipids from the animals fed the vitamin E-supplemented cod-liver oil diet. The tissues of the vitamin E-deficient corn oil-fed rats contained less linoleate and more monocarbonyl compounds than those of the vitamin E-supplemented corn oil-fed animals.The results indicate that vitamin E protection is necessary for the incorporation of C(20) and C(22) fatty acids into the tissues from the diet and that in the deficiency of vitamin E, a low level of autoxidation occurs in the tissues.