Oxygen free radicals, sources

A number of scientists in the late 1960s through the mid-1970s pointed out that many sources in biological systems produce oxygen free radicals. For example, some oxidative enzymes which contain flavin as a prosthetic group proceed by a radical mechanism. When illuminated,... 

Hyperlipidemia and the recruitment of inflammatory cells into the atherosclerotic arterial wall are suggested to cause excessive production of oxygen flee radicals [19]. Ohara et al. found that aortas from rabbits that had been fed a high cholesterol diet for several weeks produced several fold more oxygen free radicals than did control aortas [19,24]. Furthermore, removal of the endothelium resulted in reduction of free radical production, suggesting that the endothelium is a major source of the reactive oxygen species in this model. It was hypothesized that the abnormal redox state in the arterial wall may be a fundamental metabolic feature of atherosclerosis [19]. 

Product stability and performance can be affected by exposure to several oxidative sources, including oxygen, free radicals, UV radiation, oxidative enzymes, catabolic oxidation, and chemical oxidation. Many antioxidants are also good UV absorbers due to their conjugated chemical structure. Typical antioxidants found in cosmetic products are flavonoids, polyphenols, carotenoids, thiols, tocopherol (vitamin E) and ascorbic acid (vitamin C) [71,72], According to Black [73], a combination of antioxidants from different classes is more effective than a single antioxidant due to an antioxidant cascade mechanism. 

One particular relevant source of free radicals is provided by the xanthine oxidase-catalysed conversion of oxygen to the superoxide radical. This process may be initiated by tumour necrosis factor (TNFoO- Arroyo et al. (1995) have shown that sulphur mustard can induce human monocytes to release TNFa thus, a link between sulphur mustard and oxygen free radical formation has been identified. Polymorphonuclear leukocytes respond to the presence of bacteria by an... 

The loss of oxygen during an oxidation reaction is the result of a complex set of reactions. In the simplest situation where radicals are introduced into the system at a constant rate, such as by thermal decomposition of a free radical source, and where loss of radicals occurs upon every interaction of two R02, the overall scheme is... 

The flavones and catechins seem to be the most powerful flavonoids for protecting the body against ROS. Epicatechin and rutin are also powerful free-radical scavengers. Xanthine oxidase enzyme is a source of oxygen-free radicals. The scavenging ability of rutin, quercetin, and silibin may be due to its inhibitory effect on xanthine oxidase activity, thereby resulting in decreased oxidative injury [60]. 

A mixt. of isomeric prods. All eight hydroperoxides are formed by reaction with singlet oxygen. Free radical autoxidn. probably gives the 5-, 8-, 9-, 11-, 12- and 15-isomers only. Enzymic oxidn. can give rise to the 15- or 12-hydroperoxides depending on the enzyme source. 

The respiratory chain is the major source of oxygen free radicals. In theory, molecular oxygen should be completely reduced in complex IV by four electrons from water without the formation of intermediates. In practice, sometimes partial reduction occurs with oxygen being converted to superoxide anion radicals (Fig. 15.1). Also, the ubiquinone reactions in complexes I and II have an unfortunate tendency to leak electrons directly to oxygen. Overall, up to 2% of cellular oxygen forms superoxide free radicals and the body has developed defence mechanisms to counter their damaging effects. 

The reaction is initiated by a free-radical source. The initiator will be benzoyl peroxide, a relatively unstable molecule, which at 80-90°C decomposes with hemolytic cleavage of the oxygen-oxygen bond ... 

Brieland JK, Clarke SJ, Karmiol S, Phan SH, Fantone JC (1992) Transferrin a potential source of iron for oxygen free radical-mediated endothelial cell injury. Arch Biochem Biophys 294 265-270... 

The first commercial manufacture of polyethylene, using high-pressure ethylene gas in the presence of trace amounts of oxygen that acted as a free-radical source for the initiation of the polymerization process, was due to the important physical properties of polyethylene for electrical applications at the beginning of World War 11. In 1940 about 90 metric tons of polyethylene was produced by Imperial Chemical Industries (ICI) in Great Britain in support of the war effort. 

Molecular oxygen was utilized by the ICI scientists in 1933 as the free-radical source to initiate the high-pressure ethylene polymerization reaction that provided high molecular weight polyethylene. (A free radical is a highly reactive, unstable, chemical intermediate comprised of an unpaired electron designated by a [ ] symbol.) Presently, organic peroxides (R-O-O-R) are utilized as the free-radical source as shown below. 

The replacement of oxygen as the free-radical source with organic peroxides has led to a more controlled polymerization process which has essentially... 

Ide T, Tsutsui H, Kinugawa S, et al. Mitochondrial electron transport complex I is a potential source of oxygen free radicals in the failing myocardium. Circ Res 1999 85 357-363. 

---