Antioxidants secondary prevention

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. 2007. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention systematic review and meta-analysis. JAMA 297 842-857. 

Cambridge Heart Antioxidant Study DATATOR Deprenyl and Tocopherol Antioxidative Therapy of Rarkinsonism FMC, Finnish Mobile Clinic Health Examination Survey GISSI, Gruppo Italiano Studio Soprawivenza Infarto HOPE, Heart Outcome Prevention Evaluation HPFS, Health Professional Follow-up Study NHS, Nurses Health Study PPR Primary Prevention Project SPACE, Secondary Prevention with Antioxidants of Cardiovascular disease in End-stage renal disease VEAPS, Vitamin E Atherosclerosis Prevention Study VECAT Vitamin E Cataract Age-related maculopathy Trial. 

Boaz M, Smetana S, Weinstein T et al. Secondary prevention with antioxidants of cardiovascular disease in endstage renal disease (SPACE) randomised placebo-controlled trial. Lancet 2000 356 1213-1218. 

Biesalski, H.K. 1999. The role of antioxidative vitamins in primary and secondary prevention of coronary heart disease. Int. J. Vitam. Nutr. Res. 69(3) 179-186. 

Severe, life-threatening asthmatic reactions following consumption of restaurant meals and wine have occurred secondary to ingestion of the food preservative potassium metabisulfite. Sulfites have been used for centuries as preservatives in wine and food. As antioxidants, they prevent fermentation of wine and discoloration of fruits and vegeta-... 

There are many types of antioxidants. The most popular in composite materials are primary antioxidants or chain breaking antioxidants, and secondary antioxidants or preventative antioxidants. ... 

A division of antioxidants into primary (chain breaking) and secondary (preventative) is often rather arbitrary, and Irganox 1010 and Irganox 1076, for example, are considered both primary and secondary. 

The available data from such trials are not yet sufficient to fully assess the risk-to-benefit ratio for vitamin C. There are no completed large-scale trials of vitamin C in the prevention or treatment of CVD. The United States National Heart, Lung, and Blood Institute sponsored a recent conference, Antioxidants and the Prevention of Human Atherosclerosis (Steinberg and Workshop Participants, 1992). The summary statement supported the need for further large-scale randomized trials examining the role of vitamin C as well as (3-carotene and vitamin E in the primary and secondary prevention of CVD. 

Antioxidants act either by radical trapping, interfering in the radical propagation, or by decomposition of the hydroperoxide formed. In this way they inhibit the formation of new radicals. The former are known as chain breaking or chain terminator antioxidants (primary antioxidants). The latter, the hydroperoxide decomposing agents, are also known as preventive antioxidants (secondary antioxidants). 

In combination with primary antioxidants, secondary antioxidants delay the consumption of the former by decomposing hydroperoxides to non-radical compounds and by preventing the formation of new radical decomposition products. Many stabilizer types supplement each other, thus protecting against too rapid consumption and increasing their effectiveness multiple times. That is why secondary antioxidants are very often called synergists or co-stabilizers . Detailed descriptions of the secondary antioxidants mechanisms can be found in [518], [519], and [523]. 

Table 4 Summary of large intervention trials >1000 subjects) investigating the role of antioxidants and cancer in secondary prevention ...

The ability of a-tocopherol supplementation to prevent cardiovascular events in different populations was tested in four larger prospective clinical trials The a-Tocopherol, yS-Carotene Cancer Prevention (ATBC) study, the Cambridge Heart Antioxidant Study (CHAOS), the Gruppo Italiano per lo studio della Sopravvivenza nell Infarto Miocar-dito (GISSI) trial, and the Heart Outcome Prevention Evaluation (HOPE) study. In addition, at least two smaller prospective clinical trials have been completed the Secondary Prevention with... 

Another method for slowing oxidation of rubber adhesives is to add a compound which destroys the hydroperoxides formed in step 3, before they can decompose into radicals and start the degradation of new polymer chains. These materials are called hydroperoxide decomposers, preventive antioxidants or secondary antioxidants. Phosphites (phosphite esters, organophosphite chelators, dibasic lead phosphite) and sulphides (i.e. thiopropionate esters, metal dithiolates) are typical secondary antioxidants. Phosphite esters decompose hydroperoxides to yield phosphates and alcohols. Sulphur compounds, however, decompose hydroperoxides catalytically. 

The early work of Kennerly and Patterson [16] on catalytic decomposition of hydroperoxides by sulphur-containing compounds formed the basis of the preventive (P) mechanism that complements the chain breaking (CB) process. Preventive antioxidants (sometimes referred to as secondary antioxidants), however, interrupt the second oxidative cycle by preventing or inhibiting the generation of free radicals [17]. The most important preventive mechanism is the nonradical hydroperoxide decomposition, PD. Phosphite esters and sulphur-containing compounds, e.g., AO 13-18, Table la are the most important classes of peroxide decomposers. 

The detection and quantification of one or more of the above lipid peroxidation produas (primary and/or secondary) in appropriate biofluids and tissue samples serves to provide indices of lipid peroxidation both in ntro and in vivo. However, it must be stressed that it is absolutely essential to ensure that the products monitored do not arise artifactually, a very difiScult task since parameters such as the availability of catalytic trace metal ions and O2, temperature and exposure to light are all capable of promoting the oxidative deterioration of PUFAs. Indeed, one sensible precaution involves the treatment of samples for analysis with sufficient levels of a chainbreaking antioxidant [for example, butylated hydroxy-toluene (BHT)] immediately after collection to retard or prevent peroxidation occurring during periods of storage or preparation. 

Various aromatic secondary amines, substituted phenols, and pyrazoli-dones (3) that function as traps for the propagating peroxy radicals gave dead-stop induction periods when used at a concentration of 50 p.p.m. An indication of the ease of oxidation of chloroprene is that 50 p.p.m. of 2,6-di-ferf-butyl-4-methylphenol gave an induction period of only 15 minutes, while the same concentration of antioxidant prevented n-hexadecane from oxidizing for 2 hours at 160°C. 

Secondary antioxidants, i.e., sequestrants or chelators, are important compounds in the prevention of lipid oxidation. The effect of chelators tested varied with the different compounds. Of those chelators tested, ethylenediaminetetraacetic acid (EDTA, tetrasodium salt) and sodium phytate were the most effective inhibitors of lipid oxidation (so indicated by low hexanal and TEARS values) and MFD (as seen by high CBB and low PIT and CBD intensity values), see Table 5. Sodium phytate was previously shown to chelate iron and thus, was proposed as a food antioxidant(7J). Sodium citrate at a concentration of 500... 

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