review of the methodology for assessing in vivo antioxidant capacity

Oxidative stress and antioxidant deficiency have been implicated in the pathophysiology of a wide range of diseases and conditions. Consequently, over recent years many different supplementation trials have been implemented, aimed at improving clinical outcomes by boosting antioxidant levels. These trials have included supplementation with individual antioxidants, antioxidant combinations and antioxidant-rich foods, such as fruit and vegetable juices and other plant extracts. To ensure data from these trials is interpreted correctly, it is essential that suitable biomarkers are used to assess changes in in vivo antioxidant activity resulting from supplementation. This review discusses methods for measuring antioxidant activity, including direct measurement of antioxidant concentrations and assays for measuring overall reducing capacity. Antioxidant activity can also be indirectly assessed by monitoring levels of oxidative stress. This review describes biomarkers that can be used to assess oxidative damage to lipids (including F2-isoprostanes, malondialdehyde, 4-hydroxy-2-nonenal, and the hydrocarbons, ethane and pentane), protein (including protein carbonyls and nitrotyrosine) and DNA (via 8-hydroxydeoxyguanosine assay). Direct measurement of free radicals is also discussed. Useful information is provided for researchers planning animal and human intervention trials involving antioxidant-rich foods or supplements, including plant extracts. The development and use of appropriate methodologies is essential if the role of antioxidant supplementation in various diseases and conditions is to be understood.