Antioxidants and protein oxidation

Proteins are susceptible to oxidation by reactive oxy gen species, where th e type of damage induced is characteristic of the denaturing species. The i nduction of protein carbonyls is a widely applied biomarker, arising from p rimary oxidative insult. However, when applied to complex biological and pa thological conditions it can be subject to interference from lipid, carbohy drate and DNA oxidation products. More recently, interest has focused on the analysis of specific protein bou nd oxidised amino acids. Of the 22 amino acids, aromatic and sulphydryl con taining residues have been regarded as being particularly susceptible to ox idative modification, with L-DOPA from tyrosine, ortho-tyrosine from phenyl alanine; sulphoxides and disulphides from methionine and cysteine respectiv ely; and kynurenines from tryptophan. Latterly, the identification of valin e and leucine hydroxides, reduced from hydroperoxide intermediates, has bee n described and applied. In order to examine the nature of oxidative damage and protective efficacy of antioxidants the markers must be thoroughly evaluated for dosimetry in v itro following damage by specific radical species. Antioxidant protection a gainst formation of the biomarker should be demonstrated in vitro. Quantifi cation of biomarkers in proteins from normal subjects should be within the limits of detection of any analytical procedure. Further to this, the techn iques for isolation and hydrolysis of specific proteins should demonstrate that iii vitro oxidation is minimised. There is a need for the development of standards for quality assurance material to standardise procedures betwe en laboratories. At present, antioxidant effects on protein oxidation in vivo are limited to animal studies, where dietary antioxidants have been reported to reduce di tyrosine formation during rat exercise training. Two studies on humans have been reported last year. The further application of these methods to human studies is indicated, where the quality of the determinations will be enha nced through inter-laboratory validation.