Variability of oxygen radical absorbance capacity (ORAC) in different animal species

The oxygen radical absorbance capacity (ORAC) was measured both in whole (O RAC-T) and deproteinized (ORAC-AS) plasma samples of human, pig, cow, rabbi t, dog, cat, sheep, horse, dolphin, turkey, guinea-hen and chicken. In the 12 species, ORAC-T data, expressed as micromoles of peroxyl radicals trappe d by 11 of sample, were found scattered between 8,600 and 23,000 mu mol/l. The species with the highest ORAC-T values were cat among mammals and chick en among avies. ORAC-AS values ranged between 600 and 2000 mu mol/l, with t he highest values found in dolphin and sheep among mammals, while chicken w as first among avies. In the 12 species, the relative contribution of ORAC- AS in relation to ORAC-T ranged from 5% to 20%. Protein SH-groups and uric acid were measured in plasma of all species, but no significant correlation was found between thiols and ORAC-T values or between uric acid and ORAC-A S values. Our results show that: (1) the ORAC method is reproducible and se nsitive enough to be used in the comparison of the peroxyl-radical absorban ce capacity of protein and non-protein plasma components in different anima l species; (2) both in mammals and in avies, there is a deep intra-class he terogeneity of ORAC-T and ORAC-AS values; (3) by considering most species, plasma proteins and lipoproteins account for about 85-90% of the overall pe roxyl-radical trapping capacity. In the dolphin only, the protein contribut ion decreases to 80%; (4) uric acid accounts for about one-half of the ORAC -AS value in human, guinea-hen and for about one-third in chicken, while it provides a very limited contribution in other species. We conclude that sp ecies with the highest ORAC-T, like cat and chicken, or with the highest OR AC-AS, like dolphin, are interesting models to study the reasons of such a marked antioxidant defense in the plasma.