Oxidative stress as a bio-marker of estrogen exposure in healthy veal calves

In humans, the use of estrogen-based contraceptives is positively related to oxidative stress, via the formation of 2-3,4-quinone metabolites as free radicals by an E2-4-hydroxylase. These compounds are directly genotoxic and can undergo redox cycling to form toxic reactive oxygen metabolites (ROMs). This prompted us to investigate oxidative stress in terms of ROMs and of the anti-oxidant power (AOP) in sera of veal calves exposed to 17beta-estradiol (17betaE). ROMs and AOP were measured by two colorimetric methods the former based on the Fenton reaction, the latter performed as a neutralization assay of a titred HOCl solution. 17betaE Levels were screened by radio immuno assay (RIA) and confirmed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), and related for significance to the established threshold (40 ng l(-1)) in sera. Basal levels were measured in different groups of veal calves: mother suckling (MS; n = 102), free grazing (FG; n = 108), intensively farmed fed on soia and corn silage (IF-; n = 104). In calves with 17betaE above the threshold in sera (IF+; n = 16), we recorded the highest ROMs level (3.15 mM H2O2), with a negative correlation with AOP values. IF+ data significantly differed even from those of MS calves (2.61 mM H2O2) naturally exposed to colostrum hormones. The absolute ROMs value combined with an impairment of the AOP adaptive response can be considered an epidemiological bio-marker for xenobiotic estrogen treatments. (C) 2002 Elsevier Science B.V. All rights reserved.