Hepatic tyrosine aminotransferase and glucocorticoid abuse in meat cattle.

Besides being extensively applied as therapeutical remedies, glucocorticoids (GCs) - most notably dexamethasone or prednisolone - are also illegally used in livestock for growth-promoting purposes. This study was designed to assess the suitability of liver tyrosine aminotransferase (TAT), a gluconeogenic enzyme known to be induced by GCs, to act as a reliable candidate biomarker to screen for GC abuse in cattle. Enzyme activity was measured spectrophotometrically in liver cytosols or in cell extracts, and TAT gene expression was determined by real-time PCR. Compared with untreated veal calves, a notable scatter (20-fold) and much higher median values (3-fold) characterized TAT specific activity in liver samples from commercially farmed veal calves. A time-related increase in both enzyme activity and gene expression was detected in rat hepatoma cell lines treated with dexamethasone concentrations (10(-8) or 10(-9) m) in the range of those recorded in noncompliant samples from EU official controls. In experimental studies in which finishing bulls were administered GCs at growth-promoting dosages, however, no such changes were recorded in dexamethasone-treated animals; a statistically significant rise in liver TAT activity (+95%) only occurred in prednisolone-treated bulls. Although further research is needed to characterize the GC-mediated response in cattle liver, TAT does not appear to be a specific and sensitive biomarker of GC abuse in the bovine species.

Novel strategies for tracing the exposure of meat cattle to illegal growth-promoters.

Official monitoring of residues in cattle throughout the European Union in 2007 found <0.2% non-compliance for the use of illegal growth-promoters (GPs), including sex steroids, corticosteroids and ß-agonists. There is evidence, however, that these figures may underestimate the real incidence of GP abuse in meat cattle breeding. One source of evidence arises from the introduction of new detection strategies in response to the demand for safe and wholesome food. These strategies are based on the biological effects of the different GP classes in target species, with a focus on identifying reliable and cost effective biomarkers to improve detection methods. This review summarises the published data relating to experimental and field studies performed in meat cattle, emphasising the impact of the 'omic' technologies and bioinformatics to discover suitable biomarkers for residue surveillance. Further research is required before any potential biomarkers can be utilised for large scale high throughput screening tests.