The impact of stress on the prevalence of prednisolone in bovine urine: A metabolic fingerprinting approach

Effects of truck transportation and slaughtering on the occurrence of prednisolone and its metabolites in cow urine, liver, and adrenal glands

Background

The recognition of illegal administration of synthetic corticosteroids in animal husbandry has been recently challenged by the case of prednisolone, whose occasional presence in the urine of bovines under strong stressful conditions was attributed to endogenous biosynthesis, not to exogenous administration. The study of the natural stress sources possibly inducing endogenous prednisolone production represents a stimulating investigation subject. The biochemical effects of transportation and slaughtering were verified in untreated cows by studying the possible occurrence of prednisolone and its metabolites in urine, liver and adrenal glands, and the cortisol/cortisone quantification.

Results

Cortisol, cortisone, prednisolone and its metabolites were measured in urine, collected at farm under natural micturition and then at the slaughterhouse. The study was performed on 15 untreated cows reared in different farms at the end of their productive cycle. 2–3 days after the first urine collection, the animals were transported by trucks to the abattoir, slaughtered, and subjected to a second urine sampling from the bladder. Specimens of liver and adrenal gland were also collected and analysed by means of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) validated method. The stressful conditions of transportation and slaughtering proved to increase considerably the urinary levels of cortisol and cortisone as compared to those collected at farm. Prednisolone was detected in the urine collected at the slaughterhouse of two cows only, at a concentration level (≈0.6 μg L^− 1) largely below the official cut off (5.0 μg L^− 1) established to avoid false non-compliances. These two animals exhibited the highest urinary cortisol levels of the series. Prednisolone and prednisone were also detected in the adrenal glands of a different cow. Prednisolone metabolites were not detected in any urine, liver, and adrenal gland sample.

Conclusion

Within the constraints of the condition adopted, this study confirms the sporadic presence of prednisolone traces (2 samples out of 15) and the consistently increased concentration of cortisone and cortisol in the urines collected from cows subjected to truck transportation and subsequent slaughtering. No prednisolone metabolites were detected in any liver and adrenal gland samples, nor in urine specimens, unlike what was previously reported for cows artificially stressed by pharmacological treatment.

Pharmacokinetic and urinary profiling reveals the prednisolone/cortisol ratio as a valid biomarker for prednisolone administration

BACKGROUND

In Europe, synthetic corticosteroids are not allowed in animal breeding for growth-promoting purposes. Nevertheless, a high prevalence of non-compliant urine samples was recently reported for prednisolone, however, without any indication of unauthorized use. Within this context, 20β-dihydroprednisolone and the prednisolone/cortisol ratio have been suggested as potential tools to discriminate between exogenous and endogenous urinary prednisolone. In this study, the validity of these strategies was verified by investigating the plasma pharmacokinetic and urinary excretion profiles of relevant glucocorticoids in bovines, subjected to exogenous prednisolone treatment or tetracosactide hexaacetate administration to induce endogenous prednisolone formation. Bovine urine and plasma samples were analysed by liquid chromatography and mass spectrometry.

RESULTS

Based on the plasma pharmacokinetics and urinary profiles, 20β-dihydroprednisolone was confirmed as the main prednisolone-derived metabolite, being detected in the biological fluids of all 12 bovines (plasma AUC0-inf of 121 h μg L-1 and urinary concentration > 0.695 μg L-1). However, this metabolite enclosed no potential as discriminative marker as no significant concentration differences were observed upon exogenous prednisolone treatment or tetracosactide hexaacetate administration under all experimental conditions. As a second marker tool, the prednisolone/cortisol ratios were assessed along the various treatments, taking into account that endogenous prednisolone formation involves the hypothalamic-pituitary-adrenal axis and is associated with an increased cortisol secretion. Significantly lower ratios were observed in case of endogenous prednisolone formation (i.e. ratios ranging from 0.00379 to 0.129) compared to the exogenous prednisolone treatment (i.e. ratios ranging from 0.0603 to 36.9). On the basis of these findings, a discriminative threshold of 0.260 was proposed, which allowed classification of urine samples according to prednisolone origin with a sensitivity of 94.2% and specificity of 99.0%.

CONCLUSION

The prednisolone/cortisol ratio was affirmed as an expedient strategy to discriminate between endogenous and exogenous prednisolone in urine. Although the suggested threshold value was associated with high specificity and sensitivity, a large-scale study with varying experimental conditions is designated to optimize this value.

Discrimination between Synthetically Administered and Endogenous Thiouracil Based on Monitoring of Urine, Muscle, and Thyroid Tissue: An in Vivo Study in Young and Adult Bovines

Thiouracil (TU), synthesized for its thyroid-regulating capacities and alternatively misused in livestock for its weight-gaining effects, is acknowledged to have an endogenous origin. Discrimination between low-level abuse and endogenous occurrence is challenging and unexplored in an experimental setting. Therefore, cows (n = 16) and calves (n = 18) were subjected to a rapeseed-supplemented diet or treated with synthetic TU. Significant higher urinary TU levels were recorded after TU administration (<CC_α, 15 642 μg L^-1) compared to rapeseed supplementation (<CC_α, 65.8 μg L^-1), however, with overlapping values. TU was not detected in the edible meat; however, concentrations between the CC_α and 10 μg kg^-1 were noted in thyroid tissue of calves and cows following rapeseed supplementation. The latter concentrations were significantly higher in thyroid tissue of calves (22.9-41.8 μg kg^-1) and cows (16.9-36.7 μg kg^-1) after synthetic TU administration. These results strongly point toward thyroid analysis as a discriminatory tool.

Quantification of natural and synthetic glucocorticoids in calf urine following different growth-promoting prednisolone treatments

Over the last few years, low levels of prednisolone have been reported in several cattle urine samples by a number of laboratories within the EU at an average concentration of 2.0 ng mL(-1). The occurrence of prednisolone residues together with increased levels of hydrocortisone and cortisone in urine and tissue samples of untreated animals seems to demonstrate that traces of this steroid can be produced endogenously during stressful situations. Therefore, the endogenous origin of prednisolone makes difficult to correlate positive samples to a potential illicit treatment. An experimental study was developed to investigate the presence of natural and synthetic glucocorticoids and to evaluate levels of excreted prednisolone following growth-promoting treatments. Urine samples from calves undergone oral treatment with prednisolone, alone and in association with dexamethasone, were analyzed by a LC-MS/MS method, validated according to the Commission Decision 2002/657/EC. We also investigated if urinary free 6β-hydroxyhydrocortisone/hydrocortisone ratio could be a reliable biomarker of illicit treatment with prednisolone and dexamethasone in calves. Our data revealed that urinary levels of prednisolone after both oral prednisolone treatments, never exceeded the value of 1.1 ng mL(-1). Similar prednisolone levels were found in urine samples of untreated calves. Moreover the presence of 6β-hydroxyhydrocortisone below the CCα value made possible to estimate the 6β-hydroxyhydrocortisone/hydrocortisone ratio only in a very limited number of samples. Obtained data suggest that further criteria have to be considered to allow correct decisions about the urinary presence of prednisolone during control activities.