Effects of illicit dexamethasone and 17β-oestradiol on the expression of hepatic and testicular bovine responsive genes

Introduction. Since 1996, the use of growth promoters (GPs) in cattle fattening is banned at the European Union level. Despite this, the continuous illicit use of anabolic steroids (mainly androgens and estrogens), glucocorticoids (i.e. dexamethasone: DEX) or newly synthetic compounds has been demonstrated [1-2]. Besides analytical methods, a recent possible approach to detect illicit treatments consists in the identification of indirect molecular biomarkers (BMs) of effect in target tissues [3]. Therefore, a study was run in beef cattle administered illicitly either DEX or a combination of DEX plus oestradiol (OE). Pre-transcriptional effects of these GPs were investigated in liver and testis by using a set of candidate genes, including major drug metabolizing enzymes, their transcription factors and receptors as well as TAT gene, and a quantitative Real Time RT-PCR (QRT-PCR) approach. Materials and Methods. Eighteen French cross-bred beef cattle (about 500 kg bw, 13-18 months old) were used. They were divided into three groups: controls (n=6), DEX (n=6) and DEX+OE (n=6). DEX was given per os (0,75 mg/day for 42 days, layered on unifeed), while OE (20 mg) was injected sub cutis three times. Animals were slaughtered four days after the suspension of DEX administration. Liver and testis aliquots were collected in RNAlater® and stored at -80°C. Total RNA was extracted by using Invisorb® Spin Tissue RNA Mini Kit. Primers sequences for Q RT-PCR were designed by using Primer Express Software. Data were expressed as –fold change compared with controls group. The β-actin was considered as the reference gene. Results. In the liver CYP2B22 and CYP2E1 were significantly down-regulated in both treated groups. By contrast, CYP3A28, GSTA1-like, SULT1A1-like, RXRα-like and ERα-like were significantly up-regulated in DEX+OE group only. At the testis level, only CYP1A1 gene expression profile was significantly increased in DEX group; besides, CYP2E1 (in contrast to the liver) and ERα-like gene expression were significantly positively modulated only in DEX+OE group. Discussion and conclusion. In the present study, the effects of DEX, illicitly used alone or in combination with OE, were investigated at the pre-transcriptional level in cattle liver and testis. This latter was considered as a prototypical surrogate tissue. Most of genes known to be expressed in the liver were found to be constitutively expressed in the testis, too. As a whole, gene patterns of expression were similar in both tissues; however, some genes (i.e., ERα-like) were affected likewise (induction); some other, instead, were differentially modulated by GPs (i.e., CYP1A1 and CYP2E1). Molecular mechanisms by which GPs alter gene expression profiles in cattle target tissues are still unknown; therefore, further studies are required to increase knowledge on cattle responses to GPs, aiming to set up and validate BMs of exposure to assist official analytical methods in the screening of illicit GPs abuse in cattle fattening.