Testosterone metabolism of equine single CYPs of the 3A subfamily compared to the human CYP3A4

Abstract

Cytochrome P450 enzymes (CYPs) are responsible for the phase I metabolism of drugs, xenobiotics and endogenous substances. Knowledge of single CYPs and their substrates is important for drug metabolism, helps to predict adverse effects and may prevent reduced drug efficacy in polypharmacy. In this study, three equine isoenzymes of the 3A subfamily, the equine flavoprotein NADPH-P450 oxidoreductase (POR), and the cytochrome b5 (CYB5) were cloned, sequenced and heterologously expressed in a baculovirus expression system. Testosterone, the standard compound for characterization of the human CYP3A4, was used to characterize the newly expressed equine CYPs. The metabolite pattern was similar in equine and the human CYPs, but the amounts of metabolites were isoform-dependent. All equine CYPs produced 2-hydroxytestosterone (2-OH-TES), a metabolite never described in equines. The main metabolite of CYP3A4 6β-hydroxytestosterone (6β-OH-TES) was measured in CYPs 3A95 and 3A97 with levels close to the detection limit. Ketoconazole inhibited 2-OH-TES in the human CYP3A4 and the equine CYP3A94 and CYP3A97 completely, whereas a 70% inhibition was found in CYP3A95. Testosterone 6β- and 2-hydroxylation was significantly different in the equine CYPs compared to CYP3A4. The expression of single equine CYPs allows characterizing drug metabolism and may allow prevention of drug-drug interactions.

Regional Differences in Human Intestinal Drug Metabolism

“…In addition, in agreement with our findings, Ho et al (2017) described that CYP3A4 (TT as a substrate) was the most active enzyme in cryopreserved enterocytes from human small intestines followed by UGT and SULT (7-HC as a substrate), respectively. Furthermore, we also discovered a strong correlation between several products formed by CYP3A (e.g., 2b-TOH and 6b-TOH; Emoto et al, 2000b;Vimercati et al, 2017), CYP2A (15a-TOH; Honkakoski and Negishi, 1997), UGT1A (7-HC glucuronide; Wang et al, 2006), and SULT1 (7-HC sulfate, Wang et al, 2006) in both the ileum and colon. These results suggest that there might be a shared regulatory mechanism between phase I and phase II enzymes.…”

Profiling Urinary Sulfate Metabolites With Mass Spectrometry

“…The final metabolite 5α-androstane-3β,17α-diol 3-sulfate (3) has not been described in literature or in online data bases such as ChEBI (Hastings et al, 2016). The upregulated nature of these steroid sulfates also support the general idea of perturbation caused by doping with testosterone propionate (Pozo et al, 2010;Scarth et al, 2011;Vimercati et al, 2017). Future directions for this work could aim at identifying the remaining seven putative steroid sulfate metabolites against reference materials.…”