The application of in vitro technologies to study the metabolism of the androgenic/anabolic steroid stanozolol in the equine.

The research is about a case study on the use of equine liver and lung microsomes, along with S9 tissue fractions, to examine the metabolism of the steroid stanozolol. The study highlights how in vitro studies can enhance our understanding of drug metabolism while also potentially reducing the need for animal testing.

Methodology

• Equine liver and lung microsomes, as well as S9 tissue fractions, were utilized to explore the metabolism of stanozolol, an androgenic/anabolic steroid, under in vitro conditions. This was carried out to demonstrate the potential of in vitro methodologies in sports drug testing.
• In vitro incubates were analytically compared with urine samples obtained from in vivo stanozolol administrations using a variety of analytical techniques, such as LC-MS on a high-resolution accurate mass Thermo Orbitrap Discovery instrument, LC-MS/MS on an Applied Biosystems Sciex 5500 Q Trap, and GC-MS/MS on an Agilent 7000A.

Findings

• The high-resolution mass full scan analysis on the Orbitrap revealed that in vitro fractions from equine liver microsome and S9 were capable of generating all significant phase-1 metabolites observed in in vivo administrations.
• A less steep HPLC gradient combined with MS/MS functions on the 5500 Q trap led to the identification of several phase 1 metabolites, previously unreported in horses or any other species, in the liver microsomal incubates.
• Comparing liver and lung S9 metabolism, the study found that the liver was the principal site of metabolic activity in the equine.

Enzyme Inhibitor Experiment

• The study employed selective chemical enzyme inhibitors that are known to target specific isoforms in other species, suggesting that an enzyme related to CYP2C8 might be responsible for the production of 16-hydroxy-stanozolol metabolites in horses.

Conclusion

• The research concluded that the results of in vitro and in vivo phase 1 metabolism are very similar. This underscores the potential of in vitro studies not only to enhance the existing in vivo paradigm but also to promote animal welfare by minimizing and refining animal testing.