Inhibition of in vitro metabolism of testosterone in human, dog and horse liver microsomes to investigate species differences.

The research article investigates how testosterone is metabolized differently in human, canine, and equine liver microsomes, providing a better understanding of variations in testosterone biotransformation across these species.

Research Process and Methods

• The researchers studied the hydroxylation of testosterone, which is a chemical process in which an oxygen atom is added to the testosterone molecule, in liver microsomes from humans, dogs, and horses. Liver microsomes are sub-cellular components that play a key role in drug metabolism.
• They focused on the role of Cytochrome P450 (CYP) enzymes, specifically examining the CYP1, CYP2, and CYP3 families. This was done using chemical inhibitors, which are substances that slow down a chemical reaction.
• The resulting testosterone metabolites were then analyzed through High-Performance Liquid Chromatography (HPLC), a method used to separate and analyze compounds.

Findings

• Three metabolites – androstenedione, 6β-hydroxytestosterone, and 11β-hydroxytestosterone – were found across all species. However, the metabolite patterns differed among species.
• The metabolite androstenedione was more prevalent in canine and equine species, with an observable increase over time in horses.
• The hydroxylation process was primarily catalyzed by the CYP3A subfamily in all three species studied.
• Another enzyme, CYP2C9, was found not to metabolize testosterone. However, its canine equivalent, CYP2C21, produced androstenedione.
• Two inhibitors, quercetin and sulfaphenazole, were found to hinder testosterone metabolization, indicating that the enzymes CYP2C8 and possibly CYP2B6 might play a part in testosterone metabolism.
• Horse and human microsome metabolization was affected by these inhibitors, but not canine metabolism, suggesting species variation in testosterone metabolism.
• The study also indicates that 17β-hydroxysteroid dehydrogenase 2 enzyme could be involved in the formation of androstenedione in humans, with increased formation observed in horse microsomes and no involvement detected in canines.

Implications

• The study offers crucial insights into species-level differences in testosterone metabolism, which could help in refining veterinary and human medicine dosages.
• These results will equip pharmacologists with a better understanding of the role of different enzymes in testosterone hydroxylation, which can further assist in the modulation of therapeutic procedures.