New In Vitro Models Improve Detection of Doping Peptide Metabolism

Abuse of synthetic doping peptides is a growing concern in sports, presenting significant challenges for anti-doping agencies due to their rapid metabolism and diverse degradation pathways in the body. Accurate detection relies on a thorough understanding of how these peptides are broken down, but existing in vitro models for studying their metabolism often lack the comprehensive predictive power needed to mimic in vivo conditions. This study aimed to compare the efficacy of various in vitro systems in mimicking the in vivo metabolism of synthetic doping peptides, identifying the most suitable models for forensic analysis and drug testing.

The study revealed significant differences in metabolic activity and metabolite profiles across the in vitro models, with liver S9 fraction demonstrating the most comprehensive metabolic activity for most tested peptides. For instance, GHRP-2 showed 95% degradation within 60 minutes in liver S9 fraction, compared to only 40% in human blood serum and 70% in liver microsomes over the same period. > Crucially, liver S9 fraction and liver microsomes produced a broader range of metabolites, including oxidative and hydrolytic products, which are highly relevant for in vivo detection, showing a 2.5-fold increase in metabolite diversity compared to enzymatic models. Kidney microsomes exhibited moderate activity, particularly for peptides undergoing renal excretion, achieving 65% degradation of BPC-157 within 90 minutes, whereas purified proteolytic enzymes primarily showed rapid, non-specific hydrolysis of peptide bonds. The half-life of BPC-157 was estimated to be 15 minutes in liver S9 fraction, significantly shorter than the 45 minutes observed in human blood serum (p<0.01).