Analysis and Characterization of Kisspeptin and Its Analogues in Serum and Urine Samples by Liquid...

The use of testosterone-stimulating peptides for doping purposes is prohibited for male athletes by the World Anti-Doping Agency (WADA). Among these substances is kisspeptin (KP-54), its isoforms (KP-14, KP-13, and KP-10), and synthetic receptor agonists such as TAK-448. Thus, they have been included in the WADA Prohibited List in 2024. To enable effective detection of kisspeptin misuse, reliable analytical methods are required. Consequently, this study aimed to develop liquid chromatography-high-resolution mass spectrometry-based (LC-MS) methods for the detection of kisspeptin and its analogues in human serum and urine. In addition, peptide stability in different biological matrices was investigated, and metabolic stability was characterized in vitro. Extraction methods based on cation-exchange solid-phase extraction were optimized, enabling a selective and sensitive LC-MS analysis with limits of identification (LOI) ranging from 0.8 ng/mL (KP-54) to 10 pg/mL (TAK-448). Analysis of a reference population comprising n = 20 serum samples and n = 100 urine samples revealed no detectable signals of endogenous kisspeptins and/or its degradation products. All native kisspeptins investigated showed poor stability in urine and blood; however, several degradation products could be identified. These metabolites could serve as complementary target analytes and improve the detectability of kisspeptins in doping control samples. Overall, the study provides an important foundation for the confirmatory analysis of kisspeptins in doping controls and delivers in vitro insights into their metabolic behavior. Analysis of samples collected after administration of the peptides remains necessary to further assess the detectability and metabolic profiles in authentic samples.