Intra-individual variability of the human seminal plasma metabolome

In contrast to the conventional spermiogram, metabolomics approaches give insights into the molecular composition of semen and may provide more detailed information on the fertility status of the respective donor. Given the intra-individual variability of spermiogram parameters between two donations, this study sought to elucidate the biological variability of the seminal plasma metabolome over an average period of 8 weeks. Two time-shifted semen samples from 15 healthy donors were compared by a targeted metabolomics approach utilizing the Biocrates AbsoluteIDQ p180 kit. Next to intraclass correlation coefficients (ICC), which represent a measure of reliability, coefficients of variation within individuals (CVW) and coefficients of variation between individuals (CVB) were calculated for each metabolite to demonstrate its stability. Furthermore, men were divided into two cohorts, a similar sperm concentration (SSC) and a differing sperm concentration (DSC) cohort, based on the observed variance in sperm concentration between the two semen donations. The ICC was higher in the SSC compared to the DSC cohort. The levels of 18 metabolites, primarily acylcarnitines, varied between the initial and subsequent donations. After subdivision into subgroups, only ornithine and phosphatidylcholine 40:5 exhibited differential levels between the two donations in the SSC group, compared to 14 metabolites in the DSC group. CVB was higher than CVW but both differed between the metabolite subclasses. Biogenic amines were identified as the least reliable analytes over time, exhibiting the highest CVW, compared to sphingomyelins, which demonstrated the highest reliability with the lowest variation. CVB was the highest for ether-bound glycerophosphatidylcholines and the lowest for amino acids.