Exploratory seminal plasma metabolomics and independent HPLC-UV evaluation in men with impaired semen quality.

BACKGROUND: Impaired semen quality may involve concurrent abnormalities in sperm concentration, total sperm number, motility, morphology, and DNA integrity. The corresponding alterations in the seminal plasma metabolome remain incompletely characterized. OBJECTIVES: To characterize seminal plasma metabolic alterations in men with multiple concurrent semen abnormalities and identify candidate signals associated with semen quality parameters. MATERIALS AND METHODS: Untargeted LC-MS/MS metabolomics was performed in a discovery cohort comprising 10 men with impaired semen quality and 9 normozoospermic controls. Candidate metabolites were screened using nominal p value and fold-change thresholds, followed by pathway and correlation analyses, post hoc ROC analysis, and qualitative comparisons with public datasets. External-calibration-derived estimates assigned to cytidine and 2-hydroxy-3-methylbutyric acid (2-HMBA) were subsequently evaluated by HPLC-UV in an independent cohort of 18 men with impaired semen quality and 18 controls. RESULTS: Eighty-nine putatively annotated metabolites met the nominal screening criteria, but no individual metabolite remained significant after Benjamini-Hochberg false discovery rate correction. Discovery-level pathway analyses highlighted nucleotide- and nucleoside-related processes as hypothesis-generating signals. Qualitative comparison with heterogeneous publicly available reproductive metabolomics datasets provided limited directional context but was not considered formal external validation. In the independent HPLC-UV cohort, external-calibration-derived estimates assigned to 2-HMBA were nominally lower in the group with impaired semen quality (p = 0.030), but the difference did not remain significant after correction across the two candidate comparisons (q = 0.060). Cytidine showed no between-group difference (p = 0.812; q = 0.812). DISCUSSION AND CONCLUSION: The discovery-level nucleotide-related pathway signal and the independent observation concerning 2-HMBA represent distinct lines of evidence; the latter does not validate the former. Given the small sample sizes in both the discovery and independent HPLC-UV evaluation cohorts, the absence of FDR-significant metabolites, heterogeneity across the public datasets, and limitations of the HPLC-UV assay, these findings remain exploratory and hypothesis-generating. They do not constitute quantitative validation, establish a specific mechanism, or support clinical biomarker use. Larger multicenter cohorts and targeted quantitative metabolomic analyses using validated methods are needed.