Low-molecular weight compounds in human seminal plasma as potential biomarkers of male infertility

STUDY QUESTION: Is the determination of antioxidants, oxidative/nitrosative stress-related compounds, purines, pyrimidines and energy-related metabolites in human seminal plasma of utility to evidence biomarkers related to male infertility? SUMMARY ANSWER: The determination of 26 metabolites in seminal plasma allowed to evidence that 21/26 of them are biomarkers of male infertility, as well as to calculate a cumulative index, named Biomarker Score, that fully discriminates fertile controls from infertile patients and partially differentiates infertile without from infertile with spermiogram anomalies. WHAT IS KNOWN ALREADY: Epidemiological studies indicated that a male factor is involved in ∼50% of cases of pregnancy failure, with a significant percentage of infertile males having no alterations in the spermiogram. Further laboratory analyses of male infertility are mainly dedicated only to gross evaluations of oxidative stress or total antioxidant capacity. STUDY DESIGN, SIZE, DURATION: Seminal plasma of 48 fertile controls and 96 infertile patients (master group), were collected from September 2016 to February 2018. A second group of 44 infertile patients (validation group) was recruited in a second, independent centre from September 2017 to March 2018. Samples were analysed in blind using a 'Redox Energy Test' to determine various low-molecular weight compounds, with the aim of finding metabolic profiles and biomarkers related to male infertility. PARTICIPANTS/MATERIALS, SETTING, METHODS: In all seminal plasma, 26 water- and fat-soluble compounds (related to antioxidant defences, oxidative/nitrosative stress, purine, pyrimidine and energy metabolism) were analysed using high-performance liquid chromatographic methods. According to spermiogram, infertile patients of both groups were also categorized into normozoospermic (N, no anomalies in the spermiogram), or into the subgroup including all patients with anomalies in the spermiogram (asthenoteratooligozoospermic ATO + asthenozoospermic A + teratozoospermic T + oligozoospermic O). MAIN RESULTS AND THE ROLE OF CHANCE: In the master group, results indicated that 21/26 compounds assayed in seminal plasma of infertile males were significantly different from corresponding values determined in fertile controls. These 21 compounds constituted the male infertility biomarkers. Similar results were recorded in patients of the validation group. Using an index cumulating the biochemical seminal plasma anomalies (Biomarker Score), we found that fertile controls had mean Biomarker Score values of 2.01 ± 1.42, whilst infertile patients of the master and of the validation group had mean values of 12.27 ± 3.15 and of 11.41 ± 4.09, respectively (P < 0.001 compared to controls). The lack of statistical differences between the master and the validation groups, in both the metabolic profiles and the Biomarker Score values, allowed to pool patients into a single cohort of infertile males. The Biomarker Score values showed that fertile controls and infertile males clustered into two distinct groups. Infertile patients without (N, n = 42) or with (ATO + A + T + O, n = 98) spermiogram anomalies differed in some biomarkers (ascorbic acid, all-trans retinol, α-tocopherol, cytidine, uridine, guanine). These differences were reinforced by distribution frequencies and posterior probability curves of the Biomarker Score in the three groups. LIMITATIONS, REASONS FOR CAUTION: Results were obtained in relatively limited number of human seminal plasma samples. Using the 'Redox Energy Test' it was possible to associate specific metabolic profiles and values of the Biomarker Score to fertile controls or infertile males. However, it was not possible to evaluate whether the different anomalies of the spermiogram are associated with specific metabolic profiles and values of the Biomarker Score. WIDER IMPLICATIONS OF THE FINDINGS: The 'Redox Energy Test', coupled