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MP75-16 25-HYDROXYCHOLESTEROL AS A MARKER OF SPERM FUNCTION: OXYSTEROLS PROFILE OF SEMEN

INTRODUCTION AND OBJECTIVES: Cholesterol is the main lipid component of the sperm cell that is essential for sperm membrane fluidity, capacitation, and acrosomal reaction. The main objective of the study was to identify and quantify, for the first time, the different species of oxysterols in human semen from normozoospermic, oligoasthenoteratozoospermic and asthenozoospermic patients. The secondary aim was to investigate the potential role of oxysterols in sperm pathophysiology. METHODS: To investigate the profile of human sperm oxysterols in subjects with normal and altered sperm characteristics, we recruited 150 consecutive subjects aged between 18–50 years old. Therefore we investigated 134 semen samples from the same number of patients, aged 34.5±7.5. Patients were classified according to the sperm parameters: Group 1≥50th percentile (33 normozoospermic men), Group 2⩽5th percentile (32 oligoasthenoteratozoospermic men), Group 3 only progressive motility ⩽5th percentile (25 asthenozoospermic men) and Group 4 (44 patients with varicocele). Oxysterols were determined by GC-MS using deuterium-labelled internal standards. Oxysterols analyzed included seven autoxidation- and five enzymatically-generated oxysterols. RESULTS: 25-HC resulted the most abundant oxysterol in normozoospermic subjects and turned out to be the only one that differed significantly (p<0.0001) among the 4 groups. It was higher in normozoospermic group (21.63±18.47 ng/mL, mean±SD) than oligoasthenoteratozoospermic (2.59±2.93), asthenozoospermic (5.59±3.17) and varicocele (13.48±11.81) group. Furthermore, 25-HC positively correlated with the spermatozoa number (r=0.72, p<0.0001). We detected Cholesterol 25-hydroxylase, the enzyme responsible for 25-HC production, in human spermatozoa at the level of the neck and the post-acrosomal area. Upon incubation with spermatozoa, 25-HC induced calcium and cholesterol transients in connection with the acrosomal reaction. Our results support a role for 25-HC in sperm function. CONCLUSIONS: In conclusion, to the best of our knowledge, this is the first study providing evidence for the feasibility of detection and quantitation of oxysterols in human semen samples. We found in spermatozoa the presence of cholesterol 25-hydroxylase and its preferential accumulation in the neck and the post acrosomal area. 25-HC was able to induce calcium ions and cholesterol depletion in the acrosomal region, years old an extent comparable to that of a capacitating medium. These finding offers the opportunity to identify a new molecular player involved in pre-fertilization processes. Source of Funding: NONE