Metabolome and oxidative stress markers in the seminal plasma of Holstein bulls and their relationship with the characteristics of fresh and frozen/thawed sperm

Abstract

Seminal plasma composition has important role in sperm functionality and its freezability. The objective of this study was to test the hypothesis that seminal plasma (SP) oxidative status and metabolome are associated with fresh semen characteristics and freezability of bull sperm. To accomplish this objective, oxidative status markers and metabolome of SP of ejaculates obtained from 20 Holstein bulls (3 for each bull) were analyzed using spectrophotometry and nuclear magnetic resonance (¹H NMR). The ejaculates were classified into higher motility fresh semen (HMF) and lower motility fresh semen (LMF), according to total motility (TM) and progressive motility (PM) values of fresh semen. Then the ejaculates was cryopreserved and assigned to higher motility thawed group (HMT) or lower motility thawed group (LMT) according to TM and PM at 0 h post-thawing. Multivariate analyses were performed to identify the association between the functional characteristics of fresh and thawed semen and the SP parameters, in terms of the oxidative status and the metabolomic composition. According to our results, the advanced oxidative protein products (AOPP) and thiol concentrations in SP are significantly related to some physiological characteristics of the thawed sperm, such as higher viability, TM, PM and LIN and lower mitochondrial and cytoplasmic superoxide production in viable thawed cells. In contrast, a higher amount of C in the SP was negatively related to TM and PM of thawed semen and was associated with higher mitochondrial and cytoplasmic superoxide production.

In addition, partial least squares-discriminant analysis (PLS-DA) performed on the ¹H NMR spectra indicated a discrete separation between HMF and LMF groups, and good discrimination between HMT and LMT groups. Higher levels of formic acid, lactate, glycerol and phosphocholine, were found in the SP of the HMF group than in the LMF group. On the other hand, alanine, phenylalanine, and tyrosine were higher in the SP of the LMF group than in the HMF group. GABA, glutamate, histidine and glycerol were found in higher concentrations in the HMT group than in the LMT group, while fructose decreased in the HMT group. Our results showed that the oxidative and metabolomic status of SP is related to the physiological properties of semen and its freezability and open new fields in research of SP biomarkers of bull semen preservation and fertility.