A novel antioxidant formulation designed to treat male infertility associated with oxidative stress: promising preclinical evidence from animal models

STUDY QUESTION

Does a novel antioxidant formulation designed to restore redox balance within the male reproductive tract, reduce sperm DNA damage and increase pregnancy rates in mouse models of sperm oxidative stress?

SUMMARY ANSWER

Oral administration of a novel antioxidant formulation significantly reduced sperm DNA damage in glutathione peroxidase 5 (GPX5), knockout mice and restored pregnancy rates to near-normal levels in mice subjected to scrotal heat stress.

WHAT IS KNOWN ALREADY

Animal and human studies have documented the adverse effect of sperm DNA damage on fertilization rates, embryo quality, miscarriage rates and the transfer of de novo mutations to offspring. Semen samples of infertile men are known to be deficient in several key antioxidants relative to their fertile counterparts. Antioxidants alone or in combination have demonstrated limited efficacy against sperm oxidative stress and DNA damage in numerous human clinical trials, however these studies have not been definitive and an optimum combination has remained elusive.

STUDY DESIGN, SIZE, DURATION

The efficacy of the antioxidant formulation was evaluated in two well-established mouse models of oxidative stress, scrotal heating and Gpx5 knockout (KO) mice, (n = 12 per experimental group), by two independent laboratories. Mice were provided the antioxidant product in their drinking water for 2-8 weeks and compared with control groups for sperm DNA damage and pregnancy rates.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the Gpx5 KO model, oxidative DNA damage was monitored in spermatozoa by immunocytochemical detection of 8-hydroxy-2'-deoxyguanosine (8OHdG). In the scrotal heat stress model, male fertility was tested by partnering with three females for 5 days. The percentage of pregnant females, number of vaginal plugs, resorptions per litter, and litter size were recorded.

MAIN RESULTS AND ROLE OF CHANCE

Using immunocytochemical detection of 8OHdG as a biomarker of DNA oxidation, analysis of control mice revealed that around 30% of the sperm population was positively stained. This level increased to about 60% in transgenic mice deficient in the antioxidant enzyme, GPX5. Our results indicate that an 8 week pretreatment of Gpx5 KO mice with the antioxidant formulation provided complete protection of sperm DNA against oxidative damage. In mouse models of scrotal heat stress, only 35% (19/54) of female mice became pregnant resulting in 169 fetuses with 18% fetal resorption (30/169). This is in contrast to the antioxidant pretreated group where 74% (42/57) of female mice became pregnant, resulting in 427 fetuses with 9% fetal resorption (38/427). In both animal models the protection provided by the novel antioxidant was statistically significant (P < 0.01 for the reduction of 8OHdG in the spermatozoa of Gpx5 KO mice and P < 0.05 for increase in fertility in the scrotal heat stress model).

LIMITATIONS, REASONS FOR CAUTION

It was not possible to determine the exact level of antioxidant consumption for each mouse during the treatment period.

WIDER IMPLICATIONS OF THE FINDINGS

Recent clinical studies confirm moderate to severe sperm DNA damage in about 60% of all men visiting IVF centers and in about 80% of men diagnosed with idiopathic male infertility. Our results, if confirmed in humans, will impact clinical fertility practice because they support the concept of using an efficacious antioxidant supplementation as a preconception therapy, in order to optimize fertilization rates, help to maintain a healthy pregnancy and limit the mutational load carried by children.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by the Clermont Université and the University of Madrid. P.G. is the Managing Director of CellOxess LLC, which has a commercial interest in the detection and resolution of oxidative stress. A.M. and A.P. are employees of CellOxess, LLC. J.R.D., A.G.-A. and R.J.A. are honorary members of the CellOxess advisory board.

Comparative analysis of boar seminal plasma proteome from different freezability ejaculates and identification of Fibronectin 1 as sperm freezability marker

Variation in boar sperm freezability (i.e. capacity to withstand cryopreservation) between ejaculates is a limitation largely reported in the literature. Prediction of sperm freezability and classification of boar ejaculates into good (GFEs) and poor freezability ejaculates (PFEs) before cryopreservation takes place may increase the use of frozen-thawed spermatozoa. While markers of boar sperm freezability have been found from sperm cell extracts, little attention has been paid to seminal plasma. On this basis, the present study compared the fresh seminal plasma proteome of 9 GFEs and 9 PFEs through two-dimensional difference gel electrophoresis (2D-DIGE) and liquid chromatography mass spectrometry (LC-MS/MS). The ejaculates were previously classified as GFE or PFE upon their sperm viability and progressive motility assessments at 30 and 240 min post thawing. From a total of 51 spots, four were found to significantly (p < 0.05) differ between GFEs and PFEs, and two were identified as fibronectin-1 (FN1) and glutathione peroxidase 5 (GPX5). These two potential markers were further studied by western blot and correlation analysis between protein relative abundances in fresh seminal plasma and regression factors from principal component analyses (PCA) run using post-thawing sperm quality parameters. Results confirmed that FN1 is a reliable marker of boar sperm freezability, because GFEs presented significantly (p < 0.05) higher FN1-amounts than PFEs and FN1 was found to be correlated with the first PCA component at 240 min post thawing. In contrast, GPX5 was not validated as a boar sperm freezability marker. We can thus conclude that levels of FN1 in fresh seminal plasma from boar semen may be used as a sperm freezability marker, thereby facilitating the use of frozen-thawed boar spermatozoa.

Functional deletion of Txndc2 and Txndc3 increases the susceptibility of spermatozoa to age-related oxidative stress

Oxidative stress in the male germ line is known to be a key factor in both the etiology of male infertility and the high levels of DNA damage encountered in human spermatozoa. Because the latter has been associated with a variety of adverse clinical outcomes, including miscarriage and developmental abnormalities in the offspring, the mechanisms that spermatozoa use to defend themselves against oxidative stress are of great interest. In this context, the male germ line expresses three unique forms of thioredoxin, known as thioredoxin domain-containing proteins (Txndc2, Txndc3, and Txndc8). Two of these proteins, Txndc2 and Txndc3, retain association with the spermatozoa after spermiation and potentially play an important role in regulating the redox status of the mature gamete. To address this area, we have functionally deleted the sperm-specific thioredoxins from the male germ line of mice by either exon deletion (Txndc2) or mutation of the bioactive cysteines (Txndc3). The combined inactivation of these Txndc isoforms did not have an overall impact on spermatogenesis, epididymal sperm maturation, or fertility. However, Txndc deficiency in spermatozoa did lead to age-dependent changes in these cells as reflected by accelerated motility loss, high rates of DNA damage, increases in reactive oxygen species generation, enhanced formation of lipid aldehyde-protein adducts, and impaired protamination of the sperm chromatin. These results suggest that although there is considerable redundancy in the systems employed by spermatozoa to defend themselves against oxidative stress, the sperm-specific thioredoxins, Txndc2 and Txndc3, are critically important in protecting these cells against the increases in oxidative stress associated with paternal age.