Polymyxin B enhances acrosomal exocytosis triggered by calcium and the calcium ionophore A23187 in ejaculated boar spermatozoa

Polymyxin B neutralizes endotoxin and improves the quality of chicken semen during liquid storage

Despite its importance in gamete utilization for livestock production, poultry semen cryopreservation in a liquid state, is limited in the poultry industry due to a significant decline in sperm viability and functionality during liquid storage. Lipopolysaccharide (LPS) is released from gram-negative bacteria and impairs sperm function in mammals. Using exogeneous LPS, we show this endotoxin compromises sperm viability and function, including motility and penetrability to the inner peri-vitelline layer (IPVL) during liquid storage at 4 °C. This outcome was supported by LPS quantification showing an extreme increase in the first 24 h of storage. Polymyxin B (PMB) is an LPS neutralizer previously shown to improve fertility in boar semen, thus we explored the effect of PMB on chicken semen quality during liquid storage. Sperm viability and penetrability tests showed that PMB completely abolishes the deleterious effect by LPS. However, co-addition of PMB with penicillin G (PenG), an antibiotic against gram positive bacteria, reduces IPVL-penetrability while improving sperm viability post-storage. Furthermore, artificial insemination trials showed that PMB addition improves semen fertility at the post liquid storage. Our results show that chicken semen quality during liquid storage is impaired by bacterial LPS, but improved by PMB addition due to cancelled endotoxic effects, which offers a new approach for prolonged fertility of poultry semen storage in a liquid state.

OUP accepted manuscript

BACKGROUND

Oocyte activation deficiency (OAD) is attributed to the majority of cases underlying failure of ICSI cycles, the standard treatment for male factor infertility. Oocyte activation encompasses a series of concerted events, triggered by sperm-specific phospholipase C zeta (PLCζ), which elicits increases in free cytoplasmic calcium (Ca²⁺) in spatially and temporally specific oscillations. Defects in this specific pattern of Ca²⁺ release are directly attributable to most cases of OAD. Ca²⁺ release can be clinically mediated via assisted oocyte activation (AOA), a combination of mechanical, electrical and/or chemical stimuli which artificially promote an increase in the levels of intra-cytoplasmic Ca²⁺. However, concerns regarding safety and efficacy underlie potential risks that must be addressed before such methods can be safely widely used.

OBJECTIVE AND RATIONALE

Recent advances in current AOA techniques warrant a review of the safety and efficacy of these practices, to determine the extent to which AOA may be implemented in the clinic. Importantly, the primary challenges to obtaining data on the safety and efficacy of AOA must be determined. Such questions require urgent attention before widespread clinical utilization of such protocols can be advocated.

SEARCH METHODS

A literature review was performed using databases including PubMed, Web of Science, Medline, etc. using AOA, OAD, calcium ionophores, ICSI, PLCζ, oocyte activation, failed fertilization and fertilization failure as keywords. Relevant articles published until June 2019 were analysed and included in the review, with an emphasis on studies assessing large-scale efficacy and safety.

OUTCOMES

Contradictory studies on the safety and efficacy of AOA do not yet allow for the establishment of AOA as standard practice in the clinic. Heterogeneity in study methodology, inconsistent sample inclusion criteria, non-standardized outcome assessments, restricted sample size and animal model limitations render AOA strictly experimental. The main scientific concern impeding AOA utilization in the clinic is the non-physiological method of Ca²⁺ release mediated by most AOA agents, coupled with a lack of holistic understanding regarding the physiological mechanism(s) underlying Ca²⁺ release at oocyte activation.

LIMITATIONS, REASONS FOR CAUTION

The number of studies with clinical relevance using AOA remains significantly low. A much wider range of studies examining outcomes using multiple AOA agents are required.

WIDER IMPLICATIONS

In addition to addressing the five main challenges of studies assessing AOA safety and efficacy, more standardized, large-scale, multi-centre studies of AOA, as well as long-term follow-up studies of children born from AOA, would provide evidence for establishing AOA as a treatment for infertility. The delivery of an activating agent that can more accurately recapitulate physiological fertilization, such as recombinant PLCζ, is a promising prospect for the future of AOA. Further to PLCζ, many other avenues of physiological oocyte activation also require urgent investigation to assess other potential physiological avenues of AOA.

STUDY FUNDING/COMPETING INTERESTS

D.G. was supported by Stanford University’s Bing Overseas Study Program. J.K. was supported by a Healthcare Research Fellowship Award (HF-14-16) made by Health and Care Research Wales (HCRW), alongside a National Science, Technology, and Innovation plan (NSTIP) project grant (15-MED4186-20) awarded by the King Abdulaziz City for Science and Technology (KACST). The authors have no competing interests to declare.

Alterations in seminal plasma proteomic profile in men with primary and secondary infertility

Proteome of seminal plasma provides profound information related to the male reproductive health. This pilot study was conducted to characterize proteomic profile of seminal plasma from men with primary, or secondary infertility and compare it with proven fertile men. Study participants (n = 59) were recruited at the Cleveland Clinic and divided according to their fertility status: proven fertile (n = 39); primary infertility (n = 11) and secondary infertility (n = 9). Proteomic shotgun analysis revealed a total of 515 peptides common to primary infertility and control group; whereas 523 peptides were common to secondary infertility and control group. Bioinformatic analysis revealed dysregulation of biological processes such as cell secretion and vesicle mediated transport in primary infertility, whereas immune system response, regulation of proteolysis and iron homeostasis were dysregulated in secondary infertility. Western blot validation showed overexpression of ANXA2 and CDC42, and underexpression of SEMG2 proteins in primary infertility; and overexpression of ANXA2 and APP proteins in secondary infertility. This study elucidates the potential role of differentially expressed proteins in the seminal plasma as diagnostic biomarker for primary and secondary infertility. Furthermore, our results suggest maturation failure and immune reaction response as the main cause of infertility in men with primary and secondary infertility, respectively. Additional validation of the proteins involved in the above pathways is warranted.

Polymyxin B enhances acrosomal exocytosis triggered by calcium and the calcium ionophore A23187 in ejaculated boar spermatozoa

Polymyxin B (PMB) is beneficial for boar semen storage since it neutralizes the endotoxin of bacteria. However, the direct effect of PMB on boar spermatozoa has been unknown. This study aimed to examine the effect of PMB on acrosomal exocytosis, an essential process for successful fertilization in boar spermatozoa. Ejaculated spermatozoa stored with BTS extender at 17°C were washed and incubated with 0-100 μM PMB for 20 min and then examined for % total motililty, vigor grade and viability. None of the parameters was significantly different between 0 and 50 μM PMB with a gradual decline at higher concentrations. Thus the effect on acrosomal exocytosis was investigated at 0-50 μM of PMB. Spermatozoa were preincubated with PMB for 10 min, incubated for stimulation of acrosomal exocytosis with Ca²⁺ and the calcium ionophore A23187 and then fixed with glutaraldehyde at 5, 10 and 15 min. Preincubation with PMB at 0.01-50 μM and 0.05-50 μM resulted in significant enhancement of acrosomal exocytosis at 10 min and 15 min of incubation, respectively. Preincubation with PMB followed by incubation without A23187 did not affect acrosomal exocytosis. These results suggest that PMB exerts effects on the acrosomal exocytosis triggered by Ca²⁺ and A23187 in boar spermatozoa.