P-045 Effects of seminal BPA levels on human sperm parameters and gene expression
Authors: Davis O , Sabry R , Acosta J , Lagunov A , Ghaffarzadeh M , Favetta L 
Published: June 2023

Abstract

Study question
Are high BPA levels in human seminal fluid associated with low sperm metrics and changes in gene expression?

Summary answer
A trend towards an inverse relationship between seminal BPA and sperm count was observed. Expression of androgen receptor mRNA was down-regulated with high BPA exposure.

What is known already
Bisphenol A (BPA) is a widespread industrial chemical, used as the key monomer of polycarbonate plastics and epoxy resins. While some countries have introduced bans/stringent regulation for BPA, it continues to be widely used especially in North America, where its use is only limited in baby products. BPA has been detected in human seminal fluid and has been correlated with decreased sperm counts and motility - crucial factors in determining male fertility, which continue to decrease. We have demonstrated that in vitro BPA exposure can reduce motility, mitochondrial membrane potential, and capacitation in mature bovine spermatozoa.

Study design, size, duration
In collaboration with CCRM, Toronto, seminal fluid samples were collected from 90 patients undergoing fertility assessment between 2021 and 2023. Typical evaluations such as sperm counts, motility, and morphology were recorded by the clinic (following WHO guidelines). Samples were then shipped to the University of Guelph for further investigations. Information on outcomes for patients who underwent subsequent IVF cycles like fertilization rates and pregnancy rates were also recorded at the clinic.

Participants/materials, setting, methods
At the University of Guelph, seminal BPA levels were measured through an enzyme-linked immunosorbent assay (ELISA; My BioSource), then compared to sperm metrics obtained by the clinic. Next, a GeNorm analysis was performed to determine the most stable reference genes for subsequent qPCR analysis. The relative mRNA expression of three key genes related to male reproduction (androgen receptor (AR), cyp17a1 and cyp11a1) were quantified and compared between groups with high and low BPA content.

Main results and the role of chance
BPA concentrations in the seminal fluid samples ranged between 0-3000 pg/mL, with most samples containing 35-1000 pg/mL. When samples were graphed according to increasing BPA levels, no relationships were observed between BPA and motility or morphology rates. However, a negative trend between BPA and sperm count was detected, although this was not significant. Samples were then divided into high- (total 15 samples with &gt;700 pg/mL) and low- (total 15 samples with &lt;100 pg/mL) BPA content groups. The GeNorm M value indicated that HPRT1 and HMBS were the most stable reference genes across the groups. qPCR analysis on three biological replicates in technical triplicates showed that androgen receptor mRNA expression was significantly higher in sperm exposed to low seminal BPA compared to the high BPA exposure group (p = 0.03913). This finding is particularly interesting as AR expression has previously been positively correlated with sperm count, motility and morphology. cyp17a and cyp11a mRNA expression was undetectable in human spermatozoa under our experimental conditions. Future steps include increasing the sample size to increase the power of the correlation studies between sperm quality parameters and ART success rates. Furthermore, other fertility-related genes will be investigated at both the mRNA (qPCR) and protein levels (flow cytometry).

Limitations, reasons for caution
Relatively small sample size; duration of study must be extended to gain information on outcomes of ART cycles; many samples in the mid-range of BPA are excluded from gene expression studies.

Wider implications of the findings
These results can ultimately display a relationship between BPA exposure and male fertility and provide further insights into the molecular mechanisms through which BPA exerts its effects. Ultimately, this research can drive changes to guidelines/exposure limits for BPA, especially in North America.

Trial registration number
not applicable