O-053 Link between cannabis use and fertility: effects on gamete competence and early embryonic development
Authors: Favetta L 
Published: June 2023

Worldwide human fertility has been facing a significant decline over recent years. Therefore, attention has been focused on identifying environmental and lifestyle risk factors that may be contributing to impact human reproductive function. The use of alcohol, tobacco and certain medications have undergone substantial assessment into their effects on fertility. As physicians aim to offer the most appropriate recommendations to their patients, it is of utmost importance to understand the side effects of readily available substances and their mechanisms of action. Cannabis falls into this group of substances used regularly by women and men of reproductive age, with its consumption steadily rising with the onset of legalization in Canada in 2018 also amongst pregnant women. At present, the Society of Obstetricians and Gynecologists of Canada recommends that women of reproductive age, especially if considering pregnancy, discontinue cannabis use. There is, however, inconclusive evidence that links cannabis and fertility.

This presentation will outline the most recent data from our laboratory on the effects of Delta-9 tetrahydrocannabinol (THC), the main psychoactive component of cannabis, on oocytes competency and sperm fertilization capability. In fact chronic exposure to cannabis also adversely affects the male reproductive system, inducing oligospermia, morphologically abnormal sperm, and impaired sperm motility in rodents. Using a bovine model as translational model for humans, we identified effects of THC on oocyte developmental parameters, gene expression as well on sperm parameters, such as motility, morphology, capacitation and mitochondrial potential. The general hypothesis at the basis of this research program aims to elucidate the effects of THC at clinically relevant doses on gene and epigenetic modifications in sperm, oocytes and embryos, ultimately affecting fertility and pregnancy outcome. We showed a significantly reduced ability of THC-treated oocytes to undergo nuclear maturation, ultimately leading to decreased oocyte fertilization capability and poor embryonic development. We showed that THC acts as a partial agonist at the Cannabinoid receptors 1 and 2 (CB1 and CB2), as THC effects were reverted by the addition of antagonists. The significant decrease in maturation and cleavage rate of oocytes exposed to the higher doses of THC, representative of high recreational use of Cannabis, allows us to speculate that THC might act as a selection factor for only the highest quality oocytes, that overcome the THC effects. The more immature oocytes may be negatively affected by THC by being pushed towards meiotic resumption, leading to early maturation, prior to gaining developmental competence. Levels of connexin gap-junction proteins were used as indicator of oocyte competency, as they highly correlate to oocyte fertilization potential and embryo quality. Our results demonstrated a significant decrease in connexin 37 (CX37) and connexin 43 (CX43) mRNA levels measured by digital droplet PCR (ddPCR), in oocytes only in the low dose THC group, representative of the therapeutic use of Cannabis. More recently we have also shown how THC affects methylation in granulosa cells, via disrupting methylation and de-methylation enzymes, ultimately determining oocyte competency and, therefore, fertility. THC exerts parallel effects on the male gametes as well, increasing capacitation of in vitro treated sperm, affecting their mitochondrial potential and disrupting the expression of key microRNAs in sperm that are linked to early embryonic development, therefore affecting pre-implantation development and, ultimately, pregnancy outcome.

Our results suggest an overall detrimental effect of THC on the competency and fertilization potential of both female and male gametes, negatively influencing fertility and the likelihood of a viable pregnancy, especially of importance when undergoing artificial reproductive technologies procedures.

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