Abstract
Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.
Highlights
Assisted reproductive techniques (ARTs) represent an important treatment option for infertile couples and its utilization has constantly increased with growth rates between2.4% and 18.3% per annum in Europe, USA, Australia, and New Zealand in the years from 2012 to 2016 [1], resulting in about 1.3 million assisted reproductive techniques (ARTs) cycles in 2016 in these areas
Oxidative stress is defined as an imbalance between the reactive oxygen species (ROS) and the total amount of antioxidants (AOXs) in favor of the oxidants [10]
The use of frozen embryos in ART programs has considerably increased compared to the past. This is attributed to the development of the vitrification method and the adoption of the freeze-all strategy, as well as the possibility to obtain a surplus of embryos and avoid hyperstimulation syndrome [58]
Summary
Assisted reproductive techniques (ARTs) represent an important treatment option for infertile couples and its utilization has constantly increased with growth rates between. 2.4% and 18.3% per annum in Europe, USA, Australia, and New Zealand in the years from 2012 to 2016 [1], resulting in about 1.3 million ART cycles in 2016 in these areas Such an increase may be caused by several factors, including socio-economic [2] and environmental factors [3]. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos The latter may be vulnerable to OS due to a lack of the protective antioxidants in their physiological microenvironment during in vitro ART conditions [30]. The toxic effect of atmospheric oxygen levels on embryos has already been shown by Pabon et al (1989) [39] and Umaoka et al (1992) [40] This effect is mediated by excessive production of ROS causing OS [41]. Impact of OS during the entire human embryo from gametes blastocyst embryo culture period, from gametes to blastocyst stage
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