A warning sign: the impact of environmental and food contaminants on cow reproduction
|Dr. Dorit Kalo, Alisa Komsky-Elbaz, Prof. Zvi Roth, firstname.lastname@example.org|
|November 11, 2019|
Common sources of EDCs are natural compounds originating from plants or fungi (such as mold, clover, soybeans), and man-made chemicals that are manufactured for use as pesticides, drugs, and plasticizers, among others. Many more EDCs are manufacturing byproducts. EDCs can leach into the environment and contaminate food and water sources. Humans and animals are exposed to EDCs through consumption of food and water, direct skin contact, inhalation, and transfer across the placenta to the fetus or through lactation to infants.
Following consumption, DEHP is metabolized in the body to MEHP, which is considered to have a more toxic effect. ATZ is a herbicide that is most extensively used to control the growth of broadleaf and grassy weeds in agricultural crops. ATZ is considered a ubiquitous environmental contaminant that is frequently detected in ground and surface water because of its mobility in soil. The main concern with ATZ is exposure via consumption of contaminated drinking water. Once ATZ enters the body, it metabolizes into a number of metabolites, the most frequently detected being DACT.
Health and fertility concerns. EDCs are suspected of having a major impact on human health, as environmental factors are responsible for about 80% of the deadliest diseases involving the endocrine system (cancer, cardiac diseases and others). Consequently, EDC contamination of food and water poses a serious health risk. For instance, infertility is a global public health problem, defined as a "disease of the reproductive system." One of the main causes of infertility is consumption of EDC-contaminated food and water. This risk is not limited to humans; wild and domesticated animals are also exposed to environmental and food contamination. Research in our laboratory focuses on the physiological, cellular and molecular impacts of contaminants on the female (oocyte) and male (sperm) gametes and preimplantation embryos (i.e., blastocysts), using state-of-the-art reproductive technologies (Fig. 1).
Fig 1. In-vitro embryo production. Oocyte handling, including oocyte aspiration, collection and maturation. Sperm handling, including semen collection, swim-up and sperm capacitation. Matured oocytes were in-vitro fertilized with capacitated sperm and cultured for 8 days to allow embryonic development to the blastocyst stage.
Effect of phthalates on the oocyte. Using our in-vitro embryo-production system, we documented the oocyte's high sensitivity to DEHP and its metabolite MEHP. This was reflected by altered nuclear and cytoplasmic maturation of the oocyte, both required for the oocyte to be fertilizable. Disruptions included alterations in meiosis resumption and reorganization of cytoplasmic organelles (mitochondria, cortical granules and endoplasmic reticulum), impaired expression of genes associated with early embryonic development and pluripotency, and increased production of reactive oxygen species. Moreover, MEHP interfered with the oocyte's ability to be fertilized and develop into an embryo, reflected by a lower proportion of developing blastocysts.
Fig. 2. Simultaneous fluorimetric assessment of plasma and acrosome membrane integrity and mitochondrial membrane potential. Purple-stained sperm are dead sperm, stained both red (propidium iodide) and blue (DAPI). Blue-stained sperm indicate viable sperm. A green cap at the top of the sperm indicates acrosome-reacted sperm (FITC-PSA). Red or green sperm tail indicates high or low mitochondrial membrane potential, respectively (JC-1).
Effects of ATZ and DACT on sperm. Recent findings from our laboratory provide evidence of adverse effects of both ATZ and DACT on sperm, expressed by a damaged sperm membrane. Staining the sperm with specific fluorescent dyes (Fig. 2) revealed that exposure to ATZ or DACT disrupts its viability, induces spontaneous acrosome reaction and impairs mitochondrial membrane potential. Moreover, both ATZ and DACT increased the proportion of sperm with fragmented DNA, reduced the proportion of embryos that cleaved to the 2- to 4-cell stage, and reduced blastocyst-formation rate.
Fig. 3. Transcriptomic alterations in blastocysts developed from MEHP-treated oocytes (top) and ATZ-treated sperm (bottom). Presented are the alterations in biological processes in the blastocysts.
Synopsis. The potential risk of exposure to other EDCs must be taken into consideration, at least when evaluating their effect on the reproductive system. While the presented data are directly related to cows and limited to a few EDCs, they might serve as a toxicology model for other mammalian species and a variety of environmental and food contaminators.