BPS and Cell Fusion in the Human Placenta: A Separate Mechanism of Action?

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Author: Silke Schmidt
Date: June 2021
From: Environmental Health Perspectives(Vol. 129, Issue 6)
Publisher: National Institute of Environmental Health Sciences
Document Type: Report
Length: 1,410 words
Lexile Measure: 1780L

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During the past decade, the plasticizer bisphenol S (BPS) has been replacing the endocrine-disrupting chemical bisphenol A (BPA) in numerous consumer products. (1,2) As an example of its prevalence, a survey conducted in the United States and seven Asian countries found BPS in 81% of human urine samples collected. (3) Despite the two chemicals' general similarity, some of their biochemical properties differ. (4,5,6) This raises the possibility that BPS may affect endocrine organs--including the human placenta--differently than BPA does. Researchers led by Almudena Veiga-Lopez, a visiting associate professor in the Department of Pathology at the University of Illinois at Chicago, explored one such mechanism in a recent in vitro study published in Environmental Health Perspectives. (7)

Veiga-Lopez and colleagues studied cell fusion processes human placentas collected at the end of healthy pregnancies. The results of their analyses suggest that BPS may interfere with the formation of the syncytiotrophoblast (STB), a layer of epithelial cells in the placenta. The STB prevents the rejection of fetal cells by the maternal immune system, enables the exchange of nutrients and gases between mother and fetus, protects the fetus from some (although not all) harmful chemicals in maternal blood, and secretes its own hormones, such as hCG and progesterone. (8)

The STB is composed of trophoblasts, which are the first cells to differentiate after an egg is fertilized. The authors proposed that BPS interferes with the fusion of trophoblasts into the STB by competing with the epidermal growth factor (EGF) for binding to the EGF receptor (EGFR). EGF is a protein that stimulates cell growth and differentiation throughout the body. (9) The researchers analyzed trophoblasts from six term placentas and found that 200 ng/mL of BPS blocked EGF-mediated cell fusion in vitro by binding to EGFR. That concentration is at the upper end of the reported urinary range for the U.S. general population. (10)

Importantly, spontaneous cell fusion was not blocked by this dose, suggesting alternative mechanisms may be involved in the interference with STB formation. "Even if BPS were to block all of the cell fusion events that are induced by EGF, cells that were to...

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