Common plastic additives harm DNA and chromosomes

DDespite their usefulness, everyday products such as cosmetics, food packaging, and plastics can contain endocrine disrupting chemicals (EDCs). These sneaky invaders can enter the body through absorption through the skin, inhalation, or ingestion, silently causing health problems.

take Benzylbutyl phthalate (BBP) etc.¹ This additive gives plastic products flexibility and durability, but exposure to BBP can impair their functionality. hormone balance and tinker human reproductive health.^{2, 3} Although animal experiments suggest this effect, egg cell development The influence of BBP on the early stages of meiosis remains largely unexplored.⁴

This was the motivation Monica Colaiacoboa molecular cell biologist at Harvard Medical School, investigated the effects of BBP during the early stages of reproduction. Caenorhabditis elegans. of her team findingswas published in PLOS Geneticsdemonstrate that exposure to BBP levels comparable to those detected in humans caused DNA strand breaks. C.EleganceThe result is an egg cell with the wrong number of chromosomes.⁵ These insights provide a more detailed understanding of the early events of BBP exposure and its effects on animal reproduction.

largely C.Elegance Hermaphrodites are capable of self-fertilization and usually produce hermaphrodite offspring with two X chromosomes. Males with a single X chromosome, resulting from an error in X chromosome segregation, make up only 0.1 to 0.2 percent of the population. Colaiacobo sought to understand how EDC affects this process and the proportion of males in the nematode population.

Many EDCs exhibit a nonmonotonic dose response, where the relationship between dose and effect is not linear, and higher doses do not always result in stronger effects. To investigate this, the researchers used high-throughput methods to screen different doses of BBP (1, 10, 100, and 500 μM) and determined which doses caused X-chromosome nondisjunction or It was determined whether the separation caused an error. To analyze lower exposure doses, they used worms with mutations in cuticle collagen genes that make it easier for EDC compounds to penetrate the worms.

For their experiments, the researchers selected worms in their late larval stages, just before reaching adulthood, which corresponds to the peak of reproductive activity. To track male embryos, the researchers tagged the worms with green fluorescent protein (GFP), which is controlled by a male-specific promoter, and used flow cytometry to sort the embryos. They found that 10 μM was the lowest dose of BBP that produced the maximal X-chromosome nondisjunction effect, which increased male offspring. C.Elegance.

“If you prevent meiosis, you significantly increase the frequency with which these X chromosomes don’t divide properly,” Colaiácovo explains. “In many meiotic mutants, instead of 0.2% males, you end up with 30 to 40% males, so it’s much easier to see,” she said.

Using mass spectrometry, the researchers discovered that: C.Elegance They metabolized BBP in a manner similar to humans, breaking down BBP into two primary metabolites. Based on dose-response experiments, the research team tested 10 μM and 100 μM for physiologically relevant levels of BBP in C. elegans. Only the 10 μM dose resulted in BBP and metabolite concentrations comparable to levels previously reported Found in pregnant women’s urine, umbilical cord samples, and amniotic fluid.⁶

To take a closer look at the changes in chromosome composition during meiosis, the researchers tracked the behavior of the nucleus using nuclear membrane and DNA damage protein stains. These events typically occur on a timely schedule, so any delays may indicate a flaw in this process. “What we saw in this case was that these nuclei persisted. They’re falling behind, so we call them ‘latecomers.'” Colaiacobo said. “Then, even into the very late stages of meiotic prophase, they’re still sending signals.” [in the nuclei]it should already be gone. ” This stall in meiotic progression coincided with the activation of DNA damage checkpoints triggered by the formation of double-strand breaks, leading to defects such as chromosome fraying and fragmentation. Consequently, this led to increased fetal lethality.

Because exposure to BBP increases germ cell death and compromises chromosome integrity, she sought to identify genes involved in this process. Using RNA sequencing, they identified 344 genes that were differentially expressed in worms exposed to 10 μM BBP. Among the downregulated genes were genes important for extracellular matrix processes and egg cell integrity.

“What was really striking to us as we were looking at these genes was that they suggested that there might be activation of the oxidative stress response,” Coliakovo said. Ta. To dig deeper, the team nematode A strain with a fluorescent tag attached to an oxidative stress reporter. When the researchers analyzed germline cells, they observed increased fluorescence, a sign of increased oxidative stress due to BBP exposure. This increased stress caused DNA damage, compromised genome integrity, and compromised the accuracy of meiotic chromosome segregation.

Patrick AllardA developmental biologist at the University of California, Los Angeles, who was not involved in the study, said that BBP is known to cause oxidative stress associated with reproductive toxicity, but that “this paper shows that specific stages of BBP We are going even further by considering the following.” We analyze germ cell differentiation and provide detailed information about the process of meiotic recombination and how it is affected by BBP exposure. ”

Professor Colaiacobo will investigate the effects of BBP on the male germline and whether there are sexual dimorphisms that affect reproductive health. “There was a whole different and exciting new direction that we couldn’t necessarily predict. So we were very excited to look at this and try to understand why this was happening,” she said. spoke.

“This study provides insight into the mechanisms and allows people to make more educated decisions based on this research, to check what’s in the specific products they’re using, and perhaps to It serves as additional information so that you can make a choice. Alternatives,” said Colaiakovo.