Common plastic additives can damage DNA and chromosomes

DWhile everyday staples (cosmetics, food packaging, plastics) are useful, they may contain endocrine-disrupting chemicals (EDCs). These invisible invaders can sneak into the human body through skin absorption, inhalation and ingestion, quietly causing health problems.

Take butyl benzyl phthalate (BBP) as an example.¹ This additive makes plastic products flexible and durable, but exposure to BBP can disrupt hormonal balance and disrupt human reproductive health.^2,3 Although animal studies have implicated the effects of BBP on egg cell development and early embryos, the effects of BBP on early stages of meiosis remain understudied.⁴

This prompted Monica Colaiácovo, a molecular and cellular biologist at Harvard Medical School, to explore the impact of BBP on the early stages of reproduction. Caenorhabditis elegans. Her team’s findings were published in PLOS Geneticsdemonstrating that exposure to BBP at levels comparable to those detected in humans causes DNA strand breaks Nematodescausing the egg cells to have the wrong number of chromosomes.⁵ These insights provide a more detailed understanding of the early events of BBP exposure and its impact on animal reproduction.

most Nematodes Are hermaphrodites capable of self-fertilization, usually producing hermaphrodite offspring with two X chromosomes. Males have a single X chromosome, resulting from an error in the segregation of the X chromosome, and make up only 0.1% to 0.2% of the population. Colaiácovo sought to understand how EDC affects this process and the proportion of males in the nematode population.

Many EDCs exhibit nonmonotonic dose responses, where the relationship between dose and effect is not linear—higher doses do not always produce stronger effects. To explore this, the researchers used a high-throughput approach to screen different doses of BBP (1, 10, 100 and 500 μM) to determine which dose caused X chromosome non-disjunction or missegregation after 24 hours. They used nematodes with mutations in the cuticle collagen gene, which makes it easier for EDC compounds to penetrate the worms, allowing for the analysis of lower exposure doses.

For their experiments, the researchers selected worms that were in their late larval stage, before adulthood, which corresponds to the peak period of reproductive activity. To track male embryos, the researchers marked the worms with green fluorescent protein (GFP) controlled by a male-specific promoter and then used flow cytometry to sort the embryos. They found that 10 μM was the lowest dose of BBP that produced the greatest X-chromosome nondisjunction effect, thereby increasing the survival of male offspring. Nematodes.

“If you interfere with meiosis, the frequency with which these X chromosomes fail to partition correctly increases significantly,” Colaiácovo explains. “In many meiotic mutants, the proportion of males is not 0.2 percent, but 30 to 40 percent. So, it’s easy to see,” she said.

Researchers used mass spectrometry to discover Nematodes BBP is metabolized in a manner similar to humans, breaking down BBP into two major metabolites. Based on dose-response experiments, the research team examined the physiological relevance of 10 and 100 μM BBP in C. elegans . BBP and metabolite concentrations at only the 10 μM dose were comparable to previously reported levels in maternal urine, umbilical cord samples, and amniotic fluid.⁶

To amplify changes in chromosome organization during meiosis, the researchers used nuclear envelope and DNA damage protein stains to track nuclear behavior. Since these events typically follow a timely timeline, any delays may indicate flaws in the process. “What we see in this case is that these nuclei persist. We call them ‘laggards’ because they lag behind,” Kolyakovo said. “Then, very late in meiotic prophase, they still carry the signal [in the nuclei]should have disappeared. This arrest of the meiotic process coincides with activation of the DNA damage checkpoint triggered by double-strand break formation, leading to defects such as chromosome wear and breakage. Therefore, this results in increased embryonic lethality.

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

“When we looked at these genes, to our great surprise, they showed possible activation of an oxidative stress response,” Colaiácovo said. To dig deeper, the team used Nematodes Strains bearing a fluorescent tag linked to an oxidative stress reporter gene. When they analyzed germ cells, the team observed an increase in fluorescence, suggesting that BBP exposure exacerbates oxidative stress. This increase in stress causes DNA damage, compromising genome integrity, and disrupting the precision of meiotic chromosome segregation.

Patrick Allard, a 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 “this paper further investigates the mechanism of specific germ cell differentiation.” stages and provides detailed information on the meiotic recombination process and the impact of BBP exposure on it.

Colaiácovo plans to explore the effects of BBP on the male germline and whether there is sexual dimorphism affecting reproductive health. “There’s another exciting new direction that you can’t predict, so we’re really excited to see that and try to understand why this is happening,” she said.

“This study gives you some insight into the mechanism, and it can serve as additional information so people can make more educated decisions based on this work to try and see what might be in the specific products they’re using. , maybe there is another option,” commented Colaiácovo.