Micro- and nanoplastics ingested by fruit flies cause changes in heart size and function

Plastics are ubiquitous in the products we use every day, and recent studies have begun to reveal the effects of micro- and nanoplastics (MP and NP) on the health of humans and animals.

So far, most research on the health effects of plastics has focused on marine life, particularly fish. A few preliminary studies have looked at the possible toxic effects of plastics on terrestrial species such as birds, earthworms, insects, humans and other mammals, but many details remain unknown.

A team of researchers from Iowa State University, using fruit flies (Drosophila melanogaster), has now conducted the first study of the effects of MP and NP toxicity on the heart. The team’s work is published in a short research report in Frontiers in toxicology.

How big is the plastic problem?

In 2017, a study by Geyer et al. estimated that about 8,300 million tons of plastic had been produced since 1950; that more than 4,900 million tons of this plastic had ended up in landfills or elsewhere in the environment; and that without changes in production levels or waste management, this number could increase to 12,000 tons by 2050.

According to more recent research, “approximately 36 million tons of plastic waste are generated in the United States each year, most of which is released into the environment and ends up in landfills.”

In this context, and as heart disease is the leading cause of death worldwide, it becomes urgent to understand the effects of exposure to MPs and NPs on the heart.

Research and results

The hearts of fruit flies and vertebrates exhibit similar functional and genetic changes during development and aging. For this new study, the researchers obtained wild-type fruit fly larvae and divided them into a control group and two test groups.

The researchers fed all flies corn flour from early development to maturity (pupation). Flies in both test groups received corn flour to which the researchers added polystyrene MPs (larger than 100 nm and smaller than 5 mm) or NPs (smaller than 100 nm).

Five days after the flies hatched, the researchers collected about 15 flies of each sex from each of the two test groups and the control group. The team anesthetized the flies, dissected their heartbeats, and recorded high-speed videos at more than 200 frames per second for analysis.

Among the notable results, the analysis indicates that plastic exposure produces different results in males and females. The heart rate of female flies exposed to both MP and NP decreased by 13%, while their cardiac periods (time between the start of one heartbeat and the start of the next heartbeat) increased accordingly. Male flies did not show this change, but males fed MP showed greater variability than those fed NP and those in the control group.

In female flies fed NP, heart size (diastolic diameter) increased and diastolic intervals increased in females fed both MP and NP. Concurrently, heart size of male flies fed both plastic sizes showed significant changes in both diastolic and systolic diameters.

Additionally, the researchers write: “Unlike females, male flies also experience changes in systolic interval (SI) time and fractional shortening. Total SI time is reduced by 40% in flies exposed to MPs while female flies experience no change. Finally, males exposed to NPs experience an 11% reduction in fractional shortening. This phenomenon is unique to males, as females experience no change in fractional shortening following dietary exposure to either plastic format.”

Why is this important?

The researchers initially speculated that the observed changes could be due to the fact that the MPs and NPs created a physical barrier to normal heart development. They also believe that “molecular interactions between the plastics and the heart itself” are responsible for the observed sexually dimorphic changes, particularly the differences in heart size between males and females.

However, they acknowledge that “the true mechanism behind these observed changes is unknown, and further research is therefore needed to identify whether exposure to MPs and NPs interacts with genes conserved in mammals that may lead to cardiac dysfunction.”

They also suggest that further research could include a variety of ingestible forms of plastic, and that further research should also focus on identifying the specific molecular changes that cause the observed functional impairments.

“The data from this study can inform the field about potential changes in other terrestrial organisms and opens the door to future studies examining the molecular mechanism behind these changes and highlights the importance of plastic research in both sexes,” the team concludes.

© 2024 Science X Network