According to the World Health Organization, the number of people worldwide who are obese has nearly tripled since 1975. Experts think that chemical exposure may play a role in that growth. A team now reports that extracts from a variety of plastic consumer products, including food packaging materials, can induce the formation of fat cells in mouse cell culture (Environ. Sci. Technol. 2022, DOI: 10.1021/acs.est.1c06316).
The researchers used untargeted mass spectrometry to try to determine the full range of chemicals in the extracts. They went hunting for everything they could detect, not just well-known metabolism-disrupting chemicals such as phthalates, says Martin Wagner of the Norwegian University of Science and Technology, who led the research. “There’s a lot of chemical complexity in the samples,” he says.
In some products, they found more than 2,000 spectral features. The team doesn’t know how many chemicals those features correspond to, because multiple features could come from the same parent compound. But any estimate is likely to be an undercount, Wagner says, because they used only one type of mass spectrometry and positive ionization. Additional chemicals might be detected with negative ionization.
“We can’t really know the identity of the compounds, demonstrating that we have a problem of unidentifiable compounds in those plastic products,” Wagner says.
Extracts from 11 out of 34 samples induced mouse fat cell precursors to differentiate into fat cells. Extracts from four products resulted in the formation of more fat cells than are induced by rosiglitazone, an anti-diabetes drug known to cause weight gain. They assessed fat cell formation on the basis of the number and size of the lipid droplets and the fluorescence intensity of a lipid-targeting dye. The researchers found that fat cell formation didn’t correlate with the presence of known metabolism-disrupting chemicals. Wagner thinks that as-yet unidentified chemicals—either individually or as a mixture—are having a greater effect.
The researchers also found that unknown mechanisms are triggering fat cell formation. The ability of an extract to activate key known regulators of fat cell formation or lipid metabolism were not good predictors of the extract’s fat cell-inducing activity. The concern is that people could be exposed to the chemicals in the extracts through the use of everyday products.
Bruce Blumberg, a biologist at the University of California, Irvine who studies environmental factors affecting obesity, calls the work important.
“Very few studies (mostly by this group) have conducted nontargeted (i.e., unbiased) testing of chemicals for their ability to disrupt endocrine signaling pathways. Since manufacturers are permitted to keep formulations and safety information about their products as ‘trade secrets’ it is only investigations like this one that can reveal the true extent of the possible endocrine disrupting chemicals found in common plastics,” Blumberg writes in an email. “As someone who has done this type of nontargeted screening with my own hands, I can say that this work is a tour de force in the field.”
A representative of the Plastics Industry Association declined to comment on the work.
Wagner’s plans include figuring out the mechanism through which the extracts are inducing fat cell formation and whether individual chemicals or combinations are responsible.