How do environmental toxins affect the heart?
Even though the World Health Organization (WHO) estimates that up to 23 percent of the global burden of cardiovascular diseases—the leading cause of death worldwide—can be attributed to environmental chemicals, we really don’t know much about these substances.
David Threadgill, Ph.D., a university distinguished professor in the Department of Molecular & Cellular Medicine at the Texas A&M Health Science Center, had been thinking about the problem and possible ways to approach the research, so when the United States Environmental Protection Agency (EPA) put out a call for proposals to study toxicity using “organoids,” three-dimensional organ–like structures grown in cell culture, he and his collaborators jumped at the opportunity. An organoid has multiple types of cells, just like a real organ does, but it lives entirely within a dish and it is far easier to use for chemical testing. They are thought of as a kind of bridge between conventional, single-layer cell cultures and whole-animal systems.
Together with his long-term collaborator, Ivan Rusyn, M.D., Ph.D., professor of veterinary integrative biosciences at the Texas A&M College of Veterinary Medicine & Biomedical Sciences (CVM), Threadgill was awarded a $6 million grant by the EPA to fund a multi-institutional collaboration to study how heart cells react to different chemicals. The long and growing list of substances used in industry that get into the environment was what prompted the EPA to seek research that would study their toxicity. Without this information, the EPA cannot make good decisions about which substances to regulate, let alone how. This lack of regulation could turn out to have major public health implications if it is later discovered that the chemicals are harmful.
“Some of us had already been thinking about organoids and how we could use those as sensors for environmental chemicals,” said Threadgill, who is also a professor in the Department of Veterinary Pathobiology at the CVM, “and we decided to focus on cardiotoxicity, because we knew that the heart is the organ second-most (after the liver) influenced by toxins, but the one that we know least about.” Threadgill had some experience looking at cardiotoxicity in drug studies, but this was the first time he applied those techniques to chemicals in the environment—and very few other people have either. Methods for assessment of cardiac safety of non-pharmaceutical agents are lagging behind the traditional health hazards of concern to human health.
Recent advances in using stem cells to develop models of functional cardiac muscle cells has led to new prospects for simulating complex chemical outcome pathways in the beating heart. Threadgill’s lab will use induced pluripotent stem (iPS) cells to create little beating organoid “hearts” in culture, with iPS cells coming from 100 different strains of the animal model—creating variation similar to what you would see in the human population.
“We’re looking at population-level exposure,” Threadgill said. “Does everyone respond the same way, or are some people more sensitive?”
Threadgill will then test what happens to the rhythm of the organoids’ “heartbeat” after they are exposed to the nearly 200 environmental chemicals. Those chemicals that seem to have cardiotoxicity will then be tested in the actual animal models, an approach called in vitro to in vivo extrapolation modeling. If they match, that would give the researchers confidence that the data they get from cell cultures is valid.
“What we hope to be able to show—which has never been formally proven—is that all of this effort to use cultured cells or very simple systems to screen for toxicity is informative for what happens in the whole animal, with its very complex systems,” Threadgill said. “If it is indeed the case that it is predictive, we will have much greater confidence in the results coming out of cell-based research.”
Meanwhile, Rusyn will be working with human iPS cells from about 100 different adult donors to test the same chemicals, but since he can’t go back and compare his results to tests done in the donors, he will rely on Threadgill’s animal models to validate his results.
“We hope to be able to screen for a large number of chemicals that we’re all being exposed to all the time,” Threadgill said, “and the goal would be to be able to do this in cultured cells or organoids, which would be a much quicker and more efficient way of going about it.”
The other principal investigator on the project is Fred Wright, professor of statistics at the Bioinformatics Research Center at North Carolina State University (NCSU), who will be doing the computational modeling for the project.