Researchers at the National Toxicology Program (NTP) are developing cell models that better mimic the structure and function of human tissue for use in high-throughput toxicology testing. The effort is part of the Tox21 initiative to move away from animal testing, in part by using advanced tissue culture models that can quickly and reliably identify environmental toxins linked to human disease.
Sreenivasa Ramaiahgari, Ph.D., an NTP postdoctoral fellow, described his work on refining cell models for toxicity testing, during a talk Jan. 13 at the Duke University Integrated Toxicology and Environmental Health Program (ITEHP) seminar series. Ramaiahgari works in the NTP Biomolecular Screening Branch, which is the NTP lead for Tox21, and was the first presenter in the spring 2017 series.
His talk, “Organotypic In Vitro Models for Studying Chemical-induced Effects,” described his research involving three-dimensional (3D) organotypic models — models that behave like living tissue — of liver, kidney, and cancer cells.
“Cells in our bodies reside in a three-dimensional space,” Ramaiahgari explained. “Compared to conventional cell culture models, 3D models better mimic tissue functionality, and therefore, better predict responses to environmental exposures.”
Ramaiahgari’s mentor, B. Alex Merrick, Ph.D., head of the NTP Molecular Toxicology and Genomics Group, said Ramaiahgari's work on organotyping was significant. “He has advanced our ability to apply tissue-specific functionality and metabolism to high-throughput testing for chemical exposures that can cause disease,” Merrick said.
Models that mimic live tissues
Tissues and organs in the body are made up of different cell types that may be affected differently by environmental exposures. In addition, conventional cell culture methods produce models that lack the enzymes for chemical metabolism. Knowing whether and how a chemical affects cell metabolism is important when screening substances for potential toxicity.
To achieve this functionality in a tissue-specific model, Ramaiahgari developed a liver model using progenitor cells, which are a type of stem cell, that tend to differentiate into liver cells. Progenitor cell cultures are more economical than live donor cells. Furthermore, they can be kept alive as long as two months or more, Ramaiahgari pointed out, as opposed to up to a week for donor cells.
“We have already tested some model chemicals on our organotypic liver model,” Ramaiahgari said. “We found that it is more sensitive in identifying toxic chemicals than other liver tissue models.”
Early success, long-term goals
“Dr. Ramaiahgari has been extremely successful in developing a 3D spheroid model for human liver cells that demonstrates remarkably physiologically relevant liver functions,” said Rick Paules, Ph.D., acting chief of the Biomolecular Screening Branch. “It provides an unprecedented opportunity for NTP and our Tox21 colleagues to screen large numbers of chemicals. NIEHS is very fortunate to have Sreeni as part of our NTP and Tox21 team, and all the institute stands to benefit from his research.”
Ramaiahgari has also developed organotypic tissue models for breast and prostate cell types, he said. These models display tissue-specific functionalities not seen with conventional tissue culture models.
“Our ultimate goal at NTP is to have organotypic tissue culture models for all tissue types — liver, kidney, lung, heart, breast, neuronal, intestinal, and others — for predictive toxicology using high-throughput testing,” Ramaiahgari said.
Citation: Ramaiahgari SC, den Braver MW, Herpers B, Terpstra V, Commandeur JN, van de Water B, Price LS. 2014. A 3D in vitro model of differentiated HepG2 cell spheroids with improved liver-like properties for repeated dose high-throughput toxicity studies. Arch Toxicol. 88(5):1083-1095.
(John Yewell is a contract writer for the NIEHS Office of Communications and Public Liaison)