Test spares animal subjects, identifies chemicals that may cause birth defects in humans

In an effort to assess chemicals’ likelihoods of causing birth defects in humans, researchers at Yokohama National University in Japan say they’ve developed a test procedure that can be widely referenced by chemical and pharmaceutical companies, based on disturbances of the signals that are precisely programmed in human stem cells to shape parts of the body.  Birth defects occur in 7.9 million babies each year, making up approximately six percent of the world’s population.

The findings were published in iScience on February 18 and in Journal of Bioscience and Engineering.  

Testing on laboratory mice is the prevailing method for evaluating the safety of man-made chemicals, including the likelihood that the chemicals could lead to birth defects and cancers. However, some chemicals that are not found to cause birth defects in test animals can cause severe malformations in humans, a typical example of which is remembered as the tragedy of thalidomide in history. The team aims to close that gap in results between animals and humans with this new method.

“By subjecting human pluripotent stem cells to man-made chemicals and observing their influences on  precisely programed signaling within the cells, we hoped to evaluate toxicity to unborn babies with greater accuracy,” said Junji Fukuda, professor at Yokohama National University who lead the research and an expert in biomedical engineering.   

The researchers looked specifically at how different chemicals impacted controls over fibroblast growth factor chemical signals that play a key role in inducing tissue formation including limb development. They continuously observed changes in the signaling upon introducing each chemical in question. To do so, the cells were genetically edited to light up in response to temporal changes in the signaling, a method biologists refer to as using a reporter assay.

To test the feasibility of the assay system, the research team selected known chemicals that have been found to be associated with birth defects, including thalidomide. Data on thalidomide largely shapes the “ICH S5 Guideline on Reproductive Toxicology,” a pharmaceutical industry standard for evaluating drugs’ safety for use during pregnancy. Thalidomide was used in the 1950’s and early 60’s as an anti-nausea medicine for pregnant women, but quickly discontinued for that use after mounting evidence linked it with disabling birth defects such as missing and misshapen limbs. The drug is still in limited use today for specific cancers and skin conditions, but never prescribed to women who are pregnant or might become pregnant.

Fukuda’s team evaluated the assay system using 30 chemicals ranging from the relatively benign sodium saccharin and a form of penicillin to the most highly toxic substances, including all-trans-Retinoic acid and hydroxyurea.

To establish a basis for evaluating how and when certain chemicals interrupt natural growth processes, they stimulated pluripotent stem cells with fibroblast growth factor, both with and without the presence of the 30 chemicals chosen for the experiment. The researchers observed noticeable increases and decreases in the intensity of luminescence at different time points depending on chemicals. They estimated each chemicals’ likelihood of causing birth defects by integrating the difference of the signal from its original level over time.

The results were promising but left many questions for further studies.

“It was obvious that when man-made chemicals cause birth defects, associated signals are disrupted,” Fukuda said. “Our proposed process of examining pluripotent stem cells via a luminescent reporter assay is a step toward reliably predicting which man-made chemicals may put unborn children at higher risk for birth defects. In fact, our results showed that the assay provided excellent classification performance for limb malformation toxicants, including thalidomide and its derivatives, which had been difficult to predict using a test method using animals.”

Though the experiments show promise in classifying toxicants, the study authors wrote that further research will be necessary for detecting systemic developmental toxicities throughout the body. “Several other major signaling pathways are associated with birth defects, such as Wnt/b-catenin, BMP/SMAD, and Hedgehog/GLI. Combinations of reporter cells that report the activity of these signaling pathways may provide a more comprehensive assessment of developmental toxicants.,” Fukuda said.

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Yokohama National University (YNU or Yokokoku) is a Japanese national university founded in 1949. YNU provides students with a practical education utilizing the wide expertise of its faculty and facilitates engagement with the global community. YNU’s strength in the academic research of practical application sciences leads to high-impact publications and contributes to international scientific research and the global society. For more information, please see: https://www.ynu.ac.jp/english/