Planaria flatworms, as an alternative to rabbits or other animals, may be an effective model for testing topical skin therapies, potentially reducing research costs.
In a paper published online ahead of print in Toxicology In Vitro (Oct. 1, 2020), investigators from the University of Reading and Newcastle University in the U.K. detail a new assay for evaluating potential irritation. The assay involves combining a fluorescent dye with the skin product to be tested and applying it to the simple worms. Damage caused by the test agent to the outer surface of the planaria causes more dye to be absorbed.
While testing the assay, the investigators found that dye accumulation within the test worms was significantly higher when the assay had been combined with known strong irritants—benzalkonium chloride, citronellal, methyl palmitate, 1-bromohexane and carvacrol—than when the dye was combined with negative controls or common non-irritants—PEG-400, dipropylene glycol and isopropyl alcohol.
In a press release, the investigators note that this approach to testing would be less expensive and more ethical than existing animal tests, because planaria are readily available and easily cultured in a laboratory, and do not experience suffering. They note that while there is still a role for testing on human skin cells in a petri dish, the new screening method would provide a more accurate test of how a potential skin product would interact with living tissue.
“Developing more ethical alternatives to tests that others do on rabbits, known as the Draize test, has been a major challenge, especially in relation to evaluating products for sensitive human tissue,” study author Vitaliy Khutoryanskiy, PhD, said in the release. “Our tests with flatworms show that there are potential ways to screen skin irritants in a more ethically responsible way.”
Dr. Khutoryanskiy is Professor of Formulation Science at the University of Reading.
“While the vast majority of cosmetic skin products are no longer tested on animals, it remains critical that new developments for clinical treatments are tested robustly and we hope that we can find solutions that consign the Draize test to history. We also hope to continue planaria research and develop further tests for probe irritation potential of chemicals to other human tissues.”