Serious efforts are underway to significantly reduce the number of animal tests carried out for research purposes. The latest EU Cosmetics Regulation, which came into force in 2013, bans the sale of cosmetic products containing ingredients that have been tested on animals. But it is difficult to find alternatives, not only for the cosmetics industry but also in the field of pharmaceutical research. In many cases, there are no other suitable methods of toxicity testing available. Numerous research groups are therefore working on the development of new, viable test formats.
One of the most promising approaches involves the use of cultured liver cells. The liver is the most important organ when it comes to eliminating toxins from the body. It therefore makes sense to use liver cells to test the toxicity of substances. But this isn’t as easy as it sounds. It has to be ensured that all cells are equally exposed to the substance being tested. And a further problem in the case of liver cells is that they rarely survive for longer than a few days in a laboratory environment. This makes it virtually impossible to carry out experiments to determine the long-term effect of toxic substances on a living organism.
Watching how liver cells react in real time
As part of the HeMiBio (Hepatic Microfluidic Bioreactor) project, researchers at the Fraunhofer Institute for Cell Therapy and Immunology IZI in Potsdam in collaboration with partners at the Hebrew University of Jerusalem have developed a microbioreactor in which liver cells can be kept alive and observed for a period of one month. The particular advantage of this device is that it allows researchers to watch how liver cells react to toxic substances directly and in real time. “Up to now, both in animal testing and in conventional lab tests, measurements have usually only been made at the end of the test,” says Dr. Claus Duschl, head of the cellular biotechnology department at the IZI. “The procedure consists of administering different doses of an active ingredient and subsequently analyzing the areas of dead tissue or the dead animal. It is not possible to determine the precise effect of the active ingredient on the cells using this method.”
Sensors measure oxygen consumption
The microbioreactor changes all this. Its miniature sensors gather real-time data on the amount of oxygen being taken up by the liver cells at any instant. Oxygen consumption is high when the cell’s metabolism is stimulated. If the cell dies, the oxygen consumption falls. By reading this curve, cell biologists are even capable of pinpointing the metabolic processes taking place in a cell at a specific point in time. The HeMiBio project partners make use of this information. When a toxic substance is placed in the microreactor, the sensors record a detailed picture of the changing levels of oxygen consumption. These measurements make it possible to precisely identify the stages of the metabolic process that are affected or halted by the active ingredient. “While working on this project with cell biologists at the Hebrew University of Jerusalem, we have been able to verify various hypotheses by selectively replacing specific metabolic products whose synthesis had been blocked by the toxic substance,” Duschl explains. “As we had surmised, the metabolic process then continued unaffected to the next stage.”