Toxicity Test to cut Animal Testing
Milan/Rome - Italian researchers have developed a new cell culture method to test whether chemicals are toxic to humans. They engineered liver cells (hepatocytes) to secrete the human growth hormone (HGH) when exposed to toxic organic or inorganic compounds like Sodium arsenite, Benzopyrene, or Tetra-chloro hydro quinone. Additionally the transgenic hepatocyte cell line has been stably immortalized by insertion of the growth factor receptor gene c-met. As the novel cell lines can survive for longer than cultured primary liver cells, the cell type most commonly used in toxicity testing, adopting this new technique would reduce the number of animals used in such experiments.
To create the bi-transgenic cell line researchers around Marco Tripodi crossed two mice strains they previously created: A strain in which the gene for the human growth hormone (hGh) is constructed behind a heat-shock protein promotor (hsp70). Additionally, a mouse model allowing the reproducible immortalization of untransformed hepatocytes retaining complex liver functions.
To test their system the researchers added toxic arsenic and cadmium compounds to the cells and then looked for human growth hormone in the culture media. They found that even at low doses these compounds caused the cells to secrete the hormone - and were therefore deemed to be toxic. These low concentrations of the chemicals would not have been picked up by current toxicity-testing methods, which brand a chemical as ‚toxic' only if it kills liver cells.
The researchers believe that experiments using the transgenic cell lines will also be more informative than those using cultured liver cancer cell lines, the current alternative to cultured primary cells. Over time, liver cells in culture are known to alter their patterns of gene expression and no longer behave like liver cells in vivo. For example they often lose the ability to produce drug-activating and modifying enzymes. Cultured MMH-GH cell lines do not suffer from this problem, retaining features of liver cells inside the mouse. Moreover, if important changes do occur in these cells, fresh cell lines can be derived from the transgenic animals. The MMH-GH cell lines have a further advantage over current toxicity testing methods, according to the researchers. As they are derived from clonal cell populations assays using these cells should also be easier to standardize than current tests, which use heterogeneous primary cell cultures.