One possible use for controversial human embryonic stem cells, apart from possible therapies and research into genetic diseases, is testing new drugs to see whether they might be toxic in humans. Animal trials are often unreliable, as compounds which appear to be safe in animals may harm people. Now Gabriela Cezar, an animal scientist at the University of Wisconsin-Madison, has begun investigating whether the stem cells will actually work. The answer, it seems, is "not yet".

She tested a drug which is known to produce birth defects, valproate, and measured changes in the concentrations of certain molecules. However, a scientist at MIT, Steven Tannenbaum, says that whether her results are useful is still unclear. The liver metabolises drugs into other forms. "This group has taken valproic acid, which is normally extensively metabolised in the body, and exposed it under unrealistic conditions." Cezar acknowledges this and says that the problem might be overcome by morphing embryonic stem cells into liver cells before testing them. ~ Technology Review, Dec 13