In healthy animals, insulin causes the glucose levels to return to normal in 90 minutes, while in diabetic animals carrying the SIA gene the glucose levels took 120 minutes to reach the same point. These results are published in this week's issue of Nature . Key to the success of this experiment was the design of SIA, according to Jerrold Olefsky, of the University of California, San Diego. Olefsky wrote a News and Views piece that accompanies Yoon's report. The SIA gene engineered by Yoon and his colleagues produces a slightly altered version of insulin that is produced in the liver.
Natural insulin is produced in the pancreas.
In juvenile diabetes the insulin-producing cells have been mistakenly destroyed by the immune system, which necessitates that any substitute is made elsewhere in the body. There are still many hurdles to overcome before Yoon and his collaborators at Yonsei University in Seoul, can progress to human trials. The scientists used a virus to deliver SIA to the liver cells of diabetic rats and mice. The amount of virus required to treat larger animals such as dogs and monkeys must be determined before moving on to humans. Studies of how the expression of SIA changes over time are also needed.