For the cholera bacterium, it's a trick to get the intestinal cells to take up the intact cholera toxin. For the researchers, it's a trick to get the intestinal cells to take up intact proinsulin.
This system stimulates uptake by cells of the intestinal immune system as well. In NOD (nonobese diabetic -- a standard rodent model of type 1 diabetes) mice, the uptake by the immune cells resulted in a significant increase in compounds that suppress immune responses. The result was a reduction in the immune system attack on the beta cells. It is immunological attack on the beta cells that causes their destruction and is the cause of type 1 diabetes.
In the mice, eventually the beta cells recovered, and their blood glucose levels returned to normal.
Daniell said that after the proinsulin complex is taken up into the interstitial fluid, it does not get transformed into insulin and C-peptide, so there's no danger that eating a lot of the complex would have an effect on blood glucose levels.
The researchers are hoping that this technique, using insulin from modified lettuce plants, can be used to stop beta cell destruction in people who are in the very early stages of type 1 diabetes, when they still have many beta cells left. It might even work in those who have already been diagnosed with type 1 diabetes.
Like much research in mice, however, this treatment is not something that is going to be available tomorrow. Cures in mice don't always translate into human cures. But, like the Toronto work last fall that showed that type 1 diabetes could be cured in mice by manipulating the nerves to the beta cells, this research is a fascinating new approach to the complex problem of diabetes.
"This is a totally new approach. It has great promise," said Daniell. He said that human clinical trials of the lettuce system are in the works.
Read the Reuters news article on insulin produced in genetically modified plants by clicking here.