The study by University of Central Florida biomedical researchers has found that insulin capsules could someday be used to prevent diabetes before symptoms appear and treat the disease in its later stages.
Professor Henry Daniell's research team genetically engineered tobacco plants with the insulin gene and then administered freeze-dried plant cells to five-week-old diabetic mice as a powder for eight weeks. By the end of the study, the diabetic mice had normal blood and urine sugar levels, and their cells were producing normal levels of insulin.
"Those results and prior research indicate that insulin capsules could someday be used to prevent diabetes before symptoms appear and treat the disease in its later stages," Daniell said.
He has since proposed using lettuce instead of tobacco to produce the insulin because that crop can be produced cheaply and avoids the negative stigma associated with tobacco.
Insulin-dependent, or Type 1, diabetes is an autoimmune disease in which the body's immune system attacks and destroys insulin and insulin-producing beta cells in the pancreas. Insulin is a hormone that is needed to convert sugar, starches and other food into energy.
Insulin typically is given through shots and not pills so the hormone can go straight into the bloodstream. In Daniell's method, plant cell walls made of cellulose initially prevent insulin from degrading. When the plant cells containing insulin reach the intestine, bacteria living there begin to slowly break down the cell walls and gradually release insulin into the bloodstream.
"Currently, the only relief for diabetes is a momentary relief," Daniell said. "Diabetics still have to monitor their blood and urine sugar levels. They have to inject themselves with insulin several times a day. Having a permanent solution for this, I'm sure, would be pretty exciting."
Though produced in lettuce, the insulin would be delivered to human patients as a powder in capsules because the dosage must be controlled carefully.
If human trials are successful, the impact of Daniell's research could affect millions of diabetics worldwide and dramatically reduce the costs of fighting a disease that can lead to heart and kidney diseases and blindness.
The number of Americans with diabetes is projected to double by 2025, according to a study released last month by the National Changing Diabetes Program during a congressional briefing. That study by Mathematica Policy Research Inc. also reported that one of every eight federal health care dollars - 79.7 billion dollars out of 645 billion dollars is spent on treating people with diabetes.
"Diabetes is a big health and financial burden in the United States and in the rest of the world. This study would facilitate a dramatic change because so far there is no medicine that will cure insulin-dependent diabetes," Daniell said.
Daniell's method of growing insulin in plants is similar to what he used for an earlier study to produce anthrax vaccine in tobacco. In the earlier study, which also involved mice, Daniell showed and the National Institutes of Health confirmed that enough safe anthrax vaccine to inoculate everyone in the United States could be grown inexpensively in only one acre of tobacco plants.
The study is published in the July issue of Plant Biotechnology Journal.