Such a drug could offer a big advance, the group added, as no currently available therapy for diabetes actually targets the underlying causes of disease in insulin-producing pancreatic beta cells. Insulin controls blood levels of glucose, the body's main energy source. In those with diabetes, insulin deficiency or insulin resistance causes blood sugar concentrations to rise.
The team discovered that Gardenia extract contains the chemical "genipin." Previously known for its ability to cross-link proteins, they now find that the chemical also blocks the function of the enzyme called uncoupling protein 2 (UCP2) through another mechanism. In both animals and humans, high concentrations of UCP2 appear to inhibit insulin secretion from the pancreas and increase the risk of type 2 diabetes.
"We think the increase in UCP2 activity is an important component of the pathogenesis of diabetes," said Bradford Lowell of Beth Israel Deaconess Medical Center and Harvard Medical School. "Our goal therefore was to discover a UCP2 inhibitor capable of working in intact cells, as such an inhibitor could theoretically represent a lead compound for agents aimed at improving beta cell function in type 2 diabetes."
Study coauthor Chen-Yu Zhang's familiarity with traditional Chinese medicine led the team to consider the extract of Gardenia jasminoides Ellis fruits. Pancreas cells taken from normal mice secreted insulin when treated with the extract, they found, whereas the cells of mice lacking UCP2 did not. The results suggested that the extract worked through its effects on the UCP2 enzyme.