Fat cells from people who are obese don't work properly compared with those from lean people, medical researchers have found.

In Thursday's issue of the journal Diabetes, researchers in Philadelphia said they found major differences in fat cells taken from the upper thighs of six obese people and six lean subjects.

"The fat cells we found in our obese patients were deficient in several areas," said the study's lead author, Dr. Guenther Boden, chief of endocrinology at Temple University's School of Medicine.

"They showed significant stress on the endoplasmic reticulum, and the tissue itself was more inflamed than in our lean patients."

The endoplasmic reticulum, or ER, is found in every cell, helping to synthesize proteins and monitor how they are folded, which is important for proper functioning.

When the ER in fat cells were stressed, they produced proteins that lead to insulin resistance, the researchers said.

Insulin resistance occurs when the body fails to effectively regulate the metabolism of fats, proteins and sugars. The condition can lead to Type 2 diabetes.

In Type 2 diabetes, the pancreas either does not make enough insulin or makes it but the muscles, fat and liver cells may not use it properly.

Losing weight may help reduce stress on the ER, which can lower the risk of insulin resistance, the researchers said.

Transforming pancreas cells

In a related study published online in the journal Nature on Wednesday, scientists said they had transformed ordinary pancreas cells in mice into a rarer variety, called pancreatic beta cells, that secrete insulin.

The pancreatic beta cells are destroyed in people with Type 1 diabetes.

The experimental approach, which avoids the need for embryonic stem cells, is not ready to be tried in humans, cautioned study author Douglas Melton, co-director of the Harvard Stem Cell Institute and a researcher with the Howard Hughes Medical Institute.

The findings bring "more excitement to the idea of using reprogramming as a way to treat diabetes," said researcher Mark Kay of Stanford University, who is studying the approach with liver cells.

The two cell types in the mouse experiment were closely related, and many scientific questions remain about transforming other kinds of cells that may need different signals.

With files from the Associated Press