April 17, 2011 - By Krista Conger
Type-2 diabetes is likely to have its roots in an autoimmune reaction deep within the body, according to researchers at the Stanford University School of Medicine and the University of Toronto. The finding, coupled with a similar study by the same group in 2009, vaults the disorder into an entirely new, unexpected category that opens the door to novel potential therapies.
One possible therapy that proved effective in laboratory mice, an antibody called anti-CD20, is already approved for use in humans to treat some blood cancers and autoimmune diseases, although the researchers say further study is needed to determine whether it might work against diabetes in humans.
“We are in the process of redefining one of the most common diseases in America as an autoimmune disease, rather than a purely metabolic disease,” said Daniel Winer, MD, a former postdoctoral scholar in the laboratory of Stanford pathology professor Edgar Engleman, MD. “This work will change the way people think about obesity, and will likely impact medicine for years to come as physicians begin to switch their focus to immune-modulating treatments for type-2 diabetes.”
Nearly all type-2 diabetes drugs marketed today are designed to control a patient’s high blood sugar levels — a symptom of the body’s inability to respond properly to insulin. However, the researchers found that anti-CD20, which targets and eliminates mature B cells, could completely head off the development of type-2 diabetes in laboratory mice prone to the disorder and restore their blood sugar levels to normal. The researchers believe that insulin resistance arises when the B cells and other immune cells react against the body’s own tissues.
The human counterpart of anti-CD20, called rituximab, is sold under the trade names Rituxan and MabThera.
The research was published online April 17 in Nature Medicine. Engleman, who directs Stanford’s Blood Center and is a member of the Stanford Cancer Center, is the senior author of the research. Winer is one of three co-first authors; the others are his twin brother Shawn Winer, MD, PhD, of the Hospital for Sick Children at the University of Toronto; and Stanford research associate Lei Shen, MD, PhD. Daniel Winer is now an endocrine pathologist at the University Health Network of the University of Toronto.
Daniel Winer (left) and Shawn Winer collaborated on research showing that type-2 diabetes may be an autoimmune disease.
The findings blur the lines between type-2 diabetes (which has been thought to be primarily a metabolic disease) and type-1 (or juvenile) diabetes. Type-2 diabetes occurs when a person’s tissues become progressively resistant to insulin, a hormone required for the body to properly metabolize dietary glucose. Type-1 diabetes occurs when the immune system attacks and destroys insulin-producing cells in the pancreas.
The root cause of the insulin resistance in type-2 diabetes is not known, but it’s associated with obesity and can run in families. Several years ago, Daniel and Shawn Winer began to speculate that different types of immune cells, including T cells and B cells, can cause inflammation in the fatty tissue that surrounds and cushions organs in the body. This inflammation occurs in mice fed a high-fat, high-calorie diet when the rapidly growing fat cells outstrip their blood supply and begin to die. (It’s also seen in humans with type-2 diabetes.) The dying cells spew their contents, and immune system cells called macrophages are summoned to clean up the mess.
“This immune reaction causes havoc in the fatty tissue,” said Engleman, “and we’ve found that it involves two other immune system cells — T cells and B cells — in addition to macrophages.” The resulting onslaught by the immune system inhibits the ability of the remaining fat cells to respond to insulin and causes fatty acids to be shed into the blood. This sets in motion a physiological cascade that leads to fatty liver disease, high cholesterol, high blood pressure and further insulin resistance throughout the body.
To test their theory, the researchers studied the effect of blocking this early immune response to inflammation in laboratory mice fed a high-fat, high-calorie diet. Without treatment, after several weeks on the diet the mice began to grow obese and their blood sugar levels began to climb. In the 2009 work, also published in Nature Medicine (of which Shawn Winer was the first author), the researchers showed that blocking the action of disease-causing T cells could prevent the mice from going on to develop diabetes. In the current work, the researchers turned their attention to the B cells.
“The interesting thing about B cells is that, in addition to stimulating T cells, they also produce antibodies, which can have far-reaching effects,” said Shawn Winer. “Antibodies are typically involved in protecting the body from infection, but they can also cause disease.”
The researchers found that mice genetically engineered to lack B cells were protected from developing insulin resistance even when they grew obese on the high-fat diet. However, injecting these mice with B cells or purified antibodies from obese, insulin-resistant mice significantly impaired their ability to metabolize glucose and caused their fasting insulin levels to increase.
Clearly, antibodies play a significant role in insulin resistance in mice. But what about people? To find out, the researchers studied 32 age- and weight-matched overweight people who differed only in their sensitivity to insulin.
“We were able to show that people with insulin resistance make antibodies to a select group of their own proteins,” said Engleman. “In contrast, equally overweight people who are not insulin-resistant do not express these antibodies.”
“It’s highly suggestive that your body targets its own proteins as part of the development of insulin resistance,” said Daniel Winer. “It really links the concept of insulin resistance to autoimmunity. Conversely, if we could identify a panel of antibodies that might protect against developing insulin resistance, we could begin to think about a vaccine to prevent type-2 diabetes.” Vaccines could be used to induce the expression of protective, rather than harmful, antibodies and immune responses, Winer believes.
Finally, the researchers tested the effect of the anti-CD20 antibody in mice fed the high-fat diet for six weeks. Like its FDA-approved counterpart, Rituximab, the mouse anti-CD20 antibody latches onto mature B cells and targets them for destruction. It doesn’t, however, permanently stop the body from generating new B cells to replace those that are lost.
The researchers found that the mice treated with anti-CD20 showed significant improvements in their ability to metabolize glucose and in their fasting levels of insulin. One treatment lasted for about 40 days, at which time a new crop of B cells had matured and the mice again began to develop insulin resistance.
Despite the treatment’s effectiveness in mice, the researchers caution against assuming rituximab will work in humans with established type-2 diabetes.
“These animals were still in the development stage of the disease,” said Engleman, “and until we’ve done the clinical trials to evaluate this approach in humans, we can’t draw any conclusions. But our results certainly strongly suggest that immune modulation should be considered as a potential human therapy. Until then, however, diet and exercise are still the best ways to prevent type-2 diabetes in humans.”
Additional Stanford researchers involved in the study include graduate students Mike Alonso, Matt Davidson, Hweixian Leong and Justin Kenkel; postdoctoral scholars Persis Wadia, PhD, and Maria Caimol, MD; research associate Alec Glassford; assistant professor of medicine Tracey McLaughlin, MD; and assistant professor of medicine David Miklos, MD.
The research was funded by the National Institutes of Health. Daniel and Shawn Winer, along with Stanford University and The Hospital for Sick Children in Toronto, have filed joint patent applications on the use of B cell and antibody modulating agents for the treatment of insulin resistance and autoantibody diagnostic tests for the management of insulin resistance.
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