DU researchers are working on new treatments for obesity and Type 2 diabetes. Photo: Michael Richmond
We’ve all heard the jokes: “He’s so fat, he has his own area code. You’re so fat, when you step on the scale it says: One at a time, please!”
But for 69 million Americans, obesity is no laughing matter. It’s a real threat to their health and longevity. According to the American Obesity Association, obesity is associated with more than 30 medical conditions, including high blood pressure, osteoarthritis and heart disease.
One of the most devastating obesity-related diseases is Type 2 diabetes. Approximately 16 million Americans suffer from the disease, a number expected to double by 2025. Left untreated, it can lead to strokes and heart attacks, blindness, kidney failure and amputation of the lower extremities. Once called “adult-onset diabetes,” the disease today strikes a growing number of children due to America’s sedentary lifestyle and love affair with fatty foods.
New treatments for obesity and Type 2 diabetes may be on the horizon, however, thanks to Miles Brennan, an associate research professor at the University of Denver’s Eleanor Roosevelt Institute (ERI), and his longtime colleague Ute Hochgeschwender, associate member of the Oklahoma Medical Research Foundation.
In 1999, the researchers announced their finding that melanocyte-stimulating hormone (MSH) regulates fat storage and metabolism. This spring, they were awarded two patents based on the research, which could lead to drugs to reduce insulin resistance in obese patients with Type 2 diabetes, and which could safely eliminate excess fat.
Mutations and messengers
It all started in the late 1980s and early ’90s when it became possible to engineer mutations in mice. “We started to look at mutating genes that encode small protein ‘messengers’ that carry signals between cells,” explains Brennan, who met Hochgeschwender in 1986 at the Max Planck Institute in Freibourg, Germany. “We weren’t thinking about diabetes at all.”
Out of the 100,000 genes in mice, the proopiomelanocortin (POMC) gene was particularly interesting because it carries the genetic instruction manual for seven different hormones, including MSH. Secreted by the pituitary gland, MSH exists in the brains and bodies of both mice and humans. In the brain, MSH regulates appetite; in the body, it affects skin pigmentation.
“Ute had the idea that signaling modules, like MSH receptors, are expressed in the brain at different times and places during development,” Brennan recalls. So, they created mutant mice missing specific genes (called “knockout” mice because genes are “knocked out” of the genetic chain). Observing how each missing gene affects the developing animal suggests its unique role.
Because having access to mice with specific mutations is so critical to Brennan and Hochgeschwender’s research, the scientists, in essence, grow their own. They have even patented a line of mutant mice with POMC modifications.
The tricky job of creating the mutant mice is the responsibility of Stacy Forbes, ERI’s animal facility manager. About the size of an air conditioner, her microscope occupies an entire desk, and its TV monitor allows a visitor to see the whisker-size glass needles used to manipulate DNA. Forbes has her eye on a mouse egg; a circle of protoplasm surrounded by a transparent ring called the zona. In the center of the mass are two more dots, each inside a bubble-like membrane. Called pronuclei, they resemble fried chicken eggs and contain genetic material from the father and mother. Together, they will determine the physical characteristics of the unborn mouse.
Forbes deftly manipulates a joystick to punch a needle through the zona and pierce the slightly larger male pronucleus. She gently depresses a plunger and the pronucleus swells with genetically engineered DNA. By the end of her shift, Forbes will treat 210 eggs and store them to incubate overnight. She’ll then surgically implant them in the ovaries of surrogate mouse mothers using a forceps smaller than sewing needles and an insertion needle barely larger than a single egg. In three weeks, Brennan will have a new population of mutant mice to study.
“When we knocked out the POMC gene, we were sure there should be a physical difference between the mutant and the wild mouse,” Brennan explains. “For the first month, the mice showed no difference at all. But starting in the second month, they became morbidly obese, compounded by two different characteristics. One was a large increase in appetite, and the other—entirely unexpected— was a bizarre alteration of fat metabolism.”
The mice stored every gram of fat their bodies produced and didn’t metabolize a bit. Normal mice on a high-fat diet eat less, but the mutant mice did the opposite, growing more obese.
The next experiment proved equally surprising. Brennan and Hochgeschwender injected the mice with MSH, which was absent because of their tinkering with the POMC gene. The excess weight disappeared.
“What we think happens is that MSH causes the fat cells to release free fatty acids, while other cells are stimulated to remove them from the bloodstream and burn them,” Brennan explains. “It’s a way to mobilize your stored fat for current needs.”
The animals experienced no apparent ill effects, and the more obese the mouse, the more effective the treatment.
“As the animal approaches normal weight, the effect plateaus out,” Brennan continues. “This is not going to be the anorexic’s drug of choice, because when there’s no more stored fat, you can’t change the balance. We think it’s got significant potential for obesity therapies.”
Full of surprises
Brennan and Hochgeschwender’s findings were published in 1999 in Nature Medicine and confirmed in 2001 in the Proceeding of the National Academy of Sciences. In April 2004, they received a patent on the use of MSH analogs—chemicals that mimic MSH—as potential treatments for obesity.
Prevailing obesity research had focused on appetite control, and held that blood-borne MSH did not affect metabolism. Brennan and Hochgeschwender proved otherwise, despite vocal criticism from the research community, including one journal reviewer who called their ideas “wacky.”
“We applied for 10 National Institutes of Health grants, and not one has been funded, which is a remarkable track record considering we have papers published in Nature Medicine and Endocrinology,” Brennan remarks. The research has been done on a shoestring, funded almost entirely by ERI and the Oklahoma Medical Research Foundation, which have spent approximately $250,000 plus salaries and equipment.
Brennan and Hochgeschwender’s research has continued to generate surprises. The American Obesity Association estimates that 90 percent of humans with Type 2 diabetes are overweight. Therefore, the scientists expected their mutant mice to be diabetic. But when they checked their insulin levels, the mice were disease-free. “That was the first time anyone had separated obesity from the development of diabetes,” Brennan says.
To appreciate this result, one must first understand how hormones affect blood-sugar levels. The hormone insulin prompts cells to store glucose, a natural sugar, while a complementary hormone called glucagon has the opposite effect, prompting cells to release stored glucose into the bloodstream. In healthy individuals the two hormones balance each other, achieving a state called homeostasis.
Type 2 diabetes develops when the body becomes resistant to insulin, preventing it from removing glucose from the blood. Because MSH causes the pancreas to secrete glucagon, MSH must be present for Type 2 diabetes to occur.
“Because Type 2 diabetes is an insensitivity to insulin action, we can circumvent this resistance by working on the glucagon half of the circuit,” Brennan explains.
Administering an MSH antagonist, a chemical that either removes MSH from the system or which blocks the hormone’s action in the bloodstream, should correct the imbalance.
“If you’re insensitive to insulin, this approach may be able to bring you back into homeostasis by decreasing glucagons in the bloodstream,” he concludes, noting that existing Type 2 diabetes treatments alter the amount of glucose in the bloodstream.
“It’s a whole new way of looking at diabetes,” says Brennan. “This is an entirely unexpected departure, both in understanding how diabetes works and also in treating it.”
The December 2003 issue of Endocrinology described the research, and in March 2004, Brennan and Hochgeschwender were awarded a patent for a whole class of MSH antagonists that may be effective for treating diabetes. The patent also covers a method for identifying other potentially effective chemicals by administering an amino acid compound (called a peptide) with MSH to genetically engineered mice.
Not everyone in the scientific community is skeptical. One proponent of Brennan’s work is Victor Hruby, a pioneer in MSH research who began studying the hormone in the 1970s.
“It’s clear from previous work that the POMC gene and its products are involved in the brain, but Miles and his colleagues have shown that it also may be involved elsewhere in the body,” says Hruby, Regents Professor in the University of Arizona Department of Chemistry. “It continues to be an evolving, exciting story that has many implications for human health. I think they’re onto something worth pursuing.”
Possible medical applications include a test for a predisposition to diabetes, drugs to reduce insulin resistance (maybe even in patch form) and drugs to prevent or reverse obesity. But don’t expect to see them at the drugstore any time soon. ERI does not perform human clinical trials and is seeking a pharmaceutical manufacturer to license the patents and develop treatments.
Brennan already is hard at work on new MSH and POMC research that could lead to other medical breakthroughs. “Every so often when you’re doing this, you can forget just how beautiful the human body really is,” he says.