Could diabetes spread like mad cow disease?

Prions are insidious proteins that spread like infectious agents and trigger fatal conditions such as mad cow disease. A protein implicated in diabetes, a new study suggests, shares some similarities with these villains. Researchers transmitted diabetes from one mouse to another just by injecting the animals with this protein. The results don’t indicate that diabetes is contagious like a cold, but blood transfusions, or even food, may spread the disease.

The work is “very exciting” and “well-documented” for showing that the protein has some prionlike behavior, says prion biologist Witold Surewicz of Case Western Reserve University in Cleveland, Ohio, who wasn’t connected to the research. However, he cautions against jumping to the conclusion that diabetes spreads from person to person. The study raises that possibility, he says, but “it remains to be determined.”

Prions are misfolded proteins that can cause normally folded versions of the same protein to misfold themselves. When this conversion occurs in the brain, the distorted proteins bunch up inside cells and kill them. Although prion diseases are rare in people, they share some similarities with more common illnesses. In Alzheimer’s disease, for instance, globs of a misshapen protein known as β amyloid build up in the brain. Parkinson’s disease and Huntington disease, two other brain maladies, also feature aggregates, or lumps of misfolded proteins.

At first glance, type 2 diabetes, in which people lose the ability to control their blood glucose levels, doesn’t seem to have any connection to prions or neurodegenerative diseases. But in people who have this form of diabetes, cells of the pancreas amass clumps of a protein known as islet amyloid polypeptide (IAPP), which is very similar to the β amyloid that accumulates in Alzheimer’s disease. Deposits of the protein may eventually kill many of the β cells in the pancreas that manufacture the hormone insulin.

In the new study, neurobiologist and biochemist Claudio Soto of McGovern Medical School at the University of Texas Health Science Center in Houston and colleagues tested whether IAPP alone could instigate diabetes in mice. The researchers began by culturing pancreatic cells from healthy humans and from young mice that had been genetically engineered to synthesize large amounts of human IAPP. When the scientists added material from the pancreases of old engineered mice that already had diabetes, clumps of IAPP sprouted in the cultured cells. The clumps also appeared when the cells were exposed to lab-synthesized IAPP tangles, the scientists report online today in The Journal of Experimental Medicine.

Soto and his team next tested whether they could induce IAPP clumps to form in live mice. Young rodents that had been genetically modified to crank out human IAPP are normally healthy, but when the scientists injected them with synthetic IAPP or with material from the pancreases of diabetic mice, IAPP conglomerations formed in the pancreas. As with prions, a smidgen of misfolded IAPP acts like a seed that spurs new clusters of the abnormal protein to grow.

The scientists then investigated whether inducing IAPP conglomerations in mice sparked the symptoms of type 2 diabetes. It did. The affected animals’ blood glucose concentrations were higher than those of control animals. And like people with diabetes, the animals had abnormal glucose tolerance tests, which measure their ability to metabolize a dose of the sugar. Even more striking, large numbers of β cells died in each rodent’s pancreas.

“We can induce the full-blown disease just by administering these protein aggregates” Soto says. He hastens to add that the results do not mean that diabetes can be transmitted through everyday interactions among people. “It’s not like the flu.” However, he says, the researchers plan to test whether the disease spreads through the routes followed by traditional prions, such as blood transfusions or organ transplants. Soto says that people might also be exposed to the potential diabetes trigger in food, for example, if they ate meat from animals whose pancreases had begun to accumulate IAPP.

Biochemist and cell biologist David Harris, who studies prions at Boston University School of Medicine, thinks the possibility of transmission between people is “overstated.” He says that the researchers transmitted the disease through artificial means, such as the injection of pancreas extracts from mice with diabetes, and “there aren’t situations like that involving the pancreas of a human being.”

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