This is caused by a gut parasite

Nov 21, 2006 12:53 GMT  ·  By

Scientists at Penn State found that dragonflies, from the species Libellula pulchella (photo), with gut parasites suffer the same metabolic disorders encountered on humans with obesity, insulin resistance and type-2 diabetes.

This is the first study showing metabolic dysfunctions similar to the human ones in a nonmammalian species. Human intestinal microbes have been associated with metabolic dysfunctions. In mammals, metabolic disorders linked to chronic inflammatory response are believed to be triggered by an accumulation of fat. "Metabolic disease isn't some strange thing having just to do with humans," said James Marden, professor of biology and an insect physiologist.

The parasite linked with the symptoms are protozoa called gregarines, related to malaria and cryptosporidiosis agents, previously believed to be harmless. "All of these symptoms, and the underlying processes behind these symptoms that we're seeing in these dragonflies, are pretty much identical to what you see in mammalian metabolic syndrome and obesity," said Marden.

The parasitic infection in dragonflies renders the organism unable to metabolize fat, which is deposited around the muscles. "It seems plausible that disturbance in the microbial community in humans might trigger these inflammatory responses." "What we're finding in insects is that they become obese when parasites cause inflammation that affects metabolism," said Marden.

"That seems akin to what's happening in humans when they get type-2 diabetes. It's not because there's been a change in the genetic composition of the population. it's because something has changed in our environment."

Scientists suspect that behind the boom of metabolic diseases there is the dramatic increase in soft-drink containing fructose among Americans, estimated to be 500 % over 50 years from the 1940s to the 1990s.

"We looked in the literature and found that consumption of high-fructose corn syrup often is associated with gastrointestinal distress, which may be a sign that fructose affects the gut microbial flora," said Marden.

Another proof is that in AIDS patients Cryptosporidium (a parasite closely related to gregarines), the metabolism is affected in a similar fashion to what was found for infected dragonflies. "People who study metabolic disease should test the hypothesis that changes in gut microbial composition can cause these syndromes."

In dragonflies, flight muscle makes up 60 % of their body mass and powerful flight is necessary to defend pond territory in aerial constests. The muscles of some dragonflies could perform at 80 watts per kg, while others of the same species could perform at up to 220 watts per kg. If poor flight had been a genetic trait, it would have been eliminated by natural selection. But the poor fliers proved to be gut infested. "Healthy dragonflies can adjust their muscle performance according to how much fat they have available in their bodies, but the dragonflies infected with parasites weren't making that adjustment," Marden observed.

The team discovered many anatomical and physiological differences between healthy dragonflies and parasite-infected dragonflies similar to metabolic syndrome in humans. Activation of the signaling molecule called p38 MAP kinase, a stress indicator in humans and other animals, has been related to insulin resistance and metabolic disoreder in humans. The same molecule was chronically activated in the flight muscles of infected dragonflies, but not in healthy ones. "What's more, we could induce this activation in muscles from healthy individuals by exposing them to excretory-secretory products obtained from the gregarine parasites," said Schilder.

The muscles of infected dragonflies consumed only carbohydrates instead of a carbohydrate-lipid mix. In human metabolic syndrome, muscles burn very few lipids. Lipids accumulated in the parasited dragonflies' thorax, while humans with metabolic disease tend to depose fat around skeletal muscle tissue. The hemolymph (insect blood) carbohydrate level in infected dragonflies was about double as that of healthy dragonflies, and found insulin to have little effect on those concentrations, similar with what happens in human insulin resistance. Dragonflies that drank water containing trace amounts of gregarines' excretory-secretory substances presented effects in two days.

Photo credit: Penn State

Photo bellow: Gregarines inside a dragonfly gut

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