Python blood suppresses appetite without the side effects of drugs like Ozempic

Every time a Burmese python swallows a meal, something remarkable happens inside its body. Its heart expands by a quarter. Its metabolism accelerates by a factor of thousands. Organs that had shrunk during months of fasting begin to swell back to size. Then, when digestion is complete, the snake returns to a state of near-suspended animation, maintaining its muscle mass and cardiovascular health until the next meal, which might be a year away.

Researchers have been studying python physiology for decades, drawn by the sheer improbability of what these animals can do. Now, a team from the University of Colorado Boulder, Stanford, and Baylor universities has found something in python blood that no one had been looking for: a molecule that rises more than a thousandfold after the snake eats, crosses into the brain, and suppresses appetite in mice without the side effects that have limited existing weight-loss drugs.

The findings appear in the journal Nature Metabolism.

"This is a perfect example of nature-inspired biology," said Leslie Leinwand, a distinguished professor of Molecular, Cellular and Developmental Biology at CU Boulder and the study's senior author. "You look at extraordinary animals that can do things that you and I and other mammals can't do, and you try to harness that for therapeutic interventions."

Leinwand, who has studied pythons in her lab for two decades, partnered with Jonathan Long, an associate professor of pathology at Stanford University who specializes in metabolites, the chemical byproducts that circulate in blood and reflect how organisms process energy. Long's lab had recently applied a similar approach to racehorses, analyzing their blood during all-out sprints to understand extreme metabolic performance.

The logic behind using pythons as a research tool is straightforward: because their physiological swings are so dramatic, molecules that exist at barely detectable levels in other animals show up in python blood in quantities large enough to find.

"If we truly want to understand metabolism, we need to go beyond looking at mice and people and look at the greatest metabolic extremes nature has to offer," Long said.

The team measured blood samples from ball pythons and Burmese pythons fed once every 28 days, collecting samples shortly after each snake ate. Across those samples, 208 metabolites increased significantly after feeding. One molecule stood out by a wide margin. A compound called para-tyramine-O-sulfate, or pTOS, increased more than a thousandfold. Other metabolites rose by 500 to 800 percent. This one rose by 100,000 percent.

pTOS is not a newly synthesized molecule. It has been detected in human urine in scattered reports going back decades, excreted so quickly it was considered physiologically unimportant. Nobody had looked carefully at whether it circulates in blood, whether it rises after meals, or whether it does anything meaningful in the body. Part of the reason it had been overlooked is that it doesn't appear in mice or rats, the animals on which most metabolic research is conducted.

"Because most research is done in mice or rats, pTOS has been overlooked," Leinwand said.

"Our research team traced exactly how pTOS gets made. Dietary protein contains an amino acid called tyrosine. After a python eats, bacteria in the snake's large intestine convert tyrosine to tyramine. That compound then travels to the liver, where enzymes called sulfotransferases attach a sulfate group, producing pTOS," Leinwand told The Brighter Side of News.

Experiments confirmed each step: when antibiotics wiped out the gut bacteria, the postprandial spike in pTOS was largely abolished. When researchers fed tyrosine directly to fasted snakes, pTOS rose significantly in the blood.

The sulfation step turns out to be chemically important beyond simple synthesis. Tyramine itself is vasoactive, meaning it raises blood pressure and acts on receptors throughout the body in ways that limit its therapeutic usefulness. The addition of the sulfate group essentially disables those effects while simultaneously making the molecule more stable in plasma and more capable of crossing the blood-brain barrier.

When the researchers gave pTOS to mice, it showed up in cerebrospinal fluid at concentrations more than twelve times higher than in the blood, suggesting it passes readily into the central nervous system. Once there, it activated neurons in a region of the hypothalamus called the ventromedial hypothalamus, a structure known to regulate feeding and energy balance. Silencing those specific neurons using a chemogenetic technique blocked the appetite-suppressing effect of pTOS, confirming that the pathway was genuine rather than an artifact of the dose.

The appetite effects in mice were consistent across multiple experiments. Single doses of pTOS reduced food intake in both lean and obese animals. Chronic daily dosing over 28 days in obese mice durably reduced food consumption and produced a 9 percent reduction in body weight compared to controls. Throughout those experiments, energy expenditure, locomotor activity, and water intake remained unchanged, suggesting the effect was specific to appetite rather than a general disruption of metabolism.

Notably, the molecule did not cause conditioned flavor avoidance, a standard test for whether a compound produces nausea, animals trained to associate a flavor with a drug will avoid that flavor if the drug made them feel sick. pTOS-treated mice showed no such avoidance. Sucrose preference was also unaffected.

"We've basically discovered an appetite suppressant that works in mice without some of the side-effects that GLP-1 drugs have," said Leinwand, referring to medications like Ozempic and Wegovy.

GLP-1 drugs were themselves inspired by another reptile, the Gila monster, whose venom contains a hormone similar to human glucagon-like peptide-1. Those drugs are now used by millions of people, but studies suggest that as many as half of users stop taking them within a year, often because of gastrointestinal side effects or muscle loss. pTOS did not cause either in the mouse experiments.

The molecule also appears to operate through a mechanism entirely separate from GLP-1. It did not alter circulating levels of GLP-1, insulin, ghrelin, leptin, or several other hormones associated with appetite regulation. It did not slow gastric emptying, a primary mechanism of GLP-1 drugs. Something else is happening.

The path from mouse data to human therapy is long, and the researchers are clear about where they are on that path. Human beings do produce pTOS, and it does rise after meals in most of the cohorts examined, by roughly two to five times on average. But that is a modest response compared to the thousandfold surge in pythons, and the researchers don't yet know whether higher doses or specific meal compositions could amplify it.

One human study found no postprandial increase in pTOS among participants with prediabetes or type 2 diabetes, raising questions about whether the signaling pathway is already compromised in people with metabolic disease.

The specific receptor through which pTOS activates ventromedial hypothalamus neurons has not been identified. Without knowing the receptor, designing drugs that selectively target it, or predicting how such drugs might behave in people, remains speculative.

Leinwand, Long, and CU Boulder colleagues have formed a startup called Arkana Therapeutics to pursue commercial development. Future research will examine how pTOS behaves in humans and catalog the functions of the other metabolites, some rising by 500 to 800 percent, that flood python blood after a meal.

"We're not stopping with just this one metabolite," Leinwand said. "There's a lot more to be learned."

The immediate significance of the research is less about pTOS itself, which remains years from any clinical application, and more about what it demonstrates methodologically. Using an animal with extreme physiology as a discovery platform identified a molecule that standard research in mice or rats would never have found. The same logic could be applied to other metabolic questions: fasting, muscle preservation, cardiac function.

Age-related muscle loss, or sarcopenia, affects nearly everyone as they age and currently has no approved treatment to halt or reverse it. Pythons maintain remarkable muscle mass through months of fasting. Some of the other 207 metabolites identified in this study may offer leads on how that happens.

The broader argument the researchers are making is that pharmaceutical discovery has been too narrow in its choice of model organisms. By limiting the search to mice, rats, and humans, the field has implicitly excluded the vast majority of biological solutions that evolution has developed for problems mammals haven't faced in the same extreme form. Pythons, racehorses, and other physiological outliers carry solutions in their blood. The tools to read those solutions now exist.

Research findings are available online in the journal Nature Metabolism.

The original story "Python blood suppresses appetite without the side effects of drugs like Ozempic" is published in The Brighter Side of News.

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