Every living thing needs to get rid of nitrogen-based waste, but not every species does it the same way. Humans flush nitrogen compounds like urea, uric acid and ammonia in liquid form, losing precious water in the process. Reptiles and birds evolved a different strategy: they convert the waste into solids called urates and excrete those solids through a single opening called the cloaca. Scientists believe this adaptation helps conserve water—an evolutionary edge in hot, arid climates.
When uric acid levels climb too high in humans, the compound can crystallize in the body, forming kidney stones, or lodge in joints, causing gout. By examining how snakes and other reptiles safely manage these crystals, researchers hope to uncover insights that could eventually inform new approaches to preventing kidney stones and other uric acid–related conditions.
“This research was really inspired by a desire to understand the ways reptiles are able to excrete this material safely, in the hopes it might inspire new approaches to disease prevention and treatment,” said Jennifer Swift, a chemist at Georgetown University and the corresponding author of the study, published in the Journal of the American Chemical Society.
A Microscopic Marvel
To explore how reptiles manage this balancing act, the research team collected and analyzed urates from 20 species, including both primitive, non-venomous snakes and more evolved, venomous types. Both types excreted urates as nanocrystals and spherical granules, but the primitive species were more likely to contain crystals, while the advanced species were more likely to excrete uric acid in granules. Under a microscope, these granules appear as tiny, textured microspheres measuring 1 to 10 micrometers wide.
X-ray diffraction showed that these microspheres were composed of even smaller nanocrystals of uric acid and water. The structure wasn’t random. Rather, it created an intricate lattice that allowed snakes to safely pack nitrogen into a solid form without harming their tissues.
Turning a Toxin Into a Shield
The researchers discovered that uric acid does more than simply package waste—it helps detoxify it. In snakes, uric acid appears to bind with ammonia, turning this potentially deadly chemical into a stable solid called ammonium urate. This process may serve as a biological shield, preventing exposure to ammonia while snakes go about their lives on land.
The finding points to what Swift’s group describes as a previously unrecognized physiological role for uric acid—the ability to neutralize ammonia by transforming it into a solid. It is possible that uric acid acts similarly in humans.
From Snake Scales to Human Science
Swift and her colleagues are now working to pinpoint where and how these microspheres form inside the snakes — a puzzle with direct relevance to human health. The same uric acid that snakes package safely into solids is the compound that can crystallize inside people, leading to gout and kidney stones that affect millions of people worldwide. Understanding the molecular processes in snakes could reveal why their bodies avoid the painful crystal buildup that plagues humans.
This work highlights how evolutionary solutions can spark new biomedical ideas. With deeper study of how snakes assemble, transform and eliminate uric-acid crystals without harm, researchers may eventually uncover strategies to better protect human kidneys, joints and overall health.
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