Reptiles ‘pee’ crystals, and scientists are investigating what they’re made of

Unless you’ve owned reptiles, you might not know that many of them “pee” crystals. Researchers publishing in the Journal of the American Chemical Society investigated the solid urine of more than 20 reptile species and found spheres of uric acid in all of them. This work reveals how reptiles uniquely package up and eliminate crystalline waste, which could inform future treatments for human conditions that also involve uric acid crystals: kidney stones and gout.

Most living things have some sort of excretory system — after all, what goes in must come out. In humans, excess nitrogen in the form of urea, uric acid and ammonia are flushed out in the urine. But many reptiles and birds package up some of those same nitrogen-containing chemicals into solids, or “urates,” that the animals eliminate through their cloacae. Scientists believe that this process may have evolved as a way to conserve water.

While forming crystals in pee is a potential evolutionary advantage for reptiles, it is a serious issue for humans. When too much uric acid is present in the human body, it can solidify into painful shards in the joints, causing gout, or in the urinary tract as kidney stones. Jennifer Swift and colleagues investigated how reptiles excrete crystalline waste safely, studying urates from more than 20 reptile species.  

“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,” explains Swift, the corresponding author on the study.

Microscope images revealed that three species (ball pythons, Angolan pythons and Madagascan tree boas) produced urates consisting of tiny textured microspheres varying from 1 to 10 micrometers wide. X-ray studies showed that the spheres consist of even smaller nanocrystals of uric acid and water.  Additionally, they discovered that uric acid plays an important role in converting ammonia into a less toxic, solid form. They speculate that uric acid may actually play a similar protective role in humans. Though further studies are needed, this work’s insights into snake pee could one day have important implications for human health.

The authors acknowledge funding from the National Science Foundation, Georgetown University, the International Centre for Diffraction Data, and the Chiricahua Desert Museum.

The paper’s abstract will be available on Oct. 22 at 8 a.m. Eastern time here: http://pubs.acs.org/doi/abs/10.1021/jacs.5c10139  

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