A Targeted Metabolomics Assay to Measure Purines in the Diet of Managed and Free-Ranging Common Bottlenose Dolphins, Tursiops truncatus
Abstract
It is unknown why ammonium urate uroliths develop in common bottlenose dolphins (Tursiops truncatus) managed under human care, but do not occur in free-ranging dolphins.5-7 In mammals, diets rich in purines, such as the piscivorous diet of dolphins, can predispose to urate urolith formation.3,8 Usually, the total purine content of food is measured commercially by summing the concentrations of four purine metabolites: adenine, guanine, hypoxanthine, and xanthine. Nevertheless, several other dietary purine metabolites can be converted into uric acid, and individual purine metabolite concentrations can vary with fish species, cold storage methods, and storage time.2,4 Thus, a method using high-performance liquid chromatography (HPLC) with mass spectrometry (MS) was developed to better quantify and compare the purine metabolites in commercially available frozen stored and thawed whole fish fed to collection dolphins and fresh frozen whole fish species consumed by free-ranging dolphins.1 The method accurately quantifies the four purine metabolites and four additional metabolites: adenosine monophosphate, inosine monophosphate, inosine, and uric acid. Preliminary results (n = 5) in fish commonly consumed by free-ranging dolphins showed that the mean total purine content is 3 times greater for striped mullet (Mugil cephalus) when these additional metabolites are included in the total (992 vs. 360 µg/g tissue "as fed"). Additionally, mean inosine monophosphate concentrations are much higher in ladyfish (Elops saurus) than mullet (238 vs. 11 µg/g tissue "as fed"; p < 0.05). We are currently measuring the purine content of additional fish species to help assess whether diet may contribute to ammonium urate urolith development in dolphins.
Acknowledgements
We are grateful for the generous financial support of the National Marine Mammal Foundation and SeaWorld, Inc., without which this project would not have been possible. Additionally, we would like to thank SeaWorld Orlando and the U.S. Navy Marine Mammal Program, who worked together to provide the managed diet frozen fish species analyzed. We also are thankful for the support of Dr. Randall S. Wells and the Chicago Zoological Society's Sarasota Dolphin Research Program for providing me with many opportunities to procure the free-ranging fish studied in this analysis. Finally, I would like to thank Dr. Timothy J. Garrett, co-author and Principal Investigator of the University of Florida Southeast Center for Integrated Metabolomics Core Laboratory, for his time, patience, and dedication assisting me with the development of this assay.
* Presenting author
+ Student presenter
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