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Discovery of an alternate metabolic pathway for urea synthesis in adult Aedes aegypti mosquitoes

We demonstrate the presence of an alternate metabolic pathway for urea synthesis in Aedes aegypti mosquitoes that converts uric acid to urea via an amphibian-like uricolytic pathway. For these studies, female mosquitoes were fed a sucrose solution containing 15NH4Cl, [5-15N]-glutamine, [15N]-proline, allantoin, or allantoic acid. At 24 h after feeding, the feces were collected and analyzed in a mass spectrometer. Specific enzyme inhibitors confirmed that mosquitoes incorporate 15N from 15NH4Cl into [5-15N]-glutamine and use the 15N of the amide group of glutamine to produce labeled uric acid. More importantly, we found that [15N2]-uric acid can be metabolized to [15N]-urea and be excreted as nitrogenous waste through an uricolytic pathway. Ae. aegypti express all three genes in this pathway, namely, urate oxidase, allantoinase, and allantoicase. The functional relevance of these genes in mosquitoes was shown by feeding allantoin or allantoic acid, which significantly increased unlabeled urea levels in the feces. Moreover, knockdown of urate oxidase expression by RNA interference demonstrated that this pathway is active in females fed blood or 15NH4Cl based on a significant increase in uric acid levels in whole-body extracts and a reduction in [15N]-urea excretion, respectively. These unexpected findings could lead to the development of metabolism-based strategies for mosquito control.