RT Journal Article SR Electronic T1 Studies in alkaptonuria reveal new roles beyond drug clearance for phase I and II biotransformations in tyrosine metabolism JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.04.16.044347 DO 10.1101/2020.04.16.044347 A1 Brendan P Norman A1 Andrew S Davison A1 Juliette H Hughes A1 Hazel Sutherland A1 Peter J Wilson A1 Neil G Berry A1 Andrew T Hughes A1 Anna M Milan A1 Jonathan C Jarvis A1 Norman B Roberts A1 Lakshminarayan R Ranganath A1 George Bou-Gharios A1 James A Gallagher YR 2020 UL http://biorxiv.org/content/early/2020/04/16/2020.04.16.044347.abstract AB Background and Purpose alkaptonuria (AKU) is an inherited disorder of tyrosine metabolism caused by lack of the enzyme homogentisate 1,2-dioxygenase (HGD). The primary biochemical consequence of HGD-deficiency is increased circulating homogentisic acid (HGA), which is central to AKU disease pathology. The aim of this study was to investigate the wider metabolic consequences of targeted Hgd disruption.Experimental Approach the first metabolomic analysis of the Hgd−/− AKU mouse model was performed. Urinary metabolites altered in Hgd−/− were further validated by showing that the HGA-lowering drug nitisinone reversed their direction of alteration in AKUKey Results comparison of Hgd−/− (AKU) versus Hgd+/− (heterozygous control) urine revealed increases in HGA and a group of 8 previously unreported HGA-derived transformation products from phase I and II metabolism. HGA biotransformation products HGA-sulfate, HGA-glucuronide, HGA-hydrate and hydroxymethyl-HGA were also decreased in urine from both mice and patients with AKU on the HGA-lowering agent nitisinone. Hgd knockout also revealed a host of previously unrecognised associations between tyrosine, purine and TCA cycle metabolic pathways.Conclusion and Implications AKU is rare, but our findings further what is currently understood about tyrosine metabolism more generally, and show for the first time that phase I and II detoxification is recruited to prevent accumulation of endogenously-produced metabolites in inborn errors of metabolism. The data highlight the misconception that phase I and II metabolic biotransformations are reserved solely for drug clearance; these are ancient mechanisms, which represent new potential treatment targets in inherited metabolic diseases.Bullet point summary What is already known Increased circulating homogentisic acid is central to disease pathology in the inherited metabolic disease alkaptonuriaThe Hgd knockout mouse, created in our laboratory, accurately models human alkaptonuriaWhat this study adds Phase I and II biotransformations are recruited in alkaptonuria for detoxification of homogentisic acidThese data challenge misconceptions that phase I and II metabolism is solely for drug clearanceClinical significance Phase I and II metabolic processes represent new treatment targets in inherited metabolic diseasesThe molecular pathology of AKU extends much further than the known alteration to tyrosine metabolismCompeting Interest StatementThe authors have declared no competing interest.