Evaluation of the serum metabolome of patients with alkaptonuria before and after two years of treatment with nitisinone using LC‐QTOF‐MS

BACKGROUND: The homogentisic acid‐lowering therapy nitisinone is being evaluated for the treatment of alkaptonuria (AKU) at the National Centre for AKU. Beyond hypertyrosinemia, the wider metabolic consequences of its use are largely unknown. The aim of this work was to evaluate the impact of nitisinone on the serum metabolome of patients with AKU after 12 and 24 months of treatment. METHODS: Deproteinized serum from 25 patients with AKU (mean age[±SD] 51.1 ± 14.9 years, 12 male) was analyzed using the 1290 Infinity II liquid chromatography system coupled to a 6550 quadrupole time‐of‐flight mass spectrometry (Agilent, UK). Raw data were processed using a batch targeted feature extraction algorithm and an accurate mass retention time database containing 469 intermediary metabolites (MW 72‐785). Matched entities (±10 ppm theoretical accurate mass and ±0.3 minutes retention time window) were filtered based on their frequency and variability (<25% CV) in group quality control samples, and repeated measures statistical significance analysis with Benjamini‐Hochberg false discovery rate adjustment was used to assess changes in metabolite abundance. RESULTS: Eight metabolites increased in abundance (log(2) fold change [FC] 2.1‐15.2, P < .05); 7 of 8 entities were related to tyrosine metabolism, and 13 decreased in abundance (log(2) FC 1.5‐15.5, P < .05); including entities related to tyrosine (n = 2), tryptophan (n = 3), xanthine (n = 2), and citric acid cycle metabolism (n = 2). CONCLUSIONS: Evaluation of the serum metabolome of patients with AKU showed a significant difference in the abundance of several metabolites following treatment with nitisinone, including a number that have not been previously reported; several of these were not related to the tyrosine metabolic pathway. SYNOPSIS: Nitisinone therapy has a significant impact on several metabolites beyond the tyrosine metabolic pathway, several of which appear to be related to the redox state of the cell.