Metabolomics Reveals Rapid Alterations And Adaptation In Canine Plasma In Response To Changes In Dietary Methionine: Cystine And Choline

Insome species dietary methionine restriction provides health and longevitybenefits. However, the primary health concern for dogs fed commercial diets lowin dietary methionine is insufficient taurine production and its long‐term implicationsfor the development of dilated cardiomyopathy. To optimise health benefits in dogs it may be possible to provide theS‐amino acid, cysteine, or provide nutrients that support methionine function (e.g.choline). The objectives of this study were 1) to identify changes in plasmametabolite pools following a reduction in dietary methionine (1.37g to 0.55g/1000kcal), whilst maintaining total S‐aminoacids with cystine (1.31g to 2.13g/1000kcal) and 2) to determine whether additionalcholine (603mg to 1206mg/1000kcal) would support methionine functionality at the lower methionine:cystine (Me:Cy). The study was a 3‐way, crossover design with Labradorretrievers (n=18; 9 male, 9 female; mean age 4.9, range 3.4–7.7) fedeach diet for a period of 2 weeks, with a 6–7 day washout between diets. On day 2 and day 14 of each diet phase, blood samples were taken just prior to feeding(fasted), and 1 and 2 hours post feeding. Metabolic profiling (Metabolon Inc.)identified 472 plasma metabolites suitable for analysis. “Time relative to meal” was the primary driver of variance in the plasma metabolome rather than diet. Univariate analysis, followed by false discovery rate correction, identified metabolites with significant changes 1 day after a diet change and following 2 weeks of a diet change. Fastedmethionine, gamma‐glutamylmethionine and methionine sulfoxide were all significantly lower following one day of consuming a low Me:Cy diet, but were not significantly different 2 weeks later, or when choline was supplemented. Analysis of betaine pools support the hypothesisthat an initial impact on plasma methionine from reduced dietary consumption was supported by choline oxidation, and adaptation over 2 weeks to establish a largerplasma pool. Furthermore, fastedtaurine increased 1.15‐fold following 2 weeks on low Me:Cy compared to the control diet, suggesting that the low Me:Cy diet may adequately support plasma taurinepools. Analysis identified aspects of metabolism interpretable within the context of S‐aminoacid utilisation and methionine salvage pathway metabolism, as well asreflecting perturbations in the wider 1C‐related metabolic network (such asformiminoglutamate, a marker of folate deficiency). In addition, analysis indicated alterationsin BCAA oxidation reflecting negative consequences of the change in Me:Cy, whilst additional choline also increased the plasma pool of trimethylamine N‐oxide(TMAO). Metabolite Set Enrichment Analysis identified pathways associatedwith carnitine, creatine, sphingolipid and fatty acid metabolism as those mostimpacted by feeding diets with a low Me:Cy. The major effects of additional choline were in purine, secondary bile acid and fatty acid metabolism. This study highlights the wide‐ranging short‐term metabolic effects of, and adaptations to, a change in dietary S‐amino acid ratio. Future work will determine longer‐term (32 week) metabolic adaptations and their potential physiological consequences.