Fig 1: Plasma metabolome reveals chronic protein restriction affects Trp metabolism. (A) Identified differential metabolites in positive (+) ion modes (NP vs. LP groups). (B) KEGG enrichment map of different metabolites based on LC-MS/MS in positive ion mode (NP vs. LP groups). (C) Identified differential metabolites in positive (+) ion modes (LP vs. LP + RPLeu groups). (D) KEGG enrichment map of different metabolites based on LC-MS/MS in positive ion mode (LP vs. LP + RPLeu groups). (E) Identified differential metabolites in positive (+) ion modes (NP vs. LP + RPLeu groups). (F) KEGG enrichment map of different metabolites based on LC-MS/MS in positive ion mode (NP vs. LP + RPLeu groups). Red indicates significantly up-regulated metabolite levels, while purple indicates significantly down-regulated metabolite levels. NP = normal protein diet (14.24% crude protein [CP]); LP = low protein diet (8.27% CP with supplemental 1.66% rumen-protected lysine [RPLys] and 0.09% rumen-protected methionine [RPMet]); LP + RPLeu = LP with rumen-protected Leu (RPLeu) (8.75% CP with supplemental 1.66% RPLys, 0.09% RPMet and 1.46% RPLeu). The screening criteria for differential metabolites were: P < 0.05, variable importance in the projection (VIP) > 1, fold change (FC) > 2 or FC < 0.5. MAG (18:3) = monoglyceride (18:3); TPH = tryptophan hydroxylase; LLK = leucylleucyllysine; ILK = integrin-linked kinase; KPH = kalopanaxsaponin H.