Fig. 5

Histidine and tryptophan metabolism after 2-day drug treatment. A) Pathway of histidine metabolism to histamine with the metabolite products of 1-methyl-4-imidazoleacetic acid and 4-(β-acetylaminoethyl)imidazole. Illustration adapted from KEGG histidine metabolism pathway (map00340) [45]. B) Metabolite conversion ratio of 4-(β-acetylaminoethyl)imidazole to 1-methyl-4-imidazoleacetic acid, and of 1-methyl-4-imidazoleacetic acid to histidine in the four 2-day treatment groups of tacrolimus, antibiotics, tacrolimus and antibiotics together, and no treatment control. C) Tryptophan metabolism, including the kynurenine pathway, indole pyruvate pathway, and serotonin pathways. Illustration adapted from KEGG histidine metabolism pathway (map00380) [45]. D) Biplot of PCA of tryptophan metabolism pathway. Loading vectors and principal components labeled. E) IPA concentration and metabolite conversion ratio of 5-HIAA (5-hydroxyindoleacetic acid) to indole-3-propionic acid (IPA), IPA to 3-indoxylsulfuric acid (I3SA), tryptophan to IPA in the four 2-day treatment groups of tacrolimus, antibiotics, tacrolimus and antibiotics together, and no treatment control. Y axis represents the ratios normalized level between the indicated metabolites. The ROC curve used to calculate area under curve (AUC) as a metric quantifying the overall ability of the metabolite to correctly classify the experimental conditions. Closest to top-left core of ROC (red dot) as the optimal cutoff value, shown in bargraph (red line). P value was calculated using 2-sample t-tests between tacrolimus and control groups and displayed atop the boxplots. Black points representing mice, horizontal line representing mean, yellow dots presenting median, the top and bottom of the box are the lower and upper quartile