Fig. 2: Stable isotope tracing to map the conversion of phenylalanine to hippuric acid involving the fldC locus.
From: Host-microbe co-metabolism via MCAD generates circulating metabolites including hippuric acid
a Urine was collected from germ-free mice (n = 10), fldC-colonized mice (n = 4), or wild-type C. sporogenes-colonized mice (n = 5) and hippuric acid was measured using stable isotope dilution mass spectrometry (One-way ANOVA with Tukey’s post-hoc multiple comparisons, F(2, 16)=60.90). b Germ-free mice were gavaged with d9-phenylpropionic acid and incorporation of ring label into hippuric acid was quantified to determine whether phenylpropionic acid is a precursor to hippuric acid. c Administration of d9-phenylpropionic acid to germ-free mice leads to accumulation of d5-hippuric acid in urine (n = 12 mice). d Germ- free (n = 10 mice), fldC-colonized (n = 5), or WT-colonized (n = 5) mice were orally administered isotopically labeled phenylalanine and labeled hippuric acid was monitored in the urine over time. e Urine d5-hippuric acid measured 0, 3, 6, 9, or 24 h following oral administration of d5-phenylalanine using stable isotope dilution mass spectrometry. For a, c, e: boxes denote the median with inter-quartile distance; whiskers, maxima and minima. In (c), one outlier at t = 3 h (55.88 µM d5-hippuric acid) was tested for and removed with the Extreme Studentized Deviate method implemented in GraphPad Prism 8. The mouse schematic in b, d was adapted from ref. 17.
