Hippuric acid d5

Sigma Aldrich (St Quentin Fallavier, France) provided indole-3-acetic acid, indoxyl sulfate, hippuric acid, kynurenic acid, TMAO, phenylalanine, kynurenine, indole-3-acetic acid-d5, tryptophan, tyrosine, sodium hydrogen phosphate, formic acid, and dimethylsulfoxide (DMSO). Phenylacetyl-L-glutamine, Phenylacetyl-L-glutamine-d5, PCS, kynurenine-d4, p-cresyl-sulfate-d7, p-cresyl glucuronide, hippuric acid-d5, p-cresyl glucuronide-d7, TMAO-d9, tyrosine-d4, tryptophan-d5, phenylalanine-d5, kynurenic acid-d5, and 3-carboxy-4-methyl-5-propyl-2-furan were provided by Toronto Research Chemicals (North York, Toronto, ON, Canada). VWR Chemicals (Radnor, PA, USA) supplied the sodium dihydrogen phosphate and sodium chloride. Fisher Scientific (Illkirch, France) provided the LC-MS-grade methanol, water, and acetonitrile.

l-KYN and QUNA were purchased from Sigma-Aldrich (St. Louis, MO). l-TRP was purchased from Fujifilm Wako Pure Chemical Corporation (Tokyo, Japan). l-KYN sulfate (ring-D4, 3, 3-D2) (was purchased from Cambridge Isotope Laboratories (Tewksbury, MA). Hippuric acid-d5 were purchased from Toronto Research Chemicals (Toronto, Canada). All other solvents and reagents used were commercially available LC/MS or HPLC grade.
Phorbol 12-myristate 13-acetate (PMA) was obtained from Sigma-Aldrich. The recombinant human cytokines used in this study and their providers were as follows: interferon (IFN)-α 2a and IFNα-2b, PBL Assay Science (Piscataway, NJ); IFNγ and interleukin (IL)-4, Thermo Fisher Scientific (Waltham, MA); IFNβ, IL-1β, and tumor necrosis factor α (TNFα), R&D systems (Minneapolis, MN); IL-6 and IL-10, BioLegend (San Diego, CA). All cytokines were prepared at 10 µg/mL in phosphate-buffered saline (PBS) supplemented with 10% fetal bovine serum (FBS) and stored at − 80 °C.