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Liver samples were weighed and lyophilized for 72 h. The lyophilized livers were ground using Mixer Mill MM400 (Retsch GmbH & Co., Germany) and mixed with 500 μl of cold extraction solvent III (methanol:acetonitrile:water, 3:3:2, v/v/v) per 100 mg of liver sample. The mixtures were sonicated for 10 min and centrifuged for 15 min at 13 200 rpm and 4°C. The supernatants were transferred to new 1.5 ml tubes and dried completely by a speed vacuum concentrator. , Serum samples (100 μl) were extracted by 1 ml of cold extraction solvent III (methanol:acetonitrile:water, 3:3:2, v/v/v). The mixtures were sonicated for 10 min and centrifuged for 15 min at 13 200 rpm and 4°C. The supernatants were transferred to new 1.5 ml tubes and dried completely by a speed vacuum concentrator. , Caecal samples were thawed at 4°C and mixed with 1.1 ml of cold extraction solvent I (acetonitrile/water 1:1, v/v). The mixtures were vortexed for 1 min and sonicated for 5 min under ice and centrifuged at 13 200 rpm for 5 min at 4°C. 600 μl of supernatant was mixed with 600 μl of cold extraction solvent II (acetonitrile/methanol, 1:3, v/v). For the second extraction step, the mixtures were vortexed for 1 min and centrifuged at 13 200 rpm for 5 min at 4°C. The supernatants (500 μl) were aliquoted and transferred to new 1.5-ml tubes. The aliquots were concentrated to complete dryness using a speed vacuum concentrator (SCANVAC, Korea).

Mobile phase consisted of buffer A (0.1% formic acid in water) and buffer B (0.1% formic acid in 100% acetonitrile).

Mass‐spectrometric analysis was performed on a Q‐Exactive plus Orbitrap (Thermo Fisher Scientific, Waltham) with ionization polarity‐switching mode. Full MS scan was conducted on the metabolites (70–1000 m/z) with resolution of 70 000 FWHM at m/z = 200 and with automatic gain control (AGC) target of 1e6 ions and maximum injection time (IT) of 100 ms. Data‐dependent MS/MS analysis was performed on pooled samples by each ionization mode. Data‐dependent MS/MS setting was as follows: Top10 MS1 ions; resolution, 17 500 at 200 m/z; AGC target, 1e5; maximum IT, 50 ms; isolation window, 1.0 m/z; normalized collision energy (NCE), 30; intensity threshold, 2e3 ions; apex trigger, 3–6 s; dynamic exclusion, 6 s. M/Z values and retention times for seven bile acids (BAs) were added to the inclusion list for the application of higher collision energy (NCE, 70).