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Table 2 Characteristics for the putatively identified marker metabolites in liquid chromatography-mass spectrometry analysis

From: Non-targeted metabolite profiling reveals changes in oxidative stress, tryptophan and lipid metabolisms in fearful dogs

  Column Ionization mode MW m/z RT (min) Putative annotation p-valuea FDR corrected p-valueb Fold change (FC)c CID (eV) MS/MS fragmentation Identification referenced VIP
Cluster 1 RP ESI+ 821.577 822.584 10.67 PC(16:0/23:5) 0.0017 0.0226 −2.06 20 822.584, 184.074; ESI(−) 40 eV: 806.556, 343.249, 255.233 MS/MS 2.24
RP ESI+ 801.587 802.595 11.35 PC(18:0/19:1) 0.0376 0.1316 −1.98 20 184.072, 784.5833, 802.594; ESI(−) 40 eV: 295.229, 283.261, 786.565 MS/MS 1.30
RP ESI+ 204.09 205.097 2.30 Tryptophan 4.22E−04 0.0087 −1.58 10 188.0698, 146.0599, 144.0806, 130.0613, 132.0788, 159. 0881, 205.0947 Standard 0.84
RP ESI+ 537.295 538.309 10.25 LysoPC(19:0) 0.0488 0.1461 −1.53 20 104.106, 501.236, 560.310 [M + Na]+; ESI(−) 20 eV: 522.323, 297.245 MS/MS 1.68
Cluster 2 RP ESI− 579.319 578.312 8.79 Unknown LysoPC 0.0103 0.0884 −2.79 20 293.209, 578.310, 518.291; ESI(+) 20 eV: 104.107, 534.319, 184.074 MS/MS 2.08
HILIC ESI− 88.016 87.009 1.77 Unknown metabolite 0.0427 0.1108 −2.58 10  44.999, 73.857 MS/MS 1.34
RP ESI+ 809.592 810.599 12.64 PC(18:0/20:4) 0.0200 0.0965 −2.00 40 184.073, 86.095; ESI(−) 40 eV: 303.234, 283.265, 794.567 MS/MS 1.82
RP ESI+ 517.316 518.323 8.81 LysoPC(18:3) 0.0472 0.1443 −1.86 40 184.072, 104.104, 86.094, 60.082; ESI(−) 20 eV: 502.2945, 277.2162 MS/MS 1.47
RP ESI+ 499.270 500.277 9.17 LysoPE(20:5) 0.0416 0.1376 −1.64 10 500.2786, 359.2548; ESI(-) 20 eV: 498.2860, 169.1368, 301.2172 MS/MS 1.28
Cluster 3 RP ESI+ 311.319 312.326 11.01 Unknown metabolite 0.0240 0.1055 2.85 20 312.326, 57.071, 102.095, 100.075, 214.214, 81.068  MS/MS 1.88
HILIC ESI− 189.994 188.986 0.69 Pyrocatechol sulfate 0.0150 0.0734 2.36 40 108.024, 79.957, 53.042, 80.965, 109.027 Pyrocatechol standard 1.55
HILIC ESI+ 246.137 247.144 1.42 Hypaphorine 0.0485 0.1719 2.17 10 188.071, 60.081, 146.061, 55.017, 247.206, 144.079, 85.0245, 118.928 Keller et al. [34] 1.29
RP ESI− 213.009 212.002 2.43 Indoxylsulfate 0.0480 0.1870 1.78 10 212.007, 80.966, 132.043 MID 253 1.85
RP ESI+ 370.308 371.315 10.96 Unknown fatty acyl, either di-(2-ethylhexyl)adipate or dioctyl hexanedioate 0.0335 0.1253 1.55 10 129.0557, 111.0459, 147.0635, 101.0612, 57.0694, 241.1772 MS/MS 1.60
RP ESI+ 315.277 316.285 8.7 Unknown sphingosine, either dehydrophytosphingosine, 6-hydroxysphingosine, or (4OH,8Z,t18:1) sphingosine 0.0087 0.0619 1.50 40 93.071, 43.055, 57.069, 81.070, 69,069, 67.055, 95.048, 77.040 MID 392 0.68
RP ESI+ 283.287 284.294 10.59 Stearamide 0.0266 0.1108 1.28 20 284.295, 57.070, 102.091, 88.076, 71.085, 43.054 MID 34494 1.73
Cluster 4 HILIC ESI+ 136.039 137.046 1.43 Hypoxanthine 0.0250 0.1225 1.87 20 137.046, 119.035, 94.040, 110.035, 55.029, 82.038 MID 83 1.60
RP ESI− 749.54 748.531 12.51 PE(P-18:1/20:4) 0.0447 0.1866 1.81 20 748.526, 303.234; ESI(+) 20 eV: 361.275, 390.2773, 609.529, 750.551 MS/MS 1.61
  1. Also the most significant non-identified marker metabolites are included. The characteristics include both uncorrected and FDR corrected p values, fold changes, Variable influence on projection (VIP) –values, and identification references, together with parameters for the LC–MS analysis, including the chromatography (Column), ionization mode in the mass spectrometry (Ionization mode), molecular weight (MW), identified ion (m/z), retention time (RT), collision induced dissociation energy (CID), and fragment ions in the tandem mass spectrometry (MS/MS fragments). n = 20 dogs (10 fearful and 10 non-fearful dogs). Note that two metabolic features, tryptophan and unknown sphingosine, are included in the table despite their low VIP values, since they otherwise show statistical significance
  2. LysoPC lysophosphatidylcholine, LysoPE lysophosphatidylethanolamine, PC phosphatidylcholine, PE phosphatidylethanolamine
  3. aStudent’s t-test comparing the fold change against the Control group. P values <0.05 were considered as statistically significant
  4. bBenjamini–Hochberg false discovery rate (FDR) corrected p value
  5. cAverage fold change when compared against the Control group, with p values. Fold changes ≥±1.2 were considered as statistically significant. Positive values indicate increased whole blood levels in case dogs vs. control dogs, whereas negative values indicate decreased whole blood levels in case dogs vs. control dogs
  6. dIdentification of metabolites is based on manual MS/MS spectral interpretation, METLIN ID when MS/MS spectrum available, commercial standard compound, or some earlier published fragmentation patterns. Keller et al. [34]