Table 2.
Metabolites showing at least two types of evidence supporting their microbial origin [(produced by human faecal bacteria) and (reduced upon either treatment with antibiotics OR reduced in germ-free animals)].
| Metabolite class | Number of metabolites | Metabolites |
|---|---|---|
| Amino acids, peptides, and analogues | 20 | Alanine; Asparagine; Aspartic acid; Citrulline; delta-Aminovaleric acid; gamma-Aminobutyric acid; Glutamic acid; Glycine; Histidine; Homoserine; L-alpha-Aminobutyric acid; Leucine; Lysine; Methionine; Ornithine; Phenylalanine; Proline betaine; Proline; Tyrosine; Valine |
| Phenylpropanoids and polyketides | 18 | 3-Hydroxyphenylpropionic acid; 3-Phenylpropionic acid; 3,4-Dihydroxyhydrocinnamic acid; 4-Hydroxyphenylpropionic acid; 5-Hydroxyequol*; Daidzein; Dihydrodaidzein; Dihydroferulic acid; Dihydrogenistein; Equol; Ferulic acid; m-Coumaric acid; O-Desmethylangolensin; Phenyllactic acid; Quercetin; Theaflavin*; Theaflavin-3-gallic acid*; Theaflavin-3’-gallic acid* |
| Fatty Acyls | 11 | 2-Methylbutyric acid (5:0); 4-Butyric acid betaine; 5-Aminovaleric acid betaine; Behenic acid (22:0); Butyric acid (4:0); Caproic acid (6:0); Isovaleric acid (5:0); Margaric acid (17:0); Palmitic acid (16:0); Palmitoleic acid (cis-16:1n-7); Valeric acid (5:0) |
| Bile acids, alcohols and derivatives | 7 | 12-Ketolithocholic acid; 7-Ketolithocholic acid; Allodeoxycholic acid; Chenodeoxycholic acid; Deoxycholic acid; Isoursodeoxycholic acid; Lithocholic acid |
| Phenols | 8 | 1,2-Dihydroxybenzene; 3-Hydroxyphenylacetic acid; 3,4-Dihydroxyphenylacetic acid; 4-Hydroxyphenylacetic acid*; Dopamine; Homovanillic acid; p-Cresol; Phenol |
| Indoles and derivatives | 9 | Indole-3-aldehyde; Indole-3-carboxylic acid; Indole; Indoleacetic acid; Indoleethanol; Indolelactic acid; Indolepropionic acid; Tryptamine; Tryptophan |
| Organic nitrogen compounds | 7 | Alanine betaine*; Cadaverine; Dimethylamine; Methylamine; Putrescine; Spermidine; Trimethylamine |
| Benzoic acids and derivatives | 7 | 2,3-Dihydroxybenzoic acid; Benzoic acid; Gallic acid; Hippuric acid; Protocatechuic acid; Salicylic acid; Vanillic acid |
| Carboxylic acids and derivatives | 7 | Acetic acid (2:0); Formic acid; Fumaric acid; Isobutyric acid (4:0); Methylmalonic acid (MMA); Propionic acid (3:0); Succinic acid |
| Benzene and substituted derivatives | 4 | 2-Hydroxyphenylacetic acid; Phenethylamine; Phenylacetic acid; Tyramine |
| Hydroxy acids and derivatives | 1 | Lactic acid |
| Steroids and steroid derivatives | 1 | 5beta-Coprostanol |
| Tetrapyrroles and derivatives | 3 | Stercobilinogen*; Urobilin*; Urobilinogen |
| Organoheterocyclic compounds | 1 | Piperidine |
| Pteridines and derivatives | 2 | Folates; Riboflavin |
| Lignans, neolignans and related compounds | 1 | Enterolactone |
| Alkaloids and derivatives | 1 | Trigonelline |
* Concentrations in human biospecimens (blood, urine or faecal samples) are available in Exposome-Explorer for all metabolites except those marked with an asterisk.