Table 1.
Candidate Hormones of the Gut Microbiota
| Class | Examples | Functions | Comment | Reference |
|---|---|---|---|---|
| SCFAs | Acetate | Energy source | Directly produced by bacteria; epigenetic and receptor-mediated effects; CNS effects linked to autism-like behaviors | 63, 84, 94 |
| Butyrate | Host metabolism | |||
| Propionate | Signaling molecules | |||
| Neurotransmitters | Serotonin Dopamine Noradrenaline GABA |
Mood, emotion, cognition, reward (CNS) Motility/secretion (ENS) |
Can be directly produced by bacteria (see Table 2) or indirectly regulated | 61, 188, 200 |
| Precursors to neuroactive compounds | Tryptophan | Precursor to: 5-HT | Kynurenine is itself a metabolite of tryptophan, production subject to regulation by microbiota | 135, 137, 138, 194 |
| Kynurenine l-Dopa |
Kynurenic acid, quinolinic acid, Dopamine | |||
| Bile acids | Secondary bile acids | Antimicrobial | Some effects mediated by bile acid receptors | 5, 101 |
| Host metabolism | ||||
| Choline metabolites | Trimethylamine | Lipid metabolism (choline) | Metabolized in the liver to trimethylamine-N-oxide, linked to cardiovascular disease | 37, 102, 103 |
| HPA hormones | Cortisol | Stress response | Indirect regulation; HPA endocrine abnormalities prominent in stress-related psychiatric disorders | 177 |
| Host metabolism | ||||
| Anti-inflammatory | ||||
| Wound healing | ||||
| GI hormones | Ghrelin | Host metabolism | Indirect regulation; possibly mediated by SCFAs via enteroendocrine cells | 70, 128 |
| Leptin | Appetite regulation | |||
| Glucagon-like peptide-1 PYY |
GI motility/secretion |