Table 1: Indole microbial metabolites and correlation with intestinal barrier driven disease states [ 213 ].


Metabolite Compartment Disease Correlation Reference(s)

Indole feces ulcerative colitis decreases ∼ 28% [ 61 ]
Indole blood alcohol dependence Φ see notes below [ 97 ]
Indoxyl sulfate* urine acute GI GVHD decreases ∼ 92% [ 214 ]
Tryptophan serum IBS elevated ∼ 5-fold [ 215 ]
Indole propionate blood Obesity decreased pre-treatment
Indole propionate blood Obesity increased post-treatment** [ 92 ]

*Compare this to expression of Kynurenine, which are significantly increased in acute graft versus host disease (GVHD) with gastrointestinal (GI) symptoms [ 216 ].
Kynurenine is also significantly elevated downstream of Toll-like Receptor (TLR) activation in patients with Irritable bowel syndrome (IBS) [ 217 , 218 ].
Φ indole levels are lower or absent in alcohol dependent patients with high intestinal permeability as compared with alcohol dependent patients with low permeability
**treatment refers to antioxidants to reduce obesity related systemic inflammation