Liquid chromatography-mass spectrometry .. reveals increased levels of tryptophan indole metabolites in .. metabolic syndrome, 2020, Wrobel et al

Full title: Liquid chromatography-mass spectrometry untargeted metabolomics reveals increased levels of tryptophan indole metabolites in urine of metabolic syndrome patients

Paywall, https://journals.sagepub.com/doi/10.1177/1469066720964632
Sci hub, https://sci-hub.se/10.1177/1469066720964632

 

This suggests that the finding of elevated Tryptophan in cells by Phair/Davis (as suggested here) lacks specificity.

 

Or perhaps the two things are comorbid, and what's being measured is the MetS instead? It's hard to say, isn't it?

 

It isn't hard to say, if the patients don't actually have the symptoms of the "metabolic syndrome", namely high blood pressure and high blood sugar.

 

The diagnostic criteria for MetS are quite varied. So it depends which criteria you use. And unless studies into ME also screen for the traits of MetS, how do we know those patients don't have it?

 

It occurs to me that a third possibility exists, too: Ramsay mentioned blood sugar problems in his patients. It may be this that is related to the tryptophan issues, rather than the broader MetS.

These are all just musings, of course; it's not necessarily my own theory.

 

Yes Cort states "You have a vicious circle resulting in higher and higher cellular tryptophan levels." However, I assume that (to state that with confidence) you'd need to isolate all of the cell types, i.e. which rely on IDO1/2, and test them for tryptophan. Problem is there isn't a test e.g. mass spectrometry (technique used in this study) may not be sensitive enough to measure intracellular levels. I'm a bit surprised they (OMF) haven't developed a workaround but Robert Phair is due to do a lab update this month, so maybe there'll be a bit more info in that.

@Simon M highlighted a potentially significant SNIP (orthinine transporter). I find the indications of increased amino acid consumption, i.e. for energy production (Chris Armstrong & Fluge & Mella ++?), interesting. A large GWAS study might just give us the leads we need.

[https://www.omf.ngo/2018/10/19/heal...on-the-molecular-basis-of-me-cfs-at-stanford/]

 

Does it? How?

 

Seems that there's been a bit of progress i.e. Phair's found that they can replicate the trap in "human monocyte-derived macrophages" and [Davis] in yeast cells expressing the human IDO1 gene.

Problem seems to be measuring intracellular tryptophan levels and demonstrating the trap in brain serotonergic neurons.

@Hutan @Michiel Tack

 

I'll take to answering my own question!

I don't see how it does. The MetS study finds enrichment of indole pathway metabolites in urine, which are thought to result from bacterial metabolism of tryptophan. This is an entirely different pathway from the kynurenine pathway.

It doesn't look like the MetS study investigated specific cell types, nor did it measure intracellular tryptophan concentrations. Broadly speaking, the kynurenine and indole pathways are being investigated in many diseases; nowhere else has inhibition of IDO1/2 been found (as far as I know, to date). The fact that indole compounds are enriched in MetS could simply reflect a dietary component to the disease (ie. an environment in which these bacteria thrive). It could also mean that those gut bacteria predispose to MetS (not everyone might have them). Neither has any bearing on the metabolic trap theory, as far as I can see!

 

Thanks for the clarification.