Potent Activation of Indoleamine 2,3-Dioxygenase by Polysulfides, 2019, Groves et al

Andy

Retired committee member
Indoleamine 2,3-dioxygenase (IDO1) is a heme enzyme that catalyzes the oxygenation of the indole ring of tryptophan to afford N-formylkynurenine. This activity significantly suppresses the immune response, mediating inflammation and auto-immune reactions. These consequential effects are regulated through redox changes in the heme cofactor of IDO1, which autoxidizes to the inactive ferric state dur-ing turnover. This change in redox status increases the lability of the heme cofactor leading to further suppression of activity. The cell can thus regulate IDO1 activity through the supply of heme and reducing agents.

We show here that polysulfides bind to inactive ferric IDO1 and reduce it to the oxygen-binding ferrous state, thus activating IDO1 to maximal turnover even at low, physiologically significant concentrations. The on-rate for hydrogen disulfide binding to ferric IDO1 was found to be >106 M-1 s-1 at pH 7 using stopped flow-spectrometry. K-edge XANES and EPR spectroscopy indicated initial formation of a low-spin ferric sulfur-bound species followed by reduction to the ferrous state. The µM affinity of polysulfides for IDO1 implicates these polysulfides as important signaling factors in immune regulation through the kynurenine pathway. Tryptophan significantly enhanced the relatively lower-affinity binding of hydrogen sulfide to IDO1, inspiring the use of the small molecule 3-mercaptoindole (3MI), which selectively binds to and activates ferric IDO1. 3MI sustains turnover by catalytically transferring reducing equivalents from glutathione to IDO1, representing a novel strategy of upregulating innate immunosuppression for treatment of autoimmune disorders. Reactive sulfur species are thus likely unrecognized immune-mediators with potential as therapeutic agents through these interactions with IDO1.
Paywall, https://pubs.acs.org/doi/10.1021/jacs.9b07338
Sci hub, https://sci-hub.se/10.1021/jacs.9b07338
 
Something that activates IDO1 may be trialed at some point, at least in vitro. The problem with IDO2 only arises when the kinetics of IDO1 become poor. The issue here though is that the kinetics must be enhanced at high concentrations of tryptophan, and I doubt any of the drugs have been tested under those conditions.
 
I'm trying to get my head around this. So, the paper is saying that polysulfides activate IDO1, and activated IDO1 suppresses the immune response, mediating inflammation and auto-immune reactions. And the thinking around the trap idea is that IDO1 isn't working well? So maybe polysulfides might help ME?

For what it's worth:
The onset of illness for my children and I coincided with a gastrointestinal upset (well, a fairly severe one with my daughter in hospital for 3 nights due to the pain - all three of us were affected), but also a heat wave and the arrival of a container load of our personal effects from a country with very lax controls on fumigation. The goods had been treated with methyl bromide, which had reacted with some of the materials (wool, feather pillows, natural rubber mattresses, leather sofas) to create horrendously smelling polysulphides.

We were shut up in the house because the 40 degree C plus temperatures outside meant opening windows or going outside was a bad idea, and we were opening up boxes in the heat.

Methyl bromide reacts with basic amines. It also reacts with sulfur containing materials to form foul-smelling mercaptans, thio-ethers, and disulfides. This unpleasant odor can remain for several weeks.

I don't know if the skin contact and the inhalation would have affected levels of these compounds in our bodies. But, if they did, then potentially we had high levels of polysulphides, which, if I'm reading this paper right, should have activated IDO1. Which is the opposite of what the trap theory proposes?

Although, this possible perturbation of the IDO1 function was at a time when we were dealing with an infection, and so perhaps immune systems were activated. And then there was the heat and the lack of sleep due to heat. And so maybe all of that messed homeostasis up, kicking things so far into overdrive that there was a swing back in the other direction?

Thinking today is like walking through treacle, and I'm not sure that I'd do better with this on a good day. The exposure of my children and I to polysulphides around the time of illness onset seemed something worth mentioning. Maybe others can make some sense of it?

Something that activates IDO1 may be trialed at some point, at least in vitro.
There are so many unknowns. Poking a stick at things might bring change, but maybe not good change.
 
Last edited:
Indole as signalling from C difficile - interesting as gut testing via stool analysis has just highlighted c diff as being high for my daughter, but only symptom is tightness. Also gut microbioa which suggest seratonin/p[hase 2 lover detox issues. becoming very interesting.


"Clostridium difficile Modulates the Gut Microbiota by Inducing the Production of Indole, an Interkingdom Signaling and Antimicrobial Molecule" Charles Darkoh,a,b Kimberly Plants-Paris,a Dayna Bishoff,a Herbert L. DuPonta,b

https://msystems.asm.org/content/msys/4/2/e00346-18.full.pdf

tagging @Perrier
eta added tag
 
Last edited:
I'm trying to get my head around this. So, the paper is saying that polysulfides activate IDO1, and activated IDO1 suppresses the immune response, mediating inflammation and auto-immune reactions. And the thinking around the trap idea is that IDO1 isn't working well? So maybe polysulfides might help ME?

Basically Kynurenine surpresses the immune system; so low Kynurinine may mean more risk of autoimmunity. IDO1/2 convert trypotophan to Kynurinine. Yes the trap suggests that lowering intracellular tryptophan (using IDO1/2) means that you should return to normal. This suggests that polysulfides may increase the activity of IDO1 - which is what you are looking for. Check out @alex3619 comments though.

I used to be sceptical of chemical sensitivities - I'm much less so now. Good luck.
 
Back
Top Bottom