Itaconate modulates immune responses via inhibition of peroxiredoxin 5, 2025, Tomas Paulenda et al

[Snow Leopard]

I would suggest Caution with relation of itaconate and inhibition of type I interferon (IFNa and IFNb).

A side story, but the severity of COVID-19 was largely linked to impairment of type I interferon responses during the initial period of the infection and one study found lower itaconate was associated with increased COVID-19 severity. https://www.cell.com/cell-metabolism/fulltext/S1550-4131(20)30317-X

Unfortunately I haven't been able to read your primary study because it's paywalled...

 

[Turtle]

We are currently looking into obtaining patient samples to analyze.

I still believe it is possible for itaconate to play a role. You may say I'm biased and it will be true. It is my favorite molecule. But regardless of itaconate, there are gaps that need to be answered before any conclusions can be drawn.

Thank you for your dedicated, hard work and participation in the discussion on s4me!!
A fool can ask more than 10 wise people can answer. I don't mind being that fool. Due to 34 years of ME/CFS out of 68, I have no reputation to protect.

I was never tested on itaconate, but I had a 24-hour urine test that might come close to a shunt/trap, at least that's what my non-scientific brainfogged brain tells me.

All measured from creatine in mmol/mol

pyruvic acid was 0.07, lactic was 14.11. Can I conclude that's the Krebs cycle down?

succinic was high 63 Is that SDG very low performance?

Fumaric 0.17
Malic was 0.03 Both not doing much?

All messured in 1997, only once.

Is this at all connected to itaconate? Or just me being a scientific fool?

 

[hotblack]

Thanks for your involvement here @paulendat it’s been great following the discussion. Is there a way more of us can get access to the paper and/or is there a recording of the talk from last week available anywhere?

 

[Kitty]

is there a recording of the talk from last week available anywhere?

I don't know, but I watched it go out live and the red "recording" icon was on. So if it's not already accessible somewhere, it hopefully will be.

 

[hotblack]

I don't know, but I watched it go out live and the red "recording" icon was on. So if it's not already accessible somewhere, it hopefully will be.

Thanks Kitty, I hope so too. I had a look around the Wednesday Seminar Series website and Harvard Medical School youtube channel but couldn’t find anything

 

[TiredSam]

I have just read this whole thread without understanding a word of it. I find it most encouraging.

 

[Yann04]

I think I spent an hour snd a half tryong to understand the frist two pages and gave up when ghe thread balloon to loads of pages. But does sound rather interesting. And I did learn a little about cell metabolism, ROS, interferon, and itaconate.

Very mucj appreciate @Hutan 's summary thanks yo that I'm pretty sure I atleast understand the papers mechanism.

 

[arnoble]

I think I spent an hour snd a half tryong to understand the frist two pages and gave up when ghe thread balloon to loads of pages. But does sound rather interesting. And I did learn a little about cell metabolism, ROS, interferon, and itaconate.

Very mucj appreciate @Hutan 's summary thanks yo that I'm pretty sure I atleast understand the papers mechanism.

May I give my non-scientist takeaway?

a) interferons IFN make people feel lousy

b) pathogen --> IFN secretion by macrophages
... some pathogen stimulates macrophages (eg microglial cells in the hypothalamus?) to produce itaconate (by expressing IRG1/ACOD1 enzyme)
... this occurs mainly in activated macrophages (also in monocytes, neutrophils and to some extent dendritic cells)
... this itaconate inhibits a mitochondrial peroxide-detoxifying enzyme PRDX5 (peroxiredoxin5) allowing ROS to increase
... this ROS enables IFNb secretion (upregulates STING (Stimulator of Interferon Genes) pathway in cytosol)

c) this secreted IFN binds to bystander macrophage IFNa-receptors, generating more IFN (JAK/STAT1&2 pathways activate many interferon signalling genes “ISGs” including IRG1/ACOD1 producing itaconate)

d) this itaconate/IFN positive-feedback loop persists somehow in PWME
... normally, adaptive/innate immunity eventually destroys the pathogen, and the loop stops
... in PWME might there be a chronic supply of pathogen from reactivated HHV/EBV virus miRNAs, or leaky-gut, etc?

I like that all this could happen in a location with system-wide reach like the hypothalamus.

 

[RDP]

Hi Jonathan,

I completely agree, that we can't presume purely myeloid compartment playing a role. This simply doesn't exist in the body. Everything is interconnected. What is really needed now is systemic analysis of immune system. I think what I've seen so far that this analysis is warranted. We need to see how both innate and adaptive immune responses are changing in patients.

The most crucial are timing and location where we look. It is possible that in most severe cases the differences will be profound enough to manifest systemically and can be observed even from PBMCs.

We are currently looking into obtaining patient samples to analyze.

I still believe it is possible for itaconate to play a role. You may say I'm biased and it will be true. It is my favorite molecule. But regardless of itaconate, there are gaps that need to be answered before any conclusions can be drawn.

Tom and Jonathan,

Just a point of clarification: The innate immune response I'm invoking is the response of parenchymal cells to infection, not a response of the myeloid lineage. The itaconate shunt hypothesis is not about professional immune cells. Instead, it is an extension of the idea that every nucleated cell is an (innate) immune cell. I agree with Jonathan's earlier point that most blood immune cells are too short-lived to explain a chronic disease. If I see a disease phenotype in PBMCs, I assume the environment producing that phenotype is in the generative tissue, not in blood plasma. Do you agree with this point?

We're studying PBMCs only because they are available. It's nice to find a phenotype in ME PBMCs, but it surprised me. What our field needs most is a supply of ME cells that are known to express the underlying ME disease mechanism. Too often, we assume that any cell from a patient meets this criterion. But multiple lines of evidence suggest otherwise. Somewhere on S4ME I repeated my argument, based on oxygen consumption, that the fraction of patient cells that are sick may be as small as 10-15%. I'm asserting this disease is cell-autonomous. If that's true, it's an important confounder for every negative result.

Returning to the itaconate shunt, the hypothesis is that the ME trigger infection induces expression of ACOD1/CAD in parenchymal cells that happen to express a cell surface receptor for that virus. This mechanism evolved to defend parenchymal cells from acute infection by limiting host-cell resources for viral replication. ACOD1 expression should be transient. But if the normal off-switch fails for any reason, then the infected cell and its neighbors can be trapped in a pathological steady state that produces too few reducing equivalents to sustain the electron transport chain. ME symptoms then devolve from what cell types are trapped and how many are trapped and thus cannot perform their normal physiological functions. Do you think this hypothesis is too far-fetched?

 

[jnmaciuch]

Returning to the itaconate shunt, the hypothesis is that the ME trigger infection induces expression of ACOD1/CAD in parenchymal cells that happen to express a cell surface receptor for that virus. This mechanism evolved to defend parenchymal cells from acute infection by limiting host-cell resources for viral replication. ACOD1 expression should be transient. But if the normal off-switch fails for any reason, then the infected cell and its neighbors can be trapped in a pathological steady state that produces too few reducing equivalents to sustain the electron transport chain. ME symptoms then devolve from what cell types are trapped and how many are trapped and thus cannot perform their normal physiological functions. Do you think this hypothesis is too far-fetched?

This certainly fits with other threads that I have been running down in my own research. However, the main concern would be whether non-myeloid cells actually upregulate IRG1 to a sufficient extent to cause the level of TCA cycle dysregulation you hypothesize.

Tomas noted that other findings from his lab showed itaconate to be a weak SDH inhibitor, which may not be expected to have a strong physiological effect at all in neighboring cells (I will not speak for him further than this, as he has also mentioned follow-up experiments that would confirm or deny this point). This may not be a problem for e.g. macrophages, where the sheer level of itaconate produced is high enough to be locally bactericidal, and therefore are more likely to be able to affect neighboring cells than any other celltype. The question then remains as to whether non-myeloid cells are able to produce enough itaconate to sufficiently alter their own metabolism, let alone their neighbors. And even if they do, the follow-up question is whether a mild auto-inhibition in 10% of cells would be sufficient to produce the level of dysfunction seen in ME/CFS. Looking through the literature, so far it seems that only cancer cells have been shown to reach a high capacity of itaconate production. Though, as you note, we might just not have looked in the right places yet.

I am currently in the process of meeting with collaborators to discuss how my own theories might be addressed through tissue samples. If I am successful in arranging a study, it may also address parts of what you propose.

 

[Jonathan Edwards]

Tom and Jonathan,

Very fair points, Robert @RDP.

Some rogue cell population is hiding in plain sight here I think. We are just not used to the way it is tricking everything else.

 

[RDP]

This certainly fits with other threads that I have been running down in my own research. However, the main concern would be whether non-myeloid cells actually upregulate IRG1 to a sufficient extent to cause the level of TCA cycle dysregulation you hypothesize.

Tomas noted that other findings from his lab showed itaconate to be a weak SDH inhibitor, which may not be expected to have a strong physiological effect at all in neighboring cells (I will not speak for him further than this, as he has also mentioned follow-up experiments that would confirm or deny this point). This may not be a problem for e.g. macrophages, where the sheer level of itaconate produced is high enough to be locally bactericidal, and therefore are more likely to be able to affect neighboring cells than any other celltype. The question then remains as to whether non-myeloid cells are able to produce enough itaconate to sufficiently alter their own metabolism, let alone their neighbors. And even if they do, the follow-up question is whether a mild auto-inhibition in 10% of cells would be sufficient to produce the level of dysfunction seen in ME/CFS. Looking through the literature, so far it seems that only cancer cells have been shown to reach a high capacity of itaconate production. Though, as you note, we might just not have looked in the right places yet.

I am currently in the process of meeting with collaborators to discuss how my own theories might be addressed through tissue samples. If I am successful in arranging a study, it may also address parts of what you propose.

Certainly, we need evidence of ACOD1 expression in sick cells, but itaconate inhibition of SDH is not the hypothesized mechanism of TCA cycle dysfunction. What matters is not the local concentration of itaconate, but rather the fraction of TCA cycle flux that is diverted to the shunt. If itaconate is rapidly converted to itaconyl-CoA and then to citramalyl-CoA and then to pyruvate + acetyl-CoA, there is no reason to expect accumulation of itaconate, but every turn of the itaconate cycle oxidizes carbon and produces at most one NADH. Indeed, if the pyruvate re-enters the TCA cycle via PC, the itaconate cycle produces zero NADH, zero FADH2, 1 CO2, and consumes 1 ATP. This is vastly inefficient compared to the normal TCA cycle, which produces 3 NADH, 1 FADH2, and 1 ATP per turn. This dramatic inefficiency is the hypothesized cause of cell dysfunction in ME.

 

[Utsikt]

This dramatic inefficiency is the hypothesized cause of cell dysfunction in ME.

I might be completely ignorant here - but what cell dysfunction are we talking about? Is it related to a specific finding or is it a general hypothesis? And would this be a downstream effect of whatever is maintaining the illness?

 

[RDP]

Very fair points, Robert @RDP.

Some rogue cell population is hiding in plain sight here I think. We are just not used to the way it is tricking everything else.

Agreed. Could be as many rogue cell populations as there were infected cells during the "trigger" infection.

 

[jnmaciuch]

Certainly, we need evidence of ACOD1 expression in sick cells, but itaconate inhibition of SDH is not the hypothesized mechanism of TCA cycle dysfunction. What matters is not the local concentration of itaconate, but rather the fraction of TCA cycle flux that is diverted to the shunt. If itaconate is rapidly converted to itaconyl-CoA and then to citramalyl-CoA and then to pyruvate + acetyl-CoA, there is no reason to expect accumulation of itaconate, but every turn of the itaconate cycle oxidizes carbon and produces at most one NADH. Indeed, if the pyruvate re-enters the TCA cycle via PC, the itaconate cycle produces zero NADH, zero FADH2, 1 CO2, and consumes 1 ATP. This is vastly inefficient compared to the normal TCA cycle, which produces 3 NADH, 1 FADH2, and 1 ATP per turn. This dramatic inefficiency is the hypothesized cause of cell dysfunction in ME.

Thank you, yes I fully understand that, my point was mainly to address the issue of “infected cells and neighboring cells” per your previous post. All the evidence I’ve seen of viral infection leading to altered metabolic environment in nearby cells is mediated through locally activated immune cells responding to the initial signal from non-immune cells (which is not itaconate, or by detecting virus on their own), as the parenchymal response would be too weak on its own. Perhaps you have seen evidence that I haven’t seen which contradicts this.

[Edit: so while I fully understand the idea of a cell-autonomous TCA cycle problem, either those 10% dysfunctional cells alone are sufficient to create the dramatic reduction seen in ME/CFS, or another explanation is needed to explain effect on neighboring cells which effectively propagates their dysfunction]

And, to extend this, the theory needs to account for a way for this hypothesized mechanism to turn from a local signal to a global one in PEM, which is the puzzle that I’ve been putting together.

 

[RDP]

I might be completely ignorant here - but what cell dysfunction are we talking about? Is it related to a specific finding or is it a general hypothesis? And would this be a downstream effect of whatever is maintaining the illness?

Theory only at this point. Theory says parenchymal cells (afferent or efferent neurons, GI SMCs, any cell type generating symptoms) are burning carbon in the itaconate cycle and therefore are producing insufficient reducing equivalents (and ATP) to carry out their normal physiological work.

During the triggering infection, the shunt is activated via PRRs. Theory says it fails to turn off. There are several potential chronicity mechanisms, but Tom's paper, which is the source of this thread, identifies one possibility.

 

[RDP]

Thank you, yes I fully understand that, my point was mainly to address the issue of “infected cells and neighboring cells” per your previous post. All the evidence I’ve seen of viral infection leading to altered metabolic environment in nearby cells is mediated through locally activated immune cells responding to the initial signal from non-immune cells (which is not itaconate, or detecting virus on their own), as the parenchymal response would be too weak on its own. Perhaps you have seen evidence that I haven’t seen which contradicts this.

[Edit: so while I fully understand the idea of a cell-autonomous TCA cycle problem, either those 10% dysfunctional cells alone are sufficient to create the dramatic reduction seen in ME/CFS, or another explanation is needed to explain effect on neighboring cells which effectively propagates their dysfunction]

And, to extend this, the theory needs to account for a way for this hypothesized mechanism to turn from a local signal to a global one in PEM, which is the puzzle that I’ve been putting together.

Among those who think every cell is an (innate) immune cell, the signal from infected cells to neighboring cells is not metabolic, but rather type I IFNs secreted by the infected cell and activating IFNARs on neighboring cells. ACOD1 is the name given to this gene after its function was identified. Its original name was IRG1 (Immune Responsive Gene 1). ACOD1 is almost surely an ISG. This is all textbook stuff. See Abbas, for example.

I totally agree any correct theory of ME must account for PEM. Not there yet with this theory.

 

[jnmaciuch]

Among those who think every cell is an (innate) immune cell, the signal from infected cells to neighboring cells is not metabolic, but rather type I IFNs secreted by the infected cell and activating IFNARs on neighboring cells. ACOD1 is the name given to this gene after its function was identified. Its original name was IRG1 (Immune Responsive Gene 1). ACOD1 is almost surely an ISG. This is all textbook stuff. See Abbas, for example.

Thank you, I am quite aware of all of this, local interferon signaling is my research focus at the moment and exactly what I was referencing in my previous post. My point re: itaconate and SDH was towards local metabolic dysregulation in neighboring cells in response to viral infection [edit: and whether that has been actually attributed to cell-autonomous responses vs. the local effect of something like itaconate coming specifically from activated myeloid cells].

Thank you for taking the time to discuss your theory on this forum.

 

[jnmaciuch]

ACOD1 is almost surely an ISG

It is, but from my prior work in macrophages I have never seen it being stimulated by IFNAR or IFNGR activation alone. In macrophages, this is induced via co-stimulation of interferons and LPS, or another TLR activator [edit: leading to both Nf-kB and STAT TF binding to facilitate ACOD1 transcription]. You would likely need to induce a strong Nf-kB response alongside IFN, which would be confounded by the normal regulators of Nf-kB in non-immune cells. Hence my skepticism as to whether parenchymal cells can upregulate ACOD1 enough to cause this metabolic dysfunction. Of course, there might be new information in the future that challenges this.

 

[Snow Leopard]

I've read this entire thread and I still don't understand how any of this is relevant to the physiology/symptoms of ME/CFS? Maybe @jnmaciuch can enlighten me?