Urine Metabolomics Exposes Anomalous Recovery after Maximal Exertion in Female ME/CFS Patients 2023, Glass, Hanson et al

Ravn said:
There's one thing that's tying my brain into knots with studies like this one which point towards a failure of ME cells to mount an appropriate response to exertion. Why don't these studies show any difference at rest/baseline? We're most categorically ill all of the time, albeit more severely with PEM - so surely something must be measurably different already at baseline. Why does this not show up in the metobolomics?

Other studies have led to hypotheses that ME cells are stuck in a cell danger response or that they're exhausted (immune cells) or that they're running at full capacity and with all compensatory mechanisms switched on already at rest, or all of the above, and that the cells therefore are unable to respond to further demand. Which would fit the findings here that ME cells simply do nothing in response to exercise. But I would expect all of the hypotheses to impact metabolism at baseline as well as after exertion. So why do our baseline metabolomes look so seemingly normal? What are we missing? Something the tests aren't measuring? Yet they do throw up all manner of unidentified compounds. Or are the sort of pwME who participate in CPET studies so mild they're actually as well as the general population between episodes of PEM? That sounds unlikely to me.
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The apparently normal baseline urine metabolite data makes me* think that an abnormality with the process of excreting the metabolites may be a more likely explanation for these results. If that were the case, presumably that would have have other knock-on or downstream effects.

[* Edit: as a layperson who has a very limited understanding of the science.]

I note that the paper concludes:
Future work will include expanding this study to a much larger cohort that includes both sexes to validate these results, examine sex differences in the urine metabolome, and explore whether there are more subtle differences in urinary metabolites in ME/CFS patients at baseline that could potentially contribute to a diagnostic test for the disease in the future.
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Apologies if this has already been highlighted (I’ve not managed to read the whole of this thread yet) but another interesting part of the paper which caught my eye was this (my bold):
“Four compounds in the urea cycle; arginine and proline metabolism subpathway are changing differently after exercise in the ME/CFS patients and controls: carboxy-methylarginine, proline, symmetric dimethylarginine (SDMA), and dimethylarginine (ADMA) (Figure 6A). Proline is a building block of collagen and is therefore a key component of connective tissues. SDMA and ADMA are both regulators and competitive inhibitors of nitric oxide (NO) production. NO aids in vascular maintenance in healthy individuals [33], and decreased NO production is associated with endothelial dysfunction and cardiovascular disease [34]. ADMA can be removed through urinary excretion or it can be degraded in the liver [35]. The increased excretion of SDMA and ADMA in controls but not in patients after exercise implies that controls may be removing excess NO synthase inhibitors in order to maintain vascular homeostasis and that this beneficial adaptation to exertion may not be occurring in patients. The relationship of NO and ME/CFS is unclear; plasma from ME/CFS subjects at baseline was found to induce less NO production by endothelial cells in vitro [36], but it is unknown whether or not that was due to higher levels of ADMA or SDMA in ME/CFS plasma, as they were not measured in that study and NO regulation is complex.”
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This study and the recent studies on endothelial dysfunction, which appear to show abnormal NO production in response to exertion, have given me renewed hope that real progress may be starting to be made in understanding some of the mechanism. Am I being too optimistic? (If I am, please be gentle – I need every bit of hope I can get at the moment.)
 
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Drawing on comments made by @Robert 1973 and @bobbler above:
In any future replication, as well as extending the study out further in time, it might be useful to look at differences upon waking from a person's primary sleep. Perhaps there is a significant difference in the efficiency of sleep when dealing with the waste products of exertion, or something?
 
Robert 1973 said:
Apologies if this has already been highlighted (I’ve not managed to read the whole of this thread yet) but another interesting part of the paper which caught my eye was this (my bold): [...] SDMA and ADMA are both regulators and competitive inhibitors of nitric oxide (NO) production.
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They are uraemic toxins, so much of the literature seems to relate to chronic kidney disease and especially in patients having dialysis. In particular, they are being looked at in relation to the cardiovascular disease associated with renal failure. They have also been considered as markers of endothelial dysfunction in (diabetes-related) cardiovascular disease and in pre-eclampsia (also transplant medicine). From the introduction to Asymmetric and Symmetric Dimethylarginines as Renal Function Parameters in Paediatric Kidney Diseases: A Literature Review from 2003 to 2022 (2022, Children) —

The history of dimethylarginines in medicine began in 1970, when they were first isolated from human urine. At present, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are recognised uraemic toxins. We know that they play a role in many human diseases. Their wide participation in physiological and pathological processes in the organism is because they act mainly as endogenous inhibitors of nitric oxide (NO) synthesis.
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Hutan said:
Perhaps there is a significant difference in the efficiency of sleep when dealing with the waste products of exertion, or something?
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Same thought. Also, just to note the physiology of the DMAs in healthy people. From Urinary Dimethylamine (DMA) and Its Precursor Asymmetric Dimethylarginine (ADMA) in Clinical Medicine, in the Context of Nitric Oxide (NO) and Beyond (2020, J Clin Med)

In experimental and clinical studies, collection of urine for a considerable period of time, for example for 24 h, is not always feasible, notably in pediatric studies. Thus, another requirement for using urinary DMA as a measure of whole-body ADMA synthesis is the correction of the urinary concentration of DMA by the urinary concentration of creatinine measured in the same spot urine samples. The diurnal variation of DMA excretion in the urine is fairly constant, and drugs, such as the diuretic acetazolamide, which act in the proximal tubule of the nephron, do not affect the urinary excretion rate of DMA in healthy humans.
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Assuming replication and confirmation, tempting to crystal-ball gaze and wonder whether there could even be an early morning urine test that discriminates HCs from the (potentially unique??) ME symptom of "unrefreshing sleep".
 
Cheesus said:
I am also drawing deep from this hopium pipe.
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Ha! Careful, man. The come-down can be pretty heavy so I’m not drawing too deep – just enough to keep me going until the next hit.

This reminds me of a poem I wrote in 1999, when I had been told that I was going to be given Ampligen after some dodgy tests had apparently shown me to be the second most suitable candidate they had ever tested:

Let sleeping dogs lie

And now it seems there may be some hope;
A glimmer of hope, at least.
A chance to escape my Ground Hog days?
The end in sight?

No, I cannot think that.
For where hope hums his hypnotic tune, the dog of disillusion also lies,
Asleep, one ear to the floor, in anticipation of my sanguine steps.

No, I shall leave him slumbered.
He need not be stirred.
If the key fits I shall creep in through the back door and catch him unawares.
 
Robert 1973 said:
The apparently normal baseline urine metabolite data makes me* think that an abnormality with the process of excreting the metabolites may be a more likely explanation for these results. If that were the case, presumably that would have have other knock-on or downstream effects.

[* Edit: as a layperson who has a very limited understanding of the science.]
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As another lay person (and one who hasn't been able to read the whole paper yet) excretion problems make sense to me for the post-exercise findings. 24 hours is a common time point for many of us for becoming PEM-symptomatic which could be a reflection of a build-up of noxious substances overwhelming the system. This could be tested by a replication study looking at more time points after exercise.

It still wouldn't explain our seemingly normal baseline though. I guess it's possible that molecules Metabolon isn't testing for are at play, as mentioned by Strategist.
strategist said:
The assay used in this study doesn't detect small molecules. So there could be an accumulation that's not visible in the analysis.
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This raises the question, are there methods which can detect the sort of small molecules Metabolon misses?
 
Did anybody catch if the exercise event durations for each individual or clinical group were included in the paper? Can't see it at the moment. Approx 8-10 min seems to be the typical length of the exertion period but would be good to know what the difference in mechanical performance during the exercise was between the groups, if any.
 
Not absolutely clear, but I think they confirmed adequate exertion, even if the absolute amount of time or mechanical effort would have varied. It reads to me as if the two studies are using data from one experimental run-through, which for the first paper used data from two CPETs but for this paper just from the first CPET. However, the first paper said 6-14 minutes while this paper said 8-10 minutes (after 3 minutes of rest), so maybe it was a completely separate data acquisition.

Our group previously published plasma metabolomics data from these same subjects [25]. These subjects underwent the complete two-day CPET protocol and along with urine collection, blood was drawn from each subject at four time points: baseline (P1), 15–30 min after the CPET (P2), 24 h after the CPET (P3), and 15–30 min after the second CPET (P4) which was performed 24 h after the first CPET (Figure 1A in [25]).
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The CPET was performed on a stationary cycle ergometer, with the following protocol: 3 min of rest followed by continuous cycling in which the incremental workload increases 15 watts per minute of exercise until volitional exhaustion (approx. 8–10 min). The respiratory exchange ratio (RER), which is the rate of carbon dioxide production divided by the rate of oxygen consumption, was measured to ensure that participants were performing the test with sufficient effort (RER > 1.1 indicates maximal effort).
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From the prior paper [ref 25] —

The protocol was a 15-Watt ramp increment every 1 minute until the participant could no longer maintain a cadence of at least 50 rpm. The duration of cycling to maximal effort varied by participant from 6 to 14 minutes. Patients and corresponding healthy but sedentary participants were exposed to the same exercise protocol to allow statistical comparison.
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This figure got a lot of attention because of the stark differences between the two graphs. But as someone pointed out to me, these are sample averages for different metabolites which make it easier to have sharp contrasts without overlap between patients and controls.

These aren't the datapoints of patients and controls for one particular datapoint as we normally see for potential biomarkers. Such data is presented further up in the paper (e.g. figure 5 and figure 6) and do show substantial overlap between patients and controls, even though there were only 10 patients and 8 controls.

It is interesting that patients and controls show a different response post-exercise but I suspect the sharp contrast between the graphs is largely due to how the data is presented (namely the result of modelling for multiple metabolites, rather than datapoints of participants).
 
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ME/CFS Skeptic said:
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It is interesting that patients and controls show a different response post-exercise but I suspect the sharp contrast between the graphs is largely due to how the data is presented (namely the result of modelling for multiple metabolites, rather than datapoints of participants).
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In a way I see this as a positive. My biggest concern on initial viewing was that the results looked too good to be true. Understanding that the type of modelling they used makes the contrast more stark gives me more confidence in the validity of the results.
 
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Hutan said:
Drawing on comments made by @Robert 1973 and @bobbler above:
In any future replication, as well as extending the study out further in time, it might be useful to look at differences upon waking from a person's primary sleep. Perhaps there is a significant difference in the efficiency of sleep when dealing with the waste products of exertion, or something?
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I have suspected for maybe two decades and a half that our disturbed sleep might be associated with altered circadian patterns of many metabolites. This was my concern in the late 90s when early morning urinary metabolites were first being looked at. Change the time, or have patients with altered circadian patterns, and you might get different results. We cannot yet be sure that our results will be stable over the course of a sleep-wake cycle. This needs to be established, or an optimal time of day or sleep-wake cycle needs to be determined.

[Edited to correct how long its been.]
 
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