One of the frequent complaints of patients, researchers, and policymakers about ME research is that the findings are scattered, and the studies, small. One group will discover X is elevated in 20 ME patients, only to find that when the test is done on another 13 patients two years down the line, they don’t show elevated X at all. We’re also confounded by the wide array of research and clinical definitions, from Ramsay to Fukuda, to CCC, to the IOM criteria and beyond: at least 8 frequently-used definitions that describe illnesses that, if not the same, have a great deal of overlapping criteria. Critics have been known to call ME/CFS discoveries “microfindings” because of the tendency of small studies to be debunked later on.
But it may – finally – be time to put the idea to bed that patients “may or may not” have disordered cellular metabolism. The research has been piling up over the past several years and, just in the past two weeks, two studies from two different groups of researchers half a world away have results that support one another.
What this means for patients is nothing less than a potential treatment, and a serious contender for a diagnostic test. But it’s not all good news: the results of at least one of the studies appears to have found far more significant and abundant signs of dysfunction in women than men. Since there is no evidence to support that women with ME/CFS are sicker than men, we are left with the impression of a puzzle with more than a few missing pieces.
The reason that we can get energy from food is because of a process called cellular respiration. Cellular respiration is traditionally divided up into three processes: glycolysis, the citric acid (or Krebs) cycle, and the electron transport chain. The first of the three, glycolysis, involves the splitting of sugar to produce pyruvate molecules, occurs outside of the mitochondria, and does not require oxygen. The second two processes both occur in the mitochondria, and both need oxygen to work.
The goal of all these processes is to make molecules that have energy-rich chemical bonds, such as ATP and NADH. When a phosphate group breaks off of ATP, the energy that was holding it there is released, and the cell can ‘use’ that energy to do work. This is how we walk, talk, breathe, and even how our cells move fatter molecules into and out of cells.
While glycolysis is often considered the first step in the process, it isn’t truly necessary to get energy for the cell. Fats and proteins feed into the cycle as well, which is why they are considered macronutrients. Fats break down into glycerol and fatty acids, which feed into the citric acid cycle a wee bit further down. And proteins break apart into their constituent amino acids, and feed into the citric acid cycle in several spots.
However, bypassing glycolysis would rob the cell of 2 ATP molecules for every cycle, or about 5% of the energy from the cycle if we consider the ATP molecules’ removal out of context. When we consider that the pyruvate produced during glycolysis is part of what feeds the citric acid cycle, however, the loss of energy-rich molecules might in fact be far higher.
In order to transition from glycolysis to the citric acid cycle, the pyruvate produced from glucose must become Acetyl Co-A. The enzyme complex that catalyzes this process is called the pyruvate dehydrogenase complex, or PDH complex.
If the PDH complex did not function properly, or were blocked, the result would be far less pyruvate turned into Acetyl Co-A, and a dropoff in high-energy molecules down the line.
PDH activity is controlled by multiple different factors, including but not limited to:
- PDH kinases (PDKs), that inhibit activity of PDH enzymes
- PDH phosphatases that yank away PDH’s phosphate group so it does not function properly
- Sirtuin 4 (SIRT4), which is also an inhibitor for PDH
- PDK1, 2, 3, and 4
A shift in these or their expression means a shift towards higher glucose, lower pyruvate, lower Acetyl Co-A, and fewer energy-rich molecules produced in the cell to do work.
Goal: make molecules with energy-rich bonds for later use
Glucose (sugars) –> pyruvate –> acetyl Co-A
Last step requires PDH, which depends on:
PDKs, PDH phosphatases, SIRT4, PDK1—4
Citric Acid Cycle
Electron Transport Chain (ETC)
Christopher Armstrong and colleagues (out of the University of Melbourne) have been working under the theory that amino acid metabolism in ME/CFS patients is disturbed for some time. Their first metabolomics paper, Metabolic profiling reveals anomalous energy metabolism and oxidative stress pathways in chronic fatigue syndrome patients showed overall elevation of blood glucose, implying that glycolysis wasn’t happening as swiftly as in healthy controls. This study also showed signs of acceleration of other cellular processes designed to get energy-rich molecules from other methods, such as accelerated amino acid metabolism.
Then, just a few weeks ago, Armstrong’s team produced a second paper: The association of fecal microbiota and fecal, blood serum and urine metabolites in myalgic encephalomyelitis / chronic fatigue syndrome.
Armstrong’s group found once again that patients had elevated blood glucose levels that were quite significant – 124% the average of healthy controls, with a p value of 0.002. Armstrong also found blood levels of many amino acids were decreased, including glutamate, hypoxanthine, lactate, phenylalanine, and acetate.
All of Armstrong’s findings taken together strongly imply impaired glycolysis in ME/CFS patients, and a corresponding decrease in citric acid cycle activity, along with some upregulated amino acid metabolism seemingly to make up for the lack.
Armstrong had some fascinating conclusions regarding the gut environment of ME/CFS patients as well. Stay tuned for more on those findings later! However, Armstrong’s and Fluge and Mella’s findings regarding amino acid metabolism relate very closely, so let’s move on for now to their findings.
Fluge and Mella’s PDH Hypothesis:
Fluge and Mella’s hypothesis was that perhaps PDH function (and AMPK function) is impaired in ME/CFS patients. Just like Armstrong, they only included patients who met the Canadian Consensus Criteria. Their study was large, with 200 patients and over 100 healthy controls. Interestingly, they divvied their patients into male and female groups, and the results were – at least to this reader – very surprising.
First, the researchers divided the amino acids into three groups:
- Category 1, which are converted to pyruvate, and depend on PDH to be oxidized
- Category 2, which enter oxidation pathway as Acetyl Co-A
- Category 3, which are converted to citric acid cycle intermediates
Then they measured each of the levels of these amino acids in the blood.
Here is what they found:
Note that the red arrow trends depicted refer to what was found in female patients only.
You can see that the trend to dysfunction is clear from Category 2 and onward. This strongly implies that there is not a real issue with amino acids that turn into pyruvate, but a significant ‘drain’ on amino acids thereafter. This implies that the ‘issue’ is after glucose becomes pyruvate, but before pyruvate becomes Acetyl Co-A… in other words, it could well be an issue with the enzyme complex we mentioned before, since that catalyzes pyruvate into Acetyl Co-A.
Keep in mind depleted amino acids mean we’re using them up, not that we can’t make them. Amino acids here are serving as an alternate source of fuel for our cells, and that is why they are found in far lower levels in the blood than they are in healthy controls.
But amino acids have other jobs to do besides energy-molecule generation. Could their absence be the reason behind some of the symptoms that many women with ME/CFS experience?
Fluge and Mella next set out to discover just that.
Endothelial dysfunction and ME/CFS
Endothelial dysfunction is a source of concern for ME/CFS patients and may be the root of some of its symptoms. Previous studies have found evidence of disordered endothelial dysfunction in ME (Newton et al, 2012 – no, not that Newton).
Therefore, Fluge and Mella set out to see whether amino acids necessary for proper endothelial function were reduced in the blood, including arginine, asymmetric dimethylarginine, homoarginine, 1-methylhistidine, 3-methylhistidine, and symmetric dimethylarginine.
The result? Symmetric dimethylarginine was significantly reduced, as was 3-methylhistidine – the first, only in women, and the second, only in men.
Other amino acid associations
Importantly, no correlation was made between amino acids and physical activity levels. Unlike in some studies, ‘activity’ was measured objectively using a 24-hour measure of steps taken in the ME/CFS group. There was an association between cysteine levels and activity, but not in depletion of amino acids in general.
There was some correlation between some amino acid levels and body mass index (BMI), but no matter what, amino acid levels in ME/CFS patients were lower than they were for healthy controls of the same or similar BMI.
In women, a significant association was found between disease severity and phenylalanine; the longer the woman had been ill, the higher her levels of this amino acid.
Notably, the lower her category 1 amino acids, the lower a female patient’s quality of life.
PDH gene expression
So, after supposing that PDH is the step that is likely the one that’s ‘off’, Fluge and Mella and their team tested mRNA expression of all the inhibitory molecules we discussed earlier and found that their expression was elevated. Remember: increasing an inhibitor has a negative effect on PDH, which means fewer glycolysis products becoming Acetyl Co-A, and less energy!
Inhibitory kinases PDK1, 2, and 4 all had elevated mRNA expression, as did SIRT4. PPAR-gamma was increased in the peripheral mononuclear cells of patients as well.
And finally we have a result for the gentlemen! These findings were consistent across gender lines.
Moreover, PDK1 expression correlated well to severity of illness: the higher the expression of this inhibitor, the worse symptoms appeared to be.
The same association was not found for the other inhibitory molecules, but that sounds like a potential blood test to me… provided these findings can be replicated consistently in future studies.
Can ordinary cells become ‘infected’ with ME/CFS’s metabolic madness?
Here comes my favorite part: studying the effect of bathing normal skeletal muscle cells in ME/CFS blood.
Before we get there, however, it’s worth mentioning that Fluge and Mella would not be the first to study AMPK function in ME/CFS patients: Brown and colleagues, including Julie Newton, studied AMPK function in muscle cells in 2015.
The research team gathered serum from 12 patients who they classified as either severe or very severe sufferers.
They found that basal (resting) amino acid-driven respiration was moderately elevated in ME/CFS patients’ cells. This echoes similar findings from just a few months ago, when a paper reported that ME/CFS patients’ cells were just raring to go. In that study, the researchers noted that when they put their ME cells in an amino-acid-rich medium, they began producing copious energy-rich molecules, predominantly from mitochondrial processes rather than glycolytic ones. This makes sense, since they were taken out the famine and desolation of an ME patient and placed in a bath rich with delicious nutrients. Their findings appear to agree with Fluge and Mella’s.
The serum of ME/CFS patients, when cultured with ordinary skeletal muscle cells, increased the rate of mitochondrial metabolism and respiration, especially when the scientists created chemical conditions that mimicked ‘energetic strain’.
What does this all mean?
To start with, it means that ME/CFS patients are getting very little energy from sugar or carbohydrates – and there are other, good reasons to ease back from them (more on that regarding C. Armstrong’s paper, later!) Female patients especially should turn to amino-acid-rich foods and supplements.
What about our male patients, however? Could it be that if we examined their fatty acid oxidation byproducts, we’d find a similar sort of depletion we see in the amino acids of women? Only time and further experimentation will tell.
The skeletal muscle test shows us that the factors that inhibit energy metabolism are in fact blood-borne, but this does not (necessarily) mean that the disease itself is communicable by blood transfusion. It may well be that after a short period of time, a healthy person’s cells would shift back to obtaining more of their energy from glycolysis, returning to normal.
Fluge and Mella found support for the idea that PDH dysregulation / inhibition is a key factor in pathogenesis. It’s too soon to be certain, but not too soon to be hopeful: it’s possible that these findings could lead to a single-measure blood test for ME/CFS patients. What a fabulous holiday present that would be!
“Give me a lever and a place to stand and I will move the earth.” Could PDH be the ‘lever’ ME/CFS patients have been waiting for? If we can find a treatment that will ‘move’ this one target, it could make a huge difference in the quality of life of patients.
What does this have to do with pathogens? It could have quite a lot to do with them! As C. Armstrong’s paper notes, “the… microbiota has the ability to modulate host metabolism.” This may well tie in with Naviaux’s work as well! More on that down the line, folks… stay tuned.
Note that this is an opinion piece! Do not make treatment decisions based off of the word of bloggers alone. <3