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The GIST

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irritable bowel syndrome

As painful as it is, the pain in IBS isn’t caused by structural damage to the gut; instead, it appears to be caused by difficult- to-detect nerve activation.

Health Rising hasn’t published much on irritable bowel syndrome (IBS) and that’s a shame. Not only is it present in chronic fatigue syndrome (ME/CFS), fibromyalgia (FM), and long COVID, but IBS is part of a family of disorders that also includes chronic pelvic pain, interstitial cystitis, migraine, chronic low back pain, and many autoimmune diseases.

In each of these disorders, researchers have been unable to find a physical cause for the pain. For instance, despite all the bloating and pain found in the guts of people with IBS, the intestines look just fine. In fibromyalgia (FM), no one has been able to come up with enough evidence of damage to the muscles to explain the pain found in FM. Likewise, the intense pain in migraine isn’t associated with physical damage.

Diseases like these, for which clear physical causes haven’t been found and which also cause other symptoms (poor sleep, fatigue, cognitive issues, mood problems), have come to be called nociplastic disorders, and are primarily believed to be central nervous system disorders.

They also include a significant subset of people with disorders like rheumatoid arthritis/osteoarthritis and other autoimmune disorders where pain in the joints spreads beyond, producing widespread pain and other symptoms.

The GIST

  • Not only is irritable bowel syndrome (IBS) present in chronic fatigue syndrome (ME/CFS), fibromyalgia (FM), and long COVID, but it’s also part of a family of disorders that also includes chronic pelvic pain, interstitial cystitis, migraine, chronic low back pain and many autoimmune diseases.
  • These are all called nociplastic disorders. Nociplastic disorders occur when clear physical causes haven’t been found that could cause the symptoms (pain, poor sleep, fatigue, cognitive issues, mood problems) found in them. With their similar symptom presentation, ME/CFS, FM, and long COVID are all considered part of the nociplastic family of disorders.
  • Researchers have been digging deeper into the gut tissues and are making progress. For over 15 years, IBS researchers have been taking biopsies of the colon, then spinning them in a centrifuge to separate the liquid, or supernatant. Then they expose gut neurons to the supernatant – and watch as, bang! – the neurons go off like rockets – spewing out electrical signals that produce pain and other symptoms.
  • This study assessed the role mast cells play in IBS by exposing the supernatant from IBS patients, patients with a mast cell disorder called mastocytosis, and healthy controls to the nerves in the gut. It also determined if the entire gut is involved in ME/CFS.
  • Despite the fact that all the IBS and mastocytosis patients experienced the same symptoms (bloating, diarrhea, abdominal pain), only the supernatant from the gut biopsies of the IBS patients sent the gut nerves through the roof. The authors also concluded that IBS was caused by a “general phenomenon (found) throughout the gut“.
  • They did not find increased numbers of mast cell numbers in the biopsies of the IBS patients. Nor did they find any evidence of increased mast cell degranulation or histamine levels. They concluded that “mast cells are not involved in nerve activation”, and proposed that proteases (enzymes that break down proteins) are the main problem in IBS. While factors like histamine from mast cells and serotonin play a role in IBS, it’s the proteases that appear to set them off.
  • It appears that in IBS, nerve activation in the gut activates vagal nerves situated outside the spinal cord in the dorsal root ganglia (DRG). The DRG is a central gathering place where sensory signals get sent to the central nervous system, and DRG activation is found in fibromyalgia.
  • From there, the central nervous system activation spreads to cause symptoms like widespread pain, fatigue, sleep, cognitive and mood problems.
  • it’s become clear that protease-driven protein breakdown in the gut is helping to set it off, and that provides an opportunity. One review called protease inhibition “one of the most promising novel therapeutic strategies to explore” in IBS but warned that more work is needed to identify the specific proteases involved.
  • Because proteases appear to set IBS off, efforts are underway to find a way to inhibit them via gut flora modification, next-generation probiotics, fecal transplants, and drugs.
  • With their wide range of symptoms, nociplastic diseases have been assumed to be primarily central nervous system disorders. This present study suggests IBS is also a nervous system disease – but begun by an abnormal activation of the gut neurons.
  • In a recent interview, chronic pain researcher Daniel Clauw (coming up) suggested that a different kind of inflammation called “neurogenic” or nerve-associated inflammation is in play in these diseases. Something similar may have shown up recently when fibromyalgia researchers found that immune cells called neutrophils, taken from FM patients, attacked the sensory nerves in FM mice.
  • The starting point in nociplastic diseases like ME/CFS and long COVID is less clear, as no specific tissues appear to be affected; i.e. they seem more like – at least from this vantage point – purely central nervous system disorders.
  • Progress is being made in understanding what’s going on nociplastic disorders, though, and will be explored in future blogs. For now, it’s good to know that ME/CFS, FM, and long COVID belong to a larger category of nociplastic diseases. A breakthrough in one could benefit all.
  • A recent interview with chronic pain researcher Daniel Clauw (coming up) suggested that these nociplastic diseases may often begin in a difficult-to-detect activation of the peripheral nerves that progresses to a central nervous system problem. He believes that a different kind of inflammation called “neurogenic”, or nerve-associated inflammation, is in play.

With their similar symptom presentation, ME/CFS, FM, and long COVID are all considered part of the nociplastic family of disorders – and that’s a good thing. The more diseases and the more people sharing them, the more attention they will get. Breakthroughs in any of these disorders could apply to the others, and that brings us to irritable bowel syndrome (IBS).

IBS is a complicated disease. Three types of it exist and it’s embedded in a complex physical environment regulated by millions of bacteria. In a presentation last year, Laura Pace, a neurogastroenterologist, threw cold water on diagnoses of IBS and small intestinal bowel overgrowth, stating that the diagnostics are so crude that they tell us little about what’s going on in the gut. She asserted that only detailed analyses of the gut tissues are going to tell us what’s going on in IBS.

Researchers have been digging deeper into the gut tissues and are making progress, and that leads us to a set of studies that have come out of Germany for over ten years.

How deep have IBS researchers gone? For over 15 years, they’ve been taking biopsies of the colon, and then spinning them in a centrifuge to separate the liquid, or supernatant. Then they expose gut neurons to the supernatant – and watch as, bang! – the neurons go off like rockets – spewing out electrical signals that produce pain and other symptoms.

Further analyses found that while serotonin and histamine stimulate the nerves, the major players are enzymes called proteases that break down proteins.

The Mast Cell Mystery

The role mast cells play in IBS has been unclear – some studies suggest they play a role and some that they don’t. During her presentation, Pace remarked on a study finding that eosinophils, in particular, and T-cells infiltrating the gut lining were causing the most problems in IBS.

It’s not that mast cells aren’t having an impact. Activated mast cells found near nerve fibers could be having a big impact on symptoms. Interestingly, Pace believed that histamine-containing foods have, at most, a “local” impact and don’t produce the systemic effects found in these diseases. (She employs mast cell stabilizers (H2 blocker 2-3x a day, and oral Cromolyn 4x a day (slowly titrated up) and/or quercetin with her patients).

Still, while mast cell inhibitors can help, they don’t always provide relief or don’t provide total relief. We either need better mast cell inhibitors or some other cells are involved.

The Study

The present study aimed to provide insights into the mast cell question by comparing mast cell density and histamine levels in people with IBS-D (D-diarrhea), people with a systemic mast cell disease called mastocytosis, and healthy controls. In gut-associated mastocytosis-D, high levels of mast cells build up in the gut. When they dump their loads, increased fluid levels and peristalsis (gut muscle activity and rapid motility) result in vomiting and diarrhea (apparently to get rid of the excess fluid).

The small study (n=32) also expanded past gut findings by determining if nerve activation in more parts of the guts (small and large intestine) is involved.

Results

Gut-wide Problem

IBS gut

IBS appears to result from the activation of nerves across the gut.

Even though all the IBS-D and mastocytosis patients experienced the same symptoms (bloating, diarrhea, abdominal pain), only the supernatant from the gut biopsies of the IBS patients sent the gut nerves through the roof.

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(The supernatant from mastocytosis patients activated some gut neurons but to a much lesser degree, and the researchers concluded that they responded similarly to the healthy controls.)

Since the supernatant from both parts of the gut from the IBS-D patients activated the gut nerves, the authors concluded that IBS-D was caused by a “general phenomenon (found) throughout the gut“.

Mast Cells Take Second Billing

They did not find increased numbers of mast cells in the biopsies of the IBS-D patients. Nor did they find any evidence of increased mast cell degranulation or histamine levels.

They concluded that “mast cells are not involved in nerve activation, at least not in the patient groups enrolled in this study” and that, as their past studies have suggested, proteases produced by immune or epithelial cells are the main culprit in IBS. While factors like histamine from mast cells and serotonin play a role in IBS, it’s the proteases that appear to set them off.

How to explain, then, the fact that mast cell stabilizers can help in IBS? They couldn’t, except to note that mast cells may be nestled so closely next to nerves that even small (undetectable to them) amounts of mast cell activation could set them off.

Note that some studies have implicated mast cell activation in IBS as well. The situation is complicated, and factors other than mast cells must also play a role in IBS.

Prior studies have teased out the nerve connection in IBS. The nerve activation in the gut activates vagal nerves situated outside the spinal cord in the dorsal root ganglia (DRG). The DRG is a central gathering place where sensory signals get sent to the central nervous system, and DRG activation is found in fibromyalgia. From there, the central nervous system activation spreads to cause symptoms like widespread pain, fatigue, sleep, cognitive and mood problems.

The authors stated that protease finding helps explain one of the strangest findings in the field. Instead of becoming more tweaked, when the nerves in IBS biopsies were repeatedly exposed to a cocktail of IBS-activating factors (histamine, serotonin, tryptase, and TNF-α (IBS-cocktail), they became less activated; i.e. they had become desensitized. The authors of that paper proposed that a protective mechanism was trying to shut the nerves down. Proteases can do this.

IBS is a complicated disease, but it’s become clear that protease-driven protein breakdown in the gut is helping to set it off and that provides an opportunity. One review called protease inhibition “one of the most promising novel therapeutic strategies to explore” in IBS but warned that more work is needed to identify the specific proteases involved.

Because proteases are produced by the bacteria and other substances in our gut, altering our gut flora could conceivably reduce the proteolytic activity that is turning on the gut nerves. Another review suggested that next-generation probiotics will be able to turn down this activity and help return the gut to normal functioning. A fecal transplant study using stool from a donor with low proteolytic activity and containing the bacteria Alistipes putredinis is underway to see if the stool can dampen the high levels of proteolytic activity found in IBS and provide relief.

A serine protease inhibitor called nafamostad reduced the gut pain in a rat model of IBS. Another approach is to increase the levels of endogenous opioids in the gut to relieve pain.

Back to Nociplastic Disease

Because researchers have had trouble finding clear evidence of pathological problems in the tissues in pain (the gut, muscles, etc.), and because of the widespread symptoms (pain, fatigue, cognitive and mood problems), the prevailing thesis is that these diseases are primarily central nervous system directed. This present study suggests IBS is a nervous system disease as well – but one where the problem starts in an abnormal activation of the gut neurons – which took some deep digging to uncover. (No wonder it’s been such a mystery).

A recent interview with chronic pain researcher Daniel Clauw (coming up) suggested that these nociplastic diseases may often begin in a difficult-to-detect activation of the peripheral nerves that progresses to a central nervous system problem. He believes that a different kind of inflammation, called “neurogenic” or nerve-associated inflammation, is in play.

Something similar may have shown up recently when fibromyalgia researchers found that immune cells called neutrophils, taken from FM patients, attacked the sensory nerves in FM mice.

Immune Disease? Neutrophils on the Attack in Fibromyalgia

That suggests a different and hard-to-detect kind of inflammation affecting the sensory nerves, in particular, present in these mysterious diseases.

fibromyalgia conditions

Fibromyalgia and ME/CFS are one of a series of conditions featuring nervous system-derived (nociplastic) pain and other symptoms.

The starting point in nociplastic diseases like ME/CFS and long COVID is less clear, as no specific tissues appear to be affected; i.e. they seem more like – at least from this vantage point – purely central nervous system disorders.

How nerve activation in the gut turns into a nociplastic disease featuring widespread pain, fatigue, sleep problems, etc., remains a mystery, but finding a starting point – nerve activation in the gut – should help.

Progress is being made in understanding what’s going on in nociplastic disorders, and that will be explored in future blogs. For now, it’s good to know that ME/CFS, FM, and long COVID belong to a larger category of nociplastic diseases. A breakthrough in one could benefit all.

 

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