#436: Charlene Van Buiten, PhD – Coeliac Disease & the Search for Novel Therapies

1. Detailed Study Notes
2. Transcript

You are currently not signed-in as a Premium subscriber.

To view our Premium content, please log-in to your account or subscribe to Premium.

Danny’s Key Idea from this episode is noting how mechanistic nutrition research should be discussed.

Often on the podcast we’ve discussed that one of the common tactics of “quackery” is for someone to make a bold claim about human health (or give direct recommendations), and then when asked for evidence for such a position, they point to mechanistic or animal research. It is common to see mechanisms used as an explanation for their recommendation (whether that’s eating/avoiding certain foods, fasting, etc.) even if that isn’t supported by human trials, and sometimes even contradicted by human trials. One example is people who talk about linoleic acid/PUFA/omega-6/seed oils/etc. as poison capable of slowly killing you. Such arguments are based on mechanisms, not human trials with clear health outcomes.

However, this doesn’t invalidate mechanistic research. In fact, it is absolutely crucial to add knowledge and generate further hypotheses.

One form of mechanistic research in humans is done via in vitro studies. An in vitro (literally “within glass”) study is one carried out outside of a living organism. Hence, they are typically done in petri dishes or other lab equipment (and thus the name). This is really useful, as the effect of certain nutrients or other compounds can be examined to see how they impact cells, tissues, and specfic pathways in them.

Of course, given this, they cannot be used to infer with any confidence what would happen in a living organism (in vivo), and certainly not in humans or in relation to a specific disease state.

In this episode, the way Dr. Van Buiten described her own work was a great example of how such studies should be presented. Before discussing the findings she made sure to lead with all the caveats, making comments along the lines of: “this is in vitro work, this is preliminary to look at potential mechanisms, this needs to be looked at in other models, even if it were to play out we have no idea what that might look; would it be a neutraceutical? Who would it be for? What would the effect be?”

So the difference between trustworthy academics actually doing this work, and some of the online nutrition “influencers”, is telling.

You are currently not signed-in as a Premium subscriber. Key Ideas are for Premium subscribers only.

Coeliac Disease & Gluten

Coeliac disease is an autoimmune disorder stimulated by the ingestion of gluten.

Gluten is a protein found in certain grains such as wheat, barley and rye.

Gluten comprises two main subunits:

1. Glutenin
2. Gliadin

Coeliac disease prevalence is generally estimated at about 1% of the popultion. For example, a systematic review and meta-analysis of global prevalence by Singh et al. (2018) found that prevalence of coeliac disease:

• Based on serologic test results is 1.4%
• Based on biopsy results is 0.7%
• Varied slightly based on continent

“In addition to the ingestion of gluten, the development of coeliac disease requires genetic susceptibility and the disorder almost exclusively occurs in individuals with the human leukocyte antigen (HLA)-DQ2 and/or HLA-DQ8 haplotypes2. However, as only a fraction of HLA-DQ2-positive and/or HLA-DQ8-positive individuals consuming gluten develop the disorder, it is likely that other genetic and/or environmental factors play a role in the disease onset.” – Lindfors et al., 2019

Gliadins are classified as prolamins due to their richness in proline and glutamine residues.

“The viscoelasticity of gluten protein is a product of inter-and intramolecular disulfide bond formation between glutenins and gliadins, respectively, forming a gluten protein network, which contributes to the functional characteristics of gluten within a food product.” – Van Buiten & Elias, 2021

Zonulin

• One of the important processes that occurs in those with coeliac disease is gliadin-stimulated zonulin release.
• Intestinal cells have ‘tight junctions’, which regulate the permeability of the gut lining.
• Zonulin is a protein that can trigger the disassembly and downregulation of tight junction proteins
• This can then lead to increased permeability of the intestinal barrier, thus allowing large gluten proteins to pass through and can an immune response (Fasano, 2011).
• This increased permeability is likely what is being referenced when people unfortunately talk about concepts like “leaky gut”.

Fasano (2011): “Once gluten is removed from the diet, serum zonulin levels decrease, the intestine resumes its baseline barrier function, the autoantibody titers are normalized, the autoimmune process shuts off and, consequently, the intestinal damage (that represents the biological outcome of the autoimmune process) heals completely.”

In the top right hand corner of the above diagram, you’ll see that when gluten is prevented from interacting with AT1001 (i.e. from adopting a gluten-free diet), then the resulting cascade of autoimmunity does not occur.

Potential Therapies/Interventions

Dr. Van Buiten described how pharmaceutical strategies to combat celiac disease may fall into two categories:

1. Patient/pathophysiology-targeted therapies
   • These include targeting:
     • Sensitization – e.g. Nexvax2 vaccine
     • Gut barrier function enhancement – e.g. medications (e.g. larazotide acetate) or probiotics (e.g. Bifidobacterium longum CECT 7347 and Lactobacillus casei ATCC 9595)
     • Immunosuppression – via drugs or potentially probiotics
     • Disruption of antigen presentation – e.g. use of peptides to block the binding of gliadin
2. Antigen-focused therapies (Gliadin-Focused Therapies)
   • These include interventions that prevent recognition of gluten by the body via degradation. This can be achieved via either:
     • Enzymes
     • Sequestrants

While many of the pathogenesis-focused therapies target events after passage of gliadin to the lamina propria, gliadin-focused therapies instead modify the immunological potential of gluten.

Some work (e.g. Pinier et al., 2012) suggests that it may be possible to prevent the digestion and absorption of gluten proteins by sequestering the protein from interaction with the gastrointestinal tract. (Sequestering is the term used to describe when specific molecules selectively interact with a protein in a way that then inhibits its transport into parts of the cell or tissue.).

Dr. Van Buiten’s work was an attempt to see if there was a basis for possible natural and nutraceutical options. So her in vitro studies (discussed below), explored whether dietary polyphenols would be capable of sequestering gluten proteins from interacting with intestinal tissue. So in this case, the sequestering means that the gluten proteins are prevented from having their normal harmful biological activity.

Why Consider Polyphenols?

Polyphenols are non-essential, bioactive compounds found in plants. They have been shown to have a number of health-promoting effects, with a whole host of mechanisms proposed. For a deep dive on polyphenols you can see these 2 episodes:

• 406: Polyphenols & Cognitive Health
• 407: Polyphenols – Impact on Blood Pressure, Endothelial Function & Heart Disease Risk

Polyphenols were hypothesised to have a potential benefit in coeliac disease treatment due to both their anti-nutritional and anti-inflammatory properties:

• Anti-nutritional: “Despite their numerous health benefits, polyphenols are sometimes referred to as “anti-nutrients”, as polyphenol-rich diets have been associated with reduced absorption and digestibility of micro- and macronutrients. Underlying mechanisms driving the anti-nutritional effects of polyphenols in the diet include digestive enzyme inhibition and protein sequestration.” – Van Buiten & Elias, 2021
• Anti-inflammatory: “Epidemiological evidence suggests that polyphenols can beneficially impact human health, demonstrating anti-inflammatory, anti-carcinogenic and anti-obesity properties in vitro and in vivo. Often contributing to each of these is the antioxidative capacity of flavonoids. As a class of compounds, polyphenols have the ability to both scavenge free radicals and prevent radical formation, although antioxidative potential can vary between compounds and applications” – Van Buiten & Elias, 2021

Based on the mechanistic studies to date, there have been several proposed mechanisms of coeliac disease pathogenesis disruption by dietary polyphenols (as shown in diagram below):

a) physical sequestration of native gliadins
b) physical sequestration of hydrolyzed gliadins
c) digestive enzyme inhibition
d) improved barrier integrity and decreased paracellular transport of gliadins
e) anti-inflammatory activity
f) TG2 downregulation

Polyphenols are known to interact with proteins. A good example here is how polyphenols in tea can interact with milk proteins. When milk is added to tea, the polyphenols in the tea get bound up by some of the proteins in milk. This alters the bioavailability of those polyphenols.

In the context of targeting gluten (as an antigen-focused therapy), gliadins (i.e. proteins) make for a interesting target for polyphenol interactions as they are rich in proline residues and this has been shown to favor interactions with polyphenols.

Polyphenols have been shown to interact with gliadin to prevent celiac-associated inflammation and intestinal damage.

In vitro studies by Van Buiten & colleagues

Van Buiten et al., Food Funct., 2019,10, 2997-3007

• Epigallocategin gallate (EGCG), the prevalent catechin found in green tea, forms stable complexes with immunostimulatory gliadins in vitro, thereby modifying the structure of gliadin proteins.
• This structural modification may play a role in functional alterations such as decreased recognition of the protein.
• This is due to gliadin being proline-rich, which allows for recognition and binding by two critical receptors in coeliac disease transmission with HLA-DQ2.

Van Buiten, C. B., Lambert, J. D., Elias, R. J., Mol. Nutr. Food Res. 2018, 62, 1700879.

• Green tea polyphenols mitigate gliadin-mediated inflammation and permeability in vitro via multiple mechanisms, including:
  • Sequestration of gliadin protein.
  • Prevention of hydrolysis by digestive enzymes.
• The presence of green tea extract resulted in decreased formation of low molecular weight gliadins such as those implicated in coeliac disease.
• Pre-treatment of hydrolyzed gliadin with green tea extract resulted in decreased inflammation (as noted by decreased expression of IL-6 and IL-8) as well as reduced permeability of Caco-2 cell monolayers, a simple model for the intestinal brush border.

You are currently not signed-in as a Premium subscriber. Detailed study notes are for Premium subscribers only.

You are currently not signed-in as a Premium subscriber. Episode transcripts are for Premium subscribers only.