One aspect of GI permeability in particular has surfaced quite recently on my research radar, an interesting compound called zonulin.
A description first. Zonulin enjoys quite a special place in the science of the tight junctions. Tight junctions (TJs) among other roles, serve quite an important barrier function in lots of parts of the body; so making sure that things stay in and other things stay out. Zonulin seems to be part and parcel of the chemistry of tight junctions and in particular sharing quite an important relationship with the enhanced permeability of TJs.
With the gut in mind, zonulin has found quite a bit of interest. A familiar name to this blog, Dr Alessio Fasano, seems to have been present right at the beginning of interest in zonulin, with a particular focus on gut permeability tied into the presence of coeliac (celiac) disease as per this article* and write-up.
Ever since then, zonulin has just been making wave** (full-text) after wave*** (full-text) after wave**** as per its 'disassembly' activity when it comes to TJs. The initial link with coeliac disease is an interesting one given that later work suggested that gluten, or rather the gliadin fraction of gluten, has the propensity to induce zonulin release***** (at least under certain laboratory conditions).
But coeliac disease was just the starting point for zonulin, as more recent research has suggested a potential role for this protein in relation to gut permeability in type-1 diabetes (here and here), obesity (here) and potentially quite a few other conditions (here) with a specific focus on autoimmune conditions. General Zod? No, General Zonulin.
Accepting that there still remains some work to do on zonulin with regards to the methods and mode of action of zonulin on gut permeability******* this is a very interesting protein.
With my 'wondering' hat on, I have a few questions:
- Assuming the link between type-1 diabetes, gut permeability and zonulin holds up, does this mean that a gluten-free diet might be 'advantageous' for at least some people with type-1 diabetes? I'm thinking about this recent case study******* as a template. I would also add that no medical advice is given or intended by this question.
- Gut hyperpermeability, leaky gut, has been documented in other conditions including one close to my research heart, autism spectrum conditions (see here). Again noting the suggestions by de Magistris and colleagues (here) on how a gluten- & casein-free diet seemed to affect measures of gut permeability in their cohort, is it perhaps time to look at zonulin with regards to conditions like autism? How about schizophrenia also?
- Finally(!), the amino acid glutamine and its proposed tie up with gut permeability. Might glutamine affect zonulin production or even the other way around? Or am I just confusing things and heading out a step too far?
* Fasano A. et al. Zonulin, a newly discovered modulator of intestinal permeability, and its expression in coeliac disease. Lancet. 2000; 355: 1518-1519.
** Wang W. et al. Human zonulin, a potential modulator of intestinal tight junctions. Journal of Cell Science. 2000; 113: 4435-4440.
*** Fasano A. Intestinal zonulin: open sesame! Gut. 2001; 49: 159-162.
**** El Asmar R. et al. Host-dependent zonulin secretion causes the impairment of the small intestine barrier function after bacterial exposure. Gastroenterology. 2002; 123: 1607-1615.
***** Clemente MG. et al. Early effects of gliadin on enterocyte intracellular signalling involved in intestinal barrier function. Gut. 2003; 52: 218-223.
****** Fasano A. Zonulin, regulation of tight junctions, and autoimmune diseases. Annals of the New York Academy of Sciences. 2012; 1258: 25-33.
******* Sildorf SM. et al. Remission without insulin therapy on gluten-free diet in a 6-year old boy with type 1 diabetes mellitus. BMJ Case Reports. June 2012