What is Zonulin?

Zonulin, used in conjunction with other fecal inflammation markers such as calprotectin, can help clinicians to distinguish between inflammatory bowel disorders (IBD) and other inflammatory gastrointestinal disorders.  

The zonulin biomarker is available on the Advanced GI profile that reflects the level of multiple zonulin family proteins in a blood or stool sample. The zonulin family proteins all share common functions with zonulin and have been clinically associated with increased inflammation in the gut mucosa and elsewhere in the body; for convenience the family of proteins is currently referred to as “zonulin”. Zonulin can be measured in serum or in stool, but since other systemic sources of inflammation (metabolic syndrome, type II diabetes, chronic inflammatory disease, etc.) can raise serum zonulin levels, recent studies indicate that fecal zonulin results may be best when assessing gut function and gut barrier permeability.
 

Zonulin family proteins reversibly regulate the paracellular tight junctions that control the gap size between the individual cells that make up the gut mucosal lining. If the paracellular gaps are too wide, foreign proteins can invade the underlying gastrointestinal tissue layers and enter circulation (leaky gut). Circulating foreign proteins increase systemic inflammation and immune system dysregulation. Over time, these foreign proteins can contribute to the induction of environmental allergy and sensitivity. If the foreign substances are mycotoxins, toxic metals or chemicals they can also disrupt immune function and cause inflammation. High levels of both serum and fecal zonulin have been associated with inflammation and increased intestinal permeability, however serum zonulin is less discriminating when assessing gastrointestinal function. Recent human studies indicate that, when combined with other stool markers and knowledge of a patient’s HLA-DQ (Celiac) status that fecal zonulin can be an important diagnostic tool.

Gluten and other zonulin triggers

Gluten is a protein found in certain grains (wheat, rye, barley) that releases a second protein, called gliadin, during digestion. Gliadin binds to a cellular receptor that promotes the release of zonulin and increases intestinal permeability, stimulating an immune response against gliadin that sets the stage for non-Celiac gluten sensitivity (NCGS) or Celiac disease in HLA-DQ2/8+ individuals. It is likely that genetic variation in the gliadin receptor and along the immune response pathway, in addition to microbiome alterations, digestive status, and other comorbid inflammation, further influence the risk of developing Celiac disease, NCGS, or leaky gut.

Gluten is not the only trigger for intestinal inflammation and increased permeability. Increased intestinal permeability can also occur due to inflammation from:

• Active Celiac disease, inflammatory bowel disease, etc.
• Parkinson’s disease
• Food allergy or sensitivity, some non-Celiac gluten sensitivity (HLA-DQ2/8+)
• Irritation of the gut mucosa by pharmaceuticals or toxic exposures
  • Chemicals, food additives, metals, mold mycotoxins
• Pathogens, parasites, or gut microbiome dysbiosis
• Physical or psychological stress
• Cigarette smoking

Clinical utility of fecal zonulin

The inflammatory fecal markers calprotectin, secretory IgA (sIgA), zonulin, -glucuronidase, and anti-gliadin IgA help clinicians to distinguish between autoimmune inflammatory bowel disorders (IBD) and other inflammatory gastrointestinal disorders.  Zonulin is useful in the identification of barrier dysfunction in patients with the genetic markers for Celiac disease (HLA-DQ2 and DQ8). Some individuals presenting as non-Celiac gluten-sensitive have Celiac genetics – these individuals, and those with active Celiac disease tend to have elevated fecal zonulin levels. Patients with active inflammatory bowel disease (IBD) also have higher zonulin levels. 

Children with both Crohn’s disease and ulcerative colitis have higher fecal zonulin levels than normal controls, while adults with Crohn’s disease tend to have high fecal zonulin levels compared to those with ulcerative colitis or normal controls. Suspect IBD when calprotectin is also elevated. Diarrhea-predominant irritable bowel syndrome (IBS-D) has also been associated with high zonulin levels. However, while most IBS-D patients will have non-diagnostic (lower) calprotectin levels, those with comorbid digestive disorders such as fructose malabsorption, histamine intolerance, lactose intolerance or Helicobacter pylori infection may have an elevated calprotectin level in addition. Patients with Parkinson’s disease have also been shown to have elevated fecal calprotectin and zonulin levels. 

 

It is also important to be aware that the use of immunosuppressive therapies or chemotherapy may prevent the expected elevation of some of the inflammatory and immunology markers on the stool test.  Prescription anti-inflammatories, such as steroids or immunosuppressant medications, may depress the level of inflammatory markers on the GI profiles and the medications may also alter the microbiome. As always, a thorough history, review of medication use, and physical examination are just as essential as laboratory findings for correct diagnosis.

Restoration of gut barrier function

Because zonulin reversibly controls paracellular tight junctions it can be used to monitor the restoration of gut barrier function as well as detect barrier dysfunction. Reduction of inflammation and restoration of intestinal permeability may reduce zonulin levels, strengthen the gut barrier and improve gastrointestinal function. Consider:

• Amino acid supports:
  
  • Glutamine 
  • Taurine
  • Tryptophan
  • Bioactive whey proteins (lactoferrin, whey immunoglobulins, etc.)
• Consider a lower-fat diet and emphasize polyunsaturated omega-3 fatty acids.
• Flavonoids and flavones from fruits, vegetables or nutraceuticals have anti-inflammatory and antioxidant properties.
• Identify and avoid inflammatory foods and foods known to increase permeability:
  
  • Gliadin, a protein found in gluten-containing grains wheat, rye, and barley. Hidden sources of wheat/gluten may be reviewed here 
• Avoid processed foods and the pro-inflammatory preservatives, colorants, and emulsifiers they contain.
• Minerals such as calcium, selenium and zinc are essential for normal barrier function.
• Normalize intestinal motility and support gut microbiome diversity with a plant-based high-fiber diet.
• Probiotics can increase the production of beneficial short chain fatty acids and also synthesize B vitamins and vitamin K. 
• Vitamins A and D support tolerant, anti-inflammatory immune responses.

Conclusion

Zonulin, used in conjunction with other fecal inflammation markers such as calprotectin, secretory IgA (sIgA), -glucuronidase, and anti-gliadin IgA can help clinicians to distinguish between autoimmune inflammatory bowel disorders (IBD) and other inflammatory gastrointestinal disorders.  These biomarkers and markers for H. pylori infection and gut microbiome status are all available on US BioTek’s Advanced GI profile; use it today to ensure a complete assessment of your patient’s gastrointestinal health.