Dr. Ron’s Research Review – April 9, 2014

© 2014

This week’s research review focuses on Zonulin and intestinal permeability.

Zonulin is the only physiologic modulator of intercellular tight junctions described so far that is involved in trafficking of macromolecules and, therefore, in tolerance/immune response balance. When the zonulin pathway is deregulated in genetically susceptible individuals, autoimmune disorders can occur. Zonulin is the link between leaky gut and autoimmune disease. (Fasano 2012) (Fasano 2012)

A recent study found that circulating zonulin, a marker of intestinal permeability, is increased in association with obesity-associated insulin resistance. (Moreno-Navarrete, Sabater et al. 2012)

Gliadin activates zonulin signaling, leading to increased intestinal permeability to macromolecules. (de Punder and Pruimboom 2013)

Natural therapies shown to decrease zonulin include:

Probiotics (Lamprecht, Bogner et al. 2012)

Hydrolysed Casein (Visser, Lammers et al. 2010)

Inulin-enriched pasta (Russo, Linsalata et al. 2012)

Dr. Ron


Articles

The dietary intake of wheat and other cereal grains and their role in inflammation

         (de Punder and Pruimboom 2013) Download

Wheat is one of the most consumed cereal grains worldwide and makes up a substantial part of the human diet. Although government-supported dietary guidelines in Europe and the U.S.A advise individuals to eat adequate amounts of (whole) grain products per day, cereal grains contain "anti-nutrients," such as wheat gluten and wheat lectin, that in humans can elicit dysfunction and disease. In this review we discuss evidence from in vitro, in vivo and human intervention studies that describe how the consumption of wheat, but also other cereal grains, can contribute to the manifestation of chronic inflammation and autoimmune diseases by increasing intestinal permeability and initiating a pro-inflammatory immune response.

Leaky gut and autoimmune diseases

         (Fasano 2012) Download

Autoimmune diseases are characterized by tissue damage and loss of function due to an immune response that is directed against specific organs. This review is focused on the role of impaired intestinal barrier function on autoimmune pathogenesis. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, with its intercellular tight junctions, controls the equilibrium between tolerance and immunity to non-self antigens. Zonulin is the only physiologic modulator of intercellular tight junctions described so far that is involved in trafficking of macromolecules and, therefore, in tolerance/immune response balance. When the zonulin pathway is deregulated in genetically susceptible individuals, autoimmune disorders can occur. This new paradigm subverts traditional theories underlying the development of these diseases and suggests that these processes can be arrested if the interplay between genes and environmental triggers is prevented by re-establishing the zonulin-dependent intestinal barrier function. Both animal models and recent clinical evidence support this new paradigm and provide the rationale for innovative approaches to prevent and treat autoimmune diseases.

Zonulin, regulation of tight junctions, and autoimmune diseases

         (Fasano 2012) Download

Recent studies indicate that besides digestion and absorption of nutrients and water and electrolytes homeostasis, another key function of the intestine is to regulate the trafficking of environmental antigens across the host mucosal barrier. Intestinal tight junctions (TJs) create gradients for the optimal absorption and transport of nutrients and control the balance between tolerance and immunity to nonself antigens. To meet diverse physiological challenges, intestinal epithelial TJs must be modified rapidly and in a coordinated fashion by regulatory systems that orchestrate the state of assembly of the TJ multiprotein network. While considerable knowledge exists about TJ ultrastructure, relatively little is known about their physiological and pathophysiological regulation. Our discovery of zonulin, the only known physiologic modulator of intercellular TJs described so far, has increased our understanding of the intricate mechanisms that regulate the intestinal epithelial paracellular pathway and has led us to appreciate that its upregulation in genetically susceptible individuals leads to autoimmune diseases.

Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial

         (Lamprecht, Bogner et al. 2012) Download

BACKGROUND: Probiotics are an upcoming group of nutraceuticals claiming positive effects on athlete's gut health, redox biology and immunity but there is lack of evidence to support these statements. METHODS: We conducted a randomized, double-blinded, placebo controlled trial to observe effects of probiotic supplementation on markers of intestinal barrier, oxidation and inflammation, at rest and after intense exercise. 23 trained men received multi-species probiotics (1010 CFU/day, Ecologic(R)Performance or OMNi-BiOTiC(R)POWER, n = 11) or placebo (n = 12) for 14 weeks and performed an intense cycle ergometry over 90 minutes at baseline and after 14 weeks. Zonulin and alpha1-antitrypsin were measured from feces to estimate gut leakage at baseline and at the end of treatment. Venous blood was collected at baseline and after 14 weeks, before and immediately post exercise, to determine carbonyl proteins (CP), malondialdehyde (MDA), total oxidation status of lipids (TOS), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6). Statistical analysis used multifactorial analysis of variance (ANOVA). Level of significance was set at p < 0.05, a trend at p < 0.1. RESULTS: Zonulin decreased with supplementation from values slightly above normal into normal ranges (<30 ng/ml) and was significantly lower after 14 weeks with probiotics compared to placebo (p = 0.019). We observed no influence on alpha1-antitrypsin (p > 0.1). CP increased significantly from pre to post exercise in both groups at baseline and in the placebo group after 14 weeks of treatment (p = 0.006). After 14 weeks, CP concentrations were tendentially lower with probiotics (p = 0.061). TOS was slightly increased above normal in both groups, at baseline and after 14 weeks of treatment. There was no effect of supplementation or exercise on TOS. At baseline, both groups showed considerably higher TNF-alpha concentrations than normal. After 14 weeks TNF-alpha was tendentially lower in the supplemented group (p = 0.054). IL-6 increased significantly from pre to post exercise in both groups (p = 0.001), but supplementation had no effect. MDA was not influenced, neither by supplementation nor by exercise. CONCLUSIONS: The probiotic treatment decreased Zonulin in feces, a marker indicating enhanced gut permeability. Moreover, probiotic supplementation beneficially affected TNF-alpha and exercise induced protein oxidation. These results demonstrate promising benefits for probiotic use in trained men. CLINICAL TRIAL REGISTRY: http://www.clinicaltrials.gov, identifier: NCT01474629.

Circulating zonulin, a marker of intestinal permeability, is increased in association with obesity-associated insulin resistance

         (Moreno-Navarrete, Sabater et al. 2012) Download

Zonulin is the only physiological mediator known to regulate intestinal permeability reversibly by modulating intercellular tight junctions. To investigate the relationship between intestinal permeability and obesity-associated metabolic disturbances in humans, we aimed to study circulating zonulin according to obesity and insulin resistance. Circulating zonulin (ELISA) was measured in 123 caucasian men in association with inflammatory and metabolic parameters (including minimal model-measured insulin sensitivity). Circulating zonulin increased with body mass index (BMI), waist to hip ratio (WHR), fasting insulin, fasting triglycerides, uric acid and IL-6, and negatively correlated with HDL-cholesterol and insulin sensitivity. In multiple regression analysis, insulin sensitivity (p = 0.002) contributed independently to circulating zonulin variance, after controlling for the effects of BMI, fasting triglycerides and age. When circulating IL-6 was added to this model, only BMI (p = 0.01) contributed independently to circulating zonulin variance. In conclusion, the relationship between insulin sensitivity and circulating zonulin might be mediated through the obesity-related circulating IL-6 increase.

Inulin-enriched pasta improves intestinal permeability and modifies the circulating levels of zonulin and glucagon-like peptide 2 in healthy young volunteers

         (Russo, Linsalata et al. 2012) Download

Apart from the intestinal environment, inulin induces physiological effects, which includes a reduction in glucose and lipid concentrations and modulation of gastrointestinal motility through the release of different peptides. We hypothesized that inulin-enriched pasta may also improve small intestine permeability in relation to zonulin and glucagon-like peptide 2 (GLP-2) levels in healthy young subjects. Twenty healthy, young male volunteers completed a randomized, double-blind crossover study consisting of a 2-week run-in period and two 5-week study periods (11% inulin-enriched or control pasta), with an 8-week washout period in between. The intestinal barrier function was assessed by lactulose-mannitol excretion in urine. Zonulin values and GLP-2 release were evaluated by enzyme-linked immunosorbent assay. In the inulin group, the urinary lactulose recovery was significantly lower than the other 2 groups. There were no significant differences in urinary mannitol levels between groups. Accordingly, the lactulose-mannitol excretion ratio was significantly decreased in the inulin-enriched pasta group compared with the other 2 groups. The inulin-enriched pasta group had significantly lower zonulin serum values and significantly higher GLP-2 basal values when compared with the baseline and control pasta groups. The dietary use of inulin-enriched pasta preserves intestinal mucosal barrier functioning and modulates circulating levels of zonulin and GLP-2, suggesting that prebiotics could be used in the prevention of gastrointestinal diseases and metabolic disorders.

Restoration of impaired intestinal barrier function by the hydrolysed casein diet contributes to the prevention of type 1 diabetes in the diabetes-prone BioBreeding rat

         (Visser, Lammers et al. 2010) Download

AIMS/HYPOTHESIS: Impaired intestinal barrier function is observed in type 1 diabetes patients and animal models of the disease. Exposure to diabetogenic antigens from the intestinal milieu due to a compromised intestinal barrier is considered essential for induction of the autoimmune process leading to type 1 diabetes. Since a hydrolysed casein (HC) diet prevents autoimmune diabetes onset in diabetes-prone (DP)-BioBreeding (BB) rats, we studied the role of the HC diet on intestinal barrier function and, therefore, prevention of autoimmune diabetes onset in this animal model. METHODS: DP-BB rats were fed the HC diet from weaning onwards and monitored for autoimmune diabetes development. Intestinal permeability was assessed in vivo by lactulose-mannitol test and ex vivo by measuring transepithelial electrical resistance (TEER). Levels of serum zonulin, a physiological tight junction modulator, were measured by ELISA. Ileal mRNA expression of Myo9b, Cldn1, Cldn2 and Ocln (which encode the tight junction-related proteins myosin IXb, claudin-1, claudin-2 and occludin) and Il-10, Tgf-ss (also known as Il10 and Tgfb, respectively, which encode regulatory cytokines) was analysed by quantitative PCR. RESULTS: The HC diet reduced autoimmune diabetes by 50% in DP-BB rats. In DP-BB rats, prediabetic gut permeability negatively correlated with the moment of autoimmune diabetes onset. The improved intestinal barrier function that was induced by HC diet in DP-BB rats was visualised by decreasing lactulose:mannitol ratio, decreasing serum zonulin levels and increasing ileal TEER. The HC diet modified ileal mRNA expression of Myo9b, and Cldn1 and Cldn2, but left Ocln expression unaltered. CONCLUSIONS/INTERPRETATION: Improved intestinal barrier function might be an important intermediate in the prevention of autoimmune diabetes by the HC diet in DP-BB rats. Effects on tight junctions, ileal cytokines and zonulin production might be important mechanisms for this effect.


References

de Punder, K. and L. Pruimboom (2013). "The dietary intake of wheat and other cereal grains and their role in inflammation." Nutrients 5(3): 771-87. [PMID: 23482055]

Fasano, A. (2012). "Leaky gut and autoimmune diseases." Clin Rev Allergy Immunol 42(1): 71-8. [PMID: 22109896]

Fasano, A. (2012). "Zonulin, regulation of tight junctions, and autoimmune diseases." Ann N Y Acad Sci 1258: 25-33. [PMID: 22731712]

Lamprecht, M., S. Bogner, et al. (2012). "Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial." J Int Soc Sports Nutr 9(1): 45. [PMID: 22992437]

Moreno-Navarrete, J. M., M. Sabater, et al. (2012). "Circulating zonulin, a marker of intestinal permeability, is increased in association with obesity-associated insulin resistance." PLoS One 7(5): e37160. [PMID: 22629362]

Russo, F., M. Linsalata, et al. (2012). "Inulin-enriched pasta improves intestinal permeability and modifies the circulating levels of zonulin and glucagon-like peptide 2 in healthy young volunteers." Nutr Res 32(12): 940-6. [PMID: 23244539]

Visser, J. T., K. Lammers, et al. (2010). "Restoration of impaired intestinal barrier function by the hydrolysed casein diet contributes to the prevention of type 1 diabetes in the diabetes-prone BioBreeding rat." Diabetologia 53(12): 2621-8. [PMID: 20853098]