Human Zonulin ELISA Kit

The discovery of Zonulin arose from the study of Vibrio cholerae. During the development of the Vibrio cholerae vaccine, some researchers found that while the virulence of the initial recombinant Vibrio cholerae vaccine strains that removed the ctxA gene was dramatically reduced, these attenuated strains were still capable of inducing severe diarrhea even in the absence of cholera toxin. To explain this phenomenon, the researchers proposed zonula occludins toxin (Zot), a protein that regulates intestinal tight junction (TJ) exogenous toxins depolymerize the tightly junctioned structures of the intestine, which allows for increased intestinal epithelial permeability. After removal of Zot, the tight junction structure is restored. Thus, Zot is thought to regulate tight junctions in a rapidly reversible manner. The researchers then further used an affinity chromatography column with immobilized Zot antibody to isolate and purify adhesion proteins from human small intestinal tissues, and obtained an endogenous protein that functionally resembles Zot to depolymerize tightly-connected complexes, and named it zonulin.

Zonulin is a protein with a molecular mass of 47kDa, with a specific N-terminal receptor-binding domain that determines tissue specificity, and a C-terminal tau-like domain that correlates with cytoskeletal rearrangements in intercellular TJs. Proteomic analysis identified zonulin as a precursor of haptoglobin 2. This is the only human endogenous protein that has been identified that can regulate intestinal permeability by affecting the tight junction structure of the intestinal epithelium. This protein can depolymerize the intestinal epithelial tight junction structural complexes, leading to disruption of the intercellular tight junction structures and increased permeability of the intestinal epithelium, which can lead to inflammation by allowing the entry of macromolecular antigenic substances into the tissues in the intestine.

Figure 1. Mechanisms of intestinal dysbiosis due to unregulated zonulin
(Source: Heickman LK, et al. 2020)

On the other hand, studies have confirmed that zonulin is not only found in the intestinal tract, but also in various tissues and organs such as the heart and brain. However, zonulin extracted from different tissues and organs differed in their N-termini, suggesting that connexins can respond specifically to particular stimuli as needed. Therefore, the researchers hypothesized that zonulin is not only able to regulate the tight junctions between intestinal epithelial cells, but is also involved in regulating the tight junctions between extra-intestinal epithelial cells and vascular endothelial cells.