Tofacitinib Helps Restore Intestinal Epithelial Barrier
The Janus kinase inhibitor (JAKi) tofacitinib was relatively recently approved for the treatment of ulcerative colitis, but its effect on the intestinal epithelium remains a subject of research. The objective of the study presented below was to determine how tofacitinib aids in the repair of the cytokine-damaged intestinal epithelial cell barrier.
Regulation of Intestinal Epithelial Permeability
Idiopathic bowel diseases (IBD), including Crohn's disease and ulcerative colitis, are caused by an exaggerated immune response to parts of the gastrointestinal tract. Damage to intestinal epithelial cells or disruption of their apical tight junctions can weaken the epithelium's ability to act as a barrier between intestinal contents and adjacent tissues.
The intestinal mucosa consists of lamina propria and a single layer of polarized epithelial cells connected by the apical junctional complex (AJC − apical junctional complex). The apical junctional complex consists of so-called tight junctions (TJ − tight junctions), which prevent the influx of microbes and their toxins, antigens, enzymes, and degraded food components. Reconfiguration of tight junctions can increase intestinal permeability, leading to one of the main clinical symptoms of IBD − diarrhea. Changes in the localization or expression of tight junction proteins can also increase the permeability of bacterial products into the lamina propria with a subsequent exaggerated immune response observed in IBD.
The main structural component of tight junctions is transmembrane proteins from the claudin family − one of the prominent proteins being claudin 2, responsible for regulating cellular permeability. The expression of claudin 2 is increased in patients with IBD and is regulated by pro-inflammatory cytokines − e.g., interferon gamma (IFN-γ).
Tofacitinib in IBD Therapy
Currently, more than 200 genes are associated with an increased risk of developing IBD. These include genes regulating Janus kinases (the JAK/STAT pathway), which can be activated by IFN-γ and other cytokines. Therefore, attention is focused on JAK/STAT pathway inhibitors and their possibilities in IBD therapy. Tofacitinib is an orally administered JAK inhibitor that was originally approved for the treatment of rheumatoid arthritis and is now also approved for the treatment of ulcerative colitis, among other conditions. Its efficacy is also being evaluated in clinical studies in patients with Crohn's disease; other indications include psoriatic arthritis, ankylosing spondylitis, and juvenile idiopathic arthritis.
Methodology and Study Progress
Cell cultures and organoids were used to evaluate the effect of tofacitinib on JAK/STAT activation, cellular barrier permeability, and the expression and localization of tight junction proteins compared to cells activated by the cytokine IFN-γ. Untreated cells/organoids or those with added vehicles served as controls.
Findings
Exposing cells to tofacitinib before their activation by IFN-γ reduced JAK activation (phosphorylation) and completely blocked STAT activation compared to the control. This result confirms that tofacitinib can block cytokine-induced JAK/STAT pathway activation in vitro. In cells affected by IFN-γ, a reduction in transepithelial electrical resistance (higher intercellular permeability) was observed. This reduction in resistance was not observed in cells exposed to both IFN-γ and tofacitinib.
Organoids simulating the complex structure of the intestinal epithelium were used to describe tofacitinib's effect on permeability. Organoids affected by IFN-γ showed up to a fourfold increase in permeability, which was reversed by tofacitinib. IFN-γ and tofacitinib did not affect the expression of the tested tight junction proteins. IFN-γ altered the localization of tight junction proteins, and tofacitinib normalized this effect.
IFN-γ doubled the level of claudin 2 in cells compared to the control. Tofacitinib reduced the upregulation of claudin 2 expression in vitro, both before and after cell stimulation with IFN-γ. Changes in permeability are likely caused by changes in claudin 2 expression after cell stimulation with IFN-γ, as the other tested tight junction proteins did not change their expression upon cell exposure to IFN-γ.
Conclusion
Tofacitinib supports maintaining the correct function of tight junctions and permeability in vitro. These results suggest its potential therapeutic application in patients with inflammatory bowel disease.
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Source: Sayoc-Becerra A., Krishnan M., Fan S. et al. The JAK inhibitor tofacitinib rescues human intestinal epithelial cells and colonoids from cytokine-induced barrier dysfunction. Inflamm Bowel Dis 2020; 26(3): 407−422, doi: 10.1093/ibd/izz266.
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