intestinal permeability
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How open or closed the gut's physical barrier is to large molecules — a key variable in whether gluten exposure becomes disease activity.
Intestinal permeability refers to how easily substances pass through the intestinal epithelial lining from the gut lumen into the underlying tissue and bloodstream. A healthy gut maintains selective permeability — letting through nutrients while blocking bacteria, large protein fragments, and toxins. In celiac disease, this barrier is compromised.
Normal Barrier Function
The barrier has two components:
- Transcellular — through the enterocytes themselves; tightly regulated by transport proteins
- Paracellular — between enterocytes; controlled by tight-junctions
In a healthy gut, tight-junctions are the primary defence against large molecules crossing paracellularly. They are dynamic — they can tighten or loosen in response to physiological signals.
How Celiac Disease Compromises the Barrier
- gliadin triggers zonulin release → tight junctions loosen → paracellular gaps open
- Inflammation (from active disease) → cytokines (TNF-α, IFN-γ) directly disrupt tight junction protein expression → sustained permeability increase
- Villous atrophy → fewer, shorter, damaged enterocytes → physically compromised barrier
The result is a vicious cycle: more permeability → more gluten crosses → more immune activation → more inflammation → more permeability.
Measurement
Intestinal permeability is measured clinically using the lactulose:mannitol (L:M) ratio — a urine test where the patient drinks a solution of both sugars. Small mannitol crosses normally; large lactulose should not. A high ratio indicates increased permeability.
This test is used in research and in evaluating larazotide-acetate efficacy, but is not routine clinical practice.
The "Leaky Gut" Concept
Increased intestinal permeability is sometimes called "leaky gut" in popular media, where it is often overstated as a root cause of many diseases. In the context of celiac disease, the evidence is solid — increased permeability is a real, measurable phenomenon that plays a mechanistic role in disease activity. However, the term "leaky gut" as applied to other conditions remains controversial in mainstream medicine.
As a Therapeutic Target
larazotide-acetate is the primary drug candidate targeting intestinal permeability. By blocking zonulin's action on tight junctions, it aims to reduce paracellular gluten uptake. Mixed Phase 3 results suggest permeability modulation alone may be insufficient as a standalone therapy but could be valuable as part of a combination approach.
Related Concepts
tight-junctions | zonulin | enterocytes | gliadin | larazotide-acetate | villous-atrophy | cytokines-celiac