Objective: Studies of mucosal permeability to protein antigens in humans are limited to in vitro techniques. The use of surgical specimens for such studies has major shortcomings. Endoscopic biopsies in Ussing chambers have been introduced as a means of studying secretion and transepithelial permeability, but have not been evaluated for studies of protein antigen uptake in human intestine.
Material and methods: Standard forceps biopsies from the sigmoid colon of 24 healthy volunteers were mounted in Ussing chambers with an exposed tissue area of 1.76 mm2. 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP; 45 kDa protein antigen) were used as permeability markers. Mucosal permeability, electrophysiology, histology and energy contents of the biopsies were studied over time. To evaluate the ability of the technique to detect permeability changes, the mucosa was modulated with capric acid, a medium-chain fatty acid, known to affect tight junctions.
Results: In the Ussing chamber the mucosal biopsies were viable for 160 min with stable levels of ATP and lactate, and only minor changes in morphology. Steady-state permeability with low variability was seen for both markers during the 30-90 min period. Exposure to capric acid induced a rapid decrease in short-circuit current (Isc) and a slower reversible decrease in transepithelial resistance (TER), as well as an increased permeability to 51Cr-EDTA and HRP.
Conclusions: Endoscopic biopsies of human colon are viable in Ussing chambers and are reliable tools for studies of mucosal permeability to protein antigens. The technique offers a broad potential for studies of mucosal function in the pathophysiology of human gastrointestinal diseases.