Su2050 – Near Infrared (NIR) Fluorescence Readouts of Intestinal Permeability and Disease Severity in Murine IBD Models

Background: Intestinal permeability is increased in many gut disorders, but is difficult to measure in humans.Currently, intestinal permeability is assessed in people using surrogate measures of barrier function, such as concentrations of circulating bacterial lipopolysaccharide (LPS), indicators of exposure to gut bacteria such as antibodies to LPS, LPS binding protein, and α-1-acid glycoprotein, and fecal α-1-antitrypsin.Many studies have used dual sugar absorption tests to probe gut permeability, which measure the ratios in urine of a disaccharide (generally lactulose) to a monosaccharide (generally rhamnose or lactulose) following oral ingestion.If barrier function is impaired, the ratios of the heavier to the lighter sugar are elevated.This theoretically sound test is compromised by specimen handling and assay challenges, and reliance on an arbitrarily time point for assessment.Pyrazine-derived fluorophores MB-402 (MW=422, peak excitation l=500 nm, peak emission=620 nm) and MB-301 (MW=198, peak excitation l=405 nm, peak emission=540 nm) detect small bowel injury in rats challenged with indomethacin (Sci Rep 2017;7:10888).Following oral ingestion, these fluorophores can be measured through the skin using transcutaneous sensor technology, as is now employed in clinical studies to measure glomerular filtration rates, and provide more robust tracings and dynamic range in a dose response model.Methods.We tested in our rat model MB-404 (MW = 492, peak excitation=500 nm, peak emission=620 nm).MB-404 contains eight hydroxyl groups (vs.four in MB-402), retains MB-402's acid-resistance, and is soluble in water.We gavaged MB-404 ( 92mg/kg) in combination with MB-301 (16 mg/kg).Results.Urinary MB-404:MB-301 ratios recapitulate (Fig 1) MB-402:MB-301 urine ratios.Simultaneous continuous transcutaneous monitoring detects each fluorophore in the extracellular space of the rats over eight hours resemble the cumulative urinary clearance of the fluorophores, demonstrating the feasibility of measuring tracer uptake from the gut without taking possession of urine or other fluids.Transcutaneous monitoring and urinary concentrations also enabled us to test if the ratios of MB-404 and MB-301 were superior to the uptake and clearances of individual tracers.The transcutaneous assessment measurement of extracellular MB-404 by itself (Fig 2) discriminated injured vs. control rats better than did ratios of the two fluorophores.Conclusion.MB-404's greater solubility offers advantages over MB-402 in dual fluorophore tests of gut permeability.Most importantly, MB-404 uptake from the gut following oral ingestion offers greater sensitivity as a single tracer than when used in tandem with MB-301.The ability to test gut permeability with a single tracer will facilitate upcoming trials of fluorophore tracers in people with intestinal enteropathy.