Paracellular absorption in laboratory mice: Molecule size-dependent but low capacity.

Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems lower in nonfliers than in fliers, although that conclusion rests largely on a comparison of relatively larger nonflying mammals (>155g) and relatively smaller flying birds (<155g). We report on paracellular absorption in laboratory mice, the smallest nonflying mammal species studied to date. Using a standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption=f) of inert carbohydrate probes: L-arabinose (M(r)=150.13Da) and cellobiose (342.3) that are absorbed exclusively by the paracellular route, and 3-O-methyl D-glucose (3OMD-glucose) (M(r)=194) absorbed both paracellularly and transcellularly. f was measured accurately in urine collection trials of 5-10h duration. Absorption of 3OMD-glucose by mice was essentially complete (f=0.95±0.07) and much higher than that for L-arabinose (f=0.21±0.02), indicating that in mice, like other nonflying mammals, >80% of glucose is absorbed by mediated process(es) rather than the passive, paracellular route. As in all other vertebrates, absorption of cellobiose (f=0.13±0.02) was even lower than that for L-arabinose, suggesting an equivalent molecular size cut-off for flying and nonflying animals and thus a comparable effective TJ aperture. An important ecological implication is that smaller water-soluble plant secondary metabolites that have been shown to be absorbed by the paracellular path in cell culture, such as phenolics and alkaloids, might be absorbed in substantial amounts by bats and small birds relative to nonflying mammals such as mice.

Pitfalls in gastrointestinal permeability measurement in ICU patients with multiple organ failure using differential sugar absorption.

OBJECTIVE: To assess whether gastrointestinal permeability (GIP) at intensive care unit (ICU) admission, measured by differential sugar absorption, is related to severity of disease and multiple organ failure (MOF). Post hoc, to analyse the relation between the urinary sugar recovery and renal function. DESIGN: Prospective observational cohort study. SETTING: Eighteen-bed general ICU of a teaching hospital. PATIENTS: Sixty-four ventilated patients admitted with MOF. INTERVENTIONS: GIP was assessed within 24 h using cellobiose (C), sucrose (S) and mannitol (M) absorption. MEASUREMENTS AND RESULTS: Severity of disease: APACHE II and III, SAPS II and MPM II systems. Organ failure: SOFA, MODS and Goris score. The median urinary recovery of C was 0.147% (range 0.004-2.145%), of S 0.249% (0.001-3.656%) and of M 10.7% (0.6-270%). In 16 patients, M recovery was over 100% of the oral dose. They received red blood cell transfusion (RBC). In the non-transfused, the median cellobiose/mannitol (CM) ratio was 0.015 (0.0004-0.550). CM ratio was not related to severity of disease and inversely related to the SOFA score ( r=-0.30, p=0.04). Post hoc regression analysis showed that recoveries of C, S and M were positively related to urinary volume. Recoveries of C and S, but not of M, were positively related to creatinine clearance. The CM ratio corrected for diuresis, but was inversely related to creatinine clearance. CONCLUSIONS: Differential C, S and M absorption testing is unreliable after RBC transfusion, since bank blood contains mannitol. The excretion of C and S, but not of M, is limited by renal dysfunction. Differential sugar absorption is not reliable to test GIP in MOF patients, since non-permeability related factors act as confounders.

Differential sugar absorption for the assessment of canine intestinal permeability: the cellobiose/mannitol test in gluten-sensitive enteropathy of Irish setters.

Intestinal permeability was assessed in Irish setters with gluten-sensitive enteropathy by oral administration of an isotonic solution of cellobiose and mannitol, and measurement of their urinary excretion ratio. The cellobiose/mannitol ratio was increased in affected Irish setters fed a wheat-containing diet compared both with littermates reared on a cereal-free diet, with no evidence of jejunal damage, and clinically healthy Irish setters. The ratio fell following six weeks on a gluten-free diet to be comparable with control values, and subsequently increased after six weeks gluten challenge. The results indicate that the cellobiose/mannitol test may be useful for the detection of mucosal damage and for monitoring the response to therapy.

Clinical application of a simple HPLC method for the sugar intestinal permeability test.

A new high pressure liquid chromatography (HPLC) method has been used to measure urinary sugar levels for the intestinal permeability test with cellobiose and mannitol (C/M test). Urinary specimens have been prepared by simple filtration through a Millipore membrane. The method is highly sensitive (minimal detectable concentration of urinary sugars = 0.01 mg/ml) and reproducible (coefficient variation between samples = 0.47% for cellobiose and 0.25% for mannitol). By this method a C/M test has been performed in a large series of gastroenterological patients. High values of mean urinary C/M percentage recovery ratio (C/M%) were found in 30 children with active gluten-sensitive enteropathy compared with controls (0.42 +/- 0.66 versus 0.014 +/- 0.005). In 44 treated celiacs and 34 children with chronic nonspecific diarrhea the mean C/M%s were 0.027 +/- 0.018 and 0.021 +/- 0.012, respectively. The results of this study confirm that the C/M test is a valuable investigation in the diagnostic studies of children with chronic diarrhea. The simple HPLC method described for the determination of urinary sugar levels should allow a wider diffusion of this test.

Rapid and simultaneous determination of lactulose and mannitol in urine, by HPLC with pulsed amperometric detection, for use in studies of intestinal permeability.

The lactulose/mannitol dual sugar absorption test is a non-invasive test of intestinal permeability. Its widespread use has been limited by the difficulties of analysis for carbohydrates in urine at low concentrations. We describe a "high-pressure" liquid-chromatographic method for determining lactulose and mannitol in urine, in which anion-exchange chromatography and pulsed amperometric detection are used. Sample preparation is simple and fast, and lactulose and mannitol and the internal standards arabinose and cellobiose are well resolved within 15 min. Analytical response of the method is linear with concentrations to 3 g/L, and one can detect as little as 0.3 mg of lactulose per liter of urine. Analytical recovery was between 90% and 107% for all sugars analyzed, and there was good agreement with results by a gas-chromatographic method (r = 0.993 lactulose, 0.984 mannitol). The method may potentially be applied to the study of other carbohydrates present in biological fluids at low concentrations.

Gut permeability in IgA nephropathy.

Gut permeability to small molecules was assessed by the differential absorption of cellobiose and mannitolin 18 patients with IgA nephropathy (IgAN). The urinary cellobiose:mannitol excretion ratio in patients did not differ (P = 0.42) from controls. These findings do not support the hypothesis that chronic increased mucosal permeability allows excessive antigen penetration to the mucosal immune system, predisposing to glomerular IgA deposition in IgA nephropathy. However, the patient with the greatest cellobiose:mannitol ratio developed macroscopic haematuria within 3 weeks of testing, raising the possibility of a transient abnormality in gut permeability.

Lactulose/mannitol test: an ideal screen for celiac disease.

A lactulose/mannitol (La/Ma) test was compared with a standard cellobiose/mannitol test (Ce/Ma) in 17 patients with newly diagnosed celiac disease and 12 healthy controls. The mean La/Ma test was 0.163 (SEM 0.076) in celiacs and 0.016 (SEM 0.002) in controls. The mean Ce/Ma test was 0.132 (SEM 0.024) in celiacs and 0.014 (SEM 0.002) in controls (p less than 0.001). There is no significant difference between the new La/Ma test and the Ce/Ma test. Eighty-two patients referred to a general gastroenterology clinic with symptoms or signs of celiac disease performed a La/Ma test. A jejunal biopsy was indicated in 44 of these. In this selected group the sensitivity was 89%, specificity 54%, and negative predictive value of 95%. The La/Ma test fulfills the criteria of a screening test; it is sensitive, of low cost, and simple to perform, and it has the advantage of a simple enzyme assay and does not cause diarrhea in patients with hypolactasia. It can, therefore, be used in screening large patient populations.

Comparison between the cellobiose/mannitol and 51Cr-labelled ethylenediaminetetra-acetate absorption tests in the detection of coeliac disease.

1. The cellobiose/mannitol and 51Cr-labelled ethylenediaminetetra-acetate (51Cr-EDTA) absorption tests have been compared with respect to their ability to detect altered intestinal permeability in coeliac disease. 2. In patients with clinically proven coeliac disease, 13 out of 14 (93%) had abnormal urinary cellobiose/mannitol ratios, while only five out of 12 (42%) had abnormal urinary recoveries of 51Cr-EDTA. Thus, the cellobiose/mannitol absorption test is more sensitive in recognizing coeliac disease and this difference was significant (P less than 0.02). 3. Possible reasons for this difference in the sensitivity of the two absorption tests are discussed.

The double sugar test of intestinal permeability in the elderly.

Tests of intestinal permeability are used as a reflection of upper-small-intestinal mucosal damage. Thirty-two elderly in-patients aged 75-96 years, and 64 hospital volunteers aged 22-64 years with no overt gastro-intestinal disease were studied to determine whether permeability changes with increasing age. Intestinal permeability was assessed by measuring the 5-h urinary excretion of a monosaccharide, L-rhamnose, and a disaccharide, cellobiose, for 5 h after their oral administration in a hypertonic solution. While in the elderly, excretion of both mono- and di-saccharides was significantly reduced by a half to two-thirds, the ratio of the two sugars in the urine was similar in both age groups. We conclude that permeability was unimpaired in the elderly patients whom we studied. Because the test depends on a ratio of excretion rates rather than an absolute rate, accuracy of urine collection and abnormal renal function do not invalidate the results. It is therefore useful as a screening test of upper-small-intestinal mucosal damage in the elderly.

Cellobiose/mannitol test: physiological properties of probe molecules and influence of extraneous factors.

The influence of gastric emptying, intestinal transit, renal and hepatic function, and variations in the timing of urine collections, on the cellobiose/mannitol test of intestinal permeability has been studied. None of these extraneous factors influences the cellobiose/mannitol recovery ratio, and there is only a modest effect of renal function on urinary mannitol recovery. Cellobiose is almost totally recovered in the urine within 10 h of intravenous injection, whilst mannitol is less completely recovered, perhaps due to hepatic metabolism. The simultaneous administration of two probe molecules in the cellobiose/mannitol test, and the use of a ratio to express results, thus achieves the desired object of minimising the effect of extraneous factors on the test result. The cellobiose/mannitol test is therefore not subject to the limitations of previous tests of intestinal permeability using orally administered probe molecules, and is widely applicable as a screening test for coeliac disease.