Development and Validation of Test for "Leaky Gut" Small Intestinal and Colonic Permeability Using Sugars in Healthy Adults

Abstract

Background: Oral monosaccharides and disaccharides are used to measure in vivo human gut permeability through urinary excretion.

Aims: The aims were as follows: (1) to obtain normative data on small intestinal and colonic permeability; (2) to assess variance on standard 16 g fiber diet performed twice; (3) to determine whether dietary fiber influences gut permeability measurements; and (4) to present pilot data using 2 selected probes in patients with diarrhea-predominant irritable bowel syndrome (IBS-D).

Methods: Sixty healthy female and male adults, age 18-70 years, participated in 3 randomized studies (2 studies on 16.25 g and 1 study on 32.5 g fiber) in otherwise standardized diets. At each test, the following sugars were ingested: ¹²C-mannitol, ¹³C-mannitol, rhamnose (monosaccharides), sucralose, and lactulose (disaccharides). Standardized meals were administered from 24 hours before and during 24 hours post-sugars with 3 urine collections: 0-2, 2-8, and 8-24 hours. Sugars were measured using high-performance liquid chromatography-tandem mass spectrometry. Eighteen patients with IBS-D underwent 24-hour excretion studies after oral ¹³C-mannitol and lactulose.

Results: Baseline sugars (>3-fold above lower limits of quantitation) were identified in the 3 studies: ¹²C-mannitol in all participants; sucralose in 4-8, and rhamnose in 1-3. Median excretions/24 h (percentage of administered dose) for ¹³C-mannitol, rhamnose, lactulose, and sucralose were ∼30%, ∼15%, 0.32%, and 2.3%, respectively. ¹³C-mannitol and rhamnose reflected mainly small intestinal permeability. Intraindividual saccharide excretions were consistent, with minor differences with 16.25 g vs 32.5 g fiber diets. Median interindividual coefficient of variation was 76.5% (10-90 percentile: 34.6-111.0). There were no significant effects of sex, age, or body mass index on permeability measurements in health. ¹³C-mannitol measurements are feasible in IBS-D.

Conclusions: Baseline ¹²C-mannitol excretion precludes its use; ¹³C-mannitol is the preferred probe for small intestinal permeability.

Keywords: Barrier; Lactulose; Mannitol; Sucralose.

Figure 1.

Experimental protocol

Figure 2.

¹²C-mannitol in urine samples collected at baseline (upper panel) and during urine collections over 24 hours during three test days

Figure 3.

Reproducibility of small intestinal (0–2h) and colonic (8–24h) permeability measurements based on mass (mg) of saccharide excreted in urine (upper panel) or ratio of disaccharide to monosaccharide (lower panel) during 2 studies (A and B) with standardized diets containing 16.25g fiber per day. Data show median and interquartile range, IQR. LRR=lactulose to rhamnose ratio, L/13CMR=lactulose to 13C-mannitol ratio, SRR=sucralose to rhamnose ratio, S/13CMR=sucralose to 13C-mannitol ratio

Figure 4.

Comparison of small intestinal and colonic permeability measurements based on mass (mg) of saccharide excreted in urine (upper panel) or ratio of disaccharide to monosaccharide (lower panel) during two studies (A and B) with standardized diets containing 16.25g fiber per day (mean of 2 studies) and 32.5g fiber per day. Data show median and interquartile range, IQR. LRR=lactulose to rhamnose ratio, L/13CMR=lactulose to 13C-mannitol ratio, SRR=sucralose to rhamnose ratio, S/13CMR=sucralose to 13C-mannitol ratio

Figure 5.

Urine excretion of ¹²C-mannitol, ¹³C-mannitol, and lactulose in urine between 0 and 24 hours following administration of 100mg ¹³C-mannitol and 1000mg lactulose in patients with diarrhea-predominant irritable bowel syndrome. Note the significant quantities of ¹²C-mannitol particularly in the 8–24h urine sample consistent with contamination and the comparable excretion of ¹³C-mannitol and lactulose in all 3 urine samples.