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Geography of intestinal permeability and absorption

BACKGROUND

Intestinal morphology and function vary geographically.

AIMS

These functions were assessed in asymptomatic volunteers in European, North American, Middle Eastern, Asian, African, and Caribbean countries.

METHODS

Five hour urine collections were obtained from each subject following ingestion of a 100 ml iso-osmolar test solution containing 3-0-methyl-D-glucose, D-xylose, L-rhamnose, and lactulose after an overnight fast, to assess active (3-0-methyl-D-glucose) and passive (D-xylose) carrier mediated, and non-mediated (L-rhamnose) absorption capacity, as well as intestinal permeability (lactulose:rhamnose ratio).

RESULTS

A comparison of results for subjects from tropical countries (n=218) with those resident in the combined temperate and subtropical region (Europe, United States, Qatar) (n=224) showed significant differences. Residents in tropical areas had a higher mean lactulose:rhamnose ratio and lower mean five hour recoveries of 3-0-methyl-D-glucose, D-xylose, and L-rhamnose, indicating higher intestinal permeability and lower absorptive capacity. Investigation of visiting residents suggested that differences in intestinal permeability and absorptive capacity were related to the area of residence. Subjects from Texas and Qatar, although comprised of several ethnic groups and resident in a subtropical area, showed no significant difference from European subjects.

CONCLUSIONS

There are clearly demarcated variations in intestinal permeability and absorptive capacity affecting asymptomatic residents of different geographical areas which correspond with the condition described as tropical enteropathy. Results suggest the importance of environmental factors. The parameters investigated may be relevant to the predisposition of the indigenous population and travellers to diarrhoeal illness and malnutrition. Intestinal function in patients from the tropics may be difficult to interpret, but should take into account the range of values found in the asymptomatic normal population.

Small intestinal permeability to mannitol and lactulose in the three ethnic groups resident in west Birmingham

BACKGROUND/AIMS

Asymptomatic residents of tropical countries have differences in small intestinal morphology and permeability compared with residents of temperate zones. The aim of this study was to investigate small intestinal permeability and morphology in three ethnic groups resident in Birmingham, UK.

METHODS

28 white patients, 101 Indian (Indian subcontinent), and 49 Afro-Caribbean adult patients with dyspepsia had endoscopic distal duodenal biopsies and a hyperosmolar lactulose/mannitol permeability test. Twenty normal white subjects had the permeability test.

RESULTS

Lactulose/mannitol excretion ratios (LMER) were: white subjects 0.022 (median), white patients 0.022, Indians 0.031, Afro-Caribbeans 0.033. Differences between the immigrant groups and the two white groups were significant (p < 0.001); 33% of Indians and 45% of Afro-Caribbeans had LMER outside the range of the white groups. Afro-Caribbeans born in the UK had significantly lower LMER than those born abroad (p < 0.05); a similar trend was seen in Indians. Villous height/mucosal thickness ratios, calculated from small intestinal biopsy specimens, were lower in the immigrant groups and correlated inversely with LMER (r = 0.28; p < 0.05). Time resident in the tropics also correlated inversely with LMER.

CONCLUSIONS

There were significant differences in small intestinal permeability and morphology between immigrants resident in a Western country and the native white population. The data suggested that these differences were related to environmental factors.

Urinary excretion by dogs of intravenously administered simple sugars

Seven simple sugars, commonly used in intestinal function tests, were simultaneously administered intravenously to dogs and their urinary excretion was measured to assess their potential for metabolic degradation. Lactose, lactulose and 3-O-methyl-D-glucose were excreted unchanged, but small proportions of palatinose and sucrose were not, and were assumed to have been metabolised. More than half of the administered D-xylose and a quarter of L-rhamnose was not excreted and was assumed to have been metabolised. These findings may be significant for the interpretation of differential sugar absorption tests and the D-xylose tolerance test.

Intestinal permeability testing in dogs with diet-responsive intestinal disease

Fifteen dogs with signs of small and, or, large bowel disease that responded clinically to an exclusion diet were studied, using differential sugar absorption as an objective parameter of the mucosal response to the diet. Intestinal permeability and function were assessed by determining the urinary excretion ratios of lactulose/rhamnose and xylose/3-O-methylglucose, respectively, following oral administration of a mixture of these four sugars. Five dogs, all retrievers, were tentatively diagnosed as having dietary hypersensitivity, based upon resolution of clinical signs and normalisation of high intestinal permeability following an exclusion diet and recurrence of signs (in four of five dogs) upon challenge with the original diet. The fifth dog did not become symptomatic when challenged, but intestinal permeability increased. The remaining 10 dogs were diagnosed as having food intolerance, based upon clinical improvement on an exclusion diet, relapse on challenge with their original diet, but lack of improvement in intestinal permeability. These findings suggest that a differential sugar absorption test may be useful to determine the reasons for clinical response to exclusion diets. Demonstration of increased intestinal permeability with subsequent normalisation following an exclusion diet may be useful in the diagnosis of dietary hypersensitivity, while persistent abnormalities in intestinal permeability are suggestive of underlying intestinal disease and food intolerance.

Intestinal permeability: an overview

The noninvasive assessment of intestinal permeability in humans has a 20-year history. Because the tests are increasingly used in clinical practice and research and because there is much controversy, we reviewed the literature and outlined the potential and possible shortcomings of these procedures. Data was obtained from personal files and from a systemic search through MEDLINE and EMBASE. The principle of the differential urinary excretion of orally administered test markers is explained with reference to the desired physicochemical properties of the markers and how the principle can be exploited to allow assessment of various other gastrointestinal functions. The use of intestinal permeability tests for diagnostic screen for small bowel disease and assessment of responses to treatment, the pathogenesis of disease, normal intestinal physiology, and the effect of drugs and toxins on the intestine is described and reviewed. The controversy surrounding the anatomic location of the permeation pathways that the markers use is highlighted. Noninvasive tests of intestinal permeability have fulfilled early promises of usefulness in clinical practice and research. There is now a need for integrated research into the basic mechanisms of regulatory control of the intestinal barrier function.

Intestinal permeability to [51Cr]EDTA in infectious diarrhea

Orally administered [51Cr]EDTA was used to measure intestinal permeability in subjects with infectious diarrhea and in those without gastrointestinal complaints. [51Cr]EDTA was given to 87 subjects: 63 controls (32 normal controls, and 31 disease controls), and 24 patients with infectious diarrhea. Approximately 100 microCi of [51Cr]EDTA was given orally after an overnight fast. Urine was collected for the following 24 hr. Intestinal permeability to [51Cr]EDTA in both normal volunteers and in patients with a variety of diseases not associated with intestinal injury was low and results were in a relatively narrow range. Mean 24-hr urinary excretion of [51Cr]EDTA, calculated as a percent of the administered dose, in controls was 1.6% (0.2-3.5%). Patients with infectious diarrhea associated with invasive pathogens and/or intestinal inflammation had increased excretion of [51Cr]EDTA (mean 6.1%, P < 0.0001), with elevated excretions in 75%. These results demonstrate that intestinal infections must be considered as possible causes for increased intestinal permeability as assessed by the [51Cr]EDTA test.

Effects of metronidazole and misoprostol on indomethacin-induced changes in intestinal permeability

In previous open studies, misoprostol and metronidazole reduced nonsteroidal anti-inflammatory drug-induced intestinal permeability changes and inflammation respectively. We assessed the effects of indomethacin treatment (50 mg three times a day) for one week with either coadministered metronidazole (400 mg twice a day, group 1, N = 9) or misoprostol (200 micrograms four times a day, group 2, N = 7) on intestinal permeability to [51Cr]EDTA and mannitol in healthy volunteers, using double-blind, placebo-controlled, randomized techniques. Given alone, neither metronidazole nor misoprostol affected [51Cr]EDTA permeation, whereas indomethacin alone increased it from 1.20 (0.40) [mean percent urinary recovery (SD) groups 1 and 2] to 2.43 (0.72), P < 0.002. Coadministered metronidazole (group 1) prevented this increase [1.10 (0.39) before, 1.55 (0.54) after, P > 0.05], whereas misoprostol (group 2) did not [1.31 (0.51) before, 3.26 (1.10) after, P = 0.005]. No drug regimen altered mannitol permeation. Indomethacin and misoprostol did not affect urinary recovery of intravenously administered probes. The results with metronidazole, if related to its antibacterial effects, support evidence from animal models that bacteria contribute to NSAID-induced intestinal damage. The previously reported reduction of indomethacin-induced increased permeability by misoprostol during a one-day study is not seen when the drugs are used in standard clinical doses for one week.

Glucose and citrate reduce the permeability changes caused by indomethacin in humans

Nonsteroidal anti-inflammatory drug (NSAID)-induced increased intestinal permeability appears to be a prerequisite for NSAID enteropathy. It has been suggested that early metabolic events leading to the permeability changes may involve inhibition of glycolysis and the tricarboxylic acid cycle, in which case the coadministration of glucose and citrate (the substrates for these metabolic pathways) with indomethacin may afford some protection. The present study, using a combined intestinal absorption-permeability test including 3-O-methyl-D-glucose, D-xylose, L-rhamnose, and [51Cr]ethylene-diaminetetraacetic acid (EDTA) as test probes and the differential urine excretion ratio of [51Cr]-EDTA/L-rhamnose, showed that indomethacin (50 + 75 mg) increased intestinal permeability. A formulation of indomethacin containing 15 mg glucose and 15 mg citrate to each milligram of indomethacin did not increase intestinal permeability significantly above baseline values. When given alone with indomethacin, neither glucose nor citrate (45 mg to each milligram of indomethacin) had any protective effects. Pharmokinetic studies showed that the effects of glucose and citrate cannot be explained on the basis of altered drug absorption. These results suggest a new approach to reducing the small intestinal side effects of NSAIDs.

Intestinal permeability in the critically ill

Alterations in intestinal permeability reflect one component of intestinal epithelial barrier function. The objective of this study was to assess the degree of derangement of intestinal permeability in critically ill patients and to investigate the relationship of this to markers of disease severity and sepsis. Sixteen patients admitted to the intensive care unit for a variety of problems were studied with the severity of illness and degree of sepsis recorded daily. A differential sugar absorption test, using lactulose and mannitol as markers, was performed, and in 10 patients this was repeated after an interval of between 4-11 days. The use of the lactulose/mannitol (L/M) ratio corrects for variables unrelated to permeability such as gastric emptying. The L/M ratio was significantly higher in patients (median 0.98) compared to normal controls (median 0.008). The ratios showed no relation to disease severity or sepsis. These results establish that increased intestinal permeability occurs in the general ICU patient but that it is not uniquely related to sepsis. The extent of this abnormality suggests that further study is required to show the various influences on this process.

Importance of local versus systemic effects of non-steroidal anti-inflammatory drugs in increasing small intestinal permeability in man

Increased small intestinal permeability caused by non-steroidal anti-inflammatory drugs (NSAIDs) is probably a prerequisite for NSAID enteropathy, a source of morbidity in patients with rheumatoid arthritis. This increased small intestinal permeability may be a summation of a local effect during drug absorption, a systemic effect after absorption, and a local effect of the drug excreted in bile, but the relative contribution made by these factors is unknown. We assessed the effect of indomethacin and nabumetone on intestinal permeability. The principal active metabolite of nabumetone, 6-methoxy-2-naphthylacetic acid, is not subject to appreciable enterohepatic recirculation. Twelve volunteers were studied before and after one week's ingestion of indomethacin (150 mg/day) and nabumetone (1 g/day) with a combined absorption/permeability test. Neither drug had a significant effect on the permeation of 3-0-methyl-D-glucose, D-xylose, and L-rhamnose. Indomethacin increased the permeation of radioactive 51chromium ethylenediaminetetra-acetic acid (51Cr EDTA) significantly from baseline (mean (SEM) 0.63 (0.09)% v 1.20 (0.14)%, p less than 0.01) but nabumetone did not (0.70 (0.10)% p greater than 0.1). These results were supported by the 51Cr EDTA/L-rhamnose urine excretion ratios, which reflect changes in intestinal permeability. They suggest that NSAIDs increase intestinal permeability during absorption or after biliary excretion and that the systemic effect is of minor importance.