An experimental model for measuring intestinal permeability

Elemental diet and IV-TPN-induced bacterial translocation is associated with loss of intestinal mucosal barrier function against bacteria

OBJECTIVE

The goal of the current study was to directly assess the role of loss of mucosal barrier function in nutritionally induced bacterial translocation.

BACKGROUND

Parenteral and certain elemental enteral diets have been shown to promote bacterial translocation. The mechanisms underlying this observation, especially the question of whether nutritionally induced bacterial translocation is primarily related to loss of intestinal barrier function, versus an impaired immune system, remain to be fully elucidated.

METHODS

Bacterial translocation was measured in vivo, ileal mucosal membranes were harvested, and their electrophysiologic properties and barrier function were measured ex vivo in the Ussing chamber system 7 days after receiving total parenteral nutrition solution parenterally (IV-TPN) or enterally (elemental diet). Chow-fed rats served as control subjects.

RESULTS

The incidence of bacterial translocation was significantly increased both to the mesenteric lymph nodes in vivo and across the in vitro Ussing chamber-mounted ileal mucosal membranes of the elemental diet-fed and IV-TPN-fed rats. The magnitude of Escherichia coli and phenol red transmucosal passage in the Ussing chamber was significantly higher in the IV-TPN-fed rats than in the elemental diet-fed or chow-fed animals. The potential differences across the ileal membrane were similar between the three groups at all time points. However, the specific resistances of the ileal membranes of the IV-TPN and elemental diet groups were significantly less than the chow-fed animals, indicating increased membrane permeability.

CONCLUSIONS

Loss of intestinal barrier function plays a major role in nutritionally induced bacterial translocation, and the loss of mucosal barrier function to both E. coli and phenol red appeared greater in the IV-TPN than the elemental diet-fed rats.

On the absorption of alendronate in rats

Alendronate is an antiosteolytic agent under investigation for the treatment of a number of bone disorders. Since the compound is a zwitterion with five pKa values and is completely ionized in the intestine at the physiological pH, absorption is poor; less than 1% of an oral dose is available systemically in rats. In the present studies, absorption was found to be predominantly in the upper part of the small intestine. Administration of buffered solutions of alendronate (pH 2-11) did not improve absorption. Whereas food markedly impaired the absorption of alendronate, EDTA enhanced absorption in a dose-dependent manner. Pretreatment of rats with ulcerogenic agents, mepirizole, acetylsalicylic acid, or indomethacin, resulted in a 3-7-fold increase in the oral absorption of alendronate. The absorption of phenol red, added as an indicator of intestinal tissue damage, was also increased in rats with experimental peptic ulcers. The enhanced absorption of alendronate observed in rats with experimental peptic ulcers was attributed to the alteration of the integrity of the intestinal membrane.

Intestinal permeability during chemotherapy for childhood tumours

The intestinal permeability to mannitol and lactulose was measured in 29 children receiving treatment for solid tumours. At the time of study they had no gastrointestinal symptoms and appeared clinically well. However, there was a significant reduction in the absorption of mannitol when compared to normal children. This small bowel dysfunction may result in malabsorption of nutrients and drugs. There was a significant correlation between decreased mannitol absorption and low nutritional status.

Mechanisms of corneal drug penetration. I: In vivo and in vitro kinetics

Corneal penetration studies were conducted in unanesthetized albino rabbits using various organic compounds representing both polar and nonpolar species. Very low molecular weight compounds demonstrate rapid uptake into the aqueous humor despite the lipid-like barrier imposed by the corneal epithelium. Evidence that these compounds may have access to a diffusional channel for corneal transport is presented. In vitro permeability studies were also conducted in an effort to quantitate the corneal diffusion of compounds covering a range of molecular weights and partition coefficients; the results corresponded well with the results of in vivo experiments. Calculations of energies of activation, taken from Arrhenius plots, indicate that the diffusion of drug across the cornea may be by two different mechanisms that depend on the physical-chemical characteristics of the perfusant. One mechanism appears similar to drug movement in an aqueous environment and is characterized by an activation energy similar to that for diffusion in water. The other relates to the expected partitioning of a compound across cellular membranes represented by a relatively high activation energy for diffusion. For hyrdophilic compounds, the epithelium appears to be rate limiting to drug movement, whereas for hydrophobic compounds, the stroma is rate limiting. In the presence of calcium-chelating agents, glycerol demonstrated an increase in corneal penetration in vivo. This effect appears to be reversible at specific concentrations of chelator. In contrast, divalent cations reduced corneal penetration of glycerol. The known calcium chelator EDTA was shown to penetrate the cornea, conjunctiva, and iris/ciliary body from a topically applied dose. The implications of this observation pertain to toxicity effects when EDTA is incorporated into ocular drug products for stability purposes, or novel stratagems for improving ocular bioavailability of topically applied drugs are employed. The addition of calcium-chelating agents to in vivo mounted corneas demonstrated increases in permeability of the cornea to glycerol which were directly related to the concentration of chelating agent used. These results paralleled the findings of similar in vivo studies. The results of these studies are consistent with a currently proposed 'pore' model for the penetration of drugs through the cornea which demonstrates both a partition coefficient and molecular weight dependency on the permeability of the cornea to transported compounds.

Changes in intestinal permeability and epithelial differentiation during inflammation in the rat

We examined changes in gut permeability in a controlled model of inflammation produced in rats after infection with the nematode parasite, Nippostrongylus brasiliensis. The probe, 51Cr-EDTA, was injected into ligated loops of jejunum in vivo and recovery of radioactivity was measured in urine, kidney, and intact loop at five hours. Urinary recovery was significantly increased during the early (day 7) and acute (day 10) stages of the infection compared with values in control rats but subsequently returned to normal. Urinary clearance of the probe after iv injection was unaltered during infection. Villus atrophy occurred only at the stage, whereas crypt hyperplasia was evident at both the early and acute stages. The terminal ileum appeared normal and showed normal permeability when compared with controls. We conclude that permeability changes are local to the site of inflammation, are reversible after healing and may be related to an increase in the proportion of relatively undifferentiated epithelium.

Intestinal permeability in patients with coeliac disease and dermatitis herpetiformis

Intestinal permeability was investigated in patients with coeliac disease and dermatitis herpetiformis by a 51Chromium-labelled ethylenediaminetetraacetate (51Cr-EDTA) absorption test and the results correlated with histomorphometric analysis and intraepithelial lymphocyte counts of jejunal biopsies. The mean (+/- SD) 24 hour urine excretion of 51Cr-EDTA in 34 healthy volunteers was 1.9 +/- 0.5% of the orally administered test dose. Patients with untreated coeliac disease (19) or untreated dermatitis herpetiformis (five) excreted significantly more 51Cr-EDTA than controls (5.9 +/- 2.7% and 4.6 +/- 2.1%, respectively, p less than 0.001) and all were outside the normal range of 1.0-2.6%. Patients with coeliac disease (42) treated for 6 months-23 years (mean 5 years) and patients with dermatitis herpetiformis (11) treated for 6 months-8 years (mean 3 years) excreted significantly more 51Cr-EDTA than controls, 4.2 +/- 2.4% p less than 0.0001 and 3.0 +/- 0.9% p less than 0.003 respectively. Eleven of 14 (79%) treated patients with coeliac disease with an entirely normal jejunal mucosae demonstrated abnormal intestinal permeability. Intestinal permeability did not correlate significantly with either the mucosal height/crypt depth ratio or intraepithelial lymphocyte counts in jejunal biopsies from patients with untreated or treated coeliac disease. The demonstration of a persistent increase in intestinal permeability in patients with both coeliac disease and dermatitis herpetiformis may suggest a common pathogenetic mechanism in both disorders. It is postulated that altered permeability may facilitate the entry of gluten or a fraction thereof into the lamina propria where it causes a cascade of immunological events.

Intestinal permeability to 51Cr-EDTA in rats with experimentally induced enteropathy

Intestinal permeability has been investigated in the normal rat by measuring the five hour urine excretion of 51Cr-EDTA after intragastric administration. Twelve control animals excreted 2.06% +/- 0.22 (mean +/- SE) of the administered dose. Prolonged intestinal transit times with atropine had no significant effect on the apparent permeability with a urine excretion 2.31% +/- 0.36. The concomitant administration of a hypertonic, but rapidly absorbed glycerol solution, was accompanied by increased urinary excretion (3.05% +/- 0.33) while the administration of a poorly absorbed sugar, lactulose, significantly decreased the apparent permeability (urine excretion 0.61% +/- 0.14) showing that passive intestinal permeability estimations are affected by test dose composition. Enteropathy was induced by ethanol, cetrimide, or methotrexate and each was associated with increased permeability, with urine excretions of 4.19% +/- 0.47, 4.20% +/- 0.66 and 3.97% +/- 0.49 respectively. It is thus suggested that the normal rat mucosa is maximally resistant to the absorption of foreign compounds such as 51Cr-EDTA and intestinal damage will disrupt this barrier.