Impairment of the intestinal barrier by ethanol involves enteric microflora and mast cell activation in rodents

Abstract

Alcohol hepatic toxicity in heavy drinkers is associated with high endotoxin blood levels and increased intestinal permeability. Because endotoxins can cross damaged mucosa, we investigated the mechanisms through which ethanol impairs the colonic epithelium of rats submitted to acute alcohol intake. Colonic permeability to (51)Cr-ethylenediamintetraacetic acid was increased 24 hours after 3.0 g/kg ethanol intake (3.2 +/- 0.2% versus 2.2 +/- 0.2%) and was associated with significant endotoxemia. Antibiotics and doxantrazole (a mast cell membrane stabilizer) significantly inhibited the effect of ethanol. Two hours after intake, plasma concentrations of ethanol were twofold higher in antibiotic-treated rats than in controls (155.8 +/- 9.3 mg/dl versus 75.7 +/- 7.6 mg/dl, P < 0.001). Lumenal concentrations of acetaldehyde were markedly increased after ethanol intake (132.6 +/- 31.6 micromol/L versus 20.8 +/- 1.4 micromol/L, P < 0.05) and antibiotics diminished this increase (86.2 +/- 10.9 micromol/L). In colonic samples mounted in Ussing chambers, acetaldehyde but not ethanol increased dextran flux across the mucosa by 54%. Doxantrazole inhibited the effect of acetaldehyde. This study demonstrates that an acute and moderate ethanol intake alters the epithelial barrier through ethanol oxidation into acetaldehyde by the colonic microflora and downstream mast cell activation. Such alterations that remain for longer periods could result in excessive endotoxin passage, which could explain the subsequent endotoxemia frequently observed in patients with alcoholic liver disease.

Figure 1

Intestinal paracellular permeability to ⁵¹Cr-EDTA of rats receiving by gavage: ethanol (black bars), isocaloric amounts of dextrose (white bars), or water (gray bar). Data (means ± SEM) are expressed as the percentage of total radioactivity recovered in urine for 24 hours after intake. *P < 0.05.

Figure 2

Effect of antibiotics (ATB) on intestinal paracellular permeability to ⁵¹Cr-EDTA of rats receiving by gavage: 3.0 g/kg ethanol, an isocaloric amount of dextrose. Data (means ± SEM) are expressed as the percentage of total radioactivity recovered in urine for 24 hours after intake. **P < 0.01.

Figure 3

Blood ethanol concentrations measured 2 hours after a 3.0 g/kg ethanol intake in conventional and germ-free C3H/He mice, and in Sprague-Dawley rats pretreated or not with antibiotics (ATB). Data (means ± SEM) are expressed as mg/dl. ***P < 0.001.

Figure 4

Portal blood endotoxin concentration measured 90 minutes after a 3.0 g/kg ethanol intake, pretreated or not with antibiotics. Data (means ± SEM) are expressed in IU/L. **P < 0.01.

Figure 5

Lumenal acetaldehyde concentration in colonic contents of rats receiving 3.0 g/kg ethanol or an isocaloric amount of dextrose, and pretreated or not with antibiotics for 12 days. Data are expressed as μmol/L (median ± range). ns, not significant.

Figure 6

Effect of the mast cell membrane stabilizer doxantrazole (hatched bars) on intestinal paracellular permeability to ⁵¹Cr-EDTA of rats receiving by gavage ethanol (black bars) or isocaloric amounts of dextrose (white bars). *P < 0.05 and ***P < 0.001 versus dextrose-treated group; ^#P < 0.05 versus ethanol-treated group.

Figure 7

Dose-dependent effect of acetaldehyde on the dextran flux across the epithelium of rat colonic strips mounted in Ussing chambers. Acetaldehyde was added in the mucosal compartment of the chamber. Results (means ± SEM) are expressed as nmol of fluorescein isothiocyanate-dextran crossing 1 cm² of epithelium in 1 hour (nmol·h⁻¹·cm⁻²).