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Background & Aims: The gut microbiota affects intestinal permeability and mucosal mast cells (MMCs) responses. Activation of MMCs has been associated with absorption of dietary fat. We investigated whether the gut microbiota contributes to the fat-induced activation of MMCs in rats, and how antibiotics might affect this process., Methods: Adult male Sprague-Dawley rats were given streptomycin and penicillin for 4 days (n = 6-8) to reduce the abundance of their gut flora, or normal drinking water (controls, n = 6-8). They underwent lymph fistula surgery and after an overnight recovery were given an intraduodenal bolus of intralipid. We collected intestinal tissues and lymph fluid and assessed activation of MMCs, intestinal permeability, and fat transport parameters., Results: Compared with controls, intestinal lymph from rats given antibiotics had reduced levels of mucosal mast cell protease II (produced by MMCs) and decreased activity of diamine oxidase (produced by enterocytes) (P < .05). Rats given antibiotics had reduced intestinal permeability in response to dietary lipid compared with controls (P < .01). Unexpectedly, antibiotics also reduced lymphatic transport of triacylglycerol and phospholipid (P < .01), concomitant with decreased levels of mucosal apolipoproteins B, A-I, and A-IV (P < .01). No differences were found in intestinal motility or luminal pancreatic lipase activity between rats given antibiotics and controls. These effects were not seen with an acute dose of antibiotics or 4 weeks after the antibiotic regimen ended., Conclusions: The intestinal microbiota appears to activate MMCs after the ingestion of fat in rats; this contributes to fat-induced intestinal permeability. We found that the gut microbiome promotes absorption of lipid, probably by intestinal production of apolipoproteins and secretion of chylomicrons., (Copyright © 2016 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Some studies have indicated that dietary cholesterol has a role in the progression of liver fibrosis. We investigated the mechanisms by which dietary cholesterol might contribute to hepatic fibrogenesis., Methods: C57BL/6 mice were fed a high-cholesterol diet or a control diet for 4 weeks; liver fibrosis then was induced by bile-duct ligation or carbon tetrachloride administration. Hepatic stellate cells (HSCs) were isolated from mice fed high-cholesterol diets or from Niemann-Pick type C1-deficient mice, which accumulate intracellular free cholesterol., Results: After bile-duct ligation or carbon tetrachloride administration, mice fed high-cholesterol diets had significant increases in liver fibrosis and activation of HSCs compared with mice fed control diets. There were no significant differences in the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation, between mice fed high-cholesterol or control diets. Levels of free cholesterol were much higher in HSCs from mice fed high-cholesterol diets than those fed control diets. In cultured HSCs, accumulation of free cholesterol in HSCs increased levels of Toll-like receptor 4 (TLR4), leading to down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor (a pseudoreceptor for transforming growth factor [TGF]β); the HSCs became sensitized to TGFβ-induced activation. Liver fibrosis was not aggravated by the high-cholesterol diet in C3H/HeJ mice, which express a mutant form of TLR4; HSCs that express mutant TLR4 were not activated by accumulation of free cholesterol., Conclusions: Dietary cholesterol aggravates liver fibrosis because free cholesterol accumulates in HSCs, leading to increased TLR4 signaling, down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor, and sensitization of HSC to TGFβ. This pathway might be targeted by antifibrotic therapies., (Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Although the recirculation of lymphocytes through the intestinal mucosa is important for the specific immune defense, the homing of lamina propria lymphocytes (LPLs) has not been clearly understood. The aim of this study is to compare, under an intravital microscope, the dynamic process of lymphocyte-endothelium recognition and binding in the murine intestinal mucosa of T lymphocytes from the lamina propria of intestine to that of T lymphocytes from the spleen., Methods: LPLs isolated from nonlymphoid areas of the small intestine and spleen (SPL) were fluorescence-labeled and injected into a jugular vein of recipient mice. Microvessels of the villus mucosa and ileal Peyer's patches were observed under an intravital fluorescence microscope, and the effects of anti-adhesion-molecule antibodies on lymphocyte-endothelial interaction were investigated., Results: LPLs accumulated abundantly in the microvessels of villus tips but not in the submucosal venules or postcapillary venules of Peyer's patches, where SPLs migrated selectively. The accumulation of LPLs in the villus tips was almost completely inhibited by anti-beta7-integrin and was significantly inhibited by anti-mucosal addressin cell-adhesion molecule 1 (MAdCAM-1) and anti-alpha4-integrin. Significant MAdCAM-1 expression was observed in the microvessels of the villus mucosa. Some SPLs adhered to the nonlymphoid mucosa, but most soon detached., Conclusions: It was shown in vivo for the first time that T lymphocytes from the lamina propria but not from the spleen adhere selectively, mostly via alpha4beta7 and MAdCAM-1, to the microvessels of villus tips of the intestine, but not to the postcapillary venules of Peyer's patches.

Background & Aims: The basic mechanisms of food allergies are still unknown. The aims of this study were to investigate whether endothelins (ETs) in the intestinal mucosa are involved in the pathogenesis of intestinal anaphylaxis., Methods: Sprague-Dawley rats were sensitized to chicken egg albumin (EA) by intraperitoneal injection. Fourteen days after sensitization, EA was administered in the jejunal segments to induce intestinal anaphylaxis. Net water outflux and histamine release into loops and serum concentrations of rat mast cell protease II (RMCP-II) were determined. ET-1 and ET-3 concentrations in the jejunal mucosa were determined, and expression of the corresponding messenger RNAs was examined by competitive polymerase chain reaction., Results: In sensitized animals, challenge with intraluminal antigen caused a significant increase in net water outflux and histamine release together with an elevation of serum RMCP-II concentrations. Mucosal concentrations of ET-1 and ET-3 and expression of their messenger RNAs were significantly increased in sensitized animals after EA challenge. Treatment with an ETA-receptor antagonist, but not an ETB-receptor antagonist, attenuated the increase in net water outflux, histamine release, and serum RMCP-II concentrations in rats with EA-induced intestinal anaphylaxis., Conclusions: Release of ETs in the intestinal mucosa increased in sensitized animals after EA challenge. ETs may play a significant role in the development of intestinal anaphylaxis via an ETA receptor.