Influence of forskolin and carbachol on intestinal absorption of horseradish peroxidase in the goldfish (Carassius auratus)

Differences in IgY gut absorption in gastric rainbow trout (Oncorhynchus mykiss) and agastric common carp (Cyprinus carpio) assessed in vivo and in vitro

Oral IgY antibodies offer promising potential for passive immunization strategies. To evaluate barriers for successful IgY plasma recovery after oral application in vivo, gastric rainbow trout and agastric common carp were comparatively assessed. A positive control that received a low dose of unspecific IgY antibodies by intraperitoneal injection (0.0076 mg IgY g BW(-1) d(-1); BW=body mass) was compared with an oral administration of 75 and 150 fold in rainbow trout (corresponding to 0.57 and 1.14 mg g BW(-1)) and in carp (0.57 mg g BW(-1)). Dietary antibodies were delivered with the antacid sodium bicarbonate and three different putative uptake enhancers (Tween 20, vitamin E TPGS, sodium deoxycholate). IgY concentrations in the plasma were determined 1d (rainbow trout) or 5d after last feeding (both species). Irrespective of the enhancer used, ELISA revealed IgY absorption after feeding in carp, whereas IgY concentration in rainbow trout remained below the detection threshold. Intraperitoneal injections revealed IgY in plasma of both species. In vitro Ussing chamber experiments with posterior intestine tissue of carp and trout were carried out to determine whether species-specific differences in IgY translocation were due to acidic stomach passage or species-specific differences in transepithelial IgY passage. Significantly higher IgY translocation was measured in carp at high application dosage compared to all other groups, indicating that species-specific differences in IgY uptake after oral administration are not only related to peptic IgY degradation in the stomach, but also likely a result of differences in IgY transcytosis in the posterior intestine.

Ingestion of (n-3) fatty acids augments basal and platelet activating factor-induced permeability to dextran in the rat mesenteric vascular bed

Loss of intestinal barrier function and subsequent edema formation remains a serious clinical problem leading to hypoperfusion, anastomotic leakage, bacterial translocation, and inflammatory mediator liberation. The inflammatory mediator platelet activating factor (PAF) promotes eicosanoid-mediated edema formation and vasoconstriction. Fish oil-derived (n-3) fatty acids (FA) favor the production of less injurious eicosanoids but may also increase intestinal paracellular permeability. We hypothesized that dietary (n-3) FA would ameliorate PAF-induced vasoconstriction and enhance vascular leakage of dextran tracers. Rats were fed either an (n-3) FA-rich diet (EPA-rich diet; 4.0 g/kg EPA, 2.8 g/kg DHA) or a control diet (CON diet; 0.0 g/kg EPA and DHA) for 3 wk. Subsequently, isolated and perfused small intestines were stimulated with PAF and arterial pressure and the translocation of fluid and macromolecules from the vasculature to lumen and lymphatics were analyzed. In intestines of rats fed the EPA-rich diet, intestinal phospholipids contained up to 470% more EPA and DHA at the expense of arachidonic acid (AA). The PAF-induced increase in arterial pressure was not affected by the EPA-rich diet. However, PAF-induced fluid loss from the vascular perfusate was higher in intestines of rats fed the EPA-rich diet. This was accompanied by a greater basal loss of dextran from the vascular perfusate and a higher PAF-induced transfer of dextran from the vasculature to the lumen (P = 0.058) and lymphatics. Our data suggest that augmented intestinal barrier permeability to fluid and macromolecules is a possible side effect of (n-3) FA-rich diet supplementation.

GENETIC AND PHARMACOLOGIC MANIPULATION OF VACUOLAR ATPASE; EFFECTS ON ZYMOGEN ACTIVATION IN PANCREATIC ACINI

Premature activation of inactive digestive enzymes (or zymogens) within the pancreatic acinar cell is an initiating event in acute pancreatitis (AP). We have found that this response depends on the assembly and activation of an ATP-dependent proton pump, the vacuolar ATPase (vATPase). Previously, we have shown that the classic vATPase inhibitors concanamycin and bafilomycin can inhibit zymogen activation induced experimentally by high doses of the cholecystokinin orthologue, cerulein (CER) in isolated acinar cells. Recent studies have questioned the specificity of these inhibitors. In the current study we examine the role of the vATPase in pancreatitis using the newly developed novel vATPase inhibitors lobatomide-B and salicylihalamide-A as well as a genetic approach using siRNA. Both lobatomide-B and salicylihalamide-A inhibited CER stimulated zymogen (trypsinogen and chymotrypsinogen) activation but had no effect on amylase secretion. Lobatomide-B (0.1μM) was more potent, reducing activation to baseline levels. Treatment of cells with siRNA specific for the vATPase E-subunit (V1E) significantly decreased V1E expression. V1E siRNA also significantly decreased chymotrypsinogen activation, but not amylase secretion. These studies confirm a role for the vATPase in zymogen activation and demonstrate that the novel and specific inhibitors lobatomide-B and salicylihalamide-A reduce early pancreatitis responses.

Changes in macromolecular transport appear early in Caco-2 cells infected with a human rotavirus

OBJECTIVE

Rotavirus is a major cause of viral gastroenteritis, but its interaction with intestinal mucosa is poorly understood. The aim of this study was to examine the effect of Wa rotavirus (VP7 serotype 1) on barrier function in confluent Caco-2 cell monolayers. Wa is the most common serotype causing severe diarrhoea in humans. MATERIAL AND METHODS. We examined light and electron microscopic morphology, macromolecular transport, paracellular permeability, electrical parameters, disaccharidases and cytoskeletal structure in Wa- and in control sham-infected cells using a homologous human virus-cell system resembling human infection.

RESULTS

During the first 48 h following Wa infection, there was no evidence of loss of integrity or of cytopathic effect in the monolayer. A significant cytopathic effect was noticed after 48 h. Further studies examined the initial 24-h period during which there was no evidence of significant injury. Apical-to-basolateral transcytosis of the macromolecule horseradish peroxidase (HRP) was selectively inhibited at 4 and 24 h post-infection with Wa. There were no significant changes in basolateral-to-apical transcytosis, endocytosis or in apical-to-apical recycling of HRP after Wa infection. G- and F-actin levels were significantly reduced within an area corresponding to the viroplasm in Wa-infected cells but not elsewhere in the monolayer.

CONCLUSIONS

The early stages of rotavirus infection, before gross epithelial injury, are associated with a selective reduction in the apical uptake and transcytosis of macromolecules. We speculate that this is an epithelial defence mechanism.

Transcytosis of pancreatic bile salt-dependent lipase through human Int407 intestinal cells

In previous studies, we have shown that the bile-salt-dependent-lipase (BSDL), secreted by pancreatic acinar cells and secreted into the duodenal lumen, can be transcytosed through intestinal cells up to the lamina propria. In this study, we used an in vitro system to provide insights into the apical to basolateral transport of BSDL, across the intestinal barrier. The Int407 human epithelial cell line, grown under conditions that optimize polarity, was used as a tight epithelium model. We attempted to delineate uptake mechanisms and the transcytotic pathway followed by this pancreatic enzyme within the intestinal Int407 cells, which do not produce BSDL. When added to the apical reservoir of Transwell-grown Int407 cells, BSDL was shown to first interact with the apical membrane. Further, BSDL forms clusters that are internalized via clathrin-coated pits. Following endocytosis, BSDL is directed to a nocodazole- and colchicin-sensitive multivesicular compartment. Interestingly, this protein transits through the Golgi apparatus, where it was found to colocalize with the KDEL retrieval-receptor. Finally, enzymatically active intact BSDL was released at the basolateral membrane level. This is the first demonstration for an apical-to-basolateral transcytotic pathway of a secreted pancreatic digestive enzyme through polarized intestinal cells.