Mimicking Asymptomatic Infection?

The protozoan parasite Giardia duodenalis is responsible for more than 280 million cases of gastrointestinal complaints (“giardiasis”) every year, worldwide. Infections are acquired orally, mostly via uptake of cysts in contaminated drinking water. After transformation into the trophozoite stage, parasites start to colonize the duodenum and upper jejunum where they attach to the intestinal epithelium and replicate vegetatively. Outcome of Giardia infections vary between individuals, from self-limiting to chronic, and asymptomatic to severely symptomatic infection, with unspecific gastrointestinal complaints. One proposed mechanism for pathogenesis is the breakdown of intestinal barrier function. This has been studied by analyzing trans-epithelial electric resistances (TEER) or by indicators of epithelial permeability using labeled sugar compounds in in vitro cell culture systems, mouse models or human biopsies and epidemiological studies. Here, we discuss the results obtained mainly with epithelial cell models to highlight contradictory findings. We relate published studies to our own findings that suggest a lack of barrier compromising activities of recent G. duodenalis isolates of assemblage A, B, and E in a Caco-2 model system. We propose that this epithelial cell model be viewed as mimicking asymptomatic infection. This view will likely lead to a more informative use of the model if emphasis is shifted from aiming to identify Giardia virulence factors to defining non- parasite factors that arguably appear to be more decisive for disease

Gastrointestinal Tract As Entry Route for Hantavirus Infection

Background: Hantaviruses are zoonotic agents that cause hemorrhagic fevers and are thought to be transmitted to humans by exposure to aerosolized excreta of infected rodents. Puumala virus (PUUV) is the predominant endemic hantavirus in Europe. A large proportion of PUUV-infected patients suffer from gastrointestinal symptoms of unclear origin. In this study we demonstrate that PUUV infection can occur via the alimentary tract. Methods: We investigated susceptibility of the human small intestinal epithelium for PUUV infection and analyzed the resistance of virions to gastric juice. As model for intestinal virus translocation we performed infection experiments with human intestinal Caco-2 monolayers. In animal experiments we infected Syrian hamsters with PUUV via the intragastric route and tested seroconversion and protective immunity against subsequent Andes virus challenge. Results: PUUV retained infectivity in gastric juice at pH >3. The virus invaded Caco-2 monolayers in association with endosomal antigen EEA1, followed by virus replication and loss of epithelial barrier function with basolateral virus occurrence. Cellular disturbance and depletion of the tight junction protein ZO-1 appeared after prolonged infection, leading to paracellular leakage (leak flux diarrhea). Moreover, animal experiments led to dose-dependent seroconversion and protection against lethal Andes virus challenge. Conclusions: We provide evidence that hantavirus can infect the organism via the alimentary tract and suggest a novel aspect of hantavirus infection and pathogenesis. Significance: Hantaviruses are zoonotic pathogens causing severe hemorrhagic fevers worldwide. They are transmitted to humans by small mammals. To date, these viruses were thought to infect exclusively through the airborne route by inhalation of aerosols from infectious animal droppings or by rodent bites. In our work we could show that the alimentary tract is an alternative path of infection for hantaviruses, meaning a new association of virus and disease. These findings have impact on current textbook knowledge and bring many implications for hantavirus epidemiology and outbreak prevention measures

Effect of chronic Giardia lamblia infection on epithelial transport and barrier function in human duodenum

BACKGROUND: Giardia lamblia causes infection of the small intestine, which leads to malabsorption and chronic diarrhoea. AIM: To characterise the inherent pathomechanisms of G lamblia infection. METHODS: Duodenal biopsy specimens from 13 patients with chronic giardiasis and from controls were obtained endoscopically. Short‐circuit current (I(SC)) and mannitol fluxes were measured in miniaturised Ussing chambers. Epithelial and subepithelial resistances were determined by impedance spectroscopy. Mucosal morphometry was performed and tight junction proteins were characterised by immunoblotting. Apoptotic ratio was determined by terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick‐end labelling staining. RESULTS: In giardiasis, mucosal surface area per unit serosa area was decreased to 75% (3%) of control, as a result of which epithelial resistance should increase. Instead, epithelial resistance of giardiasis biopsy specimens was decreased (19 (2) vs 25 (2) Ω cm(2); p<0.05) whereas mannitol flux was not significantly altered (140 (27) vs 105 (16) nmol/h/cm(2)). As structural correlate, reduced claudin 1 expression and increased epithelial apoptosis were detected. Furthermore, basal I(SC) increased from 191 (20) in control to 261 (12) µA/h/cm(2) in giardiasis. The bumetanide‐sensitive portion of I(SC) in giardiasis was also increased (51 (5) vs 20 (9) µA/h/cm(2) in control; p<0.05). Finally, phlorizin‐sensitive Na(+)–glucose symport was reduced in patients with giardiasis (121 (9) vs 83 (14) µA/h/cm(2)). CONCLUSIONS: G lamblia infection causes epithelial barrier dysfunction owing to down regulation of the tight junction protein claudin 1 and increased epithelial apoptoses. Na(+)‐dependent d‐glucose absorption is impaired and active electrogenic anion secretion is activated. Thus, the mechanisms of diarrhoea in human chronic giardiasis comprise leak flux, malabsorptive and secretory components

Dissection of Barrier Dysfunction in Organoid-Derived Human Intestinal Epithelia Induced by Giardia duodenalis

BACKGROUND & AIMS: The protozoa Giardia duodenalis is a major cause of gastrointestinal illness worldwide, but un- derlying pathophysiological mechanisms remain obscure, partly due to the absence of adequate cellular models. We aimed at overcoming these limitations and recapitulating the authentic series of pathogenic events in the primary human duodenal tissue by using the human organoid sys- tem. METHODS: We established a compartmentalized cellular transwell system with electrophysiological and barrier properties akin to duodenal mucosa and dissected the events leading to G. duodenalis-induced barrier break- down by functional analysis of transcriptional, electro- physiological, and tight junction components. RESULTS: Organoid-derived cell layers of different donors showed a time- and parasite load-dependent leak flux indicated by collapse of the epithelial barrier upon G. duodenalis infection. Gene set enrichment analysis suggested major expression changes, including gene sets contributing to ion transport and tight junction structure. Solute carrier family 12 member 2 and cystic fibrosis transmembrane conductance regulator- dependent chloride secretion was reduced early after infec- tion, while changes in the tight junction composition, locali- zation, and structural organization occurred later as revealed by immunofluorescence analysis and freeze fracture electron microscopy. Functionally, barrier loss was linked to the adenosine 30,50-cyclic monophosphate (cAMP)/protein kinase A-cAMP response element-binding protein signaling pathway. CONCLUSIONS: Data suggest a previously unknown sequence of events culminating in intestinal barrier dysfunction upon G. duodenalis infection during which al- terations of cellular ion transport were followed by breakdown of the tight junctional complex and loss of epithelial integrity, events involving a cAMP/protein kinase A-cAMP response element-binding protein mechanism. These findings and the newly established organoid-derived model to study G. duodenalis infection may help to explore new options for intervening with disease and infection, in particular relevant for chronic cases of giardiasis.Peer Reviewe

ENaC Dysregulation Through Activation of MEK1/2 Contributes to Impaired Na+ Absorption in Lymphocytic Colitis

Background: Lymphocytic colitis (LC) causes watery diarrhea. We aimed to identify mechanisms of altered Na+ absorption and regulatory inputs in patients with LC by examining the epithelial Na+ channel (ENaC) function as the predominant Na+ transport system in human distal colon. Methods: Epithelial Na+ channel function and regulation was analyzed in biopsies from sigmoid colon of patients with LC and in rat distal colon in Ussing chambers. ENaC-subunit expression was measured by real-time PCR and RNA sequencing. Correction factors for subepithelial resistance contributions were determined by impedance spectroscopy. Upstream regulators in LC were determined by RNA sequencing. Results: Epithelial Na+ channel-mediated electrogenic Na+ transport was inhibited despite aldosterone stimulation in human sigmoid colon of patients with LC. The increase in gamma-ENaC mRNA expression in response to aldosterone was MEK1/2-dependently reduced in LC, since it could be restored toward normal by MEK1/2 inhibition through U0126. Parallel experiments for identification of signaling in rat distal colon established MEK1/2 to be activated by a cytokine cocktail of TNF alpha, IFN gamma, and IL-15, which were identified as the most important regulators in the upstream regulator analysis in LC. Conclusions: In the sigmoid colon of patients with LC, the key effector cytokines TNF alpha, IFN gamma, and IL-15 inhibited gamma-ENaC upregulation in response to aldosterone through a MEK1/2-mediated pathway. This prevents ENaC to reach its maximum transport capacity and results in Na+ malabsorption which contributes to diarrhea

Serum bile acids and leptin interact with glucose metabolism in patients with liver cirrhosis

<p>Background & aims: We investigated possible involvements of bile acids (BA) and leptin in hepatogenous insulin resistance being present in up to 90% of cirrhotic patients.</p><p>Methods: Blood was analysed in 10 cirrhotic patients (8m/2f, 48 +/- 10.4 yrs) and 10 controls (8m/2f, 43 +/- 9.3 yrs) after oral nutrition and during 1 h of parenteral feeding. In patients, leptin was additionally analysed from mesenteric and arterial blood.</p><p>Results: Cirrhosis patients showed typical signs of hepatogenous insulin resistance (hyperinsulinaemia, normoglycaemia, hyperglucagonaemia). Both fasting BA (r = .714, p = 0.047) and fasting leptin (r = .867, p = 0.001) correlated to HOMA and predicted insulin response after oral feeding (R(2)adj = .783, p = 0.002). But during parenteral nutrition only leptin predicted insulin response (p = 0.005). The prandial glucose response was negatively correlated to the BA increase after oral nutrition (r = -.733, p = 0.028) and to the change in leptin during parenteral nutrition (r = -.738, p = 0.037) pointing towards a nutritional route-dependent positive impact on glucose tolerance of both substances. Prandial glucagon response was correlated to BA under both feeding conditions (p</p><p>Conclusion: Our results suggest a substantial involvement of BA and leptin by improving postprandial glucose tolerance related to liver cirrhosis. (C) 2012 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.</p>

Epithelial barrier dysfunction in lymphocytic colitis through cytokine-dependent internalization of claudin-5 and-8

Background Watery diarrhea is the cardinal symptom of lymphocytic colitis (LC). We have previously shown that colonic Na malabsorption is one of the major pathologic alterations of LC and found evidence for an epithelial barrier defect. On these grounds, this study aimed to identify the inherent mechanisms of this epithelial barrier dysfunction and its regulatory features. Methods Epithelial resistance (R-epi) was determined by one-path impedance spectroscopy and H-3-mannitol fluxes were performed on biopsies from sigmoid colon in miniaturized Ussing chambers. Tight junction proteins were analyzed by Western blot and confocal microscopy. Inflammatory signaling was characterized in HT-29/B6 cells. Apoptosis and mucosal surface parameters were quantified morphologically. Results Repi was reduced to 53% and H-3-mannitol fluxes increased 1.7-fold in LC due to lower expression of claudin-4, -5, and -8 and altered subcellular claudin-5 and -8 distributions off the tight junction. TNF alpha and IFN gamma could mimic subcellular redistribution in HT-29/B6 cells, a process which was independent on MLCK activation. Epithelial apoptosis did not contribute to barrier dysfunction in LC and mucosal surface area was unchanged. Conclusions Epithelial barrier dysfunction in LC occurs through downregulation of claudin-4, -5, and -8, and redistribution of claudin-5 and -8 off the tight junction, which contributes to diarrhea by a leak-flux mechanism. The key effector cytokines TNF alpha and IFNc gamma turned out to be the trigger for redistribution of claudin-5 and -8. Thus, alongside sodium malabsorption, leak-flux is yet another important diarrheal mechanism in LC