Evaluation of an in vitro experimental platform of human polarized intestinal epithelial monolayers for the hazard assessment of insecticidal proteins

Previous work demonstrated the utility of using human-derived intestinal epithelial cell (IEC) lines cultured as polarized monolayers on Transwell® filters to differentiate between hazardous and non-hazardous proteins. The current study seeks to further resolve appropriate concentrations for evaluating proteins of unknown hazard potential using the IEC experimental platform and leverages these parameters for evaluating the potential toxicity of insecticidal proteins characteristic of those expressed in genetically modified (GM) agricultural biotechnology crops. To establish optimal test protein concentrations, effects of several known hazardous (C. perfringens epsilon toxin, Listeriolysin O, Phaseolus vulgaris erythroagglutinin, E. coli Shiga toxin 1, C. difficile Toxin B and wheat germ agglutinin) and non-hazardous (Ara-h2, β-lactoglobulin, fibronectin and Rubisco) proteins on IEC barrier integrity and cell viability were evaluated at concentration ranges. Two insecticidal proteins (AfIP-1A and AfIP-1B) were evaluated for effects in the IEC assay, a seven-day insecticidal bioassay, and assessed in a high-dose 14-day acute oral toxicity study in mice. The results obtained from the human in vitro IEC assay were consistent with results obtained from an in vivo acute oral toxicity study, both demonstrating that the combination of AfIP-1A and AfIP-1B do not exhibit any identifiable harmful impacts on mammalian cells.

STAT3 mutation-associated airway epithelial defects in Job syndrome

BACKGROUND

Job syndrome is a disease of autosomal dominant hyper-IgE syndrome (AD-HIES). Patients harboring STAT3 mutation are particularly prone to airway remodeling and airway infections.

OBJECTIVES

Airway epithelial cells play a central role as the first line of defense against pathogenic infection and express high levels of STAT3. This study thus interrogates how AD-HIES STAT3 mutations impact the physiological functions of airway epithelial cells.

METHODS

This study created human airway basal cells expressing 4 common AD-HIES STAT3 mutants (R382W, V463del, V637M, and Y657S). In addition, primary airway epithelial cells were isolated from a patient with Job syndrome who was harboring a STAT3-S560del mutation and from mice harboring a STAT3-V463del mutation. Cell proliferation, differentiation, barrier function, bacterial elimination, and innate immune responses to pathogenic infection were quantitatively analyzed.

RESULTS

STAT3 mutations reduce STAT3 protein phosphorylation, nuclear translocation, transcription activity, and protein stability in airway basal cells. As a consequence, STAT3-mutated airway basal cells give rise to airway epithelial cells with abnormal cellular composition and loss of coordinated mucociliary clearance. Notably, AD-HIES STAT3 airway epithelial cells are defective in bacterial killing and fail to initiate vigorous proinflammatory responses and neutrophil transepithelial migration in response to an experimental model of Pseudomonas aeruginosa infection.

CONCLUSIONS

AD-HIES STAT3 mutations confer numerous abnormalities to airway epithelial cells in cell differentiation and host innate immunity, emphasizing their involvement in the pathogenesis of lung complications in Job syndrome. Therefore, therapies must address the epithelial defects as well as the previously noted immune cell defects to alleviate chronic infections in patients with Job syndrome.

Natural infection of white grubs (Coleoptera: Scarabaeidae) with entomopathogenic nematodes in the KwaZulu-Natal province of South Africa

White grubs are root feeding larvae of beetles (Coleoptera: Scarabaeidae) that are sporadic pests in agriculture and can lead to economic damage. The grubs feed on the roots of plants, while the adult beetle can bore into underground stems, as well as cause defoliation of plants. Sporadic incidence of larvae with symptoms of nematode infections were detected in wattle and sugarcane plantations in the KwaZulu-Natal province of South Africa. The larvae with infection symptoms were isolated, washed, and put on water traps to collect infective juveniles of possible nematode infections. Three species of entomopathogenic nematodes (EPNs) were isolated from the white grub larvae. These included Steinernema bertusi isolated from Maladera sp. 4., Oscheius myriophila from Maladera sp. 4 and Schizonchya affinis, and Steinernema fabii isolated from Maladera sp. 4., Pegylis sommeri, and S. affinis. Of these S. fabii was the most common species in the sample (87%). This is the first report of such a high diversity of locally occurring EPNs found naturally associated with white grub species in this region of South Africa.

Human Airway Basal Cells Undergo Reversible Squamous Differentiation and Reshape Innate Immunity

Histological and lineage immunofluorescence examination revealed that healthy conducting airways of humans and animals harbor sporadic poorly differentiated epithelial patches mostly in the dorsal noncartilage regions that remarkably manifest squamous differentiation. In vitro analysis demonstrated that this squamous phenotype is not due to intrinsic functional change in underlying airway basal cells. Rather, it is a reversible physiological response to persistent Wnt signaling stimulation during de novo differentiation. Squamous epithelial cells have elevated gene signatures of glucose uptake and cellular glycolysis. Inhibition of glycolysis or a decrease in glucose availability suppresses Wnt-induced squamous epithelial differentiation. Compared with pseudostratified airway epithelial cells, a cascade of mucosal protective functions is impaired in squamous epithelial cells, featuring increased epithelial permeability, spontaneous epithelial unjamming, and enhanced inflammatory responses. Our study raises the possibility that the squamous differentiation naturally occurring in healthy airways identified herein may represent "vulnerable spots" within the airway mucosa that are sensitive to damage and inflammation when confronted by infection or injury. Squamous metaplasia and hyperplasia are hallmarks of many airway diseases, thereby expanding these areas of vulnerability with potential pathological consequences. Thus, investigation of physiological and reversible squamous differentiation from healthy airway basal cells may provide critical knowledge to understand pathogenic squamous remodeling, which is often nonreversible, progressive, and hyperinflammatory.

Alginates for Protection Against Pepsin-Acid Induced Aerodigestive Epithelial Barrier Disruption

OBJECTIVE

Gastroesophageal reflux disease (GERD) and laryngopharyngeal reflux (LPR) are chronic conditions caused by backflow of gastric and duodenal contents into the esophagus and proximal aerodigestive tract, respectively. Mucosal barrier dysfunction resultant from the synergistic actions of chemical injury and the mucosal inflammatory response during reflux contributes to symptom perception. Alginates effectively treat symptoms of mild to moderate GERD and have recently shown benefit for LPR. In addition to forming a "raft" over gastric contents to reduce acidic reflux episodes, alginates have been found to bind the esophageal mucosa thereby preserving functional barrier integrity measured by transepithelial electrical resistance. The aim of this study was to further examine the topical protective capacity of alginate-based Gaviscon Advance (GA) and Double Action (GDA) against pepsin-acid mediated aerodigestive epithelial barrier dysfunction in vitro.

STUDY DESIGN

Translational.

METHODS

Immortalized human esophageal and vocal cord epithelial cells cultured in transwells were pretreated with liquid formula GA, GDA, matched viscous placebo solution, or saline (control), then treated for 1 h with saline, acid (pH 3-6) or pepsin (0.1-1 mg/ml) at pH 3-6. Endpoint measure was taken of horseradish peroxidase (HRP) allowed to diffuse across monolayers for 2 h.

RESULTS

Pepsin (0.1-1 mg/ml) at pH 3-6 increased HRP flux through cultures pretreated with saline or placebo (p < 0.05); acid alone did not. GA and GDA prevented barrier dysfunction.

CONCLUSIONS

GA and GDA preserved epithelial barrier function during pepsin-acid insult better than placebo suggesting that protection was due to alginate. These data support topical protection as a therapeutic approach to GERD and LPR. Laryngoscope, 132:2327-2334, 2022.

Untapped Potential: Therapeutically Targeting Eicosanoids and Endocannabinoids in the Lung

Inflammation of the airway involves the recruitment of highly active immune cells to combat and clear microbes and toxic factors; however, this inflammatory response can result in unintended damage to lung tissue. Tissue damage resulting from inflammation is often mitigated by resolving factors that limit the scope and duration of the inflammatory response. Both inflammatory and resolving processes require the actions of a vast array of lipid mediators that can be rapidly synthesized through a variety of airway resident and infiltrating immune cells. Eicosanoids and endocannabinoids represent two major classes of lipid mediators that share synthetic enzymes and have diverse and overlapping functions. This review seeks to provide a summary of the major bioactive eicosanoids and endocannabinoids, challenges facing researchers that study them, and their roles in modulating inflammation and resolution. With a special emphasis on cystic fibrosis, a variety of therapeutics are discussed that have been explored for their potential anti-inflammatory or proresolving impact toward alleviating excessive airway inflammation and improving lung function.

Neutrophil dysfunction in cystic fibrosis

BACKGROUND

Excessive neutrophil inflammation is the hallmark of cystic fibrosis (CF) airway disease. Novel technologies for characterizing neutrophil dysfunction may provide insight into the nature of these abnormalities, revealing a greater mechanistic understanding and new avenues for CF therapies that target these mechanisms.

METHODS

Blood was collected from individuals with CF in the outpatient clinic, CF individuals hospitalized for a pulmonary exacerbation, and non-CF controls. Using microfluidic assays and advanced imaging technologies, we characterized 1) spontaneous neutrophil migration using microfluidic motility mazes, 2) neutrophil migration to and phagocytosis of Staphylococcal aureus particles in a microfluidic arena, 3) neutrophil swarming on Candida albicans clusters, and 4) Pseudomonas aeruginosa-induced neutrophil transepithelial migration using micro-optical coherence technology (µOCT).

RESULTS

Participants included 44 individuals: 16 Outpatient CF, 13 Hospitalized CF, and 15 Non-CF individuals. While no differences were seen with spontaneous migration, CF neutrophils migrated towards S. aureus particles more quickly than non-CF neutrophils (p < 0.05). CF neutrophils, especially Hospitalized CF neutrophils, generated significantly larger aggregates around S. aureus particles over time. Hospitalized CF neutrophils were more likely to have dysfunctional swarming (p < 0.01) and less efficient clearing of C. albicans (p < 0.0001). When comparing trans-epithelial migration towards Pseudomonas aeruginosa epithelial infection, Outpatient CF neutrophils displayed an increase in the magnitude of transmigration and adherence to the epithelium (p < 0.05).

CONCLUSIONS

Advanced technologies for characterizing CF neutrophil function reveal significantly altered migratory responses, cell-to-cell clustering, and microbe containment. Future investigations will probe mechanistic basis for abnormal responses in CF to identify potential avenues for novel anti-inflammatory therapeutics.

Intranasal micro-optical coherence tomography imaging for cystic fibrosis studies

Cystic fibrosis (CF) is a genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. Although impairment of mucociliary clearance contributes to severe morbidity and mortality in people with CF, a clear understanding of the pathophysiology is lacking. This is, in part, due to the absence of clinical imaging techniques capable of capturing CFTR-dependent functional metrics at the cellular level. Here, we report the clinical translation of a 1-μm resolution micro-optical coherence tomography (μOCT) technology to quantitatively characterize the functional microanatomy of human upper airways. Using a minimally invasive intranasal imaging approach, we performed a clinical study on age- and sex-matched CF and control groups. We observed delayed mucociliary transport rate at the cellular level, depletion of periciliary liquid layer, and prevalent loss of ciliation in subjects with CF. Distinctive morphological differences in mucus and various forms of epithelial injury were also revealed by μOCT imaging and had prominent effects on the mucociliary transport apparatus. Elevated mucus reflectance intensity in CF, a proxy for viscosity in situ, had a dominant effect. These results demonstrate the utility of μOCT to determine epithelial function and monitor disease status of CF airways on a per-patient basis, with applicability for other diseases of mucus clearance.

Single versus repeated exposure to human polarized intestinal epithelial monolayers for in vitro protein hazard characterization

Recent studies suggest human-derived intestinal epithelial cell (IEC) lines cultured as polarized monolayers on permeable Transwell^® filters are effective at differentiating between hazardous and non-hazardous proteins following a single exposure. In this study, IEC polarized monolayers were subjected to hazardous or non-hazardous proteins in nine exposures over 30 days and compared to a single exposure of the same protein. The objective was to evaluate whether repeated exposures to a protein differently alter barrier integrity or compromise cell viability compared to single exposures. Proteins tested included Clostridium difficile toxin A, Streptolysin O, Wheat Germ Agglutinin, Phaseolus vulgaris Hemagglutinin-E, bovine serum albumin, porcine serum albumin, and fibronectin. Evidence of diminished barrier integrity and/or cell viability following exposure to hazardous proteins was more pronounced in magnitude when IECs were subjected to multiple rather than single exposures. In some cases, an effect on IEC monolayers was observed only with repeated exposures. In general, IEC responses to non-hazardous proteins following either single or repeated exposures were minimal. Results from these studies support the utility of using cultured human IEC polarized monolayers to differentiate between hazardous and non-hazardous proteins and suggest that repeated exposures may reveal a greater magnitude of response when compared to single exposures.

Replication of the Ordered, Nonredundant Library of Pseudomonas aeruginosa strain PA14 Transposon Insertion Mutants

Pseudomonas aeruginosa is a phenotypically and genotypically diverse and adaptable Gram-negative bacterium ubiquitous in human environments. P. aeruginosa is able to form biofilms, develop antibiotic resistance, produce virulence factors, and rapidly evolve in the course of a chronic infection. Thus P. aeruginosa can cause both acute and chronic, difficult to treat infections, resulting in significant morbidity in certain patient populations. P. aeruginosa strain PA14 is a human clinical isolate with a conserved genome structure that infects a variety of mammalian and nonvertebrate hosts making PA14 an attractive strain for studying this pathogen. In 2006, a nonredundant transposon insertion mutant library containing 5,459 mutants corresponding to 4,596 predicted PA14 genes was generated. Since then, distribution of the PA14 library has allowed the research community to better understand the function of individual genes and complex pathways of P. aeruginosa. Maintenance of library integrity through the replication process requires proper handling and precise techniques. To that end, this manuscript presents protocols that describe in detail the steps involved in library replication, library quality control and proper storage of individual mutants.

Pseudomonas aeruginosa-induced lung epithelial production of IL-8 contributes to PMN sub-mucosa recruitment but not trans-epithelial migration in vitro

Background

Numerous lung associated diseased states such as acute pneumonia and cystic fibrosis (CF) are associated with increased concentrations of IL8 and infiltration of neutrophils (PMNs) in the airspace. IL8 production by lung epithelial cells (ECs) is stimulated by Pseudomonas aeruginosa infection, an opportunistic pathogen involved in acute pneumonia, and lung infection of CF patients. The exact role IL8 plays in migration of circulating PMNs into the infected lung and airspace is still uncertain.

Objective

Assess the role of IL8 in mediating PMN migration in response to P. aeruginosa infected lung epithelium.

Methods

CRISPR/Cas9 was used to delete the IL8 gene from human lung ECs, which were grown as polarized monolayers in a co-culture transwell model. Basolateral to apical PMN migration to PAO1 infection was assessed. A novel double transwell model was developed to observe PMN submucosa migration in response to PAO1 infection in the presence and absence of IL8 lung EC production.

Results

PAO1 induced PMN trans-epithelial (TE) migration was not impacted in the absence of IL8 expression. When PMNs were placed in a separate transwell suspended 5 mm above the basolateral side of the infected epithelium, the IL8 gradient produced was sufficient to cause relevant migration of PMNs to the basolateral side of the infected epithelium. The level of migrated PMNs in the double transwell system with tissues devoid of the IL8 gene was equivalent to the presence of PMNs which responded to un-infected epithelial tissues.

Conclusion

These findings further support that IL8 is integral in PMN recruitment, and suggests that IL8 is most important towards recruiting PMNs to the submucosa during P. aeruginosa PAO1 infection of lung epithelium.

Expansion of Airway Basal Cells and Generation of Polarized Epithelium

Airway basal stem cells are the progenitor cells within the airway that exhibit the capacity to self-renew and give rise to multiple types of differentiated airway epithelial cells. This stem cell-derived epithelium displays organized architecture with functional attributes of the airway mucosa. A protocol has been developed to culture and expand human airway basal stem cells while preserving their stem cell properties and capacity for subsequent mucociliary differentiation. This achievement presents a previously unrealized opportunity to maintain a durable supply of progenitor cells derived from healthy donors to differentiate into human primary airway epithelium for cellular and molecular-based studies. Further, basal stem cells can be harvested from patients with a specific airway disease, such as cystic fibrosis, enabling investigation of potentially altered behavior of disease-specific cells in the appropriate context of the airway mucosa. Here we describe, in detail, a protocol for the serial expansion of airway basal stem cells to enable the generation of nearly unlimited airway basal cells that can be stored and readily available for subsequent culturing and differentiation. In addition, we describe culturing and differentiation of airway basal stem cells on permeable transwell filters at air-liquid interface to create functional mucociliary pseudostratified polarized airway epithelial mucosa.

Neutrophil-Derived Cytosolic PLA2α Contributes to Bacterial-Induced Neutrophil Transepithelial Migration

Eicosanoids are a group of bioactive lipids that are shown to be important mediators of neutrophilic inflammation; selective targeting of their function confers therapeutic benefit in a number of diseases. Neutrophilic airway diseases, including cystic fibrosis, are characterized by excessive neutrophil infiltration into the airspace. Understanding the role of eicosanoids in this process may reveal novel therapeutic targets. The eicosanoid hepoxilin A3 is a pathogen-elicited epithelial-produced neutrophil chemoattractant that directs transepithelial migration in response to infection. Following hepoxilin A3-driven transepithelial migration, neutrophil chemotaxis is amplified through neutrophil production of a second eicosanoid, leukotriene B4 (LTB4). The rate-limiting step of eicosanoid generation is the liberation of arachidonic acid by phospholipase A2, and the cytosolic phospholipase A2 (cPLA2)α isoform has been specifically shown to direct LTB4 synthesis in certain contexts. Whether cPLA2α is directly responsible for neutrophil synthesis of LTB4 in the context of Pseudomonas aeruginosa-induced neutrophil transepithelial migration has not been explored. Human and mouse neutrophil-epithelial cocultures were used to evaluate the role of neutrophil-derived cPLA2α in infection-induced transepithelial signaling by pharmacological and genetic approaches. Primary human airway basal stem cell-derived epithelial cultures and micro-optical coherence tomography, a new imaging modality that captures two- and three-dimensional real-time dynamics of neutrophil transepithelial migration, were applied. Evidence from these studies suggests that cPLA2α expressed by neutrophils, but not epithelial cells, plays a significant role in infection-induced neutrophil transepithelial migration by mediating LTB4 synthesis during migration, which serves to amplify the magnitude of neutrophil recruitment in response to epithelial infection.

Pseudomonas aeruginosa ExoU augments neutrophil transepithelial migration

Excessive neutrophil infiltration of the lungs is a common contributor to immune-related pathology in many pulmonary disease states. In response to pathogenic infection, airway epithelial cells produce hepoxilin A₃ (HXA₃), initiating neutrophil transepithelial migration. Migrated neutrophils amplify this recruitment by producing a secondary gradient of leukotriene B₄ (LTB₄). We sought to determine whether this two-step eicosanoid chemoattractant mechanism could be exploited by the pathogen Pseudomonas aeruginosa. ExoU, a P. aeruginosa cytotoxin, exhibits phospholipase A2 (PLA2) activity in eukaryotic hosts, an enzyme critical for generation of certain eicosanoids. Using in vitro and in vivo models of neutrophil transepithelial migration, we evaluated the impact of ExoU expression on eicosanoid generation and function. We conclude that ExoU, by virtue of its PLA2 activity, augments and compensates for endogenous host neutrophil cPLA2α function, leading to enhanced transepithelial migration. This suggests that ExoU expression in P. aeruginosa can circumvent immune regulation at key signaling checkpoints in the neutrophil, resulting in exacerbated neutrophil recruitment.

Pseudomonas aeruginosa is an opportunistic pathogen that causes acute pneumonia in immune compromised patients, and infects 70–80% of patients suffering from cystic fibrosis. Infections can result in excessive airway inflammation, which lead to immune-mediated lung damage, in particular through the action of recruited white blood cells known as neutrophils. Certain strains of P. aeruginosa produce the exotoxin ExoU, which has been associated with increased virulence. ExoU causes host cell lysis by hydrolyzing host membrane lipids through its phospholipase activity. However, host phospholipases play a key role in immune signaling by mediating the production of lipids known as eicosanoids. We investigated whether separate from its cytolytic activity, ExoU could modulate host immune responses through its phospholipase activity by hijacking eicosanoid production. Using in vitro and in vivo models of neutrophil recruitment, we find that ExoU producing strains of P. aeruginosa elicit higher levels of the eicosanoid chemoattractant leukotriene B4 from migrated neutrophils. This results in increased neutrophil transepithelial migration. This work reveals a new mechanism for how bacterial pathogens alter our immune function, and highlights a new potential therapeutic strategy for moderating Pseudomonas pathogenesis in patients with cystic fibrosis and acute pneumonia.

Primary human polarized small intestinal epithelial barriers respond differently to a hazardous and an innocuous protein

An experimental platform employing human derived intestinal epithelial cell (IEC) line monolayers grown on permeable Transwell^® filters was previously investigated to differentiate between hazardous and innocuous proteins. This approach was effective at distinguishing these types of proteins and perturbation of monolayer integrity, particularly transepithelial electrical resistance (TEER), was the most sensitive indicator. In the current report, in vitro indicators of monolayer integrity, cytotoxicity, and inflammation were evaluated using primary (non-transformed) human polarized small intestinal epithelial barriers cultured on Transwell^® filters to compare effects of a hazardous protein (Clostridium difficile Toxin A [ToxA]) and an innocuous protein (bovine serum albumin [BSA]). ToxA exerted a reproducible decrease on barrier integrity at doses comparable to those producing effects observed from cell line-derived IEC monolayers, with TEER being the most sensitive indicator. In contrast, BSA, tested at concentrations substantially higher than ToxA, did not cause changes in any of the tested variables. These results demonstrate a similarity in response to certain proteins between cell line-derived polarized IEC models and a primary human polarized small intestinal epithelial barrier model, thereby reinforcing the potential usefulness of cell line-derived polarized IECs as a valid experimental platform to differentiate between hazardous and non-hazardous proteins.

Assessment of beetle diversity, community composition and potential threats to forestry using kairomone-baited traps

Traps designed to capture insects during normal movement/dispersal, or via attraction to non-specific (plant) volatile lures, yield by-catch that carries valuable information about patterns of community diversity and composition. In order to identify potential native/introduced pests and detect predictors of colonization of non-native pines, we examined beetle assemblages captured in intercept panel traps baited with kairomone lures used during a national monitoring of the woodwasp, Sirex noctilio, in Southern Africa. We identified 50 families and 436 morphospecies of beetles from nine sites sampled in both 2008 and 2009 and six areas in 2007 (trap catch pooled by region) across a latitudinal and elevational gradient. The most diverse groups were mainly those strongly associated with trees, known to include damaging pests. While native species dominated the samples in terms of richness, the dominant species was the introduced bark beetle Orthotomicus erosus (Curculionidae: Scolytinae) (22 ± 34 individuals/site). Four Scolytinae species without previous records in South Africa, namely Coccotrypes niger, Hypocryphalus robustus (formerly Hypocryphalus mangiferae), Hypothenemus birmanus and Xyleborus perforans, were captured in low abundances. Communities showed temporal stability within sites and strong biogeographic patterns across the landscape. The strongest single predictors of community composition were potential evaporation, latitude and maximum relative humidity, while the strongest multifactor model contained elevation, potential evaporation and maximum relative humidity. Temperature, land use variables and distance to natural areas did not significantly correlate with community composition. Non-phytophagous beetles were also captured and were highly diverse (32 families) perhaps representing important beneficial insects.

Commensal Bacteria-Induced Inflammasome Activation in Mouse and Human Macrophages Is Dependent on Potassium Efflux but Does Not Require Phagocytosis or Bacterial Viability

Gut commensal bacteria contribute to the pathogenesis of inflammatory bowel disease, in part by activating the inflammasome and inducing secretion of interleukin-1ß (IL-1ß). Although much has been learned about inflammasome activation by bacterial pathogens, little is known about how commensals carry out this process. Accordingly, we investigated the mechanism of inflammasome activation by representative commensal bacteria, the Gram-positive Bifidobacterium longum subspecies infantis and the Gram-negative Bacteroides fragilis. B. infantis and B. fragilis induced IL-1ß secretion by primary mouse bone marrow-derived macrophages after overnight incubation. IL-1ß secretion also occurred in response to heat-killed bacteria and was only partly reduced when phagocytosis was inhibited with cytochalasin D. Similar results were obtained with a wild-type immortalized mouse macrophage cell line but neither B. infantis nor B. fragilis induced IL-1ß secretion in a mouse macrophage line lacking the nucleotide-binding/leucine-rich repeat pyrin domain containing 3 (NLRP3) inflammasome. IL-1ß secretion in response to B. infantis and B. fragilis was significantly reduced when the wild-type macrophage line was treated with inhibitors of potassium efflux, either increased extracellular potassium concentrations or the channel blocker ruthenium red. Both live and heat-killed B. infantis and B. fragilis also induced IL-1ß secretion by human macrophages (differentiated THP-1 cells or primary monocyte-derived macrophages) after 4 hours of infection, and the secretion was inhibited by raised extracellular potassium and ruthenium red but not by cytochalasin D. Taken together, our findings indicate that the commensal bacteria B. infantis and B. fragilis activate the NLRP3 inflammasome in both mouse and human macrophages by a mechanism that involves potassium efflux and that does not require bacterial viability or phagocytosis.

Airway reflux

An ever-increasing number of adult and pediatric disorders have been shown to be influenced or caused by airway reflux. This has become a controversial and complicated aspect of medicine that requires a multidisciplinary approach. Evidence indicates that it is not only the acidic components of gastric refluxate that injure extraesophageal tissues but also the nonacidic components, such as pepsin and bile. There is a realization that proton pump inhibitors will not be effective when nonacidic components of refluxate are causing the problem. New in vitro and in vivo models for the study of airway reflux and new therapeutic and surgical approaches are discussed in this review article.

Host-pathogen interplay in the respiratory environment of cystic fibrosis

Significant advances have been made in the understanding of disease progression in cystic fibrosis (CF), revealing a complex interplay between host and pathogenic organisms. The diverse CF microbiota within the airway activates an aberrant immune response that is ineffective in clearing infection. An appreciation of how the CF host immune system interacts with these organisms is crucial to understanding the pathogenesis of CF pulmonary disease. Here we discuss the microbial complexity present in the lungs of individuals with CF, review emerging concepts of innate and adaptive immune responses to pathogens that chronically inhabit the CF lung, and discuss therapies that target the aberrant inflammatory response that characterizes CF. A greater understanding of the underlying mechanisms will shed light on pathogenesis and guide more targeted therapies in the future that serve to reduce infection, minimize lung pathology, and improve the quality of life for patients with CF.

Distinct cellular sources of hepoxilin A3 and leukotriene B4 are used to coordinate bacterial-induced neutrophil transepithelial migration

Neutrophilic infiltration is a leading contributor to pathology in a number of pulmonary disease states, including cystic fibrosis. Hepoxilin A3 (HXA3) is a chemotactic eicosanoid shown to mediate the transepithelial passage of neutrophils in response to infection in several model systems and at multiple mucosal surfaces. Another well-known eicosanoid mediating general neutrophil chemotaxis is leukotriene B4 (LTB4). We sought to distinguish the roles of each eicosanoid in the context of infection of lung epithelial monolayers by Pseudomonas aeruginosa. Using human and mouse in vitro transwell model systems, we used a combination of biosynthetic inhibitors, receptor antagonists, as well as mutant sources of neutrophils to assess the contribution of each chemoattractant in driving neutrophil transepithelial migration. We found that following chemotaxis to epithelial-derived HXA3 signals, neutrophil-derived LTB4 is required to amplify the magnitude of neutrophil migration. LTB4 signaling is not required for migration to HXA3 signals, but LTB4 generation by migrated neutrophils plays a significant role in augmenting the initial HXA3-mediated migration. We conclude that HXA3 and LTB4 serve independent roles to collectively coordinate an effective neutrophilic transepithelial migratory response.

In vitro coculture assay to assess pathogen induced neutrophil trans-epithelial migration

Mucosal surfaces serve as protective barriers against pathogenic organisms. Innate immune responses are activated upon sensing pathogen leading to the infiltration of tissues with migrating inflammatory cells, primarily neutrophils. This process has the potential to be destructive to tissues if excessive or held in an unresolved state. Cocultured in vitro models can be utilized to study the unique molecular mechanisms involved in pathogen induced neutrophil trans-epithelial migration. This type of model provides versatility in experimental design with opportunity for controlled manipulation of the pathogen, epithelial barrier, or neutrophil. Pathogenic infection of the apical surface of polarized epithelial monolayers grown on permeable transwell filters instigates physiologically relevant basolateral to apical trans-epithelial migration of neutrophils applied to the basolateral surface. The in vitro model described herein demonstrates the multiple steps necessary for demonstrating neutrophil migration across a polarized lung epithelial monolayer that has been infected with pathogenic P. aeruginosa (PAO1). Seeding and culturing of permeable transwells with human derived lung epithelial cells is described, along with isolation of neutrophils from whole human blood and culturing of PAO1 and nonpathogenic K12 E. coli (MC1000). The emigrational process and quantitative analysis of successfully migrated neutrophils that have been mobilized in response to pathogenic infection is shown with representative data, including positive and negative controls. This in vitro model system can be manipulated and applied to other mucosal surfaces. Inflammatory responses that involve excessive neutrophil infiltration can be destructive to host tissues and can occur in the absence of pathogenic infections. A better understanding of the molecular mechanisms that promote neutrophil trans-epithelial migration through experimental manipulation of the in vitro coculture assay system described herein has significant potential to identify novel therapeutic targets for a range of mucosal infectious as well as inflammatory diseases.

Pathogen induced chemo-attractant hepoxilin A3 drives neutrophils, but not eosinophils across epithelial barriers

Pathogen induced migration of neutrophils across mucosal epithelial barriers requires epithelial production of the chemotactic lipid mediator, hepoxilin A3 (HXA3). HXA3 is an eicosanoid derived from arachidonic acid. Although eosinophils are also capable of penetrating mucosal surfaces, eosinophilic infiltration occurs mainly during allergic processes whereas neutrophils dominate mucosal infection. Both neutrophils and eosinophils can respond to chemotactic gradients of certain eicosanoids, however, it is not known whether eosinophils respond to pathogen induced lipid mediators such as HXA3. In this study, neutrophils and eosinophils were isolated from human blood and placed on the basolateral side of polarized epithelial monolayers grown on permeable Transwell filters and challenged by various chemotactic gradients of distinct lipid mediators. We observed that both cell populations migrated across epithelial monolayers in response to a leukotriene B4 (LTB4) gradient, whereas only eosinophils migrated toward a prostaglandin D2 (PGD2) gradient. Interestingly, while pathogen induced neutrophil trans-epithelial migration was substantial, pathogen induced eosinophil trans-epithelial migration was not observed. Further, gradients of chemotactic lipids derived from pathogen infected epithelial cells known to be enriched for HXA3 as well as purified HXA3 drove significant numbers of neutrophils across epithelial barriers, whereas eosinophils failed to respond to these gradients. These data suggest that although the eicosanoid HXA3 serves as an important neutrophil chemo-attractant at mucosal surfaces during pathogenic infection, HXA3 does not appear to exhibit chemotactic activity toward eosinophils.

Systemic disease during Streptococcus pneumoniae acute lung infection requires 12-lipoxygenase-dependent inflammation

Acute pulmonary infection by Streptococcus pneumoniae is characterized by high bacterial numbers in the lung, a robust alveolar influx of polymorphonuclear cells (PMNs), and a risk of systemic spread of the bacterium. We investigated host mediators of S. pneumoniae-induced PMN migration and the role of inflammation in septicemia following pneumococcal lung infection. Hepoxilin A3 (HXA3) is a PMN chemoattractant and a metabolite of the 12-lipoxygenase (12-LOX) pathway. We observed that S. pneumoniae infection induced the production of 12-LOX in cultured pulmonary epithelium and in the lungs of infected mice. Inhibition of the 12-LOX pathway prevented pathogen-induced PMN transepithelial migration in vitro and dramatically reduced lung inflammation upon high-dose pulmonary challenge with S. pneumoniae in vivo, thus implicating HXA3 in pneumococcus-induced pulmonary inflammation. PMN basolateral-to-apical transmigration in vitro significantly increased apical-to-basolateral transepithelial migration of bacteria. Mice suppressed in the expression of 12-LOX exhibited little or no bacteremia and survived an otherwise lethal pulmonary challenge. Our data suggest that pneumococcal pulmonary inflammation is required for high-level bacteremia and systemic infection, partly by disrupting lung epithelium through 12-LOX-dependent HXA3 production and subsequent PMN transepithelial migration.

Hepoxilin A(3) facilitates neutrophilic breach of lipoxygenase-expressing airway epithelial barriers

A feature shared by many inflammatory lung diseases is excessive neutrophilic infiltration. Neutrophil homing to airspaces involve multiple factors produced by several distinct cell types. Hepoxilin A(3) is a neutrophil chemoattractant produced by pathogen-infected epithelial cells that is hypothesized to facilitate neutrophil breach of mucosal barriers. Using a Transwell model of lung epithelial barriers infected with Pseudomonas aeruginosa, we explored the role of hepoxilin A(3) in neutrophil transepithelial migration. Pharmacological inhibitors of the enzymatic pathways necessary to generate hepoxilin A(3), including phospholipase A(2) and 12-lipoxygenase, potently interfere with P. aeruginosa-induced neutrophil transepithelial migration. Both transformed and primary human lung epithelial cells infected with P. aeruginosa generate hepoxilin A(3) precursor arachidonic acid. All four known lipoxygenase enzymes capable of synthesizing hepoxilin A(3) are expressed in lung epithelial cell lines, primary small airway epithelial cells, and human bronchial epithelial cells. Lung epithelial cells produce increased hepoxilin A(3) and lipid-derived neutrophil chemotactic activity in response to P. aeruginosa infection. Lipid-derived chemotactic activity is soluble epoxide hydrolase sensitive, consistent with hepoxilin A(3) serving a chemotactic role. Stable inhibitory structural analogs of hepoxilin A(3) are capable of impeding P. aeruginosa-induced neutrophil transepithelial migration. Finally, intranasal infection of mice with P. aeruginosa promotes enhanced cellular infiltrate into the airspace, as well as increased concentration of the 12-lipoxygenase metabolites hepoxilin A(3) and 12-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid. Data generated from multiple models in this study provide further evidence that hepoxilin A(3) is produced in response to lung pathogenic bacteria and functions to drive neutrophils across epithelial barriers.

Selective eicosanoid-generating capacity of cytoplasmic phospholipase A2 in Pseudomonas aeruginosa-infected epithelial cells

Airway neutrophil infiltration is a pathological hallmark observed in multiple lung diseases including pneumonia and cystic fibrosis. Bacterial pathogens such as Pseudomonas aeruginosa instigate neutrophil recruitment to the air space. Excessive accumulation of neutrophils in the lung often contributes to tissue destruction. Previous studies have unveiled hepoxilin A(3) as the key molecular signal driving neutrophils across epithelial barriers. The eicosanoid hepoxilin A(3) is a potent neutrophil chemoattractant produced by epithelial cells in response to infection with P. aeruginosa. The enzyme phospholipase A(2) liberates arachidonic acid from membrane phospholipids, the rate-limiting step in the synthesis of all eicosanoids, including hepoxilin A(3). Once generated, aracidonic acid is acted upon by multiple cyclooxygenases and lipoxygenases producing an array of functionally diverse eicosanoids. Although there are numerous phospholipase A(2) isoforms capable of generating arachidonic acid, the isoform most often associated with eicosanoid generation is cytoplasmic phospholipase A(2)α. In the current study, we observed that the cytoplasmic phospholipase A(2)α isoform is required for mediating P. aeruginosa-induced production of certain eicosanoids such as prostaglandin E(2). However, we found that neutrophil transepithelial migration induced by P. aeruginosa does not require cytoplasmic phospholipase A(2)α. Furthermore, P. aeruginosa-induced hepoxilin A(3) production persists despite cytoplasmic phospholipase A(2)α suppression and generation of the 12-lipoxygenase metabolite 12-HETE is actually enhanced in this context. These results suggest that alterative phospholipase A(2) isoforms are utilized to synthesize 12-lipoxygenase metabolites. The therapeutic implications of these findings are significant when considering anti-inflammatory therapies based on targeting eicosanoid synthesis pathways.

Adhesion molecules involved in hepoxilin A3-mediated neutrophil transepithelial migration

A common feature underlying active states of inflammation is the migration of neutrophils (PMNs) from the circulation and across a number of tissue barriers in response to chemoattractant stimuli. Although our group has recently established a discreet role for the PMN chemoattractant, hepoxilin A3 (HXA3) in the process of PMN recruitment, very little is known regarding the interaction of HXA3 with PMNs. To characterize further the event of HXA3-induced PMN transepithelial migration, we sought to determine the adhesion molecules required for migration across different epithelial surfaces (T84 intestinal and A549 airway cells) relative to two well-studied PMN chemoattractants, formyl-methionyl-leucyl-phenylalanine (fMLP) and leukotriene B4 (LTB4). Our findings reveal that the adhesion interaction profile of PMN transepithelial migration in response to HXA3 differs from the adhesion interaction profile exhibited by the structurally related eicosanoid LTB4. Furthermore, unique to PMN transepithelial migration induced by gradients of HXA3 was the critical dependency of all four major surface adhesion molecules examined (i.e. CD18, CD47, CD44 and CD55). Our results suggest that the particular chemoattractant gradient imposed, as well as the type of epithelial cell monolayer, each plays a role in determining the adhesion molecules involved in transepithelial migration. Given the complexities of these interactions, our findings are important to consider with respect to adhesion molecules that may be targeted for potential drug development.

Salmonella enterica serovar Typhimurium regulates intercellular junction proteins and facilitates transepithelial neutrophil and bacterial passage

The establishment of tight junctions (TJ) between columnar epithelial cells defines the functional barrier, which enteroinvasive pathogens have to overcome. Salmonella enterica serovar Typhimurium (S. typhimurium) directly invades intestinal epithelial cells but it is not well understood how the pathogen is able to overcome the intestinal barrier and gains access to the circulation. Therefore, we sought to determine whether infection with S. typhimurium could regulate the molecular composition of the TJ and, if so, whether these modifications would influence bacterial translocation and polymorphonuclear leukocyte (PMN) movement across model intestinal epithelium. We found that infection of a model intestinal epithelium with S. typhimurium over 2 h resulted in an approximately 80% loss of transepithelial electrical resistance. Western blot analysis of epithelial cell lysates demonstrated that S. typhimurium regulated the distribution of the TJ complex proteins claudin-1, zonula occludens (ZO)-2, and E-cadherin in Triton X-100-soluble and insoluble fractions. In addition, S. typhimurium was specifically able to dephosphorylate occludin and degrade ZO-1. This TJ alteration in the epithelial monolayer resulted in 10-fold increase in bacterial translocation and a 75% increase in N-formylmethionin-leucyl-phenyalanine-induced PMN transepithelial migration. Our data demonstrate that infection with S. typhimurium is associated with the rapid targeting of the tight junctional complex and loss of barrier function. This results in enhanced bacterial translocation and initiation of PMN migration across the intestinal barrier. Therefore, the ability to regulate the molecular composition of TJs facilitates the pathogenicity of S. typhimurium by aiding its uptake and distribution within the host.

Involvement of phospholipase A2 in Pseudomonas aeruginosa-mediated PMN transepithelial migration

Inflammation resulting from bacterial infection of the respiratory mucosal surface during pneumonia and cystic fibrosis contributes to pathology. A major consequence of the inflammatory response is recruitment of polymorphonuclear cells (PMNs) to the infected site. To reach the airway, PMNs must travel through several cellular and extracellular barriers, via the actions of multiple cytokines, chemokines, and adhesion molecules. Using a model of polarized lung epithelial cells (A549 or Calu-3) grown on Transwell filters and human PMNs, we have shown that Pseudomonas aeruginosa induces PMN migration across lung epithelial barriers. The process is mediated by epithelial production of the eicosanoid hepoxilin A(3) (HXA(3)) in response to P. aeruginosa infection. HXA(3) is a PMN chemoattractant metabolized from arachidonic acid (AA). Given that release of AA is believed to be the rate-limiting step in generating eicosanoids, we investigated whether P. aeruginosa infection of lung epithelial cells resulted in an increase in free AA. P. aeruginosa infection of A549 or Calu-3 monolayers resulted in a significant increase in [(3)H]AA released from prelabeled lung epithelial cells. This was partially inhibited by PLA(2) inhibitors ONO-RS-082 and ACA as well as an inhibitor of diacylglycerol lipase. Both PLA(2) inhibitors dramatically reduced P. aeruginosa-induced PMN transmigration, whereas the diacylglycerol lipase inhibitor had no effect. In addition, we observed that P. aeruginosa infection caused an increase in the phosphorylation of cytosolic PLA(2) (cPLA(2)), suggesting a mechanism whereby P. aeruginosa activates cPLA(2) generating free AA that may be converted to HXA(3), which is required for mediating PMN transmigration.

Polymorphonuclear Cell Transmigration Induced byPseudomonas aeruginosaRequires the Eicosanoid Hepoxilin A3

Lung inflammation resulting from bacterial infection of the respiratory mucosal surface in diseases such as cystic fibrosis and pneumonia contributes significantly to the pathology. A major consequence of the inflammatory response is the recruitment and accumulation of polymorphonuclear cells (PMNs) at the infection site. It is currently unclear what bacterial factors trigger this response and exactly how PMNs are directed across the epithelial barrier to the airway lumen. An in vitro model consisting of human PMNs and alveolar epithelial cells (A549) grown on inverted Transwell filters was used to determine whether bacteria are capable of inducing PMN migration across these epithelial barriers. A variety of lung pathogenic bacteria, including Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa are indeed capable of inducing PMN migration across A549 monolayers. This phenomenon is not mediated by LPS, but requires live bacteria infecting the apical surface. Bacterial interaction with the apical surface of A549 monolayers results in activation of epithelial responses, including the phosphorylation of ERK1/2 and secretion of the PMN chemokine IL-8. However, secretion of IL-8 in response to bacterial infection is neither necessary nor sufficient to mediate PMN transepithelial migration. Instead, PMN transepithelial migration is mediated by the eicosanoid hepoxilin A3, which is a PMN chemoattractant secreted by A549 cells in response to bacterial infection in a protein kinase C-dependent manner. These data suggest that bacterial-induced hepoxilin A3 secretion may represent a previously unrecognized inflammatory mechanism occurring within the lung epithelium during bacterial infections.

Intestinal epithelial defense systems protect against bacterial threats

Numerous bacterial species inhabit the lumen of the human intestine. The epithelial cells that line the intestinal barrier are in direct contact with many of these species and have developed sophisticated strategies to prevent bacterial invasion of host tissue beyond simply providing a physical blockade. Intestinal epithelial cells (IECs) possess receptors that are capable of recognizing bacterial products, and engagement of these receptors results in the production and secretion of immunoregulatory proteins, such as cytokines and chemokines, which mobilize immune effector cells, including macrophages, dendritic cells, and neutrophils. In addition, IECs can produce various lipid-based eicosanoids that can contribute to the orchestration of the immune response. A better understanding of how the intestinal epithelium interacts with its microbial constituents may provide insight into strategies for treatment of enteric infections and inflammatory bowel disease.

Shiga toxin-producing Escherichia coli as a possible etiological agent of chronic diarrhea

We identified Shiga toxin-producing Escherichia coli (STEC) as the likely etiologic pathogen for chronic diarrhea in 2 patients, 1 of whom was immunocompromised with acquired immunodeficiency syndrome, and 1 of whom was immunocompetent. Both were treated with antibiotics, and neither developed systemic complications of the infection. These cases suggest that STEC infection should be considered in the differential diagnosis of chronic diarrhea.

Identification of hepoxilin A3 in inflammatory events: a required role in neutrophil migration across intestinal epithelia

The mechanism by which neutrophils [polymorphonuclear leukocyte (PMNs)] are stimulated to move across epithelial barriers at mucosal surfaces has been basically unknown in biology. IL-8 has been shown to stimulate PMNs to leave the bloodstream at a local site of mucosal inflammation, but the chemical gradient used by PMNs to move between adjacent epithelial cells and traverse the tight junction at the apical neck of these mucosal barriers has eluded identification. Our studies not only identify this factor, previously termed pathogen-elicited epithelial chemoattractant, as the eicosanoid hepoxilin A(3) (hepA(3)) but also demonstrate that it is a key factor promoting the final step in PMN recruitment to sites of mucosal inflammation. We show that hepA(3) is synthesized by epithelial cells and secreted from their apical surface in response to conditions that stimulate inflammatory events. Our data further establish that hepA(3) acts to draw PMNs, via the establishment of a gradient across the epithelial tight junction complex. The functional significance of hepA(3) to target PMNs to the lumen of the gut at sites of inflammation was demonstrated by the finding that disruption of the 12-lipoxygenase pathway (required for hepA(3) production) could dramatically reduce PMN-mediated tissue trauma, demonstrating that hepA(3) is a key regulator of mucosal inflammation.

Translating tissue culture results into animal models: the case of Salmonella typhimurium

Investigators use both in vitro and in vivo models to better understand infectious disease processes. Both models are extremely useful in research, but there exists a significant gap in complexity between the highly controlled reductionist in vitro systems and the largely undefined, but relevant variability encompassing in vivo animal models. In an effort to understand how Salmonella initiates disease at the intestinal epithelium, in vitro models have served a useful purpose in allowing investigators to identify molecular mechanisms responsible for Salmonella invasion of host cells and stimulation of host inflammatory responses. Identification of these molecular mechanisms has generated hypotheses that are now being tested using in vivo models. Translating the in vitro findings into the context of an animal model and subsequently to human disease remains a difficult challenge for any disease process.

Molecular and functional analysis of glutamine uptake in human hepatoma and liver-derived cells

Human hepatoma cells take up glutamine at rates severalfold faster than the system N-mediated transport rates observed in normal human hepatocytes. Amino acid inhibition, kinetic, Northern blotting, RT-PCR, and restriction enzyme analyses collectively identified the transporter responsible in six human hepatoma cell lines as amino acid transporter B(0) (ATB(0)), the human ortholog of rodent ASCT2. The majority of glutamine uptake in liver fibroblasts and an immortalized human liver epithelial cell line (THLE-5B) was also mediated by ATB(0). The 2.9-kb ATB(0) mRNA was equally expressed in all cell lines, whereas expression of the system A transporters ATA2 and ATA3 was variable. In contrast, the system N isoforms (SN1 and SN2) were expressed only in well-differentiated hepatomas. ATB(0) mRNA was also expressed in cirrhotic liver and adult and pediatric liver cancer biopsies but was not detectable in isolated human hepatocytes or fetal liver. Although the growth of all hepatomas was glutamine dependent, competitive inhibition of ATB(0)-mediated glutamine uptake blocked proliferation only in poorly differentiated cells lacking SN1 or SN2 expression and exhibiting low glutamine synthetase mRNA levels.

Shiga toxin translocation across intestinal epithelial cells is enhanced by neutrophil transmigration

Shiga toxin-producing E. coli (STEC) is a food-borne pathogen that causes serious illness, including hemolytic-uremic syndrome (HUS). STEC colonizes the lower intestine and produces Shiga toxins (Stxs). Stxs appear to translocate across intestinal epithelia and affect sensitive endothelial cell beds at various sites. We have previously shown that Stxs cross polarized intestinal epithelial cells (IECs) via a transcellular route and remain biologically active. Since acute inflammatory infiltration of the gut and fecal leukocytes is seen in many STEC-infected patients and since polymorphonuclear leukocyte (PMN) transmigration across polarized IECs diminishes the IEC barrier function in vitro, we hypothesized that PMN transmigration may enhance Stx movement across IECs. We found that basolateral-to-apical transmigration of neutrophils significantly increased the movement of Stx1 and Stx2 across polarized T84 IECs in the opposite direction. The amount of Stx crossing the T84 barrier was proportional to the degree of neutrophil transmigration, and the increase in Stx translocation appears to be due to increases in paracellular permeability caused by migrating PMNs. STEC clinical isolates applied apically induced PMN transmigration across and interleukin-8 (IL-8) secretion from T84 cells. Of the 10 STEC strains tested, three STEC strains lacking eae and espB (eae- and espB-negative STEC strains) induced significantly more neutrophil transmigration and significantly greater IL-8 secretion than eae- and espB-positive STEC or enteropathogenic E. coli. This study suggests that STEC interaction with intestinal epithelia induces neutrophil recruitment to the intestinal lumen, resulting in neutrophil extravasation across IECs, and that during this process Stxs may pass in greater amounts into underlying tissues, thereby increasing the risk of HUS.

Shiga toxins induce, superinduce, and stabilize a variety of C-X-C chemokine mRNAs in intestinal epithelial cells, resulting in increased chemokine expression

Exposure of humans to Shiga toxins (Stxs) is a risk factor for hemolytic-uremic syndrome (HUS). Because Stx-producing Escherichia coli (STEC) is a noninvasive enteric pathogen, the extent to which Stxs can cross the host intestinal epithelium may affect the risk of developing HUS. We have previously shown that Stxs can induce and superinduce IL-8 mRNA and protein in intestinal epithelial cells (IECs) in vitro via a ribotoxic stress response. We used cytokine expression arrays to determine the effect of Stx1 on various C-X-C chemokine genes in IECs. We observed that Stx1 induces multiple C-X-C chemokines at the mRNA level, including interleukin-8 (IL-8), GRO-alpha, GRO-beta, GRO-gamma, and ENA-78. Like that of IL-8, GRO-alpha and ENA-78 mRNAs are both induced and superinduced by Stx1. Furthermore, Stx1 induces both IL-8 and GRO-alpha protein in a dose-response fashion, despite an overall inhibition in host cell protein synthesis. Stx1 treatment stabilizes both IL-8 and GRO-alpha mRNA. We conclude that Stxs are able to increase mRNA and protein levels of multiple C-X-C chemokines in IECs, with increased mRNA stability at least one mechanism involved. We hypothesize that ribotoxic stress is a pathway by which Stxs can alter host signal transduction in IECs, resulting in the production of multiple chemokine mRNAs, leading to increased expression of specific proteins. Taken together, these data suggest that exposing IECs to Stxs may stimulate a proinflammatory response, resulting in influx of acute inflammatory cells and thus contributing to the intestinal tissue damage seen in STEC infection.

Shiga toxins 1 and 2 translocate differently across polarized intestinal epithelial cells

Shiga toxin-producing Escherichia coli (STEC) is an important food-borne pathogen that causes hemolytic-uremic syndrome. Following ingestion, STEC cells colonize the intestine and produce Shiga toxins (Stx), which appear to translocate across the intestinal epithelium and subsequently reach sensitive endothelial cell beds. STEC cells produce one or both of two major toxins, Stx1 and Stx2. Stx2-producing STEC is more often associated with disease for reasons as yet undetermined. In this study, we used polarized intestinal epithelial cells grown on permeable filters as a model to compare Stx1 and Stx2 movement across the intestinal epithelium. We have previously shown that biologically active Stx1 is able to translocate across cell monolayers in an energy-dependent, saturable manner. This study demonstrates that biologically active Stx2 is also capable of movement across the epithelium without affecting barrier function, but significantly less Stx2 crossed monolayers than Stx1. Chilling the monolayers to 4 degrees C reduced the amount of Stx1 and Stx2 movement by 200-fold and 20-fold respectively. Stx1 movement was clearly directional, favoring an apical-to-basolateral translocation, whereas Stx2 movement was not. Colchicine reduced Stx1, but not Stx2, translocation. Monensin reduced the translocation of both toxins, but the effect was more pronounced with Stx1. Brefeldin A had no effect on either toxin. Excess unlabeled Stx1 blocks the movement of (125)I-Stx1. Excess Stx2 failed to have any effect on Stx1 movement. Our data suggests that, despite the many common physical and biochemical properties of the two toxins, they appear to be crossing the epithelial cell barrier by different pathways.

Shiga toxins stimulate secretion of interleukin-8 from intestinal epithelial cells

In the 1980s, Shiga toxin (Stx)-producing Escherichia coli O157:H7 (STEC) was identified as a cause of hemorrhagic colitis in the United States and was found to be associated with hemolytic uremic syndrome (HUS), a microangiopathic hemolytic anemia characterized by thrombocytopenia and renal failure. The precise way that Stxs cause hemorrhagic colitis and HUS is unclear. Stxs have been thought to cause disease by killing or irreversibly harming sensitive cells through a nonspecific blockade of mRNA translation, eventually resulting in cytotoxicity by preventing synthesis of critical molecules needed to maintain cell integrity. Because STEC is noninvasive, we have been exploring the host-toxin response at the level of the gastrointestinal mucosa, where STEC infection begins. We have found that Stx is capable of interleukin-8 (IL-8) superinduction in a human colonic epithelial cell line. Despite a general blockade of mRNA translation, Stx treatment results in increased IL-8 mRNA as well as increased synthesis and secretion of IL-8 protein. Our data suggest that an active Stx A subunit is required for this activity. Ricin, which has the same enzymatic activity and trafficking pathway as Stx, has similar effects. Exploration of the effects of other protein synthesis inhibitors (cycloheximide, anisomycin) suggests a mechanism of gene regulation that is distinct from a general translational blockade. Use of the specific p38/RK inhibitor SB202190 showed that blocking of this pathway results in decreased Stx-mediated IL-8 secretion. Furthermore, Stxs induced mRNA of the primary response gene c-jun, which was subsequently partially blocked by SB202190. These data suggest a novel model of how Stxs contribute to disease, namely that Stxs may alter regulation of host cell processes in sensitive cells via activation of at least one member of the mitogen-activated protein kinase family in the p38/RK cascade and induction of c-jun mRNA. Stx-induced increases in chemokine synthesis from intestinal epithelial cells could be important in augmenting the host mucosal inflammatory response to STEC infection.

Alterations in oxidative metabolism and glutamine transport support glucose production in the tumor-influenced hepatocyte

Glutamine is the primary substrate whose hepatic transport is upregulated in the tumor-bearing host; however, the subsequent metabolism of transported glutamine is currently unknown. The purpose of this study was to determine if glutamine is an important oxidative fuel source for hepatocytes in cancer. Specifically we compare rates of glutamine transport and oxidation in hepatocytes from control and tumor-bearing animals. We also compare rates of glucose oxidation and rates of glucose production from glutamine in control hepatocytes versus those from tumor-bearing animals. Hepatocytes from rats bearing the MCA fibrosarcoma were isolated when tumors comprised 5 and 15% of total body weight and compared to sham-implanted and pair-fed control animals. [3H]GLN transport, GLN and glucose oxidation to CO2, and glucose production from glutamine were assayed. Tumor burden of 5% stimulated a 2.52-fold increase in hepatocyte glutamine transport and a 2-fold increase when tumor burden reached 15%. Rates of oxidation of glutamine were suppressed by 1.5-fold when tumors comprised 5% of body weight compared to sham animals and were equivalent to sham animals when tumors comprised 15% of body weight. Significant alterations in glucose oxidation were observed when tumors were both small and large-glucose oxidation was suppressed by 3.6- and 3.7-fold when tumors comprised 5 and 15% of body weight respectively compared to sham-implanted rats. Incubation of hepatocytes from tumor-bearing animals with glutamine as a gluconeogenic substrate induced a 1.84-fold increase in glucose production compared to sham hepatocytes. In conclusion, (i) despite a doubling of GLN transport by the tumor-influenced hepatocyte, GLN oxidation by hepatocytes was not increased. (ii) Glucose oxidation by hepatocytes from tumor-bearing animals was decreased compared to sham hepatocytes and, simultaneously, glucose production by tumor-influenced hepatocytes from glutamine was increased. The augmentation of hepatic glutamine transport and decreased glutamine oxidation seen in tumor-influenced hepatocytes appear to support hepatocyte gluconeogenesis from glutamine.

Retroperitoneal fibrosis, methysergide and malignant lymphoma

A patient who developed retroperitoneal fibrosis on low dose continuous methysergide therapy is presented. Discontinuing the drug led to rapid clinical improvement but the patient was subsequently found to have disseminated malignant lymphoma. This may have had a synergistic effect with methysergide in producing retroperitoneal fibrosis. The patient had also previously had thyrotoxicosis but no evidence of a continuing autoimmune process was found.

Hyperlipoproteinaemia and dietary fat modification in haemodialysis and renal transplant patients

A group of patients in a haemodialysis and renal transplant programme have been assessed for the frequency of lipid abnormalities. Hypercholesterolaemia was not a significant problem amongst haemodialysis patients, but mild hypercholesterolaemia was common amonst transplant patients. Mild hypertriglyceridaemia was a feature of both haemodialysis and transplant patients. Irrespective of initial lipid values, each patient was advised to undertake dietary fat modification for a period of eight months. There was a small significant lowering of plasma triglyceride values in the haemodialysis group. It is concluded that major lipid abnormalities are not a feature of this group and that the return for dietary fat modification is small, although occasional individual patients may warran hypolipidaemic therapy.