Lipopolysaccharide Causes an Increase in Intestinal Tight Junction Permeability in Vitro and in Vivo by Inducing Enterocyte Membrane Expression and Localization of TLR-4 and CD14

Bacterial-derived lipopolysaccharides (LPS) play an essential role in the inflammatory process of inflammatory bowel disease. A defective intestinal tight junction (TJ) barrier is an important pathogenic factor of inflammatory bowel disease and other inflammatory conditions of the gut. Despite its importance in mediating intestinal inflammation, the physiological effects of LPS on the intestinal epithelial barrier remain unclear. The major aims of this study were to determine the effects of physiologically relevant concentrations of LPS (0 to 1 ng/mL) on intestinal barrier function using an in vitro (filter-grown Caco-2 monolayers) and an in vivo (mouse intestinal perfusion) intestinal epithelial model system. LPS, at physiologically relevant concentrations (0 to 1 ng/mL), in the basolateral compartment produced a time-dependent increase in Caco-2 TJ permeability without inducing cell death. Intraperitoneal injection of LPS (0.1 mg/kg), leading to clinically relevant plasma concentrations, also caused a time-dependent increase in intestinal permeability in vivo. The LPS-induced increase in intestinal TJ permeability was mediated by an increase in enterocyte membrane TLR-4 expression and a TLR-4–dependent increase in membrane colocalization of membrane-associated protein CD14. In conclusion, these studies show for the first time that LPS causes an increase in intestinal permeability via an intracellular mechanism involving TLR-4–dependent up-regulation of CD14 membrane expression.An integral function of intestinal epithelial cells is to act as a physical barrier, separating the noxious luminal environment from the underlying lamina propria and the deeper intestinal layers.^1,2 The apically located tight junctions (TJs) form a paracellular seal between the lateral membranes of adjacent intestinal epithelial cells, and act as a structural and functional barrier against paracellular flux of luminal substances. Defective intestinal epithelial TJ barrier has been shown to be an important pathogenic factor of inflammatory bowel disease (IBD) and necrotizing enterocolitis (NEC) by allowing paracellular permeation of luminal antigens that elicit and promote inflammatory response.^1,2 Both clinical and animal studies have shown the importance of a defective intestinal TJ barrier in the development and prolongation of intestinal inflammation in IBD and NEC.^1–5 These studies have shown that normalization of intestinal barrier in patients with active Crohn’s disease predicts prolonged clinical remission, whereas a persistent increase in intestinal permeability portends poor clinical outcome with rapid recurrence of the disease.^6,7 Additionally, animal studies have also shown that a primary defect in intestinal junctional complexes was sufficient to induce or aggravate intestinal inflammation in murine models of IBD,^8,9 whereas therapeutic tightening or enhancement of the intestinal TJ barrier prevented the development of intestinal inflammation.^3,10The terms endotoxin and lipopolysaccharide (LPS) are used interchangeably and refer to the major cell wall component of Gram-negative bacteria.^11,12 LPS are complex amphiphilic molecules having a hydrophobic (consisting of lipid A) and a hydrophilic (consisting of carbohydrate core and polysaccharide O-antigen) component and are released from bacterial cell wall by shedding or through bacterial lysis.^11–13 LPS concentrations are highest in the gut lumen, where many trillions of commensal bacteria reside. Normally, LPS in the gut lumen do not penetrate across the healthy intestinal epithelium^14,15; however, in intestinal permeability disorders, the defective TJ barrier allows paracellular flux of LPS and other luminal antigens.^{11–13,16–19} The intestinal tissue and circulating LPS levels are markedly elevated in IBD and NEC, and play an important role in mediating inflammatory response.^{11–13,16–18} The involvement of LPS in the initiation and propagation of intestinal inflammation in IBD and NEC has been well demonstrated.^20–23 These studies have shown LPS to be an important contributing factor of intestinal inflammation, and removal of circulating LPS accelerated the clinical improvement of IBD and NEC.^20,22,23 Despite the importance of a defective intestinal barrier in the accentuation and prolongation of intestinal inflammation in IBD and NEC,^3,6,9,20,22 the effects of circulating levels of LPS on the intestinal epithelial barrier remain unknown. Because LPS levels are markedly elevated in these diseases and play an important role in the inflammatory process, understanding the effects of LPS on intestinal barrier function has important potential clinical significance.In normal healthy individuals, plasma concentrations of LPS range from undetectable levels up to 0.2 ng/mL.^11,12,20,22 A variety of physiological factors such as prolonged physical exertion, high-fat diet, physiological stresses, or heat can lead to elevated plasma LPS levels as high as 1 to 2 ng/mL.^24–27 Patients with intestinal permeability disorders such as Crohn’s disease, NEC, acute pancreatitis, alcoholic liver disease, and critical illnesses also have elevated plasma LPS levels ranging up to 2 to 10 ng/mL.^{11–13,20,22,28} Based on these reports, we consider LPS levels of 0 to 1.0 ng/mL to be physiologically relevant and 0 to 10 ng/mL to be clinically relevant. (For reference, the concentration of LPS in the gut lumen has been reported to be 1.8 μg/mL in the rat distal ileum.^29,30) Inexplicably, in most of the published studies, extreme pharmacological concentrations of LPS ranging between 50 and 1000 μg/mL, which exceed the physiologically achievable concentrations by 10⁴- to 10⁷-fold, have been used to assess various biological responses.^30–34 At these extreme concentrations, LPS causes rapid cell death in various cell types studied, including in intestinal and immune cells,^30,33–35 and does not provide accurate depiction of biological activity of LPS. Herein, we show that LPS, at physiologically and clinically relevant concentrations (0 to 10 ng/mL), does not cause intestinal epithelial cell death, but causes a selective increase in intestinal TJ permeability in vitro and in vivo. These studies also show for the first time that pattern recognition receptors Toll-like receptor 4 (TLR-4) and CD14 play a central role in the modulation of the intestinal epithelial TJ barrier.     

Woven Endobridge device for treatment of dissection-related PICA aneurysm

Ruptured vertebrobasilar dissecting aneurysms require urgent, often challenging treatment as they have with a high re-hemorrhage rate within the first 24 hours. The patient is a 57-year-old woman who presented with severe-sudden onset headache. Further work up showed a ruptured dissecting aneurysm of the caudal loop of the posterior inferior cerebellar artery (PICA) with associated narrowing distally, in the ascending limb. The aneurysm was immediately occluded with a Woven Endobridge (WEB) device (MicroVention, Tustin, CA, USA) while flow diversion treatment of the diseased ascending limb was postponed. Follow-up angiography three months later showed complete occlusion of the aneurysm, as well as healing of the diseased distal vessel, obviating the need for further intervention. WEB embolization of a ruptured dissecting posterior circulation aneurysm provided an excellent outcome for this patient.     

Fitness costs in chlorfenapyr-resistant populations of the chive maggot,Bradysia odoriphaga

The chive maggot, Bradysia odoriphaga (Yang and Zhang) is an economically important insect pest, affecting many key vegetables, including Chinese chive, especially in northern China. Chlorfenapyr, a halogenated pyrrole insecticide that interferes with mitochondrial oxidative phosphorylation is widely used against B. odoriphaga. In this study, we evaluated selection-induced resistance to chlorfenapyr and fitness costs in B. odoriphaga. The results showed that B. odoriphaga developed 43.32-fold resistance after continuous exposure to chlorfenapyr for over 10 consecutive generations. The life-history traits of chlorfenapyr-resistant and susceptible strains were compared using age-stage, two-sex life table approach. No significant effects were observed on the longevity and pre-adult period. However, reduction in the total pre-oviposition period (TPOP) and fecundity (eggs/female) were observed in the resistant strain. Moreover, the demographic parameters such as intrinsic rate of increase (r), net reproductive rate (R0) and finite rate of increase (λ) were also decreased significantly in the resistant strain compared to the susceptible strain. These results showed the potential of B. odoriphaga to develop resistance against chlorfenapyr under continuous selection pressure. Furthermore, there was a fitness cost linked with chlorfenapyr resistance in B. odoriphaga. We conclude that a better knowlegde on the trade-off at play between resistance degree and fitness cost could be crucial for developing further management of B. odoriphaga in China.     

Expression of hepcidin is down-regulated in TfR2 mutant mice manifesting a phenotype of hereditary hemochromatosis

Transferrin receptor 2 (TfR2) is a membrane glycoprotein that mediates cellular iron uptake from holotransferrin. Homozygous mutations of this gene cause one form of hereditary hemochromatosis in humans. We recently reported that homozygous TfR2(Y245X) mutant mice, which correspond to the TfR2(Y250X) mutation in humans, showed a phenotype similar to hereditary hemochromatosis. In this study, we further analyzed the phenotype as well as iron-related gene expression in these mice by comparing the TfR2-mutant and wild-type siblings. Northern blot analyses showed that the levels of expression of hepcidin mRNA in the liver were generally lower, whereas those of duodenal DMT1, the main transporter for uptake of dietary iron, were higher in the TfR2-mutant mice as compared to the wild-type siblings. Expression of hepcidin mRNA in the TfR2 mutant mice remained low even after intraperitoneal iron loading. In isolated hepatocytes from both wild-type and TfR2 mutant mice, interleukin-6 and lipopolysaccharide each induced expression of hepcidin mRNA. These results suggest that up-regulation of hepcidin expression by inflammatory stimuli is independent of TfR2 and that TfR2 is upstream of hepcidin in the regulatory pathway of body iron homeostasis.     

Erythropoietin production in a primary culture of human renal carcinoma cells maintained in nude mice

The present studies report erythropoietin (Ep) production in primary cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted to BALB/c nude mice. The levels of erythropoietin in the culture media were estimated using the exhypoxic polycythemic mouse assay (EHPCMA), fetal mouse liver erythroid colony- forming technique (FMLC), and a radioimmunoassay (RIA). The spent culture media of the exponentially growing cells contained less than 10 mU/ml of Ep measured by RIA. However, after the cells became confluent, Ep levels (RIA) in the spent media showed a marked increase to approximately 300 mU/ml. Ep levels estimated using the FMLC and EHPCMA were approximately 2/3 and 1/10, respectively, of those measured by RIA. Rabbit antiserum to highly purified human urinary Ep (70,400 U/mg protein) was utilized for immunocytochemical (peroxidase-antiperoxidase method) localization of Ep in the cultured cells. Very few of the cells in exponential growth exhibited Ep-like immunoreactivity, whereas intense Ep-like immunoreactivity was observed in the cytoplasm of the cells maintained in culture for a prolonged period after reaching confluency. The most intense staining was observed in some of the cells forming domes. The domes developed after the cells reached confluency, and their numbers increased with increasing time in confluent culture, in parallel with the increase in Ep levels in the spent media. This primary cell culture system of a renal cell carcinoma maintained in nude mice, which produces immunologically and biologically active Ep, may provide a useful model for studies of the mechanism of Ep production.     

Wound repair during arm regeneration in the red starfish Echinaster sepositus

Starfish can regenerate entire arms following their loss by both autotomic and traumatic amputation. Although the overall regenerative process has been studied several times in different asteroid species, there is still a considerable gap of knowledge as far as the detailed aspects of the repair phase at tissue and cellular level are concerned, particularly in post‐traumatic regeneration. The present work is focused on the arm regeneration model in the Mediterranean red starfish Echinaster sepositus; to describe the early cellular mechanisms of arm regeneration following traumatic amputation, different microscopy techniques were employed. In E. sepositus, the repair phase was characterized by prompt wound healing by a syncytial network of phagocytes and re‐epithelialisation followed by a localized subepidermal oedematous area formation. Scattered and apparently undifferentiated cells, intermixed with numerous phagocytes, were frequently found in the wound area during these first stages of regeneration and extensive dedifferentiation phenomena were seen at the level of the stump, particularly in the muscle bundles. A true localized blastema did not form. Our results confirm that regeneration in asteroids mainly relies on morphallactic processes, consisting in extensive rearrangement of the existing tissues which contribute to the new tissues through cell dedifferentiation, redifferentiation, and/or migration.