Effects of epidermal growth factor and Clostridium difficile toxin B in a model of mucosal injury

Murine Intrarectal Instillation of Purified Recombinant Clostridioides difficile Toxins Enables Mechanistic Studies of Pathogenesis

Clostridioides difficile is linked to nearly 225,000 antibiotic-associated diarrheal infections and almost 13,000 deaths per year in the United States. Pathogenic strains of C. difficile produce toxin A (TcdA) and toxin B (TcdB), which can directly kill cells and induce an inflammatory response in the colonic mucosa. Hirota et al. (S. A. Hirota et al., Infect Immun 80:4474-4484, 2012) first introduced the intrarectal instillation model of intoxication using TcdA and TcdB purified from VPI 10463 (VPI 10463 reference strain [ATCC 43255]) and 630 C. difficile strains. Here, we expand this technique by instilling purified, recombinant TcdA and TcdB, which allows for the interrogation of how specifically mutated toxins affect tissue. Mouse colons were processed and stained with hematoxylin and eosin for blinded evaluation and scoring by a board-certified gastrointestinal pathologist. The amount of TcdA or TcdB needed to produce damage was lower than previously reported in vivo and ex vivo Furthermore, TcdB mutants lacking either endosomal pore formation or glucosyltransferase activity resemble sham negative controls. Immunofluorescent staining revealed how TcdB initially damages colonic tissue by altering the epithelial architecture closest to the lumen. Tissue sections were also immunostained for markers of acute inflammatory infiltration. These staining patterns were compared to slides from a human C. difficile infection (CDI). The intrarectal instillation mouse model with purified recombinant TcdA and/or TcdB provides the flexibility needed to better understand structure/function relationships across different stages of CDI pathogenesis.

Periplaneta americana extract promotes intestinal mucosa repair of ulcerative colitis in rat

PURPOSE

To investigate the mechanism of Periplaneta americana extract promoting intestinal mucosal repair of OXZ-induced colitis in rat.

METHODS

All experiments used an equal number of male and female SD rats (n=48). We injected OXZ into the colon to induce UC rat model. To determine the optimal concentration of P. Americana's extract (PA-40), it was classified into low (L), medium (M), and high (H) doses. After OXZ treatment, each drug was administered by enema for 7 consecutive days. Rats were divided into the following 6 groups: (1) Saline treatment group (NC), (2) OXZ treatment UC model group (MC), (3) OXZ + budesonide group (BUN), (4) OXZ + PA-40 L group, (5) OXZ + PA-40 M group, (6) OXZ + PA-40 H group. Disease activity index (DAI) scores, colon length, histopathological score, serum cytokine level (IL-4, IL-10, iNOS, tNOS), and amount of MPO, EGF, IL-13 in colonic mucosa were measured.

RESULTS

PA treatment had a significant healing effect on the OXZ-colitis model and significantly reduced the lesioned area, especially in the PA-40H groups. PA treatment did not alter the expression of IL-10 and MPO level, but increased EGF (epidermal growth factor) and decrease IL-13 in the colonic tissue. PA inhibited the rise of NOSs (nitric oxide synthase) and decreased the serum IL-4 level.

CONCLUSIONS

The data suggest that Periplaneta americana extract may be a potential compound for the treatment of colonic lesions. The mechanism may be related to inhibiting the secretion of IL-13 and promoting the formation of EGF.

Trend, Risk Factors, and Costs of Clostridium difficile Infections in Vascular Surgery

BACKGROUND

Starting in December 2013, the Hospital Inpatient Quality Reporting Program included Clostridium difficile infection (CDI) rates as a new publically reported quality measure. Our goal was to review the trend, hospital variability in CDI rates, and associated risk factors and costs in vascular surgery.

METHODS

The rates of CDI after major vascular procedures including aortic abdominal aneurysm (AAA) repair, carotid endarterectomy or stenting, lower extremity revascularization (LER), and LE amputation were identified using Nationwide Inpatient Sample database for 2000-2011. Risk factors associated with CDI were analyzed with hierarchical multivariate logistic regression. Extra costs, length of stay (LOS), and mortality were assessed for propensity-matched hospitalizations with and without CDI.

RESULTS

During the study period, the rates of CDI after vascular procedures had increased by 74% from 0.6 in 2000 to 1.05% in 2011, whereas the case fatality rate was stable at 9-11%. In 2011, the highest rates were after ruptured aortic abdominal aneurysm (rAAA) repair (3.3%), followed by lower extremity amputations (2.3%) and elective open AAA (1.3%). The rates of CDI increased after all vascular procedures during the 12 years. The highest increase was after endovascular LER (151.8%) and open rAAA repair (135.7%). In 2011, patients who had experienced CDI had median LOS of 15 days (interquartile range, 9-25 days) compared with 8.3 days for matched patients without CDI, in-hospital mortality 9.1% (compared with 5.0%), and $13,471 extra cost per hospitalization. The estimated cost associated with CDI in vascular surgery in the United States was ∼$98 million in 2011. Hospital rates of CDI varied from 0 to 50% with 3.5% of hospitals having infection rates ≥5%. Factors associated with CDI included multiple chronic conditions, female gender, surgery type, emergent and weekend hospitalizations, hospital transfers, and urban locations.

CONCLUSIONS

Despite potential reduction of infection rates as evidenced by the experience of hospitals with effective interventions, CDI is increasing among vascular surgery patients. It is associated with prolonged LOS, increased mortality, and higher costs.

The systemic inflammatory response to Clostridium difficile infection

Background

The systemic inflammatory response to Clostridium difficile infection (CDI) is incompletely defined, particularly for patients with severe disease.

Methods

Analysis of 315 blood samples from 78 inpatients with CDI (cases), 100 inpatients with diarrhea without CDI (inpatient controls), and 137 asymptomatic outpatient controls without CDI was performed. Serum or plasma was obtained from subjects at the time of CDI testing or shortly thereafter. Severe cases had intensive care unit admission, colectomy, or death due to CDI within 30 days after diagnosis. Thirty different circulating inflammatory mediators were quantified using an antibody-linked bead array. Principal component analysis (PCA), multivariate analysis of variance (MANOVA), and logistic regression were used for analysis.

Results

Based on MANOVA, cases had a significantly different inflammatory profile from outpatient controls but not from inpatient controls. In logistic regression, only chemokine (C-C motif) ligand 5 (CCL5) levels were associated with cases vs. inpatient controls. Several mediators were associated with cases vs. outpatient controls, especially hepatocyte growth factor, CCL5, and epithelial growth factor (inversely associated). Eight cases were severe and associated with elevations in IL-8, IL-6, and eotaxin.

Conclusions

A broad systemic inflammatory response occurs during CDI and severe cases appear to differ from non-severe infections.

Serine-71 phosphorylation of Rac1/Cdc42 diminishes the pathogenic effect of Clostridium difficile toxin A

Clostridium difficile toxin A and B (TcdA/TcdB) are glucosyltransferases that glucosylate GTPases of the Rho family. The epidermal growth factor (EGF) positively modulates C. difficile toxin-induced disturbance of the intestinal barrier function by an unknown mechanism. We found that EGF-treated CaCo-2 monolayers were less susceptible to TcdA-catalysed glucosylation of Rac1 but not of RhoA, which correlated with phosphorylation of Rac1 at Ser-71. Phospho-Rac1/phospho-Cdc42 (Ser-71) still bound to the PAK-CRIB domain indicating an active state. A more detailed characterization of phospho-Rac1 was performed using the phosphomimetic mutant Rac1 S71E. Ectopic expression of Rac1 S71E induced a specific phenotype of cells showing an increase in filopodial structures that were also induced by EGF. Rac1 S71E (and Cdc42 S71E) but not Rac1 S71A was at least fivefold weaker substrate for TcdA-catalysed glucosylation compared with wild type Rac1. The protective effect was checked in transfection experiments where Rac1 S71E and, to a lesser extent, Cdc42 S71E reduced the TcdA-induced cytopathic effect. Thus, Ser-71 phosphorylation of Rac1 might be interesting for modulation of microbial pathogenesis where Rho GTPases, especially Rac1 and Cdc42, are involved. In addition, this is the first description of a specific functional outcome of Rac1 phosphorylation at Ser-71.

Necrotizing enterocolitis: a practical guide to its prevention and management

Neonatal necrotizing enterocolitis is the second most common cause of morbidity in premature infants and requires intensive care over an extended period. Despite advances in medical and surgical techniques, the mortality and long-term morbidity due to necrotizing enterocolitis remain very high. Recent advances have shifted the attention of researchers from the classic triad (ischemia, bacteria, and the introduction of a metabolic substrate into the intestine) of necrotizing enterocolitis, to gut maturation, feeding practices, and inflammation. The focus on inflammation includes proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-6, IL-18, and platelet-activating factor. Research related to the etiology of necrotizing enterocolitis has moved quickly from clostridial toxin to bacterial and other infectious agents. More recently, the pattern of bacterial colonization has been given emphasis rather than the particular species or strain of bacteria or their virulence. Gram-negative bacteria that form part of the normal flora are now speculated as important factors in triggering the injury process in a setting where there is a severe paucity of bacterial species and possible lack of protective Gram-positive organisms. Although the incidence of necrotizing enterocolitis has increased because of the survival of low birthweight infants, clinicians are more vigilant in their detection of the early gastrointestinal symptoms of necrotizing enterocolitis; however, radiographic demonstration of pneumatosis intestinalis remains the hallmark of necrotizing enterocolitis. With prompt diagnosis, a large proportion of infants with necrotizing enterocolitis are now able to be managed medically with intravenous fluid and nutrition, nasogastric suction, antibacterials, and close monitoring of physiologic parameters. In the advanced cases that require surgery, clinicians tend to opt for either simple peritoneal drainage (for very small and sick infants) or laparotomy and resection of the affected part. Intestinal transplantation later in life is available as a viable option for those who undergo resection of large segments of the intestine. It is becoming more evident that treatment of this devastating disease is expensive and comes with the toll of significant long-term sequelae. This has resulted in renewed interest in designing alternative strategies to prevent this serious gastrointestinal disease. Simple trophic feeding and the use of L-glutamine and arginine are novel avenues that have been examined. The use of probiotics ('friendly' bacterial flora) has been introduced as a promising tool for establishing healthy bacterial flora in the newborn gut to block the injury process that may ultimately lead to necrotizing enterocolitis.

The epidemiology and pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC), a syndrome characterized by crepitant necrosis of the bowel, has emerged as the most common neonatal gastrointestinal emergency in many countries of the world. In the United States, NEC strikes 1 to 8% of patients admitted to neonatal intensive care units, almost all of whom are premature infants. The incidence is low in certain countries wity a low premature birth rate, e.g., Japan. Two theories of pathogenesis are: the Santulli theory, which implicates three factors: ischaemia, bacteria and substrate; and the Lawrence theory, which stresses the injurious role of bacterial toxins on the immature gut of the preterm infant. Clinical and experimental evidence support each of the theories, but neither theory can explain certain clinical phenomena, particularly the resistance to NEC manifested by more than 90% of preterm infants, who never develop the syndrome. A unifying hypothesis of pathogenesis and a mathematical model of NEC are outlined. Because clustering of cases may occur, the design of clinical trials of preventive measures for NEC must include simultaneous control infants.

Regulation of Apoptosis by Gram-Positive Bacteria: Mechanistic Diversity and Consequences for Immunity

Apoptosis, or programmed cell death (PCD), is an important physiological mechanism, through which the human immune system regulates homeostasis and responds to diverse forms of cellular damage. PCD may also be involved in immune counteraction to microbial infection. Over the past decade, the amount of research on bacteria-induced PCD has grown tremendously, and the implications of this mechanism on immunity are being elucidated. Some pathogenic bacteria actively trigger the suicide response in critical lineages of leukocytes that orchestrate both the innate and adaptive immune responses; other bacteria proactively prevent PCD to benefit their own survival and persistence. Currently, the microbial virulence factors, which represent the keys to unlocking the suicide response in host cells, are a primary focus of this field. In this review, we discuss these bacterial "apoptosis regulatory molecules" and the apoptotic events they either trigger or prevent, the host target cells of this regulatory activity, and the possible ramifications for immunity to infection. Gram-positive pathogens including Staphylococcus, Streptococcus, Bacillus, Listeria, and Clostridia species are discussed as important agents of human infection that modulate PCD pathways in eukaryotic cells.

MAPK interacts with occludin and mediates EGF-induced prevention of tight junction disruption by hydrogen peroxide

The MAPK (mitogen-activated protein kinase) pathway is a major intracellular signalling pathway involved in EGF (epithelial growth factor) receptor-mediated cell growth and differentiation. A novel function of MAPK activity in the mechanism of EGF-mediated protection of TJs (tight junctions) from H2O2 was examined in Caco-2 cell monolayers. EGF-mediated prevention of H2O2-induced increase in paracellular permeability was associated with the prevention of H2O2-induced Tyr-phosphorylation, Thr-dephosphorylation and cellular redistribution of occludin and ZO-1 (zonula occludin-1). EGF also prevented H2O2-induced disruption of the actin cytoskeleton and the dissociation of occludin and ZO-1 from the actin-rich detergent-insoluble fractions. MEK (MAPK/ERK kinase, where ERK stands for extracellular signal related kinase) inhibitors, PD98059 and U0126, completely blocked these protective effects of EGF on TJs. EGF rapidly increased the levels of phosphorylated MEK (p-MEK) in detergent-soluble fractions and phosphorylated ERK (p-ERK) in detergent-insoluble fractions. p-ERK was colocalized and co-immunoprecipitated with occludin. GST (glutathione S-transferase) pull-down assay showed that the C-terminal tail of occludin binds to p-ERK in Caco-2 cell extracts. Pair-wise binding studies using recombinant proteins demonstrated that ERK1 directly interacts with the C-terminal tail of occludin. Therefore the present study shows that ERK interacts with the C-terminal region of occludin and mediates the prevention of H2O2-induced disruption of TJs by EGF.

Epidermal growth factor prevents acetaldehyde-induced paracellular permeability in Caco-2 cell monolayer

BACKGROUND

Intestinal permeability and endotoxemia play a crucial role in the pathogenesis of alcoholic liver disease. Previous studies showed that acetaldehyde disrupts intestinal epithelial barrier function and increases paracellular permeability by a tyrosine kinase-dependent mechanism. In the present study, the role of epidermal growth factor (EGF) in protection of epithelial barrier function from acetaldehyde was evaluated in Caco-2 intestinal epithelial cell monolayer.

METHODS

Caco-2 cells on Transwell inserts were exposed to acetaldehyde in the absence or presence of EGF, and the paracellular permeability was evaluated by measuring transepithelial electrical resistance and unidirectional flux of inulin. Integrity of epithelial tight junctions and adherens junctions was analyzed by confocal immunofluorescence microscopy and immunoblot analysis of occludin, zonula occludens (ZO)-1, E-cadherin, and beta-catenin in the actin cytoskeleton. Reorganization of actin cytoskeletal architecture was examined by confocal microscopy.

RESULTS

Acetaldehyde increased paracellular permeability to inulin and lipopolysaccharide, and EGF significantly reduced these effects of acetaldehyde in a time- and dose-dependent manner. EGF prevented acetaldehyde-induced reorganization of occludin, ZO-1, E-cadherin, and beta-catenin from the cellular junctions to the intracellular compartments. Acetaldehyde treatment induced a reorganization of actin cytoskeletal network and reduced the levels of occludin, ZO-1, E-cadherin, and beta-catenin associated with the actin cytoskeleton. EGF effectively prevented acetaldehyde-induced reorganization of actin cytoskeleton and the interaction of occludin, ZO-1, E-cadherin, and beta-catenin with the actin cytoskeleton.

CONCLUSION

These results indicate that EGF attenuates acetaldehyde-induced disruption of tight junctions and adherens junctions and prevents acetaldehyde-induced reorganization of actin cytoskeleton and its interaction with occludin, ZO-1, E-cadherin, and beta-catenin.

Key role of PKC and Ca2+ in EGF protection of microtubules and intestinal barrier against oxidants

Using monolayers of human intestinal (Caco-2) cells, we showed that growth factors (GFs) protect microtubules and barrier integrity against oxidative injury. Studies in nongastrointestinal cell models suggest that protein kinase C (PKC) signaling is key in GF-induced effects and that cytosolic calcium concentration ([Ca2+](i)) is essential in cell integrity. We hypothesized that GF protection involves activating PKC and maintaining normal ([Ca2+](i)) Monolayers were pretreated with epidermal growth factor (EGF) or PKC or Ca2+ modulators before exposure to oxidants (H2O2 or HOCl). Oxidants disrupted microtubules and barrier integrity, and EGF protected from this damage. EGF caused rapid distribution of PKC-alpha, PKC-betaI, and PKC-zeta isoforms to cell membranes, enhancing PKC activity of membrane fractions while reducing PKC activity of cytosolic fractions. EGF enhanced (45)Ca2+ efflux and prevented oxidant-induced (sustained) rises in ([Ca2+](i)). PKC inhibitors abolished and PKC activators mimicked EGF protection. Oxidant damage was mimicked by and potentiated by a Ca2+ ionophore (A-23187), exacerbated by high-Ca2+ media, and prevented by calcium removal or chelation or by Ca2+ channel antagonists. PKC activators mimicked EGF on both (45)Ca2+ efflux and ([Ca2+](i)). Membrane Ca2+-ATPase pump inhibitors prevented protection by EGF or PKC activators. In conclusion, EGF protection of microtubules and the intestinal epithelial barrier requires activation of PKC signal transduction and normalization of ([Ca2+](i)).

New concepts in necrotizing enterocolitis

Necrotizing enterocolitis is an overwhelming gastrointestinal emergency that primarily afflicts premature infants born weighing less than 1500 g. Despite years of investigation, the etiology remains unclear, and accepted prevention and treatment strategies are lacking. Studies published over the last year have provided new insight into several aspects of this complex disease. In this review, novel information is presented on (1) the epidemiology; (2) methods of early diagnosis, such as abdominal magnetic resonance imaging; (3) the importance of risk factors, including assessment of feeding strategies and role of bacterial colonization; (4) the pathophysiology, highlighting experimental and clinical trials evaluating the role of inflammatory mediators and growth factors on the disease; (5) preventive strategies, such as anaerobic bacterial supplementation; and (6) surgical interventions, including peritoneal drainage. Understanding some of these important aspects of necrotizing enterocolitis may help improve the outlook of patients with this dreaded disease. Although the incidence of neonatal necrotizing enterocolitis (NEC) and the mortality stemming from this disease have not significantly improved over the last 30 years, there is exciting new information that may significantly improve the outlook of patients with this overwhelming intestinal emergency in the near future.

Effects of Clostridium difficile toxins on epithelial cell barrier

Clostridium difficile is the primary agent responsible for many patients with antibiotic-associated diarrhea and almost all patients with pseudomembranous colitis following antibiotic therapy. C. difficile infection is the most frequent form of colitis in hospitals and nursing homes and affects millions of patients in the United States and abroad. The first event in the pathogenesis of C. difficile infection involves alterations of the indigenous colonic microflora by antibiotics, followed by colonization with C. difficile. C. difficile causes diarrhea and colitis by releasing two high molecular weight protein exotoxins, toxin A and toxin B, with potent cytotoxic and enterotoxic properties. Evidence presented here indicates that C. difficile toxins compromise the epithelial cell barrier by at least two pathophysiologic pathways, one involving disaggregation of actin microfilaments in colonocytes via glucosylation of the Rho family of proteins leading to epithelial cell destruction and opening of the tight junctions, whereas the other appears to involve early release of proinflammatory cytokines from intestinal epithelial cells probably via activation of MAP kinases. We speculate that cytokines released from intestinal epithelial cells in response to toxin A exposure will diffuse into the lamina propria and activate macrophages, enteric nerves, and sensory neurons to release SP, CGRP, and NT, which, in turn, interact with immune and inflammatory cells and amplify the inflammatory response. Dissection of this inflammatory cascade may help us understand the pathophysiology of inflammatory diarrhea caused by this important pathogen.

Necrotizing enterocolitis in infants with very low birth weight

Necrotizing enterocolitis (NEC) is a disease in which the primary risk factor is prematurity. Despite, and partially as a result of, the tremendous strides neonatal care has taken, it is a major cause of morbidity and mortality of the newborn. The infant with very low birth weight is particularly susceptible, and the management of the condition in this group differs somewhat from other neonates. The outcomes continue to improve, but there are significant sequelae. Prevention, which would be the best "cure," is elusive, in no small part because of the multifactorial nature of the etiology of NEC.

Activation of Rho GTPases by Escherichia coli cytotoxic necrotizing factor 1 increases intestinal permeability in Caco-2 cells

The cytotoxic necrotizing factor 1 (CNF1) activates Rho GTPases by deamidation of glutamine-63 and thereby induces redistribution of the actin cytoskeleton and formation of stress fibers. Here, we have studied the effects of CNF1 on the transepithelial resistance of Caco-2 cells, a human intestinal epithelial cell line, in comparison with the Rho-inactivating toxin B of Clostridium difficile. Whereas toxin B decreased the transepithelial resistance of Caco-2 cells by about 80% after 4 h, CNF1 reduced it by about 40%. Significant changes of the transepithelial resistance induced by CNF1 were detected after 3 h of incubation. Half-maximal effects were observed with 10 and 41 ng of CNF1 and toxin B per ml, respectively. Flux measurement revealed no CNF1-induced increase of fluorescein isothiocyanate-dextran permeation within the first 4 h of incubation and a 2.9-fold increase after 24 h of incubation. In contrast, toxin B induced a 28-fold increase of permeation after 24 h. As detected by rhodamine-phalloidin staining, CNF1 increased polymerization of F actin at focal contacts of adjacent cells and induced formation of stress fibers. The data indicate that not only depolymerization but also polymerization of actin and subsequent reorganization of the actin cytoskeleton alter the barrier function of intestinal tight junctions.