Clostridium difficile toxin A regulates inducible cyclooxygenase-2 and prostaglandin E2 synthesis in colonocytes via reactive oxygen species and activation of p38 MAPK

Exploring the Toxin-Mediated Mechanisms in Clostridioides difficile Infection

Clostridioides difficile infection (CDI) is the leading cause of nosocomial antibiotic-associated diarrhea, and colitis, with increasing incidence and healthcare costs. Its pathogenesis is primarily driven by toxins produced by the bacterium C. difficile, Toxin A (TcdA) and Toxin B (TcdB). Certain strains produce an additional toxin, the C. difficile transferase (CDT), which further enhances the virulence and pathogenicity of C. difficile. These toxins disrupt colonic epithelial barrier integrity, and induce inflammation and cellular damage, leading to CDI symptoms. Significant progress has been made in the past decade in elucidating the molecular mechanisms of TcdA, TcdB, and CDT, which provide insights into the management of CDI and the future development of novel treatment strategies based on anti-toxin therapies. While antibiotics are common treatments, high recurrence rates necessitate alternative therapies. Bezlotoxumab, targeting TcdB, is the only available anti-toxin, yet limitations persist, prompting ongoing research. This review highlights the current knowledge of the structure and mechanism of action of C. difficile toxins and their role in disease. By comprehensively describing the toxin-mediated mechanisms, this review provides insights for the future development of novel treatment strategies and the management of CDI.

Sebocytes contribute to melasma onset

Melasma is a hyperpigmentary disorder with photoaging features, whose manifestations appear on specific face areas, rich in sebaceous glands (SGs). To explore the SGs possible contribution to the onset, the expression of pro-melanogenic and inflammatory factors from the SZ95 SG cell line exposed to single or repetitive ultraviolet (UVA) radiation was evaluated. UVA up-modulated the long-lasting production of α-MSH, EDN1, b-FGF, SCF, inflammatory cytokines and mediators. Irradiated SZ95 sebocyte conditioned media increased pigmentation in melanocytes and the expression of senescence markers, pro-inflammatory cytokines, and growth factors regulating melanogenesis in fibroblasts cultures. Cocultures experiments with skin explants confirmed the role of sebocytes on melanogenesis promotion. The analysis on sebum collected from melasma patients demonstrated that in vivo sebocytes from lesional areas express the UVA-activated pathways markers observed in vitro. Our results indicate sebocytes as one of the actors in melasma pathogenesis, inducing prolonged skin cell stimulation, contributing to localized dermal aging and hyperpigmentation.

Streptococcus suis Induces Expression of Cyclooxygenase-2 in Porcine Lung Tissue

Streptococcus suis is a common pathogen colonising the respiratory tract of pigs. It can cause meningitis, sepsis and pneumonia leading to economic losses in the pig industry worldwide. Cyclooxygenase-2 (COX-2) and its metabolites play an important regulatory role in different biological processes like inflammation modulation and immune activation. In this report we analysed the induction of COX-2 and the production of its metabolite prostaglandin E₂ (PGE₂) in a porcine precision-cut lung slice (PCLS) model. Using Western blot analysis, we found a time-dependent induction of COX-2 in the infected tissue resulting in increased PGE₂ levels. Immunohistological analysis revealed a strong COX-2 expression in the proximity of the bronchioles between the ciliated epithelial cells and the adjacent alveolar tissue. The morphology, location and vimentin staining suggested that these cells are subepithelial bronchial fibroblasts. Furthermore, we showed that COX-2 expression as well as PGE₂ production was detected following infection with two prevalent S. suis serotypes and that the pore-forming toxin suilysin played an important role in this process. Therefore, this study provides new insights in the response of porcine lung cells to S. suis infections and serves as a basis for further studies to define the role of COX-2 and its metabolites in the inflammatory response in porcine lung tissue during infections with S. suis.

PGE2 upregulates gene expression of dual oxidase in a lepidopteran insect midgut via cAMP signalling pathway

In insect midgut, prostaglandins (PGs) play a crucial role in defending bacterial and malarial pathogens. However, little is known about the PG signalling pathway in the midgut. A dual oxidase (Se-Duox) with presumed function of catalysing reactive oxygen species (ROS) production in the midgut was identified in beet armyworm, Spodoptera exigua. Se-Duox was expressed in all developmental stages, exhibiting relatively high expression levels in the midgut of late larval instars. Se-Duox expression was upregulated upon bacterial challenge. RNA interference (RNAi) of Se-Duox expression significantly suppressed ROS levels in the midgut lumen. The suppression of ROS levels increased insecticidal activity of Serratia marcescens after oral infection. Interestingly, treatment with a PLA₂ inhibitor prevented the induction of Se-Duox expression in response to bacterial challenge. On the other hand, addition of its catalytic product rescued the induction of Se-Duox expression. Especially, PG synthesis inhibitor significantly suppressed Se-Duox expression, while the addition of PGE₂ or PGD₂ rescued the inhibition. Subsequent PG signals involved cAMP and downstream components because specific inhibitors of cAMP signal components such as adenylate cyclase (AC) and protein kinase A (PKA) significantly inhibited Se-Duox expression. Indeed, addition of a cAMP analogue stimulated Se-Duox expression in the midgut. Furthermore, individual RNAi specific to PGE₂ receptor (a trimeric G-protein subunit), AC, PKA or cAMP-responsive element-binding protein resulted in suppression of Se-Duox expression. These results suggest that PGs can activate midgut immunity via cAMP signalling pathway by inducing Se-Duox expression along with increased ROS levels.

Human intestinal enteroids as a model of Clostridioides difficile-induced enteritis

Clostridioides difficile is an important nosocomial pathogen that produces toxins to cause life-threatening diarrhea and colitis. Toxins bind to epithelial receptors and promote the collapse of the actin cytoskeleton. C. difficile toxin activity is commonly studied in cancer-derived and immortalized cell lines. However, the biological relevance of these models is limited. Moreover, no model is available for examining C. difficile-induced enteritis, an understudied health problem. We hypothesized that human intestinal enteroids (HIEs) express toxin receptors and provide a new model to dissect C. difficile cytotoxicity in the small intestine. We generated biopsy-derived jejunal HIE and Vero cells, which stably express LifeAct-Ruby, a fluorescent label of F-actin, to monitor actin cytoskeleton rearrangement by live-cell microscopy. Imaging analysis revealed that toxins from pathogenic C. difficile strains elicited cell rounding in a strain-dependent manner, and HIEs were tenfold more sensitive to toxin A (TcdA) than toxin B (TcdB). By quantitative PCR, we paradoxically found that HIEs expressed greater quantities of toxin receptor mRNA and yet exhibited decreased sensitivity to toxins when compared with traditionally used cell lines. We reasoned that these differences may be explained by components, such as mucins, that are present in HIEs cultures, that are absent in immortalized cell lines. Addition of human-derived mucin 2 (MUC2) to Vero cells delayed cell rounding, indicating that mucus serves as a barrier to toxin-receptor binding. This work highlights that investigation of C. difficile infection in that HIEs can provide important insights into the intricate interactions between toxins and the human intestinal epithelium.NEW & NOTEWORTHY In this article, we developed a novel model of Clostridioides difficile-induced enteritis using jejunal-derived human intestinal enteroids (HIEs) transduced with fluorescently tagged F-actin. Using live-imaging, we identified that jejunal HIEs express high levels of TcdA and CDT receptors, are more sensitive to TcdA than TcdB, and secrete mucus, which delays toxin-epithelial interactions. This work also optimizes optically clear C. difficile-conditioned media suitable for live-cell imaging.

Probiotic Supplementation is Associated with Increased Antioxidant Capacity and Copper Chelation in C. difficile-Infected Fecal Water

Probiotic supplementation plays a key role in maintaining intestinal homeostasis due to its ability to modulate gut microbiota. Although their potential as potent antioxidants have previously been explored, their ability to affect the redox status in the gut lumen of healthy subjects or those with gastrointestinal (GI) disorders remains unclear. In our study, we assessed the ability of single strain and multispecies probiotic supplementation to cause a change in the redox status of normal fecal water and in Clostridium (C.) difficile-infected fecal water using a simulated gastrointestinal model. Changes in redox status were assessed by ferric-reducing antioxidant power (FRAP), 2’,2’-diphenyl-1-picrylhydrazyl (DPPH), and iron and copper chelation assays. The findings from our study showed that in normal fecal water, probiotic supplements, apart from Lactobacillus (L.) rhamnosus R0011, showed a significant increase in iron chelation (p < 0.05), which was associated with lower FRAP and copper chelation. In C. difficile-infected fecal water, all probiotic supplements showed a significant increase in FRAP (p < 0.05) and were associated with increased copper chelation. The DPPH assay showed no treatment effect in either fecal water. These findings suggest that C. difficile mediates dysregulation of redox status, which is counteracted by probiotics through ferric-reducing ability and copper chelation.

Control of Clostridium difficile Infection by Defined Microbial Communities

Each year in the United States, billions of dollars are spent combating almost half a million Clostridium difficile infections (CDIs) and trying to reduce the ∼29,000 patient deaths in which C. difficile has an attributed role. In Europe, disease prevalence varies by country and level of surveillance, though yearly costs are estimated at €3 billion. One factor contributing to the significant health care burden of C. difficile is the relatively high frequency of recurrent CDIs. Recurrent CDI, i.e., a second episode of symptomatic CDI occurring within 8 weeks of successful initial CDI treatment, occurs in ∼25% of patients, with 35 to 65% of these patients experiencing multiple episodes of recurrent disease. Using microbial communities to treat recurrent CDI, either as whole fecal transplants or as defined consortia of bacterial isolates, has shown great success (in the case of fecal transplants) or potential promise (in the case of defined consortia of isolates). This review will briefly summarize the epidemiology and physiology of C. difficile infection, describe our current understanding of how fecal microbiota transplants treat recurrent CDI, and outline potential ways that knowledge can be used to rationally design and test alternative microbe-based therapeutics.

The role of toxins in Clostridium difficile infection

Clostridium difficile is a bacterial pathogen that is the leading cause of nosocomial antibiotic-associated diarrhea and pseudomembranous colitis worldwide. The incidence, severity, mortality and healthcare costs associated with C. difficile infection (CDI) are rising, making C. difficile a major threat to public health. Traditional treatments for CDI involve use of antibiotics such as metronidazole and vancomycin, but disease recurrence occurs in about 30% of patients, highlighting the need for new therapies. The pathogenesis of C. difficile is primarily mediated by the actions of two large clostridial glucosylating toxins, toxin A (TcdA) and toxin B (TcdB). Some strains produce a third toxin, the binary toxin C. difficile transferase, which can also contribute to C. difficile virulence and disease. These toxins act on the colonic epithelium and immune cells and induce a complex cascade of cellular events that result in fluid secretion, inflammation and tissue damage, which are the hallmark features of the disease. In this review, we summarize our current understanding of the structure and mechanism of action of the C. difficile toxins and their role in disease.

The American cockroach peptide periplanetasin-4 inhibits Clostridium difficile toxin A-induced cell toxicities and inflammatory responses in the mouse gut

Many reports have shown that crude extracts of the American cockroach have therapeutic effects on inflammation. In a previous study, our research group showed that an antimicrobial peptide (Periplanetasin-2) derived from the American cockroach via de novo transcriptome analysis inhibited apoptosis of human colonocytes and inflammatory responses of the mouse gut caused by Clostridium difficile toxin A. Here, we examined whether Periplanetasin-4 (Peri-4), another antimicrobial peptide identified via de novo transcriptome analysis of the American cockroach, could also inhibit the various toxicities induced by C. difficile toxin A. We found that Peri-4 significantly reduced the cell viability loss and cell apoptosis caused by toxin A in vitro. Peri-4 also ameliorated the severe inflammatory responses seen in the toxin A-induced mouse enteritis model, rescuing the villus disruption and interleukin-6 production induced by luminal injection of toxin A into the mouse gut. Mechanistically, we found that Peri-4 could reduce toxin A-induced reactive oxygen species production to inhibit the activations of p38MAPK and p21^Cip1/Waf1 , which are critical for the cell damages induced by toxin A. These results collectively suggest that the Peri-4 may be a potential therapeutic agent for treating toxin A-induced pseudomembranous colitis. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Immune responses induced by Clostridium difficile

The spectrum of Clostridium difficile infections is highly variable, ranging from asymptomatic carriage to fatal colitis depending on the strain virulence and on the host, its gut microbiota and its immune response. After disruption of the gut microbiota, C. difficile pathogenesis can be divided into three steps: 1) contamination by spores and their germination; 2) multiplication of vegetative cells and intestinal colonization using colonization factors; 3) production of the toxins TcdA and TcdB, and for some strains, the binary toxin, which are responsible for the clinical signs. Three lines of defense counteract C. difficile. The first line is the epithelial barrier, which is breached by the toxins. Then, a rapid innate immune response follows, which forms the second line of defense. It provides very quick defense reactions against C. difficile but is non-specific and does not confer memory. C. difficile and its virulence factors, the toxins and colonization factors, induce a highly pro-inflammatory response, which can be either beneficial or harmful, but triggers the adaptive immunity as the third line of defense required to control the infectious process. Adaptive immunity provides a highly specific immune response against C. difficile with memory and long lasting immunity. The innate and adaptive immune responses against the toxins and surface components are analyzed as well as their role in disease susceptibility, severity and recurrences.

The Clostridium difficile Dlt Pathway Is Controlled by the Extracytoplasmic Function Sigma Factor σV in Response to Lysozyme

Clostridium difficile (also known as Peptoclostridium difficile) is a major nosocomial pathogen and a leading cause of antibiotic-associated diarrhea throughout the world. Colonization of the intestinal tract is necessary for C. difficile to cause disease. Host-produced antimicrobial proteins (AMPs), such as lysozyme, are present in the intestinal tract and can deter colonization by many bacterial pathogens, and yet C. difficile is able to survive in the colon in the presence of these AMPs. Our prior studies established that the Dlt pathway, which increases the surface charge of the bacterium by addition of d-alanine to teichoic acids, is important for C. difficile resistance to a variety of AMPs. We sought to determine what genetic mechanisms regulate expression of the Dlt pathway. In this study, we show that a dlt null mutant is severely attenuated for growth in lysozyme and that expression of the dltDABC operon is induced in response to lysozyme. Moreover, we found that a mutant lacking the extracytoplasmic function (ECF) sigma factor σ(V) does not induce dlt expression in response to lysozyme, indicating that σ(V) is required for regulation of lysozyme-dependent d-alanylation of the cell wall. Using reporter gene fusions and 5' RACE (rapid amplification of cDNA ends) analysis, we identified promoter elements necessary for lysozyme-dependent and lysozyme-independent dlt expression. In addition, we observed that both a sigV mutant and a dlt mutant are more virulent in a hamster model of infection. These findings demonstrate that cell wall d-alanylation in C. difficile is induced by lysozyme in a σ(V)-dependent manner and that this pathway impacts virulence in vivo.

Pathogenic effects of glucosyltransferase from Clostridium difficile toxins

The glucosyltransferase domain ofClostridium difficiletoxins modifies guanine nucleotide-binding proteins of Rho family. It is the major virulent domain of the holotoxins. Various pathogenic effects ofC. difficiletoxins in response to Rho glucosylation have been investigated including cytoskeleton damage, cell death and inflammation. The most recent studies have revealed some significant characteristics of the holotoxins that are independent of glucosylating activity. These findings arouse discussion about the role of glucosyltransferase activity in toxin pathogenesis and open up new insights for toxin mechanism study. In this review, we summarize the pathogenic effects of glucosyltransferase domain of the toxins in the past years.

Reactive Oxygen Species as Additional Determinants for Cytotoxicity of Clostridium difficile Toxins A and B

Clostridium difficile infections can induce mild to severe diarrhoea and the often associated characteristic pseudomembranous colitis. Two protein toxins, the large glucosyltransferases TcdA and TcdB, are the main pathogenicity factors that can induce all clinical symptoms in animal models. The classical molecular mode of action of these homologous toxins is the inhibition of Rho GTPases by mono-glucosylation. Rho-inhibition leads to breakdown of the actin cytoskeleton, induces stress-activated and pro-inflammatory signaling and eventually results in apoptosis of the affected cells. An increasing number of reports, however, have documented further qualities of TcdA and TcdB, including the production of reactive oxygen species (ROS) by target cells. This review summarizes observations dealing with the production of ROS induced by TcdA and TcdB, dissects pathways that contribute to this phenomenon and speculates about ROS in mediating pathogenesis. In conclusion, ROS have to be considered as a discrete, glucosyltransferase-independent quality of at least TcdB, triggered by different mechanisms.

The Role of Rho GTPases in Toxicity of Clostridium difficile Toxins

Clostridium difficile (C. difficile) is the main cause of antibiotic-associated diarrhea prevailing in hospital settings. In the past decade, the morbidity and mortality of C. difficile infection (CDI) has increased significantly due to the emergence of hypervirulent strains. Toxin A (TcdA) and toxin B (TcdB), the two exotoxins of C. difficile, are the major virulence factors of CDI. The common mode of action of TcdA and TcdB is elicited by specific glucosylation of Rho-GTPase proteins in the host cytosol using UDP-glucose as a co-substrate, resulting in the inactivation of Rho proteins. Rho proteins are the key members in many biological processes and signaling pathways, inactivation of which leads to cytopathic and cytotoxic effects and immune responses of the host cells. It is supposed that Rho GTPases play an important role in the toxicity of C. difficile toxins. This review focuses on recent progresses in the understanding of functional consequences of Rho GTPases glucosylation induced by C. difficile toxins and the role of Rho GTPases in the toxicity of TcdA and TcdB.

Nicotine-induced cellular stresses and autophagy in human cancer colon cells: A supportive effect on cell homeostasis via up-regulation of Cox-2 and PGE(2) production

Nicotine, one of the active components in cigarette smoke, has been described to contribute to the protective effect of smoking in ulcerative colitis (UC) patients. Furthermore, the nicotinic acetylcholine receptor α7 subunit (α7nAChR) expressed on immune cells, is an essential regulator of inflammation. As intestinal epithelial cells also express α7nAChR, we investigated how nicotine could participate in the homeostasis of intestinal epithelial cells. First, using the human adenocarcinoma cell line HT-29, we revealed that nicotine, which triggers an influx of extracellular Ca(2+) following α7nAChR stimulation, induces mitochondrial reactive oxygen species (ROS) production associated with a disruption of the mitochondrial membrane potential and endoplasmic reticulum stress. This results in caspase-3 activation, which in turn induces apoptosis. Additionally, we have shown that nicotine induces a PI3-K dependent up-regulation of cyclooxygenase-2 (Cox-2) expression and prostaglandin E2 (PGE2) production. In this context, we suggest that this key mediator participates in the cytoprotective effects of nicotine against apoptosis by stimulating autophagy in colon cancer cells. Our results provide new insight into one potential mechanism by which nicotine could protect from UC and suggest an anti-inflammatory role for the cholinergic pathway at the epithelial cell level.

Critical roles of Clostridium difficile toxin B enzymatic activities in pathogenesis

TcdB is one of the key virulence factors of Clostridium difficile that is responsible for causing serious and potentially fatal colitis. The toxin contains at least two enzymatic domains: an effector glucosyltransferase domain for inactivating host Rho GTPases and a cysteine protease domain for the delivery of the effector domain into host cytosol. Here, we describe a novel intrabody approach to examine the role of these enzymes of TcdB in cellular intoxication. By screening a single-domain heavy chain (V(H)H) library raised against TcdB, we identified two V(H)H antibodies, 7F and E3, that specifically inhibit TcdB cysteine protease and glucosyltransferase activities, respectively. Cytoplasmic expression of 7F intrabody in Vero cells inhibited TcdB autoprocessing and delayed cellular intoxication, whereas E3 intrabody completely blocked the cytopathic effects of TcdB holotoxin. These data also demonstrate for the first time that toxin autoprocessing occurs after cysteine protease and glucosyltransferase domains translocate into the cytosol of target cells. We further determined the role of the enzymatic activities of TcdB in in vivo toxicity using a sensitive systemic challenge model in mice. Consistent with these in vitro results, a cysteine protease noncleavable mutant, TcdB-L543A, delayed toxicity in mice, whereas glycosyltransferase-deficient TcdB demonstrated no toxicity up to 500-fold of the 50% lethal dose (LD50) when it was injected systemically. Thus, glucosyltransferase but not cysteine protease activity is critical for TcdB-mediated cytopathic effects and TcdB systemic toxicity, highlighting the importance of targeting toxin glucosyltransferase activity for future therapy.

Host recognition of Clostridium difficile and the innate immune response

Clostridium difficile is a Gram-positive, spore forming bacillus and the most common cause of antibiotic-associated diarrhea in the United States. Clinical outcomes of C. difficile infection (CDI) range from asymptomatic colonization to pseudomembranous colitis, sepsis and death. Disease is primarily mediated by the action of the Rho-glucosylating toxins A and B, which induce potent pro-inflammatory signaling within the host. The role of this inflammatory response during infection is just beginning to be appreciated, with recent data suggesting inflammatory markers correlate closely with disease severity. In addition to the toxins, multiple innate immune signaling pathways have been implicated in establishing an inflammatory response during infection. In intoxication-based models of disease, inflammation typically enhances pathogenesis, while protection from infection seems to require some level of inflammatory response. Thus, the host immune response plays a key role in shaping the course of infection and a balanced inflammatory response which eradicates infection without damaging host tissues is likely required for successful resolution of disease.

Neurotropic and neuroprotective activities of the earthworm peptide Lumbricusin

We recently isolated a polypeptide from the earthworm Lumbricus terrestris that is structurally similar to defensin, a well-known antibacterial peptide. An 11-mer antibacterial peptide (NH2-RNRRWCIDQQA), designated Lumbricusin, was synthesized based on the amino acid sequence of the isolated polypeptide. Since we previously reported that CopA3, a dung beetle peptide, enhanced neuronal cell proliferation, we here examined whether Lumbricusin exerted neurotropic and/or neuroprotective effects. Lumbricusin treatment induced a time-dependent increase (∼51%) in the proliferation of human neuroblastoma SH-SY5Y cells. Lumbricusin also significantly inhibited the apoptosis and decreased viability induced by treatment with 6-hydroxy dopamine, a Parkinson's disease-mimicking agent. Immunoblot analyses revealed that Lumbricusin treatment increased ubiquitination of p27(Kip1) protein, a negative regulator of cell-cycle progression, in SH-SY5Y cells, and markedly promoted its degradation. Notably, adenoviral-mediated over-expression of p27(Kip1) significantly blocked the antiapoptotic effect of Lumbricusin in 6-hydroxy dopamine-treated SH-SY5Y cells. These results suggest that promotion of p27(Kip1) degradation may be the main mechanism underlying the neuroprotective and neurotropic effects of Lumbricusin.

Role of chemoprophylaxis with either NSAIDs or statins in patients with Barrett's esophagus

The incidence of esophageal adenocarcinoma, a poor prognosis neoplasia, has risen dramatically in recent decades. Barrett's esophagus represents the best-known risk factor for esophageal adenocarcinoma development. Non-steroidal anti-inflammatory drugs through cyclooxygenase-2 inhibition and prostaglandin metabolism regulation could control cell proliferation, increase cell apoptosis and regulate the expression of growth and angiogenic factors. Statins can achieve equivalent effects through prenylation and subsequently control of cellular signaling cascades. At present, epidemiological studies are small and underpowered. Their data could not justify either medication as a chemo-preventive agent. Population based studies have shown a 43% reduction of the odds of developing an esophageal adenocarcinoma, leaving out or stating a 25% reduction in patients consuming non-aspirin nonsteroidal anti-inflammatory drugs and a 50% reduction in those patients consuming aspirin. They have also stated a 19% reduction of esophageal cancer incidence when statins have been used. Observational studies have shown that non-steroidal anti-inflammatory drugs could reduce the adenocarcinoma incidence in patients with Barrett's esophagus by 41%, while statins could reduce the risk by 43%. The cancer preventive effect has been enhanced in those patients taking a combination of non-steroidal anti-inflammatory drugs and statins (a 74% decrease). Observational data are equivocal concerning the efficacy of non-steroidal anti-inflammatory drug subclasses. Non-steroidal anti-inflammatory drugs clearly have substantial potential for toxicity, while statins are rather safe drugs. In conclusion, both non-steroidal anti-inflammatory drugs and statins are promising chemopreventive agents and deserve further exploration with interventional studies. In the meanwhile, their use is justified only in patients with cardiovascular disease.

Probiotics for the treatment of Clostridium difficile associated disease

The purpose of this review paper is to update the current and potential future role of probiotics for Clostridium difficile-associated disease (CDAD). Included in this review, is an update on the testing of newer probiotics (e.g., Bacillus coagulans GBI-30, 6086) in animal models of CDAD. There is a focus on the modulation of signal transduction pathways (i.e., transcription factors like cAMP response element-binding, activator protein 1, and nuclear factor kappa B), as well as the inhibition of certain kinases (e.g., p38 mitogen activated protein kinases) by probiotics. Inhibition of signal transduction by probiotics, such as Saccharomyces boulardii, result in multiple effects on intestinal fluid secretion, neutrophil influx into the colon, inflammation, and colonocyte apoptosis that may positively impact CDAD. Recent clinical approaches with probiotics, for the prevention of primary and recurrent CDAD, are also summarized in this review paper. Future directions for the treatment of CDAD by probiotics are also mentioned in this review. In particular, the use of multi-strain probiotic formulations such as Ecologic^® AAD and VSL #3^® may represent a rationale pharmacological approach, particularly as adjunctive therapies for CDAD. Understanding the mechanistic basis of CDAD, and how probiotics interfere at ceratin steps in the pathogenic process, may also present the opportunity to design other multi-strain probiotics that could have a future impact on CDAD.

Human monoclonal antibodies against Clostridium difficile toxins A and B inhibit inflammatory and histologic responses to the toxins in human colon and peripheral blood monocytes

Clostridium difficile infection (CDI) is a common and debilitating nosocomial infection with high morbidity and mortality. C. difficile mediates diarrhea and colitis by releasing two toxins, toxin A and toxin B. Since both toxins stimulate proinflammatory signaling pathways in human colonocytes and both are involved in the pathophysiology of CDI, neutralization of toxin A and B activities may represent an important therapeutic approach against CDI. Recent studies indicated that human monoclonal antibodies (MAbs) against toxins A and B reduce their cytotoxic and secretory activities and prevent CDI in hamsters. Moreover, anti-toxin A and anti-toxin B MAbs together with antibiotics also effectively reduced recurrent CDI in humans. However, whether these MAbs neutralize toxin A- and toxin B-associated immune responses in human colonic mucosa or human peripheral blood monocyte cells (PBMCs) has never been examined. We used fresh human colonic biopsy specimens and peripheral blood monocytes to evaluate the effects of these antibodies against toxin A- and B-associated cytokine release, proinflammatory signaling, and histologic damage. Incubation of anti-toxin A (MK3415) or anti-toxin B (MK6072) MAbs with human PBMCs significantly inhibited toxin A- and toxin B-mediated tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) expression. MK3415 and MK6072 also diminished toxin A- and toxin B-mediated NF-κB p65 phosphorylation in human monocytes, respectively, and significantly reduced toxin A- and B-induced TNF-α and IL-1β expression as well as histologic damage in human colonic explants. Our results underline the effectiveness of MK3415 and MK6072 in blocking C. difficile toxin A- and toxin B-mediated inflammatory responses and histologic damage.

The intestinal microbiota dysbiosis and Clostridium difficile infection: is there a relationship with inflammatory bowel disease?

Gut microbiota is a compilation of microorganisms dwelling in the entire mammalian gastrointestinal tract. They display a symbiotic relationship with the host contributing to its intestinal health and disease. Even a slight fluctuation in this equipoise may be deleterious to the host, leading to many pathological conditions like Clostridium difficile infection or inflammatory bowel disease (IBD). In this review, we focus on the role of microbial dysbiosis in initiation of C. difficile infection and IBD, and we also touch upon the role of specific pathogens, particularly C. difficile, as causative agents of IBD. We also discuss the molecular mechanisms activated by C. difficile that contribute to the development and exacerbation of gastrointestinal disorders.

MAPK-activated protein kinase 2 contributes to Clostridium difficile-associated inflammation

Clostridium difficile infection (CDI) results in toxin-induced epithelial injury and marked intestinal inflammation. Fecal markers of intestinal inflammation correlate with CDI disease severity, but regulation of the inflammatory response is poorly understood. Previous studies demonstrated that C. difficile toxin TcdA activates p38 kinase in tissue culture cells and mouse ilium, resulting in interleukin-8 (IL-8) release. Here, we investigated the role of phosphorylated mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2 kinase, pMK2), a key mediator of p38-dependent inflammation, in CDI. Exposure of cultured intestinal epithelial cells to the C. difficile toxins TcdA and TcdB resulted in p38-dependent MK2 activation. Toxin-induced IL-8 and GROα release required MK2 activity. We found that p38 and MK2 are activated in response to other actin-disrupting agents, suggesting that toxin-induced cytoskeleton disruption is the trigger for kinase-dependent cytokine response. Phosphorylated MK2 was detected in the intestines of C. difficile-infected hamsters and mice, demonstrating for the first time that the pathway is activated in infected animals. Furthermore, we found that elevated pMK2 correlated with the presence of toxigenic C. difficile among 100 patient stool samples submitted for C. difficile testing. In conclusion, we find that MK2 kinase is activated by TcdA and TcdB and regulates the expression of proinflammatory cytokines. Activation of p38-MK2 in infected animals and humans suggests that this pathway is a key driver of intestinal inflammation in patients with CDI.

Bacillus coagulans GBI-30, 6086 limits the recurrence of Clostridium difficile-Induced colitis following vancomycin withdrawal in mice

Background

Recently, we found that the probiotic strain Bacillus coagulans GBI-30, 6086 (GanedenBC³⁰) improved indices of Clostridium difficile (C. difficile)-induced colitis in mice (Fitzpatrick et al., Gut Pathogens, 2011). Our goal was to determine if BC30 could also prevent the recurrence of C. difficile-induced colitis in mice, following initial treatment with vancomycin. During study days 0 through 5, mice were treated with antibiotics. On day 6, the C. difficile strain VPI 10463 was given by oro-gastric gavage at ≈ 5x10⁴ CFU to induce colitis. Mice were treated on study days 6 to 10 with vancomycin (50 mg/kg) (vanco) or vehicle (saline) by gavage. On days 10 to16, mice were dosed by gavage with saline vehicle or BC30 (2 x 10⁹ CFU per day). Mice were monitored for mortality, weight loss and diarrhea. On study days 14, 16 and 17, stools and colons were collected for analyzing other parameters of colitis.

Results

The mean stool consistency score in Vehicle/C.difficile/Vanco mice increased from 0.4 (day 10) to a range of 1.1 to 1.4 (days 14 to 17), indicating the recurrence of colitis. On days 13 through 17, the stool consistency scores for the vancomycin/BC30 mice were significantly lower (p< 0.05) than for the vancomycin/vehicle cohort of animals. On day 17, 88.9% of mice treated with BC30 had normal stools, while this value was 0% with vehicle treatment (p value = 0.0004). Colonic myeloperoxidase (Units/2 cm colon) was significantly (p < 0.05) reduced from 4.3 ± 0.7 (Vehicle/C.difficile/Vanco) to 2.6 ± 0.2 (BC30/C. Difficle/Vanco). The colonic histology score and Keratinocyte derived-chemokine level in the colon were also lower in BC30 treated mice.

Summary

In BC30-treated mice, there was evidence of better stool consistency, as well as improved biochemical and histological indices of colitis, following initial treatment of animals with vancomycin.

Conclusion

BC30 limited the recurrence of CD-induced colitis following vancomycin withdrawal in mice.

Clostridium difficile infection in HIV-seropositive individuals and transplant recipients

Immunocompromise is a commonly cited risk factor for Clostridium difficile infection (CDI). We reviewed the experimental and epidemiological literature on CDI in three immunocompromised groups, HIV-seropositive individuals, haematopoietic stem cell or bone marrow transplant recipients and solid organ transplant recipients. All three groups have varying degrees of impairment of humoral immunity, a major factor influencing the outcome of CDI. Soluble HIV proteins such as nef and immunosuppressive agents such as cyclosporin, azathioprine and mycophenalate mofetil modify signalling from the key cellular pathways triggered by C. difficile toxin A, although there is a paucity of data on how these factors may interact with pathways activated by toxin B. Despite this, there has been little direct investigation into the effect of immunosuppression on the pathogenesis of CDI. Epidemiological studies consistently show increased rates of CDI in these populations, which are higher in those with greater degrees of immunocompromise such as individuals with advanced AIDS not receiving combination antiretroviral therapy or allogeneic haematopoietic stem cell transplant recipients. Less consistently data suggests immunocompromise in each group also impacts rates of severe, recurrent or complicated CDI. However all these conditions are characterised by high levels of antibiotic use and prolonged hospital stay, both powerful drivers of CDI risk.

Hepatitis B virus induces a novel inflammation network involving three inflammatory factors, IL-29, IL-8, and cyclooxygenase-2

Chronic inflammation induced by hepatitis B virus (HBV) is a major causative factor associated with the development of cirrhosis and hepatocellular carcinoma. In this study, we investigated the roles of three inflammatory factors, IL-8, IL-29 (or IFN-λ1), and cyclooxygenase-2 (COX-2), in HBV infection. We showed that the expression of IL-29, IL-8, and COX-2 genes was enhanced in HBV-infected patients or in HBV-expressing cells. In HBV-transfected human lymphocytes and hepatocytes, IL-29 activates the production of IL-8, which in turn enhances the expression of COX-2. In addition, COX-2 decreases the production of IL-8, which in turn attenuates the expression of IL-29. Thus, we proposed that HBV infection induces a novel inflammation cytokine network involving three inflammatory factors that regulate each other in the order IL-29/IL-8/COX-2, which involves positive regulation and negative feedback. In addition, we also demonstrated that COX-2 expression activated by IL-8 was mediated through CREB and C/EBP, which maintains the inflammatory environment associated with HBV infection. Finally, we showed that the ERK and the JNK signaling pathways were cooperatively involved in the regulation of COX-2. We also demonstrated that IL-29 inhibits HBV replication and that IL-8 attenuates the expression of IL-10R2 and the anti-HBV activity of IL-29, which favors the establishment of persistent viral infection. These new findings provide insights for our understanding of the mechanism by which inflammatory factors regulate each other in response to HBV infection.

Impact of clostridial glucosylating toxins on the proteome of colonic cells determined by isotope-coded protein labeling and LC-MALDI

Background

The anaerobe Clostridium difficile produces two major virulence factors toxin A and B that inactivate Rho proteins by glucosylation of a pivotal threonine residue. Purified toxins induce reorganization of the cytoskeleton and cell death in colonic cells. Whether all toxin effects on target cells depend on catalytic glucosyltransferase activity is unclear at present. Thus, we conducted a proteome approach to compare the protein profile of target cells treated either with wild type toxin A (rTcdA wt) or with a catalytically inactive mutant toxin A (mutant rTcdA). Relative protein quantification was feasible using isotope-coded protein labeling techniques (ICPL) and mass spectrometry (LC-MALDI).

Results

Altogether we found a significant differential expression of thirty proteins after treatment with rTcdA wt or mutant rTcdA. Mutant rTcdA caused up-regulation of seven proteins and sixteen proteins were responsive to rTcdA wt after 5 h. Long-term effect of rTcdA wt on protein expression was the down-regulation of eleven proteins. Up- or down-regulation of several proteins was verified by western blot analysis confirming the MS results.

Conclusion

Our results indicate incubation time-dependent effects of the clostridial glucosylating toxin A on colonic cells. The rTcdA wt impact more cellular functions than actin cytoskeleton reorganization and apoptosis. Furthermore, these data give insight into glucosyltransferase independent effects of clostridial glucosylating toxins on target cells after short incubation time. Additionally, our data reveal pro-inflammatory and proliferative effects of mutant rTcdA after short-term incubation.

The insect peptide coprisin prevents Clostridium difficile-mediated acute inflammation and mucosal damage through selective antimicrobial activity

Clostridium difficile-associated diarrhea and pseudomembranous colitis are typically treated with vancomycin or metronidazole, but recent increases in relapse incidence and the emergence of drug-resistant strains of C. difficile indicate the need for new antibiotics. We previously isolated coprisin, an antibacterial peptide from Copris tripartitus, a Korean dung beetle, and identified a nine-amino-acid peptide in the α-helical region of it (LLCIALRKK) that had antimicrobial activity (J.-S. Hwang et al., Int. J. Pept., 2009, doi:10.1155/2009/136284). Here, we examined whether treatment with a coprisin analogue (a disulfide dimer of the nine peptides) prevented inflammation and mucosal damage in a mouse model of acute gut inflammation established by administration of antibiotics followed by C. difficile infection. In this model, coprisin treatment significantly ameliorated body weight decreases, improved the survival rate, and decreased mucosal damage and proinflammatory cytokine production. In contrast, the coprisin analogue had no apparent antibiotic activity against commensal bacteria, including Lactobacillus and Bifidobacterium, which are known to inhibit the colonization of C. difficile. The exposure of C. difficile to the coprisin analogue caused a marked increase in nuclear propidium iodide (PI) staining, indicating membrane damage; the staining levels were similar to those seen with bacteria treated with a positive control for membrane disruption (EDTA). In contrast, coprisin analogue treatment did not trigger increases in the nuclear PI staining of Bifidobacterium thermophilum. This observation suggests that the antibiotic activity of the coprisin analogue may occur through specific membrane disruption of C. difficile. Thus, these results indicate that the coprisin analogue may prove useful as a therapeutic agent for C. difficile infection-associated inflammatory diarrhea and pseudomembranous colitis.

The host immune response to Clostridium difficile

Clostridium difficile is the most common cause of nosocomial bacterial diarrhoea in the Western world. Diarrhoea and colitis are caused by the actions of toxins A and B released by pathogenic strains of C. difficile. Adaptive immune responses to these toxins influence the outcomes of C. difficile infection (CDI). Symptomless carriers of toxinogenic C. difficile and those with a single episode of CDI without recurrence show more robust antitoxin immune responses than those with symptomatic and recurrent disease. Immune-based approaches to CDI therapy and prevention have been developed using active vaccination or passive immunotherapy targeting C. difficile toxins. Innate immune responses to C. difficile and its toxins are also central to the pathophysiology of CDI. An acute intestinal inflammatory response with prominent neutrophil infiltration and associated tissue injury is characteristic of CDI. Furthermore, inhibiting this acute inflammatory response can protect against the intestinal injury that results from exposure to C. difficile toxins in animal models. Studies examining host risk factors for CDI have led to validated clinical prediction tools for risk of primary and of recurrent disease. Risk factors associated with severe CDI with poor clinical outcomes have also been identified and include marked elevation of the peripheral white blood cell count and elevated creatinine. However, further work is needed in this area to guide the clinical application of new approaches to disease prevention and treatment including new antimicrobials as well as passive and active immunization.

Rho/Ras-GTPase-dependent and -independent activity of clostridial glucosylating toxins

Clostridial glucosylating toxins are the main virulence factors of clostridia responsible for gangrene and/or colitis. These toxins have been well characterized to inactivate Rho/Ras-GTPases through glucosylation. However, the signalling pathways downstream of Rho/Ras-GTPases leading to the intracellular effects of these toxins are only partially known. Rac-dependent modification of focal adhesion complexes and phosphoinositide metabolism seem to be key processes involved in actin filament depolymerization and disorganization of intercellular junctions. In addition, clostridial glucosylating toxins induce Rho/Ras-independent intracellular effects such as activation of mitogen-activated protein kinase pathways, which are used by some of these toxins to trigger an inflammatory response.

Clostridium difficile toxin A decreases acetylation of tubulin, leading to microtubule depolymerization through activation of histone deacetylase 6, and this mediates acute inflammation

Clostridium difficile toxin A is known to cause actin disaggregation through the enzymatic inactivation of intracellular Rho proteins. Based on the rapid and severe cell rounding of toxin A-exposed cells, we speculated that toxin A may be involved in post-translational modification of tubulin, leading to microtubule instability. In the current study, we observed that toxin A strongly reduced α-tubulin acetylation in human colonocytes and mouse intestine. Fractionation analysis demonstrated that toxin A-induced α-tubulin deacetylation yielded monomeric tubulin, indicating the presence of microtubule depolymerization. Inhibition of the glucosyltransferase activity against Rho proteins of toxin A by UDP-2',3'-dialdehyde significantly abrogated toxin A-induced α-tubulin deacetylation. In colonocytes treated with trichostatin A (TSA), an inhibitor of the HDAC6 tubulin deacetylase, toxin A-induced α-tubulin deacetylation and loss of tight junction were completely blocked. Administration of TSA also attenuated proinflammatory cytokine production, mucosal damage, and epithelial cell apoptosis in mouse intestine exposed to toxin A. These results suggest that toxin A causes microtubule depolymerization by activation of HDAC6-mediated tubulin deacetylation. Indeed, blockage of HDAC6 by TSA markedly attenuates α-tubulin deacetylation, proinflammatory cytokine production, and mucosal damage in a toxin A-induced mouse enteritis model. Tubulin deacetylation is an important component of the intestinal inflammatory cascade following toxin A-mediated Rho inactivation in vitro and in vivo.

The enterotoxicity of Clostridium difficile toxins

The major virulence factors of Clostridium difficile infection (CDI) are two large exotoxins A (TcdA) and B (TcdB). However, our understanding of the specific roles of these toxins in CDI is still evolving. It is now accepted that both toxins are enterotoxic and proinflammatory in the human intestine. Both purified TcdA and TcdB are capable of inducing the pathophysiology of CDI, although most studies have focused on TcdA. C. difficile toxins exert a wide array of biological activities by acting directly on intestinal epithelial cells. Alternatively, the toxins may target immune cells and neurons once the intestinal epithelial barrier is disrupted. The toxins may also act indirectly by stimulating cells to produce chemokines, proinflammatory cytokines, neuropeptides and other neuroimmune signals. This review considers the mechanisms of TcdA- and TcdB-induced enterotoxicity, and recent developments in this field.

Clostridium difficile toxin A binds colonocyte Src causing dephosphorylation of focal adhesion kinase and paxillin

Clostridium difficile toxin A impairs tight junction function of colonocytes by glucosylation of Rho family proteins causing actin filament disaggregation and cell rounding. We investigated the effect of toxin A on focal contact formation by assessing its action on focal adhesion kinase (FAK) and the adapter protein paxillin. Exposure of NCM460 human colonocytes to toxin A for 1 h resulted in complete dephosphorylation of FAK and paxillin, while protein tyrosine phosphatase activity was reduced. Blockage of toxin A-associated glucosyltransferase activity by co-incubation with UDP-2'3' dialdehyde did not reduce toxin A-induced FAK and paxillin dephosphorylation. GST-pull down and in vitro kinase activity experiments demonstrated toxin A binding directly to the catalytic domain of Src with suppression of its kinase activity. Direct binding of toxin A to Src, independent of any effect on protein tyrosine phosphatase or Rho glucosylation, inhibits Src kinase activity followed by FAK/paxillin inactivation. These mechanisms may contribute to toxin A inhibition of colonocyte focal adhesion that occurs in human colonic epithelium exposed to toxin A.

Role of phospholipase A2 and tyrosine kinase in Clostridium difficile toxin A-induced disruption of epithelial integrity, histologic inflammatory damage and intestinal secretion

Clostridium difficile-associated disease causes diarrhea to fulminant colitis and death. We investigated the role of phospholipase A2 (PLA2) inhibitors, aristolochic acid (AA), bromophenacyl bromide (BPB) and quinacrine (QUIN) on the C. difficile toxin A-induced disruption of epithelial integrity, histologic inflammatory damage and intestinal secretion. Toxin A caused severe hemorrhagic and inflammatory fluid secretion at 6-8 h in rabbit ileal segments, an effect that was significantly inhibited by QUIN (71%, P < 0.01), AA (87%, P < 0.000l) or by BPB (51%, P < 0.01). The secretory effect of toxin A was also inhibited in segments adjacent to those with AA (89%, P < 0.01). Furthermore, QUIN or AA substantially reduced the histologic damage seen after 6-8 h in rabbit ileal segments. The cyclooxygenase inhibitor, indomethacin, also significantly inhibited (96%; n = 6) the secretory effects of toxin A in ligated rabbit intestinal segments. The destruction by toxin A of F-actin at the tight junctions of T-84 cell monolayers was not inhibited by AA or BPB. AA or QUIN had no effect on the T-84 cell tissue resistance reduction over 8-24 h after toxin A exposure. All the inhibitors were shown to be effective in the doses administered direct in ileal loops to inhibit PLA2 activity. The data suggest that PLA2 is involved in the major pathway of toxin A-induced histologic inflammatory damage and hemorrhagic fluid secretion.

Clostridium difficile toxin A promotes dendritic cell maturation and chemokine CXCL2 expression through p38, IKK, and the NF-kappaB signaling pathway

Clostridium difficile toxin A causes acute colitis associated with intense infiltrating neutrophils. Although dendritic cells (DCs) play an important role in the regulation of inflammation, little is known about the effects of toxin A on the maturation and neutrophil-attracting chemokine expression in DCs. This study investigated whether C. difficile toxin A could influence the maturation of mouse bone-marrow-derived DCs and chemokine CXCL2 expression. Toxin A increased the DC maturation which was closely related to CXCL2 upregulation. Concurrently, toxin A activated the signals of p65/p50 nuclear factor kappa B (NF-kappaB) heterodimers and phospho-I kappa B kinase (IKK) in DCs. The increased DC maturation, CXCL2 expression, and neutrophil chemoattraction were significantly downregulated in the NF-kappaB knockout mice. In addition, toxin A activated the phosphorylated signals of mitogen-activated protein kinases (MAPKs), such as ERK, p38, and JNK. Of all three MAPK signals, p38 MAPK was significantly related to DC maturation. Thus, suppression of p38 activity using SB203580 and siRNA transfection resulted in the significant reduction of IKK activity, DC maturation, and CXCL2 upregulation by toxin A. These results suggest that p38 MAPK may lead to the activation of IKK and NF-kappaB signaling, resulting in enhanced DC maturation and CXCL2 expression in response to C. difficile toxin A stimulation.

The role of the RB tumour suppressor pathway in oxidative stress responses in the haematopoietic system

Exposure to pro-oxidants and defects in the repair of oxidative base damage are associated with disease and ageing and also contribute to the development of anaemia, bone marrow failure and haematopoietic malignancies. This Review assesses emerging data indicative of a specific role for the RB tumour suppressor pathway in the response of the haematopoietic system to oxidative stress. This is mediated through signalling pathways that involve DNA damage sensors, forkhead box O (Foxo) transcription factors and p38 mitogen-activated protein kinases and has downstream consequences for cell cycle progression, antioxidant capacity, mitochondrial mass and cellular metabolism.

gp96 is a human colonocyte plasma membrane binding protein for Clostridium difficile toxin A

Clostridium difficile toxin A (TxA), a key mediator of antibiotic-associated colitis, requires binding to a cell surface receptor prior to internalization. Our aim was to identify novel plasma membrane TxA binding proteins on human colonocytes. TxA was coupled with biotin and cross-linked to the surface of HT29 human colonic epithelial cells. The main colonocyte binding protein for TxA was identified as glycoprotein 96 (gp96) by coimmunoprecipitation and mass spectrum analysis. gp96 is a member of the heat shock protein family, which is expressed on human colonocyte apical membranes as well as in the cytoplasm. TxA binding to gp96 was confirmed by fluorescence immunostaining and in vitro coimmunoprecipitation. Following TxA binding, the TxA-gp96 complex was translocated from the cell membrane to the cytoplasm. Pretreatment with gp96 antibody decreased TxA binding to colonocytes and inhibited TxA-induced cell rounding. Small interfering RNA directed against gp96 reduced gp96 expression and cytotoxicity in colonocytes. TxA-induced inflammatory signaling via p38 and apoptosis as measured by activation of BAK (Bcl-2 homologous antagonist/killer) and DNA fragmentation were decreased in gp96-deficient B cells. We conclude that human colonocyte gp96 serves as a plasma membrane binding protein that enhances cellular entry of TxA, participates in cellular signaling events in the inflammatory cascade, and facilitates cytotoxicity.

Reactive oxygen species are messengers in maintenance of human and guinea pig gallbladder tonic contraction

The tonic contraction of human and guinea pig gallbladder (GB) is dependent on basal levels of PGE(2) and thromboxane A(2) (TxA(2)). The pathway involved in the genesis of these prostaglandins has not been elucidated. We aimed to examine the source of reactive oxygen species (ROS) and whether they contribute to the genesis of GB tonic contraction by generating basal prostaglandin levels. Tonic contraction was studied in human and guinea pig GB muscle strips treated with ROS scavengers (Tiron and catalase), apocynin (an inhibitor of NADPH oxidase), and NOX-1 small interference RNA (siRNA). The subunits of NADPH oxidase and their functional roles were determined with specific antibodies in GB muscle cells. ROS scavengers reduced the GB tonic contraction and H(2)O(2) and PGE(2) levels. Apocynin also inhibited the tonic contraction. Antibodies against subunits of NADPH oxidase present in GB muscle cells lowered H(2)O(2) and PGE(2) levels. NOX-1 siRNA transfection reduced the tonic contraction, NOX-1 expression, and levels of H(2)O(2) and PGE(2). Tiron and apocynin inhibited the expected increase in tension and H(2)O(2) levels induced by stretching of muscle strips. H(2)O(2) increased the levels of PGE(2) and TxA(2) by increasing platelet-activating factor-like lipids that phosphorylate p38 and cPLA(2) sequentially. H(2)O(2) generated by NADPH oxidase participates in a signal transduction pathway that maintains the GB tonic contraction by activating PAF, p38, and cPLA(2) to generate prostaglandins.

Inflammation and apoptosis in Clostridium difficile enteritis is mediated by PGE2 up-regulation of Fas ligand

BACKGROUND & AIMS

Clostridium difficile toxin A causes acute inflammation and fluid secretion in experimental animals and patients with C difficile infection. We previously reported that toxin A increased cyclooxygenase-2/prostaglandin E(2) (PGE(2)) expression and apoptosis in human colonocytes. Here, we assessed the role of secreted PGE(2) in inflammation and enterocyte apoptosis in toxin A enteritis.

METHODS

Effects of PGE(2) and PGE(2) blockade on toxin A-induced apoptosis of human colonocytes (NCM460) and of PGE(2) or toxin A on the Fas ligand (FasL) induction were analyzed by flow cytometry and Western blot. Functional activity of elevated FasL on colonocytes was assessed by coculture of colonocytes with Fas bearing Jurkat T cells. The involvement of PGE(2)-dependent Fas/FasL activation in toxin A enteritis was further assessed in either scid or FasL and Fas deficient mice.

RESULTS

Inhibition of cyclooxygenase-2 by NS-398 and of PGE(2) using a blocking antibody markedly attenuated apoptosis in colonocytes exposed to toxin A. Enhanced expression and release of FasL followed PGE(2) or toxin A exposure in vivo and in vitro and also was significantly attenuated by treatment with NS-398 and PGE(2) blocking antibody. PGE(2) acting through an EP1 receptor activated nuclear factor-kappaB, which induced transcription of FasL. Toxin A enteritis was accompanied by increased cellular infiltration, fluid secretion, and mucosal damage in control mice, but this response was markedly reduced in both Fas(-/-) and FasL(-/-) mice.

CONCLUSIONS

Toxin A enteritis involves release of PGE(2), which activates the Fas/FasL system, causing enterocyte apoptosis and inflammation.

Clostridium difficile toxins A and B directly stimulate human mast cells

Clostridium difficile toxins A and B (TcdA and TcdB) are the causative agents of antibiotic-associated pseudomembranous colitis. Mucosal mast cells play a crucial role in the inflammatory processes underlying this disease. We studied the direct effects of TcdA and TcdB on the human mast cell line HMC-1 with respect to degranulation, cytokine release, and the activation of proinflammatory signal pathways. TcdA and TcdB inactivate Rho GTPases, the master regulators of the actin cytoskeleton. The inactivation of Rho GTPases induced a reorganization of the actin cytoskeleton accompanied by morphological changes of cells. The TcdB-induced reorganization of the actin cytoskeleton in HMC-1 cells reduced the number of electron-dense mast cell-specific granules. Accordingly, TcdB induced the release of hexosaminidase, a marker for degranulation, in HMC-1 cells. The actin rearrangement was found to be responsible for degranulation since latrunculin B induced a comparable hexosaminidase release. In addition, TcdB as well as latrunculin B induced the activation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1/2 and also resulted in a p38 MAPK-dependent increased formation of prostaglandins D(2) and E(2). The autocrine stimulation of HMC-1 cells by prostaglandins partially contributed to the degranulation. Interestingly, TcdB-treated HMC-1 cells, but not latrunculin B-treated HMC-1 cells, showed a strong p38 MAPK-dependent increase in interleukin-8 release. Differences in the mast cell responses to TcdB and latrunculin B are probably due to the presence of functionally inactive Rho GTPases in toxin-treated cells. Thus, the HMC-1 cell line is a promising model for studying the direct effects of C. difficile toxins on mast cells independently of the tissue context.

The large clostridial toxins from Clostridium sordellii and C. difficile repress glucocorticoid receptor activity

We have previously shown that Bacillus anthracis lethal toxin represses glucocorticoid receptor (GR) transactivation. We now report that repression of GR activity also occurs with the large clostridial toxins produced by Clostridium sordellii and C. difficile. This was demonstrated using a transient transfection assay system for GR transactivation. We also report that C. sordellii lethal toxin inhibited GR function in an ex vivo assay, where toxin reduced the dexamethasone suppression of the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha). Furthermore, the glucocorticoid antagonist RU-486 in combination with C. sordellii lethal toxin additively prevented glucocorticoid suppression of TNF-alpha. These findings corroborate the fact that GR is a target for the toxin and suggest a physiological role for toxin-associated GR repression in inflammation. Finally, we show that this repression is associated with toxins that inactivate p38 mitogen-activated protein kinase (MAPK).

Clostridium sordellii lethal toxin kills mice by inducing a major increase in lung vascular permeability

When intraperitoneally injected into Swiss mice, Clostridium sordellii lethal toxin reproduces the fatal toxic shock syndrome observed in humans and animals after natural infection. This animal model was used to study the mechanism of lethal toxin-induced death. Histopathological and biochemical analyses identified lung and heart as preferential organs targeted by lethal toxin. Massive extravasation of blood fluid in the thoracic cage, resulting from an increase in lung vascular permeability, generated profound modifications such as animal dehydration, increase in hematocrit, hypoxia, and finally, cardiorespiratory failure. Vascular permeability increase induced by lethal toxin resulted from modifications of lung endothelial cells as evidenced by electron microscopy. Immunohistochemical analysis demonstrated that VE-cadherin, a protein participating in intercellular adherens junctions, was redistributed from membrane to cytosol in lung endothelial cells. No major sign of lethal toxin-induced inflammation was observed that could participate in the toxic shock syndrome. The main effect of the lethal toxin is the glucosylation-dependent inactivation of small GTPases, in particular Rac, which is involved in actin polymerization occurring in vivo in lungs leading to E-cadherin junction destabilization. We conclude that the cells most susceptible to lethal toxin are lung vascular endothelial cells, the adherens junctions of which were altered after intoxication.