Host cell signalling during Listeria monocytogenes infection

Macrophages and other mammalian cells respond to infection with Listeria monocytogenes by the transient or persistent activation of host cell signal transduction pathways. In addition, L. monocytogenes infection influences expression of various host cell genes, some of which may hinder or favour bacterial replication. The observed host cell responses vary with the different subcellular locations inhabited by L. monocytogenes during its intracellular life cycle.

Listeria monocytogenes-infected human umbilical vein endothelial cells: internalin-independent invasion, intracellular growth, movement, and host cell responses

The interaction of Listeria monocytogenes with human umbilical vein endothelial cells was studied. We show that L. monocytogenes invades human umbilical vein endothelial cells independently of internalin A, internalin B, internalin C, and ActA. L. monocytogenes replicates efficiently inside the cells and moves intracellularly by the induction of actin polymerization. We further show that L. monocytogenes-infection of human umbilical vein endothelial cells induces interleukin-6 and interleukin-8 expression during the first 6 h of infection. The expression of MCP-1 and the adhesion molecules VCAM-1 and ICAM-1 was not altered under the experimental conditions used here.

Signal generation in a non-EU country

One of the most important objects of post-marketing surveillance is the early detection of serious, unknown and unexpected adverse events. As spontaneous reported adverse events vary considerably in their signal-generating value the Swiss Drug Monitoring Center SANZ implemented an early signal detection system in 1991. With a set of screening criteria the individual case reports are automatically checked by the system and read into a signal file. Subsequently these potential signals are processed to quantify the signal generating value of the particular case. According to the screening criteria 2072 (53%) of the reported cases were considered as potential signals. After validating and quantifying their signal value 27% (565) were drug-related and unlabelled, 8% (173) were also rated as serious. On the basis of these cases 114 labelling changes were made. Some of the most interesting cases are discussed. This computer-assisted early signal generation model in a small country with 7 million inhabitants has a high detectability of new, rare, serious and quality of life affecting adverse drug reactions (ADRs). These newly detected ADRs must be interpreted in cognizance of the limitations and restrictions of spontaneous reporting and do not allow pharmacoepidemiologic conclusions.

Disruption of the guanylyl cyclase-C gene leads to a paradoxical phenotype of viable but heat-stable enterotoxin-resistant mice

Heat-stable enterotoxins (STa), which cause an acute secretory diarrhea, have been suggested to mediate their actions through the guanylyl cyclase-C (GC-C) receptor. The GC-C gene was disrupted by insertion of neo into exon 1 and subsequent homologous recombination. GC-C null mice contained no detectable GC-C protein. Intestine mucosal guanylyl cyclase activity was approximately 16-fold higher in wild-type mice than in the GC-C null mice, and STa-stimulable guanylyl cyclase activity was absent in the null animals. Thus, GC-C is the major cyclase activity present in the intestine, and also completely accounts for the STa-induced elevations of cGMP. Gavage with STa resulted in marked fluid accumulation within the intestine of wild-type and heterozygous suckling mice, but GC-C null animals were resistant. In addition, infection with enterotoxigenic bacteria that produce STa led to diarrhea and death in wild-type and heterozygous mice, while the null mice were protected. Cholera toxin, in contrast, continued to cause diarrhea in GC-C null mice, demonstrating that the cAMP signaling pathway remained intact. Markedly different diets (high carbohydrate, fat, or protein) or the inclusion of high salt (K+, Na+) in the drinking water or diet also did not severely affect the null animals. Given that GC-C is a major intestinal receptor in all mammals, the pressure to retain a functional GC-C in the face of diarrhea-inflicted mortality remains unexplained. Therefore, GC-C likely provides a protective effect against stressors not yet tested, possibly pathogens other than noninvasive enterotoxigenic bacteria.

The guanylyl cyclase-deficient mouse defines differential pathways of natriuretic peptide signaling

A genetic model of salt-resistant hypertension has been developed recently through disruption of the guanylyl cyclase-A (GC-A) natriuretic peptide receptor gene (Lopez, M. J., Wong, S. K., Kishimoto, I., Dubois, S., Mach, V., Friesen, J., Garbers, D. L., and Beuve, A. (1995) Nature 378, 65-68). These genetically altered mice were used to determine which of the natural peptides with natriuretic peptide-like structures regulate blood pressure through the GC-A receptor. Atrial natriuretic peptide (ANP) or B-type natriuretic peptide (BNP) half-maximally relaxed precontracted aortic rings in wild-type mice at about 24 nM, but failed to relax such aortas in GC-A null mice, even at micromolar concentrations. C-type natriuretic peptide (CNP), in contrast, caused half-maximal relaxation at concentrations of 335 and 146 nM in aortas from either wild-type or null mice, respectively, suggesting that this peptide acted through a receptor other than GC-A. Since the in vitro results with aortic smooth muscle do not necessarily reflect the physiology of the smaller blood vessels important in blood pressure regulation, the blood pressures of conscious mice infused with the various peptides were determined. ANP caused decreases in blood pressure when infused at rates of 500 ng/kg/min, a rate which resulted in a plasma concentration of 0.8 nM. In the null mice, in contrast, ANP failed to lower blood pressure even at infusion rates of 50 microg/kg/min. Much higher infusion rates for CNP (50 microg/kg/min), which yielded final plasma concentrations of 18.3 nM, were required to lower blood pressure in wild-type mice, but the effects of CNP were not altered in GC-A null mice. Thus, two natriuretic peptides (ANP, BNP) act through GC-A whereas another (CNP) acts through another receptor to regulate blood pressure.

Synthesis, biological activity and isomerism of guanylate cyclase C-activating peptides guanylin and uroguanylin

Recently, the peptides guanylin and uroguanylin were identified as endogenous ligands of the membrane-bound guanylate cyclase C (GC-C) that is mainly expressed in the intestinal epithelium. In the present study, bioactive guanylin and uroguanylin have been prepared by solid-phase methodology using Fmoc/HBTU chemistry. The two disulfide bonds with relative 1/3 and 2/4 connectivity have been introduced selectively by air oxidation of thiol groups and iodine treatment of Cys(Acm) residues. Using this strategy, several sequential derivatives were prepared. Temperature-dependent HPLC characterization of the bioactive products revealed that guanylin-related peptides exist as a mixture of two compounds. The isoforms are interconverted within approximately 90 min, which prevents their separate characterization. This effect was not detected for uroguanylin-like peptides. Synthetic peptides were tested for their potential to activate GC-C in cultured human colon carcinoma cells (T84), known to express high levels of GC-C. The results obtained show that both disulfide bonds are necessary for GC-C activation. The presence of the amino-terminally neighboring residues of Cys104 for guanylin and Cys100 for uroguanylin has been found to be essential for GC-C stimulation. Unexpectedly, a hybrid peptide obtained from substitution of the central tripeptide AYA of guanylin by the tripeptide VNV of uroguanylin was not bioactive.

Listeria monocytogenes infection of P388D1 macrophages results in a biphasic NF-kappaB (RelA/p50) activation induced by lipoteichoic acid and bacterial phospholipases and mediated by IkappaBalpha and IkappaBbeta degradation

As previously reported, Listeria monocytogenes infection of P388D1 macrophages results in a rapid induction of NF-kappaB DNA-binding activity. Here we show that this induction of NF-kappaB activity occurs in a biphasic mode: first, a transient, IkappaBalpha degradation-dependent phase of activity, also induced by the nonvirulent species Listeria innocua, which is mediated by binding of the bacteria to the macrophage, or by adding Listeria-derived lipoteichoic acid to the macrophage; the second persistent phase of activation is only markedly induced when the bacteria enter the cytoplasm of the host cell and express the virulence genes plcA and plcB, encoding two phospholipases. We suggest that products of the enzymatic activity of phospholipases directly interfere with host cell signal transduction pathways, thus leading to persistent NF-kappaB activation via persistent IkappaBbeta degradation.

Responses by murine macrophages infected with Listeria monocytogenes crucial for the development of immunity to this pathogen

Macrophages and other mammalian cells respond to infection with Listeria monocytogenes (L. monocytogenes) by the transient or persistent activation of host cell signal transduction pathways. In addition, L. monocytogenes infection influences expression of various host cell genes, such as stress genes, genes from the MHC I and II complex, cytokine genes, and cytokine receptor genes. The possible influences of the different host cell responses on the outcome of an L. monocytogenes infection in vitro as well as for the development of immunity are discussed.

[Pneumococcal vaccination--why so rare?]

Pneumococcal infections are common even in 1997 and are still responsible for high mortality rates particularly in groups at high risk. Because of increasing resistance of streptococcus pneumoniae against antibiotics the use of pneumococcal vaccination available so far could be an important preventive measure in particular in patients at high risk. This is demonstrated by means of some proper cases and the current literature.

ANP protects against reoxygenation-induced hypercontracture in adult cardiomyocytes

It was investigated whether atrial natriuretic peptide (ANP) or the related peptide urodilatin can be used for protecting cardiomyocytes against reoxygenation-induced hypercontracture. Isolated ventricular cardiomyocytes (from adult rats) were used as the experimental model. When the cells were submitted to substrate-free anoxia (135 min) and subsequent reoxygenation (30 min), the onset of reoxygenation provoked their hypercontracture. It was studied whether the temporary presence of ANP or urodilatin (1 nM to 1 microM) or 8-bromo-guanosine 3',5'-cyclic monophosphate (8-BrcGMP; 1 microM to 1 mM) during the last 15 min of anoxia and the first 15 min of reoxygenation prevented hypercontracture. It was found that ANP (1 microM) prevented hypercontracture in 82 +/- 8% (SD), urodilatin (1 microM) in 80 +/- 9%, and 8-BrcGMP (1 mM) in 72 +/- 10% of the cells (n = 40 cells). When ANP (1 microM) was added during the last 15 min of anoxia and the first 15 min of reoxygenation, the cellular concentration of cGMP increased from 0.41 +/- 0.04 to 2.80 +/- 0.81 pmol/mg protein (n = 6 cultures). The results show that the reoxygenation-induced hypercontracture in cardiomyocytes can be attenuated by the temporary presence of the stimulators of particulate guanylate cyclase, ANP or urodilatin.

Management 1997 of chronic obstructive pulmonary disease. Working Group of the Swiss Society of Pneumology

COPD is a disorder characterized by expiratory flow limitation that does not change markedly over periods of several months' observation. When the diagnosis is suspected, COPD patients should be submitted to full assessment and initiation of therapy. Initial assessment includes a complete history, a detailed physical examination, pulmonary function tests, a chest X-ray, and blood tests. Therapy of COPD aims at reducing symptoms, preventing exacerbations and preserving optimal lung function. Many COPD patients have a bronchospastic component and usually show some response to bronchodilator therapy. Anticholinergics, beta 2-agonists or theophylline are used as monotherapy or in combination. A subgroup of patients with COPD may benefit from oral long-term corticosteroid therapy. At prime diagnosis of COPD, a trial of oral steroid under optimal bronchodilator therapy is warranted in order to identify steroid responders early in the course of the disease. Stopping smoking is the most effective preventive measure and should be combined with complementary approaches such as eviction of environmental irritants, vaccines and prescription of antioxidants. Long-term oxygen therapy is beneficial in chronically hypoxemic patients. Respiratory rehabilitation uses a multidisciplinary approach aiming at decreasing dyspnea, increasing exercise tolerance and improving quality of life. Nocturnal home noninvasive mechanical ventilatory assistance can improve arterial blood gas tensions in patients with respiratory failure, but the long-term effect on survival is still under investigation. In selected patients, surgery (bullectomy, lung volume reduction, lung transplantation) may greatly improve pulmonary function.

Listeria monocytogenes infection of HeLa cells results in listeriolysin O-mediated transient activation of the Raf-MEK-MAP kinase pathway

In this study we investigated the effect of Listeria monocytogenes infection on the activation of the Raf-MEK-MAP kinase pathway in eukaryotic host cells. HeLa cell infection with L. monocytogenes EGD resulted in a rapid, but transient, phosphorylation of the MAP kinases erk-1 and erk-2, a transient phosphorylation of the MAP kinase kinase MEK-1, and a transient activation of the MAP kinase kinase kinase Raf. In parallel to the transient phosphorylation of the MAP kinases, we detected induced expression of the MAP kinase phosphatase MKP-1. Additionally we present evidence that listeriolysin O is the inducing agent for activation of the Raf-MEK-MAP kinase pathway.

Endothelin-1 potently stimulates chloride secretion and inhibits Na(+)-glucose absorption in human intestine in vitro

1. Serosally added synthetic endothelin-1 (ET-1) increased short-circuit current (Isc) across isolated muscle-stripped human colonic mucosa in vitro. Bumetanide inhibited Isc responses, indicating that ET-1 stimulates electrogenic Cl- secretion. 2. In isolated human jejunal mucosa, ET-1 exhibited a concentration-dependent dual action. At low concentrations it induced rapid increases in Isc and these were inhibited by bumetanide. At a higher concentration (0.1 microM), ET-1 provoked a drastic and progressive decrease in Isc below the baseline value. 3. Pretreatment with phlorizin or omission of glucose from the Krebs-Ringer solution at the apical (luminal) side of the jejunal mucosa prevented the decreases in Isc evoked by ET-1, suggesting that the peptide inhibits the glucose-coupled electrogenic Na+ absorption. Indeed, flux experiments with D-[14C]glucose demonstrated that ET-1 decreases jejunal glucose absorption by approximately 80% within 30 min. 4. Electron microprobe analyses of cryosections of human jejunum showed that ET-1 (0.1 microM) evokes a significant decrease in intracellular Na+ concentrations of villus (not crypt) epithelial cells, suggesting that the peptide attenuates apical Na(+)-glucose entry by reducing the activity of the Na(+)-glucose cotransporter, SGLT1. 5. In the presence of tetrodotoxin (TTX), ET-1-induced Cl- secretion was significantly reduced, in both human jejunal and colonic mucosa. However, the inhibitory effect on jejunal Na(+)-glucose absorption was not affected by TTX. 6. ET-1 increases electrogenic Cl- secretion across human intestinal mucosa in vitro. This effect is mediated in part via the activation of enteric nerves. Responses of the human jejunal mucosa to high ET-1 concentrations exhibit a second component, namely the rapid inhibition of electrogenic Na(+)-glucose absorption, which might be mediated by an inhibition of the transport activity of SGLT1. This effect is independent from neuronal mediators. Our results suggest different cellular action sites for ET-1 in human small and large intestine.

Effects of sodium nitroprusside in the rat cortical collecting duct are independent of the NO pathway

Recently we described K+ channels in the basolateral membrane of principal cells of rat cortical collecting duct (CCD) which are regulated by a cGMP-dependent protein kinase (Pflugers Arch 429:338-344, 1995). We examined the effects of the NO-liberator sodium nitroprusside (SNP) on single channel activity and membrane voltage (Vm) in principal cells of rat CCD, and on transepithelial voltage, lumen-to-bath Na+ fluxes, and osmotic water permeability in isolated perfused rat CCD tubules. While in patch clamp experiments SNP (10 microM) hyperpolarized principal cells from -54 +/- 10 mV to -71 +/- 5 mV (N = 5) and increased the activity of the described K+ channels from 0.05 +/- 0.03 to 0.45 +/- 0.14 (N = 5) in cell-attached and from 0.04 +/- 0.02 to 0.25 +/- 0.05 (N = 4) in excised patch clamp experiments, it had no effect on basal or AVP-dependent transepithelial voltage, Na+ fluxes, or the osmotic water permeability. In addition, neither 50 microM SIN-1, another liberator of NO, nor 1 mM L-NAME, an inhibitor of the NO-synthase, changed Vm significantly. Furthermore, in cGMP-assays SNP failed to increase intracellular cGMP in CCD segments. Thus, we conclude that in the rat CCD transport is not regulated via the NO-pathway and that SNP acts as an cGMP independent activator of K+ channels in the basolateral membrane of these cells.

[Clostridium difficile associated diarrhea in cephalosporin administration: experiences of the Swiss Adverse Drug Reaction Reporting System 1981-1995]

20-25% of antibiotics-associated diarrhea cases are caused by infection with toxin-producing Clostridium difficile. Since the advent of broad-spectrum antibiotics Clostridium difficile-associated diarrhea has been observed both in ambulatory practice and as a nosocomial infection in medical and nursing institutions. Clindamycin, aminopenicillins, and cephalosporines are by far the most common triggers for this infection. We reviewed all cases of Clostridium difficile-associated diarrhea due to cephalosporines which were reported to the Swiss Drug Monitoring Center (SANZ) between 1981 and 1995. 87 cases were reported (0.9% of 9720 spontaneous reports in this period), 69 (79%) of which were considered to be due to cephalosporines. In 74% of the cases the indication for the antibiotic treatment was an upper respiratory tract infection. 61 patients received cephalosporines by oral route and 9 patients by intravenous route. Two patients had to be hospitalized. There were no deaths. The pathogenesis, clinical picture, and therapy of Clostridium difficile-associated diarrhea is discussed. We conclude from these cases in the spontaneous reporting system of SANZ that Clostridium difficile infection due to cephalosporines is a frequent occurrence. Because the course can be severe, cephalosporines should be used restrictively.

Pituitary adenylate cyclase-activating polypeptide: a potent activator of human intestinal ion transport

To investigate the effects of PACAP-27 on electrolyte transport across the isolated human intestinal mucosa, changes in short-circuit current (Isc) were measured in Ussing chamber experiments. Serosally added PACAP-27 increased Isc in a concentration-dependent manner, eliciting a similar maximal effect in both the jejunal and the colonic mucosa. Bumetanide inhibited Isc responses, indicating stimulation of Cl- secretion. The potency and efficacy of PACAP-27 were comparable to those of VIP, suggesting that both peptides activate intestinal secretion by way of a common receptor located in the basolateral membrane of the intestinal epithelium.

[Ulcer drugs: profile of side effects of proton-pump blockers in comparison to H2 blockers in the spontaneous reporting system]

Inhibition of gastric acid secretion by drugs remains the most important rational approach to the treatment of acid related diseases. Histamine H2-antagonists and more recently the proton pump blockers have become the first line treatment for acid peptic diseases. Proton pump blockers bind specifically to the proton pump of the parietal cells and thus inhibit the final acid secretion independently from the activating stimuli. Because of this specific mechanism fewer adverse effects on other systems in the body are expected with proton pump blockers than with histamine antagonists. An analysis of the spontaneous reports which the Swiss Drug Monitoring Center (SANZ) received from 1981 to 1995 showed striking differences in the adverse drug reaction profile: hypersensitivity reactions with fever and anaphylactic reactions, liver disorders such as cholestatic hepatitis, most with severe progression and requiring hospitalization, as well as endocrine disorders were reported more frequently with histamine antagonists, skin reactions and joint disorders, however, were reported more often with proton pump blockers. Our data also support the conclusion that adverse drug reactions to proton pump blockers and histamine antagonists are rare in the spontaneous reporting scheme (reporting rate < 1%). There was a somewhat higher rate of serious reports with histamine antagonists. These data do not allow conclusions concerning long-term effects or effects with larger than recommended dosages.

[Liver injury caused by coumarin anticoagulants: experience of the IKS (Intercanton Monitoring Station) and the SANZ (Swiss Center for Drug Monitoring)]

Drug-induced liver diseases are potentially avoidable. Hepatotoxic drugs can mimic virtually any form of liver disease. Among all voluntary adverse drug reaction reports to central registries, 4-7% refer to drug-induced liver diseases. We analyze all cases of coumarin-induced hepatic injuries reported on a voluntary basis to the Swiss Drug Monitoring Centre (SANZ) and the Pharmacovigilance Centre (IKS) from 1981 to 1995. During this period the SANZ collected 9720 reports, 674 of which (6.9%) referred to the liver and the biliary tract. In only 11 reports an oral anticoagulant was involved. In 8 cases we assumed at least a possible causal relationship. 2 more cases were reported directly to the IKS. Among these 10 cases 7 were related to phenprocoumon and 3 to acenocoumarol. In 4 cases elevated concentrations of liver enzymes were measured 2-7 days after the beginning of therapy. In the remaining 6 cases the clinical picture was so severe that the patients had to be hospitalized. These 10 cases are discussed and compared with the cases published in the literature. According to our data, hepatic disorders induced by coumarin-anti-coagulants are rare. If hepatitis is diagnosed in a patient treated with oral anticoagulants, the differential diagnosis of a coumarin-induced hepatic injury has to be considered. Crossreactions between the coumarin derivatives phenprocoumon and acenocoumarol are possible.