A Colonic Organoid Model Challenged with the Large Toxins of Clostridioides difficile TcdA and TcdB Exhibit Deregulated Tight Junction Proteins

BACKGROUND

Clostridioides difficile toxins TcdA and TcdB are responsible for diarrhea and colitis. Lack of functional studies in organoid models of the gut prompted us to elucidate the toxin's effects on epithelial barrier function and the molecular mechanisms for diarrhea and inflammation.

METHODS

Human adult colon organoids were cultured on membrane inserts. Tight junction (TJ) proteins and actin cytoskeleton were analyzed for expression via Western blotting and via confocal laser-scanning microscopy for subcellular localization.

RESULTS

Polarized intestinal organoid monolayers were established from stem cell-containing colon organoids to apply toxins from the apical side and to perform functional measurements in the organoid model. The toxins caused a reduction in transepithelial electrical resistance in human colonic organoid monolayers with sublethal concentrations. Concomitantly, we detected increased paracellular permeability fluorescein and FITC-dextran-4000. Human colonic organoid monolayers exposed to the toxins exhibited redistribution of barrier-forming TJ proteins claudin-1, -4 and tricellulin, whereas channel-forming claudin-2 expression was increased. Perijunctional F-actin cytoskeleton organization was affected.

CONCLUSIONS

Adult stem cell-derived human colonic organoid monolayers were applicable as a colon infection model for electrophysiological measurements. The TJ changes noted can explain the epithelial barrier dysfunction and diarrhea in patients, as well as increased entry of luminal antigens triggering inflammation.

CDT of Clostridioides difficile Induces MLC-Dependent Intestinal Barrier Dysfunction in HT-29/B6 Epithelial Cell Monolayers

Background: Clostridioides difficile binary toxin (CDT) defines the hypervirulence of strains in nosocomial antibiotic-induced colitis with the highest mortality. The objective of our study was to investigate the impact of CDT on the intestinal epithelial barrier and to enlighten the underlying molecular mechanisms. Methods: Functional measurements of epithelial barrier function by macromolecular permeability and electrophysiology were performed in human intestinal HT-29/B6 cell monolayers. Molecular analysis of the spatial distribution of tight junction protein and cytoskeleton was performed by super-resolution STED microscopy. Results: Sublethal concentrations of CDT-induced barrier dysfunction with decreased TER and increased permeability for 332 Da fluorescein and 4 kDa FITC-dextran. The molecular correlate to the functional barrier defect by CDT was found to be a tight junction protein subcellular redistribution with tricellulin, occludin, and claudin-4 off the tight junction domain. This redistribution was shown to be MLCK-dependent. Conclusions: CDT compromised epithelial barrier function in a human intestinal colonic cell model, even in sublethal concentrations, pointing to barrier dysfunction in the intestine and leak flux induction as a diarrheal mechanism. However, this cannot be attributed to the appearance of apoptosis and necrosis, but rather to an opening of the paracellular leak pathway as the result of epithelial tight junction alterations.

Human duodenal organoid-derived monolayers serve as a suitable barrier model for duodenal tissue

Usually, duodenal barriers are investigated using intestinal cell lines like Caco-2, which in contrast to native tissue are limited in cell-type representation. Organoids can consist of all intestinal cell types and are supposed to better reflect the in vivo situation. Growing three-dimensionally, with the apical side facing the lumen, application of typical physiological techniques to analyze the barrier is difficult. Organoid-derived monolayers (ODMs) were developed to overcome this. After optimizing culturing conditions, ODMs were characterized and compared to Caco-2 and duodenal tissue. Tight junction composition and appearance were analyzed, and electrophysiological barrier properties, like paracellular and transcellular barrier function and macromolecule permeability, were evaluated. Furthermore, transcriptomic data were analyzed. ODMs had tight junction protein expression and paracellular barrier properties much more resembling the originating tissue than Caco-2. Transcellular barrier was similar between ODMs and native tissue but was increased in Caco-2. Transcriptomic data showed that Caco-2 expressed fewer solute carriers than ODMs and native tissue. In conclusion, while Caco-2 cells differ mostly in transcellular properties, ODMs reflect trans- and paracellular properties of the originating tissue. If cultured under optimized conditions, ODMs possess reproducible functionality, and the variety of different cell types makes them a suitable model for human tissue-specific investigations.

Escherichia coli Alpha-Hemolysin HlyA Induces Host Cell Polarity Changes, Epithelial Barrier Dysfunction and Cell Detachment in Human Colon Carcinoma Caco-2 Cell Model via PTEN-Dependent Dysregulation of Cell Junctions

Escherichia coli (E. coli) of the B2 phylotype reside in human and animal intestines. The bacteria possess pathogenicity factors such as α-hemolysin (HlyA) that can induce intestinal epithelial leaks. We addressed the questions which host cell processes were dysregulated by E. coli HlyA that can potentiate intestinal diseases. The colon carcinoma cell line Caco-2 was infected by HlyA⁺ E. coli. Cell polarity regulation was analyzed by live cell imaging for the phosphatidylinositol-4,5-bisphosphate (PIP2) abundance. In Caco-2 monolayers, transepithelial electrical resistance was measured for characterization of barrier function. Cell proliferation and separation were assessed microscopically. Epithelial regulation and cell signaling were analyzed by RNA-Seq and Ingenuity Pathway Analysis (IPA). Our main findings from E. coli HlyA toxinogenicity in the colon carcinoma cell line are that (i) PIP2 at the membrane decrease, (ii) PTEN (phosphatase and tensin homolog) inhibition leads to cell polarity changes, (iii) epithelial leakiness follows these polarity changes by disruption of cell junctions and (iv) epithelial cell detachment increases. HlyA affected pathways, e.g., the PTEN and metastasis signaling, were identified by RNA-Seq bioinformatics calculations in IPA. In conclusion, HlyA affects cell polarity, thereby inducing epithelial barrier dysfunction due to defective tight junctions and focal leak induction as an exemplary mechanism for leaky gut.

Diet changes alter paternally inherited epigenetic pattern in male Wild guinea pigs

Epigenetic modifications, of which DNA methylation is the most stable, are a mechanism conveying environmental information to subsequent generations via parental germ lines. The paternal contribution to adaptive processes in the offspring might be crucial, but has been widely neglected in comparison to the maternal one. To address the paternal impact on the offspring's adaptability to changes in diet composition, we investigated if low protein diet (LPD) in F0 males caused epigenetic alterations in their subsequently sired sons. We therefore fed F0 male Wild guinea pigs with a diet lowered in protein content (LPD) and investigated DNA methylation in sons sired before and after their father's LPD treatment in both, liver and testis tissues. Our results point to a 'heritable epigenetic response' of the sons to the fathers' dietary change. Because we detected methylation changes also in the testis tissue, they are likely to be transmitted to the F2 generation. Gene-network analyses of differentially methylated genes in liver identified main metabolic pathways indicating a metabolic reprogramming ('metabolic shift'). Epigenetic mechanisms, allowing an immediate and inherited adaptation may thus be important for the survival of species in the context of a persistently changing environment, such as climate change.

Deactivation of the respiratory burst of human and murine macrophages by lipopolysaccharide is a receptor mediated effect independent from autocrine mechanisms

Endotoxin blunts secretion of reactive oxygen intermediates by macrophages. Because transforming growth factor β (TGFβ) or interleukin 10 (IL-10) were shown to deactivate macrophages, and are secreted by macrophages in response to LPS, we sought for autocrine mechanisms of macrophage deactivation by endotoxin. TGFβ did not deactivate the respiratory burst of human blood-derived and resident or thioglycollate-induced murine peritoneal macrophages. According to previous reports, suppression of H202 secretion by TGFβ was restricted to periodate-elicited murine peritoneal macrophages.

In contrast to TGFβ, IL-10 deactivated systems producing reactive oxygen intermediates in human blood-derived human macrophages, but neither anti-TGFβ1 nor anti-IL-10 antibodies restored LPS-mediated deactivation of macrophages.

Supernatants from LPS-treated human blood-derived macrophages could not confer deactivation to homologous macrophages.

Deactivation by LPS required the presence of serum proteins and appeared to be mediated by the CD14 antigen-related LPS receptor, because anti-CD14 antibody and IL-4, which downregulates CD14, antagonized the LPS effect.

Taken together, these observations indicate that the suppressive effect of LPS on the respiratory burst of macrophages is lipid A receptor-dependent, and results in a direct deactivation response of the cell without mediation by autocrine mechanisms.

Systemic review: the pathogenesis and pharmacological treatment of hiccups

BACKGROUND

Hiccups are familiar to everyone, but remain poorly understood. Acute hiccups can often be terminated by physical manoeuvres. In contrast, persistent and intractable hiccups that continue for days or months are rare, but can be distressing and difficult to treat.

AIM

To review the management of hiccups, including a systematic review of reported efficacy and safety of pharmacological treatments.

METHODS

Available articles were identified using three electronic databases in addition to hand searching of published articles. Inclusion criteria were any reports of pharmaceutical therapy of 'hiccup(s)', 'hiccough(s)' or 'singultus' in English or German.

RESULTS

Treatment of 341 patients with persistent or intractable hiccups was reported in 15 published studies. Management was most effective when directed at the underlying condition. An empirical trial of anti-reflux therapy may be appropriate. If the underlying cause is not known or not treatable, then a range of pharmacological agents may provide benefit; however, systematic review revealed no adequately powered, well-designed trials of treatment. The use of baclofen and metoclopramide are supported by small randomised, placebo-controlled trials. Observational data suggest that gabapentin and chlorpromazine are also effective. Baclofen and gabapentin are less likely than standard neuroleptic agents to cause side effects during long-term therapy.

CONCLUSIONS

This systematic review revealed no high quality data on which to base treatment recommendations. Based on limited efficacy and safety data, baclofen and gabapentin may be considered as first line therapy for persistent and intractable hiccups, with metoclopramide and chlorpromazine in reserve.

Disseminated Invasive Aspergillosis with Cerebral Involvement Successfully Treated with Caspofungin and Voriconazole

We describe a case of cerebral aspergillosis which was successfully treated with a combination of caspofungin and voriconazole. The patient remains in remission 18 months after stopping antifungal treatment. We discuss primary and salvage therapy of invasive aspergillosis with focus on cerebral involvement. Since historical data showed a fatal outcome in most cases, amphotericin B does not cross the blood brain barrier while voriconazole does, we chose a combination of voriconazole plus caspofungin as primary therapy.

Detection of villous conidia of Conidiobolus coronatus in a blood sample by scanning electron microscopy investigation

Conidiobolus coronatus is a major insect pathogen belonging to the fungal order Entomophthorales, causing a rare subcutaneous infection of the nasofacial region, resulting in swelling of predominantly the nose, mouth, and perinasal tissue. Later in the course of the infection firm, painless, subcutaneous nodules develop that are attached to the underlying tissues but not to the skin. No morphological studies are available in the literature on the morphology of C. coronatus in vivo and all morphological studies have been conducted on in vitro cultures. Here the authors report on the ultrastructural pathology as seen with a scanning electron microscope (SEM) of villous conidia of C. coronatus, detected in a 37-year-old woman who presented to the casualty department at Pretoria Academic Hospital, South Africa with left-sided facial pain and headache. The diagnosis of C. coronatus was confirmed by LightCycler real-time flourescence PCR technique. Research shows that typically diagnosis of the pathogen is established only on histological examination, and in over 85% of cases cultures for the causative organism is negative. This pathogen has not previously been found in a blood sample and the authors present for the first time the morphology of C. coronatus in blood using the SEM.

Life-threatening envenoming by the Saharan horned viper (Cerastes cerastes) causing micro-angiopathic haemolysis, coagulopathy and acute renal failure: clinical cases and review

BACKGROUND

The desert horned vipers (Cerastes cerastes and C. gasperettii) are the most familiar snakes of the great deserts of North Africa and the Middle East, including the plains of Iraq. They are responsible for many human snake bites. In Western countries, they are popular among exotic-snake keepers.

AIM

To investigate mechanisms of life-threatening envenoming and treatment.

DESIGN

Clinical investigation.

METHODS

Clinical and laboratory studies with measurement of serum venom antigen concentrations by enzyme immunoassay.

RESULTS

Two men bitten while handling captive Saharan horned vipers (Cerastes cerastes) in Europe developed extensive local swelling and life-threatening systemic envenoming, characterized by coagulopathy, increased fibrinolysis, thrombocytopenia, micro-angiopathic haemolytic anaemia and acute renal failure. The clinical picture is explicable by the presence in C. cerastes venom of several thrombin-like, Factor-X-activating, platelet-aggregating, haemorrhagic and nephrotoxic components. In one case, prophylactic use of subcutaneous epinephrine may have contributed to intracranial haemorrhage. The roles in treatment of heparin (rejected) and specific antivenom (recommended) are discussed.

DISCUSSION

Cerastes cerastes is capable of life-threatening envenoming in humans. Optimal treatment of envenoming is by early administration of specific antivenom, and avoidance of ineffective and potentially-dangerous ancillary methods.

Rapid detection of pathogenic fungi from clinical specimens using LightCycler real-time fluorescence PCR

In the study presented here a LightCycler real-time PCR system was used for the diagnosis of fungal infections from clinical tissue samples. Nine specimens were investigated from six patients with suspected or proven invasive fungal infections. Seven of nine samples were positive in a broad-range fungal PCR assay. In four samples, Aspergillus fumigatus was detected both by a species-specific hybridization assay as well as by sequencing of amplification products. In addition, the broad-range fungal PCR assay and PCR sequencing detected and identified, respectively, the following organisms in the specimens noted: Candida albicans in a culture-negative liver biopsy, Histoplasma capsulatum in a bone marrow sample, and Conidiobolus coronatus in a facial soft tissue specimen. Real-time PCR is a promising tool for the diagnosis of invasive fungal infections in human tissue samples and offers some advantages over culture methods, such as rapid analysis and increased sensitivity.

[Rare cause of chronic abdominal pain: retractile mesenteritis]

HISTORY AND ADMISSION FINDINGS

A 69-year-old man had a history of chronic abdominal pain and intermittent fever for more than 10 years. Due to acute epigastric pain and intermittent fever with night sweat for one week he was admitted for further investigation. On physical examination there was tenderness in the right upper and lower epigastrium without a palpable mass.

INVESTIGATIONS

Laboratory figures showed signs of inflammation with a CRP of 103 mg/l. Leucocyte counts were normal without left shift. CT and MRI scans showed a sharp-edged mass of 10 x 8 cm in diameter in the retroperitoneal area with big vessels running through it. Laparoscopic biopsy confirmed the suspected diagnosis of retractile mesenteritis.

TREATMENT AND COURSE

Under therapy with oral progesterone (Utrogestan 1 x 100 mg/d) and prednisone (Prednison 1 x 50 mg/d) there was fast symptomatic relief. A CT scan 2 months after initial diagnosis showed clear regression of the tumor.

CONCLUSION

Retractile mesenteritis is a rare cause of chronic abdominal pain with variable symptoms. Its aetiology is unknown. In case of bowel ischemia a surgical approach is preferred, milder forms may be treated with immunosuppressive agents as well as oral progesterone. Progesterone has exhibited positive effects on fatty tissue with successful treatment in desmoid tumors and retroperitoneal fibrosis. Here in we could demonstrate its safe and efficient use in a patient with retractile mesenteritis.

Marginal and subgingival plaque--a natural habitat of Tropheryma whipplei?

BACKGROUND

DNA of Tropheryma whipplei, the etiologic agent of Whipple's disease, has recently been detected in the saliva of healthy subjects. In this pilot study we searched for the habitat of T. whipplei within the oral cavity.

MATERIALS AND METHODS

Samples from different oral sites were obtained from periodontically healthy volunteers, patients with progressive periodontitis and Chinese subjects with necrotizing ulcerative gingivitis or gingivitis. Quantitative real-time PCR was performed using T. whippleispecific primers, human beta-globin-specific primers to control for tissue DNA extraction and PCR reaction and broad-range eubacterial primers to control for bacterial DNA extraction. T. whipplei specificity of multiple amplicons was confirmed by sequencing. The detection limit of the method was 10 ag of T. whipplei DNA, corresponding to one to five bacteria under reference assay conditions.

RESULTS

T. whipplei was found in the oral cavity of four out of ten healthy individuals from hospital staff and in three out of nine periodontitis patients, but in none of the individuals from China. All positive samples derived from subgingival and gingival sulcus plaque containing between 10(3) and 5 x 10(5) cells ml(-1) of plaque suspension, whereas saliva, smooth surface plaque and samples from the tongue or cheeks were negative.

CONCLUSION

Our results suggest that T. whipplei colonizes the human body via the oral cavity and that bacterial plaques of the gingival crevice and the gingival sulcus/pocket may serve as a natural primary habitat.

[Fatal brain edema after ingestion of ecstasy and benzylpiperazine]

HISTORY AND ADMISSION FINDINGS

A 23-year-old woman was hospitalized with headache, malaise and somnolence 11 hours after ingestion of A2 (benzylpiperazine), 7 hours after ingestion of ecstasy (MDMA), and large volume of fluids. On admission she had bradycardia (heart rate 48/min), hypertension (blood pressure 154/95 mm Hg), and reduced consciousness with diminished tendon reflexes and non-reacting pupils (Glasgow Coma Score 6).

INVESTIGATIONS

Serum sodium was markedly decreased (115 mmol/l [normal 135-145]) with low plasma osmolality (246 mosm/kg [normal 280-300]). Other laboratory findings were within normal limits.

TREATMENT AND COURSE

The patient had severe hypervolaemic hypotonic hyponatraemia. 40 minutes after admission she seized twice and was intubated. Brain CT scan showed massive cerebral oedema with beginning tonsillar herniation. Serum sodium concentration returned to normal within 38 hours, but the patient deteriorated neurologically with increasing tonsillar herniation detected in a second brain CT scan. The patient died 57 hours after admission.

CONCLUSION

13 cases of MDMA-associated severe hyponatraemia are reported. Intake of fluids after MDMA ingestion may lead to potentially fatal hypervolaemic hypotonic hyponatraemia with cerebral oedema. Symptoms appear about 8 hours (range 4-18) after MDMA ingestion. Even low doses of MDMA and fluids may lead to a serious outcome. The only risk factor is female gender. Measurement of serum sodium and brain CT scan is recommended in all patients with altered mental status after MDMA consumption.

Fatal hepatoxicity secondary to nimesulide

This report describes a 57-year-old female patient with chronic lumbago, who died from the sequelae of acute liver failure induced by nimesulide medication. Nimesulide is a non-steroidal anti-inflammatory drug (NSAID) which preferentially inhibits cyclo-oxygenase 2 and has been associated with a total of 13 reported cases of severe liver injury including our case. On the basis of the literature reports, the following features of nimesulide-associated hepatotoxicity were identified: female sex (84% of cases), age (mean age 62 years), jaundice as a primary manifestation (90%) and the absence of peripheral blood eosinophilia. The average duration of therapy of the published cases was 62 days (range 7-180 days). Based on spontaneous reports to the World Health Organization, nimesulide induces a high proportion of severe adverse hepatic reactions compared with other NSAIDs registered in Switzerland. Hepatotoxicity thus represents an important risk factor of nimesulide usage.

Reactive hypoglycaemia due to late dumping syndrome: successful treatment with acarbose

Reactive hypoglycaemia is a rare disease which occurs postprandially in everyday life involving blood glucose levels below 2.5 to 2.8 mmol/l. We report on a 66-year-old patient who developed symptomatic reactive hypoglycaemia due to late dumping syndrome 10 years after oesophagectomy with cervical anastomosis. A 75 g sucrose load revealed a plasma glucose level of 9.4 mmol/l after one hour, followed by symptomatic hypoglycaemia with a plasma glucose level of 1.8 mmol/l after three hours. Concomitantly, high concentrations of insulin (3216 pmol/l at a glucose level of 9.4 mmol/l and 335 pmol/l at a glucose level of 1.8 mmol/l) and glucagon-like peptide 1 (GLP-1) (375 pmol/l at a glucose level of 9.4 mmol/l and 85 pmol/l at a glucose level of 1.8 mmol/l) were measured. While the patient was under treatment with acarbose, another sucrose load did not provoke symptomatic hypoglycaemia (plasma glucose nadir of 4.6 mmol/l after two hours). Insulin and GLP-1 levels increased much less, to peak levels of 375 pmol/l and 75 pmol/l respectively, after one hour when plasma glucose was 6.8 mmol/l. We conclude that in patients with reactive hypoglycaemia due to gastrointestinal surgery, acarbose decreases rapid glucose absorption associated with hyperglycaemia and GLP-1 secretion, and thus diminishes excessive insulin release. Acarbose is therefore a successful treatment modality for reactive hypoglycaemia due to late dumping syndrome.

Reactive hypoglycaemia due to late dumping syndrome: successful treatment with acarbose

Reactive hypoglycaemia is a rare disease which occurs postprandially in everyday life involving blood glucose levels below 2.5 to 2.8 mmol/l. We report on a 66-year-old patient who developed symptomatic reactive hypoglycaemia due to late dumping syndrome 10 years after oesophagectomy with cervical anastomosis. A 75 g sucrose load revealed a plasma glucose level of 9.4 mmol/l after one hour, followed by symptomatic hypoglycaemia with a plasma glucose level of 1.8 mmol/l after three hours. Concomitantly, high concentrations of insulin (3216 pmol/l at a glucose level of 9.4 mmol/l and 335 pmol/l at a glucose level of 1.8 mmol/l) and glucagon-like peptide 1 (GLP-1) (375 pmol/l at a glucose level of 9.4 mmol/l and 85 pmol/l at a glucose level of 1.8 mmol/l) were measured. While the patient was under treatment with acarbose, another sucrose load did not provoke symptomatic hypoglycaemia (plasma glucose nadir of 4.6 mmol/l after two hours). Insulin and GLP-1 levels increased much less, to peak levels of 375 pmol/l and 75 pmol/l respectively, after one hour when plasma glucose was 6.8 mmol/l. We conclude that in patients with reactive hypoglycaemia due to gastrointestinal surgery, acarbose decreases rapid glucose absorption associated with hyperglycaemia and GLP-1 secretion, and thus diminishes excessive insulin release. Acarbose is therefore a successful treatment modality for reactive hypoglycaemia due to late dumping syndrome.

Junctional adhesion molecule, a novel member of the immunoglobulin superfamily that distributes at intercellular junctions and modulates monocyte transmigration

Tight junctions are the most apical components of endothelial and epithelial intercellular cleft. In the endothelium these structures play an important role in the control of paracellular permeability to circulating cells and solutes. The only known integral membrane protein localized at sites of membrane-membrane interaction of tight junctions is occludin, which is linked inside the cells to a complex network of cytoskeletal and signaling proteins. We report here the identification of a novel protein (junctional adhesion molecule [JAM]) that is selectively concentrated at intercellular junctions of endothelial and epithelial cells of different origins. Confocal and immunoelectron microscopy shows that JAM codistributes with tight junction components at the apical region of the intercellular cleft. A cDNA clone encoding JAM defines a novel immunoglobulin gene superfamily member that consists of two V-type Ig domains. An mAb directed to JAM (BV11) was found to inhibit spontaneous and chemokine-induced monocyte transmigration through an endothelial cell monolayer in vitro. Systemic treatment of mice with BV11 mAb blocked monocyte infiltration upon chemokine administration in subcutaneous air pouches. Thus, JAM is a new component of endothelial and epithelial junctions that play a role in regulating monocyte transmigration.

Inhalation of the nitric oxide synthase cofactor tetrahydrobiopterin in healthy volunteers

Pulmonary endothelial dysfunction is the hallmark of acute lung injury. Impaired pulmonary endothelial nitric oxide (NO) production in this event has been described. Tetrahydrobiopterin (BH4) is an essential cofactor for NO synthase and modulator of its activity. At high local concentrations, BH4 provokes local vasodilation in vivo in healthy individuals. At lower concentrations, BH4 selectively and locally restores disturbed NO-dependent vasodilation in patients with endothelial dysfunction. In this preliminary study, we therefore investigated the feasibility of BH4 inhalation in five healthy human volunteers. Inhalation of buffered, aqueous BH4-dihydrochloride solution was well tolerated; despite the buffer, BH4 stability was completely preserved. Resorption of inhaled BH4 was demonstrated by significantly increased BH4 levels in plasma and urine. Inhaled BH4 did not alter pulmonary function and had no effect on systemic hemodynamic values. Our data demonstrate that inhalation is a novel method for local BH4 administration, offering a basic therapeutic tool for investigation of restoration of impaired NO-dependent vasodilation due to pulmonary endothelial dysfunction.

Crucial role of interferon consensus sequence binding protein, but neither of interferon regulatory factor 1 nor of nitric oxide synthesis for protection against murine listeriosis

Listeria monocytogenes is widely used as a model to study immune responses against intracellular bacteria. It has been shown that neutrophils and macrophages play an important role to restrict bacterial replication in the early phase of primary infection in mice, and that the cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are essential for protection. However, the involved signaling pathways and effector mechanisms are still poorly understood. This study investigated mouse strains deficient for the IFN-dependent transcription factors interferon consensus sequence binding protein (ICSBP), interferon regulatory factor (IRF) 1 or 2 for their capacity to eliminate Listeria in vivo and in vitro and for production of inducible reactive nitrogen intermediates (RNI) or reactive oxygen intermediates (ROI) in macrophages. ICSBP-/- and to a lesser degree also IRF2-/- mice were highly susceptible to Listeria infection. This correlated with impaired elimination of Listeria from infected peritoneal macrophage (PEM) cultures stimulated with IFN-gamma in vitro; in addition these cultures showed reduced and delayed oxidative burst upon IFN-gamma stimulation, whereas nitric oxide production was normal. In contrast, mice deficient for IRF1 were not able to produce nitric oxide, but they efficiently controlled Listeria in vivo and in vitro. These results indicate that (a) the ICSBP/IRF2 complex is essential for IFN-gamma-mediated protection against Listeria and that (b) ROI together with additional still unknown effector mechanisms may be responsible for the anti-Listeria activity of macrophages, whereas IRF1-induced RNI are not limiting.

Nitrite generation in interleukin-4-treated human macrophage cultures does not involve the nitric oxide synthase pathway

The search continues for high-output nitric oxide biosynthesis in human macrophages analogous to murine phagocytes. Recently, generation of nitrite in culture supernatants of human macrophages exposed to interferon-gamma and interleukin-4 (IFN-gamma/IL-4) was reported. The present study reproduces these findings and shows that L-arginine is not consumed and L-citrulline is not produced during this process. Furthermore, the biosynthesis of the obligatory cofactor tetrahydrobiopterin is not coinduced. These biochemical data provide support against a nitric oxide synthase contribution to nitrite accumulation. Nitrite was generated from nitrate salts even in cell-free media. Nitric oxide synthase activity but not nitrate reduction depended on molecular oxygen. Nitrite accumulation in experiments with IFN-gamma/IL-4 in human monocytes appears to be an in vitro artifact produced by nitrate-reducing activities contained in cytokine preparations.

Comparison of the antimicrobial activity of deactivated human macrophages challenged with Aspergillus fumigatus and Listeria monocytogenes

The anticonidial activity of human monocytes deactivated by cytokines interleukin (IL)-4 and IL-10 and the hormone dexamethasone was studied and compared with antilisterial activity. Dexamethasone had the largest effect on the anticonidial activity and suppressed germination-inhibiting activity and elimination of ingested spores by macrophages more than the cytokines did. Maximally active concentrations of IL-10 had a similar but significantly smaller deactivating effect. IL-4, in contrast to IL-10 and dexamethasone, did not reduce anticonidial activity. However, IL-4 and IL- 10 were equally potent in deactivating human macrophages against Listeria monocytogenes, whereas dexamethasone was significantly less potent in the Listeria model. These observations indicate that all three mediators lessen antimicrobial activity but that this effect depends on the test organism studied and is apparently mediated through regulation of different antimicrobial systems operating against a particular microorganism.

Nitric oxide and infection: another view

Nitric oxide (NO) has been nicknamed "murderer" and "mediator" because it has toxic and signaling properties. We review these two aspects of NO synthesis from the perspective of the clinical infectious disease specialist by considering the potential of NO as an endothelium-derived relaxing factor (EDRF) in inflammation and sepsis and its potential as an antimicrobial system. We deviate from observations in recent authoritative reviews and point to important species differences that make it unlikely that NO serves as an EDRF mediating inflammatory vasodilatation in humans or that NO synthesized by humans phagocytes has an antimicrobial function. We propose that in humans, No synthesis is more confined and compartmentalized than in certain other animal species, and therefore, unwelcome toxicity, vasodilatation, or disturbance of paracrine signaling mechanisms (i.e., modulation of phagocytic cell functions) are avoidable during inflammation.

Modulation of the antilisterial activity of human blood-derived macrophages by activating and deactivating cytokines

A concept of macrophage deactivation by hormones and cytokines that opposes activation was recently proposed. Deactivation of the antilisterial activity of macrophages by IL-4, IL-10, and TGF-beta, as well as by dexamethasone, was studied here. IL-4, IL-10, and dexamethasone, but not TGF-beta, caused a complete loss of the competence of human blood-derived macrophages infected with Listeria monocytogenes to control or eliminate ingested bacteria. IL-10 and, to a lesser degree, dexamethasone lessened in parallel the capacity of macrophages to secrete H2O2. The antilisterial activity of cells simultaneously exposed to deactivating agents could be significantly augmented by IFN-gamma. Likewise, TNF-alpha and to a limited degree GM-CSF increased the antilisterial activity of cells treated with IL-10 and dexamethasone but not that of cells treated with IL-4. Suppression of TNF-alpha secretion in response to Listeria by TGF-beta, IL-10, dexamethasone, or pentoxifylline did not closely parallel antilisterial activity. Studies by transmission electron microscopy and actin staining suggested that deactivation by IL-10, IL-4, and dexamethasone of human blood-derived macrophages resulted in intraphagosomal multiplication of Listeria followed only then by an escape of bacteria into the cytoplasm. The antibacterial competence of human macrophages is lessened by IL-4 and IL-10 and augmented by IFN-gamma, TNF-alpha, and GM-CSF. The success of human macrophages in controlling intracellular pathogens appears to depend on the balance of activating and deactivating mediators modulating their activity.

Tetrahydrobiopterin as another EDRF in man

Endotoxin and inflammatory cytokines downregulate expression of constitutive nitric oxide synthase (cNOS) in human vascular endothelial cells with concomitant increase of tetrahydrobiopterin synthesis in these cells and parallel upregulation of inducible NOS expression in smooth muscle cells, indicating compartmentalized nitric oxide (NO) production under septic conditions in man. In this report the compartmentalization has been further studied using dual chamber cell cultures with inflammatory activated human endothelial cells. We show that endothelial cells secrete BH4 vectorially into the basal direction thereby providing underlining smooth muscle cells with the cofactor necessary for NO production. Furthermore, by laser Doppler velocimetry we show that intraarterial infusion of BH4 induces strong vasodilatation in man. Consumption of L-arginine and production of cyclic GMP increased and therefore imply NO as second messenger. Thus the discovery of an endothelium-derived factor regulating NOS activity would reconcile the concept of an inflammatory EDRF that is not NO itself but results in NO-dependent vasodilatation in man.

Nitric oxide production depends on preceding tetrahydrobiopterin synthesis by endothelial cells: selective suppression of induced nitric oxide production by sepiapterin reductase inhibitors

Using murine vascular endothelial cells expressing both constitutive and inducible nitric oxide synthases (cNOS and iNOS), we explored the feasibility of suppressing cytokine-induced nitric oxide (NO) production without affecting constitutive NO production by inhibition of the tetrahydrobiopterin (BH4) biosynthesis. We show in this study that in endothelial cells cytokine/endotoxin-activated BH4 synthesis precedes the induction of NO generation. Using the sepiapterin reductase inhibitors phenprocoumon or dicumarol as BH4 synthesis inhibitors, we achieved a pronounced and selective suppression of induced NO production in cytokine-activated endothelial cells. Addition of exogenous BH4, but not sepiapterin, restored NO production in the presence of the inhibitors. Despite profound inhibition of the BH4 biosynthesis, constitutive NO synthesis was not affected, thereby demonstrating the selectivity and specificity of the inhibitors. Suppression of enhanced NO production by sepiapterin reductase inhibitors such as cumaroles could provide pharmacologic means for therapeutic interventions in NO-mediated pathophysiologic events.

Modulation of human endothelial cell tetrahydrobiopterin synthesis by activating and deactivating cytokines: new perspectives on endothelium-derived relaxing factor

Endothelial cells, through soluble mediators, play an important role in the regulation of the vascular tone. In the present paper we investigated whether endothelial tetrahydrobiopterin (BH4), an obligatory cofactor of nitric oxide (NO) synthase, could serve as such a regulatory mediator. By studying the human vascular endothelial hybrid cells EA hy 926, we found that 1) BH4 biosynthesis is highly regulated (70-fold) by activating and deactivating cytokines; that 2) up to 90% of the induced BH4 is released by activated endothelium, and 3) while intracellular BH4 could be related to cyclic GMP concentrations within the endothelial cells, the bulk of BH4 (up to 90 pmol/10(6) cells) appears not to serve endothelial cell requirements. Activation and deactivation of BH4 synthesis by cytokines was paralleled by other endothelial cell responses reflecting their activity. We propose that BH4 serves as an endothelial mediator augmenting the activity of cytokine-inducible NO synthase in vascular smooth muscle cells. BH4 could thereby account for endothelium-derived relaxing factor activity.

Nitric oxide synthase is not a constituent of the antimicrobial armature of human mononuclear phagocytes

Nitric oxide synthase (NOS) has received immense interest as an antimicrobial and antitumoral effector system of mononuclear phagocytes from rodents. Because there is increasing doubt that an analogous system exists in human macrophages, NOS was reexamined in these cells. Under tightly controlled conditions, with murine macrophages as positive controls, human macrophages failed to secrete nitric oxide (< 0.1 mumol/10(6) cells/24 h), even after activation with endotoxin, interferon-gamma, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, bacteria, or proliferating lymphocytes. The discrepancy between murine and human macrophages depended on neither the anatomic source (blood, peritoneum), the agent used for activation, nor the duration of activation. NOS activity was paralleled by metabolization of L-arginine to L-citrulline. Exogenous tetrahydrobiopterin, an essential cofactor of NOS not synthesized by human macrophages, did not support NOS activity in human macrophages. Also, no NOS activity was found in cellular subfractions of human macrophages. It appears that in humans, the inducible high-output NOS is not conserved as an antimicrobial system of macrophages.

Regulation of the L-arginine-dependent and tetrahydrobiopterin-dependent biosynthesis of nitric oxide in murine macrophages

Nitric oxide is a recently discovered biomolecule with a broad range of actions. The present study investigated the regulation of nitric oxide synthase activity by dexamethasone and the cofactor tetrahydrobiopterin in murine macrophages. The influence of the tetrahydrobiopterin biosynthesis inhibitors 2,4-diamino-6-hydroxypyrimidine, an inhibitor of GTP cyclohydrolase I, and phenprocoumon, an inhibitor of sepiapterin reductase, on the synthesis of nitric oxide was investigated. Dexamethasone decreased the nitric oxide production due to direct inhibition of the induction of nitric oxide synthase and of GTP cyclohydrolase. Substitution of tetrahydrobiopterin via sepiapterin could not overcome the dexamethasone-mediated inhibition. 2,4-Diamino-6-hydroxypyrimidine abolished nitric oxide synthesis and synergized with dexamethasone, completely eliminating nitric oxide production. Phenprocoumon inhibited production of nitric oxide via interference with later steps of tetrahydrobiopterin biosynthesis. An exogenous supply of tetrahydrobiopterin through sepiapterin led to a further increase of nitric oxide production, even in fully activated macrophages. The amount of nitric oxide produced by murine macrophages is therefore limited by the amount of tetrahydrobiopterin present in the cells. Inhibitors of tetrahydrobiopterin biosynthesis could provide a novel approach for therapy of pathological conditions mediated by nitric oxide, such as septic shock.

Immunovascular communication: activation and deactivation of murine endothelial cell nitric oxide synthase by cytokines

A murine endothelial cell line, send1, was found to produce substantial amounts of nitric oxide, particularly after activation with cytokines. The endothelial cell activation paralleled that of macrophages. Macrophage deactivation opposing activation has recently been brought into focus. We therefore studied the cytokine-mediated deactivation of endothelial cells in send1 and vascular strips. Our observations document that activation of nitric oxide synthase of endothelial cells can be counterbalanced by deactivating cytokines such as interleukin-4, interleukin-8, interleukin-10 and transforming growth factor-beta. Deactivation of nitric oxide synthase in endothelial cells might be an essential mechanism for the control of immune-mediated vasodilatation or septic shock and represents a novel mechanism of communication between the immune and the vascular systems.

Oncogene complementation in fetal brain transplants

Using a neural transplantation model and retrovirus-mediated gene transfer, we have introduced the oncogenes v-Ha-ras and v-myc into the developing rat brain. Upon insertion of a construct encoding v-Ha-ras and the Escherichia coli beta-galactosidase marker gene, the retroviral vector was found to be expressed in neurons, astrocytes, and endothelial cells of the graft. After latency periods of several months, fascicular neoplasms with expression of S-100 protein were observed in 50% of the transplants. The foreign genes were shown to be highly expressed in the tumors and in intact donor cells, by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside histochemistry, indicating that an activated Ha-ras oncogene has the potential to initiate neoplastic transformation of glial cells. Introduction of the v-myc oncogene into 15 grafts resulted in only a single primitive neuroectodermal tumor. However, simultaneous expression of the v-Ha-ras and v-myc genes yielded highly malignant, polyclonal neoplasms in all recipient animals, as early as 13 days after transplantation, from which cell lines could be easily derived. In addition, neoplastic transformation was also observed in vitro following introduction of ras and myc into embryonic forebrain cultures and into newborn cerebellar cultures. These data indicate a powerful complementary transforming effect of ras and myc on neural progenitors in vivo and in vitro. Coexpression of ras and myc may, therefore, provide a highly efficient tool for transforming neural precursor cells in distinct segments of the central nervous system at different stages of development.