Staphylococcal alpha-toxin provokes coronary vasoconstriction and loss in myocardial contractility in perfused rat hearts: role of thromboxane generation

The Global Burden of Community-Acquired Pneumonia in Adults, Encompassing Invasive Pneumococcal Disease and the Prevalence of Its Associated Cardiovascular Events, with a Focus on Pneumolysin and Macrolide Antibiotics in Pathogenesis and Therapy

Despite innovative advances in anti-infective therapies and vaccine development technologies, community-acquired pneumonia (CAP) remains the most persistent cause of infection-related mortality globally. Confronting the ongoing threat posed by Streptococcus pneumoniae (the pneumococcus), the most common bacterial cause of CAP, particularly to the non-immune elderly, remains challenging due to the propensity of the elderly to develop invasive pneumococcal disease (IPD), together with the predilection of the pathogen for the heart. The resultant development of often fatal cardiovascular events (CVEs), particularly during the first seven days of acute infection, is now recognized as a relatively common complication of IPD. The current review represents an update on the prevalence and types of CVEs associated with acute bacterial CAP, particularly IPD. In addition, it is focused on recent insights into the involvement of the pneumococcal pore-forming toxin, pneumolysin (Ply), in subverting host immune defenses, particularly the protective functions of the alveolar macrophage during early-stage disease. This, in turn, enables extra-pulmonary dissemination of the pathogen, leading to cardiac invasion, cardiotoxicity and myocardial dysfunction. The review concludes with an overview of the current status of macrolide antibiotics in the treatment of bacterial CAP in general, as well as severe pneumococcal CAP, including a consideration of the mechanisms by which these agents inhibit the production of Ply by macrolide-resistant strains of the pathogen.

Infectious shock after liposuction

Background

Liposuction has become one of the most popular cosmetic surgeries in China. However, few studies have discussed infectious shock caused by C. perfringens as one of the causes of death after liposuction.

Case presentation

A 24-year-old woman was brought to the emergency department (ED) of Guangzhou Chinese Overseas Hospital for treatment. The patient had undergone liposuction in her bilateral lower limbs two days prior. At the ED, the patient was unconscious, and had bilateral equal-sized (diameter, 6 mm) round pupils, no light reflex, a blood pressure (BP) of 71/33 mmHg, a heart rate of 133 bpm, and an SpO2 of 70%. She had bilateral limb swelling, extensive ecchymoses in her lower abdomen and bilateral thighs, local crepitus, blisters, weak pulses on her femoral artery and dorsalis pedis, high skin tension, and hemoglobin of 32 g/L. The patient was diagnosed with Clostridium perfringens infection, and she underwent debridement surgery and supportive treatment. But the patient’s BP could not improve. At 8:28 pm on the day of admission, the patient was declared clinically dead after the electrocardiograph showed a horizontal line and spontaneous respiration ceased.

Conclusions

Failure to meet surgical disinfection and environmental standards may be the cause of infection of C. perfringens through wounds. Therefore, it is necessary to strengthen the environmental disinfection of the operating room, and standardize the sterile conditions of the operation staff and patients before and during operation. Liposuction surgery necrotizing fasciitis is a rare but fatal complications, especially if diagnosis delay, therefore it is critical for early diagnosis and treatment of gas gangrene.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07574-1.

Staphylococcus aureus-Derived α-Hemolysin Evokes Generation of Specialized Pro-resolving Mediators Promoting Inflammation Resolution

Underlying mechanisms of how infectious inflammation is resolved by the host are incompletely understood. One hallmark of inflammation resolution is the activation of specialized pro-resolving mediators (SPMs) that enhance bacterial clearance and promote tissue repair. Here, we reveal α-hemolysin (Hla) from Staphylococcus aureus as a potent elicitor of SPM biosynthesis in human M2-like macrophages and in the mouse peritoneum through selective activation of host 15-lipoxygenase-1 (15-LOX-1). S. aureus-induced SPM formation in M2 is abolished upon Hla depletion or 15-LOX-1 knockdown. Isolated Hla elicits SPM formation in M2 that is reverted by inhibition of the Hla receptor ADAM10. Lipid mediators derived from Hla-treated M2 accelerate planarian tissue regeneration. Hla but not zymosan provokes substantial SPM formation in the mouse peritoneum, devoid of leukocyte infiltration and pro-inflammatory cytokine secretion. Besides harming the host, Hla may also exert beneficial functions by stimulating SPM production to promote the resolution of infectious inflammation.

Jordan et al. reveal that α-hemolysin from Staphylococcus aureus stimulates specialized pro-resolving mediator (SPM) formation through activation of 15-lipoxygenase-1 in human macrophages involving ADAM10. The host may exploit α-hemolysin as an SPM inducer to better cope with S. aureus infections and to promote inflammation resolution and tissue regeneration.

Cardiovascular Events After Community-Acquired Pneumonia: A Global Perspective with Systematic Review and Meta-Analysis of Observational Studies

Acute cardiovascular disease after community-acquired pneumonia is a well-accepted complication for which definitive treatment strategies are lacking. These complications share some common features but have distinct diagnostic and treatment approaches. We therefore undertook an updated systematic review and meta-analysis of observational studies reporting the incidence of overall complications, acute coronary syndromes, new or worsening heart failure, new or worsening arrhythmias and acute stroke, as well as short-term mortality outcomes. To set a framework for future research, we further included a holistic review of the interplay between the two conditions. From 1984 to 2019, thirty-nine studies were accrued, involving 92,188 patients, divided by setting (inpatients versus outpatients) and clinical severity (low risk versus high risk). Overall cardiac complications occurred in 13.9% (95% confidence interval (CI) 9.6-18.9), acute coronary syndromes in 4.5% (95% CI 2.9-6.5), heart failure in 9.2% (95% CI 6.7-12.2), arrhythmias in 7.2% (95% CI 5.6-9.0) and stroke in 0.71% (95% CI 0.1-3.9) of pooled inpatients. During this period, meta-regression analysis suggests that the incidence of overall and individual cardiac complications is decreasing. After adjusting for confounders, cardiovascular events taking place after community-acquired pneumonia independently increase the risk for short-term mortality (range of odds-ratio: 1.39-5.49). These findings highlight the need for effective, large trial based, preventive and therapeutic interventions in this important patient population.

Beneficial Effects of Vaccination on Cardiovascular Events: Myocardial Infarction, Stroke, Heart Failure

Influenza and pneumococcal infections have been suggested to be potential risk factors for causing adverse cardiovascular events, especially in high-risk patients. Vaccination against respiratory infections in patients with established cardiovascular disease (CVD) could serve as a potential cost-effective intervention to improve their clinical outcomes and cardiac societies have encouraged it. Previous studies have shown that influenza vaccination reduce mortality, acute coronary syndromes and hospitalization in patients with coronary heart disease (CHD) and/or heart failure (HF). However, there is a paucity of randomized prospective clinical trials in the field of the pneumococcal vaccination, and additional higher-quality evidence is needed. Furthermore, questions around the role of vaccination in the primary prevention of CVD, the optimal dose and timing are largely unanswered. The pathophysiologic mechanism in which vaccination provides cardiovascular protection may be related to the modification of the immune-inflammatory model of atherogenesis. The present review summarizes the current evidence and understanding for vaccination against influenza and streptococcus pneumoniae in CHD, HF and stroke and highlights its beneficial effect in the reduction of adverse cardiovascular events.

High-sensitivity cardiac troponin T predicts mortality after hospitalization for community-acquired pneumonia

BACKGROUND AND OBJECTIVE

Mortality after hospitalization with community-acquired pneumonia (CAP) is high, compared with age-matched controls. Available evidence suggests a strong link with cardiovascular disease. Our aim was to explore the prognostic value of high-sensitivity cardiac troponin T (cTnT) for mortality in patients hospitalized with CAP.

METHODS

CTnT level on admission was measured (assay conducted in 2015) in 295 patients hospitalized with CAP who participated in a randomized placebo-controlled double-blind trial on adjunctive dexamethasone treatment. Outcome measures were short- (30-day) and long-term (4.1-year) mortalities.

RESULTS

CTnT levels were elevated (≥14 ng/L) in 132 patients (45%). Pneumonia severity index (PSI) class was 4-5 in 137 patients (46%). Short- and long-term mortality were significantly higher in patients with elevated cTnT levels. cTnT level on admission combined with PSI classification was significantly better in predicting short-term mortality (area under the operating curve (AUC) = 0.903; 95% CI = 0.847-0.960), compared with PSI classification alone (AUC = 0.818; 95% CI = 0.717-0.919). An optimal cTnT cut-off level of 28 ng/L was independently associated with both short- and long-term mortality (OR = 21.9; 95% CI = 4.7-101.4 and 10.7; 95% CI = 5.0-22.8, respectively).

CONCLUSION

Elevated cTnT level on admission is a strong predictor of short- and long-term mortalities in patients hospitalized with CAP.

Cardiac myocyte dysfunction induced by streptolysin O is membrane pore and calcium dependent

Septic cardiomyopathy is a severe complication among some patients who develop group A streptococcal toxic shock syndrome. Despite the importance of cardiac dysfunction in determining prognosis, very little is known about mechanisms that reduce cardiac output in association with streptococcal infection. Here, we investigated the effects of streptococcal extracellular toxins on mechanical contractility of electrically paced primary murine cardiomyocytes. Our data demonstrate that streptolysin O (SLO) is the major streptococcal toxin responsible for cardiomyocyte contractile dysfunction. Streptolysin O dose-dependently affected cardiac myocyte function in discrete stages. Exposure to SLO caused a failure of cardiac cells to respond to electrical pacing, followed by spontaneous dysregulated contractions and augmented strength of contraction. Central to these SLO-mediated effects is a marked influx of calcium into the cytosol through SLO-mediated pores in the cytoplasmic membrane. Such calcium mobilization in response to SLO correlated temporally with hypercontractility and unpaced contractions. During continued exposure to SLO, cardiomyocytes exhibited periods of reversion to normal electrical pacing suggestive of membrane lesion repair and restoration of calcium handling. Together, these observations are consistent with the clinical observation that septic cardiomyopathy is a reversible condition in patients who survive streptococcal toxic shock syndrome. These data provide strong evidence that streptococcal exotoxins, specifically SLO, can directly impact cardiac mechanical function.

Staphylococcus aureus in vitro secretion of alpha toxin (hla) correlates with the affiliation to clonal complexes

The alpha toxin of Staphylococcus aureus is a pore forming toxin that penetrates host cell membranes causing osmotic swelling, rupture, lysis and subsequently cell death. Haemolysin alpha is toxic to a wide range of different mammalian cells; i.e., neurotoxic, dermonecrotic, haemolytic, and it can cause lethality in a wide variety of animals. In this study, the in vitro alpha toxin production of 648 previously genotyped isolates of S. aureus was measured quantitatively using antibody microarrays. Isolates originated from medical and veterinary settings and were selected in order to represent diverse clonal complexes and defined clinical conditions. Generally, the production of alpha toxin in vitro is related to the clonal complex affiliation. For clonal complexes CC22, CC30, CC45, CC479, CC705 and others, invariably no alpha toxin production was noted under the given in vitro conditions, while others, such as CC1, CC5, CC8, CC15 or CC96 secreted variable or high levels of alpha toxin. There was no correlation between alpha toxin yield and clinical course of the disease, or between alpha toxin yield and host species.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Acetyl salicylic acid usage and mortality in critically ill patients with the systemic inflammatory response syndrome and sepsis

OBJECTIVE

Low doses of acetyl salicylic acid, acting through 15-epi-lipoxin A4, have been shown to be anti-inflammatory in human studies. The manifold effects of acetyl salicylic acid on human physiology potentially may benefit patients with the systemic inflammatory response syndrome after sepsis or tissue trauma. We sought to determine whether acetyl salicylic acid administration at the time of development of systemic inflammatory response syndrome is associated with reduced mortality.

DESIGN

Retrospective cohort study of consecutive intensive care unit admissions between April 2000 and November 2009.

SETTING

Australian tertiary referral center.

PATIENTS

Seven-thousand nine-hundred forty-five intensive care unit admissions examined.

MEASUREMENTS AND MAIN RESULTS

The probability of in-hospital death during admissions in which individuals were identified as having systemic inflammatory response syndrome or sepsis was analyzed according to whether they were administered acetyl salicylic acid. Propensity analysis that matched all patients for their probability of being prescribed acetyl salicylic acid was undertaken. Among 5523 patients with a first episode of systemic inflammatory response syndrome, 2082 were administered acetyl salicylic acid in a 24-hr period around the time of systemic inflammatory response syndrome recognition. Propensity analysis showed a 10.9% mortality for acetyl salicylic acid users and 17.2% mortality in the propensity-matched nonusers (absolute risk difference -6.2%; 95% confidence interval -9.5% to -3.5%). Propensity matching also found that acetyl salicylic acid administration was associated with increased risk of renal injury (6.2% vs. 2.9%; absolute risk difference 13.3%; 95% confidence interval 2.5% to 5.0%). In the 970 patients with proven sepsis, acetyl salicylic acid administration was associated with a lower mortality (27.4% vs. 42.2%; absolute risk difference -14.8%; 95% confidence interval -18.9% to -8.6%) after propensity matching. This quasi-experimental study cannot establish a causal association between acetyl salicylic acid and death from systemic inflammatory response syndrome or sepsis. Unrecognized confounders may remain but numerous covariates are included in the analyses.

CONCLUSIONS

Our study shows a strong association between acetyl salicylic acid and survival in intensive care unit systemic inflammatory response syndrome and sepsis patients. The effect of acetyl salicylic acid treatment on mortality of patients with systemic inflammatory response syndrome and sepsis needs to be evaluated with prospective randomized intervention studies.

Haemolysis induced by α-toxin from Staphylococcus aureus requires P2X receptor activation

Recently, it was documented that α-haemolysin (HlyA) from Escherichia coli uses erythrocyte P2 receptors cause lysis. This finding was surprising as it appeared firmly established that HlyA-dependent pore formation per se is sufficient for full cell lysis. We discovered that HlyA induced a sequential process of shrinkage and swelling and that the final haemolysis is completely prevented by blockers of P2X receptors and pannexin channels. This finding has potential clinical relevance as it may offer specific pharmacological interference to ameliorate haemolysis inflicted by pore-forming bacterial toxins. In this context, it is essential to know whether this is specific to HlyA-induced cell damage or if other bacterial pore-forming toxins involve purinergic signals to orchestrate haemolysis. Here, we investigate if the haemolysis produced by α-toxin from Staphylococcus aureus involves P2 receptor activation. We observed that α-toxin-induced haemolysis is completely blocked by the unselective P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid. Moreover, several selective blockers of P2X(1) and P2X(7) ionotropic receptors abolished haemolysis in murine and equine erythrocytes. Inhibitors of pannexin channels partially reduced the α-toxin induced lysis. Thus, we conclude that α-toxin, similar to HlyA from E. coli produces cell damage by specific activation of a purinergic signalling cascade. These data indicate that pore-forming toxins in general require purinergic signalling to elicit their toxicity.

Lipopolysaccharide and sepsis-associated myocardial dysfunction

PURPOSE OF REVIEW

Myocardial dysfunction in sepsis demonstrates acute reduction in left-ventricular function that is potentially reversible yet also associated with increased mortality. The purpose of this review is to discuss the most recent advances in the current knowledge regarding the pathophysiological mechanisms of septic cardiomyopathy.

RECENT FINDINGS

There are numerous candidate pathophysiologic mechanisms for the induction of myocardial dysfunction in sepsis. Sarcolemmal and myofibrillar damage to septic rat cardiomyocytes has been observed, and is likely related to oxidative stress. In a septic chimeric murine model, wild-type mice had decreased cardiac function and increased myocardial TNF-α and IL-6 levels whereas TLR-4 knockout mice had attenuated responses to lipopolysaccharide challenge; thus contributing to the increasing evidence for TLR-4's role in the myocardial inflammatory response to lipopolysaccharide. A similar finding regarding endothelial cell NF-κβ signaling inhibition was found using knockout mice.

SUMMARY

Septic cardiomyopathy is a significant morbid component of severe sepsis and septic shock. Further research into reducing cardiomyocyte damage via oxidative stress, reducing pro-inflammatory responses induced by TLR-4/NF-κβ signaling, decreasing mitochondrial dysfunction, and improving cellular respiration thereby decreasing apoptosis are examples of areas that may be future therapeutic targets.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

The effect of diazepam on myocardial function and coronary vascular tone after endotoxemia in the isolated rat heart model

OBJECTIVE AND DESIGN

Tumor necrosis factor alpha (TNF-α) has been implicated in the pathogenesis of cardiovascular disease and sepsis-associated cardiac dysfunction. Although initially described solely as a lipopolysaccharide (LPS)-induced macrophage product, evidence exists that cardiac myocytes themselves produce substantial amounts of TNF-α in response to ischemia as well as LPS. The use of phosphodiesterase inhibitors has been shown to decrease LPS-induced TNF-α elaboration. The aim of the present study was to determine the effect of diazepam (Type IV phosphodiesterase inhibitor) on (1) myocardial function and (2) coronary vascular flow after LPS-induced endotoxic shock in an isolated rat heart model.

MATERIALS AND METHODS

Endotoxemia was induced by intraperitoneal LPS administration in adult male Wistar rats. Hearts were isolated after 6 h and perfused in a working mode with oxygenated Krebs-Henseleit buffer at 37°C. Diazepam was mixed with Krebs-Henseleit buffer and administered (3.0 μg/ml) for 20 min.

RESULTS

LPS-treated hearts showed depressed cardiac function and reduced coronary flow. Myocardial functional parameters (LVDP, +dP/dt, -dP/dt, RPP) and coronary flow (ml/min) were significantly (p < 0.01) improved by diazepam administration.

CONCLUSIONS

These findings suggest that diazepam can salvage myocardial function and undo coronary vascular constriction in the endotoxemic rat heart. These findings are clinically relevant to the treatment of cardiovascular depression caused by endotoxic shock.

Role of acute infection in triggering acute coronary syndromes

Acute coronary syndromes are a leading cause of morbidity and mortality worldwide. The mechanisms underlying the triggering of these events are diverse and include increased coronary and systemic inflammatory activity, dominant prothrombotic conditions, increased biomechanical stress on coronary arteries, variations in the coronary arterial tone, disturbed haemodynamic homoeostasis, and altered myocardial metabolic balance. There is experimental evidence that acute infections can promote the development of acute coronary syndromes, and clinical data strongly support a role for acute infections in triggering these events. In our Review, we summarise the pathogenesis of coronary artery disease and present the evidence linking acute infections with the development of acute coronary syndromes. Greater awareness of this association is likely to encourage research into ways of protecting patients who are at high risk.

Apoptosis contributes to septic cardiomyopathy and is improved by simvastatin therapy

Bacterial toxins cause cardiac dysfunction and death through an inflammatory process, but the mechanism remains unclear. Simvastatin is recognized as having anti-inflammatory properties beyond its lipid-lowering effects. We examined Staphylococcus aureus alpha-toxin in isolated heart and in vivo models and tested simvastatin's effects in sepsis. Isolated Langendorff-perfused rat hearts were exposed to a recirculating perfusate containing alpha-toxin (0.5 microg mL(-1)). Compared with controls, there was a significant increase in coronary perfusion pressure and fall in myocardial performance. Significant increases in p53 expression and apoptosis (1.3 +/- 0.5 to 7.1 +/- 1.4 terminal deoxynucleaotidyl transferase nick end labeling-positive cells; P < 0.05) compared with controls were observed, but markers of necrosis were similar. In parallel experiments, anaesthetized rats receiving alpha-toxin (40 microg kg(-1), i.v.) had in vivo hemodynamic parameters and serum markers of necrosis monitored for 4 h before the hearts were analyzed for histological change, p53 expression, and apoptosis. Over 4 h, alpha-toxin exposure produced substantial hemodynamic effects. In addition, p53 expression (0.2 +/- 0.2 to 7.1 +/- 0.5 p53-positive myocytes; P < 0.05), TNF-alpha levels, the degree of apoptosis, and markers of necrosis were all significantly increased compared with control animals. Pretreatment with simvastatin protected against alpha-toxin-induced sepsis associated with reduced p53, TNF-alpha, apoptosis, and necrosis. We found significant changes in systemic hemodynamics, coronary perfusion pressure, myocardial function, and increased p53 expression with apoptosis due to bacterial exotoxin. In vivo changes were significantly inhibited by pretreatment with simvastatin. We provide novel evidence for the mechanisms by which septicemia causes myocardial depression and hint at a potential role for simvastatin as an inhibitor of apoptosis in sepsis.

Group B streptococcal beta-hemolysin/cytolysin directly impairs cardiomyocyte viability and function

Background

Group B Streptococcus (GBS) is a leading cause of neonatal sepsis where myocardial dysfunction is an important contributor to poor outcome. Here we study the effects of the GBS pore-forming β-hemolysin/cytolysin (Bh/c) exotoxin on cardiomyocyte viability, contractility, and calcium transients.

Methodology/Principal Findings

HL-1 cardiomyocytes exposed to intact wild-type (WT) or isogenic Δβh/c mutant GBS, or to cell-free extracts from either strain, were assessed for viability by trypan blue exclusion and for apoptosis by TUNEL staining. Functionality of exposed cardiomyocytes was analyzed by visual quantitation of the rate and extent of contractility. Mitochondrial membrane polarization was measured in TMRE-loaded cells exposed to GBS βh/c. Effects of GBS βh/c on calcium transients were studied in fura-2AM-loaded primary rat ventricular cardiomyocytes. Exposure of HL-1 cardiomyocytes to either WT GBS or βh/c extracts significantly reduced both rate and extent of contractility and later induced necrotic and apoptotic cell death. No effects on cardiomyocyte viability or function were observed after treatment with Δβh/c mutant bacteria or extracts. The βh/c toxin was associated with complete and rapid loss of detectable calcium transients in primary neonatal rat ventricular cardiomyocytes and induced a loss of mitochondrial membrane polarization. These effects on viability and function were abrogated by the βh/c inhibitor, dipalmitoyl phosphatidylcholine (DPPC).

Conclusions/Significance

Our data show a rapid loss of cardiomyocyte viability and function induced by GBS βh/c, and these deleterious effects are inhibited by DPPC, a normal constituent of human pulmonary surfactant.. These findings have clinical implications for the cardiac dysfunction observed in neonatal GBS infections.

Adrenomedullin reduces vascular hyperpermeability and improves survival in rat septic shock

OBJECTIVE

Current therapies of sepsis and septic shock require administration of a large volume of fluid to maintain hemodynamic stability. The vasoregulatory peptide adrenomedullin has been shown to prevent the transition to the fatal hypocirculatory septic state by poorly understood mechanisms. We tested the hypothesis that therapeutic administration of adrenomedullin would reduce vascular hyperpermeability, thereby contributing to improved hemodynamics and survival.

DESIGN

Prospective randomized controlled animal study.

SUBJECTS

Male Sprague-Dawley rats (270 g).

INTERVENTIONS

We used 4.8 x 10(3) U/kg of Staphylococcus aureus alpha-toxin, a pore-forming exotoxin, to induce vascular leakage and circulatory shock in rats. The infusion rate was 24 microg/kg per hour. Adrenomedullin was started 1 h after alpha-toxin administration.

MEASUREMENT AND RESULTS

Infusion of alpha-toxin in rats induced cardiocirculatory failure resulting in a 6-h mortality of 53%. alpha-Toxin provoked massive vascular hyperpermeability, which was indicated by an enrichment of Evans blue dye albumin in the tissues of lung, liver, ileum and kidney. Plasma fluid loss led to a significant hemoconcentration. Hemodynamic impairment observed after alpha-toxin infusion was closely correlated to vascular hyperpermeability. Therapeutic administration of 24 microg/kg per hour adrenomedullin reduced 6-h mortality from 53% to 7%. Stabilization of the endothelial barrier by adrenomedullin was indicated by reduced extravasation of albumin and plasma fluid and may have contributed to hemodynamic improvement.

CONCLUSIONS

These data suggest that adrenomedullin-related reduction of vascular hyperpermeability might represent a novel and important mechanism contributing to the beneficial effects of this endogenous vasoregulatory peptide in sepsis and septic shock.

Simvastatin improves the healing of infected skin wounds of rats

PURPOSE: This study explores the potential of the simvastatin to ameliorate inflammation and infection in open infected skin wounds of rats. METHODS: Fourteen Wistar rats weighing 285±12g were used. The study was done in a group whose open infected skin wounds were treated with topical application of sinvastatina microemulsion (SIM, n=7) and a second group with wounds treated with saline 0.9 % (SAL, n=7). A bacteriological exam of the wounds fluid for gram positive and gram negative bacteria, the tecidual expression of TNFá and IL-1â by imunohistochemical technique, and histological analysis by HE stain were performed. RESULTS: The expression of TNFa could be clearly demonstrated in lower degree in skin wounds treated with simvastatin (668.6 ± 74.7 ìm²) than in saline (2120.0 ± 327.1 ìm²). In comparison, wound tissue from SIM group displayed leukocyte infiltration significantly lower than that observed in SAL group (p<0.05). Culture results of the samples taken from wound fluid on fourth post treatment day revealed wound infection in only one rat of group simvastatin (SIM), where Proteus mirabilis, Escherchia coli and Enterobacter sp were isolated. In the rats whose wounds were treated with saline (SAL), polymicrobial infection with more than 100,000 CFU/g was detected in all the wounds. CONCLUSION: In addition to its antiinflammatory properties, the protective effects of simvastatin in infected open skin wounds is able to reduce infection and probably has antibacterial action. The potential to treat these wounds with statins to ameliorate inflammation and infection is promising.

The use of moderate hypothermia during cardiac surgery is associated with repression of tumour necrosis factor-alpha via inhibition of activating protein-1: an experimental study

Introduction

The use of moderate hypothermia during experimental cardiac surgery is associated with decreased expression of tumour necrosis factor (TNF)-α in myocardium and with myocardial protection. In order to identify the cellular mechanisms that lead to that repression, we investigated the effect of hypothermia during cardiac surgery on both main signalling pathways involved in systemic inflammation, namely the nuclear factor-κB (NF-κB) and activating protein-1 pathways.

Method

Twelve female pigs were randomly subjected to standardized cardiopulmonary bypass with moderate hypothermia or normothermia (temperature 28°C and 37°C, respectively; six pigs in each group). Myocardial probes were sampled from the right ventricle before, during and 6 hours after bypass. We detected mRNA encoding TNF-α by competitive RT-PCR and measured protein levels of TNF-α, inducible nitric oxide synthase and cyclo-oxygenase-2 by Western blotting. Finally, we assessed the activation of NF-κB and activating protein-1, as well as phosphorylation of p38 mitogen-activated protein kinase by electrophoretic mobility shift assay with super shift and/or Western blot.

Results

During and after cardiac surgery, animals subjected to hypothermia exhibited lower expression of TNF-α and cyclo-oxygenase-2 but not of inducible nitric oxide synthase. This was associated with lower activation of p38 mitogen-activated protein kinase and of its downstream effector activating protein-1 in hypothermic animals. In contrast, NF-κB activity was no different between groups.

Conclusion

These findings indicate that the repression of TNF-α associated with moderate hypothermia during cardiac surgery is associated with inhibition of the mitogen-activated protein kinase p38/activating protein-1 pathway and not with inhibition of NF-κB. The use of moderate hypothermia during cardiac surgery may mitigate the perioperative systemic inflammatory response and its complications.

Nonheart failure-associated elevation of amino terminal pro-brain natriuretic peptide in the setting of sepsis

In addition to its importance in clinical assessment, N-terminal pro-brain natriuretic peptide (NT pro-BNP) is a valuable marker for evaluation of treatment and prognosis of heart failure. However, there are situations where NT pro-BNP is not related to myocardial dysfunction. Two cases of sepsis with markedly elevated NT pro-BNP levels that are not indicative of depressed myocardial function are described.

Perturbation of endothelial junction proteins by Staphylococcus aureus alpha-toxin: inhibition of endothelial gap formation by adrenomedullin

Endothelial hyperpermeability is a hallmark of an inflammatory reaction and contributes to tissue damage in severe infections. Loss of endothelial cell-cell adhesion leads to intercellular gap formation allowing paracellular fluid flux. Although Staphylococcus aureus alpha-toxin significantly contributed to staphylococci disease, little is known about its mechanism of endothelial hyperpermeability induction. Here, we demonstrate that in a model of isolated perfused rat ileum discontinuation of capillary vascular-endothelial-cadherin (VE-cadherin) was observed after bolus application of S. aureus alpha-toxin being inhibited by the endogenous peptide adrenomedullin (ADM). In vitro, alpha-toxin exposure induced loss of immunoreactivity of VE-cadherin and occludin in human cultured umbilical vein endothelial cells. Likewise, ADM blocked alpha-toxin-related junctional protein disappearance from intercellular sites. Additionally, cyclic AMP elevation was shown to stabilize endothelial barrier function after alpha-toxin application. Although no RhoA activation was noted after endothelial alpha-toxin exposure, inhibition of Rho kinase and myosin light chain kinase blocked loss of immunoreactivity of VE-cadherin and occludin as well as intercellular gap formation. In summary, stabilization of endothelial junctional integrity as indicated by interendothelial immunostaining might be an interesting approach to stabilize endothelial barrier function in severe S. aureus infections.

Effects of statins beyond lipid lowering: Potential for clinical benefits

BACKGROUND

The role of statin drugs in the reduction of serum lipids has been well documented. More recently, evidence suggesting that statins may positively impact many organ systems and disease states independent of lipid reduction has emerged. The term "pleiotropic effects" has been used to refer to these properties. We reviewed the evidence exploring such potential effects.

METHODS

A search of the MEDLINE database was conducted for articles published between 1985 to 2005 on the pleiotropic and the lipid-lowering independent effects of statin drugs. The search terms "statin", "HMG-CoA reductase inhibitor", "pleiotropic effects", and "inflammation" were used. English language articles were selected for inclusion along with selected cross-references.

RESULTS

Numerous animal and clinical studies support the presence of a spectrum of beneficial effects for statins that are independent of their lipid-lowering properties. These effects are mediated by a variety of mechanisms and they suggest that the therapeutic role of statins may expand.

CONCLUSION

Statins have shown great promise beyond their lipid-lowering effects. Ongoing and future studies will help to further clarify the potential clinical impact of these "pleiotropic effects".

Virulence determinants in Staphylococcus aureus and their involvement in clinical syndromes

Staphylococcus aureus is a major human pathogen responsible for a variety of toxin-mediated and suppurative diseases. About 50 staphylococcal virulence factors have been described to date. In this review, we examine the clinical implications of key staphylococcal virulence factors in toxin-mediated diseases, septic shock, and severe focal infections such as arthritis, infective endocarditis, pneumonia acquired during mechanical ventilation, and necrotizing pneumonia. Staphylococcal pathogenicity is sometimes due principally to a single virulence factor, as in toxic shock syndrome and necrotizing pneumonia. In contrast, several virulence factors are involved in other staphylococcal disease, such as septic shock. A better knowledge of the mechanism of action of each virulence factor involved in the different staphylococcal diseases could open the way to the use of specific inhibitors in the clinical setting.

Free arachidonic versus eicosapentaenoic acid differentially influences the potency of bacterial exotoxins to provoke myocardial depression in isolated rat hearts

OBJECTIVE

Staphylococcal alpha-toxin and Escherichia coli hemolysin (ECH) evoke cardiac dysfunction in isolated rat hearts by provoking myocardial synthesis of arachidonic acid-derived thromboxane A2 or the cysteinyl-leukotrienes, LTC4, LTD4, and LTE4, respectively. We investigated whether low doses of either toxin, which fail to induce cardiac depression by themselves, induce cardiac dysfunction when combined with free arachidonic acid.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated hearts from male Wistar rats.

INTERVENTIONS

Hearts were perfused with low doses of ECH or alpha-toxin in the absence or presence of arachidonic acid or the alternative eicosanoid precursor eicosapentaenoic acid (EPA).

MEASUREMENTS AND MAIN RESULTS

Application of low-dose ECH with arachidonic acid increased coronary perfusion pressure, depressed left ventricular contractile function, provoked electrical instability, and induced a release of creatine kinase concomitant with the liberation of LTC4, LTD4, and LTE4 into the perfusate. All events were abolished when formation of cysteinyl-leukotrienes was blocked by the 5-lipoxygenase activity inhibitor MK-886, targeting 5-lipoxygenase activating protein. In the presence of arachidonic acid, low doses of alpha-toxin caused an increase in cerebral perfusion pressure and a decline of contractile performance, attributable to the release of thromboxane A2, as both events were mitigated by the cyclooxygenase-inhibitor indomethacin. High doses of ECH caused cardiac dysfunction even in the absence of arachidonic acid. However, in the presence of EPA, the cardiodepressant effect of ECH was blunted. Release of EPA-derived LTE5 at the expense of arachidonic acid-derived LTC4, LTD4, and LTE4 was noted in these hearts.

CONCLUSIONS

The potency of the bacterial exotoxins ECH and alpha-toxin to cause coronary vasoconstriction and myocardial depression is dependent on the availability of free arachidonic acid and may be influenced by supplying omega-3 fatty acids as alternative lipid precursors.

Adrenomedullin treatment abolishes ileal mucosal hypoperfusion induced by Staphylococcus aureus α-toxin—An intravital microscopic study on an isolated rat ileum

OBJECTIVE

Disturbances of intestinal microcirculation associated with sepsis and septic shock result in diminished mucosal oxygenation. Tissue hypoxia as well as mediator formation may lead to intestinal mucosa dysfunction. As a consequence, bacteria and their products as well as gut-derived inflammatory mediators may further perpetuate septic and inflammatory events. Adrenomedullin is produced in the mucosa of the gastrointestinal tract and has been shown to improve survival in experimental sepsis. Using pore-forming Staphylococcus aureus alpha-toxin as a potent initiator of inflammatory reactions, we tested the hypothesis that exogenously added adrenomedullin improves ileal mucosal perfusion.

DESIGN

Prospective, experimental study.

SETTING

University laboratory.

SUBJECTS

Isolated perfused ileum from male Sprague-Dawley rats

INTERVENTIONS

Adrenomedullin treatment of S. aureus alpha-toxin infused ileum.

MEASUREMENT AND MAIN RESULTS

An infusion of alpha-toxin (0.05 microg/mL) induced a significant decrease of red blood cell velocity in villus terminal arterioles from 1.7 to 0.7 mm/sec assessed by intravital microscopy. This was accompanied by a significant reduction of mucosal hemoglobin oxygenation from 71.8% to 17.5% and impaired oxygen uptake. At constant bulk flow and oxygen delivery, these data indicate a redistribution of blood perfusion away from mucosa. Subsequent intervention with 0.1 microM adrenomedullin redistributed blood flow back toward the mucosa, causing an improvement of mucosal hemoglobin oxygenation and of organ oxygen uptake.

CONCLUSION

These data suggest that exogenously added adrenomedullin protects ileum mucosa by diminishing alpha-toxin-induced microcirculatory disturbances. Further investigations will have to clarify the therapeutic potential of adrenomedullin in sepsis-related gut dysfunction.

Adrenomedullin reduces Staphylococcus aureus alpha-toxin-induced rat ileum microcirculatory damage

OBJECTIVE

Increased microvascular permeability and perfusion mismatch are hallmarks of sepsis or septic shock. The intestinal mucosa is very sensitive to tissue hypoxia. Intestinal mucosa dysfunction may allow translocation of bacteria and their products, thereby perpetuating sepsis and inflammation. Staphylococcus aureus alpha-toxin is a major pathogenicity determinant of this bacterium, provoking cardiovascular collapse. Current evidence suggests that the endogenous peptide adrenomedullin stabilizes circulatory homeostasis in systemic inflammatory response. Using alpha-toxin as a well-defined strong initiator of an inflammatory reaction, we tested the hypothesis that exogenously applied adrenomedullin stabilizes gut microcirculation.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated, perfused ileum from male Sprague-Dawley rats and human umbilical vein endothelial cells.

INTERVENTIONS

Administration of S. aureus alpha-toxin before or after infusion of adrenomedullin.

MEASUREMENTS AND MAIN RESULTS

Injection of a bolus of 1 microg of alpha-toxin in the superior mesenteric artery in a constant-flow, blood-perfused preparation of rat ileum increased perfusion pressure and relative hemoglobin concentration and decreased mucosal hemoglobin oxygen saturation. Continuous infusion of adrenomedullin (0.1 micromol/L) significantly reduced these alpha-toxin-related effects. Severe microvascular hyperpermeability observed in alpha-toxin-exposed ileum was abolished by adrenomedullin pretreatment. In addition, adrenomedullin blocked alpha-toxin-induced endothelial myosin light chain phosphorylation, endothelial cell contraction, and subsequent loss of endothelial barrier function in vitro. Treatment of alpha-toxin (infusion of 0.05 microg/mL)-exposed ileum with adrenomedullin (0.1 micromol/L) started 10 mins after onset of toxin application also significantly reduced superior mesenteric artery pressure and permeability increase.

CONCLUSIONS

In summary, these data suggest that exogenous adrenomedullin protects ileum by reducing alpha-toxin-induced microcirculatory disturbances and by stabilizing endothelial barrier function.

Effects of intraaortic balloon augmentation in a porcine model of endotoxemic shock

OBJECTIVE

Patients with septic shock commonly have myocardial dysfunction associated with lactic acid production and troponin I release. The purpose of this study was to evaluate the effects on intraaortic balloon pump (IABP) support on myocardial dysfunction.

DESIGN

Prospective, randomized controlled study.

SETTING

Animal research laboratory.

METHODS

Ten pigs had arterial, pulmonary arterial, and coronary catheters inserted. After receiving endotoxin infusion over 30 min, half the animals received IABP support.

RESULTS

Coronary sinus lactic acid levels (P< 0.05 for both 90 min versus baseline and 60 min versus baseline) and arterial lactic acid levels (P < 0.05 for both 90 min versus baseline and 60 min versus baseline) increased with time but did not differ between IABP and sham groups. While overall there was no difference with time in myocardial lactic acid consumption or production (calculated as arterial lactic acid level minus coronary sinus lactic acid level), the IABP group showed net myocardial lactic acid consumption at 90 min, while the sham group showed myocardial lactic acid production. Three of five animals in each group showed troponin I release. The levels were similar and did not differ between groups.

CONCLUSION

IABP had no benefits in this porcine model of endotoxemic shock.

Effect of a Novel Thromboxane A2 Inhibitor on Right Ventricular-Arterial Coupling in Endotoxic Shock

We investigated the effects of a dual thromboxane (TX)A2 synthase inhibitor and TXA2 receptor antagonist (BM-573) on right ventricular-arterial coupling in a porcine model of endotoxic shock. Thirty minutes before the onset of 0.5 mg/kg endotoxin infusion, six pigs (Endo group) received an infusion with a placebo solution, and six other pigs (Anta group) with BM-573. Right ventricular pressure-volume loops were obtained by the conductance catheter technique. The slope (Ees) of the end-systolic pressure-volume relationship and its volume intercept at 25 mmHg were calculated as measures of right ventricular systolic function. RV afterload was quantified by pulmonary arterial elastance (Ea), and Ees/Ea ratio represented right ventricular-arterial coupling. Mechanical efficiency was defined as the ratio of stroke work and pressure-volume area. In this model of endotoxic shock, BM-573 blunted the early phase of pulmonary hypertension, improved arterial oxygenation, and prevented a decrease in right ventricular myocardial efficiency and right ventricular dilatation. However, the drug could not prevent the loss of homeometric regulation and alterations in right ventricular-arterial coupling. In conclusion, dual TXA2 synthase inhibitor and receptor antagonists such as BM-573 have potential therapeutic applications, improving right ventricular efficiency and arterial oxygenation in endotoxic shock.

Leukotriene-mediated coronary vasoconstriction and loss of myocardial contractility evoked by low doses of Escherichia coli hemolysin in perfused rat hearts

OBJECTIVE

hemolysin has been implicated as an important pathogenic factor in extraintestinal infections including sepsis. We investigated the effects of coronary administration of hemolysin on cardiac function in isolated rat hearts perfused at constant flow.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated hearts from male Wistar rats.

INTERVENTIONS

Isolated hearts were perfused with purified hemolysin for 60 min.

MEASUREMENTS AND MAIN RESULTS

Low concentrations of the toxin in the perfusate (0.1-0.2 hemolytic units/mL) caused a dose-dependent coronary vasoconstriction with a marked increase in coronary perfusion pressure, which was paralleled by a decrease in left ventricular developed pressure (and the maximum rate of left ventricular pressure increase). Moreover, 0.2 hemolytic units/mL hemolysin evoked ventricular fibrillation within 10 mins of toxin application. These events were accompanied by the liberation of leukotrienes (LTC4, LTD4, LTE4, and LTB4), thromboxane A2, prostaglandin I2, and the cell necrosis markers lactate dehydrogenase and creatine kinase into the recirculating perfusate. The lipoxygenase inhibitor MK-886 fully blocked the toxin-induced coronary vasoconstrictor response and the loss of myocardial contractility and reduced the release of lactate dehydrogenase and creatine kinase. In contrast to this, the cyclooxygenase inhibitor indomethacin was entirely ineffective. In addition, hemolysin elicited an increase in heart weight and left ventricular end-diastolic pressure, the latter again being suppressed by MK-886.

CONCLUSIONS

Low doses of hemolysin cause strong coronary vasoconstriction, linked with loss of myocardial performance, release of cell injury enzymes, and electrical instability, with all events being largely attributable to toxin-elicited leukotriene generation in the coronary vasculature. Bacterial exotoxins such as hemolysin thus may be implicated in the cardiac abnormalities encountered in septic shock.

Staphylococcal alpha-toxin provokes neutrophil-dependent cardiac dysfunction: role of ICAM-1 and cys-leukotrienes

The role of polymorphonuclear neutrophils (PMN) in septic myocardial dysfunction is presently unknown. Staphylococcus aureus infections are frequently associated with septic sequelae. Therefore, we perfused isolated rat hearts with low doses of alpha-toxin, the major staphylococcal exotoxin, followed by application of human PMN, N-formyl-methionyl-leucyl-phenylalanine, and arachidonic acid. In contrast to sham-perfused hearts (no alpha-toxin), a rise in coronary perfusion pressure (CPP) and a reduction of contractile function were noted, and cardiac expression of intercellular adhesion molecule (ICAM)-1 was detected by immunohistochemical methods and real-time PCR. Histological analysis and myeloperoxidase activity indicated cardiac PMN accumulation in alpha-toxin-challenged hearts. Major quantities of cysteinyl (cys)-leukotrienes (LT), LTB4, and 5-hydroxyeicosatetraenoic acid (5-HETE) were found in the perfusate of alpha-toxin-exposed hearts. With an anti-ICAM-1 antibody, neutrophil accumulation, leukotriene (LT) synthesis, coronary vasoconstriction, and the accompanying cardiodepression were suppressed. Similarly, the lipoxygenase inhibitor MK-886 blocked LT synthesis and maintained cardiac function. We conclude that low-dose alpha-toxin provokes coronary endothelial ICAM-1 expression and neutrophil accumulation, with subsequent synthesis of cys-LTs, LTB4, and 5-HETE under conditions of appropriate stimulation. This response is linked with coronary vasoconstriction and contractile dysfunction, with cys-LT synthesis and maldistribution of perfusion offered as likely underlying mechanisms.

Mediator generation and signaling events in alveolar epithelial cells attacked by S. aureus alpha-toxin

Staphylococcus aureus alpha-toxin is a pore-forming bacterial exotoxin that has been implicated as a significant virulence factor in human staphylococcal diseases. In primary cultures of rat pneumocyte type II cells and the human A549 alveolar epithelial cell line, purified alpha-toxin provoked rapid-onset phosphatidylinositol (PtdIns) hydrolysis as well as liberation of nitric oxide and the prostanoids PGE(2), PGI(2), and thromboxane A(2). In addition, sustained upregulation of proinflammatory interleukin (IL)-8 mRNA expression and protein secretion occurred. "Priming" with low-dose IL-1beta markedly enhanced the IL-8 response to alpha-toxin, which was then accompanied by IL-6 appearance. The cytokine response was blocked by the intracellular Ca(2+)-chelating reagent 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, the protein kinase C inhibitor bis-indolyl maleimide I, as well as two independent inhibitors of nuclear factor-kappaB activation, pyrrolidine dithiocarbamate and caffeic acid phenethyl ester. We conclude that alveolar epithelial cells are highly reactive target cells of staphylococcal alpha-toxin. alpha-Toxin pore-associated transmembrane Ca(2+) flux and PtdIns hydrolysis-related signaling with downstream activation of protein kinase C and nuclear translocation of nuclear factor-kappaB are suggested to represent important underlying mechanisms. Such reactivity of the alveolar epithelial cells may be relevant for pathogenic sequelae in staphylococcal lung disease.

Staphylococcus aureus alpha toxin mediates polymorphonuclear leukocyte-induced vasocontraction and endothelial dysfunction

The effect of Staphylococcus aureus alpha toxin (alpha-toxin) on selectin-mediated neutrophil adhesion was investigated in polymorphonuclear leukocyte- (PMN) induced vasocontraction and endothelial dysfunction. Adherence of human PMNs to rat aortic endothelium increased significantly following stimulation of the endothelium with alpha-toxin (0.1, 0.5, and 1 microg/mL). This effect could be significantly attenuated by monoclonal antibodies directed against P-selectin or fucoidin, a carbohydrate known to block selectins. Unstimulated human PMNs (10(6)cells/mL) were added to organ chambers containing rat aortic rings stimulated with alpha-toxin (0.5 microg/mL). PMNs elicited a significant vasocontraction in alpha-toxin-stimulated, but not in control aortic, rings (142+/-12 mg versus 12+/-4 mg, P < 0.05). This PMN-induced vasocontraction was virtually blunted by pretreatment with MAb directed against P-selectin or fucoidin (P < 0.05). Endothelial function as assessed by endothelium-dependent vasorelaxation to acetylcholine was substantially inhibited after induction of PMN-induced vasocontraction in alpha-toxin-stimulated aortic rings. This endothelial dysfunction was reduced by P-selectin MAb or fucoidin. In contrast, endothelium-independent relaxation to sodium nitrite was not altered by PMN incubation, indicating that vascular smooth muscle function was unaffected. Thus, PMN-endothelial interaction following S. aureus a-toxin activation of the vascular endothelium is at least, in part, mediated by selectins. As a consequence, PMN-induced vasocontraction and endothelial dysfunction occur. Such mechanisms may be involved in microcirculation abnormalities encountered in sepsis or septic shock due to S. aureus infection.

The keratinocyte as a target for staphylococcal bacterial toxins

Skin infections with Staphylococcus aureus are not only an important cause of morbidity and even mortality, but are thought to serve as initiation and/or persistance factors for numerous inflammatory skin diseases, including psoriasis and atopic dermatitis. One mechanism by which S. aureus can modulate the immune system is through the production of proteins such as superantigenic toxins, Protein A, as well through the cytolytic alpha-toxin. This review serves to discuss the biology of these three types of proteins, with emphasis on their ability to stimulate the production of powerful pro-inflammatory lipid- and protein-derived cytokines in keratinocytes. Characterization of interactions between these proteins and the keratinocyte can provide a better understanding of how bacterial infection modulates inflammatory skin diseases, as well as provide the basis for improved therapies involving antibacterial agents.

Improved high-performance liquid chromatographic method for the combined analysis of phospholipase, lipoxygenase and cyclooxygenase activities

We report herein an improved method for the high-performance liquid chromatographic separation and analysis of eicosanoids formed during the stimulation of human platelets in vitro with collagen. Since the products of interest, excepting arachidonic acid, contain hydroxyl groups (one to several), our method involves the conversion of the hydroxyl groups into acetates (pyridine/acetic anhydride) after derivatization with anthryl diazomethane (ADAM) rendering the compounds with much decreased polarity for separation on a reversed-phase column. This procedure is superior to that involving ADAM esters only, i.e. with free hydroxyl groups, as it leads to the excellent separation of the desired compounds from each other and from extraneous peaks observed due to the ADAM reagent and sharpens the peak of thromboxane. We have successfully applied the method to investigate the formation of thromboxane B2 and 12-hydroxyheptadecatrienoic acid (HHT) (products of cyclooxygenase and thromboxane A2 synthase), 12-hydroxyeicosatetraenoic acid (12-HETE, a 12-lipoxygenase product) and arachidonic acid (AA, product of phospholipase A2) formed during the in vitro aggregation of human platelets induced by collagen. A correlation between the inhibition of aggregation by aspirin and thromboxane/HHT formation was observed. All four compounds can be chromatographed in a single run. We employed prostaglandin B1 (PGB1) as internal reference standard to quantify the products. The method is useful to investigate selectivity of drugs which may affect either or all of these enzyme pathways at the same time.

Biosynthesis of constitutive nitric oxide synthase-derived nitric oxide attenuates coronary vasoconstriction and myocardial depression in a model of septic heart failure induced by Staphylococcus aureus alpha-toxin

OBJECTIVE

Myocardial depression, which frequently occurs in the course of septic shock, has been attributed to the cardiodepressant properties of nitric oxide (NO) generated by either the inducible NO synthase (iNOS) or the constitutive isoform (cNOS). We have previously demonstrated that alpha-toxin from Staphylococcus aureus induces thromboxane-mediated vasoconstriction accompanied by severe cardiodepression in isolated rat hearts. In the present study, we investigated the role of NO in the alpha-toxin-induced vascular and contractile abnormalities.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated hearts from male Wistar rats.

INTERVENTIONS

Isolated hearts were perfused with purified staphylococcal alpha-toxin for 60 mins.

MEASUREMENTS AND MAIN RESULTS

At a concentration of 0.25 and 0.5 microg/mL, alpha-toxin induced a rise in coronary perfusion pressure, depressed myocardial contractility, and caused edema formation. Simultaneously, a time- and dose-dependent rapid release of NO into the perfusate was noted as quantified by a chemiluminescence technique. L-NMMA, a nonselective inhibitor of NOS, but not PBITU, an iNOS-selective inhibitor, blocked NO synthesis, markedly increased the rise in coronary perfusion pressure and the loss in contractility, and enhanced edema formation in response to alpha-toxin. In contrast, zaprinast, a selective inhibitor of phosphodiesterase type V that is used for stabilization of cyclic guanosine monophosphate, attenuated the toxin-induced coronary vasoconstrictor response and the myocardial depression. L-arginine, the substrate of NOS, had similar, yet less potent, effects as zaprinast and slightly increased the release of NO caused by alpha-toxin. Immunohistochemical analysis of the myocardium at the end of the perfusion period demonstrated a positive staining for cNOS but not for iNOS. In addition, no up-regulation of iNOS mRNA was detected in the tissue of toxin-exposed hearts.

CONCLUSIONS

Staphylococcal alpha-toxin provokes NO biosynthesis via activation of cNOS in rat hearts. NO partly antagonizes the deleterious effects of this pathogenicity factor on coronary vasoregulation and myocardial performance.