Multifaceted Role of Pneumolysin in the Pathogenesis of Myocardial Injury in Community-Acquired Pneumonia

Bacterial toxins and heart function: heat-labile Escherichia coli enterotoxin B promotes changes in cardiac function with possible relevance for sudden cardiac death

Bacterial toxins can cause cardiomyopathy, though it is not its most common cause. Some bacterial toxins can form pores in the membrane of cardiomyocytes, while others can bind to membrane receptors. Enterotoxigenic E. coli can secrete enterotoxins, including heat-resistant (ST) or labile (LT) enterotoxins. LT is an AB5-type toxin that can bind to specific cell receptors and disrupt essential host functions, causing several common conditions, such as certain diarrhea. The pentameric B subunit of LT, without A subunit (LTB), binds specifically to certain plasma membrane ganglioside receptors, found in lipid rafts of cardiomyocytes. Isolated guinea pig hearts and cardiomyocytes were exposed to different concentrations of purified LTB. In isolated hearts, mechanical and electrical alternans and an increment of heart rate variability, with an IC50 of ~0.2 μg/ml LTB, were observed. In isolated cardiomyocytes, LTB promoted significant decreases in the amplitude and the duration of action potentials. Na+ currents were inhibited whereas L-type Ca2+ currents were augmented at their peak and their fast inactivation was promoted. Delayed rectifier K+ currents decreased. Measurements of basal Ca2+ or Ca2+ release events in cells exposed to LTB suggest that LTB impairs Ca2+ homeostasis. Impaired calcium homeostasis is linked to sudden cardiac death. The results are consistent with the recent view that the B subunit is not merely a carrier of the A subunit, having a role explaining sudden cardiac death in children (SIDS) infected with enterotoxigenic E. coli, explaining several epidemiological findings that establish a strong relationship between SIDS and ETEC E. coli.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-023-01100-6.

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.

Interventions to improve outcomes in community-acquired pneumonia

INTRODUCTION

Community-acquired pneumonia (CAP) is a common infection associated with high morbimortality and a highly deleterious impact on patients' quality of life and functionality. We comprehensively review the factors related to the host, the causative microorganism, the therapeutic approach and the organization of health systems (e.g. setting for care and systems for allocation) that might have an impact on CAP-associated outcomes. Our main aims are to discuss the most controversial points and to provide some recommendations that may guide further research and the management of patients with CAP, in order to improve their outcomes, beyond mortality.

AREA COVERED

In this review, we aim to provide a critical account of potential measures to improve outcomes of CAP and the supporting evidence from observational studies and clinical trials.

EXPERT OPINION

CAP is associated with high mortality and a highly deleterious impact on patients' quality of life. To improve CAP-associated outcomes, it is important to understand the factors related to the patient, etiology, therapeutics, and the organization of health systems.

Risk of Acute Myocardial Infarction Among Patients With Laboratory-Confirmed Invasive Pneumococcal Disease: A Self-Controlled Case Series Study

BACKGROUND

Acute myocardial infarction (AMI) events have been reported among patients with certain viral and bacterial infections. Whether invasive pneumococcal disease (IPD) increases the risk of AMI remains unclear. We examined whether laboratory-confirmed IPD was associated with the risk of AMI.

METHODS

We conducted a self-controlled case series analysis among adult Tennessee residents with evidence of an AMI hospitalization (2003-2019). Patient follow-up started 1 year before the earliest AMI and continued through the date of death, 1 year after AMI, or study end (December 2019). Periods for AMI assessment included the 7 to 1 days before IPD specimen collection (pre-IPD detection), day 0 through day 7 after IPD specimen collection (current IPD), day 8 to 28 after IPD specimen collection (post-IPD), and a control period (all other follow-up). We used conditional Poisson regression to calculate incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for each risk period compared with control periods using within-person comparisons.

RESULTS

We studied 324 patients hospitalized for AMI with laboratory-confirmed IPD within 1 year before or after the AMI hospitalization. The incidence of AMI was significantly higher during the pre-IPD detection (IRR, 10.29; 95% CI: 6.33-16.73) and the current IPD (IRR, 92.95; 95% CI: 72.17-119.71) periods but nonsignificantly elevated in the post-IPD risk period (IRR, 1.83; 95% CI: .86-3.91) compared with control periods. The AMI incidence was higher in the post-IPD control period (29 to 365 days after IPD; IRR, 2.95; 95% CI: 2.01-4.32).

CONCLUSIONS

Hospitalizations with AMI were strongly associated with laboratory-confirmed IPD.

Acute Coronary Syndrome, Stroke, and Mortality after Community-Acquired Pneumonia: Systematic Review and Meta-Analysis

One-third of adult inpatients with community-acquired pneumonia (CAP) develop acute coronary syndrome (ACS), stroke, heart failure (HF), arrhythmias, or die. The evidence linking CAP to cardiovascular disease (CVD) events is contradictory. We aimed to systematically review the role of CAP as a CVD risk factor. We registered the protocol (CRD42022352910) and searched for six databases from inception to 31 December 2022. We included 13 observational studies, 276,109 participants, 18,298 first ACS events, 12,421 first stroke events, 119 arrhythmic events, 75 episodes of new onset or worsening HF, 3379 deaths, and 218 incident CVD events. CAP increased the odds of ACS (OR 3.02; 95% CI 1.88–4.86), stroke (OR 2.88; 95% CI 2.09–3.96), mortality (OR 3.22; 95% CI 2.42–4.27), and all CVD events (OR 3.37; 95% CI 2.51–4.53). Heterogeneity was significant (I2 = 97%, p < 0.001). Subgroup analysis found differences according to the continent of origin of the study, the follow-up length, and the sample size (I2 > 40.0%, p < 0.10). CAP is a significant risk factor for all major CVD events including ACS, stroke, and mortality. However, these findings should be taken with caution due to the substantial heterogeneity and the possible publication bias.

Risk of cardiovascular events leading to hospitalisation after Streptococcus pneumoniae infection: a retrospective cohort LIFE Study

OBJECTIVES

To elucidate the risk of cardiovascular event occurrence following Streptococcus pneumoniae infection.

DESIGN

Retrospective cohort study using a LIFE Study database.

SETTING

Three municipalities in Japan.

PARTICIPANTS

Municipality residents who were enrolled in either National Health Insurance or the Latter-Stage Elderly Healthcare System from April 2014 to March 2020.

EXPOSURE

Occurrence of S. pneumoniae infection.

PRIMARY OUTCOME MEASURES

Occurrence of one of the following cardiovascular events that led to hospitalisation after S. pneumoniae infection: (1) coronary heart disease (CHD), (2) heart failure (HF), (3) stroke or (4) atrial fibrillation (AF).

RESULTS

S. pneumoniae-infected patients were matched with non-infected patients for each cardiovascular event. We matched 209 infected patients and 43 499 non-infected patients for CHD, 179 infected patients and 44 148 non-infected patients for HF, 221 infected patients and 44 768 non-infected patients for stroke, and 241 infected patients and 39 568 non-infected patients for AF. During follow-up, the incidence rates for the matched infected and non-infected patients were, respectively, 38.6 (95% CI 19.9 to 67.3) and 30.4 (29.1 to 31.8) per 1000 person-years for CHD; 69.6 (41.9 to 108.8) and 50.5 (48.9 to 52.2) per 1000 person-years for HF; 75.4 (48.3 to 112.2) and 35.5 (34.1 to 36.9) per 1000 person-years for stroke; and 34.7 (17.9 to 60.6) and 11.2 (10.4 to 12.0) per 1000 person-years for AF. Infected patients were significantly more likely to develop stroke (adjusted HR: 2.05, 95% CI 1.22 to 3.47; adjusted subdistribution HR: 1.94, 95% CI 1.15 to 3.26) and AF (3.29, 1.49 to 7.26; 2.74, 1.24 to 6.05) than their non-infected counterparts.

CONCLUSIONS

S. pneumoniae infections elevate the risk of subsequent stroke and AF occurrence. These findings indicate that pneumococcal infections have short-term effects on patients' health and increase their midterm to long-term susceptibility to serious cardiovascular events.

Magnetic Nanoclusters Increase the Sensitivity of Lateral Flow Immunoassays for Protein Detection: Application to Pneumolysin as a Biomarker for Streptococcus pneumoniae

Lateral flow immunoassays for detecting biomarkers in body fluids are simple, quick, inexpensive point-of-care tests widely used in disease surveillance, such as during the coronavirus disease 2019 (COVID-19) pandemic. Improvements in sensitivity would increase their utility in healthcare, food safety, and environmental control. Recently, biofunctional magnetic nanoclusters have been used to selectively label target proteins, which allows their detection and quantification with a magneto-inductive sensor. This type of detector is easily integrated with the lateral flow immunoassay format. Pneumolysin is a cholesterol-dependent cytolysin and one of the most important protein virulence factors of pneumonia produced by Streptococcus pneumoniae. It is recognized as an important biomarker for diagnosis in urine samples. Pneumonia is the infectious disease that causes the most deaths globally, especially among children under five years and adults over 65 years, most of them in low- and middle-income countries. There especially, a rapid diagnostic urine test for pneumococcal pneumonia with high sensitivity and specificity would be helpful in primary care. In this work, a lateral flow immunoassay with magnetic nanoclusters conjugated to anti-pneumolysin antibodies was combined with two strategies to increase the technique's performance. First, magnetic concentration of the protein before the immunoassay was followed by quantification by means of a mobile telephone camera, and the inductive sensor resulted in detection limits as low as 0.57 ng (telephone camera) and 0.24 ng (inductive sensor) of pneumolysin per milliliter. Second, magnetic relocation of the particles within the test strip after the immunoassay was completed increased the detected signal by 20%. Such results obtained with portable devices are promising when compared to non-portable conventional pneumolysin detection techniques such as enzyme-linked immunosorbent assays. The combination and optimization of these approaches would have excellent application in point-of-care biodetection to reduce antibiotic misuse, hospitalizations, and deaths from community-acquired pneumonia.

The Yin and Yang of Pneumolysin During Pneumococcal Infection

Pneumolysin (PLY) is a pore-forming toxin produced by the human pathobiont Streptococcus pneumoniae, the major cause of pneumonia worldwide. PLY, a key pneumococcal virulence factor, can form transmembrane pores in host cells, disrupting plasma membrane integrity and deregulating cellular homeostasis. At lytic concentrations, PLY causes cell death. At sub-lytic concentrations, PLY triggers host cell survival pathways that cooperate to reseal the damaged plasma membrane and restore cell homeostasis. While PLY is generally considered a pivotal factor promoting S. pneumoniae colonization and survival, it is also a powerful trigger of the innate and adaptive host immune response against bacterial infection. The dichotomy of PLY as both a key bacterial virulence factor and a trigger for host immune modulation allows the toxin to display both "Yin" and "Yang" properties during infection, promoting disease by membrane perforation and activating inflammatory pathways, while also mitigating damage by triggering host cell repair and initiating anti-inflammatory responses. Due to its cytolytic activity and diverse immunomodulatory properties, PLY is integral to every stage of S. pneumoniae pathogenesis and may tip the balance towards either the pathogen or the host depending on the context of infection.

Neutrophil-Derived Extracellular Vesicles Activate Platelets after Pneumolysin Exposure

Pneumolysin (PLY) is a pore-forming toxin of Streptococcus pneumoniae that contributes substantially to the inflammatory processes underlying pneumococcal pneumonia and lung injury. Host responses against S. pneumoniae are regulated in part by neutrophils and platelets, both individually and in cooperative interaction. Previous studies have shown that PLY can target both neutrophils and platelets, however, the mechanisms by which PLY directly affects these cells and alters their interactions are not completely understood. In this study, we characterize the effects of PLY on neutrophils and platelets and explore the mechanisms by which PLY may induce neutrophil–platelet interactions. In vitro studies demonstrated that PLY causes the formation of neutrophil extracellular traps (NETs) and the release of extracellular vesicles (EVs) from both human and murine neutrophils. In vivo, neutrophil EV (nEV) levels were increased in mice infected with S. pneumoniae. In platelets, treatment with PLY induced the cell surface expression of P-selectin (CD62P) and binding to annexin V and caused a significant release of platelet EVs (pl-EVs). Moreover, PLY-induced nEVs but not NETs promoted platelet activation. The pretreatment of nEVs with proteinase K inhibited platelet activation, indicating that the surface proteins of nEVs play a role in this process. Our findings demonstrate that PLY activates neutrophils and platelets to release EVs and support an important role for neutrophil EVs in modulating platelet functions in pneumococcal infections.

Polyvalent immunoglobulin preparations inhibit pneumolysin-induced platelet destruction

Platelets play an important role in the development and progression of respiratory distress. Functional platelets are known to seal inflammatory endothelial gaps and loss of platelet function has been shown to result in loss of integrity of pulmonary vessels. This leads to fluid accumulation in the pulmonary interstitium, eventually resulting in respiratory distress. Streptococcus pneumoniae is one of the major pathogens causing community-acquired pneumonia. Previously, we have shown that its major toxin pneumolysin forms pores in platelet membranes and renders them nonfunctional. In vitro, this process was inhibited by polyvalent intravenous immunoglobulins (IVIGs). In this study, we compared the efficacy of a standard IVIG preparation (IVIG, 98% immunoglobulin G [IgG]; Privigen, CSL Behring, United States) and an IgM/IgA-enriched immunoglobulin preparation (21% IgA, 23% IgM, 56% IgG; trimodulin, Biotest AG, Germany) to inhibit pneumolysin-induced platelet destruction. Platelet destruction and functionality were assessed by flow cytometry, intracellular calcium release, aggregometry, platelet viability, transwell, and flow chamber assays. Overall, both immunoglobulin preparations efficiently inhibited pneumolysin-induced platelet destruction. The capacity to antagonize pneumolysin mainly depended on the final IgG content. As both polyvalent immunoglobulin preparations efficiently prevent pneumolysin-induced platelet destruction and maintain platelet function in vitro, they represent promising candidates for clinical studies on supportive treatment of pneumococcal pneumonia to reduce progression of respiratory distress.

Management of pneumonia in critically ill patients

Severe pneumonia is associated with high mortality (short and long term), as well as pulmonary and extrapulmonary complications. Appropriate diagnosis and early initiation of adequate antimicrobial treatment for severe pneumonia are crucial in improving survival among critically ill patients. Identifying the underlying causative pathogen is also critical for antimicrobial stewardship. However, establishing an etiological diagnosis is challenging in most patients, especially in those with chronic underlying disease; those who received previous antibiotic treatment; and those treated with mechanical ventilation. Furthermore, as antimicrobial therapy must be empiric, national and international guidelines recommend initial antimicrobial treatment according to the location's epidemiology; for patients admitted to the intensive care unit, specific recommendations on disease management are available. Adherence to pneumonia guidelines is associated with better outcomes in severe pneumonia. Yet, the continuing and necessary research on severe pneumonia is expansive, inviting different perspectives on host immunological responses, assessment of illness severity, microbial causes, risk factors for multidrug resistant pathogens, diagnostic tests, and therapeutic options.

Intracellularly Released Cholesterol from Polymer-Based Delivery Systems Alters Cellular Responses to Pneumolysin and Promotes Cell Survival

Cholesterol is highly abundant within all human body cells and modulates critical cellular functions related to cellular plasticity, metabolism, and survival. The cholesterol-binding toxin pneumolysin represents an essential virulence factor of Streptococcus pneumoniae in establishing pneumonia and other pneumococcal infections. Thus, cholesterol scavenging of pneumolysin is a promising strategy to reduce S. pneumoniae induced lung damage. There may also be a second cholesterol-dependent mechanism whereby pneumococcal infection and the presence of pneumolysin increase hepatic sterol biosynthesis. Here we investigated a library of polymer particles varying in size and composition that allow for the cellular delivery of cholesterol and their effects on cell survival mechanisms following pneumolysin exposure. Intracellular delivery of cholesterol by nanocarriers composed of Eudragit E100–PLGA rescued pneumolysin-induced alterations of lipid homeostasis and enhanced cell survival irrespective of neutralization of pneumolysin.

Major Adverse Cardiovascular Events During Invasive Pneumococcal Disease Are Serotype Dependent

BACKGROUND

Up to 30% of patients admitted to hospitals with invasive pneumococcal disease (IPD) experience major adverse cardiovascular event (MACE) including new/worsening heart failure, new/worsening arrhythmia, and/or myocardial infarction. Streptococcus pneumoniae (Spn) is the most frequently isolated bacterial pathogen among community-acquired pneumonia (CAP) patients and the only etiological agent linked independently to MACE. Nevertheless, no clinical data exist identifying which serotypes of Spn are principally responsible for MACE.

METHODS

This was an observational multicenter retrospective study conducted through the Public Health Secretary of Bogotá, Colombia. We included patients with a confirmed clinical diagnosis of IPD with record of pneumococcal serotyping and clinical information between 2012 and 2019. Spn were serotyped using the quellung method by the National Center of Microbiology. MACE were determined by a retrospective chart review.

RESULTS

The prevalence of MACE was 23% (71/310) in IPD patients and 28% (53/181) in patients admitted for CAP. The most prevalent S. pneumoniae serotype identified in our study was the 19A, responsible for the 13% (42/310) of IPD in our cohort, of which 21% (9/42) presented MACE. Serotypes independently associated with MACE in IPD patients were serotype 3 (odds ratio [OR] 1, 48; 95% confidence interval [CI] [1.21-2.27]; P = .013) and serotype 9n (OR 1.29; 95% CI [1.08-2.24]; P = .020). Bacteremia occurred in 87% of patients with MACE. Moreover, serum concentrations of C-reactive protein were elevated in patients with MACE versus in non-MACE patients (mean [standard deviation], 138 [145] vs 73 [106], P = .01).

CONCLUSIONS

MACE are common during IPD with serotype 3 and 9n independently of frequency.

Pneumococcal Vaccination in Immunocompromised Hosts: An Update

Infections with the pathogen, Streptococcus pneumoniae, are a common cause of morbidity and mortality worldwide. It particularly affects those at the extremes of age and immunocompromised individuals. Preventing pneumococcal disease is paramount in at risk individuals, and pneumococcal vaccination should be offered. Here, we discuss the role of pneumococcal vaccination in specific groups of immunocompromised hosts.

Pneumococcal Disease Prevention: Are We on the Right Track?

The history of Streptococcus pneumoniae diseases dramatically changed with the introduction into the immunization schedule of infants and children of the first pneumococcal conjugate vaccine, the one containing 7 (PCV7) of the most common pneumococcal serotypes (STs) causing invasive pneumococcal diseases (IPDs). Where PCV7 was largely used, incidence of both IPDs and non-invasive pneumococcal diseases (nIPDs) in vaccinated children and in unvaccinated subjects of any age, mainly the elderly, significantly decreased. Unfortunately, the impact of PCV7 administration was slightly lower than expected, as the reduction in infections due to vaccine serotypes (STs) was accompanied by a significant increase in the number of IPDs and nIPDs due to STs not included in the vaccine. To overcome this problem, two PCVs containing 10 (PCV10) and 13 (PCV13) STs, chosen among those emerging, were developed and licensed. However, ST replacement occurred again. Moreover, the new PCVs showed little effectiveness in the prevention of infection due to non-encapsulated STs and to ST3. Next-generation S. pneumoniae vaccines able to prevent pneumococcal infections regardless of infecting ST are urgently needed. For the moment, the use of available PCVs remains fundamental because their benefits far outweigh any concerns for emerging STs.

Acute cardiovascular events in patients with community acquired pneumonia: results from the observational prospective FADOI-ICECAP study

Background

The burden of cardiovascular (CV) complications in patients hospitalised for community-acquired pneumonia (CAP) is still uncertain. Available studies used different designs and different criteria to define CV complications. We assessed the cumulative incidence of acute of CV complications during hospitalisation for CAP in Internal Medicine Units (IMUs).

Methods

This was a prospective study carried out in 26 IMUs, enrolling patients consecutively hospitalised for CAP. Defined CV complications were: newly diagnosed heart failure, acute coronary syndrome, new onset of supraventricular or ventricular arrhythmias, new onset hemorrhagic or ischemic stroke or transient ischemic attack. Outcome measures were: in-hospital and 30-day mortality, length of hospital stay and rate of 30-day re-hospitalisation.

Results

A total of 1266 patients were enrolled, of these 23.8% experienced at least a CV event, the majority (15.5%) represented by newly diagnosed decompensated heart failure, and 75% occurring within 3 days. Female gender, a history of CV disease, and more severe pneumonia were predictors of CV events. In-hospital (12.2% vs 4.7%, p < 0.0001) and 30-day (16.3% vs 8.9%, p = 0.0001) mortality was higher in patients with CV events, as well as the re-hospitalisation rate (13.3% vs 9.3%, p = 0.002), and mean hospital stay was 11.4 ± 6.9 vs 9.5 ± 5.6 days (p < 0.0001). The occurrence of CV events during hospitalisation significantly increased the risk of 30-day mortality (HR 1.69, 95% CI 1.14–2.51; p = 0.009).

Conclusion

Cardiovascular events are frequent in CAP, and their occurrence adversely affects outcome. A strict monitoring might be useful to intercept in-hospital CV complications for those patients with higher risk profile.

Trial registration

NCT03798457

Registered 10 January 2019 - Retrospectively registered

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05781-w.

Sugar-Coated Killer: Serotype 3 Pneumococcal Disease

Capsular polysaccharide (CPS), which surrounds the bacteria, is one of the most significant and multifaceted contributors to Streptococcus pneumoniae virulence. Capsule prevents entrapment in mucus during colonization, traps water to protect against desiccation, can serve as an energy reserve, and protects the bacterium against complement-mediated opsonization and immune cell phagocytosis. To date, 100 biochemically and serologically distinct capsule types have been identified for S. pneumoniae; 20 to 30 of which have well-defined propensity to cause opportunistic human infection. Among these, serotype 3 is perhaps the most problematic as serotype 3 infections are characterized as having severe clinical manifestations including empyema, bacteremia, cardiotoxicity, and meningitis; consequently, with a fatality rate of 30%–47%. Moreover, serotype 3 resists antibody-mediated clearance despite its inclusion in the current 13-valent conjugate vaccine formulation. This review covers the role of capsule in pneumococcal pathogenesis and the importance of serotype 3 on human disease. We discuss how serotype 3 capsule synthesis and presentation on the bacterial surface is distinct from other serotypes, the biochemical and physiological properties of this capsule type that facilitate its ability to cause disease, and why existing vaccines are unable to confer protection. We conclude with discussion of the clonal properties of serotype 3 and how these have changed since introduction of the 13-valent vaccine in 2000.

New-onset atrial fibrillation in patients with pneumococcal pneumonia. Impact of timing and duration on short- and medium-term mortality

OBJETIVES

To assess the incidence, related factors, timing and duration of new- onset atrial fibrillation in a cohort of consecutive patients diagnosed with pneumococcal pneumonia.

METHODS

Observational study including all immunocompetent adults hospitalized for pneumococcal pneumonia. Patients were classified by time (atrial fibrillation recognized on emergency room arrival or developed during hospitalization) and duration (paroxysmal or persistent). Patients were followed-up for 6 months after discharge.

RESULTS

We included 1092 patients, of whom 109 (9.9%) had new-onset atrial fibrillation. An early event was documented in 87 (79.8%) cases. Arrhythmia was classified as paroxysmal in 78 patients. Older age, heavy drinking, respiratory rate ≥ 30/minute, leukopenia, severe inflammation and bacteremia were independent risk factors for developing new-onset atrial fibrillation on admission. Overall, 48 (4.4%) patients died during hospitalization, the rate being higher in those patients who developed new-onset arrhythmia (17.9% vs 2.9% p<0.001). Among patients with events recognized at admission, in-hospital mortality was higher in those with persistent arrhythmia (34.8% vs 6.3%, p = 0.002) and 6-month survival was better among those who developed paroxysmal event.

CONCLUSIONS

The development of new-onset atrial fibrillation was associated with pneumonia severity, and higher in-hospital mortality. Bacteremia and severe systemic inflammation were factors associated with its development.

Troponin Elevation in Older Patients with Acute Pneumonia: Frequency and Prognostic Value

Cardiovascular (CV) events are particularly frequent after acute pneumonia (AP) in the elderly. We aimed to assess whether cardiac troponin I, a specific biomarker of myocardial injury, independently predicts CV events and death after AP in older inpatients. Among 214 consecutive patients with AP aged ≥75 years admitted to a university hospital, 171 with a cardiac troponin I sample in the 72 h following diagnosis of AP were included, and 71 (42%) were found to have myocardial injury (troponin > 100 ng/L). Patients with and without myocardial injury were similar in terms of age, gender and comorbidities, but those with myocardial injury had more severe clinical presentation (median (interquartile range) Pneumonia Severity Index: 60 (40-95) vs. 45 (30-70), p = 0.003). Myocardial injury was strongly associated with in-hospital myocardial infarction (25% vs. 0%, p < 0.001), CV mortality (11 vs. 1%, p = 0.003) and all-cause mortality (34 vs. 13%, p = 0.002). After adjustment for confounders, myocardial injury remained a strong predictive factor of in-hospital mortality (odds ratio (95% confidence interval): 3.32 (1.42-7.73), p = 0.005) but not one-year mortality (1.61 (0.77-3.35), p = 0.2). Cardiac troponin I elevation, a specific biomarker of myocardial injury, was found in nearly half of an unselected cohort of older inpatients with AP and was associated with a threefold risk of in-hospital death.

Host- and Pathogen-Related Factors for Acute Cardiac Events in Pneumococcal Pneumonia

Background

Acute cardiac events (ACEs) are increasingly being recognized as a major complication in pneumococcal community-acquired pneumonia (CAP). Information regarding host- and pathogen-related factors for ACEs, including pneumococcal serotypes and clonal complexes, is scarce.

Methods

A retrospective study was conducted of a prospective cohort of patients hospitalized for CAP between 1996 and 2019. Logistic regression and funnel plot analyses were performed to determine host- and pathogen-related factors for ACEs.

Results

Of 1739 episodes of pneumococcal CAP, 1 or more ACEs occurred in 304 (17.5%) patients, the most frequent being arrhythmia (n = 207), heart failure (n = 135), and myocardial infarction (n = 23). The majority of ACEs (73.4%) occurred within 48 hours of admission. Factors independently associated with ACEs were older age, preexisting heart conditions, pneumococcal bacteremia, septic shock at admission, and high-risk pneumonia. Among 983 pneumococcal isolates, 872 (88.7%) were serotyped and 742 (75.5%) genotyped. The funnel plot analyses did not find any statistically significant association between serotypes or clonal complexes with ACEs. Nevertheless, there was a trend toward an association between CC230 and these complications. ACEs were independently associated with 30-day mortality (adjusted odds ratio, 1.88; 95% CI, 1.11-3.13).

Conclusions

ACEs are frequent in pneumococcal pneumonia and are associated with increased mortality. The risk factors defined in this study may help identify patients who must undergo close follow-up, including heart rhythm monitoring, and special care to avoid fluid overload, particularly during the first 48 hours of admission. These high-risk patients should be the target for preventive intervention strategies.

Platelets and Their Role in the Pathogenesis of Cardiovascular Events in Patients With Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) remains an important cause of morbidity and mortality throughout the world with much recent and ongoing research focused on the occurrence of cardiovascular events (CVEs) during the infection, which are associated with adverse short-term and long-term survival. Much of the research directed at unraveling the pathogenesis of these events has been undertaken in the settings of experimental and clinical CAP caused by the dangerous, bacterial respiratory pathogen, Streptococcus pneumoniae (pneumococcus), which remains the most common bacterial cause of CAP. Studies of this type have revealed that although platelets play an important role in host defense against infection, there is also increasing recognition that hyperactivation of these cells contributes to a pro-inflammatory, prothrombotic systemic milieu that contributes to the etiology of CVEs. In the case of the pneumococcus, platelet-driven myocardial damage and dysfunction is exacerbated by the direct cardiotoxic actions of pneumolysin, a major pore-forming toxin of this pathogen, which also acts as potent activator of platelets. This review is focused on the role of platelets in host defense against infection, including pneumococcal infection in particular, and reviews the current literature describing the potential mechanisms by which platelet activation contributes to cardiovascular complications in CAP. This is preceded by an evaluation of the burden of pneumococcal infection in CAP, the clinical features and putative pathogenic mechanisms of the CVE, and concludes with an evaluation of the potential utility of the anti-platelet activity of macrolides and various adjunctive therapies.

Exploration of Recombinant Fusion Proteins YAPO and YAPL as Carrier Proteins for Glycoconjugate Vaccine Design against Streptococcus pneumoniae Infection

Pneumolysin (Ply), pneumococcal surface protein A (PspA), and pneumococcal surface adhesin A (PsaA) are promising cell surface protein antigen targets for Streptococcus pneumoniae (Spn) vaccine development. Herein, we designed and recombined two fusion proteins, named YAPO and YAPL, which contained the main antigenic epitopes of Ply, PspA, and PsaA. In-depth immunological evaluations revealed that YAPO and YAPL had strong immunocompetence to be well-qualified potential carrier proteins. To verify this possibility, a serotype 3 Spn (ST3) CPS pentasaccharide was conjugated to each fusion protein to generate the resultant glycoconjugates. Immunological studies in mice revealed that, as compared with TT conjugate, YAPO and YAPL conjugates provoked robust T-cell dependent immune responses that could provide better recognition, in vitro efficient opsonophagocytosis, and in vivo effective protection against various serotypes of Spn. Collectively, YAPO and YAPL were identified as immunopotentiating carriers that could help convert immunologically inactive ST3 pentasaccharide into a T cell-dependent antigen and provide efficient and broad spectrum of immunoprotection coverage so as to formulate functional glycoconjugate vaccines against Spn infections.

Mapping of Recognition Sites of Monoclonal Antibodies Responsible for the Inhibition of Pneumolysin Functional Activity

The pathogenicity of many bacteria, including Streptococcus pneumoniae, depends on pore-forming toxins (PFTs) that cause host cell lysis by forming large pores in cholesterol-containing cell membranes. Therefore, PFTs-neutralising antibodies may provide useful tools for reducing S. pneumoniae pathogenic effects. This study aimed at the development and characterisation of monoclonal antibodies (MAbs) with neutralising activity to S. pneumoniae PFT pneumolysin (PLY). Five out of 10 produced MAbs were able to neutralise the cytolytic activity of PLY on a lung epithelial cell line. Epitope mapping with a series of recombinant overlapping PLY fragments revealed that neutralising MAbs are directed against PLY loops L1 and L3 within domain 4. The epitopes of MAbs 3A9, 6E5 and 12F11 located at L1 loop (aa 454–471) were crucial for PLY binding to the immobilised cholesterol. In contrast, the MAb 12D10 recognising L3 (aa 403–423) and the MAb 3F3 against the conformational epitope did not interfere with PLY-cholesterol interaction. Due to conformation-dependent binding, the approach to use overlapping peptides for fine epitope mapping of the neutralising MAbs was unsuccessful. Therefore, the epitopes recognised by the MAbs were analysed using computational methods. This study provides new data on PLY sites involved in functional activity.

Cardiac complications in community-acquired pneumonia and COVID-19

Community-acquired pneumonia (CAP) remains a global health problem with significant morbidity and mortality. Much recent published literature about the infection has indicated that a substantial number of patients with CAP, particularly those ill enough to be admitted to hospital, will suffer a cardiovascular event. While these may include events such as deep venous thrombosis and stroke, most of the events involve the heart and include the occurrence of an arrhythmia (most commonly atrial fibrillation), new onset or worsening of heart failure and acute myocardial infarction. While such cardiac events may occur, for example, in all-cause CAP and CAP due to influenza virus infection, and more recently described with the SARS-CoV-2 pandemic, a significant amount of research work has been investigating the pathogenic mechanisms of these cardiac events in patients with CAP due to Streptococcus pneumoniae (pneumococcus) and, more recently, COVID-19 infections. Such research has identified a number of mechanisms by which these microorganisms may cause cardiovascular events. Importantly, these cardiac events appear not only to be associated with in-hospital mortality, but they also appear to contribute to longer-term mortality of patients with CAP, even after their discharge from hospital. This review will focus initially on studies of cardiovascular events in all-cause CAP and pneumococcal CAP, excluding COVID-19 infection, and then address similar issues in the latter infection.

Immunization with Recombinant Pneumolysin Induces the Production of Antibodies and Protects Mice in a Model of Systemic Infection Caused by Streptococcus pneumoniae

Immunogenic and protective activity of recombinant pneumolysin was studied in experiments on male BALB/c mice. The mice were immunized intraperitoneally with recombinant pneumolysin sorbed on Al(OH)₃ (200 μg per mouse). In 2 weeks after immunization, the isotypes of antibodies to recombinant pneumolysin in the serum of immunized mice were determined by ELISA. The animals were infected with Streptococcus pneumoniae serotype 3. Immunization with recombinant pneumolysin induced the production of anti-pneumolysin antibodies, mainly of IgG1 subisotype. On day 21 after intraperitoneal infection with S. pneumoniae serotype 3 in a dose of 10⁶ microbial cells, the survival rate of animals immunized with recombinant pneumolysin in a dose of 25 μg/mouse was 67% vs. 0% in the control (p<0.001). Recombinant pneumolysin could be considered as a promising protective antigen for inclusion in the serotype-independent vaccine against S. pneumoniae.

Quercetin, a pneumolysin inhibitor, protects mice against Streptococcus pneumoniae infection

Pneumolysin (PLY), a pore-forming cytotoxin and a major virulence determinant, is a member of the cholesterol-dependent cytolysin (CDC) family and essential for promoting Streptococcus pneumoniae (S.pneumoniae) infection. Due to the action characteristics of hemolysin itself, the pneumolysin released after killing bacteria with conventional antibiotics still has the ability to damage host cells; therefore, drug treatments directly inhibiting hemolysin activity are the most effective. Hemolysis assays were used to confirm that quercetin can inhibit the activity of PLY, protecting cells in vitro, and an oligomerization assay was used to determine the mechanism of quercetin to suppress PLY activity. Live/Dead testing, lactate dehydrogenase (LDH) release analysis and a murine model of endonasal pulmonary infection were used to explore the capability of quercetin to protect cells and mice from S. pneumoniae-mediated damage in vivo and in vitro. The results indicated that quercetin significantly reduced PLY-induced hemolytic activity and cytotoxicity via repressing the formation of oligomers. In addition, treatment with quercetin can reduce PLY-mediated cell injury, improve the survival rate of mice infected with a lethal dose of S. pneumoniae, alleviate the pathological damage of lung tissue and inhibit the release of cytokines (IL-1β and TNF-α) in bronchoalveolar lavage fluid. Considering the importance of these events in antimicrobial resistant S. pneumoniae pathogenesis, our results indicated that quercetin may be a novel potential drug candidate for the treatment of clinical pneumococcal infections.

Aromatase inhibitors and risk of cardiovascular events in breast cancer patients: a systematic review and meta-analysis

BACKGROUND

Cardiovascular events (CVEs) was considered as one of the primary cause to reduce the quality of life in breast cancer patients with aromatase inhibitors (AIs) treatment, which has not been sufficiently addressed. The aim of this study was to assess the correlation between risk of CVEs and AIs in patients with breast cancer.

METHODS

Included studies were obtained from the databases of Embase, Pubmed, Cochrane Library, Clinical Trials.gov, and reference lists. The main outcome measures were overall incidence, odds ratios (ORs), and 95% confidence intervals (CIs). Furthermore, the association and the risk differences among different tumor types, AIs,ages,or treatment regimens were conducted. Fixed-effect or random-effect models were applied in the statistical analyses according to the heterogeneity. Our analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.

RESULTS

Seventeen studies, which included 44,411 subjects, were included in our analyses. The overall incidence of CVEs in AIs group was 13.02% (95% CI: 8.15-20.17%) and almost all of the high-grade CVEs occurred in patients treated with AIs. The pooled ORs of CVEs was 0.9940 (95% CI: 0.8545-1.1562). Under sub-group analysis, the incidence of CVEs related to exemestane was higher than that of controls (OR = 1.1564, 95% CI: 1.0656-1.2549), but no statistical differences in risk of CVEs were found in other sub-group analysis. No evidence of publication bias was found for incidence of CVEs in our meta-analysis by a funnel plot.

CONCLUSIONS

These results suggest that patients with breast cancer treated with AIs do not have a significant risk of developing CVEs in comparison with the controls, and exemestane might not be considered as the alternative AI to the breast cancer patients from the perspective of CVEs. Further studies are recommended to investigate this association and the risk differences among different tumor types, AIs or treatment regimens.

Pathogenesis and prevention of risk of cardiovascular events in patients with pneumococcal community-acquired pneumonia

It is now well recognized that cardiovascular events (CVE) occur quite commonly, both in the acute phase and in the long-term, in patients with community-acquired pneumonia (CAP). CVE have been noted in up to 30% of patients hospitalized with all-cause CAP. One systematic review and meta-analysis of hospitalized patients with all-cause CAP noted that the incidence rates for overall cardiac events were 17.7%, for incident heart failure were 14.1%, for acute coronary syndromes were 5.3% and for incident cardiac arrhythmias were 4.7%. In the case of pneumococcal CAP, almost 20% of patients studied had one or more of these cardiac events. Recent research has provided insights into the pathogenesis of the acute cardiac events occurring in pneumococcal infections. With respect to the former, key involvements of the major pneumococcal protein virulence factor, pneumolysin, are now well documented, whilst systemic platelet-driven neutrophil activation may also contribute. However, events involved in the pathogenesis of the long-term cardiovascular sequelae remain largely unexplored. Emerging evidence suggests that persistent antigenaemia may predispose to the development of a systemic pro-inflammatory/prothrombotic phenotype underpinning the risk of future cardiovascular events. The current manuscript briefly reviews the occurrence of cardiovascular events in patients with all-cause CAP, as well as in pneumococcal and influenza infections. It highlights the close interaction between influenza and pneumococcal pneumonia. It also includes a brief discussion of mechanisms of the acute cardiac events in CAP. However, the primary focus is on the prevalence, pathogenesis and prevention of the longer-term cardiac sequelae of severe pneumococcal disease, particularly in the context of persistent antigenaemia and associated inflammation.