Salmonella enterica serovar Typhimurium requires nonsterol precursors of the cholesterol biosynthetic pathway for intracellular proliferation

The antimicrobial activity of innate host-directed therapies: A systematic review

Intracellular human pathogens are the deadliest infectious diseases and are difficult to treat effectively due to their protection inside the host cell and the development of antimicrobial resistance (AMR). An emerging approach to combat these intracellular pathogens is host-directed therapies (HDT), which harness the innate immunity of host cells. HDT rely on small molecules to promote host protection mechanisms that ultimately lead to pathogen clearance. These therapies are hypothesized to: (1) possess indirect yet broad, cross-species antimicrobial activity, (2) effectively target drug-resistant pathogens, (3) carry a reduced susceptibility to the development of AMR and (4) have synergistic action with conventional antimicrobials. As the field of HDT expands, this systematic review was conducted to collect a compendium of HDT and their characteristics, such as the host mechanisms affected, the pathogen inhibited, the concentrations investigated and the magnitude of pathogen inhibition. The evidential support for the main four HDT hypotheses was assessed and concluded that HDT demonstrate robust cross-species activity, are active against AMR pathogens, clinical isolates and laboratory-adapted pathogens. However, limited information exists to support the notion that HDT are synergistic with canonical antimicrobials and are less predisposed to AMR development.

Statin Use and Reduced Risk of Pneumonia in Patients with Melioidosis: A Lung-Specific Statin Association

Rationale: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) use is associated with a lower risk of incident pneumonia and, less robustly, with nonpulmonary infections. Whether statin use is associated with a lower risk of pneumonia than other clinical presentations of infection with the same pathogen is unknown. Objectives: To assess whether preadmission statin use is associated with a lower risk of pneumonia than nonpneumonia presentations among patients hospitalized with Burkholderia pseudomallei infection (melioidosis). Methods: We performed a secondary analysis of a prospective multicenter cohort study of patients hospitalized with culture-confirmed B. pseudomallei infection (melioidosis). We used Poisson regression with robust standard errors to test for an association between statin use and pneumonia. We then performed several sensitivity analyses that addressed healthy user effect and indication bias. Results: Of 1,372 patients with melioidosis enrolled in the parent cohort, 1,121 were analyzed. Nine hundred eighty (87%) of 1,121 were statin nonusers, and 141 (13%) of 1,121 were statin users. Forty-six (33%) of 141 statin users presented with pneumonia compared with 432 (44%) of 980 statin nonusers. Statin use was associated with a lower risk of pneumonia in unadjusted analysis (relative risk, 0.74; 95% confidence interval, 0.58-0.95; P = 0.02) and, after adjustment for demographic variables, comorbidities, environmental exposures, and symptom duration (relative risk, 0.73; 95% confidence interval, 0.57-0.94; P = 0.02). The results of sensitivity analyses, including active comparator analysis and inverse probability of treatment weighting, were consistent with the primary analysis. Conclusions: In hospitalized patients with melioidosis, preadmission statin use was associated with a lower risk of pneumonia than other clinical presentations of melioidosis, suggesting a lung-specific protective effect of statins.

IL-10 Modulation Increases Pyrazinamide's Antimycobacterial Efficacy against Mycobacterium tuberculosis Infection in Mice

Mechanisms to shorten the duration of tuberculosis (TB) treatment include new drug formulations or schedules and the development of host-directed therapies (HDTs) that better enable the host immune system to eliminate Mycobacterium tuberculosis. Previous studies have shown that pyrazinamide, a first-line antibiotic, can also modulate immune function, making it an attractive target for combinatorial HDT/antibiotic therapy, with the goal to accelerate clearance of M. tuberculosis. In this study, we assessed the value of anti-IL-10R1 as an HDT along with pyrazinamide and show that short-term anti-IL-10R1 blockade during pyrazinamide treatment enhanced the antimycobacterial efficacy of pyrazinamide, resulting in faster clearance of M. tuberculosis in mice. Furthermore, 45 d of pyrazinamide treatment in a functionally IL-10-deficient environment resulted in sterilizing clearance of M. tuberculosis. Our data suggest that short-term IL-10 blockade with standard TB drugs has the potential to improve clinical outcome by reducing the treatment duration.

The effect of C/N ratio and its frequent addition on commensal and pathogenic bacterial abundances in shrimp Litopeaneus vanname gut in a biofloc system: Ratio and frequent addition interaction matters

The environmental biotic and abiotic factors form a complicated relationship with the host intestinal microbiota. In our study, we applied different levels of C/N ratio (10, 15, 20) and frequent addition times (once, twice, triple a day) in a factorial experimental design. GC/LC analysis of filtrated biofloc (BF) samples revealed the highest relative fold change for the untargeted bioactive molecules among different treatments, whereas the 16s rRNA analysis revealed the change in the shrimp gut microbiota composition. Based on the available literature on the relationship between the bioactive molecules and the available bacteria in this study, the next bioactive molecules were discussed. Proline was associated with Bacteroidota, Flavobacteriaceae, Gammaproteobacteria, and Flavobacteriales. Plumbagine was associated with Norcardiaceae. Phytosphingosin was associated with Bacteroidota. Phosphocholine compound was associated with Bacteroidota. The monobutyl ether, benzofuran, and piperidone were associated with Micobacteriaceae and Mycobacterium. Generally, C/N 15 and 20 once a day, and C/N 20 triple a day have showed a merit over other treatments in term of low pathogenic and unfavorable bacteria, and high commensal bacterial abundances. The revealed bioactive molecule composition showed the complicity of BF as a source for novel compounds as biosecurity agents in BF system. These molecules could be developed to feed additives upgrading the biosecurity level in aquaculture systems. Other bioactive molecules require future studies to reveal novel molecules in term of aquaculture biosecurity control.

Salmonella Typhimurium manipulates macrophage cholesterol homeostasis through the SseJ-mediated suppression of the host cholesterol transport protein ABCA1

Upon infection of host cells, Salmonella enterica serovar Typhimurium resides in a modified-endosomal compartment referred to as the Salmonella-containing vacuole (SCV). SCV biogenesis is driven by multiple effector proteins translocated through two type III secretion systems (T3SS-1 and T3SS-2). While many host proteins targeted by these effector proteins have been characterised, the role of host lipids in SCV dynamics remains poorly understood. Previous studies have shown that S. Typhimurium infection in macrophages leads to accumulation of intracellular cholesterol, some of which concentrates in and around SCVs; however, the underlying mechanisms remain unknown. Here, we show that S. Typhimurium utilises the T3SS-2 effector SseJ to downregulate expression of the host cholesterol transporter ABCA1 in macrophages, leading to a ~45% increase in cellular cholesterol. Mechanistically, SseJ activates a signalling cascade involving the host kinases FAK and Akt to suppress Abca1 expression. Mutational inactivation of SseJ acyltransferase activity, silencing FAK, or inhibiting Akt prevents Abca1 downregulation and the corresponding accumulation of cholesterol during infection. Importantly, RNAi-mediated silencing of ABCA1 rescued bacterial survival in FAK-deficient macrophages, suggesting that Abca1 downregulation and cholesterol accumulation are important for intracellular survival.

Various Facets of Pathogenic Lipids in Infectious Diseases: Exploring Virulent Lipid-Host Interactome and Their Druggability

Lipids form an integral, structural, and functional part of all life forms. They play a significant role in various cellular processes such as membrane fusion, fission, endocytosis, protein trafficking, and protein functions. Interestingly, recent studies have revealed their more impactful and critical involvement in infectious diseases, starting with the manipulation of the host membrane to facilitate pathogenic entry. Thereafter, pathogens recruit specific host lipids for the maintenance of favorable intracellular niche to augment their survival and proliferation. In this review, we showcase the lipid-mediated host pathogen interplay in context of life-threatening viral and bacterial diseases including the recent SARS-CoV-2 infection. We evaluate the emergent lipid-centric approaches adopted by these pathogens, while delineating the alterations in the composition and organization of the cell membrane within the host, as well as the pathogen. Lastly, crucial nexus points in their interaction landscape for therapeutic interventions are identified. Lipids act as critical determinants of bacterial and viral pathogenesis by altering the host cell membrane structure and functions.

Developing Novel Host-Based Therapies Targeting Microbicidal Responses in Macrophages and Neutrophils to Combat Bacterial Antimicrobial Resistance

Antimicrobial therapy has provided the main component of chemotherapy against bacterial pathogens. The effectiveness of this strategy has, however, been increasingly challenged by the emergence of antimicrobial resistance which now threatens the sustained utility of this approach. Humans and animals are constantly exposed to bacteria and have developed effective strategies to control pathogens involving innate and adaptive immune responses. Impaired pathogen handling by the innate immune system is a key determinant of susceptibility to bacterial infection. However, the essential components of this response, specifically those which are amenable to re-calibration to improve host defense, remain elusive despite extensive research. We provide a mini-review focusing on therapeutic targeting of microbicidal responses in macrophages and neutrophils to de-stress reliance on antimicrobial therapy. We highlight pre-clinical and clinical data pointing toward potential targets and therapies. We suggest that developing focused host-directed therapeutic strategies to enhance "pauci-inflammatory" microbial killing in myeloid phagocytes that maximizes pathogen clearance while minimizing the harmful consequences of the inflammatory response merits particular attention. We also suggest the importance of One Health approaches in developing host-based approaches through model development and comparative medicine in informing our understanding of how to deliver this strategy.

Statins & risk of Clostridium difficile infection: A meta-analysis

Background & objectives:

Clostridium difficile infection is one of the most common healthcare-associated infections worldwide. Recent epidemiologic studies have suggested that statin users may have a lower risk of C. difficile infection, although the results are inconsistent. This meta-analysis was conducted with the aim of summarizing all available data to assess the risk of C. difficile infection among statin users versus non-users.

Methods:

A literature review was performed using the MEDLINE and EMBASE databases from inception to October 2017. Cohort, case-control and cross-sectional studies that compared the risk of C. difficile infection among statin users versus non-users were included. Pooled odds ratio (OR) and 95 per cent confidence interval (CI) were calculated using a random-effect, generic inverse variance method.

Results:

Six case-control studies and two cross-sectional studies met the eligibility criteria and were included in this meta-analysis. The risk of C. difficile infection among statin users was significantly lower than non-users with the pooled OR of 0.74 (95% CI, 0.61-0.89). The statistical heterogeneity of this study was high (I²=90%).

Interpretation & conclusions:

This meta-analysis demonstrated a decreased risk of C. difficile infection among statin users versus non-users. Further studies are required to clarify the role of statins for prevention of C. difficile infection in clinical practice.

Statins: a viable candidate for host-directed therapy against infectious diseases

Statins were first identified over 40 years ago as lipid-lowering drugs and have been remarkably effective in treating cardiovascular diseases. As research advanced, the protective effects of statins were additionally attributed to their anti-inflammatory, antioxidative, anti-thrombotic and immunomodulatory functions rather than lipid-lowering abilities alone. By promoting host defence mechanisms and inhibiting pathological inflammation, statins increase survival in human infectious diseases. At the cellular level, statins inhibit the intermediates of the host mevalonate pathway, thus compromising the immune evasion strategies of pathogens and their survival. Here, we discuss the potential use of statins as an inexpensive and practical alternative or adjunctive host-directed therapy for infectious diseases caused by intracellular pathogens, such as viruses, protozoa, fungi and bacteria.

Targeting host lipid flows: Exploring new antiviral and antibiotic strategies

Bacteria and viruses pose serious challenges for humans because they evolve continuously. Despite ongoing efforts, antiviral drugs to treat many of the most troubling viruses have not been approved yet. The recent launch of new antimicrobials is generating hope as more and more pathogens around the world become resistant to available drugs. But extra effort is still needed. One of the current strategies for antiviral and antibiotic drug development is the search for host cellular pathways used by many different pathogens. For example, many viruses and bacteria alter lipid synthesis and transport to build their own organelles inside infected cells. The characterization of these interactions will be fundamental to identify new targets for antiviral and antibiotic drug development. This review discusses how viruses and bacteria subvert cell machineries for lipid synthesis and transport and summarises the most promising compounds that interfere with these pathways.

Potential Effect of Statins on Mycobacterium tuberculosis Infection

Tuberculosis is one of the 10 leading causes of death in the world. The current treatment is based on a combination of antimicrobials administered for six months. It is essential to find therapeutic agents with which the treatment time can be shortened and strengthen the host immune response against Mycobacterium tuberculosis. M. tuberculosis needs cholesterol to infect and survive inside the host, but the progression of the infection depends to a large extent on the capacity of the immune response to contain the infection. Statins inhibit the synthesis of cholesterol and have pleiotropic effects on the immune system, which have been associated with better results in the treatment of several infectious diseases. Recently, it has been reported that cells treated with statins are more resistant to M. tuberculosis infection, and they have even been proposed as adjuvants in the treatment of M. tuberculosis infection. The aim of this review is to summarize the immunopathogenesis of tuberculosis and its mechanisms of evasion and to compile the available scientific information on the effect of statins in the treatment of tuberculosis.

Sulfated vizantin induces formation of macrophage extracellular traps

Vizantin is an insoluble adjuvant that activates macrophages and lymphocytes. Recently, 2,2',3,3',4,4'-hexasulfated-vizantin (sulfated vizantin), which enables solubilization of vizantin, was developed by the present team. Sulfated vizantin was found to enhance bactericidal activity against multi-drug resistant Pseudomonas aeruginosa in RAW264.7 cells. In addition, spread of P. aeruginosa was inhibited in RAW264.7 cells treated with sulfated vizantin. When only sulfated vizantin and P. aeruginosa were incubated, sulfated vizantin did not affect growth of P. aeruginosa. Formation of DNA-based extracellular traps (ETs), a novel defense mechanism in several types of innate immune cells, helps to eliminate pathogens. In the present study, ET-forming macrophages constituted the majority of immune cells. Sulfated vizantin induced ET formation in RAW264.7 cells, whereas a Ca-chelating reagent, EDTA, and T-type calcium channel blocker, tetrandrine, inhibited ET formation and attenuated inhibition of spread of P. aeruginosa in sulfated vizantin-treated cells. Thus, sulfated vizantin induces ET formation in phagocytic cells in a Ca-dependent manner, thus preventing spread of P. aeruginosa. Hence, sulfated vizantin may be useful in the management of infectious diseases.

Lipid metabolism and intracellular bacterial virulence: key to next-generation therapeutics

Lipid metabolism is thought to play a key role in the pathogenicity of several intracellular bacteria. Bacterial lipolytic enzymes hydrolyze lipids from the host cell to release free fatty acids which are used as an energy source and building blocks for the synthesis of cell envelope and also to modulate host immune responses. In this review, we discussed the role of lipid metabolism and lipolytic enzymes in the life cycle and virulence of Mycobacterium tuberculosis and other intracellular bacteria. The lipolytic enzymes appear to be potential candidates for developing novel therapeutics by targeting lipid metabolism for controlling M. tuberculosis and other intracellular pathogenic bacteria.

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Differential Effects of Statins on Inflammatory Interleukin-8 and Antimicrobial Peptide Human Β-Defensin 2 Responses in Salmonella-Infected Intestinal Epithelial Cells

Alternative therapies are needed to reduce the use of antibiotics and incidence of drug-resistant Salmonellosis. Previous studies have revealed important roles of statins in regulating innate immunity. Therefore, we investigated the effects of statins on innate immunity in Salmonella-infected intestinal epithelial cells (IECs), which are involved in mucosal innate immunity. SW480 cells and Akt siRNA- or vitamin D receptor (VDR) siRNA-transfected SW480 cells were infected by wild-type S. Typhimurium strain SL1344 in the presence or absence of statins. The mRNA or protein expression was analyzed by real-time quantitative PCR or western blot analysis, respectively. Simvastatin or fluvastatin caused IL-8 (interleukin-8) suppression, but increased hBD-2 mRNA expression in Salmonella-infected SW480 cells. Both statins enhanced phosphorylated Akt and VDR expressions. Akt or VDR knockdown by siRNA counteracted the suppressive effect of simvastatin on IL-8 expression, whereas VDR knockdown diminished the enhanced hBD-2 expression in Salmonella-infected SW480 cells. Therefore, we observed differential regulation of statins on inflammatory IL-8 and anti-microbial hBD-2 expressions in Salmonella-infected IECs via PI3K/Akt signaling and VDR protein expression, respectively. The enhanced activity of antimicrobial peptides by statins in Salmonella-infected IECs could protect the host against infection, and modulation of pro-inflammatory responses could prevent the detrimental effects of overwhelming inflammation in the host.

Macrophage-Bacteria Interactions-A Lipid-Centric Relationship

Macrophages are professional phagocytes at the front line of immune defenses against foreign bodies and microbial pathogens. Various bacteria, which are responsible for deadly diseases including tuberculosis and salmonellosis, are capable of hijacking this important immune cell type and thrive intracellularly, either in the cytoplasm or in specialized vacuoles. Tight regulation of cellular metabolism is critical in shaping the macrophage polarization states and immune functions. Lipids, besides being the bulk component of biological membranes, serve as energy sources as well as signaling molecules during infection and inflammation. With the advent of systems-scale analyses of genes, transcripts, proteins, and metabolites, in combination with classical biology, it is increasingly evident that macrophages undergo extensive lipid remodeling during activation and infection. Each bacterium species has evolved its own tactics to manipulate host metabolism toward its own advantage. Furthermore, modulation of host lipid metabolism affects disease susceptibility and outcome of infections, highlighting the critical roles of lipids in infectious diseases. Here, we will review the emerging roles of lipids in the complex host-pathogen relationship and discuss recent methodologies employed to probe these versatile metabolites during the infection process. An improved understanding of the lipid-centric nature of infections can lead to the identification of the Achilles' heel of the pathogens and host-directed targets for therapeutic interventions. Currently, lipid-moderating drugs are clinically available for a range of non-communicable diseases, which we anticipate can potentially be tapped into for various infections.

Pulmonary Infections in the Elderly Lead to Impaired Neutrophil Targeting, Which Is Improved by Simvastatin

RATIONALE

Dysregulated neutrophil functions with age and sepsis are described. Statins are associated with improved infection survival in some observational studies, but trials in critically ill patients have not shown benefit. Statins also alter neutrophil responses in vitro.

OBJECTIVES

To assess neutrophil migratory accuracy with age during respiratory infections and determine if and how a statin intervention could alter these blunted responses.

METHODS

The migratory accuracy of blood neutrophils from young (aged <35 yr) and old (aged >60 yr) patients in health and during a lower respiratory tract infection, community-acquired pneumonia, and pneumonia associated with sepsis was assessed with and without simvastatin. In vitro results were confirmed in a double-blind randomized clinical trial in healthy elders. Cell adhesion markers were assessed.

MEASUREMENTS AND MAIN RESULTS

In vitro neutrophil migratory accuracy in the elderly deteriorated as the severity of the infectious pulmonary insult increased, without recovery at 6 weeks. Simvastatin rescued neutrophil migration with age and during mild to moderate infection, at high dose in older adults, but not during more severe sepsis. Confirming in vitro results, high-dose (80-mg) simvastatin improved neutrophil migratory accuracy without impeding other neutrophil functions in a double-blind randomized clinical trial in healthy elders. Simvastatin modified surface adhesion molecule expression and activity, facilitating accurate migration in the elderly.

CONCLUSIONS

Infections in older adults are associated with prolonged, impaired neutrophil migration, potentially contributing to poor outcomes. Statins improve neutrophil migration in vivo in health and in vitro in milder infective events, but not in severe sepsis, supporting their potential utility as an early intervention during pulmonary infections. Clinical trial registered with www.clinicaltrialsregister.eu (2011-002082-38).

Small Molecule Mediated Restoration of Mitochondrial Function Augments Anti-Mycobacterial Activity of Human Macrophages Subjected to Cholesterol Induced Asymptomatic Dyslipidemia

Mycobacterium tuberculosis (M.tb) infection manifests into tuberculosis (TB) in a small fraction of the infected population that comprises the TB susceptible group. Identifying the factors potentiating susceptibility to TB persistence is one of the prime agenda of TB control programs. Recently, WHO recognized diabetes as a risk factor for TB disease progression. The closely related pathological state of metabolic imbalance, dyslipidemia, is yet another emerging risk factor involving deregulation in host immune responses. While high cholesterol levels are clinically proven condition for perturbations in cardiac health, a significant fraction of population these days suffer from borderline risk cholesterol profiles. This apparently healthy population is susceptible to various health risks placing them in the "pre-disease" range. Our study focuses on determining the role of such asymptomatic dyslipidemia as a potential risk factor for susceptibility to TB persistence. Macrophages exposed to sub-pathological levels of cholesterol for chronic period, besides impaired release of TNF-α, could not clear intracellular pathogenic mycobacteria effectively as compared to the unexposed cells. These cells also allowed persistence of opportunistic mycobacterial infection by M. avium and M. bovis BCG, indicating highly compromised immune response. The cholesterol-treated macrophages developed a foamy phenotype with a significant increase in intracellular lipid-bodies prior to M.tb infection, potentially contributing to pre-disease state for tuberculosis infection. The foamy phenotype, known to support M.tb infection, increased several fold upon infection in these cells. Additionally, mitochondrial morphology and function were perturbed, more so during infection in cholesterol treated cells. Pharmacological supplementation with small molecule M1 that restored mitochondrial structural and functional integrity limited M.tb survival more effectively in cholesterol exposed macrophages. Mechanistically, M1 molecule promoted clearance of mycobacteria by reducing total cellular lipid content and restoring mitochondrial morphology and function to its steady state. We further supported our observations by infection assays in PBMC-derived macrophages from clinically healthy volunteers with borderline risk cholesterol profiles. With these observations, we propose that prolonged exposure to sub-pathological cholesterol can lead to asymptomatic susceptibility to M.tb persistence. Use of small molecules like M1 sets yet another strategy for host-directed therapy where re-functioning of mitochondria in cholesterol abused macrophages can improve M.tb clearance.

Statin therapy in patients with community-acquired pneumonia

Community-acquired pneumonia (CAP) is the leading cause of death from infection in developed countries. There is evidence of an association between improved survival from infection and statin use. The possible beneficial effects of statins are complicated by the common use of macrolide antibiotics for pneumonia, with current guidance suggesting that concurrent macrolide and statin use is contraindicated.We conducted an observational study of statin use in patients with CAP. Of 2,067 patients with CAP, 30.4% were on statin therapy at admission. Statin users were more likely to survive the admission (p<0.001). In addition, we conducted a survey of doctors and found that knowledge regarding concurrent macrolide and statin use was lacking.These data suggest a potential role of statins in the management of CAP. Further research using high-dose statins is required to assess their safe use in subjects with mild to moderate infections.

Human genetic variation in VAC14 regulates Salmonella invasion and typhoid fever through modulation of cholesterol

Risk, severity, and outcome of infection depend on the interplay of pathogen virulence and host susceptibility. Systematic identification of genetic susceptibility to infection is being undertaken through genome-wide association studies, but how to expeditiously move from genetic differences to functional mechanisms is unclear. Here, we use genetic association of molecular, cellular, and human disease traits and experimental validation to demonstrate that genetic variation affects expression of VAC14, a phosphoinositide-regulating protein, to influence susceptibility to Salmonella enterica serovar Typhi (S Typhi) infection. Decreased VAC14 expression increased plasma membrane cholesterol, facilitating Salmonella docking and invasion. This increased susceptibility at the cellular level manifests as increased susceptibility to typhoid fever in a Vietnamese population. Furthermore, treating zebrafish with a cholesterol-lowering agent, ezetimibe, reduced susceptibility to S Typhi. Thus, coupling multiple genetic association studies with mechanistic dissection revealed how VAC14 regulates Salmonella invasion and typhoid fever susceptibility and may open doors to new prophylactic/therapeutic approaches.

Statin Use Is Associated With a Lower Risk of TB

BACKGROUND

Statins are widely used to lower cholesterol levels and cardiovascular risk. Further, studies have shown that statins may decrease the risks of infectious diseases and infection-related mortality; however, the association between statin use and active TB disease remains unclear.

METHODS

Using the Taiwan National Health Insurance Research Database, we conducted a nationwide population-based study. Patients taking statins between 2000 and 2013, without antecedent TB disease, were included. Data from 102,424 statin users and 202,718 age-, sex-, and enrollment date-matched subjects were analyzed. The two cohorts were monitored until December 31, 2013, for incident TB disease. The definition of TB disease was validated using the claims database of Taipei Veterans General Hospital.

RESULTS

The statin and matched cohorts were observed for 571,568 and 1,027,385 person-years, respectively. Of the total 305,142 subjects, 1,264 (0.41%) developed subsequent TB disease. Validation study confirmed the accuracy of the definition of TB disease (sensitivity, 96.3%), with excellent interobserver agreement (κ = 1.00). Multivariate analysis revealed a reduced risk of TB disease among the statin cohort (hazard ratio [HR], 0.53; 95% CI, 0.47-0.61; P < .001). Compared with the matched group, statin use showed a dose-response relationship with the incident TB disease risk (<180 cumulative defined daily doses [cDDDs]: HR, 1.06; 95% CI, 0.91-1.24; P = .477; 180 to 365 cDDDs: HR, 0.57; 95% CI, 0.45-0.72; P < .001; >365 cDDDs: HR, 0.27; 95% CI, 0.22-0.33; P < .001).

CONCLUSIONS

Statin use associates with a lower risk of incident TB disease.

Roles of the Mevalonate Pathway and Cholesterol Trafficking in Pulmonary Host Defense

The mevalonic acid synthesis pathway, cholesterol, and lipoproteins play fundamental roles in lung physiology and the innate immune response. Recent literature investigating roles for cholesterol synthesis and trafficking in host defense against respiratory infection was critically reviewed. The innate immune response and the cholesterol biosynthesis/trafficking network regulate one another, with important implications for pathogen invasion and host defense in the lung. The activation of pathogen recognition receptors and downstream cellular host defense functions are critically sensitive to cellular cholesterol. Conversely, microorganisms can co-opt the sterol/lipoprotein network in order to facilitate replication and evade immunity. Emerging literature suggests the potential for harnessing these insights towards therapeutic development. Given that >50% of adults in the U.S. have serum cholesterol abnormalities and pneumonia remains a leading cause of death, the potential impact of cholesterol on pulmonary host defense is of tremendous public health significance and warrants further mechanistic and translational investigation.

The Making and Taking of Lipids: The Role of Bacterial Lipid Synthesis and the Harnessing of Host Lipids in Bacterial Pathogenesis

In order to survive environmental stressors, including those induced by growth in the human host, bacterial pathogens will adjust their membrane physiology accordingly. These physiological changes also include the use of host-derived lipids to alter their own membranes and feed central metabolic pathways. Within the host, the pathogen is exposed to many stressful stimuli. A resulting adaptation is for pathogens to scavenge the host environment for readily available lipid sources. The pathogen takes advantage of these host-derived lipids to increase or decrease the rigidity of their own membranes, to provide themselves with valuable precursors to feed central metabolic pathways, or to impact host signalling and processes. Within, we review the diverse mechanisms that both extracellular and intracellular pathogens employ to alter their own membranes as well as their use of host-derived lipids in membrane synthesis and modification, in order to increase survival and perpetuate disease within the human host. Furthermore, we discuss how pathogen employed mechanistic utilization of host-derived lipids allows for their persistence, survival and potentiation of disease. A more thorough understanding of all of these mechanisms will have direct consequences for the development of new therapeutics, and specifically, therapeutics that target pathogens, while preserving normal flora.

Host-directed therapies for infectious diseases: current status, recent progress, and future prospects

Despite extensive global efforts in the fight against killer infectious diseases, they still cause one in four deaths worldwide and are important causes of long-term functional disability arising from tissue damage. The continuing epidemics of tuberculosis, HIV, malaria, and influenza, and the emergence of novel zoonotic pathogens represent major clinical management challenges worldwide. Newer approaches to improving treatment outcomes are needed to reduce the high morbidity and mortality caused by infectious diseases. Recent insights into pathogen–host interactions, pathogenesis, inflammatory pathways, and the host's innate and acquired immune responses are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. Host-directed therapeutic strategies are now becoming viable adjuncts to standard antimicrobial treatment. Host-directed therapies include commonly used drugs for non-communicable diseases with good safety profiles, immunomodulatory agents, biologics (eg monoclonal antibodies), nutritional products, and cellular therapy using the patient's own immune or bone marrow mesenchymal stromal cells. We discuss clinically relevant examples of progress in identifying host-directed therapies as adjunct treatment options for bacterial, viral, and parasitic infectious diseases.

Is There Potential for Repurposing Statins as Novel Antimicrobials?

Statins are members of a class of pharmaceutical widely used to reduce high levels of serum cholesterol. In addition, statins have so-called "pleiotropic effects," which include inflammation reduction, immunomodulation, and antimicrobial effects. An increasing number of studies are emerging which detail the attenuation of bacterial growth and in vitro and in vivo virulence by statin treatment. In this review, we describe the current information available concerning the effects of statins on bacterial infections and provide insight regarding the potential use of these compounds as antimicrobial therapeutic agents.

Major differential gene regulation in Coxiella burnetii between in vivo and in vitro cultivation models

Background

Coxiella burnetii is the causative agent of the zoonotic disease Q fever. As it is an intracellular pathogen, infection by C. burnetii requires adaptation to its eukaryotic host and intracellular environment. The recently developed cell-free medium also allows the bacteria to propagate without host cells, maintaining its infection potential. The adaptation to different hosts or extracellular environments has been assumed to involve genome-wide modulation of C. burnetii gene expression. However, little is currently known about these adaptation events which are critical for understanding the intracellular survival of C. burnetii.

Results

We studied C. burnetii genome–wide transcriptional patterns in vivo (mice spleen) and in cell and cell-free in vitro culture models to examine its metabolic pathways and virulence associated gene expression patterns that are required to colonize and persist in different environments. Within each model, the gene expression profiles of the Dutch C. burnetii outbreak strain (602) and NM reference strains were largely similar. In contrast, modulation of gene-expression was strongly influenced by the cultivation method, indicating adaptation of the bacterium to available components. Genome–wide expression profiles of C. burnetii from in vitro cell culture were more similar to those seen for in vivo conditions, while gene expression profiles of cell-free culture were more distant to in vivo. Under in vivo conditions, significant alterations of genes involved in metabolism and virulence were identified. We observed that C. burnetii under in vivo conditions predominantly uses glucose as a carbon source (mostly for biosynthetic processes) and fatty acids for energy generation. C. burnetii experienced nutrient limitation and anaerobiosis as major stressors, while phosphate limitation was identified as an important signal for intracellular growth inside eukaryotic host cells. Finally, the in vivo environment significantly induced expression of several virulence genes, including those implicated in LPS synthesis, colonization, host component modulation and DNA repair mechanisms.

Conclusion

Our study shows that C. burnetii, with its relative small genome, requires only a subset of core gene functions to survive under in vitro conditions, but requires the induction of full repertoire of genes for successful pathogenesis and thriving in harsh environments in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2143-7) contains supplementary material, which is available to authorized users.

Effect of statins on preventing infectious complications after surgery: Systematic review and meta-analysis

OBJECTIVE

*These authors contributed equally to this work.A meta-analysis to investigate the association between preoperative statin use and the risk of postoperative infectious complications in patients undergoing surgery.

METHODS

PubMed(®) and Embase(®) databases were searched for relevant studies. Data were extracted using a standardized data collection form. The primary effect measure was the odds ratio (OR) of postoperative infectious complications. Summary OR were calculated.

RESULTS

The analysis included 10 cohort studies with a total of 147 263 participants. Statin use was associated with a lower incidence of postoperative infectious complications in all studies (summary OR 0.917, 95% confidence intervals [CI] 0.862, 0.975, fixed-effects model; summary OR 0.731, 95% CI 0.584, 0.870, random-effects model); cardiac surgery (summary OR 0.673; 95% CI 0.535, 0.847); treatment in the USA (summary OR 0.678; 95% CI 0.597, 0.770); retrospective cohort studies (summary OR 0.664; 95% CI 0.521, 0.846).

CONCLUSION

Preoperative statin use is associated with a reduced risk of postoperative infectious complications.

Antileishmanial effect of mevastatin is due to interference with sterol metabolism

Visceral leishmaniasis (VL) is one of the most severe forms of leishmaniasis which is fatal if left untreated. Sterol biosynthetic pathway in Leishmania is currently being explored for its therapeutic potential. In the present study, we have evaluated the antileishmanial efficacy of mevastatin, a known inhibitor of 3-hydroxy-3-methyl glutaryl-CoA reductase (HMGR) enzyme. Mevastatin inhibited Leishmania donovani promastigotes and intracellular amastigotes with an 50% inhibitory concentration (IC50) value of 23.8 ± 4.2 and 7.5 ± 1.1 μM, respectively, without exhibiting toxicity towards host cell line. Mevastatin also inhibited recombinant L. donovani HMGR (LdHMGR) enzyme activity with an IC50 value of 42.2 ± 3.0 μM. Kinetic analysis revealed that the inhibition of recombinant LdHMGR activity by mevastatin was competitive with HMG-CoA. Mevastatin-treated parasites exhibited 66% reduction in ergosterol levels with respect to untreated parasites. Incubation of mevastatin-treated L. donovani promastigotes with ergosterol resulted in revival of cell growth, whereas cholesterol supplementation failed to cause reversal in cell death. To further prove the specificity of mevastatin for HMGR enzyme, HMGR-overexpressing parasites were used which showed almost threefold resistance to mevastatin. It also induced morphological changes in the parasite accompanied by lipid body accumulation. Hence, antileishmanial effect of mevastatin was due to the inhibition of HMGR, which eventually leads to reduction in ergosterol levels and hence parasite death. The present study may have implications in the treatment of visceral form of leishmaniasis.

Impact of statins in outcomes of septic patients: a systematic review

BACKGROUND

The pleiotropic effects of statins have prompted considerable research in fields other than cardiovascular disease. We reviewed the literature aiming to summarize and critically evaluate the current evidence about the potential use of statins in sepsis.

MATERIALS AND METHODS

We searched the Pubmed, SciELO, and Cochrane electronic databases from inception through November 1, 2013, for randomized controlled trials (RCTs) and cohort studies that examined the association between statin use (upon hospital admission or previous users) and the risk or outcome of sepsis. Data on study characteristics, measurement of statin use, and outcomes (adjusted for potential confounders) were extracted. We structured our review according to the Principles of Reporting in Systematic Reviews and Meta-Analysis criteria. Quality assessment of cohort studies was performed using the Ottawa-Newcastle Scale.

RESULTS

Twenty-three cohort studies and 5 RCTs were eligible, comprising 42 549 statin users and 54 201 non-statin users, from 1995 to 2013. The populations included varied from patients admitted to general wards or intensive care units with bacterial infections, community-acquired pneumonia, ventilator-associated pneumonia, bacteremia, or sepsis, to outpatients with chronic kidney disease or established cardiovascular disease. Overall, 16 studies reported a benefit from statin use in morbidity or mortality outcomes (range of adjusted odds ratio, 0.06-0.62; α = 0.05). The remaining 12 studies found no protective effect associated with statin use upon hospital admission or previous users. Among the 5 RCTs, none demonstrated a reduction in mortality.

CONCLUSION

There is insufficient evidence to support the use of statins in patients with sepsis, as the existing studies failed to prove a consistent mortality benefit. More clinical trials are warranted to provide more conclusive knowledge and ultimately change clinical practice.

Association between Preoperative Statin Therapy and Postoperative Infectious Complications in Patients Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

Infectious complications of cardiac surgery are often severe and life threatening. Statins having both immunomodulatory and anti-inflammatory effects were intuitively thought to influence the development of postsurgical infections. We sought to systematically examine whether any association exists between statin use and risk of infectious complications in patients undergoing cardiac surgery. We searched Ovid MEDLINE, Ovid EMBASE, Thomson Scientific Web of Science, and Elsevier Scopus from inception through February 2011 for comparative studies examining the association between statin use and risk of postoperative infections in patients undergoing cardiac surgery. We contacted a study's author for missing information. We conducted a random-effects meta-analysis of individual studies' odds ratios (adjusted for potential confounders). We identified 6 cohort studies for inclusion, 3 of which were conducted in Canada and 3 of which were conducted in the United States. Four were single-center studies, and 2 were population based. Exposure ascertainment was based on a review of admission medication list or prescription databases. Infectious outcomes were heterogeneous and included surgical site infections within 30 days, serious infections (sepsis), or any other postoperative infection. Statin use in the preoperative period was associated with a trend toward reduction in the incidence of postoperative infections in patients who underwent cardiac surgery (odds ratio, 0.81 [95% confidence interval, 0.64–1.01]; P = .06; I2 = 75%). Heterogeneity was explained by country effect. Studies performed in Canada showed weaker associations than studies performed in the United States. This difference could not be attributed to study quality alone. We did not find good evidence to support an association between statin use and postoperative infectious complications. However, the trend toward statistical significance for this association indicates that further investigation is warranted.

Preoperative statin therapy and infectious complications in cardiac surgery

AIM

To assess whether preoperative statin therapy is associated with the risk of postoperative infection in patients undergoing cardiac surgery.

METHODS

520 patients undergoing cardiac surgery in 2010 were retrospectively examined. Data regarding statin and antibiotic use prior to and after surgery were available from the hospital pharmacy information system. Cultures and clinical data of patients on postoperative antibiotics other than standard prophylactic therapy were studied to identify postoperative infections up to 30 days from day of surgery.

RESULTS

370 (71.2 %) patients were on preoperative statin therapy. Overall, 82 patients (15.8 %) suffered from postoperative infection of which 11 were surgical site infections. In multivariable regression analysis, statin therapy was associated with a reduced risk of postoperative infection (adjusted odds ratio: 0.329, 95 %: CI 0.19-0.57; P < 0.001).

CONCLUSIONS

Preoperative statin use was associated with a considerable reduced risk of postoperative infections following cardiac surgery. Randomised controlled trials are required to clarify the role of statin therapy in the prevention of postoperative infections.

Simvastatin increases the in vivo activity of the first-line tuberculosis regimen

BACKGROUND

The need to develop new, improved treatments for tuberculosis (TB) remains urgent, and the repurposing of existing drugs represents a possible shortcut to market. Recently, there has been significant interest in host-directed adjuvant therapy to enhance bacillary killing. HMG-CoA reductase inhibitors (statins), which are among the most commonly prescribed drugs, have immunomodulatory properties and improve the clinical outcomes of bacterial infections.

METHODS

We studied the tuberculocidal activity of simvastatin alone and in combination with first-line anti-TB drugs in J774 macrophages and during chronic TB infection.

RESULTS

Exposure to 5 μM simvastatin significantly increased the tuberculocidal activity of isoniazid in J774 macrophages at Day 3 after infection versus isoniazid alone (P=0.02). Similarly, relative to the standard oral regimen of rifampicin (10 mg/kg), isoniazid (10 mg/kg) and pyrazinamide (150 mg/kg) given five times weekly, the addition of 25 mg/kg simvastatin enhanced bacillary killing, reducing the number of lung cfu by an additional 1 log10 at Day 28 (P<0.01) and by a further 1.25 log10 at Day 56 (P<0.01).

CONCLUSIONS

The potential additive activity of simvastatin to first-line TB treatment holds promise. However, further studies to identify the optimal statin and dosing are required. In addition the ability of combination treatment with statins to accelerate the time required to achieve a stable cure remains to be explored.

Exploitation of host lipids by bacteria

Bacteria that interact with eukaryotic cells have developed a variety of strategies to divert host lipids, or cellular processes driven by lipids, to their benefit. Host lipids serve as building blocks for bacterial membrane formation and as energy source. They promote the formation of specific microdomains, facilitating interactions with the host. Host lipids are also critical players in the entry of bacteria or toxins into cells, and, for bacteria growing inside parasitophorous vacuoles, in building a secure shelter. Bacterial dissemination is often dependent on enzymatic activities targeting host lipids. Finally, on a larger scale, long lasting parasitic association can disturb host lipid metabolism so deeply as to 'reprogram' it, as proposed in the case of Mycobacterium infection.

Serum lipids and lipoproteins in malaria--a systematic review and meta-analysis

BACKGROUND

Serum lipid profile changes have been observed during malaria infection. The underlying biological mechanisms remain unclear. The aim of this paper is to provide an overview on those serum lipid profile changes, and to discuss possible underlying biological mechanisms and the role of lipids in malaria pathogenesis.

METHODS

A systematic review and meta-analysis to determine lipid profile changes during malaria was conducted, following PRISMA guidelines. Without language restrictions, Medline/PubMed, Embase, Cochrane Central Register of Controlled Trials, Web of Science, LILACS, Biosis Previews and the African Index Medicus were searched for studies published up to 11 July, 2013, that measured serum lipid parameters in malaria patients. Also, major trial registries were searched. Mean differences in lipid profile parameters were combined in fixed and random effects meta-analysis, with a separate analysis for different groups of controls (healthy, other febrile illnesses or very low parasitaemia). These parameters were also compared between severe malaria and uncomplicated malaria. Funnel plots were used to test for publication bias.

RESULTS

Of 2,518 studies reviewed, 42 met the criteria for inclusion in the qualitative analysis, and of these, 15 reported the necessary data for inclusion in the meta-analysis for cholesterol; nine for high-density lipoprotein (HDL), eight for low-density lipoprotein (LDL), and nine for triglycerides, respectively. Total cholesterol, HDL and LDL concentrations were lower in malaria and other febrile diseases compared to healthy controls. The decline was more pronounced and statistically significant during malaria compared to other febrile diseases. These results were consistent across included studies. Triglycerides were raised compared to healthy controls, but not statistically significant when compared to symptomatic controls.

CONCLUSIONS

This meta-analysis suggests that the observed lipid profile changes are characteristic for malaria. Although a definite link with the pathogenesis of malaria cannot yet be demonstrated, plausible hypotheses of biological mechanisms involving host lipid alterations and the pathogenesis of malaria exist. An increased research effort to elucidate the precise pathways is warranted, since this could lead to better understanding of malaria pathophysiology and consequently to novel treatment approaches.

Toxoplasma gondii relies on both host and parasite isoprenoids and can be rendered sensitive to atorvastatin

Intracellular pathogens have complex metabolic interactions with their host cells to ensure a steady supply of energy and anabolic building blocks for rapid growth. Here we use the obligate intracellular parasite Toxoplasma gondii to probe this interaction for isoprenoids, abundant lipidic compounds essential to many cellular processes including signaling, trafficking, energy metabolism, and protein translation. Synthesis of precursors for isoprenoids in Apicomplexa occurs in the apicoplast and is essential. To synthesize longer isoprenoids from these precursors, T. gondii expresses a bifunctional farnesyl diphosphate/geranylgeranyl diphosphate synthase (TgFPPS). In this work we construct and characterize T. gondii null mutants for this enzyme. Surprisingly, these mutants have only a mild growth phenotype and an isoprenoid composition similar to wild type parasites. However, when extracellular, the loss of the enzyme becomes phenotypically apparent. This strongly suggests that intracellular parasite salvage FPP and/or geranylgeranyl diphosphate (GGPP) from the host. We test this hypothesis using inhibitors of host cell isoprenoid synthesis. Mammals use the mevalonate pathway, which is susceptible to statins. We document strong synergy between statin treatment and pharmacological or genetic interference with the parasite isoprenoid pathway. Mice can be cured with atorvastatin (Lipitor) from a lethal infection with the TgFPPs mutant. We propose a double-hit strategy combining inhibitors of host and parasite pathways as a novel therapeutic approach against Apicomplexan parasites.

Toxoplasma gondii is an obligate intracellular parasite and is not able to replicate outside the host cell. The parasite lives in a specialized parasitophorous vacuole in contact with the host cytoplasm through the parasitophorous vacuole membrane. It is highly likely that a very active exchange of metabolites occurs between parasite and host cell. We present evidence for this exchange for isoprenoids, abundant lipidic compounds essential to many cellular processes including signaling, trafficking, energy metabolism, and protein translation. Our work shows that intracellular T. gondii tachyzoites are able to salvage farnesyl diphosphate (FPP) and/or geranylgeranyl diphosphate (GGPP) from the host, and the parasite is able to grow even when its endogenous production is shut down. However, when extracellular, the parasite depends entirely on its own production of isoprenoids. We propose to use a combination of inhibitors that would hit both the host and the parasite pathways as a novel therapeutic approach against Toxoplasma gondii that could also work against other Apicomplexan parasites.

Simvastatin enhances protection against Listeria monocytogenes infection in mice by counteracting Listeria-induced phagosomal escape

Statins are well-known cholesterol lowering drugs targeting HMG-CoA-reductase, reducing the risk of coronary disorders and hypercholesterolemia. Statins are also involved in immunomodulation, which might influence the outcome of bacterial infection. Hence, a possible effect of statin treatment on Listeriosis was explored in mice. Statin treatment prior to subsequent L. monocytogenes infection strikingly reduced bacterial burden in liver and spleen (up to 100-fold) and reduced histopathological lesions. Statin-treatment in infected macrophages resulted in increased IL-12p40 and TNF-α and up to 4-fold reduced bacterial burden within 6 hours post infection, demonstrating a direct effect of statins on limiting bacterial growth in macrophages. Bacterial uptake was normal investigated in microbeads and GFP-expressing Listeria experiments by confocal microscopy. However, intracellular membrane-bound cholesterol level was decreased, as analyzed by cholesterol-dependent filipin staining and cellular lipid extraction. Mevalonate supplementation restored statin-inhibited cholesterol biosynthesis and reverted bacterial growth in Listeria monocytogenes but not in listeriolysin O (LLO)-deficient Listeria. Together, these results suggest that statin pretreatment increases protection against L. monocytogenes infection by reducing membrane cholesterol in macrophages and thereby preventing effectivity of the cholesterol-dependent LLO-mediated phagosomal escape of bacteria.

Boots for Achilles: progesterone's reduction of cholesterol is a second-order adaptation

Progesterone and cholesterol are both vital to pregnancy. Among other functions, progesterone downregulates inflammatory responses, allowing for maternal immune tolerance of the fetal allograft. Cholesterol a key component of cell membranes, is important in intracellular transport, cell signaling, nerve conduction, and metabolism Despite the importance of each substance in pregnancy, one exercises an antagonistic effect on the other, as periods of peak progesterone correspond with reductions in cholesterol availability, a consequence of progesterone's negative effects on cholesterol biosynthesis. This arrangement is understandable in light of the threat posed by pathogens early in pregnancy. Progesterone-induced immunomodulation entails increased vulnerability to infection, an acute problem in the first trimester, when fetal development is highly susceptible to insult. Many pathogens rely on cholesterol for cell entry, egress, and replication. Progesterone's antagonistic effects on cholesterol thus partially compensate for the costs entailed by progesterone-induced immunomodulation. Among pathogens to which the host's vulnerability is increased by progesterone's effects, approximately 90% utilize cholesterol, and this is notably true of pathogens that pose a risk during pregnancy. In addition to having a number of possible clinical applications, our approach highlights the potential importance of second-order adaptations, themselves a consequence of the lack of teleology in evolutionary processes.

Statin therapy is associated with fewer infections after cardiac operations

BACKGROUND

Statins interact with multiple pathways involved in infection. Therefore, we examined the association between preoperative statin therapy and infections after cardiac operations and assessed whether statin therapy was associated with lower infection-related mortality.

METHODS

From January 2005 to January 2011, 12,741 patients underwent cardiac operations. Endpoints were (1) postoperative infections and (2) mortality after an infectious complication. A propensity score was developed on the probability of patients receiving statin therapy; patients were matched in part on this score. A multivariable logistic model was developed to examine mortality. Survival of infected patients was estimated using Kaplan-Meier and multiphase hazard function methodology.

RESULTS

A total of 6,113 patients (48%) were receiving statins and 6,628 (52%) were not. Five hundred fifteen patients had postoperative infections-260 (4.3%) in the statin group and 255 (3.8%) in the no-statin group. However, patients receiving statins were older with more comorbidities and less favorable operative characteristics. Among propensity-matched groups, postoperative infections were significantly lower in patients receiving statins (n = 102 [3.1%]) than in those who were not (n = 147 [4.5%]; p = 0.004). Among patients in whom infections developed, there was no significant difference in hospital mortality between the statin and no-statin groups either before or after propensity-score matching (odds ratio, 1.38; confidence limit [CL], 0.59, 3.22; p = 0.5).

CONCLUSIONS

We observed a protective effect of statin therapy against the development of infections after cardiac operations, but not on mortality from these infections. Prospective investigations are needed to determine optimal dose and duration of statin therapy and their relationship to infectious complications.

Bacterial colonization of host cells in the absence of cholesterol

Reports implicating important roles for cholesterol and cholesterol-rich lipid rafts in host-pathogen interactions have largely employed sterol sequestering agents and biosynthesis inhibitors. Because the pleiotropic effects of these compounds can complicate experimental interpretation, we developed a new model system to investigate cholesterol requirements in pathogen infection utilizing DHCR24^−/− mouse embryonic fibroblasts (MEFs). DHCR24^−/− MEFs lack the Δ24 sterol reductase required for the final enzymatic step in cholesterol biosynthesis, and consequently accumulate desmosterol into cellular membranes. Defective lipid raft function by DHCR24^−/− MEFs adapted to growth in cholesterol-free medium was confirmed by showing deficient uptake of cholera-toxin B and impaired signaling by epidermal growth factor. Infection in the absence of cholesterol was then investigated for three intracellular bacterial pathogens: Coxiella burnetii, Salmonella enterica serovar Typhimurium, and Chlamydia trachomatis. Invasion by S. Typhimurium and C. trachomatis was unaltered in DHCR24^−/− MEFs. In contrast, C. burnetii entry was significantly decreased in −cholesterol MEFs, and also in +cholesterol MEFs when lipid raft-associated α_Vβ₃ integrin was blocked, suggesting a role for lipid rafts in C. burnetii uptake. Once internalized, all three pathogens established their respective vacuolar niches and replicated normally. However, the C. burnetii-occupied vacuole within DHCR24^−/− MEFs lacked the CD63-postive material and multilamellar membranes typical of vacuoles formed in wild type cells, indicating cholesterol functions in trafficking of multivesicular bodies to the pathogen vacuole. These data demonstrate that cholesterol is not essential for invasion and intracellular replication by S. Typhimurium and C. trachomatis, but plays a role in C. burnetii-host cell interactions.

Clustered receptors associated with cholesterol-rich microdomains, termed lipid rafts, are thought to provide plasma membrane signaling platforms that bacterial pathogens can subvert to gain entry into host cells. Moreover, cholesterol has been implicated as a critical structural lipid of several pathogen-occupied vacuoles. Cumulative data supporting these models have principally been derived using inhibitors of cholesterol metabolism and various sterol sequestering compounds, agents that can lack specificity and cause unwanted cellular affects. Here, we employed a new system to investigate pathogen reliance on cholesterol for host cell colonization that utilizes mouse embryonic fibroblasts that can synthesize precursor sterols, but not cholesterol. Cells lacking cholesterol displayed strong defects in lipid raft-based signaling. However, no defects were observed in entry, vacuole development, and growth of Salmonella enterica and Chlamydia trachomatis, bacterial pathogens previously shown to rely on cholesterol for optimal host cell parasitism. Entry by Coxiella burnetii, the bacterial cause of human Q fever, was significantly decreased in cholesterol-negative cells as was trafficking of membranous material to the pathogen vacuole. However, subsequent bacterial replication was unaltered. Our results should prompt a reevaluation of the overall importance of cholesterol in bacterial pathogenesis with the described experimental system providing an alternative approach for such studies.

The role of statins in prevention and treatment of community acquired pneumonia: a systematic review and meta-analysis

BACKGROUND

Emerging epidemiological evidence suggests that statins may reduce the risk of community-acquired pneumonia (CAP) and its complications.

PURPOSE

Performed a systematic review to address the role of statins in the prevention or treatment of CAP.

DATA SOURCE

Ovid MEDLINE, Cochrane, EMBASE, ISI Web of Science, and Scopus from inception through December 2011 were searched for randomized clinical trials, cohort and case-control studies.

STUDY SELECTION

Two authors independently reviewed studies that examined the role of statins in CAP.

DATA EXTRACTION

Data about study characteristics, adjusted effect-estimates and quality characteristics was extracted.

DATA SYNTHESIS

Eighteen studies corresponding to 21 effect-estimates (eight and 13 of which addressed the preventive and therapeutic roles of statins, respectively) were included. All studies were of good methodological quality. Random-effects meta-analyses of adjusted effect-estimates were used. Statins were associated with a lower risk of CAP, 0.84 (95% CI, 0.74-0.95), I(2) = 90.5% and a lower short-term mortality in patients with CAP, 0.68 (95% CI, 0.59-0.78), I(2) = 75.7%. Meta-regression did not identify sources of heterogeneity. A funnel plot suggested publication bias in the treatment group, which was adjusted by a novel regression method with a resultant effect-estimate of 0.85 (95% CI, 0.77-0.93). Sensitivity analyses using the rule-out approach showed that it is unlikely that the results were due to an unmeasured confounder.

CONCLUSIONS

Our meta-analysis reveals a beneficial role of statins for the risk of development and mortality associated with CAP. However, the results constitute very low quality evidence as per the GRADE framework due to observational study design, heterogeneity and publication bias.

The association of prior statin use in septic shock treated with early goal directed therapy

BACKGROUND

Previous literature suggests statins may have a therapeutic role in sepsis. No data have examined if statin use may have a positive impact beyond that afforded by early goal directed therapy (EGDT).

OBJECTIVE

To test the hypothesis that previous statin use is associated with improved clinically relevant outcomes in patients with severe sepsis and septic shock receiving EGDT.

METHODS

Retrospective cohort study of 91 patients who presented in an academic center in severe sepsis or septic shock and received EGDT. Primary outcome was mortality and secondary outcomes included mechanical ventilation days, ICU length of stay, and hospital length of stay.

RESULTS

Patients (87 of 91) presented to the Emergency Department before ICU admission. Patients (18 of 91) were receiving statin therapy before presentation. The statin group had a mortality rate of 22.2 vs. 39.7% in the nonstatin group (P=0.273). The statin group had fewer mechanical ventilation days (8.49 vs. 7.29 days, P=0.026), and a trend in improved hospital length of stay (17.9 vs. 14.4 days, P=0.065), and ICU length of stay (7.15 vs. 4.89 days, P=0.077).

CONCLUSION

Prior statin use is associated with fewer mechanical ventilation days and a trend toward improvement in other clinically relevant outcomes. This trial is limited by its retrospective nature and small sample size. These results should serve as hypothesis generating for future prospective trials, as the lack of novel drug therapy and the mortality rate of septic shock both remain unacceptable.

Uptake and persistence of Mycobacterium avium subsp. paratuberculosis in human monocytes

Mycobacterium avium subsp. paratuberculosis is a bacterium sometimes found in human blood and tissue samples that may have a role in the etiology of Crohn's disease in humans. To date, however, there have been few studies examining the interactions of these bacteria with human cells. Using the THP-1 human monocytic cell line, this study shows that the uptake and trafficking of M. avium subsp. paratuberculosis in human cells are cholesterol dependent and that these bacteria localize to cholesterol-rich compartments that are slow to acidify. M. avium subsp. paratuberculosis bacteria containing phagosomes stain for the late endosomal marker Rab7, but recruitment of the Rab7-interacting lysosomal protein that regulates the fusion of bacterium-containing phagosomes with lysosomal compartments and facilitates subsequent bacterial clearance is significantly reduced. Disruption of phagosome acidification via this mechanism may contribute to M. avium subsp. paratuberculosis persistence in human cells, but there was no evidence that internalized M. avium subsp. paratuberculosis also affects the survival of bacteria taken up during a secondary phagocytic event.

Type III effector-mediated processes in Salmonella infection

Salmonella is one of the most successful bacterial pathogens that infect humans in both developed and developing countries. In order to cause infection, Salmonella uses type III secretion systems to inject bacterial effector proteins into host cells. In the age of antibiotic resistance, researchers have been looking for new strategies to reduce Salmonella infection. To understand infection and to analyze type III secretion as a potential therapeutic target, research has focused on identification of effectors, characterization of effector functions and how they contribute to disease. Many effector-mediated processes have been identified that contribute to infection but thus far no specific treatment has been found. In this perspective we discuss our current understanding of effector-mediated processes and discuss new techniques and approaches that may help us to find a solution to this worldwide problem.

The effect of rosuvastatin in a murine model of influenza A infection

RATIONALE

HMG-CoA reductase inhibitors such as rosuvastatin may have immunomodulatory and anti-inflammatory effects that may reduce the severity of influenza A infection. We hypothesized that rosuvastatin would decrease viral replication, attenuate lung injury, and improve mortality following influenza A infection in mice.

METHODS

C57Bl/6 mice were treated daily with rosuvastatin (10 mg/kg/day) supplemented in chow (or control chow) beginning three days prior to infection with either A//Udorn/72 [H3N2] or A/WSN/33 [H1N1] influenza A virus (1×10(5) pfu/mouse). Plaque assays were used to examine the effect of rosuvastatin on viral replication in vitro and in the lungs of infected mice. We measured cell count with differential, protein and cytokines in the bronchoalveolar lavage (BAL) fluid, histologic evidence of lung injury, and wet-to-dry ratio on Day 1, 2, 4, and 6. We also recorded daily weights and mortality.

RESULTS

The administration of rosuvastatin had no effect on viral clearance of influenza A after infection. Weight loss, lung inflammation and lung injury severity were similar in the rosuvastatin and control treated mice. In the mice infected with influenza A (A/WSN/33), mortality was unaffected by treatment with rosuvastatin.

CONCLUSIONS

Statins did not alter the replication of influenza A in vitro or enhance its clearance from the lung in vivo. Statins neither attenuated the severity of influenza A-induced lung injury nor had an effect on influenza A-related mortality. Our data suggest that the association between HMG CoA reductase inhibitors and improved outcomes in patients with sepsis and pneumonia are not attributable to their effects on influenza A infection.

Role of lipids in Coxiella burnetii infection

Lipids are essential components of both eukaryotic and prokaryotic cells, serving diverse functions including energy metabolism and membrane structure. Intracellular vacuolar pathogens such as Coxiella burnetii require lipids for both normal bacterial functions as well as formation of the acidic, phagolysosomal-like parasitophorous vacuole (PV) surrounding the bacteria. As an intracellular pathogen, C. burnetii can acquire lipid through both de novo bacterial synthesis and subversion of host cell pools. The C. burnetii genome encodes enzymes required for de novo synthesis of fatty acids and phospholipids. The high percentage of branched fatty acids suggests C. burnetii modifies these molecules to generate a bacterial cell envelope that can resist the harsh environment of the PV, such as the acidic pH. In addition to fatty acids and their derivatives, C. burnetii requires isoprenoids, particularly sterols as the PV membrane is cholesterol-rich. With the exception of two eukaryote-like sterol reductases, C. burnetii does not have the capability to generate cholesterol, suggesting sterols are actively diverted from the host cell. While C. burnetii utilizes host cell lipids for membrane biogenesis and possibly energy, bacterial manipulation of host cell lipid signaling pathways may support establishment of the intracellular niche. For example, effectors secreted by the C. burnetii Type IV secretion system may either directly or indirectly modify host cell lipids. Further understanding of the lipid biosynthetic capabilities of C. burnetii, along with C. burnetii's manipulation of host cell lipids, will provide insight into the host-pathogen relationship.

Modifiers of symptomatic embolic risk in infective endocarditis

OBJECTIVE

To ascertain the impact of prior antiplatelet and statin therapy on symptomatic embolic events in [corrected] infective endocarditis (IE).

PATIENTS AND METHODS

We studied a retrospective cohort of adult patients with a diagnosis of IE who presented to Mayo Clinic (Rochester, MN) from January 1, 2003, to December 31, 2006. Patients were grouped into those who received treatment before infection or controls who did not receive treatment for both antiplatelet therapy and, separately, statin therapy. Because of the retrospective study design and thus the nonrandomized treatment groups, a propensity score approach was used to account for the confounding factors that may have influenced treatment allocation. Antiplatelet therapy included aspirin, dipyridamole, clopidogrel, ticlopidine or any combination of these agents. Statin therapy included atorvastatin, simvastatin, pravastatin, lovastatin, rosuvastatin, or fluvastatin. The primary end point was a symptomatic embolic event that occurred before or during hospitalization. Multivariable logistic regression was used to assess the propensity-adjusted effects of continuous daily therapy with antiplatelet and statin agents on risk of symptomatic emboli. Likewise, Cox proportional hazards regression was used to test for an independent association with 6-month mortality for each of the treatments.

RESULTS

The study cohort comprised 283 patients with [corrected] IE. Twenty-eight patients (24.1%) who received prior continuous antiplatelet therapy developed a symptomatic embolic event compared with 66 (39.5%) who did not receive such treatment. After adjusting for propensity to treat, the effect of antiplatelet therapy on embolic risk was not statistically significant (odds ratio, 0.71; 95% confidence interval [CI], 0.37-1.36; P=.30). Only 14 patients (18.2%) who received prior continuous statin therapy developed a symptomatic embolic event compared with 80 (39.4%) of the 203 patients who did not. After adjusting for propensity to treat with statin therapy, the benefit attributable to statins was significant (odds ratio, 0.30; 95% CI, 0.14-0.62; P=.001). The 6-month mortality rate of the entire cohort was 28% (95% CI, 23%-34%). No significant difference was found in the propensity-adjusted rate of 6-month mortality between patients who had and had not undergone prior antiplatelet therapy (P=.91) or those who had and had not undergone prior statin therapy (P=.87).

CONCLUSION

The rate of symptomatic emboli associated with IE was reduced in patients who received continuous daily statin therapy before onset of IE. Despite fewer embolic events observed in patients who received antiplatelet agents, a significant association was not found after adjusting for propensity factors. A continued evaluation of these drugs and their potential impact on subsequent embolism among IE patients is warranted.

Plasma membrane cholesterol plays a critical role in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells

Our recent study demonstrated that a phosphatidylinositol-3 kinase (PI3K)/Akt-dependent anti-inflammatory pathway was activated by Salmonella in intestinal epithelial cells. Salmonella virulence is dependent on the ability of the bacterium to invade nonphagocytic host cells and then survive and replicate within modified Salmonella-containing vacuoles where cholesterol accumulates. In addition, cholesterol in membrane lipid rafts is frequently a platform for the activation of downstream signaling pathways, including the PI3K/Akt pathway. However, the role of plasma membrane cholesterol in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells has not been elucidated. Here, we show that the effect of plasma membrane cholesterol depletion on the inhibition of Akt activation allows sustained ERK activation and the subsequent upregulation of IL-8 expression. These results demonstrate that plasma membrane cholesterol plays a critical role in the PI3K-dependent anti-inflammatory pathway activated by Salmonella in intestinal epithelial cells.