Statin inhibition of Fc receptor-mediated phagocytosis by macrophages is modulated by cell activation and cholesterol

Repurposing of statins for Buruli Ulcer treatment: antimicrobial activity against Mycobacterium ulcerans

Mycobacterium ulcerans causes Buruli Ulcer, a neglected infectious skin disease that typically progresses from an early non-ulcerative lesion to an ulcer with undermined edges. If not promptly treated, these lesions can lead to severe disfigurement and disability. The standard antibiotic regimen for Buruli Ulcer treatment has been oral rifampicin combined with intramuscular streptomycin administered daily for 8 weeks. However, there has been a recent shift toward replacing streptomycin with oral clarithromycin. Despite the advantages of this antibiotic regimen, it is limited by low compliance, associated side effects, and refractory efficacy for severe ulcerative lesions. Therefore, new drug candidates with a safer pharmacological spectrum and easier mode of administration are needed. Statins are lipid-lowering drugs broadly used for dyslipidemia treatment but have also been reported to have several pleiotropic effects, including antimicrobial activity against fungi, parasites, and bacteria. In the present study, we tested the susceptibility of M. ulcerans to several statins, namely atorvastatin, simvastatin, lovastatin and fluvastatin. Using broth microdilution assays and cultures of M. ulcerans-infected macrophages, we found that atorvastatin, simvastatin and fluvastatin had antimicrobial activity against M. ulcerans. Furthermore, when using the in vitro checkerboard assay, the combinatory additive effect of atorvastatin and fluvastatin with the standard antibiotics used for Buruli Ulcer treatment highlighted the potential of statins as adjuvant drugs. In conclusion, statins hold promise as potential treatment options for Buruli Ulcer. Further studies are necessary to validate their effectiveness and understand the mechanism of action of statins against M. ulcerans.

Computational Construction of Toxicant Signaling Networks

Humans and animals are regularly exposed to compounds that may have adverse effects on health. The Toxicity Forecaster (ToxCast) program was developed to use high throughput screening assays to quickly screen chemicals by measuring their effects on many biological end points. Many of these assays test for effects on cellular receptors and transcription factors (TFs), under the assumption that a toxicant may perturb normal signaling pathways in the cell. We hypothesized that we could reconstruct the intermediate proteins in these pathways that may be directly or indirectly affected by the toxicant, potentially revealing important physiological processes not yet tested for many chemicals. We integrate data from ToxCast with a human protein interactome to build toxicant signaling networks that contain physical and signaling protein interactions that may be affected as a result of toxicant exposure. To build these networks, we developed the EdgeLinker algorithm, which efficiently finds short paths in the interactome that connect the receptors to TFs for each toxicant. We performed multiple evaluations and found evidence suggesting that these signaling networks capture biologically relevant effects of toxicants. To aid in dissemination and interpretation, interactive visualizations of these networks are available at http://graphspace.org.

The CD47-SIRPα axis is a promising target for cancer immunotherapies

Cluster of differentiation 47(CD47) is a transmembrane protein that is ubiquitously found on the surface of many cells in the body and uniquely overexpressed by both solid and hematologic malignant cells. CD47 interacts with signal-regulatory protein α (SIRPα), to trigger a "don't eat me" signal and thereby achieve cancer immune escape by inhibiting macrophage-mediated phagocytosis. Thus, blocking the CD47-SIRPα phagocytosis checkpoint, for release of the innate immune system, is a current research focus. Indeed, targeting the CD47-SIRPα axis as a cancer immunotherapy has shown promising efficacies in pre-clinical outcomes. Here, we first reviewed the origin, structure, and function of the CD47-SIRPα axis. Then, we reviewed its role as a target for cancer immunotherapies, as well as the factors regulating CD47-SIRPα axis-based immunotherapies. We specifically focused on the mechanism and progress of CD47-SIRPα axis-based immunotherapies and their combination with other treatment strategies. Finally, we discussed the challenges and directions for future research and identified potential CD47-SIRPα axis-based therapies that are suitable for clinical application.

Crosstalk between cholesterol metabolism and psoriatic inflammation

Psoriasis is a chronic autoinflammatory skin disease associated with multiple comorbidities, with a prevalence ranging from 2 to 3% in the general population. Decades of preclinical and clinical studies have revealed that alterations in cholesterol and lipid metabolism are strongly associated with psoriasis. Cytokines (tumor necrosis factor-α (TNF-α), interleukin (IL)-17), which are important in the pathogenesis of psoriasis, have been shown to affect cholesterol and lipid metabolism. Cholesterol metabolites and metabolic enzymes, on the other hand, influence not only the biofunction of keratinocytes (a primary type of cell in the epidermis) in psoriasis, but also the immune response and inflammation. However, the relationship between cholesterol metabolism and psoriasis has not been thoroughly reviewed. This review mainly focuses on cholesterol metabolism disturbances in psoriasis and their crosstalk with psoriatic inflammation.

Simvastatin Inhibits Brucella abortus Invasion into RAW 264.7 Cells through Suppression of the Mevalonate Pathway and Promotes Host Immunity during Infection in a Mouse Model

Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase and has been found to have protective effects against several bacterial infections. In this study, we investigate the effects of simvastatin treatment on RAW 264.7 macrophage cells and ICR mice against Brucella (B.) abortus infections. The invasion assay revealed that simvastatin inhibited the Brucella invasion into macrophage cells by blocking the mevalonic pathway. The treatment of simvastatin enhanced the trafficking of Toll-like receptor 4 in membrane lipid raft microdomains, accompanied by the increased phosphorylation of its downstream signaling pathways, including JAK2 and MAPKs, upon =Brucella infection. Notably, the suppressive effect of simvastatin treatment on Brucella invasion was not dependent on the reduction of cholesterol synthesis but probably on the decline of farnesyl pyrophosphate and geranylgeranyl pyrophosphate synthesis. In addition to a direct brucellacidal ability, simvastatin administration showed increased cytokine TNF-α and differentiation of CD8+ T cells, accompanied by reduced bacterial survival in spleens of ICR mice. These data suggested the involvement of the mevalonate pathway in the phagocytosis of B. abortus into RAW 264.7 macrophage cells and the regulation of simvastatin on the host immune system against Brucella infections. Therefore, simvastatin is a potential candidate for studying alternative therapy against animal brucellosis.

Therapeutic effects of statins on osteoarthritis: A review

Osteoarthritis (OA) is a progressive joint disease. The etiology of OA is considered to be multifactorial. Currently, there is no definitive treatment for OA, and the existing treatments are not very effective. Hypercholesterolemia is considered a novel risk factor for the development of OA. Statins act as a competitive inhibitor of the β-hydroxy β-methylglutaryl-CoA (HMG-CoA) reductase and are widely used to manage hypercholesterolemia. Inhibition of HMG-CoA reductase results in reduced synthesis of a metabolite named mevalonate, thereby reducing cholesterol biosynthesis in subsequent steps. By this mechanism, statins such as atorvastatin and simvastatin could potentially have a preventive impact on joint cartilage experiencing osteoarthritic deterioration by reducing serum cholesterol levels. Atorvastatin can protect cartilage degradation following interleukin-1β-stimulation. Atorvastatin stimulates the STAT1-caspase-3 signaling pathway that was shown to be responsible for its anti-inflammatory effects on the knee joint. Simvastatin had chondroprotective effects on OA in vitro by reducing matrix metalloproteinases expression patterns. In this study, we tried to review the therapeutic effects of statins on OA.

Statins and Bempedoic Acid: Different Actions of Cholesterol Inhibitors on Macrophage Activation

Statins represent the most prescribed class of drugs for the treatment of hypercholesterolemia. Effects that go beyond lipid-lowering actions have been suggested to contribute to their beneficial pharmacological properties. Whether and how statins act on macrophages has been a matter of debate. In the present study, we aimed at characterizing the impact of statins on macrophage polarization and comparing these to the effects of bempedoic acid, a recently registered drug for the treatment of hypercholesterolemia, which has been suggested to have a similar beneficial profile but fewer side effects. Treatment of primary murine macrophages with two different statins, i.e., simvastatin and cerivastatin, impaired phagocytotic activity and, concurrently, enhanced pro-inflammatory responses upon short-term lipopolysaccharide challenge, as characterized by an induction of tumor necrosis factor (TNF), interleukin (IL) 1β, and IL6. In contrast, no differences were observed under long-term inflammatory (M1) or anti-inflammatory (M2) conditions, and neither inducible NO synthase (iNOS) expression nor nitric oxide production was altered. Statin treatment led to extracellular-signal regulated kinase (ERK) activation, and the pro-inflammatory statin effects were abolished by ERK inhibition. Bempedoic acid only had a negligible impact on macrophage responses when compared with statins. Taken together, our data point toward an immunomodulatory effect of statins on macrophage polarization, which is absent upon bempedoic acid treatment.

Exploring biological efficacy of novel benzothiazole linked 2,5-disubstituted-1,3,4-oxadiazole hybrids as efficient α-amylase inhibitors: Synthesis, characterization, inhibition, molecular docking, molecular dynamics and Monte Carlo based QSAR studies

In an effort to explore a class of novel antidiabetic agents, we have made an effort to synergize the α-amylase inhibitory potential of 1,3-benzothiazole and 1,3,4-oxadiazole scaffolds by combining the two into a single structure via an ether linkage. The structure of synthesized benzothiazole clubbed oxadiazole derivatives are established by different spectral techniques. The synthesized hybrids are evaluated for their in vitro inhibitory potential against α-amylase. Compound 8f is found to be the most potent with a significant inhibition (87.5 ± 0.74% at 50 μg/mL, 82.27 ± 1.85% at 25 μg/mL and 79.94 ± 1.88% at 12.5 μg/mL) when compared to positive control acarbose (77.96 ± 2.06%, 71.17 ± 0.60%, 67.24 ± 1.16% at 50 μg/mL, 25 μg/mL and 12.5 μg/mL concentration). Molecular docking of the most potent enzyme inhibitor, 8f, shows promising interaction with the binding site of biological macromolecule Aspergillus oryzae α-amylase (PDB ID: 7TAA) and human pancreatic α-amylase (PDB ID: 3BAJ). To a step further, in-depth QSAR studies show a significant correlation between the experimental and the predicted inhibitory activities with the best R_validation²= 0.8701. The developed QSAR model can provide ample information about the structural features responsible for the increase and decrease of inhibitory activity. The mechanistic interpretation of the structure-activity relationship (SAR) is done with the help of combined computational calculations i.e. molecular docking and QSAR. Finally, molecular dynamic simulations are performed to get an insight into the binding mode of the most potent derivative with α-amylase from A. oryzae (PDB ID: 7TAA) and human pancreas (PDB ID: 3BAJ).

Statins: Neurobiological underpinnings and mechanisms in mood disorders

Statins (3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors) treat dyslipidaemia and cardiovascular disease by inhibiting cholesterol biosynthesis. They also have immunomodulatory and anti-inflammatory properties. Beyond cardiovascular disease, cholesterol and inflammation appear to be components of the pathogenesis and pathophysiology of neuropsychiatric disorders. Statins may therefore afford some therapeutic benefit in mood disorders. In this paper, we review the pathophysiology of mood disorders with a focus on pharmacologically relevant pathways, using major depressive disorder and bipolar disorder as exemplars. Statins are discussed in the context of these disorders, with particular focus on the putative mechanisms involved in their anti-inflammatory and immunomodulatory effects. Recent clinical data suggest that statins may have antidepressant properties, however given their interactions with many known biological pathways, it has not been fully elucidated which of these are the major determinants of clinical outcomes in mood disorders. Moreover, it remains unclear what the appropriate dose, or appropriate patient phenotype for adjunctive treatment may be. High quality randomised control trials in concert with complementary biological investigations are needed if the potential clinical effects of statins on mood disorders, as well as their biological correlates, are to be better understood.

Repurposing Immunomodulatory Drugs to Combat Tuberculosis

Tuberculosis (TB) is an infectious disease caused by an obligate intracellular pathogen, Mycobacterium tuberculosis (M.tb) and is responsible for the maximum number of deaths due to a single infectious agent. Current therapy for TB, Directly Observed Treatment Short-course (DOTS) comprises multiple antibiotics administered in combination for 6 months, which eliminates the bacteria and prevents the emergence of drug-resistance in patients if followed as prescribed. However, due to various limitations viz., severe toxicity, low efficacy and long duration; patients struggle to comply with the prescribed therapy, which leads to the development of drug resistance (DR). The emergence of resistance to various front-line anti-TB drugs urgently require the introduction of new TB drugs, to cure DR patients and to shorten the treatment course for both drug-susceptible and resistant populations of bacteria. However, the development of a novel drug regimen involving 2-3 new and effective drugs will require approximately 20-30 years and huge expenditure, as seen during the discovery of bedaquiline and delamanid. These limitations make the field of drug-repurposing indispensable and repurposing of pre-existing drugs licensed for other diseases has tremendous scope in anti-DR-TB therapy. These repurposed drugs target multiple pathways, thus reducing the risk of development of drug resistance. In this review, we have discussed some of the repurposed drugs that have shown very promising results against TB. The list includes sulfonamides, sulfanilamide, sulfadiazine, clofazimine, linezolid, amoxicillin/clavulanic acid, carbapenems, metformin, verapamil, fluoroquinolones, statins and NSAIDs and their mechanism of action with special emphasis on their immunomodulatory effects on the host to attain both host-directed and pathogen-targeted therapy. We have also focused on the studies involving the synergistic effect of these drugs with existing TB drugs in order to translate their potential as adjunct therapies against TB.

Anti-tuberculous Effects of Statin Therapy: A Review of Literature

Tuberculosis (TB) is a chronic infection caused by Mycobacterium tuberculosis (M. TB). It is transmitted through respiratory droplets. Increased cholesterol level is a predisposing factor for TB. M. TB uses cholesterol in the host macrophage membranes to bind and enter the macrophages. Statins are the drugs that are prescribed to hyperlipidemic patients to maintain their lipid levels in the normal range, thereby reducing the risk of stroke and cardiovascular events. Moreover, statins aid in reducing the levels of cholesterol in human macrophages. Therefore, a reduction in the membrane cholesterol minimizes the entry of TB pathogen inside macrophages. Furthermore, acting as vitamin D3 analogs and positively influencing pancreatic beta-cell function in a chronic diabetic state, statins minimize the occurrence of M. TB infection among diabetic population as well. This review aims to provide a comprehensive detail of all in vitro, in vivo, and retrospective studies that investigated the effects of statins in relation to the prevention or treatment of TB infection.

Targeting defective pulmonary innate immunity - A new therapeutic option?

Chronic pulmonary conditions now account for 1 in 15 deaths in the US and mortality is increasing. Chronic obstructive pulmonary disease (COPD) is due to become the 3rd largest cause of mortality by 2030 and mortality from other respiratory conditions such as asthma, idiopathic pulmonary fibrosis and cystic fibrosis are not reducing. There is an urgent need for novel therapies to address this problem as many of the current strategies targeting inflammation are not sufficient. The innate immune system of the lung is an important defence against invading pathogens, but in many chronic pulmonary diseases, this system mounts an inappropriate response. In COPD, macrophages are increased in number, but fail to clear pathogens correctly and become highly activated. This leads to increased damage and remodelling of the airways. In idiopathic fibrosis, there is a switch of macrophage phenotype to a cell that promotes abnormal repair. Neutrophils also display dysfunction in COPD where aberrant migratory profiles may lead to increased damage to lung tissue and emphysema; while in cystic fibrosis the proteolytic lung environment damages neutrophil receptors leading to ineffective phagocytosis and migration. Targeting the innate immune system to restore 'normal function' could have enormous benefits. Improving phagocytosis of pathogens could reduce exacerbations and hence the associated decline in lung function, and novel therapeutics such as sulforaphane appear to do this in vitro. Other natural products such as resveratrol and derivatives also have anti-inflammatory properties. Statins have traditionally been used to manage cholesterol levels in hypercholesterolaemia, however these molecules also have beneficial effects on the innate immune cells. Statins have been shown to be anti-inflammatory and restore aberrant neutrophil chemotaxis in aged cells. Other possible agents that may be efficacious are senolytics. These compounds include natural products such as quercetin which have anti-inflammatory properties but can also suppress viral replication. As viruses have been shown to suppress phagocytosis of macrophages, it is possible that these compounds could have benefit during viral exacerbations to protect this innate response. These compounds demonstrate that it is possible to address defective innate responses in the lung but a better understanding of the mechanisms driving defective innate immunity in pulmonary disease may lead to improved therapeutics.

Statin use and risk of tuberculosis: a systemic review of observational studies

OBJECTIVES

Statin intake may be linked with a lower risk of several infectious diseases, including tuberculosis, which is an important cause of mortality worldwide. The aim of this study was to investigate the definite impacts of statins on the risk of tuberculosis (TB) in diabetic patients and in the general population.

METHODS

Four databases were thoroughly searched from inception up to July 2019. Articles in any language were included if they assessed and clarified statin intake, presented the risk of TB in diabetes mellitus (DM) patients or the general population, and reported odds ratios (ORs), relative risks (RRs), or hazard ratios (HRs) or contained data for relevant calculation. RRs with 95% confidence intervals (CIs) were pooled using random-effects models regardless of heterogeneity quantified by Cochran's Q and I² statistics.

RESULTS

Six articles reporting observational studies involving 2 073 968 patients were included. Four reported cohort studies, one a nested case-control study, and one was an abstract. Statin use significantly reduced the risk of TB in DM patients by 22% (pooled RR 0.78, 95% CI 0.63-0.95), with severe heterogeneity (I² = 76.1%). Statin intake also significantly decreased the risk of TB in the general population by 40% (pooled RR 0.60, 95% CI 0.50-0.71), with severe heterogeneity (I² = 57.7%).

CONCLUSIONS

Statin use is related to a considerably lower risk of TB in both DM patients and the general population. However, these conclusions should be interpreted with caution given the possible remaining confounding, and call for large-size and multicenter randomized controlled studies in the future.

Drug Delivery with Polymeric Nanocarriers-Cellular Uptake Mechanisms

Nanocarrier-based systems hold a promise to become “Dr. Ehrlich’s Magic Bullet” capable of delivering drugs, proteins and genetic materials intact to a specific location in an organism down to subcellular level. The key question, however, how a nanocarrier is internalized by cells and how its intracellular trafficking and the fate in the cell can be controlled remains yet to be answered. In this review we survey drug delivery systems based on various polymeric nanocarriers, their uptake mechanisms, as well as the experimental techniques and common pathway inhibitors applied for internalization studies. While energy-dependent endocytosis is observed as the main uptake pathway, the integrity of a drug-loaded nanocarrier upon its internalization appears to be a seldomly addressed problem that can drastically affect the uptake kinetics and toxicity of the system in vitro and in vivo.

Effect of Atorvastatin on PM10-induced Cytokine Production by Human Alveolar Macrophages and Bronchial Epithelial Cells

Exposure to ambient air pollution particles (PM10) has been associated with increased cardiovascular morbidity and mortality. Inhaled pollutants induce a pulmonary and systemic inflammatory response that is thought to exacerbate cardiovascular disease. The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have been shown to have anti-inflammatory effects that could contribute to their beneficial effect in cardiovascular disease. The aim of this study is to determine the effects of statins on PM10-induced cytokine production in human bronchial epithelial cells (HBECs) and alveolar macrophages (AMs). Primary HBECs and AMs are obtained from resected human lung. Cells are pretreated with different concentrations of atorvastatin for 24 hours and then exposed to 100 μg/mL urban air pollution particles (EHC-93). Cytokine levels (interleukin-1β, interleukin-8, granulocyte-macrophage colonystimulating factor, interleukin-6, and tumor necrosis factor-α) are measured at messenger RNA and protein levels using real-time polymerase chain reaction and bead-based multiplex immunoassay, respectively. PM10 exposure increases production of these cytokines by both cell types. Atorvastatin attenuates PM10-induced messenger RNA expression and cytokine production by AMs but not by HBECs. It is concluded that statins can modulate the PM10-induced inflammatory response in the lung by reducing mediator production by AMs.

Adjunctive simvastatin for treatment-resistant depression: study protocol of a 12-week randomised controlled trial

BACKGROUND

A third of patients diagnosed with major depressive disorder (MDD) experience treatment-resistant depression (TRD). Relatively few pharmacological agents have established efficacy for TRD. Therefore, the evaluation of novel treatments for TRD is a pressing priority. Statins are pleiotropic agents and preclinical studies as well as preliminary clinical trials have suggested that these drugs may have antidepressant properties.AimsTo report on a protocol for a 12-week, randomised, double-blind, placebo-controlled trial of add-on treatment with simvastatin for patients meeting DSM-5 criteria for MDD who have failed to respond to at least two adequate trials with approved antidepressants. The trial has been registered with Clinicaltrials.gov in (ClinicalTrials.gov identifier: NCT03435744).

METHOD

After screening and randomisation to the two parallel arms of the trial, 75 patients will receive simvastatin and 75 patients will receive placebo as adjuncts to treatment as usual. The primary outcome is change in Montgomery-Åsberg Depression Rating Scale scores from baseline to week 12 and secondary outcomes include changes in scores on the 24-item Hamilton Rating Scale for Depression, the Clinical Global Impression scale, the 7-item Generalized Anxiety Disorder scale and change in body mass index from baseline to week 12. Assessments will take place at screening, baseline, and weeks 2, 4, 8 and 12. Checklists for adverse effects will be undertaken at each visit. Simvastatin (20 mg) will be given once daily. Other secondary outcomes include C-reactive protein and plasma lipids measured at baseline and week 12.

RESULTS

This trial will assess simvastatin's efficacy and tolerability as an add-on treatment option for patients with TRD and provide insights into its putative mechanisms of action.

CONCLUSIONS

As the first trial investigating the use of simvastatin as an augmentation strategy in patients with TRD, if the results indicate that adjuvant simvastatin is efficacious in reducing depressive symptoms, it will deliver immediate clinical benefit.Declaration of interestI.B.C. and N.H. have given lectures and advice to Eli Lilly, Bristol Myers Squibb, Lundbeck, Astra Zeneca and Janssen pharmaceuticals for which they or their employing institution have been reimbursed. R.R. and M.M.H. have received educational grants and support for academic meetings from Pfizer, Roche, Novartis and Nabiqasim. A.H.Y. has been commissioned to provide lectures and advice to all major pharmaceutical companies with drugs used in affective and related disorders. A.H.Y. has undertaken investigator-initiated studies from Astra Zeneca, Eli Lilly, Lundbeck and Wyeth. None of the companies have a financial interest in this research.

Entry of nanoparticles into cells: the importance of nanoparticle properties

Knowledge of the interactions between nanoparticles (NPs) and cell membranes is of great importance for the design of safe and efficient nanomedicines.

Population-Based Case-Control Study Assessing the Association between Statins Use and Pulmonary Tuberculosis in Taiwan

Background and Objectives: Little evidence is available about the relationship between statins use and pulmonary tuberculosis in Taiwan. The aim of the study was to explore this issue.

Methods: Using the database of the Taiwan National Health Insurance Program, we conducted a population-based case-control study to identify 8,236 subjects aged 20 years and older with newly diagnosed pulmonary tuberculosis from 2000 to 2013 as the cases. We randomly selected 8,236 sex-matched and age-matched subjects without pulmonary tuberculosis as the controls. Subjects who had at least one prescription of statins before the index date were defined as “ever use.” Subjects who never had one prescription of statins before the index date were defined as “never use.” The odds ratio (OR) and 95% confidence interval (CI) for pulmonary tuberculosis associated with statins use was estimated by a multivariable logistic regression model.

Results: After adjustment for co-variables, the adjusted OR of pulmonary tuberculosis was 0.67 for subjects with ever use of statins (95% CI 0.59, 0.75). In a sub-analysis, the adjusted ORs of pulmonary tuberculosis were 0.87 (95% CI 0.69, 1.10) for subjects with cumulative duration of statins use <3 months, 0.77 (95% CI 0.58, 1.03) for 3–6 months, and 0.59 (95% CI 0.51, 0.68) for ≥6 months, compared with subjects with never use of statins.

Conclusions: Statins use correlates with a small but statistically significant risk reduction of pulmonary tuberculosis. The protective effect is stronger for longer duration of statins use. Due to a case-control design, a causal-relationship cannot be established in our study. A prospective cohort design is needed to confirm our findings.

The PathLinker app: Connect the dots in protein interaction networks

PathLinker is a graph-theoretic algorithm for reconstructing the interactions in a signaling pathway of interest. It efficiently computes multiple short paths within a background protein interaction network from the receptors to transcription factors (TFs) in a pathway. We originally developed PathLinker to complement manual curation of signaling pathways, which is slow and painstaking. The method can be used in general to connect any set of sources to any set of targets in an interaction network. The app presented here makes the PathLinker functionality available to Cytoscape users. We present an example where we used PathLinker to compute and analyze the network of interactions connecting proteins that are perturbed by the drug lovastatin.

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.

Cellular uptake and dynamics of unlabeled freestanding silicon nanowires

The ability to seamlessly merge electronic devices with biological systems at the cellular length scale is an exciting prospect for exploring new fundamental cell biology and in designing next-generation therapeutic devices. Semiconductor nanowires are well suited for achieving this goal because of their intrinsic size and wide range of possible configurations. However, current studies have focused primarily on delivering substrate-bound nanowire devices through mechanical abrasion or electroporation, with these bulkier substrates negating many of the inherent benefits of using nanoscale materials. To improve on this, an important next step is learning how to distribute these devices in a drug-like fashion, where cells can naturally uptake and incorporate these electronic components, allowing for truly noninvasive device integration. We show that silicon nanowires (SiNWs) can potentially be used as such a system, demonstrating that label-free SiNWs can be internalized in multiple cell lines (96% uptake rate), undergoing an active "burst-like" transport process. Our results show that, rather than through exogenous manipulation, SiNWs are internalized primarily through an endogenous phagocytosis pathway, allowing cellular integration of these materials. To study this behavior, we have developed a robust set of methodologies for quantitatively examining high-aspect ratio nanowire-cell interactions in a time-dependent manner on both single-cell and ensemble levels. This approach represents one of the first dynamic studies of semiconductor nanowire internalization and offers valuable insight into designing devices for biomolecule delivery, intracellular sensing, and photoresponsive therapies.

Changes in macrophage function modulated by the lipid environment

Macrophages (Mφs) play a critical role in the defense against pathogens, orchestrating the inflammatory response during injury and maintaining tissue homeostasis. During these processes, macrophages encounter a variety of environmental conditions that are likely to change their gene expression pattern, which modulates their function. In this study, we found that murine Mφs displayed two different subpopulations characterized by differences in morphologies, expression of surface markers and phagocytic capacity under non-stimulated conditions. These two subpopulations could be recapitulated by changes in the culture conditions. Thus, Mφs grown in suspension in the presence of serum were highly phagocytic, whereas subtraction of serum resulted in rapid attachment and reduced phagocytic activity. The difference in phagocytosis between these subpopulations was correlated with the expression levels of FcγR. These two cell subpopulations also differed in their responses to LPS and the expression of surface markers, including CD14, CD86, scavenger receptor A1, TLR4 and low-density lipoprotein receptor. Moreover, we found that the lipid/cholesterol content in the culture medium mediated the differences between these two cell subpopulations. Thus, we described a mechanism that modulates Mφ function depending on the exposure to lipids within their surrounding microenvironment.

Nature and nurture in atherosclerosis: The roles of acylcarnitine and cell membrane-fatty acid intermediates

Macrophages recycle components of dead cells, including cell membranes. When quantities of lipids from cell membranes of dead cells exceed processing capacity, phospholipid and cholesterol debris accumulate as atheromas. Plasma lipid profiles, particularly HDL and LDL cholesterol, are important tools to monitor atherosclerosis risk. Membrane lipids are exported, as triglycerides or phospholipids, or as cholesterol or cholesterol esters, via lipoproteins for disposal, for re-use in cell membranes, or for fat storage. Alternative assays evaluate other aspects of lipid pathology. A key process underlying atherosclerosis is backup of macrophage fatty acid catabolism. This can be quantified by accumulation of acylcarnitine intermediates in extracellular fluid, a direct assay of adequacy of β-oxidation to deal with membrane fatty acid recycling. Further, membranes of somatic cells, such as red blood cells (RBC), incorporate fatty acids that reflect dietary intake. Changes in RBC lipid composition occur within days of ingesting modified fats. Since diets with high saturated fat content or artificial trans-fatty acids promote atherosclerosis, RBC lipid content shifts occur with atherosclerosis, and can show cellular adaptation to pathologically stiff membranes by increased long-chain doubly unsaturated fatty acid production. Additional metabolic changes with atherosclerosis of potential utility include inflammatory cytokine production, modified macrophage signaling pathways, and altered lipid-handling enzymes. Even after atherosclerotic lesions appear, approaches to minimize macrophage overload by reducing rate of fat metabolism are promising. These include preventive measures, and drugs including statins and the newer PCSK9 inhibitors. New cell-based biochemical and cytokine assays provide data to prevent or monitor atherosclerosis progression.

Statin, calcium channel blocker and Beta blocker therapy may decrease the incidence of tuberculosis infection in elderly Taiwanese patients with type 2 diabetes

Background: It is well known that diabetes mellitus impairs immunity and therefore is an independent risk factor for tuberculosis. However, the influence of associated metabolic factors, such as hypertension, dyslipidemia and gout has yet to be confirmed. This study aimed to investigate whether the strong association between tuberculosis and diabetes mellitus is independent from the influence of hypertension and dyslipidemia, and its treatment in elderly Taiwanese patients. Methods: A total of 27,958 patients aged more than 65 years were identified from the National Health Insurance Research Database (NIHRD) in 1997 and were followed from 1998 to 2009. The demographic characteristics between the patients with and without diabetes were analyzed using the χ2 test. A total of 13,981 patients with type 2 diabetes were included in this study. Cox proportional hazard regression models were used to determine the independent effects of diabetes on the risk of tuberculosis. Results: After adjusting for age, sex, other co-morbidities and medications, calcium channel blocker, beta blocker and statin users had a lower independent association, with risk ratios of 0.76 (95% CI, 0.58–0.98), 0.72 (95% CI, 0.58–0.91) and 0.76 (95% CI, 0.60–0.97), respectively. Conclusion: Calcium channel blocker, beta blocker and statin therapy may decrease the incidence of tuberculosis infection in elderly Taiwanese patients with type 2 diabetes.

Itraconazole, a commonly used antifungal, inhibits Fcγ receptor-mediated phagocytosis: alteration of Fcγ receptor glycosylation and gene expression

Itraconazole (ICZ) is commonly used for the treatment of fungal infections, particularly in immunocompromised patients. In addition, ICZ has been recently found to have antiangiogenic effects and is currently being tested as a new chemotherapeutic agent in several cancer clinical trials. We have previously shown that ICZ impaired complex N-linked glycosylation processing, leading to the accumulation of high-mannose glycoproteins on the surface of macrophages (Møs). This investigation was directed at determining the effects of ICZ on phagocytosis as a major function of Møs. We found a significant decrease in the phagocytosis of opsonized bacterial particles in ICZ-treated murine Møs in comparison with nontreated Møs. Furthermore, the impairment of phagocytosis was associated with a decrease in cell surface expression of Fcγ receptors (FcγRs) as well as alteration of their glycosylation pattern. Concomitantly, a reduction in all three isoforms of the FcγR family (i.e., Fcgr1, Fcgr2, and Fcgr3) mRNA levels was observed after incubation with ICZ. The effect of ICZ on phagocytosis and FcγR expression was reversed by addition of low-density lipoprotein. These studies indicate that ICZ treatment certainly has a dramatic effect on macrophage function, which could result in a potential impairment of the immune system';s ability to respond to pathogens and may lead to an elevated incidence of infections.

Statin treatment affects cytokine release and phagocytic activity in primary cultured microglia through two separable mechanisms

Background

As the primary immune cells of the central nervous system, microglia contribute to development, homeostasis, and plasticity of the central nervous system, in addition to their well characterized roles in the foreign body and inflammatory responses. Increasingly, inappropriate activation of microglia is being reported as a component of inflammation in neurodegenerative and neuropsychiatric disorders. The statin class of cholesterol-lowering drugs have been observed to have anti-inflammatory and protective effects in both neurodegenerative diseases and ischemic stroke, and are suggested to act by attenuating microglial activity.

Results

We sought to investigate the effects of simvastatin treatment on the secretory profile and phagocytic activity of primary cultured rat microglia, and to dissect the mechanism of action of simvastatin on microglial activity. Simvastatin treatment altered the release of cytokines and trophic factors from microglia, including interleukin-1-β, tumour necrosis factor-α, and brain derived neurotrophic factor in a cholesterol-dependent manner. Conversely, simvastatin inhibited phagocytosis in microglia in a cholesterol-independent manner.

Conclusions

The disparity in cholesterol dependence of cytokine release and phagocytosis suggests the two effects occur through distinct molecular mechanisms. These two pathways may provide an opportunity for further refinement of pharmacotherapies for neuroinflammatory, neurodegenerative, and neuropsychiatric disorders.

Statin therapy may prevent development of tuberculosis in diabetic state

Host cholesterol is widely getting recognized as an important factor in the pathogenesis of tuberculosis in multiple ways. Therefore it is logically expected that cholesterol reduction by statins is going to have a positive outcome in the context of tuberculosis management. But at the present moment statin therapy in non diabetic individuals is believed to pose a small risk for development of diabetes mellitus, a prevalent disease throughout the globe that is known to be associated with tuberculosis infection. Consequently, in diabetic individuals statins are commonly prescribed drugs for multiple positive outcomes. Therefore it seems that statin therapy in diabetes mellitus has the potential to prevent the increased occurrence of tuberculosis in diabetic state.

Short term statin treatment improves survival and differentially regulates macrophage-mediated responses to Staphylococcus aureus

Staphylococcus aureus is the most prevalent etiologic agent of sepsis. Statins, primarily prescribed for their cholesterol-lowering capabilities, may be beneficial for treating sepsis due to their anti-inflammatory properties. This study examined the effect of low dose, short term simvastatin pretreatment in conjunction with antibiotic treatment on host survival and demonstrated that pretreatment with simvastatin increased survival of C57BL/6 mice in response to S. aureus infection. In vitro studies revealed that short term simvastatin pretreatment did not reduce S. aureus-stimulated expression of surface proteins necessary for macrophage presentation of antigen to T cells, such as MHC Class II and costimulatory molecules CD80 and CD86, but did reduce both basal and S. aureus-stimulated levels of C5aR. Additionally, this work demonstrated the ability of simvastatin to dampen macrophage responses initiated not only by bacteria directly but by membrane vesicles shed in response to infection, revealing a new mechanism of immune modulation by statins. These data demonstrate the ability of short term simvastatin pretreatment to modulate immune responses and identify new insights into the underlying mechanisms of the anti-inflammatory properties of simvastatin that may decrease the pathophysiological effects leading to sepsis.

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.

Surface acoustic waves enhance neutrophil killing of bacteria

Biofilms are structured communities of bacteria that play a major role in the pathogenicity of bacteria and are the leading cause of antibiotic resistant bacterial infections on indwelling catheters and medical prosthetic devices. Failure to resolve these biofilm infections may necessitate the surgical removal of the prosthetic device which can be debilitating and costly. Recent studies have shown that application of surface acoustic waves to catheter surfaces can reduce the incidence of infections by a mechanism that has not yet been clarified. We report here the effects of surface acoustic waves (SAW) on the capacity of human neutrophils to eradicate S. epidermidis bacteria in a planktonic state and within biofilms. Utilizing a novel fibrin gel system that mimics a tissue-like environment, we show that SAW, at an intensity of 0.3 mW/cm², significantly enhances human neutrophil killing of S. epidermidis in a planktonic state and within biofilms by enhancing human neutrophil chemotaxis in response to chemoattractants. In addition, we show that the integrin CD18 plays a significant role in the killing enhancement observed in applying SAW. We propose from out data that this integrin may serve as mechanoreceptor for surface acoustic waves enhancing neutrophil chemotaxis and killing of bacteria.

Serum allograft inflammatory factor-1 is a novel marker for diabetic nephropathy

AIMS

Recent studies have identified macrophage-mediated injury as an important component in the development of diabetic nephropathy. The aim of this study was to investigate the correlations between serum allograft inflammatory factor-1 (AIF-1) concentration, which is a marker of activated macrophages, and diabetic nephropathy.

METHODS

Serum AIF-1 concentrations were measured in 284 patients with type 2 diabetes. We evaluated relationships of serum AIF-1 concentrations to degree of urinary albumin excretion (UAE) or estimated glomerular filtration rate (eGFR) in univariate and multivariate linear regression analyses.

RESULTS

Serum AIF-1 concentrations positively correlated with logarithm of UAE (r=0.260, P<0.0001), whereas serum AIF-1 concentrations inversely correlated with eGFR (r=-0.312, P<0.0001). Mean serum AIF-1 concentration was higher in patients with macroalbuminuria than that in patients with normoalbuminuria (P=0.0001) or that in patients with microalbuminuria (P=0.0093). In multivariate linear regression analyses, serum AIF-1 concentrations were independently correlated with logarithm of UAE (β=0.213, P=0.0120) and with eGFR (β=-0.286, P=0.0011).

CONCLUSIONS

Serum AIF-1 concentration correlated with albuminuria and eGFR in patients with type 2 diabetes and it could be a marker of diabetic nephropathy as well as activated macrophages.

Ligation of macrophage Fcγ receptors recapitulates the gene expression pattern of vulnerable human carotid plaques

Stroke is a leading cause of death in the United States. As ∼60% of strokes result from carotid plaque rupture, elucidating the mechanisms that underlie vulnerability is critical for therapeutic intervention. We tested the hypothesis that stable and vulnerable human plaques differentially express genes associated with matrix degradation. Examination established that femoral, and the distal region of carotid, plaques were histologically stable while the proximal carotid plaque regions were vulnerable. Quantitative RT-PCR was used to compare expression of 22 genes among these tissues. Distal carotid and femoral gene expression was not significantly different, permitting the distal carotid segments to be used as a paired control for their corresponding proximal regions. Analysis of the paired plaques revealed differences in 16 genes that impact plaque stability: matrix metalloproteinases (MMP, higher in vulnerable), MMP modulators (inhibitors: lower, activators: higher in vulnerable), activating Fc receptors (FcγR, higher in vulnerable) and FcγR signaling molecules (higher in vulnerable). Surprisingly, the relative expression of smooth muscle cell and macrophage markers in the three plaque types was not significantly different, suggesting that macrophage distribution and/or activation state correlates with (in)stability. Immunohistochemistry revealed that macrophages and smooth muscle cells localize to distinct and non-overlapping regions in all plaques. MMP protein localized to macrophage-rich regions. In vitro, treatment of macrophages with immune complexes, but not oxidized low density lipoprotein, C-reactive protein, or TNF-α, induced a gene expression profile similar to that of the vulnerable plaques. That ligation of FcγR recapitulates the pattern of gene expression in vulnerable plaques suggests that the FcγR → macrophage activation pathway may play a greater role in human plaque vulnerability than previously appreciated.

The Role of Immune Complexes in Atherogenesis

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis. Immune complexes (ICs) may form between these antigens and autoantibodies and via Fc receptor signaling and complement activation may modulate the inflammation in atherosclerosis. Antibody isotype may direct the role that ICs play in atherogenesis, immunoglobulin G (IgG) being potentially pro-atherogenic and immunoglobulin M (IgM) playing a protective role. Therapeutic options targeting complement activation and those which are potentially Fc-receptor mediated have been investigated in animal models, though targeting Fc receptor signaling is an area that needs further investigation.

Apolipoprotein A-I mimetic 4F alters the function of human monocyte-derived macrophages

HDL and its major protein component apolipoprotein A-I (apoA-I) exert anti-inflammatory effects, inhibit monocyte chemotaxis/adhesion, and reduce vascular macrophage content in inflammatory conditions. In this study, we tested the hypothesis that the apoA-I mimetic 4F modulates the function of monocyte-derived macrophages (MDMs) by regulating the expression of key cell surface receptors on MDMs. Primary human monocytes and THP-1 cells were treated with 4F, apoA-I, or vehicle for 7 days and analyzed for expression of cell surface markers, adhesion to human endothelial cells, phagocytic function, cholesterol efflux capacity, and lipid raft organization. 4F and apoA-I treatment decreased the expression of HLA-DR, CD86, CD11b, CD11c, CD14, and Toll-like receptor-4 (TLR-4) compared with control cells, suggesting the induction of monocyte differentiation. Both treatments abolished LPS-induced mRNA for monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1 (MIP-1), regulated on activation, normal T-expressed and presumably secreted (RANTES), IL-6, and TNF-alpha but significantly upregulated LPS-induced IL-10 expression. Moreover, 4F and apoA-I induced a 90% reduction in the expression of CD49d, a ligand for the VCAM-1 receptor, with a concurrent decrease in monocyte adhesion (55% reduction) to human endothelial cells and transendothelial migration (34 and 27% for 4F and apoA-I treatments) compared with vehicle treatment. In addition, phagocytosis of dextran-FITC beads was inhibited by 4F and apoA-I, a response associated with reduced expression of CD32. Finally, 4F and apoA-I stimulated cholesterol efflux from MDMs, leading to cholesterol depletion and disruption of lipid rafts. These data provide evidence that 4F, similar to apoA-I, induces profound functional changes in MDMs, possibly due to differentiation to an anti-inflammatory phenotype.

Mechanisms of neutrophil accumulation in the lungs against bacteria

Bacterial lung diseases are a major cause of morbidity and mortality both in immunocompromised and in immunocompetent individuals. Neutrophil accumulation, a pathological hallmark of bacterial diseases, is critical to host defense, but may also cause acute lung injury/acute respiratory distress syndrome. Toll-like receptors, nucleotide-binding oligomerization domain (NOD)-like receptors, transcription factors, cytokines, and chemokines play essential roles in neutrophil sequestration in the lungs. This review highlights our current understanding of the role of these molecules in the lungs during bacterial infection and their therapeutic potential. We also discuss emerging data on cholesterol and ethanol as environmentally modifiable factors that may impact neutrophil-mediated pulmonary innate host defense. Understanding the precise molecular mechanisms leading to neutrophil influx in the lungs during bacterial infection is critical for the development of more effective therapeutic and prophylactic strategies to control the excessive host response to infection.

Impact of the FcgammaII-receptor on quartz uptake and inflammatory response by alveolar macrophages

The inflammatory response following particle inhalation is described as a key event in the development of lung diseases, e.g., fibrosis and cancer. The essential role of alveolar macrophages (AM) in the pathogenicity of particles through their functions in lung clearance and mediation of inflammation is well known. However, the molecular mechanisms and direct consequences of particle uptake are still unclear. Inhibition of different classic phagocytosis receptors by flow cytometry shows a reduction of the dose-dependent quartz particle (DQ12) uptake in the rat AM cell line NR8383. Thereby the strongest inhibitory effect was observed by blocking the FcgammaII-receptor (FcgammaII-R). Fluorescence immunocytochemistry, demonstrating FcgammaII-R clustering at particle binding sites as well as transmission electron microscopy, visualizing zippering mechanism-like morphological changes, confirmed the role of the FcgammaII-R in DQ12 phagocytosis. FcgammaII-R participation in DQ12 uptake was further strengthened by the quartz-induced activation of the Src-kinase Lyn, the phospho-tyrosine kinases Syk (spleen tyrosine kinase) and PI3K (phosphatidylinositol 3-kinase), as shown by Western blotting. Activation of the small GTPases Rac1 and Cdc42, shown by immunoprecipitation, as well as inhibition of tyrosine kinases, GTPases, or Rac1 provided further support for the role of the FcgammaII-R. Consistent with the uptake results, FcgammaII-R activation with its specific ligand caused a similar generation of reactive oxygen species and TNF-alpha release as observed after treatment with DQ12. In conclusion, our results indicate a major role of FcgammaII-R and its downstream signaling cascade in the phagocytosis of quartz particles in AM as well as in the associated generation and release of inflammatory mediators.

Atorvastatin and uptake of ultrasmall superparamagnetic iron oxide nanoparticles (Ferumoxtran-10) in human monocyte-macrophages: implications for magnetic resonance imaging

Ferumoxtran-10 is an ultrasmall superparamagnetic iron oxide nanoparticle potentially useful as a contrast material in magnetic resonance imaging for the diagnosis of inflammatory and degenerative disorders associated with high macrophage activity. In clinical trials, it is currently applied to monitor the effect of atorvastatin therapy on macrophage activity in human carotid plaques. A recent study reported the inhibition of iron oxide nanoparticle uptake in macrophages by lovastatin, an effect which could compromise the suitability of Ferumoxtran-10 as an MRI contrast material in patients on statin therapy. Therefore, we examined the effect of atorvastatin on human monocyte-macrophage uptake of Ferumoxtran-10 in vitro using biochemical assays, magnetic resonance imaging and transmission electron microscopy. Our study showed that non-toxic concentrations of atorvastatin did not affect the amount of Ferumoxtran-10 taken up by HMMs. Furthermore, the intracellular distribution of iron oxide nanoparticles and the resulting MRI signal intensities remained unchanged by statin treatment. These results were obtained using atorvastatin concentrations probably vastly exceeding those reached in patient plasma in vivo. Atorvastatin therapy itself is therefore unlikely to affect Ferumoxtran-10 based macrophage detection by MRI, a prerequisite for the use of this contrast material to monitor lesion macrophage burden during lipid-lowering therapy.

Pharmacological inhibition of endocytic pathways: is it specific enough to be useful?

Eukaryotic cells constantly form and internalize plasma membrane vesicles in a process known as endocytosis. Endocytosis serves a variety of housekeeping and specialized cellular functions, and it can be mediated by distinct molecular pathways. Among them, internalization via clathrin-coated pits, lipid raft/caveolae-mediated endocytosis and macropinocytosis/phagocytosis are the most extensively characterized. The major endocytic pathways are usually distinguished on the basis of their differential sensitivity to pharmacological/chemical inhibitors, although the possibility of nonspecific effects of such inhibitors is frequently overlooked. This review provides a critical evaluation of the selectivity of the most widely used pharmacological inhibitors of clathrin-mediated, lipid raft/caveolae-mediated endocytosis and macropinocytosis/phagocytosis. The mechanisms of actions of these agents are described with special emphasis on their reported side effects on the alternative internalization modes and the actin cytoskeleton. The most and the least-selective inhibitors of each major endocytic pathway are highlighted.

ROLE OF MACROPHAGES IN COMPLICATIONS OF TYPE 2 DIABETES

1. Macrophage accumulation is a feature of Type 2 diabetes and is associated with the development of diabetic complications (nephropathy, atherosclerosis, neuropathy and retinopathy). The present article reviews the current evidence that macrophages contribute to the complications of Type 2 diabetes. 2. Macrophage-depletion studies in rodent models have demonstrated a causal role for macrophages in the development of diabetic complications. 3. Components of the diabetic milieu (high glucose, advanced glycation end-products and oxidized low-density lipoprotein) promote macrophage accumulation (via induction of chemokines and adhesion molecules) and macrophage activation within diabetic tissues. 4. Macrophages mediate diabetic injury through a variety of mechanisms, including production of reactive oxygen species, cytokines and proteases, which result in tissue damage leading to sclerosis. 5. A number of existing and experimental therapies can indirectly reduce macrophage-mediated injury in diabetic complications. The present article discusses the use of these therapies, given alone and in combination, in suppressing macrophage accumulation and activity. 6. In conclusion, current evidence supports a critical role for macrophages in the evolution of diabetic complications. Present therapies are limited in slowing the progression of macrophage-mediated injury. Novel strategies that are more specific at targeting macrophages may provide better protection against the development of Type 2 diabetic complications.

Lipid metabolism and dynamics during phagocytosis

Phagocytosis, the engulfment of particles, mediates the elimination of invading pathogens as well as the clearance of apoptotic cells. Ingested particles reside within a vacuole or phagosome, where they are eventually destroyed and digested. The phagosomal lumen acquires microbicidal and digestive properties through interaction with various components of the endocytic pathway, a process known as maturation. Lipids are known to have numerous roles in phagosome formation and maturation; recent developments in the design of lipid-specific probes and in high-resolution imaging have revealed that lipids, notably phosphoinositides, are involved in signaling, actin assembly and the recruitment of molecular motors to sites of ingestion. In addition, phosphoinositides and other lipids also regulate multiple membrane budding, fission and fusion events required for maturation.

Lovastatin enhances clearance of apoptotic cells (efferocytosis) with implications for chronic obstructive pulmonary disease

Statins are potent, cholesterol-lowering agents with newly appreciated, broad anti-inflammatory properties, largely based upon their ability to block the prenylation of Rho GTPases, including RhoA. Because phagocytosis of apoptotic cells (efferocytosis) is a pivotal regulator of inflammation, which is inhibited by RhoA, we sought to determine whether statins enhanced efferocytosis. The effect of lovastatin on efferocytosis was investigated in primary human macrophages, in the murine lung, and in human alveolar macrophages taken from patients with chronic obstructive pulmonary disease. In this study, we show that lovastatin increased efferocytosis in vitro in an 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase-dependent manner. Lovastatin acted by inhibiting both geranylgeranylation and farnesylation, and not by altering expression of key uptake receptors or by increasing binding of apoptotic cells to phagocytes. Lovastatin appeared to exert its positive effect on efferocytosis by inhibiting RhoA, because it 1) decreased membrane localization of RhoA, to a greater extent than Rac-1, and 2) prevented impaired efferocytosis by lysophosphatidic acid, a potent inducer of RhoA. Finally, lovastatin increased efferocytosis in the naive murine lung and ex vivo in chronic obstructive pulmonary disease alveolar macrophages in an HMG-CoA reductase-dependent manner. These findings indicate that statins enhance efferocytosis in vitro and in vivo, and suggest that they may play an important therapeutic role in diseases where efferocytosis is impaired and inflammation is dysregulated.

Cytokine Secretion via Cholesterol-rich Lipid Raft-associated SNAREs at the Phagocytic Cup

Lipopolysaccharide-activated macrophages rapidly synthesize and secrete tumor necrosis factor alpha (TNFalpha) to prime the immune system. Surface delivery of membrane carrying newly synthesized TNFalpha is controlled and limited by the level of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins syntaxin 4 and SNAP-23. Many functions in immune cells are coordinated from lipid rafts in the plasma membrane, and we investigated a possible role for lipid rafts in TNFalpha trafficking and secretion. TNFalpha surface delivery and secretion were found to be cholesterol-dependent. Upon macrophage activation, syntaxin 4 was recruited to cholesterol-dependent lipid rafts, whereas its regulatory protein, Munc18c, was excluded from the rafts. Syntaxin 4 in activated macrophages localized to discrete cholesterol-dependent puncta on the plasma membrane, particularly on filopodia. Imaging the early stages of TNFalpha surface distribution revealed these puncta to be the initial points of TNFalpha delivery. During the early stages of phagocytosis, syntaxin 4 was recruited to the phagocytic cup in a cholesterol-dependent manner. Insertion of VAMP3-positive recycling endosome membrane is required for efficient ingestion of a pathogen. Without this recruitment of syntaxin 4, it is not incorporated into the plasma membrane, and phagocytosis is greatly reduced. Thus, relocation of syntaxin 4 into lipid rafts in macrophages is a critical and rate-limiting step in initiating an effective immune response.

Simvastatin protection against acute immune-mediated glomerulonephritis in mice

In addition to cholesterol lowering, 3-hydroxy-3-nethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors limit inflammatory changes associated with atherosclerosis. There is also support for their use as inhibitors of progression in chronic renal disease, irrespective of cause. In this study, their capacity to limit acute renal inflammation was evaluated. For this purpose, mice were treated with Simvastatin either prior to, at the time of, or shortly after induction of nephrotoxic nephritis. The severity of disease was determined by evaluation of blood urea nitrogen (BUN), proteinuria, and renal histologic changes. The reversibility of benefit was evaluated by the administration of mevalonic acid along with nephrotoxic serum (NTS) and Simvastatin The severity of the acute nephritis, including proteinuria, elevated BUN, and histologic changes, was ameliorated in a dose-dependent manner, when Simvastatin was administered either prior to NTS injection or at the time of NTS injection. By contrast, Simvastatin did not alter the course of established nephritis. Coadministration of mevalonic acid, the immediate substrate following HMG-CoA reductase, abolished Simvastatin's renoprotective effect, indicating that the benefit is, at least in part, due to interference with HMG-CoA reductase and biosynthetic substrates downstream from the enzyme. These findings provide the rationale for the evaluation of the efficacy of HMG-CoA reductase inhibitors in patients with recurrent forms of renal inflammation, to limit the severity of acute exacerbations of disease, prevent renal scarring and slow the rate of progression.

Human aldose reductase expression accelerates diabetic atherosclerosis in transgenic mice

Direct evidence that hyperglycemia, rather than concomitant increases in known risk factors, induces atherosclerosis is lacking. Most diabetic mice do not exhibit a higher degree of atherosclerosis unless the development of diabetes is associated with more severe hyperlipidemia. We hypothesized that normal mice were deficient in a gene that accelerated atherosclerosis with diabetes. The gene encoding aldose reductase (AR), an enzyme that mediates the generation of toxic products from glucose, is expressed at low levels in murine compared with human tissues. Mice in which diabetes was induced through streptozotocin (STZ) treatment, but not nondiabetic mice, expressing human AR (hAR) crossed with LDL receptor-deficient (Ldlr-/-) C57BL/6 male mice had increased aortic atherosclerosis. Diabetic hAR-expressing heterozygous LDL receptor-knockout mice (Ldlr+/-) fed a cholesterol/cholic acid-containing diet also had increased aortic lesion size. Lesion area at the aortic root was increased by STZ treatment alone but was further increased by hAR expression. Macrophages from hAR-transgenic mice expressed more scavenger receptors and had greater accumulation of modified lipoproteins than macrophages from nontransgenic mice. Expression of genes that regulate regeneration of glutathione was reduced in the hAR-expressing aortas. Thus, hAR increases atherosclerosis in diabetic mice. Inhibitors of AR or other enzymes that mediate glucose toxicity could be useful in the treatment of diabetic atherosclerosis.