Palmitoylethanolamide stimulates phagocytosis of Escherichia coli K1 by macrophages and increases the resistance of mice against infections

Inflammatory-Targeted Lipid Carrier as a New Nanomaterial to Formulate an Inhaled Drug Delivery System

There is a pressing need for efficacious therapies in the field of respiratory diseases and infections. Lipid nanocarriers, administered through aerosols, represent a promising tool for maximizing therapeutic concentration in targeted cells and minimizing systemic exposure. However, this approach requires the application of efficient and safe nanomaterials. Palmitoylethanolamide (PEA), an endocannabinoid-like endogenous lipid, plays a crucial role in providing protective mechanisms during inflammation, making it an interesting material for preparing inhalable lipid nanoparticles (LNPs). This report aims to preliminarily explore the in vitro behavior of LNPs prepared with PEA (PEA-LNPs), a new inhalable inflammatory-targeted nanoparticulate drug carrier. PEA-LNPs exhibited a size of about 250 nm, a rounded shape, and an marked improvement in PEA solubility in comparison to naked PEA, indicative of easily disassembled nanoparticles. A twin glass impinger instrument was used to screen the aerosol performance of PEA-LNP powders, obtained via freeze-drying in the presence of two quantities of mannose as a cryoprotectant. Results indicated that a higher amount of mannose improved the emitted dose (ED), and in particular, the fine particle fraction (FPF). A cytotoxicity assay was performed and indicated that PEA-LNPs are not toxic towards the MH-S alveolar macrophage cell line up to concentrations of 0.64 mg/mL, and using coumarin-6 labelled particles, a rapid internalization into the macrophage was confirmed. This study demonstrates that PEA could represent a suitable material for preparing inhalable lipid nanocarrier-based dry powders, which signify a promising tool for the transport of drugs employed to treat respiratory diseases and infections.

Palmitoylethanolamide shows limited efficacy in controlling cerebral cryptococcosis in vivo

Cryptococcus neoformans (Cn) is an encapsulated neurotropic fungal pathogen and the causative agent of cryptococcal meningoencephalitis (CME) in humans. Recommended treatment for CME is Amphotericin B (AmpB) and 5-fluorocytosine (5-FC). Though effective, AmpB has displayed numerous adverse side effects due to its potency and nephrotoxicity, prompting investigation into alternative treatments. Palmitoylethanolamide (PEA) is an immunomodulatory compound capable of promoting neuroprotection and reducing inflammation. To investigate the efficacy of PEA as a therapeutic alternative for CME, we intracerebrally infected mice with Cn and treated them with PEA or AmpB alone or in combination. Our results demonstrate that PEA alone does not significantly prolong survival nor reduce fungal burden, but when combined with AmpB, PEA exerts an additive effect and promotes both survivability and fungal clearance. However, we compared this combination to traditional AmpB and 5-FC treatment in a survivability study and observed lower efficacy. Overall, our study revealed that PEA alone is not effective as an antifungal agent in the treatment of CME. Importantly, we describe the therapeutic capability of PEA in the context of Cn infection and show that its immunomodulatory properties may confer limited protection when combined with an effective fungicidal agent.

Palmitoylethanolamide shows limited efficacy in controlling cerebral cryptococcosis in vivo

Cryptococcus neoformans ( Cn ) is an encapsulated neurotropic fungal pathogen and the causative agent of cryptococcal meningoencephalitis (CME) in humans. Recommended treatment for CME is Amphotericin B (AmpB) and 5-fluorocytosine (5-FC). Though effective, AmpB has displayed numerous adverse side effects due to its potency and nephrotoxicity, prompting investigation into alternative treatments. Palmitoylethanolamide (PEA) is an immunomodulatory compound capable of promoting neuroprotection and reducing inflammation. To investigate the efficacy of PEA as a therapeutic alternative for CME, we intracerebrally infected mice with Cn and treated them with PEA or AmpB alone or in combination. Our results demonstrate that PEA alone does not significantly prolong survival nor reduce fungal burden, but when combined with AmpB, PEA exerts an additive effect and promotes both survivability and fungal clearance. However, we compared this combination to traditional AmpB and 5-FC treatment in a survivability study and observed lower efficacy. Overall, our study revealed that PEA alone is not effective as an antifungal agent in the treatment of CME. Importantly, we describe the therapeutic capability of PEA in the context of Cn infection and show that its immunomodulatory properties may confer limited protection when combined with an effective fungicidal agent.

Microglia subtypes show substrate- and time-dependent phagocytosis preferences and phenotype plasticity

Microglia are phagocytosis-competent CNS cells comprising a spectrum of subtypes with beneficial and/or detrimental functions in acute and chronic neurodegenerative disorders. The heterogeneity of microglia suggests differences in phagocytic activity and phenotype plasticity between microglia subtypes. To study these issues, primary murine glial cultures were cultivated in the presence of serum, different growth factors and cytokines to obtain M0-like, M1-like, and M2-like microglia as confirmed by morphology, M1/M2 gene marker expression, and nitric oxide assay. Single-cell analysis after 3 hours of phagocytosis of E.coli particles or IgG-opsonized beads showed equal internalization by M0-like microglia, whereas M1-like microglia preferably internalized E.coli particles and M2-like microglia preferably internalized IgG beads, suggesting subtype-specific preferences for different phagocytosis substrates. Time-lapse live-cells imaging over 16 hours revealed further differences between microglia subtypes in phagocytosis preference and internalization dynamics. M0- and, more efficiently, M1-like microglia continuously internalized E.coli particles for 16 hours, whereas M2-like microglia discontinued internalization after approximately 8 hours. IgG beads were continuously internalized by M0- and M1-like microglia but strikingly less by M2-like microglia. M2-like microglia initially showed continuous internalization similar to M0-like microglia but again discontinuation of internalization after 8 hours suggesting that the time of substrate exposure differently affect microglia subtypes. After prolonged exposure to E.coli particles or IgG beads for 5 days all microglia subtypes showed increased internalization of E.coli particles compared to IgG beads, increased nitric oxide release and up-regulation of M1 gene markers, irrespectively of the phagocytosis substrate, suggesting phenotype plasticity. In summary, microglia subtypes show substrate- and time-dependent phagocytosis preferences and phenotype plasticity. The results suggest that prolonged phagocytosis substrate exposure enhances M1-like profiles and M2-M1 repolarization of microglia. Similar processes may also take place in conditions of acute and chronic brain insults when microglia encounter different types of phagocytic substrates.

Microglia subtypes show substrate- and time-dependent phagocytosis preferences and phenotype plasticity

Microglia are phagocytosis-competent CNS cells comprising a spectrum of subtypes with beneficial and/or detrimental functions in acute and chronic neurodegenerative disorders. The heterogeneity of microglia suggests differences in phagocytic activity and phenotype plasticity between microglia subtypes. To study these issues, primary murine glial cultures were cultivated in the presence of serum, different growth factors and cytokines to obtain M0-like, M1-like, and M2-like microglia as confirmed by morphology, M1/M2 gene marker expression, and nitric oxide assay. Single-cell analysis after 3 hours of phagocytosis of E.coli particles or IgG-opsonized beads showed equal internalization by M0-like microglia, whereas M1-like microglia preferably internalized E.coli particles and M2-like microglia preferably internalized IgG beads, suggesting subtype-specific preferences for different phagocytosis substrates. Time-lapse live-cells imaging over 16 hours revealed further differences between microglia subtypes in phagocytosis preference and internalization dynamics. M0- and, more efficiently, M1-like microglia continuously internalized E.coli particles for 16 hours, whereas M2-like microglia discontinued internalization after approximately 8 hours. IgG beads were continuously internalized by M0- and M1-like microglia but strikingly less by M2-like microglia. M2-like microglia initially showed continuous internalization similar to M0-like microglia but again discontinuation of internalization after 8 hours suggesting that the time of substrate exposure differently affect microglia subtypes. After prolonged exposure to E.coli particles or IgG beads for 5 days all microglia subtypes showed increased internalization of E.coli particles compared to IgG beads, increased nitric oxide release and up-regulation of M1 gene markers, irrespectively of the phagocytosis substrate, suggesting phenotype plasticity. In summary, microglia subtypes show substrate- and time-dependent phagocytosis preferences and phenotype plasticity. The results suggest that prolonged phagocytosis substrate exposure enhances M1-like profiles and M2-M1 repolarization of microglia. Similar processes may also take place in conditions of acute and chronic brain insults when microglia encounter different types of phagocytic substrates.

Collaborative Action of Microglia and Astrocytes Mediates Neutrophil Recruitment to the CNS to Defend against Escherichia coli K1 Infection

Escherichia coli K1 is a leading cause of neonatal bacterial meningitis. Recruitment of neutrophils to the central nervous system (CNS) via local immune response plays a critical role in defense against E. coli K1 infection; however, the mechanism underlying this recruitment remains unclear. In this study, we report that microglia and astrocytes are activated in response to stimulation by E. coli K1 and/or E. coli K1-derived outer membrane vesicles (OMVs) and work collaboratively to drive neutrophil recruitment to the CNS. Microglial activation results in the release of the pro-inflammatory cytokine TNF-α, which activates astrocytes, resulting in the production of CXCL1, a chemokine critical for recruiting neutrophils. Mice lacking either microglia or TNF-α exhibit impaired production of CXCL1, impaired neutrophil recruitment, and an increased CNS bacterial burden. C-X-C chemokine receptor 2 (CXCR2)-expressing neutrophils primarily respond to CXCL1 released by astrocytes. This study provides further insights into how immune responses drive neutrophil recruitment to the brain to combat E. coli K1 infection. In addition, we show that direct recognition of E. coli K1 by microglia is prevented by the K1 capsule. This study also reveals that OMVs are sufficient to induce microglial activation.

Anti-Microbial Activity of Phytocannabinoids and Endocannabinoids in the Light of Their Physiological and Pathophysiological Roles

Antibiotic resistance has become an increasing challenge in the treatment of various infectious diseases, especially those associated with biofilm formation on biotic and abiotic materials. There is an urgent need for new treatment protocols that can also target biofilm-embedded bacteria. Many secondary metabolites of plants possess anti-bacterial activities, and especially the phytocannabinoids of the Cannabis sativa L. varieties have reached a renaissance and attracted much attention for their anti-microbial and anti-biofilm activities at concentrations below the cytotoxic threshold on normal mammalian cells. Accordingly, many synthetic cannabinoids have been designed with the intention to increase the specificity and selectivity of the compounds. The structurally unrelated endocannabinoids have also been found to have anti-microbial and anti-biofilm activities. Recent data suggest for a mutual communication between the endocannabinoid system and the gut microbiota. The present review focuses on the anti-microbial activities of phytocannabinoids and endocannabinoids integrated with some selected issues of their many physiological and pharmacological activities.

The Role of PPAR Alpha in the Modulation of Innate Immunity

Peroxisome proliferator-activated receptor α is a potent regulator of systemic and cellular metabolism and energy homeostasis, but it also suppresses various inflammatory reactions. In this review, we focus on its role in the regulation of innate immunity; in particular, we discuss the PPARα interplay with inflammatory transcription factor signaling, pattern-recognition receptor signaling, and the endocannabinoid system. We also present examples of the PPARα-specific immunomodulatory functions during parasitic, bacterial, and viral infections, as well as approach several issues associated with innate immunity processes, such as the production of reactive nitrogen and oxygen species, phagocytosis, and the effector functions of macrophages, innate lymphoid cells, and mast cells. The described phenomena encourage the application of endogenous and pharmacological PPARα agonists to alleviate the disorders of immunological background and the development of new solutions that engage PPARα activation or suppression.

Palmitoylethanolamide Modulation of Microglia Activation: Characterization of Mechanisms of Action and Implication for Its Neuroprotective Effects

Palmitoylethanolamide (PEA) is an endogenous lipid produced on demand by neurons and glial cells that displays neuroprotective properties. It is well known that inflammation and neuronal damage are strictly related processes and that microglia play a pivotal role in their regulation. The aim of the present work was to assess whether PEA could exert its neuroprotective and anti-inflammatory effects through the modulation of microglia reactive phenotypes. In N9 microglial cells, the pre-incubation with PEA blunted the increase of M1 pro-inflammatory markers induced by lipopolysaccharide (LPS), concomitantly increasing those M2 anti-inflammatory markers. Images of microglial cells were processed to obtain a set of morphological parameters that highlighted the ability of PEA to inhibit the LPS-induced M1 polarization and suggested that PEA might induce the anti-inflammatory M2a phenotype. Functionally, PEA prevented Ca²⁺ transients in both N9 cells and primary microglia and antagonized the neuronal hyperexcitability induced by LPS, as revealed by multi-electrode array (MEA) measurements on primary cortical cultures of neurons, microglia, and astrocyte. Finally, the investigation of the molecular pathway indicated that PEA effects are not mediated by toll-like receptor 4 (TLR4); on the contrary, a partial involvement of cannabinoid type 2 receptor (CB2R) was shown by using a selective receptor inverse agonist.

The Potentials of Melatonin in the Prevention and Treatment of Bacterial Meningitis Disease

Bacterial meningitis (BM) is an acute infectious central nervous system (CNS) disease worldwide, occurring with 50% of the survivors left with a long-term serious sequela. Acute bacterial meningitis is more prevalent in resource-poor than resource-rich areas. The pathogenesis of BM involves complex mechanisms that are related to bacterial survival and multiplication in the bloodstream, increased permeability of blood-brain barrier (BBB), oxidative stress, and excessive inflammatory response in CNS. Considering drug-resistant bacteria increases the difficulty of meningitis treatment and the vaccine also has been limited to several serotypes, and the morbidity rate of BM still is very high. With recent development in neurology, there is promising progress for drug supplements of effectively preventing and treating BM. Several in vivo and in vitro studies have elaborated on understanding the significant mechanism of melatonin on BM. Melatonin is mainly secreted in the pineal gland and can cross the BBB. Melatonin and its metabolite have been reported as effective antioxidants and anti-inflammation, which are potentially useful as prevention and treatment therapy of BM. In bacterial meningitis, melatonin can play multiple protection effects in BM through various mechanisms, including immune response, antibacterial ability, the protection of BBB integrity, free radical scavenging, anti-inflammation, signaling pathways, and gut microbiome. This manuscript summarizes the major neuroprotective mechanisms of melatonin and explores the potential prevention and treatment approaches aimed at reducing morbidity and alleviating nerve injury of BM.

Sepsis-associated encephalopathy and septic encephalitis: an update

INTRODUCTION

Sepsis-associated encephalopathy (SAE) and septic encephalitis (SE) are associated with increased mortality, long-term cognitive impairment, and focal neurological deficits.

AREAS COVERED

The PUBMED database was searched 2016-2020. The clinical manifestation of SAE is delirium, SE additionally is characterized by focal neurological symptoms. SAE is caused by inflammation with endothelial/microglial activation, increase of permeability of the blood-brain-barrier, hypoxia, imbalance of neurotransmitters, glial activation, axonal, and neuronal loss. Septic-embolic (SEE) and septic-metastatic encephalitis (SME) are characterized by focal ischemia (SEE) and small abscesses (SME). The continuum between SAE, SME, and SEE is documented by imaging techniques and autopsies. The backbone of treatment is rapid optimum antibiotic therapy. Experimental approaches focus on modulation of inflammation, stabilization of the blood-brain barrier, and restoration of membrane/mitochondrial function.

EXPERT OPINION

The most promising diagnostic approaches are new imaging techniques. The most important measure to fight delirium remains establishment of daily structure and adequate sensory stimuli. Dexmedetomidine and melatonin appear to reduce the frequency of delirium, their efficacy in SAE and SE remains to be established. Drugs already licensed for other indications or available as food supplements which may be effective in SAE are statins, L-DOPA/benserazide, β-hydroxybutyrate, palmitoylethanolamide, and tetracyclines or other bactericidal non-lytic antibiotics.

Thermoneutral Housing Temperature Improves Survival in a Murine Model of Polymicrobial Peritonitis

Regulatory guidelines mandate housing for laboratory mice at temperatures below their thermoneutral zone, creating chronic cold stress. However, increases in housing temperature could alter immune responses. We hypothesized housing mice at temperatures within their thermoneutral zone would improve sepsis survival and alter immune responses. Male C57BL/6 mice were housed at 22°C or 30°C after cecal ligation and puncture (CLP) for 10 days. Survival of mice housed at 30°C (78%) after CLP was significantly increased compared with mice housed at 22°C (40%). Experimental groups were repeated with mice euthanized at 0, 12, 24, and 48 h post-surgery to examine select immune parameters. Raising housing temperature minimally altered systemic, peritoneal, or splenic cell counts. However, IL-6 levels in plasma and peritoneal lavage fluid were significantly lower at 12 h post-surgery in mice housed at 30°C compared with 22°C. Bacterial colony counts from peritoneal lavage fluid were significantly lower in mice housed at 30°C and in vivo studies suggested this was the result of increased phagocytosis by neutrophils. As previously demonstrated, adoptive transfer of fibrocytes significantly increased sepsis survival compared with saline at 22°C. However, there was no additive effect when adoptive transfer was performed at 30°C. Overall, the results demonstrated that thermoneutral housing improves survival after CLP by increasing local phagocytic activity and technical revisions may be necessary to standardize the severity of the model across different housing temperatures. These findings stress the pronounced impact housing temperature has on the CLP model and the importance of reporting housing temperature.

Phagocytosis by Fibrocytes as a Mechanism to Decrease Bacterial Burden and Increase Survival in Sepsis

Fibrocytes are unique cells with innate and adaptive immune functions, but these mechanisms have not been fully explored. The aim of this study was to explain the mechanism by which adoptive transfer of exogenous fibrocytes improved bacterial clearance and increased sepsis survival. Initial flow cytometry-based, in vitro assays demonstrated phagocytosis by fibrocytes and intracellular bacterial killing was confirmed by direct plating of cell lysates after exposure to live bacteria. Intravenous adoptive transfer of fibrocytes at the time of cecal ligation and puncture (CLP) or 2 h after CLP in mice increased survivability. Decreased intraperitoneal bacterial burden was also observed. Quantification of peritoneal cell populations using flow cytometry demonstrated transferred and endogenous fibrocytes were significantly increased after CLP, while macrophage and neutrophil numbers were unchanged. To determine the impact in vivo, fluorescently labeled, killed bacteria were injected i.p. into mice 10 h after CLP or sham surgery ± adoptive transfer. Two hours later, flow cytometry of peritoneal cell populations after CLP alone revealed increased phagocytosis by macrophages, neutrophils, and endogenous fibrocytes. Transferred fibrocytes had significantly increased phagocytic activity in the septic peritoneum compared with sham and greater activity than any other cell type. Therefore, adoptive transfer may enhance bacterial clearance in early sepsis through the cumulative effects of endogenous and transferred fibrocytes rather than modulating the function of other endogenous phagocytes. Direct phagocytic activity coupled with previously described influences on T cell responses may explain the benefits of fibrocyte transfer in sepsis.

N-Acylethanolamine Acid Amidase (NAAA): Structure, Function, and Inhibition

N-Acylethanolamine acid amidase (NAAA) is an N-terminal cysteine hydrolase primarily found in the endosomal-lysosomal compartment of innate and adaptive immune cells. NAAA catalyzes the hydrolytic deactivation of palmitoylethanolamide (PEA), a lipid-derived peroxisome proliferator-activated receptor-α (PPAR-α) agonist that exerts profound anti-inflammatory effects in animal models. Emerging evidence points to NAAA-regulated PEA signaling at PPAR-α as a critical control point for the induction and the resolution of inflammation and to NAAA itself as a target for anti-inflammatory medicines. The present Perspective discusses three key aspects of this hypothesis: the role of NAAA in controlling the signaling activity of PEA; the structural bases for NAAA function and inhibition by covalent and noncovalent agents; and finally, the potential value of NAAA-targeting drugs in the treatment of human inflammatory disorders.

Aged mice show an increased mortality after anesthesia with a standard dose of ketamine/xylazine

Geriatric animal models are crucial for a better understanding and an improved therapy of age-related diseases. We observed a high mortality of aged mice after anesthesia with a standard dose of ketamine/xylazine, an anesthetic regimen frequently used in laboratory veterinary medicine.

C57BL/6-N mice at the age of 2.14 ± 0.23 months (young mice) and 26.31 ± 2.15 months (aged mice) were anesthetized by intraperitoneal injection of 2 mg ketamine and 0.2 mg xylazine. 4 of 26 aged mice (15.4%) but none of 26 young mice died within 15 min after injection of the anesthetics. The weight of aged mice was significantly higher than that of young mice (32.8 ± 5.4 g versus 23.2 ± 3.4 g, p < 0.0001). Thus, aged mice received lower doses of anesthetics in relation to their body weight which are within the lower range of doses recommended in the literature or even beneath. There were no differences between deceased and surviving aged mice concerning their sex, weight and their motor performance prior to anesthesia.

Our data clearly show an age-related increase of mortality upon anesthesia with low standard doses of ketamine/xylazine. Assessment of weight and motor performance did not help to predict vulnerability of aged mice to the anesthetics. Caution is necessary when this common anesthetic regimen is applied in aged mice: lower doses or the use of alternative anesthetics should be considered to avoid unexpected mortality.

The present data from our geriatric mouse model strongly corroborate an age-adjusted reduction of anesthetic doses to reduce anesthesia-related mortality in aged individuals.

The Role of Microglia in Bacterial Meningitis: Inflammatory Response, Experimental Models and New Neuroprotective Therapeutic Strategies

Microglia have a pivotal role in the pathophysiology of bacterial meningitis. The goal of this review is to provide an overview on how microglia respond to bacterial pathogens targeting the brain, how the interplay between microglia and bacteria can be studied experimentally, and possible ways to use gained knowledge to identify novel preventive and therapeutic strategies. We discuss the dual role of microglia in disease development, the beneficial functions crucial for bacterial clearing, and the destructive properties through triggering neuroinflammation, characterized by cytokine and chemokine release which leads to leukocyte trafficking through the brain vascular endothelium and breakdown of the blood-brain barrier integrity. Due to intrinsic complexity of microglia and up until recently lack of specific markers, the study of microglial response to bacterial pathogens is challenging. New experimental models and techniques open up possibilities to accelerate progress in the field. We review existing models and discuss possibilities and limitations. Finally, we summarize recent findings where bacterial virulence factors are identified to be important for the microglial response, and how manipulation of evoked responses could be used for therapeutic or preventive purposes. Among promising approaches are: modulations of microglia phenotype switching toward anti-inflammatory and phagocytic functions, the use of non-bacterolytic antimicrobials, preventing release of bacterial components into the neural milieu and consequential amplification of immune activation, and protection of the blood-brain barrier integrity.

Prophylactic Palmitoylethanolamide Prolongs Survival and Decreases Detrimental Inflammation in Aged Mice With Bacterial Meningitis

Easy-to-achieve interventions to promote healthy longevity are desired to diminish the incidence and severity of infections, as well as associated disability upon recovery. The dietary supplement palmitoylethanolamide (PEA) exerts anti-inflammatory and neuroprotective properties. Here, we investigated the effect of prophylactic PEA on the early immune response, clinical course, and survival of old mice after intracerebral E. coli K1 infection. Nineteen-month-old wild type mice were treated intraperitoneally with two doses of either 0.1 mg PEA/kg in 250 μl vehicle solution (n = 19) or with 250 μl vehicle solution only as controls (n = 19), 12 h and 30 min prior to intracerebral E. coli K1 infection. The intraperitoneal route was chosen to reduce distress in mice and to ensure exact dosing. Survival time, bacterial loads in cerebellum, blood, spleen, liver, and microglia counts and activation scores in the brain were evaluated. We measured the levels of IL-1β, IL-6, MIP-1α, and CXCL1 in cerebellum and spleen, as well as of bioactive lipids in serum in PEA- and vehicle-treated animals 24 h after infection. In the absence of antibiotic therapy, the median survival time of PEA-pre-treated infected mice was prolonged by 18 h compared to mice of the vehicle-pre-treated infected group (P = 0.031). PEA prophylaxis delayed the onset of clinical symptoms (P = 0.037). This protective effect was associated with lower bacterial loads in the spleen, liver, and blood compared to those of vehicle-injected animals (P ≤ 0.037). PEA-pre-treated animals showed diminished levels of pro-inflammatory cytokines and chemokines in spleen 24 h after infection, as well as reduced serum concentrations of arachidonic acid and of one of its metabolites, 20-hydroxyeicosatetraenoic acid. In the brain, prophylactic PEA tended to reduce bacterial titers and attenuated microglial activation in aged infected animals (P = 0.042). Our findings suggest that prophylactic PEA can counteract infection associated detrimental responses in old animals. Accordingly, PEA treatment slowed the onset of infection symptoms and prolonged the survival of old infected mice. In a clinical setting, prophylactic administration of PEA might extend the potential therapeutic window where antibiotic therapy can be initiated to rescue elderly patients.

Activin A increases phagocytosis of Escherichia coli K1 by primary murine microglial cells activated by toll-like receptor agonists

Background

Bacterial meningitis is associated with high mortality and long-term neurological sequelae. Increasing the phagocytic activity of microglia could improve the resistance of the CNS against infections. We studied the influence of activin A, a member of the TGF-β family with known immunoregulatory and neuroprotective effects, on the functions of microglial cells in vitro.

Methods

Primary murine microglial cells were treated with activin A (0.13 ng/ml–13 μg/ml) alone or in combination with agonists of TLR2, 4, and 9. Phagocytosis of Escherichia coli K1 as well as release of TNF-α, IL-6, CXCL1, and NO was assessed.

Results

Activin A dose-dependently enhanced the phagocytosis of Escherichia coli K1 by microglial cells activated by agonists of TLR2, 4, and 9 without further increasing NO and proinflammatory cytokine release. Cell viability of microglial cells was not affected by activin A.

Conclusions

Priming of microglial cells with activin A could increase the elimination of bacteria in bacterial CNS infections. This preventive strategy could improve the resistance of the brain to infections, particularly in elderly and immunocompromised patients.

CRAMP deficiency leads to a pro-inflammatory phenotype and impaired phagocytosis after exposure to bacterial meningitis pathogens

BACKGROUND

Antimicrobial peptides are important components of the host defence with a broad range of functions including direct antimicrobial activity and modulation of inflammation. Lack of cathelin-related antimicrobial peptide (CRAMP) was associated with higher mortality and bacterial burden and impaired neutrophil granulocyte infiltration in a model of pneumococcal meningitis. The present study was designed to characterize the effects of CRAMP deficiency on glial response and phagocytosis after exposure to bacterial stimuli.

METHODS

CRAMP-knock out and wildtype glial cells were exposed to bacterial supernatants from Streptococcus pneumoniae and Neisseria meningitides or the bacterial cell wall components lipopolysaccharide and peptidoglycan. Cell viability, expression of pro- and anti-inflammatory mediators and activation of signal transduction pathways, phagocytosis rate and glial cell phenotype were investigated by means of cell viability assays, immunohistochemistry, real-time RT-PCR and Western blot.

RESULTS

CRAMP-deficiency was associated with stronger expression of pro-inflammatory and weakened expression of anti-inflammatory cytokines indicating a higher degree of glial cell activation even under resting-state conditions. Furthermore, increased translocation of nuclear factor 'kappa-light-chain-enhancer' of activated B-cells was observed and phagocytosis of S. pneumoniae was reduced in CRAMP-deficient microglia indicating impaired antimicrobial activity.

CONCLUSIONS

In conclusion, the present study detected severe alterations of the glial immune response due to lack of CRAMP. The results indicate the importance of CRAMP to maintain and regulate the delicate balance between beneficial and harmful immune response in the brain.

Fundamentals of and Critical Issues in Lipid Autacoid Medicine: A Review

The identification of a number of families of lipid signal molecules since the 1990s created new therapeutic possibilities for a great number of disorders characterized by chronic inflammation and pain. These lipid autacoids have been explored in a great variety of animal models related to inflammation, pain, (neuro-)protection, and repair. Based on the data from these models, as well as on a number of proof of principle studies in the clinic in indications such as neuropathic pain, a new chapter in medicine is about to begin. We would like to introduce the term “Autacoid Pain Medicine” for this chapter. There are, however, a number of methodological and strategic issues to overcome in this field. One of the roadblocks is related to patent strategies around families of these molecules. As this is not always recognized we will present a number of examples.

Palmitoylethanolamide induces microglia changes associated with increased migration and phagocytic activity: involvement of the CB2 receptor

The endogenous fatty acid amide palmitoylethanolamide (PEA) has been shown to exert anti-inflammatory actions mainly through inhibition of the release of pro-inflammatory molecules from mast cells, monocytes and macrophages. Indirect activation of the endocannabinoid (eCB) system is among the several mechanisms of action that have been proposed to underlie the different effects of PEA in vivo. In this study, we used cultured rat microglia and human macrophages to evaluate whether PEA affects eCB signaling. PEA was found to increase CB2 mRNA and protein expression through peroxisome proliferator-activated receptor-α (PPAR-α) activation. This novel gene regulation mechanism was demonstrated through: (i) pharmacological PPAR-α manipulation, (ii) PPAR-α mRNA silencing, (iii) chromatin immunoprecipitation. Moreover, exposure to PEA induced morphological changes associated with a reactive microglial phenotype, including increased phagocytosis and migratory activity. Our findings suggest indirect regulation of microglial CB2R expression as a new possible mechanism underlying the effects of PEA. PEA can be explored as a useful tool for preventing/treating the symptoms associated with neuroinflammation in CNS disorders.

The anti-inflammatory compound palmitoylethanolamide inhibits prostaglandin and hydroxyeicosatetraenoic acid production by a macrophage cell line

The anti‐inflammatory agent palmitoylethanolamide (PEA) reduces cyclooxygenase (COX) activity in vivo in a model of inflammatory pain. It is not known whether the compound reduces prostaglandin production in RAW264.7 cells, whether such an action is affected by compounds preventing the breakdown of endogenous PEA, whether other oxylipins are affected, or whether PEA produces direct effects upon the COX‐2 enzyme. RAW264.7 cells were treated with lipopolysaccharide and interferon‐γ to induce COX‐2. At the level of mRNA, COX‐2 was induced >1000‐fold following 24 h of the treatment. Coincubation with PEA (10 μmol/L) did not affect the levels of COX‐2, but reduced the levels of prostaglandins D₂ and E₂ as well as 11‐ and 15‐hydroxyeicosatetraenoic acid, which can also be synthesised by a COX‐2 pathway in macrophages. These effects were retained when hydrolysis of PEA to palmitic acid was blocked. Linoleic acid‐derived oxylipin levels were not affected by PEA. No direct effects of PEA upon the oxygenation of either arachidonic acid or 2‐arachidonoylglycerol by COX‐2 were found. It is concluded that in lipopolysaccharide and interferon‐γ‐stimulated RAW264.7 cells, PEA reduces the production of COX‐2‐derived oxylipins in a manner that is retained when its metabolism to palmitic acid is inhibited.

The common, autoimmunity-predisposing 620Arg > Trp variant of PTPN22 modulates macrophage function and morphology

The C1858T single nucleotide polymorphism (SNP) in PTPN22 (protein tyrosine phosphatase nonreceptor 22) leads to the 620 Arg to Trp polymorphism in its encoded human protein LYP. This allelic variant is associated with multiple autoimmune diseases, including type 1 diabetes (T1D), Crohn's disease, rheumatoid arthritis and systemic lupus erythematosus. However, the underlying mechanisms are poorly understood. To study how this polymorphism influences the immune system, we generated a mouse strain with a knock-in of the Trp allele, imitating the human disease-associated variant. We did not find significant difference between the polymorphic and the wild type mice on the proportion of total CD4 T cell, CD8 T cell, NK cell, memory T lymphocyte, macrophage, dendritic cells in both peripheral lymph nodes and spleen. However, macrophages from Trp/Trp mice showed altered morphology and enhanced function, including higher expression of MHCII and B7 molecules and increased phagocytic ability, which further leads to a higher T-cell activation by specific antigen. Our model shows no alteration in immune cell profile by the Trp allele, but brings up macrophages as an important player to consider in explaining the PTPN22 Trp allele effect on autoimmune disease risk.

Endocannabinoid signalling in innate and adaptive immunity

The immune system can be modulated and regulated not only by foreign antigens but also by other humoral factors and metabolic products, which are able to affect several quantitative and qualitative aspects of immunity. Among these, endocannabinoids are a group of bioactive lipids that might serve as secondary modulators, which when mobilized coincident with or shortly after first-line immune modulators, increase or decrease many immune functions. Most immune cells express these bioactive lipids, together with their set of receptors and of enzymes regulating their synthesis and degradation. In this review, a synopsis of the manifold immunomodulatory effects of endocannabinoids and their signalling in the different cell populations of innate and adaptive immunity is appointed, with a particular distinction between mice and human immune system compartments.