Synergistic effect of muramyldipeptide with lipopolysaccharide or lipoteichoic acid to induce inflammatory cytokines in human monocytic cells in culture

Synergistic effect of Toll-like receptor 2 ligands and alendronate on proinflammatory cytokine production in mouse macrophage-like RAW-ASC cells is accompanied by upregulation of MyD88 expression

OBJECTIVES

Toll-like receptors (TLRs) recognize whole cells or components of microorganisms. Alendronate (ALN) is an anti-bone-resorptive drug that has inflammatory side effects. The aim in this study was to examine whether ALN augments TLR2 ligand-induced proinflammatory cytokine production using mouse macrophage-like RAW264.7 cells transfected with murine apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) gene (hereafter, referred to as "RAW-ASC cells").

METHODS

RAW-ASC cells were pretreated with or without ALN and then incubated with or without TLR2 ligands. The levels of secreted mouse IL-1α, IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) in culture supernatants and the activation of activator protein-1 (AP-1) or nuclear factor-κB (NF-κB) were measured using enzyme-linked immunosorbent assay (ELISA). The expressions of myeloid differentiation factor 88 (MyD88), caspase-11, nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3), ASC, NF-κB p65, and actin were analyzed via Western blotting. TLR2 expression was analyzed using flow cytometry.

RESULTS

ALN substantially upregulated the Pam3CSK4-induced release of IL-1α, IL-1β, IL-6, and TNF-α and MyD88 expression in RAW-ASC cells. ST-2825, a MyD88 inhibitor, inhibited the ALN-augmented release of these cytokines. Pretreatment with ALN augmented Pam3CSK4-induced NF-κB activation in RAW-ASC cells and upregulated AP-1 activation. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein and ALN synergically upregulated the release of IL-1α, IL-1β, IL-6 and TNF-α in RAW-ASC cells.

CONCLUSIONS

Our findings suggest that ALN augments TLR2 ligand-induced proinflammatory cytokine production via the upregulation of MyD88 expression, and this augmentation is accompanied by the activation of NF-κB and AP-1 in RAW-ASC cells.

Decrypting the Pathological Pathways in IgA Nephropathy

IgAN is the most common form of glomerulonephritis affecting 2000000 people annually. The disease ultimately progresses to chronic renal failure and ESRD. In this article, we focused on a comprehensive understanding of the pathogenesis of the disease and thus identifying different target proteins that could be essential in therapeutic approaches in the management of the disease. Aberrantly glycosylated IgA1 produced by the suppression of the enzyme β-1, 3 galactosyltransferase ultimately triggered the formation of IgG autoantibodies which form complexes with Gd-IgA1. The complex gets circulated through the blood vessels through monocytes and ultimately gets deposited in the glomerular mesangial cells via CD71 receptors present locally. This complex triggers the inflammatory pathways activating the alternate complement system, various types of T Cells, toll-like receptors, cytokines, and chemokines ultimately recruiting the phagocytic cells to eliminate the Gd-IgA complex. The inflammatory proteins cause severe mesangial and podocyte damage in the kidney which ultimately initiates the repair process following chronic inflammation by an important protein named TGFβ1. TGF β1 is an important protein produced during chronic inflammation mediating the repair process via various downstream transduction proteins and ultimately producing fibrotic proteins which help in the repair process but permanently damage the glomerular cells.

Loss of NOD2 in macrophages improves colitis and tumorigenesis in a lysozyme-dependent manner

Background

Crohn's disease (CD) is a complex and poorly understood myeloid-mediated disorder. Genetic variants with loss of function in the NOD2 gene confer an increased susceptibility to ileal CD. While Nod2 in myeloid cells may confer protection against T-cell mediated ileopathy, it remains unclear whether it may promote resolution of the inflamed colon. In this study, we evaluated the function of Nod2 in myeloid cells in a model of acute colitis and colitis-associated colon cancer (CAC).

Methods

To ablate Nod2 specifically within the myeloid compartment, we generated LysMCre/+;Nod2fl/fl mice. The role of NOD2 was studied in a setting of Dextran Sodium Sulfate (DSS)-induced colitis and in azoxymethane (AOM)/DSS model. Clinical parameters were quantified by colonoscopy, histological, flow cytometry, and qRT-PCR analysis.

Results

Upon DSS colitis model, LysMCre/+;Nod2fl/fl mice lost less weight than control littermates and had less severe damage to the colonic epithelium. In the AOM/DSS model, endoscopic monitoring of tumor progression revealed a lowered number of adenomas within the colon of LysMCre/+;Nod2fl/fl mice, associated with less expression of Tgfb. Mechanistically, lysozyme M was required for the improved disease severity in mice with a defect of NOD2 in myeloid cells.

Conclusion

Our results indicate that loss of Nod2 signaling in myeloid cells aids in the tissue repair of the inflamed large intestine through lysozyme secretion by myeloid cells. These results may pave the way to design new therapeutics to limit the inflammatory and tumorigenic functions of NOD2.

NOD2 in monocytes negatively regulates macrophage development through TNFalpha

Objective

It is believed that intestinal recruitment of monocytes from Crohn's Disease (CD) patients who carry NOD2 risk alleles may repeatedly give rise to recruitment of pathogenic macrophages. We investigated an alternative possibility that NOD2 may rather inhibit their differentiation from intravasating monocytes.

Design

The monocyte fate decision was examined by using germ-free mice, mixed bone marrow chimeras and a culture system yielding macrophages and monocyte-derived dendritic cells (mo-DCs).

Results

We observed a decrease in the frequency of mo-DCs in the colon of Nod2-deficient mice, despite a similar abundance of monocytes. This decrease was independent of the changes in the gut microbiota and dysbiosis caused by Nod2 deficiency. Similarly, the pool of mo-DCs was poorly reconstituted in a Nod2-deficient mixed bone marrow (BM) chimera. The use of pharmacological inhibitors revealed that activation of NOD2 during monocyte-derived cell development, dominantly inhibits mTOR-mediated macrophage differentiation in a TNFα-dependent manner. These observations were supported by the identification of a TNFα-dependent response to muramyl dipeptide (MDP) that is specifically lost when CD14-expressing blood cells bear a frameshift mutation in NOD2.

Conclusion

NOD2 negatively regulates a macrophage developmental program through a feed-forward loop that could be exploited for overcoming resistance to anti-TNF therapy in CD.

Role of Myeloid Tet Methylcytosine Dioxygenase 2 in Pulmonary and Peritoneal Inflammation Induced by Lipopolysaccharide and Peritonitis Induced by Escherichia coli

Tet methylcytosine dioxygenase 2 (Tet2) mediates demethylation of DNA. We here sought to determine the expression and function of Tet2 in macrophages upon exposure to lipopolysaccharide (LPS), and in the host response to LPS induced lung and peritoneal inflammation, and during Escherichia (E.) coli induced peritonitis. LPS induced Tet2 expression in mouse macrophages and human monocytes in vitro, as well as in human alveolar macrophages after bronchial instillation in vivo. Bone marrow-derived macrophages from myeloid Tet2 deficient (Tet2^fl/flLysM^Cre) mice displayed enhanced production of IL-1β, IL-6 and CXCL1 upon stimulation with several Toll-like receptor agonists; similar results were obtained with LPS stimulated alveolar and peritoneal macrophages. Histone deacetylation was involved in the effect of Tet2 on IL-6 production, whilst methylation at the Il6 promoter was not altered by Tet2 deficiency. Tet2^fl/flLysM^Cre mice showed higher IL-6 and TNF levels in bronchoalveolar and peritoneal lavage fluid after intranasal and intraperitoneal LPS administration, respectively, whilst other inflammatory responses were unaltered. E. coli induced stronger production of IL-1β and IL-6 by Tet2 deficient peritoneal macrophages but not in peritoneal lavage fluid of Tet2^fl/flLysM^Cre mice after in vivo intraperitoneal infection. Tet2^fl/flLysM^Cre mice displayed enhanced bacterial growth during E. coli peritonitis, which was associated with a reduced capacity of Tet2^fl/flLysM^Cre peritoneal macrophages to inhibit the growth of E. coli in vitro. Collectively, these data suggest that Tet2 is involved in the regulation of macrophage functions triggered by LPS and during E. coli infection.

Role of Infections in the Pathogenesis of Rheumatoid Arthritis: Focus on Mycobacteria

Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disease characterized by chronic erosive polyarthritis. A complex interaction between a favorable genetic background, and the presence of a specific immune response against a broad-spectrum of environmental factors seems to play a role in determining susceptibility to RA. Among different pathogens, mycobacteria (including Mycobacterium avium subspecies paratuberculosis, MAP), and Epstein–Barr virus (EBV), have extensively been proposed to promote specific cellular and humoral response in susceptible individuals, by activating pathways linked to RA development. In this review, we discuss the available experimental and clinical evidence on the interplay between mycobacterial and EBV infections, and the development of the immune dysregulation in RA.

Differential Monocyte Actuation in a Three-Organ Functional Innate Immune System-on-a-Chip

A functional, human, multiorgan, pumpless, immune system-on-a-chip featuring recirculating THP-1 immune cells with cardiomyocytes, skeletal muscle, and liver in separate compartments in a serum-free medium is developed. This in vitro platform can emulate both a targeted immune response to tissue-specific damage, and holistic proinflammatory immune response to proinflammatory compound exposure. The targeted response features fluorescently labeled THP-1 monocytes selectively infiltrating into an amiodarone-damaged cardiac module and changes in contractile force measurements without immune-activated damage to the other organ modules. In contrast to the targeted immune response, general proinflammatory treatment of immune human-on-a-chip systems with lipopolysaccharide (LPS) and interferon-γ (IFN-γ) causes nonselective damage to cells in all three-organ compartments. Biomarker analysis indicates upregulation of the proinflammation cytokines TNF-α, IL-6, IL-10, MIP-1, MCP-1, and RANTES in response to LPS + IFN-γ treatment indicative of the M1 macrophage phenotype, whereas amiodarone treatment only leads to an increase in the restorative cytokine IL-6 which is a marker for the M2 phenotype. This system can be used as an alternative to humanized animal models to determine direct immunological effects of biological therapeutics including monoclonal antibodies, vaccines, and gene therapies, and the indirect effects caused by cytokine release from target tissues in response to a drug's pharmacokinetics (PK)/pharmacodynamics (PD) profile.

Two new compounds from the roots of Scrophularia ningpoensis and their anti-inflammatory activities

Aiming to investigate the bioactive constituents with anti-inflammatory activity from the roots of Scrophularia ningpoensis, two new compounds (1 and 3) were isolated from the extract of the roots of the plant. Their structures were elucidated on the basis of spectral analyses (UV, IR, NMR, and MS spectroscopy), as well as experimental and calculated electronic circular dichroism (ECD) analyses. All of the isolates were tested for their anti-inflammatory properties in terms of suppressing the production of NO in lipopolysaccharide-induced BV2 cells. Compound 2 exhibited stronger anti-inflammatory effects (77.65%) than the positive control curcumin (69.75%) at 10 μM.

NOD2 and TLR2 Signal via TBK1 and PI31 to Direct Cross-Presentation and CD8 T Cell Responses

NOD2 and TLR2 recognize components of bacterial cell wall peptidoglycan and direct defense against enteric pathogens. CD8+ T cells are important for immunity to such pathogens but how NOD2 and TLR2 induce antigen specific CD8+ T cell responses is unknown. Here, we define how these pattern recognition receptors (PRRs) signal in primary dendritic cells (DCs) to influence MHC class I antigen presentation. We show NOD2 and TLR2 phosphorylate PI31 via TBK1 following activation in DCs. PI31 interacts with TBK1 and Sec16A at endoplasmic reticulum exit sites (ERES), which positively regulates MHC class I peptide loading and immunoproteasome stability. Following NOD2 and TLR2 stimulation, depletion of PI31 or inhibition of TBK1 activity in vivo impairs DC cross-presentation and CD8+ T cell activation. DCs from Crohn's patients expressing NOD2 polymorphisms show dysregulated cross-presentation and CD8+ T cell responses. Our findings reveal unidentified mechanisms that underlie CD8+ T cell responses to bacteria in health and in Crohn's.

Role of NOD2 in antiphospholipid antibody-induced and bacterial MDP amplification of trophoblast inflammation

Women with antiphospholipid antibodies (aPL) are at high risk for pregnancy complications, such as preeclampsia. We previously demonstrated that aPL recognizing β₂GPI promote an extravillous trophoblast pro-inflammatory, anti-migratory and anti-angiogenic profile similar to that seen in preeclampsia. Since preeclampsia in the absence of aPL may have an underlying infectious element, women with aPL may be at increased risk for preeclampsia or other adverse outcomes if an infection is present. Our objective was to determine the impact the common bacterial component, muramyl dipeptide (MDP), has on trophoblast responses to aPL. Herein, we report that bacterial MDP amplifies trophoblast IL-1β expression, processing, and secretion in the presence of aPL through activation of NOD2. In the absence of MDP, NOD2 also mediates anti- β₂GPI antibody-induced trophoblast IL-1β and VEGF secretion. Additionally, we report a role for extravillous trophoblast vimentin as a novel danger signal that contributes to the aPL-induced trophoblast IL-1β production. Together our data indicate that NOD2 mediates trophoblast inflammatory and angiogenic responses to aPL alone, and mediates trophoblast inflammation in the presence of bacterial MDP. These findings suggest that a bacterial infection at the maternal-fetal interface may exacerbate the impact aPL have on trophoblast inflammation and, thus, on pregnancy outcome.

Synergistic interactions between NOD receptors and TLRs: Mechanisms and clinical implications

Interactions between pattern recognition receptors (PRRs) shape innate immune responses to particular classes of pathogens. Here, we review interactions between TLRs and nucleotide-binding oligomerization domain 1 and 2 (NOD1 and NOD2) receptors, two major groups of PRRs involved in innate recognition of bacteria. Most of experimental data both in vitro and in vivo suggest that NODs and TLRs synergize with each other at inducing the production of cytokines and antimicrobial peptides. Molecular mechanisms of this synergy remain poorly understood, although several scenarios can be proposed: (i) direct interactions of signaling pathways downstream of NODs and TLRs; (ii) mutual transcriptional regulation of unique components of NOD-dependent and TLR-dependent signaling pathways; and (iii) interactions at the post-transcriptional level. Potential practical implications of NOD-TLR synergy are dual. In sepsis, where synergistic effects probably contribute to excessive proinflammatory cytokine production, blockade of NOD1, and/or NOD2 in addition to TLR4 blockade may be required to achieve therapeutic benefit. On the other hand, synergistic combinations of relatively small doses of NOD and TLR agonists administered before infection could be used to boost innate resistance against bacterial pathogens.

Role of Muramyl Dipeptide in Lipopolysaccharide-Mediated Biological Activity and Osteoclast Activity

Lipopolysaccharide (LPS) is an endotoxin and bacterial cell wall component that is capable of inducing inflammation and immunological activity. Muramyl dipeptide (MDP), the minimal essential structural unit responsible for the immunological activity of peptidoglycans, is another inflammation-inducing molecule that is ubiquitously expressed by bacteria. Several studies have shown that inflammation-related biological activities were synergistically induced by interactions between LPS and MDP. MDP synergistically enhances production of proinflammatory cytokines that are induced by LPS exposure. Injection of MDP induces lethal shock in mice challenged with LPS. LPS also induces osteoclast formation and pathological bone resorption; MDP enhances LPS induction of both processes. Furthermore, MDP enhances the LPS-induced receptor activator of NF-κB ligand (RANKL) expression and toll-like receptor 4 (TLR4) expression both in vivo and in vitro. Additionally, MDP enhances LPS-induced mitogen-activated protein kinase (MAPK) signaling in stromal cells. Taken together, these findings suggest that MDP plays an important role in LPS-induced biological activities. This review discusses the role of MDP in LPS-mediated biological activities, primarily in relation to osteoclastogenesis.

NOD1 and NOD2: Molecular targets in prevention and treatment of infectious diseases

Nucleotide-binding oligomerization domain (NOD) 1 and NOD2 are pattern-recognition receptors responsible for sensing fragments of bacterial peptidoglycan known as muropeptides. Stimulation of innate immunity by systemic or local administration of NOD1 and NOD2 agonists is an attractive means to prevent and treat infectious diseases. In this review, we discuss novel data concerning structural features of selective and non-selective (dual) NOD1 and NOD2 agonists, main signaling pathways and biological effects induced by NOD1 and NOD2 stimulation, including induction of pro-inflammatory cytokines, type I interferons and antimicrobial peptides, induction of autophagy, alterations of metabolism. We also discuss interactions between NOD1/NOD2 and Toll-like receptor agonists in terms of synergy and cross-tolerance. Finally, we review available animal data on the role of NOD1 and NOD2 in protection against infections, and discuss how these data could be applied in human infectious diseases.

Design, synthesis and immunological evaluation of novel amphiphilic desmuramyl peptides

Muramyl dipeptide (MDP) - an essential bacterial cell wall component - is recognized by our immune system as pathogen-associated molecular pattern (PAMP) which results in immune responses with adverse toxic effects. In order to harness the beneficial properties from the pro-inflammatory characteristics of the bacterial cell wall motif, MDP was strategically re-designed while conserving the L-D configurations of the dipeptide moiety. The muramic acid was replaced with a hydrophilic arene and lipophilic chain was introduced at peptide end to give the amphiphilic desmuramyl peptides (DMPs). The novel DMPs were found to modulate the immune response by amplifying the LPS-induced surface glycoprotein (ICAM-1) expression in THP-1 cells without showing significant toxicity. Furthermore, these compounds were able to trigger the secretion of higher levels of pro-inflammatory cytokine (TNF-α) than the well-studied NOD2 agonist, Murabutide.

Efficacy of combined treatment of experimental tumors with cytostatic agents and GMDP-A

Objective of the study. To evaluate the pharmacological effects of N-acetylglucosaminyl-N-acetylmuramyl-L-alanyl-D-glutamic acid (GMDP-A) as a modifier of biological reactions, i. e. to study its modifying action in regard to traditional cytostatic chemotherapy. Materials and methods. The used drug agents were GMDP-A, cisplatinum, gemcitabine, cyclophosphamide, 5-fluorouracil. The transplanted murine tumors were Р-388 lymphocytic leukemia and S-37 sarcoma (solid and ascites variants), B-16 melanoma, CC-5 squamous cell carcinoma of the cervix uteri, C-26 adenocarcinoma of the colon, and AKATOL carcinoma of the colon (solid tumor variants). Efficacy indices were inhibition of tumor growth, and increase of life span of animals. Results. In the models of transplanted tumors in conventional mice, the influence of GMDP-A has been studied on therapeutic efficacy of cisplatinum (Р-388, S-37, В16, CC-5), 5-fluorouracyl (C-26, AKATOL), gemcitabine and cyclophosphamide (P-388) by using variations in single and total doses, time of the start of the treatment, as well as the route and site of the injection. It has been shown that GMDP-A has modified the efficacy of some cytostatic agents (cisplatinum, gemcitabine and cyclophosphamide) enhancing their antitumor activity irrespective of the location of the site of injection in regard to the tumor node. Conclusion. The obtained results proved the potency of GMDP-A as a modifier of biological reactions.

An in vitro investigation of immunomodulatory properties of Lactobacillus plantarum and L. delbrueckii cells and their extracellular polysaccharides

Many probiotic lactobacilli and their extracellular polysaccharides (EPS) have beneficial immunological properties. However, it is unclear how they elicit the host immune response. We thus investigated the immunological properties of UV-killed Lactobacillus delbrueckii TU-1 and L. plantarum KM-9 cells as well as their extracellular polysaccharides (EPSs). High-performance liquid chromatography and ion exchange chromatography analyses showed that their EPSs differ in sugar composition and sugar fractionation. The immunological properties were evaluated in a semi-intestinal model using a Transwell co-culture system that employed human intestinal epithelial (Caco-2) cells on the apical side and murine macrophage (RAW264.7) cells on the basolateral side. The UV-killed cells and EPSs were added to the apical side to allow direct contact with Caco-2 cells and incubated for 6 hr. After incubation, the amounts of tumor necrosis factor-α and several cytokines released by RAW264.7 or Caco-2 cells were quantified by cytotoxic activity on L929 cells (murine fibrosarcoma cell line) and quantitative reverse-transcriptase PCR. We found that the UV-killed cells and their EPSs had immunological effects on RAW264.7 cells via Caco-2 cells. The RAW264.7 cells showed different cytokine production profiles when treated with UV-killed cells and EPSs. The UV-killed cells and EPSs promoted a Th1-type cellular response. Furthermore, we found that the UV-killed cells sent positive signals through Toll-like receptor (TLR) 2. Meanwhile, neither EPS sent a positive signal through TLR4 and TLR2. This evidence suggests that both UV-killed cells of the lactobacillus strains and their EPSs trigger a Th1-type immune response in a human host, with the former triggering the response via the TLRs expressed on its epithelium and the latter employing a mechanism yet to be determined, possibly involving a novel receptor that is designed to recognize specific patterns of repeating sugar in the EPSs.

Toll-like Receptors, NOD1, and NOD2 in Oral Epithelial Cells

Oral epithelium might be the first barrier against oral bacteria in periodontal tissue. We hypothesized that oral epithelium is endowed with innate immune receptors for bacterial components, which play roles in host defense against bacterial infection without being accompanied by excessive inflammatory responses. We found clear expression of Toll-like receptor (TLR)4 as well as TLR2, and strong expression of NOD1 and NOD2 in normal oral epithelial tissues by immunohistochemical analysis. We also showed that primary oral epithelial cells in culture expressed these molecules using PCR, flow cytometry, and immunostaining. In inflamed oral epithelium, cell-surface localizations of TLR2 and TLR4 were more clearly observed than in healthy tissue. Upon stimulation with synthetic ligands for these receptors, the expression of β-defensin 2 was markedly up-regulated. These findings indicate that these molecules in oral epithelial cells are functional receptors that induce antibacterial responses.

Muramyl peptides activate innate immunity conjointly via YB1 and NOD2

Bacterial cell wall muramyl dipeptide (MDP) and glucosaminyl-MDP (GMDP) are potent activators of innate immunity. Two receptor targets, NOD2 and YB1, have been reported; we investigated potential overlap of NOD2 and YB1 pathways. Separate knockdown of NOD2 and YB1 demonstrates that both contribute to GMDP induction of NF-κB expression, a marker of innate immunity, although excess YB1 led to induction in the absence of NOD2. YB1 and NOD2 co-migrated on sucrose gradient centrifugation, and GMDP addition led to the formation of higher molecular mass complexes containing both YB1 and NOD2. Co-immunoprecipitation demonstrated a direct interaction between YB1 and NOD2, a major recombinant fragment of NOD2 (NACHT-LRR) bound to YB1, and complex formation was stimulated by GMDP. We also report subcellular colocalization of NOD2 and YB1. Although YB1 may have other binding partners in addition to NOD2, maximal innate immunity activation by muramyl peptides is mediated via an interaction between YB1 and NOD2.

Review: D-Galactosamine lethality model: scope and limitations

D-Galactosamine (D-galN) is well established as sensitizing mice and other animals to the lethal effects of TNF, specifically, and by several orders of magnitude. Protection by anti-TNF neutralizing antibody is complete, as is (metabolically-based) protection by uridine. Sensitization occurs regardless of the origin of the released TNF, whether it is released from macrophages and/or T-cells. The same is true for the challenging agent which leads to the release of TNF, whether it is endotoxin, a superantigen, lipoprotein, bacterial DNA, or bacteria, either killed or proliferating. Most studies have utilized endotoxin as the challenging agent, and more than 70 agents have been reported to confer protection against LPS and/or TNF challenge in the model. The model has provided new insight regarding modes of protection, including from dexamethasone, which protects against challenge from LPS but not from challenge by TNF. The D-galN lethality model has also been used to test for synergistic behavior between different bacterial components, and to test for lethality when only small amounts of the challenging agent are available (lipid A chemistry).

Three new alkaloids and three new phenolic glycosides from Liparis odorata

Three new alkaloids, liparis alkaloid A (1), B (2), C (3), and three new phenolic glycosides, liparis glycoside H (4), I (5), J (6), together with three known phenolic glycosides (7-9) were isolated from the whole plant of Liparis odorata. Their structures were characterized on the basis of extensive 1D-, 2D-NMR and HR-ESI-MS experiments. In addition, compounds 1-3 revealed hypolipidemic effects in the in vitro bioassays, and the ability to inhibit LPS-induced NO production of these isolated phenolic glycosides (4-9) was also evaluated.

Soluble β-(1,3)-glucans enhance LPS-induced response in the monocyte activation test, but inhibit LPS-mediated febrile response in rabbits: Implications for pyrogenicity tests

In the present study, we aimed to determine the influence of β-(1,3)-d-glucans on the LPS-induced pro-inflammatory cytokine response in the Monocyte Activation Test (MAT) for pyrogens, and on the LPS-induced febrile response in the Rabbit Pyrogen Test (RPT), thus evaluating the resulting effect in the outcome of each test. It was found that β-(1,3)-d-glucans elicited the production of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α, also known as endogenous pyrogens, but not enough to classify them as pyrogenic according to MAT. The same β-(1,3)-d-glucans samples were non-pyrogenic by RPT. However, β-(1,3)-d-glucans significantly enhanced the LPS-induced pro-inflammatory cytokines response in MAT, insomuch that samples containing non-pyrogenic concentrations of LPS become pyrogenic. On the other hand, β-(1,3)-d-glucans had no effect on sub-pyrogenic LPS doses in the RPT, but surprisingly, inhibited the LPS-induced febrile response of pyrogenic LPS concentrations. Thus, while β-(1,3)-d-glucans could mask the LPS pyrogenic activity in the RPT, they exerted an overstimulation of pro-inflammatory cytokines in the MAT. Hence, MAT provides higher safety since it evidences an unwanted biological response, which is not completely controlled and is overlooked by the RPT.

New Butyrolactone Type Lignans from Arctii Fructus and Their Anti-inflammatory Activities

Arctiidilactone (1), a novel rare butyrolactone lignan with a 6-carboxyl-2-pyrone moiety, and 11 new butyrolactone lignans (2-12) were isolated from the fruits of Arctium lappa L., together with 5 known compounds (13-17). Their structures were elucidated by interpretation of their spectroscopic data (1D and 2D NMR, UV, IR, ORD, and HRESIMS) and comparison to literature data. The absolute configurations of compounds 1-12 were determined by a combination of rotating-frame nuclear Overhauser effect spectroscopy (ROESY), circular dichroism (CD) spectroscopy, and Rh2(OCOCF3)4-induced CD spectroscopy. All of the compounds were tested for their anti-inflammatory properties in terms of suppressing the production of NO in lipopolysaccharide-induced BV2 cells. Compounds 1, 6, 8, and 10 exhibited stronger anti-inflammatory effects than the positive control curcumin, particularly 1, which exhibited 75.51, 70.72, and 61.17% inhibition at 10, 1, and 0.1 μM, respectively.

Macrophages polarization is mediated by the combination of PRR ligands and distinct inflammatory cytokines

Macrophages recognize microbes through Pattern Recognition Receptors (PRRs), and then release pro-inflammatory and anti-inflammatory cytokines. Recent studies have highlighted that collaboration between different PRRs. However, these studies have neglected the crosstalk between various PRRs on macrophages. In the present study, we investigated the interplay of nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) (NOD1, NOD2) and TLRs (TLR1, 2, 3, 4, 5, 6, 7, 8) in terms of macrophage activation, the expression and production of cytokines. The macrophages were stimulated with a single PRR ligand or a combination of TLR and NOD ligands. After 8 h of incubation, the mRNA expression of interleukin-1β (IL-1β), IL-4, IL-6, IL-10, IL-12p35, IL-12p40, IL-13, and interferon-γ (IFN-γ) was evaluated. The production of these cytokines was also measured. NOD2 synergized with TLR3 agonists on enhancement of IL-10 release. However, the combination of NOD1 with TLR3 ligands showed little effect on IL-10 production. Moreover, NOD2 inhibited the percentages of CD11b + F4/80 + cells activated by TLR3 agonist.

Innate immunity: Bacterial cell-wall muramyl peptide targets the conserved transcription factor YB-1

The bacterial cell wall muramyl dipeptides MDP and glucosaminyl-MDP (GMDP) are powerful immunostimulators but their binding target remains controversial. We previously reported expression cloning of GMDP-binding polypeptides and identification of Y-box protein 1 (YB-1) as their sole target. Here we show specific binding of GMDP to recombinant YB-1 protein and subcellular colocalization of YB-1 and GMDP. GMDP binding to YB-1 upregulated gene expression levels of NF-κB2, a mediator of innate immunity. Furthermore, YB-1 knockdown abolished GMDP-induced Nfkb2 expression. GMDP/YB-1 stimulation led to NF-κB2 cleavage, transport of activated NF-κB2 p52 to the nucleus, and upregulation of NF-κB2-dependent chemokine Cxcr4 gene expression. Therefore, our findings identify YB-1 as new target for muramyl peptide signaling.

Muramyl dipeptide enhances lipopolysaccharide-induced osteoclast formation and bone resorption through increased RANKL expression in stromal cells

Lipopolysaccharide (LPS) is bacterial cell wall component capable of inducing osteoclast formation and pathological bone resorption. Muramyl dipeptide (MDP), the minimal essential structural unit responsible for the immunological activity of peptidoglycans, is ubiquitously expressed by bacterium. In this study, we investigated the effect of MDP in LPS-induced osteoclast formation and bone resorption. LPS was administered with or without MDP into the supracalvariae of mice. The number of osteoclasts, the level of mRNA for cathepsin K and tartrate-resistant acid phosphatase (TRAP), the ratio of the bone destruction area, the level of tartrate-resistant acid phosphatase form 5b (TRACP 5b), and C-terminal telopeptides fragments of type I collagen as a marker of bone resorption in mice administrated both LPS and MDP were higher than those in mice administrated LPS or MDP alone. On the other hand, MDP had no effect on osteoclastogenesis in parathyroid hormone administrated mice. MDP enhanced LPS-induced receptor activator of NF-κB ligand (RANKL) expression and Toll-like receptor 4 (TLR4) expression in vivo and in stromal cells in vitro. MDP also enhanced LPS-induced mitogen-activated protein kinase (MAPK) signaling, including ERK, p38, and JNK, in stromal cells. These results suggest that MDP might play an important role in pathological bone resorption in bacterial infection diseases.

Hm-MyD88 and Hm-SARM: two key regulators of the neuroimmune system and neural repair in the medicinal leech

Unlike mammals, the CNS of the medicinal leech can regenerate damaged neurites, thus restoring neural functions after lesion. We previously demonstrated that the injured leech nerve cord is able to mount an immune response promoting the regenerative processes. Indeed neurons and microglia express sensing receptors like Hm-TLR1, a leech TLR ortholog, associated with chemokine release in response to a septic challenge or lesion. To gain insights into the TLR signaling pathways involved during these neuroimmune responses, members of the MyD88 family were investigated. In the present study, we report the characterization of Hm-MyD88 and Hm-SARM. The expression of their encoding gene was strongly regulated in leech CNS not only upon immune challenge but also during CNS repair, suggesting their involvement in both processes. This work also showed for the first time that differentiated neurons of the CNS could respond to LPS through a MyD88-dependent signalling pathway, while in mammals, studies describing the direct effect of LPS on neurons and the outcomes of such treatment are scarce and controversial. In the present study, we established that this PAMP induced the relocalization of Hm-MyD88 in isolated neurons.

The intracellular sensor NOD2 induces microRNA-29 expression in human dendritic cells to limit IL-23 release

NOD2 is an intracellular sensor that contributes to immune defense and inflammation. Here we investigated whether NOD2 mediates its effects through control of microRNAs (miRNAs). miR-29 expression was upregulated in human dendritic cells (DCs) in response to NOD2 signals, and miR-29 regulated the expression of multiple immune mediators. In particular, miR-29 downregulated interleukin-23 (IL-23) by targeting IL-12p40 directly and IL-23p19 indirectly, likely via reduction of ATF2. DSS-induced colitis was worse in miR-29-deficient mice and was associated with elevated IL-23 and T helper 17 signature cytokines in the intestinal mucosa. Crohn's disease (CD) patient DCs expressing NOD2 polymorphisms failed to induce miR-29 upon pattern recognition receptor stimulation and showed enhanced release of IL-12p40 on exposure to adherent invasive E. coli. Therefore, we suggest that loss of miR-29-mediated immunoregulation in CD DCs might contribute to elevated IL-23 in this disease.

Therapeutic targeting of NOD1 receptors

The nucleotide-binding oligomerization domain 1 (NOD1) protein is an intracellular receptor for breakdown products of peptidoglycan (PGN), an essential bacterial cell wall component. NOD1 responds to γ-D-glutamyl-meso-diaminopimelic acid, which is an epitope unique to PGN structures from all Gram-negative bacteria and certain Gram-positive bacteria. Upon ligand recognition, NOD1 undergoes conformational changes and self-oligomerization mediated by the nucleotide-binding NACHT domains, followed by the recruitment and activation of the serine threonine kinase receptor-interacting protein 2 leading to the activation of NF-κB and MAPK pathways and induction of inflammatory genes. Much of our knowledge is derived from seminal studies using mice deficient in NOD1 and confirming an essential role for NOD1 in the host immune response against gastrointestinal and respiratory pathogens. In addition, recent studies have revealed a role for intracellular NOD1 receptors in the regulation of vascular inflammation and metabolism. This review will discuss our current understanding of intracellular NOD1 receptors in host immunity and chronic inflammatory disorders with a focus on cardiovascular diseases. Although therapeutic advances may have to wait until the complex interplay with pathogens, danger signals, other pattern recognition receptors and overlapping metabolic pathways is further unravelled, the steadily growing body of knowledge suggest that NOD1 antagonism might represent attractive candidate to reduce excessive inflammation associated to intestinal, cardiovascular and metabolic diseases.

Macrophages in tuberculosis: friend or foe

Tuberculosis (TB) remains one of the greatest threats to human health. The causative bacterium, Mycobacterium tuberculosis (Mtb), is acquired by the respiratory route. It is exquisitely human adapted and a prototypic intracellular pathogen of macrophages, with alveolar macrophages (AMs) being the primary conduit of infection and disease. The outcome of primary infection is most often a latently infected healthy human host, in whom the bacteria are held in check by the host immune response. Such individuals can develop active TB later in life with impairment in the immune system. In contrast, in a minority of infected individuals, the host immune response fails to control the growth of bacilli, and progressive granulomatous disease develops, facilitating spread of the bacilli via infectious aerosols coughed out into the environment and inhaled by new hosts. The molecular details of the Mtb-macrophage interaction continue to be elucidated. However, it is clear that a number of complex processes are involved at the different stages of infection that may benefit either the bacterium or the host. Macrophages demonstrate tremendous phenotypic heterogeneity and functional plasticity which, depending on the site and stage of infection, facilitate the diverse outcomes. Moreover, host responses vary depending on the specific characteristics of the infecting Mtb strain. In this chapter, we describe a contemporary view of the behavior of AMs and their interaction with various Mtb strains in generating unique immunologic lung-specific responses.

Lipopolysaccharide induces the expression of an autocrine prolactin loop enhancing inflammatory response in monocytes

Background

Prolactin from pituitary gland helps maintain homeostasis but it is also released in immune cells where its function is not completely understood. Pleiotropic functions of prolactin (PRL) might be mediated by different isoforms of its receptor (PRLr).

Methods

The aim of this study was to investigate the relationship between the eventual synthesis of PRL and PRLr isoforms with the inflammatory response in monocytes. We used THP-1 and monocytes isolated from healthy subjects stimulated with lipopolysaccharide (LPS). Western blot, real time PCR and immunocytochemistry were performed to identify both molecules. The bioactivity of the PRL was assessed using a bioassay and ELISA to detect pro inflammatory cytokines.

Results

PRLr mRNA and PRL mRNA were synthesized in THP-1 monocytes activated with LPS with peaks of 300-fold and 130-fold, respectively. The long (100 kDa) and the intermediate (50 kDa) isoforms of PRLr and big PRL (60 kDa) were time-dependent upregulated for monocytes stimulated with LPS. This expression was confirmed in monocytes from healthy subjects. The PRLr intermediate isoform and the big PRL were found soluble in the culture media and later in the nucleus in THP-1 monocytes stimulated with LPS. Big PRL released by monocytes showed bioactivity in Nb2 Cells, and both PRL and PRLr, synthesized by monocytes were related with levels of nitrites and proinflammatory citokines.

Conclusions

Our results suggest the expression of a full-autocrine loop of PRL enhances the inflammatory response in activated monocytes. This response mediated by big PRL may contribute to the eradication of potential pathogens during innate immune response in monocytes but may also contribute to inflammatory disorders.

Alveolar macrophage phagocytic activity is enhanced with LPS priming, and combined stimulation of LPS and lipoteichoic acid synergistically induce pro-inflammatory cytokines in pigs

The objective of the present study was to investigate LPS and lipoteichoic acid (LTA)-induced TLRs, associated signaling molecules and inflammatory mediators, as well as to compare their combined effect in porcine alveolar macrophages. Macrophages were incubated for 24 h with various concentrations of LPS, LTA, LPS + LTA or control. Multiple concentrations of LPS elicited marked up-regulation in mRNA for TLR2 and TLR4, CD14, MD2, MyD88, IRAK-4 and TRAF6 compared with the control. LTA had no effect on TLR4 and MD2; only higher doses up-regulated TLR2, CD14, MyD88, IRAK-4 and TRAF6 mRNA. LPS-activated cells released IL1-β, IL12-β, TNF-α, IL-6, IL-8, IFN-γ and IL-10 in a dose-dependent manner, while LTA had no effect on IL-1β, IL-6 and IFN-γ. Higher doses of LTA induced IL-12β, TNF-α, IL-8 and IL-10. Combined stimulation augmented TLR2, CD14 and MyD88 mRNA, and subsequently produced elevated levels of IL-6, TNF-α and IL-8 when compared with LPS and LTA alone. Additionally, phagocytosis of macrophages was significantly increased following low concentration of LPS treatment. Only low levels of NO (nitric oxide) were detected in the LPS group. Overall, compared with LPS, LTA was a relatively weak inducer, and co-stimulation accelerated gene and cytokine production associated with pulmonary innate immune function.

Nucleotide-binding oligomerization domain 2 signaling promotes hyperresponsive macrophages and colitis in IL-10-deficient mice

IL-10 contributes to the maintenance of intestinal homeostasis via the regulation of inflammatory responses to enteric bacteria. Loss of IL-10 signaling results in spontaneous colitis in mice and early onset enterocolitis in humans. Nucleotide-binding oligomerization domain (NOD) 2 is an intracellular receptor of bacterial peptidoglycan products, and, although NOD2 mutations are associated with Crohn's disease, the precise role of NOD2 in the development of intestinal inflammation remains undefined. To determine the role of NOD2 in the development of colitis on the clinically relevant genetic background of IL-10-deficient signaling, we generated mice lacking IL-10 and NOD2 (IL-10(-/-)NOD2(-/-)). Loss of NOD2 in IL-10(-/-) mice resulted in significant amelioration of chronic colitis, indicating that NOD2 signaling promotes the development of intestinal inflammation in IL-10(-/-) mice. Contrary to previous reports investigating immune function in NOD2(-/-) mice, T cell proliferative capacity and IL-2 production were not impaired, and immune polarization toward type 1 immunity was not affected. However, loss of NOD2 in IL-10-deficient macrophages reduced IL-6, TNF-α, and IL-12p40 production in response to bacterial stimulation. Further analysis of the intrinsic macrophage response before the onset of inflammation revealed that, in the absence of IL-10, synergistic signaling between various TLRs and NOD2 resulted in hyperresponsive, proinflammatory macrophages, thus providing the appropriate immune environment for the development of colitis. Data presented in this study demonstrate that NOD2 signaling contributes to intestinal inflammation that arises through loss of IL-10 and provides mechanistic insight into the development of colitis in inflammatory bowel disease patients with impaired IL-10 signaling.

Bioactives from probiotics for dermal health: functions and benefits

Probiotics have been extensively reviewed for decades, emphasizing on improving general gut health. Recently, more studies showed that probiotics may exert other health-promoting effects beyond gut well-being, attributed to the rise of the gut-brain axis correlations. Some of these new benefits include skin health such as improving atopic eczema, atopic dermatitis, healing of burn and scars, skin-rejuvenating properties and improving skin innate immunity. Increasing evidence has also showed that bacterial compounds such as cell wall fragments, their metabolites and dead bacteria can elicit certain immune responses on the skin and improve skin barrier functions. This review aimed to underline the mechanisms or the exact compounds underlying the benefits of bacterial extract on the skin based on evidences from in vivo and in vitro studies. This review could be of help in screening of probiotic strains with potential dermal enhancing properties for topical applications.

Adherent lipopolysaccharide inhibits the osseointegration of orthopedic implants by impairing osteoblast differentiation

Osseointegration is the process by which an orthopedic implant makes direct bone-to-implant contact and is crucial for the long-term function of the implant. Surface contaminants, such as bacterial debris and manufacturing residues, may remain on orthopedic implants after sterilization and impair osseointegration. For example, specific lots of implants that were associated with impaired osseointegration and high failure rates were discovered to have contaminants including bacterial debris. Therefore, the goals of this study were to determine if bacterial debris exists on sterile orthopedic implants and if adherent bacterial debris inhibits the osseointegration of orthopedic implants. We found that debris containing lipopolysaccharide (LPS) from Gram-negative bacteria exists on both sterile craniofacial implants and wrist implants. Levels of bacterial debris vary not only between different lots of implants but within an individual lot. Using our murine model of osseointegration, we found that ultrapure LPS adherent to the implants inhibited bone-to-implant contact and biomechanical pullout measures. Analysis of osseointegration in knock-out mice demonstrated that adherent LPS inhibited osseointegration by signaling through its primary receptor, Toll-like receptor 4, and not by signaling through Toll-like receptor 2. Ultrapure LPS adherent to titanium alloy discs had no detectable effect on early stages of MC3T3-E1 osteogenesis in vitro such as attachment, spreading or growth. However, later stages of osteogenic differentiation and mineralization were inhibited by adherent LPS. Thus, LPS may inhibit osseointegration in part through cell autonomous effects on osteoblasts. These results highlight bacterial debris as a type of surface contaminant that can impair the osseointegration of orthopedic implants.

A vitamin D3 analog augmented interleukin-8 production by human monocytic cells in response to various microbe-related synthetic ligands, especially NOD2 agonistic muramyldipeptide

Active metabolite vitamin D(3), 1α,25-dihydroxyvitamin D(3), is a pleiotropic factor and exhibits various physiological functions, including immunomodulating activities. In this study, the possible regulation of innate immune responses of human monocytic cells by a vitamin D(3) analog was examined. Human monocytic THP-1 cells were pre-treated with OCT, vitamin D(3) analog, 1α,25-dihydroxy-22-oxavitamin D(3), followed by stimulation with various chemically synthesized Toll-like receptors (TLR) and NOD1 and NOD2 ligands. OCT-treated cells produced more IL-8 than non-treated cells upon stimulation with various chemically-synthesized ligands: TLR2-agonistic lipopeptide (FSL-1), TLR3-agonistic poly I:C, TLR4-agonistic lipid A (E. coli-type LA-15-PP), NOD1-agonistic FK565 and NOD2-agonistic muramyldipeptide (MDP). Among the ligands, MDP was the highest inducer of IL-8 production in OCT-treated THP-1 cells, and IL-8 production increased depending on the treatment time until 72h. OCT up-regulated the expression of NOD2 in THP-1 cells, and OCT-treated cells exhibited higher activation of p38, JNK and ERK in the MAPK pathway, IκBα in the NF-κB pathway, and TAK1 upstream in response to MDP than non-treated cells. Analysis using siRNA against NOD2 and inhibitors of specific signal molecules indicated that the existence of NOD2 and activation of the above signaling molecules are required for enhanced production of IL-8 in OCT-treated THP-1 cells. These findings suggested that NOD2, NF-κB and MAPK pathways are involved in the activity of OCT to augment the response of human monocytic cells to MDP.

NOD2 signaling and role in pathogenic mycobacterium recognition, infection and immunity

The Mycobacterium pathogens acquire additional properties to expand their pathogenicity and existence spaces. The interaction between pathogenic Mycobacterium components and receptors of host innate immune system is critical for the infection outcome, particularly for the macrophage activation. NOD2 (Nucleotide binding oligomerization domain 2), an intracellular pathogen recognition sensor, attenuates two key putative host bacterial killing mechanisms: interfering the production of TNF-alpha and inducing resistance to apoptosis. Multiple evidences have shown that NOD2 acts as a non-redundant recognition system of Mycobacterium, a successful pathogen with many mechanisms to evade host immunity and leading to insidious disease. Understanding the complex interaction between host and pathogen mediated by NOD2 signaling, might provide novel insight into the pathogenesis of pathogenic Mycobacterium and inform the development of more effective vaccines and therapeutics.

Essential role of toll-like receptor 4 in Acinetobacter baumannii-induced immune responses in immune cells

TLR4 is a membrane sensor for lipopolysaccharide (LPS), a major cell wall component of gram-negative bacteria. In this study, we investigated the role of TLR4 on innate immune responses in immune cells against Acinetobacter baumannii. Bone marrow-derived macrophages (BMDMs) and dendritic cells (BMDCs) were isolated from WT and TLR4-deficient mice and infected with A. baumannii ATCC 15150. ELISA assay revealed that the production of IL-6 and TNF-α by A. baumannii was impaired in TLR4-deficient macrophages. However, absence of TLR2 did not affect A. baumannii-induced cytokines production in BMDMs. In addition, TLR4 was required for the optimal production of IL-6, TNF-α, and IL-12 in BMDCs in response to A. baumannii. Western blot analysis showed that A. baumannii leads to the activation of NF-κB and MAPKs (p38, ERK, and JNK) in macrophages via TLR4-dependent pathway. mRNA expression of iNOS and NO production was elicited in WT BMDMs in response to A. baumannii, which was abolished in TLR4-deficienct cells. Bacterial killing ability against A. baumannii was impaired in TLR4-deficient BMDMs. In addition, A. baumannii induced apoptosis in BMDMs via TLR4-independent pathway. Our results demonstrate that TLR4 is essential for initiating innate immune response of macrophages against A. baumannii infection.

Regulation of Salmonella flagellin-induced interleukin-8 in intestinal epithelial cells by muramyl dipeptide

Toll-like receptor 5 (TLR5) and nucleotide-binding oligomerization domain 2 (Nod2) are two important pattern recognition receptors involved in innate immunity to invading pathogens. Flagellin, recognized by TLR5, is Salmonella's dominant pro-inflammatory determinant in intestinal epithelial cells (IECs). Nod2 has played a pivotal role in protecting against intestinal bacterial infection. Therefore the aim of the study is to investigate regulation of Salmonella flagellin-induced interleukin (IL)-8 (IL-8) in IECs by Nod2 agonist, muramyl dipeptide (MDP). We found that MDP by itself induced only a weak IL-8 secretion in Caco-2 cells. However, it did show synergistic enhancement on flagellin-induced IL-8 production in Caco-2 cells, possibly caused by flagellin-mediated enhanced Nod2 recruitment into cell membrane. By Western blot and siRNA, we showed ERK and NF-κB, Nod2 and Rip2 were involved in the synergistic effect of MDP. These findings suggested that the cooperation of TLR5 and Nod2 in IECs regulates inflammatory response to Salmonella infection.

Probiotic genomic DNA reduces the production of pro-inflammatory cytokine tumor necrosis factor-alpha

The effect of Lactobacillus plantarum genomic DNA on lipopolysaccharide (LPS)-induced mitogen-activated protein kinase (MAPK) activation, nuclear factor-kappa B activation, and the expressions of tumor necrosis factor-alpha, interleukin-1 receptor-associated kinase M, and the pattern recognition receptor were examined. Pretreatment of p-gDNA inhibited the phosphorylation of MAPKs and nuclear factor-kappa B, and also inhibited LPS-induced TNF-α production in response to subsequent LPS stimulation. L. plantarum genomic DNA-mediated inhibition of signaling pathway and tumor necrosis factor-alpha was accompanied by the suppression of toll-like receptor (TLR) 2, TLR4, and TLR9 and the induction of interleukin-1 receptor-associated kinase M, a negative regulator of TLR. This study can extend our understanding of the biological function of probiotic genomic DNA as an anti-inflammatory agent.