Gram-Negative Bacteria Salmonella typhimurium Boost Leukotriene Synthesis Induced by Chemoattractant fMLP to Stimulate Neutrophil Swarming

Leukotriene synthesis in neutrophils is critical for host survival during infection. In particular, leukotriene B4 (LTB4) is a powerful neutrophil chemoattractant that plays a crucial role in neutrophil swarming. In this work, we demonstrated that preincubation of human neutrophils with Salmonella typhimurium strongly stimulated LTB4 production induced by the bacterial chemoattractant, peptide N-formyl-L-methionyl-L-leucyl-l-phenylalanine (fMLP), while the reverse sequence of additions was ineffective. Preincubation with bacterial lipopolysaccharide or yeast polysaccharide zymosan particles gives weaker effect on fMLP-induced LTB4 production. Activation of 5-lipoxygenase (5-LOX), a key enzyme in leukotrienes biosynthesis, depends on rise of cytosolic concentration of Ca2+ and on translocation of the enzyme to the nuclear membrane. Both processes were stimulated by S. typhimurium. With an increase in the bacteria:neutrophil ratio, the transformation of LTB4 to ω-OH-LTB4 was suppressed, which further supported increased concentration of LTB4. These data indicate that in neutrophils gathered around bacterial clusters, LTB4 production is stimulated and at the same time its transformation is suppressed, which promotes neutrophil swarming and elimination of pathogens simultaneously.

Efficacy of Oregano Essential Oil Extract in the Inhibition of Bacterial Lipopolysaccharide (LPS)-Induced Osteoclastogenesis Using RAW 264.7 Murine Macrophage Cell Line—An In-Vitro Study

Gram-negative, anaerobic bacterias are predominate in periapical infections. The bacterial lipopolysaccharide (LPS) initiates the process of inflammation and periapical bone resorption. Usage of various medicaments retards or inactivates the bacterial endotoxin (LPS). However, the results are not highly effective. In recent years, owing to antimicrobial resistance, the shift from conventional agents to herbal agents has been increased tremendously in research. Keeping this in mind, the present study was formulated to evaluate the efficacy of oregano essential oil in inhibiting bacterial LPS- induced osteoclastogenesis. Four different concentrations (0 ng/mL, 25 ng/mL, 50 ng/mL, and 100 ng/mL) of oregano essential oil extract were added into 96-well culture plate. Under light microscope, quantification of osteoclast cells was performed. One-way ANOVA with post-hoc Tukey test was carried out on SPSS v21. A significant reduction (p < 0.001) in the osteoclast was observed in the experimental groups compared to no oregano essential oil extract (control). A dose-dependent significant reduction (p < 0.001) in osteoclast formation was observed among the experimental groups, with lesser osteoclast seen in group IV with 100 ng/mL of oregano essential oil extract. Thus, it can be concluded that oregano essential oil extract can be utilized as a therapeutic agent that can target bacterial LPS-induced osteoclastogenesis. However, randomized controlled studies should be conducted to assess the potential use of this extract in the periapical bone resorption of endodontic origin.

SARS-CoV-2 spike protein as a bacterial lipopolysaccharide delivery system in an overzealous inflammatory cascade

Accumulating evidence indicates a potential role for bacterial lipopolysaccharide (LPS) in the overactivation of the immune response during SARS-CoV-2 infection. LPS is recognised by Toll-like receptor 4 (TLR4) in innate immunity. Here, we showed that LPS binds to multiple hydrophobic pockets spanning both the S1 and S2 subunits of the SARS-CoV-2 spike (S) protein. LPS binds to the S2 pocket with a lower affinity compared to S1, suggesting its possible role as an intermediate in the TLR4 cascade. Congruently, nuclear factor-kappa B (NF-κB) activation in vitro is strongly boosted by S2. In vivo, however, a boosting effect is observed for both S1 and S2, with the former potentially facilitated by proteolysis. Collectively, our study suggests the S protein may act as a delivery system for LPS in host innate immune pathways. The LPS binding pockets are highly conserved across different SARS-CoV-2 variants and therefore represent potential therapeutic targets.

Cytosolic Sensor of Bacterial Lipopolysaccharide in Human Macrophages

Inflammasomes are cytosolic supramolecular organizing centers that, in response to pathogen-derived molecules and endogenous danger signals, assemble and activate innate immune responses. Bacterial lipopolysaccharide (LPS) is an inflammasome trigger and a major mediator of inflammation during infection, including during the potentially lethal condition sepsis. Activation of most inflammasomes is triggered by sensing of pathogen products by a specific host cytosolic nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain containing protein (NLRP) or other sensor protein that in turn activates a pro-inflammatory caspase. LPS that accesses the cell cytosol (cLPS) induces cell-autonomous activation of a non-canonical inflammasome that contains caspases-4/5 in humans or caspase-11 in mice1-3. Whereas the NLRPs that sense most pathogen triggers have been identified, no NLRP is known to sense cLPS, which together with the observation that caspases-4, -5, and -11 bind LPS in vitro4, has led to the postulate that inflammasome activation by cLPS occurs independent of an NLRP. Here we show that primate-specific NLRP11 senses cLPS and promotes the activation of caspase-4. We found that in response to infection by each of several gram-negative intracellular bacterial pathogens or to LPS transfection, efficient activation of the non-canonical pathway in human-derived macrophages depends on NLRP11. Further, we found that in both immortalized human-derived macrophages and primary human macrophages, the dependence of the non-canonical pathway on NLRP11 is due to detection of cLPS. Moreover, in cell lysates, NLRP11 binds LPS independently of caspase-4 and binds caspase-4 independently of LPS. Our results demonstrate that NLRP11 senses cLPS and promotes LPS-dependent activation of caspase-4. NLRP11 is a previously missing link in the human non-canonical inflammasome activation pathway.

Gram-Negative Bacterial Lipopolysaccharide Promotes Tumor Cell Proliferation in Breast Implant-Associated Anaplastic Large-Cell Lymphoma

Breast implant-associated anaplastic large-cell lymphoma (BIA-ALCL) is a distinct malignancy associated with textured breast implants. We investigated whether bacteria could trigger the activation and multiplication of BIA-ALCL cells in vitro. BIA-ALCL patient-derived BIA-ALCL tumor cells, BIA-ALCL cell lines, cutaneous ALCL cell lines, an immortal T-cell line (MT-4), and peripheral blood mononuclear cells (PBMC) from BIA-ALCL, capsular contracture, and primary augmentation patients were studied. Cells were subjected to various mitogenic stimulation assays including plant phytohemagglutinin (PHA), Gram-negative bacterial lipopolysaccharide (LPS), Staphylococcal superantigens enterotoxin A (SEA), toxic shock syndrome toxin-1 (TSST-1), or sterilized implant shells. Patient-derived BIA-ALCL tumor cells and BIA-ALCL cell lines showed a unique response to LPS stimulation. This response was dampened significantly in the presence of a Toll-like receptor 4 (TLR4) inhibitor peptide. In contrast, cutaneous ALCL cells, MT-4, and PBMC cells from all patients responded significantly more to PHA, SEA, and TSST-1 than to LPS. Breast implant shells of all surface grades alone did not produce a proliferative response of BIA-ALCL cells, indicating the breast implant does not act as a pro-inflammatory stimulant. These findings indicate a possible novel pathway for LPS to promote BIA-ALCL cell proliferation via a TLR4 receptor-mediated bacterial transformation of T-cells into malignancy.

Necrotizing Enterocolitis: LPS/TLR4-Induced Crosstalk Between Canonical TGF-β/Wnt/β-Catenin Pathways and PPARγ

Necrotizing enterocolitis (NEC) represents one of the major causes of morbidity and mortality in premature infants. Several recent studies, however, have contributed to a better understanding of the pathophysiology of this dreadful disease. Numerous intracellular pathways play a key role in NEC, namely: bacterial lipopolysaccharide (LPS), LPS toll-like receptor 4 (TLR4), canonical Wnt/β-catenin signaling and PPARγ. In a large number of pathologies, canonical Wnt/β-catenin signaling and PPARγ operate in opposition to one another, so that when one of the two pathways is overexpressed the other is downregulated and vice-versa. In NEC, activation of TLR4 by LPS leads to downregulation of the canonical Wnt/β-catenin signaling and upregulation of PPARγ. This review aims to shed light on the complex intracellular mechanisms involved in this pathophysiological profile by examining additional pathways such as the GSK-3β, NF-κB, TGF-β/Smads, and PI3K-Akt pathways.

Morphofunctional Parameters of the Spleen Under Immobilization Stress and the Use of Bacterial Lipopolysaccharide

The aimof this study was to determine the morphofunctional features of the spleen in rats under immobilization stress and administration of bacterial lipopolysaccharide.Material and methods.60 white Wistar rats were divided into 4 groups. The animals of the first control group were injected with saline. The rats of the second control group were injected with lipopolysaccharide. In the rats of the third group, immobilization stress was induced and the animals of this group were injectedwith saline. In rats of the fourth group, immobilization stress was also caused and lipopolysaccharide was administered in the form of the drug Pyrogenal (Medgamal, Russia) in a dose of 100 µg/kg of body weight. Fragments of the spleen were fixed in a 10% solution of neutral formalin, dehydrated in alcohols of increasing strength, and embedded in paraffin. Thin paraffin sections 4–5 µm thick were stained with hematoxylin and eosin. The area of longitudinal sections of the spleen, the area of the white and red pulp were determined planimetrically. Using a screw m icrometer eyepiece, the width of the reactive center of the lymph nodes of the white pulp, the width of the mantle and marginal zone of the nodules, as well as the width of the periarterial lymphoid sheath were measured (40–50 measurements for each animal).Results.It was found that on the 3rd day after the stress morphological signs of a sharp decrease in the activity of the white pulp were revealed. On the 8th day, pronounced recovery processes in the spleen were noted, however, complete restoration of the structure of the spleen did not occur. On the 3rd and 8th days after stress and administration of lipopolysaccharide, no signs of inhibition of the activity of the white and red pulp were found in the spleen; morphological parameters of the spleen did not differ from the control values.