Intrinsic nitric oxide-stimulatory activity of lipoteichoic acids from different Gram-positive bacteria

Lactobacillus rhamnosus Affects Rat Peritoneal Cavity Cell Response to Stimulation with Gut Microbiota: Focus on the Host Innate Immunity

Gut microbiota contribute to shaping the immune repertoire of the host, whereas probiotics may exert beneficial effects by modulating immune responses. Having in mind the differences in both the composition of gut microbiota and the immune response between rats of Albino Oxford (AO) and Dark Agouti (DA) rat strains, we investigated if intraperitoneal (i.p.) injection of live Lactobacillus rhamnosus (LB) may influence peritoneal cavity cell response to in vitro treatments with selected microbiota in the rat strain-dependent manner. Peritoneal cavity cells from AO and DA rats were lavaged two (d2) and seven days (d7) following i.p. injection with LB and tested for NO, urea, and H₂O₂ release basally, or upon in vitro stimulation with autologous E.coli and Enterococcus spp. Whereas the single i.p. injection of LB nearly depleted resident macrophages and increased the proportion of small inflammatory macrophages and monocytes on d2 in both rat strains, greater proportion of MHCII^hiCD163^- and CCR7⁺ cells and increased NO/diminished H₂O₂ release in DA compared with AO rats suggest a more intense inflammatory priming by LB in this rat strain. Even though E.coli- and/or Enterococcus spp.-induced rise in H₂O₂ release in vitro was abrogated by LB in cells from both rat strains, LB prevented microbiota-induced increase in NO/urea ratio only in cells from AO and augmented it in cells from DA rats. Thus, the immunomodulatory properties may not be constant for particular probiotic bacteria, but shaped by innate immunity of the host.

Enterococcus faecalis and Staphylococcus aureus stimulate nitric oxide production in macrophages and fibroblasts in vitro

Aim: Nitric oxide (NO) is an important mediator related to damage of the pulp tissue and at the same time to regenerative pulp processes. However, it is not clear how common endodontic microorganisms can regulate this mediator. This study aimed to investigate NO production by macrophages and fibroblasts against Enterococcus faecalis- and Staphylococcus aureus-antigens. Methods: RAW 264.7 macrophages and L929 fibroblast cell lines were stimulated with different heat-killed (HK) antigen concentrations (105-108 colony forming units - CFU) from E. faecalis and S. aureus with or without interferon-gamma (IFN-γ). Cell viability by MTT colorimetric assay and NO production from the culture supernatants were evaluated after 72 h. Results: Data here reported demonstrated that none of the antigen concentrations decreased cell viability in macrophages and fibroblasts. The presence of HK-S. aureus and HK-E. faecalis antigen- stimulated NO production with or without IFN-γ on RAW 264.7. The HK-S. aureus antigen stimulated NO production in L929 fibroblasts with or without IFN-γ, and the highest concentration of HK-E. faecalis with IFN-γ also stimulated NO production by these cells. Conclusion: The amount of NO produced by macrophages and fibroblasts may be involved in the concentration and type of prevalent endodontic microorganisms, generating new answers for the understanding of pulpal revascularization/regeneration processes.

Ability of Lactobacillus plantarum lipoteichoic acid to inhibit Vibrio anguillarum-induced inflammation and apoptosis in silvery pomfret (Pampus argenteus) intestinal epithelial cells

Lipoteichoic acid (LTA) is a major constituent of the cell wall of Gram-positive bacteria. The structure and immunomodulation of LTA vary greatly between different species. LTA from Lactobacillus plantarum has been shown to exert anti-pathogenic effects. Vibrio anguillarum is a major causative agent of vibriosis, one of the most prevalent fish diseases. The purpose of this study was to examine the effects of L. plantarum LTA on V. anguillarum growth, adhesion, and induced inflammation and apoptosis in intestinal epithelial cells of silvery pomfret (Pampus argenteus). Our results showed that L. plantarum LTA was unable to inhibit V. anguillarum growth; however, it significantly inhibited adhesion of V. anguillarum. It also showed significant inhibitory effects on EHEC-induced inflammation and apoptosis by modulating the expression of NF-κB (nuclear factor kappa B), IκB (inhibitor of NF-κB), Bcl2 (B-cell leukemia/lymphoma-2), BAX (Bcl-2-associated X protein), IL-8 (interleukin 8) and TNF-α (tumor necrosis factor-α), and via inhibition of caspase-9 and caspase-3 activation. These data extend our understanding of the beneficial effects of L. plantarum LTA, which is related to the inhibition of V. anguillarum, and suggest that L. plantarum LTA has potential as a new therapeutic agent against V. anguillarum-caused vibriosis in fish.

Dual inhibition of nitric oxide and prostaglandin E2 production by polysubstituted 2-aminopyrimidines

The present in vitro experiments demonstrate inhibitory effects of polysubstituted 2-aminopyrimidines on high output production of nitric oxide (NO) and prostaglandin E2 (PGE2) stimulated by interferon-γ and lipopolysaccharide (LPS) in peritoneal macrophages of mouse and rat origin. PGE2 production was inhibited also in LPS-activated human peripheral blood mononuclear cells. A tight dependence of the suppressive activities on chemical structure of pyrimidines was observed. Derivatives containing hydroxyl groups at the C-4 and C-6 positions of pyrimidine ring were devoid of any influence on NO and PGE2. Remarkable inhibitory potential was acquired by the replacement of hydroxyl groups with chlorine, the 4,6-dichloro derivatives being more effective than the monochloro analogues. The effects were further intensified by modification of the amino group at the C-2 position, changing it to the (N,N-dimethylamino)methyleneamino or the formamido ones. There was no substantial difference in the expression of NO-inhibitory effects among derivatives containing distinct types of substituents at the C-5 position (hydrogen, methyl, ethyl, propyl, butyl, phenyl, and benzyl). In contrast to NO, larger substituents then methyl were required to inhibit PGE2 production. Overall, no significant correlation between the extent of NO and PGE2 suppression was observed. The IC50s of derivatives with the strongest effects on both NO and PGE2 were within the range of 2-10 μM. Their NO-inhibitory potential of pyrimidines was stronger than that of non-steroidal anti-inflammatory drugs (NSAIDs) aspirin and indomethacin. The PGE2-inhibitory effectiveness of pyrimidines was about the same as that of aspirin, but weaker as compared to indomethacin. The NO- and PGE2-inhibitory activity of tested pyrimidines has been found associated with decreased expression of iNOS mRNA and COX-2 mRNA, respectively, and with post-translation interactions. Selected NO-/PGE2-inhibitory derivatives decreased severity of intestinal inflammation in murine model of ulcerative colitis.

HMGB1 Binds to Lipoteichoic Acid and Enhances TNF-α and IL-6 Production through HMGB1-Mediated Transfer of Lipoteichoic Acid to CD14 and TLR2

Lipoteichoic acid (LTA) is a component of the cell wall of Gram-positive bacteria and induces a toll-like receptor 2 (TLR2)-mediated inflammatory response upon initial binding to lipopolysaccharide-binding protein (LBP) and subsequent transfer to CD14. In this study, we identified a novel role for the nuclear protein high-mobility group box 1 (HMGB1) in LTA-mediated inflammation. Results of ELISA, surface plasmon resonance and native PAGE electrophoretic mobility shift analyses indicated that HMGB1 binds to LTA in a concentration-dependent manner and that this binding is inhibited by LBP. Native PAGE, fluorescence-based transfer and confocal imaging analyses indicated that HMGB1 catalytically disaggregates LTA and transfers LTA to CD14. NF-κB p65 nuclear transmigration, degradation of IκBα and reporter assay results demonstrated that NF-κB activity in HEK293-hTLR2/6 cells is significantly upregulated by a mixture of LTA and soluble CD14 in the presence of HMGB1. Furthermore, the production of TNF-α and IL-6 in J774A.1 and RAW264.7 cells increased significantly following treatment with a mixture of LTA and HMGB1 compared with treatment with LTA or HMGB1 alone. Thus, we propose that HMGB1 plays an important role in LTA-mediated inflammation by binding to and transferring LTA to CD14, which is subsequently transferred to TLR2 to induce an inflammatory response.

Circulating microRNA signatures in mice exposed to lipoteichoic acid

Background

Previously, we had identified a specific whole blood–derived microRNAs (miRNAs) signature in mice following in vivo injection of lipopolysaccharide (LPS) originated from Gram-negative bacteria. This study was designed to profile the circulating miRNAs expression in mice exposed to lipoteichoic acid (LTA) which is a major component of the wall of Gram-positive bacteria.

Results

C57BL/6 mice received intraperitoneal injections of 100 μg of LTA originated from Bacillus subtilis, Streptococcus faecalis, and Staphylococcus aureus were killed 6 h and the whole blood samples were obtained for miRNA expression analysis using a miRNA array (Phalanx miRNA OneArray® 1.0). Up-regulated expression of miRNA targets in the whole blood, serum and white blood cells (WBCs) of C57BL/6 and Tlr2^−/− mice upon LTA treatment in 10, 100, or 1000 ug concentrations was quantified at indicated time (2, 6, 24, and 72 h) using real-time RT-PCR and compared with that in the serum of C57BL/6 mice injected with 100 ug of LPS. A significant increase of 4 miRNAs (miR-451, miR-668, miR-1902, and miR-1904) was observed in the whole blood and the serum in a dose- and time-dependent fashion following LTA injection. Induction of miRNA occurred in the serum after 2 h and persisted for at least 6 h. No increased expression of these 4 miRNAs was found in the WBCs. Higher but not significant expression level of these 4 miRNAs were observed following LTA treatment in the serum of Tlr2^−/−against that of C57BL6 mice. In contrast, LPS exposure induced moderate expression of miR-451 but not of the other 3 miRNA targets.

Conclusions

We identified a specific circulating miRNA signature in mice exposed to LTA. That expression profile is different from those of mice exposed to LPS. Those circulating miRNAs induced by LTA or LPS treatment may serve as promising biomarkers for the differentiation between exposures to Gram-positive or Gram-negative bacteria.

Microfiltration method of removal of bacterial contaminants and their monitoring by nitric oxide and Limulus assays

Similar to lipopolysaccharide (LPS), a product of Gram-negative bacteria, the signal macromolecules of Gram-positive bacteria lipoteichoic acid (LTA) and peptidoglycan (PGN) possess multiple biological activities. They may be a source of misinterpretation of experimental findings. We have found that not only LPS but also LTA and PGN can be detected by the Limulus amebocyte lysate (LAL) assay. All of them stimulate the high output in vitro nitric oxide (NO) production of in rat peritoneal cells. The onset of the NO enhancement was observed with 25-100pg/ml of LPS and 25-100ng/ml of PGN and LTA. Polymyxin B (PMX), if applied at concentration 10,000-fold higher than that of LPS, can completely inhibit the NO and LAL binding responses of LPS. The NO-stimulatory and LAL-binding properties of LTA and PGN are not eliminated by PMX. Handling of LPS contamination with PMX may be associated with serious problems because it possesses intrinsic biological activity and becomes cytotoxic at concentration >25μg/ml. The present findings suggest a convenient alternative avoiding these issues. As monitored by the NO and LAL assays, even high amounts of LPS as well as PGN and LTA can be removed by molecular mass cutoff microfiltration. All types of the filters (3kDa to 100kDa) are equally effective. It is suggested that the microfiltration procedure may be considered as a preferable, general and easy method of sample decontamination.

Induction of intestinal pro-inflammatory immune responses by lipoteichoic acid

Background

The cellular and molecular mechanisms of inflammatory bowel disease are not fully understood; however, data indicate that uncontrolled chronic inflammation induced by bacterial gene products, including lipoteichoic acid (LTA), may trigger colonic inflammation resulting in disease pathogenesis. LTA is a constituent glycolipid of Gram-positive bacteria that shares many inflammatory properties with lipopolysaccharide and plays a critical role in the pathogenesis of severe inflammatory responses via Toll-like receptor 2. Accordingly, we elucidate the role of LTA in immune stimulation and induced colitis in vivo.

Methods

To better understand the molecular mechanisms utilized by the intestinal microbiota and their gene products to induce or subvert inflammation, specifically the effect(s) of altered surface layer protein expression on the LTA-mediated pro-inflammatory response, the Lactobacillus acidophilus surface layer protein (Slp) genes encoding SlpB and SlpX were deleted resulting in a SlpB^- and SlpX^- mutant that continued to express SlpA (assigned as NCK2031).

Results

Our data show profound activation of dendritic cells by NCK2031, wild-type L. acidophilus (NCK56), and purified Staphylococcus aureus-LTA. In contrary to the LTA-deficient strain NCK2025, the LTA-expressing strains NCK2031 and NCK56, as well as S. aureus-LTA, induce pro-inflammatory innate and T cell immune responses in vivo. Additionally, neither NCK2031 nor S. aureus-LTA supplemented in drinking water protected mice from DSS-colitis, but instead, induced significant intestinal inflammation resulting in severe colitis and tissue destruction.

Conclusions

These findings suggest that directed alteration of two of the L. acidophilus NCFM-Slps did not ameliorate LTA-induced pro-inflammatory signals and subsequent colitis.