lipid-a and Gonorrhea

Neisseria gonorrhoeae is an exclusively human pathogen that commonly infects the urogenital tract resulting in gonorrhoea. Empirical treatment of gonorrhoea with antibiotics has led to multidrug resistance and the need for new therapeutics. Inactivation of lipooligosaccharide phosphoethanolamine transferase A (EptA), which attaches phosphoethanolamine to lipid A, results in attenuation of the pathogen in infection models. Small molecules that inhibit EptA are predicted to enhance natural clearance of gonococci via the human innate immune response.. A library of small-fragment compounds was tested for the ability to enhance susceptibility of the reference strain N. gonorrhoeae FA1090 to polymyxin B. The effect of these compounds on lipid A synthesis and viability in models of infection were tested.. Three compounds, 135, 136 and 137, enhanced susceptibility of strain FA1090 to polymyxin B by 4-fold. Pre-treatment of bacterial cells with all three compounds resulted in enhanced killing by macrophages. Only lipid A from bacterial cells exposed to compound 137 showed a 17% reduction in the level of decoration of lipid A with phosphoethanolamine by MALDI-TOF MS analysis and reduced stimulation of cytokine responses in THP-1 cells. Binding of 137 occurred with higher affinity to purified EptA than the starting material, as determined by 1D saturation transfer difference NMR. Treatment of eight MDR strains with 137 increased susceptibility to polymyxin B in all cases.. Small molecules have been designed that bind to EptA, inhibit addition of phosphoethanolamine to lipid A and can sensitize N. gonorrhoeae to killing by macrophages.

Topics: Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Antimicrobial Peptides; Drug Resistance, Bacterial; Ethanolaminephosphotransferase; Ethanolamines; Gonorrhea; Humans; Lipid A; Microbial Sensitivity Tests; Neisseria gonorrhoeae; Polymyxin B

Neisseria meningitidis (Nm) and N. gonorrhoeae (Ng) express a Macrophage Infectivity Potentiator (MIP, NMB1567/NEIS1487) protein in their outer membrane (OM). In this study, we prepared independent batches of liposomes (n = 3) and liposomes + MonoPhosphoryl Lipid A (MPLA) (n = 3) containing recombinant truncated Nm-MIP protein encoded by Allele 2 (rT-Nm-MIP, amino acids 22-142), and used these to immunize mice. We tested the hypothesis that independent vaccine batches showed similar antigenicity, and that antisera could recognise both meningococcal and gonococcal MIP and induce cross-species bactericidal activity. The different batches of M2 rT-Nm-MIP-liposomes ± MPLA showed no significant (P > 0.05) batch-to-batch variation in antigenicity. Anti-rT-Nm-MIP sera reacted equally and specifically with Nm-MIP and Ng-MIP in OM and on live bacterial cell surfaces. Specificity was shown by no antiserum reactivity with Δmip bacteria. Using human complement/serum bactericidal assays, anti-M2 rT-Nm-MIP sera killed homologous meningococcal serogroup B (MenB) strains (median titres of 32-64 for anti-rT-Nm-MIP-liposome sera; 128-256 for anti-rT-Nm-MIP-liposome + MPLA sera) and heterologous M1 protein-expressing MenB strains (titres of 64 for anti rT-Nm-MIP-liposome sera; 128-256 for anti-rT-Nm-MIP-liposome + MPLA sera). Low-level killing (P < 0.05) was observed for a MenB isolate expressing M7 protein (titres 4-8), but MenB strains expressing M6 protein were not killed (titre < 4-8). Killing (P < 0.05) was observed against MenC and MenW bacteria expressing homologous M2 protein (titres of 8-16) but not against MenA or MenY bacteria (titres < 4-8). Antisera to M2 rT-Nm-MIP showed significant (P < 0.05) cross-bactericidal activity against gonococcal strain P9-17 (expressing M35 Ng-MIP, titres of 64-512) and strain 12CFX_T_003 (expressing M10 Ng-MIP, titres 8-16) but not against FA1090 (expressing M8 Ng-MIP). As an alternative to producing recombinant protein, we engineered successfully the Nm-OM to express M2 Truncated-Nm-MIP, but lipooligosaccharide-extraction with Na-DOC was contra-indicated. Our data suggest that a multi-component vaccine containing a select number of Nm- and Ng-MIP type proteins would be required to provide broad coverage of both pathogens.

Topics: Adjuvants, Immunologic; Animals; Antibodies, Bacterial; Antigens, Bacterial; Bacterial Proteins; Cross Reactions; Gonorrhea; Humans; Immune Sera; Immunization; Lipid A; Liposomes; Meningitis, Meningococcal; Mice; Mice, Inbred BALB C; Neisseria gonorrhoeae; Neisseria meningitidis; Recombinant Proteins

During infection, the sexually transmitted pathogen Neisseria gonorrhoeae (the gonococcus) encounters numerous host-derived antimicrobials, including cationic antimicrobial peptides (CAMPs) produced by epithelial and phagocytic cells. CAMPs have both direct and indirect killing mechanisms and help link the innate and adaptive immune responses during infection. Gonococcal CAMP resistance is likely important for avoidance of host nonoxidative killing systems expressed by polymorphonuclear granulocytes (e.g., neutrophils) and intracellular survival. Previously studied gonococcal CAMP resistance mechanisms include modification of lipid A with phosphoethanolamine by LptA and export of CAMPs by the MtrCDE efflux pump. In the related pathogen Neisseria meningitidis, a two-component regulatory system (2CRS) termed MisR-MisS has been shown to contribute to the capacity of the meningococcus to resist CAMP killing. We report that the gonococcal MisR response regulator but not the MisS sensor kinase is involved in constitutive and inducible CAMP resistance and is also required for intrinsic low-level resistance to aminoglycosides. The 4- to 8-fold increased susceptibility of misR-deficient gonococci to CAMPs and aminoglycosides was independent of phosphoethanolamine decoration of lipid A and the levels of the MtrCDE efflux pump and seemed to correlate with a general increase in membrane permeability. Transcriptional profiling and biochemical studies confirmed that expression of lptA and mtrCDE was not impacted by the loss of MisR. However, several genes encoding proteins involved in membrane integrity and redox control gave evidence of being MisR regulated. We propose that MisR modulates the levels of gonococcal susceptibility to antimicrobials by influencing the expression of genes involved in determining membrane integrity.

Topics: Aminoglycosides; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Bacterial Proteins; Drug Resistance, Bacterial; Gonorrhea; Humans; Lipid A; Neisseria gonorrhoeae; Neisseria meningitidis

Neisseria gonorrhoeae causes gonorrhea, a sexually transmitted infection characterized by inflammation of the cervix or urethra. However, a significant subset of patients with N. gonorrhoeae remain asymptomatic, without evidence of localized inflammation. Inflammatory responses to N. gonorrhoeae are generated by host innate immune recognition of N. gonorrhoeae by several innate immune signaling pathways, including lipooligosaccharide (LOS) and other pathogen-derived molecules through activation of innate immune signaling systems, including toll-like receptor 4 (TLR4) and the interleukin-1β (IL-1β) processing complex known as the inflammasome. The lipooligosaccharide of N. gonorrhoeae has a hexa-acylated lipid A. N. gonorrhoeae strains that carry an inactivated msbB (also known as lpxL1) gene produce a penta-acylated lipid A and exhibit reduced biofilm formation, survival in epithelial cells, and induction of epithelial cell inflammatory signaling. We now show that msbB-deficient N. gonorrhoeae induces less inflammatory signaling in human monocytic cell lines and murine macrophages than the parent organism. The penta-acylated LOS exhibits reduced toll-like receptor 4 signaling but does not affect N. gonorrhoeae-mediated activation of the inflammasome. We demonstrate that N. gonorrhoeae msbB is dispensable for initiating and maintaining infection in a murine model of gonorrhea. Interestingly, infection with msbB-deficient N. gonorrhoeae is associated with less localized inflammation. Combined, these data suggest that TLR4-mediated recognition of N. gonorrhoeae LOS plays an important role in the pathogenesis of symptomatic gonorrhea infection and that alterations in lipid A biosynthesis may play a role in determining symptomatic and asymptomatic infections.

Topics: Acylation; Acyltransferases; Analysis of Variance; Animals; Caspase 1; Cells, Cultured; Chemokines; Cytokines; Disease Models, Animal; Female; Gonorrhea; Humans; Inflammation; Lipid A; Lipopolysaccharides; Macrophages; Mice; Mice, Inbred BALB C; Monocytes; Neisseria gonorrhoeae; Signal Transduction

In this article, we report that retreatment of human monocytic THP-1 cells and primary monocytes with pathogenic Neisseria or with purified lipooligosaccharides (LOS) after previous exposure to LOS induced immune tolerance, as evidenced by reduced TNF-α and IL-1β cytokine expression. LOS that we have previously shown to vary in their potential to activate TLR4 signaling, which was correlated with differences in levels of lipid A phosphorylation, had similarly variable ability to induce tolerance. Efficacy for induction of tolerance was proportional to the level of lipid A phosphorylation, as LOS from meningococcal strain 89I with the highest degree of phosphorylation was the most tolerogenic following retreatment with LOS or whole bacteria, compared with LOS from gonococcal strains 1291 and GC56 with reduced levels of phosphorylation. Hydrogen fluoride treatment of 89I LOS to remove phosphates rendered the LOS nontolerogenic. Tolerance induced by the more highly inflammatory meningococcal LOS was correlated with significantly greater downregulation of p38 activation, greater induction of the expression of A20 and of microRNA-146a, and greater reductions in IL-1R-associated kinase 1 and TRAF6 levels following LOS retreatment of cells. The role of miR-146a in regulation of induction of TNF-α was confirmed by transfecting cells with an inhibitor and a mimic of miR-146a. Our results provide a mechanistic framework for understanding the variable pathophysiology of meningococcal and gonococcal infections given that after an initial exposure, greater upregulation of microRNA-146a by more highly inflammatory LOS conversely leads to the suppression of immune responses, which would be expected to facilitate bacterial survival and dissemination.

Topics: DNA-Binding Proteins; Endotoxins; Enzyme Activation; Gonorrhea; Humans; Hydrofluoric Acid; Immune Tolerance; Inflammation; Interleukin-1 Receptor-Associated Kinases; Interleukin-1beta; Intracellular Signaling Peptides and Proteins; Lipid A; Lipopolysaccharides; Meningitis, Meningococcal; MicroRNAs; Monocytes; Neisseria gonorrhoeae; Neisseria meningitidis; Nuclear Proteins; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Signal Transduction; TNF Receptor-Associated Factor 6; Toll-Like Receptor 4; Tumor Necrosis Factor alpha-Induced Protein 3; Tumor Necrosis Factor-alpha

The induction of an intense inflammatory response by Neisseria gonorrhoeae and the persistence of this pathogen in the presence of innate effectors is a fascinating aspect of gonorrhea. Phosphoethanolamine (PEA) decoration of lipid A increases gonococcal resistance to complement-mediated bacteriolysis and cationic antimicrobial peptides (CAMPs), and recently we reported that wild-type N. gonorrhoeae strain FA1090 has a survival advantage relative to a PEA transferase A (lptA) mutant in the human urethral-challenge and murine lower genital tract infection models. Here we tested the immunostimulatory role of this lipid A modification. Purified lipooligosaccharide (LOS) containing lipid A devoid of the PEA modification and an lptA mutant of strain FA19 induced significantly lower levels of NF-κB in human embryonic kidney Toll-like receptor 4 (TLR4) cells and murine embryonic fibroblasts than wild-type LOS of the parent strain. Moreover, vaginal proinflammatory cytokines and chemokines were not elevated in female mice infected with the isogenic lptA mutant, in contrast to mice infected with the wild-type and complemented lptA mutant bacteria. We also demonstrated that lptA mutant bacteria were more susceptible to human and murine cathelicidins due to increased binding by these peptides and that the differential induction of NF-κB by wild-type and unmodified lipid A was more pronounced in the presence of CAMPs. This work demonstrates that PEA decoration of lipid A plays both protective and immunostimulatory roles and that host-derived CAMPs may further reduce the capacity of PEA-deficient lipid A to interact with TLR4 during infection.

Topics: Animals; Anti-Bacterial Agents; Cathelicidins; Cell Line, Transformed; Chemokines; Complement System Proteins; Cytokines; Ethanolamines; Female; Fibroblasts; Gonorrhea; Humans; Lipid A; Mice; Mice, Inbred BALB C; Microbial Sensitivity Tests; Neisseria gonorrhoeae; NF-kappa B; Reproductive Tract Infections; Toll-Like Receptor 4; Vagina

The acyl chain length, number, and distribution have been considered the major factors contributing to this biological activity of lipid A. The charged head groups on the dihexosamine backbone have also been implicated in contributing to this biology. In Neisseria, it has now been shown that loss of the 4' phosphoethanolamine has an impact on virulence in an animal model and on the organism's susceptibility to cationic antimicrobial peptides. Such studies offer potential insight into targets for novel antimicrobial agents.

Topics: Animals; Cathelicidins; Female; Gonorrhea; Humans; Lipid A; Neisseria gonorrhoeae; Reproductive Tract Infections

Phosphoethanolamine (PEA) on Neisseria gonorrhoeae lipid A influences gonococcal inflammatory signaling and susceptibility to innate host defenses in in vitro models. Here, we evaluated the role of PEA-decorated gonococcal lipid A in competitive infections in female mice and in male volunteers. We inoculated mice and men with mixtures of wild-type N. gonorrhoeae and an isogenic mutant that lacks the PEA transferase, LptA. LptA production conferred a marked survival advantage for wild-type gonococci in the murine female genital tract and in the human male urethra. Our studies translate results from test tube to animal model and into the human host and demonstrate the utility of the mouse model for studies of virulence factors of the human-specific pathogen N. gonorrhoeae that interact with non-host-restricted elements of innate immunity. These results validate the use of gonococcal LptA as a potential target for development of novel immunoprophylactic strategies or antimicrobial treatments.. Gonorrhea is one of the most common bacterial sexually transmitted infections, and increasing antibiotic resistance threatens the use of currently available antimicrobial therapies. In this work, encompassing in vitro studies and in vivo studies of animal and human models of experimental genital tract infection, we document the importance of lipid A's structure, mediated by a single bacterial enzyme, LptA, in enhancing the fitness of Neisseria gonorrhoeae. The results of these studies suggest that novel agents targeting LptA may offer urgently needed prevention or treatment strategies for gonorrhea.

Topics: Animals; Disease Models, Animal; Ethanolaminephosphotransferase; Ethanolamines; Female; Gene Knockout Techniques; Gonorrhea; Healthy Volunteers; Humans; Lipid A; Male; Mice; Microbial Viability; Neisseria gonorrhoeae; Virulence; Virulence Factors

The capacity of Neisseria gonorrhoeae to cause disseminated gonococcal infection requires that such strains resist the bactericidal action of normal human serum. The bactericidal action of normal human serum against N. gonorrhoeae is mediated by the classical complement pathway through an antibody-dependent mechanism. The mechanism(s) by which certain strains of gonococci resist normal human serum is not fully understood, but alterations in lipooligosaccharide structure can affect such resistance. During an investigation of the biological significance of phosphoethanolamine extensions from lipooligosaccharide, we found that phosphoethanolamine substitutions from the heptose II group of the lipooligosaccharide beta-chain did not impact levels of gonococcal (strain FA19) resistance to normal human serum or polymyxin B. However, loss of phosphoethanolamine substitution from the lipid A component of lipooligosaccharide, due to insertional inactivation of lptA, resulted in increased gonococcal susceptibility to polymyxin B, as reported previously for Neisseria meningitidis. In contrast to previous reports with N. meningitidis, loss of phosphoethanolamine attached to lipid A rendered strain FA19 susceptible to complement killing. Serum killing of the lptA mutant occurred through the classical complement pathway. Both serum and polymyxin B resistance as well as phosphoethanolamine decoration of lipid A were restored in the lptA-null mutant by complementation with wild-type lptA. Our results support a role for lipid A phosphoethanolamine substitutions in resistance of this strict human pathogen to innate host defenses.

Topics: Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Complement System Proteins; Drug Resistance, Microbial; Ethanolamines; Gonorrhea; Humans; Lipid A; Neisseria gonorrhoeae; Polymyxin B; Serum; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization