Rifampin reduces production of reactive oxygen species of cerebrospinal fluid phagocytes and hippocampal neuronal apoptosis in experimental Streptococcus pneumoniae meningitis

Ceftaroline + Rifampin Versus Vancomycin + Rifampin in the Treatment of Methicillin-Resistant Staphylococcus aureus Meningitis in an Experimental Rabbit Model

Background/Aim: To compare the effectiveness ceftaroline-rifampicin (CR) and vancomycin-rifampicin (VR), against methicillin-resistant Staphylococcus aureus (MRSA) in a rabbit meningitis model, to compare the effects on brain tissues in terms of inflammation and apoptosis and to test the antibiotics via in vitro time-kill and synergy tests. Method: Meningitis was induced using MRSA strain ATCC 43300. After 28 hours, the rabbits were split into three groups: control, VR, and CR. A CSF culture was taken at the start (T0) and end of treatment (EOT)-the 24th hour of treatment. At EOT, the animals' brain tissues were examined for inflammation and apoptosis. The study strain was tested for a 24-hour time kill assay. Results: At the EOT, statistically significant differences were observed between the treatment groups in terms of reducing the cerebrospinal fluid (CSF) bacterial count, achieving partial or complete treatment response, and exhibiting lower levels of neuronal apoptosis compared with the control group. However, there was no significant difference in all three parameters and in survival between the two treatment groups. The CR group exhibited a noticeable decrease in inflammation than the control group, but no significant difference was found between the control group versus VR and VR versus CR group. Rifampicin did not improve antibacterial efficacy in the in vitro time-kill assay. Conclusion: The CR arm showed better complete response and inflammation, but both treatments were similar in other parameters. CR combination was found as effective as VR combination for treating MRSA meningitis.

Streptococcus pneumoniae exerts oxidative stress, subverts antioxidant signaling and autophagy in human corneal epithelial cells that is alleviated by tert-Butylhydroquinone

Streptococcus pneumoniae is one of the leading causes of bacterial keratitis in the developing world and globally. In the current study, we have determined oxidative stress as pathogenesis of S. pneumoniae infection in corneal tissues and human corneal epithelial cells (HCEC) and explored host immune response of HCEC towards S. pneumoniae. We also determined whether treatment with tert-Butylhydroquinone (tBHQ), a Nrf2 inducer, could alleviate oxidative stress and reduce bacterial cytotoxicity in these cells. Oxidative stress was determined in corneal tissues of patients and HCEC by immunohistochemistry and immunofluorescence analysis, respectively. The expression of antioxidant genes, cytokines and antimicrobial peptides was determined by quantitative PCR. Infection of HCEC by S. pneumoniae was determined by colony-forming units. The autophagy and cell death were determined by fluorescence microscopy. The phosphorylation of signaling proteins was evaluated by immunoblot analysis. S. pneumoniae induced oxidative stress during corneal infections and inhibited antioxidant signaling pathways and immune responses like autophagy. tBHQ aided in restoring Nrf2 activation, reduced reactive oxygen species generation and prevented cytotoxicity and cell death in S. pneumoniae-infected HCEC. tBHQ also induced autophagy in a Nrf2-dependent manner and reduced bacterial survival in HCEC. Increased expression of antimicrobial peptides by tBHQ might have contributed to a reduction of bacterial load and cytotoxicity, as exemplified in LL-37 depleted corneal epithelial cells exposed to S. pneumoniae compared to control siRNA-transfected cells. tBHQ mediates alleviation of oxidative stress induced by S. pneumoniae by activating Nrf2-mediated antioxidant signaling in corneal epithelial cells. tBHQ also enhances expression of antimicrobial peptides in corneal cells and aids in inhibition of bacterial survival and cytotoxicity of HCEC.

High-dose rifampin improves bactericidal activity without increased intracerebral inflammation in animal models of tuberculous meningitis

Tuberculous meningitis (TB meningitis) is the most severe form of tuberculosis (TB), requiring 12 months of multidrug treatment for cure, and is associated with high morbidity and mortality. High-dose rifampin (35 mg/kg/d) is safe and improves the bactericidal activity of the standard-dose (10 mg/kg/d) rifampin-containing TB regimen in pulmonary TB. However, there are conflicting clinical data regarding its benefit for TB meningitis, where outcomes may also be associated with intracerebral inflammation. We conducted cross-species studies in mice and rabbits, demonstrating that an intensified high-dose rifampin-containing regimen has significantly improved bactericidal activity for TB meningitis over the first-line, standard-dose rifampin regimen, without an increase in intracerebral inflammation. Positron emission tomography in live animals demonstrated spatially compartmentalized, lesion-specific pathology, with postmortem analyses showing discordant brain tissue and cerebrospinal fluid rifampin levels and inflammatory markers. Longitudinal multimodal imaging in the same cohort of animals during TB treatment as well as imaging studies in two cohorts of TB patients demonstrated that spatiotemporal changes in localized blood-brain barrier disruption in TB meningitis are an important driver of rifampin brain exposure. These data provide unique insights into the mechanisms underlying high-dose rifampin in TB meningitis with important implications for developing new antibiotic treatments for infections.

Neuroprotective effects of some epigenetic modifying drugs' on Chlamydia pneumoniae-induced neuroinflammation: A novel model

Chlamydia pneumoniae (Cpn) is a gram-negative intracellular pathogen that causes a variety of pulmonary diseases, and there is growing evidence that it may play a role in Alzheimer's disease (AD) pathogenesis. Cpn can interact functionally with host histones, altering the host's epigenetic regulatory system by introducing bacterial products into the host tissue and inducing a persistent inflammatory response. Because Cpn is difficult to propagate, isolate, and detect, a modified LPS-like neuroinflammation model was established using lyophilized cell free supernatant (CFS) obtained from infected cell cultures, and the effects of CFS were compared to LPS. The neuroprotective effects of Trichostatin A (TSA), givinostat, and RG108, which are effective on epigenetic mechanisms, and the antibiotic rifampin, were studied in this newly introduced model and in the presence of amyloid beta (Aβ) 1-42. The neuroprotective effects of the drugs, as well as the effects of CFS and LPS, were evaluated in Aβ-induced neurotoxicity using a real-time cell analysis system, total ROS, and apoptotic impact. TSA, RG108, givinostat, and rifampin all demonstrated neuroprotective effects in both this novel model and Aβ-induced neurotoxicity. The findings are expected to provide early evidence on neuroprotective actions against Cpn-induced neuroinflammation and Aβ-induced neurotoxicity, which could represent a new treatment option for AD, for which there are currently few treatment options.

Rifampicin ameliorates lithium-pilocarpine-induced seizures, consequent hippocampal damage and memory deficit in rats: Impact on oxidative, inflammatory and apoptotic machineries

Epilepsy is one of the serious neurological sequelae of bacterial meningitis. Rifampicin, the well-known broad spectrum antibiotic, is clinically used for chemoprophylaxis of meningitis. Besides its antibiotic effects, rifampicin has been proven to be an effective neuroprotective candidate in various experimental models of neurological diseases. In addition, rifampicin was found to have promising antioxidant, anti-inflammatory and anti-apoptotic effects. Herein, we investigated the anticonvulsant effect of rifampicin at experimental meningitis dose (20 mg/kg, i.p.) using lithium-pilocarpine model of status epilepticus (SE) in rats. Additionally, we studied the effect of rifampicin on seizure induced histopathological, neurochemical and behavioral abnormalities. Our study showed that rifampicin pretreatment attenuated seizure activity and the resulting hippocampal insults marked by hematoxylin and eosin. Markers of oxidative stress, neuroinflammation and apoptosis were evaluated, in the hippocampus, 24 h after SE induction. We found that rifampicin pretreatment suppressed oxidative stress as indicated by normalized malondialdehyde and glutathione levels. Rifampicin pretreatment attenuated SE-induced neuroinflammation and decreased the hippocampal expression of interleukin-1β, tumor necrosis factor-α, nuclear factor kappa-B, and cyclooxygenase-2. Moreover, rifampicin mitigated SE-induced neuronal apoptosis as indicated by fewer positive cytochrome c immunostained cells and lower caspase-3 activity in the hippocampus. Furthermore, Morris water maze testing at 7 days after SE induction showed that rifampicin pretreatment can improve cognitive dysfunction. Therefore, rifampicin, currently used in the management of meningitis, has a potential additional advantage of ameliorating its epileptic sequelae.

Structural and biochemical characterization of GTP cyclohydrolase II from Helicobacter pylori reveals its redox dependent catalytic activity

GTP cyclohydrolase II (GCHII), catalyzes the conversion of GTP to 2,5-diamino-6-β-ribosyl-4(3H)-pyrimidinone-5'-phosphate and has been shown to be essential for pathogens. Here we describe the biochemical, kinetic and structural characterization of GCHII from Helicobacter pylori (hGCHII). The crystal structure of hGCHII, unlike other GCHII structures, revealed that cysteines at the active site existed in oxidized state forming two disulfide bonds and lacked Zn(2+) that was shown to be indispensable for catalytic activity in other species. However, incubation of hGCHII with hydrogen peroxide, an oxidizing agent, followed by PAR-assay showed that Zn(2+) was intrinsically present, indicating that all cysteines at the catalytic site remained in reduced state. Moreover, site directed mutagenesis of catalytic site cysteines revealed that only three, out of four cysteines were essential for hGCHII activity. These results, though, indicated that hGCHII crystallized in oxidized form, the expulsion of Zn(2+) upon oxidation of catalytic cysteines revealed its ability to act in response to the redox environment. Exploring further, incubation of hGCHII with reversible thiol modifying agent S-methyl-methane-thiosulfonate resulted in loss of GCHII activity due to oxidation of its cysteine residues as revealed by mass spectrometry studies. However, addition of reducing agent DTT partially restored the hGCHII catalytic activity. Taken together, these results demonstrate that hGCHII can regulate its catalytic activity depending on the redox environment, a function hitherto unknown for GCHII.

Mitochondria are targets for the antituberculosis drug rifampicin in cultured epithelial cells

Rifampicin is a widely used drug for antituberculosis therapy. Its target is the bacterial RNA polymerase. After entry into the human or mammalian organism, rifampicin is accumulated in cells of epithelial origin (kidneys, liver, lungs) where it induces apoptosis, necrosis, and fibrosis. The purpose of this study was to determine the intracellular mechanisms leading to rifampicin-induced pathological changes and cell death. We analyzed the survival and state of the chondriome of cultured epithelial cells of the SPEV line under the influence of rifampicin. Our data show that the drug induces pronounced pathological changes in the network and ultrastructure of mitochondria, and their dysfunction results in excessive production of reactive oxygen species and release of cytochrome c. These data suggest the initiation of the mitochondrial pathway of apoptosis. Simultaneously, we observed inhibition of cell proliferation and changes in morphology of the epithelial cells toward fibroblast-like appearance, which could indicate induction of epithelial-mesenchymal transition. Thus, mitochondria are the main potential target for rifampicin in cells of epithelial origin. We suggest that similar mechanisms of pathological changes can be induced in vivo in organs and tissues accumulating rifampicin during chemotherapy of bacterial infectious diseases.

RIFAMPICIN: an antibiotic with brain protective function

Besides its well known antibiotic activity rifampicin exerts multiple brain protective functions in acute cerebral ischemia and chronic neurodegeneration. The present mini-review gives an update of the unique activity of rifampicin in different diseases including Parkinson's disease, meningitis, stroke, Alzheimer's disease and optic nerve injury.

Rifampicin and Parkinson's disease

Rifampicin is a macrocyclic antibiotic used extensively for the treatment of Mycobacterium tuberculosis and other mycobacterial infections. Recently, it was discovered that rifampicin exhibits neuroprotective effects. It has been shown to protect PC12 cells against MPP(+)-induced apoptosis and inhibit the expression of α-synuclein multimers. In in vitro studies, rifampicin pretreatment protects PC12 cells against rotenone-induced cell death. Qualitative and quantitative analyses uncover that rifampicin significantly suppresses rotenone-induced apoptosis by ameliorating mitochondrial oxidative stress. It reduces microglial inflammation and improves neuron survival. Our results indicate that rifampicin is cytoprotective under a variety of experimental conditions, and suggest that it may be useful in PD therapeutics. It is the aim of this paper to review the experimental neuroprotection data reported using rifampicin with a focus on the molecular and cellular mechanisms of cytoprotective effect in in vitro models of PD.

Adjunctive daptomycin attenuates brain damage and hearing loss more efficiently than rifampin in infant rat pneumococcal meningitis

Exacerbation of cerebrospinal fluid (CSF) inflammation in response to bacteriolysis by beta-lactam antibiotics contributes to brain damage and neurological sequelae in bacterial meningitis. Daptomycin, a nonlytic antibiotic acting on Gram-positive bacteria, lessens inflammation and brain injury compared to ceftriaxone. With a view to a clinical application for pediatric bacterial meningitis, we investigated the effect of combining daptomycin or rifampin with ceftriaxone in an infant rat pneumococcal meningitis model. Eleven-day-old Wistar rats with pneumococcal meningitis were randomized to treatment starting at 18 h after infection with (i) ceftriaxone (100 mg/kg of body weight, subcutaneously [s.c.], twice a day [b.i.d.]), (ii) daptomycin (10 mg/kg, s.c., daily) followed 15 min later by ceftriaxone, or (iii) rifampin (20 mg/kg, intraperitoneally [i.p.], b.i.d.) followed 15 min later by ceftriaxone. CSF was sampled at 6 and 22 h after the initiation of therapy and was assessed for concentrations of defined chemokines and cytokines. Brain damage was quantified by histomorphometry at 40 h after infection and hearing loss was assessed at 3 weeks after infection. Daptomycin plus ceftriaxone versus ceftriaxone significantly (P < 0.04) lowered CSF concentrations of monocyte chemoattractant protein 1 (MCP-1), MIP-1α, and interleukin 6 (IL-6) at 6 h and MIP-1α, IL-6, and IL-10 at 22 h after initiation of therapy, led to significantly (P < 0.01) less apoptosis, and significantly (P < 0.01) improved hearing capacity. While rifampin plus ceftriaxone versus ceftriaxone also led to lower CSF inflammation (P < 0.02 for IL-6 at 6 h), it had no significant effect on apoptosis and hearing capacity. Adjuvant daptomycin could therefore offer added benefits for the treatment of pediatric pneumococcal meningitis.

Bacterial meningitis: current therapy and possible future treatment options

Despite targeted therapy, case-fatality rates and neurologic sequelae of bacterial meningitis remain unacceptably high. The poor outcome is mainly due to secondary systemic and intracranial complications. These complications seem to be both a consequence of the inflammatory response to the invading pathogen and release of bacterial components by the pathogen itself. Therefore, within the last decades, research has focused on the mechanism underlying immune regulation and the inhibition of bacterial lysis in order to identify new targets for adjuvant therapy. The scope of this article is to give an overview on current treatment strategies of bacterial meningitis, to summarize new insights on the pathophysiology of bacterial meningitis, and to give an outlook on new treatment strategies derived from experimental models.

Pathogenesis and pathophysiology of pneumococcal meningitis

Pneumococcal meningitis continues to be associated with high rates of mortality and long-term neurological sequelae. The most common route of infection starts by nasopharyngeal colonization by Streptococcus pneumoniae, which must avoid mucosal entrapment and evade the host immune system after local activation. During invasive disease, pneumococcal epithelial adhesion is followed by bloodstream invasion and activation of the complement and coagulation systems. The release of inflammatory mediators facilitates pneumococcal crossing of the blood-brain barrier into the brain, where the bacteria multiply freely and trigger activation of circulating antigen-presenting cells and resident microglial cells. The resulting massive inflammation leads to further neutrophil recruitment and inflammation, resulting in the well-known features of bacterial meningitis, including cerebrospinal fluid pleocytosis, cochlear damage, cerebral edema, hydrocephalus, and cerebrovascular complications. Experimental animal models continue to further our understanding of the pathophysiology of pneumococcal meningitis and provide the platform for the development of new adjuvant treatments and antimicrobial therapy. This review discusses the most recent views on the pathophysiology of pneumococcal meningitis, as well as potential targets for (adjunctive) therapy.

Modulation of brain injury as a target of adjunctive therapy in bacterial meningitis

Despite effective antimicrobial therapy, mortality and morbidity from bacterial meningitis remain unacceptably high. Meningitis deaths occur as a consequence of intracranial and systemic complications. The neurologic and otologic sequelae reflect structural injury to brain and cochlear tissues. Over the past decade, experimental studies have demonstrated that meningitis-related vascular and cortical injury is largely caused by the massive neutrophilic inflammatory reaction, whereas hippocampal and cochlear injury is driven by both the host response and bacterial toxins. The benefit of adjunctive corticosteroid therapy proves the principle that the key to improve clinical outcome is combining antibiotics with drugs directed against pathophysiologically relevant targets; its limitations in efficacy and applicability highlight the need for novel adjunctive therapies. Promising targets were identified recently through animal studies, and include limiting the release of toxic bacterial products (by using nonbacteriolytic antibiotics) and interfering with the generation of host-derived cytotoxins (by using neutrophil apoptosis-inducing agents).

New understandings on the pathophysiology of bacterial meningitis

PURPOSE OF REVIEW

Currently, dexamethasone is the only adjuvant of proven benefit in bacterial meningitis. Dexamethasone halves the risk of poor outcome, but only in selected patient groups. New therapies based upon an understanding of the pathophysiology are needed. This article summarizes our knowledge on the pathophysiology of bacterial meningitis with special emphasis on pneumococcal meningitis, the experimentally best characterized subtype.

RECENT FINDINGS

Experimental studies made clear that the harmful inflammatory reaction is initiated by the interaction of bacterial products with host pattern recognition receptors (PRRs) such as Toll-like receptors. PRR signalling leads to MyD88-dependent production of proinflammatory cytokines of the interleukin-1 family. Secretion of interleukin-1 family cytokines forms a positive feedback loop that boosts MyD88-dependent production of proinflammatory mediators. As a consequence, great numbers of neutrophils are recruited to the subarachnoid space. Activated neutrophils release many potentially cytotoxic agents including oxidants and matrix metalloproteinases that can cause collateral damage to brain tissue. Additionally to the inflammatory response, direct bacterial cytotoxicity has been identified as a contributor to tissue damage.

SUMMARY

Promising pathophysiologically targeted approaches for adjunctive therapy of acute bacterial meningitis include limiting the release of toxic bacterial products (e.g. nonbacteriolytic antibiotics) and interfering in the generation of host-derived cytotoxins.

Strategies and new developments in the management of bacterial meningitis

The principles of antimicrobial therapy for acute bacterial meningitis include use of agents that penetrate well into cerebrospinal fluid and attain appropriate cerebrospinal fluid concentrations, are active in purulent cerebrospinal fluid, and are bactericidal against the infecting pathogen. Recommendations for treatment of bacterial meningitis have undergone significant evolution in recent years, given the emergence of pneumococcal strains that are resistant to penicillin. Clinical experience with use of newer agents is limited to case reports, but these agents may be necessary to consider in patients who are failing standard therapy.

Short-term rifampicin pretreatment reduces inflammation and neuronal cell death in a rabbit model of bacterial meningitis

OBJECTIVE

In bacterial meningitis, severe systemic and local inflammation causes long-term impairment and death of affected patients. The current antibiotic therapy relies on cell wall-active beta-lactam antibiotics, which rapidly sterilize the cerebrospinal fluid (CSF). However, beta-lactams inhibit cell wall synthesis, induce bacteriolysis, and thereby evoke a sudden release of high amounts of toxic and proinflammatory bacterial products. Because tissue damage in bacterial meningitis is the result of bacterial toxins and the inflammatory host response, any reduction of free bacterial compounds promises to prevent neuronal damage.

DESIGN

In vitro experiments and randomized prospective animal study.

SETTING

University research laboratories.

SUBJECTS

Streptococcus pneumoniae broth cultures and New Zealand White rabbits.

INTERVENTIONS

We evaluated a concept to improve bacterial meningitis therapy in which a short-term pretreatment with the protein synthesis-inhibiting antibiotic rifampicin precedes the standard antibiotic therapy with ceftriaxone. First, logarithmically growing pneumococcal cultures were subdivided and exposed to different antibiotics. Then, rabbits suffering from pneumococcal meningitis were randomized to receive rifampicin pretreatment or ceftriaxone alone.

MEASUREMENTS AND MAIN RESULTS

In pneumococcal cultures, quantitative immunoblotting and real-time polymerase chain reaction revealed a reduced release of pneumolysin and bacterial DNA by rifampicin pretreatment for 30 minutes in comparison with ceftriaxone treatment alone. In vivo, a 1-hour rifampicin pretreatment reduced the release of bacterial products and attenuated the inflammatory host response, as demonstrated by decreased CSF levels of prostaglandin E2 and total protein and increased glucose CSF/plasma ratios. Rifampicin pretreatment reduced infection-associated neuronal apoptotic cell loss compared with ceftriaxone-treated controls.

CONCLUSIONS

A short-term pretreatment with rifampicin reduced the beta-lactam-induced release of deleterious bacterial products, attenuated inflammation, and thereby decreased neuronal cell loss in experimental bacterial meningitis. This concept has the potential to reduce inflammation-associated neuronal injury in bacterial meningitis and should be evaluated in a clinical trial.

[Treatment of community acquired bacterial meningitis, after microbiological identification]

INTRODUCTION

Are the 1996 SPILF consensus conference recommendations on bacterial meningitis (BM) still adequate?

OBJECTIVE

The literature published after 1996 was analyzed and the reviewers summarized the available data on antibiotic treatment once BM microbiological diagnosis made or strongly suspected.

METHOD

A review was made using PubMed, 10,015 references were examined. Only articles published after 1997 were analyzed.

RESULTS

No study allowed to recommend other regimens than those previously recommended in 1996, in case of meningococcal or pneumococcal infection: 3rd generation cephalosporin or amoxicillin, combined with vancomycin in case of penicillin-intermediate or resistant pneumococcus. In some cases, alternatives are possible, in case of pneumococcal infection: meropenem or antipneumococcal fluoroquinolone were recommended by US guidelines. New antibiotics available on the market were tested using experimental pneumococcal meningitis models: daptomycin and ertapenem seemed to be useful but linezolid was not. Among the antibiotic combinations tested, ceftriaxone+rifampicine demonstrated a better efficacy than ceftriaxone+vancomycin. There was not contributive published data on the length of treatment for bacterial meningitis.

CONCLUSION

No assessed arguments could be found to modify previous guidelines. In case of problem with penicillin-resistant pneumococci, penem or a combination using ceftriaxone and rifampicin may be used.

Elevated exhalation of hydrogen peroxide and circulating IL-18 in patients with pulmonary tuberculosis

Mycobacteria are the strong stimulators of respiratory burst, resulting in production of reactive oxygen species and nitrogen intermediates. The aim of our study was to assess the concentration of hydrogen peroxide (H(2)O(2)) in expired breath condensate (EBC) and the serum level of interleukin-18 (IL-18) in patients with active pulmonary tuberculosis (TB) before introduction of chemotherapy and after 2 months of treatment. Sixteen patients, current cigarette smokers, with advanced pulmonary TB were enrolled into the study. As a control served two groups: I group--16 asymptomatic cigarette smokers, II group--17 healthy never smoked subjects. The level of H(2)O(2) in EBC was significantly higher in patients with TB (1.3+/-0.7 microM) as compared to cigarette are healthy nonsmoker subjects (0.4+/-0.1 and 0.2+/-0.1 microM, respectively, P<0.05). Two months of treatment significantly decreased the level of H(2)O(2) exhalation in TB patients (0.5+/-0.3 microM) to the value that was not different from that in asymptomatic smokers but was still higher than in never smoked subjects. Serum concentration of IL-18 in TB patients was higher than that found in both control groups either before and after antituberculous treatment (P<0.05). Exhaled H(2)O(2) did not correlate with circulating IL-18 in TB patients before or after treatment. These results demonstrated the occurrence of oxidative stress in the airways of TB patients completely attenuating after 2 months of successful antituberculous treatment.

Horseradish peroxidase-catalyzed oxidation of rifampicin: reaction rate enhancement by co-oxidation with anti-inflammatory drugs

The tuberculostatic drug rifampicin has been described as a scavenger of reactive species. Additionally, the recent demonstration that oral therapy with a complex of rifampicin and horseradish peroxidase (HRP) was more effective than rifampicin alone, in an animal model of experimental leprosy, suggested the importance of redox reactions involving rifampicin and their relevance to the mechanism of action. Hence, we studied the oxidation of rifampicin catalyzed by HRP, since this enzyme may represent the prototype of peroxidation-mediated reactions. We found that the antibiotic is efficiently oxidized and that rifampicin-quinone is the product, in a reaction dependent on both HRP and hydrogen peroxide. The steady-state kinetic constants Km(app) (101+/-23 micromol/l), Vmax(app) (0.78+/-0.09 micromol/l.s(-1)) and kcat (5.1+/-0.6 s(-1)) were measured (n=4). The reaction rate was increased by the addition of co-substrates such as tetramethylbenzidine, salicylic acid, 5-aminosalicylic acid and paracetamol. This effect was explained by invoking an electron-transfer mechanism by which these drugs acted as mediators of rifampicin oxidation. We suggested that this drug interaction might be important at the inflammatory site.

Interaction of rifalazil with oxidant-generating systems of human polymorphonuclear neutrophils

It is well acknowledged that ansamycins display immunosuppressive and anti-inflammatory properties in vitro and in vivo. Rifalazil, a new ansamycin derivative, has not been studied in the context of inflammation. In particular, there are no data on the possible interference of rifalazil with oxidant production by phagocytes. We have compared the antioxidant properties of rifalazil to those of rifampin, a drug well known in this context, by using cellular and acellular oxidant-generating systems. Oxidant production by polymorphonuclear neutrophils was measured in terms of cytochrome c reduction, lucigenin-amplified chemiluminescence (Lu-ACL), and the 2',7'-dichlorofluorescin diacetate H2 (DCFDA-H2) technique (intracellular oxidant production). Rifalazil impaired O2- production in a concentration-dependent manner, with 50% inhibitory concentrations (IC50) (concentrations which inhibit 50% of the response) of 5.4 (30 and 60 min of incubation) and 6.4 (30 min) mg/liter, respectively, for phorbol myristate acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (fMLP) stimulation. In agreement with the published fMLP-like activity of rifampin, the inhibitory effect of rifampin was significantly greater for fMLP (IC50 of 5.6 mg/liter) than for PMA (IC50 of 58 mg/liter) stimulation. Alteration of intracellular oxidant production was also observed with IC50 values similar to those obtained by the cytochrome assay. In addition, rifalazil and rifampin (> or = 25 mg/liter) scavenged O2-, as demonstrated by the acellular (hypoxanthine-xanthine oxidase) system. Interference with light detection systems was evidenced for both drugs by Lu-ACL. The clinical relevance of the antioxidant effect of rifalazil demonstrated in vitro, in particular its potential anti-inflammatory activity, requires further investigation.

Amyloid beta peptide 1-40 enhances the action of Toll-like receptor-2 and -4 agonists but antagonizes Toll-like receptor-9-induced inflammation in primary mouse microglial cell cultures

The interaction of endogenous and exogenous stimulators of innate immunity was examined in primary cultures of mouse microglial cells and macrophages after application of defined Toll-like receptor (TLR) agonists [lipopolysaccharide (LPS) (TLR4), the synthetic lipopeptide Pam3Cys-Ser-Lys4 (Pam3Cys) (TLR2) and single-stranded unmethylated CpG-DNA (CpG) (TLR9)] alone and in combination with amyloid beta peptide (Abeta) 1-40. Abeta1-40 stimulated microglial cells and macrophages primed by interferon-gamma in a dose-dependent manner. Co-administration of Abeta1-40 with LPS or Pam3Cys led to an additive release of nitric oxide (NO) and tumour necrosis factor alpha (TNF-alpha). This may be one reason for the clinical deterioration frequently observed in patients with Alzheimer's disease during infections. In contrast, co-application of Abeta1-40 with CpG led to a substantial decrease of NO and TNF-alpha release compared with stimulation with CpG alone. Abeta1-40 and CpG did not co-localize within the same subcellular compartment, making a direct physicochemical interaction as the cause of the observed antagonism very unlikely. This suggests that not all TLR agonists enhance the stimulatory effect of A beta on innate immunity.

Anti-inflammatory activity of ansamycins

Inflammation represents a complex biologic and biochemical process involving cells of the immune system and a plethora of biologic mediators in response to mechanical, chemical or infectious injuries. When mobilization of effector cells and molecules becomes excessive, the beneficial aspect of this response--to limit damage and promote healing, can be overriden, resulting in host-cell and tissue dysfunction. Based on the hypothesis that chronic infections underly some inflammatory diseases, antibacterial therapy has long been assessed in various inflammatory settings. Recently, the anti-inflammatory activity of some antibacterial agents has also been suspected. Of these duel-action drugs, ansamycins represent an interesting family. Although their therapeutic use is restricted to potentially infectious inflammatory diseases, many experimental data suggest that these drugs also possess direct inhibitory activity on some crucial proinflammatory effectors. To date, the potent antimycobacterial activity of the therapeutically useful ansamycins precludes their widespread use in inflammatory diseases. However, biosynthetic manipulation remains an attractive route for the generation of pharmacologically useful analogs.

Minimizing the release of proinflammatory and toxic bacterial products within the host: A promising approach to improve outcome in life-threatening infections

Various bacterial components (e.g., endotoxin, teichoic and lipoteichoic acids, peptidoglycans, DNA) induce or enhance inflammation by stimulating the innate immune system and/or are directly toxic in eukariotic cells (e.g., hemolysins). When antibiotics which inhibit bacterial protein synthesis kill bacteria, smaller quantities of proinflammatory or toxic compounds are released in vitro and in vivo than during killing of bacteria by beta-lactams and other cell-wall active drugs. In general, high antibiotic concentrations liberate lower quantities of bacterial proinflammatory or toxic compounds than concentrations close to the minimum inhibitory concentration. In animal models of Escherichia coli Pseudomonas aeruginosa and Staphylococcus aureus peritonitis/sepsis and of Streptococcus pneumoniae meningitis, a lower release of proinflammatory bacterial compounds was associated with a reduced mortality or neuronal injury. Pre-treatment with a bacterial protein synthesis inhibitor reduced the strong release of bacterial products usually observed during treatment with a beta-lactam antibiotic. Data available strongly encourage clinical trials comparing antibiotic regimens with different release of proinflammatory/toxic bacterial products. The benefit of the approach to reduce the liberation of bacterial products should be greatest in patients with a high bacterial load.

Group B streptococci exposed to rifampin or clindamycin (versus ampicillin or cefotaxime) stimulate reduced production of inflammatory mediators by murine macrophages

Streptococcus agalactiae (group B Streptococcus, GBS) is an important cause of sepsis and meningitis in neonates, and excessive production of the inflammatory mediators tumor necrosis factor (TNF) and nitric oxide (NO) causes tissue injury during severe infections. We hypothesized that exposure of GBS to different antimicrobial agents would affect the magnitude of the macrophage inflammatory response to this organism. We stimulated RAW 264.7 murine macrophages with a type-Ia GBS isolate in the presence of ampicillin, cefotaxime, rifampin, clindamycin, or gentamicin, singly or in combination. We found that GBS exposed to rifampin or clindamycin (versus beta-lactam antibiotics) stimulated less TNF secretion and inducible nitric oxide synthase (iNOS) protein accumulation in RAW 264.7 cells. Furthermore, GBS exposed to combinations of antibiotics that included a protein synthesis inhibitor stimulated less macrophage TNF and iNOS production than did organisms exposed to beta-lactam antibiotics singly or in combination. We conclude that exposure of GBS to rifampin or clindamycin leads to a less pronounced macrophage inflammatory mediator response than does exposure of the organism to cell wall-active antibiotics.

Clindamycin is neuroprotective in experimental Streptococcus pneumoniae meningitis compared with ceftriaxone

In animal models of Streptococcus pneumoniae meningitis, rifampin is neuroprotective in comparison to ceftriaxone. So far it is not clear whether this can be generalized for other protein synthesis-inhibiting antimicrobial agents. We examined the effects of the bactericidal protein synthesis-inhibiting clindamycin (n = 12) on the release of proinflammatory bacterial components, the formation of neurotoxic compounds and neuronal injury compared with the standard therapy with ceftriaxone (n = 12) in a rabbit model of pneumococcal meningitis. Analysis of the CSF and histological evaluation were combined with microdialysis from the hippocampal formation and the neocortex. Compared with ceftriaxone, clindamycin reduced the release of lipoteichoic acids from the bacteria (p = 0.004) into the CSF and the CSF leucocyte count (p = 0.011). This led to lower extracellular concentrations of hydroxyl radicals (p = 0.034) and glutamate (p = 0.016) in the hippocampal formation and a subsequent reduction of extracellular glycerol levels (p = 0.018) and neuronal apoptosis in the dentate gyrus (p = 0.008). The present data document beneficial effects of clindamycin compared with ceftriaxone on various parameters linked with the pathophysiology of pneumococcal meningitis and development of neuronal injury. This study suggests neuroprotection to be a group effect of bactericidal protein synthesis-inhibiting antimicrobial agents compared with the standard therapy with beta-lactam antibiotics in meningitis.

Acute Bacterial Meningitis in Children

Despite advances in recent decades in management, including new and effective antimicrobials, children with bacterial meningitis still incur significant morbidity and mortality. Pathophysiologic processes including colonization and migration of the bacteria to blood, seeding of the meninges, and meningeal and brain inflammation have been largely elucidated, but more specific knowledge could lead to new effective therapies. Outside of the neonatal period, the most common causative organisms have been Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. However, conjugate vaccines, especially the H influenzae type b preparation, have contributed significantly to steep declines in the incidence of meningitis. Optimal management consists of rapid diagnosis and administration of bactericidal antibiotics with properties allowing adequate penetration of the inflamed blood-brain barrier. Recently, development of microbial resistance has resulted in changes to recommended empiric antibiotic regimens. Novel therapies are under investigation; however, until controlled trials can be conducted, these therapies cannot be recommended.

Expression of proinflammatory cytokines tumor necrosis factor-α and interleukin-1β in the brain during experimental Group B streptococcal meningitis

We performed mRNA in situ hybridization for TNF-alpha and IL-1beta from infant rats with group B streptococcal meningitis. Induction of both cytokines was seen in the ependyma and the meninges at 4 h. Both cytokines were expressed in the brain parenchyma at 12 h. Induction of IL-1beta mRNA was seen in vessels within the brain cortex. Neutrophilic infiltrate at all time points examined was minimal and could not account for the observed cytokine expression.

Experimental pneumococcal meningitis: impaired clearance of bacteria from the blood due to increased apoptosis in the spleen in Bcl-2-deficient mice

Necrotic and apoptotic neuronal cell death can be found in pneumococcal meningitis. We investigated the role of Bcl-2 as an antiapoptotic gene product in pneumococcal meningitis using Bcl-2 knockout (Bcl-2(-/-)) mice. By using a model of pneumococcal meningitis induced by intracerebral infection, Bcl-2-deficient mice and control littermates were assessed by clinical score and a tight rope test at 0, 12, 24, 32, and 36 h after infection. Then mice were sacrificed, the bacterial titers in blood, spleen, and cerebellar homogenates were determined, and the brain and spleen were evaluated histologically. The Bcl-2-deficient mice developed more severe clinical illness, and there were significant differences in the clinical score at 24, 32, and 36 h and in the tight rope test at 12 and 32 h. The bacterial titers in the blood were greater in Bcl-2-deficient mice than in the controls (7.46 +/- 1.93 log CFU/ml versus 5.16 +/- 0.96 log CFU/ml [mean +/- standard deviation]; P < 0.01). Neuronal damage was most prominent in the hippocampal formation, but there were no significant differences between groups. In situ tailing revealed only a few apoptotic neurons in the brain. In the spleen, however, there were significantly more apoptotic leukocytes in Bcl-2-deficient mice than in controls (5,148 +/- 3,406 leukocytes/mm2 versus 1,070 +/- 395 leukocytes/mm2; P < 0.005). Bcl-2 appears to counteract sepsis-induced apoptosis of splenic lymphocytes, thereby enhancing clearance of bacteria from the blood.

Reduced release of pneumolysin by Streptococcus pneumoniae in vitro and in vivo after treatment with nonbacteriolytic antibiotics in comparison to ceftriaxone

Pneumolysin, a virulence factor of Streptococcus pneumoniae with cytotoxic and proinflammatory activities, occurs at concentrations from 0.85 to 180 ng/ml in cerebrospinal fluid (CSF) of meningitis patients. In pneumococcal cultures and in a rabbit meningitis model, the concentrations of pneumolysin in supernatant and CSF were lower after addition of nonbacteriolytic bactericidal antibiotics (rifampin and clindamycin) than after incubation with ceftriaxone.

Differential effect of p47phox and gp91phox deficiency on the course of Pneumococcal Meningitis

Bacterial meningitis is a severe inflammatory disease of the central nervous system and is characterized by massive infiltration of granulocytes into the cerebrospinal fluid (CSF). To assess the role of NADPH oxidase-derived reactive oxygen species (ROS) in pneumococcal meningitis, mice deficient in either the gp91 subunit (essential for functioning of the phagocyte enzyme) or the p47 subunit (essential for functioning of homologous enzymes in nonphagocytic cells) were intracisternally infected with live Streptococcus pneumoniae, and defined disease parameters were measured during the acute stage of infection. While none of the parameters measured (including CSF bacterial titers) were significantly different in gp91(-/-) and wild-type mice, the infection in p47(-/-) mice was associated with significantly increased inflammation of the subarachnoid and ventricular space, disruption of the blood-brain barrier, and the presence of interleukin-1 beta, tumor necrosis factor alpha, and matrix metalloproteinase 9 in the cortex. These changes were associated with approximately 10-fold-higher CSF bacterial titers in p47(-/-) mice than in wild-type mice (P < 0.001). In contrast to infection with live bacteria, the inflammatory response, including CSF leukocytosis, was significantly attenuated in p47(-/-) mice (but not gp91(-/-) mice) challenged with a fixed number of heat-inactivated pneumococci. Impairment of the host defense appeared to be responsible for the higher bacterial titers in p47(-/-) mice. Therefore, these results indicate that ROS generated by a gp91-independent NADPH oxidase(s) are important for establishing an adequate inflammatory response to pneumococcal CSF infection.

Diagnosis and treatment of bacterial meningitis

This review focuses on recent advances of topical interest regarding the diagnosis and treatment of common causes of bacterial meningitis occurring in children beyond the neonatal period. Tuberculous meningitis is beyond the scope of this review.

Reprogramming the host response in bacterial meningitis: how best to improve outcome?

Despite effective antibiotic therapy, bacterial meningitis is still associated with high morbidity and mortality in both children and adults. Animal studies have shown that the host inflammatory response induced by bacterial products in the subarachnoid space is associated with central nervous system injury. Thus, attenuation of inflammation early in the disease process might improve the outcome. The feasibility of such an approach is demonstrated by the reduction in neurologic sequelae achieved with adjuvant dexamethasone therapy. Increased understanding of the pathways of inflammation and neuronal damage has suggested rational new targets to modulate the host response in bacterial meningitis, but prediction of which agents would be optimal has been difficult. This review compares the future promise of benefit from the use of diverse adjuvant agents. It appears unlikely that inhibition of a single proinflammatory mediator will prove useful in clinical practice, but several avenues to reprogram a wider array of mediators simultaneously are encouraging. Particularly promising are efforts to adjust combinations of cytokines, to inhibit neuronal apoptosis and to enhance brain repair.

Rifampin followed by ceftriaxone for experimental meningitis decreases lipoteichoic acid concentrations in cerebrospinal fluid and reduces neuronal damage in comparison to ceftriaxone alone

Rifampin (RIF) releases smaller quantities of lipoteichoic acids (LTAs) from Streptococcus pneumoniae than ceftriaxone (CRO). Due to the rapid development of resistance, RIF cannot be used as a single agent for therapy of bacterial meningitis. For this reason, we compared the effect of treatment with RIF followed by treatment with CRO (RIF-CRO) or the effect of treatment with clindamycin (CLI) followed by treatment with CRO (CLI-CRO) to that of CRO alone on the concentrations of LTAs and teichoic acids in vitro. The effects of RIF-CRO on LTA concentrations in cerebrospinal fluid (CSF) and on neuronal injury were investigated in a rabbit model of S. pneumoniae meningitis. In vitro, bacterial titers were effectively reduced by CRO, RIF-CRO, and CLI-CRO when each drug was used at 10 micro g/ml. The levels of release of LTAs after the initiation of therapy were lower in RIF-CRO- and CLI-CRO-treated cultures than in cultures treated with CRO alone (P < 0.05 from 3 to 12 h after initiation of treatment). Similarly, in rabbits, the increase in the amount of LTAs in CSF was lower in RIF-CRO-treated animals than in CRO-treated animals (P = 0.02). The density of dentate apoptotic granular cells was lower after RIF-CRO therapy than after CRO therapy (medians, 58.4 and 145.6/mm(2), respectively; 25th quartiles, 36.3 and 81.7/mm(2), respectively; 75th quartiles, 100.7 and 152.3/mm(2), respectively; P = 0.03). Therefore, initiation of therapy with a protein synthesis-inhibiting antibacterial and continuation of therapy with a combination that includes a beta-lactam may be a strategy to decrease neuronal injury in bacterial meningitis.

Modulation of release of proinflammatory bacterial compounds by antibacterials: potential impact on course of inflammation and outcome in sepsis and meningitis

Several bacterial components (endotoxin, teichoic and lipoteichoic acids, peptidoglycan, DNA, and others) can induce or enhance inflammation and may be directly toxic for eukaryotic cells. Bactericidal antibiotics which inhibit bacterial protein synthesis release smaller quantities of proinflammatory/toxic bacterial compounds than B-lactams and other cell wall-active drugs. Among the B-lactams, compounds binding to penicillin-binding protein 2 (PBP-2) release smaller amounts of bacterial substances than antibacterials inhibiting PBP-3. Generally, high antibiotic concentrations (more than 10 times the MIC) induce the release of fewer bacterial proinflammatory/toxic compounds than concentrations close to the MIC. In several in vitro and in vivo systems, bacteria treated with protein synthesis inhibitors or B-lactams inhibiting PBP-2 induce less inflammation than bacteria treated with PBP-3-active B-lactams. In mouse models of Escherichia coli peritonitis sepsis and of Streptococcus pneumoniae meningitis, lower release of proinflammatory bacterial compounds was associated with reduced mortality. In conclusion, sufficient evidence for the validity of the concept of modulating the release of proinflammatory bacterial compounds by antibacterials has been accumulated in vitro and in animal experiments to justify clinical trials in sepsis and meningitis. A properly conducted study addressing the potential benefit of bacterial protein synthesis inhibitors versus B-lactam antibiotics will require both strict selection and inclusion of a large number of patients. The benefit of this approach should be greatest in patients with a high bacterial load.

Neuronal injury in bacterial meningitis: mechanisms and implications for therapy

In bacterial meningitis, long-term neurological sequelae and death are caused jointly by several factors: (1) the systemic inflammatory response of the host, leading to leukocyte extravasation into the subarachnoid space, vasculitis, brain edema and secondary ischemia; (2) stimulation of resident microglia within the CNS by bacterial compounds; and (3) possible direct toxicity of bacterial compounds on neurons. Neuronal injury is mediated by the release of reactive oxygen intermediates, proteases, cytokines and excitatory amino acids, and is executed by the activation of transcription factors, caspases and other proteases. In experimental meningitis, dexamethasone as an adjunct to antibiotic treatment leads to an aggravation of neuronal damage in the hippocampal formation, suggesting that corticosteroids might not be the ideal adjunctive therapy. Several approaches that interfere selectively with the mechanisms of neuronal injury are effective in animal models, including the use of nonbacteriolytic protein synthesis-inhibiting antibiotics, antioxidants and inhibitors of transcription factors, matrix metalloproteinases, and caspases.