Bacteremia causes hippocampal apoptosis in experimental pneumococcal meningitis

Background

Bacteremia and systemic complications both play important roles in brain pathophysiological alterations and the outcome of pneumococcal meningitis. Their individual contributions to the development of brain damage, however, still remain to be defined.

Methods

Using an adult rat pneumococcal meningitis model, the impact of bacteremia accompanying meningitis on the development of hippocampal injury was studied. The study comprised of the three groups: I. Meningitis (n = 11), II. meningitis with attenuated bacteremia resulting from iv injection of serotype-specific pneumococcal antibodies (n = 14), and III. uninfected controls (n = 6).

Results

Pneumococcal meningitis resulted in a significantly higher apoptosis score 0.22 (0.18-0.35) compared to uninfected controls (0.02 (0.00-0.02), Mann Whitney test, P = 0.0003). Also, meningitis with an attenuation of bacteremia by antibody treatment resulted in significantly reduced apoptosis (0.08 (0.02-0.20), P = 0.01) as compared to meningitis.

Conclusions

Our results demonstrate that bacteremia accompanying meningitis plays an important role in the development of hippocampal injury in pneumococcal meningitis.

Expression and regulation of antimicrobial peptide rCRAMP after bacterial infection in primary rat meningeal cells

Bacterial meningitis is characterized by an inflammation of the meninges and continues to be an important cause of mortality and morbidity. Meningeal cells cover the cerebral surface and are involved in the first interaction between pathogens and the brain. Little is known about the role of meningeal cells and the expression of antimicrobial peptides in the innate immune system. In this study we characterized the expression, secretion and bactericidal properties of rat cathelin-related antimicrobial peptide (rCRAMP), a homologue of the human LL-37, in rat meningeal cells after incubation with different bacterial supernatants and the bacterial cell wall components lipopolysaccharide (LPS) and peptidoglycan (PGN). Using an agar diffusion test, we observed that supernatants from meningeal cells incubated with bacterial supernatants, LPS and PGN showed signs of antimicrobial activity. The inhibition of rCRAMP expression using siRNA reduced the antimicrobial activity of the cell culture supernatants. The expression of rCRAMP in rat meningeal cells involved various signal transduction pathways and was induced by the inflammatory cytokines interleukin-1, -6 and tumor necrosis factor alpha. In an experimental model of meningitis, infant rats were intracisternally infected with Streptococcus pneumoniae and rCRAMP was localized in meningeal cells using immunohistochemistry. These results suggest that cathelicidins produced by meningeal cells play an important part in the innate immune response against pathogens in CNS bacterial infections.

Chorioretinal nocardiosis

PURPOSE

Description of ocular involvement in a case of disseminated nocardiosis.

METHODS

Case report of an immunosuppressed patient displaying a unilateral extramacular choroidal lesion presumed to be due to nocardia species. The patient received sulfonamide treatment for a culture-proven generalized nocardia infection.

RESULTS

During follow-up, demarcation, resolution, and secondary development of macular pucker with vitreoretinal traction and macular edema was observed. Visual acuity of the affected eye recovered from initially 20/100 to 20/32 at the end of follow-up.

CONCLUSION

Early and appropriate treatment of ocular endogenous nocardiosis can result in a favorable outcome.

A case of maternal herpes simplex virus encephalitis during late pregnancy

BACKGROUND

A pregnant 25-year-old woman at 32 weeks' gestation was admitted to an emergency unit after her husband had found her drowsy and with her tongue bitten. The day before admission, the patient had developed a fever of 39 degrees C, was suffering from headaches, was nauseated and had vomited. On admission, she had anterograde and retrograde amnesia, but no somatic neurological deficits were detected.

INVESTIGATIONS

Routine laboratory testing, lumbar puncture, cerebrospinal fluid analysis, routine bacteriology, brain MRI, and polymerase chain reaction testing for neurotropic viruses including herpes simplex virus types 1 and 2.

DIAGNOSIS

Maternal herpes simplex virus type 1 encephalitis.

MANAGEMENT

Antiviral and anticonvulsive therapy, supportive treatment, and cesarean section.

Effects of Toll-like receptor 2 agonist Pam(3)CysSK(4) on inflammation and brain damage in experimental pneumococcal meningitis

TLR2 signaling participates in the pathogenesis of pneumococcal meningitis. In infant rats, the TLR2 agonist Pam(3)CysSK(4) was applied intracisternally (0.5 microg in 10 microl saline) alone or after induction of pneumococcal meningitis to investigate the effect of TLR2 activation on cerebrospinal fluid (CSF) inflammation and hippocampal apoptosis. A dose effect of Pam(3)CysSK(4) on apoptosis was investigated by intracisternal application of 0.5 microg in 10 microl saline and 40 microg in 20 microl saline. Pam(3)CysSK(4) neither induced apoptosis in sham-operated mice nor aggravated apoptosis in acute infection. However, Pam(3)CysSK(4) induced pleocytosis, TNF-alpha and MMP-9 in CSF in sham-infection but not during acute meningitis. We conclude that TLR2 signaling triggered by Pam(3)CysSK(4) at a dosage capable to induce a neuroinflammatory response does not induce hippocampal apoptosis in the infant rat model of experimental pneumococcal meningitis.

Essential role of choline for pneumococcal virulence in an experimental model of meningitis

OBJECTIVES

The goal of the present study was to elucidate the contribution of the newly recognized virulence factor choline to the pathogenesis of Streptococcus pneumoniae in an animal model of meningitis.

RESULTS

The choline containing strain D39Cho(-) and its isogenic choline-free derivative D39Cho(-)licA64--each expressing the capsule polysaccharide 2--were introduced intracisternally at an inoculum size of 10(3) CFU into 11 days old Wistar rats. During the first 8 h post infection both strains multiplied and stimulated a similar immune response that involved expression of high levels of proinflammatory cytokines, the matrix metalloproteinase 9 (MMP-9), IL-10, and the influx of white blood cells into the CSF. Virtually identical immune response was also elicited by intracisternal inoculation of 10(7) CFU equivalents of either choline-containing or choline-free cell walls. At sampling times past 8 h strain D39Cho(-) continued to replicate accompanied by an intense inflammatory response and strong granulocytic pleiocytosis. Animals infected with D39Cho(-) died within 20 h and histopathology revealed brain damage in the cerebral cortex and hippocampus. In contrast, the initial immune response generated by the choline-free strain D39Cho(-)licA64 began to decline after the first 8 h accompanied by elimination of the bacteria from the CSF in parallel with a strong WBC response peaking at 8 h after infection. All animals survived and there was no evidence for brain damage.

CONCLUSION

Choline in the cell wall is essential for pneumococci to remain highly virulent and survive within the host and establish pneumococcal meningitis.

JNK is activated but does not mediate hippocampal neuronal apoptosis in experimental neonatal pneumococcal meningitis

Pneumococcal meningitis is associated with caspase 3-dependent apoptosis of recently post-mitotic immature neurons in the dentate gyrus of the hippocampus. The death of these cells is implicated in the learning and memory deficits in patients surviving the disease. The stress-activated protein kinase c-Jun N-terminal kinase (JNK) has been shown to be an important mediator of caspase 3-dependent neuronal apoptosis. However, whether JNK is involved in hippocampal apoptosis caused by pneumococcal meningitis has so far not been investigated. Here we show in a neonatal rat model of pneumococcal meningitis that JNK3 but not JNK1 or JNK2 is activated in the hippocampus during the acute phase of infection. At the cellular level, JNK3 activation was accompanied in the dentate gyrus by markedly increased phosphorylation of its major downstream target c-Jun in early immature (Hu-positive) neurons, but not in migrating (doublecortin-positive) neurons, the cells that do undergo apoptosis. These findings suggested that JNK may not be involved in pneumococcal meningitis-induced hippocampal apoptosis. Indeed, although intracerebroventricular administration of D-JNKI-1 or AS601245 (two highly specific JNK inhibitors) inhibited c-Jun phosphorylation and protein expression in the hippocampus, hippocampal apoptosis was unaffected. Collectively, these results demonstrate that JNK does not mediate hippocampal apoptosis in pneumococcal meningitis, and that JNK may be involved in processes unrelated to apoptosis in this disease.

Atorvastatin does not alter serum levels of sCD95 and sCD95L in multiple sclerosis

Elimination of autoreactive T cells by apoptosis is critical for restricting immune responses to self-antigens. An errant lytic interaction between the CD95 death receptor and its ligand CD95L is presumed to be involved in the pathogenesis of multiple sclerosis (MS). Statins are promising agents for the treatment of MS and were shown to modulate levels of soluble death receptors. Here, we evaluated the in vivo effects by interferon (IFN)-beta and atorvastatin on soluble CD95 (sCD95) and sCD95L in serum of patients with MS. Concentrations of sCD95 and sCD95L did not show any differences between MS and healthy control subjects. In patients with MS, treatment with IFN-beta increased serum levels of sCD95 and sCD95L significantly (P < 0.01 and P < 0.05 respectively). Addition of atorvastatin to IFN-beta did not alter serum levels of sCD95 and sCD95L significantly. Our study suggests that atorvastatin does not affect IFN-beta-induced increases of the soluble death receptors in the serum of patients with MS.

An infant mouse model of brain damage in pneumococcal meningitis

Bacterial meningitis due to Streptococcus pneumoniae is associated with an significant mortality rate and persisting neurologic sequelae including sensory-motor deficits, seizures, and impairments of learning and memory. The histomorphological correlate of these sequelae is a pattern of brain damage characterized by necrotic tissue damage in the cerebral cortex and apoptosis of neurons in the hippocampal dentate gyrus. Different animal models of pneumococcal meningitis have been developed to study the pathogenesis of the disease. To date, the infant rat model is unique in mimicking both forms of brain damage documented in the human disease. In the present study, we established an infant mouse model of pneumococcal meningitis. Eleven-days-old C57BL/6 (n = 299), CD1 (n = 42) and BALB/c (n = 14) mice were infected by intracisternal injection of live Streptococcus pneumoniae. Sixteen hours after infection, all mice developed meningitis as documented by positive bacterial cultures of the cerebrospinal fluid. Sixty percent of infected C57BL/6 mice survived more than 40 h after infection (50% of CD1, 0% of BALB/c). Histological evaluations of brain sections revealed apoptosis in the dentate gyrus of the hippocampus in 27% of infected C57BL/6 and in 5% of infected CD1 mice. Apoptosis was confirmed by immunoassaying for active caspase-3 and by TUNEL staining. Other forms of brain damage were found exclusively in C57BL/6, i.e. caspase-3 independent (pyknotic) cell death in the dentate gyrus in 2% and cortical damage in 11% of infected mice. This model may prove useful for studies on the pathogenesis of brain injury in childhood bacterial meningitis.

Gene and protein expression of galectin-3 and galectin-9 in experimental pneumococcal meningitis

Inflammation of the subarachnoid and ventricular space contributes to the development of brain damage i.e. cortical necrosis and hippocampal apoptosis in pneumococcal meningitis (PM). Galectin-3 and -9 are known pro-inflammatory mediators and regulators of apoptosis. Here, the gene and protein expression profile for both galectins was assessed in the disease progression of PM. The mRNA of Lgals3 and Lgals9 increased continuously in the cortex and in the hippocampus from 22 h to 44 h after infection. At 44 h after infection, mRNA levels of Lgals9 in the hippocampus were 7-fold and those of Lgals3 were 30-fold higher than in uninfected controls (P<0.01). Galectin-9 protein did not change, but galectin-3 significantly increased in cortex and hippocampus with the duration of PM. Galectin-3 was localized to polymorphonuclear neutrophils, microglia, monocytes and macrophages, suggesting an involvement of galectin-3 in the neuroinflammatory processes leading to brain damage in PM.

Rapid diagnosis of experimental meningitis by bacterial heat production in cerebrospinal fluid

Background

Calorimetry is a nonspecific technique which allows direct measurement of heat generated by biological processes in the living cell. We evaluated the potential of calorimetry for rapid detection of bacterial growth in cerebrospinal fluid (CSF) in a rat model of bacterial meningitis.

Methods

Infant rats were infected on postnatal day 11 by direct intracisternal injection with either Streptococcus pneumoniae, Neisseria meningitidis or Listeria monocytogenes. Control animals were injected with sterile saline or heat-inactivated S. pneumoniae. CSF was obtained at 18 hours after infection for quantitative cultures and heat flow measurement. For calorimetry, 10 μl and 1 μl CSF were inoculated in calorimetry ampoules containing 3 ml trypticase soy broth (TSB).

Results

The mean bacterial titer (± SD) in CSF was 1.5 ± 0.6 × 10⁸ for S. pneumoniae, 1.3 ± 0.3 × 10⁶ for N. meningitidis and 3.5 ± 2.2 × 10⁴ for L. monocytogenes. Calorimetric detection time was defined as the time until heat flow signal exceeded 10 μW. Heat signal was detected in 10-μl CSF samples from all infected animals with a mean (± SD) detection time of 1.5 ± 0.2 hours for S. pneumoniae, 3.9 ± 0.7 hours for N. meningitidis and 9.1 ± 0.5 hours for L. monocytogenes. CSF samples from non-infected animals generated no increasing heat flow (<10 μW). The total heat was the highest in S. pneumoniae ranging from 6.7 to 7.5 Joules, followed by L. monocytogenes (5.6 to 6.1 Joules) and N. meningitidis (3.5 to 4.4 Joules). The lowest detectable bacterial titer by calorimetry was 2 cfu for S. pneumoniae, 4 cfu for N. meningitidis and 7 cfu for L. monocytogenes.

Conclusion

By means of calorimetry, detection times of <4 hours for S. pneumoniae and N. meningitidis and <10 hours for Listeria monocytogenes using as little as 10 μl CSF were achieved. Calorimetry is a new diagnostic method allowing rapid and accurate diagnosis of bacterial meningitis from a small volume of CSF.

A model of cerebral aspergillosis in non-immunosuppressed nursing rats

Central nervous system aspergillosis is an often fatal complication of invasive Aspergillus infection. Relevant disease models are needed to study the pathophysiology of cerebral aspergillosis and to develop novel therapeutic approaches. This study presents a model of central nervous system aspergillosis that mimics important aspects of human disease. Eleven-day-old non-immunosuppressed male Wistar rats were infected by an intracisternal injection of 10 mul of a conidial suspension of Aspergillus fumigatus. An inoculum of 7.18 log(10) colony-forming units (CFU) consistently produced cerebral infection and resulted in death of all animals (n = 25) within 3-10 days. Median survival time was 3 days. Histomorphologically, all animals developed intracerebral abscesses (2-26 per brain) containing abundant fungal hyphae and neutrophils. Fungal culture of cortical homogenates yielded maximal growth on day 3 after infection (5.4 log(10) CFU/g, n = 15) that declined over time. Galactomannan concentrations in cortical homogenates, assessed as an index for hyphal burden, peaked on days 3-5. Fungal infection spread to peripheral organs in 83% of animals. Fungal burden in lung, liver, spleen and kidney was two orders of magnitude lower than in the brain. The successful establishment of a model of cerebral aspergillosis in a non-immunosuppressed host provides the opportunity to investigate mechanisms of disease and to develop novel treatment regimens for this commonly fatal infection.

Limited efficacy of adjuvant therapy with dexamethasone in preventing hearing loss due to experimental pneumococcal meningitis in the infant rat

Sensorineural hearing loss (SNHL) is the most common sequel of bacterial meningitis (BM) and is observed in up to 30% of survivors when the disease is caused by Streptococcus pneumoniae. BM is the single most important origin of acquired SNHL in childhood. Anti-inflammatory dexamethasone holds promises as potential adjuvant therapy to prevent SNHL associated with BM. However, in infant rats, pneumococcal meningitis (PM) increased auditory brainstem response (ABR) thresholds [mean difference = 54 decibels sound pressure level (dB SPL)], measured 3 wk after infection, irrespective to treatment with ceftriaxone plus dexamethasone or ceftriaxone plus saline (p < 0.005 compared with mock-infected controls). Moreover, dexamethasone did not attenuate short- and long-term histomorphologic correlates of SNHL. At 24 h after infection, blood-labyrinth barrier (BLB) permeability was significantly increased in infected animals of both treatment groups compared with controls. Three weeks after the infection, the averaged number of type I neurons per square millimeter of the Rosenthal's canal dropped from 0.3019 +/- 0.0252 in controls to 0.2227 +/- 0.0635 in infected animals receiving saline (p < 0.0005). Dexamethasone was not more effective than saline in preventing neuron loss (0.2462 +/- 0.0399; p > 0.05). These results suggest that more efficient adjuvant therapies are needed to prevent SNHL associated with pediatric PM.

Prevention of brain injury by the nonbacteriolytic antibiotic daptomycin in experimental pneumococcal meningitis

Bacteriolytic antibiotics cause the release of bacterial components that augment the host inflammatory response, which in turn contributes to the pathophysiology of brain injury in bacterial meningitis. In the present study, antibiotic therapy with nonbacteriolytic daptomycin was compared with that of bacteriolytic ceftriaxone in experimental pneumococcal meningitis, and the treatments were evaluated for their effects on inflammation and brain injury. Eleven-day-old rats were injected intracisternally with 1.3 x 10(4) +/- 0.5 x 10(4) CFU of Streptococcus pneumoniae serotype 3 and randomized to therapy with ceftriaxone (100 mg/kg of body weight subcutaneously [s.c.]; n = 55) or daptomycin (50 mg/kg s.c.; n = 56) starting at 18 h after infection. The cerebrospinal fluid (CSF) was assessed for bacterial counts, matrix metalloproteinase-9 levels, and tumor necrosis factor alpha levels at different time intervals after infection. Cortical brain damage was evaluated at 40 h after infection. Daptomycin cleared the bacteria more efficiently from the CSF than ceftriaxone within 2 h after the initiation of therapy (log(10) 3.6 +/- 1.0 and log(10) 6.3 +/- 1.4 CFU/ml, respectively; P < 0.02); reduced the inflammatory host reaction, as assessed by the matrix metalloproteinase-9 concentration in CSF 40 h after infection (P < 0.005); and prevented the development of cortical injury (cortical injury present in 0/30 and 7/28 animals, respectively; P < 0.004). Compared to ceftriaxone, daptomycin cleared the bacteria from the CSF more rapidly and caused less CSF inflammation. This combined effect provides an explanation for the observation that daptomycin prevented the development of cortical brain injury in experimental pneumococcal meningitis. Further research is needed to investigate whether nonbacteriolytic antibiotic therapy with daptomycin represents an advantageous alternative over current bacteriolytic antibiotic therapies for the treatment of pneumococcal meningitis.

Pneumococcal Meningitis Induces Apoptosis in Recently Postmitotic Immature Neurons in the Dentate Gyrus of Neonatal Rats

Bacterial meningitis is associated with high rates of morbidity and mortality, despite advances in antibiotic therapy. Meningitis caused by Streptococcus pneumoniae is associated with a particularly high incidence of neurological sequelae including deficits resulting from damage to the hippocampus. Previous studies have documented that in neonatal rats with experimental pneumococcal meningitis, cells in the subgranular layer of the dentate gyrus undergo apoptosis. The aim of the present study was to define in more detail the nature of the dying cells in the dentate gyrus. Using bromodeoxyuridine labeling at different times before infection combined with immunocytochemistry, we identified the vulnerable cells as those which underwent mitosis 6-10 days before infection. A majority of these cells are of neuronal lineage. Thus, immature neuronal cells several days after the last cell division are preferentially triggered into apoptosis during pneumococcal meningitis. The loss of these cells may contribute to the long-lasting impairment of hippocampal function identified in animal models and in humans after bacterial meningitis.

Induction of haem oxygenase-1 causes cortical non-haem iron increase in experimental pneumococcal meningitis: evidence that concomitant ferritin up-regulation prevents iron-induced oxidative damage

Desferrioxamine inhibits cortical necrosis in neonatal rats with experimental pneumococcal meningitis, suggesting that iron-induced oxidative damage might be responsible for neuronal damage. We therefore examined the spatial and temporal profile of changes in cortical iron and iron homeostatic proteins during pneumococcal meningitis. Infection was associated with a steady and global increase of non-haem iron in the cortex, particularly in neuronal cell bodies of layer II and V, and in capillary endothelial cells. The non-haem iron increase was associated with induction of haem oxygenase (HO)-1 in neurones, microglia and capillary endothelial cells, whereas HO-2 levels remained unchanged, suggesting that the non-haem iron increase might be the result of HO-1-mediated haem degradation. Indeed, treatment with the haem oxygenase inhibitor tin protoporphyrin (which completely blocked the accumulation of bilirubin detected in HO-1-positive cells) completely prevented the infection-associated non-haem iron increase. The same cells also displayed markedly increased ferritin staining, the increase of which occurred independently of HO activity. At the same time, no increase in DNA/RNA oxidation was observed in infected animals (as assessed by in situ detection of 8-hydroxy[deoxy]guanosine), strongly suggesting that ferritin up-regulation protected the brain from iron-induced oxidative damage. Thus, although pneumococcal meningitis leads to an increase of cortical non-haem iron, protective mechanisms up-regulated in parallel prevent iron-induced oxidative damage. Cortical damage does not appear to be a direct consequence of increased iron, therefore.

Herpes-simplex virus encephalitis is characterized by an early MMP-9 increase and collagen type IV degradation

Cerebrovascular complications including cerebral edema, raised intracranial pressure and hemorrhage contribute to the high mortality and morbidity of herpes-simplex virus encephalitis (HSE). We examined changes of collagen type IV, the major constituent of the neurovascular matrix, together with expression and localization of matrix-degrading enzymes during the development of acute HSE. In an experimental model of focal HSE, we found that early, symptomatic HSE (3 days after infection) and acute, fully developed HSE (7 days after infection) are associated with significantly raised levels of matrix-metalloproteinase-9 (MMP-9) (both P<0.05). In situ zymography of brain sections revealed that the increase of MMP-9 was restricted to the cerebral vasculature in early HSE and further expanded towards the perivascular space and adjacent tissue in acute HSE. Around the cerebral vasculature, we observed that MMP-9 activity was insufficiently counterbalanced by its endogenous tissue inhibitor of MMP (TIMP) TIMP-1, resulting in loss of collagen type IV. Our findings suggest that MMP-9 is involved in the evolution of HSE by causing damage to the cerebral vasculature. The degradation of the neurovascular matrix in HSE facilitates the development of cerebrovascular complications and may represent a target for novel adjuvant treatment strategies.

[Invasive meningococcal infections: two cases that demonstrate the broad spectrum in clinical manifestation and outcome]

Invasive meningococcal infections show a broad clinical picture including sepsis and meningitis. Here we report on a case of sepsis and a case of meningitis, two clinical manifestations of meningococcal infections with striking differences in the clinical presentation and outcome. Meningococcal sepsis is characterized by a systemic release of endotoxins, that triggers an intense cytokine response of the host that can lead to shock and multi organ failure and death within hours. Meningococcal meningitis occurs when bacteria breach into the subarachnoidal and ventricular space during bacteremia and mortality is much lower that in sepsis. Thus meningitis may be seen as a consequence of lower pathogenicity and/or more efficient host control of the meningococci compared to sepsis.

Pneumococcal meningitis causes accumulation of neurotoxic kynurenine metabolites in brain regions prone to injury

Pneumococcal meningitis (PM) is characterized by an intense inflammatory host reaction that contributes to the development of cortical necrosis and hippocampal apoptosis. Inflammatory conditions in the brain are known to induce tryptophan degradation along the kynurenine pathway, resulting in accumulation of neurotoxic metabolites. In the present study, we investigated the contribution of the kynurenine pathway to brain injury in experimental PM by measuring the concentration of its metabolites and the enzymatic activities and mRNA levels of its major enzymes in the vulnerable brain regions. In the late phase of acute PM, we found a significant transcriptional upregulation of kynurenine-3-hydroxylase and an accumulation of the neurotoxic metabolites 3-hydroxykynurenine (3-HKYN) and 3-hydroxyanthranilic acid in cortex and hippocampus. The positive correlation between the concentration of 3-HKYN and the extent of hippocampal apoptosis adds support to the concept that 3-HKYN contributes to brain injury in PM.