Protective role of NF-κB1 (p50) in experimental pneumococcal meningitis

Does Infection-Induced Immune Activation Contribute to Dementia?

The central nervous system (CNS) is protected by a complex blood-brain barrier system; however, a broad diversity of virus, bacteria, fungi, and protozoa can gain access and cause illness. As pathogens replicate, they release molecules that can be recognized by innate immune cells. These molecules are pathogen-associated molecular patterns (PAMP) and they are identified by pattern-recognition receptors (PRR) expressed on antigen-presenting cells. Examples of PRR include toll-like receptors (TLR), receptors for advanced glycation endproducts (RAGE), nucleotide binding oligomerisation domain (NOD)-like receptors (NLR), c-type lectin receptors (CLR), RIG-I-like receptors (RLR), and intra-cytosolic DNA sensors. The reciprocal action between PAMP and PRR triggers the release of inflammatory mediators that regulate the elimination of invasive pathogens. Damage-associated molecular patterns (DAMP) are endogenous constituents released from damaged cells that also have the ability to activate the innate immune response. An increase of RAGE expression levels on neurons, astrocytes, microglia, and endothelial cells could be responsible for the accumulation of αβ-amyloid in dementia and related to the chronic inflammatory state that is found in neurodegenerative disorders.

B7 homolog 3 aggravates brain injury in a murine model of Streptococcus pneumoniae-induced meningitis

Despite the application of antibiotics, Streptococcus pneumoniae (SP)-induced meningitis continues to be a life-threatening disease with a high fatality rate and an elevated risk of serious neurological sequelae, particularly in developing countries. In this study, the contribution of the co-stimulatory molecule B7 homolog 3 (B7-H3) to the pathogenesis of experimental SP-induced meningitis was investigated. Mice were challenged with the intracerebroventricular injection of serotype 3 SP with or without B7-H3. The clinical status of mice with SP-induced meningitis was examined by body weight loss and spontaneous motor activity with neurological scoring. Coronal brain sections were analyzed by counting Nissl-positive neurons and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells. Protein expression of neuron-specific enolase (NSE) and S100B in brain tissues was examined with immunohistochemical staining. All experiments were performed in a randomized and blinded setting. By the intracerebroventricular injection of SP suspension, a murine model of pneumococcal meningitis was successfully established. In this SP-induced meningitis model, B7-H3 deteriorated the clinical status, as manifested by a decreased neurological score and increased body weight loss. Following the B7-H3 challenge, the number of Nissl-positive cells decreased and TUNEL-stained positive cells increased in the brain tissues of mice with SP meningitis, which demonstrates the enhancement of neuronal necrosis and apoptosis, respectively. Protein expression of NSE was decreased, while that of S100B was increased. These in vivo findings indicate that B7-H3 aggravates brain injury during the pathological process of experimental SP-induced meningitis.

Treatment and prevention strategies to combat pediatric pneumococcal meningitis

Pneumococcal meningitis is a severe, life-threatening infection of the nervous system affecting infants, children and adults alike. The incidence of pneumococcal meningitis in infants and children less than 2 years of age in Europe is approximately 10 out of 100,000 per year, rising to approximately 148 out of 100,000 per year in Gambian infants. The use of highly sensitive tests such as PCR may increase the likelihood of detecting the infection by 20% or more. Epidemics of serotype 1 pneumococcal meningitis in northern Ghana, have had many of the characteristics of meningococcal meningitis epidemics. Neurologic sequelae may occur in 28-63% of cases, and serotype 3 is associated with a 2.54 relative risk of death. The pathogenic process can be divided into invasion, inflammatory pathways, bacterial toxicity and damage; pneumolysin being particularly associated with apoptosis. In the future, neuroprotection may be achieved, targeting this process at all these levels. Therapeutic guidelines have been published by the Infectious Diseases Society of America. Standard empiric therapy, in those aged greater than or equal to 1 month, is a third-generation cephalosporin plus vancomycin. There is insufficient evidence relating to the use or otherwise of corticosteroids in pneumococcal meningitis to make a firm recommendation. The advent of a pneumococcal conjugate vaccine is the most powerful tool available for the prevention of pneumococcal meningitis in all parts of the world.

Pathophysiology of neonatal acute bacterial meningitis

Neonatal meningitis is a severe acute infectious disease of the central nervous system and an important cause of morbidity and mortality worldwide. The inflammatory reaction involves the meninges, the subarachnoid space and the brain parenchymal vessels and contributes to neuronal injury. Neonatal meningitis leads to deafness, blindness, cerebral palsy, seizures, hydrocephalus or cognitive impairment in approximately 25-50 % of survivors. Bacterial pathogens can reach the blood-brain barrier and be recognized by antigen-presenting cells through the binding of Toll-like receptors. They induce the activation of NFκB or mitogen-activated protein kinase pathways and subsequently upregulate leukocyte populations and express numerous proteins involved in inflammation and the immune response. Many brain cells can produce cytokines, chemokines and other pro-inflammatory molecules in response to bacterial stimuli, and polymorphonuclear leukocytes are attracted, activated and released in large amounts of superoxide anion and nitric oxide, leading to peroxynitrite formation and generating oxidative stress. This cascade leads to lipid peroxidation, mitochondrial damage and breakdown of the blood-brain barrier, thus contributing to cell injury during neonatal meningitis. This review summarizes information on the pathophysiology and adjuvant treatment of acute bacterial meningitis in neonates.

Pathophysiology of acute meningitis caused by Streptococcus pneumoniae and adjunctive therapy approaches

Pneumococcal meningitis is a life-threatening disease characterized by an acute purulent infection affecting piamater, arachnoid and the subarachnoid space. The intense inflammatory host's response is potentially fatal and contributes to the neurological sequelae. Streptococcus pneumoniae colonizes the nasopharynx, followed by bacteremia, microbial invasion and blood-brain barrier traversal. S. pneumoniae is recognized by antigen-presenting cells through the binding of Toll-like receptors inducing the activation of factor nuclear kappa B or mitogen-activated protein kinase pathways and subsequent up-regulation of lymphocyte populations and expression of numerous proteins involved in inflammation and immune response. Many brain cells can produce cytokines, chemokines and others pro-inflammatory molecules in response to bacteria stimuli, as consequence, polymorphonuclear are attracted, activated and released in large amounts of superoxide anion and nitric oxide, leading to the peroxynitrite formation, generating oxidative stress. This cascade leads to lipid peroxidation, mitochondrial damage, blood-brain barrier breakdown contributing to cell injury during pneumococcal meningitis.

Dexamethasone in adults with community-acquired bacterial meningitis

Bacterial meningitis in adults is a severe disease with high fatality and morbidity rates. Experimental studies have shown that the inflammatory response in the subarachnoid space is associated with an unfavourable outcome. In these experiments, corticosteroids, and in particular dexamethasone, were able to reduce the inflammatory cascades in the subarachnoid space. The use of corticosteroids as adjunctive therapy in adults with bacterial meningitis has been evaluated in six studies, performed over a time period of 40 years. Most studies on adjunctive dexamethasone therapy in adults with bacterial meningitis were limited by methodological flaws. In 2002, a study with sufficient statistical power to show significant differences was published. This European Dexamethasone Study showed that adjunctive dexamethasone therapy reduced the rate of unfavourable outcomes in adults with bacterial meningitis from 25% to 15%. In this study, adjunctive treatment with dexamethasone was given before or with the first dose of antibacterials, without serious adverse effects. A quantitative review showed a consistent beneficial effect of dexamethasone on mortality and a borderline statistical beneficial effect on neurological sequelae. On the basis of the available evidence, adjunctive dexamethasone therapy should be initiated before or with the first dose of antibacterials and continued for 4 days in all adults with suspected or proven bacterial meningitis, regardless of bacterial aetiology. In patients with both meningitis and septic shock, dexamethasone therapy cannot be unequivocally recommended, but the use of lower doses seems reasonable at present. Since prompt use of dexamethasone and appropriate antibacterials improves the prognosis of adults with bacterial meningitis, hospitals will require protocols to include dexamethasone with the initial antibacterial therapy.

Drug Insight: adjunctive therapies in adults with bacterial meningitis

Despite the availability of effective antibiotics, mortality and morbidity rates associated with bacterial meningitis are high. Studies in animals have shown that bacterial lysis, induced by treatment with antibiotics, leads to inflammation in the subarachnoid space, which might contribute to an unfavorable outcome. The management of adults with bacterial meningitis can be complex, and common complications include meningoencephalitis, systemic compromise, stroke and raised intracranial pressure. Various adjunctive therapies have been described to improve outcome in such patients, including anti-inflammatory agents, anticoagulant therapies, and strategies to reduce intracranial pressure. Although a recent randomized trial provided evidence in favor of dexamethasone treatment, few randomized clinical studies are available for other adjunctive therapies in adults with bacterial meningitis. This review briefly summarizes the pathogenesis and pathophysiology of bacterial meningitis, and focuses on the evidence for and against use of the available adjunctive therapies in clinical practice.

Pneumococcal meningitis in adults: new approaches to management and prevention

Since the virtual eradication of meningitis due to Haemophilus influenzae type B by vaccination in the developed world, pneumococcal meningitis has become the leading cause of bacterial meningitis beyond the neonatal period. Clinical and experimental research has increased our knowledge about the pathophysiology and pathogenesis of the disease over the past decades. Despite the availability of effective antibiotics, supportive care facilities, and recent advances in adjunctive strategies-ie, adjunctive dexamethasone-mortality and morbidity rates associated with pneumococcal meningitis remain unacceptably high. Although preliminary results after the introduction of the pneumococcal conjugate vaccine are promising, the incidence of multidrug-resistant pneumococcal strains is rising worldwide. Here we discuss clinical aspects of pneumococcal meningitis in adults, with focus on pathophysiology, and stress the urgent need for adequate preventive measures and new effective treatments.