Roland Nau

Penetration of Drugs through the Blood-Cerebrospinal Fluid/Blood-Brain Barrier for Treatment of Central Nervous System Infections

SUMMARY The entry of anti-infectives into the central nervous system (CNS) depends on the compartment studied, molecular size, electric charge, lipophilicity, plasma protein binding, affinity to active transport systems at the blood-brain/blood-cerebrospinal fluid (CSF) barrier, and host factors such as meningeal inflammation and CSF flow. Since concentrations in microdialysates and abscesses are not frequently available for humans, this review focuses on drug CSF concentrations. The ideal compound to treat CNS infections is of small molecular size, is moderately lipophilic, has a low level of plasma protein binding, has a volume of distribution of around 1 liter/kg, and is not a strong ligand of an efflux pump at the blood-brain or blood-CSF barrier. When several equally active compounds are available, a drug which comes close to these physicochemical and pharmacokinetic properties should be preferred. Several anti-infectives (e.g., isoniazid, pyrazinamide, linezolid, metronidazole, fluconazole, and some fluoroquinolones) reach a CSF-to-serum ratio of the areas under the curves close to 1.0 and, therefore, are extremely valuable for the treatment of CNS infections. In many cases, however, pharmacokinetics have to be balanced against in vitro activity. Direct injection of drugs, which do not readily penetrate into the CNS, into the ventricular or lumbar CSF is indicated when other effective therapeutic options are unavailable.

The varicella zoster virus vasculopathies: Clinical, CSF, imaging, and virologic features

Background: Varicella zoster virus (VZV) vasculopathy produces stroke secondary to viral infection of cerebral arteries. Not all patients have rash before cerebral ischemia or stroke. Furthermore, other vasculitides produce similar clinical features and comparable imaging, angiographic, and CSF abnormalities. Methods: We review our 23 published cases and 7 unpublished cases of VZV vasculopathy. All CSFs were tested for VZV DNA by PCR and anti-VZV IgG antibody and were positive for either or both. Results: Among 30 patients, rash occurred in 19 (63%), CSF pleocytosis in 20 (67%), and imaging abnormalities in 29 (97%). Angiography in 23 patients revealed abnormalities in 16 (70%). Large and small arteries were involved in 15 (50%), small arteries in 11 (37%), and large arteries in only 4 (13%) of 30 patients. Average time from rash to neurologic symptoms and signs was 4.1 months, and from neurologic symptoms and signs to CSF virologic analysis was 4.2 months. CSF of 9 (30%) patients contained VZV DNA while 28 (93%) had anti-VZV IgG antibody in CSF; in each of these patients, reduced serum/CSF ratio of VZV IgG confirmed intrathecal synthesis. Conclusions: Rash or CSF pleocytosis is not required to diagnose varicella zoster virus (VZV) vasculopathy, whereas MRI/CT abnormalities are seen in almost all patients. Most patients had mixed large and small artery involvement. Detection of anti-VZV IgG antibody in CSF was a more sensitive indicator of VZV vasculopathy than detection of VZV DNA (p < 0.001). Determination of optimal antiviral treatment and benefit of concurrent steroid therapy awaits studies with larger case numbers. GLOSSARY: EIA = enzyme immunoabsorbent assay; VZV = varicella zoster virus.

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.

Modulation of Release of Proinflammatory Bacterial Compounds by Antibacterials: Potential Impact on Course of Inflammation and Outcome in Sepsis and Meningitis

SUMMARY 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 Β-lactams and other cell wall-active drugs. Among the Β-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 Β-lactams inhibiting PBP-2 induce less inflammation than bacteria treated with PBP-3-active Β-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 Β-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.

Apoptosis of Neurons in the Dentate Gyrus in Humans Suffering from Bacterial Meningitis

Apoptosis of granular cells in the dentate gyrus frequently occurs in animal models of bacterial meningitis. In 37 autopsy cases of bacterial meningitis we evaluated, by light microscopy and in-situ tailing, whether this pattern of neuronal damage is of relevance in humans. Neuronal apoptoses in the dentate gyrus (density 1 to 19/mm2) were observed in 26 cases of bacterial meningitis and in none of 10 aged-matched control cases dying from non-neurological diseases. The density of apoptotic neurons depended on the interval between the onset of symptoms of meningitis and death (death within the first 2 days: 1.8+/-2.8 apoptoses/mm2; later than 18 days: 1.8+/-1.7/mm2; compared to death between days 3 and 18: 7.4+/-6.6 apoptoses/mm2, p = 0.007 and 0.004, respectively). Neuronal apoptosis in the dentate gyrus was not linked to neuronal damage in other parts of the brain or previous treatment with corticosteroids. Since learning deficits are frequently observed in survivors of bacterial meningitis, strategies to reduce the density of apoptotic neurons in the dentate gyrus may decrease the frequency of neurological sequela in patients surviving bacterial meningitis.

Anti-Inflammatory Treatment Influences Neuronal Apoptotic Cell Death in the Dentate Gyrus in Experimental Pneumococcal Meningitis

Apoptotic neuronal death and the increase of neuron-specific enolase (NSE) in cerebrospinal fluid (CSF) were studied in a rabbit model of experimental pneumococcal meningitis after treatment with antimicrobial (ceftriaxone) and antiinflammatory agents (dexamethasone, monoclonal antibodies against the β-subunit of β2-integrins [anti-CD18 mAb]). Twenty-four hours after infection, apoptotic cell death was found solely in the granular cell layer of the dentate gyrus. Neurons with DNA fragmentation were quantified with the in situ tailing (IST) reaction. Dexamethasone and anti-CD18 mAb inhibited the NSE increase in CSF significantly (p=0.003, p=0.011). After administration of dexamethasone the density of apoptotic neurons was significantly higher than in control animals receiving only ceftriaxone (p=0.044). The median of the density of apoptotic neurons was lower in the dentate gyrus in animals receiving anti-CD18 mAb and ceftriaxone vs those receiving only ceftriaxone, although the difference did not reach statistic significance (p=0.058). In conclusion, apoptotic cell death occurs in the dentate gyrus during the early phase of bacterial meningitis. The extent was influenced by antiinflammatory therapy. The systemic administration of glucocorticoids increased the quantity of apoptotic neurons in the dentate gyrus but reduced overall neuronal damage as indicated by low levels of NSE concentration in CSF.

PavA of Streptococcus pneumoniae Modulates Adherence, Invasion, and Meningeal Inflammation

ABSTRACT Pneumococcal adherence and virulence factor A (PavA) is displayed to the cell outer surface of Streptococcus pneumoniae and mediates pneumococcal binding to immobilized fibronectin. PavA, which lacks a typical gram-positive signal sequence and cell surface anchorage motif, is essential for pneumococcal virulence in a mouse infection model of septicemia. In this report the impact of PavA on pneumococcal adhesion to and invasion of eukaryotic cells and on experimental pneumococcal meningitis was investigated. In the experimental mouse meningitis model, the virulence of the pavA knockout mutant of S. pneumoniae D39, which did not show alterations of subcellular structures as indicated by electron microscopic studies, was strongly decreased. Pneumococcal strains deficient in PavA showed substantially reduced adherence to and internalization of epithelial cell lines A549 and HEp-2. Similar results were obtained with human brain-derived microvascular endothelial cells and human umbilical vein-derived endothelial cells. Attachment and internalization of pneumococci were not significantly affected by preincubation or cocultivations of pneumococci with anti-PavA antisera. Pneumococcal adherence was also not significantly affected by the addition of PavA protein. Complementation of the pavA knockout strain with exogenously added PavA polypeptide did not restore adherence of the mutant. These data suggest that PavA affects pneumococcal colonization by modulating expression or function of important virulence determinants of S. pneumoniae.

Neuronal injury mediated via stimulation of microglial toll-like receptor-9 (TLR9)

Innate immune cells express toll‐like receptor‐9 (TLR9) and respond to unmethylated, CG dinucleotide motif‐rich DNA released from bacteria during infection or endogenous cells during autoimmune tissue injury. Oligonucleotides containing CG dinucleotide (CpG‐DNA) mimic the effect of unmethylated DNA and stimulate TLR9. CpG‐DNA was cytotoxic to neurons in organotypic brain cultures. Neurotoxicity of CpG‐DNA was mediated via microglial cells and started primarily from neurites as determined by time‐lapse imaging of enhanced green fluorescent protein (EGFP)‐transfected neurons. Cultured brain microglial cells expressed TLR9 and responded to CpG‐DNA by production of the inflammatory mediators nitric oxide (NO) and tumor necrosis factor‐α (TNF‐α). Blockade of NO synthase and TNF‐α prevented damage of neurites and neurotoxicity of CpG‐DNA. The data suggest that stimulation of microglia via TLR9 and subsequent release of NO and TNF‐α is a major source of neurotoxicity in bacterial and autoimmune brain tissue injury.

Rifampin Reduces Early Mortality in Experimental Streptococcus pneumoniae Meningitis

Compared with beta-lactam antibiotics, rifampin releases smaller quantities of proinflammatory cell wall products from Streptococcus pneumoniae in vitro. Mice infected intracerebrally with S. pneumoniae were treated subcutaneously with 2-mg doses of rifampin or ceftriaxone (n=43 each) every 12 h for 3 days and then observed for another 3 days. Rifampin reduced overall mortality from 49% to 26% (P=.04). Kaplan-Meyer analysis revealed a substantial reduction of mortality during the first 24 h in mice receiving rifampin (difference in survival time: P=.007). Eight h after receiving a single 2-mg dose of rifampin or ceftriaxone, rifampin-treated mice had lower serum and cerebrospinal fluid concentrations of lipoteichoic and teichoic acids than did ceftriaxone-treated mice (median serum level: <0.5 vs. 27.0 ng/mL, P=.02; median cerebrospinal fluid level of pooled specimens: 97.5 vs. 206.0 ng/mL). Thus, the use of rifampin appears promising for reducing the release of proinflammatory bacterial components and decreasing early mortality in bacterial meningitis.

Conversion of Neuropeptide K to Neurokinin A and Vesicular Colocalization of Neurokinin A and Substance P in Neurons of the Guinea Pig Small Intestine

Abstract: The highest concentration of neurokinin A‐like immunoreactivity and substance P‐like immunoreactivity in the guinea pig small intestine was associated with the myenteric plexus‐containing longitudinal muscle layer. Chromatographic analysis of extracts of this tissue demonstrated the presence of neurokinin A and neuropeptide K but the probable absence of neurokinin B. A fraction of synaptic vesicles of density 1.133 ± 0.003 g/ml was prepared from the myenteric plexus‐containing tissue by density gradient centrifugation in a zonal rotor and was enriched 29 ± 12‐fold in the concentration of neurokinin A‐like immunoreactivity and 43 ± 13‐fold in the concentration of substance P‐like immunoreactivity. This fraction was separated from the fraction of vasoactive intestinal peptide‐containing vesicles (density, 1.154 ± 0.009 g/ml). Chromatographic analysis of lysates of the vesicles indicated the presence of neurokinin A but not neuropeptide K. It is postulated that β‐pre‐protachykinin is processed to substance P, neurokinin A, and neuropeptide K in the cell bodies of myenteric plexus neurons but that conversion of neuropeptide K to neurokinin A takes place during packaging into storage vesicles for axonal transport. The data are consistent with the proposal that neurokinin A and substance P are stored in the same synaptic vesicle, but the possibility of cosedimentation of different vesicles of very similar density cannot be excluded.