Changes in MMP-9 and TIMP-1 Concentrations in Cerebrospinal Fluid after 1 Week of Treatment of Childhood Bacterial Meningitis

Infections in the Developing Brain: The Role of the Neuro-Immune Axis

Central nervous system (CNS) infections occur more commonly in young children than in adults and pose unique challenges in the developing brain. This review builds on the distinct vulnerabilities in children's peripheral immune system (outlined in part 1 of this review series) and focuses on how the developing brain responds once a CNS infection occurs. Although the protective blood-brain barrier (BBB) matures early, pathogens enter the CNS and initiate a localized innate immune response with release of cytokines and chemokines to recruit peripheral immune cells that contribute to the inflammatory cascade. This immune response is initiated by the resident brain cells, microglia and astrocytes, which are not only integral to fighting the infection but also have important roles during normal brain development. Additionally, cytokines and other immune mediators such as matrix metalloproteinases from neurons, glia, and endothelial cells not only play a role in BBB permeability and peripheral cell recruitment, but also in brain maturation. Consequently, these immune modulators and the activation of microglia and astrocytes during infection adversely impact normal neurodevelopment. Perturbations to normal brain development manifest as neurodevelopmental and neurocognitive impairments common among children who survive CNS infections and are often permanent. In part 2 of the review series, we broadly summarize the unique challenges CNS infections create in a developing brain and explore the interaction of regulators of neurodevelopment and CNS immune response as part of the neuro-immune axis.

Increased MMP-9 levels with strain-dependent stress resilience and tunnel handling in mice

Increased perineuronal net (PNN) deposition has been observed in association with corticosteroid administration and stress in rodent models of depression. PNNs are a specialized form of extracellular matrix (ECM) that may enhance GABA-mediated inhibitory neurotransmission to potentially restrict the excitation and plasticity of pyramidal glutamatergic neurons. In contrast, antidepressant administration increases levels of the PNN-degrading enzyme matrix metalloproteinase-9 (MMP-9), which enhances glutamatergic plasticity and neurotransmission. In the present study, we compare pro-MMP-9 levels and measures of stress in females from two mouse strains, C57BL/6 J and BALB/cJ, in the presence or absence of tail grasping versus tunnel-associated cage transfers. Prior work suggests that C57BL/6 J mice show relatively enhanced neuroplasticity and stress resilience, while BALB/c mice demonstrate enhanced susceptibility to adverse effects of stress. Herein we observe that as compared to the C57BL/6 J strain, BALB/c mice demonstrate a higher level of baseline anxiety as determined by elevated plus maze (EPM) testing. Moreover, as determined by open field testing, anxiety is differentially reduced in BALB/c mice by a choice-driven tunnel-entry cage transfer technique. Additionally, as compared to tail-handled C57BL/6 J mice, tail-handled BALB/c mice have reduced brain levels of pro-MMP-9 and increased levels of its endogenous inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1); however, tunnel-associated cage transfer increases pro-MMP-9 levels in BALB/c mice. BALB/c mice also show increases in Western blot immunoreactive bands for brevican, a constituent of PNNs. Together, these data support the possibility that MMP-9, an effector of PNN remodeling, contributes to the phenotype of strain and handling-associated differences in behavior.

CSF Levels of Elongation Factor Tu Is Associated With Increased Mortality in Malawian Adults With Streptococcus pneumoniae Meningitis

Background

Mortality from bacterial meningitis, predominately caused by Streptococcus pneumoniae, exceeds 50% in sub-Saharan African countries with high HIV prevalence. Underlying causes of high mortality are poorly understood. We examined the host and pathogen proteome in the CSF of adults with proven pneumococcal meningitis (PM), testing if there was an association between differentially expressed proteins and outcome.

Materials/Methods

CSF proteomes were analyzed by quantitative Mass-Spectrometry. Spectra were identified using the Swissprot human and TIGR4 pneumococcal protein libraries. Proteins were quantitated and analyzed against mortality. Unique proteins in PM were identified against published normal CSF proteome. Random-Forest models were used to test for protein signatures discriminating outcome. Proteins of interest were tested for their effects on growth and neutrophil opsonophagocytic killing of S. pneumoniae.

Results

CSF proteomes were available for 57 Adults with PM (median age 32 years, 60% male, 70% HIV-1 co-infected, mortality 63%). Three hundred sixty individual human and 23 pneumococcal proteins were identified. Of the human protein hits, 30% were not expressed in normal CSF, and these were strongly associated with inflammation and primarily related to neutrophil activity. No human protein signature predicted outcome. However, expression of the essential S. pneumoniae protein Elongation Factor Tu (EF-Tu) was significantly increased in CSF of non-survivors [False Discovery Rate (q) <0.001]. Expression of EF-Tu was negatively co-correlated against expression of Neutrophil defensin (r 0.4 p p < 0.002), but not against complement proteins C3 or Factor H. In vitro, addition of EF-Tu protein impaired S. pneumoniae neutrophil killing in CSF.

Conclusions

Excessive S. pneumoniae EF-Tu protein in CSF was associated with reduced survival in meningitis in a high HIV prevalence population. We show EF-Tu may inhibit neutrophil mediated killing of S. pneumoniae in CSF. Further mechanistic work is required to better understand how S. pneumoniae avoids essential innate immune responses during PM through production of excess EF-Tu.

Pneumococcal serotype determines growth and capsule size in human cerebrospinal fluid

Background

The polysaccharide capsule is a major virulence factor of S. pneumoniae in diseases such as meningitis. While some capsular serotypes are more often found in invasive disease, high case fatality rates are associated with those serotypes more commonly found in asymptomatic colonization. We tested whether growth patterns and capsule size in human cerebrospinal fluid depends on serotype using a clinical isolate of S. pneumoniae and its capsule switch mutants.

Results

We found that the growth pattern differed markedly from that in culture medium by lacking the exponential and lysis phases. Growth in human cerebrospinal fluid was reduced when strains lost their capsules. When a capsule was present, growth was serotype-specific: high carriage serotypes (6B, 9 V, 19F and 23F) grew better than low carriage serotypes (7F, 14, 15B/C and 18C). Growth correlated with the case-fatality rates of serotypes reported in the literature. Capsule size in human cerebrospinal fluid also depended on serotype.

Conclusions

We propose that serotype-specific differences in disease severity observed in meningitis patients may, at least in part, be explained by differences in growth and capsule size in human cerebrospinal fluid. This information could be useful to guide future vaccine design.

The Potential Role of Matrix Metalloproteinases 8 and 9 and Myeloperoxidase in Predicting Outcomes of Bacterial Meningitis of Childhood

Background

Matrix metalloproteinases (MMPs) and myeloperoxidase (MPO) contribute to the inflammatory cascade in the cerebrospinal fluid (CSF) during bacterial meningitis. We determined levels of MPO, MMP-8, MMP-9, and tissue inhibitor of metalloproteinase- (TIMP-) 1 in the CSF of children with bacterial meningitis and investigated how these inflammatory mediators relate to each other and to the disease outcomes.

Methods

Clinical data and the diagnostic CSF samples from 245 children (median age eight months) with bacterial meningitis were obtained from a clinical trial in Latin America in 1996–2003. MMP-9 levels in the CSF were assessed by zymography, while MMP-8, MPO, and TIMP-1 concentrations were determined with immunofluorometric and enzyme-linked immunosorbent assays.

Results

MPO correlated positively with MMP-8 (rho 0.496, P < 0.001) and MMP-9 (rho 0.153, P = 0.02) but negatively with TIMP-1 (rho -0.361, P < 0.001). MMP-8 emerged as the best predictor of disease outcomes: a CSF MMP-8 concentration above the median increased the odds of death 4.9-fold (95% confidence interval 1.8–12.9).

Conclusions

CSF MMP-8 presented as an attractive prognostic marker in children with bacterial meningitis.

MMPs and ADAMs in neurological infectious diseases and multiple sclerosis

Metalloproteinases-such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs)-are involved in various diseases of the nervous system but also contribute to nervous system development, synaptic plasticity and neuroregeneration upon injury. MMPs and ADAMs proteolytically cleave many substrates including extracellular matrix components but also signaling molecules and receptors. During neuroinfectious disease with associated neuroinflammation, MMPs and ADAMs regulate blood-brain barrier breakdown, bacterial invasion, neutrophil infiltration and cytokine signaling. Specific and broad-spectrum inhibitors for MMPs and ADAMs have experimentally been shown to decrease neuroinflammation and brain damage in diseases with excessive neuroinflammation as a common denominator, such as pneumococcal meningitis and multiple sclerosis, thereby improving the disease outcome. Timing of metalloproteinase inhibition appears to be critical to effectively target the cascade of pathophysiological processes leading to brain damage without inhibiting the neuroregenerative effects of metalloproteinases. As the critical role of metalloproteinases in neuronal repair mechanisms and regeneration was only lately recognized, the original idea of chronic MMP inhibition needs to be conceptually revised. Recently accumulated research urges for a second chance of metalloproteinase inhibitors, which-when correctly applied and dosed-harbor the potential to improve the outcome of different neuroinflammatory diseases.

Matrix metalloproteinases: Expression, regulation and role in the immunopathology of tuberculosis

Mycobacterium tuberculosis (Mtb) leads to approximately 1.5 million human deaths every year. In pulmonary tuberculosis (TB), Mtb must drive host tissue destruction to cause pulmonary cavitation and dissemination in the tissues. Matrix metalloproteinases (MMPs) are endopeptidases capable of degrading all components of pulmonary extracellular matrix (ECM). It is well established that Mtb infection leads to upregulation of MMPs and also causes disturbance in the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thus altering the extracellular matrix deposition. In TB, secretion of MMPs is mainly regulated by NF-κB, p38 and MAPK signalling pathways. In addition, recent studies have demonstrated the immunomodulatory roles of MMPs in Mtb pathogenesis. Researchers have proposed a new regimen of improved TB treatment by inhibition of MMP activity to hinder matrix destruction and to minimize the TB-associated morbidity and mortality. The proposed regimen involves adjunctive use of MMP inhibitors such as doxycycline, marimastat and other related drugs along with front-line anti-TB drugs to reduce granuloma formation and bacterial load. These findings implicate the possible addition of economical and well-tolerated MMP inhibitors to current multidrug regimens as an attractive mean to increase the drug potency. Here, we will summarize the recent advancements regarding expression of MMPs in TB, their immunomodulatory role, as well as their potential as therapeutic targets to control the deadly disease.

Expression of MMP-2 and TIMP-1 in cerebrospinal fluid and the correlation with dynamic changes of serum PCT in neonatal purulent meningitis

Matrix metalloproteinase 2 (MMP-2) and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels in cerebrospinal fluid of pediatric patients with neonatal purulent meningitis were observed to analyze changes in serum procalcitonin (PCT) and the correlation among the three factors (MMP-2, TIMP-1 and PCT). Sixty pediatric patients with neonatal purulent meningitis from April 2015 to December 2016 were enrolled as the purulent meningitis group and 60 pediatric patients with viral encephalitis treated during the same period were enrolled as the viral encephalitis group. Additionally, 60 healthy newborns who underwent physical examinations in our hospital during the same period were enrolled as the control group. The levels of MMP-2 were 136.73±25.42 ng/ml in the purulent meningitis group, 45.32±6.57 ng/ml in the viral encephalitis group and 1.32±0.51 ng/ml in the control group and the differences between the three groups were statistically significant (F=15.052, p<0.05). The levels of TIMP-1 in cerebrospinal fluid were 374.55±36.04 ng/ml in the purulent meningitis group, 176.61±21.06 ng/ml in the viral encephalitis group and 7.72±2.44 ng/ml in the control group. The serum levels of PCT were 14.56±2.21 ng/ml in the purulent meningitis group, 9.04±1.17 ng/ml in the viral encephalitis group and 0.38±0.14 ng/ml in the control group. The level of MMP-2 in cerebrospinal fluid of pediatric patients in the purulent meningitis group was positively correlated with the level of serum PCT (r=0.582, p<0.05); the level of TIMP-1 in cerebrospinal fluid of pediatric patients in the viral encephalitis group was positively correlated with the level of serum PCT (r=0.635, p<0.05). In conclusion, MMP-2 and TIMP-1 were positively correlated with the levels of serum PCT, suggesting that MMP-2, TIMP-1 and PCT were involved in the occurrence and development of neonatal purulent meningitis.

Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an in vitro model of CNS tuberculosis

Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB.

Predicting Outcome of Childhood Bacterial Meningitis With a Single Measurement of C-Reactive Protein

INTRODUCTION

C-reactive protein (CRP), a marker of inflammation, shows high serum levels in invasive bacterial infections. We investigated the potential of a single CRP measurement at different phases of acute childhood bacterial meningitis to predict outcomes.

METHODS

Using whole-blood finger-prick samples with no centrifugation, CRP was measured quantitatively on arrival and on day 3 or 4 in children participating in 2 prospective, randomized, double-blind treatment studies conducted in Latin America or Angola. The results were compared with patient outcomes.

RESULTS

Although initial CRP values from 669 children gave useful prognostic information, the 3rd or 4th day measurements taken from 275 children associated significantly with seizures, slow recovery and low scores on the Glasgow Outcome Scale, with odds ratios for CRP values above the median (62 mg/L) ranging from 2 to 6, 2 to 5, and 3 to 5 (Latin America-Angola), respectively. Hearing impairment, although not full deafness, was 3 to 7 times more likely if CRP was above the median soon after hospitalization.

CONCLUSIONS

Especially in resource-poor settings, clinicians have few simple-enough tools to identify the child with meningitis who requires maximum attention. CRP is a worthy addition.