In vivo study of experimental pneumococcal meningitis using magnetic resonance imaging

Bacterial association with metals enables in vivo monitoring of urogenital microbiota using magnetic resonance imaging

Bacteria constitute a significant part of the biomass of the human microbiota, but their interactions are complex and difficult to replicate outside the host. Exploiting the superior resolution of magnetic resonance imaging (MRI) to examine signal parameters of selected human isolates may allow tracking of their dispersion throughout the body. Here we investigate longitudinal and transverse MRI relaxation rates and found significant differences between several bacterial strains. Common commensal strains of lactobacilli display notably high MRI relaxation rates, partially explained by elevated cellular manganese content, while other species contain more iron than manganese. Lactobacillus crispatus show particularly high values, 4-fold greater than any other species; up to 60-fold greater signal than relevant tissue background; and a linear relationship between relaxation rate and fraction of live cells. Different bacterial strains have detectable, repeatable MRI relaxation rates that in the future may enable monitoring of their persistence in the human body for enhanced molecular imaging.

The effect on brain volume in HIV-negative and non-transplant cryptococcal meningitis

To explore the brain volume (BV) changes of HIV-negative and non-transplant cryptococcal meningitis (CM) in one year after initial therapy. Case data were collected from 78 CM patients who underwent magnetic resonance imaging (MRI) scanning at least 3 times in one-year interval after initial therapy. The assessment of BV was measured by a non-commercial software, uAI Research Portal. Linear mixed model was used to investigate the association between clinical characteristics and the changes of BV. Longitudinal study showed a decrease in total brain volume (-4.65 cm3, p = 0.005), regional brain volume including white matter (-2.86 cm3, p = 0.031) and basal ganglia (-0.25 cm3, p = 0.007), and an increase in cerebrospinal fluid (CSF) volume (3.58 cm3, p = 0.013) in CM patients in one year after initial therapy. Ventricular volume in patients with ventriculoperitoneal shunts (VPS) was lower than that in patients without VPS (-7.5 cm3, p < 0.05). Ventricular volume in patients with post-infectious inflammatory response syndrome (PIIRS) was larger than that in patients without PIIRS (7.1 cm3, p < 0.01). In addition, temporal lobe atrophy was associated with corticosteroid therapy (-6.8 cm3, p < 0.01). The present study suggested that brain atrophy, especially regional BV decrease, could happen in the HIV-negative and non-transplant CM patients over a one-year interval.

Assessment of Blood-Brain Barrier Integrity in Tuberculous Meningitis Using Dynamic Contrast-Enhanced MR Perfusion

Objective Tuberculous meningitis (TBM) is the most common form of central nervous system tuberculosis. The aim of the study was to quantitatively evaluate blood-brain barrier (BBB) perfusion changes in TBM patients using dynamic contrast-enhanced (DCE) MR perfusion. Methods and Material Thirty untreated patients of TBM and 10 healthy controls were prospectively evaluated by conventional imaging and DCE MR perfusion. Mean permeability indices- K trans and Ve-were calculated from multiple regions of interest (ROIs) placed in basal cisterns and comparison was done between the patients and controls. Results The permeability indices were significantly higher (where p < 0.001) in cisterns of TBM patients who showed basal meningeal enhancement when compared with healthy controls. Significant differences in permeability were observed between "enhancing" cases and controls as well as in "enhancing" cases when compared with the "non-enhancing" cases. However, no significant difference was observed in the mean cisternal value between "non-enhancing" cases and the controls. K trans with a cutoff value of > 0.0838 had 81.6% sensitivity and 78.6% specificity in differentiating cases and controls while V e mean value with a cutoff value of 0.0703 showed 86.8% sensitivity and 91.4% specificity in predicting the permeability difference between the cases and controls. Conclusion DCE MR perfusion is useful in the quantitative measurement of disruption of BBB and perfusion alterations in patients of TBM.

Radical Dendrimers Based on Biocompatible Oligoethylene Glycol Dendrimers as Contrast Agents for MRI

Finding alternatives to gadolinium (Gd)-based contrast agents (CA) with the same or even better paramagnetic properties is crucial to overcome their established toxicity. Herein we describe the synthesis and characterization of entirely organic metal-free paramagnetic macromolecules based on biocompatible oligoethylene glycol dendrimers fully functionalized with 5 and 20 organic radicals (OEG Gn-PROXYL (n = 0, 1) radical dendrimers) with the aim to be used as magnetic resonance imaging (MRI) contrast agents. Conferring high water solubility on such systems is often a concern, especially in large generation dendrimers. Our approach to overcome such an issue in this study is by synthesizing dendrimers with highly water-soluble branches themselves. In this work, we show that the highly water-soluble OEG Gn-PROXYL (n = 0, 1) radical dendrimers obtained showed properties that convert them in good candidates to be studied as contrast agents for MRI applications like diagnosis and follow-up of infectious diseases, among others. Importantly, with the first generation radical dendrimer, a similar r1 relaxivity value (3.4 mM-1s-1) in comparison to gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) used in clinics (3.2 mM-1s-1, r.t. 7T) has been obtained, and it has been shown to not be cytotoxic, avoiding the toxicity risks associated with the unwanted accumulation of Gd in the body.

A functional observational battery for evaluation of neurological outcomes in a rat model of acute bacterial meningitis

BACKGROUND

Acute bacterial meningitis is a disease with a high mortality and a high incidence of neurological sequelae in survivors. There is an acute need to develop new adjuvant therapies. To ensure that new therapies evaluated in animal models are translatable to humans, studies must evaluate clinically relevant and patient-important outcomes, including neurological symptoms and sequelae.

METHODS

We developed and tested a functional observational battery to quantify the severity of a variety of relevant neurological and clinical symptoms in a rat model of bacterial meningitis. The functional observational battery included symptoms relating to general clinical signs, gait and posture abnormalities, involuntary motor movements, focal neurological signs, and neuromotor abnormalities which were scored according to severity and summed to obtain a combined clinical and neurological score. To test the functional observational battery, adult Sprague-Dawley rats were infected by intracisternal injection of a clinical isolate of Streptococcus pneumoniae. Rats were evaluated for 6 days following the infection.

RESULTS

Pneumococcal meningitis was not lethal in this model; however, it induced severe neurological symptoms. Most common symptoms were hearing loss (75% of infected vs 0% of control rats; p = 0.0003), involuntary motor movements (75% of infected vs 0% of control rats; p = 0.0003), and gait and posture abnormality (67% of infected vs 0% of control rats; p = 0.0013). Infected rats had a higher combined score when determined by the functional observational battery than control rats at all time points (24 h 12.7 ± 4.0 vs 4.0 ± 2.0; 48 h 17.3 ± 7.1 vs 3.4 ± 1.8; 6 days 17.8 ± 7.4 vs 1.7 ± 2.4; p < 0.0001 for all).

CONCLUSIONS

The functional observational battery described here detects clinically relevant neurological sequelae of bacterial meningitis and could be a useful tool when testing new therapeutics in rat models of meningitis.

Developing a newborn rat model of ventriculitis without concomitant bacteremia by intraventricular injection of K1 (-) Escherichia coli

BACKGROUND

Neonatal meningitis caused by Escherichia coli results in high mortality and neurological disabilities, and the concomitant systemic bacteremia confounds its mortality and brain injury. This study developed an experimental model of neonatal ventriculitis without concomitant systemic bacteremia by determining the bacterial inoculum of K1 capsule-negative E. coli by intraventricular injection in newborn rats.

METHODS

We carried out intraventricular injections 1 × 10² (low dose), 5 × 10² (medium dose), or 1 × 10³ (high dose) colony-forming units (CFU) of K1 (-) E. coli (EC5ME) in Sprague-Dawley rats at postnatal day (P) 11. Ampicillin was started at P12. Blood and cerebrospinal fluid (CSF) cultures were performed at 6 h, 1 day, and 6 days after inoculation. Brain magnetic resonance imaging (MRI) was performed at P12 and P17. Survival was monitored, and brain tissue was obtained for histological and biochemical analyses at P12 and P17.

RESULTS

Survival was inoculum dose-dependent, with the lowest survival in the high-dose group (20%) compared with the medium- (67%) or low- (73%) dose groups. CSF bacterial counts in the low- and medium-dose groups were significantly lower than that in the high-dose group at 6 h, but not at 24 h after inoculation. No bacteria were isolated from the blood throughout the experiment or from the CSF at P17. Brain MRI showed an inoculum dose-dependent increase in the extent of brain injury and inflammatory responses.

CONCLUSIONS

We developed a newborn rat model of bacterial ventriculitis without concomitant systemic bacteremia by intraventricular injection of EC5ME.

Mesenchymal stem cells transplantation attenuates brain injury and enhances bacterial clearance in Escherichia coli meningitis in newborn rats

OBJECTIVE

Neonatal meningitis caused by Escherichia coli results in significant mortality and neurological disabilities, with few effective treatments. Recently, we demonstrated that human umbilical cord blood-derived mesenchymal stem cell (hUCB-MSC) transplantation attenuated E. coli-induced severe pneumonia, primarily by reducing inflammation and enhancing bacterial clearance. This study aimed to determine whether intraventricular transplantation of hUCB-MSCs attenuated the brain injury in E. coli meningitis in newborn rats.

METHODS

Meningitis without concomitant bacteremia was induced by intraventricular injection of 5 × 10² colony forming units of K1 (-) E. coli in rats at postnatal day (P)11, and hUCB-MSCs (1 × 10⁵) were transplanted intraventricularly 6 h after induction of meningitis. Antibiotics was started 24 h after modeling.

RESULT

Meningitis modeling induced robust proliferation of E. coli in the cerebrospinal fluid and increased mortality in rat pups, and MSC transplantation significantly reduced this bacterial growth and the mortality rate. Impaired sensorimotor function in the meningitis rats was ameliorated by MSCs injection. MSCs transplantation also attenuated meningitis caused brain injury including cerebral ventricular dilatation, brain cell death, reactive gliosis, and inflammatory response.

CONCLUSION

Intraventricular transplantation of hUCB-MSCs significantly improved survival and attenuated the brain injury via anti-inflammatory and antibacterial effects in experimental neonatal E. coli meningitis.

Blood-Brain Barrier Disruption After Cardiopulmonary Bypass: Diagnosis and Correlation to Cognition

BACKGROUND

Cardiopulmonary bypass (CPB) elicits a systemic inflammatory response that may impair blood-brain barrier (BBB) integrity. BBB disruption can currently be detected by dynamic contrast enhancement magnetic resonance imaging (MRI), reflected by an increase in the permeability constant (K^trans). We aimed to determine (1) whether CPB induces BBB disruption, (2) duration until BBB disruption resolution, and (3) the obtainable correlation between BBB injury (location and intensity) and neurocognitive dysfunction.

METHODS

Seven patients undergoing CPB with coronary artery bypass grafting (CABG) were assigned to serial cerebral designated MRI evaluations, preoperatively and on postoperative day (POD) 1 and 5. Examinations were analyzed for BBB disruption and microemboli using dynamic contrast enhancement MRI and diffusion-weighted imaging methods, respectively. Neuropsychologic tests were performed 1 day preoperatively and on POD 5.

RESULTS

A significant local K^trans increase (0.03 min^-1 vs 0.07 min^-1, p = 0.033) compatible with BBB disruption was evident in 5 patients (71%) on POD 1. Resolution was observed by POD 5 (mean, 0.012 min^-1). The location of the disruption was most prominent in the frontal lobes (400% vs 150% K^trans levels upsurge, p = 0.05). MRI evidence of microembolization was demonstrated in only 1 patient (14%). The postoperative global cognitive score was reduced in all patients (98.2 ± 12 vs 95.1 ± 11, p = 0.032), predominantly in executive and attention (frontal lobe-related) functions (91.8 ± 13 vs 86.9 ± 12, p = 0.042). The intensity of the dynamic contrast enhancement MRI BBB impairment correlated with the magnitude of cognition reduction (r = 0.69, p = 0.04).

CONCLUSIONS

BBB disruption was evident in most patients, primarily in the frontal lobes. The location and intensity of the BBB disruption, rather than the microembolic load, correlated with postoperative neurocognitive dysfunction.

Brain ventricular dimensions and relationship to outcome in adult patients with bacterial meningitis

Background

Experimental studies suggest that changes in brain ventricle size are key events in bacterial meningitis. This study investigated the relationship between ventricle size, clinical condition and risk of poor outcome in patients with bacterial meningitis.

Methods

Adult patients diagnosed with bacterial meningitis admitted to two departments of infectious diseases from 2003 through 2010 were identified. Clinical and biochemical data as well as cerebral computed tomographic images were collected. The size of the brain ventricles were presented as a Ventricle to Brain Ratio (VBR). Normal range of VBR was defined from an age matched control group. A multivariate analysis was performed to identify predictors of 30-day mortality.

Results

One hundred and seven patients were included. Eighty-one patients had a CT scan at the time of diagnosis. VBR was identified as an independent risk factor of 30-day mortality, Mortality Rate Ratio: 6.03 (95 % confidence interval: 1.61-22.64, p = 0.008) for highest versus lowest tertile. A VBR deviating more than 2 standard deviations from the normal range was associated with increased mortality.

Conclusions

Brain ventricles are commonly subject to marked changes in size as a consequence of meningitis. Increased brain ventricle size in the acute phase of bacterial meningitis was associated with increased mortality.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1097-3) contains supplementary material, which is available to authorized users.

Assessment of blood-brain barrier disruption using dynamic contrast-enhanced MRI. A systematic review

There is increasing recognition of the importance of blood-brain barrier (BBB) disruption in aging, dementia, stroke and multiple sclerosis in addition to more commonly-studied pathologies such as tumors. Dynamic contrast-enhanced MRI (DCE-MRI) is a method for studying BBB disruption in vivo. We review pathologies studied, scanning protocols and data analysis procedures to determine the range of available methods and their suitability to different pathologies. We systematically review the existing literature up to February 2014, seeking studies that assessed BBB integrity using T1-weighted DCE-MRI techniques in animals and humans in normal or abnormal brain tissues. The literature search provided 70 studies that were eligible for inclusion, involving 417 animals and 1564 human subjects in total. The pathologies most studied are intracranial neoplasms and acute ischemic strokes. There are large variations in the type of DCE-MRI sequence, the imaging protocols and the contrast agents used. Moreover, studies use a variety of different methods for data analysis, mainly based on model-free measurements and on the Patlak and Tofts models. Consequently, estimated K (Trans) values varied widely. In conclusion, DCE-MRI is shown to provide valuable information in a large variety of applications, ranging from common applications, such as grading of primary brain tumors, to more recent applications, such as assessment of subtle BBB dysfunction in Alzheimer's disease. Further research is required in order to establish consensus-based recommendations for data acquisition and analysis and, hence, improve inter-study comparability and promote wider use of DCE-MRI.

Increase in hippocampal water diffusion and volume during experimental pneumococcal meningitis is aggravated by bacteremia

Background

The hippocampus undergoes apoptosis in experimental pneumococcal meningitis leading to neurofunctional deficits in learning and memory function. The aim of the present study was 1) to investigate hippocampal apparent diffusion coefficient (ADC) and volume with MRI during the course of experimental pneumococcal meningitis, 2) to explore the influence of accompanying bacteremia on hippocampal water distribution and volume, 3) and to correlate these findings to the extent of apoptosis in the hippocampus.

Methods

Experimental meningitis in rats was induced by intracisternal injection of live pneumococci. The study comprised of four experimental groups. I. Uninfected controls (n = 8); II. Meningitis (n = 11); III. Meningitis with early onset bacteremia by additional i.v. injection of live pneumococci (n = 10); IV. Meningitis with attenuated bacteremia by treatment with serotype-specific anti-pneumococcal antibodies (n = 14). T2 and diffusion weighted MR images were used to analyze changes in hippocampus volume and water diffusion (ADC). The results were correlated to ADC of the cortex, to ventricular volume, and to the extent of hippocampal apoptosis.

Results

Both ADC and the volume of hippocampus were significantly increased in meningitis rats compared to uninfected controls (Kruskal-Wallis test, p = 0.0001, Dunns Post Test, p < 0.05), and were significantly increased in meningitis rats with an early onset bacteremia as compared to meningitis rats with attenuated bacteremia (p < 0.05). Hippocampal ADC and the volume and size of brain ventricles were positively correlated (Spearman Rank, p < 0.05), whereas no association was found between ADC or volume and the extent of apoptosis (p > 0.05).

Conclusions

In experimental meningitis increase in volume and water diffusion of the hippocampus are significantly associated with accompanying bacteremia.

A novel method for long-term monitoring of intracranial pressure in rats

BACKGROUND

In preclinical neurological studies, monitoring intracranial pressure (ICP) in animal models especially in rodents is challenging. Further, the lack of methods for long-term ICP monitoring has limited the possibilities to conduct prolonged studies on ICP fluctuations in parallel to disease progression or therapeutic interventions. For these reasons we aimed to set up a simple and valid method for long-term ICP recordings in rats.

NEW METHOD

A novel ICP method employing epidural probes was developed and validated by simultaneously ICP recordings in the lateral ventricle and in the epidural space. The two pressures were recorded twice a week for 59 days and the correlation was studied.

RESULTS

The two pressure recordings correlated exceptionally well and the R(2) values on each recording day ranged between 0.99 and 1.00. However, the ventricular probes caused a number of complications including loss of patency and tissue damage probably due to cerebral infection, whereas the epidural probes were safe and reliable throughout the entire study.

COMPARISON WITH EXISTING METHODS

Epidural probes are much easier to implant than ventricular probes. In addition, these new probes are far less invasive and induce no apparent mechanical tissue damage and highly decrease the infection risk associated with ICP recordings.

CONCLUSION

Epidural ICP recorded with this new method is identical to the ventricular ICP for at least 59 days but is far less complicated and safer for the animals. The long-term method described is reliable, valid, inexpensive, and may be used in multiple disease models to study ICP.

Magnetic resonance imaging characterization of microbial infections

The investigation of microbial infections relies to a large part on animal models of infection, if host pathogen interactions or the host response are considered. Especially for the assessment of novel therapeutic agents, animal models are required. Non-invasive imaging methods to study such models have gained increasing importance over the recent years. In particular, magnetic resonance imaging (MRI) affords a variety of diagnostic options, and can be used for longitudinal studies. In this review, we introduce the most important MRI modalities that show how MRI has been used for the investigation of animal models of infection previously and how it may be applied in the future.

Hydrocephalus induces dynamic spatiotemporal regulation of aquaporin-4 expression in the rat brain

BACKGROUND

The water channel protein aquaporin-4 (AQP4) is reported to be of possible major importance for accessory cerebrospinal fluid (CSF) circulation pathways. We hypothesized that changes in AQP4 expression in specific brain regions correspond to the severity and duration of hydrocephalus.

METHODS

Hydrocephalus was induced in adult rats (~8 weeks) by intracisternal kaolin injection and evaluated after two days, one week and two weeks. Using magnetic resonance imaging (MRI) we quantified lateral ventricular volume, water diffusion and blood-brain barrier properties in hydrocephalic and control animals. The brains were analysed for AQP4 density by western blotting and localisation by immunohistochemistry. Double fluorescence labelling was used to study cell specific origin of AQP4.

RESULTS

Lateral ventricular volume was significantly increased over control at all time points after induction and the periventricular apparent diffusion coefficient (ADC) value significantly increased after one and two weeks of hydrocephalus. Relative AQP4 density was significantly decreased in both cortex and periventricular region after two days and normalized after one week. After two weeks, periventricular AQP4 expression was significantly increased. Relative periventricular AQP4 density was significantly correlated to lateral ventricular volume. AQP4 immunohistochemical analysis demonstrated the morphological expression pattern of AQP4 in hydrocephalus in astrocytes and ventricular ependyma. AQP4 co-localized with astrocytic glial fibrillary acidic protein (GFAP) in glia limitans. In vascular structures, AQP4 co-localized to astroglia but not to microglia or endothelial cells.

CONCLUSIONS

AQP4 levels are significantly altered in a time and region dependent manner in kaolin-induced hydrocephalus. The presented data suggest that AQP4 could play an important neurodefensive role, and may be a promising future pharmaceutical target in hydrocephalus and CSF disorders.

Genome-wide identification of Streptococcus pneumoniae genes essential for bacterial replication during experimental meningitis

Meningitis is the most serious of invasive infections caused by the Gram-positive bacterium Streptococcus pneumoniae. Vaccines protect only against a limited number of serotypes, and evolving bacterial resistance to antimicrobials impedes treatment. Further insight into the molecular pathogenesis of invasive pneumococcal disease is required in order to enable the development of new or adjunctive treatments and/or pneumococcal vaccines that are efficient across serotypes. We applied genomic array footprinting (GAF) in the search for S. pneumoniae genes that are essential during experimental meningitis. A total of 6,000 independent TIGR4 marinerT7 transposon mutants distributed over four libraries were injected intracisternally into rabbits, and cerebrospinal fluid (CSF) was collected after 3, 9, and 15 h. Microarray analysis of mutant-specific probes from CSF samples and inocula identified 82 and 11 genes mutants of which had become attenuated or enriched, respectively, during infection. The results point to essential roles for capsular polysaccharides, nutrient uptake, and amino acid biosynthesis in bacterial replication during experimental meningitis. The GAF phenotype of a subset of identified targets was followed up by detailed studies of directed mutants in competitive and noncompetitive infection models of experimental rat meningitis. It appeared that adenylosuccinate synthetase, flavodoxin, and LivJ, the substrate binding protein of a branched-chain amino acid ABC transporter, are relevant as targets for future therapy and prevention of pneumococcal meningitis, since their mutants were attenuated in both models of infection as well as in competitive growth in human cerebrospinal fluid in vitro.

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.