Klebsiella pneumoniae meningitis induces memory impairment and increases pro-inflammatory host response in the central nervous system of Wistar rats

The Role of HMGB1 in Infection-Related Cognitive Deficits

Infectious diseases caused by fungi, viruses, or bacteria can have a profound impact on human cognition. This can be due to either direct spread to the central nervous system (CNS) or indirect neuroinflammation. Ultimately causing neuronal damage and even neurodegeneration. Deteriorations in cognition, such as poor encoding and attention deficits, have been reported secondary to infectious diseases. Preclinical studies have identified the underlying mechanisms of these infection-related cognitive effects, such as through blood-brain barrier (BBB) disruption and M1 microglial polarization. These mechanisms are spearheaded by inflammatory markers that are released/initiated by the pathogens over the course of the infection. Among them, the high mobility group box 1 (HMGB1) protein is a common biomarker implicated across several infection-related cognitive deficits. Understanding these effects and mechanisms is crucial for the development of strategies to prevent and treat infection-related cognitive impairment. This review will thus consolidate and elucidate the current knowledge on the potential role of HMGB1 as a therapeutic target for infection-related cognitive impairments. This review will not only advance scientific understanding but also have significant clinical and public health implications, especially considering recent global health challenges. Based on the selected articles, extracellular HMGB1, as opposed to intracellular HMGB1, acts as damage-associated molecular patterns (DAMPs) or alarmins when released in the peripheries secondary to inflammasome activation. Due to their low molecular weight, they then enter the CNS through routes such as retrograde transport along the afferent nerves, or simple diffusion across the impaired BBB. This results in further disruption of the brain microenvironment due to the dysregulation of other regulatory pathways. The outcome is structural neuronal changes and cognitive impairment. Given its key role in neuroinflammation, HMGB1 holds promise as both a biomarker for diagnostic detection and a potential therapeutic target candidate for preventing infection-related cognitive impairment.

Nano-phytosome loaded Retama raetam extract/colistin: antibacterial, antioxidant activities and in vivo lipopolysaccharide-induced-neurotoxicity inhibition

Antibiotics are misused nowadays, leading to the prevalence of antibiotic resistant bacterial strains; causing the world to move towards natural medicine. Retama raetam had wide medicinal use. In the present study, R. raetam ethanolic extract proved to be active against Pseudomonas aeruginosa with MIC values ranged from 15.62 to 250 µg/ml. Antioxidant analysis showed that the extract had high scavenging activity reached 92.40%. GC/MS analysis revealed that Sparteine and Tributyl acetylcitrate represent the extract major components. Furthermore, the combination between Retama raetam extract and colistin showed a synergistic effect. Moreover, nano-phytosome was designated and optimized to encapsulate Retama raetam extract/Colistin. Nano-phytosome characterized by particle size, Zeta potential, polydispersity index and Entrapment efficiency percentage of 16.92-32.85 nm, -30.40 mV, 0.26 and 89% respectively. The antibacterial activity of the prepared nano-phytosome formula against P. aeruginosa showed promising MIC, MBC, MIC index, and IZ diameter reaching 7.81, 15.62 µg/ml, 2, and 39 mm, respectively. While TEM examination of P. aeruginosa cells treated with nano-phytosome formula revealed cell wall breakage which led to cell death. Finally, P. aeruginosa LPS was used to induce neurodegenerative disease in rat model. Rats treated with nano-phytosome formula showed normal histoarchitecture organization and the cerebral cortex was partially restored compared to control groups.

An Enteric Bacterial Infection Triggers Neuroinflammation and Neurobehavioral Impairment in 3xTg-AD Transgenic Mice

BACKGROUND

Klebsiella pneumoniae is infamous for hospital-acquired infections and sepsis, which have also been linked to Alzheimer disease (AD)-related neuroinflammatory and neurodegenerative impairment. However, its causative and mechanistic role in AD pathology remains unstudied.

METHODS

A preclinical model of K. pneumoniae enteric infection and colonization is developed in an AD model (3xTg-AD mice) to investigate whether and how K. pneumoniae pathogenesis exacerbates neuropathogenesis via the gut-blood-brain axis.

RESULTS

K. pneumoniae, particularly under antibiotic-induced dysbiosis, was able to translocate from the gut to the bloodstream by penetrating the gut epithelial barrier. Subsequently, K. pneumoniae infiltrated the brain by breaching the blood-brain barrier. Significant neuroinflammatory phenotype was observed in mice with K. pneumoniae brain infection. K. pneumoniae-infected mice also exhibited impaired neurobehavioral function and elevated total tau levels in the brain. Metagenomic analyses revealed an inverse correlation of K. pneumoniae with gut biome diversity and commensal bacteria, highlighting how antibiotic-induced dysbiosis triggers an enteroseptic "pathobiome" signature implicated in gut-brain perturbations.

CONCLUSIONS

The findings demonstrate how infectious agents following hospital-acquired infections and consequent antibiotic regimen may induce gut dysbiosis and pathobiome and increase the risk of sepsis, thereby increasing the predisposition to neuroinflammatory and neurobehavioral impairments via breaching the gut-blood-brain barrier.

Gut bacterial profiles in Parkinson's disease: A systematic review

INTRODUCTION

Recent advances have highlighted the relationships between gut dysbiosis and Parkinson's disease (PD). Microbiota transplantation from PD patients to mice can induce increased alpha-synuclein-mediated motor deficits. Human studies have identified differences in the gut microbiota of PD patients compared to healthy controls. We undertook a systematic review to evaluate the available evidence for the involvement of gut bacteria in the etiology of PD.

METHODS

The PubMed databank, the China National Knowledge Infrastructure databank, and Wanfang Data were searched from inception until June 2021 to identify human case-control studies that investigated relationships between PD and microbiota quantified from feces. We evaluated the resulting studies focusing on bacterial taxa that were different between PD patients and healthy controls.

RESULTS

Twenty-six studies were found in which 53 microbial families and 98 genera exhibited differences between patients with PD and healthy controls. The genera identified by more than two studies as increased in PD were Bifidobacterium, Alistipes, Christensenella, Enterococcus, Oscillospira, Bilophila, Desulfovibrio, Escherichia/Shigella, and Akkermansia, while Prevotella, Blautia, Faecalibacterium, Fusicatenibacter, and Haemophilus had three or more reports of being lower in PD patients. More than one report demonstrated that Bacteroides, Odoribacter, Parabacteroides, Butyricicoccus, Butyrivibrio, Clostridium, Coprococcus, Lachnospira, Lactobacillus, Megasphaera, Phascolarctobacterium, Roseburia, Ruminococcus, Streptococcus, and Klebsiella were altered in both directions.

CONCLUSION

Our review shows that the involvement of the gut microbiome in the etiology of PD may involve alterations of short-chain fatty acids (SCFAs)-producing bacteria and an increase in putative gut pathobionts. SCFAs-producing bacteria may vary above or below an "optimal range," causing imbalances. Considering that Bifidobacterium, Lactobacillus, and Akkermansia are beneficial for human health, increased Bifidobacterium and Lactobacillus in the PD gut microbiome may be associated with PD medications, especially COMT inhibitors, while a high level of Akkermansia may be associated with aging.

Memory Impairment, Pro-Inflammatory Host Response and Brain Histopathologic Severity in Rats Infected with K. pneumoniae or P. aeruginosa Meningitis

Meningitis caused by Klebsiella pneumoniae and Pseudomonas aeruginosa has lately become a prevalent cause of the central nervous system (CNS) infection. Bacterial invasion into the subarachnoid space prompts the releasing mechanism of chemokines and pro-inflammatory cytokines. The present study aimed to compare K. pneumoniae and P. aeruginosa meningitis concerning the memory, pro-inflammatory mediators and brain histopathological changes at different time intervals in adult Albino rats. The animals were sacrificed at three time intervals comprising 5, 10 and 15 days after meningitis induction. Cerebrospinal fluid (CSF) culture, relative brain weights, complete blood analysis, biochemical markers, levels of cytokine, chemokine and brain-derived neurotrophic factor (BDNF), neurotransmitter acetylcholine esterase (AChE) activity, and the brain histopathology of the infected rats in comparison to those in the control group were assessed. There was a significant increase in the levels of pro-inflammatory cytokines and chemokines including TNF-α, IL-1β, IL-6 and AChE after 5 days of bacterial meningitis infection with both K. pneumoniae and P. aeruginosa. The histopathological analysis of the cerebral cortex in the P. aeruginosa meningitis model at different time intervals revealed abundant numbers of dilated and congested blood vessels with severe hemorrhage, cerebral infarct, intracellular and extracellular vacuoles, and gliosis. Fifteen days post infection, a significant reduction in the brain tissue weight was observed. The meningitis model employing P. aeruginosa exhibited more evident time-dependent severity compared to K. pneumoniae, which may advocate its validity as a simple and effective research model to study meningitis of the CNS. This model may be utilized for further investigation to ascertain the molecular and biological association between bacterial meningitis and the development of the pathophysiological hallmarks underlying Alzheimer's disease in preclinical and clinical setups. Clinical extrapolation based on studies employing animal disease models should be carefully interpreted.

Systemic Response to Infection Induces Long-Term Cognitive Decline: Neuroinflammation and Oxidative Stress as Therapeutical Targets

In response to pathogens or damage signs, the immune system is activated in order to eliminate the noxious stimuli. The inflammatory response to infectious diseases induces systemic events, including cytokine storm phenomenon, vascular dysfunction, and coagulopathy, that can lead to multiple-organ dysfunction. The central nervous system (CNS) is one of the major organs affected, and symptoms such as sickness behavior (depression and fever, among others), or even delirium, can be observed due to activation of endothelial and glial cells, leading to neuroinflammation. Several reports have been shown that, due to CNS alterations caused by neuroinflammation, some sequels can be developed in special cognitive decline. There is still no any treatment to avoid cognitive impairment, especially those developed due to systemic infectious diseases, but preclinical and clinical trials have pointed out controlling neuroinflammatory events to avoid the development of this sequel. In this minireview, we point to the possible mechanisms that triggers long-term cognitive decline, proposing the acute neuroinflammatory events as a potential therapeutical target to treat this sequel that has been associated to several infectious diseases, such as malaria, sepsis, and, more recently, the new SARS-Cov2 infection.

Infectious disease-associated encephalopathies

Infectious diseases may affect brain function and cause encephalopathy even when the pathogen does not directly infect the central nervous system, known as infectious disease-associated encephalopathy. The systemic inflammatory process may result in neuroinflammation, with glial cell activation and increased levels of cytokines, reduced neurotrophic factors, blood-brain barrier dysfunction, neurotransmitter metabolism imbalances, and neurotoxicity, and behavioral and cognitive impairments often occur in the late course. Even though infectious disease-associated encephalopathies may cause devastating neurologic and cognitive deficits, the concept of infectious disease-associated encephalopathies is still under-investigated; knowledge of the underlying mechanisms, which may be distinct from those of encephalopathies of non-infectious cause, is still limited. In this review, we focus on the pathophysiology of encephalopathies associated with peripheral (sepsis, malaria, influenza, and COVID-19), emerging therapeutic strategies, and the role of neuroinflammation.

Neuroinflammation trajectories precede cognitive impairment after experimental meningitis-evidence from an in vivo PET study

Background

Bacterial meningitis is a devastating central nervous system (CNS) infection with acute and long-term neurological consequences, including cognitive impairment. The aim of this study was to understand the association between activated microglia-induced neuroinflammation and post-meningitis cognitive impairment.

Method

Meningitis was induced in male Wistar rats by injecting Streptococcus pneumoniae into the brain through the cisterna magna, and rats were then treated with ceftriaxone. Twenty-four hours and 10 days after meningitis induction, rats were imaged with positron emission tomography (PET) using [¹¹C]PBR28, a specific translocator protein (TSPO) radiotracer, to determine in vivo microglial activation. Following imaging, the expression of TSPO, cardiolipin, and cytochrome c, inflammatory mediators, oxidative stress markers, and glial activation markers were evaluated in the prefrontal cortex and hippocampus. Ten days after meningitis induction, animals were subjected to behavioral tests, such as the open-field, step-down inhibitory avoidance, and novel object recognition tests.

Results

Both 24-h (acute) and 10-day (long-term) groups of rats demonstrated increased [¹¹C]PBR28 uptake and microglial activation in the whole brain compared to levels in the control group. Although free from infection, 10-day group rats exhibited increased expression levels of cytokines and markers of oxidative stress, microglial activation (IBA-1), and astrocyte activation (GFAP) similar to those seen in the 24-h group. Acute meningitis induction also elevated TSPO, cytochrome c, and caspase-3 levels with no change in caspase-9 levels. Furthermore, upregulated levels of TSPO, cytochrome c, and caspase-3 and caspase-9 were observed in the rat hippocampus 10 days after meningitis induction with a simultaneous reduction in cardiolipin levels. Animals showed a cognitive decline in all tasks compared with the control group, and this impairment may be at least partially mediated by activating a glia-mediated immune response and upregulating TSPO.

Conclusions

TSPO-PET could potentially be used as an imaging biomarker for microglial activation and long-term cognitive impairment post-meningitis. Additionally, this study opens a new avenue for the potential use of TSPO ligands after infection-induced neurological sequelae.

Colibactin Contributes to the Hypervirulence of pks+ K1 CC23 Klebsiella pneumoniae in Mouse Meningitis Infections

Klebsiella pneumoniae is the most common pathogen of community-acquired meningitis in Taiwan. However, the lack of a physiologically relevant meningitis model for K. pneumoniae has impeded research into its pathogenesis mechanism. Based on the core genome MLST analyses, the hypervirulent K1 K. pneumoniae strains, which are etiologically implicated in adult meningitis, mostly belong to a single clonal complex, CC23. Some K1 CC23 K. pneumoniae strains carry a gene cluster responsible for colibactin production. Colibactin is a small genotoxic molecule biosynthesized by an NRPS-PKS complex, which is encoded by genes located on the pks island. Compared to other hypervirulent K. pneumoniae which primarily infect the liver, the colibactin-producing (pks⁺) K1 CC23 strains had significant tropism toward the brain of BALB/c mice. We aimed in this study to develop a physiologically relevant meningitis model with the use of pks⁺ K1 CC23 K. pneumoniae. Acute meningitis was successfully induced in adult BALB/c male mice through orogastric, intranasal, and intravenous inoculation of pks⁺ K1 CC23 K. pneumoniae. Besides the typical symptoms of bacterial meningitis, severe DNA damages, and caspase 3-independent cell death were elicited by the colibactin-producing K1 CC23 K. pneumoniae strain. The deletion of clbA, which abolished the production of colibactin, substantially hindered K. pneumoniae hypervirulence in the key pathogenic steps toward the development of meningitis. Our findings collectively demonstrated that colibactin was necessary but not sufficient for the meningeal tropism of pks⁺ K1 CC23 K. pneumoniae, and the mouse model established in this study can be applied to identify other virulence factors participating in the development of this life-threatening disease.

Evidence for the contribution of adult neurogenesis and hippocampal cell death in experimental cerebral malaria cognitive outcome

Cognitive dysfunction is a major sign of cerebral malaria (CM). However, the underlying mechanisms of CM cognitive outcome remain poorly understood. A body of evidence suggests that adult neurogenesis may play a role in learning and memory processes. It has also been reported that these phenomena can be regulated by the immune system. We hypothesized that memory dysfunction in CM results from hippocampal neurogenesis impairment mediated by the deregulated immune response during the acute phase of CM. C57Bl/6 mice were infected with Plasmodium berghei ANKA (PbA) strain, using a standardized inoculation of 10(6) parasitized erythrocytes. Long-term working memory was evaluated using the novel object recognition test. The mRNA expression of brain-derived neurotrophic factor (BDNF), tropomyosin-receptor-kinase (TRK-B) and nerve growth factor (NGF) in the frontal cortex and hippocampus was estimated by real-time polymerase chain reaction (PCR). The protein levels of cytokine interleukin-2 (IL-2), IL-4, IL-6, IL-10, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and CCL11 and neurotrophins BDNF and NGF were determined using a cytometric bead array (CBA) kit or enzyme-linked immunosorbent assay. Cell viability in the hippocampus was analyzed by Confocal Microscopy. Neurogenesis in the dentate gyrus was determined through quantification of doublecortin (DCX) positive cells. PbA-infected mice presented working memory impairment on day 5 post-infection. At this same time point, CM mice exhibited a decrease in DCX-positive cells in the dentate gyrus in parallel with increased cell death and elevated inflammatory cytokines (IL-6, TNF-α, IFN-γ and CCL11) in the hippocampus and frontal cortex. A significant reduction of BDNF mRNA expression was also found. IL-6 and TNF-α correlated negatively with BDNF and NGF levels in the hippocampus of CM mice. In summary, we provide further evidence that neuroinflammation following PbA-infection influences neurotrophin expression, impairs adult hippocampal neurogenesis and increases hippocampal cell death in association with memory impairment following CM course. The current study identified potential mediators of memory impairment in CM.