Sepsis-Associated Encephalopathy and Blood-Brain Barrier Dysfunction

Pathophysiology of Sepsis and Genesis of Septic Shock: The Critical Role of Mesenchymal Stem Cells (MSCs)

The treatment of sepsis and septic shock remains a major public health issue due to the associated morbidity and mortality. Despite an improvement in the understanding of the physiological and pathological mechanisms underlying its genesis and a growing number of studies exploring an even higher range of targeted therapies, no significant clinical progress has emerged in the past decade. In this context, mesenchymal stem cells (MSCs) appear more and more as an attractive approach for cell therapy both in experimental and clinical models. Pre-clinical data suggest a cornerstone role of these cells and their secretome in the control of the host immune response. Host-derived factors released from infected cells (i.e., alarmins, HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (e.g., LPS, peptidoglycans) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of cytokines/chemokines and growth factors that influence, respectively, immune cell recruitment and stem cell mobilization. However, the way in which MSCs exert their beneficial effects in terms of survival and control of inflammation in septic states remains unclear. This review presents the interactions identified between MSCs and mediators of immunity and tissue repair in sepsis. We also propose paradigms related to the plausible roles of MSCs in the process of sepsis and septic shock. Finally, we offer a presentation of experimental and clinical studies and open the way to innovative avenues of research involving MSCs from a prognostic, diagnostic, and therapeutic point of view in sepsis.

Distinct post-sepsis induced neurochemical alterations in two mouse strains

Sepsis associated encephalopathy, occurs in 70% of severe septic cases, following which survivors exhibit long-term cognitive impairment or global loss of cognitive function. Currently there is no clearly defined neurochemical basis of septic encephalopathy. Moreover, the lingering neurological complications associated with the severe acute respiratory syndrome CoV 2 (SARS-CoV-2) and the significant worsening in outcomes for those individuals with SARS-Cov-2 following sepsis underscore the need to define factors underlying the susceptibility to acute toxic encephalitis. In this study, differential neurochemical sequelae in response to sepsis (lipopolysaccharide (LPS)-induced endotoxemia and caecal ligation and puncture (CLP)), were evaluated in two inbred mouse strains, known to differ in behaviour, immune profile, and neurotransmitter levels, namely BALB/c and C57BL/6J. It was hypothesized that these strains would differ in sepsis severity, cytokine profile, peripheral tryptophan metabolism and central monoamine turnover. BALB/c mice exhibited more pronounced sickness behavioural scores, hypothermia, and significant upregulation of cytokines in the LPS model relative to C57BL/6J mice. Increased plasma kynurenine/tryptophan ratio, hippocampal serotonin and brainstem dopamine turnover were evident in both strains, but the magnitude was greater in BALB/c mice. In addition, CLP significantly enhanced kynurenine levels and hippocampal serotonergic and dopaminergic neurotransmission in C57BL/6J mice. Overall, these studies depict consistent changes in kynurenine, serotonin, and dopamine post sepsis. Further evaluation of these monoamines in the context of septic encephalopathy and cognitive decline is warranted. Moreover, these data suggest the continued evaluation of altered peripheral kynurenine metabolism as a potential blood-based biomarker of sepsis.

Central role of microglia in sepsis-associated encephalopathy: From mechanism to therapy

Sepsis-associated encephalopathy (SAE) is a cognitive impairment associated with sepsis that occurs in the absence of direct infection in the central nervous system or structural brain damage. Microglia are thought to be macrophages of the central nervous system, devouring bits of neuronal cells and dead cells in the brain. They are activated in various ways, and microglia-mediated neuroinflammation is characteristic of central nervous system diseases, including SAE. Here, we systematically described the pathogenesis of SAE and demonstrated that microglia are closely related to the occurrence and development of SAE. Furthermore, we comprehensively discussed the function and phenotype of microglia and summarized their activation mechanism and role in SAE pathogenesis. Finally, this review summarizes recent studies on treating cognitive impairment in SAE by blocking microglial activation and toxic factors produced after activation. We suggest that targeting microglial activation may be a putative treatment for SAE.

Sepsis modulates cortical excitability and alters the local and systemic hemodynamic response to seizures

Non-convulsive seizures and status epilepticus are frequent and associated with increased mortality in septic patients. However, the mechanism through which seizures impact outcome in these patients is unclear. As previous studies yielded an alteration of neurovascular coupling (NVC) during sepsis, we hypothesized that non-convulsive seizures, might further impair NVC, leading to brain tissue hypoxia. We used a previously developed ovine model of sepsis. Animals were allocated to sham procedure or sepsis; septic animals were studied either during the hyperdynamic phase (sepsis group) or after septic shock occurrence (septic shock group). After allocation, seizures were induced by cortical application of penicillin. We recorded a greater seizure-induced increase in the EEG gamma power in the sepsis group than in sham. Using a neural mass model, we also found that the theoretical activity of the modeled inhibitory interneurons, thought to be important to reproduce gamma oscillations, were relatively greater in the sepsis group. However, the NVC was impaired in sepsis animals, despite a normal brain tissue oxygenation. In septic shock animals, it was not possible to induce seizures. Cortical activity declined in case of septic shock, but it did not differ between sham or sepsis animals. As the alteration in NVC preceded cortical activity reduction, we suggest that, during sepsis progression, the NVC inefficiency could be partially responsible for the alteration of brain function, which might prevent seizure occurrence during septic shock. Moreover, we showed that cardiac output decreased during seizures in sepsis animals instead of increasing as in shams. The alteration of the seizure-induced systemic hemodynamic variations in sepsis might further affect cerebrovascular response to neuronal activation. Our findings support the hypothesis that anomalies in the cerebral blood flow regulation may contribute to the sepsis-associated encephalopathy and that seizures might be dangerous in such a vulnerable setting.

Sepsis-Associated Encephalopathy: A Mini-Review of Inflammation in the Brain and Body

Sepsis is defined as a life-threatening multi-organ dysfunction triggered by an uncontrolled host response to infectious disease. Systemic inflammation elicited by sepsis can cause acute cerebral dysfunction, characterized by delirium, coma, and cognitive dysfunction, known as septic encephalopathy. Recent evidence has reported the underlying mechanisms of sepsis. However, the reasons for the development of inflammation and degeneration in some brain regions and the persistence of neuroinflammation remain unclear. This mini-review describes the pathophysiology of region-specific inflammation after sepsis-associated encephalopathy (SAE), clinical features, and future prospects for SAE treatment. The hippocampus is highly susceptible to inflammation, and studies that perform treatments with antibodies to cytokine receptors, such as interleukin-1β, are in progress. Future development of clinically applicable therapies is expected.

Molecular Mechanisms in the Genesis of Seizures and Epilepsy Associated With Viral Infection

Seizures are a common presenting symptom during viral infections of the central nervous system (CNS) and can occur during the initial phase of infection ("early" or acute symptomatic seizures), after recovery ("late" or spontaneous seizures, indicating the development of acquired epilepsy), or both. The development of acute and delayed seizures may have shared as well as unique pathogenic mechanisms and prognostic implications. Based on an extensive review of the literature, we present an overview of viruses that are associated with early and late seizures in humans. We then describe potential pathophysiologic mechanisms underlying ictogenesis and epileptogenesis, including routes of neuroinvasion, viral control and clearance, systemic inflammation, alterations of the blood-brain barrier, neuroinflammation, and inflammation-induced molecular reorganization of synapses and neural circuits. We provide clinical and animal model findings to highlight commonalities and differences in these processes across various neurotropic or neuropathogenic viruses, including herpesviruses, SARS-CoV-2, flaviviruses, and picornaviruses. In addition, we extensively review the literature regarding Theiler's murine encephalomyelitis virus (TMEV). This picornavirus, although not pathogenic for humans, is possibly the best-characterized model for understanding the molecular mechanisms that drive seizures, epilepsy, and hippocampal damage during viral infection. An enhanced understanding of these mechanisms derived from the TMEV model may lead to novel therapeutic interventions that interfere with ictogenesis and epileptogenesis, even within non-infectious contexts.

Lysophosphatidic Acid Receptor 5 (LPA5) Knockout Ameliorates the Neuroinflammatory Response In Vivo and Modifies the Inflammatory and Metabolic Landscape of Primary Microglia In Vitro

Systemic inflammation induces alterations in the finely tuned micromilieu of the brain that is continuously monitored by microglia. In the CNS, these changes include increased synthesis of the bioactive lipid lysophosphatidic acid (LPA), a ligand for the six members of the LPA receptor family (LPA_1-6). In mouse and human microglia, LPA₅ belongs to a set of receptors that cooperatively detect danger signals in the brain. Engagement of LPA₅ by LPA polarizes microglia toward a pro-inflammatory phenotype. Therefore, we studied the consequences of global LPA₅ knockout (^-/-) on neuroinflammatory parameters in a mouse endotoxemia model and in primary microglia exposed to LPA in vitro. A single endotoxin injection (5 mg/kg body weight) resulted in lower circulating concentrations of TNFα and IL-1β and significantly reduced gene expression of IL-6 and CXCL2 in the brain of LPS-injected LPA₅^-/- mice. LPA₅ deficiency improved sickness behavior and energy deficits produced by low-dose (1.4 mg LPS/kg body weight) chronic LPS treatment. LPA₅^-/- microglia secreted lower concentrations of pro-inflammatory cyto-/chemokines in response to LPA and showed higher maximal mitochondrial respiration under basal and LPA-activated conditions, further accompanied by lower lactate release, decreased NADPH and GSH synthesis, and inhibited NO production. Collectively, our data suggest that LPA₅ promotes neuroinflammation by transmiting pro-inflammatory signals during endotoxemia through microglial activation induced by LPA.

Chromogranin A-derived peptide CGA47-66 protects against septic brain injury by reducing blood-brain barrier damage through the PI3K/AKT pathway

CGA_47-66 (Chromofungin, CHR), is a peptide derived from the N-terminus of chromogranin A (CgA), has been proven to inhibit the lipopolysaccharide (LPS)-induced brain injury. However, the underlying mechanism is still unknown. We found that CGA_47-66 exerted a protective effect on cognitive impairment by inhibiting the destruction of the blood-brain barrier (BBB) in the LPS-induced sepsis mice model. In addition, the hCMEC/D3 cell line was used to establish an in vitro BBB model. Under LPS stimulation, CGA_47-66 could significantly alleviate the hyperpermeability of the BBB, the destruction of tight junction proteins, and the rearrangement of F-actin. To investigate the underlying mechanism, we used LY294002, a PI3K inhibitor, which partially reduced the protective effect of CGA_47-66 on the integrity of BBB. Indicating that the PI3K/AKT pathway plays a vital role in the brain-protective function of CGA_47-66, which might be a potential therapeutic target for septic brain injury.

Influence of age and sex on microRNA response and recovery in the hippocampus following sepsis

Sepsis, defined as a dysregulated host immune response to infection, is a common and dangerous clinical syndrome. The excessive host inflammatory response can induce immediate and persistent cognitive decline, which can be worse in older individuals. Sex-specific differences in the outcome of infectious diseases and sepsis appear to favor females. We employed a murine model to examine the influence of age and sex on the brain's microRNA (miR) response following sepsis. Young and old mice of both sexes underwent cecal ligation and puncture (CLP) with daily restraint stress. Expression of hippocampal miR was examined in age- and sex-matched controls at 1 and 4 days post-CLP. Few miR were modified in a similar manner across age or sex and these few miR were generally associated with neuroprotection against inflammation. Similar to previous work examining transcription, young females exhibited a better recovery of the miR profile from day 1 to day 4, relative to young males and old females. For young males and all female groups, the initial response mainly involved a decrease in miR expression. In contrast, old males exhibited only upregulated miR on day 1 and day 4 and many of the miR upregulated on day 1 and day 4 were linked to neurodegeneration, increased neuroinflammation, and cognitive impairment. The results emphasize age and sex differences in epigenetic mechanisms that likely contribute to susceptibility or resilience to cognitive impairment due to sepsis.

Selegiline Protects Against Lipopolysaccharide (LPS)-Induced Impairment of the Blood-Brain Barrier Through Regulating the NF-κB/MLCK/p-MLC Signaling Pathway

Disruption of the blood-brain barrier (BBB) is an important hallmark of sepsis-associated encephalopathy (SAE). Selegiline, a selective and irreversible inhibitor of monoamine oxidase type B, has been applied for the treatment of nervous disorders. In this study, we aimed to investigate whether selegiline has a protective capacity in the impairment of the BBB in both in vivo and in vitro experiments. In a sepsis mouse model, administration of selegiline ameliorated lipopolysaccharide (LPS)-induced impairment of BBB integrity. Additionally, treatment with selegiline increased the expression of the tight junction protein junctional adhesion molecule A (JAM-A) against LPS. Also, we found that selegiline inhibited the production of the proinflammatory cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-1β. In an in vitro experimental model, bEnd.3 brain endothelial cells were exposed to LPS. Results indicate that stimulation with LPS significantly increased the permeability of bEnd.3 cells and reduced the expression of JAM-A, both of which were rescued by treatment with selegiline. Additionally, selegiline prevented the activation of the NF-κB/MLCK/p-MLC signaling pathway in LPS-challenged bEnd.3 cells. These results indicate that selegiline exerted a protective effect on BBB dysfunction, which might be attributed to the inhibition of the NF-κB/MLCK/p-MLC signaling pathway. These findings provide a basis for further research into the neuroprotective mechanism of selegiline.

Cognitive Trajectories Following Acute Infection in Older Patients With and Without Cognitive Impairment: An 1-Year Follow-Up Study

Introduction: Dementia is a known risk factor for both delirium and acute systemic infections which may also play a significant role in promoting or accelerating neurodegenerative disease. Infections are both the main causes of hospitalization of dementia patients and can be a major precipitant of delirium but currently it is not possible to predict the risk of cognitive decline in older patients exposed to acute infection. Objectives: We aimed to determine the level of cognitive change at 1-year follow up in individuals with different patterns of cognitive function (dementia, delirium, delirium superimposed on dementia) at the time of their hospitalization due to a systemic infection and to correlate these cognitive patterns with clinical status variables. Methods: We recruited 53 hospitalized geriatric patients with a systemic infection, and we collected 12-months follow up data for 34 patients. These patients were classified in four groups: no cognitive impairment (controls-C), delirium only (D), dementia only (Dem), and delirium superimposed to dementia (DD). Cognitive performance was measured by change in score on the Montreal Cognitive Assessment (MoCA) and delirium was identified using Confusion Assessment Measure (CAM). We examined performance on the MoCA in the first year after hospitalization, controlling for demographic characteristics, coexisting medical conditions, and type of infection. Results: For the 34 patients to whom follow-up data was available, delirium presence in individuals with prior dementia (DD group) was associated with a negative mean change score of 3-point (p < 0.02) at 1 year follow up, whereas dementia patients without delirium had a mean change score of 1.5-point lower at 12-months (p = 0.04), when comparing follow-up and baseline MoCA scores. Cognitively healthy patients did not significantly decrease their MoCA score at follow-up (p = 0.15). MoCA and NPI scores during hospitalization were significantly correlated with the level of cognitive decline in the four groups (r = 0.658, p < 0.01 and r = 0.439, p = 0.02, respectively). Conclusions: Premorbid dementia and delirium superimposed on dementia during hospitalization in older patients with acute infections predict cognitive decline at 1 year following admission. Taken together, our findings suggest a pathophysiological interaction between neurodegenerative changes, acute infection, and delirium.

Neural autoantibodies in delirium

BACKGROUND

Delirium in hospitalized and intensive care unit patients is an emerging condition due to its rapid-onset requiring fast action to mitigate a worse clinical outcome. Although several causes and conditions are known, the association between delirium and neural autoantibodies has often been neglected in cohort studies and reviews as causing delirium. The aim of our review is to delineate the occurrence and type of neural autoantibodies and to depict other biological markers of autoimmunity in relationship to delirium.

METHODS

For this narrative review Pubmed research was done to select articles about delirium and neural autoantibodies.

RESULTS

We can report on several cell-surface autoantibodies such as anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, anti-contactin associated protein 2, anti-Leucin rich glioma inactivated protein 1, anti-dipeptidyl-peptidase-like 6 protein, anti-glycine receptor and anti-myelin autoantibodies, as well as intracellular autoantibodies such as anti-glutamic acid decarboxylase 65 (GAD65), anti-CV2 and anti-Hu associated with delirium in patients. Our case reports and case series screening revealed that 20 of 63 patients with delirium presented neural autoantibodies, thus revealing a 32% frequency of autoantibody-associated delirium in delirium patients. Our main finding is that delirium's hyperactive form is associated with neural autoantibodies. Diagnosing delirium differentially is difficult, as in patients with delirium and GAD65 autoantibodies, as it must be distinguished from other psychopathological excitation states such as mania. We also describe autoimmune delirium's potential pathophysiologic pathways.

CONCLUSIONS

The existence of neural autoantibodies in delirious patients is scientifically and clinically highly relevant in its diagnosis, therapy, and pathogenesis. More large-scale studies should be conducted to evaluate their significance and prevalence in delirium.

Blood-Brain Barrier Dysfunction in CNS Disorders and Putative Therapeutic Targets: An Overview

The blood-brain barrier (BBB) is a fundamental component of the central nervous system (CNS). Its functional and structural integrity is vital to maintain the homeostasis of the brain microenvironment by controlling the passage of substances and regulating the trafficking of immune cells between the blood and the brain. The BBB is primarily composed of highly specialized microvascular endothelial cells. These cells’ special features and physiological properties are acquired and maintained through the concerted effort of hemodynamic and cellular cues from the surrounding environment. This complex multicellular system, comprising endothelial cells, astrocytes, pericytes, and neurons, is known as the neurovascular unit (NVU). The BBB strictly controls the transport of nutrients and metabolites into brain parenchyma through a tightly regulated transport system while limiting the access of potentially harmful substances via efflux transcytosis and metabolic mechanisms. Not surprisingly, a disruption of the BBB has been associated with the onset and/or progression of major neurological disorders. Although the association between disease and BBB disruption is clear, its nature is not always evident, specifically with regard to whether an impaired BBB function results from the pathological condition or whether the BBB damage is the primary pathogenic factor prodromal to the onset of the disease. In either case, repairing the barrier could be a viable option for treating and/or reducing the effects of CNS disorders. In this review, we describe the fundamental structure and function of the BBB in both healthy and altered/diseased conditions. Additionally, we provide an overview of the potential therapeutic targets that could be leveraged to restore the integrity of the BBB concomitant to the treatment of these brain disorders.

Electroacupuncture prevents LPS- induced neuroinflammation via upregulation of PICK-TLR4 complexes in the microglia of hippocampus

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis caused by neuroinflammation. Electroacupuncture (EA) can be used to treat SAE, but the underlying mechanism is not clear. Lack of PICK1 further aggravates the inflammatory response in mice with sepsis. Therefore, we sought to investigate whether PICK1 is involved in the protective effects of electroacupuncture to SAE. In this study, mice were treated with EA after lipopolysaccharide (LPS) treatment. Behavioral tests; microglial activity of hippocampus; neuron survival and the inflammatory factors PICK1 and TLR4, as well as TLR4-related proteins, such as ERK, JNK, and P38, were assessed after EA treatment. PICK1, TLR4, and TLR4-related proteins, as well as PICK1-TLR4 complex levels were assessed in BV2 cells treated with LPS, PICK1 siRNA, or PICK1 polypeptide. The results indicated that EA could improve neurological assessment and reduce activation of microglial and TLR4 and expression of proinflammatory cytokines. EA also reduced the expression of TLR4 and phosphorylation of ERK/JNK/P38 while, increased the expression of PICK1 and TLR4 complexes. PICK1 knockdown further promoted the expression of TLR4 and phosphorylation of ERK/JNK/P38 in BV2 cells, but this effect was reversed by PICK1 polypeptides. These results suggest that EA may reduce neuroinflammation responses, decrease inflammatory factors, and finally, protect SAE by increasing the formation of PICK1-TLR4 complexes in microglia.