Cellular pathophysiology of sepsis associated encephalopathy (SAE) remains poorly characterised. Brain pathology in SAE, which is manifested by impaired perception, consciousness and cognition, results from multifactorial events, including high levels of systemic cytokines, microbial components and endotoxins, which all damage the brain barriers, instigate neuroinflammation and cause homeostatic failure. Astrocytes, being the principal homeostatic cells of the central nervous system contribute to the brain defence against infection. Forming multifunctional anatomical barriers, astroglial cells maintain brain-systemic interfaces and restrict the damage to the nervous tissue. Astrocytes detect, produce and integrate inflammatory signals between immune cells and cells of brain parenchyma, thus regulating brain immune response. In SAE astrocytes are present in both reactive and astrogliopathic states; balance between these states define evolution of pathology and neurological outcomes. In humans pathophysiology of SAE is complicated by frequent presence of comorbidities, as well as age-related remodelling of the brain tissue with senescence of astroglia; these confounding factors further impact upon SAE progression and neurological deficits.
Perivascular spaces (PVS) and their enlargement (EPVS) have been gaining interest as EPVS can be visualized non-invasively by magnetic resonance imaging (MRI) when viewing T-2-weighted images. EPVS are most commonly observed in the regions of the basal ganglia and the centrum semiovale; however, they have also been identified in the frontal cortex and hippocampal regions. EPVS are known to be increased in aging and hypertension, and are considered to be a biomarker of cerebral small vessel disease (SVD). Interest in EPVS has been significantly increased because these PVS are now considered to be an essential conduit necessary for the glymphatic pathway to provide the necessary efflux of metabolic waste. Metabolic waste includes misfolded proteins of amyloid beta and tau that are known to accumulate in late-onset Alzheimer’s disease (LOAD) within the interstitial fluid that is delivered to the subarachnoid space and eventually the cerebral spinal fluid (CSF). The CSF acts as a sink for accumulating neurotoxicities and allows clinical screening to potentially detect if LOAD may be developing early on in its clinical progression via spinal fluid examination. EPVS are thought to occur by obstruction of the PVS that associates with excessive neuroinflammation, oxidative stress, and vascular stiffening that impairs flow due to a dampening of the arterial and arteriolar pulsatility that aids in the convective flow of the metabolic debris within the glymphatic effluxing system. Additionally, increased EPVS has also been associated with Parkinson’s disease and non-age-related multiple sclerosis (MS).
The blood–brain barrier (BBB) is an interface primarily comprised of brain endothelial cells (BECs), separating the central nervous system (CNS) from the systemic circulation while carefully regulating the transport of molecules and inflammatory cells, and maintaining the required steady-state environment. Inflammation modulates many BBB functions, but the ultrastructural cytoarchitectural changes of the BBB with inflammation are understudied. Inflammation was induced in male 8–10-week-old CD-1 mice with intraperitoneal lipopolysaccharide (LPS), using a regimen (3 mg/kg at 0, 6, and 24 h) that caused robust BBB disruption but had minimal lethality at the study timepoint of 28 h. Perfusion-fixed brains were collected and the frontal cortical layer III regions were analyzed using a transmission electron microscopy (TEM). The LPS-treated mice had pronounced ultrastructural remodeling changes in BECs that included plasma membrane ruffling, increased numbers of extracellular microvesicles, small exosome formation, aberrant BEC mitochondria, increased BEC transcytosis, while tight junctions appeared to be unaltered. Aberrant pericytes were contracted with rounded nuclei and a loss of their elongated cytoplasmic processes. Surveilling microglial cells were attracted to the neurovascular unit (NVU) of BECs, and astrocyte detachment and separation were associated with the formation of a perivascular space and pericapillary edema. The LPS treatment resulted in numerous ultrastructural aberrant remodeling changes to the neurovascular unit’s BECs, microglia, pericytes, and astrocytes. In summary, a disturbance of the NVU morphology is a consequence of LPS treatment.
Background. The problem of acute and chronic forms of hepatic encephalopathy (HE) is not clearly identified among modern problems of hepatology and neuroscience in Ukraine. Despite the significant contribution to the development of lethal complications in patients with liver pathology and long history of the study of this issue, there is still no unified opinion on the links of HE pathogenesis.The aim of this review is to conduct a comprehensive analysis of current data on the spreading and mechanisms of development of HE.HE is a complex of potentially reversible neurocognitive disorders in patients with chronic or acute hepatic failure (ALF). HE is more often a complication of liver cirrhosis and is the second most frequent cause of hospitalization of such patients after ascites. When decompensating liver failure in acute or chronic hepatic pathology in patients severe forms of HE develop, accompanied by a progressive increase in intracranial pressure and the development of coma, which often ends lethal due to poor corrigibility of intracranial hypertension while maintaining hepatogenic neurointoxication. HE is considered as the end result of the accumulation of a number of neurotoxic substances in the brain, among which are ammonia, mercaptans, short chain fatty acids, false neurotransmitters, gamma-aminobutyric acid, manganese. The most popular among the reasons for the development of HE is the neurotoxic theory of ammonia. Ammonia is subjected to detoxification in the liver, turning into urea, a smaller fraction with the participation of glutamine synthetase is used in the synthesis of glutamine in muscles, liver and astrocytes of brain. In case of hepatic dysfunction and/or portosystemic shunting, the concentration of ammonia in blood increases up to 10 times and the main load for its detoxification is shifted to myocytes and astroglia. In ALF glutamine overload of astrocytes occurs with a change in intracellular osmolarity and subsequent edema of astroglia, which is accompanied by the development of cytotoxic edema of the brain. In this case, in astrocytes damaging of mitochondrial respiratory chain occurs and mitochondrial insufficiency develops, as well as processes of nitrosative-oxidative stress and oxidation of astrocytic and neuronal RNA, disruption of gene expression, synthesis of neuro-and gliotransmitters and synaptic plasticity. The increased influx of aromatic amino acids into brain leads to the synthesis of false neurotransmitters, which worsens serotoninergic, GABA-ergic, dopaminergic and glutamatergic neurotransmission. Damage to the components of the blood-brain barrier leads to aggravation of the water imbalance, penetration of hematogenous cytokines, endotoxins and other products of systemic inflammatory reaction into the cerebral parenchyma and development of neuroinflammation, which makes an important contribution to the further progression of cerebral edema.Conclusions: despite a comprehensive study of the problem, many open questions remain in the pathogenesis of HE. Special attention ...
The aim of the study was to determine the immunohistochemical level of glutamine synthetase (GS) expression in different brain regions in the conditions of experimental acute liver failure in rats. Materials and methods. The study was conducted in Wistar rats: 5 sham (control) animals and 10 rats with acetaminophen induced liver failure model (AILF). The immunohistochemical study of GS expression in the sensorimotor cortex, white matter, hippocampus, thalamus, caudate nucleus/putamen was carried out in the period of 12-24 h after acetaminophen treatment. Results. Beginning from the 6th hour after acetaminophen treatment all AILF-animals showed the progressive increase in clinical signs of acute brain disfunction finished in 6 rats by comatose state up to 24 h - they constituted subgroup AILF-B, “non-survived”. 4 animals survived until the 24 h - subgroup AILF-A, “survived”. In the AILF-B group, starting from 16 to 24 hours after treatment, a significant (relative to control) regionally-specific dynamic increase in the level of GS expression was observed in the brain: in the cortex – by 307.33 %, in the thalamus – by 249.47%, in the hippocampus – by 245.53%, in the subcortical white matter – by 126.08%, from 12th hour – in the caudate nucleus/putamen, by 191.66 %; with the most substantive elevation of GS expression in the cortex: by 4.07 times. Conclusion. Starting from the 16th hours after the acetaminophen treatment (from the 12th h in the caudate nucleus/putamen region) and up to 24 h, it is observed reliable compared to control dynamic increase in GS protein expression in the cortex, white matter, hippocampus, thalamus, caudate nucleus/putamen of the rat brain with the most significant elevation in the cortex among other regions. The heterogeneity in the degree of GS expression rising in different brain regions potentially may indicate regions more permeable for ammonia and/or other systemic toxic factors as well as heterogeneous sensitivity of brain regions to deleterious agents in conditions of AILF. Subsequently, revealed diversity in the GS expression reflects the specificity of reactive response of local astroglia in the condition of AILF-encephalopathy during specific time-period. The dynamic increase in the GS expression associated with impairment of animal state, indicates involvement of increased GS levels in the mechanisms of experimental acute hepatic encephalopathy.
Hepatic encephalopathy (HE) is a syndrome of impaired brain function in patients with advanced liver failure and it manifests in form of psychometric tests alterations up to decreased consciousness and coma. The current knowledge about HE mainly focused on the theory of ammonia neurotoxicity and neuroinflammation. Microglia being resident innate immune cells of the brain when activated are responsible for the neuroinflammatory reactions. The aim – immunohistochemical study of the microglial changes in different rat brain regions in conditions of experimental acute HE (AHE). Materials and methods. We used acetaminophen induced liver failure model in Wistar rats. Four from 10 animals that survived up to 24 h after acetaminophen injection constituted “compensated group”; 6 animals which died within 24 h – “decompensated group”. Microglial reactive changes were analysed by the evaluation of the relative area (S rel., %) of CD68+ expression in the brain cells not associated with meninges and vessels, as well as the changing in shape and number of these cells. Results. Acetaminophen-induced AHE in rats was characterized by the regional- and time-dependent dynamic increase in CD68 expression level in the rat brain in form of significant (relatively to control) increase of CD68+ S rel. in brain cells and the number of such cells. The medians of CD68+ S rel. and their numbers in significantly changed regions of non-survived rats were, respectively: subcortical white matter – 0.24 (0.20; 0.26) and 11.00 (8.00; 13.00); thalamus – 0.13 (0.90; 0.18) and 6.00 (3.00; 7.00); caudate/putamen – 0.13 (0.12; 0.18) and 7.00 (4.00; 11.00) – all indicators were statistically significant compared to control. In the survived animals, indicators were, respectively: subcortical white matter – 0.24 (0.16; 0,26) and 10.00 (8.00; 12.00); caudate/putamen – 0.12 (0.10; 0.15) and 6.00 (4.00; 10.00) – the differences were significant compared to control. Conclusions. The highest and significant indicators were revealed at 24 h (compared to earlier time points) of the experiment in the white matter, thalamus and caudate/putamen. This fact reflects time-dependent dynamic boosting of reactive changes in microglia and presumably may indicate the regions of the most active neuroinflammatory response within the brain parenchyma in the conditions of AHE. The appearing of a small percentage of cells with amoeboid transformation among CD68+-cells may mean partial functional insufficiency of such cells due to probable suppressive impact of ammonia or other influencing factors, as well as insignificance of the material that needs to be phagocytosed under established conditions.
Pathophysiology of sepsis-associated encephalopathy (SAE) is linked to blood-brain barrier breakdown, neuroinflammation and neurotransmitter imbalance in the brain. Astroglia, the most abundant cell population within the brain, plays the critical role in control of all kinds of homeostatic processes, thereby regulating the adaptive reactions of the brain to various challenges. Astroglia are highly heterogenous across the brain regions, therefore, damaging factors stimulate heterogenous astroglial reactivity and response in different brain regions. The aim of this study was determining immunohistochemical features of GFAP expression in various brain regions in the model of rodent experimental sepsis. Materials and methods. The experiment was performed in Wistar rats: control group of 5 sham-operated rats and the main group of 20 rats subjected to cecum ligation and puncture (CLP) procedure. The immunohistochemical study of GFAP expression in the sensorimotor cortex, subcortical white matter, hippocampal, thalamic and caudate nucleus/putamen regions was performed from 20 to 48 hours of the postoperative period. Results. Starting from the 12th hour after CLP, animals began display progressive increase in signs of periorbital exudation, piloerection, fever-/hypothermia, diarrhea, social isolation, lethargy, and respiratory impairment. In the period of 20–38 hours, 9 animals showed expressed previously listed symptoms and were euthanized (CLP-B – lethal group), 11 rats survived until 48 hours of the experiment (CLP-A – survived group). In the lethal group, starting from 20 to 38 hours after the CLP procedure, a significant (relative to control) regionally-specific dynamic increase in the level of GFAP expression was observed in the brain: in the cortex – by 465 %, in the subcortical white matter – by 198 %, in the hippocampus – by 250 %, from the 23rd hour – in the caudate nucleus/putamen by 18 %. In the thalamus, no significant changes in the level of GFAP expression were observed. In the cortex and hippocampus of survived animals, 48 h after CLP, higher values of GFAP expression were observed comparing to the group of non-survived animals. Conclusions. Under conditions of the experimental SAE, an early dynamic increase in the astroglial reactivity was observed in the cortex, hippocampus, white matter, and caudate nucleus/putamen of the brain with the most significant increase of indicators in the cortex and hippocampus, which potentially indicates relatively more vulnerable areas of the brain to damaging factors, as well as places of the most active intercellular interaction in the condition of systemic inflammation. Higher values of GFAP expression in the cortex and hippocampus of survived animals at 48 hours of the experiment, compared with indicators of non-survived group, indicate increased astroglial reactivity in these brain regions at the noted time period, accompanied by relatively more favorable clinical course of the disease.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.