An alteration in the gamma-aminobutyric acid receptor system in experimentally induced septic shock in rats

Research progress in the pathogenesis of sepsis-associated encephalopathy

Sepsis is a syndrome that causes dysfunction of multiple organs due to the host's uncontrolled response to infection and is a significant contributor to morbidity and mortality in intensive care units worldwide. Surviving patients are often left with acute brain injury and long-term cognitive impairment, known as sepsis-associated encephalopathy (SAE). In recent years, researchers have directed their focus towards the pathogenesis of SAE. However, due to the complexity of its development, there remains a lack of effective treatment measures that arise as a serious issue affecting the prognosis of sepsis patients. Further research on the possible causes of SAE aims to provide clinicians with potential therapeutic targets and help develop targeted prevention strategies. This paper aims to review recent research on the pathogenesis of SAE, in order to enhance our understanding of this syndrome.

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.

Glutamate and GABA in Microglia-Neuron Cross-Talk in Alzheimer's Disease

The physiological balance between excitation and inhibition in the brain is significantly affected in Alzheimer’s disease (AD). Several neuroactive compounds and their signaling pathways through various types of receptors are crucial in brain homeostasis, among them glutamate and γ-aminobutyric acid (GABA). Activation of microglial receptors regulates the immunological response of these cells, which in AD could be neuroprotective or neurotoxic. The novel research approaches revealed the complexity of microglial function, including the interplay with other cells during neuroinflammation and in the AD brain. The purpose of this review is to describe the role of several proteins and multiple receptors on microglia and neurons, and their involvement in a communication network between cells that could lead to different metabolic loops and cell death/survival. Our review is focused on the role of glutamatergic, GABAergic signaling in microglia–neuronal cross-talk in AD and neuroinflammation. Moreover, the significance of AD-related neurotoxic proteins in glutamate/GABA-mediated dialogue between microglia and neurons was analyzed in search of novel targets in neuroprotection, and advanced pharmacological approaches.

Sepsis impairs the propagation of cortical spreading depression in rats and this effect is prevented by antioxidant extract

Sepsis is a clinical syndrome with high morbidity and mortality. It is characterized by acute inflammatory response and oxidative stress, which is implicated in cerebral dysfunction. Murici (Byrsonimacrassifolia (L.) Kunth) is a fruit rich in antioxidant compounds, which could be an alternative to prevent damage to tissues induced by sepsis . Here, we evaluated the effects of sepsis on the propagation of cortical spreading depression (CSD) and oxidative stress, and tested the action of murici antioxidant extract in prevention against the effect of sepsis. Male Wistar rats (90-210 days, n = 40) were previously supplemented, orogastrically, with murici extract (150 mg/kg/day or 300 mg/kg/day), or an equivalent volume of the vehicle solution, for fifteen days. Then the animals were subjected to experimental sepsis through cecal ligation and perforation (CLP). Subsequently, CSD recordings were obtained and brain oxidative stress was evaluated. Sepsis decelerated CSD and increased the malondialdehyde (MDA) levels in the brain cortex of the animals. In contrast, septic rats that had been previously supplemented with murici antioxidant extract in doses of 150 and 300 mg/kg/day showed an increase in CSD propagation velocity, low levels of MDA and GSH/GSSG ratio and an increase of superoxide dismutase (SOD) activity, regardless of the dose tested. Our results demonstrate that sepsis affects brain excitability and that this effect can be prevented by murici antioxidant extract. The effects of sepsis and/or murici extract on CSD may be due to the oxidative state of the brain.

Sepsis-associated encephalopathy and septic encephalitis: an update

INTRODUCTION

Sepsis-associated encephalopathy (SAE) and septic encephalitis (SE) are associated with increased mortality, long-term cognitive impairment, and focal neurological deficits.

AREAS COVERED

The PUBMED database was searched 2016-2020. The clinical manifestation of SAE is delirium, SE additionally is characterized by focal neurological symptoms. SAE is caused by inflammation with endothelial/microglial activation, increase of permeability of the blood-brain-barrier, hypoxia, imbalance of neurotransmitters, glial activation, axonal, and neuronal loss. Septic-embolic (SEE) and septic-metastatic encephalitis (SME) are characterized by focal ischemia (SEE) and small abscesses (SME). The continuum between SAE, SME, and SEE is documented by imaging techniques and autopsies. The backbone of treatment is rapid optimum antibiotic therapy. Experimental approaches focus on modulation of inflammation, stabilization of the blood-brain barrier, and restoration of membrane/mitochondrial function.

EXPERT OPINION

The most promising diagnostic approaches are new imaging techniques. The most important measure to fight delirium remains establishment of daily structure and adequate sensory stimuli. Dexmedetomidine and melatonin appear to reduce the frequency of delirium, their efficacy in SAE and SE remains to be established. Drugs already licensed for other indications or available as food supplements which may be effective in SAE are statins, L-DOPA/benserazide, β-hydroxybutyrate, palmitoylethanolamide, and tetracyclines or other bactericidal non-lytic antibiotics.

Astroglia in Sepsis Associated Encephalopathy

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.

General Pathophysiology of Astroglia

Astroglial cells are involved in most if not in all pathologies of the brain. These cells can change the morpho-functional properties in response to pathology or innate changes of these cells can lead to pathologies. Overall pathological changes in astroglia are complex and diverse and often vary with different disease stages. We classify astrogliopathologies into reactive astrogliosis, astrodegeneration with astroglial atrophy and loss of function, and pathological remodelling of astrocytes. Such changes can occur in neurological, neurodevelopmental, metabolic and psychiatric disorders as well as in infection and toxic insults. Mutation in astrocyte-specific genes leads to specific pathologies, such as Alexander disease, which is a leukodystrophy. We discuss changes in astroglia in the pathological context and identify some molecular entities underlying pathology. These entities within astroglia may repent targets for novel therapeutic intervention in the management of brain pathologies.

Septic Encephalopathy

PURPOSE OF THE REVIEW

To discuss the diagnostic approach to patients with septic encephalopathy as well as the need for specific neuro-monitoring and the perspectives on future therapeutic approaches in this setting.

RECENT FINDINGS

Most of data-concern experimental studies evaluating the pathophysiology of septic encephalopathy. A combination of neurodegenerative pathways with neurovascular injury is the cornerstone for the development of such complication and the long-term neurological sequelae among survivors. Septic encephalopathy is a common complication in septic patients. Clinical presentation may range from mild confusion and disorientation to convulsions and deep coma. The diagnosis of septic encephalopathy is made difficult by the lack of any specific clinical and non-clinical feature, in particular among sedated patients in whom neurological examination is unreliable. In spite of the high mortality rate associated with this condition, there is no prophylactic or targeted therapy to reduce or minimize brain damage in septic patients and clinical management is limited to the treatment of the underlying infection.

Activation of central GABAB receptors offsets the cyclosporine counteraction of endotoxic cardiovascular outcomes in conscious rats

We have previously shown that cyclosporine (CSA) counteracts cardiovascular manifestations induced by endotoxemia (lipopolysaccharide, LPS) such as hypotension and cardiac autonomic dysfunction in conscious rats. In this study, we investigated whether the facilitation of central γ-amino butyric acid (GABA) neurotransmission blunts these favorable influences of CSA. The LPS-CSA interaction was determined in the absence and presence of drugs that activate GABA_A or GABA_B receptors or elevate synaptic GABA levels in the central nervous system. The consequent i.v. administration of CSA (10 mg/kg) blunted the LPS-evoked hypotension, tachycardia, and reductions in time- and frequency-domain indices of heart rate variability (measures of cardiac autonomic control) evoked by LPS (10 mg/kg i.v.). The ability of CSA to reverse the LPS effects disappeared in rats treated intracisternally (i.c.) with baclofen (selective GABA_B agonist, 2 μg/rat) but not muscimol (selective GABA_A agonist, 1 μg/rat), indicating a preferential compromising action for central GABA_B receptors on the advantageous effects of CSA. Moreover, the improvement by CSA of LPS-evoked cardiovascular derangements was also eliminated after concurrent i.c. administration of vigabatrin (GABA transaminase inhibitor, 200 μg/rat) or tiagabine (GABA reuptake inhibitor, 100 μg/rat). These results demonstrate that the activation of central GABA_B receptors either directly via baclofen or indirectly following interventions that boost GABA levels in central synapses counterbalances the rectifying action of CSA on endotoxemia.

Mass spectrometry for the discovery of biomarkers of sepsis

Sepsis is a serious medical condition that occurs in 30% of patients in intensive care units (ICUs). Early detection of sepsis is key to prevent its progression to severe sepsis and septic shock, which can cause organ failure and death. Diagnostic criteria for sepsis are nonspecific and hinder a timely diagnosis in patients. Therefore, there is currently a large effort to detect biomarkers that can aid physicians in the diagnosis and prognosis of sepsis. Mass spectrometry is often the method of choice to detect metabolomic and proteomic changes that occur during sepsis progression. These "omics" strategies allow for untargeted profiling of thousands of metabolites and proteins from human biological samples obtained from septic patients. Differential expression of or modifications to these metabolites and proteins can provide a more reliable source of diagnostic biomarkers for sepsis. Here, we focus on the current knowledge of biomarkers of sepsis and discuss the various mass spectrometric technologies used in their detection. We consider studies of the metabolome and proteome and summarize information regarding potential biomarkers in both general and neonatal sepsis.

Neuroanatomy of sepsis-associated encephalopathy

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Originally published in the Annual Update in Intensive Care and Emergency Medicine 2017. The number of authors differs in the two versions due to constraints regarding the number of authors in the Annual Update in Intensive Care and Emergency Medicine. In the Annual Update version of the review, the three senior authors appear in the acknowledgement section. In the Critical Care version, these three senior authors appear as full authors of the manuscript. All authors helped draft and revise the manuscript for critical intellectual content.

Neuroanatomy and Physiology of Brain Dysfunction in Sepsis

Sepsis-associated encephalopathy (SAE), a complication of sepsis, is often complicated by acute and long-term brain dysfunction. SAE is associated with electroencephalogram pattern changes and abnormal neuroimaging findings. The major processes involved are neuroinflammation, circulatory dysfunction, and excitotoxicity. Neuroinflammation and microcirculatory alterations are diffuse, whereas excitotoxicity might occur in more specific structures involved in the response to stress and the control of vital functions. A dysfunction of the brainstem, amygdala, and hippocampus might account for the increased mortality, psychological disorders, and cognitive impairment. This review summarizes clinical and paraclinical features of SAE and describes its mechanisms at cellular and structural levels.

Preventive strategies and potential therapeutic interventions for delirium in sepsis

Delirium is the most frequent and severe clinical presentation of brain dysfunction in critically ill septic patients with an incidence ranging from 9% to 71%. Delirium represents a significant burden for patients and relatives, as well as to the health care system, resulting in higher costs, long-term cognitive impairment and significant risk of death after 6 months. Current interventions for the prevention of delirium typically involve early recognition and amelioration of modifiable risk factors and treatment of underlying conditions that predisposes the individual to delirium. Several pharmacological interventions to prevent and treat delirium have been tested, although their effectiveness remains uncertain, especially in larger and more homogeneous subgroups of ICU patients, like in patients with sepsis. To date, there is inconsistent and conflicting data regarding the efficacy of any particular pharmacological agent, thus substantial attention has been paid to non-pharmacological interventions and preventive strategies should be applied to every patient admitted in the ICU. Future trials should be designed to evaluate the impact of these pharmacologic interventions on the prevention and treatment of delirium on clinically relevant outcomes such as length of stay, hospital mortality and long-term cognitive function. The role of specific medications like statins in delirium prevention is also yet to be evaluated.

Peripheral T-lymphocyte and natural killer cell population imbalance is associated with septic encephalopathy in patients with severe sepsis

Septic encephalopathy (SE) is a diffuse cerebral dysfunction resulting from a systemic inflammatory response, and is associated with an increased risk of mortality. The pathogenesis of SE is complex and multifactorial, but unregulated immune imbalance may be an important factor. The current retrospective study examined the clinical data of 86 patients with severe sepsis who were admitted to the Intensive Care Unit at Zhongshan Hospital, Xiamen University (Xiamen, China) from January, 2014 to January, 2015. The patients were assigned to SE and non-SE patient groups according to the presence or absence of SE. The proportion of T-lymphocyte subsets and natural killer (NK) cells in the immune cell population, representing the function of the immune system, were analyzed for their association with SE and compared with other clinical predictors and biomarkers. The incidence of SE in the patients was 39.5%, and this group demonstrated higher mortality rates (38 vs. 10% in non-SE patients; P=0.001). Univariate analysis revealed that the SE patients reported a lower percentage of cluster of differentiation 4⁺(CD4⁺) T-lymphocytes (51.67±7.12 vs. 60.72±3.70% in non-SE patients; P<0.01), a lower CD4⁺/cluster of differentiation 8⁺(CD8⁺) ratio (1.59±0.32 vs. 1.85±0.26% in non-SE patients; P<0.01) and a higher percentage of NK cells (11.80±1.44 vs. 9.19±2.36% in non-SE patients; P<0.01). Using a binary logistic regression model, the Acute Physiology and Chronic Health Evaluation II score and the percentage of CD4⁺ T-lymphocytes were demonstrated to be independently associated with SE (respectively, P=0.012 and OR, 4.763; P=0.005 and OR, 0.810). An area under the curve analysis of a receiver operating characteristic curve of the two indicators revealed that these were equally powerful measures in prediction of SE (Z=1.247, P>0.05). The present results confirm that SE leads to higher mortality in patients with severe sepsis, and demonstrate that immune imbalance is important in the development of SE. The proportion of CD4⁺ T-lymphocytes present were revealed in the current study to be a powerful predictor of SE in patients with severe sepsis.

Central GABAA receptors are involved in inflammatory and cardiovascular consequences of endotoxemia in conscious rats

γ-Aminobutyric acid (GABA), the principal brain inhibitory neurotransmitter, modulates inflammatory and neurodegenerative disease. Here, we tested the hypothesis that central GABAergic neurotransmission mediates the detrimental inflammatory, hemodynamic, and cardiac autonomic actions of endotoxemia. The effects of drugs that block GABA receptors or interfere with GABA uptake or degradation on blood pressure (BP), heart rate (HR), and HR variability (HRV) responses elicited by i.v. lipopolysaccharide (LPS) were assessed in conscious rats. The hypotensive effect of LPS (10 mg/kg) was blunted after intracisternal (i.c.) administration of bicuculline (GABAA receptor antagonist) or saclofen (GABAB receptor antagonist). By contrast, the concomitant LPS-evoked tachycardia and decreases in time domain and frequency domain indices of HRV (measures of cardiac autonomic control) were abolished upon treatment with bicuculline but not saclofen. Increases in serum tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) caused by LPS disappeared in the presence of bicuculline or saclofen, whereas LPS-evoked increases in serum nitric oxide metabolites (NOx) were counteracted by bicuculline only. None of the endotoxemia effects was altered in rats treated with i.c. tiagabine (GABA reuptake inhibitor) or vigabatrin (GABA transaminase inhibitor). These data suggest a major role for central GABAA receptors in the inflammatory and cardiovascular effects of endotoxemia.

Discrimination of sepsis stage metabolic profiles with an LC/MS-MS-based metabolomics approach

Background

To identify metabolic biomarkers that can be used to differentiate sepsis from systemic inflammatory response syndrome (SIRS), assess severity and predict outcomes.

Methods

65 patients were involved in this study, including 35 patients with sepsis, 15 patients with SIRS and 15 normal patients. Small metabolites that were present in patient serum samples were measured by liquid chromatography mass spectrometry techniques and analysed using multivariate statistical methods.

Results

The metabolic profiling of normal patients and patients with SIRS or sepsis was markedly different. A significant decrease in the levels of lactitol dehydrate and S-phenyl-d-cysteine and an increase in the levels of S-(3-methylbutanoyl)-dihydrolipoamide-E and N-nonanoyl glycine were observed in patients with sepsis in comparison to patients with SIRS (p<0.05). Patients with severe sepsis and septic shock displayed lower levels of glyceryl-phosphoryl-ethanolamine, Ne, Ne dimethyllysine, phenylacetamide and d-cysteine (p<0.05) in their sera. The profiles of patients with sepsis 48 h before death illustrated an obvious state of metabolic disorder, such that S-(3-methylbutanoyl)-dihydrolipoamide-E, phosphatidylglycerol (22:2 (13Z, 16Z)/0:0), glycerophosphocholine and S-succinyl glutathione were significantly decreased (p<0.05). The receiver operating characteristic curve of the differential expression of these metabolites was also performed.

Conclusions

The body produces significant evidence of metabolic disorder during SIRS or sepsis. Seven metabolites may potentially be used to diagnose sepsis.

Trial registration number

ClinicalTrial.gov identifier NCT01649440.

Cognitive decline after sepsis

The modern era of sepsis management is characterised by a growing number of patients who survive in the short term and are discharged from hospital. Increasing evidence suggests that these survivors exhibit long-term neurological sequelae, particularly substantial declines in cognitive function. The exact prevalence and outcomes of these neuropsychological sequelae are unclear. The mechanisms by which sepsis induces cognitive dysfunction probably include vascular injuries and neuroinflammation that are mediated by systemic metabolism disorders and overwhelming inflammation, a disrupted blood-brain barrier, oxidative stress, and severe microglial activation, particularly within the limbic system. Interventions targeting the blood-brain barrier, glial activation, and oxidative stress have shown promise in prevention of cognitive dysfunction in various experimental models of sepsis. The next step should be to translate these favourable effects into positive clinical results.

Sepsis Associated Encephalopathy

Sepsis associated encephalopathy (SAE) is a common but poorly understood neurological complication of sepsis. It is characterized by diffuse brain dysfunction secondary to infection elsewhere in the body without overt CNS infection. The pathophysiology of SAE is complex and multifactorial including a number of intertwined mechanisms such as vascular damage, endothelial activation, breakdown of the blood brain barrier, altered brain signaling, brain inflammation, and apoptosis. Clinical presentation of SAE may range from mild symptoms such as malaise and concentration deficits to deep coma. The evaluation of cognitive dysfunction is made difficult by the absence of any specific investigations or biomarkers and the common use of sedation in critically ill patients. SAE thus remains diagnosis of exclusion which can only be made after ruling out other causes of altered mentation in a febrile, critically ill patient by appropriate investigations. In spite of high mortality rate, management of SAE is limited to treatment of the underlying infection and symptomatic treatment for delirium and seizures. It is important to be aware of this condition because SAE may present in early stages of sepsis, even before the diagnostic criteria for sepsis can be met. This review discusses the diagnostic approach to patients with SAE along with its epidemiology, pathophysiology, clinical presentation, and differential diagnosis.

Imaging in sepsis-associated encephalopathy--insights and opportunities

Sepsis-associated encephalopathy (SAE) refers to a clinical spectrum of acute neurological dysfunction that arises in the context of sepsis. Although the pathophysiology of SAE is incompletely understood, it is thought to involve endothelial activation, blood-brain barrier leakage, inflammatory cell migration, and neuronal loss with neurotransmitter imbalance. SAE is associated with a high risk of mortality. Imaging studies using MRI and CT have demonstrated changes in the brains of patients with SAE that are also seen in disorders such as stroke. Next-generation imaging techniques such as magnetic resonance spectroscopy, diffusion tensor imaging and PET, as well as experimental imaging modalities, provide options for early identification of patients with SAE, and could aid in identification of pathophysiological processes that represent possible therapeutic targets. In this Review, we explore the recent literature on imaging in SAE, relating the findings of these studies to pathological data and experimental studies to obtain insights into the pathophysiology of sepsis-associated neurological dysfunction. Furthermore, we suggest how novel imaging technologies can be used for early-stage proof-of-concept and proof-of-mechanism translational studies, which may help to improve diagnosis in SAE.

Sepsis-induced brain dysfunction

Systemic infection is often revealed by or associated with brain dysfunction, which is characterized by alteration of consciousness, ranging from delirium to coma, seizure or focal neurological signs. Its pathophysiology involves an ischemic process, secondary to impairment of cerebral perfusion and its determinants and a neuroinflammatory process that includes endothelial activation, alteration of the blood-brain barrier and passage of neurotoxic mediators. Microcirculatory dysfunction is common to these two processes. This brain dysfunction is associated with increased mortality, morbidity and long-term cognitive disability. Its diagnosis relies essentially on neurological examination that can lead to specific investigations, including electrophysiological testing or neuroimaging. In practice, cerebrospinal fluid analysis is indisputably required when meningitis is suspected. Hepatic, uremic or respiratory encephalopathy, metabolic disturbances, drug overdose, sedative or opioid withdrawal, alcohol withdrawal delirium or Wernicke's encephalopathy are the main differential diagnoses. Currently, treatment consists mainly of controlling sepsis. The effects of insulin therapy and steroids need to be assessed. Various drugs acting on sepsis-induced blood-brain barrier dysfunction, brain oxidative stress and inflammation have been tested in septic animals but not yet in patients.

Understanding brain dysfunction in sepsis

Sepsis often is characterized by an acute brain dysfunction, which is associated with increased morbidity and mortality. Its pathophysiology is highly complex, resulting from both inflammatory and noninflammatory processes, which may induce significant alterations in vulnerable areas of the brain. Important mechanisms include excessive microglial activation, impaired cerebral perfusion, blood-brain-barrier dysfunction, and altered neurotransmission. Systemic insults, such as prolonged inflammation, severe hypoxemia, and persistent hyperglycemia also may contribute to aggravate sepsis-induced brain dysfunction or injury. The diagnosis of brain dysfunction in sepsis relies essentially on neurological examination and neurological tests, such as EEG and neuroimaging. A brain MRI should be considered in case of persistent brain dysfunction after control of sepsis and exclusion of major confounding factors. Recent MRI studies suggest that septic shock can be associated with acute cerebrovascular lesions and white matter abnormalities. Currently, the management of brain dysfunction mainly consists of control of sepsis and prevention of all aggravating factors, including metabolic disturbances, drug overdoses, anticholinergic medications, withdrawal syndromes, and Wernicke's encephalopathy. Modulation of microglial activation, prevention of blood-brain-barrier alterations, and use of antioxidants represent relevant therapeutic targets that may impact significantly on neurologic outcomes. In the future, investigations in patients with sepsis should be undertaken to reduce the duration of brain dysfunction and to study the impact of this reduction on important health outcomes, including functional and cognitive status in survivors.

Neuro-oxidative-nitrosative stress in sepsis

Neuro-oxidative-nitrosative stress may prove the molecular basis underlying brain dysfunction in sepsis. In the current review, we describe how sepsis-induced reactive oxygen and nitrogen species (ROS/RNS) trigger lipid peroxidation chain reactions throughout the cerebrovasculature and surrounding brain parenchyma, due to failure of the local antioxidant systems. ROS/RNS cause structural membrane damage, induce inflammation, and scavenge nitric oxide (NO) to yield peroxynitrite (ONOO(-)). This activates the inducible NO synthase, which further compounds ONOO(-) formation. ROS/RNS cause mitochondrial dysfunction by inhibiting the mitochondrial electron transport chain and uncoupling oxidative phosphorylation, which ultimately leads to neuronal bioenergetic failure. Furthermore, in certain 'at risk' areas of the brain, free radicals may induce neuronal apoptosis. In the present review, we define a role for ROS/RNS-mediated neuronal bioenergetic failure and apoptosis as a primary mechanism underlying sepsis-associated encephalopathy and, in sepsis survivors, permanent cognitive deficits.

Sepsis-associated encephalopathy: not just delirium

Sepsis is a major cause of mortality and morbidity in intensive care units. Organ dysfunction is triggered by inflammatory insults and tissue hypoperfusion. The brain plays a pivotal role in sepsis, acting as both a mediator of the immune response and a target for the pathologic process. The measurement of brain dysfunction is difficult because there are no specific biomarkers of neuronal injury, and bedside evaluation of cognitive performance is difficult in an intensive care unit. Although sepsis-associated encephalopathy was described decades ago, it has only recently been subjected to scientific scrutiny and is not yet completely understood. The pathophysiology of sepsis-associated encephalopathy involves direct cellular damage to the brain, mitochondrial and endothelial dysfunction and disturbances in neurotransmission. This review describes the most recent findings in the pathophysiology, diagnosis, and management of sepsis-associated encephalopathy and focuses on its many presentations.

Sepsis-associated encephalopathy and its differential diagnosis

Sepsis-associated encephalopathy (SAE) is defined as a diffuse cerebral dysfunction resulting from the systemic inflammatory response to an infection without direct infestation of the CNS. Although the pathophysiology of SAE is as yet unknown, some mechanisms have been suggested that involve BBB disruption as a consequence of proinflammatory mediators’ effects on endothelial cells. This leads to an increased passage of neurotoxic and proinflammatory mediators into the brain parenchyma, as well as an impairment of the movements of oxygen and metabolites through the BBB. Both neurons and glial cells are affected, resulting in neural functioning and neurotransmission impairment. The clinical translation of this process is an alteration of consciousness and awareness. SAE is a frequent condition in septic patients. Despite being considered reversible, SAE appears to be associated with long-term cognitive impairment. Detection and diagnosis can be challenging; it requires daily neurological assessment with the assistance of clinical scores. Use of biomarkers and neurophysiological testing is discussed. The aim of this article is to provide practical tools for detection of SAE, as well as an updated overview of its pathophysiology and therapeutic perspectives.

[Delirium in the intensive care unit]

In recent years delirium in the intensive care unit (ICU) has internationally become a matter of rising concern for intensive care physicians. Due to the design of highly sophisticated ventilators the practice of deep sedation is nowadays mostly obsolete. To assess a ventilated ICU patient for delirium easy to handle bedside tests have been developed which permit a psychiatric scoring. The significance of ICU delirium is equivalent to organ failure and has been proven to be an independent prognostic factor for mortality and length of ICU and hospital stay. The pathophysiology and risk factors of ICU delirium are still insufficiently understood in detail. A certain constellation of pre-existing patient-related conditions, the current diagnosis and surgical procedure and administered medication entail a higher risk for the occurrence of ICU delirium. A favored hypothesis is that an imbalance of the neurotransmitters acetylcholine and dopamine serotonin results in an unpredictable neurotransmission. Currently, the administration of neuroleptics, enforced physiotherapy, re-orientation measures and appropriate pain treatment are the basis of the therapeutic approach.

Sepsis-associated encephalopathy and its differential diagnosis

Sepsis is often complicated by an acute and reversible deterioration of mental status, which is associated with increased mortality and is consistent with delirium but can also be revealed by a focal neurologic sign. Sepsis-associated encephalopathy is accompanied by abnormalities of electroencephalogram and somatosensory-evoked potentials, increased in biomarkers of brain injury (i.e., neuron-specific enolase, S-100 beta-protein) and, frequently, by neuroradiological abnormalities, notably leukoencephalopathy. Its mechanism is highly complex, resulting from both inflammatory and noninflammatory processes that affect all brain cells and induce blood-brain barrier breakdown, dysfunction of intracellular metabolism, brain cell death, and brain injuries. Its diagnosis relies essentially on neurologic examination that can lead one to perform specific neurologic tests. Electroencephalography is required in the presence of seizure; neuroimaging in the presence of seizure, focal neurologic signs or suspicion of cerebral infection; and both when encephalopathy remains unexplained. In practice, cerebrospinal fluid analysis should be performed if there is any doubt of meningitis. Hepatic, uremic, or respiratory encephalopathy, metabolic disturbances, drug overdose, withdrawal of sedatives or opioids, alcohol withdrawal delirium, and Wernicke's encephalopathy are the main differential diagnoses of sepsis-associated encephalopathy. Patient management is based mainly on controlling infection, organ system failure, and metabolic homeostasis, at the same time avoiding neurotoxic drugs.

Low dose dexamethasone reverses depressive-like parameters and memory impairment in rats submitted to sepsis

Sepsis is characterized by a systemic inflammatory response of the immune system against an infection, presenting with hypothalamic-pituitary-adrenal (HPA) axis dysfunction, behavior alterations, and high mortality. In this study, we aimed to evaluate the effects of dexamethasone on mortality, anhedonia, circulating corticosterone and adrenocorticotropin hormone (ACTH) levels, body and adrenal gland weight, and aversive memory in sepsis survivor rats. Male Wistar rats underwent sham operation or cecal ligation and perforation (CLP) procedure. Rats subjected to CLP were treated with "basic support" and dexamethasone (at 0.2 and 2mg/kg daily for 7 days after CLP, intraperitonially) or saline. After 10 days of sepsis procedure, it was evaluated aversive memory, sweet food consumption, and body and adrenal gland weight. Serum and plasma were also obtained. It was observed that low dose dexamethasone reverted anhedonia, normalized adrenal gland and body weight, corticosterone and ACTH levels, and decreased mortality and avoidance memory impairment, demonstrating that low doses of dexamethasone for moderate periods may be beneficial for sepsis treatment and its sequelae-depressive-like parameters and memory impairment.

Cerebral net exchange of large neutral amino acids after lipopolysaccharide infusion in healthy humans

INTRODUCTION

Alterations in circulating large neutral amino acids (LNAAs), leading to a decrease in the plasma ratio between branched-chain and aromatic amino acids (BCAA/AAA ratio), may be involved in sepsis-associated encephalopathy. We hypothesised that a decrease in the BCAA/AAA ratio occurs along with a net cerebral influx of the neurotoxic AAA phenylalanine in a human experimental model of systemic inflammation.

METHODS

The BCAA/AAA ratio, the cerebral delivery, and net exchange of LNAAs and ammonia were measured before and 1 hour after a 4-hour intravenous infusion of Escherichia coli lipopolysaccharide (LPS) in 12 healthy young men.

RESULTS

LPS induced systemic inflammation, reduced the BCAA/AAA ratio, increased the cerebral delivery and unidirectional influx of phenylalanine, and abolished the net cerebral influx of the BCAAs leucine and isoleucine. Furthermore, a net cerebral efflux of glutamine, which was independent of the cerebral net exchange of ammonia, was present after LPS infusion.

CONCLUSIONS

Systemic inflammation may affect brain function by reducing the BCAA/AAA ratio, thereby changing the cerebral net exchange of LNAAs.

The encephalopathy in sepsis

Brain dysfunction is a severe complication of sepsis with an incidence ranging from 9% to 71% that is associated with increased morbidity and mortality. Its diagnosis relies mainly on neurologic examination with clinical manifestations ranging from confusion to coma. An electroencephalogram, somatosensory evoked potentials, and measurement of plasma S-100b protein and neuron-specific enolase can be useful for the detection of brain dysfunction. Brain MRI can identify brain lesions such as cerebral infarction, posterior reversible encephalopathy syndrome, and leukoencephalopathy. The mechanism of sepsis-associated encephalopathy involves inflammatory and non-inflammatory processes that affect endothelial cells, glial cells, and neurons and induce blood-brain barrier breakdown, derangements of intracellular metabolism, and cell death. Specific treatments for sepsis-associated encephalopathy need to be developed. Currently, treatment is mainly the management of sepsis.

Comparative effects of propofol vs dexmedetomidine on cerebrovascular carbon dioxide reactivity in patients with septic shock

BACKGROUND

The use of sedative drugs is reportedly related to altered cerebrovascular CO2 reactivity. The present study examined the comparative effects of propofol vs dexmedetomidine on cerebrovascular CO2 reactivity in patients with septic shock.

METHODS

A total of 20 patients with septic shock who required mechanical ventilation were included in this study. Sedation during mechanical ventilation was maintained using either propofol or dexmedetomidine. A 2.5 MHz pulsed transcranial Doppler probe was attached to the head of the patient at the right temporal window for continuous measurement of mean blood flow velocity in the middle cerebral artery (V(mca)). After establishing baseline values of V(mca) and cardiovascular haemodynamics, end-tidal CO2 was increased by decreasing ventilatory frequency by 5-8 bpm.

RESULTS

The absolute and relative CO2 reactivity values in patients with septic shock were lower for both propofol and dexmedetomidine than those for control groups, with significant differences between these values in the two septic shock groups (absolute CO2 reactivity in septic shock under propofol: 2.6 (sd 0.3) cm s(-1) mm Hg(-1); absolute CO2 reactivity in septic shock under dexmedetomidine: 2.0 (0.3) cm s(-1) mm Hg(-1); P<0.01).

CONCLUSIONS

This study showed that cerebrovascular CO2 reactivity was lower under dexmedetomidine sedation than under propofol sedation during almost identical sedation in patients with septic shock.

Sepsis-associated delirium

OBJECTIVE

Sepsis-associated delirium is a common and poorly understood neurological complication of sepsis. This review provides an update of the diagnostic criteria and treatment strategies and the current knowledge about the mechanisms involved in sepsis associated brain dysfunction.

DATA SOURCES

Articles published between 1981 and 2006 were identified through a Medline search for "encephalopathy" and "sepsis" and by hand searching of articles cited in the identified publications. The immune response to sepsis results in multiorgan failure including brain dysfunction.

DISCUSSION

The potential mechanisms for sepsis-associated delirium include vascular damage, endothelial activation, breakdown of the blood-brain barrier, metabolic disorders, brain inflammation and apoptosis. On the other hand, there is evidence for distinct neuroprotective factors, such as anti-inflammatory mediators and glial cell activity.

CONCLUSIONS

The diagnosis of sepsis-associated delirium relies mainly on clinical and electrophysiological criteria, and its treatment is entirely based on general management of sepsis.

Pathogenesis of hepatic encephalopathy: the tumour necrosis factor-alpha theory

Hepatic encephalopathy (HE) is a major complication for acute and chronic liver failure. Despite several decades of intensive clinical and basic research, the pathogenesis of HE is still incompletely understood, and the precise mechanisms causing brain dysfunction in liver failure are still not fully established. Several theories concerning the pathogenesis of HE have been previously suggested, including the ammonia theory, which received the most attention. These theories are not mutually exclusive and the validity of none of them has been definitely proved experimentally. In this review article, an attractive theory concerning the pathogenesis of HE, the tumour necrosis factor-alpha (TNF) theory, is presented and comprehensively discussed after accumulation of sufficient data which indicate that the pro-inflammatory cytokine, TNF, is strongly involved in the pathogenesis of HE associated with both acute and chronic liver failure. This theory seems to be superior to all other previous theories in the pathogenesis of HE, and may induce development of other beneficial therapeutical modalities for HE directed towards inhibition of TNF production and/or action, and towards enhancement of its degradation.

Hormone, cytokine, and nutritional regulation of sepsis-induced increases in atrogin-1 and MuRF1 in skeletal muscle

Various atrophic stimuli increase two muscle-specific E3 ligases, muscle RING finger 1 (MuRF1) and atrogin-1, and knockout mice for these "atrogenes" display resistance to denervation-induced atrophy. The present study determined whether increased atrogin-1 and MuRF1 mRNA are mediated by overproduction of endogenous glucocorticoids or inflammatory cytokines in adult rats and whether atrogene expression can be downregulated by anabolic agents such as insulin-like growth factor (IGF)-I and the nutrient-signaling amino acid leucine. Both atrogin-1 and MuRF1 mRNA in gastrocnemius was upregulated dose and time dependently by endotoxin. Additionally, peritonitis produced by cecal ligation and puncture increased atrogin-1 and MuRF1 mRNA in gastrocnemius (but not soleus or heart) by 8 h, which was sustained for 72 and 24 h, respectively. Whereas the sepsis-induced increase in atrogin-1 expression was completely prevented by IGF-I, the increased MuRF1 was not altered. In contrast to the IGF-I effect, the sepsis-induced increased mRNA of both atrogenes was unresponsive to either acute or repetitive administration of leucine. Whereas exogenous infusion of TNF-alpha increased atrogin-1 and MuRF1 in gastrocnemius, pretreatment of septic rats with the TNF antagonist TNF-binding protein did not prevent increased expression of either atrogene. Similarly, whereas dexamethasone increased atrogene expression, pretreatment with the glucocorticoid receptor antagonist RU-486 failed to ameliorate the sepsis-induced increase in atrogin-1 and MuRF1. Thus, under in vivo conditions in mature adult rats, the sepsis-induced increase in muscle atrogin-1 and MuRF1 mRNA appears both glucocorticoid and TNF independent and is unresponsive to leucine.

Effects of AM281, a cannabinoid antagonist, on circulatory deterioration and cytokine production in an endotoxin shock model: comparison with norepinephrine

PURPOSE

The purpose of this study was to examine the comparative effects of AM281, a cannabinoid antagonist, and norepinephrine (NE) on systemic hemodynamics, and renal and mesenteric artery blood flow in an endotoxin shock model.

METHODS

The study was designed to include two sets of experiments: (1) measurements of changes in systemic hemodynamics and organ artery blood flows (n = 20), and (2) measurements of biochemical variables (n = 20). For each set of experiments, male 7-week-old Wistar rats were randomly divided into four groups: group 1, controls (n = 5); group 2, receiving lipopolysaccharide (LPS: Escherichia coli endotoxin, 10.0 mg.kg(-1) intravenous bolus) (n = 5); group 3, receiving intravenous LPS and NE (continuous infusion at 0.2 microg.kg.min(-1)) (n = 5); group 4, receiving LPS and AM281 (0.1 mg.kg.min(-1)) (n = 5). Systemic hemodynamics, regional artery blood flow changes, and biochemical variables were assessed before treatment and 1 and 3 h after treatment.

RESULTS

Infusion of NE or AM281 prevented endotoxin-induced decreases in systemic arterial pressure, aortic blood flow, carotid artery blood flow, and renal artery blood flow. Both AM281 and NE inhibited endotoxin-induced increases in cytokine production, with significant differences observed among the three groups at 1 and 3 h after treatment. Endotoxin-induced decreases in mesenteric arterial blood flow were restored by AM281 but not by NE. AM281 improved arterial oxygenation and reduced lactate overproduction and body temperature elevation induced by endotoxin.

CONCLUSIONS

Although NE and AM281 both prevented endotoxin-induced deterioration of systemic hemodynamics, AM281 yielded better preservation of mesenteric blood flow and attenuation of cytokine production than NE.

Environmental and immune stressors enhance alcohol-induced motor ataxia in rat

Infection is now accepted as a stressor, consequently we sought to compare the short- and longer-term consequences of several environmental stressors versus an endotoxin challenge on alcohol-induced motor ataxia. The present set of studies examined the impact of intermittent electric shock (SHOCK), intermittent cold water swim (ICWS), or lipopolysaccharide (LPS) administration on the motor ataxic effects of an intraperitoneal (i.p.) injection of alcohol (ETOH). In Experiment 1 SHOCK, but not ICWS, enhanced the motor ataxic effects of ethanol at both 2 and 24 h post-stress. In Experiment 2 administration of LPS did not affect the motor ataxic effects of ETOH 4 h later, but enhanced the ataxic potency of ETOH 24 h later. The results indicate that certain environmental and immune stressors have the potential to alter the long-term behavioral reactivity to alcohol. These examples of stress-induced enhancement of the motor ataxic effects of ETOH may have important implications for the development of alcohol dependence.

Cannabinoid antagonist AM 281 reduces mortality rate and neurologic dysfunction after cecal ligation and puncture in rats

OBJECTIVES

The purpose of this study was to examine whether anandamide, an endogenous cannabinoid receptor ligand, is involved in the pathogenesis of septic encephalopathy.

DESIGN

Prospective, controlled study.

SUBJECTS

Male Wistar rats (7 wks old) were randomly divided into four groups as follows: group 1, control (0.5 mL of saline injected subcutaneously); group 2, sham (surgical abdominal incision and suturing were performed, but ligation and puncture of the cecum were omitted); group 3, cecal ligation and puncture (CLP); group 4, CLP + AM 281 ([N-morpholin-4-yl]-5-[2,4-yl]-5-[2,4-dichlorophenyl]-4-methyl-1H-pyrazole-3-carboxamide) as the cannabinoid receptor antagonist (1 mg/kg intraperitoneally).

INTERVENTIONS

Sepsis was induced by CLP under pentobarbital anesthesia (10 mg/kg intraperitoneally) with 1% isoflurane. A 2-Fr high-fidelity micromanometer catheter was inserted into the left ventricle via the right carotid artery to assess hemodynamics. Each of the rats was neurologically assessed at 30 mins and 12, 24, and 48 hrs after the treatment. The cytoplasmic levels of caspase-3 in the hippocampi were assayed before surgery and at 30 mins and 24 and 48 hrs after surgery using Western blotting techniques. To examine the effects of AM 281 on neurologic function and mortality rate, we set another control group treated solely with AM 281. Selective inducible nitric oxide synthase inhibitor, L-N6-(1-iminoethyl)-lysine (4 mg/kg), was injected intraperitoneally immediately after CLP to produce the CLP + L-N6-(1-iminoethyl)-lysine group to exclude the influence of depressed hemodynamics on neurologic impairment.

MEASUREMENTS AND MAIN RESULTS

It was found that administration of AM 281 could prevent the hemodynamic changes induced by sepsis. Reflex responses, including the pinna, corneal, paw or tail flexion, and righting reflexes, and the escape response significantly decreased in the CLP and CLP + L-N6-(1-iminoethyl)-lysine groups at 48 hrs after the surgery. In contrast, no changes in these reflex responses were found between the CLP + AM 281 and control and sham groups. In addition, no effects of the administration of AM 281 on neurologic function and mortality rate in the control group were found. Tissue caspase-3 levels were elevated at 48 hrs after CLP in the CLP alone group (means +/- sd: control, 3.9 +/- 0.4; sham, 4.2 +/- 0.4; CLP, 7.1 +/- 1.0 [p < .01]; CLP + AM 281, 4.0 +/- 0.5 densitometric units). In addition, administration of AM 281 also decreased the mortality rate (p < .05).

CONCLUSIONS

Administration of AM 281 prevented the hemodynamic changes and development of neurologic dysfunction occurring in association with septic shock, and could decrease the mortality rate in experimentally induced septic shock in rats. Although further studies are necessary to determine whether endogenous cannabinoids cause septic encephalopathy in rats directly or via their effects on systemic hemodynamics, the beneficial effects of AM 281 on these rats might have significant therapeutic implications in cases of septic encephalopathy.

Effects of AM281, a cannabinoid antagonist, on systemic haemodynamics, internal carotid artery blood flow and mortality in septic shock in rats

INTRODUCTION

The purpose of this study was to examine the effects of AM281, a cannabinoid receptor antagonist, on systemic haemodynamics, internal carotid artery blood flow and mortality during septic shock in rats.

METHODS

The study included three sets of experiments: measurements of changes in systemic haemodynamics and left internal carotid artery flow (30 animals divided into three groups of 10); measurements of biochemical variables (n=30); assessment of mortality (n=30). Male Wistar rats (7 weeks old) were randomly divided into three groups: group 1, control; group 2, lipopolysaccharide (LPS) i.v., Escherichia coli endotoxin 10.0 mg kg(-1) i.v., bolus; group 3, LPS 10.0 mg kg(-1) i.v.+AM281 1 mg kg(-1) i.v. Systemic haemodynamics, carotid artery flow changes and biochemical variables were assessed at pretreatment and 1, 2 and 3 h after the treatment was performed.

RESULTS

Administration of AM281 could prevent the haemodynamic changes induced by sepsis. Tumour necrosis factor-alpha and interleukin 1-beta increased in the LPS i.v. and LPS i.v.+AM281 groups at 1, 2 and 3 h after treatment; significant differences were observed in these levels in the two groups at these times. Internal carotid artery blood flow remained fairly constant in the control and LPS i.v.+AM281 groups compared with baseline values. In the LPS i.v. group, it decreased at 2 and 3 h after the treatment compared with baseline values [at 2 h: control 12.7 (SD 0.9) ml min(-1), LPS i.v. 8.7 (1.4) ml min(-1) (P<0.05), LPS i.v.+AM281 11.5 (0.9) ml min(-1); at 3 h: control 12.7 (0.4) ml min(-1), LPS i.v. 7.7 (1.3) ml min(-1) (P<0.05), LPS i.v.+AM281 11.6 (1.0) ml min(-1)]. Significant differences in mortality within 6 and 12 h were found between the LPS i.v. and LPS i.v.+AM281 groups [6 h mortality: LPS i.v. 5/10 (50%), LPS i.v.+AM281 2/10 (20%), P<0.05; 12 h mortality: LPS i.v. group 10/10 (100%), LPS i.v.+AM281 5/10 (50%), P<0.05].

CONCLUSIONS

Administration of AM281 prevented changes in systemic haemodynamic and internal carotid artery blood flow and could improve mortality in experimentally induced septic shock in rats. These findings may have significant therapeutic implications in the treatment of septic shock.

Science review: The brain in sepsis--culprit and victim

On one side, brain dysfunction is a poorly explored complication of sepsis. On the other side, brain dysfunction may actively contribute to the pathogenesis of sepsis. The current review aimed at summarizing the current knowledge about the reciprocal interaction between the immune and central nervous systems during sepsis. The immune-brain cross talk takes part in circumventricular organs that, being free from blood-brain-barrier, interface between brain and bloodstream, in autonomic nuclei including the vagus nerve, and finally through the damaged endothelium. Recent observations have confirmed that sepsis is associated with excessive brain inflammation and neuronal apoptosis which clinical relevance remains to be explored. In parallel, damage within autonomic nervous and neuroendocrine systems may contribute to sepsis induced organ dysfunction.

Relationship between tumor necrosis factor-alpha and ammonia in patients with hepatic encephalopathy due to chronic liver failure

BACKGROUND

We have recently demonstrated that in humans, circulating levels of tumor necrosis factor-alpha (TNF) correlate positively with severity of hepatic encephalopathy (HE) due to chronic liver failure.AIM. The main aim of this larger population study is to determine the relationship between TNF and ammonia in patients with HE and chronic liver failure due to liver cirrhosis.

METHODS

Circulating levels of TNF and ammonia were measured in 108 patients with liver cirrhosis due to various etiologies in various clinical grades of HE (grades 0-4). TNF concentrations were measured in venous serum using commercially available solid-phase high sensitivity enzyme-linked immunosorbent assay. Ammonia levels were determined in venous plasma by the enzymatic method, using the glutamate dehydrogenase reaction.

RESULTS

The mean+/-SEM values of circulating levels of TNF and ammonia at presentation in patients with grade 0 of HE (n = 30) were 3.89+/-0.2 pg/mL and 49.8+/-2.8 microg/mL respectively, in patients with grade 1 of HE (n = 26) were 8.56+/-0.34 pg/mL and 101.6+/-6.5 microg/mL respectively, in patients with grade 2 of HE (n = 22) were 11.59+/-0.48 pg/mL and 160.3+/-10.7 microg/mL respectively, in patients with grade 3 of HE (n = 20) were 19.98+/-0.94 pg/mL and 228.8+/-16.1 microg/mL respectively, and in patients with grade 4 of HE (n = 10) were 51.53+/-8.59 pg/mL and 284.2+/-20.3 microg/mL respectively. A significant positive correlation was found between circulating levels of TNF and those of ammonia (r = 0.62, P< 0.0001), and also between circulating levels of both substances and severity of HE in these patients (r = 0.95, P<0.0001, and r = 0.9, P<0.0001 respectively). TNF and ammonia were both significant independent predictors of severity of HE (P<0.0001 for both variables).

CONCLUSION

The results of this study demonstrate a significant relationship between TNF and ammonia in patients with chronic liver failure and HE, and so strengthen the suggestion that TNF could be strongly involved in the pathogenesis of HE in these patients. Hence, we suggest a new theory in the pathogenesis of HE, the "TNF theory".

Selective inducible nitric oxide inhibition can restore hemodynamics, but does not improve neurological dysfunction in experimentally-induced septic shock in rats

In this study, we evaluated the time course of changes in inducible nitric oxide synthase (iNOS) in the brain by using the rat model of sepsis induced by cecal ligation and puncture (CLP) and examined whether selective iNOS inhibition can prevent the hemodynamic and neurological changes induced by sepsis. Male Wistar rats were randomly divided into four groups: control, sham, CLP, and CLP + the selective iNOS inhibitor L-N6-(1-iminoethyl)-lysine (L-NIL). Septic shock was induced in the rats by CLP under pentobarbital anesthesia, and then we measured hemodynamic variables, neurological indicators, blood gases, plasma levels of nitrate/nitrite (an indicator of the biosynthesis of NO), and brain iNOS activity and nitrotyrosine levels after 1, 6, 12, and 24 h. Plasma nitrite was increased at 12 and 24 h in the CLP group. The activity of iNOS in the brain was increased at 12 and 24 h after CLP (at 12 h: control, 0.3 +/- 0.05; sham, 0.3 +/- 0.1; CLP, 1.3 +/- 0.08*; CLP + L-NIL, 0.33 +/- 0.1 fmol x mg(-1) x min(-1); at 24 h: control, 0.27 +/- 0.08; sham, 0.31 +/- 0.1; CLP, 1.0 +/- 0.3*; CLP + L-NIL, 0.34 +/- 0.1 fmol x mg(-1) x min(-1); mean +/- SD; *P < 0.05). Brain nitrotyrosine was increased at 24 h after CLP (at 24 h: control, 6.7 +/- 0.4; sham, 6.7 +/- 0.5; CLP, 11.2 +/- 2.8*; CLP + L-NIL, 7.52 +/- 0.5 densitometric units; means +/- SD; *P < 0.01). In contrast, in both the CLP and CLP + L-NIL groups, the consciousness reflex was significantly decreased at 24 h after CLP. Selective iNOS inhibition restored the hemodynamic changes induced by sepsis but could not improve neurological dysfunction.

Serum levels of tumor necrosis factor-alpha correlate with severity of hepatic encephalopathy due to chronic liver failure

BACKGROUND

Several studies have shown that serum levels of tumor necrosis factor-alpha (TNF) are significantly elevated in patients with acute and chronic liver diseases, where these elevations are independent of the etiology of the underlying disease. Serum levels of TNF are significantly higher in patients with cirrhosis than in those without cirrhosis, reaching the highest levels in decompensated cirrhosis. It has also been shown that plasma levels of TNF correlate with the severity of hepatic encephalopathy (HE) in fulminant hepatic failure. However, still there are no published data regarding the relationship between blood levels of TNF and the presence or severity of HE in patients with chronic liver failure.

AIM

The aim of this study is to determine the relationship between serum levels of TNF and clinical grades of HE in patients with liver cirrhosis.

METHODS

Using a commercially available high-sensitivity enzyme-linked immunosorbent assay kit, serum levels of TNF were measured in 74 patients with liver cirrhosis in various clinical grades of HE (grades 0-4).

RESULTS

The mean+/-SEM values of serum levels of TNF at presentation in patients with grade 0 of HE (n=23), grade 1 (n=12), grade 2 (n=14), grade 3 (n=16), and grade 4 (n=9) were 4.50+/-0.46, 9.10+/-1.0, 12.98+/-1.22, 21.51+/-2.63, and 58.26+/-19.7 pg/ml, respectively. A significant positive correlation was found between serum levels of TNF and the severity of HE (P<0.0001).

CONCLUSION

Serum levels of TNF correlate positively with the severity of HE in patients with chronic liver failure.

The neuropathology of septic shock

The neuropathological correlates of encephalopathy and autonomic dysfunction in septic shock are unclear. We performed post mortem analysis of 5 brain areas susceptible to ischemia and 5 autonomic nuclei (AN) in 23 patients who had died in our intensive care unit (ICU) from septic shock and 8 dying from non-septic shock as well as 5 controls who had died suddenly from extracranial injury. Proinflammatory cytokine (IL1-beta and TNF-alpha) and inducible nitric oxide synthase (iNOS) expression was assessed by immunocytochemistry. Abnormalities in septic shock were: hemorrhages (26%), hypercoagulability syndrome (9%), micro-abscesses (9%), multifocal necrotizing leukoencephalopathy (9%) and ischemia (100%). The incidence of cerebral hemorrhage or hypercoagulability syndrome was not related to clotting disturbances. The intensity of ischemia within susceptible areas was the same in both ICU groups, but more pronounced in the autonomic centers of septic patients (P < 0.0001). Neuronal apoptosis assessed using anti-caspase 3 immunocytochemistry and in situ end labeling was more pronounced in the autonomic nuclei of septic patients. (P < 0.0001). TNF-alpha expression did not differ between groups but vascular iNOS expression assessed by immunocytochemistry was higher in sepsis (P<0.0001) and correlated with autonomic center neuronal apoptosis (P < 0.02). We conclude that septic shock is associated with diffuse cerebral damage and specific autonomic neuronal apoptosis which may be due to circulating factors particularly iNOS.