Impairment In Sepsis Survivors Research Articles

Potential of piperine for neuroprotection in sepsis-associated encephalopathy

AimsSepsis-associated encephalopathy (SAE) is a common complication that increases mortality and leads to long-term cognitive impairment in sepsis survivors. However, no specific or effective therapy has been identified for this complication. Piperine is an alkaloid known for its anti-inflammatory, antioxidant, and neuroprotective properties, which are important characteristics for treatment of SAE. The objective of this study was to evaluate the neuroprotective effect of piperine on SAE in C57BL/6 mice that underwent cecum ligation and perforation surgery (CLP). Main methodsC57BL/6 male mice were randomly assigned to groups that underwent SHAM surgery or CLP. Mice in the CLP group were treated with piperine at doses of 20 or 40 mg/kg for short- (5 days) or long-term (10 days) periods after CLP. Key findingsOur results revealed that untreated septic animals exhibited increased concentrations of IL-6, TNF, VEGF, MMP-9, TBARS, and NLRP3, and decreased levels of BDNF, sulfhydryl groups, and catalase in the short term. Additionally, the levels of carbonylated proteins and degenerated neuronal cells were increased at both time points. Furthermore, short-term and visuospatial memories were impaired. Piperine treatment reduced MMP-9 activity in the short term and decreased the levels of carbonylated proteins and degenerated neuronal cells in the long term. It also lowered IL-6 and TBARS levels at both time points evaluated. Moreover, piperine increased short-term catalase and long-term BDNF factor levels and improved memory at both time points. SignificanceIn conclusion, our data demonstrate that piperine exerts a neuroprotective effect on SAE in animals that have undergone CLP.

Rosmarinic acid against cognitive impairment via RACK1/HIF-1α regulated microglial polarization in sepsis-surviving mice

Microglial polarization modulation has been considered the potential therapeutic strategy for relieving cognitive impairment in sepsis survivors. Rosmarinic acid (RA), a water-soluble polyphenolic natural compound, processes a strong protective effect on various types of neurological disorders including Parkinson's disease, depression, and anxiety. However, its role and potential molecular mechanisms in sepsis-associated cognitive impairment remain unclear. To investigate the preventive and therapeutic effect of RA on sepsis-associated cognitive impairment and elucidate the potential mechanism of RA on regulating microglial polarization, we established a CLP-induced cognitive impairment model in mice and a lipopolysaccharide-induced microglia polarization cell model in BV-2. RACK1 siRNA was designed to identify the potential molecular mechanism of RACK1 on microglial polarization. The preventive and therapeutic effect of RA on cognitive impairment followed by PET-CT and behavioral tests including open-field test and tail suspension test. RACK1/HIF-1α pathway and microglial morphology in the hippocampus or BV-2 cells were measured. The results showed that RA significantly ameliorated the CLP-induced depressive and anxiety-like behaviors and promoted whole-brain glucose uptake in mice. Moreover, RA markedly improved CLP-induced hippocampal neuron loss and microglial activation by inhibiting microglial M1 polarization. Furthermore, experiments showed RACK1 was involved in the regulation of LPS-induced microglial M1 polarization via HIF-1α, and RA suppressed lipopolysaccharide or sepsis-associated microglial M1 polarization via RACK1/HIF-1α pathway (rescued the decrease of RACK1 and increase of HIF-1α). Taken together, RA could be a potential preventive and therapeutic medication in improving cognitive impairment through RACK1/HIF-1α pathway-regulated microglial polarization.

A crosstalk between gut and brain in sepsis-induced cognitive decline

BackgroundSepsis is a potentially fatal disease characterized by acute organ failure that affects more than 30 million people worldwide. Inflammation is strongly associated with sepsis, and patients can experience impairments in memory, concentration, verbal fluency, and executive functioning after being discharged from the hospital. We hypothesize that sepsis disrupts the microbiota–gut–brain axis homeostasis triggering cognitive impairment. This immune activation persists during treatment, causing neurological dysfunction in sepsis survivors.MethodsTo test our hypothesis, adult Wistar rats were subjected to cecal–ligation and perforation (CLP) or sham (non-CLP) surgeries. The animals were subjected to the [11C]PBR28 positron emission tomography (PET)/computed tomography (CT) imaging at 24 h and 10 days after CLP and non-CLP surgeries. At 24 h and 10 days after surgery, we evaluated the gut microbiome, bacterial metabolites, cytokines, microglia, and astrocyte markers. Ten days after sepsis induction, the animals were subjected to the novel object recognition (NOR) and the Morris water maze (MWM) test to assess their learning and memory.ResultsCompared to the control group, the 24-h and 10-day CLP groups showed increased [11C]PBR28 uptake, glial cells count, and cytokine levels in the brain. Results show that sepsis modulates the gut villus length and crypt depth, alpha and beta microbial diversities, and fecal short-chain fatty acids (SCFAs). In addition, sepsis surviving animals showed a significant cognitive decline compared with the control group.ConclusionsSince several pharmacological studies have failed to prevent cognitive impairment in sepsis survivors, a better understanding of the function of glial cells and gut microbiota can provide new avenues for treating sepsis patients.

Mitochondrial Transplantation Attenuates Brain Dysfunction in Sepsis by Driving Microglial M2 Polarization.

Activation of microglia and mitochondrial dysfunction are two major contributors to the pathogenesis of sepsis-associated brain dysfunction. Mitochondrial dysfunction can alter the immunological profile of microglia favoring to a pro-inflammatory phenotype. Mitochondrial transplantation, as an emerging mitochondria-targeted therapy, possesses considerable therapeutic potential in various central nervous system injuries or diseases. However, the effects of mitochondrial transplantation on microglial polarization and neuroprotection after sepsis remain unclear. In this study, lipopolysaccharide (LPS)/interferon-γ (IFN-γ) and interleukin-4 (IL-4)/interleukin-13 (IL-13) were used to induce different phenotypes of BV2 microglial cells. We observed that mitochondrial content and function were enhanced in IL-4-/IL-13-stimulated microglia. In vitro, mitochondria treatment conferred neuroprotection by enhancing microglial polarization from the M1 phenotype to the M2 phenotype and suppressing microglial-derived inflammatory cytokine release. Furthermore, microglial phenotypes and behavior tests were assessed after mice were subjected to sepsis by cecal ligation and puncture (CLP) followed by intracerebroventricular injection of exogenous functional mitochondria. We found that mitochondrial transplantation induced microglial M2 rather than M1 response 24h after sepsis. Mitochondrial transplantation improved behavioral deficits by increasing the latency time in inhibitory avoidance test and decreasing the number of crossing and rearing in the test session of open field test 10days after CLP onset. These findings indicate that mitochondrial transplantation promotes the phenotypic conversion of microglia and improves cognitive impairment in sepsis survivors, supporting the potential use of exogenous mitochondrial transplantation therapy that may be a potential therapeutic opportunity for sepsis-associated brain dysfunction.

Sepsis-Associated Encephalopathy: From Delirium to Dementia?

Sepsis is a major cause of death in intensive care units worldwide. The acute phase of sepsis is often accompanied by sepsis-associated encephalopathy, which is highly associated with increased mortality. Moreover, in the chronic phase, more than 50% of surviving patients suffer from severe and long-term cognitive deficits compromising their daily quality of life and placing an immense burden on primary caregivers. Due to a growing number of sepsis survivors, these long-lasting deficits are increasingly relevant. Despite the high incidence and clinical relevance, the pathomechanisms of acute and chronic stages in sepsis-associated encephalopathy are only incompletely understood, and no specific therapeutic options are yet available. Here, we review the emergence of sepsis-associated encephalopathy from initial clinical presentation to long-term cognitive impairment in sepsis survivors and summarize pathomechanisms potentially contributing to the development of sepsis-associated encephalopathy.

Mitochondrial dysfunction is associated with long-term cognitive impairment in an animal sepsis model.

Background: Several different mechanisms have been proposed to explain long-term cognitive impairment in sepsis survivors. The role of persisting mitochondrial dysfunction is not known. We thus sought to determine whether stimulation of mitochondrial dynamics improves mitochondrial function and long-term cognitive impairment in an experimental model of sepsis.Methods: Sepsis was induced in adult Wistar rats by cecal ligation and perforation (CLP). Animals received intracerebroventricular injections of either rosiglitazone (biogenesis activator), rilmenidine, rapamycin (autophagy activators), or n-saline (sham control) once a day on days 7-9 after the septic insult. Cognitive impairment was assessed by inhibitory avoidance and object recognition tests. Animals were killed 24 h, 3 and 10 days after sepsis with the hippocampus and prefrontal cortex removed to determine mitochondrial function.Results: Sepsis was associated with both acute (24 h) and late (10 days) brain mitochondrial dysfunction. Markers of mitochondrial biogenesis, autophagy and mitophagy were not up-regulated during these time points. Activation of biogenesis (rosiglitazone) or autophagy (rapamycin and rilmenidine) improved brain ATP levels and ex vivo oxygen consumption and the long-term cognitive impairment observed in sepsis survivors.Conclusion: Long-term impairment of brain function is temporally related to mitochondrial dysfunction. Activators of autophagy and mitochondrial biogenesis could rescue animals from cognitive impairment.

PET imaging of TSPO in a rat model of sepsis induced by peritoneal polymicrobial infection

Abstract Background Sepsis is a life-threatening acute organ dysfunction secondary to infection that affects more than 30 million people worldwide. In the USA, 1.5 million people develop sepsis, and at least 250,000 Americans die from sepsis each year. After hospitalization, patients suffer from long-term impairments in memory, attention, verbal fluency, and executive functioning. The translocator protein (TSPO), marker of activated microglia astrocytes cells, can be measured in vivo using positron emission tomography (PET). Our working hypothesis is that systemic inflammation associated with sepsis activate microglia cells, which will later lead to further long-term cognitive impairment in sepsis survivors. Methods To test this hypothesis, adult male Wistar rats were subjected to a gold standard sepsis model induced by cecal ligation and perforation (CLP) surgery to induce peritoneal poly microbial sepsis or sham surgery as a control group. At 24 hour after the surgery the animals were subjected to translocator protein (TSPO) microPET imaging with [11C]PBR28. Following the imaging, TSPO, cytochrome C, cytokines/chemokines, microglia (Iba-1) and astrocyte marker (GFAP) were measured in the prefrontal cortex and hippocampus of the septic animals. Results septic animals presented and increased uptake of [11C]PBR28-microglia activation in the whole brain compared to control at 24 after the CLP surgery. The expression of IL-1α, IL-1β, IL-6, IL-18, TNF-α, IFN-γ and Iba-1 increased in the hippocampus of septic rat. Conclusion The upregulation of TSPO expression in the hippocampus of septic rat brain is a possible mechanism associated with long-term cognitive impairment in sepsis survivors.

Targeting the Blood-Brain Barrier to Prevent Sepsis-Associated Cognitive Impairment.

Sepsis is a systemic inflammatory disease resulting from an infection. This disorder affects 750 000 people annually in the United States and has a 62% rehospitalization rate. Septic symptoms range from typical flu-like symptoms (eg, headache, fever) to a multifactorial syndrome known as sepsis-associated encephalopathy (SAE). Patients with SAE exhibit an acute altered mental status and often have higher mortality and morbidity. In addition, many sepsis survivors are also burdened with long-term cognitive impairment. The mechanisms through which sepsis initiates SAE and promotes long-term cognitive impairment in septic survivors are poorly understood. Due to its unique role as an interface between the brain and the periphery, numerous studies support a regulatory role for the blood-brain barrier (BBB) in the progression of acute and chronic brain dysfunction. In this review, we discuss the current body of literature which supports the BBB as a nexus which integrates signals from the brain and the periphery in sepsis. We highlight key insights on the mechanisms that contribute to the BBB’s role in sepsis which include neuroinflammation, increased barrier permeability, immune cell infiltration, mitochondrial dysfunction, and a potential barrier role for tissue non-specific alkaline phosphatase (TNAP). Finally, we address current drug treatments (eg, antimicrobials and intravenous immunoglobulins) for sepsis and their potential outcomes on brain function. A comprehensive understanding of these mechanisms may enable clinicians to target specific aspects of BBB function as a therapeutic tool to limit long-term cognitive impairment in sepsis survivors.

Constitutive Vagus Nerve Activation Modulates Immune Suppression in Sepsis Survivors.

Patients surviving a septic episode exhibit persistent immune impairment and increased mortality due to enhanced vulnerability to infections. In the present study, using the cecal ligation and puncture (CLP) model of polymicrobial sepsis, we addressed the hypothesis that altered vagus nerve activity contributes to immune impairment in sepsis survivors. CLP-surviving mice exhibited less TNFα in serum following administration of LPS, a surrogate for an infectious challenge, than control-operated (control) mice. To evaluate the role of the vagus nerve in the diminished response to LPS, mice were subjected to bilateral subdiaphragmatic vagotomy at 2 weeks post-CLP. CLP-surviving vagotomized mice exhibited increased serum and tissue TNFα levels in response to LPS-challenge compared to CLP-surviving, non-vagotomized mice. Moreover, vagus nerve stimulation in control mice diminished the LPS-induced TNFα responses while having no effect in CLP mice, suggesting constitutive activation of vagus nerve signaling in CLP-survivors. The percentage of splenic CD4+ ChAT-EGFP+ T cells that relay vagus signals to macrophages was increased in CLP-survivors compared to control mice, and vagotomy in CLP-survivors resulted in a reduced percentage of ChAT-EGFP+ cells. Moreover, CD4 knockout CLP-surviving mice exhibited an enhanced LPS-induced TNFα response compared to wild-type mice, supporting a functional role for CD4+ ChAT+ T cells in mediating inhibition of LPS-induced TNFα responses in CLP-survivors. Blockade of the cholinergic anti-inflammatory pathway with methyllcaconitine, an α7 nicotinic acetylcholine receptor antagonist, restored LPS-induced TNFα responses in CLP-survivors. Our study demonstrates that the vagus nerve is constitutively active in CLP-survivors and contributes to the immune impairment.

Vagal tonic activity modulates immune suppression in sepsis survivors

Abstract Sepsis survivors exhibit persistent immune dysfunction and compromised quality of life with premature mortality due to increased vulnerability to infections. Previously we demonstrated in a cecal ligation and puncture (CLP) model, sepsis survivors had a reduced TNFα response to LPS-challenge in vivo. The vagus nerve is known to modulate TNFα production. To evaluate the role of the vagus nerve in the diminished TNFα production, sepsis-surviving mice were subjected to bilateral subdiaphragmatic vagotomy 2 weeks post-CLP. CLP-surviving vagotomized mice exhibit increased (p<0.05) TNFα levels in response to LPS-challenge 4 weeks post surgery compared to CLP. Moreover, vagus nerve stimulation in sham mice dampened (p<0.05) the LPS-induced TNFα response while it had no effect in CLP-surviving mice; suggesting that vagus nerve signaling is constitutively active in CLP-sepsis survivors. To identify whether there was an alteration in the number of acetylcholine-producing T cells that relay the vagus signal to splenic macrophages, we used ChAT-EGFP mice. Our findings show that the frequency of splenic ChAT-EGFP+ cells among memory CD4+CD44highCD62LlowT cells is increased (p<0.001) in CLP-surviving mice compared to sham, and vagotomy in these mice resulted in decreased (p<0.01) frequency of ChAT-EGFP+ cells, buttressing the conclusion that the vagus nerve is constitutively firing action potentials to activate more ChAT+ T cells. Methyllycaconitine, the α7 nicotinic acetylcholine receptor antagonist, increased (p<0.01) LPS-induced TNFα secretion in CLP-surviving mice compared to saline treated-CLP. In summary, our study demonstrates that altered vagus nerve activity contributes to the immune impairment in sepsis survivors.

Brain-Defective Insulin Signaling Is Associated to Late Cognitive Impairment in Post-Septic Mice.

Sepsis survivors frequently develop late cognitive impairment. Because little is known on the mechanisms of post-septic memory deficits, there are no current effective approaches to prevent or treat such symptoms. Here, we subjected mice to severe sepsis induced by cecal ligation and puncture (CLP) and evaluated the sepsis-surviving animals in the open field, novel object recognition (NOR), and step-down inhibitory avoidance (IA) task at different times after surgery. Post-septic mice (30days post-surgery) failed in the NOR and IA tests but exhibited normal performance when re-evaluated 45days after surgery. Cognitive impairment in post-septic mice was accompanied by reduced hippocampal levels of proteins involved in synaptic plasticity, including synaptophysin, cAMP response element-binding protein (CREB), CREB phosphorylated at serine residue 133 (CREBpSer133), and GluA1 phosphorylated at serine residue 845 (GluA1pSer845). Expression of tumor necrosis factor α (TNF-α) was increased and brain insulin signaling was disrupted, as indicated by increased hippocampal IRS-1 phosphorylation at serine 636 (IRS-1pSer636) and decreased phosphorylation of IRS-1 at tyrosine 465 (IRS-1pTyr465), in the hippocampus 30days after CLP. Phosphorylation of Akt at serine 473 (AktpSer473) and of GSK3 at serine 9 (GSK3βpSer9) were also decreased in hippocampi of post-septic animals, further indicating that brain insulin signaling is disrupted by sepsis. We then treated post-septic mice with liraglutide, a GLP-1 receptor agonist with insulinotropic activity, or TDZD-8, a GSK3β inhibitor, which rescued NOR memory. In conclusion, these results establish that hippocampal inflammation and disrupted insulin signaling are induced by sepsis and are linked to late memory impairment in sepsis survivors.

CD40-CD40 Ligand Pathway is a Major Component of Acute Neuroinflammation and Contributes to Long-term Cognitive Dysfunction after Sepsis.

Sepsis-associated encephalopathy (SAE) is associated with an increased rate of morbidity and mortality. It is not understood what the exact mechanism is for the brain dysfunction that occurs in septic patients, but brain inflammation and oxidative stress are a possible theory. Such events can occur through the alteration of molecules that perpetuate the inflammatory response. Thus, it is possible to postulate that CD40 may be involved in this process. The aim of this work is to evaluate the role of CD40-CD40L pathway activation in brain dysfunction associated with sepsis in an animal model. Microglia activation induces the upregulation of CD40-CD40L, both in vitro and in vivo. The inhibition of microglia activation decreases levels of CD40-CD40L in the brain and decreases brain inflammation, oxidative damage and blood brain barrier dysfunction. Despite this, anti-CD40 treatment does not improve mortality in this model. However, it is able to improve long-term cognitive impairment in sepsis survivors. In conclusion, there is a major involvement of the CD40-CD40L signaling pathway in long-term brain dysfunction in an animal model of sepsis.

The role of microglia activation in the development of sepsis-induced long-term cognitive impairment.

Oxidative stress and inflammation is likely to be a major step in the development of sepsis-associated encephalopathy (SAE) and long-term cognitive impairment. To date, it is not known whether brain inflammation and oxidative damage are a direct consequence of systemic inflammation or whether these events are driven by brain resident cells, such as microglia. Therefore, the aim of this study is to evaluate the effect of minocycline on behavioral and neuroinflammatory parameters in rats submitted to sepsis. Male Wistar rats were subjected to sepsis by cecal ligation and puncture (CLP). The animals were divided into sham-operated (Sham+control), sham-operated plus minocycline (sham+MIN), CLP (CLP+control) and CLP plus minocycline (CLP+MIN) (100 μg/kg, administered as a single intracerebroventricular (ICV) injection). Some animals were killed 24h after surgery to assess the breakdown of the blood brain barrier, cytokine levels, oxidative damage to lipids (TBARS) and proteins in the hippocampus. Some animals were allowed to recover for 10 days when step-down inhibitory avoidance and open-field tasks were performed. Treatment with minocycline prevented an increase in markers of oxidative damage and inflammation in the hippocampus after sepsis. This was associated with an improvement in long-term cognitive performance. In conclusion, we demonstrated that the inhibition of the microglia by an ICV injection of minocycline was able to decrease acute brain oxidative damage and inflammation as well as long-term cognitive impairment in sepsis survivors.

HMGB1 mediates splenomegaly and expansion of splenic CD11b+ Ly-6C(high) inflammatory monocytes in murine sepsis survivors.

BackgroundMore than 500,000 hospitalized patients survive severe sepsis annually in the USA. Recent epidemiological evidence, however, demonstrated that these survivors have significant morbidity and mortality, with 3-year fatality rates higher than 70%. To investigate the mechanisms underlying persistent functional impairment in sepsis survivors, here we developed a model to study severe sepsis survivors following cecal ligation and puncture (CLP).MethodsSepsis was induced in mice by CLP and survivors were followed for twelve weeks. Spleen and blood were collected and analyzed at different time points post-sepsis.ResultsWe observed that sepsis survivors developed significant splenomegaly. Analysis of the splenic cellular compartments revealed a major expansion of the inflammatory CD11b+ Ly-6CHigh pool. Serum high-mobility group box 1 (HMGB1) levels in the sepsis surviving mice were significantly elevated for 4-6 weeks after post-sepsis, and administration of an anti-HMGB1 monoclonal antibody significantly attenuated splenomegaly as well as splenocyte priming. Administration of recombinant HMGB1 to naive mice induced similar splenomegaly, leukocytosis and splenocyte priming as observed in sepsis survivors. Interestingly analysis of circulating HMGB1 from sepsis survivors by mass spectroscopy demonstrated a stepwise increase of reduced form of HMGB1 (with known chemo-attractant properties) during the first 3 weeks, followed by disulphide form (with known inflammatory properties) 4-8 weeks after CLP.DiscussionOur results indicate that prolonged elevation of HMGB1 is a necessary and sufficient mediator of splenomegaly and splenocyte expansion, as well as splenocyte inflammatory priming in murine severe sepsis survivors.

Correlation of Acute Phase Inflammatory and Oxidative Markers With Long-term Cognitive Impairment in Sepsis Survivors Rats

Oxidative damage and inflammation occur early in the brain after sepsis and are resolved when long-term cognitive impairment occurs. There is no information of a direct relation between acute levels of brain inflammation and oxidative damage and long-term cognitive deficits. We hypothesized that higher levels of early oxidative damage and inflammation are followed by long-term cognitive deficits, and this is related to a decrease in the levels of brain-derived neurotropic factor (BDNF). Wistar rats were subjected to sham operation or cecal ligation and perforation and the cerebrospinal fluid (CSF) was obtained 6 and 24 h after the determination of thiobarbituric acid-reactive species, interleukin 1 (IL-1), IL-10, and tumor necrosis factor α (TNF-α). Animals were followed until 30 days after surgery and were subjected to the step-down inhibitory avoidance (IA) task, and the hippocampus levels of BDNF were determined. At 6 h, higher CSF levels of thiobarbituric acid-reactive species and TNF-α were observed in septic animals that had a better performance in the IA task and presented higher BDNF levels in the hippocampus. At 24 h, higher CSF levels of IL-1β and TNF-α were observed in septic animals that had a worse performance in the IA task, and this was associated with lower BDNF levels. The persistence of brain inflammation during the acute phase of sepsis is associated with long-term hippocampus levels of BDNF and memory impairment in sepsis survivors.

Is There a Role for High Mobility Group Box 1 and the Receptor for Advanced Glycation End Products in the Genesis of Long-term Cognitive Impairment in Sepsis Survivors?

Recently, Chavan et al.(1) demonstrated the major role of high mobility group box 1 (HMGB1) in cognitive dysfunction in sepsis survivors. By using a severe sepsis mice model, they clearly showed that serum HMGB1 levels were elevated 4 wks after sepsis (1). In addition, these animals had significant long-term impairments in learning and memory that were reversed by the administration of anti-HMGB1 antibody (1). The fact that HMGB1 can be one of the major mediators that leads to cognitive impairment suggests that some of its receptors can be a therapeutic target in this context. The interactions involving HMGB1, Toll-like receptors (TLRs) and the receptor for advanced glycation end products (RAGE) are considered relevant in some diseases (2), and these are one of the postulated mechanisms raised by Chavan et al.(1) to explain their results. In fact, TLR upregulation was demonstrated after endotoxemia (3), but no direct evidence of an upregulation of RAGE was found in the literature. Thus, by using a rat model of sepsis (4), we looked for the content of RAGE in the brain 30 d after sepsis, when these animals presented impairments of learning and memory (5,6). RAGE content was determined by Western blot by using anti-RAGE antibodies (R5278; Sigma, St. Louis, MO, USA). RAGE content, in hippocampus and prefrontal cortex, of septic animals was increased when compared with sham animals (Figures 1A, B). Figure 1 Immunocontent of RAGE in the hippocampus and prefrontal cortex of sepsis survivor animals. Sepsis was induced by cecal ligation and perforation and, after 30 d, the immunocontent of RAGE was evaluated in samples from the hippocampus (A) and prefrontal ... It is well described that HMGB1 can bind RAGE, and the activation of RAGE in the central nervous system has been increasingly implicated in the progression of neurodegeneration (7). The neurotoxicity related to RAGE signaling in the brain is believed to be associated with mechanisms that enhance RAGE expression and/or the production and secretion of RAGE ligands (8). One of the main intracellular targets of RAGE activation is the transcription factor nuclear factor (NF)-κB, which activates microglia, thus perpetuating brain inflammatory response (9). Thus, taken together, these results pointed to a role of HMGB1-RAGE signaling activation as a major pathway for the long-term cognitive impairment observed in sepsis survivors. A great effort must be done to clearly demonstrate the relevance of HMGB1-TLR-RAGE signaling as the major mediator of long-term cognitive impairment in sepsis survivors.

Response to “HMGB1 Mediates Cognitive Impairment in Sepsis Survivors”

The letter from Dal-Pizzol et al.(1) addresses the question of brain cell activation in sepsis survivors. The data demonstrate that RAGE (receptor for advanced glycation end products) expression in the hippocampus and in the prefrontal cortex is significantly increased 4 wks after septic insult. This is an interesting observation because it indicates that altered expression of specific brain proteins can be sustained for weeks after sepsis. The significance of these findings can be considered in light of our recent report showing that HMGB1 (high mobility group box 1), one of the putative RAGE ligands, mediates memory loss in sepsis survivors (2). The novel findings by Dal-Pizzol et al.(1), combined with Chavan et al.(2), raise additional questions: What is the time course for the elevation of RAGE levels? Is it an immediate increase after septic insult, indicating a direct link between sepsis-mediated systemic inflammation and increased RAGE expression? Alternatively, is it a late effect, suggesting it is caused by sepsis-induced changes in brain physiology and not by the systemic inflammation? Which molecular cascade induces RAGE expression? What sustains the high expression of RAGE? Do receptors besides RAGE mediate HMGB1-dependent alteration of memory function, as suggested in a recent report by Mazarati et al.(3)? Which brain cells express RAGE? Is HMGB1 directly affecting neurons, or is it altering glial cell biology? A recent report by Pedrazzi et al.(4) shows that HMGB1 potentiates N-methyl-d-aspartate receptor activation, a process that might be critical for memory formation. This finding is consistent with the hypothesis that HMGB1 acts directly on neurons, but it may also activate glial cells, which in turn can modulate neuronal signaling via other cytokine networks. Finally, it is worth mentioning that HMGB1 may be deleterious to neurons or may function to compensate for previous injury. In sum, we agree with the authors of the letter that this is an important area of research with significant implications for medical practice.

HMGB1 Mediates Cognitive Impairment in Sepsis Survivors

Severe sepsis, a syndrome that complicates infection and injury, affects 750,000 annually in the United States. The acute mortality rate is approximately 30%, but, strikingly, sepsis survivors have a significant disability burden: up to 25% of survivors are cognitively and physically impaired. To investigate the mechanisms underlying persistent cognitive impairment in sepsis survivors, here we developed a murine model of severe sepsis survivors following cecal ligation and puncture (CLP) to study cognitive impairments. We observed that serum levels of high mobility group box 1 (HMGB1), a critical mediator of acute sepsis pathophysiology, are increased in sepsis survivors. Significantly, these levels remain elevated for at least 4 wks after CLP. Sepsis survivors develop significant, persistent impairments in learning and memory, and anatomic changes in the hippocampus associated with a loss of synaptic plasticity. Administration of neutralizing anti-HMGB1 antibody to survivors, beginning 1 wk after onset of peritonitis, significantly improved memory impairments and brain pathology. Administration of recombinant HMGB1 to naïve mice recapitulated the memory impairments. Together, these findings indicate that elevated HMGB1 levels mediate cognitive decline in sepsis survivors, and suggest that it may be possible to prevent or reverse cognitive impairments in sepsis survivors by administration of anti-HMGB1 antibodies.

Long-Term Cognitive Impairment in Sepsis Survivors

Barichello, Tatiana PharmD, MSc; Martins, Márcio R. BSc; Reinke, Adalisa BSc; Feier, Gustavo Bsc; Ritter, Cristiane MD, MSc; Quevedo, João MD, PhD; Dal-Pizzol, Felipe MD, PhD Author Information

Cognitive impairment in sepsis survivors from cecal ligation and perforation*

Critical illness survivors present long-term cognitive impairment, including problems with memory and learning. We evaluated cognitive performance in rats that survived from sepsis induced by cecal ligation and puncture (CLP). Prospective, controlled experiment. Animal basic science laboratory. Male Wistar rats, weighing 300-350 g. The rats underwent CLP (sepsis group) with "basic support" (saline at 50 mL/kg immediately and 12 hrs after CLP plus ceftriaxone at 30 mg/kg and clindamycin at 25 mg/kg 6, 12, and 18 hrs after CLP) or sham-operated (control group). Ten days after surgery, the animals underwent three behavioral tasks: a) inhibitory avoidance task; b) habituation to an open field; and c) continuous multiple-trials step-down inhibitory avoidance task (CMSIA). In the habituation to an open-field task, there were no differences in the number of crossings and rearings. The sepsis group showed significantly decreased performance in latency retention compared with the sham group in inhibitory avoidance. Furthermore, when tested by the habituation to an open-field task, the sepsis group did not show any difference between training and test, indicating memory impairment. In the CMSIA, the sepsis group showed a significant increase in the number of training trials required to reach the acquisition criterion. Our data provide the first experimental demonstration that survivors from CLP show learning and memory impairment after complete physical recovery from sepsis.