Alterations in hypothalamic synaptophysin and death markers may be associated with vasopressin impairment in sepsis survivor rats

Potential of piperine for neuroprotection in sepsis-associated encephalopathy

AIMS

Sepsis-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 METHODS

C57BL/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 FINDINGS

Our 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.

SIGNIFICANCE

In conclusion, our data demonstrate that piperine exerts a neuroprotective effect on SAE in animals that have undergone CLP.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

Autonomic Disbalance During Systemic Inflammation is Associated with Oxidative Stress Changes in Sepsis Survivor Rats

Sepsis affects 31.5 million people worldwide. It is characterized by an intense drop in blood pressure driving to cardiovascular morbidity and mortality. Modern supportive care has increased survival in patients; however, after experiencing sepsis, several complications are observed, which may be potentiated by new inflammatory events. Nevertheless, the interplay between sepsis survivors and a new immune challenge in cardiovascular regulation has not been previously defined. We hypothesized that cecal ligation and puncture (CLP) cause persistent cardiovascular dysfunctions in rats as well as changes in autonomic-induced cardiovascular responses to lipopolysaccharide (LPS). Male Wistar rats had mean arterial pressure (MAP) and heart rate (HR) recorded before and after LPS or saline administration to control or CLP survivor rats. CLP survivor rats had similar baseline MAP and HR when compared to control. LPS caused a drop in MAP accompanied by tachycardia in control, while CLP survivor rats had a noteworthy enhanced MAP and a blunted tachycardia. LPS-induced hemodynamic changes were related to an autonomic disbalance to the heart and resistance vessels that were expressed as an increased low- and high-frequency power of pulse interval in CLP survivors after saline and enhancement in the low-frequency power of systolic arterial pressure in control rats after LPS. LPS-induced plasma interferon γ, but not interleukin-10 surges, was blunted in CLP survivor rats. To further access whether or not LPS-induced autonomic disbalance in CLP survivor rats was associated with oxidative stress dysregulation, superoxide dismutase (SOD) activity and thiobarbituric acid reactive substances (TBARS) plasma levels changes were measured. LPS-induced oxidative stress was higher in CLP survivor rats. These findings indicate that key changes in hemodynamic regulation of CLP survivors rats take place in response to LPS that are associated with oxidative stress changes, i.e., reduced SOD activity and increased TBARS levels.

Environmental Enrichment Protects Against Sepsis-Associated Encephalopathy-Induced Learning and Memory Deficits by Enhancing the Synthesis and Release of Vasopressin in the Supraoptic Nucleus

Background

As a severe complication of sepsis, sepsis-associated encephalopathy (SAE) usually manifests as impaired learning and memory ability in survivors. Previous studies have reported that environmental enrichment (EE) can increase the learning and memory ability in different brain injury models. However, there has been no research on the possible positive effect of EE on SAE.

Aim

The present study aimed to test the effect of EE on SAE-induced impairment of learning and memory and its related mechanisms.

Methods

A Morris water maze test (MWM) was used to evaluate the learning and memory ability of SAE rats that received EE housing or not. The expression of vasopressin (VP) was assessed using immunofluorescence microscopy and enzyme-linked immunosorbent assays (ELISAs). The synthesis of VP in the supraoptic nucleus (SON) was determined using quantitative real-time reverse transcription-PCR analysis. Moreover, inflammatory markers and brain-derived neurotrophic factor (BDNF) were detected using ELISA.

Results

The results showed that SAE induced a decreased learning and memory ability, while EE reversed this impairment. EE also enhanced the synthesis and secretion of VP in the SON. Blocking the action of VP in the hippocampus interrupted the EE-induced amelioration of learning and memory impairment. Moreover, EE induced changes to the levels of BDNF and cytokines in the hippocampus and these effects were mediated by VP binding to the VP receptor 1a.

Conclusion

Our findings demonstrated that the enhanced synthesis and secretion of VP in the SON are a key determinant responsible for EE-induced alleviation of learning and memory deficits caused by SAE.

Precise gene delivery systems with detachable albumin shell remodeling dysfunctional microglia by TREM2 for treatment of Alzheimer's disease

Intervention of the over-activated microglia-aggravated neuroinflammation represents a promising therapeutic strategy for Alzheimer's disease (AD). Upregulation of triggering receptor expressed on myeloid cells-2 (TREM2) attenuates the neuroinflammatory processes and normalizes the dysfunctional microglia. However, Trem2-gene therapy for AD by the effective non-invasive delivery systems is unexploited. Herein, we report the microglia-targeted gene delivery systems (PHSA@PF/pTREM2) composed of a core of fluorinated polyethylenimine condensing the TREM2-encoding plasmid (PF/pTREM2) and a shell of human serum albumin conjugated with both cis-aconitic anhydride and neural cell adhesion molecule-mimetic peptide P2 (PHSA). Thanks to the shedding effect of the albumin coated, PHSA@PF/pTREM2 exhibit prolonged blood circulation and low cytotoxicity. PHSA@PF/pTREM2 achieve brain accumulation as high as 2.17% injected dose per gram of brain and the microglial-targeting effect (targeting specificity of 41.9%) via the systemic administration. The nanocomplexes can be detached PHSA-shell in the acidic endo-lysosomes via the cleavage of cis-aconitic amide bond, resulting in PF/pTREM2 exposure for efficient endo-lysosomal escape and gene transfection. PHSA@PF/pTREM2 upregulate the TREM2 level and regulate microglial polarization toward M2-phenotype for remodeling the inflammatory microenvironment and enhanced Aβ clearance, leading to an improvement of cognitive performance in APP/PS1 mice. This work provides a promising gene delivery platform to reverse dysfunctional microglia for AD therapy.

Inflammatory, synaptic, motor, and behavioral alterations induced by gestational sepsis on the offspring at different stages of life

BACKGROUND

The term sepsis is used to designate a systemic condition of infection and inflammation associated with hemodynamic changes that result in organic dysfunction. Gestational sepsis can impair the development of the central nervous system and may promote permanent behavior alterations in the offspring. The aim of our work was to evaluate the effects of maternal sepsis on inflammatory cytokine levels and synaptic proteins in the hippocampus, neocortex, frontal cortex, and cerebellum of neonatal, young, and adult mice. Additionally, we analyzed the motor development, behavioral features, and cognitive impairments in neonatal, young and adult offspring.

METHODS

Pregnant mice at the 14th embryonic day (E14) were intratracheally instilled with saline 0.9% solution (control group) or Klebsiella spp. (3 × 108 CFU) (sepsis group) and started on meropenem after 5 h. The offspring was sacrificed at postnatal day (P) 2, P8, P30, and P60 and samples of liver, lung, and brain were collected for TNF-α, IL-1β, and IL-6 measurements by ELISA. Synaptophysin, PSD95, and β-tubulin levels were analyzed by Western blot. Motor tests were performed at all analyzed ages and behavioral assessments were performed in offspring at P30 and P60.

RESULTS

Gestational sepsis induces a systemic pro-inflammatory response in neonates at P2 and P8 characterized by an increase in cytokine levels. Maternal sepsis induced systemic downregulation of pro-inflammatory cytokines, while in the hippocampus, neocortex, frontal cortex, and cerebellum an inflammatory response was detected. These changes in the brain immunity were accompanied by a reduction of synaptophysin and PSD95 levels in the hippocampus, neocortex, frontal cortex, and cerebellum, in all ages. Behavioral tests demonstrated motor impairment in neonates, and depressive-like behavior, fear-conditioned memory, and learning impairments in animals at P30 and P60, while spatial memory abilities were affected only at P60, indicating that gestational sepsis not only induces an inflammatory response in neonatal mouse brains, but also affects neurodevelopment, and leads to a plethora of behavioral alterations and cognitive impairments in the offspring.

CONCLUSION

These data suggest that maternal sepsis may be causatively related to the development of depression, learning, and memory impairments in the litter.

Simvastatin Prevents Long-Term Cognitive Deficits in Sepsis Survivor Rats by Reducing Neuroinflammation and Neurodegeneration

Sepsis-associated encephalopathy causes brain dysfunction that can result in cognitive impairments in sepsis survivor patients. In previous work, we showed that simvastatin attenuated oxidative stress in brain structures related to memory in septic rats. However, there is still a need to evaluate the long-term impact of simvastatin administration on brain neurodegenerative processes and cognitive damage in sepsis survivors. Here, we investigated the possible neuroprotective role of simvastatin in neuroinflammation, and neurodegeneration conditions of brain structures related to memory in rats at 10 days after sepsis survival. Male Wistar rats (250-300 g) were submitted to cecal ligation and puncture (CLP, n = 42) or remained as non-manipulated (naïve, n = 30). Both groups were treated (before and after the surgery) by gavage with simvastatin (20 mg/kg) or an equivalent volume of saline and observed for 10 days. Simvastatin-treated rats that survived to sepsis showed a reduction in the levels of nitrate, IL1-β, and IL-6 and an increase in Bcl-2 protein expression in the prefrontal cortex and hippocampus, and synaptophysin only in the hippocampus. Immunofluorescence revealed a reduction of glial activation, neurodegeneration, apoptosis, and amyloid aggregates confirmed by quantification of GFAP, Iba-1, phospho Ser₃₉₆-tau, total tau, cleaved caspase-3, and thioflavin-S in the prefrontal cortex and hippocampus. In addition, treated animals presented better performance in tasks involving habituation memory, discriminative, and aversive memory. These results suggest that statins exert a neuroprotective role by upregulation of the Bcl-2 and gliosis reduction, which may prevent the cognitive deficit observed in sepsis survivor animals.

Sepsis-induced encephalopathy impairs descending nociceptive pathways in rats

Sepsis-associated encephalopathy (SAE) is a significant problem in patients with sepsis, and it is associated with a decrease in cognitive and sensitivity capability induced by systemic inflammation. SAE is implicated in reversible brain damage of several regions related to cognition, emotion, and sensation; however, it is not well established if it could affect brain regions associated with nociceptive modulation. Here were evaluated the nociceptive thresholds in rats with systemic inflammation induced by cecal ligation puncture (CLP). After 24 h of CLP, it was observed an increase in nociceptive threshold in all tests. Periaqueductal gray, rostroventral medulla, critical regions for descending nociceptive modulation, were evaluated and showed enhanced pro-inflammatory cytokines as well as glial activation. These results suggest that systemic inflammation could compromise descending facilitatory pathways, impairing nociceptive sensory functioning.

Role of AMPA and NMDA receptors on vasopressin and oxytocin secretion induced by hypertonic extracellular volume expansion

Vasopressin (AVP) and oxytocin (OT) are essential for the control of extracellular fluid osmolality and volume. Secretion of these hormones is modulated by several mechanisms, including NMDA and AMPA L-glutamate receptors in magnocellular cells of paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei. Thus, to better understand the participation of L-glutamate on the neuroendocrine control of AVP and OT, this work evaluated the effects of intracerebroventricular (icv) NMDA and AMPA receptor antagonists on plasma AVP and OT levels induced by extracellular volume expansion (EVE). Cannulated rats received icv NMDA (AP5) and AMPA (NBQX) antagonists in 10 and 30nmol/5μl/rat doses and were subjected to either isotonic (0.15 M NaCl, 2ml/100g) or hypertonic (0.30 M NaCl, 2ml/100g) EVE. Blood samples were collected for plasma AVP and OT determination. Isotonic EVE did not change plasma AVP and OT levels, but hypertonic EVE increased both AVP and OT plasma levels. AP5 reduced plasma AVP, but it did not change the OT level induced by hypertonic EVE. On the other hand, NBQX reduced plasma OT, but did not alter the AVP plasma level. Our data shows that L-glutamate controls the secretion of neurohypophyseal hormones through the NMDA receptor for AVP release, and through the AMPA receptor for OT release, both in response to hypertonic EVE. This article is protected by copyright. All rights reserved.