Acute neuroinflammation provokes intracellular acidification in mouse hippocampus

Neuroinflammation increases oxygen extraction in a mouse model of Alzheimer's disease

BACKGROUND

Neuroinflammation, impaired metabolism, and hypoperfusion are fundamental pathological hallmarks of early Alzheimer's disease (AD). Numerous studies have asserted a close association between neuroinflammation and disrupted cerebral energetics. During AD progression and other neurodegenerative disorders, a persistent state of chronic neuroinflammation reportedly exacerbates cytotoxicity and potentiates neuronal death. Here, we assessed the impact of a neuroinflammatory challenge on metabolic demand and microvascular hemodynamics in the somatosensory cortex of an AD mouse model.

METHODS

We utilized in vivo 2-photon microscopy and the phosphorescent oxygen sensor Oxyphor 2P to measure partial pressure of oxygen (pO2) and capillary red blood cell flux in cortical microvessels of awake mice. Intravascular pO2 and capillary RBC flux measurements were performed in 8-month-old APPswe/PS1dE9 mice and wildtype littermates on days 0, 7, and 14 of a 14-day period of lipopolysaccharide-induced neuroinflammation.

RESULTS

Before the induced inflammatory challenge, AD mice demonstrated reduced metabolic demand but similar capillary red blood cell flux as their wild type counterparts. Neuroinflammation provoked significant reductions in cerebral intravascular oxygen levels and elevated oxygen extraction in both animal groups, without significantly altering red blood cell flux in capillaries.

CONCLUSIONS

This study provides evidence that neuroinflammation alters cerebral oxygen demand at the early stages of AD without substantially altering vascular oxygen supply. The results will guide our understanding of neuroinflammation's influence on neuroimaging biomarkers for early AD diagnosis.

The proton-sensing receptors TDAG8 and GPR4 are differentially expressed in human and mouse oligodendrocytes: Exploring their role in neuroinflammation and multiple sclerosis

Acidosis is one of the hallmarks of demyelinating central nervous system (CNS) lesions in multiple sclerosis (MS). The response to acidic pH is primarily mediated by a family of G protein-coupled proton-sensing receptors: OGR1, GPR4 and TDAG8. These receptors are inactive at alkaline pH, reaching maximal activation at acidic pH. Genome-wide association studies have identified a locus within the TDAG8 gene associated with several autoimmune diseases, including MS. Accordingly, we here found that expression of TDAG8, as opposed to GPR4 or OGR1, is upregulated in MS plaques. This led us to investigate the expression of TDAG8 in oligodendrocytes using mouse and human in vitro and in vivo models. We observed significant upregulation of TDAG8 in human MO3.13 oligodendrocytes during maturation and in response to acidic conditions. However, its deficiency did not impact normal myelination in the mouse CNS, and its expression remained unaltered under demyelinating conditions in mouse organotypic cerebellar slices. Notably, our data revealed no expression of TDAG8 in primary mouse oligodendrocyte progenitor cells (OPCs), in contrast to its expression in primary human OPCs. Our investigations have revealed substantial species differences in the expression of proton-sensing receptors in oligodendrocytes, highlighting the limitations of the employed experimental models in fully elucidating the role of TDAG8 in myelination and oligodendrocyte biology. Consequently, the study does not furnish robust evidence for the role of TDAG8 in such processes. Nonetheless, our findings tentatively point towards a potential association between TDAG8 and myelination processes in humans, hinting at a potential link between TDAG8 and the pathophysiology of MS and warrants further research.

Cytomegalovirus antibodies are associated with mood disorders, suicide, markers of neuroinflammation, and microglia activation in postmortem brain samples

Cytomegalovirus (CMV) is a common, neurotrophic herpesvirus that can be reactivated by inflammation and cause central nervous system disease. We hypothesize that CMV may contribute to the neuroinflammation that underlies some psychiatric disorders by (1) exacerbating inflammation through the induction of anti-viral immune responses, and (2) translating peripheral inflammation into neuroinflammation. We investigated whether the presence of anti-CMV antibodies in blood were associated with mental illness, suicide, neuroinflammation, and microglial density in the dorsolateral prefrontal cortex (DLPFC) in postmortem samples. Data (n = 114 with schizophrenia; n = 78 with bipolar disorder; n = 87 with depression; n = 85 controls) were obtained from the Stanley Medical Research Institute. DLPFC gene expression data from a subset of 82 samples were categorized into "high" (n = 30), and "low" (n = 52) inflammation groups based on a recursive two-step cluster analysis using expression data for four inflammation-related genes. Measurements of the ratio of non-ramified to ramified microglia, a proxy of microglial activation, were available for a subset of 49 samples. All analyses controlled for age, sex, and ethnicity, as well as postmortem interval, and pH for gene expression and microglial outcomes. CMV seropositivity significantly increased the odds of a mood disorder diagnosis (bipolar disorder: OR = 2.45; major depression: OR = 3.70) and among the psychiatric samples, of suicide (OR = 2.09). Samples in the upper tercile of anti-CMV antibody titers were more likely to be members of the "high" inflammation group (OR = 4.41, an effect driven by schizophrenia and bipolar disorder samples). CMV positive samples also showed an increased ratio of non-ramified to ramified microglia in layer I of the DLPFC (Cohen's d = 0.81) as well as a non-significant increase in this ratio for the DLPFC as a whole (d = 0.56). The results raise the possibility that the reactivation of CMV contributes to the neuroinflammation that underlies some cases of psychiatric disorders.

Inflammatory processes in the prefrontal cortex induced by systemic immune challenge: Focusing on neurons

Peripheral immune challenge induces neurobiological alterations in the brain and related neuropsychiatric symptoms both in humans and other mammals. One of the best known physiological effects of systemic inflammation is sickness behavior. However, in addition to this depression-like state, there are other cognitive outcomes of peripherally induced neuroinflammation that can be linked to the dysfunction of higher-order cortical areas, such as the prefrontal cortex (PFC). As the physiological activity of the PFC is largely based on the balanced interplay of excitatory pyramidal cells and inhibitory interneurons, it may be hypothesized that neuroinflammatory processes result in a shift of excitatory/inhibitory balance, which is a common hallmark of several neuropsychiatric conditions. Indeed, many data suggest that peripherally induced neuroinflammation is strongly associated with molecular and functional changes in PFC neurons leading to disturbances in their synaptic networks. Different experimental approaches may cause some incongruence in the reviewed data. However, it is commonly agreed that acute systemic inflammation leads to changes in the excitatory/inhibitory balance in the PFC by proinflammatory signaling at the brain borders and in the brain parenchyma. These cellular changes result in altered local and brain-wide network activity inducing disturbances in the top-down control of goal-directed behavior and cognition regulated by the PFC. Lipopolysaccharide (LPS)-treated rodents are the most widely used experimental models of peripherally induced neuroinflammation, so the majority of the reviewed data come from studies utilizing the LPS model. This may limit their general interpretation regarding the neuronal effects of peripheral immune activation. In addition, several biological variables (e.g., sex, age) can influence the PFC effects of systemic immune challenge, not only the nature and severity of immune activation. Therefore, it would be desirable to investigate inflammation-related neuronal changes in the PFC using other models of systemic inflammation as well, and to focus on the targeted fine-tuning of the affected cell types via common molecular mechanisms of the immune and nervous systems.

Using the LeiCNS-PK3.0 Physiologically-Based Pharmacokinetic Model to Predict Brain Extracellular Fluid Pharmacokinetics in Mice

INTRODUCTION

The unbound brain extracelullar fluid (brainECF) to plasma steady state partition coefficient, Kp,uu,BBB, values provide steady-state information on the extent of blood-brain barrier (BBB) transport equilibration, but not on pharmacokinetic (PK) profiles seen by the brain targets. Mouse models are frequently used to study brain PK, but this information cannot directly be used to inform on human brain PK, given the different CNS physiology of mouse and human. Physiologically based PK (PBPK) models are useful to translate PK information across species.

AIM

Use the LeiCNS-PK3.0 PBPK model, to predict brain extracellular fluid PK in mice.

METHODS

Information on mouse brain physiology was collected from literature. All available connected data on unbound plasma, brainECF PK of 10 drugs (cyclophosphamide, quinidine, erlotonib, phenobarbital, colchicine, ribociclib, topotecan, cefradroxil, prexasertib, and methotrexate) from different mouse strains were used. Dosing regimen dependent plasma PK was modelled, and Kpuu,BBB values were estimated, and provided as input into the LeiCNS-PK3.0 model to result in prediction of PK profiles in brainECF.

RESULTS

Overall, the model gave an adequate prediction of the brainECF PK profile for 7 out of the 10 drugs. For 7 drugs, the predicted versus observed brainECF data was within two-fold error limit and the other 2 drugs were within five-fold error limit.

CONCLUSION

The current version of the mouse LeiCNS-PK3.0 model seems to reasonably predict available information on brainECF from healthy mice for most drugs. This brings the translation between mouse and human brain PK one step further.

ROS-responsive 18β-glycyrrhetic acid-conjugated polymeric nanoparticles mediate neuroprotection in ischemic stroke through HMGB1 inhibition and microglia polarization regulation

Ischemic stroke is an acute and serious cerebral vascular disease, which greatly affects people's health and brings huge economic burden to society. Microglia, as important innate immune components in central nervous system (CNS), are double-edged swords in the battle of nerve injury, considering their polarization between pro-inflammatory M1 or anti-inflammatory M2 phenotypes. High mobility group box 1 (HMGB1) is one of the potent pro-inflammatory mediators that promotes the M1 polarization of microglia. 18β-glycyrrhetinic acid (GA) is an effective intracellular inhibitor of HMGB1, but of poor water solubility and dose-dependent toxicity. To overcome the shortcomings of GA delivery and to improve the efficacy of cerebral ischemia therapy, herein, we designed reactive oxygen species (ROS) responsive polymer-drug conjugate nanoparticles (DGA) to manipulate microglia polarization by suppressing the translocation of nuclear HMGB1. DGA presented excellent therapeutic efficacy in stroke mice, as evidenced by the reduction of infarct volume, recovery of motor function, suppressed of M1 microglia activation and enhanced M2 activation, and induction of neurogenesis. Altogether, our work demonstrates a close association between HMGB1 and microglia polarization, suggesting potential strategies for coping with inflammatory microglia-related diseases.

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We synthesized GA-boronate ester-conjugated diethylaminoethylen-dextran polymer-drug conjugate nanoparticles.

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The DGA nanoparticles achieve ROS-responsive drug release.

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The DGA nanoparticles inhibit cytoplasmic translocation of nuclear HMGB1, thus modulate microglia to M2 phenotype.

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The DGA nanoparticles effectively alleviate the pathology of stroke, reduce infarct volume, and enhance neurogenesis.

Simultaneous Antagonism at H3R/D2R/D3R Reduces Autism-like Self-Grooming and Aggressive Behaviors by Mitigating MAPK Activation in Mice

Dysregulation in brain neurotransmitters underlies several neuropsychiatric disorders, e.g., autism spectrum disorder (ASD). Also, abnormalities in the extracellular-signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway pave the way for neuroinflammation, neurodegeneration, and altered learning phenotype in ASD. Therefore, the effects of chronic systemic administration of the multiple-targeting antagonist ST-713 at the histamine H3 receptor (H3R) and dopamine D2/D3 receptors (D2/D3R) on repetitive self-grooming, aggressive behaviors, and abnormalities in the MAPK pathway in BTBR T + Itpr3tf/J (BTBR) mice were assessed. The results showed that ST-713 (2.5, 5, and 10 mg/kg, i.p.) mitigated repetitive self-grooming and aggression in BTBR mice (all p < 0.05), and the ameliorative effects of the most promising dose of ST-713 (5 mg/kg, i.p.) on behaviors were completely abrogated by co-administration of the H3R agonist (R)-α-methylhistamine or the anticholinergic drug scopolamine. Moreover, the elevated levels of several MAPK pathway proteins and induced proinflammatory markers such as tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), and IL-6 were significantly suppressed following chronic administration of ST-713 (5 mg/kg, i.p.) (all p < 0.01). Furthermore, ST-713 significantly increased the levels of histamine and dopamine in hippocampal tissue of treated BTBR mice (all p < 0.01). The current observations signify the potential role of such multiple-targeting compounds, e.g., ST-713, in multifactorial neurodevelopmental disorders such as ASD.

Inflammation-related transcripts define "high" and "low" subgroups of individuals with schizophrenia and bipolar disorder in the midbrain

Dopamine dysregulation in schizophrenia may be associated with midbrain inflammation. Previously, we found elevated levels of pro-inflammatory cytokine mRNAs in the post-mortem midbrain of people with schizophrenia (46%) but not from unaffected controls (0%) using a brain cohort from Sydney, Australia. Here, we measured cytokine mRNAs and proteins in the midbrain in the Stanley Medical Research Institute (SMRI) array cohort (N = 105). We tested if the proportions of individuals with schizophrenia and with high inflammation can be replicated, and if individuals with bipolar disorder with elevated midbrain cytokines can be identified. mRNA levels of 7 immune transcripts from post-mortem midbrain tissue were measured via RT-PCR and two-step recursive clustering analysis was performed using 4 immune transcripts to define "high and low" inflammatory subgroups. The clustering predictors used were identical to our earlier midbrain study, and included: IL1B, IL6, TNF, and SERPINA3 mRNA levels. 46% of schizophrenia cases (16/35 SCZ), 6% of controls (2/33 CTRL), and 29% of bipolar disorder cases (10/35 BPD) were identified as belonging to the high inflammation (HI) subgroups [χ² (2) = 13.54, p < 0.001]. When comparing inflammatory subgroups, all four mRNAs were significantly increased in SCZ-HI and BPD-HI compared to low inflammation controls (CTRL-LI) (p < 0.05). Additionally, protein levels of IL-1β, IL-6, and IL-18 were elevated in SCZ-HI and BPD-HI compared to all other low inflammatory subgroups (all p < 0.05). Surprisingly, TNF-α protein levels were unchanged according to subgroups. In conclusion, we determined that almost half of the individuals with schizophrenia were defined as having high inflammation in the midbrain, replicating our previous findings. Further, we detected close to one-third of those with bipolar disorder to be classified as having high inflammation. Elevations in some pro-inflammatory cytokine mRNAs (IL-1β and IL-6) were also found at the protein level, whereas TNF mRNA and protein levels were not concordant.

Effects of pH alterations on stress- and aging-induced protein phase separation

Upon stress challenges, proteins/RNAs undergo liquid–liquid phase separation (LLPS) to fine-tune cell physiology and metabolism to help cells adapt to adverse environments. The formation of LLPS has been recently linked with intracellular pH, and maintaining proper intracellular pH homeostasis is known to be essential for the survival of organisms. However, organisms are constantly exposed to diverse stresses, which are accompanied by alterations in the intracellular pH. Aging processes and human diseases are also intimately linked with intracellular pH alterations. In this review, we summarize stress-, aging-, and cancer-associated pH changes together with the mechanisms by which cells regulate cytosolic pH homeostasis. How critical cell components undergo LLPS in response to pH alterations is also discussed, along with the functional roles of intracellular pH fluctuation in the regulation of LLPS. Further studies investigating the interplay of pH with other stressors in LLPS regulation and identifying protein responses to different pH levels will provide an in-depth understanding of the mechanisms underlying pH-driven LLPS in cell adaptation. Moreover, deciphering aging and disease-associated pH changes that influence LLPS condensate formation could lead to a deeper understanding of the functional roles of biomolecular condensates in aging and aging-related diseases.

VIP alleviates sepsis-induced cognitive dysfunction as the TLR-4/NF-κB signaling pathway is inhibited in the hippocampus of rats

Cognitive dysfunction caused by sepsis-associated encephalopathy (SAE) is still poorly understood. It is reported that vasoactive intestinal peptide (VIP) exerts its anti-inflammatory effects in multiple diseases, while its biological function in SAE remains unclear. We aimed to figure out whether VIP has influence on sepsis-induced neuroinflammation and cognitive dysfunction. To induce sepsis, rats were subjected to cecal ligation and puncture (CLP) operation. Morris water maze test and fear conditioning test were conducted to reveal cognitive dysfunctions. TUNEL assay was performed to evaluate apoptosis. We found out that the expression of VIP was downregulated in the hippocampus of septic rats. VIP was verified to attenuate sepsis-induced memory impairment following CLP. Additionally, we examined apoptosis and inflammation in rats' hippocampus. It is worth noting that VIP inhibited the apoptosis in the hippocampus and reduced the productions of proinflammatory cytokines TNF-α, IL-6 and IL-1β. Furthermore, our data confirmed that VIP was involved in regulating the TLR-4/NF-κB signaling. In conclusion, VIP inhibited neuroinflammation and cognitive impairment in hippocampus of septic rats through the TLR-4/NF-κB signaling pathway.

Neurodegenerative Disease: What Potential Therapeutic Role of Acid-Sensing Ion Channels?

Acidic pH shift occurs in many physiological neuronal activities such as synaptic transmission and synaptic plasticity but also represents a characteristic feature of many pathological conditions including inflammation and ischemia. Neuroinflammation is a complex process that occurs in various neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and Huntington’s disease. Acid-sensing ion channels (ASICs) represent a widely expressed pH sensor in the brain that play a key role in neuroinflammation. On this basis, acid-sensing ion channel blockers are able to exert neuroprotective effects in different neurodegenerative diseases. In this review, we discuss the multifaceted roles of ASICs in brain physiology and pathology and highlight ASIC1a as a potential pharmacological target in neurodegenerative diseases.

Brain Energy Metabolism in Two States of Mind Measured by Phosphorous Magnetic Resonance Spectroscopy

Introduction: Various functional neuroimaging studies help to better understand the changes in brain activity during meditation. The purpose of this study was to investigate how brain energy metabolism changes during focused attention meditation (FAM) state, measured by phosphorous magnetic resonance spectroscopy (³¹P-MRS).

Methods:³¹P-MRS imaging was carried out in 27 participants after 7 weeks of FAM training. Metabolite ratios and the absolute values of metabolites were assessed after meditation training in two MRI measurements, by comparing effects in a FAM state with those in a distinct focused attention awake state during a backwards counting task.

Results: The results showed decreased phosphocreatine/ATP (PCr/ATP), PCr/ inorganic phosphate (Pi), and intracellular pH values in the entire brain, but especially in basal ganglia, frontal lobes, and occipital lobes, and increased Pi/ATP ratio, cerebral Mg, and Pi absolute values were found in the same areas during FAM compared to the control focused attention awake state.

Conclusions: Changes in the temporal areas and basal ganglia may be interpreted as a higher energetic state induced by meditation, whereas the frontal and occipital areas showed changes that may be related to a down-regulation in ATP turnover, energy state, and oxidative capacity.

Regulation of RNA editing by intracellular acidification

The hydrolytic deamination of adenosine-to-inosine (A-to-I) by RNA editing is a widespread post-transcriptional modification catalyzed by the adenosine deaminase acting on RNA (ADAR) family of proteins. ADAR-mediated RNA editing modulates cellular pathways involved in innate immunity, RNA splicing, RNA interference, and protein recoding, and has been investigated as a strategy for therapeutic intervention of genetic disorders. Despite advances in basic and translational research, the mechanisms regulating RNA editing are poorly understood. Though several trans-acting regulators of editing have been shown to modulate ADAR protein expression, previous studies have not identified factors that modulate ADAR catalytic activity. Here, we show that RNA editing increases upon intracellular acidification, and that these effects are predominantly explained by both enhanced ADAR base-flipping and deamination rate at acidic pH. We also show that the extent of RNA editing increases with the reduction in pH associated with conditions of cellular hypoxia.

Dichloroacetic acid-induced dysfunction in rat hippocampus and the protective effect of curcumin

The present study was designed to evaluate the role of cAMP-PKA-CREB signaling in mediating the neuroprotective effects of curcumin against DCAA-induced oxidative stress, inflammation and impaired synaptic plasticity in rats. Sixty Sprague-Dawley rats were randomly divided into five groups, and we assessed the histomorphological, behavioral and biochemical characteristics to investigate the beneficial effects of different concentrations of curcumin against DCAA-induced neurotoxicity in rat hippocampus. The results indicated that animal weight gain and food consumption were not significantly affected by DCAA. However, behavioral tests, including morris water maze and shuttle box, showed varying degrees of alterations. Additionally, we found significant changes in hippocampal neurons by histomorphological observation. DCAA exposure could increase lipid peroxidation, reactive oxygen species (ROS), inflammation factors while reducing superoxide dismutase (SOD) activity and glutathione (GSH) level accompanied by DNA damage in the hippocampus. Furthermore, we found that DCAA exposure could cause a differential modulation of mRNA and proteins (cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), cAMP-response element-binding protein (CREB), p-CREB, brain-derived neurotrophic factor (BDNF), postsynaptic density-95 (PSD-95), synaptophysin (SYP)). Conversely, various doses of curcumin attenuated DCAA-induced oxidative stress, inflammation response and impaired synaptic plasticity, while elevating cAMP, PKA, p-CREB, BDNF, PSD-95, SYP levels. Thus, curcumin could activate the cAMP-PKA-CREB signaling pathway, conferring neuroprotection against DCAA-induced neurotoxicity.

The Role of TRP Channels and PMCA in Brain Disorders: Intracellular Calcium and pH Homeostasis

Brain disorders include neurodegenerative diseases (NDs) with different conditions that primarily affect the neurons and glia in the brain. However, the risk factors and pathophysiological mechanisms of NDs have not been fully elucidated. Homeostasis of intracellular Ca²⁺ concentration and intracellular pH (pH_i) is crucial for cell function. The regulatory processes of these ionic mechanisms may be absent or excessive in pathological conditions, leading to a loss of cell death in distinct regions of ND patients. Herein, we review the potential involvement of transient receptor potential (TRP) channels in NDs, where disrupted Ca²⁺ homeostasis leads to cell death. The capability of TRP channels to restore or excite the cell through Ca²⁺ regulation depending on the level of plasma membrane Ca²⁺ ATPase (PMCA) activity is discussed in detail. As PMCA simultaneously affects intracellular Ca²⁺ regulation as well as pH_i, TRP channels and PMCA thus play vital roles in modulating ionic homeostasis in various cell types or specific regions of the brain where the TRP channels and PMCA are expressed. For this reason, the dysfunction of TRP channels and/or PMCA under pathological conditions disrupts neuronal homeostasis due to abnormal Ca²⁺ and pH levels in the brain, resulting in various NDs. This review addresses the function of TRP channels and PMCA in controlling intracellular Ca²⁺ and pH, which may provide novel targets for treating NDs.

N-Docosahexanoylethanolamine Reduces Microglial Activation and Improves Hippocampal Plasticity in a Murine Model of Neuroinflammation

Chronic neuroinflammation is a common pathogenetic link in the development of various neurological and neurodegenerative diseases. Thus, a detailed study of neuroinflammation and the development of drugs that reduce or eliminate the negative effect of neuroinflammation on cognitive processes are among the top priorities of modern neurobiology. N-docosahexanoylethanolamine (DHEA, synaptamide) is an endogenous metabolite and structural analog of anandamide, an essential endocannabinoid produced from arachidonic acid. Our study aims to elucidate the pharmacological activity of synaptamide in lipopolysaccharide (LPS)-induced neuroinflammation. Memory deficits in animals were determined using behavioral tests. To study the effects of LPS (750 µg/kg/day, 7 days) and synaptamide (10 mg/kg/day, 7 days) on synaptic plasticity, long-term potentiation was examined in the CA1 area of acute hippocampal slices. The Golgi-Cox method allowed us to assess neuronal morphology. The production of inflammatory factors and receptors was assessed using ELISA and immunohistochemistry. During the study, functional, structural, and plastic changes within the hippocampus were identified. We found a beneficial effect of synaptamide on hippocampal synaptic plasticity and morphological characteristics of neurons. Synaptamide treatment recovered hippocampal neurogenesis, suppressed microglial activation, and significantly improved hippocampus-dependent memory. The basis of the phenomena described above is probably the powerful anti-inflammatory activity of synaptamide, as shown in our study and several previous works.

Genomic DNA i-motifs as fast sensors responsive to near-physiological pH microchanges

We report the design of robust sensors for measuring intracellular pH, based on the native DNA i-motifs (iMs) found in neurodegeneration- or carcinogenesis-related genes. Those iMs appear to be genomic regulatory elements and might modulate transcription in response to pH stimuli. Given their intrinsic sensitivity to minor pH changes within the physiological range, such noncanonical DNA structures can be used as sensor core elements without additional modules other than fluorescent labels or quenchers. We focused on several iMs that exhibited fast folding/unfolding kinetics. Using stopped-flow techniques and FRET-melting/annealing assays, we confirmed that the rates of temperature-driven iM-ssDNA transitions correlate with the rates of the pH-driven transitions. Thus, we propose FRET-based hysteresis analysis as an express method for selecting sensors with desired kinetic characteristics. For the leading fast-response sensor, we optimized the labelling scheme and performed intracellular calibration. Unlike the commonly used small-molecule pH indicators, that sensor was transferred efficiently to cell nuclei. Considering its favourable kinetic characteristics, the sensor can be used for monitoring proton dynamics in the nucleus. These results argue that the 'genome-inspired' design is a productive approach to the development of biocompatible molecular tools.

Proton extrusion during oxidative burst in microglia exacerbates pathological acidosis following traumatic brain injury

Acidosis is among the least studied secondary injury mechanisms associated with neurotrauma. Acute decreases in brain pH correlate with poor long‐term outcome in patients with traumatic brain injury (TBI), however, the temporal dynamics and underlying mechanisms are unclear. As key drivers of neuroinflammation, we hypothesized that microglia directly regulate acidosis after TBI, and thereby, worsen neurological outcomes. Using a controlled cortical impact model in adult male mice we demonstrate that intracellular pH in microglia and extracellular pH surrounding the lesion site are significantly reduced for weeks after injury. Microglia proliferation and production of reactive oxygen species (ROS) were also increased during the first week, mirroring the increase in extracellular ROS levels seen around the lesion site. Microglia depletion by a colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622, markedly decreased extracellular acidosis, ROS production, and inflammation in the brain after injury. Mechanistically, we identified that the voltage‐gated proton channel Hv1 promotes oxidative burst activity and acid extrusion in microglia. Compared to wildtype controls, microglia lacking Hv1 showed reduced ability to generate ROS and extrude protons. Importantly, Hv1‐deficient mice exhibited reduced pathological acidosis and inflammation after TBI, leading to long‐term neuroprotection and functional recovery. Our data therefore establish the microglial Hv1 proton channel as an important link that integrates inflammation and acidosis within the injury microenvironment during head injury.

A New Perspective on Ameliorating Depression-Like Behaviors: Suppressing Neuroinflammation by Upregulating PGC-1α

Inflammation plays an important role in depression pathology, making it a promising target for ameliorating depression-like behaviors. The peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a transcriptional coactivator being able to constrain inflammatory events through NF-κB signaling. However, the role of PGC-1α in depression is not yet clear. This study was designed to investigate the role of PGC-1α in depression and explore the underlying mechanisms. Mice modeled with chronic unpredictable mild stimulation (CUMS) were explored for the relationship between depression-like behaviors and PGC-1α. Baicalin was used to evaluate the effect regulating PGC-1α. Furthermore, the anti-neuroinflammatory effect of baicalin was investigated both in BV2-SH-SY5Y co-culture system and in mice by LPS challenge. The role of PGC-1α in neuroinflammation was explored in cell co-culture systems under gene silencing conditions targeting NF-κB signaling. We found that the expression of PGC-1α was inhibited in the hippocampus of mice exposed to CUMS or LPS, while baicalin could increase the expression of PGC-1α and alleviate the depression-like behaviors. Furthermore, baicalin attenuated neuroinflammation in the hippocampus of mice and BV2-SH-SY5Y co-culture system by LPS challenge via regulating NF-κB signaling; however, knockdown of the PGC-1α could reverse the effect of baicalin on neuroinflammation and NF-κB signaling. Our results revealed a vital role for PGC-1α in attenuating neuroinflammation in depression, indicating that PGC-1α might be a therapeutic target for depression.

The anti-neuroinflammatory effects of Clinacanthus nutans leaf extract on metabolism elucidated through 1H NMR in correlation with cytokines microarray

Clinacanthus nutans (CN) (Acanthaceae) is well-known for its anti-inflammatory properties among Asian communities; however, there are currently no data specifically focused on the anti-inflammatory effects of CN on the brain tissue. Neuroinflammation is a common consequence of toxin intrusion to any part of the central nervous system (CNS). As an innate immune response, the CNS may react through both protective and/or toxic actions due to the activation of neuron cells producing pro- and/or anti-inflammatory cytokines in the brain. The unresolved activation of the inflammatory cytokines' response is associated with the pathogenesis of neurological disorders. The present study aimed to decipher the metabolic mechanism on the effects of 14 days oral treatment with CN aqueous extract in induced-lipopolysaccharides (LPS) rats through 1H NMR spectroscopic biomarker profiling of the brain tissue and the related cytokines. Based on the principal component analysis (PCA) of the nuclear magnetic resonance (NMR) spectral data, twenty-one metabolites in the brain tissue were profiled as biomarkers for the LPS (10 μL)-induced neuroinflammation following intracerebroventricular injection. Among the twenty-one biomarkers in the neuroinflammed rats, CN treatment of 1000 and 500 mg/kg BW successfully altered lactate, pyruvate, phosphorylcholine, glutamine, and α-ketoglutarate when compared to the negative control. Likewise, statistical isolinear multiple component analysis (SIMCA) showed that treatments by CN and the positive control drug, dextromethorphan (DXM, 5 mg/kg BW), have anti-neuroinflammatory potential. A moderate correlation, in the orthogonal partial least squares (OPLS) regression model, was found between the spectral metabolite profile and the cytokine levels. The current study revealed the existence of high levels of pro-inflammatory cytokines, namely IL-1α, IL-1β, and TNF-α in LPS-induced rats. Both CN dose treatments lowered IL-1β significantly better than DXM Interestingly, DXM and CN treatments both exhibited the upregulation of the anti-inflammatory cytokines IL-2 and 4. However, DXM has an advantage over CN in that the former also increased the expression of IL-10 of anti-inflammatory cytokines. In this study, a metabolomics approach was successfully applied to discover the mechanistic role of CN in controlling the neuroinflammatory conditions through the modulation of complex metabolite interactions in the rat brain.

Topiramate Decelerates Bicarbonate-Driven Acid-Elimination of Human Neocortical Neurons: Strategic Significance for its Antiepileptic, Antimigraine and Neuroprotective Properties

BACKGROUND

Mammalian central neurons regulate their intracellular pH (pHi) strongly and even slight pHi-fluctuations can influence inter-/intracellular signaling, synaptic plasticity and excitability.

OBJECTIVE

For the first time, we investigated topiramate´s (TPM) influence on pHi-behavior of human central neurons representing a promising target for anticonvulsants and antimigraine drugs.

METHODS

In slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal lobe epilepsy, BCECF-AM-loaded neocortical pyramidal-cells were investigated by fluorometry. The pHi-regulation was estimated by using the recovery-slope from intracellular acidification after an Ammonium-Prepulse (APP).

RESULTS

Among 17 pyramidal neurons exposed to 50 μM TPM, seven (41.24%) responded with an altered resting-pHi (7.02±0.12), i.e., acidification of 0.01-0.03 pH-units. The more alkaline the neurons, the greater the TPM-related acidifications (r=0.7, p=0.001, n=17). The recovery from APPacidification was significantly slowed under TPM (p<0.001, n=5). Further experiments using nominal bicarbonate-free (n=2) and chloride-free (n=2) conditions pointed to a modulation of the HCO3 -- driven pHi-regulation by TPM, favoring a stimulation of the passive Cl-/HCO3 --antiporter (CBT) - an acid-loader predominantly in more alkaline neurons.

CONCLUSION

TPM modulated the bicarbonate-driven pHi-regulation, just as previously described in adult guinea-pig hippocampal neurons. We discussed the significance of the resulting subtle acidifications for beneficial antiepileptic, antimigraine and neuroprotective effects as well as for unwanted cognitive deficits.

Electrochemical detection of exogenously administered melatonin in the brain

Melatonin (MT) is an important electroactive hormone that regulates different physiological actions in the brain, ranging from circadian clock to neurodegeneration. An impressive number of publications have highlighted the effectiveness of MT treatments in different types of sleep and neurological disorders, including Alzheimer's and Parkinson's disease. The ability to detect MT in different regions of the brain would provide further insights into the physiological roles and therapeutic effects of MT. While multiple electrochemical methods have been used to detect MT in biological samples, monitoring MT in the brain of live animals has not been demonstrated. Here, we optimized a square wave voltammetry (SWV) electroanalytical method to evaluate the MT detection performance at CFEs in vitro and in vivo. SWV was able to sensitively detect the MT oxidation peak at 0.7 V, and discriminate MT from most common interferents in vitro. More importantly, using the optimized SWV, CFEs successfully detected and reliably quantified MT concentrations in the visual cortex of anesthetized mice after intraperitoneal injections of different MT doses, offering stable MT signals for up to 40 minutes. To the best of our knowledge, this is the first electrochemical measurement of exogenously administered MT in vivo. This electrochemical MT sensing technique will provide a powerful tool for further understanding MT's action in the brain.

A novel role of NLRP3-generated IL-1β in the acute-chronic transition of peripheral lipopolysaccharide-elicited neuroinflammation: implications for sepsis-associated neurodegeneration

BACKGROUND

Sepsis-associated acute brain inflammation, if unresolved, may cause chronic neuroinflammation and resultant neurodegenerative diseases. However, little is known how the transition from acute to chronic neuroinflammation, which is critical for the following progressive neurodegeneration, occurs in sepsis. The goal of this study was to investigate potential immune factors regulating the transition process using a widely used endotoxemia LPS mouse model. This model shows distinct acute and chronic phases of neuroinflammation and recapitulates many cardinal features of Parkinson's disease, thus, providing a unique opportunity for studying phase transition of neuroinflammation.

METHODS

C57BL/6 J, NLRP3-/-, and IL-1R1-/- mice were employed. Mild and severe endotoxemia were produced by LPS ip injection at 1 or 5 mg/kg. Neuroinflammation in vitro and in vivo was assessed with proinflammatory cytokine expression by qPCR or ELISA and microglial activation by immunohistochemical analysis. Neurodegeneration was measured by manual and stereological counts of nigral dopaminergic neurons and immunohistochemical analysis of protein nitrosylation and α-synuclein phosphorylation.

RESULTS

LPS-elicited initial increases in mouse brain mRNA levels of TNFα, IL-6, IL-1β, and MCP-1, and nigral microglial activation were not dose-related. By contrast, the delayed increase in brain mature IL-1β levels was dependent on LPS doses and protracted nigral microglial activation was only observed in high dose of LPS-treated mice. LPS-elicited increase in brain mature IL-1β but not IL-1α level was NLRP3-dependent. After high dose LPS treatment, deficiency of NLRP3 or IL-1R1 did not prevent the initiation of acute neuroinflammation but abolished chronic neuroinflammation. Genetic or pharmacological inhibition of the NLRP3-IL-1β axis repressed LPS-stimulated upregulation of chronic neuroinflammatory mediators including MHC-II, NOX2, and Mac1, and protected dopaminergic neurons. Ten months after LPS-elicited severe endotoxemia, nigral persisted microglial activation, elevated nitrosylated proteins and phosphorylated α-synuclein, and significant neuronal degeneration developed in wild-type mice but not in NLRP3-/- or IL-1R1-/- mice.

CONCLUSIONS

This study uncovers a novel role of the NLRP3-IL-1β signaling pathway in gauging the severity of sepsis-associated inflammation and determining whether acute neuroinflammation will resolve or transition to low grade chronic neuroinflammation. These findings also provide novel targets for developing therapy for severe systemic infection-related neurodegeneration.

Demarcation of Sepsis-Induced Peripheral and Central Acidosis with pH (Low) Insertion Cycle Peptide

Acidosis is a key driver for many diseases, including cancer, sepsis, and stroke. The spatiotemporal dynamics of dysregulated pH across disease remain elusive, and current diagnostic strategies do not provide localization of pH alterations. We sought to explore if PET imaging using hydrophobic cyclic peptides that partition into the cellular membrane at low extracellular pH (denoted as pH [low] insertion cycles, or pHLIC) can permit accurate in vivo visualization of acidosis. Methods: Acid-sensitive cyclic peptide c[E₄W₅C] pHLIC was conjugated to bifunctional maleimide-NO2A and radiolabeled with ⁶⁴Cu (half-life, 12.7 h). C57BL/6J mice were administered lipopolysaccharide (15 mg/kg) or saline (vehicle) and serially imaged with [⁶⁴Cu]Cu-c[E₄W₅C] over 24 h. Ex vivo autoradiography was performed on resected brain slices and subsequently stained with cresyl violet to enable high-resolution spatial analysis of tracer accumulation. A non-pH-sensitive cell-penetrating control peptide (c[R₄W₅C]) was used to confirm specificity of [⁶⁴Cu]Cu-c[E₄W₅C]. CD11b (macrophage/microglia) and TMEM119 (microglia) immunostaining was performed to correlate extent of neuroinflammation with [⁶⁴Cu]Cu-c[E₄W₅C] PET signal. Results: [⁶⁴Cu]Cu-c[E₄W₅C] radiochemical yield and purity were more than 95% and more than 99%, respectively, with molar activity of more than 0.925 MBq/nmol. Significantly increased [⁶⁴Cu]Cu-c[E₄W₅C] uptake was observed in lipopolysaccharide-treated mice (vs. vehicle) within peripheral tissues, including blood, lungs, liver, and small intestines (P < 0.001-0.05). Additionally, there was significantly increased [⁶⁴Cu]Cu-c[E₄W₅C] uptake in the brains of lipopolysaccharide-treated animals. Autoradiography confirmed increased uptake in the cerebellum, cortex, hippocampus, striatum, and hypothalamus of lipopolysaccharide-treated mice (vs. vehicle). Immunohistochemical analysis revealed microglial or macrophage infiltration, suggesting activation in brain regions containing increased tracer uptake. [⁶⁴Cu]Cu-c[R₄W₅C] demonstrated significantly reduced uptake in the brain and periphery of lipopolysaccharide mice compared with the acid-mediated [⁶⁴Cu]Cu-c[E₄W₅C] tracer. Conclusion: Here, we demonstrate that a pH-sensitive PET tracer specifically detects acidosis in regions associated with sepsis-driven proinflammatory responses. This study suggests that [⁶⁴Cu]Cu-pHLIC is a valuable tool to noninvasively assess acidosis associated with both central and peripheral innate immune activation.

Photobiomodulation therapy in knee osteoarthritis reduces oxidative stress and inflammatory cytokines in rats

Knee osteoarthritis (OA) is a chronic disease that causes pain and gradual degeneration of the articular cartilage. In this study, MIA-induced OA knee model was used in rats to test the effects of the photobiomodulation therapy (PBM). We analyzed the inflammatory process (pain and cytokine levels), and its influence on the oxidative stress and antioxidant capacity. Knee OA was induced by monosodium iodoacetate (MIA) intra-articular injection (1.5 mg/50 μL) and the rats were treated with eight sessions of PBM 3 days/week (904 nm, 6 or 18 J/cm² ). For each animal, mechanical and cold hyperalgesia and spontaneous pain were evaluated; biological analyses were performed in blood serum, intra-articular lavage, knee structures, spinal cord and brainstem. Cytokine assays were performed in knee, spinal cord and brainstem samples. The effects of the 18 J/cm² dose of PBM were promising in reducing pain and neutrophil activity in knee samples, together with reducing oxidative stress damage in blood serum and spinal cord samples. PBM improved the antioxidant capacity in blood serum and brainstem, and decreased the knee pro-inflammatory cytokine levels. Our study demonstrated that PBM decreased oxidative damage, inflammation and pain. Therefore, this therapy could be an important tool in the treatment of knee OA.

Active Fraction Combination from Liuwei Dihuang Decoction (LW-AFC) Alleviated the LPS-Induced Long-Term Potentiation Impairment and Glial Cells Activation in Hippocampus of Mice by Modulating Immune Responses

Neuroinflammation is known as a typical feature associated with many neurodegenerative diseases including Alzheimer's disease (AD) and impairs the synaptic plasticity of the hippocampus. LW-AFC is an active fraction combination being extracted from Liuwei Dihuang decoction, a classic traditional Chinese medicine prescription. This study aimed to investigate the effects of LW-AFC on synaptic plasticity in mice with lipopolysaccharide (LPS) treatment. The results showed that the administration of LPS caused fever and long-term potentiation (LTP) impairment in mice. The pretreatment with LW-AFC had an antipyretic effect on fever and improved the impaired LTP induced by LPS, alleviated the microglia and astrocytes activation in the hippocampus, regulated the abnormal T-lymphocyte subpopulation in the spleen and blood caused by LPS, and reduced the aberrant secretion of cytokines in the brain and plasma. The compounds paeoniflorin, morroniside, and loganic acid in LW-AFC regulated the TNF-α secretion in non-LPS- and LPS-stimulated BV-2 cells. These data suggest that LW-AFC improves the LPS-induced impairment of LTP and alleviates the activation of glial cells in the hippocampus, which might be associated with modulating immune responses.

The effect of red-to-near-infrared (R/NIR) irradiation on inflammatory processes

Introduction: Near-infrared (NIR) and red-to-near-infrared (R/NIR) radiation are increasingly applied for therapeutic use. R/NIR-employing therapies aim to stimulate healing, prevent tissue necrosis, increase mitochondrial function, and improve blood flow and tissue oxygenation. The wide range of applications of this radiation raises questions concerning the effects of R/NIR on the immune system. Methods: In this review, we discuss the potential effects of exposure to R/NIR light on immune cells in the context of physical parameters of light. Discussion: The effects that R/NIR may induce in immune cells typically involve the production of reactive oxygen species (ROS), nitrogen oxide (NO), or interleukins. Production of ROS after exposure to R/NIR can either be inhibited or to some extent increased, which suggests that detailed conditions of experiments, such as the spectrum of radiation, irradiance, exposure time, determine the outcome of the treatment. However, a wide range of immune cell studies have demonstrated that exposure to R/NIR most often has an anti-inflammatory effect. Finally, photobiomodulation molecular mechanism with particular attention to the role of interfacial water structure changes for cell physiology and regulation of the inflammatory process was described. Conclusions: Optimization of light parameters allows R/NIR to act as an anti-inflammatory agent in a wide range of medical applications.

Effects of in vivo conditions on amyloid aggregation

One of the grand challenges of biophysical chemistry is to understand the principles that govern protein misfolding and aggregation, which is a highly complex process that is sensitive to initial conditions, operates on a huge range of length- and timescales, and has products that range from protein dimers to macroscopic amyloid fibrils. Aberrant aggregation is associated with more than 25 diseases, which include Alzheimer's, Parkinson's, Huntington's, and type II diabetes. Amyloid aggregation has been extensively studied in the test tube, therefore under conditions that are far from physiological relevance. Hence, there is dire need to extend these investigations to in vivo conditions where amyloid formation is affected by a myriad of biochemical interactions. As a hallmark of neurodegenerative diseases, these interactions need to be understood in detail to develop novel therapeutic interventions, as millions of people globally suffer from neurodegenerative disorders and type II diabetes. The aim of this review is to document the progress in the research on amyloid formation from a physicochemical perspective with a special focus on the physiological factors influencing the aggregation of the amyloid-β peptide, the islet amyloid polypeptide, α-synuclein, and the hungingtin protein.

Levetiracetam mediates subtle pH-shifts in adult human neocortical pyramidal cells via an inhibition of the bicarbonate-driven neuronal pH-regulation - Implications for excitability and plasticity modulation

The intracellular pH (pHi) of mammalian central neurons is tightly regulated and small pHi-fluctuations can fine-tune inter-/intracellular signaling, excitability, and synaptic plasticity. The research-gap about the pHi-regulation of human brain neurons is addressed here by testing possible influences of the anticonvulsant levetiracetam (LEV). BCECF-AM-loaded neocortical pyramidal cells were fluorometrically investigated in slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal-lobe epilepsy. Recovery-slope from intracellular acidification following an ammonium prepulse (APP) was used to measure the pHi-regulation. Among twenty pyramidal cells exposed to 50 μM LEV, the resting pHi (7.09 ± 0.14) was lowered in eight (40%) neurons, on average by 0.02 ± 0.011 pH-units. In three (15%) and nine (45%) neurons, a minimal alkaline shift (0.017 ± 0.004 pH-units) and no pHi-shift occurred, respectively. The LEV-induced pHi-shifts were positively correlated with the resting pHi (r = 0.6, p = 0.006, n = 20). In five neurons, which all had responded on LEV with an acidification before, the recovery from APP-acidification was significantly delayed during LEV (p < 0.001). This inhibitory LEV-effect on pHi-regulation i) was similar to that of 200 μM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (n = 2) and ii) did not occur under nominal bicarbonate-free conditions (n = 2). Thus, LEV lowered the pHi of human neocortical pyramidal cells most likely by a weakening of the transmembrane HCO3(-)-mediated acid-extrusion. This might contribute to LEV's anticonvulsive potency. Neurons with more acidic resting pHi-values showed a minimal alkalization upon LEV providing a mechanism for paradoxical proconvulsive LEV-effects rarely observed in epilepsy patients. The significance of these subtle pHi-shifts for cortical excitability and plasticity is discussed.

Copper mediated amyloid-β binding to Transthyretin

Transthyretin (TTR), a homotetrameric protein that transports thyroxine and retinol both in plasma and in cerebrospinal (CSF) fluid provides a natural protective response against Alzheimer's disease (AD), modulates amyloid-β (Aβ) deposition by direct interaction and co-localizes with Aβ in plaques. TTR levels are lower in the CSF of AD patients. Zn²⁺, Mn²⁺ and Fe²⁺ transform TTR into a protease able to cleave Aβ. To explain these activities, monomer dissociation or conformational changes have been suggested. Here, we report that when TTR crystals are exposed to copper or iron salts, the tetramer undergoes a significant conformational change that alters the dimer-dimer interface and rearranges residues implicated in TTR's ability to neutralize Aβ. We also describe the conformational changes in TTR upon the binding of the various metal ions. Furthermore, using bio-layer interferometry (BLI) with immobilized Aβ(1-28), we observe the binding of TTR only in the presence of copper. Such Cu²⁺-dependent binding suggests a recognition mechanism whereby Cu²⁺ modulates both the TTR conformation, induces a complementary Aβ structure and may participate in the interaction. Cu²⁺-soaked TTR crystals show a conformation different from that induced by Fe²⁺, and intriguingly, TTR crystals grown in presence of Aβ(1-28) show different positions for the copper sites from those grown its absence.

The histamine H3R antagonist DL77 attenuates autistic behaviors in a prenatal valproic acid-induced mouse model of autism

Autistic spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairment in social communication and restricted/repetitive behavior patterns or interests. Antagonists targeting histamine H3 receptor (H3R) are considered potential therapeutic agents for the therapeutic management of different brain disorders, e.g., cognitive impairments. Therefore, the effects of subchronic treatment with the potent and selective H3R antagonist DL77 (5, 10, or 15 mg/kg, i.p.) on sociability, social novelty, anxiety, and aggressive/repetitive behavior in male Tuck-Ordinary (TO) mice with ASD-like behaviors induced by prenatal exposure to valproic acid (VPA, 500 mg/kg, i.p.) were evaluated using the three-chamber test (TCT), marble burying test (MBT), nestlet shredding test (NST), and elevated plus maze (EPM) test. The results showed that VPA-exposed mice exhibited significantly lower sociability and social novelty preference compared to VPA-exposed mice that were pretreated with DL77 (10 or 15 mg/kg, i.p.). VPA-exposed mice presented a significantly higher percentage of buried marbles in MBT and shredded nestlet significantly more in NST compared to the control groups. However, VPA-exposed animals pretreated with DL77 (10 or 15 mg/kg, i.p.) buried a reduced percentage of marbles in MBT and presented a significantly lower percentage of shredding behavior in NST. On the other hand, pretreatment with DL77 (5, 10, or 15 mg/kg, i.p.) failed to restore the disturbed anxiety levels and hyperactivity observed in VPA-exposed animals in EPM, whereas the reference drug donepezil (DOZ, 1 mg/kg, i.p.) significantly palliated the anxiety and reduced the hyperactivity measures of VPA-exposed mice. Furthermore, pretreatment with DL77 (10 or 15 mg/kg, i.p.) modulated oxidative stress status by increasing GSH and decreasing MDA, and it attenuated the proinflammatory cytokines IL-1β, IL-6 and TNF-α exacerbated by lipopolysaccharide (LPS) challenge, in VPA-exposed mouse brain tissue. Taken together, these results provide evidence that modulation of brain histaminergic neurotransmission, such as by subchronic administration of the H3R antagonist DL77, may serve as an effective pharmacological therapeutic target to rescue ASD-like behaviors in VPA-exposed animals, although further investigations are necessary to corroborate and expand these initial data.

Aging is associated with a mild acidification in neocortical human neurons in vitro

The intracellular pH (pHi) in the cytosol of mammalian central neurons is tightly regulated and small pHi-fluctuations are deemed to modulate inter-/intracellular signaling, excitability, and synaptic plasticity. The resting pHi of young rodent hippocampal pyramidal neurons is known to decrease alongside aging for about 0.1 pH-units. There is no information about the relationship between age and pHi of human central neurons. We addressed this knowledge gap using 26 neocortical slices from 12 patients (1-56-years-old) who had undergone epilepsy surgery. For fluorometric recordings, the slice-neurons were loaded with the pHi-sensitive dye BCECF-AM. We found that the pyramidal cells' resting pHi (n = 26) descended linearly alongside aging (r = - 0.71, p < 0.001). This negative relationship persisted, when the sample was confined to specific brain regions (i.e., middle temporal gyrus, 23 neurons, r = - 0.68, p < 0.001) or pathologies (i.e., hippocampus sclerosis, 8 neurons, r = - 0.78, p = 0.02). Specifically, neurons (n = 9, pHi 7.25 ± 0.12) from young children (1.5 ± 0.46-years-old) were significantly more alkaline than neurons from adults (n = 17, 38.53 ± 12.38 years old, pHi 7.08 ± 0.07, p < 0.001). Although the samples were from patients with different pathologies the results were in line with those from the rodent hippocampal pyramidal neurons. Like a hormetin, the age-related mild pHi-decrease might contribute to neuroprotection, e.g., via limiting excitotoxicity. On the other hand, aging cortical neurons could become more vulnerable to metabolic overstress by a successive pHi-decrease. Certainly, its impact for the dynamics in short and long-term synaptic plasticity and, ultimately, learning and memory provides a challenge for further research.

Plant Polyphenols and Exendin-4 Prevent Hyperactivity and TNF-α Release in LPS-Treated In vitro Neuron/Astrocyte/Microglial Networks

Increasing evidence supports a decisive role for neuroinflammation in the neurodegenerative process of several central nervous system (CNS) disorders. Microglia are essential mediators of neuroinflammation and can regulate a broad spectrum of cellular responses by releasing reactive oxygen intermediates, nitric oxide, proteases, excitatory amino acids, and cytokines. We have recently shown that also in ex-vivo cortical networks of neurons, astrocytes and microglia, an increased level of tumor necrosis factor-alpha (TNF-α) was detected a few hours after exposure to the bacterial endotoxin lipopolysaccharide (LPS). Simultaneously, an atypical “seizure-like” neuronal network activity was recorded by multi-electrode array (MEA) electrophysiology. These effects were prevented by minocycline, an established anti-inflammatory antibiotic. We show here that the same inhibitory effect against LPS-induced neuroinflammation is exerted also by natural plant compounds, polyphenols, such as curcumin (CU, curcuma longa), crocin (CR, saffron), and resveratrol (RE, grape), as well as by the glucagon like peptide-1 receptor (GLP-1R) agonist exendin-4 (EX-4). The drugs tested also caused per-se early transient (variable) changes of network activity. Since it has been reported that LPS-induced neuroinflammation causes rearrangements of glutamate transporters in astrocytes and microglia, we suggest that neural activity could be putatively increased by an imbalance of glial glutamate transporter activity, leading to prolonged synaptic glutamatergic dysregulation.