Species-Dependent Blood-Brain Barrier Disruption of Lipopolysaccharide: Amelioration by Colistin In Vitro and In Vivo

2-(3,4-Dihydroxyphenyl)ethyl 3-hydroxybutanoate Ameliorates Cognitive Dysfunction and Inflammation Via Modulating Gut Microbiota in Aged Senescence-Accelerated Mouse Prone8 Mice

Numerous studies have indicated a close association between gut microbiota dysbiosis, inflammation, and cognitive impairment, highlighting their crucial role in the aging process. 2-(3,4-Dihydroxyphenyl)ethyl 3-hydroxybutanoate (HTHB), a novel derivative of hydroxytyrosol, known for its metabolic and anti-inflammatory properties, was investigated for its effects on memory, inflammation, and gut microbiota in senescence-accelerated mouse prone 8 mice. The study employed behavioral testing, biochemical detection, and 16S RNA analysis. Results revealed that HTHB mitigated memory decline and lymphocyte aberrance, reduced inflammation in the brain cortex, intestine and peripheral system, and modulated gut microbiota dysbiosis. Interestingly, the cognitive function and serum inflammation of mice significantly correlated with differences in gut microbiota in senescence-accelerated mouse prone 8 mice. Furthermore, HTHB treatment exhibited an enhancement of gut barrier integrity in colon tissue in SAMP8 mice. In vitro experiments using HCT116 and DLD1 cells further evidenced that HTHB rescued the tight junction protein levels impaired by lipopolysaccharide. These findings demonstrate that HTHB effectively ameliorates cognitive dysfunction in aged mice, by modulating gut microbiota, suppressing inflammation, and promoting intestinal barrier integrity. This highlights the potential of HTHB as a therapeutic agent for age-related cognitive loss.

From Gut Microbiomes to Infectious Pathogens: Neurological Disease Game Changers

Gut microbiota and infectious diseases affect neurological disorders, brain development, and function. Compounds generated in the gastrointestinal system by gut microbiota and infectious pathogens may mediate gut-brain interactions, which may circulate throughout the body and spread to numerous organs, including the brain. Studies shown that gut bacteria and disease-causing organisms may pass molecular signals to the brain, affecting neurological function, neurodevelopment, and neurodegenerative diseases. This article discusses microorganism-producing metabolites with neuromodulator activity, signaling routes from microbial flora to the brain, and the potential direct effects of gut bacteria and infectious pathogens on brain cells. The review also considered the neurological aspects of infectious diseases. The infectious diseases affecting neurological functions and the disease modifications have been discussed thoroughly. Recent discoveries and unique insights in this perspective need further validation. Research on the complex molecular interactions between gut bacteria, infectious pathogens, and the CNS provides valuable insights into the pathogenesis of neurodegenerative, behavioral, and psychiatric illnesses. This study may provide insights into advanced drug discovery processes for neurological disorders by considering the influence of microbial communities inside the human body.

Inter-alpha inhibitor proteins attenuate lipopolysaccharide-induced blood-brain barrier disruption in neonatal mice

There is a paucity of information regarding efficacious pharmacological neuroprotective strategies to attenuate or reduce brain injury in neonates. Lipopolysaccharide (LPS) disrupts blood-brain barrier (BBB) function in adult rodents and increases inflammation in adults and neonates. Human blood-derived Inter-alpha Inhibitor Proteins (IAIPs) are neuroprotective, improve neonatal survival after LPS, and attenuate LPS-induced disruption of the BBB in adult male mice. We hypothesized that LPS also disrupts the function of the BBB in neonatal mice and that IAIPs attenuate the LPS-induced BBB disruption in male and female neonatal mice. IAIPs were administered to neonatal mice after LPS and BBB permeability quantified with intravenous 14C-sucrose and 99mTc-albumin. Although repeated high doses (3 mg/kg) of LPS in neonates resulted in high mortality rates and a robust increase in BBB permeability, repeated lower doses (1 mg/kg) of LPS resulted in lower mortality rates and disruption of the BBB in both male and female neonates. IAIP treatment attenuated disruption of the BBB similarly to sucrose and albumin after exposure to low-dose LPS in neonatal mice. Exposure to low-dose LPS elevated IAIP concentrations in blood, but it did not appear to increase the systemic levels of Pre-alpha inhibitor (PaI), one of the family members of the IAIPs that contains heavy chain 3. We conclude that IAIPs attenuate LPS-related disruption of the BBB in both male and female neonatal mice.

Chaihu Shugan San ameliorated cognitive deficits through regulating gut microbiota in senescence-accelerated mouse prone 8

Background: Traditional Chinese medicines exhibit promising preventive effects on Alzheimer's disease. Chaihu Shugan San (CSS) is a well-known traditional herbal formula whose several kinds of ingredients have the potential of ameliorating Alzheimer's disease. The present study aimed to evaluate the effects of CSS on the microbiota-gut-brain axis and cognitive deficits of senescence-accelerated mouse prone 8 (SAMP8) mice as well as investigate the underlying mechanisms. Methods: Thirty 5-month-old SAMP8 mice were randomly divided into the model group (SAMP8), CSS low-dose treatment group (CSSL), and CSS high-dose treatment group (CSSH). Ten SAMR1 mice were used as the normal control, and ten SAMP8 mice treated with donepezil were used as the positive control of cognitive function. CSS was orally administrated to SAMP8 mice for 8 weeks. The Morris water maze test was used to evaluate cognitive function. Histological staining was used to observe neuronal injury and Aβ deposition. Transmission electron microscopy was used to observe the synaptic ultrastructure. 16S rRNA gene analysis was performed to measure the changes in intestinal microbiota. Results: The results showed that CSS significantly improved the learning function and memory deficits of aged SAMP8 mice in the Morris water maze examination. CSS ameliorated neuronal injury, synaptic injuries, and Aβ deposition in the brain of SAMP8 mice. In addition, CSS also significantly improved microbiota composition in terms of elevating Lactobacillus reuteri and decreasing Staphylococcus xylosus in the feces of aged SAMP8 mice. Conclusion: These findings suggested that CSS might have a preventive potential for cognitive deficits in aging through regulating gut microbiota, which paved the way for the application of CSS for prevention and therapeutic purposes for mild cognitive impairment as well as Alzheimer's disease.

Dynamic Interleukin-1 Receptor Type 1 Signaling Mediates Microglia-Vasculature Interactions Following Repeated Systemic LPS

Introduction

Lipopolysaccharide (LPS) preconditioning involves repeated, systemic, and sub-threshold doses of LPS, which induces a neuroprotective state within the CNS, thus preventing neuronal death and functional losses. Recently, proinflammatory cytokine, Interleukin-1 (IL-1), and its primary signaling partner, interleukin-1 receptor type 1 (IL-1R1), have been associated with neuroprotection in the CNS. However, it is still unknown how IL-1/IL-1R1 signaling impacts the processes associated with neuroprotection.

Methods

Using our IL-1R1 restore genetic mouse model, mouse lines were generated to restrict IL-1R1 expression either to endothelia (Tie2-Cre-Il1r1^r/r) or microglia (Cx3Cr1-Cre-Il1r1 ^r/r), in addition to either global ablation (Il1r1 ^r/r) or global restoration of IL-1R1 (Il1r1 ^GR/GR). The LPS preconditioning paradigm consisted of four daily i.p. injections of LPS at 1 mg/kg (4d LPS). 24 hrs following the final i.p. LPS injection, tissue was collected for qPCR analysis, immunohistochemistry, or FAC sorting.

Results

Following 4d LPS, we found multiple phenotypes that are dependent on IL-1R1 signaling such as microglia morphology alterations, increased microglial M2-like gene expression, and clustering of microglia onto the brain vasculature. We determined that 4d LPS induces microglial morphological changes, clustering at the vasculature, and gene expression changes are dependent on endothelial IL-1R1, but not microglial IL-1R1. A novel observation was the induction of microglial IL-1R1 (mIL-1R1) following 4d LPS. The induced mIL-1R1 permits a unique response to central IL-1β: the mIL-1R1 dependent induction of IL-1R1 antagonist (IL-1RA) and IL-1β gene expression. Analysis of RNA sequencing datasets revealed that mIL-1R1 is also induced in neurodegenerative diseases.

Discussion

Here, we have identified cell type-specific IL-1R1 mediated mechanisms, which may contribute to the neuroprotection observed in LPS preconditioning. These findings identify key cellular and molecular contributors in LPS-induced neuroprotection.

Rescuing the Last-Line Polymyxins: Achievements and Challenges

Antibiotic resistance is a major global health challenge and, worryingly, several key Gram negative pathogens can become resistant to most currently available antibiotics. Polymyxins have been revived as a last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacterales. Polymyxins were first discovered in the late 1940s but were abandoned soon after their approval in the late 1950s as a result of toxicities (e.g., nephrotoxicity) and the availability of "safer" antibiotics approved at that time. Therefore, knowledge on polymyxins had been scarce until recently, when enormous efforts have been made by several research teams around the world to elucidate the chemical, microbiological, pharmacokinetic/pharmacodynamic, and toxicological properties of polymyxins. One of the major achievements is the development of the first scientifically based dosage regimens for colistin that are crucial to ensure its safe and effective use in patients. Although the guideline has not been developed for polymyxin B, a large clinical trial is currently being conducted to optimize its clinical use. Importantly, several novel, safer polymyxin-like lipopeptides are developed to overcome the nephrotoxicity, poor efficacy against pulmonary infections, and narrow therapeutic windows of the currently used polymyxin B and colistin. This review discusses the latest achievements on polymyxins and highlights the major challenges ahead in optimizing their clinical use and discovering new-generation polymyxins. To save lives from the deadly infections caused by Gram negative "superbugs," every effort must be made to improve the clinical utility of the last-line polymyxins. SIGNIFICANCE STATEMENT: Antimicrobial resistance poses a significant threat to global health. The increasing prevalence of multidrug-resistant (MDR) bacterial infections has been highlighted by leading global health organizations and authorities. Polymyxins are a last-line defense against difficult-to-treat MDR Gram negative pathogens. Unfortunately, the pharmacological information on polymyxins was very limited until recently. This review provides a comprehensive overview on the major achievements and challenges in polymyxin pharmacology and clinical use and how the recent findings have been employed to improve clinical practice worldwide.

Lipopolysaccharide influences the plasma and brain pharmacokinetics of subcutaneously-administered HsTX1[R14A], a KV1.3-blocking peptide

K_V1.3 is a voltage-gated potassium channel that is upregulated in neuroinflammatory conditions, such as Alzheimer's disease and Parkinson's disease. HsTX1[R14A] is a potent and selective peptide blocker of K_V1.3 with the potential to block microglial K_V1.3, but its brain uptake is expected to be limited owing to the restrictive nature of the blood-brain barrier. To assess its peripheral and brain exposure, a LC-MS/MS assay was developed to quantify HsTX1[R14A] concentrations in mouse plasma and brain homogenate that was reliable and reproducible in the range of 6.7-66.7 nM (r² = 0.9765) and 15-150 pmol/g (r² = 0.9984), respectively. To assess if neuroinflammation affected HsTX1[R14A] disposition, C57BL/6 mice were administered HsTX1[R14A] subcutaneously (2 mg/kg) 24 h after an intraperitoneal dose of Escherichia coli lipopolysaccharide (LPS), which is commonly used to induce neuroinflammation; brain and plasma concentrations of HsTX1[R14A] were then quantified over 120 min. LPS treatment significantly retarded the decline in HsTX1[R14A] plasma concentrations, presumably as a result of reducing renal clearance, and led to substantial brain uptake of HsTX1[R14A], presumably through disruption of brain inter-endothelial tight junctions. This study suggests that HsTX1[R14A] may reach microglia in sufficient concentrations to block K_V1.3 in neuroinflammatory conditions, and therefore has the potential to reduce neurodegenerative diseases.

Preventive electroacupuncture ameliorates D-galactose-induced Alzheimer's disease-like inflammation and memory deficits, probably via modulating the microbiota-gut-brain axis

OBJECTIVES

We aimed to observe the effects of preventive electroacupuncture (EA) on the microbiota-gut-brain axis and spatial learning and memory deficits and to investigate the possible mechanism using D-galactose (D-gal)-induced aging rats.

MATERIALS AND METHODS

D-gal was intraperitoneally injected to establish the aging model. We used Morris water maze to detect spatial learning and memory function of rats. RT-PCR was applied to test targeted gut microbes. The expression of zonula occludens-1 (ZO-1) and Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB pathway proteins were detected by Western blotting. ELISA was employed to evaluate the level of lipopolysaccharides (LPS), diamine oxidase (DAO) and S-100β. Additionally, we observed ionized calcium-binding adapter molecule-1 (Iba-1) expression in the hippocampal CA1 area by immunofluorescence.

RESULTS

Morris water maze test showed decreased mean escape latency and increased target quadrant time after EA treatment. The gut microbiota composition has been modified in EA treated rats. Molecular examination indicated that expression of ZO-1 was improved and the the concentration of LPS in blood and hippocampus were reduced in EA treated rats. Further, we observed an inhibition of activated microglia and TLR4/NF-κB pathway in EA groups.

CONCLUSION

Preventive EA may alleviate the impairments of the microbiota-gut-brain axis and spatial learning and memory in aging, and the mechanism may be related to the inhibition of TLR4/NF-kB signaling pathway. The combination of acupoints GV20 and ST36 can enhance the therapeutic effect in aging rats.

Polymyxins-Curcumin Combination Antimicrobial Therapy: Safety Implications and Efficacy for Infection Treatment

The emergence of antimicrobial resistance in Gram-negative bacteria poses a huge health challenge. The therapeutic use of polymyxins (i.e., colistin and polymyxin B) is commonplace due to high efficacy and limiting treatment options for multidrug-resistant Gram-negative bacterial infections. Nephrotoxicity and neurotoxicity are the major dose-limiting factors that limit the therapeutic window of polymyxins; nephrotoxicity is a complication in up to ~60% of patients. The emergence of polymyxin-resistant strains or polymyxin heteroresistance is also a limiting factor. These caveats have catalyzed the search for polymyxin combinations that synergistically kill polymyxin-susceptible and resistant organisms and/or minimize the unwanted side effects. Curcumin—an FDA-approved natural product—exerts many pharmacological activities. Recent studies showed that polymyxins–curcumin combinations showed a synergistically inhibitory effect on the growth of bacteria (e.g., Gram-positive and Gram-negative bacteria) in vitro. Moreover, curcumin co-administration ameliorated colistin-induced nephrotoxicity and neurotoxicity by inhibiting oxidative stress, mitochondrial dysfunction, inflammation and apoptosis. In this review, we summarize the current knowledge-base of polymyxins–curcumin combination therapy and discuss the underlying mechanisms. For the clinical translation of this combination to become a reality, further research is required to develop novel polymyxins–curcumin formulations with optimized pharmacokinetics and dosage regimens.

Inter-alpha inhibitor proteins attenuate lipopolysaccharide-induced blood-brain barrier disruption and downregulate circulating interleukin 6 in mice

Circulating levels of inter-alpha inhibitor proteins change dramatically in acute inflammatory disorders, which suggest an important contribution to the immunomodulatory system. Human blood-derived inter-alpha inhibitor proteins are neuroprotective and improve survival of neonatal mice exposed to lipopolysaccharide. Lipopolysaccharide augments inflammatory conditions and disrupts the blood-brain barrier. There is a paucity of therapeutic strategies to treat blood-brain barrier dysfunction, and the neuroprotective effects of human blood-derived inter-alpha inhibitor proteins are not fully understood. To examine the therapeutic potential of inter-alpha inhibitor proteins, we administered human blood-derived inter-alpha inhibitor proteins to male and female CD-1 mice after lipopolysaccharide exposure and quantified blood-brain barrier permeability of intravenously injected 14C-sucrose and 99mTc-albumin. We hypothesized that human blood-derived inter-alpha inhibitor protein treatment would attenuate lipopolysaccharide-induced blood-brain barrier disruption and associated inflammation. Lipopolysaccharide increased blood-brain barrier permeability to both 14C-sucrose and 99mTc-albumin, but human blood-derived inter-alpha inhibitor protein treatment only attenuated increases in 14C-sucrose blood-brain barrier permeability in male mice. Lipopolysaccharide stimulated a more robust elevation of male serum inter-alpha inhibitor protein concentration compared to the elevation measured in female serum. Lipopolysaccharide administration also increased multiple inflammatory factors in serum and brain tissue, including interleukin 6. Human blood-derived inter-alpha inhibitor protein treatment downregulated serum interleukin 6 levels, which were inversely correlated with serum inter-alpha inhibitor protein concentration. We conclude that inter-alpha inhibitor proteins may be neuroprotective through mechanisms of blood-brain barrier disruption associated with systemic inflammation.

Probiotics modulate the microbiota-gut-brain axis and improve memory deficits in aged SAMP8 mice

ProBiotic-4 is a probiotic preparation composed of Bifidobacterium lactis, Lactobacillus casei, Bifidobacterium bifidum, and Lactobacillus acidophilus. This study aims to investigate the effects of ProBiotic-4 on the microbiota–gut–brain axis and cognitive deficits, and to explore the underlying molecular mechanism using senescence-accelerated mouse prone 8 (SAMP8) mice. ProBiotic-4 was orally administered to 9-month-old SAMP8 mice for 12 weeks. We observed that ProBiotic-4 significantly improved the memory deficits, cerebral neuronal and synaptic injuries, glial activation, and microbiota composition in the feces and brains of aged SAMP8 mice. ProBiotic-4 substantially attenuated aging-related disruption of the intestinal barrier and blood–brain barrier, decreased interleukin-6 and tumor necrosis factor-α at both mRNA and protein levels, reduced plasma and cerebral lipopolysaccharide (LPS) concentration, toll-like receptor 4 (TLR4) expression, and nuclear factor-κB (NF-κB) nuclear translocation in the brain. In addition, not only did ProBiotic-4 significantly decreased the levels of γ-H2AX, 8-hydroxydesoxyguanosine, and retinoic-acid-inducible gene-I (RIG-I), it also abrogated RIG-I multimerization in the brain. These findings suggest that targeting gut microbiota with probiotics may have a therapeutic potential for the deficits of the microbiota–gut–brain axis and cognitive function in aging, and that its mechanism is associated with inhibition of both TLR4-and RIG-I-mediated NF-κB signaling pathway and inflammatory responses.

Pioglitazone Increases Blood-Brain Barrier Expression of Fatty Acid-Binding Protein 5 and Docosahexaenoic Acid Trafficking into the Brain

Brain levels of docosahexaenoic acid (DHA), an essential cognitively beneficial fatty acid, are reduced in Alzheimer's disease (AD). We have demonstrated in an AD mouse model that this is associated with reduced blood-brain barrier (BBB) transport of DHA and lower expression of the key DHA-trafficking protein, fatty acid-binding protein 5 (FABP5). This study focused on assessing the impact of activating peroxisome proliferator-activated receptor (PPAR) isoforms on FABP5 expression and function at the BBB. Using immortalized human brain endothelial (hCMEC/D3) cells, a 72 h treatment with the PPARα agonist clofibrate (100 μM), and PPARβ/δ agonists GW0742 (1 μM) and GW501506 (0.5 μM), did not affect FABP5 protein expression. In contrast, the PPARγ agonists rosiglitazone (5 μM), pioglitazone (25 μM), and troglitazone (1 μM) increased FABP5 protein expression by 1.15-, 1.18-, and 1.24-fold in hCMEC/D3 cells, respectively, with rosiglitazone and pioglitazone also increasing mRNA expression of FABP5. In line with an increase in FABP5 expression, pioglitazone increased ¹⁴C-DHA uptake into hCMEC/D3 cells 1.20- to 1.33-fold over a 2 min period, and this was not associated with increased expression of membrane transporters involved in DHA uptake. Furthermore, treating male C57BL/6J mice with pioglitazone (40 mg/kg/day for 7 days) led to a 1.79-fold increase in BBB transport of ¹⁴C-DHA over 1 min, using an in situ transcardiac perfusion technique, which was associated with a 1.82-fold increase in brain microvascular FABP5 protein expression. Overall, this study demonstrated that PPARγ can regulate FABP5 at the BBB and facilitate DHA transport across the BBB, important in restoring brain levels of DHA in AD.

Molecular Mechanisms of Neurotoxicity Induced by Polymyxins and Chemoprevention

Neurotoxicity is one major unwanted side-effects associated with polymyxin (i.e., colistin and polymyxin B) therapy. Clinically, colistin neurotoxicity is characterized by neurological symptoms including dizziness, visual disturbances, vertigo, confusion, hallucinations, seizures, ataxia, and facial and peripheral paresthesias. Pathologically, colistin-induced neurotoxicity is characterized by cell injury and death in neuronal cell. This Review covers our current understanding of polymyxin-induced neurotoxicity, its underlying mechanisms, and the discovery of novel neuroprotective agents to limit this neurotoxicity. In recent years, an increasing body of literature supports the notion that polymyxin-induced nerve damage is largely related to oxidative stress and mitochondrial dysfunction. P53, PI3K/Akt, and MAPK pathways are also involved in colistin-induced neuronal cell death. The activation of the redox homeostasis pathways such as Nrf2/HO-1 and autophagy have also been shown to play protective roles against polymyxin-induced neurotoxicity. These pathways have been demonstrated to be upregulated by neuroprotective agents including curcumin, rapamycin and minocycline. Further research is needed toward the development of novel polymyxin formulations in combination with neuroprotective agents to ameliorate this unwanted adverse effect during polymyxins therapy in patients.

Leaky brain in neurological and psychiatric disorders: Drivers and consequences

BACKGROUND

The blood-brain barrier acts as a highly regulated interface; its dysfunction may exacerbate, and perhaps initiate, neurological and neuropsychiatric disorders.

METHODS

In this narrative review, focussing on redox, inflammatory and mitochondrial pathways and their effects on the blood-brain barrier, a model is proposed detailing mechanisms which might explain how increases in blood-brain barrier permeability occur and can be maintained with increasing inflammatory and oxidative and nitrosative stress being the initial drivers.

RESULTS

Peripheral inflammation, which is causatively implicated in the pathogenesis of major psychiatric disorders, is associated with elevated peripheral pro-inflammatory cytokines, which in turn cause increased blood-brain barrier permeability. Reactive oxygen species, such as superoxide radicals and hydrogen peroxide, and reactive nitrogen species, such as nitric oxide and peroxynitrite, play essential roles in normal brain capillary endothelial cell functioning; however, chronically elevated oxidative and nitrosative stress can lead to mitochondrial dysfunction and damage to the blood-brain barrier. Activated microglia, redox control of which is mediated by nitric oxide synthases and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, secrete neurotoxic molecules such as reactive oxygen species, nitric oxide, prostaglandin, cyclooxygenase-2, quinolinic acid, several chemokines (including monocyte chemoattractant protein-1 [MCP-1], C-X-C motif chemokine ligand 1 [CXCL-1] and macrophage inflammatory protein 1α [MIP-1α]) and the pro-inflammatory cytokines interleukin-6, tumour necrosis factor-α and interleukin-1β, which can exert a detrimental effect on blood-brain barrier integrity and function. Similarly, reactive astrocytes produce neurotoxic molecules such as prostaglandin E2 and pro-inflammatory cytokines, which can cause a 'leaky brain'.

CONCLUSION

Chronic inflammatory and oxidative and nitrosative stress is associated with the development of a 'leaky gut'. The following evidence-based approaches, which address the leaky gut and blood-brain barrier dysfunction, are suggested as potential therapeutic interventions for neurological and neuropsychiatric disorders: melatonin, statins, probiotics containing Bifidobacteria and Lactobacilli, N-acetylcysteine, and prebiotics containing fructo-oligosaccharides and galacto-oligosaccharides.

Effects of hepatic ischemia-reperfusion injury on the blood-brain barrier permeability to [14C] and [13C]sucrose

Hepatic encephalopathy that is associated with severe liver failure may compromise the blood-brain barrier (BBB) integrity. However, the effects of less severe liver diseases, in the absence of overt encephalopathy, on the BBB are not well understood. The goal of the current study was to investigate the effects of hepatic ischemia-reperfusion (IR) injury on the BBB tight junction permeability to small, hydrophilic molecules using the widely used [¹⁴C]sucrose and recently-proposed alternative [¹³C]sucrose as markers. Rats were subjected to 20 min of hepatic ischemia or sham surgery, followed by 8 h of reperfusion before administration of a single bolus dose of [¹⁴C] or [¹³C]sucrose and collection of serial (0-30 min) blood and plasma and terminal brain samples. The concentrations of [¹⁴C] and [¹³C]sucrose in the samples were determined by measurement of total radioactivity (nonspecific) and LC-MS/MS (specific), respectively. IR injury significantly increased the blood, plasma, and brain concentrations of both [¹⁴C] and [¹³C]sucrose. However, when the brain concentrations were corrected for their respective area under the blood concentration-time curve, only [¹⁴C]sucrose showed significantly higher (30%) BBB permeability values in the IR animals. Because [¹³C]sucrose is a more specific BBB permeability marker, these data indicate that our animal model of hepatic IR injury does not affect the BBB tight junction permeability to small, hydrophilic molecules. Methodological differences among studies of the effects of liver diseases on the BBB permeability may confound the conclusions of such studies.

Polymyxins for CNS infections: Pharmacology and neurotoxicity

Central nervous system (CNS) infections caused by multi-drug resistant (MDR) Gram-negative bacteria present a major health and economic burden worldwide. Due to the nearly empty antibiotic discovery pipeline, polymyxins (i.e. polymyxin B and colistin) are used as the last-line therapy against Gram-negative 'superbugs' when all other treatment modalities have failed. The treatment of CNS infections due to multi-drug resistant Gram-negative bacteria is problematic and associated with high mortality rates. Colistin shows significant efficacy for the treatment of CNS infections caused by MDR Gram-negative bacteria that are resistant to all other antibiotics. In particular, MDR Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae which are resistant to expanded-spectrum and fourth-generation cephalosporins, carbapenems and aminoglycosides, represent a major therapeutic challenge, although they can be treated with colistin or polymyxin B. However, current dosing recommendations of intrathecal/intraventricular polymyxins are largely empirical, as we have little understanding of the pharmacokinetics/pharmacodynamics and, importantly, we are only starting to understand the mechanisms of potential neurotoxicity. This review covers the current knowledge-base on the mechanisms of disposition and potential neurotoxicity of polymyxins as well as the combined use of neuroprotective agents to alleviate polymyxins-related neurotoxicity. Progress in this field will provide the urgently needed pharmacological information for safer and more efficacious intrathecal/intraventricular polymyxin therapy against life-threatening CNS infections caused by Gram-negative 'superbugs'.

Sepsis-Associated Encephalopathy: The Blood-Brain Barrier and the Sphingolipid Rheostat

Sepsis is not only a significant cause of mortality worldwide but has particularly devastating effects on the central nervous system of survivors. It is therefore crucial to understand the molecular structure, physiology, and events involved in the pathogenesis of sepsis-associated encephalopathy, so that potential therapeutic advances can be achieved. A key determinant to the development of this type of encephalopathy is morphological and functional modification of the blood–brain barrier (BBB), whose function is to protect the CNS from pathogens and toxic threats. Key mediators of pathologic sequelae of sepsis in the brain include cytokines, including TNF-α, and sphingolipids, which are biologically active components of cellular membranes that possess diverse functions. Emerging data demonstrated an essential role for sphingolipids in the pulmonary vascular endothelium. This raises the question of whether endothelial stability in other organs systems such as the CNS may also be mediated by sphingolipids and their receptors. In this review, we will model the structure and vulnerability of the BBB and hypothesize mechanisms for therapeutic stabilization and repair following a confrontation with sepsis-induced inflammation.

Evaluation of [14C] and [13C]Sucrose as Blood-Brain Barrier Permeability Markers

Nonspecific quantitation of [¹⁴C]sucrose in blood and brain has been routinely used as a quantitative measure of the in vivo blood-brain barrier (BBB) integrity. However, the reported apparent brain uptake clearance (K_in) of the marker varies widely (∼100-fold). We investigated the accuracy of the use of the marker in comparison with a stable isotope of sucrose ([¹³C]sucrose) measured by a specific liquid chromatography-tandem mass spectrometry method. Rats received single doses of each marker, and the K_in values were determined. Surprisingly, the K_in value of [¹³C]sucrose was 6- to 7-fold lower than that of [¹⁴C]sucrose. Chromatographic fractionation after in vivo administration of [¹⁴C]sucrose indicated that the majority of the brain content of radioactivity belonged to compounds other than the intact [¹⁴C]sucrose. However, mechanistic studies failed to reveal any substantial metabolism of the marker. The octanol:water partition coefficient of [¹⁴C]sucrose was >2-fold higher than that of [¹³C]sucrose, indicating the presence of lipid-soluble impurities in the [¹⁴C]sucrose solution. Our data indicate that [¹⁴C]sucrose overestimates the true BBB permeability to sucrose. We suggest that specific quantitation of the stable isotope (¹³C) of sucrose is a more accurate alternative to the current widespread use of the radioactive sucrose as a BBB marker.

The impact of inflammation on respiratory plasticity

Breathing is a vital homeostatic behavior and must be precisely regulated throughout life. Clinical conditions commonly associated with inflammation, undermine respiratory function may involve plasticity in respiratory control circuits to compensate and maintain adequate ventilation. Alternatively, other clinical conditions may evoke maladaptive plasticity. Yet, we have only recently begun to understand the effects of inflammation on respiratory plasticity. Here, we review some of common models used to investigate the effects of inflammation and discuss the impact of inflammation on nociception, chemosensory plasticity, medullary respiratory centers, motor plasticity in motor neurons and respiratory frequency, and adaptation to high altitude. We provide new data suggesting glial cells contribute to CNS inflammatory gene expression after 24h of sustained hypoxia and inflammation induced by 8h of intermittent hypoxia inhibits long-term facilitation of respiratory frequency. We also discuss how inflammation can have opposite effects on the capacity for plasticity, whereby it is necessary for increases in the hypoxic ventilatory response with sustained hypoxia, but inhibits phrenic long term facilitation after intermittent hypoxia. This review highlights gaps in our knowledge about the effects of inflammation on respiratory control (development, age, and sex differences). In summary, data to date suggest plasticity can be either adaptive or maladaptive and understanding how inflammation alters the respiratory system is crucial for development of better therapeutic interventions to promote breathing and for utilization of plasticity as a clinical treatment.

Metabolic consequences of inflammatory disruption of the blood-brain barrier in an organ-on-chip model of the human neurovascular unit

Background

Understanding blood-brain barrier responses to inflammatory stimulation (such as lipopolysaccharide mimicking a systemic infection or a cytokine cocktail that could be the result of local or systemic inflammation) is essential to understanding the effect of inflammatory stimulation on the brain. It is through the filter of the blood-brain barrier that the brain responds to outside influences, and the blood-brain barrier is a critical point of failure in neuroinflammation. It is important to note that this interaction is not a static response, but one that evolves over time. While current models have provided invaluable information regarding the interaction between cytokine stimulation, the blood-brain barrier, and the brain, these approaches—whether in vivo or in vitro—have often been only snapshots of this complex web of interactions.

Methods

We utilize new advances in microfluidics, organs-on-chips, and metabolomics to examine the complex relationship of inflammation and its effects on blood-brain barrier function ex vivo and the metabolic consequences of these responses and repair mechanisms. In this study, we pair a novel dual-chamber, organ-on-chip microfluidic device, the NeuroVascular Unit, with small-volume cytokine detection and mass spectrometry analysis to investigate how the blood-brain barrier responds to two different but overlapping drivers of neuroinflammation, lipopolysaccharide and a cytokine cocktail of IL-1β, TNF-α, and MCP1,2.

Results

In this study, we show that (1) during initial exposure to lipopolysaccharide, the blood-brain barrier is compromised as expected, with increased diffusion and reduced presence of tight junctions, but that over time, the barrier is capable of at least partial recovery; (2) a cytokine cocktail also contributes to a loss of barrier function; (3) from this time-dependent cytokine activation, metabolic signature profiles can be obtained for both the brain and vascular sides of the blood-brain barrier model; and (4) collectively, we can use metabolite analysis to identify critical pathways in inflammatory response.

Conclusions

Taken together, these findings present new data that allow us to study the initial effects of inflammatory stimulation on blood-brain barrier disruption, cytokine activation, and metabolic pathway changes that drive the response and recovery of the barrier during continued inflammatory exposure.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0760-y) contains supplementary material, which is available to authorized users.

Assessment of blood-brain barrier function and the neuroinflammatory response in the rat brain by using cerebral open flow microperfusion (cOFM)

Blood-brain barrier (BBB) impairment in systemic inflammation leads to neuroinflammation. Several factors including cytokines, chemokines and signal transduction molecules are implicated in BBB dysfunction in response to systemic inflammation. Here, we have adopted a novel in vivo technique; namely, cerebral open flow microperfusion (cOFM), to perform time-dependent cytokine analysis (TNF-alpha, IL-6 and IL-10) in the frontal cortex of the rat brain in response to a single peripheral administration of lipopolysaccharide (LPS). In parallel, we monitored BBB function using sodium fluorescein as low molecular weight reporter in the cOFM sample. In response to the systemic LPS administration, we observed a rapid increase of TNF-alpha in the serum and brain, which coincides with the BBB disruption. Brain IL-6 and IL-10 synthesis was delayed by approximately 1 h. Our data demonstrate that cOFM can be used to monitor changes in brain cytokine levels and BBB disruption in a rat sepsis model.

Converging actions of alcohol on liver and brain immune signaling

Chronic excessive alcohol consumption results in inflammation in multiple organs, including the brain. While the contribution of neuroinflammation to alcohol-related cognitive dysfunction and behavioral alterations is established, the mechanisms by which alcohol triggers inflammation in the brain are only partially understood. There are acute and long-term alterations in brain function due to intercellular and intracellular changes of different cell types as a result of alcohol consumption. This review focuses on the alcohol-induced proinflammatory cellular and molecular changes in the central nervous system. Alcohol passes through the blood-brain barrier and alters neurotransmission. Alcohol use activates microglia and astrocyte, contributing to neurodegeneration and impaired regeneration. Alcohol-induced cell injury in the brain results in release of damage-associated molecular patterns, such as high mobility group box 1, that trigger inflammatory changes through activation of pattern recognition receptors. In addition, alcohol consumption increases intestinal permeability and results in increased levels of pathogen-associated molecular pattern such as endotoxin in the systemic circulation that triggers PRRs and inflammation. The Toll-like receptor-4 pathway that activates nuclear factor-κB and secretion of proinflammatory cytokines, tumor necrosis factor-α, interleukin-1-beta, and chemokines, including monocyte chemotactic protein-1, has been suggested to contribute to alcohol-induced neuroinflammation. Alcohol-induced IL-1β secretion also requires Nod-like receptor-mediated inflammasome and caspase-1 activation, and, consistent with this, disruption of IL-1/IL-1-receptor signaling prevents alcohol-induced neuroinflammation. Delicate regulators of inflammatory gene expressions are micro-RNAs (miRs) that have recently been identified in alcohol-related neuroinflammation. Alcohol induces miR155, a regulator of inflammation in the brain, and deficiency in miR-155 in mice was protective from neuroinflammatory changes. These observations suggest that manipulation of miR pathways and cytokine induction may reduce alcohol-induced proinflammatory processes.