No increase in blood-brain barrier permeability after intraperitoneal injection of endotoxin in the rat

Methods used for the measurement of blood-brain barrier integrity

The blood-brain barrier (BBB) comprises the interface between blood, brain and cerebrospinal fluid. Its primary function, which is mainly carried out by tight junctions, is to stabilize the tightly controlled microenvironment of the brain. To study the development and maintenance of the BBB, as well as various roles their intrinsic mechanisms that play in neurological disorders, suitable measurements are required to demonstrate integrity and functional changes at the interfaces between the blood and brain tissue. Markers and plasma proteins with different molecular weight (MW) are used to measure the permeability of BBB. In addition, the expression changes of tight-junction proteins form the basic structure of BBB, and imaging modalities are available to study the disruption of BBB. In the present review, above mentioned methods are depicted in details, together with the pros and cons as well as the differences between these methods, which maybe benefit research studies focused on the detection of BBB breakdown.

Rg1 improves LPS-induced Parkinsonian symptoms in mice via inhibition of NF-κB signaling and modulation of M1/M2 polarization

Ginsenoside Rg1 is one of the most active ingredients in ginseng, which has been reported to protect dopaminergic neurons and improve behavioral defects in MPTP model, 6-OHDA model and rotenone model. However, it is unclear whether Rg1 exerted neuroprotection in LPS-induced sub-acute PD model. In this study, we investigated the neuroprotective effect of Rg1 in the sub-acute PD mouse model and explored the related mechanisms. Rg1 (10, 20, 40 mg·kg^-1·d^-1) was orally administered to mice for 18 days. A sub-acute PD model was established in the mice through LPS microinjection into the substantia nigra (SN) from D8 to D13. We found that Rg1 administration dose-dependently inhibited LPS-induced damage of dopaminergic neurons and activation of glial cells in the substantia nigra pars compacta (SNpc). The neuroprotective effects of Rg1 were associated with the reduction of pro-inflammatory cytokines and the improvement of anti-inflammatory cytokines and neurotrophin in the midbrain. Rg1 shifted the polarization of microglia towards the M2 phenotype from M1, evidenced by decreased M1 markers (inducible NO synthase, CD16, etc.) and increased M2 markers (arginase 1 (Arg1), CD206, etc) in the midbrain. Furthermore, Rg1 administration markedly inhibited nuclear translocation of NF-κB in midbrain microglia. In conclusion, Rg1 protects PD mice induced by continuous LPS injection by inhibiting the nuclear entry of NF-κB and regulating the polarization balance of microglia, shedding new light on a disease-modifying therapy of PD.

Anti-Tumor Necrosis Factor Therapy and Incidence of Parkinson Disease Among Patients With Inflammatory Bowel Disease

Importance

Despite established genetic and pathophysiologic links between inflammatory bowel disease (IBD) and Parkinson disease (PD), clinical data supporting this association remain scarce. Although systemic inflammation is considered a potential biological mechanism shared between the 2 diseases, the role of reduced systemic inflammation through IBD-directed anti-tumor necrosis factor (anti-TNF) therapy in PD risk is largely unknown.

Objective

To compare the incidence of PD among individuals with or without IBD and to assess whether PD risk among patients with IBD is altered by anti-TNF therapy.

Design, Setting, and Participants

This is a retrospective cohort study analyzing information in the Truven Health MarketScan administrative claims database and the Medicare Supplemental Database between January 1, 2000, and March 31, 2016. Individuals were selected who had at least 2 claims for IBD diagnoses, at least 6 months of follow-up, and no prior diagnosis of PD on or before the IBD index date. Exposure to Anti-TNF therapy was measured from the anti-TNF index date to the last date of anti-TNF coverage or the end of enrollment or PD index date, whichever was earliest. Incidence rates per 1000 person-years were calculated, and crude and adjusted incidence rate ratios were estimated by Poisson regression models and presented with 95% CIs.

Main Outcomes and Measures

Incidence of PD among patients with IBD with or without exposure to anti-TNF therapy.

Results

In total, 144 018 individuals with IBD were matched on age, sex, and year of index date with 720 090 unaffected controls. Of them, 1796 individuals had at least 2 PD diagnoses and at least 1 filled PD-related prescription. The mean (SD) age of individuals with IBD was 51 (17) years, and 44% were men. The incidence of PD among patients with IBD was 28% higher than that among unaffected matched controls (adjusted incidence rate ratio, 1.28; 95% CI, 1.14-1.44; P < .001). A 78% reduction in the incidence rate of PD was detected among patients with IBD who were exposed to anti-TNF therapy compared with those who were not exposed (adjusted incidence rate ratio, 0.22; 95% CI, 0.05-0.88; P = .03).

Conclusions and Relevance

A higher incidence of PD was observed among patients with IBD than among individuals without IBD. Early exposure to antiinflammatory anti-TNF therapy was associated with substantially reduced PD incidence. These findings support a role of systemic inflammation in the pathogenesis of both diseases. Further studies are required to determine whether anti-TNF treatment administered to high-risk individuals may mitigate PD risk.

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.

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 blood-brain barrier in systemic inflammation

The blood-brain barrier (BBB) plays a key role in maintaining the specialized microenvironment of the central nervous system (CNS), and enabling communication with the systemic compartment. BBB changes occur in several CNS pathologies. Here, we review disruptive and non-disruptive BBB changes in systemic infections and other forms of systemic inflammation, and how these changes may affect CNS function in health and disease. We first describe the structure and function of the BBB, and outline the techniques used to study the BBB in vitro, and in animal and human settings. We then summarise the evidence from a range of models linking BBB changes with systemic inflammation, and the underlying mechanisms. The clinical relevance of these BBB changes during systemic inflammation are discussed in the context of clinically-apparent syndromes such as sickness behaviour, delirium, and septic encephalopathy, as well as neurological conditions such as Alzheimer's disease and multiple sclerosis. We review emerging evidence for two novel concepts: (1) a heightened sensitivity of the diseased, versus healthy, BBB to systemic inflammation, and (2) the contribution of BBB changes induced by systemic inflammation to progression of the primary disease process.

Parkinson's disease and enhanced inflammatory response

Parkinson's disease (PD) is the first and second most prevalent motor and neurodegenerative disease, respectively. The clinical symptoms of PD result from a loss of midbrain dopaminergic (DA) neurons. However, the molecular cause of DA neuron loss remains elusive. Mounting evidence implicates enhanced inflammatory response in the development and progression of PD pathology. This review examines current research connecting PD and inflammatory response.

Effects of short-term portacaval anastomosis on the peripheral and brain disposition of the blood-brain barrier permeability marker sodium fluorescein in rats

Contradictory results have been reported with regard to the effects of various models of hepatic encephalopathy on the blood-brain barrier (BBB) permeability, which may be due partly to the use of brain concentrations of BBB markers without attention to their peripheral pharmacokinetics. The purpose of the current study was to investigate the effects of short-term portacaval anastomosis (PCA), a type B model of hepatic encephalopathy, on the peripheral pharmacokinetics and brain distribution of sodium fluorescein (FL), which is a small molecule marker of BBB passive permeability. A single 25mg/kg dose of FL was administered intravenously to 10-day PCA and sham-operated rats, and serial blood and bile (0-30min) and terminal (30min) brain samples were collected, and the concentrations of FL and its glucuronidated metabolite (FL-Glu) were measured by HPLC. Additionally, the free fractions of FL (fu) in all the plasma samples were determined, and the effects of bile salts on fu were investigated in vitro. Passive permeability of BBB to FL was estimated by brain uptake clearance (Kin) based on both the brain concentrations of FL and plasma concentrations of free (unbound) FL. PCA caused a 26% increase in the fu of FL in plasma, which was due to competition of bile acids with FL for binding to plasma proteins. Additionally, PCA reduced the biliary excretion of FL-Glu by 55%. However, free Kin values (µl/min/g brain) for the sham (0.265±0.034) and PCA (0.228±0.038) rats were not significantly different. It is concluded that whereas 10-day PCA alters the peripheral pharmacokinetics of FL, it does not significantly affect the BBB permeability to the marker.

Activated protein C improves pial microcirculation in experimental endotoxemia in rats

INTRODUCTION

The brain is one of the first organs affected clinically in sepsis. Microcirculatory alterations are suggested to be a critical component in the pathophysiology of sepsis. The aim of this study was to investigate the effects of recombinant human activated protein C (rhAPC) on the pial microcirculation in experimental endotoxemia using intravital microscopy. Our hypothesis is rhAPC protects pial microcirculation in endotoxemia.

METHODS

Endotoxemia was generated in Lewis rats with intravenous injection of lipopolysaccharide (LPS, 5 mg/kg i.v.). Dura mater was removed through a cranial window to expose pial vessels on the brain surface. The microcirculation, including leukocyte-endothelial interaction, functional capillary density (FCD) and plasma extravasation of pial vessels was examined by fluorescent intravital microscopy (IVM) 2 h after administration of LPS, LPS and rhAPC or equivalent amount of saline (used as Control group). Plasma cytokine levels of interleukin 1 alpha (IL1-α), tumor necrosis factor-α (TNF-α), interferon γ (IFN-γ), Monocyte chemotactic protein-1 (MCP-1) and Granulocyte-macrophage colony-stimulating factor (GM-CSF) were evaluated after IVM.

RESULTS

LPS challenge significantly increased leukocyte adhesion (773±190 vs. 592±152 n/mm(2) Control), decreased FCD (218±54 vs. 418±74 cm/cm(2) Control) and increased proinflammatory cytokine levels (IL-1α: 5032±1502 vs. 8±21 pg/ml; TNF-α: 1823±1007 vs. 168±228 pg/ml; IFN-γ: 785±434 vs. 0 pg/ml; GM-CSF: 54±52 vs. 1±3 pg/ml) compared to control animals. rhAPC treatment significantly reduced leukocyte adhesion (599±111 n/mm(2)), increased FCD (516±118 cm/cm(2)) and reduced IL-1α levels (2134±937 pg/ml) in the endotoxemic rats.

CONCLUSION

APC treatment significantly improves pial microcirculation by reducing leukocyte adhesion and increasing FCD.

Systemic inflammation induces axon injury during brain inflammation

OBJECTIVE

Axon injury is a key contributor to the progression of disability in multiple sclerosis (MS). Systemic infections, which frequently precede relapses in MS, have been linked to clinical progression in Alzheimer's disease. There is evidence of a role for the innate immune system in MS lesions, as axonal injury is associated with macrophage activation. We hypothesize that systemic inflammation leads to enhanced axonal damage in MS as a consequence of innate immune system activation.

METHODS

Monophasic experimental allergic encephalomyelitis (EAE) was induced in a cohort of Lewis rats. The animals received a systemic challenge with either an inflammagen (lipopolysaccharide [LPS]) or saline as a control, at 1, 3, or 6 weeks into the remission phase of the disease. The clinical outcome, cellular recruitment to lesions, degree of tissue damage, and cytokine profiles were measured.

RESULTS

We found that systemic inflammation activates the central nervous system (CNS) innate immune response and results in a switch in the macrophage/microglia phenotype. This switch was accompanied by inducible nitric oxide synthase (iNOS) and interleukin-1β (IL-1β) expression and increased axon injury. This increased injury occurred independently of the re-emergence of overt clinical signs.

INTERPRETATION

Our evidence indicates that microglia/macrophages, associated with lesions, respond to circulating cytokines, produced in response to an inflammatory event outside the CNS, by producing immune mediators that lead to tissue damage. This has implications for people with MS, in which prevention and stringent management of systemic infectious diseases may slow disease progression.

IL-1β induction and IL-6 suppression are associated with aggravated neuronal damage in a lipopolysaccharide-pretreated kainic acid-induced rat pup seizure model

OBJECTIVES

Reportedly, hippocampal neuronal degeneration by kainic acid (KA)-induced seizures in rats <14 days old was enhanced by lipopolysaccharide (LPS). This study was to test the hypothesis that cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor-α are associated with aggravated neuronal damage.

MATERIALS AND METHODS

Sixty male Sprague-Dawley, 14-day-old rats were used. Experiments were conducted in saline, LPS + saline, saline + KA and LPS + KA groups. Intraperitoneal LPS injections (0.04 mg/kg) were administered 3 h prior to KA injection (3 mg/kg).

RESULTS

The LPS + KA group showed a tendency toward shorter latency to seizure onset (p = 0.086) and significantly longer seizure duration (p < 0.05) compared with the KA group. Induction of the proconvulsant cytokine IL-1β in rat pup brains was significantly greater in the LPS + KA group compared to the KA group (38.8 ± 5.5 vs. 9.2 ± 1.0 pg/µg; p < 0.05); however, IL-6 levels were higher in the KA group than in the LPS + KA group (108.7 ± 6.8 vs. 60.9 ± 4.7 pg/µg; p < 0.05). The difference in tumor necrosis factor-α between the LPS + KA group and the KA group was insignificant (12.1 ± 0.6 vs. 10.9 ± 2.3 pg/µg; p = 0.64).

CONCLUSIONS

Our results showed an increase in the proconvulsant cytokine IL-1β and a decrease in a potentially neuroprotective cytokine, IL-6, in rat pups treated with LPS + KA. These results warrant further investigation into the possible role of IL-1β induction and IL-6 suppression in LPS-promoted neuronal damage.

Experimental Endotoxemia Induces Leukocyte Adherence and Plasma Extravasation Within the Rat Pial Microcirculation

Disturbance of capillary perfusions due to leukocyte adhesion, disseminated intravascular coagulation, tissue edema is critical components in the pathophysiology of sepsis. Alterations in brain microcirculation during sepsis are not clearly understood. The aim of this study is to gain an improved understanding of alterations through direct visualization of brain microcirculations in an experimental endotoxemia using intravital microscopy (IVM). Endotoxemia was induced in Lewis rats with Lipopolysaccharide (LPS, 15 mg/kg i.v.). The dura mater was removed via a cranial window to expose the pial vessels on the brain surface. Using fluorescence dyes, plasma extravasation of pial venous vessels and leukocyte-endothelial interaction were visualized by intravital microscopy 4 h after LPS administration. Plasma cytokine levels of IL1-β, IL-6, IFN-γ, TNF-α and KC/GRO were evaluated after IVM. A significant plasma extravasation of the pial venous vessels was found in endotoxemia rats compared to control animals. In addition, a significantly increased number of leukocytes adherent to the pial venous endothelium was observed in septic animals. Endotoxemia also induced a significant elevation of plasma cytokine levels of IL1-β, IL-6, IFN-γ, TNF-α and KC/GRO. Endotoxemia increased permeability in the brain pial vessels accompanied by an increase of leukocyte-endothelium interactions and an increase of inflammatory cytokines in the plasma.

Lipopolysaccharide animal models for Parkinson's disease

Lipopolysaccharide (LPS), an endotoxin from Gram-negative bacteria, acts as a potent stimulator of microglia and has been used to study the inflammatory process in the pathogenesis of Parkinson's disease (PD) and anti-inflammatory therapy for PD treatment. Here, we review the growing body of literature on both in vitro and in vivo LPS PD models. Primary cell cultures from mesencephalic tissue were exposed to LPS in vitro; LPS was stereotaxically injected into the substantia nigra, striatum, or globus pallidus of brain or injected into the peritoneal cavity of the animal in vivo. In conclusion, the LPS PD models are summarized as (1) local and direct LPS treatment and (2) systemic LPS treatment. Mechanisms underlying the PD models are investigated and indicated that LPS induces microglial activation to release a variety of neurotoxic factors, and damaged neurons may trigger reactive microgliosis, which lead to progressive dopaminergic neurodegeneration.

Quantification of metformin by the HPLC method in brain regions, cerebrospinal fluid and plasma of rats treated with lipopolysaccharide

Recently, it has been reported that metformin may attenuate inflammation and directly act on the central nervous system. Using the HPLC method, in Wistar rats, we assessed the changes in metformin concentrations in various brain regions (pituitary gland, olfactory bulb, hypothalamus, cerebellum, hippocampus, striatum, frontal cortex), cerebrospinal fluid and plasma after single and chronic oral administration, in the model of systemic inflammation induced by lipopolysaccharide (ip). Regarding the influence of systemic inflammation on metformin distribution, the pituitary gland demonstrated the highest its level after single and chronic administration (28.8 ± 3.5 nmol/g and 24.9 ± 3.2 nmol/g, respectively). We concluded that orally-dosed metformin rapidly crosses the blood-brain barrier and differently accumulates in structures of the central nervous system.

Re-exposure to endotoxin induces differential cytokine gene expression in the rat hypothalamus and spleen

This study was designed to investigate whether the pattern of hypothalamic and splenic cytokine expression induced by peripheral administration of a bacterial lipopolysaccharide (LPS) is affected by prior exposure to LPS derived from another bacterial strain. Injection of LPS from Salmonella enteritidis (LPS(2)) alone resulted in increased hypothalamic gene expression of IL-1beta, IL-6, TNFalpha, IL-1ra and IL-10. However, pre-exposure to LPS derived from Escherichia coli (LPS(1)) 3 weeks before, significantly attenuated hypothalamic IL-1ra, IL-6 and IL-10 expression. IL-1beta expression also tended to be lower. This pattern contrasted with the robust cytokine expression in the spleen of LPS(2)-treated rats previously exposed to LPS(1), since pre-treatment with endotoxin resulted in a significantly greater response of IL-1beta and IL-1ra to LPS(2). Expression of TNFalpha and IL-10 also tended to be higher. Pre-treatment with LPS(1) did not significantly affect the marked increase in corticosterone and adrenaline blood levels induced by LPS(2). Thus, while endotoxin pre-exposure seemed not to induce a "tolerant" state in the periphery as judged by the immune and endocrine parameters evaluated upon re-stimulation, expression of four of the six cytokines measured was decreased in the hypothalamus. This is the first demonstration that endotoxin priming can differentially affect cytokine expression in the central nervous system and peripheral tissues when a host is confronted with a second, acute, pro-inflammatory stimulus. These results may provide new evidence for the involvement of cytokine pathways in the central nervous system in modulating peripheral inflammation and mediating cognitive and behavioural alterations during inflammatory diseases.

Systemic inflammatory response reactivates immune-mediated lesions in rat brain

The potential association between microbial infection and reactivation of a multiple sclerosis (MS) lesion is an important issue that remains unresolved, primarily because of the absence of suitable animal models and imaging techniques. Here, we have evaluated this question in an empirical manner using immunohistochemistry and magnetic resonance imaging (MRI), before and after the induction of a systemic inflammatory response in two distinct models of MS. In a pattern-II-type focal myelin oligodendrocyte glycoprotein-experimental autoimmune encephalomyelitis model, systemic endotoxin injection caused an increase in regional cerebral blood volume (rCBV) around the lesion site after 6 h, together with a reduction in the magnetization transfer ratio of the lesioned corpus callosum. These changes were followed by an increase in the diffusion of tissue water within the lesion 24 h after endotoxin challenge and new leukocyte recruitment as revealed both immunohistochemically and by MRI tracking of ultrasmall superparamagnetic iron oxide-labeled macrophages. Importantly, we detected in vivo expression of E- and P-selectin in quiescent lesions by MRI-detectable glyconanoparticles conjugated to sialyl Lewis(X). This finding may explain, at least in part, the ability of quiescent MS lesions to rapidly reinitiate the cell recruitment processes. In a pattern-I-type delayed-type hypersensitivity response model, a similar effect of endotoxin challenge on rCBV was observed, together with delayed breakdown of the blood-brain barrier, showing that systemic infection can alter the pathogenesis of MS-like lesions regardless of lesion etiology. These findings will have important implications for the management and monitoring of individuals with MS.

Neuronal activation in the nucleus of the solitary tract following jejunal lipopolysaccharide in the rat

INTRODUCTION

Inflammation during systemic lipopolysaccharide (LPS) seems to be modulated by the CNS via afferent and efferent vagal pathways. We hypothesized that similar to systemic inflammation, local LPS in the gut lumen may also activate central neurons and aimed to identify potential molecular mechanisms.

METHODS

Male Wistar rats were equipped with an exteriorized canula in the proximal jejunum. LPS or vehicle were administered into the jejunum (10 mg ml(-1)). For further study of molecular mechanisms, LPS or vehicle were administered systemically (1 mg kg(-1)). Brain stem activation was quantified by Fos-immunohistochemistry in the vagal nucleus of the solitary tract (NTS) and the Area postrema which is exposed to systemic circulation. Serum LPS concentrations were also determined.

RESULTS

Jejunal LPS exposure entailed 91+/-12 (n=7) Fos-positive neurons in the NTS compared to 39+/-9 in controls (n=6; p<0.01), while serum LPS concentrations and Fos-positive neurons in the Area postrema were not different. Systemic LPS triggered 150+/-25 (n=6) and vehicle 52+/-6 Fos-positive neurons (n=7; p<0.01). The Fos count after systemic LPS was reduced to 99+/-30 following pretreatment with the cyclooxygenase inhibitor Naproxen (10 mg kg(-1); p>0.05 versus vehicle controls) and increased to 242+/-66 following the iNOS-inhibitor Aminoguanidine (15 mg kg(-1); p<0.01). In the Area postrema, 97+/-17 (n=6) neurons were counted in animals pretreated with systemic LPS compared to 14+/-4 in controls (n=7, p<0.001).

CONCLUSIONS

Central neuronal activation following inflammation after systemic LPS is modulated by cyclooxygenase and NO pathways. Local exposure to bacterial LPS in the gut lumen activates the NTS which may set the stage for efferent vagal modulation of intestinal inflammation.

The neuronal excitability time-dependently changes after lipopolysaccharide administration in mice: Possible role of cyclooxygenase-2 induction

The parameters of pentylenetetrazol (PTZ)-induced seizures have been evaluated at various time intervals after lipopolysaccharide (LPS; Escherichia coli O111:B4, 100 microg/kg, i.p.) administration in mice. A proconvulsant effect occurred 4h after LPS injection with decreased seizure latency and enhanced seizure intensity. In contrast, the incidence of seizures was reduced 18 h after LPS injection. There were no significant alterations on seizure parameters 2, 8, 12, and 24h after LPS treatment. SC-58236, a selective cyclooxygenase (COX)-2 inhibitor (20 or 40 mg/kg, s.c.) treatment alone had no effect on PTZ-induced seizures, but reversed the antiseizure activity observed 18 h after LPS injection. However, SC-58236 treatment partially restored the proconvulsant changes that were observed 4h after LPS administration. On the other hand, COX-1-selective inhibitor valeryl salicylate (20 or 40 mg/kg, s.c.) itself facilitated PTZ-induced seizures. Thus, it was not possible to evaluate the effects of valeryl salicylate on the excitability changes after LPS injection. These results indicate that the parameters of PTZ-induced seizures change time-dependently after LPS treatment, in which proconvulsant and anticonvulsant states could be seen in a sequence. It seems that COX-2 isoenzyme may be involved in the neuronal excitability changes due to LPS.

Effects of lipopolysaccharide on blood-brain barrier permeability during pentylenetetrazole-induced epileptic seizures in rats

We investigated the effects of lipopolysachharide (LPS) on functional and structural properties of the blood-brain barrier (BBB) during pentylenetetrazole (PTZ)-induced epileptic seizures in rats. Arterial blood pressure was significantly elevated during epileptic seizures irrespective of LPS pretreatment. Plasma levels of interleukin (IL)-1, interleukin (IL)-6, nitric oxide (NO) and malondialdehyde (MDA) increased while catalase concentrations decreased in animals treated with LPS, PTZ and LPS plus PTZ. The significantly increased BBB permeability to Evans blue (EB) dye in the cerebral cortex, diencephalon and cerebellum regions of rats by PTZ-induced seizures was markedly reduced upon LPS pretreatment. Immunoreactivity for tight junction proteins, zonula occludens-1 and occludin, did not change in brain vessels of animals treated with PTZ and LPS plus PTZ. Glial fibrillary acidic protein immunoreactivity was increased in LPS, but not in PTZ and LPS plus PTZ. These results indicate that LPS pretreatment reduces the passage of EB dye bound to albumin into the brain, at least partly, by increasing plasma NO and IL-6 levels during PTZ-induced epileptic seizures. We suggest that LPS may provide protective effects on the BBB integrity during epileptic seizures through transcellular pathway, since the paracellular route remained unaffected by LPS and LPS plus PTZ.

Chronic systemic endotoxin exposure: an animal model in experimental hepatic encephalopathy

Plasma levels of gut-derived endotoxins (lipopolysaccharides, LPS) are often elevated in cirrhotics and are thought to contribute to hepatic encephalopathy. Circulating LPS activates macrophages to produce tumor necrosis factor alpha (TNF-alpha) and other potentially cytotoxic proinflammatory mediators. A pathogenic role for endotoxins is supported by studies showing that treatment with Lacto-bacillusor antibiotics, both of which reduce LPS-producing intestinal Gram-negative bacteria, alleviates experimental liver damage. To mimic the "leaky gut" syndrome with endotoxin translocation into the circulation in cirrhotics, a new animal model was developed. Rats were chronically exposed to ethanol and for the four last weeks also infused with endotoxin into the jugular vein from subcutaneously implanted osmotic minipumps. Animals receiving endotoxin had elevated hepatic expression of both pro- and anti-inflammatory cytokines, but compared to ethanol treatment alone hepatic steatosis and inflammatory changes were only marginally increased. This demonstrates marked endotoxin tolerance, probably as a consequence of a counteracting anti-inflammatory cytokine response. The role of gut-derived endotoxin in hepatic encephalopathy has recently received considerable attention. To further delineate the role and actions of endotoxin and its extrahepatic effects, studies applying both acute challenge and chronic infusion seem warranted. The chronic endotoxin model, mimicking the "leaky gut," may best be combined with more robust ways to impair liver function, such as carbon tetrachloride treatment, bile duct ligation, or galactosamine administration.

Breakdown of the blood-brain barrier to proteins in white matter of the developing brain following systemic inflammation

Compromised blood-brain barrier permeability resulting from systemic inflammation has been implicated as a possible cause of brain damage in fetuses and newborns and may underlie white matter damage later in life. Rats at postnatal day (P) 0, P8 and P20 and opossums (Monodelphis domestica) at P15, P20, P35, P50 and P60 and adults of both species were injected intraperitoneally with 0.2-10 mg/kg body weight of 055:B5 lipopolysaccharide. An acute-phase response occurred in all animals. A change in the permeability of the blood-brain barrier to plasma proteins during a restricted period of postnatal development in both species was determined immunocytochemically by the presence of proteins surrounding cerebral blood vessels and in brain parenchyma. Blood vessels in white matter, but not grey matter, became transiently permeable to proteins between 10 and 24 h after lipopolysaccharide injection in P0 and P8 rats and P35-P60 opossums. Brains of Monodelphis younger than P35, rats older than P20 and adults of both species were not affected. Permeability of the blood-cerebrospinal fluid (CSF) barrier to proteins was not affected by systemic inflammation for at least 48 h after intraperitoneal injection of lipopolysaccharide. These results show that there is a restricted period in brain development when the blood-brain barrier, but not the blood-CSF barrier, to proteins is susceptible to systemic inflammation; this does not appear to be attributable to barrier "immaturity" but to its stage of development and only occurs in white matter.

Effects of lipopolysaccharide on the blood-brain barrier permeability in prolonged nitric oxide blockade-induced hypertensive rats

The authors investigated the effects of lipopolysaccharide (LPS) on the blood-brain barrier (BBB) integrity and the activity of astrocytes during the Nw-nitro-L-arginine methyl ester (L-NAME) hypertension followed by angiotensin (ANG) II in rats. They measured the changes in the BBB permeability using the Evans blue (EB) dye and concomitantly in the levels of TNF-a, IL-1b, and IL-6 in serum and nitric oxide in plasma. The authors performed two tight junction-specific proteins, zonula occludens-1 and occludin, and glial fibrillary acidic protein, by using immunohisto-chemical method. The serum levels of TNF-a, IL-1 IL-6, and the plasma level of nitric oxide significantly increased in LPS-treated rats (p<.01). The EB dye extravasation increased in cerebellum (p<.001) and diencephalon (p<.05) of L-NAME plus ANG II-treated animals. However, LPS reduced the increased EB dye extravasation in the brain regions of L-NAME-induced hypertensive rats treated with ANG II (p<.001). In L-NAME, there was a considerable loss of staining in both zonula occludens-1 and occludin. Staining for zonula occludens-1 and occludin was highly intensive in animals treated with LPS. Glial fibrillary acidic protein staining was seen in a few astrocytes in brains of L-NAME-treated animals. However, this staining showed an increased intensity in the brain sections of animals treated with LPS. This study indicates that, in L-NAME hypertensive rats, ANG II leads to an increase in the extravasation of EB dye to brain as a result of decreased activity of tight junction proteins and astrocytes, and LPS could significantly attenuate the EB dye transport to the brain through the increased activity of tight junction proteins and astrocytes.

Effects of lipopolysaccharide on the radiation-induced changes in the blood-brain barrier and the astrocytes

The use of radiation to improve the efficacy of chemotherapy on malignant brain tumors is also known to cause side effects on vascular endothelial cells and astrocytes in normal parts of the brain. We investigated the effects of lipopolysaccharide (LPS) on the functional and structural properties of blood-brain barrier (BBB) and the activity of astrocytes during whole-brain irradiation in rats. The permeability of the BBB to Evans blue (EB) dye significantly increased in the cerebral cortex, diencephalon and cerebellum regions of rats exposed to irradiation (P<0.01). In contrast, the BBB permeability in irradiated rats was significantly reduced by LPS (P<0.05). Tumor necrosis factor-alpha (TNF-alpha) levels were increased following LPS, irradiation and irradiation plus LPS (P<0.05, P<0.01). Irradiated brain vessels showed a considerable loss of staining intensity of tight junction proteins Zonula occludens-1 (ZO-1) and occludin. Staining for Zonula occludens-1 and occludin was intensive in animals treated with LPS and irradiation plus LPS. Glial fibrillary acidic protein (GFAP) immunoreactivity was seen in very few astrocytes of irradiated brains. However, this staining showed an increased positive intensity in the brain sections of LPS-treated as well as of irradiation plus LPS-treated animals. These results indicate that LPS reduces the passage of exogenous vascular tracer EB-binding albumin into the brain, at least partly, by increasing the expression of tight junction proteins and GFAP, following the irradiation. We suggest that irradiation may affect paracellular permeability through disruption of tight junction proteins, Zonula occludens-1 and occludin, and LPS could provide beneficial effects on the BBB integrity and the astrocytes against irradiation damage.

How does peripheral lipopolysaccharide induce gene expression in the brain of rats?

Lipopolysaccharide (LPS), the principal cell-wall component of gram-negative bacteria, is responsible for alterations in the central and peripheral tissues associated with gram-negative infections. However, the mechanism by which peripheral LPS cause central effects is not fully known. This study showed that peripheral LPS sequentially increased IL-1beta and iNOS mRNA levels, NO2 level, and CRF mRNA level in the hypothalamic PVN, and corticosterone concentration in blood. Brain-endothelium, but not hypothalamic PVN samples, from LPS injected rats contained ions for LPS lipids, bound BODIPY-LPS (bLPS), and expressed TLR-4, TLP-2 and CD14 mRNAs. This suggests that (1) LPS does not cross the blood-brain barrier, and (2) brain-endothelial cells contain LPS binding sites, TLR-4, TLR-2 and CD14. Systemic LPS injection increased [14C]sucrose uptake, but did not affect [14C]dextran uptake into the brain. Thus, when injected systemically, LPS binds to its receptor and enter the endothelial cells where it increase BBB permeation in a mass-selective manner and triggers a series of signaling events leading to the development of inflammatory response in the brain.

The effects of endogenous interleukin-1 bioactivity on locus coeruleus neurons in response to bacterial and viral substances

In a previous study, we found that microinjection of the cytokine interleukin-1 (IL-1) into the locus coeruleus (LC) increased the electrophysiological activity of LC neurons. To determine if endogenous IL-1 similarly affects the LC, brain IL-1 was induced with lipopolysaccharide (LPS), a substance derived from Gram-negative bacteria. LPS microinjected directly into the LC increased the activity of LC neurons in anesthetized rats, and this effect was blocked by microinfusion of the IL-1 receptor antagonist (IL-1RA) protein into the LC indicating the involvement of IL-1 receptors. Similarly, intraperitoneal (i.p.) LPS injection increased the activity of LC neurons in a dose- and time-related manner that was sensitive to IL-1RA. The change in the activity of LC neurons caused by a single i.p. injection of LPS was surprisingly long-lasting, and evolved over a period of at least 3 weeks. Other microbial substances-namely, peptidoglycan from Gram-positive bacteria and poly-inosine/poly-cytosine (poly(I)/(C)), which resembles RNA viruses-were used to determine the generality of the findings with LPS. Both i.p. peptidoglycan and poly(I)/(C) increased LC activity but with lesser efficacy than LPS. IL-1RA reversed the increase in the activity of LC neurons caused by i.p. peptidoglycan treatment; however, that caused by i.p. Poly(I)/(C) was not diminished by IL-1RA. Thus, the increased activity of LC neurons caused by LPS and peptidoglycan requires IL-1 receptor binding, suggesting the involvement of endogenously-produced IL-1. In contrast, poly(I)/(C) increased the activity of LC neurons but this did not critically involve IL-1 receptors in the LC.

Effect of endotoxin on expression of TNF receptors and transport of TNF-alpha at the blood-brain barrier of the rat

The transport mechanism mediating brain uptake of tumor necrosis factor (TNF)-alpha has been studied. When (125)I-labeled rat TNF-alpha was used in internal carotid artery perfusions in rats, the cytokine showed transcytosis through the blood-brain barrier in intact form (permeability-surface area product 0.34 +/- 0.13 microl. min(-1). g(-1)). Uptake was inhibited by low nanomolar concentrations of unlabeled rat TNF-alpha. Human TNF-alpha, which does not interact with the p80 TNF receptor in rodents, showed no brain uptake. mRNA expression of both p60 and p80 receptors could be demonstrated in native brain microvessel preparations. These transcripts increased to 149% (p60) and 127% (p80) of control 4 h after a systemic immune stimulation (2 mg/kg bacterial endotoxin ip). Lipopolysaccharide treatment did not alter the rate of brain uptake of TNF-alpha measured between 4 and 24 h later. In conclusion, a receptor-mediated mechanism is responsible for the transcytosis of TNF-alpha. Saturable transport, requiring the p80 receptor, occurs at concentrations encountered under pathophysiological conditions and therefore constitutes a relevant mechanism of communication between the immune system and the brain.

Effect of endotoxin on doxorubicin transport across blood-brain barrier and P-glycoprotein function in mice

The aim of this study was to investigate whether Klebsiella pneumoniae endotoxin modifies transport of doxorubicin, a P-glycoprotein substrate, across the blood-brain barrier and P-glycoprotein function in mice. Doxorubicin (30 mg/kg) was administered into the tail vein or fluorescein isothiocyanate-labeled dextran (FD-4) was infused (20 microg/min) into the right jugular vein of mice intravenously injected with endotoxin (10 mg/kg) 6 or 24 h earlier. Blood and brain samples were collected 4 h after injection of doxorubicin or 1 h after infusion of FD-4. We examined using Western blotting the influence of endotoxin on the expression of P-glycoprotein in brains obtained 6, 12 and 24 h after injection. Endotoxin did not change the plasma and brain concentrations and brain-to-plasma concentration ratio (K(p) value) of FD-4. No histopathological changes in brain capillaries were observed. These results suggest that endotoxin does not cause damage to brain capillaries. Plasma and brain concentrations of doxorubicin in mice treated 6 h earlier with endotoxin were significantly higher than those in control and mice treated 24 h earlier. However, endotoxin did not significantly change the K(p) value of doxorubicin. The protein level of P-glycoprotein was significantly, but slightly down-regulated 6 h after endotoxin treatment. However, the levels remained almost unchanged after 12 and 24 h. The present results suggest that Klebsiella pneumoniae endotoxin has no effect on the brain capillary integrity and doxorubicin transport across the blood-brain barrier in mice. It is likely that P-glycoprotein function might be sufficient to transport doxorubicin in spite of decreased levels of P-glycoprotein in the brain.

Prenatal exposure to maternal infection alters cytokine expression in the placenta, amniotic fluid, and fetal brain

Prenatal exposure to infection appears to increase the risk of schizophrenia and other neurodevelopmental disorders. We have hypothesized that cytokines, generated in response to maternal infection, play a key mechanistic role in this association. E16 timed pregnancy rats were injected i.p. with Escherichia coli lipopolysaccharide (LPS) to model prenatal exposure to infection. Placenta, amniotic fluid and fetal brains were collected 2 and 8h after LPS exposure. There was a significant treatment effect of low-dose (0.5mg/kg) LPS on placenta cytokine levels, with significant increases of interleukin (IL)-1beta (P<0.0001), IL-6 (P<0.0001), and tumor necrosis factor-alpha (TNF-alpha) (P=0.0001) over the 2 and 8h time course. In amniotic fluid, there was a significant effect of treatment on IL-6 levels (P=0.0006). Two hours after maternal administration of high-dose (2.5mg/kg) LPS, there were significant elevations of placenta IL-6 (P<0.0001), TNF-alpha (P<0.0001), a significant increase of TNF-alpha in amniotic fluid (P=0.008), and a small but significant decrease in TNF-alpha (P=0.035) in fetal brain. Maternal exposure to infection alters pro-inflammatory cytokine levels in the fetal environment, which may have a significant impact on the developing brain.