MyD88-mediated signaling is critical for the generation of seizure responses and cognitive impairment in a model of anti-N-methyl-D-aspartate receptor encephalitis.

OBJECTIVE: We previously demonstrated that interleukin-1 receptor-mediated immune activation contributes to seizure severity and memory loss in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis. In the present study, we assessed the role of the myeloid differentiation primary response gene 88 (MyD88), an adaptor protein in Toll-like receptor signaling, in the key phenotypic characteristics of anti-NMDAR encephalitis. METHODS: Monoclonal anti-NMDAR antibodies or control antibodies were infused into the lateral ventricle of MyD88 knockout mice (MyD88-/-) and control C56BL/6J mice (wild type [WT]) via osmotic minipumps for 2 weeks. Seizure responses were measured by electroencephalography. Upon completion of the infusion, the motor, anxiety, and memory functions of the mice were assessed. Astrocytic (glial fibrillary acidic protein [GFAP]) and microglial (ionized calcium-binding adaptor molecule 1 [Iba-1]) activation and transcriptional activation for the principal inflammatory mediators involved in seizures were determined using immunohistochemistry and quantitative real-time polymerase chain reaction, respectively. RESULTS: As shown before, 80% of WT mice infused with anti-NMDAR antibodies (n = 10) developed seizures (median = 11, interquartile range [IQR] = 3-25 in 2 weeks). In contrast, only three of 14 MyD88-/- mice (21.4%) had seizures (0, IQR = 0-.25, p = .01). The WT mice treated with antibodies also developed memory loss in the novel object recognition test, whereas such memory deficits were not apparent in MyD88-/- mice treated with anti-NMDAR antibodies (p = .03) or control antibodies (p = .04). Furthermore, in contrast to the WT mice exposed to anti-NMDAR antibodies, the MyD88-/- mice had a significantly lower induction of chemokine (C-C motif) ligand 2 (CCL2) in the hippocampus (p = .0001, Sidak tests). There were no significant changes in the expression of GFAP and Iba-1 in the MyD88-/- mice treated with anti-NMDAR or control antibodies. SIGNIFICANCE: These findings suggest that MyD88-mediated signaling contributes to the seizure and memory phenotype in anti-NMDAR encephalitis and that CCL2 activation may participate in the expression of these features. The removal of MyD88 inflammation may be protective and therapeutically relevant.

Presynaptic Inhibitory Effects of Acetylcholine in the Hippocampus: A 40-Year Evolution of a Serendipitous Finding.

Cholinergic regulation of hippocampal circuit activity has been an active area of neurophysiological research for decades. The prominent cholinergic innervation of intrinsic hippocampal circuitry, potent effects of cholinomimetic drugs, and behavioral responses to cholinergic modulation of hippocampal circuitry have driven investigators to discover diverse cellular actions of acetylcholine in distinct sites within hippocampal circuitry. Further research has illuminated how these actions organize circuit activity to optimize encoding of new information, promote consolidation, and coordinate this with recall of prior memories. The development of the hippocampal slice preparation was a major advance that accelerated knowledge of how hippocampal circuits functioned and how acetylcholine modulated these circuits. Using this preparation in the early 1980s, we made a serendipitous finding of a novel presynaptic inhibitory effect of acetylcholine on Schaffer collaterals, the projections from CA3 pyramidal neurons to dendrites of CA1 pyramidal cells. We characterized this effect at cellular and pharmacological levels, published the findings in the first volume of the Journal of Neuroscience, and proceeded to pursue other scientific directions. We were surprised and thrilled to see that, nearly 40 years later, the paper is still being cited and downloaded because the data became an integral piece of the foundation of the science of cholinergic regulation of hippocampal function in learning and memory. This Progressions article is a story of how single laboratory findings evolve through time to be confirmed, challenged, and reinterpreted by other laboratories to eventually become part of the basis of fundamental concepts related to important brain functions.

Peripheral Myeloid Cell EP2 Activation Contributes to the Deleterious Consequences of Status Epilepticus.

A multidimensional inflammatory response ensues after status epilepticus (SE), driven partly by cyclooxygenase-2-mediated activation of prostaglandin EP2 receptors. The inflammatory response is typified by astrocytosis, microgliosis, erosion of the blood-brain barrier (BBB), formation of inflammatory cytokines, and brain infiltration of blood-borne monocytes. Our previous studies have shown that inhibition of monocyte brain invasion or systemic administration of an EP2 receptor antagonist relieves multiple deleterious consequences of SE. Here we identify those effects of EP2 antagonism that are reproduced by conditional ablation of EP2 receptors in immune myeloid cells and show that systemic EP2 antagonism blocks monocyte brain entry in male mice. The induction of hippocampal IL-6 after pilocarpine SE was nearly abolished in EP2 conditional KO mice. Serum albumin levels in the cortex, a measure of BBB breakdown, were significantly higher after SE in EP2-sufficient mice but not in EP2 conditional KOs. EP2 deficiency in innate immune cells accelerated the recovery from sickness behaviors following SE. Surprisingly, neurodegeneration was not alleviated in myeloid conditional KOs. Systemic EP2 antagonism prevented monocyte brain infiltration and provided broader rescue of SE-induced effects than myeloid EP2 ablation, including neuroprotection and broader suppression of inflammatory mediators. Reporter expression indicated that the cellular target of CD11b-driven Cre was circulating myeloid cells but, unexpectedly, not microglia. These findings indicate that activation of EP2 receptors on immune myeloid cells drives substantial deficits in behavior and disrupts the BBB after SE. The benefits of systemic EP2 antagonism can be attributed, in part, to blocking brain recruitment of blood-borne monocytes.SIGNIFICANCE STATEMENT Unabated seizures reduce quality of life, promote the development of epilepsy, and can be fatal. We previously identified activation of prostaglandin EP2 receptors as a driver of undesirable consequences of seizures. However, the relevant EP2-expressing cell types remain unclear. Here we identify peripheral innate immune cells as a driver of the EP2-related negative consequences of seizures. Removal of EP2 from peripheral immune cells was beneficial, abolishing production of a key inflammatory cytokine, accelerating weight regain, and limiting behavioral deficits. These findings provide evidence that EP2 engagement on peripheral immune and brain endothelia contributes to the deleterious effects of SE, and will assist in the development of beneficial therapies to enhance quality of life in individuals who suffer prolonged seizures.

Prostaglandin EP2 receptor antagonist ameliorates neuroinflammation in a two-hit mouse model of Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) causes substantial medical and societal burden with no therapies ameliorating cognitive deficits. Centralized pathologies involving amyloids, neurofibrillary tangles, and neuroinflammatory pathways are being investigated to identify disease-modifying targets for AD. Cyclooxygenase-2 (COX-2) is one of the potential neuroinflammatory agents involved in AD progression. However, chronic use of COX-2 inhibitors in patients produced adverse cardiovascular effects. We asked whether inhibition of EP2 receptors, downstream of the COX-2 signaling pathway, can ameliorate neuroinflammation in AD brains in presence or absence of a secondary inflammatory stimuli. METHODS: We treated 5xFAD mice and their non-transgenic (nTg) littermates in presence or absence of lipopolysaccharide (LPS) with an EP2 antagonist (TG11-77.HCl). In cohort 1, nTg (no-hit) or 5xFAD (single-hit-genetic) mice were treated with vehicle or TG11-77.HCl for 12 weeks. In cohort 2, nTg (single-hit-environmental) and 5xFAD mice (two-hit) were administered LPS (0.5 mg/kg/week) and treated with vehicle or TG11-77.HCl for 8 weeks. RESULTS: Complete blood count analysis showed that LPS induced anemia of inflammation in both groups in cohort 2. There was no adverse effect of LPS or EP2 antagonist on body weight throughout the treatment. In the neocortex isolated from the two-hit cohort of females, but not males, the elevated mRNA levels of proinflammatory mediators (IL-1ß, TNF, IL-6, CCL2, EP2), glial markers (IBA1, GFAP, CD11b, S110B), and glial proteins were significantly reduced by EP2 antagonist treatment. Intriguingly, the EP2 antagonist had no effect on either of the single-hit cohorts. There was a modest increase in amyloid-plaque deposition upon EP2 antagonist treatment in the two-hit female brains, but not in the single-hit genetic female cohort. CONCLUSION: These results reveal a potential neuroinflammatory role for EP2 in the two-hit 5xFAD mouse model. A selective EP2 antagonist reduces inflammation only in female AD mice subjected to a second inflammatory insult.

A Glutamate N-Methyl-d-Aspartate (NMDA) Receptor Subunit 2B-Selective Inhibitor of NMDA Receptor Function with Enhanced Potency at Acidic pH and Oral Bioavailability for Clinical Use.

We describe a clinical candidate molecule from a new series of glutamate N-methyl-d-aspartate receptor subunit 2B-selective inhibitors that shows enhanced inhibition at extracellular acidic pH values relative to physiologic pH. This property should render these compounds more effective inhibitors of N-methyl-d-aspartate receptors at synapses responding to a high frequency of action potentials, since glutamate-containing vesicles are acidic within their lumen. In addition, acidification of penumbral regions around ischemic tissue should also enhance selective drug action for improved neuroprotection. The aryl piperazine we describe here shows strong neuroprotective actions with minimal side effects in preclinical studies. The clinical candidate molecule NP10679 has high oral bioavailability with good brain penetration and is suitable for both intravenous and oral dosing for therapeutic use in humans. SIGNIFICANCE STATEMENT: This study identifies a new series of glutamate N-methyl-d-aspartate (NMDA) receptor subunit 2B-selective negative allosteric modulators with properties appropriate for clinical advancement. The compounds are more potent at acidic pH, associated with ischemic tissue, and this property should increase the therapeutic safety of this class by improving efficacy in affected tissue while sparing NMDA receptor block in healthy brain.

Seizures and memory impairment induced by patient-derived anti-N-methyl-D-aspartate receptor antibodies in mice are attenuated by anakinra, an interleukin-1 receptor antagonist.

OBJECTIVE: Neuroinflammation associated with anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis may facilitate seizures. We previously showed that intraventricular administration of cerebrospinal fluid from patients with anti-NMDAR encephalitis to mice precipitates seizures, thereby confirming that antibodies are directly pathogenic. To determine whether interleukin (IL)-1-mediated inflammation exacerbates autoimmune seizures, we asked whether blocking the effects of IL-1 by anakinra, a selective IL-1 receptor antagonist, blunts antibody-induced seizures. METHODS: We infused C57BL/6 mice intraventricularly with purified serum IgG from patients with anti-NMDAR encephalitis or monoclonal anti-NMDAR IgG; subdural electroencephalogram was continuously recorded. After a 6-day interval, mice received anakinra (25 mg/kg sc, twice daily) or vehicle for 5 days. Following a 4-day washout period, we performed behavioral tests to assess motor function, anxiety, and memory, followed by hippocampus tissue analysis to assess astrocytic (glial fibrillary acidic protein [GFAP]) and microglial (ionized calcium-binding adapter molecule [Iba]-1) activation. RESULTS: Of 31 mice infused with purified patient NMDAR-IgG (n = 17) or monoclonal NMDAR-IgG (n = 14), 81% developed seizures. Median baseline daily seizure count during exposure to antibodies was 3.9; most seizures were electrographic. Median duration of seizures during the baseline was 82.5 s. Anakinra administration attenuated daily seizure frequency by 60% (p = .02). Anakinra reduced seizure duration; however, the effect was delayed and became apparent only after the cessation of treatment (p = .04). Anakinra improved novel object recognition in mice with antibody-induced seizures (p = .03) but did not alter other behaviors. Anakinra reduced the expression of GFAP and Iba-1 in the hippocampus of mice with seizures, indicating decreased astrocytic and microglial activation. SIGNIFICANCE: Our evidence supports a role for IL-1 in the pathogenesis of seizures in anti-NMDAR encephalitis. These data are consistent with therapeutic effects of anakinra in other severe autoimmune and inflammatory seizure syndromes. Targeting inflammation via blocking IL-1 receptor-mediated signaling may be promising for developing novel treatments for refractory autoimmune seizures.

Urethane attenuates early neuropathology of diisopropylfluorophosphate-induced status epilepticus in rats.

Seizures can be evident within minutes of exposure to an organophosphorus (OP) agent and often progress to status epilepticus (SE) resulting in a high mortality if left untreated. Effective medical countermeasures are necessary to sustain patients suffering from OP poisoning and to mitigate the ensuing brain injury. Here, the hypothesis was tested that a single subanesthetic dose of urethane prevents neuropathology measured 24 h following diisopropylfluorophosphate (DFP)-induced SE. Adult Sprague-Dawley rats were injected with DFP to induce SE. During SE rats displayed increased neuronal activity in the hippocampus and an upregulation of immediate early genes as well as pro-inflammatory mediators. In additional experiments rats were administered diazepam (10 mg/kg, ip) or urethane (0.8 g/kg, sc) 1 h after DFP-induced SE and compared to rats that experienced uninterrupted SE. Cortical electroencephalography (EEG) and power analysis strengthen the conclusion that urethane effectively terminates SE and prevents the overnight return of seizure activity. Neurodegeneration in limbic brain regions and the seizure-induced upregulation of key inflammatory mediators present 24 h after DFP-induced SE were strongly attenuated by administration of urethane. A trivial explanation for these beneficial effects, that urethane simply reactivates acetylcholinesterase, has been ruled out. These findings indicate that, by contrast to rats administered diazepam or rats that experience uninterrupted SE, the early neuropathology after SE is prevented by subanesthetic urethane, which terminates rather than interrupts, SE.

A rat model of organophosphate-induced status epilepticus and the beneficial effects of EP2 receptor inhibition.

This review describes an adult rat model of status epilepticus (SE) induced by diisopropyl fluorophosphate (DFP), and the beneficial outcomes of transient inhibition of the prostaglandin-E2 receptor EP2 with a small molecule antagonist, delayed by 2-4 h after SE onset. Administration of six doses of the selective EP2 antagonist TG6-10-1 over a 2-3 day period accelerates functional recovery, attenuates hippocampal neurodegeneration, neuroinflammation, gliosis and blood-brain barrier leakage, and prevents long-term cognitive deficits without blocking SE itself or altering acute seizure characteristics. This work has provided important information regarding organophosphate-induced seizure related pathologies in adults and revealed the effectiveness of delayed EP2 inhibition to combat these pathologies.

A mouse model of seizures in anti-N-methyl-d-aspartate receptor encephalitis.

OBJECTIVE: Seizures develop in 80% of patients with anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis, and these represent a major cause of morbidity and mortality. Anti-NMDAR antibodies have been linked to memory loss in encephalitis; however, their role in seizures has not been established. We determined whether anti-NMDAR antibodies from autoimmune encephalitis patients are pathogenic for seizures. METHODS: We performed continuous intracerebroventricular infusion of cerebrospinal fluid (CSF) or purified immunoglobulin (IgG) from the CSF of patients with anti-NMDAR encephalitis or polyclonal rabbit anti-NMDAR IgG, in male C57BL/6 mice. Seizure status during a 2-week treatment was assessed with video-electroencephalography. We assessed memory, anxiety-related behavior, and motor function at the end of treatment and assessed the extent of neuronal damage and gliosis in the CA1 region of hippocampus. We also performed whole-cell patch recordings from the CA1 pyramidal neurons in hippocampal slices of mice with seizures. RESULTS: Prolonged exposure to rabbit anti-NMDAR IgG, patient CSF, or human IgG purified from the CSF of patients with encephalitis induced seizures in 33 of 36 mice. The median number of seizures recorded in 2 weeks was 13, 39, and 35 per mouse in these groups, respectively. We observed only 18 brief nonconvulsive seizures in 11 of 29 control mice (median seizure count of 0) infused with vehicle (n = 4), normal CSF obtained from patients with noninflammatory central nervous system (CNS) conditions (n = 12), polyclonal rabbit IgG (n = 7), albumin (n = 3), and normal human IgG (n = 3). We did not observe memory deficits, anxiety-related behavior, or motor impairment measured at 2 weeks in animals treated with CSF from affected patients or rabbit IgG. Furthermore, there was no evidence of hippocampal cell loss or astrocyte proliferation in the same mice. SIGNIFICANCE: Our findings indicate that autoantibodies can induce seizures in anti-NMDAR encephalitis and offer a model for testing novel therapies for refractory autoimmune seizures.

Infiltrating monocytes promote brain inflammation and exacerbate neuronal damage after status epilepticus.

The generalized seizures of status epilepticus (SE) trigger a series of molecular and cellular events that produce cognitive deficits and can culminate in the development of epilepsy. Known early events include opening of the blood-brain barrier (BBB) and astrocytosis accompanied by activation of brain microglia. Whereas circulating monocytes do not infiltrate the healthy CNS, monocytes can enter the brain in response to injury and contribute to the immune response. We examined the cellular components of innate immune inflammation in the days following SE by discriminating microglia vs. brain-infiltrating monocytes. Chemokine receptor 2 (CCR2(+)) monocytes invade the hippocampus between 1 and 3 d after SE. In contrast, only an occasional CD3(+) T lymphocyte was encountered 3 d after SE. The initial cellular sources of the chemokine CCL2, a ligand for CCR2, included perivascular macrophages and microglia. The induction of the proinflammatory cytokine IL-1ß was greater in FACS-isolated microglia than in brain-invading monocytes. However, Ccr2 knockout mice displayed greatly reduced monocyte recruitment into brain and reduced levels of the proinflammatory cytokine IL-1ß in hippocampus after SE, which was explained by higher expression of the cytokine in circulating and brain monocytes in wild-type mice. Importantly, preventing monocyte recruitment accelerated weight regain, reduced BBB degradation, and attenuated neuronal damage. Our findings identify brain-infiltrating monocytes as a myeloid-cell subclass that contributes to neuroinflammation and morbidity after SE. Inhibiting brain invasion of CCR2(+) monocytes could represent a viable method for alleviating the deleterious consequences of SE.

Candidate drug targets for prevention or modification of epilepsy.

Epilepsy is a prevalent neurological disorder afflicting nearly 50 million people worldwide. The disorder is characterized clinically by recurrent spontaneous seizures attributed to abnormal synchrony of brain neurons. Despite advances in the treatment of epilepsy, nearly one-third of patients are resistant to current therapies, and the underlying mechanisms whereby a healthy brain becomes epileptic remain unresolved. Therefore, researchers have a major impetus to identify and exploit new drug targets. Here we distinguish between epileptic effectors, or proteins that set the seizure threshold, and epileptogenic mediators, which control the expression or functional state of the effector proteins. Under this framework, we then discuss attempts to regulate the mediators to control epilepsy. Further insights into the complex processes that render the brain susceptible to seizures and the identification of novel mediators of these processes will lead the way to the development of drugs to modify disease outcome and, potentially, to prevent epileptogenesis.

Commonalities in epileptogenic processes from different acute brain insults: Do they translate?

The most common forms of acquired epilepsies arise following acute brain insults such as traumatic brain injury, stroke, or central nervous system infections. Treatment is effective for only 60%-70% of patients and remains symptomatic despite decades of effort to develop epilepsy prevention therapies. Recent preclinical efforts are focused on likely primary drivers of epileptogenesis, namely inflammation, neuron loss, plasticity, and circuit reorganization. This review suggests a path to identify neuronal and molecular targets for clinical testing of specific hypotheses about epileptogenesis and its prevention or modification. Acquired human epilepsies with different etiologies share some features with animal models. We identify these commonalities and discuss their relevance to the development of successful epilepsy prevention or disease modification strategies. Risk factors for developing epilepsy that appear common to multiple acute injury etiologies include intracranial bleeding, disruption of the blood-brain barrier, more severe injury, and early seizures within 1 week of injury. In diverse human epilepsies and animal models, seizures appear to propagate within a limbic or thalamocortical/corticocortical network. Common histopathologic features of epilepsy of diverse and mostly focal origin are microglial activation and astrogliosis, heterotopic neurons in the white matter, loss of neurons, and the presence of inflammatory cellular infiltrates. Astrocytes exhibit smaller K+ conductances and lose gap junction coupling in many animal models as well as in sclerotic hippocampi from temporal lobe epilepsy patients. There is increasing evidence that epilepsy can be prevented or aborted in preclinical animal models of acquired epilepsy by interfering with processes that appear common to multiple acute injury etiologies, for example, in post-status epilepticus models of focal epilepsy by transient treatment with a trkB/PLCγ1 inhibitor, isoflurane, or HMGB1 antibodies and by topical administration of adenosine, in the cortical fluid percussion injury model by focal cooling, and in the albumin posttraumatic epilepsy model by losartan. Preclinical studies further highlight the roles of mTOR1 pathways, JAK-STAT3, IL-1R/TLR4 signaling, and other inflammatory pathways in the genesis or modulation of epilepsy after brain injury. The wealth of commonalities, diversity of molecular targets identified preclinically, and likely multidimensional nature of epileptogenesis argue for a combinatorial strategy in prevention therapy. Going forward, the identification of impending epilepsy biomarkers to allow better patient selection, together with better alignment with multisite preclinical trials in animal models, should guide the clinical testing of new hypotheses for epileptogenesis and its prevention.

Neuroinflammatory targets and treatments for epilepsy validated in experimental models.

A large body of evidence that has accumulated over the past decade strongly supports the role of inflammation in the pathophysiology of human epilepsy. Specific inflammatory molecules and pathways have been identified that influence various pathologic outcomes in different experimental models of epilepsy. Most importantly, the same inflammatory pathways have also been found in surgically resected brain tissue from patients with treatment-resistant epilepsy. New antiseizure therapies may be derived from these novel potential targets. An essential and crucial question is whether targeting these molecules and pathways may result in anti-ictogenesis, antiepileptogenesis, and/or disease-modification effects. Therefore, preclinical testing in models mimicking relevant aspects of epileptogenesis is needed to guide integrated experimental and clinical trial designs. We discuss the most recent preclinical proof-of-concept studies validating a number of therapeutic approaches against inflammatory mechanisms in animal models that could represent novel avenues for drug development in epilepsy. Finally, we suggest future directions to accelerate preclinical to clinical translation of these recent discoveries.

Inhibition of the prostaglandin receptor EP2 following status epilepticus reduces delayed mortality and brain inflammation.

Prostaglandin E2 is now widely recognized to play critical roles in brain inflammation and injury, although the responsible prostaglandin receptors have not been fully identified. We developed a potent and selective antagonist for the prostaglandin E2 receptor subtype EP2, TG6-10-1, with a sufficient pharmacokinetic profile to be used in vivo. We found that in the mouse pilocarpine model of status epilepticus (SE), systemic administration of TG6-10-1 completely recapitulates the effects of conditional ablation of cyclooxygenase-2 from principal forebrain neurons, namely reduced delayed mortality, accelerated recovery from weight loss, reduced brain inflammation, prevention of blood-brain barrier opening, and neuroprotection in the hippocampus, without modifying seizures acutely. Prolonged SE in humans causes high mortality and morbidity that are associated with brain inflammation and injury, but currently the only effective treatment is to stop the seizures quickly enough with anticonvulsants to prevent brain damage. Our results suggest that the prostaglandin receptor EP2 is critically involved in neuroinflammation and neurodegeneration, and point to EP2 receptor antagonism as an adjunctive therapeutic strategy to treat SE.

EP2 Receptor Signaling Regulates Microglia Death.

The timely resolution of inflammation prevents continued tissue damage after an initial insult. In the brain, the death of activated microglia by apoptosis has been proposed as one mechanism to resolve brain inflammation. How microglial death is regulated after activation is still unclear. We reported that exposure to lipopolysaccharide (LPS) and interleukin (IL)-13 together initially activates and then kills rat microglia in culture by a mechanism dependent on cyclooxygenase-2 (COX-2). We show here that activation of the E prostanoid receptor 2 (EP2, PTGER2) for prostaglandin E2 mediates microglial death induced by LPS/IL-13, and that EP2 activation by agonist alone kills microglia. Both EP2 antagonists and reactive oxygen scavengers block microglial death induced by either LPS/IL-13 or EP2 activation. By contrast, the homeostatic induction of heme oxygenase 1 (Hmox1) by LPS/IL-13 or EP2 activation protects microglia. Both the Hmox1 inducer cobalt protoporphyrin and a compound that releases the Hmox1 product carbon monoxide (CO) attenuated microglial death produced by LPS/IL-13. Whereas CO reduced COX-2 protein expression, EP2 activation increased Hmox1 and COX-2 expression at both the mRNA and protein level. Interestingly, caspase-1 inhibition prevented microglial death induced by either LPS/IL-13 or low (but not high) concentrations of butaprost, suggestive of a predominantly pyroptotic mode of death. Butaprost also caused the expression of activated caspase-3 in microglia, pointing to apoptosis. These results indicate that EP2 activation, which initially promotes microglial activation, later causes delayed death of activated microglia, potentially contributing to the resolution phase of neuroinflammation.

Uptake and metabolism of fructose by rat neocortical cells in vivo and by isolated nerve terminals in vitro.

Fructose reacts spontaneously with proteins in the brain to form advanced glycation end products (AGE) that may elicit neuroinflammation and cause brain pathology, including Alzheimer's disease. We investigated whether fructose is eliminated by oxidative metabolism in neocortex. Injection of [(14) C]fructose or its AGE-prone metabolite [(14) C]glyceraldehyde into rat neocortex in vivo led to formation of (14) C-labeled alanine, glutamate, aspartate, GABA, and glutamine. In isolated neocortical nerve terminals, [(14) C]fructose-labeled glutamate, GABA, and aspartate, indicating uptake of fructose into nerve terminals and oxidative fructose metabolism in these structures. This was supported by high expression of hexokinase 1, which channels fructose into glycolysis, and whose activity was similar with fructose or glucose as substrates. By contrast, the fructose-specific ketohexokinase was weakly expressed. The fructose transporter Glut5 was expressed at only 4% of the level of neuronal glucose transporter Glut3, suggesting transport across plasma membranes of brain cells as the limiting factor in removal of extracellular fructose. The genes encoding aldose reductase and sorbitol dehydrogenase, enzymes of the polyol pathway that forms glucose from fructose, were expressed in rat neocortex. These results point to fructose being transported into neocortical cells, including nerve terminals, and that it is metabolized and thereby detoxified primarily through hexokinase activity. We asked how the brain handles fructose, which may react spontaneously with proteins to form 'advanced glycation end products' and trigger inflammation. Neocortical cells took up and metabolized extracellular fructose oxidatively in vivo, and isolated nerve terminals did so in vitro. The low expression of fructose transporter Glut5 limited uptake of extracellular fructose. Hexokinase was a main pathway for fructose metabolism, but ketohexokinase (which leads to glyceraldehyde formation) was expressed too. Neocortical cells also took up and metabolized glyceraldehyde oxidatively.

Therapeutic window for cyclooxygenase-2 related anti-inflammatory therapy after status epilepticus.

As a prominent inflammatory effector of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2) mediates brain inflammation and injury in many chronic central nervous system (CNS) conditions including seizures and epilepsy, largely through its receptor subtype EP2. However, EP2 receptor activation might also be neuroprotective in models of excitotoxicity and ischemia. These seemingly incongruent observations expose the delicacy of immune and inflammatory signaling in the brain; thus the therapeutic window for quelling neuroinflammation might vary with injury type and target molecule. Here, we identify a therapeutic window for EP2 antagonism to reduce delayed mortality and functional morbidity after status epilepticus (SE) in mice. Importantly, treatment must be delayed relative to SE onset to be effective, a finding that could be explained by the time-course of COX-2 induction after SE and compound pharmacokinetics. A large number of inflammatory mediators were upregulated in hippocampus after SE with COX-2 and IL-1ß temporally leading many others. Thus, EP2 antagonism represents a novel anti-inflammatory strategy to treat SE with a tightly-regulated therapeutic window.

Small molecule antagonist reveals seizure-induced mediation of neuronal injury by prostaglandin E2 receptor subtype EP2.

With interest waning in the use of cyclooxygenase-2 (COX-2) inhibitors for inflammatory disease, prostaglandin receptors provide alternative targets for the treatment of COX-2-mediated pathological conditions in both the periphery and the central nervous system. Activation of prostaglandin E2 receptor (PGE(2)) subtype EP2 promotes inflammation and is just beginning to be explored as a therapeutic target. To better understand physiological and pathological functions of the prostaglandin EP2 receptor, we developed a suite of small molecules with a 3-aryl-acrylamide scaffold as selective EP2 antagonists. The 12 most potent compounds displayed competitive antagonism of the human EP2 receptor with K(B) 2-20 nM in Schild regression analysis and 268- to 4,730-fold selectivity over the prostaglandin EP4 receptor. A brain-permeant compound completely suppressed the up-regulation of COX-2 mRNA in rat cultured microglia by EP2 activation and significantly reduced neuronal injury in hippocampus when administered in mice beginning 1 h after termination of pilocarpine-induced status epilepticus. The salutary actions of this novel group of antagonists raise the possibility that selective block of EP2 signaling via small molecules can be an innovative therapeutic strategy for inflammation-related brain injury.

The prostaglandin EP1 receptor potentiates kainate receptor activation via a protein kinase C pathway and exacerbates status epilepticus.

Prostaglandin E2 (PGE2) regulates membrane excitability, synaptic transmission, plasticity, and neuronal survival. The consequences of PGE2 release following seizures has been the subject of much study. Here we demonstrate that the prostaglandin E2 receptor 1 (EP1, or Ptger1) modulates native kainate receptors, a family of ionotropic glutamate receptors widely expressed throughout the central nervous system. Global ablation of the EP1 gene in mice (EP1-KO) had no effect on seizure threshold after kainate injection but reduced the likelihood to enter status epilepticus. EP1-KO mice that did experience typical status epilepticus had reduced hippocampal neurodegeneration and a blunted inflammatory response. Further studies with native prostanoid and kainate receptors in cultured cortical neurons, as well as with recombinant prostanoid and kainate receptors expressed in Xenopus oocytes, demonstrated that EP1 receptor activation potentiates heteromeric but not homomeric kainate receptors via a second messenger cascade involving phospholipase C, calcium and protein kinase C. Three critical GluK5 C-terminal serines underlie the potentiation of the GluK2/GluK5 receptor by EP1 activation. Taken together, these results indicate that EP1 receptor activation during seizures, through a protein kinase C pathway, increases the probability of kainic acid induced status epilepticus, and independently promotes hippocampal neurodegeneration and a broad inflammatory response.

Cyclooxygenase-2 in epilepsy.

Epilepsy is one of the more prevalent neurologic disorders in the world, affecting approximately 50 million people of different ages and backgrounds. Epileptic seizures propagating through both lobes of the forebrain can have permanent debilitating effects on a patient's cognitive and somatosensory brain functions. Epilepsy, defined by the sporadic occurrence of spontaneous recurrent seizures (SRS), is often accompanied by inflammation of the brain. Pronounced increases in the expression of key inflammatory mediators (e.g., interleukin -1ß [IL-1ß], tumor necrosis factor alpha [TNFα], cyclooxygenase-2 [COX-2], and C-X-C motif chemokine 10 [CXCL10]) after seizures may cause secondary damage in the brain and increase the likelihood of repetitive seizures. The COX-2 enzyme is induced rapidly during seizures. The increased level of COX-2 in specific areas of the epileptic brain can help to identify regions of seizure-induced brain inflammation. A good deal of effort has been expended to determine whether COX-2 inhibition might be neuroprotective and represent an adjunct therapeutic strategy along with antiepileptic drugs used to treat epilepsy. However, the effectiveness of COX-2 inhibitors on epilepsy animal models appears to depend on the timing of administration. With all of the effort placed on making use of COX-2 inhibitors as therapeutic agents for the treatment of epilepsy, inflammation, and neurodegenerative diseases there has yet to be a selective and potent COX-2 inhibitor that has shown a clear therapeutic outcome with acceptable side effects.