Prostaglandin D2 DP1 receptor is beneficial in ischemic stroke and in acute exicitotoxicity in young and old mice

Analysis of the brain transcriptome, microbiome and metabolome in ketogenic diet and experimental stroke

The ketogenic diet (KD) has been shown to be effective in treating various brain pathologies. In this study, we conducted detailed transcriptomic and metabolomic profiling of rat brains after KD and ischemic stroke in order to investigate the effects of KD and its underlying mechanisms. We evaluated the effect of a two-month KD on gene expression in intact brain tissue and after middle cerebral artery occlusion (MCAO). We analyzed the effects of KD on gut microbiome composition and blood metabolic profile as well as investigated the correlation between severity of neurological deficits and KD-induced changes. We found transcriptional reprogramming in the brain after stroke and KD treatment. The KD altered the expression of genes involved in the regulation of glucose and fatty acid metabolism, mitochondrial function, the immune response, Wnt-associated signaling, stem cell development, and neurotransmission, both in intact rats and after MCAO. The KD led to a significant change in the composition of gut microbiome and the levels of amino acids, acylcarnitines, polyunsaturated fatty acids, and oxylipins in the blood. However, the KD slightly worsened the neurological functions after MCAO, so that the therapeutic effect of the diet remained unproven.

The vasoconstrictor activities of prostaglandin D2 via the thromboxane prostanoid receptor and E prostanoid receptor-3 outweigh its concurrent vasodepressor effect mainly through D prostanoid receptor-1 ex vivo and in vivo

Prostaglandin (PG) D2, a commonly considered vasodilator through D prostanoid receptor-1 (DP1), might also evoke vasoconstriction via acting on the thromboxane (Tx)-prostanoid receptor (the original receptor of TxA2; TP) and/or E prostanoid receptor-3 (one of the vasoconstrictor receptors of PGE2; EP3). This study aimed to test the above hypothesis in the mouse renal vascular bed (main renal arteries and perfused kidneys) and/or mesenteric resistance arteries and determine how the vasoconstrictor mechanism influences the overall PGD2 effect on systemic blood pressure under in vivo conditions. Experiments were performed on control wild-type (WT) mice and mice with deficiencies in TP (TP-/-) and/or EP3 (EP3-/-). Here we show that PGD2 indeed evoked vasoconstrictor responses in the above-mentioned tissues of WT mice, which were however not only reduced by TP-/- or EP3-/-, but also reversed by TP-/-/EP3-/- in some of the above tissues (mesenteric resistance arteries or perfused kidneys) to dilator reactions that were reduced by non-selective DP antagonism. A slight or mild pressor response was also observed with PGD2 under in vivo conditions, and this was again reversed to a depressor response in TP-/- or TP-/-/EP3-/- mice. Non-selective DP antagonism reduced the PGD2-evoked depressor response in TP-/-/EP3-/- mice as well. These results thus demonstrate that like other PGs, PGD2 activates TP and/or EP3 to evoke vasoconstrictor activities, which can outweigh its concurrent vasodepressor activity mediated mainly through DP1, and hence result in a pressor response, although the response might only be of a slight or mild extent.

Identification and Imaging of Prostaglandin Isomers Utilizing MS3 Product Ions and Silver Cationization

Prostaglandins (PGs) are important lipid mediators involved in physiological processes, such as inflammation and pregnancy. The pleiotropic effects of the PG isomers and their differential expression from cell types impose the necessity for studying individual isomers locally in tissue to understand the molecular mechanisms. Currently, mass spectrometry (MS)-based analytical workflows for determining the PG isomers typically require homogenization of the sample and a separation method, which results in a loss of spatial information. Here, we describe a method exploiting the cationization of PGs with silver ions for enhanced sensitivity and tandem MS to distinguish the biologically relevant PG isomers PGE2, PGD2, and Δ12-PGD2. The developed method utilizes characteristic product ions in MS3 for training prediction models and is compatible with direct infusion approaches. We discuss insights into the fragmentation pathways of Ag+ cationized PGs during collision-induced dissociation and demonstrate the high accuracy and robustness of the model to predict isomeric compositions of PGs. The developed method is applied to mass spectrometry imaging (MSI) of mouse uterus implantation sites using silver-doped pneumatically assisted nanospray desorption electrospray ionization and indicates localization to the antimesometrial pole and the luminal epithelium of all isomers with different abundances. Overall, we demonstrate, for the first time, isomeric imaging of major PG isomers with a simple method that is compatible with liquid-based extraction MSI methods.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Astrocytes as a Therapeutic Target in Alzheimer's Disease-Comprehensive Review and Recent Developments

Alzheimer's disease (AD) is a frequent and disabling neurodegenerative disorder, in which astrocytes participate in several pathophysiological processes including neuroinflammation, excitotoxicity, oxidative stress and lipid metabolism (along with a critical role in apolipoprotein E function). Current evidence shows that astrocytes have both neuroprotective and neurotoxic effects depending on the disease stage and microenvironmental factors. Furthermore, astrocytes appear to be affected by the presence of amyloid-beta (Aβ), with alterations in calcium levels, gliotransmission and proinflammatory activity via RAGE-NF-κB pathway. In addition, astrocytes play an important role in the metabolism of tau and clearance of Aβ through the glymphatic system. In this review, we will discuss novel pharmacological and non-pharmacological treatments focused on astrocytes as therapeutic targets for AD. These interventions include effects on anti-inflammatory/antioxidant systems, glutamate activity, lipid metabolism, neurovascular coupling and glymphatic system, calcium dysregulation, and in the release of peptides which affects glial and neuronal function. According to the AD stage, these therapies may be of benefit in either preventing or delaying the progression of the disease.

Timapiprant, a prostaglandin D2 receptor antagonist, ameliorates pathology in a rat Alzheimer's model

We investigated the relevance of the prostaglandin D2 pathway in Alzheimer's disease, because prostaglandin D2 is a major prostaglandin in the brain. Thus, its contribution to Alzheimer's disease merits attention, given the known impact of the prostaglandin E2 pathway in Alzheimer's disease. We used the TgF344-AD transgenic rat model because it exhibits age-dependent and progressive Alzheimer's disease pathology. Prostaglandin D2 levels in hippocampi of TgF344-AD and wild-type littermates were significantly higher than prostaglandin E2. Prostaglandin D2 signals through DP1 and DP2 receptors. Microglial DP1 receptors were more abundant and neuronal DP2 receptors were fewer in TgF344-AD than in wild-type rats. Expression of the major brain prostaglandin D2 synthase (lipocalin-type PGDS) was the highest among 33 genes involved in the prostaglandin D2 and prostaglandin E2 pathways. We treated a subset of rats (wild-type and TgF344-AD males) with timapiprant, a potent highly selective DP2 antagonist in development for allergic inflammation treatment. Timapiprant significantly mitigated Alzheimer's disease pathology and cognitive deficits in TgF344-AD males. Thus, selective DP2 antagonists have potential as therapeutics to treat Alzheimer's disease.

Maternal Prenatal Inflammation Increases Brain Damage Susceptibility of Lipopolysaccharide in Adult Rat Offspring via COX-2/PGD-2/DPs Pathway Activation

A growing body of research suggests that inflammatory insult contributes to the etiology of central nervous system diseases, such as depression, Alzheimer’s disease, and so forth. However, the effect of prenatal systemic inflammation exposure on offspring brain development and cerebral susceptibility to inflammatory insult remains unknown. In this study, we utilized the prenatal inflammatory insult model in vivo and the neuronal damage model in vitro. The results obtained show that prenatal maternal inflammation exacerbates LPS-induced memory impairment, neuronal necrosis, brain inflammatory response, and significantly increases protein expressions of COX-2, DP2, APP, and Aβ, while obviously decreasing that of DP1 and the exploratory behaviors of offspring rats. Meloxicam significantly inhibited memory impairment, neuronal necrosis, oxidative stress, and inflammatory response, and down-regulated the expressions of APP, Aβ, COX-2, and DP2, whereas significantly increased exploring behaviors and the expression of DP1 in vivo. Collectively, these findings suggested that maternal inflammation could cause offspring suffering from inflammatory and behavioral disorders and increase the susceptibility of offspring to cerebral pathological factors, accompanied by COX-2/PGD-2/DPs pathway activation, which could be ameliorated significantly by COX-2 inhibitor meloxicam treatment.

G-Protein-Coupled Receptors and Ischemic Stroke: a Focus on Molecular Function and Therapeutic Potential

In ischemic stroke, there is only one approved drug, tissue plasminogen activator, to be used in clinical conditions for thrombolysis. New neuroprotective therapies for ischemic stroke are desperately needed. Several targets and pathways have been shown to confer neuroprotective effects in ischemic stroke. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system disorders. GPCRs are a large family of cell surface receptors that response to a wide variety of extracellular stimuli. GPCRs are involved in a wide range of physiological and pathological processes. More than 90% of the identified non-sensory GPCRs are expressed in the brain, where they play important roles in regulating mood, pain, vision, immune responses, cognition, and synaptic transmission. There is also good evidence that GPCRs are implicated in the pathogenesis of stroke. This review narrates the pathophysiological role and possible targeted therapy of GPCRs in ischemic stroke.

Blocking pro-inflammatory platelet-activating factor receptors and activating cell survival pathways: A novel therapeutic strategy in experimental ischemic stroke

OBJECTIVE

Acute ischemic stroke triggers complex neurovascular, neuroinflammatory, and synaptic alterations. This study explores whether blocking pro-inflammatory platelet-activating factor receptor (PAF-R) plus selected docosanoids after middle cerebral artery occlusion (MCAo) would lead to neurological recovery. The following small molecules were investigated: (a) LAU-0901, a PAF-R antagonist that blocks pro-inflammatory signaling; and (b) derivatives of docosahexaenoic acid (DHA), neuroprotectin D1 (NPD1), and aspirin-triggered NPD1 (AT-NPD1), which activates cell survival pathways and are exert potent anti-inflammatory activity in the brain.

MATERIALS AND METHODS

Sprague-Dawley rats received 2 h MCAo and LAU-0901 (30 or 60 mg/kg, 2 h after stroke), NPD1, and AT-NPD1 (333 μg/kg), DHA (5 mg/kg), and their combination were administered intravenous at 3 h after stroke. Behavior testing and ex vivo magnetic resonance imaging were conducted on day 3 or 14 to assess lesion characteristics and lipidomic analysis on day 1. Series 1 (LAU-0901 + NPD1, 14d), Series 2 (LAU-0901 + AT-NPD1, 3d), and Series 3 (LAU-0901 + DHA, 1d).

RESULTS

All combinatory groups improved behavior compared to NPD1, AT-NPD1, or DHA treatments alone. Total lesion volumes were reduced with LAU-0901 + NPD1 by 62% and LAU-0901 + AT-NPD1 by 90% treatments versus vehicle groups. LAU-0901 and LAU-0901 + DHA increased the production of vasoactive lipid mediators (prostaglandins: PGE₂, PGF_{2- α}, 6-keto-PGF_{1- α}, and PGD₂) as well an inflammatory regulating mediator hydroxyoctadecadienoic acid. In contrast, LAU-0901 and LAU-0901 + DHA decreased the production of 12-hydroxyeicosatetraenoic acid, a pro-inflammatory mediator.

CONCLUSION

Combination therapy with LAU-0901 and selected docosanoids is more effective than the single therapy, affording synergistic neuroprotection, with restored pro-homeostatic lipid mediators and improved neurological recovery. Altogether, our findings support the combinatory therapy as the basis for future therapeutics for ischemic stroke.

Why PGD2 has different functions from PGE2

Prostaglandin (PG) D₂ and PGE₂ are positional isomers; however, they sometimes exhibit opposite physiological functions, such as in cancer development. Because DP receptors are considered to be a duplicated copy of EP2 receptors, PGD₂ and PGE₂ cross-react with both receptors. These prostanoids may act as biased agonists for each receptor. In reviewing this field, a hypothesis was proposed to explain the opposed effects of these prostanoids from the viewpoints of the evolution of, mutations in, and biased activities of their receptors. Previous findings showing more mutations/variations in DP receptors than EP2 receptors among individuals worldwide indicate that DP receptors are still in a rapid evolutionary stage. The opposing effects of these prostanoids on cancer development may be attributed to the biased activity of PGE₂ for DP receptors, which may incidentally develop during the process of the old ligand, PGE₂ gaining selectivity to newly diverged DP receptors.

Prostaglandin D2 signaling in dendritic cells is critical for the development of EAE

Priming of autoreactive T cells in lymph nodes by dendritic cells (DCs) is critical for the pathogenesis of experimental autoimmune encephalitis (EAE). DC activation reflects a balance of pro- and anti-inflammatory signals. One anti-inflammatory factor is prostaglandin D2 signaling through its cognate receptor, D-prostanoid receptor 1 (PTGDR), on myeloid cells. Loss of PTGDR signaling might be expected to enhance DC activation and EAE but here we show that PTGDR^−/− mice developed only mild signs of MOG_35-55 peptide immunization-induced EAE. Compared to wild type mice, PTGDR^−/− mice exhibited less demyelination, decreased leukocyte infiltration and diminished microglia activation. These effects resulted from increased pro-inflammatory responses in the lymph nodes, most notably in IL-1β production, with the unexpected consequence of increased activation-induced apoptosis of MOG_35-55 peptide-specific T cells. Conditional deletion of PTGDR on DCs, and not other myeloid cells ameliorated EAE. Together, these results demonstrate the indispensable role that PGD₂/PTGDR signaling on DCs has in development of pathogenic T cells in autoimmune demyelination.

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Increased T cell activation occurred in PTGDR^−/- mice resulting in T cell apoptosis.

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AICD decreased T cell infiltration into, and demyelination in CNS during EAE.

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Decreased PGD₂/PTGDR signaling in DCs resulted in increased IL-1β expression.

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Anakinra treatment in PTGDR^−/- mice increased EAE severity.

DP1 Activation Reverses Age-Related Hypertension Via NEDD4L-Mediated T-Bet Degradation in T Cells

BACKGROUND

Blood pressure often rises with aging, but exact mechanisms are still not completely understood. With aging, the level of proinflammatory cytokines increases in T lymphocytes. Prostaglandin D₂, a proresolution mediator, suppresses Type 1 T helper (Th1) cytokines through D-prostanoid receptor 1 (DP1). In this study, we aimed to investigate the role of the prostaglandin D₂/DP1 axis in T cells on age-related hypertension.

METHODS

To clarify the physiological and pathophysiological roles of DP1 in T cells with aging, peripheral blood samples were collected from young and older male participants, and CD4⁺ T cells were sorted for gene expression, prostaglandin production, and Western blot assays. Mice blood pressure was quantified by invasive telemetric monitor.

RESULTS

The prostaglandin D₂/DP1 axis was downregulated in CD4⁺ T cells from older humans and aged mice. DP1 deletion in CD4⁺ T cells augmented age-related hypertension in aged male mice by enhancing Th1 cytokine secretion, vascular remodeling, CD4⁺ T cells infiltration, and superoxide production in vasculature and kidneys. Conversely, forced expression of exogenous DP1 in T cells retarded age-associated hypertension in mice by reducing Th1 cytokine secretion. Tumor necrosis factor α neutralization or interferon γ deletion ameliorated the age-related hypertension in DP1 deletion in CD4⁺ T cells mice. Mechanistically, DP1 inhibited Th1 activity via the PKA (protein kinase A)/p-Sp1 (phosphorylated specificity protein 1)/neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) pathway-mediated T-box-expressed-in-T-cells (T-bet) ubiquitination. T-bet deletion or forced NEDD4L expression in CD4⁺ T cells attenuated age-related hypertension in CD4⁺ T cell-specific DP1-deficient mice. DP1 receptor activation by BW245C prevented age-associated blood pressure elevation and reduced vascular/renal superoxide production in male mice.

CONCLUSIONS

The prostaglandin D₂/DP1 axis suppresses age-related Th1 activation and subsequent hypertensive response in male mice through increase of NEDD4L-mediated T-bet degradation by ubiquitination. Therefore, the T cell DP1 receptor may be an attractive therapeutic target for age-related hypertension.

Role of the L-PGDS-PGD2-DP1 receptor axis in sleep regulation and neurologic outcomes

To meet the new challenges of modern lifestyles, we often compromise a good night's sleep. In preclinical models as well as in humans, a chronic lack of sleep is reported to be among the leading causes of various physiologic, psychologic, and neurocognitive deficits. Thus far, various endogenous mediators have been implicated in inter-regulatory networks that collectively influence the sleep-wake cycle. One such mediator is the lipocalin-type prostaglandin D2 synthase (L-PGDS)-Prostaglandin D2 (PGD2)-DP1 receptor (L-PGDS-PGD2-DP1R) axis. Findings in preclinical models confirm that DP1R are predominantly expressed in the sleep-regulating centers. This finding led to the discovery that the L-PGDS-PGD2-DP1R axis is involved in sleep regulation. Furthermore, we showed that the L-PGDS-PGD2-DP1R axis is beneficial in protecting the brain from ischemic stroke. Protein sequence homology was also performed, and it was found that L-PGDS and DP1R share a high degree of homology between humans and rodents. Based on the preclinical and clinical data thus far pertaining to the role of the L-PGDS-PGD2-DP1R axis in sleep regulation and neurologic conditions, there is optimism that this axis may have a high translational potential in human therapeutics. Therefore, here the focus is to review the regulation of the homeostatic component of the sleep process with a special focus on the L-PGDS-PGD2-DP1R axis and the consequences of sleep deprivation on health outcomes. Furthermore, we discuss whether the pharmacological regulation of this axis could represent a tool to prevent sleep disturbances and potentially improve outcomes, especially in patients with acute brain injuries.

Bioactive Lipids in Inflammation After Central Nervous System Injury

Despite the progress made over the last decades to understand the mechanisms underlying tissue damage and neurological deficits after neurotrauma, there are currently no effective treatments in the clinic. It is well accepted that the inflammatory response in the CNS after injury exacerbates tissue loss and functional impairments. Unfortunately, the use of potent anti-inflammatory drugs, such as methylprednisolone, fails to promote therapeutic recovery and also gives rise to several undesirable side effects related to immunosuppression. The injury-induced inflammatory response is complex, and understanding the mechanisms that regulate this inflammation is therefore crucial in the quest to develop effective treatments. Bioactive lipids have emerged as potent molecules in controlling the initiation, coordination, and resolution of inflammation and in promoting tissue repair and recovery of homeostasis. These bioactive lipids are produced by cells involved in the inflammatory response, and their defective synthesis leads to persistent chronic inflammation, tissue damage, and fibrosis. The present chapter discusses recent evidence for the role of some of these bioactive lipids, in particular, eicosanoid and pro-resolving lipid mediators, in the regulation of inflammation after neurotrauma and highlights the therapeutic potential of some of these lipids in enhancing neurological outcomes after CNS injuries.

Efficacy of Laropiprant in Minimizing Brain Injury Following Experimental Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is one of the most devastating and disabling forms of stroke, yet effective treatments are still lacking. Prostaglandins and their receptors have been implicated in playing vital roles in ICH outcomes. Recently, laropiprant, a DP1 receptor antagonist, has been used in combination with niacin to abolish the prostaglandin D2-(PGD2)-induced flushing. Here, we test the hypothesis that laropiprant limits bleeding and rescues the brain from ICH. Wildtype (WT) and DP1-/- mice were subjected ICH and neurologic deficits and hemorrhagic lesion outcomes were evaluated at 72 hours after the ICH. To test the therapeutic potential of laropiprant, WT mice subjected to ICH were treated with laropiprant at 1 hour after the ICH. The putative effect of laropiprant on limiting hematoma expansion was tested by an in vivo tail bleeding cessation method and an ex vivo coagulation method. Finally, the roles of laropiprant on gliosis and iron accumulation were also investigated. A significant decrease in the injury volume was observed in DP1-/- as well as laropiprant-treated WT mice. The tail bleeding time was significantly lower in laropiprant group as compared with the vehicle group. Significantly lower Iba-1 and Perls' iron staining in DP1-/- and laropiprant-treated WT groups were observed. Altogether, the data suggest that laropiprant treatment post-ICH attenuates brain damage by targeting primary as well as secondary injuries.

Virus-induced inflammasome activation is suppressed by prostaglandin D2/DP1 signaling

Prostaglandin D2 (PGD₂), an eicosanoid with both pro- and anti-inflammatory properties, is the most abundantly expressed prostaglandin in the brain. Here we show that PGD₂ signaling through the D-prostanoid receptor 1 (DP1) receptor is necessary for optimal microglia/macrophage activation and IFN expression after infection with a neurotropic coronavirus. Genome-wide expression analyses indicated that PGD₂/DP1 signaling is required for up-regulation of a putative inflammasome inhibitor, PYDC3, in CD11b⁺ cells in the CNS of infected mice. Our results also demonstrated that, in addition to PGD₂/DP1 signaling, type 1 IFN (IFN-I) signaling is required for PYDC3 expression. In the absence of Pydc3 up-regulation, IL-1β expression and, subsequently, mortality were increased in infected DP1^-/- mice. Notably, survival was enhanced by IL1 receptor blockade, indicating that the effects of the absence of DP1 signaling on clinical outcomes were mediated, at least in part, by inflammasomes. Using bone marrow-derived macrophages in vitro, we confirmed that PYDC3 expression is dependent upon DP1 signaling and that IFN priming is critical for PYDC3 up-regulation. In addition, Pydc3 silencing or overexpression augmented or diminished IL-1β secretion, respectively. Furthermore, DP1 signaling in human macrophages also resulted in the up-regulation of a putative functional analog, POP3, suggesting that PGD₂ similarly modulates inflammasomes in human cells. These findings demonstrate a previously undescribed role for prostaglandin signaling in preventing excessive inflammasome activation and, together with previously published results, suggest that eicosanoids and inflammasomes are reciprocally regulated.

Excitotoxicity-induced prostaglandin D2 production induces sustained microglial activation and delayed neuronal death

Excitotoxicity is the pivotal mechanism of neuronal death. Prostaglandins (PGs) produced during excitotoxicity play important roles in neurodegenerative conditions. Previously, we demonstrated that initial burst productions of PGD2, PGE2, and PGF2α are produced by cyclooxygenase-2 (COX-2) in the hippocampus following a single systemic kainic acid (KA) administration. In addition, we showed that blocking of all PG productions ameliorated hippocampal delayed neuronal death at 30 days after KA administration. To investigate the role of individual PGs in the delayed neuronal death, we performed intracerebroventricular injection of PGD2, PGE2, or PGF2α in rats whose hippocampal PG productions were entirely blocked by pretreatment of NS398, a COX-2 selective inhibitor. Administration of PGD2 and PGF2α had a latent contribution to the delayed neuronal death, sustained over 30 days after a single KA treatment. Furthermore, PGD2 enhanced microglial activation, which may be involved in the delayed neuronal death in the hippocampus. These findings suggest that excitotoxic delayed neuronal death is mediated through microglia activated by PGD2.

Amyloid proteotoxicity initiates an inflammatory response blocked by cannabinoids

The beta amyloid (Aβ) and other aggregating proteins in the brain increase with age and are frequently found within neurons. The mechanistic relationship between intracellular amyloid, aging and neurodegeneration is not, however, well understood. We use a proteotoxicity model based upon the inducible expression of Aβ in a human central nervous system nerve cell line to characterize a distinct form of nerve cell death caused by intracellular Aβ. It is shown that intracellular Aβ initiates a toxic inflammatory response leading to the cell's demise. Aβ induces the expression of multiple proinflammatory genes and an increase in both arachidonic acid and eicosanoids, including prostaglandins that are neuroprotective and leukotrienes that potentiate death. Cannabinoids such as tetrahydrocannabinol stimulate the removal of intraneuronal Aβ, block the inflammatory response, and are protective. Altogether these data show that there is a complex and likely autocatalytic inflammatory response within nerve cells caused by the accumulation of intracellular Aβ, and that this early form of proteotoxicity can be blocked by the activation of cannabinoid receptors.

Effect of the PGD2-DP signaling pathway on primary cultured rat hippocampal neuron injury caused by aluminum overload

In the present study, the agonists and antagonists of DP receptor were used to examine whether the PGD₂-DP signaling pathway affects neuronal function. Primary cultured hippocampal neuron was prepared and treated with aluminum maltolate (100 μM) to establish the neuronal damage model. PGD₂ and cAMP content was detected by ELISA. L-PGDS and DPs mRNA and protein expression were measured by RT-PCR and Western blotting, respectively. The aluminium-load neuron was treated with the DP₁ agonist BW245C, the DP₁ antagonist BWA868C, the DP₂ agonist DK-PGD_2, and the DP₂ antagonist CAY10471, respectively. Neuronal pathomorphology was observed using H-E staining. The cell viability and the lactate dehydrogenase leakage rates of neurons were measured with MTT and LDH kit, respectively. Ca²⁺ level was detected by Fluo-3/AM. In the model group, the MTT values obviously decreased; LDH leakage rates and PGD₂ content increased significantly; L-PGDS, DP₁ mRNA and protein expressions increased, and DP₂ level decreased. BW245C reduced the Ca²⁺ fluorescence intensity and protected the neurons. DK-PGD₂ increased the intensity of Ca²⁺ fluorescence, while CAY10471 had the opposite effect. In conclusion, contrary to the effect of DP₂, the PGD₂-DP₁ signaling pathway protects against the primary cultured rat hippocampal neuronal injury caused by aluminum overload.

Method parameters' impact on mortality and variability in mouse stroke experiments: a meta-analysis

Although hundreds of promising substances have been tested in clinical trials, thrombolysis currently remains the only specific pharmacological treatment for ischemic stroke. Poor quality, e.g. low statistical power, in the preclinical studies has been suggested to play an important role in these failures. Therefore, it would be attractive to use animal models optimized to minimize unnecessary mortality and outcome variability, or at least to be able to power studies more exactly by predicting variability and mortality given a certain experimental setup. The possible combinations of methodological parameters are innumerous, and an experimental comparison of them all is therefore not feasible. As an alternative approach, we extracted data from 334 experimental mouse stroke articles and, using a hypothesis-driven meta-analysis, investigated the method parameters’ impact on infarct size variability and mortality. The use of Swiss and C57BL6 mice as well as permanent occlusion of the middle cerebral artery rendered the lowest variability of the infarct size while the emboli methods increased variability. The use of Swiss mice increased mortality. Our study offers guidance for researchers striving to optimize mouse stroke models.

Hippocampal neuronal cyclooxygenase-2 downstream signaling imbalance in a rat model of chronic aluminium gluconate administration

BACKGROUND

Acute and chronic brain damages including neurodegenerative diseases are a group of neuroinflammation-associated diseases characterized by cognitive function defect and progressive neuron loss. The pathophysiological procession of brain damages involves the overexpression of cyclooxygenase (COX)-2. Owing to the limited benefit to chronic brain damage and the late adverse effect of COX-2 inhibitors, the COX downstream signaling pathway has become a focus in neurological research. In order to explore the mechanism of aluminum neurotoxicity and the importance of COX2 downstream signaling pathways to chronic brain damage, the present study was designed to simultaneously observe the prostaglandin (PG) contents, and the expressions of PG synthases and PG receptors of hippocampus in a rat model induced by chronic administration of aluminium gluconate.

METHODS

A rat model of chronic brain damage was established by chronic intragastric administration of aluminium gluconate (Al3+ 200 mg/kg per day, 5d a week for 20 weeks). PG contents, the expressions of PG synthases, and the expressions of PG receptors in rats were measured by ELISA, RT-PCR and Western blotting, respectively.

RESULTS

Chronic aluminium gluconate administration resulted in hippocampal neuron injury and learning and memory disorders in rats. Aluminium gluconate administration also resulted in increased levels of PGE2, PGD2, TXA2, PGI2, and PGF2α in rat hippocampus. The DP1, EP2, IP, mPGES-1, EP4, PGIS and TXAS mRNA expressions, and the DP1, EP2 and IP protein expressions significantly increased in the Al-treated hippocampus, while the EP3 and FP mRNA and protein expressions and the TP mRNA expression decreased.

CONCLUSIONS

The PGS/PGs/PG receptors signaling pathway in chronic aluminium gluconate-overloaded rat hippocampus is disturbed, which may be involved in the mechanism of aluminium neurotoxicity.

Neuroinflammation and J2 prostaglandins: linking impairment of the ubiquitin-proteasome pathway and mitochondria to neurodegeneration

The immune response of the CNS is a defense mechanism activated upon injury to initiate repair mechanisms while chronic over-activation of the CNS immune system (termed neuroinflammation) may exacerbate injury. The latter is implicated in a variety of neurological and neurodegenerative disorders such as Alzheimer and Parkinson diseases, amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain injury, HIV dementia, and prion diseases. Cyclooxygenases (COX-1 and COX-2), which are key enzymes in the conversion of arachidonic acid into bioactive prostanoids, play a central role in the inflammatory cascade. J2 prostaglandins are endogenous toxic products of cyclooxygenases, and because their levels are significantly increased upon brain injury, they are actively involved in neuronal dysfunction induced by pro-inflammatory stimuli. In this review, we highlight the mechanisms by which J2 prostaglandins (1) exert their actions, (2) potentially contribute to the transition from acute to chronic inflammation and to the spreading of neuropathology, (3) disturb the ubiquitin-proteasome pathway and mitochondrial function, and (4) contribute to neurodegenerative disorders such as Alzheimer and Parkinson diseases, and amyotrophic lateral sclerosis, as well as stroke, traumatic brain injury (TBI), and demyelination in Krabbe disease. We conclude by discussing the therapeutic potential of targeting the J2 prostaglandin pathway to prevent/delay neurodegeneration associated with neuroinflammation. In this context, we suggest a shift from the traditional view that cyclooxygenases are the most appropriate targets to treat neuroinflammation, to the notion that J2 prostaglandin pathways and other neurotoxic prostaglandins downstream from cyclooxygenases, would offer significant benefits as more effective therapeutic targets to treat chronic neurodegenerative diseases, while minimizing adverse side effects.

Inflammation after stroke: mechanisms and therapeutic approaches

Reperfusion of ischemic brain can reduce injury and improve outcome, but secondary injury due to inflammatory mechanisms limits the efficacy and time window of such treatments for stroke. This review summarizes the cellular and molecular basis of inflammation in ischemic injury as well as possible therapeutic strategies.

Sustained neuroprotection from a single intravitreal injection of PGJ2 in a rodent model of anterior ischemic optic neuropathy

PURPOSE

Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common cause of sudden optic nerve-related vision loss in persons older than 50 in the United States. There currently is no treatment for this disorder. We previously showed that systemic administration of 15-deoxy, delta (12, 14) prostaglandin J2 (PGJ2) is neuroprotective in our rodent model of AION (rAION). In this study, we determined if a single intravitreal (IVT) injection of PGJ2 is neuroprotective after rAION, and if this method of administration is toxic to the retina, optic nerve, or both.

METHODS

TOXICITY was assessed after a single IVT injection of PGJ2 in one eye and PBS in the contralateral eye of normal, adult Long-Evans rats. EFFICACY was assessed by inducing rAION in one eye and injecting either PGJ2 or vehicle immediately following induction, with the fellow eye serving as naïve control. Visual evoked potentials (VEPs) and ERGs were performed before induction and at specific intervals thereafter. Animals were euthanized 30 days after induction, after which immunohistochemistry, transmission electron microscopy, and quantitative stereology of retinal ganglion cell (RGC) numbers were performed.

RESULTS

TOXICITY

IVT PGJ2 did not alter the VEP or ERG compared with PBS-injected control eyes, and neither IVT PGJ2 nor PBS reduced overall RGC numbers.

EFFICACY

IVT PGJ2 preserved VEP amplitude, reduced optic nerve edema, and resulted in significant preservation of RGCs and axons in eyes with rAION.

CONCLUSIONS

A single IVT injection of PGJ2 is nontoxic to the retina and optic nerve and neuroprotective when given immediately after rAION induction.

Lipoxygenase: an emerging target for stroke therapy

Neuroprotection as approach to stroke therapy has recently seen a revival of sorts, fueled in part by the continuing necessity to improve acute stroke care, and in part by the identification of novel drug targets. 12/15- Lipoxygenase (12/15-LOX), one of the key enzymes of the arachidonic acid cascade, contributes to both neuronal cell death and vascular injury. Inhibition of 12/15-LOX may thus provide multifactorial protection against ischemic injury. Targeting 12/15-LOX and related eicosanoid pathways is the subject of this brief review.

Prostaglandin D2 toxicity in primary neurons is mediated through its bioactive cyclopentenone metabolites

Prostaglandin D2 (PGD2) is the most abundant prostaglandin in brain but its effect on neuronal cell death is complex and not completely understood. PGD2 may modulate neuronal cell death via activation of DP receptors or its metabolism to the cyclopentenone prostaglandins (CyPGs) PGJ2, Δ(12)-PGJ2 and 15-deoxy-Δ(12,14)-PGJ2, inducing cell death independently of prostaglandin receptors. This study aims to elucidate the effect of PGD2 on neuronal cell death and its underlying mechanisms. PGD2 dose-dependently induced cell death in rat primary neuron-enriched cultures in concentrations of ≥10μM, and this effect was not reversed by treatment with either DP1 or DP2 receptor antagonists. Antioxidants N-acetylcysteine (NAC) and glutathione which contain sulfhydryl groups that can bind to CyPGs, but not ascorbate or tocopherol, attenuated PGD2-induced cell death. Conversion of PGD2 to CyPGs was detected in neuronal culture medium; treatment with these CyPG metabolites alone exhibited effects similar to those of PGD2, including apoptotic neuronal cell death and accumulation of ubiquitinated proteins. Disruption of lipocalin-type prostaglandin D synthase (L-PGDS) protected neurons against hypoxia. These results support the hypothesis that PGD2 elicits its cytotoxic effects through its bioactive CyPG metabolites rather than DP receptor activation in primary neuronal culture.

Putative role of prostaglandin receptor in intracerebral hemorrhage

Each year, approximately 795,000 people experience a new or recurrent stroke. Of all strokes, 84% are ischemic, 13% are intracerebral hemorrhage (ICH) strokes, and 3% are subarachnoid hemorrhage strokes. Despite the decreased incidence of ischemic stroke, there has been no change in the incidence of hemorrhagic stroke in the last decade. ICH is a devastating disease 37–38% of patients between the ages of 45 and 64 die within 30 days. In an effort to prevent ischemic and hemorrhagic strokes we and others have been studying the role of prostaglandins and their receptors. Prostaglandins are bioactive lipids derived from the metabolism of arachidonic acid. They sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. Most prostaglandins are produced from specific enzymes and act upon cells via distinct G-protein coupled receptors. The presence of multiple prostaglandin receptors cross-reactivity and coupling to different signal transduction pathways allow differentiated cells to respond to prostaglandins in a unique manner. Due to the number of prostaglandin receptors, prostaglandin-dependent signaling can function either to promote neuronal survival or injury following acute excitotoxicity, hypoxia, and stress induced by ICH. To better understand the mechanisms of neuronal survival and neurotoxicity mediated by prostaglandin receptors, it is essential to understand downstream signaling. Several groups including ours have discovered unique roles for prostaglandin receptors in rodent models of ischemic stroke, excitotoxicity, and Alzheimer disease, highlighting the emerging role of prostaglandin receptor signaling in hemorrhagic stroke with a focus on cyclic-adenosine monophosphate and calcium (Ca²⁺) signaling. We review current ICH data and discuss future directions notably on prostaglandin receptors, which may lead to the development of unique therapeutic targets against hemorrhagic stroke and brain injuries alike.

Therapeutic implications of disorders of cell death signalling: membranes, micro-environment, and eicosanoid and docosanoid metabolism

Disruptions of cell death signalling occur in pathological processes, such as cancer and degenerative disease. Increased knowledge of cell death signalling has opened new areas of therapeutic research, and identifying key mediators of cell death has become increasingly important. Early triggering events in cell death may provide potential therapeutic targets, whereas agents affecting later signals may be more palliative in nature. A group of primary mediators are derivatives of the highly unsaturated fatty acids (HUFAs), particularly oxygenated metabolites such as prostaglandins. HUFAs, esterified in cell membranes, act as critical signalling molecules in many pathological processes. Currently, agents affecting HUFA metabolism are widely prescribed in diseases involving disordered cell death signalling. However, partly due to rapid metabolism, their role in cell death signalling pathways is poorly characterized. Recently, HUFA-derived mediators, the resolvins/protectins and endocannabinoids, have added opportunities to target selective signals and pathways. This review will focus on the control of cell death by HUFA, eicosanoid (C20 fatty acid metabolites) and docosanoid (C22 metabolites), HUFA-derived lipid mediators, signalling elements in the micro-environment and their potential therapeutic applications. Further therapeutic approaches will involve cell and molecular biology, the multiple hit theory of disease progression and analysis of system plasticity. Advances in the cell biology of eicosanoid and docosanoid metabolism, together with structure/function analysis of HUFA-derived mediators, will be useful in developing therapeutic agents in pathologies characterized by alterations in cell death signalling.

The transcriptome of cerebral ischemia

The molecular causality and response to stroke is complex. Yet, much of the literature examining the molecular response to stroke has focused on targeted pathways that have been well-characterized. Consequently, our understanding of stroke pathophysiology has made little progress by way of clinical therapeutics since tissue plasminogen activator was approved for treatment nearly a decade ago. The lack of clinical translation is in part due to neuron-focused studies, preclinical models of cerebral ischemia and the paradoxical nature of neuro-inflammation. With the evolution of the Stroke Therapy Academic Industry Roundtable criteria streamlining research efforts and broad availability of genomic technologies, the ability to decipher the molecular fingerprint of ischemic stroke is on the horizon. This review highlights preclinical microarray findings of the ischemic brain, discusses the transcriptome of cerebral preconditioning and emphasizes the importance of further characterizing the role of the neurovascular unit and peripheral white blood cells in mediating stroke damage and repair within the penumbra.

Extended release niacin-laropiprant in patients with hypercholesterolemia or mixed dyslipidemias improves clinical parameters

The progression of atherosclerosis remains a major cause of morbidity and mortality. Plaque formation is an immunological response driven by a number of risk factors, and reduction of risk is the primary goal of treatment. The role of LDL-C is well established and statins have proved effective drugs, although the relative risk reduction is only around 30%. The importance of other factors-notably low HDL-C and high TGs-has become increasingly clear and the search for alternative strategies continues. Niacin is particularly effective in achieving normalization of HDL-C but is clinically underutilized due to the side effect of cutaneous flushing. The discovery that flushing is mediated by mechanisms distinct from the lipid-lowering effects has led to the development of combination drugs with reduced side effects. This review considers the evidence regarding the clinical efficacy of extended-release niacin and the DP1 antagonist laropiprant in the treatment of hypercholesterolemia and mixed dyslipidemias.