Upregulation of ceramide and its regulating mechanism in a rat model of chronic cerebral ischemia

Advances in Engineered Nanoparticles for the Treatment of Ischemic Stroke by Enhancing Angiogenesis

Angiogenesis, or the formation of new blood vessels, is a natural defensive mechanism that aids in the restoration of oxygen and nutrition delivery to injured brain tissue after an ischemic stroke. Angiogenesis, by increasing vessel development, may maintain brain perfusion, enabling neuronal survival, brain plasticity, and neurologic recovery. Induction of angiogenesis and the formation of new vessels aid in neurorepair processes such as neurogenesis and synaptogenesis. Advanced nano drug delivery systems hold promise for treatment stroke by facilitating efficient transportation across the the blood-brain barrier and maintaining optimal drug concentrations. Nanoparticle has recently been shown to greatly boost angiogenesis and decrease vascular permeability, as well as improve neuroplasticity and neurological recovery after ischemic stroke. We describe current breakthroughs in the development of nanoparticle-based treatments for better angiogenesis therapy for ischemic stroke employing polymeric nanoparticles, liposomes, inorganic nanoparticles, and biomimetic nanoparticles in this study. We outline new nanoparticles in detail, review the hurdles and strategies for conveying nanoparticle to lesions, and demonstrate the most recent advances in nanoparticle in angiogenesis for stroke treatment.

Sphingomyelinases in retinas and optic nerve heads: Effects of ocular hypertension and ischemia

Sphingomyelinases (SMase), enzymes that catalyze the hydrolysis of sphingomyelin to ceramide, are important sensors for inflammatory cytokines and apoptotic signaling. Studies have provided evidence that increased SMase activity can contribute to retinal injury. In most tissues, two major SMases are responsible for stress-induced increases in ceramide: acid sphingomyelinase (ASMase) and Mg2+-dependent neutral sphingomyelinase (NSMase). The purposes of the current study were to determine the localization of SMases and their substrates in the retina and optic nerve head and to investigate the effects of ocular hypertension and ischemia on ASMase and NSMase activities. Tissue and cellular localization of ASMase and NSMase were determined by immunofluorescence imaging. Tissue localization of sphingomyelin in retinas was further determined by Matrix-Assisted Laser Desorption/Ionization mass spectrometry imaging. Tissue levels of sphingomyelins and ceramide were determined by liquid chromatography with tandem mass spectrometry. Sphingomyelinase activities under basal conditions and following acute ischemic and ocular hypotensive stress were measured using the Amplex Red Sphingomyelinase Assay Kit. Our data show that ASMase is in the optic nerve head and the retinal ganglion cell layer. NSMase is in the optic nerve head, photoreceptor and retinal ganglion cell layers. Both ASMase and NSMase were identified in human induced pluripotent stem cell-derived retinal ganglion cells and optic nerve head astrocytes. The retina and optic nerve head each exhibited unique distribution of sphingomyelins with the abundance of very long chain species being higher in the optic nerve head than in the retina. Basal activities for ASMase in retinas and optic nerve heads were 54.98 ± 2.5 and 95.6 ± 19.5 mU/mg protein, respectively. Ocular ischemia significantly increased ASMase activity to 86.2 ± 15.3 mU/mg protein in retinas (P = 0.03) but not in optic nerve heads (81.1 ± 15.3 mU/mg protein). Ocular hypertension significantly increased ASMase activity to 121.6 ± 7.3 mU/mg protein in retinas (P < 0.001) and 267.0 ± 66.3 mU/mg protein in optic nerve heads (P = 0.03). Basal activities for NSMase in retinas and optic nerve heads were 12.3 ± 2.1 and 37.9 ± 8.7 mU/mg protein, respectively. No significant change in NSMase activity was measured following ocular ischemia or hypertension. Our results provide evidence that both ASMase and NSMase are expressed in retinas and optic nerve heads; however, basal ASMase activity is significantly higher than NSMase activity in retinas and optic nerve heads. In addition, only ASMase activity was significantly increased in ocular ischemia or hypertension. These data support a role for ASMase-mediated sphingolipid metabolism in the development of retinal ischemic and hypertensive injuries.

Sphingolipid metabolism and signaling in cardiovascular diseases

Sphingolipids are a structural component of the cell membrane, derived from sphingosine, an amino alcohol. Its sphingoid base undergoes various types of enzymatic transformations that lead to the formation of biologically active compounds, which play a crucial role in the essential pathways of cellular signaling, proliferation, maturation, and death. The constantly growing number of experimental and clinical studies emphasizes the pivotal role of sphingolipids in the pathophysiology of cardiovascular diseases, including, in particular, ischemic heart disease, hypertension, heart failure, and stroke. It has also been proven that altering the sphingolipid metabolism has cardioprotective properties in cardiac pathologies, including myocardial infarction. Recent studies suggest that selected sphingolipids may serve as valuable biomarkers useful in the prognosis of cardiovascular disorders in clinical practice. This review aims to provide an overview of the current knowledge of sphingolipid metabolism and signaling in cardiovascular diseases.

Administration of an Acidic Sphingomyelinase (ASMase) Inhibitor, Imipramine, Reduces Hypoglycemia-Induced Hippocampal Neuronal Death

Severe hypoglycemia (below 35 mg/dL) appears most often in diabetes patients who continuously inject insulin. To rapidly cease the hypoglycemic state in this study, glucose reperfusion was conducted, which can induce a secondary neuronal death cascade following hypoglycemia. Acid sphingomyelinase (ASMase) hydrolyzes sphingomyelin into ceramide and phosphorylcholine. ASMase activity can be influenced by cations, pH, redox, lipids, and other proteins in the cells, and there are many changes in these factors in hypoglycemia. Thus, we expect that ASMase is activated excessively after hypoglycemia. Ceramide is known to cause free radical production, excessive inflammation, calcium dysregulation, and lysosomal injury, resulting in apoptosis and the necrosis of neurons. Imipramine is mainly used in the treatment of depression and certain anxiety disorders, and it is particularly known as an ASMase inhibitor. We hypothesized that imipramine could decrease hippocampal neuronal death by reducing ceramide via the inhibition of ASMase after hypoglycemia. In the present study, we confirmed that the administration of imipramine significantly reduced hypoglycemia-induced neuronal death and improved cognitive function. Therefore, we suggest that imipramine may be a promising therapeutic tool for preventing hypoglycemia-induced neuronal death.

Acid sphingomyelinase deactivation post-ischemia promotes brain angiogenesis and remodeling by small extracellular vesicles

Antidepressants have been reported to enhance stroke recovery independent of the presence of depressive symptoms. They have recently been proposed to exert their mood-stabilizing actions by inhibition of acid sphingomyelinase (ASM), which catalyzes the hydrolysis of sphingomyelin to ceramide. Their restorative action post-ischemia/reperfusion (I/R) still had to be defined. Mice subjected to middle cerebral artery occlusion or cerebral microvascular endothelial cells exposed to oxygen-glucose deprivation were treated with vehicle or with the chemically and pharmacologically distinct antidepressants amitriptyline, fluoxetine or desipramine. Brain ASM activity significantly increased post-I/R, in line with elevated ceramide levels in microvessels. ASM inhibition by amitriptyline reduced ceramide levels, and increased microvascular length and branching point density in wildtype, but not sphingomyelinase phosphodiesterase-1 ([Smpd1]^-/-) (i.e., ASM-deficient) mice, as assessed by 3D light sheet microscopy. In cell culture, amitriptyline, fluoxetine, and desipramine increased endothelial tube formation, migration, VEGFR2 abundance and VEGF release. This effect was abolished by Smpd1 knockdown. Mechanistically, the promotion of angiogenesis by ASM inhibitors was mediated by small extracellular vesicles (sEVs) released from endothelial cells, which exhibited enhanced uptake in target cells. Proteomic analysis of sEVs revealed that ASM deactivation differentially regulated proteins implicated in protein export, focal adhesion, and extracellular matrix interaction. In vivo, the increased angiogenesis was accompanied by a profound brain remodeling response with increased blood-brain barrier integrity, reduced leukocyte infiltrates and increased neuronal survival. Antidepressive drugs potently boost angiogenesis in an ASM-dependent way. The release of sEVs by ASM inhibitors disclosed an elegant target, via which brain remodeling post-I/R can be amplified.

Updates on sphingolipids: Spotlight on retinopathy

The sphingolipids ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (Sph), and sphingosine-1-phosphate (S1P)) are key signaling molecules that regulate many patho-biological processes. During the last decade, they have gained increasing attention since they may participate in important and numerous retinal processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Cer for instance has emerged as a key mediator of inflammation and death of neuronal and retinal pigment epithelium cells in experimental models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. S1P may have opposite biological actions, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1- phosphate may also contribute to uveitis. Furthermore, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), have been shown to preserve neuronal viability and retinal function. Collectively, the expanding role for these sphingolipids in the modulation of vital processes in retina cell types and in their dysregulation in retinal degenerations makes them attractive therapeutic targets.

Raw and wine processed Schisandra chinensis attenuate anxiety like behavior via modulating gut microbiota and lipid metabolism pathway

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, the fruit of Schisandra chinensis (Turcz.) Baill (SC) is used to treat various nervous system diseases, such as dysphoria, anxiety, insomnia and many dreams. It is worthy to be noted that wine processed Schisandra chinensis (WSC) has been applied in clinic for thousands of years.

AIM OF STUDY

This study aimed to investigate the possible mechanism and related metabolism of SC and WSC ameliorating anxiety behavior through modulating gut microbiota.

MATERIALS AND METHODS

The ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) was used for the quality control of chemical components in SC and WSC. Chronic unpredictable stress procedure (CUSP)-induced anxiety rats were administrated with SC and WSC via gavage for five weeks. An untargeted UPLC/LTQ-Orbitrap MS metabolomic analysis of plasma was conducted to understand the effects of long-term intake of WSC and SC extracts on anxious rats. 16S rRNA microbial sequencing technology was applied to investigate gut microbiota structure. Expression of GPR81, TNF-α, S1PR2 as well as molecules in cAMP pathway was assayed by immunohistochemistry staining, RT-qPCR, or Western blot, respectively.

RESULTS

12 compounds were identified using UPLC-QTOF-MS technology, all of which are lignans. Results demonstrate that the amounts of 6-O-Benzoylgomisin O, Schisandrin, Gomisin D, Schizandrin A, Gomisin T, Schizandrin B, Schisandrin C were higher in wine-processed samples than in raw samples. Furthermore, both SC and WSC significantly ameliorated anxiety- and depression-like behavior and lipid metabolism dysfunction and attenuated hippocampal neuritis in anxiety rats. After WSC treatment, the structure and composition of gut microbiota in anxiety rats changed significantly, and gut microbiota derivatives lactate level was significantly lower in the plasma and feces. WSC treatment help restore gut microbial ecosystem dysbiosis and reverse the changes in Lachnospiraceae, Lactobacillus, Alloprevotella, and Bacteroidales in anxiety rat. In addition, the expression of liver GPR81 was decreased, and the molecules in cAMP pathway were increased in SC and WSC-treated anxiety rat.

CONCLUSION

Raw and wine processed Schisandra chinensis treatment improved anxiety- and depression-like behavior through modulating gut microbiota derivatives in association with GPR81 receptor-mediated lipid metabolism pathway. And WSC has more exhibition than SC.

Ceramide/Sphingomyelin Rheostat Regulated by Sphingomyelin Synthases and Chronic Diseases in Murine Models

Ceramide and sphingomyelin (SM) are major components of the double membrane-bound sphingolipids. Ceramide is an essential bioactive lipid involved in numerous cell processes including apoptosis, necrosis, and autophagy-dependent cell death. Inversely, SM regulates opposite cellular processes such as proliferation and migration by changing receptor-mediated signal transduction in the lipid microdomain. SM is generated through a transfer of phosphocholine from phosphatidylcholine to ceramide by SM synthases (SMSs). Research during the past several decades has revealed that the ceramide/SM balance in cellular membranes regulated by SMSs is important to decide the cell fate, survival, and proliferation. In addition, recent experimental studies utilizing SMS knockout mice and murine disease models provide evidence that SMS-regulated ceramide/SM balance is involved in human diseases. Here, we review the basic structural and functional characteristics of SMSs and focus on their cellular functions through the regulation of ceramide/SM balance in membrane microdomains. In addition, we present the pathological or physiological implications of SMSs by analyzing their role in SMS-knockout mice and human disease models. This review finally presents evidence indicating that the regulation of ceramide/SM balance through SMS could be a therapeutic target for human disorders.

Metabolomic Analysis of Mouse Brain after a Transient Middle Cerebral Artery Occlusion by Mass Spectrometry Imaging

We performed metabolomic analyses of mouse brain using a transient middle cerebral artery occlusion (tMCAO) model with Matrix Assisted Laser Desorption/Ionization (MALDI)-mass spectrometry imaging (MSI) to reveal metabolite changes after cerebral ischemia. We selected and analyzed three metabolites, namely creatine (Cr), phosphocreatine (P-Cr), and ceramides (Cer), because these metabolites contribute to cell life and death. Eight-week-old male C57BL/6J mice were subjected to tMCAO via the intraluminal blockade of the middle cerebral artery (MCA) and reperfusion 60 min after the induction of ischemia. Each mouse was randomly assigned to one of the three groups; the groups were defined by the survival period after reperfusion: control, 1 h, and 24 h. Corrected samples were analyzed using MALDI-MSI. Results of MSI analysis showed the presence of several ionized substances and revealed spatial changes in some metabolites identified as precise substances, including Cr, P-Cr, Cer d18:1/18:0, phosphatidylcholine, L-glutamine, and L-histidine. Cr, P-Cr, and Cer d18:1/18:0 were changed after tMCAO, and P-Cr and Cer d18:1/18:0 accumulated over time in ischemic cores and surrounding areas following ischemia onset. The upregulation of P-Cr and Cer d18:1/18:0 was detected 1 h after tMCAO when no changes were evident on hematoxylin and eosin staining and immunofluorescence assay. P-Cr and Cer d18:1/18:0 can serve as neuroprotective therapies because they are biomarker candidates for cerebral ischemia.

Beta adrenoceptor blockade ameliorates impaired glucose tolerance and alterations of the cerebral ceramide metabolism in an experimental model of ischemic stroke

Background:

Sphingolipids are versatile signaling molecules derived from membrane lipids of eukaryotic cells. Ceramides regulate cellular processes such as proliferation, differentiation and apoptosis and are involved in cellular stress responses. Experimental evidence suggests a pivotal role of sphingolipids in the pathogenesis of cardiovascular diseases, including ischemic stroke. A neuroprotective effect has been shown for beta-adrenergic antagonists in rodent stroke models and supported by observational clinical data. However, the exact underlying pathophysiological mechanisms are still under investigation. We aimed to examine the influence of propranolol on the ceramide metabolism in the stroke-affected brain.

Methods:

Mice were subjected to 60 or 180 min transient middle cerebral artery occlusion (tMCAO) and infarct size, functional neurological deficits, glucose tolerance, and brain ceramide levels were assessed after 12, 24, and 72 h to evaluate whether the latter two processes occur in a similar time frame. Next, we assessed the effects of propranolol (10 mg/kg bw) at 0, 4 and 8 h after tMCAO and FTY720 (fingolimod; 1 mg/kg) on infarct size, functional outcome, immune cell counts and brain ceramide levels at 24 h after 60 min tMCAO.

Results:

We found a temporal coincidence between stroke-associated impaired glucose tolerance and brain ceramide accumulation. Whereas propranolol reduced ischemic lesion size, improved functional outcome and reduced brain ceramide accumulation without an effect on circulating immune cells, FTY720 showed the known neuroprotective effect and strong reduction of circulating immune cells without affecting brain ceramide accumulation.

Conclusions:

Propranolol ameliorates both stroke-associated impairment of glucose tolerance and brain ceramide accumulation which are temporally linked, strengthening the evidence for a role of the sympathetic nervous system in regulating post-stroke glucose metabolism and its metabolic consequences in the brain.

Metabolomics and Lipidomics of Ischemic Stroke

Ischemic stroke is a sudden loss of brain function due to the reduction of blood flow. Brain tissues cease to function with subsequent activation of the ischemic cascade. Metabolomics and lipidomics are modern disciplines that characterize the metabolites and lipid components of a biological system, respectively. Because the pathogenesis of ischemic stroke is heterogeneous and multifactorial, it is crucial to establish comprehensive metabolomic and lipidomic approaches to elucidate these alterations in this disease. Fortunately, metabolomic and lipidomic studies have the distinct advantages of identifying tissue/mechanism-specific biomarkers, predicting treatment and clinical outcome, and improving our understanding of the pathophysiologic basis of disease states. Therefore, recent applications of these analytical approaches in the early diagnosis of ischemic stroke were discussed. In addition, the emerging roles of metabolomics and lipidomics on ischemic stroke were summarized, in order to gain new insights into the mechanisms underlying ischemic stroke and in the search for novel metabolite biomarkers and their related pathways.

Imaging mass spectrometry of frontal white matter lipid changes in human alcoholics

BACKGROUND

Chronic alcohol use disorders (AUD) are associated with white matter (WM) degeneration with altered myelin integrity. Matrix assisted laser desorption ionization-imaging mass spectrometry (MALDI-IMS) enables high throughput analysis of myelin lipid biochemical histopathology to help characterize disease mechanisms.

PURPOSE

This study utilized MALDI-IMS to investigate frontal lobe WM myelin lipid abnormalities in AUD.

METHODS

Standardized cores of formalin-fixed WM from Brodmann Area 4 (BA4) and BA8/9 of 20 postmortem AUD and 19 control adult human brains were embedded in carboxymethyl-cellulose, cryo-sectioned (8 μm), thaw-mounted onto indium tin oxide (ITO) -coated glass slides, and sublimed with 2,5-dihydroxybenzxoic acid (DHB) matrix. Lipids were imaged by MALDI-time of flight in the negative ionization mode. Data were visualized with FlexImaging software v4.0 and analyzed with ClinProTools v3.0.

RESULTS

Principal component analysis (PCA) and data bar plots of MALDI-IMS data differentiated AUD from control WM. The dominant effect of AUD was to broadly reduce expression of sphingolipids (sulfatides and ceramides) and phospholipids. Data bar plots demonstrated overall similar responses to AUD in BA4 and BA8/9. However, differential regional effects of AUD on WM lipid profiles were manifested by non-overlapping expression or discordant responses to AUD for a subset of lipid ions.

CONCLUSIONS

Human AUD is associated with substantial inhibition of frontal lobe WM lipid expression with regional variability in these effects. MALDI-IMS can be used to characterize the nature of AUD-associated lipid biochemical abnormalities for correlation with lifetime exposures and WM degeneration, altered gene expression, and responses to abstinence or treatment.

Puerarin Up-regulates Methyl-CpG Binding Protein 2 Phosphorylation in Hippocampus of Vascular Dementia Rats

OBJECTIVE

To observe the effect of puerarin on methyl-CpG binding protein 2 (MeCP2) phosphorylation (pMeCP2) in the hippocampus of a rat model of vascular dementia (VD).

METHODS

Thirty-six healthy Sprague-Dawley rats were randomly assigned to the sham-operated group, dementia group and puerarintreated group using a random number table (n=12 per group). The modifified permanent bilateral common carotid artery occlusion method was used to establish the VD model. The sham-operated and dementia groups were given 2 mL/d of saline, while the puerarin-treated group was given 100 mg/(kg•d) of puerarin for 17 days. The learning and memory abilities were evaluated by the Morris water maze test. Hematoxylin-eosin staining, immunohistochemical (IHC) staining and Western blot analysis were carried out to observe changes in neuron morphology and in level of pMeCP2 in the hippocampus, respectively.

RESULTS

The morphologies of rat hippocampal neurons in the puerarintreated group were markedly improved compared with the dementia group. The escape latency of the dementia group was significantly longer than the sham-operated group (P<0.05), while the puerarin-treated group was obviously shorter than the dementia group (P<0.05). Cross-platform times of the dementia group were signifificantly decreased compared with the sham-operated group (P<0.05), while the puerarin-treated group was obviously increased compared with the dementia group (P<0.05). IHC staining showed no significant difference in the number of MeCP2 positive cells among 3 groups (P>0.05). The number of pMeCP2 positive cells in the CA1 region of hippocampus in the dementia group was signifificantly increased compared with the sham-operated group, and the puerarin-treated group was signifificantly increased compared with the dementia group (both P<0.05). Western blot analysis showed no signifificant difference of MeCP2 expression among 3 groups (P>0.05). The expression of pMeCP2 in the dementia group was signifificantly increased compared with the sham-operated group, while it in the puerarin-treated group was signifificantly increased compared with the dementia group (P<0.05).

CONCLUSION

Puerarin could play a role in the protection of nerve cells through up-regulating pMeCP2 in the hippocampus, improving neuron morphologies, and enhancing learning and memory ablities in a rat model of VD.

Acid sphingomyelinase promotes mitochondrial dysfunction due to glutamate-induced regulated necrosis

Inhibiting the glutamate/cystine antiporter system x_c^-, a key antioxidant defense machinery in the CNS, could trigger a novel form of regulated necrotic cell death, ferroptosis. The underlying mechanisms of system x_c^--dependent cell demise were elucidated using primary oligodendrocytes (OLs) treated with glutamate to block system x_c^- function. Pharmacological analysis revealed ferroptosis as a major contributing factor to glutamate-initiated OL death. A sphingolipid profile showed elevations of ceramide species and sphingosine that were preventable by inhibiting of an acid sphingomyelinase (ASM) activity. OL survival was enhanced by both downregulating ASM expression and blocking ASM activity. Glutamate-induced ASM activation seems to involve posttranscriptional mechanisms and was associated with a decreased GSH level. Further investigation of the mechanisms of OL response to glutamate revealed enhanced reactive oxygen species production, augmented lipid peroxidation, and opening of the mitochondrial permeability transition pore that were attenuated by hindering ASM. Of note, knocking down sirtuin 3, a deacetylase governing the mitochondrial antioxidant system, reduced OL survival. The data highlight the importance of the mitochondrial compartment in regulated necrotic cell death and accentuate the novel role of ASM in disturbing mitochondrial functions during OL response to glutamate toxicity, which is essential for pathobiology in stroke and traumatic brain injury.

Suppression of Acid Sphingomyelinase Protects the Retina from Ischemic Injury

PURPOSE

Acid sphingomyelinase (ASMase) catalyzes the hydrolysis of sphingomyelin to ceramide and mediates multiple responses involved in inflammatory and apoptotic signaling. However, the role ASMase plays in ischemic retinal injury has not been investigated. The purpose of this study was to investigate how reduced ASMase expression impacts retinal ischemic injury.

METHODS

Changes in ceramide levels and ASMase activity were determined by high performance liquid chromatography-tandem mass spectrometry analysis and ASMase activity. Retinal function and morphology were assessed by electroretinography (ERG) and morphometric analyses. Levels of TNF-α were determined by ELISA. Activation of p38 MAP kinase was assessed by Western blot analysis.

RESULTS

In wild-type mice, ischemia produced a significant increase in retinal ASMase activity and ceramide levels. These increases were associated with functional deficits as measured by ERG analysis and significant structural degeneration in most retinal layers. In ASMase+/- mice, retinal ischemia did not significantly alter ASMase activity, and the rise in ceramide levels were significantly reduced compared to levels in retinas from wild-type mice. In ASMase+/- mice, functional and morphometric analyses of ischemic eyes revealed significantly less retinal degeneration than in injured retinas from wild-type mice. The ischemia-induced increase in retinal TNF-α levels was suppressed by the administration of the ASMase inhibitor desipramine, or by reducing ASMase expression.

CONCLUSIONS

Our results demonstrate that reducing ASMase expression provides partial protection from ischemic injury. Hence, the production of ceramide and subsequent mediators plays a role in the development of ischemic retinal injury. Modulating ASMase may present new opportunities for adjunctive therapies when treating retinal ischemic disorders.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)2 D3 and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)2 D3 have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)2 D3 , will focus on the potential crosstalk between sphingolipids and 1,25(OH)2 D3 in neural cells.

Relative quantification of neuronal polar lipids by UPLC-MS reveals the brain protection mechanism of Danhong injection

Promising results from clinical trials have fueled a growing acceptance of Danhong injection (DHI) as a Chinese Materia Medica standardized product for the treatment of ischemic stroke.

Regulation of sphingomyelin metabolism

Sphingolipids (SFs) represent a large class of lipids playing diverse functions in a vast number of physiological and pathological processes. Sphingomyelin (SM) is the most abundant SF in the cell, with ubiquitous distribution within mammalian tissues, and particularly high levels in the Central Nervous System (CNS). SM is an essential element of plasma membrane (PM) and its levels are crucial for the cell function. SM content in a cell is strictly regulated by the enzymes of SM metabolic pathways, which activities create a balance between SM synthesis and degradation. The de novo synthesis via SM synthases (SMSs) in the last step of the multi-stage process is the most important pathway of SM formation in a cell. The SM hydrolysis by sphingomyelinases (SMases) increases the concentration of ceramide (Cer), a bioactive molecule, which is involved in cellular proliferation, growth and apoptosis. By controlling the levels of SM and Cer, SMSs and SMases maintain cellular homeostasis. Enzymes of SM cycle exhibit unique properties and diverse tissue distribution. Disturbances in their activities were observed in many CNS pathologies. This review characterizes the physiological roles of SM and enzymes controlling SM levels as well as their involvement in selected pathologies of the Central Nervous System, such as ischemia/hypoxia, Alzheimer disease (AD), Parkinson disease (PD), depression, schizophrenia and Niemann Pick disease (NPD).

SIRT3 Deacetylates Ceramide Synthases: IMPLICATIONS FOR MITOCHONDRIAL DYSFUNCTION AND BRAIN INJURY

Experimental evidence supports the role of mitochondrial ceramide accumulation as a cause of mitochondrial dysfunction and brain injury after stroke. Herein, we report that SIRT3 regulates mitochondrial ceramide biosynthesis via deacetylation of ceramide synthase (CerS) 1, 2, and 6. Reciprocal immunoprecipitation experiments revealed that CerS1, CerS2, and CerS6, but not CerS4, are associated with SIRT3 in cerebral mitochondria. Furthermore, CerS1, -2, and -6 are hyperacetylated in the mitochondria of SIRT3-null mice, and SIRT3 directly deacetylates the ceramide synthases in a NAD(+)-dependent manner that increases enzyme activity. Investigation of the SIRT3 role in mitochondrial response to brain ischemia/reperfusion (IR) showed that SIRT3-mediated deacetylation of ceramide synthases increased enzyme activity and ceramide accumulation after IR. Functional studies demonstrated that absence of SIRT3 rescued the IR-induced blockade of the electron transport chain at the level of complex III, attenuated mitochondrial outer membrane permeabilization, and decreased reactive oxygen species generation and protein carbonyls in mitochondria. Importantly, Sirt3 gene ablation reduced the brain injury after IR. These data support the hypothesis that IR triggers SIRT3-dependent deacetylation of ceramide synthases and the elevation of ceramide, which could inhibit complex III, leading to increased reactive oxygen species generation and brain injury. The results of these studies highlight a novel mechanism of SIRT3 involvement in modulating mitochondrial ceramide biosynthesis and suggest an important role of SIRT3 in mitochondrial dysfunction and brain injury after experimental stroke.

Dietary fats significantly influence the survival of penumbral neurons in a rat model of chronic ischemic by modifying lipid mediators, inflammatory biomarkers, NOS production, and redox-dependent apoptotic signals

OBJECTIVE

Brain stroke is the third most important cause of death in developed countries. We studied the effect of different dietary lipids on the outcome of a permanent ischemic stroke rat model.

METHODS

Wistar rats were fed diets containing 7% commercial oils (S, soybean; O, olive; C, coconut; G, grape seed) for 35 d. Stroke was induced by permanent middle cerebral artery occlusion. Coronal slices from ischemic brains and sham-operated animals were supravitally stained. Penumbra and core volumes were calculated by image digitalization after 24, 48, and 72 h poststroke. Homogenates and mitochondrial fractions were prepared from different zones and analyzed by redox status, inflammatory markers, ceramide, and arachidonate content, phospholipase A2, NOS, and proteases.

RESULTS

Soybean (S) and G diets were mainly prooxidative and proinflammatory by increasing the liberation of arachidonate and its transformation into prostaglandins. O was protective in terms of redox homeostatic balance, minor increases in lipid and protein damage, conservation of reduced glutathione, protective activation of NOS in penumbra, and net ratio of anti-to proinflammatory cytokines. Apoptosis (caspase-3, milli- and microcalpains) was less activated by O than by any other diet.

CONCLUSION

Dietary lipids modulate NOS and PLA2 activities, ceramide production, and glutathione import into the mitochondrial matrix, finally determining the activation of the two main protease systems involved in programmed cell death. Olive oil appears to be a biological source for the isolation of protective agents that block the expansion of brain core at the expense of penumbral neurons.

Alterations of the Ceramide Metabolism in the Peri-Infarct Cortex Are Independent of the Sphingomyelinase Pathway and Not Influenced by the Acid Sphingomyelinase Inhibitor Fluoxetine

Ceramides induce important intracellular signaling pathways, modulating proliferation, migration, apoptosis, and inflammation. However, the relevance of the ceramide metabolism in the reconvalescence phase after stroke is unclear. Besides its well-known property as a selective serotonin reuptake inhibitor, fluoxetine has been reported to inhibit the acid sphingomyelinase (ASM), a key regulator of ceramide levels which derives ceramide from sphingomyelin. Furthermore, fluoxetine has shown therapeutic potential in a randomized controlled rehabilitation trial in stroke patients. Our aim was to investigate and modulate ceramide concentrations in the peri-infarct cortex, whose morphological and functional properties correlate with long-term functional outcome in stroke. We show that certain ceramide species are modulated after experimental stroke and that these changes do not result from alterations of ASM activity, but rather from nontranscriptional induction of the ceramide de novo pathway. Unexpectedly, although reducing lesion size, fluoxetine did not improve functional outcome in our model and had no significant influence on ASM activity or the concentration of ceramides. The ceramide metabolism could emerge as a potential therapeutic target in the reconvalescence phase after stroke, as its accumulation in the peri-infarct cortex potentially influences membrane functions as well as signaling events in the tissue essential for neurological recovery.

Changes in the metabolism of sphingolipids after subarachnoid hemorrhage

We previously described how ceramide (Cer), a mediator of cell death, increases in the cerebrospinal fluid (CSF) of subarachnoid hemorrhage (SAH) patients. This study investigates the alterations of biochemical pathways involved in Cer homeostasis in SAH. Cer, dihydroceramide (DHC), sphingosine-1-phosphate (S1P), and the activities of acid sphingomyelinase (ASMase), neutral sphingomyelinase (NSMase), sphingomyelinase synthase (SMS), S1P-lyase, and glucosylceramide synthase (GCS) were determined in the CSF of SAH subjects and in brain homogenate of SAH rats. Compared with controls (n = 8), SAH patients (n = 26) had higher ASMase activity (10.0 ± 3.5 IF/µl· min vs. 15.0 ± 4.6 IF/µl • min; P = 0.009) and elevated levels of Cer (11.4 ± 8.8 pmol/ml vs. 33.3 ± 48.3 pmol/ml; P = 0.001) and DHC (1.3 ± 1.1 pmol/ml vs. 3.8 ± 3.4 pmol/ml; P = 0.001) in the CSF. The activities of GCS, NSMase, and SMS in the CSF were undetectable. Brain homogenates from SAH animals had increased ASMase activity (control: 9.7 ± 1.2 IF/µg • min; SAH: 16.8 ± 1.6 IF/µg • min; P < 0.05) and Cer levels (control: 3,422 ± 26 fmol/nmol of total lipid P; SAH: 7,073 ± 2,467 fmol/nmol of total lipid P; P < 0.05) compared with controls. In addition, SAH was associated with a reduction of 60% in S1P levels, a 40% increase in S1P-lyase activity, and a twofold increase in the activity of GCS. In comparison, NSMase and SMS activities were similar to controls and SMS activities similar to controls. In conclusion, our results show an activation of ASMase, S1P-lyase, and GCS resulting in a shift in the production of protective (S1P) in favor of deleterious (Cer) sphingolipids after SAH. Additional studies are needed to determine the effect of modulators of the pathways described here in SAH.

The effect of scalp point cluster-needling on learning and memory function and neurotransmitter levels in rats with vascular dementia

We observed the effect of scalp point cluster-needling treatment on learning and memory function and neurotransmitter levels in rats with vascular dementia (VD). Permanent ligation of the bilateral carotid arteries was used to create the VD rat model. A Morris water maze was used to measure the rats' learning and memory function, and the changes in neurotransmitter levels in the rats' hippocampus were analyzed. The results show that scalp point cluster-needling can increase the VD rat model's learning and memory score. The VD rat model's learning and memory score was significantly different when compared with that of the sham operation group (P < 0.05). Hippocampal acetylcholine (ACh), dopamine (DA), and 5-hydroxytryptamine (5-HT) concentrations significantly decreased in the rat model. Compared with the model group, the scalp point cluster-needling group's ACh concentration markedly increased and DA and 5-HT levels increased as well. In conclusion, scalp point cluster-needling can improve learning and memory function in VD rats, and its function may be related to an increase in neurotransmitter release.

Ceramide in the molecular mechanisms of neuronal cell death. The role of sphingosine-1-phosphate

Ceramide and sphingosine-1-phosphate (S1P), two important bioactive sphingolipids, have been suggested as being key players in the pathology of Alzheimer’s disease in inflammation and cancer. However, their role in the molecular mechanisms of neuronal death has not been fully elucidated. Our study indicated that ceramide significantly enhanced the level of free radicals and decreased the viability of the human neuroblastoma cell line (SH-SY5Y) through inhibition of the prosurvival PI3-K/Akt pathway. Ceramide also decreased anti-apoptotic (Bcl-2) and increased pro-apoptotic (Bax, Hrk) mRNA/protein levels. Concomitantly, our study indicated that ceramide induced poly(ADP-ribose) polymerase-1 (PARP-1) activation and accumulation of poly(ADP-ribose) PAR, a signalling molecule involved in mitochondria-nucleus cross-talk and mitochondria integrity. Ceramide treatment significantly decreased the level of apoptosis-inducing factor (AIF) in the mitochondria. The PARP-1 inhibitor (PJ-34) prevented AIF release from the mitochondria. In addition, our data showed that exogenously added S1P increased the viability of SH-SY5Y through the S1P (1,3) receptor-dependent mechanism. It was also revealed that the S1P and PARP-1 inhibitor (PJ-34) decreased oxidative stress, gene expression of the pro-apoptotic Hrk protein and up-regulated the anti-apoptotic Bcl-2 protein. Our data demonstrate that neuronal cell death evoked by ceramide is regulated by PARP/PAR/AIF and by S1P receptor signalling. In summary, our results suggest that PARP-1 inhibitor(s) and modulators of sphingosine-1-phosphate receptor(s) should be considered in potential therapeutic strategies directed at neurodegenerative diseases.

Sphingolipid profiles are altered in prefrontal cortex of rats under acute hyperglycemia

Diabetes type 1 is a common autoimmune disease manifesting by insulin deficiency and hyperglycemia, which can lead to dementia-like brain dysfunctions. The factors triggering the pathological processes in hyperglycemic brain remain unknown. We reported in this study that brain areas with different susceptibility to diabetes (prefrontal cortex (PFC), hippocampus, striatum and cerebellum) revealed differential alterations in ceramide (Cer) and sphingomyelin (SM) profiles in rats with streptozotocin-induced hyperglycemia. Employing gas-liquid chromatography, we found that level of total Cer increased significantly only in the PFC of diabetic animals, which also exhibited a broad spectrum of sphingolipid (SLs) changes, such as elevations of Cer-C16:0, -C18:0, -C20:0, -C22:0, -C18:1, -C24:1 and SM-C16:0 and -C18:1. In opposite, only minor changes were noted in other examined structures. In addition, de novo synthesis pathway could play a role in generation of Cer containing monounsaturated fatty acids in PFC during hyperglycemia. In turn, simultaneous accumulation of Cers and their SM counterparts may suggest that overproduced Cers are converted to SMs to avoid excessive Cer-mediated cytotoxicity. We conclude that broad changes in SLs compositions in PFC induced by hyperglycemia may provoke membrane rearrangements in some cell populations, which can disturb cellular signaling and cause tissue damage.

Fetal asphyxia induces acute and persisting changes in the ceramide metabolism in rat brain

Fetal asphyctic preconditioning, induced by a brief episode of experimental hypoxia-ischemia, offers neuroprotection to a subsequent more severe asphyctic insult at birth. Extensive cell stress and apoptosis are important contributing factors of damage in the asphyctic neonatal brain. Because ceramide acts as a second messenger for multiple apoptotic stimuli, including hypoxia/ischemia, we sought to investigate the possible involvement of the ceramide pathway in endogenous neuroprotection induced by fetal asphyctic preconditioning. Global fetal asphyxia was induced in rats by clamping both uterine and ovarian vasculature for 30 min. Fetal asphyxia resulted in acute changes in brain ceramide/sphingomyelin metabolic enzymes, ceramide synthase 1, 2, and 5, acid sphingomyelinase, sphingosine-1-phosphate phosphatase, and the ceramide transporter. This observation correlated with an increase in neuronal apoptosis and in astrocyte number. After birth, ceramide and sphingomyelin levels remained high in fetal asphyxia brains, suggesting that a long-term regulation of the ceramide pathway may be involved in the mechanism of tolerance to a subsequent, otherwise lethal, asphyctic event.

Ceramide from sphingomyelin hydrolysis differentially mediates mitogen-activated protein kinases (MAPKs) activation following cerebral ischemia in rat hippocampal CA1 subregion

Objective

To explore the role that ceramide plays in the activation of mitogen-activated protein kinases (MAPKs) during cerebral ischemia and reperfusion.

Methods

Rats were subjected to ischemia by the four-vessel occlusion (4-VO) method. The sphingomyelinase inhibitor TPCK was administered to the CA1 subregion of the rat hippocampus before inducing ischemia. Western blot was used to examine the activity of extracellular-signal regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK) using antibodies against ERK, JNK and diphosphorylated ERK and JNK.

Results

At 1h reperfusion post-ischemia, JNK reached its peak activity while ERK was undergoing a sharp inactivation (P < 0.05). The level of diphosphorylated JNK was significantly reduced but the sharp inactivation of ERK was visibly reversed (P < 0.05) by the sphingomyelinase inhibitor.

Conclusion

The ceramide signaling pathway is up-regulated through sphingomyelin hydrolysis in brain ischemia, promoting JNK activation and suppressing ERK activation, culminating in the ischemic lesion.

The effects of fetal and perinatal asphyxia on neuronal cytokine levels and ceramide metabolism in adulthood

In a rat model of global fetal and perinatal asphyxia, we investigated if asphyxia and long-lasting brain tolerance to asphyxia (preconditioning) are mediated by modifications in inflammatory cytokines and ceramide metabolism genes in prefrontal cortex, hippocampus and caudate-putamen at the age of 8months. Most significant changes were found in prefrontal cortex, with reduced LAG1 homolog ceramide synthase 1 expression after both types of asphyxia. Additionally, sphingosine kinase 1 was upregulated in those animals that experienced the combination of fetal and perinatal asphyxia (preconditioning), suggesting increased cell proliferation. While cytokine levels are normal, levels of ceramide genes were modulated both after fetal and perinatal asphyxia in the adult prefrontal cortex. Moreover, the combination of two subsequent asphyctic insults provides long-lasting neuroprotection in the prefrontal cortex probably by maintaining normal apoptosis and promoting cell proliferation. Better understanding of the effects of asphyxia on ceramide metabolism will help to understand the changes leading to brain tolerance and will open opportunities for the development of new neuroprotective therapies.

Changes in the cerebrospinal fluid ceramide profile after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The purpose of this study was to investigate changes in the cerebrospinal fluid sphingolipid profile in patients with subarachnoid hemorrhage in relation to the occurrence of symptomatic vasospasm and outcome at hospital discharge.

METHODS

The ceramide profile in the cerebrospinal fluid was determined by mass spectrometry in control subjects and patients with Fisher 3 grade subarachnoid hemorrhage within 48 hours of the bleed. Patients were prospectively followed and subcategorized based on the occurrence of symptomatic vasospasm and modified Rankin Scale at discharge.

RESULTS

Compared to control subjects, patients with subarachnoid hemorrhage had higher cerebrospinal fluid levels of total ceramide (12.4±8.8 versus 54.6±49.3 pmol/mL; P<0.001). In the subgroup analysis, total ceramide levels in individuals with symptomatic vasospasm (104.2±57.0 pmol/mL) were higher than in those with asymptomatic vasospasm (32.4±25.7 pmol/mL; P=0.006) and no vasospasm (30.9±15.7 pmol/mL; P=0.003). In addition, compared to patients with a good outcome (modified Rankin Scale ≤3), individuals with poor outcome (modified Rankin Scale ≥4) had higher cerebrospinal fluid levels of total ceramide (79±25 versus 23±6 pmol/mL; P=0.008). When the relative contributions of the different ceramide species were calculated, a higher relative concentration of C(18:0) ceramide was observed in individuals with symptomatic vasospasm (P=0.018) and poor outcome (P=0.028).

CONCLUSIONS

Ceramide profile changes occur in subarachnoid hemorrhage. In this small case-based series elevation of levels of this sphingolipid, particularly C(18:0), was associated with the occurrence of symptomatic vasospasm and poor neurological outcome after subarachnoid hemorrhage.

Anti-apoptotic and anti-oxidative mechanisms of minocycline against sphingomyelinase/ceramide neurotoxicity: implication in Alzheimer's disease and cerebral ischemia

Sphingolipids represent a major class of lipids in which selected family members act as bioactive molecules that control diverse cellular processes, such as proliferation, differentiation, growth, senescence, migration and apoptosis. Emerging evidence reveals that sphingomyelinase/ceramide pathway plays a pivotal role in neurodegenerative diseases that involve mitochondrial dysfunction, oxidative stress and apoptosis. Minocycline, a semi-synthetic second-generation tetracycline derivative in clinical use for infection control, is also considered an effective protective agent in various neurodegenerative diseases in pre-clinical studies. Acting via multiple mechanisms, including anti-inflammatory, anti-oxidative and anti-apoptotic effects, minocycline is a desirable candidate for clinical trials in both acute brain injury as well as chronic neurodegenerative disorders. This review is focused on the anti-apoptotic and anti-oxidative mechanisms of minocycline against neurotoxicity induced by sphingomyelinase/ceramide in relation to neurodegeneration, particularly Alzheimer's disease and cerebral ischemia.

Ceramide profiles in the brain of rats with diabetes induced by streptozotocin

Diabetes is associated with disturbances of brain activity and cognitive impairment. We hypothesize that ceramides may constitute an important contribution to diabetes-linked neuro-dysfunction. In our study we used rats injected with streptozotocin (STZ) as a model of severe hyperglycemia. Using the gas-liquid chromatography technique we found a significant increase of ceramide content in brains and a decrease in plasma of diabetic rats. The inhibitor of serine palmitoyltransferase, myriocin, reduced ceramide generation in hyperglycemic brains, although injected alone it exerted a paradoxical effect of ceramide upregulation. Myriocin had no impact on ceramide concentration in the plasma of either control or diabetic rats. The level of ceramide saturated fatty acids was elevated whereas the level of ceramide poly-unsaturated fatty acids was downregulated in brains of all experimental groups. The concentration of ceramide mono-unsaturated fatty acids remained unchanged. The pattern of individual ceramide species was altered depending on treatment. We noted an STZ-evoked increase of brain ceramide C16:0, C18:0 and C20:0 and a strong decline in ceramide C18:2 fatty acid levels. Some changes of brain ceramide pattern were modified by myriocin. We found a decreased amount of total ceramide-ω-6 fatty acids in STZ-treated rat brains and no changes in ceramide-ω-3 concentration. We conclude that ceramides may be important mediators of diabetes-accompanied brain dysfunction.

Protection of murine neural progenitor cells by the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin in the low nanomolar concentration range

Stem cell-based approaches provide hope as a potential therapy for neurodegenerative diseases and stroke. One of the major scientific hurdles for stem cell therapy is the poor survival rate of the newly formed or transplanted neural stem cells. In this study, we found that low-dose treatment with the Heat shock protein 90 (Hsp90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heavily investigated anti-cancer drug, prevented neural progenitor cells from either naturally-occurring or stress-induced apoptosis, although it induced apoptosis at higher doses. This stress adaptation effect mediated by low-dose 17-AAG is accompanied by activation of multiple cell survival pathways, including the stress response pathway (induction of Hsp70), the MAPK pathway, and the PI3K/Akt pathway. When administered in vivo, 17-AAG led to Akt and glycogen synthase kinase 3β phosphorylation, and more 5-bromo-2'-deoxyuridine positive cells in the mouse brain. These findings could have profound implications in stem cell therapy for neurodegenerative diseases and stroke.

Neuroprotective mechanisms of minocycline against sphingomyelinase/ceramide toxicity: Roles of Bcl-2 and thioredoxin

In this study, we determined whether minocycline may protect rat cortical cultures against neurotoxicity induced by sphingomyelinase/ceramide and explored the underlying mechanisms. We found that minocycline exerted strong neuroprotective effects against toxicity induced by bacterial sphingomyelinase and synthetic C2 ceramide. Minocycline enhanced the production of nitric oxide (NO) with resultant increases in cellular cGMP content. Consistently, minocycline-dependent neuroprotection was abolished by the nitric oxide synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) and the soluble guanylate cyclase (sGC) inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). Western blotting revealed that minocycline restored the expression levels of cGMP-dependent protein kinase (PKG)-1, antioxidative thioredoxin-1, and antiapoptotic Bcl-2 that were down-regulated by bacterial sphingomyelinase. Accordingly, the PKG inhibitor KT5823, the thioredoxin reductase inhibitor 1-chloro-2,4-dinitrobenzene (DNCB), and a Bcl-2 inhibitor significantly abolished the minocycline neuroprotection. The minocycline-dependent restoration of Bcl-2 was abolished by L-NAME, ODQ, and KT5823, but not by DNCB, suggesting the involvement of NO/sGC/PKG but not thioredoxin. Furthermore, minocycline-dependent recovery of thioredoxin-1 was PKG-independent. Taken together, our results indicate that minocycline protects rat cortical neurons against bacterial sphingomyelinase/ceramide toxicity via an NO/cGMP/PKG pathway with induction of Bcl-2 and PKG-independent stimulation of thioredoxin-1.

Sphingomyelinase-induced ceramide production stimulate calcium-independent JNK and PP2A activation following cerebral ischemia

PRIMARY OBJECTIVE

Intracellular calcium overload is considered to be a key pathologic factor for ischemic stroke; however, there are other signal molecules produced in response to ischemic stimuli. The present study investigated the ceramide signal pathway, which is associated with cerebral ischemia in a calcium-independent manner.

METHODS

Male Sprague-Dawley rats were subjected to 10-minute four-vessel occlusion. Ketamine, a blocker of calcium-ion channels, or TPCK or fumonisin B1, inhibitors of ceramide production in the sphingomyelinase and de novo pathways, respectively, were administrated to the rats prior to inducing ischemia. Ceramide levels were determined by immunofluorescence, protein activity was assessed by immunoblotting and PP2A activity was measured using a protein phosphatase assay system.

RESULTS

The morphologic data indicated that ischemia-induced ceramide production was largely restricted to glia cells in the rat hippocampus. TPCK, but not ketamine or fumonisin B1, blocked the ceramide pathway and its downstream molecules, JNK and PP2A.

CONCLUSIONS

Cerebral ischemia up-regulates the sphingomyelin-ceramide pathway, which involves calcium-independent JNK and PP2A activation in hippocampal glia; this may play a significant role in cerebral lesions post-ischemia.

Ceramide and mitochondria in ischemia/reperfusion

A hallmark of tissue injury in various models of ischemia/reperfusion (IR) is mitochondrial dysfunction and the release of mitochondrial proapoptotic proteins leading to cell death. Although IR-induced mitochondrial injury has been extensively studied and key mitochondrial functions affected by IR are chiefly characterized, the nature of the molecule that causes loss of mitochondrial integrity and function remains obscure. It has become increasingly clear that ceramide, a membrane sphingolipid and a key mediator of cell stress responses, could play a critical role in IR-induced mitochondrial damage. Emerging data point to excessive ceramide accumulation in tissue and, specifically, in mitochondria after IR. Exogenously added to isolated mitochondria, ceramide could mimic some of the mitochondrial dysfunctions occurring in IR. The recent identification and characterization of major enzymes in ceramide synthesis is expected to contribute to the understanding of molecular mechanisms of ceramide involvement in mitochondrial damage in IR. This review will examine the experimental evidence supporting the important role of ceramide in mitochondrial dysfunction in IR to highlight potential targets for pharmacological manipulation of ceramide levels.

Neutral sphingomyelinase-induced ceramide accumulation by oxidative stress during carbon tetrachloride intoxication

Ceramide is a biologically active lipid causing apoptosis in a variety of cells. In this study, we examined the effect of CCl4 on the ceramide metabolism and indicators of oxidative stress. After 12 h of oral administration of CCl4 (4 ml/kg body weight as a 1:1 mixture of CCl4 and mineral oil) to rats, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were increased. Antioxidants such as vitamins C and E were decreased in the liver and kidney. In addition, the ratio of GSH/GSSG in the liver, plasma, kidney, and brain decreased at 2h. The total ceramide in the liver significantly increased as early as 2h after CCl4 administration. After 24 and 36 h, the total ceramide in plasma and the kidney was also augmented. In the brain, the total ceramide dramatically increased at 36 h. These results suggested that the increased ceramide in plasma was transferred to the kidney and the brain. The activity of neutral sphingomyelinase (SMase), which was reported to be enhanced by the decrease of GSH, was significantly increased after CCl4 treatment in the liver, kidney, and brain. However, acid SMase activities were not increased in the liver and kidney. Thus, the activation of neutral SMase via oxidative stress induced the increase of ceramide during CCl4 intoxication in not only the liver but also other tissues. These results suggested that the excess accumulation of ceramide causes damage in other organs including the kidney and brain during fulminant hepatic failure.

Ceramide and neurodegeneration: susceptibility of neurons and oligodendrocytes to cell damage and death

Neurodegenerative disorders are marked by extensive neuronal apoptosis and gliosis. Although several apoptosis-inducing agents have been described, understanding of the regulatory mechanisms underlying modes of cell death is incomplete. A major breakthrough in delineation of the mechanism of cell death came from elucidation of the sphingomyelin (SM)-ceramide pathway that has received worldwide attention in recent years. The SM pathway induces apoptosis, differentiation, proliferation, and growth arrest depending upon cell and receptor types, and on downstream targets. Sphingomyelin, a plasma membrane constituent, is abundant in mammalian nervous system, and ceramide, its primary catabolic product released by activation of either neutral or acidic sphingomyelinase, serves as a potential lipid second messenger or mediator molecule modulating diverse cellular signaling pathways. Neutral sphingomyelinase (NSMase) is a key enzyme in the regulated activation of the SM cycle and is particularly sensitive to oxidative stress. In a context of increasing clarification of the mechanisms of neurodegeneration, we thought that it would be useful to review details of recent findings that we and others have made concerning different pro-apoptotic neurotoxins including proinflammatory cytokines, hypoxia-induced SM hydrolysis and ceramide production that induce cell death in human primary neurons and primary oligodendrocytes: redox sensitive events. What has and is emerging is a vista of therapeutically important ceramide regulation affecting a variety of different neurodegenerative and neuroinflammatory disorders.

Regulation of ceramide-induced neuronal death: cell metabolism meets neurodegeneration

The present review explores the role of ceramides in neuronal apoptosis, as well as the recent discovery of the signaling pathways involved in this process placing particular emphasis on the correlation between cellular metabolism and neuronal death. Endogenous levels of ceramides are increased following various pro-apoptotic stimuli which have been identified as potential causes of chronic and acute neurodegenerative diseases. Ceramides induce changes in multiple enzymes and cell signaling components. The early inhibition of the neuronal survival pathway regulated by phosphatidil-inositol-3-kinase/protein kinase B or AKT mediated by ceramide may be a relevant early event in the decision of neuronal survival/death. It may perturb several molecular and metabolic functions. In particular it might decrease glycolysis through rapid modulation of hexokinase activity. This would in turn generate limited amounts of mitochondrial substrates leading to mitochondrial dysfunction and neuronal apoptosis. Subtle and early metabolic alterations caused by inhibition of the PI3K/AKT pathway mediated by ceramide may potentially work with genes associated with neurodegenerative diseases such as Parkinson's and Alzheimer's disease. Together they may be determinant steps in downstream events leading to neuronal apoptosis. Therefore, reinforcement of the PI3K/AKT pathway could constitute an important neuroprotective strategy.

Expression of sphingomyelin synthase 1 gene in rat brain focal ischemia

Metabolites of the sphingomyelin cycle are reported to play an important role in neuronal death after ischemia. To elucidate the involvement of the key enzyme of this cycle, sphingomyelin synthase (SMS), in the mechanism underlying cerebral ischemia, we, for the first time, investigated changes in the mRNA expression of the SMS1 gene in rats after focal cerebral ischemia. According to our histological analysis, the damaged area is localized only in the ipsilateral cortex. In the ischemic cortex, the level of SMS1 transcripts was decreased at 3 and 24 h after occlusion, and at 72 h it had returned to the control level. A reduced level of SMS1 mRNA expression in the subcortex of rats with occlusion and sham-operated animals also was appeared during the first 24 h after surgery. This could be attributed to the effect of surgical stress. Seventy-two hours after occlusion, SMS1 mRNA expression in subcortex of ischemic rats was still at a decreased level; this may be considered to be a somewhat distant extended effect. Our results show the early response of the SMS1 gene that can be induced by both ischemia and stress. The results also suggest that inhibition of SMS1 mRNA expression may contribute to ceramide accumulation in a damaged cortex.

JNK3 signaling pathway activates ceramide synthase leading to mitochondrial dysfunction

A cardinal feature of brain tissue injury in stroke is mitochondrial dysfunction leading to cell death, yet remarkably little is known about the mechanisms underlying mitochondrial injury in cerebral ischemia/reperfusion (IR). Ceramide, a naturally occurring membrane sphingolipid, functions as an important second messenger in apoptosis signaling and is generated by de novo synthesis, sphingomyelin hydrolysis, or recycling of sphingolipids. In this study, cerebral IR-induced ceramide elevation resulted from ceramide biosynthesis rather than from hydrolysis of sphingomyelin. Investigation of intracellular sites of ceramide accumulation revealed the elevation of ceramide in mitochondria because of activation of mitochondrial ceramide synthase via post-translational mechanisms. Furthermore, ceramide accumulation appears to cause mitochondrial respiratory chain damage that could be mimicked by exogenously added natural ceramide to mitochondria. The effect of ceramide on mitochondria was somewhat specific; dihydroceramide, a structure closely related to ceramide, did not inflict damage. Stimulation of ceramide biosynthesis seems to be under control of JNK3 signaling: IR-induced ceramide generation and respiratory chain damage was abolished in mitochondria of JNK3-deficient mice, which exhibited reduced infarct volume after IR. These studies suggest that the hallmark of mitochondrial injury in cerebral IR, respiratory chain dysfunction, is caused by the accumulation of ceramide via stimulation of ceramide synthase activity in mitochondria, and that JNK3 has a pivotal role in regulation of ceramide biosynthesis in cerebral IR.

Interactions between neural membrane glycerophospholipid and sphingolipid mediators: A recipe for neural cell survival or suicide

The neural membranes contain phospholipids, sphingolipids, cholesterol, and proteins. Glycerophospholipids and sphingolipids are precursors for lipid mediators involved in signal transduction processes. Degradation of glycerophospholipids by phospholipase A(2) (PLA(2)) generates arachidonic acid (AA) and docosahexaenoic acids (DHA). Arachidonic acid is metabolized to eicosanoids and DHA is metabolized to docosanoids. The catabolism of glycosphingolipids generates ceramide, ceramide 1-phosphate, sphingosine, and sphingosine 1-phosphate. These metabolites modulate PLA(2) activity. Arachidonic acid, a product derived from glycerophospholipid catabolism by PLA(2), modulates sphingomyelinase (SMase), the enzyme that generates ceramide and phosphocholine. Furthermore, sphingosine 1-phosphate modulates cyclooxygenase, an enzyme responsible for eicosanoid production in brain. This suggests that an interplay and cross talk occurs between lipid mediators of glycerophospholipid and glycosphingolipid metabolism in brain tissue. This interplay between metabolites of glycerophospholipid and sphingolipid metabolism may play an important role in initiation and maintenance of oxidative stress associated with neurologic disorders as well as in neural cell proliferation, differentiation, and apoptosis. Recent studies indicate that PLA(2) and SMase inhibitors can be used as neuroprotective and anti-apoptotic agents. Development of novel inhibitors of PLA(2) and SMase may be useful for the treatment of oxidative stress, and apoptosis associated with neurologic disorders such as stroke, Alzheimer disease, Parkinson disease, and head and spinal cord injuries.

Effect of tricyclodecan-9-yl potassium xanthate (D609) on phospholipid metabolism and cell death during oxygen-glucose deprivation in PC12 cells

Alterations in lipid metabolism play an integral role in neuronal death in cerebral ischemia. Here we used an in vitro model, oxygen-glucose deprivation (OGD) of rat pheochromocytoma (PC12) cells, and analyzed changes in phosphatidylcholine (PC) and sphingomyelin (SM) metabolism. OGD (4-8 h) of PC12 cells triggered a dramatic reduction in PC and SM levels, and a significant increase in ceramide. OGD also caused increases in phosphatidylcholine-phospholipase C (PC-PLC) and phospholipase D (PLD) activities and PLD2 protein expression, and reduction in cytidine triphosphate:phosphocholine cytidylyltransferase-alpha (CCTalpha, the rate-limiting enzyme in PC synthesis) protein expression and activity. Phospholipase A2 activity and expression were unaltered during OGD. Increased neutral sphingomyelinase activity during OGD could account for SM loss and increased ceramide. Surprisingly, treatment with PC-PLC inhibitor tricyclodecan-9-yl potassium xanthate (D609) aggravated cell death in PC12 cells during OGD. D609 was cytotoxic only during OGD; cell death could be prevented by inclusion of sera, glucose or oxygen. During OGD, D609 caused further loss of PC and SM, depletion of 1,2-diacylglycerol (DAG), increase in ceramide and free fatty acids (FFA), cytochrome c release from mitochondria, increases in intracellular Ca2+ ([Ca2+]i), poly-ADP ribose polymerase (PARP) cleavage and phosphatidylserine externalization, indicative of apoptotic cell death. Exogenous PC during OGD in PC12 cells with D609 attenuated PC, SM loss, restored DAG, attenuated ceramide levels, decreased cytochrome c release, PARP cleavage, annexin V binding, attenuated the increase in [Ca2+]i, FFA release, and significantly increased cell viability. Exogenous PC may have elicited these effects by restoring membrane PC levels. A tentative scheme depicting the mechanism of action of D609 (inhibiting PC-PLC, SM synthase, PC synthesis at the CDP-choline-1,2-diacylglycerol phosphocholine transferase (CPT) step and causing mitochondrial dysfunction) has been proposed based on our observations and literature.

Gene expression alterations in the sphingolipid metabolism pathways during progression of dementia and Alzheimer's disease: a shift toward ceramide accumulation at the earliest recognizable stages of Alzheimer's disease?

There is mounting evidence linking Abeta42 generation in Alzheimer's disease (AD) with sphingomyelin catabolism. Using microarray technology to study 17 brain regions from subjects with varying severity of AD and dementia we detected multiple gene expression abnormalities of the key enzymes that control sphingolipid metabolism. These changes were correlated with the progression of clinical dementia. The upregulation of gene expression of the enzymes controlling synthesis de novo of Cer and the downregulation of the enzymes involved in glycosphingolipid synthesis was evident as early in disease progression as in mild dementia. Together these changes suggest a shift in sphingolipid metabolism towards accumulation of Cer, depletion of glycosphingolipids and the reduction of synthesis of the anti-apoptosis signaling lipid-sphingosine 1-phosphate as a function of disease progression. This disrupted balance within the sphingolipid metabolism may trigger signaling events promoting neurodegeneration across cortical regions. This potential mechanism may provide a link between lipid metabolism disturbance and AD.

Expression, activity, and role of serine palmitoyltransferase in the rat hippocampus after kainate injury

An increase in ceramide species has been shown recently by lipidomic analysis of the rat hippocampus after kainate-induced excitotoxic injury (Guan et al. [2006] FASEB J 20:1152-1161). In this study, we showed increased expression of serine palmitoyltransferase (SPT), the first enzyme in the ceramide biosynthetic pathway, in reactive astrocytes of the hippocampus after kainate injections. The increase in enzyme expression was paralleled by increased SPT enzyme activity in the hippocampus at 2 weeks post-kainate injection. In vitro studies showed that treatment of hippocampal slice cultures with SPT inhibitor ISP-1 (myriocin) or L-cycloserine modulated increases in 16:0, 18:0, and 20:0 ceramide species, and partially reduced kainate-induced cell death. The above findings indicate a role of SPT in ceramide increase after kainate injury, although additional effects of sphingomyelinase cannot be ruled out. They also suggest that SPT activity might contribute to neuronal injury after kainate excitotoxicity.

N-tosyl-l-phenylalanyl-chloromethyl ketone reduces ceramide during hypoxic–ischemic brain injury in newborn rat

N-tosyl-L-phenylalanyl-chloromethyl ketone (TPCK) suppresses apoptosis and protects neurons from damage in animal models. TPCK is thought to act by inhibiting ceramide production by sphingomyelinase. Ceramide is a proapoptotic intracellular signal that is involved in the cerebral ischemia. We wished to see whether ceramide contributes to TPCK's neuroprotective effects in vivo. Seven-day-old rat pups had the right carotid arteries permanently ligated followed by 2.5 h of hypoxia (8% oxygen). TPCK (10 mg/kg, n=62) or vehicle (n=63) was administered by i.p. 5 min prior to hypoxia. The level of ceramide in brain cortex both in lesioned and unlesioned hemispheres was measured at 8 h, 18 h, 24 h, 2 and 5 days after hypoxia-ischemia using reversed phase high performance liquid chromatography. The level of ceramide significantly increased due to hypoxic-ischemia at 18, 24 h and 2 days after hypoxia (P<0.05 or P<0.01) but not at 8 h or 5 days after hypoxia as compared to the contralateral hemisphere or a sham group. Pretreatment with TPCK reduced this increase. We also examined the level of sphingomyelin and the activities of the ceramide synthesizing sphingomyelinase enzymes by thin layer chromatography. The activities of acidic and neutral sphingomyelinase significantly increased due to hypoxic ischemia at 24 h after hypoxia. TPCK significantly reduced this increase (P<0.05 vs. vehicle) but did not affect the level of sphingomyelin. The results are consistent with the hypothesis that ceramide is involved in TPCK's neuroprotective effects in hypoxic-ischemic brain injury in the newborn rat.

Inhibitory effect of sesaminol glucosides on lipopolysaccharide-induced NF-κB activation and target gene expression in cultured rat astrocytes

The inflammatory reaction plays an important role in the pathogenesis of the neurodegenerative disorder including Alzheimer's disease (AD). Sesame lignan compounds such as sesaminol glucosides (SG) exhibit a range of pharmacological activities including anti-oxidative and anti-inflammatory action. In this study, we tried to elucidate possible effects of SG on lipopolysaccharide (LPS)-induced inflammatory reaction and its underlying mechanism in cultured astrocytes. SG (10-100 microg/ml) inhibited LPS-induced generation of nitric oxide (NO) and reactive oxygen species (ROS), as well as inhibited LPS-induced cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) expression dose-dependently. This inhibitory effect of SG on NO and ROS generation was enforced by addition of glutathione (GSH) in culture. In addition, SG prevented LPS-induced DNA binding and transcriptional activity of nuclear factor KappaB (NF)-kappaB. Consistent with the inhibitory effect on NF-kappaB activity, SG inhibits phosphorylation and degradation of inhibitory KappaB (IkappaB), thereby translocation of p50 of NF-kappaB. These data show that SG has an anti-inflammatory effect through inhibition of NF-kappaB, and may be a useful agent for prevention of inflammatory disease like AD.

Astroglial expression of ceramide in Alzheimer's disease brains: a role during neuronal apoptosis

Accumulating evidences indicate that ceramide is closely involved in apoptotic cell death in neurodegenerative disorders and aging. We examined ceramide levels in the cerebrospinal fluid (CSF) or brain tissues from patients with neurodegenerative disorders and the mechanism of how intra- and extracellular ceramide was regulated during neuronal apoptosis. We screened the ceramide levels in the CSF of patients with neurodegenerative disorders, and found that ceramide was significantly increased in patients with Alzheimer's disease (AD) than in patients with age-matched amyotrophic lateral sclerosis (ALS) and other neurological controls. With immunohistochemistry in AD brains, ceramide was aberrantly expressed in astroglia in the frontal cortices, but not detected in ALS and control brains. To explore for the regulation of ceramide in astroglia in Alzheimer's disease brains, we examined the metabolism of ceramide during neuronal apoptosis. In retinoic acid (RA)-induced neuronal apoptosis, RA slightly increased de novo synthesis of ceramide, but interestingly, RA dramatically inhibited conversion of [14C] ceramide to glucosylceramide (GlcCer), suggesting that the increase of ceramide mass is mainly due to inhibition of the ceramide-metabolizing enzyme GlcCer synthase. In addition, a significant increase of the [14C] ceramide level in the culture medium was detected by chasing and turnover experiments without alteration of extracellular [14C] sphingomyelin levels. A 2.5-fold increase of ceramide mass in the supernatant was also detected after 48 h of treatment with RA. These results suggest a regulatory mechanism of intracellular ceramide through inhibition of GlcCer synthase and a possible role of ceramide as an extracellular/intercellular mediator for neuronal apoptosis. The increased ceramide level in the CSF from AD patients, which may be derived from astroglia, raises a possibility of neuronal apoptosis by the response to intercellular ceramide in AD.