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

Subcellular imaging of lipids and sugars using genetically encoded proximity sensors

Live cell imaging of lipids and other metabolites is a long-standing challenge in cell biology. Bioorthogonal labeling tools allow for the conjugation of fluorophores to several phospholipid classes, but cannot discern their trafficking between adjacent organelles or asymmetry across individual membrane leaflets. Here we present fluorogen-activating coincidence sensing (FACES), a chemogenetic tool capable of quantitatively imaging subcellular lipid pools and reporting their transbilayer orientation in living cells. FACES combines bioorthogonal chemistry with genetically encoded fluorogen-activating proteins (FAPs) for reversible proximity sensing of conjugated molecules. We first validate this approach for quantifying discrete phosphatidylcholine pools in the ER and mitochondria that are trafficked by lipid transfer proteins. We then show that transmembrane domain-containing FAPs can be used to reveal the membrane asymmetry of multiple lipid classes that are generated in the trans-Golgi network. Lastly, we demonstrate that FACES is a generalizable tool for subcellular bioorthogonal imaging by measuring changes in mitochondrial N -acetylhexosamine levels. These results demonstrate the use of fluorogenic tags for spatially-defined molecular imaging.

Does mask wearing affect skin health? An untargeted skin metabolomics study

Wearing masks is used as an effective way to prevent the spread of viruses. However, the effect of wearing masks on skin health requires further assessment. In this study, a non-invasive D-squame sampling method coupled with an untargeted metabolomics analysis by liquid chromatography high-resolution mass spectrometry was developed to identify the changes in the skin metabolome caused by wearing masks. D-squame method was found to have advantages over the commonly used sterile gauze method, especially for the lipids and lipid-like molecules. A total of 356 skin metabolites were putatively identified from the stratum corneum of 10 volunteers, and 17 differential metabolites were significantly downregulated after wearing surgical masks or N95 respirators. The downregulation of metabolites such as phosphatidylethanolamine and sphingomyelin might be related to hypoxia or increased skin moisture caused by wearing masks. Changes in skin metabolomics indicated a potential risk of skin barrier disruption and skin inflammation. Intermittent removal of the masks can effectively alleviate changes in the skin metabolome.

Analysis of glycerophospholipid metabolism after exposure to PCB153 in PC12 cells through targeted lipidomics by UHPLC-MS/MS

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that have neurotoxicity, reproductive toxicity, hepatotoxicity and immunotoxicity in both animals and humans. Few studies have focused on the changes to endogenous glycerophospholipid metabolism caused by PCB153. To evaluate the relationships between exposure to PCB153 and specific endogenous glycerophospholipid metabolism, an ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was implemented in this study. Twenty-two endogenous glycerophospholipids in PC12 cells were analyzed after exposure to PCB153 at dosages of 0.05 μg mL^-1, 0.5 μg mL^-1 or 20 μg mL^-1 for 120 h. PC(14:0/14:0), PE(16:0/18:1), PE(16:0/18:2), PS(18:0/18:1) and PI(16:0/18:1) were identified as potential biomarkers under the rules of t-test (P) value < 0.05 and variable importance at projection (VIP) value > 1. It was also found that the alterations at 0.05 μg mL^-1 and 20 μg mL^-1 PCB153 were similar at 120 h, while 0.5 μg mL^-1 PCB153 presented an opposite trend. Additionally, significant upregulation of PC, PE and PS with the same fatty acid chains of 18:0/18:2 was found after exposure to 0.05 μg mL^-1 and 20 μg mL^-1 PCB153 at 120 h. This study revealed that PCB153 exposure modulated 22 endogenous glycerophospholipids in PC12 cells and provided the basis for the further study of PCB153 on the effects of glycerophospholipids on PC12 cells.

Vitexin protects against hypoxic-ischemic injury via inhibiting Ca2+/Calmodulin-dependent protein kinase II and apoptosis signaling in the neonatal mouse brain

Neonatal hypoxic-ischemic is a major cause of death and disability in neonates. In this study, we suggest for the first time that pretreatment with vitexin may suppress a pro-apoptotic signaling pathway in hypoxic-ischemic neuronal injury in neonates by inhibition of the phosphorylation of Ca²⁺/Calmodulin-dependent protein kinase II. Here we found that vitexin pretreatment reduced brain infarct volume in a dose-dependent manner. In addition, vitexin decreased the number of TUNEL-positive cells and brain atrophy. Furthermore, vitexin improved neurobehavioral outcomes. Vitexin also reduced oxygen glucose deprivation-induced neuronal injury and calcium entry. Vitexin pretreatment increased the Bcl-2/Bax protein ratio and decreased phosphorylation of Ca²⁺/Calmodulin-dependent protein kinase II and NF-κB, cleaved caspase-3 protein expression 24 hours after injury. Our data indicate that pretreatment with vitexin protects against neonatal hypoxic-ischemic brain injury and thus has potential as a treatment for hypoxic-ischemic brain injury.

Inhibition of sphingomyelin synthase 1 affects ceramide accumulation and hydrogen peroxide-induced apoptosis in Neuro-2a cells

Oxidative stress plays a key role in brain injury after cerebral ischemia-reperfusion, which contributes toward excessive apoptosis of nerve cells. Therefore, it would be beneficial to identify a therapy that could interfere with the progression of apoptosis and protect the brain from ischemia-reperfusion injury. As ceramide, a well-known second messenger of apoptosis, can be metabolized by sphingomyelin synthase 1 (SMS1), recent research has focused on the link between SMS1 and apoptosis in different cells. To investigate whether SMS1 is involved in the process of oxidative stress-induced apoptosis in neurons and to explore the possible underlying mechanism, we treated mouse neuroblastoma Neuro-2A (N2a) cells with hydrogen peroxide (H2O2). Incubation with H2O2 significantly upregulated the expression of SMS1, increased the intracellular levels of ceramide and sphingomyelin synthase activity, and induced apoptosis. Moreover, pretreatment of N2a cells with D609, an sphingomyelin synthase inhibitor, or SMS1-silencing RNA (siRNA) further increased ceramide and potentiated H2O2-induced apoptosis which could be reversed by SB203580 (a p38 inhibitor). Thus, our study has shown that SMS1 regulates ceramide levels in N2a cells and plays a potent protective role in this oxidative stress-induced apoptosis partly through the p38 pathway.

Application of nanostructured lipid carriers: the prolonged protective effects for sesamol in in vitro and in vivo models of ischemic stroke via activation of PI3K signalling pathway

BACKGROUND

Treatment of the ischemic stroke has remained a major healthcare challenge. The phenolic compound, sesamol, has shown promising antioxidant and neuroprotective effects, however, fast clearance may negatively affect its efficiency. This, prompted us to incorporate sesamol into the nanostructured lipid carriers (S-NLCs) and evaluate its therapeutic potential in in vitro and in vivo models of ischemic stroke.

METHODS

S-NLCs formulations were prepared by high-pressure homogenization followed by physicochemical characterization, evaluation of the bioactivity of the optimal formulation in oxygen-glucose deprivation (OGD) and global cerebral ischemia/reperfusion (I/R) injury and implication of phosphatidylinositol 3-kinase (PI3K) pathway in this regard. Two- or three-way ANOVA, Mann-Whitney U test, and Student's t-test were used for data analysis.

RESULTS

Formation of S-NLCs which exhibited a controlled release profile, was confirmed by scanning electron microscope and differential scanning calorimetry. 1- and 8-h OGD followed by 24 h re-oxygenation significantly reduced PC12 cell viability, increased lactate dehydrogenase activity and the number of condensed nuclei, and induced oxidative stress as revealed by increased malondialdehyde level and decreased glutathione content and superoxide dismutase and catalase activities. Sesamol (80 and 100 μM) reduced the cytotoxicity, oxidative stress, and cellular damage only after 1-h OGD, while, S-NLCs (containing 80 and 100 μM of sesamol) were effective at both time points. Intravenous injections of S-NLCs (20 and 25 mg/kg) into rats markedly attenuated I/R-induced neurobehavioural deficits, cellular damage, and oxidative stress, while, free sesamol failed. Pre-treatment with PI3K inhibitor, LY294002, abolished the protective effects against OGD or I/R.

CONCLUSIONS

S-NLCs improve the pharmacological profile of sesamol and provide longer lasting protective effects for this phenolic phytochemical. This nanoformulation by activating PI3K pathway may serve as a promising candidate for neuroprotection against the cerebral stroke or other neurodegenerative disorders. Sesamol-loaded NLCs, a promising nanoformulation against the ischemic stroke.

Ferulic acid-loaded nanostructured lipid carriers: A promising nanoformulation against the ischemic neural injuries

AIMS

Treatment of the ischemic stroke has remained a major healthcare challenge. The phenolic compound, ferulic acid (FA), has shown promising antioxidant and neuroprotective effects, however, low bioavailability may negatively affect its efficiency. This, prompted us to incorporate FA into the nanostructured lipid carriers (FA-NLCs) and evaluate its therapeutic potential in in vitro and in vivo models of ischemic stroke.

MAIN METHODS

FA-NLCs were prepared by high-pressure homogenization followed by physicochemical characterization, evaluation of the bioactivity of FA-NLCs in oxygen-glucose deprivation (OGD) and global cerebral ischemia/reperfusion (I/R) injury and implication of phosphatidylinositol 3-kinase (PI3K) pathway in this regard.

KEY FINDINGS

Formation of FA-NLCs which exhibited a controlled release profile, was confirmed by scanning electron microscope and differential scanning calorimetry. 1- and 8-h OGD followed by 24h re-oxygenation significantly reduced PC12 cell viability, increased lactate dehydrogenase activity and number of condensed nuclei, and induced oxidative stress as revealed by increased malondialdehyde and decreased glutathione content and superoxide dismutase and catalase activities. FA (80 and 100μM) reduced the cytotoxicity, oxidative stress, and cellular damage only after 1-h OGD, while, FA-NLCs (containing 80 and 100μM of FA) were effective at both time points. Intravenous injections of FA-NLCs (20 and 25mg/kg) into rats significantly attenuated I/R-induced neurobehavioural deficits, cellular damage, and oxidative stress, while, FA failed. Pre-treatment with PI3K inhibitor, LY294002, abolished the protective effects against OGD or I/R.

SIGNIFICANCE

FA-NLCs by improving the pharmacological profile of FA and activating PI3K pathway might be of therapeutic value in cerebral stroke.

Electronic structure determination using an assembly of conventional and synchrotron techniques: The case of a xanthate complex

The electronic properties of the coordination complex nickel (II) bis-n-propylxanthate, Ni(CH₃(CH₂)₂OC(S)S)₂, were studied by a combination of complementary experimental (both laboratory and synchrotron based techniques) and theoretical methods. Energy differences between HOMOs and LUMOs were determined from UV-visible spectroscopy. The assignment of the transitions were performed with the aid of TD-DFT calculations and based in symmetry considerations. The analysis of the Raman excitation profiles of selected vibrational modes of the complex, taken in resonance with a particular electronic transition, was found to reinforce the electronic assignment. Experimental binding energies of inner and core electrons were determined by PES measurements. Ni K-edge, S K-edge, Ni L-edge, O K-edge and C K-edge XANES spectra were interpreted in terms of the promotion of core electrons to unoccupied electronic levels. An experimental quantitative molecular orbital diagram was constructed using the information extracted from the different techniques.

The effects of NONRATT021972 lncRNA siRNA on PC12 neuronal injury mediated by P2X7 receptor after exposure to oxygen-glucose deprivation

Adenosine triphosphate (ATP) participates in signal transmission by acting on P2X receptors, and the P2X7 receptor is involved in the pathophysiological changes of ischemic injury. The PC12 cell line is a popular model system to study sympathetic neuronal function. Long noncoding RNAs (lncRNAs) are highly expressed in the nervous system and serve as regulatory RNAs. In this study, the effects of NONRATT021972 lncRNA siRNA on P2X7-mediated PC12 neuronal injury after exposure to oxygen-glucose deprivation (OGD) were investigated. Our results showed that the viability of PC12 cells cultured with OGD or the P2X7 agonist BzATP was significantly decreased. Treatment with NONRATT021972 siRNA reversed the decreased viability of PC12 cells under OGD conditions. The upregulated P2X7 mRNA and protein levels in PC12 cells under OGD conditions or BzATP treatment were significantly decreased when pretreated with NONRATT021972 siRNA. Moreover, NONRATT021972 siRNA treatment effectively suppressed the increase in [Ca(2+)]i induced by OGD or P2X7 agonists (ATP or BzATP) in PC12 cells. Therefore, treatment with NONRATT021972 siRNA may decrease sympathetic neuronal injury induced by ischemia.

Host sphingomyelin increases West Nile virus infection in vivo

Flaviviruses, such as the dengue virus and the West Nile virus (WNV), are arthropod-borne viruses that represent a global health problem. The flavivirus lifecycle is intimately connected to cellular lipids. Among the lipids co-opted by flaviviruses, we have focused on SM, an important component of cellular membranes particularly enriched in the nervous system. After infection with the neurotropic WNV, mice deficient in acid sphingomyelinase (ASM), which accumulate high levels of SM in their tissues, displayed exacerbated infection. In addition, WNV multiplication was enhanced in cells from human patients with Niemann-Pick type A, a disease caused by a deficiency of ASM activity resulting in SM accumulation. Furthermore, the addition of SM to cultured cells also increased WNV infection, whereas treatment with pharmacological inhibitors of SM synthesis reduced WNV infection. Confocal microscopy analyses confirmed the association of SM with viral replication sites within infected cells. Our results unveil that SM metabolism regulates flavivirus infection in vivo and propose SM as a suitable target for antiviral design against WNV.

The role of P2X7 receptor in PC12 cells after exposure to oxygen-glucose deprivation

Adenosine triphosphate (ATP) plays an important role in signal transmission via acting on P2X receptors. P2X7 receptor is involved in pathophysiological changes of ischemic diseases. The PC12 cell line is a popular model system to study sympathetic neuronal function. In this study, the effects of P2X7 on the viability or [Ca(2+)]i in PC12 cells after exposure to oxygen-glucose deprivation (OGD) were investigated. The results showed that the viability of PC12 cells was decreased under the condition of OGD. BzATP, a P2X7 agonist, decreased the viability, while P2X7 antagonist oxATP or P2X7 siRNA reversed the viability of PC12 cells under the condition of OGD. The expression levels of P2X7 mRNA and protein in PC12 cells were up-regulated under the condition of OGD or BzATP treatment. The expression levels of P2X7 mRNA and protein were significantly decreased in OGD PC12 cells, which were pretreated with oxATP or P2X7 siRNA. It was also found that oxATP or P2X7 siRNA effectively suppressed the increase of [Ca(2+)]i induced by OGD. P2X7 agonist ATP or BzATP enhanced the [Ca(2+)]i rise induced by OGD in PC12 cells. The [Ca(2+)]i peak induced by ATP or BzATP in OGD group was decreased by ERK inhibitor U0126. Therefore, P2X7 antagonists or P2X7 siRNA could depress the sympathetic neuronal damage induced by ischemia.

Cinepazide maleate protects PC12 cells against oxygen-glucose deprivation-induced injury

Our previous study showed that cinepazide maleate (CM) was as effective and safe as mildronate in the treatment of acute ischemic stroke in a randomized, double-blind, active-controlled phase II multicenter trial, but underlying mechanism(s) is not well understood. As an extending study, here we demonstrated that CM could protect neuronal cells by affecting mitochondrial functions. PC12 cells were exposed to 2.5 h oxygen-glucose deprivation (OGD) followed by a 24 h reoxygenation, and then treated with different concentrations (1, 10, 100 μM) of CM. Among various concentrations, 10 μM CM exhibited most significant protection on PC12 cells against OGD injury. CM was found to suppress OGD-induced oxidative stress, as supported by its capability of reducing intracellular reactive oxygen species and malondialdehyde production and enhancing superoxide dismutase activity. Importantly, our results showed that CM could preserve mitochondrial functions, as revealed by its capability of stabilizing mitochondrial membrane potential, improving OGD-induced suppression of mitochondrial respiratory complex activities and enhancing ATP production. In summary, our present study provides the first evidence that CM can protect neuronal cells against OGD injury by preserving mitochondrial functions.

Anti-proliferative effects of tricyclodecan-9-yl-xanthogenate (D609) involve ceramide and cell cycle inhibition

Tricyclodecan-9-yl-xanthogenate (D609) inhibits phosphatidylcholine (PC)-phospholipase C (PLC) and/or sphingomyelin (SM) synthase (SMS). Inhibiting SMS can increase ceramide levels, which can inhibit cell proliferation. Here, we examined how individual inflammatory and glia cell proliferation is altered by D609. Treatment with 100-μM D609 significantly attenuated the proliferation of RAW 264.7 macrophages, N9 and BV-2 microglia, and DITNC(1) astrocytes, without affecting cell viability. D609 significantly inhibited BrdU incorporation in BV-2 microglia and caused accumulation of cells in G(1) phase with decreased number of cells in the S phase. D609 treatment for 2 h significantly increased ceramide levels in BV-2 microglia, which, following a media change, returned to control levels 22 h later. This suggests that the effect of D609 may be mediated, at least in part, through ceramide increase via SMS inhibition. Western blots demonstrated that 2-h treatment of BV-2 microglia with D609 increased expression of the cyclin-dependent kinase (Cdk) inhibitor p21 and down-regulated phospho-retinoblastoma (Rb), both of which returned to basal levels 22 h after removal of D609. Exogenous C8-ceramide also inhibited BV-2 microglia proliferation without loss of viability and decreased BrdU incorporation, supporting the involvement of ceramide in D609-mediated cell cycle arrest. Our current data suggest that D609 may offer benefit after stroke (Adibhatla and Hatcher, Mol Neurobiol 41:206-217, 2010) through ceramide-mediated cell cycle arrest, thus restricting glial cell proliferation.

Tricyclodecan-9-yl-xanthogenate (D609) mechanism of actions: a mini-review of literature

Tricyclodecan-9-yl-xanthogenate (D609) is known for its antiviral and antitumor properties. D609 actions are widely attributed to inhibiting phosphatidylcholine (PC)-specific phospholipase C (PC-PLC). D609 also inhibits sphingomyelin synthase (SMS). PC-PLC and/or SMS inhibition will affect lipid second messengers 1,2-diacylglycerol (DAG) and/or ceramide. Evidence indicates either PC-PLC and/or SMS inhibition affected the cell cycle and arrested proliferation, and stimulated differentiation in various in vitro and in vivo studies. Xanthogenate compounds are also potent antioxidants and D609 reduced Aß-induced toxicity, attributed to its antioxidant properties. Zn²⁺ is necessary for PC-PLC enzymatic activity; inhibition by D609 might be attributed to its Zn²⁺ chelation. D609 has also been proposed to inhibit acidic sphingomyelinase or down-regulate hypoxia inducible factor-1α; however these are down-stream events related to PC-PLC inhibition. Characterization of the mammalian PC-PLC is limited to inhibition of enzymatic activity (frequently measured using Amplex red assay with bacterial PC-PLC as a standard). The mammalian PC-PLC has not been cloned; sequenced and structural information is unavailable. D609 showed promise in cancer studies, reduced atherosclerotic plaques (inhibition of PC-PLC) and cerebral infarction after stroke (PC-PLC or SMS). D609 actions as an antagonist to pro-inflammatory cytokines have been attributed to PC-PLC. The purpose of this review is to comprehensively evaluate the literature and summarize the findings and relevance to cell cycle and CNS pathologies.

Proteases inhibition assessment on PC12 and NGF treated cells after oxygen and glucose deprivation reveals a distinct role for aspartyl proteases

Hypoxia is a severe stressful condition and induces cell death leading to neuronal loss both to the developing and adult nervous system. Central theme to cellular death is the activation of different classes of proteases such as caspases calpains and cathepsins. In the present study we investigated the involvement of these proteases, in the hypoxia-induced PC12 cell death. Rat PC12 is a model cell line for experimentation relevant to the nervous system and several protocols have been developed for either lethal hypoxia (oxygen and glucose deprivation OGD) or ischemic preconditioning (IPS). Nerve Growth Factor (NGF) treated PC12 differentiate to a sympathetic phenotype, expressing neurites and excitability. Lethal hypoxia was established by exposing undifferentiated and NGF-treated PC12 cells to a mixture of N₂/CO₂ (93:5%) in DMEM depleted of glucose and sodium pyruvate for 16 h. The involvement of caspases, calpains and lysosomal cathepsins D and E to the cell death induced by lethal OGD was investigated employing protease specific inhibitors such as z-VAD-fmk for the caspases, MDL28170 for the calpains and pepstatin A for the cathepsins D and E. Our findings show that pepstatin A provides statistically significant protection from cell death of both naive and NGF treated PC12 cells exposed to lethal OGD. We propose that apart from the established processes of apoptosis and necrosis that are integral components of lethal OGD, the activation of cathepsins D and E launches additional cell death pathways in which these proteases are key partners.

The role of phospholipase D in osteoblast response to titanium surface microstructure

Biomaterial surface properties such as microtopography and energy can change cellular responses at the cell-implant interface. Phospholipase D (PLD) is required for the differentiation of osteoblast-like MG63 cells on machined and grit-blasted titanium surfaces. Here, we determined if PLD is also required on microstructured/high-energy substrates and the mechanism involved. shRNAs for human PLD1 and PLD2 were used to silence MG63 cells. Wild-type and PLD1 or PLD1/2 silenced cells were cultured on smooth-pretreatment surfaces (PT); grit-blasted, acid-etched surfaces (SLA); and SLA surfaces modified to have higher surface energy (modSLA). PLD was inhibited with ethanol or activated with 24,25-dihydroxyvitamin-D(3) [24R,25(OH)(2)D(3)]. As surface roughness/energy increased, PLD mRNA and activity increased, cell number decreased, osteocalcin and osteoprotegerin increased, and protein kinase C (PKC) and alkaline phosphatase specific activities increased. Ethanol inhibited PLD and reduced surface effects on these parameters. There was no effect on these parameters after knockdown of PLD1, but PLD1/2 double knockdown had effects comparableto PLD inhibition. 24R,25(OH)(2)D(3) increased PLD activity and the production of osteocalcin and osteoprotegerin, but decreased cell number on the rough/high-energy surfaces. These results confirm that surface roughness/energy-induced PLD activity is required for osteoblast differentiation and that PLD2 is the main isoform involved in this pathway. PLD is activated by 24R,25(OH)(2)D(3) in a surface-dependent manner and inhibition of PLD reduces the effects of surface microstructure/energy on PKC, suggesting that PLD mediates the stimulatory effect of microstructured/high-energy surfaces via PKC-dependent signaling.

Plant phosphatidylcholine-hydrolyzing phospholipases C NPC3 and NPC4 with roles in root development and brassinolide signaling in Arabidopsis thaliana

Phosphatidylcholine-hydrolyzing phospholipase C (PC-PLC) catalyzes the hydrolysis of phosphatidylcholine (PC) to generate phosphocholine and diacylglycerol (DAG). PC-PLC has a long tradition in animal signal transduction to generate DAG as a second messenger besides the classical phosphatidylinositol splitting phospholipase C (PI-PLC). Based on amino acid sequence similarity to bacterial PC-PLC, six putative PC-PLC genes (NPC1 to NPC6) were identified in the Arabidopsis genome. RT-PCR analysis revealed overlapping expression pattern of NPC genes in root, stem, leaf, flower, and silique. In auxin-treated P(NPC3):GUS and P(NPC4):GUS seedlings, strong increase of GUS activity was visible in roots, leaves, and shoots and, to a weaker extent, in brassinolide-treated (BL) seedlings. P(NPC4):GUS seedlings also responded to cytokinin with increased GUS activity in young leaves. Compared to wild-type, T-DNA insertional knockouts npc3 and npc4 showed shorter primary roots and lower lateral root density at low BL concentrations but increased lateral root densities in response to exogenous 0.05-1.0 μM BL. BL-induced expression of TCH4 and LRX2, which are involved in cell expansion, was impaired but not impaired in repression of CPD, a BL biosynthesis gene, in BL-treated npc3 and npc4. These observations suggest NPC3 and NPC4 are important in BL-mediated signaling in root growth. When treated with 0.1 μM BL, DAG accumulation was observed in tobacco BY-2 cell cultures labeled with fluorescent PC as early as 15 min after application. We hypothesize that at least one PC-PLC is a plant signaling enzyme in BL signal transduction and, as shown earlier, in elicitor signal transduction.

Protection by D609 through cell-cycle regulation after stroke

Expressions of cell-cycle regulating proteins are altered after stroke. Cell-cycle inhibition has shown dramatic reduction in infarction after stroke. Ceramide can induce cell-cycle arrest by up-regulation of cyclin-dependent kinase (Cdk) inhibitors p21 and p27 through activation of protein phosphatase 2A (PP2A). Tricyclodecan-9-yl-xanthogenate (D609)-increased ceramide levels after transient middle cerebral artery occlusion (tMCAO) in spontaneously hypertensive rat (SHR) probably by inhibiting sphingomyelin synthase (SMS). D609 significantly reduced cerebral infarction and up-regulated Cdk inhibitor p21 and down-regulated phospho-retinoblastoma (pRb) expression after tMCAO in rat. Others have suggested bFGF-induced astrocyte proliferation is attenuated by D609 due to an increase in ceramide by SMS inhibition. D609 also reduced the formation of oxidized phosphatidylcholine (OxPC) protein adducts. D609 may attenuate generation of reactive oxygen species and formation of OxPC by inhibiting microglia/macrophage proliferation after tMCAO (please also see note added in proof: D609 may prevent mature neurons from entering the cell cycle at the early reperfusion, however may not interfere with later proliferation of microglia/ macrophages that are the source of brain derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF-1) in offering protection). It has been proposed that D609 provides benefit after tMCAO by attenuating hypoxia-inducible factor-1alpha and Bcl2/adenovirus E1B 19 kDa interacting protein 3 expressions. Our data suggest that D609 provides benefit after stoke through inhibition of SMS, increased ceramide levels, and induction of cell-cycle arrest by up-regulating p21 and causing hypophosphorylation of Rb (through increased protein phosphatase activity and/or Cdk inhibition).

Lipid oxidation and peroxidation in CNS health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) are produced at low levels in mammalian cells by various metabolic processes, such as oxidative phosphorylation by the mitochondrial respiratory chain, NAD(P)H oxidases, and arachidonic acid oxidative metabolism. To maintain physiological redox balance, cells have endogenous antioxidant defenses regulated at the transcriptional level by Nrf2/ARE. Oxidative stress results when ROS production exceeds the cell's ability to detoxify ROS. Overproduction of ROS damages cellular components, including lipids, leading to decline in physiological function and cell death. Reaction of ROS with lipids produces oxidized phospholipids, which give rise to 4-hydroxynonenal, 4-oxo-2-nonenal, and acrolein. The brain is susceptible to oxidative damage due to its high lipid content and oxygen consumption. Neurodegenerative diseases (AD, ALS, bipolar disorder, epilepsy, Friedreich's ataxia, HD, MS, NBIA, NPC, PD, peroxisomal disorders, schizophrenia, Wallerian degeneration, Zellweger syndrome) and CNS traumas (stroke, TBI, SCI) are problems of vast clinical importance. Free iron can react with H(2)O(2) via the Fenton reaction, a primary cause of lipid peroxidation, and may be of particular importance for these CNS injuries and disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Atherosclerosis, the major risk factor for ischemic stroke, involves accumulation of oxidized LDL in the arteries, leading to foam cell formation and plaque development. This review will discuss the role of lipid oxidation/peroxidation in various CNS injuries/disorders.

Ceramide generated by sphingomyelin hydrolysis and the salvage pathway is involved in hypoxia/reoxygenation-induced Bax redistribution to mitochondria in NT-2 cells

Ceramide functions as an important second messenger in apoptosis signaling pathways. In this report, we show that treatment of NT-2 neuronal precursor cells with hypoxia/reoxygenation (H/R) resulted in ceramide up-regulation. This elevation in ceramide was primarily due to the actions of acid sphingomyelinase and ceramide synthase LASS 5, demonstrating the action of the salvage pathway. Hypoxia/reoxygenation treatment led to Bax translocation from the cytoplasm to mitochondria and cytochrome c release from mitochondria. Down-regulation of either acid sphingomyelinase or LASS 5-attenuated ceramide accumulation and H/R-induced Bax translocation to mitochondria. Overall, we have demonstrated that ceramide up-regulation following H/R is pertinent to Bax activation to promote cell death.

Altered lipid metabolism in brain injury and disorders

Deregulated lipid metabolism may be of particular importance for CNS injuries and disorders, as this organ has the highest lipid concentration next to adipose tissue. Atherosclerosis (a risk factor for ischemic stroke) results from accumulation of LDL-derived lipids in the arterial wall. Pro-inflammatory cytokines (TNF-alpha and IL-1), secretory phospholipase A2 IIA and lipoprotein-PLA2 are implicated in vascular inflammation. These inflammatory responses promote atherosclerotic plaques, formation and release of the blood clot that can induce ischemic stroke. TNF-alpha and IL-1 alter lipid metabolism and stimulate production of eicosanoids, ceramide, and reactive oxygen species that potentiate CNS injuries and certain neurological disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Low levels of neurosteroids were related to poor outcome in many brain pathologies. Apolipoprotein E is the principal cholesterol carrier protein in the brain, and the gene encoding the variant Apolipoprotein E4 is a significant risk factor for Alzheimer's disease. Parkinson's disease is to some degree caused by lipid peroxidation due to phospholipases activation. Niemann-Pick diseases A and B are due to acidic sphingomyelinase deficiency, resulting in sphingomyelin accumulation, while Niemann-Pick disease C is due to mutations in either the NPC1 or NPC2 genes, resulting in defective cholesterol transport and cholesterol accumulation. Multiple sclerosis is an autoimmune inflammatory demyelinating condition of the CNS. Inhibiting phospholipase A2 attenuated the onset and progression of experimental autoimmune encephalomyelitis. The endocannabinoid system is hypoactive in Huntington's disease. Ethyl-eicosapetaenoate showed promise in clinical trials. Amyotrophic lateral sclerosis causes loss of motorneurons. Cyclooxygenase-2 inhibition reduced spinal neurodegeneration in amyotrophic lateral sclerosis transgenic mice. Eicosapentaenoic acid supplementation provided improvement in schizophrenia patients, while the combination of (eicosapentaenoic acid + docosahexaenoic acid) provided benefit in bipolar disorders. The ketogenic diet where >90% of calories are derived from fat is an effective treatment for epilepsy. Understanding cytokine-induced changes in lipid metabolism will promote novel concepts and steer towards bench-to-bedside transition for therapies.

Altered lipid metabolism in brain injury and disorders

Deregulated lipid metabolism may be of particular importance for CNS injuries and disorders, as this organ has the highest lipid concentration next to adipose tissue. Atherosclerosis (a risk factor for ischemic stroke) results from accumulation of LDL-derived lipids in the arterial wall. Pro-inflammatory cytokines (TNF-alpha and IL-1), secretory phospholipase A2 IIA and lipoprotein-PLA2 are implicated in vascular inflammation. These inflammatory responses promote atherosclerotic plaques, formation and release of the blood clot that can induce ischemic stroke. TNF-alpha and IL-1 alter lipid metabolism and stimulate production of eicosanoids, ceramide, and reactive oxygen species that potentiate CNS injuries and certain neurological disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Low levels of neurosteroids were related to poor outcome in many brain pathologies. Apolipoprotein E is the principal cholesterol carrier protein in the brain, and the gene encoding the variant Apolipoprotein E4 is a significant risk factor for Alzheimer's disease. Parkinson's disease is to some degree caused by lipid peroxidation due to phospholipases activation. Niemann-Pick diseases A and B are due to acidic sphingomyelinase deficiency, resulting in sphingomyelin accumulation, while Niemann-Pick disease C is due to mutations in either the NPC1 or NPC2 genes, resulting in defective cholesterol transport and cholesterol accumulation. Multiple sclerosis is an autoimmune inflammatory demyelinating condition of the CNS. Inhibiting phospholipase A2 attenuated the onset and progression of experimental autoimmune encephalomyelitis. The endocannabinoid system is hypoactive in Huntington's disease. Ethyl-eicosapetaenoate showed promise in clinical trials. Amyotrophic lateral sclerosis causes loss of motorneurons. Cyclooxygenase-2 inhibition reduced spinal neurodegeneration in amyotrophic lateral sclerosis transgenic mice. Eicosapentaenoic acid supplementation provided improvement in schizophrenia patients, while the combination of (eicosapentaenoic acid + docosahexaenoic acid) provided benefit in bipolar disorders. The ketogenic diet where >90% of calories are derived from fat is an effective treatment for epilepsy. Understanding cytokine-induced changes in lipid metabolism will promote novel concepts and steer towards bench-to-bedside transition for therapies.

Role of Lipids in Brain Injury and Diseases

Lipid metabolism is of particular interest due to its high concentration in CNS. The importance of lipids in cell signaling and tissue physiology is demonstrated by many CNS disorders and injuries that involve deregulated metabolism. The long suffering lipid field is gaining reputation and respect as evidenced through the Center of Biomedical Research Excellence in Lipidomics and Pathobiology (COBRE), Lipid MAPS (Metabolites And Pathways Strategy) Consortium sponsored by NIH, European initiatives for decoding the lipids through genomic approaches, and Genomics of Lipid-associated Disorder (GOLD) project initiated by Austrian government. This review attempts to provide an overview of the lipid imbalances associated with neurological disorders (Alzheimer's, Parkinson's; Niemann-Pick; Multiple sclerosis, Huntington, amyotrophic lateral sclerosis, schizophrenia, bipolar disorders and epilepsy) and CNS injury (Stroke, traumatic brain injury; and spinal cord injury) and a few provocative thoughts. Lipidomic analyses along with RNA silencing will provide new insights into the role of lipid intermediates in cell signaling and hopefully open new avenues for prevention or treatment options.