Ceramide signaling in cancer and stem cells

Modulation of Ceramide-Induced Apoptosis in Enteric Neurons by Aryl Hydrocarbon Receptor Signaling: Unveiling a New Pathway beyond ER Stress

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a persistent organic pollutant and a potent aryl hydrocarbon receptor (AHR) ligand, causes delayed intestinal motility and affects the survival of enteric neurons. In this study, we investigated the specific signaling pathways and molecular targets involved in TCDD-induced enteric neurotoxicity. Immortalized fetal enteric neuronal (IM-FEN) cells treated with 10 nM TCDD exhibited cytotoxicity and caspase 3/7 activation, indicating apoptosis. Increased cleaved caspase-3 expression with TCDD treatment, as assessed by immunostaining in enteric neuronal cells isolated from WT mice but not in neural crest cell-specific Ahr deletion mutant mice (Wnt1Cre+/-/Ahrb(fl/fl)), emphasized the pivotal role of AHR in this process. Importantly, the apoptosis in IM-FEN cells treated with TCDD was mediated through a ceramide-dependent pathway, independent of endoplasmic reticulum stress, as evidenced by increased ceramide synthesis and the reversal of cytotoxic effects with myriocin, a potent inhibitor of ceramide biosynthesis. We identified Sptlc2 and Smpd2 as potential gene targets of AHR in ceramide regulation by a chromatin immunoprecipitation (ChIP) assay in IM-FEN cells. Additionally, TCDD downregulated phosphorylated Akt and phosphorylated Ser9-GSK-3β levels, implicating the PI3 kinase/AKT pathway in TCDD-induced neurotoxicity. Overall, this study provides important insights into the mechanisms underlying TCDD-induced enteric neurotoxicity and identifies potential targets for the development of therapeutic interventions.

Supplementation of amylase or amylase + xylanase improves performance and metabolism of broilers fed with diets containing newly harvested maize

How supplementation with amylase or amylase + xylanase in newly harvested maize-based diets affects broiler nutrient metabolism and performance is unclear. Thus, this study evaluated whether the supplementation of amylase (CN) or amylase + xylanase (CAX) improves performance and metabolism of broilers fed with newly harvested maize-based diets during a 6-week production. The results showed that the body weight gain of broilers fed with CA or CAX diet was higher than that with the control (CN) diet at 1-21 d of age; however, an opposite trend was observed for feed/gain (p < 0.05). Furthermore, 150, 64 and 35 different metabolites were found between CA/CN, CAX/CN and CAX/CA, respectively. Overall, amylase supplementation improved broiler growth performance at 1-21 d of age, and the positive effects of amylase on nutrient utilization were mostly related to nicotinate, retinol and glutathione metabolism improvement. Moreover, CAX diet increased apparent metabolizable energy and growth performance of broilers at 22-42 d of age, and the difference might be related to sphingolipid, porphyrin and chlorophyll metabolism regulation. The findings prove amylase + xylanase supplementation is an effective method to improve the nutritional value of newly harvested maize for broilers.

The SIRT1-c-Myc axis in regulation of stem cells

SIRT1 is the most conserved mammalian NAD+-dependent protein deacetylase. Through deacetylation of transcriptional factors and co-factors, this protein modification enzyme is critically involved in metabolic and epigenetic regulation of stem cells, which is functionally important in maintaining their pluripotency and regulating their differentiation. C-Myc, a key member of Myc proton-oncogene family, is a pivotal factor for transcriptional regulation of genes that control acquisition and maintenance of stemness. Previous cancer research has revealed an intriguing positive feedback loop between SIRT1 and c-Myc that is crucial in tumorigenesis. Recent literature has uncovered important functions of this axis in regulation of maintenance and differentiation of stem cells, including pluripotent stem cells and cancer stem cells. This review highlights recent advances of the SIRT1-c-Myc axis in stem cells.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

Metabolomics and Transcriptomics Analysis on Metabolic Characteristics of Oral Lichen Planus

Objective

To explore metabolic biomarkers related to erosive and reticulated oral lichen planus (OLP) by non-targeted metabolomics methods and correlate metabolites with gene expression, and to investigate the pathological network pathways of OLP from the perspective of metabolism.

Methods

A total of 153 individuals were enrolled in this study, including 50 patients with erosive oral lichen planus (EOLP), 51 patients with reticulated oral lichen planus (ROLP), and 52 healthy controls (HC). The ultra-high-performance liquid chromatography quadrupole-Orbitrap high-resolution accurate mass spectrometry (UHPLC/Q-Orbitrap HRMS) was used to analyze the metabolites of 40 EOLP, 40 ROLP, and 40 HC samples, and the differential metabolic biomarkers were screened and identified. The regulatory genes were further screened through the shared metabolites between EOLP and ROLP, and cross-correlated with the OLP-related differential genes in the network database. A “gene-metabolite” network was constructed after finding the key differential genes. Finally, the diagnostic efficiency of the biomarkers was verified in the validation set and a diagnostic model was constructed.

Result

Compared with HC group, a total of 19 and 25 differential metabolites were identified in the EOLP group and the ROLP group, respectively. A total of 14 different metabolites were identified between EOLP and ROLP. Two diagnostic models were constructed based on these differential metabolites. There are 14 differential metabolites shared by EOLP and ROLP. The transcriptomics data showed 756 differentially expressed genes, and the final crossover network showed that 19 differential genes were associated with 12 metabolites. Enrichment analysis showed that alanine, aspartate and glutamate metabolism were closely associated with the pathogenesis of OLP.

Conclusion

The metabolic change of different types of OLP were clarified. The potential gene perturbation of OLP was provided. This study provided a strong support for further exploration of the pathogenic mechanism of OLP.

Preparation of Nitrogen Analogues of Ceramide and Studies of Their Aggregation in Sphingomyelin Bilayers

Ceramides can regulate biological processes probably through the formation of laterally segregated and highly packed ceramide-rich domains in lipid bilayers. In the course of preparation of its analogues, we found that a hydrogen-bond-competent functional group in the C1 position is necessary to form ceramide-rich domains in lipid bilayers [Matsufuji; Langmuir 2018]. Hence, in the present study, we newly synthesized three ceramide analogues: CerN₃, CerNH₂, and CerNHAc, in which the 1-OH group of ceramide is substituted with a nitrogen functionality. CerNH₂ and CerNHAc are capable of forming hydrogen bonds in their headgroups, whereas CerN₃ is not. Fluorescent microscopy observation and differential scanning calorimetry analysis disclosed that these ceramide analogues formed ceramide-rich phases in sphingomyelin bilayers, although their thermal stability was slightly inferior to that of normal ceramides. Moreover, wide-angle X-ray diffraction analysis showed that the chain packing structure of ceramide-rich phases of CerNHAc and CerN₃ was similar to that of normal ceramide, while the CerNH₂-rich phase showed a slightly looser chain packing due to the formation of CerNH₃⁺. Although the domain formation of CerN₃ was unexpected because of the lack of hydrogen-bond capability in the headgroup, it may become a promising tool for investigating the mechanistic link between the ceramide-rich phase and the ceramide-related biological functions owing to its Raman activity and applicability to click chemistry.

Crucial role of glucosylceramide synthase in the regulation of stem cell-like cancer cells in B16F10 murine melanoma

Cancer stem cells render a complex cascade of events that facilitates highly invasive melanoma malignancy. Interplay between immunocytes and cancer stem cells within tumor microenvironment with the participation of sphingolipid signaling mediators skews the immune evasion strategies toward metastatic neoplasm. In this context, we aimed to explore the functional aspect of glucosylceramide synthase (GCS), a key enzyme of sphingolipid biosynthesis in the maintenance of melanoma stem cell-like cancer cells (CSCs). Our findings demonstrated that tumor hypoxia was responsible for elevated GCS expression in melanoma, which was correlated with substantially increased melanoma CSCs. Moreover, hypoxia-induced TGF-β from TAMs and Tregs promoted GCS induction in B16F10 murine melanoma CSCs via PKCα signaling and facilitated the expansion of melanoma CSCs. Interestingly, GCS ablation hindered the immunosuppressiveness of TAMs and Tregs. Therefore, our study for the first time demonstrated a novel paracrine pathway of melanoma CSC maintenance and tumorigenicity, exploiting the bidirectional signaling with immunocytes. Furthermore, our study showed that the combinatorial immunotherapy involving immunomodulators like Mw and DTA-1 repressed CSC pool affecting GCS functions in advanced-stage B16F10 murine melanoma tumor. Moreover, GCS inhibition sensitized conventional chemotherapeutic drug-resistant melanoma CSCs to the genotoxic drugs paving the way toward selective melanoma treatment. Better therapeutic efficacy with inhibition of GCS and CSC depletion suggests a crucial role of GCS in melanoma treatment, therefore, implying its application concerning clinical challenges of chemotherapy resistance leading to prolonged survival.

S1P signaling, its interactions and cross-talks with other partners and therapeutic importance in colorectal cancer

Sphingosine-1-Phosphate (S1P) plays an important role in normal physiology, inflammation, initiation and progression of cancer. Deregulation of S1P signaling causes aberrant proliferation, affects survival, leads to angiogenesis and metastasis. Sphingolipid rheostat is crucial for cellular homeostasis. Discrepancy in sphingolipid metabolism is linked to cancer and drug insensitivity. Owing to these diverse functions and being a potent mediator of tumor growth, S1P signaling might be a suitable candidate for anti-tumor therapy or combination therapy. In this review, with a focus on colorectal cancer we have summarized the interacting partners of S1P signaling pathway, its therapeutic approaches along with the contribution of S1P signaling to various cancer hallmarks.

SIRT1 regulates sphingolipid metabolism and neural differentiation of mouse embryonic stem cells through c-Myc-SMPDL3B

Sphingolipids are important structural components of cell membranes and prominent signaling molecules controlling cell growth, differentiation, and apoptosis. Sphingolipids are particularly abundant in the brain, and defects in sphingolipid degradation are associated with several human neurodegenerative diseases. However, molecular mechanisms governing sphingolipid metabolism remain unclear. Here, we report that sphingolipid degradation is under transcriptional control of SIRT1, a highly conserved mammalian NAD⁺-dependent protein deacetylase, in mouse embryonic stem cells (mESCs). Deletion of SIRT1 results in accumulation of sphingomyelin in mESCs, primarily due to reduction of SMPDL3B, a GPI-anchored plasma membrane bound sphingomyelin phosphodiesterase. Mechanistically, SIRT1 regulates transcription of Smpdl3b through c-Myc. Functionally, SIRT1 deficiency-induced accumulation of sphingomyelin increases membrane fluidity and impairs neural differentiation in vitro and in vivo. Our findings discover a key regulatory mechanism for sphingolipid homeostasis and neural differentiation, further imply that pharmacological manipulation of SIRT1-mediated sphingomyelin degradation might be beneficial for treatment of human neurological diseases.

All cells in the brain start life as stem cells which are yet to have a defined role in the body. A wide range of molecules and chemical signals guide stem cells towards a neuronal fate, including a group of molecules called sphingolipids. These molecules sit in the membrane surrounding the cell and play a pivotal role in a number of processes which help keep the neuronal cell healthy.

Various enzymes work together to break down sphingolipids and remove them from the membrane. Defects in these enzymes can result in excess levels of sphingolipids, which can lead to neurodegenerative diseases, such as Alzheimer’s, Parkinson’s and Huntington’s disease. But how these enzymes are used and controlled during neuronal development is still somewhat of a mystery. To help answer this question, Fan et al. studied an enzyme called SIRT1 which has been shown to alleviate symptoms in animal models of neurodegenerative diseases.

Stem cells were extracted from a mouse embryo lacking the gene for SIRT1 and cultured in the laboratory. These faulty cells were found to have superfluous amounts of sphingolipids, which made their membranes more fluid and reduced their ability to develop into neuronal cells. Further investigation revealed that SIRT1 regulates the degradation of sphingolipids by promoting the production of another enzyme called SMPDL3B. Fan et al. also found that when female mice were fed a high-fat diet, this caused sphingolipids to accumulate in their embryos which lacked the gene for SIRT1; this, in turn, impaired the neural development of their offspring.

These findings suggest that targeting SIRT1 may offer new strategies for treating neurological diseases. The discovery that embryos deficient in SIRT1 are sensitive to high-fat diets implies that activating this enzyme might attenuate some of the neonatal complications associated with maternal obesity.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

Insights into the lipidome and primary metabolome of the uterus from day 14 cyclic and pregnant sheep†

In ruminants, conceptus elongation requires the endometrium and its secretions. The amino acid, carbohydrate, and protein composition of the uterine lumen during early pregnancy has been defined in sheep; however, a comprehensive understanding of metabolomic changes in the uterine lumen is lacking, particularly with respect to lipids. Here, the lipidome and primary metabolome of the uterine lumen, endometrium, and/or conceptus was determined on day 14 of the estrous cycle and pregnancy. Lipid droplets and select triglycerides were depleted in the endometrium of pregnant ewes. In contrast, select ceramides, diglycerides, and non-esterified fatty acids as well as several phospholipid classes (phosphatidylcholine, phosphatidylinositol, phosphatidylglycerols, and diacylglycerols) were elevated in the uterine lumen of pregnant ewes. Lipidomic analysis of the conceptus revealed that triglycerides are particularly abundant within the conceptus. Primary metabolite analyses found elevated amino acids, carbohydrates, and energy substrates, among others, in the uterine lumen of pregnant ewes. Collectively, this study supports the hypothesis that lipids are important components of the uterine lumen that govern conceptus elongation and growth during early pregnancy.

Overriding sorafenib resistance via blocking lipid metabolism and Ras by sphingomyelin synthase 1 inhibition in hepatocellular carcinoma

BACKGROUND

The survival benefit of sorafenib, the most used drug for advanced hepatocellular carcinoma (HCC), is unsatisfactory due to the development of adaptive resistance. Exploring the mechanisms underlying sorafenib resistance is important to develop sensitizing strategy. Sphingomyelin synthase (SMS) plays a critical role in sphingolipid metabolism which is involved in oncogenesis and drug resistance.

METHODS

SMS1 and SMS2 levels in HCC cells in response to prolonged chemotherapy were analyzed using ELISA. mRNA and protein levels of SMS in HCC and adjacent normal tissues were analyzed by ELISA and real-time PCR. The roles of SMS and its downstream targets were investigated using cellular and biochemical assays and mass spectrometry.

RESULTS

SMS1, but not SMS2, was upregulated in HCC in response to sorafenib treatment, although HCC displayed similar RNA and protein level of SMS1 compared to adjacent normal liver tissues. Overexpression of SMS1 promoted HCC growth and migration, and alleviated sorafenib's toxicity. SMS1 inhibition via genetic and pharmacological approaches consistently resulted in inhibition of growth and migration, and apoptosis induction in sorafenib-resistance HCC cells. SMS1 inhibition also augmented the efficacy of sorafenib in sensitive HCC cells. SMS1 inhibition disrupted sphingolipid metabolism via accumulating ceramide and decreasing sphingomyelin, inducing mitochondrial dysfunction and oxidative stress, and decreasing Ras activity in resistant cells. Overexpression of constitutively active Ras reversed the inhibitory effects of SMS1 inhibition. Although SMS1 overexpression did not affect Ras expression and activity, Pearson correlation coefficient analysis of SMS1 and Ras expression demonstrated that there was positive correlation between SMS1 and RAS (NRAS, R = 0.55, p < 0.01; KRAS, R = 0.44, p < 0.01).

CONCLUSIONS

Our work is the first to suggest that SMS1 plays a more important role in sorafenib resistance than tumorigenesis, and provides preclinical evidence to overcome sorafenib resistance with SMS1 inhibition in HCC.

Cancer stem cells and ceramide signaling: the cutting edges of immunotherapy

The multipotent, self renewing "cancer stem cells" (CSCs), a small population within tumor microenvironment facilitates transformed cells to grow and propagate within the body. The CSCs are discovered as resistant to the chemotherapeutic drug with distinct immunological characteristics. In recent years, immunologically targeting CSCs have emerged as an integral part of effective and successful cancer therapy. CSCs notably exhibit dysregulation in conventional sub-cellular sphingolipid metabolism. Recently, ceramide decaying enzymes have been shown to activate alternative ceramide signaling pathways leading to reduction in efficacy of the chemotherapeutic drugs. Therefore, a control over ceramide mediated modulations of CSCs offers an attractive dimension of effective cancer treatment strategy in future. In this review, we focused on the recent findings on broad spectrum of ceramide mediated signaling in CSCs within the tumor niche and their role in potential cancer immunotherapy.

Brain Cancer-Activated Microglia: A Potential Role for Sphingolipids

Almost no neurological disease exists without microglial activation. Microglia has exert a pivotal role in the maintenance of the central nervous system and its response to external and internal insults. Microglia have traditionally been classified as, in the healthy central nervous system, "resting", with branched morphology system and, as a response to disease, "activated", with amoeboid morphology; as a response to diseases but this distinction is now outmoded. The most devastating disease that hits the brain is cancer, in particular glioblastoma. Glioblastoma multiforme is the most aggressive glioma with high invasiveness and little chance of being surgically removed. During tumor onset, many brain alterations are present and microglia have a major role because the tumor itself changes microglia from the pro-inflammatory state to the anti-inflammatory and protects the tumor from an immune intervention. What are the determinants of these changes in the behavior of the microglia? In this review, we survey and discuss the role of sphingolipids in microglia activation in the progression of brain tumors, with a particular focus on glioblastoma.

Sphingolipids in Alzheimer's disease, how can we target them?

Altered levels of sphingolipids and their metabolites in the brain, and the related downstream effects on neuronal homeostasis and the immune system, provide a framework for understanding mechanisms in neurodegenerative disorders and for developing new intervention strategies. In this review we will discuss: the metabolites of sphingolipids that function as second messengers; and functional aberrations of the pathway resulting in Alzheimer's disease (AD) pathophysiology. Focusing on the central product of the sphingolipid pathway ceramide, we describ approaches to pharmacologically decrease ceramide levels in the brain and we argue on how the sphingolipid pathway may represent a new framework for developing novel intervention strategies in AD. We also highlight the possible use of clinical and non-clinical drugs to modulate the sphingolipid pathway and sphingolipid-related biological cascades.

Drugging cancer metabolism: Expectations vs. reality

As compared to their normal counterparts, neoplastic cells exhibit a variety of metabolic changes that reflect not only genetic and epigenetic defects underlying malignant transformation, but also the nutritional and immunobiological conditions of the tumor microenvironment. Such alterations, including the so-called Warburg effect (an increase in glucose uptake largely feeding anabolic and antioxidant metabolism), have attracted considerable attention as potential targets for the development of novel anticancer therapeutics. However, very few drugs specifically conceived to target bioenergetic cancer metabolism are currently approved by regulatory agencies for use in humans. This reflects the elevated degree of heterogeneity and redundancy in the metabolic circuitries exploited by neoplastic cells from different tumors (even of the same type), as well as the resemblance of such metabolic pathways to those employed by highly proliferating normal cells. Here, we summarize the major metabolic alterations that accompany oncogenesis, the potential of targeting bioenergetic metabolism for cancer therapy, and the obstacles that still prevent the clinical translation of such a promising therapeutic paradigm.

Body Mass Index in Multiple Sclerosis modulates ceramide-induced DNA methylation and disease course

BACKGROUND

Multiple Sclerosis (MS) results from genetic predisposition and environmental variables, including elevated Body Mass Index (BMI) in early life. This study addresses the effect of BMI on the epigenome of monocytes and disease course in MS.

METHODS

Fifty-four therapy-naive Relapsing Remitting (RR) MS patients with high and normal BMI received clinical and MRI evaluation. Blood samples were immunophenotyped, and processed for unbiased plasma lipidomic profiling and genome-wide DNA methylation analysis of circulating monocytes. The main findings at baseline were validated in an independent cohort of 91 therapy-naïve RRMS patients. Disease course was evaluated by a two-year longitudinal follow up and mechanistic hypotheses tested in human cell cultures and in animal models of MS.

FINDINGS

Higher monocytic counts and plasma ceramides, and hypermethylation of genes involved in negative regulation of cell proliferation were detected in the high BMI group of MS patients compared to normal BMI. Ceramide treatment of monocytic cell cultures increased proliferation in a dose-dependent manner and was prevented by DNA methylation inhibitors. The high BMI group of MS patients showed a negative correlation between monocytic counts and brain volume. Those subjects at a two-year follow-up showed increased T1 lesion load, increased disease activity, and worsened clinical disability. Lastly, the relationship between body weight, monocytic infiltration, DNA methylation and disease course was validated in mouse models of MS.

INTERPRETATION

High BMI negatively impacts disease course in Multiple Sclerosis by modulating monocyte cell number through ceramide-induced DNA methylation of anti-proliferative genes. FUND: This work was supported by funds from the Friedman Brain Institute, NIH, and Multiple Sclerosis Society.

Ceramide Suppresses Influenza A Virus Replication In Vitro

Annual influenza outbreaks are associated with significant morbidity and mortality worldwide despite the availability of seasonal vaccines. Influenza pathogenesis depends on the manipulation of host cell signaling to promote virus replication. Ceramide is a sphingosine-derived lipid that regulates diverse cellular processes. Studies highlighted the differential role of ceramide de novo biosynthesis on the propagation of various viruses. Whether ceramide plays, a role in influenza virus replication is not known. In this study, we assessed the potential interplay between the influenza A (IAV) and ceramide biosynthesis pathways. The accumulation of ceramide in human lung epithelial cells infected with influenza A/H1N1 virus strains was evaluated using thin-layer chromatography and/or confocal microscopy. Virus replication was assessed upon the regulation of the de novo ceramide biosynthesis pathway. A significant increase in ceramide accumulation was observed in cells infected with IAV in a dose- and time-dependent manner. Inoculating the cells with UV-inactivated IAV did not result in ceramide accumulation in the cells, suggesting that the induction of ceramide required an active virus replication. Inhibiting de novo ceramide significantly decreased ceramide accumulation and enhanced virus replication. The addition of exogenous C₆-ceramide prior to infection mediated an increase in cellular ceramide levels and significantly attenuated IAV replication and reduced viral titers (≈1 log10 PFU/ml unit). Therefore, our data demonstrate that ceramide accumulation through de novo biosynthesis pathway plays a protective and antiviral role against IAV infection. These findings propose new avenues for development of antiviral molecules and strategies.IMPORTANCE Understanding the effect of sphingolipid metabolism on viral pathogenesis provide important insights into the development of therapeutic strategies against microbial infections. In this study, we demonstrate a critical role of ceramide during influenza A virus infection. We demonstrate that ceramide produced through de novo biosynthesis possess an antiviral role. These observations unlock new opportunities for the development of novel antiviral therapies against influenza.

Mechanism of Rapid Nuclear Factor-E2-Related Factor 2 (Nrf2) Activation via Membrane-Associated Estrogen Receptors: Roles of NADPH Oxidase 1, Neutral Sphingomyelinase 2 and Epidermal Growth Factor Receptor (EGFR)

Membrane-associated estrogen receptors (ER)-α36 and G protein-coupled estrogen receptor (GPER) play important roles in the estrogen’s rapid non-genomic actions including stimulation of cell proliferation. Estrogen via these receptors induces rapid activation of transcription factor nuclear factor-E2-related factor 2 (Nrf2), a master regulator of detoxification and antioxidant systems, playing a key role in the metabolic reprogramming to support cell proliferation. This review highlights the possible mechanism underlying rapid Nrf2 activation via membrane-associated estrogen receptors by estrogen and phytoestrogens. Stimulation of ER-α36-GPER signaling complex rapidly induces Src-mediated transactivation of epidermal growth factor receptor (EGFR) leading to a kinase-mediated signaling cascade. We propose a novel hypothesis that ER-α36-GPER signaling initially induces rapid and temporal activation of NADPH oxidase 1 to generate superoxide, which subsequently activates redox-sensitive neutral sphingomyelinase 2 generating the lipid signaling mediator ceramide. Generation of ceramide is required for Ras activation and ceramide-protein kinase C ζ-casein kinase 2 (CK2) signaling. Notably, CK2 enhances chaperone activity of the Cdc37-Hsp90 complex supporting activation of various signaling kinases including Src, Raf and Akt (protein kinase B). Activation of Nrf2 may be induced by cooperation of two signaling pathways, (i) Nrf2 stabilization by direct phosphorylation by CK2 and (ii) EGFR-Ras-PI 3 kinase (PI3K)-Akt axis which inhibits glycogen synthase kinase 3β leading to enhanced nuclear transport and stability of Nrf2.

Imbalanced sphingolipid signaling is maintained as a core proponent of a cancerous phenotype in spite of metabolic pressure and epigenetic drift

Tumor heterogeneity may arise through genetic drift and environmentally driven clonal selection for metabolic fitness. This would promote subpopulations derived from single cancer cells that exhibit distinct phenotypes while conserving vital pro-survival pathways. We aimed to identify significant drivers of cell fitness in pancreatic adenocarcinoma (PDAC) creating subclones in different nutrient formulations to encourage differential metabolic reprogramming. The genetic and phenotypic expression profiles of each subclone were analyzed relative to a healthy control cell line (hTert-HPNE). The subclones exhibited distinct variations in protein expression and lipid metabolism. Relative to hTert-HPNE, PSN-1 subclones uniformly maintained modified sphingolipid signaling and specifically retained elevated sphingosine-1-phosphate (S1P) relative to C16 ceramide (C16 Cer) ratios. Each clone utilized a different perturbation to this pathway, but maintained this modified signaling to preserve cancerous phenotypes, such as rapid proliferation and defense against mitochondria-mediated apoptosis. Although the subclones were unique in their sensitivity, inhibition of S1P synthesis significantly reduced the ratio of S1P/C16 Cer, slowed cell proliferation, and enhanced sensitivity to apoptotic signals. This reliance on S1P signaling identifies this pathway as a promising drug-sensitizing target that may be used to eliminate cancerous cells consistently across uniquely reprogrammed PDAC clones.

Metabolomics of Green-Tea Catechins on Vascular-Endothelial-Growth-Factor-Stimulated Human-Endothelial-Cell Survival

Neovascularization causes serious oculopathy related to upregulation of vascular-endothelial-growth factor (VEGF) causing new capillary growth via endothelial cells. Green-tea-extract (GTE) constituents possess antiangiogenesis properties. We used VEGF to induce human umbilical-vein endothelial cells (HUVECs) and applied GTE, epigallocatechin gallate (EGCG), and mixtures of different compositions of purified catechins (M1 and M2) to evaluate their efficacies of inhibition and their underlying mechanisms using cell-cycle analysis and untargeted metabolomics techniques. GTE, EGCG, M1, and M2 induced HUVEC apoptosis by 22.1 ± 2, 20.0 ± 0.7, 50.7 ± 8.5, and 69.8 ± 4.1%, respectively. GTE exerted a broad, balanced metabolomics spectrum, involving suppression of the biosynthesis of cellular building blocks and oxidative-phosphorylation metabolites as well as promotion of the biosynthesis of membrane lipids and growth factors. M2 mainly induced mechanisms associated with energy and biosynthesis suppression. Therefore, GTE exerted mechanisms involving both promotion and suppression activities, whereas purified catechins induced extensive apoptosis. GTE could be a more promising antineovascularization remedy for ocular treatment.

The crosstalk between glycosphingolipids and neural stem cells

Until a few years ago, the majority of cell functions were envisioned as the result of protein and DNA activity. The cell membranes were considered as a mere structure of support and/or separation. In the last years, the function of cell membranes has, however, received more attention and their components of lipid nature have also been depicted as important cell mediators and the membrane organization was described as an important determinant for membrane-anchored proteins activity. In particular, because of their high diversity, glycosphingolipids offer a wide possibility of regulation. Specifically, the role of glycosphingolipids, in the fine-tuning of neuron activity, has recently received deep attention. For their pivotal role in vertebrate and mammals neural development, neural stem cells regulation is of main interest especially concerning their further functions in neurological pathology progression and treatment. Glycosphingolipids expression present a developmental regulation. In this view, glycosphingolipids can hold an important role in neural stem cells features because of their heterogeneity and their consequent capacity for eclectic interaction with other cell components.

Sphingolipids and lipid rafts: Novel concepts and methods of analysis

About twenty years ago, the functional lipid raft model of the plasma membrane was published. It took into account decades of research showing that cellular membranes are not just homogenous mixtures of lipids and proteins. Lateral anisotropy leads to assembly of membrane domains with specific lipid and protein composition regulating vesicular traffic, cell polarity, and cell signaling pathways in a plethora of biological processes. However, what appeared to be a clearly defined entity of clustered raft lipids and proteins became increasingly fluid over the years, and many of the fundamental questions about biogenesis and structure of lipid rafts remained unanswered. Experimental obstacles in visualizing lipids and their interactions hampered progress in understanding just how big rafts are, where and when they are formed, and with which proteins raft lipids interact. In recent years, we have begun to answer some of these questions and sphingolipids may take center stage in re-defining the meaning and functional significance of lipid rafts. In addition to the archetypical cholesterol-sphingomyelin raft with liquid ordered (Lo) phase and the liquid-disordered (Ld) non-raft regions of cellular membranes, a third type of microdomains termed ceramide-rich platforms (CRPs) with gel-like structure has been identified. CRPs are "ceramide rafts" that may offer some fresh view on the membrane mesostructure and answer several critical questions for our understanding of lipid rafts.

Lipidated cyclopropenes via a stable 3-N spirocyclopropene scaffold

Lipidated cyclopropenes serve as useful bioorthogonal reagents for imaging cell membranes due to the cyclopropene's small size and ability to ligate with pro-fluorescent tetrazines. Previously, the lipidation of cyclopropenes required modification at the C3 position because methods to append lipids at C1/C2 were not available. Herein, we describe C1/C2 lipidation with the biologically active lipid ceramide and a common phospholipid using a cyclopropene scaffold whose reactivity with 1,2,4,5-tetrazines has been caged.

Ceramide Metabolism Balance, a Multifaceted Factor in Critical Steps of Breast Cancer Development

Ceramides are key lipids in energetic-metabolic pathways and signaling cascades, modulating critical physiological functions in cells. While synthesis of ceramides is performed in endoplasmic reticulum (ER), which is altered under overnutrition conditions, proteins associated with ceramide metabolism are located on membrane arrangement of mitochondria and ER (MAMs). However, ceramide accumulation in meta-inflammation, condition that associates obesity with a chronic low-grade inflammatory state, favors the deregulation of pathways such as insulin signaling, and induces structural rearrangements on mitochondrial membrane, modifying its permeability and altering the flux of ions and other molecules. Considering the wide biological processes in which sphingolipids are implicated, they have been associated with diseases that present abnormalities in their energetic metabolism, such as breast cancer. In this sense, sphingolipids could modulate various cell features, such as growth, proliferation, survival, senescence, and apoptosis in cancer progression; moreover, ceramide metabolism is associated to chemotherapy resistance, and regulation of metastasis. Cell–cell communication mediated by exosomes and lipoproteins has become relevant in the transport of several sphingolipids. Therefore, in this work we performed a comprehensive analysis of the state of the art about the multifaceted roles of ceramides, specifically the deregulation of ceramide metabolism pathways, being a key factor that could modulate neoplastic processes development. Under specific conditions, sphingolipids perform important functions in several cellular processes, and depending on the preponderant species and cellular and/or tissue status can inhibit or promote the development of metabolic and potentially breast cancer disease.

Caveolae-mediated effects of TNF-α on human skeletal muscle cells

Chronic diseases are characterized by the production of pro-inflammatory cytokines such than TNF-α and are frequently correlated with muscle wasting conditions. Among the pleiotropic effects of TNF-α within the cell, its binding to TNFR1 receptor has been shown to activate sphingomyelinases leading to the production of ceramides. Sphingomyelinases and TNF receptor have been localized within caveolae which are specialized RAFT enriched in cholesterol and sphingolipids. Because of their inverted omega shape, maintained by the oligomerization of specialized proteins, caveolins and cavins, caveolae serve as membrane reservoir therefore providing mechanical protection to plasma membranes. Although sphingolipids metabolites, caveolins and TNF-α/TNFR1 have been shown to independently interfere with muscle physiology, no data have clearly demonstrated their concerted action on muscle cell regeneration. In this context, our study aimed at studying the molecular mechanisms induced by TNF-α at the level of caveolae in LHCN-M2 human muscle satellite cells. Here we showed that TNF-α-induced production of ROS and nSMase activation requires caveolin. More strikingly, we have demonstrated that TNF-α induces the formation of additional caveolae at the plasma membrane of myoblasts. Furthermore, TNF-α prevents myoblast fusion suggesting that inflammation could modulate caveolae organization/function and satellite cell function.

Role of caveolin-1 in hepatocellular carcinoma arising from non-alcoholic fatty liver disease

The molecular features of hepatocellular carcinoma arising from non-alcoholic fatty liver disease (NAFLD-HCC) are not well known. In this study, we investigated the mechanism by which NAFLD-HCC survives in a fat-rich environment. We found that caveolin (CAV)-1 was overexpressed in clinical specimens from NAFLD-HCC patients. HepG2, HLE, and HuH-7 HCC cell lines showed decreased proliferation in the presence of the saturated fatty acids palmitic acid and stearic acid, although only HLE cells expressed high levels of CAV-1. HLE cells treated with oleic acid (OA) showed robust proliferation, whereas CAV-null HepG2 cells showed reduced proliferation and increased apoptosis. CAV-1 knockdown in HLE cells attenuated the OA-induced increase in proliferation and enhanced apoptosis. Liquid chromatography-tandem mass spectrometry analysis revealed that the levels of OA-containing ceramide, a pro-apoptotic factor, were higher in HepG2 and CAV-1-deficient HLE cells than in HLE cells, suggesting that CAV-1 inhibits apoptosis by decreasing the level of OA-containing ceramide. These results indicate that CAV-1 is important for NAFLD-HCC survival in fatty acid-rich environments and is a potential therapeutic target.

Molecular Markers of Therapy-Resistant Glioblastoma and Potential Strategy to Combat Resistance

Glioblastoma (GBM) is the most common primary malignant tumor of the central nervous system. With its overall dismal prognosis (the median survival is 14 months), GBMs demonstrate a resounding resilience against all current treatment modalities. The absence of a major progress in the treatment of GBM maybe a result of our poor understanding of both GBM tumor biology and the mechanisms underlying the acquirement of treatment resistance in recurrent GBMs. A comprehensive understanding of these markers is mandatory for the development of treatments against therapy-resistant GBMs. This review also provides an overview of a novel marker called acid ceramidase and its implication in the development of radioresistant GBMs. Multiple signaling pathways were found altered in radioresistant GBMs. Given these global alterations of multiple signaling pathways found in radioresistant GBMs, an effective treatment for radioresistant GBMs may require a cocktail containing multiple agents targeting multiple cancer-inducing pathways in order to have a chance to make a substantial impact on improving the overall GBM survival.

Ceramide and Exosomes: A Novel Target in Cancer Biology and Therapy

Exosomes are secreted extracellular vesicles (EVs) that carry micro RNAs and other factors to reprogram cancer cells and tissues affected by cancer. Exosomes are exchanged between cancer cells and other tissues, often to prepare a premetastatic niche, escape immune surveillance, or spread multidrug resistance. Only a few studies investigated the function of lipids in exosomes although their lipid composition is different from that of the secreting cells. Ceramide is one of the lipids critical for exosome formation, and it is also enriched in these EVs. New research suggests that lipids in the exosomal membrane may organize and transmit "mobile rafts" that turn exosomes into extracellular signalosomes spreading activation of cell signaling pathways in oncogenesis and metastasis. Ceramide may modulate the function of mobile rafts and their effect on these cell signaling pathways. The critical role of lipids and, in particular, ceramide for formation, secretion, and function of exosomes may lead to a radically new understanding of cancer biology and therapy.

Molecular Targeting of Acid Ceramidase in Glioblastoma: A Review of Its Role, Potential Treatment, and Challenges

Glioblastoma is the most common, malignant primary tumor of the central nervous system. The average prognosis for life expectancy after diagnosis, with the triad of surgery, chemotherapy, and radiation therapy, is less than 1.5 years. Chemotherapy treatment is mostly limited to temozolomide. In this paper, the authors review an emerging, novel drug called acid ceramidase, which targets glioblastoma. Its role in cancer treatment in general, and more specifically, in the treatment of glioblastoma, are discussed. In addition, the authors provide insights on acid ceramidase as a potential druggable target for glioblastoma.

Acid ceramidase is a novel drug target for pediatric brain tumors

Pediatric brain tumors are the most common solid tumors in children and are also a leading culprit of cancer-related fatalities in children. Pediatric brain tumors remain hard to treat. In this study, we demonstrated that medulloblastoma, pediatric glioblastoma, and atypical teratoid rhabdoid tumors express significant levels of acid ceramidase, where levels are highest in the radioresistant tumors, suggesting that acid ceramidase may confer radioresistance. More importantly, we also showed that acid ceramidase inhibitors are highly effective at targeting these pediatric brain tumors with low IC₅₀ values (4.6–50 μM). This data suggests acid ceramidase as a novel drug target for adjuvant pediatric brain tumor therapies. Of these acid ceramidase inhibitors, carmofur has seen clinical use in Japan since 1981 for colorectal cancers and is a promising drug to undergo further animal studies and subsequently a clinical trial as a treatment for pediatric patients with brain tumors.

Ceramide and S1P Signaling in Embryonic Stem Cell Differentiation

Bioactive sphingolipids are important regulators for stem cell survival and differentiation. Most recently, we have coined the term "morphogenetic lipids" for sphingolipids that regulate stem cells during embryonic and postnatal development. The sphingolipid ceramide and its derivative, sphingosine-1-phosphate (S1P), can act synergistically as well as antagonistically on embryonic stem (ES) cell differentiation. We show here simple as well as state-of-the-art methods to analyze sphingolipids in differentiating ES cells and discuss new protocols to use ceramide and S1P analogs for the guided differentiation of mouse ES cells toward neuronal and glial lineage.

Lysosphingolipids and sphingolipidoses: Psychosine in Krabbe's disease

Until recently, lipids were considered inert building blocks of cellular membranes. This changed three decades ago when lipids were found to regulate cell polarity and vesicle transport, and the "lipid raft" concept took shape. The lipid-driven membrane anisotropy in form of "rafts" that associate with proteins led to the view that organized complexes of lipids and proteins regulate various cell functions. Disturbance of this organization can lead to cellular, tissue, and organ malfunction. Sphingolipidoses, lysosomal storage diseases that are caused by enzyme deficiencies in the sphingolipid degradation pathway, were found to be particularly detrimental to the brain. These enzyme deficiencies result in accumulation of sphingolipid metabolites in lysosomes, although it is not yet clear how this accumulation affects the organization of lipids in cellular membranes. Krabbe's disease (KD), or globoid cell leukodystrophy, was one of the first sphingolipidosis for which the raft concept offered a potential mechanism. KD is caused by mutations in the enzyme β-galactocerebrosidase; however, elevation of its substrate, galactosylceramide, is not observed or considered detrimental. Instead, it was found that a byproduct of galactosylceramide metabolism, the lysosphingolipid psychosine, is accumulated. The "psychosine hypothesis" has been refined by showing that psychosine disrupts lipid rafts and vesicular transport critical for the function of glia and neurons. The role of psychosine in KD is an example of how the disruption of sphingolipid metabolism can lead to elevation of a toxic lysosphingolipid, resulting in disruption of cellular membrane organization and neurotoxicity. © 2016 Wiley Periodicals, Inc.

Acid ceramidase and its inhibitors: a de novo drug target and a new class of drugs for killing glioblastoma cancer stem cells with high efficiency

Glioblastoma remains the most common, malignant primary cancer of the central nervous system with a low life expectancy and an overall survival of less than 1.5 years. The treatment options are limited and there is no cure. Moreover, almost all patients develop recurrent tumors, which typically are more aggressive. Therapeutically resistant glioblastoma or glioblastoma stem-like cells (GSCs) are hypothesized to cause this inevitable recurrence. Identifying prognostic biomarkers of glioblastoma will potentially advance knowledge about glioblastoma tumorigenesis and enable discovery of more effective therapies. Proteomic analysis of more than 600 glioblastoma-specific proteins revealed, for the first time, that expression of acid ceramidase (ASAH1) is associated with poor glioblastoma survival. CD133+ GSCs express significantly higher ASAH1 compared to CD133- GSCs and serum-cultured glioblastoma cell lines, such as U87MG. These findings implicate ASAH1 as a plausible independent prognostic marker, providing a target for a therapy tailored toward GSCs. We further demonstrate that ASAH1 inhibition increases cellular ceramide level and induces apoptosis. Strikingly, U87MG cells, and three different patient-derived glioblastoma stem-like cancer cell lines were efficiently killed, through apoptosis, by three different known ASAH1 inhibitors with IC50's ranging from 11–104 μM. In comparison, the standard glioblastoma chemotherapy agent, temozolomide, had minimal GSC-targeted effects at comparable or even higher concentrations (IC50 > 750 μM against GSCs). ASAH1 is identified as a de novo glioblastoma drug target, and ASAH1 inhibitors, such as carmofur, are shown to be highly effective and to specifically target glioblastoma GSCs. Carmofur is an ASAH1 inhibitor that crosses the blood-brain barrier, a major bottleneck in glioblastoma treatment. It has been approved in Japan since 1981 for colorectal cancer therapy. Therefore, it is poised for repurposing and translation to glioblastoma clinical trials.

Monascus purpureus induced apoptosis on gastric cancer cell by scavenging mitochondrial reactive oxygen species

Monascus purpureus is a red dye derived from yeast rice and has been used as color additives for food in East Asia. Monascus purpureus consists of several bioactive components. Some of these components work as a radical scavenger, thus monascus purpureus would also eliminate reactive oxygen species. Cancer cells maintain the high level of reactive oxygen species than normal cell and are death by imbalance in pro-oxidant/antioxidant homeostasis. In this study, we investigated whether monascus purpureus induced cancer specific cell death by scavenging reactive oxygen species. Compared to normal cell, monascus purpureus had cancer specific cytotoxicity. Monascus purpureus and lovastatin, its component, scavenged free radicals caused by a xanthine/xanthine oxidase system, thus Monascus purpureus is likely to scavenge reactive oxygen species by a synergistic effect between lovastatin and other components. Monascus purpureus also decreased reactive oxygen species derived from mitochondria in cancer cells, and cellular apoptosis was induced via activation of caspase-9. Induction of apoptosis by reduction of reactive oxygen species generation decreased acid ceramidase, and this mechanism could be involved with increasing ceramide accumulation in cells.

Complete Acid Ceramidase ablation prevents cancer-initiating cell formation in melanoma cells

Acid ceramidase (AC) is a lysosomal cysteine hydrolase that catalyzes the conversion of ceramide into fatty acid and sphingosine. This reaction lowers intracellular ceramide levels and concomitantly generates sphingosine used for sphingosine-1-phosphate (S1P) production. Since increases in ceramide and consequent decreases of S1P reduce proliferation of various cancers, AC might offer a new target for anti-tumor therapy. Here we used CrispR-Cas9-mediated gene editing to delete the gene encoding for AC, ASAH1, in human A375 melanoma cells. ASAH1-null clones show significantly greater accumulation of long-chain saturated ceramides that are substrate for AC. As seen with administration of exogenous ceramide, AC ablation blocks cell cycle progression and accelerates senescence. Importantly, ASAH1-null cells also lose the ability to form cancer-initiating cells and to undergo self-renewal, which is suggestive of a key role for AC in maintaining malignancy and self-renewal of invasive melanoma cells. The results suggest that AC inhibitors might find therapeutic use as adjuvant therapy for advanced melanoma.

tsRNA signatures in cancer

Small, noncoding RNAs are short untranslated RNA molecules, some of which have been associated with cancer development. Recently we showed that a class of small RNAs generated during the maturation process of tRNAs (tRNA-derived small RNAs, hereafter "tsRNAs") is dysregulated in cancer. Specifically, we uncovered tsRNA signatures in chronic lymphocytic leukemia and lung cancer and demonstrated that the ts-4521/3676 cluster (now called "ts-101" and "ts-53," respectively), ts-46, and ts-47 are down-regulated in these malignancies. Furthermore, we showed that tsRNAs are similar to Piwi-interacting RNAs (piRNAs) and demonstrated that ts-101 and ts-53 can associate with PiwiL2, a protein involved in the silencing of transposons. In this study, we extended our investigation on tsRNA signatures to samples collected from patients with colon, breast, or ovarian cancer and cell lines harboring specific oncogenic mutations and representing different stages of cancer progression. We detected tsRNA signatures in all patient samples and determined that tsRNA expression is altered upon oncogene activation and during cancer staging. In addition, we generated a knocked-out cell model for ts-101 and ts-46 in HEK-293 cells and found significant differences in gene-expression patterns, with activation of genes involved in cell survival and down-regulation of genes involved in apoptosis and chromatin structure. Finally, we overexpressed ts-46 and ts-47 in two lung cancer cell lines and performed a clonogenic assay to examine their role in cell proliferation. We observed a strong inhibition of colony formation in cells overexpressing these tsRNAs compared with untreated cells, confirming that tsRNAs affect cell growth and survival.

The 5XFAD Mouse Model of Alzheimer's Disease Exhibits an Age-Dependent Increase in Anti-Ceramide IgG and Exogenous Administration of Ceramide Further Increases Anti-Ceramide Titers and Amyloid Plaque Burden

We present evidence that 5XFAD Alzheimer's disease model mice develop an age-dependent increase in antibodies against ceramide, suggesting involvement of autoimmunity against ceramide in Alzheimer's disease pathology. To test this, we increased serum anti-ceramide IgG (2-fold) by ceramide administration and analyzed amyloid plaque formation in 5XFAD mice. There were no differences in soluble or total amyloid-β levels. However, females receiving ceramide had increased plaque burden (number, area, and size) compared to controls. Ceramide-treated mice showed an increase of serum exosomes (up to 3-fold using Alix as marker), suggesting that systemic anti-ceramide IgG and exosome levels are correlated with enhanced plaque formation.

A Diet Rich in Medium-Chain Fatty Acids Improves Systolic Function and Alters the Lipidomic Profile in Patients With Type 2 Diabetes: A Pilot Study

CONTEXT

Excessive cardiac long-chain fatty acid (LCFA) metabolism/storage causes cardiomyopathy in animal models of type 2 diabetes. Medium-chain fatty acids (MCFAs) are absorbed and oxidized efficiently. Data in animal models of diabetes suggest MCFAs may benefit the heart.

OBJECTIVE

Our objective was to test the effects of an MCFA-rich diet vs an LCFA-rich diet on plasma lipids, cardiac steatosis, and function in patients with type 2 diabetes.

DESIGN

This was a double-blind, randomized, 2-week matched-feeding study.

SETTING

The study included ambulatory patients in the general community.

PATIENTS

Sixteen patients, ages 37-65 years, with type 2 diabetes, an ejection fraction greater than 45%, and no other systemic disease were included.

INTERVENTION

Fourteen days of a diet rich in MCFAs or LCFAs, containing 38% as fat in total, was undertaken.

MAIN OUTCOME MEASURES

Cardiac steatosis and function were the main outcome measures, with lipidomic changes considered a secondary outcome.

RESULTS

The relatively load-independent measure of cardiac contractility, S', improved in the MCFA group (P < .05). Weight-adjusted stroke volume and cardiac output decreased in the LCFA group (both P < .05). The MCFA, but not the LCFA, diet decreased several plasma sphingolipids, ceramide, and acylcarnitines implicated in diabetic cardiomyopathy, and changes in several sphingolipids correlated with improved fasting insulins.

CONCLUSIONS

Although a diet high in MCFAs does not change cardiac steatosis, our findings suggest that the MCFA-rich diet alters the plasma lipidome and may benefit or at least not harm cardiac function and fasting insulin levels in humans with type 2 diabetes. Larger, long-term studies are needed to further evaluate these effects in less-controlled settings.

Assaying Ceramide Synthase Activity In Vitro and in Living Cells Using Liquid Chromatography-Mass Spectrometry

Sphingolipids are one the major lipid families in eukaryotes, incorporating a diverse array of structural and signaling lipids such as sphingomyelin and gangliosides. The core lipid component for all complex sphingolipids is ceramide, a diacyl lipid consisting of a variable length fatty acid linked through an amide bond to a long chain base such as sphingosine or dihydrosphingosine. This reaction is catalyzed by a family of six ceramide synthases (CERS1-6), each of which preferentially catalyzes the synthesis of ceramides with different fatty acid chain lengths. Ceramides are themselves potent cellular and physiological signaling molecules heavily implicated in diabetes and neurodegenerative diseases, making it important for researchers to have access to sensitive and accurate assays for ceramide synthase activity. This chapter describes methods for assaying ceramide synthase activity in cell or tissue lysates, or in cultured cells (in situ), using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the readout. LC-MS/MS is a very sensitive and accurate means for assaying ceramide synthase reaction products.

Fluorescent Assays for Ceramide Synthase Activity

Ceramides are the central lipid metabolite of the sphingolipid family, and exert a potent influence over cell polarity, differentiation, and survival through their biophysical properties and their specific interactions with cell signaling proteins. Literature on the importance of ceramides in physiology and pathological conditions continues to grow, with ceramides having been identified as central effectors in major human pathologies such as diabetes and neurodegenerative conditions. In mammals, ceramide synthesis from a sphingoid base and a variable length fatty acid is catalyzed by a family of six ceramide synthases (CERS1-6), whose active sites exhibit differential specificity for different length fatty acids. CERS activity has traditionally been measured using radioactive substrates. More recently mass spectrometry has been used. In this chapter, we describe a fluorescent CERS assay, the results of which can be quantified using thin-layer chromatography (TLC) or high-performance liquid chromatography (HPLC). Methods for quantification with either TLC or HPLC are described.

In situ characterizing membrane lipid phenotype of breast cancer cells using mass spectrometry profiling

Lipid composition in cell membrane is closely associated with cell characteristics. Here, matrix-assisted laser desorption/ionization- Fourier transform ion cyclotron resonance mass spectrometry was employed to in situ determine membrane components of human mammary epithelial cells (MCF-10 A) and six different breast cancer cell lines (i.e., BT-20, MCF-7, SK-BR-3, MDA-MB-231, MDA-MB-157, and MDA-MB-361) without any lipid extraction and separation. Partial least-square discriminant analysis indicated that changes in the levels of these membrane lipids were closely correlated with the types of breast cell lines. Elevated levels of polyunsaturated lipids in MCF-10 A cells relative to six breast cancer cells and in BT-20 cells relative to other breast cancer cell lines were detected. The Western blotting assays indicated that the expression of five lipogenesis-related enzymes (i.e., fatty acid synthase 1(FASN1), stearoyl-CoA desaturase 1 (SCD1), stearoyl-CoA desaturase 5 (SCD5), choline kinase α (CKα), and sphingomyelin synthase 1) was associated with the types of the breast cells, and that the SCD1 level in MCF-7 cells was significantly increased relative to other breast cell lines. Our findings suggest that elevated expression levels of FASN1, SCD1, SCD5, and CKα may closely correlated with enhanced levels of saturated and monounsaturated lipids in breast cancer cell lines.

Rapid evaluation of 25 key sphingolipids and phosphosphingolipids in human plasma by LC-MS/MS

We report on a new, sensitive, and fast LC-MS/MS method for the simultaneous determination of 25 key sphingolipid components in human plasma, including phosphorylated sphinganine and sphingosine, in a single 9-min run. This method enables an effective and high-throughput coverage of the metabolic changes involving the sphingolipidome during physiological or pathological states. The method is based on liquid–liquid extraction followed by reversed-phase LC-MS/MS. Exogenous odd-chain lipids are used as cost-effective but reliable internal standards. The method was fully validated in surrogate matrix and naive human plasma following FDA guidelines. Sample stability and dilution integrity were also tested and verified.

Overexpressed PKCδ downregulates the expression of PKCα in B16F10 melanoma: induction of apoptosis by PKCδ via ceramide generation

In the present study, we observed a marked variation in the expression of PKCα and PKCδ isotypes in B16F10 melanoma tumor cells compared to the normal melanocytes. Interestingly, the tumor instructed expression or genetically manipulated overexpression of PKCα isotype resulted in enhanced G1 to S transition. This in turn promoted cellular proliferation by activating PLD1 expression and subsequent AKT phosphorylation, which eventually resulted in suppressed ceramide generation and apoptosis. On the other hand, B16F10 melanoma tumors preferentially blocked the expression of PKCδ isotype, which otherwise could exhibit antagonistic effects on PKCα-PLD1-AKT signaling and rendered B16F10 cells more sensitive to apoptosis via generating ceramide and subsequently triggering caspase pathway. Hence our data suggested a reciprocal PKC signaling operational in B16F10 melanoma cells, which regulates ceramide generation and provide important clues to target melanoma cancer by manipulating the PKCδ-ceramide axis.