Long chain-polyunsaturated fatty acids modulate membrane phospholipid composition and protein localization in lipid rafts of neural stem cell cultures

Lipid Peroxidation Drives Liquid-Liquid Phase Separation and Disrupts Raft Protein Partitioning in Biological Membranes

The peroxidation of membrane lipids by free radicals contributes to aging, numerous diseases, and ferroptosis, an iron-dependent form of cell death. Peroxidation changes the structure and physicochemical properties of lipids, leading to bilayer thinning, altered fluidity, and increased permeability of membranes in model systems. Whether and how lipid peroxidation impacts the lateral organization of proteins and lipids in biological membranes, however, remains poorly understood. Here, we employ cell-derived giant plasma membrane vesicles (GPMVs) as a model to investigate the impact of lipid peroxidation on ordered membrane domains, often termed membrane rafts. We show that lipid peroxidation induced by the Fenton reaction dramatically enhances the phase separation propensity of GPMVs into coexisting liquid-ordered (Lo) and liquid-disordered (Ld) domains and increases the relative abundance of the disordered phase. Peroxidation also leads to preferential accumulation of peroxidized lipids and 4-hydroxynonenal (4-HNE) adducts in the disordered phase, decreased lipid packing in both Lo and Ld domains, and translocation of multiple classes of raft proteins out of ordered domains. These findings indicate that the peroxidation of plasma membrane lipids disturbs many aspects of membrane rafts, including their stability, abundance, packing, and protein and lipid composition. We propose that these disruptions contribute to the pathological consequences of lipid peroxidation during aging and disease and thus serve as potential targets for therapeutic intervention.

Lipid peroxidation drives liquid-liquid phase separation and disrupts raft protein partitioning in biological membranes

The peroxidation of membrane lipids by free radicals contributes to aging, numerous diseases, and ferroptosis, an iron-dependent form of cell death. Peroxidation changes the structure, conformation and physicochemical properties of lipids, leading to major membrane alterations including bilayer thinning, altered fluidity, and increased permeability. Whether and how lipid peroxidation impacts the lateral organization of proteins and lipids in biological membranes, however, remains poorly understood. Here, we employ cell-derived giant plasma membrane vesicles (GPMVs) as a model to investigate the impact of lipid peroxidation on ordered membrane domains, often termed membrane rafts. We show that lipid peroxidation induced by the Fenton reaction dramatically enhances phase separation propensity of GPMVs into co-existing liquid ordered (raft) and liquid disordered (non-raft) domains and increases the relative abundance of the disordered, non-raft phase. Peroxidation also leads to preferential accumulation of peroxidized lipids and 4-hydroxynonenal (4-HNE) adducts in the disordered phase, decreased lipid packing in both raft and non-raft domains, and translocation of multiple classes of proteins out of rafts. These findings indicate that peroxidation of plasma membrane lipids disturbs many aspects of membrane rafts, including their stability, abundance, packing, and protein and lipid composition. We propose that these disruptions contribute to the pathological consequences of lipid peroxidation during aging and disease, and thus serve as potential targets for therapeutic intervention.

Biosynthesis and Significance of Fatty Acids, Glycerophospholipids, and Triacylglycerol in the Processes of Glioblastoma Tumorigenesis

One area of glioblastoma research is the metabolism of tumor cells and detecting differences between tumor and healthy brain tissue metabolism. Here, we review differences in fatty acid metabolism, with a particular focus on the biosynthesis of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) by fatty acid synthase (FASN), elongases, and desaturases. We also describe the significance of individual fatty acids in glioblastoma tumorigenesis, as well as the importance of glycerophospholipid and triacylglycerol synthesis in this process. Specifically, we show the significance and function of various isoforms of glycerol-3-phosphate acyltransferases (GPAT), 1-acylglycerol-3-phosphate O-acyltransferases (AGPAT), lipins, as well as enzymes involved in the synthesis of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and cardiolipin (CL). This review also highlights the involvement of diacylglycerol O-acyltransferase (DGAT) in triacylglycerol biosynthesis. Due to significant gaps in knowledge, the GEPIA database was utilized to demonstrate the significance of individual enzymes in glioblastoma tumorigenesis. Finally, we also describe the significance of lipid droplets in glioblastoma and the impact of fatty acid synthesis, particularly docosahexaenoic acid (DHA), on cell membrane fluidity and signal transduction from the epidermal growth factor receptor (EGFR).

Effects of the Combined Treatment with a G-Quadruplex-Stabilizing Ligand and Photon Beams on Glioblastoma Stem-like Cells: A Magnetic Resonance Study

Glioblastoma multiforme is a malignant primary brain tumor with a poor prognosis and high rates of chemo-radiotherapy failure, mainly due to a small cell fraction with stem-like properties (GSCs). The mechanisms underlying GSC response to radiation need to be elucidated to enhance sensitivity to treatments and to develop new therapeutic strategies. In a previous study, two GSC lines, named line #1 and line #83, responded differently to carbon ions and photon beams, with the differences likely attributable to their own different metabolic fingerprint rather than to radiation type. Data from the literature showed the capability of RHPS4, a G-quadruplex stabilizing ligand, to sensitize the glioblastoma radioresistant U251MG cells to X-rays. The combined metabolic effect of ligand #190, a new RHPS4-derivative showing reduced cardiotoxicity, and a photon beam has been monitored by magnetic resonance (MR) spectroscopy for the two GSC lines, #1 and #83, to reveal whether a synergistic response occurs. MR spectra from both lines were affected by single and combined treatments, but the variations of the analysed metabolites were statistically significant mainly in line #1, without synergistic effects due to combination. The multivariate analysis of ten metabolites shows a separation between control and treated samples in line #1 regardless of treatment type, while separation was not detected in line #83.

Effects of Dietary Food Components on Cognitive Functions in Older Adults

Population aging has recently been an important issue as the number of elderly people is growing worldwide every year, and the extension of social security costs is financially costly. The increase in the number of elderly people with cognitive decline is a serious problem related to the aging of populations. Therefore, it is necessary to consider not only physical care but also cognitive patterns in the future care of older adults. Since food contains a variety of bioactive substances, dietary patterns may help improve age-related cognitive decline. However, the relationship between cognitive function and individual food components remains ambiguous as no clear efficacy or mechanism has been confirmed. Against this background, this review summarizes previous reports on the biological process of cognitive decline in the elderly and the relationship between individual compounds in foods and cognitive function, as well as the role of individual components of food in cognitive function, in the following order: lipids, carotenoids, vitamins, phenolic compounds, amino acids, peptides, and proteins. Based on the research presented in this review, a proper diet that preserves cognitive function has the potential to improve age-related cognitive decline, Alzheimer's disease, and Parkinson's disease. Hopefully, this review will help to trigger the development of new foods and technologies that improve aging and cognitive functions and extend the healthy life span.

Maternal omega-3 intake differentially affects the endocannabinoid system in the progeny`s neocortex and hippocampus: Impact on synaptic markers

Omega-3 (n-3) polyunsaturated fatty acids (PUFA) and the endocannabinoid system (ECS) modulate several functions through neurodevelopment including synaptic plasticity mechanisms. The interplay between n-3PUFA and the ECS during the early stages of development, however, is not fully understood. This study investigated the effects of maternal n-3PUFA supplementation (n-3Sup) or deficiency (n-3Def) on ECS and synaptic markers in postnatal offspring. Female rats were fed with a control, n-3Def, or n-3Sup diet from 15 days before mating and during pregnancy. The cerebral cortex and hippocampus of mothers and postnatal 1-2 days offspring were analyzed. In the mothers, a n-3 deficiency reduced CB1 receptor (CB1R) protein levels in the cortex and increased CB2 receptor (CB2R) in both cortex and hippocampus. In neonates, a maternal n-3 deficiency reduced the hippocampal CB1R amount while it increased CB2R. Additionally, total GFAP isoform expression was increased in both cortex and hippocampus in neonates of the n-3Def group. Otherwise, maternal n-3 supplementation increased the levels of n-3-derived endocannabinoids, DHEA and EPEA, in the cortex and hippocampus and reduced 2-arachidonoyl-glycerol (2-AG) concentrations in the cortex of the offspring. Furthermore, maternal n-3 supplementation also increased PKA phosphorylation in the cortex and ERK phosphorylation in the hippocampus. Synaptophysin immunocontent in both regions was also increased. In vitro assays showed that the increase of synaptophysin in the n-3Sup group was independent of CB1R activation. The findings show that variations in maternal dietary omega-3 PUFA levels may impact differently on the ECS and molecular markers in the cerebral cortex and hippocampus of the progeny.

Brain foods - the role of diet in brain performance and health

The performance of the human brain is based on an interplay between the inherited genotype and external environmental factors, including diet. Food and nutrition, essential in maintenance of brain performance, also aid in prevention and treatment of mental disorders. Both the overall composition of the human diet and specific dietary components have been shown to have an impact on brain function in various experimental models and epidemiological studies. This narrative review provides an overview of the role of diet in 5 key areas of brain function related to mental health and performance, including: (1) brain development, (2) signaling networks and neurotransmitters in the brain, (3) cognition and memory, (4) the balance between protein formation and degradation, and (5) deteriorative effects due to chronic inflammatory processes. Finally, the role of diet in epigenetic regulation of brain physiology is discussed.

Different Mechanisms Underlie the Metabolic Response of GBM Stem-Like Cells to Ionizing Radiation: Biological and MRS Studies on Effects of Photons and Carbon Ions

Glioblastoma multiforme (GBM) is a malignant primary brain tumor with very poor prognosis, high recurrence rate, and failure of chemo-radiotherapy, mainly due to a small fraction of cells with stem-like properties (GSCs). To study the mechanisms of GSCs resistance to radiation, two GSC lines, named line #1 and line #83, with different metabolic patterns and clinical outcome, were irradiated with photon beams and carbon ions and assessed by ¹H Magnetic Resonance Spectroscopy (MRS). Both irradiation modalities induced early cytotoxic effects in line #1 with small effects on cell cycle, whereas a proliferative G2/M cytostatic block was observed in line #83. MR spectroscopy signals from mobile lipids (ML) increased in spectra of line #1 after photon and C-ion irradiation with effects on lipid unsaturation level, whereas no effects were detected in line #83 spectra. Gamma-Aminobutyric Acid (GABA), glutamic acid (glu) and Phosphocreatine (pCr) signals showed a significant variation only for line #1 after carbon ion irradiation. Glucose (glc) level and lactate (Lac) extrusion behaved differently in the two lines. Our findings suggest that the differences in irradiation response of GSCs #1 and #83 lines are likely attributable to their different metabolic fingerprint rather than to the different radiation types.

The Implications for Cells of the Lipid Switches Driven by Protein-Membrane Interactions and the Development of Membrane Lipid Therapy

The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist-receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane's lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell's physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes "lipid switches", as they alter the cell's status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer's lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.

PUFAs supplementation affects the renal expression of pannexin 1 and connexins in diabetic kidney of rats

In diabetic nephropathy (DN), intercellular communication is disrupted. Connexins (Cx) have a crucial role in that process. Dietary ratios and supplementation with polyunsaturated fatty acids (PUFAs) can alleviate diabetic complications and cause alterations in Cx levels. Although pannexins (Panx) share similarities with members of the Cx family, their function in diabetic nephropathy has still not been fully determined. We studied the influence of PUFA supplementation on the immunoexpression of Px1 and Cx family members in diabetic kidneys of rats. Four groups of rats in experimental DM1 model were supplemented with different dietary n-6/n-3 ratios; ≈7 in control (C) and diabetic groups (STZ), ≈ 60 in the STZ + N6 group and ≈ 1 (containing 16% EPA and 19% DHA) in the STZ + N3 group. Immunoexpression of Cx40, Cx43, Cx45 and Panx1 was evaluated in the renal tissue of diabetic rats using immunohistochemistry. Diabetes significantly decreased the protein expression of Cx40 and Cx43 and increased Panx1 protein expression in the renal cortex (p < 0.05-p < 0.01). There was a significant impact of diet on Cx and Panx1 immunoexpression. Dietary supplementation with a high n-6/n-3 ratio downregulated the protein expression of Cx45 and Panx1 in diabetic rats (p < 0.05-p < 0.01), while Cx43 immunoexpression was increased in diabetic rats fed with high and low n-6/n-3 ratios (p < 0.01-p < 0.001). Hyperglycaemic conditions in DN interfere with cell-to-cell communication and disturb the connection between cells and their immediate environment due to variations in connexin and pannexin immunoexpression. These variations can be regulated by PUFA dietary intake, suggesting their beneficial effect and possible therapeutic option.

Docosahexaenoic Acid Serving As Sensitizing Agents And Gefitinib Resistance Revertants In EGFR Targeting Treatment

Objective

Due to the resistance of cancer cells, chemotherapy has been severely restricted. Docosahexaenoic acid (DHA) has been broadly identified as the chemo-sensitizing agent and revertant of multidrug resistance owing to its pleiotropic characteristics; however, it has not been well interpreted. The purpose of this research was to identify the anticancer role of DHA and its combination with the chemotherapeutic agent Gefitinib in non-small cell lung cancer (NSCLC).

Methods

Human chemo-sensitive NSCLC PC-9 cells and the Gefitinib-resistant counterpart PC-9/GR cells were adopted to assess the effects of the integrated DHA and Gefitinib treatments in vitro and vivo, for which the combination index (CI), apoptosis rate and the epithelial growth factor receptor (EGFR) pathway were analyzed.

Results

Comparing with the control cells, the DHA-treated PC-9/GR cells triggered the increase of drug absorption and sensitivity, suggesting that the sensitivity of chemotherapeutic drug could be induced by DHA. Moreover, the elevation of phosphorylation levels of EGFR and the downstream extracellular signal-regulated kinase (ERK) in the cellular lysates were induced by the DHA+Gefitinib treatment. Additionally, the long-term Gefitinib stimulated PC-9 model revealed that DHA could revert the Gefitinib resistance.

Conclusion

This is the first research that indicated the novel biochemical effect of DHA, which can help in overcoming the resistance of EGFR-TKI in NSCLC cells and broaden the horizon of the DHA supplementation during the NSCLC therapy.

Dietary Polar Lipids and Cognitive Development: A Narrative Review

Polar lipids are amphiphilic lipids with a hydrophilic head and a hydrophobic tail. Polar lipids mainly include phospholipids and sphingolipids. They are structural components of neural tissues, with the peak rate of accretion overlapping with neurodevelopmental milestones. The critical role of polar lipids in cognitive development is thought to be mediated through the regulation of signal transduction, myelination, and synaptic plasticity. Animal products (egg, meat, and dairy) are the major dietary sources of polar lipids for children and adults, whereas human milk and infant formula provide polar lipids to infants. Due to the differences observed in both concentration and proportion of polar lipids in human milk, the estimated daily intake in infants encompasses a wide range. In addition, health authorities define neither intake recommendations nor guidelines for polar lipid intake. However, adequate intake is defined for 2 nutrients that are elements of these polar lipids, namely choline and DHA. To date, limited studies exist on the brain bioavailability of dietary polar lipids via either placental transfer or the blood-brain barrier. Nevertheless, due to their role in pre- and postnatal development of the brain, there is a growing interest for the use of gangliosides, which are sphingolipids, as a dietary supplement for pregnant/lactating mothers or infants. In line with this, supplementing gangliosides and phospholipids in wild-type animals and healthy infants does suggest some positive effects on cognitive performance. Whether there is indeed added benefit of supplementing polar lipids in pregnant/lactating mothers or infants requires more clinical research. In this article, we report findings of a review of the state-of-the-art evidence on polar lipid supplementation and cognitive development. Dietary sources, recommended intake, and brain bioavailability of polar lipids are also discussed.

Adipocytes promote ovarian cancer chemoresistance

Ovarian cancer (OvCa), while accounting for only 3% of all women’s cancer, is the fifth leading cause of cancer death among women. One of the most significant obstacles to successful OvCa treatment is chemoresistance. The current lack of understanding of the driving mechanisms underlying chemoresistance hinders the development of effective therapeutics against this obstacle. Adipocytes are key components of the OvCa microenvironment and have been shown to be involved in OvCa cell proliferation, however, little is known about their impact on OvCa chemoresistance. In the current study, we found that adipocytes, of both subcutaneous and visceral origin, secrete factors that enhance the resistance of OvCa cells against chemotherapeutic drugs by activating the Akt pathway. Importantly, we have demonstrated that secreted lipids mediate adipocyte-induced chemoresistance. Through a comprehensive lipidomic analysis, we have identified this chemo-protective lipid mediator as arachidonic acid (AA). AA acts on OvCa cells directly, not through its downstream derivatives such as prostaglandins, to activate Akt and inhibit cisplatin-induced apoptosis. Taken together, our study has identified adipocytes and their secreted AA as important mediators of OvCa chemoresistance. Strategies that block the production of AA from adipocytes or block its anti-apoptotic function may potentially inhibit chemoresistance in OvCa patients.

Omega-3 Docosahexaenoic Acid Is a Mediator of Fate-Decision of Adult Neural Stem Cells

The mammalian brain is enriched with lipids that serve as energy catalyzers or secondary messengers of essential signaling pathways. Docosahexaenoic acid (DHA) is an omega-3 fatty acid synthesized de novo at low levels in humans, an endogenous supply from its precursors, and is mainly incorporated from nutrition, an exogeneous supply. Decreased levels of DHA have been reported in the brains of patients with neurodegenerative diseases. Preventing this decrease or supplementing the brain with DHA has been considered as a therapy for the DHA brain deficiency that could be linked with neuronal death or neurodegeneration. The mammalian brain has, however, a mechanism of compensation for loss of neurons in the brain: neurogenesis, the birth of neurons from neural stem cells. In adulthood, neurogenesis is still present, although at a slower rate and with low efficiency, where most of the newly born neurons die. Neural stem/progenitor cells (NSPCs) have been shown to require lipids for proper metabolism for proliferation maintenance and neurogenesis induction. Recent studies have focused on the effects of these essential lipids on the neurobiology of NSPCs. This review aimed to introduce the possible use of DHA to impact NSPC fate-decision as a therapy for neurodegenerative diseases.

Reduced level of docosahexaenoic acid shifts GPCR neuroreceptors to less ordered membrane regions

G protein-coupled receptors (GPCRs) control cellular signaling and responses. Many of these GPCRs are modulated by cholesterol and polyunsaturated fatty acids (PUFAs) which have been shown to co-exist with saturated lipids in ordered membrane domains. However, the lipid compositions of such domains extracted from the brain cortex tissue of individuals suffering from GPCR-associated neurological disorders show drastically lowered levels of PUFAs. Here, using free energy techniques and multiscale simulations of numerous membrane proteins, we show that the presence of the PUFA DHA helps helical multi-pass proteins such as GPCRs partition into ordered membrane domains. The mechanism is based on hybrid lipids, whose PUFA chains coat the rough protein surface, while the saturated chains face the raft environment, thus minimizing perturbations therein. Our findings suggest that the reduction of GPCR partitioning to their native ordered environments due to PUFA depletion might affect the function of these receptors in numerous neurodegenerative diseases, where the membrane PUFA levels in the brain are decreased. We hope that this work inspires experimental studies on the connection between membrane PUFA levels and GPCR signaling.

Our current picture of cellular membranes depicts them as laterally heterogeneous sheets of lipids crowded with membrane proteins. These proteins often require a specific lipid environment to efficiently perform their functions. Certain neuroreceptor proteins are regulated by membrane cholesterol that is considered to be enriched in ordered membrane domains. In the brain, these very same domains also contain a fair amount of polyunsaturated fatty acids (PUFAs) that have also been discovered to interact favorably with many receptor proteins. However, certain neurological diseases—associated with the inadequate functioning of the neuroreceptors—seem to result in the decrease of brain PUFA levels. We hypothesized that this decrease in PUFA levels somehow inhibits receptor partitioning to cholesterol-rich domains, which could further compromise their function. We verified our hypothesis by an extensive set of computer simulations. They demonstrated that the PUFA–receptor interaction indeed leads to favorable partitioning of the receptors in the cholesterol-rich ordered domains. Moreover, the underlying mechanism based on the shielding of the rough protein surface by the PUFAs seems to be exclusive for multi-helical protein structures, of which neuroreceptors are a prime example.

Low omega-6/omega-3 ratio in a maternal protein-deficient diet promotes histone-3 changes in progeny neural cells and favors leukemia inhibitory factor genetranscription

Omega-3 (n-3) fatty acids modulate epigenetic changes critical to genesis and differentiation of neural cells. Conversely, maternal protein-malnutrition can negatively modify these changes. This study investigated whether a low n-6/n-3 ratio in a maternal diet could favor histone-3 (H3) modifications, gene transcription and differentiation in the offspring neural cells even under protein-deficiency. Female rats fed a control (Ct), or 3 types of multideficient diets differing in protein levels or linoleic/alpha-linolenic fatty acid ratios (RBD, RBD-C, RBD-SO) from 30 days prior to mating and during pregnancy. Cerebral cortex tissue and cortical cultures of progeny embryonic neurons and postnatal astrocytes were analyzed. H3K9 acetylation and H3K27 or H3K4 di-methylation levels were assessed by flow cytometry and/or immunocytochemistry. In astrocyte cultures and cortical tissue, the GFAP protein levels were assessed. Glial derived neurotrophic factor (GDNF) and leukemia inhibitory factor (LIF) gene expression were evaluated in the cortical tissue. GFAP levels were similar in astrocytes of Ct, RBD and RBD-C, but 65% lower in RBD-SO group. Higher levels of H3K9Ac were found in the neurons and H3K4Me2 in the astrocytes of the RBD group. No intergroup difference in the cortical GDNF mRNA expression or the H3K27Me2 levels in astrocytes was detected. LIF mRNA levels were higher in the RDB (P=.002) or RBD-C (P=.004) groups than in the control. The findings indicate the importance of dietary n-3 availability for the brain, even under a protein-deficient condition, inducing Histone modifications and increasing LIF gene transcription, involved in neural cell differentiation and reactivity.

Opportunities and Challenges in the Discovery of Allosteric Modulators of GPCRs

From the pharmacological point of view, allosteric modulators may present numerous advantages over orthosteric ligands. Growing availability of novel tools and experimental data provides a tempting opportunity to apply computational methods to improve known modulators and design novel ones. However, recent progress in understanding of complexity of allostery increases awareness of problems involved in design of modulators with desired properties. Deeper insight into phenomena such as probe dependence, altering signaling bias with minor changes in ligand structure, as well as influence of subtle endogenous allosteric factors turns out to be fundamental. These effects make the design of a modulator with precise pharmacological outcome a very challenging task, and need to be taken into consideration throughout the design process. In this chapter, we focus on nuances of targeting GPCR allosteric sites in computational drug design efforts, in particular with application of docking, virtual screening, and molecular dynamics.

The Role of Lipid Metabolism for Neural Stem Cell Regulation

Neural stem/progenitor cells (NSPCs) give rise to billions of cells during development and are critical for proper brain formation. The finding that NSPCs persist throughout adulthood has challenged the view that the brain has poor regenerative abilities and raised hope for stem cell-based regenerative therapies. For decades there has been a strong movement towards understanding the requirements of NSPCs and their regulation, resulting in the discovery of many transcription factors and signaling pathways that can influence NSPC behavior and neurogenesis. However, the role of metabolism for NSPC regulation has only gained attention recently. Lipid metabolism in particular has been shown to influence proliferation and neurogenesis, offering exciting new possible mechanisms of NSPC regulation, as lipids are not only the building blocks of membranes, but can also act as alternative energy sources and signaling entities. Here I review the recent literature examining the role of lipid metabolism for NSPC regulation and neurogenesis.

Is cytotoxicity a determinant of the different in vitro and in vivo effects of bioactives?

BACKGROUND

Foodstuffs of both plant and animal origin contain a wide range of bioactive compounds. Although human intervention studies are mandatory to assess the health effects of bioactives, the in vitro approach is often used to select the most promising molecules to be studied in vivo. To avoid misleading results, concentration and chemical form, exposure time, and potential cytotoxicity of the tested bioactives should be carefully set prior to any other experiments.

METHODS

In this study the possible cytotoxicity of different bioactives (docosahexaenoic acid, propionate, cyanidin-3-O-glucoside, protocatechuic acid), was investigated in HepG2 cells using different methods. Bioactives were supplemented to cells at different concentrations within the physiological range in human blood, alone or in combination, considering two different exposure times.

RESULTS

Reported data clearly evidence that in vitro cytotoxicity is tightly related to the exposure time, and it varies among bioactives, which could exert a cytotoxic effect even at a concentration within the in vivo physiological blood concentration range. Furthermore, co-supplementation of different bioactives can increase the cytotoxic effect.

CONCLUSIONS

Our results underline the importance of in vitro cytotoxicity screening that should be considered mandatory before performing studies aimed to evaluate the effect of bioactives on other cellular parameters. Although this study is far from the demonstration of a toxic effect of the tested bioactives when administered to humans, it represents a starting point for future research aimed at verifying the existence of a potential hazard due to the wide use of high doses of multiple bioactives.

Oral feeding with polyunsaturated fatty acids fosters hematopoiesis and thrombopoiesis in healthy and bone marrow-transplanted mice

Hematopoietic stem cells play the vital role of maintaining appropriate levels of cells in blood. Therefore, regulation of their fate is essential for their effective therapeutic use. Here we report the role of polyunsaturated fatty acids (PUFAs) in regulating hematopoiesis which has not been explored well so far. Mice were fed daily for 10 days with n-6/n-3 PUFAs, viz. linoleic acid (LA), arachidonic acid (AA), alpha-linolenic acid and docosahexanoic acid (DHA) in four separate test groups with phosphate-buffered saline fed mice as control set. The bone marrow cells of PUFA-fed mice showed a significantly higher hematopoiesis as assessed using side population, Lin-Sca-1⁺ckit+, colony-forming unit (CFU), long-term culture, CFU-spleen assay and engraftment potential as compared to the control set. Thrombopoiesis was also stimulated in PUFA-fed mice. A combination of DHA and AA was found to be more effective than when either was fed individually. Higher incorporation of PUFAs as well as products of their metabolism was observed in the bone marrow cells of PUFA-fed mice. A stimulation of the Wnt, CXCR4 and Notch1 pathways was observed in PUFA-fed mice. The clinical relevance of this study was evident when bone marrow-transplanted recipient mice, which were fed with PUFAs, showed higher engraftment of donor cells, suggesting that the bone marrow microenvironment may also be stimulated by feeding with PUFAs. These data indicate that oral administration of PUFAs in mice stimulates hematopoiesis and thrombopoiesis and could serve as a valuable supplemental therapy in situations of hematopoietic failure.

Arachidonic acid and Docosahexanoic acid enhance platelet formation from human apheresis-derived CD34+ cells

An Aberration in megakaryopoiesis and thrombopoiesis, 2 important processes that maintain hemostasis, leads to thrombocytopenia. Though platelet transfusions are used to treat this condition, blood banks frequently face a shortage of platelets. Therefore, methods to generate platelets on a large scale are strongly desirable. However, to generate megakaryocytes (MKs) and platelets (PLTs) in numbers sufficient for clinical application, it is essential to understand the mechanism of platelet production and explore efficient strategies accordingly. We have earlier reported that the N-6 and N-3 poly-unsaturated fatty acids (PUFAs), Arachidonic acid (AA)/Docosahexanoic acid (DHA) have beneficial effect on the generation of MKs and PLTs from umbilical cord blood derived CD34⁺ cells. Here we tested if a similar effect is observed with peripheral blood derived CD34⁺ cells, which are more commonly used in transplantation settings. We found a significant enhancement in cell numbers, surface marker expression, cellular ploidy and expression of cytoskeletal components during PLT biogenesis in cultures exposed to media containing AA/DHA than control cultures that were not exposed to these PUFAs. The test cells engrafted more efficiently in NOD/SCID mice than control cells. AA/DHA appears to have enhanced MK/PLT generation through upregulation of the NOTCH and AKT pathways. Our data show that PUFAs could be valuable additives in the culture system for large scale production of platelets for clinical applications.

Regional changes in CNS and retinal glycerophospholipid profiles with age: a molecular blueprint

We present here a quantitative molecular blueprint of the three major glycerophospholipid (GPL) classes, phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE), in retina and six regions of the brain in C57Bl6 mice at 2, 10, and 26 months of age. We found an age-related increase in molecular species containing saturated and monoenoic FAs and an overall decrease in the longer-chain PUFA molecular species across brain regions, with loss of DHA-containing molecular species as the most consistent and dramatic finding. Although we found very-long-chain PUFAs (VLC-PUFAs) (C28) in PC in the retina, no detectable levels were found in any brain region at any of the ages examined. All brain regions (except hippocampus and retina) showed a significant increase with age in PE plasmalogens. All three retina GPLs had di-PUFA molecular species (predominantly 44:12), which were most abundant in PS (∼30%). In contrast, low levels of di-PUFA GPL (1-2%) were found in all regions of the brain. This study provides a regional and age-related assessment of the brain's lipidome with a level of detail, inclusion, and quantification that has not heretofore been published.

Maintenance of membrane organization in the aging mouse brain as the determining factor for preventing receptor dysfunction and for improving response to anti-Alzheimer treatments

Although a major risk factor for Alzheimer's disease (AD), the "aging" parameter is not systematically considered in preclinical validation of anti-AD drugs. To explore how aging affects neuronal reactivity to anti-AD agents, the ciliary neurotrophic factor (CNTF)-associated pathway was chosen as a model. Comparison of the neuroprotective properties of CNTF in 6- and 18-month old mice revealed that CNTF resistance in the older animals is associated with the exclusion of the CNTF-receptor subunits from rafts and their subsequent dispersion to non-raft cortical membrane domains. This age-dependent membrane remodeling prevented both the formation of active CNTF-receptor complexes and the activation of prosurvival STAT3 and ERK1/2 pathways, demonstrating that age-altered membranes impaired the reactivity of potential therapeutic targets. CNTF-receptor distribution and CNTF signaling responses were improved in older mice receiving dietary docosahexaenoic acid, with CNTF-receptor functionality being similar to those of younger mice, pointing toward dietary intervention as a promising adjuvant strategy to maintain functional neuronal membranes, thus allowing the associated receptors to respond appropriately to anti-AD agents.

Regulation of Connexin-Based Channels by Fatty Acids

In this mini-review, we briefly summarize the current knowledge about the effects of fatty acids (FAs) on connexin-based channels, as well as discuss the limited information about the impact FAs may have on pannexins (Panxs). FAs regulate diverse cellular functions, some of which are explained by changes in the activity of channels constituted by connexins (Cxs) or Panxs, which are known to play critical roles in maintaining the functional integrity of diverse organs and tissues. Cxs are transmembrane proteins that oligomerize into hexamers to form hemichannels (HCs), which in turn can assemble into dodecamers to form gap junction channels (GJCs). While GJCs communicate the cytoplasm of contacting cells, HCs serve as pathways for the exchange of ions and small molecules between the intra and extracellular milieu. Panxs, as well as Cx HCs, form channels at the plasma membrane that enable the interchange of molecules between the intra and extracellular spaces. Both Cx- and Panx-based channels are controlled by several post-translational modifications. However, the mechanism of action of FAs on these channels has not been described in detail. It has been shown however that FAs frequently decrease GJC-mediated cell-cell communication. The opposite effect also has been described for HC or Panx-dependent intercellular communication, where, the acute FA effect can be reversed upon washout. Additionally, changes in GJCs mediated by FAs have been associated with post-translational modifications (e.g., phosphorylation), and seem to be directly related to chemical properties of FAs (e.g., length of carbon chain and/or degree of saturation), but this possible link remains poorly understood.

Distinctive effects of eicosapentaenoic and docosahexaenoic acids in regulating neural stem cell fate are mediated via endocannabinoid signalling pathways

Emerging evidence suggests a complex interplay between the endocannabinoid system, omega-3 fatty acids and the immune system in the promotion of brain self-repair. However, it is unknown if all omega-3 fatty acids elicit similar effects on adult neurogenesis and if such effects are mediated or regulated by interactions with the endocannabinoid system. This study investigated the effects of DHA and EPA on neural stem cell (NSC) fate and the role of the endocannabinoid signalling pathways in these effects. EPA, but not DHA, significantly increased proliferation of NSCs compared to controls, an effect associated with enhanced levels of the endocannabinoid 2-arachidonylglycerol (2-AG) and p-p38 MAPK, effects attenuated by pre-treatment with CB1 (AM251) or CB2 (AM630) receptor antagonists. Furthermore, in NSCs derived from IL-1β deficient mice, EPA significantly decreased proliferation and p-p38 MAPK levels compared to controls, suggesting a key role for IL-1β signalling in the effects observed. Although DHA similarly increased 2-AG levels in wild-type NSCs, there was no concomitant increase in proliferation or p-p38 MAPK activity. In addition, in NSCs from IL-1β deficient mice, DHA significantly increased proliferation without effects on p-P38 MAPK, suggesting effects of DHA are mediated via alternative signalling pathways. These results provide crucial new insights into the divergent effects of EPA and DHA in regulating NSC proliferation and the pathways involved, and highlight the therapeutic potential of their interplay with endocannabinoid signalling in brain repair.

Dietary macronutrients and the aging liver sinusoidal endothelial cell

Fenestrations are pores within the liver sinusoidal endothelial cells (LSECs) that line the sinusoids of the highly vascularized liver. Fenestrations facilitate the transfer of substrates between blood and hepatocytes. With pseudocapillarization of the hepatic sinusoid in old age, there is a loss of fenestrations. LSECs are uniquely exposed to gut-derived dietary and microbial substrates delivered by the portal circulation to the liver. Here we studied the effect of 25 diets varying in content of macronutrients and energy on LSEC fenestrations using the Geometric Framework method in a large cohort of mice aged 15 mo. Macronutrient distribution rather than total food or energy intake was associated with changes in fenestrations. Porosity and frequency were inversely associated with dietary fat intake, while fenestration diameter was inversely associated with protein or carbohydrate intake. Fenestrations were also linked to diet-induced changes in gut microbiome, with increased fenestrations associated with higher abundance of Firmicutes and reduced abundance of Bacteroidetes Diet-induced changes in levels of several fatty acids (C16:0, C19:0, and C20:4) were also significantly inversely associated with fenestrations, suggesting a link between dietary fat and modulation of lipid rafts in the LSECs. Diet influences fenestrations and these data reflect both the key role of the LSECs in clearing gut-derived molecules from the vascular circulation and the impact these molecules have on LSEC morphology.

Docosahexaenoic acid (DHA) prevents corticosterone-induced changes in astrocyte morphology and function

The many functions of astrocytes, such as glutamate recycling and morphological plasticity, enable them to stabilize synapses environment and protect neurons. Little is known about how they adapt to glucocorticoid-induced stress, and even less about the influence of dietary factors. We previously showed that omega-3 polyunsaturated fatty acids (ω3PUFA), dietary fats which alleviate stress responses, influence the way astroglia regulate glutamatergic synapses. We have explored the role of docosahexaenoic acid (DHA), the main ω3PUFA, in the astroglial responses to corticosterone, the main stress hormone in rodents to determine whether ω3PUFA help astrocytes resist stress. Cultured rat astrocytes were enriched in DHA or arachidonic acid (AA, the main ω6PUFA) and given 100 nM corticosterone for several days. Corticosterone stimulated astrocyte glutamate recycling by increasing glutamate uptake and glutamine synthetase (GS), and altered the astrocyte cytoskeleton. DHA-enriched astrocytes no longer responded to the action of corticosterone on glutamate uptake, had decreased GS, and the cytoskeletal effect of corticosterone was delayed, while AA-enriched cells were unaffected. The DHA-dependent anti-corticosterone effect was related to fewer glucocorticoid receptors, while corticosterone increased DHA incorporation into astrocyte membranes. Thus, DHA helps astrocytes resist the influence of corticosterone, so perhaps promoting a sustainable response by the stressed brain. We show that corticosterone increases the glutamate recycling capacity of rat cortical astrocytes in culture, and alters their morphology, which may be detrimental in the long term. Increasing the membrane incorporation of docosahexaenoic acid (DHA), the main omega-3 in brain, reduces the amount of glucocorticoid receptors (GR) and prevents the effects of corticosterone. This may help the astrocytes maintain a functional phenotype in chronic stress situations.

Role of Polyunsaturated Fatty Acids and Their Metabolites on Stem Cell Proliferation and Differentiation

The nervous system is highly enriched with long-chain polyunsaturated fatty acids (PUFAs). Essential fatty acids, namely, ω-6 (n - 6) and ω-3 (n - 3) PUFA, and their metabolites are critical components of cell structure and function and could therefore influence stem cell fate. The available supporting experimental data reveal that n - 6 and n - 3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. PUFAs and their mediators regulate several processes within the brain, such as neurotransmission, cell survival and neuroinflammation, and thereby mood and cognition. PUFA levels and the signaling pathways that they regulate are altered in various neurological disorders, including Alzheimer's disease and major depression. Therefore, elucidating the role of PUFAs and their metabolites in stem cell fate regulation is important for stem cell biology as well as stem cell therapy. PUFA-based interventions to generate a positive environment for stem cell proliferation or differentiation might be a promising and practical approach to controlling stem cell fate for clinical applications.

Pathways of polyunsaturated fatty acid utilization: implications for brain function in neuropsychiatric health and disease

Essential polyunsaturated fatty acids (PUFAs) have profound effects on brain development and function. Abnormalities of PUFA status have been implicated in neuropsychiatric diseases such as major depression, bipolar disorder, schizophrenia, Alzheimer's disease, and attention deficit hyperactivity disorder. Pathophysiologic mechanisms could involve not only suboptimal PUFA intake, but also metabolic and genetic abnormalities, defective hepatic metabolism, and problems with diffusion and transport. This article provides an overview of physiologic factors regulating PUFA utilization, highlighting their relevance to neuropsychiatric disease.

Concise review: Regulation of stem cell proliferation and differentiation by essential fatty acids and their metabolites

Stem cell therapy holds great promise for regenerative medicine and the treatment of numerous diseases. A key issue of stem cell therapy is the control of stem cell fate, but safe and practical methods are limited. Essential fatty acids, namely ω-6 (n-6) and ω-3 (n-3) polyunsaturated fatty acids (PUFA), and their metabolites are critical components of cell structure and function, and could therefore influence stem cell fate. The available evidence demonstrates that n-6 and n-3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. Therefore, elucidating the role of PUFA and their metabolites in stem cell fate regulation is both a challenge and an opportunity for stem cell biology as well as stem cell therapy. PUFA-based interventions to create a favorable environment for stem cell proliferation or differentiation may thus be a promising and practical approach to controlling stem cell fate for clinical applications.

Recent developments in lipid metabolism in ruminants – the role of fat in maintaining animal health and performance

Optimising farm animal performance has long been the key focus of worldwide livestock production research. Advances in the understanding of metabolism/phenotype associations have outlined the central role of the lipid metabolism of farm animals for economically relevant phenotypic traits, such as animal health (immune status, fertility/reproductive capacity, adaptability/metabolic flexibility, robustness, well being) and performance aspects (meat/milk quality and quantity) and have led to an extensive exploitation of lipid metabolism manipulation strategies (e.g. tailored nutritional regimes, alimentary/intravenous fat supplementation, rumen-protected fat feeding, hormone application). This contribution gives an overview of established concepts to tailor animals’ lipid metabolism and highlights novel strategies to expand these application-oriented approaches via improved analysis tools, omics-approaches, cell model systems and systems biology methods.

Dexamethasone inhibits the maturation of newly formed neurons and glia supplemented with polyunsaturated fatty acids

Stress bears a negative impact on adult neurogenesis. High levels of corticoids have been shown to inhibit neural stem cell proliferation, and are considered responsible for the loss of neural precursors. Their effects on the differentiation of the glial and neuronal lineages have been less studied. We examined the effect of dexamethasone (Dex), a synthetic glucocorticoid, on the differentiation of rat neural stem cells in vitro. Dex had no effect on the differentiation of cells cultured under standard conditions. Since we previously determined that NSC, when cultured under classical conditions, were deprived of polyunsaturated fatty acids (PUFA), and displayed phospholipid compositions very different from the in vivo figures [1], we examined the effect of Dex under PUFA supplementation. Dex impaired neuron and oligodendrocyte maturation in PUFA-supplemented cells, demonstrated by the reduction of neurite lengths and oligodendrocyte sizes. This effect was mediated by the glucocorticoid receptor (GR), since it was eliminated by mifepristone, a GR antagonist, and could be relayed by a reduction of ERK phosphorylation. We determined that GR was associated with PPAR β and α under basal conditions, and that this association was disrupted when PUFA were added in combination with Dex. We assumed that this effect on the receptor status enabled the effect of Dex on PUFA supplemented cells, since we determined that the binding to the glucocorticoid response element was higher in cells incubated with PUFA and Dex. In conclusion, corticoids can impair NSC differentiation, and consequently impact the entire process of neurogenesis.

Using neurolipidomics to identify phospholipid mediators of synaptic (dys)function in Alzheimer's Disease

Not all of the mysteries of life lie in our genetic code. Some can be found buried in our membranes. These shells of fat, sculpted in the central nervous system into the cellular (and subcellular) boundaries of neurons and glia, are themselves complex systems of information. The diversity of neural phospholipids, coupled with their chameleon-like capacity to transmute into bioactive molecules, provides a vast repertoire of immediate response second messengers. The effects of compositional changes on synaptic function have only begun to be appreciated. Here, we mined 29 neurolipidomic datasets for changes in neuronal membrane phospholipid metabolism in Alzheimer's Disease (AD). Three overarching metabolic disturbances were detected. We found that an increase in the hydrolysis of platelet activating factor precursors and ethanolamine-containing plasmalogens, coupled with a failure to regenerate relatively rare alkyl-acyl and alkenyl-acyl structural phospholipids, correlated with disease severity. Accumulation of specific bioactive metabolites [i.e., PC(O-16:0/2:0) and PE(P-16:0/0:0)] was associated with aggravating tau pathology, enhancing vesicular release, and signaling neuronal loss. Finally, depletion of PI(16:0/20:4), PI(16:0/22:6), and PI(18:0/22:6) was implicated in accelerating Aβ₄₂ biogenesis. Our analysis further suggested that converging disruptions in platelet activating factor, plasmalogen, phosphoinositol, phosphoethanolamine (PE), and docosahexaenoic acid metabolism may contribute mechanistically to catastrophic vesicular depletion, impaired receptor trafficking, and morphological dendritic deformation. Together, this analysis supports an emerging hypothesis that aberrant phospholipid metabolism may be one of multiple critical determinants required for Alzheimer disease conversion.

Omega-3 fatty acids and brain resistance to ageing and stress: body of evidence and possible mechanisms

The increasing life expectancy in the populations of rich countries raises the pressing question of how the elderly can maintain their cognitive function. Cognitive decline is characterised by the loss of short-term memory due to a progressive impairment of the underlying brain cell processes. Age-related brain damage has many causes, some of which may be influenced by diet. An optimal diet may therefore be a practical way of delaying the onset of age-related cognitive decline. Nutritional investigations indicate that the ω-3 poyunsaturated fatty acid (PUFA) content of western diets is too low to provide the brain with an optimal supply of docosahexaenoic acid (DHA), the main ω-3 PUFA in cell membranes. Insufficient brain DHA has been associated with memory impairment, emotional disturbances and altered brain processes in rodents. Human studies suggest that an adequate dietary intake of ω-3 PUFA can slow the age-related cognitive decline and may also protect against the risk of senile dementia. However, despite the many studies in this domain, the beneficial impact of ω-3 PUFA on brain function has only recently been linked to specific mechanisms. This review examines the hypothesis that an optimal brain DHA status, conferred by an adequate ω-3 PUFA intake, limits age-related brain damage by optimizing endogenous brain repair mechanisms. Our analysis of the abundant literature indicates that an adequate amount of DHA in the brain may limit the impact of stress, an important age-aggravating factor, and influences the neuronal and astroglial functions that govern and protect synaptic transmission. This transmission, particularly glutamatergic neurotransmission in the hippocampus, underlies memory formation. The brain DHA status also influences neurogenesis, nested in the hippocampus, which helps maintain cognitive function throughout life. Although there are still gaps in our knowledge of the way ω-3 PUFA act, the mechanistic studies reviewed here indicate that ω-3 PUFA may be a promising tool for preventing age-related brain deterioration.

L1 cell adhesion molecule signaling is inhibited by ethanol in vivo

BACKGROUND

Fetal alcohol spectrum disorder is an immense public health problem. In vitro studies support the hypothesis that L1 cell adhesion molecule (L1) is a target for ethanol (EtOH) developmental neurotoxicity. L1 is critical for the development of the central nervous system. It functions through signal transduction leading to phosphorylation and dephosphorylation of tyrosines on its cytoplasmic domain. The function of L1 is also dependent on trafficking through lipid rafts (LRs). Our hypothesis is that L1 is a target for EtOH neurotoxicity in vivo. Our objective is to demonstrate changes in L1 phosphorylation/dephosphorylation and LR association in vivo.

METHODS

Rat pups on postnatal day 6 are administered 4.5, 5.25, and 6 g/kg of EtOH divided into 2 doses 2 hours apart, then killed. Cerebella are rapidly frozen for assay. Blood is analyzed for blood EtOH concentration. L1 tyrosine phosphorylation is determined by immunoprecipitation and dephosphorylation of tyrosine 1176 determined by immunoblot. LRs are isolated by sucrose density gradient, and the distribution of L1 in LRs is determined.

RESULTS

EtOH at all doses reduced the relative amount of Y1176 dephosphorylation as well as the relative amount of L1 phosphorylated on other tyrosines. The proportion of L1 present in LRs is significantly increased in pups who received 6 g/kg EtOH compared to intubated controls.

CONCLUSIONS

L1 is a target for EtOH developmental neurotoxicity in vivo.

Profiling changes triggered during maturation of dendritic cells: a lipidomic approach

Lipids are important in several biological processes because they act as signalling and regulating molecules, or, locally, as membrane components that modulate protein function. This paper reports the pattern of lipid composition of dendritic cells (DCs), a cell type of critical importance in inflammatory and immune responses. After activation by antigens, DCs undergo drastic phenotypical and functional transformations, in a process known as maturation. To better characterize this process, changes of lipid profile were evaluated by use of a lipidomic approach. As an experimental model of DCs, we used a foetal skin-derived dendritic cell line (FSDC) induced to mature by treatment with lipopolysaccharide (LPS). The results showed that LPS treatment increased ceramide (Cer) and phosphatidylcholine (PC) levels and reduced sphingomyelin (SM) and phosphatidylinositol (PI) content. Mass spectrometric analysis of a total lipid extract and of each class of lipids revealed that maturation promoted clear changes in ceramide profile. Quantitative analysis enabled identification of an increase in the total ceramide content and enhanced Cer at m/z 646.6, identified as Cer(d18:1/24:1), and at m/z 648.6, identified as Cer(d18:1/24:0). The pattern of change of these lipids give an extremely rich source of data for evaluating modulation of specific lipid species triggered during DC maturation.

Nutrigenomics and Cancer Prevention

Mounting evidence continues to point to dietary habits as a modifier of cancer risk and tumor behavior; although it is clear that considerable variability occurs across studies. While genetic public health messages can be developed, the use of mean values may result in underexposure to some essential and nonessential food components, yet precipitate overexposure to nutrients. Undeniably, inconsistencies in the literature may reflect variation in timing of exposures to specific dietary constituents, interactions with the food matrix, processing technologies, or the genomic variation among individuals, which can influence absorption, metabolism, and/or the molecular target. Inter-individual variability in genetics, epigenetics, transcriptomics, proteomics, metabolomics, or microbiomics can influence the magnitude and direction of response to bioactive food components, as briefly reviewed in this article. Unquestionably, understanding nutrigenomics holds promise to reveal those who will benefit most from dietary interventions plus identify any who might be placed at risk due to overexposures.

Biophysical and biochemical mechanisms by which dietary N-3 polyunsaturated fatty acids from fish oil disrupt membrane lipid rafts

N-3 polyunsaturated fatty acids (PUFAs) from fish oil exert their functional effects by targeting multiple mechanisms. One mechanism to emerge in the past decade is the ability of n-3 PUFA acyl chains to perturb the molecular organization of plasma membrane sphingolipid/cholesterol-enriched lipid raft domains. These domains are nanometer-scale assemblies that coalesce to compartmentalize select proteins for optimal function. Here we review recent evidence on how n-3 PUFAs modify lipid rafts from biophysical and biochemical experiments from several different model systems. A central theme emerges from these studies. N-3 PUFA acyl chains display tremendous conformational flexibility and a low affinity for cholesterol and saturated acyl chains. This unique flexibility of n-3 PUFA acyl chains impacts the organization of inner and outer leaflet lipid rafts by disrupting acyl chain packing and molecular order within rafts. Ultimately, the disruption in raft organization has consequences for protein clustering and thereby signaling. Overall, elucidating the complex mechanisms by which n-3 PUFA acyl chains reorganize membrane architecture will enhance the translation of these fatty acids into the clinic for treating several diseases.

Systems virology identifies a mitochondrial fatty acid oxidation enzyme, dodecenoyl coenzyme A delta isomerase, required for hepatitis C virus replication and likely pathogenesis

We previously employed systems biology approaches to identify the mitochondrial fatty acid oxidation enzyme dodecenoyl coenzyme A delta isomerase (DCI) as a bottleneck protein controlling host metabolic reprogramming during hepatitis C virus (HCV) infection. Here we present the results of studies confirming the importance of DCI to HCV pathogenesis. Computational models incorporating proteomic data from HCV patient liver biopsy specimens recapitulated our original predictions regarding DCI and link HCV-associated alterations in cellular metabolism and liver disease progression. HCV growth and RNA replication in hepatoma cell lines stably expressing DCI-targeting short hairpin RNA (shRNA) were abrogated, indicating that DCI is required for productive infection. Pharmacologic inhibition of fatty acid oxidation also blocked HCV replication. Production of infectious HCV was restored by overexpression of an shRNA-resistant DCI allele. These findings demonstrate the utility of systems biology approaches to gain novel insight into the biology of HCV infection and identify novel, translationally relevant therapeutic targets.

Dietary lipids from an evolutionary perspective: sources, structures and functions

Lipids are a complex group of biomolecules whose precise functions remain poorly understood. As a result of this poor understanding, it is difficult to make mechanistically based recommendations for appropriate dietary intakes. It is equally difficult to develop methods that are capable of diagnosing functional impairments because of insufficiencies or excesses in particular fatty acids. Lipids are abundant building blocks of cellular membranes, supply components for lipid particle assembly and substrates for metabolic fuel, and provide a precursor pool for an astonishingly diverse range of signalling molecules. In each of these broad functions, the functional consequences of different structures of fatty acids are not fully understood. According to research on membrane functions through early evolution, docosahexaenoic acid provides two biophysical properties to membranes - accelerating the lateral motion of lipids and proteins within the plane of the membrane and simultaneously slowing the rate of diffusion/leakage of charged species across the plane of the membrane. The range of fatty acid structures used as substrates for assembly of either lipoproteins or milk fat globules is broad, yet the functional consequences of differences are not known. Different lipids signal into a remarkable range of biological processes. Saturated and monounsaturated fatty acids are becoming recognized as signal molecules in their own right. The complex composition of human milk lipids implies that diets with a diversity of fatty acids in complex lipid forms and structures is more beneficial than a narrow range of any particular group of fatty acids.

Nutritional deficiencies and phospholipid metabolism

Phospholipids are important components of the cell membranes of all living species. They contribute to the physicochemical properties of the membrane and thus influence the conformation and function of membrane-bound proteins, such as receptors, ion channels, and transporters and also influence cell function by serving as precursors for prostaglandins and other signaling molecules and modulating gene expression through the transcription activation. The components of the diet are determinant for cell functionality. In this review, the effects of macro and micronutrients deficiency on the quality, quantity and metabolism of different phospholipids and their distribution in cells of different organs is presented. Alterations in the amount of both saturated and polyunsaturated fatty acids, vitamins A, E and folate, and other micronutrients, such as zinc and magnesium, are discussed. In all cases we observe alterations in the pattern of phospholipids, the more affected ones being phosphatidylcholine, phosphatidylethanolamine and sphingomyelin. The deficiency of certain nutrients, such as essential fatty acids, fat-soluble vitamins and some metals may contribute to a variety of diseases that can be irreversible even after replacement with normal amount of the nutrients. Usually, the sequelae are more important when the deficiency is present at an early age.

Docosahexaenoic acid reduces amyloid beta production via multiple pleiotropic mechanisms

Alzheimer disease is characterized by accumulation of the β-amyloid peptide (Aβ) generated by β- and γ-secretase processing of the amyloid precursor protein (APP). The intake of the polyunsaturated fatty acid docosahexaenoic acid (DHA) has been associated with decreased amyloid deposition and a reduced risk in Alzheimer disease in several epidemiological trials; however, the exact underlying molecular mechanism remains to be elucidated. Here, we systematically investigate the effect of DHA on amyloidogenic and nonamyloidogenic APP processing and the potential cross-links to cholesterol metabolism in vivo and in vitro. DHA reduces amyloidogenic processing by decreasing β- and γ-secretase activity, whereas the expression and protein levels of BACE1 and presenilin1 remain unchanged. In addition, DHA increases protein stability of α-secretase resulting in increased nonamyloidogenic processing. Besides the known effect of DHA to decrease cholesterol de novo synthesis, we found cholesterol distribution in plasma membrane to be altered. In the presence of DHA, cholesterol shifts from raft to non-raft domains, and this is accompanied by a shift in γ-secretase activity and presenilin1 protein levels. Taken together, DHA directs amyloidogenic processing of APP toward nonamyloidogenic processing, effectively reducing Aβ release. DHA has a typical pleiotropic effect; DHA-mediated Aβ reduction is not the consequence of a single major mechanism but is the result of combined multiple effects.

Liposome-incorporated DHA increases neuronal survival by enhancing non-amyloidogenic APP processing

The fluidity of neuronal membranes plays a pivotal role in brain aging and neurodegeneration. In this study, we investigated the role of the omega-3 fatty acid docosahexaenoic acid (DHA) in modulation of membrane fluidity, APP processing, and protection from cytotoxic stress. To this end, we applied unilamellar transfer liposomes, which provided protection from oxidation and effective incorporation of DHA into cell membranes. Liposomes transferring docosanoic acid (DA), the completely saturated form of DHA, to the cell cultures served as controls. In HEK-APP cells, DHA significantly increased membrane fluidity and non-amyloidogenic processing of APP, leading to enhanced secretion of sAPPα. This enhanced secretion of sAPPα was associated with substantial protection against apoptosis induced by ER Ca(2+) store depletion. sAPPα-containing supernatants obtained from HEK-APP cells exerted similar protective effects as DHA in neuronal PC12 cells and HEK293 control cells. Correlating to further increased sAPPα levels, supernatants obtained from DHA-treated HEK-APP cells enhanced protection, whereas supernatants obtained from DHA-treated HEK293 control cells did not inhibit apoptosis, likely due to the low expression of endogenous APP and negligible sAPPα secretion in these cells. Further experiments with the small molecule inhibitors LY294002 and SP600125 indicated that sAPPα-induced cytoprotection relied on activation of the anti-apoptotic PI3K/Akt pathway and inhibition of the stress-triggered JNK signaling pathway in PC12 cells. Our data suggest that liposomal DHA is able to restore or maintain physiological membrane properties, which are required for neuroprotective sAPPα secretion and autocrine modulation of neuronal survival.