Phospholipid Composition Of Plasma Membranes Research Articles

The Role of Alpha Linolenic Acid on Neuroinflammation: A Systemic Review

Neuroinflammation, an inflammatory response within the central nervous system (CNS), plays a critical role in various neurological disorders, including neurodegenerative diseases. Alpha linolenic acid (ALA), an essential omega-3 polyunsaturated fatty acid, has shown promising health benefits due to its antioxidant and anti-inflammatory properties. This article aims to thoroughly examine the potential effects of ALA in reducing neuroinflammation, emphasizing its roles as an anti-inflammatory and antioxidant agent. The review focuses on studies published between 2018 and 2023, sourced from reputable academic databases such as PubMed, Semantic Scholar, Google Scholar, and ScienceDirect, with nine key papers selected. The findings indicate that ALA significantly mitigates neuroinflammation by decreasing reactive oxygen species (ROS) via the Nrf-2/HO-1/JNK signaling pathway. Additionally, ALA reduces inflammatory cytokines by inhibiting p-JNK activation, disrupting lipid rafts, blocking the pro-inflammatory transcription factor NF-κB, and altering cell membrane phospholipid composition. The review concludes that ALA may have potential therapeutic effects in reducing neuroinflammation through its antioxidant and anti-inflammatory actions, offering possible benefits for various neurological conditions, including Alzheimer's and Parkinson's diseases.

ACSL4-Mediated Membrane Phospholipid Remodeling Induces Integrin β1 Activation to Facilitate Triple-Negative Breast Cancer Metastasis.

ACSL4 upregulation in triple-negative breast cancer alters cell membrane phospholipid composition to increase integrin β1 activation and drive metastasis, indicating that targeting ACSL4 could potentially block metastasis and improve patient outcomes.

Omega-3 and -6 Fatty Acids Alter the Membrane Lipid Composition and Vesicle Size to Regulate Exocytosis and Storage of Catecholamines.

The two essential fatty acids, alpha-linolenic acid and linoleic acid, and the higher unsaturated fatty acids synthesized from them are critical for the development and maintenance of normal brain functions. Deficiencies of these fatty acids have been shown to cause damage to the neuronal development, cognition, and locomotor function. We combined electrochemistry and imaging techniques to examine the effects of the two essential fatty acids on catecholamine release dynamics and the vesicle content as well as on the cell membrane phospholipid composition to understand how they impact exocytosis and by extension neurotransmission at the single-cell level. Incubation of either of the two fatty acids reduces the size of secretory vesicles and enables the incorporation of more double bonds into the cell membrane structure, resulting in higher membrane flexibility. This subsequently affects proteins regulating the dynamics of the exocytotic fusion pore and thereby affects exocytosis. Our data suggest a possible pathway whereby the two essential fatty acids affect the membrane structure to impact exocytosis and provide a potential treatment for diseases and impairments related to catecholamine signaling.

Acyl-CoA synthase ACSL4: an essential target in ferroptosis and fatty acid metabolism.

Long-chain acyl-coenzyme A (CoA) synthase 4 (ACSL4) is an enzyme that esterifies CoA into specific polyunsaturated fatty acids, such as arachidonic acid and adrenic acid. Based on accumulated evidence, the ACSL4-catalyzed biosynthesis of arachidonoyl-CoA contributes to the execution of ferroptosis by triggering phospholipid peroxidation. Ferroptosis is a type of programmed cell death caused by iron-dependent peroxidation of lipids; ACSL4 and glutathione peroxidase 4 positively and negatively regulate ferroptosis, respectively. In addition, ACSL4 is an essential regulator of fatty acid (FA) metabolism. ACSL4 remodels the phospholipid composition of cell membranes, regulates steroidogenesis, and balances eicosanoid biosynthesis. In addition, ACSL4-mediated metabolic reprogramming and antitumor immunity have attracted much attention in cancer biology. Because it facilitates the cross-talk between ferroptosis and FA metabolism, ACSL4 is also a research hotspot in metabolic diseases and ischemia/reperfusion injuries. In this review, we focus on the structure, biological function, and unique role of ASCL4 in various human diseases. Finally, we propose that ACSL4 might be a potential therapeutic target.

Relationship between obesity, insulin resistance and cell membrane properties

Introduction and aim. The obesity is one of the greatest public health problems in developing countries and it is a triggering factor for diabetes associated with insulin resistance. The importance of cell membrane lipids as essential regulators of insulin resistance, since changes in the dynamic properties of the cell membrane (e.g., membrane fluidity), could be one of the events by which obesity affects insulin sensitivity. Thus, the insulin resistance may not only be a cause but also a consequence of lipid disorders such as dyslipidemia and/or cell membrane phospholipid composition change. The modification of plasma membrane lipid composition can change membrane biophysical properties and thus influencing protein-lipid interactions, enzymatic activity and regulation of surface receptors. Alterations in the lipid composition modify the fluidity of plasma membranes and the expression of membrane functions, such as receptor binding and enzyme activities. This review summarizes the current knowledge on the effects of the modulation of plasma membrane lipid composition and membrane fluidity in the functionality of membrane proteins involved in insulin activity, including the insulin receptor, glucose transport and Na + /K + ATPase and, in turn, the key features of the metabolic syndrome. Material and methods. References for that article were found through PubMed and Google Scholar, using terms: “obesity”, “insulin resistance” and “membrane properties”. The research was limited to abstracts and available full-text articles. Analysis of the literature. There is a strong relationship between dietary lipids, membrane lipid profiles and insulin resistance. The changes in the dynamic properties of the cell membrane (e.g., membrane fluidity), could be one of the events by which obesity affects insulin sensitivity. The modification of plasma membrane lipid composition can change membrane biophysical properties and thus influencing protein–lipid interactions, enzymatic activity, and regulation of surface receptors. Modifications of membrane phospholipid composition could have a role in the insulin action by altering membrane fluidity and, as a consequence, the insulin signaling pathway. Conclusion. As conclusion the membrane-lipid therapy approach can be used to treat important pathologies such as obesity and many others diseases such as : cancer, cardiovascular pathologies, neurodegenerative processes, obesity, metabolic disorders, inflammation, and infectious and autoimmune diseases. This pharmacological strategy aims to regulate cell functions by influencing lipid organization and membrane fluidity, inducing a concomitant modulation of membrane protein localization and activity which might serve to reverse the pathological state. Through this review we suggest an in-depth analysis of the membrane lipid therapy field, especially its molecular bases and its relevance to the development of innovative therapeutic approaches.

Tuberculosis: The tug of war between pathogen and inflammasome

A new study reveals how Mycobacterium tuberculosis evades anti-bacterial immunity by modifying the plasma membrane phospholipid composition of infected macrophages, thereby blocking the host's pyroptosis response and supporting chronic infection.

Antioxidant protection in patients with pulmonary tuberculosis

The literature review summarizes the data on the classification and characteristics of the antioxidant defense system. This model combines a number of different substances. Each of the components of the antioxidant system acts in close connection with its other structural elements, harmoniously complements, and in many cases – enhances the action of each other. The functional basis of the system of antioxidant protection is formed by the glutathione system, the constituent elements of which are actually glutathione and enzymes that catalyze the reactions of its reverse transformation (oxidation ↔ reduction). Most researchers conventionally divide the system of antioxidant protection into enzymatic and non-enzymatic. The enzyme links of the antioxidant defense system include: catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase, glutathione transferase and other enzymes. The non-enzymatic system includes fat-soluble vitamins A, E and K, water-soluble vitamins C and PP, biogenic amines, glutathione, carotenoids, ubiquinone, sterols. Both enzymatic and non-enzymatic antioxidant defense systems are present in the bloodstream. The activity of the enzymatic antioxidant system is very well regulated and depends on age, physiological condition, hormone dynamics, intensity of antioxidant enzyme synthesis, pH, presence of coenzymes, inhibitors, activators and other factors. The non-enzymatic part of the antioxidant system does not require as many regulators as the chemical itself - the antioxidant - reacts chemically with the radical. Only the reaction rate can change. The lungs are directly exposed to oxygen and oxidants of polluted air, they are most sensitive to oxidative damage, so they have an increased possibility of free radical reactions. Protection against the damaging effects of reactive oxygen species and free radicals is provided by anti-radical protective systems, especially the glutathione system and its enzymes. Numerous papers have obtained clinical and experimental data on the important role of free radical oxidation of lipids (FROL) and antioxidant systems (AOS) protection in the development of many diseases, including pulmonary tuberculosis (TB). The review presents modern views on the state of the system of lipid peroxidation (LPO) and antioxidant protection in TB. The main topic of the review is information on the generation of free radical compounds by different populations of leukocytes with further enhancement of LPO and secondary deepening of functional disorders. The article substantiates the feasibility of identifying LPO products as non-specific markers of aseptic inflammation in TB and the need to develop new generations of antioxidants. One of the universal mechanisms of damage to cell membranes is LPO, the excessive activation of which is normally prevented by factors of the antioxidant defense system. Membrane-bound enzymes involved in the formation of LPO products include lipoxy and cyclooxygenases. Lipoperoxidation processes change the structure and phospholipid composition of cell membranes, which negatively affects the cellular immune response due to damage to the mechanisms of information transfer from extracellular regulators to intracellular effector systems.

Quercetin affects membrane lipids and apoptosis in three-dimensional fibroblast cultures

The polyphenol quercetin is associated with numerous beneficial health effects in various pathologies such as oxidative stress, neurodegenerative disorders, inflammation, neoplastic processes, age-related diseases, and so on. However, the molecular mechanisms underlying the effects of quercetin and its implication in the pharmaceutical practice require additional clarification. In this study we analyzed the biochemical mechanisms of quercetin effect on membrane lipids of fibroblasts cultured as three-dimensional (3D) cultures, which resemble living tissues more adequately compared to cellular monolayers. Quercetin treatment of 3D fibroblasts induced alterations of the plasma membrane phospholipid and fatty acid composition as well as in the phospholipid metabolizing enzymes sphingomyelinase and phospholipase A2. The level of sphingomyelin (SM), which acts as endogenous membrane antioxidant, was elevated due to quercetin action. Incubation of 3D fibroblasts with quercetin induced augmentation in the saturated fatty acids and reduction of all polyunsaturated fatty acids in the membrane phospholipid molecules of the plasma membranes, indicating an additional increase of the resistance to oxidative damage. Quercetin treatment reduced cholesterol susceptibility to oxidation, a phenomenon which is probably related to the observed increase in the level of SM. In addition, Western blot analysis showed augmented phosphorylation of Akt and expression of Bcl-2 in quercetin-treated cell, indicating that apoptosis was suppressed by quercetin. In conclusion, the reported results contribute to a better understanding of the beneficial effects of quercetin on the structure and functions of plasma membranes of 3D cell cultures, which are a more adequate model of living tissues.

Plasma membrane phosphatidylinositol (4,5)-bisphosphate promotes Weibel-Palade body exocytosis.

Weibel-Palade bodies (WPB) are specialized secretory organelles of endothelial cells that control vascular hemostasis by regulated, Ca2+-dependent exocytosis of the coagulation-promoting von-Willebrand factor. Some proteins of the WPB docking and fusion machinery have been identified but a role of membrane lipids in regulated WPB exocytosis has so far remained elusive. We show here that the plasma membrane phospholipid composition affects Ca2+-dependent WPB exocytosis and von-Willebrand factor release. Phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] becomes enriched at WPB-plasma membrane contact sites at the time of fusion, most likely downstream of phospholipase D1-mediated production of phosphatidic acid (PA) that activates phosphatidylinositol 4-phosphate (PI4P) 5-kinase γ. Depletion of plasma membrane PI(4,5)P2 or down-regulation of PI4P 5-kinase γ interferes with histamine-evoked and Ca2+-dependent WPB exocytosis and a mutant PI4P 5-kinase γ incapable of binding PA affects WPB exocytosis in a dominant-negative manner. This indicates that a unique PI(4,5)P2-rich environment in the plasma membrane governs WPB fusion possibly by providing interaction sites for WPB-associated docking factors.

Phospholipid-Dependent Mechanisms of Platelet Dysfunction in Rabbits with Hemorrhagic Shock.

The time course of phospholipid composition of platelet plasma membranes at the peak of hemorrhagic shock were studied in rabbit experiments. The results indicate the key role of impairment of the structure of platelet membrane phospholipid bilayer in the pathogenesis of shockogenic thrombocytopathy.

T-2 Mycotoxin Treatment of Newborn Rat Pups does not Significantly Affect Nervous System Functions in Adulthood

T-2 toxin is primarily produced by Fusarium sp. abundant under temperate climatic conditions. Its main harmful effect is the inhibition of protein synthesis. Causing oxidative stress, it also promotes lipid peroxidation and changes plasma membrane phospholipid composition; this may lead to nervous system alterations. The aim of the present study was to examine whether a single dose of T-2 toxin administered at newborn age has any long-lasting effects on nervous system functions. Rat pups were treated on the frst postnatal day with a single intraperitoneal dose of T-2 toxin (0.2 mg/bwkg). Body weight of treated pups was lower during the second and third week of life, compared to littermates; later, weight gain was recovered. At young adulthood, behavior was tested in the open feld, and no difference was observed between treated and control rats. Field potential recordings from somatosensory cortex and hippocampus slices did not reveal any signifcant difference in neuronal network functions. In case of neocortical feld EPSP, the shape was slightly different in treated pups. Long-term synaptic plasticity was also comparable in both groups. Seizure susceptibility of the slices was not different, either. In conclusion, T-2 toxin did not signifcantly affect basic nervous system functions at this dose.

Lipid Droplet Fusion in Mammary Epithelial Cells is Regulated by Phosphatidylethanolamine Metabolism.

Mammary epithelial cells (MEC) secrete fat in the form of milk fat globules (MFG) which are found in milk in diverse sizes. MFG originate from intracellular lipid droplets, and the mechanism underlying their size regulation is still elusive. Two main mechanisms have been suggested to control lipid droplet size. The first is a well-documented pathway, which involves regulation of cellular triglyceride content. The second is the fusion pathway, which is less-documented, especially in mammalian cells, and its importance in the regulation of droplet size is still unclear. Using biochemical and molecular inhibitors, we provide evidence that in MEC, lipid droplet size is determined by fusion, independent of cellular triglyceride content. The extent of fusion is determined by the cell membrane's phospholipid composition. In particular, increasing phosphatidylethanolamine (PE) content enhances fusion between lipid droplets and hence increases lipid droplet size. We further identified the underlying biochemical mechanism that controls this content as the mitochondrial enzyme phosphatidylserine decarboxylase; siRNA knockdown of this enzyme reduced the number of large lipid droplets threefold. Further, inhibition of phosphatidylserine transfer to the mitochondria, where its conversion to PE occurs, diminished the large lipid droplet phenotype in these cells. These results reveal, for the first time to our knowledge in mammalian cells and specifically in mammary epithelium, the missing biochemical link between the metabolism of cellular complex lipids and lipid-droplet fusion, which ultimately defines lipid droplet size.

Abstract 2048: Saturated fatty acids in cell membrane phospholipids play an important role in chemoresistance in colorectal cancer

Abstract [Background and Aim] Resistance to chemotherapy represents the major obstacle to survival in patients with chemoresistant colorectal cancer. Various factors, such as drug efflux, autocrine survival signaling, and alterations in DNA damage repair mechanisms, can contribute to chemoresistance; however, the actual underlying mechanism is yet to be elucidated. The aim of this study was to elucidate the mechanism behind anticancer drug resistance based on lipidomics. [Materials and Methods] 1) Spheroids were derived from three colorectal cancer patient-derived xenograft models (A, B, and C) that were incubated with chemotherapeutic agents, such as 5-fluorouracil (5-FU). We analyzed the response rate of spheroids under 5-FU treatment. Global lipid analysis was performed on 5-FU resistance spheroids (A) and sensitive spheroids (C) using a Q Exactive LC-MS/MS mass spectrometer, and lipid identification was performed using the Lipid Search software. 2) We tried to identify genes that were responsible for changes in phospholipid profiles in the cell membrane. 3) To determine phospholipid profile changes in the cell membrane that occur in colon cancer cell lines (HCT116, SW480) during anticancer drug resistance, the genes responsible for such resistance were knocked down using siRNA. [Results and discussion] 1) Response to 5-FU was different in individual spheroids. Global lipid analysis and chemosensitivity assay revealed that phospholipids of 5-FU resistant spheroids were rich in saturated fatty acids (SFAs), while those of the 5-FU sensitive spheroids were rich in monounsaturated fatty acids (MUFAs). 2) The enzyme stearoyl-CoA desaturase (SCD) converts SFAs to MUFAs in the phospholipids. Based on these findings we hypothesized that decreased SCD expression is possibly associated with chemoresistance. 3) Cell lines with SCD knock down demonstrated increased SFA containing phospholipids and chemoresistance towards 5-FU. Viable cells after the administration of the anti-cancer agent confirmed that the expression of CD44 was upregulated. Therefore, changes in the phospholipid composition of cell membranes regulate 5-FU resistance in colon cancer. [Conclusions] Identification and analysis of the role of membrane lipids has become possible using high-sensitivity and high-resolution mass spectrometers and the relevant software, such as Lipid Search. Changes of phospholipid composition regulates chemoresistance. In future, investigation of the pathophysiology of membrane lipids in cancer may help to reveal novel strategies for cancer therapy. Citation Format: Takanori Hiraide, Takanori Sakaguchi, Satoru Furuhashi, Tomohiro Matsumoto, Yusuke Ozaki, Ryota Kiuchi, Makoto Takeda, Yasushi Shibasaki, Yoshifumi Morita, Hirotoshi Kikuchi, Megumi Baba, Mitsutoshi Setou, Hiroyuki Konno. Saturated fatty acids in cell membrane phospholipids play an important role in chemoresistance in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2048. doi:10.1158/1538-7445.AM2017-2048

Organ and phospholipid class fatty acid specificity in response to dietary depletion of essential n-3 fatty acids in Atlantic salmon (Salmo salarL.)

The cell membrane phospholipid composition is of major importance for normal cell functions. However, it is not known how complete depletion of both shorter and longer chain omega-3 fatty acids in salmon diets influences fatty acid composition of phospholipid subclasses in different organs of Atlantic salmon. We describe here the fatty acid composition in phospholipid subclasses of liver, muscle, heart and intestine in Atlantic salmon after 18 months of dietary n-3 essential fatty acids deprivation. The percentage of 22:6n-3 was markedly reduced in almost all phospholipid subclasses, and except for muscle phosphatidylcholine, phosphatidylethanolamine (PE) and phosphatidylinositol (PI), phospholipids in deficient fish were totally devoid of 20:5n-3. As compensation, we observed significant increases in 20:4n-6, and especially in 20:3n-9 (Mead acid) and 22:5n-6, varying among phospholipids and organs. High amounts of 20:3n-9 were found in liver and intestinal PE, little in PE from heart and muscle. For 22:5n-6, we saw a small incorporation in PI in liver and intestine compared to heart and muscle. Generally in PI, the preference for 20:4n-6 to 20:5n-3 differed significantly between organs. Overall, changes upon n-3 deprivation seemed to be strongest in liver and intestine, the lipid-secreting organs, and less in muscle and heart.

Effects of Different Maturation Systems on Bovine Oocyte Quality, Plasma Membrane Phospholipid Composition and Resistance to Vitrification and Warming.

The objective of this study was to evaluate the effects of different maturation systems on oocyte resistance after vitrification and on the phospholipid profile of the oocyte plasma membrane (PM). Four different maturation systems were tested: 1) in vitro maturation using immature oocytes aspirated from slaughterhouse ovaries (CONT; n = 136); 2) in vitro maturation using immature oocytes obtained by ovum pick-up (OPU) from unstimulated heifers (IMA; n = 433); 3) in vitro maturation using immature oocytes obtained by OPU from stimulated heifers (FSH; n = 444); and 4) in vivo maturation using oocytes obtained from heifers stimulated 24 hours prior by an injection of GnRH (MII; n = 658). A sample of matured oocytes from each fresh group was analyzed by matrix associated laser desorption-ionization (MALDI-TOF) to determine their PM composition. Then, half of the matured oocytes from each group were vitrified/warmed (CONT VIT, IMA VIT, FSH VIT and MII VIT), while the other half were used as fresh controls. Afterwards, the eight groups underwent IVF and IVC, and blastocyst development was assessed at D2, D7 and D8. A chi-square test was used to compare embryo development between the groups. Corresponding phospholipid ion intensity was expressed in arbitrary units, and following principal components analyses (PCA) the data were distributed on a 3D graph. Oocytes obtained from superstimulated animals showed a greater rate of developmental (P<0.05) at D7 (MII = 62.4±17.5% and FSH = 58.8±16.1%) compared to those obtained from unstimulated animals (CONT = 37.9±8.5% and IMA = 50.6±14.4%). However, the maturation system did not affect the resistance of oocytes to vitrification because the blastocyst rate at D7 was similar (P>0.05) for all groups (CONT VIT = 2.8±3.5%, IMA VIT = 2.9±4.0%, FSH VIT = 4.3±7.2% and MII VIT = 3.6±7.2%). MALDI-TOF revealed that oocytes from all maturation groups had similar phospholipid contents, except for 760.6 ([PC (34:1) + H]+), which was more highly expressed in MII compared to FSH (P<0.05). The results suggest that although maturation systems improve embryonic development, they do not change the PM composition nor the resistance of bovine oocytes to vitrification.

A defensin fragment regulates CHO-K1 cell spreading and induces renewal of fatty acid composition in cell membrane phospholipids.

A tetrapeptide defensin fragment has been shown to stimulate the spreading of CHOK1 cells. The tetrapeptide investigated had virtually no effect on the composition of cell membrane phospholipids but participated in the regulation of the renewal of fatty acid composition of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. Incubation of cells with the peptide resulted in a change in the composition of the unsaturated fatty acid residues in the phospholipids investigated: specifically, the content of monoenoic and/or dienoic acids increased and that of polyenoic acids decreased. The possible role of the peptide investigated (1) in the regulation of the functional activity of integrin receptors, and (2) in changes in the packing density of the phospholipid acyl chains in cell membrane microdomains, which affects the rates of integrin clustering and adhesion complex formation, is discussed.

Membrane adaptation in phospholipids and cholesterol in the widely distributed, freeze-tolerant wood frog, Rana sylvatica

Maintaining proper membrane phase and fluidity is important for preserving membrane structure and function, and by altering membrane lipid composition many organisms can adapt to changing environmental conditions. We compared the phospholipid and cholesterol composition of liver and brain plasma membranes in the freeze-tolerant wood frog, Rana sylvatica, from southern Ohio and Interior Alaska during summer, fall, and winter. We also compared membranes from winter-acclimatized frogs from Ohio that were either acclimated to 0, 4, or 10 °C, or frozen to -2.5 °C and sampled before or after thawing. Lipids were extracted from isolated membranes, separated by one-dimensional thin-layer chromatography, and analyzed via densitometry. Liver membranes underwent seasonal changes in phospholipid composition and lipid ratios, including a winter increase in phosphatidylethanolamine, which serves to increase fluidity. However, whereas Ohioan frogs decreased phosphatidylcholine and increased sphingomyelin, Alaskan frogs only decreased phosphatidylserine, indicating that these phenotypes use different adaptive strategies to meet the functional needs of their membranes. Liver membranes showed no seasonal variation in cholesterol abundance, though membranes from Alaskan frogs contained relatively less cholesterol, consistent with the need for greater fluidity in a colder environment. No lipid changed seasonally in brain membranes in either population. In the thermal acclimation experiment, cold exposure induced an increase in phosphatidylethanolamine in liver membranes and a decrease in cholesterol in brain membranes. No changes occurred during freezing and thawing in membranes from either organ. Wood frogs use tissue-specific membrane adaptation of phospholipids and cholesterol to respond to changing environmental factors, particularly temperature, though not with freezing.

Diurnal ammonia and urea excretion rates in European sea bass, Dicentrarchus labrax fed diets containing mixtures of canola and cotton seed oil at two different ambient temperature

The knowledge about the combined effects of higher temperature and dietary nutrient quality on the diurnal nitrogenous excretion rates is very limited in farmed fish species including European sea bass. Therefore this study investigated the combined effects of increasing levels (30 vs. 60 %) of dietary fish oil replacement by equal mixture of cotton seed oil (CSO) and canola oils (CO) and two different ambient temperature (24 vs. 30°C) on diurnal total ammonia and Urea–N excretion rates in European sea bass (Dicentrarchus labrax). Experimental diets were fed to fish three times (08:30–13:30–18:30h) at a fixed rate of 3 % BW.d−1. The daily consumed nitrogen and energy intake of fish were similar during the investigation in different dietary treatments. However, the daily excretion rates of TAN, total nitrogen (TAN+Urea–N) and total nitrogen expressed as a proportion of consumed nitrogen by the European sea bass maintained at 30°C were found to be significantly (P<0.001) higher (40 to 50%) than fish maintained at 24°C in all the dietary treatments suggesting higher rates of deamination of ingested amino acids with increased temperature. Daily urea–nitrogen excretion of fish accounted for between 20–30 % of total ammonia–nitrogen excretion rates for each dietary treatment at 24 and 30°C and appeared to be slightly increased by the temperature but neither the temperature nor the amount of plant oil mixture inclusion in diets or the interaction of these two factors had a significant effect on the urea nitrogen excretion rates of fish in different dietary treatments. However, Urea–N excretion rates in fish fed fish oil only (FO) diet were significantly higher (P<0.05) compared to that of fish fed diets containing increasing amount of plant oil mixture (VOM30 and VOM 60) during the light-on phase of the sampling period at 24°C indicating periodic enhancement of permeability for urea at excretion sites. Further research is needed in order to elucidate the mechanism of nitrogenous excretion in European sea bass fed plant oil containing diets under extreme summer time temperatures employing total dietary fish oil replacement to reveal the possible effects of alteration in cell membrane phospholipid composition on enzymes responsible for nitrogenous excretion and/or detoxification.

Disruption of phospholipase B‐mediated turnover upon loss of Ypk1 in S. cerevisiae

Ypk1, the yeast homolog of the human serum‐ and glucocorticoid‐induced kinase (Sgk1), is a serine/threonine protein kinase known to affect various downstream processes, including plasma membrane flippase activity and sphingolipid homeostasis. The results described here indicate that Ypk1 also impinges upon the turnover of phospholipids. Pulse‐chase experiments reveal that a ypk1 mutant exhibits alterations in phospholipid deacylation and resultant glycerophosphodiester production as compared to a wild type strain. Furthermore, loss of Plb1, a plasma membrane (PM) associated phospholipase, in a ypk1 background results in further alterations in phospholipid deacylation and a growth defect. We are in the process of examining potential explanations for the altered Plb1 activity in the ypk1 mutant. Strains in which other phospholipase B‐encoding genes are deleted in combination with YPK1 do not display a growth defect, suggesting a specific functional interaction between Plb1 and Ypk1. Preliminary studies have identified model PM proteins, including the Git1 permease, whose activity is affected by loss of Ypk1 and/or Plb1. Our data is consistent with the idea that Ypk1 and Plb1 alter plasma membrane phospholipid composition, which in turn impinges upon the activity of integral plasma membrane proteins.

Peculiarities of the phospholipid and fatty acid composition of erythrocyte plasma membranes of the black sea fish

The phospholipid and the fatty acid composition of the main phospholipids families of erythrocyte plasma membranes was studied in two species of cartilaginous fish: the common thrasher (Raja clavata L.) and the common stingray (Dasyatis pastinaca) and three bony fish species: the scorpion fish (Scorpaena porcus L.), the smarida (Spicara flexuosa Raf.), and the horse mackerel (Trachurus mediterraneus ponticus Aleev). It was shown that in the studied fish, 70.0-80.0 % of all membrane phospholipids were composed of phosphatidylcholine and phosphatidylethanolamine. Phosphatidylserine, monophosphoinositide, and sphingomyelin were minor components whose content in the erythrocyte membrane fluctuated from 3.0 % to 13.0 %. The fatty acid phospholipids composition was represented by a large specter of acids. From saturated acids, basic for plasma membranes are palmitic (C16: 0) and stearic (C18: 0) acids. From unsaturated acids, the larger part belong to mono-, tetra-, penta-, and hexaenoic acids in fish phospholipids. The calculation of the double bond index and of the unsaturation coefficient showed difference in the deformation ability of erythrocyte membranes of the studied fish.