Lipids of whole cells and plasma membrane fractions from Balb/c3T3, SV3T3, and concanavalin A-selected revertant cells

Unveiling the MUFA-Cancer Connection: Insights from Endogenous and Exogenous Perspectives

Monounsaturated fatty acids (MUFAs) have been the subject of extensive research in the field of cancer due to their potential role in its prevention and treatment. MUFAs can be consumed through the diet or endogenously biosynthesized. Stearoyl-CoA desaturases (SCDs) are key enzymes involved in the endogenous synthesis of MUFAs, and their expression and activity have been found to be increased in various types of cancer. In addition, diets rich in MUFAs have been associated with cancer risk in epidemiological studies for certain types of carcinomas. This review provides an overview of the state-of-the-art literature on the associations between MUFA metabolism and cancer development and progression from human, animal, and cellular studies. We discuss the impact of MUFAs on cancer development, including their effects on cancer cell growth, migration, survival, and cell signaling pathways, to provide new insights on the role of MUFAs in cancer biology.

Impact of Hydrophobic Chains in Five-Coordinate Glucoconjugate Pt(II) Anticancer Agents

This study describes new platinum(II) cationic five-coordinate complexes (1-R,R') of the formula [PtR(NHC)(dmphen)(ethene)]CF₃SO₃ (dmphen = 2,9-dimethyl-1,10-phenanthroline), containing in their axial positions an alkyl group R (methyl or octyl) and an imidazole-based NHC-carbene ligand with a substituent R' of variable length (methyl or octyl) on one nitrogen atom. The Pt-carbene bond is stable both in DMSO and in aqueous solvents. In DMSO, a gradual substitution of dmphen and ethene is observed, with the formation of a square planar solvated species. Octanol/water partitioning studies have revealed the order of hydrophobicity of the complexes (1-Oct,Me > 1-Oct,Oct > 1-Me,Oct > 1-Me,Me). Their biological activity was investigated against two pairs of cancer and non-cancer cell lines. The tested drugs were internalized in cancer cells and able to activate the apoptotic pathway. The reactivity of 1-Me,Me with DNA and protein model systems was also studied using UV-vis absorption spectroscopy, fluorescence, and X-ray crystallography. The compound binds DNA and interacts in various ways with the model protein lysozyme. Remarkably, structural data revealed that the complex can bind lysozyme via non-covalent interactions, retaining its five-coordinate geometry.

Stearoyl-CoA desaturase and tumorigenesis

Stearoyl-CoA desaturase (SCD) generates monounsaturated fatty acids (MUFAs) which contribute to cell growth, survival, differentiation, metabolic regulation and signal transduction. Overexpression of SCD is evident and implicated in metabolic diseases such as diabetes and non-alcoholic fatty liver disease. SCD also stimulates canonical Wnt pathway and YAP activation in support of stemness and tumorigenesis. SCD facilitates metabolic reprogramming in cancer which is mediated, at least in part, by regulation of AKT, AMPK, and NF-kB via MUFAs. Our research has revealed the novel positive loop to amplify Wnt signaling through stabilization of LRP5/6 in both hepatic stellate cells and liver tumor-initiating stem cell-like cells. As such, this loop is pivotal in promoting liver fibrosis and liver tumor development. This review summarizes the mechanisms of SCD-mediated tumor promotion described by recent studies and discusses the future prospect for SCD-mediated signaling crosstalk as a potential therapeutic target for cancer.

The highly unnatural fatty acid profile of cells in culture

The fatty acid profile of cells in culture are unlike those of natural cells with twice the monounsaturated (MUFA) and half the polyunsaturated fatty acids (PUFA) level (Mol%). This is not due to cell lines primarily being derived from cancers but is due to limited access to lipid and an inability to make PUFA de novo as vertebrate cells. Classic culture methods use media with 10% serum (the only exogenous source of lipid). Fetal bovine serum (FBS), the serum of choice has a low level of lipid and cholesterol compared to other sera and at 10% of media provides 2-3% of the fatty acid and cholesterol, 1% of the PUFA and 0.3% of the essential fatty acid linoleic acid (18:2n-6) available to cells in the body. Since vertebrate cell lines cannot make PUFA they synthesise MUFA, offsetting their PUFA deficit and reducing their fatty acid diversity. Stem and primary cells in culture appear to be similarly affected, with a rapid loss of their natural fatty acid compositions. The unnatural lipid composition of cells in culture has substantial implications for examining natural stems cell in culture, and for investigations of cellular mechanisms using cell lines based on the pervasive influence of fats.

Stearoyl-CoA Desaturase 1 as a Therapeutic Target for the Treatment of Cancer

A distinctive feature of cancer cells of various origins involves alterations of the composition of lipids, with significant enrichment in monounsaturated fatty acids. These molecules, in addition to being structural components of newly formed cell membranes of intensely proliferating cancer cells, support tumorigenic signaling. An increase in the expression of stearoyl-CoA desaturase 1 (SCD1), the enzyme that converts saturated fatty acids to ∆9-monounsaturated fatty acids, has been observed in a wide range of cancer cells, and this increase is correlated with cancer aggressiveness and poor outcomes for patients. Studies have demonstrated the involvement of SCD1 in the promotion of cancer cell proliferation, migration, metastasis, and tumor growth. Many studies have reported a role for this lipogenic factor in maintaining the characteristics of cancer stem cells (i.e., the population of cells that contributes to cancer progression and resistance to chemotherapy). Importantly, both the products of SCD1 activity and its direct impact on tumorigenic pathways have been demonstrated. Based on these findings, SCD1 appears to be a significant player in the development of malignant disease and may be a promising target for anticancer therapy. Numerous chemical compounds that exert inhibitory effects on SCD1 have been developed and preclinically tested. The present review summarizes our current knowledge of the ways in which SCD1 contributes to the progression of cancer and discusses opportunities and challenges of using SCD1 inhibitors for the treatment of cancer.

Betulinic acid induces a novel cell death pathway that depends on cardiolipin modification

Cancer is associated with strong changes in lipid metabolism. For instance, normal cells take up fatty acids (FAs) from the circulation, while tumour cells generate their own and become dependent on de novo FA synthesis, which could provide a vulnerability to target tumour cells. Betulinic acid (BetA) is a natural compound that selectively kills tumour cells through an ill-defined mechanism that is independent of BAX and BAK, but depends on mitochondrial permeability transition-pore opening. Here we unravel this pathway and show that BetA inhibits the activity of steroyl-CoA-desaturase (SCD-1). This enzyme is overexpressed in tumour cells and critically important for cells that utilize de novo FA synthesis as it converts newly synthesized saturated FAs to unsaturated FAs. Intriguingly, we find that inhibition of SCD-1 by BetA or, alternatively, with a specific SCD-1 inhibitor directly and rapidly impacts on the saturation level of cardiolipin (CL), a mitochondrial lipid that has important structural and metabolic functions and at the same time regulates mitochondria-dependent cell death. As a result of the enhanced CL saturation mitochondria of cancer cells, but not normal cells that do not depend on de novo FA synthesis, undergo ultrastructural changes, release cytochrome c and quickly induce cell death. Importantly, addition of unsaturated FAs circumvented the need for SCD-1 activity and thereby prevented BetA-induced CL saturation and subsequent cytotoxicity, supporting the importance of this novel pathway in the cytotoxicity induced by BetA.

Decreasing stearoyl-CoA desaturase-1 expression inhibits β-catenin signaling in breast cancer cells

Stearoyl-CoA desaturase-1 (SCD1) is an endoplasmic reticulum anchored enzyme catalyzing the synthesis of monounsaturated fatty acids, mainly palmytoleyl-CoA and oleyl-CoA. Recent studies have revealed a function for SCD1 in the modulation of signaling processes related to cell proliferation, survival and transformation to cancer. We used MCF7 and MDA-MB-231 cells to analyze the role of SCD1 in the metastatic acquisition of breast cancer cells. Silencing SCD1 expression in breast cancer cells has no effect on cell viability but the levels of cell proliferation, cell cycle genes' expressions and the phosphorylation state of ERK1/2 MAPK are significantly reduced. Decreasing SCD1 expression also reduces the level of GSK3 phosphorylation, indicating higher activity of the kinase. Using cells fractionation, immunofluorescence and a β-catenin/TCF-responsive reporter construct, we demonstrate that lowering SCD1 expression leads to a decrease of β-catenin amounts within the nucleus and to inhibition of its transactivation capacity. Moreover, MDA-MB-231 cells transfected with the SCD1 siRNA show a lower invasive potential than the control cells. Taken together, our data demonstrate that low SCD1 expression is associated with a decrease in the proliferation rate of breast cancer cells associated with a decrease in ERK1/2 activation. SCD1 silencing also inhibits GSK3 phosphorylation, lowering β-catenin translocation to the nucleus, and, subsequently, its transactivation capacity and the expression of its target genes. Finally, we show that silencing SCD1 impairs the epithelial to mesenchymal transition-like behavior of the cells, a characteristic of metastatic breast cancer.

Inhibition of stearoylCoA desaturase-1 inactivates acetyl-CoA carboxylase and impairs proliferation in cancer cells: role of AMPK

Cancer cells activate the biosynthesis of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) in order to sustain an increasing demand for phospholipids with appropriate acyl composition during cell replication. We have previously shown that a stable knockdown of stearoyl-CoA desaturase 1 (SCD1), the main Δ9-desaturase that converts SFA into MUFA, in cancer cells decreases the rate of lipogenesis, reduces proliferation and in vitro invasiveness, and dramatically impairs tumor formation and growth. Here we report that pharmacological inhibition of SCD1 with a novel small molecule in cancer cells promoted the activation of AMP-activated kinase (AMPK) and the subsequent reduction of acetylCoA carboxylase activity, with a concomitant inhibition of glucose-mediated lipogenesis. The pharmacological inhibition of AMPK further decreased proliferation of SCD1-depleted cells, whereas AMPK activation restored proliferation to control levels. Addition of supraphysiological concentrations of glucose or pyruvate, the end product of glycolysis, did not reverse the low proliferation rate of SCD1-ablated cancer cells. Our data suggest that cancer cells require active SCD1 to control the rate of glucose-mediated lipogenesis, and that when SCD1 activity is impaired cells downregulate SFA synthesis via AMPK-mediated inactivation of acetyl-CoA carboxylase, thus preventing the harmful effects of SFA accumulation.

Second-harmonic generation sensitivity to transmembrane potential in normal and tumor cells

Second-harmonic generation (SHG) is emerging as a powerful tool for the optical measurement of transmembrane potential in live cells with high sensitivity and temporal resolution. Using a patch clamp, we characterize the sensitivity of the SHG signal to transmembrane potential for the RH 237 dye in various normal and tumor cell types. SHG sensitivity shows a significant dependence on the type of cell, ranging from 10 to 17% per 100 mV. Furthermore, in the samples studied, tumor cell lines display a higher sensitivity compared to normal cells. In particular, the SHG sensitivity increases in the cell line Balb/c3T3 by the transformation induced with SV40 infection of the cells. We also demonstrate that fluorescent labeling of the membrane with RH 237 at the concentration used for SHG measurements does not induce any measurable alteration in the electrophysiological properties of the cells investigated. Therefore, SHG is suitable for the investigation of outstanding questions in electrophysiology and neurobiology.

High stearoyl-CoA desaturase protein and activity levels in simian virus 40 transformed-human lung fibroblasts

The precise role of monounsaturated fatty acid (MUFA) synthesis in cell proliferation and programmed cell death remains unknown. The strong correlation of high levels of MUFA and neoplastic phenotype suggest that the regulation of stearoyl CoA desaturase (SCD) must play a significant role in cancer development. In this study, the levels of SCD protein and activity were investigated in normal (WI38) and SV40-transformed (SV40-WI38) human lung fibroblasts. Thus, the activity of SCD on exogenous [14C]stearic acid and endogenous [14C]acetate-labeled fatty acids was increased by 2.2- and 2.6-fold, respectively, in SV40-WI38 compared to WI38 fibroblasts. Concomitantly, a 3.3-fold increase in SCD protein content was observed in SV40-transformed cells. Cell transformation also led to high levels of MUFA, which was paralleled by a more fluid membrane environment. Furthermore, the levels of PPAR-gamma, a well-known activator of SCD expression, were highly increased in SV40-transformed fibroblasts. SCD activity appeared linked to the events of programmed cell death, since incubations with 40 microM etoposide induced apoptosis in SV40 cells, and led to a decrease in fatty acid synthesis, SCD activity and in MUFA cellular levels. Taken together, these results suggest that SCD protein and activity levels are associated with the events of neoplastic cell transformation and programmed cell death.

Vaccenic acid (t11-18:1) is converted to c9,t11-CLA in MCF-7 and SW480 cancer cells

The aims of this study were to determine whether vaccenic acid (VA; t11-18:1) is converted to c9,t11-CLA in human mammary (MCF-7) and colon (SW480) cancer cell lines and whether VA influences cell viability and other CLA-bioresponsive markers. When cells were incubated in the presence of VA at concentrations of 5 to 20 microg/mL, both VA and c9,t11-CLA increased in cellular lipids in a dose-dependent manner. After 4 d of incubation of SW480 and MCF-7 cells with VA (20 microg/mL), c9,t11-CLA increased from undetectable levels to 8.57 and 12.14 g/100 g FAME in cellular lipids, respectively. VA supplementation for 4 d at 5, 10, and 15 microg/mL had no effect on cell growth, whereas 20 microg/mL significantly (P < 0.05) reduced cell growth in both cell lines. VA (20 microg/mL) treatment induced DNA fragmentation and significantly (P < 0.05) depleted cytosolic GSH levels in the SW480 cell line after 4 d of incubation, suggesting that apoptosis was the mode of cell death induced by VA. Both VA and c9,t11-CLA reduced (P < 0.05) total ras expression in SW480 cells. 14C-Arachidonic acid uptake into the MG fraction was significantly increased (P < 0.05) in both cell lines while uptake into the phospholipid fraction decreased in response to VA. VA treatment significantly (P < 0.05) increased 8-epi-prostaglandin F2alpha in both cell lines. The data indicate that growth suppression and cellular responses of both cells lines are likely mediated by VA desaturation to c9,t11-CLA via delta9-desaturase.

Comparison of the fatty acid compositions in intraepithelial and infiltrating lesions of the cervix: part I, total fatty acid profiles

In the first part of this study, the possible role of essential total fatty acids and their metabolites during cervical carcinogenesis was investigated. Since membrane lipids play a key role in cell proliferation and differentiation, disturbances in the fatty acid compositions of cell membranes and the modulation of membrane fatty acid compositions received attention in several in vitro studies. There are, however, no reported studies where the actual total and free (unesterified) fatty acid compositions have been determined during the different stages of cervical carcinogenesis. In part I of this ex vivo study, the total fatty acid compositions of normal tissue, intraepithelial and infiltrating lesions of the cervix were compared. The fatty acid profiles that were determined make it possible to speculate about the metabolic pathways followed during cervical carcinogenesis. Lipids were extracted from biopsies of normal tissue (n=36), cervical intraepithelial lesions (n=47) and infiltrating lesions (n=47). Samples, from which the total fatty acid compositions were determined, were saponified, methylated and analysed by gas liquid chromatography (GLC). Essential fatty acid deficiency (EFAD) in the intraepithelial lesions, compared with normal tissue (linoleic acid, P< 0.01), and infiltrating lesions, compared with intraepithelial lesions (linoleic acid and arachidonic acid, P< 0.01) were observed. High levels of oleic acid were also observed when infiltrating lesions were compared with normal tissue (P< 0.01). This EFAD in cancer cells may result in many defective cell mechanisms. Although there are many risk factors for cervical cancer, the human papilloma virus has emerged over the past decade as the leading candidate to be an aetiological factor. There is ample evidence that human viral infections are associated with reduced levels of linoleic acid and thus participate in the depletion of essential fatty acids in cancer cells.

Lipid changes in HL-60 cells on differentiation into macrophages by treatment with a phorbol ester

We studied changes in lipid composition of human promyelocytic leukemia cells (HL-60) on differentiation to the macrophage/monocytic lineage by treatment with the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate. Differentiation was accompanied by: (i) a decrease in the level of phospholipids; (ii) a greater amount of triacylglycerols; (iii) an increase in 1-alk-1'-enyl-2-acyl- and 1-alkyl-2-acyl-sn-glycero-3-phosphoethanolamine and a decrease in 1-alkyl-2-acyl-sn-glycero-3-phosphocholine; and (iv) an increase in the level of arachidonic acid in ethanolamine phospholipids. The increased levels of ether-linked lipids and of arachidonic acid in ethanolamine phospholipids are consistent with an enhanced biosynthesis of platelet-activating factor and eicosanoids, which are particularly important in the macrophage function.

Effect of phosphatidylcholine structure on the adenylate cyclase activity of a murine fibroblast cell line

To determine which structural characteristics of membrane phospholipids influence adenylate cyclase activity, we measured basal and sodium fluoride-or forskolin-stimulated activity in a murine fibroblast cell line, i.e., Balb/c3T3 cells grown in media supplemented with fetal calf serum (FCS), lipid-depleted FCS (LD-FCS) or LD-FCS complexed with different phosphatidylcholine (PC) molecular species. Cells grown in the presence of LD-FCS showed a substantial decrease in their basal and NaF-stimulated adenylate cyclase activities; however, their forskolin-stimulated activity was not altered, suggesting that the enzyme's catalytic site is not affected by changes in membrane lipids. Media supplemented with different LD-FCS/PC complexes were shown to prevent the LD-FCS-mediated reduction of basal and NaF-stimulated adenylate cyclase activity to different extents. Addition of cis-9-16:1, cis-9-18:1/cis-9-18:1 or cis-9-18:1/cis-9,12-18:2 sn-glycerophosphocholine (GPC) completely restored adenylate cyclase activity, while cis-11-18:1/cis-11-18:1 GPC was not effective and only a partial recovery was observed with 16:0/16:0, 16:0/cis-9-18:1 and trans-9-18:1 GPC. Considering the structural features of these seven PC molecular species, the findings suggest that an optimal lipid environment is conferred to the enzyme by the presence of two cis double bonds, each located in delta 9 position of the PC acyl chains. The limited effect of cis-9-16:1/cis-9-18:1 GPC and cis-9-18:1/cis-9-16:1 GPC suggests that an equal length of the terminal hydrocarbon chains extending beyond the delta 9 double bonds is also important.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid composition of normal and malignant cells and cytotoxicity of stearic, oleic and sterculic acids in vitro

The aim of this study was to investigate the hypothesis that saturated fatty acids are differentially cytotoxic to cancer cells. Three studies were undertaken to: (1) measure the toxicities of stearic and oleic acids to normal and malignant cells in vitro, (2) assess if there is any relationship between toxicity and relative fatty acid composition and (3) determine whether the relative fatty acid composition of a cancer cell line could be modified by sterculic acid, an inhibitor of delta-9-desaturase. Stearic (18:0) and oleic (18:1) acids inhibited the colony-forming abilities of five human cancer cell lines and two non-neoplastic cell lines in a dose-dependent fashion. The concentration of oleic acid required to reduce colony formation ability by 50% was 2.5-6.0-fold greater than that of stearic acid. Addition of sterculic acid to a cancer cell line resulted in steady-state levels of stearic acid and increasing percentage of oleic acid.

Age-related changes in red blood cell lipids

Red blood cell (RBC) lipid composition was investigated in 81 healthy subjects aged twenty to sixty-nine years, having similar dietary habits, and living in the same geographic area in order to search for changes referable to aging. A significant increase in RBC cholesterol and total phospholipid content with aging was found (p less than 0.001), whereas no differences were observed in cholesterol/phospholipid molar ratio. Significant increases in palmitic acid 16:0 esterified in phosphatidylcholine and in stearic acid 18:0 esterified in phosphatidylethanolamine (p less than 0.001) were observed with aging. Moreover, a decrease in 18:2 n6 was observed in all three phosphoglyceride fractions investigated (p less than 0.001). These results suggest that modifications in RBC lipid composition occur with aging, possibly causing a reduction of membrane fluidity.

Lipid characteristics of RSV-transformed Balb/c 3T3 cell lines with different spontaneous metastatic potentials

To determine whether a metastatic phenotype may be correlated with a characteristic lipid pattern, we compared the lipid composition of low metastasizing Balb/c 3T3 cells transformed by the B77 strain of Rous sarcoma virus (B77-3T3 cells) with that of a subclone isolated by growth in 0.6% agar, the B77-AA6 cells, which exhibit a high capacity for spontaneous metastasis. B77-3T3 cells revealed characteristics in their lipid composition common to other systems of transformed cells, i.e., an accumulation of ether-linked lipids, a reduction of the more complex gangliosides, an increase of oleic acid (18:1) and a decrease of arachidonic (20:4) and C22 polyunsaturated fatty acids in phospholipids. High metastatic B77-AA6 cells showed: a) an even more marked decrease of complex gangliosides; b) a more pronounced increase of 18:1 and decrease of 20:4 and 22 polyunsaturated fatty acids in certain phospholipid classes; and c) a higher percentage of alkyl-acyl subfractions in both phosphatidylcholine and phosphatidylethanolamine than B77-3T3 cells. Comparing the data for other systems of metastatic cells with those of lipid studies of spontaneously metastasizing B77-AA6 cell system leads us to conclude that the metastatic phenotype is characterized by a change in ether-linked lipids, rather than in fatty acids.

Altered lipid composition and thromboxane A2 formation in platelets from patients affected by IIa hyperlipoproteinemia

Platelets from patients with familial hypercholesterolemia (type IIa hyperlipoproteinemia), a condition associated with high prevalence of atherosclerosis and of its thrombotic complications, are known to be hyperresponsive to aggregating stimuli and to synthesize increased amounts of thromboxane A2 (TxA2) in comparison to platelets from normal subjects. In order to search if these functional alterations are linked to a different platelet lipid composition, we studied a group of young patients affected by IIa hyperlipoproteinemia and a group of suitable controls with similar dietary habits. Both cholesterol and phospholipid content of platelets were higher in patients than in controls with a significant increase of cholesterol/phospholipid molar ratio (at least p less than 0.05). The percent contents of the main platelet phospholipid fractions were not altered, while an increase in saturated fatty acids, both unesterified and esterified in different lipid fractions, was observed. Moreover, an increased TxA2 production by platelets and a significantly increased number of megathrombocytes occur in patients with respect to controls (p less than 0.001). Our results indicates that platelets from patients with IIa hyperlipoproteinemia have an altered lipid composition which could explain, at least in part, the enhanced platelet reactivity reported in these patients.

Lipid composition of cultured B16 melanoma cell variants with different lung-colonizing potential

Lipid components influence several cell surface properties that are critical in different stages of the metastatic process. In this study, we examined whether the different lung-colonizing potential of B16-F1 and B16-F10 melanoma cells could be related to a characteristic lipid profile. The lipid analyses, carried out on the same cell cultures used for the assay of lung-colonizing potential, revealed characteristics in the lipid composition of both B16-F1 and B16-F10 melanoma cells that are common to other systems of malignant cells: a high level of 18:1 associated with low proportions of polyunsaturated fatty acids in phospholipids, accumulation of ether-linked lipids and absence of complex gangliosides. The two B16 melanoma variants differed significantly only with respect to ether-linked lipids, due to a higher level of alkyl-PC in B16-F10 than in B16-F1.

Lipid changes associated with erythroid differentiation of Friend erythroleukemia cells

Friend erythroleukemia cells were induced to differentiate by dimethyl sulfoxide (DMSO) and hexamethylene-bis-acetamide (HBMA) in order to investigate whether their lipid characteristics, common to other systems of transformed cells, revert to a normal differentiation pattern. DBA/2 mouse erythrocytes were examined as a model of terminal differentiation in erythroid lineage. Variants of erythroleukemia cells not inducible to erythroid differentiation by DMSO and HMBA were also used in this study, in order to test whether lipid modifications occurring in differentiated erythroleukemia cells were related to the differentiation process or caused by specific effects of the inducers. Friend erythroleukemia cells showed the same lipid characteristics as those found in other transformed cell types. That is, a high level of ether-linked lipids and low percentages of long chain polyunsaturated fatty acids along with an accumulation of monoenoic fatty acids in phospholipids. These lipid characteristics remained unchanged when erythroleukemia cells were induced to differentiation by either DMSO or HMBA. However, other lipid components of erythroleukemia cells, e.g., phosphatidylethanolamine and triglycerides, were affected by erythroid differentiation. There were also changes of some lipid components of erythroleukemia cells, such as cholesteryl esters, which were related to specific effects of the inducers. Both DMSO- and HMBA-resistant variants differed from the inducible erythroleukemia cells, mainly in their ether-linked phospholipid pattern.

Age related changes in platelet lipid composition

Platelet lipid composition was investigated in 52 healthy subjects aged 20 to 68 years with similar dietary habits and living in a narrow geographic area in order to search possible changes referrable to aging. No significant variations were observed when platelet cholesterol, total phospholipids and different phospholipid fractions were considered, whereas cholesterol/phospholipid (C/PL) molar ratio significantly increased with aging (p less than 0.01). Moreover, a significant increase in 16:0 + 16:1 fatty acids was found in phosphatidylcholine (PC) and in sphingomyelin (SP) (r = 0.62, p less than 0.001 and r = 0.30, p less than 0.05 respectively) and a decrease in 18:2 n6 in the phospholipid fractions considered (at least p less than 0.05). These results indicate that modifications in platelet lipid composition occur with aging and that they could affect platelet functions so playing a role in the onset of atherosclerosis and in thrombotic phenomena occurring with increasing frequency in the elderly.

Increased thromboxane A2 generation and altered membrane fatty acid composition in platelets from patients with active angina pectoris

Lipid composition of platelet membranes and thromboxane A2 (TxA2) generation by platelets were investigated in eighty-seven anginal patients (forty-two with resting angina in active phase and forty-five with effort stable angina or rest angina in inactive phase) and in forty-five clinically healthy subjects of similar age. All subjects were on the same dietary regimen and the adherence to diet was checked by analysis of red blood cell lipids. Platelets from active angina patients produced more TxA2 than platelets from both inactive patients and controls (p less than 0.001). Moreover patients with active angina had higher arachidonic acid (AA, p less than 0.001) and lower eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) levels in phosphatidylcholine (PC, p less than 0.001), than inactive patients and controls. AA and EPA changes in membrane PC significantly correlated with TxA2 production (p less than 0.001) but not with coronary pathoanatomy. Plasma lipids, content of cholesterol, total phospholipids (and their saturated and unsaturated fatty acids) and the different phospholipid fractions in platelet membrane were not different in the three groups. Present results indicate that in platelets from anginal patients phospholipid fatty acid composition is at least in part independent of plasma composition and that in active angina there are modifications leading to increased TxA2 formation and possibly contributing to the occurrence of ischemic attacks.

Incorporation and turnover of phospholipid precursors in normal and tumoral glial cells in culture

The incorporation and turnover of phospholipid precursors in cultured normal and tumoral glial cells was investigated during the plateau phase of growth. Glycerol was incorporated similarly by all cell types, and was renewed with a half-life of 19-37 hr. Acetate had a much longer half-life in primary cultures (50-75 hr) than in proliferative tumor cells (20-40 hr). Phosphate had a more rapid turnover rate in primary cultures (25 hr) than in proliferative tumor cells (50 hr). For all precursors, inositol- and choline phosphoglycerides had a faster turnover rate than other phospholipids.

Ganglioside composition of substrate-adhesion sites of normal and virally-transformed Balb/c 3T3 cells

The ganglioside composition of the so-called substrate-attached material (SAM), which remains tightly bound to the tissue culture dish after cells are detached by chelating agents, was compared with the ganglioside composition of released cell bodies in the cultures of normal and various virally-transformed Balb/c 3T3 cells. Regardless of whether the cells were untransformed or transformed, the SAM of their cultures shows a ganglioside structure characterized by a prevalence of the higher homologs, mainly GD1a, over the simpler gangliosides, even when the level of higher homologs was reduced in the cell bodies of transformed cells. This result cannot be ascribed to the presence of plasmamembranes in the SAM as shown by ganglioside analysis of the plasmamembranes of some of the cells under study. Only in a highly metastatic transformed cell line did the SAM contain the same low GD1a level as found in the cell bodies.

Roles of gangliosides in the surface properties of normal and malignant cells

Gangliosides are ubiquitous plasma membrane components whose structural characteristics make it possible to establish multiple interactions with the pericellular microenvironment. Several receptorial activities of gangliosides have already been recognized and the possible involvement of gangliosides in growth control, adhesion, differentiation, and immunologic recognition is at present under study. The study of the role of gangliosides in cell growth control has been approached in our laboratory by investigating whether the ganglioside changes found in SV40-transformed Balb/c3T3 cells (SV3T3 cells) revert to a normal pattern in a variant of SV3T3 cells with growth properties similar to those of normal parental cells, the concanavalin A-selected SV3T3 revertant cells. These latter cells showed the same reduction of the more complex gangliosides as found in SV3T3 cells, while their amount of II3NeuAC-LacCer (GM3) was greatly increased compared to that found in either normal or transformed 3T3 cells. In order to study the role of gangliosides in the adhesion process, we analyzed the ganglioside structure of the so-called substrate-attached material, a cell surface structure involved in the adhesion of cells to substrate, from cultures of Balb/c3T3, SV3T3, and concanavalin A-selected SV3T3 revertant cells and from cultures of a system of transformed cells with different metastatic potential: the nonmetastatic B77-3T3 and the highly metastatic AA6 cells. Compared to normal cells, all the transformed cells contained smaller quantities of gangliosides in their substrate-attached material.(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation and metabolism of exogenous fatty acids by cultured normal and tumoral glial cells

We have investigated the transformation of exogenous radioactive free fatty acids by cultured glial cells and their incorporation into complex lipids. The cells were either tumor lines (C6 and NN) or primary cultures from newborn rat hemispheres. The tumor lines could undergo morphological differentiation with dibutyryl cyclic AMP or bromodeoxyuridine. The fatty acid precursors used were palmitic, stearic, oleic, linoleic and linolenic acids. Tumor cells presented a higher incorporation of the precursors in the cell lipid acyl groups than did normal cells. Tumor cells desaturated and/or elongated palmitic, stearic and oleic acid to a higher extent than did normal cells. In contrast, tumor cells transformed linoleic and linolenic acids to their polyunsaturated derivatives to a lower extent than did normal cells. In differentiated tumor cells, these patterns of metabolism were shifted toward the patterns of normal cells. Tumor cells did not exhibit delta 4-desaturase activity, but such activity was restored in the C6 line upon dibutyryl cyclic AMP-induced differentiation. Transformation of linoleic and linolenic acid is likely to proceed through initial delta 6 desaturation. Phospholipids were preferentially labelled with the radioactive fatty acids, and only a little radioactivity was found in the neutral lipid fraction, mainly in diacylglycerols. Each fatty acid precursor label was incorporated in individual phospholipids to a proportion which reflected the typical acyl group composition of glycerophospholipids; we observed high levels of incorporation of palmitic acid and its derivatives into choline glycerophospholipids, and high levels of incorporation of linolenic acid and its derivatives into ethanolamine glycerophospholipids. This pattern was more marked in tumor cells than in normal cells, and the differentiation of tumor cells partially restored the normal pattern, mainly in bromodeoxyuridine-treated NN cells. Both types of differentiation of glial cell lines can be useful as models for the understanding of membrane physiology in normal and tumor cells.

Liposome induction or enhancement of macrophage-mediated cancer cell lysis

Liposomes of different composition have been used to modify macrophage-mediated destruction of syngeneic cancer cells through a modulation of membrane lipid content of macrophages and/or tumor cells. Dipalmitoylphosphatidylcholine (DPPC)1 liposomes induce cancer cell lysis by normal, non-tumoricidal, peritoneal macrophages and enhance tumor cell destruction by BCG-activated macrophages. This effect was produced by large and small unilamellar liposomes, which are in the 25,000 g supernatant of sonicated preparations. Addition of cholesterol or negative charges carried by dicetylphosphate supressed the effect of DPPC liposomes on macrophage-mediated cytolysis. Enhancement of macrophage-mediated tumor cell lysis was observed when both cancer cells and macrophages were incubated with DPPC liposomes, but not when macrophages and/or tumor cells were preincubated with liposomes prior to their coincubation. Liposomes did not promote the binding of the cancer cells to the macrophages. Liposomes could promote formation of phospholipid domains within the plasma membrane of both tumor cells and macrophages leading to the destruction of cancer cells through a temporary fusion with the macrophages.

Ether-linked lipids of Balb/c3T3, SV3T3 and concanavalin A-selected SV3T3 revertant cells

Ether-linked lipids were analyzed in Balb/c3T3, SV3T3 and Concanavalin A-selected SV3T3 revertant cells. The three cell lines were found to contain significant quantities of alk-1-enyl- and alkyl-linked phosphatidylethanolamine (PE) and phosphatidylcholine (PC) and small amounts of alkyldiacylglycerols. Compared to 3T3 cells, SV3T3 cells contain a higher amount of alk-1-enyl-linked PC, while in SV3T3 revertant cells the concentrations of the various ether lipids are similar to those of 3T3 cells. The major difference in the composition of ether groups of SV3T3 cells, compared to 3T3 cells, is an increase of 18:0 accompanied by a decrease of 18:1 in the alk-1-enyl-linked PE and PC. Alk-1-enyl-linked PC of SV3T3 revertant cells also shows an increase of 18:0, while the decrease of 18:1 was not statistically significant.

Cell growth and the regulation of prostaglandin synthesis

Prostaglandin (PG) synthesis was determined in human embryo lung fibroblasts (HELF) during active, slowed and non-growing phases. Bradykinin and ascorbic acid were used to induce PG synthesis. The cells were also exposed to arachidonic acid, a PG precursor. During active growth, PGE2 synthesis in response to stimulation by either bradykinin or ascorbic acid was low. As growth slowed the cellular response changed. During quiescence bradykinin and ascorbic acid stimulated PG production markedly while the conversion of free arachidonic acid to PGE2 also increased markedly. This change in response by quiescent cells was not due to an increase in cell density. When growing and quiescent cells at the same cell density were compared, the growing cells showed very little response to bradykinin while the quiescent cells were very responsive. The change in response was also not due to any difference in arachidonic acid concentrations in the culture medium during growth and non-growth.

Phospholipid acyl group composition in normal and tumoral nerve cells in culture

We have studied the fatty acid composition of total phosphoglycerides from various types of nerve cells in culture. Primary cell cultures were compared with tumoral cell strains. Glial cells exhibited no characteristic pattern when compared to neurons. Tumoral cell phosphoglycerides contained much higher levels of octadecenoic acid and lower levels of C-20 to C-22 polyunsaturated fatty acids than normal cell phosphoglycerides. This observation seems to be a general feature in tumoral cell membranes. It could be of interest in respect to the membrane fluidity of cancer cells.