Activation of protein kinase C by cis- and trans-octadecadienoic acids in intact human platelets and its potentiation by diacylglycerol

Octadecadienoic acids (linoleic acid and linolelaidic acid) and the diacylglycerol, 1-oleoyl-2-acetyl-rac-glycerol (OAG) concentration-dependently induced activation of gel-filtered human platelets, i.e. aggregation and phosphorylation of 20 kDa and 47 kDa peptides. In contrast, octadecenoic acids (oleic and elaidic acid) and octadecanoic (stearic) acid were inactive. Octadecadienoic acid-induced platelet activation was suppressed by the protein kinase C inhibitor, polymyxin B, but not by the cyclooxygenase inhibitor, indomethacin. OAG-induced activation was potentiated by octadecadienoic acids present at non-stimulatory concentrations. Our data suggest that octadecadienoic acids and diacylglycerol synergistically induce platelet activation via protein kinase C. Furthermore, linolelaidic acid may provide a useful experimental tool to study fatty acid regulation of protein kinase C in intact cells.     

Induction of apoptosis and lipogenesis in human preadipocyte cell line by n −3 PUFAs

We examined the effect of n ?3 PUFAs (polyunsaturated fatty acids) on the growth and maturation of human preadipocyte cell line AML‐I. On day 3 of the culture, n ?3 fatty acids such as DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), but not n ?6 fatty acid LA (linoleic acid), induced growth arrest accompanied by the appearance of characteristics of apoptosis in AML‐I cells at concentrations between 250 and 500 μM by Annexin V‐FITC staining. In Western blotting analysis, the loss of NF‐κB, Bcl‐2 and p‐Akt and the accumulation of Bad and Akt were observed in the cytoplasmic protein from the EPA‐treated cells. Exposure of AML‐I to EPA or DHA increased the cytoplasmic lipid accumulation compared with the vehicle‐treated cells in a time‐dependent manner during 4 and 6 days culture period by Oil Red O staining. The expression of FAS (fatty acid synthase) and PPAR‐γ (peroxisome proliferator‐activated receptor‐γ) were increased in EPA‐treated cells. These results suggest that EPA and DHA promote differentiation, inhibit proliferation and induce apoptosis in preadipocyte cell line AML‐I.     

Regulation of human lymphocyte proliferation by fatty acids

In the present study, the effect of increasing concentrations of palmitic (PA, C16:0), stearic (SA, C18:0), oleic (OA, C18:1, n-9), linoleic (LA, C18:2n-6), docosahexaenoic (DHA, C22:6 n-3) and eicosapentaenoic (EPA, C20:5 n-3) acids on lymphocyte proliferation was investigated. The maximal non-toxic concentrations of these fatty acids for human lymphocytes in vitro were determined. It was also evaluated whether these fatty acids at non-toxic concentrations affect IL-2 induced lymphocyte proliferation and cell cycle progression. OA and LA at 25 microM increased lymphocyte proliferation and at higher concentrations (75 microM and 100 microM) inhibited it. Both fatty acids promoted cell death at 200 microM concentration. PA and SA decreased lymphocyte proliferation at 50 microM and promoted cell death at concentrations of 100 microM and above. EPA and DHA decreased lymphocyte proliferation at 25 and 50 microM being toxic at 50 and 100 microM, respectively. PA, SA, DHA and EPA decreased the stimulatory effect of IL-2 on lymphocyte proliferation, increasing the percentage of cells in G1 phase and decreasing the proportion of cells in S and G2/M phases. OA and LA caused an even greater pronounced effect. The treatment with all fatty acids increased neutral lipid accumulation in the cells but the effect was more pronounced with PA and DHA. In conclusion, PA, SA, DHA and EPA decreased lymphocyte proliferation, whereas OA and LA stimulated it at non-toxic concentrations.     

Modulation of voltage-dependent Ca channel current by arachidonic acid and other long-chain fatty acids in rabbit intestinal smooth muscle.

The effects of arachidonic acid (AA) and other long-chain fatty acids on voltage-dependent Ca channel current (ICa) were investigated, with the whole cell patch clamp method, in longitudinal smooth muscle cells of rabbit ileum. 10-30 microM AA caused a gradual depression of ICa. The inhibitory effect of AA was not prevented by indomethacin (10 microM) (an inhibitor of cyclooxygenase) or nordihydroguaiaretic acid (10 microM) (an inhibitor of lipoxygenase). 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine (H7; 25-50 microM) or staurosporine (2 microM) (inhibitors of protein kinase C) did not block the AA-induced inhibition of ICa, and application of phorbol ester (a protein kinase C activator) (phorbol-12,13-dibutyrate, 0.2 microM) did not mimic the AA action. Some other cis-unsaturated fatty acids (palmitoleic, linoleic, and oleic acids) were also found to depress ICa, while a trans-unsaturated fatty acid (linolelaidic acid) and saturated fatty acids (capric, lauric, myristic, and palmitic acids) had no inhibitory effects on ICa. Myristic acid consistently increased the amplitude of ICa at negative membrane potentials. The present results suggest the possible role of AA, and perhaps other fatty acids, in the physiological and/or pathological modulation of ICa in smooth muscle.     

Effects of fatty acids on lysis of Streptococcus faecalis.

Palmitic, stearic, oleic, and linoleic acids at concentrations of 200 nmol/ml all inhibited autolysin activity 80% or more in whole cells or cell-free extracts. This concentration of the saturated fatty acids palmitic acid and stearic acid had little or no effect on the growth of whole cells or protoplasts. However, the unsaturated fatty acids oleic acid and linoleic acid induced lysis in both situations. This lytic effect is apparently not related to any uncoupling activity or inhibition of energy catabolism by unsaturated fatty acids. It is concluded that unsaturated fatty acids induce cell and protoplast lysis by acting as more potent membrane destabilizers than saturated fatty acids.     

Differential effects of temperature and exogenous fatty acids on mitogen-induced proliferation in channel catfish T and B lymphocytes

1. Exogenously supplied, BSA complexed saturated and unsaturated fatty acids were compared for their effects on mitogen-induced DNA synthesis in channel catfish T and B lymphocytes. 2. At "permissive" in vitro temperatures (27 degrees C), high concentrations (greater than or equal to 240 microM) of all the fatty acids used were inhibitory. However, at lower concentrations (80-160 microM), differences were noted in the ability of some fatty acids to modulate mitogen responses. While palmitic acid (16:0) and linoleic acid (18:2) had little effect on LPS-induced B cell- or Con A-induced T cell proliferation, stearic acid (18:0) suppressed while oleic acid (18:1) enhanced T cell responses only. 3. Adding equimolar amounts of 18:0 and 18:1 obviated the effects of singularly added fatty acids on T cell mitogenesis. 4. 18:1 was used to successfully "rescue" approximately 60% of the Con A-induced T cell proliferation normally inhibited at "nonpermissive" in vitro temperatures (17 degrees C). 5. While B cells readily appear to desaturate 18:0 and synthesize unsaturated fatty acids, T cells accumulate comparatively large amounts of 18:0 in membrane associated phospholipids. 6. It is proposed that 18:1 enhances T cell responses at permissive high temperatures and rescues suppressed T cell responses at nonpermissive low temperatures by increasing membrane fluidity.     

Application of a continuous bioreactor cascade to study the effect of linoleic acid on hybridoma cell physiology

The aim of the present study is to demonstrate the use of controlled bioreactors for toxicological studies. As a model system the effect of linoleic acid on hybridoma cells is studied in two well-controlled continuously operated bioreactors placed in series. In the first reactor the effect on rapid proliferating cells can be studied, while in the second reactor a special steady state is created, which allows studying the effect on apoptotic cells. Experiments are done at 0, 25, and 50 microM linoleic acid. At the end of the experiment with 50 microM linoleic acid, the concentration of linoleic acid is increased stepwise to determine the cytotoxic level. For rapid proliferating cells exposed to 25 and 50 microM stimulation of growth was observed. At 50 microM there was at the same time an increase in cell death through apoptosis. For stressed apoptotic cells linoleic acid caused partial growth inhibition at 25 and 50 microM and arrest of cell proliferation in the G(2)/M phase at 50 microM. For both, rapid proliferating cells and stressed apoptotic cells, complete growth inhibition occurred at 85 microM, with cells being arrested in the G(2)/M phase and dying mainly through necrosis. Cells in the bioreactor system appeared to be more sensitive towards linoleic acid than cells grown in multi-well plates. (IC(50) = 300 microM; IC(100) = 400 microM). Altogether the results of the present study reveal that the biostat experiments allow detailed analysis of the effect of a bioactive ingredient on cell physiology and behavior.     

Differential inhibition of thromboxane B2 and leukotriene B4 biosynthesis by two naturally occurring acetylenic fatty acids

The seed oil of the plant Ixiolaena brevicompta is a rich source of crepenynic acid (octadec-cis-9-en-12-ynoic acid), which has been linked with extensive sheep mortalities in Western New South Wales and Queensland, Australia. A number of acetylenic fatty acids have been found to interfere with lipid and fatty acid metabolism and inhibit cyclooxygenase and lipoxygenase enzymes in a variety of tissues. We have investigated the effects of crepenynic acid and ximenynic acid (octadec-trans-11-en-9-ynoic acid) on leukotriene B4 and thromboxane B2 production in rat peritoneal leukocytes and compare them with non-acetylenic compounds linoleic and ricinoleic acids. In concentrations ranging from 10 to 100 microM linoleic acid and ricinoleic acid had only minimal effects on leukotriene B4 and thromboxane B2 production in ionophore-stimulated cells. Ximenynic acid gave dose-dependent inhibition of leukotriene B4, thromboxane B2 and 6-ketoprostaglandin F1 alpha production. Ximenynic acid appears to be a more effective inhibitor of leukotriene B4 than crepenynic acid with an IC50 of 60 microM compared to 85 microM. On the other hand, crepenynic acid is a much more effective inhibitor of the cyclooxygenase products, having an IC50 for thromboxane B2 of less than 10 microM. Both acetylenic fatty acids inhibited phospholipase activity in these cells by 40-50% at a concentration of 100 microM but had no inhibitory effect at 10 microM. These results indicate that crepenynic acid and ximenynic acid differentially inhibit the cyclooxygenase and lipoxygenase products of stimulated leukocytes, and that at high doses of these fatty acids the effect on these products may be partially due to inhibition of phospholipase A2.     

Differential regulation of calmodulin-dependent and -independent cyclic AMP phosphodiesterases from oviduct by fatty acids.

Regulation of calmodulin-independent and -dependent cAMP phosphodiesterases from quail oviduct by various fatty acids was studied. The calmodulin-independent form was slightly activated by low concentrations (20 microM) of oleic, linoleic and arachidonic acid, higher concentrations were inhibitory. The basal activity of the calmodulin-dependent form was activated by linoleic acid and to a lesser extent by arachidonic acid at low concentrations and inhibited by higher concentrations of the two fatty acids. In contrast, arachidonic acid was a potent reversible inhibitor of calmodulin in the activation of this enzyme (IC50: 20 microM) whereas linoleic acid was inactive from 10 to 150 microM. The present results strongly suggest that the differential regulation of cAMP phosphodiesterases by these fatty acids could profoundly influence the level of cAMP in the oviduct and thus its subsequent effects.     

Modulation of native T-type calcium channels by omega-3 fatty acids

Low voltage-activated, rapidly inactivating T-type Ca(2+) channels are found in a variety of cells where they regulate electrical activity and Ca(2+) entry. In whole-cell patch clamp recordings from bovine adrenal zona fasciculata cells, cis-polyunsaturated omega-3 fatty acids including docosahexaenoic acid (DHA), eicosapentaenoic acid, and alpha-linolenic acid inhibited T-type Ca(2+) current (I(T-Ca)) with IC(50)s of 2.4, 6.1, and 14.4microM, respectively. Inhibition of I(T-Ca) by DHA was partially use-dependent. In the absence of stimulation, DHA (5microM) inhibited I(T-Ca) by 59.7+/-8.1% (n=5). When voltage steps to -10mV were applied at 12s intervals, block increased to 80.5+/-7.2%. Inhibition of I(T-Ca) by DHA was accompanied by a shift of -11.7mV in the voltage dependence of steady-state inactivation, and a smaller -3.3mV shift in the voltage dependence of activation. omega-3 fatty acids also selectively altered the gating kinetics of T-type Ca(2+) channels. DHA accelerated T channel recovery from inactivation by approximately 3-fold, but did not affect the kinetics of T channel activation or deactivation. Arachidonic acid, an omega-6 polyunsaturated fatty acid, also inhibited T-type Ca(2+) current at micromolar concentrations, while the trans polyunsaturated fatty acid linolelaidic acid was ineffective. These results identify cis polyunsaturated fatty acids as relatively potent, new T-type Ca(2+) channel antagonists. omega-3 fatty acids are essential dietary components that have been shown to possess remarkable neuroprotective and cardioprotective properties that are likely mediated through suppression of electrical activity and associated Ca(2+) entry. Inhibition of T-type Ca(2+) channels in neurons and cardiac myocytes could contribute significantly to their protective actions.     

Abortive infection of the virulent phage 9NA in a fatty acid auxotroph of Salmonella typhimurium: effect of fatty acid supplementation

A conditional (temperature sensitive) fatty acid biosynthetic mutant (fabB2) of Salmonella typhimurium does not support the development of the virulent bacteriophage 9NA even at permissive temperature (30 degrees C). A limited amount of phage DNA synthesis takes place at this temperature. When the fatty acid composition of the host membrane is altered by growing the cells at 37 degrees C in the presence of exogenous unsaturated fatty acid, differential expression of phage genes was observed. Phage specific lysozyme is induced when the cultures are supplemented with elaidic, palmitelaidic, linoleic and linolelaidic acids but not with oleic and plamitoleic acids. However, in no case were infective particles produced. Under conditions where no lysozyme is synthesized the infected cells increase in length and become filamentous.     

Growth temperature affects accumulation of exogenous fatty acids and fatty acid composition in <Emphasis Type="Italic">Schizosaccharomyces pombe</Emphasis>

The incorporation of exogenously supplied fatty acids, palmitic acid, palmitoleic acid, oleic acid and linoleic acid, was examined in the yeast Schizosaccharomyces pombe at two growth temperatures, 20 °C and 30 °C. Fatty acids supplied to S. pombe in the growth medium were found to be preferentially incorporated into the cells, becoming a dominant species. The relative increase in exogenous fatty acids in cells came at the expense of endogenous oleic acid as a proportion of total fatty acids. Lowering the temperature at which the yeast were grown resulted in decreased levels of incorporation of the fatty acids palmitic acid, palmitoleic acid and linoleic acid compared to cells supplemented at 30 °C. In addition, the relative amount of the endogenously produced unsaturated fatty acid oleic acid, while greatly reduced compared to unsupplemented cells, was increased in cells supplemented with fatty acids at 20 °C compared to supplemented cells at 30 °C. The differential production of oleic acid in S. pombe cells indicates that regulation of unsaturated fatty acid levels, possibly by control of the stearoyl-CoA desaturase, is an important control point in membrane composition in response to temperature and diet in this species.     

Antifungal Activities of Four Fatty Acids against Plant Pathogenic Fungi

The effect of the fatty acids linolenic acid, linoleic acid, erucic acid and oleic acid on the growth of the plant pathogenic fungi Rhizoctonia solani, Pythium ultimum, Pyrenophora avenae and Crinipellis perniciosa were examined in in vitro studies. Linolenic and linoleic acids exhibited activity against all of the fungi. However, whereas linolenic acid reduced mycelial growth of R. solani and C. perniciosa at 100 microM, the concentration had to be increased to 1000 microM before any effect on mycelial growth of P. ultimum and P. avenae was observed. Linoleic acid only reduced mycelial growth of R. solani, P. ultimum and P. avenae at 1000 microM, but led to a significant reduction in growth of C. perniciosa at 100 microM. In contrast, oleic acid had no significant effect on growth of R. solani or P. avenae, but gave significant reductions in mycelial growth of P. ultimum at 100 microM and reduced growth of C. perniciosa significantly at 1000 microM. All of the fatty acids reduced biomass production by all of the fungi significantly in liquid culture when added to the media at 100 microM. Erucic acid had no effect on fungal growth at any concentration examined. The antifungal activities exhibited by linolenic, linoleic and oleic acids may be useful in the search for alternative approaches to controlling important plant pathogens, such as those examined in this study.     

The effects of unsaturated fatty acids on the synthesis of arachidonic acid in rat kidney cells

Cultured rat kidney cells absorbed exogenous linoleic acid (cic, cis-18:2n-6) and esterified it mostly into glycerophospholipids. As the concentration of 18:2 was increased (5-200 microM) the quantity absorbed increased linearly and the amount esterified in the triacylglycerol increased. The cells possessed active acyl delta 6-desaturase and elongase which facilely converted 18:2n-6 to 20:4n-6. At low intracellular concentrations of 18:2n-6 other unsaturated fatty acids, i.e., gamma-linolenic (18:3n-6), alpha-linolenic (18:3n-3), dihomo-gamma-linolenic (20:3n-6), and especially trans, trans-linoleic acid (trans, trans-18:2n- -6) at concentrations ranging from 25 to 200 microM depressed delta 6-desaturase activity. However, suppression of 20:4 synthesis even by trans, trans-18:2 was readily overcome by increasing the concentration of available cis, cis-18:2n-6.     

The aldehydic metabolites of linoleic acid are cytotoxic against human breast cancer cells

The cytotoxic effect of aldehydic metabolites of linoleic acid, 13-oxo-tridecadienoic acids, on MCF-7 human breast cancer cells was investigated. The metabolites inhibited the growth of the cancer cells and the effect was dependent on both time of exposure and concentration of the metabolites; 50% growth inhibition occurred at approximately 55 and 33 microM, after 3- and 5-day incubations, respectively. The metabolites had greater cytotoxicity than parent linoleic acid or other polyunsaturated fatty acids tested. The antiproliferative effect was partially reversed by 10 microM of dithiothreitol suggesting that attack on thiol groups in cancer cells by highly reactive alpha, beta-unsaturated carbonyl moiety in the metabolites was responsible for the cytotoxic actions.     

Inhibition of brain prostaglandin D synthetase and prostaglandin D2 dehydrogenase by some saturated and unsaturated fatty acids

The activities of rat brain prostaglandin D synthetase and swine brain prostaglandin D2 dehydrogenase were inhibited by some saturated and unsaturated fatty acids. Myristic acid was most potent among saturated straight-chain fatty acids so far tested. The IC50 values of this acid were 80 microM for prostaglandin D synthetase and 7 microM for prostaglandin D2 dehydrogenase, respectively. Little inhibition was found with methyl myristate and myristyl alcohol. The IC50 values of these derivatives were more than 200 microM for both enzymes, suggesting that the free carboxyl group was essential for the inhibition. The effects of cis double bond structure of fatty acids on the inhibition potency were examined by the use of the carbon 18 and 20 fatty acids. The inhibition potencies for both enzymes increased with the number of cis double bonds; the IC50 values of stearic, oleic, linoleic and linolenic acid were, respectively, more than 200, 60, 30 and 30 microM for prostaglandin D synthetase, and 20, 10, 8.5 and 7 microM for prostaglandin D2 dehydrogenase. Arachidonic acid also inhibited the activities of both enzymes with respective IC50 values of 40 microM for prostaglandin D synthetase and 3.9 microM for prostaglandin D2 dehydrogenase, while arachidic acid showed little inhibition. The kinetic studies with myristic acid and arachidonic acid demonstrated that the inhibition by these fatty acids was competitive and reversible for both enzymes. Myristic acid and other fatty acids also inhibited the activities of several enzymes in prostaglandin metabolism, although to a lesser extent. The IC50 values of myristic acid for prostaglandin E isomerase, thromboxane synthetase and NAD-linked prostaglandin dehydrogenase (type I) were 200, 700 and 100 microM, respectively. However, this fatty acid showed little inhibition on fatty acid cyclooxygenase (20% at 800 microM), glutathione-requiring prostaglandin D synthetase from rat spleen (20% at 800 microM), and NADP-linked prostaglandin dehydrogenase (type II) (no inhibition at 200 microM).     

Dietary oxidized fatty acids may enhance intestinal apolipoprotein A-I production

Apolipoprotein (apo)A-I, the major protein component of HDL, is synthesized principally in the small intestine and liver. Recently we observed an increase in plasma apoA-I level in humans who were on an oxidized fat diet. To test whether oxidized fatty acids could affect apoA-I synthesis, we incubated day 4 (undifferentiated) and day 14 (differentiated) Caco-2 cells with varying concentrations of oxidized linoleic acid (ox-linoleic acid) (5, 10, and 25 microM) and unoxidized linoleic acid for 24 h. Ox-linoleic acid caused a dose-dependent increase in the levels of apoA-I protein in both differentiated and undifferentiated Caco-2 cells as assessed by ELISA and Western blot analysis. Whereas apoB production was not increased by ox-linoleic acid in both day 4 and day 14 Caco-2 cells. The mRNA expression for apoA-I paralleled the protein expression when measured by RT-PCR. We also found that both day 4 and day 14 Caco-2 cells did express peroxisomal proliferator-activated receptor-gamma (PPAR-gamma). mRNA and PPAR-gamma ligand could increase apoA-I secretion in these cells.Therefore we propose that the mechanism for the induction of apoA-I might include PPAR-gamma for which oxidized fatty acid is a ligand.     

Unsaturated fatty acids induce mesenchymal stem cells to increase secretion of angiogenic mediators

Mesenchymal stem cells (MSC) represent emerging cell-based therapies for diabetes and associated complications. Ongoing clinical trials are using exogenous MSC to treat type 1 and 2 diabetes, cardiovascular disease and non-healing wounds due to diabetes. The majority of these trials are aimed at exploiting the ability of these multipotent mesenchymal stromal cells to release soluble mediators that reduce inflammation and promote both angiogenesis and cell survival at sites of tissue damage. Growing evidence suggests that MSC secretion of soluble factors is dependent on tissue microenvironment. Despite the contribution of fatty acids to the metabolic environment of type 2 diabetes, almost nothing is known about their effects on MSC secretion of growth factors and cytokines. In this study, human bone marrow-derived MSC were exposed to linoleic acid, an omega-6 polyunsaturated fatty acid, or oleic acid, a monounsaturated fatty acid, for seven days in the presence of 5.38 mM glucose. Outcomes measured included MSC proliferation, gene expression, protein secretion and chemotaxis. Linoleic and oleic acids inhibited MSC proliferation and altered MSC expression and secretion of known mediators of angiogenesis. Both unsaturated fatty acids induced MSC to increase secretion of interleukin-6, VEGF and nitric oxide. In addition, linoleic acid but not oleic acid induced MSC to increase production of interleukin-8. Collectively these data suggest that exposure to fatty acids may have functional consequences for MSC therapy. Fatty acids may affect MSC engraftment to injured tissue and MSC secretion of cytokines and growth factors that regulate local cellular responses to injury.     

Fatty acid control of nitric oxide production by macrophages

Modulation of macrophage functions by fatty acids (FA) has been studied by several groups, but the effect of FA on nitric oxide production by macrophages has been poorly examined. In the present study the effect of palmitic, stearic, oleic, linoleic, arachidonic, docosahexaenoic and eicosapentaenoic acids on NF-kappaB activity and NO production in J774 cells (a murine macrophage cell line) was investigated. All FA tested stimulated NO production at low doses (1-10 microM) and inhibited it at high doses (50-200 microM). An increase of iNOS expression and activity in J774 cells treated with a low concentration of FA (5 microM) was observed. The activity of NF-kappaB was time-dependently enhanced by the FA treatment. The inhibitory effect of FA on NO production may be due to their cytotoxicity, as observed by loss of membrane integrity and/or increase of DNA fragmentation in cells treated for 48 h with high concentrations. The results indicate that, at low concentrations FA increase NO production by J774 cells, whereas at high concentrations they cause cell death.     

Manipulation of fatty acid composition of membrane phospholipid and its effects on cell growth in mouse LM cells

Fatty acid composition of the phospholipids of mouse LM cells grown in suspension culture in serum-free chemically defined medium was modified by supplementing the medium with various fatty acids bound to bovine serum albumin.Following supplementation with saturated fatty acids of longer than 15 carbons (100 μM) profound inhibition of cell growth occurred; this inhibitory effect was completely abolished when unsaturated fatty acids were added at the same concentration. Supplementing with unsaturated fatty acids such as linoleic acid, linolenic acid or arachidonic acid had no effect on the cell growth.Fatty acid composition of membrane phospholipids could be manipulated by addition of different fatty acids. The normal percentage of unsaturated fatty acids in LM cell membrane phospholipids (63%) was reduced to 35–41% following incorporation of saturated fatty acids longer than 15 carbon atoms and increased to 72–82% after addition of unsaturated fatty acids.A good correlation was found between the unsaturated fatty acid content of membrane phospholipids and cell growth. When incorporated saturated fatty acids reduced the percentage of unsaturated fatty acids in membrane phospholipids to less than 50%, severe inhibition of the cell growth was found. Simultaneous addition of an unsaturated fatty acid completely abolished this effect of saturated fatty acids.