Free fatty acids as modulators of the steroid hormone message

Effects of ω3- and ω6-polyunsaturated fatty acids on RANKL-induced osteoclast differentiation of RAW264.7 cells: a comparative in vitro study

Polyunsaturated fatty acids (PUFAs) have been reported to have an anabolic effect on bone in vivo, but comparative studies to identify inhibitors of osteoclast formation amongst ω3- and ω6-PUFAs are still lacking. Here we assessed the effects of the ω3-PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and the ω6-PUFAs, arachidonic acid (AA) and γ-linolenic acid (GLA) on a RAW264.7 osteoclast differentiation model. The effects of PUFAs on RANKL-induced osteoclast formation were evaluated by counting tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells. PUFAs significantly inhibited RANKL-induced osteoclast formation in a dose-dependent manner with AA- and DHA-mediated inhibition being the strongest. Furthermore, RANKL-induced mRNA- and protein expression of the key osteoclastogenic genes cathepsin K and TRAP were inhibited by AA and more potently by DHA. Owing to the attenuated osteoclastogenesis by DHA and AA, actin ring formation and bone resorptive activity of these cells as evaluated on bone-mimetic plates were severely compromised. Hence, of the tested PUFAs, AA and DHA were found to be the most effective in inhibiting RANKL-induced osteoclast formation with the latter providing the strongest inhibitory effects. Collectively, the data indicates that these PUFAs may play an important role in regulating bone diseases characterized by excessive osteoclast activity.

Effects of arachidonic acid, docosahexaenoic acid and prostaglandin E(2) on cell proliferation and morphology of MG-63 and MC3T3-E1 osteoblast-like cells

During bone remodelling bone is resorbed by osteoclasts and replaced again by osteoblasts through the process of bone formation. Clinical trials and in vivo animal studies suggest that specific polyunsaturated fatty acids (PUFAs) might benefit bone health. As the number of functional osteoblasts is important for bone formation the effects of specific PUFAs on in vitro osteoblastic cell proliferation were investigated. Morphological studies were conducted to determine whether exposure of the cells to these agents caused structural damage to the cells thereby yielding invalid results. Results from this study showed that arachidonic acid (AA) and docosahexaenoic acid (DHA) both inhibit cell growth significantly at high concentrations. The anti-mitotic effect of AA is possibly independent of PGE(2) production, as PGE(2) per se had little effect on proliferation. Further study is required to determine whether reduced proliferation due to fatty acids could be due to increased differentiation of osteoblasts to the mature mineralising osteoblastic phenotype.

Omega-3 fatty acids modulate ATPases involved in duodenal Ca absorption

Dietary supplementation with fish oil that contains omega-3 polyunsaturated fatty acids has been shown to enhance bone density as well as duodenal calcium uptake in rats. The latter process is supported by membrane ATPases. The present in vitro study was undertaken to test the effect of omega-3 fatty acids on ATPase activity in isolated basolateral membranes from rat duodenal enterocytes. Ca-ATPase in calmodulin-stripped membranes was activated in a biphasic manner by docosahexanoic acid (DHA) (10-30 microg/ml) but not by eicosapentanoic acid (EPA). This effect was blocked partially by 0.5 microM calphostin (a protein kinase C blocker). DHA inhibited Na,K-ATPase (-49% of basal activity, [DHA]=30 microg/ml, P <0.01). This effect could be reversed partially by 50 microM genistein, a tyrosine kinase blocker. EPA also inhibited Na,K-ATPase: (-47% of basal activity, [EPA]=30 microg/ml, P <0.01), this effect was partially reversed by 100 microM indomethacin, a cyclo-oxygenase blocker. Omega-3 fatty acids are thus involved in multiple signalling effects that effect ATPases in BLM.

The effect of omega-3 fatty acids on Ca-ATPase in rat cerebral cortex

Neuronal Ca-ATPase has the essential function of keeping intracellular Ca levels in the micromolar range. This is a prerequisite for normal neurotransmission. This study was designed to determine whether Ca-ATPase is a target for docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) action: results show that both these fatty acids are inhibitors of Ca-ATPase activity in synaptosomal membranes isolated from rat cerebral cortex (-65+/-5% at [DHA]=20 microg/ml, -59+/-7% at [EPA]=20 microg/ml). The inhibition caused by EPA, but not that of DHA, could be reversed completely by the addition of calphostin, a protein kinase C blocker. In contrast, DHA could stimulate Ca-ATPase activity (+132+/-5% at [DHA]=30 microg/ml) only in calmodulin-depleted membranes. In addition, Na,K-ATPase (which drives the Na-Ca exchanger) was inhibited by both DHA and EPA, both at 30 microg/ml (-15+/-0.7% and -42+/-1%, respectively). These results suggest a mechanism that explains the dampening effect of omega-3 fatty acids on neuronal activity.

Effect of arachidonic acid on duodenal enterocyte ATPases

Duodenal ion transport processes are supported by ATPase enzymes in basolateral membranes of the enterocyte. In vivo studies have shown that long term n-6 poly-unsaturated fatty acid (PUFA) supplementation in rats causes increases in intestinal Ca absorption, coupled with a higher total calcium balance and bone calcium content. The present in vitro study was undertaken to test the effect of arachidonic acid (AA), a highly unsaturated (and thus physiologically potent) member of the n-6 PUFA family, on ATPases in enterocyte basolateral membranes isolated with a sorbitol density gradient procedure. This paper presents results which show that AA inhibits Na+,K+-ATPase in a dose-dependent manner (-67% of basal activity at a concentration of 30 microg/ml, P < 0.005) but that this effect is not mediated by protein kinase C, as shown by the use of the protein kinase C blocker calphostin (0.5 microM). Indomethacin (IDM) at 0.1 mM, a cyclo-oxygenase blocker, could also not reverse the inhibitory effect of AA on Na+,K+-ATPase. Ca2+-ATPase, on the other hand, is not affected significantly (-10%, P > 0.05) by arachidonic acid at 30 microg/ml.

Upregulation of duodenal calcium absorption by poly-unsaturated fatty acids: events at the basolateral membrane

Poly-unsaturated fatty acids, especially of the n-3 series, have a beneficial effect in treatment of osteoporosis in the elderly. Duodenal calcium absorption is a particularly vulnerable aspect of the development of this disease. It has been shown that the process of calcium transport through the rat duodenal enterocyte takes place in essentially three steps: entry of calcium through channels in the brush border (apical membrane), transcellular transport through the cytoplasm by calbindin and extrusion at the basolateral membrane by Ca(2+)-ATPase and a Ca(2+)-Na(+)exchanger which is driven by Na(+), K(+)-ATPase. This paper presents a hypothesis that poly-unsaturated fatty acids can modulate both Ca(2+)-ATPase and Na(+), K(+)-ATPase activity either by a direct action on the enzyme or by phosphorylation processes via protein kinases A and C and thus exert their positive influence on calcium absorption in this manner.

Changes in enzymatic activities involved in glucose metabolism by acyl-CoAs in Trypanosoma cruzi

This study describes the effect of some saturated and unsaturated free fatty acids and acyl-CoA thioesters on Trypanosoma cruzi glucose 6-phosphate dehydrogenase and hexokinase activities. Glucose 6-phosphate dehydrogenase was sensitive to the destabilizing effect provoked by free fatty acids, while hexokinase remained unaltered. Glucose 6-phosphate dehydrogenase inhibition by free fatty acids was dependent on acid concentration and chain length. Both enzymes were inhibited when they were incubated with acyl-CoA thioesters. The acyl-CoA thioesters inhibited glucose 6-phosphate dehydrogenase at a lower concentration than the free fatty acids; the ligands glucose 6-phosphate and NADP+ afforded protection. The inhibition of hexokinase by acyl-CoAs was not reverted when the enzyme was incubated with ATP. The type of inhibition found with acyl-CoAs in relation to glucose 6-phosphate dehydrogenase and hexokinase suggests that this type inhibition may produce an in vivo modulation of these enzymatic activities.Key words: Trypanosoma cruzi, fatty acids, acyl-CoAs, glucose 6-phosphate dehydrogenase, hexokinase.

The levels of lipid peroxidation products in bovine retained and not retained placenta

Unsaturated fatty acids undergo peroxidation processes. The presence of elevated levels of metabolites of lipid peroxidation processes may cause alterations in metabolic pathways which may lead to disturbances and clinical symptoms of illnesses. One such illness may be retention of fetal membranes (RFM) in cows. The aim of the study was the determination of thiobarbituric acid (TBA) reactive substances, conjugated dienes and hydroperoxides in bovine retained and not retained placenta in order to describe the oxidative status of cows affected with RFM. Placental samples were collected immediately after spontaneous delivery or caesarian section before term and at term and divided into 6 groups, with 16 animals in each group, as follows: A) caesarian section before term without RFM: B) caesarian section before term with RFM: C) caesarian section at term without RFM: D) caesarian section at term with RFM: E) spontaneous delivery at term without RFM; F) spontaneous delivery with RFM. The levels of TBA reactive substances, conjugated dienes and hydroperoxides were measured spectrophotometrically. The levels of all parameters were statistically significantly higher in the maternal than in the fetal part of placenta and the lowest in preterm groups. Statistically significantly higher concentrations in retained placenta samples than in control animals were observed. In conclusion, the metabolites of lipid peroxidation processes are elevated in cases of retained placenta and their presence might influence directly and/or indirectly the improper release of fetal membranes in cows.

Review: the role of omega 3 fatty acids in intestinal inflammation

The role of polyunsaturated fatty acids (PUFAs) in inflammatory lesions of the intestines is the subject of increasing research. This review begins with a background discussion of the source, elongation, and desaturation of PUFAs, as well as the role they have played in the human diet through evolution. The available data and hypotheses as to how manipulation of PUFAs might effect the various components of the immune system are then provided. Possible mechanisms by which PUFAs result in immunomodulation include alterations in eicosanoid synthesis, membrane fluidity, signal transduction, intraluminal bacteria, and gene expression. Attention is then turned to the known effects that these polyunsaturated fatty acids have on the various individual components of the immune system including lymphocytes, neutrophils, and antigen presenting cells, as well as the immunoregulatory process of apoptosis. Finally, laboratory data on the role of PUFAs in necrotizing enterocolitis, and to a greater extent inflammatory bowel disease, first as demonstrated in animal models of the disease, and second in human studies are then summarized.

Inhibition of duodenal enterocyte Mg2+-ATPase by arachidonic acid is not mediated by an effect on protein kinase C

Active absorption processes in the duodenal enterocyte are driven by various ATPases. It is known that the activity of Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase can be modulated by polyunsaturated fatty acids of the n-6 series, for example by linoleic and gamma-linolenic acids. These effects may be achieved by protein phosphorylation via protein kinase C. The present study was undertaken to determine the effect of arachidonic acid on Mg2+-ATPase (measured colorimetrically) activity in basolateral membranes prepared from rat duodenum. It shows, for the first time, significant dose-dependent inhibition of Mg2+-ATPase (26-62%) by arachidonic acid (10-50 microg/ml) which already takes place after one minute of exposure, indicating involvement of a rapid signal transduction mechanism. Addition of the protein kinase C inhibitors bisimidolylmaleimide (2.5 microM) and calphostin (0.5 microM) did not influence the action of arachidonic acid on Mg2+-ATPase; protein kinase C involvement in this process is thus not indicated.

Oestrogen and essential fatty acid supplementation corrects bone loss due to ovariectomy in the female Sprague Dawley rat

Essential fatty acid deficient animals develop osteoporosis. Eicosapentaenoic acid and gamma-linoleic acid have been reported to have positive effects on bone metabolism in both the growing male rat and the ovariectomized (OVX) female rat. These effects have been further investigated using a novel gamma-linolenic/eicosapentaenoic acid diester together with an oestrogen implant in the ovariectomized, female Sprague Dawley rat. Rats were sham-operated or ovariectomized at age 11 weeks. Two groups of OVX rats received an oestrogen implant at ovariectomy. Animals received fatty acids, linoleic acid (control) or a diester with gamma-linolenic acid and eicosapentaenoic acid as part of a semi-synthetic diet. Bone calcium content and excretion of deoxypyridinolines as marker of bone degradation were measured at 14 weeks. Oestrogen, as well as diester alone, increased calcium/femur to sham levels. Oestrogen plus diester potentiated the effect of oestrogen on bone calcium (P < 0.05 vs OVX). At the same time, oestrogen alone and the combination of oestrogen plus diester significantly reduced (P < 0.05 vs OVX) urinary deoxypyridinoline and hydroxyproline excretion. Again, the diester potentiated the effect of oestrogen. The effects of the diester alone, together with the potentiated effects of oestrogen by the essential fatty acids on osteoporosis, are novel findings.

Cytokine levels affected by gamma-linolenic acid

This study was undertaken to assess whether gamma-linolenic acid (GLA) in the form of evening primrose oil (EPO) could affect rat serum cytokines, interferon-gamma (IFN-gamma), monocyte chemotactic protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha). The following diets were administered: control, glucan, Freund's adjuvant and glucan plus Freund's adjuvant with and without GLA. In the presence of GLA, the IFN-gamma and MCP-1 levels were significantly decreased in contrast to the control group of TNF-alpha, which was significantly stimulated. On account of interaction between diets and GLA, the remaining diet groups of TNF-alpha were either not affected or were inhibited in the presence of GLA. The observations indicate that GLA may modulate the level of serum IFN-gamma, MCP-1 and TNF-alpha, which may be a worthwhile line of treatment in certain human diseases.

Expression of retinoic acid, triiodothyronine, and glucocorticoid hormone nuclear receptors is decreased in the liver of rats fed a hypercholesterolemia-inducing diet

Several studies have shown that dietary factors modulate cell signaling pathways. The aim of this study was to determine whether a hypercholesterolemia-inducing diet rich in saturated fat and cholesterol modifies rat liver expression of the nuclear receptors of retinoic acid (RAR), triiodothyronine (TR), and glucocorticoid hormone (GR), which are transcriptional factors. The experimental diet contained coconut oil 25 g/100 g as a source of lipids, cholesterol 1 g/100 g, and cholic acid 0.5 g/100 g, and the control diet contained olive oil 5 g/100 g. After 26 days of feeding the hypercholesterolemia-inducing diet, a lower binding capacity of the nuclear receptors and a smaller amount of their mRNA were observed. Moreover, the activities of malic enzyme (ME) and tyrosine aminotransferase (TAT), whose gene promotors contain a response element to TR and GR, respectively, were significantly decreased. These changes occurred in a cellular environment characterized by a high level of cholesterol and free fatty acids (FFAs). Thus, two nonexclusive hypotheses can be proposed to explain this decreased expression of nuclear receptors, one emphasizing the effect of lipidic components on the cellular amount of receptor ligands (retinoic acid [RA] and triiodothyronine [T3]), the other emphasizing a modification of the balance between nuclear receptors that could impede the upregulation of TR and RAR.

N-3 polyunsaturated fatty acids and immune cell function

The amount and type of eicosanoids made can be affected by the type of fat consumed in the diet. It is now apparent that both eicosanoids and n-3 PUFAs are potent modulators of lymphocyte and M phi functions in vitro. Inclusion in the diet of high levels of certain lipids containing n-3 PUFAs markedly affects the functions of cells of the immune system subsequently tested in vitro. Cellular components of both natural and acquired immunity are affected. In vivo tests are perhaps the most appropriate approach for determining the effect of different dietary n-3 PUFAs upon immune function. Several studies indicate that diets rich in n-3 PUFAs are anti-inflammatory and immunosuppressive in vivo, although there have been relatively few studies in man. Although some of the effects of n-3 PUFAs may be brought about by modulation of the amount and types of eicosanoids made, it is clear that these fatty acids can also elicit their effects by eicosanoid-independent mechanisms (Fig. 12). Such n-3 PUFA-induced effects may be of use as a therapy for acute and chronic inflammation, for disorders which involve an inappropriately-activated immune response and for the enhancement of graft survival.

Fatty acids involved in signal cross-talk between cell membrane and nucleus

The results presented underline the fact that the nature and the concentration of the non-esterified fatty acids (NEFAs) liberated from membrane lipids, particularly the essential ones issued from lipid nutrition, clearly belong to a large group of factors (hormones, retinoids, growth factors, cytokines...) which control the shift between cell multiplication and differentiation. NEFAs act on this shift, per se or after being metabolized, by influencing, as second messengers or modulators, the intertwined mechanisms of action of growth factors and steroid hormones. These results may explain the molecular links which exist between endocrinology, oncology and nutrition.

Biological complexity is under the 'strange attraction' of non-esterified fatty acids

It is now clear from numerous data that non-esterified fatty acids (NEFAs) can act without any metabolic modification as second messengers or modulators of the complex signalling network which is characteristic of mammals. This network can respond differently to adapt the organism to the various endogenous and exogenous environmental situations. NEFAs have a wide range of molecular structures, and thus can exert different specific modulatory actions on this signalling network, such as amplification, inhibition or signal redirection. We have chosen the term 'strange attractions' to describe these signalling modulations by analogy with the 'strange attractions' concept introduced in deterministic chaos theory. NEFAs can modulate the functions of mammals at all levels of organization (molecular, cellular, tissue, organ, etc).

Abnormal membrane concentrations of 20 and 22-carbon essential fatty acids: a common link between risk factors and coronary and peripheral vascular disease?

Although elevated levels of cholesterol are associated with increased risks of coronary and peripheral vascular disease, the association frequently fails to provide a causative explanation at the individual level. New hypotheses are required which, whether or not they are correct, will provide new lines of research. It is proposed here that the causes of vascular disease are abnormal membrane phospholipid concentrations of the 20-carbon and 22-carbon essential fatty acids (EFAs) of the n-6 and n-3 series. These levels become abnormal with ageing, with stress and in response to smoking, high cholesterol levels and high saturated fat intakes. They are also abnormal in patients with diabetes and hypertension. The effects of these EFAs and their metabolites include lowering of triglycerides, elevation of high-density lipoprotein (HDL)-cholesterol, reduction of blood pressure, vasodilatation, reduction of fibrinogen levels and inhibition of platelet aggregation and of cardiac arrhythmias. Prospective studies have shown that abnormal levels of these fatty acids are predictive of future coronary death. Controlled trials of treatment have demonstrated that provision of the fatty acids reduces both coronary and total mortality. Further experimental and clinical investigations of the roles of appropriate membrane concentrations of these fatty acids are justified.

Arachidonic acid inhibits hCG-stimulated progesterone production by corpora lutea of primates: potential mechanism of action

Arachidonic acid (AA) is a precursor of metabolites known to affect the corpus luteum (CL) in many species, including primates. We have shown that some of these products (prostaglandins F2 alpha and E2) inhibit pro-gesterone (P4) production and activate the phosphatidylinositol (PI) pathway in CL of rhesus monkeys. A direct role of AA in luteal function has also been suggested. The current experiments were designed to investigate the effect of AA on P4 synthesis and to examine the ability of AA to activate the PI pathway in CL of rhesus monkeys. Basal and hCG-stimulated P4 production by luteal cells collected during the midluteal phase was measured after treatment with AA (1, 5, and 10 microM) or linoleic acid (1, 5, and 10 microM). Dispersed cells (50,000/tube) were incubated at 37 degrees C for 2 h. AA elicited a dose-dependent decrease in hCG-stimulated, but not in basal, P4 production. hCG-stimulated P4 production was reduced (P < 0.01) at AA doses of 5 microM (12.1 +/- 1.5 ng/mL) and 10 microM (8.6 +/- 1.8 mg/mL) to hCG alone (18 +/- 1.6 ng/mL). There was no significant effect of 1 microM AA (15.2 +/- 1.6). Response to linoleic acid was dissimilar and was not dose-dependent. Viability of cells was not affected by any treatment. Indomethacin, a prostaglandin synthesis inhibitor, and nordihydroguaiaretic acid, an inhibitor of lipoxygenase, did not interfere with the inhibitory effect of AA. Activation of the PI pathway was assessed by monitoring the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PIP2) to inositol phosphates and by monitoring increases in intracellular free calcium concentrations ([Ca2+]i) in individual cells. Moreover, the ability of AA to activate protein kinase C (PKC) in luteal cells was measured using a [3H]phorbol dibutyrate (PDBu) binding assay. AA did not alter PIP2 hydrolysis or [Ca2+]i, however, AA (10 microM) increased specific binding of [3H]PDBu to luteal cells (P < 0.05). We conclude that AA inhibits hCG-stimulated P4 production by primate luteal cells. AA exerts this action without being converted to prostaglandins or leukotrienes. This inhibition may be mediated through the activation of PKC. These results suggest a possible role for AA in the regulation of luteal function in primates, and that PKC-activation by AA may promote its effects.

Unsaturated fatty acids synergistically enhance glucocorticoid-induced gene expression

Regulation by unsaturated fatty acids of glucocorticoid-sensitive gene transcription was studied in HeLa cells transiently transfected with a mouse mammary tumour virus-luciferase reporter gene. Arachidonic acid and docosahexaenoic acid by themselves had no effect on basal levels of luciferase expression. However, they were able to enhance dexamethasone-induced transcription by 1.4-2.3 times (25-42 times the control levels) in a dose-dependent manner (ED50: 18 and 8 microM) for arachidonic and docosahexaenoic acid, respectively. The glucocorticoid antagonist RU486 effectively antagonized the dexamethasone response as well as the synergistic effect observed in the presence of arachidonic and docosahexaenoic acids, suggesting that the glucocorticoid receptor was an intermediate in the fatty acid synergism of the dexamethasone response. These studies show that fatty acids may be playing a role in modulating the intracellular steroid hormone signalling pathway to co-regulate a glucocorticoid-sensitive promoter.

1,25-Dihydroxyvitamin D3 or dexamethasone modulate arachidonic acid uptake and distribution into glycerophospholipids by normal adult human osteoblast-like cells

The effects of treatment with the osteotropic steroids 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), 17 beta-estradiol, or dexamethasone on [1-14C]arachidonic acid (AA) uptake and distribution into glycerophospholipid classes by normal adult human osteoblast-like (hOB) cells were investigated. Total uptake of [1-14C]AA was decreased in cells treated with dexamethasone when assayed after a 24-, 48-, or 96-h exposure to the hormone. Specific radiolabel incorporation into phosphatidylcholine was reduced by a 48-h treatment with dexamethasone with a concurrent increase in the radiolabeling of phosphatidylethanolamine. However, these changes were transient, and by 96 h of dexamethasone treatment the distribution of the radiolabeled fatty acid had reequilibrated to resemble the pattern found for vehicle treated samples. Total uptake of [1-14C]AA was diminished by 96-h treatment with 1,25(OH)2D3 (79 +/- 3% of control, P < 0.01); at that time point, a significant decrease in the proportional radiolabeling of the phosphatidylinositol pool was identified (92 +/- 2% of control, P < 0.05). The 1,25(OH)2D3-dependent decrease in total uptake and in phosphatidylinositol incorporation of [1-14C]AA were found to be hormone dose dependent. Treatment with 24,25(OH)2D3 was without effect on either total [1-14C]AA uptake or the specific [1-14C]AA radiolabeling of the phosphatidylinositol pool. 1,25(OH)2D3 treatment decreased hOB cell uptake of [1-14C]oleic acid and decreased its proportional incorporation into the phosphatidylinositol pool. Gas chromatographic analyses revealed no 1,25(OH)2D3-dependent effects on total phosphatidylinositol lipid mass or on the mole percent of arachidonic acid within the phosphatidylinositol pool, leaving the mechanism of the effects of the secosteroid on hOB cell AA metabolism unexplained. 17 beta-Estradiol had no effects on the parameters of AA metabolism measured. As a consequence of their modulation of arachidonic acid uptake and its distribution into hOB cellular phospholipids, steroids might alter the biological effects of other hormones whose actions include the stimulated production of bioactive AA metabolites, such as prostaglandins or the various lipoxygenase products.

Arachidonic acid and free fatty acids as second messengers and the role of protein kinase C

In addition to serving as the precursor to a plethora of eicosanoids and other bioactive molecules, arachidonate may function as a bona fide second messenger. A number of studies have documented the ability of arachidonate to regulate the function of multiple targets in vitro systems. This has been particularly well established and studied with the activation of protein kinase C by arachidonate in a mechanism distinct from activation by diacylglycerol. In cells, arachidonate induces a number of activities, many of which may be independent of further metabolism to eicosanoids; suggesting possible direct action of arachidonate. This review summarizes the current state of knowledge on the possible second messenger function of arachidonate with specific emphasis on the regulation of protein kinase C.

Fatty acids: ancestral ligands and modern co-regulators of the steroid hormone receptor cell signalling pathway

Long chain fatty acids derived from endogenous metabolism and/or nutrition are regulators of cell signalling pathways. They can be lipid second messengers of signal transduction systems or modulators and regulators of intracellular signalling pathways such as those involved in the mechanism of action of steroid hormones. Fatty acids have been shown to activate gene transcription under the control of some evolutionarily primitive members of the steroid/thyroid superfamily of receptors. They may represent ancestral ligands of this superfamily of receptors. Fatty acids are also known to regulate the activity of protein kinases, particularly protein kinase C, and thereby phosphorylation of intracellular proteins involved in regulation of gene transcription. Fatty acids may be co-regulators in the cross-talk between membrane-triggered signal transduction and the intracellular steroid hormone signalling pathway. Fatty acids are known to affect either negatively and/or positively the binding of steroid hormones to their specific plasma transport proteins and their specific intracellular receptors and, very recently, fatty acids have also been shown to co-regulate glucocorticoid-dependent gene expression. The mechanism of action of steroid hormones will be used as an illustration of how fatty acids can intervene at different levels of cellular organization to regulate biological activity, with a focus on the glucocorticoid receptor.

Fatty acids in cell signalling: modulation by lipid binding proteins

Long-chain fatty acids and several of their metabolites have now been shown to be involved as primary or secondary messengers in specific cell signalling pathways. In view of their extremely low aqueous solubility, the extracellular as well as intracellular transport of these compounds is assumed to be facilitated by specific lipid binding proteins, such as cytoplasmic fatty acid-binding protein (FABP). In this paper a survey is given on the biological significance and possible modulatory action of intracellular lipid binding proteins for fatty acid-mediated signal transduction pathways.

Characterization of platelet-activating factor binding to human airway epithelial cells: modulation by fatty acids and ion-channel blockers

Radioligand-binding studies were performed in primary cultured human airway epithelial cells with [3H]PAF to determine whether these cells express platelet-activating factor (PAF) receptors. Scatchard analysis of PAF binding data revealed a single class of PAF binding sites with Kd 1.8 +/- 0.2 nM and Bmax. 21.0 +/- 2.1 fmol/10(6) cells (13,000 receptors/cell). PAF binding increased the intracellular free Ca2+ concentration ([Ca2+]i), indicating functional PAF receptors. Palmitate (C16:0), linoleic acid (C18:2 omega 6) or eicosapentaenoic acid (C20:5 omega 3) was incubated with the cells to test the effect on PAF binding. Incorporation of each fatty acid into cellular phospholipid occurred. [3H]PAF (1 nM) binding decreased in cells supplemented with C20:5 omega 3, but increased in the cells supplemented with C16:0. Scatchard analysis revealed that the inhibition of PAF binding by supplementation with C20:5 omega 3 was due to a decrease in both affinity and number of PAF receptors. PAF-stimulated increase in [Ca2+]i was also decreased by 60% in cells supplemented with C20:5 omega 3. Verapamil, a Ca(2+)-channel blocker, and amiloride, a Na(+)-channel blocker, inhibited specific binding of [3H]PAF to the cells, with IC50 4-5 microM and 0.2 mM respectively. Diphenylamine-2-carboxylate (DPC), a Cl(-)-channel blocker, dramatically increased PAF binding to the cell in a dose-dependent manner. Scatchard analysis revealed that verapamil and amiloride decreased both binding affinity and number of PAF receptors, whereas DPC increased PAF binding sites without affecting binding affinity. These results demonstrate that human airway epithelial cells have a functional receptor for PAF and that PAF receptor binding can be modulated by exogenous fatty acids and by ion-channel blockers.

Differential cytotoxic effects of gamma-linolenic acid on MG-63 and HeLa cells

Gamma-linolenic acid (GLA) inhibited cell proliferation in MG-63 and HeLa cells. Different morphological lesions were present in dividing cells; abnormal spindle formation in MG-63 cells and chromosome hypercondensation in HeLa cells. Different types of cell death were also present in interphase cells, no apoptosis but only 6% pycnosis in MG-63 cells and 90% apoptosis in HeLa cells. In MG-63 cells immunofluorescence showed segregation of nucleoli components, abnormal spindle formation and decreased labelling of microtubuli during interphase. In HeLa interphase cells prominently labelled abnormally arranged microtubuli were observed. The effects of GLA on protein synthesis in synchronized cells were determined with [35S]-methionine incorporation and SDS-PAGE. Decreased protein synthesis in both G1- and S-phase MG-63 cells was present. In S-phase HeLa cells, proteins of approximately 40, 92 and 150 kD were markedly expressed. Signalling mechanisms involved in cell proliferation and cell death may be differently affected in MG-63 and HeLa cells.