Cellular uptake of long-chain fatty acids: role of membrane-associated fatty-acid-binding/transport proteins

The critical importance of long-chain fatty acids in cellular homeostasis demands an efficient uptake system for these fatty acids and their metabolism in tissues. Increasing evidence suggests that the plasma-membrane-associated and cytoplasmic fatty-acid-binding proteins are involved in cellular fatty acid uptake, transport and metabolism in tissues. These binding proteins may also function in the fine tuning of cellular events by modulating the metabolism of long-chain fatty acids implicated in the regulation of cell growth and various cellular functions. Several membrane-associated fatty-acid-binding/transport proteins such as plasma membrane fatty-acid-binding protein (FABPpm, 43 kDa), fatty acid translocase (FAT, 88 kDa) and fatty acid transporter protein (FATP, 63 kDa) have been identified. In the feto-placental unit, preferential transport of maternal plasma arachidonic and docosahexaenoic acids across the placenta is of critical importance for fetal growth and development. Our studies have shown that arachidonic and docosahexaenoic acids are preferentially taken up by placental trophoblasts for fetal transport. The existence of a fatty-acid-transport system comprising multiple membrane-binding proteins (FAT, FATP and FABPpm) in human placenta may be essential to facilitate the preferential transport of maternal plasma fatty acids in order to meet the requirements of the growing fetus. The preferential uptake of arachidonic and docosahexaenoic acids by the human placenta has the net effect of shunting these maternal plasma fatty acids towards the fetus. The roles of plasma membrane-associated binding/transport proteins (FABPpm, FAT and FATP) in tissue-specific fatty acid uptake and metabolism are discussed.     

Chemie und Stoffwechsel der Polyenfettsäuren

Summary The chemical structure of the polyenoic fatty acids occuring in organ phosphatides and in fish oils is reviewed. The double bonds of all these polyenoic acids are arranged in divinylmethane pattern. Except some of the C₁₆-polyenoic acids of fish oils, these polyenoic acids belong either to the oleic, linoleic or linolenic acid type and have chain lengths C₁₈, C₂₀, and C₂₂. Polyenoic acids of the oleic acid type are present only in small amounts in phosphatides of mammalian origin. Fish oils are lacking in these but predominantly contain polyenoic acids of the linolenic acid type.Metabolic studies have shown that polyenoic acids of linoleic acid type (e.g. arachidonic acid) originate from linoleic acid and those of the linolenic acid type (e.g. C₂₀-pentaenoic and C₂₂-hexaenoic acid) from linolenic acid-both supplemented exogenous-by extension of the carbon chain by acetate on the side of the carboxylic acid group and introduction of additional double bonds in the divinylmethane pattern directed toward the carboxylic acid group. There is some evidence, however, that a total synthesis of the polyenoic acids of the oleic acid type occurs in the animal body.The transformation of linolenic to C₂₂-hexaenoic acid and some intermediate reactans have been investigated more precisely by means of the tracer method. As far as the biosynthesis of the polyenoic fatty acids is concerned there are no fundamental differences in different vertebrates.

---

---

Nach einem Vortrag auf der gemeinsamen Tagung der deutschen, französischen und schweizerischen Biochemiker in Zürich vom 10.–12. Oktober 1960.     

Intracellular localization of alpha-fetoprotein and serum albumin in the central nervous system of the rat during fetal and postnatal development]

The morphological localisation of alphafetoprotein (AFP), serumalbumin (SA), transferrin and immunoglobulins (IgG) has been studied in the developing central nervous system of the Rat by immunocytochemical methods. Evidence is presented of a highly selective staining for AFP and SA, both proteins exhibiting the same topographical distribution. Practically all the areas of the brain and the spinal cord are stained at a given moment of the developmental process. The labeling is cytoplasmic and in the neuronal elements extends to their axonic and dendritic prolongations. The localization of AFP and SA in the nervous system may be related to the well known binding properties of these proteins for varied substances (estrogen and/or fatty acids). The morphological data presented here suggest that both proteins may be actively involved in the uptake of such substances by the cellular structures of the nervous tissue.     

Antiproliferative effect of polyunsaturated fatty acids and interleukin-2 on normal and abnormal human lymphocytes

The polyunsaturated fatty acids (PUFAs), linoleic acid (LA), alpha linolenic acid (ALA), gamma linolenic acid (GLA), arachidonic acid (AA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), showed inhibition of growth of both normal and abnormal (Molt-4) human lymphocytes, and inhibition was concentration-dependent. Interestingly, the production of the lymphokine Interleukin-2 (IL-2) was elevated in Molt-4 cells, but it was reduced in the normal human lymphocytes. Addition of GLA or IL-2 or a combination of both showed enhancement of SO ₂ ^– and of lipid peroxidation levels, which were significantly higher in Molt-4 cells than in the normal lymphocytes. Reduction of protein concentration was also observed in both types of cells during this treatment. The data showed that the antiproliferative effects of GLA and IL-2 may partly be exerted through the elevated production of superoxide free radicals and peroxidatin products. This is a novel finding and therefore, further exploitation of combinations of PUFAs and IL-2 may be a possible way of combating cancer cell growth.     

Über die Fettsäuren aus Spinatchloroplasten

Summary The fatty acids of two samples of chloroplasts fromSpinacia oleracea have been investigated quantitatively. They contain many polyenoic fatty acids (more than 70% of the total fatty acids); amongst these, a relatively high content of C¹⁶-trienoic acid is remarkable. Moreover, the presence of the ³-trans-hexadecenoic acid, recently detected in plants, is noteworthy.     

Factors controlling the chain length of fatty acids synthesized by the intestinal mucosa of guinea-pig

Conclusion It has been shown that alteration in the pattern of fatty acids synthesized is not confined to extracts of mammary gland, but can be achieved with extracts of guinea-pig intestinal mucosa. With all these tissues, the proportion of long chain fatty acids synthesized increased with increasing rate of synthesis. The results presented support the suggestion that the chain length of the synthesized fatty acids is, at least in part, controlled by the concentration of malonyl-CoA available to the fatty acid synthetase. The mechanism of this control is now being investigated.

---

Résumé Nous avons montré que la longueur de la chaÎne des acides gras synthétisés par les extraits solubles de la muqueuse intestinale du cobaye peut Être modifiée. Cette longueur dépend, au moins en partie, de la concentration du malonyl-CoA.

     

Der Einfluss der experimentellen Leberschädigung auf Gesamtfett und ungesättigte Fettsäuren in Serum und Leber

Summary In experiments on rats with CCl₄-induced liver damage the total lipids and the di- to tetra-enoic fatty acids were estimated. The acute experiment of 72 h duration showed a strong augmentation of total lipids and a transitory diminution of arachidonic acid in serum and liver which two months after the intoxication still persisted together with a marked rise in linolenic acid. The parallelism of changes of saturation of the fatty acids in serum and liver being statistically significant indicates that the process of desaturation is most probably localized in the liver itself.     

Effect of maternal under-nutrition on pup body weight and hypothalamic endocannabinoid levels

Dietary long-chain polyunsaturated fatty acids are known to influence brain levels of the endocannabinoid anandamide in newborn pigs and mice. Furthermore, endocannabinoids were shown to control pup suckling and body weight in mice, and food intake in adult rodents. Here we determined the effect of maternal under-nutrition during gestation, lactation, or both, on body weight, and on the levels of endocannabinoids and expression of cannabinoid CB₁ receptors and fatty acid amide hydrolase in the hypothalamus of rat pups at weaning (21 days old) or adult rats (4 months old). Maternal under-nutrition resulted in a striking decrease in body weight of weaning rats, paralleled by a decrease in the hypothalamic levels of the endocannabinoid anandamide, but not of 2-arachidonoylglycerol. No significant change in the hypothalamic expression of either cannabinoid CB₁ receptors or fatty acid amide hydrolase mRNA was detected in any of the three groups of weaned pups. The decrease in pup body weight and hypothalamic anandamide levels was not observable in 4-month-old rats from any of the three groups. These data suggest that maternal under-nutrition causes a decrease in hypothalamic anandamide levels and loss of body weight, and confirm a crucial role for endocannabinoid signalling in neonatal development. Received 4 November 2002; received after revision 29 November 2002; accepted 16 December 2002 RID="*" ID="*"Corresponding author.     

Inhibition of high affinity uptake of GABA by branched fatty acids

Summary Several branched fatty acids including an antiepileptic agent nDPA were tested as potential inhibitors of high affinity uptake of GABA by brain slices and synaptosomes. Only three compounds (2-butyl-3-propylhexanoic acid, 5-propyloctanoic acid, 2-propylpenten-2-oic acid) were found to be relatively weak inhibitors of the uptake system. There was no correlation between anticonvulsant properties of the branched fatty acids and their potencies as inhibitors of high affinity uptake of GABA.     

The egg-lipid composition of the ‘living fossil’ reptile tuatara (Sphenodon punctatus)

Summary The lipid composition of two tuatara eggs was examined. The eggs contained triacylglycerol (80%) and phospholipid (12%) as their major lipid fractions. Fatty acid analyses of the individual lipid classes indicated the presence of essential fatty acids, linoleic and arachidonic acids. The quantity of such acids in the egg yolk lipids would suggest they are factors for survival as illustrated in other species.     

Enzymatic reduction of fatty acids and acyl-CoAs to long chain aldehydes and alcohols

Summary The properties of enzymatic systems involved in the synthesis of long chain aldehydes and alcohols have been reviewed. Fatty acid and acyl-CoA reductases are widely distributed and generate fatty alcohols for ether lipid and was ester synthesis as well as fatty aldehydes for bacterial bioluminescence. Fatty alcohol is generally the major product of fatty acid reduction in crude or membrane systems, although reductases which release fatty aldehydes as products have also been purified. The reduction of fatty acid proceeds through the ATP-dependent formation of acyl intermediates such as acyl-CoA and acyl protein, followed by reduction to aldehyde and alcohol with NAD(P)H. In most cases, both the rate of fatty acid conversion and acyl chain specificity of the reaction are determined at the level of reduction of the intermediate. The reduction of fatty acids represents the major pathway for the control of the synthesis of fatty aldehydes and alcohols. Several other enzymatic reactions involved in lipid degradation also release fatty aldehydes but do not apear to play an important role in long chain alcohol synthesis.     

Enzymatic reduction of fatty acids and acyl-CoAs to long chain aldehydes and alcohols

The properties of enzymatic systems involved in the synthesis of long chain aldehydes and alcohols have been reviewed. Fatty acid and acyl-CoA reductases are widely distributed and generate fatty alcohols for ether lipid and wax ester synthesis as well as fatty aldehydes for bacterial bioluminescence. Fatty alcohol is generally the major product of fatty acid reduction in crude or membrane systems, although reductases which release fatty aldehydes as products have also been purified. The reduction of fatty acid proceeds through the ATP-dependent formation of acyl intermediates such as acyl-CoA and acyl protein, followed by reduction to aldehyde and alcohol with NAD(P)H. In most cases, both the rate of fatty acid conversion and acyl chain specificity of the reaction are determined at the level of reduction of the intermediate. The reduction of fatty acids represents the major pathway for the control of the synthesis of fatty aldehydes and alcohols. Several other enzymatic reactions involved in lipid degradation also release fatty aldehydes but do not appear to play an important role in long chain alcohol synthesis.     

Cholesterol esterification activities in the intestines and pancreas of the albino rat

Summary Cholesterol esterification activities in intestines and pancreas are much greater with unsaturated fatty acids than with the saturated ones; the maximum activity is with arachidonic acid in intestines and with oleic acid in pancreas. The pancreatic cholesterol esterification activity is higher than the intestinal one.     

The presence of free D-amino acids in mouse tissues

The presence of free D-amino acids in mouse kidney, liver, brain, heart, lung, thymus and serum has been shown with an enzymic microdetermination method. The D-amino acid levels were higher in the extracts of kidney and liver than in those from other organs.     

The presence of free D-amino acids in mouse tissues

Summary The presence of free D-amino acids in mouse kidney, liver, brain, heart, lung, thymus and serum has been shown with an enzymic microdetermination method. The D-amino acid levels were higher in the extracts of kidney and liver than in those from other organs.     

Lipoxygenase - a versatile biocatalyst for biotransformation of endobiotics and xenobiotics

Lipoxygenase, a member of the arachidonate cascade enzymes, dioxygenates polyenoic fatty acids to finally yield products with profound and distinct biological activity. This review summarizes the available evidence for another role played by lipoxygenases in the metabolism of endobiotics and xenobiotics. Although other mechanisms exist, a direct hydrogen abstraction by the enzyme and the peroxyl radical-dependent chemical oxidation appear to be central to the co-oxidase activity of lipoxygenases. Besides polyunsaturated fatty acids, H2O2, fatty acid hydroperoxides, and synthetic organic hydroperoxides support the lipoxygenase-catalyzed xenobiotic oxidation. The major reactions documented thus far include oxidation, epoxidation, hydroxylation, sulfoxidation, desulfuration, dearylation, and N-dealkylation. It is noteworthy that lipoxygenases are also capable of glutathione conjugation of certain xenobiotics. The enzyme system appears to be inducible following exposure to chemicals. Lipoxygenases are inhibited by a large number of chemicals, some of which also serve as co-substrates. Available data suggest that lipoxygenases contribute to in vivo metabolism of xenobiotics in mammals.     

The effect of endotoxin on membrane fatty acid composition in BCG-sensitized mice

The effects of endotoxin on mouse liver phospholipid fatty acid composition have been investigated. Administration of endotoxin from Salmonella abortus equi led to a decrease in the polyunsaturated fatty acid content of livers from mice sensitized with Bacille Calmette Guérin (BCG). The content of arachidonic acid fell significantly in both the phosphatidylcholine and phosphatidylinositol fractions whereas in the phosphatidylethanolamine fraction the linoleic acid content was significantly reduced. The polyunsaturated fatty acids were replaced by increased amounts of oleic acid and palmitic acid, leading to a reduction in the polyunsaturated to saturated fatty acid ratio.     

Fatty acid profiles of major food sources of howler monkeys (Alouatta palliata) in the neotropics

Wild howler monkeys (Alouatta palliata) get most of their calories from carbohydrates (65%) and fats (18%) of native tropical plants, but little is known about their intake of individual fatty acids. The fatty acid composition of several natural food sources of howler monkeys collected in Panama was determined by gas-liquid chromatography. The predominant fatty acids were palmitic (30%), linoleic (23%), linoleic (23%), -linolenic (16%) and oleic (15%). Fatty acids with less than 16, and more than 18, carbon chains were uncommon (0–7%). Although total saturated fatty acids were high in some specific food sources (22–54% of total fatty acids and 8 energy %), most of the calories from fat in the animals' diets are derived from mono-and polyunsaturated fatty acids (9.75 energy %) All food sources had significant amounts of the -3 fatty acid, -linolenic acid (2.9 energy %). In terms of human diets, the howler monkey's fat consumption would not be considered atherogenic. Unless these animals show a particular adverse susceptibility to dietary fat, it is unlikely that their fat intake is the primary cause of the low, but significant, incidence of atherosclerosis that develops in these animals in the wild state.     

The effect of endotoxin on membrane fatty acid composition in BCG-sensitized mice

Summary The effects of endotoxin on mouse liver phospholipid fatty acid composition have been investigated. Administration of endotoxin fromSalmonella abortus equi led to a decrease in the polyunsaturated fatty acid content of livers from mice sensitized with Bacille Calmette Guérin (GCG). The content of arachidonic acid fell significantly in both the phosphatidylcholine and phosphatidylinositol fractions whereas in the phosphatidylethanolamine fraction the linoleic acid content was significantly reduced. The polyunsaturated fatty acids were replaced by increased amounts of oleic acid and palmitic acid, leading to a reduction in the polyunsaturated to saturated fatty acid ratio.     

Pyruvate dehydrogenase kinase 4 expression is synergistically induced by AMP-activated protein kinase and fatty acids

Organs are flexible as to which substrates they will use to maintain energy homeostasis. Under well-fed conditions, glucose is a preferred substrate for oxidation. During fasting, fatty acid oxidation will become a more important energy source. Glucose oxidation is decreased by fatty acids, a process in which the pyruvate dehydrogenase complex (PDH) and its regulator pyruvate dehydrogenase kinase 4 (PDK4) play important roles. It is currently unknown how energy status influences PDH activity. We show that AMP-activated protein kinase (AMPK) activation by hypoxia and AICAR treatment combined with fatty acid administration synergistically induce PDK4 expression. We provide evidence that AMPK activation modulates ligand-dependent activation of peroxisome proliferator-activated receptor. Finally, we show that this synergistic induction of PDK4 decreases cellular glucose oxidation. In conclusion, AMPK and fatty acids play a direct role in fuel selection in response to cellular energy status in order to spare glucose. S. M. Houten, M. Chegary: These two authors contributed equally to this work. Received 11 July 2008; received after revision 26 January 2009; accepted 02 February 2009