Aerobic glycolysis of bone and cartilage: The possible involvement of fatty acid oxidation

The apparent paradox of aerobic glycolysis has been investigated in bone and in cartilage. A new cytochemical procedure for hydroxyacyl dehydrogenase (HOAD) activity showed that the maximal activity of this enzyme in both tissues was equivalent to the maximal activity of glyceraldehyde 3-phosphate dehydrogenase (GAPD). The sum of these activities gave a measure of the maximum amount of acetyl-coenzyme A that could be produced. In these tissues, but not in liver which does not exhibit aerobic glycolysis, this summed value exceeded the maximal activity of succinate dehydrogenase (SDH). Consequently, it suggested that where fatty acid oxidation is sufficient to supply all the acetyl-coenzyme A required for the Krebs' cycle, that derived from fatty acid oxidation may inhibit pyruvate dehydrogenase causing accumulation of pyruvate which must be converted to lactate if pentose-shunt activity is to be maintained.     

PDK4 dictates metabolic resistance to ferroptosis by suppressing pyruvate oxidation and fatty acid synthesis

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Fatty acid-binding protein and its relation to fatty acid oxidation

A relation between fatty acid oxidation capacity and cytosolic FABP content was found in heart and various muscles of the rat. Other tissues do not show such a relation, since they are involved in more or other pathways of fatty acid metabolism. At postnatal development FABP content and fatty acid oxidation capacity rise concomitantly in heart and quadriceps muscle in contrast to in liver and kidney. A dietary fat content of 40 en. % increased only the FABP content of liver and adipose tissue. Peroxisomal proliferators increased fatty acid oxidation in both liver and kidney, but only the FABP content of liver, and had no effect on heart and skeletal muscle. The FABP content of muscle did not show adaptation to various conditions. Only it increased in fast-twitch muscles upon chronic electrostimulation and endurance training.     

Fatty acid biosynthesis from glutamate and glutamine is specifically induced in neuronal cells under hypoxia

Hypoxia is involved in many neuronal and non‐neuronal diseases, and defining the mechanisms for tissue adaptation to hypoxia is critical for the understanding and treatment of these diseases. One mechanism for tissue adaptation to hypoxia is increased glutamine and/or glutamate (Gln/Glu) utilization. To address this mechanism, we determined incorporation of Gln/Glu and other lipogenic substrates into lipids and fatty acids in both primary neurons and a neuronal cell line under normoxic and hypoxic conditions and compared this to non‐neuronal primary cells and non‐neuronal cell lines. Incorporation of Gln/Glu into total lipids was dramatically and specifically increased under hypoxia in neuronal cells including both primary (2.0‐ and 3.0‐fold for Gln and Glu, respectively) and immortalized cultures (3.5‐ and 8.0‐fold for Gln and Glu, respectively), and 90% to 97% of this increase was accounted for by incorporation into fatty acids (FA) depending upon substrate and cell type. All other non‐neuronal cells tested demonstrated decreased or unchanged FA synthesis from Gln/Glu under hypoxia. Consistent with these data, total FA mass was also increased in neuronal cells under hypoxia that was mainly accounted for by the increase in saturated and monounsaturated FA with carbon length from 14 to 24. Incorporation of FA synthesized from Gln/Glu was increased in all major lipid classes including cholesteryl esters, triacylglycerols, diacylglycerols, free FA, and phospholipids, with the highest rate of incorporation into triacylglycerols. These results indicate that increased FA biosynthesis from Gln/Glu followed by esterification may be a neuronal specific pathway for adaptation to hypoxia.

     

The metabolic switch and its regulation in cancer cells

The primary features of cancer are maintained via intrinsically modified metabolic activity, which is characterized by enhanced nutrient supply, energy production, and biosynthetic activity to synthesize a variety of macromolecular components during each passage through the cell cycle. This metabolic shift in transformed cells, as compared with non-proliferating cells, involves aberrant activation of aerobic glycolysis, de novo lipid biosynthesis and glutamine-dependent anaplerosis to fuel robust cell growth and proliferation. Here, we discuss the unique metabolic characteristics of cancer, the constitutive regulation of metabolism through a variety of signal transduction pathways and/or enzymes involved in metabolic reprogramming in cancer cells, and their implications in cancer diagnosis and therapy.     

Maturation of fatty acid and carbohydrate metabolism in the newborn heart

During fetal life, myocardial ATP is derived predominantly from glycolysis and lactate oxidation. Following birth, a rapid maturational increase in fatty acid oxidation occurs along with a decline in glycolytic and lactate oxidative rates, thus changing the major source of myocardial ATP production. This shift in energy substrate preference occurs in response to changes in the circulating substrate content of newborn plasma with the onset of suckling, and is also due to alterations in circulating levels of hormones, such as insulin and glucagon. Important changes in subcellular regulatory mechanisms of both fatty acid and carbohydrate metabolism in the heart also characterize this response. This review deals with recent advances in the understanding of these subcellular mechanisms which regulate this important shift in myocardial energy metabolism, with particular emphasis on the molecular events occurring in the heart during the transition from fetal to newborn life.     

病毒感染影响宿主细胞代谢研究进展

作为专性的细胞内寄生物,病毒没有独立代谢的能力,因此完全依赖于宿主细胞的代谢机制。病毒利用宿主细胞代谢网络提供的能量和生物合成前体物质来驱动其复制、装配和释放。因此,病毒挟持宿主细胞代谢以实现自身的复制和增殖。此外,病毒还可以通过编码辅助代谢基因(auxiliary metabolic genes,AMGs)调控宿主的细胞代谢,影响碳、氮、磷、硫循环,参与微生物驱动的生物地球化学循环。本文主要从细胞葡萄糖代谢、谷氨酰胺代谢、脂肪酸代谢、病毒AMGs调控宿主代谢影响生物地球化学循环4个方面总结病毒感染对宿主核心代谢途径影响的研究,以期为深入理解病毒-宿主相互作用提供参考,也将为通过代谢干预治疗病毒性疾病提供一定的理论依据。     

Diltiazem inhibits fatty acid oxidation in the isolated perfused rat liver

The effects of diltiazem on fatty acid metabolism were measured in the isolated perfused rat liver and in isolated mitochondria. In the perfused rat liver diltiazem inhibited oxygen uptake and ketogenesis from endogenous substrates. Ketogenesis from exogenously supplied palmitate was also inhibited. The β-hydroxybutyrate/acetoacetate ratio in the presence of palmitate alone was equal to 3·2. When the fatty acid and diltiazem were present simultaneously this ratio was decreased to 0·93, suggesting that, in spite of the inhibition of oxygen uptake, the respiratory chain was not rate limiting for the oxidation of the reducing equivalents coming from β-oxidation. In experiments with isolated mitochondria, incubated in the presence of all intermediates of the Krebs cycle, pyruvate or glutamate, no significant inhibition of oxygen uptake by diltiazem was detected. Inhibition of oxygen uptake in isolated mitochondria was found only when palmitoyl CoA was the source of the reducing equivalents. It was concluded that a direct effect on β-oxidation may be a major cause for the inhibition of oxygen uptake caused by diltiazem in the perfused liver. © 1997 John Wiley & Sons, Ltd.     

Alterations in fatty acid oxidation in ischemic and reperfused myocardium

Summary The focus of this review centered on describing the effects of excess fatty acids on myocardial recovery during reperfusion following ischemic stress. Effects on mechanical function were modest in our studies and are likely to remain difficult/impossible to measure due to the independent phenomenon of stunning which obfuscates and no doubt dominates the influences of other mechanical determinants. Mitochondria appear capable of again using long-chain fatty acids as a preferred substrate and in the presence of restored oxygen delivery can produce normal levels of CO₂. These changes in oxidative metabolism are not mirrored by equal recoveries in mitochondrial energetics. Because of inefficiencies in electron transport and oxidative phosphorylation together with moderate uncoupling of electron transport from oxidative phosphorylation, ATP resynthesis is blunted. This explains in part the absolute decrease in contents of exchangeable nucleotides noted both in cytosol and mitochondria. Further impairments in recovery reside in the inability of the mitochondria to exchange adenine nucleotides into cytosol through the adenine nucleotide translocase antiport. These findings contribute to our understanding of mechanical stunning and may be of value in designing future strategies to optimize the handling of substrates during myocardial reperfusion.Visiting scientist from the Shang Hai Second Medical University, Peoples Republic of China.     

Fatty acid oxidation capacity and fatty acid-binding protein content of different cell types isolated from rat heart

Summary Heart tissue contains appreciable amounts of fatty acid-binding protein (FABP). FABP is thought to play a crucial role in the transport of fatty acids from the cellular membrane to the intracellular site of oxidation and also, in case of endothelial cells, in the transfer of fatty acids from the vascular to the interstitial compartment through the endothelial cytoplasm. The present study was designed to delineate a possible quantitative relationship between the capacity of different cell types in the heart to oxidize fatty acids and the presence of FABP. Palmitate oxidation capacity, measured in homogenates of cells isolated from adult rat hearts, was 2 nmol/min per mg tissue protein in freshly isolated cardiomyocytes (CMC), but only 0.09 and 0.31 nmol/min per mg tissue protein in cultivated endothelial (CEC) and fibroblast-like cells (CFLC), respectively. Palmitate oxidation rates were closely related to the cytochrome C oxidase activity and, hence, to the mitochondrial density in the cells under investigation. In CMC the content of cytosolic H-FABP (H-FABP_c) was about 4.51 µg/mg tissue protein. However, in CEC and CFLC the FABP content was less than 0.01 and 0.004 µg/mg tissue protein, respectively, corresponding to at maximum 0.2% of the FABP content of CMC. These findings indicate a marked difference between CMC and non-myocytal cells in the heart regarding their capacity to oxidize fatty acids, and a marked disproportion between the fatty acid oxidation capacity and immunochemically determined FABP content in both CEC and CFLC. The functional implication of these observations remains to be elucidated.     

Fatty acid metabolism in human breast cancer cells (MCF7) transfected with heart-type fatty acid binding protein

The human breast cancer cell line MCF7 does not express heart-type fatty acid binding protein (H-FABP), a marker protein for differentiated mammary gland. MCF7 cells transfected with the bovine H-FABP cDNA expressed the corresponding protein and were characterized by growth inhibition and lower tumorgenicity in nude mice [22]. By enzyme linked immunoassay we now determined the amount of bovine H-FABP in these cells as 638 ± 80 ng/mg protein and used the transfected cells to study the role of H-FABP in fatty acid metabolism. Compared to control cells the uptake of radioactively labelled palmitic acid and oleic acid into MCF7 cells after 30 or 60 min was increased by 67% in H-FABP expressing transfectants, demonstrating a stimulatory role for this FABP-type in fatty acid metabolism. However, preferential targeting of [¹⁴C]oleic acid into neutral or phospholipid classes was not observed by the criterion of high performance thin layer chromatography followed by autoradiography. A reason for the modest increase of fatty acid uptake in H-FABP transfected MCF7 cells may be the basal expression of epidermal-type FABP, which was detected for the first time in these cells. It appears that the small amount of E-FABP expressed in MCF7 cells fulfils the need of the cells for a cytosolic fatty acid carrier under culture conditions and that even high concentrations of another FABP do only slightly increase the uptake due to limitations of fatty acid transport through the plasma membrane or of metabolism.     

Role of fatty acid-binding protein in cardiac fatty acid oxidation

Summary Although abundant in most biological tissues and chemically well characterized, the fatty acid-binding protein (FABP) was until recently in search of a function. Because of its strong affinity for long chain fatty acids and its cytoplasmic origin, this protein was repeatedly claimed in the literature to be the transcytoplasmic fatty acid carrier. However, techniques to visualize and quantify the movements of molecules in the cytoplasm are still in their infancy. Consequently the carrier function of FABP remains somewhat speculative. However, FABP binds not only fatty acids but also their CoA and carnitine derivatives, two typical molecules of mitochondrial origin. Moreover, it has been demonstrated and confirmed that FABP is not exclusively cytoplasmic, but also mitochondrial. A function for FABP in the mitochondrial metabolism of fatty acids plus CoA and carnitine derivatives would therefore be anticpated. Using spin-labelling techniques, we present here evidence that FABP is a powerful regulator of acylcarnitine flux entering the mitochondrial -oxidative system. In this perspective FABP appears to be an active link between the cytoplasm and the mitochondria, regulating the energy made available to the cell. This active participation of FABP is shown to be the consequence of its gradient-like distribution in the cardiac cell, and also of the coexistence of multispecies of this protein produced by self-aggregation.     

Glucose is essential for the initiation of fatty acid oxidation in ATP-depleted cultured ventricular myocytes

Cultured cardiac myocytes were depleted of ATP by incubation with oligomycin (1 mg/ml). Then the ability of the cells to oxidize various substrates and to restore ATP levels was studied. Following ATP depletion, the cells were found to be able to oxidize glucose given alone, but not palmitate. However, with both substrates, palmitate was oxidized in the presence of glucose and ATP recovery was enhanced. Pyruvate had a minor effect on palmitate oxidation, while acetate given alone was oxidized, but did not enhance cellular ATP content. These results show that glucose is essential for restoration of mitochondrial function and the coupling between oxidation and ATP synthesis.     

Altered fatty acid metabolism and composition in cultured astrocytes under hyperammonemic conditions

In vitro ¹H- and ¹³C-NMR spectroscopy was used to investigate the effect of ammonia on fatty acid synthesis and composition in cultured astrocytes. Cells were incubated 3 and 24 h with 5 mM ammonia in the presence or absence of the glutamine synthetase inhibitor methionine sulfoximine. An increase of de novo synthesized fatty acids and the glycerol subunit of lipids was observed after 3 h treatment with ammonia (35% and 40% over control, respectively), the initial time point examined. Both parameters further increased significantly to 85% and 60% over control after 24 h ammonia treatment. Three hours incubation with ammonia increased the synthesis of diacylglycerides, while formation of triacylglycerides was decreased (40% over and 15% under control, respectively). The degradation of fatty acids was not affected by ammonia treatment. Furthermore, ammonia caused alterations in the composition of fatty acids, e.g. increased mono- and decreased polyunsaturated fatty acids (85% over and 15% under control concentrations, respectively). The decrease of polyunsaturated fatty acids was even more pronounced in isolated astrocytic mitochondria (39% lower than controls). Our results suggest ammonia-induced abnormalities in astrocytic membranes, which may be related to astrocytic mitochondrial dysfunction in hyperammonemic states. Most of the observed effects of ammonia on fatty acid synthesis and composition were ameliorated when glutamine synthetase was inhibited by methionine sulfoximine, supporting a pathological role of glutamine in ammonia toxicity. This study further emphasizes the importance of investigating the relative contribution of exogenous ammonia, effects of glutamine and of glutamine-derived ammonia on astrocytes and astrocytic mitochondria.     

Identification of diarylsulfonamides as agonists of the free fatty acid receptor 4 (FFA4/GPR120)

The exploration of a diarylsulfonamide series of free fatty acid receptor 4 (FFA4/GPR120) agonists is described. This work led to the identification of selective FFA4 agonist 8 (GSK137647A) and selective FFA4 antagonist 39. The in vitro profile of compounds 8 and 39 is presented herein.     

Glyoxylate metabolism and fatty acid oxidation in mango fruit during development and ripening

Throughout the development (maturation) of mango fruit the contents of citric and glyoxylic acids increased steadily. As the fruit matured the levels of isocitrate lyase, malate lyase and alanine: glyoxylate aminotransferase increased and reached maximum values prior to the time of harvesting. At and after harvest the levels of malate lyase and alanine : glyoxylate aminotransferase began to decrease but that of isocitrate lyase remained high until after the harvest when it decreased. The level of glyoxylate reductase was highest in the early developmental stage but declined as the fruit matured and ripened. As the fruit ripened, after harvest, the amounts of citric and glyoxylic acids decreased concomitant with a considerable increase in the levels of isocitrate dehydrogenase, malic dehydrogenase, malic enzyme and glyoxylate dehydrogenase.Fatty acid oxidizing capacity of mitochondria isolated from immature (developing) and postclimacteric fruit pulps was much less than that observed with mitochondria from preclimacteric and climacteric fruit. Glyoxylate stimulated the oxidation of caprylic, lauric, myristic and palmitic acids and inhibited the activity of isocitrate dehydrogenase in vitro.     

Myocardial fatty acid oxidation during ischemia and reperfusion

Inhibition of fatty acid oxidation is an early event in myocardial ischemia that most likely contributes to tissue injury by the accumulation of potentially toxic intermediates such as acylCoA and acylcarnitine. After reperfusion both myocardial oxygen consumption and fatty acid oxidation may rapidly recover to preischemic levels, even when contractile function remains depressed. The mechanisms underlying the apparent dissociation between contractile function and oxidative metabolism early during reperfusion are still controversial. In isolated rat hearts subjected to 60 min of no-flow ischemia myocardial oxygen consumption and oxidation of palmitate were lowered during reperfusion by 3 mM of NiCl₂ and by 6 µM of ruthenium red. The results provide indirect evidence for the hypothesis that intracellular calcium transport may be involved in the mechanisms responsible for the high oxidative metabolic rate early after reperfusion