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Fatty acid metabolism in adipocytes: functional analysis of fatty acid transport proteins 1 and 4.

The role of fatty acid transport protein 1 (FATP1) and FATP4 in facilitating adipocyte fatty acid metabolism was investigated using stable FATP1 or FATP4 knockdown (kd) 3T3-L1 cell lines derived from retrovirus-delivered short hairpin RNA (shRNA). Decreased expression of FATP1 or FATP4 did not affect preadipocyte differentiation or the expression of FATP1 (in FATP4 kd), FATP4 (in FATP1 kd), fatty acid translocase, acyl-coenzyme A synthetase 1, and adipocyte fatty acid binding protein but did lead to increased levels of peroxisome proliferator-activated receptor gamma and CCAAT/enhancer binding protein alpha. Both FATP1 and FATP4 kd adipocytes exhibited reduced triacylglycerol deposition and corresponding reductions in diacylglycerol and monoacylglycerol levels compared with control cells. FATP1 kd adipocytes displayed an approximately 25% reduction in basal (3)H-labeled fatty acid uptake and a complete loss of insulin-stimulated (3)H-labeled fatty acid uptake compared with control adipocytes. In contrast, FATP4 kd adipocytes as well as HEK-293 cells overexpressing FATP4 did not display any changes in fatty acid influx. FATP4 kd cells exhibited increased basal lipolysis, whereas FATP1 kd cells exhibited no change in lipolytic capacity. Consistent with reduced triacylglycerol accumulation, FATP1 and FATP4 kd adipocytes exhibited enhanced 2-deoxyglucose uptake compared with control adipocytes. These findings define unique and distinct roles for FATP1 and FATP4 in adipose fatty acid metabolism.

3T3-L1 Cells↗

Zonation of fatty acid metabolism in rat liver.

Fatty acid metabolism was studied in periportal and perivenous hepatocytes isolated by the method of Chen & Katz [Biochem. J. (1988) 255, 99-104]. The rate of fatty acid synthesis and the activity of acetyl-CoA carboxylase were markedly enhanced in perivenous hepatocytes as compared with periportal cells. However, the response of these two parameters to short-term modulation by cellular effectors such as the hormones insulin and glucagon, the phorbol ester 4 beta-phorbol 12 beta-myristate 13 alpha-acetate and the xenobiotics ethanol and acetaldehyde was similar in the two zones of the liver. In addition, perivenous hepatocytes showed a higher capacity of esterification of exogenous fatty acids into both cellular and very-low-density-lipoprotein lipids. Nevertheless, no difference between the two cell sub-populations seemed to exist in relation to the secretion of very-low-density lipoproteins. On the other hand, the rate of fatty acid oxidation was increased in periportal cells. This could be accounted for by a higher activity of carnitine palmitoyltransferase I and a lower sensitivity of this enzyme to inhibition by malonyl-CoA in the periportal zone. No differences were observed between periportal and perivenous hepatocytes in relation to the short-term response of fatty acid oxidation and carnitine palmitoyltransferase I activity to the cellular modulators mentioned above. In conclusion, our results show that: (i) lipogenesis is achieved at higher rates in the perivenous zone of the liver, whereas the fatty-acid-oxidative process occurs with a certain preference in the periportal area of this organ; (ii) the short-term response of the different fatty-acid-metabolizing pathways to cellular effectors is quantitatively similar in the two zones of the liver.

Acetyl-CoA Carboxylase↗

Ventricular function and fatty acid metabolism in neonatal piglet heart.

Studies in which subcellular systems were used suggest that neonatal myocardium has a sharply limited capacity to metabolize fatty acids. The relationship of these findings to the intact heart was tested on piglets, 8 h to 12 days of age. Left ventricular (LV) performance, O2 consumption (MVO2), and fatty acid (FA) uptake and oxidation were measured. Hearts were perfused at 70 cmH2O pressure with buffer containing 2% bovine serum albumin, insulin (100 microU/ml), 5 mM glucose, and 1.5 mM lactate. 14C-labeled palmitate was added (net FA, 0.5 mM). Washed erythrocytes were used to assure adequate O2 delivery. LV end-diastolic pressure (EDP) was controlled with a fluid-filled balloon. FA oxidation was estimated by measuring 14CO2 production. Hearts less than 24 h (group I, n = 6), those approximately 3 days (group II, n = 5), and those 6-12 days of age (group III, n = 10) were compared. Measurements at a low EDP (2-4 cmH2O) and at a higher EDP (7-9 cmH2O) were compared. At the low EDP, rates of FA oxidation for groups I-III averaged 30.0 +/- 3.0, 31.4 +/- 2.9, and 50.2 +/- 2.6 nmol.min-1.g-1, respectively. These values increased to 43.8 +/- 3.7, 42.6 +/- 2.5, and 63.8 +/- 4.0 nmol.min-1.g-1, respectively, at the higher EDP level (P less than 0.01 for each group). Thus within a few hours of birth, pig hearts are able to oxidize long-chain FA, and the rate of oxidation is linked to mechanical function. However, both the oxidation rate and the percentage of MVO2 accounted for by FA oxidation are greater in older hearts.

Algorithms↗

Radionuclide assessment of myocardial fatty acid metabolism by PET and SPECT.

Although fatty acid is a major energy source in the normal myocardium, fatty acid oxidation is easily suppressed in a variety of cardiac disorders. Therefore assessment of fatty acid metabolism may hold an important role for early detection of myocardial abnormalities and provide insights into cardiac pathologic states. C-11 palmitate is a well-established PET tracer to probe myocardial fatty acid metabolism. On the other hand, a variety of iodinated fatty acid compounds have been introduced for assessment of fatty acid metabolism with conventional gamma cameras. These include straight-chain, such as iodopheyl pentadecanoic acid (IPPA), and branch-chain fatty acid compounds, such as beta-methyl iodopheyl pentadecanoic acid (BMIPP). This review article includes the characterization of these tracers and clinical experiences with these tracers for detection and characterizing patients with ischemic heart disease and cardiomyopathy.

Animals↗

Fatty acid metabolism in Paramecium. Oleic acid metabolism and inhibition of polyunsaturated fatty acid synthesis by triparanol.

Paramecium requires oleic acid for growth and can grow in media containing no other fatty acids. In the present study, we have shown that this ciliate utilized oleate mainly as a carbon and energy source, even though this fatty acid was the only substrate available for synthesis of polyunsaturated fatty acids. Culture growth was inhibited by the addition of the drug triparanol. Triparanol decreased the formation of polyunsaturated fatty acids from oleate by preventing desaturation to form the dienoic acid, linoleate. Triparanol inhibition resulted in an altered phospholipid fatty acyl composition, an increased fragility and an altered behavioral response of the cells to a depolarizing stimulation solution. Therefore, although most of the dietary oleate was not used by the cells for polyunsaturated fatty acid synthesis, the desaturation of oleic acid was critical for normal culture growth, cell integrity and swimming behavior, all of which are expected to be dependent on normal membrane lipid composition.

Animals↗

Alterations in fatty acid metabolism in adriamycin cardiomyopathy.

Myocardial fatty acid metabolism may be impaired in adriamycin cardiomyopathy. In order to determine the extent of fatty acid metabolism alterations, we measured steady state [14C]palmitate oxidation and the incorporation of [14C]palmitate into the neutral lipid pool in a rat model of adriamycin cardiomyopathy. Isolated hearts from control rats and rats treated with adriamycin were perfused with 1.2 mmol/l of [14C]palmitate for 30 min to achieve steady state oxidation measured as [14C]O2 production; then perfused with 1.2 nmol/l of unlabelled palmitate. Hearts were killed early (0-5 min) or late (10-30 min) after the [14C]palmitate perfusion, to determine incorporation into the neutral lipid pool, and neutral lipid utilization. In the control group steady state oxidation was reached in 10 min ([14C]O2 production = 580 +/- 61 nmol/min/g dry wt) of perfusion. In the adriamycin treated group, mean CO2 production was significantly reduced at 10 min (329 +/- 44 nmol/min/g dry wt, P < 0.01 v control). At 30 min, [14C]O2 production in the treated group was not significantly different than controls (521 +/- 65 nmol/min/g dry wt v 617 +/- 36 nmol/min/g dry wt, P = N.S.). The incorporation of [14C]palmitate into the neutral lipid pool measured in the early subgroup was significantly reduced for adriamycin treated hearts v controls (7.2 +/- 0.6 v 12.0 +/- 1.4 mumol/g dry wt respectively, P < 0.01). In the control group 14C labelled neutral lipid reduced with time to 8.4 +/- 1.1 mumol/g dry wt (P < 0.05) in the late group. The adriamycin group demonstrated no significant change between early and late measurements. In conclusion, in adriamycin cardiomyopathy: (1) there is significant delay in achieving steady state palmitate oxidation, although the steady state rate is near normal; (2) palmitate incorporation into the neutral lipid pool is reduced; (3) neutral lipid pool utilization may also be reduced. These data suggest impaired uptake of palmitate into the cell in adriamycin cardiomyopathy, with a relatively maintained capacity for oxidative metabolism.

Animals↗

Myocardial fatty acid metabolism during acute cardiac allograft rejection.

Fatty acids are promptly taken up, metabolised and eliminated by healthy cardiomyocytes. Cardiomyopathy, coronary heart disease and chronic rejection are known to be associated with an impaired fatty acid metabolism. It was the aim of this study to investigate fatty acid metabolism in a rat heart transplant model and to correlate scintigraphic findings with histological changes. After right-side nephrectomy of Lewis recipients Brown Norway cardiac allografts were anastomosed to the renal vessels. Animals were given no immunosuppression. The metabolism of carrier-free 17-123 jodo-heptadecanoic acid (123J-HDA) with a specific activity of > 2 x 10(17) Bq/ml was scintigraphically measured between days 1 and 11. An increase in the grade of rejection was observed over time. Fifty-six frames of 30 s duration each were recorded. For the region of interest (native heart, transplanted heart, left kidney) frames 10-56 were superimposed, time-activity curves generated and monoexponentially fitted. Furthermore, elimination half-life and intercepts were calculated. Following scintigraphic evaluation the animals were killed and graft as well as native hearts excised for histological examination. The uptake of the tracer identified severe grades of rejection. Elimination half-life of the tracer was twice as long from hearts with mild rejection and more than 14 times as long in severe rejection compared with no rejection. Elimination half-life and amplitude did not permit discrimination between grades 1, 2 and 3 a, but significantly decreased in groups 3 b and 4. This method therefore seems to be a valuable tool for the noninvasive detection of severe acute cardiac allograft rejection. Since fatty acid metabolism is clearly stress-dependent it remains to be seen whether this method allows detection of earlier rejection in loaded hearts.

Animals↗

Fatty acid metabolism in liver of rats treated with hypolipidemic sulphur-substituted fatty acid analogues.

The purpose of this study was to investigate early biochemical changes and possible mechanisms via which alkyl(C12)thioacetic acid (CMTTD, blocked for beta-oxidation), alkyl(C12)thiopropionic acid (CETTD, undergo one cycle of beta-oxidation) and a 3-thiadicarboxylic acid (BCMTD, blocked for both omega- (and beta-oxidation) influence the peroxisomal beta-oxidation in liver of rats. Treatment of rats with CMTTD caused a stimulation of the palmitoyl-CoA synthetase activity accompanied with increased concentration of hepatic acid-insoluble CoA. This effect was already established during 12-24 h of feeding. From 2 days of feeding, the cellular level of acid-insoluble CoA began to decrease, whereas free CoASH content increased. Stimulation of [1-14C]palmitoyl-CoA oxidation in the presence of KCN, palmitoyl-CoA-dependent dehydrogenase (termed peroxisomal beta-oxidation) and palmitoyl-CoA hydrolase activities were revealed after 36-48 h of CMTTD-feeding. Administration of BCMTD affected the enzymatic activities and altered the distribution of CoA between acid-insoluble and free forms comparable to what was observed in CMTTD-treated rats. It is evident that treatment of peroxisome proliferators (BCMTD and CMTTD), the level of acyl-CoA esters and the enzyme activity involved in their formation precede the increase in peroxisomal and palmitoyl-CoA hydrolase activities. In CMTTD-fed animals the activity of cyanide-insensitive fatty acid oxidation remained unchanged when the mitochondrial beta-oxidation and carnitine palmitoyltransferase operated at maximum rates. The sequence and redistribution of CoA and enzyme changes were interpreted as support for the hypothesis that substrate supply is an important factor in the regulation of peroxisomal fatty acid metabolism, i.e., the fatty acyl-CoA species appear to be catabolized by peroxisomes at high rates only when uptake into mitochondria is saturated. Administration of CETTD led to an inhibition of mitochondrial fatty acid oxidation accompanied with a rise in the concentration of acyl-CoA esters in the liver. Consequently, fatty liver developed. The peroxisomal beta-oxidation was marginally affected. Whether inhibition of mitochondrial beta-oxidation may be involved in regulation of peroxisomal fatty acid metabolism and in development of fatty liver should be considered.

Animals↗

Expression and functional profiling reveal distinct gene classes involved in fatty acid metabolism.

Cells respond to fatty acid exposure by metabolic reorganization and proliferation of peroxisomes. Described here is the development and application of a genome-wide screen to identify nonessential yeast genes necessary for efficient metabolism of myristic and oleic acids. Comparison of the resultant fitness data set with an integrated data set of genes transcriptionally responsive to fatty acids revealed very little overlap between the data sets. Furthermore, the fitness data set enriched for genes involved in peroxisome biogenesis and other processes related to cell morphology, whereas the expression data set enriched for genes related to metabolism. These data suggest that in response to fatty acid exposure, transcriptional control is biased towards metabolic reorganization, and structural changes tend to be controlled post-transcriptionally. They also suggest that fatty acid responsive metabolic networks are more robust than those related to cell structure. Statistical analyses of these and other global data sets suggest that the utilization of distinct control mechanisms for the execution of morphological versus metabolic responses is widespread.

Fatty Acids↗

[Effect of nerobolil on higher fatty acid metabolism in the rat liver normally and in disordered protein metabolism].

Metabolism of fatty acids in rat liver tissue and content of albumin in blood of control rats as well as in the animals with impaired protein metabolism as a result of thermic trauma were studied under conditions of nerobolyl treatment (5 mg per kg of body mass within a day) of different duration. After daily administration of the drug (within 13 days) into control rats and into the animals with burns, content of oleic and linoleic acids was decreased in liver tissue but the content of 5,8,11-eicosatrienic acid and total monoenic acids with uneven amount of carbon atoms was increased with simultaneous decrease in albumin concentration in blood. Metabolism of fatty acids was altered only slightly in liver tissue of healthy animals after nerobolyl administration within three weeks (with an interval for 3-4 days); under conditions of the thermic trauma nerobolyl normalized the fatty acids metabolism in liver tissue and increased the albumin content in blood.

Anabolic Agents↗

Quantitation of myocardial fatty acid metabolism using PET.

UNLABELLED: Abnormalities of fatty acid metabolism in the heart presage contractile dysfunction and arrhythmias. This study was performed to determine whether myocardial fatty acid metabolism could be quantified noninvasively using PET and 1-(11)C-palmitate. METHODS: Anesthetized dogs were studied during control conditions; during administration of dobutamine; after oxfenicine; and during infusion of glucose. Dynamic PET data after administration of 1-(11)C-palmitate were fitted to a four-compartment mathematical model. RESULTS: Modeled rates of palmitate utilization correlated closely with directly measured myocardial palmitate and total long-chain fatty acid utilization (r = 0.93 and 0.96, respectively, p < 0.001 for each) over a wide range of arterial fatty acid levels and altered patterns of myocardial substrate use (fatty acid extraction fraction ranging from 1% to 56%, glucose extraction fraction from 1% to 16% and myocardial fatty acid utilization from 1 to 484 nmole/g/ min). The percent of fatty acid undergoing oxidation could also be measured. CONCLUSION: The results demonstrate the ability to quantify myocardial fatty acid utilization with PET. The approach is readily applicable for the determination of fatty acid metabolism noninvasively in patients.

Animals↗

FATTY ACID METABOLISM IN SERRATIA MARCESCENS I. : Oxidation of Saturated Fatty Acids by Whole Cells.

Bishop, D. G. (University of Sydney, Sydney, Australia), and J. L. Still. Fatty acid metabolism in Serratia marcescens. J. Bacteriol. 82:370-375. 1961.-A study has been made of the oxidation of saturated fatty acids containing between two and 18 carbon atoms by whole cells of the bacterium, Serratia marcescens. This organism was found to be capable of oxidizing all of the acids tested, but variations in the rate and total oxygen uptake were found. These variations were dependent on the length of the carbon chain in the substrate molecule and the pH of the reaction mixture. The concept that these variations are due to a cellular permeability barrier to the substrate is discussed.

Journal Article↗