Hepatic Fatty Acid Synthetase Activity Research Articles

Altered hepatic glycolysis, lipogenesis, and blood biochemistry of tiger puffer (Takifugu rubripes) under two different culture systems

Tiger puffer (Takifugu rubripes) is one of the most commercially important fish species cultivated and consumed in East Asian countries, including Japan, South Korea and China. In this study, the hepatic glycolysis, and lipogenesis, and serum biochemistry of tiger puffers subjected to short-term culture in offshore sea cage aquaculture system (OSCS) and recirculating aquaculture system (RAS) were evaluated. Results showed that the activity of hepatic phosphofructokinase, and lipoprotein lipase, ATP level, and serum cortisol content of the male tiger puffers reared in OSCS were significantly higher than those of female tiger puffers reared in OSCS and those of fish reared in RAS. The lowest hepatic fatty acid synthetase activity, lipid droplet number, serum aspartate aminotransferase activity, Na+ and Cl− concentrations were observed in male tiger puffers reared in OSCS. However, serum glucose, triglyceride, total cholesterol, K+ concentrations and alanine aminotransferase activity of tiger puffers reared in RAS and OSCS showed no significant differences. Hepatic glycolysis and lipogenesis were profoundly affected by rearing system and gender. The interaction effect of gender and rearing system on hepatic lipoprotein lipase activity, lipid droplet number and serum Na+ level was observed. These results indicate male tiger puffers exhibited different metabolic status in hepatic glycolysis, lipogenesis, and serum biochemical parameters when reared under two different culture systems. These findings will provide important information for improving tiger puffer (Takifugu rubripes) farming and profitable production using the RAS and OSCS aquaculture systems in the north coast of China.

The effect of different dietary unsaturated to saturated fatty acids ratios on the performance and serum lipids in broiler chickens

Fat saturation degree and the age of bird are two important factors for broilers’ ability to digest fats. It has been shown that hepatic fatty acid synthetase activity is decreased by diets with added sunflower oil (rich in PUFA of n-6 series) compared with those fed lard and this can result in abdominal fat pad reduction. (Sanzet al., 2000). It is well known that dietary intake of n-6 and n-3 PUFAs is effective in lowering blood lipid level, but they differ in their effect on serum lipid concentrations. It has been observed that n-6 fatty acids lower serum cholesterol level, but not triacylglycerol; n-3 fatty acids lower both serum cholesterol and serum triacylglycerol level in experimental animals (Berret al., 1993). The objective of this study was to survey the effects of different dietary unsaturated to saturated fatty acids ratio on performance, abdominal fat pad and serum lipids in broiler chickens.

Ornithine decarboxylase, fatty acid synthetase, and lipid levels in selected organs of the postnatal developing male miniature pig

Ornithine decarboxylase (ODC) and fatty acid synthetase (FAS) activities were determined in tissues from male neonate and juvenile miniature swine (Hormel-Hanford strain) at various ages. ODC activity was measured in liver, brain, kidney, pancreas, and spleen at one day and at 1, 4, 8, 12 and between 24 and 32 weeks. Hepatic FAS activity, total lipid, triglyceride, and total cholesterol were measured at 2, 8, 16, and 32 weeks. Generally, tissue ODC activity was highest in the spleen at all ages. Three postnatal patterns of ODC activity were observed for the different organs. The mean values of FAS activity, total lipid, and cholesterol were highest at 8 weeks compared to other sampling periods.

Estrogens and antiestrogens: actions and interactions with fluphenazine on food intake and body weight in rats.

Treatment of ovariectomized rats for 3 days with 2 micrograms estradiol benzoate (E2B), 6 micrograms ethinyl estradiol, or 1-2 mg of either of the antiestrogens nafoxidine or tamoxifen led to similar decreases in food intake, body weight gain, adipose tissue lipoprotein lipase activity, and hepatic fatty acid synthetase activity, despite their different effects on uterine growth and induction of progestin receptors in pituitary and adipose tissue. Longer-term (2 wk) treatment with tamoxifen resulted in similar transient changes in food intake and body weight gain, as did treatment with E2B. Daily administration of 50 micrograms fluphenazine (FLU) led to significant decreases in body weight, although there was no change in food intake. Concurrent administration of FLU with either E2B or tamoxifen led to additive effects on body weight and food intake change. None of the treatments had any effect on in vitro binding of [3H]tamoxifen to antiestrogen binding sites in pooled hypothalamic-preoptic area samples.

Temporal Effect of Change in Diet Composition on Plasma Estradiol and Thyroxine Concentrations and Hepatic Lipogenesis in Laying Hens

Temporal effects of feeding isocaloric and isonitrogenous diets with and without 10% menhaden fish meal (FM) on plasma estradiol and thyroxine concentrations, hepatic fatty acid synthetase activity and lipid content were significantly increased Hepatic fatty acid synthetase activity and lipid content were significantly increased at 7 days and 14 days, respectively, after feeding the corn-soybean meal (CS) diet. Plasma thyroxine concentration was significantly reduced at 3 days after feeding the FM diet. Plasma estradiol concentration was immediately and gradually elevated after feeding the CS diet and reduced after changing from the CS to the FM diet. A significant positive correlation was observed between plasma estradiol, but not plasma thyroxine, and hepatic fatty acid synthetase activity. These findings suggest that tissue estradiol concentration responds early to dietary changes followed by stimulated hepatic lipogenesis, and steatosis in laying hens.

Effect of dietary polyunsaturated fatty acids on the activity and content of fatty acid synthetase in mouse liver

When mice, previously fed a standard laboratory mouse chow diet, were fed a high carbohydrate (50% glucose) diet containing 15% (w/w) hydrogenated cottonseed oil, the activity of hepatic fatty acid synthetase per mg cytosolic protein increased approximately 3-fold over an 11-day period. However, when mice were placed on an isocaloric diet containing 15% (w/w) corn oil, the specific activity of the enzyme did not increase above the chow-fed levels. Using antibody prepared against pure mouse liver fatty acid synthetase, we showed that the increase in the specific activity of fatty acid synthetase in the hydrogenated cottonseed oil-fed animals resulted from an elevation in the hepatic content of the enzyme. This increase was a result of (a) an increase in the rate of synthesis of the enzyme relative to that of total protein and (b) a decrease in the enzyme's degradative rate, when compared to these parameters measured in the livers of the corn oil-fed animals. Furthermore, these dietary-induced changes in enzyme specific activity were not accompanied by changes in the catalytic efficiency of fatty acid synthetase; since both hydrogenated cottonseed oil-fed and corn oil-fed animals showed identical immunoequivalences and contained similar amounts of immunoprecipitable 3H-labeled enzyme protein per unit enzyme activity (in mice pulse-labeled with [ 3H]leucine). The results of experiments in which we administered pure fatty acids (oleic (cis- Δ 9-18:1), ricinoleic (12-hydroxy-cis- Δ 9-18:1), Iinoleic (cis, cis- Δ 9,12-18:2), α-linoleic ( cis, cis, cis- Δ 9,12,15-18:3), columbinic ( trans, cis, cis- Δ 5,9,12-18:3) and arachidonic (all-cis- Δ 5,8,11,14-20:4)) to mice maintained on a 50% glucose diet suggested that the ability of a fatty acid to inhibit hepatic fatty acid synthetase activity and to prevent an increase in hepatic fatty acid synthetase protein was related to the degree and position of unsaturation of the fatty acid administered and not to the ability of the fatty acid to act as prostaglandin precursor. Those 18-carbon fatty acids which possessed a double bond at positions Δ 9,12 (linoleic, columbinic and α-linolenic) were the most effective at inhibiting hepatic fatty acid synthetase activity and in preventing an increase in enzyme content.

Studies on the mechanism of the effects of experimental inflammation on adaptive synthesis of rat liver fatty acid synthetase

The mechanism of suppression, by experimental inflammation of the usual increase in hepatic fatty acid synthetase activity resulting from fat-free feeding following starvation (adaptive synthesis), was investigated immunochemically. That suppression results from changes in amount of hepatic fatty acid synthetase was shown by the observation that fatty acid synthetase preparations from inflamed and uninflamed animals, exhibiting a wide variety of specific enzyme activities, had identical immunochemical equivalence points. In confirmation of this, the amounts of fatty acid synthetase, determined by radial immunodiffusion in gels containing anti-fatty acid synthetase serum, varied concomitantly with changes in enzyme activity regardless of the relative times of inflammation and onset of adaptive synthesis. Serum insulin levels were not dramatically elevated during the first 48 h of fat-free feeding, but rose markedly thereafter. Inflammation, either alone or combined with fat-free feeding, resulted in increased serum glucose levels, followed by a similar pattern of increased serum insulin levels some 12 h later. Fat-free feeding did not affect serum cortisol levels, but depressed liver cyclic AMP. Inflammation invariably resulted in a marked increase in serum cortisol within 12 h and a concomitant elevation of hepatic cyclic AMP, indicating possible roles for cortisol and cyclic AMP in suppression of hepatic fatty acid synthetase synthesis.

Time Sequence of Changes in Hepatic Fatty Acid Synthesis in Rats Meal-Fed Polyunsaturated Fatty Acids

Rats were meal-fed once daily methyl esters of palmitate (C16:0); stearate (C18:0); linoleate (C18:2) and linolenate (C18:8) to determine the influence of these fatty acids on glucokinase and fatty acid synthetase activities and on in vivo rates of fatty acid synthesis in the liver. Addition of 7% C16:0 or 3% C18:3 to a fat-free basal diet did not alter the rate at which the diet was removed from the stomach and small intestine. Consumption of a diet containing C18:2 for eight meals significantly reduced hepatic fatty acid synthetase activity and in vivo rates of fatty acid synthesis by 40%, but did not alter glucokinase activity. At least three meals of a diet containing C18:2 or C18:3 were required to inhibit hepatic fatty acid synthesis. Conversely, after rats consumed C18:2, more than two meals of a fat-free diet were required to increase hepatic rates of fatty acid synthesis. Dietary C16:0 and C18:0 did not alter rates of fatty acid synthesis in rat liver. Glucokinase was not influenced by any of the methyl esters fed in all trials except one. The results of this study suggest that polyunsaturated fatty acids can specifically influence hepatic fatty acid synthesis and fatty acid synthetase activity without altering glucokinase activity, and that meal-fed rats must consume at least three meals containing polyunsaturated fatty acids before hepatic fatty acid synthesis or fatty acid synthetase activity is altered.

Stimulation of hepatic fatty acid synthetase activity in chick embryo by cycloheximide

Liver fatty acid synthetase activity is increased up to 25-fold at 10–24 h after administration of cycloheximide in 16-, 18-, and 20-day-old chick embryos. The extent of stimulation of the synthetase activity depended on the dose of the protein synthesis inhibitor, larger doses elevating the enzyme activity to a greater degree than smaller doses. Quantitative precipitin reactions using goat antibodies against chicken liver synthetase and partially purified liver extracts from normal and cycloheximide-treated embryos gave identical equivalence points, suggesting that the increase in the synthetase activity following cycloheximide injection resulted from an increase in the content of the enzyme and not from its activation. Although there was a strong inhibition of protein and fatty acid synthetase syntheses after cycloheximide injection, a twofold increase in the rate of enzyme synthesis, compared to saline-treated embryos, was observed at 12 h after injection of the antibiotic. During the period of active inhibition of synthetase synthesis in cycloheximide-treated embryos, the synthetase activity did not diminish. The results support the conclusion that a decrease in degradation and a subsequent increase in the synthesis of the enzyme are responsible for an increase in the content of the synthetase after cycloheximide treatment. Absence of a stimulatory effect of cycloheximide on synthetase activity of cultured avian liver expiants indicate that cycloheximide stimulates synthetase activity, in ovo, by an indirect action mediated by extrahepatic events. These results emphasize the ambiguity involved in interpretation of data derived from in vivo experiments with inhibitors of protein synthesis.

Specific inhibition of hepatic fatty acid synthesis exerted by dietary linoleate and linolenate in essential fatty acid adequate rats.

Dietary linoleate and linolenate were investigated for their ability to specifically inhibit liver and adipose tissue lipogenesis in meal-fed (access to food 900-1,200 hr), essential fatty acid (EFA) adequate rats. Supplementing a high carbohydrate diet containing 2.5% safflower oil with 3% palmitate 16:0, oleate 18:1, or linoleate 18:2 did not affect in vivo liver or adipose tissue fatty acid synthesis. However, 18:2 addition to the basal diet did result in a significant (P less than 0.05) decline of liver fatty acid synthetase (FAS) and glucose-6-phosphate dehydrogenase (G6PD) activities. When the safflower oil content of the basal diet was reduced to 1%, the addition of 3% 18:2 or linolenate 18:3 significantly (P less than 0.05) depressed hepatic FAS, G6PD, and in vivo fatty acid synthesis by 50%. Addition of 18:1 caused no depression in hepatic FAS activity but did result in a significant (P less than 0.05) decline in liver G6PD activity and fatty acid synthesis which was intermediate between basal and basal +18:2- or +18:3-fed animals. Adipose tissue rates of lipogenesis were completely unaffected by dietary fatty acid supplementation. Similarly, the addition of 3 or 5% 18:3 to a basal diet for only one meal resulted in no change in lipogenesis relative to that in animals fed the basal diet. The data indicate that, like rats fed EFA-deficient diets, dietary 18:2 and 18:3 exert a specific capacity to depress rat liver FAS and G6PD activities and rate of fatty acid synthesis.

Mercury inhibition of avian fatty acid synthetase complex

( 1) Subcutaneous or intra-abdominal injections of 8 mg of HgCl 2/100 g body weight markedly depressed hepatic fatty acid synthetase activity of chicks at l h postinjection. The depression occurred despite the fact that the chicks continued to eat up until the time they were killed. Under these same conditions, the hepatic activity of acetyl-CoA car☐ylase (EC 6.4.1.2) was not affected by HgCl 2, while the activity of the mitochondrial system of fatty acid elongation was stimulated. ( 2) When 2-mercaptoethanol was included in the incubation medium for a highly purified preparation of fatty acid synthetase, 500 μ M HgCl 2 was required to show definite inhibition of the enzyme. When 2-mercaptoethanol was omitted, 50 μ M HgCl 2 was inhibitory and 100 μ M HgCl 2 abolished enzyme activity. ( 3) 2 m M dithiothreitol completely protected the purified fatty acid synthetase preparation from inhibition by 100 μ M HgCl 2. When dithiothreitol was added after the addition of enzyme to the mercury-containing medium, protection of the enzyme was not complete. ( 4) Dialysis of cytosol fractions from chicks injected with HgCl 2 against 500 vol. of 0.2 M potassium phosphate buffer (pH 7.0) containing 1 m M EDTA and 10 m M dithiothreitol for 4 h at 4° stimulated the fatty acid synthetase activity of the fractions. Dialysis of cytosol fractions from noninjected chicks under the same conditions was without effect on fatty acid synthetase activity. ( 5) These data support the nypothesis that the inhibitory effect of HgCl 2 administered in vivo on hepatic fatty acid synthetase activity in chicks is mediated through the interaction of mercury with the sulfhydryl groups of the enzyme.

Mercury inhibition of fatty acid synthesis in chicks

Male chicks were fed a commercial ration and were given drinking water which contained 0, 50, 100, 150, 200 or 300 mug of mercury/ml as mercuric chloride from hatching to 3 weeks of age. In one experiment, the mercuric chloride was administered by injection into the abdominal cavity rather than in the drinking water. At 3 weeks the chicks were killed, and the livers were removed and weighed. The activity of fatty acid synthetase in the 800 X gav supernatant fractions of the liver homogenates and in vivo incorporation of [14C]acetate into liver and carcass fatty acids and respiratory 14CO2 was determined as indicated. Administration of mercury at a treatment level of 300 mug/ml of drinking water depressed growth, feed and water consumption, liver weight, hepatic fatty acid synthetase activity, and in vivo incorporation of [14C]acetate into liver and carcass fatty acids, and increased the production of respiratory 14CO2 as compared with controls. In experiments in which graded doses of mercury were administered, body weights, liver weights, and feed and water intakes of the chicks receiving 0, 50 and 100 mug of mercury/ml of drinking water were similar to each other, but these parameters were severely depressed by 200 mug of mercury/ml of drinking water. Mercury caused a dose-related decrease of fatty acid synthetase activity. Incorporation of [14C]acetate into carcass fatty acid was depressed by 50 and 200 mug of mercury/ml of drinking water; incorporation into liver fatty acids and production of respiratory 14CO2 was not affected by mercury. Intra-abdominal injection of 6 mg of mercury/100 g body weight (as mercuric chloride) into well alimented chicks depressed hepatic fatty acid synthetase activity at 1 h post-injection. The data are consistent with the hypothesis that a portion of the effects of mercury on fatty acid synthesis are direct rather than a secondary effect of inanition.

Some effects of different dietary carbohydrates on pregnancy and lactation in rats.

Female rats were fed from weaning on diets with sucrose, starch, glucose or fructose as the carbohydrate source. Animals were killed at various stages throughout pregnancy and early lactation. Maternal plasma triglycerides (TG), cholesterol, free fatty acids, glucose, insulin and corticosteroids were measured. Lipogenic activity was assayed in the livers, adipose tissue and mammary tissue, and the results compared with those from non-pregnant rats. Insulin, corticosteroids and hepatic lipogenesis were also assayed in the embryos and in newborn pups. Dietary sucrose and fructose produced a significantly higher concentration of plasma TG in the non-pregnant, pregnant and lactating rats than did starch and glucose. All the diets led to an increase in TG concentration at the 20th day of pregnancy, which returned to the original concentration 2 days post-partum. The hypertriglyceridaemia of late pregnancy was accentuated by the feeding of sucrose and fructose. Maternal concentrations of plasma glucose were significantly reduced towards the end of pregnancy in all dietary groups. The replacement of starch by sucrose, or of glucose by fructose, enhanced hepatic lipogenesis. Fructose but not sucrose depressed fat synthesis in the adipose tissue. Hepatic fatty acid synthetase activity was increased in late pregnancy on all diets except that with starch. Late pregnancy intensified hepatic lipogenesis in rats fed sucrose or fructose. The results are discussed in relation to the metabolic changes during pregnancy and to sucrose feeding.

Effect of vitamin B-12 deprivation on the rates of synthesis and degradation of rat liver fatty acid synthetase

To characterize the basis for the increased hepatic fatty acid synthetase activity in vitamin B-12 deprivation, the content and rates of synthesis and degradation for the enzyme were determined. Animals were in a dietary steady state on normal chow or a B-12-deprived diet; animals on the latter diet were further divided into a “supplemented” group given B-12 and those “B-12-deprived.” The B-12-deprived animals had tissue B-12 depletion. Both total and specific activity of fatty acid synthetase were increased in the B-12-deprived animals, and this was due to increased enzyme protein. Rates of synthesis and degradation were studied in each group after a pulse of 20 μCi of l-[U- 14C]leucine. Radioactivity was determined in the immunoprecipitate of the purified enzyme. Relative rates of synthesis in the B-12-deprived group were increased 8.8-fold over the normal and 3.6-fold over the B-12-supplemented group. Degradation of hepatic fatty acid synthetase was 63 hr ( t 1 2 ) in the normal and 65 hr in the B-12-supplemented group. The t 1 2 in the B-12-deprived group was 35 hr. Degradation rates for the soluble protein pool were not affected by B-12 deprivation. The rate constant for synthesis of hepatic fatty acid synthetase in the B-12-deprived group was 14-fold that of the normal and 6-fold that of the B-12-supplemented animals. Thus, although vitamin B-12 deprivation results in increased rate of degradation of fatty acid synthetase, enzyme synthesis is markedly increased yielding a severalfold net increase in synthetase content and activity.

Fatty acid synthetase activity in the liver and adipose tissue of rats fed with various carbohydrates.

1. The inclusion of sucrose in the diet of rats led to an increase in hepatic fatty acid synthetase activity compared with that of rats fed with starch as the sole carbohydrate. The higher activity occurred within 18h of the introduction of sucrose and persisted with fluctuations for the 30 days of the experiment. Reversal of the diets in some rats after 21 days led to changes in the enzyme activity to values appropriate to the second diet. The plasma triglyceride concentration followed a similar pattern. 2. A comparison of the effects of diets with starch, glucose, maltose, sucrose or fructose showed that fructose gave the highest values of triglyceride content and of fatty acid synthetase activity in liver, but the lowest values of the synthetase activity in adipose tissue and the lowest values of plasma insulin concentration. These effects may perhaps be attributed to the low insulin response to fructose and to the high affinity of the liver for this sugar. 3. When the diet contained fructose or sucrose there was a correlation between hepatic synthetase activity and plasma triglyceride concentration. Neither of these, however, was related to plasma insulin concentration. On the other hand, there was a correlation between plasma insulin concentration and fatty acid synthetase activity in adipose tissue. 4. When rats were starved and then re-fed the differences in enzyme activities induced by fructose or glucose were minimized. This, together with the varying degree of difference during the course of the experiments, may explain why other workers, using the starvation-re-feeding technique and making measurements on one day only, have failed to observe differences in the activities of lipogenic enzymes in animals fed with either fructose or glucose.

Activity of lipogenic enzymes and plasma triglyceride levels in the rat and the chicken as determined by the nature of the dietary fat and dietary carbohydrate.

The plasma triglyceride levels of rats fed diets containing sucrose were higher than those of rats fed starch. The presence of saturated fat in the diet further elevated these levels. No significant differences were found in the activities of hepatic lipogenic enzymes in groups fed saturated or polyunsaturated fat, although these activities were much higher after feeding sucrose. The activities of lipogenic enzymes in the adipose tissue were very low. It is suggested that sucrose elevates plasma triglycerides by stimulating hepatic lipogenesis, whereas saturated fat may produce the same effect by reducing plasma clearance. In cockerels, no significant difference was found in the plasma triglyceride levels of those fed either sucrose or starch or with saturated or polyunsaturated fat. Sucrose increased hepatic fatty acid synthetase activity, while polyunsaturated fat decreased it. It was presumed that efficient plasma clearance prevented any rise in plasma triglyceride concentrations.