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PubMed1970

Lipolysis and lipogenesis from glucose in human fat cells of different sizes. Effects of insulin, epinephrine, and theophylline.

Lipogenesis from glucose and lipolysis in human omental and subcutaneous fat cells were studied as functions of adipose cell size and number in adult females. Since subcutaneous fat cells were larger than those prepared from the greater omentum, a comparison could be made of the metabolism of different sizes of cells within individual subjects. Rates per cell of glyceride-glycerol and glyceride-fatty acid synthesis from glucose were similar in omental and subcutaneous fat cells incubated in the presence or absence of insulin. However, subcutaneous fat cells exhibited higher rates of basal lipolysis than omental fat cells and these differences were maintained when lipolysis was stimulated with theophylline. Different rates of lipolysis were not demonstrable after incubations with epinephrine, indicating that subcutaneous fat cells were less responsive to this hormone than smaller omental fat cells. Correlation and partial correlation analysis showed that differences in basal and theophylline-stimulated lipolysis between fat cells prepared from different subjects and between omental and subcutaneous fat cells could be accounted for by differences in adipose cell volume. In subcutaneous fat cells highly significant intercorrelations were demonstrated between cell volume, basal lipolysis, and the basal conversion of glucose to glyceride-glycerol. There was no correlation between fat cell volume, age, or relative obesity and the effects of theophylline or insulin on lipolysis or lipogenesis from glucose in vitro when the data were expressed as percentage changes above basal values.

Adipose Tissue↗
PubMed1972

Lipogenesis in human adipose tissue: some effects of nibbling and gorging.

Six grossly obese patients were fed 5000 calorie diets for 4 wk. During one period of 2 wk, the calories were consumed over 4 hr (gorging) and during the other 2 wk, the dietary intake was spread over 20 hr (nibbling). Each of these periods followed a low caloric intake which lasted at least 10 days. Three male patients (group I) were studied at or near their maximal weight and three females (group II) after a weight loss of 50-70 kg. The patients in group II gained more weight than those in group I. Lipogenesis from pyruvate was greater in group II than in group I. Rapid ingestion of food (gorging) was accompanied by a significant increase in glyceride-glycerol-(14)C and fatty acids-(14)C from pyruvate-(14)C. The enzymatic activity of sn-glycerol 3-phosphate dehydrogenase and mitochondrial glycerophosphate oxidase paralleled the rate of formation of glyceride-glycerol. Lipogenesis from pyruvate was significantly lower when the bicarbonate concentration was reduced from 25 to 10 mM. Citrate and acetate were also converted to fatty acids but there was no difference between gorging and nibbling. An inhibitor of carbonic anhydrase significantly reduced the conversion of pyruvate into CO(2), glyceride-glycerol, and fatty acids. These data on gorging and nibbling have been related to other studies suggesting that the frequency of food intake may be inversely related to obesity.

Acetates↗
PubMed1975

Structure and synthesis of milk fat XI. Effects of heparin on paths of incorporation of glucose and palmitic acid into milk fat.

Intravenous injection of heparin increases lipoprotein lipase activity of circulating serum presumably by removing the enzyme from its location on the capillary endothelium. The incorporation of carbon-14 uniformly labeled glucose and carbon-14 1-labeled palmitic acid into fractionated milk fat triglycerides was studied in both normal and heparin treated lactating goats. The objective was to remove lipoprotein lipase from the mammary gland capillaries and to contrast normal milk fat synthesis with a situation presumed to cause the gland to be solely dependent on the phosphatidic acid pathway. The studies with labeled glucose indicated that under normal conditions there are two sources of milk glyceride glycerol; while following heparin injections, there is a single glycerol pool providing most of the glyceride glycerol. The investigations with labeled palmitic acid indicated that under normal conditions there are two sources of palmitic acid coming from the blood which enter nonequilibrating cellular pools. Palmitic acid from both pools is available for triglyceride synthesis. Following heparin injections there appears to be a common intracellular pool of pre-formed palmitic acid derived from the blood. The data indicate that lipoprotein lipase operating on blood triglycerides yields a 2-mono-glyceride which subsequently enters the gland and is utilized for milk fat synthesis.

Animals↗
PubMed1976

Bovine pancreatic lipase. III. Lipolysis of oils and fats and fatty acid specificity.

Purified bovine pancreatic lipase hydrolyzed butteroil, vegetable oils, and synthetic glycerides. The enzyme hydrolyzed triglycerides more rapidly than di- and monoglycerides and tripropionin faster than any other synthetic glyceride. Triacetin was the least hydrolyzed glyceride. Gas-liquid chromatographic analysis of the free fatty acids liberated by the lipase from milk fat indicated that the enzyme selectively liberated butyric acid in higher proportion than the relative amount originally in the fat. The enzyme released saturated as well as unsaturated fatty acids from commericial vegetable oils. With regard to the lipolytic behavior, in general, the bovine pancreatic lipase closely resembled milk lipase.

Animals↗
PubMed1985

A radioisotopic method for the measurement of free fatty acid turnover and adrenoceptor response in small fragments of human adipose tissue.

New techniques for measuring rates of triglyceride hydrolysis and the re-esterification of resultant free fatty acids (FFA) in small fragments of human adipose tissue are described. Buffered medium containing [14C]-glucose and [3H]-palmitate of high specific activity is used to label newly synthesized acylglycerides in incubated tissue. 14C is incorporated only into the glyceride 'back bone' of acylglycerides, and the rate of incorporation may be used as a measure of the rate of synthesis of each glyceride molecular species. Due to mixing of exogenous [3H]-palmitate with endogenously released FFA, the actual specific activity of FFA esterified to [14C]-glycerides is always less than that of the [3H]-palmitate in the medium. The degree of dilution of [3H]-palmitate with unlabelled FFA is directly proportional to the rate of lipolysis. Thus, determination of the 14C/3H ratio in newly synthesized triglycerides permits the assessment of adrenoceptor dose-response characteristics (lipolysis) of unweighed fragments of adipose tissue. If rates of 14C-tri- and diglyceride accumulation are measured in tissue fragments whose cellularity and rate of glycerol release has been determined, the fraction of newly lipolyzed FFA which are re-esterified can be calculated. This 'cycle' of re-esterification controls the ratio of FFA: glycerol leaving the adipocyte. These techniques can be applied to serial subcutaneous adipose tissue samples from awake subjects in various clinical and experimental states.

Adipose Tissue↗
PubMed1968

Hydrolysis of primary and secondary esters of glycerol by pancreatic juice.

The relative rates of hydrolysis of the secondary ester in glycerol 1,3-benzylidene 2-oleate and in glycerol 1,3-dihexadecyl ether 2-oleate, and of the primary and secondary esters in triolein were determined. Both unaltered and selectively inactivated rat pancreatic juice were used as sources of enzyme. It was found that rat pancreatic juice contains an enzyme that can hydrolyze fatty acids esterified at the 2-position of a glyceride. This enzyme is not pancreatic lipase. It may be sterol ester hydrolase. Partial glycerides, as well as complete glycerides, can serve as substrates. Pancreatic lipase, if it can hydrolyze the 2-positioned fatty acids of a triglyceride, does so at a very slow rate.

Animals↗
PubMed1974

Hepatic microbody proliferation and catalase synthesis induced by methyl clofenapate, a hypolipidemic analog of CPIB.

The effects of the administration of methyl clofenapate (methyl-2-[4-(p-chlorophenyl)phenoxy]2-methylpropionate) on the inducibility of hepatic microbody (peroxisome) proliferation and catalase synthesis were studied in male rats and in both sexes of wild type (Cs(a) strain) and acatalasemic (Cs(b) strain) mice. These investigations included electron microscopic examination of livers, assay of liver catalase activity, quantitation of catalase protein by immunotitration procedure, and measurements of serum cholesterol and glyceride-glycerol levels. In all groups of animals administration of methyl clofenapate at dietary concentrations of 0.015, 0.05 and 0.125% produced a significant and sustained increase in number of hepatic microbody (peroxisome) profiles. There was no appreciable increase in mitochondrial population, but several mitochondria were markedly enlarged and possessed numerous cristae. The hepatic microbody proliferation in male rats and in both sexes of wild type mice following methyl clofenapate administration was associated with a twofold increase in catalase activity and in the concentration of catalase protein. The increase in microbody population in acatalasemic mice, however, was not accompanied by a significant elevation of the catalase activity, which is due to the unusual heat lability of the mutant catalase enzyme. A marked decrease in serum cholesterol and glyceride-glycerol levels was observed in male rats following methyl clofenapate administration which paralleled the increase in liver catalase activity. In both strains of mice there was a significant reduction in serum glyceride-glycerol concentrations. All the above effects of methyl clofenapate were fully reversed when the drug was withdrawn from the diet of male wild type mice. The demonstration of microbody proliferation and catalase induction with hypolipidemic compounds, CPIB, nafenopin and, in these studies, with methyl clofenapate suggests a possible but as yet unclarified relationship between microbodies and hypolipidemia.

Animals↗
PubMed1969

Early effects of feeding excess vitamin A: mechanism of fatty liver production in rats.

Oral administration of vitamin A (30,000 IU daily for 2 days) to young rats caused a marked increase in hepatic glycogen, cholesterol, and glycerides, while hepatic phospholipid content remained almost unaltered. In an examination of the pathogenesis of the lipid accumulation, it was found that more glucose-(14)C was incorporated into liver lipids in vitamin A-fed rats, whereas incorporation of glucose-(14)C and dl-glycine-(14)C into liver protein remained unaltered. The increase in glucose-(14)C incorporation was confined to the glyceride-glycerol portion of the lipids; incorporation into liver fatty acids was inhibited. Plasma free fatty acid concentrations were elevated. It is postulated that in the vitamin A-fed rats, increased accumulation of lipids in the liver is caused by a stimulation of fatty acid mobilization from adipose tissue and enhanced formation of glycerophosphate through glycolysis, with consequent increase in the glyceride synthesis in the liver. The weight of the adrenals was increased, whereas cholesterol concentration in the gland was decreased, after administration of vitamin A to rats. This indicates adrenocortical stimulation. Interestingly enough, vitamin A feeding did not affect either the level of liver lipids or of plasma FFA in adrenalectomized rats.

Adrenal Glands↗
PubMedDate not supplied

[Effect of hydrazine sulfate on lipid composition in rat liver homogenates and plasma membranes].

Introduction of hydrazine-sulphate to experimental animals decreases the total content of lipids in homogenates, but in plasmatic membranes of the liver it increases. The composition of certain classes of neutral lipids under these conditions is also changed. In particular, the contents of cholesterol and its esters as well as of free fatty acids decrease in the homogenate. The amount of glycerides remains unchanged. In the plasmatic membranes under the effect of hydrazine-sulphate the contents of cholesterol and its esters lowers and, vice versa, those of free fatty acids and glycerides rise. The molar glycerides-to-phospholipids ratio in the homogenates is unchanged but in the plasmatic membranes it increases, whereas the molar cholesterol-to-phospholipids ratio in the homogenates as well as in plasmatic membranes decreases.

Animals↗
PubMed1983

Metabolism of fatty acid, glycerol and a monoglyceride analogue by rat cardiac myocytes and perfused hearts.

Studies have been conducted on the uptake and metabolism of unesterified fatty acid, free glycerol and 1-hexadecyl glyceryl ether by rat cardiac myocytes, and of fatty acid, intact triglyceride and the glyceryl ether by perfused rat hearts. Cardiac myocytes efficiently extracted, oxidized and esterified oleic acid, but demonstrated little ability to utilize free glycerol. Although the glyceryl ether was efficiently extracted by myocytes, it was neither hydrolyzed or esterified. The perfused heart also extracted and metabolized unesterified fatty acid, and the fatty acid released during lipolysis of circulating lipoprotein triglyceride. The glyceride glycerol, however, was largely recovered (90%) in the perfusate suggesting inefficient myocardial utilization of either free glycerol or partial glycerides. Myocardial extraction of glyceryl monoether was demonstrated, but the monoglyceride analogue was also unmetabolized by intact heart tissue. The results suggest that if monoglycerides are produced by the action of lipoprotein lipase on circulating triglycerides, reutilization of intact monoglycerides for higher glyceride synthesis is not a major fate of these products.

Animals↗
PubMed1986

Comparative utilization of glycerol and alanine as liver gluconeogenic substrates in the fed late pregnant rat.

The appearance of plasma [14C]glucose in the inferior cava vein after a pulse of 0.2 mmol of [U-14C]L-alanine or [U-14C]glycerol/200 g body wt given through the portal vein was studied in fed 21 day pregnant rats and virgin controls under pentobarbital anesthesia. In both groups values were much higher when [U-14C]glycerol was the administered tracer than when [U-14C]L-alanine, and they were augmented in pregnant versus virgin animals at 1 min when receiving [U-14C]glycerol and at 2 min when receiving [U-14C]L-alanine. 20 min after the tracers rats receiving [U-14C]glycerol showed much higher liver [14C]glycogen and [14C]glyceride glycerol than those receiving [U-14C]L-alanine. Radioactivity present in liver as [14C]glyceride glycerol was greater in pregnant than in virgin rats receiving [U-14C]glycerol whereas radioactivity corresponding to [14C]fatty acids was lower in the former group receiving either tracer. At 20 min after maternal treatments fetuses showed lower plasma [14C]glycerol than [14C]alanine values but plasma [14C]glucose and liver [14C]glycogen values were much greater in fetuses from mothers receiving [U-14C]glycerol than [U-14C]L-amine. Besides showing the higher gluconeogenic efficiency in pregnant than in virgin rats, results indicate that at late gestation glycerol is used as a preferential substrate for both glucose and glyceride glycerol synthesis in liver.

Alanine↗
PubMed1987

The effect of malathion and gamma-BHC on the lipid metabolism in relation to reproduction in the tropical teleost, Clarias batrachus.

In the present study, female Clarias batrachus were exposed to two sublethal concentrations of gamma-BHC (2 and 8 microg litre(-1)) and malathion (1 and 4 microl litre(-1)) for 4 weeks during different phases of their reproductive cycle. Impact of these pesticides on free fatty acids, monoglycerides, diglycerides, triglycerides, phospholipids, free and esterified cholesterol in the liver, plasma, ovary and muscle was assessed. During the pre-vitellogenic and regressed phases, they suppressed the levels of fatty acids and glycerides in the liver, but had no effect on their levels in the plasma, ovary and muscle. However, in the vitellogenic phase, fatty acids in the liver and plasma were increased, but were decreased in the ovary and muscle. Glycerides were also decreased in the studied tissues. In the post-vitellogenic phase, these pesticides increased the levels of fatty acids and glycerides in the liver and ovary, but decreased their levels in the plasma. Both pesticides decreased hepatic phospholipids in the pre-vitellogenic phase, while in the vitellogenic phase only gamma-BHC reduced its levels in the liver. These pesticides also restricted their mobilisation to the ovary. Cholesterol biosynthesis seemed unaffected, but the hydrolysis of esterified cholesterol to free cholesterol was adversely affected during the period of estrogen biosynthesis.

Journal Article↗
PubMed1990

Adrenergic blockade paradoxically increases lipogenic response of brown adipose tissue to sympathetic nerve stimulation.

Intermittent electrical stimulation of sympathetic nerves entering the interscapular brown adipose tissue (BAT) in rats increased the rate of glyceride glycerol synthesis in BAT but the fatty acid synthesis did not change. Simultaneous administration of phenoxybenzamine and propranolol paradoxically increased the fatty acid synthesis in response to the nerve stimulation whereas the glyceride glycerol synthesis was inhibited. Propranolol alone was also effective in mimicking the effects of adrenergic blockade, but guanethidine selectively eliminated the lipogenic response to the nerve stimulation. These results indicate that synthesis of glyceride glycerol induced by sympathetic nerve stimulation is largely due to beta-adrenergic action of noradrenaline, whereas synthesis of fatty acids may be mediated by non-adrenergic transmission of the sympathetic nerves.

Adipose Tissue, Brown↗
PubMed2001

Combining solvent engineering and thermodynamic modeling to enhance selectivity during monoglyceride synthesis by lipase-catalyzed esterification.

Monoglyceride synthesis by Rhyzomucor miehei lipase was investigated via direct esterification between glycerol (adsorbed onto silica gel) and oleic acid in organic solvents. The main difficulty is to avoid the unwanted production of di- and tri-glycerides. It was demonstrated that an increase in solvent polarity, using mixtures of n-hexane and 2-methyl-2-butanol (2M2B), improves drastically the selectivity toward monoglyceride formation. In pure n-hexane, the monoglyceride represents only 6 molar % of the total products at the thermodynamic equilibrium (34 and 60% for di- and tri-glyceride respectively). Use of an equivolume mixture of n-hexane/2M2B enables a product mixture to be obtained containing 94% of monoglyceride at equilibrium (2.4 and 0% for di- and tri-glyceride respectively). This positive effect is counterbalanced by a decrease both in initial velocities and in substrate conversion at thermodynamic equilibrium.A modeling, able to predict the three thermodynamic equilibria governing the 3 consecutive reactions, based on activity coefficient calculations using the UNIFAC model, is proposed. It takes into account both the partition of water between solvent and immobilized catalyst, and the partition of glycerol between solvent and silica gel. A good correlation with experimental data obtained in n-hexane/2M2B mixtures was observed.

Journal Article↗
PubMed1982

Capillary gas chromatographic analysis of human skin surface lipids after microsampling on ground-glass platelets.

Small amounts of human skin surface lipids, in the 1-20 micrograms range, sampled on ground-glass platelets are investigated using capillary gas chromatography. A first system allows the separation of the neutral lipids, up to the triglyceride fraction. A second system reveals the distribution of the free fatty acids or of the free + glyceride fatty acids, after a methylation or transesterification step. Examination of samples from nine subjects shows that the unsaturation of the free fatty acids increases during a four-day period of accumulation. Comparison of the free fatty acid fraction and the free + glyceride fatty acid fraction shows that the fraction is more saturated than the latter. It is concluded that the bacterial lipases which cleave the fatty acids from the ester bond favor the liberation of straight-chain saturated fatty acids from sebum triglycerides. This result is confirmed by comparison of the free fatty acid fraction with the glyceride fatty acid fraction separated from bulk samples of skin surface lipids from hair and scalp.

Chromatography, Gas↗
PubMed2003

Intestinal lymphatic transport of halofantrine occurs after oral administration of a unit-dose lipid-based formulation to fasted dogs.

PURPOSE: To examine whether the small quantities of lipid present in unit-dose microemulsion formulations comprising medium- (C8-10) or long-chain (C18) glyceride lipids can stimulate the intestinal lymphatic transport of halofantrine (Hf), a model lymphatically transported drug. METHODS: Hf (50 mg) was administered to thoracic lymph duct- and cephalic vein-cannulated fasted greyhound dogs. Drug was formulated as a single soft gelatin capsule containing approximately 1 g of a microemulsion preconcentrate based on either medium- or long-chain glycerides. Thoracic lymph was collected, and systemic plasma samples taken over 10 h postdose. RESULTS: The extent of lymphatic transport of Hf after administration of the long-chain lipid formulation was high (28.3% of dose), and significantly higher than that seen after administration of the medium-chain formulation (5.0% of dose). Plasma levels of Hf were not significantly different across the two formulations when assessed by AUC0-10h. CONCLUSIONS: This is the first study to demonstrate that the small amounts of lipid present within a single lipid-based dose form can support substantial intestinal lymphatic transport in the fasted state. Furthermore, microemulsions based on long-chain glycerides appear to be more effective with respect to lymphatic transport than the equivalent medium-chain formulation.

Absorption↗
PubMed1966

Studies on lipogenesis in vivo. Effect of dietary fat or starvation on conversion of [14]glucose into fat ad turnover of newly synthsized fat.

1. Lipogenesis was studied in vivo by giving mice 250mg. meals of [U-(14)C]glucose and measuring the disposition and incorporation of label. About 48% of the (14)C dose was eliminated as (14)CO(2) in the first 2hr. At 60min. after administration, 1.0, 1.9 and 11.9% of the dose was recovered as liver glycogen, liver fatty acid and carcass fatty acid respectively. Of the [(14)C]glucose converted into fat in the epididymal pads about 90% was present as glyceride fatty acid and 10% as glyceride glycerol. 2. Hepatic synthesis of fatty acid was depressed by dietary fat to a much greater extent than was synthesis outside the liver. Both feeding with fat and starvation decreased the proportion of the label taken up by adipose tissue present as fat (triglyceride) and increased the proportion of triglyceride label present as glyceride glycerol. These results are consistent with the hypothesis that the primary action of both these conditions in decreasing fat synthesis is to inhibit synthesis of fatty acids. 3. Turnover of body fat labelled in vivo from [U-(14)C]glucose was estimated from the decline in radioactivity measured over the first 24hr. of the experiment. The half-life of liver and extrahepatic fatty acids (excluding epididymal fat) was 16hr. and 3 days respectively. In contrast, no measurable decrease in radioactivity of the fatty acids of epididymal fat was observed for 7 days after administration of the [U-(14)C]glucose.

Adipose Tissue↗
PubMed1976

Phosphatidylcholine synthesis in castor bean endosperm.

Three pathways for phosphatidylcholine synthesis were assayed in castor bean (Ricinus communis var. Hale) endosperm. Phosphatidylethanolamine: S-adenosylmethionine methyl transferase occurred predominantly in the endoplasmic reticulum fraction, but some activity appeared in the mitochondria. Phosphorylcholine glyceride transferase occurred exclusively in the endoplasmic reticulum. The phosphorylcholine glyceride transferase activity was approximately 20-fold greater than the methylation pathway in the endoplasmic reticulum. No exchange activity was found. The Michaelis constant for the methylation was 31 mum for S-adenosylmethionine; phosphatidylethanolamine promoted the reaction slightly while other intermediates stimulated it by about 50%. The pH optimum was 9. Phosphorylcholine glyceride transferase had a Michaelis constant of 9.7 mum for cytidine diphosphate choline but variable results were obtained from diglycerides. The pH optimum was 7.5 and a divalent cation was required, Mg(2+) giving the greatest stimulation.

Journal Article↗