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At least 865 records · Page 48Linked to original sources
PubMed1971

Mass spectrometry of the phosphatidylcholines: dipalmitoyl, dioleoyl, and stearoyl-oleoyl glycerylphosphorylcholines.

Mass spectra of the diacyl glycerylphosphorylcholines have been obtained using a direct insertion probe, with a source temperature of 250 degrees C at an ionizing potential of 70 ev. Fragmentation patterns are described for dipalmitoyl, dioleoyl, and 1-stearoyl-2-oleoyl glycerylphosphorylcholines. Significant differences are observed in the fragmentation patterns, and the fragment ions have been identified by high resolution mass measurements. Ions associated with the hydrocarbon chains, glycerol esters, and phosphorylcholine have been identified, and the presence of metastable transitions have been used as confirmatory evidence for some of the steps involved in the fragmentation sequence. A molecular ion was tentatively identified in the case of dioleoyl glycerylphosphorylcholine. The mass spectrum of 1-stearoyl-2-oleoyl glycerylphosphorylcholine shows an important rearrangement ion at m/e 604 and some evidence for the differential cleavage, or stability, of the stearoyl- and oleoyl-containing fragments. Strong similarities exist between the observed spectra for the diacyl glycerylphosphorylcholines and those for the corresponding glycerides.

Chemical Phenomena↗
PubMed1968

Lipogenesis in human adipose tissue.

The pathways and some critical enzymes involved in lipogenesis in adipose tissue from 82 patients have been studied. Of the glucose-(14)C metabolized to lipid by isolated adipose cells, approximately 0.6% was recovered in fatty acids and the rest in glyceride-glycerol. Palmitate-1-(14)C was readily incorporated into neutral lipid. Homogenates of human adipose tissue contained an active alpha-glycerophosphate dehydrogenase which was approximately twice as active as malate dehydrogenase. Mitochondria of human adipose tissue contained an NAD-independent alpha-glycerophosphate dehydrogenase; the reaction product, di-hydroxyacetone phosphate, was recovered extramitochondrially. Homogenates of human adipose tissue also contained an active fatty acyl CoA synthetase which required ATP, CoA, and Mg(++) for maximal activity. The activity of acyl CoA synthetase varied greatly in a group of 40 patients. By contrast, the range of activity of malate dehydrogenase assayed in the same group of patients was much smaller. When palmitate or palmitoyl CoA was used as substrate, no difference was found in the rate of incorporation of alpha-glycerol-1,3-(14)C phosphate into neutral lipid. If time was allowed for activation of palmitate, the incorporation of alpha-glycerol-1,3-(14)C phosphate into lipid was 3.5 times greater than for unactivated palmitate. Palmitate (200 mM) stimulated lipogenesis in homogenates of human adipose tissue and then caused a severe inhibition at 700 mM. Arachidate over the same concentration range did not depress lipogenesis below initial values.

Adenosine Triphosphate↗
PubMed1968

Specific distribution of short-chain fatty acids in molecular distillates of bovine milk fat.

Triglycerides with a total of 34-44 acyl carbon atoms have previously been shown to account for nearly 50% of bovine milk fat. About 80% of this material was isolated by molecular distillation and a representative fraction of these glycerides was subjected to a stereospecific analysis. Of the 29 moles % of C(4)-C(8) fatty acids present in the analyzed fraction, at least 95% were specifically attached to the glycerol molecule in the position corresponding to carbon 3 of sn-glycerol 3-(dihydrogen phosphate) (L-alpha-glycerophosphate). The distribution of the other fatty acids (C(10) or greater) did not show such marked specificity for either the 1- or the 2-position. The data support the hypothesis that the short-chain fatty acids are esterified with long-chain diglycerides, or are substituted in glycerophosphatide intermediates, during the final step in the biosynthesis of milk fat triglycerides.

Animals↗
PubMed1966

Metabolism of phytol-U-14C and phytanic acid-U-14C in the rat.

The metabolism of uniformly-labeled (14)C-phytol, (14)C-phytenic acid, and (14)C-phytanic acid was studied in the rat. Conversion of both phytol and phytenic acid to phytanic acid was demonstrated. Tracer doses of phytol-U-(14)C given orally were well absorbed (30-66%), and approximately 30% of the absorbed dose was converted to (14)CO(2) in 18 hr. After intravenous injection, 20% appeared in (14)CO(2) in 4 hr. Phytanic acid-U-(14)C given intravenously was oxidized at a comparable rate (22-37% in 4 hr) and was as rapidly oxidized as palmitic acid-1-(14)C (21% in 4 hr). Metabolism of these substrates was also studied in rats previously maintained on a diet containing 5% phytol by weight, which causes accumulation of phytanic acid, phytenic acid, and, to a lesser extent, phytol in blood and tissues. Despite the large body pools of preformed, unlabeled substrate in these animals, the fraction of an administered dose of phytol-U-(14)C or phytanic acid-U-(14)C converted to (14)CO(2) was not significantly diminished. These studies indicate that the rat has an appreciable capacity to degrade the highly branched carbon skeleton of phytol and its derivatives. Twenty-four hours after administration of phytol-U-(14)C, the lipid radioactivity remaining in the body was widely distributed among the tissues, highest concentrations being found in liver and adipose tissue. Four hours after intravenous administration of phytanic acid-U-(14)C, all of the major lipid classes in the liver contained radioactivity, most in triglycerides and phospholipids and least in cholesterol esters and lower glycerides. There was no demonstrable incorporation of mevalonate-2-(14)C or acetate-1-(14)C into liver phytanic acid when they were given intravenously to a rat previously fed phytol. Endogenous biosynthesis, if it occurs at all, must be extremely limited.

Adipose Tissue↗
PubMed1967

Effects of insulin on glucose metabolism in isolated human fat cells.

Isolated fat cells were used for the study of in vitro effects of insulin on glucose metabolism in human and rat adipose tissue. In human subcutaneous fat cells, effects of insulin could be detected at concentrations of glucose in the medium from 1 to 10 micro moles/ml. Cellular responsiveness was inversely proportional to the glucose level. At a constant concentration of 6 micro moles of glucose per ml, the effects of insulin at various concentrations up to 500 micro U/ml were investigated. At the highest concentration, which gave the maximal response, there was a 100% increase in the conversion of glucose-U-(14)C to glyceride-glycerol and a 40% increase in glucose oxidation. The dose-response curve was steepest between 2 and 20 micro U/ml. Rat epididymal fat cells were much more responsive to insulin. Glucose lipogenesis and pentose cycle activity could also be demonstrated in rat cells, whereas these activities could not be shown in fat cells from human omental and subcutaneous tissue. The findings for human cells are attributed to changes in cellular activity during preparation.

Adipose Tissue↗
PubMed1983

Extent of retention of 2-monoglyceride backbone of diet fat in alcohol-induced fatty liver.

This study was carried out to determine whether hepatic triglyceride (TG) synthesis is a major determinant in the development of fatty liver induced by chronic ethanol ingestion. For this purpose, the degree to which the 2-monoglyceride (MG) backbone of dietary fat was retained in the accumulated TG of fatty liver was examined. Triglycerides were isolated from diet and from the liver and plasma of rats maintained for four weeks on a Lieber-DeCarli liquid ethanol diet. Pancreatic lipase hydrolysis of the TG from these three sources was carried out and the MG produced was analyzed for the fatty acid composition. Almost all of TG in fatty liver and that released to plasma retained the MG structure which originated from diet fat. This result demonstrates that the de novo glyceride synthesis or transacylation reactions do not have a major role in the production of TG in alcohol-induced fatty liver.

Animals↗
PubMed1984

Influence of diet on de novo lipogenesis in artificially-fed 15- and 20-day-old Zucker fatty rats.

Lean and obese Zucker rat pups were artificially fed high-fat and high-carbohydrate diets from 10-20 d of age to determine the effect of early diet composition on de novo lipogenesis and the development of obesity in the Zucker fatty rat. Amounts fed were the same as that consumed by suckling Zucker rat pups, which also were used as dam-fed controls. Lipogenic rates were measured by in vivo incorporation of tritium from 3H2O into total lipids and fatty acid and glyceride-glycerol fractions of liver, carcass and adipose tissue. Expressed on a per g tissue basis there was no difference in lipogenic rates between lean and obese pups in any tissues, even though pups accumulated a significantly higher percentage of carcass fat. High carbohydrate feeding accelerated growth and lipogenic rates in both lean and obese rats. Dam-fed pups had the lowest rates of lipogenesis and percentage of carcass fat. Thus, diet composition and method of feeding were important determinants of de novo lipogenic rates and body energy stores at this early age, but their influence was similar in lean and genetically obese animals.

Adipose Tissue↗
PubMed1982

Characterization of serum and liver lipids of gallstone-forming humans.

Liver biopsy and serum specimens obtained from patients with cholesterol gallstones and from a control group were analysed for their different lipids and lipoprotein fractions. The ratio of free cholesterol to esterified cholesterol (CF/CE) was significantly (P less than 0.001) higher in the livers of gallstone-forming patients. There was no significant difference in the levels of total lipids, total cholesterol, phospholipids and glycerides. Beta-lipoprotein fraction (LDL) was higher in gallstone-forming patients. It is concluded that the decrease in esterified cholesterol of gallstone-formers may provide an important clue to an understanding of the physiology and chemistry of stone-formation in humans.

Cholelithiasis↗
PubMed1993

Elongation, desaturation, and esterification of essential fatty acids by fetal rat brain in vivo.

Tracer amounts of either [1-14C]linolenic (18:3n-3, LNA), or [1-14C]linoleic (18:2n-6, LA) acids were intracranially injected into 19- to 20-day-old rat fetuses, and the time course of the in vivo formation and esterification of their long chain polyenoic metabolites was determined for up to 20 h. A rapid disappearance of free LNA and LA, with apparent half-lives of 60 and 40 min, respectively, was noticed. One hour after LNA injection, 32.3% and 14.3% of the total brain radioactivity was found in the neutral glyceride (NG) and phospholipid (PL) fractions, respectively. After 20 h, PL radioactivity attained a level of 75%. Phosphatidylcholine (PC), diacylglycerol (DG), and triacylglycerol (TG) constituted 40%, 23%, and 9% of the total brain label at 1 h, and 35%, 10% and 14% at 20 h, respectively. Ethanolamine-containing PL (including plasmalogen) radioactivity accounted for about 10% up to 6 h and increased nearly 3-fold at 20 h, primarily due to an increase in the amount of labeled docosapentaenoic and docosahexaenoic acids (DHA), the elongation-desaturation products of LNA. A similar pattern of incorporation into NG and PL fraction was observed after the administration of [1-14C]LA. After 1 h, PC, DG, and TG species constituted 23%, 10%, and 23% of the total brain radioactivity, whereas after 20 h it accounted for 44%, 6%, and 10%, respectively. Although radioactivity in the ethanolamine PL also increased substantially from 4% at 1 h to 29% at 20 h, the main labeled fatty acid in this fraction was LA. Labeled arachidonic acid (AA) constituted 42.7% of the total radioactivity in phosphatidylinositol (PI) at 20 h. At this time, it comprised 12.5% and 14% of the total radioactivity in PC and ethanolamine PL, respectively, suggesting a high degree of esterification selectivity. Comparison of the total amounts of LA and LNA and their corresponding labeled AA and DHA metabolites in brain and liver after 3 and 6 h indicated that the contribution of liver metabolism to the elongation-desaturation under these conditions was negligible. One hour after intracerebral injection of [3H]DHA (22:6n-3) or [3H]AA (20:4n-6), 29.2% and 12% of total radioactivity, respectively, was found in the ethanolamine PL while 20% and 40% was incorporated in PC, respectively. PI labeling by [3H]AA was 6- to 8-fold higher than that seen in the presence of DHA. A high percent of radioactivity (26.9% and 18.2%) was found in DG and TG species.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetyltransferases↗
PubMed1994

Pancreatic lipase assays with triglycerides as substrate: contribution of each sequential reaction to product formation.

Human pancreatic lipase assays are usually performed in the presence of either emulsified triglycerides or diglycerides within the limits of their solubility. Two reactions are catalyzed in the presence of triglycerides: hydrolysis of triglycerides to diglycerides, and diglycerides to monoglycerides. The contribution of each reaction to the final result was determined after extensive kinetic studies on the appearance and/(or) accumulation of intermediates and/(or) products. Acylated glycerides were analyzed after extraction from the reaction mixture, separation of lipid classes by thin-layer chromatography, and quantification by capillary gas chromatography. The results show that after 10 min of reaction in the presence of high concentrations of triolein, 75% of the released fatty acids arise from the first reaction. Relative merits and disadvantages of each substrate (triglyceride or diglyceride) are discussed in terms of practicability.

Acylation↗
PubMed1977

Lipids from subcellular fractions of the tegument of Hymenolepis diminuta.

Lipids comprised 37% and 22.1%, respectively, of the day weights of brush border- and vesicle-rich fractions separated by differential centrifugation of isolated H. diminuta tegument. Neutral lipids of both fractions were rich in cholesterol, but also contained small amounts of glycerides, sterol esters, and (in brush borders) free fatty acids. Phosphatidyl ethanolamine was the most prevalent polar lipid in both fractions, and was particularly abundant (63.4% of total polar lipids) in vesicles; sphingomyelin, not previously reported from H. diminuta, was also present. Polar lipids of both tegumental fractions resembled each other but differed from whole worm polar lipids in fatty acid composition. Tegumental polar lipids contained lower levels of long-chain, polyunsaturated fatty acids than reported for corresponding lipids of whole worms.

Cestoda↗
PubMed1976

Lipids of two Cassia species and Datura stramonium seeds.

The fatty acid constitution of three seed-oils, namely, Cassia alexandrina, Cassia italica and Datura stramonium, were carried out using gas chromatographic analysis. The glyceride structure of these oils was computed using the technique of pancreatic lipase hydrolysis. The phospholipids fraction of these oils were identified using thin layer chromatography, also the fatty acid constitution of the phosphilipids were determined quantitatively by gas liquid chromatography.

Fatty Acids↗
PubMed1976

Factors affecting fatty acid oxidation in fat cells isolated from rat white adipose tissue.

Fat cells isolated from rat epididymal adipose tissue were incubated with albumin-bound [14C]palmitate. Incorporation of 14C into 14CO2 and glycerides was measured. Some evidence is presented to suggest that the exogenous palmitate pool is in isotopic equilibrium with intracellular precursors for these metabolic processes. Precautions were taken to minimize dilution of the exogenous palmitate pool by fatty acids released from the cells. 14CO2 production from [1-14C]palmitate was 3 times that from [16-14C]palmitate. Octanoate increased this differential oxidation of palmitate carbons and also inhibited palmitate oxidation without similarly affecting esterification. Glucose increases palmitate esterification in cells from fed or starved rats. Insulin potentiated this effect of glucose. Glucose influenced palmitate oxidation in a more complex manner, dependent upon the glucose concentration. Both the observation that esterification constitutes 99% of the metabolic flux of fatty acid and the manner in which glucose, insulin, or starvation influence palmitate esterification and oxidation suggested that factors controlling esterification may alter oxidation as a secondary effect, but not vice versa. It is suggested that oxidation and esterification compete for a single intracellular precursor, possibly extramitochondrial long chain fatty acyl CoA.

Adipose Tissue↗
PubMed1997

Lipid composition in epithelium and stroma of human benign prostatic hyperplasia.

The lipid composition and concentration in human benign prostatic hyper-plasia (BPH) were investigated. The reason was to shed some light onto the lipid environment of cellular membranes, in which the epithelial and stromal 5 alpha-reductase of the human prostate have apparently to be embedded in order to gain an active state. The phospholipids were found to be the major portion (67% +/- 1.1) of total lipids in whole BPH homogenate, followed by cholesterol (29% +/- 1.1) and glyceride glycerols (4% +/- 0.9). In BPH epithelium, the lipid concentration related to wet weight and to protein was two to three-fold higher than in stroma. Assigning the lipid concentration on a per-cell basis (i.e., related to DNA), a significantly lower lipid concentration was found in the epithelium as compared to the stroma. In the stroma, a significantly higher phospholipid and lower cholesterol portion were found than in the epithelium. Moreover, sphingomyelin was found to comprise a higher portion in stromal than in epithelial phospholipids, whereas the percentage of phosphatidylserine was higher in the epithelial phospholipids. We discuss whether the significant differences in lipid concentration and composition between the epithelium and stroma of human BPH could have an impact on the activity of the membrane-bound 5 alpha-reductase, or whether such differences in the lipid environment are due to a different hormonal milieu in the epithelium and stroma of BPH.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1999

Hydrolysis of menhaden oil by a Candida cylindracea lipase immobilized in a hollow-fiber reactor.

A lipase from Candida cylindracea immobilized by adsorption on microporous polypropylene fibers was used to selectively hydrolyze the saturated and monounsaturated fatty acid residues of menhaden oil at 40 degrees C and pH 7.0. At a space time of 3.5 h, the shell and tube reactor containing these hollow fibers gives a fractional release of each of the saturated and monounsaturated fatty acid residues (i.e., C14, C16, C16:1, C18:1) of ca. 88% of the corresponding possible asymptotic value. The corresponding coproduct glycerides retained over 90% of the initial residues of both eicosapentaenoic (EPA; C20:5) and docosahexaenoic (DHA; C22:6) acids. The half-life of the immobilized lipase was 170 h when the reactor was operated at the indicated (optimum) conditions. Rate expressions associated with a generic ping-pong bi-bi mechanism were used to fit the experimental data for the lipase catalyzed reaction. Both uni- and multiresponse nonlinear regression methods were employed to determine the kinetic parameters associated with these rate expressions. The best statistical fit of the uniresponse data was obtained for a rate expression, which is formally equivalent to a general Michaelis-Menten mechanism. After reparameterization, this rate expression reduced to a pseudo-first-order model. For the multiresponse analysis, a model that employed a normal distribution of the ratio of Vmax/Km with respect to the chain length of the fatty acid residues provided the best statistical fit of the experimental data.

Bioreactors↗
PubMed1999

Biotechnology for the production of nutraceuticals enriched in conjugated linoleic acid: I. Uniresponse kinetics of the hydrolysis of corn oil by a pseudomonas sp. lipase immobilized in a hollow fiber reactor

The kinetics of the hydrolysis of corn oil in the presence of a lipase from Pseudomonas sp. immobilized within the walls of a hollow fiber reactor can be modeled in terms of a three-parameter rate expression. This rate expression consists of the product of a two-parameter rate expression for the hydrolysis reaction itself (which is of the general Michaelis-Menten form) and a first-order rate expression for deactivation of the enzyme. Optimum operating conditions correspond to 30 degrees C and buffer pH values of 7.0 during both immobilization of the enzyme and the hydrolysis reaction. Under these conditions, the total fatty acid concentration in the effluent oil stream for a fluid residence time of 4 h is approximately 1.6 M. This concentration corresponds to hydrolysis of approximately 50% of the glyceride bonds present in the feedstock corn oil. The fatty acid of primary interest in the effluent stream is linoleic acid. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗
PubMed2000

Effect of pH on the production of lipolyzed butter oil by a calf pregastric esterase immobilized in a hollow-fiber reactor: I. uniresponse kinetics.

A calf pregastric esterase immobilized in a hollow-fiber reactor was employed to hydrolyze milkfat, thereby producing a lipolyzed butteroil. The reaction kinetics can be modeled by a two-parameter model of the general Michaelis-Menten form based on a ping-pong bi-bi mechanism; the rate of enzyme deactivation can be modeled as a first-order reaction. The initial concentration of accessible glyceride bonds, [G](O), was estimated by complete saponification of the substrate butteroil as 2400 mM. An extra sum of squares test indicated that not only the parameters of the kinetic generalized Michaelis-Menten model, but also the deactivation-rate constant varied significantly with pH. The optimum pH, for lypolysis is near 6.0 at a temperature of 40 degrees C because at this pH the rate of deactivation of the esterase is minimized.

Animals↗
PubMed2000

Intestinal permeation enhancers.

This review addresses the field of improving oral bioavailability through the use of excipients that increase intestinal membrane permeability. The critical issues to consider in evaluating these approaches are 1) the extent of bioavailability enhancement achieved, 2) the influence of formulation and physiological variables, 3) toxicity associated with permeation enhancement, and 4) the mechanism of permeation enhancement. The categories of permeation enhancers discussed are surfactants, fatty acids, medium chain glycerides, steroidal detergents, acyl carnitine and alkanoylcholines, N-acetylated alpha-amino acids and N-acetylated non-alpha-amino acids, and chitosans and other mucoadhesive polymers. Some of these approaches have been developed to the stage of initial clinical trials. Several seem to have potential to improve oral bioavailabilities of poorly absorbed compounds without causing significant intestinal damage. In addition, the possible use of excipients that inhibit secretory transport is reviewed.

Animals↗