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PubMed2001

Hydrophobic ligand binding by Zn-alpha 2-glycoprotein, a soluble fat-depleting factor related to major histocompatibility complex proteins.

Zn-alpha(2)-glycoprotein (ZAG) is a member of the major histocompatibility complex (MHC) class I family of proteins and is identical in amino acid sequence to a tumor-derived lipid-mobilizing factor associated with cachexia in cancer patients. ZAG is present in plasma and other body fluids, and its natural function, like leptin's, probably lies in lipid store homeostasis. X-ray crystallography has revealed an open groove between the helices of ZAG's alpha(1) and alpha(2) domains, containing an unidentified small ligand in a position similar to that of peptides in MHC proteins (Sanchez, L. M., Chirino, A. J., and Bjorkman, P. J. (1999) Science 283, 1914-1919). Here we show, using serum-derived and bacterial recombinant protein, that ZAG binds the fluorophore-tagged fatty acid 11-(dansylamino)undecanoic acid (DAUDA) and, by competition, natural fatty acids such as arachidonic, linolenic, eicosapentaenoic, and docosahexaenoic acids. Other MHC class I-related proteins (FcRn, HFE, HLA-Cw*0702) showed no such evidence of binding. Fluorescence and isothermal calorimetry analysis showed that ZAG binds DAUDA with K(d) in the micromolar range, and differential scanning calorimetry showed that ligand binding increases the thermal stability of the protein. Addition of fatty acids to ZAG alters its intrinsic (tryptophan) fluorescence emission spectrum, providing a strong indication that ligand binds in the expected position close to a cluster of exposed tryptophan side chains in the groove. This study therefore shows that ZAG binds small hydrophobic ligands, that the natural ligand may be a polyunsaturated fatty acid, and provides a fluorescence-based method for investigating ZAG-ligand interactions.

Binding Sites↗
PubMed1983

Lipid deposition in different fiber types of skeletal muscle of periparturient dairy cows.

The intracellular deposition of neutral lipid in skeletal muscle of dairy cows before and after calving has been studied in biopsy samples taken from 72 cows in three herds. The amounts of neutral lipid in individual fibers were estimated using Oil red O-stained sections and an average value was calculated for each fiber type within a sample. Intracellular lipid deposition occurred mainly in type 1 fibers and reached its highest level one week after calving. The amount of lipid in muscle at this time showed a high correlation with the amount of lipid in liver and with the rate of lipid mobilization from tissue reserves.

Animals↗
PubMed1988

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced alterations in lipid peroxidation, enzymes, and divalent cations in rat testis.

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) produces atrophy, morphological changes, impaired spermatogenesis, and epididymal lesions in testis of experimental animals. The effects of TCDD administration to male rats on various parameters in the testes were examined. 2. Nine days after TCDD administration, significant decreases in body and testes weights occurred. However, the testes weight as a percent of body weight was higher in treated than control animals. 3. An increase in lipid peroxidation (content of thiobarbituric acid reactive substances) occurred in conjunction with the decrease in testicular weights. 4. TCDD administration produced a 3-fold increase in protein kinase C activity, small but significant decrease is superoxide dismutase and glutathione peroxidase activities, and no effect on catalase, glutathione reductase or glutathione S-transferase activities in the testes. 5. Nine days after treatment with TCDD, in the testes the iron content of whole tissue and cytosol increased while a decrease in microsomal iron was observed. The copper content of mitochondria and microsomes decreased with a corresponding increase in cytosol copper content. A small increase in the zinc content of whole testes occurred. 6. The data indicate that testicular atrophy due to TCDD may be associated with lipid mobilization and peroxidation.

Animals↗
PubMed1995

Differences in fat balance underlying obesity.

Energy balance occurs under free-living conditions when macronutrient balance is achieved (i.e., the intake of each macronutrient corresponds to its use). Among the components of macronutrient balance, fat balance is the one which is at greater risk of large deviations because of a reduced potential of fat to decrease food intake acutely and to promote its oxidation. This may represent a problem for individuals predisposed to obesity who are characterized by an increased taste preference for fat and a reduced capacity to oxidize fat when their body weight is normal. When these individuals are exposed to a lifestyle favouring a positive fat balance, a greater demand is imposed on sympathetic nervous system activity which is stimulated by hyperinsulinaemia. Accordingly, muscle sympathetic nerve activity (MSNA) is greater in obese hyperinsulinaemic individuals in the basal state, whereas they display a blunted response in MSNA to the acute administration of insulin. In this context, where the ability to further stimulate sympathetic activity is low, fat gain and its related increased lipid mobilization and oxidation remain the ultimate means to restore fat balance.

Body Composition↗
PubMed1969

Respiratory changes during seed germination. Histological distribution of respiratory enzymes and mobilization of fat reserves in castor bean endosperm and peanut cotyledons.

Germinating peanut cotvledons and germinating castor bean endosperm have been compared with respect to their rates of fat dissimilation and with respect to the anatomical distribution of respiratory activity. The lipid mobilization is much slower in peanut cotyledons than in castor bean endosperm. Light has essentially no effect on either system. As germination progresses, the majority of the succinic dehydrogenase and cytochrome oxidase activities become localized in the vein regions of peanut cotyledons. In the castor bean endosperm these two activities are uniformly distributed throughout the storage parenchyma and increase with germination until the organ becomes soft and visibly senescent.

Arachis↗
PubMed2004

Organochlorine contaminants in sea turtles: correlations between whole blood and fat.

Monitoring toxic organochlorine (OC) compounds is an important aspect in wildlife studies, especially in protected species such as sea turtles. The goal of this study was to determine whether blood OC concentrations can predict those in adipose tissue of sea turtles. Blood offers many benefits for monitoring OCs. It can be collected nondestructively from live turtles and can be sampled repeatedly for continuous monitoring. Organochlorine concentrations in blood may better represent the exposure levels of target tissues, but blood concentrations may fluctuate more than those in fatty tissues following recent dietary exposure or lipid mobilization. Paired fat and blood samples were collected from 44 live, juvenile loggerhead sea turtles and 10 juvenile Kemp's ridley sea turtle carcasses. Organochlorines were analyzed using gas chromatography with electron capture detection and mass spectrometry. Lipid-normalized OC concentrations measured in the blood significantly correlated to levels found in the fat samples of both species. This result suggests that sea turtle blood is a suitable alternative to fatty tissues for measuring OCs because blood concentrations reasonably represent those observed in the paired fat samples. However, blood OC concentrations calculated on a wet-mass basis were significantly and inversely correlated to lipid content in the fat samples. Therefore, caution should be used when monitoring spatial or temporal trends, as OC levels may increase in the blood following mobilization of fat stores, such as during long migrations, breeding, or disease events.

Adipose Tissue↗
PubMed2003

The effect of lipid demixing on the electrostatic interaction of planar membranes across a salt solution.

We study the effect of lipid demixing on the electrostatic interaction of two oppositely-charged membranes in solution, modeled here as an incompressible two-dimensional fluid mixture of neutral and charged mobile lipids. We calculate, within linear and nonlinear Poisson-Boltzmann theory, the membrane separation at which the net electrostatic force between the membranes vanishes, for a variety of different system parameters. According to Parsegian and Gingell, contact between oppositely-charged surfaces in an electrolyte is possible only if the two surfaces have exactly the same charge density (sigma(1) = -sigma(2)). If this condition is not fulfilled, the surfaces can repel each other, even though they are oppositely charged. In our model of a membrane, the lipidic charge distribution on the membrane surface is not homogeneous and frozen, but the lipids are allowed to freely move within the plane of the membrane. We show that lipid demixing allows contact between membranes even if there is a certain charge mismatch, /sigma(1)/ not equal /sigma(2)/, and that in certain limiting cases, contact is always possible, regardless of the value of sigma(1)/sigma(2) (if sigma(1)/sigma(2) < 0). We furthermore find that of the two interacting membranes, only one membrane shows a major rearrangement of lipids, whereas the other remains in exactly the same state it has in isolation and that, at zero-disjoining pressure, the electrostatic mean-field potential between the membranes follows a Gouy-Chapman potential from the more strongly charged membrane up to the point of the other, more weakly charged membrane.

Adsorption↗
PubMed2003

Parameterized evaluation of macromolecules and lipids in proton MR spectroscopy of brain diseases.

Short echo time (TE) proton MR spectra of the brain include signals of several metabolites as well as macromolecules. In various pathologies, such as brain tumors and multiple sclerosis (MS), the presence of mobile lipids or pathologically altered macromolecules may provide useful additional diagnostic information. A reliable quantitation of these resonances, however, is often not possible due to the lack of adequate prior knowledge. Furthermore, even if advanced fitting procedures are used, a reliable evaluation of metabolites in the presence of pathological lipids or macromolecules often fails if the latter are omitted in the spectral evaluation. In this study, a method is presented for the simultaneous evaluation of all visible components, including metabolites, lipids, and macromolecules, by the use of the fitting procedure LCModel. A standard basis set of brain metabolites was extended by inclusion of parameterized components for macromolecules and lipids that were derived from metabolite-nulled in vivo spectra of normal brain and high-grade gliomas, respectively. The improved spectral quantitation is demonstrated in glial brain tumors and MS lesions as well as in normal brain. It is pointed out that both macromolecules and lipids must be included to provide a proper spectral evaluation.

Brain Chemistry↗
PubMed1993

Carbon-13 "magic-angle" sample-spinning nuclear magnetic resonance studies of human myelin, and model membrane systems.

We have obtained high-field (11.7 Tesla), high-resolution carbon-13 solid-state "magic-angle" sample-spinning nuclear magnetic resonance (NMR) spectra of a variety of phospholipids, sphingolipids, myelin and white matter samples, resolving and assigning over 40 resonances in the spectra of human and bovine myelin. The NMR results indicated no large spectral changes due to sample preparation, sample freezing, or brain location, and also no changes in myelin structure detectable via light microscopy, electron microscopy, thin layer chromatography, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, attributable to the sometimes lengthy NMR data acquisition process. Human myelin and white matter chemical shift assignments were made based on 13C "magic angle" sample spinning (MAS) NMR spectra of individual model lipids, as well as on spectra of lipid mixtures. In all myelin samples there were essentially no features attributable to membrane proteins, with the exception of one small feature due to C zeta of Arg residues, primarily in the myelin basic proteins. The general similarity between the model lipid and intact myelin spectra suggested no major effects of protein on lipid mobility. We have also investigated human myelin samples as a function of developmental age (4, 15, 48 months and adult), and our results showed only small changes in overall lipid composition, although there were significant decreases in lipid hydrocarbon chain unsaturation with age, as determined by computer line-shape simulations of myelin and model compounds. The spectrum of an infant leukoencephalopathy myelin showed marked decreases in galactocerebrosides. Overall, the ability to resolve and assign over 40 resonances in the 13C MAS NMR spectra of myelin, and to detect changes as a function of development and disease, should provide a useful starting point for further more detailed studies of myelin membrane molecular motions, and function.

Adult↗
PubMed1996

Growth hormone-induced insulin resistance and its relationship to lipid availability in the rat.

The role of increased lipid availability in the generation of insulin resistance by growth hormone has not been established. We investigated this in rats infused with saline (controls) or human growth hormone (hGH) (500 micrograms x kg-1 x 24 h-1) for 5 h or 3 days. hGH infusion increased basal plasma insulin at 5 h (335 +/- 33 vs. 197 +/- 15 [controls]; P < 0.005) and at 3 days (396 +/- 34 vs. 218 +/- 14 pmol/l; P < 0.0001). Plasma nonesterified fatty acid (0.26 +/- 0.01 vs. 0.21 +/- 0.01 [controls] g/l) and liver long-chain acyl-CoA (21.2 +/- 1.9 vs. 14.1 +/- 1.1 [controls] nmol/g wet wt) were elevated at 5 h (P < 0.01 for both) but were below control levels after 3 days of hGH infusion (P < 0.01 for both); indirect calorimetry after 3 days demonstrated decreased lipid oxidation. Clamp studies showed similar degrees of peripheral insulin resistance at 5-h and 3-day hGH infusion (glucose disposal reduced by 25% versus controls). Insulin-stimulated glucose metabolic index (Rg') in red gastrocnemius muscle (red muscle) was reduced (P < 0.05 and P < 0.01) at 5 h and 3 days of hGH infusion, respectively (e.g., 5 h, 10.0 +/- 1.8 vs. 24.1 +/- 4.4 [controls] micromol x 100 g-1 x min-1), whereas insulin-mediated muscle glycogen synthesis was reduced (P < 0.03) only in rats infused with hGH for 3 days. We conclude that in the rat, hGH rapidly induces persistent peripheral insulin resistance and basal hyperinsulinemia. However, the transient nature of increased lipid mobilization suggests that it is not an important factor in the manifestation of muscle insulin resistance during prolonged hGH elevation. The persistent insulin resistance is not associated with increased lipid oxidation but is associated with hyperinsulinemia and reduced insulin-mediated muscle glycogen synthesis.

Adipose Tissue↗
PubMed2004

Tumor-host interactions.

A number of malignant tumors interact with the host to cause a syndrome of cachexia, characterized by extensive loss of adipose tissue and skeletal muscle mass, but with preservation of proteins in visceral tissues. Although anorexia is frequently present, the body composition changes in cancer cachexia cannot be explained by nutritional deprivation alone. Loss of skeletal muscle mass is a result of depression in protein synthesis and an increase in protein degradation. The main degradative pathway that has been found to have increased expression and activity in the skeletal muscle of cachectic patients is the ubiquitin-proteasome proteolytic pathway. Cachexia-inducing tumors produce catabolic factors such as proteolysis-inducing factor (PIF), a 24 kDa sulfated glycoprotein, which inhibit protein synthesis and stimulate degradation of intracellular proteins in skeletal muscle by inducing an increased expression of regulatory components of the ubiquitin-proteasome proteolytic pathway. While the oligosaccharide chains in PIF are required to initiate protein degradation the central polypeptide core may act as a growth and survival factor. Only cachexia-inducing tumors are capable of elaborating fully glycosylated PIF, and the selectivity of production possibly rests with the acquisition of the necessary glycosylating enzymes, rather than expressing the gene for the polypeptide core. Loss of adipose tissue is probably the result of an increase in catabolism rather than a defect in anabolism. A lipid mobilizing factor (LMF), identical with the plasma protein Zn-alpha2-glycoprotein (ZAG) is found in the urine of cachectic cancer patients and is produced by tumors causing a decrease in carcass lipid. LMF causes triglyceride hydrolysis in adipose tissue through a cyclic AMP-mediated process by interaction with a beta3-adrenoreceptor. Thus, by producing circulating factors certain malignant tumors are able to interfere with host metabolism even without metastasis to that particular site.

Adipose Tissue↗
PubMed2003

Metabolism of hydrogen peroxide during reserve mobilization and programmed cell death of barley (Hordeum vulgare L.) aleurone layer cells.

During germination, aleurone layer cells of barley (Hordeum vulgare) grains synthesize and secrete hydrolytic enzymes (principally alpha-amylase) in response to gibberellic acid (GA); shortly thereafter, the aleurone layer cells undergo programmed death. Gluconeogenesis of lipid reserves within aleurone cells, which supports this hydrolytic enzyme synthesis, results in the generation of H(2)O(2), which is catabolized by glyoxysomal catalase. Lowered amounts of catalase may contribute to aleurone cell death because of a compromised capacity to cope with reactive oxygen species generated by glyoxysomes and mitochondria. In the presence of GA, cells of intact aleurone layers underwent programmed death between 18 and 48 h; in the presence of ABA, no cell death was evident over 60 h. The capacity of GA-treated layers to metabolize exogenous H(2)O(2) increased steadily over the first 24 h, during the stage of lipid mobilization and the major synthesis and secretion of alpha-amylase; thereafter, this capacity declined markedly. In contrast, cells of ABA-treated aleurone layers exhibited little change in their capacity for H(2)O(2)-metabolism. Glyoxysomal catalase increased in activity over the first 12-24 h of GA treatment, which was accompanied by an increase in catalase-1 transcripts between 12 and 18 h. Catalase protein and activity declined after 24 h in GA-treated layers, prior to the onset of rapid programmed death at 30 h. These data suggest that a decline in glyoxysomal catalase precedes death of aleurone cells and may indeed contribute to an increase in cellular oxidative stress.

Abscisic Acid↗
PubMed1979

Roles for insulin and glucagon in the development of ruminant ketosis -- a review.

Ketonemia can be a physiological response to a reduction in dietary intake. It also may occur when energy demands exceed the energy intake. Normally, alimentary ketogenesis is the major source of ketone bodies in ruminants. During ketonemia there is increased hepatic ketone body production. During physiological ketosis, the mobilization of free fatty acids is inadequate to support a high rate of hepatic ketogenesis. However, during clinical ketosis, the hormonal status (low insulin, high glucagon/insulin ratio) in combination with hypoglycemia promotes excessive lipid mobilization and a greater hepatic removal of fatty acids and switches the liver to a higher rate of ketogenesis. The low insulin, furthermore, can impair maximal ketone body utilization, thus exacerbating the hyperketonemia.

Acidosis↗
PubMed1993

Anomalously slow mobility of fluorescent lipid probes in the plasma membrane of the yeast Saccharomyces cerevisiae.

We measured the lateral mobility of two fluorescent lipid probes dioctadecylindocarbocyanine (diI) and tetramethyl rhodamine phosphatidylethanolamine (R-PE) in the plasma membranes of Saccharomyces cerevisiae ino1 and opi3 spheroplasts. These are well-characterized strains with mutations in the inositol and phosphatidylcholine biosynthetic pathways. Membrane phospholipid composition was altered by growing these mutants in the presence or absence of inositol and choline. Lateral mobility was measured by fluorescence recovery after photobleaching (FRAP). Microscopic fluorescence polarization employing CCD digital imaging produced an ordered orientation distribution of the lipid probe diI, confirming that at least one of the probes was largely incorporated into the bilayer membrane. Our results demonstrated anomalously slow mobility of both lipid probes for both mutants, regardless of whether the lipid composition was near normal or dramatically altered in relative composition of phosphatidylinositol and phosphatidylcholine. Trypsinization of the spheroplasts to remove surface proteins resulted in markedly increased lateral mobility. However, even in trypsinized spheroplasts, mobility was still somewhat lower than the mobility observed in the membrane of mammalian cells, such as rat smooth muscle culture cells tested here for comparison.

Carbocyanines↗
PubMed1989

Lipid metabolism in shorn and unshorn pregnant sheep.

The aim of the present study was to determine how the long-term metabolic adaptations to winter shearing of the pregnant ewe result in significant changes in the rates of lipid mobilization and utilization of non-esterified fatty acids (NEFA) in comparison with unshorn controls. Continuous infusions of [1-14C]palmitic acid, [2-3H]glycerol and NaH14CO3 were used to measure whole-body lipid metabolism in fed (estimated metabolizable energy (ME) intake 9.54 MJ/d) and under-fed (estimated ME intake of 3 MJ/d), shorn and unshorn sheep over the final 4 weeks of pregnancy. Whole-body carbon dioxide, estimated heat production, total NEFA entry and oxidation rates were all significantly higher in fed shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma NEFA concentration. These differences may be mediated via an increase in the plasma concentrations of thyroid hormones in shorn animals. As a result of under-feeding any significant differences in lipid metabolism between shorn and unshorn groups were removed. In all sheep the mean total NEFA entry rate as measured using [1-14C]palmitic acid was 3.4 times the value obtained using [2-3H]glycerol. It is concluded that when sheep are fed on a diet from which no more than half the required ME for late pregnancy is obtained, then lipolysis of body fat depots occurs via the incomplete breakdown of adipose tissue triglycerides. This effect is significantly greater in the fed shorn pregnant ewe which exhibits higher entry and oxidation rates of NEFA.

Adaptation, Physiological↗
PubMed1986

Effect of physical training in humans on the response of isolated fat cells to epinephrine.

Endurance training helps muscle tissue oxidize lipids and therefore helps conserve glycogen. It was thought interesting to find out if, in addition to this preferential use of fatty acids by muscle tissue, there is an increase in the capacity of adipose tissue to mobilize lipids. So the response to epinephrine of collagenase-isolated fat cells obtained after biopsies of fat performed in the periumbilical region of 10 trained marathon runners (T) and 10 sedentary subjects (S), all males, was studied in vitro. Glycerol release, chosen as adipocyte lipolysis indicator, was measured by bioluminescence. Lipolysis was studied with increased epinephrine concentration. This caused a significant increase in lipolysis only in the T subjects. The dose-response curves were significantly different for T and S subjects at 10(-6) M and above (P less than 0.05). To determine the modification mechanisms observed, lipolysis with isoproterenol and epinephrine plus propranolol were studied. Isoproterenol significantly increased lipolysis in both groups. The dose-response curves were significantly different at 10(-7) M (P less than 0.01) and above. In both groups, epinephrine plus propranolol significantly decreased lipolysis without distinction between T and S. It is concluded that in male subjects endurance training increases the sensitivity of subcutaneous abdominal adipose tissue to the lipolytic action of epinephrine; this effect seems to be related to an increased response of the beta-adrenergic pathways.

Adipose Tissue↗
PubMed1993

Yield and composition of milk from lactating mares: effect of body condition at foaling.

The yield and composition of milk from nursing mares were studied during the first 2 months of lactation in two groups of six and five saddle mares respectively made thin or fat before foaling, then fed ad lib. post partum. Milk yield did not significantly vary with body condition (16.5 and 15.4 kg/d for fat and thin mares respectively). Milk from fat mares had a higher fat content than milk from thin mares; the reverse was found for protein. The composition of milk fat was modified: milk of fat mares was poorer in short- and medium-chain fatty acids (C8-C14). Milk fat output was affected by body condition: 252 and 187 g/d for fat and thin mares respectively. This can be explained by a difference in lipid mobilization, as shown by variations in non-esterified fatty acids.

Animals↗
PubMed2005

Study of muscle regeneration using in vitro 2D 1H spectroscopy.

The in vivo spectrum of regenerating muscles shows a specific cross-correlation signal assigned to the (n-3) fatty acyl chain, which peaks during the myoblast fusion phase. In order to identify the origin of this signal and to take all the lipid metabolites into account, we investigated the degeneration-regeneration process by 1H 2D NMR of lipid muscle extracts. We observed an increase in the total amount of lipids during the regeneration process, although the lipid profile did not show any drastic change during this process. The changes in the NMR signal observed in vivo and, in particular, the appearance of the specific (n-3) fatty acyl chain signal appears to arise from mobile lipid compartments located in fusing cells.

Animals↗