Labeling of adipocyte membranes by sulfo-N-succinimidyl derivatives of long-chain fatty acids: Inhibition of fatty acid transport

Summary Sulfo-N-succinimidyl derivatives of the long-chain fatty acids, oleic and myristic, were synthesized and covalently reacted with isolated rat adipocytes. The plasma membrane proteins labeled by these compounds and the effect of labeling on the transport of long-chain fatty acids were investigated. Sulfo-N-succinimidyl oleate (SSO) and myristate (SSM) inhibited the transport of fatty acids (by about 70%). Inhibition of fatty acid transport was not a result of alterations in cell integrity, as intracellular water volume was not changed. It did not reflect effects on fatty acid metabolism, since it was observed under conditions where greater than 90% of the fatty acid taken up was recovered in the free form. The inhibitory effect was specific to the fatty acid transport system, as the transport of glucose and the permeation of retinoic acid, a substance with structural similarities to long-chain fatty acids, were unaffected. Sulfosuccinimidyl oleate reacted exclusively with a plasma membrane protein with an apparent size of 85 kDa while sulfosuccinimidyl myristate also labeled a 75-kDa while sulfosuccinimidyl myristate also labeled a 75-kDa protein. These proteins were among the ones labeled by diisothiocyanodisulfonic acid (DIDS) which also inhibits fatty acid transport irreversibly. The data suggest that the 85-kDa protein, which is the only one labeled by all three inhibitors is involved in facilitating membrane permeation of long-chain fatty acids.     

Uptake of glucose and release of fatty acids and glycerol by rat brown adipose tissue in vivo

The net in vivo uptake or release of free fatty acids glycerol, glucose, lactate, and pyruvate by the interscapular brown adipose tissue (IBAT) of barbital-anesthetized, cold-acclimated rats was determined from measurements of plasma arteriovenous concentration differences across IBAT and tissue blood flow. Measurements were made without stimulation of the tissue and also during submaximal and maximal stimulation by infused noradrenaline (NA), the physiological activator of BAT thermogenesis. There was no appreciable uptake of glucose or release of fatty acids and glycerol by the nonstimulated tissue. At both levels of stimulation there was significant uptake of glucose (1.7 and 2.0 mumol/min) and release of glycerol (0.9 and 1.2 mumol/min), but only at maximal stimulation was there significant release of fatty acids (1.9 mumol/min). Release of lactate and pyruvate accounted for 33% of the glucose taken up at submaximal stimulation and 88% at maximal stimulation. By calculation, the remainder of the glucose taken up was sufficient to have fueled about 12% of the thermogenesis at submaximal stimulation, but only about 2% at maximal stimulation. As estimated from the rate of glycerol release, the rate of triglyceride hydrolysis was sufficient at submaximal stimulation to fuel IBAT thermogenesis entirely with the resulting fatty acids, but it was not sufficient to do so at maximal stimulation when some of the fatty acid was exported. It is suggested that at maximal NA-induced thermogenesis a portion of lipolysis proceeded only to the level of mono- and di-glycerides with the result that glycerol release did not fully reflect the rate of fatty acid formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ca2+ effects on glucose transport and fatty acid oxidation in L6 skeletal muscle cell cultures

We examined the effect of Ca²⁺ on skeletal muscle glucose transport and fatty acid oxidation using L6 cell cultures. Ca²⁺ stimulation of glucose transport is controversial. We found that caffeine (a Ca²⁺ secretagogue) stimulation of glucose transport was only evident in a two-part incubation protocol (“post-incubation”). Caffeine was present in the first incubation, the media removed, and labeled glucose added for the second. Caffeine elicited a rise in Ca²⁺ in the first incubation that was dissipated by the second. This post-incubation procedure was insensitive to glucose concentrations in the first incubation. With a single, direct incubation system (all components present together) caffeine caused a slight inhibition of glucose transport. This was likely due to caffeine induced inhibition of phosphatidylinositol 3-kinase (PI3K), since nanomolar concentrations of wortmannin, a selective PI3K inhibitor, also inhibited glucose transport, and previous investigators have also found this action.We did find a Ca²⁺ stimulation (using either caffeine or ionomycin) of fatty acid oxidation. This was observed in the absence (but not the presence) of added glucose. We conclude that Ca²⁺ stimulates fatty acid oxidation at a mitochondrial site, secondary to malonyl CoA inhibition (represented by the presence of glucose in our experiments). In summary, the experiments resolve a controversy on Ca²⁺ stimulation of glucose transport by skeletal muscle, introduce an important experimental consideration for the measurement of glucose transport, and uncover a new site of action for Ca²⁺ stimulation of fatty acid oxidation.     

Adipose differentiation related protein (ADRP) expressed in transfected COS-7 cells selectively stimulates long chain fatty acid uptake.

Adipose differentiation related protein (ADRP) is a 50-kDa novel protein cloned from a mouse 1246 adipocyte cDNA library, rapidly induced during adipocyte differentiation. We have examined ADRP function, and we show here that ADRP facilitates fatty acid uptake in COS cells transfected with ADRP cDNA. We demonstrate that uptake of long chain fatty acids was significantly stimulated in a time-dependent fashion in ADRP-expressing COS-7 cells compared with empty vector-transfected control cells. Oleic acid uptake velocity increased significantly in a dose-dependent manner in ADRP-expressing COS-7 cells compared with control cells. The transport Km was 0.051 microM, and Vmax was 57.97 pmol/10(5) cells/min in ADRP-expressing cells, and Km was 0.093 microM and Vmax was 20.13 pmol/10(5) cells/min in control cells. The oleate uptake measured at 4 degrees C was only 10% that at 37 degrees C. ADRP also stimulated uptake of palmitate and arachidonate but had no effect on uptake of medium chain fatty acid such as octanoic acid and glucose. These data suggest that ADRP specifically enhances uptake of long chain fatty acids by increasing the initial rate of uptake and provide novel information about ADRP function as a saturable transport component for long chain fatty acids.     

On the effects of propionate and other short-chain fatty acids on sodium transport by the toad bladder.

1. Propionate and other unbranched short-chain fatty acids, butyrate, pentanoate, hexanoate and octanoate were found to both stimulate and inhibit active sodium transport by the toad bladder, as measured by the short-circuit current (s.c.c.). 2. Stimulation alone followed addition of low concentrations of fatty acids (0.1-1.0 mM) to either the serosal or mucosal bathing medium; stimulation was also seen after an initial period of inhibition in response to higher concentrations (approx. 5 mM) of some compounds. 3. Inhibition alone followed addition of high concentrations (5-20 mM) of these compounds. The duration and magnitude of the inhibition varied with increasing concentration and chain length of the fatty acid, and was greater following mucosal addition than serosal addition. 4. The inhibitory effect of mucosal propionate increased with decreasing pH of the mucosal bathing medium. 5. Inhibition by the fatty acids was completely reversed upon removing the compound from the bathing medium, and stimulation characteristically followed. 6. In studies designed to evaluate the role of metabolism of the fatty acids in their mucosal inhibitory effects it was found that 14-c-labelled propionate, when added to the mucosal surface of the bladder, was converted to 14-CO2, and mucosal succinate and alpha-oxoglutaric acid at 20 mM inhibited the s.c.c. slightly. However, malonate did not interfere with inhibition by mucosal propionate and two non-metabolizable acids, dimethylpropionate and benzoate, induced inhibition (and no stimulation) of the s.c.c. 7. In the presence of an inhibitory concentration of fatty acid, the ability of the bladder to respond to added pyruvate was reduced in proportion to the reduction in the level of the s.c.c., whereas the natriferic response to vasopressin was largely intact. 8. We conclude that stimulation of sodium transport by propionate and other short-chain fatty acids is due to metabolism of the compounds and provision of energy to the sodium transport mechanism. The basis of the inhibition appears complex. It may in part depend on metabolism of the fatty acids and/or uncoupling of oxidative phosphorylation, with resultant reduction in net ATP production for the sodium transport mechanism. However, the inhibition may also be caused in part by a direct effect on the mucosal entry of sodium into the transporting epithelial cells.     

Plasma free fatty acid transport during prolonged glucose consumption and its relationship to plasma triglyceride fatty acids in man

Plasma free fatty acid (FFA) transport in human subjects has been studied during the course of prolonged ingestion of different amounts of glucose. Compared with the fasting state, hypocaloric glucose intake resulted in marked suppression of net transport of FFA with no change in (fractional) turnover rate. There was no further suppression of net transport of FFA when the intake was increased to isocaloric or hypercaloric levels, but there was a significant increase in the (fractional) turnover rate, indicating an enhancement of clearance mechanisms. During the 20-24-hr period of fasting after isocaloric glucose consumption, the (fractional) turnover rate quickly fell to that found in the fasting individual, whereas net transport remained suppressed for much longer. This suggested that ingestion of glucose maintains an influence on lipolysis longer than on esterification. During this period of fasting after glucose administration, the contribution of plasma FFA to circulating triglyceride fatty acids increased with time and was positively and significantly correlated with the changes in the net transport of plasma FFA.     

Serum factors that stimulate fatty acid oxidation: physiological specificity

In the accompanying paper (Wice et al., 1986) we reported that serum from chickens contains small molecular weight compounds that stimulate long-chain fatty acid oxidation ten fold or more in HeLa cells. Here we show that this response is not limited to specific sera or to specific target cells. The specificity of the metabolic response to these factors was also investigated. They had no effect on the following major pathways of HeLa cell metabolism: 1) the oxidation of the medium-chain fatty acid, octanoic acid, 2) the rate of glycolysis of glucose, 3) the flux of glucose carbon through the oxidative arm of the pentose cycle, 4) the entry of pyruvate into the citrate cycle, 5) the oxidation of glutamine carbon, 6) the utilization rate of oxygen or 7) the rate of fatty acid synthesis. Furthermore, the increased oxidation of long-chain fatty acids was not a result of an increased uptake into the cells. Thus, the serum factors appear to be very specific for the oxidation of long-chain fatty acids for energy. Since carnitine also stimulates long-chain fatty acid oxidation in these cells, it seems likely that these compounds either facilitate the activity of carnitine or provide the same function--presumably the transport of long-chain fatty acid into and out of the mitochondria.     

The influence of insulin on glucose and fatty acid metabolism in the isolated perfused rat hind quarter.

Glucose and fatty acid metabolism of resting skeletal muscle were studied by perfusion of the isolated rat hind leg with a hemoglobin-free medium. Tissue integrity was demonstrated by normal ATP, ADP and creatine phosphate levels, by a sufficient oxygen supply, and by a normal appearance of perfused muscle specimens under the electron microscope. The rates of glucose and fatty acid uptake, and of lactate, alanine, glycerol and fatty acid release were constant over a perfusion period of 60 min. Insulin (1 unit/l) caused a more than threefold increase in glucose uptake, a stimulation of lactate production, and a 20% increase in the muscular glycogen levels. Fatty acids and alanine release were significantly diminished by insulin, but glycerol release did not change. The uptake of oleate by the rat hind leg was dependent on the medium concentration in a range of 0.7-1.9mM oleate, and was stimulated by insulin. Glucose uptake was not influenced by oleate, whether sodium was present or not. When the leg was perfused with [1-14C]oleate, 75% of the incorporated fatty acids were found in muscle lipids, 10% were oxidized to CO2, and 5% were recovered in bone lipids. The absolute amount of oleate oxidation was not altered by insulin. In all experiments with and without glucose in the medium, 70-80% of the 14C label incorporated into muscle lipids was found in the triglyceride fraction. In the presence of glucose, insulin significantly increased the incorporation of [1-14C]oleate into muscle triglycerides, whereas no insulin effect, either on fatty acid uptake or on triglyceride formation, could be observed when glucose was omitted from the perfusate. The present results indicate that a "glucose-fatty acid cycle" as found in rat heart muscle does not operate in resting peripheral skeletal muscle tissue. They also demonstrate that the stimulating effect of insulin on muscular fatty acid uptake and triglyceride synthesis is dependent on glucose supply. This finding can be intrepreted as a stimulation of fatty acid esterification by sn-glycerol 3-phosphate derived from an increased glucose turnover, which is in turn due to insulin.     

Fatty acids decrease mitochondrial generation of reactive oxygen species at the reverse electron transport but increase it at the forward transport

Long-chain nonesterified (“free”) fatty acids (FFA) can affect the mitochondrial generation of reactive oxygen species (ROS) in two ways: (i) by depolarisation of the inner membrane due to the uncoupling effect and (ii) by partly blocking the respiratory chain. In the present work this dual effect was investigated in rat heart and liver mitochondria under conditions of forward and reverse electron transport. Under conditions of the forward electron transport, i.e. with pyruvate plus malate and with succinate (plus rotenone) as respiratory substrates, polyunsaturated fatty acid, arachidonic, and branched-chain saturated fatty acid, phytanic, increased ROS production in parallel with a partial inhibition of the electron transport in the respiratory chain, most likely at the level of complexes I and III. A linear correlation between stimulation of ROS production and inhibition of complex III was found for rat heart mitochondria. This effect on ROS production was further increased in glutathione-depleted mitochondria. Under conditions of the reverse electron transport, i.e. with succinate (without rotenone), unsaturated fatty acids, arachidonic and oleic, straight-chain saturated palmitic acid and branched-chain saturated phytanic acid strongly inhibited ROS production. This inhibition was partly abolished by the blocker of ATP/ADP transfer, carboxyatractyloside, thus indicating that this effect was related to uncoupling (protonophoric) action of fatty acids. It is concluded that in isolated rat heart and liver mitochondria functioning in the forward electron transport mode, unsaturated fatty acids and phytanic acid increase ROS generation by partly inhibiting the electron transport and, most likely, by changing membrane fluidity. Only under conditions of reverse electron transport, fatty acids decrease ROS generation due to their uncoupling action.     

Fatty acids decrease mitochondrial generation of reactive oxygen species at the reverse electron transport but increase it at the forward transport

Long-chain nonesterified ("free") fatty acids (FFA) can affect the mitochondrial generation of reactive oxygen species (ROS) in two ways: (i) by depolarisation of the inner membrane due to the uncoupling effect and (ii) by partly blocking the respiratory chain. In the present work this dual effect was investigated in rat heart and liver mitochondria under conditions of forward and reverse electron transport. Under conditions of the forward electron transport, i.e. with pyruvate plus malate and with succinate (plus rotenone) as respiratory substrates, polyunsaturated fatty acid, arachidonic, and branched-chain saturated fatty acid, phytanic, increased ROS production in parallel with a partial inhibition of the electron transport in the respiratory chain, most likely at the level of complexes I and III. A linear correlation between stimulation of ROS production and inhibition of complex III was found for rat heart mitochondria. This effect on ROS production was further increased in glutathione-depleted mitochondria. Under conditions of the reverse electron transport, i.e. with succinate (without rotenone), unsaturated fatty acids, arachidonic and oleic, straight-chain saturated palmitic acid and branched-chain saturated phytanic acid strongly inhibited ROS production. This inhibition was partly abolished by the blocker of ATP/ADP transfer, carboxyatractyloside, thus indicating that this effect was related to uncoupling (protonophoric) action of fatty acids. It is concluded that in isolated rat heart and liver mitochondria functioning in the forward electron transport mode, unsaturated fatty acids and phytanic acid increase ROS generation by partly inhibiting the electron transport and, most likely, by changing membrane fluidity. Only under conditions of reverse electron transport, fatty acids decrease ROS generation due to their uncoupling action.     

Effects of oleate,palmitate, and octanoate on gluconeogenesis in isolated rabbit liver cells

The effect of oleate, palmitate, and octanoate on glucose formation was studied with lactate or pyruvate as substrate. Octanoate was much more quickly oxidized and utilized for ketone body production than were oleate and palmitate. Among fatty acids studied, only octanoate resulted in a marked increase of the 3-hydroxybutyrate/acetoacetate (3-$\text{OHB}\text{AcAc}$) ratio. Each of the fatty acids studied stimulated glucose synthesis from pyruvate. The enhancement of gluconeogenesis by long-chain fatty acids was abolished after the addition of ammonia. As concluded from the “crossover” plot, the stimulatory effect of fatty acids was due to: (i) a stimulation of pyruvate carboxylation, (ii) a provision of reducing equivalents for glyceraldehyde phosphate dehydrogenase, and (iii) an acceleration of flux through hexose diphosphatase. Moreover, palmitate and oleate resulted in an increased generation of mitochondrial phosphpenolpyruvate, while in the presence of octanoate, the activity of mitochondrial phosphoenolpyruvate carboxykinase was diminished. When lactate was used as the glucose precursor, palmitate and oleate increased glucose production by about 50% but did not affect the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis. In contrast, in spite of the stimulation of both pyruvate carboxylase and hexose diphosphatase, as judged from the crossover plot, the addition of octanoate resulted in a marked inhibition of both glucose formation and mitochondrial generation of phosphoenolpyruvate. The inhibitory effect of octanoate was reversed by ammonia. Results indicate that fatty acids and ammonia are potent regulatory factors of both the rate of glucose formation and the contribution of mitochondrial phosphoenolpyruvate carboxykinase to gluconeogenesis in hepatocytes of the fasted rabbit.     

Deterrent effect of carboxylic acids on cabbage root fly oviposition

In laboratory experiments, 11 selected carboxylic acids were tested to determine which part of the sinapic acid molecule is responsible for deterring cabbage root fly from laying its eggs on otherwise-acceptable cauliflower host-plants. The deterrent effect was only obtained with compounds containing at least one carboxylic group in the molecule. Hence, the aliphatic acids were as deterrent as the aromatic acids to the fly and all the carboxylic acids were as deterrent as sinapic acid, reducing oviposition by > 50%. The inclusion of two carboxylic groups in the molecule, (e.g. phthalic acid and oxalic acid) did not increase the deterrent effect observed with sinapic acid. Some of the long chain fatty acids, with low volatility, low water solubility and thus greater persistence, offer practical opportunities for deterring Delia radicurn from laying its eggs on plants in the field.     

Contribution of fatty acids to olfactory host finding of female Aedes aegypti

Single carbon to 18 carbon n-aliphatic carboxylic acids were tested for their attractive effects on female Aedes aegypti in a Y-tube olfactometer. Each acid was tested over a wide range of concentrations together with L-(+)-lactic acid, the indispensable synergist for other attractive components emitted from human hosts. The attractiveness of lactic acid was significantly augmented when combined with fatty acids of chain length C(1)-C(3), C(5)-C(8) and C(13)-C(18), respectively. The addition of the C(9) and C(11) acids reduced the attractive effect of lactic acid. According to experiments showing a further increase of attractiveness by adding a second fatty acid, we suggest two groups of attractive carboxylic acids: C(1)-C(3) and C(5)-C(8). The addition of a fatty acid from one group to a mixture of lactic acid and an acid from the other group augmented the attraction to the mixture. Together with ammonia, a previously demonstrated attractant for Aedes aegypti, lactic acid plus two fatty acids from the different groups formed the hitherto most attractive, artificially composed blend. Two of the carboxylic acids which were found to be attractive together with lactic acid were also tested alone and in combination with CO(2), the major attractant in human breath. In both cases no attractive effect of the carboxylic acids could be observed.     

Spectrum of effects of dietary long-chain fatty acids on rat intestinal glucose and lipid uptake

Isocaloric modification in the ratio of dietary polyunsaturated-to-saturated fatty acids influences intestinal uptake of actively and passively transported nutrients. This study was undertaken to determine which dietary fatty acid was responsible for these alterations in absorption. Adult female rats were fed isocaloric semisynthetic diets high in palmitic and stearic acids (SFA), oleic acid (OA), linoleic acid (LA), or linolenic acid (LNA). An in vitro technique was used to measure the uptake of varying concentrations of glucose as well as a series of fatty acids and cholesterol. Jejunal uptake of 40 mM glucose was highest in rats fed SFA and lowest in those fed LA; ileal glucose uptake was similar in OA, LA, and LNA, but was lowest in SFA. Jejunal uptake of medium-chain fatty acids (8:0-12:0) was higher in OA than in other diet groups; ileal uptake of medium-chain fatty acids was unaffected by diet. Jejunal and ileal uptake of 18:2 was higher in LNA than in SFA or OA; the uptake of the other long-chain saturated or unsaturated fatty acids was unchanged by diet. The ileal but not the jejunal uptake of cholesterol was increased in LA as compared with SFA or OA, and reduced in LNA as compared with LA. These transport changes were not explained by differences in the animals' food consumption, body weight gain, intestinal mass, or mucosal surface area. We postulate that these diet-induced transport alterations may be mediated via changes in brush border membrane phospholipid fatty acyl composition. Thus, intestinal transport of nutrients may be varied by isocaloric changes in the dietary content of individual fatty acids.     

Cis-unsaturated fatty acids induce both lipogenesis and calcium binding in adipocytes

The addition of 0.4-3 mM of cis-unsaturated fatty acids such as oleic acid (18:1) or linoleic acid (18:2) to intact rat adipocytes stimulated lipogenesis at 37 degrees C. Saturated or trans-unsaturated fatty acids were ineffective. Fluorescence photobleaching recovery studies performed under similar conditions indicated that the cis-unsaturated fatty acids do not alter lateral mobility of either a lipid probe or a general protein marker in the plasma membrane. A high concentration (7 mM) of Ca2+, which by itself has some stimulatory effect on lipogenesis, significantly potentiated the effect of oleic acid on this insulin-like activity. Measurement of 45Ca2+ binding by fat cells has indicated that cis-unsaturated (but not saturated) fatty acids increased 12- to 20-fold the amount of Ca2+ associated with the cells. The dependence of this effect on the fatty acid concentration correlates well with the effect of the fatty acid on the induction of lipogenesis. Our results suggest that cis-unsaturated fatty acids affect membrane organization in a manner which induces a significant increase in membrane associated or intracellular Ca2+. This increase may be responsible for inducing exocytotic-like processes which facilitate translocation of glucose transport activity from storage sites to the plasma membrane and thus produce an insulin-like effect.     

The regulation of peroxisomal enzyme systems of Tetrahymena pyriformis by fatty acid composition, glucose and oxygen in the medium

The effect of the chain length of fatty acids on peroxisomal enzyme activities of Tetrahymena pyriformis was investigated. The growth of cells and the activities of peroxisomal enzymes were inhibited markedly by the addition of medium-chain fatty acids (C6-C12) to the culture medium, whereas the addition of longer-chain fatty acids (C14-C18) resulted in a slight increase of growth and in the marked stimulation of enzyme activities concerned with fatty acid beta-oxidation and the glyoxylate cycle in peroxisomes. Peroxisomal beta-oxidation (fatty acyl-CoA oxidase) was more potent towards longer-chain fatty acids than the mitochondrial activity (fatty acyl-CoA dehydrogenase). The induction of the peroxisomal beta-oxidation system by palmitate was repressed both by the addition of glucose and the aeration of the culture medium, whereas that of the peroxisomal glyoxylate cycle was repressed only by the addition of glucose to the medium. These results indicate that peroxisomal enzyme systems related to the beta-oxidation of fatty acids and the glyoxylate cycle are regulated by the compositions of fatty acids, glucose, and oxygen in the medium.     

Metformin activates AMP kinase through inhibition of AMP deaminase

The mechanism for how metformin activates AMPK (AMP-activated kinase) was investigated in isolated skeletal muscle L6 cells. A widely held notion is that inhibition of the mitochondrial respiratory chain is central to the mechanism. We also considered other proposals for metformin action. As metabolic pathway markers, we focused on glucose transport and fatty acid oxidation. We also confirmed metformin actions on other metabolic processes in L6 cells. Metformin stimulated both glucose transport and fatty acid oxidation. The mitochondrial Complex I inhibitor rotenone also stimulated glucose transport but it inhibited fatty acid oxidation, independently of metformin. The peroxynitrite generator 3-morpholinosydnonimine stimulated glucose transport, but inhibited fatty acid oxidation. Addition of the nitric oxide precursor arginine to cells did not affect glucose transport. These studies differentiate metformin from inhibition of mitochondrial respiration and from active nitrogen species. Knockdown of adenylate kinase also failed to affect metformin stimulation of glucose transport. Hence, any means of increase in ADP appears not to be involved in the metformin mechanism. Knockdown of LKB1, an upstream kinase and AMPK activator, did not affect metformin action. Having ruled out existing proposals, we suggest a new one: metformin might increase AMP through inhibition of AMP deaminase (AMPD). We found that metformin inhibited purified AMP deaminase activity. Furthermore, a known inhibitor of AMPD stimulated glucose uptake and fatty acid oxidation. Both metformin and the AMPD inhibitor suppressed ammonia accumulation by the cells. Knockdown of AMPD obviated metformin stimulation of glucose transport. We conclude that AMPD inhibition is the mechanism of metformin action.     

Studies on mediators of manganese peroxidase for bleaching of wood pulps

In order to enhance the bleaching effect of manganese peroxidase (MnP), unsaturated fatty acids, thiol-containing compounds and various other organic compounds were applied in pulp bleaching experiments with MnP. Thiol-containing compounds did not improve the pulp bleaching effect by MnP. Some unsaturated fatty acids, linoleic acid and linolenic acid provided a better pulp bleaching effect than Tween 80. The correlation between the number of C=C bonds in a fatty acid and its pulp bleaching effect was also investigated. The MnP pulp bleaching capability was shown to depend on the carboxylic acid used. A combination of Tween 80 and a carboxylic acid resulted in higher pulp brightness than that obtained with Tween 80 alone. A laccase mediator, 3-hydroxy-1,2,3-benzotriazin-4(3H)-one, could also enhance the MnP pulp bleaching effect.     

Effects of mebendazole on the absorption of low molecular weight nutrients by Ascaris suum

Van Den Bossche H. and De Nollin S. 1973. Effects of mebendazole on the absorption of low molecular weight nutrients by Ascaris suum. International Journal for Parasitology3: 401–407. The effect of the anthelmintic drug, mebendazole, on the uptake and/or transport of glucose, fructose, 3-O-methylglucose, glycine, proline, methionine and palmitic acid was studied on in vitro incubated Ascaris suum. The experiments presented indicate that mebendazole inhibits the uptake and/or transport of glucose by A. suum. This inhibition is followed by a marked decrease in the glycogen content of the ascaris muscle. The addition of glucose to the incubation medium significantly enhanced the rate of uptake and/or transport of 3-O-methylglueose, glycine, methionine, proline and palmitic acid indicating that the absorption mechanisms depend on energy.Therefore, the inhibitory effect of mebendazole on the glucose uptake also results in a decreased uptake of 3-O-methylglucose and of the amino acids and fatty acid studied. The fructose uptake was not affected by the addition of glucose.Although mebendazole decreased the uptake of the hexoses and of the amino acids whether or not glucose was added, the uptake of palmitic acid was not affected when glucose was omitted from the medium. Mebendazole failed to exhibit an effect on the uptake, transport and/or utilization of glucose in rat.     

Inhibition by potential metabolic inhibitors of in vitro adipose tissue lipogenesis

To study the pathway of lactate utilization as a carbon source for fatty acid synthesis, the effect of (-)-hydroxycitrate, agaric acid, sodium oxamate, 2-n-butyl malonate and alpha-cyano-4-hydroxycinnamate on the rate of in vitro conversion of lactate, acetate and glucose to fatty acids was measured in bovine and rat adipose tissues. Sodium oxamate and hydroxycitrate caused less fatty acid to be synthesized from lactate in bovine adipose tissue. Hydroxycitrate depressed fatty acid synthesis from glucose in rat adipose tissue. alpha-Cyano-4-hydroxycinnamate was an effective inhibitor of lipogenesis from all substrates and may act as a specific inhibitor in adipose tissue. Although the inhibitors were absorbed poorly into adipocytes, the results indicate that conversion of lactate to fatty acids probably occurs by way of the citrate cleavage pathway.