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PubMed2000

Cholesterol-lowering effects of guar gum: changes in bile acid pools and intestinal reabsorption.

Soluble fibers such as guar gum (GG) may exert cholesterol-lowering effects. It is generally accepted that bile acid (BA) reabsorption in portal blood is reduced, thus limiting the capacity of BA to down-regulate liver cholesterol 7alpha-hydroxylase, the rate-limiting enzyme of BA synthesis. In the present work, rats were adapted to fiber-free (FF) or 5% GG diets (supplemented or not with 0.25% cholesterol), to investigate various aspects of enterohepatic BA cycling. GG in the diet at a level of 5% elicited a significant lowering of plasma cholesterol during the absorptive period, in cholesterol-free (-13%) or 0.25% cholesterol (-20%) diet conditions. In rats adapted to the GG diets, the small intestinal and cecal BA pools and the ileal vein-artery difference for BA were markedly enhanced; reabsorption in the cecal vein was also enhanced in these rats. [14C]Taurocholate absorption, determined in perfused ileal segments, was not significantly different in rats adapted to the FF or GG diet, suggesting that a greater flux of BA in the ileum might support a greater ileal BA reabsorption in rats adapted to the GG diet. In contrast, capacities for [14C]cholate absorption from the cecum at pH 6.5 were higher in rats adapted to the GG diet than to the FF diet. Acidification of the bulk medium in isolated cecum (from pH 7.1 down to pH 6.5 or 5.8) or addition of 100 mM volatile fatty acids was also found to stimulate cecal [14C]cholate absorption. These factors could contribute to accelerated cecal BA absorption in rats fed the GG diet. The effects of GG on steroid fecal excretion thus appear to accompany a greater intestinal BA absorption and portal flux to the liver. These results suggest that some mechanisms invoked to explain cholesterol-lowering effect of fibers should be reconsidered.

Animals↗

PubMed2001

Effects of dietary maritime pine seed oil on lipoprotein metabolism and atherosclerosis development in mice expressing human apolipoprotein B.

BACKGROUND: Conifer seeds are used for food preparation in several countries. Aim of the study To assess the lipid-lowering and antiatherogenic properties of maritime pine (Pinuspinaster) seed oil. METHODS: The effects of maritime pine oil supplementation (20% w/w) for 2 weeks were compared to those of coconut and sunflower oil in mice expressing human apolipoprotein B (hApoB). Atherosclerosis lesion development was measured in hApoB mice fed 1.25% (w/w) cholesterol and 0.05% (w/w) sodium cholate and either coconut, sunflower or maritime pine oil (20% w/w) for 8 weeks. RESULTS: After 2 weeks of dietary treatment, plasma cholesterol (p < 0.0001), triglyceride (p < 0.0003), phospholipid (p < 0.0001) and apolipoprotein B (p < 0.0001) levels were lower in mice supplemented with maritime pine oil than in those treated with coconut oil. These effects were accounted for by a lowering of LDL-cholesterol, LDL-phospholipids and LDL-triglycerides, as well as a decrease in HDL-cholesterol and HDL-phospholipids. After 8 weeks of dietary treatment cholesterol and cholate, the mean area of aortic lesions was not statistically different between fat groups. CONCLUSIONS: Feeding maritime pine oil is associated with major changes of lipid and lipoprotein levels in hApoB mice. However, in the long term, maritime pine oil has no preventive effect on cholesterol-induced aortic lesion development in hApoB mice.

Animals↗

PubMed1985

Changes in bile salt composition after cholecystectomy and ileal resection.

The effect of ileal resection and cholecystectomy on bile salt metabolism was studied in female prairie dogs 4 weeks after either a sham laparotomy, cholecystectomy, ileal resection, or cholecystectomy and ileal resection. Bile was collected from a common bile duct cannula at hourly intervals for 12 hours. Pool sizes and synthetic rates of primary and secondary bile salts were determined from washout curves. Cholate, chenodeoxycholate, deoxycholate, and lithocholate levels were determined by gas chromatography from pooled collections of bile. After cholecystectomy and ileal resection, the pool sizes of primary and secondary bile salts were significantly reduced to amounts that were much less than the pool sizes after either procedure alone. Primary bile salt synthesis was significantly increased after combined cholecystectomy and ileal resection, to the same degree as cholecystectomy alone. After the combined procedures, there was a decrease in the proportion of cholate in hepatic bile associated with an increase in chenodeoxycholate, deoxycholate, and lithocholate levels. The data suggest that after the loss of both ileum and gallbladder the bile salt pool sizes are drastically reduced, the synthesis of primary bile salts is increased, and the proportion of secondary bile salts is increased. Cholecystectomy should be avoided, if possible, in patients with ileal resection in order to conserve the bile salt pool and prevent severe fat malabsorption.

Animals↗

PubMed1983

Purification of human milk bile salt-activated lipase.

A modified procedure for a large-scale purification of human milk bile salt-activated lipase (BAL) has been devised. An initial step used cholate-Sepharose affinity chromatography for the partial purification of the enzyme followed by the removal of cholate with a Bio-Rex 5 anion-exchange resin. The final step of purification used heparin-Sepharose affinity chromatography. This procedure of purification resulted in a 50-fold purification of BAL from human skim milk and a specific activity of 50-60 mumol/min/mg with p-nitrophenyl acetate as substrate. From 450 ml of human skim milk, approximately 30 mg of purified enzyme could be obtained. The N-terminal-region amino acid sequence of the purified BAL was determined as follows: Ala-Lys-Leu-Gly-Ala-Val-Tyr-Thr-Glu-Gly-Lys-Phe-Val-Glu-Gly-Val-Asn-Lys-Lys-Leu-Gly-Leu-. Despite the finding that BAL interacts with heparin-Sepharose, soluble heparin had no effect on BAL activity. The possible physiological role of BAL-heparin interaction has also been discussed.

Amino Acid Sequence↗

PubMed1986

Purification of human placental glucocerebrosidase using a two-step high-performance hydrophobic and gel permeation column chromatography method.

Glucocerebrosidase was purified from human placenta approximately 10,600-fold to apparent homogeneity with an overall yield of 37% using cholate extraction, ammonium sulfate fractionation, butanol delipidation, and a two-step high-performance hydrophobic and gel permeation column chromatography method. A Phenyl-5PW (21.5 X 150 mm) column was used in the first step. Approximately one litre of delipidated and dialysed extract containing 3.7 X 10(6) units of enzyme activity from 1 kg of placental tissue was processed by the column at a flow rate of 5 ml/min. Glucocerebrosidase was eluted using a linear cholate gradient (2-3%). There was a 50-fold purification and 89% recovery. The run was completed in about 7 h. In the second step, the concentrated enzyme preparation from the phenyl column was run through two Bio-Sil TSK 250 gel permeation columns (21.5 X 600 mm) connected in series at a flow rate of 1.5 ml/min. A symmetrical peak of glucocerebrosidase activity (Ve = 253 ml) which had constant specific activity (47,000 units/h/mg protein) was noted. There was a 17-fold purification and 80% recovery in this run which was completed in 4 h. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and protein staining with silver compounds of the purified preparation revealed the presence of one band of Mr 68,000.

Chromatography, Gel↗

PubMed1983

Functional modification of the guanine nucleotide regulatory protein after desensitization of turkey erythrocytes by catecholamines.

Densensitization of turkey erythrocytes by exposure to the beta-adrenergic agonist (-)isoproterenol leads to decreased activation of adenylate cyclase by agonist, NaF, and guanyl-5'-yl imido diphosphate, with no reduction in the number of beta-adrenergic receptors. Interactions between the receptor and the guanine nucleotide regulatory protein (N protein) also seem to be impaired. These observations suggest that a component distal to the beta-adrenergic receptor may be a locus of modification. Accordingly we examined the N protein to determine whether it was altered by desensitization. The rate at which (-)isoproterenol stimulated the release of [3H]GDP from the N protein was substantially lower in membranes prepared from desensitized cells, providing further evidence for uncoupling of the receptor and the N protein. The amount of N protein in membranes from control and desensitized cells was compared by labeling the 42,000 Mr component of the N protein with [32P]NAD+ and cholera toxin; no significant difference was found. However, significantly more N protein (p less than .001) was solubilized by cholate extraction of desensitized membranes, suggesting an altered association of the N protein with the membrane after desensitization. The functional activity of the N protein was measured by reconstitution of cholate extracts of turkey erythrocyte membranes into S49 lymphoma cyc- membranes. Reconstitution of (-)isoproterenol stimulation of adenylate cyclase activity was reduced significantly (p less than .05) after desensitization. These observations suggest that desensitization of the turkey erythrocyte by (-)isoproterenol results in functional modifications of the guanine nucleotide regulatory protein, leading to impaired interactions with the beta-adrenergic receptor and reduced activation of adenylate cyclase.

Adenylyl Cyclases↗

PubMed1989

The role of peroxisomal fatty acyl-CoA beta-oxidation in bile acid biosynthesis.

The physiological role of the peroxisomal fatty acyl-CoA beta-oxidizing system (FAOS) is not yet established. We speculated that there might be a relationship between peroxisomal degradation of long-chain fatty acids in the liver and the biosynthesis of bile acids. This was investigated using [1-14C]butyric acid and [1-14C]lignoceric acid as substrates of FAOS in mitochondria and peroxisomes, respectively. The incorporation of [14C]lignoceric acid into primary bile acids was approximately four times higher than that of [14C]butyric acid (in terms of C-2 units). The pools of these two fatty acids in the liver were exceedingly small. The incorporations of radioactivity into the primary bile acids were strongly inhibited by administration of aminotriazole, which is a specific inhibitor of peroxisomal FAOS in vivo [F. Hashimoto and H. Hayashi (1987) Biochim. Biophys. Acta 921, 142-150]. Aminotriazole inhibited preferentially the formation of cholate, the major primary bile acid, from both [14C]lignoceric acid and [14C]butyric acid, rather than the formation of chenodeoxycholate. The former inhibition was about 70% and the latter was approximately 40-50%. In view of reports that cholate is biosynthesized from endogenous cholesterol, the above results indicate that peroxisomal FAOS may have an anabolic function, supplying acetyl CoA for bile acid biosynthesis.

Acyl Coenzyme A↗

PubMed1979

The reconstitution of energy transfer in membranes from a bacteriochlorophyll-less mutant of Rhodopseudomonas sphaeroides by addition of light-harvesting and reaction centre pigment-protein complexes.

Antenna and reaction centre complexes purified from photosynthetically-grown cells of Rhodopseudomonas sphaeroides have been mixed with cytoplasmic membranes prepared from an aerobically-grown bacteriochlorophyll-less mutant of Rp. sphaeroides (designated 01) in the presence of 1% sodium cholate. After removal of the cholate by dislysis, the dislysate was subjected to isopycnic centrifugation. Reconstituted cytochrome c2 photooxidation and cytochrome b photoreduction was demonstrated in a pigmented fraction recovered from the sucrose gradient, suggesting that the pigment-proteins were incorporated into the 01 membrane. The fluorescence properties of the system were examined. The appearance of a variable component after the initial fast fluorescence rise indicated that energy transfer occurred between the antenna and reaction centre proteins in the presence of 01 membrane. The order in which the system was assembled was important. Reconstituted energy transfer with a pre-dialysed reaction centre-antenna complex was more effective than when all the components were mixed at once. Energy transfer was also reconstituted between added reaction centre protein and the endogenous antenna present in membranes from the pigmented, but aerobically-grown reaction centre-less mutant PM8dp of Rp. sphaeroides. Preparations of 01 membranes reconstituted with reaction centre exhibited a light intensity dependent cytochrome c2 photooxidation. At low exciting light intensities, preparations containing reconstituted antenna protein in addition to reaction centres showed greated membrane cytochrome c2 photooxidation than preparations with the antenna omitted; this improvement was maximal when a pre-dialysed antenna-reaction centre complex was used.

Aerobiosis↗

PubMed1979

The incorporation of reaction centres into membranes from a bacteriochlorophyll-less mutant of Rhodopseudomonas sphaeroides.

Reaction centres purified from a blue-green mutant R-26 of Rhodopseudomonas sphaeroides can be incorporated into bacteriochlorophyll-less membranes purified from an aerobically-grown bacteriochlorophyll-less mutant 01 of R. sphaeroides. This can be accomplished by raising the temperature of the mixture or by addition of the detergent sodium cholate and its subsequent removal by dilution or dialysis. Optimum conditions for the reconstitution are at 4 degrees C in the presence of 1% cholate and soybean phospholipid (2 : 1, w/w, with membrane protein). Isopycnic sucrose density gradient centrifugation of such preparations shows that reaction centres and light-harvesting pigment-protein complex bind to the membranes. Reconstituted membranes exhibit light-induced steady-state cytochrome absorbance changes resembling those observed in chromatophores prepared from the photosynthetically-grown mutant R-26. The effect on these absorbance changes of varying reaction centre content in the membrane has been studied, and the time course of the interaction between 01 membrane cytochrome c2 and added reaction centre examined. Cytochrome b photoreduction and cytochrome c2 photo-oxidation were observed in the reconstituted preparation; each increased following the addition of antimycin A, suggesting that a cyclic light-driven system had been reconstituted.

Bacterial Chromatophores↗

PubMed1976

Single bilayer vesicles prepared without sonication. Physico-chemical properties.

Single shelled lecithin vesicles of uniform size (diameter = 300 A) are prepared without sonication by solubilizing unsonicated lecithin dispersions with sodium cholate and removing the detergent from the mixed lecithin - cholate micelles by gel filtration on Sephadex G-50. A homogeneous population of pure lecithin single-bilayer vesicles free of multilamellar structures is obtained. The vesicle diameter is somewhat larger than the average diameter of sonicated vesicles. The curvature of the bilayer seems to be sufficiently large to allow for similar packing densities (areas/molecule) on the outer and inner layer of the bilayer. The morphology and some physico-chemical properties of these vesicles are described and compared with those of sonicated vesicles.

Cholic Acids↗

PubMed1976

Investigations on the sodium dependence of bile acid fluxes in the isolated perfused rat liver.

At [Na+]o = 118 mM the concentrative transfer of cholic and taurocholic acid from the perfusate into the isolated rat liver displays saturation kinetics (taurocholate: V = 299 nmol-min-1-g-1, Km = 61 muM; Cholate: V=327 nmol-min-1-g-1, Km = 436 muM). Perfusion with an isotonic sodium-free medium did not change the feature of a carrier-mediated transport but did markedly reduce V without affecting Km (taurocholate: V = 65 nmol-min-1-g-1, Km = 78 muM; cholate: V = 104 nmol-min-1-g-1, Km = 354 muM). It was experimentally assured that the observed reduction of bile salt uptake was not a consequence of regurgitation of bile salts or due to an excessive intracellular accumulation during cholestasis in the sodium-free state. The rate of taurocholate efflux is very low when compared with the rapid rate of the uptake. A stimulatory action of extracellular sodium on this pathway was also observed. Inhibition of the (Na+ + K+)-ATPase by 1 mM ouabain resulted in a decrease of bile salt uptake. Activation of the enzyme by potassium readmission to a K+-deprived liver enhanced bile salt uptake. The immediate response to alteration of the enzyme activity suggests a close association of a fraction of bile acid active transport with the sodium pump.

Adenosine Triphosphatases↗

PubMed1977

Distribution of lysophosphatidylcholine in single bilayer vesicles prepared without sonication.

The cholate method originally introduced by Kagawa et al. (J. Biol. Chem. (1973) 248, 676-684) and further developed by Brunner et al. (Biochim. Biophys. Acta (1976) 455, 322-331) has been used to prepare single bilayer vesicles containing 5 mol% lysophosphatidylcholine embedded in a matrix of phosphatidylcholine. The distribution of lysophosphatidylcholine over outer and inner monolayer was found to be highly asymmetric (ratio 9:1), as determined by lysophospholipase treatment of the vesicles. This distribution is similar to the value found in sonicated vesicles. Up to 20 mol% cholesterol could be incorporated in the vesicles by the cholate method. The method was succesfully used also for the preparation of single bilayer vesicles from total rat liver microsomal lipids, to which 5 mol% of 1-[1-14C]palmitoyl lysophosphatidylcholine had been added. Surprisingly, almost 100% of lysophosphatidylcholine in the latter vesicles was directly available for hydrolysis by sophospholipase. In contrast, only 70% of the lysophosphatidylcholine is sonicated vesicles of similar composition could be hydrolyzed by lysophospholipase.

Animals↗

PubMed1978

Association of Pseudomonas cytochrome oxidase with liposomes.

Purified Pseudomonas cytochrome oxidase has been associated with asolectin liposomes by two different methods. Firstly, the enzyme was attached to liposomic membranes by adding it to a cholate-phospholipid dispersion and subsequently dialyzing the detergent out of suspension. In the second case the enzyme was adsorbed on the preformed liposomes when added to them after the dialysis. A stimulation of the cytochrome oxidase activity approximately twenty-fold was observed by the first method. In contrast, the activation was absent in the second type of preparation, indicating that interaction between the enzyme and phospholipids is very different in the two types of vesicles. The cholate-dialysis method for reconstitution of protein-phospholipid vesicles seems to lead to rather heterogenous preparations. These can be further fractionated, not only according to their size but also to the protein/phospholipid ratio, by gel chromatography.

Centrifugation, Density Gradient↗

PubMed1980

Incorporation of purified components of the rabbit liver microsomal hydroxylase system into phospholipid vesicles.

Methods are described for incorporation of purified forms of rabbit liver microsomal NADPH-cytochrome P-450 reductase and cytochrome P-450LM2, P-450LM3 and P-450LM4 (LM, liver microsomes) into phospholipid vesicles. It was found that each cytochrome could individually be incorporated into preformed phospholipid vesicles in the absence of cholate. However, NADPH-cytochrome P-450 reductase prevented incorporation of P-450 by this method, a phenomenon possibly inherent in the formation of complexes between P-450 and the reductase in solution. Using the cholate-gel filtration technique it was possible to prepare monolamellar phosphatidylcholine vesicles containing any of the cytochromes and P-450 reductase in good yields. It was found that P-450LM3-containing vesicles had a mean diameter of 47 nm, whereas vesicles formed under the same conditions but containing P-450LM4 were much smaller (mean diameter 33 nm). Vesicles formed with P-450LM2 were homogeneous in density (1.04 g/cm3) according to isopycnic centrifugation in Ficoll but not in size (44-72 nm). These findings, taken together with results obtained from treatment of the cytochromes in soluble form and in reconstituted vesicles with the non-penetrating reagent, p-diazobenzene sulphonate, indicate a unidirectional, relatively peripheral orientation of P-450LM4 with the major part localized on the outside of the vesicles. Experiments with trypsin and cytochrome c-reduction demonstrated a unidirectional orientation of P-450 reductase towards the outside of the vesicles.

Animals↗

PubMed1980

The glucose transport activity of human erythrocyte membranes. Reconstitution in phospholipid liposomes and fractionation by molecular sieve and ion exchange chromatography.

Human erythrocyte membranes, at a protein concentration of 1-2 g/l, were solubilized with 0.12 M cholate in the presence of 0.06 M phospholipid (egg yolk phospholipids or phosphatidylcholine). More than 40% of the protein was solubilized. Cholate was removed by molecular sieve chromatography, whereby liposomes formed. These liposomes exchanged D-glucose faster than L-glucose. The recovery of glucose transport activity in the reconstituted system was estimated to be higher than 16%. The liposomes were heterogenous in size, as shown by molecular sieve chromatography on Sepharose 4B, and small liposomes predominated. In liposomes formed with phosphatidylcholine, the distribution of glucose transport activity did not parallel the distribution of protein or phospholipid, and the activity was found mainly in the smallest liposomes. The proteins were incorporated mainly in the liposomes that eluted at the lowest ionic strength upon ion exchange chromatography. The glucose transport activity separated into three main peaks upon ion exchange chromatography of egg yolk phospholipid liposomes. The activity eluted at low ionic strength. The liposomes contained proteins mainly from the 3- and 4.5-regions (nomenclature according to Steck, T.L. (1974) J. Cell Biol. 62, 1-19). The activity peaks were highest in the first part of the chromatogram. The protein distribution did not coincide with the variation in activity over each peak. Therefore, it cannot be excluded that a minor component not seen in the electrophoretic analyses might be responsible for the glucose transport activity.

Biological Transport, Active↗

PubMed1981

Characterization of cytochrome P-450scc-containing liposomes.

Purified cytochrome P450scc from bovine adrenocortical mitochondria was incorporated into liposomes by the cholate-dilution method utilizing either dialysis or Sephadex gel filtration. Among synthetic phospholipids tested, dioleoylglycerophosphocholine showed the best stability during the incorporation of P450scc into liposomes. A maximum amount of heme was incorporated into liposomes at a molar ratio of phospholipid to the cytochrome of approx. 200. When P450scc was incorporated into the dioleoylglycerophosphocholine liposomes by the cholate-filtration method, the P450scc-containing liposomes showed two major populations on the elution pattern of the Sepharose 4B gel filtration, and were seen at a diameter of 200-600 A and its aggregated forms. When the cytochrome was incorporated into dioleoylglycerophosphocholine liposomes or cholesterol-free adrenocortical mitochondrial liposomes, P450scc was less stable than P450scc in aqueous solution. Cholesterol or adrenodoxin markedly stabilized the liposomal P450scc. Liposomal P450scc required cholesterol for its optimum reduction with adrenodoxin, adrenodoxin reductase, and NADPH in the presence of CO. About 70% of the total heme in the dioleoylglycerophosphocholine liposomes was reduced by the enzymatic reduction in the presence of cholesterol, indicating that 70% of the total molecules are exposed to the surface of the outer monolayer. In order to see the location of the heme in membrane, the dioleoylglycerophosphocholine-liposomal P450scc was subjected to p-chloromercuriphenyl sulfonic acid treatment. This reagent destroyed the liposomal P450scc. These results suggest that the heme is located in the proximity of the p-chloromercuriphenyl sulfonic acid reacting sites which are exposed to the surface, or located on the vincinity of polar heads of the membrane.

Adrenal Cortex↗

PubMed1984

Partial purification and characterization of rabbit-kidney brush-border (Ca2+ or Mg2+)-dependent adenosine triphosphatase.

The ATPase activity of rabbit-kidney brush border can be activated almost equally well by Ca2+ and Mg2+ and, therefore, should be called (Ca2+ or Mg2+)-ATPase. This enzyme was solubilized and enriched 14-fold by the following steps: pretreatment with papain removed 69% of alkaline phosphatase without attacking a significant portion of the ATPase activity. Addition of 1% cholate removed 65% of the protein but no ATPase activity. The combination of cholate (0.5%) and deoxycholate (0.4%) solubilized most of the ATPase activity and most of the remaining protein. A column chromatography of the extract on Sepharose CL-2B resulted in an 6.5-fold increase of specific ATPase activity. A precipitation by ammonium sulfate (40% saturation) produced an additional 1.9-fold increase. The yield of this partial purification was 16%. Towards the nucleotides UTP and GTP the enzyme showed an activity slightly higher, and towards ITP and CTP an activity slightly lower than that with ATP. ADP was split about half as fast as ATP. AMP was not accepted by the enzyme. Replacing MgCl2 by CaCl2 resulted in an ATPase activity of 92% of that with MgCl2. Using calcium- and magnesium-ATP as substrates, apparent Km values of 0.22 and 0.33 mM, respectively, were obtained. The gel electrophoresis revealed the enrichment of a protein with an apparent Mr of 95000 and also that of microvillus actin.

Adenosine Triphosphatases↗

PubMed1985

Solubilization and reconstitution of cholinephosphotransferase from sarcoplasmic reticulum: stabilization of solubilized enzyme by diacylglycerol and glycerol.

Cholinephosphotransferase (CDPcholine: 1,2-diacylglycerol cholinephosphotransferase, EC 2.7.8.2), which catalyzes the terminal step in phosphatidylcholine synthesis via the CDPcholine pathway, is present in sarcoplasmic reticulum from rabbit skeletal muscle (Cornell, R. and MacLennan, D.H. (1985) Biochim. Biophys. Acta 835, 567-576). The conditions for solubilization and reconstitution of this enzyme were investigated as a preliminary step towards its eventual purification. The activity was not released by treatment of membranes with 1 M KCl, but was solubilized after dissolution of membranes with detergents. Cholinephosphotransferase was inactivated by cholate, deoxycholate, Triton X-100, octylglucoside, Tween-20 or SDS at concentrations which solubilize the membrane. However, the activity could be fully recovered after reconstituting the membrane by adding excess lipid (soybean) and removing detergent by gel filtration, dialysis or by absorption to Bio-Beads. When the membrane was solubilized with octylglucoside or cholate at weight ratios of detergent: membrane protein of at least 10, the activity was irreversibly lost unless stabilizers were added with detergent. The substrate diacylglycerol and glycerol were effective stabilizers.

Animals↗