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Biomedical subjects

D M Small

Publications and source records attributed to D M Small.

At least 109 records · Page 6Linked to original sources
PubMed1983

Triolein-cholesteryl oleate-cholesterol-lecithin emulsions: structural models of triglyceride-rich lipoproteins.

The organization of lipids within emulsions composed of triolein (TO), cholesteryl oleate (CO), cholesterol (C), and egg yolk phosphatidylcholine (L) was examined. CO was substituted for TO in a series of emulsions to obtain TO:CO ratios comparable to the triglyceride:cholesterol ester ratios observed in subfractions of triglyceride-rich lipoproteins. The weight fraction of TO in the surface phase (0.02-0.05) was independent of the TO content of the emulsions. However, the weight fraction of CO in the surface phase depended upon the percentage of CO in the emulsions and was less than 0.004 even when 13.7% CO was present in the emulsion. When CO was substituted for TO, the percent of the total particle C which was carried in the droplet oil phase was increased. The interparticle equilibration of lipids was studied in subfractions of sonicated emulsions with particle sizes comparable to triglyceride-rich lipoproteins. The TO:CO ratios of the subfractions of a given emulsion were constant and independent of size, but the C:L ratio decreased in particles of smaller diameter. However, the surface C:L ratio was the same in all particles from a given emulsion. The size dependence of the C:L ratios was attributed to the partitioning of C into the oil cores of the emulsions. Because large droplets have the greatest core:surface mass ratios, more of their total particle C is carried in the core.

Chemical Phenomena↗
PubMed1983

Relationship of an abnormal plasma lipoprotein to protection from atherosclerosis in the cholesterol-fed diabetic rabbit.

Alloxan-diabetic rabbits develop a pronounced hypercholesterolemia and hypertriglyceridemia in response to cholesterol feeding. Despite higher levels of plasma cholesterol, these animals have much less atherosclerosis than cholesterol-fed nondiabetics. To determine whether this effect is due to properties of the lipoproteins, we compared chemical, physical, and metabolic characteristics of a very low density lipoprotein (VLDL) fraction (d less than 1.019 g/ml) from the diabetic and nondiabetic cholesterol-fed rabbits. The molar ratio of triglyceride to cholesteryl ester in the particles from diabetic animals ranged from 2:1 to 6:1, and this ratio remained constant in subfractions from individual rabbits. Triglyceride from nondiabetic control animals was a minor component. Differential scanning calorimetry showed a distinct order-disorder phase transition for cholesteryl ester at approximately 42 degrees C in the fractions from control animals, whereas in fractions from most of the diabetics no such transition was observed, indicating that both triglyceride and cholesteryl ester are present in the core of the same particle. The relative amount of apoprotein E in particles from diabetic animals was much less than that of cholesterol-fed controls. The ability of the lipoproteins from both groups to stimulate cholesteryl ester formation in mouse peritoneal macrophages also was tested. Lipoproteins from cholesterol-fed controls stimulated cholesteryl ester formation in a dose-dependent manner, but particles from the diabetic group had little or no effect. The results suggest that the presence of unusual VLDL particles in diabetic cholesterol-fed rabbits is responsible, at least in part, for the reduced incidence of atherosclerosis in this animal model.

Animals↗
PubMed1982

Temperature-dependent molecular motions of cholesterol esters: a carbon-13 nuclear magnetic resonance study.

Carbon-13 NMR spectroscopy at 50.3 MHz has been used to study four long-chain cholesterol esters with a double bond in the omega-9 position: cholesteryl oleate, C18:1, omega-9; cholesteryl linoleate, C18:2, omega-6,9; cholesteryl erucate, C22:1, omega-9; cholesteryl nervonate, C24:1, omega-9. The linoleate and oleate esters exhibit two metastable liquid-crystalline phases (cholesteric and smectic), whereas the longer chain esters form a stable smectic phase but no cholesteric phase [Ginsburg, G. S., & Small, D. M. (1981) Biochim. Biophys. Acta 664, 98-107]. Line widths (nu 1/2), spin--lattice relaxation times (T1), and nuclear Overhauser enhancements (NOE) were measured for all well-resolved resonances from ring and fatty acyl (FA) carbons at different temperatures in the isotropic liquid of each ester. T1 and NOE values of FA resonances were constant between the FA-2 carbon and olefinic region of each acyl chain and increased markedly for carbons near the chain terminus. FA carbon motions are thus restricted and/or highly correlated in the region between the ring and the olefinic carbons, suggesting that strong interactions occur between cholesterol ester molecules in this region of the FA chain. These results also suggest that the FA chains are approximately extended in the isotropic liquid. Steroid ring methine C-6 and C-3 nu 1/2's increased differentially on cooling to the liquid leads to liquid crystal transition temperature (Tm) of each ester, indicative of increasingly anisotropic ring rotations. The rotational anisotropy was quantitated by using a prolate ellipsoid model for the cholesterol ester molecule for which two correlation times (corresponding to rotations about the long and short molecular axes) were calculated from the C-3 and C-6 nu 1/2 values. The C-3/C-6 nu 1/2 ratio was directly proportional to the anisotropy of the ring motions as measured by the ratio of the two correlation times. At any given temperature relative to Tm, the C-3 and C-6 nu 1/2's and the C-3/C-6 nu 1/2 ratios were larger for cholesterol esters which have a cholesteric phase than for esters which have no cholesteric phase, showing that steroid ring motions were more restricted and more anisotropic prior to the formation of a cholesteric phase. Cholesteryl erucate and cholesteryl nervonate have longer regions of FA chain interactions which result in greater chain cooperativity, apparently preventing the preordering of steroid rings to the degree necessary for formation of a cholesteric phase. Thus, these esters form the smectic phase directly from the isotropic liquid. These results are applied to the cholesterol ester transition in plasma low-density lipoproteins.

Carbon Isotopes↗
PubMed1982

Solubilization and localization of cholesteryl oleate in egg phosphatidylcholine vesicles. A carbon 13 NMR study.

Co-sonicated mixtures of egg phosphatidylcholine and small amounts (less than or equal to 4%, w/w) of [carbonyl-13C]cholesteryl oleate have been studied by 13C NMR spectroscopy at 50.3 MHz. The carbonyl chemical shift from cholesteryl oleate solubilized in vesicles was 1 ppm downfield from the carbonyl chemical shift of cholesteryl oleate present in a separate oil phase. The maximum solubility of the steroid in vesicles determined by chemical analysis of purified vesicles was 1.6 weight % (approximately 2 mol %), in close agreement with the maximum solubility estimated from NMR speak intensity measurements (1.4 weight %). The downfield shift indicates hydrogen bonding of solvent (H2O) molecules with the cholesteryl oleate carbonyl group, suggesting that vesicle-solubilized cholesteryl oleate molecules are located in the phospholipid bilayer with the carbonyl group close to the aqueous interface and the sterol ring and fatty acyl chain approximately parallel to the fatty acyl chains of the phospholipid. Such a folded conformation and localization of the carbonyl group at the aqueous interface may facilitate interactions of sterol esters with cholesterol ester transfer proteins and cholesterol esterases.

Cholesterol Esters↗
PubMed1982

Mobilization of cholesterol from cholesterol ester-enriched tissue culture cells by phospholipid dispersions.

The accumulation of cholesterol esters in foam cells of the arterial intima is an important characteristic of fatty streak lesions of atherosclerosis. We wished to know if cholesterol ester accumulations in cells could be mobilized by altering their external milieu. Thus, phospholipid dispersions were used to remove cholesterol from a cholesterol ester-enriched cell line. Rat hepatoma cells, Fu5AH, were loaded with cholesterol esters by incubation in medium supplemented with hyperlipemic rabbit serum. After removing the loading medium, we incubated the cells in serum-free medium containing egg phosphatidylcholine dispersions. Unesterified cellular cholesterol level decreased in the first 4 h and then remained at a constant level. The cholesterol esters decreased after a lag time of about 2 h and the triacylglycerol level increased after 3 h. The decrease in cellular cholesterol ester depended on the amount of phospholipid in the medium. Cellular cholesterol ester decreased with increasing concentration of medium phospholipid to 2 mumols/ml and then plateaued. The removed cellular sterols appeared in the medium as free cholesterol. Since there was no measurable cholesterol esterase activity in the medium, the cholesterol ester in the cells was hydrolyzed before it appeared in the medium. The fatty acyl composition of the cellular cholesterol esters remained unchanged after significant reduction, suggesting that the hydrolysis of cholesterol esters was not specific for the acyl chain. Sphingomyelin and dimyristoyl phosphatidylcholine dispersions, though cytotoxic, were also effective in reducing cellular cholesterol esters. These experiments demonstrate that cholesterol ester accumulations in these cells can be reduced when phospholipid dispersions are used as cholesterol acceptors in the extracellular medium.

Animals↗
PubMed1982

Transluminal angioplasty in experimental atherosclerosis. Analysis for embolization using an in vivo perfusion system.

We used polarized light microscopy and thin-layer chromatography to determine whether embolization of atherosclerotic material occurs after transluminal angioplasty. The experimental model consisted of an in vivo perfusion system of the atherosclerotic rabbit left iliac artery. Of eight rabbits that underwent successful angioplasty, four had angiographic evidence of dissection and three showed aneurysm formation. Histologic studies demonstrated fracture of the intimal plaque, dissection, and stretching of the noninvolved portion of the vessel. Perfusate analysis revealed no detectable cholesterol by thin-layer chromatography in six of eight rabbits. In two rabbits, a very small amount of cholesterol was measured, which was totally accounted for by hemorrhage into the perfusate rather than from cholesterol in the plaque. No evidence of arterial wall embolic debris could be detected by polarized light microscopy in seven rabbits, but lipid debris from the plaque was found in the perfusate of one rabbit that had excessive arterial trauma. We conclude that the major mechanism of successful transluminal angioplasty in this experimental model is intimal fracture combined with stretching of a noninvolved portion of the vessel. Furthermore, embolization of atheromatous lipid debris was an uncommon event related to arterial trauma during catheter placement rather than transluminal angioplasty itself.

Angioplasty, Balloon↗
PubMed1982

National Cooperative Gallstone Study: the effect of chenodeoxycholic acid on lipoproteins and apolipoproteins.

Subjects in the National Cooperative Gallstone Study undergoing 12 mo of therapy with chenodeoxycholic acid for the dissolution of gallstones (low-dose, 375 mg/day, n =252; high-dose, 750 mg/day, n = 253) had a mean increase in serum cholesterol of 20 mg/dl as compared with a 5 mg/dl increase in the placebo group (n = 258). The effect of chenodeoxycholic acid on lipoproteins was determined in a random subset of the high-dose (n = 136) and placebo (n = 143) groups. For men, the mean baseline adjusted estimated low-density lipoprotein cholesterol level at 12 mo was significantly higher in the high-dose group than in the placebo group (159 vs. 148 mg/dl, p less than 0.01), whereas among women this difference was not demonstrated. Change in low-density lipoprotein cholesterol level was inversely related to baseline cholesterol to an equivalent degree in each group among men and women. Women in the high-dose group had significantly lower very-low-density lipoprotein cholesterol levels than did the corresponding placebo group (27 vs. 32 mg/dl, p less than 0.003). Very-low-density lipoprotein cholesterol levels did not differ significantly between the high-dose and placebo group in men. Treatment did not significantly affect the levels of high-density lipoprotein cholesterol or apoproteins A-I, A-II, or B. Chenodeoxycholic acid therapy produces an increase in total cholesterol and low-density lipoprotein cholesterol but does not alter high-density lipoprotein cholesterol levels.

Apolipoprotein A-I↗
PubMed1982

The effect of elevated biliary tract pressure on biliary lipid metabolism and bile flow in nonhuman primates.

The effects of low (control), moderate, and high biliary tract pressures on biliary lipid metabolism and bile flow were studied in six rhesus monkeys and two baboons. Moderate pressures did not influence bile flow or biliary lipid metabolism. High biliary tract pressures produced significant reductions in bile flow and the secretion rates of bile salts, phospholipids, and cholesterol, but cholesterol saturation in bile improved. High pressure also completely inhibited bile salt synthesis, and the bile salt pool size decreased slightly due to continuing small losses in urine and bile samples. During the high pressure period bile salts accumulated in the liver and peripheral tissues. After pressure had been returned to control levels, bile flow and biliary lipid secretion rates returned to normal levels. Bile salt secretion recovered more slowly than secretion of the other lipids and bile became more saturated with cholesterol than in the control period. Bile salt synthesis resumed approximately 10 hr after pressure had been returned to control levels. The high biliary tract pressures induced in these studies are no known to occur in about 25% of normal human subjects. (J Lab Clin Med 99:342, 1982.)

Animals↗
PubMed1982

Rapid method for determining cholesteryl ester transitions of apoB-containing lipoproteins.

A wide variety of cholesteryl ester-rich apoB-containing lipoproteins undergo an order-disorder transition in the cholesteryl ester core at approximately normal body temperature. The transition occurs over several degrees C with the mid-point being as high as 57 degrees C in some cholesterol-fed animals. The transition mid-point of normal human low density lipoprotein (LDL) appears to vary from as low as 26 degrees C to about body temperature. However, to screen a large population of patients at risk for atheroscerlotic cardiovascular disease (ACD), a rapid method for determining the transition temperature of LDL is needed. Since apoB-containing lipoproteins (VLDL and LDL) are readily precipitated from plasma by dextran sulfate and magnesium sulfate, we have studied the thermal properties of this precipitate using differential scanning calorimetry (DSC). The VLDL-LDL precipitate undergoes a reversible thermal transition similar in transition temperature and enthalpy to the cholesteryl ester transition of isolated pure LDL. The transition is seen with the precipitate from VLDL-free plasma, but no transition is seen when VLDL and LDL have been removed. Cholesteryl ester-rich apoB containing lipoproteins were isolated from a variety of sources (man, cholesterol-fed monkeys, and rabbits) and their transition temperatures compared with the apoB-containing lipoprotein precipitates from the same source. The mid-point of individual transitions varied over a wide range (17-57 degrees C) and the correlation between the pure lipoprotein and the plasma precipitate was strong (r = 0.98, P < 0.001. Thus, DSC of the plasma apoB precipitate may be used as a rapid method of determining the cholesteryl ester transition of LDL and other apoB-containing lipoproteins.-Waugh, D. A., and D. M. Small. Rapid method for determining cholesteryl ester transitions of apoB-containing lipoproteins.

Adult↗
PubMed1982

Physical studies of d less than 1.006 g/ml lymph lipoproteins from rats fed palmitate-rich diets.

At body temperature the stable form of triglycerides rich in saturated fatty acids is crystalline. We examined the physical state of triglyceride-rich lymph lipoproteins from rats fed saturated fat, as a function of temperature. When chylomicrons and very low density lipoproteins were collected, isolated, and examined at 37 degrees C, they were liquid as judged by differential scanning calorimetry, x-ray diffraction analysis and proton nuclear magnetic resonance spectroscopy, and they appeared spherical by electron microscopy. At 23-26 degrees C, triglyceride began to crystallize in the alpha form, which transformed to the stable beta form at lower temperatures. On cooling from 23 degrees C to 17 degrees C, considerable crystallization occurred and the particle density was increased significantly. When lipoproteins were held at 0-7 degrees C, about 75% of the triglyceride crystallized, distorting the lipoprotein shape. Reheating from 0 degrees C to 37 degrees C left 25% of the triglyceride unmelted. Heating to 58 degrees C was necessary to melt all the crystallized triglyceride and to restore the spherical lipoprotein shape. After complete melting of cooled lipoproteins, the liquid state was maintained on recooling to 37 degrees C, with formation of a metastable particle similar to the nascent lipoprotein. Isolation of lipoproteins containing highly saturated triglyceride at temperatures below 23-26 degrees C results in partial crystallization, alters their physical properties, and may affect their metabolism.

Animals↗
PubMed1982

Cholesterol turnover in lipid phases of human atherosclerotic plaque.

The turnover of free cholesterol in atheromatous plaque lipid phases was studied in a patient undergoing peripheral vascular surgery. [14C]Cholesterol was injected intravenously 139 days prior to surgery, and [3H]cholesterol was injected 12 days pre-op. The plasma cholesterol specific radioactivity decay curves were determined from the times of isotope injection until surgery. At surgery, atheroma, skin, muscle, and tendon were obtained. Lipid phases of plaque homogenate were isolated by density gradient centrifugation. The top layer of the gradient, layer 1, contained the cholesteryl ester oil droplet phase, layer 2 was enriched in phospholipid bilayer phase, layer 3 contained cholesterol monohydrate crystals and the pellet, layer 4 had more dense plaque components such as collagen and elastin. The tissue:plasma specific radioactivity ratios on days 12 and 139 respectively were muscle, 0.86, 2.47; skin, 0.74, 1.20; tendon, 0.18, 1.45; total plaque, 0.22, 1.39; plaque layer 1, 0.31, 1.50; layer 2, 0.22, 1.53; layer 3, 0.08, 0.61; and layer 4, 0.20, 0.88. Thus, plaque atheroma, which contains physically distinct forms of cholesterol, had correspondingly different rates of cholesterol turnover. Cholesterol solubilized in liquid oil droplets (layer 1) and liquid crystalline phospholipid bilayers (layer 2) had specific radioactivity values similar to those of tendon cholesterol, and represented tissue cholesterol that was undergoing slow equilibration with the plasma cholesterol pool. Pellet cholesterol (layer 4), which is probably connective tissue-associated, had lower specific radioactivity values, well below those of plasma cholesterol even after 5 months. Crystalline cholesterol (layer 3) had the lowest specific radioactivity values of all tissues and plaque fractions. Therefore, cholesterol in the crystalline state is relatively inert. Since crystalline cholesterol can account for over 40% of plaque free cholesterol, resistance to mobilization of this lipid may be an important obstacle to plaque regression.

Aged↗
PubMed1982

Ionization behavior of aqueous short-chain carboxylic acids: a carbon-13 NMR study.

The 13C chemical shift of each carbon of aqueous acetic, propionic, and butyric acids has been measured as a function of pH or of added equivalents of base. A plot of chemical shifts for the carboxyl, alpha, and beta carbons as a function of pH is sigmoidal and yields pKa values that agree closely with values obtained by potentiometric titration. In contrast, a plot of chemical shift as a function of added equivalents of base is linear and has a sharp break at the equivalence point. Based on this result, we propose that the local (microscopic) ionization state of the carboxyl group can be determined directly by NMR without need for pH or pK determinations. In addition to titration curves, the effects of concentration, ionic strength, and temperature upon fatty acid chemical shifts are reported. For aqueous acids, changes in ionic strength and temperature have no effect on chemical shifts. However, changes in concentration do affect chemical shifts, probably as a result of changes in the relative degree of acid-acid and acid-water hydrogen bonding. Our results provide necessary background data for 13C NMR studies of higher fatty acids in lipid-lipid and lipid-protein systems.

Acetates↗
PubMed1981

Physical characterization of lymph chylomicrons and very low density lipoproteins from nonhuman primates fed saturated dietary fat.

Differential scanning calorimetry (DSC) and x-ray diffraction studies were performed on chylomicrons and very low density lipoproteins (VLDL), from nonhuman primates fed saturated fat, isolated from lymph at two different temperatures (15 and 39 degrees C). When heated from -10 leads to 60 degrees C, chylomicrons and VLDL isolated at 15 degrees C had two endothermic transitions resulting from the melting of triglycerides (TG). Cooling resulted in the onset of crystallization of the TG core at 16-19 degrees C; 50% of the TG in the particles remained fluid at 4 degrees C. The initial DSC pattern was reproduced not on immediate reheating, but by storing samples at 4 degrees C overnight. Chylomicrons isolated at 39 degrees C contained a metastable (undercooled) TG core until cooled to the onset of TG crystallization at 16-19 degrees C. Reheating the particles with crystalline TG to body temperature (39 degrees C) resulted in a partially crystalline TG core, not an undercooled liquid. To ascertain the effect of particle structure on the TG physical properties, intact particles were compared with heat denatured particles and extracted lipids. The onset of crystallization was lower and the time necessary for isothermal crystallization was much greater for intact versus denatured particles or lipids. Only minor differences in physical properties as a function of particle size were found. It was concluded that: 1) the physical state of chylomicrons and VLDL TG core can be modified by isolation temperature; 2) particle structure affects crystallization but not melting of chylomicrons and VLDL TG; and 3) chylomicrons particle size does not markedly influence the physical properties of the TG core.

Animals↗
PubMed1981

X-ray diffraction and calorimetric study of anhydrous and hydrated N-palmitoylgalactosylsphingosine (cerebroside).

Differential scanning calorimetry and X-ray diffraction of anhydrous and hydrated N-palmitoylgalactosylsphingosine (NPGS) show evidence of complex polymorphic behavior and interconversions between stable and metastable structural forms. Anhydrous NPGS exhibits three lamellar crystal forms (A, B, and B') at temperatures below 143 degrees C and a liquid-crystal form between 143 and 180 degrees C before melting to an isotropic liquid at 180 degrees C. The crystal B leads to liquid-crystal transition is accompanied by an enthalpy change, delta H, of 11.2 kcal/mol of NPGS, while a relatively small enthalpy change (delta H = 0.8 kcal/mol) marks the liquid-crystal leads to liquid transition. The A and B' crystal forms do not hydrate readily at room temperature. When heated, crystal form A in the presence of water undergoes an exothermic transition at 52 degrees C to produce a thermodynamically stable hydrated crystal E form. X-ray diffraction shows that this stable bilayer crystal form has a highly ordered hydrocarbon chain packing arrangement; melting to the bilayer liquid-crystal form occurs at 82 degrees C with a large enthalpy change, delta H = 17.5 kcal/mol of NPGS. A complex liquid-crystal leads to crystal transition is observed on cooling; the cooling rate independent exotherm involves the transition of the hydrated liquid crystal to an intermediate metastable crystal form identical with anhydrous crystal form A. The subsequent cooling rate dependent step involves the conversion of the metastable crystal form A to the stable crystal form E. We suggest that hydrated crystal form E is stabilized by both a highly ordered chain packing mode and a lateral intermolecular hydrogen bonding network involving the sphingosine backbone, the galactosyl group, and interbilayer water molecules. Although disruption of both the specific hydrogen chain packing and H-bonding networks occurs at the high enthalpy transition to the bilayer liquid-crystal L alpha form, these two types of interactions are not reestablished simultaneously on cooling. First, recrystallization of the hydrocarbon chain accompanies removal of water from the lipid interface, leading to "dehydrated" metastable crystal form A. This is followed by a time-dependent, temperature-dependent hydration process which allows a rearrangement of the hydrogen-bonding matrix. Alterations in the NPGS-NPGS and NPGS-water interactions accompany further changes in the hydrocarbon chain packing and lead to the formation of the stable E form.

Animals↗