Hypertension exacerbates coronary artery disease in transgenic hyperlipidemic Dahl salt-sensitive hypertensive rats

BACKGROUND

The mechanisms underlying the known interaction of two complex polygenic traits, hypertension and hyperlipidemia, resulting in exacerbation of coronary artery disease have not been elucidated. Identification of critical pathways underlying said exacerbation could identify mechanism-based targets for intervention and prevention.

MATERIALS AND METHODS

To investigate hypertension- atherosclerosis interaction, we studied the inbred transgenic atherosclerosis-polygenic hypertension Dahl salt-sensitive (S) rat model (Tg53), which over-expresses human cholesteryl ester transfer protein (hCETP) in the liver, and exhibits coronary artery disease and decreased survival compared with control non-transgenic Dahl S rats. Using serial-section histopathological and immunohistochemical analyses, we analyzed the coronary artery disease phenotype of Tg53 rats at end-stage marked by cardio-respiratory compromise as the experimental equivalent of acute coronary syndromes, and determined the effects of reduction of blood pressure through low salt diet (0.008% NaCl) on the coronary artery disease phenotype and survival.

RESULTS

End-stage Tg53 rats exhibit coronary artery lesions in the proximal right coronary artery system which exhibit "culprit plaque" features such as plaque inflammation, matrix degradation, apoptosis, neovascularization, thrombosis and hemorrhage recapitulating said features and heterogeneity of human coronary "culprit plaques". Comparative analysis of 6 month vs end-stage lesions reveals distinct lesion development profiles of proximal coronary lesions which quickly progress from eccentric non-occlusive foam-cell rich lesions at 6 months to occlusive "culprit plaques", compared with more distal coronary lesions which exhibit occlusive thick-cap atheroma that remain relatively unchanged from 6 months to end stage. Reduction of hypertension through a low-salt (0.008% NaCl) diet increased survival (P < 0.0001) of Tg53 rats and significantly attenuated the coronary artery disease phenotype detected at 10 months of age marked by diminished apoptosis, neovascularization, matrix degradation compared with end-stage lesions detected at <8 months of age.

CONCLUSIONS

End stage coronary lesions in the Tg53 rats recapitulate many, albeit not all, features of "culprit plaques" in humans supporting proposed paradigms of plaque vulnerability implicating lesion macrophage enrichment, apoptosis, matrix degradation and pathological neovascularization. Comparative time course analysis of coronary lesions reveals that plaques which develop into end-stage "culprit plaques" are distinct from "stable plaques" by location and early lesion morphology, suggesting distinct lesion development and progression pathways. The significant effects of low-salt diet-induced decrease in hypertension on right coronary disease phenotype provides compelling evidence that polygenic hypertension accelerates coronary plaque progression and complication independent of cardiac hypertrophy, and more importantly provides paradigmatic support for public health policy.

Diffusion behavior of lipid vesicles in entangled polymer solutions

Dynamic light scattering was used to follow the tracer diffusion of phospholipid/cholesterol vesicles in aqueous polyacrylamide solutions and compared with the diffusive behavior of polystyrene (PS) latex spheres of comparable diameters. Over the range of the matrix concentration examined (Cp = 0.1-10 mg/ml), the diffusivities of the PS spheres and the large multilamellar vesicles exhibited the Stokes-Einstein (SE) relation, while the diffusivity of the unilamellar vesicles did not follow the increase of the solution's viscosity caused by the presence of the matrix molecules. The difference between the diffusion behaviors of unilamellar vesicles and hard PS spheres of similar size is possibly due to the flexibility of the lipid bilayer of the vesicles. The unilamellar vesicles are capable of changing their shape to move through the entangled polymer solution so that the hindrance to their diffusion due to the presence of the polymer chains is reduced, while the rigid PS spheres have little flexibility and they encounter greater resistance. The multilamellar vesicles are less flexible, thus their diffusion is similar to the hard PS spheres of similar diameter.

Monoacylglycerols alter the lipid composition and molecular mobility of phosphatidylcholine bilayers: 13C NMR evidence of dynamic lipid remodeling

The physical effects of monoacylglycerols (MAG) in small unilamellar vesicles composed of phosphatidyl-choline (PC), triolein, cholesterol, and varying amounts of monopalmitin and monoolein were studied by 13C-NMR. The signal to noise ratio of the carbonyls of PC and triolein were enhanced by the addition of 1,2-di-[1-13C]palmitoylphosphatidylcholine and tri-[1-13C]oleoylglycerol. The linewidths of the carbonyl-13C, choline methyl, olefinic carbon, and terminal methyl resonances were measured digitally from vesicles with 0 to 42 mol % of MAG. Significant increases in the linewidth of carbonyl (P < 0.05), olefinic and terminal methyl carbons (P < 0.01) of vesicles containing 42 mol % monopalmitin indicated that these groups experienced restricted molecular mobility at high monopalmitin concentrations. However, more striking was the apparent displacement of triolein from the surface environment of PC bilayers to an oil-like environment in systems containing only 8 mol % monopalmitin. Displacement of triolein from the surface by monoolein occurred only above 15 mol %. Thus, saturated and monounsaturated monoacylglycerols, natural products of lipoprotein metabolism, dynamically alter both the lipid composition and molecular mobility of lipoprotein surfaces in distinct ways.

Calorimetry of apolipoprotein-A1 binding to phosphatidylcholine-triolein-cholesterol emulsions

The thermotropic properties of triolein-rich, low-cholesterol dipalmitoyl phosphatidylcholine (DPPC) emulsion particles with well-defined chemical compositions (approximately 88% triolein, 1% cholesterol, 11% diacyl phosphatidylcholine) and particle size distributions (mean diameter, approximately 1000-1100 A) were studied in the absence and presence of apolipoprotein-A1 by a combination of differential scanning and titration calorimetry. The results are compared to egg yolk PC emulsions of similar composition and size. Isothermal titration calorimetry at 30 degrees C was used to saturate the emulsion surface with apo-A1 and rapidly quantitate the binding constants (affinity Ka = 11.1 +/- 3.5 x 10(6) M-1 and capacity N = 1.0 +/- 0.09 apo-A1 per 1000 DPPC) and heats of binding (enthalpy H = -940 +/- 35 kcal mol-1 apo-A1 or -0.92 +/- 0.12 kcal mol-1 DPPC). The entropy of association is -3070 cal deg-1 mol-1 protein or -3 cal deg-1 mol-1 DPPC. Without protein on the surface, the differential scanning calorimetry heating curve of the emulsion showed three endothermic transitions at 24.3 degrees C, 33.0 degrees C, and 40.0 degrees C with a combined enthalpy of 1.53 +/- 0.2 kcal mol-1 DPPC. With apo-A1 on the surface, the heating curve showed the three transitions more clearly, in particular, the second transition became more prominent by significant increases in both the calorimetric and Van't Hoff enthalpies. The combined enthalpy was 2.70 +/- 0.12 kcal mol-1 DPPC and remained constant upon repeated heating and cooling. Indicating that the newly formed DPPC emulsion-Apo-A1 complex is thermally reversible during calorimetry. Thus there is an increase in delta H of 1.17 kcal mol-1 DPPC after apo-A1 is bound, which is roughly balanced by the heat released during binding (-0.92 kcal) of apo-A1. The melting entropy increase, +3.8 cal deg-1 mol-1 DPPC of the three transitions after apo-A1 binds, also roughly balances the entropy (-3 cal deg-1 mol-1 DPPC) of association of apo-A1. These changes indicate that apo-A1 increases the amount of ordered gel-like phase on the surface of DPPC emulsions when added at 30 degrees C. From the stoichiometry of the emulsions we calculate that the mean area of DPPC at the triolein/DPPC interface is 54.5 A2 at 41 degrees C and 54.2 A2 at 30 degrees C. The binding of apo-A1 at 30 degrees C to the emulsion reduces the surface area per DPPC molecule from 54.2 A2 to 50.8 A2. At 30 degrees apo-A1 binds with high affinity and low capacity to the surface of DPPC emulsions and increases the packing density of the lipid domain to which it binds. Apo-A1 was also titrated onto DPPC emulsions at 45 degrees C. This temperature is above the gel liquid crystal transition. No heat was released or adsorbed. Furthermore, egg yolk phosphatidylcholine emulsions of nearly identical composition were also titrated at 30 degrees C with apo-A1 and were euthermic. Association constants were previously measured using a classical centrifugation assay and were used to calculate the entropy of apo-A1 binding (+28 cal deg-1 mol-1 apo-A1). This value indicates that apo-A1 binding to a fluid surface like egg yolk phosphatidylcholine or probably DPPC at 45 degrees C is hydrophobic and is consistent with hydrocarbon lipid or protein moities coming together and excluding water. Thus the binding of apo-A1 to partly crystalline surfaces is entropically negative and increases the order of the already partly ordered phases, whereas binding to liquid surfaces is mainly an entropically driven hydrophobic process.

Mucin-vesicle interactions in model bile: evidence for vesicle aggregation and fusion before cholesterol crystal formation

Nucleation of cholesterol monohydrate crystals from bile is a critical step in the formation of cholesterol gallstones. Measurement of nucleation in model bile system and the characteristics of the initial nucleus have proven elusive. In this study we have used three separate physical chemical techniques to examine vesicle aggregation and fusion, including dynamic light scattering (DLS), transmission electron microscopy (TEM), and fluorescent biochemical assays. These assays enabled us to quantify the effect of biliary proteins, such as gallbladder mucin, on vesicle fusion and aggregation. In the absence of mucin, fusion is a relatively slow process occurring over 24 hours, whereas physiological concentrations of mucin are able to accelerate almost complete fusion of vesicles within 6 hours. Vesicle fusion and aggregation as characterized by TEM result in the formation of aggregates of multilamellar vesicles and giant fusion bodies associated with a background of mucin. These mucin-vesicle aggregate bodies may represent true nuclei and precede cholesterol monohydrate crystal nucleation. In future studies, these vesicle fusion assays can be used to quantitatively examine the effect of putative pro- and anti-nucleating proteins on the earliest steps of cholesterol crystal nucleation.

Bile acid derived HMG-CoA reductase inhibitors

The target organ for HMG-CoA reductase inhibitors to decrease cholesterol biosynthesis in hypercholesterolemic patients is the liver. Since bile acids undergo an enterohepatic circulation showing a strict organotropism for the liver and the small intestine, the structural elements of an inhibitor for HMG-CoA reductase were combined with those for specific molecular recognition of a bile acid molecule for selective uptake by hepatocytes. Either, the HMG-CoA reductase inhibitors HR 780 and mevinolin were covalently attached to 3 xi-(omega-aminoalkoxy)-7 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acids to obtain bile acid prodrugs, or the side chain of bile acids at C-17 was replaced by 3,5-dihydroxy-heptanoic acid--a structural element essential for inhibition of HMG-CoA reductase--to obtain hybrid bile acid: HMG-CoA reductase inhibitors. The prodrugs could, as expected, not inhibit rat liver HMG-CoA reductase to a significant extent, whereas the hybrid inhibitors showed a stereospecific inhibition of HMG-CoA reductase from rat liver microsomes with an IC50-value of 0.7 microM for the most potent compound S 2467 and 6 microM for its diastereomere S 2468. Uptake measurements with isolated rat hepatocytes and ileal brush-border membrane vesicles from rabbit small intestine revealed a specific interaction of both classes of bile acid-derived HMG-CoA reductase inhibitors with the hepatocyte and ileocyte bile acid uptake systems. Photoaffinity labeling studies using 3-azi- or 7-azi-derivatives of taurocholate with freshly isolated rat hepatocytes or rabbit ileal brush-border membrane vesicles revealed a specific interaction of bile acid derived HMG-CoA reductase inhibitors with the respective putative bile acid transporters in the liver and the ileum demonstrating the bile acid character of these derivatives, both for the prodrugs and the hybrids. Cholesterol biosynthesis in Hep G2 cells was inhibited by the bile acid prodrugs with IC50-values in the range of 68 nM to 600 nM compared to 13 nM for HR 780 and 130 nM for mevinolin. Among the hybrid inhibitors, S 2467 was the most active compound with an IC50-value of 16 microM compared to 55 microM for its diastereomere S 2468. Preliminary in vivo experiments showed an inhibition of hepatic cholesterol biosynthesis after oral dosage only with prodrugs such as S 3554, whereas the hybrid molecules were inactive after oral application.(ABSTRACT TRUNCATED AT 400 WORDS)

Bovine gallbladder mucin accelerates cholesterol monohydrate crystal growth in model bile

BACKGROUND

Gallbladder mucin accelerates cholesterol crystal nucleation, an early step in the pathogenesis of gallstones. To examine the role of gallbladder mucin in postnucleation gallstone maturation, the influence of mucin on cholesterol monohydrate crystal growth was studied in a novel model system.

METHODS

Cholesterol crystals of a uniform size were incubated in model biles at 37 degrees C with varying cholesterol saturation indices. Crystal size was quantitated by measuring the width and length of individual crystals under polarizing light microscopy and calculating average crystal area.

RESULTS

Crystal growth was dependent on the degree of cholesterol supersaturation of bile. Bovine gallbladder mucin (0.5-8 mg/mL) accelerated crystal growth in supersaturated model bile in a concentration- and time-dependent fashion compared with control incubations with bovine serum albumin or model bile alone (P < 0.05). Cholesterol crystal growth was accompanied by a progressive decrease in cholesterol saturation and an increase in total cholesterol crystal mass. Crystal growth was also accompanied by a decrease in total crystal number, suggesting net transfer of cholesterol to larger crystals.

CONCLUSIONS

The acceleration of cholesterol crystal growth by gallbladder mucin may be of pathophysiological importance in the postnucleation maturation of cholesterol gallstones.

Expression of human apolipoprotein E but not that of apolipoprotein A-I by mouse C127 cells is associated with increased secretion of lipids in the form of vesicles and discs

Transfected mouse mammary-derived cells (C127) expressing human apolipoprotein (apo) E (C127E) were used a) to determine whether the lipid-binding character of apoE is sufficient to promote its assembly with lipid to form lipoprotein-like particles when expressed by cells not normally expressing apolipoproteins; b) to characterize the secreted complexes in terms of morphology, size, and composition; and finally c) to determine whether apoE or apoA-I gene expression by these transfected cells has any effect on the levels and the profiles of the synthesized and secreted lipids. The findings of the present study demonstrate that: a) as determined by density gradient ultracentrifugation and gel filtration chromatography, about 20% of the secreted [35S]methionine-labeled apoE expressed by C127E cells is lipid-associated. b) Negative-stain electron microscopic analysis of the lipid-protein complexes recovered in the lipoprotein fractions (d less than 1.21 g/ml) revealed that approximately 13% of the total population of particles were discs (16 +/- 5 nm mean diameter and 4-6 nm thick), resembling nascent high density lipoproteins (HDL). The majority of the particles however (greater than 82%) appeared vesicular with varying diameters (48 +/- 40 nm mean diameter). The discoidal and the vesicular appearance of the particles secreted by C127E cells is consistent with the composition of lipids. These consisted mostly of surface lipids, phospholipids (45 +/- 18%), diacylglycerols (36 +/- 17%), and free cholesterol (17 +/- 7%) (by weight). c) Expression of apoE by C127E cells was associated with an increased release of [35S]methionine-labeled protein and [3H]glycerol-labeled lipid (3- to 5- and 4- to 8-fold, respectively) compared to nontransfected C127 cells. Expression of mutant apoE or normal apoA-I, however, was not associated with increased release of the major lipid classes compared to the parent C127 cells, strongly suggesting that this character of C127E cells is specific to apoE expression. The release of lipids by C127E cells could be reduced considerably by the addition of the metabolic inhibitors, colchicine or cycloheximide (10 and 1 microM, respectively), suggesting that lipid release by C127E cells is an active process requiring both protein synthesis and functional secretory mechanisms. Taken together the findings suggest that apoE expression by C127 cells promotes the formation of nascent discoidal lipoprotein-like particles and enhances the release of vesicular lipids, possibly by promoting shedding of cell plasma membrane fragments.

A comparison of lipoprotein secretion, bile production and hepatic morphology in isolated rat livers perfused with a perfluorocarbon emulsion or rat erythrocytes

Isolated rat livers were perfused with an oxygenated perfluorocarbon emulsion, FC-43 emulsion for 1 to 4 hr. FC-43 emulsion contained 20% FC-43 (wt/vol) perfluorotributylamine (the fluorocarbon component for the transport of oxygen and carbon dioxide) emulsified with 2.56% Pluronic F-68 (a nonionic surfactant) in Krebs-Ringer bicarbonate buffer. FC-43 emulsion also contained 3% hydroxyethyl starch as an oncotic agent and 1.8 mg/ml glucose. The viability (oxygen consumption), bile secretion, structural integrity and secretion of nascent lipoproteins by FC-43-perfused rat livers was compared with livers perfused with Krebs-Henseleit bicarbonate buffer that contained rat erythrocytes (25% hematocrit) and 1.5 mg/ml glucose (red blood cell medium). Oxygen consumption was somewhat higher in livers perfused with FC-43 emulsion. Bile secretion of livers perfused with FC-43 emulsion for 4 hr was reduced significantly to 40% of that by red blood cell medium. The structural integrity of livers perfused with FC-43 emulsion varied from normal to marked cellular damage. Light-microscopical examination of rat livers perfused with FC-43 emulsion showed ballooning of sinusoids, presence of vacuoles in sinusoidal lining cells in some hepatocytes and detachment of endothelium in sinusoids. The number of vacuoles progressively increased in longer perfusions. Electron-microscopical studies showed the presence of small (60 to 100 nm) vesicles of varying electron density, presumably fluorocarbon particles inside the vacuoles in sinusoidal lining cells (Kupffer and endothelial) and hepatocytes. After 4 hr of perfusion with FC-43 emulsion, most of the sinusoidal endothelia were denuded, and the microvilli of the hepatocytes all but disappeared. In contrast, the ultrastructure of rat livers perfused with red blood cell medium for 4 hr was unaltered. The accumulation of nascent lipoproteins in perfusates of FC-43-perfused livers was markedly reduced, and no normal very-low-density lipoprotein, low-density lipoprotein or high-density lipoprotein were isolated. Chemical analysis showed the presence of Pluronic F-68 in all lipoprotein fractions. Our data strongly suggest that, during recirculating liver perfusions with FC-43 emulsion (between 1 and 4 hr), the nonionic surfactant detergent Pluronic F-68 dissociated from the emulsion and markedly affected hepatic structure, lipoprotein secretion and the composition of lipoproteins isolated from perfusate. Therefore FC-43 emulsion is not a suitable liver-perfusion medium for studies of lipoprotein metabolism.

Size and shape determination of fixed chylomicrons and emulsions with fluid or solid surfaces by three-dimensional analysis of shadows

Chylomicrons and chylomicron-sized emulsions are spherical particles in suspension but their shape and apparent size may be distorted by electron microscopy processing. To assess adsorption to grids, flattening, and shrinkage, chylomicrons and emulsions were fixed with osmium tetroxide and together with polystyrene beads were shadowed with platinum. Vertical profiles projected from particle shadows indicated that the chylomicrons and emulsions were slightly shrunken, slightly truncated, oblate spheroids while the polystyrene beads were spheres. Particle diameters were corrected by assuming that volumes of oblate spheroids on the grid surface were equal to volumes of spheres in the original lipid suspension. Because of the compensating effects of shrinkage (decreases diameter) and flattening (increases diameter) the differences between the means of measured diameters and corrected diameters were less than or equal to 5%.

Natural history of restricted synthesis and expression of measles virus genes in subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a slow infection caused by measles virus in which several years separate recovery from typical acute measles and the development of a slowly progressive neurological disease. We have investigated replication of measles virus in brain tissue obtained after the onset of neurological disease and in the terminal phase. With a hybridization tomographic technique that combines in situ hybridization with macroradioautographic screening of large areas of tissue, we analyzed the spatial and temporal distribution of virus genes in vivo, using region- and strand-specific probes for the nucleocapsid and matrix genes. We show that early in the course of SSPE there is a global repression in the synthesis and expression of the genome. In the final stage of SSPE most infected cells still have depressed levels of plus- and minus-strand viral RNA and contain nucleocapsid protein but lack matrix protein. These findings provide further evidence for a unified view of slow infections of the nervous system, where the general constraints on virus gene expression provide an explanation for persistence of virus in the face of the host's immune response, and the slow evolution of pathological change. In the final phases of SSPE the more specific block in virus replication accounts for the cell-associated state of the virus and the difficulty in virus isolation.

Kinetics and metabolism of clobazam in animals and man

1 The pharmacokinetic behaviour of the psychotropic drug clobazam, a 1,5 benzodiazepine, and its metabolism were studied with the ¹⁴C-labelled compound in rats, dogs, monkeys and man. The absorption was practically complete in all three animal species. Clobazam was not excreted in the unchanged form by all species. The main metabolite in plasma of monkeys, dogs and man was N-demethylclobazam. The metabolites were partially in the conjugated form.

2 The binding to serum proteins (concentration range 0.05-10 μg/ml serum) amounted to between 66% (in rats) and 85% (in man). The maximal levels of total radioactivity (original compound and metabolites) in blood were 0.24 ± 0.043 μg Equ/ml (2-4 h) in doses and 0.67-0.82 μg Equ/ml (0.5-1 h) in rhesus monkeys. These levels were markedly higher than those in rats with values of 0.064 ± 0.012 μg Equ/ml (∼0.5 h). The elimination of radioactivity from blood occurred in two phases.

3 After repeated daily administration of oral doses, the 24-h blood levels accumulated in rats to about three times the initial value. In dogs the 24-h serum concentrations remained practically unchanged. Long-term treatment with clobazam in monkeys neither caused enzyme induction nor other processes retarding metabolism and elimination.

4 Both after a single oral and intravenous dose, more than two-thirds of the radioactivity administered to rats was excreted with the faeces. Dogs, however, excreted about three-quarters of the radioactivity with the urine, irrespective of the route of administration. In monkeys, the excretion also occurred mainly in the urine. In all three species, renal excretion was similarly rapid to that from blood or plasma.

5 Apart from gastro-intestinal tract, liver and kidneys, the distribution in rats and dogs was remarkably even within the range of maximal blood levels. In the rat brain, the concentration amounted to only one-third of that in the blood. Special accumulations were not found. In dogs, the concentration in the brain was as high as that in the blood.

6 In rats, kinetics and metabolism were not significantly changed by pregnancy.

7 For metabolism studies in the four species (man, monkey, dog and rat) urine and faeces (and in some cases also serum) were examined after a single dose or repeated administration. The number and kind of metabolites detected in the individual species were partially different. In autoradiographic studies, exceptionally up to 14 radioactive spots were found for clobazam.

8 The structures of the metabolites were elucidated by independent methods, mainly mass spectrometry. In addition to the original substance, eight metabolites were identified for clobazam amounting to 70-90% of the total number of metabolites, depending on the species.

The two most important chemical changes of clobazam during metabolism are dealkylation and hydroxylation. Dealkylation at nitrogen-(1), particularly pronounced in the species dog, does not differ between the 1,4- and 1,5-benzodiazepines. The difference in metabolism is only pronounced in oxidative decomposition.

9 In contrast to diazepam, the 4′ position of the phenyl ring of clobazam seems to be particularly favourable for introduction of a hydroxyl function. In dogs, hydroxylation at the 9 position plays an additional important role. It results in the formation of the metabolite 9-hydroxy-N-demethylclobazam by which this species is markedly distinguished from the other three species.

It is remarkable that clobazam is not hydroxylated at the 3-position. This is obviously a characteristic of the 1,5-benzodiazepines and helps to distinguish them from the 1,4-benzodiazepines such as diazepam.