Isolation of calcifiable vesicles from human atherosclerotic aortas

Advanced mineralization can cause brittleness of aortic walls with decreased elasticity thereby causing the wall to rupture. Although the precise mechanisms of dystrophic calcification remain unknown, morphological evidence reveals the presence of mineral-associated vesicles in the lesions and defective bioprosthetic valves. In an attempt to demonstrate the calcifiability of the vesicles, small segments of human atherosclerotic aortas with calcified lesions were removed at autopsy and then digested in a crude collagenase solution to release vesicles. A differential centrifugation was then used to isolate calcifiable vesicles, which was precipitated at 300,000 x g for 20 min. An exposure of the vesicles to a calcifying medium containing physiologic levels of Ca2+, Pi, and 1 mM ATP caused Ca deposition in a vesicle protein-concentration dependent manner. The calcifiability of the vesicles was further demonstrated by electron microscopy. Fourier transform spectroscopic analysis of the deposited mineral revealed the presence of a hydroxyapatite phase, closely resembling the native form of mineral in atherosclerotic plaques. In addition, calcifiable vesicles were enriched in ATP-hydrolyzing enzymes including Mg2+ or Ca2+-ATPase and NTP pyrophosphohydrolase that may be involved in normal and pathological calcification. Triton X-100 at 0.01% abolished 80% of both ATPase activity and ATP-initiated calcification. A comparison of vesicles isolated from non-atherosclerotic and atherosclerotic aortas indicated that atherosclerotic vesicles tended to have higher calcifiability. These observations suggest that the calcifiable vesicles play a part in dystrophic calcification of aortas in atherosclerosis.     

Induction of calcification in rabbit aortas by high cholesterol diets: roles of calcifiable vesicles in dystrophic calcification

Atherosclerotic calcification may weaken the aorta wall and thereby lead to rupture of the vessel. The mechanism whereby aortas undergo calcification remains unclear. Previous reports in this laboratory showed that, after 2 months of cholesterol-supplemental feeding, an increase in calcifiability of membrane vesicles isolated from rabbit aortas precedes substantial arterial calcification. Further, the mineral was deposited by isolated calcifiable vesicles as an amorphous phase similar to minerals in human aortas at an early stage of atherosclerosis. In the current study, atherosclerotic calcification was induced by exposing rabbits to a 1% cholesterol-rich diet for 3 or 6 months. After 3 months of dietary interventions, atherosclerotic lesions were fully developed. Fatty streaks were evident in areas proximal to the heart and became less frequent in the distal areas. However, calcification was not yet identifiable histologically or by using Fourier transform spectroscopy (FT-IR). After 6 months of high cholesterol treatment, aortas were partially calcified. Histochemical staining for mineral revealed that calcification appeared to occur predominantly in the intimal areas immediately adjacent to the media. Fourier Transform Imaging analysis demonstrated that the mineral deposited in atherosclerotic rabbit aortas was a hydroxyapatite-like phase. To determine whether aorta vesicles play a role in mineral formation in aortas, vesicles were isolated from calcified aortas and then their calcifiability was compared to that in normal vesicles. Interestingly, during the course of vesicle isolation, we found that calcifiable vesicles with much higher calcifiability than normal vesicles could be readily isolated from atherosclerotic aortas simply by suspending minced tissues in PBS. The characteristics of the calcification process and the enzymatic contents of isolated vesicles were similar to those obtained using collagenase digestion. Correlatively, mineral deposited by calcifiable vesicles isolated from the calcified aortas was also of hydroxyapatite-like phases. Altogether, these observations indicate that (1) aortic calcification is a later event during atherogenesis, (2) calcifiable vesicles are loosely bound to the matrices of the lesions as the result of the disease process and (3) similarities in the mineral phases between those in aortas and by vesicles during atherogenesis further support the role of calcifiable vesicles in dystrophic calcification.     

Are calcifying matrix vesicles in atherosclerotic lesions of cellular origin?

Over recent years, the role of matrix vesicles in the initial stages of arterial calcification has been recognized. Matrix calcifying vesicles have been isolated from atherosclerotic arteries and the biochemical composition of calcified vesicles has been studied. No studies have yet been carried out to examine the fine structure of matrix vesicles in order to visualize the features of the consequent stages of their calcification in arteries. In the present work, a high resolution ultrastructural analysis has been employed and the study revealed that matrix vesicles in human atherosclerotic lesions are heterogeneous with two main types which we classified. Type I calcified vesicles were presented by vesicles surrounded by two electron-dense layers and these vesicles were found to be resistant to the calcification process in atherosclerotic lesions in situ. Type II matrix vesicles were presented by vesicles surrounded by several electron-dense layers and these vesicles were found to represent calcifying vesicles in atherosclerotic lesions.To test the hypothesis that calcification of matrix vesicles surrounded by multilayer sheets may occur simply as a physicochemical process, independently from the cell regulation, we produced multilamellar liposomes and induced their calcification in vitro in a manner similar to that occurring in matrix vesicles in atherosclerotic lesions in situ.     

A comparative study of atherosclerosis and osteopenia in elderly and young hemodialysis patients

The effects of aging on atherosclerosis and osteopenia in hemodialysis patients were investigated. Eighty patients on maintenance hemodialysis were subdivided according to age into old (greater than or equal to 65 years old, N = 40) and young (less than 65 years old, N = 40). Biochemical, radiologic, and biophysical studies were performed in each patient to assess the degree of atherosclerosis and osteopenia. Compared to age-matched controls, patients in the old group exhibited a significantly higher aortic pulse wave velocity (PWV), and old female patients had a significantly lower bone mineral content/bone width (BMC/W). Elderly patients also had a significantly higher aortic PWV and higher grade of aortic calcification as assessed radiologically; in contrast, the BMC/W was lower. Concerning sex differences, elderly male patients had the highest average grade of aortic calcification, the lowest serum Pi, [Ca] x [Pi], and immunoreactive parathyroid hormone concentrations, while elderly female patients had the lowest BMC/W and highest incidence of osteopenia. These observations suggest that elderly male hemodialysis patients are more prone to develop atherosclerosis and elderly female hemodialysis patients to develop advanced osteopenia.     

Pathophysiology of coronary calcification

Calcification is a prominent feature of atherosclerosis, frequently associated with myocardial infarction and other adverse cardiovascular outcomes. Currently, calcification is widely viewed as an end-stage, degenerative process which is inevitable in advanced atherosclerosis. Pathologists, however, have long noted that calcification may occur early in atherosclerosis and, at times, may appear histologically identical to organized bone, including areas resembling bone marrow. These observations suggest that rather than being a passive process, atherosclerotic calcification may instead be an active, regulated process similar to that of osteogenesis. Using an in-vitro model of arterial calcification a subpopulation of artery wall cells, capable of producing hydroxyapatite mineral in vitro was discovered. This article discusses some of the cellular and molecular mechanisms of arterial calcification identified utilizing this in-vitro model of vascular calcification.     

Immunolocalization of apolipoproteins in aortic atherosclerosis in American youths and young adults: findings from the PDAY study

The immunohistochemical distribution of apolipoproteins in the abdominal aortas of 142 men, 15-34 years of age, collected in a cooperative multicenter study group (Pathobiological Determinants of Atherosclerosis in Youth) was examined in relationship to serum VLDL+LDL+HDL cholesterol levels. ApoB deposits were limited to the intima of specimens with intimal fibro cellular thickening or atherosclerotic lesions. Apo A-I, E and J were observed in both the intima and media of the aortas with intimal lesions. The pattern of apoJ distribution was similar to that of apoA-I and E. The distribution patterns of these apolipoproteins in these young adults were very similar to those in adults and old men seen in an earlier study. The extent of apolipoprotein distribution in the intima and media increased with age and the stage of atherosclerosis development, but was not correlated significantly with serum VLDL+LDL or HDL cholesterol levels. The infiltration of lipoprotein particles into the aortic wall seems to be more strongly associated with the progression of intimal lesions rather than with serum cholesterol levels.     

Clearance of fetuin-a-containing calciprotein particles is mediated by scavenger receptor-a

Rationale: Fetuin-A is a liver-derived plasma protein involved in the regulation of calcified matrix metabolism. Biochemical studies showed that fetuin-A is essential for the formation of protein-mineral complexes, called calciprotein particles (CPPs). CPPs must be cleared from circulation to prevent local deposition and pathological calcification. Objective: We studied CPP clearance in mice and in cell culture to identify the tissues, cells, and receptors involved in the clearance. Methods and Results: In mice, fetuin-A-containing CPPs were rapidly cleared by the reticuloendothelial system, namely Kupffer cells of the liver and marginal zone macrophages of the spleen. Macrophages from scavenger receptor-AI/II (SR-A)-deficient mice cleared CPPs less efficiently than macrophages from wild-type mice, suggesting that SR-AI/II is involved in CPP binding and endocytosis. Accordingly, we found reduced clearance of CPPs in SR-A/MARCO-deficient mice. Conclusions: We could demonstrate that fetuin-A-containing CPPs facilitate the clearance of mineral debris by macrophages via SR-A. Since the same receptor also contributes to the uptake of modified low-density lipoprotein particles in atherosclerosis, defective endocytosis of both types of particle may impinge on lipid as well as mineral debris clearance in calcifying atherosclerosis.     

Expression and localization of the proteoglycan decorin during the progression of cholesterol induced atherosclerosis in Japanese quail: implications for interaction with collagen type I and lipoproteins.

The temporal and spatial distribution, and relative levels of the proteoglycan decorin and collagen type I were examined during the progression of atherosclerosis in the dorsal aortas of Japanese quail selected for cholesterol induced atherosclerosis. The quail were placed on either a control or 0.5% added cholesterol diet at approximately 16 weeks of age. Dorsal aortas were collected at 1- or 2-week intervals over a 15-week period after initiating cholesterol feeding. Biochemical analysis for decorin and collagen type I showed that both increased in the cholesterol-fed birds compared to control-fed birds beginning at 9 weeks and continued through the duration of the study. Through immunohistochemical staining for decorin and collagen type I, the spatial localization of decorin and collagen type I in control and less severe plaques in cholesterol-fed birds was most prominent in the arterial adventitia. However, in severe atherosclerotic plaques, decorin was localized in foam cell regions and collagen type I was found surrounding the foam cell regions where decorin accumulated. These results demonstrated a localization of decorin in the core of the atherosclerotic plaque foam cell region with collagen type I being located on the plaque surface.     

CD68-阳性巨噬细胞在人冠状动脉粥样硬化病变中的分布特点及其意义

目的 探讨人冠状动脉粥样硬化病变中CD68-阳性巨噬细胞的分布以及与冠状动脉粥样硬化病变类型、管腔狭窄之间的关系及其意义.方法 选用53例尸检病例的312块冠状动脉组织标本,光镜下诊断弥漫性内膜增厚和冠状动脉粥样硬化病变及其类型,用免疫组织化学计数冠状动脉粥样硬化病变中CD68-阳性巨噬细胞,用Scion图像软件系统检测和计算冠状动脉标本中管腔狭窄程度、脂质坏死核心和钙化基质面积.结果 在冠状动脉粥样病变中, 40% (124/312)为弥漫性内膜增厚, 5% (16/312)为Ⅰ型, 10% (31/312)为Ⅱ型, 21% (66/312)为Ⅲ型, 4% (14/312)为Ⅳ型, 18% (55/312)为Ⅴ型和2% (6/312)为Ⅵ型.脂质坏死核心面积在高胆固醇组明显大于正常胆固醇组(P<0.05),而钙化基质面积在早期病变(Ⅰ～Ⅲ型)和进展期病变(Ⅳ～Ⅵ型)之间有显著性差异(P<0.05);冠状动脉粥样硬化病变CD68-阳性巨噬细胞随着冠状动脉粥样硬化病变进展和管腔狭窄程度的加重而增多,分别呈正相关(P<0.01),且不同病变类型、管腔狭窄程度之间以及正常胆固醇组与高胆固醇组之间有显著性差异(P<0.05).结论 CD68-阳性巨噬细胞随着人冠状动脉粥样硬化病变进展和管腔狭窄程度的加重而增多,表明巨噬细胞浸润始终始发和加重冠状动脉粥样硬化病变,大量巨噬细胞主要在斑块肩部区浸润和脂质坏死核心的增大与冠状动脉粥样硬化病变进展、不稳定性斑块破裂及并发症的发生有关.     

Effect of calcification on in vivo mechanical response of rabbit arteries to balloon dilation

BACKGROUND. Atherosclerosis has been associated with loss of artery wall distensibility in human cadavers and in experimental animal models, giving it the lay term "hardening of the arteries." METHODS AND RESULTS. To assess the effect of calcification on arterial distensibility, balloon pressure and volume were recorded during dilation of calcified aortas in Watanabe heritable hyperlipidemic (WHHL) rabbits in vivo. Calcification was induced by dietary supplements of cholesterol, vitamin D2, and calcium. Balloon pressure, volume, and time signals were acquired at high frequency with controls for temperature and balloon inflation rate. Resistance to balloon dilation was minimal in control rabbit aortas (delta Vmax = 5.0 +/- 3.5 microliters) and in excised nonatherosclerotic human coronary arteries, and it was small in aortas from cholesterol-fed rabbits (12.3 +/- 8 microliters), even when lipid levels were markedly elevated by a high cholesterol diet (611 +/- 347 mg/dl). With dietary cholesterol, vitamin D2, and calcium supplements, WHHL rabbits developed mild hypercalcemia (15 +/- 1.9 mg/dl), hypercholesterolemia (1,100 +/- 633 mg/dl), moderate-to-marked aortic calcification, and high resistance to balloon dilation (38 +/- 27) comparable to that seen in angioplasty patients. CONCLUSIONS. It is concluded that experimentally induced calcification decreases the distensibility of the rabbit aorta in vivo and that it yields to balloon dilation by plastic deformation closely resembling that seen in balloon angioplasty of human coronary arteries. These findings suggest that calcification contributes to arterial "hardening" associated with atherosclerosis.     

Vitamin E inhibits CD36 scavenger receptor expression in hypercholesterolemic rabbits

A numerous studies suggest that Vitamin E has a preventive role in atherosclerosis, although the mechanism of action still remains unclear. CD36, a member of the scavenger receptor family is centrally involved in the uptake of oxidized low density proteins (oxLDLs) from bloodstream. During the atherosclerotic process, the lipid cargo of oxLDL accumulates in macrophages and smooth muscle cells, inducing their pathological conversion to foam cells. In the present study, we investigate the role of Vitamin E on CD36 expression in an in vivo model. Atherosclerosis was induced by a 2% cholesterol containing Vitamin E poor diet. Three groups of six rabbits each were studied. The first group (control) was fed on Vitamin E poor diet. The second group was fed with Vitamin E poor diet containing 2% cholesterol and the rabbits in the third group were fed with Vitamin E poor diet containing 2% cholesterol and received injections of 50 mg/kg of Vitamin E i.m. After 4 weeks, aortas were removed and analysed by light microscopy for atherosclerotic lesions. Aortic samples were analysed for CD36 mRNA expression. The aortas of cholesterol-fed rabbits showed typical atherosclerotic lesions, detected by macroscopic and microscopic examination, and exhibited an increase in CD36 mRNA expression. Vitamin E fully prevented cholesterol induced atherosclerotic lesions and the induction of CD36 mRNA expression. The effects observed at the level of CD36 scavenger receptor expression in vivo suggest an involvement of reduced foam cell formation in the protective effect of Vitamin E against atherosclerosis.     

Matrix vesicles and calcification

Matrix vesicles (MVs) are extracellular, 100 nM in diameter, membrane-invested particles selectively located at sites of initial calcification in cartilage, bone, and predentin. The first crystals of apatitic bone mineral are formed within MVs close to the inner surfaces of their investing membranes. Matrix vesicle biogenesis occurs by polarized budding and pinching-off of vesicles from specific regions of the outer plasma membranes of differentiating growth plate chondrocytes, osteoblasts, and odontoblasts. Polarized release of MVs into selected areas of developing matrix determines the nonrandom distribution of calcification. Initiation of the first mineral crystals, within MVs (phase 1), is augmented by the activity of MV phosphatases (eg, alkaline phosphatase, adenosine triphosphatase and pyrophosphatase) plus calcium-binding molecules (eg, annexin I and phosphatidyl serine), all of which are concentrated in or near the MV membrane. Phase 2 of biologic mineralization begins with crystal release through the MV membrane, exposing preformed hydroxyapatite crystals to the extracellular fluid. The extracellular fluid normally contains sufficient Ca2+ and PO4 3- to support continuous crystal proliferation, with preformed crystals serving as nuclei (templates) for the formation of new crystals by a process of homologous nucleation. In diseases such as osteoarthritis, crystal deposition arthritis, and atherosclerosis, MVs initiate pathologic calcification, which, in turn, augments disease progression.     

Mechanism of calcification in atherosclerosis

Calcification is commonly associated with atherosclerosis, and it has important clinical implications, especially in coronary arteries. The mineral has been identified as the same mineral as in bone, hydroxyapatite, and several features of its development suggest a mechanism similar to osteogenesis and not merely passive precipitation. The artery wall has been shown to contain several bone-related proteins, including those for osteopontin, osteonectin, and osteocalcin, as well as proteoglycan core proteins homologous with bone biglycan. Our laboratory recently demonstrated that a potent osteogenic differentiation factor, bone morphogenetic protein 2a, is expressed in calcified human atherosclerotic lesions, suggesting that arterial calcification may be initiated by an osteogenic differentiation. In addition, a cell capable of calcium mineral formation in vitro has been isolated from bovine and human aorta and identified by immunostaining as having a surface marker characteristic of microvascular pericytes. These findings suggest the possibility that plaque calcification develops when a signal from atherosclerotic plaque or a factor associated with atherosclerosis induces expression of bone morphogenetic protein, leading to osteogenic differentiation of pluripotential, pericytelike cells located in the arterial intima, which then produce bonelike matrix and hydroxyapatite mineral. These findings also raise questions as to whether osteogenic-promoting factors used to prevent osteoporosis may also increase risk of arterial calcification.     

Beta-migrating very low density lipoprotein attenuates endothelium-dependent relaxation in rabbit atherosclerotic aortas

We studied the effects of beta-migrating very low density lipoprotein (beta-VLDL) on the vascular responses of isolated thoracic aortic preparations taken from normal and hypercholesterolemic rabbits. The endothelium-dependent relaxation induced by acetylcholine or adenosine triphosphate (ATP) was attenuated in the arteries from hypercholesterolemic rabbits that were fed a cholesterol-rich diet for 12 weeks. In these aortas, the lesional circumference of the atherosclerotic plaques (fatty streaks) was only 12.18 +/- 1.98%. The relaxation induced by the Ca2+ ionophore A23187 or nitroglycerin was not altered. Preincubation with beta-VLDL significantly inhibited the relaxation due to acetylcholine, ATP, or A23187, especially in the aortas of hypercholesterolemic rabbits. However, beta-VLDL did not alter the response to nitroglycerin. Preincubation with high density lipoprotein had no significant effect on vessel relaxation. These results indicated that endothelium-dependent relaxation was already inhibited in the early stages of atherosclerosis, and that the atherogenic lipoprotein, beta-VLDL, further inhibited endothelium-dependent relaxation in atherosclerotic aortas. It may be that beta-VLDL also plays a role in determining the level of vascular tonus in atherosclerosis.     

Vascular calcification in chronic kidney disease: mechanisms and clinical implications

Vascular calcification is a well-known complication of chronic kidney disease and one of the main predictors for increased cardiovascular morbidity and mortality in these patients. It may happen in 2 main types of intimal calcification, as a part of diffuse atherosclerosis, and medial calcification, which is generally focal in distribution, unrelated to atherosclerotic risk factors, and seen in younger hemodialysis patients. Pathogenesis may be genetic, mineral metabolism related, or nonmineral metabolism related. Increased calcium, phosphorus, and calcium- phosphorus product; decreased parathyroid hormone level; and overzealous use of active vitamin D supplements are the main mineral metabolism-related mechanisms of vascular calcification. Other mechanisms are formation of matrix vesicles and cellular apoptosis, with generation of hydroxyapatite crystals within vesicles and apoptotic bodies. The interplay of various activator proteins of vascular calcification such as bone morphogenetic proteins and receptor activator of nuclear factor-kappa B ligand, or inhibitor proteins like matrix Gla protein, bone morphogenetic protein-7, osteopontin, osteoprotegerin, fetuin-A, Smad6, and pyrophosphate are important in establishment of vascular calcification. Vascular calcification is related to all-cause and cardiovascular mortality both in general population and dialysis patients. Minimizing traditional risk factors of vascular calcification, prevention of hypercalcemia, and avoidance of high doses of calcium-based phosphate binders and vitamin D analogues are important measures for prevention or attenuation of progression of vascular calcification. Sevelamer and cinacalcet may prevent progression of vascular calcification. With the evolving knowledge of the pathogenesis of vascular calcification, we can look forward to emergence of novel therapies for this complication in the future.     

Primary culture of endothelial cells from atherosclerotic human aorta. Part 1. Identification, morphological and ultrastructural characteristics of two endothelial cell subpopulations

Endothelial cells (EC) were harvested by 0.1% collagenase treatment for adult human thoracic aortas obtained 1-3 h after sudden death. At least 35-70% of EC were removed from the intimal surface of aorta, 90-95% of them being viable. Plating efficiency was 70-80%. Monolayer formation was achieved at a seeding density of 5-8 X 10(2) cells/mm2. The cells were identified as endothelium by the presence of Factor VIII antigen, Weigel-Palade bodies and typically endothelial morphology at confluence. Unlike endothelial cultures derived from human umbilical veins and infant aortas, primary cultures obtained from human adult aortas contain multinuclear EC with Factor VIII antigen and Weibel-Palade bodies. The number of multinuclear EC in cultures isolated from aortas affected by atherosclerosis was 2-fold higher (P less than 0.05) than in cultures obtained from grossly normal aortas taken from donors of the same age. EC with numerous lipid inclusions revealed by oil-red-O staining were present in all the EC primary cultures derived from aortas affected by atherosclerosis. No oil-red-O-positive cells were detected among the EC cultured from infant aorta, aorta of young donors, and umbilical vein. An electron microscopic examination of EC from atherosclerotic aorta in culture and in situ failed to reveal any ultrastructural peculiarities distinguishing multinuclear EC from the mononuclear EC.     

Localization of human ATP-binding cassette transporter 1 (ABC1) in normal and atherosclerotic tissues

The present study examines the expression of ATP-binding cassette transporter 1 (ABC1) mRNA in normal and atherosclerotic tissues by using in situ hybridization in an effort to better understand the function of this cholesterol transport protein. Samples of normal baboon tissues as well as human normal and atherosclerotic aortas were hybridized with (35)S-labeled ABC1 sense and antisense riboprobes. Widespread expression of ABC1 was observed generally in tissues containing inflammatory cells and lymphocytes. Other noninflammatory cells that were also sites of ABC1 synthesis included the ductal cells of the kidney medulla, Leydig cells in the testis, and glial cells in the baboon cerebellum. Although normal veins and arteries did not express ABC1 mRNA, it was found to be upregulated in the setting of atherosclerosis, where widespread expression was found in macrophages within atherosclerotic lesions. These results are consistent with the proposed role of ABC1 in cholesterol transport in inflammatory cells. The specific upregulation of ABC1 mRNA in the setting of atherosclerosis probably reflects the response of leukocytes to cholesterol loading. However, the presence of ABC1 in ductal cells of the kidney medulla and in the small intestine suggest a more general role for this protein in cholesterol transport in other cell types.     

The hyperlipidemic hamster as an atherosclerosis model.

The descending thoracic and abdominal aortas of normal and hypercholesterolemic Golden Syrian hamsters were examined with transmission electron microscopy and immunofluorescence microscopy. Serum cholesterol distribution in lipoproteins was determined by gradient ultracentrifugation. Luminal surfaces appeared free of lesions and no intimal thickening or foam cells were seen. The main rise of cholesterol during the hypercholesterolemic diet was in the VLDL + IDL fraction. These findings suggest differences in the localization of atherosclerotic lesions and lipoprotein cholesterol distribution between humans and hamsters, which hamper the use of this species as a model for human atherosclerosis.     

Oxidative phosphorylation and aspects of calcium metabolism in myocardia of hypercholesterolaemic swine with moderate coronary atherosclerosis.

Aspects of myocardial oxidative phosphorylation and Ca2+ metabolism were studied in a swine model in which coronary atherosclerosis was induced by a combination of denudation of the endothelium of the coronary arteries plus 7--11 months of feeding a high fat--high cholesterol diet. By microscopy, a moderate amount of coronary atherosclerosis was present at the time of sacrifice, and 2 of the 14 swine hearts had old myocardial infarcts. Myocardial mitochondria from grossly normal areas showed partial uncoupling and decreased state 3 O2 uptake with 3 of 4 substrates tested. In addition, Ca2+ stimulated mitochondrial respiration was decreased in the atherosclerotic swine. In the sarcoplasmic reticulum Ca2+ uptake under conditions of heavy loading was greater in the atherosclerotic swine than in control animals. The degree of atherosclerosis was not great enough to suggest that persistent myocardial ischaemia was present. Possibly coronary artery spasm induced an intermittent ischaemia resulting in the metabolic abnormalities observed, or the changes may have been brought about by the effects of the high fat--high cholesterol diet on subcellular membranes.     

Apoprotein B quantification in rhesus and cynomolgus monkey atherosclerotic lesions

The concept that much of the cholesterol deposition in atherosclerotic plaque development is provided by ingress of blood-derived apo B-rich lipoproteins into the arterial intima is given support by the study of arterial apo B accumulation. To compare the arterial wall level of immunoreactive apo B during the progression of diet-induced atherosclerosis in two widely used animal models of atherosclerosis, rhesus and cynomolgus monkeys were fed an atherogenic diet for 4, 8, and 12 months and their abdominal aortas quantitated for apo B. Apo B was extracted from aortic intima-media homogenates in two forms: Tris-buffer extractable or ‘loosely bound’ and detergent (Triton X-100) extractable or ‘tightly bound’. The aortic extracts were quantitated for apo B by radial immunodiffusion, using goat antirhesus apo B along with serum LDL standards of the appropriate species diluted in the two extract solutions.

The control monkeys' aortas contained only buffer-extractable apo B. The atherosclerotic aortas of both species of monkeys progressively increased their levels of loosely bound and tightly bound apo B through 4, 8, and 12 months of atherogenic diet feeding, with the 8- and 12-month cynomolgus aortas containing much larger amounts of apo B than the rhesus aortas. These differences in aortic apo B content could be accounted for by the greater rate at which the cynomolgus atherosclerotic lesions developed at the later time points. When the total lesion apo B levels were correlated with representative morphometrically-quantitated histopathologic sections of the homogenized aortas, a highly significant correlation was seen between the total aortic apo B values and both the absolute area of the intimal lesions and the total area of oil red O stainable lipid in the lesions (P < 0.001). These data indicate that as atherosclerotic lesions become larger and richer in lipid with progression of the disease, the amount of apo B-associated lipoproteins which are deposited unmetabolized in the lesions increases. These lipoproteins are increased in both the tightly bound and loosely bound forms.