Biomedical subjects

H F Hoff

Publications and source records attributed to H F Hoff.

At least 55 records · Page 3Linked to original sources

PubMed1991

Modified low density lipoprotein isolated from atherosclerotic lesions does not cause lipid accumulation in aortic smooth muscle cells.

Foam cells in atherosclerotic lesions are derived not only from blood monocytes but also from smooth muscle cells (SMC). To better understand the mechanisms by which SMC may become lipid-laden, we have studied the catabolism by cultured rabbit aortic SMC of LDL derived from atherosclerotic lesions (A-LDL) previously shown to be chemically modified. A-LDL was isolated either from homogenates of atherosclerotic plaques in human aortas by affinity chromatography and gel filtration, or from nonhomogenized extracts of plaque minces by ultracentrifugation and gel filtration. Internalization of A-LDL by SMC or fibroblasts appeared to be mediated primarily via the LDL receptor since: 1) either unlabeled LDL or A-LDL could inhibit the degradation of 125I-labeled A-LDL or of 125I-labeled LDL, 2) the uptake of both A-LDL and LDL, as estimated by their abilities to stimulate cholesterol esterification, was reduced in cells in which LDL receptor expression was down-regulated; and 3) the uptake of both [3H]cholesteryl ether-labeled A-LDL and LDL by normal fibroblasts was significant and could be inhibited by excess LDL, but was negligible in receptor-negative fibroblasts. At saturating concentrations of lipoproteins, maximum cholesterol esterification in SMC was greater for LDL than for A-LDL. Over a 48-h incubation, A-LDL, like LDL, was unable to induce cellular cholesteryl ester accumulation. Cross-competition studies suggested that either the affinity of A-LDL for the LDL receptor was less than that of LDL, or that some particles in A-LDL are not internalized by SMC. The latter alternative was supported by the observations that some A-LDL particles had undergone aggregation, especially at high concentrations, and that aggregated forms of A-LDL or plasma LDL failed to be internalized and degraded by SMC. Collectively, these results are consistent with recognition of some of the A-LDL particles by the LDL receptor, but also suggest that, at least under in vitro conditions, A-LDL is unlikely to induce lipid accumulation in SMC resulting in SMC-derived foam cells.

Adult↗

PubMed1990

Macrophage uptake of cholesterol-containing particles derived from LDL and isolated from atherosclerotic lesions.

A variety of different cholesterol-rich particles with different physical and chemical structures can be isolated from human atherosclerotic lesions. Many of these particles are internalized in an unregulated fashion by macrophages in culture, leading to lipid loading of these cells. However, the in vivo relevance of this uptake is still uncertain. In this overview, we have summarized data obtained primarily in our laboratory on low density lipoprotein (LDL)-like particles (A-LDL) and large cholesterol-rich droplets isolated from human atherosclerotic lesions. Based on our studies, we propose a variety of different mechanisms of uptake. A-LDL can be internalized by the LDL receptor or the scavenger receptor on macrophages in culture; the latter uptake mechanism can lead to lipid loading. In addition, at high concentrations A-LDL can undergo aggregation, possibly due to intermolecular cross-bridging by aldehydes released during oxidation of these particles. The aggregates are subsequently internalized by macrophages by phagocytosis, a process which appears to be independent of the LDL or scavenger receptor. By contrast, arterial smooth muscle cells do not take up these aggregates. Large cholesteryl ester-rich particles isolated from human lesions, and derived from LDL that had been degraded by hydrolytic enzymes in the extracellular space of the arterial wall, or from inclusions released from lysed foam cells, are also internalized via phagocytosis by macrophages in culture. Since some of these particles contain apoliproteins and/or proteins that are ligands for receptors on macrophages, initial receptor-mediated binding may precede and facilitate subsequent phagocytosis in some cases. Uptake of the diverse group of cholesteryl ester-rich particles in plaques can induce lipid loading of macrophages and therefore may lead to further growth of the atherosclerotic plaque.

Arteriosclerosis↗

PubMed1989

LDL accumulation in the grossly normal human iliac bifurcation and common iliac arteries.

We had previously used an electrophoretic transfer procedure to determine the topographic distribution of low density lipoprotein (LDL) accumulation in the aortic intima of normolipemic swine. In this present study we have employed a similar procedure to assess whether LDL-rich sites consistently demonstrate increased intimal thickening at the iliac bifurcation and common iliac arteries. The topographic distribution of LDL-rich sites was determined in the aortas of six subjects ranging in age from 16 to 36 years, by transferring LDL by electrophoresis from the tissue into an agarose gel containing anti-LDL, and then staining the immunofixed LDL in the gel for lipid. LDL-rich sites were found in all but two of these cases. On the basis of control studies establishing the level of nonspecific staining, we determined that the cutoff between LDL-rich and LDL-poor zones was 37 mg apoB protein/mm2 intimal surface area. Intimal thickening was found to be threefold greater in LDL-rich than in LDL-poor regions. These results confirm and extend earlier immunohistochemical studies suggesting a preferential accumulation of LDL at sites of intimal thickening in human arteries.

Adolescent↗

PubMed1988

Extracts of human atherosclerotic lesions can modify low density lipoproteins leading to enhanced uptake by macrophages.

Plasma low density lipoproteins (LDL) and/or other lipoproteins containing apo B that accumulate in atherosclerotic lesions of human aortas exhibit structural changes that are associated with enhanced uptake in an unregulated fashion by macrophages in culture, resulting in the formation of foam cells in vitro. In an attempt to better characterize the structure-function modifications, we have incubated plasma LDL with extracts of human atherosclerotic plaques obtained at surgery, and determined whether such plaque-modified LDL also demonstrates enhanced uptake by cultured mouse peritoneal macrophages (MPM). Enhanced uptake was found which was linear over a concentration range of 100 micrograms lipoprotein protein/ml, as assessed by enhanced degradation of [125I]LDL and by stimulation of cholesterol esterification. Extracts of non-arterial human tissue were unable to induce this modification, suggesting tissue specificity. When delipidated apo B from tissue-treated [125I]LDL was subjected to SDS-PAGE, autoradiograms demonstrated, in addition to the B-100 band of apo B, a doublet of higher molecular weight than B-100 and a band just entering the gel, both at the expense of the B-100 band. No lower molecular weight bands suggestive of apo B degradation were seen. Modest increases in LDL electrophoretic mobility and thiobarbituric acid reactive substances were found following the incubation of LDL with plaque extracts. These changes could be inhibited by butylated hydroxytoluene (BHT), suggesting that free radical-induced lipid peroxidation was responsible for these modifications. However, since BHT did not inhibit the uptake of the tissue-incubated LDL by macrophages, the actual modification responsible for enhanced macrophage recognition did not appear to be free radical-induced. Uptake of plaque-modified [125I]LDL was inhibited by only 22% by a 20-fold excess of acetyl LDL or plaque-modified LDL. If the latter did not represent a mixture of modified and unmodified particles, this result would suggest that uptake was not mediated by the scavenger receptor. It is possible that foam cells are formed in vivo when LDL particles, which have been modified by interacting with components of the arterial wall, are taken up by tissue macrophages.

Animals↗

PubMed1988

Serum Lp(a) level as a predictor of vein graft stenosis after coronary artery bypass surgery in patients.

Although the serum lipoprotein fraction Lp(a) has been associated with coronary artery atherosclerosis, its relationship to narrowing of saphenous vein grafts has not previously been elucidated. We therefore measured serum Lp(a) levels in 167 symptomatic patients undergoing cardiac catheterization who had had coronary artery bypass surgery 0.7 to 14.3 years earlier. Lp(a), total cholesterol, and total triglyceride levels were compared with the degree of saphenous vein graft stenosis to test for any association. Serum Lp(a) levels were significantly associated with the degree of stenosis of saphenous vein grafts (r = .24, p = .002). Mean Lp(a) levels (mg/dl) in the 135 patients with stenosis were almost double (32.0 +/- 32.7, mean +/- SD) those in the 32 patients with no graft stenosis (16.7 +/- 22.6; p = .002). Graft stenosis was not associated with previous myocardial infarction, hypertension, obesity, diabetes, or smoking. Serum cholesterol levels (mg/dl) were slightly higher in the stenosis group (251.3 +/- 69) than in the no-stenosis group (231.8 +/- 48.8), but the difference was of borderline significance (p = .06). A stepwise increase in mean Lp(a) was found in groups of patients with increasing vein graft stenosis. At a serum Lp(a) level of 31.6 mg/dl or above, 92% of the patients demonstrated vein graft stenosis. Thus, patients with elevated Lp(a) levels have an increased risk of developing saphenous vein graft stenosis after coronary bypass surgery.

Cardiac Catheterization↗

PubMed1987

Uptake by mouse peritoneal macrophages of large cholesteryl ester-rich particles isolated from human atherosclerotic lesions.

We have previously shown that a lipoprotein fraction consisting of large cholesteryl ester-rich particles can be isolated from homogenates of human aortic plaques by gel exclusion chromatography. This fraction was recognized by a high-affinity binding site on mouse peritoneal macrophages (MPM) resulting in unregulated uptake, stimulation of cholesterol esterification, and massive accumulation of cholesteryl esters. In this report we have further characterized such a fraction, designated lipid-protein complex (LP), which can be isolated from the void volume fraction of a Bio-Gel A-150m column following chromatography of plaque extracts. LP possessed a mean cholesterol-to-protein ratio of 2.3; it was heterogeneous in size and structure as observed by electron microscopy after negative staining, and it stimulated cholesterol esterification in MPM in a linear fashion over a 48-hr time interval, suggesting that the binding site on MPM recognizing LP was not down-regulated by intracellular cholesterol content. This uptake resulted in the presence of oil red O-positive intracellular droplets and numerous vacuoles containing electron-dense structures, whereas MPM incubated without lipoprotein showed few vacuoles or lipid droplets. Using SDS-PAGE and immunoblot and dot-blot techniques, we found that the major proteins associated with LP were albumin and fibronectin, whereas apoB and apoE were present in lower amounts. These proteins may be responsible for opsonization of LP, making it recognizable to receptors on MPM and facilitating LP uptake by MPM. LP isolated from tissue extracts without homogenization had the same structural and functional characteristics, suggesting that homogenization per se was not responsible for creating a particle that was recognized by MPM. However, homogenization yielded two to three times more LP. MPM uptake of LP derived from lysed foam cells may represent one of the mechanisms by which fatty streak lesions may grow to larger atherosclerotic lesions.

Aged↗

PubMed1986

Plasma low density lipoprotein accumulation in aortas of hypercholesterolemic swine correlates with modifications in aortic glycosaminoglycan composition.

Arterial wall sulfated glycosaminoglycans (GAG) of matrix proteoglycans have been implicated in the retention of plasma low density lipoproteins in the early stages of atherosclerosis. We have studied modifications in porcine aortic GAG composition after 4 and 11 weeks of diet-induced hypercholesterolemia. After these time intervals no grossly visible atherosclerotic lesions were discerned. GAG changes were correlated with tissue LDL accumulation estimated by quantification of immunochemically-identifiable apolipoprotein B (apoB). Values of apoB ranged from less than 10 to 250 ng/mg wet weight of aorta, and correlated significantly with tissue total cholesterol contents. Although total GAG concentrations did not differ between a normolipemic control and the two diet groups, apoB showed a significantly positive correlation with the percent of total GAG that was chondroitin sulfate and a significantly negative correlation with the percent of total GAG that was dermatan sulfate. Total tissue cholesterol likewise demonstrated similar correlations with GAG. Since areas of the aorta were chosen that were devoid of intimal thickening, these metabolic changes may occur in the inner part of the arterial tunica media. The results suggest that the accumulation of plasma LDL in the arterial wall following hypercholesterolemia may induce alterations in arterial GAG composition, presumably by affecting GAG synthesis by medial smooth muscle cells.

Animals↗

PubMed1986

Spatial distribution and accumulation of low density lipoproteins in the abdominal aorta of swine: determination by a novel electrotransfer procedure.

An immunotransfer procedure has been developed which can determine both the spatial distribution of low density lipoproteins (LDL) along the intima-media of large blood vessels such as the aorta, and can quantify LDL accumulation along its length. Aortas which were opened longitudinally along their ventral aspect were positioned so that their intimal side abutted against a gel containing glyoxyl agarose to which anti-LDL had been covalently coupled. LDL was electrophoresed out of the agarose gel where it was immunofixed. This distribution was then visualized first by incubating the gel with 125I-anti-LDL which bound to free epitopes on the immunofixed LDL, and second by subjecting the washed and dried gel to autoradiography. Plasma LDL was applied to wells of different shapes and sizes in an agarose gel substituting for aortic tissue, and the transfer procedure was performed as described. The resultant patterns matched those of the original wells, suggesting that the spatial distribution of LDL in the autoradiogram probably mimicked that in the aortic tissue. The transfer procedure appeared to be specific for the antigen under study since minimal silver grains were observed in autoradiograms when an IgG fraction of nonimmune serum was used in place of anti-LDL. Application of increasing concentrations of LDL to wells in a gel substituting for tissue, resulted in a dose-dependent increase in autoradiographic grain density. If such standards were applied to gels adjacent to tissue samples, the amounts of LDL in the tissue could be quantified from the standard curve of grain density versus LDL concentration. The distribution of LDL along the abdominal aortas of 10- and 31-week-old swine was determined by converting autoradiographic grain densities to isopleths of LDL concentrations by computer assisted image analysis. These distributions were focal and were found to range between 10 and 225 ng of apoB/mm2 of intimal surface area. This procedure lends itself not only to studies relating lipoprotein accumulation to atherogenesis, but also to any studies dealing with tissue accumulation of macromolecules.

Animals↗

PubMed1986

A low density lipoprotein-sized particle isolated from human atherosclerotic lesions is internalized by macrophages via a non-scavenger-receptor mechanism.

A lipoprotein particle designated A-LDL, which contains apolipoprotein B (apoB) and which is the size of plasma low density lipoproteins (LDL), was isolated from homogenates of human aortic athersclerotic plaques by a combination of affinity chromatography and gel-filtration. Compared to plasma LDL, A-LDL was more electronegative, its hydrated density was lower and more heterogeneous, and its protein-to-lipid ratio was lower. In addition, apoB in A-LDL was highly degraded, and A-LDL was recognized by mouse peritoneal macrophages (MPM) as indicated by its ability to stimulate cholesterol esterification. Cholesterol esterification was saturable with an apparent Km of 100 micrograms of A-LDL cholesterol/ml. Stimulation of cholesterol esterification was linear with time, leading to extensive accumulation of cholesteryl ester in MPM over a 48-hr time interval. The uptake or degradation of acetyl-LDL (radiolabeled either in the protein with 125I or hydrophobic core with [3H]cholesteryl ether) was markedly decreased by excess unlabeled acetyl-LDL but not by A-LDL, and excess acetyl-LDL did not inhibit the uptake or degradation of labeled A-LDL. However, a 10-fold excess of A-LDL also failed to inhibit the uptake of labeled A-LDL. This finding was consistent with the observation that, unlike the saturable stimulation of cholesterol esterification in MPM induced by A-LDL, the uptake of cholesteryl ether-labeled A-LDL was almost linear over a 0-400 micrograms cholesterol/ml range. This discrepancy between dose response curves for A-LDL, which did not occur for acetyl-LDL, could be eliminated by a 24-hr postincubation period in the absence of lipoprotein, suggesting that A-LDL is catabolized less efficiently than acetyl-LDL following internalization. In summary, we conclude that A-LDL uptake by MPM occurs via a low affinity-high capacity process. Although the uptake of A-LDL is not readily saturated, it is of sufficient affinity to lead to lipid loading of macrophages even when A-LDL is present at relatively low concentrations. If these mechanisms are operative in vivo, they could explain how foam cells in human fatty streak lesions develop.

Amino Acids↗

PubMed1986

Exchange and mass efflux of cholesterol in macrophages. Evidence for a common mechanism and a role for plasma membrane proteins.

Exchange and net mass efflux of cholesterol were investigated in [3H]cholesterol-labeled or cholesteryl ester-loaded murine peritoneal macrophages, respectively. Macrophages were subjected to mild proteolysis prior to measurements of mass efflux or exchange to assess whether plasma membrane proteins participated in either process. Cholesterol exchange and mass efflux were inhibited up to 70% following trypsinization. The inhibitory effect was reversible as cells regained normal efflux and exchange 6-8 hr following treatment. Incubation of trypsinized cells with cycloheximide prevented recovery, indicating that protein synthesis was necessary for restoration of normal cholesterol efflux. Studies with peptide and nonpeptide inhibitors of proteolysis suggested that active catalytic activity of trypsin was necessary for the inhibitory effect to be expressed. The degree of inhibition for both cholesterol exchange and mass efflux was dependent in a quantitatively similar manner on the time of incubation and the concentration of trypsin, suggesting that the mechanism of cholesterol exchange and mass efflux were similar at the level of the plasma membrane. Two other serine-proteases, thrombin and elastase, were also capable of inhibiting cholesterol removal in a similar manner. No cell death was observed by altered morphology, detachment, changes in DNA or protein content, or trypan blue exclusion even under the most severe proteolytic conditions. These studies suggest that protease-sensitive plasma membrane proteins play a role in cholesterol efflux in macrophages.

Animals↗

PubMed1985

Reduction in tissue LDL accumulation during coronary artery regression in cynomolgus macaques.

The aim of this study was to determine whether the amount of LDL that had accumulated in the coronary arteries of cynomolgus monkeys during an 18-month period on a hypercholesterolemic (H) diet was reduced during subsequent periods of 6 and 12 months on a normolipemic (N) diet. This was performed by assessing the accumulation of LDL in the left anterior descending (LAD) branch of the left coronary artery within an area 4 mm from its origin, since this region contained the largest lesions in the LAD. LDL accumulation was estimated by measuring the percent cross-sectional area of artery occupied by reaction product depicting apo B by an immunoperoxidase procedure. The following reduction in mean (+/- SD) percent cross-sectional area occupied by reaction product was found in 8 animals on the progression diet (group I), 7 animals on the 6-month regression diet (group II), and 9 animals on the 12-month regression diet (group III), respectively: 21.7 +/- 4.7, 6.9 +/- 5.5, and 2.3 +/- 1.3. Differences between group I and either group II or III were statistically significant (using the Wilcoxon signed-ranks test). In group I, LDL was localized primarily in the necrotic core and around pools of foam cells. In groups II and III fewer foam cells and smaller pools of extracellular debris were qualitatively evident, and LDL was localized closer to the lumen and along collagen fibers. These results suggest that lowering of the plasma LDL level following termination of a hypercholesterolemic diet also induces a decrease in the LDL content in coronary artery lesions, even without significant reductions in lesion size, and that this decrease might be responsible for the decrease in foam cells.

Animals↗

PubMed1985

Lipoproteins containing apo B extracted from human aortas. Structure and function.

We have isolated, by anti-LDL affinity chromatography, apo B-containing lipoproteins from homogenates of atherosclerotic plaques excised from the human aorta. This fraction, called A-LP, has similarities with plasma LDL, such as having similar size and relative lipid composition, along with containing apo B. However, the fraction also contains some particles larger than LDL, it is more electronegative than LDL, the relative protein content is less than in LDL, and its apo B is highly degraded. A-LP is recognized by a high affinity binding site on mouse peritoneal macrophages (MPM), as suggested by dose-response curves of stimulation of cholesterol esterification. The interaction is inhibited by negatively-charged carbohydrates such as fucoidin, but excess A-LP did not inhibit the degradation of labeled acetyl-LDL by MPM, suggesting that the binding site recognizing A-LP may not be the scavenger receptor. Finally, stimulation of cholesterol esterification by A-LP in MPM is unregulated over a 48 hr time interval, leading to massive accumulations of cholesteryl esters and a transition of these MPM to a morphology characteristic of foam cells. It is possible that when monocytes enter the arterial intima at specific sites and become tissue macrophages, they internalize A-LP in an unregulated fashion. This, in turn, would make the monocyte-macrophage lipid-laden, and could explain the etiology of foam cells in fatty streak lesions. The modification in A-LP relative to P-LDL responsible for the enhanced recognition still needs to be elucidated.

Animals↗

PubMed1984

Apolipoprotein B accumulation and development of foam cell lesions in coronary arteries of hypercholesterolemic swine.

We wished to determine whether plasma low density lipoproteins (LDL) preferentially accumulate at specific anatomical sites in swine coronary arteries that are predisposed to atherosclerotic lesion development, and if so, to determine what alteration in wall structure may be responsible for this accumulation. Therefore, we measured the accumulation of apolipoprotein B (apo B), the major protein in LDL, by electroimmunoassay in seven separate segments of coronary arteries from swine fed a hypercholesterolemic or normolipemic control diet for periods of 4 to 15 weeks. Apo B accumulation was greater in segments from swine fed a hypercholesterolemic diet than in segments for corresponding time intervals from swine fed a normolipemic diet and was greater in proximal than in distal segments (nonbranch points) of coronary arteries. This accumulation of apo B generally increased with time on the hypercholesterolemic diet, already appearing elevated relative to controls at 4 weeks on the hypercholesterolemic diet, whereas the initial appearance of foam cells in these regions occurred at 6 weeks. Apo B was localized by immunofluorescence almost exclusively to areas of diffuse intimal thickening in the proximal portions of the coronary arteries and to focal areas of intimal thickening or cushions at branch points in more distal segments. In these regions, apo B was found primarily in edematous, cell-sparse zones close to the lumen surface, rather than the smooth muscle cell-rich areas making up most of the thickened intima. Apo B in these areas was associated with Alcian blue-positive areas suggested to contain sulfated glycosaminoglycans, which may be responsible for the preferential LDL accumulation. The diffuse and focal intimal thickening does not appear to have been induced by the hypercholesterolemia or the subsequent deposition of LDL, since such thickening was found at the same sites and to about the same degree in the normolipemic control animals. Thus, this study has shown that the areas of earliest and preferential accumulation of LDL are sites of intimal thickening containing deposits of sulfated glycosaminoglycan, and that these are the regions at which the first foam cell lesions eventually appear. These findings add additional strong circumstantial data linking LDL deposition in arteries to the atherosclerotic process.

Animals↗

PubMed1984

Immunohistochemical localization of apoprotein B in aortas from hyperlipemic swine. Preferential accumulation in lesion-prone areas.

In hyperlipemic swine, areas of the aortic arch that accumulate intravenously injected Evans blue dye (blue areas) appear to be more susceptible to early atherogenesis than adjacent areas that are devoid of dye uptake (white areas). We used immunofluorescence microscopy to determine the localization of apoprotein-B (apoB) in these blue and white areas, and in intimal cell masses (ICMs) of the abdominal aortas obtained from hyperlipemic and normolipemic swine. The results showed that before aortic lesions were visible grossly or microscopically, extracellular accumulations of apoB occurred preferentially in the thickened intima of blue areas and in ICMs of the abdominal aorta. Normal white areas in the aortic arch and abdominal aortas, and in the aortas obtained from control swine showed negligible immunoreactivity. Thus, the accumulation of apoB at anatomic sites predilected to early atherogenesis lends further evidence linking these lipoproteins with atherogenesis.

Animals↗

PubMed1983

Localization of LDL in arteries: improvements in immunofluorescence procedures.

We have described the development of procedures used to localize LDL in arteries with atherosclerotic lesions from humans and experimental animal models. We have first illustrated data obtained from earlier cryostat studies, described the procedures, given examples of results of LDL localization in sections of paraffin-embedded blocks, and finally outlined the procedures used and examples for LDL localization in epoxy-embedded blocks. Future improvements in resolution of LDL localization will probably require performing electron microscopy on ultrathin sections of epoxy-embedded arteries followed by immunocytochemistry.

Animals↗

PubMed1983

Apolipoprotein B localization in coronary atherosclerotic plaques from cynomolgus monkeys.

The presence of apolipoprotein B (apo B) was determined in atherosclerotic lesions of coronary arteries from cynomolgus monkeys placed on a hypercholesterolemic diet for one year. Immunofluorescence techniques were applied to sections of arteries that were fixed by perfusion with formalin and embedded in paraffin. Segments of right coronary, left anterior descending, and left circumflex arteries were observed. All segments demonstrated substantial intimal thickening, accompanied by areas of necrosis at the base of the plaque, usually located on the luminal side of the internal elastic lamina. Large clusters of foam cells could be found at the base of such plaques, between intimal smooth muscle cells in the fibromuscular cap, and frequently in the tunica media in regions of necrosis. Immunofluorescence depicting apo B was usually confined to the intima, especially in the necrotic core, but could also be seen in the media in regions in which the internal elastic lamina was missing. Apo B often filled the extracellular space between smooth muscle cells and groups of foam cells but was not identified in the cytoplasm of intact cells. Apo B-positive areas were usually also positive for alcian blue staining, suggesting LDL-sulfated glycosaminoglycan coexistence at such sites. The localization pattern of apo B in lesioned coronary arteries from cynomolgus monkeys was consistent with that found in human coronary lesions, suggesting that diet-induced hypercholesterolemia in such monkeys may be a valid model for studying the role of LDL in human atherogenesis.

Animals↗

PubMed1983

Quantitation of apolipoprotein B in aortas of hypercholesterolemic swine.

An electroimmunoassay has been developed to quantify apolipoprotein B (apoB) in samples of aorta from normolipemic and hypercholesterolemic (diet-induced) swine. Acceptability of the assay was demonstrated using tests for specificity, sensitivity, accuracy, and validity. Specific sites in the grossly normal aortic arch of hypercholesterolemic animals were macroscopically demarcated after the injection of the dye, Evans blue. These blue sites, previously shown to be regions of early lesion formation, contained significantly greater amounts of apoB than adjacent nonblue (white) zones. By contrast, in normolipemic swine no difference in apoB content was found between blue and white regions of the arch. Likewise, the apoB content did not differ among various white regions of grossly normal aortas of hypercholesterolemic swine when no lesions were present. Also, once gross lesions were found in white regions, the apoB content was at least as great as in blue regions. The differences in apoB content between lesioned and nonlesioned areas were greatest in the abdominal aorta. The results of this study are consistent with an enhanced interstitial accumulation of lipoproteins containing apoB, especially low-density lipoprotein, occurring prior to lesion formation in this experimental model.

Animals↗

PubMed1982

Lipoproteins containing apolipoprotein A-I extracted from human aortas.

Apolipoprotein A-I was quantitated by electroimmunoassay in buffer-soluble fractions of both grossly normal intima and raised atherosclerosis lesions of the human aorta. The mean value for apolipoprotein A-I content in microgram/mg tissue dry weight of normal intima (12 cases) was 0.71 +/- 0.10 S.E. and of aortic plaques (19 cases) was 0.64 +/- 0.40 S.E. When compared to the buffer-extractable apolipoprotein B content measured in these same cases from both regions, the ratio of apolipoprotein B to apolipoprotein A-I was approximately 6. No apolipoprotein A-I was measurable in tunica media. Following differential ultracentrifugation into d less than 1.063, d 1.063-1.21 and d greater than 1.21 fractions, the distributions of recovered apolipoprotein A-I were, respectively: 1, 94 and 5% for normal intima, 19, 31 and 50% for plaques and 1, 89 and 10% for plasma. Characterization of a chromatographically purified d 1.063-1.21 or HDL density fraction from fatty-fibrous plaques demonstrated particles of between 60 and 120 A diameter, a characteristic apolipoprotein A-I band by SDS-polyacrylamide gel electrophoresis, and a precipitin peak closely migrating with that for plasma HDL by two-dimensional immunoelectrophoresis. The d greater than 1.21 density fraction from plaques isolated by affinity chromatography on a Sepharose-anti-apolipoprotein A-I column contained small amounts of phospholipid but no measurable cholesterol. The d 1.063-1.21 density fraction from plaques showed a significant increase in percent free cholesterol and phospholipid contents and decrease in cholesteryl ester content relative to plasma HDL. This increase in free cholesterol could represent evidence for an anti-atherogenic mechanism wherein infiltrated HDL removes cholesterol together with phospholipid from the arterial wall.

Adult↗