Degradation Of Low Density Lipoprotein Research Articles

インスリンによるLDL pathwayの調節

Effects of insulin and growth factors on low-density lipoprotein (LDL) metabolism were studied in cultured human fibroblasts. Epidemal growth factor (EGF), fibroblast growth factor (FGF), and insulin increased LDL binding, internalization, and degradation in a serum free system by approximately 39%, 25%, and 75% respectively. Both EGF and FGF had additive effects on the insulin stimulated LDL metabolism in the cells. In the presence of 2mM hydroxyurea an inhibitor of DNA synthesis, basal acivities of LDL pathway were declined, however the insulin stimulation was not altered. Insulin also stimulated (U-14C) D-glucose incorporation into the same fibroblasts, and the half maximal effects were observed at the insulin concentration of 5ng/m/. Dose-response curves of glucose incorporation to insulin were similar to those of LDL pathway to insulin.Results indicate that the stimulatory effects of insulin on LDL pathway is independent of cell proliferation, and also suggest that insulin plays a physiological role in LDL metabolism comparable to that in carbohydrate metabolism.

Diabetic lipoprotein deficient serum: Its effect in low density lipoprotein (LDL) uptake and degradation by fibroblasts

Low density lipoproteins (LDL) isolated from poorly controlled diabetic patients are known to be taken up and degraded by fibroblasts at a lower rate than LDL isolated from normal subjects. This aberrant metabolic behavior has been attributed to a diabetic-related abnormality in LDL composition yet to be characterized. The studies reported in this article show that the decrease in uptake and intracellular degradation of LDL from diabetic patients is further enhanced when the cells are exposed to lipoprotein deficient serum (LPDS) isolated from the same poorly controlled diabetic patients. Comparative studies of the composition of LPDS obtained from normal donors and poorly controlled diabetic patients showed an increase in saturated and total unesterified fatty acids (UFA), lecithin, apolipoprotein A 1, and immunoreactive insulin in the LPDS from diabetic patients. We postulate that exposure of cells to LPDS obtained from poorly controlled diabetic patients may induce changes in the composition of the fibroblast membrane and alter its fluidity, leading to further decrease in the uptake and degradation of LDL. During poor diabetic control, cell membrane changes, and modification of LDL composition are likely to act either additively or synergistically to induce an abnormal LDL-cell interaction. This abnormal interaction may be a relevant factor to explain the greater incidence of arteriosclerosis in diabetes mellitus.

Complexes of low-density lipoproteins and arterial proteoglycan aggregates promote cholesteryl ester accumulation in mouse macrophages

We studied the effect of complexes of low-density lipoproteins (LDL) and different proteoglycan preparations from bovine aorta on LDL degradation and cholesteryl ester accumulation in mouse peritoneal macrophages. Native proteoglycan aggregate containing proteoglycan monomers, hyaluronic acid and link protein was isolated by associative extraction of aortic tissue, while proteoglycan monomer was obtained by dissociative isopycnic centrifugation of the native proteoglycan aggregate. In vitro proteoglycan aggregates were prepared by reaction of the proteoglycan monomer with exogenous hyaluronic acid. 125I-labeled LDL-proteoglycan complexes were formed in the presence of 30 mM Ca 2+ and incubated with macrophages. At equivalent uronic acid levels in the proteoglycans the degradation of 125I-labeled LDL contained in the native proteoglycan aggregate complex was 3.7–7.5-fold greater than the degradation of the lipoprotein in the proteoglycan monomer complex. Degradation of 125I-LDL in the in vitro aggregate complex, while higher than that in the monomer complex, was markedly less than that in the native aggregate complex. The larger size and the greater complex-forming ability of the native proteoglycan aggregate might account for the greater capacity of the aggregate to promote LDL degradation in macrophages. The proteoglycan-stimulated degradation of LDL produced a marked increase in cholesteryl ester synthesis and content in macrophages. The LDL-proteoglycan complex was degraded with saturation kinetics, suggesting that these complexes are internalized through high-affinity receptors. Degradation was inhibited by the lysosomotropic agent, chloroquine. Acetyl-LDL, but not native LDL, competitively inhibited the degradation of the 125I-LDL component of the complex. Polyanionic compounds such as polyinosinic acid and fucoidin, while completely blocking the acetyl-LDL-stimulated cholesteryl ester formation, had no effect on the proteoglycan aggregate-stimulated cholesterol esterification. This suggests that LDL-proteoglycan complex and acetyl-LDL are not entering the cells through the same receptor pathway. These results demonstrate that the interaction of LDL with arterial wall proteoglycan aggregates results in marked cholesteryl ester accumulation in macrophages, a process likely to favor foam cell formation. A role for arterial proteoglycans in atherosclerosis is obvious.

Involvement of microtubules in lipoprotein degradation and utilization for steroidogenesis in cultured rat luteal cells.

Cells isolated from superovulated rat ovaries metabolize low density lipoprotein (LDL) and high density lipoprotein (HDL) of human or rat origin and use the lipoprotein-derived cholesterol as a precursor for progesterone production. Under in vitro conditions, both lipoproteins are internalized and degraded in the lysosomes, although degradation of HDL is of lower magnitude than that of LDL. In this report we have examined the role of cellular microtubules in the internalization and degradation of human LDL and HDL in cultured rat luteal cells. The microtubule depolymerizing agents colchicine, podophyllotoxin, vinblastine, and nocodazole as well as taxol, deuterium oxide, and dimethyl sulfoxide, which are known to rapidly polymerize cellular tubulin into microtubules, were used to block the function of microtubules. When these antimicrotubule agents were included in the incubations, degradation of the apolipoproteins of [125I]iodo-LDL and [125I]iodo-HDL by the luteal cells was inhibited by 50-85% compared to untreated control values. Maximum inhibitory effects were observed when the cells were preincubated with the inhibitor for at least 4 h at 37 C before treatment with the labeled lipoprotein. Lipoprotein-stimulated progesterone production by luteal cells was also inhibited by 50% or more in the presence of antimicrotubule agents. However, basal and hCG-stimulated progesterone production were unaffected by these inhibitors. The binding of [125I]iodo-LDL and [125I]iodo-HDL to luteal cell plasma membrane receptors was not affected by the microtubule inhibitors. Although binding was unaffected and degradation was impaired in the presence of the inhibitors, there was no detectable accumulation of undegraded lipoprotein within the cells during the 24 h of study. From this study we conclude that the uptake and utilization of LDL and HDL by cultured rat luteal cells are mediated by cellular microtubules.

The effect of mevalonate on 3-hydroxy-3-methylglutaryl-CoA reductase activity and the absolute rate of cholesterol biosynthesis in human monocyte-derived macrophages.

Normal monocyte-derived macrophages maintained in medium containing 20% whole serum exhibited a high activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase while expressing appreciable, but not maximal receptor-mediated uptake and degradation of low-density lipoprotein (LDL). Addition of extracellular mevalonate led to a concentration-dependent fall in both processes, although a higher concentration was required to produce the same effect on LDL degradation as on HMG-CoA reductase activity. The true rate of cholesterol synthesis by the cells was already high without mevalonate and was not further increased when the intracellular pool of mevalonate was expanded. After preincubation with lipoprotein-deficient serum receptor-mediated degradation of LDL was increased but HMG-CoA reductase activity was decreased. Both were more sensitive to extracellular mevalonate and a given concentration of mevalonate now produced the same percentage fall in LDL degradation and reductase activity. The amount of cholesterol synthesized by the cells was markedly reduced during incubation with lipoprotein-deficient serum, probably as a result of the decreased reductase activity compounded by a lack of endogenous substrate. If these were circumvented by adding mevalonate, cholesterol synthesis was restored to normal. These results suggest that the fall in HMG-CoA reductase activity during incubation with lipoprotein-deficient serum resulted from repression by some non-sterol product of mevalonate metabolism. They imply that the need for this product by cells growing in whole serum leads to a particularly high HMG-CoA reductase activity and could account for their apparent preference for endogenous synthesis of cholesterol rather than for receptor-mediated uptake of LDL.

Lipoproteins of the extravascular space: enhanced macrophage degradation of low density lipoproteins from interstitial inflammatory fluid

Current evidence has demonstrated that cholesteryl ester-loaded macrophages are important components of the atherosclerotic lesion. Additional studies have implicated low density lipoproteins (LDL) and circulating monocytes as central to the origin of lipid-laden foam cells found in the arterial wall. This is a result of the finding of accelerated macrophage uptake of LDL chemically modified by reaction with malondialdehyde (MDA-LDL), acetic anhydride (Ac-LDL), or incubation with arterial cells in vitro. In concert with these chemical modifications, we have previously demonstrated selective in vivo modification of LDL isolated from interstitial inflammatory fluid (IF) of the rabbit. Utilizing the polyvinyl sponge implant model, we reported that IF-LDL had an altered chemical composition, electrophoretic mobility, and particle size distribution when compared to LDL isolated from homologous plasma (WP-LDL). In this study reported herein, we examined the metabolism of IF-LDL by resident mouse peritoneal macrophages (MPM) in culture. IF-LDL was degraded substantially faster by MPM, and resulted in a substantial increase in cellular cholesteryl ester when compared to cells incubated with WP-LDL. IF-LDL binding to MPM was inhibited by Ac-LDL derived from WP-LDL, but only minimally by unmodified WP-LDL. Transmission electron microscopy of MPM revealed extensive lipid deposition in cells incubated with Ac-LDL and IF-LDL. These results implicate LDL from interstitial inflammatory fluid as an in vivo modified lipoprotein that can enhance uptake via the acetyl LDL receptor pathway in resident macrophages.

Low density lipoprotein degradation by rat mast cells. Demonstration of extracellular proteolysis caused by mast cell granules.

The interaction between rat serosal mast cells and low density lipoproteins (LDL) was studied in vitro. When rat 125I-LDL was incubated with mast cells, it was bound to a binding site on the mast cell surface but was not internalized by the cells. Even though 125I-LDL was not internalized, its protein component, apolipoprotein B, was rapidly degraded. The proteolytic activity responsible for the degradation of apolipoprotein B was present in the extracellular fluid of mast cells. It could be shown that the degradation was caused entirely by specific cell organelles of mast cells, the granules, which were spontaneously released into the extracellular fluid during preparation and incubation of the cells. In contrast to uncontrolled spontaneous degranulation, a controlled specific degranulation of mast cells can be induced by treating the cells with the compound 48/80. When increasing amounts of 48/80 were added to mast cell suspensions, a dose-dependent release of granules was observed and an increase in the rate of 125I-LDL degradation resulted. The increase in 125I-LDL degradation closely followed the increase in granule release. Thus, a quantitative relationship between the amount of granules present in the extracellular fluid and the amount of degradation of 125I-LDL could be established. The apolipoprotein part of LDL was extensively degraded by isolated mast cell granules. Analysis by polyacrylamide gel electrophoresis showed that upon incubation of LDL with isolated granules, the apolipoprotein B band rapidly disappeared with simultaneous appearance of several low molecular weight bands. The degradation of 125I-LDL by mast cell granules proceeded optimally at neutral pH and at physiological ionic strength. The results show that mast cell granules are able to efficiently degrade LDL in vitro, once released from mast cells into the extracellular fluid.

HYPOCHOLESTEROLAEMIA IN MALIGNANCY DUE TO ELEVATED LOW-DENSITY-LIPOPROTEIN-RECEPTOR ACTIVITY IN TUMOUR CELLS: EVIDENCE FROM STUDIES IN PATIENTS WITH LEUKAEMIA

59 patients with acute leukaemia were examined to see if hypocholesterolaemia, which is commonly found in acute leukaemia, was due to the high low-density-lipoprotein (LDL)-receptor activity of leukaemic cells. LDL-receptor activity was found to be inversely correlated with plasma-cholesterol concentration. Patients with both a high LDL-receptor activity per cell and a high white-blood-cell count had the lowest cholesterol concentrations. During chemotherapy, cholesterol levels rose concomitantly with the disappearance from the peripheral blood of leukaemic cells. Hypocholesterolaemia in leukaemia and other neoplastic disorders may be due to increased LDL-receptor activity in the malignant cells. This high uptake and degradation of LDL by malignant cells could be utilised to target neoplastic cells with LDL-bound chemotherapeutic agents.

Mechanisms Involved in the Uptake and Degradation of Low Density Lipoprotein by the Artery Wall in Vivoa

Mechanisms Involved in the Uptake and Degradation of Low Density Lipoprotein by the Artery Wall <i>in Vivo</i>^a

Human chorionic gonadotropin and 8-bromo-adenosine 3',5'-monophosphate stimulate [125I]low density lipoprotein uptake and metabolism by luteinized human granulosa cells in culture.

In nonsteroidogenic cells, cellular cholesterol requirements and sterol availability determine low density lipoprotein (LDL) receptor expression and LDL metabolism. We wished to learn if hCG and cAMP increase LDL metabolism by cultured luteinized human granulosa cells and whether this increase is dependent on enhanced metabolism of cellular cholesterol stores to steroid. Granulosa cells were cultured for 48 h in medium containing 20% human male serum and then for 48 h in serum- and hormone-free medium. The cells then received either fresh medium (no additions) or one of the following treatments: 500 mIU hCG/ml, 1.5 mM 8-bromo-cAMP, 100 micrograms aminoglutethimide (AG)/ml to inhibit cholesterol metabolism to steroid hormones, hCG plus AG, or 8-bromo-cAMP plus AG. After 6-48 h of exposure to tropic agents, specific metabolism of [125I]LDL was determined. hCG and 8-bromo-cAMP significantly increased (P less than 0.05) the amount of [125I]LDL bound (2.2-fold), internalized (2.3-fold), and degraded (2.9-fold) by the luteinized granulosa cells. The apparent Km values for LDL degradation in control and hCG-treated cells were similar (2.0 and 2.6 micrograms/ml, respectively). As little as 10 mIU hCG/ml stimulated LDL metabolism in a time-dependent fashion: a stimulatory effect was detected within 6 h of exposure to hCG and was greater after 24 h. AG attenuated but did not prevent the hCG- or 8-bromo-cAMP-stimulated increase in both LDL uptake and metabolism, although it completely inhibited the steroidogenic response. AG alone had no significant effect on [125I] LDL metabolism. We conclude that hCG and cAMP increase LDL metabolism by luteinized human granulosa cells. These effects are apparently not simply a consequence of enhanced cellular cholesterol metabolism to steroids.

Properties of low density lipoprotein binding by cultured swine granulosa cells.

The properties of low density lipoprotein (LDL) binding to ovarian cells were investigated in cultured swine granulosa cells in serum-free monolayer cultures. Swine and human LDL bound with high affinity and specificity, with apparent dissociation constant (Kd) values for swine and human LDL of 1.1 and 3.6 micrograms/ml at 4 C, and 2.7 and 4.8 micrograms/ml at 37 C. In contrast, high density lipoprotein competed sparingly with [125I]iodo-LDL with an apparent half-maximally inhibitory concentration of 650 micrograms/ml. Binding of LDL was dependent upon arginine residues within the apoprotein B moiety, since covalent modification of LDL with 1,2-cyclohexanedione markedly reduced its ability to compete for binding or degradation and to support progesterone biosynthesis. This specific, high affinity saturable binding of LDL to pig granulosa cells exhibited a maximal binding capacity of 0.7 micrograms LDL protein/mg DNA, which corresponds to approximately 5500 LDL receptors per cell. The relative time course of LDL binding, internalization, and degradation by swine granulosa cells was assessed by examining trypsin-releasable (surface-bound) and trypsin-resistant (internalized) [125I]iodo-LDL. At 37 C, granulosa cells exhibited a rapid increase in surface-bound lipoprotein, followed by delayed but subsequently progressive increases in internalized and degraded LDL. LDL degradation by swine granulosa cells was a saturable, temperature- and time-dependent process, with half-maximal degradation occurring at a concentration of 16 micrograms/ml LDL. This correlates closely with the half-maximal concentration of LDL that stimulates progesterone secretion. Degradation of [125I]iodo-LDL was not attributable to bulk fluid-phase pinocytosis, since the cellular ingestion of an impermeant probe, [125I]iodo-polyvinylpyrrolidone, occurred at 1/40 the rate of lipoprotein degradation. In addition, degradation of [125I]iodo-LDL was specifically inhibited by excess unlabeled LDL, decreased by prior exposure of granulosa cells to the soluble sterol, 25-hydroxycholesterol, and antagonized by the lysosomotrophic agent, chloroquine. Moreover, in separate experiments, rates of degradation of LDL were found to be significantly correlated with progesterone one production (r = +0.88, P less than 0.01). In summary, swine granulosa cells exhibit specific, high affinity, saturable, and low capacity receptors for homologous and heterologous LDL. These LDL recognition sites on ovarian cells depend upon cyclohexanedione-sensitive arginine residues with the apoprotein B moiety for effective binding, internalization, and functional (steroidogenic) responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic cooperation between vascular endothelial cells and smooth muscle cells in co-culture: changes in low density lipoprotein metabolism.

A microcarrier co-culture system for aortic endothelial cells and smooth muscle cells (SMCs) was developed as a model for metabolic interactions between cells of the vessel wall. Low density lipoprotein (LDL) metabolism in SMCs was significantly influenced by co-culture with endothelium. The numbers of high affinity receptors for LDL was increased more than twofold (range, 2.1-5.6), with concomitant increases in LDL receptor-mediated endocytosis and degradation. These effects reached a plateau at an endothelial cell/SMC ratio of 1. Kinetic analysis of the endocytic pathway for LDL in SMCs indicated that, in co-culture with endothelium, there was no alteration in the binding affinity of LDL to its receptors but that the internalization rate constant declined and the rate constant for degradation increased. This analysis suggested that the formation and migration of endocytic vesicles was the rate-limiting step of enhanced LDL metabolism under co-culture conditions. Two mechanisms by which endothelial cells influenced smooth muscle LDL metabolism were identified. First, mitogen(s) derived from endothelial cells stimulated entry of SMCs into the growth cycle, and the changes in LDL metabolism occurred as a consequence of G1-S transition. Second, SMC lipoprotein metabolism was stimulated in the absence of mitogens by a low molecular weight (less than 3,500) factor or factors. Co-culture was a required condition for the latter effect, suggesting that the mediator(s) may be unstable or that cell-cell communication was necessary for expression. These results (a) demonstrate that vascular cell interactions can modify LDL metabolism in SMCs, (b) provide some insights into the mechanisms responsible, and (c) identify co-culture as an experimental approach appropriate to certain aspects of vascular cell biology.

Receptor-independent low density lipoprotein transport in the rat in vivo. Quantitation, characterization, and metabolic consequences.

Receptor-independent low density lipoprotein (LDL) transport plays a critical role in the regulation of plasma cholesterol levels; hence, these studies were done to characterize this process in the tissues of the rat. High rates of receptor-independent clearance were found in the spleen, but other organs, like liver, gastrointestinal tract, and endocrine glands manifested lower clearance rates that varied from 3 to 9 microliter/h per g, while the rates in nervous tissue, muscle, and adipose tissue were less than 1 microliter/h per g. Receptor-dependent uptake was much higher in liver (85 microliter/h per g) and adrenal gland (219 microliter/h per g), but was also low in most other tissues. At normal plasma LDL concentrations, 67% of the receptor-dependent transport in the whole animal was accounted for by LDL uptake in the liver. In contrast, the receptor-independent uptake found in the whole animal took place in many organs, including skeletal muscle (20%), liver (16%), small bowel (15%), skin (10%), and spleen (7%). Furthermore, in liver, the rate of cholesterol synthesis could be varied 11-fold, yet the rate of receptor-independent LDL clearance remained constant at approximately 8 microliter/h per g. When the circulating levels of LDL were systematically increased, receptor-independent LDL clearance also remained constant, so that hepatic LDL-cholesterol uptake by this mechanism increased linearly, from 1 to 20 micrograms/h per g, as the plasma LDL-cholesterol level was increased from 10 to 250 mg/dl. Finally, when equal amounts of LDL-cholesterol were delivered into the liver by either the receptor-dependent or receptor-independent mechanism, there was significant suppression of cholesterol synthesis and an increase in cholesteryl esters. Thus, in any situation in which receptor-dependent LDL degradation is lost, cholesterol balance in the whole animal and across individual organs is maintained by receptor-independent mechanisms, although when the new steady state is achieved, circulating levels of LDL must necessarily be very much increased.

The effect of calcium antagonists on the proteolytic degradation of low-density lipoprotein in HeLa cells

The degradation of 125I-labelled low-density lipoproteins (LDL) in HeLa cells was significantly inhibited when the cells were incubated either with the calcium channel blocking agents D600 and verapamil, or with the lysosomotropic agent chloroquine. However, nifedipine, another blocker of Ca 2+ channels, did not affect the degradation of 125I-labelled LDL. The association of 125I-labelled LDL with HeLa cells was increased in proportion to the concentration of D600, and 125I-labelled LDL was accumulated in lysosomal fractions as assessed by Percoll density gradient analysis. Some 80% of 125I-labelled LDL in lysosomes of HeLa cells treated with D600 was acid-insoluble. The rate of incorporation of [ 3H]acetate into digitonin-precipitable material was increased 4-fold in the cells treated with 40 μg/ml D600 compared with untreated cells, but that of [ 3H]mevalonate was not enhanced. About 8 h of preincubation of the cells with D600 or verapamil was required to inhibit the LDL degradation by 50% of the control activity. It was also found that the inhibitory action of D600 could be reversed by removal of D600 from the medium. The activities of lysosomal enzymes, cathepsin B, β-hexosaminidase, and acid phosphatase, were significantly decreased when the cells were treated with D600 and chloroquine, but not with nifedipine. Blockers of Ca 2+ channels which effect the activity of lysosomal enzymes, should be useful for the study of the lysosomal function.

High-affinity association and degradation of 125I-labelled low density lipoproteins by human hepatocytes in primary culture

Catabolism of homologous low density lipoproteins (LDL) was studied in primary culture of human hepatocytes (HH). The cell association and degradation of 125I-labeled LDL ( 125I-LDL) were curvilinear functions of substrate concentration. Cell association and degradation of 125I-LDL were inhibited by excess unlabeled LDL. Reductive methylation of unlabeled LDL abolished its ability to compete with 125I-LDL for cell association and degradation. Preincubation of HH with unlabeled LDL caused a 63% inhibition of the 125I-LDL degradation. It is concluded that the catabolism of LDL by HH proceeds in part through a receptor-mediated pathway similar to that demonstrated on extrahepatic cells. Human hepatocyte LDL Cell association Degradation High affinity association

In vivo catabolism of human low density lipoprotein in the rat is mediated by a nonsaturable, low-affinity mechanism

The degradation of human low density lipoprotein (LDL) was analyzed in fasted rats treated for 3 days with either 4-aminopyrazolo-(3,4-d)pyrimidine (4APP) or saline. Treatment with 4APP caused an 80% decrease in serum cholesterol concentration. The mono-exponential serum decay of a tracer amount of labelled LDL was changed neither by 4APP treatment, nor by the simultaneous injection of a bolus of unlabelled LDL. The sites of degradation of human LDL were determined using the nondegradable labelling compound O-(4-diazo-3-[ 125I]iodobenzoyl)sucrose (D 125IBS). The sites of degradation and the rate of degradation of D 125IBS labelled LDL were also not affected by 4APP treatment or by injection of a bolus of unlabelled LDL. It is concluded that human LDL is catabolised in the rat by way of a nonsaturable, low-affinity mechanism. Low density lipoprotein 4-Aminopyrazolo-(3,4-d)pyrimidine Catabolic site LDL receptor B/E receptor O-(4-Diazo-3-[ 125I]iodobenzoyl)sucrose

Effects of ammonium ion derived from bovine endothelial cells upon low density lipoprotein degradation in cultured vascular smooth muscle cells

Low density lipoprotein (LDL) metabolism in bovine arterial smooth muscle cells (SMC) was increased upon exposure to endothelial cell conditioned medium. The mass of LDL degraded in the SMC lysosomal system was increased, and kinetic analysis demonstrated that the rate constant for LDL degradation arising from receptor-mediated endocytis was unchanged. The effects on LDL metabolism were accompanied by stimulation of DNA synthesis in the SMC. These results are in contrast to reports concerning a porcine endothelial cell system where LDL degradation was inhibited by endothelial-derived NH 4 +. We show that bovine endothelial cells produce insufficient NH 4 + to inhibit LDL degradation and conclude that endothelial cell-derived NH 4 + is unlikely to be a factor affecting LDL metabolism in the bovine vascular cell culture system.

Cell density dependent uptake of LDL in cultured rat hepatocytes

An inverse relationship between low-density lipoprotein uptake and cell density was observed in rat hepatocyte monolayers incubated with lipoprotein-deficient serum. This was also true for cell association, binding and degradation of low-density lipoproteins. Compactin stimulated cell association and degradation of low-density lipoproteins both at low and high concentrations. Insulin, on the other hand, had no consistent effect on low-density lipoprotein cell association or degradation.

Normalization of low-density lipoprotein levels and disappearance of xanthomas during pregnancy in a woman with heterozygous familial hypercholesterolemia

Serum lipids and lipoproteins were studied prior to conception, during pregnancy, and after delivery in a woman heterozygous for familial hypercholesterolemia. Prior to conception, serum and low-density lipoprotein (LDL) cholesterol levels were 613 and 528 mg/dL, respectively. At 37-week gestation, serum and LDL cholesterols decreased to the normal levels, 226 and 90 mg/dL, respectively. At two-week postpartum serum and LDL cholesterols returned to the preconception levels, 547 and 427 mg/dL, respectively. At delivery her cutaneous xanthomas almost disappeared. The patient was challenged by ethinyl estradiol of 120 μg/d for two months, as a result serum cholesterol decreased from 565 to 385 mg/dL, and LDL cholesterol fell from 460 to 208 mg/dL. During her second pregnancy, serum and LDL cholesterol decreased again significantly. Thus, this case, which showed dramatic reductions of serum and LDL cholesterol levels, may be considered a new variant of heterozygous familial hypercholesterolemia, and the reductions were probably brought about by the action of estrogens, which are known to increase LDL degradation through LDL receptors.

Proliferation, morphology, and low-density lipoprotein metabolism of arterial endothelial cells cultured from normal and diabetic minipigs

Aortic endothelial cells from control and streptozotocin diabetic minipigs were cultured. Both groups of cells exhibited the typical cobblestone-like appearance and gap junction formation. Endothelial cells derived from diabetic minipigs differed, however, from those from control animals by a higher rate of proliferation and a higher percentage of large and often multinucleated cells. In these cells the specific binding of low-density lipoproteins (LDL) to coated pits on the cell surface, the LDL uptake, and the intracellular transport of LDL to lysosomes were visualized by gold-labeled LDL complexes. The binding, internalization, and degradation of LDL by subconfluent, non-contact-inhibited endothelial cells was quantified using 125I-labeled LDL. The LDL metabolism of endothelial cells derived from diabetic animals was increased by about 40% compared to endothelial cells derived from nondiabetic animals.