Human Native Low-density Lipoprotein Research Articles

The role of dendritic cells the in development of atherosclerosis of coronary vessels in the experiment.

The dynamics of quantitative and qualitative changes of the dendritic cells (DC) of coronary arteries wall at different stages of atherosclerosis development was investigated. Animals received human native low density lipoproteins. Dendritic cells were detected by using polyclonal antibodies S-100 and monoclonal antibodies CD1a (clone O10). A semiquantitative scale from 0 to 3 points was used to determine the intensity of expression of immunohistochemical markers. Histological examination of coronary arteries wall was perfomed by hemothoxylin-eosin, orsein andsudanIII. The first increase of the number of dendritic cells was observed at the 10th week after start of experiment, which corresponded to prelipid stage of atherosclerosis. The second increase of the number of dendritic cells was noted at the 13week and was characterized by moderate expression of markers (2 points) and morphologically responded to the stage of lipoidosis. The late stages of the experiment (18-20 week) were characterized by the maximal increase of DC and a high expression of immunohistochemical markers (3 points).

Features of histologiacal morfology of components of the coronary arterial wall in experimental atherosclerosis.

Background. Atherosclerosis is a multifactorial chronic disease, which is associated with immune inflammation of the arteries. The main role in the development of atherosclerotic lesions belongs to the dendritic cells. Objective. To investigate the components of coronary arteries wall and their interrelationships in the experimental atherosclerosis. Methods. Animals received human native low density lipoproteins. Standard histological and immunehistochemical methods were used to detect dendritic cells and other components into coronary arteries wall. Results. On the 4-6 th weeks of the experiment it was observed that dendritic cells form contacts with isolated lymphocytes and macrophages, and they were located mainly in the subendothelial layer. On the 12 th week the artery wall has changed its structure and the composition of the cellular elements. After 16 th week, dendritic cells were found in all layers of the coronary arteries and foam cells were revealed at this period. 18-20 th weeks of the experiment were characterized by the phenomena of liposclerosis. Conclusion. It was established that under the normal condition the intima of coronary arteries in rats contains dendritic cells. There is a complex relationships between dendritic cells with other cells. The number of dendritic cells increases with the progression of atherosclerotic lesions. It was observed the redistribution of cells in the intima depends on the stage of atherosclerosis.

N‐acetylcysteine prevents in vivo oxidation of native low‐density lipoprotein

ObjectiveLow‐density lipoprotein (LDL) is not atherogenic. Oxidized LDL (ox‐LDL) produces reactive oxidative species (ROS) and is critical to atherosclerosis. N‐acetylcysteine (NAC) has anti‐atherosclerotic effect with largely unknown mechanisms. The present study aimed to determine if NAC could attenuate LDL oxidation in vivo.Approach and ResultsMeasurable serum level of human ox‐LDL was detected 30 min after a single dose intravenous injection of human native LDL into male C57BL/6 mice, reached the peak in 3 hours, then started to decline, and became undetectable in 12 hours. NAC treatment significantly reduced serum ox‐LDL level with no detectable serum ox‐LDL 6 hours after injection. No difference in ox‐LDL clearance was observed in NAC‐treated animals. NAC treatment also significantly decreased serum ox‐LDL level in patients with coronary artery disease and hyperlipidemia with no effect on LDL level. Intracellular and extracellular ROS production was significantly increased in the mice treated with native LDL, or ox‐LDL that was completely prevented with NAC treatment.ConclusionNAC attenuated native LDL in vivo oxidation and ROS formation from ox‐LDL.Sources of fundingNIH R01 HL094650

Redox regulation of 14-3-3ζ controls monocyte migration.

Metabolic stress primes monocytes for accelerated chemokine-mediated adhesion, migration, and recruitment into vascular lesions by increasing actin remodeling. The mechanism linking metabolic stress to accelerated actin turnover and enhanced monocyte migration was not known. We tested the hypothesis that in metabolically primed monocytes, the acceleration of monocyte chemoattractant protein-1-induced chemotaxis is mediated by the hyperactivation of cofilin. Metabolic priming was induced by exposing human THP-1 monocytes to diabetic conditions, that is, human native low-density lipoprotein plus high glucose concentrations. In healthy monocytes, monocyte chemoattractant protein-1 induced the phosphorylation and inactivation of cofilin. This response was completely blocked in metabolically primed monocytes but restored by overexpression of the thiol transferase, glutaredoxin 1. Cofilin kinase, LIM kinase 1, and cofilin phosphatase, Slingshot-1L, were not affected by metabolic stress. However, metabolic priming increased 3.8-fold the S-glutathionylation of the Slingshot-1L-binding protein 14-3-3ζ (zeta), resulting in its caspase-dependent degradation. Glutaredoxin 1 overexpression inhibited low-density lipoprotein plus high glucose-induced S-glutathionylation and degradation of 14-3-3ζ. The C25S mutant of 14-3-3ζ was resistant to both S-glutathionylation and degradation induced by low-density lipoprotein plus high glucose. Overexpression of the C25S mutant restored monocyte chemoattractant protein-1-induced cofilin phosphorylation and prevented accelerated migration of metabolically stressed monocytes, suggesting that loss of 14-3-3ζ increases the pool of free Slingshot-1L phosphatase, thereby preventing the phosphorylation and deactivation of cofilin in response to chemokine activation. By preventing the inactivation of cofilin, metabolic stress-induced degradation of 14-3-3ζ promotes the conversion of blood monocytes into a hypermigratory, proatherogenic phenotype.

Oxidized Low Density Lipoprotein (LDL) Affects Hyaluronan Synthesis in Human Aortic Smooth Muscle Cells

Thickening of the vessel in response to high low density lipoprotein(s) (LDL) levels is a hallmark of atherosclerosis, characterized by increased hyaluronan (HA) deposition in the neointima. Human native LDL trapped within the arterial wall undergoes modifications such as oxidation (oxLDL). The aim of our study is to elucidate the link between internalization of oxLDL and HA production in vitro, using human aortic smooth muscle cells. LDL were used at an effective protein concentration of 20-50 μg/ml, which allowed 80% cell viability. HA content in the medium of untreated cells was 28.9 ± 3.7 nmol HA-disaccharide/cell and increased after oxLDL treatment to 53.9 ± 5.6. OxLDL treatments doubled the transcripts of HA synthase HAS2 and HAS3. Accumulated HA stimulated migration of aortic smooth muscle cells and monocyte adhesiveness to extracellular matrix. The effects induced by oxLDL were inhibited by blocking LOX-1 scavenger receptor with a specific antibody (10 μg/ml). The cholesterol moiety of LDL has an important role in HA accumulation because cholesterol-free oxLDL failed to induce HA synthesis. Nevertheless, cholesterol-free oxLDL and unmodified cholesterol (20 μg/ml) induce only HAS3 transcription, whereas 22,oxysterol affects both HAS2 and HAS3. Moreover, HA deposition was associated with higher expression of endoplasmic reticulum stress markers (CHOP and GRP78). Our data suggest that HA synthesis can be induced in response to specific oxidized sterol-related species delivered through oxLDL.

Atherosclerosis in rats after immunization with human native low-density lipoproteins

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Activated platelets contribute to oxidized low‐density lipoproteins and dysfunctional high‐density lipoproteins through a phospholipase A2‐dependent mechanism

Plasma activity of secretory phospholipase A2 (sPLA2) increases in patients with cardiovascular disease. The present study investigated whether platelet-released sPLA2 induces low-density lipoprotein (LDL) and high-density lipoprotein (HDL) modifications that translate into changes in lipoprotein function. Activated but not resting platelets induced oxidative modifications of human native LDLs and HDLs, which render these particles dysfunctional. Platelet-incubated LDLs stimulated the incorporation of cholesterol oleate into macrophages, and modified HDLs lost their cholesterol efflux capacity and antioxidant properties. In vitro and ex vivo experiments showed that lysophophatidylcholine accumulated in the platelet-modified LDLs and HDLs of mice expressing sPLA2 (Balb/c and transgenic C57Bl/6 mice expressing human sPLA2) but not in the lipoproteins of naturally sPLA2-deficient mice (C57Bl/6). Unlike C57Bl/6 mice, Balb/c mice injected with leptin (67 μg/mouse, i.p.) as an in vivo prothrombotic agent displayed increased plasma sPLA2 activity, reduced clotting time, higher plasma levels of oxidation products, increased production of nonesterified fatty acids, and more substantial platelet-mediated modification of lipoproteins. These effects were blocked completely by injection of the platelet inhibitor ticlopidine (5 mg/kg, i.p.) or by a sPLA2 inhibitor (LY311727, 3 mg/kg, i.p.). These results demonstrate that stimulated platelets are major contributors to plasma sPLA2 activity in vivo and account to a large extent for the adverse modification of circulating lipoproteins.

Ceruloplasmin and oxidized LDL colocalize in atherosclerotic lesions of hamster

Abstract Epidemiological studies show that the risk for cardiovascular diseases increases with increasing levels of free-copper in plasma. It is known that intact ceruloplasmin (CP), the major protein transporter of copper in human plasma, oxidizes low density lipoproteins (LDL) in vitro. Our aim was to study the interaction between LDL and CP in vitro and in vivo, in an animal model of diet-induced atherosclerosis. In order to visualize the pathway of LDL into the arterial wall, human native LDL was labeled with fluorescent DiI and injected into male, Golden Syrian hyperlipemic hamsters. In vitro results demonstrated that slightly degraded CP has a significant oxidation potential against LDL at neutral pH. In vivo, after 24 hours circulation, LDL-DiI was taken up by the enlarged intima and fatty streaks of the arterial wall. Immunohistochemical localization of oxidized LDL and CP revealed their presence in the same areas of the arteries that take up LDL-DiI. Co-localization of LDL and CP in the enlarged intima of pro-atherosclerotic areas might explain the possible copper-induced oxidation process that might occur after native LDL is taken-up from the blood, transcytosed through the endothelium and accumulated in focalized deposits.

Systematic comparison of two novel, thiol-reactive prosthetic groups for 18F labeling of peptides and proteins with the acylation agent succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)

A systematic comparison of 4-[18F]fluorobenzaldehyde-O-(2-{2-[2-(pyrrol-2,5-dione-1-yl)ethoxy]-ethoxy}-ethyl)oxime ([18F]FBOM) and 4-[18F]fluorobenzaldehyde-O-[6-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-hexyl]oxime ([18F]FBAM) as prosthetic groups for the mild and efficient 18F labeling of cysteine-containing peptides and proteins with the amine-group reactive acylation agent, succinimidyl-4-[18F]fluorobenzoate ([18F]SFB), is described. All three prosthetic groups were prepared in a remotely controlled synthesis module. Synthesis of [18F]FBOM and [18F]FBAM was accomplished via oxime formation through reaction of appropriate aminooxy-functionalized labeling precursors with 4-[18F]fluorobenzaldehyde. The obtained radiochemical yields were 19% ([18F]FBOM) and 29% ([18F]FBAM), respectively. Radiolabeling involving [18F]FBAM and [18F]FBOM was exemplified by the reaction with cysteine-containing tripeptide glutathione (GSH), a cysteine-containing dimeric neurotensin derivative, and human native low-density lipoprotein (nLDL) as model compounds. Radiolabeling with the acylation agent [18F]SFB was carried out using a dimeric neurotensin derivative and nLDL. Both thiol-group reactive prosthetic groups show significantly better labeling efficiencies for the peptides in comparison with the acylation agent [18F]SFB. The obtained results demonstrate that [18F]FBOM is especially suited for the labeling of hydrophilic cysteine-containing peptides, whereas [18F]FBAM shows superior labeling performance for higher molecular weight compounds as exemplified for nLDL apolipoprotein constituents. However, the acylation agent [18F]SFB is the preferred prosthetic group for labeling nLDL under physiological conditions.

Carbamylated low-density lipoprotein induces death ofendothelial cells: A link to atherosclerosis in patients with kidney disease

The presence of accelerated atherosclerosis in patients with kidney disease cannot be entirely explained by traditional cardiovascular risk factors. Exposure to urea, which is normally present in human blood plasma and elevated in patients with kidney disease, leads to the carbamylation of proteins. We postulated that low-density lipoprotein (LDL) carbamylated by urea has biologic effects relevant to atherosclerosis. To produce carbamylated LDL (cLDL), human native LDL (nLDL) was chemically modified in vitro by exposure to potassium cyanate. Human coronary artery endothelial cells (HCAECs) and human coronary artery smooth muscle cells (CASMCs) were treated in vitro with cLDL or nLDL. Irreversible cell death was measured using the lactate dehydrogenase (LDH) assay, apoptosis was assessed by annexin V binding, and proliferation was determined using bromodeoxyuridine (BrdU) incorporation. Total plasma protein carbamylation and plasma cLDL were measured in hemodialysis patients using the homocitrulline assay and enzyme-linked immunosorbent assay (ELISA). Our studies demonstrated that cLDL but not nLDL induced dose-dependent vascular cell injuries relevant to atherosclerosis, which included the proliferation of vascular smooth muscle cells and endothelial cell death. Under light microscopy, endothelial cells treated with cLDL showed signs of morphologic alterations. The injury to endothelial cells measured by LDH release was time-dependent and correlated with the degree of LDL carbamylation. At least a part of the endothelial cell population treated with cLDL died by apoptosis. In patients with advanced renal disease on hemodialysis, total plasma protein carbamylation and plasma cLDL were several times higher than in control healthy individuals. Collectively these data suggest the potential role of carbamylated LDL in accelerated atherosclerosis in patients with chronic renal disease and, possibly, in healthy individuals.

Mechanisms of gastroprotection by lansoprazole pretreatment against experimentally induced injury in rats: role of mucosal oxidative damage and sulfhydryl compounds

This study investigated the mechanisms involved in the protective actions exerted by lansoprazole against experimental gastric injury. Following the intraluminal injection of ethanol–HCl, the histomorphometric analysis of rat gastric sections demonstrated a pattern of mucosal lesions associated with a significant increase in the mucosal contents of malondialdehyde and 8- iso-prostaglandin F 2α (indices of lipid peroxidation), as well as a decrease in the levels of mucosal sulfhydryl compounds, assayed as reduced glutathione (GSH). Pretreatment with lansoprazole 90 μmol/kg, given intraduodenally as single dose or once daily by intragastric route for 8 days, significantly prevented ethanol–HCl-induced gastric damage. The concomitant changes in the mucosal levels of malondialdehyde, 8- iso-prostaglandin F 2α and GSH elicited by ethanol–HCl were also counteracted by lansoprazole. In separate experiments, performed on animals undergoing 2-h pylorus ligation, lansoprazole did not enhance the concentration of prostaglandin E 2, bicyclo-prostaglandin E 2, or nitric oxide (NO) metabolites into gastric juice. Western blot analysis revealed the expression of both type 1 and 2 cyclooxygenase (COX) isoforms in the gastric mucosa of pylorus-ligated rats. These expression patterns were not significantly modified by single-dose or repeated treatment with lansoprazole. Lansoprazole also exhibited direct antioxidant properties by reducing 8- iso-prostaglandin F 2α generation in an in vitro system where human native low-density lipoproteins were subjected to oxidation upon exposure to CuSO 4. The present results suggest that the protective effects of lansoprazole can be ascribed to a reduction of gastric oxidative injury, resulting in an increased bioavailability of mucosal sulfhydryl compounds. It is also proposed that lansoprazole does not exert modulator effects on the gastric expression of COX isoforms as well as on the activity of NO pathways.

Protein Kinase Cα Regulates Human Monocyte O·̄2Production and Low Density Lipoprotein Lipid Oxidation

Our previous studies have shown that human native low density lipoprotein (LDL) can be oxidized by activated human monocytes. In this process, both activation of protein kinase C (PKC) and induction of superoxide anion (O-2) production are required. PKC is a family of isoenzymes, and the functional roles of individual PKC isoenzymes are believed to differ based on subcellular location and distinct responses to regulatory signals. We have shown that the PKC isoenzyme that is required for both monocyte O-2 production and oxidation of LDL is a member of the conventional PKC group of PKC isoenzymes (Li, Q., and Cathcart, M. K. (1994) J. Biol. Chem. 269, 17508-17515). The conventional PKC group includes PKCalpha, PKCbetaI, PKCbetaII, and PKCgamma. With the exception of PKCgamma, each of these isoenzymes was detected in human monocytes. In these studies, we investigated the requirement for select PKC isoenzymes in the process of monocyte-mediated LDL lipid oxidation. Our data indicate that PKC activity was rapidly induced upon monocyte activation with the majority of the activity residing in the membrane/particulate fraction. This enhanced PKC activity was sustained for up to 24 h after activation. PKCalpha, PKCbetaI, and PKCbetaII protein levels were induced upon monocyte activation, and PKCalpha and PKCbetaII substantially shifted their location from the cytosol to the particulate/membrane fraction. To distinguish between these isoenzymes for regulating monocyte O-2 production and LDL oxidation, PKCalpha or PKCbeta isoenzyme-specific antisense oligonucleotides were used to selectively suppress isoenzyme expression. We found that suppression of PKCalpha expression inhibited both monocyte-mediated O-2 production and LDL lipid oxidation by activated human monocytes. In contrast, inhibition of PKCbeta expression (including both PKCbetaI and PKCbetaII) did not affect O-2 production or LDL lipid oxidation. Further studies demonstrated that the respiratory burst oxidase responsible for O-2 production remained functionally intact in monocytes with depressed levels of PKCalpha because O-2 production could be restored by treating the monocytes with arachidonic acid. Taken together, our data reveal that PKCalpha, and not PKCbetaI or PKCbetaII, is the predominant isoenzyme required for O-2 production and maximal oxidation of LDL by activated human monocytes.

Effects of Iodotyrosines, Thyronines, Iodothyroacetic Acids and Thyromimetic Analogues on In Vitro Copper-Induced Oxidation of Low-Density Lipoproteins

We studied the effect of different thyroid compounds [(I 2, monoiodo- l-tyrosine (MIT), diiodo- l-tyrosine (DIT), l-thyronine (T 0), 3,5-diiodo- l-thyronine (T 2), 3,5,3′-triiodo- l-thyronine (T 3), 3,3′,5′-triiodo- l-thyronine (rT 3), 3,5,3′,5′-tetraiodo- l-thyronine (T 4), 3,5-diiodothyroacetic acid (TA 2), 3,5,3′-triiodothyroacetic acid (TA 3) and 3,5,3′,5′-tetraiodothyroacetic acid (TA 4)] or thyromimetics [(3,5-dimethyl-3′-isopropyl- l-thyronine (DIMIT) and 3,5-diiodo-3′-isopropyl-thyroacetic acid (IpTA 2)] on in vitro copper-induced oxidation of low-density lipoproteins (LDL). Human native LDL (0.05 g protein/L) oxidation was induced by 2.5 μmol/L of CuCl 2. Conjugated dienes were measured spectrophotometrically for up to 10 hr. The length of the lag phase (T lag), maximum velocity of the reaction (V max) and the maximum amount of generated dienes were obtained from kinetic data. T 3 increased T lag and decreased V max with a dependence upon concentration (0 to 3 μmol/L). There was no difference between the D max obtained with Cu 2+ alone or in the presence of the various compounds (1 μmol/L). I 2, MIT and DIT did not modify any parameter of the oxidation kinetic. T 0 and T 2 had the same antioxidant efficiency as T 3, whereas T 4 only decreased V max. rT 3 increased T lag less than did T 3, whereas DIMIT was the thyronine that had the most important effect. TA 2 and TA 3 were the most efficient antioxidant compounds. TA 4 decreased T lag less than TA 3 did, whereas IpTA 2 had an effect weaker than that of the physiological acetic derivatives. The data suggest that thyroid hormones and derivatives have LDL-antioxidant properties, their importance being related to their 4′-hydroxy diphenyl ether structure and depending upon the nature and the position of substituents in this structure.

Characteristics of ten charge-differing subfractions isolated from human native low-density lipoproteins (LDL). No evidence of peroxidative modifications

Native plasma low-density lipoproteins (LDL) were fractionated into ten subfractions with increasingly negative charges (LDL-1, the least electronegative, to LDL-10) using an anion-exchange column coupled to a fast protein-liquid chromatography system. Prior to fractionation, contaminating Lp(a) and apo A-I-containing lipoproteins were removed from LDL preparations by immunoaffinity chromatography. No significant difference in thiobarbituric acid-reactive substances, vitamin E or free aminogroup content was found among subfractions, and no peptide with a higher molecular weight than apo B was observed on SDS-PAGE. We observed a gradual increase in cholesterol esters and a concomitant decrease in triglycerides from LDL-1 to LDL-7, and a reverse tendency from LDL-8 to LDL-10 ( P < 0.01). Free cholesterol increased linearly from LDL-1 to LDL-10 ( P < 0.01). LDL-1 to -3 had a homogeneous density profile, while other more electronegative subfractions showed a bimodal distribution with a second, minor peak of slightly higher density. A gradual increase in apolipoprotein C-III content related to LDL electronegativity was observed ( P < 0.01). Apolipoprotein E content was also increased in the last two subfractions ( P < 0.01). LDL subfractions displayed a similar binding fate on human fibroblasts, with the exception of the most electronegative subfractions [LDL-(9 ± 10)], which bound more actively to apo9 B/E receptors ( P < 0.05). This study shows that charge heterogeneity of native LDL is not related to lipid peroxidation or derivatization of free aminogroups of apolipoprotein B. In contrast, the enrichment of LDL in apolipoproteins other than apo B may explain, in part, the difference in their particle charge.

Targeting of an antitumor agent, RS-1541 (palmitoyl-rhizoxin), via low-density lipoprotein receptor

RS-1541 is a 13- O-palmitoyl derivative of rhizoxin, an inhibitor of tubulin polymerization. RS-1541 has been shown to bind preferentially to plasma lipoproteins and to exhibit selective uptake by tumors in mice. We demonstrated that: (1) 99% of RS-1541 bound to human lipoproteins after incubation with human serum, among which the low-density lipoprotein (LDL) fraction attained 10%; (2) RS-1541/LDL complex was obtained by simply incubating human native LDL with a detergent-aided RS-1541 solution; (3) uptake of the [ 14C]RS-1541/LDL complex in cultured human skin fibroblasts was dependent on the LDL receptor activities of the cells; (4) excess amounts of native LDL or 10 μM monensin, a proton ionophore, significantly inhibited the uptake; and (5) the detergent-aided solution of [ 14C]RS-1541 showed very low cellular uptake. These results suggest the possibility of LDL as an endogenous targeting carrier of RS-1541 into tumor cells, which have higher LDL receptor activities.

Low density lipoproteins bind more to type I and III collagens by negative charge-dependent mechanisms than to type IV and V collagens

The accumulation of low density lipoprotein (LDL) in the arterial intima is an important characteristic of atherosclerosis. We investigated the mechanisms by which LDL binds to different types of collagen. The binding activities of 125I-labeled human native LDL (nLDL) and copper-oxidized LDL (oxLDL) with different collagen gels prepared in type I collagen-based mixtures with types I, III, IV and V (I+I, I+III, I+IV and I+V, respectively) were examined. A concentration of 20 μg LDL protein/150 μg collagen/well was used. The diffusion of both nLDL and oxLDL into the collagen gels reached an equilibrium after 48 h. All of the collagen gels showed the same rates of diffusion with both LDLs. The binding activities of oxLDL were significantly greater than those of nLDL ( P < 0.001%), while the binding activities for both LDLs followed the order I+I and I+III > I+V > I+IV. However, the increased binding rate of oxLDL compared to nLDL was 1.66 for I+IV, 1.50 for I+V, 1.33 for I+I and 1.19 for I+III. When a 10-fold higher dose of NaCl (1 M) was added to the oxLDL medium, the binding rate of oxLDL was reduced (rate of reduction: 52% (I+I), 48% (I+III), 35% (I+IV), 13% (I+V)). These results suggest that oxLDL binds more to type I and III collagens by negative charge-dependent mechanisms than to type IV and V collagens. Therefore, types I and III collagens may play an important role in trapping LDL, especially oxLDL. Therefore, oxidatively modified LDL may contribute to atherogenesis due to its longer retention in the arterial wall.

Effect of copper deficiency on the plasma clearance of native and acetylated human low density lipoproteins

The rates of plasma clearance of human native low density lipoproteins (LDL) and acetylated human low density lipoproteins (acetyl-LDL) were compared between copper-deficient (CuD) and copper-adequate (CuA) rats. Purified human LDL (d 1.02–1.063) were labeled with 125I and injected to fasted recipient rats intravenously. At different time intervals plasma clearance of 125I radioactivity was measured. The percent of clearance was calculated based on the total plasma volume, as determined by a radioisotopic dilution method. Native human 125I-LDL were cleared at a faster rate in CuD, compared with CuA rats. The half-times (t 1 2 ) of 125I-LDL clearance are 4.90 ± 0.20 and 5.80 ± 0.30 hours in CuD and CuA rats, respectively. The plasma trichloroacetic acid-soluble 125I-radioactivity was significantly and steadily increased in CuD rats at each interval, reflecting the faster clearance and degradation of LDL in those rats. The plasma removal of 125I-acetyl-LDL was faster compared with that of 125I-LDL. The half-times (t 1 2 ) of acetyl-LDL in CuD and CuA rats are 5.20 ± 0.06 and 5.16 ± 0.08 minutes, respectively, with no significant difference between the groups. The data indicates that the uptake of LDL via the “scavenger” receptor remains unaffected in copper-deficient rats. The faster removal of the unmodified (native) LDL in CuD group suggests that the apoB,E receptor is up-regulated in copper-deficient rats and that the hypercholesterolemia observed in copper deficiency is not associated with the defective uptake of LDL by the apoB,E-receptor dependent mechanism.