Plasma kinetics of an LDL-like nanoemulsion and lipid transfer to HDL in subjects with glucose intolerance

OBJECTIVE

Glucose intolerance is frequently associated with an altered plasma lipid profile and increased cardiovascular disease risk. Nonetheless, lipid metabolism is scarcely studied in normolipidemic glucose-intolerant patients. The aim of this study was to investigate whether important lipid metabolic parameters, such as the kinetics of LDL free and esterified cholesterol and the transfer of lipids to HDL, are altered in glucose-intolerant patients with normal plasma lipids.

METHODS

Fourteen glucose-intolerant patients and 15 control patients were studied; none of the patients had cardiovascular disease manifestations, and they were paired for age, sex, race and co-morbidities. A nanoemulsion resembling a LDL lipid composition (LDE) labeled with 14C-cholesteryl ester and ³H-free cholesterol was intravenously injected, and blood samples were collected over a 24-h period to determine the fractional clearance rate of the labels by compartmental analysis. The transfer of free and esterified cholesterol, triglycerides and phospholipids from the LDE to HDL was measured by the incubation of the LDE with plasma and radioactivity counting of the supernatant after chemical precipitation of non-HDL fractions.

RESULTS

The levels of LDL, non-HDL and HDL cholesterol, triglycerides, apo A1 and apo B were equal in both groups. The 14C-esterified cholesterol fractional clearance rate was not different between glucose-intolerant and control patients, but the ³H-free-cholesterol fractional clearance rate was greater in glucose-intolerant patients than in control patients. The lipid transfer to HDL was equal in both groups.

CONCLUSION

In these glucose-intolerant patients with normal plasma lipids, a faster removal of LDE free cholesterol was the only lipid metabolic alteration detected in our study. This finding suggests that the dissociation of free cholesterol from lipoprotein particles occurs in normolipidemic glucose intolerance and may participate in atherogenic signaling.

Effects of metformin plus gliclazide compared with metformin alone on circulating endothelial progenitor cell in type 2 diabetic patients

Circulating endothelial progenitor cells (EPCs) play an important role in the development and progression of diabetic vascular complications. The aim of this study was to investigate the effects of gliclazide plus metformin (GLIMET) compared with metformin alone (MET) on number and function of circulating EPCs in T2DM patients. Patients with newly diagnosed T2DM were randomly divided into two groups, receiving the following treatments for 16 weeks: MET group (assuming metformin 500-2500 mg/day, n=24) and GLIMET group [assuming gliclazide (modified release, 30-60 mg/day)+metformin (250-1000 mg/day), n=23]. Circulating EPCs were quantified by flow cytometry, and the ability to uptake LDL and stain for lectin were used as another method of characterizing EPCs ex vivo. The functions of circulating EPCs were evaluated by colony-forming units (CFU) and migration. The status of oxidative stress was analyzed by serum-free malonaldehyde (MDA) and superoxide dismutase (SOD). There were no significant differences in clinical characteristics and number and function of circulating EPCs between two groups at baseline. Glycemic responses were similar after treatments. Compared with MET group, GLIMET group was associated with an increase in circulating EPCs number, DiLDL-lectin-positive EPCs, and migration. The mean improvements in MDA and SOD of GLIMET group were more strongly upregulated than those of MET group. This study demonstrated that both metformin mono-treatment and metformin plus gliclazide combination treatment provided with improvements in number and function of circulating EPCs. Compared with metformin mono-treatment, early use of combination therapy with gliclazide plus metformin made more effective improvements in circulating EPCs.

Metabolism of a lipid nanoemulsion resembling low-density lipoprotein in patients with grade iii obesity

INTRODUCTION

Obesity increases triglyceride levels and decreases high-density lipoprotein concentrations in plasma. Artificial emulsions resembling lipidic plasma lipoprotein structures have been used to evaluate low-density lipoprotein metabolism. In grade III obesity, low density lipoprotein metabolism is poorly understood.

OBJECTIVE

To evaluate the kinetics with which a cholesterol-rich emulsion (called a low-density emulsion) binds to low-density lipoprotein receptors in a group of patients with grade III obesity by the fractional clearance rate.

METHODS

A low-density emulsion was labeled with [(14)C]-cholesterol ester and [(3)H]-triglycerides and injected intravenously into ten normolipidemic non-diabetic patients with grade III obesity [body mass index higher than 40 kg/m(2)] and into ten non-obese healthy controls. Blood samples were collected over 24 hours to determine the plasma decay curve and to calculate the fractional clearance rate.

RESULTS

There was no difference regarding plasma levels of total cholesterol or low-density lipoprotein cholesterol between the two groups. The fractional clearance rate of triglycerides was 0.086 +/- 0.044 in the obese group and 0.122 +/- 0.026 in the controls (p = 0.040), and the fractional clearance rate of cholesterol ester (h(-1)) was 0.052 +/- 0.021 in the obese subjects and 0.058 +/- 0.015 (p = 0.971) in the controls.

CONCLUSION

Grade III obese subjects exhibited normal low-density lipoprotein removal from plasma as tested by the nanoemulsion method, but triglyceride removal was slower.

Low density lipoprotein adsorption on sol-gel derived alumina for blood purification therapy

Among the clinical treatments of Familial Hyper cholesterolemia patients to reduce the concentration of low density lipoprotein (LDL), blood purification therapy is most suitable in which a blood-compatible adsorbent is employed. In the present study, alumina powders were prepared via a sol-gel route to develop a LDL-adsorbent Aluminum tri2-propoxide was hydrolyzed and subsequently calcined up to 1200 degrees C. Surface charge density and pore size distribution were measured, and the phases were identified. The alumina calcined above 400 degrees C had excellent blood compatibility in terms of endogenous clotting parameters, i.e., partial thromboplastin time: (PTT), prothrombin time: (PT), and the amount of fibrinogen: (Fib). The amount of LDL-adsorption (DeltaW(LDL)) increased with the calcining temperature, showing a good linear correlation to surface charge density. The 1200 degrees C sample consisted only of alpha-alumina, and was greatest in DeltaW(LDL). All samples involved pores smaller than 20 nm but not the pores large enough to accommodate LDL molecules (20-25 nm). From those results, it was concluded for the present alumina particles that the surface charge density was the primary factor and that the chemical activity of alpha-alumina also contributed to the excellent LDL-adsorption for the 1200 degrees C sample, while entrapping LDL in the pores was not an active mechanism.

Effects of lipoprotein lipase and statins on cholesterol uptake into heart and skeletal muscle

Regulation of cholesterol metabolism in cultured cells and in the liver is dependent on actions of the LDL receptor. However, nonhepatic tissues have multiple pathways of cholesterol uptake. One possible pathway is mediated by LPL, an enzyme that primarily hydrolyzes plasma triglyceride into fatty acids. In this study, LDL uptake and tissue cholesterol levels in heart and skeletal muscle of wild-type and transgenic mice with alterations in LPL expression were assessed. Overexpression of a myocyte-anchored form of LPL in heart muscle led to increased uptake of LDL and greater heart cholesterol levels. Loss of LDL receptors did not alter LDL uptake into heart or skeletal muscle. To induce LDL receptors, mice were treated with simvastatin. Statin treatment increased LDL receptor expression and LDL uptake by liver and skeletal muscle but not heart muscle. Plasma creatinine phosphokinase as well as muscle mitochondria, cholesterol, and lipid droplet levels were increased in statin-treated mice overexpressing LPL in skeletal muscle. Thus, pathways affecting cholesterol balance in heart and skeletal muscle differ.

The expression of recombinant human LOX-1 and identifying its mimic ligands by fluorescence polarization-based high throughput screening

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) was identified as a major receptor for oxidized low-density lipoprotein (oxLDL) in endothelial cells. LOX-1 critically mediates the endothelial dysfunction and the progression of atherosclerosis by oxLDL stimulation. It might be an important target for vascular endothelium. In order to obtain human LOX-1 and identify its mimic ligand for facilitating the study of LOX-1 function, a recombinant plasmid pPIC9K-His-hLOX-1 was structured and expressed human LOX-1 in Pichia pastoris GS115. Western blot analysis ensured the expressed recombinant human LOX-1 protein and a receptor-ligand binding assay showed that it had high binding affinity with oxLDL. With this receptor protein, a competitive fluorescence polarization-based high throughput screening method was established in a 384-well microplate to isolate the mimic ligands of human LOX-1. The evaluating parameter Z' value of 0.72 for this method showed that fluorescence polarization-based high throughput screening assay was robust and the results had a high reliability. By the fluorescence polarization-based high throughput screening assay, a total of 20,316 chemicals were screened, and 2 chemicals were identified that they have a high affinity with human LOX-1. Competitive uptake DiI-oxLDL assay by human LOX-1 transfected CHO-K1 cells further confirmed that two chemicals block the uptake of DiI-oxLDL. And the preliminary results indicated that isolated mimic ligands may act as a function of antagonist. The discovery of human LOX-1 mimic ligand would benefit to further study the function of LOX-1 and identify a novel avenue for prevention and treatment atherosclerosis.

A single common portal for clathrin-mediated endocytosis of distinct cargo governed by cargo-selective adaptors

Sorting of transmembrane cargo into clathrin-coated vesicles requires endocytic adaptors, yet RNA interference (RNAi)-mediated gene silencing of the AP-2 adaptor complex only disrupts internalization of a subset of clathrin-dependent cargo. This suggests alternate clathrin-associated sorting proteins participate in cargo capture at the cell surface, and a provocative recent proposal is that discrete endocytic cargo are sorted into compositionally and functionally distinct clathrin coats. We show here that the FXNPXY-type internalization signal within cytosolic domain of the LDL receptor is recognized redundantly by two phosphotyrosine-binding domain proteins, Dab2 and ARH; diminishing both proteins by RNAi leads to conspicuous LDL receptor accumulation at the cell surface. AP-2-dependent uptake of transferrin ensues relatively normally in the absence of Dab2 and ARH, clearly revealing delegation of sorting operations at the bud site. AP-2, Dab2, ARH, transferrin, and LDL receptors are all present within the vast majority of clathrin structures at the surface, challenging the general existence of specialized clathrin coats for segregated internalization of constitutively internalized cargo. However, Dab2 expression is exceptionally low in hepatocytes, likely accounting for the pathological hypercholesterolemia that accompanies ARH loss.

Platelet-activating factor (PAF) increase intracellular lipid accumulation by increasing both LDL and scavenger receptors in human mesangial cells

Intra- and extracellular lipid accumulation and the production of inflammatory mediators by renal and accessory cells may play an important role in the initiation and progression of these lesions. Platelet activating factor (PAF) is a biologically active phospholipid that is produced by various cells upon activation by different stimuli. It has been suggested that PAF plays a role in atherogenesis, and several studies indicated its participation in the pathogenesis of renal diseases. The aim of this study is to investigate the role of PAF on intracellular lipid accumulation and gene regulation of lipoprotein receptors in human mesangial cells (HMCs). A human mesangial cell line (HMC) was used to study the effects of PAF on foam cell formation by Oil red O staining and on the expression of LDLr, SR-AI, and PAF-R mRNA using RT-PCR. Native LDL caused foam cell formation in HMC in the presence of PAF. PAF enhanced LDLr expression and overrode LDL receptor suppression induced by a high concentration of LDL. Moreover, it enhanced SR-AI expression. PAF also caused increase in PAF-R expression. The above data suggest that PAF enhances its own receptor expression and then increases lipid accumulation by dysregulating LDL receptor regulation and inducing scavenger receptor expression in HMCs. These results suggest that PAF has a potential role in lipid mediated renal injury.

Cholesteryl Esters of Aggregated LDL Are Internalized by Selective Uptake in Human Vascular Smooth Muscle Cells

Objective— Low-density lipoprotein (LDL) receptor-related protein (LRP1) mediates the internalization of aggregated LDL (agLDL)–LDL trapped in the arterial intima bound to proteoglycans–into human vascular smooth muscle cells (VSMC). LRP1-mediated agLDL uptake induces high-intracellular cholesteryl ester (CE) accumulation. The aim of this study was to characterize the mechanism of agLDL internalization in human VSMC.

Methods and Results— The lipidic component of LDL was labeled with [ 3 H] and the apolipoprotein component with [ 125 I]. We found that >90% of intracellular CE derived from agLDL uptake was not associated with apoB100 degradation but was selectively taken up from agLDL. The inhibition of LRP1 expression by small interfering RNA treatment led to a decrease of 80±0.05% in agLDL-CE selective uptake. AgLDL induced intracellular CE accumulation without a concomitant CE synthesis. Cytosolic and cytoskeletal proteins were not required for CE transport. Electron and confocal microscopy experiments indicate that CE derived from agLDL accumulated in adipophilin-stained lipid droplets that were not removable by high-density lipoprotein.

Conclusions— Taken together, these results demonstrate that LRP1 mediates the selective uptake of CE from agLDL and that CE derived from agLDL is not intracellularly processed but stored in lipid droplets in human VSMC.

In vivo cholesteryl ester selective uptake of mildly and standardly oxidized LDL occurs by both parenchymal and nonparenchymal mouse hepatic cells but SR-BI is only responsible for standardly oxidized LDL selective uptake by nonparenchymal cells

In blood circulation, low density lipoproteins (LDL) can undergo modification, such as oxidation, and become key factors in the development of atherosclerosis. Although the liver is the major organ involved in the elimination of oxidized LDL (oxLDL), the identity of the receptor(s) involved remains to be defined. Our work aims to clarify the role of the scavenger receptor class B type I (SR-BI) in the hepatic metabolism of mildly and standardly oxLDL as well as the relative contribution of parenchymal (hepatocytes) and nonparenchymal liver cells with a special emphasis on CE-selective uptake. The association of native LDL and mildly or standardly oxLDL labeled either in proteins or in cholesteryl esters (CE) was measured on primary cultures of mouse hepatocytes from normal and SR-BI knock-out (KO) mice. These in vitro assays demonstrated that hepatocytes are able to mediate CE-selective uptake from both LDL and oxLDL and that SR-BI KO hepatocytes have a 60% reduced ability to selectively take CE from LDL but not towards mildly or standardly oxLDL. When lipoproteins were injected in the mouse inferior vena cava, parenchymal and nonparenchymal liver cells accumulated more CE than proteins from native, mildly and standardly oxLDL, indicating that selective uptake of CE from these lipoproteins occurs in vivo in these two cell types. The parenchymal cells contribute near 90% of the LDL-CE selective uptake and SR-BI for 60% of this pathway. Nonparenchymal cells capture mainly standardly oxLDL while parenchymal and nonparenchymal cells equally take up mildly oxLDL. An 82% reduction of standardly oxLDL-CE selective uptake by the nonparenchymal cells of SR-BI KO mice allowed emphasizing the contribution of SR-BI in hepatic metabolism of standardly oxLDL. However, SR-BI is not responsible for mildly oxLDL metabolism. Thus, SR-BI is involved in LDL- and standardly oxLDL-CE selective uptake in parenchymal and nonparenchymal cells, respectively.

State of the Art of Low-density Lipoprotein Apheresis in the Year 2003

Low-density lipoprotein (LDL) apheresis is a last-resort treatment for hypercholesterolemic patients resistant to conservative lipid-lowering therapy. In the extracorporeal circuit, LDL, Lp(a) and coagulation factors are selectively eliminated, while the beneficial proteins like high-density lipoprotein, albumin and immunoglobulins are returned to the patient. Clinical effects of LDL apheresis comprise improvement of symptoms like angina and exercise tolerance, reduction of clinical coronary events like unstable angina, need for angioplasty or bypass operation, myocardial infarction and ultimately coronary mortality. The reduction of atherogenic lipoproteins and of coagulation factors by LDL apheresis (LA) positively influences hemorheology, endothelial function and coronary reserve. In the controlled LAARS, LA significantly improved the electrocardiographic signs of myocardial ischemia in the treadmill test. In angiographically controlled trials such as LARS and L-CAPS, a reduction of progression of coronary lesions was observed; in favorable cases, regression of the stenoses could be documented. In addition, in the LDL apheresis coronary morphology trial, LA decreased the coronary plaque area. The Hokuriku trial documented a 72% decrease of coronary events (MACE) in the LA group vs. controls treated only by statins. In longitudinal studies, the incidence of MACE after regular LA decreased compared with the preapheresis period in the same patients. Apart from coronary heart disease, recent studies indicate a positive effect of LA also on carotid artery stenoses and peripheral vascular disease. Prospective randomized studies showed the beneficial effects of cascade filtration on age-related macular degeneration and of heparin-induced LDL precipitation apheresis on acute inner ear deafness.

Cells derived from regenerated endothelium of the porcine coronary artery contain more oxidized forms of apolipoprotein-B-100 without a modification in the uptake of oxidized LDL

Increased accumulation of lipoproteins and cholesterol within cells from regenerated endothelium may be responsible for their reported dysfunction. This study compared the presence and uptake of oxidized forms of low-density lipoprotein (LDL) in cells derived from native and regenerated endothelium. Four weeks after balloon denudation, primary cultures of native and regenerated endothelial cells were prepared from porcine coronary arteries. Regenerated endothelium stained more strongly using an antibody against oxidized lipoproteins. The increase in oxidized forms of apolipoprotein-B-100 exhibited by cells from regenerated endothelium was not due to an increase in extracellular-induced oxidation of native LDL, measured as the production of thiobarbituric-acid-reactive substances, being identical in both cell types. Intracellular cholesterol and cholesterol ester content were unchanged in regenerated cells. Using flow cytometry, accumulation of oxidized LDL was investigated further by quantifying the uptake of a mildly oxidized preparation of 1,1'-dioctadecyl-3,3,3',3-tetramethyl-indocarbocyanine perchlorate-labelled LDL. The parameters of uptake, EC(50) and E(max), were not different between cells from native and regenerated endothelium suggesting that the number of LOX-1 receptors was identical in the two cell types. Moreover, a negative correlation between the increased uptake of acetylated LDL and decreased cGMP production in response to bradykinin was observed in cells from regenerated endothelium. Thus, the increased incorporation of modified LDL and their intracellular oxidation could be responsible for the alteration in NO production. The presence of oxidized forms of LDL may be a marker of endothelium regeneration and could be involved in the endothelial dysfunction of pig coronary arteries 4 weeks after balloon denudation.

Establishment of immortalized human hepatic stellate scavenger cells to develop bioartificial livers

BACKGROUND

Maintenance of liver-specific functions has been shown to be stabilized by co-cultivation of hepatocytes with hepatic stellate cells (HSC). Because the limited lifespan of human HSC is a major hurdle to their use, the authors report here the amplification of human HSC populations in vitro by retroviral transfer of human telomerase reverse transcriptase (hTERT).

METHODS

Human HSC strain LI 90 cells were transduced with a retroviral vector SSR#197 expressing hTERT and green fluorescent protein (GFP) cDNA flanked by a pair of loxP. TWNT-1, one of SSR#197-immortalized HSC, was characterized. Differentiated liver functions were evaluated in an immortalized human hepatocyte NKNT-3-TWNT-1 co-culture system.

RESULTS

TWNT-1 cells showed differential functions of HSC, including uptake of acetylated low-density lipoproteins and synthesis of collagen type I and hepatocyte growth factor. Efficient excision of the retrovirally transferred hTERT and GFP cDNAs was achieved by TAT-mediated expression of the Cre recombinase and subsequent GFP-negative cell sorting. When co-cultured with TWNT-1 cells, NKNT-3 increased protein expression of the detoxifying cytochrome P450-associated protein isoenzymes 3A4 and 2C9 and urea synthesis.

CONCLUSIONS

TWNT-1 cells could be valuable in the study of integrated liver functions and contribute to the optimization of liver cell therapies and bioartificial livers.

Multinucleated variant endothelial cells (MVECs) have a greater capacity for LDL cholesterol uptake than typical mononuclear endothelial cells (TECs)

The existence of large endothelial cells in the human aorta, especially on atherosclerotic lesions has been reported. They have multiple nuclei and are called "multinucleated variant endothelial cells (MVECs)". In the present study caveolin expression was demonstrated in both MVECs and small typical endothelial cells (TECs). Caveolin was expressed diffusely as fine particles, and caveoles were expressed as prominent accumulations of caveolin in the cytoplasm. LDL was bound to the endothelial surface. With double immunostaining for caveolin and LDL, the location of LDL corresponded to the immunoreactive caveoles. Over time, large dots of LDL appeared in MVECs, whereas a few fine particles remained in TECs. An electron microscopic chase study of LDL-gold uptake identified many LDL-gold particles in plasmalemmal vesicles and in endosomes or lysosomes of MVECs, but only a few particles were found in TECs. Gold containing vesicles often were located near the abluminal surface. The number of LDL-gold particles was 4.5 times greater per unit area in MVECs than in TECs. Some of the gold particles were located in the subendothelial collagen matrix. These findings indicate that MVECs have a greater capacity of LDL cholesterol uptake followed by transport to the subendothelial matrices than TECs, and that MVECs contribute to the development and advancement of atherosclerotic lesions.

Tricarbocyanine cholesteryl laurates labeled LDL: new near infrared fluorescent probes (NIRFs) for monitoring tumors and gene therapy of familial hypercholesterolemia

For monitoring low-density lipoprotein receptors (LDLr) in tumors and in livers of patients with familial hypercholesterolemia (FH) treated with gene therapy, a series of tricarbocyanine cholesteryl laurates were synthesized with the cholesteryl laurate moiety serving as the lipid-chelating anchor for low-density lipoprotein (LDL). One of these conjugates, TCL17, was successfully used to label LDL to give a new NIRF, TCL17-LDL. Ex vivo biological studies on an LDLr overexpressing tumor model, human hepatoblastoma G(2) (HepG(2)), confirmed that this NIRF were internalized selectively by the tumor and detected with high sensitivity by a low-temperature 3-D redox scanner.

Preservation of human cell bioassay device for the on-site evaluation of environmental waters

We have already developed a novel disposable bioassay device based on the low-density lipoprotein (LDL) uptaking activity of human hepatoblastoma Hep G2 cells in our previous work. However, this device is not readily applicable to evaluate river water toxicity on-site because it cannot be preserved for more than one week. In this work, we developed the method for preservation of the device to enable it to be preserved for at least one month. The device can be supplied to individual environmental sites without any facilities for cell culture. We can evaluate river water toxicity by 2 hours of exposure after thawing. Therefore, this kind of device could be a promising tool for daily water quality management.

Response of mesangial cells to low-density lipoprotein and angiotensin II in diabetic (OLETF) rats

BACKGROUND

Progression of diabetic nephropathy is closely associated with morphological changes in glomeruli, such as thickening of the glomerular basement membrane, mesangial expansion, and glomerulosclerosis. To elucidate early glomerular events, we compared the mitogenic activity and extracellular matrix production in mesangial cells (MC) isolated from diabetic rats prior to the manifestation of nephropathy and those showing overt nephropathy. This study may help to clarify the mechanisms underlying diabetic nephropathy and provide clues about early therapeutic interventions for preventing or slowing this process.

METHODS

Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a chronic model for human type 2 diabetes mellitus, and age-matched control (LETO) rats were used. Glomerular cell numbers, expression of immediate early genes (c-Fos and c-Myc) and proliferating cell nuclear antigen (PCNA), and low-density lipoprotein (LDL) deposition were determined in renal tissue sections from rats aged 15 to 75 weeks. Mesangial cells (MCs) from OLETF rats at two different stages of the disease, that is, young (12- to 14-week-old) OLETF rats (y-OLETF) prior to the manifestation of nephropathy and old (48- to 50-week-old) OLETF rats (o-OLETF) showing nephropathy, were isolated and cultured. After stimulation with native (n-) or oxidized (ox-) LDL or angiotensin II (Ang II), DNA synthesis and extracellular matrix (ECM) production were examined. Cellular expression of LDL/scavenger receptors was analyzed using fluorescence-labeled LDL and binding to 125I-labeled-LDL.

RESULTS

The number of cells per glomerular cross section was significantly higher in OLETF rats than in LETO rats between 25 and 65 weeks of age. In OLETF glomeruli, c-Fos, c-Myc, and PCNA were transiently expressed in the early phase. Glomerular LDL deposition increased with the age of OLETF rats. Addition of a low dose of n-LDL (10 microg/mL) to the culture medium significantly stimulated DNA synthesis of y-OLETF MCs, as compared with o-OLETF MCs and LETO MCs (P < 0.05). A high dose of n-LDL (100 microg/mL) caused cytotoxic effects in all cells. Exposure to ox-LDL minimally affected DNA synthesis of OLETF or LETO MCs. LDL receptors and scavenger receptors were predominant in y-OLETF and o-OLETF, respectively. After stimulation with n-LDL and ox-LDL, expression of type I and type III collagen, along with transforming growth factor-beta (TGF-beta), was higher in o-OLETF MCs that in y-OLETF MCs or LETO MCs. Exposure to Ang II markedly induced DNA synthesis and ECM mRNA expression in y-OLETF MCs and o-OLETF MCs, respectively.

CONCLUSIONS

These findings indicate that the cell proliferation process precedes the evolution of diabetic glomerulopathy. The responses of OLETF MCs to n-LDL/ox-LDL and Ang II differed depending on the stage of diabetes. In the early phase, MCs were prone to proliferate, whereas in the late stage, MCs, which expressed higher levels of TGF-beta, tended to synthesize ECM. A functional switch in MCs may contribute to the development of glomerulosclerosis in diabetic nephropathy.

Uptake of a cholesterol-rich emulsion by neoplastic ovarian tissues

OBJECTIVE

Previously, it was shown that a lipidic emulsion (LDE) composed of phospholipids and cholesterol esters which binds to low-density lipoprotein (LDL) receptors may concentrate in acute myeloid leukemia cells. In this study, we aimed to verify whether LDE also has the ability to concentrate in malignant ovarian cancer after being injected into the blood circulation of the patients.

METHODS

Three groups of women scheduled for surgery were included in the survey: 13 bearing malignant tumors, 9 with benign ovarian tumors, and 13 without ovarian tumor who were scheduled to undergo oophorectomy due to malignant disease of the uterine cervix or endometrium. On the day prior to surgery they were injected with LDE labeled with [(14)C]cholesteryl oleate. Specimens of tumors and normal ovaries excised during surgery were lipid extracted and analyzed for radioactivity counting. Results were expressed in radioactive count (cpm) per gram of tissue.

RESULTS

The mean of the uptakes of the emulsion radioactivity by the malignant tumors was roughly eightfold greater when compared with that of the contralateral normal ovaries (2261 +/- 1444 and 275 +/- 137 cpm/g, respectively, P < 0.012), benign tumors, and normal ovaries of the patients without ovarian tumors.

CONCLUSION

LDE has the ability to concentrate in malignant ovarian tumor tissue. Therefore, it can be used as a vehicle to direct cytotoxic drugs against malignant ovarian tumors, thus diminishing the side effects of chemotherapy.

[Stanols--a new perspective in treatment of hypercholesterolemia?]

Since the unfavorable impact of hypercholesterolemia on the cardiovascular system has been proven, effective, inexpensive and easy to use cholesterol-lowering treatment options have been looked for. In the 1990s as the effect of a few decades of research, stanols have been introduced as new cholesterol-lowering agents. Stanols are derivates of plant sterols, which act through inhibition of intestinal cholesterol absorption. Their incorporation into normal diet fats has led to a significant reduction of both total and LDL cholesterol in investigated subjects, also in those on cholesterol-lowering diet or taking cholesterol-lowering drugs. When the dose considered optimal, i.e. 2-3 g/d, was used, the average reduction was 10% for total and 14% for LDL cholesterol. So far no adverse effects of stanols and no influence on the taste of food have been observed. The possible role of stanols in primary and secondary prevention of cardiovascular diseases still remains to be verified. It seems, however, that stanols have a potential to become a significant element in the treatment of hypercholesterolemia and in preventing its consequences.

Depletion of rafts in late endocytic membranes is controlled by NPC1-dependent recycling of cholesterol to the plasma membrane

In mammalian cells, cholesterol is thought to associate with sphingolipids to form lateral membrane domains termed rafts. Increasing evidence suggests that rafts regulate protein interactions, for example, during signalling, intracellular transport and host-pathogen interactions. Rafts are present in cholesterol-sphingolipid-enriched membranes, including early and recycling endosomes, but whether rafts are found in late endocytic organelles has not been analyzed. In this study, we analyzed the association of cholesterol and late endosomal proteins with low-density detergent-resistant membranes (DRMs) in normal cells and in cells with lysosomal cholesterol-sphingolipid accumulation. In normal cells, the majority of [(3)H]cholesterol released from [(3)H]cholesterol ester-LDL associated with detergent-soluble membranes, was rapidly transported to the plasma membrane and became increasingly insoluble with time. In Niemann-Pick C1 (NPC1) protein-deficient lipidosis cells, the association of LDL-cholesterol with DRMs was enhanced and its transport to the plasma membrane was inhibited. In addition, the NPC1 protein was normally recovered in detergent-soluble membranes and its association with DRMs was enhanced by lysosomal cholesterol loading. Moreover, lysosomal cholesterol deposition was kinetically paralleled by the sequestration of sphingolipids and formation of multilamellar bodies in late endocytic organelles. These results suggest that late endocytic organelles are normally raft-poor and that endocytosed LDL-cholesterol is efficiently recycled to the plasma membrane in an NPC1-dependent process. The cholesterol-sphingolipid accumulation characteristic to NPC disease, and potentially to other sphingolipidoses, causes an overcrowding of rafts forming lamellar bodies in the degradative compartments.

Embryonic striatal neurons from niemann-pick type C mice exhibit defects in cholesterol metabolism and neurotrophin responsiveness

Niemann-Pick type C (NP-C) disease is a progressive and fatal neuropathological disorder previously characterized by abnormal cholesterol metabolism in peripheral tissues. Although a defective gene has been identified in both humans and the npc(nih) mouse model of NP-C disease, how this leads to abnormal neuronal function is unclear. Here we show that whereas embryonic striatal neurons from npc(nih) mice can take up low density lipoprotein-derived cholesterol, its subsequent hydrolysis and esterification are significantly reduced. Given the importance of cholesterol to a variety of signal transduction mechanisms, we assessed the effect of this abnormality on the ability of these neurons to respond to brain-derived neurotrophic factor (BDNF). In contrast to its effects on wild type neurons, BDNF failed to induce autophosphorylation of the TrkB receptor and to increase neurite outgrowth in npc(nih) neurons, despite expression of TrkB on the cell surface. The results suggest that abnormal cholesterol metabolism occurs in neurons in the brain during NP-C disease, even at embryonic stages of development prior to the onset of phenotypic symptoms. Moreover, this defect is associated with a lack of TrkB function and BDNF responsiveness, which may contribute to the loss of neuronal function observed in NP-C disease.

Uptake of lipoprotein-associated alpha-tocopherol by primary porcine brain capillary endothelial cells

From the severe neurological syndromes resulting from vitamin E deficiency, it is evident that an adequate supply of the brain with alpha-tocopherol (alphaTocH), the biologically most active member of the vitamin E family, is of utmost importance. However, uptake mechanisms of alphaTocH in cells constituting the blood-brain barrier are obscure. Therefore, we studied the interaction of low (LDL) and high (HDL) density lipoproteins (the major carriers of alphaTocH in the circulation) with monolayers of primary porcine brain capillary endothelial cells (pBCECs) and compared the ability of these two lipoprotein classes to transfer lipoprotein-associated alphaTocH to pBCECs. With regard to potential binding proteins, we could identify the presence of the LDL receptor and a putative HDL3 binding protein with an apparent molecular mass of 100 kDa. At 4 degrees C, pBCECs bound LDL with high affinity (K(D) = 6 nM) and apolipoprotein E-free HDL3 with low affinity (98 nM). The binding capacity was 20,000 (LDL) and 200,000 (HDL3) lipoprotein particles per cell. alphaTocH uptake was approximately threefold higher from HDL3 than from LDL when [14C]alphaTocH-labeled lipoprotein preparations were used. The majority of HDL3-associated alphaTocH was taken up in a lipoprotein particle-independent manner, exceeding HDL3 holoparticle uptake 8- to 20-fold. This uptake route is less important for LDL-associated alphaTocH (alphaTocH uptake approximately 1.5-fold higher than holoparticle uptake). In line with tracer experiments, mass transfer studies with unlabeled lipoproteins revealed that alphaTocH uptake from HDL3 was almost fivefold more efficient than from LDL. Biodiscrimination studies indicated that uptake efficacy for the eight different stereoisomers of synthetic alphaTocH is nearly identical. Our findings indicate that HDL could play a major role in supplying the central nervous system with alphaTocH in vivo.

Estrogen and progesterone reduce lipid accumulation in human monocyte-derived macrophages: a sex-specific effect

BACKGROUND

Males have an earlier onset and greater prevalence of clinical atherosclerosis than age-matched females, which is consistent with an atheroprotective effect of the female sex steroids, estrogen and progesterone. We therefore examined the effects of estrogen and progesterone on human foam cell formation, a key early event in atherogenesis.

METHODS AND RESULTS

Monocytes from healthy female and male donors were obtained from white cell concentrates and allowed to differentiate into macrophages over 10 days. These human monocyte-derived macrophages (MDMs) were exposed to either control (0.1% vol/vol ethanol) or estrogen or progesterone treatment on days 3 through 10. Lipid loading was achieved on days 8 through 10 by incubation with acetylated LDL. Lipid from the MDMs was then extracted for analysis of cholesteryl ester (CE) content. 17beta-Estradiol at both physiological (2 nmol/L) and supraphysiological (20 and 200 nmol/L) concentrations produced a significant reduction in macrophage CE content (88+/-3%, 88+/-2%, and 85+/-4%, respectively; P<0.02 compared with control). Physiological and supraphysiological levels of progesterone (2, 10, and 200 nmol/L) produced an even more dramatic reduction in CE content (74+/-9%, 56+/-10%, and 65+/-8%, respectively; P<0.002 compared with control). This effect could be abrogated by coincubation with the progesterone receptor antagonist RU486. Neither estrogen nor progesterone produced a reduction in lipid loading in male-donor-derived MDMs. Detailed lipid trafficking studies demonstrated that both estrogen and progesterone altered macrophage uptake and/or processing of modified LDL.

CONCLUSIONS

Physiological levels of estrogen and progesterone are associated with a female-sex-specific reduction in human macrophage lipid loading, which is consistent with an atheroprotective effect.

Cholesterol-lowering action of plant sterols

Plant sterols have an extended history of use as cholesterol-lowering agents. Until the 1970s, the principal interest in plant sterols lay in effects of sitosterol, but over the past decade interest has reemerged in using plant sterols in functional foods. Hydrogenated plant sterols have been shown efficacious in lowering lipid levels, inhibiting cholesterol absorption and regressing plaque in animals. Hydrogenated versus unhydrogenated plant sterol esters have been demonstrated to possess equal efficacy in low-density lipoprotein cholesterol lowering in humans. Unhydrogenated plants sterol esters show consistency in cholesterol-lowering across dosage levels in humans. Unhydrogenated, unesterifed plant sterols yield similar low-density lipoprotein cholesterol lowering efficacy as achieved with hydrogenated sitostanol esters. Solubility and miscibility are likely more important determinants in cholesterol-lowering potential of plant sterols than their specific composition.

Cholesterol accumulation in tissues of the Niemann-pick type C mouse is determined by the rate of lipoprotein-cholesterol uptake through the coated-pit pathway in each organ

Niemann-Pick type C (NPC) disease is associated with the accumulation of unesterified cholesterol in nearly all tissues and with progressive neurodegeneration. A murine model of this disease, the NPC mouse, was used to determine whether this sequestered cholesterol represented sterol carried in low density lipoprotein (LDL) and chylomicrons (CMs) taken up into the tissues through the coated-pit pathway. By 7 weeks of age, the sterol pool in the NPC mice had increased from 2,165 to 5,669 mg/kg body weight because of the daily sequestration of 67 mg of cholesterol per kg in the various organs. This was 7-fold greater than the rate of accumulation in control mice. The rate of LDL clearance in the NPC mouse was normal (523 ml/day per kg) and accounted for the uptake of 78 mg/day per kg of cholesterol in LDL whereas 8 mg/day per kg was taken up from CMs. Deletion of the LDL receptor in NPC mice altered the concentration of unesterified cholesterol in every organ in a manner consistent with the changes also observed in the rate of LDL cholesterol uptake in those tissues. Similarly, altering the flow of cholesterol to the liver through the CM pathway changed the concentration of unesterified cholesterol in that organ. Together, these observations strongly support the conclusion that, in NPC disease, it is cholesterol carried in LDL and CMs that is sequestered in the tissues and not sterol that is newly synthesized and carried in high density lipoprotein.

Human mesangial cells express inducible macrophage scavenger receptor

BACKGROUND

Type A scavenger receptors (Scr) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipids via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMCs) have not been previously shown to express Scr in normal culture. We therefore investigated whether there is an inducible form of Scr in a human mesangial cell line (HMCL).

METHODS

Scr activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. Scr mRNA expression was examined using reverse transcription-polymerase chain reaction, followed by Southern blotting. To investigate the molecular mechanism of Scr expression, several reporter gene constructs were designed. The first contained a full Scr promoter, the second a part of the Scr promoter that has both AP-1 and ets transcription factor binding sites. Other constructs were identical to the second, except that they contained either AP-1 or ets motif mutations.

RESULTS

Phorbol 12-Myristate 13-acetate (PMA) and angiotensin II (Ang II) increased both the percentage of Scr-positive cells and the Scr mean fluorescence intensity. PMA and Ang II also increased Scr mRNA and promoter activity in a time- and dose-responsive manner. Protein kinase C and calmodulin transduction pathways were involved in Scr up-regulation induced by PMA and Ang II. Additionally, a serine/threonine kinase was involved in PMA stimulation. Functional analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCLs.

CONCLUSIONS

This study suggests that HMCs may express an inducible Scr, by which cells can acquire lipids and convert to foam cells in developing glomerulosclerosis.

Effects of alcohol and cholesterol feeding on lipoprotein metabolism and cholesterol absorption in rabbits

Alcohol fed to rabbits in a liquid formula at 30% of calories increased plasma cholesterol by 36% in the absence of dietary cholesterol and by 40% in the presence of a 0.5% cholesterol diet. The increase was caused almost entirely by VLDL, IDL, and LDL. Cholesterol feeding decreased the fractional catabolic rate for VLDL and LDL apoprotein by 80% and 57%, respectively, and increased the production rate of VLDL and LDL apoprotein by 75% and 15%, respectively. Alcohol feeding had no effect on VLDL apoprotein production but increased LDL production rate by 55%. The efficiency of intestinal cholesterol absorption was increased by alcohol. In the presence of dietary cholesterol, percent cholesterol absorption rose from 34.4+/-2.6% to 44.9+/-2.5% and in the absence of dietary cholesterol, from 84.3+/-1.4% to 88.9+/-1.0%. Increased cholesterol absorption and increased LDL production rate may be important mechanisms for exacerbation by alcohol of hypercholesterolemia in the cholesterol-fed rabbit model.

Tissue factor expression by cells used for sodding of prosthetic vascular grafts

Sodding of vascular grafts involves coating the biomaterial with cells prepared from collagenase-digested fat tissue after removal of the adipocytes by centrifugation. The goal of this study was to investigate the staining characteristics of the sodding cells as well as their ability to express the procoagulant protein tissue factor, and to compare these findings to those found with extensively purified microvascular endothelial cells (MEC) prepared from similar tissue. Sodding cells and MEC, isolated using immunomagnetic separation with anti-PECAM antibodies, were prepared from liposuction material and endothelial-specific staining was compared. The expression of tissue factor on these cells was examined using both an ELISA and a chromogenic assay to assess the rate of generation of factor Xa. Sodding cells expressed significantly more tissue factor than the unstimulated MEC in which the expression was undetectable (sodding cells 2466 +/- 830 pg/mL, P < 0.05). There was no further increase in tissue factor expression in the sodding cells with stimulation with lipopolysaccharide (LPS); however, purified MEC expressed significantly more tissue factor after exposure to LPS (1247 +/- 356 pg/mL, P < 0.05). These results were confirmed by the determination of procoagulant activity of the cells whereby the procoagulant activity on unstimulated MEC was significantly less than that found after stimulation of these cells, and it was also less than stimulated and unstimulated sodding cells (absorbance at 405 nm: 0.423 +/- 0.125, unstimulated MEC; 1.000 +/- 0.438, stimulated MEC; 1.129 +/- 0.396, unstimulated sodding cells; 1.171 +/- 0.254, stimulated sodding cells, P < 0.05). Staining of these two cells types also demonstrated significant uptake of acetylated LDL (Ac-LDL) in the purified MEC which was essentially absent in the sodding cells. Further, vWf staining was found to a greater degree in the purified MEC than in the sodding cells. These experiments demonstrated that the cells prepared for cell sodding express large amounts of tissue factor. The sodding cells do not stain for antigens known to be specific for endothelial cells, whereas MEC do and therefore the concentration of endothelial cells in the sodding cells is small. The significance of the tissue factor expression on the surface of sodded grafts is not yet known.

In vivo kinetics of lipoprotein(a) in homozygous Watanabe heritable hyperlipidaemic rabbits

In vivo kinetics of lipoprotein(a) [Lp(a)] were investigated in homozygous Watanabe heritable hyperlipidaemic (WHHL) rabbits (an animal model of familial hypercholesterolemia (FH)), and in normolipidemic Japanese White rabbits (controls). 125I-labelled Lp(a) and 131I-labelled LDL were simultaneously injected intravenously. Blood samples were then taken periodically. Kinetic parameters were calculated from the plasma radioactivity decay curves. The fractional catabolic rates (FCRs) of both Lp(a) and LDL (1.355 +/- 0.189 pools per day and 1.278 +/- 0.397 pools per day, respectively) in the WHHL rabbits were significantly (P < 0.005) smaller than those in the control rabbits (2.008 +/- 0.083 pools per day and 2.855 +/- 0.759 pools per day, respectively). In WHHL rabbits, the FCRs of Lp(a) and LDL were similar. However, in control rabbits, the FCR of Lp(a) was significantly (P < 0.01) smaller than that of LDL. In WHHL rabbit organs, the mean ratio of 125I-Lp(a): 131I-LDL, 48 h after injection, normalized to the corresponding isotope ratio in plasma, were 1.525, 1.020, 1.819 and 1.967, in liver, kidney, spleen and bile, respectively. These values were significantly higher than the corresponding values in control rabbits (0.590, 0.677, 0.862 and 0.766, respectively). Our data strongly suggest that Lp(a) clearance is not entirely dependent upon LDL receptors and may be mediated by some other mechanisms.

Cholesterol absorption, elimination, and synthesis related to LDL kinetics during varying fat intake in men with different apoprotein E phenotypes

Cholesterol absorption, fecal elimination, and synthesis and low density lipoprotein (LDL) metabolism were measured in 29 middle-aged men while on their normal diet and a diet low in fat and cholesterol, and the obtained values were related to apoprotein (apo) E phenotypes. Basal cholesterol absorption efficiency was positively related to production rate (PR) for LDL apo B and negatively to cholesterol synthesis (measured by fecal steroids and dietary cholesterol), which in turn was negatively associated with the LDL level and positively with the fractional removal (FCR) of LDL apo B. The apo E subscript (e.g., E2/2 = 1, E2/3 = 2, etc.) was positively associated with cholesterol absorption and the LDL apo B and cholesterol levels and negatively with cholesterol synthesis and FCR for LDL apo B. Effective bile acid and cholesterol synthesis, fecal elimination of cholesterol, removal of LDL apo B, and low cholesterol absorption characterized men with the epsilon 2 allele. Reduction of dietary fat and cholesterol intakes lowered LDL cholesterol levels and cholesterol absorption but increased cholesterol synthesis proportionally to the apo E subscript; the FCR and PR for LDL apo B were significantly increased and decreased, respectively. The decrease in absorption was related to enhanced removal of LDL apo B and synthesis of cholesterol. During the modified diet, cholesterol metabolism was poorly related to LDL, apo E phenotypes, and LDL apo B kinetics. A positive correlation of cholesterol absorption with dietary fat intake in combined studies suggests that a dietary fat reduction-associated decrease in LDL cholesterol is at least partly caused by reduced cholesterol absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of liver endothelial and Kupffer cells in clearing low density lipoprotein from blood in hypercholesterolemic rabbits

The role of liver endothelial and Kupffer cells in the hepatic uptake of cholesterol-rich low density lipoprotein (LDL) was studied in rabbits fed a diet containing 2% (w/w) cholesterol for 3 weeks. 125I-labeled tyramine cellobiose-labeled cholesterol-rich LDL was injected intravenously into rabbits, and parenchymal and nonparenchymal liver cells were isolated 24 h after injection. The hepatic uptake was 9 +/- 3% of injected dose in cholesterol-fed rabbits 24 h after injection, as compared to 36 +/- 9% in control-fed rabbits (n = 6 in each group; significant difference, P less than 0.005). Endothelial and Kupffer cells took up 2.7 +/- 0.5% and 1.2 +/- 0.8% of injected dose in the hypercholesterolemic rabbits, as compared to 1.9 +/- 0.8% and 0.8 +/- 0.3% in control animals. The amount accounted for by the parenchymal cells was markedly reduced in the cholesterol-fed rabbits to 7.3 +/- 2.7% of injected dose, as compared to 32.8 +/- 7.6% in controls (P less than 0.02). On a per cell basis, the nonparenchymal cells of cholesterol-fed rabbits took up as much LDL as the parenchymal cells (0.6 +/- 0.2, 0.7 +/- 0.1, and 0.6 +/- 0.4% of injected dose per 10(9) parenchymal, endothelial, and Kupffer cells, respectively). This is in marked contrast to the control animals, in which parenchymal cells took up about 6 times more LDL per cell than endothelial and Kupffer cells (3.2 +/- 0.9, 0.7 +/- 0.3, and 0.5 +/- 0.1% of injected dose per 10(9) cells). Thus, 30% of the hepatic uptake of LDL in the cholesterol-fed rabbits took place in nonparenchymal cells, as compared to 6% in controls. Consistent with these data, the concentrations of cholesteryl ester in endothelial and Kupffer cells in rabbits fed the high cholesterol diet were about twofold higher than in parenchymal cells (428 +/- 74 and 508 +/- 125 micrograms/mg protein, respectively, vs. 221 +/- 24 micrograms/mg protein in parenchymal cells). In contrast to cells from normal rabbits, Kupffer and endothelial cells from cholesterol-fed rabbits accumulated significant amounts of Oil Red O-positive material (neutral lipids). Electron microscopic examination of these cells in situ as well as in culture revealed numerous intracellular lipid droplets. Slot blot hybridization of RNA from liver parenchymal, endothelial, and Kupffer cells showed that cholesterol feeding reduced the level of mRNA specific for the apoB,E receptor to a small and insignificant extent in all three cell types (to 70-80% of that observed in control animals).(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic epidemiology of differences in low-density lipoprotein (LDL) cholesterol concentration: possible involvement of variation at the apolipoprotein B gene locus in LDL kinetics

Circulating levels of low-density lipoprotein (LDL) vary considerably within and between populations, paralleled by differing coronary heart disease (CHD) mortality rates. We have previously shown that variation in the apolipoprotein (apo) B gene as associated with certain restriction fragment length polymorphisms (RFLPs) influences the metabolism of LDL in the U.K. population. To investigate a possible genetic contribution to variation in LDL levels in differing populations we have extended this original study. RFLPs of the apo B gene were determined in samples of individuals from the United Kingdom, Finland, Italy, Spain, and Africa. Significant associations of LDL fractional catabolic rate with the apo B EcoRI and XbaI RFLP genotypes were detected only in the two North European populations. In the African population sample, the XbaI RFLP displayed a significant association with LDL apo B synthesis. The data suggest that variation in the apo B gene influences the metabolism of LDL and that it is different in individuals of different ethnic background.

Probucol does not alter acetylated low density lipoprotein uptake by murine peritoneal macrophages

It has been suggested that the anti-atherogenic effect of probucol (MDL 11,309) in familial hypercholesterolemic rabbits may be due in part to the inhibition of the uptake of modified low density lipoproteins by macrophages in the arterial wall. To test this hypothesis, mice were treated with dietary probucol (0.25%) for fourteen days, peritoneal macrophages were isolated and the uptake of acetylated low density lipoprotein (ALDL) was studied. In addition, peritoneal macrophages from control animals were treated with probucol (200 micrograms/ml) for 24 h in vitro prior to the ALDL uptake assay. The assay involved a fluorescent ALDL probe (dioctadecyltetramethylindocarbocyanine perchlorate-labeled ALDL), and measurement of uptake with a flow cytometer. No differences in ALDL uptake were detected between the control macrophages and macrophages treated with probucol in vitro or macrophages taken from probucol-treated mice.

Hepatic uptake and metabolism of free cholesterol from different lipoprotein classes. An in vivo study in the rat

Hepatic metabolism of [14C]cholesterol, vehiculated by LDL, HDL2 and HDL3 lipoprotein particles, has been studied in rats with a permanent biliary drainage. The lipoprotein fractions were infused individually by a jugular vein catheter and bile was collected for 180 min after the administration. At the end of this period, the animals were killed and the blood and livers were collected. The free cholesterol of the HDL2 fraction was secreted into bile, mainly as bile salt, preferentially to that associated with HDL3 and LDL fractions (11.7% vs. 2.3% and 0.3%, respectively). The free cholesterol of the HDL3 fraction, on the other hand, was taken up by liver more quickly and in a higher proportion than that associated with other lipoprotein fractions. The label incorporation in this lipoprotein fraction was secreted earlier and not transformed into bile. The contribution of LDL-vehiculated free cholesterol to bile secretion was small and the hepatic uptake amounted to no more than 12% of the injected label.

Characterization of apoB, E receptor function in the luteinized ovary

Recent findings from this laboratory have led to the suggestion that the hormone-producing cells of the rat luteinized ovary in situ may obtain a large share of low density lipoprotein (LDL) cholesterol without actually internalizing the intact lipoprotein particles. We have shown that the lipoproteins are trapped at the surface of the luteal cells in a rich network of "microvillar channels" and have theorized that these channel membranes, with their large surface area for interacting with lipoprotein particles, may function in the cholesterol transfer process. In the current study, we try to establish what proportion of the human (h)LDL-cholesterol transfer in the in situ perfused tissue occurs by a classical apoB, E receptor-mediated process versus a surface extraction process. We examine the tissue for the presence of apoB, E receptors, and characterize the structural/functional interaction of hLDL with the apoB, E receptor utilizing a variety of modified hLDL particles as probes. Then, using nonmetabolizable radiolabels for both the protein and cholesteryl ester moieties of these LDL probes, we attempt to quantify the extent to which apoB, E receptors in the ovary contribute to the uptake of hLDL-cholesterol during steroidogenesis. Our experiments show that although the luteinized ovary contains apoB, E receptor protein, hLDL interacts with the tissue atypically. That is, despite modifications of LDL amino acid residues to prevent interaction with the apoB, E receptor, the modified ligands continue to contribute cholesterol for luteal cell internalization and/or steroidogenesis. We conclude, therefore, that in this tissue much of the LDL-cholesterol is not delivered by the apoB, E receptor pathway.