Addition Of Low Density Lipoprotein Research Articles

Effect of egg yolk lipoproteins on foaming properties and interfacial behavior of egg white: Insights into implications for aerated food production

Chicken eggs are often used as an ingredient in oil-containing aerated foods. Different egg yolk lipids have different influence on the foaming properties of egg white, but the exact mechanism behind this influence is not well understood. In this study, we aimed to investigate how high and low-density lipoproteins present in egg yolks impact the macroscopic foam characteristics, rheological properties, and air/water (a/w) interfacial behavior in egg white foams. We found that the addition of low-density lipoprotein (LDL) at a concentration as low as 0.1 % led to a significant decrease in foaming ability (FA) by 284.67–66.67 %. Conversely, high-density lipoproteins (HDL) improved the FA from 284.67 % to 340.67 % within the concentration range of 0.024–0.16 %. Rheological properties showed that the addition of LDL caused a decrease in the viscoelasticity of the interfacial membrane, while HDL had no significant effect on viscoelasticity. Interfacial behavior results suggested that LDL and HDL were detrimental to the diffusion of protein molecules at the a/w interface. This implied that the effects of LDL and HDL on the foaming properties of EWP were mainly due to the competitive adsorption of lipids and proteins at the A/W interface, as well as the interactions between them. This work provides new insights into the effect mechanism of different forms of egg yolk lipids on the foaming properties of egg white, which can be beneficial for regulating oil-containing aerated foods to meet production demands.

Influence of selected factors on bovine spermatozoa cold shock resistance

The objectives of this study were to determine the effects of sire, extender, and addition of Low Density Lipoprotein (LDL) to extenders used on the percentage rate of spermatozoa survival after cold shock. Two groups of extenders were compared: without LDL addition (control variants) and LDL enriched (experimental variants). Three extenders were used: AndroMed®, Bioxcell®, and Triladyl®. Experimental variants included 4–8% LDL addition into the AndroMed® and Bioxcell® extenders, and 6–10% LDL addition into the Triladyl® extender. In total, 12 samples of fresh semen were collected from 4 bulls during a period of 8 weeks. Bovine spermatozoa cold shock resistance (1 ± 1 °C, 10 min) was evaluated by the percentage rate of live sperm using eosin-nigrosine staining immediately and after heat incubation (37 ± 1 °C, 120 min). The results showed the effect of sire as important and individual differences between selected sires in their sperm resistance against cold shock were confirmed. AndroMed® and Bioxcell® were found to be providing better protection of bull semen to cold shock compared to Triladyl® due to lower decline of live sperm proportion. Our results detected a positive effect of LDL addition on sperm resistance against cold shock, especially on lower decrease of live sperm percentage rate after 120 min of the heat test (P < 0.05). Further studies are needed to assess the optimal concentration of LDL in various kinds of extenders as well to state ideal time and temperature conditions for ensuring LDL reaction with sperm.

Itraconazole, a Commonly Used Antifungal, Inhibits Fcγ Receptor–Mediated Phagocytosis

Itraconazole (ICZ) is commonly used for the treatment of fungal infections, particularly in immunocompromised patients. In addition, ICZ has been recently found to have antiangiogenic effects and is currently being tested as a new chemotherapeutic agent in several cancer clinical trials. We have previously shown that ICZ impaired complex N-linked glycosylation processing, leading to the accumulation of high-mannose glycoproteins on the surface of macrophages (Møs). This investigation was directed at determining the effects of ICZ on phagocytosis as a major function of Møs. We found a significant decrease in the phagocytosis of opsonized bacterial particles in ICZ-treated murine Møs in comparison with nontreated Møs. Furthermore, the impairment of phagocytosis was associated with a decrease in cell surface expression of Fcγ receptors (FcγRs) as well as alteration of their glycosylation pattern. Concomitantly, a reduction in all three isoforms of the FcγR family (i.e., Fcgr1, Fcgr2, and Fcgr3) mRNA levels was observed after incubation with ICZ. The effect of ICZ on phagocytosis and FcγR expression was reversed by addition of low-density lipoprotein. These studies indicate that ICZ treatment certainly has a dramatic effect on macrophage function, which could result in a potential impairment of the immune system';s ability to respond to pathogens and may lead to an elevated incidence of infections.

凍結用希釈液への鶏卵黄由来低密度リポタンパク質(LDL)添加による沖縄在来豚アグー精子性状の改良効果

凍結用希釈液への鶏卵黄由来低密度リポタンパク質(LDL)添加による沖縄在来豚アグー精子性状の改良効果

P-Glycoprotein Is Downregulated in KG1a Primitive Leukaemia Cells by LDL Cholesterol Deprivation and by HMG-CoA Reductase Inhibitors.

P-glycoprotein (pgp) is a membrane transporter encoded by the multidrug resistance (MDR1, ABCB1) gene. Pgp is a poor prognostic factor in elderly patients with acute myeloid leukaemia (AML). In addition to its role in drug efflux, pgp has been implicated in cellular cholesterol homeostasis. We investigated the effects of exogenous cholesterol removal on pgp expression and function. KG1a drug-naïve, primitive leukaemia cells were cultured in serum free medium with or without the addition of low density lipoprotein (LDL) cholesterol. After 72 hours pgp expression and function was assessed by flow cytometry and total cholesterol content of the KG1a cells was determined by the Amplex Red® cholesterol assay. The addition of clinically available cholesterol lowering agents, HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibitors to KG1a cells was also assessed. There was a 39% (SEM 8.3% P=0.03) decrease in pgp protein expression after 3 days of serum free culture without HMG-CoA reductase inhibitors. Message was decreased by 40% (P=0.01) and pgp function was also reduced by 40% (P=0.005). The addition of low density lipoprotein (LDL) cholesterol restored pgp expression to 86% of the basal value. The addition of a HMG-CoA reductase inhibitor to KG1a cells in serum free culture resulted in a further 26% (lovastatin, P=0.03) and 16% (pravastatin, P=0.05) reduction in pgp respectively. Lovastatin also significantly reduced cellular cholesterol levels by 47% (P=0.002) under serum free conditions. Furthermore, the toxicity of the pgp substrate drug daunorubicin was significantly enhanced following lovastatin pre-culture (P=0.04). We conclude that LDL/cholesterol contributes to pgp expression and chemoresistance in primitive leukaemia cells. The use of HMG-CoA reductase inhibitors may be of clinical value in lowering pgp expression in AML.

P-glycoprotein is downregulated in KG1a-primitive leukemia cells by LDL cholesterol deprivation and by HMG-CoA reductase inhibitors

P-glycoprotein (pgp) is a membrane transporter encoded by the multidrug resistance (MDR1, ABCB1) gene. Pgp is a poor prognostic factor in elderly patients with acute myeloid leukemia (AML). In addition to its role in drug efflux, pgp has been implicated in cellular cholesterol homeostasis. We investigated the effects of exogenous cholesterol removal on pgp expression and function. KG1a drug-naïve, primitive leukemia cells were cultured in serum-free medium with or without the addition of low-density lipoprotein (LDL) cholesterol. After 72 hours, pgp expression and function was assessed by flow cytometry and total cholesterol content of the KG1a cells was determined by the Amplex Red cholesterol assay. The addition of clinically available cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors to KG1a cells was also assessed. There was a 39% (SEM = 8.3%; p = 0.03) decrease in pgp protein expression after 3 days of serum-free culture. The decrease was also observed at the message and functional levels. In the presence of low-density lipoprotein cholesterol, pgp expression was restored to 86% of the basal value. Addition of a HMG-CoA reductase inhibitor to KG1a cells resulted in an additional 26% (lovastatin, p = 0.03) and 16% (pravastatin, p = 0.05) reduction in pgp, respectively. Furthermore, toxicity of the pgp substrate drug daunorubicin was enhanced following lovastatin preculture (p = 0.04). LDL cholesterol contributes to pgp expression and chemoresistance in primitive leukemia cells. Use of HMG-CoA reductase inhibitors may be of clinical value in lowering pgp expression in AML.

ApoE Gene Deficiency Enhances the Reduction of Bone Formation Induced by a High-Fat Diet Through the Stimulation of p53-Mediated Apoptosis in Osteoblastic Cells

Osteoblast apoptosis increased in the tibias of apoE(-/-) mice fed with a high-fat diet, decreasing bone formation. The expression of p53 mRNA in marrow adherent cells increased. LDL or oxidized LDL increased apoptosis in the calvarial cells of apoE(-/-) mice. The increase in p53-mediated apoptosis is apparently related to a high-fat diet-induced osteopenia in apoE(-/-) mice. The effects of high-fat loading and the apolipoprotein E (apoE) gene on bones have not been elucidated. We hypothesized that apoE gene deficiency (apoE(-/-)) modulates the effects of high-fat loading on bones. We assessed this hypothesis using wildtype (WT) and apoE(-/-) mice fed a standard (WTS and ApoES groups) or a high-fat diet (WTHf and ApoEHf groups). The concentration of serum lipid levels and bone chemical markers were measured. Histomorphometry of the femurs was performed using microCT and a microscope. Bone marrow adherent cells from the femurs were used for colony-forming unit (CFU)-fibroblastic (CFU-f) assay and mRNA expressions analysis. The apoptotic cells in the tibias were counted. TUNEL fluorescein assay and Western analysis were performed in cultures of calvarial cells by the addition of low-density lipoprotein (LDL) or oxidized LDL. In the ApoEHf group, the values of cortical bone volume and trabecular and endocortical bone formation of the femurs decreased, and urinary deoxypyridinoline increased. Subsequent analysis revealed that the number of apoptotic cells in the tibias of the ApoES group increased, and more so in the ApoEHf group. The ratio of alkaline phosphatase-positive CFU-f to total CFU-f was decreased in the ApoEHf group. p53 mRNA expression in adherent cells of the apoE(-/-) mice increased and had a significantly strong positive correlation with serum LDL. TUNEL fluorescein assay of osteoblastic cells revealed an increase of apoptotic cells in the apoE(-/-) mice. The number of apoptotic cells in the apoE(-/-) mice increased with the addition of 100 microg/ml LDL or oxidized LDL. The p53 protein expression in apoE(-/-) cells exposed to 100 microg/ml LDL or oxidized LDL increased. We concluded that apoE gene deficiency enhances the reduction of bone formation induced by a high-fat diet through the stimulation of p53-mediated apoptosis in osteoblastic cells.

136 ADDITION OF LOW DENSITY LIPOPROTEIN TO CHEMICALLY DEFINED PORCINE EMBRYO CULTURE MEDIUM CAN PARTIALLY REPLACE BOVINE SERUM ALBUMIN

Embryo culture media typically contain undefined biologicals such as BSA. Our goal is to develop chemically defined culture media that are based on the biology and physiology of the embryo. To that end we evaluated the presence of message in embryos at various stages of development and determined that the message for the low density lipoprotein receptor (LDLR) increased from the germinal vesicle and 4-cell stage to the blastocyst stage of porcine embryogenesis. Thus, this study was conducted to determine if the addition of low density lipoprotein (LDL) would enhance the development and quality of in vitro produced porcine embryos in an already chemically defined culture medium. Slaughterhouse ovaries were aspirated, cumulous–oocyte complexes (COC) identified, and the COC were matured for 42 h in M199 base medium supplemented with EGF, FSH, and LH. Metaphase II oocytes were then selected. Fertilization was then preformed in modified Tris buffered medium and cocultured with 0.25 � 106/mL frozen thawed porcine semen for 5 h. The presumptive zygotes were then transferred to either porcine zygote medium with 0.3% BSA or 0.1% PVA (PZM3, PZM4). After 28 h, cleaved embryos were then sorted into six treatment groups (1. PZM3, 2. PZM3 + 20 µg mL–1 LDL, 3. PZM4, 4. PZM4 + 10 µg mL–1 LDL, 5. PZM4 + 20 µg mL–1 LDL, 6. PZM4 + 50 µg mL–1 LDL). The embryos were cultured in 5%O2 5%CO2 90%N until day 7. The percentage of development to the blastocyst stage was determined and analyzed with the SAS Proc GENMOD Procedure (a–cP ≤ 0.05). The percentage blastocyst was 51.3 � 0.09a, 51.6 � 0.09a, 33.1 � 0.99c, 35.8 � 0.09c, 36.9 � 0.09c, and 41.3 � 0.06b, for treatments 1–6, respectively. Culture in PZM4 (without BSA) significantly reduced development. However, addition of 50 µg mL–1 of LDL to PZM4 improved development above PZM4 alone. We interpret these data to indicate that a high concentration of LDL in the PZM4 media did improve embryo development and that LDL could partially substitute for BSA. Differential staining was performed on the blastocysts, and preliminary results suggest that the ICM to trophectoderm ratio in the high LDL treatment group is closer to the ratio found in in vivo produced embryos. This project was supported by USDA CSREES NRI (2006-35203-17282) and Food for the 21st Century.

Selective aggregation of zinc phthalocyanines in the skin

In photodynamic therapy it is important to avoid undesirable side effects caused by photodynamic reactions with accumulated photosensitizers, especially in the skin. Although phthalocyanine monomers can serve as photosensitizers, aggregated phthalocyanines are inactive. In this study the aggregations of five zinc phthalocyanines (MSPc, TSPc, TX-101A, TX-105A and TX-106A) in the skin and in the tumor are compared. Every phthalocyanine was more dissociated in the tumor than in the skin. In particular, TX-101A and TX-106A remained in monomeric form in the tumor but were aggregated in the skin. The aggregation effects of phthalocyanines in organic solvents and biological materials were also investigated. These phthalocyanines were aggregated in water and ethanol and also by the addition of bovine serum albumin and ghosts of red cells. On the other hand, they were dissociated in propanol and also by the addition of low-density lipoprotein. It was found that the dissociation of these phthalocyanines depended strongly on the polarity of the solvents and on the biological microenvironment.

Effects of fluvastatin on growth of porcine and human vascular smooth muscle cells in vitro

The effects of fluvastatin, a new fully synthetic inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, on growth and cell-cycle kinetics of porcine and human vascular smooth muscle cells (SMC) were studied by growth curves and flow cytometric determination of cellcycle distribution. Growth curves were obtained from counting after 2, 4, 7, 9, 11, and 14 days of incubation in Dulbecco's minimum essential medium and 10% fetal calf serum (FCS). For cell-cycle phase determination, cells were synchronized in Go by 48 hours of incubation in serum-free medium, then stimulated by incubation in 10% FCS, with or without fluvastatin. There was a concentration-dependent decrease in the proliferation of human and porcine SMC when cells were incubated in the presence of fluvastatin. The reduction in the number of cells was significant with 10−5 M and 10−4 M fluvastatin. The G/S-phase transition of human and porcine vascuar SMC was reduced to 50% of controls by 10−4M fluvastatin, as revealed by cell-cycle analysis. The effects of fluvastatin on growth kinetics and cell-cycle distribution could be completely reversed by the addition of 1 mM mevalonolactone, indicating that the fluvastatin effects are due to specific inhibition of HMG-CoA reductase. The addition of low density lipoprotein as a source of cholesterol failed to support SMC growth and phase transition. Addition of squalene or cholesterol to the culture medium also failed to normalize cell growth. It is concluded that nonsterol products synthesized from mevalonate are necessary for the growth of SMC. HMG-CoA reductase inhibitors, such as fluvastatin, block the synthesis of these nonsterol precursors in human and porcine vascular SMC in vitro and are therefore growth inhibitory.

Effects of flwastatin on growth of porcine and human vascular smooth muscle cells in vitro

The effects of fluvastatin, a new fully synthetic inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, on growth and cell-cycle kinetics of porcine and human vascular smooth muscle cells (SMC) were studied by growth curves and flow cytometric determination of cellcycle distribution. Growth curves were obtained from counting after 2, 4, 7, 9, 11, and 14 days of incubation in Dulbecco's minimum essential medium and 10% fetal calf serum (FCS). For cell-cycle phase determination, cells were synchronized in G o by 48 hours of incubation in serum-free medium, then stimulated by incubation in 10% FCS, with or without fluvastatin. There was a concentration-dependent decrease in the proliferation of human and porcine SMC when cells were incubated in the presence of fluvastatin. The reduction in the number of cells was significant with 10 −5 M and 10 −4 M fluvastatin. The G/S-phase transition of human and porcine vascuar SMC was reduced to 50% of controls by 10 −4 M fluvastatin, as revealed by cell-cycle analysis. The effects of fluvastatin on growth kinetics and cell-cycle distribution could be completely reversed by the addition of 1 mM mevalonolactone, indicating that the fluvastatin effects are due to specific inhibition of HMG-CoA reductase. The addition of low density lipoprotein as a source of cholesterol failed to support SMC growth and phase transition. Addition of squalene or cholesterol to the culture medium also failed to normalize cell growth. It is concluded that nonsterol products synthesized from mevalonate are necessary for the growth of SMC. HMG-CoA reductase inhibitors, such as fluvastatin, block the synthesis of these nonsterol precursors in human and porcine vascular SMC in vitro and are therefore growth inhibitory.

Activation of Acyl-Coenzyme A:Cholesterol Acyltransferase by Cholesterol or by Oxysterol in a Cell-free System

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes the conjugation of long chain fatty acid and cholesterol to form cholesteryl esters. It is an integral membrane protein located in the endoplasmic reticulum. Experiments performed in intact mammalian cells have shown that the rate of cholesteryl ester synthesis in intact cells, as well as the ACAT activity from cell extracts, are greatly activated by the addition of low density lipoprotein (LDL) or oxygenated sterols such as 25-hydroxycholesterol to the growth medium. However, the molecular mechanism(s) by which sterol(s) stimulate the ACAT activity remains to be elucidated. Recently, our laboratory reported the expression cloning of human ACAT cDNA (Chang, C. C. Y., Huh, H. Y., Cadigan, K. M., and Chang, T. Y. 1993) J. Biol. Chem. 268, 20747-20755). In the current study, we report the expression of human ACAT cDNA in insect Sf9 cells. Uninfected Sf9 cells do not express detectable ACAT-like activity. Infecting these cells with recombinant virus containing ACAT cDNA caused these cells to express high levels of ACAT protein and high levels of ACAT activity when assayed in vitro. The catalytic properties of ACAT expressed in these cells were found to be similar to those found in human tissue culture cells. The combination of high level of ACAT protein expression and the low level of cellular cholesterol content in the infected cells have provided us a novel opportunity to establish a simple cell-free system, whereby stimulation of ACAT by sterols can be readily demonstrated. Using this system, we have shown that cholesterol itself can serve as an ACAT activator in vitro, in addition to its role as an ACAT substrate. The current work provides the experimental basis to hypothesize that, inside mammalian cells, cholesterol itself may serve as a physiological regulator of ACAT.

Cell surface assembly of lipoprotein(a) in primary cultures of baboon hepatocytes.

Lipoprotein(a) (Lp(a)) consists of a low density lipoprotein particle in which apolipoprotein(a) (apo(a)), is disulfide linked to apoB. Lp(a) is produced by the liver, and high plasma levels represent an independent risk factor for cardiovascular diseases. However, pathways of production and metabolism of Lp(a) are poorly understood. We used primary cultures of baboon hepatocytes to analyze the steps involved in Lp(a) biogenesis. The results demonstrated that Lp(a) assembly was extracellular, since it was inhibited when anti-apo(a) antiserum was present in the culture medium. In addition, free apo(a) produced by hepatocytes could associate extracellularly with apoB in either very low density or low density lipoproteins. Lp(a) assembly required lysine-binding pockets in apo(a) kringles, as it was inhibited by the lysine analog, 6-amino hexanoic acid. A portion of apo(a) was also bound to the cell surface via its kringle domains and could be released into the medium by 6-amino hexanoic acid or proline. In add-back experiments, apo(a), but not Lp(a), bound to the cell surface. Addition of low density lipoprotein or very low density lipoprotein to hepatocyte cultures released apo(a) from the cell surface into the lipoprotein fraction of culture medium. We conclude that assembly of Lp(a) can occur at the cell surface. This represents one potential mechanism of Lp(a) production in vivo.

Increased cholesterol synthesis in Chinese hamster ovary cells deficient in peroxisomes

In a previous study we have shown that Chinese hamster ovary (CHO) cells deficient in intact peroxisomes, lack the nonspecific lipid transfer protein (nsL-TP; sterol carrier protein 2) (van Heusden, G.P.H., Bos, K., Raetz, C.R.H. and Wirtz, K.W.A. (1990) J. Biol. Chem. 265, 4105-4110). The consequences of the absence of peroxisomes and of nsL-TP on intracellular cholesterol metabolism have been investigated in two peroxisome-deficient CHO cell lines (CHO-82 and CHO-78). Compared with wild-type cells (CHO-K1), the incorporation of [3H]acetate into cholesterol was 3-fold higher in the CHO-82 cells and 2-fold higher in the CHO-78 cells. In agreement with an increased synthesis of cholesterol, a 2-3-fold higher 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was measured in both mutant cell lines. On the other hand, addition of low density lipoprotein (LDL), mevalonate (30 mM) or 25-hydroxycholesterol (2 micrograms/ml) to cells grown in lipoprotein-deficient serum, demonstrated that in both mutant cell lines the down-regulation of HMG-CoA reductase and of cholesterol synthesis were comparable to that in wild-type cells. These results strongly suggest that, in addition to down-regulation by LDL-derived cholesterol, mevalonate and 25-hydroxycholesterol, HMG-CoA reductase activity is under control of peroxisomes and/or nsL-TP.

Possible Inhibitory Effect of Lipid Peroxides on Acid Lipase Activity via Low-Density Lipoprotein in Human Mononuclear Leukocytes.

Acid lipase (AL) activity was measured in mononuclear leukocytes (MNL) isolated from 214 subjects. An inverse relation was observed between the AL activity and serum cholesterol (CHO) with age variation: The age groups above 30, which showed low AL activities in their MNL, exhibited high serum CHO; whereas the 20-to-29 age group, which had the highest AL activity among the age groups, showed the lowest CHO value. Moreover, the hypercholesterolemic group with high apo-B levels showed significantly low AL activity in both sexes when compared with the normolipidemic group. Significant negative correlations were also observed in the hypercholesterolemic group between the AL activity and both CHO and apo-B, and between the AL activity and lipid peroxides (LPO). On the other hand, while the addition of low-density lipoprotein (LDL) from patients with type II hypercholesterolemia to the AL assay system and the culture medium of MNL resulted in the inhibition of the AL activity, the inhibitory effect was prevented by preincubation of LDL with anti apo-B serum. These data suggest a certain regulatory mechanism of LDL, the physiological substrate of AL, on the AL activity; this action possibly occurs through lipid peroxides in LDL.

Inhibition by 6-fluoromevalonate demonstrates that mevalonate or one of the mevalonate phosphates is necessary for lymphocyte proliferation.

The sterol synthesis inhibitor 6-fluoromevalonate (Fmev) was used to explore the role of mevalonate products in lymphocyte proliferation. Fmev blocks the synthesis of isopentenyl pyrophosphate and all more distal products in the sterol pathway. When cells were cultured in lipoprotein-deficient medium, Fmev (200 microM) completely inhibited mitogen-stimulated human lymphocyte proliferation, quantified by measuring DNA synthesis. The addition of low density lipoprotein (LDL) restored lymphocyte responses to normal, whereas mevalonate was totally ineffective. Similar results were obtained with concentrations of Fmev up to 1 mM. These results contrast with those observed when sterol biosynthesis was blocked with lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. When lymphocyte proliferation was blocked with lovastatin (5 microM), either high concentrations of mevalonate or LDL together with low concentrations of mevalonate was required to restore responses. In contrast, neither LDL nor low concentrations of mevalonate when alone was able to restore lymphocyte DNA synthesis in cultures blocked with 5 microM lovastatin. The effect of Fmev on the capacity of exogenous mevalonate to restore proliferation of lovastatin-blocked lymphocytes was directly examined. Fmev had no effect on the capacity of LDL plus low concentrations of mevalonate to restore DNA synthesis to lovastatin-blocked lymphocytes, indicating that the synthesis of the necessary factor from mevalonate was unaltered by Fmev. Fmev profoundly blocked lymphocyte endogenous sterol synthesis, decreasing incorporation of radiolabeled acetate into digitonin-precipitable sterols by up to 98%. LDL did not alter the capacity of Fmev to block sterol synthesis. The possibility that Fmev allowed shunting of endogenous mevalonate into essential lipid products was assessed by examining the incorporation of radiolabeled mevalonate. Fmev (200 microM) inhibited the incorporation of mevalonate into all lipids, including ubiquinone, dolichol, and other non-sterol lipids by up to 98%, and this was not altered by LDL. Furthermore, Fmev (200 microM) suppressed the incorporation of radiolabeled mevalonate into protein by up to 97%. These data confirm that a product of mevalonate is essential for cell proliferation. However, the results indicate that the required product is directly synthesized from mevalonate or mevalonate phosphates rather than from a more distal isoprenoid metabolite.

Abnormal cholesterol metabolism in imipramine-treated fibroblast cultures. Similarities with Niemann-Pick type C disease

Addition of low-density lipoprotein (LDL) to cholesterol-deprived human skin fibroblast cultures treated by imipramine at a 20 μ M concentration induced a significant intracellular accumulation of unesterified cholesterol. Intracytoplasmic inclusions were already visible by histochemical filipin staining after 2 h of LDL uptake and were progressively mobilized towards the perinuclear region within 24 h. At this concentration of the drug, the rate of proteolytic 125I-LDL hydrolysis was similar in treated and untreated cells. Treated cells maintained in lipoprotein-deficient medium showed no abnormality, indicating the exogenous origin of the accumulated sterol. Further, the drug induced a drastic dose-dependent impairment of LDL-stimulated cholesterol esterification, not related to an inhibition of acyl CoA: cholesterol acyltransferase, and a significant delay in down-regulation of de novo cholesterol synthesis. However, imipramine did not affect 25-hydroxycholesterol-mediated regulation of the two latter processes. These results resemble those observed in Niemann-Pick type C disease and suggest an impaired mobilization of LDL-derived cholesterol in imipramine-treated cells.

Low density lipoprotein-induced growth of U937 cells: a novel method to determine the receptor binding of low density lipoprotein.

U937 is a monocytic cell-line originally derived from a histiocytic lymphoma. In serum-free medium the growth of U937 cells was stimulated by addition of low density lipoprotein (LDL). Methylation of LDL impaired its ability to be taken up in U937 cells as well as the capacity to stimulate the growth of these cells. Pretreatment of U937 cells with a monoclonal antibody against the LDL receptor was also found to completely block the growth-promoting effect of LDL. Exposure of U937 cells to liposomes with a lipid composition similar to that of LDL did not stimulate the growth rate. These findings demonstrate that growth of U937 cells under serum-free conditions is related to the amount of LDL ingested by the cells and that this uptake is mediated by binding of LDL to the LDL receptor. To determine if LDL-induced growth of U937 cells can be used to identify LDL with decreased binding to the LDL receptor, U937 cells were incubated with LDL isolated from a patient with familial defective apolipoprotein B-100 and from subjects with various lipoprotein phenotypes. LDL containing defective apolipoprotein B-100 was found to be less than half as effective as LDL from normolipidemic controls in stimulating growth of U937 cells. LDL isolated from patients with hyperlipoproteinemia type IIa and IV did not differ from normal LDL in their ability to promote growth of U937 cells. The present results suggest that LDL-induced growth of U937 cells may be used as an assay to identify defective receptor binding of LDL.

Coordinate Regulation of 3-Hydroxy-3-methylglutaryl-coenzyme A Synthase, 3-Hydroxy-3-methylglutaryl-coenzyme A Reductase, and Prenyltransferase Synthesis but Not Degradation in HepG2 Cells

Human hepatoma HepG2 cells were used to demonstrate coordinate regulation of three enzymes of cholesterol synthesis under a variety of conditions. Addition of either delipidized serum and mevinolin or low density lipoprotein, 25-hydroxycholesterol, or mevalonic acid to HepG2 cells resulted in rapid changes both in the levels of the mRNAs and in the rates of synthesis of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase, HMG-CoA reductase, and farnesyl pyrophosphate synthetase (prenyltranferase). In all cases, the changes in mRNA levels were paralleled by changes in the rates of specific protein synthesis. Pulse-chase techniques were used to determine the half-lives of all three proteins. Addition of low density lipoprotein to the media during the chase increased the rate of degradation of HMG-CoA reductase 4.6-fold but had no affect on the half-lives of HMG-CoA synthase or prenyltransferase. Therefore, we conclude that the coordinate regulation of these three enzymes under a variety of conditions occurs at the level of enzyme synthesis and not at the level of protein stability.

Regulation of sterol synthesis and of 3-hydroxy-3-methylglutaryl coenzyme A reductase by lipoproteins in glial cells in primary culture.

Although plasma lipoproteins have been demonstrated to have a major role in regulating cholesterol biosynthesis in extraneural cells, no data concerning such regulation are available for developing brain, when cholesterol synthesis is especially active. Glial primary cultures derived from neonatal rat brain and by morphological and biochemical criteria essentially exclusively composed of astrocytes were utilized to examine such regulation. When the primary cultures, which had been maintained in 10% fetal calf serum, were placed in 10% lipoprotein-poor serum on day 7 of culture, an induction of sterol synthesis (1.6-2.2-fold) and of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase-specific activity (1.5-2-fold) resulted after 24 hr. Addition of low-density lipoprotein (LDL) to the 10% lipoprotein-poor serum prevented the induction of both sterol synthesis and HMG-CoA reductase. However, addition of high-density lipoprotein (HDL) to the 10% lipoprotein-poor serum caused a 1.5-2-fold further induction of sterol synthesis relative to that in cultures containing 10% lipoprotein-poor serum alone. In contrast to the glial primary cultures, cultures of C-6 glioma cells responded to replacement of 10% fetal calf serum with 10% lipoprotein-poor serum with much more marked increases of sterol synthesis and HMG-CoA reductase. Although, as with the primary cultures, addition of LDL to the C-6 glioma cell cultures prevented the increases in sterol synthesis and reductase activity, addition of HDL had no effect. Thus, these results indicate that in developing glial cells in primary culture, cholesterol synthesis and HMG-CoA reductase are capable of responsiveness to both LDL and HDL.(ABSTRACT TRUNCATED AT 250 WORDS)