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Biomedical subjects

O Stein

Publications and source records attributed to O Stein.

At least 37 records · Page 2Linked to original sources
PubMed1997

Scavenger receptor activity and expression of apolipoprotein E mRNA in monocyte-derived macrophages of young and old healthy men.

The aim of this study was to compare some aspects of lipid metabolism in monocyte-derived macrophages isolated from young males, aged 18-24 years, and old males, aged 74-90 years, who were found healthy in accordance with the Senieur protocol. The parameters tested were metabolism of 125I-acetylated low-density lipoproteins (LDL) and oxidized LDL, incorporation of [3H]cholesterol into cholesteryl ester and expression of apolipoprotein E (apo E) mRNA. Cell association and degradation of 125I-acetylated LDL by macrophages of old and young subjects, respectively, was 15,978 +/- 2492 and 9300 +/- 1416 ng/mg cell protein per 24 h. Incorporation of [3H]cholesterol into cellular [3H]cholesteryl ester in the presence of acetylated LDL in cells isolated from old subjects was twice that in cells from young subjects. The macrophages from both age groups metabolized less 125I-oxidized LDL than 125I-acetylated LDL. Cell association and degradation of 125I-oxidized LDL in cells from old and young subjects, respectively, was 6779 +/- 1398 and 3219 +/- 643 ng/mg cell protein per 24 h. Expression of apo E mRNA was determined by reverse transcriptase polymerase chain reaction. In the basal state, it was 5.8 +/- 0.4 and 2.4 +/- 0.2 photo-stimulated luminescence (PSL) units in cells from the old and young subjects, respectively, and increased after exposure to acetylated LDL. In conclusion, these findings suggest that a combination of higher scavenger receptor activity and increased expression of apo E mRNA in macrophages could contribute to (a) enhanced metabolism of modified LDL and (b) more efficient removal of cholesterol from arteries, thus leading to healthy old age.

Acetylation↗
PubMed1997

Cholesterol efflux in vivo from a depot of cationized LDL injected into a thigh muscle of small rodents.

We have developed a model system to measure quantitatively removal of cholesterol from a well-defined depot in vivo. To that end, lipoproteins were injected into the rectus femoris muscle of small rodents, using a 25 microliters Hamilton syringe and a 27-gauge needle. In most experiments, the injected volume was 10 microliters containing 200 micrograms of cholesterol. The lipoproteins tested were native or modified LDL labeled with trace amounts of [3H]free cholesterol ([3H]FC). The amount of label or of cholesterol mass recovered at various time intervals after injection was normalized to that found after 10 min (designated time 0). In mice, the highest recovery of the [3H]cholesterol 24 h after injection was found with cationized LDL, and ranged between 78% and 84%, whereas retention of native LDL did not exceed 24%. Based on results of 9 experiments with cationized LDL, the loss of [3H]FC was mono-exponential between 1 and 14 days and the t1/2 was about 4 days. The disappearance curve of cholesterol mass showed an initial slow and a later more rapid component, the latter with a t1/2 of 4 days. The initial lag is most probably due to the presence of cholesteryl ester, which needs to be hydrolyzed prior to egress. This assumption was verified by injection of cat-LDL labeled with [3H]cholesteryl oleate and finding a similar lag as well as evidence of [3H]cholesteryl ester hydrolysis. Histological examination of the injected muscle 1-4 days after injection of cat LDL showed infiltration with mononuclear cells in an area limited to the site of injection. The presently described model system, which mimics to some extent events occurring during atherogenesis, permits quantitative evaluation of egress of deposited cholesterol and may allow to study the role of HDL in such a process.

Animals↗
PubMed1997

Prevalence of antibodies to cytomegalovirus in a parturient population in Israel.

The aim of our study was to assess the serologic immunity to cytomegalovirus (CMV) in a population of pregnant women in Israel. We measured the titers of both IgG and IgM to CMV in 6,126 pregnant women by enzyme immunoassay. Of these, 84.3% were found to be positive for anti-CMV IgG and 15.7% were seronegative, and thus susceptible to primary infection. The total number of women positive for anti-CMV IgM, and hence suspected of being infected with the virus during or shortly before their pregnancy, was 43 (0.7%). An acute infection was therefore diagnosed in 4.35% of IgG seronegative women. A significantly higher CMV seropositivity rate was found in the parturient population as compared to surveys conducted in Israel in the 1970's. The seropositivity rates found in Israel are similar to those reported in Asia and Africa. The rate of serosusceptibility and the risk of primary CMV infection in pregnancy are lower in Israel than in Europe and North America. According to the observed incidence of primary CMV infection in pregnant women, it can be estimated that approximately 280 cases of fetal infection occur in Israel every year, potentially resulting in 56 symptomatic newborns.

Adult↗
PubMed1996

Relative resistance of the hamster to aortic atherosclerosis in spite of prolonged vitamin E deficiency and dietary hypercholesterolemia. Putative effect of increased HDL?

UNLABELLED: Male golden hamsters were rendered hypercholesterolemic by feeding diets enriched with cholesterol and fat. In the first series of experiments, 5% butter and 1% cholesterol were added to a chow diet and plasma cholesterol levels were maintained at 350-390 mg/dl over the entire experimental period. Groups of hamsters and their age controls consuming the chow diet, were killed after 7, 15 and 20 months when the aorta was examined for atherosclerosis by determination of cholesterol mass. In the controls, aortic total cholesterol (TC) increased with age by 28% and esterified cholesterol increased to 11% of TC. In the hypercholesterolemic animals aortic TC was only 28% higher than in the controls and cholesteryl ester was also 11.5% of TC. In the second series, one group of hamsters were fed a semi-purified diet deficient in vitamin E, containing 1% cholesterol and 10% lard; a second group received the same diet, but supplemented with vitamin E. Controls consumed local chow. After 7 months on the vitamin E deficient diet plasma alpha-tocopherol was 0.05 mg/l, in those supplemented with vitamin E it was 20 mg/l, while in the controls it was 3.3 mg/l. Plasma thiobarbituric acid reactive substances (TBARS) were higher in the vitamin E deficient group and there was a greater propensity of lipoproteins (d < 1.063 g/ml) to peroxidation in vitro than in the vitamin E supplemented group. Plasma cholesterol was 366 mg/dl in the vitamin E deficient, 336 mg/dl in the vitamin E supplemented group, and 64 mg/dl in controls. Aortic cholesterol was 79.1 in vitamin E supplemented and 84.4 micrograms/10 mg dry weight in vitamin E deficient hamsters. In both series of experiments, HDL amounted to 36-41% of plasma TC in the hypercholesterolemic animals and 59-62% in the controls. IN CONCLUSION: the hamster appears to be quite resistant to atherosclerosis in face of sustained hypercholesterolemia, even in the presence of increased peroxidative stress caused by vitamin E deficiency. This relative resistance could be related to commensurate increase in plasma HDL which was observed in both series of experiments. Since vitamin E deficiency did not enhance aortic cholesteryl ester deposition, the protective effect of HDL seems to be related to its role in reverse cholesterol transport, rather than in prevention of peroxidation.

Animals↗
PubMed1996

Study of causes underlying the low atherosclerotic response to dietary hypercholesterolemia in a selected strain of rabbits.

We have recently characterized a strain of rabbits that shows a low atherosclerotic response (LAR) to dietary hypercholesterolemia in contrast to the usual high atherosclerotic response (HAR) of rabbits [1]. Presently, we have focused on three well established and important stages of atherogenesis, i.e., monocyte adhesion to endothelium, cell mediated peroxidative modification of lipoproteins and induction of a receptor that recognizes modified low density lipoprotein (LDL). The results obtained show that (1) beta-very low density lipoprotein (beta-VLDL) from LAR and HAR rabbits enhanced monocyte adhesion to endothelial cells to the same extent; (2) Cell mediated peroxidation of LDL and beta-VLDL, tested by loss of alpha-tocopherol and formation of thiobarbituric acid reacting substances (TBARS), was compared using macrophages, fibroblasts and smooth muscle cells (SMC) of LAR and HAR rabbits and no significant differences were found; (3) Induction of scavenger receptor by phorbol ester (phorbol 12-myristate 13-acetate (PMA)) and platelet-derived growth factor-BB (PDGF-BB) was determined in SMC or fibroblasts from LAR and HAR rabbits using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-acetylated LDL (DiL-acLDL). We found a significantly higher uptake of DiI-acLDL in SMC and fibroblasts derived from HAR rabbits as compared with cells from LAR rabbits. Similar results were also obtained with [125I]-acLDL in fibroblasts from LAR and HAR rabbits with respect to cellular lipoprotein degradation after PMA pretreatment. Even though the attenuated atherosclerotic response to hypercholesterolemia of LAR rabbits may have multiple underlying causes, the most prominent so far is an apparent difference in inducibility of scavenger receptor in SMC and fibroblasts.

Animals↗
PubMed1995

Effects of interactions of apolipoprotein A-II with apolipoproteins A-I or A-IV on [3H]cholesterol efflux and uptake in cell culture.

Conflicting evidence has accumulated with years regarding the putative negative effect of apolipoprotein A-II on apo A-I mediated cholesterol efflux. In this study, this question was reexamined and in addition to the interaction of apo A-II with apo A-I, its possible effect on apo E and apo A-IV was investigated as well. Free cholesterol (FC) donors were the main components of atheroma, namely, mouse peritoneal macrophages (MP), bovine aortic smooth muscle (SMC) and fibroblasts labeled with [3H]FC. Acceptors of FC were dioleoylphosphatidylcholine (DOPC) liposomes containing apo A-I, rh-apo A-IV or rh-apo E alone or together with apo A-II. When [3H]FC labeled MP were incubated for 2 or 4 h with equimolar concentrations of apo A-I, A-II, A-IV or E, the lowest [3H]cholesterol efflux occurred with apo A-II. Exposure of [3H]FC MP to liposomes containing apo A-I/A-II at 1:2 M/M (keeping the total protein concentration at 50 micrograms/ml), resulted in a lower [3H]FC efflux as compared to apo A-I alone. However, when apo A-I or apo A-IV protein concentration was kept constant and supplemented with apo A-II, a lower [3H]FC efflux was found only at 1:3 M/M of apo A-I/A-II. Apo A-II added to apo E had no effect on FC efflux. With aortic SMC and fibroblasts, no inhibitory effect of addition of apo A-II to apo A-I or apo A-IV on cholesterol efflux was seen at apo A-I/A-II of 1:1 or 1:2 M/M. The uptake of macrophage derived [3H]FC by SMC or HepG2 cells was studied using the serum-free efflux media, containing PC liposomes + apolipoproteins, from 3H-labeled macrophages. The cellular uptake of [3H]FC was higher when apo A-II had been added to apo A-I or apo A-IV than when the apolipoproteins were added alone. In conclusion, apo A-II was found to be less effective in cholesterol efflux and to interfere with the action of A-I only when the cholesterol donors were macrophages and when the relative amount of apo A-I to apo A-II was low. This was not the case when SMC or fibroblasts served as cholesterol donors. In the presence of apo A-II, enhanced [3H]cholesterol delivery to cells was seen which could contribute to the proatherogenic activity of apo A-II.

Animals↗
PubMed1995

Effect of transforming growth factor-beta on lipoprotein lipase in rat mesenchymal heart cell cultures.

The effect of recombinant transforming growth factor-beta 2 (rTGF-beta 2) on lipoprotein lipase (LPL) synthesis was studied in mesenchymal rat heart cell cultures. Addition of rTGF-beta 2 to culture medium containing 20% serum resulted in a time-dependent decrease in LPL activity. With 10 ng/ml a 30% fall occurred after 12 h and only 20% of enzyme activity remained after 24 h with 5 or 10 ng/ml. The minimal effective dose of rTGF-beta 2 was 0.1 ng/ml and a 20% decrease occurred after exposure for 24 h. Antibodies specific to TGF-beta 2 blocked this effect. The decrease in enzymic activity was accompanied by a decrease in enzyme mass and LPL mRNA. Addition of rTGF-beta 2 was effective only during the first week in culture, when enzyme activity was increasing but not after 12 days when the cultures were overconfluent, and the enzyme activity was high.

Animals↗
PubMed1995

Smooth muscle cells and atherosclerosis.

The role of smooth muscle cells in atherogenesis involves cell proliferation and accretion of cholesteryl ester. Smooth muscle cell proliferation, controlled by growth factors produced locally, contributes to progression of atheroma and to restenosis after percutaneous transluminal coronary angioplasty. Accretion of cholesteryl ester in smooth muscle cells is mediated by factors secreted by macrophages. Induction of the scavenger receptor in smooth muscle cells may promote the transformation to foam cells. Novel approaches to combat restenosis include gene transfer into smooth muscle cells using different vectors.

Angioplasty, Balloon, Coronary↗
PubMed1994

Murine macrophages secrete factors that enhance uptake of non-lipoprotein [3H]cholesteryl ester by aortic smooth muscle cells.

We have recently demonstrated that macrophage conditioned medium (MP medium) and beta VLDL enhance cholesterol esterification in cultured aortic smooth muscle cells by LDL receptor mediated and other pathways (Stein, O. et al. (1993) Arteroscl. Thromb. 13, 1350-1358). In view of the presence of extracellular non-lipoprotein cholesteryl ester (in the form of lipid droplets) in the atheroma, the effect of MP medium on the cellular uptake of liposomal cholesteryl linoleyl ether (CLE) or cholesteryl ester (CE) was studied. After 4 h incubation in MP medium, the uptake of liposomal [3H]CLE was up to 10-fold higher than in the presence of control medium of the same composition but not conditioned with macrophages (DV medium). Similar results were seen also with HSF derived from LDL receptor negative donors. The MP medium-stimulated uptake of liposomal [3H]CE resulted also in hydrolysis of 70-90% of the labeled compound, indicating that the [3H]CE was intracellular. While the MP medium effect on liposomal [3H]CLE uptake was evident after 4 h, its effect on [3H]cholesterol esterification by SMC in the presence of beta VLDL could be demonstrated only after 24 h. Addition of apoE to MP medium resulted in a small (30-40%) increase in the uptake of liposomal [3H]CLE; however, it was augmented more than 4-fold when apoE was added to DV medium. The MP medium effect on the uptake of liposomal [3H]CLE was interfered with by heparin, anti-LPL antibody or heparinase, while these treatments did not affect [3H]cholesterol esterification in the presence of beta VLDL. These results suggest that the interaction between SMC and two potential sources of lipids in atheroma, i.e., lipoproteins and non-lipoprotein lipid droplets, could be governed by different components of the MP medium. In the case of the lipid droplets, as modeled here in the form of liposomes, macrophage-derived lipoprotein lipase could play a major role in cholesteryl ester transfer into SMC.

Animals↗
PubMed1994

Metabolic effects of nicotine on human adipose tissue in organ culture.

Fragments of human adipose tissue were maintained in culture for 1 week in a medium containing 1 mU/ml insulin and 100 ng/ml dexamethasone. Under these conditions lipoprotein lipase activity was present in human adipose tissue fragments which converted [14C]glucose to 14CO2 and [14C]triglyceride. Both metabolic parameters studied were affected by human tumor necrosis factor and brefeldin A. When fragments of human adipose tissue after 1 week in culture were incubated with nicotine tartrate for 20 h, a slight but significant increase in lipoprotein lipase activity was observed, and an increased conversion of [14C]glucose to 14CO2 and [14C]triglyceride occurred. Nicotine was taken up by human adipose tissue, but no conversion to cotinine was observed. Our data demonstrate a direct effect of nicotine on human adipose tissue metabolism. Furthermore, it is suggested that weight loss in smokers is a multifactorial phenomenon, and one of the important factors to be considered is the direct effect of nicotine within the tissue.

Adipose Tissue↗
PubMed1993

Can lipoprotein lipase be the culprit in cholesteryl ester accretion in smooth muscle cells in atheroma?

Bovine aortic smooth muscle cells and human skin fibroblasts were incubated with beta-very low density lipoprotein (beta VLDL) isolated from cholesterol-fed rabbits and labeled with [3H]cholesteryl oleate. Addition of lipoprotein lipase resulted in a 3.2-4.8-fold increase in cell associated radioactivity of which 45-61% was in free cholesterol, i.e., derived after intracellular hydrolysis. After exposure of smooth muscle cells to beta VLDL for up to 9 days and 60 min sodium heparin wash at 4 degrees C to remove extracellular surface bound lipoprotein, cellular cholesterol increase was 2 micrograms in controls and in the presence of lipoprotein lipase (LPL) it was tenfold higher. Addition of [3H]cholesteryl ester labeled beta VLDL during the last 48 h of incubation showed that 30-40% of total cellular label was in free cholesterol. This value represents the minimal cellular uptake of the added lipoprotein cholesteryl ester. Addition of recombinant apolipoprotein (apo) E to smooth muscle cells incubated with beta VLDL and [3H]oleate induced no further increase in [3H]cholesteryl oleate. We propose that following LPL-mediated binding of beta VLDL to heparan sulphate, this complex either undergoes endocytosis, or translocation of cholesteryl ester into the smooth muscle cells (SMC) occurs without endocytosis of the entire particle. The present results indicate that in the aortic wall macrophage-derived lipoprotein lipase could play a role in cholesteryl ester accretion in smooth muscle cells during atherogenesis.

Animals↗
PubMed1993

Macrophage-conditioned medium and beta-VLDLs enhance cholesterol esterification in SMCs and HSFs by LDL receptor-mediated and other pathways.

Thioglycolate-elicited mouse peritoneal macrophages were incubated for 24 hours in serum-free Dulbecco-Vogt medium containing 0.5% fatty acid-poor bovine serum albumin. This conditioned medium, designated MP medium, was used for experiments with bovine aortic smooth muscle cells (SMCs) or human skin fibroblasts (HSFs). Dulbecco-Vogt medium of the same albumin content but without macrophages served as a control medium. In SMCs labeled from plating the [3H]cholesterol and incubated with hypercholesterolemic rabbit beta-very-low-density lipoprotein (beta-VLDL) in Dulbecco-Vogt medium for 24 hours, there was an increase in cellular [3H]cholesteryl ester (CE) content compared with cells incubated without lipoprotein. When MP medium was used for the incubation of SMCs with beta-VLDL, cellular [3H]cholesteryl ester content increased threefold compared with cells incubated with Dulbecco-Vogt medium. A smaller increase in cholesterol esterification in the presence of MP medium was also encountered with low-density lipoprotein (LDL). The MP medium-induced increase in [3H]cholesterol esterification was not evident up to 6 hours of incubation. Similar results were also obtained with HSFs. The increase in [3H]cholesterol esterification with MP medium in the presence of beta-VLDL was also elicited in cells obtained from LDL receptor-negative donors with familial hypercholesterolemia (FH-HSF), even though in these cells significantly less [3H]cholesteryl ester was formed in the presence of beta-VLDL. MP medium contains numerous agents that could be responsible for the increase in cellular [3H]cholesteryl ester induced by lipoproteins. The first considered was lipoprotein lipase, but lack of inhibition of the MP medium effect by antiserum to lipoprotein lipase did not support this possibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Persistence of increased cholesteryl ester in human skin fibroblasts is caused by residual exogenous sphingomyelinase and is reversed by phospholipid liposomes.

Human skin fibroblasts (HSF) were exposed to sphingomyelinase 50 or 5 mU/ml for 60 min, washed with 5 mM EDTA or 20% serum and with phosphate-buffered saline, and postincubated for 24 h in the presence of [14C]16:0 sphingomyelin (SP) liposomes. The recovery of up to 48% of label in the medium in ceramide provided evidence of persistence of sphingomyelinase activity. The rate of hydrolysis of [14C]16:0 SP remained the same irrespective of whether the liposomes were added immediately after the wash, or 3 or 6 h thereafter. In HSF labeled with [3H]cholesterol exposure to 50 mU/ml of sphingomyelinase for 60 min resulted in an increase in labeled cholesteryl ester (CE) at 6 and 24 h of postincubation. Addition of sphingomyelin liposomes reduced markedly the fraction of cellular labeled cholesteryl ester recovered after 24 h, while phosphatidylcholine liposomes were not effective. When the enzyme concentration had been reduced 5-20 fold the effect of sphingomyelin liposomes on cellular 3H-CE was evident already after 6 h of postincubation and some effect was seen also with phosphatidylcholine liposomes. Increase in the concentrations of SP liposomes to 150 micrograms/ml restored labeled cholesteryl ester to control values at 24 h. A significant reduction occurred also with 18:1 phosphatidylcholine liposomes but labeled cholesteryl ester remained 50-100% higher when compared with 18:1 or 18:2 SP. No correlation was seen between the rates of cholesteryl ester decrease and free cholesterol efflux into the medium. The inability to remove residual sphingomyelinase by regular washing procedures exaggerates and prolongs the recovery period of sphingomyelin during postincubation and delays the return of the cholesteryl ester pool to control levels. This can be counteracted by addition of phospholipid liposomes that can compete for the enzyme with the plasma membrane sphingomyelin and also substitute the hydrolyzed molecule in the plasma membrane to impede cholesterol flow to cell interior.

Cells, Cultured↗
PubMed1992

Regulation of lipoprotein lipase by dibutyryl cAMP, cholera toxin, Hepes and heparin in F1 heart-cell cultures.

Regulation of lipoprotein lipase was studied in mesenchymal rat heart-cell cultures. Treatment of the cultures with dibutyryl cyclic AMP or with cholera toxin resulted in an increase in LPL activity and a comparable increase in LPL mRNA. When the cells were exposed to 100 mM Hepes for 24 h, total enzyme activity rose 2-fold and LPL mRNA increased 2.4-fold. After 72 h, there was a 3-fold increase in LPL mRNA and a 4-fold rise in cellular LPL activity, while medium activity increased 20-fold. Exposure of the cultures to heparin for 24 h resulted in a 3.2-fold increase in total activity and a 36-fold increase in medium activity. This increase was not accompanied by any rise in LPL mRNA. Addition of actinomycin D to control dishes for 24 h resulted in a 33% reduction in LPL mRNA and a 43% reduction in enzyme activity. These values were 71% and 56%, respectively, in Hepes-treated cells, indicating that no stabilization of LPL mRNA occurred under these conditions. It can be concluded that in mesenchymal rat heart-cells in culture cAMP and cholera toxin upregulate lipoprotein lipase at the level of transcription. The increase in LPL activity after 24 h exposure to Hepes could be compatible with transcriptional regulation, while exposure to heparin is not accompanied by a change in LPL mRNA.

Animals↗
PubMed1992

Modulation of sphingomyelinase-induced cholesterol esterification in fibroblasts, CaCo2 cells, macrophages and smooth muscle cells.

The present study has focused on three questions concerning the effect of sphingomyelinase on release of free cholesterol from the plasma membrane and its intracellular translocation: (i) Can one change the direction of the flow of cholesterol? (ii) Can one modulate the flow? (iii) May such a mechanism be relevant in atherogenesis? (i) The results obtained show that even in the presence of potent nonlipoprotein cholesterol acceptors in the medium, the intracellular flow of cholesterol is not reduced as measured by cholesterol esterification. Moreover, in sphingomyelinase-treated cells, cholesterol efflux in presence of nonlipoprotein acceptors was not enhanced even when intracellular esterification was inhibited. (ii) Modulation of the sphingomyelinase induced cholesterol flow can be obtained by 100 microM verapamil which reduces it. In human skin fibroblast, interference with the delivery of free cholesterol to its site of esterification was found in the presence of brefeldin A. (iii) Aortic smooth muscle cells in culture are sensitive to low concentrations of sphingomyelinase and the increase in esterified cholesterol is evident also after exposure to the enzyme for 24 h. The present results suggest that in the plasma membrane, free cholesterol bound to sphingomyelin may be in a compartment which renders it more available for transport to the cell interior than for efflux. In view of the sensitivity of aortic smooth muscle cells to sphingomyelinase, this mechanism for enhanced esterification of cholesterol could be relevant to the transformation of arterial smooth muscle cells into foam cells in the process of atherogenesis.

Brefeldin A↗
PubMed1992

Dissimilar effects of Brefeldin A on cholesteryl ester and triacylglycerol metabolism in CaCo2 and HepG2 cells as compared to peritoneal macrophages.

The effect of Brefeldin A (BFA) on lipid metabolism was studied in two cell lines and in primary cultures of peritoneal macrophages. In both CaCo2 and HepG2 cells, which are models for human liver and intestine, addition of BFA resulted in a 2-10-fold increase in recovery of labeled cholesteryl ester when the cells had been prelabeled with free cholesterol or with [3H]oleic acid. This effect was linear for up to 6 h and could be elicited with doses of BFA as low as 0.03 micrograms/ml. The increase in cholesteryl ester induced by BFA was completely abolished by the ACAT inhibitor (Sandoz 58-035) and partly by forskolin. Intracellular hydrolysis of labeled cholesteryl ester was studied in the presence of the ACAT inhibitor and while in the controls 30-40% was hydrolyzed in 6 h, the values were 7-16% in the BFA treated cells. The slower rate of hydrolysis in the BFA treated cells could not account for the entire increase of cholesteryl ester and there was also no decrease in cholesteryl ester secretion. Even though activation of acyl-CoA:cholesterol acyltransferase by BFA was not demonstrated in cell homogenates, we hypothesize that in the intact cell the BFA induced increase in cholesteryl ester might have been related to the pronounced increase in modified endoplasmic reticulum which results from the dispersion of the Golgi apparatus. In the macrophages, BFA at doses of 0.25-1 micrograms/ml resulted in a 90% reduction in the incorporation of [3H]oleic acid into triacyglycerol. Incorporation of [3H]oleic acid into triacyglycerol in CaCo2 cells was not affected by BFA. In view of the ever-increasing use of BFA in cell biology, it seems important to emphasize that BFA may affect different pathways of lipid metabolism in various cells.

Acetylation↗