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Biomedical subjects

Y Stein

Publications and source records attributed to Y Stein.

At least 181 records · Page 10Linked to original sources
PubMed1979

The role of lysophosphatidylcholine and apolipoprotein A in the cholesterol-removing capacity of lipoprotein-deficient serum in tissue culture.

Lipoprotein-deficient serum (d greater than 1.21 or 1.25 g/ml fraction) is commonly used to deplete cellular cholesterol from cultured cells and presently we have studied some of the potential promoters of this process. Although serum albumin is the main protein component of the fraction, its cholesterol-removing capacity was quite limited, even in the presence of lysophosphatidylcholine, which is the major phospholipid of the d greater than 1.25 g/ml infranatant of serum. On the other hand, apolipoprotein A1 especially when complexed with lysophosphatidylcholine promoted considerable release of cellular cholesterol. The cholesterol-removing capacity of lysophosphatidylcholine alone was related to the fatty acid chain length and was low when the fatty acid chain length was below C-14. The release of cellular cholesterol is not related to shedding of surface glycoproteins and depends on the presence of suitable acceptors in the medium. Such acceptors were presently found in an ultrafiltrate of serum prepared by membrane filtration. It is proposed that in human serum there are low molecular weight protein-phospholipid complexes (less than 100,000), which can cross the capillary endothelial barrier, in preference to lipoproteins, and promote cholesterol removal from peripheral cells.

Adult↗
PubMed1979

Lipoprotein lipase of cultured mesenchymal rat heart cells. IV. Modulation of enzyme activity by VLDL added to the culture medium.

Lipoprotein lipase activity was studied in rat heart cell cultures grown in the presence of 20% fetal calf and horse serum and a medium concentration of triacylglycerol of 0.03 mg/ml. After 6--8 days, when the enzyme activity had reached high levels, the cells were incubated for 24 h in a medium containing 20% serum derived from fasted or fed rats. No change in enzyme activity occurred in the presence of fasted rat serum, but a 50% fall was observed with fed rat serium. When the complete culture medium was supplemented with rat plasma VLDL (0.075--0.75 mg triacylglycerol) a pronounced decrease in lipoprotein lipase activity occurred after 3--5 h of incubation. Similar extent of enzyme fall was observed also in the presence of triacylglycerol-rich lipoproteins isolated from rat plasma after feeding of safflower oil or lard, even though the fatty acid composition of the triacylgylcerol varied markedly. As the addition of VLDL to the culture medium resulted in a lesser fall of heparin releasable than residual activity it seems that there was no direct inhibition of surface bound enzyme activity and that the transport of the enzyme to the cell surface was not affected. These data indicate that addition of VLDL to the culture medium resulted in a fall in enzyme synthesis, while total protein synthesis as determined by incorporation of [3H]leucine, remained unchanged. This inhibition could be reproduced by increasing free fatty acid concentration of the medium, however addition of excess albumin to VLDL-containing medium did not prevent the fall in enzyme activity. The present results obtained with cultured rat hearts cells suggest that in vivo plasma levels of triacylglycerol-rich lipoproteins could modulate the lipoproteins could modulate the lipoprotein lipase activity of the heart.

Animals↗
PubMed1979

Uptake and degradation of low density lipoproteins (LDL) by confluent, contact-inhibited bovine and human endothelial cells exposed to physiological concentrations of LDL.

Metabolism of low density lipoproteins (LDL) was studied in cultures of endothelial cells derived from bovine aorta or heart and from human umbilical veins. At low LDL concentrations nonconfluent cultures of bovine endothelial cells catabolized more LDL protein than contact-inhibited confluent cultures but this difference was reduced at high LDL concentrations. Nonconfluent human endothelial cells displayed also a higher rate of LDL degradation than their contact-inhibited counterparts, but this difference was less pronounced than in the bovine cells. Bovine endothelial cells grown in the presence of fibroblast growth factor metabolized less LDL than those cultured without fibroblast growth factor (FGF), but this difference was not consistent in the human endothelial cells. The data presented provide evidence that contact-inhibited confluent human endothelial cells are capable of catabolizing LDL when exposed to physiological concentrations of this lipoprotein.

Animals↗
PubMed1979

Modulation by sodium ascorbate of the effect of chloroquine on low density lipoprotein retention and degradation in cultured human skin fibroblasts.

Human skin fibroblasts in culture were incubated for 48 h with 125I-labelled low density lipoprotein and chloroquine in the presence and absence of sodium ascorbate. Pretreatment of the cells for 3 days with sodium ascorbate and addition of the vitamin during incubation resulted in a decrease in cellular retention and an increase in degradation of the labelled low density lipoprotein. Similar results were obtained when the cells were pretreated for 3 days but the vitamin was not added during the final 48 h of incubation. Pretreatment of the cells with dithiothreitol, butylated hydroxy-toluene, beta-mercaptoethanol and D-alpha-tocopherol had a similar effect to that of ascorbate, i.e. reduction in low density lipoprotein retention and increase in degradation. Neither ascorbate nor the other reducing agents affected low density lipoprotein catabolism in control cells not treated with chloroquine. Sodium ascorbate pretreatment resulted also in a slight but significant alleviation of the chloroquine-induced inhibition of hydrolysis of cholesterol linoleate. It is proposed that sodium ascorbate by virtue of its reducing properties provides some protection to the intralysosomal hydrolases against the inhibitory action of chloroquine. If cholesterol accumulation in human and experimental atheroma is caused by partial inhibition of lysosomal enzymes, sodium ascorbate could play a role in the alleviation of such an inhibition.

Adult↗
PubMed1978

Lipoprotein lipase of cultured mesenchymal rat heart cells. III. Effect of glucocorticoids and insulin on enzyme formation.

Lipoprotein lipase activity was studied in mesenchymal cells isolated from rat hearts and cultured for up to 8 days. The enzyme activity increased markedly between day 3 and 5 while the subsequent increase was less pronounced. Addition of hydrocortisone to complete culture medium resulted in an increase in lipoprotein lipase activity at all stages of culture. Lipoprotein lipase activity did not increase after addition of insulin to the complete culture medium. In the presence of serum-poor medium between day 3 and 6, the increase in lipoprotein lipase activity was much lower than in the presence of complete culture medium. Addition of hydrocortisone and insulin to the serum-poor medium resulted in a significant rise in lipoprotein lipase activity while less consistent effects were obtained after addition of each hormone alone. Transfer of cells to serum-poor medium between day 6 and 7 of culture caused a fall in enzyme activity. Addition of hydrocortisone alone and with insulin restored enzyme activity to control values. No effect on lipoprotein lipase was seen with estradiol, growth hormone, or glucagon when added to serum-containing medium, or serum-poor medium. These results indicate that the lipoprotein lipase of heart is controlled by glucocorticoids and that this control might require the presence of insulin for optimal expression.

Animals↗
PubMed1978

Intralysosomal hydrolysis of cholesterol esters of varying fatty acid composition in cultured human skin fibroblasts.

Intralysosomal accumulation of low density lipoprotein-cholesterol ester was achieved during incubation of cultured human skin fibroblasts in the presence of chloroquine and the subsequent hydrolysis of the cholesterol ester was studied after removal of chloroquine. The fall in the ratio of cholesterol linoleate to cholesterol oleate during recovery from chloroquine inhibition suggested preferential hydrolysis of cholesterol linoleate. To verify this assumption, low density lipoprotein (labeled with [3H] cholesterol linoleate, oleate, palmitate or stearate) was sequestered in the lysosomes as described above. The rate of hydrolysis of the different cholesterol esters was determined 24 and 48 h after removal of chloroquine from the medium and was found to be similar for the four cholesterol esters studied. These findings indicate that enrichment in cholesterol oleate in atheromatous lesions does not result from preferential hydrolysis of intralysosomal cholesterol linoleate, but rather could be due to preferential utilization of oleic acid for the esterification in the cytoplasm of free cholesterol released from the lysosomal compartment.

Cells, Cultured↗
PubMed1978

Lipoprotein lipase of cultured mesenchymal rat heart cells. I. Synthesis, secretion and releasability by heparin.

Cell suspensions prepared from rat hearts were separated by replating into F1, F2 and M cultures, and cultured for 3--11 days. Lipoprotein lipase activity was highest in the F1 cultures which consisted mainly of non-beating, mesenchymal cells. The enzyme activity was released into the medium only after addition of heparin. The release occurred by an initial rapid phase and a continuous slow phase. Both the rapid and the slow release of enzyme activity by heparin were inhibited by about 70% after a 4 h pretreatment with colchicine. Thus, it seems that the vesicular transport is responsible for the translocation of lipoprotein lipase to the cell surface also during the slow process of release. The residual activity in the colchicine treated cultures was higher than in the controls indicating that no inhibition of enzyme synthesis occurred. The slow phase of enzyme release continued also after removal of heparin from the medium but was reduced markedly when protein synthesis was inhibited by cycloheximide. Thus the increase in total enzyme activity encountered after exposure to heparin resulted from stimulation of new enzyme synthesis. The half-time of lipoprotein lipase in the F1 cultures was 35 min and full restoration of enzyme activity was found 60 min after complete removal of cycloheximide from the system. These data indicate that the culture system can be used to study regulation of new enzyme synthesis and its turnover.

Animals↗
PubMed1978

Study of cultured skin fibroblasts from patients with and without ischemic heart disease. Metabolism of low density lipoprotein and cholesterol ester, synthesis of cellular lipids and effect of chloroquine on accumulation of cholesterol ester.

The aim of the present study was to determine whether skin fibroblasts derived from patients with ischemic heart disease (IHD), which could not be related to accepted risk factors, would show a metabolic abnormality with respect to lipid or lipoprotein metabolism. Male patients 30-52 years old suffering from IHD were subdivided into two groups: those in whom IHD was not associated with risk factors such as hypertension, hyperlipoproteinemia, diabetes or smoking (group I); and those in whom heavy smoking was the only major risk factor recognized (group II). The controls were patients with angiographically normal coronary arteries (group III). Skin fibroblasts obtained from these patients were cultured and investigated with respect to metabolism of low density lipoprotein (LDL), synthesis of cellular lipids and induction of cholesterol ester accumulation in the presence of chloroquine, an inhibitor of lysosomal hydrolases. After 24 h incubation, the uptake and degradation of LDL protein in cells from patients of group II was significantly higher than in the controls, group III, but not different from those of group I. Hydrolysis of [3H] cholesterol linoleate, and incorporation of [3H] oleic acid into total lipids and into cholesterol esters was similar in cell cultures of the 3 groups studied. After exposure to chloroquine and LDL, the cells from the different donors accumulated cholesterol ester to a similar extent. Thus, whereas no significant difference was encountered in the lipid and lipoprotein metabolism in cells of patients with IHD without risk factors and controls, some increase in LDL metabolism was seen in cells from patients with IHD and with a history of smoking. It remains to be determined whether this increase was causally related to smoking.

Adult↗
PubMed1977

Rat heart in culture as a tool to elucidate the cellular origin of lipoprotein lipase.

Lipoprotein lipase was determined in 5-day old cell cultures derived from hearts of newborn rats. With the help of the preplating method the cells were subdivided into cultures containing predominantly cardiac myocytes and into those composed mainly of mesenchymal cells. Lipoprotein lipase activity, associated with the mesenchymal cells was ten times higher than the activity found in the cultures containing mainly the myogenic cells. It is suggested that the mesenchymal cells are the progenitors of lipoprotein lipase in rat heart.

Animals↗