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Biomedical subjects

A A Spector

Publications and source records attributed to A A Spector.

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

Reconstitution of the solubilized insulin receptor in phospholipid vesicles.

The insulin receptor was solubilized from turkey erythrocyte membranes by extraction with 1% beta-octylglucopyranoside. Insulin binding was enhanced when the solubilized material was reconstituted in phospholipid vesicles. The affinity of the reconstituted vesicles for various insulins was similar to that of the intact membranes: porcine insulin greater than proinsulin greater than desoctapeptide insulin. A curvilinear Scatchard plot was obtained for insulin binding to the reconstituted system at 15 degrees C. A high affinity association constant of 1.4 x 10(9) M-1 was obtained from the Scatchard plot. This is a four-fold increase over the value for the turkey erythrocyte membrane, which contains more highly saturated phospholipids. This suggests that the insulin receptor may be sensitive to the lipid composition of the membranes in which it is embedded.

Animals↗
PubMed1979

Modification of the fatty acid composition of cultured human fibroblasts.

The fatty acid composition of human skin fibroblasts grown in 10% dialyzed fetal calf serum can be modified considerably by adding supplemental fatty acids to the culture medium. The degree of modification was dependent on the concentration of added fatty acid over the range tested, 2.5 X 10(-5) to 1 X 10(-4) M. At the higher concentration, the extent of the modifications was as those which can be produced in nonhuman or malignant cell lines. Although the greatest changes were produced in the neutral lipid fraction, the cellular phospholipids also exhibited appreciable modifications. The phospholipids isolated from a microsomal fraction prepared from the cell homogenate exhibited similar changes in fatty acyl composition. These findings indicate that the human fibroblast can tolerate considerable variability in fatty acid composition, even in membrane phospholipids. The triglyceride content of the cells increased when they were grown in the presence of added fatty acids, but the phospholipid and cholesterol content remained unchanged. Growth was not affected by either oleic or linoleic acids, but it was reduced up to 50% when palmitic linolenic, or arachidonic acid was added in concentrations of 5 X 10(-5) M or above. Extensive modifications in phospholipid fatty acid composition also were produced in confluent monolayers of these fibroblasts. This suggest that some membrane lipid turnover occurs even when the cultures are not rapidly growing. Fatty acid modifications also were produced in the commercially available IMR-90 strain of human lung fibroblasts, suggesting that the ability to tolerate considerable differences in fatty acid composition is not a special property of the skin fibroblast line that was isolated locally.

Cell Line↗
PubMed1978

Fatty acid metabolism in L1210 murine leukemia cells: differences in modification of fatty acids incorporated into various lipids.

L1210 leukemia cells can utilize all of the main fatty acids that normally are present in the ascites fluid in which they grow. This finding is consistent with the view that L1210 cells derive most of their fatty acids from the ascites fluid. From 80--90% of each fatty acid was incorporated into cell lipids without structural modification, suggesting that the lipid composition of these cells can be altered by changing the type of fatty acids to which they are exposed. Most importantly, the palmitate that was subsequently incorporated into total cell phospholipids was elongated and desaturated somewhat more than that incorporated into triglycerides. This difference was due primarily to more extensive modification of the palmitate incorporated into the ethanolamine phosphoglycerides fraction. Although there was no difference between total phospholipids and triglycerides with linoleate, more of the linoleate incorporated into ethanolamine phosphoglycerides was elongated and further desaturated than that incorporated into choline phosphoglycerides and triglycerides. These findings indicate fatty acids incorporated into various cell lipid fractions are not structurally modified to the same extent. There appears to be greater modification of fatty acid used for ethanolamine phosphoglyceride synthesis as compared with triglyceride and choline phosphoglyceride synthesis.

Animals↗
PubMed1978

Effects of dietary fat composition on the Ehrlich ascites tumor fluid lipoproteins.

Mice bearing the Ehrlich ascites tumor were fed diets rich in either coconut oil or sunflower oil. From 20 to 40% less lipid was present in the ascites tumor fluid when the mice were fed the sunflower oil diet. This was associated with a reduction in the amount of very low density lipoproteins (VLDL) and high density lipoproteins (HDL), the main lipoprotein fractions present in the ascites tumor fluid. The VLDL from the mice fed sunflower oil contained more cholesteryl esters and a lower free to esterified cholesterol ratio than those from the mice fed coconut oil. Very little change occurred in the composition of the HDL. All of the lipids contained in both lipoprotein fractions exhibited appreciable differences in fatty acid composition. Much more monoenoic and less polyenoic fatty acid were present in the lipids from the mice fed the coconut oil diet, but no appreciable change in saturated fatty acid content occurred. Similar changes in fatty acid composition were observed in the blood plasma of the tumor-bearing mice. There was no qualitative difference in the apolipoprotein patterns of either the ascites fluid VLDL or HDL. Pyrene fluorescence studies indicated that the fluidity of the VLDL was increased when the mice were fed the sunflower oil diets. No difference in HDL fluidity, however, was observed by this technique. These results indicate that the amount, composition, and physical properties of certain of the lipoproteins contained in the ascites tumor fluid can be modified by changing the composition of the dietary fat fed to mice bearing the Ehrlich ascites tumor.

Animals↗
PubMed1978

Effect of dietary fat saturation on survival of mice with L1210 leukemia.

We examined L1210 murine leukemia growth rate and survival of host male DBA/2J mice fed a diet rich in either polyunsaturated fat (16% sunflower oil) or saturated fat (16% coconut oil). The survival of mice that received transplants of L1210 leukemia cells was longer among the animals that had ingested a diet rich in the saturated fat as compared to those fed the more unsaturated fat. In duplicate experiments, the mean survivals of mice fed coconut oil were 200.9 +/- 1.6 and 202.5 +/- 3.4 hours compared to 188.7 +/- 5.3 and 187.6 +/- 3.5 hours for those fed sunflower oil. Tumor growth rate or the rate of DNA synthesis by the leukemia cells did not differ between the two experimental groups. Therefore, the alteration in survival was apparently due to an effect of the diets on the responses of the hosts rather than their effect on tumor size or growth rate.

Animals↗
PubMed1977

Regulation of fatty acid biosynthesis in Ehrlich cells by ascites tumor plasma lipoproteins.

Fatty acid biosynthesis in Ehrlich cells in vitro was reduced when very low density lipoproteins (VLDL) isolated from the ascites tumor plasma were added to the incubation medium. The degree of inhibition was dependent on the VLDL concentration. At the VLDL concentrations usually present in the ascites plasma, there was a 30% decrease in biosynthesis as measured by (3)H(2)O incorporation into fatty acids. Analysis of the labeled fatty acids by gas liquid chromatography indicated that this decrease was due to a reduction in fatty acid de novo biosynthesis and that chain elongation actually was increased when VLDL were present. Although ascites plasma low- and high density lipoproteins also produced a concentration-dependent inhibition of fatty acid biosynthesis, their effects were much smaller than those of the VLDL. Studies employing VLDL and radioactive free fatty acids indicated that the cells took up utlilzed fatty acids derived from these lipoproteins. When VLDL were present, labeled free fatty acid incorporation into cell phospholipids, cholesteryl esters, and CO(2) decreased, whereas its incorporation into the cell free fatty acid pool increased. By contrast, the cells incorporated only very small amounts of fatty acid from either low- or high density lipoproteins. This suggests that the VLDL exert their inhibitory effect on fatty acid synthesis by supplying exogenous fatty acids to the cells.

Animals↗
PubMed1977

Effect of dietary fat saturation on acylcoenzyme A:-cholesterol acyltransferase activity of Ehrlich cell microsomes.

Ehrlich cells grown in mice fed coconut oil diets (highly saturated) contain about twice as much cholesteryl ester as those grown in mice fed sunflower oil diets (highly polyunsaturated). Acylcoenzyme A: cholesterol acyltransferase (ACAT) activity was 30-100% higher in microsomes prepared from the cells grown on coconut oil (M(c)) than in those prepared from the cells grown on sunflower oil (M(s)). Increased ACAT activity was noted in M(c) with either [1-(14)C]palmitoyl CoA or [1,2-(3)H]cholesterol as the labeled substrate. This occurred at all acyl CoA concentrations tested and, in the [1,2-(3)H]cholesterol assay, with palmitoyl, oleoyl, or linoleoyl CoA as the substrate. The pH optimum for ACAT activity was the same with M(c) and M(s), pH 7.0. ACAT activity obeyed Michaelis-Menten kinetics at palmitoyl CoA concentrations between 1 and 10 micro M. Substrate inhibition occurred at higher concentrations. Kinetic analysis with [1-(14)C]palmitoyl CoA as the substrate indicated that the apparent K(m) for M(c) was 33% smaller than for M(s). There was no difference, however, in apparent V(max) values. The cholesterol and phospholipid contents of M(c) and M(s) were similar, but their fatty acid compositions differed considerably. M(c) contained 2.7 times more monoenoic fatty acid and only half as much polyenoic fatty acid as M(s). Our results indicate that dietary modification of the microsomal fatty acid composition is associated with alterations in the activity of ACAT, an enzyme that is tightly bound to the microsomes. These changes in ACAT activity may be partly responsible for the differences in cholesteryl ester contents of Ehrlich cells grown in mice fed the coconut and sunflower oil diets.

Acyltransferases↗
PubMed1977

Utilization of long-chain free fatty acids and glucose by human leukemic blast cells.

We have studied the utilization of free fatty acid and glucose by human leukemic blast cells. Palmitate was both incorporated into complex cellular lipids, primarily phospholipids and triglycerides, and oxidized to CO2. The predominant phospholipid synthesized was phosphatidylcholine. Only a small proportion of the incoming fatty acid was modified structurally before incorporation into lipid esters. After incubation with [1-14 C]palmitate, 91% of the radioactivity recovered in cell lipids remained in fatty acids containing 16 carbon atoms. Studies with labeled glucose revealed little de novo synthesis of fatty acid, and the majority of the radioactivity from glucose was located in the water-soluble fraction after saponification of the esters. We conclude that the free fatty acids contained in the extracellular fluid provide much of the fatty acid for required cellular lipid synthesis in human leukemic blast cells. Since there is little elongation of incoming palmitate before incorporation into cellular lipids, it may be possible to alter the fatty acid composition of membrane phospholipids by changing the proportion of the various free fatty acids available to the leukemic cells.

Carbon Dioxide↗
PubMed1977

Fatty acid utilization by L1210 murine leukemia cells.

L1210 murine leukemia cells grow in an ascites plasma that contains lipids, including 0.62 +/- 0.046 (S.E.) MICRONEq free fatty acid per ml. in vitro incubations demonstrated that isolated L1210 cells readily utilize free fatty acid that is added to the incubation medium. When the cells were incubated with albumin-bound [1-14C]palmitate, about 12 times more radioactivity was incorporated into cell lipids than was oxidized to CO2. Triacylglycerols contained 1.5 to 4 times more radioactivity than phospholipids, and from 48 to 69% of the phospholipid radioactivity was recovered in the choline phosphoglycerides. [1-14C]Palmitate utilization increased as the fatty acid concentration of the medium was raised, the largest increase occurring in the triacylglycerol fraction. Palmitate utilization also was increased by the presence of carbohydrates in the medium, their effectiveness (in descending order) being glucose, mannose, galactose, fructose, and glycerol. By contrast, ribose did not produce any stimulatory effect. During a 1-hr incubation, between 82 and 87% of the [1-14C]palmitate that was taken up remained as palmitic acid. From 8 to 15% was elongated to stearate, and only 2 to 3% was desaturated to palmitoleate and oleate. Based upon the lipid content, growth rate, and palmitate utilization rate of the cells, it appears that a major portion of the lipid requirements of the L1210 cell may be supplied by the fatty acid contained in the ascites plasma. In addition, our results suggest that most of the saturated fatty acid taken up is incorporated into cell lipids without structural modification.

Animals↗