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Biomedical subjects

A A Spector

Publications and source records attributed to A A Spector.

At least 217 records · Page 12Linked to original sources
PubMed1974

Utilization of ascites plasma very low density lipoprotein triglycerides by Ehrlich cells.

Much of the lipid present in the ascites plasma in which Ehrlich cells grow is contained in very low density lipoproteins (VLDL). Chemical measurements indicated that triglycerides were taken up by the cells during in vitro incubation with ascites VLDL. When tracer amounts of radioactive triolein were incorporated into the ascites VLDL, the percentage uptakes of glyceryl tri[1-(14)C]oleate and triglycerides measured chemically were similar. The cells also took up [2-(3)H]glyceryl trioleate that was added to VLDL, but the percentage of available (3)H recovered in the cell lipids was 30-40% less than that of (1 4)C from glyceryl tri[1-(1 4)C]oleate. This difference was accounted for by water-soluble (3)H that accumulated in the incubation medium, suggesting that extensive hydrolysis accompanied the uptake of VLDL triglycerides. Radioactive fatty acids derived from the VLDL triglycerides were incorporated into cell phospholipids, glycerides, and free fatty acids, and they also were oxidized to CO(2). Triglyceride utilization increased as the VLDL concentration was raised. These results suggest that one function of the ascites plasma VLDL may be to supply fatty acid to the Ehrlich cells and that the availability of fatty acid to this tumor is determined in part by the ascites plasma VLDL concentration. Although Ehrlich cells incorporate almost no free glycerol into triglycerides, considerable amounts of [2-(3)H]glyceryl trioleate radioactivity were recovered in cell triglycerides. This indicates that at least some VLDL triglycerides were taken up intact. The net uptake of VLDL protein and cholesterol was very small relative to the triglyceride uptake, suggesting that intact triglycerides are transferred from the ascites VLDL to the Ehrlich cells and that hydrolysis occurs after the triglyceride is associated with the cells.

Animals↗
PubMed1974

Partition of fatty acids.

The partition ratios of radioactive fatty acids between n-heptane and a physiological buffer at 37 degrees C were measured. The fatty acids included the saturated acids with an even number of carbons from 10 to 18 and the unsaturated acids oleic, linoleic, and linolenic. In addition, the partition ratios of decanoate, myristate, and palmitate were determined over a wide pH range. Any single plot of partition ratio vs. aqueous concentration of an acid gave a nearly straight line, a finding consistent with very little association in the aqueous phase. In the case of the acids with 16 and 18 carbon atoms, however, comparison of the constants calculated from these plots with the assumption of no aqueous phase association revealed several inconsistencies. These inconsistencies cannot be resolved completely by assuming the existence of fatty acid association in the aqueous solution. We believe that at least some of the deviations are due to the presence of trace quantities of radioactive impurities in the labeled fatty acids. For example, purification of a sample of supposedly pure [1-(14)C]myristate by a series of solvent extractions increased the partition ratio by a factor of 1.5. Although all of the observations cannot be explained by this interpretation, we believe that our studies suggest that there is no appreciable association of fatty acids under the usual physiological conditions.

Alkanes↗
PubMed1972

Excretion of sterols from the skin of normal and hypercholesterolemic humans. Implications for sterol balance studies.

The 24 hr sterol excretion from the entire skin surface was determined in six normal and five hypercholesterolemic (Type II) patients fed a controlled, eucaloric diet containing 400 mg of plant sterols. All subjects received radiolabeled cholesterol intravenously in order to measure cholesterol turnover and exchange. The 24 hr skin surface lipids were collected subsequently at intervals of 7-10 days. Sterols were quantified and identified by a combination of thin-layer and gas-liquid chromatographic methods. The mean 24 hr excretion of cholesterol in milligrams was 82.6 in the normal subjects and 82.7 in the hypercholesterolemic patients. Cholesterol constituted 89% of the total sterol excretion through the skin surface in both groups. The specific radioactivity of cholesterol in the skin surface lipids increased gradually after the intravenous administration of the isotope. Within 4-5 wk the specific activity equaled and then remained higher than that of the plasma up to 10 wk. These specific activity curves suggested that, for at least some of skin surface cholesterol, there was a precursor-product relationship between the plasma cholesterol and the skin cholesterol. The presence of plant sterols, beta-sitosterol, campesterol, and stigmasterol in the skin surface lipids of man has not been reported previously. We identified these sterols in the skin surface lipids of all of our subjects. They constituted about 7% of the total skin surface sterols. The occurrence of plant sterols in the skin surface lipids suggested that plasma sterols were transferred from the plasma into the skin. 1-2% of the skin surface sterols were tentatively identified as lathosterol and lanosterol. The present study documented that a significant amount of cholesterol was excreted from the skin surface and that probably there was a net transfer of plasma cholesterol into the skin surface lipids. Both normal subjects and hypercholesterolemic patients excreted similar amounts of cholesterol per day into the skin surface lipids. We suggest that this daily loss of cholesterol from the skin surface may need to be considered in sterol balance studies.

Adult↗
PubMed1972

Studies on the cellular mechanism of free fatty acid uptake using an analog, hexadecanol.

Hexadecanol was employed as a fatty acid analog in an attempt to elucidate the role of the carboxyl group in free fatty acid uptake. Large quantities of albumin-bound [1-(14)C]hexadecanol were taken up by Ehrlich ascites cells during in vitro incubation. More than 90% of the (14)C that was taken up remained as hexadecanol even after 1 hr of incubation at 37 degrees C. Addition of unlabeled hexadecanol did not appreciably alter the rate of [U-(14)C]glucose oxidation or incorporation into total lipids, suggesting that the slow rate of hexadecanol metabolism was not due to a toxic effect of this analog. However, more of the labeled glucose was incorporated into phospholipids and less into glycerides, indicating that hexadecanol did exert some metabolic effect on the cells. Uptake was temperature dependent but relatively unresponsive to the presence of glucose or fluoride and cyanide. Hexadecanol was incorporated into exchangeable and nonexchangeable cellular pools as determined by its availability for release to a medium containing albumin. These results indicate that a mammalian cell can rapidly take up large amounts of a long-chain hydrocarbon derivative that does not contain a carboxyl group. Furthermore, the data are compatible with the hypothesis that free fatty acids are taken up by a nonenzymatic process such as diffusion into the lipid phase of the cell membrane.

Animals↗
PubMed1972

Quantitative analysis of uptake of free fatty acid by mammalian cells: lauric acid and human erythrocytes.

Quantitative aspects of the binding of free fatty acid to human erythrocytes were studied by measuring the distribution of various amounts of [1-(14)C]lauric acid between washed human erythrocytes and defatted human plasma albumin. Incubations were done at 37 degrees C in an isotonic phosphate-buffered salt solution. Laurate uptake approached a steady state value within 1 hr of incubation over the range of laurate-albumin molar ratios that were tested. Uptake was due primarily to a transfer of laurate from albumin to the cell, not to incorporation of the intact laurate-albumin complex. The fatty acid binding sites of the erythrocyte are located predominantly on or within the cell membrane. The binding model which best fitted the laurate uptake data consisted of two classes of erythrocyte binding sites. This model contains a small number of sites, 2.0 x 10(-13) moles/10(6) cells, that have an average apparent association constant of 1.8 x 10(6) m(-1) for laurate. Thus, the average strength of these sites is of the same order of magnitude as the stronger laurate binding sites of albumin. The binding model also contains a relatively large number of weaker fatty acid binding sites, 1.3 x 10(-11) moles/10(6) cells, that have an average apparent association constant of 1.3 x 10(4) m(-1) for laurate. These sites are too weak to bind appreciable amounts of laurate unless the fatty acid-albumin molar ratio is elevated.

Binding Sites↗
PubMed1971

Utilization of free fatty acids complexed to human plasma lipoproteins by mammalian cell suspensions.

The purpose of this study was to determine whether lipoprotein-bound free fatty acid could be utilized by isolated mammalian cells. Ehrlich ascites tumor cells were incubated in vitro with radioactive free fatty acids that were bound to human plasma lipoproteins. Under these conditions, lipoprotein-bound free fatty acids were readily taken up by the cells. After 2 min of incubation with free fatty acids bound to low density lipoproteins, most of the radioactivity that was associated with the cells was in the form of free fatty acids. As the incubation continued, increasing amounts of radioactivity were incorporated into CO(2) and cell lipids, particularly phospholipids. Most of the free fatty acid uptake was the result of fatty acid transfer from low density lipoproteins to the cell, not from irreversible incorporation of the intact free fatty acid-low density lipoprotein complex. Fatty acid uptake increased as the ratio of free fatty acid to low density lipoprotein was raised. When albumin was added to the medium, free fatty acid uptake decreased. A large percentage of the newly incorporated cellular radioactivity was released into the medium if the cells were exposed subsequently to a solution containing albumin. Most of the released radioactivity was in the form of free fatty acid. The results with this experimental model suggest that lipoprotein-bound free fatty acid, like albumin-bound free fatty acid, is readily available for uptake by isolated cells. The mechanism of free fatty acid utilization by the Ehrlich cell is similar when either low density lipoprotein or serum albumin serves as the fatty acid carrier.

Animals↗