Comparison of the intracellular lipids of cultured vascular endothelial cells and fibroblasts

The effect of shear stress on the uptake and metabolism of arachidonic acid by human endothelial cells

The uptake and metabolism of arachidonic acid (AA) by human umbilical vein endothelial cells was studied for cells in stationary culture and for cells exposed to physiological levels of shear stress. For cells grown in stationary culture, the initial incorporation of arachidonic acid was primarily into diacylglycerol and phospholipids. Cells exposed to flow incorporated labeled arachidonic acid at a similar rate as cells maintained in stationary culture; however, the distribution of the label was altered by flow. The incorporation of arachidonic acid into diacylglycerol and phosphatidylinositol was increased in cells exposed to flow. The largest increase occurred for cells exposed to arterial levels of shear stress for the shortest time period studied, 0.5 h. Prostacyclin (PGI2) and PGF2 alpha were the principal arachidonic acid metabolites formed. Shear stress-stimulated cells preferentially produced PGI2 relative to other eicosanoid products. The initiation of flow caused a burst of AA metabolism which was highly specific for PGI2. This might represent an increase in the turnover of phosphatidylinositol-bound arachidonic acid which is specifically converted to PGI2 as a result of flow-induced membrane stresses.

Influence of environmental medium on fatty acid composition of human cells: leukocytes and fibroblasts

Fibroblasts in culture and leukocytes have been widely used to study fatty acid and lipoprotein cellular metabolism. The present investigations were designed to study the role of nutritional and environmental factors on lipid metabolism in these two types of cells. Leukocytes freshly isolated from human blood and fibroblasts cultured in media enriched in human serum (HS) have relatively similar fatty acid distributions. However, more important differences are observed in fibroblasts cultured in media enriched with HS or with fetal bovine serum (FBS). It is obvious that the quantity and quality of fatty acids are very different in FBS and HS, but intracellular regulation ensures relative homogeneity of saturated (SFA) and monounsaturated fatty acids (MUFA) in the cells, particularly in phospholipids. The first modifications induced by different media (FBS or HS) are detected on cellular growth; the differences seem to be due more to the fatty acid (FA) quantitative supply than to the FA quality of each culture medium. The major modifications in FA composition induced by different culture media concern the polyunsaturated fatty acids (PUFA) of phospholipids, especially the n-6 family. The intracellular linoleic acid level depends on the level in the medium, but intracellular n-6 metabolite levels depend both on the level in the medium and on the growth state of the cells. The n-3 family seems to be less affected by the quality of the medium in our experiment, and the cells maintain a stable docosahexaenoic acid (22:6n-3) level. A higher content of the n-3 family in the medium induces a higher level of eicosa- or docosapentaenoic acid, rather than docosahexaenoic acid itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of intracellular arachidonate in normal and stressed endothelial cells

The uptake of arachidonate and stearate from serum-free media by endothelial cells was investigated over a 48 h period. Arachidonate was rapidly incorporated into both the phospholipids and triacylglycerols. Triacylglycerol incorporation reached a maximum at 2 h and then rapidly declined with a concomitant increase in phospholipid incorporation. High initial arachidonate incorporation into phosphatidylcholine was followed by a partial transfer of that arachidonate to phosphatidylethanolamine. In contrast, stearate was slowly incorporated into all of the phospholipids and was not incorporated into the triacylglycerols. Cells stimulated with A23187 for 24 h cleaved stearate from all the phospholipids equally, whereas more arachidonate was cleaved from phosphatidylethanolamine than from the other phospholipids. Released arachidonate was both metabolized and reacylated into the triacylglycerols. Our results suggest that triacylglycerols serve as a modulator of intracellular arachidonate concentrations in endothelial cells.

Fatty acid composition in native and cultured human endothelial cells

Endothelial cells from human umbilical veins were isolated by collagenase treatment. Cells were cultured in the presence of either 20% fetal bovine serum (FBS) or 20% human serum (HS). At confluency, endothelial cell lipids were labeled with tracer concentrations of tritiated arachidonic acid, then extracted and separated into lipid subclasses by thin layer chromatography. The fatty acid composition of each lipid class was determined by glass capillary gas-liquid chromatography analysis and compared to that of cells freshly isolated from the cord (NC cells). The fatty acid compositions differed only in phospholipids. Polyunsaturated fatty acids (PFAs), arachidonic, and linoleic acids were depleted in FBS cell phospholipids and replaced by both stearic and oleic acids. No significant difference could be observed between NC cell and HS cell phospholipids. We conclude that PFAs might be decreased in FBS cells because of the relative paucity of PFAs in FBS as compared to HS. It seems therefore more convenient to cultivate endothelial cells in the presence of HS, especially in respect to their phospholipid content of arachidonic acid, which is the physiological reservoir for prostacyclin synthesis.

The effect of ionophore A23187 on albumin internalization in cultured human umbilical vein endothelial cells

The effects of calcium and the calcium ionophore A23187 on endocytosis were studied in cultured human umbilical vein endothelial cells using iodinated human albumin to measure bulk phase endocytosis. In the absence of the ionophore, varying the levels of extracellular calcium did not affect endocytosis. In the presence of 10 microM A23187, the endocytic clearance of albumin decreased approx. 50% when exposed to physiological concentrations of extracellular calcium, but increased approx. 50% at lower calcium concentrations. Since the ionophore is known to alter cellular calcium levels, these results are compatible with a role for intracellular calcium in the modulation of endothelial cell endocytosis.

Fatty acyl delta 6 desaturation activity of cultured human endothelial cells. Modulation by fetal bovine serum

Human endothelial cells from umbilical vein actively desaturate [14C]linoleate and synthesize icosatrienoate, arachidonate and docosatetraenoate. Desaturation and chain elongation of 9,12,15-[14 C]linolenate (n - 3) by these cells is more extensive than that of [14 C]linoleate. Both confluent primary monolayers and subconfluent subcultures exhibit greater fatty acyl CoA delta 6-desaturase activity when growth and incubation media contain 2.5% fetal bovine serum instead of 10%. Prior growth with 20% serum diminishes the extent of subsequent linoleate desaturation. Use of medium supplemented with 20-100 microM oleate results in up to 67% inhibition of [14 C]arachidonate synthesis. These results indicate that, despite previously published reports to the contrary, human vascular endothelial cells are similar to other normal mammalian cells in having fatty acyl delta 6-desaturase activity. Suppression of endogenous arachidonate synthesis by elevated levels of serum lipids may impair endothelial cell function.

Formation of elastic fibers and elastin in rabbit aortic smooth muscle cell cultures

Cultured rabbit aortic smooth muscle cells produce elastic fibers and elastin in their extracellular matrix. Morphological analyses of elastic fibers indicate that they consist of two distinct components which play a major role in elastic early fiber formation namely, the amorphous component and the "microfibrillar" component. During elastogenesis, the early fiber consists of small bundles of filaments. Later, clearly distinguishable small conglomerates of amorphous material are found distributed among the bundles of filaments. The mature elastic fibers have large conglomerates of amorphous material with the filaments present within the interstices. Long term cultures of these cells in the second passage continue to accumulate elastin. The crosslinking amino acid isomers desmosine and isodesmosine, which are unique to insoluble elastin, increase with time in culture. Twenty-four hour pulses with 14C-proline followed by measurements of 14C-hydroxyproline in the collagenase resistant protein of the cell layer show that the synthesis of insoluble elastin is constant up to the 14 week period studied from the time the amorphous material becomes evident ultrastructurally.