Evidence that prostaglandins modulate lipogenesis in cultured lymphocytes--a comparison with its effect on macrophages and tumour cells.

Lipogenesis is essential for the rapid proliferation of cells and it is established that the biosynthesis of selected lipids precedes S-phase, DNA synthesis and the initiation of cell division. Pyruvate was previously shown to be an important lipid precursor for lymphocytes, macrophages and tumour cells. This study now reports the role of prostaglandins (PG) on the regulation of lipogenesis from [3-14C] pyruvate in 24-h cultured lymphocytes. It is shown that indomethacin (10 microM) and ibuprofen (10 microM), both inhibitors of PG biosynthesis, increased [3-14C] pyruvate incorporations into phospholipid and cholesterol fractions in resting lymphocytes but reduced its incorporation into these fractions in concanavalin A (Con A)-stimulated lymphocytes and tumour cells. These two agents also affected [2-14C] thymidine incorporation into the DNA of these cells in the same manner. Lipids produced from [3-14C] pyruvate and exported into the cell culture medium were also measured. The PG biosynthesis inhibitions reduced the transfer to culture medium of arachidonic acid, phospholipids, cholesterol and fatty acids higher than C20 by lymphocytes and tumour cells. Although macrophages are not proliferative cells, the cytoplasmic export measurement is important because these cells have a high capacity for lipid secretion. The results show that the PG biosynthesis inhibitors do not affect the export of phospholipids and cholesterol in macrophages. They do however markedly change the export of arachidonic acid and fatty acids higher than C20 produced from [3-14C] pyruvate in macrophages. It is also reported that a cell-stimulating response diminished the above fatty acid outcome in resting cells and augmented it in thioglycollate-stimulated macrophages. The findings suggest that PG modulation of lipogenesis may depend on cell cycle phase as well as the intrinsic lipid metabolic diversity and capacity.

Pyruvate is a lipid precursor for rat lymphocytes in culture: evidence for a lipid exporting capacity.

Since acetyl-CoA produced through pyruvate dehydrogenase reaction is poorly oxidized by the Krebs cycle in rat lymphocytes, the fate of acetyl units was investigated in these cells. The results presented here show that 24-h cultured lymphocytes actively synthesize lipids from [3-14C]pyruvate. Furthermore, a considerable amount of these lipids have shown to be exported into the culture medium. Experiments with [1-14C] acetate as a lipid precursor showed a close similarity with the rates of incorporation of [3-14C] pyruvate into the same lipid fractions. Treatment of lymphocytes with the mitogen concanavalin A (Con A) markedly enhanced [1-14C] acetate incorporation into a variety of lipids, but the lectin did not affect [3-14C] pyruvate incorporation. The results suggest that lymphocytes convert pyruvate into lipids via the acetyl-CoA pathway and that Con A interferes in lymphocyte lipogenesis but does not seem to affect the pyruvate dehydrogenase reaction. The ability to incorporate pyruvate into certain lipids may have an important role for the rapidly dividing capacity of lymphocytes since the human cancer strain HeLa 155 (a quickly proliferating cell line) also exhibits this feature by converting much more [3-14C] pyruvate into lipids than do lymphocytes. In addition, comparative experiments with lymphocytes, peritoneal macrophages and HeLa cells indicate that pyruvate may provide precursors for cells with active lipid producing and exporting capacities.