Modulation of polyunsaturated fatty acid metabolism in human umbilical vein endothelial cell cultures by antioxidants
Primary cultures of human umbilical vein endothelial cells were incubated with n-3 and n-6 fatty acids for a maximum of 24 hours, to investigate their distribution in membrane neutral lipids and phospholipid. Furthermore, the release of labelled free fatty acids due to induction of PLA2 by cytokines and the further production of PGI2 in cells supplemented with different PUFA was investigated in the present study to elucidate the metabolism of lipids in these cells. In addition, the extent of lipid peroxidation and the potency of antioxidants in inhibiting the formation of lipid peroxides due to dietary modification in cells were also investigated in relation to their effects on essential fatty acid metabolism. Endothelial cells in the present study had a significant capacity to metabolise PUFA which was supplied exogenously. PUFA of n-3 and n-6 families behaved differently with respect to their incorporation into membrane lipids. ARA of n-6 family had the greatest incorporation into the total lipids compared to n-3 PUFA ie, EPA and DHA. About 80% of PUFA was incorporated into the phospholipid fraction and another 20% was found in neural lipids. [14C]-ARA and [14C]-DHA when co-incubated with endothelial cells for longer incubation periods were found mainly incorporated into TAG. In contrast, [14C]-EPA was distributed significantly into other fractions of neutral lipids with no significant increase in the TAG fraction. TAG is important as a fatty acid store in the cells including essential PUFA which can be metabolised and utilised for PG synthesis during the deficiency of eicosanoid precursor (PUFA) in the phospholipids of cell membranes. All the PUFA tested were incorporated into PC to a similar extent with time. Transfer between PC and PE during the longer incubation time was observed in the present study which indicated that PE may be important in the storage of fatty acids in phospholipids since PC and PI were the most preferred substrates for the phospholipases.