Differential metabolism of hydroxyeicosatetraenoic acid isomers by mouse cerebromicrovascular endothelium

Arachidonic acid diols produced by cytochrome P-450 monooxygenases are incorporated into phospholipids of vascular endothelial cells

Epoxyeicosatrienoic acids (EETs) are synthesized by cytochrome P-450 monooxygenases and released into the blood. When taken up by vascular endothelial and smooth muscle cells, the EETs are primarily esterified to phospholipids or converted to dihydroxyeicosatetraenoic acids (DHETs) and released. In the present studies, radiolabeled 8,9-, 11,12-, and 14,15-DHETs released into the medium from vascular smooth muscle cells were isolated and incubated for 4-16 h with cultured bovine aortic endothelial cells. The uptake ranged from 2 to 50% for the three regioisomers. Hydrolysis of the endothelial lipids and gas chromatographic-mass spectral analyses of the products indicated that all three DHET regioisomers were incorporated intact into phosphatidylcholine and phosphatidylinositol. Similar incubations with EETs confirmed that small amounts of DHETs were also esterified to endothelial phospholipids. These studies indicate that DHETs are incorporated into phospholipids either at the time of EET conversion to DHET or upon release and re-uptake of DHETs. Beside demonstrating for the first time that fatty acid diols are incorporated intact into endothelial lipids, these studies raise the possibility that both EETs and DHETs remain long enough in the vascular wall to produce chronic vasoactive effects.

Cerebral microvessel phospholipase A2 activity in senescent mouse

Phospholipase A2 activity was measured in cerebral microvessels isolated from 5 to 6 month (young adult) and 21 to 24 month (aged adult) old mice. Radiolabeled 1-stearoyl-2-[1-14C]arachidonyl choline phosphoglyceride was used as the enzyme substrate, and enzyme activity determined at pH 8 and pH 9. Activity in older animals was significantly less than in younger animals at both pH's. With choline phosphoglyceride as a substrate, phospholipase A2 activity was predominantly Ca(2+)-dependent, although a small, but measurable Ca(2+)-independent component was present. Negligible production of diacylglycerol indicated little or no phospholipase C activity. These findings indicate that activity of a phospholipase A2, which utilizes choline phosphoglyceride as a substrate, is affected by the aging process. Moreover, a change in PLA2 activity would result in altered metabolism of specific phosphoglycerides and turnover of fatty acids at the sn-2 position in cerebral microvessels.