Generation of Arachidonic Acid and Diacylglycerol Second Messengers from Polyphosphoinositides in Ischemic Fetal Brain

Abstract

Intracerebral administration of [3H]arachidonic acid ([3H]ArA) into 19-20-day-old rat embryos, resulted in a rapid incorporation of label into brain lipids. One hour after injection, 55.6 +/- 8.2, 18.0 +/- 3.4, and 13.7 +/- 1.3% of the total radioactivity was associated with phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine, respectively. Approximately 10% of radioactivity was found acylated in neutral lipids of which free ArA comprised only 1.5 +/- 0.2% of the total radioactivity. Complete restriction of the maternal-fetal circulation for < or = 40 min did not affect the rate of [3H]ArA incorporation (t1/2 = 2 min) into fetal brain lipids, suggesting an effective acylation mechanism that proceeds irrespective of the impaired blood flow. After a short restriction period (5 min), the radioactivity in diacylglycerol was elevated by 50%. After a longer restriction period (20 min), the radioactivity in the free fatty acid and diacylglycerol fractions increased to values of 130 and 87%, respectively. Polyphosphoinositides prelabeled with either [3H]ArA or 32P were rapidly degraded after 5 min of ischemia. After 20 min, the decrease in phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate radioactivity was 47 and 70%, respectively. Double labeling of phospholipids with [14C]palmitic acid and [3H]ArA indicated a preferential loss of [3H]ArA within the polyphosphoinositide species after 20 min, but not after 5 min of ischemia. The specific activity of [14C]palmitate remained unchanged. The current data suggest phospholipase C-mediated diacylglycerol formation at the beginning of the insult followed by a phospholipase A2-mediated ArA liberation at a later time, both enzymes presumably acting preferentially on polyphosphoinositide species.

Elevated production of 20-HETE in the cerebral vasculature contributes to severity of ischemic stroke and oxidative stress in spontaneously hypertensive rats

“…20-hydroxyeicosatetraenoic acid; middle cerebral artery occlusion; cytochrome P-450A; N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine HYPERTENSION IS A MAJOR RISK factor for stroke, but the factors that contribute to the increased incidence and severity of ischemic stroke in hypertension remain to be determined (46). Previous studies have indicated that arachidonic acid (AA) is released into cerebrospinal fluid following cerebral ischemia (1,31,42,56). AA is converted by cytochrome P-450 (CYP) enzymes in cerebral arteries to a potent vasoconstrictor, 20-hydroxyeicosatetraenoic acid (20-HETE) (15,16,32).…”

NMDA receptor-mediated Ca2+ influx triggers nucleocytoplasmic translocation of diacylglycerol kinase ζ under oxygen–glucose deprivation conditions, an in vitro model of ischemia, in rat hippocampal slices

“…As described, prominent changes in lipids are reportedly accompanied in the ischemic brain, where a rapid decrease in phosphatidylinositol-4,5-bisphosphate (PIP 2 ) levels together with a parallel accumulation of diacylglycerol (DG) is observed (Kunievsky et al 1992). In addition, levels of PIP, PIP 2 , and DG approach plateau values after 10 min of ischemia ), a 30 min recirculation period after 15 min of ischemia engenders increases in PIP and PIP 2 , whereas levels of DG decrease promptly toward control values (Moto et al 1991;Yoshida et al 1986).…”

“…Glutamate excitotoxicity causes a massive inXux of Ca 2+ that activates various catabolic processes, culminating in neuronal cell death (Choi 1985(Choi , 1995Lau and Tymianski 2010). Furthermore, previous reports show that prominent changes in lipids are accompanied in the ischemic brain, in which a rapid decrease in phosphatidylinositol-4,5-bisphosphate (PIP2) levels together with a parallel accumulation of diacylglycerol (DG) occurs (Kunievsky et al 1992). These Wndings suggest that phosphoinositide (PI) pathway is involved in this process.…”

mRNA levels of Ca2+-independent forms of protein kinase C in postischemic gerbil brain by Northern blot analysis

“…Intrauterine ischemia leads to rapid translocation of PKC from the cytosol to the membrane fraction followed by loss in the content and activity of the enzyme (Louis et al, 1988). Polyphosphoinositides are hydrolyzed by a phospholipase C with formation of diacylglycerol at the beginning of ischemic insult followed by a phospholipase A 2 mediated liberation of arachidonic acid as 8 Savithiry and Kumar ischemia progresses (Kunievsky et al, 1992). It appears that the release of arachidonic acid from polyphosphoinositides could be part of a signal transduction chain responsible for PKC activation (Kunievsky et al, 1992).…”

“…Polyphosphoinositides are hydrolyzed by a phospholipase C with formation of diacylglycerol at the beginning of ischemic insult followed by a phospholipase A 2 mediated liberation of arachidonic acid as 8 Savithiry and Kumar ischemia progresses (Kunievsky et al, 1992). It appears that the release of arachidonic acid from polyphosphoinositides could be part of a signal transduction chain responsible for PKC activation (Kunievsky et al, 1992). Gangliosides administered prior to the ischemic episode prevent downregulation of PKC in ischemic fetal rat brain (Magal et al, 1990).…”