Nitric oxide alters arachidonic acid turnover in brain cortex synaptoneurosomes.

Nitric oxide (NO) and arachidonic acid (AA) and also its metabolites are very important inter- and intracellular second messengers. They are involved in mechanisms of learning and memory. However, liberated in excessive amount in brain ischemia, Parkinson and Alzheimer diseases they are responsible for cell degeneration and death. Previously, we could show that Alzheimer disease's amyloid-beta protein enhanced nitric oxide liberation. The role of NO in AA metabolism is till now not well understood. Therefore, the aim of the present study was to investigate the mechanisms of NO-evoked activation of AA release and inhibition of AA incorporation into phospholipids of cortical rat brain synaptoneurosomes. The studies were carried out using NO donors, butyryl-cGMP (b-cGMP) and H2O2. All these compounds enhanced AA liberation from phosphatydilinositol (PI) and phosphatidylcholine (PC). Protein kinase ERK1/2, protein kinase C (PKC), cGMP-dependent protein kinase G (PKG) were involved in basal and NO-induced cytosolic phospholipase A2 (cPLA2) activation. Moreover, NO donors, b-cGMP and hydrogen peroxide (H2O2) exerted inhibitory effect on AA incorporation into PI and PC influencing arachidonyl-CoA transferase (AA-CoA-T) activity. AA-CoA synthase (AA-CoA-S) activity did not change. Specific inhibitors of protein kinase ERK1/2 (UO126), PKC (GF109203X), PKG (KT5823) had no effect on NO-mediated lowering of AA incorporation into PI and PC but inhibited the basal AA-CoA-S activity. Our data indicated that AA (10 microM) itself markedly decreased AA incorporation by about 50% into phospholipids of synaptoneurosomes membranes. Increasing release of AA and its metabolites causes the lowering of AA incorporation evoked by NO, b-cGMP and H2O2. Antioxidant, Resveratrol (100 microM) prevented NO- and cGMP-evoked inhibition of AA incorporation. These results suggest that NO affects the intracellular level of AA through alteration of cPLA2 and AA-CoA acyltransferase activities and may have an important implication in alterations of nerve endings properties and function.