Synergy by secretory phospholipase A(2) and glutamate on inducing cell death and sustained arachidonic acid metabolic changes in primary cortical neuronal cultures

Secretory and cytosolic phospholipases A(2) (sPLA(2) and cPL(2)) may contribute to the release of arachidonic acid and other bioactive lipids, which are modulators of synaptic function. In primary cortical neuron cultures, neurotoxic cell death and [H-3]arachidonate metabolism was studied after adding glutamate and sPLA(2) from bee venom. sPLA(2), at concentrations eliciting low neurotoxicity (less than or equal to 100 ng/ml), induced a decrease of [H-3]arachidonate-phospholipids and preferential reesterification of the fatty acid into triacylglycerols. Free [H-3]arachidonic acid accumulated at higher enzyme concentrations, below those exerting highest toxicity. Synergy in neurotoxicity and [H-3]arachidonate release was observed when low, nontoxic (10 ng/ml, 0.71 nm), or mildly toxic (25 ng/ml, 1.78 nM) concentrations of sPLA(2) were added together with glutamate (80 mu M). A similar synergy was observed with the sPLA(2) OS2, from Taipan snake venom. The NMDA receptor antagonist MK-801 blocked glutamate effects and partially inhibited sPLA(2) OS2 but not sPLA(2) from bee venom-induced arachidonic acid release. Thus, the synergy with glutamate and very low concentrations of exogenously added sPLA(2) suggests a potential role for this enzyme in the modulation of glutamatergic synaptic function and of excitotoxicity.