Phospholipase A 2-induced neurotoxicity in vitro and in vivo in rats

Abstract

The present study evaluated the neurotoxic potential of phospholipase A 2 (PLA 2) in vitro (primary neuronal cultures) and in vivo (EEG and behavior) rat models of CNS excitability. In vitro, PLA 2 (0.0038-5.8 nM) or melittin (a potent activator of endogenous PLA 2; 100–5000 nM), were highly neurotoxic, causing approximately 500 units/ml LDH release. The neurotoxic EC 50s for PLA 2 and melittin were 1.8 (1.4-2.3) and 848 (501–1280) nM, respectively. Neurotoxic concentrations of PLA 2 stimulated neuronal release of [ 3H]AA. Preliminary in vitro experiments evaluating changes in neuronal calcium flux indicated that PLA 2 caused transient, and melittin sustained, increases in [Ca 2+] i. In vivo, PLA 2 (0.5-5 μg i.c.v.) or melittin (2.5-20 μg i.c.v.) produced nonconvulsive EEG seizures, which generalized to status epilepticus. While the onset of seizure development was markedly delayed for PLA 2 (1.5-4.5 h), the seizure inducing effects of melittin were evident within 3.5 ± 0.2 min and more severe. Both PLA 2 and melittin were lethal, exhibiting LD 50s of 0.62 μg and 8.4 μg, respectively. Pretreatment with (+)-MK801 (5 μg, i.c.v.) significantly attenuated melittin, but not PLA 2, in vivo neurotoxicity. PLA 2 induced neuropathology in surviving rats revealed extensive cortical and subcortical injury to forebrain neurons and fibre pathways. Collectively, these results demonstrate the potent neurotoxic potential of PLA 2, the delayed clinical nature of its in vivo neurotoxicity and the applicability of these model systems to future studies on mechanisms of PLA 2 neurotoxicity and the development of potential PLA 2 antagonists.