Phospholipase A2, hydroxyl radicals, and lipid peroxidation in transient cerebral ischemia

Phospholipid degradation is an important promoter of neuronal death after transient cerebral ischemia. Phospholipid hydrolysis by phospholipase A(2) (PLA(2)) after transient cerebral ischemia releases arachidonic acid. Arachidonic acid metabolism results in formation of reactive oxygen species, lipid peroxides, and toxic aldehydes (malondialdehyde, 4-hydroxynonenal, and acrolein). Citicoline (cytidine-5'-diphosphocholine), an intermediate in phosphatidylcholine synthesis, has undergone 13 phase III clinical trials for stroke, and is being evaluated for treatment of Alzheimer's and Parkinson's diseases. Here we examined the effect of citicoline on PLA(2) activity in relationship to attenuating hydroxyl radical (OH.) generation and lipid peroxidation after transient forebrain ischemia in gerbil. High Ca2+ dependency (millimolar range) of PLA(2) activity suggests that secretory PLA(2) is the predominant isoform in membrane and mitochondria. Citicoline attenuated the increase in PLA(2) activity in both membrane and mitochondrial fractions. In vitro, citicoline and its components choline and cytidine had no effect on the PLA(2) activity. Thus, citicoline is not a "direct PLA(2) inhibitor." Citicoline also significantly attenuated loss of cardiolipin and arachidonic acid release from phosphatidylcholine and phosphatidylethanolamine. Transient cerebral ischemia resulted in significant formation of OH. and malondialdehyde, and citicoline significantly attenuated their formation. These results suggest that citicoline provides neuroprotection by attenuating the stimulation of PLA(2).