Nanomolar vitamin E alpha-tocotrienol inhibits glutamate-induced activation of phospholipase A2 and causes neuroprotection

J Neurochem. 2010 Mar;112(5):1249-60. doi: 10.1111/j.1471-4159.2009.06550.x. Epub 2009 Dec 17.

Abstract

Our previous works have elucidated that the 12-lipoxygenase pathway is directly implicated in glutamate-induced neural cell death, and that such that toxicity is prevented by nM concentrations of the natural vitamin E alpha-tocotrienol (TCT). In the current study we tested the hypothesis that phospholipase A(2) (PLA(2)) activity is sensitive to glutamate and mobilizes arachidonic acid (AA), a substrate for 12-lipoxygenase. Furthermore, we examined whether TCT regulates glutamate-inducible PLA(2) activity in neural cells. Glutamate challenge induced the release of [(3)H]AA from HT4 neural cells. Such response was attenuated by calcium chelators (EGTA and BAPTA), cytosolic PLA(2) (cPLA(2))-specific inhibitor (AACOCF(3)) as well as TCT at 250 nM. Glutamate also caused the elevation of free polyunsaturated fatty acid (AA and docosahexaenoic acid) levels and disappearance of phospholipid-esterified AA in neural cells. Furthermore, glutamate induced a time-dependent translocation and enhanced serine phosphorylation of cPLA(2) in the cells. These effects of glutamate on fatty acid levels and on cPLA(2) were significantly attenuated by nM TCT. The observations that AACOCF(3), transient knock-down of cPLA(2) as well as TCT significantly protected against the glutamate-induced death of neural cells implicate cPLA(2) as a TCT-sensitive mediator of glutamate induced neural cell death. This work presents first evidence recognizing glutamate-induced changes in cPLA(2) as a novel mechanism responsible for neuroprotection observed in response to nanomolar concentrations of TCT.

MeSH terms

  • Animals
  • Arachidonic Acid / metabolism
  • Arachidonic Acid / pharmacology
  • Arachidonic Acids / pharmacology
  • Calcium / metabolism
  • Cell Death / drug effects
  • Cell Line, Transformed
  • Cell Size / drug effects
  • Chelating Agents / pharmacology
  • Dose-Response Relationship, Drug
  • Down-Regulation / drug effects
  • Drug Interactions
  • Egtazic Acid / pharmacology
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Fatty Acids / metabolism
  • Glutamic Acid / pharmacology*
  • Hippocampus / cytology
  • Mice
  • Neurons / drug effects*
  • Neuroprotective Agents / pharmacology*
  • Phospholipase A2 Inhibitors
  • Phospholipases A2 / genetics
  • Phospholipases A2 / metabolism*
  • RNA, Small Interfering / pharmacology
  • Subcellular Fractions / drug effects
  • Tocotrienols
  • Transfection / methods
  • Vitamin E / analogs & derivatives*
  • Vitamin E / pharmacology

Substances

  • Arachidonic Acids
  • Chelating Agents
  • Enzyme Inhibitors
  • Fatty Acids
  • Neuroprotective Agents
  • Phospholipase A2 Inhibitors
  • RNA, Small Interfering
  • Tocotrienols
  • arachidonyltrifluoromethane
  • Vitamin E
  • Arachidonic Acid
  • Glutamic Acid
  • Egtazic Acid
  • tocotrienol, alpha
  • Phospholipases A2
  • Calcium