Tournefolic acid B attenuates amyloid β protein-mediated toxicity by abrogating the calcium overload in mitochondria and retarding the caspase 8-truncated Bid-cytochrome c pathway in rat cortical neurons

The effect of tournefolic acid B (TAB) on amyloid beta protein-mediated neurotoxicity and the underlying mechanisms were investigated. Amyloid beta protein 25-35 elicited neuronal death as determined by calcein/ethidium homodimer-1 staining. 10 mu M amyloid beta protein 25-35 caused cell death at a level of 41.5 +/- 3.8% by MTT reduction. 50 mu M TAB attenuated the amyloid beta protein 25-35-induced cell death by 49.7 +/- 11.1%. TAB also abrogated amyloid protein-induced activation of caspases 8 and 9 by about 50-60%. Furthermore, TAB significantly diminished the amyloid beta protein 25-35-induced elevation of calcium level in mitochondria, whereas it did not affect the calcium level in cytosol or endoplasmic reticulum. TAB markedly retarded the amyloid beta protein-mediated release of cytochrome c from mitochondria. Amyloid beta protein 25-35 elevated mitochondrial truncated BH3 interacting domain death agonist (tBid) and decreased the level of B-cell leukemia/lymphoma-2 alpha (Bcl-2 alpha) in mitochondria. Moreover, amyloid beta protein induced a slight up-regulation of Bcl-2 agonist killer 1 (Bak) in cytosol. 50 mu M TAB decreased the amyloid beta protein-induced elevation of mitochondrial tBid and the level of Bak, whereas it did not affect the amyloid beta protein-mediated decrease in mitochondrial Bcl-2 alpha. Caspase 8 inhibitor significantly inhibited the amyloid beta protein-mediated increase in mitochondrial tBid and the release of cytochrome c. Therefore, TAB blocked the overload of calcium in mitochondria and impaired the amyloid beta protein-mediated activation of the caspase 8-tBid-cytochrome c pathway, thereby conferring its neuroprotective effects on amyloid beta protein-mediated neurotoxicity. (C) 2009 Elsevier B.V. All rights reserved.