Neurodegenerative disorders such as
Alzheimer's disease (AD) are associated with oxidative stress, and it has been suggested that apoptosis is a crucial pathway in neuronal cell death in AD patients.
4-Hydroxynonenal (HNE), one of the aldehydic products of
membrane lipid peroxidation, is reported to be elevated in the brains of AD patients and mediates the induction of neuronal apoptosis in the presence of oxidative stress. In this study, we investigated the HNE-induced apoptosis mechanism and the protective effects of the cocoa
procyanidin fraction (CPF) and its major
antioxidant procyanidin B2 against the apoptosis induced by HNE in rat
pheochromocytoma (PC12) cells. HNE-induced nuclear condensation and increased sub-G1 fraction, both of which are markers of apoptotic cell death, were inhibited by CPF and
procyanidin B2. Intracellular
reactive oxygen species (ROS) accumulation was attenuated by pretreatment with CPF and
procyanidin B2. CPF and
procyanidin B2 also prevented HNE-induced
poly(ADP-ribose) polymerase cleavage, antiapoptotic
protein (Bcl-2 and Bcl-X(L)) down-regulation, and
caspase-3 activation. Activation of c-Jun N-terminal
protein kinase (JNK) and
mitogen-activated protein kinase kinase 4 (MKK4) was attenuated by CPF and
procyanidin B2. Moreover, CPF and
procyanidin B2 bound directly to MKK4 and inhibited its activity. Data obtained with
SP600125, a selective inhibitor of JNK, revealed that JNK is involved in HNE-induced apoptosis through the inhibition of PARP cleavage and
caspase-3 activation in PC12 cells. Collectively, these results indicate that CPF and
procyanidin B2 protect PC12 cells against HNE-induced apoptosis by blocking MKK4 activity as well as ROS accumulation.