The Neuroprotective Effects of Uncaria Hirsute Haviland on Amyloid β Protein-induced Toxicity in Rat Cortical Neurons

Abstract

Amyloid β protein (Aβ) elicits a toxic effect on neurons in vitro and in vivo and has been proposed to play an important role in the pathogenesis of Alzheimer’s disease (AD). Previous studies have shown that aggregated Aβ can induce caspase-dependent apoptosis by oxidative stress in cultured neurons. Uncaria rhynchophylla (miq.) Jacks., a traditional Chinese herbal medicine, has been used in combination with other herbs for the treatment of cognitive disorders. The major components responsible for the neuroprotective effect remains unclear In the present study, 23 fractions (UR-EAs) and 24 subfractions (UR-EA-As and UR-EA-Bs) were isolated from the ethyl acetate extracts of Uncaria hirsuta Haviland, a Taiwanese Uncaria. Five fractions, UR-EA-8, -16, -17, -18 and -19, and 5 subfractions, UR-EA-A567, -B3, -B8, -B9 and -BlO, and a pure compound, catechin, purified from UR-EA-19, were identified as neuroprotective components. The neuroprotective mechanism of UR-EA-A567, -B3 and -B9 were studied. All three fractions reduced Aβ-induced cytochome c release and nucleus condensation suggesting that Aβ-induced apoptosis was inhibited by the fractions. Nevertheless, three fractions had distinct effects on the activity of caspases. UR-EA-A567 abrogated Aβ-induced activation of caspase 2, 3, and 8. UR-EA-B3 reduced Aβ-induced activation of caspase 2 and 3, and promoted Aβ-induced activation of caspase 9. In contrast, UR-EA-B9 enhanced the Af3-induced activation of caspase 2, 3, 8, and 9. These results indicate that these fractions affect different targets in the apoptotic pathway. Moreover, UR-EAB9 possessed antioxidant capacity, whereas UR-EA-A567 and -B3 lacked this activity, implying that antioxidative activity may not play a role to protect neurons against Aβ-mediated toxicity for UR-EA-A567 and -B3. However, three fractions were able to eliminate reactive oxygen species (ROS) induced by Af3. Moreover, antioxidants such as epigallocatechin and probucol facilitated the caspase-dependent neuroprotective effects of UR-EA-A567. These results indicate that ROS elimination is essential for neurorpotection. Our results demonstrate that the neuroprotective mechanisms of Uncaria hirsuta Haviland on Af3-induced toxicity is mediated by abrogating the activation of the caspase cascade. The inhibition of the caspase cascade in combination with antioxidative activity will further eliminate Aβ-mediated neurotoxicity.