Isoamericanin A ameliorates neuronal damage and alleviates vascular cognitive impairments by inhibiting oxidative stress through activation of the Nrf2 pathway.

Oxidative stress is critically involved in the cognitive dysfunction and neuronal progressive degeneration in the vascular cognitive impairment (VCI). The natural lignan molecular isoamericanin A (ISOA) containing multiple hydroxyl groups has great potential for suppressing oxidative stress in VCI. The primary objective of this study was to delve into the pharmacological properties of ISOA against VCI, as well as to elucidate the mechanisms driving this effect from the perspective of antioxidative stress. Transient bilateral common carotid arteries occlusion (tBCCAO) mice model and hydrogen peroxide (H₂O₂) treated N2a cells were employed in vivo and in vitro, respectively. Behavioral tests showed that ISOA (5, 10 mg/kg) treatment alleviated learning, memorizing, and recognition in tBCCAO model mice. ISOA alleviated the neuronal damages by increasing the number of NeuN-positive cells, decreasing the TUNEL-positive cells density, up-regulating MAP-2 expression, lighting the damage of neuronal nucleus and synapse. Mechanistically, we found that ISOA reduced the oxidative stress in neurons, which manifested by reduction on the expressions of superoxide, H₂O₂, intercellular reactive oxygen species (ROS) and malondialdehyde (MDA) level, and up-regulations on the expressions of anti-oxidant enzymes superoxide dismutase, heme oxygenase-1, glutathione peroxidase 4, glutathione, and NAD(P)H: quinone oxidoreductase 1. Further investigation showed that ISOA activated nuclear factor erythroid 2-related factor 2 (Nrf2) pathway by downregulating the expression of kelch-like ECH-associated protein 1, upregulating the nuclear translocation and expression of Nrf2, and augmenting antioxidant response elements (ARE) promotor activity. The ISOA-mediated promotion on ARE promotor activity and anti-oxidant enzymes expressions, and suppression on superoxide and ROS expressions and MDA levels were weakened by pharmacological inhibition or genetic knockdown of Nrf2. These effects were enhanced after knockdown Keap1 in H₂O₂-treated cells. Our study demonstrates that ISOA alleviates the cognitive impairments and neuronal loss in VCI by attenuating oxidative stress through promoting the activation of Nrf2 pathway.