Andrographolide attenuates PM2.5-induced blood-brain barrier damage via antioxidant and PI3K/AKT/mTOR/NRF2 pathways

Fine particulate matter (PM2.5) may trigger ischemic cerebrovascular diseases, although the molecular mechanisms remain unclear. Andrographolide (AG), a Chinese herbal ingredient, exhibits anti-cancer, anti-inflammation, and anti-oxidation activities in many diseases. However, the efficacy of AG for treatment of cerebrovascular diseases remains unclear. This study evaluated the effects of PM2.5 on the blood-brain barrier (BBB) integrity and AG's efficacy, along with the underlying mechanisms. Cell viability, apoptosis, inflammatory responses, mitochondrial oxidative stress, and adenosine triphosphate levels, in addition to tight junction protein levels of brain microvascular endothelial cells (BMECs) were assessed following treatment with PM2.5, AG, and LY294002 (the PI3K inhibitor). Furthermore, the effects of AG on lung and brain tissue damage, systemic inflammation, BBB permeability, and ultrastructural changes were investigated in mice exposed to PM2.5. Results revealed that PM2.5 was cytotoxic to BMECs, and the mRNA sequencing suggested significant upregulation of the PI3K-AKT pathway. AG inhibited PM2.5-induced apoptosis and attenuated oxidative stress and inflammatory responses in BMECs. AG also ameliorated mitochondrial oxidative stress and barrier dysfunction by activation of the PI3K/AKT/mTOR and NRF2/HO-1 pathways. Moreover, molecular docking confirmed AG binding to the PI3K protein. In vivo experiments showed that AG alleviated PM2.5-induced lung and brain tissue damage and systemic inflammation, thereby improving disruption of the BBB and ultrastructural damage of vascular endothelial cells. These protective effects were reversed by LY294002. Overall, the protective effects of AG against PM2.5-induced BBB impairment were mainly associated with suppression of mitochondrial oxidative stress and activation of the PI3K/AKT/mTOR/NRF2 signaling.