Autophagy is involved in the neuroprotective effect of nicotiflorin

Nicotiflorin is a flavonoid glycoside derived from the traditional Chinese medicine FlosCarthami, dried petals of Carthamus tinctorius L., and has been confirmed to be a promising novel drug candidate for ischemic stroke. Yet, the exact role of nicotiflorin in cerebral I/R injury is uncharacterized and the possible mechanisms have not been clearly expounded.

The present study was designed to determine the effect of nicotiflorin on cerebral ischemia/reperfusion (I/R) injury and its relationship with autophagy.

Middle cerebral artery occlusion (MCAO) in rats and oxygen-glucose deprivation and reintroduction (OGD/R) in SH-SY5Y cells were established in in vivo and in vitro models, respectively. The severity of MCAO was assessed by brain infarct size, neurological scores and survival rate. The severity of OGD/R was evaluated by cell viability, lactate dehydrogenase (LDH) release and cell apoptosis. The level of autophagy was evaluated both in vivo and in vitro. Autophagosomes were observed using transmission electron microscopy and autophagic flux was measured using mRFP-GFP-tandem fluorescent LC3 adenovirus. Autophagy-related proteins (LC3-II/I, SQSTM1, beclin-1, Phospho-mTOR/mTOR) were measured by immunoblot. Autophagy-related mRNA levels (Becn1, Atg7) were detected by Real-Time PCR. Inhibition of autophagy was implemented by 3-Methyladenine (3-MA) or chloroquine in vitro.

In vivo, nicotiflorin treatment alleviated brain damage and neurological deficit while it dramatically increased 72 h survival rate in rats. In vitro, nicotiflorin treatment also ameliorated the severity of OGD/R. Moreover, nicotiflorin treatment increased ischemic penumbra autophagy (autophagosomes, BECN1, LC3-II/I ratio, SQSTM1, Phospho-mTOR/mTOR, Atg7). In vitro, nicotiflorin likewise enhanced autophagy and promoted autophagy flux. Furthermore, the blockade of autophagy by 3-MA or chloroquine disabled the efficacic of nicotiflorin in preventing cell damage upon OGD/R insult.

These findings suggest that autophagy plays a significant role in the protective effect of nicotiflorin against ischemic stroke.