NAD replenishment with nicotinamide mononucleotide protects blood-brain barrier integrity and attenuates delayed tissue plasminogen activator-induced haemorrhagic transformation after cerebral ischaemia.

Abstract

Tissue plasminogen activator (tPA) is the only approved pharmacological therapy for acute brain ischaemia; however, a major limitation of tPA is the haemorrhagic transformation that follows tPA treatment. Here, we determined whether nicotinamide mononucleotide (NMN), a key intermediate of nicotinamide adenine dinucleotide biosynthesis, affects tPA-induced haemorrhagic transformation. Middle cerebral artery occlusion (MCAO) was achieved in CD1 mice by introducing a filament to the left MCA for 5h. When the filament was removed for reperfusion, tPA was infused via the tail vein. A single dose of NMN was injected i.p. (300mg·kg-1 ). Mice were killed at 24h post ischaemia, and their brains were evaluated for brain infarction, oedema, haemoglobin content, apoptosis, neuroinflammation, blood-brain barrier (BBB) permeability, the expression of tight junction proteins (TJPs) and the activity/expression of MMPs. In the mice infused with tPA at 5h post ischaemia, there were significant increases in mortality, brain infarction, brain oedema, brain haemoglobin level, neural apoptosis, Iba-1 staining (microglia activation) and myeloperoxidase staining (neutrophil infiltration). All these tPA-induced alterations were significantly prevented by NMN administration. Mechanistically, the delayed tPA treatment increased BBB permeability by down-regulating TJPs, including claudin-1, occludin and zonula occludens-1, and enhancing the activities and protein expression of MMP9 and MMP2. Similarly, NMN administration partly blocked these tPA-induced molecular changes. Our results demonstrate that NMN ameliorates tPA-induced haemorrhagic transformation in brain ischaemia by maintaining the integrity of the BBB.