Effects of nitric oxide on blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats

Release of Matrix Metalloproteinases-2 and 9 by S-Nitrosylated Caveolin-1 Contributes to Degradation of Extracellular Matrix in tPA-Treated Hypoxic Endothelial Cells

Intracranial hemorrhage remains the most feared complication in tissue plasminogen activator (tPA) thrombolysis for ischemic stroke. However, the underlying molecular mechanisms are still poorly elucidated. In this study, we reported an important role of caveolin-1 (Cav-1) s-nitrosylation in matrix metalloproteinase (MMP)-2 and 9 secretion from tPA-treated ischemic endothelial cells. Brain vascular endothelial cells (bEND3) were exposed to oxygen-glucose deprivation (OGD) for 2 h before adding recombinant human tPA for 6 h. This treatment induced a significant increase of MMP2 and 9 in the media of bEND3 cells and a simultaneous degradation of fibronectin and laminin β-1, the two main components of extracellular matrix (ECM). Inhibition of MMP2 and 9 with SB-3CT completely blocked the degradation of fibronectin and laminin β-1. ODG+tPA treatment led to Cav-1 shedding from bEND3 cells into the media. Notably, OGD triggered nitric oxide (NO) production and S-nitrosylationof Cav-1 (SNCav-1). Meanwhile tPA induced activation of ERK signal pathway and stimulates the secretion of SNCav-1. Pretreatment of bEND3 cells with C-PTIO (a NO scavenger) or U0126 (a specific ERK inhibitor) significantly reduced OGD-induced S-nitrosylation of Cav-1 in cells and blocked the secretion of Cav-1 and MMP2 and 9 into the media as well as the degradation of fibronectin and laminin β-1 in OGD and tPA-treated cells. These data indicate that OGD-triggered Cav-1 S-nitrosylation interacts with tPA-induced ERK activation to augment MMP2 and 9 secretion and subsequent ECM degradation, which may account for the exacerbation of ischemic blood brain barrier damage following tPA thrombolysis for ischemic stroke.

Modulation of Hyperosmotic and Immune-Induced Disruption of the Blood-Brain Barrier by the Nitric Oxide System

OBJECTIVES

The role of nitric oxide (NO) in modulating the blood-brain barrier (BBB) is not entirely clear. We examined the effect of different NO synthase (NOS) inhibitors and NO donors on the permeability of the BBB in animals with normally functioning brain blood vessels, following disruption by hyperosmotic mannitol and during immune inflammation.

METHODS

We administered L-NAME, aminoguanidine, S-methyl-thiocitrulline (SMT) and 7-indazole (NOS inhibitors) and NOR-4 (an NO donor) into the cerebral ventricle of rats. Disruption of the BBB was induced by intracarotid injection of mannitol (25%). Experimental autoimmune encephalomyelitis (EAE) was induced by brain homogenate. The extent of disruption was evaluated by Evans blue (2%) dye extravasation.

RESULTS

L-NAME (a nonspecific NOS inhibitor) and SMT (a neuronal and endothelial NOS inhibitor) increased mannitol-induced disruption of BBB. This effect was inhibited by NO donors. In animals with a normally functioning BBB, none of these inhibitors or NO donors caused a change in the permeability. 7-indazole (a specific neuronal NOS inhibitor) and aminoguanidine (an inducible NOS inhibitor) had no facilitatory effect on BBB permeability, either alone or in combination with hyperosmotic mannitol. Administration of L-NAME and SMT to rats with EAE significantly aggravated the clinical outcome. In contrast, the administration of NOR-4 diminished clinical signs of EAE.

CONCLUSION

The NOS system does not play a role in BBB permeability in naïve animals. Only endothelial NOS takes part in the facilitation of BBB compromised by mannitol and EAE. Extrinsic NO decreases this facilitatory effect.

Osmotic opening of the blood-brain barrier: principles, mechanism, and therapeutic applications

1. Osmotic opening of the blood-brain barrier by intracarotid infusion of a hypertonic arabinose or mannitol solution is mediated by vasodilatation and shrinkage of cerebrovascular endothelial cells, with widening of the interendothelial tight junctions to an estimated radius of 200 A. The effect may be facilitated by calcium-mediated contraction of the endothelial cytoskeleton. 2. The marked increase in apparent blood-brain barrier permeability to intravascular substances (10-fold for small molecules) following the osmotic procedure is due to both increased diffusion and bulk fluid flow across the tight junctions. The permeability effect is largely reversed within 10 min. 3. In experimental animals, the osmotic method has been used to grant wide access to the brain of water-soluble drugs, peptides, antibodies, boron compounds for neutron capture therapy, and viral vectors for gene therapy. The method also has been used together with anticancer drugs to treat patients with metastatic or primary brain tumors, with some success and minimal morbidity.