The Bradykinin B2 Receptor Agonist NG291 Causes Rapid, Transient Blood‐Brain Barrier Disruption Without Evidence of Persistent Brain Injury: Implications for Drug Delivery to the Brain.

Abstract

The blood brain barrier (BBB) is a term used to describe the highly specialized capillaries of the brain which forms a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, through its barrier functions which prevent entry of potentially harmful circulating molecules into the brain. However, the barrier activities of the BBB are also an obstacle to the delivery of therapeutics to the brain. One strategy to facilitate the delivery of therapeutics into the brain is to transiently induce BBB disruption. Bradykinins are one class of molecule produced endogenously and contribute to transient BBB disruption through agonist activity on the bradykinin B2 receptor (B2R).Unfortunately, the endogenous peptide bradykinin is of little therapeutic value because of its short half‐life and because it also activates the bradykinin B1 receptor that generates an exaggerated inflammatory response. We have been studying NG291, a physiologically stable bradykinin analogue that has selective agonist activity on B2R, and its ability to disrupt the BBB. Sprague Dawley (SD) rats and CD‐1 mice were subjected to NG291 treatment (either 50μg/Kg or 100μg/Kg, IV). BBB disruption was measured by Evans blue extravasation in SD rats in a time and dose dependent fashion. Disruption was evaluated in mice using the large and small sized radioactive tracers 99mTc‐Albumin (66.5KDa) and 14C‐Sucrose (340Da), respectively. We evaluated the potential harm of NG291 administration in rats via changes in brain water content and detection of cellular death via Fluoro‐Jade C staining. Evans blue studies in rats confirmed that NG291 is disrupting the BBB in a time and dose dependent fashion with the BBB regaining function 2hr after 50μg/Kg and 4hr after 100μg/Kg of NG291 administration. In mice, both albumin and sucrose tissue/serum ratio were significantly increased within 15 minutes of NG291 injection vs vehicle controls. We have observed no increased cell death nor change in water content in groups treated with NG291 when compared to saline injected controls. We conclude that NG291 has the potential to acutely disrupt the BBB, generating a window where potential CNS therapies can be more effectively delivered to the brain. This has the potential to speed up drug development process, increase the number of CNS therapies that reach the market, and help those in dire need of such treatments.