Blodhjernebarieren

Blodhjernebarrieren, or the blood-brain barrier (BBB), is a selective border that separates circulating blood from the brain extracellular fluid. It protects neural tissue from toxins and pathogens while regulating the transport of essential nutrients, ions, and other molecules necessary for brain function.

The barrier is formed by brain microvascular endothelial cells connected by tight junctions and supported by a neurovascular unit that includes pericytes, the basement membrane, and astrocyte endfeet. This structure creates a highly regulated interface that limits the passage of large molecules and plasma proteins, helping maintain CNS homeostasis and stable neural activity.

Transport across the BBB is tightly controlled. Small lipophilic molecules can diffuse passively, while essential nutrients such as glucose use specific transporters (e.g., GLUT1). Large or charged molecules may require receptor-mediated or adsorptive transcytosis. Active efflux transporters, such as P-glycoprotein, remove certain xenobiotics from the brain. The balance of selective permeability and protective barriers is crucial for normal brain function but also poses challenges for drug delivery.

BBB disruption occurs in various conditions, including stroke, traumatic brain injury, infection, and neurodegenerative diseases, potentially leading to edema and immune cell infiltration. Conversely, an intact barrier can impede the delivery of therapeutic agents to the CNS, influencing treatment strategies.

In research and clinical contexts, approaches to overcome the BBB include designing small, lipophilic drugs, exploiting endogenous transport systems, nanoparticle carriers, and techniques such as focused ultrasound to transiently increase permeability. Intranasal or intrathecal administration is also explored for targeting the CNS while aiming to minimize systemic exposure.