The blood-brain barrier protects the brain from harmful substances in the blood, but it also protects the brain from potentially therapeutic chemicals that may reduce the size of brain tumors by killing cancer cells, alleviate depression, and aid in patient recovery from stroke or spinal cord injury. Two methods are currently being rigorously researched to get these helpful chemicals past the

Question

blood-brain barrier. The two methods are termed "molecular Trojan Horse" and osmotic "blood-brain barrier disruption." Based on their names, hypothesize how these methods might allow chemicals to pass through the blood-brain barrier.

What will be an ideal response?

Answer 1

(Note to instructor: You may have to explain enough of the legend of the Trojan Horse for this to be a fair question.)
The molecular Trojan Horse method delivers specific substances to the brain by attaching them to a protein that is
normally able to cross the barrier. The therapeutic chemicals are ferried across by piggybacking a substance that can
cross the barrier. Once across the barrier, these substances can reach almost every neuron through the blood vessels
that nourish the brain.
The blood-brain barrier disruption method is a technique that uses a concentrated mannitol (sugar) solution.
Because this solution is more concentrated than the endothelial cells of the capillaries that make up the blood-brain
barrier, these cells will experience shrinkage (Chapter 5, hypertonicity). When these cells decrease in volume the
tight junctions that exist between them are temporarily opened and chemicals in that area can pass through the
blood-brain barrier. In actual patients who experimentally undergo this therapy, an infusion of this solution, via a
catheter, temporarily opens the tight junction by osmotically disrupting the endothelial cells that make up the
blood-brain barrier. Immediately after the mannitol solution, the patients receive the chemotherapy treatment
intra-arterially through the same catheter.