Why We Can’t Deliver Drugs to the Brain

This is Elise. She suffers from a brain tumor,
which causes blurred vision and confusion. But when doctors try and treat brain cancers
and other disorders, the brain blocks roughly 95% of medicine taken orally or intravenously. That’s a problem! So what is going on inside
your brain? And why is it just ignoring medicine? In your body, you have (on average) 5 litres
of blood that travels through 96,000 kilometres of blood vessels every day and it’s full
of different types of cells, nutrients, hormones, and gases. In their journey, they travel to your brain
and come face to face with the Blood Brain Barrier. It’s what’s stopping that 95%
of medicine getting in – it’s tough! It controls what is and what is not allowed
to leave your blood supply and enter your brain. The Blood Brain Barrier is made up of endothelial
cells and other specialised cells. The endothelial cells form tight junctions, like small gates,
between each other to restrict the transport of substances that can pass through. The barrier needs to recognize the substance
before letting it in. Luckily, iron and nutrients like glucose have
a way of getting through. They’re both recognized by specialized proteins on the surface of
the cells. When glucose or iron bind to these proteins,
they get shuttled through the gatekeeper cells and into the brain. But when the majority of medicines try to
get through, they get rejected! The gatekeeper cells treat them like blood-borne
pathogens or toxins. It’s like a paradox of our biology: The
blood brain barrier protects your brain from harm, but it’s also keeps out medicine when
people need it the most. And this is where the scientists step in – to
try and sneak medicine into your brain. One way is to disguise medicine as substances
the barrier does let through. Some scientists package medicine in nanoparticles
coated in proteins that look similar to the iron-carrying protein; in the hope it’ll
“trick” the gatekeeper cells to bind with it and let the nanoparticle into the brain,
just like they let in iron. Similarly, other scientists engineer harmless
viruses, hijacking their natural ability to enter cells. And they work as delivery vehicles
to transport medicine across the barrier. And more scientists are trying to push through
the barrier, by using magnetic nanoparticles to heat up and open the gate. Or, tiny bubbles to force it open. Seeing if these tiny bubbles can help deliver
a chemotherapy drug across the barrier is being tested right now to treat brain tumors. And as scientists continue to come up with
clever ways of getting medicine into the brain, there will be many more trials to come. Elise
and other patients suffering from brain disorders will hopefully have better treatment options
to choose from. And that’s what I would call a breakthrough!


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