There are three primary sorts of barriers of the BBB, the vascular brain barrier, blood-CSF barrier, and the specialty CNS barriers such as the blood-retinal barrier. They transport molecules in by pores, the opening of tight junctions and receptors. (1) One can also bypass the BBB by going through the nose or injecting directly into the cerebral spinal fluid. This even works for larger molecules like peptides and other proteins.(1) Injecting insulin through the nose has been helpful for Alzheimer’s for instance. And they injected stem cells into the middle turbinate of my nose as one form of administration. It was weird but topical lidocaine prevented pain.
However researchers also found that mannose IV infusions open pores in the BBB and increase enzyme passage 10 fold (2). In fact mannose infusion has become a standalone therapy as well as a way of getting drugs to the brain.
StemGenex, the center that performed my stem cell administration, started using mannose infusions long before they started using intranasal injection. It increased the success for neurological conditions. Their mannose solution increases the diameter of pores for 20 minutes, so it is immediately followed by injected and IV stem cell administration.
If you are academically inclined, the following articles give the science behind getting through the BBB. Our understanding of the BBB is growing every day.