Joop,
Dank U wel, Ik kan alleen een beetje Nederlands spreken.
First why are you surprised that substances like homocystine which damages the BBB, affects other illnesses besides PD? Most substances have one or more substantial effects on a particular illness, as well as lots of side effects on other illnesses.
For example, hypertension drugs which are normally used to lower blood pressure, also reduce the BBB permeabilty, and have been shown to be of value in PD.
Again, you say,
"Further heavy metals are known to interfere with the BBB. They are also associated with lots of neurological disorders."
This is what we would expect if the theory is correct. It goes for many other toxic compounds, like pesticides.
You say why does a PWP have a defective BBB? But why do some people have a defective heart, a defective lung , kidney etc. It is presumably the luck of the draw. Why are some people fair and others darK?
Normally with a healthy BBB, levodopa can pass, carbidopa can't.
This fits in with the fact that levodopa has the lower molecular weight. The solubility of the molecule is critical also. Low molecular weight molecules which are fat soluble can pass the BBB. The difference may be small, but carbidopa has a -NH-NH2 group that levodopa hasn't. This will make carbidopa more polar, less fat soluble, and less able to cross the BBB.
Hope this helps
Ron
PS THere is something we can do to put this theory to the test.
Take a group of PWP with ascending PD progression, and measure their BBB permeability (This can be done).
If the theory is correct, we should get a table where the newly diagnosed has the lowest BBB permeability, and the most advanced PWP has the highest.