Another theory on why levodopa becomes less effective over time ?
 

"The cause of Parkinson’s isn’t well understood, but the reason the drug wears off is. It’s because the brain also starts losing an enzyme known as aromatic L-amino acid decarboxylase, or AADC, that is needed to convert L-Dopa into dopamine."

https://www.technologyreview.com/s/6...-gene-therapy/

I've not heard this before, and I suspect it might be a technical writer's (mis)understanding, rather than the researcher's view.

However, the underlying premise seems sound to me, and they are getting some results. That is, as more neurons die, if you can boost (e.g. by gene therapy) the amount of AADC (the enzyme that catalyzes the conversion of levodopa to dopamine) in the brain, then this might boost the amount of dopamine produced by the remaining neurons.

Carbidopa does this with side effects, it would be nice to get AADC from Gene therapy combined with pure levodopa.

Carbidopa correction
 

Hercules957 said:

"Carbidopa does this . . ."

This is wrong, and I'll correct it for the record. You never know who reads this stuff, seeking to learn from what we write.

Carbidopa doesn't boost AADC, it inhibits AADC. Carbidopa can't cross the blood-brain barrier so it only inhibits AADC outside of the brain, allowing more levodopa to reach the brain.

Carbidopa has no role to play in the topic of this thread, since this thread is about things occurring on the brain side of the blood brain barrier, and Carbidopa can't get there to join the discussion. :-)

On the other hand, Carbidopa has everything to do with the current discussion on the Hinz thread, and I've posted something (hopefully) appropriate over there.