Fig. 4
From: Parkinson’s disease and gut microbiota: from clinical to mechanistic and therapeutic studies
Effect of intestinal microbes on the metabolic pathway of levodopa. After oral administration, L-dopa enters the circulation through active transport in the intestine and crosses the blood–brain barrier into the brain, where it exerts anti-Parkinson’s disease effects by restoring striatal dopaminergic neurotransmission. However, only a small fraction of the drug eventually reaches the brain due to interference by various factors. Studies have revealed that tyrDC from Enterococcus faecalis can convert L-dopa to dopamine in the intestine and affect its absorption. a Elevated E. feacalis and tyrDC levels enable more L-dopa to be metabolized to dopamine in the intestine, resulting in impaired L-dopa absorption. b Conversely, a decrease in tyrDC allows more L-dopa to be absorbed and utilized. In addition, the small molecule inhibitor (S)-α-fluoromethyltyrosine (AFMT) can suppress tyrDC, thereby increasing the bioavailability of L-dopa