Totally agree about the phenylalanine, I also supplement some n-acetyl-tyrosine. Elevated cAMP seems to cause DA to be synthesized very quickly from nat, I actually feel a bit of a body buzz sometimes. Slightly worried about the buildup of dopamine metabolites over the long term. I also take rhodiola so that combined with the COMT inhibition of quercetin should mitigate this to some degree. Any idea if you can build up too much l-DOPA this way? My understanding is that tyrosine hydroxylase is always the rate limiting enzyme, so it shouldn't be an issue?
The mechanisms of L-DOPA supplementation leading to toxicity in Parkinsons patients is a bit of a mystery, especially since the ongoing Parkinsons neuropathology complicates investigating it a bit. The theory that L-DOPA is responsible for accelerated neurodegeneration
is even somewhat controversial. Dopamine converted by MAO-B to DOPAL and the inability to clear the DOPAL is
suggested to be the cause of the
Parkinsons pathology which is why MAOB inhibitors are regularly prescribed for Parkinsons issues, but this is not the confirmed mechanism of action for L-DOPA toxicity. L-DOPA makes up for the
inhibition of tyrosine hydroxylase caused by Parkinsons pathology.
L-DOPA converts directly into dopamine via
DOPA decarboxylase in the
presence of vitamin B6. So far so good. From here there are two ways the dopamine degrades, via COMT and MAOB.
Does a COMT inhibitor make the L-DOPA problem worse?
This study says "meh":
http://www.ncbi.nlm....ubmed/19058133/Dyskinesia was observed in 11 (5.3%) subjects in the LCE group and 16 (7.4%) in the LC group (P = 0.367).
...
LCE provided greater symptomatic benefit than LC and did not increase motor complications.
Does A MAOB inhibitor make things worse?
This study says yes..sort of... Some symptoms got worse, others got better.
http://www.ncbi.nlm....pubmed/12112107Levodopa-treated Parkinson's disease patients who had been treated with deprenyl for up to 7 years, compared with patients who were changed to a placebo after about 5 years, experienced slower motor decline and were more likely to develop dyskinesias but less likely to develop freezing of gait.
So by upregulating tyrosine hydroxylase are we creating too much L-DOPA? How much is that enzyme being upregulated? If so, could it possibly metabolize enough tyrosine into L-DOPA to cause problems? I don't know. I don't think
upregulating tyrosine hydroxylase via cAMP has never been tried as a treatment for Parkinsons because nobody in the traditional scientific community has even looked at it
since 1984. The army looked at it a while back
according to Wikipedia and got promising results.
What about studies on healthy rats given L-DOPA? This would get all the confusion caused by the on-going Parkinson's pathology in most L-DOPA studies out of the way.
http://www.ncbi.nlm..../pubmed/8479601L-dopa, the major treatment for Parkinson's disease (PD), depletes S-adenosyl-L-methionine (SAM). Since SAM causes PD-like symptoms in rodents, the decreased efficacy of chronic L-dopa administered to PD patients may result from a rebound increase in SAM via methionine adenosyl transferase (MAT), which produces SAM from methionine and ATP. This was tested by administering intraperitoneally saline, or L-dopa to mice and assaying for brain MAT activity. As compared to controls, L-dopa (100 mg/kg) treatments of 1 and 2 times per day for 4 days did not significantly increase MAT activity. However, treatments of 3 times per day for 4 and 8 days did significantly increase the activity of MAT by 21.38% and 28.37%, respectively. These results show that short interval, chronic L-dopa treatments significantly increases MAT activity, which increases the production of SAM. SAM may physiologically antagonize the effects of L-dopa and biochemically decrease the concentrations of L-dopa and dopamine. Thus, an increase in MAT may be related to the decreased efficacy of chronic L-dopa therapy in PD.
So the theory is that L-DOPA depletes SAM(S-adenosyl-L-methionine) which causes MAT to upregulate which causes more SAM which causes decreased concentrations of L-Dopa and Dopamine. Thereby losing its effectiveness in Parkinsons disease.
Then there's the other theory that it
downregulates DAT, but only in rats first injected with a parkinsons causing neurotoxin, so again the confound of the Parkinsons pathology.
And then there's this study.
http://www.ncbi.nlm..../pubmed/6147392Nigrostriatal dopaminergic neurons remain undamaged in rats given high doses of L-DOPA and carbidopa chronically.
Perry TL, Yong VW, Ito M, Foulks JG, Wall RA, Godin DV, Clavier RM.
Abstract
Rats were fed maximally tolerated doses of L-3,4-Dihydroxyphenylalanine (L-DOPA) and carbidopa daily for 120 days in order to achieve a sustained elevation in brain dopamine levels. Some animals were also given buthionine sulfoximine, a gamma-glutamylcysteine synthetase inhibitor, in an unsuccessful effort to reduce brain glutathione contents. L-DOPA- and carbidopa-treated animals displayed no behavioral changes suggestive of nigrostriatal dopaminergic neuronal loss. When sacrificed 60 days after L-DOPA treatment ended, all rats had normal tyrosine hydroxylase activities and dopamine contents in their striata, and cell counts were normal in the substantia nigra. It therefore seems unlikely that a model of Parkinson's disease, suitable for exploring the etiological importance of glutathione deficiency, can be produced in rats merely by administering the largest tolerable doses of L-DOPA.
Another study says that the
L-DOPA itself causes apoptosis to cell cultures and says that it doesn't show up in vivio because apoptotic neurons are rapidly disposed of. Still, it's a culture study and not in vivio and the in vivio study said it did not cause any measurable signs of neurodegeneration.
Given all this confusion and controversy, I'm going to stick to L-Phenylalanine supplementation because that isn't converted directly to L-DOPA by Tyrosine Hydroxylase and there's a rate limiting enzyme that limits its rate of conversion to Tyrosine:
Phenylalanine hydroxylase.
Here's one more interesting study:
http://www.ncbi.nlm....pubmed/22583428CNS Neurol Disord Drug Targets. 2012 Jun 1;11(4):450-5.
Current status of tyrosine hydroxylase in management of Parkinson's disease.
Feve AP.
Source
Neurology Department, Parkinson Unit, Leopold Bellan Hospital, 19-21 rue Vercingetorix, 75014 Paris, France. afeve@aol.com.
Abstract
Tyrosine hydroxylase (TH) is the rate limiting enzyme responsible for converting tyrosine to L-DOPA in the dopamine synthesis pathway. The pathophysiology of Parkinson's disease (PD) is largely due to the nigrostriatal dopaminergic system, with a decrease in TH activity, TH synthesis and TH mRNA in the striatum of PD and animal experimental models. TH is thus one of the main targets for gene therapy in PD. TH activity variations during L-DOPA and new antiparkinsonian treatments have been extensively studied. Pharmacological trials with neuroprotective treatments could modify these variations, suggesting a direct involvement of TH cells in the neurodegenerative process. α- Synuclein, the main component of Lewy bodies regulates the production of dopamine through its interaction with TH. Over-expression of α-synuclein reduces the levels of TH mRNA and protein in the brain and in this way links the histological description of PD and its pathological biochemistry.
This study says that the cause of parkinsons is due to a decrease in Tyrosine Hydroxylase activity. Interesting... I wonder if this stack would help someone with Parkinsons?
Edited by abelard lindsay, 12 August 2012 - 07:49 AM.