L-Dopa And Pyridoxine by Trần Mạnh Ngô, M.D., Ph.D.
Further comments on the Role of L-Dopa and Pyridoxine in parkinsonism
by Lương Vinh Quốc Khanh, M.D., Ph.D.

L-Dopa And Pyridoxine: published in The Lancet (England), July 1 1972, 2 (2776), p45-6 by Ngo Tran
SIR,-I have read the letters of Dr. Evered (1) and Dr. Johnston (2) on L-dopa and pyridoxine with great interest. Although Dr. Evered’s important hypothesis suggested that a chemical reaction between L-dopa and pyridoxal 5’-phosphate might explain the clinically (3) and experimentally (4) observed antagonism between L-dopa and pyridoxine, the role of the tetrahydroisoquinolines possibly formed is still unknown.
The formation of L-dopa/pyridoxal-5’-phosphate complexes has been demonstrated by Clark et al.,(6) Evered,(1) and Fellman and Roth. (6) Using radioisotope techniques, Dr. Vogel and we (8-10) have found that large doses of pyridoxal 5’-phosphate inhibited both a nonenzymatic and enzymatic oxidation of dopa. The results obtained suggested that large doses of L-dopa and pyridoxine given to patients with Parkinson’s disease might
enhance the formation of L-dopa-pyridoxal 5’-phosphate complexes in the human body, which in turn could inhibit dopa-decarboxylase activity.(8-10) Perhaps a fall in dopamine
production due to the inhibition of dopa decarboxylation by pyridoxal 5’-phosphate may explain the antagonism of the activity of L-dopa by pyridoxine in the treatment of
parkinsonism. Also, this may explain the role of pyridoxine in the production of many beneficial effects (3,11,12) as well as side-effects (3,11) of L-dopa. A fall in plasma-L-dopa levels and in urinary excretion of L-dopa and dopamine was found in patients with parkinsonism who received both L-dopa and pyridoxine; unfortunately, no method is known for isolating these L-dopa-pyridoxal 5’ phosphate complexes from living tissues.
References:
1. Evered, D. F. Lancet, 1971, i, 914.
2. Johnston, G. A. R. ibid. 1971, ii, 220.
3. Boudin, G., Castaigne, P., Lhermitte, F., Beck, H., Guillard, A., Marteau, P., Pepin, B., Rondot, P., Raphy, B. Rev. neurol. 1970, 122, 80.
4. Lechat, P., Streichenberger, G., Boismare, F., Letteron, N. J. Pharmac. 1970, 1, 525.
5. Clark, C. T., Weissback, H., Udenfriend, S. J. biol. Chem. 1954, 210, 139.
6. Fellman, J. H., Roth, E. S. Biochemistry, 1971, 10, 408.
7. Vogel, W. H. Naturwissenschaften, 1969, 56, 462.
8. Tran, N., Laplante, M. Int. J. Biochem. (in the press).
9. Tran, N. J. Nucl. Med. 1972, 13, 349.
10. Tran, N. Un. med. Can. 1972, 101, 746.
11. Jameson, H. D. J. Am. med. Ass. 1970, 211, 1700.
12. Leon, A. S., Spiegel, H. E., Thomas, G., Abrams, W. B. ibid. 1971, 218, 1924.
Department of Nuclear Medicine and Radiobiology, Centre Hospitalier Universitaire,
Sherbrooke, Quebec, Canada.
NGO TRAN

Comments on the Role of L-Dopa and Vitamine B6 in Parkinsonism by Lương Vinh Quốc Khanh, M.D.,Ph.D.
Dear Dr. Ngo,
Thank you very much for your question regarding the role of L-Dopa & Vitamin B6 in Parkinsonism. As you know, I am not an expert in Parkinson Disease as well as in the Neurology field. However, I might add some information from medical literature after your excellent comment in Lancet (1).
There were many articles dealing with the role of vitamin B6. Unfortunately, These articles are in foreign languages. Interestingly, Sandyk and Pardeshi (2) reported a case of schizophrenic patient with severe neurologic-induced Parkinsonism and Tardive Dyskinesia in whom administration of vitamin B6 (100mg/day) resulted in dramatic and persistent attenuation of the movement disorders as well as reduction of psychotic behavior. However, Chen et al. (3) investigated whether higher intake of folate, vitamin B6, or vitamin B12 was related to a lower risk of Parkinson's diseases (248 men and 167 women). They found that higher intake of folate or related vitamin B did not lower the risk of parkinson's disease.
Sincerely,
Khanh v.q. Luong, M.D.
References:
1. Ngo Tran, M.D as noted.
2. Sandyk R and Pardeshi R. Pyridoxine improves drug-induced parkinsonsm and psychosis in a schizophrenic patient. Int J Neurosci. 1990; 52:225-232.
3. Chen et al. Folate intake and risk of Parkinson's disease. Am J Epidemiol. 2004;
160:368-375.

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