Importance of membrane-bound catechol-O-methyltransferase in L-DOPA metabolism: a pharmacokinetic study in two types of Comt gene modified mice.
OBJECTIVE
Catechol-O-methyltransferase (COMT) metabolizes compounds containing catechol structures and has two forms: soluble (S-COMT) and membrane-bound (MB-COMT). Here we report the generation of a mouse line that expresses MB-COMT but not S-COMT. We compared the effects of deleting S-COMT only or both COMT forms on the pharmacokinetics of oral L-DOPA.


METHODS
L-DOPA (10 mg kg(-1)) and carbidopa (30 mg kg(-1)) were given to mice by gastric tube, and samples were taken at various times. HPLC was used to measure L-DOPA in plasma and tissue samples, and dopamine and its metabolites in brain. Immunohistochemistry and Western blotting were used to characterize the distribution of COMT protein isoforms.


RESULTS
Lack of S-COMT did not affect the levels of L-DOPA in plasma or peripheral tissues, whereas in the full COMT-knock-out mice, these levels were increased. The levels of 3-O-methyldopa were significantly decreased in the S-COMT-deficient mice. In the brain, L-DOPA levels were not significantly increased, and dopamine was increased only in females. The total COMT activity in the S-COMT-deficient mice was 22-47% of that in the wild-type mice. In peripheral tissues, female mice had lower COMT activity than the males.


CONCLUSIONS
In S-COMT-deficient mice, MB-COMT in the liver and the duodenum is able to O-methylate about one-half of exogenous L-DOPA. Sexual dimorphism and activity of the two COMT isoforms seems to be tissue specific and more prominent in peripheral tissues than in the brain.
Käenmäki
M
M
Division of Pharmacology and Toxicology, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland. mikko.kaenmaki@helsinki.fi
Tammimäki
A
A
Garcia-Horsman
J A
JA
Myöhänen
T
T
Schendzielorz
N
N
Karayiorgou
M
M
Gogos
J A
JA
Männistö
P T
PT
D000284:Administration, Oral; D000818:Animals; D000978:Antiparkinson Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D015153:Blotting, Western; D002230:Carbidopa / Q000494:pharmacology*; D002394:Catechol O-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007150:Immunohistochemistry; D007527:Isoenzymes; D007980:Levodopa / Q000493:pharmacokinetics*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D012737:Sex Factors; D013997:Time Factors
D000978:Antiparkinson Agents; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D007980:Levodopa; D002394:Catechol O-Methyltransferase; D002230:Carbidopa