Intrastriatal grafting of Cos cells stably expressing human aromatic L-amino acid decarboxylase: neurochemical effects.
To study the possibility that increasing striatal activity of aromatic L-amino acid decarboxylase (AADC; EC 4.1.1.28) can increase dopamine production in dopamine denervated striatum in response to L-3,4-dihydroxy-phenylalanine (L-DOPA) administration, we grafted Cos cells stably expressing the human AADC gene (Cos-haadc cells) into 6-hydroxydopamine denervated rat striatum. Before grafting, the catalytic activity of the enzyme was assessed in vitro via the generation of 14CO2 from L-[14C]DOPA. The Km value for L-DOPA in intact and disrupted cells was 0.60 and 0.56 mM, respectively. The cofactor, pyridoxal 5-phosphate, enhanced enzymatic activity with maximal effect at 0.1 mM. The pH optimum for enzyme activity was 6.8. Grafting Cos-haadc cells into denervated rat striatum enhanced striatal dopamine levels measured after systemic administration of L-DOPA. When measured 2 h after L-DOPA administration, the mean dopamine level in the striata of Cos-haadc-grafted animals was 2 micrograms/g of tissue, representing 31% of normal striatal dopamine concentration. The mean dopamine concentration in the striata grafted with untransfected Cos cells (Cos-ut cells) was 1 microgram/g. At 6-8 h after L-DOPA administration, striatal dopamine content in the Cos-haadc-grafted animals was 0.67 microgram/g of tissue weight, representing 9% of intact striatum dopamine content. By contrast, the average dopamine content in the Cos-ut-grafted animals was undetectable. These findings demonstrate that enhancing striatal AADC activity can improve dopamine bioformation in response to systemically administered L-DOPA.
Kaddis
F G
FG
Department of Medicine, University of Colorado School of Medicine, Denver 80262, USA.
Clarkson
E D
ED
Weber
M J
MJ
Vandenbergh
D J
DJ
Donovan
D M
DM
Mallet
J
J
Horellou
P
P
Uhl
G R
GR
Freed
C R
CR
D000818:Animals; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells / Q000201:enzymology / Q000637:transplantation*; D003714:Denervation; D004298:Dopamine / Q000096:biosynthesis; D015259:Dopamine Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006801:Humans; D007980:Levodopa / Q000493:pharmacokinetics / Q000494:pharmacology*; D017072:Neostriatum / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology; D016627:Oxidopamine; D051381:Rats; D017207:Rats, Sprague-Dawley; D013565:Sympatholytics; D014162:Transfection
D015259:Dopamine Agents; D013565:Sympatholytics; D007980:Levodopa; D016627:Oxidopamine; D001142:Aromatic-L-Amino-Acid Decarboxylases; D004298:Dopamine