title: Catechol-O-methyltransferase inhibition protects against 3,4-dihydroxyphenylalanine (DOPA) toxicity in primary mesencephalic cultures: new insights into levodopa toxicity.
abstract: Inhibition of catechol-O-methyltransferase (COMT) has protective effects on levodopa (L-DOPA), but not D-DOPA toxicity towards dopamine (DA) neurons in rat primary mesencephalic cultures [Mol. Pharmacol. 57 (2000) 589]. Here, we extend our recent studies to elucidate the mechanisms of these protective effects. Thus, we investigated the effects of all main L-DOPA/DA metabolites on survival of tyrosine hydroxylase immunoreactive (THir) neurons in primary rat mesencephalic cultures. 3-O-Methyldopa, homovanillic acid, dihydroxyphenyl acetate and 3-methoxytyramine had no effects at concentrations up to 300 micro M after 24h, whereas DA was more toxic than L-DOPA with toxicity at concentrations of >or=1 micro M. The coenzyme of COMT, S-adenosyl-L-methionine (SAM), and its demethylated product S-adenosylhomocystein caused no relevant alteration of THir neuron survival or L-DOPA toxicity. In contrast, inhibition of SAM synthesis by selenomethionine showed time- and dose-dependent increase of THir neuron survival, but did not affect L-DOPA toxicity. L-DOPA-induced lipid peroxidation in mesencephalic cultures was not modified by the COMT inhibitor Ro 41-0960 (1 micro M). Increased contamination of the cultures with glial cells attenuated L- and D-DOPA toxicity, but caused significant enhancement of protection by COMT inhibitors against L-DOPA toxicity only. Investigations of L-DOPA uptake in rat striatal cultures using HPLC revealed a significant reduction of extracellular L-DOPA concentrations by Ro 41-0960. Our data confirm that L-DOPA toxicity towards DA neurons is mediated by an autooxidative process, which is attenuated by glial cells. In addition, we demonstrate a second mechanism of L-DOPA toxicity in vitro mediated by a COMT- and glia-dependent pathway, which is blocked by COMT inhibitors, most likely due to enhanced glial uptake of L-DOPA.
authors.affiliation: Department of Neurology, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Blessing
authors.forename: Markus
authors.initials: M
authors.lastname: Bareiss
authors.forename: Heinz
authors.initials: H
authors.lastname: Zettlmeisl
authors.forename: Johannes
authors.initials: J
authors.lastname: Schwarz
authors.forename: Alexander
authors.initials: A
authors.lastname: Storch
mesh_terms: D000818:Animals; D001577:Benzophenones / Q000494:pharmacology; D065098:Catechol O-Methyltransferase Inhibitors; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000378:metabolism; D015259:Dopamine Agents / Q000378:metabolism / Q000633:toxicity*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D007980:Levodopa / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000633:toxicity*; D015227:Lipid Peroxidation / Q000187:drug effects; D008636:Mesencephalon / Q000166:cytology* / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000201:enzymology; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D012436:S-Adenosylmethionine / Q000494:pharmacology; D012645:Selenomethionine / Q000494:pharmacology; D013237:Stereoisomerism
chemical_list: D001577:Benzophenones; D065098:Catechol O-Methyltransferase Inhibitors; D015259:Dopamine Agents; D004791:Enzyme Inhibitors; C071721:Ro 41-0960; D007980:Levodopa; D012436:S-Adenosylmethionine; D012645:Selenomethionine; D004298:Dopamine