Selective dopaminergic neurotoxicity of isoquinoline derivatives related to Parkinson's disease: studies using heterologous expression systems of the dopamine transporter.
Endogenous isoquinoline (IQ) derivatives structurally related to the selective dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenylpyridine (MPP(+)) may contribute to dopaminergic neurodegeneration in Parkinson's disease. We addressed the importance of the DAT molecule for selective dopaminergic toxicity by testing the differential cytotoxicity of 22 neutral and quaternary compounds from three classes of isoquinoline derivatives (3, IQs; 4,3,4-dihydroisoquinolines and 15, 1,2,3,4-tetrahydroisoquinolines) as well as MPP(+) in non-neuronal and neuronal heterologous expression systems of the DAT gene (human embryonic kidney HEK-293 and mouse neuroblastoma Neuro-2A cells, respectively). Cell death was estimated using the MTT assay and the Trypan blue exclusion method. Nine isoquinolines and MPP(+) showed general cytotoxicity in both parental cell lines after 72hr with half-maximal toxic concentrations (TC(50) values) in the micromolar range. The rank order of toxic potency was: papaverine>salsolinol=tetrahydropapaveroline=1-benzyl-TIQ=norsalsolinol>tetrahydropapaverine>2[N]-methyl-salsolinol>2[N]-methyl-norsalsolinol>2[N]-Me-IQ(+)=MPP(+). Besides MPP(+), only the 2[N]-methylated compounds 2[N]-methyl-IQ(+), 2[N]-methyl-norsalsolinol and 2[N]-methyl-salsolinol showed enhanced cytotoxicity in both DAT expressing cell lines with 2- to 14-fold reduction of TC(50) values compared to parental cell lines. The rank order of selectivity in both cell systems was: MPP(+)>>2[N]-Me-IQ(+)>2[N]-methyl-norsalsolinol=2[N]-methyl-salsolinol. Our results suggest that 2[N]-methylated isoquinoline derivatives structurally related to MPTP/MPP(+) are selectively toxic to dopaminergic cells via uptake by the DAT, and therefore may play a role in the pathogenesis of Parkinson's disease.
Storch
Alexander
A
Department of Neurology, University of Ulm Medical School, Oberer Eselsberg 45, 89081, Ulm, Germany. alexander.storch@medizin.uni-ulm.de
Ott
Stefanie
S
Hwang
Yu I
YI
Ortmann
Rainer
R
Hein
Andreas
A
Frenzel
Stefan
S
Matsubara
Kazuo
K
Ohta
Shigeru
S
Wolf
Hans Uwe
HU
Schwarz
Johannes
J
D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D050483:Dopamine Plasma Membrane Transport Proteins; D015870:Gene Expression; D006801:Humans; D007546:Isoquinolines / Q000009:adverse effects* / Q000737:chemistry / Q000494:pharmacology; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D009419:Nerve Tissue Proteins; D020258:Neurotoxicity Syndromes / Q000209:etiology*; D009498:Neurotoxins / Q000009:adverse effects* / Q000494:pharmacology; D010300:Parkinson Disease / Q000209:etiology*; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism; D044005:Tetrahydroisoquinolines; D014162:Transfection; D014407:Tumor Cells, Cultured
D050483:Dopamine Plasma Membrane Transport Proteins; D007546:Isoquinolines; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; D011954:Receptors, Dopamine; C493214:SLC6A3 protein, human; C493215:Slc6a3 protein, mouse; D044005:Tetrahydroisoquinolines; C014843:1,2,3,4-tetrahydroisoquinoline; C039109:isoquinoline