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In Vitro Reactivation of Rat Cortical Tryptophan Hydroxylase Following In Vivo Inactivation by Methylenedioxymethamphetamine
Author(s) -
Stone Donna M.,
Hanson Glen R.,
Gibb James W.
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb07372.x
Subject(s) - dithiothreitol , tryptophan hydroxylase , in vivo , enzyme , tryptophan , chemistry , methamphetamine , cycloheximide , biochemistry , mdma , tyrosine hydroxylase , monoamine oxidase , tranylcypromine , enzyme assay , serotonin , pharmacology , biology , receptor , amino acid , protein biosynthesis , microbiology and biotechnology , serotonergic
The activity of tryptophan hydroxylase (EC 1.14.16.4) from rat brain was significantly decreased 1 h following a single systemic injection of 3,4‐methylenedioxy‐methamphetamine (MDMA) when assessed ex vivo by ra‐dioenzymatic assay or in vivo by the quantitation of 5‐hy‐droxytryptophan accumulation following central L‐aromatic amino acid decarboxylase inhibition. Recovery of enzymatic activity in vivo, which occurred within 24 h of low‐dose MDMA treatment, appeared not to involve synthesis of new enzyme protein, because the return of enzymatic activity was not prevented by prior cycloheximide. Acutely MDMA‐depressed cortical tryptophan hydroxylase activity could be completely restored in vitro by a prolonged (20‐24 h) anaerobic incubation in the presence of dithiothreitol and Fe 2+ at 25°C; partial reconstitution occurred when 2‐mercapto‐ethanol was substituted for dithiothreitol. Cortical tryptophan hydroxylase acutely inactivated by methamphetamine or p ‐chloroamphetamine could be similarly reactivated. MDMA‐inactivated cortical tryptophan hydroxylase derived from rats killed later than 3 days after drug treatment could not be significantly reactivated under the conditions described above, indicating the development of irreversible enzymatic damage. Kinetic analysis of enzyme reactivation revealed an approximate doubling of enzyme V max with no change in enzyme affinity for either substrate, tryptophan, or pterin cofactor. These studies suggest that MDMA and its congeners inactivate central tryptophan hydroxylase by inducing oxidation of key enzyme sulfhydryl groups. The reactivation capacity of drug‐inactivated enzyme at various times after MDMA treatment may provide a means of assessing the development of MDMA‐induced neurotoxicity.