title: Studies on the mechanisms of 6-hydroxydopamine cytotoxicity.
abstract: The uptake-accumulation and binding of radioactivity in mouse heart after administration of the catecholamine neurotoxin [3H]6-hydroxydopamine (6-OH-DA, 1 or 3 mg/kg, i.v.) has been investigated. It was confirmed that a substantial portion (8--20%) of the radioactivity taken up and retained by the heart could not be extracted with perchloric acid, in all probability representing covalently bound oxidation products of 6-OH-DA to tissue proteins. Pharmacological analysis showed that a large part of this fraction was associated with the adrenergic nerves. The time-course of the perchloric acid resistant binding to the adrenergic nerves was found to parallel that of the neurotoxic action of 6-hydroxydopamine as evaluated by monitoring the change in [3H]noradrenaline uptake. Calculation of the intranelronal 6-hydroxydopamine concentration (average) needed to induce degeneration showed it to be in the order of 50 mM. The binding ratio for tritium deriving from [3H]6-OH-DA between the intraneuronal and extraneuronal compartments was found to be 10,000 to 30,000, pointing to a very high neuronal specificity for 6-hydroxydopamine. The 'covalent' binding of oxidation products of [3H]6-OH-DA was considerably reduced after desipramine or 1-phenyl-3(2-thiazolyl)-2-thiourea administration, treatments both known to protect the adrenergic nerves from undergoing degeneration. Conversely it was found that the binding increased during conditions known to potentiate the neurotoxic action of 6-hydroxydopamine, e.g., after monoamine oxidase inhibition with nialamide. Subcellular fractionation studies indicated that the predominant site of interaction between 6-hydroxydopamine oxidation products and neuronal proteins is the cytoplasm and the axonal membrane. Analysis of the effect in vivo administration of 6-hydroxydopamine on the field-stimulated induced release of [3H]noradrenaline previously taken up in the adrenergic nerves showed a 6-hydroxydopamine indiced reduction in [3H]noradrenaline release which was approximately proportional to the reduction in the number of nerve terminals. These findings further support the view that 6-hydroxydopamine acts largely in an "all-or-none' fashion with respect to the neurodegenerative action. Administration of [3H]dopamine also resulted in a fraction which was not extractable with perchloric acid, although this fraction was very small compared to that found after an equal dose of [3H]6-hydroxydopamine. These data may indicate that oxidation products of dopamine can interact with tissue proteins. From the present results it can be concluded that there is a close relationship between 'covalent' binding of 6-hydroxydopamine oxidation products to neuronal elements and the cytotoxic action of 6-hydroxydopamine, indicating that this binding may play an important role in the neurodegenerative action of 6-hydroxydopamine on catecholamine neurons.
mesh_terms: D000320:Adrenergic Fibers / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D003891:Desipramine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D006801:Humans; D006860:Hydrogen Bonding; D006892:Hydroxydopamines / Q000378:metabolism / Q000633:toxicity*; D008297:Male; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D009410:Nerve Degeneration / Q000187:drug effects; D009526:Nialamide / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010668:Phenylthiazolylthiourea / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects; D013890:Thiourea / Q000494:pharmacology
chemical_list: D006892:Hydroxydopamines; D011941:Receptors, Adrenergic; D010668:Phenylthiazolylthiourea; D013890:Thiourea; D009526:Nialamide; D003891:Desipramine; D004298:Dopamine; D009638:Norepinephrine