In Vivo and in Vitro Studies on the Neurotoxic Potential of 6-Hydroxydopamine Analogs

Abstract

In an attempt to determine which physical and biological properties could best be correlated with neurotoxic potential, seven analogs of 1-(2,4,5-trihydroxyphenyl)-2-aminoethane (1), better known as 6-hydroxydopamine, were synthesized and compared to 1 in a variety of ways both in vivo and in vitro. The analogs, in combination with the standard 1, include all eight of the 2,4,5-trisubstituted-phenyl derivatives of phenethylamine and alpha-methylphenethylamine in which the substitution is of the trihydroxy or aminodihydroxy form. Low (60 nmol) and high (300 nmol) intracerebroventricular doses of all analogs produced long-term (7 day) reduction of mouse whole brain norepinephrine (NE) and lesser depletions of dopamine (DA), and effects on serotonin were varied. The analog 1-(5-amino-2,4-dihydroxyphenyl)-2-aminopropane (8) was both more complete and more selective than the standard 1 in depleting NE. Using a histofluorometric glyoxylic acid method and Fink-Heimer silver degeneration stain, it was determined that overt neural degeneration was produced by 8. In vitro, the ease of oxidation of the eight analogs was found to be represented by a formal potential range of -130 to -212 mV vs SCE. However, there was no obvious relationship between ease of oxidation and the extent of monoamine depletion from mouse brain. Using kinetic analysis of synaptosomal accumulation of [3H]NE and [3H]DA, it was found that the standard 1 is more potent in its interaction with the DA uptake site (Ki = 12 +/- 0 microM) than the NE uptake site (Ki = 51 +/- 1 microM). A correlation analysis was used to determine that differences in NE and DA depletion by each analog could not be explained by differences in potency for in vitro uptake blockade. However, there was a correlation between the Ki for [3H]NE uptake blockade and the EC50 for synaptosomal release of preloaded [3H]NE for the eight analogs (R2 = 0.96; for log:log plot, R2 = 0.54), indicating that the results for these two in vitro tests both reflect interaction with the same NE neuronal membrane transport site. A similar correlation between Ki and EC50 was shown for all eight analogs using [3H]DA (R2 = 0.92; for log:log plot, R2 = 0.52), indicating interaction with the same DA neuronal membrane transport site. These findings demonstrate that there is no single property that can account for selectivity of action and/or potency of catecholamine neurotoxins related to 6-hydroxydopamine.

Synthesis and Cytotoxic Profile of 3,4-Methylenedioxymethamphetamine (“Ecstasy”) and Its Metabolites on Undifferentiated PC12 Cells: A Putative Structure−Toxicity Relationship

“…10, 1297 dark oil at room temperature and when exposed to air. The data obtained was in accordance with that described in the literature (10)(11)(12)(13) (6)), 6.59 (1H, d, J ) 1.9, H (2)), 6.68 (1H, d, J ) 8.0, H (5)), 7.78 (3H, bs, NH 3 + ), 8.85 (2H, bs, 2×OH); 13 General Synthetic Procedure for the O-Debenzylation. The synthesis was carried out by catalytic hydrogenolysis of compounds 15 and 18 as described earlier (46).…”

“…Briefly, the synthesis of the target compounds was performed in a straightforward manner, starting from the appropriate substituted benzaldehydes (1)(2)(3)(4)(5), which were converted into the corresponding phenylisopropylamines (11)(12)(13)(14)(15) Via -methyl--nitrostyrenes (6-10) intermediates. First, a Knoevenagel condensation between the aldehyde, with the corresponding aromatic substitution pattern, and nitroethane was carried out, yielding the nitrostyrene derivatives (53).…”

“…From the analysis of the electrochemical data of the drug and metabolites, it was possible to clearly distinguish two sets of compounds ( Figure 7): one containing the metabolites with a catecholic group (R-MeDA (19), 6-OH-R-MeDA (20), N-Me-R-MeDA (21)) and the other including the compounds with a substituted catechol function (MDA (11), 3-O-Me-R-MeDA (13), MDMA (16)).…”

“…Dimethoxy--methyl--nitrostyrene(7). Yield 95%; 1 H NMR δ: 2.44 (3H, s, CH 3 ),3.80 (3H, s, 3-OCH 3 ),3.82 (3H, s, 4-OCH 3 ), 7.08 (1H, d, J ) 8.5, H (5)), 7.22 (1H, s, H (2)), 7.23 (1H, d, J ) 8.5, H (6)), 8.08 (1H, s, H(R));13 C NMR δ: 14.0 CH 3 , 55.6 (4-OCH 3 ), 55.7 (3-OCH 3 ), 111.8, 113.9 C (2) and C (5), 124.3 C (6), 124.4 C (1), 133.8 C(R), 145.6 C( ), 148.7 C (4), 150.7 C (3); EI-MS m/z (%): 223 (M +• , 100), 176 (78), 165 (22), 161 (37), 146 (47), 131 (46), 119 (36), 103 (37), 91 (47), 77 (38), 65 (34); mp 71-72°C (lit (43). mp 72-74°C).…”

Selective neurotoxins, chemical tools to probe the mind: The first Thirty years and beyond

“…Many analogues of 6-OHDA have been,synthesized, having a somewhat different action profile or spectrum of selectivity (Azevedo and Osswald, 1977;Blank et aI., 1972b,c;1976;Borchardt et al, 1977;Cheng and Castagnoli, 1984;Ho et al, 1973;Lundstrom et al, 1973;Ma et al, 1995;Tranzer and Thoenen, 1973). Among these is 6-hydroxydopa (6-OHDOPA) Stone et al, 1963), a metabolic precursor of 6-OHDA (Jacobowitz and Kostrzewa, 1971;Ong et al, 1969).…”