Jesse L. Cashaw

Dopamine-derived tetrahydroisoquinoline alkaloids—Inhibitors of neuroamine metabolism☆

Abstract The formation of salsolinol and tetrahydropapaveroline (THP) in vitro as aberrant metabolites of dopamine has been established previously. Demonstrating the formation of these compounds in vivo is complicated by the probability that they are extensively metabolized. The present studies indicate that a primary metabolic route for these compounds may be methylation of one or more of the free hydroxyl groups catalyzed by catechol-O-methyl transferase (COMT). Through the use of a partially purified COMT preparation from rat liver, the maximal velocities of salsolinol and THP O-methylation proved to be three to five times the maximal velocities of norepinephrine and dopamine O-methylation. The Michaelis constants determined for salsolinol, norepinephrine and dopamine are similar, whereas the Km of COMT for THP (0.03 mM) is approximately one-tenth that of the above substrates. Salsolinol and THP are competitive inhibitors of dopamine O-methylation in vitro, their calculated inhibitor constants (ki values) being 0.13 and 0.02 mM respectively. The effects of these two alkaloids on rat brain monoamine oxidase (MAO) activity were also measured. They were found to be equally potent substrate competitive inhibitors of rat brain MAO in vitro, with calculated Ki values of 0.14 mM (salsolinol) and 0.20 mM (THP). These data suggest that, if formed in vivo under certain pharmacological conditions, aberrant neuroamme derived alkaloids may alter the metabolic disposition of endogenous neuroamines with resultant modification of adrenergic function.

Identification of catecholamine-derived alkaloids in mammals by gas chromatography and mass spectrometry

Abstract Tetrahydropapaveroline, the tetrahydroisoquinoline alkaloid derived from dopamine, is convertedin vivo by rats and by rat-liver and brain preparations to tetrahydropprotoberberine alkaloids. The latter alkaloids have also been identified for the first time in the urine of parkinsonian patients receiving l -DOPA therapy. These findings suggest that man, like plants, may have the ability to elaborate several classes of alkaloids with potentially important pharmacological consequences.

Stereoselective enzymatic O-methylation of tetrahydropapaveroline and tetrahydroxyberbine alkaloids

Abstract Modification of neuroamine metabolism leading to the formation of isoquinoline alkaloids has been the target of several investigations. This study describes the differential enzymatic O -methylation pattern of the racemates and optical isomers of tetrahydropapaveroline (THP) and 2,3,10,11-tetrahydroxy-berbine (THB) by a rat liver catechol O -methyltransferase (COMT) preparation. Reaction products were separated and isolated by high-pressure liquid chromatography, and structural identity was confirmed by synthesis and gas chromatography/mass spectrometry. The positions of enzymatic O -methylations were markedly influenced by the particular optical isomeric form of substrate employed. The optical isomers and racemates of THP and THB were mainly mono- O -methylated with trace amounts of di- O -methylation. The mono- O -methylations of THP were contained exclusively in the isoquinoline ring at positions 6 or 7, while mono- O -methylations of THB occurred at the vicinal hydroxyl groups of both rings A and D. This enzymatic process was evaluated further by examining the effect of classical inhibitors of COMT on these O -methylations. The results presented demonstrate that vicinal hydroxyl moieties of THP and THB are mono- O -methylated at either of the sites and that the magnitude of the positional isomer product ratio results from the optical isomeric orientation in which the substrate binds to the enzyme.

Identification of 5-Hydroxytryptophol as a Serotonin Metabolite In Man.∗

Summary 5-Hydroxytryptophol has been isolated, identified, and measured in urine of subjects with carcinoid tumors. In the urine of normal subjects and of patients with carcinoid tumors who ingested 5-HT-C14, 2.3% of the excreted C14 was attributable to 5-HTOH and its conjugates and 82.3% to 5-HIAA. These data show that 5-HTOH is a 5-HT metabolite in man as well as in animals.

Tetrahydropapaveroline in brain regions of rats after acute ethanol administration

Tetrahydropapaveroline (THP), the condensation product of dopamine, and its aldehyde, dopaldehyde, have been detected in brain regions of rats after acute ethanol administration. THP levels were determined in eight brain regions of animals that received ethanol (3.0 g/kg) by intraperitoneal injection 100 or 120 minutes before decapitation. The levels of THP in two brain regions, i.e., the midbrain and striatum, were determined at time intervals ranging from 50 to 120 minutes after ethanol administration. THP was not found in brain regions of untreated animals. However, significant levels of THP were found in pooled midbrains (0.50 pmol/g tissue) and pooled hypothalami (0.20 pmol/g tissue) of animals that received ethanol 120 minutes before decapitation. Most brain regions had detectable levels of THP 100 minutes after the animals received ethanol and the striatum contained the highest concentration of the alkaloid. The concentration of THP in striata tissue of rats at 50, 70, 90, or 100 minutes after ethanol administration were 0.33, 0.38, 0.33, and 0.33 pmol/g tissue, respectively. These results demonstrate that THP can be detected in specific brain regions of the rat after acute ethanol administration.

A novel synthesis of Aporhoeadanes

Abstract A one-pot synthesis of aporhoeadanes from the reaction of 3,4-dihydro-isoquinolines, 2-chloromethylbenzoyl chloride and sodium hydroxide, is described.

Alteration of endogenous catecholamine metabolism by ethanol ingestion.

Summary Ingestion of moderate amounts of ethanol by normal human subjects results in a striking decrease in excretion of 3-methoxy-4-hydroxymandelic acid and a compensatory increase in excretion of 3-methoxy-4-hydroxyphenylglycol. These findings are supported by previous studies using C14-norepinephrine and indicate that ethanol ingestion diverts the intermediate metabolism of both epinephrine and norepinephrine from the normal oxidative route to a reductive pathway.

Disposition of Catecholamine-Derived Alkaloids in Mammalian Systems

Tetrahydropapaveroline, the tetrahydroisoquinoline alkaloid derived from dopamine, is converted in vivo by rats and by rat liver and brain preparations to tetrahydroprotoberberine alkaloids. The latter alkaloids have also been identified for the first time in the urine of parkinsonian patients receiving L-dopa therapy. These findings suggest that man, like plants, may have the ability to elaborate several classes of alkaloids with potentially important pharmacological consequences. Thus, this newly demonstrated ability of mammalian systems to evoke the biosynthesis of benzyl-tetrahydroisoquinoline-derived alkaloids - a capability previously considered unique to plants - elects the tetrahydroprotoberberine alkaloids as representative of the first class of a possible constellation of complex mammalian alkaloids elaborated from the neuroamines.

Alteration of norepinephrine metabolism by barbiturates

Abstract Competitive inhibition of NAD-linked aldehyde dehydrogenase by acetaldehyde, the primary metabolite of ethanol, enhances the formation in vitro of tetrahydropapaveroline (THF), a tetrahydroisoquinoline (THIQ) alkaloid derived from the condensation of dopamine (DA) with 3,4-dihydroxyphenylacetaldehyde. Unlike the DA-derived aldehyde, the aldehyde derivative of norepinephrine (NE) is not appreciably oxidized in brain tissue to the corresponding acid by brain aldehyde dehydrogenase, but is primarily reduced to the glycol, 3,4-dihydroxyphenylglycol (DHPG), by an NADPH-dependent aldehyde reductase. Since it has been demonstrated that this partially purified aldehyde reductase from bovine brain is inhibited by barbiturates, an investigation was conducted to define the effects of barbiturates on the over-all metabolism of 14 C-NE and its aldehyde by rat brainstem homogenates. In the absence of exogenous NAD or NADPH, the major metabolite of deaminated NE was found in a fraction that would contain the THIQ alkaloids. A smaller portion of the deaminated NE was isolated as the DHPG and the 3,4-dihydroxymandelic acid (DHMA) metabolites. A substantial amount of the deaminated NE was also accounted for as the free aldehyde. Adding NADPH markedly increased DHPG formation while decreasing alkaloid synthesis. Incorporating barbiturates into incubation mixtures containing NADPH, or a mixture of NAD and NADPH, appreciably inhibited DHPG production, thereby enhancing free glycolaldehyde levels and augmenting alkaloid formation. Thus, barbiturates-like ethanol, as mediated by acetaldehyde-markedly modify neuroamine-derived aldehyde metabolism.

High pressure cation exchange chromatography of biogenic amines

Fourteen selected neuroamines and related compounds (phenethylamines, β-hydroxyphenethylamines, and indoleamines) were chromatographed by high pressure cation exchange chromatography using ammonium phosphate solutions as elutants. The capacity factor (k′) values for all compounds studied exhibited linear relationships with respect to both elutant concentration and pH. Values of k′ were strongly dependent on the degree of hydrophilicity or hydrophobicity of the individual bases. The method proved capable of quantitation of 1–5 nmol of most biogenic amines. Sensitivity to serotonin was even greater, with detectability extending into the picomole range.