Albert N. Nelson

Binding of antidepressants to human brain receptors: focus on newer generation compounds.

Using radioligand binding assays and postmortem normal human brain tissue, we obtained equilibrium dissociation constants (Kds) for 17 antidepressants and two of their metabolites at histamine H1, muscarinic, α1-adrenergic, α2-adrenergic, dopamine D2, serotonin 5-HT1A, and serotonin 5-HT2 receptors. Several newer antidepressants were compared with older drugs. In addition, we studied some antimuscarinic, antiparkinson, antihistamine, and neuroleptic compounds at some of these receptors. For the antidepressants, classical tricyclic antidepressants were the most potent drugs at five of the seven receptors (all but α2-adrenergic and 5-HT1A receptors). The chlorophenylpiperazine derivative antidepressants (etoperidone, nefazodone, trazodone) were the most potent antidepressants at α2-adrenergic and 5-HT1A receptors. Of ten antihistamines tested, none was more potent than doxepin at histamine H1 receptors. At muscarinic receptors antidepressants and antihistamines had a range of potencies, which were mostly weaker than those for antimuscarinics. From the in vitro data, we expect adinazolam, bupropion, fluoxetine, sertraline, tomoxetine, and venlafaxine not to block any of these five receptors in vivo. An antidepressants potency for blocking a specific receptor is predictive of certain side effects and drug-drug interactions. These studies can provide guidelines for the clinician in the choice of antidepressant.

Antagonism by neuroleptics of neurotransmitter receptors of normal human brain in vitro.

Using radioligand binding techniques, we determined the equilibrium dissociation constants (KDs) for a series of neuroleptics at the dopamine (D-2), muscarinic, histamine H1, alpha 1- and alpha 2-adrenergic receptors of normal human brain tissue obtained at autopsy. Seventeen different compounds were studied at the D-2 receptor and 15 compounds at the remaining receptors. At the D-2 receptor of caudate nucleus, spiperone was the most potent compound (KD = 0.16 nM); clozapine the least potent (KD = 180 nM). The KDs for six compounds at the D-2 receptor of nucleus accumbens were not significantly different from their respective KDs in the caudate nucleus. The most potent and least potent compounds at the other receptors were clozapine and molindone at the muscarinic receptor, mesoridazine and molindone at the H1 receptor, spiperone and molindone at the alpha 1-receptor, and clozapine and haloperidol at the alpha 2-receptor, respectively.

[3H]Neurotensin(8–13) Binds in Human Brain to the Same Sites as Does [3H]Neurotensin but with Higher Affinity

Abstract: The binding of [3H]neurotensin(8–13) to membranes from human frontal cortex at 0°C was time dependent, specific, saturable, and reversible. Saturation isotherms provided an equilibrium dissociation constant (KD) of 0.52 nM, and the maximal number of binding sites (B max) was 3.5 pmol/g original wet weight of tissue. Scat‐chard analysis yielded a straight line, and the Hill coefficient was equal to 1, a result indicating that [3H]‐neurotensin(8–13) bound to single, noncooperative sites. The KD values of several analogs of neurotensin determined in competition with [3H]neurotensin(8–13) were similar to those previously determined in competition with [3H]‐neurotensin. The regional distribution of binding sites for [3H]neurotensin(8–13) was also similar to that for [3H]‐neurotensin. These results suggest that [3H]neurotensin(8–13) binds to the same sites as [3H]neurotensin and that [3H]neurotensin(8–13) has a higher affinity than [3H]‐neurotensin for these sites in human brain.

S-Methyl N,N-diethylthiocarbamate sulfone, a potential metabolite of disulfiram and potent inhibitor of low Km mitochondrial aldehyde dehydrogenase

Disulfiram inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. It is thought that disulfiram is too short-lived in vivo to directly inhibit ALDH, but instead is biotransformed to reactive metabolites that inhibit the enzyme. S-Methyl N,N-diethylthiocarbamate (MeDTC) sulfoxide has been identified in the blood of animals given disulfiram and is a potent inhibitor of ALDH (Hart and Faiman, Biochem Pharmacol 46: 2285-2290, 1993). MeDTC sulfone is a logical metabolite of MeDTC sulfoxide. Therefore, we investigated the effects of MeDTC sulfone on the activity of rat hepatic low Km mitochondrial ALDH, the major enzyme in the metabolism of acetaldehyde. MeDTC sulfone inhibited the low Km mitochondrial ALDH in vitro with an IC50 of 0.42 +/- 0.04 microM (mean +/- SD, N = 5) compared with disulfiram, which had an IC50 of 7.5 +/- 1.2 microM under the same conditions. The inhibition of ALDH by MeDTC sulfone was time dependent. The decline in ALDH activity followed pseudo first-order kinetics with an apparent half-life of 2.1 min at 0.6 microM MeDTC sulfone. Inhibition of ALDH by MeDTC sulfone was apparently irreversible; dilution of the inhibited enzyme did not restore lost activity. The substrate (acetaldehyde, 80 microM) and cofactor (NAD, 0.5 mM) together completely protected ALDH from inhibition by MeDTC sulfone; substrate alone partially protected the enzyme. Addition of either thiol-containing compound glutathione (GSH) or dithiothreitol (DTT) to MeDTC sulfone before incubation with the enzyme increased the IC50 of MeDTC sulfone by 7- to 14-fold. Neither GSH nor DTT could restore lost ALDH activity after exposure of the enzyme to MeDTC sulfone. Results of these studies indicate that MeDTC sulfone, a potential metabolite of disulfiram, is a potent, irreversible inhibitor of low Km mitochondrial ALDH.

Simultaneous structure-activity determination of disulfiram photolysis products by on-line continuous-flow liquid secondary ion mass spectrometry and enzyme inhibition assay.

Disulfiram (DSF) is used in the treatment of recovering alcoholics and exerts its effect by inhibiting the enzyme aldehyde dehydrogenase (ALDH). We analyzed a mixture of products derived photochemically from DSF with on-line microbore HPLC-continuous-flow liquid secondary ion mass spectrometry (HPLC-CF-LSI-MS). By utilizing the post-HPLC column split of solvent flow, a small proportion (ca. 5%) was sent directly into the mass spectrometer, and the remainder was collected. Simultaneous MS analysis and enzyme inhibition studies on ALDH were then possible. Furthermore, using HPLC-CF-LSI-MS-MS, we were able to structurally characterize an interesting sulfine compound that inhibited ALDH.

Determination of urinary tetrahydroaldosterone glucosiduronic acid by radioimmunoassay

Abstract A procedure is described for determining tetrahydroaldosterone 3-glucosiduronic acid in unprocessed human urine by radioimmunoassay. The procedure is simple, accurate and requires relatively little time. Data on cross reactivity, on within-assay and betweeen-assay variability, and on reliability are given. Values for urinary excretion of tetrahydroaldosterone, aldosterone and sodium are given for a group of 72 normal individuals (35 M; 37 F) who were on ad libitum salt intake. The average excretion of tetrahydroaldosterone is 5.3 times as great as that of aldosterone and the range of deviation (in percent) from the mean value is the same for tetrahydroaldosterone as for aldosterone.

C-3 glucosiduronates of metabolites of adrenal steroids

On treatment with methyl 2,3,4-tri-O-acetyl-1-bromo-1-deoxy-alpha-D-glucuronate and silver carbonate, tetrahydrocortisone 21-acetate gave the corresponding 3-glucosiduronate triacetyl methyl ester. This product was converted into the 20-semicarbazone which, by treatment with alkali to hydrolyze the ester functions and acid to hydrolyze the semicarbazone moiety, gave tetrahydrocortisone 3-glucosiduronic acid. The acid was converted into the crystalline barium salt and into the methyl ester. An analogous series of reactions was carried out on tetrahydrocortexolone 21-acetate. Treatment of the 20-semicarbazone of tetrahydrocortisone 3-glucosiduronic acid with potassium borohydride reduced the 11-oxo function to an 11 beta hydroxyl group; acid-catalyzed removal of the semicarbazone group produced tetrahydrocortisol 3-glucosiduronic acid which also was obtained as the barium salt and the methyl ester.

Photolysis of sulfiram: a mechanism for its disulfiram-like reaction.

Sulfiram, a drug applied topically to treat scabies, produces effects similar to those of disulfiram after subsequent ingestion of ethanol. Disulfiram, used in aversion therapy in the treatment of alcoholism, inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. The increased tissue levels of acetaldehyde cause a spectrum of undesirable side-effects including flushing, nausea, vomiting, and tachycardia, which are referred to as the disulfiram reaction. Previous studies have shown that in vitro sulfiram is a very weak inhibitor of ALDH, but solutions of sulfiram markedly increase in potency with time. In the present study, fresh solutions of sulfiram were exposed to fluorescent room light under ambient conditions and analyzed at timed intervals by HPLC. At least eight products, including disulfiram, were formed in the light-exposed sulfiram solutions, but not in solutions kept in the dark. Structural characterization of two of the photolysis products was obtained by on-line microbore HPLC-mass spectrometry (mu LC-MS) and on-line microbore HPLC-tandem mass spectrometry (mu LC-MS/MS) using continuous flow-liquid secondary ion mass spectrometry (CF-LSIMS) as the primary ionization method. Sulfiram was converted to disulfiram at an initial rate of 0.7%/hr, and the formation of disulfiram correlated with the increase in ALDH inhibition in vitro. The results of this investigation show that while sulfiram is a weak inhibitor of ALDH in vitro, it is readily photoconverted to disulfiram, a very potent inhibitor of ALDH, which may explain the adverse reaction to ethanol after sulfiram therapy.

Preparation of 3β,16β-dihydroxyandrost-5-en-17-one: Stabilization of its α-ketolic group toward alkali by formation of a semicarbazone

Abstract Alkaline hydrolysis of a 16β-acetoxy-17-oxo steroid is accompanied by almost complete rearrangement of the product to a 16-oxo-17β-hydroxy steroid. Hydrolysis can be achieved without rearrangement by 1) formation of a C-17 semicarbazone, 2) alkaline removal of the acetate group, and 3) removal of the semicarbazone group in the presence of pyruvic acid-acetic acid. By employing this technique, the title compound was obtained from its diacetate in a yield of 65%.

Chemical synthesis of glucuronidated metabolites of cortisol

During in vivo metabolism the addition of six atoms of hydrogen to cortisone at the appropriate location and configuration can lead to formation of either 3 alpha,17,20 alpha,21-tetrahydroxy 5 beta-pregnan-11-one (cortolone) or 3 alpha,17,20 beta,21-tetrahydroxy-5 beta-pregnan-11-one (beta-cortolone). Likewise, metabolic reduction of cortisol can lead to formation of either 5 alpha-pregnane-3 alpha,11 beta,17,20 alpha,21-pentol (cortol) or the 20 beta isomer (beta-cortol). This paper describes the chemical syntheses of the C-3 beta-D-glucosiduronates of cortolone, beta-cortolone, cortol and beta-cortol-conjugates which are normal excretory products of man. The foregoing conjugates are characterized as free acids (or salts), as methyl esters and as polyacetate methyl esters.