Biomedical subjects

E Richelson

Publications and source records attributed to E Richelson.

At least 73 records · Page 4Linked to original sources

PubMed1994

Pharmacology of antidepressants--characteristics of the ideal drug.

OBJECTIVE: To describe the clinical and basic pharmacologic properties of antidepressants and thus define the pharmacologic criteria for the ideal antidepressant. DESIGN: A review of the pharmacologic characteristics of the newer second-generation antidepressants is presented in relationship to those of the older compounds. MATERIAL AND METHODS: Clinical pharmacologic and in vitro data on the synaptic effects of antidepressants (inhibition of synaptosomal uptake and blockade of neurotransmitter receptors) were obtained for the older antidepressants and for the more recently marketed and approved drugs. The group of antidepressants includes six new antidepressants approved for marketing since 1988 and two additional drugs marketed outside the United States as antidepressants but approved for use in the United States for obsessive-compulsive disorder. Thus, 18 antidepressant drugs are discussed. RESULTS: All antidepressants seem to be equally efficacious in treating depression, and no drug seems to work more rapidly than another. Nonetheless, antidepressant drugs differ substantially in pharmacokinetic variables (elimination half-lives); in their effects on the metabolism of other drugs (by inhibiting the cytochrome P450 system); in their potencies for blocking the reuptake of norepinephrine, serotonin, and dopamine; and in their affinities for blocking histamine H1, muscarinic acetylcholine, alpha 1-adrenergic, and dopamine D2 receptors. Most side effects of antidepressants can be explained by their effects on blocking uptake and on blocking neurotransmitter receptors. CONCLUSION: The newer second-generation antidepressants have distinct pharmacologic advantages in comparison with the tricyclic antidepressants and the older second-generation compounds. These advantages are clearly seen from their synaptic effects, in which most newer second-generation antidepressants are practically devoid of blocking effects at neurotransmitter receptors. Although the newer second-generation antidepressants are much closer to being the ideal antidepressant than are the older compounds, none completely fulfills the criteria for being the ideal drug.

Antidepressive Agents↗

PubMed1994

Inhibition by lithium of cyclic GMP formation without inhibition of nitric oxide generation in the mouse neuroblastoma cell (N1E-115).

We investigated the effects of lithium ion (Li+) on muscarinic receptor-mediated nitric oxide (NO) generation, and guanylate cyclase (GCase) activation using the mouse neuroblastoma clone, N1E-115. The levels of released NO were determined by measuring the levels of nitrite/nitrate in the incubation medium, and the activity of GCase was measured with an assay for cellular cyclic [3H] GMP levels. We determined that Li+ had no effects on muscarinic receptor-activated elevation of nitrite/nitrate levels, which were significantly inhibited by 100 microM L-NG-monomethylarginine, although it has been reported that Li+ inhibits muscarinic receptor-activated cyclic GMP formation in the cells. In addition, Li+ inhibited the cyclic GMP formation induced by an NO donor, sodium nitroprusside (SNP), in both intact cells and a crude cellular homogenate; thus, the inhibition by Li+ of muscarinic receptor-mediated cyclic GMP synthesis appeared to be at the level of GCase, but not NO synthase.

Animals↗

PubMed1994

Affinity of neuroleptics for D1 receptor of human brain striatum.

We determined the inhibition-dissociation constant (Ki) of a number of neuroleptics for D1 receptors of normal human brain tissue using [3H]SCH23390 [R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3[benzazepine-7- ol]. SCH23390 had the highest affinity with a Ki of 0.76 nM. Among clinically used drugs, propericiazine showed the highest affinity with a Ki of 10 nM. When neuroleptics were classified according to chemical structures, the Ki values were as follows. Phenothiazines ranged from 10 nM to 250 nM. Butyrophenones ranged from 45 nM to 250 nM. Thioxanthenes ranged from 12 nM to 340 nM. Orthopramines were more than 10,000 nM. The Ki values for the binding site of this study were significantly correlated with those reported in studies using animal brain. The possible relationship between D1 receptors and negative symptoms is discussed.

Aged↗

PubMed1994

Deletion mutation in the putative third intracellular loop of the rat neurotensin receptor abolishes polyphosphoinositide hydrolysis but not cyclic AMP formation in CHO-K1 cells.

The tridecapeptide neurotensin is a putative neurotransmitter in the central nervous system. Previously, we showed that the rat neurotensin receptor expressed in CHO-K1 cells mediates polyphosphoinositide hydrolysis and cAMP formation. To further investigate these neurotensin receptor-mediated signal transduction systems, we constructed three deletion mutations in the putative third intracellular loop of this receptor and transfected these mutated genes into CHO-K1 cells. The equilibrium dissociation constants for specific [3H]neurotensin binding to these mutants were not different from that for the wild-type receptor. However, one mutant, which lacked 27 amino acids (amino acids 270-296), did not stimulate polyphosphoinositide hydrolysis, whereas it retained its ability to stimulate cAMP formation. In addition, as found for the wild-type receptor, sequestration occurred with this mutant. We demonstrated here that the putative third intracellular loop of this receptor plays a role in coupling to certain G proteins that induce polyphosphoinositide hydrolysis but not in coupling to cAMP formation or in ligand binding. The two different signal transduction systems may be induced by different G proteins that couple at different sites of the neurotensin receptor protein in CHO-K1 cells. Furthermore, our data show that neurotensin receptor sequestration is independent of agonist-induced polyphosphoinositide hydrolysis.

Amino Acid Sequence↗

PubMed1994

The pharmacology of antidepressants at the synapse: focus on newer compounds.

This paper reviews the in vitro effects of antidepressants on blockade of uptake of norepinephrine, serotonin, and dopamine at the synapse (rat synaptosomal preparations), as well as blockade of histamine H1, muscarinic, alpha 1-adrenergic, and dopamine D2 receptors in human brain tissue. The potency of an antidepressant at this blockade is predictive of the likelihood of its causing certain side effects and drug-drug interactions.

Animals↗

PubMed1993

Antagonism of the five cloned human muscarinic cholinergic receptors expressed in CHO-K1 cells by antidepressants and antihistaminics.

Based on molecular cloning studies, five different muscarinic receptor subtypes exist: m1, m2, m3, m4, and m5. We determined the affinity and selectivity of binding for sixteen antidepressants, two of their metabolites, and three antihistaminics (H1) at these subtypes. Using Chinese hamster ovary cells (CHO-K1) transfected with genes for the human muscarinic receptor subtypes, we obtained equilibrium dissociation constants (Kds) from competitive radioligand binding studies with [3H]-quinuclidinyl benzilate ([3H]QNB) and membranal preparations of these cells. QNB was the most potent compound studied (Kd 30-80 pM). Mequitazine (Kd 6-14 nM) and amitriptyline (Kd 7-16 nM) exhibited the highest affinity among the antihistaminics and antidepressants, respectively. Among the antidepressants examined were the serotonin-selective drugs sertraline and fluoxetine, both of which displayed Kd values > 1 microM. The remaining antidepressants were moderate to weak antagonists with some eliciting no radioligand competition at high concentrations. The compounds studied showed no significant selectivity among the five cloned subtypes.

Animals↗

PubMed1993

Further characterization of neurotensin receptor desensitization and down-regulation in clone N1E-115 neuroblastoma cells.

Murine neuroblastoma clone N1E-115 cells possess neurotensin receptors that are coupled to polyphosphoinositide hydrolysis and cyclic guanosine 3',5'-monophosphate (cGMP) formation. These responses rapidly desensitize and these receptors rapidly down-regulate nearly completely in about 15 min. Although neurotensin is rapidly degraded by peptidases, in this study we show that at 37 degrees neurotensin (100 nM) in the absence of peptidase inhibitors caused this rapid desensitization and down-regulation (32 +/- 5 and 24 +/- 2% of control, respectively) of neurotensin receptors in N1E-115 cells. In addition, we demonstrated that this desensitization, resensitization, down-regulation and recovery of binding sites were temperature dependent. These data suggest that a certain degree of phospholipid fluidity or activity of some enzymes is required for these processes to occur. After addition of sodium nitroprusside or ionomycin to cells, cGMP increased in desensitized cells to the same degree as in control cells. Additionally, desensitization and down-regulation occurred in the absence of a change in the affinity of neurotensin for the remaining sites. These data suggest that desensitization is not caused by changes in nitric oxide synthesis, guanylyl cyclase activity or receptor affinity, but predominantly by a decrease in receptor number.

Animals↗

PubMed1993

Neurotensin stimulates cyclic AMP formation in CHO-rNTR-10 cells expressing the cloned rat neurotensin receptor.

Recently, we reported that the rat neurotensin receptor expressed in transfected Chinese hamster ovary cells (CHO-rNTR-10) mediates the hydrolysis of polyphosphoinositides. In this study, we show that neurotensin stimulated cyclic AMP formation in CHO-rNTR-10 cells in a dose-dependent manner (EC50 = 34 nM). Neurotensin also stimulated cyclic AMP formation in membranal preparations under Ca(2+)-free conditions. These results suggest that this cyclic AMP formation occurs from direct coupling of the neurotensin receptor to a type of GTP binding protein, mediating synthesis of cyclic AMP, and not from an increase in intracellular Ca2+ concentration from polyphosphoinositide hydrolysis.

Animals↗

PubMed1993

Facilitation of adaptation and acute tolerance to stressful sensory input by doxepin and scopolamine plus amphetamine.

This work characterizes a new methodologic and pharmacologic approach to control terrestrial and space motion sickness (SMS). The experimental design allowed separate evaluation of drug action on susceptibility and adaptability, and used repeated measures to approximate the chronic stressful motion of microgravity. Daily exposure to cross-coupled angular acceleration for 5 consecutive days demonstrated that the efficacy of doxepin and scopolamine plus amphetamine in the prevention of autonomic system dysfunction was not only apparent on the first test day (P < .01), but was also evident in the substantially enhanced resistance developed over the 5-day test period (P < .01) as compared with placebo. This indicates that daily use of these medications does not diminish therapeutic efficacy (tolerance). The efficacy of doxepin was anticipated because it possesses pharmacologic properties similar to those of established anti-motion sickness drugs. Comparable efficacy after doxepin loading for 4 hours, 3 days, or 21 days suggests a mechanism distinct from its antidepressant effects, possibly related to its potent antihistaminergic actions. Use of doxepin has operational significance to the National Aeronautics and Space Administration, in comparison with current preparations of scopolamine plus amphetamine, because of doxepin's minimal impact on cognitive performance, and most importantly, its favorable pharmacokinetic profile, particularly its long half-life.

Adaptation, Physiological↗

PubMed1993

Blockade by newly-developed antidepressants of biogenic amine uptake into rat brain synaptosomes.

We determined the uptake blockade produced by eight new antidepressant drugs (etoperidone, femoxetine, lofepramine, nefazodone, paroxetine, sertraline, tomoxetine, and venlafaxine), two metabolites of newer antidepressants (desmethylsertraline and norfluoxetine), seven previously reported antidepressants, and carbamazepine. Inhibitor constants (Kis) for uptake blockade were obtained from competitive uptake studies with [3H]norepinephrine, [3H]5-hydroxytryptamine, and [3H]dopamine in rat brain synaptosomes prepared from hippocampus, frontal cortex, and striatum, respectively. Among the newer compounds, tomoxetine (Ki = 0.7 nM) and lofepramine (Ki = 1.9 nM) were potent and selective [3H]norepinephrine uptake blockers; paroxetine (Ki = 0.73 nM), sertraline (Ki = 3.4 nM), and femoxetine (Ki = 22 nM) potently and selectively inhibited [3H]5-hydroxytryptamine uptake. Although none of the drugs was potent for [3H]dopamine uptake blockade, sertraline was the most potent (Ki = 260 nM). These data are useful in predicting adverse effects and drug-drug interactions of antidepressants.

Animals↗

PubMed1993

Identification of a polymorphism in the human neurotensin receptor gene.

A complementary DNA (cDNA) clone encoding the neurotensin receptor was isolated from a human substantia nigra cDNA library. The deduced amino acid sequence of this clone was almost identical to that of a cDNA for this receptor cloned from a previously described HT29 human colonic adenocarcinoma cell line. We found three base changes between the previously reported HT29 cDNA clone and the current cDNA clone. We investigated these changes by using polymerase chain reactions to amplify these areas from various human samples. One of the differences, which resulted in an amino acid change at AA194 (a leucine in the HT29 sequence was a phenylalanine in the current sequence), was found in some, but not in all, human samples. This finding represents genetic variability in human neurotensin receptors, the first such report for a peptide receptor. Both of these receptors, however, when expressed separately in transfected cell lines, had similar affinities for neurotensin and some related peptides.

Amino Acid Sequence↗

PubMed1993

Haloperidol but not clozapine increases neurotensin receptor mRNA levels in rat substantia nigra.

We examined the effects of chronic (2 weeks) treatment with a typical neuroleptic, haloperidol (1 mg/kg, s.c.), and an atypical neuroleptic, clozapine (20 mg/kg, s.c.), on neurotensin receptor (NTR) mRNA levels by in situ hybridization histochemistry. Quantitative OD analysis showed haloperidol-induced NTR mRNA levels in the substantia nigra/ventral tegmental area (SN/VTA) 110% over control levels (significant difference from the control, p < 0.05). In contrast, the same analysis applied to the sections from clozapine-treated animals showed no significant change in NTR mRNA levels compared with matched control sections (p > 0.05). Thus, chronic treatment with haloperidol but not clozapine resulted in elevated levels of NTR mRNA within the SN/VTA. These results suggest that the high incidence of extrapyramidal side effects of typical neuroleptics could result from changes in NTR expression in the SN/VTA.

Animals↗

PubMed1993

A method for radioligand binding assays using a robotic workstation.

Radioligand binding assays provide a powerful tool for screening drug candidates at many receptors. We present a method utilizing a robotic workstation, the Biomek 1000, which automates the tedious and repetitive tasks of these assays. First, the robot handles the serial dilution of up to 8 drugs with 11 concentrations per drug. The sequential addition of diluting buffer, non-radioactively labeled ligand, radioactive ligand, and finally the tissue homogenate or membrane preparation, is fully automated. A novel rack design allows the use of tubes with a maximum capacity of 2 ml, providing a total assay volume of 1 ml. Final filtration on a Brandel cell harvester outfitted with a uniquely designed head allows for processing of 48 samples simultaneously from the rack holder. We have employed this method for the determination of equilibrium dissociation constants (Kds) for drugs at the 5 human muscarinic acetylcholine receptor subtypes expressed in cultured cells, as well as histamine H1, dopamine D2, serotonin 5HT1A, alpha 1- and alpha 2-adrenergic receptors in human brain tissue homogenates. Our results compare favorably with manual methods reported for these receptors, and exhibit a very high degree of reproducibility and throughput, with a minimum of operator input.

Animals↗

PubMed1993

Role of signal transduction systems in neurotensin receptor down-regulation induced by agonist in murine neuroblastoma clone N1E-115 cells.

Murine neuroblastoma clone N1E-115 cells possess neurotensin (NT) receptors, which are coupled to signal transduction systems resulting in polyphosphoinositide (Pl) hydrolysis and cyclic GMP synthesis. Previously, we have demonstrated that the process of down-regulation of NT receptors in N1E-115 cells involves intracellular sequestration of recyclable receptors followed by receptor degradation, causing true down-regulation. In this study, agonist-induced sequestration of NT receptors in N1E-115 cells was inhibited by an aminosteroid, 1-(6-([17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino)hexyl)-1H-pyrrole- 2,5-diane (U-73122). Pl hydrolysis elicited by NT or sodium fluoride, which stimulates GTP binding proteins, was also inhibited by U-73122, whereas Pl hydrolysis elicited by calcium ionophores, ionomycin or A23187, was not apparently affected. These data suggest that U-73122 affects a process that is distal to the cell surface receptor but not involving the sites just proximal to Pl hydrolysis or cyclic GMP synthesis. It is suggested that U-73122 may affect the coupling of GTP binding proteins and the NT receptor. We conclude that GTP binding proteins play an important role in the mechanism of agonist-induced down-regulation of NT receptors in N1E-115 cells. These results may indicate that GTP binding proteins also play a role in the mechanism of internalization of this receptor in the central nervous system in vivo.

Animals↗

PubMed1993

Pharmacological studies on novel neurotensin mimetics: discovery of a pharmacologically unique agent exhibiting concentration-dependent dual effects as antagonist and agonist.

We report the development of two novel neurotensin mimetics (mimics 1 and 2). These compounds were rationally designed and synthesized according to the multiple template approach. We present results of experiments designed to define their pharmacological profiles. In radioligand binding assays with murine neuroblastoma clone N1E-115, we determined the equilibrium dissociation constants for these compounds at the neurotensin receptor. The Kd values for mimic 1 and mimic 2 were 3.3 microM and 1.9 microM, respectively. Functionally, both mimetics antagonized the neurotensin-stimulated production of cGMP, with Kd values in the low micromolar range. Interestingly, mimic 2 displayed a dualistic pharmacological profile, which was concentration dependent. At doses in the 10-100 microM range, mimic 2 became a full agonist, stimulating cGMP production in N1E-115 cells with an EC50 value of 19 microM. Furthermore, mimic 1 did not antagonize the cGMP response elicited by mimic 2. When the neurotensin receptor was desensitized with a neurotensin receptor agonist, mimic 2 failed to stimulate significant cGMP production. We propose that mimic 2 binds to a higher affinity site when acting as an antagonist and binds to a lower affinity and different site when acting as an agonist. Thus, mimic 2 would appear to represent a unique pharmacological tool to characterize the neurotensin receptor and its diverse binding sites in N1E-115 cells.

Amino Acid Sequence↗

PubMed1993

Desensitization and down-regulation of neurotensin receptors in murine neuroblastoma clone N1E-115 by [D-Lys8] neurotensin(8-13).

Clone N1E-115 cells have specific, high-affinity binding sites for neurotensin (NT). These receptors mediate formation of cyclic GMP and other second messengers. We studied the effects of extended exposure of cells to [D-Lys8]NT(8-13) (NT2), a peptidase-resistant NT analog, on NT's ability to stimulate cyclic GMP synthesis and to bind [3H]NT to its sites on these cells. When intact N1E-115 cells were preincubated with NT2 (1 microM) for various times (15 min to 12 hr) at 37 degrees C, maximal desensitization and binding site (Bmax) loss occurred after only 15 min. Receptor affinity for [3H]NT did not change. At 0 degrees C NT2 for 15 min caused no down-regulation. After 15 min of preincubation with NT2 at 37 degrees C, the recovery of receptor binding and function after a 10 to 20 min lag-time was rapid (T1/2 = 15 min and 19 min, for binding and cyclic GMP response, respectively). After 12 hr of NT2 preincubation, it was slow (T1/2 = 212 min). Incubation of cells with cycloheximide (70 microM) for 5 hr after their exposure to NT2 for 15 min did not change the rate or extent of recovery of NT Bmax. However, cycloheximide did decrease the recovery of NT Bmax after exposure of cells to NT2 for 12 hr. Cycloheximide alone did not change NT Bmax. These data suggest that this decrease of NT receptor binding after short (15 min) and long (12 hr) exposure times to agonist involves two consecutive steps: intracellular sequestration of recyclable NT receptors, followed by receptor degradation causing true down-regulation.

Animals↗

PubMed1993

Treatment of acute depression.

This article presents information needed by the clinician to diagnose and treat acute depression. The emphasis is on the pharmacologic treatment of depression. Both clinical and preclinical pharmacology of antidepressants are reviewed. The data presented will help the clinician make a rational choice of antidepressant for his or her patient. In particular, these data will help the clinician avoid or minimize certain adverse effects and drug-drug interactions. Guidelines for treating depression as well as strategies for treating the refractory patient are presented.

Antidepressive Agents↗

PubMed1992

Block of neurotensin receptor down-regulation by an aminosteroid in N1E-115 cells.

We have demonstrated that the aminosteroid, U-73122 (1-(6-([17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino)hexyl)-1H-pyrrole- 2,5-dione) blocks agonist induced down-regulation of neurotensin receptors in murine neuroblastoma clone N1E-115 cells. U-73122 is known to inhibit polyphosphoinositide hydrolysis by affecting the coupling of GTP-binding proteins. Our results may indicate that GTP-binding proteins play a role in the mechanism of down-regulation of the neurotensin receptor.

Down-Regulation↗