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Biomedical subjects

Richard B Rothman

Publications and source records attributed to Richard B Rothman.

At least 19 recordsLinked to original sources
PubMed2007

A comparison of noninternalizing (herkinorin) and internalizing (DAMGO) mu-opioid agonists on cellular markers related to opioid tolerance and dependence.

Previous studies established that Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) and (2S,4aR,6aR,7R,9S,10aS,10bR)-9-(Benzoyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho-[2,1-c]pyran-7-carboxylic acid methyl ester (herkinorin) are fully efficacious mu-agonists. Herkinorin (HERK), unlike DAMGO, does not recruit beta-arrestin and promote mu-receptor internalization, even in cells that over express beta-arrestin. We hypothesized that chronic HERK and DAMGO treatment will differentially affect cellular markers of tolerance and dependence. CHO cells expressing the cloned human mu-receptor were treated for 20 h with 10 microM DAMGO, HERK, morphine, or medium. Both DAMGO and HERK acted as full agonists in the [(35)S]GTP-gamma-S binding assay with E(MAX) values of 230% and EC(50) values of 12.8 and 92.5 nM, respectively. In the cAMP assay, DAMGO and HERK had similar E(MAX) values of approximately 80% and EC(50) values of 3.23 and 48.7 nM, respectively. Chronic exposure to both drugs produced moderate tolerance to both drugs ( approximately 2 to 5 fold) in the [(35)S]GTP-gamma-S binding assay. In the cAMP assay, chronic DAMGO produced tolerance to both drugs ( approximately 3 to 4 fold). Chronic HERK eliminated the ability of either drug to inhibit forskolin-stimulated cAMP accumulation. Chronic DAMGO increased, and chronic HERK decreased, forskolin-stimulated cAMP accumulation. Naloxone, after chronic HERK (but not DAMGO) induced a large increase in forskolin-stimulated cAMP accumulation. Viewed collectively with published data, the current data indicate that both internalizing and noninternalizing mu-agonists produce cellular signs of tolerance and dependence.

Analgesics, Opioid↗
PubMed2006

Dual dopamine-5-HT releasers: potential treatment agents for cocaine addiction.

Biogenic amine transporters (BATs) are integral membrane proteins that translocate biogenic amine neurotransmitters [norepinephrine, dopamine (DA) and 5-hydroxytryptamine (5-HT)] across cell membranes. BATs are the principal sites of action for many psychotropic drugs, including abused stimulants such as cocaine and methamphetamine. Preclinical and human data demonstrate that withdrawal from long-term cocaine administration produces a dual deficit of synaptic DA and 5-HT in the brain, indicating the advantage of developing medications that normalize impairments in both neurotransmitter systems. In this article, we review data supporting the notion that stimulant effects normally produced by increased levels of extracellular DA can be antagonized by concurrent increases in levels of extracellular 5-HT. Accordingly, nonselective BAT substrates that can release both DA and 5-HT, such as the novel compound PAL287, have low abuse potential while maintaining the ability to suppress drug-seeking behavior. The collective findings indicate that such drugs will provide neurochemical normalization therapy for cocaine addiction and might also be useful for treating depression, obsessive-compulsive disorder, attention deficit disorder and obesity.

Animals↗
PubMed2006

Salvinorin A: allosteric interactions at the mu-opioid receptor.

Salvinorin A [(2S,4aR,6aR,7R,9S,10aS,10bR)-9-(acetyloxy)-2-(3-furanyl)-dodecahydro-6a,10b-dimethyl-4,10-dioxo-2h-naphtho[2,1-c]pyran-7-carboxylic acid methyl ester] is a hallucinogenic kappa-opioid receptor agonist that lacks the usual basic nitrogen atom present in other known opioid ligands. Our first published studies indicated that Salvinorin A weakly inhibited mu-receptor binding, and subsequent experiments revealed that Salvinorin A partially inhibited mu-receptor binding. Therefore, we hypothesized that Salvinorin A allosterically modulates mu-receptor binding. To test this hypothesis, we used Chinese hamster ovary cells expressing the cloned human opioid receptor. Salvinorin A partially inhibited [(3)H]Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) (0.5, 2.0, and 8.0 nM) binding with E(MAX) values of 78.6, 72.1, and 45.7%, respectively, and EC(50) values of 955, 1124, and 4527 nM, respectively. Salvinorin A also partially inhibited [(3)H]diprenorphine (0.02, 0.1, and 0.5 nM) binding with E(MAX) values of 86.2, 64, and 33.6%, respectively, and EC(50) values of 1231, 866, and 3078 nM, respectively. Saturation binding studies with [(3)H]DAMGO showed that Salvinorin A (10 and 30 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Saturation binding studies with [(3)H]diprenorphine showed that Salvinorin A (10 and 40 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Similar findings were observed in rat brain with [(3)H]DAMGO. Kinetic experiments demonstrated that Salvinorin A altered the dissociation kinetics of both [(3)H]DAMGO and [(3)H]diprenorphine binding to mu receptors. Furthermore, Salvinorin A acted as an uncompetitive inhibitor of DAMGO-stimulated guanosine 5'-O-(3-[(35)S]thio)-triphosphate binding. Viewed collectively, these data support the hypothesis that Salvinorin A allosterically modulates the mu-opioid receptor.

Allosteric Regulation↗
PubMed2006

DAT/SERT selectivity of flexible GBR 12909 analogs modeled using 3D-QSAR methods.

The dopamine reuptake inhibitor GBR 12909 (1-{2-[bis(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)piperazine, 1) and its analogs have been developed as tools to test the hypothesis that selective dopamine transporter (DAT) inhibitors will be useful therapeutics for cocaine addiction. This 3D-QSAR study focuses on the effect of substitutions in the phenylpropyl region of 1. CoMFA and CoMSIA techniques were used to determine a predictive and stable model for the DAT/serotonin transporter (SERT) selectivity (represented by pK(i) (DAT/SERT)) of a set of flexible analogs of 1, most of which have eight rotatable bonds. In the absence of a rigid analog to use as a 3D-QSAR template, six conformational families of analogs were constructed from six pairs of piperazine and piperidine template conformers identified by hierarchical clustering as representative molecular conformations. Three models stable to y-value scrambling were identified after a comprehensive CoMFA and CoMSIA survey with Region Focusing. Test set correlation validation led to an acceptable model, with q(2)=0.508, standard error of prediction=0.601, two components, r(2)=0.685, standard error of estimate=0.481, F value=39, percent steric contribution=65, and percent electrostatic contribution=35. A CoMFA contour map identified areas of the molecule that affect pK(i) (DAT/SERT). This work outlines a protocol for deriving a stable and predictive model of the biological activity of a set of very flexible molecules.

Cluster Analysis↗
PubMed2006

Serotonergic responsiveness in human cocaine users.

BACKGROUND: Animal experiments show that repeated cocaine injections induce changes in brain serotonin (5-hydroxytryptamine, or 5-HT) function which can be detected by altered neuroendocrine responsiveness to serotonergic drug challenge. Studies of human cocaine users given a serotonergic challenge have produced inconsistent results. METHODS: Hormone responses evoked by the 5-HT releaser D,L-fenfluramine (FEN) were examined in eight human cocaine users who resided on a closed research ward. FEN (60 mg oral) was given after a 7-day cocaine-free period and 3 days after a 5-day period of daily double-blind administration of intranasal cocaine (96 mg) and active placebo (4 mg cocaine). Plasma cortisol and prolactin levels were measured after FEN challenges, and after cocaine and placebo administration. RESULTS: Cocaine significantly elevated plasma cortisol levels to a similar degree on the first and fifth days of administration, but did not alter prolactin levels on either day. The first FEN challenge significantly increased plasma prolactin and cortisol, whereas the second challenge increased only prolactin. CONCLUSIONS: Intranasal cocaine increases plasma cortisol without affecting prolactin, with no evidence for tolerance. The reduction in FEN-induced cortisol secretion after cocaine exposure suggests that deficits in 5-HT transmission during early cocaine abstinence might contribute to the maintenance of drug dependence.

Adult↗
PubMed2006

Interaction of amphetamines and related compounds at the vesicular monoamine transporter.

Amphetamine-type agents interact with the vesicular monoamine transporter type 2 (VMAT(2)), promoting the release of intravesicular neurotransmitter and an increase in cytoplasmic neurotransmitter. Some compounds, such as reserpine, "release" neurotransmitter by inhibiting the ability of VMAT(2) to accumulate neurotransmitter in the vesicle, whereas other types of compounds can release neurotransmitter via a carrier-mediated exchange mechanism. The purpose of this study was to determine, for 42 mostly amphetamine-related compounds, their mode of interaction with the VMAT(2). We used a crude vesicular fraction prepared from rat caudate to assay VMAT(2) activity. Test compounds were assessed in several assays, including 1) inhibition of [(3)H]dihydrotetrabenazine binding, 2) inhibition of vesicular [(3)H]dopamine uptake, and 3) release of preloaded [(3)H]dopamine and [(3)H]tyramine. Several important findings derive from this comprehensive study. First, our work indicates that most agents are VMAT(2) substrates. Second, our data strongly suggest that amphetamine-type agents deplete vesicular neurotransmitter via a carrier-mediated exchange mechanism rather than via a weak base effect, although this conclusion needs to be confirmed via direct measurement of vesicular pH. Third, our data fail to reveal differential VMAT(2) interactions among agents that do and do not produce long-term 5-hydroxytryptamine depletion. Fourth, the data reported revealed the presence of two pools of [(3)H]amine within the vesicle, one pool that is free and one pool that is tightly associated with the ATP/protein complex that helps store amine. Finally, the VMAT(2) assays we have developed should prove useful for guiding the synthesis and evaluation of novel VMAT(2) agents as possible treatment agents for addictive disorders.

Amphetamines↗
PubMed2006

TDIQ (5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline) inhibits the consumption of "snacks" in mice.

There is considerable evidence that alpha2-adrenergic receptor activity exerts a pivotal role in initiation of feeding behavior. The appetite suppressant and monoamine release effects of TDIQ (5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline), a putative selective alpha2-adrenergic compound, were compared to those of fenfluramine, a reference drug that produces an anorectic effect via presynaptic release and reuptake inhibition of serotonin. The drugs were administered to two groups of mice that had learned to consume either sweet milk or chocolate pellets (i.e. "snacks") during the low-activity/reduced-feeding "light" portion of their light/dark cycle. The selectivity of the drugs to suppress the consumption of snacks was determined by comparing doses of each drug that inhibited the animals' consumption of snacks to doses of each drug that have been shown, or were shown, to impact the motor (i.e. locomotor, rotarod, and inclined-screen side effect-like tests) or conditioned taste aversion (CTA) behavior of mice. An evaluation of TDIQ as a releaser of monoamines was determined in rodent brain synaptosomes. The administration of TDIQ or fenfluramine inhibited the consumption of the snacks, and a comparison of their ED50 doses indicated that TDIQ is about 3 times more potent than fenfluramine (1.3 mg/kg vs. 4.2 mg/kg, respectively) in the sweet milk test and almost equipotent to fenfluramine (19.4 mg/kg vs. 18.4 mg/kg, respectively) in the chocolate pellet assay. The selectivity of the appetite suppressant effect of TDIQ was differentiated from that of fenfluramine on the basis that TDIQ exhibited a wide separation between its dose-response effects that suppressed snack consumption and its minimal effects in tests that measured behavioral impairment. Moreover, TDIQ was distinguished from fenfluramine in that it displayed very low potencies as a presynaptic releaser of monoamines. Finally, TDIQ (0.3 mg/kg-30.0 mg/kg) did not induce a conditioned taste aversion. TDIQ may represent a novel chemical entity that exhibits a significantly favorable therapeutic-like (i.e. appetite suppressant) effect to side effect-like ratio.

Animals↗
PubMed2006

Antinociceptive and hypothermic effects of Salvinorin A are abolished in a novel strain of kappa-opioid receptor-1 knockout mice.

Salvia divinorum is a natural occurring hallucinogen that is traditionally used by the Mazatec Indians of central Mexico. The diterpene salvinorin A was identified as an active component of S. divinorum over 20 years ago, but only recently has biochemical screening indicated that a molecular target of salvinorin A in vitro is the kappa-opioid receptor. We have examined whether salvinorin A, the C2-substituted derivative salvinorinyl-2-propionate, and salvinorin B can act as kappa-opioid receptor agonists in vivo. We found that following intracerebroventricular injection over a dose range of 1 to 30 microg of both salvinorin A and salvinorinyl-2-propionate produces antinociception in wild-type mice but not in a novel strain of kappa-opioid receptor knockout mice. Moreover, both salvinorin A and salvinorinyl-2-propionate reduce rectal body temperature, similar to conventional kappa-opioid receptor agonists, in a genotype-dependent manner. In addition, we determined that salvinorin A has high affinity for kappa 1- but not kappa 2-opioid receptors, demonstrating selectivity for this receptor subclass. Finally, treatment over the same dose range with salvinorin B, which is inactive in vitro, produced neither antinociceptive nor hypothermic effects in wild-type mice. These data demonstrate that salvinorin A is the active component of S. divinorum, selective for kappa(1)-opioid receptors, and that salvinorin A and specific structurally related analogs produce behavioral effects that require the kappa-opioid receptor.

Analgesics↗
PubMed2006

Amphetamine analogs increase plasma serotonin: implications for cardiac and pulmonary disease.

Elevations in plasma serotonin (5-HT) have been implicated in the pathogenesis of cardiac and pulmonary disease. Normally, plasma 5-HT concentrations are kept low by transporter-mediated uptake of 5-HT into platelets and by metabolism to 5-hydroxyindoleacetic acid (5-HIAA). Many abused drugs (e.g., substituted amphetamines) and prescribed medications (e.g., fluoxetine) target 5-HT transporters and could thereby influence circulating 5-HT. We evaluated the effects of amphetamines analogs [(+/-)-fenfluramine, (+/-)-3,4-methylenedioxymethamphetamine, (+)-methamphetamine, (+)-amphetamine, phentermine] on extracellular levels (i.e., plasma levels) of 5-HT and 5-HIAA in blood from catheterized rats. Effects of the 5-HT uptake blocker fluoxetine were examined for comparison. Drugs were tested in vivo and in vitro; plasma indoles were measured using a novel microdialysis method in whole blood. We found that baseline dialysate levels of 5-HT are approximately 0.22 nM, and amphetamine analogs evoke large dose-dependent increases in plasma 5-HT ranging from 4 to 20 nM. The ability of drugs to elevate plasma 5-HT is positively correlated with their potency as 5-HT transporter substrates. Fluoxetine produced small, but significant, increases in plasma 5-HT. Although the drug-evoked 5-HT concentrations are below the micromolar levels required for contraction of pulmonary arteries, they approach concentrations reported to stimulate mitogenesis in pulmonary artery smooth muscle cells. Additional studies are needed to determine the effects of chronic administration of amphetamines on circulating 5-HT.

Amphetamines↗
PubMed2006

Synthetic studies of neoclerodane diterpenes from Salvia divinorum: selective modification of the furan ring.

A synthetic sequence has been developed to selectively functionalize the furan ring of the natural product salvinorin A (2a). The synthetic routes described convert the furan ring in 2a into an N-sulfonylpyrrole, oxazole or an oxadiazole. In addition, a procedure has been found to remove the furan skeleton completely. Biological results indicate that replacement of the furan ring with an N-sulfonylpyrrole leads to reduced affinity and efficacy at kappa opioid receptors.

Animals↗
PubMed2006

Structure-activity relationships of substituted N-benzyl piperidines in the GBR series: Synthesis of 4-(2-(bis(4-fluorophenyl)methoxy)ethyl)-1-(2-trifluoromethylbenzyl)piperidine, an allosteric modulator of the serotonin transporter.

A series of 4-(2-(bis(4-fluorophenyl)methoxy)ethyl)-(substituted benzyl) piperidines with substituents at the ortho and meta positions in the aromatic ring of the N-benzyl side chain were synthesized and their affinities and selectivities for the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET) were determined. One analogue, 4-(2-(bis(4-fluorophenyl)methoxy)ethyl)-1-(2-trifluoromethylbenzyl)piperidine (the C(2)-trifluoromethyl substituted compound), has been found to act as an allosteric modulator of hSERT binding and function. It had little affinity for any of the transporters. Several compounds showed affinity for the DAT in the low nanomolar range and displayed a broad range of SERT/DAT selectivity ratios and very little affinity for the NET. The pharmacological tools provided by the availability of compounds with varying transporter affinity and selectivity could be used to obtain additional information about the properties a compound should have to act as a useful pharmacotherapeutic agent for cocaine addiction and help unravel the pharmacological mechanisms relevant to stimulant abuse.

Allosteric Regulation↗
PubMed2006

3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) is a widely abused illicit drug. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been interpreted as neurotoxicity. Whether such 5-HT deficits reflect neuronal damage is a matter of ongoing debate. OBJECTIVE: The present paper reviews four specific issues related to the hypothesis of MDMA neurotoxicity in rats: (1) the effects of MDMA on monoamine neurons, (2) the use of "interspecies scaling" to adjust MDMA doses across species, (3) the effects of MDMA on established markers of neuronal damage, and (4) functional impairments associated with MDMA-induced 5-HT depletions. RESULTS: MDMA is a substrate for monoamine transporters, and stimulated release of 5-HT, NE, and DA mediates effects of the drug. MDMA produces neurochemical, endocrine, and behavioral actions in rats and humans at equivalent doses (e.g., 1-2 mg/kg), suggesting that there is no reason to adjust doses between these species. Typical doses of MDMA causing long-term 5-HT depletions in rats (e.g., 10-20 mg/kg) do not reliably increase markers of neurotoxic damage such as cell death, silver staining, or reactive gliosis. MDMA-induced 5-HT depletions are accompanied by a number of functional consequences including reductions in evoked 5-HT release and changes in hormone secretion. Perhaps more importantly, administration of MDMA to rats induces persistent anxiety-like behaviors in the absence of measurable 5-HT deficits. CONCLUSIONS: MDMA-induced 5-HT depletions are not necessarily synonymous with neurotoxic damage. However, doses of MDMA which do not cause long-term 5-HT depletions can have protracted effects on behavior, suggesting even moderate doses of the drug may pose risks.

Animals↗
PubMed2006

Design and synthesis of promiscuous high-affinity monoamine transporter ligands: unraveling transporter selectivity.

A series of 4-[2-[bis(4-fluorophenyl)methoxy]ethyl]-piperidines and 4-[2-[(bisphenyl)methoxy]ethyl]-piperidines with different types of substituents in the phenylpropyl side-chain were synthesized and examined for their ability to bind to the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET). All of the compounds showed high binding affinities for the DAT in the low to subnanomolar range. Their ability to bind to the SERT and the NET, while maintaining their high affinity for the DAT, could be altered by substitution in positions C2 and C3 of the phenylpropyl side-chain. This approach gave rise to a new set of compounds with selectivity for the DAT, the DAT and the SERT, or the DAT and the NET. Six compounds (7, 9, 11, 12, 14, and 20) with relatively low SERT/DAT ratios were selected for additional study in biogenic amine uptake inhibition assays based on the biogenic amine transporter binding results. Some of the new ligands can serve as pharmacological tools to block DAT or DAT and another transporter simultaneously.

Adrenergic Uptake Inhibitors↗
PubMed2006

Synthetic studies of neoclerodane diterpenes from Salvia divinorum: semisynthesis of salvinicins A and B and other chemical transformations of salvinorin A.

Salvinorin A (1) is a hallucinogenic neoclerodane diterpene isolated from the widely available psychoactive plant Salvia divinorum and is the first example of a non-nitrogenous opioid receptor ligand. At present, there is little information available as to why this compound is selective for kappa opioid receptors. One approach to better understanding the mode of binding of 1 at kappa receptors is to systematically alter the structure of 1 and examine the effects on opioid receptor affinity and activity. Currently, there is a paucity of methods described for the preparation of analogues derived from 1. Here, we report the investigation of several chemical transformations of 1 isolated from S. divinorum. In particular, this work provides a semisynthesis of salvinicins A (2) and B (3) and has identified 10a as the first neoclerodane diterpene with delta opioid antagonist activity.

Diterpenes↗
PubMed2006

Synthesis of salvinorin A analogues as opioid receptor probes.

Several neoclerodanes, such as salvinorin A (1) and herkinorin (3), have recently been shown to possess opioid receptor activity in vitro and in vivo. To explore the structure-affinity relationships of this interesting class of compounds, we have synthesized a series of analogues from 1 isolated from Salvia divinorum. Here, we report the semisynthesis of neoclerodane diterpenes and their structure-affinity relationships at opioid receptors. This work will allow the further development of novel opioid receptor ligands.

Crystallography, X-Ray↗
PubMed2006

Balance between dopamine and serotonin release modulates behavioral effects of amphetamine-type drugs.

The abuse of illicit stimulants is a worldwide crisis, yet few medicines are available for treating stimulant addiction. We have advocated the idea of "agonist therapy" for cocaine dependence. This strategy involves administration of stimulant-like medications (e.g., monoamine releasers) to alleviate cocaine withdrawal symptoms and prevent relapse. A chief limitation of this strategy is that many candidate medicines possess high abuse liability due to activation of mesolimbic dopamine (DA) neurons in reward pathways. Evidence suggests that serotonin (5-HT) neurons can provide an inhibitory influence over mesolimbic DA neurons. Thus, it might be predicted that the balance between DA and 5-HT transmission is a critical variable when developing medications with reduced stimulant side effects. In this article, we review recent studies from our laboratory that examined neurochemical and behavioral effects of a series of monoamine releasers which displayed different potencies at DA and 5-HT transporters. The data show that increasing 5-HT release can attenuate stimulant effects mediated by DA release, such as motor stimulation and drug self-administration. Our findings support the work of others and indicate that elevated synaptic 5-HT can dampen certain behavioral effects of DA-releasing agents. Moreover, the relationship between DA and 5-HT releasing potency is an important determinant in developing new agonist medications with reduced stimulant properties.

Amphetamine↗
PubMed2006

Therapeutic potential of monoamine transporter substrates.

Monoamine transporter proteins are targets for many psychoactive compounds, including therapeutic and abused stimulant drugs. This paper reviews recent work from our laboratory investigating the interaction of stimulants with transporters in brain tissue. We illustrate how determining the precise mechanism of stimulant drug action (uptake inhibitor vs. substrate) can provide unique opportunities for medication discovery. An important lesson learned from this work is that drugs which display equipotent substrate activity at dopamine (DA) and serotonin (5-HT) transporters have minimal abuse liability and few stimulant side-effects, yet are able to suppress ongoing drug-seeking behavior. As a specific example, we describe the development of PAL-287 (alpha-methylnapthylethylamine), a dual DA/5-HT releasing agent that suppresses cocaine self-administration in rhesus monkeys, without the adverse effects associated with older phenylethylamine 5-HT releasers (e.g., fenfluramine) and DA releasers (e.g., amphetamine). Our findings demonstrate the feasibility of developing non-amphetamine releasing agents as potential treatments for substance abuse disorders and other psychiatric conditions.

Animals↗