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Biomedical subjects

F I Carroll

Publications and source records attributed to F I Carroll.

At least 73 records · Page 4Linked to original sources
PubMed1997

Serotonin transporter binding sites and mRNA levels in depressed persons committing suicide.

The serotonin transporter (5-HTT) has been found altered in postmortem brain samples from persons committing suicide, but the results of radioligand binding studies have been inconsistent. In the present series of experiments, autoradiographic radioligand binding and in situ hybridization techniques were utilized to examine 5-HTT function in the brains of 8 depressed subjects who had committed suicide, and matched controls. It was hypothesized that depressed subjects would demonstrate decreased numbers of 5-HTT binding sites and mRNA; however, [125I]RTI-55 binding to the 5-HTT was not different in the midbrain, hippocampus, or frontal cortex of depressed subjects. Also, 5-HTT mRNA levels in dorsal and median raphe nuclei were not different between controls and depressed subjects. The current results, although limited in scope because of the small number of subjects included, offer no evidence that alterations in the 5-HTT occur in pertinent brain regions of depressed individuals.

Adult↗
PubMed1997

Synthesis and transporter binding properties of 2,3-diphenyltropane stereoisomers. Comparison to 3beta-phenyltropane-2beta-carboxylic acid esters.

2beta,3beta-Diphenyl-(5), 2alpha,3alpha-diphenyl-(6), and 2alpha,3beta-diphenyltropane (3) as well as 2,3-diphenyltrop-2-ene (4) were prepared in racemic form and assayed for inhibition of radioligand binding at the dopamine (DA), serotonin (5-HT), and norepinephrine (NE) transporters. Among all three transporters, compounds 4-6 bound the DA transporter with the highest affinity. The 2beta,3beta-diphenyltropane (5) bound the DA transporter with an IC50 value (28 nM) almost identical to that of 3beta-phenyltropane-2beta-carboxylic acid methyl ester (WIN 35,065-2) and has much greater selectivity relative to binding to the serotonin transporter. A comparison of the radioligand data from this study to radioligand data obtained on other WIN 35,065-2 analogs suggests that hydrophobicity of the C-2 substituent of some analogs of the WIN 35,065-2 class may be an important contributing factor to binding at the DA transporter.

Binding, Competitive↗
PubMed1997

Synthesis and characterization of [125I]3'-(-)-iodopentazocine, a selective sigma 1 receptor ligand.

Pentazocine is a potent ligand at both opioid and sigma receptors, but with opposite stereoselectivities. Whereas (-)-pentazocine has high affinity for a number of opioid receptors, (+)-pentazocine labels sigma 1 receptors. Iodination of (-)-pentazocine at the 3'-position reverses its selectivity for opioid and sigma 1 receptors. 3'-(-)-Iodopentazocine competes at sigma 1 receptor binding sites with a Ki value of 8 nM, compared to approximately 40 nM for (-)-pentazocine. 3'-(-)-Iodopentazocine also has lost its affinity for opioid receptors. In contrast, iodination of (+)-pentazocine lowers its affinity at sigma 1 receptors. Synthesis of [125I]3'-(-)-iodopentazocine is readily performed with incorporations of up to 80%. Binding is of high affinity and shows the selectivity anticipated for a sigma 1 receptor-selective ligand. Exposing membranes prebound with [125I]3'-(-)-iodopentazocine to ultraviolet light can covalently couple the ligand into the membranes. Polyacrylamide gel electrophoresis reveals a major band at about 25 kDa and a minor one at about 20 kDa, indicating photolabeling of sigma 1 receptors with minor incorporation into sigma 2 sites.

Affinity Labels↗
PubMed1997

N-substituted phenyltropanes as in vivo binding ligands for rapid imaging studies of the dopamine transporter.

Variously substituted phenyltropanes are proven as superb binding ligands for the dopamine transporter (DAT). In this study, we examine four N-substituted phenyltropanes which are derivatives of RTI-55 as in vivo binding ligands in mice. In this series, the methyl group on the nitrogen was replaced by a propyl (RTI-310), an allyl (RTI-311), a butyl (RTI-312), or a fluoropropyl (RTI-313) group. The in vitro binding potencies of these compounds at rat striatal DAT varied somewhat but were about 1 nM. While these compounds did not display marked selectivity for the dopamine transporter, they were more selective than RTI-55. Injection of the radiolabeled compound into mice resulted in striatal-to-cerebellar ratios that varied from about 4.5-6.5. The ratios peaked most rapidly for RTI-311 and RTI-313, at about 20 min. Pharmacological inhibition studies indicated that these compounds were binding to DATs in the striatum, as expected. These findings suggest that some compounds of this type may be excellent in vivo binding ligands for rapid imaging studies of the DAT.

Analysis of Variance↗
PubMed1997

Fluoro-norchloroepibatidine: preclinical assessment of acute toxicity.

18Fluoro-norchloroepibatidine (exo-2-(6-fluoro-3-pyridyl)-7-azabicyclo-[2.2.1]heptane [NFEP]), a labeled derivative of epibatidine, has shown promise for imaging brain nicotinic acetylcholine receptors with PET. We determined the dose-dependent effects of NFEP in conscious rats. NFEP (1.5 microg/kg; administered intravenously) resulted in 30% mortality. Neither 0.5 microg/kg or 0.25 microg/kg NFEP resulted in any significant changes in cardiorespiratory parameters, but plasma catecholamines increased (2- to 3-fold). Further studies are needed to determine the safety of NFEP that are specifically designed to assess the catecholamine response. Our results suggest that it is not advisable to initiate human PET studies with [18F]-NFEP without further evidence supporting its safety.

Animals↗
PubMed1996

Lack of dopamine receptor agonists effect on striatal dopamine transporter binding sites.

Depending on experimental conditions, chronic cocaine exposure can induce an increase in binding to the dopamine transporter (DAT). One possible mechanism for the cocaine-induced-upregulation in DAT binding sites is through stimulation of presynaptic D2 receptors by excess synaptic dopamine. To test this hypothesis, the present experiment examined in rats the effect of chronic quinpirole and apomorphine treatments on striatal DAT binding sites. Rats were chronically injected subcutaneously with either: quinpirole, 0.7 mg/kg body weight, apomorphine, 2.0 mg/kg body weight, or vehicle. Striatal DAT binding was then examined autoradiographically using the DAT-selective cocaine congeners [125I]RTI-121 and [3H]WIN 35428. Analysis of the results indicated that quinpirole and apomorphine administration did not alter DAT cocaine binding sites.

Animals↗
PubMed1996

Synthesis and transporter binding properties of 3 beta-(4'-alkyl-, 4'-alkenyl-, and 4'-alkynylphenyl)nortropane-2 beta-carboxylic acid methyl esters: serotonin transporter selective analogs.

New methods for the synthesis of 3 beta-(4'-alkyl-, 4'-alkenyl-, and 4'-alkynylphenyl)nortropane-2 beta-carboxylic acid methyl esters 2-4, respectively, were developed. These methods involved coupling of the appropriate organometallic reagents to 3 beta-(4'-iodophenyl)tropane-2 beta-carboxylic acid methyl ester (6a, RTI-55) or to an N-protected derivative of 6a followed by N-demethylation or removal of the protecting group. Some analogs were prepared by catalytic reduction of the alkene and alkene analogs 3 and 4 or by isomerization of the alkenes 3. The analogs 2-4 were evaluated for inhibition of radioligand binding to the serotonin (5-HT), dopamine (DA), and norepinephrine (NE) transporters. 3 beta-(4'-Isopropenyl- and 4'-cis-propenylphenyl)nortropane-2 beta-carboxylic acid methyl esters (3b,d), which possessed IC50 values of 0.6 and 1.15 nM, respectively, were the most potent analogs at the 5-HT transporter, and with NE/5-HT IC50 ratios of 240 and 128 nM, respectively, they were selective for the 5-HT relative to the NE transporter. Since interaction with the serotonin transporter may modulate the pharmacological effects resulting from binding to the dopamine transporter, 3 beta-(4'-isopropenylphenyl)tropane-2 beta-carboxylic acid methyl ester (11b) which has good affinity for both the 5-HT and DA transporters but low affinity at the NE transporter may be useful for studying this interaction.

Animals↗
PubMed1996

Highly potent cocaine analogs cause long-lasting increases in locomotor activity.

Three cocaine analogs were compared with cocaine for the capacity to affect: (1) dopamine transporter binding and function; and (2) locomotor activity. RTI-55 (3 beta-[4-iodophenyl]tropane-2 beta-carboxylic acid methyl ester tartrate), RTI-121 (3 beta-[4-iodophenyl] tropan-2 beta-carboxylic acid isopropyl ester hydrochloride) and RTI-130 (3 beta-[4-chlorophenyl-2 beta-[1,2,4-oxadiazol-3-phenyl-5-yl]tropane hydrochloride) competed for [3H]WIN 35428 binding in rat striatum in vitro, with IC50 values at least 50-fold less than that of cocaine. These analogs inhibited [3H]dopamine transport into rat striatal synaptosomes, with IC50 values again less (at least 100-fold) than that for cocaine. Intravenous RTI-55, RTI-121 or RTI-130 injection effected dose-related increases in locomotor activity in mice, with estimated relative potencies at least 10-fold greater than that of cocaine. These increases were long lasting: whereas increased activity ceased within 2 h after cocaine administration, increased locomotion was observed at least 10 h after RTI-55, RTI-121, or RTI-130 administration. Parallel line analysis indicated that the slopes of the ascending portion of the RTI-121 and RTI-130 dose-response curves differed from that of cocaine, suggesting the involvement of mechanisms different from that of cocaine.

Analysis of Variance↗
PubMed1996

Effects of sphingosine stereoisomers on P-glycoprotein phosphorylation and vinblastine accumulation in multidrug-resistant MCF-7 cells.

To investigate the role of protein kinase C (PKC) in the regulation of multidrug resistance and P-glycoprotein (P-gp) phosphorylation, the natural isomer of sphingosine (SPH), D-erythro sphingosine (De SPH), and its three unnatural stereoisomers were synthesized. The SPH isomers showed similar potencies as inhibitors of in vitro PKC activity and phorbol binding, with IC50 values of approximately 50 microM in both assays. Treatment of multidrug-resistant MCF-7ADR cells with SPH stereoisomers increased vinblastine (VLB) accumulation up to 6-fold at 50 microM but did not alter VLB accumulation in drug-sensitive MCF-7 wild-type (WT) cells or accumulation of 5-fluorouracil in either cell line. Phorbol dibutyrate treatment of MCF-7ADR cells increased phosphorylation of P-gp, and this increase was inhibited by prior treatment with SPH stereoisomers. Treatment of MCF-7ADR cells with SPH stereoisomers decreased basal phosphorylation of the P-gp, suggesting inhibition of PKC-mediated phosphorylation of P-gp. Most drugs that are known to reverse multidrug resistance, including several PKC inhibitors, have been shown to directly interact with P-gp and inhibit drug binding. SPH stereoisomers did not inhibit specific binding of [3H] VLB to MCF-7ADR cell membranes or [3H]azidopine photoaffinity labeling of P-gp or alter P-gp ATPase activity. These results suggest that SPH isomers are not substrates of P-gp and suggest that modulation of VLB accumulation by SPH stereoisomers is associated with inhibition of PKC-mediated phosphorylation of P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Synthesis, ligand binding, and quantitative structure-activity relationship study of 3 beta-(4'-substituted phenyl)-2 beta-heterocyclic tropanes: evidence for an electrostatic interaction at the 2 beta-position.

A set of 3 beta-(4'-substituted phenyl)-2 beta-heterocyclic tropanes was designed, synthesized, and characterized. We discovered that these compounds can function as bioisosteric replacements for the corresponding WIN 35,065-2 analogs which possess a 2 beta-carbomethoxy group. Several of the compounds showed high affinity and selectivity for the dopamine transporter (DAT) relative to the serotonin and norepinephrine transporters. From the structure-activity relationship study, the 3 beta-(4'-chlorophenyl)-2 beta-(3'-phenylisoxazol-5-yl)tropane (5d) emerged as the most potent and selective compound. The binding data for 2 beta-heterocyclic tropanes were found to show a high correlation with molecular electrostatic potential (MEP) minima near one of the heteroatoms in the 2 beta-substituents. In contrast, low correlations were found for other MEP minima near the 2 beta-substituent as well as for calculated log P or substituent volume. These quantitative structure-activity relationship studies are consistent with an electrostatic contribution to the binding potency of these WIN 35,065-2 analogs at the DAT.

Animals↗
PubMed1996

Displacement of RTI-55 from the dopamine transporter by cocaine.

The cocaine analog 3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid methyl ester (RTI-55 or beta CIT) has a higher affinity for the dopamine transporter and may be potentially useful in interfering with cocaine's actions in brain. However, imaging studies have demonstrated displacement of tracer doses of [123I]RTI-55 by a subsequent dose of cocaine. Similar displacement of pharmacological doses of RTI-55 might compromize therapy with RTI-55 in cocaine abuse. The reduction in dopamine transporter availability, assessed in vivo in mouse striatum using [3H]cocaine, caused by pretreatment with RTI-55 was significantly mitigated by subsequent administration of cocaine. In a similar experiment using a tracer dose of [123I]RTI-55 significant reductions of striatal radioligand binding by pretreatment with cocaine or RTI-55 were not observed. These results suggest that: (1) cocaine can displace pharmacological doses of RTI-55 from striatum, and (2) radioligands used to assess binding site occupancy should have a lower affinity than the occupying drug.

Animals↗
PubMed1996

Ibogaine block of the NMDA receptor: in vitro and in vivo studies.

Ibogaine is an hallucinogenic indole alkaloid claimed to have anti-addictive properties. Although its mechanism of action is unknown, binding studies have indicated that the drug may interact with N-methyl-D-aspartate (NMDA) receptors. We further investigated the nature of the interaction between ibogaine and NMDA receptors in voltage clamp and binding studies, and sought to confirm that the drug has NMDA receptor blocking activity in vivo. In whole-cell recordings from cultured rat hippocampal neurons, ibogaine caused a slow, concentration-dependent block of NMDA-induced currents (IC50, 3.1 microM at -60 mV). In contrast, ibogaine failed to affect either kainate- or gamma-aminobutyric acid-evoked currents. The blockade of NMDA currents was use- and voltage-dependent, and the long lasting ibogaine block could be occluded by co-application of Mg2+. Ibogaine also inhibited equilibrium [3H]dizocilpine binding to NMDA receptors in rat forebrain membranes (IC50, 3.2 microM). We conclude that ibogaine is an open channel NMDA receptor antagonist. Administration of ibogaine to mice resulted in complete protection in the maximal electroshock test (ED50, 31 mg/kg, i.p.) and partial protection against NMDA-induced lethality, confirming that ibogaine can block NMDA receptors in vivo.

Animals↗
PubMed1996

3 Beta-(p-trimethylsilylphenyl)tropane-2 beta-carboxylic acid methyl ester: a new precursor for the preparation of [123I]RTI-55.

Here we report the synthesis of 3 beta-(p-trimethylsilylphenyl)tropane-2 beta-carboxylic acid methyl ester, a new, easily prepared precursor for the synthesis of radioiodinated versions of RTI-55. In contrast to the 3 beta-(p-trimethylstannylated) precursor for radioiodination, the aryl silane is prepared directly by the 1,4 addition of p-trimethylsilylphenylmagnesium iodide to anhydroecgonine methyl ester in 49% yield (Scheme 1). Radioiododesilylation proceeded smoothly (approx. 85% radioincorporation after 15 min at room temperature) using 1 microgram of the novel precursor in trifluoroacetic acid and chloramine-T as oxidant. Isolated radiochemical yields for 125I and 123I radiolabelings were 72 and 48%, respectively, with a calculated specific activity for [123I]RTI-55 of > 2000 mCi/mumol.

Chromatography, High Pressure Liquid↗