Biomedical subjects

S Caccia

Publications and source records attributed to S Caccia.

At least 37 records · Page 2Linked to original sources

PubMed1998

Modulation of the association reaction between hemoglobin and carbon monoxide by proton and chloride.

A cryogenic technique for the isolation of the ligation intermediates in the association reaction between hemoglobin and carbon monoxide at 20 degrees C [Perrella, M., Davids, N., and Rossi-Bernardi, L. (1992) J. Biol. Chem. 267, 8744-8751] was used to study the effects of proton and chloride concentrations on the rates of the stepwise reactions. The reaction rate was observed to increase continuously in the course of the ligation process, yet the acceleration of the reaction after the binding of two ligand molecules, observed previously in 100 mM KCl, pH 7, was not observed at other pH values. At pH 6.3, such an acceleration occurred after the binding of three ligands, and at pH 8.5, a large acceleration was observed after the binding of the first ligand molecule. Greater CO binding to the beta chains was observed under all conditions, as in the previous study. The functional heterogeneity of the chains in the first ligation step increased with pH. The chloride concentration did not influence the distribution of the ligand between the alpha and beta chains at pH 6.3 and 8.5. At pH 7, less binding to the alpha chains was observed at 7 mM chloride with respect to 100 mM. The nature of the biliganded component isolated at pH 7 in 100 mM KCl and unresolved by the cryogenic technique was studied using a combination of cryogenic and noncryogenic isoelectric focusing. This component was a mixture of intermediates (alpha beta) (alpha CO beta CO), about 65%, and (alpha beta CO) (alpha CO beta), about 35%. The experimental data were compared with the distributions of intermediates calculated according to the Monod kinetic model assuming rapid and concerted transitions between two quaternary structures at each ligation step. The model provided a qualitative fit of the observed distributions of intermediates at acidic and neutral pH. A large discrepancy between the experimental observations and the predictions of the model was found at alkaline pH. The mechanism of the association reaction is discussed in the light of the available information on the tertiary/quaternary structures of the intermediates, as obtained from the studies of the deoxy/cyanomet model of ligation.

Carbon Monoxide↗

PubMed1998

Citalopram-induced hypophagia is enhanced by blockade of 5-HT(1A) receptors: role of 5-HT(2C) receptors.

The selective 5-hydroxytryptamine reuptake inhibitor citalopram (10 and 20 mg kg(-1), i.p.) significantly reduced food intake in male rats (CD-COBS) habituated to eat their daily food during a 4-h period. The 5-HT1A receptor antagonist WAY100635 (0.3 mg kg(-1)) administered systemically did not modify feeding but significantly potentiated the reduction in food intake caused by 10 mg kg(-1) i.p. citalopram. The dose of 5 mg kg(-1) i.p. citalopram was not active in animals pretreated with vehicle but significantly reduced feeding in animals pretreated with WAY100635. WAY100635 (0.1 microg 0.5 microl(-1)) injected into the dorsal raphe significantly potentiated the hypophagic effect of 10 mg kg(-1) citalopram. WAY100635 (1.0 microg 0.5 microl(-1)) injected into the median raphe did not modify feeding or the hypophagic effect of 10 mg kg(-1) citalopram. The 5-HT2B/2C receptor antagonist SB206553 (10 mg kg(-1), p.o.) slightly reduced feeding by itself but partially antagonized the effect of WAY100635 administered systemically (0.3 mg kg(-1), s.c.) or into the dorsal raphe (0.1 microg 0.5 microl(-1)) in combination with 10 mg kg(-1) i.p. citalopram. The hypophagic effect of 10 mg kg(-1) i.p. citalopram alone was not significantly modified by SB206553. Brain concentrations of citalopram and its metabolite desmethylcitalopram in rats pretreated with SB206553, WAY100635 and their combination were comparable to those of vehicle-pretreated rats, 90 min after citalopram injection. The hypophagic effect of citalopram was potentiated by blocking 5-HT1A receptors. Only the effect of the WAY100635/citalopram combination seemed to be partially mediated by central 5-HT2C receptors.

Animals↗

PubMed1998

Brain-to-blood partition and in vivo inhibition of 5-hydroxytryptamine reuptake and quipazine-mediated behaviour of nefazodone and its main active metabolites in rodents.

The brain/plasma partition of nefazodone, hydroxynefazodone (OHNFZ) and m-chlorophenyl-piperazine (mCPP) and their antagonism of p-chloroamphetamine (PCA)-induced 5-hydroxytryptamine (5-HT) depletion and quipazine-induced head twitches were compared in rodents. Nefazodone (30 mg kg(-1), i.p.) rapidly entered the brain but concentrations were exceeded by mCPP, the metabolic ratio being 47 and 10 in the mouse and rat respectively. OHNFZ was detectable in plasma but never in brain. Brain concentrations of OHNFZ in the mouse (30 mg kg(-1), i.p.) were less than 10% of those in plasma, confirming a poor blood-brain barrier penetration. Concentrations of its metabolite mCPP were similar to those after 5 mg kg(-1)(i.p.) mCPP. In the mouse, nefazodone (30 mg kg(-1)) antagonized the 5-HT depleting effect of PCA 2 h after dosing, when it had disappeared from brain but when mCPP concentrations were similar to those after 5 mg kg(-1) (i.p.) mCPP. However, mCPP antagonized PCA less than nefazodone. In the rat, nefazodone pretreatment (30 mg kg(-1), 15 min) prevented (97% of inhibition) quipazine-induced head twitches. The effect was weaker (65% of inhibition) but significant when only mCPP was detected in brain. Analysis of brain concentrations of the two compounds after their ED50 against quipazine indicated that both contributed to the effect, although nefazodone was more active than mCPP in terms of concentrations required to obtain a comparable reduction of twitches. These findings show that mCPP concentrates in the brain following injection of nefazodone and may play a role in preventing quipazine-induced behaviour and PCA-induced 5-HT depletion. In contrast OHNFZ poorly enters the brain and its in vivo activity is mostly due to its biotransformation to mCPP.

Animals↗

PubMed1998

Acid-catalysed hydrolysis and benzodiazepine-like properties of 5-(dialkylamino)- and 5-(alkylthio)-substituted 8-chloro-6-phenyl-6H-[1,2,4]triazolol[4,3-a][1,5]benzodiazepines in mice.

The in-vitro and in-vivo hydrolysis of two benzodiazepine compounds has been studied to evaluate their in-vivo activity in mice. Compounds RL 218 and RL 236, selected as representative examples of N,N-dialkyl-8-chloro-6-phenyl-6H-[1,2,4]triazolo[4,3-a][1,5]benzodiaz epin-5-amines (1) and of their 5-(alkylthio) substituted analogues (2), were rapidly hydrolysed to the corresponding 8-chloro-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5(6H )-one 3 (RL 214) in aqueous acidic solution at pH 1.5. This reaction also occurred extensively in mice when compounds RL 218 and RL 236 were given orally but not intraperitoneally. Both compounds were active against pentylenetetrazole-induced lethal convulsions in mice only when administered orally. After administration of pharmacologically effective oral doses (ED50, the dose protecting 50% of mice), at the time of assessment of the anti-pentylenetetrazole activity, mean brain concentrations of RL 218 and RL 236 were below the limits of sensitivity of the analytical procedure whereas brain concentrations of their metabolite RL 214 were comparable with that present after an oral equiactive dose of this compound itself. RL 214 but not RL 218 or RL 236 had in-vitro affinity for brain benzodiazepine receptors. These results indicate that the anticonvulsant activity of RL 218 and RL 236 in mice depends essentially on their in-vivo transformation into the common active metabolite RL 214 which most probably arises as a result of acid catalysed hydrolysis in the gastric juice.

Administration, Oral↗

PubMed1998

Metabolism of the newer antidepressants. An overview of the pharmacological and pharmacokinetic implications.

Several chemically unrelated agents has been developed and introduced in the past decade, to supplement the earlier antidepressants. These include inhibitors of the reuptake of serotonin [the selective serotonin reuptake inhibitors (SSRI)] or noradrenaline (reboxetine) or both (milnacipran and venlafaxine), as well as drugs with distinct neurochemical profiles such as mirtazapine, nefazodone, moclobemide and tianeptine. Like the earlier drugs, these newer antidepressants are almost totally biotransformed before excretion, except for milnacipran whose clearance appears to be due equally to both urinary excretion and metabolism. Sometimes--as in the case of moclobemide--up to 20 metabolites have been identified in body fluids. In some cases, however, only a few metabolites have been detected, and a substantial proportion of the dose remains unaccounted for (e.g. fluoxetine and fluvoxamine). Metabolism generally proceeds through sequential or parallel oxidative pathways. These may be affected to varying degrees by physiological and pathological factors and those mediated by cytochrome P450 (CYP) 2D6 and CYP2C19 through genetic polymorphism. Some are influenced by chirality (e.g. the dealkylation of citalopram and fluoxetine), although information on this aspect of disposition is still lacking for other drugs existing as racemates (e.g. mirtazapine and tianeptine) and milnacipran, which is probably a mixture of 4 stereoisomers. Others again are saturable within the therapeutic range of doses (e.g. some pathways of metabolism of fluoxetine, fluvoxamine, nefazodone, paroxetine and venlafaxine). This may explain the individual variability with all these drugs which, from the pharmacokinetic point of view, is the same as with tricyclic agents. Our knowledge of the isoenzymes involved in the various oxidation pathways and their relevance for potential drug interactions varies from a considerable amount for most of the SSRI and nefazodone, to minimal for reboxetine and tianeptine. This information is useful for predicting the pharmacokinetic interactions mediated through inhibition of specific isoenzymes. This would be better appreciated if the enzymatic mechanisms involved in the biotransformation of the metabolite(s), and their role in drug interactions, were also known. This information is still lacking for some drugs, although metabolites may exhibit in vitro inhibitory potencies of similar to (paroxetine and its M2 metabolite as inhibitors of CYP2D6) or even greater than that of the parent drug (norfluoxetine is more potent than fluoxetine as an inhibitor of CYP3A3/4, and in view of the longer half-life (t1/2) of the metabolite the potential for interactions may persist for weeks after discontinuation of the parent drug). While we do know something about the biological activity of the metabolites of some of these drugs, we know very little about others. With few exceptions this knowledge refers only to the major metabolite(s) and regards the main in vitro effects as exerted by the parent drug. However, in vitro potency and selectivity may not translate directly into in vivo, and either major or minor metabolites may have characteristic in vitro and in vivo properties. For example, unlike the parent drug some minor ring-opened metabolites of moclobemide have monoamine oxidase-B inhibitory activity in the rat, and the nefazodone metabolite m-chlorophenyl-piperazine shows activity on 5-HT2C receptors in rats and humans. Data on the brain-to-blood partition of metabolites compared with their parent drug are available only in a few cases. They are still not known for the main metabolites of fluvoxamine, milnacipran, mirtazapine, moclobemide, nefazodone, paroxetine, reboxetine and venlafaxine, despite the fact that total blood concentrations do not always reflect the metabolite: parent drug ratio in brain. Thus, in most cases, we do not really know what part hepatic metabolism plays in the overall effect of the administered parent drug.

Adrenergic Uptake Inhibitors↗

PubMed1997

Effect of piribedil and its metabolite, S584, on brain lipid peroxidation in vitro and in vivo.

We studied the effect of piribedil (1-3,4-methylendioxybenzyl-4-(2-pyrimidyl) piperazine) and its catechol metabolite, S584 (1-(3,4-dihydroxybenzyl-4-(2-pyrimidinyl)-piperazine), on rat brain lipid peroxidation (a) in vitro in rat synaptosomes and cortical slices after induction of an oxidative stress and (b) in vivo in mouse brain after short-term exposure (two and three 4-h cycles) to O2/CO2 (95%:5%). The metabolite (10[-4]-10[-5] M), but not piribedil, prevented Fe3+-stimulated lipid peroxidation in rat synaptosomes and in rat cortical slices incubated with high oxygen concentrations. Piribedil (7.5 and 30 mg/kg, orally), counteracted the increase in thiobarbituric reactive substances in the brain of mice only when these were exposed to two or three cycles of a high oxygen concentration. S584 (30 mg/kg, orally) reduced thiobarbituric acid reactive substances in brain in mice exposed either to air (control) or to three cycles of a high oxygen concentration. These results suggest that piribedil has an antiperoxidative effect in brain, which may be partly related to the in vivo formation of the catechol metabolite, S584.

Animals↗

PubMed1997

Novel and highly potent 5-HT3 receptor agonists based on a pyrroloquinoxaline structure.

The synthesis and the biological evaluation of a series of novel pyrroloquinoxaline derivatives are described. In binding studies several compounds proved to be potent and selective 5-HT3 receptor ligands. The most active pyrroloquinoxalines, 11d and 11e, showed a subnanomolar affinity for 5-HT3 receptor and were able to functionally discriminate the central and peripheral 5-HT3 receptor, being agonists and antagonists, respectively. In functional studies ([14C]-guanidinium accumulation test in NG 108-15 cells, in vitro) most of the synthesized compounds showed clear-cut 5-HT3 agonist properties. In in vivo studies on the von Bezold-Jarisch reflex test (a peripheral interaction model) the behavior of the tested compounds ranged from agonist to antagonist, while clear agonist properties were obtained with 12a on cortical acetylcholine release in freely moving rats. Pharmacokinetic studies with 11e and 12c indicate that the compounds easily cross the blood-brain barrier (BBB) after systemic administration with a brain/plasma ratio of 17.5 and 37.5, respectively. Thus compounds 11e and 12c represent the most potent central 5-HT3 agonists identified to date that are able to cross the blood-brain barrier.

Animals↗

PubMed1997

Pharmacokinetics of isosorbide dinitrate in healthy volunteers after 24-hour intravenous infusion.

No studies have examined the pharmacokinetics of isosorbide dinitrate (ISDN) after infusion of long duration, even though such infusions are used in patients. We therefore measured ISDN and its active metabolites, isosorbide-5-mononitrate (IS5MN) and isosorbide-2-mononitrate (IS2MN), in plasma of 9 healthy volunteers who received a continuous intravenous infusion of ISDN for 24 hours at a dose rate that lowered diastolic blood pressure by 10% during the first 30 minutes of infusion. All subjects tolerated the infusion except one who experienced intolerable headache. Five subjects received 1 microgram.min-1.kg-1, one 2 micrograms.min-1.kg-1, and two 4 micrograms.min-1.kg-1 ISDN, whereas the full rate of 6 micrograms.min-1.kg-1 was used continuously in one subject. At all infusion rates the plasma concentrations of ISDN were higher at 24 hours than at earlier times, suggesting that a steady-state condition had not been reached at that time. The same was true for the mononitrate metabolites, which reached higher plasma concentrations and were cleared more slowly than the parent compound after the end of the infusion. Apparent elimination half-lives of ISDN, IS2MN, and IS5MN were 67 +/- 10 minutes, 115 +/- 13 minutes, and 272 +/- 38 minutes, respectively. Comparison of low-rate infusions (1 and 2 micrograms.min-1.kg-1) with high-rate infusions (4 and 6 micrograms.min-1.kg-1) showed that the plasma concentration ratios at 24 hours of mononitrate metabolites to parent drug and apparent plasma clearance of ISDN were almost halved at the higher infusion rates.

Adult↗

PubMed1997

Neuropharmacological effects of low and high doses of repeated oral dexfenfluramine in rats: a comparison with fluoxetine.

The neuropharmacological effects of repeated oral doses of dexfenfluramine (DF; 1.25-10 mg/kg, twice daily for 21 days) were examined in rats and related to the drug brain levels. Results were compared with fluoxetine (FL) given at similar doses relative to its anorectic ED50. Both drugs dose-dependently slowed body weight gain and reduced brain serotonin (5-HT). However, at 1.25 mg/kg DF caused only a slight and transient decrease in cortical 5-HT. Comparable doses of FL (6.25-12.5 mg/kg) lowered 5-HT more than DF, besides slightly reducing striatal dopamine. At higher doses DF markedly reduced 5-HT in all regions, and to a lesser extent noradrenaline in hippocampus. There was a negative relationship between 5-HT and log total active drug levels and the indole was approximately halved at drug levels about 50 times lower with DF than FL. However, the ratio between drug levels causing marked 5-HT reductions and those considered anorectic was similar for DF and FL because brain levels at the anorectic ED50 were higher with FL than DF. Long-lasting reductions of 5-HT were also observed but recovery was only consistently slow beginning from 5 mg/ kg DF. Comparable doses of FL could not be used because its general toxicity leads to the death of rats after only 2-4 multiples of its anorectic ED50.

Administration, Oral↗

PubMed1997

Persistent excitability changes in the piriform cortex of the isolated guinea-pig brain after transient exposure to bicuculline.

The development of long-lasting excitability changes after a single intracerebral injection of bicuculline (1 mM) in a restricted region of the anterior piriform cortex was studied by means of simultaneous intra- and extracellular recordings in the isolated guinea-pig brain preparation maintained in vitro by arterial perfusion. The transitory disinhibition induced by bicuculline revealed transient afterdischarges that were followed by the activation of a synaptic potential mediated by the recurrent propagation of the focal epileptiform activity along cortico-cortical associative fibres. The epileptiform associative potential persisted for the duration of the experiment. Both the induction and the long-term expression of the epileptiform associative potential were dependent on the activation of glutamatergic receptors of the NMDA type, as demonstrated by perfusion with the NMDA receptor antagonist 2-aminopentanoic acid (AP5) (100 microM). After bicuculline washout, piriform cortex neurons responded to afferent stimulation with a burst discharge superimposed on a paroxysmal depolarizing potential. The early component of the burst was mediated by a Ca(2+)-dependent, non-synaptic potential located at the proximal apical dendrites and soma of layer II-III cells, since (i) it was abolished by membrane hyperpolarization, (ii) it was not affected by AP5, (iii) it was correlated with a current sink in layer II, as demonstrated by current source density analysis of field potential laminar profiles, and (iv) it was abolished by cadmium (2-5 mM) applied locally in layer II. The late component of the burst response (i) coincided in time with the extracellular epileptiform associative potential, (ii) increased linearly in amplitude during membrane hyperpolarization, (iii) was blocked by AP5, and (iv) was correlated with an extracellular sink in layer Ib, where the associative fibres contact the distal apical dendrites of piriform cortex neurons. The results presented here indicate that a transient focal disinhibition promotes persistent intrinsic and synaptic excitability changes in piriform cortex neurons. These changes may be responsible for the propagation of epileptiform activity and for the induction of secondary epileptogenesis.

Animals↗

PubMed1996

Effects of repeated oral doses of dexnorfenfluramine on 5-HT levels and 5-HT uptake sites in rat brain.

The effects of oral dexnorfenfluramine (DNF; 1-4 mg/kg, twice daily for 4 days), the active metabolite of dexfenfluramine, were examined on rat regional brain indole contents and [3H]citalopram binding. Two hours after the last dose, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were dose-dependently lowered at doses above 1.5 mg/kg, with slight regional differences. Cortical 5-HT uptake sites were reduced only at the highest dose. Above 2 mg/kg DNF also caused a more lasting reduction (4 weeks) of regional indoles and cortical 5-HT uptake sites. At this longer time while the decrease in hippocampal 5-HT levels and cortical 5-HT uptake sites remained essentially constant, cortical and striatal 5-HT levels were lowered less than at 2 h, suggesting a return toward control values.

Administration, Oral↗

PubMed1996

Dopamine-N-methyl-D-aspartate interactions in the modulation of locomotor activity and memory consolidation in mice.

This study explores the functional interaction between glutamatergic and dopaminergic systems in the modulation of two behavioral responses: locomotor activity and memory consolidation assessed with one-trial inhibitory avoidance. In agreement with previous reports, the NMDA receptor antagonist, (+)-MK-801 ((+)-5-methyl-10,11-dihydro(a,d) cyclohepten-5,10-imine hydrogen maleate), dose dependently enhanced locomotor activity in mice. The selective dopamine D1 receptor antagonist SCH 23390 at doses up to 0.05 mg/kg was unable to affect MK-801-induced locomotor activity, while (-)-sulpiride, but only at high doses (30 mg/kg), and haloperidol (0.05 mg/kg) blocked the MK-801 effect. Hypermotility induced by MK-801 was enhanced by repeated administration of haloperidol (once daily administration for 14 days of 4 mg/kg) or (-)-sulpiride (125 mg/kg), but not SCH 23390 (0.5 mg/kg). Dopamine D1 (SKF 38393)- and D2 (quinpirole)-selective agonists enhanced retention of one-trial inhibitory avoidance performance whilst NMDA receptor antagonists 3-(2-D-carboxypiperazin-4-yl)propyl-1-phosphoric acid (CPP) and MK-801 impaired it. Moreover we observed that the NMDA receptor antagonist-induced impairment of memory consolidation was attenuated by subeffective doses of SKF 38393 (5 mg/kg) and quinpirole (0.25 mg/kg). Impairment of the response induced by post-trial injections of CPP and MK-801, in the one-trial inhibitory avoidance test, was highly enhanced by 14 days of daily administration of haloperidol (4 mg/kg), sulpiride (25 mg/kg) but also SCH 23390 (0.5 mg/kg). These results suggest that different neural mechanisms underlie the functional interaction between the two neural systems in the modulation of these behavioral responses. Further, the results of the chronic study revealed a possible heterologous regulation of NMDA receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1996

Isocratic reversed-phase liquid chromatography of all-trans-retinoic acid and its major metabolites in new potential supplementary test systems for developmental toxicology.

An isocratic reversed-phase high-performance liquid chromatographic procedure for the determination of all-trans-retinoic acid (all-trans-RA) and its metabolites, all-trans-4-oxo-RA, 5,6-epoxy-RA, 9-cis-RA and 13-cis-RA, in mouse plasma and embryo and in new in vitro potential test systems for developmental toxicology has been developed. These compounds, their biological precursor retinol (vitamin A) and the internal standard were resolved on a Spherisorb ODS-2 (5 microns) column (250 x 4.6 mm I.D.) with acetonitrile-water-methanol-n-butyl alcohol (56:37:4:3, v/v) containing 100 mM ammonium acetate and 70 mM acetic acid as the elution system, with a total run time of 23 min. The assay was linear over a wide range, with a lower limit of quantitation of 50 ng/ml or 10 ng/mg of protein for all-trans-RA, 13-cis-RA and 9-cis-RA and of 25 ng/ml or 5 ng/mg protein for the 4-oxo- and 5,6-epoxy-metabolites. At these concentrations, intra-assay coefficients of variation (C.V.) of the retinoids were 3-9%. Mean intra-assay C.V. averaged 5-7% in the tissues studied. Its use is discussed for RA measurements in some of the new test systems--Drosophila melanogaster, sea urchin embryos and cultured human keratinocytes--that have to be evaluated in toxicological testing, supplementary to standard assays in mammals.

Animals↗

PubMed1996

AM580, a stable benzoic derivative of retinoic acid, has powerful and selective cyto-differentiating effects on acute promyelocytic leukemia cells.

All-trans retinoic acid (ATRA) is successfully used in the cyto-differentiating treatment of acute promyelocytic leukemia (APL). Paradoxically, APL cells express PML-RAR, an aberrant form of the retinoic acid receptor type alpha (RAR alpha) derived from the leukemia-specific t(15;17) chromosomal translocation. We show here that AM580, a stable retinobenzoic derivative originally synthesized as a RAR alpha agonist, is a powerful inducer of granulocytic maturation in NB4, an APL-derived cell line, and in freshly isolated APL blasts. After treatment of APL cells with AM580 either alone or in combination with granulocyte colony-stimulating factor (G-CSF), the compound induces granulocytic maturation, as assessed by determination of the levels of leukocyte alkaline phosphatase, CD11b, CD33, and G-CSF receptor mRNA, at concentrations that are 10- to 100-fold lower than those of ATRA necessary to produce similar effects. By contrast, AM580 is not effective as ATRA in modulating the expression of these differentiation markers in the HL-60 cell line and in freshly isolated granulocytes obtained from the peripheral blood of chronic myelogenous leukemia patients during the stable phase of the disease. In NB4 cells, two other synthetic nonselective RAR ligands are capable of inducing LAP as much as AM580, whereas RAR beta- or RAR gamma-specific ligands are totally ineffective. These results show that AM580 is more powerful than ATRA in modulating the expression of differentiation antigens only in cells in which PML-RAR is present. Binding experiments, using COS-7 cells transiently transfected with PML-RAR and the normal RAR alpha, show that AM580 has a lower affinity than ATRA for both receptors. However, in the presence of PML-RAR, the synthetic retinoid is a much better transactivator of retinoic acid-responsive element-containing promoters than the natural retinoid, whereas, in the presence of RAR alpha, AM580 and ATRA have similar activity. This may explain the strong cyto-differentiating potential of AM580 in PML-RAR-containing leukemic cells.

Alkaline Phosphatase↗

PubMed1996

In vitro and in vivo effects of the anorectic agent dexfenfluramine on the central serotoninergic neuronal systems of non-human primates. A comparison with the rat.

The effects of repeated subcutaneous (s.c) injections of dexfenfluramine (d-F; 10 mg/kg, twice daily, for 4 days) on the contents of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the brain were assessed in primates (cynomolgus and rhesus monkeys) and compared with the regional brain concentrations of unchanged drug and its active metabolite, dexnorfenfluramine (d-NF). This four-day, high-dose, regimen caused a large depletion of 5-HT (more than 95%) and of 5-HIAA (80-90%) in all brain areas studied (cortex, hippocampus, putamen, caudate nucleus and hypothalamus) 2 h after the last injection of d-F. Analysis of the plasma and brain contents of d-F and d-NF confirmed that both compounds were concentrated as in other species, in regions of the primate brain. However, d-NF was concentrated to a greater extent than d-F, and there were differences between the two primate species. Unlike in the rat brain, concentrations of d-NF greatly exceeded those of d-F in the primate brain suggesting that in these primates the d-NF may play a major role in the overall neurochemical response. The effects of d-F and d-NF on different in vitro parameters of serotoninergic neuronal function did not show appreciable differences between cynomolgus or rhesus monkeys when compared to rats, the ability of the two compounds to inhibit 5-HT reuptake, to enhance its release, and to affect the binding of [3H] -d-F or of [3H] -mesulergine (a ligand for 5-HT2C receptors) being similar. Kinetic differences in the disposition of d-F appear to have more relevance than biochemical effects in providing an explanation for the more marked brain depletion induced by d-F in primates than in rodents.

Animals↗

PubMed1996

In vivo and in vitro interaction of flunarizine with D-fenfluramine serotonergic effects.

Flunarizine (35 mg/kg), but not haloperidol and trifluperazine, counteracted the initial indole depletion induced by D-fenfluramine (dF) in vivo (5 mg/kg), without affecting ex vivo [3H]-serotonin (5-HT) uptake by synaptosomes or changing the brain concentrations of the parent drug and its main active metabolite, D-norfenfluramine (dNF). The long-term indole depletion induced by repeated doses of dF (5 mg/kg, b.i.d. for 4 days) was also reversed by flunarizine pretreatment. Flunarizine, methiothepin, and trifluperazine, but not haloperidol, reduced in vitro the Ca(2+)-dependent [3H]5-HT release stimulated by 0.5 microM dF and dNF from superfused synaptosomes. At the concentrations used in release experiments the drugs were not active on [3H]5-HT uptake nor on the calcium-calmodulin protein kinase activity, thus excluding an effect on the uptake carrier or on phosphorylation of synaptic proteins involved in exocytosis, respectively. The drugs did not consistently affect [3H]5-HT release induced by depolarization, or dNF-induced [3H]dopamine release in vitro. The fact that flunarizine, as methiothepin and 5-HT uptake inhibitors, counteract dF-induced indole depletion in vivo suggests a relation between the reduction of the Ca(2+)-dependent release of [3H]5-HT induced by dF in vitro and the protective effect on the short- and long-lasting depletion of indoles induced in vivo by high doses of dF.

Animals↗

PubMed1995

Determination of the retinobenzoic acid derivative Am580 in rat plasma by high-performance liquid chromatography.

A specific liquid chromatographic method for the determination of 4-[[(5,6,7,8,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthalenyl)carbonyl]amino]benzoic acid (Am580) in rat plasma is described. The procedure includes one-step isolation of the compound and the internal standard (naphthol AS) from protein precipitated with acetonitrile, resolution on a reversed-phase column (Supelcosil LC18-DB, 5 microns) with water-acetonitrile-methanol-n-butanol (45:40:14:1, v/v) containing 65 mM ammonium acetate as elution system and UV absorbance detection at 280 nm. The assay was linear over a wide range (25-5000 ng ml-1) and the limit of quantitation was 25 ng ml-1 using 0.2 ml of plasma. It was precise and reproducible enough for pharmacokinetic studies. Application to a preliminary disposition study in the rat indicated that Am580 was characterized by a relatively large apparent volume of distribution (1.1-1.5 1 kg-1) and small clearance (8.8-9.7 ml min-1 kg-1). Its pharmacokinetic behaviour was linear within the dose range considered (2 and 10 mg kg-1, i.p.).

Acetonitriles↗

PubMed1995

Effect of d-fenfluramine on the indole contents of the rat brain after treatment with different inducers of cytochrome P450 isoenzymes.

The effects of pretreatment with inducers of hepatic cytochrome P450 isoenzymes (phenobarbital, dexamethasone and beta-naphthoflavone) on the metabolism of d-fenfluramine (d-F) and its acute and long-lasting indole-depleting effects were studied in rats, in an effort to obtain further information on the importance of hepatic drug metabolism in relation to its neurochemical actions. Twenty-four hours after the last dose of each inducer, rats were injected with d-F hydrochloride (5 mg/kg, IP) and killed at various times thereafter for parallel determination of indoles and drug concentrations in plasma and brain. Additional rats were treated as above and killed 1 week after d-F hydrochloride (5 and 10 mg/kg) to study the recovery of indole in the cortex, a particularly sensitive brain area. Phenobarbital and beta-naphthoflavone and, to a lesser degree, dexamethasone, stimulated the metabolism of d-F, as evidenced by a decrease in plasma and brain areas under the curve (AUC) compared to vehicle-treated rats. This indicated that multiple isoenzymes are capable of mediating the drug's metabolism, primarily by N-dealkylation to d-norfenfluramine (d-NF). None of the inducers raised plasma and brain AUC of the nor-derivative, and in fact phenobarbital and particularly beta-naphthoflavone reduced it. These different effects were even apparent in rats given d-NF (2.5 mg/kg), indicating that both phenobarbital and beta-naphthoflavone also stimulate the sequential metabolism of the nor-metabolite (by N-deamintaion) which, however, is apparently enhanced most actively by beta-naphthoflavone-inducible forms of P-450.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗