Biomedical subjects

R Zini

Publications and source records attributed to R Zini.

At least 37 records · Page 2Linked to original sources

PubMed1996

Desipramine treatment differently down-regulates beta-adrenoceptors of freshly isolated neurons and astrocytes.

Eight days' desipramine administration (16 mg/kg per day i.p.) to rats resulted in a significant decrease in the density of beta-adrenoceptors in neuronal and astroglial cells from rat forebrain and cerebellum without modification of their corresponding affinity. beta-Adrenoceptor subtypes, beta 1 and beta 2, which coexist in neurons and astrocytes, are differently distributed in the brain and differently modified by desipramine administration which down-regulates beta 1-adrenoceptor in forebrain neurons and astrocytes and beta 2-adrenoceptor in cerebellum neurons. This down-regulation affects the predominant subtype, beta 1 or beta 2, of the relevant structure. Astroglial and neuronal beta-adrenoceptors are differently coupled to G-proteins. Only neuronal cells contain the high-affinity conformational state of the beta-adrenoceptors which is sensitive to GTP. The percentage of neuronal receptors in the high-affinity state differs according to brain area. Desipramine treatment decreases the neuronal density of both cerebellar high- and low-affinity sites and only the forebrain high-affinity site. The desipramine effects are thus subtype-dependent and differ between the two brain areas selected.

Adrenergic Uptake Inhibitors↗

PubMed1996

Tobacco smoking induces expression of very-high-affinity nicotine binding sites on blood polymorphonuclear cells.

The targets of nicotine in the central nervous system (CNS) have been identified as nicotinic acetylcholine (ACh) receptors. Because of their localization in the brain, no data are available about their in vivo modifications. However, nonneuronal nicotine binding sites have been identified on peripheral blood cells. The present study was designed to evaluate the effects of tobacco smoking on granulocyte nicotine binding sites. Binding assays were performed on granulocyte membranes using (-)(3H)nicotine and were analyzed by the Scatchard method in nonsmokers (n=10), smokers (n=10), and ex-smokers (n=10). In nonsmokers, a single-affinity binding site was detected with Kd = 1.08 +/- 0.05 x 10 -9 M. In contrast, in smokers, two different classes of binding sites were identified: one with Kd1 = 2.80 +/- 0.81 x 10 -11 M and another with Kd2 = 3.92 +/- 0.58 x 10 -9 M, similar to the binding site in nonsmokers. Moreover, a twofold increase in nicotine binding-site density was observed in smokers. Ex-smokers recovered a single class of binding sites similar to those observed in nonsmokers when they had stopped smoking for more than 1 yr, whereas recent ex-smokers (1 to 8 mo) displayed a pattern similar to that in smokers, as demonstrated by the persistence of two classes of nicotine binding sites. Chronic nicotine exposure induces modifications of nicotine binding sites on granulocytes. It is noteworthy that the persistence of such alterations corresponds to the very high rate of relapse into smoking observed during the early stages of tobacco cessation. Consequently, monitoring of nicotine binding sites could constitute an interesting approach to understanding the pharmacologic mechanisms involved in tobacco dependence.

Adult↗

PubMed1996

Inhibition of rat cerebral mitochondrial respiration by cyclosporins A, D, and G and restoration with trimetazidine.

The aim of this work was to investigate possible inhibitory effects of Ca+ and different cyclosporins (Cs) on the rat brain mitochondrial respiratory control ratio (RCR) and whether or not these effects could be antagonized by trimetazidine (TMZ). The RCR was evaluated as the state 3/state 4 ratio of oxidative phosphorylation. CsA, D, and G inhibited about 10% of RCR in a concentration-dependent manner with EC50 of 57, 19 and 7 nM, respectively, whereas CsH did not modify RCR. TMZ was able to fully antagonize this inhibitory effect in a concentration-dependent manner with EC50 of 5,200, 180, and 1 nM, respectively. The Ca2+ added to the mitochondrial preparation decreased RCR in a concentration-dependent manner with a maximal effect of 46% obtained with 100 microM Ca2+. In the presence of TMZ (100 microM), the inhibitory effect of Ca2+ was partly reversed (9%). TMZ alone showed no inhibitory or stimulant effect on RCR. These results show that restoration of RCR by TMZ is due to a Ca(2+)-dependent mechanism, promoting Ca2+ efflux from the mitochondrial matrix. However, Ca2+ efflux is only partial in case of Ca2+ overload. These data suggest that TMZ may restore ATP synthesis in circumstances where neither Ca2+ overload, nor a prooxidant have generated a RCR decrease.

Analysis of Variance↗

PubMed1994

Isoproterenol interacts differently with beta-adrenoceptors in astrocytes and neurons isolated from the adult rat brain.

The interaction of isoproterenol with beta-adrenoceptors has been investigated in astroglial and neuronal cells isolated from adult rat cerebral cortices. Using the non-selective beta-adrenergic antagonist (3H)CGP-12177 as a ligand, binding experiments revealed that both types of cells exhibit beta-adrenoceptors. However the analysis of the isoproterenol displacement curve indicated that only neuronal cells contained the high affinity conformational state of the beta-adrenoceptor.

Animals↗

PubMed1994

Cyclic AMP and inositol phosphate accumulations in rat brain cortical slices following chronic citalopram or desipramine administration.

The influence of chronic administration of desipramine (16 mg/kg per day for 8 days) or citalopram (1 mg/kg per day for 8 days) on the serotonergic and noradrenergic stimulations of phosphoinositide hydrolysis and cyclic AMP formation was investigated in rat cerebral cortical slices. This was done by means of a prelabelling method allowing the simultaneous measurement of the accumulations of (3H) inositol phosphates ((3H)IP) and of (14C) cyclic AMP. Our results show that neither of the two drugs altered the inhibition of adenylate cyclase activity induced by serotonin1 (5-HT1) receptor agonists nor did they alter 5-HT1A and 5-HT1B receptor densities. Similarly they did not modify the stimulation of the inositol phosphate metabolism induced by 5-HT or norepinephrine (NE). Desipramine treatment decreased both beta-adrenoceptor-elicited cyclic AMP accumulation (-37%) and beta-adrenoceptor density (-29%), whereas citalopram was without effect. These results reinforce the idea that the ability of antidepressants to decrease the activity of the beta-adrenoceptor-adenylate cyclase complex is not common to all antidepressants, and provide no evidence for the involvement of 5-HT1A and/or 5-HT1B in the mechanism of action of these drugs.

Animals↗

PubMed1993

Nucleotides modulate the low affinity binding sites for [3H]glibenclamide in the rat brain.

Receptors for hypoglycemic sulfonylureas, such as glibenclamide, are commonly linked to the activity of ATP-sensitive K+ channels (K-ATP). High and low affinity binding sites for glibenclamide were described previously in numerous tissues. High affinity binding sites have been thought to be responsible of the modulation of K-ATP, but new evidences suggest that low affinity ones could also regulate these channels. In order to clarify the properties of the two binding sites, with respect to their interaction with K-ATP, we characterized biochemically and pharmacologically [3H]glibenclamide binding in the rat brain cortex. Competitive inhibition plots with [3H]glibenclamide performed on membranes of adult and neonatal rat brain cortex exhibited a biphasic pattern with similar binding parameters, indicating the presence of two similar binding sites in adult as well as in neonatal animals. Membranes of adult rat cortex treated with thiol groups modifying agents, N-ethylmaleimide or 1,4-dithiothreitol, increased the inhibition constant of glibenclamide for the low affinity binding sites (K(i)L) by about 4-fold. The divalent cations Mg++ and Ca++ also increased K(i)L by 3- to 6-fold and enhanced the low affinity binding capacity (BmaxL) by 55 and 103%, respectively, both cations increasing BmaxL by 144%. Among the numerous nucleotides studied, adenine and guanidine triphosphate nucleotides were the most potent to affect the low affinity binding sites. ATP, ADP, GTP and respective nonhydrolysable nucleotides increased K(i)L by 7- to 12-fold and decreased BmaxL by 10 to 30%. The effects of nucleotides were not Mg++ dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1992

Albumin binding and brain uptake of 6-fluoro-DL-tryptophan: competition with L-tryptophan.

We investigated potential competition between L-tryptophan (TRP) and 6-fluoro-DL-tryptophan (6-F-TRP) for binding to albumin and for passage through the blood-brain barrier (BBB). In experiments based on equilibrium dialysis, albumin (600 microM) bound about 80% of TRP and 50% of 6-F-TRP with affinity constants (Ka) of 3.7 +/- 0.04 x 10(4) and 0.62 +/- 0.01 x 10(4) M-1, respectively. Competitive inhibition was assessed as the decrease in the apparent Ka (K' a) of TRP in the presence of 6-F-TRP, with no modification of the N value. Competition between TRP, 6-F-TRP and L-valine (VAL) for passage across the BBB was demonstrated using two approaches. When administered concomitantly with TRP or 6-F-TRP to rats, VAL decreased brain uptake of TRP and 6-F-TRP and reversed their action on serotonin. In Oldendorf's model, 6-F-TRP and VAL decreased the brain uptake of TRP.

Animals↗

PubMed1992

Evaluation of central adrenergic receptor signal transmissions after an antidepressant administration to the rat.

The effects of several antidepressants, amitriptyline, citalopram, desipramine, fluoxetine, maprotiline, mianserin, nialamide, nomifensine, tranylcypromine and viloxazine, on the accumulation of cyclic AMP and inositol monophosphates were studied in rat cerebral cortical slices. The two enzymatic systems were stimulated either by adrenergic agonists or by forskolin. Cyclic AMP and inositol monophosphates (IPs) formed were determined by a double label method. In vitro all drugs, except inhibitors of monoamine oxidase, nialamide and tranylcypromine, inhibited alpha 1-agonist-mediated production but did not modify the cyclic AMP accumulation. Otherwise, chronic desipramine but not citalopram administration decreased the accumulation of cyclic AMP (-39%) elicited by beta-adrenoceptor agonists; no change was observed in inositol phosphate metabolism after administration of these two drugs. These data support previous investigations showing a decrease in cyclic AMP production after chronic treatment with norepinephrine uptake blockers but do not confirm the hypothesis of a modification of alpha 1-adrenoceptor-stimulated inositol phosphate metabolism.

Animals↗

PubMed1992

Serotonin enhances the beta-adrenergic response in rat brain cortical slices.

Serotonin increased the isoproterenol-induced cyclic AMP accumulation in rat brain cortical slices but did not itself stimulate the production of cyclic AMP in this area. This effect appeared to be inhibited by the 5-HT2 receptor antagonist, ritanserin. This potentiation was not observed in the hippocampus. These data reinforce the hypothesis of a coupling between the noradrenergic and serotonergic systems, which may be involved in the mechanism of action of antidepressant drugs.

Animals↗

PubMed1992

Labelling of rat brain beta-adrenoceptors: (3H)CGP-12177 or (125I)iodocyanopindolol?

Binding of (125I)iodocyanopindolol (ICYP) and (3H)CGP-12177 to rat brain homogenates was characterized and compared. ICYP was shown to bind to both beta-adrenergic and serotonin1B (5HT1B) receptors whereas (3H)CGP-12177 only labelled the first ones. The addition of 10 microM serotonin (5HT) prevented ICYP binding to 5HT receptors and under these experimental conditions both ligands labelled a similar total number of beta-adrenoceptors in the different rat brain regions. ICYP displayed a higher affinity for cerebellar (mainly beta 2-subtype) than for cerebral cortex beta-adrenoceptors (mainly beta 1-subtype) suggesting a subtype selectivity. A multiple displacement binding approach using CGP-20712A, a beta 1-subtype ligand, as competitor revealed a 2.6 fold selectivity of ICYP for the beta 2-adrenoceptor subtype. On the other hand, (3H)CGP-12177 binds only to beta-adrenoceptors and is not subtype selective in the rat brain homogenate. Considering both its high specificity and its lack of subtype selectivity (3H)CGP-12177 seems to be a more suitable ligand than ICYP to non-selectively label beta-adrenoceptors in rat brain.

Adrenergic beta-Antagonists↗

PubMed1991

A method to measure simultaneously cyclic AMP and inositol phosphate accumulation in rat brain slices.

The simultaneous measurement of the accumulation of cyclic AMP and inositol phosphates in rat cerebral cortical slices is described. After stimulation, the separation of cyclic AMP and inositol phosphates was achieved using ion-exchange chromatography and their concentrations were determined by means of a double-labeling technique, the substrates adenine and inositol being labeled with 14C and 3H, respectively. The recoveries were 70-80% for inositol phosphates and 40-50% for cyclic AMP. To test the applicability of the method, norepinephrine was chosen as an agonist, because it is known to stimulate the production of these two second messengers by interacting with alpha- and beta-adrenergic receptors. This procedure is an improvement over existing methods, because we obtained the simultaneous formation of 3H-inositol phosphates and [14C]cyclic AMP in a concentration-dependent process. EC50 values were similar for the two, 8.5 +/- 3.9 microM for 3H-inositol phosphates and 20.2 +/- 6.3 microM for [14C]cyclic AMP, and close to the values obtained when each process was studied alone. The action of adrenergic antagonists was also tested. Propranolol blocked the norepinephrine stimulation of [14C]cyclic AMP, but did not inhibit the norepinephrine stimulation of 3H-inositol phosphates. The opposite results were observed with prazosin. Our results suggest that this method could be a useful tool to examine the interaction between these two receptor-coupled effectors.

1-Methyl-3-isobutylxanthine↗

PubMed1991

The blood binding of cefotiam and cyclohexanol, metabolites of the prodrug cefotiam hexetil, in-vitro.

The binding of cefotiam and cyclohexanol to human serum, isolated proteins and erythrocytes has been studied in-vitro by equilibrium dialysis. The two molecules are 50% bound to serum proteins and the free fraction for both compounds remained constant within the therapeutic concentration range. Human serum albumin (HSA) was exclusively responsible for the cefotiam binding (48%) with a saturable process characterized by one binding site (n = 1.00 +/- 0.14) with a very weak affinity (Ka = 1457 +/- 352 M-1). Like other cephalosporins, cefotiam showed no binding to alpha 1-acid glycoprotein, lipoproteins or gamma-globulins. Cyclohexanol is mainly bound to HSA with a weak affinity (Ka approximately 1,800 M-1) but lipoproteins and alpha 1-acid glycoprotein bind about 30% of bound cyclohexanol in serum. Interactions with free fatty acids (FFA) or bilirubin were studied at physiopathological concentrations. HSA-bound cefotiam was displaced by FFA (1260 microM) and bilirubin (330 microM), whereas the cyclohexanol binding was inhibited only by FFA. The cefotiam binding site seems to be close to the warfarin site (site I) whereas cyclohexanol probably shares the diazepam site (site II) on HSA. There is no mutual inhibition of binding between cefotiam and cyclohexanol at therapeutic levels. The binding of both compounds to erythrocytes is low and restricted when measured in the presence of plasma.

Bilirubin↗

PubMed1991

Interactions of flerobuterol, an antidepressant drug candidate, with beta adrenoceptors in the rat brain.

Interactions of dl-flerobuterol with central beta adrenoceptors were investigated. It inhibited the binding of [3H]CGP 12177, a selective beta adrenoceptor ligand, to membranes prepared from rat cerebral cortex, cerebellum, heart and lung. The affinity of dl-flerobuterol was very close in all tissues (Ki approximately 1 microM). In cerebral cortex, binding inhibition of [3H]CGP 12177 was stereospecific, l-flerobuterol (Ki = 483 nM) being 70-fold more potent than d-flerobuterol (Ki = 34 microM). Moreover, dl-flerobuterol (Ki = 926 nM) was 7-fold less potent than isoproterenol (Ki = 140 nM) to displace [3H]CGP 12177 binding, but 5-fold more potent than salbutamol (Ki = 4600 nM). Flerobuterol did not inhibit the radioligand binding to the other receptors at the highest concentration tested, thus leading to a very high beta adrenergic selectivity. Flerobuterol increased the concentration of cyclic AMP in slices of rat cerebral cortex in a dose-dependent manner; this effect was antagonized by atenolol and propranolol. Compared to isoproterenol or norepinephrine, which produced cyclic AMP maximal increases of 380 and 460%, respectively, it showed a weaker activity with a maximal stimulation obtained at 100 microM, corresponding to a cAMP increase of 140% over basal value (100%). These data revealed that flerobuterol possessed a beta adrenergic agonist activity. Moreover, it antagonized competitively the isoproterenol- or norepinephrine-stimulated accumulation of cAMP. At low concentrations of isoproterenol or norepinephrine, the stimulation of adenylate cyclase was only due to the action of flerobuterol, but at higher concentrations, the response of isoproterenol or norepinephrine was competitively blocked by flerobuterol. At 10 microM, isoproterenol surmounted fully this antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗

PubMed1991

Blood binding of selezen (imidazole salicylate) in man.

The interactions of selezen (imidazole salicylate) with human blood components were studied by equilibrium dialysis. These interactions were limited to the binding of salicylate to human serum albumin (HSA). The binding was saturable and involved several classes of binding sites with different association constants. A competition study indicated that salicylic acid at high concentration was able to displace warfarin and digitoxin but not glibenclamide from their HSA sites. On the other hand, selezen serum binding was decreased in renal impaired patients and this result was probably linked to the decreases in HSA concentration. So the use of small dosage regimens of selezen to these patients can be proposed. The same recommendation may be done for cirrhotic patients, where the decrease of selezen binding percentage was observed and due to both hypoalbuminemia and hyperbilirubinemia.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1991

The influence of various drugs on the binding of tianeptine to human plasma proteins.

The plasma binding of the atypical tricyclic antidepressant tianeptine was studied in combination with six drugs, at therapeutic concentrations: cyamemazine, levomepromazine, flunitrazepam, oxazepam, diclofenac and salicylic acid. Of these drugs, only salicylic acid at high plasma concentrations impaired tianeptine binding and thus may potentiate its effects.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1990

Separation procedures used to reveal and follow drug-protein binding.

The review gives a critical evaluation of the different separation procedures used to study drug-protein interactions and describes their various fields of application. For pharmacological studies, the most widely used methods are dialysis and ultrafiltration, because they allow measurements with solutions of high protein concentrations, such as those found in therapeutic conditions. Both techniques use membrane devices, which may induce additional binding effects. Another drawback of these techniques is the need for radiolabelled compounds. Chromatographic methods, which now take advantage of the technology of high-performance liquid chromatography, are generally faster and do not use drug labelling because of the higher sensitivities of the detectors. Two different approaches are possible: either all the interacting species (protein and drug) are dissolved in the mobile phase, or one of them (protein or drug) is immobilized on the support. Several chromatographic methods are available for studies in solution that differ according to the sample injection mode (frontal or zonal elution) and the nature of the mobile phase used. They include quantitation of the drug-protein complex by zonal elution, the Hummel and Dreyer method, frontal elution, the vacancy peak method, and retention analysis by zonal elution. Frontal elution is the most rigorous method since all the species at equilibrium are present in the mobile phase with known and constant concentrations. The most promising one is the Hummel and Dreyer method, because of the very small amount of protein injected in the mobile phase containing the drug. Drug-protein interactions may be studied by affinity chromatography by immobilizing one of the interacting species on the support. Comparison of the constants obtained with methods when both the drug and the protein are in solution is questionable, since the immobilized species in affinity separations differ in their physical properties from those in solution. The main advantage with studies on immobilized proteins is the easy comparison of the binding properties of various drugs, especially when they are enantiomeric. The results of the binding constants measured by different separation methods are given for the albumin-phenylbutazone and albumin-warfarin systems. Good agreement is generally obtained, which proves the validity of using chromatography as a tool to study drug-protein interactions.

Chromatography, Affinity↗

PubMed1990

Use of 1-anilino-8-naphthalene sulfonate as a fluorescent probe in the investigation of drug interactions with human alpha-1-acid glycoprotein and serum albumin.

We report a rapid method for the characterization of the human serum albumin (HSA) and alpha-1-acid glycoprotein (AAG) interactions with drugs. The binding of 1-anilino-8-naphthalene sulfonate (ANS) to AAG and HSA was measured by fluorescence spectroscopy. Fluorescence data indicated that ANS was bound tightly to at least one site on AAG, with an affinity constant of 1.35 x 10(6) M-1. The fluorescence of an ANS:AAG complex was quenched by the binding of various drugs. Fluorescence quenching of the HSA:ANS complex showed a single site with an affinity constant of 0.72 x 10(6) M-1. The interaction of AAG and HSA with ANS or other drugs was also studied by comparative equilibrium dialysis. [14C]Pipequaline was used as an AAG and HSA site marker. [14C]Pipequaline seems to share sites I (azapropazone) and II (diazepam and ibuprofen) of HSA. However, high concentrations of warfarin were unable to displace [14C]pipequaline. On the other hand, it was shown that palmitic acid decreased, whereas bilirubin increased the pipequaline binding.

Anilino Naphthalenesulfonates↗

PubMed1990

Tianeptine binding to human plasma proteins and plasma from patients with hepatic cirrhosis or renal failure.

1. The binding of tianeptine to human plasma, isolated plasma proteins, red blood cells and to plasma from patients with cirrhosis or renal failure was studied in vitro by equilibrium dialysis. 2. Tianeptine is highly bound to plasma (95%) at therapeutic concentrations (0.3-1 microM). No saturation of the binding sites was seen. 3. Human serum albumin (HSA) was shown to be mainly responsible for this binding (94%) with a saturable process characterized by one binding site with a moderate affinity (Ka = 4.2 x 10(4) M-1) and a non-saturable process with a low total affinity (nKa = 1.2 x 10(4) M-1). 4. Like many basic and amphoteric drugs, tianeptine showed a saturable binding to alpha 1-acid glycoprotein (AAG) with one site and a moderate affinity (Ka = 3.7 x 10(4) M-1). Its binding to lipoproteins and red blood cells (RBC) was weak and non-saturable. Over the range of therapeutic drug concentrations (0.3-1 microM), the unbound fraction in blood remains constant (4.5%). 5. Interactions were studied using non-esterified fatty acids (NEFA) at pathological concentrations; they altered tianeptine binding to plasma and to isolated HSA. Tianeptine seems to bind to a HSA site different from sites I (warfarin) and II (diazepam), but close to site II. It also shares the only basic-site on AAG. However, at therapeutic drug concentrations (0.3-1 microM), not all of these interactions occur. 6. The binding of tianeptine varied according to HSA, AAG and NEFA concentrations both in patients and healthy subjects. In patients with chronic renal failure having high NEFA concentrations the unbound fraction of tianeptine (fu) increased from 0.045 to 0.153 compared with normal (P less than 0.001). In cirrhotic patients, with relatively low HSA concentrations, the fu of tianeptine increased from 0.045 to 0.088 compared with normal (P less than 0.01). 7. Multiple regression analysis of all of the data indicated that the fu of tianeptine was related significantly to HSA, NEFA and AAG concentrations, with a particularly strong correlation with NEFA concentrations. Therefore, variation of HSA and NEFA concentrations in patients on maintenance therapy may cause an increase of tianeptine fu.

Adult↗