Biomedical subjects

V Calderone

Publications and source records attributed to V Calderone.

At least 19 recordsLinked to original sources

PubMed2002

Large-conductance, ca(2+)-activated k(+) channels: function, pharmacology and drugs.

Because of the physiological role played by the hyperpolarisation process resulting from a K(+) outflow, it is not surprising that compounds able to activate outward K(+) channels are considered as promising drugs, with exciting perspectives for the treatment of several cardiovascular, respiratory, neurological and urological diseases. Among the different and numerous K(+) channel families, medicinal chemistry has focused its major interest onto two channel types: the ATP-sensitive channels (K(ATP)) and the large conductance subtype (BK), that belongs to the wide family of calcium-activated K(+) channels. BK channels are almost ubiquitous and exhibit single channel conductance of 100-300 pS, a property which justifies the potent role of these channels in the control of the membrane potential. BK channels have been investigated as potential therapeutic targets for different neuropathies, because of their profound influence on the neuronal activity. Moreover, BK channels are expected to have applications for the therapy of cardiovascular diseases. A potent feed-back control of the vascular and non-vascular smooth muscle tone is mediated by these channels, whose activation can be promoted by both a rise of the intracellular free calcium concentration as well as a membrane depolarisation. Additionally, BK channel activation can also be induced by other factors, such as cAMP-mediated phosphorylation, G-proteins, GMP and cGMP. The aim of this paper is to give a concise overview of the biological and pharmacological properties and potential therapeutic applications of activators of BK channels present at the vascular level. The "state of the art" in the pharmaceutical development of natural and synthetic BK-activators, with a description of the lead chemical structures, will be also described.

Animals↗

PubMed2002

[Ventricular arrhythmias. A potential risk associated with the use of non-cardiovascular drugs prolonging the QT interval].

The electrocardiogram shows a sequence of cardiac electrical events generated by individual electrical currents generated mainly by sodium (Na+), potassium (K+) and calcium (Ca++) ions transiting via specialized transport pathways, such as ion channels, inserted in the membranes of excitable cardiac cells. Na+ and Ca++, entering the cells, are messengers of activating, inward, depolarizing currents (INa, ICa), generating the QRS wave of the electrocardiogram, whereas K+, leaving the cells, carries outward repolarizing currents (e.g. Ito, IKr, IKs and IK1), generating the T wave of the electrocardiogram, which drives the cell to a rest condition. Therefore, a significantly prolonged repolarization process results in a prolonged QT interval which can initiate ectopic cardiac beats that may evolve into a potentially lethal ventricular tachyarrhythmia, called torsades de pointes. This implies that the measurement of QT interval, appropriately corrected (QTc) for heart rate values by applying available algorithms, is a current tool of diagnostic investigation to reveal abnormalities of the cardiac repolarisation process. Numerous non cardiovascular drugs in general clinical use (psychotropics, prokinetics, antimalarials, antibiotics, antihistamines, etc.) can prolong QT interval, often by a mechanism not necessary for their therapeutic effects, which is a reduction of the potassium current IKr conveyed by the HERG channel. The torsadogenic potential of these drugs can be facilitated by factors (female gender, bradycardia, electrolyte imbalances, cardiac diseases, simultaneous use of multiple drugs prolonging QT interval, etc.) known to have the propensity to reduce the redundant cardiac repolarization reserve, characterizing the healthy myocardium. Presently, drug candidates are routinely subjected to preclinical and clinical examination for cardiac safety, a property required by health authorities for any new medicine before allowing marketing authorization. Finally, before prescribing a medicinal product prolonging QT interval, a physician should carefully evaluate not only the disease he wants to treat but also the availability of equally effective, alternative drugs. The golden rule, to which such a prescription has always to abide, requires that the beneficial effects expected from a therapy should for each treated patient outweigh any possible adverse consequence, particularly when the latter one could be of lethal nature.

Action Potentials↗

PubMed2001

Structure of chicken plasma retinol-binding protein.

The crystal structure of the specific carrier of retinol (retinol-binding protein, RBP) purified from chicken plasma has been determined (space group P2(1)2(1)2(1), with a=46.06(5) A, b=53.56(6) A, c=73.41(8) A, and one protein molecule in the asymmetric unit). Despite being obtained from a species phylogenetically distant from mammals, chicken holoRBP has an overall structure that closely resembles the previously determined structures of mammalian holoRBPs. The lack in chicken RBP of eight carboxy-terminal amino acid residues characteristic of mammalian RBPs does not significantly affect the protein structure. A distinctive feature of the avian protein is a better definition of the loop 63-67, close to the opening of the beta-barrel cavity accommodating the retinol molecule, which is rather disordered in the structures of mammalian RBPs.

Animals↗

PubMed2001

Identification, retinoid binding, and x-ray analysis of a human retinol-binding protein.

Two cellular retinol-binding proteins (CRBP I and II) with distinct tissue distributions and retinoid-binding properties have been recognized thus far in mammals. Here, we report the identification of a human retinol-binding protein resembling type I (55.6% identity) and type II (49.6% identity) CRBPs, but with a unique H residue in the retinoid-binding site and a distinctively different tissue distribution. Additionally, this binding protein (CRBP III) exhibits a remarkable sequence identity (62.2%) with the recently identified iota-crystallin/CRBP of the diurnal gecko Lygodactylus picturatus [Werten, P. J. L., Röll, B., van Alten, D. M. F. & de Jong, W. W. (2000) Proc. Natl. Acad. Sci. USA 97, 3282-3287 (First Published March 21, 2000; 10.1073/pnas.050500597)]. CRBP III and all-trans-retinol form a complex (K(d) approximately 60 nM), the absorption spectrum of which is characterized by the peculiar fine structure typical of the spectra of holo-CRBP I and II. As revealed by a 2.3-A x-ray molecular model of apo-CRBP III, the amino acid residues that line the retinol-binding site in CRBP I and II are positioned nearly identically in the structure of CRBP III. At variance with the human CRBP I and II mRNAs, which are most abundant in ovary and intestine, respectively, the CRBP III mRNA is expressed at the highest levels in kidney and liver thus suggesting a prominent role for human CRBP III as an intracellular mediator of retinol metabolism in these tissues.

Amino Acid Sequence↗

PubMed2001

New 5-substituted-1-(2-hydroxybenzoyl)-benzotriazoles, potassium channel activators. IV.

This paper reports the synthesis of a series of new 5-substituted-1-(2-hydroxybenzoyl)-benzotriazoles, which have been tested for their activity as possible activators of potassium channels. In rat aortic rings, the 'opened' derivatives 1a-f, intermediates of synthesis, showed vasorelaxing properties, with appreciable values of potency. However, the most remarkable effects were recorded for the 2-hydroxybenzoylbenzotriazoles 3a-f, which showed full vasorelaxing efficacy and high potency values. The introduction of a 2-hydroxybenzyl substituent in the 1 position of the benzotriazole ring (compound 7) strongly decreased the activity, showing the importance of the electron-acceptor carbonyl function. The best compound, 3b, was further investigated, in order to evaluate the possible mechanism of action involved in the vasodilator activity. In the vascular model, different potassium channel blockers inhibited the effects of the compound, and an increase of the levels of membrane depolarisation induced a significant reduction of the recorded responses. Compound 3b was also tested in a model of isolated rat heart, retroperfused through the aorta and submitted to a global ischemia/reperfusion cycle. In such an experimental condition, 3b showed an interesting cardioprotective activity. All the above observations are in agreement with the hypothesis of a mechanism linked to the activation of potassium channels.

Animals↗

PubMed2001

Some structural changes on triazolyl-benzotriazoles and triazolyl-benzimidazolones as potential potassium channel activators. III.

This paper reports the synthesis and pharmacological evaluation of some compounds, obtained by structural modifications of 1,2,3-triazolyl-benzotriazoles and 1,2,3-triazolyl-benzimidazolones, which had shown activity as potential activators of the big-conductance calcium-activated potassium channels (BK(Ca)). Changes have concerned the introduction of a hinderer substituent in the 5-position of the benzimidazolone (4a, b) and benzotriazole (5a, b) rings, opening of the benzimidazolone ring (7) and substitution of the 1,2,3-triazole ring with a 2-hydroxyphenyl ring (10). Furthermore a series of 3-aryl-benzotriazin-4-one derivatives (13a-e) has been studied, which appears as a modification and/or combination of the benzimidazolone and benzotriazole rings. Only compound 10 shows interesting activity, while the other structural modifications either do not increase (compounds 4 and 5) or reduce (compounds 7 and 13) the pharmacological activity. However, these results provide useful information about structure-activity relationships.

Animals↗

PubMed2001

Adenosine-mediated hypotension in in vivo guinea-pig: receptors involved and role of NO.

1. Adenosine produced a biphasic lowering of the mean BP with a drastic bradycardic effect at the highest doses. The first phase hypotensive response was significantly reduced by the nitric oxide (NO) synthase inhibitor L-NAME. 2. The A(2a)/A(2b) agonist NECA produced hypotensive and bradycardic responses similar to those elicited by adenosine, which were not significantly modified by the A(2b) antagonist enprofylline. 3. The A(2a) agonist CGS 21680 did not significantly influence basal HR while induced a hypotensive response antagonized by the A(2a) selective antagonist ZM 241385, and reduced by both L-NAME and the guanylate cyclase inhibitor methylene blue. 4. The A(1) agonist R-PIA showed a dose-dependent decrease in BP with a drastic decrease in HR at the highest doses. The A(1) selective antagonist DPCPX significantly reduced the bradycardic activity and also the hypotensive responses obtained with the lowest doses while it increased those obtained with the highest ones. 5. The A(1)/A(3) agonist APNEA, in the presence of the xanthinic non-selective antagonist 8-pSPT, maintained a significant hypotensive, but not bradycardic, activity, not abolished by the histamine antagonist diphenhydramine. 6. The selective A(3) agonist IB-MECA revealed a weak hypotensive and bradycardic effect, but only at the highest doses. 7. In conclusion, in the systemic cardiovascular response to adenosine two major components may be relevant: an A(2a)- and NO-mediated hypotension, and a bradycardic effect with a consequent hypotension, via atypical A(1) receptors. Finally, an 8-pSPT-resistant hypotensive response not attributable to A(3) receptor-stimulation or to release of histamine by mastocytes or other immune cells was observed.

Adenosine↗

PubMed2000

Synthesis and beta-blocking activity of (R,S)-(E)-oximeethers of 2, 3-dihydro-1,8-naphthyridine and 2,3-dihydrothiopyrano[2, 3-b]pyridine:potential antihypertensive agents - part IX.

The synthesis of oximeethers of 2,3-dihydro-1,8-naphthyridine and 2, 3-dihydrothiopyrano[2,3-b]pyridine is described. These compounds exhibit a selective beta-blocking activity, with a selectivity towards beta(2)-receptors. Groups in the N(1) position giving rise to a considerable steric hindrance led to a higher beta(2)-blocking selectivity, whereas groups creating a moderate hindrance caused a weak but significant decrease in beta(2)-antagonist potency. Substitution of the N(1)-R group with a sulfur atom led to compounds possessing beta(1)-, beta(2)- and beta(3)-blocking properties. Compounds 9c(1) and 10a(1) showed a beta(3)-antagonist activity slightly lower than that of propranolol.

Adipose Tissue↗

PubMed2000

Triazolyl-benzimidazolones and triazolyl-benzotriazoles: new potential potassium channel activators. II.

This paper reports the synthesis and pharmacological evaluation of a series of 5-substituted-triazolyl benzotriazoles (2a-f) and the corresponding series of 5-substituted-triazolyl-benzimidazolones (6a-f), as potential activators of the big-conductance calcium-activated potassium channels (BK(Ca)). The synthesis and structure demonstration of the stock compounds of the two series have been described in our previous works, as well as the common starting compounds 4-carboxamido-5-(4-substituted-2amino-anilino)-1,2,3-triazoles (1a-f). The triazolyl-benzotriazoles were obtained by diazotization, while the triazolyl-benzimidazolones were obtained by thermal intramolecular cyclization of ethoxycarbonylamino derivatives or directly with phosgene. Benzimidazolone compounds generally showed little effect whilst the compounds with a benzotriazole ring showed full efficacy, with vasorelaxing properties and potency parameters a little lower than that of the reference compound NS 1619. These effects were significantly reduced by an increased membrane depolarization. This depolarization-sensitive response is in agreement with the pharmacodynamic hypothesis of activation of potassium channels.

Animals↗

PubMed2000

The structure of human aldose reductase bound to the inhibitor IDD384.

The crystallographic structure of the complex between human aldose reductase (AR2) and one of its inhibitors, IDD384, has been solved at 1.7 A resolution from crystals obtained at pH 5.0. This structure shows that the binding of the inhibitor's hydrophilic head to the catalytic residues Tyr48 and His110 differs from that found previously with porcine AR2. The difference is attributed to a change in the protonation state of the inhibitor (pK(a) = 4.52) when soaked with crystals of human (at pH 5.0) or pig lens AR2 (at pH 6.2). This work demonstrates how strongly the detailed binding of the inhibitor's polar head depends on its protonation state.

Aldehyde Reductase↗

PubMed1999

Antiviral properties of a crude extract from a green alga Caulerpa taxifolia (Vahl) C. Agardh.

A crude extract of Caulerpa taxifolia was tested for its antiviral activity. The chloroform-methanol residue showed an interesting inhibitor effect in vitro toward the feline immunodeficiency virus (FIV), a valid model for studying the acquired immunodeficiency syndrome. This extract reduced the virus-induced syncytia in the cultured cells, the viral reverse transcriptase activity and the viral capsid protein P24 expression.

Animals↗

PubMed1999

Vascular effects of aqueous crude extracts of Artemisia verlotorum Lamotte (Compositae): in vivo and in vitro pharmacological studies in rats.

Artemisia verlotorum Lamotte (Compositae), growing in almost all the northern hemisphere, is used in folk medicine of some countries of Tuscany, Italy, as a remedy for hypertension. The pharmacological evaluation of the responses evoked by an aqueous dried extract of Artemisia verlotorum on the blood pressure of anaesthetized rats and on in vitro rat isolated aortae showed a marked, but transient, hypotensive activity. This effect was mediated by a strong vasodilator action, closely linked to the release of endothelial nitric oxide and to the nitric oxide-guanosine 3'-5'-cyclic monophosphate (cGMP) pathway, caused by a muscarinic receptor agonism.

Acetylcholine↗

PubMed1999

Experimental and theoretical comparisons between the classical Schild analysis and a new alternative method to evaluate the pA2 of competitive antagonists.

The Schild analysis is undoubtedly the most frequently used powerful diagnostic tool to investigate the nature of an antagonist and, consequently, to evaluate its potency, often expressed as pA2. Nevertheless, different reasons often prevent the experimenter from applying this analysis, leading to use an inhibition curve for the antagonist and to evaluate its potency by means of several approaches, which are generally considered theoretically invalid. In a recent work, a new theoretical approach, mathematically analogous to the Schild one, has been shown. By means of a simplified experimental protocol based on an antagonist inhibition curve (following a control concentration-response curve for the agonist), this method allows a linear regression analysis, giving a slope value absolutely equivalent to the Schild slope and a reliable estimation of the pA2 of a competitive antagonist. In this paper, this new method has been compared with the Schild analysis, to determine the parameters of potency relative to well-known competitive antagonists, on different in vitro isolated preparations. In strips of guinea pig isolated gastric smooth muscle, pirenzepine antagonised the effects of bethanechol. In guinea pig isolated ileum, atropine blocked the contracturant effects of carbamylcholine, while in electrostimulated ileum segments, the inhibitory responses to alpha-methylnoradrenaline were reduced by idazoxan. Finally, in guinea pig isolated spontaneously beating atria, the negative inotropic effects of 5'-N-ethylcarboxamidoadenosine were antagonised by 8-cyclopentyl-1,3-dipropylxanthine. The parameters of potency, relative to all the above competitive antagonists and expressed as pA2, resulted almost equivalent, when calculated by the Schild analysis or by the alternative method. Furthermore, when tested also for the well-known irreversible alkylating agent dibenamine in rat aortic rings stimulated by noradrenaline, the alternative method furnished a profile of clear nonlinearity, unmasking the nature of the antagonism. Finally, the relationships between the results calculated by the alternative analysis or by the Schild analysis and different levels of computer-generated "random noise" (affecting the shape and the position of theoretical curves) were also evaluated, in order to know the robustness of the new method. The two methods proved reliable and almost equivalent in robustness, when applied with different levels of "random noise". These results confirm the Schild analysis as the most accurate tool to study antagonists, since this analysis can furnish the highest number of information and observations on the behaviour of an antagonist. Nevertheless, when limiting conditions prevent a classical Schild analysis and impose the use of an inhibition curve, the new method probably represents the most preferable experimental approach. Indeed, it allows to calculate the antagonist potency, after the evaluation of a slope parameter giving an important information about the possible nature of the antagonism.

Animals↗

PubMed1998

Influence of depolarization on vasorelaxant potency and efficacy of Ca2+ entry blockers, K+ channel openers, nitrate derivatives, salbutamol and papaverine in rat aortic rings.

We examined the effects of various KCl concentrations on the actions of some vasodilators belonging to different pharmacological classes in rat aortic rings. In some experiments, tissues were precontracted with noradrenaline after blocking voltage-dependent channels to assess the effects of depolarisation unaccompanied by the entry of extracellular Ca2+ into the cytosol. Concentration/response curves for the vasorelaxant effect of calcium entry blockers (e.g. diltiazem), K+ channel openers (e.g. aprikalim), nitrate derivatives (e.g. nitroglycerin), a beta2-adrenergic agonist (salbutamol) and papaverine were obtained by using endothelium-denuded rat aortic rings precontracted with KC1 (20-60 mM) to determine the potencies and efficacies of the drugs. The efficacies and potencies of calcium entry inhibitors were virtually independent of the [KCl]. A reduction in the potency (up to 18-fold) of papaverine occurred without changes in efficacy when the [KCl] was raised from 20 to 60 mM. The decline in potency was even greater for nitrate-like compounds. The potency of K+ channel openers in aortic rings precontracted with 30 mM KCI decreased by three- to sixfold compared with those precontracted with 20 mM KCl. With the exception of pinacidil, the efficacy of these agents already started to decline in preparations precontracted with 25 mM KCI and was virtually zero in preparations precontracted with 60 mM KCI. In contrast to other K+ channel openers, the vasorelaxant action of pinacidil was relatively resistant to glibenclamide. Salbutamol produced only a slight relaxation even in preparations precontracted with 20 mM KCl. In nitrendipine-pretreated, noradrenaline-precontracted aortic rings, the vasorelaxant effects of aprikalim, but not those of linsidomine or papaverine, declined when the [KCl] of the bathing medium was increased. In conclusion, the vasorelaxant potency and efficacy of calcium entry blockers is independent of the [KCI] used to precontract rat aortic rings, and thus, of the degree of membrane depolarisation. In contrast, increasing the [KCl] strongly reduces the potency and the efficacy of K+ channel openers not only in this preparation but also in noradrenaline-precontracted rings in which the entry of extracellular Ca2+ was prevented with nitrendipine. This indicates that, with the exception of pinacidil, the vasorelaxant activity of K+ channel openers depends on the degree of membrane depolarisation. Finally, the vasorelaxant potency and efficacy of nitrate-like compounds and papaverine are independent of depolarisation per se but they are markedly affected by the influx of Ca2+ accompanying elevated [KCI]. Thus, the degree of vessel depolarisation should be taken into consideration when attempting to compare potencies and efficacies among vasorelaxant agents.

Albuterol↗

PubMed1998

An alternative method to evaluate the nature of an antagonist and its potency: a theoretical approach.

The Schild analysis is certainly the most reliable method for antagonism studies. The Schild regression allows one to determine the parameter of the Schild-slope, which represents a powerful diagnostic tool when investigating the nature of an antagonist and, consequently, to evaluate its potency. Nevertheless, in functional pharmacology, often practical reasons lead the experimenter to obtain an inhibition curve for the antagonist and calculate its potency by means of equations, which can be considered as a derivation of the Cheng-Prusoff analysis. This approach is considered theoretically invalid, because it does not allow to know the exact nature of the antagonism, and thus the evaluation of the antagonist dissociation constant can be meaningless. In this paper, a new method is proposed, which, by means of an equation closely similar to the Schild one, permits one to obtain a linear regression analysis, giving a slope value absolutely equivalent to the Schild-slope. This method allows us to determine both the nature and the potency of an antagonist, and requires an experimental procedure substantially analogous to the one performed to obtain an inhibition curve.

Binding, Competitive↗

PubMed1998

A simplified empirical approach to evaluate the dissociation constant of a full agonist by the irreversible receptor inactivation method.

The estimation of the dissociation constant (Ka) of full agonists represents an essential tool for the classification of drugs and drug receptors, in functional pharmacology. The evaluation of the Ka was a problem until the development of the Furchgott's method (irreversible partial receptor inactivation method), which surely represents the most used analysis for the evaluation of the agonist Ka in experimental protocols on isolated tissues. The Furchgott's method can furnish a reliable estimation of the Ka, but it requires a relatively complicated manipulation of experimental data. In this article, an alternative approach for the evaluation of the Ka is proposed, on the basis of empirical considerations. This method, also based on the partial alkylation of a fraction of receptors, needs only the knowledge of the location parameters of the concentration-response curves and the application of a very simple equation, without any complicated intermediate interpolation of the experimental data.

Algorithms↗

PubMed1998

Intrinsic activity and EC50: the simplest tools for the evaluation of the dissociation constant of a partial agonist.

In functional pharmacology, the Furchgott's analysis and the Waud's analysis are the most widely used among the reliable different methods actually available, for the determination of the dissociation constant of partial agonists. However, they need the application of relatively complicated procedures of manipulation and interpolation of raw data. On the basis of empirical assumptions, this article proposes a new approach, which probably can be considered the simplest method to determine the dissociation constant of a partial agonist, because of the rapid experimental protocol and the easy calculation procedure. Computer-generated concentration-response curves (CRC) for hypothesised partial agonists were analysed by the widely known Waud's analysis and by this new approach. Furthermore, this new analysis was also used to evaluate experimental data from literature, relative to the dissociation constants of alpha-adrenoceptor partial agonists, recorded in rabbit and rat aortae and calculated by the Waud's method. The results obtained by the new approach, both for the computer-generated and for the experimentally studied partial agonists, showed a high level of accuracy, when compared with the classical Waud's analysis.

Adrenergic alpha-Agonists↗

PubMed1998

New 1,2,3-triazole derivatives (ureas, amides, urethanes) with a potential biological interest.

This paper reports the preparation of three series of 1,2,3-triazole derivatives bearing an ureido substituent (compounds 5a-h), a carboxamido substituent (compounds 6a-f) or an urethane substituent (compounds 7a-l). Some compounds were submitted to in vitro functional tests on guinea-pig isolated intestinal preparations and/or to in vitro antitumor and antiviral screening. The tested compounds showed no activity on guinea-pig ileum, except compound 7g, provided of contracturant properties; similarly, no anticancer or antiviral significant activity was found.

Animals↗