María Dolores Ivorra

Tetrahydroisoquinolines as dopaminergic ligands: 1-Butyl-7-chloro-6-hydroxy-tetrahydroisoquinoline, a new compound with antidepressant-like activity in mice.

Three series of 1-substituted-7-chloro-6-hydroxy-tetrahydroisoquinolines (1-butyl-, 1-phenyl- and 1-benzyl derivatives) were prepared to explore the influence of each of these groups at the 1-position on the affinity for dopamine receptors. All the compounds displayed affinity for D(1)-like and/or D(2)-like dopamine receptors in striatal membranes, and were unable to inhibit [(3)H]-dopamine uptake in striatal synaptosomes. Different structure requirements have been observed for adequate D(1) or D(2) affinities. This paper details the synthesis, structural elucidation, dopaminergic binding assays, structure-activity relationships (SAR) of these three series of isoquinolines. Moreover, 1-butyl-7-chloro-6-hydroxy-tetrahydroisoquinoline (1e) with the highest affinity towards D(2)-like receptors (K(i) value of 66nM) and the highest selectivity (49-fold D(2) vs D(1)) by in vitro binding experiments was then evaluated in behavioral assays (spontaneous activity and forced swimming test) in mice. Compound 1e increased locomotor activity in a large dose range (0.04-25mg/kg). Furthermore, this lead compound produced reduction in immobility time in the forced swimming test at a dose (0.01mg/kg) that did not modify locomotor activity. The haloperidol (0.03mg/kg), a D(2) receptor preferred antagonist, blocked the antidepressant-like effect of compound 1e.

A possible structural determinant of selectivity of boldine and derivatives for the α1A-adrenoceptor subtype

1 The selectivity of action of boldine and the related aporphine alkaloids, predicentrine (9‐O‐methylboldine) and glaucine (2,9‐O‐dimethylboldine) on α1‐adrenoceptor subtypes was studied by examining [3H]‐prazosin competition binding in rat cerebral cortex. WB 4101 and benoxathian were used as selective α1A‐adrenoceptor antagonists. 2 In the competition experiments [3H]‐prazosin (0.2 nM) binding was inhibited by WB 4101 and benoxathian. The inhibition curves displayed shallow slopes which could be subdivided into high and low affinity components (pKi = 9.92 and 8.29 for WB 4101, 9.35 and 7.94 for benoxathian). The two antagonists recognized approximately 37% of the sites with high affinity from among the total [3H]‐prazosin specific binding sites. 3 Boldine, predicentrine and glaucine also competed for [3H]‐prazosin (0.2 nM) binding with shallow and biphasic curves recognizing 30–40% of the sites with high affinity. Drug affinities (pKi) at the high and low affinity sites were, 8.31 and 6.50, respectively, for boldine, 8.13 and 6.39 for predicentrine, and 7.12 and 5.92 for glaucine. The relative order of selectivity for α1A‐adrenoceptors was boldine (70 fold α1A‐selective) = predicentrine (60 fold, α1A‐selective) > glaucine (15 fold, α1A‐selective). 4 Pretreatment of rat cerebral cortex membranes with chloroethylclonidine (CEC, 10 μm) for 30 min at 37°C followed by thorough washing out reduced specific [3H]‐prazosin binding by approximately 70%. The CEC‐insensitive [3H]‐prazosin binding was inhibited by boldine monophasically (Hill slope = 0.93) with a single pKi value (7.76). 5 These results suggest that whereas the aporphine structure shared by these alkaloids is responsible for their selectivity of action for the a α1A‐adrenoceptor subtype in rat cerebral cortex, defined functional groups, namely the 2‐hydroxy function, induces a significant increase in α1A‐subtype selectivity and affinity.

Different expression of adrenoceptors and GRKs in the human myocardium depends on heart failure ethiology and correlates to clinical variables

Downregulation of β(1)- adrenergic receptors (β(1)-ARs) and increased expression/function of G-protein-coupled receptor kinase 2 (GRK2) have been observed in human heart failure, but changes in expression of other ARs and GRKs have not been established. Another unresolved question is the incidence of these compensatory mechanisms depending on heart failure etiology and treatment. To analyze these questions, we quantified the mRNA/protein expressions of six ARs (α(1A), α(1B), α(1D), β(1), β(2), and β(3)) and three GRKs (GRK2, GRK3, and GRK5) in left (LV) and right ventricle (RV) from four donors, 10 patients with ischemic cardiomyopathy (IC), 14 patients with dilated cardiomyopathy (DC), and 10 patients with nonischemic, nondilated cardiopathies (NINDC). We correlated the changes in the expressions of ARs and GRKs with clinical variables such as left ventricular ejection fraction (LVEF) and left ventricular end-systolic and left ventricular end-diastolic diameter (LVESD and LVEDD, respectively). The main findings were 1) the expression of the α(1A)-AR in the LV positively correlates with LVEF; 2) the expression of GRK3 and GRK5 inversely correlates with LVESD and LVEDD, supporting previous observations about a protective role for both kinases in failing hearts; and 3) β(1)-AR expression is downregulated in the LV and RV of IC, in the LV of DC, and in the RV of NINDC. This difference, better than an increased expression of GRK2 (not observed in IC), determines the lower LVEF in IC and DC vs. NINDC.

2,3,9- and 2,3,11-Trisubstituted tetrahydroprotoberberines as D2 dopaminergic ligands

Dopamine-mediated neurotransmission plays an important role in relevant psychiatric and neurological disorders. Nowadays, there is an enormous interest in the development of new dopamine receptors (DR) acting drugs as potential new targets for the treatment of schizophrenia or Parkinsons disease. Previous studies have revealed that isoquinoline compounds such as tetrahydroisoquinolines (THIQs) and tetrahydroprotoberberines (THPBs) can behave as selective D2 dopaminergic alkaloids since they share structural similarities with dopamine. In the present study we have synthesized eleven 2,3,9- and 2,3,11-trisubstituted THPB compounds (six of them are described for the first time) and evaluated their potential dopaminergic activity. Binding studies on rat striatal membranes were used to evaluate their affinity and selectivity towards D1 and D2 DR and establish the structure-activity relationship (SAR) as dopaminergic agents. In general, all the tested THPBs with protected phenolic hydroxyls showed a lower affinity for D1 and D2 DR than their corresponding homologues with free hydroxyl groups. In previous studies in which dopaminergic affinity of 1-benzyl-THIQs (BTHIQs) was evaluated, the presence of a Cl into the A-ring resulted in increased affinity and selectivity towards D2 DR. This is in contrast with the current study since the existence of a chlorine atom into the A-ring of the THPBs caused increased affinity for D1 DR but dramatically reduced the selectivity for D2 DR. An OH group in position 9 of the THPB (9f) resulted in a higher affinity for DR than its homologue with an OH group in position 11 (9e) (250 fold for D2 DR). None of the compounds showed any cytotoxicity in freshly isolated human neutrophils. A molecular modelling study of three representative THPBs was carried out. The combination of MD simulations with DFT calculations provided a clear picture of the ligand binding interactions from a structural and energetic point of view. Therefore, it is likely that compound 9d (2,3,9-trihydroxy-THPB) behave as D2 DR agonist since serine residues cluster are crucial for agonist binding and receptor activation.

Tetrahydroisoquinolines acting as dopaminergic ligands. A molecular modeling study using MD simulations and QM calculations

A molecular modeling study on 16 1-benzyl tetrahydroisoquinolines (BTHIQs) acting as dopaminergic ligands was carried out. By combining molecular dynamics simulations with ab initio and density functional theory (DFT) calculations, a simple and generally applicable procedure to evaluate the binding energies of BTHIQs interacting with the human dopamine D2 receptor (D2 DR) is reported here, providing a clear picture of the binding interactions of BTHIQs from both structural and energetic viewpoints. Molecular aspects of the binding interactions between BTHIQs and the D2 DR are discussed in detail. A significant correlation between binding energies obtained from DFT calculations and experimental pKi values was obtained, predicting the potential dopaminergic effect of non-synthesized BTHIQs.

Vasodilator Effects of Liriodenine and Norushinsunine, Two Aporphine Alkaloids Isolated from Annona cherimolia, in Rat Aorta

The effect of two aporphines, liriodenine and norushinsunine, isolated from Annona cherimolia, were studied in the rat aorta in order to examine their mechanism of action. Both alkaloids (10(-7) - 10(-4) mol/l) showed relaxant effects on the contractions elicited by 10(-6) mol/l noradrenaline (NA) or 80 mmol/1 KCl, but, while liriodenine showed a nonspecific relaxant action on both spasmogens, norushinsunine was more potent on KCl-induced contraction. In Ca2+ free medium, both alkaloids (0.1 mmol/l) inhibited the responses elicited by NA, but not those elicited by caffeine. This inhibitory action occurred when the alkaloids were present during the release of the Ca2+ internal stores or during the refilling process. These results suggest that the two aporphines show a relaxant action in rat aorta which is mediated by an interaction with alpha1-adrenoceptors and an alteration of the Ca2+ entry via voltage-operated channels. Norushinsunine exhibits a certain degree of selectivity as an L-type Ca2+ channel blocker.

Relationships between structure and vascular activity in a series of benzylisoquinolines

1 1In the present work, the properties of 3‐methyl isoquinoline, 3,4‐dihydropapaverine, tetrahydropapaverine and tetrahydropapaveroline were compared with those of papaverine and laudanosine. The work includes functional studies on rat isolated aorta contracted with noradrenaline, caffeine or KC1, and a determination of the affinity of the compounds for α1‐adrenoceptors and calcium channel binding sites, with [#H]‐prazosin, [#H]‐nitrendipine and [#H]‐(+)‐cis‐diltiazem binding to rat cerebral cortical membranes. The effects of papaverine derivatives on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were also determined. 2 2The three papaverine derivatives show greater affinity than papaverine for the [#H]‐prazosin binding site. They are therefore more selective as inhibitors of [#H]‐prazosin binding as opposed to [#H]‐(+)‐cis‐diltiazem, while papaverine appears to have approximately equal affinity for both. [#H]‐nitrendipine binding was not affected by either papaverine or papaverine derivatives in concentrations up to 100 μM. 3‐Methylisoquinoline had no effect on any of the binding sites assayed. 3 3Contractions evoked by noradrenaline (1 μM) in rat aorta were inhibited in a concentration‐dependent manner by 3,4‐dihydropapaverine, tetrahydropapaverine and with a lower potency, by tetrahydropapaveroline. In Ca2+‐free solution, tetrahydropapaverine and to a lesser extent, tetrahydropapaveroline, inhibited the noradrenaline (1 μM) evoked contraction in a concentration‐dependent manner and did not modify the phasic contractile response evoked by caffeine (10 mM). This suggests that these alkaloids do not act at the intracellular level, unlike papaverine which inhibits the contractile response to caffeine and noradrenaline. 4 4Inositol phosphates formation induced by noradrenaline (1 μM) in rat aorta was inhibited by tetrahydropapaverine (100 μM) and tetrahydropapaveroline (300 μM), thus suggesting that α1D‐adrenoceptors are coupled to phosphoinositide metabolism in rat aorta. 5 5Unlike papaverine, which has a significant effect on all the PDE isoforms, the three alkaloids assayed did not have an inhibitory effect on the different forms of PDE isolated from bovine aorta. 6 6These results provide evidence that papaverine derivatives with a partially or totally reduced isoquinoline ring have a greater affinity for α1‐adrenoceptors and a lower affinity for benzothiazepine sites in the Ca2+‐channel than papaverine. This structural feature also implies a loss of the inhibitory activity on PDE isoforms. The planarity of the isoquinoline ring (papaverine) impairs the interaction with the α1‐adrenoceptor site and facilitates it with the Ca2+‐channels and PDEs, whereas the more flexible tetrahydroisoquinoline ring increases the binding to α1‐adrenoceptors.

Intervention of two voltage-dependent calcium-entry pathways in the contractile response to acetylcholine and KCl in rat uterus

The contractile response of rat uterine smooth muscle was investigated. Verapamil and diltiazem concentration-dependently relax the sustained contractions induced by KCl (56 mmol/l) or acetylcholine (10(-4) mol/l). This inhibitory effect was not not freely reversed by washing the tissue and subsequently no contractile response was obtained in depolarized tissue, but a lower biphasic response (phasic and tonic) to acetylcholine was observed. Addition of cumulative concentrations of CaCl2 (1.2-19.2 mmol/l) induced a partial recovery of the contractile response to acetylcholine or KCl, but addition of MgCl2 (1.2-19.2 mmol/l did not. When the channel was reactivated by a third addition of KCl or acetylcholine after treatment with Ca2+, both spasmogens-induced phasic contractions recovered towards the initial configuration but the tonic component was not restored under any conditions. No recovery of mechanical response could be observed after Mg2+ treatment.

Relaxant activity of three aporphine alkaloids from Annona cherimolia on isolated aorta of rat

In the present study we tested the relaxant effect of three aporphine alkaloids—roemerine, anonaine and dehydroroemerine—isolated from the roots of Annona cherimolia, on isolated strips of rat thoracic aorta.

Effect of boldine, secoboldine, and boldine methine on angiotensin II‐induced neurtrophil recruitment in vivo

Angiotensin‐II (Ang‐II) has inflammatory activity and is involved in different diseases associated with the cardiovascular system. This study has evaluated the effect of boldine (B), and two phenanthrene alkaloids semisynthesized by us, secoboldine (SB) and boldine methine (BM), on Ang‐II‐induced neutrophil recruitment. Intraperitoneal administration of 1 nM Ang‐II induced significant neutrophil accumulation, which was maximal at 4–8 h. BM inhibited neutrophil infiltration into the peritoneal cavity at 4 h and 8 h by 73% and 77%, respectively, SB at 8 h by 55%, and B had no effect on this response. Although BM inhibited the release of cytokine‐inducible neutrophil chemoattractant/keratinocyte‐derived chemokine, macrophage inflammatory protein‐2 (MIP‐2), and platelet‐activating factor (PAF) elicited by Ang‐II, SB only reduced the release of MIP‐2 after 4 h of its administration. Sixty‐minute superfusion of the rat mesentery with 1 nM Ang‐II induced a significant increase in the leukocyte‐endothelial cell interactions and P‐selectin up‐regulation, which were inhibited by 1 μM BM and SB. The generation of reactive oxygen species (ROS) in endothelial cells stimulated with Ang‐II was inhibited significantly by the three alkaloids tested. BM also diminished Ang‐II‐induced interleukin‐8 release from endothelial cells and blocked the PAF receptor on human neutrophils (concentration of the compound needed to produce 50% inhibition value: 28.2 μM). Therefore, BM is a potent inhibitor of Ang‐II‐induced neutrophil accumulation in vivo. This effect appears to be mediated through inhibition of CXC chemokine and PAF release, ROS scavenging activity, and blockade of the PAF receptor. Thus, it may have potential therapeutic interest for the control of neutrophil recruitment that occurs in inflammation associated with elevated levels of Ang‐II.