Synthesis, structure and antiarrhythmic properties evaluation of new basic derivatives of 5,5-diphenylhydantoin

The synthesis of 1-N and 3-N aminoalkyl derivatives of 5,5-diphenylhydantoin is described. Structural elucidation based on X-ray analysis was performed for two representative compounds 4a and 9b. The effect of tested compounds on the electrocardiogram was examined in vitro in the non-working heart perfusion test and antiarrhythmic activity in the rat coronary artery ligation-reperfusion model. The most active 1-N derivatives 4a and 7b have shown properties of the compounds belonging to class Ia, according to the Vaughan Williams classification. The spatial organisation of the chosen compounds necessary for their pharmacological activity was discussed.

[2-(2'-hydroxy 2'-substituted) ethyl-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines--a novel group of substances with anti-arrhythmia activity]

The antiarrhythmic activity and acute toxicity of a series of 2-(2'-hydroxy-2'-substituted) ethyl-1,2,3,4-tetrahydropyrrolo[1,2- a]pyrazines were studied. Two most promising compounds (PV-168 PV-174) are characterized by a high antiarrhythmic activity, a broad spectrum of action, and low toxicity.

Solution and solid state properties of a set of procaine and procainamide derivatives

A set of potential Class III antiarrhythmic agents of structure p-HOOC-R-CO-NH-C(6)H(4)-CO-X-C(2)H(5)-N(C(2)H(5))(2) were isolated as crystalline solids of the amide and ester derivatives, I: succinylprocainamide (X=-NH-, R=-C(2)H(4)-); II: succinylprocaine (X=-O-, R=-C(2)H(4)-); III: maleylprocainamide (X=-NH-, R=-C(2)H(2)-) and IV: maleylprocaine (X=-O-, R=-C(2)H(2)-). Although compounds I-IV exhibit similar solution properties (i.e. acid-base speciation, with zwitterionic (+-) to neutral (00) form ratios higher than 10(4)), aqueous solubility of -NH- derivatives is significantly higher than that of -O- derivatives and also, solvent effects on solubility (i.e. the change of water by ethanol) is clearly different in both series. Solution and solid-state properties of I-IV were characterized to account for the observed differences. Results indicate that procainamide derivatives I and III crystallizes as (+-)(s) but procaine derivatives II and IV as (00)(s). Besides, I is anhydrous but II-IV are hydrates. Aqueous solubility and solvent effect on solubility are controlled by the intrinsic solubility of the species (+-) in I and III and (00) in II and IV. The rise of hydrophilicity of species (00) due to the structural change from -O- to -NH- would determine the change in the structure of the precipitating crystals from (00)(s) to (+-)(s). Solid structure (zwitterionic or neutral), as well as composition (anhydrous or hydrated) may be recognized as the main factors in determining the rank of aqueous solubility of the set: (+-)>(+-.H(2)O)>(00.H(2)O).

Can the USP paddle method be used to represent in-vivo hydrodynamics?

Experiments in-vitro and in dogs were conducted to find in-vitro hydrodynamic conditions that can be used to represent gastrointestinal motility patterns. Specifically, the dissolution performance of micronised and coarse-grade felodipine (a poorly soluble, neutral, lipophilic drug) was studied in a biorelevant medium in the USP paddle apparatus at various paddle speeds. Ratios of percentage dissolved (slower:faster rev min(-1)) were calculated pairwise. These ratios were then compared with AUC ratios obtained in a corresponding pharmacokinetic study in Labradors, in which the absorption of both the micronised and coarse-grade felodipine had been compared under two gastrointestinal hydrodynamic conditions. Using a paddle speed combination of 75 and 125 rev min(-1) to represent the motility patterns in response to administration of normal saline and 5% glucose, respectively, the in-vitro ratios (75:125 rev min(-1) dissolution ratio was 91% for the micronised and 46% for the coarse-grade powder) showed good agreement with the pharmacokinetic data (saline-to-glucose absorption ratio was 98% for the micronised and 46% for the coarse-grade powder). It was concluded that, provided an appropriate composition is chosen for the dissolution test, the USP paddle apparatus can be used to reflect variations in hydrodynamic conditions in the upper gastrointestinal tract.

Stability of sotalol in two liquid formulations at two temperatures

BACKGROUND

Sotalol is used in certain pediatric patients to treat, suppress, or prevent the recurrence of life-threatening ventricular arrhythmias. However, it is commercially unavailable in a liquid dosage form. The use of an extemporaneously prepared liquid dosage form must be supported by the documentation of the chemical and physical stability of sotalol.

OBJECTIVE

To determine the stability of sotalol hydrochloride extemporaneously prepared from tablets in 2 oral suspensions stored at 2 temperatures.

METHODS

Five bottles contained Ora Plus:Ora Sweet (1:1) and the other 5 bottles had 1% methylcellulose:simple syrup NF (1:9), with a sotalol concentration of 5 mg/mL. Three samples were collected from each bottle at 0, 7, 14, 28, 42, 56, 70, and 91 days and analyzed by a stability-indicating HPLC analytical method (n = 15).

RESULTS

At 4 degrees C, the mean concentration of sotalol was at least 98.9% of the original concentration in Ora Plus:Ora Sweet suspension and 95.5% of the initial concentration in 1% methylcellulose:simple syrup during storage for 3 months. At 25 degrees C, the mean concentration of sotalol was >/=95.5% of the original concentration in Ora Plus:Ora Sweet suspension and 94.4% of the initial concentration in 1% methylcellulose:simple syrup during storage for 3 months. The pH did not change substantially during the study period. Further, no changes in physical appearance were seen during the study.

CONCLUSIONS

Sotalol hydrochloride can be prepared in either of 2 liquid dosage forms and stored in plastic bottles for 13 weeks at 4 or 25 degrees C without substantial loss of potency.

Efficient generation, storage, and manipulation of fully flexible pharmacophore multiplets and their use in 3-D similarity searching

Pharmacophore triplets and quartets have been used by many groups in recent years, primarily as a tool for molecular diversity analysis. In most cases, slow processing speeds and the very large size of the bitsets generated have forced researchers to compromise in terms of how such multiplets were stored, manipulated, and compared, e.g., by using simple unions to represent multiplets for sets of molecules. Here we report using bitmaps in place of bitsets to reduce storage demands and to improve processing speed. Here, a bitset is taken to mean a fully enumerated string of zeros and ones, from which a compressed bitmap is obtained by replacing uniform blocks ("runs") of digits in the bitset with a pair of values identifying the content and length of the block (run-length encoding compression). High-resolution multiplets involving four features are enabled by using 64 bit executables to create and manipulate bitmaps, which "connect" to the 32 bit executables used for database access and feature identification via an extensible mark-up language (XML) data stream. The encoding system used supports simple pairs, triplets, and quartets; multiplets in which a privileged substructure is used as an anchor point; and augmented multiplets in which an additional vertex is added to represent a contingent feature such as a hydrogen bond extension point linked to a complementary feature (e.g., a donor or an acceptor atom) in a base pair or triplet. It can readily be extended to larger, more complex multiplets as well. Database searching is one particular potential application for this technology. Consensus bitmaps built up from active ligands identified in preliminary screening can be used to generate hypothesis bitmaps, a process which includes allowance for differential weighting to allow greater emphasis to be placed on bits arising from multiplets expected to be particularly discriminating. Such hypothesis bitmaps are shown to be useful queries for database searching, successfully retrieving active compounds across a range of structural classes from a corporate database. The current implementation allows multiconformer bitmaps to be obtained from pregenerated conformations or by random perturbation on-the-fly. The latter application involves random sampling of the full range of conformations not precluded by steric clashes, which limits the usefulness of classical fingerprint similarity measures. A new measure of similarity, The Stochastic Cosine, is introduced here to address this need. This new similarity measure uses the average number of bits common to independently drawn conformer sets to normalize the cosine coefficient. Its use frees the user from having to ensure strict comparability of starting conformations and having to use fixed torsional increments, thereby allowing fully flexible characterization of pharmacophoric patterns.

Identification, synthesis, and activity of novel blockers of the voltage-gated potassium channel Kv1.5

The voltage-gated potassium channel Kv1.5 is regarded as a promising target for the development of new atrial selective drugs with fewer side effects. In the present study the discovery of ortho,ortho-disubstituted bisaryl compounds as blockers of the Kv1.5 channel is presented. Several compounds of this new class were synthesized and screened for their ability to block Kv1.5 channels expressed in Xenopus oocytes. The observed structure-activity relationship (SAR) is described by a pharmacophore model that consists of three hydrophobic centers in a triangular arrangement. The hydrophobic centers are matched by a phenyl or pyridyl ring of the bisaryl core and both ends of the side chains. The most potent compounds (e.g., 17c and 17o) inhibited the Kv1.5 channel with sub-micromolar half-blocking concentrations and displayed 3-fold selectivity over Kv1.3 and no significant effect on the HERG channel and sodium currents. In addition, compounds 17c and 17m have already shown antiarrhythmic effects in a pig model.

Dronerarone acts as a selective inhibitor of 3,5,3'-triiodothyronine binding to thyroid hormone receptor-alpha1: in vitro and in vivo evidence

Dronedarone (Dron), without iodine, was developed as an alternative to the iodine-containing antiarrhythmic drug amiodarone (AM). AM acts, via its major metabolite desethylamiodarone, in vitro and in vivo as a thyroid hormone receptor alpha(1) (TRalpha(1)) and TRbeta(1) antagonist. Here we investigate whether Dron and/or its metabolite debutyldronedarone inhibit T(3) binding to TRalpha(1) and TRbeta(1) in vitro and whether dronedarone behaves similarly to amiodarone in vivo. In vitro, Dron had a inhibitory effect of 14% on the binding of T(3) to TRalpha(1), but not on TRbeta(1). Desethylamiodarone inhibited T(3) binding to TRalpha(1) and TRbeta(1) equally. Debutyldronedarone inhibited T(3) binding to TRalpha(1) by 77%, but to TRbeta(1) by only 25%. In vivo, AM increased plasma TSH and rT(3), and decreased T(3). Dron decreased T(4) and T(3), rT(3) did not change, and TSH fell slightly. Plasma total cholesterol was increased by AM, but remained unchanged in Dron-treated animals. TRbeta(1)-dependent liver low density lipoprotein receptor protein and type 1 deiodinase activities decreased in AM-treated, but not in Dron-treated, animals. TRalpha(1)-mediated lengthening of the QTc interval was present in both AM- and Dron-treated animals. The in vitro and in vivo findings suggest that dronedarone via its metabolite debutyldronedarone acts as a TRalpha(1)-selective inhibitor.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

The antiarrhythmic drug BRL-32872

BRL-32872 is a new antiarrhythmic drug with balanced class-III and class-IV actions as categorized by the Vaughan-Williams classification. BRL-32872 blocks the rapid component of the cardiac delayed rectifier potassium channel IK(r) (IC(50) = 28 nM) and its molecular correlate HERG ("Human-ether-a-go-go related gene," IC(50) of 19.8 nM in cell lines) at low concentrations. It also inhibits the L-type calcium current (ICa) at higher concentrations (IC(50) = 2.8 microM). This dual concentration-dependent profile of action at higher concentrations may possibly prevent "torsades de pointes" ventricular arrhythmias, which is a dangerous side effect of many other class-III antiarrhythmic drugs. With BRL-32872, an excessive prolongation of the action potential duration and consecutive QTc prolongation is prevented by a concentration-dependent increase of calcium channel block, resulting in the so-called "bell-shaped" profile of antiarrhythmic drug action. BRL-32872 is very effective in the treatment of ventricular arrhythmias in animal models of cardiac ischemia. In the ischemic hearts of animals the drug significantly reduced early afterdepolarization and ventricular tachycardia. The antiarrhythmic effect of BRL-32872 has not yet been demonstrated in humans.

Molecular cloning and functional expression of a gene encoding an antiarrhythmia peptide derived from the scorpion toxin

From a cDNA library of Chinese scorpion Buthus martensii Karsch, full-length cDNAs of 351 nucleotides encoding precursors (named BmKIM) that contain signal peptides of 21 amino acid residues, a mature toxin of 61 residues with four disulfide bridges, and an extra Gly-Lys-Lys tail, were isolated. The genomic sequence of BmKIM was cloned and sequenced; it consisted of two exons disrupted by an intron of 1622 bp, the largest known in scorpion toxin genomes, inserted in the region encoding the signal peptide. The cDNA was expressed in Escherichia coli. The recombinant BmKIM was toxic to both mammal and insects. This is the first report that a toxin with such high sequence homology with an insect-specific depressant toxin group exhibits toxicity to mammals. Using whole cell patch-clamp recording, it was discovered that the recombinant BmKIM inhibited the sodium current in rat dorsal root ganglion neurons and ventricular myocytes and protected against aconitine- induced cardiac arrhythmia.

Toward a pharmacophore for drugs inducing the long QT syndrome: insights from a CoMFA study of HERG K(+) channel blockers

In this paper, we present a pharmacophore for QT-prolonging drugs, along with a 3D QSAR (CoMFA) study for a series of very structurally variegate HERG K(+) channel blockers. The blockade of HERG K(+) channels is one of the most important molecular mechanisms through which QT-prolonging drugs increase cardiac action potential duration. Since QT prolongation is one of the most undesirable side effects of drugs, we first tried to identify the minimum set of molecular features responsible for this action and then we attempted to develop a quantitative model correlating the 3D stereoelectronic characteristics of the molecules with their HERG blocking potency. Having considered an initial set of 31 QT-prolonging drugs for which the HERG K(+) channel blocking activity was measured on mammalian transfected cells, we started the construction of a theoretical screening tool able to predict whether a new molecule can interact with the HERG channel and eventually induce the long QT syndrome. This in silico tool might be useful in the design of new drug candidates devoid of the physicochemical features likely to cause the above-mentioned side effect.

Effects of quinine and quinidine on the transient outward and on the L-type Ca(2+) current in rat ventricular cardiomyocytes

The effects of the enantiomers quinine and quinidine on the transient outward current (I(to)) and on the L-type Ca(2+) current (I(ca)) were investigated in rat ventricular cardiomyocytes using the patch-clamp technique. At a stimulation frequency of 2 Hz, both quinine and quinidine depressed the magnitude of I(to) and I(Ca); the half-maximal effects on I(to) were achieved at 11 and 15 micromol/l, respectively, and those on I(Ca) at 14 and 10 micromol/l, respectively. At 0.2 Hz, both drugs depressed the magnitude of I(to), but not that of I(Ca). A change in extracellular pH from 7.3 to 8.3 did not significantly influence the effects of the drugs(which are protonated to 98% at pH 7.3) on I(to) or I(Ca). It is concluded that neither the different chemical structure nor the amount of protonation of quinine and quinidine controls their effects on I(to) or I(Ca).

A three-layer guar gum matrix tablet for oral controlled delivery of highly soluble metoprolol tartrate

The objective of the study is to design oral controlled drug delivery systems for highly water-soluble drugs using guar gum as a carrier in the form of a three-layer matrix tablet. Metoprolol tartrate was chosen as a model drug because of its high water solubility. Matrix tablets containing either 30 (M1), 40 (M2) or 50% (M3) of guar gum were prepared by wet granulation technique using starch paste as a binder. Three-layer matrix tablets of metoprolol tartrate were prepared by compressing on both sides of guar gum matrix tablet granules of metoprolol tartrate M1, M2 or M3 with either 50 (TL1M1, TL1M2 or TL1M3) or 75 mg (TL2M1, TL2M2 or TL2M3) of guar gum granules as release retardant layers. Both the matrix and three-layer matrix tablets were evaluated for hardness, thickness, drug content uniformity, and subjected to in vitro drug release studies. The amount of metoprolol tartrate released from the matrix and three-layer matrix tablets at different time intervals was estimated by using a HPLC method. Matrix tablets of metoprolol tartrate were unable to provide the required drug release rate. However, the three-layer guar gum matrix tablets (TL2M3) provided the required release rate on par with the theoretical release rate for metoprolol tartrate formulations meant for twice daily administration. The three-layer guar gum matrix tablet (TL2M3) showed no change either in physical appearance, drug content or in dissolution pattern after storage at 40 degrees C/75% RH for 6 months. The FT-IR study did not show any possibility of metoprolol tartrate/guar gum interaction with the formulation excipients used in the study. The results indicated that guar gum, in the form of three-layer matrix tablets, is a potential carrier in the design of oral controlled drug delivery systems for highly water-soluble drugs such as metoprolol tartrate.

A quantitative method for the determination of amphiphilic drug release kinetics from nanoparticles using a Langmuir balance

Amiodarone is a drug that is widely used in the treatment of heart disease. To circumvent side effects, colloidal drug carriers have been designed to deliver the drug specifically to the site of action. For the purposes of in vitro characterization of such particles, difficult test systems are employed that usually require the quantitative separation of the drug carrier from the release medium before analysis. In this work, a Langmuir balance was used to characterize amiodarone release. Drug-loaded nanoparticles were prepared from a biodegradable polyester and assayed for their drug release kinetics. Simultaneously, nanoparticles were analyzed for their drug release by a standard procedure based on dialysis tubes combined with high-performance, liquid chromatography. The results obtained by the Langmuir balance experiments were compared with those obtained from high-performance liquid chromatography and were found to correlate well. The interexperimental variation was 4.4% for the Langmuir method (n = 4), and the interexperimental variation for HPLC was 2.9% (n = 3). The major advantage of this new method is the possibility diminishing significantly the required sample amount for the experiment, allowing drug detection in the lower nanomolar range. Moreover, the avoidance of prior nanoparticle separation from the release medium provides important progress of this technique. The Langmuir balance has proven its adaptability as a new sensitive tool for the characterization of amphiphilic drug release kinetics.

Development of level A, B and C in vitro-in vivo correlations for modified-release levosimendan capsules

The aim of this study was to investigate the possibility of developing different levels of correlation between in vitro release and in vivo absorption rate for four modified-release levosimendan capsule formulations. Differences and similarities in the in vitro dissolution curves were compared with pharmacokinetic parameters describing absorption rate. Formulations F, G, H and I differed in the amounts of the delaying excipients alginic acid and HPMC. In vitro release rate was studied by the USP basket method using the following conditions: pH 5.8 or 7.4 and a rotation speed of 50 or 100 rpm. In vivo bioavailability was tested in nine healthy male volunteers and the fractions absorbed were calculated by the Wagner-Nelson method. Dissolution conditions pH 5.8 and a rotation speed of 100 rpm predicted best the similarities and differences in absorption rates among different formulations, and levels C and B correlation coefficients were 0.85 and 0.97, respectively. For formulation H level A correlation (r=0.997) was found when in vitro lag time was 0.2 h and time scale factor 1.9. This study indicated that dissolution tests developed can be used as a surrogate for human bioequivalence studies, for development processes of final commercial products, to ensure batch to batch bioequivalence and in the future in possible scale-up and post approval change cases for modified-release levosimendan formulation H.

Buccal transport of flecainide and sotalol: effect of a bile salt and ionization state

Patients with infrequent attacks of supraventricular arrhythmia may benefit from self administration of antiarrhythmic drugs on an 'as required' basis. The oral cavity is easily accessible and the potential for rapid absorption exists. The effects of ionization state and sodium glycocholate on the ex vivo transport of sotalol and flecainide across porcine buccal mucosa were studied. The permeated amounts at 3 h (Q) and fluxes (J) of sotalol in an aqueous solution at pH 7.4 and 9.0 were similar. At pH 7.4, in contrast to pH 9.0, the addition of 1.0% (w/v) sodium glycocholate decreased Q and J four and five fold. Flecainide base in propylene glycol resulted in a nine and 12 fold higher Q and J as compared with an aqueous solution of flecainide acetate at pH 5.8. The presence of sodium glycocholate reduced the transport rate of the flecainide base. However, Q and J were increased 110 and 75 fold by adding 1.0% (w/v) sodium glycocholate to a solution of flecainide acetate at pH 5.8. Sodium glycocholate seems to be an effective penetration enhancer for the buccal absorption of the more polar ionized form of flecainide in an aqueous solution. Sodium glycocholate does not seem to improve the transport of sotalol.

New p-methylsulfonamido phenylethylamine analogues as class III antiarrhythmic agents: design, synthesis, biological assay, and 3D-QSAR analysis

Class III antiarrhythmic agents selectively delay the effective refractory period (ERP) and increase the transmembrane action potential duration (APD). Using dofetilide (2) as a template of class III antiarrhythmic agents, we designed and synthesized 16 methylsulfonamido phenylethylamine analogues (4a-d and 5a-l). Pharmacological assay indicated that all of these compounds showed activity for increasing the ERP in isolated animal atrium; among them, the effective concentration of compound 4a is 1.6 x 10(-8) mol/L in increasing ERP by 10 ms, slightly less potent than that of 2, 1.1 x 10(-8) mol/L. Compound 4a also produced a slightly lower change in ERP at 10(-5) M, DeltaERP% = 17.5% (DeltaERP% = 24.0% for dofetilide). On the basis of this bioassay result, these 16 compounds together with dofetilide were investigated by the three-dimensional quantitative structure-activity relationship (3D-QSAR) techniques of comparative molecular field analysis (CoMFA), comparative molecular similarity index analysis (CoMSIA), and the hologram QSAR (HQSAR). The 3D-QSAR models were tested with another 11 compounds (4e-h and 5m-s) that we synthesized later. Results revealed that the CoMFA, CoMSIA, and HQSAR predicted activities for the 11 newly synthesized compounds that have a good correlation with their experimental value, r(2) = 0.943, 0.891, and 0.809 for the three QSAR models, respectively. This indicates that the 3D-QSAR models proved a good predictive ability and could describe the steric, electrostatic, and hydrophobic requirements for recognition forces of the receptor site. On the basis of these results, we designed and synthesized another eight new analogues of methanesulfonamido phenylethyamine (6a-h) according to the clues provided by the 3D-QSAR analyses. Pharmacological assay indicated that the effective concentrations of delaying the ERP by 10 ms of these newly designed compounds correlated well with the 3D-QSAR predicted values. It is remarkable that the percent change of delaying ERP at 10(-5) M compound 6c is much higher than that of dofetilide; the effective concentration of compound 6c is 5.0 x 10(-8)mol/L in increasing the ERP by 10 ms, which is slightly lower than that of 2. The results showed that the 3D-QSAR models are reliable and can be extended to design new antiarrhythmic agents.

Current and new drugs for the treatment of arrhythmias

Sudden cardiac death is a leading cause of mortality in industrialized nations, accountingfor 50% of all cardiovascular deaths. Carefully performed randomized trials, technological advances and better understanding of arrhythmia mechanisms have resulted in improved approaches to rhythm disturbances. Risk assessment has to be individualized and can be approached through an analysis based upon all other clinical characteristics of the patient. The need for long-term therapy must be carefully individualized to each patient, since the severity and importance of symptoms are highly variable. This review will summarize the classification of antiarrhythmic drugs and main pharmacokinetic properties. Newer antiarrhythmic drugs either block a specific ionic current (eg, dofetilide-induced blockade of the rapidly activating component of the delayed rectifier potassium current) or block multiple ionic channels (eg, ibutilide and azimilide) in order to prolong atrial and ventricular action potentials without other specific pharmacological effects. Additionally, this manuscript reviews the newer class III agents' effectiveness in treating atrial and ventricular arrhythmias, and the development of novel antiarrhythmic drugs that act specifically to alter cell communication.

Sodium channel blocking and antiarrhythmic actions of the novel arylpiperazine rsd992

Bolus doses (4-128 micromolkg(-1)) and infusions (2-32 micromolkg(-1)min(-1)) of the novel arylpiperazine drug RSD992 produced bradycardia in rats and guinea pigs but had minimal effect on ECG variables. RSD992 (2-32 micromolkg(-1)min(-1)) increased threshold current (I(T)) for induction of extra-systoles and induction of sustained ventricular fibrillation (VF(T)) and also increased the effective refractory period (ERP) and decreased the maximum following frequency (MFF) in rat and guinea pig hearts. RSD992 (32-512 microM) significantly increased PR and QRS intervals in isolated rat hearts subjected to conditions that mimic ischaemia (pH 6.4, K(+) 11mM) but not in isolated hearts under normal perfusion conditions (pH 7.4, K(+) 3mM). RSD992 (0.1-3.0mM) reduced peak sodium current in rat cardiac (rNa(v)1.5) sodium channels more potently than neuronal (rNa(v)1.2a) sodium channels expressed in Xenopus oocytes. The voltage-dependence of sodium channel activation was unaffected whereas inactivation was shifted in a hyperpolarized direction thus suggesting RSD992 may preferentially interact with the inactive state of the sodium channel, a state usually associated with myocardial cell depolarization in ischaemic myocardium. RSD992 (2-24 micromolkg(-1)min(-1)) decreased the incidence of ventricular arrhythmias and mortality in rats subject to coronary artery ligation. RSD992 exhibits frequency- and ischaemia-selective actions on myocardial sodium currents and antiarrhythmic actions in ischaemic rat myocardium.

Vomilenine reductase--a novel enzyme catalyzing a crucial step in the biosynthesis of the therapeutically applied antiarrhythmic alkaloid ajmaline

Delineation of the biochemical pathway leading to the antiarrhythmic Rauvolfia alkaloid ajmaline has been an important target in biosynthetic research for many years. The biosynthetic sequence starting with tryptamine and the monoterpene secologanin consists of about 10 different steps. Most of the participating enzymes have been detected and characterized previously, except those catalyzing the reduction of the intermediate vomilenine. A novel NADPH-dependent enzyme that reduces the intermediate has been isolated from Rauvolfia serpentina cell suspension cultures. Vomilenine reductase (M(r )43 kDa, temp opt 30 degrees C, pH opt 5.7-6.2), saturates the indolenine double bond of vomilenine with stereospecific formation of 2beta(R)-1,2-dihydrovomilenine. The described detection, enrichment and properties of the reductase not only closes a gap in ajmaline biosynthesis but is also a prerequisite for overexpressing the protein heterologously for final clarification of its molecular properties.

A review of HNS-32: a novel azulene-1-carboxamidine derivative with multiple cardiovascular protective actions

HNS-32 [N(1),N(1)-dimethyl-N(2)-(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1- carboxamidine] (CAS Registry Number: 186086-10-2) is a newly synthesized azulene derivative. Computer simulation showed that its three dimensional structure is similar to that of the class Ib antiarrhythmic drugs, e.g., lidocaine or mexiletine. HNS-32 potently suppressed ventricular arrhythmias induced by ischemia due to coronary ligation and/or ischemia-reperfusion in dogs and rats. In the isolated dog and guinea pig cardiac tissues, HNS-32 had negative inotropic and chronotropic actions, prolonged atrial-His and His-ventricular conduction time and increased coronary blood flow. In the isolated guinea pig ventricular papillary muscle, HNS-32 decreased maximal rate of action potential upstroke (Vmax) and shortened action potential duration (APD). These findings suggest that HNS-32 inhibits inward Na+ and Ca2+ channel currents. In the isolated pig coronary and rabbit conduit arteries, HNS-32 inhibited both Ca2+ channel-dependent and -independent contractions induced by a wide variety of chemical stimuli. HNS-32 is a potent inhibitor of protein kinase C (PKC)-mediated constriction of cerebral arteries. It is likely to block both, Na+ and Ca2+ channels expressed in cardiac and vascular smooth muscles. These multiple ion channel blocking effects are largely responsible for the antiarrhythmic and vasorelaxant actions of HNS-32. This drug may represent a novel approach to the treatment of arrhythmias.

Chronic and acute effects of dronedarone on the action potential of rabbit atrial muscle preparations: comparison with amiodarone

Dronedarone, a noniodinated derivative of amiodarone, is under evaluation as a potentially less toxic anti-arrhythmic alternative to amiodarone. The acute and chronic electrophysiologic effects of dronedarone and amiodarone were compared in isolated rabbit atrial muscle by microelectrode techniques. Four-week PO treatment with dronedarone or amiodarone increased action potential duration (APD90) (58 +/- 4 ms control versus 69 +/- 2 ms dronedarone, p < 0.01; 68 +/- 3 ms amiodarone, p < 0.01 for a 100-mg/kg/d dose) and effective refractory period (49 +/- 6 ms control versus 68 +/- 4 ms dronedarone, p < 0.01; 63 +/- 3 ms amiodarone, p < 0.01). The APD90 prolonged reverse rate-dependency. In contrast, acute superfusion with 10 microM dronedarone or amiodarone decreased APD90 (61 +/- 6 ms control versus 53 +/- 4 ms dronedarone, p < 0.05; 52 +/- 6 ms amiodarone, p < 0.05), effective refractory period (50 +/- 5 ms control versus 44 +/- 4 ms dronedarone, p < 0.05; 43 +/- 6 ms amiodarone, p < 0.05), and the maximum upstroke slope of the action potential (Vmax) (188 +/- 9 V/s control versus 182 +/- 11 V/s dronedarone p < 0.05; 182 +/- 11 V/s amiodarone, p < 0.05). Thus, chronic and acute electrophysiologic effects of dronedarone on rabbit atrial muscle are similar to those of amiodarone, suggesting a similar potential against atrial arrhythmias.

[Structure and activity relationship of propafenone and alkylesters of 2-and 4-[(3-propylamino-2-hydroxy)-propoxy]-phenylcarbamic acid]

Conformation analysis was performed in propaphenone and two potential antiarrhythmic agents of the carbamate type, employing the method of molecular mechanics for calculations. Energetically stable conformers were optimized by means of the quantumchemical method AM1 and the optimized structures were used to construct the pharmacophore. Using the programme Chem-X, four groups of stable conformations of these drug were found, and comparisons by means of the molecular graphic method were employed to graphically visualize the degree of their similarity and to determine the interatomic distances of the groups with free electron pairs and a lipophilic aromatic nucleus.