Studies of the potential genotoxic effects of furoxans: the case of CAS 1609 and of the water-soluble analogue of CHF 2363.

CAS 1609 (compound 1) and CHF 2363 (compound 2) are two furoxan derivatives able to release nitric oxide (NO) under physiological conditions, and display typical NO-dependent vasodilator activity. The potential genotoxic effects of compound 1 and of the water-soluble analogue of CHF 2363 (compound 2a) were investigated. The results show that the two compounds induce genotoxic effects only at concentrations that significantly reduce cell viability. However, in the case of compound 1 this range of concentrations is one order of magnitude higher than the one leading to the beneficial effects, while in the case of compound 2a these ranges partially overlap. In both cases the release of NO plays a key role in the induction of the cytotoxic and genotoxic effects, since the non-NO-donating furazan analogues display a different toxicological profile, and since the effects were reduced in the presence of oxyhaemoglobin, a well-known NO-scavenger.

Focus on recent approaches for the development of new NO-donors.

Recent research developments in the field of NO-donor compounds have concerned conjugation of NO-donor moieties with antioxidant groups, NO-donor targeting, design of NO-donor hybrid drugs and of NO-delivery systems. These new approaches are illustrated and discussed through selected examples.

Identification of 2,3-diaminophenazine and of o-benzoquinone dioxime as the major in vitro metabolites of benzofuroxan.

1. The results of an in vitro study of the metabolism of benzofuroxan using either cytosolic or microsomal fractions obtained from rat liver are reported. 2. Benzofuroxan was incubated with an appropriate volume of cytosol or microsomal suspension; control incubations were performed without the beta-nicotinamide adenine dinucleotide phosphate-generating system or, alternatively, by using the subcellular fractions inactivated by heating. Incubation mixtures were analysed by high-performance liquid chromatography. Two principal metabolites (M1, M2) were identified in the cytosolic fraction only. The dependence of M2 formation on thiol cofactors, incubation time and protein concentration was examined. 3. The two metabolites were isolated and characterized by their 1H-, 13C-nuclear magnetic resonance, infrared and mass spectra. The structures of o-benzoquinonedioxime (2) and 2,3-diaminopleuozuc (3), were arranged to M1 and M2 respectively. The proposed structures were confirmed by the identity of the metabolites with authentic samples obtained by synthesis. X-ray analysis showed that the dioxime metabolite had an amphy configuration. 4. A metabolic scheme for the formation of the two products is proposed.

Effect of the leaving group on the electrodic reduction mechanism of anti-Helicobacter pylori metronidazole derivatives, in aprotic and protic media.

Because redox properties are central to bioreductive drug activity and selectivity, six 2-methyl-5-nitroimidazole, substituted at the N1-ethyl side chain with I, Br, Cl, OAc, OMs and NH(3)(+) were synthesized and submitted to cyclic voltammetry and electrolyses, in order to define their electrodic reduction mechanism, in aprotic [dimethylsulphoxide (DMSO)+0.1 mol l(-1) tetrabuthylammonium perchlorate (TBAP)] and phosphate-buffered media, on glassy carbon electrode, in comparison with metronidazole. Three of these compounds, namely, the iodo, bromo and ammonium salt derivatives showed significant anti-Helicobacter pylori (strain resistant to metronidazole) activity. All the cyclic voltammograms (CV), in aprotic medium, are similar to the one for metronidazole, except for -I, -Br and -NH(3)(+) derivatives. The CV of the N1-ethylhalide (-I, -Br) 5-nitroimidazole showed more intense and irreversible first waves, even at faster sweep rates (nu<2 V s(-1)). The absence of the first wave anodic counterpart, along with analysis of the dependence of E(p), I(p) and other parameters with nu, and results from electrolysis (consumption of two electrons) showed the process to be an ECE system, with halide release, after uptake of two electrons. This behaviour represents a case of dissociative electron transfer (ET). For the ammonium salt, self-protonation mechanism was evident. The facility of reduction represented by the first wave potential and concerning the substituents is NH(3)(+)>Br>I>Cl>OMs>OH>OAc. In aqueous phosphate-buffered medium, the electrochemical behaviour of all the compounds is similar to the one of metronidazole, represented by a unique and irreversible 4e(-)/4H(+) wave. The order of reduction ease is NH(3)(+)>Br approximately OMs>I>OH>OAc. Aprotic medium allows a better discrimination between the substituents. Concerning biological activity, despite the impossibility of establishing a correlation, it has been observed that the more electrophilic compounds showed better anti-H. pylori activity.

Synthesis and vasodilating properties of N-alkylamide derivatives of 4-amino-3-furoxancarboxylic acid and related azo derivatives.

A series of N-alkylamide derivatives of 4-amino-3-furoxancarboxylic acids 5a-11a and their oxidation products, the azo derivatives 5b-11b, were synthesised and studied for their vasodilating properties. All the products were able to release rat aorta strips precontracted with (-)noradrenaline. Azo derivatives proved to be 20-200 times more potent than the parent amines. The large variation of lipophilicity within the two series does not seem to influence significantly the activity. Experiments carried out in the presence of oxyhaemoglobin (HbO(2)) suggest the involvement of nitric oxide (NO*) in the vasodilation.

Nitroanilines are the reduction products of benzofuroxan system by oxyhemoglobin (HbO2 2+).

Benzofuroxans are interesting compounds which display several biochemical and pharmacological properties. Recent studies from our laboratory demonstrate that they are reduced by ferrous salts at room temperature and that the principal reaction products are o-nitroanilines. This paper shows that simple benzofuroxan derivatives are also able to oxidise HbO2 2+ to methemoglobin (MetHb3+) (UV detection) and to form o-nitroanilines (HPLC detection). From a toxicological point of view this reaction is interesting, since it indicates that the blood is a site for metabolism of these compounds with consequent methemoglobinemia and formation of toxic compounds.

A new class of ibuprofen derivatives with reduced gastrotoxicity.

A new series of nonsteroidal antiinflammatory drugs (NSAIDs) obtained by linking ibuprofen to selected furoxan moieties and to related furazans were synthesized and tested for their antiinflammatory, antiaggregatory, and ulcerogenic properties. All the derivatives are endowed with antiinflammatory activity comparable to that of ibuprofen, but, unlike this drug, they display reduced acute gastrotoxicity. The masking of the ibuprofen-free carboxylic group seems to be principally at the basis of this reduced topical irritant action. The two furoxan derivatives 8 and 9 also trigger potent antiaggregatory effects, principally as a consequence of their NO-donor ability.

Searching for balanced hybrid NO-donor 1,4-dihydropyridines with basic properties.

PURPOSE: Model compounds containing NO-donor furoxan moieties at the 3-positioned basic lateral chain of 1, a 1,4-dihydropyridine related to nicardipine, were synthesized in order to study their vasodilating activity as well as their basic and lipophilic behaviour. METHODS: All the compounds were obtained by a modified Hantzsch approach. Potentiometry was used to determine pKa and lipophilicity descriptors. The furoxan 4-aryl-1,4-dihydropyridines were assessed for their ability to release nitrite, in the presence of a large excess of cysteine, by the Griess reaction. Vasodilating activity of the products in the absence and in the presence of ODQ, a well-known guanylate cyclase inhibitor, was evaluated on rat thoracic aorta. RESULTS: The compounds display low basicity values and for this reason their log Ds at physiological pH are identical to the log Ps of the neutral forms. Products 2, 3 display vasodilating action principally dependent on their Ca2+-antagonist properties, whereas 4 behaves as a well-balanced hybrid with mixed Ca2+-channel blocker and NO-dependent vasodilator activities. CONCLUSIONS. Nitrogen containing lateral chain at the 3-position of 1 is a suitable molecular region to be modified in order to obtain well-balanced furoxan NO-donor 1,4-DHPs. This manipulation produces a decrease in the basicity. General analysis of pKa and lipophilicity descriptors of these new DHPs suggest that molecular flexibility could influence both their basicity and log PI.

Lipophilicity behaviour of the Zwitterionic antihistamine cetirizine in phosphatidylcholine liposomes/water systems.

PURPOSE: The partitioning of cetirizine in a phosphatidylcholine liposomes/water system was compared with that of hydroxyzine and acrivastine to gain insight into the mechanisms of interaction of its various electrical species with membranes. METHODS: The lipophilicity profiles of the compounds were obtained from equilibrium dialysis and potentiometry, and compared with changes in NMR relaxation rates. RESULTS: The neutral form of hydroxyzine interacted mainly via hydrophobic interactions with the bilayer lipid core of the membrane, whereas for the cationic form both hydrophobic and electrostatic interactions were involved. Zwitterionic and anionic cetirizine were less lipophilic than its cation, which behaved like the corresponding species of hydroxyzine. Zwitterionic cetirizine interacted more by weak electrostatic interactions with the polar headgroups of phospholipids than by hydrophobic interactions with the membrane interior. The lipophilicity of its anion reflected the balance of repulsive electrostatic interactions between the carboxylate and phosphate groups and the hydrophobic interactions with the lipid core. CONCLUSION: The study confirms that various mechanisms influence the interaction of solutes with liposomes. Combining experimental techniques and using suitable reference compounds proves useful.

Studies on agents with mixed NO-dependent and calcium channel antagonistic vasodilating activities.

PURPOSE: To obtain new cardiovascular agents with mixed Ca2+-channel antagonistic and NO-donor properties, a series of "hybrid" 1,4-dihydropyridines (1,4-DHPs), bearing NO-donating furoxan moieties on the 3-positioned lateral ester chain were synthesized and pharmacologically characterized. Furazan analogues were also prepared and investigated for control purposes, because they are unable to release NO. METHODS: Synthesis of the models was achieved by a modified Hantzsch approach. All of the final furoxan 1,4-DHPs were assessed for their ability to produce nitrite in the presence of a large excess of cysteine by the Griess reaction. Vasodilating activity was evaluated on rat aorta and expressed as EC50 and EC50MB values, obtained in the absence and in the presence of methylene blue (MB) respectively, a well-known guanylate cyclase inhibitor. Affinities to 1,4-DHP receptor on Ca2+-channels, expressed as IC50 values, were determined through displacement experiments of [3H]-nitrendipine on rat cortex homogenates. RESULTS: Some hybrid compounds (derivatives 15a, 15b, 16a, and 16b) displayed vasodilating activity depending predominantly on their Ca2+-channel blocker properties. By contrast, some others (derivatives 17a, 17b, and 21) behaved as well-balanced hybrids with mixed Ca2+-channel blocking and NO-dependent vasodilating activities. CONCLUSION: This work demonstrates the possibility of obtaining well-balanced hybrids endowed with mixed NO-donor and Ca2+-channel blocker properties using appropriate 1,4-DHP and furoxan moieties. A procedure for the individual evaluation of the NO-dependent vasodilator component and that due to Ca2+-channel blocking is proposed.

Nicorandil analogues containing NO-donor furoxans and related furazans.

The synthesis and in vitro vasodilating properties of hybrid compounds in which furoxan (1,2,5-oxadiazole 2-oxide) moieties, endowed with different NO-donor properties, were substituted for the nitroxy function of Nicorandil are reported. The corresponding cyanoguanidine analogues are also considered. This approach has led to a series of vasorelaxing compounds devoid of affinity for K(ATP) channels, whose activity is prevalently due to their ability to activate sGC, at the concentrations of the experiments. Related furazan (1,2,5-oxadiazole) derivatives, unable to release nitric oxide were also prepared and studied for control. The amide analogues of Nicorandil display feeble vasorelaxing action not involving the activation of K+ channels, while in the guanidine analogues, this mechanism seems to underlie this action.

NO donor and biological properties of different benzofuroxans.

PURPOSE: To investigate the effect of benzofusion on NO donor properties and related biological activities of the furoxan system. The biological properties considered were the ability to increase the cytosolic levels of cGMP in C6 cells and vasodilation. METHODS: NO donor properties were investigated either in the presence or the absence of cysteine by using the Griess reaction, chemiluminescence, and gas chromatography. Increase of cytosolic cGMP levels were evaluated by radioimmunoassay. Vasodilating activity was assessed on rat aorta strips precontracted with noradrenaline, in the presence and the absence of oxyhemoglobin (HbO2) and methylene blue (MB), respectively. RESULTS: Benzofuroxan and its methyl and cyano derivatives were unable to release NO under the experimental conditions. Generally these compounds displayed feeble vasodilating properties and were able to weakly stimulate soluble guanylate cyclase (sGC). By contrast, benzodifuroxan and benzotrifuroxan were able to produce both NO* and its reduced form NO- , the nitroxyl anion. They displayed potent vasodilating properties and were able to increase cytosolic levels of cGMP in a concentration-dependent manner. CONCLUSIONS: The simple benzofuroxans considered here are devoid of the capability to release NO, they weakly stimulate sGC as well as manifest feeble vasodilating properties by a mechanism that does not involve a thiol-induced NO production. By contrast, benzodifuroxan and benzotrifuroxan behave as typical NO donor furoxans.

N-Substituted analogues of S-nitroso-N-acetyl-D,L-penicillamine: chemical stability and prolonged nitric oxide mediated vasodilatation in isolated rat femoral arteries.

Previous studies show that linking acetylated glucosamine to S-nitroso-N-acetyl-D,L-penicillamine (SNAP) stabilizes the molecule and causes it to elicit unusually prolonged vasodilator effects in endothelium-denuded, isolated rat femoral arteries. Here we studied the propanoyl (SNPP; 3 carbon side-chain), valeryl (SNVP; 5C) and heptanoyl (SNHP; 7C) N-substituted analogues of SNAP (2C), to further investigate other molecular characteristics that might influence chemical stability and duration of vascular action of S-nitrosothiols. Spectrophotometric analysis revealed that SNVP was the most stable analogue in solution. Decomposition of all four compounds was accelerated by Cu(II) and cysteine, and neocuproine, a specific Cu(I) chelator, slowed decomposition of SNHP. Generation of NO from the compounds was confirmed by electrochemical detection at 37 degrees C. Bolus injections of SNAP (10 microl; 10(-8)-10(-3) M) into the perfusate of precontracted, isolated rat femoral arteries taken from adult male Wistar rats (400-500 g), caused concentration-dependent, transient vasodilatations irrespective of endothelial integrity. Equivalent vasodilatations induced by SNVP and SNHP were transient in endothelium-intact vessels but failed to recover to pre-injection pressures at moderate and high concentrations (10(-6)-10(-3) M) in those denuded of endothelium. This sustained effect (> 1 h) was most prevalent with SNHP and was largely reversed by the NO scavenger, haemoglobin. We suggest that increased lipophilicity of SNAP analogues with longer sidechains facilitates their retention by endothelium-denuded vessels; subsequent slow decomposition within the tissue generates sufficient NO to cause prolonged vasodilatation. This is a potentially useful characteristic for targeting NO delivery to areas of endothelial damage.

Synthesis and voltage-clamp studies of methyl 1,4-dihydro-2, 6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine-3-carboxylate racemates and enantiomers and of their benzofuroxanyl analogues.

Racemic methyl 1,4-dihydro-2, 6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine-3-carboxylates (+/-)-10 and (+/-)-11 and their benzofuroxanyl analogues (+/-)-12 and (+/-)-13 were prepared using a modified Hantzsch reaction that involved the condensation of nitroacetone with methyl 3-aminocrotonate and the appropriate aldehydes. The racemic mixtures were resolved into the corresponding enantiomers. Whole-cell voltage-clamp studies on L-type Ca2+ channels expressed in a rat insulinoma cell line (RINm5F) showed that all the dextrorotatory antipodes were effective agonists of L-type Ca2+ currents, while the levorotatory ones were weak Ca2+ entry blockers. The (+)-enantiomer of benzofurazan-5'-yl derivative 11 demonstrated unusual activity in that, in addition to producing a potentiation of L-type currents, it interfered with the voltage-dependent gating of L-type channels by producing a net delay of their activation at low voltages. This compound represents an interesting tool to probe L-type Ca2+ channel structure and function.

Mechanisms of liposomes/water partitioning of (p-methylbenzyl)alkylamines.

PURPOSE: The objective of this study was to compare and interpret the variations in lipophilicity of homologous (p-methylbenzyl)alkylamines (MBAAs) in isotropic (octanol/water) and anisotropic (zwitterionic liposomes/water) system. METHODS: Two experimental approaches were used, namely the pH-metric method to measure lipophilicity parameters in octanol/water and liposomes/water systems, and changes in NMR relaxation rates to validate the former method and to gain additional insights into the mechanisms of liposomes/water partitioning. RESULTS: For long-chain homologues (N-butyl to N-heptyl), the octanol/water and liposomes/water systems mostly expressed hydrophobicity. In contrast, the lipophilicity of the shorter homologues (N-methyl to N-propyl) in the two systems expressed various electrostatic and polar interactions. CONCLUSIONS: The study sheds light on the molecular interactions between zwitterionic liposomes and amphiphilic solutes in neutral and cationic form.

Bacteriemia por Stenotrophomona maltophilia asociada a neoplasia oculta / Bacteremia due to Stenotrophomona maltophilia associated with occult neoplasia

La S.maltophilia es un germen ubícuo de los suelos y el agua, que además con frecuencia coloniza la orofaringe de adultos normales. Se han documentado infecciones por S.maltophilia como causa de bacteriemia, contaminación de heridas, neumonías e infecciones del tracto urinario. Se considera un patógeno hospitalario emergente, en especial en pacientes inmunocomprometidos por neoplasias y en sujetos transplantados. La susceptibilidad antimicrobiana varía con la cepa identificada, pero casi todos los aislamientos son sensibles a la combinación de trimetoprima/sulfametoxazol. Se presenta una paciente de sexo femenino, de 66 años de edad, que ingresa al servicio de clínica médica para ser estudiada por síndrome febril prolongado. Una ecografía abdominal mostró un hígado heterogéneo, cuya biopsia informó metástasis de adenocarcinoma. Se realizaron tres tomas de hemocultivos que fueron positivas para S.maltophilia. Se realizó tratamiento con cotrimoxazol con buena respuesta clínica: no se pudo hallar la neoplasia primitiva. Se concluye afirmando que debe incluirse a la S.maltophilia dentro de los gérmenes oportunistas, teniendo especial atención en su particular sensibilidad antibiótica

Inhibition of human placenta glutathione transferase P1-1 by the antibiotic calvatic acid and its diazocyanide analogue--evidence for multiple catalytic intermediates.

The inhibition mechanism of the dimeric human placenta glutathione transferase (GST) P1-1 by calvatic acid and the reaction intermediates, i.e. the diazocyanide analogue of calvatic acid, has been investigated at pH 7.0 and 30.0 degrees C. Experiments performed at different molar ratios of inhibitor/GST P1-1 indicate that 1 mol calvatic acid inactivates 1 mol GST P1-1, containing two catalytically equivalent active sites. However, 2 mol of the diazocyanide analogue of calvatic acid inactivate 1 mol GST P1-1. Two disulfide bridges/dimer, probably between Cys47 and Cys101, have been formed during the reaction of GST P1-1 with calvatic acid and its diazocyanide analogue. The apparent second-order rate constants for GST P1-1 inactivation by calvatic acid and its diazocyanide analogue are 2.4+/-0.3 M(-1) s(-1) and (8.5+/-0.7) x 10(3) M(-1) s(-1), respectively. The reaction of calvatic acid with free L-cysteine can be described by a simple process with an apparent second-order rate constant of (5.0+/-0.4) x 10(1) M(-1) s(-1). In contrast, a transient species occurs during the reaction of the diazocyanide analogue of calvatic acid with free L-cysteine. Kinetics may be described by a second-order process [the rate constant being (8.0+/-0.5) x 10(3) M(-1) s(-1)] followed by a first-order decay [the rate constant corresponding to (1.2+/-0.1) x 10(1) s(-1)]. Calvatic acid represents an enzyme inhibitor acting much slower than its reaction intermediates (i.e. its diazocyanide analogue).

Water soluble furoxan derivatives as NO prodrugs.

The synthesis, characterization, NO donor properties, and in vitro vasodilating activity of a series of water soluble furoxans (5-14a,b) are described. All of the compounds released NO when treated with a large excess of cysteine under physiological conditions (pH 7.4; 37 degrees C). The amount of NO produced after 1 h of incubation was evaluated by detecting nitrites, via the Griess reaction. Derivatives 5b, 7b, and 14b were able to release nitric oxide also in the absence of the thiol cofactor. The initial rates of NO release were determined at different concentrations, using a spectrophotometric technique based on the NO-induced oxidation of oxyhemoglobin (HbO2) to methemoglobin (MetHb). The initial rates of NO release were linearly dependent on the concentrations of the single compounds. The vasodilating potency (EC50) of all the derivatives was assessed on rat aortic strips precontracted with noradrenaline. Correlation between potency and initial NO release rate is discussed.

Studies on agents with mixed NO-dependent vasodilating and beta-blocking activities.

PURPOSE: A series of derivatives having a propranolol-like moiety linked to NO-donor furoxan substructures were synthesized. The main objective of this investigation was to obtain agents with mixed NO-dependent vasodilating and beta-blocking activities. METHODS: Most of the target compounds were synthesized from the appropriate furoxans bearing XCH2CH2NH2 (X = O, S, SO2) chains at the 4 position of the ring, using Al(C2H5)3 in methylene chloride solution and (+/-)2,3-epoxypropyl 1-naphtyl ether. Two of the final products (X = CONH) were obtained by coupling the appropriate furoxancarboxylic acids with N-[2-hydroxy-3-(1-naphthoxy)propyl]-ethylenediamine. beta 1- and beta 2-blocking activities were examined on isolated guinea pig right atria and on guinea pig trachea respectively. Vasodilating properties were assessed on endothelium denuded strips of rat aorta. RESULTS: Some derivatives behave as well balanced "hybrids" displaying NO-dependent vasodilating and beta-blocking properties in the same concentration range. Some others display either prevalent beta-blocking or vasodilating activity. Generally speaking hybrid formation lowers the affinity for beta-receptors, in particular for beta 2-type, to give an increase in beta 1/beta 2 selectivity. CONCLUSIONS: The furoxan system is a flexible tool in designing analogues of propranolol whose NO-donating and beta-blocking properties are modulated over a wide range.