Efectos del triflusal y la aspirina sobre los mediadores inflamatorios cardiovasculares inducidos por NF- kB / Effects of trifusal and aspirin over imflamatory cardiovascular mediators mediated by NF-kB

El factor de transcripción nuclear NF-kB controla la expresión de diversos genes implicados en la patogénesis de la ateroclerosis. El triflusal (ácido 2-acetoxi-4-trifluorometilbenzoico) es un fármaco antiagregante que, aunque relacionado estructuralmente con la aspirina y otros salicilatos, muestra un perfil farmacológico y farmacocinético característico. Dado que recientemente se ha demostrado que los salicilatos pueden inhibir el NF-kB, el objetivo del presente estudio ha sido probar la actividad inhibitoria tanto del triflusal como de su metabolito desacetilado, el HTB, sobre la activación de NF-kB. Los resultados aquí descritos muestran que ambos compuestos, trifulsal y HTB, son inhibidores de la activación de NF-kB más potentes que la aspirina o el salicilato, y como consecuencia de ello, pueden bloquear la inducción de la síntesis de citocinas (TNF-a), quimiocinas (MCP-1), moléculas de adhesión (VCAM-1) y enzimas proinflamatorios (COX-2, NOS 2).Además, a diferencia de la aspirina, estos efectos antiinflamatorios del trifulsal se alcanzan a concentraciones similares a las obtenidas en su uso terapeútico como fármaco antiagregante plaquetario. El trifulsal puede ejercer efectos antiinflamatorios en trastornos cardiovasculares en los que se ha observado que genes controlados por el NF-kB están sobrexpresados (AU)

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Inhibition of cyclooxygenase-2 expression by 4-trifluoromethyl derivatives of salicylate, triflusal, and its deacetylated metabolite, 2-hydroxy-4-trifluoromethylbenzoic acid.

The therapeutic potential of drugs that block the induction of cyclooxygenase-2 has been emphasized. When two 4-trifluoromethyl salicylate derivatives [2-acetoxy-4-trifluoromethyl-benzoic acid (triflusal) and its deacetylated metabolite 2-hydroxy-4-trifluoromethylbenzoic acid (HTB)] were compared with aspirin and sodium salicylate as cyclooxygenase-2 (COX-2) inhibitors, we observed that in bacterial lipopolysaccharide-activated human blood, triflusal, aspirin, and HTB, but not sodium salicylate, inhibited COX-2-mediated prostaglandin E2 (PGE2) production (IC50 = 0.16, 0.18, 0.39, and >10 mM, respectively). However, only triflusal and aspirin inhibited purified COX-2 enzyme. To test this apparent discrepancy, we realized that HTB and triflusal (but neither aspirin nor salicylate) produced a concentration-dependent inhibition of COX-2 protein expression in peripheral human mononuclear cells. This observation was further confirmed in a rat air pouch model in vivo, in which both aspirin and triflusal inhibited PGE2 production (ID50 = 18.9 and 11.4 mg/kg p.o., respectively) but only triflusal-treated animals showed a decrease in COX-2 expression. This different behavior may be, at least in part, due to the ability of HTB and triflusal to block the activation of the transcription factor nuclear factor-kappaB to a higher extent than aspirin and sodium salicylate. Thus, in addition to inhibiting the COX-2 activity at therapeutic concentrations, triflusal is able to block through its metabolite HTB the expression of new enzyme, and hence the resumption of PGE2 synthesis. Triflusal and HTB may exert beneficial effects in processes in which de novo COX-2 expression is involved and, in a broader sense, in pathological situations in which genes under nuclear factor-kappaB control are up-regulated.

Studies on the time-dependent activation of microsomal semicarbazide-sensitive amine oxidase.

The semicarbazide-sensitive amine oxidase (SSAO) from bovine lung microsomes was activated in a temperature- and time-dependent process. This behaviour was observed when the enzyme was preincubated at 25 degrees C, 37 degrees C and 50 degrees C but not at 4 degrees C. This activation was only observed when benzylamine was used as substrate but not when methylamine, histamine or 2-phenylethylamine were used. The activation was independent of pH, ionic strength and the nature of the buffer used. At 37 degrees C the specific activity had risen to a value that was about 7 times higher than that of the starting material after 120 min. This process affected only the maximum velocity of the reaction with the Km value remaining essentially unchanged. Treatment of SSAO with phospholipases and detergents did not affect this behaviour. Incubation of the enzyme with serine proteases, metal chelating agents, reducing agents or protease inhibitors, had no effect on the activation. The fact that both forms of the enzyme (activated and non-activated), showed the same Mr values on gel filtration chromatography excluded the possibility of an enzyme aggregation and/or degradation being involved in this process.

Inhibition of bovine lung semicarbazide-sensitive amine oxidase (SSAO) by some hydrazine derivatives.

Microsomal semicarbazide-sensitive amine oxidase (SSAO) from bovine lung was shown to be inhibited by a number of hydrazine derivatives, but the mechanisms of inhibition were found to differ. Hydralazine behaved as an irreversible and partially time-dependent inhibitor with an IC50 value of 1 microM under the conditions used. Phenylhydrazine was found to be a potent irreversible inhibitor of SSAO (IC50 30 nM). Semicarbazide behaved as a specific irreversible inhibitor (active-site-directed irreversible inhibitor) in first forming a non-covalent enzyme-semicarbazide complex (with a Ki value of 85 microM), which then reacted to give an irreversibly inhibited enzyme species in a reaction defined by the first-order rate constant k2 = 0.065 min-1. Phenelzine behaved as a reversible inhibitor, but dialysis at 37 degrees C was found to be necessary to obtain full recovery of enzyme activity. The dependence of inhibition on phenelzine concentration was complex and consistent with multiple binding sites for this inhibitor. This diversity in the action of a family of compounds with the same functional group must be taken into account in attempts to design more specific inhibitors of this enzyme.

Inhibition of monoamine oxidase from bovine retina by beta-carbolines.

The behaviour of some beta-carboline derivatives as inhibitors of monoamine oxidase has been studied in bovine retina. Inhibition was found not to show any significant time dependence. Di- and tetrahydro-beta-carbolines were shown to behave as reversible and competitive inhibitors. In contrast, the fully unsaturated beta-carbolines harmane, harmine and harmaline, which showed deviation from linearity at high substrate concentrations, behaved as tight-binding inhibitors. In these cases, the concentration of the enzyme and the inhibitor were of the same order. This was confirmed by the Ki values for these compounds in the nanomolar concentration range. Consistent with this was that inhibition was only partly reversed by dialysis for 18 h at 4 degrees C, although complete reversal was observed after dialysis for the same period at 37 degrees C. Structure-activity relationships indicated that substitution of a methoxy group at the C7 position of the aromatic ring is determinant for this tight-binding behaviour; a substitution of this group at the C6 position greatly reduced inhibition. Since beta-carbolines have been reported to be formed endogenously, this suggests that they might have important physiological actions on monoamine oxidase activity in-vivo. In contrast, all the beta-carbolines investigated in this study had low potencies as inhibitors of monoamine oxidase B.

Several aspects on the amine oxidation by semicarbazide-sensitive amine oxidase (SSAO) from bovine lung.

The lung has been shown to be potentially important in the metabolism of amines. Since SSAO has been demonstrated to be active towards some volatile short-chain aliphatic amines in other tissues, the current study determined the specificity and kinetic constants for the metabolism by bovine lung SSAO, of several aliphatic and aromatic amines some of which have been suggested to be physiological substrates (e.g. methylamine, aminoacetone and beta-phenylethylamine), and others (e.g. benzylamine) which are non-physiological. In the case of benzylamine, an inhibition at high substrate concentration was observed. Kinetic assays ruled out the possibility that this inhibition was caused by products of the deamination of benzylamine, and consequently it is suggested that these results may indicate the presence of two binding sites for the interaction of benzylamine with SSAO.

Contribution of different amine oxidases to the metabolism of dopamine in bovine retina.

The contribution of monoamine oxidase (MAO) A, MAO B and semicarbazide-sensitive amine oxidase (SSAO) to the metabolism of dopamine in the bovine retina was studied. These activities were present in the optic nerve, iris, choroid and bovine retina, but they were absent in the lens. SSAO activity towards dopamine was present in the choroid and the retina, but not in the iris or the optic nerve. The corresponding kinetic values for this substrate in the retina and the choroid showed higher affinity for MAO A (Km 271 and 197 microM, respectively) than for MAO B (Km 861 and 404 microM, respectively). This effect was counteracted by the higher Vmax value for MAO B resulting in the Vmax/Km ratio being similar for both cases. The absence of detectable SSAO activity towards dopamine in these last two tissues contrasts with the presence of that enzyme when benzylamine was studied as substrate. These results indicate that two different SSAO activities could be present in the bovine eye.

Monoamine oxidase and semicarbazide-sensitive amine oxidase activities in bovine eye.

The activities of MAO-A, MAO-B and the semicarbazide-sensitive amine oxidase (SSAO) were determined in bovine lens, retina, optic nerve, iris and epithelium. No activities were detected in lens but the SSAO activity was found to be rather evenly distributed in the other tissues. The SSAO activities determined with 1 microM benzylamine were about half those determined for MAO-B. MAO-A activity, measured with 5-HT as substrate, was considerably greater than those of MAO-B and SSAO, determined with 2-phenylethylamine and benzylamine, respectively, in all the eye tissues.