RESUMEN
INTRODUCTION: In vitro and in vivo studies were performed to elucidate the pathogenesis of amiodarone toxicity. METHODS AND RESULTS: Rats were treated with amiodarone alone (500 mg/kg body weight per day) or together with antioxidants (silibinin or MTDQ-DA: 50 mg/kg body weight per day) or with either antioxidant alone. They received amiodarone for 30 days and antioxidant for 33 days (3 days pretreatment). In vitro, amiodarone induced a dose-dependent chemiluminescence signal, which was inhibited by the two dihydroquinolin-type antioxidants (MTDQ-DA, CH 402). Chemiluminometric results from liver homogenate demonstrated that simultaneous treatment with silibinin partially prevented the liver homogenate superoxide anion radical scavenger capacity decreasing effect of amiodarone. Amiodarone treatment caused a significant increase of NADPH and Fe3+ induced lipid peroxidation in the liver microsomal fraction, which antioxidants (silibinin, MTDQ-DA) were unable to prevent. Light microscopy of the lung tissue in amiodarone-treated rats showed accumulation of foamy macrophages with thickening of the interalveolar septa, pneumonitis, and variable interstitial fibrosis. Antioxidant treatment did not prevent these changes. Electron micrographs of lung from amiodarone-treated rats showed lysosomal phospholipoidosis, intralysosomal electron dense deposits, and increased lysosome number and size. In contrast to rats treated with amiodarone alone, those treated with both amiodarone and silibinin had significantly fewer lysosomes (P < 0.01); the lysosome size, shape, and internal characteristics remained the same. Simultaneous treatment with silibinin and amiodarone decreased lysosomal phospholipoidosis compared to amiodarone treatment alone. Simultaneous treatment with MTDQ-DA and amiodarone did not show any beneficial effect. Pulse radiolysis and cobalt 60-gamma (60Co-gamma) radiolysis studies showed that the main free radical product in a reducing environment was a very reactive aryl radical formed after the partial deiodination of the amiodarone molecule. The radiosensitizing effect of amiodarone was also verified in rat liver microsomal preparations using in vivo amiodarone with or without MTDQ-DA pretreatment and 60Co-gamma irradiation with or without the in vitro addition of antioxidants (CH 402, MTDQ-DA). In vivo, the MTDQ-DA treatment also had a radiosensitizing effect; however, the in vitro addition of both antioxidants resulted in a radioprotective effect. The aryl radical also may emerge in vivo during the metabolism of amiodarone. CONCLUSION: These observations suggest that amiodarone in vitro and in vivo generates free radicals that may play a role in the pathogenesis of amiodarone toxicity beside other well-established mechanisms, and antioxidants may have a partial protective effect against amiodarone toxicity.
Asunto(s)
Amiodarona/toxicidad , Animales , Antioxidantes/farmacología , Radicales Libres , Técnicas In Vitro , Peroxidación de Lípido , Hígado/efectos de los fármacos , Hígado/patología , Hígado/ultraestructura , Mediciones Luminiscentes , Pulmón/efectos de los fármacos , Pulmón/patología , Pulmón/ultraestructura , Masculino , Microscopía Electrónica , Ratas , Ratas WistarRESUMEN
Silybin dihemisuccinate sodium salt, a flavonoid used in human therapy of liver dysfunction, has an inhibitory effect in vivo on radiation-induced deactivation of enzymes and peroxidation of membrane lipids in rat liver microsomes. The reactivity of silybin and its phenolic OH groups towards free radicals (OH, N3., (SCN)2.-, Cl3CO2.) in aqueous solution was studied by pulse radiolysis. Absorption spectra for the phenoxyl-type radicals were assigned using structurally similar models. The one-electron reduction potential for silybin at pH 7 (E07 = 0.76 V), determined using the p-methoxy-phenoxyl/phenolate redox couple as reference standard (E07 = 0.72 V, Lind et al. 1990), is related to the 3'-methoxy-4'-OH structure, the exclusive target for one-electron oxidation at pH 7, while the 7-OH and 5-OH groups are prevented from oxidation by 4-keto substitution and intramolecular H-bonding, respectively. The free radical reactivity of silybin compares favourably with poly-OH-substituted flavonoids; however, the latter compounds have been reported to generate potentially toxic oxygen species at a biologically relevant pH.
Asunto(s)
Silimarina , Animales , Radicales Libres , Hidróxidos , Radical Hidroxilo , Masculino , Microsomas Hepáticos/efectos de los fármacos , Microsomas Hepáticos/enzimología , Microsomas Hepáticos/efectos de la radiación , Oxidación-Reducción , Radiólisis de Impulso , Ratas , Ratas Endogámicas , Silimarina/farmacologíaRESUMEN
The authors demonstrated the generation of a very reactive phenyl radical from amiodarone in a reducing molecular environment by pulse radiolysis study. The various antioxidants are probably not capable of preventing the generation of phenyl radical, as well as to protect against its damaging effects on the neighboring molecules. Electron microscopic studies from lung tissue of in vivo treated rats showed that the simultaneous Silibinin (a flavonoid type antioxidant) treatment with amiodarone decreased significantly the lysosomal phospholipoidosis induced by amiodarone compared with the amiodarone treated group, but it didn't prevent entirely the accumulation of lysosomal phospholipids. The in vitro lysosomal beta-glucuronidase enzyme release measured from the liver tissue of in vivo treated rats increased significantly on amiodarone treatment, the antioxidants used (Silibinin, and the dihydroquinoline type MTDQ-DA) didn't exert any favorable effect. The authors discuss in details the possible relationships between free radical reactions and lysosomal phospholipoidosis.
Asunto(s)
Amiodarona/efectos adversos , Antioxidantes/farmacología , Amiodarona/antagonistas & inhibidores , Animales , Enfermedad Hepática Inducida por Sustancias y Drogas/prevención & control , Evaluación Preclínica de Medicamentos/métodos , Radicales Libres , Técnicas In Vitro , Hígado/enzimología , Hígado/ultraestructura , Lisosomas/efectos de los fármacos , Radiólisis de Impulso , Ratas , Análisis EspectralRESUMEN
The non-toxic and water soluble dihydroquinoline type antioxidants: CH 402 (Na-2,2-dimethyl-1,2-dihydroquinoline-4-yl methane sulphonate) and MTDQ-DA (6,6-methylene bis 2,2-dimethyl-4-methane sulphonic acid: Na-1,2-dihydroquinoline) were studied in various in vitro tests in which oxygen free radicals were generated. Both compounds were shown to scavenge superoxide radical anions O2- produced in aqueous solution by pulse radiolysis with rate constants k (O2- + MTDQ-DA) = 4.10(8) dm3 mol-1 s-1 and k (O2- + CH 402) = 1.5.10(7) dm3 mol-1 s-1. CH 402 and MTDQ-DA reduced the H2O2 produced in the glucose-glucose oxidase reaction, which was detected by the luminol + hemin reaction with a chemiluminometric method. The dihydroquinoline type substrates inhibited the NADPH-induced and Fe3+ - stimulated lipid peroxidation and the ascorbic acid-induced non-enzymatic peroxidation pathways in microsomal fractions of rat and mouse liver.