The Role of Free Radicals in the Pathogenesis of Amiodarone Toxicity

Free Radicals and Amiodarone Toxicity. 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 antioxidanl 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 amtodarone. Amiodarone treatment caused a significant increase of NADPH and Fe³⁺ induced lipid peroxidalion 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 tibrosis. Antioxidant treatment did not prevent these changes. Electron micrographs of lung from amiodarone-treated ruts 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 he 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-γ) 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 radioseasitizing effect of amiodarone was also verified in rat liver microsomal preparations using in vivo amiodarone with or without MTDQ-DA pretreatment and ⁶⁰Co-γ 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 radio-protective 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.     

Clinical Significance of Sleep-Related Breathing Disorders in Patients with Implantable Cardioverter Defibrillators

The prevalence and clinical significance of sleep-related breathing disorders (SRBDs) in patients with cardiac disease and a history of life-threatening ventricular tachyarrhythmias is unclear. Forty consecutive recipients of implantable cardioverter defibrillators (ICDs) with cardiac disease and a documented history of spontaneous, life-threatening, ventricular tachyarrhythmias underwent full night polysomnography. SRBDs were diagnosed if the apnea/hypopnea index was > 10. SRBD were diagnosed in 16 of 40 patients (40%): central sleep apnea (CSA) was present in 9 of these 16 patients (56%), 8 of whom had associated Cheyne-Stoke respiration. Seven of the 16 patients with SRBD (44%) had obstructive sleep apnea (OSA). Patients with and without SRBDs were comparable with respect to left ventricular ejection fraction, NYHA classification, underlying heart disease, ICD indications, and concomitant antiarrhythmic drug and beta-blocker therapy. Patients were followed prospectively for 2 years. ICD-treated ventricular tachyarrhythmias occurred in 10 of 24 patients (42%) without SRBD, in 4 of 9 patients (44%) with CSA, and in 3 of 7 patients (44%) with OSA (NS). The numbers and circadian distributions of episodes recorded during follow-up in patients without SRBD versus with CSA or OSA were not significantly different (14 ± 25, median = 4 vs 4 ± 5, median = 2.5 vs 15 ± 15, median = 7, respectively). The 2-year mortality, which was entirely attributable to nonsudden cardiac events, was highest in patients with CSA (4/9 [44%], vs 0/7 [0%] with OSA, vs 3/24 patients (12.5%) without SRBD; P < 0.05).     

Effect of Human Seminal Plasma on the Lytic Activity of Natural Killer Cells and Presumptive Identification of Participant Macromolecules

ABSTRACT: Using the lytic activity of natural killer (NK) cells as an in vitro parameter, the immunoregulatory properties of human seminal plasma (SeP1) and participant macromolecules have been investigated. Significant (P < 0.05) suppression of NK cell activity by SeP1 and chromatographically separable fractions was demonstrated in association with high and low molecular weight (M_r) macromolecules. SePl suppression was retained after heating to 56°C for 30 min, and appeared to function at the level of the effector, rather than target cell. Physicochemical characterization of high and low M_r fractions provided presumptive identification of the participation of transglutaminase and prostaglandins as the principal molecules contributory to SeP1 immunosuppression.     

The fate of Staphylococcal exfoliatin in newborn and adult mice*

The distribution and excretion of the staphylococcal exfoliatin was investigated following in vivo administration of highly purified ¹²⁵I-labelled exfoliatin fractions to adult and newborn mice. Adult mice excrete approximately one-third of a test dose by 3 hours as compared to a fifteenth of a test dose excreted by newborn mice. Accordingly, blood tracer radioactivity reaches a relatively higher peak and shows a slower decline in newborns than in adults. The urine of adult mice contains considerable biologically active exfoliating material. Both nephrectomized and carbon tetrachloride-poisoned adult mice injected with exfoliatin develop generalized exfoliation whereas comparable doses in untreated controls have no effect. On the other hand, subtotal hepatectomy, followed by injection of exfoliatin, does not lead to exfoliation. We conclude that renal immaturity is a critical factor responsible for the susceptibility of neonates to generalized staphylococcal scalded skin syndrome.     

Effect of Selective Inhibition of Potassium Channels on Vasorelaxing Response to Cromakalim,Nitroglycerin and Nitric Oxide of Canine Coronary Arteries

A comparative study was performed on the sensitivity of in-vitro vasorelaxation by nitroglycerin and cromakalim to block glibenclamide, a blocker of ATP-sensitive potassium channels, and iberiotoxin, a selective inhibitor of large-conductance calcium-activated potassium channels. In isolated canine coronary arteries preconstricted with 25 μM prostaglandin F_2α, nitroglycerin (0.005–1.8 μM) and cromakalim (0.15–9.6 μM) produced dose-dependent vasodilations. Glibenclamide (30 μM) had no significant effect on relaxation of the dose-response curve to nitroglycerin and almost completely abolished the relaxation by cromakalim, a known opener of ATP-sensitive potassium channels. Iberiotoxin (90 nM) decreased the maximal response to nitroglycerin and had no effect on the vasodilation induced by cromakalim. The effect of iberiotoxin on the vasorelaxing action of nitric oxide, the active metabolite of nitroglycerin, was also examined. In a low potassium chloride (14.4–20.4 mM) medium, as a contractile stimulus, iberiotoxin inhibited relaxations by exogenous nitric oxide (100–200 nM). Enhancement of potassium concentrations to 35.4–40.4 mM significantly decreased relaxation by nitric oxide and under these conditions the inhibitory action of iberiotoxin disappeared. The present study demonstrated that in canine coronary arteries, the functional role of two potassium channels can be separated by pharmacological means. Nitroglycerin-induced vasorelaxation may be mediated, at least in part, by its enzymatic breakdown product, nitric oxide that activates large-conductance calcium-activated potassium channels.