Amiodarone-induced lymphocyte toxicity and mitochondrial function

Amiodarone Advances the Apoptosis of Cardiomyocytes by Repressing Sigmar1 Expression and Blocking KCNH2-related Potassium Channels

BACKGROUND

Heart failure (HF) is the ultimate transformation result of various cardiovascular diseases. Mitochondria-mediated cardiomyocyte apoptosis has been uncovered to be associated with this disorder.

OBJECTIVE

This study mainly delves into the mechanism of the anti-arrhythmic drug amiodarone on mitochondrial toxicity of cardiomyocytes.

METHODS

The viability of H9c2 cells treated with amiodarone at 0.5, 1, 2, 3, and 4 μM was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and Sigmar1 expression was examined by quantitative real-time PCR (qRTPCR). After transfection, the viability, apoptosis, reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), and potassium voltage-gated channel subfamily H member 2 (KCNH2) expression in H9c2 cells were assessed by MTT, flow cytometry, ROS assay kit, mitochondria staining kit, and Western blot.

RESULTS

Amiodarone at 1-4 μM notably weakened H9c2 cell viability with IC50 value of 2.62 ± 0.43 μM. Amiodarone at 0.5-4 μM also evidently suppressed the Sigmar1 level in H9c2 cells. Amiodarone repressed H9c2 cell viability and KCNH2 level and triggered apoptosis, ROS production and mitochondrial depolarization, while Sigmar1 upregulation reversed its effects. Moreover, KCNH2 silencing neutralized the effect of Sigmar1 up-regulation on H9c2 cell viability, apoptosis, and ROS production.

CONCLUSION

Amiodarone facilitates the apoptosis of H9c2 cells by restraining Sigmar1 expression and blocking KCNH2-related potassium channels.

miR-155 influences cell-mediated immunity in Balb/c mice treated with aflatoxin M1

Aflatoxin M1 (AFM1) is a 4-hydroxylated metabolite of aflatoxin B1 (AFB1). It induces various toxicological effects including immunotoxicity. In the present study, we investigated the effects of AFM1 on immune system and its modulation by MicroRNA (miR)-155. AFM1 was administered intraperitoneally at doses of 25 and 50 µg/kg for 28 days to Balb/c mice and different immune system parameters were analyzed. The levels of miR-155 and targeted proteins were evaluated in isolated T cells from spleens of mice. Spleen weight was reduced in mice exposed to AFM1 compared to negative control. Proliferation of splenocytes in response to phytohemagglutinin-A was reduced in mice exposed to AFM1. IFN-γ was decreased in mice exposed to AFM1, whereas IL-10 was increased. Concentration of IL-4 did not change different in mice exposed to AFM1 compared to negative control. Exposure to AFM1 reduced the expression of miR-155. Significant upregulation of phosphatidylinositol-3, 4, 5-trisphosphate 5-phosphatase 1 (Ship1) and suppressor of cytokine signaling 1 (Socs1) was observed in isolated T cells from spleens of mice treated with AFM1, but the transcription factor Maf (c-MAF) was not affected. These results suggest that miR-155 and targeted proteins might be involved in the immunotoxicity observed in mice exposed to AFM1.

Effect of grapefruit juice on amiodarone induced nephrotoxicity in albino rats

Amiodarone is a potent antiarrhythmic drug that is used to treat ventricular and supraventricular tachyarrhythmias. The present work studied the effect of amiodarone on the kidney of albino rats and the possible ameliorative role of grapefruit juice. Administration of amiodarone by gastric intubation (18 mg/kg body weight (b.w.), daily for 5 weeks) caused many histological alterations including intertubular leucocytic infiltrations, degeneration of the renal tubules, and atrophy of the glomeruli. Amiodarone caused marked elevation in serum creatinine and blood urea nitrogen. Histochemical examination of the renal tubules revealed depletion of glycogen and total proteins. Besides, animals administered with amiodarone showed an increase of apoptotic bands as detected by gel electrophoresis. Treating animals with amiodarone and grapefruit juice (27 ml/kg b.w.) caused an improvement in histological and histochemical appearance of the kidney together with decrease of serum creatinine and blood urea nitrogen. Moreover, the apoptosis was decreased. It is concluded from the obtained results that grapefruit juice ameliorates the nephrotoxicity of amiodarone in albino rats and this may be due to the potent antioxidant effects of its components.

Identification of drugs inducing phospholipidosis by novel in vitro data

Drug-induced phospholipidosis (PLD) is a lysosomal storage disorder characterized by the accumulation of phospholipids within the lysosome. This adverse drug effect can occur in various tissues and is suspected to impact cellular viability. Therefore, it is important to test chemical compounds for their potential to induce PLD during the drug design process. PLD has been reported to be a side effect of many commonly used drugs, especially those with cationic amphiphilic properties. To predict drug-induced PLD in silico, we established a high-throughput cell-culture-based method to quantitatively determine the induction of PLD by chemical compounds. Using this assay, we tested 297 drug-like compounds at two different concentrations (2.5 μM and 5.0 μM). We were able to identify 28 previously unknown PLD-inducing agents. Furthermore, our experimental results enabled the development of a binary classification model to predict PLD-inducing agents based on their molecular properties. This random forest prediction system yields a bootstrapped validated accuracy of 86 %. PLD-inducing agents overlap with those that target similar biological processes; a high degree of concordance with PLD-inducing agents was identified for cationic amphiphilic compounds, small molecules that inhibit acid sphingomyelinase, compounds that cross the blood-brain barrier, and compounds that violate Lipinski's rule of five. Furthermore, we were able to show that PLD-inducing compounds applied in combination additively induce PLD.

Hepatotoxicity after intravenous amiodarone

Amiodarone is a class III antiarrhythmic agent with a long half-life which is used to control atrial and ventricular arrhythmias, including atrial flutter and fibrillation. We describe here the case of an elderly woman (77 years of age) who was hospitalized for acute atrial fibrillation, abdominal pain, and dyspnea. In the Emergency Department, treatment with intravenous amiodarone was begun. The following day, the patient developed acute liver damage; improved liver function occurred following the withdrawal of amiodarone. Complete recovery of liver function was documented after three weeks. Unfortunately, the patient died from a severe infectious disease, with multiple organ failure.

Interaction with the hERG channel and cytotoxicity of amiodarone and amiodarone analogues

BACKGROUND AND PURPOSE

Amiodarone (2-n-butyl-3-[3,5 diiodo-4-diethylaminoethoxybenzoyl]-benzofuran, B2-O-CH(2)CH(2)-N-diethyl) is an effective class III antiarrhythmic drug demonstrating potentially life-threatening organ toxicity. The principal aim of the study was to find amiodarone analogues that retained human ether-a-go-go-related protein (hERG) channel inhibition but with reduced cytotoxicity.

EXPERIMENTAL APPROACH

We synthesized amiodarone analogues with or without a positively ionizable nitrogen in the phenolic side chain. The cytotoxic properties of the compounds were evaluated using HepG2 (a hepatocyte cell line) and A549 cells (a pneumocyte line). Interactions of all compounds with the hERG channel were measured using pharmacological and in silico methods.

KEY RESULTS

Compared with amiodarone, which displayed only a weak cytotoxicity, the mono- and bis-desethylated metabolites, the further degraded alcohol (B2-O-CH(2)-CH(2)-OH), the corresponding acid (B2-O-CH(2)-COOH) and, finally, the newly synthesized B2-O-CH(2)-CH(2)-N-pyrrolidine were equally or more toxic. Conversely, structural analogues such as the B2-O-CH(2)-CH(2)-N-diisopropyl and the B2-O-CH(2)-CH(2)-N-piperidine were significantly less toxic than amiodarone. Cytotoxicity was associated with a drop in the mitochondrial membrane potential, suggesting mitochondrial involvement. Pharmacological and in silico investigations concerning the interactions of these compounds with the hERG channel revealed that compounds carrying a basic nitrogen in the side chain display a much higher affinity than those lacking such a group. Specifically, B2-O-CH(2)-CH(2)-N-piperidine and B2-O-CH(2)-CH(2)-N-pyrrolidine revealed a higher affinity towards hERG channels than amiodarone.

CONCLUSIONS AND IMPLICATIONS

Amiodarone analogues with better hERG channel inhibition and cytotoxicity profiles than the parent compound have been identified, demonstrating that cytotoxicity and hERG channel interaction are mechanistically distinct and separable properties of the compounds.

Rapid succession of peripheral blood progenitor cell mobilization cycles in patients with chronic heart failure: effects on the hematopoietic system

BACKGROUND

Circulating hematopoietic peripheral blood progenitor cells (PBPCs) may contribute to the regeneration of nonhematopoietic organs. An increase in circulating PBPC numbers may enhance this process. Therefore, an exploratory trial of repeated PBPC mobilization in patients with chronic heart failure was conducted. The safety and cardiovascular efficacy data have been described elsewhere. In the hematopoietic system, the trial offered an opportunity to study several new aspects of granulocyte-colony-stimulating factor (G-CSF) action.

STUDY DESIGN AND METHODS

Fourteen male patients with chronic heart failure were treated successively with G-CSF (four 10-day treatment periods interrupted by treatment-free intervals of equal length; daily dose adjustment to maintain a white blood cell [WBC] count of 45 x 10(9)-50 x 10(9)/L).

RESULTS

G-CSF induced a rapid increase in cells of all WBC lineages with return to levels equal to (neutrophilic, eosinophilic, and basophilic granulocytes) or lower than those before treatment (monocytes, lymphocytes) during the treatment-free intervals. Red cell counts remained unchanged, but platelet counts decreased followed by rebound thrombocytosis. The extent of CD34+ cell mobilization was highly variable. For each patient, the changes induced were identical through all cycles, but the G-CSF dose required in the first cycle was significantly higher than in subsequent cycles. In the cohort of patients, an inverse correlation was observed between the WBC level reached and the dose of G-CSF administered.

CONCLUSIONS

Rapid alternation between PBPC mobilization and recovery periods is feasible, with identical alterations in all treatment cycles. G-CSF responsiveness varies among patients and is increased by pretreatment with G-CSF.

Attenuation of amiodarone-induced pulmonary fibrosis by vitamin E is associated with suppression of transforming growth factor-beta1 gene expression but not prevention of mitochondrial dysfunction

Amiodarone (AM) is an efficacious antidysrhythmic agent that can cause numerous adverse effects, including potentially life-threatening pulmonary fibrosis. The current study was undertaken to investigate potential protective mechanisms of vitamin E against AM-induced pulmonary toxicity (AIPT) in the hamster. Three weeks after intratracheal administration of AM (1.83 micromol), increased pulmonary hydroxyproline content and histological damage were observed, indicative of fibrosis. These effects were preceded by increased pulmonary levels of transforming growth factor (TGF)-beta1 mRNA at 1 week post-AM, which remained elevated 3 weeks post-AM. Dietary supplementation with vitamin E resulted in rapid pulmonary accumulation of the vitamin, and prevention of AM-induced increases in TGF-beta1, hydroxyproline, and histological damage. Although dietary supplementation also markedly elevated lung mitochondrial vitamin E content, it did not attenuate AM-induced inhibition of mitochondrial respiration or disruption of mitochondrial membrane potential in vitro, or lung mitochondrial respiratory inhibition resulting from in vivo AM administration. These results suggest that vitamin E reduces the extent of pulmonary damage after AM administration via down-regulating TGF-beta1 overexpression but that it does not modify AM-induced mitochondrial dysfunction, a potential initiating event in AIPT.

Amiodarone inhibits lung degradation of SP-A and perturbs the distribution of lysosomal enzymes

Amiodarone may induce lung damage by direct toxicity or indirectly through inflammation. To clarify the mechanism of direct toxicity, we briefly exposed rabbit alveolar macrophages to amiodarone and analyzed their morphology, synthesis, and degradation of dipalmitoylphosphatidylcholine (DPPC); distribution of lysosomal enzymes; and uptake of diphtheria toxin and surfactant protein (SP) A used as tracers of the endocytic pathway. Furthermore, in newborn rabbits, we studied the clearance of DPPC and SP-A instilled into the trachea together with increasing amounts of amiodarone. We found that in vitro amiodarone decreases the surface density of mitochondria and lysosomes while increasing the surface density of inclusion bodies, increases the incorporation of choline into DPPC, modifies the distribution of lysosomal enzymes, and does not affect the uptake and processing of diphtheria toxin but inhibits the degradation of SP-A. In vivo amiodarone inhibits the degradation of SP-A but not of DPPC. We conclude that the acute exposure to amiodarone perturbs the endocytic pathway acting after the early endosomes, alters the traffic of lysosomal enzymes, and interferes with the turnover of SP-A.

Amiodarone-induced disruption of hamster lung and liver mitochondrial function: lack of association with thiobarbituric acid-reactive substance production

Amiodarone (AM) is an efficacious antidysrhythmic agent that is limited clinically by numerous adverse effects. Of greatest concern is AM-induced pulmonary toxicity (AIPT) due to the potential for mortality. Mitochondrial alterations and free radicals have been implicated in the etiology of AM-induced toxicities, including AIPT. Isolated hamster lung and liver mitochondria were assessed for AM-induced effects on respiration, membrane potential, and lipid peroxidation. AM (50-400 microM) stimulated state 4 (resting) respiration at complexes I and II of tightly coupled lung mitochondria, with higher concentrations (200 and 400 microM) resulting in a subsequent inhibition. This biphasic effect of AM (200 microM) was also observed with isolated liver mitochondria. Only inhibition of respiration was observed with AM (50-400 microM) in less tightly coupled lung mitochondria. Based on safranine fluorescence, 200 microM AM decreased lung mitochondrial membrane potential (p < 0.05), while a concentration-dependent (50-200 microM) decrease of membrane potential was observed with liver mitochondria exposed to AM (p < 0.05). Formation of thiobarbituric acid-reactive substances (TBARS) was not altered by AM (50-400 microM) in incubations lasting up to 1 h. These results indicate that lipid peroxidation, as indicated by levels of TBARS, does not play a role in AM-induced alterations in mitochondrial respiration and membrane potential.