Toxicity of amiodarone and amiodarone analogues on isolated rat liver mitochondria

doi:10.1016/S0168-8278(01)00189-1

Journal of Hepatology

Volume 35, Issue 5, November 2001, Pages 628-636

https://doi.org/10.1016/S0168-8278(01)00189-1 Get rights and content

Abstract

Background: Amiodarone is a well-known mitochondrial toxin consisting of a benzofuran ring (ring A) coupled to a p-OH-benzene structure substituted with 2 iodines and a diethyl-ethanolamine side chain (ring B).

Aim: To find out which part of amiodarone is responsible for mitochondrial toxicity.

Methods: Amiodarone, ring A and B without the ethanolamine side-chain and iodines (B0), ring A and B with iodines but no ethanolamine (B2), ring B with 1 iodine and no ethanolamine (C1) and ring B with ethanolamine and 2 iodines (D2) were studied.

Results: In freshly isolated rat liver mitochondria, amiodarone inhibited state 3 glutamate and palmitoyl-CoA oxidation and decreased the respiratory control ratios. B0 and B2 were more potent inhibitors than amiodarone and B2 more potent than B0. C1 and D2 showed no significant mitochondrial toxicity. After disruption, mitochondrial oxidases and complexes of the electron transport chain were inhibited by amiodarone, B0 and B2, whereas C1 and D2 revealed no inhibition. Beta-oxidation showed a strong inhibition by amiodarone, B0 and B2 but not by C1 or D2. Ketogenesis was almost unaffected.

Conclusions: Amiodarone, B0 and B2 are uncouplers of oxidative phosphorylation, and inhibit complexes I, II and III, and β-oxidation. The benzofuran structure is responsible for mitochondrial toxicity of amiodarone and the presence of iodine is not essential.

Introduction

Amiodarone is a highly effective antiarrhythmic agent with class III activity according to the classification of Vaughan-Williams [1]. It is used in the treatment and prophylaxis of both ventricular and supraventricular arrhythmias [1], in particular in patients with heart insufficiency [2], [3], because it has no significant negative inotropic effect.

Amiodarone has several adverse effects including corneal deposits, hypo- and hyperthyreosis, pulmonary fibrosis and hepatocellular liver damage [1]. About 1–3% of the patients treated with amiodarone suffer from symptomatic liver disease which may histologically be similar to alcoholic liver lesions [4], [5]. One of the reasons for hepatic toxicity of amiodarone may be impairment of the function of liver mitochondria. It has been shown in mice that amiodarone inhibits mitochondrial β-oxidation of fatty acids, leading to microvesicular steatosis of the liver [6]. In addition, amiodarone has an uncoupling effect on oxidative phosphorylation and inhibits the function of the electron transport chain in isolated mice liver mitochondria [7].

The current study was undertaken to find out which part of the amiodarone molecule is responsible for mitochondrial toxicity. Amiodarone is composed of a diiodobenzene ring carrying a diethylaminoethoxy side chain, and a benzofuran ring carrying a C₄H₉ side chain (Fig. 1). In order be able to answer our question, we synthesized four amiodarone analogues composed of different parts of the amiodarone molecule and investigated their effect on the function of isolated rat liver mitochondria.

Section snippets

Reagents

Amiodarone hydrochloride and the amiodarone analogues were synthesized as described previously [8]. Duroquinol (durohydroquinone) was purchased from ReseaChem GmbH (Burgdorf, Switzerland). [1–¹⁴C]Palmitic acid was purchased from Amersham Pharmacia Biotech (Dübendorf, Switzerland). All other chemicals were purchased from Sigma Chemical Co. (Buchs, Switzerland).

Animals

Male Sprague–Dawley rats were purchased from BRL Biological Research (Füllinsdorf, Switzerland). They were fed ad libitum and held on a

Results

The toxicity of amiodarone and the structural analogues B0, B2, C1 and D2 (structures shown in Fig. 1) was tested in isolated rat liver mitochondria. The effect of amiodarone and analogues on oxidative mitochondrial metabolism using glutamate or palmitoyl-CoA as substrate is shown in Table 1. In the presence of glutamate as substrate, amiodarone, B0 and B2 revealed a dose dependent toxic effect on mitochondrial metabolism. Glutamate is metabolized by glutamate dehydrogenase to α-ketoglutarate

Discussion

Our study shows that amiodarone, B0 and B2 are uncouplers of oxidative phosphorylation, inhibit various enzyme complexes of the electron transport chain and also mitochondrial β-oxidation. The essential structure associated with mitochondrial toxicity appears to be the benzofuran ring, whereas the presence of iodine is not essential for mitochondrial toxicity of amiodarone and analogues.

As shown in Table 1, amiodarone, B0 and B2 are more potent as uncouplers than as inhibitors of enzyme

Acknowledgements

The study has been supported by grant 31-59812.99 from the Swiss National Science Foundation to S.K.

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Toxicity of amiodarone and amiodarone analogues on isolated rat liver mitochondria

Abstract

Introduction

Section snippets

Reagents

Animals

Results

Discussion

Acknowledgements

Lancet

J Biol Chem

J Biol Chem

J Biol Chem

Methods Enzymol

Clin Chim Acta

Clin Chim Acta

J Hepatol

Biochim Biophys Acta

Pharmacol Ther

J Hepatol

J Hepatol

Amiodarone

N Engl J Med