Amiodarone decreases gene expression of low-density lipoprotein receptor at both the mRNA and the protein level

Desmosterol accumulation in users of amiodarone

BACKGROUND

Amiodarone is an effective and widely used antiarrhythmic drug with many possible adverse effects including hypercholesterolaemia and hepatotoxicity.

OBJECTIVE

Our aim was to evaluate how long-term amiodarone treatment affects cholesterol metabolism.

METHODS

The study population consisted of 56 cardiac patients, of whom 20 were on amiodarone (amiodarone + group) and 36 did not use the drug (amiodarone - group). We also studied a control group of 124 individuals selected randomly from the population. Cholesterol metabolism was evaluated by analysis of serum noncholesterol sterols by gas-liquid chromatography and gas chromatography-mass spectrometry.

RESULTS

Comparisons of serum lipids and noncholesterol sterols across the three groups showed increased serum triglyceride in users of amiodarone but no statistically significant group differences in total, LDL or HDL cholesterol or serum proprotein convertase subtilisin/kexin type 9 concentrations. Nor did the groups differ in the ratios of cholestanol or plant sterols to cholesterol in serum, suggesting that cholesterol absorption was unaltered. However, all users of amiodarone had very markedly elevated serum desmosterol concentrations: the desmosterol-to-cholesterol ratio (10² × μmol mmol^-1 ) averaged 1030.7 ± 115.7 (mean ± SE) in the amiodarone + group versus 82.7 ± 3.4 and 75.9 ± 1.4 in the amiodarone - and the population control groups (P < 0.001), respectively.

CONCLUSION

Use of amiodarone was associated with on average 12-fold serum desmosterol concentrations compared with the control groups. This observation is fully novel and suggests that amiodarone interferes with the conversion of desmosterol to cholesterol in the cholesterol synthesis pathway. Whether accumulation of desmosterol plays a role in amiodarone-induced hepatotoxicity deserves to be studied in the future.

Amiodarone inhibits the entry and assembly steps of hepatitis C virus life cycle

HCV (hepatitis C virus) infection affects an estimated 180 million people in the world's population. Adverse effects occur frequently with current standard treatment of interferon and ribavirin, while resistance of new direct anti-viral agents, NS3 protease inhibitors, is a major concern because of their single anti-HCV mechanism against the viral factor. New anti-viral agents are needed to resolve the problems. Amiodarone, an anti-arrhythmic drug, has recently been shown to inhibit HCV infection in vitro. The detailed mechanism has yet to be clarified. The aim of the present study was to elucidate the molecular mechanism of the inhibitory effect of amiodarone on HCV life cycle. The effect of amiodarone on HCV life cycle was investigated in Huh-7.5.1 cells with HCVcc (cell culture-derived HCV), HCVpp (HCV pseudoviral particles), sub-genomic replicons, IRES (internal ribosomal entry site)-mediated translation assay, and intracellular and extracellular infectivity assays. The administration of amiodarone appeared to inhibit HCV entry independent of genotypes, which was attributed to the down-regulation of CD81 receptor expression. The inhibitory effect of amiodarone also manifested in the HCV assembly step, via the suppression of MTP (microsomal triacylglycerol transfer protein) activity. Amiodarone revealed no effects on HCV replication and translation. With the host factor-targeting characteristics, amiodarone may be an attractive agent for the treatment of HCV infection.

Iodine excess induces hepatic steatosis through disturbance of thyroid hormone metabolism involving oxidative stress in BALB/c mice

Iodine excess is emerging as a new focus. A better understanding of its hazardous effects on the liver will be of great benefit to health. The aim of this study is to illustrate the effects of iodine excess on hepatic lipid homeostasis and explore its possible mechanisms. One hundred twenty BaLB/c mice were given iodine at different levels (0, 0.3, 0.6, 1.2, 2.4, and 4.8 mg I/L) in drinking water for 1 or 3 months. Lipid parameters and serum thyroid hormones were measured. Hepatic type 1 deiodinase activity and oxidative stress parameters were evaluated. The mRNA expression of sterol regulatory element-binding protein-1c (SREBP-1c) and fatty acid synthase (FAS) was detected by real-time polymerase chain reaction. Dose-dependent increase of hepatic triglyceride content was detected (r = 0.680, P < 0.01) in iodine-loaded groups. Evident hepatic steatosis was observed in 2.4 and 4.8 mg I/L iodine-loaded groups. The activities of antioxidant enzymes (glutathione peroxidase and superoxide dismutase) were decreased, and the malondialdehyde level was increased by excessive iodine in both serum and liver in a dose-dependent manner, accompanying the decrease of hepatic D1 activity. That resulted in the increase of serum total thyroxine and the decrease of serum total triiodothyronine in iodine-loaded groups. The mRNA expression of SREBP-1c and FAS was increased in iodine-loaded groups in response to the change of serum triiodothyronine. Present findings demonstrated that iodine excess could dose dependently induce hepatic steatosis. Furthermore, our data suggested that the disturbance of thyroid hormone metabolism involving oxidative stress may play a critical role in iodine excess-induced hepatic steatosis.

Amiodarone and the thyroid: a 2012 update

Amiodarone-induced thyroid dysfunction occurs in 15-20% of amiodarone-treated patients. Amiodarone-induced hypothyroidism (AIH) does not pose relevant problems, is easily controlled by L-thyroxine replacement, and does not require amiodarone withdrawal. Most frequently AIH develops in patients with chronic autoimmune thyroiditis. Amiodarone- induced thyrotoxicosis (AIT) is most frequently due to destructive thyroiditis (type 2 AIT) causing discharge of thyroid hormones from the damaged, but otherwise substantially normal gland. Less frequently AIT is a form of hyperthyroidism (type 1 AIT) caused by the iodine load in a diseased gland (nodular goiter, Graves' disease). A clearcut differentiation between the two main forms is not always possible, despite recent diagnostic advances. As a matter of fact, mixed or indefinite forms do exist, contributed to by both thyroid damage and increased thyroid hormone synthesis. Treatment of type 1 (and mixed forms) AIT is based on the use of thionamides, a short course of potassium perchlorate and, if treatment is not rapidly effective, oral glucocorticoids. Glucocorticoids are the first-line treatment for type 2 AIT. Amiodarone should be discontinued, if feasible from a cardiac standpoint. Continuation of amiodarone has recently been associated with a delayed restoration of euthyroidism and a higher chance of recurrence after glucocorticoid withdrawal. Whether amiodarone treatment can be safely reinstituted after restoration of euthyroidism is still unknown. In rare cases of AIT resistance to standard treatments, or when a rapid restoration of euthyroidism is advisable, total thyroidectomy represents a valid alternative. Radioiodine treatment is usually not feasible due to the low thyroidal iodine uptake.

Statin resistant dyslipidemia in a patient treated with amiodarone

The authors describe a patient treated with amiodarone presented with high low-density lipoprotein cholesterol (LDL-C) levels who did not respond to treatment with a statin. Both amiodarone and amiodarone induced hypothyroidism influence the synthesis of LDL-receptor which may explain the lack of effect of statin. This was confirmed by normalisation of LDL-C upon discontinuation of amiodarone and treatment with thyroxine.

Amiodarone and thyroid

Assessment of TSH and TPO-Ab before starting amiodarone (AM) treatment is recommended. The usefulness of periodic TSH measurement every 6 months during AM treatment is limited by the often sudden explosive onset of AIT, and the spontaneous return of a suppressed TSH to normal values in half of the cases. AM-induced hypothyroidism develops rather early after starting treatment, preferentially in iodine-sufficient areas and in females with TPO-Ab; it is due to failure to escape from the Wolff-Chaikoff effect, resulting in preserved radioiodine uptake. AM-induced thyrotoxicosis (AIT) occurs at any time during treatment, preferentially in iodine-deficient regions and in males. AIT can be classified in type 1 (iodide-induced thyrotoxicosis, best treated by potassium perchlorate in combination with thionamides and discontinuation of AM) and type 2 (destructive thyrotoxicosis, best treated by prednisone; discontinuation of AM may not be necessary). AIT is associated with a higher rate of major adverse cardiovascular events (especially of ventricular arrhythmias). Uncertainty continues to exist with respect to the feasibility of continuation of AM despite AIT, the appropriate methods to distinguish between AIT type 1 and 2 as well as the advantages of AIT classification into subtypes in view of possible mixed cases, and the best policy when AM needs to be restarted.

Amiodarone inhibits arterial thrombus formation and tissue factor translation

BACKGROUND

In patients with coronary artery disease and reduced ejection fraction, amiodarone reduces mortality by decreasing sudden death. Because the latter may be triggered by coronary artery thrombosis as much as ventricular arrhythmias, amiodarone might interfere with tissue factor (TF) expression and thrombus formation.

METHODS AND RESULTS

Clinically relevant plasma concentrations of amiodarone reduced TF activity and impaired carotid artery thrombus formation in a mouse photochemical injury model in vivo. PTT, aPTT, and tail bleeding time were not affected; platelet number was slightly decreased. In human endothelial and vascular smooth muscle cells, amiodarone inhibited tumor necrosis factor (TNF)-alpha and thrombin-induced TF expression as well as surface activity. Amiodarone lacking iodine and the main metabolite of amiodarone, N-monodesethylamiodarone, inhibited TF expression. Amiodarone did not affect mitogen-activated protein kinase activation, TF mRNA expression, and TF protein degradation. Metabolic labeling confirmed that amiodarone inhibited TF protein translation.

CONCLUSIONS

Amiodarone impairs thrombus formation in vivo; in line with this, it inhibits TF protein expression and surface activity in human vascular cells. These pleiotropic actions occur within the range of amiodarone concentrations measured in patients, and thus may account at least in part for its beneficial effects in patients with coronary artery disease.

Amiodarone reversibly decreases sodium-iodide symporter mRNA expression at therapeutic concentrations and induces antioxidant responses at supraphysiological concentrations in cultured human thyroid follicles

CONTEXT

Amiodarone, a potent antiarrhythmic, iodine-containing agent, is a highly active oxidant exerting cytotoxic effects on thyrocytes at pharmacological concentrations. Patients receiving amiodarone usually remain euthyroid, but occasionally develop thyroid dysfunction. Although there is a general consensus that amiodarone-associated hypothyroidism is iodine induced, the destructive mechanism of thyroid follicles in amiodarone-induced thyrotoxicosis remains unknown.

OBJECTIVE

To elucidate the mechanism by which amiodarone elicits thyroid dysfunction.

DESIGN

Human thyroid follicles were cultured with thyroid-stimulating hormone (TSH) and amiodarone at therapeutic (1-2 microM) and pharmacological (10-20 microM) concentrations, and the drug-induced effect on whole human gene expression was analyzed by cDNA microarray. Microarray data were confirmed by real-time PCR and Western blot.

MAIN OUTCOMES

Amiodarone at 1-2 muM decreased the expression level of the sodium-iodide symporter (NIS) to nearly half, but did not affect genes participating in thyroid hormonogenesis (thyroid peroxidase, thyroglobulin, pendrin, and NADPH oxidase). Higher concentrations (10-20 microM) decreased the expression of all these genes, accompanied by increased expression of antioxidant proteins such as heme oxygenase 1 and ferritin. When thyroid follicles obtained from a patient with Graves' disease who had been treated with amiodarone were cultured in amiodarone-free medium, TSH-induced thyroid function was intact, suggesting that amiodarone at a maintenance dose did not elicit any cytotoxic effect on thyrocytes. The ultrastructural features of cultured thyroid follicles were compatible with these in vitro findings.

CONCLUSION

These in vitro and ex vivo findings suggest that patients taking maintenance doses of amiodarone usually remain euthyroid, probably due to escape from the Wolff-Chaikoff effect mediated by decreased expression of NIS mRNA. Further, amiodarone is not cytotoxic for thyrocytes at therapeutic concentrations but elicits cytotoxicity through oxidant activity at supraphysiological concentrations. We speculate that when amiodarone-induced prooxidant activity somehow exceeds the endogenous antioxidant capacity, the thyroid follicles will be destroyed and amiodarone-induced destructive thyrotoxicosis may develop.

Uptake of amiodarone by thyroidal and non-thyroidal cell lines

Amiodarone perturbs thyroid function, causing overt hypothyroidism or hyperthyroidism in 15% of patients. Changes in thyroid function are likely due, at least in part, to amiodarone and/or desethylamiodarone (DEA) concentration into the thyroid gland, but mechanisms whereby the drug uptake occurred are not known. Thyroidal (FRTL-5) or non-thyroidal [Chinese hamster ovary wild-type (CHOwt) or CHO stably transfected with NIS (CHO-NIS)] cells were exposed to 10 microM amiodarone or DEA. Cellular content of both drugs was measured by HPLC and normalized by protein concentration. Cellular concentration of the two drugs was higher in FRTL-5 (mean +/- SD 17.2 +/- 1.2 microg/mg protein of amiodarone and 18.9 +/- 0.7 microg/mg protein of DEA) than in CHO-NIS and CHOwt cells (10.8 +/- 0.8 microg/mg protein and 12.8 +/- 0.2 microg/mg protein, respectively, of amiodarone (p < 0.004); 11.9 +/- 0.1 microg/mg protein and 11 +/- 0.2 microg/mg protein, respectively, of DEA (p < 0.0002). DEA concentration was higher than that of amiodarone in all cell lines (p < 0.002). Differences between FRTL-5 and CHO cell lines were not dependent on TSH: in fact, cellular content of either drug did not change in the presence or absence of TSH in the culture medium. NIS did not intervene in amiodarone or DEA entry into thyroid cells, since amiodarone and DEA content was the same in CHOwt and CHO-NIS cells; in addition, KClO4 inhibited NIS function, but had no effect on drug uptake by the cells. At variance, 80 microM DEA reduced 125I uptake by CHO-NIS cells by 40% at 30 min without affecting cell viability. In conclusion, mechanisms whereby amiodarone is taken up by thyroid cells remain largely unknown, but the two main factors involved in thyroid-specific cellular transport, ie, NIS and TSH, seem to be excluded.

Microarray analysis reveals pivotal divergent mRNA expression profiles early in the development of either compensated ventricular hypertrophy or heart failure

Myocardial right ventricular (RV) hypertrophy due to pulmonary hypertension is aimed at normalizing ventricular wall stress. Depending on the degree of pressure overload, RV hypertrophy may progress to a state of impaired contractile function and heart failure, but this cannot be discerned during the early stages of ventricular remodeling. We tested whether critical differences in gene expression profiles exist between ventricles before the ultimate development of either a compensated or decompensated hypertrophic phenotype. Both phenotypes were selectively induced in Wistar rats by a single subcutaneous injection of either a low or a high dose of the pyrrolizidine alkaloid monocrotaline (MCT). Spotted oligonucleotide microarrays were used to investigate pressure-dependent cardiac gene expression profiles at 2 wk after the MCT injections, between control rats and rats that would ultimately develop either compensated or decompensated hypertrophy. Clustering of significantly regulated genes revealed specific expression profiles for each group, although the degree of hypertrophy was still similar in both. The ventricles destined to progress to failure showed activation of pro-apoptotic pathways, particularly related to mitochondria, whereas the group developing compensated hypertrophy showed blocked pro-death effector signaling via p38-MAPK, through upregulation of MAPK phosphatase-1. In summary, we show that, already at an early time point, pivotal differences in gene expression exist between ventricles that will ultimately develop either a compensated or a decompensated phenotype, depending on the degree of pressure overload. These data reveal genes that may provide markers for the early prediction of clinical outcome as well as potential targets for early intervention.

The various effects of amiodarone on thyroid function

Amiodarone, a benzofuranic-derivative iodine-rich drug used mostly for tachyarrhythmias, often causes changes in the peripheral metabolism of thyroid hormones mainly due to the inhibition of 5'-deiodinase activity: an increase in serum thyroxine and reverse triiodothyronine, and a decrease in serum triiodothyronine concentrations. Overt thyroid dysfunction, either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH), occurring in 14% to 18% of patients receiving long-term treatment, may develop both in apparently normal thyroid glands and in glands with preexisting abnormalities. AIH is mainly due to the failure to escape from the acute Wolff-Chaikoff effect, and, in patients with thyroid autoimmune phenomena, to concomitant Hashimoto's thyroiditis. AIT is due to excess iodine-induced thyroid hormone synthesis (type I AIT) or to amiodarone-related destructive thyroiditis (type II AIT), although mixed forms often occur. Treatment of AIH consists of levothyroxine replacement therapy while continuing amiodarone therapy; alternatively, amiodarone can be discontinued, if possible, and the natural course toward euthyroidism can be accelerated by a short trial of potassium perchlorate. In type I AIT, the simultaneous administration of thionamides and potassium perchlorate is the treatment of choice, while in type II AIT steroids are the most useful therapeutic option. Mixed forms are best treated with a combination of thionamides, potassium perchlorate, and glucocorticoids. The low thyroidal 131I uptake usually makes radioiodine therapy not feasible, while thyroidectomy is a valid alternative in cases resistant to medical therapy.

The effects of amiodarone on the thyroid

Amiodarone is a benzofuranic-derivative iodine-rich drug widely used for the treatment of tachyarrhythmias and, to a lesser extent, of ischemic heart disease. It often causes changes in thyroid function tests (typically an increase in serum T(4) and rT(3), and a decrease in serum T(3), concentrations), mainly related to the inhibition of 5'-deiodinase activity, resulting in a decrease in the generation of T(3) from T(4) and a decrease in the clearance of rT(3). In 14-18% of amiodarone-treated patients, there is overt thyroid dysfunction, either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH). Both AIT and AIH may develop either in apparently normal thyroid glands or in glands with preexisting, clinically silent abnormalities. Preexisting Hashimoto's thyroiditis is a definite risk factor for the occurrence of AIH. The pathogenesis of iodine-induced AIH is related to a failure to escape from the acute Wolff-Chaikoff effect due to defects in thyroid hormonogenesis, and, in patients with positive thyroid autoantibody tests, to concomitant Hashimoto's thyroiditis. AIT is primarily related to excess iodine-induced thyroid hormone synthesis in an abnormal thyroid gland (type I AIT) or to amiodarone-related destructive thyroiditis (type II AIT), but mixed forms frequently exist. Treatment of AIH consists of L-T(4) replacement while continuing amiodarone therapy; alternatively, if feasible, amiodarone can be discontinued, especially in the absence of thyroid abnormalities, and the natural course toward euthyroidism can be accelerated by a short course of potassium perchlorate treatment. In type I AIT the main medical treatment consists of the simultaneous administration of thionamides and potassium perchlorate, while in type II AIT, glucocorticoids are the most useful therapeutic option. Mixed forms are best treated with a combination of thionamides, potassium perchlorate, and glucocorticoids. Radioiodine therapy is usually not feasible due to the low thyroidal radioiodine uptake, while thyroidectomy can be performed in cases resistant to medical therapy, with a slightly increased surgical risk.