Functional Analysis of Wild-Type and 27 CYP3A4 Variants on Dronedarone Metabolism In vitro.

BACKGROUND: Cytochrome P450 (P450) is the largest family of enzymatic proteins in the human liver, and its features have been studied in physiology, medicine, biotechnology, and phytoremediation. OBJECTIVE: The aim of this study was to assess the catalytic activities of 28 human CYP3A4 alleles by using dronedarone as a probe drug in vitro, including 7 novel alleles recently found in the Han Chinese population. METHODS: We expressed 28 CYP3A4 alleles in insect microsomes and incubated them with 1-100 µM of dronedarone at 37 °C for 40 minutes to obtain the metabolites of N-debutyl-dronedarone. RESULTS: Compared with the wild type of CYP3A4, the 27 defective alleles can be classified into four categories. Three alleles had no detectable enzyme activity leading to a lack of kinetic parameters of N-debutyl-dronedarone; the other three alleles slightly despaired when it comes to intrinsic clearance values compared with the features of the wild type. Sixteen alleles exhibited 35.91%~79.70% relative values (in comparison to the wild-type) and could be defined as the "moderate decrease group". The rest of the alleles showed a considerable decrease in intrinsic clearance values, ranging from 11.88%~23.34%. Therefore they were classified as a "significantly decreased group". More specifically, 18 CYP3A4 alleles exhibited a substrate inhibition trend toward dronedarone when the concentration rises to 20 µM. CONCLUSION: The outcomes of this novel study on the metabolism of dronedarone by CYP3A4 alleles can be used as experimental data support for the individualized use of this modern drug.

Inhibitory Effects of Dronedarone on Small Conductance Calcium Activated Potassium Channels in Patients with Chronic Atrial Fibrillation: Comparison to Amiodarone.

BACKGROUND Dysfunction of small conductance calcium activated potassium (SK) channels plays a vital role in atrial arrhythmogenesis. Amiodarone and dronedarone are the most effective class III antiarrhythmic drugs. It is unclear whether the antiarrhythmic effect of amiodarone and dronedarone is related to SK channel inhibition. MATERIAL AND METHODS Tissue samples were obtained from the right atria of 46 patients with normal sinus rhythm and 39 patients with chronic atrial fibrillation. Isolated atrial myocytes were obtained by enzymatic dissociation. KCNN2 (SK2) channels were transiently expressed in human embryonic kidney (HEK)-293 cells. SK currents were recorded using whole-cell conventional patch clamp techniques. RESULTS Amiodarone and dronedarone showed a concentration-dependent inhibitory effect on SK currents (IKAS) in atrial myocytes from normal sinus rhythm patients and chronic atrial fibrillation patients. The suppressed efficacy of dronedarone and amiodarone on IKAS was greater in atrial myocytes from chronic atrial fibrillation patients than that from normal sinus rhythm patients. Furthermore, in patients with chronic atrial fibrillation, the IC50 value was 2.42 µM with dronedarone and 8.03 µM with amiodarone. In HEK-293 cells with transiently transfected SK2 channels, both dronedarone and amiodarone had a dose-dependent inhibitory effect on IKAS. The IC50 value was 1.7 µM with dronedarone and 7.2 µM with amiodarone in cells from patients with chronic atrial fibrillation. Compared to amiodarone, dronedarone is more efficacy to inhibit IKAS and could be a potential intervention for patients with chronic atrial fibrillation. CONCLUSIONS Dronedarone provides a great degree of IKAS inhibition in atrial myocytes from chronic atrial fibrillation than amiodarone. IKAS might be a potential target of amiodarone and dronedarone for the management of chronic atrial fibrillation.

Dronedarone: the effect of diet-induced obesity on its metabolism and experimental hyperlipidemia on its metabolism and tissue distribution in the rat.

Dronedarone biodistribution in hyperlipidemia and dronedarone metabolism in hyperlipidemia or obesity were assessed. Male Sprague-Dawley rats were given either normal standard chow with water or various high-fat or high-carbohydrate diets for 14 weeks. There was also a nonobese hyperlipidemic group given poloxamer 407 intraperitoneally. Liver and intestinal microsomes were prepared and the metabolic conversion of dronedarone to desbutyldronedarone was followed. A biodistribution study of dronedarone given orally was conducted in hyperlipidemic and control normolipidemic rats. The metabolism of dronedarone to desbutyldronedarone in control rats was consistent with substrate inhibition. However in the treatment groups, the formation of desbutyldronedarone did not follow substrate inhibition; hyperlipidemia and high-calorie diets created remarkable changes in dronedarone metabolic profiles and reduction in formation velocities. Tissue concentrations of dronedarone were much higher than in plasma. Furthermore, in hyperlipidemia, plasma and lung dronedarone concentrations were significantly higher compared to normolipidemia.

The role of hepatic cytochrome P450s in the cytotoxicity of dronedarone.

Dronedarone is used to treat patients with cardiac arrhythmias and has been reported to be associated with liver injury. Our previous mechanistic work demonstrated that DNA damage-induced apoptosis contributes to the cytotoxicity of dronedarone. In this study, we examined further the underlying mechanisms and found that after a 24-h treatment of HepG2 cells, dronedarone caused cytotoxicity, G1-phase cell cycle arrest, suppression of topoisomerase II, and DNA damage in a concentration-dependent manner. We also investigated the role of cytochrome P450s (CYPs)-mediated metabolism in the dronedarone-induced toxicity using our previously established HepG2 cell lines expressing individually 14 human CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrated that CYP3A4, 3A5, and 2D6 were the major enzymes that metabolize dronedarone, and that CYP3A7, 2E1, 2C19, 2C18, 1A1, and 2B6 also metabolize dronedarone, but to a lesser extent. Our data showed that the cytotoxicity of dronedarone was decreased in CYP3A4-, 3A5-, or 2D6-overexpressing cells compared to the control HepG2 cells, indicating that the parent dronedarone has higher potency than the metabolites to induce cytotoxicity in these cells. In contrast, cytotoxicity was increased in CYP1A1-overexpressing cells, demonstrating that CYP1A1 exerts an opposite effect in dronedarone's toxicity, comparing to CYP3A4, 3A5, or 2D6. We also studied the involvement of topoisomerase II in dronedarone-induced toxicity, and demonstrated that the overexpression of topoisomerase II caused an increase in cell viability and a decrease in γ-H2A.X induction, suggesting that suppression of topoisomerase II may be one of the mechanisms involved in dronedarone-induced liver toxicity.