The Action of a Novel Fluoroquinolone Antibiotic Agent Antofloxacin Hydrochloride on Human-Ether-à-go-go-Related Gene Potassium Channel

In vivo and in silico evaluations of survival and cardiac developmental toxicity of quinolone antibiotics in zebrafish embryos (Danio rerio)

Quinolones are ranked as the second most commonly used class of antibiotics in China, despite their adverse clinical and environmental effects. However, information on their cardiac developmental toxicity to zebrafish is limited. This study investigates the relationships between different quinolone structures and toxicity in zebrafish embryos using in vivo and in silico methods. All of the experimentally tested quinolones show cardiac developmental toxicity potential and present mortality and teratogenic effects in a dose-dependent manner. Theoretically, the acute toxicity values predicted using quantitative structure-toxicity relationship (QSTR) modeling based on previously reported LC₅₀ values are in good agreement with the in vivo results. Further investigation demonstrates that the hormetic concentration response of some quinolones may be related to methylation on the piperazine ring at the C-7 position. The amino group at the C-5 position, the methylated or ethylated piperazine group at the C-7 position, halogens at the C-8 position and a cyclopropyl ring at N1 position may be responsible for cardiac developmental toxicity. In terms of survival (key ecological endpoint), the naridine ring is more toxic than the quinoline ring. This combined approach can predict the acute and cardiac developmental toxicity of other quinolones and impurities.

Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias

Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.

The protease inhibitor atazanavir blocks hERG K(+) channels expressed in HEK293 cells and obstructs hERG protein transport to cell membrane

AIM

Atazanavir (ATV) is a HIV-1 protease inhibitor for the treatment of AIDS patients, which is recently reported to provoke excessive prolongation of the QT interval and torsades de pointes (TdP). In order to elucidate its arrhythmogenic mechanisms, we investigated the effects of ATV on the hERG K(+) channels expressed in HEK293 cells.

METHODS

hERG K(+) currents were detected using whole-cell patch clamp recording in HEK293 cells transfected with EGFP-hERG plasmids. The expression of hERG protein was measured with Western blotting. Two mutants (Y652A and F656C) were constructed in the S6 domain within the inner helices of hERG K(+) channels that were responsible for binding of various drugs. The trafficking of hERG protein was studied with confocal microscopy.

RESULTS

Application of ATV (0.01-30 μmol/L) concentration-dependently decreased hERG K(+) currents with an IC50 of 5.7±1.8 μmol/L. ATV (10 μmol/L) did not affect the activation and steady-state inactivation of hERG K(+) currents. Compared with the wild type hERG K(+) channels, both Y652A and F656C mutants significantly reduced the inhibition of ATV on hERG K(+) currents. Overnight treatment with ATV (0.1-30 μmol/L) concentration-dependently reduced the amount of fully glycosylated 155 kDa hERG protein without significantly affecting the core-glycosylated 135 kDa hERG protein in the cells expressing the WT-hERG protein. Confocal microscopy studies confirmed that overnight treatment with ATV obstructed the trafficking of hERG protein to the cell membrane.

CONCLUSION

ATV directly blocks hERG K(+) channels via binding to the residues Y652 and F656 in the S6 domain, and indirectly obstructs the transport of the hERG protein to the cell membrane.

Antiarrhythmic efficacy of CPUY102122, a multiple ion channel blocker, on rabbits with ischemia/reperfusion injury

BACKGROUND

The antiarrhythmic potential of a novel multichannel blocker CPUY102122 (CY22) was investigated in the present study.

METHODS

The effect of CY22 on rapid delayed rectifier potassium channel current (IKr) was studied using whole-cell patch clamp techniques in Chinese Hamster Ovary cells stably expressing human Ether-à-go-go-Related Gene. We further evaluated the antioxidant effects of CY22 and demonstrated the reversal of connexin down-regulation in the development of cardiac ventricular arrhythmias, which was produced using coronary ligation/reperfusion in rabbits. CY22 and Amiodarone were administered 30min prior to the procedure. Next, electrocardiograms were recorded, protein expression of left ventricular Connexin43 (Cx43), non-phosphorylation-Cx43 (np-Cx43), Rac-1 and gp-91[phox] were assayed using Western blot analysis, microstructural changes in the myocardium were observed and redox system activity was assayed.

RESULTS

CY22 inhibited IKr in a concentration-dependent manner with IC50 value of 2.8±0.8μmol/L. CY22 treatment significantly decreased T-wave amplitude and QTc arrhythmic scores and ameliorated the shape of the infarcted myocardium compared to the model group. CY22 decreased the serum levels of creatine kinase, lactate dehydrogenase, and myocardial levels of malondialdehyde, as well as increased superoxide dismutase activity. Cx43 expression in the left ventricle was significantly increased by CY22 treatment, which significantly decreased np-43 expression, Rac-1 activity and gp-91[phox] protein expression.

CONCLUSIONS

These results indicated that CY22 has both antiarrhythmic and cardiovascular protective effects partly by blocking IKr, the production of antioxidants and protection of Cx43.

Blockage of hERG current and the disruption of trafficking as induced by roxithromycin

Roxithromycin is an oral macrolide antibiotic agent that has been repeatedly reported to provoke excessive prolongation of the Q–T interval and torsades de pointes in clinical settings. To investigate the mechanisms underlying the arrhythmogenic side effects of roxithromycin, we studied the molecular mechanisms of roxithromycin on human ether-à-go-go-related gene (hERG) K+ channels expressed in human embryonic kidney (HEK293) cells. Roxithromycin was found to inhibit wild-type (WT) hERG currents in a concentration-dependent manner with a half-maximum block concentration (IC50) of 55.8 ± 9.1 μmol/L. S6 residue hERG mutants (Y652A and F656C) showed reduced levels of hERG current blockage attributable to roxithromycin. Roxithromycin also inhibited the trafficking of hERG protein to the cell membrane, as confirmed by Western blot analysis and confocal microscopy. These findings indicate that roxithromycin may cause acquired long-QT syndrome via direct inhibition of hERG current and by disruption of hERG protein trafficking. Mutations in drug-binding sites (Y652A or F656C) of the hERG channel were found to attenuate hERG current blockage by roxithromycin, but did not significantly alter the disruption of trafficking.

A422T mutation in HERG potassium channel retained in ER is rescurable by pharmacologic or molecular chaperones

In the present study, we characterized biologic and electrophysiologic consequences of A422T mutation in HERG K(+) channel and the role of pharmacologic or molecular chaperons by employing a heterogeneous expression system in HEK 293 cells. It was found that A422T mutation led to a marked decrease in whole-cell recording currents, and that a complexly glycosylated form protein band at 155 kDa was missing by Western blotting analysis compared to wild type (WT). And the mutant protein was mainly located in the cytoplasm as illustrated in immunocytochemical assay, indicating that the mutation underwent a trafficking defect. In addition, A422T mutation exerted remarkable dominant-negative suppression on WT, resulting in the alteration in the kinetic processes. Strikingly, trafficking-deficient A422T mutation was partially rescued by incubating the cells at a lower temperature, administration of pharmacologic chaperon, E4031 or overexpression of a chaperon molecule, Hsp90, but not Hsp70. In conclusion, missense A422T mutation in HERG K(+) channel results in its trafficking defect, which is rescurable by pharmacologic or molecular chaperones.

The synthesized novel fluorinated compound (LJJ-10) induces death receptor- and mitochondria-dependent apoptotic cell death in the human osteogenic sarcoma U-2 OS cells

We designed the 6-fluoro-2-(3-fluorophenyl)-4-substituted anilinoquinazoline derivatives as less toxic anti-cancer candidates. Our result demonstrated that LJJ-10 has greater cytotoxicity than that of the other compounds in human osteogenic sarcoma U-2 OS cells. LJJ-10-induced apoptosis was associated with enhancing ROS generation, DNA damage, and an increase of the protein levels of Fas, FasL, FADD, caspase-8, cytochrome c, Apaf-1, AIF, Endo G, caspase-9 and caspase-3 in U-2 OS cells. LJJ-10-triggered growth inhibition was significantly attenuated by N-acetylcysteine, cyclosporine A, anti-FasL monoclonal antibody, and caspase-8, -9 and -3 specific inhibitors in U-2 OS cells. We suggest that LJJ-10-induced apoptotic cell death in U-2 OS cells through death receptor- and mitochondria-dependent apoptotic signaling pathways.