RESUMEN
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.
Asunto(s)
Síndrome de QT Prolongado/tratamiento farmacológico , Potenciales de la Membrana/efectos de los fármacos , Roxitromicina/farmacología , Transactivadores/metabolismo , Línea Celular , Membrana Celular/efectos de los fármacos , Membrana Celular/genética , Membrana Celular/metabolismo , Células HEK293 , Humanos , Síndrome de QT Prolongado/metabolismo , Potenciales de la Membrana/genética , Mutación/genética , Transporte de Proteínas/efectos de los fármacos , Transporte de Proteínas/genética , Transactivadores/genética , Regulador Transcripcional ERGRESUMEN
QT interval prolongation, a risk factor for arrhythmias, may be associated with genetic variants in genes governing cardiac repolarization. Long QT syndrome type 2 (LQT2) is caused by mutations in the human ether-a-gogo-related gene (hERG). This gene encodes a voltage-gated potassium channel comprised of 4 subunits, and the formation of functional channels requires the proper assembly of these 4 subunits. In the present study, we investigated the role of the LQT2 mutation, Q738X, which causes truncation of the C-terminus of hERG channels, in the assembly and function of hERG channels. When expressed in HEK293 cells, Q738X did not generate an hERG current. The co-expression of Q738X with wild-type (WT)-hERG did not cause the dominant-negative suppression of the WT-hERG current. Western blot analysis and confocal microscopy revealed that the Q738X mutation caused defective trafficking of hERG channel proteins. Co-immunoprecipitation demonstrated that Q738X did not exhibit dominant-negative effects due to the failure of the mutant and WT subunits to co-assemble. In conclusion, the functional loss caused by the Q738X mutation in hERG K+ channels may be attributed to the disruption of tetrameric assembly.
Asunto(s)
Canales de Potasio Éter-A-Go-Go/genética , Predisposición Genética a la Enfermedad , Síndrome de QT Prolongado/genética , Mutación/genética , Canal de Potasio ERG1 , Células HEK293 , Humanos , Activación del Canal Iónico , TransfecciónRESUMEN
Response to statin therapy for cardiovascular disease is variable among different individuals. The authors aimed to investigate the effect of the CYP3AP1*3 polymorphism on the lipid-lowering efficacy of statins. They recruited 379 unrelated hyperlipidemic patients: 202 (103 men) treated with simvastatin and 177 (87 men) with atorvastatin as single-agent therapy (20 mg day(-1) orally) for 4 weeks. CYP3AP1*3(-44G>A) was genotyped using the PCR restriction fragment-length polymorphism method. Serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TGs) were determined before and after treatment. The frequency of the CYP3AP1*3 variant allele in Chinese hyperlipidemic patients was 70.6%. In the simvastatin treatment group, the percentage reduction of LDL-C level was greater in the CYP3AP1*3/*3 carriers than in the CYP3AP1*1 carriers. This difference was statistically significant for women but not for men. In contrast, the authors found no significant association between the lipid-lowering efficacy of atorvastatin and the CYP3AP1*3 polymorphism in all participants. However, in women, the percentage change of the TC level was significantly lower in the CYP3AP1*3/*3 carriers than in the CYP3AP1*1 carriers. These findings suggest that the CYP3AP1*3 allele may be a biomarker for the lipid-lowering efficacy of simvastatin and atorvastatin in Chinese women with hyperlipidemia.