Impaired tissue clearance of verapamil in rat cardiac hypertrophy results in transcriptional repression of ion channels.

Heart hypertrophy is a common cardiac complication of sustained arterial hypertension and is accompanied by an increased incidence of supraventricular tachyarrhythmia, such as atrial fibrillation and atrial flutter. Verapamil, a phenyalkylamine, belongs to the group of calcium channel antagonists (class IV antiarrhythmic drugs) and is frequently used for the management of supraventricular tachycardia and for ventricular rate control in atrial fibrillation and atrial flutter. Verapamil heart tissue and plasma levels after intraperitoneal dosing of spontaneously hypertensive and normotensive rats were investigated. Transcript expression of various ion channels, ion transporters, calcium handling, and cytoskeletal proteins by reverse transcriptase-polymerase chain reaction (RT-PCR) were further investigated. There was no difference in plasma pharmacokinetics when hypertensive and normotensive animals were compared. Strikingly, the tissue clearance of verapamil was highly significantly impaired in heart tissue of hypertensive animals. Gene expression analysis showed the repression of many cardiac-specific genes in spontaneously hypertensive but not in normotensive rats, therefore providing evidence for different modes of action in healthy and hypertrophic hearts. Verapamil heart tissue levels differed dramatically between normotensive and hypertensive rats and resulted in repression of many cardiac ion channels, ion transporters, and calcium handling proteins. A disturbed ion homeostasis induced by critical tissue levels of verapamil is therefore proposed as a molecular rational for its pro-arrhythmogenic activity. The observed changes can be a significant determinant of spatial electrophysiological heterogeneity, thereby contributing to increased conductance disturbance as observed with some patients.

Expression of drug-metabolizing enzymes, nuclear transcription factors and ABC transporters in Caco-2 cells.

1. Caco-2 cells are frequently used in intestinal drug absorption and metabolism studies, but little is known about the effects of drugs on the simultaneous expression of genes coding for drug-metabolizing enzymes (DMEs), nuclear transcription factors and ABC transporters. 2. The gene expression and enzyme activities of control and Aroclor 1254-treated cultures were therefore explored, the latter being a powerful inducer of DMEs. Fourteen- and 80-fold induction of CYP1A1 and CYP1A2 mRNA were shown, whereas expression of other DMEs was either increased (CYP2C8-2C19, 10-fold; CYP3A5, twofold; FMO1, 2 and 5, twofold; epoxide hydrolase, threefold) or repressed (CYP2D6 and CYP2E1 to 75% of control values). 3. Notably, gene copies of CYP3A4 and CYP2B6/7 were below the limit of detection, but a three- and 10-fold induction of HNF 1alpha + beta, HNF-4alpha4 and a similar 10-fold increase in STAT 3 and 4 was observed. 4. Similarly, c/EBP transcripts were only detected in treated cell cultures, but MRP1, its isoforms 3-5 as well as MDR-1 were increased threefold after dosing with Aroclor 1254. 5. Overall, CYP gene expression correlated well with the cognate enzyme activity using testosterone as a marker substrate.