Serum cardiac troponin I concentrations transiently increase in rats given rosiglitazone.

Rosiglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) agonist of the thiazolidinedione class, is a major insulin-sensitizing drug widely used to treat type-2 diabetes. Rosiglitazone causes myocardial hypertrophy in rodents and increases the risk of cardiac events in man. To better characterize its cardiac effects, male Wistar rats were orally administered 0, 10 or 80 mg/kg/day rosiglitazone. Myocardial gene expression profiling, hematology, histopathology and clinical chemistry, including measurement of serum cardiac troponin (cTn) I concentration with the ultrasensitive assay, were evaluated after 6 and 24h and 7 and 14 days of dosing. Heart weight was increased 10% after 7 days and 16% after 14 days of dosing at 80 mg/kg/day in the absence of microscopic changes. At the transcriptomic level, the number of differentially expressed probes was small: it was most at 24h in rats given 80 mg/kg rosiglitazone with 356 differentially regulated probes (fold change >1.3 fold, p<0.05). Also, gene categories typically associated with myocardial damage were not over-represented. Most importantly, serum cTnI concentrations in 5/9 rats after 7 days of dosing at 80 mg/kg/day were above the upper limit of serum cTnI concentration. cTnI concentrations after 14 days of dosing were similar between rats given the vehicle and rosiglitazone at 80 mg/kg. This is the first study to detect increases of serum cTnI concentrations in rats administered rosiglitazone. In light of reported cardiac events in patients chronically dosed with PPARγ agonists, our results support serum cTnI concentrations as an early biomarker of cardiac liability.

Bidirectional on/off switch for controlled targeting of proteins to subcellular compartments.

A regulatable fusion protein was constructed for controlling the localization of plasmid products. A ligand-inducible nuclear localization signal, nuclear export signal (NES) and a truncated form of the ligand binding domain of the progesterone receptor were attached to the desired protein. Enhanced green fluorescent protein (EGFP) was used as a model protein and its trafficking between the nucleus and cytoplasm was studied using fluorescence microscopy in response to the ligand, mifepristone. It was found that the protein trafficking into the nucleus was dose dependent with ligand concentration. Increasing the ligand dose from 1 to 100 nM enhanced import and reduced the rate of export of the fusion protein from the nucleus to the cytoplasm. This study demonstrates the feasibility of using an export signal and a ligand-inducible nuclear import signal as a bi-directional on/off switch with potential use for controlled targeting of therapeutic proteins to subcellular compartments.