Andrea Szebeni

Effects of rosiglitazone on the configuration of action potentials and ion currents in canine ventricular cells

BACKGROUND AND PURPOSE In spite of its widespread clinical application, there is little information on the cellular cardiac effects of the antidiabetic drug rosiglitazone in larger experimental animals. In the present study therefore concentration‐dependent effects of rosiglitazone on action potential morphology and the underlying ion currents were studied in dog hearts.

Th1 and Th2 cell responses of type 1 diabetes patients and healthy controls to human heat-shock protein 60 peptides AA437-460 and AA394-408.

Abstract.Rationale: Type 1 diabetes mellitus (T1) is considered to be an immune mediated disease. Based on previous findings it might be suggested that heat shock protein 60 (Hsp60) could be involved in the mediation of the development of the disease. Furthermore a bias toward Th1 immune response was observed in T1D patients where the level of Th1 cytokines was elevated, while the level of Th2 was decreased.Aim of the study: To determine Th1 (IFN-γ) and Th2 (IL-13) cytokine levels in T1 diabetic and control subjects as well as to determine whether there is a shift towards Th1 or Th2 immune response.Materials and methods: ELISPOT (Enzyme-linked ImmunoSPOT) analysis was employed to differentiate antigen specific T-cell responses of a Th1 (IFN-γ) or Th2 (IL-13) type. 11 T1 diabetic patients and 9 healthy controls were investigated. For T-cell stimulation, we used a polyclonal mitogen or Tetanus toxoid (TT) as positive controls and two peptide antigens Hsp60 AA394–408 and Hsp60 AA437–460.Results: In case of Hsp60 AA437–460 we found significantly decreased Th2 response in patients, although there was no significant difference in Th1 response. In case of Hsp60 AA394–408 and positive controls there was no significant difference.Conclusion: Comparing the control and diabetic subjects a significant shift towards Th1 response in T1 diabetes mellitus for Hsp60 AA437–460 was observed.

Effects of vaccination with heat shock proteins on streptozotocin induced diabetes in histidine decarboxylase knockout mice

Abstract.Rationale:Type 1 diabetes mellitus (T1D) is an immune mediated disease in which heat shock proteins (hsps) may be involved in the development of the disease. Furthermore, vaccination with different hsps prevented the development of multiple low-dose streptozotocin (STZ) induced autoimmune diabetes in C57BL/KSJ mice. Histamine influences many aspects of the immune response, including Th1/Th2 balance and antibody production. Therefore, a study of diabetes-related immune processes was considered of interest in histidine decarboxylase knockout (HDC-KO) mice.Aim of the study:The aim of our study was i) to characterize antibody production in response to vaccination with p277 or hsp65 in wild type (WT) BALB/c and HDC-KO mice, and ii) to establish a possible correlation between vaccination and the changes in the pattern of STZ diabetes.Materials and methods:An ELISA was employed to measure the hsp65- and p277-specific antibody levels. To induce diabetes multiple low-dose of STZ was used.Results:Vaccination with p277 and hsp65 altered the pattern of STZ diabetes both in HDC-KO and WT animals, characterized by a transient increase followed by sustained reduction of blood sugar levels as compared to controls. However, vaccination with hsp65 and p277 caused a significant anti-p277 and anti-hsp65 antibody level increase only in WT animals.Conclusion:Multiple low-doses of STZ were able to induce diabetes in HDC-KO mice and the development of diabetes was prevented by vaccination with hsps. This protection developed in spite of the fact that vaccination caused a significant antibody level increase only in WT animals. To explain the therapeutic effect of vaccination we need further examination of the HDC KO strain.

Effects of pioglitazone on cardiac ion currents and action potential morphology in canine ventricular myocytes

Despite its widespread therapeutical use there is little information on the cellular cardiac effects of the antidiabetic drug pioglitazone in larger mammals. In the present study, therefore, the concentration-dependent effects of pioglitazone on ion currents and action potential configuration were studied in isolated canine ventricular myocytes using standard microelectrode, conventional whole cell patch clamp, and action potential voltage clamp techniques. Pioglitazone decreased the maximum velocity of depolarization and the amplitude of phase-1 repolarization at concentrations ≥3 μM. Action potentials were shortened by pioglitazone at concentrations ≥10 μM, which effect was accompanied with significant reduction of beat-to-beat variability of action potential duration. Several transmembrane ion currents, including the transient outward K(+) current (Ito), the L-type Ca(2+) current (ICa), the rapid and slow components of the delayed rectifier K(+) current (IKr and IKs, respectively), and the inward rectifier K(+) current (IK1) were inhibited by pioglitazone under conventional voltage clamp conditions. Ito was blocked significantly at concentrations ≥3 μM, ICa, IKr, IKs at concentrations ≥10 μM, while IK1 at concentrations ≥30 μM. Suppression of Ito, ICa, IKr, and IK1 has been confirmed also under action potential voltage clamp conditions. ATP-sensitive K(+) current, when activated by lemakalim, was effectively blocked by pioglitazone. Accordingly, action potentials were prolonged by 10 μM pioglitazone when the drug was applied in the presence of lemakalim. All these effects developed rapidly and were readily reversible upon washout. In conclusion, pioglitazone seems to be a harmless agent at usual therapeutic concentrations.

Can the electrophysiological action of rosiglitazone explain its cardiac side effects

Recent large clinical trials found an association between the antidiabetic drug rosiglitazone therapy and increased risk of cardiovascular adverse events. The aim of this report is to elucidate the cardiac electrophysiological properties of rosiglitazone (R) on isolated rat and murine ventricular papillary muscle cells and canine ventricular myocytes using conventional microelectrode, whole cell voltage clamp, and action potential (AP) voltage clamp techniques. In histidine-decarboxylase knockout mice as well as in their wild types R (1-30 µM) shortened AP duration at 90% level of repolarization (APD(90)) and increased the AP amplitude (APA) in a concentration-dependent manner. In rat ventricular papillary muscle cells R (1-30 µM) caused a significant reduction of APA and maximum velocity of depolarization (V(max)) which was accompanied by lengthening of APD(90). In single canine ventricular myocytes at concentrations ≥10 µM R decreased the amplitude of phase-1 repolarization, the plateau potential and reduced V(max). R suppressed several ion currents in a concentration-dependent manner under voltage clamp conditions. The EC(50) value for this inhibition was 25.2±2.7 µM for the transient outward K(+ ) current (I(to)), 72.3±9.3 µM for the rapid delayed rectifier K(+ ) current (I(Kr)), and 82.5±9.4 µM for the L-type Ca(2+ ) current (I(Ca)) with Hill coefficients close to unity. The inward rectifier K(+ ) current (I(K1)) was not affected by R up to concentrations of 100 µM. Suppression of I(to), I(Kr), and I(Ca) has been confirmed under action potential voltage clamp conditions as well. The observed alterations in the AP morphology and densities of ion currents may predict serious proarrhythmic risk in case of intoxication with R as a consequence of overdose or decreased elimination of the drug, particularly in patients having multiple cardiovascular risk factors, such as elderly diabetic patients.

Electrophysiological effects of rosiglitazone on heart ventricular papillary muscles of control and diabetic histidine decarboxylase knock-out and wild-type mice

Background Rosiglitazone is a thiazolidinedione derivative oral hypoglycemic agent active in both diabetic animal models and type 2 diabetic patients. Rosiglitazone is a high affinity ligand for the peroxisome proliferator-activated receptor gamma, which is responsible for the insulin-sensitizing action of the compound. Recent large clinical trials found an association between the antidiabetic drug rosiglitazone therapy and increased risk of cardiovascular adverse events.

Electrophysiological characteristics of heart ventricular papillary muscles in diabetic histidine decarboxylase knockout and wild-type mice

Objective The diabetes-induced action potential (AP) abnormalities have been studied mainly in rats where significant prolongation of repolarization and reduced maximum rate of depolarization (V max) was detected. Histidine decarboxylase knockout (HDC-KO) mice lack endogenous histamine and they are characterized by impaired glucose tolerance. Furthermore they have autoantibodies reactive to glutamic acid decarboxylase (GAD). These findings suggested that this model might have an increased susceptibility to autoimmune diabetes.

The electrophysiological and hemodynamical effects of pyruvate on diabetic and control rat hearts

Background Pyruvate, as an end-product of glycolysis, might influence the electrophysiological parameters of the heart by several mechanisms: Pyruvate enhances the phosphorylating potency of the cytosol; it can facilitate the reduction of inorganic phosphate and finally can influence the cytoplasamatic redox state by decreasing the H+ concentration. According to the literature, pyruvate enhances the amplitude of the action potential (APA) and also reduces the duration of the action potential (APD); hereby, it might be used to enhance the contractility in case of heart failure. Our aim was to determine the electrophysiological and hemodynamical effects of pyruvate on diabetic and control rat hearts.

Electrophysiological effects of heat shock proteins and dofetilide on cardiac preparations of streptozotocin-induced diabetic rats

Vaccination with different heat shock proteins (HSP60, HSP65) prevented the development of low-dose streptozotocin (STZ)-induced autoimmune diabetes in C57BL/ KSJ mice. The aim of our work was to examine whether the vaccination with HSP65 can prevent the well-known cardiac electrophysiological characteristics of diabetes. The electrophysiological effects of dofetilide (a class III antiarrhythmic drug) were also studied. Diabetes was induced by a low dose of STZ (3 × 30 mg/kg i.p.), the vaccination with HSP65 (100 μg/animal) occurred 7 days before STZ treatment. The parameters of transmembrane action potentials (APs) of right ventricular papillary muscles in rats were studied by the microelectrode technique. The previously observed prolongation of AP duration in diabetes induced by a high dose of STZ was recorded in the case of low dose of STZ too. The vaccination with HSP65 could not modify the increase of AP duration. Dofetilide (1–10 μM) did not cause any significant alterations in the parameters of AP either in diabetic or in the HSP-treated animals. Our results with dofetilide differ from published data. This result could be due to the fact that the ion current characteristic of the rat ventricular repolarization phase highly differs from that of other species. We need further experiments to find out additional explanations of our results.

Electrophysiological characteristics of heart ventricular papillary muscles from histidine decarboxylase knockout and wild-type mice: effects of rosiglitazone

Conclusion The most important difference in the electrophysiological parameters (APD, Vmax) between HDC KO and WT mice could be due to the fact that HDC KO mice are more susceptible for hyperglycaemia. The results also suggest that rosiglitazone might act on K+ channels and this effect might take part in the protective effect of rosiglitazone in ischemia/reperfusion injury observed in rats, but further, direct ionic current measurements need to support this explanation.