Thyroid hormone changes cardiomyocyte shape and geometry via ERK signaling pathway: potential therapeutic implications in reversing cardiac remodeling?

It has previously been shown that thyroid hormone can reverse cardiac remodeling in failing hearts by reducing myocardial wall stress due to the unique changes induced in cardiac myocyte shape. This effect may be of therapeutic relevance. Therefore, the present study has investigated potential signaling mechanisms underlying the thyroid hormone action on cardiac myocyte shape and geometry. Neonatal cardiomyocytes were treated with T(3) while untreated cells served as controls. T(3) administration for 48 h significantly increased the ratio of the major to minor cell axis and changed their shape from an almost circular to an elongated form. Cell area and protein synthesis were increased and T(3) treated cells expressed 51% alpha-MHC and 49% beta-MHC as compared to 100% beta-MHC expression in non-treated cells. This response was accompanied by a 1.9-fold increase in phospho-ERK levels early at 8 min which, within 60 min, returned to the levels of the untreated cells. Phospho-JNK levels were significantly reduced within 60 min after T(3) treatment while no changes in the expression of phospho-Akt and phospho-p38 MAPK were found between the T(3) treated and untreated cells. Administration of PD98059 (an inhibitor of ERK signaling) prevented the thyroid hormone induced changes in cardiomyocyte geometry and shape without a significant reduction in cell area and protein synthesis. In conclusion, T(3) induced changes in cardiomyocyte shape and geometry involve the ERK kinase signaling. This response is independent of the effects of T(3) on cell size and protein synthesis.

High glucose protects embryonic cardiac cells against simulated ischemia.

In the present study we investigated whether acute glucose administration could be protective against hypoxic stress. H9c2 cells were exposed to either 4.5 mM or 22 mM of glucose for 15,min and then were submitted to simulated ischemia. Cell death was microscopically assessed by combined staining with propidium iodide (PI) and Hoeschst 33358. Intracellular content of glucose was measured by enzymatic analysis. Clucose content of H9c2 cells was 48.24+/- 7.94 micromol/L in the 22 mM vs 23.86+/- 4.8 micromol/L in the 4.5 mM group (p < 0.05). PKCepsilon expression was increased 1.6 fold in the membrane fraction after pretreatment with high glucose (p < 0.05), while was decreased 1.6 fold in the cytosol (p < 0.05). In addition, no difference to PKCdelta translocation was observed after pretreatment with low glucose. After hypoxia, in the 22 mM group, cell death was found to be 17.36+/- 2.66% vs 38.2+/- 5.4% in the 4.5 mM group (p < 0.05). In the presence of iodoacetic acid, a glycolytic inhibitor, cell death was not different between the two groups (23.54+/- 3.2% in 22 mM vs 22.06+/- 5.3% in 4.5 mM). Addition of chelerythrine did not change the protective effect of high glucose (13.4+/- 1.7% cell death in 22 mM vs 27.5+/- 5.5% in 4.5 mM, p < 0.05). In conclusion, short pretreatment with high glucose protects H9c2 cells against hypoxia. Although this protective effect is associated with translocation of PKCepsilon and increased glucose uptake, it was abrogated only by inhibition of glycolysis.

Dronedarone administration prevents body weight gain and increases tolerance of the heart to ischemic stress: a possible involvement of thyroid hormone receptor alpha1.

Hypothyroid heart displays a phenotype of cardioprotection against ischemia and this study investigated whether administration of dronedarone, an amiodarone-like compound that has been shown to preferentially antagonize thyroid hormone binding to thyroid hormone receptor alpha1 (TRalpha1), results in a similar effect. Dronedarone was given in Wistar rats (90 mg/kg, once daily (od) for 2 weeks) (DRON), while untreated animals served as controls (CONT). Hypothyroidism (HYPO) was induced by propylthiouracil administration. Isolated rat hearts were perfused in Langendorff mode and subjected to 20 minutes of zero-flow global ischemia (I) followed by 45 minutes of reperfusion (R). 3,5,3' Triiodothyronine remained unchanged while body weight and food intake were reduced. alpha-Myosin heavy chain (alpha-MHC) decreased in DRON while beta-myosin heavy chain (beta-MHC) and sarcoplasmic reticulum Ca2+ adenosine triphosphatase (ATPase) expression (SERCA) was similar to CONT. In HYPO, alpha-MHC and SERCA were decreased while beta-MHC was increased. Myocardial glycogen content was increased in both DRON and HYPO. In DRON, resting heart rate and contractility were reduced and ischemic contracture was significantly suppressed while postischemic left ventricular end-diastolic pressure and lactate dehydrogenase release (IU/L min) after I/R were significantly decreased. In conclusion, dronedarone treatment results in cardioprotection by selectively mimicking hypothyroidism. This is accompanied by a reduction in body weight because of the suppression of food intake. TRs might prove novel pharmacologic targets for the treatment of cardiovascular illnesses.

Trimetazidine protects isolated rat hearts against ischemia-reperfusion injury in an experimental timing-dependent manner.

The present study investigated the tolerance of the isolated rat heart to ischemia-reperfusion after administration of trimetazidine (TMZ) at different experimental phases, as well as the possible involvement of p38 MAPK and JNKs in this response. Isolated rat hearts were perfused in Langendorff mode. Untreated hearts after stabilization (S) were subjected to 20 min of zero-flow global ischemia (I) and 45 min of reperfusion (R), (NORM), n = 9. TMZ (10(-5) M) was administered (in the perfusate): a) only at S phase, (TMZ-STAB), n = 8, b) only at R, (TMZ-REP), n = 8 and c) during both S and R, (TMZ-STAB+REP), n = 8. Recovery of left ventricular developed pressure at 45 min of R (Rec) was significantly higher in TMZ-STAB and TMZ-STAB+REP and LDH release was lower in TMZ-STAB+REP and TMZ-STAB than NORM, [1153.2 (121.0) and 1152.1 (86.8) vs 1573.5 (138.2), P < 0.05]. TMZ induced cardioprotection did not involve p38 MAPK and JNKs. Phospho-p38 MAPK and JNKs levels after I/R were not changed with TMZ treatment. In TMZ-REP, Rec and LDH release were similar to NORM, but the rate of functional recovery (ratio of Rec at 10 min of R to Rec) was 86.7% (13.3) for TMZ-REP vs 53.8% (7.7) for NORM, P < 0.05. This effect was associated with decreased myocardial lactate content early at reperfusion. In conclusion, preischemic administration of TMZ protects against I/R injury while TMZ given only at reperfusion accelerates recovery of function without reducing the extent of injury.

Thyroid hormone and phenotypes of cardioprotection.

Thyroid hormone has multiple effects on the cardiovascular system with important physiological consequences. Several genes that encode important regulatory and structural proteins in the heart have been shown to be thyroid hormone responsive. More notably, certain effects of thyroid hormone have been exploited therapeutically. Thyroid hormone is currently being evaluated as an inotrope and vasodilator in various clinical settings. Furthermore, new information has been recently accumulated on the role of thyroid hormone in the response of the heart to ischaemic stress. In fact, hyperthyroid and hypothyroid hearts display a phenotype of cardioprotection against ischaemia-reperfusion. Based on this evidence, the various actions of thyroid hormone on the cardiovascular system are highlighted in this review. Thyroid hormone, although limited by its adverse effects, might prove a suitable treatment for cardiovascular illnesses. Various thyroid hormone analogues are currently under development.

Thyroxine pretreatment increases basal myocardial heat-shock protein 27 expression and accelerates translocation and phosphorylation of this protein upon ischaemia.

Thyroxine pretreatment increases the tolerance of the heart to ischaemia, and heat-shock protein 27 (HSP27) is considered to play an important role in cardioprotection. The present study investigated whether long-term thyroxine administration can induce changes in the expression, translocation and phosphorylation of HSP27 at baseline and upon ischaemic stress. L-Thyroxine (T(4)) was administered to Wistar rats (25 microg/100 g/day s.c.) for 2 weeks, while normal animals served as controls. Hearts from normal and thyroxine-treated rats were perfused in Langendorff mode and subjected to 10 or 20 min of zero-flow global ischaemia only or to 20 min of ischaemia followed by 45 min of reperfusion. Total and phospho-HSP27 expression were assessed at different times in the Triton-soluble (cytosol-membrane), S fraction, and the Triton-insoluble (cytoskeleton-nucleus) fraction, P fraction. Postischaemic recovery of left ventricular developed pressure at 45 min of reperfusion was expressed as % of the initial value. In hearts from thyroxine-treated animals, the levels of basal total HSP27 and phospho-HSP27 in the P fraction were significantly increased as compared to normal. In response to ischaemia, in hearts from thyroxine-treated rats, the levels of total HSP27 and phospho-HSP27 were found to be significantly increased in the P fraction at 10 and 20 min of ischaemia as compared to preischaemic values, whereas in normal hearts, the levels of total HSP27 and phospho-HSP27 were significantly increased at 20 min only. Postischaemic functional recovery was significantly greater in thyroxine-treated than in untreated hearts. In summary, long-term thyroxine pretreatment results in an increased basal expression and phosphorylation of HSP27 and in an earlier and sustained redistribution of HSP27 from the S to the P fraction in response to ischaemia. This effect might be of important therapeutic relevance.

Involvement of p38 MAPK and JNK in heat stress-induced cardioprotection.

The present study investigated whether heat stress-induced cardioprotection involves alterations in the pattern of p38 mitogen activated protein kinase (p38MAPK) and c-Jun NH2 - terminal kinase (JNK) activation during ischaemia - reperfusion in a model of isolated perfused rat heart. Wistar rats were subjected to whole-body hyperthermia at 42 degrees C for 15 min (HS), while untreated animals served as controls (CON). Twenty four hours later, CON and HS isolated hearts were perfused in a Langendorff mode and subjected to 20 min of zero-.ow global ischaemia followed by 45 min of reperfusion. Postischaemic recovery of left ventricular developed pressure at 45 min of reperfusion was expressed as % of the initial value (LVDP%). Activation of p38 MAPK and JNK was assessed by standard Western blotting techniques using a dual phospho-p38 MAPK and phospho-p46 JNK and p54 JNK antibodies. The levels of phospho-p38 MAPK at the end of reperfusion were not different in HS as compared to CON hearts. The levels of phospho-p46 JNK and p54 JNK were 1.4- and 1.6-fold less in HS than in CON hearts respectively, p < 0.05. LVDP% was 60.3 (s.e.m., 6.3) for HS and 42.9 (4.1) for CON, p < 0.05. In summary, heat stress pretreatment improves postischaemic recovery of function in isolated rat hearts and this is associated with suppressed JNK activation in response to ischaemia-reperfusion.

Thyroid hormone and cardioprotection: study of p38 MAPK and JNKs during ischaemia and at reperfusion in isolated rat heart.

It has been recently shown that long-term thyroxine administration increases the tolerance of the heart to ischaemia. The present study investigated whether thyroxine induced cardioprotection involves alterations in the pattern of p38 mitogen activated protein kinase (p38MAPK) and c-Jun NH2-terminal kinases (JNKs) activation during ischaemia-reperfusion. L-thyroxine (T4) was administered in Wistar rats (25 microg/100 g/day, subcutaneously) for 2 weeks (THYR), while normal animals served as controls (NORM). NORM and THYR isolated rat hearts were perfused in Langendorff mode and subjected to 10 or 20 min of zero-flow global ischaemia only and also to 20 min of ischaemia followed by 10, 20 or 45 min of reperfusion. Postischaemic recovery of left ventricular developed pressure at 45 min of reperfusion was expressed as % of the initial value. Activation of p38 MAPK and JNKs was assessed at the different times of the experimental setting by standard Western blotting techniques using a dual phospho p38MAPK and phospho JNKs (p46/p54) antibodies. Activation of p38 MAPK was significantly attenuated during ischaemia and reperfusion in thyroxine treated hearts compared to normal hearts. JNKs were found to be activated only during the reperfusion period. The levels of phospho JNKs were found to be lower in thyroxine treated hearts as compared to untreated hearts, though not at a statistically significant level. Postischaemic functional recovery was higher in THYR as compared to NORM, p < 0.05. In summary, in hearts pretreated with thyroxine, p38 MAPK was attenuated during ischaemia and at reperfusion and this was associated with improved postischaemic recovery of function.

Dobutamine administration exacerbates postischaemic myocardial dysfunction in isolated rat hearts: an effect reversed by thyroxine pretreatment.

The present study has investigated the effects of dobutamine on postischaemic dysfunction in the setting of global ischaemia and reperfusion in a model of isolated heart preparation. Isolated rat hearts were subjected to 20 min of zero-flow global ischaemia followed by 45 min of reperfusion. Dobutamine administration (10 microg/kg/min) during the reperfusion period resulted in deterioration of functional recovery, which was abolished by propranolol administration. Long-term thyroxine pretreatment (12.5 microg 100 g(-1) body weight, b.i.d., s.c., for 2 weeks) reversed the detrimental effect of dobutamine and increased postischaemic recovery of function. We conclude that the combination of thyroxine pretreatment and dobutamine administration could potentially be a new therapeutic strategy to improve postischaemic dysfunction particularly in clinical settings such as cardiopulmonary bypass and/or myocardial infarction.

Effects of dronedarone and amiodarone on plasma thyroid hormones and on the basal and postischemic performance of the isolated rat heart.

The present study investigated the effects of dronedarone and amiodarone on plasma thyroid hormones and the possible consequences on the response of the heart to ischemia. Amiodarone (30 mg/kg/day per os) or dronedarone (30 mg/kg/day per os) were administered for 2 weeks in normal and thyroxine-treated animals (25 microg/100 g body weight od sc, for 2 weeks), while animals without amiodarone and dronedarone served as controls. Isolated rat hearts were perfused in a Langendorff mode and subjected to 20 and 30 min of zero-flow global ischemia followed by 45 min of reperfusion. Functional changes were assessed by measuring left ventricular developed pressure (LVDP) under resting conditions and in response to ischemia-reperfusion, LVDP%, as well as the severity of ischemic contracture. Amiodarone resulted in increased T4, T4/T3 and rT3, whereas dronedarone did not alter the thyroid hormone profile in normal animals. In thyroxine-treated animals, amiodarone increased T4/T3 ratio but T4, T3 and rT3 levels were not altered. Basal functional parameters and ischemic contracture did not change by amiodarone and/or dronedarone neither in normal nor in thyroxine-treated hearts. In normal hearts, postischemic functional recovery, LVDP%, was not altered by amiodarone or dronedarone administration. LVDP% was statistically higher in thyroxine-treated hearts than in normal and this beneficial effect was not abolished by amiodarone or dronedarone treatment.

Long-term thyroxine administration protects the heart in a pattern similar to ischemic preconditioning.

We have previously shown that long-term thyroxine administration can protect the heart against ischemia. In the present study, we investigated whether thyroxine-induced cardioprotection can mimic the pattern of protection that is afforded by a well-established cardioprotective means such as ischemic preconditioning. In a Langendorff-perfused rat heart preparation, after an initial stabilization, normal and thyroxine-treated hearts were subjected to 20 minutes of zero-flow global ischemia followed by 45 minutes of reperfusion. In thyroxine-treated hearts, phospho-p38 mitogen-activated protein kinase (MAPK) was found to be less at the end of the ischemic period, whereas ischemic contracture was accelerated and postischemic recovery was increased in comparison to normal hearts. In addition, normal hearts were subjected to a four-cycle preconditioning protocol before ischemia. Phospho-p38 MAPK was found to be less at the end of the ischemic period in preconditioned hearts, whereas ischemic contracture was accelerated and postischemic functional recovery was increased in those hearts in comparison to nonpreconditioned hearts. An increase in basal expression and phosphorylation of PKCdelta was also found to occur after long-term thyroxine administration. We conclude that long-term thyroxine administration can protect the heart from ischemic injury through a pattern of protection that closely resembles that of ischemic preconditioning.