A randomised, double-blind, dose-finding, phase II multicentre study of ODX in the treatment of patients with castration-resistant prostate cancer and skeletal metastases

AIMS

This study aimed to assess the efficacy and safety of ODX, a novel, cytotoxic, bone-targeting drug candidate, in castration-resistant prostate cancer bone metastatic disease.

METHODS

Patients with progressive disease were randomised to ten cycles of ODX, intravenous infusion Q2W (3, 6, and 9 mg/kg, respectively). The primary objective was to assess the relative change from baseline in bone alkaline phosphatase (B-ALP) and serum-aminoterminal-propeptide of Type I procollagen (S-P1NP) at 12 weeks. The inclusion criteria selected were broad, and a double-blind design was used to ensure objective recruitment of patients for the assessment of efficacy. None of the patients received bone-protecting agents during the ODX treatment period.

RESULTS

Fifty-five 21,20 and 14) patients were randomised to ODX (3, 6 and 9 mg/kg), respectively. The lower number of patients in arm 3 was due to too low a recruitment rate towards the end of the study. The median treatment time were 14, 13 and 14 weeks, respectively. The decrease in B-ALP at 12 weeks in study arms 3, 6 and 9 mg/kg was seen in 6/15 (40%), 8/12 (67%) and 5/12 (42%) patients, respectively, whereas the corresponding numbers for P1NP were 8/15 (53%), 8/12 (67%), and 4/12 (33%), respectively. The median decrease in B-ALP and P1NP at 12 weeks for study arms 3, 6 and 9 mg/kg were 37%, 14% and 43%, respectively, and 51%, 40% and 64%, respectively. The decrease in serum C-terminal telopeptide at 12 weeks was seen in the vast majority of patients and in about one-third of patients in bone scan index. ODX was well tolerated, and no drug-related serious adverse events occurred. There were no significant differences between study arms regarding efficacy and safety.

CONCLUSIONS

ODX was well tolerated and demonstrated inhibitory effects on markers related to the vicious cycle in bone at all three doses. The reduction in metastatic burden, assessed with bone scan index, supports this finding. Studies with continued ODX treatment until disease progression are being planned (ClinicalTrials.gov Identifier: NCT02825628).

Changes in therapy and survival of metastatic renal cell carcinoma in Estonia

Background

Before the era of targeted therapies, cytokines were the main therapy for metastatic renal cell carcinoma (mRCC). Our aim was to analyze the changes in treatments and overall survival (OS) of all mRCC patients in Estonia in relation to the introduction of new medications.

Methods

All patients with mRCC who started medical therapy in Estonia during the years 2004–2012 were identified using the database of the Estonian Health Insurance Fund. Tumor and treatment data were gathered from medical records. Vital status data were obtained from the Estonian Population Registry. The only available therapy before 2008 was interferon alpha-2A (INFa2A), targeted agents added from 2008. For survival analysis, patients were divided into 2 groups: INFa therapy only (group 1) and INFa followed by targeted agents or targeted agents therapy only (group 2).

Results

Out of 416 identified patients, 380 were eligible for analysis. The most common 1st-line treatments were INFa (55%), sunitinib (32%) and INFa+bevacizumab (13%). 28% of patients received 2nd-line therapies and 15% 3rd-line treatments. Median survival of all patients was 13.7 months [95% confidence interval (CI) 11.3–16.2]; 7.6 months (CI 6.4–8.6) for group 1 and 19.8 months (CI 15.6–22.9) for group 2. In multivariate analysis, group 1 had nearly four times higher risk of dying than group 2 [hazard ration (HR) 3.88, 95% CI 2.64–5.72].

Conclusions

The implementation of targeted therapies significantly changed the outcomes of mRCC in Estonia: it prolonged median survival, reduced the risk of death and also enlarged the proportion of patients who received medical therapy.

Pembrolizumab for Treatment-Refractory Metastatic Castration-Resistant Prostate Cancer: Multicohort, Open-Label Phase II KEYNOTE-199 Study

PURPOSE

Pembrolizumab has previously shown antitumor activity against programmed death ligand 1 (PD-L1)-positive metastatic castration-resistant prostate cancer (mCRPC). Here, we assessed the antitumor activity and safety of pembrolizumab in three parallel cohorts of a larger mCRPC population.

METHODS

The phase II KEYNOTE-199 study included three cohorts of patients with mCRPC treated with docetaxel and one or more targeted endocrine therapies. Cohorts 1 and 2 enrolled patients with RECIST-measurable PD-L1-positive and PD-L1-negative disease, respectively. Cohort 3 enrolled patients with bone-predominant disease, regardless of PD-L1 expression. All patients received pembrolizumab 200 mg every 3 weeks for up to 35 cycles. The primary end point was objective response rate per RECIST v1.1 assessed by central review in cohorts 1 and 2. Secondary end points included disease control rate, duration of response, overall survival (OS), and safety.

RESULTS

Two hundred fifty-eight patients were enrolled: 133 in cohort 1, 66 in cohort 2, and 59 in cohort 3. Objective response rate was 5% (95% CI, 2% to 11%) in cohort 1 and 3% (95% CI, < 1% to 11%) in cohort 2. Median duration of response was not reached (range, 1.9 to ≥ 21.8 months) and 10.6 months (range, 4.4 to 16.8 months), respectively. Disease control rate was 10% in cohort 1, 9% in cohort 2, and 22% in cohort 3. Median OS was 9.5 months in cohort 1, 7.9 months in cohort 2, and 14.1 months in cohort 3. Treatment-related adverse events occurred in 60% of patients, were of grade 3 to 5 severity in 15%, and led to discontinuation of treatment in 5%.

CONCLUSION

Pembrolizumab monotherapy shows antitumor activity with an acceptable safety profile in a subset of patients with RECIST-measurable and bone-predominant mCRPC previously treated with docetaxel and targeted endocrine therapy. Observed responses seem to be durable, and OS estimates are encouraging.

Increasing incidence and survival of corpus uteri cancer in Estonia over the past two decades

BACKGROUND

Corpus uteri cancer has become the fourth most common female cancer in Europe. In Estonia, the prevalence of obesity is increasing, and corpus uteri cancer survival has been relatively low. The aim of the study was to evaluate incidence, mortality and survival trends of corpus uteri cancer in Estonia by age, stage and histological subtypes with an emphasis on surgical treatment.

METHODS

Estonian Cancer Registry data on incident cases of corpus uteri cancer were used to examine incidence trends (1995-2016) and calculate relative survival ratios (RSR) (1996-2016). Cases were classified by morphology and FIGO stage. Causes of Death Registry data were used to analyse corrected mortality (1995-2017).

RESULTS

A total of 4281 cases were diagnosed in 1996-2016. A significant increase was seen in age-standardized incidence from 2009, while mortality remained stable throughout the study period. Significant increases were observed for type I cancers and age groups ≥65 years. Overall age-standardized 5-year RSR improved from 70% in 1996-2002 to 78% in 2010-2016. Survival increased for type I cancers, all age groups and all stages (significantly for stage IV). The proportion of surgically treated cases increased significantly from 85% to 89%, with the largest increases seen in older age groups and later stages.

DISCUSSION

The rising corpus uteri cancer incidence in Estonia is driven by the type I cancer trend. Survival gain for later stages and older age groups likely reflected more frequent surgical treatment. To reduce mortality, further efforts are necessary to ensure appropriate care for all patients.

Trends in cervical cancer incidence and survival in Estonia from 1995 to 2014

Background

Cervical cancer (CC) incidence in Estonia is the third highest in Europe, even though an organised nation-wide screening program has been in place since 2006.

The aim of the study was to analyse the incidence and survival of CC in Estonia, focusing on age, morphology and stage at diagnosis.

Methods

Data from Estonian Cancer Registry were used to analyse age-standardized (world) and age-specific incidence for 1968–2014 rates. Joinpoint regression was used to estimate the annual percentage change (APC) for incidence trends. Age-period-cohort model was used to summarise time trends in terms of cohort and period effects. Relative survival ratios (RSR) were calculated for cases diagnosed in 1995–2014. Union for International Cancer Control version 7 of the TNM classification for malignant tumours was used to categorise stage.

Results

The age-standardized incidence of CC increased since 1980s at a rate of 0.8% per year. A significant increase was seen for all age groups except for 70+. The incidence of squamous cell carcinoma mimicked the overall trend, while adenocarcinoma showed increase since mid-1990s (APC 6.7). Age-period-cohort modelling showed strong cohort effects with the lowest risk for birth-cohorts born around 1940 and significantly increasing risks for successive cohorts born thereafter. No period effects were seen.

The proportion of stage IV cases increased from 13% in 2005–2009 to 18% in 2010–2014. A significant increase was seen in the overall 5-year RSR from 1995 to 1999 to 2010–2014 (58% vs 66%). In 2010–2014, the 5-year RSRs ranged from 89% in women aged 15–39 to 41% in age group 70+. For stages I to IV, the respective RSRs were 98, 74, 57 and 22%.

Conclusions

The inadequate uptake and insufficient quality of the Pap-smear based screening program has not brought along a decline in the incidence of CC in Estonia. Stage distribution has shifted towards later stages. New approaches are needed to prevent CC in Estonia.

Time Trends in Ovarian Cancer Survival in Estonia by Age and Stage

OBJECTIVE

The objective of the study was to examine temporal trends in ovarian cancer (OC) survival in Estonia during 1995 to 2009 in relation to age and stage.

MATERIALS AND METHODS

Estonian Cancer Registry data on all adult cases of primary OC diagnosed during 1995 to 2009 and followed up for vital status until 2014 were used to estimate relative survival ratios (RSRs). Cohort analysis was used to estimate 1-, 2-, and 5-year RSRs for patients diagnosed in 1995 to 1999, 2000 to 2004, and 2005 to 2009. Analysis was performed by age at diagnosis (<50; 50-59; 60-69; 70+ years) and stage (International Federation of Gynecology and Obstetrics 1988).

RESULTS

Among 2296 women included in the study, the age-adjusted 5-year RSR improved from 27% in 1995 to 1999 to 38% in 2005 to 2009. Survival increase of 10% units from 1995 to 1999 to 2005 to 2009 was seen for women aged 50 to 59 and 60 to 69 years. Among younger and older women, the respective changes were smaller. In 1995 to 1999, the difference in survival between the youngest and oldest age groups was 41% units. This decreased over the study period to 37% units. From 1995 to 1999 to 2005 to 2009, the 5-year RSR increased from 82% to 91% for stage I patients; from 48% to 67% for stage II patients; from 25% to 35% for stage III patients; and from 11% to 16% for stage IV patients.

CONCLUSIONS

The study showed an improvement of OC survival in Estonia in all age and stage groups, but particularly among younger women and those with early stage disease. Slower progress among older women is of great concern.

P1: CHOLINERGIC RECEPTOR FUNCTION IN CARDIAC ISCHEMIC PRECONDITIONING

Purpose of Study

Cardiac acetylcholine (ACh) signaling is protective, but the role of ACh in ischemic preconditioning (IPC) remains largely unknown. We studied the effect of selective alpha-7 nicotinic ACh receptor (a7nAChR) antagonism by methyllycaconitine (MLA) on the functional benefits of IPC and the effects of this on mitochondrial complexity and inner mitochondrial membrane potential (ψM).

Methods Used

Male Sprague Dawley rats (n=17, 322±17 g) were heparinized and anesthetized with 80 mg/kg pentobarbital IP, and their hearts excised and perfused at constant pressure with a non-circulating Langendorff apparatus. Left ventricular (LV) pressure (LVDP) and heart rate (HR) were continually measured with a fluid filled latex balloon attached to a pressure transducer. Treatment groups were: ischemia-reperfusion (IR)(n=6): 20 min. perfusion, 30 min. of global ischemia, 45 min. of reperfusion; IPC (n=5): 10 min. perfusion, 3 min. ischemia with 2 min. reperfusion repeated 3 times prior to IR protocol, IPC+MLA (n=6): 6 min. perfusion, 4 min. of infusion of MLA at 233 nM, IPC with MLA during reperfusion periods, then IR. Mitochondria were isolated from the LV free wall, stained for ψM and for size, and examined by Flow Cytometry with a BD LSRFortessa. Controls (C) (n=4) were freshly excised hearts from similar animals with identical anesthesia.

Summary of Results

IPC increased LV work product (LVDP times HR) as a percent of pre-ischemia (%P) during reperfusion compared to IR control, and this effect was attenuated by MLA pretreatment (IR=24.1±4.5%P, IPC=49.8±2.8%P, IPC+MLA=33.8±3.5%P, p<0.01). IPC reduced end diastolic pressure from IR levels, and this was partially prevented by MLA treatment (IR=78.8±7.7 mm Hg, IPC=18.8±6.6 mm Hg, IPC+MLA=46.3±8.6 mm Hg, p<0.05). IPC maintained mitochondrial structural complexity compared to IR (C=65±6% of total mitochondria, IPC=61±5%, IR=32±4%, p<0.01). MLA reduced the effect of IPC on ψM in intact mitochondria to IR levels (IR=67±10% of intact population, IPC=88±3%, IPC+MLA=71±4%, p<0.01).

Conclusions

Signaling through the a7nAChR is necessary for the effect of IPC on maintaining ψM and cardiac contractile function after IR injury.

Differential regulation of SR calcium transporters by thyroid hormone in rat atria and ventricles

Thyroid hormone exerts positive inotropic effects on the heart mediated in part by its regulation of calcium transporter proteins, including sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2), phospholamban (PLB), and Na(+)/Ca(2+) exchanger (NCX). To further understand the potential cardiac chamber-specific effects of thyroid hormone action, we compared the triiodo-L-thyronine (T(3)) responsiveness of calcium transporter proteins in atrial versus ventricular tissues. Rats were rendered hypothyroid by ingestion of propylthiouracil, and a subgroup of animals was treated with T(3) for 7 days (7 microg/day by constant infusion). Atrial and left ventricular (LV) tissue homogenates were analyzed for expression of SERCA2, PLB, and NCX proteins by Western blot analysis. SERCA2 protein significantly decreased by 50% in hypothyroid LV and was normalized by T(3) treatment. In contrast, SERCA2 protein in atria was unaltered in the hypothyroid state. PLB protein expression significantly increased by 1.6- and 5-fold in the hypothyroid LV and atria, respectively, and returned to euthyroid levels with T(3) treatment. Expression of NCX protein showed a greater response to T(3) treatment in atria tissue than in ventricular tissue. Sarcoplasmic reticulum calcium cycling is determined in part by the ratio of SERCA2 to PLB. This ratio was sixfold higher in the atria compared with LV, suggesting that PLB may play a minor role in the regulation of SERCA2 function in normal atria. We conclude that calcium transporter proteins are responsive to thyroid hormone in a chamber-specific manner, with atria showing a greater change in protein content in response to T(3). The differential effect on atria may account for the occurrence of atrial rather than ventricular arrhythmias in response to even mild degrees of thyrotoxicosis.

Thyroid hormone increases pacemaker activity in rat neonatal atrial myocytes

The effects of thyroid hormone (3,3',5-triiodo- L -thyronine, T3) on pacemaker activity were studied with electrophysiological and pharmacological approaches using spontaneously beating neonatal atrial myocytes cultured from 2-day-old rats. Treatment with T3 (10(-8)m) for 24-48 h led to a positive chronotropic effect. The beating rate of T3-treated cells was 244+/-19 beats/min and for control cells it was 122+/-10 beats/min (P<0.05). Action potentials were recorded and showed that the predominant effect of T3 was to increase the diastolic depolarization rate (99.5+/-9.8 in T3-treated group v 44.0+/-7.8 mV/s in untreated group). Some cells that exhibited pacemaker activity lacked a pacemaker current (I(f)) under voltage clamp conditions I(f)was recorded in 5 of 12 spontaneously active control cells and in 6 of 10 T3-treated cells. In those cells exhibiting the pacemaker current, the I(f)density was significantly larger in T3-treated cells (-7.9+/-2.6 pA/pF v-1.8+/-0.5 pA/pF in control). The L-type Ca2+ current density was similar in the two groups (at -7 mV, -7.5+/-1.5 in treated group v-8.6+/-1.0 pA/pF in control). In the presence of T3, the Na+-Ca2+ exchanger current (I(Na/Ca)) density was larger (e.g. at +60 mV, it was 4.8+/-0.5 v 3.5+/-0.2 pA/pF in control cells, P<0.05). As intracellular Ca2+ is extruded from the cell, the electrogenic Na+-Ca2+ exchanger causes a declining inward current, which may contribute to the pacemaker potential-this declining inward current was demonstrated using the action potential voltage clamp technique and was shown to be larger in T3-treated myocytes. Our data demonstrate that thyroid hormone enhances pacemaker activity and that this may be due in part to an increased Na+-Ca2+ exchanger activity.

Thyroid hormone metabolism and cardiac gene expression after acute myocardial infarction in the rat

In a rat model of acute myocardial infarction (MI) produced by coronary artery ligation, thyroid hormone metabolism was altered with significant reductions (54%) in serum triiodo-L-thyronine (T(3)), the cellular active hormone metabolite. T(3) has profound effects on the heart; therefore, rats were treated with T(3) after acute MI for 2 or 3 wk, at either replacement or elevated doses, to determine whether cardiac function and gene expression could be normalized. Acute MI resulted in a 50% (P < 0.001) decrease in percent ejection fraction (%EF) with a 32-35% increase (P < 0.01) in compensatory left ventricle (LV) hypertrophy. Treatment of the MI animals with either replacement or elevated doses of T(3) significantly increased %EF to 64 and 73% of control, respectively. Expression levels of several T(3)-responsive genes were altered in the hypertrophied LV after MI, including significant decreases in alpha-myosin heavy chain (MHC), sarcoplasmic reticulum calcium-activated ATPase (SERCA2), and Kv1.5 mRNA, whereas beta-MHC and phospholamban (PLB) mRNA were significantly increased. Normalization of serum T(3) did not restore expression of all T(3)-regulated genes, indicating altered T(3) responsiveness in the postinfarcted myocardium. Although beta-MHC and Kv1.5 mRNA content was returned to control levels, alpha-MHC and SERCA2 were unresponsive to T(3) at replacement doses, and only at higher doses of T(3) was alpha-MHC mRNA returned to control values. The present study showed that acute MI in the rat was associated with a fall in serum T(3) levels, LV dysfunction, and altered expression of T(3)-responsive genes and that T(3) treatment significantly improved cardiac function, with normalization of some, but not all, of the changes in gene expression.

Thyroid hormone stimulates Na, K-ATPase gene expression in the hemodynamically unloaded heterotopically transplanted rat heart

Regulation of myocardial Na, K-ATPase gene expression by thyroid hormone was investigated in the heterotopically transplanted rat heart to distinguish the direct effects of the hormone on the heart from effects secondary to increased hemodynamic workload. In this model, the transplanted heart is histologically normal and spontaneously beating, but hemodynamically unloaded. Three days after transplantation, relative contents of ventricular Na, K-ATPase alpha2- and beta1-mRNAs and alpha1- and alpha2-proteins were increased twofold to threefold in the transplanted heart, but these changes were transient. We next determined the maximal triiodothyronine (T3)-induced changes that are observed in various parameters of Na, K-ATPase expression in the heart: treatment of nontransplanted euthyroid rats with T3 to reach hyperthyroid steady state resulted in significant increases in heart weight, RNA and RNA/protein ratio, Na, K-ATPase activity, Na, K-ATPase alpha2-protein and enzyme activity, and approximately threefold increase in both alpha2- and beta1-mRNA content. The effect of treatment with thyroxine (T4) on the heterotopically transplanted and the in situ heart was then examined. T4 treatment (of the host) resulted in a significant increase in Na, K-ATPase alpha1-, alpha2-, and beta1-mRNAs in transplanted hearts (1.6 +/- 0.1-, 2.4 +/- 0.2-, and 1.7 +/- 0.1-fold, respectively), that was associated with a 2.2 +/- 0.2-fold increase in alpha2 protein as compared to transplanted hearts in diluent-treated euthyroid hosts (p < 0.05 for all changes). In addition, T4-induced increments in transplanted hearts were similar to those observed in the corresponding in situ hearts of host rats treated with T4. We conclude that the increase in Na, K-ATPase expression by thyroid hormone largely occurs independently of increased cardiac work elicited by the hormone and reflects a direct action of the hormone on Na, K-ATPase gene expression.

Thyroid hormone regulation of phospholamban phosphorylation in the rat heart

Thyroid hormone exerts predictable effects on the contractile performance of the heart in part by regulating the transcription of genes encoding specific calcium transporter proteins. In a rat model of hypothyroidism, left ventricular (LV) contractile function as measured by ejection fraction was decreased by 22% (P < 0.05), and this was returned to control values with T3 treatment. In confirmation of prior studies, LV phospholamban (PLB) protein content was significantly decreased by 25% and 40% compared with hypothyroid LV when the animals were treated with T3 at two doses, 2.5 and 7.0 microg/day, respectively. The ratio of sarcoplasmic reticulum calcium adenosine triphosphatase (SERCA2) to PLB protein content was thus increased by 171% and 207%, respectively (P < 0.01). Resolution of the phosphorylated PLB pentamers by SDS-PAGE showed that T3 infusion at 2.5 and 7.0 microg/day decreased (P < 0.001) the amount nonphosphorylated pentamers by 82% and 95%, respectively, in a dose-dependent manner. T3 treatment produced an increase in the proportion of highly phosphorylated PLB pentamers (more than five phosphates) when expressed as a fraction of total pentameric molecules (P < 0.05). Site-specific antibodies showed that the T3-induced increase in phosphorylated PLB pentamers was the result of an increase in both serine 16 and threonine 17 phosphorylation. We conclude that thyroid hormone, in addition to regulating the expression of cardiac PLB, is able to alter the degree of PLB phosphorylation, which correlates with enhancement of LV contractile function. These studies suggest that T3 may augment myocyte calcium cycling via changes in both cAMP- and calcium/calmodulin-dependent protein kinase activities.

Changes in adenylyl cyclase isoforms as a mechanism for thyroid hormone modulation of cardiac beta-adrenergic receptor responsiveness

Although thyroid hormones are known to modulate cardiac beta-adrenergic receptor expression, the physiologic implications of these changes in the cardiac manifestations of altered thyroid hormone metabolism have been disputed. This study examined whether thyroid hormone modulates signaling via the cyclic adenosine monophosphate (cAMP) pathway by regulating cardiac adenylyl cyclase (AC) isoform expression. Northern blot analyses and AC enzyme assays were performed on preparations from hypothyroid, euthyroid, and hyperthyroid rat ventricles. Steady-state levels of cardiac AC mRNA types V and VI in hypothyroid ventricles were 173% +/- 8% and 149% +/- 12%, respectively, of the values in euthyroid ventricles (P < .01). This increase in AC mRNA isoforms was accompanied by a 1.5-fold increase (P < .05) in the activation of catalytic AC by forskolin and Mn. In contrast, the relative abundance of transcripts for types V and VI AC was similar in hyperthyroid and euthyroid ventricles, but catalytic AC activation by forskolin and Mn was significantly reduced by 35% in membranes obtained from hyperthyroid ventricles. AC activation through beta-adrenergic receptor stimulation by isoproterenol was not altered by thyroid hormone status. Thus, the effect of thyroid hormone to repress AC catalytic activity would be anticipated to offset the increase in beta-adrenergic receptor expression in hyperthyroidism. These studies identify cardiac AC enzymes as important targets for thyroid hormone-dependent regulation of signaling via the cAMP pathway, and support the finding that cardiac adrenergic responsiveness is unaltered in thyroid disease states.

Effects of thyroid hormone on action potential and repolarizing currents in rat ventricular myocytes

Thyroid hormones play an important role in cardiac electrophysiology through both genomic and nongenomic mechanisms of action. The effects of triiodothyronine (T(3)) on the electrophysiological properties of ventricular myocytes isolated from euthyroid and hypothyroid rats were studied using whole cell patch clamp techniques. Hypothyroid ventricular myocytes showed significantly prolonged action potential duration (APD(90)) compared with euthyroid myocytes, APD(90) of 151 +/- 5 vs. 51 +/- 8 ms, respectively. Treatment of hypothyroid ventricular myocytes with T(3) (0.1 microM) for 5 min significantly shortened APD by 24% to 115 +/- 10 ms. T(3) similarly shortened APD in euthyroid ventricular myocytes, but only in the presence of 4-aminopyridine (4-AP), an inhibitor of the transient outward current (I(to)), which prolonged the APD by threefold. Transient outward current (I(to)) was not affected by the acute application of T(3) to either euthyroid or hypothyroid myocytes; however, I(to) density was significantly reduced in hypothyroid compared with euthyroid ventricular myocytes.

Usefulness of triiodothyronine (T3) treatment after surgery for complex congenital heart disease in infants and children

This is a study of the use of T3 infusion in the postoperative period in 6 pediatric patients who underwent complex cardiac surgical procedures under cardiopulmonary bypass. Normalization of serum T3 levels was reflected in a marked decrease in requirement of inotropic support, conversion to normal sinus rhythm, and progressively improving clinical course.

Regulation of rat cardiac Kv1.5 gene expression by thyroid hormone is rapid and chamber specific

Thyroid hormone affects the contractile and electrophysiological properties of the cardiac myocyte that result in part from changes in the expression of thyroid hormone-responsive cardiac genes, including those that regulate membrane ion currents. To determine the molecular mechanisms underlying this effect, expression of a voltage-gated K+ channel, Kv1.5, was measured in response to thyroid hormone. Using quantitative RT-PCR methodology, the content of Kv1.5 messenger RNA (mRNA) in left ventricles of euthyroid rats was 4.25+/-0.6x10(-20) mol/microg total RNA and was decreased by 70% in the hypothyroid rat ventricle to 1.27+/-0.80x10(-20) mol/microg RNA (P<0.01). Administration of T3 to hypothyroid animals restored ventricular Kv1.5 mRNA to control levels within 1 h of treatment, making this the most rapid T3-responsive cardiac gene reported to date. The half-life of Kv1.5 mRNA was 1.9 h and 2.0 h in euthyroid and hypothyroid ventricles, respectively, and T3 treatment of the rats did not alter its half-life. In atrial myocardium, expression of Kv1.5 mRNA (6.10+/-0.37x10(-20) mol/microg RNA) was unaltered by thyroid hormone status. The myocyte-specific and chamber-selective expression of Kv1.5 mRNA was confirmed in primary cultures of rat atrial and ventricular myocytes.

Regulation of Na/K-ATPase gene expression by thyroid hormone and hyperkalemia in the heart

Hypothermic hyperkalemic circulatory arrest has been widely used for myocardial protection during heart surgery. Recent data showed that administration of triiodo-L-thyronine (T3) postoperatively enhanced ventricular function. The effect of hyperkalemic arrest in conjunction with thyroid hormone on the plasma membrane enzyme sodium/potassium-adenosine triphosphatase (Na/K-ATPase), was determined in cultured neonatal rat atrial and ventricular myocytes. Exposure of ventricular myocytes to hyperkalemic medium (50 mM KCl) in the absence of T3 increased expression of the Na/K-ATPase catalytic subunit mRNAs, alpha1 and alpha3 isoforms, by 1.9- and 1.5-fold, respectively (p<0.01), which were accompanied by similar increases (1.4- and 1.8-fold) in protein content. Addition of T3 to the hyperkalemic cultures attenuated these increases in Na/K-ATPase mRNA isoforms to levels of expression observed in cells treated with T3 (10(-8) M) alone. Similarly, expression of the alpha1 mRNA isoform in atrial myocytes was increased (p<0.05) by hyperkalemic conditions, and T3 treatment attenuated this effect. In contrast, although expression of the Na/K-ATPase beta1 mRNA in both atrial and ventricular myocytes was significantly increased by hyperkalemia, addition of T3 did not prevent the hyperkalemic response, and in atrial myocytes T3 significantly increased beta1 mRNA expression 1.8-fold. These results show that expression of cardiac Na/K-ATPase is regulated by T3 and hyperkalemia in an isoform and chamber specific manner, and suggest that use of hyperkalemic cardioplegia during heart surgery may alter plasma membrane ion function.

Thyrotoxicosis and the heart

This review examines the molecular mechanisms by which thyroid hormone affects the cardiovascular system in naturally occurring thyroid disease states. The potential utility of thyroid hormone therapy in the management of patients with various forms of cardiovascular disease is also discussed.

Regulation of cardiac alpha-myosin heavy chain gene transcription by a contractile-responsive E-box binding protein

The hemodynamic workload imposed on the heart modulates the expression of the cardiac-specific alpha-myosin heavy chain (MHC) gene. A hemodynamic responsive element (HME) has been mapped to an E box motif (CACGTG) located at position -47 of the promoter. The present studies showed that the HME is sufficient to confer contractile responsiveness to a heterologous promoter, the simian virus thymidine kinase gene, when expressed in cultured neonatal rat ventricular myocytes. Proximity of the HME to the TATA box of the alpha-MHC promoter appear necessary for high levels of basal transcription and for the four-fold induction in response to the contractile stimulus. An HME binding protein, approximately 43 kDa, was isolated from a neonatal rat ventricular myocyte cDNA library with sequence homology to the human upstream stimulatory factor-1 (hUSF1). Electrophoretic mobility shift assay showed that the in vitro translation product of the rat USF1 cDNA bound to the alpha-MHC HME motif and was recognized by an antibody to hUSF1. Overexpression of recombinant rat USF1 in spontaneously contracting cultured cardiomyocytes significantly increased activity of a cotransfected alpha-MHC promoter/luciferase reporter plasmid containing the HME motif plus core promoter elements (-40/+32), suggesting a role of rat USF1 in the contractile-mediated activation of the gene.

Alterations in cardiac contractility and gene expression during low-T3 syndrome: prevention with T3

The low-T3 syndrome is a metabolic response resulting in a decreased serum triiodothyronine (T3) concentration that has uncertain effects on thyroid hormone-responsive gene expression and function. We measured cardiac myocyte gene expression and cardiac contractility in young adult female rats using chronic calorie deprivation as a model of the low-T3 syndrome. Sarcoplasmic reticulum calcium adenosinetriphosphatase (SERCA2) and myosin heavy chain (MHC) isoform mRNA content were measured after 28 days on a 50% calorie-restricted diet (low T3) with or without T3 treatment (6 micrograms.kg body wt-1.day-1). The low-T3 animals had decreased maximal rates of contraction (-13%; P < 0.05) and relaxation (-18%; P < 0.05) compared with the control and the T3-treated groups. There was a 21% (P < 0.05) increase in left ventricular (LV) relaxation time in the low-T3 animals vs. both control and T3-treated groups. The LV content of the SERCA2 mRNA was decreased significantly (37%) in the low-T3 rats and was increased (P < 0.05) with T3 treatment vs. controls. The alpha-MHC mRNA isoform decreased in the low-T3 animals but was unchanged in the T3-treated animals. T3 supplementation normalized both cardiac function and phenotype of calorie-restricted animals, suggesting a role for the low-T3 syndrome in the pathophysiological response to calorie restriction.

The direct vasomotor effect of thyroid hormones on rat skeletal muscle resistance arteries

The present study examines the hypothesis that the hormones have direct vasodilatory effects and attempts to determine whether the effects are endothelium-dependent. Rat skeletal muscle resistance arteries of approximately 100 microns were dissected, and vessel diameter changes were monitored using a videodetection system. After equilibration at 37 degrees C, each vessel was preconstricted with the thromboxane analog U46619 1 microM, and the percentage of dilation was measured after exposure to increasing concentrations of triiodothyronine (T3) or levothyroxine (T4) (10(-10) to 10(-7) M). Dilation in response to T3 was also measured after endothelial denudation and pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) 10 microM, the cyclooxygenase inhibitor indomethacin 10 microM, the adenosine triphosphate-sensitive K+ channel blocker glibenclamide 1 microM, or the beta-adrenergic antagonist propranolol 1 microM. Both T3 and T4 demonstrated concentration-dependent dilation of the U46619-preconstricted vessels (P < 0.001 each), with T3 having a greater effect than T4 (P < 0.05) (36% +/- 9% [mean +/- SD] dilation at 10(-7) M T3 vs 24% +/- 6% dilation at 10(-7) M T4). In comparison, isoproterenol 10(-7) M produced 56% +/- 6% dilation. T3-mediated vasodilation was attenuated but not abolished by endothelial denudation (18% +/- 3% dilation at 10(-7) M T3) (P < 0.01), L-NNA (15% +/- 7% dilation at 10(-7) M T3) (P < 0.01), indomethacin (20% +/- 9% dilation at 10(-7) M T3) (P < 0.05), and glibenclamide (22% +/- 7% dilation at 10(-7) M T3) (P < 0.01), but it was not affected by propranolol (37% +/- 20% dilation at 10(-7) M T3) (P = 0.99). We conclude that thyroid hormones possess direct vasodilatory effects with both endothelium-independent and endothelium-dependent components.

IMPLICATIONS

Thyroid hormones may have modest direct vasodilatory effects. This may partially account for the cardiovascular actions of the hormones in hyperthyroidism or when administered pharmacologically in cardiac surgery.

Myosin heavy chain gene expression in neonatal rat heart cells: effects of [Ca2+]i and contractile activity

To determine if mechanical signals or alterations in intracellular Ca2+ concentration ([Ca2+]i) affect myosin heavy chain (MHC) gene expression in spontaneously beating, neonatal rat ventricular myocytes, contractile activity was inhibited with verapamil, KCl, or 2,3-butanedione monoxime (BDM), and their acute and chronic effects on myocyte shortening, [Ca2+]i, and MHC gene expression were examined. Despite their differing effects on [Ca2+]i, verapamil, KCl, and BDM all inhibited contractile activity and markedly downregulated beta-MHC mRNA levels to 24 +/- 5, 21 +/- 7, and 6 +/- 2% of contracting cells, respectively. In contrast, these inhibitors of contraction upregulated alpha-MHC mRNA levels to 163 +/- 19, 156 +/- 7, and 198 +/- 20% of contracting cells, respectively. Transient transfection with a rat beta-MHC promoter-luciferase expression plasmid demonstrated that all inhibitors of contraction significantly decreased beta-MHC promoter activity. Paradoxically, contractile arrest also inhibited alpha-MHC promoter activity, suggesting that increased alpha-MHC mRNA levels resulted from posttranscriptional mechanisms. Actinomycin D mRNA stability assays indicated that alpha-MHC mRNA half-life was prolonged in noncontracting cells (33 h) compared with contracting myocytes (14 h). Contraction-dependent alterations in MHC gene expression were not dependent on release of angiotensin II or other growth factors into the culture medium. Thus intrinsic mechanical signals rather than alterations in [Ca2+]i regulate alpha-MHC and beta-MHC gene expression by both transcriptional and posttranscriptional mechanisms.

Long-term gene transfer in porcine myocardium after coronary infusion of an adeno-associated virus vector

BACKGROUND

Viral vector-mediated gene transfer into the heart represents a potentially powerful tool for studying both cardiac physiology as well as gene therapy of cardiac disease. We report here the use of a defective viral vector, which expresses no viral gene products, for gene transfer into the mammalian heart. Previous studies have used recombinant viral vectors, which retained viral genes and yielded mostly short-term expression, often with significant inflammation.

METHODS

An adeno-associated virus vector was used that contains no viral genes and is completely free of contaminating helper viruses. The adeno-associated virus vector was applied to rat hearts by direct intramuscular injection; adeno-associated virus was also infused into pig hearts in vivo via percutaneous intraarterial infusion into the coronary vasculature using routine catheterization techniques.

RESULTS

Gene transfer into rat heart yielded no apparent inflammation, and expression was observed for at least 2 months after injection. Infusion into pig circumflex coronary arteries resulted in successful transfer and expression of the reporter gene in cardiac myocytes without apparent toxicity or inflammation; gene expression was observed for at least 6 months after infusion.

CONCLUSIONS

We report the use of adeno-associated virus vectors in the cardiovascular system as well as successful myocardial gene transfer after percutaneous coronary artery infusion of viral vectors in a large, clinically relevant mammalian model. These results suggest that safe and stable gene transfer can be achieved in the heart using standard outpatient cardiac catheterization techniques.

Acute effects of thyroid hormone on vascular smooth muscle

The enhanced cardiovascular hemodynamics associated with triiodo-L-thyronine (T3) treatment is in part mediated by a decrease in systemic vascular resistance. To determine the molecular mechanisms for the vasoactive properties of T3, we studied primary cultures of aortic endothelial and vascular smooth muscle (VSM) cells. Active tension development by the VSM cells was measured by deformation lines within a siloxane matrix on which the cells were grown. Exposure to T3 (10(-10) M) resulted in cellular relaxation within 10 min. Hormone binding studies to purified VSM cell plasma membranes identified two binding sites specific for T3 with Kd of 1 x 10(-11) and 6.1 x 10(-8) M. L-Thyroxine and reverse T3 did not compete for the L-T3 binding sites. To determine an intracellular signaling pathway of T3 action, cAMP and cGMP content were measured in VSM cell cultures treated with T3. No quantitative changes were observed in a time frame known to cause VSM cell relaxation. The level of myosin light chain phosphorylation is a major determinant of smooth muscle contraction. Thus, treatment of VSM cells with isoproterenol, a vasodilator, caused a significant decrease in radiolabeled phosphate incorporation into the myosin light chains, whereas T3 had no effect on phosphorylation of these proteins. Primary cultures of vascular endothelial cells exposed to T3 showed no nitric oxide production as measured by cellular cGMP content and nitrite release, suggesting that T3 acted directly on the VSM cell to cause vascular relaxation.

Triiodothyronine therapy lowers the incidence of atrial fibrillation after cardiac operations

BACKGROUND

Cardiopulmonary bypass results in a euthyroid sick state, and recent evidence suggests that perioperative triiodothyronine (T3) supplementation may have hemodynamic benefits. In light of the known effects of thyroid hormone on atrial electrophysiology, we investigated the effects of perioperative T3 supplementation on the incidence of postoperative arrhythmias.

METHODS

One hundred forty-two patients with depressed left ventricular function (ejection fraction < 0.40) undergoing coronary artery bypass grafting were randomized to either T3 or placebo treatment groups in a prospective, double-blind fashion. Triiodothyronine was administered as a 0.8 micrograms/kg intravenous bolus at the time of aortic cross-clamp removal followed by an infusion of 0.113 micrograms.kg-1.h-1 for 6 hours. Patients were monitored for the development of arrhythmias during the first 5 postoperative days.

RESULTS

The incidence of sinus tachycardia and ventricular arrhythmias were similar between groups. Triiodothyronine-treated patients had a lower incidence of atrial fibrillation (24% versus 46%; p = 0.009), and fewer required cardioversion (0 versus 6; p = 0.012) or anticoagulation (2 versus 10; p = 0.013) during hospitalization. Six patients in the T3 group versus 16 in the placebo group required antiarrhythmic therapy at discharge (p = 0.019).

CONCLUSIONS

Perioperative T3 administration decreased the incidence and need for treatment of postoperative atrial fibrillation.

Thyroid hormone and hemodynamic regulation of beta-myosin heavy chain promoter in the heart

Thyroid hormone exerts marked effects on cardiovascular function. Expression of cardiac alpha- and beta-myosin heavy chain (MHC) isoforms can be altered in response to thyroid hormone as well as by hemodynamic changes imposed on the heart. The molecular mechanisms that mediate these changes are not completely known. We studied the contractile and thyroid hormone responsiveness of the betaMHC promoter in both cultured cardiac myocytes and in vivo by direct DNA transfer. Using transient transfection of neonatal rat cardiomyocytes, the activities of recombinant reporter plasmids containing betaMHC 5'-flanking sequences terminating at positions -2250, -1145, -670, and -354 were decreased significantly in cultures containing L-T3 (50 nM). Similar deletion analysis showed that 5'-flanking regions terminating within -2250 to -151 bp were contractility responsive; however, deletion to position -126 attenuated this response. In vivo betaMHC promoter activity, determined by injecting the recombinant plasmid into the myocardium, was significantly higher by 2-fold in hyperthyroid than in euthyroid ventricles (2.47 +/- 0.41 vs. 1.33 +/- 0.25 luciferase/ chloramphenicol acetyltransferase; P<0.05). Increased ventricular workload, produced by aortic coarctation for 5 days, resulted in ventricular hypertrophy (heart/body weight, 4.05 +/- 0.19 vs. 3.42 +/- 0.16 mg/g; P < 0.02) and a 3.4-fold increase in betaMHC messenger RNA content. However, betaMHC promoter activity in vivo was not significantly different between rats experiencing aortic coarctation and sham-operated rats (1.49 +/- 0.41 vs. 0.96 +/- 0.27 luciferase chloramphenicol acetyltransferase, respectively) and was similar to that in euthyroid animals. These results show that betaMHC promoter activity is T3 responsive in cultured myocytes and in vivo, but that the increase in betaMHC messenger RNA observed in the in vivo pressure overloaded myocardium cannot be explained entirely by transcription control mechanisms.

Thyroid hormone therapy in cardiovascular disease

The relationship between thyroid disease states and cardiovascular hemodynamics is well recognized. Although the long-term effects of thyroid hormone are thought to result from changes in myocardial gene expression, attention has recently focused on acute, non-nuclear-mediated actions of L-triidothyronine (T3), the biologically active form of the hormone. Various lines of evidence have documented that T3 can act as a vasodilator and inotrope. With this recognition have come novel treatment strategies targeted at specific clinical conditions including heart failure and cardiac surgery that are associated with impaired cardiovascular performance and low serum T3 levels. An understanding of the mechanisms of action of thyroid hormone on the heart and peripheral vasculature is essential for the rational implementation of thyroid hormone as a therapeutic agent. As outlined in this review, initial clinical experience suggests that the ability of thyroid hormone to increase cardiac output and to lower systemic vascular resistance may provide a novel treatment option for physicians caring for patients with cardiovascular illness.

Identification of a contractile-responsive element in the cardiac alpha-myosin heavy chain gene

The mechanisms by which the cardiac-specific alpha-myosin heavy chain (alpha-MHC) gene responds to contractile activity was studied in cultured cardiomyocytes and in vivo. Deletion analysis of the alpha-MHC promoter transiently transfected into neonatal rat cardiomyocytes localized the contractile-responsive element within -80 to -40 base pairs of the transcriptional start site. Mutational analysis of an E-box motif at position -47 showed that it was necessary for the contractile response both in cultured cardiomyocytes and in the intact heart. Competition gel mobility shift experiments indicated that the protein-DNA complex formed within the -39 to -59 base pair region could be competed by the E-box element at -309 of the alpha-MHC gene and that base substitutions within an E-box motif at -47 eliminated the protein-DNA complex. To identify the contractile-responsive nuclear protein, antibodies specific for E12/E47, an E-box binding basic-helix-loop-helix (bHLH) protein, and antibodies recognizing upstream stimulatory factor (USF), a widely expressed bHLH-leucine zipper transcription factor, were studied for their ability to inhibit cardiomyocyte nuclear protein binding to the E-box motif at -47. Anti-USF antibody abolished formation of the protein-DNA complex, thus identifying the protein as antigenically related to USF and demonstrating that bHLH-leucine zipper proteins are involved in the contractile-induced expression of the cardiac alpha-MHC gene.

Thyroid hormone treatment after coronary-artery bypass surgery

BACKGROUND

Thyroid hormone has many effects on the cardiovascular system. During and after cardiopulmonary bypass, serum triiodothyronine concentrations decline transiently, which may contribute to postoperative hemodynamic dysfunction. We investigated whether the perioperative administration of triiodothyronine (liothyronine sodium) enhances cardiovascular performance in high-risk patients undergoing coronary-artery bypass surgery.

METHODS

We administered triiodothyronine or placebo to 142 patients with coronary artery disease and depressed left ventricular function. The hormone was administered as an intravenous bolus of 0.8 microgram per kilogram of body weight when the aortic cross-clamp was removed after the completion of bypass surgery and then as an infusion of 0.113 microgram per kilogram per hour for six hours. Clinical and hemodynamic responses were serially recorded, as was any need for inotropic or vasodilator drugs.

RESULTS

The patients' preoperative serum triiodothyronine concentrations were normal (mean [+/- SD] value, 81 +/- 22 ng per deciliter [1.2 +/- 0.3 nmol per liter]), and they decreased by 40 percent (P < 0.001) 30 minutes after the onset of cardiopulmonary bypass. The concentrations in patients given intravenous triiodothyronine became supranormal and were significantly higher than those in patients given placebo (P < 0.001). However, the concentrations were once again similar in the two groups 24 hours after surgery. The mean postoperative cardiac index was higher in the triiodothyronine group (2.97 +/- 0.72 vs. 2.67 +/- 0.61 liters per minute per square meter of body-surface area, P = 0.007), and systemic vascular resistance was lower (1073 +/- 314 vs. 1235 +/- 387 dyn.sec.cm-5, P = 0.003). The two groups did not differ significantly in the incidence of arrhythmia or the need for therapy with inotropic and vasodilator drugs during the 24 hours after surgery, or in perioperative mortality and morbidity.

CONCLUSIONS

Raising serum triiodothyronine concentrations in patients undergoing coronary-artery bypass surgery increases cardiac output and lowers systemic vascular resistance, but does not change outcome or alter the need for standard postoperative therapy.

Triiodothyronine improves left ventricular function without oxygen wasting effects after global hypothermic ischemia

Cardiopulmonary bypass results in a "euthyroid sick" state. Recently, interest has focused on the relationship between low serum triiodothyronine levels and postoperative cardiovascular hemodynamics. The present study was undertaken to more clearly define the acute effects of triiodothyronine on myocardial mechanics and energetics after hypothermic global ischemia using an ex-vivo canine heart preparation to model the clinical condition. Experiments were performed on isolated hearts subjected to hyperkalemic arrest with 90 minutes of hypothermic (10 degrees C) ischemia. Isolated hearts were cross-perfused by euthyroid support dogs in which triiodothyronine levels spontaneously decreased by 65% to 75% (p < 0.01) after the initiation of cross-perfusion. In nine heart preparations, triiodothyronine (Triostat) was given as a bolus dose (0.2 micrograms/kg) after 1 hour of baseline data collection with a subsequent measurable rise in serum triiodothyronine levels (p < 0.01). In six postischemic hearts, reverse triiodothyronine was given as a 0.2 micrograms/kg bolus. Triiodothyronine was also administered to a group of eight nonischemic, continuously perfused isolated hearts. Intrinsic myocardial contractility was assessed by analysis of the preload recruitable stroke work area, energetic efficiency from the myocardial oxygen consumption-pressure-volume area relationship, and coronary vascular resistance from analysis of coronary flow and perfusion pressure. Acute administration of triiodothyronine to postischemic hearts improved the preload recruitable stroke work area from 9.5 +/- 1.42 to 14.9 +/- 2.03 x 10(7) erg/ml, a 56% increase from baseline (p < 0.001), but had no effect on the preload recruitable stroke work area of the nonischemic hearts. The inotropic response resulting from triiodothyronine treatment did not alter the myocardial oxygen consumption-pressure-volume area relationship. Triiodothyronine treatment was associated with significantly decreased coronary resistance and increased coronary flow through a range of diastolic loading conditions in the postischemic hearts. The biologically inactive thyroid hormone metabolite reverse triiodothyronine was without effect on any of the measured parameters. On the basis of these results, we conclude that the low triiodothyronine state of cardiopulmonary bypass can be reproduced in this isolated heart model and that acute triiodothyronine treatment results in a unique inotropic action manifest only in the postischemic reperfused myocardium and is accomplished without oxygen wasting effects.

Effects of adrenergic agonists on the growth and gene expression of the transplanted heart

Cardiac growth occurs in response to changes in hemodynamic demand and results primarily from cellular hypertrophy without cellular hyperplasia. In addition to changes in cardiac work, various reports have demonstrated that adrenergic stimulation, specifically of the alpha 1 adrenergic receptor of cultured myocytes, can produce changes in cardiac-specific gene expression and increases in protein synthesis and cell growth. To study the effects of adrenergic stimulation in the absence of alterations in cardiac work we have used the model of the heterotopically transplanted heart, which is a spontaneously beating, vascularly perfused, and histologically normal heart that is hemodynamically unloaded. Seventy-two hours after transplantation, the hemodynamically unloaded transplanted heart had decreased in size by 20% when compared with the control host heart that was growing in situ. Treatment with either the alpha-adrenergic agonist phenylephrine (2.5 mg/kg/day) or the beta-adrenergic agonist isoproterenol (250 micrograms/kg/day) while increasing the spontaneous heart rate had no effect on the size of the transplanted heart. Simultaneous measurements demonstrated that both of these drugs produced a 10% increase in weight of the corresponding hemodynamically loaded host heart. We previously demonstrated that cardiac unloading caused a change in the expression of the myosin heavy chain (MHC) genes with a significant increase in the beta MHC isoform. In the present studies treatment with either isoproterenol or phenylephrine did not alter MHC gene expression either in the in situ host or transplanted hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of rat ventricular myosin heavy chain expression by serum and contractile activity

To quantitatively analyze the effects of serum stimulation and contractile activity and their interaction on cellular growth and cardiac myosin heavy chain (MHC) gene expression, spontaneously contracting neonatal rat ventricular myocytes in primary culture were maintained in serum-free growth medium or growth medium supplemented with fetal bovine serum. Contractile activity in paired cultures was inhibited by addition of the calcium channel blocker verapamil (10 microM) to the culture medium. Both serum stimulation and contractile activity produced myocyte hypertrophy as assessed by increases in total protein, total RNA, protein-to-DNA ratios, and total MHC protein content. MHC isoenzyme analysis indicated that both MHC-alpha and MHC-beta proteins accumulated in response to serum stimulation and/or contractile activity. The increases in MHC-beta protein resulting from serum stimulation and contractile activity occurred in parallel with increases in MHC-beta mRNA. In contrast, MHC-alpha mRNA levels were relatively unaffected by serum stimulation but appeared to decrease in response to contractile activity. The protein kinase inhibitor staurosporine (5 nM) reduced MHC-beta expression in serum-free, contracting cultures and also prevented the serum-induced increase in MHC-beta mRNA observed in both contracting and arrested myocytes. Staurosporine also increased MHC-alpha mRNA levels in serum-free, contracting, and verapamil-arrested myocytes. These data suggest that both humoral and mechanical factors regulate MHC isoenzyme expression and cellular growth in neonatal ventricular myocytes.

Posttranscriptional modification of myosin heavy-chain gene expression in the hypertrophied rat myocardium

Hypertrophy of the myocardium in response to pressure or volume overload elicits a change in myofibrillar protein content as a result of changes in both transcriptional and translational regulation of gene expression. Hemodynamic overload caused by aortic constriction produced changes in the expression of the two isoforms of myosin heavy chain (MHC) with a 319% increase in beta-MHC mRNA and a 54% decrease in alpha-MHC mRNA (P < 0.01). Cardiac unloading as a result of heterotopic transplantation resulted in a decrease in cardiac mass and a similar shift in MHC isoform expression. In this study. We investigated cardiac gene transcription to understand how different hemodynamic stimuli produce similar cardiac phenotypes. We studied the in vivo activity of the alpha-MHC promoter (-2564 to +421 bp of the transcriptional start site) by directly injecting a recombinant expression plasmid (pAM3LUC) into the ventricular tissue of coarctated animals as well as into the unloaded heterotopic transplanted heart. When expressed as a function of the activity of a constitutively active viral promoter (pSVCAT), pAM3LUC activities were 18.4 +/- 2.9, 24.6 +/- 2.6, and 25.0 +/- 4.5 (x10(4)) luciferase/chloramphenicol acetyltransferase units in the hypertrophied ventricles of 2-, 3-, and 7-day coarctated animals, respectively. These values were not statistically different from pAM3LUC activity in control hearts of sham operated animals even though alpha-MHC mRNA content was decreased by 54% in the hypertrophied myocardium. This disparity between transcriptional activity and mRNA content suggests that alpha-MHC expression in the hypertrophic ventricle is in part regulated by a posttranscriptional mechanism. In contrast, alpha-MHC promoter activity in the unloaded transplanted hearts decreased significantly by 37% compared to control working hearts and suggests that a transcriptional mechanism of regulation of the alpha-MHC gene may account for the phenotypic expression observed in the unloaded myocardium.

Acute effects of triiodothyronine on arterial smooth muscle cells

Thyroid hormone has profound effects on the heart and cardiovascular system. Systemic vascular resistance is uniformly decreased in both naturally occurring and experimental hyperthyroidism, and it is increased in thyroid hormone deficiency. Because vascular smooth muscle cell contraction is a major determinant of systemic vascular resistance, the present studies were designed to address the acute effects of the thyroid hormones, specifically triiodothyronine, on vascular smooth muscle cell contractile activity. Our data indicate that triiodothyronine causes smooth muscle relaxation; this property may account for some of its marked effects on the cardiovascular system. As a novel vasodilatory agent, the potential therapeutic implications for triiodothyronine may be numerous.

In vivo regulation of recombinant cardiac myosin heavy chain gene expression by thyroid hormone

Cardiac myocytes have the unique ability to express exogenous genes that have been injected directly into the heart tissue in vivo. This technique makes it possible to identify cis-acting DNA sequences responsible for the regulation of myocyte-specific genes in a working heart. In these studies we introduced recombinant plasmids containing 5'-flanking sequences of the alpha-myosin heavy chain (alpha MHC) gene into the rat myocardium in order to identify sufficient promoter/enhancer sequences that faithfully reproduced the activity of the endogenous gene. The transcriptional activity of the alpha MHC promoter sequence was measured by the level of activity of the firefly luciferase reporter gene and was reported as the activity relative to a coinjected constitutively active viral promoter construct (pRSVCAT) which corrected for variations in DNA uptake and posttranscriptional events. We report that a recombinant plasmid containing 5'-flanking sequences -2560 to +421 basepairs of the transcriptional start site of the alpha MHC gene was appropriately inactive in the hypothyroid rat heart, in which expression of the endogenous gene was also inhibited. The activity of this promoter sequence was increased 44-fold by thyroid hormone in the hearts of thyroidectomized rats. In contrast, although this recombinant plasmid was appropriately active in the euthyroid myocardium, its activity could not be further stimulated by thyroid hormone. The observation that regulation of the transcriptional activity of the alpha MHC promoter by thyroid hormone was different in euthyroid and hypothyroid hearts suggests that the participation of nuclear regulatory factors, including the thyroid hormone/retinoid family of receptors, may differ according to thyroid status.

Thyroid hormone effects on cardiac gene expression independent of cardiac growth and protein synthesis

Prior studies have demonstrated the importance of hemodynamic loading in mediating thyroxine (T4)-induced cardiac hypertrophy. Direct cellular effects of thyroid hormone have been implicated in modulating the expression of the myosin heavy chain (MHC) genes and the slow sarcoplasmic reticulum calcium adenosine triphosphatase (SR Ca(2+)-ATPase) gene. In the present report, administration of T4 for 72 h did not stimulate growth of the hemodynamically unloaded heterotopic isograft. The synthetic rates of total cardiac proteins and MHC in the isograft remained significantly lower at 64 and 53% of the respective rates measured simultaneously in the in situ working heart. Although total left ventricle RNA content in the isograft was unchanged by T4, alpha-MHC and SR Ca(2+)-ATPase mRNA concentrations were increased 181 and 208%, respectively, and the previously observed beta-MHC expression was completely prevented. These data indicate that, although T4 requires an increased hemodynamic load to stimulate cardiac protein synthesis, it is capable of directly altering the expression of at least two myocyte-specific genes. Therefore some of the phenotypic alterations observed with thyroid hormone treatment are the result of direct effects of the hormones on specific cardiac genes and independent of changes in cardiac growth.