Low THRB (thyroid hormone receptor beta) Promoter Methylation Levels in Peripheral Blood Leukocytes Induced By Systematic Inflammation Are Involved in Low Thyroid Hormone Function in Metabolic Syndrome

[Figure: see text].

Triiodothyronine maintains cardiac transverse-tubule structure and function

Subclinical hypothyroidism and low T3 syndrome are commonly associated with an increased risk of cardiovascular disease (CVD) and mortality. We examined effects of T3 on T-tubule (TT) structures, Ca²⁺ mobilization and contractility, and clustering of dyadic proteins. Thyroid hormone (TH) deficiency was induced in adult female rats by propyl-thiouracil (PTU; 0.025%) treatment for 8 weeks. Rats were then randomized to continued PTU or triiodo-L-thyronine (T3; 10 μg/kg/d) treatment for 2 weeks (PTU + T3). After in vivo echocardiographic and hemodynamic recordings, cardiomyocytes (CM) were isolated to record Ca²⁺ transients and contractility. TT organization was assessed by confocal microscopy, and STORM images were captured to measure ryanodine receptor (RyR2) cluster number and size, and L-type Ca²⁺ channel (LTCC, Ca_v1.2) co-localization. Expressed genes including two integral TT proteins, junctophilin-2 (Jph-2) and bridging integrator-1 (BIN1), were analyzed in left ventricular (LV) tissues and cultured CM using qPCR and RNA sequencing. The T3 dosage used normalized serum T3, and reversed adverse effects of TH deficiency on in vivo measures of cardiac function. Recordings of isolated CM indicated that T3 increased rates of Ca²⁺ release and re-uptake, resulting in increased velocities of sarcomere shortening and re-lengthening. TT periodicity was significantly decreased, with reduced transverse tubules but increased longitudinal tubules in TH-deficient CMs and LV tissue, and these structures were normalized by T3 treatment. Analysis of STORM data of PTU myocytes showed decreased RyR2 cluster numbers and RyR localizations within each cluster without significant changes in Ca_v1.2 localizations within RyR clusters. T3 treatment normalized RyR2 cluster size and number. qPCR and RNAseq analyses of LV and cultured CM showed that Jph2 expression was T3-responsive, and its increase with treatment may explain improved TT organization and RyR-LTCC coupling.

Ignoring a basic pathophysiological mechanism of heart failure progression will not make it go away

A link between heart failure (HF) and low thyroid hormone (TH) function has been known for over a century. Nonetheless, there is a general belief that TH treatment of patients with HF may not be worth the risk. This is largely based on two clinical trials where heart patients were treated with excessive doses of TH analogs, not actual THs. Further complicating the matter is the fact that normalization of THs in noncardiac patients can often be challenging. This issue is not going away as noted by a steady increase in TH-HF citations in recent years. In this article, we discuss what we know and how we may move the field forward.

Chronic dantrolene treatment attenuates cardiac dysfunction and reduces atrial fibrillation inducibility in a rat myocardial infarction heart failure model

Background

Cardiac ryanodine receptor 2 (RyR2) dysfunction and elevated diastolic Ca²⁺ leak have been linked to arrhythmogenesis not only in inherited arrhythmia syndromes but also in acquired forms of heart disease including heart failure (HF) and atrial fibrillation (AF). Thus, stabilizing RyR2 may exert therapeutic effects in these conditions.

Objective

The purpose of this study was to investigate the effects of stabilizing RyR2 with chronic dantrolene treatment on HF development and AF inducibility in a myocardial infarction (MI)-induced HF model in rats.

Methods

MI was induced in adult Sprague-Dawley rats by ligation of the left anterior descending coronary artery. Two weeks after MI surgery, rats with large MI (≥40%) were randomly assigned to MI-vehicle (n = 14) or MI-dantrolene (10 mg/kg/d; n = 13) groups. Sham-surgery rats (n = 7) served as controls.

Results

Compared to the MI-vehicle group, 4-week dantrolene treatment significantly improved cardiac function, with increased left ventricular (LV) fractional shortening (19.48% ± 3.61% vs 15.43% ± 2.65%; P <.01), and decreased LV end-diastolic pressure (12.58 ± 8.52 mm Hg vs 21.91 ± 7.25 mm Hg; P <.01), left atrial diameter (4.97 ± 0.75 mm vs 6.09 ± 1.53 mm; P <.05), and fibrosis content (6.42% ± 0.78% vs 9.76% ± 2.25%; P <.001). Dantrolene significantly decreased AF inducibility (69% in MI-vehicle vs 23% in MI-dantrolene; P <.05). Dantrolene treatment was associated with reduced RyR2 phosphorylation and favorably altered gene expression involving ion channels, sympathetic signaling, oxidative stress, and inflammatory markers.

Conclusion

Chronic dantrolene treatment attenuated LV dysfunction and reduced AF inducibility, which was associated with decreased RyR2 phosphorylation and normalization of many adverse changes in gene expression. Thus, stabilizing RyR2 with chronic dantrolene treatment is a promising novel strategy for decreasing AF in HF.

Chronic Dantrolene Treatment Does Not Affect Hypertension, but Attenuates Sympathetic Stimulation Enhanced Atrial Fibrillation Inducibility in SHR

BACKGROUND

Ryanodine receptor (RyR) dysfunction in skeletal muscle (RyR1) leads to malignant hyperthermia, and in cardiac muscle (RyR2) triggers cardiac arrhythmias. We hypothesized that RyR dysfunction in vascular smooth muscle could increase vascular resistance and hypertension, and may contribute to increased atrial fibrillation (AF) in hypertension. Thus, stabilizing RyR function with chronic dantrolene treatment may attenuate hypertension and AF inducibility in spontaneously hypertensive rats (SHR).

METHODS

Male SHR (16 weeks old) were randomized into vehicle- (n = 10) and dantrolene-treated (10 mg/kg/day, n = 10) groups for 4 weeks. Wistar Kyoto (WKY, n = 11) rats served as controls. Blood pressures (BP) were monitored before and during the 4-week treatment. After 4-week treatment, direct BP, echocardiography, and hemodynamics were recorded. AF inducibility tests were performed in vivo at baseline and repeated under sympathetic stimulation (SS).

RESULTS

Compared with WKY, SHR had significantly higher BP throughout the experimental period. Dantrolene treatment had no effect on BP levels in SHR (final systolic BP 212 ± 9 mm Hg in vehicle group vs. 208 ± 16 mm Hg in dantrolene group, P > 0.05). AF inducibility was very low and not significantly different between 5-month-old WKY and SHR at baseline. However, under SS, AF inducibility and duration were significantly increased in SHR (20% in WKY vs. 60% in SHR-vehicle, P<0.05). Dantrolene treatment significantly attenuated AF inducibility under SS in SHR (60% in vehicle vs. 20% in dantrolene, P < 0.05).

CONCLUSIONS

Stabilizing RyR with chronic dantrolene treatment does not affect hypertension development in SHR. SHR has increased vulnerability to AF induction under SS, which can be attenuated with dantrolene treatment.

Triiodothyronine Reduces Vascular Dysfunction Associated with Hypertension by Attenuating Protein Kinase G/Vasodilator-Stimulated Phosphoprotein Signaling

Vascular dysfunction associated with hypertension comprises hypercontractility and impaired vasodilation. We have previously demonstrated that triiodothyronine (T3), the active form of thyroid hormone, has vasodilatory effects acting through rapid onset mechanisms. In the present study, we examined whether T3 mitigates vascular dysfunction associated with hypertension. To test the direct effects of T3 in hypertensive vessels, aortas from female Dahl salt-sensitive (Dahl SS) rats fed a high-salt diet (8% NaCl, HS group) and their age-matched controls fed a standard low-salt diet (0.3% NaCl, LS group) for 16 weeks were isolated and used in ex vivo vascular reactivity studies. We confirmed that the HS group exhibited a higher systolic blood pressure in comparison with the control LS group and displayed aortic remodeling. Aortas from both groups were pretreated with T3 (0.1 μM) for 30 minutes at 37°C in a 5% CO₂ incubator before functional vascular studies. T3 treatment significantly attenuated hypercontractility and improved impaired endothelium-dependent vasodilation in aortas from the HS group. These vascular improvements in response to T3 were accompanied by increased phosphorylation of vasodilator-stimulated phosphoprotein (VASP) at serine 239, a vasodilatory factor of the cGMP-dependent protein kinase (PKG)/VASP signaling pathway in vascular smooth muscle cells. Moreover, increased production of reactive oxygen species in aortas from the HS group were significantly reduced by T3, suggesting a potential antioxidant effect of T3 in the vasculature. These results demonstrate that T3 can mitigate hypertension-related vascular dysfunction through the VASP signaling pathway and by reducing vascular ROS production. SIGNIFICANCE STATEMENT: This study demonstrates that triiodothyronine (T3) directly acts on vascular tone and has a beneficial effect in hypertension-induced vascular dysfunction. T3 augmented vasodilation and diminished vasoconstriction in blood vessels from hypertensive rats in association with activation of the protein kinase G/vasodilator-stimulated phosphoprotein signaling pathway that activates vascular relaxation and exerted an antioxidant effect. Collectively, these results show that T3 is a potential vasoprotective agent with rapid action on hypertension-related vascular dysfunction.

Western diet triggers Toll-like receptor 4 signaling-induced endothelial dysfunction in female Wistar rats

Overconsumption of a diet rich in fat and carbohydrates, called the Western diet, is a major contributor to the global epidemic of cardiovascular disease. Despite previously documented cardiovascular protection exhibited in female rats, this safeguard may be lost under certain metabolic stressors. We hypothesized that female Wistar rats challenged by a Western diet composed of 21% fat and 50% carbohydrate (34.1% sucrose) for 17 wk would develop endothelial dysfunction via endothelial Toll-like receptor 4 (TLR4) signaling. Western diet-fed female rats exhibited dysregulation of metabolism, revealing increased body weight and abdominal fat, decreased expression of adiponectin in white adipose tissue, glucose intolerance, and impaired insulin sensitivity. Western diet exposure increased hepatic triglycerides and cholesterol alongside hepatic steatosis, categorizing nonalcoholic fatty liver disease. Moreover, a Western diet negatively affected vascular function, revealing hypertension, impaired endothelium-dependent vasorelaxation, aortic remodeling, and increased reactive oxygen species (ROS) production. Aortic protein expression of TLR4 and its downstream proteins were markedly increased in the Western diet-fed group in association with elevated serum levels of free fatty acids. In vitro experiments were conducted to test whether free fatty acids contribute to vascular ROS overproduction via the TLR4 signaling pathway. Cultured endothelial cells were stimulated with palmitate in the presence of TAK-242, a TLR4 signaling inhibitor. Palmitate-induced overgeneration of ROS in endothelial cells was abolished in the presence of TAK-242. Our data show that a Western diet induced endothelial dysfunction in female rats and suggest that endothelial TLR4 signaling may play a key role in abolishing female cardiovascular protection. NEW & NOTEWORTHY A Western diet induced elevated levels of free fatty acids, produced nonalcoholic fatty liver disease, and provoked endothelial dysfunction in female rats in association with Toll-like receptor 4 signaling-mediated vascular reactive oxygen species production. Limited consumption of a Western diet in premenopausal women may decrease their risk of cardiovascular complications.

Failing Hearts Are More Vulnerable to Sympathetic, but Not Vagal Stimulation-Induced, Atrial Fibrillation-Ameliorated with Dantrolene Treatment

BACKGROUND

Both vagal (VS) and sympathetic (SS) stimulations can increase atrial fibrillation (AF) inducibility, with VS being known as more arrhythmogenic in normal hearts. Heart failure (HF) results in autonomic dysfunction (characterized by sympathetic activation and vagal withdrawal) and is associated with an increased AF incidence. This study investigated whether failing hearts, compared with normal control hearts, respond differently to autonomic stimulation-induced AF arrhythmogenesis and the effect of dantrolene on SS-enhanced AF in HF.

METHODS AND RESULTS

A rat myocardial infarction (MI) HF model was used. In experiment 1, AF inducibility was compared in 9 MI-HF rats versus 10 sham-control animals at baseline, during VS, and during SS with isoproterenol infusion. In experiment 2, dantrolene treatment (n = 8) was compared with placebo-control (n = 9) on SS-induced AF inducibility in HF. Compared with the sham-control, baseline AF inducibility was higher in the MI-HF group. AF inducibility was augmented in both groups by autonomic stimulation. However, under VS the increased magnitude was less in the MI-HF group (49% ± 11% vs 80% ± 10%; P = .029), but under SS was significantly more (53% ± 8% vs 6% ± 7%; P < .001), compared with sham-control. Dantrolene significantly attenuated SS-enhanced AF in HF (69% ± 6% vs 29% ± 9%; P = .006).

CONCLUSIONS

Failing hearts are less sensitive to VS, but more vulnerable to SS-induced AF compared with normal-control hearts. Dantrolene can significantly attenuate SS-enhanced AF in HF, indicating that cardiac ryanodine receptor dysfunction may play a critical role in SS-enhanced AF in HF, and stabilizing leaky ryanodine receptor with the use of dantrolene may be a new treatment option in this condition.

Comparison of Therapeutic Triiodothyronine Versus Metoprolol in the Treatment of Myocardial Infarction in Rats

BACKGROUND

Beta blockers are standard therapy for myocardial infarction (MI). Preclinical studies have shown efficacy and safety of thyroid hormone (TH) treatment of cardiovascular disorders. Since THs interact with the sympathoadrenergic system, this study aimed to compare triiodothyronine (T3) and metoprolol (Met) in the treatment of rats with MI on pathophysiology and TH-adrenergic signaling.

METHODS

Female Sprague-Dawley rats aged 12 weeks underwent left anterior descending coronary artery ligation (MI) or sham surgeries. T3 (5 μg/kg/day) or Met (100 mg/kg/day) was given in drinking water immediately after surgery for eight weeks. At the terminal of the experiments, the rats were subjected to morphological, functional, and molecular examination.

RESULTS

T3 and Met significantly enhanced left ventricular contractility (left ventricular fractional shortening 21.37 ± 2.58% and 21.14 ± 3.71%, respectively) compared to untreated MI (17.88 ± 1.23%), and decreased the incidence of inducible atrial tachyarrhythmia by 87.5% and 62.5%, respectively. Although both treatments showed efficacy, T3 but not Met showed statistically significant improvements compared to MI in arrhythmia duration, left atrial diameter (T3 vs. MI 4.33 ± 0.63 vs. 5.65 ± 1.32 mm; p < 0.05), fibrosis (6.1 ± 0.6%, 6.6 ± 0.6% vs. 8.2 ± 0.7%, T3, Met vs. MI, respectively), and aortic vasorelaxation responsiveness to acetylcholine (pD2 6.97 ± 0.22, 6.83 ± 0.21 vs. 6.66 ± 0.22, T3, Met vs. MI, respectively). Quantitative polymerase chain reaction showed that T3 and Met attenuated expression of genes associated with inflammation and oxidative stress and restored expression of ion channels and contractile proteins.

CONCLUSION

These results support comparable efficacy of T3 and Met treatments, suggesting that T3 may provide a therapeutic alternative to standard β-receptor blockade, especially for patients intolerant to treatment with β-blockers after MI.

Long-term prognostic value of combined free triiodothyronine and late gadolinium enhancement in nonischemic dilated cardiomyopathy

BACKGROUND

Thyroid dysfunction and myocardial fibrosis are both associated with cardiovascular events in patients with dilated cardiomyopathy (DCM).

HYPOTHESIS

The combination of thyroid hormone (TH) and myocardial fibrosis (detected by late gadolinium enhancement [LGE]) is an independent and incremental predictor of adverse events in DCM.

METHODS

We consecutively enrolled 220 idiopathic DCM patients with thyroid function and LGE assessment at Fuwai Hospital (China) from January 2010 to October 2011 and followed up through December 2015. Patients were divided into 4 groups according to the presence or absence of LGE and FT3 value (median level of 2.79 pg/mL): LGE-positive + FT3 < 2.79 pg/mL, LGE-positive + FT3 ≥ 2.79 pg/mL, LGE-negative + FT3 < 2.79 pg/mL, and LGE-negative + FT3 ≥ 2.79 pg/mL.

RESULTS

During a median follow-up of 61 months, 56 patients (25.5%) died, with 27/56 (48.2%), 8/45 (17.8%), 12/54 (22.2%), and 9/65 (13.8%) among 4 groups (P = 0.009), respectively. Multivariable Cox regression analysis identified LGE-positive and FT3 < 2.79 pg/mL as a significant independent predictor of all-cause mortality (hazard ratio: 2.893, 95% confidence interval: 1.323-6.326, P = 0.008). Combining the predictive value of FT3 and LGE status significantly improved risk reclassification for all-cause mortality, as indicated by the net reclassification improvement (0.28; P = 0.005) and integrated discrimination improvement (0.058; P = 0.001).

CONCLUSIONS

The findings suggest that the combination of FT3 and LGE yielded a more accurate predictive value for long-term prognosis in patients with DCM, which may improve patient selection for intensive interventions.

Ellagic Acid Reduces High Glucose-Induced Vascular Oxidative Stress Through ERK1/2/NOX4 Signaling Pathway

BACKGROUND/AIMS

Elevated production of reactive oxygen species (ROS) is linked to endothelial dysfunction and is one of the key contributors to the pathogenesis of diabetic vascular complications. Emerging evidence has indicated that ellagic acid (EA), a polyphenol found in fruits and nuts, possesses numerous biological activities including radical scavenging. However, whether EA exerts a vasculo-protective effect via antioxidant mechanisms in blood vessels exposed to diabetic conditions remains unknown. Accordingly, the goal of this current study was to determine whether EA decreases vascular ROS production and thus ameliorates endothelial dysfunction in the diabetic milieu.

METHODS

Intact rat aortas and human aortic endothelial cells (HAEC) were stimulated with 30mM high glucose (HG) with and without EA co-treatment. Endothelium-dependent vasodilation was measured using a wire myograph. Gene and protein expression of non-phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidases 4 (NOX4) were detected using RT-PCR and western blotting, respectively. Oxidative stress was determined by measuring ROS levels using dihydroethidium (DHE) staining.

RESULTS

Intact aortas exposed to HG condition displayed exacerbated ROS production and impairment of endothelium-dependent vasodilation, characterizing endothelial dysfunction. These effects were markedly reduced with EA treatment. HG enhanced ROS production in HAEC, paralleled by increased ERK1/2 activation and NOX4 expression. EA treatment blunted the increase of ROS generation, ERK1/2 activation and decreased NOX4.

CONCLUSIONS

EA significantly decreases endothelial ROS levels and ameliorates the impairment of vascular relaxation induced by HG. Our results suggest that EA exerts a vasculo-protective effect under diabetic conditions via an antioxidant effect that involves inhibition of ERK1/2 and downregulation of NOX4.

Overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelial cells accelerates coronary artery disease in a mouse model of familial hypercholesterolemia

OBJECTIVE

Overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelium leads to arterial calcification in mice. The purpose of this study was to examine the effect of elevated endothelial TNAP on coronary atherosclerosis. In addition, we aimed to examine endogenous TNAP activity in human myocardium.

APPROACH AND RESULTS

A vascular pattern of TNAP activity was observed in human non-failing, ischemic, and idiopathic dilated hearts (5 per group); no differences were noted between groups in this study. Endothelial overexpression of TNAP was achieved in mice harboring a homozygous recessive mutation in the low density lipoprotein receptor (whc allele) utilizing a Tie2-cre recombinase (WHC-eTNAP mice). WHC-eTNAP developed significant coronary artery calcification at baseline compared WHC controls (4312 vs 0μm2 alizarin red area, p<0.001). Eight weeks after induction of atherosclerosis, lipid deposition in the coronary arteries of WHC-eTNAP was increased compared to WHC controls (121633 vs 9330μm2 oil red O area, p<0.05). Coronary lesions in WHC-eTNAP mice exhibited intimal thickening, calcifications, foam cells, and necrotic cores. This was accompanied by the reduction in body weight and left ventricular ejection fraction (19.5 vs. 23.6g, p<0.01; 35% vs. 47%, p<0.05). In a placebo-controlled experiment under atherogenic conditions, pharmacological inhibition of TNAP in WHC-eTNAP mice by a specific inhibitor SBI-425 (30mg*kg-1*d-1, for 5 weeks) reduced coronary calcium (78838 vs.144622μm2) and lipids (30754 vs. 77317μm2); improved body weight (22.4 vs.18.8g) and ejection fraction (59 vs. 47%). The effects of SBI-425 were significant in the direct comparisons with placebo but disappeared after TNAP-negative placebo-treated group was included in the models as healthy controls.

CONCLUSIONS

Endogenous TNAP activity is present in human cardiac tissues. TNAP overexpression in vascular endothelium in mice leads to an unusual course of coronary atherosclerosis, in which calcification precedes lipid deposition. The prevalence and significance of this mechanism in human atherosclerosis requires further investigations.

Abstract P247: Triiodothyronine Ameliorates Endothelial Dysfunction in Rats Following Acute Myocardial Infarction

Background: Low thyroid hormone (TH) function is recognized as a significant contributor in the pathogenesis after acute myocardial infarction (MI). Endothelial dysfunction contributes significantly to the poor prognosis of MI. We hypothesize that long-term treatment with low dose T3 improves endothelial function and cardiac contractile activity compared to beta blocker, the current recommended therapy for MI.

Methods: Adult female Sprague-Dawley rats were subjected to left anterior descending coronary artery ligation (MI) or sham surgeries. Survivors were randomly assigned to vehicle (MI, n=11), T3 (MI+T3, n=11) and metoprolol (MI+Meto, n=11). Vehicle, T3 (5 ug/kg/day) and metoprolol (2 mg/kg/day) were supplied in drinking water ad libitum immediately following MI for 2 months. Heart function and LV hemodynamics were measured. Isolated thoracic aortic rings were used to test relaxation response to acetylcholine (ACh) in a wire myograph. The maximal effect elicited by ACh (E max ) and the sensitivity to ACh (pEC 50 ) were analyzed. One-way ANOVA with Bonferroni correction was used for multiple comparisons.

Results: Serum concentration of free and total T3 were normal in all the experimental groups. T3 and metoprolol improved LV contractile function measured by fractional shortening (21.88±2.06 vs 17.88±1.23%, p<0.01, T3 vs MI; 21.12±3.88 vs 17.88±1.23%, p<0.05, Meto vs MI; 46.86±1.84% for sham) and LV +d p /d t (7307±1128 vs 5479±810 mmHg/s, p<0.01, T3 vs MI; 7022±695 vs 5479±810 mmHg/s, p<0.05; Meto vs MI; 9160±1881 mmHg/s for sham). Aortas from vehicle-treated group exhibited a marked impairment of endothelial-dependent relaxation measured by pEC 50 (6.65±0.22 vs 7.19±0.16, p<0.001, MI vs Sham), which was significantly improved in the T3 treated group (6.96±0.22 vs. 6.65±0.22, p<0.01, T3 vs MI) but not in metoprolol group (6.85±0.21 versus 6.65±0.22, p=0.22, Meto vs MI). T3 and metoprolol increased maximal relaxation measured by E max (90.56±3.55 vs 79.50±3.98%, p<0.001, T3 vs MI; 89.81±6.75% vs 79.50±3.98%, P<0.001, Meto vs MI; 96.93±1.91% for sham).

Conclusion: Long-term treatment with a physiological dose of T3 following MI is equally effective as metoprolol on LV function while improving endothelial function as an additional benefit.

Abstract P205: Short-term Western Diet Induced Hypertension in Female Rats is Associated With Vascular Epigenetic Modification

Over consumption of the western diet (WD) is a major contributor to the global epidemic of metabolic syndrome. Studies on the impact of WD on vascular complications related to hypertension have revealed contradictory results. Moreover, reports on the effect of WD on female cohorts is limited. Results from our lab have indicated that transient diabetic conditions increase vascular lysine acetylation levels, a post-translational epigenetic modification. Therefore, we hypothesized that short-term exposure to WD causes vascular endothelial dysfunction and hypertension in association with increased vascular lysine acetylation. Adult female Wistar rats were assigned either a control diet (13.4% fat, 56% carbohydrate, and 29.8% protein; n=4) or a WD (41% fat, 43% carbohydrates, and 17% protein; n=6) for 17 weeks. Results showed the WD group exhibited increased body weight (376 ± 49 vs 305 ± 41g, p<0.05), periabdominal fat content (30 ±11 vs 11 ±2g, p<0.01), % body fat (8.1 ±1.0 vs 3.6 ±0.4%, p<0.01), and serum triglycerides levels (56 ± 13 vs 25 ± 4mg/dl, p<0.01) compared to controls. Blood glucose and free fatty acid levels did not differ between groups. Vascular reactivity studies, using wire myography, showed WD aortas had impaired acetylcholine-induced endothelial-dependent relaxation (83.5 ±4.2 vs 93.1 ±3.0%, p<0.001). Invasive left ventricular (LV) catheterization demonstrated that the WD group had increased systolic (147 ±12 vs 120 ±6mmHg, p<0.01) and diastolic blood pressures (105 ±9 vs 87± 4mmHg, p<0.01), and rate of LV relaxation (-dP/dt: 13.5 ±1.3 vs 9.4 ±2.4mmHg/ms, p<0.01) compared to controls. Histological orcein staining and morphometric analysis showed that WD aortas displayed severe elastic fiber derangement and medial thickening (150.6 ±13.5 vs 110.5 ±20.2μm, p<0.05). Lysine acetylation levels were significantly increased in WD vascular tissue (1.5-fold increase vs control, p<0.05). Additionally, levels of KAT2B/HAT, an acetyltransferase protein, were elevated in aortas from WD (2.0-fold increase vs control, n=2). Our results support our hypothesis that endothelial dysfunction and hypertension induced by WD in female rats correlates with increased epigenetic markers in vascular tissue.

Abstract P174: Free Triiodothyronine Level Correlates with Statin Responsiveness in Acute Myocardial Infarction

Background: Although thyroid hormone (TH) has important effects on lipid metabolism, the relationship between TH and statin responsiveness has never been investigated. We hypothesized that TH plays an important role in statin responsiveness in AMI patients.

Methods: Consecutive 1091 hospitalized AMI patients in Fuwai hospital were enrolled. The study population was divided into three groups based on the intensity of statin treatment: low (n=221), moderate (n=712) and high (n=158). Lipid levels were measured after statin therapy lasting for 10-14 days. We explored the association between TH, lipid levels and achievement of low density lipoprotein cholesterol (LDL-C) lowering goals in patients with acute myocardial infarction (AMI) on statin therapy.

Results: By general linear analysis, a significant linear trend between FT3 and LDL-C level (linear coefficient=-0.082, P =0.001) and FT3 and total cholesterol (TC) level (linear coefficient=-0.105, P =0.031) was observed in the moderate-intensity statin group. A more apparent linear trend was detected in the high-intensity statin group (for LDL-C: linear coefficient=-0.113, P =0.005; for TC: linear coefficient=-0.172, P=0.029, respectively). However, no significant correlation was observed in the low-intensity statin group. Compared with the low-T3 group (defined as FT3<1.79 pg/ml), the OR (95% CI) for attaining a LDL-C<3.0mmol/L was found to be 2.217 (1.001-4.839) in the higher FT3 group (>2.95 pg/ml).The OR for attaining the more intensive goal (LDL-C<1.8mmol/L) (95% CI) was 2.836 (1.014-5.182).

Conclusions: Variation in FT3 levels is related to the lipid-lowering responsiveness of statins in AMI patients.

Abstract 456: High Fat Diet-Induced Atherosclerosis-Driven Myocardial Infarction: Role of Cardiac Long Noncoding RNAs in Triiodo-L-Thyronine-Mediated Protection

Novel mechanisms associated with therapeutically safe thyroid hormone (TH) therapy are emerging. We have shown that oral triiodo-L-thyronine (T3) offers safe cardioprotection in coronary ligation myocardial infarction (MI), ligation ischemia-reperfusion injury, diabetic cardiomyopathy, etc. via restoration of gene expression. However, safe therapeutic effects following atherosclerosis-driven MI and role of long noncoding RNAs (lncRNAs) is unknown. We employed a mouse model of scavenger receptor B1 knockout with hypomorphic apolipoprotein E. Young adult heterozygote littermates served as controls and all mice received high fat (HF) diet for one month. Along with HF diet, a cohort of homozygotes (HypoE) received therapeutic dose of T3 (5.5 μg/kg/d) in drinking water ad libitum. In HypoE mice, Paigen HF diet induced interstitial fibrotic MI with severe hypertrophic (Heart wt./Body wt., HW/BW: control:4.6±0.14; HypoE:12.9±0.75; p<0.0001) heart failure, depressed left ventricular (LV) contractility, increased end-diastolic pressure, myocyte disarray/loss, vacuolization and inflammatory cell infiltration. Aortic root showed atheromatous lipid deposits and median survival time was 26 days. Cholate-free paigen HF diet, used to achieve more gradual transition showed moderate hypertrophy (HW/BW: control:4.9±0.1; HypoE:7.9±0.95; ; p<0.01), decreased LV contractility, increasing atrial effective refractory period with a median survival of 41.5 days. Other changes include decreased serum thyroxine, increased serum cholesterol, significant splenomegaly and alterations in real-time gene expression of numerous cardiac lncRNAs and limited serum lncRNAs involved in inflammatory and immune responses (>2-fold; p<0.05). Oral T3 therapy with cholate-free diet partially restored LV contractility, atrial refractory period and cardiac lncRNAs without significantly affecting serum lncRNAs. These were accompanied by expected feedback inhibition of thyroxine without negatively impacting hypertrophy or heart rate. This is the first study to show a novel role of lncRNAs in TH-mediated cardioprotection. It also demonstrates possibility of safe preventive T3 therapy in a clinically relevant early coronary artery disease model.

Modified Low-Dose Triiodo-L-thyronine Therapy Safely Improves Function Following Myocardial Ischemia-Reperfusion Injury

Background: We have shown that thyroid hormones (THs) are cardioprotective and can be potentially used as safe therapeutic agents for diabetic cardiomyopathy and permanent infarction. However, no reliable, clinically translatable protocol exists for TH treatment of myocardial ischemia-reperfusion (IR) injury. We hypothesized that modified low-dose triiodo-L-thyronine (T3) therapy would confer safe therapeutic benefits against IR injury.

Methods: Adult female rats underwent left coronary artery ligation for 60 min or sham surgeries. At 2 months following surgery and T3 treatment (described below), the rats were subjected to functional, morphological, and molecular examination.

Results: Following surgery, the rats were treated with T3 (8 μg/kg/day) or vehicle in drinking water ad libitum following IR for 2 months. Oral T3 significantly improved left ventricular (LV) contractility, relaxation, and relaxation time constant, and decreased beta-myosin heavy chain gene expression. As it takes rats ~6 h post-surgery to begin drinking water, we then investigated whether modified T3 dosing initiated immediately upon reperfusion confers additional improvement. We injected an intraperitoneal bolus of T3 (12 μg/kg) upon reperfusion, along with low-dose oral T3 (4.5 μg/kg/day) in drinking water for 2 months. Continuous T3 therapy (bolus + low-dose oral) enhanced LV contractility compared with oral T3 alone. Relaxation parameters were also improved compared to vehicle. Importantly, these were accomplished without significant increases in hypertrophy, serum free T3 levels, or blood pressure.

Conclusions: This is the first study to provide a safe cardiac therapeutic window and optimized, clinically translatable treatment-monitoring protocol for myocardial IR using commercially available and inexpensive T3. Low-dose oral T3 therapy supplemented with bolus treatment initiated upon reperfusion is safer and more efficacious.

Triiodothyronine Potentiates Vasorelaxation via PKG/VASP Signaling in Vascular Smooth Muscle Cells

BACKGROUND/AIMS

Vascular relaxation caused by Triiodothyronine (T3) involves direct activation of endothelial cells (EC) and vascular smooth muscle cells (VSMC). Activation of protein kinase G (PKG) has risen as a novel contributor to the vasorelaxation mechanism triggered by numerous stimuli. We hypothesize that T3-induced vasorelaxation involves PKG/vasodilator-stimulated phosphoprotein (VASP) signaling pathway in VSMC.

METHODS

Human aortic endothelial cells (HAEC) and VSMC were treated with T3 for short (2 to 60 minutes) and long term (24 hours). Nitric oxide (NO) production was measured using DAF-FM. Expression of protein targets was determined using western blot. For functional studies, rat aortas were isolated and treated with T3 for 20 minutes and mounted in a wire myograph. Relaxation was measured by a concentration-dependent response to acetylcholine (ACh) and sodium nitroprusside (SNP).

RESULTS

Aortas stimulated with T3 exhibited augmented sensitivity to ACh and SNP-induced relaxation, endothelium-dependent and endothelium-independent responses, respectively. T3 directly increased vasorelaxation, which was abolished in the presence of a PKG inhibitor. T3 markedly induced phosphorylation of Akt, eNOS and consequently increased NO production in EC. Likewise, T3 induced phosphorylation of VASP at serine 239 via the PKG pathway in VSMC.

CONCLUSION

Our findings have uncovered a PKG/VASP signaling pathway in VSMC as a key molecular mechanism underlying T3-induced vascular relaxation.

Disease pattern in Danish patients with Peutz-Jeghers syndrome

PURPOSE

In this paper, we aimed to collect genetic and medical information on all Danish patients with Peutz-Jeghers syndrome (PJS), in order to contribute to the knowledge of phenotype and genotype. Peutz-Jeghers syndrome is a hereditary syndrome characterized by multiple hamartomatous polyps in the GI tract, mucocutaneous pigmentations, and an increased risk of cancer in the GI tract and at extraintestinal sites. Over 90 % of patients harbour a pathogenic mutation in STK11.

METHODS

Based on the Danish Pathology Data Bank, the Danish National Patient Register, as well as information from relevant departments at Danish hospitals, we identified patients and collected clinical and genetic information.

RESULTS

We identified 43 patients of which 14 were deceased. The prevalence was estimated to be ∼1 in 195,000 individuals. The median age at first symptom was 27.5 with invagination of the small bowel as the most frequent presenting symptom. We noted 18 occurrences of cancer at various anatomical sites, including a case of thyroid cancer and penile cancer. Eight of the deceased patients had died of cancer. Eighteen different mutations in STK11 had been detected in 28 patients.

CONCLUSION

This is the first comprehensive study of patients with Peutz-Jeghers syndrome in the Danish population identified from nationwide registers and databases. We have demonstrated that the expressivity of Peutz-Jeghers syndrome varies greatly among the patients, even within the same families, underlining the great phenotypic spectrum. Patients with PJS should be offered surveillance from childhood in order to prevent morbidity and reduce mortality.

MuRF1 mono-ubiquitinates TRα to inhibit T3-induced cardiac hypertrophy in vivo

Thyroid hormone (TH) is recognized for its role in cellular metabolism and growth and participates in homeostasis of the heart. T3 activates pro-survival pathways including Akt and mTOR. Treatment with T3 after myocardial infarction is cardioprotective and promotes elements of physiological hypertrophic response after cardiac injury. Although T3 is known to benefit the heart, very little about its regulation at the molecular level has been described to date. The ubiquitin proteasome system (UPS) regulates nuclear hormone receptors such as estrogen, progesterone, androgen, and glucocorticoid receptors by both degradatory and non-degradatory mechanisms. However, how the UPS regulates T3-mediated activity is not well understood. In this study, we aim to determine the role of the muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) in regulating T3-induced cardiomyocyte growth. An increase in MuRF1 expression inhibits T3-induced physiological cardiac hypertrophy, whereas a decrease in MuRF1 expression enhances T3's activity both in vitro and in cardiomyocytes in vivo MuRF1 interacts directly with TRα to inhibit its activity by posttranslational ubiquitination in a non-canonical manner. We then demonstrated that a nuclear localization apparatus that regulates/inhibits nuclear receptors by sequestering them within a subcompartment of the nucleus was necessary for MuRF1 to inhibit T3 activity. This work implicates a novel mechanism that enhances the beneficial T3 activity specifically within the heart, thereby offering a potential target to enhance cardiac T3 activity in an organ-specific manner.

Safe Oral Triiodo-L-Thyronine Therapy Protects from Post-Infarct Cardiac Dysfunction and Arrhythmias without Cardiovascular Adverse Effects

Background

A large body of evidence suggests that thyroid hormones (THs) are beneficial for the treatment of cardiovascular disorders. We have shown that 3 days of triiodo-L-thyronine (T3) treatment in myocardial infarction (MI) rats increased left ventricular (LV) contractility and decreased myocyte apoptosis. However, no clinically translatable protocol is established for T3 treatment of ischemic heart disease. We hypothesized that low-dose oral T3 will offer safe therapeutic benefits in MI.

Methods and Results

Adult female rats underwent left coronary artery ligation or sham surgeries. T3 (~6 μg/kg/day) was available in drinking water ad libitum immediately following MI and continuing for 2 month(s) (mo). Compared to vehicle-treated MI, the oral T3-treated MI group at 2 mo had markedly improved anesthetized Magnetic Resonance Imaging-based LV ejection fraction and volumes without significant negative changes in heart rate, serum TH levels or heart weight, indicating safe therapy. Remarkably, T3 decreased the incidence of inducible atrial tachyarrhythmias by 88% and improved remodeling. These were accompanied by restoration of gene expression involving several key pathways including thyroid, ion channels, fibrosis, sympathetic, mitochondria and autophagy.

Conclusions

Low-dose oral T3 dramatically improved post-MI cardiac performance, decreased atrial arrhythmias and cardiac remodeling, and reversed many adverse changes in gene expression with no observable negative effects. This study also provides a safe and effective treatment/monitoring protocol that should readily translate to humans.

Role of thyroid hormones in ventricular remodeling

Cardiac remodeling includes alterations in molecular, cellular, and interstitial systems contributing to changes in size, shape, and function of the heart. This may be the result of injury, alterations in hemodynamic load, neurohormonal effects, electrical abnormalities, metabolic changes, etc. Thyroid hormones (THs) serve as master regulators for diverse remodeling processes of the cardiovascular system-from the prenatal period to death. THs promote a beneficial cardiomyocyte shape and improve contractility, relaxation, and survival via reversal of molecular remodeling. THs reduce fibrosis by decreasing interstitial collagen and reduce the incidence and duration of arrhythmias via remodeling ion channel expression and function. THs restore metabolic function and also improve blood flow both by direct effects on the vessel architecture and decreasing atherosclerosis. Optimal levels of THs both in the circulation and in cardiac tissues are critical for normal homeostasis. This review highlights TH-based remodeling and clinically translatable strategies for diverse cardiovascular disorders.

Long-term physiological T3 supplementation in hypertensive heart disease in rats

Animal studies suggest that hypertension leads to cardiac tissue hypothyroidism, a condition that can by itself lead to heart failure. We have previously shown that short-term thyroid hormone treatment in Spontaneously Hypertensive Heart Failure (SHHF) rats near heart failure is beneficial. This study tested the hypothesis that therapeutic, long-term T3 treatment in SHHF rats can prevent or attenuate cardiac dysfunction. Female SHHF rats were treated orally with a physiological T3 dose (0.04 μg/ml) from 12 to 24 mo of age. Age-matched female SHHF and Wistar-Kyoto rats served as hypertensive and normotensive controls, respectively. SHHF rats had reduced serum free thyroid hormone levels and cardiac tissue T3 levels, LV dysfunction, and elevated LV collagen content compared with normotensive controls. Restoration of serum and cardiac tissue thyroid hormone levels in T3-treated rats was associated with no change in heart rate, but strong trends for improvement in LV systolic function and collagen levels. For instance, end-systolic diameter, fractional shortening, systolic wall stress, and LV collagen levels were no longer significantly different from controls. In conclusion, longstanding hypertension in rats led to chronic low serum and cardiac tissue thyroid hormone levels. Long-term treatment with low-dose T3 was safe. While cardiac dysfunction could not be completely prevented in the absence of antihypertensive treatment, T3 may offer additional benefits as an adjunct therapy with possible improvement in diastolic function.

Thyroid Status, Cardiac Function, and Mortality in Patients With Idiopathic Dilated Cardiomyopathy

CONTEXT

Previous studies claiming a relationship between thyroid dysfunction and poor prognosis of heart failure (HF) had a major limitation in that they included patients with different etiologies.

OBJECTIVE

With complete information of thyroid function profile from 458 consecutive patients with idiopathic dilated cardiomyopathy, we tested the hypothesis that thyroid status can independently influence mortality in patients with HF. Design, Patients, and Outcome Measure: The original cohort consisted of 572 consecutive patients with idiopathic dilated cardiomyopathy, and 458 patients remained at the end of follow-up. All patients took thyroid function tests and other regular examinations in hospital. The risk of mortality was evaluated based on free T3, TSH, and the whole thyroid function profile, respectively.

RESULTS

The most frequent thyroid dysfunction was subclinical hypothyroidism (n = 41), followed by subclinical hyperthyroidism (n = 35), low-T3 syndrome (n = 17), and hypothyroidism (n = 12). Logistic analysis showed log-TSH and free T3 as independent predictors of exacerbated cardiac function (New York Heart Association stages III-IV vs New York Heart Association stages I-II). During the follow-up (17 ± 8 mo), 111 cumulative deaths occurred. Hypothyroidism was the strongest predictor of mortality [hazard ratio (HR) 4.189; 95% confidence interval (CI) 2.118-8.283)], followed by low-T3 syndrome (HR 3.147; 95% CI 1.558-6.355) and subclinical hypothyroidism (HR 2.869; 95% CI 1.817-4.532). Subclinical hyperthyroidism showed no significant impact.

CONCLUSIONS

We found a clear association between thyroid dysfunction and increased risk of mortality in idiopathic dilated cardiomyopathy with HF. These results suggest that monitoring thyroid function in HF patients is necessary, and further studies on the treatment of HF with thyroid dysfunction are needed.

How to improve the overall quality of cardiac morphometric data

By the mid-1990s, experts realized that drugs leading to improved ventricular remodeling were doing something remarkable in cardiac patients. The "age of cardiac remodeling" had begun. This created an experimental need for high-quality assessment of changes in cardiac tissue composition, including myocyte shape, myocardial fibrosis/collagen, and vascular remodeling. Many working in the field today have little or no training related to recognition of fixation artifacts or common errors associated with quantitative morphology. Unfortunately, such skills had become somewhat of a lost art during the ages of cardiac physiology in the mid-20th century and molecular biology, gaining prominence by the mid-1970s. Consequently, cardiac remodeling studies today are often seriously flawed to the point where data are not reproducible and subsequent researchers may be chasing the molecular basis of a nonexistent or erroneous phenotype. The current unacceptably high incidence of irreproducible data is a serious waste of time and resources as recently noted in comments by the National Institutes of Health director. The goal of this "how to" article is to share some lessons I have learned during nearly 40 years of assessing morphological changes in the heart. It is possible for any laboratory to routinely publish highly reproducible morphological data that stand the test of time and contribute to our fundamental knowledge of cardiac remodeling and the molecular mechanisms that drive it.

Thyroid hormone replacement therapy attenuates atrial remodeling and reduces atrial fibrillation inducibility in a rat myocardial infarction-heart failure model

BACKGROUND

Heart failure (HF) is associated with increased atrial fibrillation (AF) risk. Accumulating evidence suggests the presence of myocardial tissue hypothyroidism in HF, which may contribute to HF development. In a recent report we demonstrated that hypothyroidism, like hyperthyroidism, leads to increased AF inducibility. The present study was designed to investigate the effect of thyroid hormone (TH) replacement therapy on AF arrhythmogenesis in HF.

METHODS AND RESULTS

Myocardial infarction (MI) was produced in rats by means of coronary artery ligation. Rats with large MIs (>40%) were randomized into L-thyroxine (T4; n = 14) and placebo (n = 15) groups 2 weeks after MI. Rats received 3.3 mg T4 (in 60-day release form) or placebo pellets for 2 months. Compared with the placebo, T4 treatment improved cardiac function and decreased left ventricular internal diameters as well as left atrial diameter. T4 treatment attenuated atrial effective refractory period prolongation (45 ± 1.5 ms in placebo group vs 37 ± 1.6 ms in T4 group; P < .01) and reduced AF inducibility (AF/atrial flutter/tachycardia were inducible in 11/15 rats [73%] in the placebo- vs 4/14 rats [29%] in the T4-treated group; P < .05). Arrhythmia reduction was associated with decreased atrial fibrosis but was not associated with connexin 43 changes.

CONCLUSIONS

To our knowledge this is the first study demonstrating that TH replacement therapy in HF attenuates atrial remodeling and reduces AF inducibility after MI-HF. Clinical studies are needed to confirm such benefits in human patients.

Restoration of thyroid hormone balance: a game changer in the treatment of heart failure?

The link between low thyroid hormone (TH) function and heart failure is reviewed in the present report. The idea that TH dysfunction may contribute to diseases leading to HF has been discussed for over 60 yr. A growing body of evidence from animal and human studies, particularly in recent years, suggests that TH treatment may improve clinical outcomes. Indeed, if a similar amount of positive information were available for a newly developed heart drug, there is little doubt that large-scale clinical trials would be underway with considerable excitement. THs offer the promise of improving ventricular contraction and relaxation, improving coronary blood flow, and inhibiting atherosclerosis, and new results suggest they may even reduce the incidence of arrhythmias in heart diseases. Are the potential clinical benefits worth the risk of possible overdosing? After so many years, why has this question not been answered? Clearly, the concept has not been disproven. This review explores the body of clinical evidence related to TH dysfunction and heart failure, discuss insights into pathophysiological, cellular, and molecular mechanisms provided by animal research, and discuss what is needed to resolve this long-standing issue in cardiology and move forward.

Low-dose T₃ replacement restores depressed cardiac T₃ levels, preserves coronary microvasculature and attenuates cardiac dysfunction in experimental diabetes mellitus

Thyroid dysfunction is common in individuals with diabetes mellitus (DM) and may contribute to the associated cardiac dysfunction. However, little is known about the extent and pathophysiological consequences of low thyroid conditions on the heart in DM. DM was induced in adult female Sprague Dawley (SD) rats by injection of nicotinamide (N; 200 mg/kg) followed by streptozotocin (STZ; 65 mg/kg). One month after STZ/N, rats were randomized to the following groups (N = 10/group): STZ/N or STZ/N + 0.03 μg/mL T3; age-matched vehicle-treated rats served as nondiabetic controls (C). After 2 months of T3 treatment (3 months post-DM induction), left ventricular (LV) function was assessed by echocardiography and LV pressure measurements. Despite normal serum thyroid hormone (TH) levels, STZ/N treatment resulted in reductions in myocardial tissue content of THs (T3 and T4: 39% and 17% reduction versus C, respectively). Tissue hypothyroidism in the DM hearts was associated with increased DIO3 deiodinase (which converts THs to inactive metabolites) altered TH transporter expression, reexpression of the fetal gene phenotype, reduced arteriolar resistance vessel density, and diminished cardiac function. Low-dose T3 replacement largely restored cardiac tissue TH levels (T3 and T4: 43% and 10% increase versus STZ/N, respectively), improved cardiac function, reversed fetal gene expression and preserved the arteriolar resistance vessel network without causing overt symptoms of hyperthyroidism. We conclude that cardiac dysfunction in chronic DM may be associated with tissue hypothyroidism despite normal serum TH levels. Low-dose T3 replacement appears to be a safe and effective adjunct therapy to attenuate and/or reverse cardiac remodeling and dysfunction induced by experimental DM.

Thyroid hormone induces sprouting angiogenesis in adult heart of hypothyroid mice through the PDGF-Akt pathway

Study of physiological angiogenesis and associated signalling mechanisms in adult heart has been limited by the lack of a robust animal model. We investigated thyroid hormone-induced sprouting angiogenesis and the underlying mechanism. Hypothyroidism was induced in C57BL/6J mice by feeding with propylthiouracil (PTU). One year of PTU treatment induced heart failure. Both 12 weeks- (young) and 1 year-PTU (middle age) treatment caused a remarkable capillary rarefaction observed in capillary density. Three-day Triiodothyronine (T3) treatment significantly induced cardiac capillary growth in hypothyroid mice. In cultured left ventricle (LV) tissues from PTU-treated mice, T3 also induced robust sprouting angiogenesis where pericyte-wrapped endothelial cells formed tubes. The in vitro T3 angiogenic response was similar in mice pre-treated with PTU for periods ranging from 1.5 to 12 months. Besides bFGF and VEGF₁₆₄, PDGF-BB was the most robust angiogenic growth factor, which stimulated notable sprouting angiogenesis in cultured hypothyroid LV tissues with increasing potency, but had little effect on tissues from euthyroid mice. T3 treatment significantly increased PDGF receptor beta (PDGFR-β) protein levels in hypothyroid heart. PDGFR inhibitors blocked the action of T3 both on sprouting angiogenesis in cultured LV tissue and on capillary growth in vivo. In addition, activation of Akt signalling mediated in T3-induced angiogenesis was blocked by PDGFR inhibitor and neutralizing antibody. Our results suggest that hypothyroidism leads to cardiac microvascular impairment and rarefaction with increased sensitivity to angiogenic growth factors. T3-induced cardiac sprouting angiogenesis in adult hypothyroid mice was associated with PDGF-BB, PDGFR-β and downstream activation of Akt.

Both hypothyroidism and hyperthyroidism increase atrial fibrillation inducibility in rats

BACKGROUND

Evidence indicates that cardiac hypothyroidism may contribute to heart failure progression. It is also known that heart failure is associated with an increased risk of atrial fibrillation (AF). Although it is established that hyperthyroidism increases AF incidence, the effect of hypothyroidism on AF is unclear. This study investigated the effects of different thyroid hormone levels, ranging from hypothyroidism to hyperthyroidism on AF inducibility in thyroidectomized rats.

METHODS AND RESULTS

Thyroidectomized rats with serum-confirmed hypothyroidism 1 month after surgery were randomized into hypothyroid (N=9), euthyroid (N=9), and hyperthyroid (N=9) groups. Rats received placebo, 3.3-mg l-thyroxine (T4), or 20-mg T4 pellets (60-day release form) for 2 months, respectively. At the end of treatment, hypothyroid, euthyroid, and hyperthyroid status was confirmed. Hypothyroid animals showed cardiac atrophy and reduced cardiac systolic and diastolic functions, whereas hyperthyroid rats exhibited cardiac hypertrophy and increased cardiac function. Hypothyroidism and hyperthyroidism produced opposite electrophysiological changes in heart rates and atrial effective refractory period, but both significantly increased AF susceptibility. AF incidence was 78% in hypothyroid, 67% in hyperthyroid, and the duration of induced AF was also longer, compared with 11% in the euthyroid group (all P<0.05). Hypothyroidism increased atrial interstitial fibrosis, but connexin 43 was not affected.

CONCLUSIONS

Both hypothyroidism and hyperthyroidism lead to increased AF vulnerability in a rat thyroidectomy model. Our results stress that normal thyroid hormone levels are required to maintain normal cardiac electrophysiology and to prevent cardiac arrhythmias and AF.

Restoration of cardiac tissue thyroid hormone status in experimental hypothyroidism: a dose-response study in female rats

Thyroid hormones (THs) play a pivotal role in regulating cardiovascular homeostasis. To provide a better understanding of the coordinated processes that govern cardiac TH bioavailability, this study investigated the influence of serum and cardiac TH status on the expression of TH transporters and cytosolic binding proteins in the myocardium. In addition, we sought to determine whether the administration of T(3) (instead of T(4)) improves the relationship between THs in serum and cardiac tissue and cardiac function over a short-term treatment period. Adult female Sprague Dawley rats were made hypothyroid by 7 weeks treatment with the antithyroid drug 6-n-propyl-2-thiouracil (PTU). After establishing hypothyroidism, rats were assigned to 1 of 5 graded T(3) dosages plus PTU for a 2-week dose-response experiment. Untreated, age-matched rats served as euthyroid controls. PTU was associated with depressed serum and cardiac tissue T(3) and T(4) levels, arteriolar atrophy, altered TH transporter and cytosolic TH binding protein expression, fetal gene reexpression, and cardiac dysfunction. Short-term administration of T(3) led to a mismatch between serum and cardiac tissue TH levels. Normalization of serum T(3) levels was not associated with restoration of cardiac tissue T(3) levels or cardiac function. In fact, a 3-fold higher T(3) dosage was necessary to normalize cardiac tissue T(3) levels and cardiac function. Importantly, this study provides the first comprehensive data on the relationship between altered TH status (serum and cardiac tissue), cardiac function, and the coordinated in vivo changes in cardiac TH membrane transporters and cytosolic TH binding proteins in altered TH states.

Metabolic adaptations of skeletal muscle to voluntary wheel running exercise in hypertensive heart failure rats

The Spontaneously Hypertensive Heart Failure (SHHF) rat mimics the human progression of hypertension from hypertrophy to heart failure. However, it is unknown whether SHHF animals can exercise at sufficient levels to observe beneficial biochemical adaptations in skeletal muscle. Thirty-seven female SHHF and Wistar-Furth (WF) rats were randomized to sedentary (SHHFsed and WFsed) and exercise groups (SHHFex and WFex). The exercise groups had access to running wheels from 6-22 months of age. Hindlimb muscles were obtained for metabolic measures that included mitochondrial enzyme function and expression, and glycogen utilization. The SHHFex rats ran a greater distance and duration as compared to the WFex rats (P<0.05), but the WFex rats ran at a faster speed (P<0.05). Skeletal muscle citrate synthase and beta-hydroxyacyl-CoA dehydrogenase enzyme activity was not altered in the SHHFex group, but was increased (P<0.05) in the WFex animals. Citrate synthase protein and gene expression were unchanged in SHHFex animals, but were increased in WFex rats (P<0.05). In the WFex animals muscle glycogen was significantly depleted after exercise (P<0.05), but not in the SHHFex group. We conclude that despite robust amounts of aerobic activity, voluntary wheel running exercise was not sufficiently intense to improve the oxidative capacity of skeletal muscle in adult SHHF animals, indicating an inability to compensate for declining heart function by improving peripheral oxidative adaptations in the skeletal muscle.

Longstanding hyperthyroidism is associated with normal or enhanced intrinsic cardiomyocyte function despite decline in global cardiac function

Thyroid hormones (THs) play a pivotal role in cardiac homeostasis. TH imbalances alter cardiac performance and ultimately cause cardiac dysfunction. Although short-term hyperthyroidism typically leads to heightened left ventricular (LV) contractility and improved hemodynamic parameters, chronic hyperthyroidism is associated with deleterious cardiac consequences including increased risk of arrhythmia, impaired cardiac reserve and exercise capacity, myocardial remodeling, and occasionally heart failure. To evaluate the long-term consequences of chronic hyperthyroidism on LV remodeling and function, we examined LV isolated myocyte function, chamber function, and whole tissue remodeling in a hamster model. Three-month-old F1b hamsters were randomized to control or 10 months TH treatment (0.1% grade I desiccated TH). LV chamber remodeling and function was assessed by echocardiography at 1, 2, 4, 6, 8, and 10 months of treatment. After 10 months, terminal cardiac function was assessed by echocardiography and LV hemodynamics. Hyperthyroid hamsters exhibited significant cardiac hypertrophy and deleterious cardiac remodeling characterized by myocyte lengthening, chamber dilatation, decreased relative wall thickness, increased wall stress, and increased LV interstitial fibrotic deposition. Importantly, hyperthyroid hamsters demonstrated significant LV systolic and diastolic dysfunction. Despite the aforementioned remodeling and global cardiac decline, individual isolated cardiac myocytes from chronically hyperthyroid hamsters had enhanced function when compared with myocytes from untreated age-matched controls. Thus, it appears that long-term hyperthyroidism may impair global LV function, at least in part by increasing interstitial ventricular fibrosis, in spite of normal or enhanced intrinsic cardiomyocyte function.

Regulation of gene expression with thyroid hormone in rats with myocardial infarction

Introduction

The expression of hundreds of genes is altered in response to left ventricular (LV) remodeling following large transmural myocardial infarction (MI). Thyroid hormone (TH) improves LV remodeling and cardiac performance after MI. However, the molecular basis is unknown.

Methods

MI was produced by ligation of the left anterior descending coronary artery in female SD rats. Rats were divided into the following groups: (1) Sham MI, (2) MI, and (3) MI+T4 treatment (T4 pellet 3.3 mg, 60 days release, implanted subcutaneously immediately following MI). Four weeks after surgery, total RNA was isolated from LV non-infarcted areas for microarray analysis using the Illumina RatRef-12 Expression BeadChip Platform.

Results

Signals were detected in 13,188 genes (out of 22,523), of which the expression of 154 genes were decreased and the expression of 200 genes were increased in MI rats compared with Sham MI rats (false discovery rate (FDR) <0.05). Compared to MI rats, T4 treatment decreased expression of 27 genes and increased expression of 28 genes. In particular, 6 genes down-regulated by MI and 12 genes up-regulated by MI were reversed by T4. Most of the 55 genes altered by T4 treatment are in the category of molecular function under binding (24) and biological processes which includes immune system process (9), multi-organism process (5) and biological regulation (19) nonexclusively.

Conclusions

These results suggest that altered expression of genes for molecular function and biological process may be involved in the beneficial effects of thyroid hormone treatment following MI in rats.

Thyroid hormone promotes remodeling of coronary resistance vessels

Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced density of small arterioles, and heart failure. Nonetheless, little is known about the mechanisms by which THs regulate coronary microvascular remodeling. The current study examined the initial cellular events associated with coronary remodeling induced by triiodothyronine (T3) in hypothyroid rats. Rats with established hypothyroidism, eight weeks after surgical thyroidectomy (TX), were treated with T3 for 36 or 72 hours. The early effects of T3 treatment on coronary microvasculature were examined morphometrically. Gene expression changes in the heart were assessed by quantitative PCR Array. Hypothyroidism resulted in arteriolar atrophy in the left ventricle. T3 treatment rapidly induced small arteriolar muscularization and, within 72 hours, restored arteriolar density to control levels. Total length of the capillary network was not affected by TX or T3 treatment. T3 treatment resulted in the coordinate regulation of Angiopoietin 1 and 2 expression. The response of Angiopoietins was consistent with vessel enlargement. In addition to the well known effects of THs on vasoreactivity, these results suggest that THs may affect function of small resistance arteries by phenotypic remodeling of vascular smooth muscle cells (VSMC).

Omega-3 fatty acids prevent pressure overload-induced cardiac fibrosis through activation of cyclic GMP/protein kinase G signaling in cardiac fibroblasts

BACKGROUND

Omega-3 polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid) from fish oil ameliorate cardiovascular diseases. However, little is known about the effects of ω-3 polyunsaturated fatty acids on cardiac fibrosis, a major cause of diastolic dysfunction and heart failure. The present study assessed the effects of ω-3 polyunsaturated fatty acids on cardiac fibrosis.

METHODS AND RESULTS

We assessed left ventricular fibrosis and pathology in mice subjected to transverse aortic constriction after the consumption of a fish oil or a control diet. In control mice, 4 weeks of transverse aortic constriction induced significant cardiac dysfunction, cardiac fibrosis, and cardiac fibroblast activation (proliferation and transformation into myofibroblasts). Dietary supplementation with fish oil prevented transverse aortic constriction-induced cardiac dysfunction and cardiac fibrosis and blocked cardiac fibroblast activation. In heart tissue, transverse aortic constriction increased active transforming growth factor-β1 levels and phosphorylation of Smad2. In isolated adult mouse cardiac fibroblasts, transforming growth factor-β1 induced cardiac fibroblast transformation, proliferation, and collagen synthesis. Eicosapentaenoic acid and docosahexaenoic acid increased cyclic GMP levels and blocked cardiac fibroblast transformation, proliferation, and collagen synthesis. Eicosapentaenoic acid and docosahexaenoic acid blocked phospho-Smad2/3 nuclear translocation. DT3, a protein kinase G inhibitor, blocked the antifibrotic effects of eicosapentaenoic acid and docosahexaenoic acid. Eicosapentaenoic acid and docosahexaenoic acid increased phosphorylated endothelial nitric oxide synthase and endothelial nitric oxide synthase protein levels and nitric oxide production.

CONCLUSION

Omega-3 fatty acids prevent cardiac fibrosis and cardiac dysfunction by blocking transforming growth factor-β1-induced phospho-Smad2/3 nuclear translocation through activation of the cyclic GMP/protein kinase G pathway in cardiac fibroblasts.