Prevalence and clinical implications of abnormal thyroid hormone metabolism in advanced heart failure

Gene signature and immune cell profiling by high-dimensional, single-cell analysis in COVID-19 patients, presenting Low T3 syndrome and coexistent hematological malignancies

Background

Low T3 syndrome is frequent in patients admitted to intensive care units for critical illness and pneumonia. It has been reported also in patients with COVID-19, Hodgkin disease and chronic lymphocytic leukemia. We analyzed the clinical relevance of Low T3 syndrome in COVID-19 patients and, in particular, in those with associated hematological malignancies.

Methods

Sixty-two consecutive patients, hospitalized during the first wave of SARS-CoV-2 outbreak in Sant’Andrea University Hospital in Rome, were subdivided in 38 patients (Group A), showing low levels of FT3, and in 24 patients (Group B), with normal FT3 serum values. During the acute phase of the disease, we measured serum, radiologic and clinical disease severity markers and scores, in search of possible correlations with FT3 serum values. In addition, in 6 COVID-19 patients, 4 with Low T3 syndrome, including 2 with a hematological malignancy, and 2 with normal FT3 values, we performed, high-dimensional single-cell analysis by mass cytometry, multiplex cytokine assay and gene expression profiling in peripheral blood mononuclear cells (PBMC).

Results

Low FT3 serum values were correlated with increased Absolute Neutrophil Count, NLR and dNLR ratios and with reduced total count of CD3+, CD4+ and CD8+ T cells. Low FT3 values correlated also with increased levels of inflammation, tissue damage and coagulation serum markers as well as with SOFA, LIPI and TSS scores. The CyTOF analysis demonstrated reduction of the effector memory and terminal effector subtypes of the CD4+ T lymphocytes. Multiplex cytokine assay indicates that mainly IL-6, IP-10 and MCAF changes are associated with FT3 serum levels, particularly in patients with coexistent hematological malignancies. Gene expression analysis using Nanostring identified four genes differently expressed involved in host immune response, namely CD38, CD79B, IFIT3 and NLRP3.

Conclusions

Our study demonstrates that low FT3 serum levels are associated with severe COVID-19. Our multi-omics approach suggests that T3 is involved in the immune response in COVID-19 and coexistent hematological malignancy and new possible T3 target genes in these patients have been identified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02805-6.

Thyroid Abnormalities in Heart Failure

The effects of hyperthyroidism and hypothyroidism on the heart and cardiovascular system are well documented. It has also been shown that various forms of heart disease including but not limited to congenital, hypertensive, ischemic, cardiac surgery, and heart transplantation cause an alteration in thyroid function tests including a decrease in serum liothyronine (T₃). This article discusses the basic science and clinical data that support the hypothesis that these changes pose pathophysiologic and potential novel therapeutic challenges.

Thyroxine increases Serca2 and Ryr2 gene expression in heart failure rats with euthyroid sick syndrome

OBJECTIVE

The current study was aimed at analyzing sarcoplasmic reticulum Ca2+ ATPase (Serca2) and ryanodine receptor type 2 (Ryr2) gene expression in rats subjected to surgery that induced HF and were subsequently treated with T4 using physiological doses.

MATERIALS AND METHODS

HF was induced in 18 male Wistar rats by clipping the ascending thoracic aorta to generate aortic stenosis (HFS group), while the control group (9-sham) underwent thoracotomy. After 21 weeks, the HFS group was subdivided into two subgroups. One group (9 Wistar rats) with HF received 1.0 µg of T4/100 g of body weight for five consecutive days (HFS/T4); the other group (9 Wistar rats) received isotonic saline solution (HFS/S). The animals were sacrificed after this treatment and examined for signs of HF. Samples from the left ventricles of these animals were analyzed by RT-qPCR for the expression of Serca2 and Ryr2 genes.

RESULTS

Rats with HF developed euthyroid sick syndrome (ESS) and treatment with T4 restored the T3 values to the Sham level and increased Serca2 and Ryr2 gene expression, thereby demonstrating a possible benefit of T4 treatment for heart function in ESS associated with HF.

CONCLUSION

The T4 treatment can potentially normalize the levels of T3 as well elevated Serca2 and Ryr2 gene expression in the myocardium in heart failure rats with euthyroid sick syndrome.

Nonthyroidal illness and the cardiorenal syndrome

The cardiorenal syndrome represents a final common pathway for renal and congestive heart failure and heralds a poor prognosis. Factors that link the failing heart and the failing kidneys--the so-called cardiorenal connectors--are, therefore, of clinical and therapeutic interest. Alterations in the levels and function of thyroid hormones that fit the spectrum of nonthyroidal illnesses could be considered to be cardiorenal connectors as both renal failure and heart failure progress with the development of nonthyroidal illness. In addition, circumstantial evidence suggests that nonthyroidal illness can induce deterioration in the function of the heart and the kidneys via multiple pathways. As a consequence, these reciprocal associations could result in a vicious cycle of deterioration that likely contributes to increased mortality. In this Review, we describe the evidence for a pathophysiological role of nonthyroidal illness in the cardiorenal syndrome. We also discuss the available data from studies that have investigated the efficacy of thyroid hormone replacement therapy in patients with renal failure and the rationale for interventional trials to examine the effects of normalization of the thyroid hormone profile in patients with renal failure and congestive heart failure.

Reverse T3 as a parameter of myocardial function impairment in heart failure

Sick Euthyroid Syndrome (SES) has been defined as low T(3) levels in the presence of normal TSH concentrations. The purpose of this study was to assess the relationship between heart failure functional classes (NYHA) and the presence of SES, as well as to estimate an index of myocardial function impairment (MFI). Forty-six patients were evaluated and 66 clinical laboratory assessments were performed. Clinical laboratory assessment reports (CLAR) were categorized according to heart failure functional class. The levels of rT(3) and fT(3)/rT(3) ratios were significantly higher and lower in class IV, respectively. In all CLAR reviewed, rT(3) positively correlated with functional classes II, III and IV. By adding the mean of the rT3 values found in Group I to one SD, MFI was estimated as 0.47 µg/mL. In 24 of the 66 CLAR reviewed MFI>0.47 µg/mL. Of these 24 CLAR, 92% were in Group II, and 8% were in Group I. MFI was low in 42 CLAR; 74% in Group II and 26% in Group I. MFI and rT(3) levels could be used for the evaluation of the prognosis of patients with heart failure in addition to (or even replacing) NYHA functional classification given that rT(3)>MFI suggests that the patient has a 92% possibility to be in NYHA functional class III or IV.

Heart failure after aortic valve substitution due to severe hypothyroidism

We report a case of a 70-year-old female with considerable co-morbidities (Type 2 diabetes, Leiden factor V mutation, mild to moderate chronic obstructive pulmonary disease) and a recent biological aortic valve substitution, who was admitted due to circulatory collapse caused by severe heart failure with an ejection fraction of 10%. The patient was treated with diuretics and inotropic drugs with only a minor effect on the condition. A thyroid status disclosed a condition of overt hypothyreosis (TSH: 70 miu/L, T4: 19 nmol/L, T3 0.8: nmol/L). Cautious treatment with peroral Levothyroxin and hydrocortisone was given as a supplement to the heart failure treatment and the condition improved gradually. Within 3 months the patient was euthyroid and had regained her habitual LV function.

Correlates of non-thyroidal illness syndrome in chronic obstructive pulmonary disease

Non-thyroidal illness syndrome (NTIS) is frequently detected in chronic, systemic diseases. The objectives of the current study is to assess the alterations of thyroid hormones during exacerbation period, recovery of exacerbation and stable phase of chronic obstructive pulmonary disease (COPD) and correlates of these hormonal alterations. A total of 83 stable COPD patients, 20 patients with acute exacerbation and 30 control subjects were evaluated. TT3, fT3, TT3/TT4 levels of both stable and exacerbation COPD groups were lower than control subjects. TSH was also decreased during exacerbation period. In follow-up of COPD exacerbation group, TSH, TT3, fT3 and TT3/TT4 were found to be increased in measurements on the day of discharge from hospital and after 1 month, compared to baseline values. TT3 and TT3/TT4 were lower in severe COPD; whereas TSH, fT3, TT3 and TT3/TT4 were lower in patients with severe hypoxemia. IL-6 and TNF-alpha were higher in both stable and exacerbation phase COPD groups and IL-6 was correlated to TT3 in stable COPD. As a result, there are significant alterations in thyroid hormones of stable COPD patients, which are related to severity of disease and hypoxemia. The hormonal changes are more significant during exacerbation and partially regress after 1 month when the disease is stabilized. We conclude that COPD patients should not be evaluated for thyroid disease during exacerbation of the disease, and thyroid function alterations during stable phase of the disease should be considered cautiously, since thyroid function abnormalities in non-thyroid illness may mimic or mask biochemical abnormalities observed in true thyroid disease.

Year in review 2005: critical care--cardiology

This review summarizes key research papers published in the fields of cardiology and intensive care during 2005 in Critical Care. The papers have been grouped into categories: haemodynamic monitoring; goal-directed therapy; cardiac enzymes and critical care; metabolic considerations in cardiovascular performance; thrombosis prevention; physiology; and procedures and techniques.

Clinical investigation: thyroid function test abnormalities in cardiac arrest associated with acute coronary syndrome

INTRODUCTION

It is known that thyroid homeostasis is altered during the acute phase of cardiac arrest. However, it is not clear under what conditions, how and for how long these alterations occur. In the present study we examined thyroid function tests (TFTs) in the acute phase of cardiac arrest caused by acute coronary syndrome (ACS) and at the end of the first 2 months after the event.

METHOD

Fifty patients with cardiac arrest induced by ACS and 31 patients with acute myocardial infarction (AMI) who did not require cardioversion or cardiopulmonary resuscitation were enrolled in the study, as were 40 healthy volunteers. The patients were divided into three groups based on duration of cardiac arrest (<5 min, 5-10 min and >10 min). Blood samples were collected for thyroid-stimulating hormone (TSH), tri-iodothyronine (T3), free T3, thyroxine (T4), free T4, troponin-I and creatine kinase-MB measurements. The blood samples for TFTs were taken at 72 hours and at 2 months after the acute event in the cardiac arrest and AMI groups, but only once in the control group.

RESULTS

The T3 and free T3 levels at 72 hours in the cardiac arrest group were significantly lower than in both the AMI and control groups (P < 0.0001). On the other hand, there were no significant differences between T4, free T4 and TSH levels between the three groups (P > 0.05). At the 2-month evaluation, a dramatic improvement was observed in T3 and free T3 levels in the cardiac arrest group (P < 0.0001). In those patients whose cardiac arrest duration was in excess of 10 min, levels of T3, free T3, T4 and TSH were significantly lower than those in patients whose cardiac arrest duration was under 5 min (P < 0.001, P < 0.001, P < 0.005 and P < 0.05, respectively).

CONCLUSION

TFTs are significantly altered in cardiac arrest induced by ACS. Changes in TFTs are even more pronounced in patients with longer periods of resuscitation. The changes in the surviving patients were characterized by euthyroid sick syndrome, and this improved by 2 months in those patients who did not progress into a vegetative state.

Nonthyroidal illness syndrome or euthyroid sick syndrome?

OBJECTIVE

To characterize the nonthyroidal illness syndrome (NTIS) and to discuss various underlying potential biochemical mechanisms for this condition.

METHODS

The pertinent medical literature was reviewed, and studies of thyroid function in systemic non-thyroidal illnesses were summarized.

RESULTS

Abnormalities of thyroid function in the NTIS have been classified into four major categories: (1) low triiodothyronine (T3) syndrome, (2) a combination of low T3 and low thyroxine (T4), (3) high T4 syndrome, and (4) other abnormalities. The NTIS has been noted in essentially all severe systemic illnesses and after caloric deprivation, major operations, and administration of some drugs. Some mechanisms that may contribute to low serum T3 in the NTIS are decreased type I 5 -monodeiodinase in tissues, decreased uptake of T4 by tissues, decreased serum binding, increased reverse T3, alterations in selenium status, cytokines, and a decrease in thyrotropin. Decreased thyrotropin may also contribute to low T4 levels in NTIS, as may decreased serum T4-binding proteins, abnormalities in T4-binding globulin, and circulating inhibitors of binding of T4 to serum proteins. Although T4 treatment of patients with NTIS has yielded little improvement, administration of T3 has produced some beneficial effects.

CONCLUSION

Further studies should be conducted to determine appropriate patient populations, dose-response ratios, and possible adverse effects of treatment of the NTIS with T3.

Identifying infants at risk of marked thyroid suppression post-cardiopulmonary bypass

OBJECTIVE

The clinical benefit of tri-iodothyrinone (T(3)) replacement following congenital heart surgery with cardiopulmonary bypass (CPB) is not clear in unselected cohorts of children. Infants with more marked thyroid hormone suppression or prolonged post-CPB recovery may benefit from T(3) replacement. This study aimed to identify infants at risk of more marked suppression by examining the relationship between organ support parameters during CPB and post-operative thyroid hormone levels.

DESIGN AND SETTING

Prospective observational study in a tertiary referral centre for congenital heart surgery.

PATIENTS

36 infants less than 12 months of age were recruited following CPB.

MEASUREMENTS AND RESULTS

Thyroid hormone levels were measured on admission to the intensive care unit and on post-operative days 1 and 2. Increasing CPB time was associated with decreasing admission free T(3) and thyroid-stimulating hormone. Younger, smaller infants had lower admission levels of free T(3) on univariant analysis. Infants who continued to require ventilation 48 h after admission to the ICU had a mean free T(3) level on post-operative day 2 that was 0.9 pmol/l lower than in those who had been extubated.

CONCLUSIONS

Prospective studies of T(3) replacement in selected young infants (less than 3 months) with long CPB time (greater than 120 min) during congenital heart surgery are warranted.

Low triiodothyronine (T3) or reverse triiodothyronine (rT3) syndrome modifies gene expression in rats with congestive heart failure

Heart failure (HF) is frequently associated with euthyroid "sick" syndrome (low T3 and elevated rT3). We investigated if altered thyroid hormone in HF could affect expression of the TH receptor (TRalpha1), and alpha and beta myosin heavy chains (alpha-MHC, beta-MHC). HF was provoked in rats by aortic stenosis. We showed that rT3 generated from liver and kidney deiodination significantly increased and T3 decreased in HF; there was significantly higher TRalpha1 expression, no alpha-MHC expression, but beta-MHC expression. Changes in TRalpha could be compensating for low T3 from HF.

Thyronin treatment in adult and pediatric heart surgery: clinical experience and review of the literature

Thyroid hormone has multiple direct and indirect effects on the heart and the vasculature. Many signs and symptoms of thyroid dysfunction are manifest by the cardiovascular system. Furthermore, many cardiovascular diseases are adversely affected by the concomitant presence of either hyper- or hypothyroidism: it is still being debated whether these alterations are the consequence of increased cardiac workload alone or are due to the intrinsic properties of thyroid hormone. There are three potential mechanisms by which thyroid hormone might exert a cardiovascular action: (1) direct effects at the cellular level (inotropic and chronotropic effect); (2) interaction with the sympathetic nervous system; and (3) alteration of the peripheral circulation through changes in preload, afterload and energy metabolism. We treated 54 adult and seven pediatric patients suffering from severe low cardiac output in different clinical conditions with a mean bolus dosage of 2+/-1.5 microg h(-1) of T(3), followed by a continuous infusion of 0.4+/-0.3 microg h(-1) for a mean duration of 48+/-12 h. In 45 patients, stabilization of the hemodynamic situation with a decrease in inotropic support requirement was observed; however, in 11 patients no beneficial effects were observed. From this experience we suggest that T(3) treatment may improve hemodynamics in a substantial proportion of cardiac and cardiosurgical patients in whom more conventional treatment is unsuccessful.

Thyroid hormone metabolism in patients with congestive heart failure: the low triiodothyronine state

Thyroid hormone has multiple effects on the cardiovascular system, ranging from molecular and cellular effects to the consequent hemodynamic alterations. Consequently, thyroid function has been evaluated in small cohorts of patients with advanced heart failure that indicate a significant prevalence of morphologic or functional thyroid disorders. We sought to determine the prevalence of altered thyroid hormone metabolism in a broad spectrum of ambulatory heart failure patients. Thyroid function tests were evaluated in 132 ambulatory patients (98 males, 32 females, mean age, 67 years) with left ventricular systolic dysfunction (EF < 35%) and New York Heart Association (NYHA) class I-IV symptoms. Hypothyroidism was defined as serum thyroid-stimulating hormone (TSH) > 4.25 U/mL and low triiodothyronine (T3) state was defined as T3 levels < 80 ng/dL, with normal thyroxine (T4) and TSH level. Seven percent of patients were found to have primary hypothyroidism and 34% have a low T3 state. Of patients receiving amiodarone, 21% had elevated TSH levels and 76% had low T3 levels. The prevalence of abnormal thyroid function correlated with NYHA class. There is an unexpectedly high risk of hypothyroidism and low T3 syndrome in patients regardless of treatment with amiodarone, which appears to correlate with disease severity that requires further investigation.

Clinical and experimental studies on the use of 3,5-diiodothyropropionic acid, a thyroid hormone analogue, in heart failure

Thyroid hormone has unique actions that make it a novel and possibly useful agent for treatment of heart failure. Because of potential adverse effects of thyroid hormone, however, there has been interest in developing analogues with fewer undesirable side effects. Screening of compounds structurally related to levothyroxine identified 3,5-diiodothyropropionic acid (DITPA) as an analogue with inotropic selectivity and low metabolic activity in hypothyroid rats. When DITPA was administered alone or in combination with captopril in rat and rabbit postinfarction models of heart failure, cardiac output was increased and left ventricular end-diastolic pressure (LV EDP) was decreased without increasing heart rate. A pilot clinical study was undertaken to evaluate the safety and efficacy of DITPA. In a dose-ranging study in 7 normal volunteers the drug was well tolerated. A double-blind comparison then was made of DITPA versus placebo in a group of 19 patients with moderately severe heart failure. Patients were randomly assigned to receive either 1.875 mg/kg of DITPA or placebo daily. After 2 weeks the drug was increased to 3.75 mg/kg daily for an additional 2 weeks. In heart failure patients receiving the drug for 4 weeks, cardiac index was increased (p = 0.04) and systemic vascular resistance index was decreased (p = 0.02). Total serum cholesterol (p = 0.013) and triglycerides (p = 0.005) also were decreased significantly. These results indicate that DITPA is well tolerated and could represent a useful new agent for treatment of congestive heart failure.

Association between increased levels of reverse triiodothyronine and mortality after acute myocardial infarction

PURPOSE

The thyroid hormone system may be downregulated temporarily in patients who are severely ill. This "euthyroid sick syndrome" may be an adaptive response to conserve energy. However, thyroid hormone also has beneficial effects on the cardiovascular system, such as improving cardiac function, reducing systemic vascular resistance, and lowering serum cholesterol levels. We investigated whether thyroid hormone levels obtained at the time of myocardial infarction are associated with subsequent mortality.

PATIENTS AND METHODS

Serum levels of thyroid hormones (triiodothyronine [T3], reverse T3, free thyroxine [T4], and thyroid-stimulating hormone) were measured in 331 consecutive patients with acute myocardial infarction (mean age [+/- SD], 68 +/- 12 years), from samples obtained at the time of admission.

RESULTS

Fifty-three patients (16%) died within 1 year. Ten percent (16 of 165) of patients with reverse T3 levels (an inactive metabolite) >0.41 nmol/L (the median value) died within the first week after myocardial infarction, compared with none of the 166 patients with lower levels (P <0.0004). After 1 year, the corresponding figures were 24% (40 of 165) versus 7.8% (13 of 166; P <0.0001). Reverse T3 levels >0.41 nmol/L were associated with an increased risk of 1-year mortality (hazard ratio = 3.0; 95% confidence interval: 1.4 to 6.3; P = 0.005), independent of age, previous myocardial infarction, prior angina, heart failure, serum creatinine level, and peak serum creatine kinase-MB fraction levels.

CONCLUSION

Determination of reverse T3 levels may be a valuable and simple aid to improve identification of patients with myocardial infarction who are at high risk of subsequent mortality.

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (1H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a 1H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation of T2 was made by Carr Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T21) values for bound water and long (T22) values for free water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease of T22, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue water (H2Ot%), measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H2Ot%. The decrease of T21 seems to be proportional with the level of left ventricle hypertrophy in female groups. The 1H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.

Acute effects of triiodothyronine on glucose and fatty acid metabolism during reperfusion of ischemic rat hearts

Clinical studies have demonstrated improved myocardial recovery after severe ischemia in response to acute triiodothyronine (T3) treatment. We determined whether T3 improves the recovery of ischemic hearts by improving energy substrate metabolism. Isolated working rat hearts were perfused with 5.5 mM glucose and 1.2 mM palmitate and were subjected to 30 min of no-flow ischemia. Glycolysis, glucose oxidation, and palmitate oxidation were measured during aerobic reperfusion by adding [5-3H]glucose, [U-14C]glucose, or [9,10-3H]palmitate to the perfusate, respectively. During reperfusion, cardiac work in untreated hearts recovered to a lesser extent than myocardial O2 consumption (MVO2), resulting in a decreased recovery of cardiac efficiency, which recovered to only 25% of preischemic values. Treatment of hearts with T3 (10 nM) before ischemia increased glucose oxidation during reperfusion, which was associated with a significant increase in pyruvate dehydrogenase (PDH) activity, the rate-limiting enzyme for glucose oxidation. In contrast, T3 had no effect on MVO2, glycolysis, or palmitate oxidation. This resulted in a significant decrease in H+ production from glycolysis uncoupled from glucose oxidation (2.7 +/- 0.3 and 1.9 +/- 0.3 micromol . g dry wt-1 . min-1 in control and T3-treated hearts, respectively, P < 0.05), as well as a 3.2-fold improvement in cardiac work and a 2.3-fold increase in cardiac efficiency compared with untreated postischemic hearts (P < 0.05). These data suggest that T3 can exert acute effects that improve the coupling of glycolysis to glucose oxidation, thereby decreasing H+ production and increasing cardiac efficiency as well as contractile function during reperfusion of the postischemic heart.

Safety and hemodynamic effects of intravenous triiodothyronine in advanced congestive heart failure

Most patients with advanced congestive heart failure have altered thyroid hormone metabolism. A low triiodothyronine level is associated with impaired hemodynamics and is an independent predictor of poor survival. This study sought to evaluate safety and hemodynamic effects of short-term intravenous administration of triiodothyronine in patients with advanced heart failure. An intravenous bolus dose of triiodothyronine, with or without a 6- to 12-hour infusion (cumulative dose 0. 1 5 to 2.7 microg/kg), was administered to 23 patients with advanced heart failure (mean left ventricular ejection fraction 0.22 +/- 0.01). Cardiac rhythm and hemodynamic status were monitored for 12 hours, and basal metabolic rate by indirect calorimetry, echocardiographic parameters of systolic function and valvular regurgitation, thyroid hormone, and catecholamine levels were measured at baseline and at 4 to 6 hours. Triiodothyronine was well tolerated without episodes of ischemia or clinical arrhythmia. There was no significant change in heart rate or metabolic rate and there was minimal increase in core temperature. Cardiac output increased with a reduction in systemic vascular resistance in patients receiving the largest dose, consistent with a peripheral vasodilatory effect. Acute intravenous administration of triiodothyronine is well tolerated in patients with advanced heart failure, establishing the basis for further investigation into the safety and potential hemodynamic benefits of longer infusions, combined infusion with inotropic agents, oral triiodothyronine replacement therapy, and new triiodothyronine analogs.

Sick Euthyroid Syndrome

Critical illness causes multiple alterations in thyroid hormone concentrations in patients who have no intrinsic thyroid disease. These effects are nonspecific, and they relate to the severity of illness. Because a wide variety of illnesses tend to result in the same changes in serum thyroid hormone levels, such alterations in thyroid hormone indexes has been termed the sick euthyroid syndrome. These changes are rarely isolated, and they are often associated with alterations in other endocrine systems. Similar changes in endocrine function has been shown experimentally by administration of cytokines from the interleukin and interferon families, as well as tumor necrosis factor-α. Thus, the sick euthyroid syndrome should not be viewed as an isolated pathological event, but as part of a coordinated systemic reaction to illness that involves both the immune and the endocrine systems. Recovery from the illness usually results in resolution of the alterations in thyroid hormone parameters. Supplemental thyroid hormone therapy in patients with the sick euthyroid syndrome is of no benefit and is not indicated.

Characterization of AT-1 cardiomyocytes as a model for studies of T3 effects on cardiac cells

AT-1 cardiomyocyte derive from atrial tumors in transgenic mice. Earlier studies have indicated a highly differentiated, contracting, cardiac phenotype in primary cultures and the AT-1 cardiomyocyte may thus be an excellent in vitro model in cardiac research. Thyroid hormone (T3) has positive inotropic and chronotropic effects and is clinically known to be relevant in various pathological heart conditions. Thyroid Hormone Receptors (TR) are ligand regulated transcriptional activators who mediate the effects of T3. The aim of this study was to determine whether AT-1 cardiomyocytes express TR. Regular binding competition assays showed a Kd of 370 +/- 105 for 125I-T3 binding to TR. Reverse transcription-PCR in mouse showed that TRalpha1, alpha2, beta1 and beta2 mRNA were expressed in AT-1 cardiomyocytes and mouse myocardium. Western blot with polyclonal rabbit antibodies against human TR revealed the presence of TRalpha1, beta2 and low levels of TRbeta1 while TRalpha2 was not detectable. Generally, for the detected subtypes the intensities of the bands were weaker for AT-1 cardiomyocytes in comparison to mouse heart. We conclude that the AT-1 cardiomyocytes express both protein and mRNA for TR and may provide a useful model for studying T3 effects in cultured cardiac myocytes.

Development of a thyroid hormone analogue for the treatment of congestive heart failure

The possibility that thyroid hormone or a thyroid hormone analogue that improves cardiac performance might be useful in the treatment of heart failure has-been examined. In the rat postinfarction model of heart failure, treatment with low doses (1.5 micrograms/100 g) of thyroxine (T4) for 3 days produced a positive inotropic response, including an increase in left ventricular (LV) dP/dt and a decrease in LV end-diastolic pressure (LVEDP). When treatment with T4 was continued at the same or higher doses (3 to 15 micrograms/100 g) for 10-12 days, heart rate was increased and improvement in LVEDP was not sustained. To identify an analogue with a more favorable hemodynamic profile, single- and double-ring compounds related to T4 were screened for thyromimetic activity in heart cell cultures and for their ability to bind thyroid hormone receptors. One of the analogues selected, 3,5-diiodothyropropionic acid (DITPA), was found to have inotropic selectivity in hypothyroid rats. When administered (375 micrograms/100 g) to rats with ventricular dysfunction after myocardial infarction in combination with captopril, there was improvement of the resting and stressed cardiac index and LV filling pressure. Similar improvement in cardiac performance was obtained when DITPA was administered to rabbits after infarction. Thus a thyroid hormone analogue with inotropic selectivity may be a useful adjunct to other measures in the treatment of heart failure.

Thyroid hormone abnormalities in heart failure: possibilities for therapy

Though thyroid hormone abnormalities have been identified in many cardiac conditions, the role of thyroid hormones in congestive heart failure has not been well defined. In a population of patients with advanced heart failure, a reduction in triiodothyronine (T3) with an increase in reverse T3 was identified in many patients, with an abnormally low ratio of T3/reverse T3 being the strongest predictor of mortality. Normalization of thyroid indices appeared to be necessary for prolonged survival to occur. To address the concern of T3 administration possibility exacerbating a hypermetabolic state, basal metabolic rate was measured in a group of advanced heart failure patients and was found to be generally within the normal range. A preliminary safety study of short-term intravenous T3 administration (bolus +/- 6 h infusion, total dose 0.15-2.7 micrograms/kg) was then performed in 23 patients under hemodynamic and electrocardiographic monitoring. There were neither adverse events nor substantial hemodynamic changes, but some patients had an increase in cardiac output, consistent with a peripheral vasodilatory effect. With this foundation, further investigation into the possible role of T3 and its analogs in congestive heart failure therapy may be pursued.

Pretreatment with 3,5,3'triiodo-L-thyronine (T3). Effects on myocyte contractile function after hypothermic cardioplegic arrest and rewarming

Circulating levels of 3,5,3'triiodo-L-thyronine are depressed after cardiopulmonary bypass and have been implicated to play a contributory role in the alterations in left ventricular function after hypothermic cardioplegic arrest and rewarming. The central hypothesis of the present study was that pretreatment of isolated myocytes with triiodothyronine will have a direct and beneficial effect on contractile performance after hypothermic cardioplegic arrest and rewarming. Contractile function in isolated pig left ventricular myocytes was examined by video microscopy after the following treatment protocols: (1) 37 degrees C incubation in medium (normothermia) for 2 hours with triiodothyronine followed by a 2-hour normothermic incubation with no triiodothyronine, (2) 4 hours of normothermic incubation with no triiodothyronine, (3) normothermic incubation for 2 hours with triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest ([K+]:24 mmol/L; 4 degrees C) and subsequent rewarming, and (4) normothermic incubation for 2 hours with no triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest and rewarming. Two hours of normothermia with triiodothyronine increased myocyte contractile function by 30% compared with values in untreated control myocytes, and this increase persisted after a subsequent 2-hour incubation under normothermic conditions with no triiodothyronine. For example, myocyte velocity of shortening in triiodothyronine-pretreated myocytes was 84 +/- 4.9 microns/sec compared with 62 +/- 2.8 microns/sec in control myocytes (p < 0.05). Cardioplegic arrest and subsequent rewarming caused a significant reduction in myocyte velocity of shortening from normothermic values (37 +/- 3.4 microns/sec, p < 0.05). However, in myocytes pretreated with triiodothyronine, myocyte contractile function was significantly higher after hypothermic cardioplegic arrest and rewarming (54 +/- 2.5 microns/sec, p < 0.05). In a second series of experiments, beta-adrenergic responsiveness was examined after pretreatment with triiodothyronine. In the presence of the beta-adrenergic agonist isoproterenol (25 nmol/L), myocyte contractile function was increased by 26% in the triiodothyronine-treated myocytes compared with that in untreated control myocytes. This enhanced beta-adrenergic responsiveness with triiodothyronine pretreatment persisted with subsequent exposure to hypothermic cardioplegic arrest and rewarming. In summary, triiodothyronine pretreatment caused an increase in myocyte contractile function and beta-adrenergic responsiveness under normothermic conditions and after hypothermic cardioplegic arrest and rewarming. Thus the present study provides direct evidence to suggest that preemptive treatment with triiodothyronine may improve left ventricular contractile performance after hypothermic cardioplegic arrest and rewarming.

3,5,3' Triiodo-L-thyronine pretreatment with cardioplegic arrest and chronic left ventricular dysfunction

BACKGROUND

The active form of thyroid hormone, T3, may be an important determinant of left ventricular (LV) function after hypothermic cardioplegic arrest and rewarming, particularly in patients with preexisting LV dysfunction. Thus, the present project tested the hypothesis that T3 pretreatment will improve myocyte contractile performance after hypothermic cardioplegic arrest and rewarming in the setting of chronic LV dysfunction.

METHODS

Control LV porcine myocytes (n = 160) and cardiomyopathic LV (rapid pacing for 3 weeks at 240 beats/min) myocytes (n = 100) were treated with or without 80 pmol/L T3. Myocytes then were maintained in normothermic conditions (2 hours at 37 degrees C in media) or exposed to hypothermic cardioplegic arrest ([K+], 24 mmol/L; 2 hours at 4 degrees C) with subsequent rewarming.

RESULTS

After cardioplegic arrest and rewarming, T3 pretreatment increased myocyte velocity of shortening by 41% in control myocytes and by 35% in cardiomyopathic myocytes when compared to untreated myocytes. Furthermore, T3 pretreatment followed by beta-adrenergic receptor stimulation with isoproterenol (25 nmol/L) improved myocyte velocity of shortening by 24% in control myocytes and 90% in cardiomyopathic myocytes after hypothermic cardioplegic arrest and rewarming, as compared with untreated myocytes.

CONCLUSIONS

In summary, this study provides evidence to suggest that preemptive treatment with T3 may improve LV pump function and beta-adrenergic responsiveness after hypothermic cardioplegic arrest and rewarming in patients with underlying LV dysfunction.

Direct effects of acute administration of 3, 5, 3' triiodo-L-thyronine on myocyte function

Recent studies have suggested that acute administration of 3, 5, 3' triiodo-L-thyronine (T3) may increase ventricular performance; however, the direct cellular effects of acute T3 administration are not understood. The objectives of this study were to determine (1) whether T3 acts directly on the cardiac muscle cell (myocyte) itself, and (2) whether T3 acts independently of the myocyte beta-adrenergic receptor. Accordingly, isolated myocyte function was examined using video-microscopy in normal porcine myocytes (n = 60) in the control state and in the presence of increasing T3 concentrations (10 to 500 pmol/L). T3 caused myocyte shortening extent, shortening velocity, and lengthening velocity to increase in a dose-dependent manner. For example, shortening velocity increased from 49.2 +/- 4.3 microns/s at baseline to 66.5 +/- 6.1 microns/s with 100 pmol/L T3 (p < 0.05). beta-Adrenergic stimulation with 25 nmol/L isoproterenol increased shortening velocity to 97.6 +/- 5.7 microns/s; isoproterenol with T3 increased shortening velocity further to 168.5 +/- 10.9 microns/s. Analysis of variance revealed that this increase with T3 was independent of and additive to the beta-adrenergic receptor system. In summary, T3 caused a dose-dependent increase in myocyte contractile performance, and these effects were independent of and additive to beta-adrenergic receptor stimulation. Thus, acute T3 administration may provide a novel modality to improve left ventricular contractile function independent of the beta-adrenergic receptor system.

Studies on the use of thyroid hormone and a thyroid hormone analogue in the treatment of congestive heart failure

In heart failure, cardiac output is insufficient to meet the needs of the body for oxygen delivery. Available data suggest that alterations in thyroid hormone metabolism may contribute to defective myocardial performance. Accordingly, thyroid hormone or a thyroid hormone analogue that improves cardiac performance might be useful in the treatment of heart failure and has been studied. Experimental and theoretical results of these studies are reviewed and indicate that thyroid hormone increases cardiac output by a combination of effects on the heart and peripheral circulation, specifically by increasing myocardial contractile performance and decreasing venous compliance. In the rat postinfarction model of heart failure, treatment with low doses of thyroxine (1.5 micrograms/100 g) for 3 days produced a positive inotropic response, including an increase in rate of change of left ventricular pressure and a decrease in left ventricular end-diastolic pressure. These changes could be attributed to conversion to triiodothyronine, the active intracellular form of thyroid hormone. When treatment with thyroxine was continued at the same or higher doses (3 to 15 micrograms/100 g) for 10 to 12 days, heart rate increased and improvement in left ventricular end-diastolic pressure was not sustained. More favorable results were obtained with 3,5-diiodothyropropionic acid, a cardiotonic thyroid hormone analogue administered at doses of 375 microgram/100 g, given in combination with captopril. Thus, triiodothyronine or a thyroid hormone analogue may be a useful adjunct to other measures in the treatment of heart failure.