Second Department of Cardiovascular Medicine, Onassis Cardiac Surgery Center, Athens, Greece
* Correspondence to: Stamatis Adamopoulos, MD, PhD (London), FESC, Zinonos 9, 15234 Halandri, Athens, Greece. Tel: +30-210-6848463; Fax: +30-210-9493373
E-mail address: sadamo{at}bigfoot.com
Received 17 April 2003; revised 19 July 2003; accepted 31 July 2003
Abstract
Background Recent experimental and clinical data indicate that abnormal central and peripheral immune reactions contribute to the progression of chronic heart failure, and that immunomodulation may be an important therapeutic approach in this syndrome.
Aims We sought to study the effects of growth hormone (GH) administration on circulating pro-inflammatory/anti-inflammatory cytokine balance, and to investigate whether these GH-induced immunomodulatory effects are associated with the improvement of left ventricular (LV) contractile performance in idiopathic dilated cardiomyopathy (DCM) patients.
Methods Plasma pro-inflammatory cytokines tumour necrosis factor- (TNF-
), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF) and its soluble receptor (sGM-CSFR), chemotactic cytokine macrophage chemoattractant protein-1 (MCP-1), soluble adhesion molecules intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1), and, finally, anti-inflammatory cytokines interleukin-10 (IL-10) and transforming growth factor-ß2 (TGF-ß2) were measured (ELISA method) in 12 patients with DCM (NYHA class III; LV ejection fraction: 23.6±1.7%) before and after a 3-month subcutaneous administration of GH 4IU every other day (randomized crossover design). Peak oxygen uptake (VO2 max), LV dimensions, LV mass index, end-systolic wall stress (ESWS), mean velocity of circumferential fibre shortening (Vcfc), and contractile reserve (change of ratio Vcfc/ESWS after dobutamine administration) were also determined at the same period.
Results Treatment with GH produced a significant reduction in plasma TNF- (7.8±1.1 vs 5.5±0.9pg/ml, P=0.013), IL-6 (5.7±0.5 vs 4.7±0.4pg/ml, P=0.043), GM-CSF (27.3±1.7 vs 23.3±1.8pg/ml, P=0.042), sGM-CSFR (4.0±0.4 vs 3.2±0.4ng/ml, P=0.039), MCP-1 (199±5 vs 184±6pg/ml, P=0.048), sICAM-1 (324±34 vs 274±27ng/ml, P=0.008) and sVCAM-1 (1238±89 vs 1043±77ng/ml, P=0.002) in DCM patients. A significant increase in ratios IL-10/TNF-
(1.9±0.3 vs 3.5±0.9, P=0.049), IL-10/IL-6(2.6±0.6 vs 3.2±0.5, P=0.044) and TGF-ß2/TNF-
(3.1±0.6 vs 4.4±0.6, P=0.05) was alsofound with GH therapy. A significant reduction in ESWS (841±62 vs 634±48gr/cm2, P=0.0026) and LV end-systolic volume index (LVESVI, 128±12 vs 102±12ml, P=0.035) as well as a significant increase in posterior wall thickness (PWTH, 9.2±0.5 vs 10.3±0.6mm, P=0.034), contractile reserve (0.00029±0.0001 vs 0.00054±0.0001circ*cm2/gr*s, P=0.00028) and VO2max (15.3±0.7 vs 17.1±0.9ml/kg/min, P=0.002) were observed after GH administration. Good correlations were found between GH-induced increase in contractile reserve and the increases in VO2max (r=0.63, P=0.028), IL-10/TNF-
(r=0.69, P=0.011) and TGF-ß2/TNF-
(r=0.58, P=0.046) ratios, as well as the reduction in plasma TNF-
levels (r=0.86, P=0.0004).
Conclusions GH administration modulates beneficially circulating cytokine network and soluble adhesion molecules in patients with DCM, whilst enhancing contractile reserve and diminishing LV volumes. These GH-induced anti-inflammatory effects may be associated with the improvement in LV contractile performance and exercise capacity as well as with the reverse of LV remodelling of patients with DCM.
Key Words: Cytokines Adhesion molecules Inflammation Growth hormone Contractile performance Cardiac remodelling Dilated cardiomyopathy Chronic heart failure
1. Introduction
Both experimental and clinical studies have shown a role for inflammation in the pathogenesis and progression of chronic heart failure (CHF).1,2This seems to be related to an imbalance between proinflammatory and anti-inflammatory factors, favouring inflammatory effects on cardiovascular system of CHF patients.3,4More specifically, the existence of an abnormal inflammatory response mediated mainly by the complex cytokine network, is responsible for some aspects of syndrome phenotype, such as the adverse left ventricular (LV) remodelling, endothelial dysfunction and peripheralmyopathy.1,2Thus, the modulation of immunologic variables may be an important therapeutic approach in CHF, possibly intervening in the progression of the syndrome.5
On the other hand, experimental studies have demonstrated that growth hormone (GH) administration can influence LV myocardial growth and geometry in the setting of CHF.6,7Thus, an improvement of cardiac contractility and performance, as well as a reduction in end-systolic wall stress, have been noted in animalmodels.6,7Additionally, few clinical studies810showed that GH treatment improves cardiac systolic function and corrects the abnormal endothelial function in patients with CHF. These beneficial effects were associated with better functional status and exercise capacity of CHF patients. We have recently focused on the anti-inflammatory and anti-apoptotic role of GH in a smaller group of patients with idiopathic dilated cardiomyopathy (DCM) by using very few markers indicative of inflammation (TNF- and IL-6) and apoptosis (sFas and sFasLigand). To our knowledge, no in vivo data exist regarding the GH effects on a broad spectrum of peripheral monocyte-related inflammatory markers of the complex cytokine network in relation to echocardiographic parameters of cardiac contractile performance and remodelling. We, therefore, sought to investigate whether GH treatment affects plasma proinflammatory cytokines tumour necrosis factor-
(TNF-
) and interleukin-6 (IL-6), plasma anti-inflammatory cytokines interleukin-10 (IL-10) and transforming growth factor-ß2 (TGF-ß2), chemotacticcytokine macrophage chemoattractant protein-1 (MCP-1), the granulocyte-macrophage colony-stimulating factor (GM-CSF) and its soluble receptor (sGM-CSFR) and soluble cellular adhesion molecules intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1) in 12 patients with CHF secondary to DCM. Furthermore, we examined whether these GH-induced changes are correlated with the GH-induced changes in exercise capacity, expressed by peak oxygen uptake (VO2 max), and in echocardiographic markers of cardiac remodelling and contractile performance,11expressed mainly by LV end-systolic volume index (LVESVI), end-systolic wall stress (ESWS) and myocardial contractile reserve (
Vcfc/ESWS).
2. Methods
2.1. Study group
Twelve patients with moderate to severe CHF secondary to DCM (age: 50±4 years; eight men and four women; New York Heart Association class III; LVEF: 23.6±1.7%) gave informed, written consent and were studied in our Cardiology Department, in compliance with the approval of Ethics Committee. The clinical diagnosis of DCM as a cause of CHF was established on the basis of a normal coronary angiogram, clinical history, and histological findings of endomyocardial biopsy. All CHF patients were treated with angiotensin-converting enzyme inhibitors and diuretics. Additionally, 10 patients were taking ß-blockers, three patients digoxin and two patients anti-coagulants. Medication remained unchanged throughout the various phases of the study.
This study was a randomized crossover comparison of 12-week treatment with subcutaneous administration of 4IU GH every other day against 12-week period without treatment with GH. Baseline measurements were performed 1 week before the randomization and, therefore, the initiation of the study. After baseline measurements, six patients received GH therapy for 12 weeks (with GH treatment period) followed by another 12 weeks without GH therapy, whereas the remaining six patients continued their conventional treatment for 12 weeks (without GH treatment period) followed by another 12 weeks of GH therapy.
Patients with infections, malignancies, pulmonary disease, thyroid disease, renal failure, collagen or other inflammatory disease, as well as patients taking anti-inflammatory or immunosuppressive agents for the last 2 weeks, were excluded from our study. For baseline comparisons, 10 age- and sex-matched control subjects, without acute or chronic illness or any symptoms related to the cardiovascular system were also studied.
2.2. Cardiopulmonary exercise testing
Exercise testing with respiratory gas exchange measurements was performed while patients exercised on a treadmill according to the Dargie protocol.12
Oxygen uptake, carbon dioxide production and respiratory exchange ratio were measured continuously during exercise using the Medgraphics CPX/MAX (Medical Graphics Corp., St Paul, Minnesota) automated gas exchange data for each individual breath (which can then be averaged over a 5s interval). Blood pressure was measured with a mercury sphygmomanometer and the electrocardiogram was monitored continuously with a computer-assisted system (Marcquette Electronics Inc.) All patients quit the test because of dyspnoea or fatigue, and in all patients the gas exchange anaerobic threshold and a respiratory exchange ratio >1.0 were reached. Peak oxygen uptake (ml/kg/min) at peak exercise was calculated as the mean of values during the last minute of exercise.
2.3. Echocardiographic measurements
Left ventricular dimensions and wall thickness were measured from parasternal targeted M-mode echocardiographic recordings. Care was taken to record the largest and smallest LV dimensions present between the tips of the mitral valve leaflets and the superior aspect of the papillary muscles. Left ventricular end-diastolic diameter (LVEDD) was taken at the Q wave of the electrocardiogram. Left ventricular end-systolic dimension (LVESD) was determined to be the shortest distance between walls rather than at the time of peak downward septal motion. Using a Hewlett-Packard septal motion (Sonos 1000 or 2500) ultrasound device the following echocardiographic variables were measured at baseline and after the end of 10µg/kgr/min of dobutamine infusion: (1) the LV fractional shortening (LVFS), LVFS=[(LVEDD-LVESD)/LVEDD] x100; (2) maximal ventricular septum and posterior wall thickness (PWTH) in systole; (3) end-systolic meridional wall stress (ESWS), calculated using the formula: systolic blood pressurexLVESDx1.35/4xPWTHsx[(1+PWTHs)/LVESD]13(systolic blood pressure was represented by brachial artery systolic pressure and measured every minute with a cuff sphygmomanometer); (4) LV heart-rate corrected mean velocity of circumferential fibre shortening (Vcfc), calculated as follows: Vcfc=(%FS/LVET)xRR). (LVET represents LV ejection time in msecs from the opening to the closing clicks of the aortic valve flow velocity envelope by continuous-wave Doppler imaging); (5) Vcfc/ESWS ratio changes after dobutamine administration (Vcfc/ESWS) as an index of myocardial contractile reserve;14From 2D echocardiography end-diastolic and end-systolic volumes were calculated and LV ejection fraction (LVEF) was derived [(end-diastolicend-systolic volume)/end-diastolic volume]x100 according to the modified Simpson's formula. Changes represent the values obtained after inotropic stimulation minus those obtained at baseline. Inotropic stimulation was done by dobutamine, which was infused intravenously in two steps after establishment of a stable haemodynamic state (heart rate, blood pressure). The duration of each step was 5min and the maximal end dose of dobutamine infused was 10µg/kg/min.15At each step dobutamine infusion was increased by 5µg/kg/min, reaching 10µg/kg/min at the second step. Every minute during the protocol, systolic, diastolic and hence mean arterial blood pressure (Siemens, Sirecust 888 device), heart rate and a 12-lead electrocardiogram were recorded. As a limitation of the study, we recognize that brachial artery pressure is only an estimate of LV ejection pressure, and not a direct measurement. In addition, there is a lack of synchrony between estimates of ventricular pressure (which occurred at early or mid ejection) and those of cavity dimensions and wall thickness (which occurred at the end of ejection). However, the main purpose of the study was to estimate wall stress before and after GH therapy, and we, therefore, assumed that the method used for the measurement of peak systolic blood pressure had little influence on the final results. All measurements were made at a speed paper of 100mm/s and represent the average of the measurements of five consecutive beats. In all cases echocardiograms were analysed by two independent expert observers. Finally, LV mass (LVM) was determined according to Penn convention.16The LVM was then divided by the body surface area to provide the LVM index (LVMI). All the above echocardiographic variables were measured in patients of our study at baseline, as well as at the end of each treatment period.
Cardiopulmonary exercise testing and echocardiograms were both performed and analysed by blinded observers, who were unaware of the current phase of the study.
2.4. Laboratory measurements
For the biochemical measurements, blood samples were obtained by standard venipuncture from CHF patients at baseline, before and after the 3-month treatment with GH. For plasma sampling, blood was drawn into pyrogen-free blood collection tubes (Becton Dickinson) with EDTA as anticoagulant. Tubes were immediately immersed in melting ice and centrifuged within 15min (1000xg at 4°C). Plasma were stored at 80°C in multiple aliquots until analysis. Samples were frozen and thawed only once. Plasma samples were assayed in duplicate for TNF-, IL-6, IL-10, TGF-ß2, MCP-1, GM-CSF, sGM-CSFR, sICAM-1 and sVCAM-1 concentrations using commercially available enzyme-linked immunosorbent assay (ELISA) kits (R&D systems, Minneapolis Minnesota) according to the manufactures descriptions. All kits had the following sandwich ELISA format: the microtitre plates were already precoated with a murine monoclonal antibody against the human monocyte-related inflammatory marker being measured. Standards of the analyte and plasma samples-in-duplicate were added, along with another antibody against another epitope of the analyte conjugated to horse radish peroxidase for TNF-
, IL-6, IL-10, TGF-ß2, MCP-1, GM-CSF, sGM-CSFR, sICAM-1 and sVCAM-1 measurements. To test the validity of assays, we also used control plasma samples that contains known concentrations of all nine molecules. The samples were incubated for 1.5h at room temperature. Finally, for all them, the chromogen tetra-methyl-benzidine was added and incubated for 30min in the dark. After addition of 2N H2SO4, the optical densities at 450nm (reference filter 620nm) were read, and standard curves were plotted in an Organon Technika 530 (Turnhout, Belgium) microplate reader. The intra-assay and interassay coefficients of variation were <8% for all ELISA assays in our laboratory. All tests were performed before daily medication had been taken and were conducted by staff who was blinded to the treatment status of the individual subjects. Table 1summarizes the clinical, echocardiographic (LV volumes, end-systolic wall stress and contractile reserve) and biochemical (monocyte-related inflammatory factors) characteristics of patients with CHF during the various phases of the study.
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3. Results
We demonstrated that a 3-month therapy with GH induced a significant reduction in the whole spectrum of peripheral monocyte-related inflammatory markers of the cytokine network (P<0.01 by ANOVA) as well as a reduction in end-systolic volume and wall stress (P<0.001 by ANOVA) associated with an increase in myocardial wall thickness and contractile reserve (P<0.001 by ANOVA) in the group of patients with IDC. Thus, as shown in Table 1, compared to without GH treatment period GH administration causes a significant reduction in plasma concentrations of circulating proinflammatory cytokines TNF- (P=0.013) and IL-6 (P=0.043), inflammatory cell-growth factor GM-CSF (P=0.042) and its soluble receptor sGM-CSFR (P=0.039), chemotactic cytokine MCP-1 (P=0.048), and soluble adhesion molecules sICAM-1 (P=0.008) and sVCAM-1 (P=0.002). In contrast, no change was found in serum anti-inflammatory cytokines IL-10 and TGF-ß2. However, the ratio of IL-10/TNF-
(P=0.049) and IL-10/IL-6 (P=0.044), as well as the ratio of TGF-ß2/TNF-
(P=0.05) were significantly increased. Fig. 1describes the effects of GH administration on plasma activity of TNF-
, IL-6, IL-10/TNF-
and IL-10/IL-6 ratios, while Fig. 2describes the effects of GH administration on plasma levels of inflammatory cell-growth factor (GM-CSF), chemotactic cytokine MCP-1 and soluble adhesion molecules sICAM-1 and sVCAM-1. Exercise capacity of CHF patients, expressed by VO2max, was also improved with GH treatment (P=0.002) (Table 1; Fig. 3). A significant reduction in ESWS (P=0.0026) and LV end-systolic volume index (LVESVI, P=0.035) and end-diastolic volume index (LVEDVI, P=0.034) as well as a significant increase in posterior wall thickness (P=0.014), and contractile reserve (P=0.00028) were also observed in IDC patients after GH administration (Table 1; Fig. 3). Significant and perhaps important correlations were found between the GH-induced improvement in contractile reserve and the increase in VO2max (r=0.63, P=0.028), IL-10/TNF-
(r=0.69, P=0.011) and TGF-ß2/TNF-
(r=0.58, P=0.046),as well as the reduction in plasma TNF-
levels (r=0.86, P=0.0004) (Fig. 4). Significant correlations were also observed between GH-induced reduction in ESWS and the increase in IL-10/IL-6 (r=0.60, P=0.04) and TGF-ß2/IL-6 (r=0.67, P=0.016), as well as the reduction in plasma MCP-1 levels (r=0.58, P=0.049) (Fig. 5). In addition, good correlations were found between GH-induced improvement in VO2max and respective reduction of sVCAM-1 values (r=0.57, P=0.05) or increase of ratio IL-10/TNF-
(r=0.77, P=0.0032) and TGF-ß2/TNF-
(r=0.84, P=0.0008) (Fig. 6). Finally, a correlation of borderline significance was found between LV reverse remodelling, expressed by the percentage reduction in LVESVI, and percentage increase in exercise tolerance, expressed by VO2max (r=0.55, P=0.05).
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4. Discussion
Recent investigations indicate that pro-inflammatory cytokines (TNF-, IL-6 and IL-1) and other cytokine-related inflammatory factors are capable of modulating cardiac, muscular and vascular functions, by a variety of mechanisms including activation of tissue and circulating monocytes, production of oxygen free radicals and apoptosis.18,19These deleterious effects of pro-inflammatory cytokines are clinically translated into cardiac, skeletal and respiratory muscle dysfunction and fatigability, impaired peripheral tissue perfusion, poor oxygen consumption and tissue wasting, all of which are associated with exercise intolerance, and all of which are hallmarks of patients with advanced CHF and adverse prognosis.2022
It is known that GH administration has beneficial effects on myocardial function and peripheral circulation in animal models with CHF, including peripheral vasodilatation, enhancement in cardiac contractility, improvement in cardiomyocyte metabolic dysbalance, stimulation of cardiac hypertrophy, increase in calcium sensitivity of cardiac myofilaments and prevention of cardiomyocyte apoptosis.2325Small clinical studies confirm these beneficial effects by showing improvement in LV mechanical efficiency and correction, at least partial, of both endothelium and non-endothelium dependent vasodilatation in patients with DCM.10,26
In this report, we have shown that a 3-month therapy with GH intervenes in the various stages of inflammatory process in patients with DCM by reducing not only the major pro-inflammatory cytokines TNF- and IL-6, which initiate or stimulate the cytokine cascade and are potent inducers of apoptosis,2,3but also the growth factor GM-CSF, which (apart from differentiating and proliferating myeloid progenitor cells) generates free radicals and potentiates cytokine production;27the chemotactic cytokine MCP-1, which promotes the migration of mononuclear phagocytes into the injured myocardial tissue and endothelial cells;28,29and the soluble adhesion molecules ICAM-1 and VCAM-1, which are cleaved into the circulation by the activated monocytes and endothelial cells, and may be products of endothelial activation or damage.30
Another indication that GH administration normalizes abnormal inflammatory responses emerges from the GH-induced increase in the ratio of plasma anti-inflammatory to pro-inflammatory cytokines (IL-10/IL-6, IL-10/TNF- and TGF-ß2/TNF-
), which has been used to predict survival of patients with systemic inflammatory response syndrome and may be also used as a marker to describe the inflammatory load in CHF.4,31
We have, also, shown that GH therapy attenuates or even reverses the progress towards maladaptive remodelling by reducing LV end-systolic and end-diastolic volumes as well as end-systolic wall stress with simultaneous improvement of LV contractile reserve.
Despite some evidence from the literature of either teratogenic or cancerogenic or atherogenic effects of GH, our 3-month therapy, in keeping with previous studies,32,33was safe and without serious side effects including abnormalities in glucose control.
4.1. Growth hormone and immunomodulation
Despite the growing interest in the contribution of cytokine activation to the pathophysiology of CHF progression, few data exist regarding the influence of traditional pharmacological interventions on the dysregulated cytokine network in human (angiotensin converting enzyme inhibitor and beta-blockers)34,35and experimental (aldosterone antagonists)36CHF. We have also found that physical training programmes in patients with moderate to severe CHF cause a significant decrease in circulating pro-inflammatory cytokines and apoptosis mediators.37,38Additionally, we have recently demonstrated the immunoregulatory role of recombinant GH administration in a smaller group of DCM patients, manifested with significant reductions in circulating levels of the pro-inflammatory cytokines TNF- and IL-6, and of apoptotic markers of the sFas/sFas Ligand system.39
The present study demonstrates, for the first time, that GH administration downregulates not only the expression of circulating major pro-inflammatory cytokines (TNF- and IL-6) but also the activation of the monocyte/macrophage-myocyte/endothelial cell self-propelled axis consisted of the growth factor GM-CSF and its cellular receptor GM-CSFR, the chemoattractant protein-1 (MCP-1), and the adhesion molecules sICAM-1 and sVCAM-1.
In particular, the elevated plasma levels of GM-CSF in patients with CHF we demonstrated in a previous study,27which were associated with haemodynamic deterioration and neurohormonal overactivation, and which were reduced with GH therapy in this study, might interfere with the progression of the syndrome of heart failure by virtue of this factor's characteristics to modulate monocyte/macrophage function in vivo via specific cell surface receptors (GM-CSFR) and subsequently to generate free radicals and enhance cytokine production. The extracellular domain of human GM-CSF receptor on activated monocytes, can be detected as the soluble form (sGM-CSFR) into the circulation of patients with CHF. Although the clinical significance of elevated sGM-CSFR in CHF remains uncertain, it has been postulated that, similar to the TNF- system, overactivation mechanisms may be responsible for sGM-CSFR release into the circulation of patients with CHF. A GH-induced decrease in sGM-CSFR levels, associated with a parallel reduction in GM-CSF levels, reflects a deactivation of the GM-CSF system, another multifunctional cytokine that mediates both the immune and inflammatory responses. Furthermore, GH by reducing MCP-1 attenuates the strength of an important chemoattractant signal, which seems to play a role in the recruitment and activation of monocytes/macrophages and migration to areas of inflammation in myocardial tissue and vascular wall of patients with CHF, thus facilitating cardiomyocyte and endothelial cell apoptosis and, therefore, potentiating left ventricular and endothelial dysfunction. Finally, GH significantly reduced soluble adhesion molecules ICAM-1 and VCAM-1, which may be characterized as the end products of the interaction between activated monocytes and endothelial cells, and may reflect the degree of endothelial dysfunction in CHF.30
Interleukin-10 and TGF-ß2 are potent anti-inflammatory cytokines which are activated in an attempt to neutralize the overexpression of pro-inflammatory cytokines characterizing CHF, thus representing important inherent components of the cytokine network in CHF.4,40A significant reduction in IL-10/TNF- and TGF-ß2/TNF-
ratios was observed, indicating restoration, at least partial, of the impaired inflammatory balance associated with advanced CHF. These ratios, pathophysiologically more meaningful in describing the inflammatory status of patients with CHF, might acquire prognostic significance greater to each individualcomponent alone (IL-10 and TGF-ß2 or TNF-
and IL-6) and may alternatively be used as a marker not only of the severity of CHF but also of the effectiveness of a therapeutic intervention in this syndrome.
4.2. Growth hormone and contractile performance
Small human studies confirm previous experimental findings by demonstrating GH-induced improvement in mechanical efficiency, attributed, mainly, to enhancement of LV muscle mass.8,41
A slightly different perspective to explain the mechanisms underlying the beneficial effects of GH on myocardial contractility is offered by our study. Growth hormone significantly improves myocardial contractility (expressed by Vcfc), even if it is corrected by LV afterload (expressed by the ratio Vcfc/ESWS) and even more important it enhances contractile reserve (expressed by the dobutamine-induced changes in Vcfc/ESWS ratio). Moreover, additional echocardiographic measurements reveal significant reduction in ESWS associated with smaller end-diastolic and end-systolic volumes, all indicative of attenuation or even reverse of LV remodelling with GH therapy.
Although the mechanisms underlying these beneficial effects on echocardiographic variables, reflecting cardiac structure and function, remain unclear, both central and peripheral GH properties seem to be involved. Thus, GH, administered for 3 months to patients with DCM, increased myocardial mass whilst doubled the serum concentrations of IGF-1,8,41,42which seems to normalize the anatomical and functional properties of the myopathic heart, by enhancing growth and viability of myocytes in a transgenic mouse model of CHF. Furthermore, a significant improvement in vascular function has been recently described with 3-month therapy with GH, which corrected endothelial dysfunction and non-endothelium dependent vasodilatation in patients with CHF.10,26This finding is in keeping with the reduction of adhesion molecules sICAM-1 and sVCAM-1 we observed, indicating a down-regulation in the excessive monocyte-endothelial cell adhesive interaction, which is associated with impaired endothelial function in CHF.
Both aforementioned mechanisms (myocyte hypertrophy or even replication and improvement in vascular function) might explain, to a great extent, the GH-induced reduction in ESWS we found. However, afterload reduction, alone, cannot explain the significant enhancement of myocardial contractility, because this improvement still holds even if it is corrected by LV afterload, as indicated by the improvement of Vcfc/ESWS ratio (either at baseline or after dobutamine infusion reflecting contractile reserve). Here, therefore, emerges the anti-inflammatory, anti-apoptotic and potential proliferative effects of GH on the myopathic heart to explain the beneficial role of GH on ventricular hemodynamics we found in our study.
Growth hormone reduces plasma levels of the major proinflammatory cytokines TNF- and IL-6 as well as the cytokine inducer GM-CSF, all facilitating cardiomyocyte apoptosis and all inducing overexpression of chemotactic chemokines, such as MCP-1 (self-perpetuating locally an inflammatory vicious circle by attracting macrophages in the myocardium), of inducible form of NO synthase (overproducing oxygen free radicals and, thus, exhausting energy stores) and of metalloproteinases (causing myocyte slippage and, therefore, promoting ventricular dilatation) in the myocardial tissue.3,19
In addition, GH reduces MCP-1 itself, which levels are associated with the severity of the syndrome, further attenuating the deleterious effects of chemotactic and pro-inflammatory cytokines on cardiac muscle by breaking their unfavourable interaction.
These beneficial anti-inflammatory GH properties we demonstrated in this study extend our initial observation,39offering at the same time the pathophysiologic background to understand the anti-apoptotic effects of GH in our previous study. Down-regulation of the apoptotic system sFas/sFas Ligand, as a result of GH therapy, contributes further to the geometrical and functional improvement of cardiac muscle.
Finally, GH, acting either directly on the heart or via the induction of local or systemic insulin-like growth factor-1 (IGF-1), may enhance not only growth but also viability of cardiac myocytes, as evidenced by cellular analyses, which revealed that IGF-1 inhibits cardiomyocyte elongation in dilated hearts and restored calcium dynamics comparable to that observed in normal cells.42
4.3. Correlations between central hemodynamics, immunologic responses and exercise tolerance
The good correlation between GH-induced improvement in exercise capacity (expressed by the increase in VO2max) and restoration of abnormal inflammatory response (expressed by the increase in TGF-ß2/TNF- and IL-10/TNF-
ratios) indicates that therapy with GH may exert its beneficial effects, at least partially, by shifting cytokine balance towards to anti-inflammatory predominance.
A good correlation between GH-induced improvement in exercise capacity and reduction in adhesion molecule sVCAM-1 (an indirect measure of endothelial function) was also shown in our study. This might imply that partial correction of inflammatory dysbalance, apart from improving cardiac structure and function, may also influence favourably impaired endothelial function, thus offering an additional mechanism to elucidate the increase in exercise tolerance with GH.43
Apart from the peripheral contribution (possible correction of endothelial function) to the improvement of exercise tolerance with GH therapy, a central element (reverse remodelling and enhancement of intrinsic contractile performance) seems to play an important role, given the good correlation between GH-induced beneficial changes in VO2max and LV end-systolic volume and contractile reserve.
Immunomodulation with GH therapy in DCM patients appears to shed light on the fundamental mechanisms implicated in the pathogenesis of impaired contractility, a cardinal characteristic of the syndrome. Thus, the good correlations between GH-induced decrease in ESWS or enhancement of contractile reserve, and decrease in chemotactic protein MCP-1 or the major pro-inflammatory cytokine TNF- render the anti-inflammatory effects of GH therapy not a simple epiphenomenon or therapeutic coincidence but an interesting pathophysiologic mechanism implicated in the favourable modification of myocardial structure and function. This interpretation is reinforced by the good correlation between GH-induced favourable shift of overall inflammatory balance (expressed by the ratios IL-10/IL-6 and TGF-ß2/IL-6 or IL-10/TNF-
and TGF-ß2/TNF-
) and either decrease in ESWS or increase in contractile reserve.
5. Conclusions
We demonstrated that a 3-month therapy with GH causes a significant decrease in the circulating pro-inflammatory cytokines (TNF-, IL-6, GM-CSF and its soluble receptor GM-CSFR), chemotactic chemokines (MCP-1) and soluble adhesion molecules (sICAM-1 and sVCAM-1), as well as an increase in the serum anti-inflammatory/pro-inflammatory balance ((IL-10/IL-6,IL-10/TNF-
and TGF-ß2/TNF-
) whilst enhancing contractile reserve and reducing LV dimensions. This GH-induced favourable shift in inflammatory balance towards anti-inflammatory predominance may be associated with the improvement in LV contractile performance and functional status as well as with the reverse of LV remodelling of patients with CHF, suggesting that persistent immune activation appears to be involved in the impaired central and peripheral haemodynamics and exercise capacity characterizing this syndrome. Modulation of immuno-inflammatory variables emerges as a major therapeutic strategy in the treatment of patients with CHF secondary to DCM, and GH (in addition to other therapeutic modalities (i.e. ACE inhibition, beta-blockade, physical training) may represent another important immunomodulatory option that may possibly intervene in the disease process by attenuating or even reversing its progression.
References
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