a Department of Internal Medicine and Cardiovascular Sciences, University Federico II,Via Sergio Pansini 5, Naples 80131, Italy
b Department of Clinical and Experimental Medicine, Second University, Naples, Italy
c Department of Endocrinology, University Federico II, Via Sergio Pansini 5, Naples 80131, Italy
d Department of Internal Medicine, Second University, Naples, Italy
* Corresponding author. Tel.: +39-081-746-4375; fax: +39- 081-746-3199
E-mail address: cittadin{at}unina.it
Received 22 July 2002; revised 8 October 2002; accepted 9 October 2002
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Abstract |
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Methods and results Patients were randomized to receive for 3 months either placebo or recombinant human GH, in a double-blind fashion. In GH-treated patients, left ventricular (LV) mass increased by 16% in BMD and by 29% in DMD (both ), with a significant increase of relative wall thickness (+19%). Systemic blood pressure remained unchanged, while LV end-systolic stress fell significantly by 13% in BMD and by 33% in DMD, with a slight increase of systolic function indexes. No changes were observed related to cardiac arrhythmias and skeletal muscle function in the patient groups during the treatment period, nor any side effects were observed. Brain natriuretic peptide, interleukin-6, and tumor necrosis factor-
circulating levels were elevated at baseline. While brain natriuretic peptide decreased by 40%, cytokine levels did not exhibit significant variations during the treatment period.
Conclusions The 3-month GH therapy in patients with DMD and BMD induces a hypertrophic response associated with a significant reduction of brain natriuretic peptide plasma levels and a slight improvement of systolic function, no changes in skeletal muscle function, and no side effects.
Key Words: Growth hormone X-linked muscular dystrophy Cytokines
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1. Introduction |
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The role of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis in the modulation of cardiac structure and function under normal circumstances and in diseased states has recently been delineated in a series of animal and human studies.410 However, the use of GH as an adjunctive therapy in heart failure is still controversial. In fact, while several uncontrolled studies have documented a major improvement of clinical status, myocardial function, and energetics in patients with idiopathic dilated cardiomyopathy, recent randomized trials did not show significant changes in baseline left ventricular (LV) function despite confirming the growth-promoting effect of GH therapy.810
In addition to cardiac muscle, skeletal muscle is a typical target tissue for the anabolic and growth-promoting actions of GH, and its involvement is prominent in all muscular dystrophies.1 Moreover, it has been documented that the well-knownbeneficial effects of corticosteroids in DMD are associated with increased circulating IGF-1 levels, suggesting a link between augmented GH/IGF-1 axis activity and clinical improvement.11 Further support for the use of GH in muscular dystrophies comes from two recent animal studies performed in the Syrian cardiomyopathic hamster. Takeshi et al. demonstrated that 3-week GH treatment prevented the development of heart failure, significantly attenuated LV dilation, and improved cardiac function.12 More recently, Ross Jr.'s group showed decreased end-systolic wall stress and improved systolic function in young cardiomyopathic hamsters after GH treatment.13
The aim of the current study was to evaluate the effects of a 3-month GH therapy on cardiac structure and function in patients with X-linked muscular dystrophy. We also measured circulating levels of brain natriuretic peptide (BNP) and cytokines, since they have been shown to correlate with heart failure severity and prognosis.14 In view of the lack of data about the safety of GH administration in this specific patient population, we planned a pilot study, with a double-blind, placebo-controlleddesign, on 16 subjects.
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2. Methods |
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2.2. Laboratory evaluation
Before study entry, all subjects underwent the following pharmacological tests to evaluate GHsecretion: (1) Growth hormone-releasing hormone (GHRH); and (2) Arginine tolerance test (ATT), as previously described.16 In addition, routine analysis, creatine kinase, IGF-1, thyroid hormone, testosterone, and insulin levels were measured at baseline and after the treatment phase wereassayed using commercial kits.17 Serum GH and plasma IGF-I levels were assessed by IRMA, using DSL kits (Diagnostic System Laboratories, Inc,Webster, TX, USA). The normal IGF-I range in our laboratory for age- and sex-matched individuals was 215290µg/l in adults and 245365µg/l in prepubertal children. Serum IGF-I showed an intra-assay cv of 3.4, 3.0, and 1.5%, and inter-assay cv of 8.2, 1.5, and 3.7% at 10.4, 53.8, and 255.9µg/l. Testosterone and insulin were assayed by RIA method using a commercial kit (DSL, Diagnostic System Laboratories, Inc) Evaluation of plasma TSH levels was performed by an ultrasensitive immunoradiometric assay (Bouty, Milan, Italy) with a detection limit of 0.05mU/l. The intra- and inter-assay variability were 3.1 and 3.8%, respectively, at 0.2550mU/l. Serum FT4and FT3were measured using the Lisophase Kits (Bouty, Milan, Italy). The intra-and inter-assay variations and sensitivities were 2.9%, 4.7%, and 0.8pmol/l, respectively, for FT3and 4.1%, 5.9%, and 1.0pmol/l, respectively, for FT4. Reference ranges in our laboratory were: TSH, 0.23.0 mU/l; FT3, 4.09.2pmol/l; and FT4, 7.720.6pmol/l. Plasma levels of BNP weremeasured with a commercially available specific immunoradiometric assay kit for human BNP. Plasma interleukin-6 (IL-6) and tumor necrosis factor- (TNF-
) were determined by enzymeimmunoassay using commercial kits (MedgenixDiagnostics SA), with detection limits of 2 and 3ng/l, respectively. Values of BNP, IL-6, and TNF-
in age- and sex-matched normal individuals in our laboratory were 13±3pg/ml, 0.85±0.2ng/l, and 19±2ng/l, respectively. Laboratory staff were blinded as to the treatment code.
2.3. Cardiac evaluation
ECG included cardiomyopathic index (the QT:PQ ratio, normal values 2.24.6s) which was assessed as previously described.3 Twenty-four-hour ECGmonitoring was performed to detect rhythm disturbances. The print-outs were analyzed blindlyby two observers. The complexity of ventricular premature beats was graded according to theLown classification.18 Complete M-mode, two-dimensional (2D), and Doppler echocardiographic analysis was performed according to the standardization of the American Society of Echocardiography,19 as previously described.8,17 LV volumeswere calculated according to a biplane arealength method. The investigator reading the echoes was blinded as to whether the recordings hewas interpreting were of placebo or GH-treatedpatients.
2.4. Skeletal muscle function evaluation
The parameters assessed were: (1) timed functional testingtests included measurement of the time needed to rise to a standing position from a lying position on the floor (Gowers time), to climb four standard-size stairs, and travel 10m as fastas possible; and (2) Dynamic index, which was assessed as previously described.3
2.5. Pulmonary-function tests
Assessment included measurements of forcedvital capacity, maximal voluntary ventilation, and maximal expiratory pressure.
2.6. Statistical analysis
All values are given as mean±SE. Statistical analysis was performed using the STATISTICA package. Between-group comparisons of echocardiographic indexes were performed using the two-way ANOVA with repeated measures in one factor (time). One-way ANOVA was used for the other comparisons. Where appropriate, comparisons to determine the significance of changes within the same group over time and between the groups at each time point were performed with NeumanKeuls test. Linear regression analysis was used as appropriate. A value of was considered significant. Due to the small sample size of the Duchenne group (three patients in both the GH and the placebo group), we did not perform ANOVA analyses. The use of corresponding nonparametric tests yielded similar levels of significance.
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3. Results |
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3.4. Pulmonary-function tests
No changes were observed among the four study groups during the treatment period.
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4. Discussion |
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These cardiovascular effects are reminiscent of those observed after GH administration in human dilated cardiomyopathy.810 The effects of theactivation of the GH/IGF-1 axis on the loading conditions and myocardial contractility57 mayindeed underlie these findings. In fact, LV concentric remodeling with consequent reduction of wall stress and GH's mediated vasodilatory actions may both have contributed to after-load reduction.Interestingly, both DMD and BMD displayed similar response to GH's growth-promoting and hemodynamic properties, despite the different muscle dystrophin content and clinical progression.
In patients treated with GH, no significantimprovement of exercise capacity could bedetected as assessed by timed functionalindexes. Since, in addition to cardiovascular status, respiratory and skeletal muscle functions are also major determinants of exercise capacity, such finding might reflect GH's inability to act on these target tissues. This may be owing to the more advanced damage of skeletal compared to heart muscle usually found at the histological level in muscular dystrophies. Alternatively, the short treatment duration might have precluded an effect of GH. This latter speculation is supported by previous studies in GH-deficient patients treated with GH replacement therapy, in whom 6-month period is usually the minimum time-range employed in most clinical trials to observe changes in cardiac and skeletal muscle function.20 In GH deficiency, cardiovascular function is generally restored sooner than skeletal muscle function, clinical indexes of which show initial modifications after at least1 year of GH treatment.17 In this regard, most of our patients display abnormalities of the GH/IGF-1 axis similar to those observed in GH deficiency.
Whether the reactivation of cardiac growth in the setting of muscular dystrophies may improve survival remains to be addressed by futurelonger term investigations. On one hand, such hypertrophic response might be viewed as anunpropitious component of LV remodeling, since LV hypertrophy is associated with increasedcardiovascular mortality. On the other hand,experimental data support the notion that, at variance with pathologic hypertrophy, GH-induced cardiac growth displays unique features, such as preserved capillary density and diastolic function, improvements of intracellular calcium dynamics, and systolic performance despite less energetic cost.57 The unchanged diastolic filling in GH-treated patients despite the increased LV mass appears congruent with this concept. The significant reduction of BNP plasma levels (40%) lends support to the hypothesis that GH-induced structural and functional changes in X-linked muscular dystrophies may indeed be beneficial. BNP is a ventricular hormone whose circulating levels are directly related to LV end-diastolic pressures, to the degree of LV damage, and to LV mass, andhas recently been demonstrated to be a strong prognostic indicator of morbidity and mortality in patients with heart failure following optimized treatment.14 Therefore, the novel finding related to elevated baseline BNP circulating levels inpatients with X-linked muscular dystrophy, herein reported, supports the known impairment of LV structure and mechanics of this patient population, and, probably, its adverse prognosis despite optimal medical treatment. On the other hand, BNP reduction after GH therapy may reflect an improved hemodynamic profile and, possibly, a better outcome of the active treatment group, and appears particularly relevant insofar as itoccurs in the setting of increased LV mass induced by GH.
Patients with X-linked muscular dystrophy presented with elevated plasma levels of cytokines, that were not significantly changed after 3 months of GH therapy. Such pattern of chronic inflammation is commonly seen in chronic heart failure and is probably causally related to its pathogenesis and progression,21 as well as to muscle dysfunction in DMD.22 Moreover, since experimental modelsof inflammation also inhibit GH signaling,23 it is possible that high circulating levels of IL-6 and TNF- may contribute to the observed impairment of the GH/IGF-1 axis (vide infra). This contentionis supported by our finding that the response toGH therapy, expressed as percent change in IGF-1 circulating levels, was inversely correlated with baseline TNF-
levels. At variance with BNP, the absence of IL-6 and TNF-
plasma levels changes after 3-month GH therapy either suggests theinability of GH therapy to modify the cytokine pattern in this clinical stetting or that a longer treatment period would be needed. This lastspeculation is congruent with a previous report showing that changes of inflammatory cytokines usually occur only after at least 6 months of therapy.24
Forty-four percent of our patient population displayed abnormalities of the GH/IGF-1 axis, similar to those observed in GH deficiency, i.e. low IGF-1 circulating levels and an altered response to GH stimulatory tests. Possible explanations for this finding include indirect mechanisms, such as physical inactivity or concomitant corticosteroid treatment, or alternatively it may reflect a primary unknown disorder of GH secretion.
Previous studies have addressed the role of GH/IGF-1 axis in patients with muscular dystrophies, in particular DMD.2527 Conflicting results have been reported. The observation of a slower progression of DMD in a patient with dwarfism lead to the hypothesis that a low activity of the GH/IGF-1 axis might be beneficial in muscular dystrophy.25 Two lines of evidence have challenged this initialspeculation. First, the frequent finding of impaired GH secretion, particularly in patients with DMD, was not associated with a milder form of disease, in keeping with our findings.26 Second, clinical trials with a GH inhibitor, mazindolol, have been unable to show any beneficial effect of GH-reduced secretion on clinical status and natural history of DMD.27
An obvious limitation of the current preliminary trial is the limited sample size, which hampers definite conclusions related to GH efficacy in DMD and BMD. However, while larger and/or long-term trials are needed to confirm and expand on our findings, the presence of borderline statistical significance or trends toward significance, despitethe small number of patients studied, might point toward a strong biological cardiovascular effectof GH.
The 3-month therapy in DMD and BMD did not cause any clinical relevant side effect. The safety of GH therapy was also documented by the absence of cardiac arrhythmias at Holter monitoring, and by the stability of all hematological parameters.
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Acknowledgments |
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References |
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