Improvement of doxorubicin induced cardiomyopathy in rats treated with insulin-like growth factor I

Underlying the Mechanisms of Doxorubicin-Induced Acute Cardiotoxicity: Oxidative Stress and Cell Death

Cancer is a destructive disease that causes high levels of morbidity and mortality. Doxorubicin (DOX) is a highly efficient antineoplastic chemotherapeutic drug, but its use places survivors at risk for cardiotoxicity. Many studies have demonstrated that multiple factors are involved in DOX-induced acute cardiotoxicity. Among them, oxidative stress and cell death predominate. In this review, we provide a comprehensive overview of the mechanisms underlying the source and effect of free radicals and dependent cell death pathways induced by DOX. Hence, we attempt to explain the cellular mechanisms of oxidative stress and cell death that elicit acute cardiotoxicity and provide new insights for researchers to discover potential therapeutic strategies to prevent or reverse doxorubicin-induced cardiotoxicity.

MicroRNAs in Cancer Treatment-Induced Cardiotoxicity

Cancer treatment has made significant progress in the cure of different types of tumors. Nevertheless, its clinical use is limited by unwanted cardiotoxicity. Aside from the conventional chemotherapy approaches, even the most newly developed, i.e., molecularly targeted therapy and immunotherapy, exhibit a similar frequency and severity of toxicities that range from subclinical ventricular dysfunction to severe cardiomyopathy and, ultimately, congestive heart failure. Specific mechanisms leading to cardiotoxicity still remain to be elucidated. For instance, oxidative stress and DNA damage are considered key players in mediating cardiotoxicity in different treatments. microRNAs (miRNAs) act as key regulators in cell proliferation, cell death, apoptosis, and cell differentiation. Their dysregulation has been associated with adverse cardiac remodeling and toxicity. This review provides an overview of the cardiotoxicity induced by different oncologic treatments and potential miRNAs involved in this effect that could be used as possible therapeutic targets.

Insulin-Like Growth Factor 1 in the Cardiovascular System

Non-communicable diseases, such as cardiovascular diseases, are the leading cause of mortality worldwide. For this reason, a tremendous effort is being made worldwide to effectively circumvent these afflictions, where insulin-like growth factor 1 (IGF1) is being proposed both as a marker and as a central cornerstone in these diseases, making it an interesting molecule to focus on. Firstly, at the initiation of metabolic deregulation by overfeeding, IGF1 is decreased/inhibited. Secondly, such deficiency seems to be intimately related to the onset of MetS and establishment of vascular derangements leading to atherosclerosis and finally playing a definitive part in cerebrovascular and myocardial accidents, where IGF1 deficiency seems to render these organs vulnerable to oxidative and apoptotic/necrotic damage. Several human cohort correlations together with basic/translational experimental data seem to confirm deep IGF1 implication, albeit with controversy, which might, in part, be given by experimental design leading to blurred result interpretation.

Efficient expression of stable recombinant human insulin-like growth factor-1 fusion with human serum albumin in Chinese hamster ovary cells

Insulin-like growth factor-1 (IGF-1) plays a crucial role in cell development, differentiation, and metabolism, and has been a potential therapeutic agent for many diseases. Chinese hamster ovary (CHO) cells are widely used for production of recombinant therapeutic proteins, but the expression level of IGF-1 in CHO cells is very low (1,500 µg/L) and the half-life of IGF-1 in blood circulation is only 4.5 min according to previous studies. Therefore, IGF-1 was fused to long-circulating serum protein human serum albumin (HSA) and expressed in CHO cells. After 8-day fed-batch culture, the expression level of HSA-IGF-1 reached 100 mg/L. The fusion protein HSA-IGF-1 was purified with a recovery of 35% using a two-step chromatographic procedure. According to bioactivity assay, the purified HSA-IGF-1 could stimulate the proliferation of NIH3T3 cells in a dose-dependent fashion and promote the cell-cycle progression. Besides this, HSA-IGF-1 could bind to IGF-1 receptor on cell membrane and activate the intracellular PI3K/AKT signaling pathway. Our study suggested that HSA fusion technology carried out in CHO cells not only provided bioactivity in HSA-IGF-1 for further research but also offered a beneficial strategy to produce other similar cytokines in CHO cells.

miR-320a mediates doxorubicin-induced cardiotoxicity by targeting VEGF signal pathway

Background

Vascular homeostasis abnormalities may involve in doxorubicin induced cardiotoxicity.

Methods

Enhanced cardiac miR-320a expression, reduced cardiac microvessel density and impaired cardiac function were observed in mice treated by anthracycline doxorubicin. To further explore the role of miR-320a in doxorubicin induced cardiotoxicity, microRNA mimics/inhibitor in vitro and rAAV administration in vivo were employed in mice.

Results

Knockdown of miR-320a not only resulted in enhanced proliferation and inhibited apoptosis in cultured endothelial cells, but also attenuated cardiac abnormalities induced by doxorubicin. On the contrary, overexpression of miR-320a enhanced apoptosis in vitro, and aggravated vessel abnormalities in heart and subsequent cardiac dysfunction in mice. Furthermore, Western blot assays showed that VEGF-A was a potential target of miR-320a, which was verified by anti-Ago2 co-immunoprecipitation. Moreover, as same as miR-320a, siRNA against VEGF-A reinforced doxorubicin induced endothelial cells injury. Finally, the negative effects of miR-320a on vascular homeostasis and cardiac function were alleviated by VEGF-A re-expression in doxorubicin treated mice.

Conclusion

Our observations demonstrate that miR-320a play important roles in doxorubicin induced cardiotoxicity via vessel homeostasis in heart and thus, inhibition of miR-320a may be applied to the treatment of cardiac dysfunction induced by anthracycline.

Insulin-like growth factor 1 treatment of MSCs attenuates inflammation and cardiac dysfunction following MI

It has been reported that insulin-like growth factor 1 (IGF-1) promoted migration of endothelial cells and cardiac resident progenitor cells. In the previous study, we found the time-dependent and dose-dependent effects of IGF-1 treatment on the CXCR4 expression in MSCs in vitro, but it is still not clear whether IGF-1 pretreatment of MSCs may play anti-apoptotic and anti-inflammation role in myocardial infarction. In this study, we demonstrated that IGF-1-treated MSCs' transplantation attenuate cardiac dysfunction, increase the survival of engrafted cells in the ischemic heart, decrease myocardium cells apoptosis, and inhibit protein production and gene expression of inflammation cytokines tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6. IGF-1 pretreatment of MSCs may play anti-apoptotic and anti-inflammation roles in post-myocardial infarction.

Increased expression of integrin-linked kinase improves cardiac function and decreases mortality in dilated cardiomyopathy model of rats

Aims

Integrin-linked kinase (ILK) is a multifunctional kinase linking the extracellular matrix to intracellular signaling pathways, whose activation in the heart gives rise to a number of functional consequences. The aim of this study is to demonstrate the therapeutic and survival benefit of cardiac ILK overexpression in a rat model of dilated cardiomyopathy.

Methods and Results

The dilated cardiomyopathy model was generated in rats by intraperitoneal administration of six equal doses of doxorubicin over a 2 week period. Five weeks after the first injection, echocardiographic analysis demonstrated impaired cardiac function and, at that point, recombinant adenoviral vector harboring ILK cDNA or vehicle was injected into the myocardium, and the rats re-studied 4 weeks later. Compared with vehicle injection, ILK treatment ameliorated inflammatory cell infiltration and cardiomyocyte degeneration, as well as left ventricular dilation and dysfunction. ILK treatment was also associated with a reduction in apoptosis and an increase in proliferation of cardiomyocytes, as well as decreased oxidative stress and autophagic vacuole accumulation. Importantly, mortality was lower in rats following ILK treatment than in those following vehicle injection. In cultured neonatal rat cardiomyocytes, we also found that ILK overexpression protected against doxorubicin-induced apoptosis, giving rise to an increase in their proliferation.

Conclusions

These data demonstrate for the first time that ILK gene therapy improves cardiac function and survival in a model of dilated cardiomyopathy, and this may be mediated through suppression of inflammation, prevention of ventricular remodeling, inhibition of cardiomyocyte apoptosis and autophagy, and stimulation of cardiomyocyte proliferation.

The GH/IGF-1 Axis and Heart Failure

The growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis regulates cardiac growth, stimulates myocardial contractility and influences the vascular system. The GH/IGF-1 axis controls intrinsic cardiac contractility by enhancing the intracellular calcium availability and regulating expression of contractile proteins; stimulates cardiac growth, by increasing protein synthesis; modifies systemic vascular resistance, by activating the nitric oxide system and regulating non-endothelial-dependent actions. The relationship between the GH/IGF-1 axis and the cardiovascular system has been extensively demonstrated in numerous experimental studies and confirmed by the cardiac derangements secondary to both GH excess and deficiency. Several years ago, a clinical non-blinded study showed, in seven patients with idiopathic dilated cardiomyopathy and chronic heart failure (CHF), a significant improvement in cardiac function and structure after three months of treatment with recombinant GH plus standard therapy for heart failure. More recent studies, including a small double-blind placebo-controlled study on GH effects on exercise tolerance and cardiopulmonary performance, have shown that GH benefits patients with CHF secondary to both ischemic and idiopathic dilated cardiomyopathy. However, conflicting results emerge from other placebo-controlled trials. These discordant findings may be explained by the degree of CHF-associated GH resistance. In conclusion, we believe that more clinical and experimental studies are necessary to exactly understand the mechanisms that determine the variable sensitivity to GH and its positive effects in the failing heart.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Activation of mitochondrial energy metabolism protects against cardiac failure

Cardiac failure is the most prevalent cause of death at higher age, and is commonly associated with impaired energy homeostasis in the heart. Mitochondrial metabolism appears critical to sustain cardiac function to counteract aging. In this study, we generated mice transgenically over-expressing the mitochondrial protein frataxin, which promotes mitochondrial energy conversion by controlling iron-sulfur-cluster biogenesis and hereby mitochondrial electron flux. Hearts of transgenic mice displayed increased mitochondrial energy metabolism and induced stress defense mechanisms, while overall oxidative stress was decreased. Following standardized exposure to doxorubicin to induce experimental cardiomyopathy, cardiac function and survival was significantly improved in the transgenic mice. The insulin/IGF-1 signaling cascade is an important pathway that regulates survival following cytotoxic stress through the downstream targets protein kinase B, Akt, and glycogen synthase kinase 3. Activation of this cascade is markedly inhibited in the hearts of wild-type mice following induction of cardiomyopathy. By contrast, transgenic overexpression of frataxin rescues impaired insulin/IGF-1 signaling and provides a mechanism to explain enhanced cardiac stress resistance in transgenic mice. Taken together, these findings suggest that increased mitochondrial metabolism elicits an adaptive response due to mildly increased oxidative stress as a consequence of increased oxidative energy conversion, previously named mitohormesis. This in turn activates protective mechanisms which counteract cardiotoxic stress and promote survival in states of experimental cardiomyopathy. Thus, induction of mitochondrial metabolism may be considered part of a generally protective mechanism to prevent cardiomyopathy and cardiac failure.

Insulin-like growth factor 1 improves the efficacy of mesenchymal stem cells transplantation in a rat model of myocardial infarction

BACKGROUND

Previous study demonstrated the improvement of cardiac function was proportional to the number of cells implanted. Therefore, increasing cell survival in the infarcted myocardium might contribute to the improvement of the functional benefit of cell transplantation.

METHODS AND RESULTS

MSCs were treated with IGF-1 in vitro and infused into the acute myocardial infarction rats via the tail vein. After treatment of MSCs with IGF-1 for 48 h, flow cytometric analysis showed marked enhancement of expression of CXCR4 in the cell surface. After 4 weeks of transplantation, we found 1) a greater number of engrafted MSCs arrived and survived in the peri-infarct region; 2) TnT protein expression and capillary density were enhanced; 3) LV cavitary dilation, transmural infarct thinning, deposition of total collagen in the peri-infarct region and cardiac dysfunction were attenuated.

CONCLUSION

1) IGF-1 treatment has time-dependent and dose-dependent effects on CXCR4 expression in MSCs in vitro. 2) IGF-1 improves the efficacy of MSCs transplantation in a rat model of myocardial infarction mainly via enhancement of the number of cells attracted into the infarcted heart. These findings provide a novel stem cell therapeutic avenue against ischemic heart disease.

Growth hormone therapy in heart failure: a novel therapy worthy of further consideration?

Despite the improvements in survival with angiotensin-converting enzyme inhibitors and beta-blockers, the clinical events for patients with heart failure remain elevated. New therapies for heart failure are required to improve the functional capacity, quality of life and prognosis. Growth hormone exerts both direct and indirect effects on cardiac structure and function. Experimental models of heart failure and small studies have demonstrated significant improvements in cardiac function, haemodynamical parameters, functional capacity and quality of life. The results from randomised controlled studies have been mixed with others showing benefit and some that do not. The randomised studies showing benefit consistently used growth hormone every other day. Further studies are needed to assess the potential role of this adjuvant therapy in patients with heart failure.

The role of insulin-like growth factor during a postischemic period - new insights into pathophysiologic pathways in cardiac tissue

Despite an improvement in the therapeutic strategies available for an acute ischemic event, cardiac disease is still the principal cause of morbidity and mortality in Western societies. A shift from acute towards more chronic heart disease due to atherosclerotic disease has been recognized. Modification of adaptive capacities of the cardiac muscle after damage remains a key component in the prevention of chronic cardiac disease, such as overt heart failure. It has recently been demonstrated that local insulin-like growth factor (IGF)-1 homeostasis in the cardiac tissue is closely involved in postischemic adaptation, such as the process of remodeling. Both experimental and clinical data support the theory that IGF-1 plays a key role in the adaptive response of the myocardium during both acute myocardial ischemia and chronic myocardial failure, regulating left ventricular remodeling and thereby restoring left ventricular architecture. This eventually leads to improvement in the function of the failing heart. While most experimental data support the beneficial role of IGF-1 in restoring architecture and function of the failing heart, clinical trials investigating the role of IGF-1 treatment of patients in cardiac failure show conflicting results. In this bench-to-bedside review, the authors aim to highlight recent advances in knowledge of the role of paracrine and autocrine IGF balances during postischemic cardiac adaptation, in order to present possible new initiatives concerning therapeutic strategies in maladaptive cardiac performance, such as the syndrome of heart failure.

Intrapericardial IGF-I Improves Cardiac Function in an Ovine Model of Chronic Heart Failure

BACKGROUND

Following myocardial infarction, progressive deterioration of left ventricular function often follows, leading eventually to overt heart failure. In the myocardium, there is increased expression of insulin-like growth factor I (IGF-I) mRNA, protein and receptor levels, particularly in the peri-infarct zone, suggesting that IGF-I has a role to play in post-infarct cardiac structure and function. In this study, we examine the effects of exogenous IGF-I on cardiac function.

METHODS

Intrapericardial IGF-I (15 microg/kg/d, n=3) or vehicle (sterile saline, n=3) was administered to sheep in chronic heart failure and the results of intrapericardial delivery compared with those of subcutaneous delivery. Left ventricular ejection fraction (EF) was measured to assess cardiac performance. Concentrations of plasma IGF-I were quantified by radioimmunoassay.

RESULTS

Intrapericardial delivery of IGF-I resulted in a rapid and sustained increase (P<0.001) in EF, which remained elevated 14 days after cessation of treatment. Subcutaneous IGF-I treatment did not affect EF. Both subcutaneous and intrapericardial IGF-I administration increased concentrations of plasma IGF-I, although concentrations declined prior to the cessation of treatment.

CONCLUSIONS

We conclude that the higher concentration of IGF-I in the myocardium, which results from intrapericardial delivery significantly increases EF in chronic heart failure but that subcutaneous delivery of IGF-I does not.

Risk factors for heart failure

Despite remarkable therapeutic advances in the management of patients with heart failure (HF), the mortality due to this syndrome remains high. Identifying free-living individuals who are at high risk for developing HF may allow implementing strategies that can prevent HF. Prospective epidemiologic studies have identified several risk factors and risk markers for HF. This article reviews current knowledge regarding conventional and newer risk markers for HF, outlines possible underlying mechanisms for the increased HF risk, and provides a framework for clinical multivariate risk prediction using HF risk factors.

Endogenous production of ghrelin and beneficial effects of its exogenous administration in monocrotaline-induced pulmonary hypertension

We investigated the endogenous production of ghrelin as well as cardiac and pulmonary vascular effects of its administration in a rat model of monocrotaline (MCT)-induced pulmonary hypertension (PH). Adult Wistar rats randomly received a subcutaneous injection of MCT (60 mg/kg) or an equal volume of vehicle. One week later, animals were randomly assigned to receive a subcutaneous injection of ghrelin (100 mug/kg bid for 2 wk) or saline. Four groups were analyzed: normal rats treated with ghrelin (n=7), normal rats injected with saline (n=7), MCT rats treated with ghrelin (n=9), and MCT rats injected with saline (n=9). At 22-25 days, right (RV) and left ventricular (LV) pressures were measured, heart and lungs were weighted, and samples were collected for histological and molecular analysis. Endogenous production of ghrelin was almost abolished in normal rats treated with ghrelin. In MCT-treated animals, pulmonary expression of ghrelin was preserved, and RV myocardial expression was increased more than 20 times. In these animals, exogenous administration of ghrelin attenuated PH, RV hypertrophy, wall thickening of peripheral pulmonary arteries, and RV diastolic disturbances and ameliorated LV dysfunction, without affecting its endogenous production. In conclusion, decreased tissular expression of ghrelin in healthy animals but not in PH animals suggests a negative feedback in the former that is lost in the latter. A selective increase of ghrelin mRNA levels in the RV of animals with PH might indicate distinct regulation of its cardiac expression. Finally, ghrelin administration attenuated MCT-induced PH, pulmonary vascular remodeling, and RV hypertrophy, indicating that it may modulate PH.

Enhanced IGF-1 expression improves smooth muscle cell engraftment after cell transplantation

The functional benefit of cell transplantation after a myocardial infarction is diminished by early cell losses. IGF-1 enhances cell proliferation and survival. We hypothesized that IGF-1-transfected smooth muscle cells (SMCs) would enhance cell survival and improve engraftment after cell transplantation. The IGF-1 gene was transfected into male SMCs and compared with SMCs transfected with a plasmid vector (vector control) and nontransfected SMCs (cell control). IGF-1 mRNA (n=10/group) and protein levels (n=6/group) were higher (P <0.05 for all groups) at 3, 7, and 14 days compared with controls. VEGF was also increased in parallel to enhanced IGF-1 expression. IGF-1-transfected cells demonstrated greater cell proliferation, stimulated angiogenesis, and decreased caspase-3 activity after simulated ischemia and reperfusion (P <0.05 for all groups compared with vector or cell controls). A uniform left ventricular injury was produced in female rats using a cryoprobe. Three weeks later, 2 x 10(6) cells from three groups were implanted into the scar. One week later, IGF-1-transfected SMCs had increased myocardial IGF-1 and VEGF levels, increased Bcl2 expression, limited cell apoptosis, and enhanced vessel formation in the myocardial scar compared with the two control groups (P <0.05 for all groups). The proportion of SMCs surviving in the implanted region was greater (P <0.05) in the IGF-1-transfected group than in the vector or cell controls. Gene enhancement with IGF-1 improved donor cell proliferation, survival, and engraftment after cell transplantation, perhaps mediated by enhanced angiogenesis and reduced apoptosis.

Growth hormone therapy in heart failure: where are we now?

Despite improvement in survival with angiotensin-converting enzyme inhibitors and beta blockers, clinical events for patients with heart failure remain elevated. New therapies for heart failure are needed to improve functional capacity, quality of life, and prognosis. Growth hormone exerts direct and indirect effects on cardiac structure and function. Experimental models of heart failure and small studies have demonstrated significant improvements in cardiac function, hemodynamic parameters, functional capacity, and quality of life. Despite the lack of benefit demonstrated in small, short-term, randomized clinical trials, further studies are needed to assess the potential role of this adjuvant therapy in heart failure patients.

Elevated myocardial Akt signaling ameliorates doxorubicin-induced congestive heart failure and promotes heart growth

Doxorubicin is a chemotherapeutic agent that can induce cardiotoxicity and congestive heart failure (CHF). In this study we tested whether intracoronary Akt1 gene delivery could inhibit doxorubicin-induced CHF. Saline or a replication defective adenoviral vector expressing constitutively-active Akt1 (myrAkt) or beta-galactosidase (betagal) was delivered to the myocardium of 8 week old rats one day prior to initiating doxorubicin administration. In animals receiving saline or betagal, doxorubicin resulted in significant decreases in cardiac function and retarded post-natal heart growth at the 5 weeks time point. In contrast, transduction of myrAkt protected hearts against doxorubicin-induced decreases in fractional shortening and cardiac index, and improved left ventricular function at 5 weeks time point. Delivery of myrAkt also reversed the doxorubicin-induced reduction in post-natal heart growth and diminished lung edema. These data show that myocardial Akt can inhibit doxorubicin-induced reductions in cardiac function and growth, suggesting that manipulation of this signaling pathway may have utility for the treatment of congestive heart failure.

Cardiomyocyte resistance to doxorubicin mediated by A(3) adenosine receptor

Recently, we reported that the activation of A(3) adenosine receptor (A(3)R) in newborn cultured cardiomyocytes by highly selective agonist Cl-IB-MECA (2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide) induces protection against the anthracycline antibiotic doxorubicin (DOX) cardiotoxicity. The present study was undertaken to further characterize the cardioprotective action of A(3)R activation by revealing the structural changes in cardiomyocytes elicited upon exposure to DOX. Morphological observations (ultrastructural and immunocytochemical) indicate that after DOX treatment, the cardiomyocytes undergo destructive alterations, and protective action of A(3)R is not connected with its anti-apoptotic activity. A(3)R activation appeared to prevent destructive alterations of cardiomyocyte mitochondria and dissipation of mitochondrial membrane potential. In DOX-treated cardiomyocytes, appearance of disorganized desmin and contractile filaments was related to detrimental alterations in the mitochondrial structure, in particular their position and transmembrane potential. In intact cardiomyocytes, diazoxide, a selective mitochondrial K(ATP) channel opener, induced an increase in ATP synthesis within 15 min of application. Similar effect was obtained by activation of adenosine A(1)R. However, A(3)R agonist Cl-IB-MECA did not affect ATP synthesis. Neither A(1)R agonist CCPA (2-chloro-N(6)-cyclopentyladenosine) nor diazoxide protected cardiomyocytes from the detrimental effects of DOX. Thus, the opening of mitochondrial K(ATP) channels does not seem to be effective during the slow development of anthracycline cytotoxicity. Our results indicate that DOX increases the activity of lysosomes, which may contribute to cell injury in an "oncotic" manner and also demonstrate the proinflammatory potency of the drug. Furthermore, the decreased acidification of cytoplasm upon activation of A(3)R may attenuate the ongoing inflammatory response. The present study identifies a novel role for A(3)R selective agonist Cl-IB-MECA and suggests its importance in regulating cardiac cellular function.

Effects of rhIGF-I and insulin-induced hypoglycaemia on cardiovascular parameters recorded with telemetry in the conscious dog

Using telemetry, the effects on cardiovascular parameters after single intravenous administration (0.5 mg/kg) of recombinant human insulin-like growth factor-I (rhIGF-I) were studied in conscious and unrestrained dogs. Insulin (1.1 IU/kg) was used as a reference compound. Telemetry transmitters were implanted subcutaneously with a pressure catheter in the femoral artery and electrodes for ECG subcutaneously. Cardiovascular effects and changes in blood glucose levels induced with rhlGF-I were similar to those induced with insulin. Heart rate increased continuously for about 90 min. after treatment, regardless of compound. Thereafter, heart rate slowly decreased but did not fully reach predose values 4 hr after treatment. Both systolic and diastolic blood pressure decreased continuously for about 90 min. and remained low for up to 4 hr after treatment. Treatment with rhIGF-I or insulin did not influence dp/dt values. Treatment with glucose intravenously to abolish the rhIGF-I-induced hypoglycaemia reduced the heart rate, but caused a substantial increase in dp/dt and a slight increase in blood pressure. RhIGF-I and insulin induced an almost identical onset and degree of hypoglycaemia. Blood glucose reached a minimum level 1 hr after treatment and was almost returned to normal 4 hr after treatment. There was an increase in the amplitude of the T-waves, though this effect occurred earlier and was longer lasting with insulin than with rhIGF-I. After 4 hr, the T-wave amplitude was normal with rhIGF-I but remained high with insulin. These T-wave effects were probably due to an increase in the transport of potassium or calcium since they decreased in plasma. This suggests that the effects of rhIGF-I and insulin are highly comparable and that the cardiovascular changes induced by rhIGF-I are likely caused by its insulin-like activity. As shown by the recorded cardiovascular responses induced by rhIGF-1 and insulin, the telemetric recording system makes it possible to evaluate the effects of different drugs in a continuous way that is not possible with conventional techniques. This new telemetric technique can be of significant importance in the process of future drug development.

Insulin-like growth factor I and II preserve myocardial structure in postinfarct swine

BACKGROUND

Insulin-like growth factors (IGF) I and II improve myocardial function after coronary occlusion in different animal models.

OBJECTIVES

To investigate the mechanism of improved myocardial function after administration of IGF-I or IGF-II in acute myocardial infarction.

METHODS

Female pigs (mean (SD) weight 25 (5) kg) were subjected to acute myocardial infarction by microembolisation with 75-150 micrometer affigel blue beads. The beads contained and slowly released 150 microgram/pig of IGF-I (n = 6), IGF-II (n = 6), or pig albumin (n = 6). Echocardiography, perfusion imaging, and haemodynamic measurements were performed before infarction and during four weeks after infarction. Regional wall motion of different left ventricular segments was scored semiquantitatively on the basis of a three point scoring system, from normal = 0 to dyskinesia = 3. Serum cardiac troponin I concentration was measured before, immediately after, and three hours after the infarct. Excised hearts were analysed for actin, desmin, blood vessel density, and DNA laddering within the infarct, border, and normal myocardial areas.

RESULTS

Myocardial function of the infarct related area improved significantly during the four weeks of follow up in both the IGF groups (p = 0.01). Myocardial perfusion, heart rate, and blood pressure were similar in all the animals during the study. Treated animals had lower serum cardiac troponin I concentration (p = 0.001), more actin in the border area (p = 0.01) and infarct area (p = 0.0001), and reduced DNA laddering in the infarct area compared with the controls (p < 0.05). IGF groups had more blood vessels in the border area (p = 0.04) and the infarct area (p = 0.003).

CONCLUSIONS

Both types of IGF improved myocardial function and the improvement was associated with preservation of myocardial structure. IGF-I was more effective than IGF-II.

IGF-I treatment reduces hyperphagia, obesity, and hypertension in metabolic disorders induced by fetal programming

The discovery of a link between in utero experience and later metabolic and cardiovascular disease is one of the most important advances in epidemiology research of recent years. There is increasing evidence that alterations in the fetal environment may have long-term consequences on cardiovascular, metabolic, and endocrine pathophysiology in adult life. This process has been termed programming, and we have shown that undernutrition of the mother during gestation leads to programming of hyperphagia, obesity, hypertension, hyperinsulinemia, and hyperleptinemia in the offspring. Using this model of maternal undernutrition throughout pregnancy combined with postnatal hypercaloric nutrition of the offspring, we examined the effects of IGF-I therapy. Virgin Wistar rats (age 75 +/- 5 d, n = 20 per group) were time mated and randomly assigned to receive food either ad libitum or 30% of ad libitum intake (UN) throughout pregnancy. At weaning, female offspring were assigned to one of two diets (control or hypercaloric [30% fat]). Systolic blood pressure was measured at day 175 and following infusion with 3 microg/g per day recombinant human IGF-1 (rh-IGF-I) by minipump for 14 d. Before treatment, UN offspring were hyperinsulinemic, hyperleptinemic, hyperphagic, obese, and hypertensive on both diets, compared with ad libitum offspring and this was exacerbated by hypercaloric nutrition. IGF-I treatment increased body weight in all treated animals. However, systolic blood pressure, food intake, retroperitoneal and gonadal fat pad weights, and plasma leptin and insulin concentrations were markedly reduced with IGF-I treatment. IGF-I treatment resulted in a 3- to 5-fold increase in 38--44 kDa and 28--30 kDa IGF binding proteins, although in UN animals, there was an impaired and differential up-regulation of these insulin-like growth factor binding proteins following IGF-I treatment. The 24-kDa IGF binding protein representing IGF binding protein-4 was down-regulated in all IGF-I-treated animals, but the decrease was more marked in UN animals. Our data suggest that IGF-I treatment alleviates hyperphagia, obesity, hyperinsulinemia, hyperleptinemia, and hypertension in rats programmed to develop the metabolic syndrome X.

Doxorubicin and mechanical performance of cardiac trabeculae after acute and chronic treatment: a review

Doxorubicin, a very potent and often used anti-cancer drug, has a wide spectrum of biological activity. Classic studies have demonstrated that doxorubicin and other members of the anthracycline family intercalate with DNA and partially uncoil the double-stranded helix. Doxorubicin has a high affinity for cell nuclei: as much as 60% of the total intracellular amount of doxorubicin is found in the nucleus. Once binding to DNA occurs, several consequences may ensue. The binding of anthracyclines to DNA inhibits DNA polymerase and nucleic acid synthesis. In addition, anthracyclines are known to stabilize the otherwise cleavable complex between DNA and homodimeric topoisomerase II enzyme subunits, resulting in the formation of protein-linked DNA double strand breaks. In tumor cells, these anthracycline-induced perturbations are believed to result in a final common pathway of endonucleolytic DNA fragmentation known as apoptosis. Because proliferation is an important determinant of tumor growth, interference with the genome is regarded as the primary cause of the anti-tumor action of doxorubicin. Intercalation with DNA may not be important in the cardiotoxicity associated with doxorubicin therapy (see next section), because cardiac cell proliferation in humans stops after 2 months of age. This review is focussed on the effects of doxorubicin on mechanical performance in skinned cardiac trabeculae after acute and chronic administration of doxorubicin. We look especially at the mechanical performance and the molecular changes observed and related to mechanical performance.

Characterization of insulin-like growth factor-1-induced activation of the JAK/STAT pathway in rat cardiomyocytes

This study was designed to investigate whether insulin-like growth factor-1 (IGF-1) transduces signaling through the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway in cardiomyocytes and to assess the upstream signals of serine and tyrosine phosphorylation of STAT family proteins. Primary cultured neonatal rat cardiomyocytes were stimulated with IGF-1 (10(-8) mol/L). JAK1, but not JAK2 or Tyk2, was phosphorylated by IGF-1 as early as 2 minutes and peaked at 5 minutes. IGF-1 induced both tyrosine and serine phosphorylation of STAT1 and STAT3. Tyrosine phosphorylation of STAT1 peaked at 15 minutes and correlated with that of JAK1, whereas that of STAT3 was sustained up to 120 minutes and was dissociated from the activation of JAK1. Tyrosine phosphorylation of STAT3 was unaffected by the preincubation with CV11974 (AT(1) blocker), TAK044 (endothelin-1 receptor blocker), RX435 (anti-gp130 blocking antibody), PD98058, wortmannin, EDTA, or KN62 but was significantly attenuated by BAPTA-AM and chelerythrine. The time course of a gel mobility shift of SIE (sis-inducing element) coincided with the phosphorylation of STAT3. Serine phosphorylation of STAT1 peaked at 30 minutes and that of STAT3 was observed from 5 to 60 minutes. These results indicated that (1) IGF-1 activated JAK1 but not JAK2 or Tyk2 in rat cardiomyocytes; (2) IGF-1 induced both tyrosine and serine phosphorylation of STAT1 and STAT3; and (3) the tyrosine phosphorylation of STAT3 was not caused by JAK1 alone, and protein kinase C and intracellular Ca(2+) were required for phosphorylation.

Insulin-like growth factor I: an attractive option for chronic heart failure?

Chronic congestive heart failure is a syndrome with a poor prognosis. Currently, the only therapy providing the possibility of long term survival is heart transplantation. Therefore, new therapeutic strategies continue to be investigated. One such new approach may be the application of recombinant human insulin-like growth factor (IGF)-1. IGF-1 has both acute and long term cardiovascular effects. Acute administration of IGF-1 resulted in a reduction in afterload and positive inotropic effects in patients with heart failure. In vitro and animal studies have demonstrated that IGF-1 can stimulate myofibril formation. In addition, IGF-1 administration has beneficial metabolic effects. The benefits of prolonged IGF-1 therapy have yet to be investigated.

Insulin-like growth factor I improves cardiovascular function and suppresses apoptosis of cardiomyocytes in dilated cardiomyopathy

To investigate how insulin-like growth factor I (IGF-I) modulates cardiovascular function and myocardial apoptosis in heart failure, the therapeutic effects of IGF-I were determined in a canine model of dilated cardiomyopathy. The animals were paced at 220 beats/min, and the left ventricular (LV) chamber became dilated after 2 weeks. A subset of paced dogs was treated with s.c. injections of IGF-I from week 3 to week 4. After 4 weeks of pacing, untreated paced dogs developed significant ventricular dysfunction. IGF-I-treated paced dogs showed better cardiac output, stroke volume, LV end-systolic pressure, and LV end-diastolic pressure. Moreover, pulmonary wedge pressure and systemic vascular resistance were increased in the untreated group and decreased in the IGF-I-treated group. IGF-I treatment was associated with less thinning of the ventricular wall. Compared with the controls, untreated paced dogs showed increased apoptosis of cardiac muscle cells, which was partially suppressed by IGF-I treatment. The myocardial apoptotic index was negatively related to the thickness of the ventricular wall and to cardiac output, suggesting that ventricular remodeling/dysfunction involves the occurrence of myocardial apoptosis. Due to the close resemblance between this experimental model of dilated cardiomyopathy and human heart failure, the results of this study provide evidence that IGF-I may be a potential therapeutic agent for the failing human heart.

Endocrine predictors of acute hemodynamic effects of growth hormone in congestive heart failure

BACKGROUND

The aim of our study was to assess whether there could be any clinical and/or endocrine (spontaneous growth hormone [GH] secretion rate, baseline insulin-like growth factor-1 [IGF-1]) predictors and/or determinants of the acute effects of continuous intravenous infusion of recombinant human GH on hemodynamic parameters in 12 patients with dilated cardiomyopathy and congestive heart failure (CHF).

METHODS AND RESULTS

The study involved 12 male patients with chronic CHF (ischemic in 8 patients and idiopathic in 4). Ten patients were in New York Heart Association functional class III or IV and 2 in class II. The first 24 hours were considered the control period; in fact, during the following 24 hours, all the patients underwent intravenous constant pump infusion of recombinant human GH. Blood samples for GH assay were taken every 20 minutes during the first night of the study (from 10 PM to 6 AM). Moreover, blood samples for GH assay were also taken during exogenous GH infusion. Blood samples for IGF-1 assays were taken at 8 AM of each of the 3 days of the study. Pulmonary artery pressure (PAP) and capillary wedge (PCWP) pressure, cardiac index, and arterial blood pressure were measured 30 minutes after right heart catheterization (baseline 1), at the end of the control period (baseline 2), and every 4 hours during GH infusion. A negative correlation has been found between mean nocturnal GH levels and baseline IGF-1 levels (r = -0.47, P =.124) and between mean nocturnal GH levels and both postinfusion absolute (r = -0.67, P <.05) and delta (postinfusion-preinfusion) (r = -0.58; P < 005) IGF-1 levels. No significant correlations have been found between several parameters of liver function (albumin, bilirubin, and pseudocholinesterase) and mean nocturnal GH. However, baseline IGF-1 levels showed a negative significant correlation (r = -0.76, P <.01) with total bilirubin and a positive correlation (r = 0.72, P <.01) with pseudocholinesterase. Baseline IGF-1 levels showed a significant negative correlation with baseline mean PAP (r = -0.68, P <.05) and PCWP (r = -0.70, P <.05) and a positive correlation with baseline cardiac index (r = 0.71, P <.05). Baseline IGF-1 levels also showed a significant negative correlation with absolute mean PAP (r = -0.63, P <.05) and mean PCWP (r = -0.67, P <.05) after GH infusion. After GH infusion, IGF-1 levels also negatively correlated with post-GH infusion mean PAP (r = -0.50, P =.09) and mean PCWP (r = -0.66, P <.05). The positive correlation between either baseline or postinfusion IGF-1 and the postinfusion cardiac index (r = 0.40 and 0.43, respectively) did not reach statistical significance.

CONCLUSIONS

GH has acute functional effects on the heart in patients with CHF, including both an increase in myocardial contractility and a decrease in vascular resistances, and among patients with CHF, those with low baseline IGF-1 are likely to have fewer beneficial effects from GH infusion.

IGF-I in experimental daunorubicin-induced cardiomyopathy in rabbits

1. The occurrence of IGF-I was investigated in rabbits with experimentally daunorubicin-induced cardiomyopathy. IGF-I was measured in the heart, serum, liver and skeletal muscle. 2. A significant increase in the IGF-I was found in the left heart ventricle in daunorubicin cardiomyopathy (152.9 +/- 10.0 ng/g vs 95.1 +/- 4.2 ng/g in the control group). This site of increased IGF-I activity corresponded well with the maximum of morphological changes (dispersed cytolysis of cardiomyocytes mostly without developed subsequent interstitial myofibrosis). 3. The highest levels of IGF-I were present in right and left cardiac atrium (but without significant differences between the groups). Furthermore, in skeletal muscle, the levels of IGF-I in the daunorubicin group (839.0 +/- 142.1 ng/g) were significantly higher in comparison with the control group (482.5 +/- 83.1 ng/g). 4. The level of IGF-I in the left ventricle in the daunorubicin group (but not in the control group) was significantly higher than that in the liver. There were no correlations observed between the levels of IGF-I in the heart and in the serum. 5. The increase in IGF-I concentrations in the left heart ventricle after the administration of daunorubicin may thus reflect possible autocrine/paracrine role of IGF-I in cardiomyopathy.

Growth hormone preserves cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors) and enhances cardiac function in cardiomyopathic hamsters

OBJECTIVE

Growth hormone (GH) improves cardiac function in experimental models of heart failure and human dilated cardiomyopathy. However, the mechanism by which GH increases myocardial contractility is not entirely clear. Our aim was to examine the effects of GH on cardiac function and cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors, RyR) in the hearts of UM-X7.1 cardiomyopathic hamsters during the development of heart failure.

METHODS

Experimental and healthy control hamsters were examined at the age of 20 weeks. Recombinant human GH (2 mg/kg/day, s.c.) or vehicle was then administered for 3 weeks. We examined (i) the in vivo left ventricular (LV) size and LV systolic function using transthoracic echocardiography, (ii) the density (Bmax) and affinity (Kd) of high-affinity [3H] ryanodine binding sites in crude homogenates from normal and cardiomyopathic hamster hearts.

RESULTS

Vehicle-treated UM-X7.1 hamsters exhibited significant increases in left ventricular end-diastolic diameter and end-systolic diameter (LVESd), and a significant decrease in LV fractional shortening (FS). GH-treatment attenuated the increase in LVESd and reduced the LV chamber size, and also significantly increased LVFS. Vehicle-treated UM-X7.1 hamsters exhibited a significantly lower Bmax than control hamsters (0.34 +/- 0.04 vs 0.44 +/- 0.06 pmol/mg, p < 0.05), and the treatment with GH in UM-X7.1 hamsters significantly attenuated the reduction of Bmax (0.42 +/- 0.03 pmol/mg vs vehicle-treated group (0.34 +/- 0.04 pmol/mg), p < 0.05). Kd did not differ significantly between the experimental groups. In normal control hamsters, GH treatment with this dose did not significantly enhance LV systolic function or the density of RyRs. There was no significant difference in terms of the connective-tissue volume-fraction, myocyte size and capillary density between the GH- and vehicle-treated groups of UM-X7.1 hamsters.

CONCLUSIONS

GH treatment may improve cardiac function by preserving the density of RyRs and enhancing cellular function in cardiomyopathic hamster hearts.

Regulation of cardiomyocyte apoptotic signaling by insulin-like growth factor I

Apoptosis is regulated by specific intracellular signaling pathways. The development of cardiomyopathy involves the apoptosis of cardiomyocytes; however, the details of their apoptotic signaling are not yet known. Insulin-like growth factor I (IGF I) is an important survival growth factor for myocardium and other tissues, but the effects of IGF I on apoptotic signaling remain largely unknown. To study apoptotic signaling pathways in cardiomyocytes and to understand IGF I actions on the apoptotic signaling of cardiac muscle cells, we have defined the effects of IGF I on Bcl-2, Bax, caspase 3, DNA fragmentation, and cell survival in primary cardiomyocytes. Compared with Bax levels, the levels of Bcl-2 were found to be quite low in these cells. Serum withdrawal and doxorubicin reduced cell viability, increased fragmentation of DNA, increased cellular contents of Bax, and activated caspase 3. IGF I enhanced cell viability, suppressed DNA fragmentation, attenuated Bax induction, and suppressed caspase 3 activation. The levels of Bcl-2-associated Bax were increased after serum withdrawal and incubation with doxorubicin and were reduced by IGF I. Thus, cardiomyocyte apoptosis induced by serum withdrawal and doxorubicin likely results, in part, from the induction of Bax and activation of caspase 3, but IGF I may inhibit cardiomyocyte apoptosis by attenuating Bax induction and caspase 3 activation. These findings provide new insight into the mechanisms of cardiomyocytes apoptosis and may help elucidate how IGF I modulates apoptotic signaling in cardiac muscle.

IGF I induction of p53 requires activation of MAP kinase in cardiac muscle cells

The aim of this study was to investigate whether IGF I induction of p53 expression and p21 promoter require activation of MAP kinase in cardiac muscle cells. Compared to cardiomyocytes transfected with control vector, activation of MAP kinase by IGF I was decreased by approximately 60-70% in the cells transfected with dominant negative MAP kinase Y185. Transfection with Y185 also resulted in decreased induction of p53 mRNA by IGF I (70% reduction). In the cells transfected with a wildtype p21WAF1/CIP1 promoter construct, activation of luciferase reporter gene by IGF I was decreased in the cells co-transfected with Y185. To further confirm these findings, cells were preincubated with PD98059, a specific MAP kinase kinase inhibitor. As expected, PD98059 inhibited induction of p53 mRNA and p21WAF1/CIP1 promoter by IGF I. These data indicate that transcriptional activation of p53 and p21WAF1/CIP1 by IGF I involves MAP kinase pathway in cardiomyocytes, and thus link MAP kinase to negative modulation of the cell cycle in cardiac muscle cells.

Continuous administration of insulin-like growth factor-I and basic fibroblast growth factor does not affect left ventricular geometry after acute myocardial infarction in rats

We examined the long-term effect of exogenous administration of bFGF and IGF-I on myocardial geometry in 72 Sprague-Dawley male rats subjected to AMI. A preloaded miniature osmotic pump subsequently implanted in the peritoneum for continuous infusion (1 week) of IGF-I, bFGF, IGF-I+bFGF or rat albumin. Six weeks following AMI the rats were killed and cross-section slices were analyzed for left ventricular geometry. No differences were observed between IGF-I-treated, bFGF-treated, IGF-I+bFGF-treated and control groups in all parameters of the left ventricle.

The role of insulin-like and basic fibroblast growth factors on ischemic and infarcted myocardium: a mini review

Current therapeutic techniques in acute myocardial infarction (AMI) are inadequate since restoration of blood flow through the obstructed coronary artery does not always preserve the ischemic myocardium. Therefore, deterioration of cardiac function and detrimental left ventricular remodeling may follow. Alternative therapeutic modalities are now being actively sought. Insulin-like growth factor (IGF) and fibroblast growth factor (FGF) are two polypeptides found in wide distribution and high concentrations in the normal myocardium. They play a key role in vascular growth (FGF) and affect the differentiation of cardiac myocytes (IGF). IGF has been found to promote physiological forms of cardiac hypertrophy, and FGF induces neovascularization. During myocardial ischemia and infarction there is a marked elevation in the concentration of these growth promoting factors in the myocardium concomitant with increased coronary collateral blood flow, neovascularization and peri-infarct hypertrophy. In animal models of myocardial infarction, exogenous administration of FGF and IGF induced neovascularization and cardiac hypertrophy thus, preserving cardiac function. We assume that these growth factors may become an additional tool in the future treatment of patients with AMI.

Differential cardiac effects of growth hormone and insulin-like growth factor-1 in the rat. A combined in vivo and in vitro evaluation

BACKGROUND

Despite their increasing clinical use and recent evidence that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) target the heart, there has been no systematic investigation of the effects of GH and IGF-1 on the cardiovascular system.

METHODS AND RESULTS

Sixty normal but growing adult female rats were randomized to receive 4 weeks of treatment with GH (3.5 mg.kg-1.d-1), IGF-1 (3 mg.kg-1.d-1), a combination of the two, or placebo. Transthoracic echocardiograms were performed at baseline and at 2 weeks and 4 weeks of treatment. After the final echocardiography, rats underwent either closed-chest left ventricular (LV) catheterization or Langendorff perfusion studies. Myocyte diameter and interstitial tissue fraction were assessed by morphometric histology. Echocardiographic and ex vivo data demonstrated a LV hypertrophic response in all three groups of treated animals that was most marked in the GH group, which alone exhibited a concentric growth pattern (relative wall thickness, 0.52 versus 0.42 to 0.44 in the other groups; P < .001). At 4 weeks, cardiac index was significantly higher and total systemic vascular resistance was lower in all groups of treated animals than in control animals (both P < .001), whereas arterial blood pressure did not differ significantly. All indexes of in vivo and in vitro cardiac function were higher in GH- and IGF-1-treated rats than in control animals, whereas combination therapy yielded a blunted effect. Myocyte diameter was increased in all three treated groups without an increase in interstitial tissue.

CONCLUSIONS

Exogenous administration of GH and IGF-1 in the normal adult rat induces a cardiac hypertrophic response without development of significant fibrosis. Cardiac performance is increased both in vivo and in the isolated heart.

Growth hormone improves cardiac performance in experimental heart failure

BACKGROUND

Growth hormone has been shown to increase maximum isometric active force of the left ventricular papillary muscle of rats in vitro. Administration of growth hormone causes an increase in myocardial contractility in normal humans. Our preliminary study suggests that treatment with growth hormone results in increased ventricular contractility in rats with left ventricular dysfunction. In the present study, the effects of growth hormone on cardiac function, including cardiac output, stroke volume, and peripheral vascular resistance, were determined in a rat model of heart failure.

METHODS AND RESULTS

Ligation of the left coronary artery or sham operation was performed; 4 weeks after surgery, recombinant human growth hormone (2 mg/kg per day SC) or vehicle then was administered for 15 days. The animals were catheterized after 13 days of the treatment. Cardiac output, measured by a thermodilution method, and other hemodynamic parameters were measured in the conscious animals 2 days after catheterization. The infarct sizes induced by left coronary ligation were comparable between growth hormone-treated and vehicle-treated rats. Six weeks after ligation, rats treated with vehicle exhibited significant decreases in cardiac index, stroke volume index, and left ventricular maximum dP/dt and increases in left ventricular end-diastolic pressure compared with sham rats. In the ligated rats, treatment with growth hormone increased cardiac index, stroke volume index, and left ventricular maximum dP/dt (P < .05) and reduced left ventricular end-diastolic pressure and systemic vascular resistance (P < .05). In sham rats, growth hormone slightly reduced arterial pressure but did not significantly alter cardiac performance. There was no significant difference in heart rate between the experimental groups.

CONCLUSIONS

These results suggest that growth hormone treatment may improve cardiac function by both increased myocardial contractility and decreased peripheral vascular resistance in heart failure.

Insulin-like growth factor-1 enhances ventricular hypertrophy and function during the onset of experimental cardiac failure

To determine whether additional hypertrophy would be beneficial or maladaptive in cardiac failure, the effects of insulin-like growth factor (IGF-1) were investigated in rats with left ventricular (LV) dysfunction. In normal rats, 3 mg/kg per d of recombinant human IGF-1 for 14 d augmented LV wt (32%) and increased LV/body wt ratio (P < 0.01). 2 d after coronary occlusion, rats were randomized to IGF-1 (3 mg/kg per d) or placebo. After 2 wk, IGF-1-treated rats showed significant increases in LV wt (13%) and LV wt/tibial length ratio, but LV/body wt ratio was unchanged. By microangiography, compared with controls (n = 12) IGF-1-treated rats (n = 16) showed increased LV end-diastolic volume (19%) and stroke volume (31%) (both significant normalized to tibial length, but not to body wt). Average infarct size did not differ between groups. The LV ejection fraction (EF) was not significantly different between groups, but estimated cardiac output was higher in treated rats; there was a significant interaction for the EF between infarct size and treatment (P = 0.029) and a trend for EF to be higher in treated rats with large infarctions (EF 33.4 vs 25.1% in controls). Myocyte cross-sectional areas in noninfarcted LV zones tended to be larger in treated rats (232.1 vs 205.4 microns 2; P = 0.10), but there was no difference in capillary density and collagen content did not differ between groups. In conclusion, IGF-1 administration caused hypertrophy of the normal heart in vivo. When stimulated by IGF-1, the severely dysfunctional heart in evolving myocardial infarction is capable of undergoing additional hypertrophy with evidence of improved function, suggesting a beneficial effect. Further investigation of the potential role of growth factor therapy in heart failure appears warranted.