Cardiac iron overload in thalassemic patients: an endomyocardial biopsy study

In vivo calibration of the T2* cardiovascular magnetic resonance method at 1.5 T for estimation of cardiac iron in a minipig model of transfusional iron overload

BACKGROUND

Non-invasive estimation of the cardiac iron concentration (CIC) by T2* cardiovascular magnetic resonance (CMR) has been validated repeatedly and is in widespread clinical use. However, calibration data are limited, and mostly from post-mortem studies. In the present study, we performed an in vivo calibration in a dextran-iron loaded minipig model.

METHODS

R2* (= 1/T2*) was assessed in vivo by 1.5 T CMR in the cardiac septum. Chemical CIC was assessed by inductively coupled plasma-optical emission spectroscopy in endomyocardial catheter biopsies (EMBs) from cardiac septum taken during follow up of 11 minipigs on dextran-iron loading, and also in full-wall biopsies from cardiac septum, taken post-mortem in another 16  minipigs, after completed iron loading.

RESULTS

A strong correlation could be demonstrated between chemical CIC in 55 EMBs and parallel cardiac T2* (Spearman rank correlation coefficient 0.72, P < 0.001). Regression analysis led to [CIC] = (R2* - 17.16)/41.12 for the calibration equation with CIC in mg/g dry weight and R2* in Hz. An even stronger correlation was found, when chemical CIC was measured by full-wall biopsies from cardiac septum, taken immediately after euthanasia, in connection with the last CMR session after finished iron loading (Spearman rank correlation coefficient 0.95 (P < 0.001). Regression analysis led to the calibration equation [CIC] = (R2* - 17.2)/31.8.

CONCLUSIONS

Calibration of cardiac T2* by EMBs is possible in the minipig model but is less accurate than by full-wall biopsies. Likely explanations are sampling error, variable content of non-iron containing tissue and smaller biopsies, when using catheter biopsies. The results further validate the CMR T2* technique for estimation of cardiac iron in conditions with iron overload and add to the limited calibration data published earlier.

Evaluation of myocardial perfusion and function in patients with asymptomatic beta-thalassemia major using myocardial gated single-photon-emission computed tomography

This study was conducted to evaluate the cardiac perfusion and function of patients with beta-thalassemia major (TM) using^99mTc-MIBI cardiac gated single-photon-emission computed tomography (SPECT) and to compare the obtained indices with echocardiographic and hematological parameters. Patients with TM who were referred for regular blood transfusion and periodic checkup were included in this study. A questionnaire containing demographic and medical data was provided for all patients by an expert pediatrician. All of the patients were on Desferal chelation therapy and none of them had clinical signs of heart failure. Myocardial gated perfusion SPECT, echocardiography, and complete blood tests were performed for each patient. In total, 24 patients including 14 men (58.3%) and 10 women (41.7%) aged 15-36 years with a mean age of 24.3 ± 6.5 years' old were enrolled in this study. Myocardial perfusion scan (MPS) was normal in all patients. The mean value of the measured left ventricular ejection fraction (LVEF) was 58.88 ± 13.45%. There was no significant association between measured LVEF on scan and echocardiography (P > 0.05). In terms of hematological results, there was a significant association between the hemoglobin and ferritin level and the amount of blood transfusion (P = 0.02 and P= 0.00, respectively). According to the results of myocardial perfusion imaging (MPI), cardiac perfusion and LVEF were within normal limits in all asymptomatic patients. In the absence of any perfusion abnormality, the use of MPI in patients with asymptomatic beta-TM is not recommended for diagnosing myocardial ischemia.

Myocardial deformation in iron overload cardiomyopathy: speckle tracking imaging in a beta-thalassemia major population

Traditional echocardiography is unable to detect neither the early stages of iron overload cardiomyopathy nor myocardial iron deposition. The aim of the study is to determine myocardial systolic strain indices in thalassemia major (TM), and assess their relationship with T2*, a cardiac magnetic resonance index of the severity of cardiac iron overload. 55 TM cases with recent cardiac magnetic resonance (CMR-T2*) underwent speckle tracking analysis to assess regional myocardial strains and rotation. The results were compared with a normal control group (n = 20), and were subsequently analyzed on the basis of the CMR-T2* values. Two TM groups were studied: TM with significant cardiac iron overload ("low" T2*, ≤20 ms; n = 21), and TM with normal T2* values ("normal" T2*, >20 ms; n = 34). TM patients show significant, uniform decrease in circumferential and radial strain (P < 0.05), and a remarkable reduction in end-systolic rotation, both global, and for all segments (P < 0.001). No significant differences were found between the low- and the normal T2* group either in regional strains and rotation or in standard echocardiographic and CMR parameters. Spearman's correlation coefficient shows no significant correlation between myocardial strains, rotation and cardiac T2* values. In conclusion, our results are in accordance with recent evidence that myocardial iron overload is not the only mechanism underlying iron cardiomyopathy in TM. Strain imaging can predict subclinical myocardial dysfunction irrespective of CMR-T2* values, although it cannot replace CMR-T2* in assessing cardiac iron overload. Finally, it might be useful to appropriately time cardioactive treatment.

Cardiac complications in beta-thalassemia: From mice to men

Beta-thalassemia is an inherited hemoglobin disorder caused by reduced or absent synthesis of the beta globin chains of hemoglobin. This results in variable outcomes ranging from clinically asymptomatic to severe anemia, which then typically requires regular blood transfusion. These regular blood transfusions can result in an iron overload condition. The iron overload condition can lead to iron accumulation in various organs, especially in the heart, leading to iron overload cardiomyopathy, which is the major cause of mortality in patients with thalassemia. In the past decades, there is no doubt that the use of β-thalassemic mice as a study model to investigate the pathophysiology of iron overload cardiomyopathy and the role of various pharmacological interventions, has shed some light in understanding this serious complication and in improving the associated cardiac dysfunction. In this review, the effects that iron overload has on the hearts of β-thalassemic mice under conditions of iron overload as well as the efficacy of pharmacological interventions to combat these adverse effects on the heart are reviewed and discussed. The in-depth understanding of biomolecular alterations in the heart of these iron overload thalassemic mice will help give guidance for more effective therapeutic approaches in the near future. Impact statement Iron overload cardiomyopathy is a major cause of morbidity and mortality in patients with thalassemia. Since investigation of iron overload cardiomyopathy in thalassemia patients has many limitations, a search for an animal model for this condition has been ongoing for decades. In the past decades, there is no doubt that the use of β-thalassemic mice as a study model to investigate the pathophysiology of iron overload cardiomyopathy and the role of various pharmacological interventions, has shed some light in understanding this serious complication and in improving the associated cardiac dysfunction. In this review, the effects of iron overload on the hearts of β-thalassemic mice under conditions of iron overload as well as the efficacy of pharmacological interventions to combat these adverse effects on the heart are reviewed and discussed.

Histopathology of thalassemic heart disease: an endomyocardial biopsy study

Right ventricle endomyocardial biopsies were obtained from 13 thalassemic patients. Clinical profiles were investigated, and serum ferritin tests were assessed using diagnostic kits. Histochemical iron detection (Perls method) and immunohistochemical stain for ferritin were performed in the endomyocardial samples. Histologic iron overload was observed in eight patients, and variable iron deposits were recognized by a semiquantitative method. There was a statistically evident correlation between serum ferritin and myocardial iron storage. Marked iron deposition was associated with higher immunohistologic ferritin concentration. Iron-negative tissue samples showed bland immunohistochemical positivity. Myocardial interstitial fibrosis was observed in 12 cases; diffuse perimyocytic or perivascular fibrosis and endocardium thickening were the main histologic patterns identified. One biopsy was characterized by marked fibrolipomatous infiltration. Myocyte hypertrophy, myocytolysis, and severe capillary congestion also were observed.

Deferasirox for the treatment of iron overload in non-transfusion-dependent thalassemia

Non-transfusion-dependent thalassemia (NTDT) defines a group of patients who do not require regular transfusions for survival, but are at significant risk of iron accumulation from underlying disease-related mechanisms distinct from transfusional iron overload. Management of iron overload in NTDT has received little attention compared with that of β-thalassemia major, despite evidence of significant iron-induced complications with advancing age. The efficacy and safety of the iron chelator deferasirox in NTDT has been evaluated in two pilot studies and the first prospective, randomized, placebo-controlled study (THALASSA) of any chelator in NTDT. Treatment with deferasirox for up to 2 years yielded a sustained reduction in iron burden, with a clinically manageable safety profile. Following these trial data, deferasirox is the first iron chelator approved for use in NTDT patients, and with NTDT guidelines now available, physicians are better equipped to achieve effective monitoring and management of iron burden in NTDT.

Evidence for a novel mechanism independent of myocardial iron in β-thalassemia cardiac pathogenesis

Human β-thalassemia major is one of the most prevalent genetic diseases characterized by decrease/absence of β-globin chain production with reduction of erythrocyte number. The main cause of death of treated β-thalassemia major patients with chronic blood transfusion is early cardiac complications that have been attributed to secondary iron overload despite optimal chelation. Herein, we investigated pathophysiological mechanisms of cardiovascular dysfunction in a severe murine model of β-thalassemia from 6 to 15-months of age in the absence of confounding effects related to transfusion. Our longitudinal echocardiography analysis showed that β-thalassemic mice first display a significant increase of cardiac output in response to limited oxygen-carrying erythrocytes that progressed rapidly to left ventricular hypertrophy and structural remodeling. Following this compensated hypertrophy, β-thalassemic mice developed age-dependent deterioration of left ventricular contractility and dysfunction that led toward decompensated heart failure. Consistently, murine β-thalassemic hearts histopathology revealed cardiac remodeling with increased interstitial fibrosis but virtual absence of myocardial iron deposits. Importantly, development of thalassemic cardiac hypertrophy and dysfunction independently of iron overload has uncoupled these cardiopathogenic processes. Altogether our study on β-thalassemia major hemoglobinopathy points to two successive phases resulting from severe chronic anemia and from secondarily induced mechanisms as pathophysiologic contributors to thalassemic cardiopathy.

Iron overload in non-transfusion-dependent thalassemia: a clinical perspective

Iron overload due to increased intestinal iron absorption represents an important clinical problem in patients with non-transfusion-dependent thalassemia (NTDT), particularly as they advance in age. Current models for iron metabolism in patients with beta (β)-thalassemia intermedia (TI) suggest that suppression of serum hepcidin results in increased iron absorption and release of iron from the reticuloendothelial system, leading to depletion of macrophage iron, relatively low levels of serum ferritin, and liver iron loading. The clinical consequences of iron overload in patients with NTDT are multifactorial and include endocrinopathy, bone disease, thromboembolism, pulmonary hypertension, cerebrovascular and neuronal damage, liver fibrosis or cirrhosis, and increased risk of hepatocellular carcinoma. Although serum ferritin levels correlate with liver iron concentration (LIC), they underestimate iron load in these patients compared with transfusion-dependent patients with equivalent LIC. Therefore, direct measurement of LIC is recommended with chelation therapy as indicated.

d-Propranolol protects against oxidative stress and progressive cardiac dysfunction in iron overloaded rats

d-Propranolol (d-Pro: 2-8 mg·(kg body mass)(-1)·day(-1)) protected against cardiac dysfunction and oxidative stress during 3-5 weeks of iron overload (2 mg Fe-dextran·(g body mass)(-1)·week(-1)) in Sprague-Dawley rats. At 3 weeks, hearts were perfused in working mode to obtain baseline function; red blood cell glutathione, plasma 8-isoprostane, neutrophil basal superoxide production, lysosomal-derived plasma N-acetyl-β-galactosaminidase (NAGA) activity, ventricular iron content, and cardiac iron deposition were assessed. Hearts from the Fe-treated group of rats exhibited lower cardiac work (26%) and output (CO, 24%); end-diastolic pressure rose 1.8-fold. Further, glutathione levels increased 2-fold, isoprostane levels increased 2.5-fold, neutrophil superoxide increased 3-fold, NAGA increased 4-fold, ventricular Fe increased 4.9-fold; and substantial atrial and ventricular Fe-deposition occurred. d-Pro (8 mg) restored heart function to the control levels, protected against oxidative stress, and decreased cardiac Fe levels. After 5 weeks of Fe treatment, echocardiography revealed that the following were depressed: percent fractional shortening (%FS, 31% lower); left ventricular (LV) ejection fraction (LVEF, 17%), CO (25%); and aortic pressure maximum (P(max), 24%). Mitral valve E/A declined by 18%, indicating diastolic dysfunction. Cardiac CD11b+ infiltrates were elevated. Low d-Pro (2 mg) provided modest protection, whereas 4-8 mg greatly improved LVEF (54%-75%), %FS (51%-81%), CO (43%-78%), P(max) (56%-100%), and E/A >100%; 8 mg decreased cardiac inflammation. Since d-Pro is an antioxidant and reduces cardiac Fe uptake as well as inflammation, these properties may preserve cardiac function during Fe overload.

β-thalassemia intermedia: a clinical perspective

Our understanding of the molecular and pathophysiological mechanisms underlying the disease process in patients with β-thalassemia intermedia has substantially increased over the past decade. Earlier studies observed that patients with β-thalassemia intermedia experience a clinical-complications profile that is different from that in patients with β-thalassemia major. In this article, a variety of clinical morbidities are explored, and their associations with the underlying disease pathophysiology and risk factors are examined. These involve several organs and organ systems including the vasculature, heart, liver, endocrine glands, bone, and the extramedullary hematopoietic system. The effects of some therapeutic interventions on the development of clinical complications are also discussed.

Diagnostic Biopsies of the Native Heart

Endomyocardial biopsy in the nontransplant setting can be diagnostic for particular diseases. Such disorders include amyloidosis, myocarditis, sarcoidosis, iron overload, glycogen storage disorders, and lysosomal storage disorders. The diagnostic features of these disorders on endomyocardial biopsy will be discussed along with the impact of endomyocardial biopsy-based diagnoses on patient management and prognosis.

2011 consensus statement on endomyocardial biopsy from the Association for European Cardiovascular Pathology and the Society for Cardiovascular Pathology

The Association for European Cardiovascular Pathology and the Society for Cardiovascular Pathology have produced this position paper concerning the current role of endomyocardial biopsy (EMB) for the diagnosis of cardiac diseases and its contribution to patient management, focusing on pathological issues, with these aims: • Determining appropriate EMB use in the context of current diagnostic strategies for cardiac diseases and providing recommendations for its rational utilization • Providing standard criteria and guidance for appropriate tissue triage and pathological analysis • Promoting a team approach to EMB use, integrating the competences of pathologists, clinicians, and imagers.

Establishment of secondary iron overloaded mouse model: evaluation of cardiac function and analysis according to iron concentration

Periodic blood transfusion can lead to secondary iron overload in patients with hematologic and oncologic diseases. Iron overload can result in iron deposition in heart tissue, which decreases cardiac function and can ultimately lead to death due to dilated cardiomyopathy and cardiac failure. In this study, we established murine model of secondary iron overload, studied the changes in cardiac function with echocardiography, and examined the histopathologic changes. Three experimental groups of the six week-old C57/BL mice (H-2(b)) were injected intraperitoneally with 10 mg of iron dextran daily 5 days a week for 2, 4, and 6 weeks. Cumulative doses of iron for the three experimental groups were 100, 200, and 300 mg, while the control groups were injected with the same amounts of phosphate-buffered saline. We studied the cardiac function under anesthesia with echocardiography using a GE Vivid7 Dimension system. Plasma iron levels and liver iron contents were measured. The hearts and livers were harvested and stained with H&E and Perls Prussian blue for iron, and the levels of iron deposit were examined. We assessed the cardiac measurements after adjustment for weight. On echocardiography, thicknesses of the interventricular septum and posterior ventricular wall (PS) during diastole showed correlation with the amount of iron deposit (P < 0.01). End-diastolic volume showed dilatation of the left ventricle in the 300 mg group (P < 0.01). Changes in the fractional shortening were not statistically significant (P = 0.07). Plasma iron levels and liver iron contents were increased proportionally according to the amount of iron loaded. The histopathologic findings of PS and liver showed higher grade of iron deposit proportional to the cumulated iron dose. In this study, we present an animal model which helps understand the cardiac function changes in patients with secondary iron overload due to repeated blood transfusions. Our results may help characterize the pathophysiologic features of cardiomyopathy in patients with secondary iron overload, and our model may be applied to in vivo iron-chelating therapy studies.

Iron overload decreases CaV1.3-dependent L-type Ca2+ currents leading to bradycardia, altered electrical conduction, and atrial fibrillation

BACKGROUND

Chronic iron overload (CIO) is associated with blood disorders such as thalassemias and hemochromatosis. A major prognostic indicator of survival in patients with CIO is iron-mediated cardiomyopathy characterized by contractile dysfunction and electrical disturbances, including slow heart rate (bradycardia) and heart block.

METHODS AND RESULTS

We used a mouse model of CIO to investigate the effects of iron on sinoatrial node (SAN) function. As in humans, CIO reduced heart rate (≈20%) in conscious mice as well as in anesthetized mice with autonomic nervous system blockade and in isolated Langendorff-perfused mouse hearts, suggesting that bradycardia originates from altered intrinsic SAN pacemaker function. Indeed, spontaneous action potential frequencies in SAN myocytes with CIO were reduced in association with decreased L-type Ca(2+) current (I(Ca,L)) densities and positive (rightward) voltage shifts in I(Ca,L) activation. Pacemaker current (I(f)) was not affected by CIO. Because I(Ca,L) in SAN myocytes (as well as in atrial and conducting system myocytes) activates at relatively negative potentials due to the presence of Ca(V)1.3 channels (in addition to Ca(V)1.2 channels), our data suggest that elevated iron preferentially suppresses Ca(V)1.3 channel function. Consistent with this suggestion, CIO reduced Ca(V)1.3 mRNA levels by ≈40% in atrial tissue (containing SAN) and did not lower heart rate in Ca(V)1.3 knockout mice. CIO also induced PR-interval prolongation, heart block, and atrial fibrillation, conditions also seen in Ca(V)1.3 knockout mice.

CONCLUSIONS

Our results demonstrate that CIO selectively reduces Ca(V)1.3-mediated I(Ca,L), leading to bradycardia, slowing of electrical conduction, and atrial fibrillation as seen in patients with iron overload.

Iron overload cardiomyopathy: better understanding of an increasing disorder

The prevalence of iron overload cardiomyopathy (IOC) is increasing. The spectrum of symptoms of IOC is varied. Early in the disease process, patients may be asymptomatic, whereas severely overloaded patients can have terminal heart failure complaints that are refractory to treatment. It has been shown that early recognition and intervention may alter outcomes. Biochemical markers and tissue biopsy, which have traditionally been used to diagnose and guide therapy, are not sensitive enough to detect early cardiac iron deposition. Newer diagnostic modalities such as magnetic resonance imaging are noninvasive and can assess quantitative cardiac iron load. Phlebotomy and chelating drugs are suboptimal means of treating IOC; hence, the roles of gene therapy, hepcidin, and calcium channel blockers are being actively investigated. There is a need for the development of clinical guidelines in order to improve the management of this emerging complex disease.

Iron-loaded cardiac myocytes stimulate cardiac myofibroblast DNA synthesis

Cardiac fibrosis in iron overload disorders may arise from activation of the interstitial fibroblast. However, the cardiac myocyte, and not the fibroblast, is the main target for iron deposition. We hypothesized that fibroblasts respond to the presence of iron-loaded myocytes with increased proliferative capacity. Cardiac fibroblasts were either co-cultured with myocytes on porous filters or treated with medium conditioned by growth of myocyte cultures. In both circumstances myocytes suppressed [(3)H]thymidine incorporation by fibroblasts over 24 h, compared to stimulation of quiescent fibroblasts with fresh, unconditioned medium. However, when the myocytes were preloaded with iron, the suppressive effect was lost and DNA synthesis was restored to levels seen in unconditioned medium. This effect was not due to early events in cell cycle entry; activation of Erk at 15 min and expression of c-fos mRNA at 30 min were similar in media from control and iron-loaded myocytes. Early markers of progression of G1, namely cyclin D and phosphoretinoblastoma protein, were not significantly different in fibroblasts treated with either conditioned medium. However, cyclin E expression, a marker of the G1/S transition, was significantly increased by conditioned medium from the iron-loaded cells, compared to control-conditioned medium. We conclude that myocytes can suppress proliferation of fibroblasts by cumulative effects on late G1 events leading to DNA synthesis, and these effects are diminished with myocyte iron accumulation.

Antioxidant and lysosomotropic properties of acute D-propranolol underlies its cardioprotection of postischemic hearts from moderate iron-overloaded rats

The benefits of acute D-propranolol (D-Pro, non-beta-adrenergic receptor blocker) pretreatment against enhanced ischemia/reperfusion (I/R) injury of hearts from moderate iron-overloaded rats were examined. Perfused hearts from iron-dextran-treated rats (450 mg/kg/week for 3 weeks, intraperitoneal administration) exhibited normal control function, despite iron treatment that elevated plasma iron and conjugated diene levels by 8.1-and 2.5-fold, respectively. However, these hearts were more susceptible to 25 mins of global I/R stress compared with non-loaded hearts; the coronary flow rate, aortic output, cardiac work, left ventricular systolic pressure, positive differential left ventricular pressure (dP/dt), and left ventricular developed pressure displayed 38%, 60%, 55%, 13%, 41%, and 15% lower recoveries, respectively, and a 6.5-fold increase in left ventricular end-diastolic pressure. Postischemic hearts from iron-loaded rats also exhibited 5.6-, 3.48-, 2.43-, and 3.45-fold increases in total effluent iron content, conjugated diene levels, lactate dehydrogenase (LDH) activity, and lysosomal N-acetyl-beta-glucosaminidase (NAGA) activity, respectively, compared with similarly stressed non-loaded hearts. A comparison of detection time profiles during reperfusion suggests that most of the oxidative injury (conjugated diene) in hearts from iron-loaded rats occurred at later times of reperfusion (8.5-15 mins), and this corresponded with heightened tissue iron and NAGA release. D-Pro (2 microM infused for 30 mins) pretreatment before ischemia protected all parameters compared with the untreated iron-loaded group; pressure indices improved 1.2- to 1.6-fold, flow parameters improved 1.70- to 2.96-fold, cardiac work improved 2.87-fold, and end-diastolic pressure was reduced 56%. D-Pro lowered total release of tissue iron, conjugated diene content, LDH activity, and NAGA activity 4.59-, 2.55-, 3.04-, and 4.14-fold, respectively, in the effluent of I/R hearts from the iron-loaded group. These findings suggest that the enhanced postischemic dysfunction and tissue injury of hearts from iron-loaded rats was caused by excessive iron-catalyzed free radical stress, and that the membrane antioxidant properties of D-Pro and its stabilization of sequestered lysosomal iron by D-Pro may contribute to the cardioprotective actions of D-Pro.

An approach to endomyocardial biopsy interpretation

The endomyocardial biopsy (EMB) remains the gold standard mode of investigation for diagnosing many primary and secondary cardiac conditions. Through a percutaneous and transvenous route, tissue fragments are generally procured from the right ventricular septum, with very few complications. Widespread use of EMB followed the development of heart transplantation as a means to follow allograft rejection. It has since been useful in helping to diagnose conditions affecting the heart, including cardiomyopathies, myocarditis, infiltrative lesions, arrhythmias, and drug toxicities. The procedure has also been used as a research tool to investigate the natural history of disease and the cardiotoxicity of new medications. This review presents an approach to the evaluation of the EMB, which is particularly directed towards those who may be asked to interpret such biopsies, but are not dedicated cardiovascular pathologists. Through a systematic evaluation of the endocardium, myocardium, interstitium, and intramural vessels, in the context of a complete clinical history, enough information can be deduced to diagnose or exclude specific conditions of clinical value.

Assessment of cardiac function in iron-deficient children without anemia

Iron deficiency anemia may lead to impairment of many vital functions, including those in the cardiovascular system. However, the effects of iron depletion on cardiac function in the absence of anemia are not well known. In this study the authors examined the effects of iron deficiency without overt anemia on cardiac function in 59 children. Complete blood count, serum iron, serum iron-binding capacity, and serum ferritin levels were measured in all children. The children were divided into two groups according to serum ferritin levels: an iron-depleted group (n = 28) and a non-iron-depleted control group (n = 31). Echocardiographic examinations were performed using M mode and Doppler echocardiographic methods in all children to assess cardiac function. No statistically significant difference was found between the two groups in terms of echocardiographic indices. Although the number of subjects in this study was small, the authors conclude that iron deficiency in the absence of overt anemia does not lead to important changes in cardiac function.

Endomyocardial biopsy for non-transplant-related disorders

Endomyocardial biopsy (EMB) remains the "gold standard" for diagnosing rejection after cardiac transplantation. In addition, it has value in monitoring patients during treatment with doxorubicin. It also is important in the setting of acute-onset heart failure for the diagnosis of myocarditis, particularly giant cell myocarditis because earlier transplantation usually is undertaken in patients with giant cell morphologic features. EMB has a role in the unexplained cardiomyoapthy for excluding specific disease processes that might lead to similar morphofunctional changes but might be reversible or a contraindication for transplantation. This review focuses on the growing number of diseases that can be diagnosed by EMB in adult and pediatric age groups.

Genetic regulation of cell function in response to iron overload or chelation

Iron influences many aspects of cell function on different biochemical levels. This review considers effects mediated through iron-dependent changes in gene expression in mammalian cells. Several classes of related genes are responsive to cellular iron levels, but no clear patterns readily account for the toxicity of iron overload or the consequences of removal of iron with chelating agents. Here we group some of the genes influenced by iron status into those related to iron metabolism, oxygen and oxidative stress, energy metabolism, cell cycle regulation, and tissue fibrosis. Iron excess and chelation do not generally result in a continuous or graded transcriptional response, but indicate operation of distinct mechanisms. An emerging concept is that iron signals through generation of reactive oxygen species to activate transcription factors such as NF-kappaB, whereas iron removal mimics hypoxia, perhaps by disrupting iron-based O(2) sensors and influencing gene expression through, e.g., the hypoxia-inducible factor, HIF-1. Heme and other metalloporphyrins have other distinct mechanisms for regulating transcription. Regulation of gene expression through iron-responsive elements in mRNAs coded by several genes is one of the best understood mechanisms of translational control.

Iron metabolism in mice with partial frataxin deficiency

Friedreich ataxia (FRDA), the most common autosomal recessive inherited ataxic disorder, is the consequence of deficiency of the mitochondrial protein frataxin, typically caused by homozygous intronic GAA expansions in the corresponding gene. The yeast frataxin homologue (yfh1p) is required for cellular respiration. Yfh1p appears to regulate mitochondrial iron homeostasis and protect from free radical toxicity. Complete loss of frataxin in knockout mice leads to early embryonic lethality, indicating an important role for frataxin during development. Heterozygous littermates with partial frataxin deficiency are apparently healthy and have no obvious phenotype. Here we evaluate iron metabolism and sensitivity to dietary and parenteral iron loading in heterozygote frataxin knockout mice (Fx(+/-)). Iron concentrations in the liver, heart, pancreas and spleen, and cellular iron distribution patterns were compared between wild type and Fx(+/-) mice. Response to parenteral iron challenge was not different between Fx(+/-) mice and wild type littermates, while sporadic iron deposits were observed in the hearts of dietary iron-loaded Fx(+/-) mice. Finally, we evaluated the effect of partial frataxin deficiency on susceptibility to cardiac damage in the mouse model of hereditary hemochromatosis (HH), the Hfe knockout mice. HH, an iron overload disease, is one of the most frequent genetic diseases in populations of European origin. By breeding Hfe(-/-) with Fx(+/-) mice, we obtained compound mutant mice lacking both Hfe and one frataxin allele. Sparse iron deposits in areas of mild to moderate cardiac fibrosis were found in the majority of these mice. However, they did not develop any neurological symptoms. Our studies indicate an association between frataxin deficiency, iron deposits and cardiac fibrosis, but no obvious association between iron accumulation and neurodegeneration similar to FRDA could be detected in our model. In addition, these results suggest that frataxin mutations may have a modifier role in HH, that predisposes to cardiomyopathy.

Clinical management of beta-thalassemia major

Management of patients with beta-thalassemia is based on adequate, safe blood transfusions (free of transfusion-transmitted diseases) and prevention of iron overload. Iron overload causes multiple endocrinopathies, contributes to osteoporosis, and is the cause of cardiac disease. Cardiac disease, secondary to iron damage, causes death in developed countries as a result of noncompliance to deferoxamine from the third decade of life. In underdeveloped countries, cardiac death starts from 12 years of age, due to nonavailability of deferoxamine. With the emergence of the advanced cardiac magnetic resonance imaging technique, early diagnosis of heart iron will allow the currently available iron-chelating agents (oral and parenteral) to be used in an innovative way to improve the quality of life and improve survival of patients with beta-thalassemia.

Changes in gene expression with iron loading and chelation in cardiac myocytes and non-myocytic fibroblasts

Iron overload is associated with long-term cardiac iron accumulation and tissue changes such as fibrosis. To determine short-term iron-dependent changes in expression of genes associated with iron homeostasis and fibrosis we measured mRNA on Northern blots prepared from cultured rat neonatal cardiomyocytes and non-myocytes (fibroblasts) as a function of iron loading and chelation. Transferrin receptor mRNA was reduced in myocytes exposed to various concentrations of iron for 3 days and this decline was associated with a 63% decline in iron-response element (IRE) binding of iron regulatory protein-1, indicating that myocytes utilize IRE-dependent mechanisms to modulate gene expression. In myocytes iron caused a dose-dependent decline in mRNAs coding for transforming growth factor- beta(1)(TGF- beta(1)), biglycan, and collagen type I while plasminogen activator inhibitor-1 mRNA was unaffected by iron loading and decorin mRNA doubled. Total TGF- beta bioactivity was also decreased by iron loading. Thus, the effects of iron loading on genes related to cardiac fibrosis are gene-specific. Addition of deferoxamine for 1 day did not have any significant effect on any of these genes. Parallel changes in gene expression were exhibited by non-myocytes (fibroblasts), where chelation also decreased TGF- beta(1)mRNA and activity, and mRNA for collagen type I and biglycan, and collagen synthesis. In addition to these changes in transcripts associated with matrix formation the mRNA of the metabolic enzyme glyceraldehyde-3-phosphate dehydrogenase was unaffected by iron loading but doubled in both cell types upon treatment with deferoxamine. These findings suggest that in both cardiac myocytes and non-myocyte fibroblasts gene expression is coupled to intracellular iron pools by gene-specific and IRE-dependent and idependent mechanisms. This linkage may influence matrix deposition, a significant component of cardiac injury.

Evaluation of cardiac functions in patients with thalassemia major

It is known that a blood transfusion is necessary for survival in patients with thalassemia, but it may cause myocardial dysfunction due to myocardial siderosis as in other organs. The aim of this study was to evaluate myocardial perfusion by means of stress thallium scanning (MPS) and left ventricular functions by rest radionuclide ventriculography (RNV). Twenty-one patients at ages 9-16 (mean 12.1 +/- 3.2) who have been diagnosed with thalassemia for 4-15 years (mean 12.7 +/- 4.8) were included in the study. They had blood transfusions 78-318 times (mean 162.1 +/- 71). MPS and RNV was performed within two days after the any transfusion. MPS showed ischemia in 3 patients and normal perfusion in 18 patients. RNV revealed normal systolic parameters (wall motion, EF, PER, TPE) but diminished diastolic parameters (TPF, PFR) compared with normal values (p < 0.05). We conclude that ischemia or fixed defects may be seen in stress MPS as a result of cardiac involvement in patients with thalassemia. But, RNV is an important and preferable test for the early detection of subclinic cardiomyopathy. RNV may therefore show diastolic abnormalities before the systolic abnormalities show up.