Nrf2 Plays a Key Role in Iron-Overload Cardiomyopathy

Cardiomyopathy due to iron-overload is a severe complication of patients undergoing chronic transfusion regimen such as β-thalassemia and myelodysplastic syndromes. Previous studies have shown the key role of Nrf2, a redox-related transcriptional factor, in both β-thalassemia erythropoiesis and iron homeostasis (Matte A et al. ARS 2018, 2019; Lim PJ et al Nat Metab, 2019). Here, we compared Nrf2 knockout male mice (Nrf2 -/-) and C57BL-6J as wild-type (WT) controls, with a focus on cardiac function. Nrf2 -/- mice were characterized by a mild chronic hemolytic anemia associated with ineffective erythropoiesis, similar to what observed in murineβ-thalassemia (Toya SCM et al., Blood, 2019). Aging Nrf2 -/- mice developed systolic and diastolic dysfunction, associated with increased cardiac oxidative stress, degradation of the calcium-dependent SERCA2A transporter and activation of metalloproteinase MMP9, involved in both SERCA2A degradation and heart remodeling. In Nrf2 -/- mice, we observed increased plasma NTBI, heart iron deposition and elevated expression of cardiac ferroportin when compared to WT animals. Moreover, cardiac Hamp mRNA levels were down-regulated in aging Nrf2 -/- mice when compared to WT mice. This pattern was consistent with progressive cardiac iron overload in absence of Nrf2. Interestingly, activation of TGF-b receptor and PDGF-B-related pathway as well as increased collagen deposition were observed in hearts from 12 months old Nrf2 -/- mice. Taken together our data suggest an aging-associated development of iron-overload cardiomyopathy in mice genetically lacking Nrf2. To evaluate the role of Nrf2 in iron overload cardiomyopathy, Nrf2 -/- and WT mice were exposed to dietary iron supplementation (2.5% w/w carbonyl iron for 28 days). Nrf2 -/- mice developed cardiac hypertrophy which was accompanied by a worsening in collagen deposition and persistent activation of PDGF-B pathway. This was associated with inflammatory vasculopathy. The biologic importance of Nrf2 is supported by the cardiac activation of Nrf2, degradation of SERC2A and activation of TGF-b receptor and PDGF-B pathway in a mouse model of beta thalassemia intermedia, the Hbb3th/+ mice. Collectively our data support the crucial role of Nrf2 in the protection of cardiomyocytes against iron cytotoxicity which significantly develops in aging as well as in β-thalassemia. Disclosures Vinchi: Silence Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Vifor Pharma: Research Funding; PharmaNutra: Research Funding; Novartis: Research Funding. Ghigo: Kither Biotech: Other: Board member and Co-Founder. Iolascon: Bluebird Bio: Other: Advisory Board; Celgene: Other: Advisory Board.

Multimodality imaging for the diagnosis of infiltrative cardiomyopathies

Infiltrative cardiomyopathies result from the deposition or anomalous storage of specific substances in the heart, leading to impaired cardiac function and heart failure. In this review, we describe the utility of a variety of imaging modalities for the diagnosis of infiltrative cardiomyopathies and provide algorithms for clinicians to use to evaluate patients with these disorders. We have divided infiltrative cardiomyopathies into two different categories: (1) infiltrative cardiomyopathies characterised by increased wall thickness (eg, cardiac amyloidosis and Anderson-Fabry disease (AFD)) and (2) infiltrative cardiomyopathies that can mimic ischaemic or dilated cardiomyopathies (eg, cardiac sarcoidosis (CS) and iron overload cardiomyopathy). Echocardiography is the first modality of choice for the evaluation of cardiomyopathies in either category, and the differential can be narrowed using cardiac magnetic resonance (CMR) and nuclear imaging techniques. The diagnosis of cardiac amyloidosis is supported with key findings seen on echocardiography, CMR and nuclear imaging, whereas AFD can be suggested by unique features on CMR. CMR and nuclear imaging are also important modalities for the diagnosis of CS, while iron overload cardiomyopathy is mostly diagnosed using tissue characterisation on CMR. Overall, multimodality imaging is necessary for the accurate non-invasive diagnosis of infiltrative cardiomyopathies, which is important to ensure appropriate treatment and prognostication.

Myocardial Iron Overload in an Experimental Model of Sudden Unexpected Death in Epilepsy

Uncontrolled repetitive generalized tonic-clonic seizures (GTCS) are the main risk factor for sudden unexpected death in epilepsy (SUDEP). GTCS can be observed in models such as Pentylenetetrazole kindling (PTZ-K) or pilocarpine-induced Status Epilepticus (SE-P), which share similar alterations in cardiac function, with a high risk of SUDEP. Terminal cardiac arrhythmia in SUDEP can develop as a result of a high rate of hypoxic stress-induced by convulsions with excessive sympathetic overstimulation that triggers a neurocardiogenic injury, recently defined as “Epileptic Heart” and characterized by heart rhythm disturbances, such as bradycardia and lengthening of the QT interval. Recently, an iron overload-dependent form of non-apoptotic cell death called ferroptosis was described at the brain level in both the PTZ-K and SE-P experimental models. However, seizure-related cardiac ferroptosis has not yet been reported. Iron overload cardiomyopathy (IOC) results from the accumulation of iron in the myocardium, with high production of reactive oxygen species (ROS), lipid peroxidation, and accumulation of hemosiderin as the final biomarker related to cardiomyocyte ferroptosis. Iron overload cardiomyopathy is the leading cause of death in patients with iron overload secondary to chronic blood transfusion therapy; it is also described in hereditary hemochromatosis. GTCS, through repeated hypoxic stress, can increase ROS production in the heart and cause cardiomyocyte ferroptosis. We hypothesized that iron accumulation in the “Epileptic Heart” could be associated with a terminal cardiac arrhythmia described in the IOC and the development of state-potentially in the development of SUDEP. Using the aforementioned PTZ-K and SE-P experimental models, after SUDEP-related repetitive GTCS, we observed an increase in the cardiac expression of hypoxic inducible factor 1α, indicating hypoxic-ischemic damage, and both necrotic cells and hemorrhagic areas were related to the possible hemosiderin production in the PTZ-K model. Furthermore, we demonstrated for the first time an accumulation of hemosiderin in the heart in the SE-P model. These results suggest that uncontrolled recurrent seizures, as described in refractory epilepsy, can give rise to high hypoxic stress in the heart, thus inducing hemosiderin accumulation as in IOC, and can act as an underlying hidden mechanism contributing to the development of a terminal cardiac arrhythmia in SUDEP. Because iron accumulation in tissues can be detected by non-invasive imaging methods, cardiac iron overload in refractory epilepsy patients could be treated with chelation therapy to reduce the risk of SUDEP.