Voltage-gated Ca2+ channels as key mediators of iron-transport and iron-overload cardiomyopathy: L-type vs. T-type Ca+ channels

Iron deficiency and supplementation in heart failure

Non-anaemic iron deficiency (NAID) is a strategic target in cardiovascular medicine because of its association with a range of adverse effects in various conditions. Endeavours to tackle NAID in heart failure have yielded mixed results, exposing knowledge gaps in how best to define 'iron deficiency' and the handling of iron therapies by the body. To address these gaps, we harness the latest understanding of the mechanisms of iron homeostasis outside the erythron and integrate clinical and preclinical lines of evidence. The emerging picture is that current definitions of iron deficiency do not assimilate the multiple influences at play in patients with heart failure and, consequently, fail to identify those with a truly unmet need for iron. Additionally, current iron supplementation therapies benefit only certain patients with heart failure, reflecting differences in the nature of the unmet need for iron and the modifying effects of anaemia and inflammation on the handling of iron therapies by the body. Building on these insights, we identify untapped opportunities in the management of NAID, including the refinement of current approaches and the development of novel strategies. Lessons learned from NAID in cardiovascular disease could ultimately translate into benefits for patients with other chronic conditions such as chronic kidney disease, chronic obstructive pulmonary disease and cancer.

Comparison of the effects of calcium channel blockers plus iron chelation therapy versus chelation therapy only on iron overload in children and young adults with transfusion-dependent thalassemia: A randomized double-blind placebo-controlled trial

BACKGROUND

Myocardial iron deposition is a significant cause of morbidity and mortality in patients with transfusion-dependent thalassemia (TDT). Amlodipine, L-type calcium channel blocker with regular chelation therapy may reduce myocardial iron overload. Lack of randomized trials prompted this study to assess the effect of calcium channel blocker (amlodipine) in combination with iron chelation therapy on iron overload in patients with TDT.

METHODS

Sixty-four eligible patients were randomized to receive either amlodipine and chelation (group A) or chelation alone (group B) in double-blind placebo-controlled trial. Myocardial iron concentration (MIC) using T2* magnetic resonance imaging (MRI), liver iron concentration (LIC), left ventricular ejection fraction (LVEF), and serum ferritin were measured at baseline and 12 months.

RESULTS

In the amlodipine group, mean cardiac T2* value significantly increased from 18.11 ± 8.47 to 22.15 ± 7.61 (p = .002) at 12 months, whereas in control group, there was a nonsignificant increase (p = .62) in cardiac T2* value from 19.50 ± 8.84 to 20.03 ± 9.07. There was a significant decrease in MRI-derived MIC in the amlodipine group compared to control group (1.93 ± 1.61 to 1.29 ± 0.90, p = .01). Changes in the LVEF (p = .45), MRI-derived LIC (p = .09), and serum ferritin (p = .81) were not significant between the two groups.

CONCLUSION

Amlodipine is safe and when combined with chelation therapy appears to be more effective in reducing cardiac iron overload than chelation only in children and young adults with TDT.

L-type calcium channel blockers decrease the iron overload-mediated oxidative stress in renal epithelial cells by reducing iron accumulation

Iron-mediated oxidative stress has been recognized as one of the leading causes of chronic kidney injury. The effect of L-type calcium channel (LTCC) blocker on iron overload has been shown in cardiomyocytes, liver cells, and nerve cells. So far, few studies have examined whether blockers improve kidney iron-mediated oxidative stress. Yet, the precise mechanism through which blockers regulate kidney iron transport still remains unclear. In the present work, treatment with nifedipine or verapamil decreased oxidative stress and reduced the cell apoptosis-induced by ferric ammonium citrate (P < 0.05), decreased cellular iron contents, and prevented the rising of iron level-induced by ferric ammonium citrate (P > 0.05) in HK-2 and HEK293 cells. Besides, nifedipine and verapamil treatments increased the expression of divalent metal transporter 1, divalent metal transporter ZIP14, and ferroportin1 in HK-2 cells and increased ferroportin1 expression in HEK293 cells. In summary, LTCC blockers alleviate iron overload-induced oxidative stress in renal epithelial cells by blocking the iron uptake and enhancing cellular iron transport and/or iron export, thus synergistically reducing the cellular iron accumulation. Consequently, LTCC blockers may be used as a novel treatment for the prevention of primary or secondary iron overload-kidney injury.

Restoring the impaired cardiac calcium homeostasis and cardiac function in iron overload rats by the combined deferiprone and N-acetyl cysteine

Intracellular calcium [Ca²⁺]_i dysregulation plays an important role in the pathophysiology of iron overload cardiomyopathy. Although either iron chelators or antioxidants provide cardioprotection, a comparison of the efficacy of deferoxamine (DFO), deferiprone (DFP), deferasirox (DFX), N-acetyl cysteine (NAC) or a combination of DFP plus NAC on cardiac [Ca²⁺]_i homeostasis in chronic iron overload has never been investigated. Male Wistar rats were fed with either a normal diet or a high iron (HFe) diet for 4 months. At 2 months, HFe rats were divided into 6 groups and treated with either a vehicle, DFO (25 mg/kg/day), DFP (75 mg/kg/day), DFX (20 mg/kg/day), NAC (100 mg/kg/day), or combined DFP plus NAC. At 4 months, the number of cardiac T-type calcium channels was increased, whereas cardiac sarcoplasmic-endoplasmic reticulum Ca²⁺ ATPase (SERCA) was decreased, leading to cardiac iron overload and impaired cardiac [Ca²⁺]i homeostasis. All pharmacological interventions restored SERCA levels. Although DFO, DFP, DFX or NAC alone shared similar efficacy in improving cardiac [Ca²⁺]i homeostasis, only DFP + NAC restored cardiac [Ca²⁺]i homeostasis, leading to restoring left ventricular function in the HFe-fed rats. Thus, the combined DFP + NAC was more effective than any monotherapy in restoring cardiac [Ca²⁺]_i homeostasis, leading to restored myocardial contractility in iron-overloaded rats.

Iron toxicity and its possible association with treatment of Cancer: lessons from hemoglobinopathies and rare, transfusion-dependent anemias

Exposure to elevated levels of iron causes tissue damage and organ failure, and increases the risk of cancer. The toxicity of iron is mediated through generation of oxidants. There is also solid evidence indicating that oxidant stress plays a significant role in a variety of human disease states, including malignant transformation. Iron toxicity is the main focus when managing thalassemia. However, the short- and long-term toxicities of iron have not been extensively considered in children and adults treated for malignancy, and only recently have begun to draw oncologists' attention. The treatment of malignancy can markedly increase exposure of patients to elevated toxic iron species without the need for excess iron input from transfusion. This under-recognized exposure likely enhances organ toxicity and may contribute to long-term development of secondary malignancy and organ failure. This review discusses the current understanding of iron metabolism, the mechanisms of production of toxic free iron species in humans, and the relation of the clinical marker, transferrin saturation (TS), to the presence of toxic free iron. We will present epidemiological data showing that high TS is associated with poor outcomes and development of cancer, and that lowering free iron may improve outcomes. Finally, we will discuss the possible relation between some late complications seen in survivors of cancer and those due to iron toxicity.

Physiology and pathophysiology of iron in hemoglobin-associated diseases

Iron overload and iron toxicity, whether because of increased absorption or iron loading from repeated transfusions, can be major causes of morbidity and mortality in a number of chronic anemias. Significant advances have been made in our understanding of iron homeostasis over the past decade. At the same time, advances in magnetic resonance imaging have allowed clinicians to monitor and quantify iron concentrations noninvasively in specific organs. Furthermore, effective iron chelators are now available, including preparations that can be taken orally. This has resulted in substantial improvement in mortality and morbidity for patients with severe chronic iron overload. This paper reviews the key points of iron homeostasis and attempts to place clinical observations in patients with transfusional iron overload in context with the current understanding of iron homeostasis in humans.

Blocking of L-type calcium channels protects hippocampal and nigral neurons against iron neurotoxicity. The role of L-type calcium channels in iron-induced neurotoxicity

Iron plays an important role in maintaining normal brain function. However, iron overload and enhanced hydroxyl radical formation have been implicated as the causative factors of some neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. Calcium is also required for diverse physiological process including secretion of neurotransmitters, synaptic plasticity, gene expression and axonal growth. Iron and calcium are essential for neuronal function but, when present in excessive level, they induce neuronal damage and may even cause neuronal death. Some reports suggest that voltage gated calcium channels (VGCCs) are an alternate route for iron entry into neuronal cell lines under conditions of iron overload. The aim of the present study was to investigate the effects of L-type VGCCs on iron-induced neurotoxicity. Iron neurotoxicity was generated by intracerebroventricular FeCl₃ injection. Nicardipine treatment (10 mg/kg/d) was applied to block L-type VGCCs for 10 d. Rats were perfused intracardially under deep urethane anaesthesia after treatment period. Removed brains were processed using the standard histological techniques. The numbers of neurons in hippocampus and substantia nigra of all rats were estimated by stereological techniques. Results of present study show that nicardipine decreased hippocampal and nigral neuron loss from 43.9% to 18.4% and 41.0% to 12.1%, respectively. Outcomes of the present study propose that blocking of L-type VGCCs may reduce the neurotoxic effects of iron by inhibiting the cellular influx of excessive calcium and/or iron ions.

Verapamil reverses cardiac iron overload in streptozocin-induced diabetic rats

Accumulating evidence shows that iron overload is a new risk factor for diabetes mellitus. L-type Ca(2+) channel (LTCC) has been identified as an important mediator for ferrous iron uptake into cardiomyocytes. In this study, we aimed to examine the effects of verapamil, the LTCC blocker, on myocardial iron metabolism in diabetic rats. Diabetes was induced by intraperitoneal injection of streptozocin after intragastric administration of fat emulsion, and then treated by verapamil (5 mg · kg(-1) · day(-1)) for 1 week. The results showed that verapamil did not alter the blood glucose level of diabetic rats. However, elevated levels of superoxide dismutase, malonaldehyde, and serum ferritin in diabetic rats were decreased significantly by verapamil treatment. Moreover, serum, myocardial, and urine iron were elevated remarkably along with a decrease of hepatic iron in diabetic rats. After verapamil administration, serum and myocardial iron in diabetic rats were reduced significantly but urine and hepatic iron were increased. Furthermore, confocal microscopy demonstrated that intracellular-free iron concentration was elevated dramatically in cardiomyocytes of diabetic rats, which was markedly attenuated after verapamil treatment. In summary, our data demonstrated that verapamil prevented myocardial iron overload by inhibiting intracellular iron accumulation in diabetic cardiomyocytes.