The C57BL/6 genetic background confers cardioprotection in iron-overloaded mice

Research advances on molecular mechanism and natural product therapy of iron metabolism in heart failure

The progression of heart failure (HF) is complex and involves multiple regulatory pathways. Iron ions play a crucial supportive role as a cofactor for important proteins such as hemoglobin, myoglobin, oxidative respiratory chain, and DNA synthetase, in the myocardial energy metabolism process. In recent years, numerous studies have shown that HF is associated with iron dysmetabolism, and deficiencies in iron and overload of iron can both lead to the development of various myocarditis diseases, which ultimately progress to HF. Iron toxicity and iron metabolism may be key targets for the diagnosis, treatment, and prevention of HF. Some iron chelators (such as desferrioxamine), antioxidants (such as ascorbate), Fer-1, and molecules that regulate iron levels (such as lactoferrin) have been shown to be effective in treating HF and protecting the myocardium in multiple studies. Additionally, certain natural compounds can play a significant role by mediating the imbalance of iron-related signaling pathways and expression levels. Therefore, this review not only summarizes the basic processes of iron metabolism in the body and the mechanisms by which they play a role in HF, with the aim of providing new clues and considerations for the treatment of HF, but also summarizes recent studies on natural chemical components that involve ferroptosis and its role in HF pathology, as well as the mechanisms by which naturally occurring products regulate ferroptosis in HF, with the aim of providing reference information for the development of new ferroptosis inhibitors and lead compounds for the treatment of HF in the future.

Comparison of the effects of high dietary iron levels on bone microarchitecture responses in the mouse strains 129/Sv and C57BL/6J

Iron is an essential nutrient for all living organisms. Both iron deficiency and excess can be harmful. Bone, a highly metabolic active organ, is particularly sensitive to fluctuations in iron levels. In this study, we investigated the effects of dietary iron overload on bone homeostasis with a specific focus on two frequently utilized mouse strains: 129/Sv and C57BL/6J. Our findings revealed that after 6 weeks on an iron-rich diet, 129/Sv mice exhibited a decrease in trabecular and cortical bone density in both vertebral and femoral bones, which was linked to reduced bone turnover. In contrast, there was no evidence of bone changes associated with iron overload in age-matched C57BL/6J mice. Interestingly, 129/Sv mice exposed to an iron-rich diet during their prenatal development were protected from iron-induced bone loss, suggesting the presence of potential adaptive mechanisms. Overall, our study underscores the critical role of genetic background in modulating the effects of iron overload on bone health. This should be considered when studying effects of iron on bone.

[Effect of cyclophosphamide on hematopoietic stem cells in mice with iron overload]

OBJECTIVE

To explore the effect of cyclophosphamide on hematopoietic stem cells (HSCs) in mice with iron overload.

METHODS

Mouse models of iron overload were established in 30 male C57BL/6 mice by intraperitoneal injections of iron dextran at low (0.25 g/kg), moderate (0.5 g/kg), and high (1 g/kg) doses (n=10), with another 10 PBS-treated mice as the control group. The changes in body weight, liver, spleen and bone marrow of the mice were recorded, and serum level of ferritin was detected. The mice receiving a moderate dose of iron dextran were further divided into 8 groups for observation at different time points (D1, D2, D3, D4, D5, D6, D7, and D14 groups) and were given intraperitoneal injection of 50 mg/kg cyclophosphamide (Cy) for 2 consecutive days. Peripheral blood cells, bone marrow mononuclear cells (BMMNCs), and the frequencies of different HSCs (HPCs, HSCs, LT-HSCs) in the BMMNCs were monitored. The cell cycle distribution in the HSCs, level of reactive oxygen species and the microenvironment of the HSCs were analyzed using flow cytometry.

RESULTS

Compared with the control mice, the mice with iron overload showed obvious weight loss with significantly increased serum ferritin level, enlargement of the liver and spleen, and iron deposition in the organs (P < 0.05). No significant changes were noted in the peripheral blood of the mice with iron overload. The cyclophosphamide-treated mice exhibited significantly decreased number of WBCs and lymphocyte ratio at days 1 to 4 (P < 0.05). The numbers of BMMNCs and HPCs in mice with iron overload did not show significant changes as compared with those in the control mice, but the numbers of HSCs and LTHSCs decreased significantly in the mice with iron overload (P < 0.05). In cyclophosphamide-treated mice, the number of HSCs increased since day 1 and reached the peak level on day 3 (P < 0.05). Compared with those in the control group, the HSCs did not exhibit significant changes in cell cycle distribution in mice with iron overload, but the proportion of G0/G1 cells decreased significantly in cyclophosphamide group since day 1 and reached the lowest level on day 3 (P < 0.05).

CONCLUSIONS

Iron deposition in the bone marrow causes long- term damages of the HSCs in the bone marrow but does not induce obvious changes in the peripheral blood. In mice with iron overload, intraperitoneal injection of 50 mg/kg cyclophosphamide for two days promotes cell cycle changes of the resting HSCs to mobilize the HSCs, and this effect is the most obvious on day 4.

Assessment of MR-based R2* and quantitative susceptibility mapping for the quantification of liver iron concentration in a mouse model at 7T

PURPOSE

To assess the feasibility of quantifying liver iron concentration (LIC) using R2* and quantitative susceptibility mapping (QSM) at a high field strength of 7 Tesla (T).

METHODS

Five different concentrations of Fe-dextran were injected into 12 mice to produce various degrees of liver iron overload. After mice were sacrificed, blood and liver samples were harvested. Ferritin enzyme-linked immunosorbent assay (ELISA) and inductively coupled plasma mass spectrometry were performed to quantify serum ferritin concentration and LIC. Multiecho gradient echo MRI was conducted to estimate R2* and the magnetic susceptibility of each liver sample through complex nonlinear least squares fitting and a morphology enabled dipole inversion method, respectively.

RESULTS

Average estimates of serum ferritin concentration, LIC, R2*, and susceptibility all show good linear correlations with injected Fe-dextran concentration; however, the standard deviations in the estimates of R2* and susceptibility increase with injected Fe-dextran concentration. Both R2* and susceptibility measurements also show good linear correlations with LIC (R2  = 0.78 and R2  = 0.91, respectively), and a susceptibility-to-LIC conversion factor of 0.829 ppm/(mg/g wet) is derived.

CONCLUSION

The feasibility of quantifying LIC using MR-based  R2* and QSM at a high field strength of 7T is demonstrated. Susceptibility quantification, which is an intrinsic property of tissues and benefits from being field-strength independent, is more robust than R2* quantification in this ex vivo study. A susceptibility-to-LIC conversion factor is presented that agrees relatively well with previously published QSM derived results obtained at 1.5T and 3T.

Tom20 senses iron-activated ROS signaling to promote melanoma cell pyroptosis

Iron has been shown to trigger oxidative stress by elevating reactive oxygen species (ROS) and to participate in different modes of cell death, such as ferroptosis, apoptosis and necroptosis. However, whether iron-elevated ROS is also linked to pyroptosis has not been reported. Here, we demonstrate that iron-activated ROS can induce pyroptosis via a Tom20-Bax-caspase-GSDME pathway. In melanoma cells, iron enhanced ROS signaling initiated by CCCP, causing the oxidation and oligomerization of the mitochondrial outer membrane protein Tom20. Bax is recruited to mitochondria by oxidized Tom20, which facilitates cytochrome c release to cytosol to activate caspase-3, eventually triggering pyroptotic death by inducing GSDME cleavage. Therefore, ROS acts as a causative factor and Tom20 senses ROS signaling for iron-driven pyroptotic death of melanoma cells. Since iron activates ROS for GSDME-dependent pyroptosis induction and melanoma cells specifically express a high level of GSDME, iron may be a potential candidate for melanoma therapy. Based on the functional mechanism of iron shown above, we further demonstrate that iron supplementation at a dosage used in iron-deficient patients is sufficient to maximize the anti-tumor effect of clinical ROS-inducing drugs to inhibit xenograft tumor growth and metastasis of melanoma cells through GSDME-dependent pyroptosis. Moreover, no obvious side effects are observed in the normal tissues and organs of mice during the combined treatment of clinical drugs and iron. This study not only identifies iron as a sensitizer amplifying ROS signaling to drive pyroptosis, but also implicates a novel iron-based intervention strategy for melanoma therapy.

Females Are Protected From Iron-Overload Cardiomyopathy Independent of Iron Metabolism: Key Role of Oxidative Stress

Background

Sex‐related differences in cardiac function and iron metabolism exist in humans and experimental animals. Male patients and preclinical animal models are more susceptible to cardiomyopathies and heart failure. However, whether similar differences are seen in iron‐overload cardiomyopathy is poorly understood.

Methods and Results

Male and female wild‐type and hemojuvelin‐null mice were injected and fed with a high‐iron diet, respectively, to develop secondary iron overload and genetic hemochromatosis. Female mice were completely protected from iron‐overload cardiomyopathy, whereas iron overload resulted in marked diastolic dysfunction in male iron‐overloaded mice based on echocardiographic and invasive pressure‐volume analyses. Female mice demonstrated a marked suppression of iron‐mediated oxidative stress and a lack of myocardial fibrosis despite an equivalent degree of myocardial iron deposition. Ovariectomized female mice with iron overload exhibited essential pathophysiological features of iron‐overload cardiomyopathy showing distinct diastolic and systolic dysfunction, severe myocardial fibrosis, increased myocardial oxidative stress, and increased expression of cardiac disease markers. Ovariectomy prevented iron‐induced upregulation of ferritin, decreased myocardial SERCA2a levels, and increased NCX1 levels. 17β‐Estradiol therapy rescued the iron‐overload cardiomyopathy in male wild‐type mice. The responses in wild‐type and hemojuvelin‐null female mice were remarkably similar, highlighting a conserved mechanism of sex‐dependent protection from iron‐overload‐mediated cardiac injury.

Conclusions

Male and female mice respond differently to iron‐overload‐mediated effects on heart structure and function, and females are markedly protected from iron‐overload cardiomyopathy. Ovariectomy in female mice exacerbated iron‐induced myocardial injury and precipitated severe cardiac dysfunction during iron‐overload conditions, whereas 17β‐estradiol therapy was protective in male iron‐overloaded mice.

A beta-blocker, propranolol, decreases the efficacy from enzyme replacement therapy in Pompe disease

Enzyme replacement therapy (ERT) with recombinant human acid α-glucosidase (rhGAA) fails to completely reverse muscle weakness in Pompe disease. β2-agonists enhanced ERT by increasing receptor-mediated uptake of rhGAA in skeletal muscles.

PURPOSE

To test the hypothesis that a β-blocker might reduce the efficacy of ERT, because the action of β-blockers opposes those of β2-agonists.

METHODS

Mice with Pompe disease were treated with propranolol (a β-blocker) or clenbuterol in combination with ERT, or with ERT alone.

RESULTS

Propranolol-treated mice had decreased weight gain (p<0.01), in comparison with clenbuterol-treated mice. Left ventricular mass was decreased (and comparable to wild-type) in ERT only and clenbuterol-treated groups of mice, and unchanged in propranolol-treated mice. GAA activity increased following either clenbuterol or propranolol in skeletal muscles. However, muscle glycogen was reduced only in clenbuterol-treated mice, not in propranolol-treated mice. Cell-based experiments confirmed that propranolol reduces uptake of rhGAA into Pompe fibroblasts and also demonstrated that the drug induces intracellular accumulation of glycoproteins at higher doses.

CONCLUSION

Propranolol, a commonly prescribed β-blocker, reduced weight, increased left ventricular mass and decreased glycogen clearance in skeletal muscle following ERT. β-Blockers might therefore decrease the efficacy from ERT in patients with Pompe disease.

Iron excretion in iron dextran-overloaded mice

BACKGROUND

Iron homeostasis in humans is tightly regulated by mechanisms aimed to conserve iron for reutilisation, with a negligible role played by excretory mechanisms. In a previous study we found that mice have an astonishing ability to tolerate very high doses of parenterally administered iron dextran. Whether this ability is linked to the existence of an excretory pathway remains to be ascertained.

MATERIALS AND METHODS

Iron overload was generated by intraperitoneal injections of iron dextran (1 g/kg) administered once a week for 8 weeks in two different mouse strains (C57bl/6 and B6D2F1). Urinary and faecal iron excretion was assessed by inductively coupling plasma-mass spectrometry, whereas cardiac and liver architecture was evaluated by echocardiography and histological methods. For both strains, 24-hour faeces and urine samples were collected and iron concentration was determined on days 0, 1 and 2 after iron administration.

RESULTS

In iron-overloaded C57bl/6 mice, the faecal iron concentration increased by 218% and 157% on days 1 and 2, respectively (p<0.01). The iron excreted represented a loss of 14% of total iron administered. Similar but smaller changes was also found in B6D2F1 mice. Conversely, we found no significant changes in the concentration of iron in the urine in either of the strains of mice. In both strains, histological examination showed accumulation of iron in the liver and heart which tended to decrease over time.

CONCLUSIONS

This study indicates that mice have a mechanism for removal of excess body iron and provides insights into the possible mechanisms of excretion.

Seizure resistance without parkinsonism in aged mice after tau reduction

Tau is an emerging target for Alzheimer's disease (AD) and other conditions with epileptiform activity. Genetic tau reduction (in Tau(+/-) and Tau(-/-) mice) prevents deficits in AD models and has an excitoprotective effect, increasing resistance to seizures, without causing apparent neuronal dysfunction. However, most studies of tau reduction have been conducted in <1-year-old mice, and the effects of tau reduction in aged mice are less clear. Specifically, whether the excitoprotective effects of tau reduction persist with aging is unknown and whether tau reduction causes neuronal dysfunction, including parkinsonism, with aging is controversial. Here, we performed a comprehensive analysis of 2-year-old Tau(+/+), Tau(+/-), and Tau(-/-) mice. In aged mice, tau reduction still conferred resistance to pentylenetetrazole-induced seizures. Moreover, tau reduction did not cause parkinsonian abnormalities in dopamine levels or motor function and did not cause iron accumulation or impaired cognition, although Tau(-/-) mice had mild hyperactivity and decreased brain weight. Importantly, the excitoprotective effect in aged Tau(+/-) mice was not accompanied by detectable abnormalities, indicating that partially reducing tau or blocking its function may be a safe and effective therapeutic approach for AD and other conditions with increased excitability.