Influence of cytokines on Dmt1 iron transporter and ferritin expression in insulin-secreting cells

Ferroptosis Signaling in Pancreatic β-Cells: Novel Insights & Therapeutic Targeting

Metabolic stress impairs pancreatic β-cell survival and function in diabetes. Although the pathophysiology of metabolic stress is complex, aberrant tissue damage and β-cell death are brought on by an imbalance in redox equilibrium due to insufficient levels of endogenous antioxidant expression in β-cells. The vulnerability of β-cells to oxidative damage caused by iron accumulation has been linked to contributory β-cell ferroptotic-like malfunction under diabetogenic settings. Here, we take into account recent findings on how iron metabolism contributes to the deregulation of the redox response in diabetic conditions as well as the ferroptotic-like malfunction in the pancreatic β-cells, which may offer insights for deciphering the pathomechanisms and formulating plans for the treatment or prevention of metabolic stress brought on by β-cell failure.

A novel chronic in vivo oral cadmium exposure-washout mouse model for studying cadmium toxicity and complex diabetogenic effects

Type II diabetes mellitus (T2DM) is characterized by insulin resistance, β-cell dysfunction and hyperglycemia. In addition to well known risk factors such as lifestyle and genetic risk score, accumulation of environmental toxicants in organs relevant to glucose metabolism is increasingly recognized as additional risk factors for T2DM. Here, we describe the development of an in vivo oral cadmium (Cd) exposure model. It was shown that oral Cd exposure in drinking water followed by washout and high fat diet (HFD) in C57BL/6N mice results in islet Cd bioaccumulation comparable to that found in native human islets while mitigating the anorexic effects of Cd to achieve the same weight gain required to induce insulin resistance as in Cd naïve control mice. Inter individual variation in plasma glucose and insulin levels as well as islet Cd bioaccumulation was observed in both female and male mice. Regression analysis showed an inverse correlation between islet Cd level and plasma insulin following a glucose challenge in males but not in females. This finding highlights the need to account for inter individual target tissue Cd concentrations when interpreting results from in vivo Cd exposure models. No effect of Cd on insulin secretion was observed in islets ex vivo, highlighting differences between in vivo and ex vivo cadmium exposure models. In summary, our oral in vivo Cd exposure-washout with HFD model resulted in islet Cd bioaccumulation that is relevant in the context of environmental cadmium exposure in humans. Here, we showed that islet Cd bioaccumulation is associated with complex cadmium-mediated changes in glucose clearance and β-cell function. The model described here will serve as a useful tool to further examine the relationship between Cd exposure, islet Cd bioaccumulation, dysglycemia and their underlying mechanisms.

Synchrotron fluorescence imaging of individual mouse beta-cells reveals changes in zinc, calcium, and iron in a model of low-grade inflammation

Pancreatic beta-cells synthesize and secrete insulin maintaining an organism's energy homeostasis. In humans, beta-cell dysfunction and death contribute to the pathogenesis of type 2 diabetes (T2D). Although the causes of beta-cell dysfunction are complex, obesity-induced low-grade systemic inflammation plays a role. For example, obese individuals exhibiting increased levels of proinflammatory cytokines IL-6 and IL-1beta have a higher risk of beta-cell dysfunction and T2D. Interestingly, obesity-induced inflammation changes the expression of several cellular metal regulating genes, prompting this study to examine changes in the beta-cell metallome after exposure to proinflammatory-cytokines. Primary mouse beta-cells were exposed to a combination of IL-6 and IL-1beta for 48 hours, were chemically fixed and imaged by synchrotron X-ray fluorescent microscopy. Quantitative analysis showed a surprising 2.4-fold decrease in the mean total cellular content of zinc from 158 ± 57.7 femtograms (fg) to 65.7 ± 29.7 fg; calcium decreased from 216 ± 67.4 to 154.3 ± 68.7 fg (control vs. cytokines, respectively). The mean total cellular iron content slightly increased from 30.4 ± 12.2 to 47.2 ± 36.4 fg after cytokine treatment; a sub-population of cells (38%) exhibited larger increases of iron density. Changes in the subcellular distributions of zinc and calcium were observed after cytokine exposure. Beta-cells contained numerous iron puncta that accumulated still more iron after exposure to cytokines. These findings provide evidence that exposure to low levels of cytokines is sufficient to cause changes in the total cellular content and/or subcellular distribution of several metals known to be critical for normal beta-cell function.

Ferroptosis and Its Potential Role in Metabolic Diseases: A Curse or Revitalization?

Ferroptosis is classified as an iron-dependent form of regulated cell death (RCD) attributed to the accumulation of lipid hydroperoxides and redox imbalance. In recent years, accumulating researches have suggested that ferroptosis may play a vital role in the development of diverse metabolic diseases, for example, diabetes and its complications (e.g., diabetic nephropathy, diabetic cardiomyopathy, diabetic myocardial ischemia/reperfusion injury and atherosclerosis [AS]), metabolic bone disease and adrenal injury. However, the specific physiopathological mechanism and precise therapeutic effect is still not clear. In this review, we summarized recent advances about the development of ferroptosis, focused on its potential character as the therapeutic target in metabolic diseases, and put forward our insights on this topic, largely to offer some help to forecast further directions.

The central role of glutathione peroxidase 4 in the regulation of ferroptosis and its implications for pro-inflammatory cytokine-mediated beta-cell death

Pro-inflammatory cytokines are crucial mediators of beta-cell destruction in type 1 diabetes mellitus (T1DM). The involvement of ferroptosis as a form of oxidative non-apoptotic cell death in T1DM pathogenesis has not been elucidated so far. Moreover, the role of glutathione peroxidase 4 (GPx4) as an antioxidative enzyme and a major regulator of ferroptosis remains elusive. Assessment of GPx4 expression in different pancreatic islet cell types revealed a predominant expression in beta-cells. Silencing of GPx4 by RNA interference and exposure to tert-butyl hydroperoxide (tert-BHP) caused ferroptosis in rat pancreatic beta-cells as evidenced by non-apoptotic cell death in association with increased lipid peroxidation, disturbed ATP synthesis, reduced GSH content, and GPx4 degradation. GPx4 overexpression as well as the ferroptosis inhibitor ferrostatin-1 effectively attenuated beta-cell death induced by tert-BHP. Notably, beta-cell toxic cytokines did not induce ferroptosis although beta-cells underwent cell death. Inhibition of iNOS by Nω-nitro-L-arginine however led to a massive lipid peroxidation upon exposure to pro-inflammatory cytokines. Hence, nitric oxide produced during pro-inflammatory cytokine action prevents the induction of ferroptosis, thereby favouring apoptosis as a primary cell death mechanism. The extraordinarily high abundance of the phospholipid hydroperoxidase GPx4 in beta-cells in contrast to the very low expression in other islet cell types points to a susceptibility of beta-cells to the accumulation of toxic lipid peroxides. Overall, these data strongly suggest that GPx4 is indispensable for beta-cell function under physiological conditions. On the other hand, our results exclude an involvement of ferroptosis as an alternative beta-cell death mode under pro-inflammatory cytokine attack.

The problem with transferrin saturation as an indicator of iron 'sufficiency' in chronic kidney disease

After a brief review of physiological iron metabolism, we describe diagnostic tests for iron status and iron deficiency anemia in patients without chronic kidney disease (CKD) or inflammation. Thereafter we review the dysregulation of iron metabolism in CKD. Specific emphasis is placed on the role of the 'inflammatory' state that develops with the progression of CKD. It invokes changes in iron metabolism that are the exact opposite of those occurring during pure iron deficiency. As a result, transferrin saturation (TSAT) becomes a poorer index of iron availability to the bone marrow and serum ferritin no longer represents iron that can be used during erythropoiesis. We argue that serum iron may provide more information to guide iron therapy than TSAT. In other words, the emphasis on TSAT is misplaced. With the development of a number of hypoxia-inducible factor prolyl hydroxylase inhibitors, which restore iron metabolism toward the 'physiologic state', the iron indices indicating sufficient iron availability to avoid functional iron deficiency during therapy of CKD-associated anemia are likely to change. We summarize these changes in the section 'A peek into things to come!', citing the available data.

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BACKGROUND

Diabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.

SCOPE REVIEW

This review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.

MAJOR CONCLUSION

The weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress. Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.

GENERAL SIGNIFICANCE

Diabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.

Anaemia of Chronic Disease: An In-Depth Review

Anaemia is the most common haematological disorder affecting humanity and is usually observed in chronic disease states such as non-specific anaemia, which may cause diagnostic difficulties. In chronically ill patients with anaemia, this has a negative impact on quality of life as well as survival. This paper aims at reviewing the pathogenesis of this form of anaemia with a view to suggesting future targets for therapeutic intervention. The ability to diagnose this disorder depends on the ability of the physician to correlate the possible clinical pathways of the underlying disease with the patients' ferrokinetic state. It is important to rule out iron deficiency and other causes of anaemia as misdiagnosis will in most cases lead to refractoriness to standard therapy. The cytokines and acute-phase proteins play important roles in the pathogenesis of anaemia of chronic disease. Alterations in the metabolism of iron via the molecule hepcidin and ferritin are largely responsible for the consequent anaemia. Concomitant iron deficiency might be present and could affect the diagnosis and therapeutic protocol. Treatment options involve the use of erythropoiesis-stimulating agents, blood transfusion, and iron supplementation, in addition to treating the underlying disease.

Endometrial expression and in vitro modulation of the iron transporter divalent metal transporter-1: implications for endometriosis

OBJECTIVE

To evaluate divalent metal transporter-1 (DMT1) expression in healthy women's and endometriosis patients' endometrium and to analyze DMT1 and ferritin light chain (Fn-L) expression modulation by iron overload and IL-1β in endometrial stromal cells (ESCs).

DESIGN

Observational and experimental study.

SETTING

University hospital research laboratory.

PATIENT(S)

Thirty-one healthy women and 24 endometriosis patients.

INTERVENTION(S)

Menstrual, proliferative, and secretory endometrial biopsies. Isolated ESCs from seven endometrial biopsies incubated with IL-1β or FeSO4 overload for 24 hours.

MAIN OUTCOME MEASURE(S)

Divalent metal transporter-1 endometrial protein expression assessed by immunohistochemistry and Western blot. Divalent metal transporter-1 and Fn-L proteins expression in stimulated ESCs evaluated by Western blot.

RESULT(S)

Divalent metal transporter-1 is expressed throughout the menstrual cycle in human endometrium. Four endometrial DMT1 variants were identified accordingly to their molecular weight: DMT-80, -65, -55, and -50. Endometrial expression of DMT-80 and -55 is higher in endometriosis patients than in healthy women. In ESCs, iron overload induces an overexpression of DMT-80, DMT-50, and Fn-L, whereas IL-1β increases DMT-80 and -50 expressions and decreases Fn-L expression.

CONCLUSION(S)

Divalent metal transporter-1 overexpression in endometriosis patients' endometrium can increase iron influx to endometrial cells, inducing oxidative stress-mediated proinflammatory signaling. In turn, endometriosis-related conditions, as iron overload and inflammation (IL-1β), enhance endometriosis patients endometrial DMT1 expression, creating a vicious circle on DMT-1-modulated pathways.

In Situ OH Generation from O2- and H2O2 Plays a Critical Role in Plasma-Induced Cell Death

Reactive oxygen and nitrogen species produced by cold atmospheric plasma (CAP) are considered to be the most important species for biomedical applications, including cancer treatment. However, it is not known which species exert the greatest biological effects, and the nature of their interactions with tumor cells remains ill-defined. These questions were addressed in the present study by exposing human mesenchymal stromal and LP-1 cells to reactive oxygen and nitrogen species produced by CAP and evaluating cell viability. Superoxide anion (O2-) and hydrogen peroxide (H2O2) were the two major species present in plasma, but their respective concentrations were not sufficient to cause cell death when used in isolation; however, in the presence of iron, both species enhanced the cell death-inducing effects of plasma. We propose that iron containing proteins in cells catalyze O2- and H2O2 into the highly reactive OH radical that can induce cell death. The results demonstrate how reactive species are transferred to liquid and converted into the OH radical to mediate cytotoxicity and provide mechanistic insight into the molecular mechanisms underlying tumor cell death by plasma treatment.