Increased intracellular iron in mouse primary hepatocytes in vitro causes activation of the Akt pathway but decreases its response to insulin

Antagonizing Effects of Chromium Against Iron-Decreased Glucose Uptake by Regulating ROS-Mediated PI3K/Akt/GLUT4 Signaling Pathway in C2C12

To investigate the effect of chromium and iron on glucose metabolism via the PI3K/Akt/GLUT4 signaling pathway. Skeletal muscle gene microarray data in T2DM (GSE7014) was selected using Gene Expression Omnibus database. Element-gene interaction datasets of chromium and iron were extracted from comparative toxicogenomics database (CTD). Gene ontology (GO)and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed using DAVID online tool. Cell viability, insulin-stimulated glucose uptake, intracellular reactive oxygen species (ROS) level, and protein expression level were measured in C2C12 cells. The bioinformatics research indicated that PI3K/Akt signaling pathway participated in the effects of chromium and iron associated with T2DM. Insulin-stimulated glucose uptake level was significantly higher in chromium picolinate (Cr group) and lower in ammonium iron citrate (FA group) than that for the control group (P < 0.05); chromium picolinate + ammonium iron citrate (Cr + FA group) glucose uptake level was higher than that for the FA group (P < 0.05). Intracellular ROS level was significantly higher in the FAC group than that for the control group (P < 0.05), and that for the Cr + FA group was lower than that for the FA group (P < 0.05). p-PI3K/PI3K, p-Akt/Akt, and GLUT4 levels were significantly lower in the FA group than that for the control group (P < 0.05), and the Cr + FA group had higher levels than the FA group (P < 0.05). Chromium might have a protective effect on iron-induced glucose metabolism abnormalities through the ROS-mediated PI3K/Akt/GLUT4 signaling pathway.

Cyclovirobuxine D pretreatment ameliorates septic heart injury through mitigation of ferroptosis

Myocardial dysfunction is a frequent complication in patients with severe sepsis. However, effective drugs for the prevention of myocardial dysfunction and the molecular mechanisms of the disease remain elusive. The present study demonstrated that Cyclovirobuxine D (CVB-D) could improve cardiac dysfunction in a cecal ligation and puncture (CLP) model in rodents and in a lipopolysaccharide (LPS) model in vitro. Echocardiography and histopathological examination were used to detect changes in cardiac structure and function. Kits were used to detect indicators of cardiac injury, transmission electron microscopy to detect structural changes in mitochondria and reverse transcription-quantitative PCR to detect prostaglandin-endoperoxide synthase 2 and hamp expression levels. L-Glutathione and malondialdehyde levels and superoxide dismutase activity were measured using kits. Cell viability was measured with the Cell Counting Kit-8. Iron metabolism-related proteins, inflammatory factor levels and related pathway proteins were detected using western blot analysis. Changes in L-type calcium currents were detected by membrane clamp, and contractility of cardiomyocytes was measured by Ion Optix. CVB-D attenuated CLP-induced cardiac malfunction in septic rats, with changes observed in myocardial pathological structure, creatine kinase isoenzyme (CK-MB), lactate dehydrogenase (LDH) and cardiac troponin I (cTnI). CVB-D attenuated sepsis-induced lipid peroxidation and iron overload. In addition, CVB-D decreased the expression of CK-MB, LDH and cTnI, suppressed oxidative stress index levels and reduced the production of reactive oxygen species. CVB-D decreased LPS-induced cytoplasmic iron overload by increasing upregulation of iron uptake molecules. Conversely, CVB-D significantly increased the upregulation of ferroportin 1. CVB-D pretreatment significantly reduced the levels of hamp mRNA compared with the LPS-treated group. CVB-D pretreatment significantly reduced inflammatory factor levels and the ratio of phosphorylated vs. total signal transducer and activator of transcription 3. The expression of SLC7A11 and GPX4 was upregulated in septic cells pretreated with CVB-D, however treatment with ML385 largely decreased this upregulation. Of note, CVB-D inhibited the inward flow of calcium ions through the LTCC. In conclusion, these findings suggest that CVB-D alleviated sepsis-induced cardiac iron toxicity by alleviating iron metabolism.

Exposure to multiple metals and diabetes mellitus risk in dong ethnicity in China: from the China multi-ethnic cohort study

Metals play an important role in the development of diabetes mellitus (DM). The association of metals with diabetes among the Dong ethnicity in China remains poorly understood. The current study aimed to evaluate the association of single metal exposure and multi-metal co-exposure with DM risk. Urinary concentrations of arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, molybdenum, nickel, strontium, vanadium, and zinc were measured using inductively coupled plasma-mass spectrometry (ICP-MS) among 4479 Dong ethnic participants aged 30-79 years from the China Multi-Ethnic Cohort (CMEC) study. Based on tertiles, the metal exposure can be divided into three groups: low, middle, and high exposure. Multivariate logistic regression models and principal component analysis were performed to determine exposure to single-metal and multi-metal co-exposure in relation to DM. A decrease in risk of DM was associated with iron (OR = 0.78, 95% CI: 0.61-1.00 and 0.68, 0.53-0.88 for the middle and high vs. low) and strontium (OR = 0.87, 95% CI: 0.69-1.12 and 0.67, 0.51-0.86 for the middle and high vs. low), respectively. A principal component 3 (PC3) characterized by iron and strontium showed an inverse association with DM. A principal component 4 (PC4) characterized by manganese and lead positively associated with DM. Exposure to high concentrations of urinary iron and strontium may reduce the risk of diabetes mellitus. This study revealed an increase in the risk of diabetes mellitus by co-exposure to high concentrations of urinary manganese and lead.

Insulin resistance and adipose tissue inflammation induced by a high-fat diet are attenuated in the absence of hepcidin

Increased body iron stores and inflammation in adipose tissue have been implicated in the pathogenesis of insulin resistance (IR) and type 2 diabetes mellitus. However, the underlying basis of these associations is unclear. To attempt to investigate this, we studied the development of IR and associated inflammation in adipose tissue in the presence of increased body iron stores. Male hepcidin knock-out (Hamp1^-/-) mice, which have increased body iron stores, and wild-type (WT) mice were fed a high-fat diet (HFD) for 12 and 24 weeks. Development of IR and metabolic parameters linked to this, insulin signaling in various tissues, and inflammation and iron-related parameters in visceral adipose tissue were studied in these animals. HFD-feeding resulted in impaired glucose tolerance in both genotypes of mice. In response to the HFD for 24 weeks, Hamp1^-/- mice gained less body weight and developed less systemic IR than corresponding WT mice. This was associated with less lipid accumulation in the liver and decreased inflammation and lipolysis in the adipose tissue in the knock-out mice, than in the WT animals. Fewer macrophages infiltrated the adipose tissue in the knockout mice than in wild-type mice, with these macrophages exhibiting a predominantly anti-inflammatory (M2-like) phenotype and indirect evidence of a possible lowered intracellular iron content. The absence of hepcidin was thus associated with attenuated inflammation in the adipose tissue and increased whole-body insulin sensitivity, suggesting a role for it in these processes.

Iron Homeostasis and Energy Metabolism in Obesity

Iron plays a role in energy metabolism as a component of vital enzymes and electron transport chains (ETCs) for adenosine triphosphate (ATP) synthesis. The tricarboxylic acid (TCA) cycle and oxidative phosphorylation are crucial in generating ATP in mitochondria. At the mitochondria matrix, heme and iron-sulfur clusters are synthesized. Iron-sulfur cluster is a part of the aconitase in the TCA cycle and a functional or structural component of electron transfer proteins. Heme is the prosthetic group for cytochrome c, a principal component of the respiratory ETC. Regarding fat metabolism, iron regulates mitochondrial fat oxidation and affects the thermogenesis of brown adipose tissue (BAT). Thermogenesis is a process that increases energy expenditure, and BAT is a tissue that generates heat via mitochondrial fuel oxidation. Iron deficiency may impair mitochondrial fuel oxidation by inhibiting iron-containing molecules, leading to decreased energy expenditure. Although it is expected that impaired mitochondrial fuel oxidation may be restored by iron supplementation, its underlying mechanisms have not been clearly identified. Therefore, this review summarizes the current evidence on how iron regulates energy metabolism considering the TCA cycle, oxidative phosphorylation, and thermogenesis. Additionally, we relate iron-mediated metabolic regulation to obesity and obesity-related complications.

Iron overload, oxidative stress and vascular dysfunction: Evidences from clinical studies and animal models

Although iron is a metal involved in many in vital processes due to its redox capacity, body iron overloads lead to tissue damage, including the cardiovascular system. While cardiomyopathy was the focus since the 1960s, the impact on the vasculature was comparatively neglected for about 40 years, when clinical studies correlating iron overload, oxidative stress, endothelial dysfunction, arterial stiffness and atherosclerosis reinforced an "iron hypothesis". Due to controversial results from some epidemiological studies investigating atherosclerotic events and iron levels, well-controlled trials and animal studies provided essential data about the influence of iron, per se, on the vasculature. As a result, the pathophysiology of vascular dysfunction in iron overload have been revisited. This review summarizes the knowledge obtained from epidemiological studies, animal models and "in vitro" cellular systems in recent decades, highlighting a more harmful than innocent role of iron excess for the vascular homeostasis, which supports our proposal to hereafter denominate "iron overload vasculopathy". Additionally, evidence-based therapeutic targets are pointed out to be tested in pre-clinical research that may be useful in cardiovascular protection for patients with iron overload syndromes.

Research Progress on Relationship Between Iron Overload and Lower Limb Arterial Disease in Type 2 Diabetes Mellitus

Iron is one of the most important trace elements in life activities. It participates in a variety of important physiological processes in the body through oxidation-reduction reaction. A large number of studies show that iron overload (IO) is closely related to the progression of diabetes and its various chronic complications. However, the mechanism of iron overload in the pathogenesis of diabetes and the mechanism of iron overload in atherosclerosis (AS) are still controversial, and the relationship between iron overload and diabetic lower extremity arterial disease (LEAD) remains still unclear. Some recent reviews and original research articles suggest further studies to explain the complex relationship between iron metabolism and atherosclerosis. This article reviews the relationship between iron overload and diabetes and its relationship with LEAD, and discusses its mechanisms from various aspects, such as lipid peroxidation induced by iron overload, so as to provide clinical diagnosis and treatment ideas for diabetic lower extremity arterial disease. It is hoped that early evaluation, diagnosis and treatment of LEAD will be inspired.

Optimized 3D Culture of Hepatic Cells for Liver Organoid Metabolic Assays

The liver is among the principal organs for glucose homeostasis and metabolism. Studies of liver metabolism are limited by the inability to expand primary hepatocytes in vitro while maintaining their metabolic functions. Human hepatic three-dimensional (3D) organoids have been established using defined factors, yet hepatic organoids from adult donors showed impaired expansion. We examined conditions to facilitate the expansion of adult donor-derived hepatic organoids (HepAOs) and HepG2 cells in organoid cultures (HepGOs) using combinations of growth factors and small molecules. The expansion dynamics, gluconeogenic and HNF4α expression, and albumin secretion are assessed. The conditions tested allow the generation of HepAOs and HepGOs in 3D cultures. Nevertheless, gluconeogenic gene expression varies greatly between conditions. The organoid expansion rates are limited when including the TGFβ inhibitor A8301, while are relatively higher with Forskolin (FSK) and Oncostatin M (OSM). Notably, expanded HepGOs grown in the optimized condition maintain detectable gluconeogenic expression in a spatiotemporal distribution at 8 weeks. We present optimized conditions by limiting A8301 and incorporating FSK and OSM to allow the expansion of HepAOs from adult donors and HepGOs with gluconeogenic competence. These models increase the repertoire of human hepatic cellular tools available for use in liver metabolic assays.

Adaptation of the heart to Frataxin depletion: Evidence that integrated stress response can predominate over mTORC1 activation

Friedreich's ataxia (FRDA) is an inherited disorder caused by depletion of frataxin (FXN), a mitochondrial protein required for iron-sulfur cluster (ISC) biogenesis. Cardiac dysfunction is the main cause of death. Yet pathogenesis, and, more generally, how the heart adapts to FXN loss, remain poorly understood, though are expected to be linked to an energy deficit. We modified a transgenic (TG) mouse model of inducible FXN depletion that permits phenotypic evaluation of the heart at different FXN levels, and focused on substrate-specific bioenergetics and stress signaling. When FXN protein in the TG heart was 17% of normal, bioenergetics and signaling were not different from control. When, 8 weeks later, FXN was ~ 97% depleted in the heart, TG heart mass and cardiomyocyte cross-sectional area were less, without evidence of fibrosis or apoptosis. mTORC1 signaling was activated, as was the integrated stress response, evidenced by greater phosphorylation of eIF2α relative to total eIF2α, and decreased protein translation. We interpret these results to suggest that, in TG hearts, an anabolic stimulus was constrained by eIF2α phosphorylation. Cardiac contractility was maintained in the 97%-FXN-depleted hearts, possibly contributed by an unexpected preservation of β-oxidation, though pyruvate oxidation was lower. Bioenergetics alterations were matched by changes in the mitochondrial proteome, including a non-uniform decrease in abundance of ISC-containing proteins. Altogether, these findings suggest that the FXN depleted heart can suppress a major ATP demanding process such as protein translation, which, together with some preservation of β-oxidation, could be adaptive, at least in the short term.

Myeloid-specific deletion of ferroportin impairs macrophage bioenergetics but is disconnected from systemic insulin action in adult mice

Tissue iron overload is associated with insulin resistance and mitochondrial dysfunction in rodents and humans; however, the mechanisms or cell types that mediate this phenotype are not completely understood. Macrophages (Mɸs) are known to contribute to iron handling; thus, we hypothesized that perturbed iron handling by Mɸs impairs mitochondrial energetics and evokes systemic insulin resistance in mice. Male and female mice with myeloid-targeted (LysMCre) deletion of the canonical iron exporter, ferroportin (Fpn, encoded by Slc40a1), floxed littermates, and C57BL/6J wild-type mice were used to test our hypotheses. Myeloid-targeted deletion of Fpn evoked multitissue iron accumulation and reduced mitochondrial respiration in bone marrow-derived Mɸs, liver leukocytes, and Mɸ-enriched populations from adipose tissue (AT). In addition, a single bolus of exogenous iron administered to C57BL/6J mice phenocopied the loss of Fpn, resulting in a reduction in maximal and mitochondrial reserve capacity in Mɸ-enriched cellular fractions from liver and AT. In vivo exogenous iron chelation restored mitochondrial reserve capacity in liver leukocytes from Fpn LysMCre mice, but had no effect in AT myeloid populations. However, despite the impairments in mitochondrial respiration, neither loss of myeloid-specific Fpn nor exogenous iron overload perturbed glucose homeostasis or systemic insulin action in lean or obese mice, whereas aging coupled with lifelong loss of Fpn unmasked glucose intolerance. Together these data demonstrate that iron handling is critical for the maintenance of macrophage mitochondrial function, but perturbing myeloid iron flux via the loss of Fpn action is not sufficient to evoke systemic insulin resistance in young adult mice. These findings also suggest that if Mɸs are capable of storing iron properly, they have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance that may be age dependent.NEW & NOTEWORTHY We used myeloid-specific knockout of ferroportin to determine whether macrophage iron enrichment alters systemic metabolism. We found that macrophages in several tissues showed mitochondrial defects such as a reduction in mitochondrial reserve capacity. However, insulin action in the mice was preserved. These findings also suggest that Mɸs have a pronounced ability to withstand iron excess without evoking overt collateral damage and associated insulin resistance, which appears to be age dependent.

Dietary iron overload mitigates atherosclerosis in high-fat diet-fed apolipoprotein E knockout mice: Role of dysregulated hepatic fatty acid metabolism

The atherosclerosis "iron hypothesis" generates a fair amount of debate since it has been proposed. Here, we revisited the "iron hypothesis" by examining whether dietary iron overload would intensify iron deposition in plaques and thus lead to further exacerbation of atherosclerosis in apolipoprotein E knockout (ApoE KO) mice. ApoE KO mice were fed either a normal chow diet (ND) or a high fat diet (HFD) supplemented with or without 2% carbonyl iron (Fe) for 16 weeks. However, contrary to our assumption, dietary iron overloading did not intensify, but rather diminished the atherosclerotic lesion area by 65.3%, which was accompanied by significantly decreased serum total cholesterol, triglyceride and low-density lipoprotein cholesterol contents, together with hepatic lipid accumulation decline, despite the evident existence of aortic iron accumulation and the typical signs of iron overload in ApoE KO mice. Using isobaric tag for absolute quantification (iTRAQ) proteomics approach, hepatic CD36 and fatty acid binding proteins-mediated fatty acid (FA) uptake and trafficking impairment were identified as the key potential pathomechanisms by which iron overload diminishes atherosclerotic lesions. Furthermore, downstream hepatic FA de novo biosynthesis was enhanced and FA oxidation was inhibited to compensate for the FA deficiency triggered by iron overload-impaired fatty acid uptake and trafficking. Our findings suggested that dietary iron overload is not atherogenic in ApoE KO mice, and more research efforts are warranted to revisit the "iron hypothesis" of atherosclerosis.

Non-Enzymatic Glycation of Transferrin and Diabetes Mellitus

Diabetes is a metabolic disease characterized by high blood sugar. Its complications may damage multiple organs, such as eyes, kidneys, heart, blood vessels, and nerves, severely threatening human health. Transferrin (Tf) is a major iron transport protein in the body. Recent studies have shown that the degree of non-enzymatic glycated modification of Tf is increased in diabetic patients, and glycated Tf is closely related to the occurrence and development of diabetes and diabetic complications. However, the molecular mechanisms underlying this glycated modification in diabetes and diabetic complications are still unclear. It is speculated that the mechanism may be that glycated modification reduces the binding ability of Tf and its receptor TfR, followed by excessive iron accumulation in the body. Iron overload in the body may further lead to the death of pancreatic beta cells and insulin resistance by increasing oxidative stress, inducing iron death, interfering with the insulin signaling pathway, and causing autophagy deficiency. In addition, non-enzymatic glycation affects the binding of Tf with chromium and reduces the ability of Tf to transport chromium into tissues, resulting in a decrease in the levels of chromium in tissues and ultimately affecting the sensitivity of tissues to insulin. In diabetic patients, the concentrations of glycated Tf in serum were significantly correlated with those of fructosamine.Tf has a shorter half-life, and not affected by anemia or hypoalbuminemia and less negative charge under physiological conditions, while glycated modification could not change the isoelectric point of Tf, which easily passes through the negatively charged basement membrane of the glomerulus. Therefore, compared to glucosamine, HbA1C, etc., glycated Tf may be a future biomarker for evaluating short-term glycemic control and early renal damage in diabetic patients.

Regulatory Connections between Iron and Glucose Metabolism

Iron is essential for energy metabolism, and states of iron deficiency or excess are detrimental for organisms and cells. Therefore, iron and carbohydrate metabolism are tightly regulated. Serum iron and glucose levels are subjected to hormonal regulation by hepcidin and insulin, respectively. Hepcidin is a liver-derived peptide hormone that inactivates the iron exporter ferroportin in target cells, thereby limiting iron efflux to the bloodstream. Insulin is a protein hormone secreted from pancreatic β-cells that stimulates glucose uptake and metabolism via insulin receptor signaling. There is increasing evidence that systemic, but also cellular iron and glucose metabolic pathways are interconnected. This review article presents relevant data derived primarily from mouse models and biochemical studies. In addition, it discusses iron and glucose metabolism in the context of human disease.

Targeting DUSP7 signaling alleviates hepatic steatosis, inflammation and oxidative stress in high fat diet (HFD)-fed mice via suppression of TAK1

The non-alcoholic fatty liver disease (NAFLD), as a critical liver disease, is still lack of effective treatments because the molecular mechanism revealing the NAFLD pathogenesis remains unclear. Dual specific phosphatase 6 (DUSP7) shows effects on inflammatory response and is a negative feedback mechanism of the mitogen-activated protein kinase (MAPK) superfamily, which are critical factors in regulating NAFLD progression. However, the effects of DUSP7 on hepatic steatosis are still not fully understood. Here, we found that DUSP7 functioned as a negative regulator of NAFLD and in various metabolic disorders. DUSP7 expression was markedly reduced in liver samples from patients with simple hepatic steatosis or non-alcoholic steatohepatitis (NASH), as well as in liver tissues from high fat diet (HFD)-challenged mice or genetically obese (ob/ob) mice. DUSP7 knockout markedly accelerated insulin resistance, glucose intolerance, liver dysfunction, fibrosis and hepatic steatosis in HFD-fed mice. In addition, inflammatory response was significantly exacerbated in HFD-challenged mice with DUSP7 deletion, which was associated with the elevated activation of nuclear factor-κB (NF-κB) and MAPKs signaling pathways. Moreover, oxidative stress was detected in liver of HFD-induced mice, and this phenomenon was aggravated in mice with DUSP7 knockout. Importantly, we demonstrated that DUSP7 physically interacted with transforming growth factor β (TGF-β)-activated kinase (TAK1). DUSP7 deletion considerably promoted the activation of TAK1 in mice after HFD feeding, contributing to the lipid deposition, inflammatory response and reactive oxygen species (ROS) production. Taken together, DUSP7 might function as a protective factor against NAFLD development and metabolic disorder through alleviating dyslipidemia, inflammation and oxidative stress by directly interacting with TAK1 in hepatocytes, which was involved in the suppression of fibrosis. Thus, we may provide an effective strategy for the treatment of hepatic steatosis via targeting DUSP7.

Iron overload inhibits late stage autophagic flux leading to insulin resistance

Iron overload, a common clinical occurrence, is implicated in the metabolic syndrome although the contributing pathophysiological mechanisms are not fully defined. We show that prolonged iron overload results in an autophagy defect associated with accumulation of dysfunctional autolysosomes and loss of free lysosomes in skeletal muscle. These autophagy defects contribute to impaired insulin-stimulated glucose uptake and insulin signaling. Mechanistically, we show that iron overload leads to a decrease in Akt-mediated repression of tuberous sclerosis complex (TSC2) and Rheb-mediated mTORC1 activation on autolysosomes, thereby inhibiting autophagic-lysosome regeneration. Constitutive activation of mTORC1 or iron withdrawal replenishes lysosomal pools via increased mTORC1-UVRAG signaling, which restores insulin sensitivity. Induction of iron overload via intravenous iron-dextran delivery in mice also results in insulin resistance accompanied by abnormal autophagosome accumulation, lysosomal loss, and decreased mTORC1-UVRAG signaling in muscle. Collectively, our results show that chronic iron overload leads to a profound autophagy defect through mTORC1-UVRAG inhibition and provides new mechanistic insight into metabolic syndrome-associated insulin resistance.