Short-term hyperglycemia increases arterial superoxide production and iron dysregulation in atherosclerotic monkeys

Targeting PKCα alleviates iron overload in diabetes and hemochromatosis through the inhibition of ferroportin

ABSTRACT

Ferroportin (Fpn) is the only iron exporter, playing a crucial role in systemic iron homeostasis. Fpn is negatively regulated by its ligand hepcidin, but other potential regulators in physiological and disease conditions remain poorly understood. Diabetes is a metabolic disorder that develops body iron loading with unknown mechanisms. By using diabetic mouse models and human duodenal specimens, we demonstrated that intestinal Fpn expression was increased in diabetes in a hepcidin-independent manner. Protein kinase C (PKC) is hyperactivated in diabetes. We showed that PKCα was required to sustain baseline Fpn expression and diabetes-induced Fpn upregulation in the enterocytes and macrophages. Knockout of PKCα abolished diabetes-associated iron overload. Mechanistically, activation of PKCα increased the exocytotic trafficking of Fpn and decreased the endocytic trafficking of Fpn in the resting state. Hyperactive PKCα also suppressed hepcidin-induced ubiquitination, internalization, and degradation of Fpn. We further observed that iron loading in the enterocytes and macrophages activated PKCα, acting as a novel mechanism to enhance Fpn-dependent iron efflux. Finally, we demonstrated that the loss-of-function of PKCα and pharmacological inhibition of PKC significantly alleviated hereditary hemochromatosis-associated iron overload. Our study has highlighted, to our knowledge, for the first time, that PKCα is an important positive regulator of Fpn and a new target in the control of iron homeostasis.

Non-coding RNAs in diabetic foot ulcer- a focus on infected wounds

Diabetes mellitus is associated with a wide range of neuropathies, vasculopathies, and immunopathies, resulting in many complications. More than 30% of diabetic patients risk developing diabetic foot ulcers (DFUs). Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), play essential roles in various biological functions in the hyperglycaemic environment that determines the development of DFU. Ulceration results in tissue breakdown and skin barrier scavenging, thereby facilitating bacterial infection and biofilm formation. Many bacteria contribute to diabetic foot infection (DFI), including Staphylococcus aureus (S. aureus) et al. A heterogeneous group of "ncRNAs," termed small RNAs (sRNAs), powerfully regulates biofilm formation and DFI healing. Multidisciplinary foot care interventions have been identified for nonhealing ulcers. With an appreciation of the link between disease processes and ncRNAs, a novel therapeutic model of bioactive materials loaded with ncRNAs has been developed to prevent and manage diabetic foot complications.

Targeting PKC alleviates iron overload in diabetes and hemochromatosis

Diabetes is one of the most prevalent chronic diseases worldwide. Iron overload increases the incidence of diabetes and aggravates diabetic complications that cause mortality. Reciprocally, diabetes potentially promotes body iron loading, but the mechanism remains not well understood. In this study, we demonstrated systemic iron excess and the upregulation of iron exporter ferroportin (Fpn) in the enterocytes and macrophages of multiple diabetic mouse models. Increased Fpn expression and iron efflux was also seen in the enterocytes of type 2 diabetic human patients. We further showed that protein kinase C (PKC), which is activated in hyperglycemia, was responsible for the sustained membrane expression of Fpn in physiological and in diabetic settings. For the first time, we identified that PKCs were novel binding proteins and positive regulators of Fpn. Mechanistically, hyperactive PKC promoted exocytotic membrane insertion while inhibited the endocytic trafficking of Fpn in the resting state. PKC also protected Fpn from internalization and degradation by its ligand hepcidin dependent on decreased ubiquitination and increased phosphorylation of Fpn. Importantly, the loss-of-function and pharmacological inhibition of PKC alleviated systemic iron overload in diabetes and hemochromatosis. Our study thus highlights PKC as a novel target in the control of systemic iron homeostasis.

A Role of Glucose Overload in Diabetic Cardiomyopathy in Nonhuman Primates

Type 2 diabetes (T2D) plays a major role in the development of heart failure. Patients with T2D have an increased risk to develop HF than healthy subjects, and they always have very poor outcomes and survival rates. However, the underlying mechanisms for this are still unclear. To help develop new therapeutic interventions, well-characterized animal models for preclinical and translational investigations in T2D and HF are urgently needed. Although studies in rodents are more often used, the research findings in rodents have often failed to be translated into humans due to the significant metabolic differences between rodents and humans. Nonhuman primates (NHPs) serve as valuable translational models between basic studies in rodent models and clinical studies in humans. NHPs can recapitulate the natural progress of these diseases in humans and study the underlying mechanism due to their genetic similarity and comparable spontaneous T2D rates to humans. In this review, we discuss the importance of using NHPs models in understanding diabetic cardiomyopathy (DCM) in humans with aspects of correlations between hyperglycemia and cardiac dysfunction progression, glucose overload, and altered glucose metabolism promoting cardiac oxidative stress and mitochondria dysfunction, glucose, and its effect on cardiac resynchronization therapy with defibrillator (CRT-d), the currently available diabetic NHPs models and the limitations involved in the use of NHP models.

In vitro and in vivo anti-diabetic and anti-oxidant activities of methanolic leaf extracts of Ocimum canum

Background:

Diabetes is a metabolic disorder with a highly complex, multifaceted and intricate etiologies and thus may require management options that proffers multimodal mechanism of action. This present study evaluated the antidiabetic and antioxidant potential of the methanolic extract/fractions of leaves of Ocimum canum.

Methods:

The antidiabetic potential was evaluated and using STZ-induced diabetic Wistar rat model (in vivo) and inhibition of α-amylase and α-glucosidase activity (in vitro). Antioxidant activity was assessed in vitro by free radical scavenging and reducing power assays and in vivo via monitoring SOD and CAT activities; GSH and MDA levels.

Results:

The total phenolic content (221.0±3.0 mg catechol/g of sample) and tannins (146.0±4.0 mg tannic acid/g of sample) of the crude extract; and flavonoid of the aqueous-methanol fraction (216.0.0±1.0 mg of rutin/g of sample) were found to be significantly higher relative to others. The crude extract and the aqueous-methanol fraction exhibited a significantly (p<0.05) higher percentage reduction in fasting blood glucose and a concomitant increase in serum insulin level relative to the diabetic control group. The highest radical scavenging activity and reducing power were observed in the aqueous-methanol fraction. The aqueous-methanol solvent fraction also significantly reversed the alterations in oxidative stress markers occasioned by the diabetic condition.

Conclusion:

In conclusion, the result of the present study has demonstrated evidently that extracts of Ocimum canum leaves ameliorates hyperglycemia and the associated oxidative stress in STZ-induced rats.

Hyperglycemia promotes microvillus membrane expression of DMT1 in intestinal epithelial cells in a PKCα-dependent manner

Excessive iron increases the incidence of diabetes and worsens diabetic complications. Reciprocally, diabetes induces iron loading, partially attributable to elevated intestinal iron export according to a recent report. Herein, we show that iron uptake and the mRNA expression of iron importer divalent metal transporter 1 (DMT1) were significantly increased in the duodenum of streptozotocin-induced diabetic mice. Immunofluorescence staining of human intestinal biopsies revealed increased brush border membrane (BBM) and decreased cytoplasmic DMT1 expression in patients with diabetes, suggesting translocation of DMT1. This pattern of DMT1 regulation was corroborated by immunoblotting results in diabetic mice showing that BBM DMT1 expression was increased by 210%, in contrast to a 60% increase in total DMT1. PKC mediates many diabetic complications, and PKCα activity was increased in diabetic mouse intestine. Intriguingly, diabetic mice with PKCα deficiency did not show increases in iron uptake and BBM DMT1 expression. High-glucose treatment increased plasma membrane DMT1 expression via the activation of PKCα in cultured IECs. Inhibition of PKCα potentiated the ubiquitination and degradation of DMT1 protein. We further showed that high glucose suppressed membrane DMT1 internalization. These findings demonstrate that PKCα promotes microvillus membrane DMT1 expression and intestinal iron uptake, contributing to diabetic iron loading.-Zhao, L., Bartnikas, T., Chu, X., Klein, J., Yun, C., Srinivasan, S., He, P. Hyperglycemia promotes microvillus membrane expression of DMT1 in intestinal epithelial cells in a PKCα-dependent manner.

Prion protein modulates glucose homeostasis by altering intracellular iron

The prion protein (PrP^C), a mainly neuronal protein, is known to modulate glucose homeostasis in mouse models. We explored the underlying mechanism in mouse models and the human pancreatic β-cell line 1.1B4. We report expression of PrP^C on mouse pancreatic β-cells, where it promoted uptake of iron through divalent-metal-transporters. Accordingly, pancreatic iron stores in PrP knockout mice (PrP^-/-) were significantly lower than wild type (PrP^+/+) controls. Silencing of PrP^C in 1.1B4 cells resulted in significant depletion of intracellular (IC) iron, and remarkably, upregulation of glucose transporter GLUT2 and insulin. Iron overloading, on the other hand, resulted in downregulation of GLUT2 and insulin in a PrP^C-dependent manner. Similar observations were noted in the brain, liver, and neuroretina of iron overloaded PrP^+/+ but not PrP^-/- mice, indicating PrP^C-mediated modulation of insulin and glucose homeostasis through iron. Peripheral challenge with glucose and insulin revealed blunting of the response in iron-overloaded PrP^+/+ relative to PrP^-/- mice, suggesting that PrP^C-mediated modulation of IC iron influences both secretion and sensitivity of peripheral organs to insulin. These observations have implications for Alzheimer's disease and diabetic retinopathy, known complications of type-2-diabetes associated with brain and ocular iron-dyshomeostasis.

Iron reduction response and demographic differences between diabetics and non-diabetics with cardiovascular disease entered into a controlled clinical trial

Filings of elemental iron separated magnetically from a homogenate of breakfast cereal implicated in the risk of cardiovascular disease and diabetes.

Hepcidin is directly regulated by insulin and plays an important role in iron overload in streptozotocin-induced diabetic rats

Iron overload is frequently observed in type 2 diabetes mellitus (DM2), but the underlying mechanisms remain unclear. We hypothesize that hepcidin may be directly regulated by insulin and play an important role in iron overload in DM2. We therefore examined the hepatic iron content, serum iron parameters, intestinal iron absorption, and liver hepcidin expression in rats treated with streptozotocin (STZ), which was given alone or after insulin resistance induced by a high-fat diet. The direct effect of insulin on hepcidin and its molecular mechanisms were furthermore determined in vitro in HepG2 cells. STZ administration caused a significant reduction in liver hepcidin level and a marked increase in intestinal iron absorption and serum and hepatic iron content. Insulin obviously upregulated hepcidin expression in HepG2 cells and enhanced signal transducer and activator of transcription 3 protein synthesis and DNA binding activity. The effect of insulin on hepcidin disappeared when the signal transducer and activator of transcription 3 pathway was blocked and could be partially inhibited by U0126. In conclusion, the current study suggests that hepcidin can be directly regulated by insulin, and the suppressed liver hepcidin synthesis may be an important reason for the iron overload in DM2.

A role for diallyl trisulfide in mitochondrial antioxidative stress contributes to its protective effects against vascular endothelial impairment

Persistent hyperglycemia increases a systemic oxidative stress, causing the onset of vascular endothelial dysfunction and atherosclerosis. Diallyl trisulfide (DAT), a natural organosulfur compound in garlic, has been reported to have actions of dilating blood vessels and antibacteria, etc. In this study, models of obese diabetic rat in vivo and high glucose concentration (HG)-induced endothelial cell injury in vitro were used to investigate the protective effects of DAT on vascular endothelial injury and its underlying mechanisms. In the in vivo model, the obese diabetic rats were injected venously with DAT (5.0 mg kg(-1)d(-1)) and Vitamin E (1.0 mg kg(-1)d(-1)) respectively, once daily for 7 consecutive days. In the in vitro model, HG-injured HUVEC were treated with or without DAT (25 µmol L(-1), 50 µmol L(-1), 100 µmol L(-1)) or Vitamin E (25 µmol L(-1)) respectively for 24h. The extents of vascular endothelial injury and protective effects of DAT were evaluated. The results both in vivo and in vitro displayed that DAT-treatment significantly attenuated the endothelial cell impairments. Besides, DAT-treatment markedly decreased the levels of malondialdehyde (MDA) and reactive oxygen species, whereas elevated the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in mitochondrium. Moreover, DAT-treatment considerably improved mitochondrial respiration function. Taken together, our results suggest that DAT protects vascular endothelium from HG or hyperglycemia induced-injury by reducing mitochondrial oxidative stress. The findings provide a novel insight for DAT to potentially treat the oxidative stress diseases, i.e., atherosclerosis, diabetes, and neurodegenerative diseases.

Exacerbation of glycoprotein VI-dependent platelet responses in a rhesus monkey model of Type 1 diabetes

Thrombosis is a life-threatening complication of diabetes. Platelet reactivity is crucial to thrombus formation, particularly in arterial vessels and in thrombotic complications causing myocardial infarction or ischaemic stroke, but diabetic patients often respond poorly to current antiplatelet medication. In this study, we used a nonhuman primate model of Type 1 diabetes to measure early downstream signalling events following engagement of the major platelet collagen receptor, glycoprotein (GP)VI. Diabetic monkeys were given enough insulin to maintain their blood glucose levels either at ~8 mM (well-controlled diabetes) or ~15 mM (poorly controlled diabetes). Flow cytometric analysis was used to measure platelet reactive oxygen species (ROS) generation, calcium mobilisation, receptor surface expression, and immature platelet fraction. We observed exacerbated intracellular ROS and calcium flux associated with engagement of GPVI in monkeys with poorly controlled diabetes. GPVI surface levels did not differ between healthy monkeys or the two diabetic groups. Treatment of platelets with the specific Syk inhibitor BAY61-3606 inhibited GPVI-dependent ROS and, importantly, reduced ROS generation in the poorly controlled diabetes group to that observed in healthy monkeys. These data indicate that glycaemic control is important in reducing GPVI-dependent platelet hyperreactivity and point to a potential antithrombotic therapeutic benefit of Syk inhibition in hyperglycaemic diabetes.

Nonhuman primates and other animal models in diabetes research

Animal models are important for determining the pathogenesis of and potential treatments for obesity and diabetes. Nonhuman primates (NHPs) are particularly useful for studying these disorders. As in humans, type 2 diabetes mellitus is the most common form of diabetes in NHPs and occurs more often in older obese animals, with a metabolic progression from insulin resistance (IR) and impaired glucose tolerance to overt diabetes. Histopathologic changes in pancreatic islets are also similar to those seen in humans with diabetes. Initially, there is islet hyperplasia with abundant insulin production to compensate for IR, followed by insufficient insulin production with replacement of islets with islet-associated amyloid. Diabetic NHPs also have adverse changes in plasma lipid and lipoprotein concentrations, biomarkers of obesity, inflammation, and oxidative stress, and protein glycation that contribute to the numerous complications of the disease. Furthermore, sex hormones, pregnancy, and environmental factors (e.g., diet and stress) affect IR and can also contribute to diabetes progression in NHPs. Additionally, due to their similar clinical and pathologic characteristics, NHPs have been used in many pharmacological studies to assess new therapeutic agents. For these reasons, NHPs are particularly valuable animal models of obesity and diabetes for studying disease pathogenesis, risk factors, comorbidities, and therapeutic interventions.

Reduced metal ion concentrations in atherosclerotic plaques from subjects with type 2 diabetes mellitus

AIMS

Transition metal ions have been implicated in atherosclerosis. The goal of this study was to investigate whether metal ion levels were higher in people with diabetes, in view of their increased risk of aggravated atherosclerosis.

METHODS AND RESULTS

Absolute concentrations of iron, copper, zinc and calcium, and products of protein and lipid oxidation were quantified in atherosclerotic lesions from subjects with (T2DM, n=27), without Type 2 diabetes (nonDM, n=22), or hyperglycaemia (HG, n=17). Iron (P<0.05), zinc (P<0.01) and calcium (P=0.01) were lower in T2DM compared to nonDM subjects. Copper levels were comparable. A strong correlation (r=0.618; P<0.001) between EPR-detectable and total iron in nonDM patients was not seen in T2DM. X-ray fluorescence microscopy revealed "hot spots" of iron in both T2DM and nonDM. Calcium and zinc co-localised and levels correlated strongly. F(2)-isoprostanes (P<0.05) and di-Tyr/Tyr ratio (P<0.025), oxidative damage markers were decreased in T2DM compared to nonDM, or HG.

CONCLUSION

Advanced atherosclerotic lesions from T2DM subjects unexpectedly contained lower levels of transition metal ions, and protein and lipid oxidation products, compared to nonDM and HG. These data do not support the hypothesis that elevated metal ion levels may be a major causative factor in the aggravated atherosclerosis observed in T2DM patients.