Intracellular zinc in insulin secretion and action: a determinant of diabetes risk?

Marginal Zinc Deficiency Promotes Pancreatic Islet Enlargement While Zinc Supplementation Improves the Pancreatic Insulin Response in Zucker Diabetic Fatty Rats

Zinc deficiency has been associated with the worsening of diabetes while zinc supplementation has been proposed to ameliorate diabetes. This study examined the effects of marginal zinc deficiency (MZD) and zinc supplementation (ZS) on obesity, glycemic control, pancreatic islets, hepatic steatosis and renal function of Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed an MZD, zinc control (ZC) or ZS diet (4, 30 and 300 mg Zn/kg diet, respectively), and lean Zucker rats were fed a ZC diet for 8 weeks. MZD and ZS did not alter body weight or whole-body composition in ZDF rats. MZD ZDF rats had reduced zinc concentrations in the femur and pancreas, a greater number of enlarged pancreatic islets and a diminished response to an oral glucose load based on a 1.8-fold greater incremental area-under-the-curve (AUC) for glucose compared to ZC ZDF. ZS ZDF rats had elevated serum, femur and pancreatic zinc concentrations, unchanged pancreatic parameters and a 50% reduction in the AUC for insulin compared to ZC ZDF rats, suggesting greater insulin sensitivity. Dietary zinc intake did not alter hepatic steatosis, creatinine clearance, or levels of proteins that contribute to insulin signaling, inflammation or zinc transport in epididymal fat. Potential adverse effects of ZS were suggested by reduced hepatic copper concentrations and elevated serum urea compared to ZC ZDF rats. In summary, ZS improved the pancreatic insulin response but not the glucose handling. In contrast, reduced zinc status in ZDF rats led to impaired glucose tolerance and a compensatory increase in the number and size of pancreatic islets which could lead to β-cell exhaustion.

Development of a live cell assay for the zinc transporter ZnT8

Zinc is an essential trace element that is involved in many biological processes and in cellular homeostasis. In pancreatic β-cells, zinc is crucial for the synthesis, processing, and secretion of insulin, which plays a key role in glucose homeostasis and which deficiency is the cause of diabetes. The accumulation of zinc in pancreatic cells is regulated by the solute carrier transporter SLC30A8 (or Zinc Transporter 8, ZnT8), which transports zinc from cytoplasm in intracellular vesicles. Allelic variants of SLC30A8 gene have been linked to diabetes. Given the physiological intracellular localization of SLC30A8 in pancreatic β-cells and the ubiquitous endogenous expression of other Zinc transporters in different cell lines that could be used as cellular model for SLC30A8 recombinant over-expression, it is challenging to develop a functional assay to measure SLC30A8 activity. To achieve this goal, we have firstly generated a HEK293 cell line stably overexpressing SLC30A8, where the over-expression favors the partial localization of SLC30A8 on the plasma membrane. Then, we used the combination of this cell model, commercial FluoZin-3 cell permeant zinc dye and live cell imaging approach to follow zinc flux across SLC30A8 over-expressed on plasma membrane, thus developing a novel functional imaging- based assay specific for SLC30A8. Our novel approach can be further explored and optimized, paving the way for future small molecule medium-throughput screening.

Multiple genetic variants at the SLC30A8 locus affect local super-enhancer activity and influence pancreatic β-cell survival and function

Variants at the SLC30A8 locus are associated with type 2 diabetes (T2D) risk. The lead variant, rs13266634, encodes an amino acid change, Arg325Trp (R325W), at the C-terminus of the secretory granule-enriched zinc transporter, ZnT8. Although this protein-coding variant was previously thought to be the sole driver of T2D risk at this locus, recent studies have provided evidence for lowered expression of SLC30A8 mRNA in protective allele carriers. In the present study, we examined multiple variants that influence SLC30A8 allele-specific expression. Epigenomic mapping has previously identified an islet-selective enhancer cluster at the SLC30A8 locus, hosting multiple T2D risk and cASE associations, which is spatially associated with the SLC30A8 promoter and additional neighboring genes. Here, we show that deletion of variant-bearing enhancer regions using CRISPR-Cas9 in human-derived EndoC-βH3 cells lowers the expression of SLC30A8 and several neighboring genes and improves glucose-stimulated insulin secretion. While downregulation of SLC30A8 had no effect on beta cell survival, loss of UTP23, RAD21, or MED30 markedly reduced cell viability. Although eQTL or cASE analyses in human islets did not support the association between these additional genes and diabetes risk, the transcriptional regulator JQ1 lowered the expression of multiple genes at the SLC30A8 locus and enhanced stimulated insulin secretion.

Mediation effect of serum zinc on insulin secretion inhibited by methyl tert-butyl ether in gas station workers

Methyl tert-butyl ether (MTBE), a type of gasoline additive, has been found to affect insulin function and glucose homeostasis in animal experiments, but there is still no epidemiological evidence. Zinc (Zn) is a key regulatory element of insulin secretion and function, and Zn homeostasis can be disrupted by MTBE exposure through inducing oxidative stress. Therefore, we suspected that Zn might be involved and play an important role in the process of insulin secretion inhibited by MTBE exposure. In this study, we recruited 201 male subjects including occupational and non-occupational MTBE exposure from Anhui Province, China in 2019. Serum insulin and functional analog fibroblast growth factor 1 (FGF1) and blood MTBE were detected by Elisa and headspace solid-phase microextraction and gas chromatography-high-resolution mass spectrometry. According to MTBE internal exposure level, the workers were divided into low- and high-exposed groups and found that the serum insulin level in the high-exposed group was significantly lower than that in the low-exposed group (p = 0.003) while fasting plasma glucose (FPG) level increased obviously in the high-exposed group compared to the low-exposed group (p = 0.001). Further analysis showed that MTBE exposure level was positively correlated with FPG level, but negatively correlated with serum insulin level, which suggested that the FPG level increase might be related to the decrease of serum insulin level induced by MTBE exposure. The results of further mediation effect analysis showed that changes in serum zinc levels played a major intermediary role in the process of insulin secretion inhibition and blood glucose elevation caused by MTBE exposure. In addition, a significant negative correlation was found between MTBE exposure and serum Zn level, which might play a strong mediating effect on the inhibition of insulin secretion induced by MTBE exposure. In conclusion, our study provided evidence that MTBE could inhibit insulin secretion and interfere with Zn metabolism in gas station workers for the first time, and found that Zn might play an important mediation effect during the process of inhibiting insulin secretion and interfering with glucose metabolism induced by MTBE exposure.

"Green" synthesized versus chemically synthesized zinc oxide nanoparticles: In vivo antihyperglycemic activity and pharmacokinetics

Zinc is one of the most studied trace elements, commonly used as supplement in diabetes treatment. By its involvement in the synthesis, secretion of insulin, promotion of insulin sensitivity and its multiple enzymatic functions it is known to contribute to reduce hyperglycemia. Researchers have shown that zinc administered under the form of zinc oxide nanoparticles (ZnONPs) is more effective than under its ionic form. Studies evaluating the antihyperglycemic activity of these nanocarriers include both ZnONPs synthesised using plants (i.e. green synthesized) or chemically synthesized. The present work aims to compare green synthesized ZnONPs with the marketed chemically synthesized ones. Green ZnONPs were synthesized using the aqueous extract of the stem bark of the medicinal plant Panda oleosa and zinc nitrate hexahydrate. Both nanocarriers were compared in terms of optical properties, morphology, composition, chemical functions, resistance to oxidation, in vivo antihyperglycemic activity via oral glucose tolerance test (OGTT) and pharmacokinetics in relation to zinc in C57BL/6J mice. A UV absorption peak was observed at 354 nm and 374 nm for the green and marketed ZnONPs, respectively. The shape and hydrodynamic diameters were anisotropic and of 228.8 ± 3.0 nm for the green ZnONPs and spherical and of 225.6 ± 0.9 nm for the marketed ZnONPs. Phenolic compounds accounted for 2.58 ± 0.04% of the green ZnONPs and allowed them to be more stable and unaffected by an oxidizing agent during the experiment, while the marketed chemically synthesized ZnONPs aggregated with or without contact with an oxidizing agent. No significant differences were observed on the amounts of zinc absorbed when comparing green ZnONPs, chemically synthesized ZnONPs and zinc sulfate in a pharmacokinetics study in normoglycemic mice. When evaluating the in vivo hypoglycemic activity of the nanocarriers in obese/diabetic mice, green synthesized ZnONPs displayed a significant hypoglycemic effect compared with the chemically synthesized nanoparticles following an OGTT. Altogether, these data indicate that phytocompounds, as catechin derivatives and polyphenols, attached to the green synthesized ZnONPs' surface, could contribute to their hypoglycemic activity. The comparison thus demonstrated that green synthesized ZnONPs are significantly more efficient than chemically ones at reducing hyperglycemia regardless of their absorption.

Absence of Slc39a14/Zip14 in mouse pancreatic beta cells results in hyperinsulinemia

Zinc is an essential component of the insulin protein complex synthesized in β cells. The intracellular compartmentalization and distribution of zinc are controlled by 24 transmembrane zinc transporters belonging to the ZnT or Zrt/Irt-like protein (ZIP) family. Downregulation of SLC39A14/ZIP14 has been reported in pancreatic islets of patients with type 2 diabetes (T2D) as well as mouse models of high-fat diet (HFD)- or db/db-induced obesity. Our previous studies observed mild hyperinsulinemia in mice with whole body knockout of Slc39a14 (Zip14 KO). Based on our current secondary data analysis from an integrative single-cell RNA-seq dataset of human whole pancreatic tissue, SLC39A14 (coding ZIP14) is the only other zinc transporter expressed abundantly in human β cells besides well-known zinc transporter SLC30A8 (coding ZnT8). In the present work, using pancreatic β cell-specific knockout of Slc39a14 (β-Zip14 KO), we investigated the role of SLC39A14/ZIP14-mediated intracellular zinc trafficking in glucose-stimulated insulin secretion and subsequent metabolic responses. Glucose-stimulated insulin secretion, zinc concentrations, and cellular localization of ZIP14 were assessed using in vivo, ex vivo, and in vitro assays using β-Zip14 KO, isolated islets, and murine cell line MIN6. Metabolic evaluations were done on both chow- and HFD-fed mice using time-domain nuclear magnetic resonance and a comprehensive laboratory animal monitoring system. ZIP14 localizes on the endoplasmic reticulum regulating intracellular zinc trafficking in β cells and serves as a negative regulator of glucose-stimulated insulin secretion. Deletion of Zip14 resulted in greater glucose-stimulated insulin secretion, increased energy expenditure, and shifted energy metabolism toward fatty acid utilization. HFD caused β-Zip14 KO mice to develop greater islet hyperplasia, compensatory hyperinsulinemia, and mild insulin resistance and hyperglycemia. This study provided new insights into the contribution of metal transporter ZIP14-mediated intracellular zinc trafficking in glucose-stimulated insulin secretion and subsequent metabolic responses.NEW & NOTEWORTHY Metal transporter SLC39A14/ZIP14 is downregulated in pancreatic islets of patients with T2D and mouse models of HFD- or db/db-induced obesity. However, the function of ZIP14-mediated intracellular zinc trafficking in β cells is unknown. Our analyses revealed that SLC39A14 is the only Zn transporter expressed abundantly in human β cells besides SLC30A8. Within the β cells, ZIP14 is localized on the endoplasmic reticulum and serves as a negative regulator of insulin secretion, providing a potential therapeutic target for T2D.

Multiple genetic variants at the SLC30A8 locus affect local super-enhancer activity and influence pancreatic β-cell survival and function

Variants at the SLC30A8 locus are associated with type 2 diabetes (T2D) risk. The lead variant, rs13266634, encodes an amino acid change, Arg325Trp (R325W), at the C-terminus of the secretory granule-enriched zinc transporter, ZnT8. Although this protein-coding variant was previously thought to be the sole driver of T2D risk at this locus, recent studies have provided evidence for lowered expression of SLC30A8 mRNA in protective allele carriers. In the present study, combined allele-specific expression (cASE) analysis in human islets revealed multiple variants that influence SLC30A8 expression. Epigenomic mapping identified an islet-selective enhancer cluster at the SLC30A8 locus, hosting multiple T2D risk and cASE associations, which is spatially associated with the SLC30A8 promoter and additional neighbouring genes. Deletions of variant-bearing enhancer regions using CRISPR-Cas9 in human-derived EndoC-βH3 cells lowered the expression of SLC30A8 and several neighbouring genes, and improved insulin secretion. Whilst down-regulation of SLC30A8 had no effect on beta cell survival, loss of UTP23, RAD21 or MED30 markedly reduced cell viability. Although eQTL or cASE analyses in human islets did not support the association between these additional genes and diabetes risk, the transcriptional regulator JQ1 lowered the expression of multiple genes at the SLC30A8 locus and enhanced stimulated insulin secretion.

Investigations into the Signaling Pathways Involving Glucose-Stimulated Zinc Secretion (GSZS) from Prostate Epithelial Cells In Vitro and In Vivo

PURPOSE

Recently, we reported that exposure of prostate cells in vitro or the in vivo prostate to high glucose results in release of Zn2+ ions, a process now referred to as glucose-stimulated zinc secretion (GSZS). To our knowledge, the metabolic event(s) that trigger GSZS remain largely unknown. Here, we explore several signaling pathways both in vitro using a prostate epithelial cell line and in vivo from the rat prostate.

METHODS

PNT1A cells grown to confluence were washed and tagged with ZIMIR to monitor zinc secretion by optical methods. The expression levels of GLUT1, GLUT4, and Akt in cells cultured in either zinc-rich or zinc-poor media and after exposure to high versus low glucose were determined. Zinc secretion from the rat prostate in vivo as detected by MRI was compared in control animals after injection of glucose, deoxyglucose, or pyruvate to initiate zinc secretion and in animals pre-treated with WZB-117 (a GLUT1 inhibitor) or S961 (a peripheral insulin receptor inhibitor).

RESULTS

PNT1A cells exposed to high levels of glucose secrete zinc whereas cells exposed to an equivalent amount of deoxyglucose or pyruvate do not. Expression of Akt was dramatically altered by zinc supplementation of the culture media but not after exposure to glucose while GLUT1 and GLUT4 levels were less affected. Rats pre-treated with WZB-117 prior to imaging showed a reduction in GSZS from the prostate compared to controls whereas rats pre-treated with S961 showed no difference. Interestingly, in comparison to PNT1A cells, pyruvate and deoxyglucose also stimulate zinc secretion in vivo likely through indirect mechanisms.

CONCLUSIONS

GSZS requires metabolism of glucose both in vitro (PNT1A cells) and in vivo (rat prostate). Pyruvate also stimulates zinc secretion in vivo but likely via an indirect pathway involving rapid production of glucose via gluconeogenesis. These combined results support the conclusion that glycolytic flux is required to trigger GSZS in vivo.

The relationship between beta cell activation and SLC30A8/ZnT8 levels of the endocrine pancreas and maternal zinc deficiency in rats

OBJECTIVES

Zinc, which is found in high concentrations in the β-cells of the pancreas, is also a critical component for the endocrine functions of the pancreas. SLC30A8/ZnT8 is the carrier protein responsible for the transport of zinc from the cytoplasm to the insulin granules. The aim of this study was to investigate how dietary zinc status affects pancreatic beta cell activation and ZnT8 levels in infant male rats born to zinc-deficient mothers.

METHODS

The study was performed on male pups born to mothers fed a zinc-deficient diet. A total of 40 male rats were divided into 4 equal groups. Group 1: In addition to maternal zinc deficiency, this group was fed a zinc-deficient diet. Group 2: In addition to maternal zinc deficiency, this group was fed a standard diet. Group 3: In addition to maternal zinc deficiency, this group was fed a standard diet and received additional zinc supplementation. Group 4: Control group. Pancreas ZnT8 levels were determined by ELISA method and insulin-positive cell ratios in β-cells by immunohistochemistry.

RESULTS

The highest pancreatic ZnT8 levels and anti-insulin positive cell ratios in the current study were obtained in Group 3 and Group 4. In our study, the lowest pancreatic ZnT8 levels were obtained in Group 1 and Group 2, and the lowest pancreatic anti-insulin positive cell ratios were obtained in Group 1.

CONCLUSION

The results of the present study; in rats fed a zinc-deficient diet after maternal zinc deficiency has been established shows that ZnT8 levels and anti-insulin positive cell ratios in pancreatic tissue, which is significantly suppressed, reach control values with intraperitoneal zinc supplementation.

Novel ketamine and zinc treatment for anorexia nervosa and the potential beneficial interactions with the gut microbiome

Anorexia nervosa (AN) is a severe illness with diverse aetiological and maintaining contributors including neurobiological, metabolic, psychological, and social determining factors. In addition to nutritional recovery, multiple psychological and pharmacological therapies and brain-based stimulations have been explored; however, existing treatments have limited efficacy. This paper outlines a neurobiological model of glutamatergic and γ-aminobutyric acid (GABA)-ergic dysfunction, exacerbated by chronic gut microbiome dysbiosis and zinc depletion at a brain and gut level. The gut microbiome is established early in development, and early exposure to stress and adversity contribute to gut microbial disturbance in AN, early dysregulation to glutamatergic and GABAergic networks, interoceptive impairment, and inhibited caloric harvest from food (e.g., zinc malabsorption, competition for zinc ions between gut bacteria and host). Zinc is a key part of glutamatergic and GABAergic networks, and also affects leptin and gut microbial function; systems dysregulated in AN. Low doses of ketamine in conjunction with zinc, could provide an efficacious combination to act on NMDA receptors and normalise glutamatergic, GABAergic and gut function in AN.

Setting the Stage for Insulin Granule Dysfunction during Type-1-Diabetes: Is ER Stress the Culprit?

Type-1-diabetes (T1D) is a multifactorial disorder with a global incidence of about 8.4 million individuals in 2021. It is primarily classified as an autoimmune disorder, where the pancreatic β-cells are unable to secrete sufficient insulin. This leads to elevated blood glucose levels (hyperglycemia). The development of T1D is an intricate interplay between various risk factors, such as genetic, environmental, and cellular elements. In this review, we focus on the cellular elements, such as ER (endoplasmic reticulum) stress and its consequences for T1D pathogenesis. One of the major repercussions of ER stress is defective protein processing. A well-studied example is that of islet amyloid polypeptide (IAPP), which is known to form cytotoxic amyloid plaques when misfolded. This review discusses the possible association between ER stress, IAPP, and amyloid formation in β-cells and its consequences in T1D. Additionally, ER stress also leads to autoantigen generation. This is driven by the loss of Ca++ ion homeostasis. Imbalanced Ca++ levels lead to abnormal activation of enzymes, causing post-translational modification of β-cell proteins. These modified proteins act as autoantigens and trigger the autoimmune response seen in T1D islets. Several of these autoantigens are also crucial for insulin granule biogenesis, processing, and release. Here, we explore the possible associations between ER stress leading to defects in insulin secretion and ultimately β-cell destruction.

Screening of Relevant Metabolism-Disrupting Chemicals on Pancreatic β-Cells: Evaluation of Murine and Human In Vitro Models

Endocrine-disrupting chemicals (EDCs) are chemical substances that can interfere with the normal function of the endocrine system. EDCs are ubiquitous and can be found in a variety of consumer products such as food packaging materials, personal care and household products, plastic additives, and flame retardants. Over the last decade, the impact of EDCs on human health has been widely acknowledged as they have been associated with different endocrine diseases. Among them, a subset called metabolism-disrupting chemicals (MDCs) is able to promote metabolic changes that can lead to the development of metabolic disorders such as diabetes, obesity, hepatic steatosis, and metabolic syndrome, among others. Despite this, today, there are still no definitive and standardized in vitro tools to support the metabolic risk assessment of existing and emerging MDCs for regulatory purposes. Here, we evaluated the following two different pancreatic cell-based in vitro systems: the murine pancreatic β-cell line MIN6 as well as the human pancreatic β-cell line EndoC-βH1. Both were challenged with the following range of relevant concentrations of seven well-known EDCs: (bisphenol-A (BPA), bisphenol-S (BPS), bisphenol-F (BPF), perfluorooctanesulfonic acid (PFOS), di(2-ethylhexyl) phthalate (DEHP), cadmium chloride (CdCl2), and dichlorodiphenyldichloroethylene (DDE)). The screening revealed that most of the tested chemicals have detectable, deleterious effects on glucose-stimulated insulin release, insulin content, electrical activity, gene expression, and/or viability. Our data provide new molecular information on the direct effects of the selected chemicals on key aspects of pancreatic β-cell function, such as the stimulus-secretion coupling and ion channel activity. In addition, we found that, in general, the sensitivity and responses were comparable to those from other in vivo studies reported in the literature. Overall, our results suggest that both systems can serve as effective tools for the rapid screening of potential MDC effects on pancreatic β-cell physiology as well as for deciphering and better understanding the molecular mechanisms that underlie their action.

Lack of ZnT8 protects pancreatic islets from hypoxia- and cytokine-induced cell death

Pancreatic β-cells depend on the well-balanced regulation of cytosolic zinc concentrations, providing sufficient zinc ions for the processing and storage of insulin, but avoiding toxic effects. The zinc transporter ZnT8, encoded by SLC30A8,is a key player regarding islet cell zinc homeostasis, and polymorphisms in this gene are associated with altered type 2 diabetes susceptibility in man. The objective of this study was to investigate the role of ZnT8 and zinc in situations of cellular stress as hypoxia or inflammation. Isolated islets of WT and global ZnT8-/- mice were exposed to hypoxia or cytokines and cell death was measured. To explore the role of changing intracellular Zn2+ concentrations, WT islets were exposed to different zinc concentrations using zinc chloride or the zinc chelator N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN). Hypoxia or cytokine (TNF-α, IFN-γ, IL1-β) treatment induced islet cell death, but to a lesser extent in islets from ZnT8-/- mice, which were shown to have a reduced zinc content. Similarly, chelation of zinc with TPEN reduced cell death in WT islets treated with hypoxia or cytokines, whereas increased zinc concentrations aggravated the effects of these stressors. This study demonstrates a reduced rate of cell death in islets from ZnT8-/- mice as compared to WT islets when exposed to two distinct cellular stressors, hypoxia or cytotoxic cytokines. This protection from cell death is, in part, mediated by a reduced zinc content in islet cells of ZnT8-/- mice. These findings may be relevant for altered diabetes burden in carriers of risk SLC30A8 alleles in man.

The role of zinc in the prevention and treatment of nonalcoholic fatty liver disease

The zinc element is an essential nutrient for human health. Zinc is involved in the glucose, lipid, and protein metabolism and antioxidant processes in biological pathways. Zinc deficiency can lead to several chronic liver diseases. Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases where zinc deficiency plays a critical role in pathogenesis. Human and animal studies showed that both NAFLD risk factors (i.e., insulin resistance, diabetes mellitus, dyslipidemia, obesity, hypertension) and NAFLD itself are associated with decreased blood levels of zinc. Additionally, endoplasmic reticulum stress and inflammation due to unfolded protein response, inadequate dietary zinc intake, and decreased zinc absorption from the gastrointestinal tract can result in zinc deficiency leading to NAFLD. Herein, we reviewed the mechanistic links between zinc deficiency and NAFLD development and the role of zinc in the prevention and treatment of NAFLD.

Inside the Insulin Secretory Granule

The pancreatic β-cell is purpose-built for the production and secretion of insulin, the only hormone that can remove glucose from the bloodstream. Insulin is kept inside miniature membrane-bound storage compartments known as secretory granules (SGs), and these specialized organelles can readily fuse with the plasma membrane upon cellular stimulation to release insulin. Insulin is synthesized in the endoplasmic reticulum (ER) as a biologically inactive precursor, proinsulin, along with several other proteins that will also become members of the insulin SG. Their coordinated synthesis enables synchronized transit through the ER and Golgi apparatus for congregation at the trans-Golgi network, the initiating site of SG biogenesis. Here, proinsulin and its constituents enter the SG where conditions are optimized for proinsulin processing into insulin and subsequent insulin storage. A healthy β-cell is continually generating SGs to supply insulin in vast excess to what is secreted. Conversely, in type 2 diabetes (T2D), the inability of failing β-cells to secrete may be due to the limited biosynthesis of new insulin. Factors that drive the formation and maturation of SGs and thus the production of insulin are therefore critical for systemic glucose control. Here, we detail the formative hours of the insulin SG from the luminal perspective. We do this by mapping the journey of individual members of the SG as they contribute to its genesis.

Diabetes Risk Data Mining Method Based on Electronic Medical Record Analysis

In today's society, the development of information technology is very rapid, and the transmission and sharing of information has become a development trend. The results of data analysis and research are gradually applied to various fields of social development, structured analysis, and research. Data mining of electronic medical records in the medical field is gradually valued by researchers and has become a major work in the medical field. In the course of clinical treatment, electronic medical records are edited, including all personal health and treatment information. This paper mainly introduces the research of diabetes risk data mining method based on electronic medical record analysis and intends to provide some ideas and directions for the research of diabetes risk data mining method. This paper proposes a research strategy of diabetes risk data mining method based on electronic medical record analysis, including data mining and classification rule mining based on electronic medical record analysis, which are used in the research experiment of diabetes risk data mining method based on electronic medical record analysis. The experimental results in this paper show that the average prediction accuracy of the decision tree is 91.21%, and the results of the training set and the test set are similar, indicating that there is no overfitting of the training set.

Emerging Roles of Metallothioneins in Beta Cell Pathophysiology: Beyond and Above Metal Homeostasis and Antioxidant Response

Simple Summary

Defective insulin secretion by pancreatic beta cells is key for the development of type 2 diabetes but the precise mechanisms involved are poorly understood. Metallothioneins are metal binding proteins whose precise biological roles have not been fully characterized. Available evidence indicated that Metallothioneins are protective cellular effectors involved in heavy metal detoxification, metal ion homeostasis and antioxidant defense. This concept has however been challenged by emerging evidence in different medical research fields revealing novel negative roles of Metallothioneins, including in the context of diabetes. In this review, we gather and analyze the available knowledge regarding the complex roles of Metallothioneins in pancreatic beta cell biology and insulin secretion. We comprehensively analyze the evidence showing positive effects of Metallothioneins on beta cell function and survival as well as the emerging evidence revealing negative effects and discuss the possible underlying mechanisms. We expose in parallel findings from other medical research fields and underscore unsettled questions. Then, we propose some future research directions to improve knowledge in the field.

Abstract

Metallothioneins (MTs) are low molecular weight, cysteine-rich, metal-binding proteins whose precise biological roles have not been fully characterized. Existing evidence implicated MTs in heavy metal detoxification, metal ion homeostasis and antioxidant defense. MTs were thus categorized as protective effectors that contribute to cellular homeostasis and survival. This view has, however, been challenged by emerging evidence in different medical fields revealing novel pathophysiological roles of MTs, including inflammatory bowel disease, neurodegenerative disorders, carcinogenesis and diabetes. In the present focused review, we discuss the evidence for the role of MTs in pancreatic beta-cell biology and insulin secretion. We highlight the pattern of specific isoforms of MT gene expression in rodents and human beta-cells. We then discuss the mechanisms involved in the regulation of MTs in islets under physiological and pathological conditions, particularly type 2 diabetes, and analyze the evidence revealing adaptive and negative roles of MTs in beta-cells and the potential mechanisms involved. Finally, we underscore the unsettled questions in the field and propose some future research directions.

Harnessing reaction-based probes to preferentially target pancreatic β-cells and β-like cells

Highly sensitive approaches to target insulin-expressing cells would allow more effective imaging, sorting, and analysis of pancreatic β-cells. Here, we introduce the use of a reaction-based probe, diacetylated Zinpyr1 (DA-ZP1), to image pancreatic β-cells and β-like cells derived from human pluripotent stem cells. We harness the high intracellular zinc concentration of β-cells to induce a fluorescence signal in cells after administration of DA-ZP1. Given its specificity and rapid uptake by cells, we used DA-ZP1 to purify live stem cell-derived β-like cells as confirmed by immunostaining analysis. We tested the ability of DA-ZP1 to image transplanted human islet grafts and endogenous mouse pancreatic islets in vivo after its systemic administration into mice. Thus, DA-ZP1 enables purification of insulin-secreting β-like cells for downstream applications, such as functional studies, gene-expression, and cell-cell interaction analyses and can be used to label engrafted human islets and endogenous mouse islets in vivo.

The role of labile Zn2+ and Zn2+-transporters in the pathophysiology of mitochondria dysfunction in cardiomyocytes

An important energy supplier of cardiomyocytes is mitochondria, similar to other mammalian cells. Studies have demonstrated that any defect in the normal processes controlled by mitochondria can lead to abnormal ROS production, thereby high oxidative stress as well as lack of ATP. Taken into consideration, the relationship between mitochondrial dysfunction and overproduction of ROS as well as the relation between increased ROS and high-level release of intracellular labile Zn²⁺, those bring into consideration the importance of the events related with those stimuli in cardiomyocytes responsible from cellular Zn²⁺-homeostasis and responsible Zn²⁺-transporters associated with the Zn²⁺-homeostasis and Zn²⁺-signaling. Zn²⁺-signaling, controlled by cellular Zn²⁺-homeostatic mechanisms, is regulated with intracellular labile Zn²⁺ levels, which are controlled, especially, with the two Zn²⁺-transporter families; ZIPs and ZnTs. Our experimental studies in mammalian cardiomyocytes and human heart tissue showed that Zn²⁺-transporters localizes to mitochondria besides sarco(endo)plasmic reticulum and Golgi under physiological condition. The protein levels as well as functions of those transporters can re-distribute under pathological conditions, therefore, they can interplay among organelles in cardiomyocytes to adjust a proper intracellular labile Zn²⁺ level. In the present review, we aimed to summarize the already known Zn²⁺-transporters localize to mitochondria and function to stabilize not only the cellular Zn²⁺ level but also cellular oxidative stress status. In conclusion, one can propose that a detailed understanding of cellular Zn²⁺-homeostasis and Zn²⁺-signaling through mitochondria may emphasize the importance of new mitochondria-targeting agents for prevention and/or therapy of cardiovascular dysfunction in humans.

The Potential Role of Zinc Oxide Nanoparticles in MicroRNAs Dysregulation in STZ-Induced Type 2 Diabetes in Rats

Diabetes mellitus (DM) is a group of metabolic disorders that are characterized by a loss of glucose homeostasis and insufficiency in production or action of insulin. Development of newly antidiabetic molecules using a variety of organic compounds and biomolecules has been in practice for a long time. Recently, nanomaterials are also being used in antidiabetic studies for their unique properties. In this context, zinc nanoparticles have drawn attention due to the relationship between diabetes and imbalance of zinc homeostasis. Few studies have attempted to investigate the effect of zinc oxide nanoparticles (ZON) in microRNA dysregulations in diabetes. To evaluate the therapeutic effect of ZON on streptozotocin (STZ)-induced diabetic rats as well as its role in microRNA dysregulations. Diabetes was induced in rats by 60 mg/kg body weight (bwt) of STZ and then treated with ZON (5 mg/kg bwt) for 15 consecutive days. The levels of glucose, insulin, oxidative stress markers, and microRNAs expression were measured in liver and pancreas tissues. Intraperitoneal injection of 60 mg/kg bwt of STZ to Wistar rats caused significant decreases in the body weight and Zn contents of pancreas, liver, and kidney. Also, STZ injection increased the blood glucose level and oxidative stress (lipid peroxidation (LPO) and nitric oxide (NO). Meanwhile, STZ decreased blood insulin and pancreatic anti-oxidants. STZ also resulted in β cell dysfunction and destruction and altered the expression of certain pancreatic and liver microRNAs. ZON treatment for 15 days, at a dose of 5 mg/kg bwt resulted in marked improvements in the blood insulin, glucose tolerance, and structure and function of the pancreatic β cells. Furthermore, ZON administration reduced LPO and NO, and increased the levels of enzymatic and non-enzymatic anti-oxidants in STZ-induced diabetic rats. It was found also that ZON specifically regulated the expression of pancreatic and liver microRNAs that involved in diabetes development. The obtained results revealed that ZON is a promising antidiabetic agent. The antidiabetic effect of ZON was partially mediated by restoring the oxidants/antioxidants balance and by modulating the alerted microRNAs.

Divalent Cations: A Molecular Glue for Protein Materials

Among inorganic materials, divalent cations modulate thousands of physiological processes that support life. Their roles in protein assembly and aggregation are less known, although they are progressively being brought to light. We review the structural roles of divalent cations here, as well as the novel protein materials that are under development, in which they are used as glue-like agents. More specifically, we discuss how mechanically stable nanoparticles, fibers, matrices, and hydrogels are generated through their coordination with histidine-rich proteins. We also describe how the rational use of divalent cations combined with simple protein engineering offers unexpected and very simple biochemical approaches to biomaterial design that might address unmet clinical needs in precision medicine.

Targeted pancreatic beta cell imaging for early diagnosis

Pancreatic beta cells are important in blood glucose level regulation. As type 1 and 2 diabetes are getting prevalent worldwide, we need to explore new methods for early detection of beta cell-related afflictions. Using bioimaging techniques to measure beta cell mass is crucial because a decrease in beta cell density is seen in diseases such as diabetes and thus can be a new way of diagnosis for such diseases. We also need to appraise beta cell purity in transplanted islets for type 1 diabetes patients. Sufficient amount of functional beta cells must also be determined before being transplanted to the patients. In this review, indirect imaging of beta cells will be discussed. This includes membrane protein on pancreatic beta cells whereby specific probes are designed for different imaging modalities mainly magnetic resonance imaging, positron emission tomography and fluorescence imaging. Direct imaging of insulin is also explored though probes synthesized for such function are relatively fewer. The path for successful pancreatic beta cell imaging is fraught with challenges like non-specific binding, lack of beta cell-restricted targets, the requirement of probes to cross multiple lipid layers to bind to intracellular insulin. Hence, there is an urgent need to develop new imaging techniques and innovative probing constructs in the entire imaging chain of bioengineering to provide early detection of beta cell-related pathology.

Combined effect of high-dose vitamin A, vitamin E supplementation, and zinc on adult patients with diabetes: A randomized trial

In type 2 diabetes mellitus (T2DM), hyperglycemia leads to oxidative insult. Vitamins A and E have antioxidant potentials and may help in managing diabetes. The combined effect of high-dose vitamin A plus E supplementation with and without zinc on T2DM, has never been examined. Thus, this study aimed to evaluate and compare the effect of high-dose vitamin A plus E supplementation (AE) versus high-dose vitamin A plus E with zinc (AEZ), on different diabetic parameters. Ninety-eight patients with T2DM were randomized to receive either: 50,000 IU vitamin A and 100 mg vitamin E (AE group, N = 36), an equivalent dose of vitamin A and E combined with 25 mg zinc (AEZ group, N = 35), or no supplements (control group, N = 27) for three months. Compared to control, AEZ group showed significant reductions in fasting blood glucose, 2 h postprandial blood glucose, and glycated hemoglobin (HbA1c) with significant increases in homeostasis model assessment of beta-cell function and difference value of fasting insulin. Two hair loss cases were recorded in both treated groups. Although vitamin A needs dose moderation, these results suggest that, high-dose vitamin A plus E supplementation combined with zinc may improve glycemic control, β-cell function, and insulin secretion in adults with T2DM.

Mediator subunit MDT-15/MED15 and Nuclear Receptor HIZR-1/HNF4 cooperate to regulate toxic metal stress responses in Caenorhabditis elegans

Zinc is essential for cellular functions as it is a catalytic and structural component of many proteins. In contrast, cadmium is not required in biological systems and is toxic. Zinc and cadmium levels are closely monitored and regulated as their excess causes cell stress. To maintain homeostasis, organisms induce metal detoxification gene programs through stress responsive transcriptional regulatory complexes. In Caenorhabditis elegans, the MDT-15 subunit of the evolutionarily conserved Mediator transcriptional coregulator is required to induce genes upon exposure to excess zinc and cadmium. However, the regulatory partners of MDT-15 in this response, its role in cellular and physiological stress adaptation, and the putative role for mammalian MED15 in the metal stress responses remain unknown. Here, we show that MDT-15 interacts physically and functionally with the Nuclear Hormone Receptor HIZR-1 to promote molecular, cellular, and organismal adaptation to cadmium and excess zinc. Using gain- and loss-of-function mutants and qRT-PCR and reporter analysis, we find that mdt-15 and hizr-1 cooperate to induce zinc and cadmium responsive genes. Moreover, the two proteins interact physically in yeast-two-hybrid assays and this interaction is enhanced by the addition of zinc or cadmium, the former a known ligand of HIZR-1. Functionally, mdt-15 and hizr-1 mutants show defective storage of excess zinc in the gut and are hypersensitive to zinc-induced reductions in egg-laying. Furthermore, mdt-15 but not hizr-1 mutants are hypersensitive to cadmium-induced reductions in egg-laying, suggesting potential divergence of regulatory pathways. Lastly, mammalian MDT-15 orthologs bind genomic regulatory regions of metallothionein and zinc transporter genes in a cadmium and zinc-stimulated fashion, and human MED15 is required to induce a metallothionein gene in lung adenocarcinoma cells exposed to cadmium. Collectively, our data show that mdt-15 and hizr-1 cooperate to regulate cadmium detoxification and zinc storage and that this mechanism is at least partially conserved in mammals.

Role of Tmem163 in zinc-regulated insulin storage of MIN6 cells: Functional exploration of an Indian type 2 diabetes GWAS associated gene

Genome wide association study for type 2 diabetes discovered TMEM163 as a risk locus. Perturbations in TMEM163 expression was reported to be associated with impaired intracellular zinc homeostasis. Physiological concentration of zinc is instrumental to maintain insulin storage and functionality in pancreatic β cells. We found abundant TMEM163 expression in human pancreas, both at transcriptional and translational levels. Knockdown of endogenous Tmem163 in MIN6 cells resulted in increased intracellular zinc and total insulin content, coupled with compromised insulin secretion at high glucose stimuli. Furthermore, Tmem163 knockdown led to enhanced cellular glucose uptake. Upon next generation sequencing, one-third of the studied T2D patients were found to have a novel missense variant in TMEM163 gene. Study participants harboring this missense variant displayed a trend of higher glycemic indices. This is the first report on exploring the biological role of TMEM163 in relation to T2D pathophysiology.

Zinc and its regulators in pancreas

Studies have demonstrated that susceptibility to type 2 diabetes (T2D) is influenced by common polymorphism in the zinc transporter 8 gene SLC30A8, providing novel insight into the role of zinc in diabetes. Intriguingly, zinc participates in every step of the process, including insulin synthesis, crystallization, storage, secretion and signaling. Zinc deficiency or overload is associated with various disorders, such as diabetes, cardiovascular disease and obesity. Zinc supplementation is considered as an effective means of treating or preventing T2D in people with certain SLC30A8 genotypes. Three important protein families-zinc transporters (ZnTs), zinc importers (ZiPs) and metallothionein (MT)-participate in maintaining zinc homeostasis. Here, we review research on the physiological characteristics of zinc and its role in the pancreas and homeostasis regulation mechanisms, along with the latest research on the structure and function of ZnT/ZiP and MT. In addition, we summarize the advancements in research on SLC30A8 gene polymorphism in search of a mechanism to explain the relationship between the R risk allele and zinc transporter activity.

Sensors for measuring subcellular zinc pools

Zinc homeostasis is essential for normal cellular function, and defects in this process are associated with a number of diseases including type 2 diabetes (T2D), neurological disorders and cardiovascular disease. Thus, variants in the SLC30A8 gene, encoding the vesicular/granular zinc transporter ZnT8, are associated with altered insulin release and increased T2D risk while the zinc importer ZIP12 is implicated in pulmonary hypertension. In light of these, and findings in other diseases, recent efforts have focused on the development of refined sensors for intracellular free zinc ions that can be targeted to subcellular regions including the cytosol, endoplasmic reticulum (ER), secretory granules, Golgi apparatus, nucleus and the mitochondria. Here, we discuss recent advances in Zn²⁺ probe engineering and their applications to the measurement of labile subcellular zinc pools in different cell types.

ICP-DRC-MS analysis of serum essential and toxic element levels in postmenopausal prediabetic women in relation to glycemic control markers

PURPOSE

Assessment of the influence of prediabetes on serum trace element and electrolyte levels in postmenopausal women.

METHODS

A total of 80 prediabetic and 80 healthy postmenopausal women took part in the present study. Serum was analyzed for glucose, insulin, insulin resistance index (HOMA-IR), total cholesterol (TC), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT). Glycated haemoglobin (HbA1c) levels were also assessed. Serum levels of 28 elements were estimated using inductively-coupled plasma mass spectrometry with dynamic reaction cell technology (ICP-DRC-MS).

RESULTS

Prediabetic women were characterized by significantly higher HbA1c, glucose, insulin, HOMA-IR, ALT, and GGT values. Of trace elements, only serum zinc (Zn) levels were significantly lower in prediabetics by 10% (p=0.001) when compared to the controls. Serum Zn levels were characterized by a significant inverse correlation with HbA1c (r=- 0.205; p=0.009), insulin (r=- 0.246; p=0.002), and HOMA-IR (r=- 0.227; p=0.004). Multiple regression analysis demonstrated a significant inverse association between serum Zn (β=-0.169; p=0.031) and Sr (β=-0.192; p=0.012) and HOMA-IR values after adjustment for anthropometric and biochemical parameters (p for a model <0.001). Although serum Zn was significantly associated with HbA1c both in crude and adjusted models, no significant relationship was detected after adjustment for age and anthropometric parameters.

CONCLUSIONS

Prediabetic postmenopausal women are characterized by significantly lower levels of serum Zn concentration, whereas serum Zn and Sr levels were inversely associated with insulin resistance.

Zinc supplementation reduces diet-induced obesity and improves insulin sensitivity in rats

Rates of obesity have been growing at alarming rates, compromising the health of the world population. Thus, the search for interventions that address the metabolic repercussions of obesity are necessary. Here we evaluated the metabolic and antioxidant effects of zinc and branched-chain amino acids (BCAA) supplementation on obese rats. Male Wistar rats were fed either a high-fat/high-fructose diet (HFD) or a standard diet (SD) for 19 weeks. From the fifteenth week until the end of the experiment, HFD- and SD-fed rats received zinc (6 mg/kg) or BCAA (750 mg/kg) supplementation. Body weight, abdominal fat, lipid profile, blood glucose, insulin, leptin, and hepatic transaminases were evaluated. In the liver, superoxide dismutase and catalase activities and lipid peroxidation were also analyzed. HFD-fed animals showed increased weight gain, abdominal fat pad, plasma insulin, leptin, and triglycerides levels in comparison with SD-fed rats. Zinc supplementation reduced all these parameters, suggesting a beneficial role for the treatment of obesity. BCAA, on the other hand, did not show any beneficial effect. Liver antioxidant enzymes and hepatic transaminases plasma levels did not change among groups. Lipid peroxidation was higher in HFD-fed rats and was not reverted by zinc or BCAA supplementation. In conclusion, zinc supplementation may be a useful strategy for the treatment of the metabolic dysfunction associated with obesity.

The zinc transporter Slc39a5 controls glucose sensing and insulin secretion in pancreatic β-cells via Sirt1- and Pgc-1α-mediated regulation of Glut2

Zinc levels are high in pancreatic β-cells, and zinc is involved in the synthesis, processing and secretion of insulin in these cells. However, precisely how cellular zinc homeostasis is regulated in pancreatic β-cells is poorly understood. By screening the expression of 14 Slc39a metal importer family member genes, we found that the zinc transporter Slc39a5 is significantly down-regulated in pancreatic β-cells in diabetic db/db mice, obese ob/ob mice and high-fat diet-fed mice. Moreover, β-cell-specific Slc39a5 knockout mice have impaired insulin secretion. In addition, Slc39a5-deficient pancreatic islets have reduced glucose tolerance accompanied by reduced expression of Pgc-1α and its downstream target gene Glut2. The down-regulation of Glut2 in Slc39a5-deficient islets was rescued using agonists of Sirt1, Pgc-1α and Ppar-γ. At the mechanistic level, we found that Slc39a5-mediated zinc influx induces Glut2 expression via Sirt1-mediated Pgc-1α activation. These findings suggest that Slc39a5 may serve as a possible therapeutic target for diabetes-related conditions.

Prolonged stimulation of insulin release from MIN6 cells causes zinc depletion and loss of β-cell markers

Zinc is integral for the normal function of pancreatic β-cells in glycaemic control. Large amounts of zinc are secreted from β-cells following insulin exocytosis and regulated replenishment is required, which is thought to be mediated by the ZIP family of zinc importer proteins. Within Type 2 Diabetic patients, β-cells are stressed through prolonged stimulation by hyperglycaemia and this is thought to be a major factor contributing to loss of β-cell identity and mass. However, the consequences for the β-cell zinc status remain largely unexplored. We used inductively coupled plasma mass spectrometry (ICP-MS) to show that 24 h treatment of MIN6 cells with potassium chloride, mimicking hyperglycaemic stimulation, reduces the total cellular zinc content 2.8-fold, and qPCR to show an increase in mRNA expression for metallothioneins (Mt1 and Mt2) following 4 and 24 h of stimulation, suggestive of an early rise in cytosolic zinc. To determine which ZIP paralogues may be responsible for zinc replenishment, we used immunocytochemistry, Western blot and qPCR to demonstrate initial ZIP1 protein upregulation proceeded by downregulation of mRNA coding for ZIP1, ZIP6, ZIP7 and ZIP14. To assign a biological significance to the decreased total cellular zinc content, we assessed expression of key β-cell markers to show downregulation of mRNA for MafA, Mnx-1, Nkx2.2 and Pax6. Our data suggest hyperglycaemia-induced zinc depletion may contribute to loss of β-cell markers and promote β-cell dedifferentiation through disrupting expression of key transcription factors.

Mice harboring the human SLC30A8 R138X loss-of-function mutation have increased insulin secretory capacity

SLC30A8 encodes a zinc transporter that is primarily expressed in the pancreatic islets of Langerhans. In β-cells it transports zinc into insulin-containing secretory granules. Loss-of-function (LOF) mutations in SLC30A8 protect against type 2 diabetes in humans. In this study, we generated a knockin mouse model carrying one of the most common human LOF mutations for SLC30A8, R138X. The R138X mice had normal body weight, glucose tolerance, and pancreatic β-cell mass. Interestingly, in hyperglycemic conditions induced by the insulin receptor antagonist S961, the R138X mice showed a 50% increase in insulin secretion. This effect was not associated with enhanced β-cell proliferation or mass. Our data suggest that the SLC30A8 R138X LOF mutation may exert beneficial effects on glucose metabolism by increasing the capacity of β-cells to secrete insulin under hyperglycemic conditions.

Mouse models of peripheral metabolic disease

Metabolic disease risk is driven by defects in the function of cells that regulate energy homeostasis, as well as altered communication between the different tissues or organs that these cells occupy. Thus, it is desirable to use model organisms to understand the contribution of different cells, tissues and organs to metabolism. Mice are widely used for metabolic research, since well-characterised mouse strains (in terms of their genotype and phenotype) allow comparative studies and human disease modelling. Such research involves strains containing spontaneous mutations that lead to obesity and diabetes, surgically- and chemically-induced models, those that are secondary to caloric excess, genetic mutants created by transgenesis and gene knockout technologies, and peripheral models generated by Cre-Lox or CRISPR/Cas9 approaches. Focussing on obesity and type 2 diabetes as relevant metabolic diseases, we systematically review each of these models, discussing their use, limitations, and future potential.

Biogenesis of zinc storage granules in Drosophila melanogaster

Membrane transporters and sequestration mechanisms concentrate metal ions differentially into discrete subcellular microenvironments for use in protein cofactors, signalling, storage or excretion. Here we identify zinc storage granules as the insect's major zinc reservoir in principal Malpighian tubule epithelial cells of Drosophila melanogaster The concerted action of Adaptor Protein-3, Rab32, HOPS and BLOC complexes as well as of the white-scarlet (ABCG2-like) and ZnT35C (ZnT2/ZnT3/ZnT8-like) transporters is required for zinc storage granule biogenesis. Due to lysosome-related organelle defects caused by mutations in the homologous human genes, patients with Hermansky-Pudlak syndrome may lack zinc granules in beta pancreatic cells, intestinal paneth cells and presynaptic vesicles of hippocampal mossy fibers.

Role of Zinc Homeostasis in the Pathogenesis of Diabetes and Obesity

Zinc deficiency is a risk factor for obesity and diabetes. However, until recently, the underlying molecular mechanisms remained unclear. The breakthrough discovery that the common polymorphism in zinc transporter SLC30A8/ZnT8 may increase susceptibility to type 2 diabetes provided novel insights into the role of zinc in diabetes. Our group and others showed that altered ZnT8 function may be involved in the pathogenesis of type 2 diabetes, indicating that the precise control of zinc homeostasis is crucial for maintaining health and preventing various diseases, including lifestyle-associated diseases. Recently, the role of the zinc transporter ZIP13 in the regulation of beige adipocyte biogenesis was clarified, which indicated zinc homeostasis regulation as a possible therapeutic target for obesity and metabolic syndrome. Here we review advances in the role of zinc homeostasis in the pathophysiology of diabetes, and propose that inadequate zinc distribution may affect the onset of diabetes and metabolic diseases by regulating various critical biological events.

Zinc stimulates glucose oxidation and glycemic control by modulating the insulin signaling pathway in human and mouse skeletal muscle cell lines

Zinc is a metal ion that is an essential cell signaling molecule. Highlighting this, zinc is an insulin mimetic, activating cellular pathways that regulate cellular homeostasis and physiological responses. Previous studies have linked dysfunctional zinc signaling with several disease states including cancer, obesity, cardiovascular disease and type 2 diabetes. The present study evaluated the insulin-like effects of zinc on cell signaling molecules including tyrosine, PRSA40, Akt, ERK1/2, SHP-2, GSK-3β and p38, and glucose oxidation in human and mouse skeletal muscle cells. Insulin and zinc independently led to the phosphorylation of these proteins over a 60-minute time course in both mouse and human skeletal muscle cells. Similarly, utilizing a protein array we identified that zinc could active the phosphorylation of p38, ERK1/2 and GSK-3B in human and ERK1/2 and GSK-3B in mouse skeletal muscle cells. Glucose oxidation assays were performed on skeletal muscle cells treated with insulin, zinc, or a combination of both and resulted in a significant induction of glucose consumption in mouse (p<0.01) and human (p<0.05) skeletal muscle cells when treated with zinc alone. Insulin, as expected, increased glucose oxidation in mouse (p<0.001) and human (0.001) skeletal muscle cells, however the combination of zinc and insulin did not augment glucose consumption in these cells. Zinc acts as an insulin mimetic, activating key molecules implicated in cell signaling to maintain glucose homeostasis in mouse and human skeletal muscle cells. Zinc is an important metal ion implicated in several biological processes. The role of zinc as an insulin memetic in activating key signaling molecules involved in glucose homeostasis could provide opportunities to utilize this ion therapeutically in treating disorders associated with dysfunctional zinc signaling.

Hypoglycemic and Hypolipidemic Effects of Leucine, Zinc, and Chromium, Alone and in Combination, in Rats with Type 2 Diabetes

For the increasing development of diabetes, dietary habits and using appropriate supplements can play important roles in the treatment or reduction of risk for this disease. The objective of this study was to investigate the effects of leucine (Leu), zinc (Zn), and chromium (Cr) supplementation, alone or in combination, in rats with type 2 diabetes (T2D). Seventy-seven adult male Wistar rats were randomly assigned in 11 groups, using nutritional supplements and insulin (INS) or glibenclamide (GLC). Supplementing Leu significantly reduced blood glucose, triglycerides (TG), nonesterified fatty acids (NEFA), low-density lipoprotein (LDL), and increased high-density lipoprotein (HDL) concentrations compared to vehicle-treated T2D animals, and those improvements were associated with reduced area under the 2-h blood glucose response curve (AUC). Supplementation of T2D animals with Zn improved serum lipid profile as well as blood glucose concentrations but was not comparable with the INS, GLC, and Leu groups. Supplementary Cr did not improve blood glucose and AUC in T2D rats, whereas it reduced serum TG and LDL and increased HDL concentrations. In conclusion, supplementation of diabetic rats with Leu was more effective in improving blood glucose and consequently decreasing glucose AUC than other nutritional supplements. Supplementary Zn and Cr only improved serum lipid profile. The combination of the nutritional supplements did not improve blood glucose level. Nevertheless, supplementation with Leu-Zn, Leu-Cr, Zn-Cr, and Leu-Zn-Cr led to an improved response in serum lipid profile over each supplement given alone.

Zinc transporters and insulin resistance: therapeutic implications for type 2 diabetes and metabolic disease

BACKGROUND

Zinc is a metal ion that is essential for growth and development, immunity, and metabolism, and therefore vital for life. Recent studies have highlighted zinc's dynamic role as an insulin mimetic and a cellular second messenger that controls many processes associated with insulin signaling and other downstream pathways that are amendable to glycemic control.

MAIN BODY

Mechanisms that contribute to the decompartmentalization of zinc and dysfunctional zinc transporter mechanisms, including zinc signaling are associated with metabolic disease, including type 2 diabetes. The actions of the proteins involved in the uptake, storage, compartmentalization and distribution of zinc in cells is under intense investigation. Of these, emerging research has highlighted a role for several zinc transporters in the initiation of zinc signaling events in cells that lead to metabolic processes associated with maintaining insulin sensitivity and thus glycemic homeostasis.

CONCLUSION

This raises the possibility that zinc transporters could provide novel utility to be targeted experimentally and in a clinical setting to treat patients with insulin resistance and thus introduce a new class of drug target with utility for diabetes pharmacotherapy.

Impact of Labile Zinc on Heart Function: From Physiology to Pathophysiology

Zinc plays an important role in biological systems as bound and histochemically reactive labile Zn²⁺. Although Zn²⁺ concentration is in the nM range in cardiomyocytes at rest and increases dramatically under stimulation, very little is known about precise mechanisms controlling the intracellular distribution of Zn²⁺ and its variations during cardiac function. Recent studies are focused on molecular and cellular aspects of labile Zn²⁺ and its homeostasis in mammalian cells and growing evidence clarified the molecular mechanisms underlying Zn²⁺-diverse functions in the heart, leading to the discovery of novel physiological functions of labile Zn²⁺ in parallel to the discovery of subcellular localization of Zn²⁺-transporters in cardiomyocytes. Additionally, important experimental data suggest a central role of intracellular labile Zn²⁺ in excitation-contraction coupling in cardiomyocytes by shaping Ca²⁺ dynamics. Cellular labile Zn²⁺ is tightly regulated against its adverse effects through either Zn²⁺-transporters, Zn²⁺-binding molecules or Zn²⁺-sensors, and, therefore plays a critical role in cellular signaling pathways. The present review summarizes the current understanding of the physiological role of cellular labile Zn²⁺ distribution in cardiomyocytes and how a remodeling of cellular Zn²⁺-homeostasis can be important in proper cell function with Zn²⁺-transporters under hyperglycemia. We also emphasize the recent investigations on Zn²⁺-transporter functions from the standpoint of human heart health to diseases together with their clinical interest as target proteins in the heart under pathological condition, such as diabetes.

A prospective study of dietary and supplemental zinc intake and risk of type 2 diabetes depending on genetic variation in SLC30A8

Background

The solute carrier family 30 member 8 gene (SLC30A8) encodes a zinc transporter in the pancreatic beta cells and the major C-allele of a missense variant (rs13266634; C/T; R325W) in SLC30A8 is associated with an increased risk of type 2 diabetes (T2D). We hypothesized that the association between zinc intake and T2D may be modified by the SLC30A8 genotype.

Results

We carried out a prospective study among subjects with no history cardio-metabolic diseases in the Malmö Diet and Cancer Study cohort (N = 26,132, 38% men; 86% with genotype data). Zinc intake was assessed using a diet questionnaire and food record. During a median follow-up of 19 years, 3676 T2D cases occurred. A BMI-stratified Cox proportional hazards regression model with attained age as the time scale was used to model the association between total and dietary zinc intake, zinc supplement use, zinc to iron ratio, and risk of T2D adjusting for putative confounding factors.

The median total zinc intake was 11.4 mg/day, and the median dietary zinc intake was 10.7 mg/day. Zinc supplement users (17%) had a median total zinc intake of 22.4 mg/day. Dietary zinc intake was associated with increased risk of T2D (P_trend < 0.0001). In contrast, we observed a lower risk of T2D among zinc supplement users (HR = 0.79, 95% CI 0.70–0.89). The SLC30A8 CC genotype was associated with a higher risk of T2D (HR = 1.16, 95% CI 1.07–1.24), and the effect was stronger among subjects with higher BMI (P_interaction = 0.007). We observed no significant modification of the zinc-T2D associations by SLC30A8 genotype. However, a three-way interaction between SLC30A8 genotype, BMI, and zinc to iron ratio was observed (P_interaction = 0.007). A high zinc to iron ratio conferred a protective associated effect on T2D risk among obese subjects, and the effect was significantly more pronounced among T-allele carriers.

Conclusions

Zinc supplementation and a high zinc to iron intake ratio may lower the risk of T2D, but these associations could be modified by obesity and the SLC30A8 genotype. The findings implicate that when considering zinc supplementation for T2D prevention, both obesity status and SLC30A8 genotype may need to be accounted for.

Electronic supplementary material

The online version of this article (10.1186/s12263-017-0586-y) contains supplementary material, which is available to authorized users.

Expression of the ZIP/SLC39A transporters in β-cells: a systematic review and integration of multiple datasets

BACKGROUND

Pancreatic β-cells require a constant supply of zinc to maintain normal insulin secretory function. Following co-exocytosis with insulin, zinc is replenished via the Zrt- and Irt-like (ZIP; SLC39A) family of transporters. However the ZIP paralogues of particular importance for zinc uptake, and associations with β-cell function and Type 2 Diabetes remain largely unexplored. We retrieved and statistically analysed publically available microarray and RNA-seq datasets to perform a systematic review on the expression of β-cell SLC39A paralogues. We complemented results with experimental data on expression profiling of human islets and mouse β-cell derived MIN6 cells, and compared transcriptomic and proteomic sequence conservation between human, mouse and rat.

RESULTS

The 14 ZIP paralogues have 73-98% amino sequence conservation between human and rodents. We identified 18 datasets for β-cell SLC39A analysis, which compared relative expression to non-β-cells, and expression in response to PDX-1 activity, cytokines, glucose and type 2 diabetic status. Published expression data demonstrate enrichment of transcripts for ZIP7 and ZIP9 transporters within rodent β-cells and of ZIP6, ZIP7 and ZIP14 within human β-cells, with ZIP1 most differentially expressed in response to cytokines and PDX-1 within rodent, and ZIP6 in response to diabetic status in human and glucose in rat. Our qPCR expression profiling data indicate that SLC39A6, -9, -13, and - 14 are the highest expressed paralogues in human β-cells and Slc39a6 and -7 in MIN6 cells.

CONCLUSIONS

Our systematic review, expression profiling and sequence alignment reveal similarities and potentially important differences in ZIP complements between human and rodent β-cells. We identify ZIP6, ZIP7, ZIP9, ZIP13 and ZIP14 in human and rodent and ZIP1 in rodent as potentially biologically important for β-cell zinc trafficking. We propose ZIP6 and ZIP7 are key functional orthologues in human and rodent β-cells and highlight these zinc importers as important targets for exploring associations between zinc status and normal physiology of β-cells and their decline in Type 2 Diabetes.

Hyperglycemia-Induced Changes in ZIP7 and ZnT7 Expression Cause Zn2+ Release From the Sarco(endo)plasmic Reticulum and Mediate ER Stress in the Heart

Changes in cellular free Zn²⁺ concentration, including those in the sarco(endo)plasmic reticulum [S(E)R], are primarily coordinated by Zn²⁺ transporters (ZnTs) whose identity and role in the heart are not well established. We hypothesized that ZIP7 and ZnT7 transport Zn²⁺ in opposing directions across the S(E)R membrane in cardiomyocytes and that changes in their activity play an important role in the development of ER stress during hyperglycemia. The subcellular S(E)R localization of ZIP7 and ZnT7 was determined in cardiomyocytes and in isolated S(E)R preparations. Markedly increased mRNA and protein levels of ZIP7 were observed in ventricular cardiomyocytes from diabetic rats or high-glucose-treated H9c2 cells while ZnT7 expression was low. In addition, we observed increased ZIP7 phosphorylation in response to high glucose in vivo and in vitro. By using recombinant-targeted Förster resonance energy transfer sensors, we show that hyperglycemia induces a marked redistribution of cellular free Zn²⁺, increasing cytosolic free Zn²⁺ and lowering free Zn²⁺ in the S(E)R. These changes involve alterations in ZIP7 phosphorylation and were suppressed by small interfering RNA-mediated silencing of CK2α. Opposing changes in the expression of ZIP7 and ZnT7 were also observed in hyperglycemia. We conclude that subcellular free Zn²⁺ redistribution in the hyperglycemic heart, resulting from altered ZIP7 and ZnT7 activity, contributes to cardiac dysfunction in diabetes.

Lifestyle and precision diabetes medicine: will genomics help optimise the prediction, prevention and treatment of type 2 diabetes through lifestyle therapy?

Precision diabetes medicine, the optimisation of therapy using patient-level biomarker data, has stimulated enormous interest throughout society as it provides hope of more effective, less costly and safer ways of preventing, treating, and perhaps even curing the disease. While precision diabetes medicine is often framed in the context of pharmacotherapy, using biomarkers to personalise lifestyle recommendations, intended to lower type 2 diabetes risk or to slow progression, is also conceivable. There are at least four ways in which this might work: (1) by helping to predict a person's susceptibility to adverse lifestyle exposures; (2) by facilitating the stratification of type 2 diabetes into subclasses, some of which may be prevented or treated optimally with specific lifestyle interventions; (3) by aiding the discovery of prognostic biomarkers that help guide timing and intensity of lifestyle interventions; (4) by predicting treatment response. In this review we overview the rationale for precision diabetes medicine, specifically as it relates to lifestyle; we also scrutinise existing evidence, discuss the barriers germane to research in this field and consider how this work is likely to proceed.

Copper in Diabetes Mellitus: a Meta-Analysis and Systematic Review of Plasma and Serum Studies

Copper (Cu) is an important trace element involved in oxidative stress, which is associated with the onset and progression of diabetes mellitus (DM). However, clinical studies comparing plasma or serum Cu levels in patients with DM and in healthy individuals report conflicting findings. Therefore, in this meta-analysis, we analyzed the circulating levels of Cu associated with DM (including type 1 diabetes mellitus [T1DM] and type 2 diabetes mellitus [T2DM]). We searched the articles indexed in PubMed, OVID, and Cochrane databases, published through January 2016 and meeting our predefined criteria. Requisite data were extracted, and a random-effect model or a fixed-effect model was used to conduct the meta-analysis. Fifteen eligible studies involving a total of 1079 DM patients and 561 healthy controls were identified. Overall, the DM patients showed higher Cu levels than the healthy controls (plasma Cu mean difference [MD] = 1.69 μmol/L, p < 0.0001; serum Cu MD = 4.06 μmol/L, p = 0.005; plasma and serum Cu MD = 2.67 μmol/L, p = 0.006). Stratification based on the type of diabetes also indicated higher levels of Cu in the plasma and serum of DM patients than in healthy controls, respectively. Stratification of DM patients associated with and without complications also revealed similar results. This meta-analysis suggests that DM patients carried higher levels of Cu than healthy individuals. However, international cohort studies are needed to corroborate our findings.

The Role of Oxidative Stress and Hypoxia in Pancreatic Beta-Cell Dysfunction in Diabetes Mellitus

SIGNIFICANCE

Metabolic syndrome is a frequent precursor of type 2 diabetes mellitus (T2D), a disease that currently affects ∼8% of the adult population worldwide. Pancreatic beta-cell dysfunction and loss are central to the disease process, although understanding of the underlying molecular mechanisms is still fragmentary. Recent Advances: Oversupply of nutrients, including glucose and fatty acids, and the subsequent overstimulation of beta cells, are believed to be an important contributor to insulin secretory failure in T2D. Hypoxia has also recently been implicated in beta-cell damage. Accumulating evidence points to a role for oxidative stress in both processes. Although the production of reactive oxygen species (ROS) results from enhanced mitochondrial respiration during stimulation with glucose and other fuels, the expression of antioxidant defense genes is unusually low (or disallowed) in beta cells.

CRITICAL ISSUES

Not all subjects with metabolic syndrome and hyperglycemia go on to develop full-blown diabetes, implying an important role in disease risk for gene-environment interactions. Possession of common risk alleles at the SLC30A8 locus, encoding the beta-cell granule zinc transporter ZnT8, may affect cytosolic Zn2+ concentrations and thus susceptibility to hypoxia and oxidative stress.

FUTURE DIRECTIONS

Loss of normal beta-cell function, rather than total mass, is increasingly considered to be the major driver for impaired insulin secretion in diabetes. Better understanding of the role of oxidative changes, its modulation by genes involved in disease risk, and effects on beta-cell identity may facilitate the development of new therapeutic strategies to this disease. Antioxid. Redox Signal. 26, 501-518.

Expression Patterns and Correlations with Metabolic Markers of Zinc Transporters ZIP14 and ZNT1 in Obesity and Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is associated with infertility, increased androgen levels, and insulin resistance. In adipose tissue, zinc facilitates insulin signaling. Circulating zinc levels are altered in obesity, diabetes, and PCOS; and zinc supplementation can ameliorate metabolic disturbances in PCOS. In adipose tissue, expression of zinc influx transporter ZIP14 varies with body mass index (BMI), clinical markers of metabolic syndrome, and peroxisome proliferator-activated receptor gamma (PPARG). In this study, we investigated expression levels of ZIP14 and PPARG in subcutaneous adipose tissue of 36 PCOS women (17 lean and 19 obese women) compared with 23 healthy controls (7 lean and 16 obese women). Further, expression levels of zinc transporter ZIP9, a recently identified androgen receptor, and zinc efflux transporter ZNT1 were investigated, alongside lipid profile and markers of glucose metabolism [insulin degrading enzyme, retinol-binding protein 4 (RBP4), and glucose transporter 4 (GLUT4)]. We find that ZIP14 expression is reduced in obesity and positively correlates with PPARG expression, which is downregulated with increasing BMI. ZNT1 is upregulated in obesity, and both ZIP14 and ZNT1 expression significantly correlates with clinical markers of altered glucose metabolism. In addition, RBP4 and GLUT4 associate with obesity, but an association with PCOS as such was present only for PPARG and RBP4. ZIP14 and ZNT1 does not relate to clinical androgen status and ZIP9 is unaffected by all parameters investigated. In conclusion, our findings support the existence of a zinc dyshomeostasis in adipose tissue in metabolic disturbances including PCOS-related obesity.