IIb Group Metal Ions (Zn2+, Cd2+, Hg2+) Stimulate Glucose Transport Activity by Post-insulin Receptor Kinase Mechanism in Rat Adipocytes

A review on the relationship between Arachidonic acid 15-Lipoxygenase (ALOX15) and diabetes mellitus

Arachidonic acid 15-lipoxygenase (ALOX15), as one of the lipoxygenase family, is mainly responsible for catalyzing the oxidation of various fatty acids to produce a variety of lipid components, contributing to the pathophysiological processes of various immune and inflammatory diseases. Studies have shown that ALOX15 and its related products are widely distributed in human tissues and related to multiple diseases such as liver, cardiovascular, cerebrovascular diseases, diabetes mellitus and other diseases. Diabetes mellitus (DM), the disease studied in this article, is a metabolic disease characterized by a chronic increase in blood glucose levels, which is significantly related to inflammation, oxidative stress, ferroptosis and other mechanisms, and it has a high incidence in the population, accompanied by a variety of complications. Figuring out how ALOX15 is involved in DM is critical to understanding its role in diseases. Therefore, ALOX15 inhibitors or combination therapy containing inhibitors may deliver a novel research direction for the treatment of DM and its complications. This article aims to review the biological effect and the possible function of ALOX15 in the pathogenesis of DM.

The ameliorative effect of zinc acetate with caffeic acid in the animal model of type 2 diabetes

Recently the complexation-mediated antioxidative and glycaemic control synergism between zinc(II) and caffeic acid was demonstrated in vitro. The present study evaluated the complexation-mediated antidiabetic and antioxidative synergism between zinc(II) and caffeic acid in diabetic rats and the possible underlying mechanisms. Male SD rats were induced with diabetes using 10% fructose and 40 mg/kg bw streptozotocin. The diabetic rats were treated with Zn(II)-caffeic acid complex and its precursors (caffeic acid and zinc acetate) for 4 weeks at predetermined doses. The effect of the treatments on diabetes and oxidative stress was measured. The complex ameliorated diabetic alterations. It reduced polyphagia and polydipsia and recovered weight loss. It increased insulin secretion, insulin sensitivity, hepatic and muscle glycogen, muscle hexokinase activity and Akt phosphorylation, which resulted in improved glucose tolerance and reduced blood glucose in the diabetic rats. The complex concomitantly reduced systemic and tissue lipid peroxidation and increased antioxidant enzymes activity in the diabetic rats. The complex outperformed the antidiabetic and antioxidative action of its precursors and had a broader bioactivity profile. Complexing zinc acetate with caffeic acid improved their ameliorative effect on insulin resistance by ∼24% and 42%, respectively, as well as their anti-hyperglycaemic action by ∼24 - 36% and ∼42 - 47%, respectively, suggesting a complexation-mediated synergism. In some instances, the antidiabetic action of the complex was comparable to metformin, while its antioxidant effect was better than that of metformin. Zinc(II)-caffeic acid complexation may be an alternative approach to improving the efficacy of antidiabetic and antioxidative therapy with minimal adverse or side effects.

The Assessment of Dietary Organic Zinc on Zinc Homeostasis, Antioxidant Capacity, Immune Response, Glycolysis and Intestinal Microbiota in White Shrimp (Litopenaeus vannamei Boone, 1931)

This study aimed to assess dietary organic zinc on zinc homeostasis, antioxidant capacity, immune response, glycolysis and intestinal microbiota in white shrimp (Litopenaeus vannamei Boone, 1931). Six experimental diets were formulated: Control, zinc free; S120, 120 mg·kg⁻¹ zinc from ZnSO₄·7H₂O added into control diet; O30, O60, O90 and O120, 30, 60, 90 and 120 mg·kg⁻¹ zinc from Zn-proteinate added into control diet, respectively. The results showed that organic zinc significantly promoted zinc content and gene expression of ZnT1, ZIP11 and MT in the hepatopancreas and enhanced antioxidant capacity and immunity (in terms of increased activities of T-SOD, Cu/Zn SOD, PO, LZM, decreased content of MDA, upregulated expressions of GST, G6PDH, ProPO, LZM and Hemo, and increased resistance to Vibrio parahaemolyticus). Organic zinc significantly upregulated GluT1 expression in the intestine, increased glucose content of plasma and GCK, PFK and PDH activities of hepatopancreas, and decreased pyruvate content of hepatopancreas. Organic zinc improved intestinal microbiota communities, increased the abundance of potentially beneficial bacteria and decreased the abundance of potential pathogens. Inorganic zinc (S120) also had positive effects, but organic zinc (as low as O60) could achieve better effects. Overall, organic zinc had a higher bioavailability and was a more beneficial zinc resource than inorganic zinc in shrimp feeds.

Lead, mercury, and cadmium exposures are associated with obesity but not with diabetes mellitus: Korean National Environmental Health Survey (KoNEHS) 2015-2017

BACKGROUND

Associations of heavy metal exposures with obesity and obesity-related traits have been suggested, while those with nonalcoholic fatty liver disease (NAFLD) and diabetes mellitus (DM) are often inconsistent.

METHODS

This study included 3787 adults aged ≥19 years who participated in the Korean National Environmental Health Survey 2015-2017, and investigated the association of toxic heavy metals with metabolic diseases. Lead (Pb), mercury (Hg), and cadmium (Cd) were measured either in urine (uHg, uCd) or total blood (bPb, bHg). Body mass index (BMI) was calculated, and DM cases were identified through a self-answered medication history. Hepatic Steatosis Index (HSI) as a surrogating index of NAFLD, was calculated using hepatic enzyme measurements, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

RESULTS

Adults in the highest quartile of bPb, bHg, and uHg showed significantly elevated odds of obesity (BMI ≥25 kg/m²), compared to the lowest quartile (OR 1.58 for bPb, 1.92 for bHg, and 1.81 for uHg). HSI was positively correlated with bHg, uHg, and uCd concentrations. The odds of NAFLD (HSI ≥36) were also increased with increasing quartile of bHg, uHg, and uCd concentrations. For DM, bPb showed a significant negative association, while bHg and uCd exhibited non-monotonic and inconclusive associations.

CONCLUSIONS

Among the general adult population of Korea, both Pb and Hg exposures were associated with an increased risk of obesity. In addition, both Hg and Cd exposures were associated with increased odds of NAFLD. These metals, however, were not associated with an increased risk of DM.

Vanillic acid-Zn(II) complex: a novel complex with antihyperglycaemic and anti-oxidative activity

OBJECTIVES

Our aim was to synthesize, characterize and evaluate the antihyperglycaemic and anti-oxidative properties of a new Zn(II) complex of vanillic acid.

METHODS

The complex was synthesized using ZnSO4.7H2O and vanillic acid as precursors. NMR and FTIR techniques were used to characterize the synthesized complex. The cytotoxicity of the complex was measured. The antihyperglycemic and anti-oxidative properties of the complex were evaluated using in vitro, cell-based and ex vivo models and compared with those of its precursors.

KEY FINDINGS

Zn(II) coordinated with vanillic acid via a Zn(O6) coordination, with the complex having three moieties of vanillic acid. The radical scavenging, Fe3+ reducing and hepatic antilipid peroxidative activity of the complex were, respectively, 2.3-, 1.8- and 9.7-folds more potent than vanillic acid. Complexation increased the α-glucosidase and glycation inhibitory activity of vanillic acid by 3- and 2.6-folds, respectively. Zn(II) conferred potent L-6 myotube (EC50 = 20.4 μm) and muscle tissue (EC50 = 612 μm) glucose uptake effects on vanillic acid. Cytotoxicity evaluation showed that the complex did not reduce the viability of L-6 myotubes and Chang liver cells.

CONCLUSIONS

The data suggest that Zn(II)-vanillic acid complex had improved bioactivity relative to vanillic acid. Thus, Zn(II) may be further studied as an antihyperglycaemic and anti-oxidative adjuvant for bioactive phenolic acids.

The Effect of Inorganic and Organic Zinc Supplementation on Growth Performance, Mineral Profile and Gene Expression Pattern of GLUT1 in Malabari Kids

The objective of this experiment was to study and compare the effects of dietary supplementation of organic and inorganic zinc (Zn) on growth performance, nutrient utilisation and gene expression pattern of glucose transporter protein in peripheral blood mononuclear cells (PBMC) in Malabari kids. Fifteen, 3-4-month-old goat kids were divided into three groups uniformly by using completely randomised design (CRD). Group G1 was fed on basal diet as per NRC requirement, and G2 and G3 were fed on basal diet + 40 ppm Zn as inorganic zinc sulphate (ZnSO₄) and 40 ppm Zn as organic Zn methionine, respectively, for a period of 91 days. Supplementation of inorganic and organic Zn had no significant effect on dry matter (DM) intake. The digestibility of crude protein (CP), ether extract (EE), neutral detergent fibre (NDF), hemicellulose and cellulose was significantly more in the organic Zn-supplemented group. The average daily gain and feed:gain ratio were significantly (p < 0.05) better in group G3 in comparison to G1 and G2, while the nitrogen retention was found to be (p < 0.01) higher in group G3 than in group G1. Zinc balance was found to be significantly (p < 0.01) increased in both supplemented groups with respect to unsupplemented group G1. The blood glucose level was (p < 0.01) lower in group G3 compared to group G1 suggesting the insulin-like activity of Zn. Serum Zn concentration was significantly (p < 0.01) increased in both Zn-supplemented groups. There was a significant (p < 0.05) rise in glucose transporter GLUT1 expression in groups G2 and G3 when compared to control group G1. Moreover, GLUT1 expression was found to be higher (p < 0.05) in group G3 as against the animals of group G2. Lowered blood glucose level might have stimulated more glucose transporter GLUT1 expression in PBMC. Organic Zn supplemented at 40 ppm level resulted in better growth performance, nutrient digestibility and nitrogen as well as Zn retention in goat kids. There was better absorption, and hence, less amount of Zn got excreted in the organic Zn-supplemented group.

Zinc(II) mineral increased the in vitro, cellular and ex vivo antihyperglycemic and antioxidative pharmacological profile of p-hydroxybenzoic acid upon complexation

In this study, zinc was complexed with p-hydroxybenzoic acid to synthesize a complex with improved pharmacological profile. Proton NMR and FTIR analysis were used to characterize the complex. Several in vitro, cellular and ex vivo antihyperglycemic and antioxidative assays were used to evaluate the potency of the complex, relative to its precursors, while molecular docking was used to investigate interactions with insulin signaling targets (GLUT-4 and PKB). Also, the cytotoxicity of the complex was evaluated in Chang liver cells and L-6 myotubes using MTT assay. Complexation was through a Zn(O₄ ) coordination. This afforded the complex two moieties of p-hydroxybenzoic acid, which influenced its activities. While the complex retained the α-glucosidase and α-amylase inhibitory activity of its phenolic acid precursor, complexation increased in vitro and ex vivo antioxidant activity of the phenolic acid by 1.4 to 10.5-folds. Complexation, further, conferred a potent antiglycation activity and L-6 myotube and psoas muscle glucose uptake properties (2.1 to 3.5-folds more than p-hydroxybenzoic acid) on the phenolic acid, without notably inhibiting or reducing the viability of Chang liver cells (IC₅₀  = 5,120 μM) and L-6 myotubes (IC₅₀  = 2,172 μM). Docking studies showed the complex had better interactions with insulin signaling targets (GLUT-4 and PKB) than p-hydrobenzoic acid, which may influence its glucose uptake effects. Data suggest that Zn(II) complexation improved and/or broadened the pharmacological profile of p-hydroxybenzoic acid, thus, may be further studied as a promising adjuvant for phenolic acids. PRACTICAL APPLICATIONS: Most antidiabetic drugs are used as two or more combinations to achieve better efficacy, which may cause drug interaction and increase the risk of side effects associated with these drugs. This study takes advantage of the glycemic control property of zinc and the antioxidant and/or diabetes-related pharmacological properties of p-hydroxybenzoic acid to form a complex with improved and broader antioxidant and antihyperglycemic profile and minimal toxicity concerns. With appropriate further studies, Zn(II)-phenolic acid complexes may be safe nutraceuticals for diabetes and related oxidative complications.

Diabetes and zinc dyshomeostasis: Can zinc supplementation mitigate diabetic complications?

Zinc present in the islet cells of the pancreas is crucial for the synthesis, storage, and secretion of insulin. The excretion of large amounts of zinc from the body is reported in diabetic situations. Zinc depletion and increased oxidative stress have a major impact on the pathogenesis of diabetic complications. It would be most relevant to ascertain if intervention with supplemental zinc compensating for its depletion would beneficially mitigate hyperglycemia and the attendant metabolic abnormalities, and secondary complications in diabetes. An exhaustive literature search on this issue indicates: (1) Concurrent hypozincemia and decreased tissue zinc stores in diabetes as a result of its increased urinary excretion and/or decreased intestinal absorption, (2) Several recent experimental studies have documented that supplemental zinc has a potential hypoglycemic effect in the diabetic situation, and also beneficially modulate the attendant metabolic abnormalities and compromised antioxidant status, and (3) Supplemental zinc also alleviates renal lesions, cataract and the risk of cardiovascular disease accompanying diabetes mellitus, and help restore gastrointestinal health in experimental diabetes. These studies have also attempted to identify the precise mechanisms responsible for zinc-mediated beneficial effects in diabetic situation. The evidence discussed in this review highlights that supplemental zinc may significantly contribute to its clinical application in the management of diabetic hyperglycemia and related metabolic abnormalities, and in the alleviation of secondary complications resulting from diabetic oxidative stress.

Zinc(II) complexes in diabetes management: Plant-derived phenolics as understudied promising ligands

Zinc mineral has been known as a supplement for diabetics due to its deficiency in diabetics. Its glycemic control and insulin mimetic properties have been reported. Thus, it has been complexed with numerous types of ligands to improve the glycemic control property of the ligands. Unfortunately, mostly synthetic ligands with little or no bioactive properties and toxicity concerns have been complexed with Zn, while plant-derived dietary phenolics have rarely been explored as ligand for Zn complexation, despite their medicinal credence and minimal toxicity concern. In this letter, plant-derived phenolics have been presented as promising ligands for Zn(II) in developing potent antidiabetic and antioxidative nutraceutical complexes with improved and multi-facet bioactivity profile, as well as minimal toxicity concerns. Thus, fostering the paradigm shift from synthetic medicine toward dietary and functional medicine. PRACTICAL APPLICATIONS: Potentially, complexing Zn(II) with bioactive plant-derived dietary phenolics could result in novel nutraceuticals and/or supplements with improved and multi-facet bioactivity profile, as well as minimal toxicity concerns.

Synthesis, characterization, antidiabetic and antioxidative evaluation of a novel Zn(II)-gallic acid complex with multi-facet activity

Objectives

This study was done to synthesize a novel Zn(II)-gallic acid complex with improved antidiabetic and antioxidative properties.

Methods

The complex was synthesized and characterized using Fourier Transform Infrared (FT-IR) and 1H NMR. Cytotoxicity was evaluated using Chang liver cells and L6 myotubes. Radical scavenging and Fe3+-reducing, as well as α-glucosidase, α-amylase and glycation inhibitory properties were measured. Glucose uptake was measured in L6 myotubes, while the complex was docked against glucose transporter type 4 (GLUT-4) and protein kinase B (PKB).

Key findings

Analysis showed that complexation occurred through a Zn(O4) coordination; thus, the complex acquired two moieties of gallic acid, which suggests why complexation increased the DPPH (IC50 = 48.2 µm) and ABTS (IC50 = 12.7 µm) scavenging and α-glucosidase inhibitory (IC50 = 58.5 µm) properties of gallic acid by several folds (5.5, 3.6 and 2.7 folds; IC50 = 8.79, 3.51 and 21.5 µm, respectively). Zn(II) conferred a potent dose-dependent glucose uptake activity (EC50 = 9.17 µm) on gallic acid, without reducing the viability of L6 myotubes and hepatocytes. Docking analysis showed the complex had stronger interaction with insulin signalling proteins (GLUT-4 and PKB) than its precursor.

Conclusions

Data suggest that complexation of Zn(II) with gallic acid resulted in a complex with improved and multi-facet antioxidative and glycaemic control properties.

Effects of Zinc Supplementation on Cardiometabolic Risk Factors: a Systematic Review and Meta-analysis of Randomized Controlled Trials

The prevalence of cardiometabolic risk factors has been increasing worldwide. The results of reported studies on the effects of zinc supplementation on cardiometabolic risk factors are unequivocal. This systematic review and meta-analysis of randomized controlled trials was conducted to evaluate the effects of zinc supplementation on cardiometabolic risk factors. A systematic search was conducted through international databases (PubMed/Medline, Institute of Scientific Information, and Scopus) until December 2018 to include all randomized controlled trials (RCT), quasi-RCT, and controlled clinical trials which assessed the effect of zinc supplementation on cardiometabolic risk factors including lipid profile, glycemic indices, blood pressure, and anthropometric indices. Random- or fixed-effects meta-analysis method was used to estimate the standardized mean difference (SMD) and 95% confidence interval (CI). A total of 20 studies were included in the meta-analysis, which included a total of 1141 participants in the intervention group. Meta-analysis showed that zinc supplementation significantly decreased plasma levels of triglyceride (SMD - 0.66, 95% CI - 1.27, - 0.06), very-low-density lipoprotein (SMD - 1.59, 95% CI - 2.86, - 0.31), and total cholesterol (SMD - 0.65, 95% CI - 1.15, - 0.15). Similarly, zinc supplementation significantly decreased fasting blood glucose (SMD - 0.52, 95% CI - 0.96, - 0.07) and HbA1c (SMD - 0.64, 95% CI - 1.27, - 0.02). The effects of zinc supplementation on blood pressure and anthropometric indices were not statistically significant (P > 0.05). Zinc supplements had beneficial effects on glycemic indices and lipid profile. Thus, it appeared that zinc supplementation might be associated with a decrease in cardiometabolic risk factors contributing to a reduction in risk of atherosclerosis.

A comprehensive review on zinc(II) complexes as anti-diabetic agents: The advances, scientific gaps and prospects

Zinc has gained notable attention in the development of potent anti-diabetic agents, due to its role in insulin storage and secretion, as well as its reported insulin mimetic properties. Consequently, zinc(II) has been complexed with numerous organic ligands as an adjuvant to develop anti-diabetic agents with improved and/or broader scope of pharmacological properties. This review focuses on the research advances thus far to identify the major scientific gaps and prospects. Peer-reviewed published data on the anti-diabetic effects of zinc(II) complexes were sourced from different scientific search engines, including, but not limited to "PubMed", "Google Scholar", "Scopus" and ScienceDirect to identify potent anti-diabetic zinc(II) complexes. The complexes were subcategorized according to their precursor ligands. A critical analysis of the outcomes from published studies shows promising leads, with Zn(II) complexes having a "tri-facet" mode of exerting pharmacological effects. However, the promising leads have been flawed by some major scientific gaps. While zinc(II) complexes of synthetic ligands with little or no anti-diabetic pharmacological history remain the most studied (about 72 %), their toxicity profile was not reported, which raises safety concerns for clinical relevance. The zinc(II) complexes of plant polyphenols; natural ligands, such as maltol and hinokitiol; and supplements, such as ascorbic acid (a natural antioxidant), l-threonine and l-carnitine, showed promising insulin mimetic and glycemic control properties but remain understudied and lack clinical validation, in spite of their minimal safety concerns and health benefits. A paradigm shift toward probing (including clinical studies) supplements, plant polyphenol and natural ligands as anti-diabetic zinc(II) complex is, therefore, recommended. Also, promising anti-diabetic Zn(II) complexes of synthetic ligands should undergo critical toxicity evaluation to address possible safety concerns.

Urinary cadmium concentrations and metabolic syndrome in U.S. adults: The National Health and Nutrition Examination Survey 2001-2014

BACKGROUND

Low to moderate acute cadmium exposure has been associated with increased risk of chronic diseases, such as cardiovascular and kidney disease. Little is known about the association between urinary cadmium levels-an indicator of longer-term exposure-and metabolic syndrome (MetS).

METHODS

We analysed data from 3982 participants aged 20-<80 years of the National Health and Nutrition Examination Survey 2001-2014. Urinary cadmium levels were measured and adjusted for creatinine using spot urine samples. Cadmium levels were evaluated in quintiles (Q). MetS was defined by National Cholesterol Education Program's Adult Treatment Panel III report criteria. Prevalence odds ratios (OR) and 95% confidence intervals (CI) were calculated using multivariable logistic regression accounting for complex survey design, while adjusting for potential confounders and stratifying by sex and smoking status.

RESULTS

In the overall study population, there was a marginal inverse association between urinary cadmium and MetS (adj. OR for Q5 versus Q1: 0.7; 95% CI: 0.5-1.0). Sex stratified models were similar. When examining individual components of MetS, participants with higher levels of urinary cadmium had decreased odds of abdominal obesity (adj. OR for Q5 versus Q1 0.4; 95% CI: 0.3-0.6), but increased odds for low HDL (adj. OR for Q5 versus Q1 2.1; 95% CI: 1.4-3.1). Among current smokers, higher urinary cadmium was associated with increased odds of MetS, hypertension, and low HDL even after accounting for serum cotinine-a marker of smoking intensity.

CONCLUSIONS

Higher levels of urinary cadmium, a marker of long term exposure, were not associated with an increased risk of MetS in the overall study population. However, higher urine cadmium was associated with altered MetS components. Current smokers were the most vulnerable group, with higher long-term cadmium exposure being associated with increased risk of MetS, low HDL, and hypertension.

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.

Is mercury exposure causing diabetes, metabolic syndrome and insulin resistance? A systematic review of the literature

INTRODUCTION

Several populations are exposed to mercury (Hg) via their environment, occupation or diet. It is hypothesized that Hg exposure can lead to the development of diabetes mellitus (DM). Metabolic syndrome (MS) is also a possible outcome as its symptoms are closely linked to those of DM.

METHOD

We conducted a systematic review of the literature by screening Web of Science, MEDLINE, SciFinder and Embase and we included original studies pertaining to the relationship of total Hg exposure (elemental, inorganic or organic) to DM, MS or insulin resistance. The studies were selected based on the PICOS (patients, intervention, comparator, outcomes and study design) criteria and their quality assessed using a nine-point scale. Study characteristics and results were extracted and presented in structured tables. We also extracted covariates entered as confounding factors to evaluate possible biases in selected studies. Finally, a weight of evidence approach was used to assess the causality of the relationship.

RESULTS

A total of 34 studies were included in the present review. Epidemiological data assessment suggests a possible association between total Hg concentrations in different biological matrices and incidence of DM or MS, but the relationship is not consistent. In vivo and in vitro studies support the biological plausibility of the relation between Hg exposure and DM or MS. Five out of nine of Bradford Hill's criteria were fulfilled: strength, temporality, plausibility, coherence and analogy.

CONCLUSION

Increased total Hg exposure may augment the risk of DM and MS, but the lack of consistency of the epidemiological evidence prevents inference of a causal relationship. Additional prospective cohort studies and careful consideration of confounding variables and interactions are required to conclude on the causal relationship of total Hg exposure on the development of DM or MS.

Metabolic relationship between diabetes and Alzheimer's Disease affected by Cyclo(His-Pro) plus zinc treatment

BACKGROUND

Association of Alzheimer's Disease (AD) with Type 2 Diabetes (T2D) has been well established. Cyclo(His-Pro) plus zinc (Cyclo-Z) treatment ameliorated diabetes in rats and similar improvements have been seen in human patients. Treatment of amyloid precursor protein (APP) transgenic mice with Cyclo-Z exhibited memory improvements and significantly reduced Aβ-40 and Aβ-42 protein levels in the brain tissues of the mice.

SCOPE OF REVIEW

Metabolic relationship between AD and T2D will be described with particular attention to insulin sensitivity and Aβ degradation in brain and plasma tissues. Mechanistic effect of insulin degrading enzyme (IDE) in decreasing blood glucose and brain Aβ levels will be elucidated. Cyclo-Z effects on these biochemical parameters will be discussed.

MAJOR CONCLUSION

Stimulation of IDE synthesis is effective for the clinical treatment of metabolic diseases including AD and T2D.

GENERAL SIGNIFICANCE

Cyclo-Z might be the effective treatment of AD and T2D by stimulating IDE synthesis.

MicroRNA Expression Varies according to Glucose Tolerance, Measurement Platform, and Biological Source

Dysregulated microRNA (miRNA) expression is observed during type 2 diabetes (T2D), although the consistency of miRNA expression across measurement platform and biological source is uncertain. Here we report miRNA profiling in the whole blood and serum of South African women with different levels of glucose tolerance, using next generation sequencing (NGS) and quantitative real time PCR (qRT-PCR). Whole blood-derived miRNAs from women with newly diagnosed T2D (n = 4), impaired glucose tolerance (IGT) (n = 4), and normal glucose tolerance (NGT) (n = 4) were subjected to NGS, whereafter transcript levels of selected miRNAs were quantified in the whole blood and serum of these women using qRT-PCR. Of the five significantly differentially expressed miRNAs identified by NGS, only the directional increase of miR-27b in women with IGT compared to NGT was confirmed in whole blood and serum, using qRT-PCR. Functional enrichment of miR-27b gene targets identified biological pathways associated with glucose transport and insulin regulation. In conclusion, this study showed poor correlation in miRNA expression profiled using NGS and qRT-PCR and in whole blood and serum. The consistent increased expression of miR-27b in women with IGT compared to NGT across measurement platform and biological source holds potential as a biomarker for risk stratification in our population.

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.

Dual Effect of Curcumin-Zinc Complex in Controlling Diabetes Mellitus in Experimentally Induced Diabetic Rats

Ultrasound-assisted extraction of curcumin from Curcuma longa was performed in an ultrasonic bath at 30°C using ethanol for 40 min. A successful attempt has been made to prepare curcumin-zinc (Zn) complex using a simple chemical procedure. The complex formation and its stoichiometry were characterized using elemental analysis, Fourier transform (FT)-IR and UV spectroscopy which revealed the interaction of Zn(II) ion (M) with curcumin (ligand, L) to proceed via (ML) complex type formation. Oral administration of curcumin-Zn complex at a concentration of 150 mg/kg body weight/rat/d for 45 d in streptozotocin-induced diabetic rats in comparison to curcumin and/or Zn administration exerted a hypoglycemic effect. A significant reduction in blood glucose, glycosylated hemoglobin (Hb)A1c, and lipid profile parameters with an excellent improvement in plasma insulin levels have been attained. Also, the reduced activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea, and creatinine in the diabetic rats treated with the complex exhibited the non-toxic nature of the curcumin-Zn complex. Finally, the larger extent of the complex in hyperglycemic improvement in comparison to curcumin and/or Zn supplementation was interpreted by its dual action on glucose and insulin maintenance.

Administration of Zinc plus Cyclo-(His-Pro) Increases Hippocampal Neurogenesis in Rats during the Early Phase of Streptozotocin-Induced Diabetes

The effects of zinc supplementation on hippocampal neurogenesis in diabetes mellitus have not been studied. Herein, we investigated the effects of zinc plus cyclo-(His-Pro) (ZC) on neurogenesis occurring in the subgranular zone of dentate gyrus after streptozotocin (STZ)-induced diabetes. ZC (27 mg/kg) was administered by gavage once daily for one or six weeks from the third day after the STZ injection, and histological evaluation was performed at 10 (early phase) or 45 (late phase) days after STZ injection. We found that the proliferation of progenitor cells in STZ-induced diabetic rats showed an increase in the early phase. Additionally, ZC treatment remarkably increased the number of neural progenitor cells (NPCs) and immature neurons in the early phase of STZ-induced diabetic rats. Furthermore, ZC treatment showed increased survival rate of newly generated cells but no difference in the level of neurogenesis in the late phase of STZ-induced diabetic rats. The present study demonstrates that zinc supplementation by ZC increases both NPCs proliferation and neuroblast production at the early phase of diabetes. Thus, this study suggests that zinc supplemented with a histidine/proline complex may have beneficial effects on neurogenesis in patients experiencing the early phase of Type 1 diabetes.

Anti-Hyperglycemic Activity of Zinc Plus Cyclo (His-Pro) in Genetically Diabetic Goto-Kakizaki and Aged Rats

We previously reported that treatment of streptozotocin-induced diabetic rats with zinc plus cyclo (his-pro) (CHP) decreased fed blood glucose levels and water intake. The present study was conducted to examine the dose-dependent, acute, and chronic treatment effects of CHP on oral glucose tolerance (OGT), fed blood glucose levels, water intake, and plasma insulin levels in young and aged Sprague-Dawley (S-D) rats, nondiabetic Wistar rats, and genetically diabetic Goto-Kakizaki (G-K) rats. Acute gastric gavage of 10 mg zinc plus 1.0 mg CHP/kg body weight significantly improved OGT in 4- and 13-month-old nondiabetic S-D rats and in 2-month-old diabetic G-K rats. Young S-D and G-K rats returned to pretreatment OGT values 1 week after acute gavage of zinc plus CHP (ZC), but improved OGT values persisted for at least 1 week after gavage in aged S-D rats. OGT values and fed blood glucose decreased to the greatest extent among other treatments when G-K rats were given free access to drinking water containing 1.0 to 1.5 mg CHP/L plus 10 mg zinc/L for 2 weeks. Although food and water intake showed a tendency to decrease, no statistically significant differences were observed in young G-K rats. Plasma insulin levels and blood glucose levels in both normal and diabetic G-K rats decreased with 2-week treatment with ZC. To test the direct effects of ZC on muscle tissue, we observed the effect of various doses of ZC on normal and G-K rat muscle slices. The optimal level of CHP alone for maximal muscle glucose uptake in muscle slices from normal rats was 10 microg/mL and 5.0 microg/mL in G-K rats, and ZC stimulated glucose uptake. However, no statistically significant difference was demonstrated between normal and G-K rat tissues in this study. These results indicate that oral intake of an optimal dose of ZC stimulates blood glucose metabolism, probably by stimulating muscle glucose utilization.

Bis(hinokitiolato)zinc complex ([Zn(hkt)2]) activates Akt/protein kinase B independent of insulin signal transduction

Since many Zn complexes have been developed to enhance the insulin-like activity and increase the exposure and residence of Zn in the animal body, these complexes are recognized as one of the new candidates with action mechanism different from existing anti-diabetic drugs. However, the molecular mechanism by which Zn complexes exert an anti-DM effect is unknown. Therefore, we evaluated the activity of Zn complexes, especially related to the phosphorylation of insulin signaling pathway components. We focused on the insulin-like effects of the bis(hinokitiolato)zinc complex, [Zn(hkt)2], using 3T3-L1 adipocytes. [Zn(hkt)2] was taken up by cells and induced Akt phosphorylation in a time-dependent manner. Additionally, it showed inhibitory activity against PTP1B and PTEN, which are major negative regulators of insulin signaling. It did not promote the phosphorylation of IR (insulin receptor)-β or IRS (insulin receptor substrate)-1 by itself, but in combination with insulin, it enhanced the phosphorylation of IRβ. We conclude that [Zn(hkt)2] has effects on the proteins of insulin signaling pathway without insulin receptor mediation, and [Zn(hkt)2] promotes insulin function and shows the anti-DM effects. Thus, [Zn(hkt)2] may be the basis for improved DM treatments.

Effect of Trace and Toxic Elements of Different Brands of Cigarettes on the Essential Elemental Status of Irish Referent and Diabetic Mellitus Consumers

Cigarette smoking interferes with the metal homeostasis of the human body, which plays a crucial role for maintaining the health. A significant flux of heavy metals, among other toxins, reaches the lungs through smoking. In the present study, the relationship between toxic element (TE) exposure via cigarette smoking and diabetic mellitus incidence in population living in Dublin, Ireland is investigated. The trace [zinc (Zn) and selenium (Se)] and toxic elements arsenic (As), aluminum (Al), cadmium (Cd), nickel (Ni), mercury (Hg), and lead (Pb) were determined in biological (scalp hair and blood) samples of patients diagnosed with diabetic mellitus, who are smokers living in Dublin, Ireland. These results were compared with age- and sex-matched healthy, nonsmokers controls. The different brands of cigarette (filler tobacco, filter, and ash) consumed by the studied population were also analyzed for As, Al, Cd, Ni, Hg, and Pb. The concentrations of TEs in biological samples and different components of cigarette were measured by inductively coupled plasma atomic emission spectrophotometer after microwave-assisted acid digestion. The validity and accuracy of the methodology were checked using certified reference materials (CRM). The recovery of all the studied elements was found to be in the range of 96.4-99.7% in certified reference materials. The filler tobacco of different branded cigarettes contains Hg, As, Al, Cd, Ni, and Pb concentrations in the ranges of 9.55-12.4 ng/cigarette, 0.432-0.727 μg/cigarette, 360-496 μg/cigarette, 1.70-2.12 μg/cigarette, 0.715-1.52 μg/cigarette, and 0.378-1.16 μg/cigarette, respectively. The results of this study showed that the mean values of Al, As, Cd, Hg, Ni, and Pb were significantly higher in scalp hair and blood samples of diabetic mellitus patients in relation to healthy controls, while the difference was significant in the case of smoker patients (p < 0.001). The levels of all six toxic elements were twofolds to threefolds higher in scalp hair and blood samples of nondiabetic mellitus smoker subjects as compared to nonsmoker controls. The high exposure of toxic metals as a result of cigarette smoking may be synergistic with risk factors associated with diabetic mellitus.

Zinc and diabetes mellitus: understanding molecular mechanisms and clinical implications

Background

Diabetes mellitus is a leading cause of morbidity and mortality worldwide. Studies have shown that Zinc has numerous beneficial effects in both type-1 and type-2 diabetes. We aim to evaluate the literature on the mechanisms and molecular level effects of Zinc on glycaemic control, β-cell function, pathogenesis of diabetes and its complications.

Methods

A review of published studies reporting mechanisms of action of Zinc in diabetes was undertaken in PubMed and SciVerse Scopus medical databases using the following search terms in article title, abstract or keywords; (“Zinc” or “Zn”) and (“mechanism” or “mechanism of action” or “action” or “effect” or “pathogenesis” or “pathology” or “physiology” or “metabolism”) and (“diabetes” or “prediabetes” or “sugar” or “glucose” or “insulin”).

Results

The literature search identified the following number of articles in the two databases; PubMed (n = 1799) and SciVerse Scopus (n = 1879). After removing duplicates the total number of articles included in the present review is 111. Our results show that Zinc plays an important role in β-cell function, insulin action, glucose homeostasis and the pathogenesis of diabetes and its complications.

Conclusion

Numerous in-vitro and in-vivo studies have shown that Zinc has beneficial effects in both type-1 and type-2 diabetes. However further randomized double-blinded placebo-controlled clinical trials conducted for an adequate duration, are required to establish therapeutic safety in humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s40199-015-0127-4) contains supplementary material, which is available to authorized users.

Jasada bhasma, a Zinc-Based Ayurvedic Preparation: Contemporary Evidence of Antidiabetic Activity Inspires Development of a Nanomedicine

The roles of metals in human physiology are well established. It is also known that many metals are required in trace amounts for normal metabolism and their deficiency leads to diseases. In Ayurveda, metal-based preparations, that is, bhasmas, are indicated for the treatment of several diseases. Standard textbooks of Ayurveda recommend Jasada bhasma (zinc based bhasma) as the treatment of choice for diabetes. Modern medicine also recognizes the important role of zinc in glucose homeostasis. Yet, studies that validate the use of Jasada bhasma are few and uncomprehensive. There is an imminent need for a systematic study on physicochemical characterization, pharmacological efficacy, and toxicity assessment of several bhasma preparations to generate scientific evidence of their utility and safety. Interestingly, recent studies suggest that bhasmas comprise submicronic particles or nanoparticles. Thus a bhasma-inspired new drug discovery approach could emerge in which several metal based nanomedicines could be developed. This would help in utilizing the age old, time-tested wisdom of Ayurveda in modern medicine. One such study on antidiabetic activity of Jasada bhasma and the corresponding new drug, namely, zinc oxide nanoparticles, is briefly discussed, as an example.

Cadmium exposure in relation to insulin production, insulin sensitivity and type 2 diabetes: a cross-sectional and prospective study in women

BACKGROUND

Cadmium is a wide-spread pollutant. Observational studies suggest associations between cadmium and prevalence of type 2 diabetes. Experimental studies indicate that cadmium may cause impaired insulin production.

OBJECTIVES

To examine whether cadmium exposure is associated with impaired glucose tolerance and type 2 diabetes and impaired pancreatic beta-cell function.

METHODS

Oral glucose tolerance tests were used in a screening examination of 64-year old women (n=2595) to identify all with diabetes, impaired (IGT) and normal (NGT) glucose tolerance. Random samples of women with type 2 diabetes (n=215), IGT (n=207) and NGT (n=194) were recruited in a cross-sectional examination including measurement of pancreatic insulin production (acute insulin response) and insulin sensitivity (homeostasis model assessment). Cadmium concentrations were measured in blood and urine. A follow-up examination was performed after 5.4 years with assessment of new cases with diabetes or impaired glucose tolerance.

RESULTS

At baseline, neither blood nor urinary cadmium concentrations showed any statistically significant differences between women with type 2 diabetes, IGT or NGT. The prospective analysis included 68 cases with incident diabetes, 58 with IGT and 118 women with NGT and no associations with cadmium levels at baseline were observed. Blood and urinary cadmium at baseline were not associated with insulin production, blood glucose, HbA1c, or changes in HbA1c during follow-up.

CONCLUSIONS

This is the first study of cadmium and diabetes with detailed data on pancreatic beta-cell function, insulin sensitivity and glucose tolerance. Cadmium exposure was not associated with increased risk of type 2 diabetes or IGT.

Zinc transporters, mechanisms of action and therapeutic utility: implications for type 2 diabetes mellitus

Zinc is an essential trace element that plays a vital role in maintaining many biological processes and cellular homeostasis. Dysfunctional zinc signaling is associated with a number of chronic disease states including cancer, cardiovascular disease, Alzheimer's disease, and diabetes. Cellular homeostasis requires mechanisms that tightly control the uptake, storage, and distribution of zinc. This is achieved through the coordinated actions of zinc transporters and metallothioneins. Evidence on the role of these proteins in type 2 diabetes mellitus (T2DM) is now emerging. Zinc plays a key role in the synthesis, secretion and action of insulin in both physiological and pathophysiological states. Moreover, recent studies highlight zinc's dynamic role as a "cellular second messenger" in the control of insulin signaling and glucose homeostasis. This suggests that zinc plays an unidentified role as a novel second messenger that augments insulin activity. This previously unexplored concept would raise a whole new area of research into the pathophysiology of insulin resistance and introduce a new class of drug target with utility for diabetes pharmacotherapy.

Comparative metal distribution in scalp hair of Pakistani and Irish referents and diabetes mellitus patients

BACKGROUND

The essential metals, chromium (Cr), magnesium (Mg), manganese (Mn) and zinc (Zn), are necessary for many metabolic processes and their homeostasis is crucial for life. The toxic metals, cadmium (Cd) and lead (Pb), have no beneficial role in human metabolism. The aim of this study was to investigate the levels of Cd, Cr, Mg, Mn, Pb, and Zn in scalp hair samples of type 2 diabetes mellitus patients of both genders, ages ranging from 30 to 50 y, and belong to urban areas of Ireland and Pakistan. For comparison purposes, age matched non-diabetic subjects of both countries were selected as referents.

METHODS

The concentrations of metals in scalp hair samples were measured by inductively coupled plasma atomic emission spectrophotometer and atomic absorption spectrophotometer after microwave-assisted acid digestion. The validity and accuracy of the methodology were checked by conventional wet-acid-digestion method and using certified reference materials.

RESULTS

The mean values of Cd and Pb were significantly higher in scalp hair samples of both Pakistani and Irish diabetic patients as compared to referents of both countries (P<0.001). In contrast, lower Cr, Mg, Mn, and Zn (P<0.01) concentrations were detected in scalp hair derived from patients with type 2 diabetes versus healthy subjects of both countries.

CONCLUSION

This study showed that, increased toxic elements and decreased essential elements are associated with diabetes mellitus. Therefore, these elements may play a role in the development and pathogenesis of diabetes mellitus.

Differential effects of cobalt and mercury on lipid metabolism in the white adipose tissue of high-fat diet-induced obesity mice

Metals and metalloid species are involved in homeostasis in energy systems such as glucose metabolism. Enlarged adipocytes are one of the most important causes of obesity-associated diseases. In this study, we studied the possibility that various metals, namely, CoCl(2), HgCl(2), NaAsO(2) and MnCl(2) pose risk to or have beneficial effects on white adipose tissue (WAT). Exposure to the four metals resulted in decreases in WAT weight and the size of enlarged adipocytes in mice fed a high-fat diet (HFD) without changes in liver weight, suggesting that the size and function of adipocytes are sensitive to metals. Repeated administration of CoCl(2) significantly increased serum leptin, adiponectin and high-density lipoprotein (HDL) cholesterol levels and normalized glucose level and adipose cell size in mice fed HFD. In contrast, HgCl(2) treatment significantly decreased serum leptin level with the down-regulation of leptin mRNA expression in WAT and a reduction in adipocyte size. Next, we tried to investigate possible factors that affect adipocyte size. Repeated exposure to HgCl(2) significantly decreased the expression levels of factors upon the regulation of energy such as the PPARα and PPARγ mRNA expression levels in adipocytes, whereas CoCl(2) had little effect on those genes expressions compared with that in the case of the mice fed HFD with a vehicle. In addition, repeated administration of CoCl(2) enhanced AMPK activation in a dose-dependent manner in the liver, skeletal muscle and WAT; HgCl(2) treatment also enhanced AMPK activation in the liver. Thus, both Co and Hg reduced WAT weight and the size of enlarged adipocytes, possibly mediated by AMKP activation in the mice fed HFD. However, inorganic cobalt may have a preventive role in obesity-related diseases through increased leptin, adiponectin and HDL-cholesterol levels, whereas inorganic mercury may accelerate the development of such diseases. These results may lead to the development of new approaches to establishing the role of metals in adipose tissue of obesity-related diseases.

Status of toxic metals in biological samples of diabetic mothers and their neonates

The mechanism of transport of trace elements from the mother to the newborn is still not well known. The aim of present study was to compare the status of trace toxic elements, arsenic (As), cadmium (Cd), and lead (Pb) in biological samples (whole blood, urine and scalp hair) of insulin-dependent diabetic mothers (age ranged 30-40) and their newly born infants (n = 76). An age and socioeconomics matched 68 nondiabetic mothers and their infants, residing in the same locality, who were selected as referents. The elemental concentrations in all three biological samples were determined by an electrothermal atomic absorption spectrometer, prior to microwave-assisted acid digestion. The mean values of As, Cd, and Pb in all biological samples of diabetic mothers and their infants were significantly higher as compared to the referent mother-infant pair samples (p < 0.01). The high levels of As, Cd, and Pb in biological samples of diabetic women may play a role in the pathogenesis of diabetes mellitus and impacts on their neonates.

Evaluation of insulin-mimetic trace metals as insulin replacements in mammalian cell cultures

Insulin is involved in a number of cellular functions, including the stimulation of cell growth, cell cycle progression and glucose uptake and is a common protein supplement in serum-free mammalian cell culture media. However, several trace metals have previously been reported to exhibit insulin-like effects on specific cell types. As a step towards developing chemically-defined, protein-free media for mammalian cells, we tested the effectiveness of five trace metals (cadmium, nickel, lithium, vanadium and zinc) as a replacement for insulin. Four cell lines of biotechnological relevance were used, including the hybridoma CRL1606, the myeloma NS0, and the Chinese hamster ovary cell lines CHO-IFN and CHO-K1. Zinc was found to be an effective insulin replacement for the hybridoma, myeloma and CHO-K1 cells. Cell growth, cell cycle progression and antibody production was not affected by the substitution. Furthermore, no adaptation procedure was required.

Cell-type-specific roles of IGF-1R and EGFR in mediating Zn2+-induced ERK1/2 and PKB phosphorylation

Zn(2+) exerts insulin-mimetic and antidiabetic effects in rodent models of insulin resistance, and activates extracellular-signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase B (PKB), key components of the insulin signaling pathway. Zn(2+)-induced signaling has been shown to be associated with an increase in the tyrosine phosphorylation of insulin receptor (IR), as well as of insulin-like growth factor 1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) in several cell types. However, the specific contribution of these receptor protein tyrosine kinases (R-PTKs) in mediating Zn(2+)-induced responses in a cell-specific fashion remains to be established. Therefore, using a series of pharmacological inhibitors and genetically engineered cells, we have investigated the roles of various R-PTKs in Zn(2+)-induced ERK1/2 and PKB phosphorylation. Pretreatment of Chinese hamster ovary (CHO) cells overexpressing a human IR (CHO-HIR cells) with AG1024, an inhibitor for IR protein tyrosine kinase (PTK) and IGF-1R-PTK, blocked Zn(2+)-induced ERK1/2 and PKB phosphorylation, but AG1478, an inhibitor for EGFR, was without effect in CHO cells. On the other hand, both of these inhibitors were able to attenuate Zn(2+)-induced phosphorylation of ERK1/2 and PKB in A10 vascular smooth muscle cells. In addition, in CHO cells overexpressing tyrosine kinase deficient IR, Zn(2+) was still able to induce the phosphorylation of these two signaling molecules, whereas the insulin effect was significantly attenuated. Furthermore, both Zn(2+) and insulin-like growth factor 1 failed to stimulate ERK1/2 and PKB phosphorylation in IGF-1R knockout cells. Also, Zn(2+)-induced responses in CHO-HIR cells were not associated with an increase in the tyrosine phosphorylation of the IR beta-subunit and insulin receptor substrate 1 in CHO-HIR cells. Taken together, these data suggest that distinct R-PTKs mediate Zn(2+)-evoked ERK1/2 and PKB phosphorylation in a cell-specific manner.

Zinc and diabetes--clinical links and molecular mechanisms

Zinc is an essential trace element crucial for the function of more than 300 enzymes and it is important for cellular processes like cell division and apoptosis. Hence, the concentration of zinc in the human body is tightly regulated and disturbances of zinc homeostasis have been associated with several diseases including diabetes mellitus, a disease characterized by high blood glucose concentrations as a consequence of decreased secretion or action of insulin. Zinc supplementation of animals and humans has been shown to ameliorate glycemic control in type 1 and 2 diabetes, the two major forms of diabetes mellitus, but the underlying molecular mechanisms have only slowly been elucidated. Zinc seems to exert insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Furthermore, zinc might play a role in the development of diabetes, since genetic polymorphisms in the gene of zinc transporter 8 and in metallothionein (MT)-encoding genes could be demonstrated to be associated with type 2 diabetes mellitus. The fact that antibodies against this zinc transporter have been detected in type 1 diabetic patients offers new diagnostic possibilities. This article reviews the influence of zinc on the diabetic state including the molecular mechanisms, the role of the zinc transporter 8 and MT for diabetes development and the resulting diagnostic and therapeutic options.

Cadmium reduces adipocyte size and expression levels of adiponectin and Peg1/Mest in adipose tissue

Adipose tissue dysfunction has been associated with diabetogenic effects. The effects of repeated Cd exposure on adipocytes remain largely unknown. We administered Cd at doses of 0, 5, 10, and 20 micromol/kgbw sc for 2 weeks (3.5 times/week) to mice and assessed the possible alteration of epididymal white adipose tissue (WAT), including histological difference, adipocyte differentiation and functional capacity. Whereas hepatic weight did not differ between the control and Cd-exposed groups, WAT weight, as well as adipose cell mass, significantly decreased in a dose-dependent manner in Cd-treated mice. The Cd concentration in WAT significantly increased in Cd-treated groups after 2 weeks of exposure. Next, we examined the effects of Cd on adipocyte differentiation and hypertrophy. Cd exposure significantly decreased the paternally expressed gene 1/Mesoderm-specific transcript mRNA expression levels. Both peroxisome proliferator-activated receptor gamma2 and CCAAT/enhancer-binding protein alpha mRNA expression levels in WAT tended to decrease in the Cd-treated groups. Next, we determined the effects of Cd exposure on the mRNA expression levels of adipose-derived hormones, such as adiponectin and resistin. The adiponectin mRNA expression level in WAT decreased after both 6h and 2 weeks of exposure to a high dose of Cd, and the reduction in resistin mRNA expression levels was observed after 2 weeks of exposure. These results suggest that Cd exposure causes abnormal adipocyte differentiation, expansion, and function, which might lead to development of insulin resistance, hypertension, and cardiovascular disease.

Zinc fingers as biologic redox switches?

Despite zinc ions being redox inert in biologic systems, zinc-finger structures act as redox-sensitive molecular switches controlling several crucial cellular processes. Oxidative or nitrosative stress, via modification of zinc finger cysteine thiols, leads to a release of Zn(2+) from these structures, causing not only a loss of zinc-finger function but also an increase of cytoplasmic or nuclear free Zn(2+) that may, in turn, stimulate and interfere with cellular signaling cascades. A signaling cascade stimulated by exposure of cells to zinc ions or to stressful stimuli that are reported to cause an intracellular release of zinc ions involves phosphoinositide 3'-kinases and the Ser/Thr protein kinase Akt, resulting in an inactivation of transcriptional regulators of the FoxO family. Possible modes of action of zinc ions to stimulate this signaling cascade and consequences of stimulation are discussed. Moreover, we present an overview on human diseases or disorders characterized by an intracellular Zn(2+) dyshomeostasis.

A [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(ii) complex as an oral therapeutic for the treatment of type 2 diabetic KKA(y) mice

We prepared and characterized [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(II) ([Zn(tpps)]), and investigated its in vitro insulin-mimetic activity and in vivo hypoglycemic effect in type 2 diabetic KKA(y) mice. The results were compared with those of previously proposed insulin-mimetic zinc(II) complexes and zinc sulfate (ZnSO(4)). The in vitro insulin-mimetic activity of [Zn(tpps)] was considerably better than that of bis(allixinato)zinc(II) ([Zn(alx)(2)]), bis(maltolato)zinc(II) ([Zn(mal)(2)]), bis(2-aminomethylpyridinato)zinc(II) ([Zn(2-ampy)(2)](2+)), and ZnSO(4). In particular, the order of in vitro insulin-mimetic activity of the complexes was determined to be: [Zn(tpps)]>[Zn(alx)(2)]>[Zn(mal)(2)]>[Zn(2-ampy)](2+)>ZnSO(4). [Zn(tpps)] normalized the hyperglycemia of KKA(y) mice within 21 days when administered orally at doses of 10-20 mg (0.15-0.31 mmol) Zn per kg body mass for 28 days. In addition, metabolic syndromes such as insulin resistance, the degree of renal disturbance, and the degree of liver disturbance were significantly improved in [Zn(tpps)]-treated KKA(y) mice relative to those administered with saline and ZnSO(4). The improvement in diabetes was validated by the results of oral glucose-tolerance tests and the decrease in the HbA(1c) level observed. In contrast, ZnSO(4) and the ligand H(2)tpps did not lower the elevated blood glucose level under the same experimental conditions. Based on these observations, [Zn(tpps)] is proposed to be the first orally active zinc(II)-porphyrin complex for the efficacious treatment of not only type 2 diabetes but also metabolic syndromes in animals.

Evaluation of status of toxic metals in biological samples of diabetes mellitus patients

There is accumulating evidence that the metabolism of several trace elements is altered in diabetes mellitus and that these nutrients might have specific roles in the pathogenesis and progress of this disease. The aim of present study was to compare the level of toxic elements, lead (Pb), cadmium (Cd), and arsenic (As) in biological samples (whole blood, urine, and scalp hair) of patients having diabetes mellitus type-2 age ranged (31-60) (n=238), with those of age matched non-diabetics (ND) as control subjects (n=196), of both genders. The concentrations of elements were measured by means of an atomic absorption spectrophotometer after microwave-assisted acid digestion. The validity and accuracy was checked by conventional wet acid digestion method and using certified reference materials. The overall recoveries of all elements were found in the range of 98.1-99.4% of certified values. The results of this study showed that the mean values of Pb, Cd and, As were significantly higher in scalp hair samples of smoker and non-smoker diabetic patients as compared to control subjects (p<0.001). The concentration of understudy toxic metals was also high in blood and urine samples of DM patient but difference was more significant in smoker DM patients. These results are consistent with those obtained in other studies, confirming that toxic metals may play a role in the development of diabetes mellitus.

Arachidonic Acid Can Significantly Prevent Early Insulin Resistance Induced by a High-Fat Diet

AIM

To investigate whole-body metabolic disorder and hepatic glucose output (HGO) disturbance in rats with insulin resistance induced by a short-term high-fat diet, and the effect of arachidonic acid (AA).

METHODS

Twenty-four normal male Wistar rats (230-250 g) were randomly divided into 3 groups according to their weight and fed for 12 weeks: control group, n = 8, fed with standard chow diet; high-fat (HF) group, n = 8, fed with a high-fat diet; HF+AA group, n = 8, fed with a high-fat diet and administered orally 3 mg x kg(-1) x day(-1)AA.

RESULTS

Early insulin resistance was successfully induced in HF-fed rats with hyperinsulinemia (p < 0.05), higher plasma triglyceride (TG) (p < 0.05), higher fasting liver glycogen content (p < 0.01) and higher glucose-insulin index (p < 0.01) during an oral glucose tolerance test (OGTT). The AA treatment significantly decreased the glucose-insulin index (p < 0.01), blood TG (p < 0.05) and glycogen content (p < 0.05) in liver. Both activity of phosphoenolpyruvate carboxykinase (PEPCK) (p < 0.05) and mRNA levels of PEPCK (p < 0.05) and glucose-6-phosphatase (G-6-Pase) (p < 0.01) in liver were also observed to be significantly decreased. But there were significant differences in the glucose-insulin index (p < 0.01) during OGTT, and glycogen content (p < 0.01) between the HF+AA and control groups.

CONCLUSION

AA can significantly prevent whole-body insulin resistance induced by a high-fat diet, as well as accompanied HGO disturbance in the overnight fasting state, but not thoroughly.

Stimulation of phosphoinositide 3-kinase/Akt signaling by copper and zinc ions: mechanisms and consequences

The phosphoinositide 3'-kinase (PI3K)/Akt signaling cascade controls cellular processes such as apoptosis and proliferation. Moreover, it is a mediator of insulin effects on target cells and as such is a major regulator of fuel metabolism. The PI3K/Akt cascade was demonstrated to be activated by stressful stimuli, including heat shock and reactive oxygen species (ROS). This minireview focuses on activation of the pathway by exposure of cells to heavy metal ions, Cu2+ and Zn2+. It is hypothesized that stimulation of PI3K/Akt is the molecular mechanism underlying the known insulin-mimetic effects of copper and zinc ions. Following a brief summary of PI3K/Akt signaling and of activation of the cascade by Cu2+ and Zn2+, mechanisms of metal-induced PI3K/Akt activation are discussed with a focus on the role of ROS and of cellular thiols (glutathione, thioredoxin) and protein tyrosine phosphatases in Cu2+ and Zn2+ signaling. Finally, consequences of metal-induced PI3K/Akt activation are discussed, focusing on the modulation of FoxO-family transcription factors by Cu2+ and Zn2+.