Zinc modulates high glucose-induced apoptosis by suppressing oxidative stress in renal tubular epithelial cells

Vascular protection afforded by zinc supplementation in human coronary artery smooth muscle cells mediated by NRF2 signaling under hypoxia/reoxygenation

Zinc (Zn) has antioxidant, anti-inflammatory and anti-proliferative actions, with Zn dysregulation associated with coronary ischemia/reperfusion injury and smooth muscle cell dysfunction. As the majority of studies concerning Zn have been conducted under non-physiological hyperoxic conditions, we compare the effects of Zn chelation or supplementation on total intracellular Zn content, antioxidant NRF2 targeted gene transcription and hypoxia/reoxygenation-induced reactive oxygen species generation in human coronary artery smooth muscle cells (HCASMC) pre-adapted to hyperoxia (18 kPa O2) or normoxia (5 kPa O2). Expression of the smooth muscle marker SM22-α was unaffected by lowering pericellular O2, whereas calponin-1 was significantly upregulated in cells under 5 kPa O2, indicating a more physiological contractile phenotype under 5 kPa O2. Inductively coupled plasma mass spectrometry established that Zn supplementation (10 μM ZnCl2 + 0.5 μM pyrithione) significantly increased total Zn content in HCASMC under 18 but not 5 kPa O2. Zn supplementation increased metallothionein mRNA expression and NRF2 nuclear accumulation in cells under 18 or 5 kPa O2. Notably, NRF2 regulated HO-1 and NQO1 mRNA expression in response to Zn supplementation was only upregulated in cells under 18 but not 5 kPa. Furthermore, whilst hypoxia increased intracellular glutathione (GSH) in cells pre-adapted to 18 but not 5 kPa O2, reoxygenation had negligible effects on GSH or total Zn content. Reoxygenation-induced superoxide generation in cells under 18 kPa O2 was abrogated by PEG-superoxide dismutase but not by PEG-catalase, and Zn supplementation, but not Zn chelation, attenuated reoxygenation-induced superoxide generation in cells under 18 but not 5kPaO2, consistent with a lower redox stress under physiological normoxia. Our findings highlight that culture of HCASMC under physiological normoxia recapitulates an in vivo contractile phenotype and that effects of Zn on NRF2 signaling are altered by oxygen tension.

ZnT8 Loss of Function Mutation Increases Resistance of Human Embryonic Stem Cell-Derived Beta Cells to Apoptosis in Low Zinc Condition

The rare SLC30A8 mutation encoding a truncating p.Arg138* variant (R138X) in zinc transporter 8 (ZnT8) is associated with a 65% reduced risk for type 2 diabetes. To determine whether ZnT8 is required for beta cell development and function, we derived human pluripotent stem cells carrying the R138X mutation and differentiated them into insulin-producing cells. We found that human pluripotent stem cells with homozygous or heterozygous R138X mutation and the null (KO) mutation have normal efficiency of differentiation towards insulin-producing cells, but these cells show diffuse granules that lack crystalline zinc-containing insulin granules. Insulin secretion is not compromised in vitro by KO or R138X mutations in human embryonic stem cell-derived beta cells (sc-beta cells). Likewise, the ability of sc-beta cells to secrete insulin and maintain glucose homeostasis after transplantation into mice was comparable across different genotypes. Interestingly, sc-beta cells with the SLC30A8 KO mutation showed increased cytoplasmic zinc, and cells with either KO or R138X mutation were resistant to apoptosis when extracellular zinc was limiting. These findings are consistent with a protective role of zinc in cell death and with the protective role of zinc in T2D.

Urine trace element disorder along with renal function injury in vitamin D deficient diabetic rats and intervention effect of 1α,25-dihydroxyvitamin D3

Introduction

Trace element metabolism disorders are often secondary to disorders of glucose metabolism in diabetes. Although 1α,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] could ameliorate abnormal glucose metabolism in the development of diabetes, the effect on trace element metabolism is unclear. The objective of this study was to evaluate the influence of 1,25(OH)₂D₃ on urinary excretions of trace elements in Zucker diabetic fatty (ZDF) rats.

Methods

At 6 weeks of age, male ZDF (n = 40) rats were subdivided into four groups: diabetic model (ZDF), low-dose (ZDF + VL, 2 μg/kg⋅bw), middle-dose (ZDF + VM, 8 μg/kg⋅bw) and high-dose (ZDF + VH, 16 μg/kg⋅bw) 1,25(OH)₂D₃ groups. Another 10 Zucker lean (ZL) rats served as a control group. All rats were given vitamin D deficient Purina #5008 chow and the intervention groups were given the corresponding dose of 1,25(OH)₂D₃ by gavage on alternate days for 7 weeks. Microalbuminuria (MALB) and urinary creatinine concentration were detected by a biochemical autoanalyzer. Urine trace element concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS) and were corrected by urinary creatinine.

Results

Throughout the intervention phase, MALB, UACR and urinary creatinine levels in the ZDF group were significantly higher than those in the ZL group, and showed a gradual increase with the prolongation of the intervention time. These changes were reversed in a dose-dependent manner after 1,25(OH)₂D₃ intervention (P < 0.05). Correspondingly, most of the urinary trace element excretions in the ZDF rats were significantly increased compared with the ZL group, and 1,25(OH)₂D₃ intervention significantly reduced the urinary copper (Cu), zinc (Zn), selenium (Se) and molybdenum (Mo) levels in the ZDF rats (P < 0.05), especially in the medium and high dose groups.

Conclusion

1,25(OH)₂D₃ had improvement effects on urinary Cu, Zn, Se, and Mo excretions in ZDF rats, suggesting that it may be related to the reduction of diabetic renal impairment and renal oxidative damage.

The impact of zinc on the molecular signaling pathways in the diabetes disease

Since there's been an upsurge in people with diabetes or pre-diabetes conditions, many studies have been conducted to evaluate approaches for reducing the complications of diabetes. One of the most common therapeutic elements suggested for this purpose is zinc (Zn). Zn has long been shown to positively improve complications of both type 1 and type 2 diabetes. This review aims to provide comprehensive information about the influence of Zn on the various signaling pathways in multiple tissues with diabetic conditions, with great attention to the treatment period and effective dose of Zn.

Recent Advances in KEAP1/NRF2-Targeting Strategies by Phytochemical Antioxidants, Nanoparticles, and Biocompatible Scaffolds for the Treatment of Diabetic Cardiovascular Complications

Significance: Modulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated antioxidant response is a key aspect in the onset of diabetes-related cardiovascular complications. With this review, we provide an overview of the recent advances made in the development of Nrf2-targeting strategies for the treatment of diabetes, with particular attention toward the activation of Nrf2 by natural antioxidant compounds, nanoparticles, and oxidative stress-modulating biocompatible scaffolds. Recent Advances: In the past 30 years, studies addressing the use of antioxidant therapies to treat diabetes have grown exponentially, showing promising but yet inconclusive results. Animal studies and clinical trials on the Nrf2 pathway have shown promising results, suggesting that its activation can delay or reverse some of the cardiovascular impairments in diabetes. Critical Issues: Hyperglycemia- and oscillating glucose levels-induced reactive oxygen species (ROS) accumulation is progressively emerging as a central factor in the onset and progression of diabetes-related cardiovascular complications, including endothelial dysfunction, retinopathy, heart failure, stroke, critical limb ischemia, ulcers, and delayed wound healing. In this context, accumulating evidence suggests a central role for Nrf2-mediated antioxidant response, one of the most studied cellular defensive mechanisms against ROS accumulation. Future Directions: Innovative approaches such as tissue engineering and nanotechnology are converging toward targeting oxidative stress in diabetes. Antioxid. Redox Signal. 36, 707-728.

Role of Zinc in Diabetic Kidney Disease

Diabetic Kidney Disease (DKD) represents the most common cause of Chronic Kidney Disease (CKD) in developed countries. Approximately 30% to 40% of diabetes mellitus (DM) subjects develop DKD, and its presence significantly increases the risk for morbidity and mortality. In this context, Zinc seems to have a potential role in kidney and body homeostasis in diabetic individuals as well as in patients at a high risk of developing this condition. This essential element has functions that may counteract diabetes-related risk factors and complications, which include stabilization of insulin hexamers and pancreatic insulin storage and improved glycemic control. In our review, we analyzed the current knowledge on the role of zinc in the management of renal impairment in course of DM. Several studies underline the critical role of zinc in reducing oxidative stress levels, which is considered the common denominator of the mechanisms responsible for the progression of kidney disease. Reaching and maintaining a proper serum zinc level could represent a valuable target to reduce symptoms related to DM complications and contrast the progression of kidney impairment in patients with the high risk of developing end-stage renal disease. In conclusion, analyzing the beneficial role of zinc in this review would advance our knowledge on the possible strategies of DM and DKD treatment.

Burdock Fructooligosaccharide Attenuates High Glucose-Induced Apoptosis and Oxidative Stress Injury in Renal Tubular Epithelial Cells

Hyperglycemia-induced apoptosis and oxidative stress injury are thought to play important roles in the pathogenesis of diabetic nephropathy (DN). Attenuating high glucose (HG)-induced renal tubular epithelial cell injury has become a potential approach to ameliorate DN. In recent years, burdock fructooligosaccharide (BFO), a water-soluble inulin-type fructooligosaccharide extracted from burdock root, has been shown to have a wide range of pharmacological activities, including antiviral, anti-inflammatory, and hypolipidemic activities. However, the role and mechanism of BFO in rat renal tubular epithelial cells (NRK-52E cells) have rarely been investigated. The present study investigated the protective effect of BFO on HG-induced damage in NRK-52E cells. BFO could protect NRK-52E cells against the reduced cell viability and significantly increased apoptosis rate induced by HG. These anti-oxidative stress effects of BFO were related to the significant inhibition of the production of reactive oxygen species, stabilization of mitochondrial membrane potential, and increased antioxidant (superoxide dismutase and catalase) activities. Furthermore, BFO increased the expression of Nrf2, HO-1, and Bcl-2 and decreased the expression of Bax. In conclusion, these findings suggest that BFO protects NRK-52E cells against HG-induced damage by inhibiting apoptosis and oxidative stress through the Nrf2/HO-1 signaling pathway.

MicroRNA (miR)-590-3p alleviates high-glucose induced renal tubular epithelial cell damage by targeting C-X3-C motif chemokine ligand 1 (CX3CL1) in diabetic nephropathy

We attempted to analyze the clinical value of microRNA (miR)-590-3p in diabetic nephropathy (DN) patients and its role in high glucose (HG)-induced renal tubular epithelial cell (HK-2) injury. Serum levels of miR-590-3p were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Spearman correlation coefficient analysis of the correlation between miR-590-3p and clinical indicators. The diagnostic value of miR-590-3p was analyzed by the receiver operating characteristic (ROC) curve. Then, the DN cell model induced by HG in HK-2 cells was established. Enzyme-linked immunosorbent assay (ELISA), flow cytometry, and CCK-8 assay were employed to assess cell inflammation, oxidative stress, apoptosis, and proliferation. Dual-luciferase reporter assay confirmed the target of miR-590-3p. Serum miR-590-3p was reduced in patients of DN, which was positively correlated with eGFR and negatively associated with albuminuria. Furthermore, miR-590-3p also can diagnose patients of DN from healthy subjects or patients of T2DM. Furthermore, miR-590-3p was decreased in a concentration- and time-dependent manner during HG-induction. miR-590-3p overexpression bated HG-induced inhibition effect on cell proliferation and promotion effects on apoptosis, oxidative stress, and inflammation. C-X3-C motif chemokine ligand1 (CX3CL1) is the target of miR-590-3p, whose levels were enhanced in DN patients and are negatively regulated by miR-590-3p. Our discoveries offered new insights that reduced miR-590-3p as a potential biomarker for the diagnosis of DN, and elevated miR-590-3p can alleviate renal tubular injury by HG-induced through targeting CX3XL1, which may be a novel target for improving the development of DN.

Nrf2 participates in the anti-apoptotic role of zinc in Type 2 diabetic nephropathy through Wnt/β-catenin signaling pathway

Zinc (Zn), as an essential trace element, has been approved to serve many roles in diabetic studies. Also Zn deficiency will aggravate renal damage in diabetes through suppression of nuclear factor-erythroid 2-related factor 2 (Nrf2) expression and function. The purpose of this study was to illustrate the role of Zn in renal apoptosis in diabetes and whether Nrf2 participated in the process. Type 2 diabetes mice model was induced by a single dose of streptozotocin (STZ) injection after high-fat diet (HFD) feeding for 3 months, then the mice were given diets supplemented with different concentrations of Zn (control, 30 ppm; low-concentration, 0.85 ppm). After 12-week treatment, morphology and associated protein expressions were examined. The results showed that low Zn diet significantly aggravated the level of renal apoptosis during diabetes, performed as the upregulation of caspase-3 expression. In addition, either low Zn diet or diabetes or both dramatically decreased the expression of Nrf2 and P-AKT in kidney. Moreover, the expression of β-catenin in kidney was increased markedly in diabetic groups. Mechanistic study applying human renal tubular epithelial cells (HK11) confirmed the role of Nrf2, as silencing Nrf2 expression abolished Zn supplementation protection against high sugar + high fat + low Zn-induced apoptosis and downregulation of β-catenin expression. All these results suggest that Nrf2 plays a key role in Zn protection against Type 2 diabetes induced renal apoptosis, which might be through Wnt/β-catenin signaling pathway.

Regulation of P300 and HDAC1 on endoplasmic reticulum stress in isoniazid-induced HL-7702 hepatocyte injury

P300 and HDAC1 can be involved in the development of various liver diseases by regulating gene transcription. Endoplasmic reticulum stress (ERS) is one of the main pathways of apoptosis and is activated during inflammatory responses, but the roles of P300 and HDAC1 in ERS in antituberculosis drug-induced liver injury (ADLI) are not clear. This study confirms that isoniazid can change the states of P300 and HDAC1 in HL-7702 hepatocyte metabolism and induce ERS, causing hepatocyte injury and apoptosis. When combined with C646, however, P300 can be reduced. HL-7702 cells were flattened, and the cytoplasm became crinkled. To a certain extent, ERS was relieved, but hepatocytes suffered worse damage, and the rate of cell apoptosis markedly increased. When MS-275 was applied, HDAC1 level was increased, cell fusion appeared, and fluorescence intensity of endoplasmic reticulum was weakened. In addition, ERS was aggravated, but liver injury was relieved, and the apoptosis rate significantly decreased. Therefore, alteration of P300 and HDAC1 status and ERS are involved in ADLI, and changes in P300 and HDAC1 can regulate ERS and then affect cell damage.

Apigenin Protects Against Renal Tubular Epithelial Cell Injury and Oxidative Stress by High Glucose via Regulation of NF-E2-Related Factor 2 (Nrf2) Pathway

Background

Diabetic nephropathy (DN) is a disease characterized by oxidative stress and apoptosis of renal tubular epithelial cells driven by hyperglycemia. Apigenin is a flavonoid compound that possesses potent anti-apoptotic properties. The present study aimed to explore the protective effects and underlying mechanisms of apigenin on renal tubular epithelial cells exposed to hyperglycemia.

Material/Methods

Human renal epithelial cell HK-2 were incubated to D-glucose to establish in vitro DN model. The cell viability, lactate dehydrogenase (LDH) release, apoptosis and oxidative stress were evaluated. qRT-PCR was performed to determine the mRNA levels of NF-E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). Western blot analysis was performed to measure the protein expressions of Nrf2.

Results

In HK-2 cells, high glucose reduced cell viability in a concentration- and time-dependent manner. Apigenin suppressed the decrease in cell viability and increase in supernatant LDH release at 100 and 200 μM after 48-h treatment. Apigenin reduced apoptotic rate and pro-inflammatory cytokines production. Apigenin suppressed oxidative stress and increased mRNA expressions of Nrf2 and HO-1. Inhibition of Nrf2 using small interfering RNA (siRNA), or cotreatment with LY294002, an inhibitor of PI3K/Akt, abolished the protective effect on high glucose-induced injury, oxidative stress, and pro-inflammatory cytokines production by apigenin. LY294002 also attenuated the increase in Nrf2 protein by apigenin in high glucose-treated HK-2 cells.

Conclusions

Apigenin protects renal tubular epithelial cells against high glucose-induced injury through suppression of oxidative stress and inflammation via activation of the Nrf2 pathway.

Effects of transcription factor EB on oxidative stress and apoptosis induced by high glucose in podocytes

The aim of the present study was to investigate the effects of transcription factor EB (TFEB) overexpression on oxidative stress, mitochondrial function and apoptosis in podocytes induced with high glucose. High glucose-induced time-dependent changes in TFEB expression were identified and nuclear translocation of TFEB was observed in podocytes. Overexpression of TFEB markedly reduced high glucose-induced oxidative stress in podocytes, and increased the expression of superoxide dismutase 2 and heme oxygenase 1 antioxidant enzymes. It was further observed that TFEB overexpression could partially restore the expression of peroxisome proliferator-activated receptor-γ coactivator-1α, transcription factor A, mitochondrial, and cytochrome c oxidase subunit 4, thereby enhancing mitochondrial biosynthesis. Furthermore, overexpression of TFEB reduced mitochondrial swelling and fragmentation, restored mitochondrial membrane potential, and contributed to the restoration of mitochondrial function. By overexpressing TFEB, it was revealed that TFEB increased the ratios of phosphorylated (p)-Akt/Akt and p-Bad/Bad, and the expression of downstream Bcl-xl, and reduced the ratio of Bax/Bcl-2 and the expression of cleaved-caspase-3 compared with high glucose-treatment. Furthermore, when the Akt phosphorylation inhibitor Ly294002 was added, the improvement by TFEB to high glucose-induced apoptosis was significantly reduced. These findings suggest that overexpressing TFEB could reduce the production of reactive oxygen species in podocytes in a high glucose environment, relieve oxidative stress, promote mitochondrial biogenesis and renewal functions, and reduce high glucose-induced podocyte apoptosis by activating the Akt/Bad pathway.

Erianin protects against high glucose-induced oxidative injury in renal tubular epithelial cells

Erianin is the major bibenzyl compound found in Dendrobium chrysotoxum Lindl. The current study was designed to investigate the protective effects of erianin on high glucose-induced injury in cultured renal tubular epithelial cells (NRK-52E cells) and determine the possible mechanisms for its effects. NRK-52E cells were pretreated with erianin (5, 10, 25 or 50 nmol/L) for 1 h followed by further exposure to high glucose (30 mmol/L, HG) for 48 h. Erianin concentration dependently enhanced cell viability followed by HG treatment in NRK-52E cells. HG induced reactive oxygen species (ROS) generation, malondialdehyde production, and glutathione deficiency were recovered in NRK-52E cells pretreated with erianin. HG triggered cell apoptosis via the loss of mitochondrial membrane potential, depletion of adenosine triphosphate, upregulation of caspases 9 and 3, enhancement of cytochrome c release, and subsequent interruption of the Bax/Bcl-2 balance. These detrimental effects were ameliorated by erianin. HG also induced activation of p53, JNK, p38 mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) in NRK-52E cells, which were blocked by erianin. The results suggest that treatment NRK-52E cells with erianin halts HG-induced renal dysfunction through the suppression of the ROS/MAPK/NF-κB signaling pathways. Our findings provide novel therapeutic targets for diabetic nephropathy.

Daily rhythms of cloacal temperature in broiler chickens of different age groups administered with zinc gluconate and probiotic during the hot-dry season

The aim of the experiment was to evaluate effects of zinc gluconate (ZnGlu) and probiotic administration on the daily rhythm of cloacal temperature (t_cloacal) in broiler chickens of different age groups during the hot-dry season. One-day-old broiler chicks (n = 60) were divided into groups I-IV of 15 chicks per group, and treated for 35 days: Group I (control) was given deionized water; Group II, ZnGlu (50 mg/kg); Group III, probiotic (4.125 × 10⁶ cfu/100 mL), and Group IV, ZnGlu (50 mg/kg) + probiotic (4.125 × 10⁶ cfu/100 mL). Air dry-bulb temperature (t_db), relative humidity (RH), and temperature-humidity index (THI) inside the pen, and t_cloacal of each broiler chick were obtained bihourly over a 24-h period; on days 21, 28, and 35 of the study. Values of t_db (32.10 ± 0.49°C), RH (49.94 ± 1.91%), and THI (38.85 ± 0.42) obtained were outside the thermoneutral zone for broiler chickens, and suggested that the birds were subjected to heat stress. Application of the periodic model showed disruption of daily rhythm of t_cloacal in broilers on day 21, which was synchronized by probiotic administration. The administration of probiotics or ZnGlu + probiotics to a greater extent decreased the mesor and amplitude, delayed the acrophases of t_cloacal in broilers, especially at day 35, as compared to the controls. Overall, the t_cloacal values in broiler chickens administered with probiotic alone (41.25 ± 0.05°C) and ZnGlu + probiotic (41.52 ± 0.05°C) were lower (P < 0.001) than that of the controls (41.94 ± 0.06°C). In conclusion, probiotic alone synchronized t_cloacal of the birds at day 21, and, in addition, decreased t_cloacal response most, followed by its coadministration with ZnGlu, the antioxidants may be beneficial in modulating daily rhythmicity of t_cloacal and alleviating adverse effects of heat stress on broiler chickens during the hot-dry season.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Role of Nuclear Factor Erythroid 2-Related Factor 2 in Diabetic Nephropathy

Diabetic nephropathy (DN) is manifested as increased urinary protein level, decreased glomerular filtration rate, and final renal dysfunction. DN is the leading cause of end-stage renal disease worldwide and causes a huge societal healthcare burden. Since satisfied treatments are still limited, exploring new strategies for the treatment of this disease is urgently needed. Oxidative stress takes part in the initiation and development of DN. In addition, nuclear factor erythroid 2-related factor 2 (Nrf2) plays a key role in the cellular response to oxidative stress. Thus, activation of Nrf2 seems to be a new choice for the treatment of DN. In current review, we discussed and summarized the therapeutic effects of Nrf2 activation on DN from both basic and clinical studies.

Chk1 and DNA-PK mediate TPEN-induced DNA damage in a ROS dependent manner in human colon cancer cells

Recently, we showed that the metal chelator TPEN targets colon cancer cells through redox cycling of copper. Here, we studied the DNA damage potential of TPEN and deciphered the role of Chk1, ATM and DNA-PK in TPEN-induced toxicity in 3 human colon cancer cell lines, HCT116, SW480 and HT29. We also investigated the role of reactive oxygen species (ROS) in TPEN-induced DNA damage. TPEN reduced cell viability in a dose- and time-dependent manner. Cytotoxicity was associated with significant DNA damage and higher expression of γ-H2AX protein and activation of ATM/ATR signaling pathway. Cell death by TPEN was dependent on ROS generation as evidenced by the reversal of cell viability, and DNA damage and the abrogation of γ-H2AX levels in the presence of antioxidants. Treatment with antioxidants, however, failed to reverse cytotoxicity at high TPEN concentrations (10µM). TPEN-induced cell death was also dependent on the redox cycling of copper since the copper chelator neocuproine inhibited DNA damage and reduced pChk1, γ-H2AX, and ATM protein expression. Cell death by low TPEN concentrations, involved ATM/ATR signaling in all 3 cell lines, since pre-incubation with specific inhibitors of ATM and DNA-PK led to the recovery of cells from TPEN-induced DNA damage. In addition, siRNA silencing of Chk1, DNA-PK and ATM abrogated the expression of γ-H2AX and reversed cell death, suggesting that Chk1 and DNA-PK mediate TPEN-induced cytotoxicity in colon cancer cells. This study shows for the first time the involvement of Chk1, DNA-PK and ATM in TPEN-induced DNA damage and confirms our previous findings that ROS generation and the redox cycling of copper in response to TPEN are the main mechanisms by which this compound induces cell death in human colon cancer cells. Inhibition of ATM or DNA-PK did not reverse cytotoxicity at high TPEN concentrations that cause excessive levels of ROS and irreversible cellular damage.

Overexpression of DJ-1 reduces oxidative stress and attenuates hypoxia/reoxygenation injury in NRK-52E cells exposed to high glucose

Patients with diabetes are more vulnerable to renal ischemia/reperfusion (I/R) injury, which is implicated in hyperglycemia-induced oxidative stress. We previously reported that the hyperglycemia-induced inhibition of DJ-1, a novel oncogene that exhibits potent antioxidant activity, is implicated in the severity of myocardial I/R injury. In the present study, we aimed to explore the role of DJ-1 in hypoxia/reoxygenation (H/R) injury in renal cells exposed to high glucose (HG). For this purpose, NRK-52E cells were exposed to HG (30 mM) for 48 h and then exposed to hypoxia for 4 h and reoxygenation for 2 h, which significantly decreased cell viability and superoxide dismutase (SOD) activity, and increased the malondialdehyde (MDA) content, accompanied by a decrease in DJ-1 protein expression. The overexpression of DJ-1 by transfection with a DJ-1 overexpression plasmid exerted protective effects against HG-induced H/R injury, as evidenced by increased CCK-8 levels and SOD activity, the decreased release of lactate dehydrogenase (LDH) and the decreased MDA content, and increased nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase-1 (HO-1) expression. Similar effects were observed following treatment with the antioxidant, N-acetylcysteine. These results suggest that the overexpression of DJ-1 reduces oxidative stress and attenuates H/R injury in NRK-52E cells exposed to HG.

Diosmectite-zinc oxide composite improves intestinal barrier restoration and modulates TGF-β1, ERK1/2, and Akt in piglets after acetic acid challenge

The present study evaluated the beneficial effect of diosmectite-zinc oxide composite (DS-ZnO) on improving intestinal barrier restoration in piglets after acetic acid challenge and explored the underlying mechanisms. Twenty-four 35-d-old piglets (Duroc × Landrace × Yorkshire), with an average weight of 8.1 kg, were allocated to 4 treatment groups. On d 1 of the trial, colitis was induced via intrarectal injection of acetic acid (10 mL of 10% acetic acid [ACA] solution for ACA, DS-ZnO, and mixture of diosmectite [DS] and ZnO [DS+ZnO] groups) and the control group was infused with saline. Twenty-four hours after challenged, piglets were fed with the following diets: 1) control group (basal diet), 2) ACA group (basal diet), 3) DS-ZnO group (basal diet supplemented with DS-ZnO), and 4) DS+ZnO group (mixture of 1.5 g diosmectite [DS]/kg and 500 mg Zn/kg from ZnO [equal amount of DS and ZnO in the DS-ZnO treatment group]). On d 8 of the trial, piglets were sacrificed. The results showed that DS-ZnO supplementation improved (P < 0.05) ADG, ADFI, and transepithelial electrical resistance and decreased (P < 0.05) fecal scores, crypt depth, and fluorescein isothiocyanate-dextran 4 kDa (FD4) influx as compared with ACA group. Moreover, DS-ZnO increased (P < 0.05) occludin, claudin-1, and zonula occluden-1 expressions; reduced (P < 0.05) caspase-9 and caspase-3 activity and Bax expression; and improved (P < 0.05) Bcl2, XIAP, and PCNA expression. Diosmectite-zinc oxide composite supplementation also increased (P < 0.05) TGF-β1 expression and ERK1/2 and Akt activation. These results suggest that DS-ZnO attenuates the acetic acid-induced colitis by improving mucosa barrier restoration, inhibiting apoptosis, and improving intestinal epithelial cells proliferation and modulation of TGF-β1 and ERK1/2 and Akt signaling pathway.

Valproate attenuates diabetic nephropathy through inhibition of endoplasmic reticulum stress‑induced apoptosis

Previous studies have suggested that endoplasmic reticulum stress (ERS) is one of the mechanisms responsible for the pathogenesis of diabetic nephropathy (DN). Histone acetylation modification can regulate the transcription of genes and is involved in the regulation of ERS. Valproate (VPA), a nonselective histone deacetylase inhibitor, has been reported to have a protective role in kidney tissue injury, however, whether VPA can prevent DN remains to be elucidated. In the present study, it was found that VPA increases the expression of glucose-regulated protein (GRP78) and reduces the protein expression of C/EBP-homologous protein (CHOP), growth arrest and DNA-damage-inducible gene 153 and caspase-12 in a rat model of DN. VPA can reduce renal cell apoptosis and alleviate proteinuria and alterations in serum creatinine. VPA also upregulates the acetylation level of histone H4 in the promoter of GRP78 and downregulates the acetylation level of histone H4 in the promoter of CHOP. Collectively, the data indicate that VPA can relieve ERS and reduce renal cell apoptosis, and thus attenuate renal injury in a rat model of DN by regulating the acetylation level of histone H4 in ERS-associated protein promoters.

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.

Inhibitory effect of zinc on the advanced glycation end product-induced apoptosis of mouse osteoblastic cells

Osteoporosis and diabetes have become serious health problems worldwide. Previous studies have suggested that diabetes is associated with osteoporosis and increased fracture risk. However, the mechanism underlying diabetes‑induced osteoporosis remains to be elucidated. Therefore, the present study aimed to examine the mechanism underlying diabetes‑induced osteoporosis, and determine the protective effects of zinc, which is known to be closely associated with osteoporosis and diabetes. The results of the present study demonstrated that zinc inhibited advanced glycation end product (AGE)‑induced MC3T3‑E1 cell apoptosis by attenuating the production of reactive oxygen species, inhibiting caspase‑3 and caspase‑9 activation, and inhibiting the release of cytochrome c from between the mitochondria and the cytosol. Furthermore, zinc was found to protect cells against AGE‑induced apoptosis via the mitogen‑activated protein kinase/extracellular signal‑regulated kinase and phosphoinositide 3‑kinase/AKT signaling pathways. In conclusion, these findings enable a better understanding of the mechanism underlying diabetes‑induced osteoporosis, and may indicate a novel target for its prevention and treatment.

Natural Nrf2 activators in diabetes

Prediabetes and diabetes are rising worldwide. Control of blood glucose is crucial to prevent or delay diabetic complications that frequently result in increased morbidity and mortality. Most strategies include medical treatment and changes in lifestyle and diet. Some nutraceutical compounds have been recognized as adjuvants in diabetes control. Many of them can activate the nuclear factor (erythroid-derived 2)-like 2 (Nrf2), which has been recognized as a master regulator of the antioxidant response. Recent studies have described the role of Nrf2 in obesity, metabolic syndrome, nephropathy, retinopathy and neuropathy, where its activation prevents the development of diabetes and its complications. It has been demonstrated that natural compounds derived from plants, vegetables, fungi and micronutrients (such as curcumin, sulforaphane, resveratrol and vitamin D among others) can activate Nrf2 and, thus, promote antioxidant pathways to mitigate oxidative stress and hyperglycemic damage. The role of some natural Nrf2 activators and its effect in diabetes is discussed.

Curcumin protects renal tubular epithelial cells from high glucose-induced epithelial-to-mesenchymal transition through Nrf2-mediated upregulation of heme oxygenase-1

Curcumin has been observed to exhibit an anti-fibrotic effect in the liver, lung and gallbladder. However, the mechanisms underlying the cytoprotective effects of curcumin remain to be elucidated. The epithelial-to-mesenchymal transition (EMT) of mature tubular epithelial cells in the kidney is considered to contribute to the renal accumulation of matrix proteins associated with diabetic nephropathy. The EMT is also closely associated with the progression of renal interstitial fibrosis and oxidative stress. This process may occur through abrogation of high glucose (HG)-induced oxidative stress via activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase-1 (HO-1) in kidney tubular epithelial cells. In the present study, the effect of curcumin on HG-induced EMT in the NRK-52E normal rat kidney tubular epithelial cell line was investigated, and whether the effect of curcumin was mediated by the induction of Nrf2 and HO-1 expression was examined. The present study revealed that curcumin was able to prevent events associated with EMT, including the downregulation of E-cadherin and the increased expression of α-smooth muscle actin. Further analysis revealed that the expression levels of Nrf2 and HO-1 protein were elevated to a greater extent in the curcumin pretreated NRK-52E cells compared with those of the control. Notably, knockdown of Nrf2 with small interfering RNA prevented the curcumin-induced elevation in expression of HO-1 and the associated anti-fibrotic effects. In conclusion, the present findings suggested that curcumin may be significant in cellular antioxidant defense, through the activation of Nrf2 and HO-1, thereby protecting the NRK-52E cells from HG-induced EMT.

Effect of LIV1 on the sensitivity of ovarian cancer cells to trichostatin A

In a previous study, we used a functional gene screen approach to identify the key genes responsible for the tumor-selective action of trichostatin A (TSA), of which LIV1, a novel zinc transporter, was isolated by its marked ability to confer resistance against TSA-induced apoptosis. The aim of the present study was to investigate the effect of LIV1 expression on the sensitivity of ovarian cancer cells to TSA. We tested the induction of LIV1 in ovarian cancer cells and clinical samples after TSA treatment by real-time PCR and western blot analysis. We investigated the effect of LIV1 expression on the sensitivity of ovarian cancer cells to TSA by MTT assay, flow cytometry and colony forming assays. Finally, we analyzed the mechanism of LIV1 in ovarian cancer cells by western blot analysis. We found that the levels of LIV1 mRNA and protein were significantly upregulated after TSA treatment. The viability and colony forming rates of the ovarian cancer cells transfected with AS-LIV1 (pCEP4 carrying antisense LIV1 cDNA) were obviously higher than the rates of the control as detected by MTT and colony forming assays, which could be reversed by FL-LIV1 (pCEP4 carrying full-length LIV1 cDNA). The apoptotic rate of the AS-LIV1 cells was markedly lower than the rate of the control as determined FACS. Using western blot analysis, we demostrated that the inhibition of TSA-induced apoptosis by knockdown of LIV1 might be associated with decreased endogenous levels of Bcl-2, enhanced levels of Bax and cleavage of procaspase-3. The present study suggests that the drug resistance of ovarian cancer cells to TSA may be related to expression of the LIV1 gene, and targeting LIV1 could be exploited as a novel strategy to more effectively kill ovarian cancer cells.