Advanced glycation end products accelerate ischemia/reperfusion injury through receptor of advanced end product/nitrative thioredoxin inactivation in cardiac microvascular endothelial cells

Thioredoxin reductase as a pharmacological target

Thioredoxin reductases (TrxRs) belong to the pyridine nucleotide disulfide oxidoreductase family enzymes that reduce thioredoxin (Trx). The couple TrxR and Trx is one of the major antioxidant systems that control the redox homeostasis in cells. The thioredoxin system, comprised of TrxR, Trx and NADPH, exerts its activities via a disulfide-dithiol exchange reaction. Inhibition of TrxR is an important clinical goal in all conditions in which the redox state is perturbed. The present review focuses on the most critical aspects of the cellular functions of TrxRs and their inhibition mechanisms by metal ions or chemicals, through direct targeting of TrxRs or their substrates or protein interactors. To update the involvement of overactivation/dysfunction of TrxRs in various pathological conditions, human diseases associated with TrxRs genes were critically summarized by publicly available genome-wide association study (GWAS) catalogs and literature. The pieces of evidence presented here justify why TrxR is recognized as one of the most critical clinical targets and the growing current interest in developing molecules capable of interfering with the functions of TrxR enzymes.

Biomarkers of Unfavorable Outcome in Acute Ischemic Stroke Patients with Successful Recanalization by Endovascular Thrombectomy

<b><i>Background:</i></b> We aimed to identify plasma markers of unfavorable outcomes for patients with acute ischemic stroke (AIS) after recanalization by endovascular thrombectomy (EVT). <b><i>Methods:</i></b> From November 2017 to May 2019, we prospectively collected 61 AIS patients due to anterior large vessel occlusion who achieved recanalization by EVT. Plasma samples were obtained between 18 and 24 h after recanalization. Unfavorable outcomes included futile recanalization at 90 days and overall early complications within 7 days after EVT. <b><i>Results:</i></b> After adjustment for age and initial National Institute of Health Stroke Scale (NIHSS), matrix metalloproteinase-9 (MMP-9), tenascin-C, thioredoxin, ADAMTS13, and gelsolin were independently associated with both futile recanalization and overall early complications significantly (all <i>p</i> &#x3c; 0.05), while C-reactive protein (CRP) was independently associated with overall early complications (<i>p</i> = 0.031) but at the limit of significance for futile recanalization (<i>p</i> = 0.051). The baseline clinical model (BCM) (including age and initial NIHSS) demonstrated discriminating ability to indicate futile recanalization (area under the curve [AUC] 0.807, 95% confidence interval [CI] 0.693–0.921) and overall early complications (AUC 0.749, 95% CI 0.611–0.887). BCM+MMP-9+thioredoxin enhanced discrimination (AUC 0.908, 95% CI 0.839–0.978, <i>p</i> = 0.043) and reclassification (net reclassification improvement [NRI] 67.2%, <i>p</i> &#x3c; 0.001) to indicate futile recanalization. With respect to overall early complications, BCM+MMP-9+tenascin-C, BCM+MMP-9+CRP, BCM+MMP-9+ADAMTS13, BCM+tenascin-C+ADAMTS13, and BCM+CRP+ADAMTS13, all improved discrimination (AUC [95% CI]: 0.868 [0.766–0.970], 0.882 [0.773–0.990], 0.886 [0.788–0.984], 0.880 [0.783–0.977], and 0.863 [0.764–0.962], respectively, all <i>p</i> &#x3c; 0.05 by the DeLong method) and reclassification (NRI 59.1%, 71.8%, 51.1%, 67.4%, and 38.3%, respectively, all <i>p</i> &#x3c; 0.05). <b><i>Conclusions:</i></b> The increased levels of MMP-9, tenascin-C, CRP, thioredoxin, and decreased levels of ADAMTS13 and gelsolin were independent predictors of futile recanalization in AIS patients after recanalization by EVT.

Trans, trans-2,4-decadienal impairs vascular endothelial function by inducing oxidative/nitrative stress and apoptosis

Aldehydes are implicated in the development of hypertension. Trans, trans-2,4-decadienal (tt-DDE), a dietary α,β-unsaturated aldehyde, is widespread in many food products. However, the role of tt-DDE in the pathophysiology of hypertension remains unknown. This study was designed to investigate whether tt-DDE consumption evokes hypertension and to explore the mechanisms underlying such a role. Sprague-Dawley rats were administered different concentrations of tt-DDE. After 28 days, blood pressure and endothelial function of mesenteric arteries were measured. Results showed that tt-DDE treatment significantly increased blood pressure and impaired endothelial function based on endothelium-dependent vasorelaxation and p-VASP levels. Mechanistically, tt-DDE induced oxidative/nitrative stress in the arteries of rats as evidenced by overproductions of superoxide and peroxynitrite, accompanied with increased expressions of iNOS and gp91^phox. To further investigate the effects of tt-DDE on endothelial cells and underlying mechanisms, human umbilical vein endothelial cells (HUVECs) were treated with different concentrations of tt-DDE. tt-DDE induced oxidative/nitrative stress in HUVECs. Moreover, tt-DDE induced endothelial cells apoptosis through JNK-mediated signaling pathway. These results show, for the first time, that oral intake of tt-DDE elevates blood pressure and induces endothelial dysfunction in rats through oxidative/nitrative stress and JNK-mediated apoptosis signaling, indicating that excess ingestion of tt-DDE is a potential risk factor for endothelial dysfunction and hypertension.

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Trans, trans-2,4-decadienal (tt-DDE) is a dietary α,β-unsaturated aldehyde.

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tt-DDE raised blood pressure and impaired endothelial function in rats.

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Oxidative/nitrative stress was induced by tt-DDE in both rats and HUVECs.

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HUVEC apoptosis in response to tt-DDE exposure was mediated by JNK signaling.

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tt-DDE may be a risk factor for hypertension and associated cardiovascular disease.

Advanced glycation end products facilitate the proliferation and reduce early apoptosis of cardiac microvascular endothelial cells via PKCβ signaling pathway: Insight from diabetic cardiomyopathy

Objective:

To investigate the effects of advanced glycation end products (AGEs) on the proliferation and apoptosis of cardiac microvascular endothelial cells (CMECs) in rats and their underlying signaling pathway.

Methods:

CMECs were isolated from Sprague–Dawley rats. We first examined the effects of AGEs on the proliferation and apoptosis of CMECs and then tested whether protein kinase C (PKC) β blockers could counteract the effects of AGEs. The PKC agonists phorbol 12-myristate 13-acetate (PMA) and PKCβ blockers were also used to verify whether PKC could act independently on CMECs. The receptor for AGEs (RAGE)–small interfering RNA (siRNA) transfection was used to verify the effect of AGEs on PKC. Following the above steps, we explained whether AGEs regulated the CMEC proliferation and early apoptosis through the PKCβ signaling pathway. Proliferation of CMECs was detected using the Cell Counting Kit-8 (CCK-8) assay, and early apoptosis was determined using the Annexin V- Fluorescein Isothiocyanate (FITC)/propidium iodide (PI) double staining. Expression of proliferation and apoptosis-related proteins and PKC phosphorylation were determined by western blotting analysis. Cell cycle distributions were assayed using a BD FACSCalibur cell-sorting system.

Results:

AGEs facilitated the proliferation of CMECs, upregulated phosphorylated extracellular signal regulated kinase (p-ERK), and accelerated the entry of cells from G1 phase to the S+G2/M phase, which was consistent with the upregulated cyclin D1 by AGEs. AGEs inhibited early apoptosis of CMECs by increasing the expression of survivin and decreasing the expression of cleaved-caspase3. All these effects can be reversed by PKCβ1/2inhibitors. In addition, AGE upregulated the RAGE expression and phosphorylation of PKCβ1/2 in CMECs, while the inhibition of RAGE reversed the phosphorylation, as well as the effects of AGEs on proliferation and apoptosis in CMECs.

Conclusion:

The study indicated that AGEs facilitated the proliferation and reduced early apoptosis of CMECs via the PKCβ signaling pathway.

Redox Signaling and Advanced Glycation Endproducts (AGEs) in Diet-Related Diseases

Diets are currently characterized by elevated sugar intake, mainly due to the increased consumption of processed sweetened foods and drinks during the last 40 years. Diet is the main source of advanced glycation endproducts (AGEs). These are toxic compounds formed during the Maillard reaction, which takes place both in vivo, in tissues and fluids under physiological conditions, favored by sugar intake, and ex vivo during food preparation such as baking, cooking, frying or storage. Protein glycation occurs slowly and continuously through life, driving AGE accumulation in tissues during aging. For this reason, AGEs have been proposed as a risk factor in the pathogenesis of diet-related diseases such as diabetes, insulin resistance, cardiovascular diseases, kidney injury, and age-related and neurodegenerative diseases. AGEs are associated with an increase in oxidative stress since they mediate the production of reactive oxygen species (ROS), increasing the intracellular levels of hydrogen peroxide (H₂O₂), superoxide (O₂⁻), and nitric oxide (NO). The interaction of AGEs with the receptor for AGEs (RAGE) enhances oxidative stress through ROS production by NADPH oxidases inside the mitochondria. This affects mitochondrial function and ultimately influences cell metabolism under various pathological conditions. This short review will summarize all evidence that relates AGEs and ROS production, their relationship with diet-related diseases, as well as the latest research about the use of natural compounds with antioxidant properties to prevent the harmful effects of AGEs on health.

Plin5/p-Plin5 Guards Diabetic CMECs by Regulating FFAs Metabolism Bidirectionally

Background

Hyper-free fatty acidemia (HFFA) impairs cardiac capillaries, as well as type 2 diabetes mellitus (T2DM). Perilipin 5 (Plin5) maintains metabolic balance of free fatty acids (FFAs) in high oxidative tissues via the states of nonphosphorylation and phosphorylation. However, when facing to T2DM-HFFA, Plin5's role in cardiac microvascular endothelial cells (CMECs) is not defined.

Methods

In mice of WT or Plin5^−/−, T2DM models were rendered by high-fat diet combined with intraperitoneal injection of streptozocin. CMECs isolated from left ventricles were incubated with high glucose (HG) and high FFAs (HFFAs). Plin5 phosphorylation was stimulated by isoproterenol. Plin5 expression was knocked down by small interfering RNA (siRNA). We determined cardiac function by small animal ultrasound, apoptotic rate by flow cytometry, microvessel quantity by immunohistochemistry, microvascular integrity by scanning electron microscopy, intracellular FFAs by spectrophotometry, lipid droplets (LDs) by Nile red staining, mRNAs by quantitative real-time polymerase chain reaction, proteins by western blots, nitric oxide (NO) and reactive oxygen species (ROS) by fluorescent dye staining and enzyme-linked immunosorbent assay kits.

Results

In CMECs, HFFAs aggravated cell injury induced by HG and activated Plin5 expression. In mice with T2DM-HFFA, Plin5 deficiency reduced number of cardiac capillaries, worsened structural incompleteness, and enhanced diastolic dysfunction. Moreover, in CMECs treated with HG-HFFAs, both ablation and phosphorylation of Plin5 reduced LDs content, increased intracellular FFAs, stimulated mitochondrial β-oxidation, added ROS generation, and reduced the expression and activity of endothelial nitric oxide synthase (eNOS), eventually leading to increased apoptotic rate and decreased NO content, all of which were reversed by N-acetyl-L-cysteine.

Conclusion

Plin5 preserves lipid balance and cell survival in diabetic CMECs by regulating FFAs metabolism bidirectionally via the states of nonphosphorylation and phosphorylation.

Specific Inhibition of CYP4A Alleviates Myocardial Oxidative Stress and Apoptosis Induced by Advanced Glycation End-Products

High exposure to advanced glycation end-products (AGEs) may induce cardiotoxicity. However, the effects and mechanisms remain to be further clarified. CYP4A plays an important role in the pathophysiological process of myocardial abnormalities by modulating oxidative stress and apoptosis (OS/Apop) signaling pathway. The present work aimed to investigate whether CYP4A mediates AGEs-induced myocardial injury. AGEs solution was administered intragastrically to C57BL/6 mice for 60 days, while the specific inhibitor of CYP4A, HET0016, was given from the 47th day via intraperitoneal injection for 2 weeks. Levels of OS/Apop in heart tissue were measured. The effects on the cell viability and apoptosis were detected in primary rat cardiomyocytes. To further investigate the mechanism, H9c2 cells were treated with HET0016 or small interfering RNAs (siRNAs) against CYP4a mRNA before incubation with AGEs. Exposure to AGEs led to significantly increased expression of CYP4A and levels of OS/Apop in heart and H9c2 cells both in vivo and in vitro. The OS/Apop pathway was activated with increased expression of NOX2, p-JNK, and cleaved caspase-3 (c-caspase-3) and decreased expression of p-Akt and Bcl-xL both in vivo and in vitro. Specific CYP4A suppression by HET0016 or siRNA exerted significant protective effects by attenuating AGEs-induced OS/Apop pathways in vitro. Our results demonstrate that specific inhibition of CYP4A might be a potential therapeutic option for myocardial injury induced by AGEs.

Advanced glycation end-products disrupt human endothelial cells redox homeostasis: new insights into reactive oxygen species production

Advanced glycation end-products (AGEs) trigger multiple metabolic disorders in the vessel wall that may in turn lead to endothelial dysfunction. The molecular mechanisms by which AGEs generate these effects are not completely understood. Oxidative stress plays a key role in the development of deleterious effects that occur in endothelium during diabetes. Our main objectives were to further understand how AGEs contribute to reactive oxygen species (ROS) overproduction in endothelial cells and to evaluate the protective effect of an antioxidant plant extract. The human endothelial cell line EA.hy926 was treated with native or modified bovine serum albumin (respectively BSA and BSA-AGEs). To monitor free radicals formation, we used H₂DCF-DA, dihydroethidium (DHE), DAF-FM-DA and MitoSOX Red dyes. To investigate potential sources of ROS, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial inhibitors were used. The regulation of different types of ROS by the polyphenol-rich extract from the medicinal plant Doratoxylon apetalum was also studied for a therapeutic perspective. BSA-AGEs exhibited not only less antioxidant properties than BSA, but also pro-oxidant effects. The degree of albumin glycoxidation directly influenced oxidative stress through a possible communication between NADPH oxidase and mitochondria. D. apetalum significantly decreased intracellular hydrogen peroxide and superoxide anions mainly detected by H₂DCF-DA and DHE respectively. Our results suggest that BSA-AGEs promote a marked oxidative stress mediated at least by NADPH oxidase and mitochondria. D. apetalum plant extract appeared to be an effective antioxidant compound to protect endothelial cells.

Autophagy inhibits high glucose induced cardiac microvascular endothelial cells apoptosis by mTOR signal pathway

Cardiac microvascular endothelial cells (CMECs) dysfunction is an important pathophysiological event in the cardiovascular complications induced by diabetes. However, the underlying mechanism is not fully clarified. Autophagy is involved in programmed cell death. Here we investigated the potential role of autophagy on the CMECs injury induced by high glucose. CMECs were cultured in normal or high glucose medium for 6, 12 and 24 h respectively. The autophagy of CMECs was measured by green fluorescence protein (GFP)-LC3 plasmid transfection. Moreover, the apoptosis of CMEC was determined by flow cytometry. Furthermore, 3-Methyladenine (3MA), ATG7 siRNA and rapamycin were administrated to regulate the autophagy state. Moreover, Western blotting assay was performed to measure the expressions of Akt, mTOR, LC3 and p62. High glucose stress decreased the autophagy, whereas increased the apoptosis in CMECs time dependently. Meanwhile, high glucose stress activated the Akt/mTOR signal pathway. Furthermore, autophagy inhibitor, 3-MA and ATG7 siRNA impaired the autophagy and increased the apoptosis in CMECs induced by high glucose stress. Conversely, rapamycin up-regulated the autophagy and decreased the apoptosis in CMECs under high glucose condition. Our data provide evidence that high glucose directly inhibits autophagy, as a beneficial adaptive response to protect CMECs against apoptosis. Furthermore, the autophagy was mediated, at least in part, by mTOR signaling.

The pathological role of advanced glycation end products-downregulated heat shock protein 60 in islet β-cell hypertrophy and dysfunction

Heat shock protein 60 (HSP60) is a mitochondrial chaperone. Advanced glycation end products (AGEs) have been shown to interfere with the β-cell function. We hypothesized that AGEs induced β-cell hypertrophy and dysfunction through a HSP60 dysregulation pathway during the stage of islet/β-cell hypertrophy of type-2-diabetes. We investigated the role of HSP60 in AGEs-induced β-cell hypertrophy and dysfunction using the models of diabetic mice and cultured β-cells. Hypertrophy, increased levels of p27Kip1, AGEs, and receptor for AGEs (RAGE), and decreased levels of HSP60, insulin, and ATP content were obviously observed in pancreatic islets of 12-week-old db/db diabetic mice. Low-concentration AGEs significantly induced the cell hypertrophy, increased the p27Kip1 expression, and decreased the HSP60 expression, insulin secretion, and ATP content in cultured β-cells, which could be reversed by RAGE neutralizing antibody. HSP60 overexpression significantly reversed AGEs-induced hypertrophy, dysfunction, and ATP reduction in β-cells. Oxidative stress was also involved in the AGEs-decreased HSP60 expression in β-cells. Pancreatic sections from diabetic patient showed islet hypertrophy, increased AGEs level, and decreased HSP60 level as compared with normal subject. These findings highlight a novel mechanism by which a HSP60-correlated signaling pathway contributes to the AGEs-RAGE axis-induced β-cell hypertrophy and dysfunction under diabetic hyperglycemia.

Resveratrol Cardioprotection Against Myocardial Ischemia/Reperfusion Injury Involves Upregulation of Adiponectin Levels and Multimerization in Type 2 Diabetic Mice

Downregulation of adiponectin (APN) multimerization is significantly correlated with the aggravation of myocardial ischemia/reperfusion (MI/R) injury in type 2 diabetes mellitus (T2DM). Resveratrol (RSV) upregulates APN multimerization in adipocytes, but whether RSV improves endogenous APN multimerization and thus attenuates MI/R injury in T2DM mice has never been investigated. T2DM mice were treated with 10 mg/kg RSV daily for 3 weeks, followed by 30 minutes of myocardial ischemia and 3 hours or 24 hours of reperfusion. RSV administration alleviated MI/R injury in diabetic mice, as evidenced by reduced infarct size, cardiomyocyte apoptosis, and caspase-3 activity, and improved cardiac function. Moreover, RSV reversed the downregulated APN levels and multimerization both in plasma and adipose tissue, accompanied by increased disulfide bond A oxidoreductase-like protein (DsbA-L) expression in T2DM mice. Conversely, serving as a key downstream molecule of APN in ameliorating MI/R injury, inhibition of AMP-activated protein kinase (AMPK) significantly attenuated the cardioprotective effects of RSV. In conclusion, long-term administration of RSV upregulates adiponectin levels and multimerization in T2DM mice, consequently attenuating MI/R injury partially through APN-AMPK signaling.

Advanced glycation end-product (AGE)-albumin from activated macrophage is critical in human mesenchymal stem cells survival and post-ischemic reperfusion injury

Post-ischemic reperfusion injury (PIRI) triggers an intense inflammatory response which is essential for repair but is also implicated in pathogenesis of post-ischemic remodeling in several organs in human. Stem cell therapy has recently emerged as a promising method for treatment of PIRI in human. However, satisfactory results have not been reported due to severe loss of injected stem cells in PIRI including critical limb ischemia (CLI). For investigating the advanced glycation end-product-albumin (AGE-albumin) from activated macrophages is critical in both muscle cell and stem cell death, we evaluated the recovery of PIRI-CLI by injection of human bone marrow derived mesenchymal stem cells (hBD-MSCs) with or without soluble receptor for AGEs (sRAGE). Our results showed that activated M1 macrophages synthesize and secrete AGE-albumin, which induced the skeletal muscle cell death and injected hBD-MSCs in PIRI-CLI through RAGE increase. Combined injection of sRAGE and hBD-MSCs resulted in enhanced survival of hBD-MSCs and angiogenesis in PIRI-CLI mice. Taken together, AGE-albumin from activated macrophages is critical for both skeletal muscle cell and hBD-MSCs death in PIRI-CLI. Therefore, the inhibition of AGE-albumin from activated macrophages could be a successful therapeutic strategy for treatment of PIRI including CLI with or without stem cell therapy.

RAGE-NF-κB-PPARγ Signaling is Involved in AGEs-Induced Upregulation of Amyloid-β Influx Transport in an In Vitro BBB Model

The receptor for advanced glycation end products (RAGE) at the blood-brain barrier (BBB) is critical for regulation of amyloid-β (Aβ) homeostasis in the diabetic brain. In this study, we used an in vitro BBB model consisting of mouse brain capillary endothelial cells (MBCECs) to investigate whether advanced glycation end products (AGEs) increase Aβ influx transport across the BBB and the underlying mechanisms. We found that AGEs induced Aβ influx transport across the BBB in concentration- and time-dependent manner, accompanied by increased RAGE expression and nuclear factor-kappa B p65 (NF-κB p65), and decreased nuclear peroxisome proliferator-activated receptor γ (PPARγ). Blockade of RAGE with its antibody and inhibition of NF-κB signaling with PDTC as well as activation of PPARγ with rosiglitazone significantly decreased Aβ transport across the BBB from the periphery to the brain. These treatments also pronouncedly suppressed AGEs-induced increases in RAGE expression and nuclear NF-κB p65 and reversed the decrease in nuclear PPARγ. These results suggest that RAGE-NF-κB-PPARγ signaling is involved in regulation of AGEs-induced influx transport of Aβ across the BBB and targeting the signaling pathway could serve as a novel strategy to modify such Aβ transport.

Hypoxia/ischemia promotes CXCL10 expression in cardiac microvascular endothelial cells by NFkB activation

CXCL10, the chemokine with potent chemotactic activity on immune cells and other non-immune cells expressing its receptor CXCR3, has been demonstrated to involve in myocardial infarction, which was resulted from hypoxia/ischemia. The cardiac microvascular endothelial cells (CMECs) are the first cell type which is implicated by hypoxia/ischemia. However, the potential molecular mechanism by which hypoxia/ischemia regulates the expression of CXCL10 in CMECs remains unclear. In the present study, the expression of CXCL10 was firstly examined by real-time PCR and ELISA analysis. Several potential binding sites (BS) for transcription factors including NF-kappaB (NFkB), HIF1 alpha (HIF1α) and FoxO3a were identified in the promoter region of CXCL10 gene from -2000 bp to -1 bp using bioinformatics software. Luciferase reporter gene vectors for CXCL10 promoter and for activation of above transcription factors were constructed. The activation of NFkB, hypoxia-inducible transcription factor-1 alpha (HIF-1α) and FoxO3a was also analyzed by Western blotting. It was shown that the production of CXCL10 in CMECs was significantly increased by hypoxia/ischemia treatment, in parallel with the activation of CXCL10 promoter examined by reporter gene vector system. Furthermore, transcription factors including NFkB, HIF1α and FoxO3a were activated by hypoxia/ischemia in CMECs. However, over-expression of NFkB, but not that of HIF1α or FoxO3a, significantly promoted the activation of CXCL10 promoter reporter gene. These findings indicated that CXCL10 production in CMECs was significantly increased by hypoxia/ischemia, at least in part, through activation of NFkB pathway and subsequently binding to CXCL10 promoter, finally promoted the transcription of CXCL10 gene.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Ameliorating Effect of Akebia quinata Fruit Extracts on Skin Aging Induced by Advanced Glycation End Products

The accumulation of free radicals and advanced glycation end products (AGEs) in the skin plays a very important role in skin aging. Both are known to interact with each other. Therefore, natural compounds or extracts that possess both antioxidant and antiglycation activities might have great antiageing potential. Akebia quinata fruit extract (AQFE) has been used to treat urinary tract inflammatory disease in traditional Korean and Chinese medicines. In the present study, AQFE was demonstrated to possess antioxidant and antiglycation activity. AQFE protects human dermal fibroblasts (HDFs) from oxidative stress and inhibits cellular senescence induced by oxidative stress. We also found that AQFE inhibits glycation reaction between BSA and glucose. The antiglycation activity of AQFE was dose-dependent. In addition, the antiglycation activity of AQFE was confirmed in a human skin explant model. AQFE reduced CML expression and stimulated fibrillin-1 expression in comparison to the methyglyoxal treatment. In addition, the possibility of the extract as an anti-skin aging agent has also been clinically validated. Our analysis of the crow’s feet wrinkle showed that there was a decrease in the depth of deep furrows in RI treated with AQFE cream over an eight-week period. The overall results suggest that AQFE may work as an anti-skin aging agent by preventing oxidative stress and other complications associated with AGEs formation.

TNF-α antagonism ameliorates myocardial ischemia-reperfusion injury in mice by upregulating adiponectin

Tumor necrosis factor-α (TNF-α) antagonism alleviates myocardial ischemia-reperfusion (MI/R) injury. However, the mechanisms by which the downstream mediators of TNF-α change after acute antagonism during MI/R remain unclear. Adiponectin (APN) exerts anti-ischemic effects, but it is downregulated during MI/R. This study was conducted to investigate whether TNF-α is responsible for the decrease of APN, and whether antagonizing TNF-α affects MI/R injury by increasing APN. Male adult wild-type (WT), APN knockout (APN KO) mice, and those with cardiac knockdowns of APN receptors via siRNA injection were subjected to 30 min of MI followed by reperfusion. The TNF-α antagonist etanercept or globular domain of APN (gAD) was injected 10 min before reperfusion. Etanercept ameliorated MI/R injury in WT mice as evidenced by improved cardiac function, and reduced infarct size and cardiomyocyte apoptosis. APN concentrations were augmented in response to etanercept, followed by an increase in AMP-activated protein kinase phosphorylation. Etanercept still increased cardiac function and reduced infarct size and apoptosis in both APN KO and APN receptors knockdown mice. However, its potential was significantly weakened in these mice compared with the WT mice. TNF-α is responsible for the decrease in APN during MI/R. The cardioprotective effects of TNF-α neutralization are partially due to the upregulation of APN. The results provide more insight into the TNF-α-mediated signaling effects during MI/R and support the need for clinical trials to validate the efficacy of acute TNF-α antagonism in the treatment of MI/R injury.

Effect of PKC-β Signaling Pathway on Expression of MCP-1 and VCAM-1 in Different Cell Models in Response to Advanced Glycation End Products (AGEs)

Advanced glycation end products (AGEs) are compounds classified as uremic toxins in patients with chronic kidney disease that have several pro-inflammatory effects and are implicated in the development of cardiovascular diseases. To explore the mechanisms of AGEs–endothelium interactions through the receptor for AGEs (RAGE) in the PKC-β pathway, we evaluated the production of MCP-1 and VCAM-1 in human endothelial cells (HUVECs), monocytes, and a coculture of both. AGEs were prepared by albumin glycation and characterized by absorbance and electrophoresis. The effect of AGEs on cell viability was assessed with an MTT assay. The cells were also treated with AGEs with and without a PKC-β inhibitor. MCP-1 and VCAM-1 in the cell supernatants were estimated by ELISA, and RAGE was evaluated by immunocytochemistry. AGEs exposure did not affect cell viability, but AGEs induced RAGE, MCP-1, and VCAM-1 expression in HUVECs. When HUVECs or monocytes were incubated with AGEs and a PKC-β inhibitor, MCP-1 and VCAM-1 expression significantly decreased. However, in the coculture, exposure to AGEs and a PKC-β inhibitor produced no significant effect. This study demonstrates, in vitro, the regulatory mechanisms involved in MCP-1 production in three cellular models and VCAM-1 production in HUVECs, and thus mimics the endothelial dysfunction caused by AGEs in early atherosclerosis. Such mechanisms could serve as therapeutic targets to reduce the harmful effects of AGEs in patients with chronic kidney disease.

TXNIP mediates NLRP3 inflammasome activation in cardiac microvascular endothelial cells as a novel mechanism in myocardial ischemia/reperfusion injury

NLRP3 inflammasome is necessary for initiating acute sterile inflammation. Recent studies have demonstrated that NLRP3 inflammasome is up-regulated and mediates myocardial ischemia/reperfusion (MI/R) injury. However, the signaling pathways that lead to the activation of NLRP3 inflammasome by MI/R injury have not been fully elucidated. C57BL/6J mice were subjected to 30 min ischemia and 3 or 24 h reperfusion. The ischemic heart exhibited enhanced inflammasome activation as evidenced by increased NLRP3 expression and caspase-1 activity and increased IL-1β and IL-18 production. Intramyocardial NLRP3 siRNA injection or an intraperitoneal injection of BAY 11-7028, an inflammasome inhibitor, attenuated macrophage and neutrophil infiltration and decreased MI/R injury, as measured by cardiomyocyte apoptosis and infarct size. The ischemic heart also exhibited enhanced interaction between Txnip and NLRP3, which has been shown to be a mechanism for activating NLRP3. Intramyocardial Txnip siRNA injection also decreased infarct size and NLRP3 activation. In vitro experiments revealed that NLRP3 was expressed in cardiac microvascular endothelial cells (CMECs), but was hardly expressed in cardiomyocytes. Simulated ischemia/reperfusion (SI/R) stimulated NLRP3 inflammasome activation in CMECs, but not in cardiomyocytes. Moreover, CMECs subjected to SI/R injury increased interactions between Txnip and NLRP3. Txnip siRNA diminished NLRP3 inflammasome activation and SI/R-induced injury, as measured by LDH release and caspase-3 activity in CMECs. ROS scavenger dissociated TXNIP from NLRP3 and inhibited the activation of NLRP3 inflammasome in the CMECs. For the first time, we demonstrated that TXNIP-mediated NLRP3 inflammasome activation in CMECs was a novel mechanism of MI/R injury. Interventions that block Txnip/NLRP3 signaling to inhibit the activation of NLRP3 inflammasomes may be novel therapies for mitigating MI/R injury.

NADPH oxidase 4 promotes cardiac microvascular angiogenesis after hypoxia/reoxygenation in vitro

Microvascular endothelial cell dysfunction plays a key role in myocardial ischemia/reperfusion (I/R) injury, wherein reactive oxygen species (ROS)-dependent signaling is intensively involved. However, the roles of the various ROS sources remain unclear. This study sought to investigate the role of NADPH oxidase 4 (Nox4) in the cardiac microvascular endothelium in response to I/R injury. Adult rat cardiac microvascular endothelial cells (CMECs) were isolated and subjected to hypoxia/reoxygenation (H/R). Our results showed that Nox4 was highly expressed in CMECs, was significantly increased at both mRNA and protein levels after H/R injury, and contributed to H/R-stimulated increase in Nox activity and ROS generation. Downregulation of Nox4 by small interfering RNA transfection did not affect cell viability or ROS production under normoxia, but exacerbated H/R injury as evidenced by increased apoptosis and inhibited cell survival, migration, and angiogenesis after H/R. Nox4 inhibition also increased prolyl hydroxylase 2 (PHD2) expression and blocked H/R-induced increases in HIF-1α and VEGF expression. Pretreatment with DMOG, a specific competitive PHD inhibitor, upregulated HIF-1α and VEGF expression and significantly reversed Nox4 knockdown-induced injury. However, Nox2 was scarcely expressed and played a minimal role in CMEC survival and angiogenesis after H/R, though a modest upregulation of Nox2 was observed. In conclusion, this study demonstrated a previously unrecognized protective role of Nox4, a ROS-generating enzyme and the major Nox isoform in CMECs, against H/R injury by inhibiting apoptosis and promoting migration and angiogenesis via a PHD2-dependent upregulation of HIF-1/VEGF proangiogenic signaling.

Overexpression of RAGE contributes to cigarette smoke-induced nitric oxide generation in COPD

BACKGROUND

Receptor for advanced glycation end products (RAGE), a multiple-ligands receptor, is implicated in chronic obstructive pulmonary disease (COPD). This study was designed to investigate the potential role of RAGE in nitric oxide (NO) generation, an endogenous marker of nitrosative stress in COPD.

METHODS

Lung tissues from COPD patients were used to describe the relationship between RAGE expression and NO level. RAGE expression was assessed by immunohistochemistry, western blot, and ELISA. Human bronchial epithelial cells (16HBE) were cultured with cigarette smoke extract (CSE). Neutralizing antibody against RAGE was used to detect the role of RAGE in CSE-induced NO generation by 16HBE cells.

RESULTS

Compared with nonsmoker controls, overexpression of RAGE was significantly detected in COPD smokers (p < 0.01), but not healthy smokers and nonsmokers with COPD, which was dominantly expressed at bronchiolar epithelia. Correlation analysis showed that RAGE in COPD smokers was positively related to NO level, smoking status, and lung function decline. In cultured 16HBE cells treated with CSE, soluble RAGE was reduced; however, full-length RAGE was enhanced significantly as the same trend as NO generation. Moreover, increased NO level and NO synthase activity, decreased total glutathione (a major cellular antioxidant), enhanced nuclear translocation of p65 (a key molecule of nuclear factor (NF)-κB) and release of NF-κB-dependent proinflammatory cytokines were all reversed by pretreatment of anti-RAGE antibody.

CONCLUSIONS

These findings suggest that overexpression of RAGE contributes to CS-induced NO generation in COPD with involvement in NF-κB activation.

Myocardial protective effect of extracellular superoxide dismutase gene modified bone marrow mesenchymal stromal cells on infarcted mice hearts

Aim: Extracellular superoxide dismutase (ecSOD) is a unique scavenger of superoxide anions and a promising target of gene therapy for ischemia/reperfusion injury (I/R). However, conventional gene therapies have limitation in effectiveness and efficiency. This study aimed to investigate the protective effects of ecSOD gene modified bone marrow mesenchymal stromal cells (BMSCs) on cardiac function improvement in mice infarcted heart. METHODS & RESULTS: BMSCs were isolated from Fluc⁺ transgenic mice (Tg FVB[Fluc⁺]) and transfected by adenovirus combined with human ecSOD gene. ELISA was performed to determine ecSOD protein level. Female syngeneic FVB mice were randomized into 5 groups: (1) Sham group (sham); (2) MI group (MI); (3) MI+BMSCs group (BMSC); (4) MI+BMSCs-vector group (BMSC-vector); (5) MI+ BMSCs-ecSOD group (BMSC-ecSOD). MI was accomplished by ligation of the left anterior descending artery. BMSCs (2x10⁶) were injected into the border zone of infarction. In vivo bioluminescence imaging (BLI) was performed to monitor transplanted BMSCs viability. Echocardiography and histological staining revealed that BMSCs-ecSOD significantly reduced myocardial infarction size and improved cardiac function. Lucigenin chemiluminescence, DHE and TUNEL staining demonstrated that BMSCs-ecSOD delivery reduced ROS level and cell apoptosis both in vivo and in vitro. Western blot assay revealed that ecSOD supplementation increased FoxO3a phosphorylation in cardiomyocytes. Moreover, quantitative real-time PCR showed that pro-apoptotic factors (bim and bax) were decreased while the anti-apoptotic factor mir-21 expression was increased after ecSOD intervention. CONCLUSION: Intra-myocardial transplantation of adenovirus-ecSOD transfected BMSCs could exert potential cardiac protection against MI, which may be partly through reduction of oxidative stress and improvement of BMSCs survival.

Metallothionein prevents cardiac pathological changes in diabetes by modulating nitration and inactivation of cardiac ATP synthase

Mitochondrial ATP production is the main energy source for the cell. Diabetes reduces the efficient generation of ATP, possibly due to the inactivation of ATP synthase. However, the exact mechanism by which diabetes induces inactivation of ATP synthase remains unknown, as well as whether such inactivation has a role in the development of pathological abnormalities of the diabetic heart. To address these issues, we used cardiac metallothionein-transgenic (MT-TG) and wild-type (WT) mice with streptozotocin-induced diabetes, since we have demonstrated previously that diabetes-induced cardiac damage and remodeling were found in WT diabetic mice, but not in MT-TG diabetic mice. Immunohistochemical and biochemical assays were used to compare pathological and biochemical changes of the heart between MT-TG and WT diabetic mice, and a proteomic assay to evaluate ATP synthase expression and tyrosine nitration, with its activity. LC/MS analysis revealed that diabetes increased tyrosine nitration of the ATP synthase α subunit at Tyr(271), Tyr(311), and Tyr(476), and the β subunit at Tyr(269) and Tyr(508), and also significantly reduced ATP synthase activity by ~32%. These changes were not observed in MT-TG diabetic mice. Furthermore, parallel experiments with induced expression of cardiac MT by zinc supplementation in diabetic mice produced similar effects. These results suggest that MT can preserve ATP synthase activity in streptozotocin-induced diabetes, probably through the inhibition of ATP synthase nitration.

Radical roles for RAGE in the pathogenesis of oxidative stress in cardiovascular diseases and beyond

Oxidative stress is a central mechanism by which the receptor for advanced glycation endproducts (RAGE) mediates its pathological effects. Multiple experimental inquiries in RAGE-expressing cultured cells have demonstrated that ligand-RAGE interaction mediates generation of reactive oxygen species (ROS) and consequent downstream signal transduction and regulation of gene expression. The primary mechanism by which RAGE generates oxidative stress is via activation of NADPH oxidase; amplification mechanisms in the mitochondria may further drive ROS production. Recent studies indicating that the cytoplasmic domain of RAGE binds to the formin mDia1 provide further support for the critical roles of this pathway in oxidative stress; mDia1 was required for activation of rac1 and NADPH oxidase in primary murine aortic smooth muscle cells treated with RAGE ligand S100B. In vivo, in multiple distinct disease models in animals, RAGE action generates oxidative stress and modulates cellular/tissue fate in range of disorders, such as in myocardial ischemia, atherosclerosis, and aneurysm formation. Blockade or genetic deletion of RAGE was shown to be protective in these settings. Indeed, beyond cardiovascular disease, evidence is accruing in human subjects linking levels of RAGE ligands and soluble RAGE to oxidative stress in disorders such as doxorubicin toxicity, acetaminophen toxicity, neurodegeneration, hyperlipidemia, diabetes, preeclampsia, rheumatoid arthritis and pulmonary fibrosis. Blockade of RAGE signal transduction may be a key strategy for the prevention of the deleterious consequences of oxidative stress, particularly in chronic disease.

Involvement of the FoxO3a pathway in the ischemia/reperfusion injury of cardiac microvascular endothelial cells

FoxO3a, a member of the forkhead transcription factors, has been demonstrated to be involved in myocardial ischemia/reperfusion (I/R) injury. Cardiac microvascular endothelial cells (CMECs) are some of the predominant cells damaged immediately after myocardial I/R injury. Despite the importance of injured CMECs in an ischemic heart, little is known about the involvement of FoxO3a in regulating CMECs injury. Thus, we used rat CMECs following simulated I/R to examine FoxO3a activation and signaling in relation to survival, the cell cycle and apoptosis in CMECs. We found that Akt negatively regulates activation of the FoxO3a pathway by phosphorylating FoxO3a in CMECs as demonstrated with an Akt inhibitor and activator. Upon I/R injury, the FoxO3a pathway was significantly activated in CMECs, which was accompanied by Akt deactivation. In parallel, the I/R of CMECs induced G1-phase arrest through p27(Kip1) up-regulation and significant activation of caspase-3. Accordingly, inhibition of the FoxO3a pathway by IGF-1, an Akt activator, could significantly block the I/R-enhanced activation of p27(Kip1) and caspase-3 in CMECs. Collectively, our results indicate that the FoxO3a pathway is involved in the I/R injury of CMECs at least in part through the regulation of cell cycle arrest and apoptosis, suggesting that the FoxO3a pathway may be a novel therapeutic target that protects against microvascular endothelial damage in ischemic hearts.

Advanced glycation end products induce human corneal epithelial cells apoptosis through generation of reactive oxygen species and activation of JNK and p38 MAPK pathways

Advanced Glycation End Products (AGEs) has been implicated in the progression of diabetic keratopathy. However, details regarding their function are not well understood. In the present study, we investigated the effects of intracellular reactive oxygen species (ROS) and JNK, p38 MAPK on AGE-modified bovine serum albumin (BSA) induced Human telomerase-immortalized corneal epithelial cells (HUCLs) apoptosis. We found that AGE-BSA induced HUCLs apoptosis and increased Bax protein expression, decreased Bcl-2 protein expression. AGE-BSA also induced the expression of receptor for advanced glycation end product (RAGE). AGE-BSA-RAGE interaction induced intracellular ROS generation through activated NADPH oxidase and increased the phosphorylation of p47phox. AGE-BSA induced HUCLs apoptosis was inhibited by pretreatment with NADPH oxidase inhibitors, ROS quencher N-acetylcysteine (NAC) or neutralizing anti-RAGE antibodies. We also found that AGE-BSA induced JNK and p38 MAPK phosphorylation. JNK and p38 MAPK inhibitor effectively blocked AGE-BSA-induced HUCLs apoptosis. In addition, NAC completely blocked phosphorylation of JNK and p38 MAPK induced by AGE-BSA. Our results indicate that AGE-BSA induced HUCLs apoptosis through generation of intracellular ROS and activation of JNK and p38 MAPK pathways.

The alternative crosstalk between RAGE and nitrative thioredoxin inactivation during diabetic myocardial ischemia-reperfusion injury

The receptor for advanced glycation end products (RAGE) and thioredoxin (Trx) play opposing roles in diabetic myocardial ischemia-reperfusion (MI/R) injury. We recently demonstrated nitrative modification of Trx leads to its inactivation and loss of cardioprotection. The present study is to determine the relationship between augmented RAGE expression and diminished Trx activity pertaining to exacerbated MI/R injury in the diabetic heart. The diabetic state was induced in mice by multiple intraperitoneal low-dose streptozotocin injections. RAGE small-interfering RNA (siRNA) or soluble RAGE (sRAGE, a RAGE decoy) was via intramyocardial and intraperitoneal injection before MI/R, respectively. Mice were subjected to 30 min of myocardial infarction followed by 3 or 24 h of reperfusion. At 10 min before reperfusion, diabetic mice were randomized to receive EUK134 (peroxynitrite scavenger), recombinant hTrx-1, nitrated Trx-1, apocynin (a NADPH oxidase inhibitor), or 1400W [an inducible nitric oxide synthase (iNOS) inhibitor] administration. The diabetic heart manifested increased RAGE expression and N(ε)-(carboxymethyl)lysine (CML, major advanced glycation end product subtype) content, reduced Trx-1 activity, and increased Trx nitration after MI/R. RAGE siRNA or administration of sRAGE in diabetic mice decreased MI/R-induced iNOS and gp91(phox) expression, reduced Trx nitration, preserved Trx activity, and decreased infarct size. Apocynin or 1400W significantly decreased nitrotyrosine production and restored Trx activity. Conversely, administration of either EUK134 or reduced hTrx, but not nitrated hTrx, attenuated MI/R-induced superoxide production, RAGE expression, and CML content and decreased cardiomyocyte apoptosis in diabetic mice. Collectively, we demonstrate that RAGE modulates the MI/R injury in a Trx nitrative inactivation fashion. Conversely, nitrative modification of Trx blocked its inhibitory effect upon RAGE expression in the diabetic heart. This is the first direct evidence demonstrating the alternative cross talk between RAGE overexpression and nitrative Trx inactivation, suggesting that interventions interfering with their interaction may be novel means of mitigating diabetic MI/R injury.

O-GlcNAcylation and oxidation of proteins: is signalling in the cardiovascular system becoming sweeter?

O-GlcNAcylation is an unusual form of protein glycosylation, where a single-sugar [GlcNAc (N-acetylglucosamine)] is added (via β-attachment) to the hydroxyl moiety of serine and threonine residues of nuclear and cytoplasmic proteins. A complex and extensive interplay exists between O-GlcNAcylation and phosphorylation. Many phosphorylation sites are also known glycosylation sites, and this reciprocal occupancy may produce different activities or alter the stability in a target protein. The interplay between these two post-translational modifications is not always reciprocal, as some proteins can be concomitantly phosphorylated and O-GlcNAcylated, and the adjacent phosphorylation or O-GlcNAcylation can regulate the addition of either moiety. Increased cardiovascular production of ROS (reactive oxygen species), termed oxidative stress, has been consistently reported in various chronic diseases and in conditions where O-GlcNAcylation has been implicated as a contributing mechanism for the associated organ injury/protection (for example, diabetes, Alzheimer's disease, arterial hypertension, aging and ischaemia). In the present review, we will briefly comment on general aspects of O-GlcNAcylation and provide an overview of what has been reported for this post-translational modification in the cardiovascular system. We will then specifically address whether signalling molecules involved in redox signalling can be modified by O-GlcNAc (O-linked GlcNAc) and will discuss the critical interplay between O-GlcNAcylation and ROS generation. Experimental evidence indicates that the interactions between O-GlcNAcylation and oxidation of proteins are important not only for cell regulation in physiological conditions, but also under pathological states where the interplay may become dysfunctional and thereby exacerbate cellular injury.

A soluble receptor for advanced glycation end-products inhibits hypoxia/reoxygenation-induced apoptosis in rat cardiomyocytes via the mitochondrial pathway

Severe myocardial dysfunction and tissue damage resulting from ischemia/reperfusion (I/R) is a common clinical scenario in patients with certain types of heart diseases and therapies such as thrombolysis, percutaneous coronary intervention, coronary artery bypass grafting, and cardiac transplantation. The underlining mechanism of endogenous cardiac protection after I/R injury has been a focus of current research. Growing evidences suggests that soluble receptor for advanced glycation end-products (sRAGE) has a cardioprotective effect; however, its role in I/R injury remains unclear. We hypothesized that exogenous administration of sRAGE during hypoxia/reoxygenation (H/R) induces cardioprotection by inhibiting cardiomyocyte apoptosis via multiple signals, involving mitochondrial membrane potential (MMP), the mitochondrial permeability transition pore (mPTP), mitochondrial cytochrome c, caspase-3, Bcl-2 and Bax. Neonatal rat cardiomyocytes underwent hypoxia for 3-h followed by 2-h reoxygenation or were treated with sRAGE for 10 min before H/R. Compared with H/R alone, sRAGE pretreatment reduced H/R-induced cardiomyocyte apoptosis from 27.9% ± 5.9% to 9.4% ± 0.7% (p < 0.05). In addition, sRAGE treatment significantly inhibited H/R-induced mitochondrial depolarization and mPTP opening, reduced mitochondrial cytochrome c leakage, caspase-3 and caspase-9 activity, and decreased the ratio of Bax to Bcl-2. Therefore, we conclude that the exogenous administration of sRAGE during H/R is involved in cardioprotection by inhibiting apoptosis via the mitochondrial pathway, which, if further confirmed in vivo, may have important clinical implications during H/R.

FTY720 protects cardiac microvessels of diabetes: a critical role of S1P1/3 in diabetic heart disease

Background: Diabetes is associated with an increased risk of cardiac microvascular disease. The mechanisms by which this damage occurs are unknown. However, research suggests that signaling through the sphingosine-1-phosphates receptor 1 and 3 (S1P1/3) by FTY720, a sphiongolipid drug that is structually similar to SIP, may play a role in the treatment on cardiac microvascular dysfunction in diabetes. We hypothesized that FTY720 might exert the cardioprotective effects of S1P1 and S1P3 viaprotein kinase C-beta (PKCβ II) signaling pathway.

Methodology/Principal Findings: Transthoracic echocardiography was performed to detect the change of cardiac function. Scanning and transmission electron microscope with lanthanum tracer were used to determine microvascular ultrastructure and permeability in vivo. Apoptosis was detected by TUNEL and CD31 dual labeling in paraffin-embedded sections. Laser capture miscrodissection was used to assess cardiac micovascular endothelial cells (CMECs) in vivo. RT-PCR and Western blot analysis were used to determine the mRNA levels and protein expression of S1P1, S1P3, and PKCβ II. In the diabetic rats vs. controls, cardiac capillaries showed significantly higher density; CD31 positive endothelial cells were significantly reduced; the apoptosis index of cardiac endothlial cells was significantly higher. And FTY720 could increase the expressional level of S1P1 and boost S1P3 trasnslocation from membrane to nuclear, then ameliorate cardiac microvascular barrier impairment and pathologic angiogenesis induced by diabetes. In addition, overexpression of PKCβ II significantly decreased the protective effect of FTY720.

Conclusions: Our study represents that the deregulation of S1P1 and S1P3 is an important signalresponsible for cardiac microvascular dysfunction in diabetes. FTY720 might be competent to serve as a potential therapeutic approach for diabetic heart disease through ameliorating cardiac microvascular barrier impairment and pathologic angiogenesis, which might be partly dependent on PKCβII-mediated signaling pathway.

Redox-regulating role of insulin: the essence of insulin effect

It is well-known that insulin acts as an important hormone, controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Over the past few years, intensive insulin therapy has been believed to be benefit for the outcome of diabetic patients, in which the suppression of oxidative stress plays a role. Moreover, insulin is accepted as a key component of glucose-insulin-potassium, a treatment which has been believed to exert significant cardiovascular protective effect via the reduction of oxidative stress. Furthermore, accumulating evidence has suggested that insulin exerts important redox-regulating actions in various insulin-sensitive target organs, implying the systematic antioxidative role of insulin as a hormone. It is time for us to revisit insulin effects, through summarizing and evaluating the novel functions of insulin and their mechanisms. This review focuses on the antioxidative effect of insulin and highlights insulin-induced regulation of various antioxidant enzymes via insulin signaling pathways and the cross talk between key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NF-κB) which are responsible for the transcription of antioxidant enzymes, leading to reduced generation of reactive oxygen species (ROS) and the enhancement of the elimination of ROS.