HMGB1 is activated in type 2 diabetes mellitus patients and in mesangial cells in response to high glucose

Diabetic nephropathy (DN) is one of the most devastating complications of diabetes, leading the cause of end-stage renal disease (ESRD). And investigations into mechanisms underlying renal inflammation may provide new insight into novel therapeutic targets for patients with DN. However, little is known about the promotion of inflammation in DN. In the present study, we examined the promotion by high glucose to High-mobility group box-1 (HMGB1) in patients with type 2 diabetes mellitus or in renal mesangial SV40 MES 13 cells. Results demonstrated that high glucose promoted the pre-inflammatory cytokines, such as TNF-α, IL-1β and IL-6 in patients with T2DM or in SV40 MES 13 cells. And the serum HMGB1 was also upregulated in T2DM patients, correlating with serum IL-6 and TNFα. The in vitro results indicated that HMGB1 mediated the D-glucose-induced pro-inflammatory cytokines in mesangial cells. And the NF-κB signaling pathway involved in the promotion of pro-inflammatory cytokines by D-glucose. In summary, the present study indicated that HMGB1 was significantly promoted by the glucose in vivo or in vitro, in an association with an upregulation of pro-inflammatory cytokines, via activating NF-κB signaling pathway. And the strategy of HMGB1 inhibition reduced the upregulation of pro-inflammatory cytokines in response to high glucose, via inhibiting the NF-κB signaling pathway. It implies the regulatory role of HMGB1 in the inflammatory responses in DN.

A natural product, resveratrol, protects against high-glucose-induced developmental damage in chicken embryo

Resveratrol, a famous plant-derived polyphenolic phytoalexin, has been considered to play physiological roles such as antioxidative, neuroprotective, and anticancer effects in adults. However, its antioxidative activity and neuroprotective effect were seldom discussed in the embryonic system. In this study, the effect of resveratrol on chicken embryo development under high glucose and its underlying mechanism of resveratrol were investigated. High glucose administrated to chicken embryo at embryonic Day 1 induced stillbirth, growth retardation, and impaired blood vessel development on yolk sac. However, resveratrol supplementation before glucose exposure showed significant effect on decreasing the death rate, developmental damage, and vessel injury. In addition, oxidative stress was caused by high-glucose exposure, and resveratrol could rescue this high-glucose-induced oxidative stress. Moreover, the neural developmental marker paired box 3 was significantly decreased by high glucose and recovered by resveratrol. Cell cycle-regulated gene expression was also intervened by resveratrol. This study had found an association between resveratrol and hyperglycemia-induced embryonic damage, which suggested a potential protective effect of resveratrol on gestational diabetes.

Overexpression of miR-34c inhibits high glucose-induced apoptosis in podocytes by targeting Notch signaling pathways

Recent findings have shown that microRNAs play critical roles in the pathogenesis of diabetic nephropathy. miR-34c has been found to inhibit fibrosis and the epithelial-mesenchymal transition of kidney cells. However, the role of miR-34c in diabetic nephropathy has not been well studied. The current study was designed to investigate the role and potential underlying mechanism of miR-34c in regulating diabetic nephropathy. After treating podocytes with high glucose (HG) in vitro, we found that miR-34c was downregulated and that overexpression of miR-34c inhibited HG-induced podocyte apoptosis. The direct interaction between miR-34c and the 3'-untranslated region (UTR) of Notch1 and Jagged1 was validated by dual-luciferase reporter assay. Moreover, Notch1 and Jagged1 as putative targets of miR-34c were downregulated by miR-34c overexpression in HG-treated podocytes. Overexpression of miR-34c inhibited HG-induced Notch signaling pathway activation, as indicated by decreased expression of the Notch intracellular domain (NICD) and downstream genes including Hes1 and Hey1. Furthermore, miR-34c overexpression increased the expression of the anti-apoptotic gene Bcl-2, and decreased the expression of the pro-apoptotic protein Bax and cleaved Caspase-3. Additionally, the phosphorylation of p53 was also downregulated by miR-34c overexpression. Taken together, our findings suggest that miR-34c overexpression inhibits the Notch signaling pathway by targeting Notch1 and Jaggged1 in HG-treated podocytes, representing a novel and potential therapeutic target for the treatment of diabetic nephropathy.

Glucotoxicity inhibits cAMP-protein kinase A-potentiated glucose-stimulated insulin secretion in pancreatic β-cells

BACKGROUND

The effect of incretin is markedly blunted in patients with type 2 diabetes (T2D), and this reduced effect of incretin is correlated with a diminished insulintropic potency of glucagon-like peptide-1 (GLP-1). We reported recently that GLP-1 potentiates glucose-stimulated insulin secretion (GSIS) mainly via activation of the cAMP-protein kinase A (PKA) signaling pathway in INS-1E cells under hyperglycemic conditions. In the present study, we further explored whether glucotoxicity impairs cAMP-PKA-mediated effects and its relevance to the reduced insulinotropic action of GLP-1 in hyperglycemia.

METHODS

Mouse islets and INS-1E cells were cultured in 30 mmol/L glucose for 72 h. The effects of glucotoxicity on cAMP-PKA-linked pathways and its insulinotropic action were then evaluated.

RESULTS

Chronic exposure of INS-1E cells and primary mouse islets to 30 mmol/L glucose almost abolished GSIS. The cAMP-elevating agent forskolin produced an approximate 1.9-fold increase in GSIS, significantly lower than that observed with 5.5 mmol/L glucose (~3.3-fold). Moreover, 72 h culture in the presence of 30 mmol/L glucose reduced forskolin-stimulated cAMP accumulation in β-cells. Notably, glucotoxicity reduced the expression and activity of PKA, as well as PKA-mediated effects. In contrast, glucotoxicity had no effect on the expression of Epac2, another cAMP effector.

CONCLUSIONS

Glucotoxicity-induced reductions in PKA and its signaling account, at least in part, for the decreased incretin effect under conditions of glucotoxicity.

Lack of PGC-1α exacerbates high glucose-induced apoptosis in human umbilical vein endothelial cells through activation of VADC1

Endothelial cells (ECs) apoptosis induced by hyperglycemia is intimately involved in the pathophysiology of diabetes and its complication. Although PGC-1α is known for its role in glucose metabolism, its role in ECs injury caused by high glucose milieu is still unclear. Therefore, this study aims to investigate whether PGC-1α participates in ECs apoptosis under high glucose condition. Human umbilical vein endothelial cells (HUVECs) were down-regulated PGC-1α expression by adenovirus-mediated PGC-1α specific siRNA (Ad-shPGC-1α) and exposed to high glucose. Cell viability, apoptosis, mitochondrial membrane permeability, apoptotic marker, reactive oxygen species (ROS), and expression of PGC-1α and VDAC isoforms were studied. Our results showed that high glucose-induced cell apoptosis was associated with an obvious decrease in PGC-1α expression. Lack of PGC-1α exacerbated high glucose-induced cell apoptosis, inner mitochondrial membrane permeabilization, mitochondrial cytochrome c release into cytoplasm and caspases activation; while further decreased cell viability and mitochondrial membrane potential. Analysis of apoptotic markers (Bcl-2, Bax), intracellular ROS and endoplasmic reticulum stress revealed that these mechanisms were not accounted for the effects of Ad-shPGC-1α on apoptosis. However, we found silencing PGC-1α further increased high glucose-induced VDAC1 expression. The pharmacological inhibition of VDAC1 with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibited the increased apoptosis in high glucose-treated PGC-1α knockdown cells. These findings strongly suggest that PGC-1α defect is one of the major mechanisms for ECs apoptosis under high glucose condition, and provide a novel strategy to prevent endothelial dysfunction in diabetes.

SIRT1 is a regulator in high glucose-induced inflammatory response in RAW264.7 cells

Sepsis is defined as a systemic inflammatory response syndrome that disorders the functions of host immune system, including the imbalance between pro- and anti-inflammatory responses mediated by immune macrophages. Sepsis could also induce acute hyperglycemia. Studies have shown that the silent mating type information regulation 2 homolog 1 (SIRT1), an NAD⁺-dependent deacetylase, mediates NF-κb deacetylation and inhibits its function. Therefore, SIRT1 is likely to play an important role in high glucose-mediated inflammatory signalings. Here we demonstrate that high glucose significantly downregulates both the mRNA and protein levels of SIRT1 and upregulates the mRNA level and the release of two pro-inflammatory cytokines, IL-1β and TNF-α, in RAW264.7 macrophages. Interestingly, the reduced level of SIRT1 by high glucose is remarkably upregulated by SIRT1 activator SRT1720, while the level and the release of IL-1β and TNF-α significantly decrease with the use of SRT1720. However, when the function of SIRT1 is inhibited by EX527 or its expression is suppressed by RNAi, the upregulated level and release of IL-1β and TNF-α by high glucose are further increased. Taken together, these findings collectively suggest that SIRT1 is an important regulator in many high glucose-related inflammatory diseases such as sepsis.

Histone acetyltransferase inhibitor C646 reverses epithelial to mesenchymal transition of human peritoneal mesothelial cells via blocking TGF-β1/Smad3 signaling pathway in vitro

Peritoneal fibrosis resulting from long-term peritoneal dialysis is a major cause of failure of peritoneal ultrafiltration function and main reason of dropout from peritoneal dialysis. Epithelial-mesenchymal transition (EMT) of peritoneal mesochelial cells (HPMCs) is a major contributor of peritoneal fibrosis. Recently, the association between histone acetylation and kinds of fibrosis including liver, lung and kidney fibrosis is well established. Thus, in this study we tried to profile whether histone acetylation is also operates EMT process in HPMCs and what's the regulatory mechanism. We established an EMT model of HPMCs through high glucose treatment. And hyperacetylation of H3 histone was found using western blot in EMT model. After treated with C646, a histone acetyltransferase (HAT) inhibitor, high glucose-induced EMT in HPMCs was counteracted. To further understand the molecular mechanism of C646 rescues high glucose-induced EMT, CHIP-qPCRwas used to examine the modulation of histone H3 acetylation at promoters of series signaling target genes. We found that the H3 acetylation level at TGF-β1 gene promoter was down-regulation by C646 treatment. Moreover, we also found that TGF-β1/Smad3 signaling was blocked. Hence, our results suggest that histone H3 acetylation activated TGF-β1/Smad3 signaling during EMT of HPMCs, and C646 can rescue the mesenchymal phenotype transition. These findings may provide a novel pathogenic mechanism and therapeutic target for peritoneal fibrosis.

Testosterone reduces AGTR1 expression to prevent β-cell and islet apoptosis from glucotoxicity

Hypogonadism in men is associated with an increased incidence of type 2 diabetes. Supplementation with testosterone has been shown to protect pancreatic β-cell against apoptosis due to toxic substances including streptozotocin and high glucose. One of the pathological mechanisms of glucose-induced pancreatic β-cell apoptosis is the induction of the local rennin-angiotensin-aldosterone system (RAAS). The role of testosterone in regulation of the pancreatic RAAS is still unknown. This study aims to investigate the protective action of testosterone against glucotoxicity-induced pancreatic β-cell apoptosis via alteration of the pancreatic RAAS pathway. Rat insulinoma cell line (INS-1) cells or isolated male mouse islets were cultured in basal and high-glucose media in the presence or absence of testosterone, losartan, and angiotensin II (Ang II), then cell apoptosis, cleaved caspase 3 expression, oxidative stress, and expression of angiotensin II type 1 receptor (AGTR1) and p47(phox) mRNA and protein were measured. Testosterone and losartan showed similar effects in reducing pancreatic β-cell apoptosis. Testosterone significantly reduced expression of AGTR1 protein in INS-1 cells cultured in high-glucose medium or high-glucose medium with Ang II. Testosterone decreased the expression of AGTR1 and p47(phox) mRNA and protein in comparison with levels in cells cultured in high-glucose medium alone. Furthermore, testosterone attenuated superoxide production when co-cultured with high-glucose medium. In contrast, when cultured in basal glucose, supplementation of testosterone did not have any effect on cell apoptosis, oxidative stress, and expression of AGT1R and p47(phox). In addition, high-glucose medium did not increase cleaved caspase 3 in AGTR1 knockdown experiments. Thus, our results indicated that testosterone prevents pancreatic β-cell apoptosis due to glucotoxicity through reduction of the expression of ATGR1 and its signaling pathway.

Protection of vascular endothelial cells from high glucose-induced cytotoxicity by emodin

Induction of endothelial cytotoxicity by hyperglycemia in diabetes has been widely accepted. Emodin is a natural anthraquinone in rhubarb used for treatment of diabetes, but its mechanism of action is not fully understood. This study aimed to examine the potential beneficial effects of emodin on endothelial cytotoxicity caused by high glucose milieu. Culture of human umbilical vein endothelial cells (HUVECs) with high concentrations of glucose resulted in damage to the cells, leading to decreased formazan products by 14-27%, reduced DNA contents by 12-19%, and increased hypodiploid apoptosis by 40-109%. These adverse effects of high glucose could be prevented to a large extent by co-culture with 3 μM of emodin which per se did not affect HUVECs viability. In addition, CCL5 expression of HUVECs cultured in high glucose medium was significantly elevated at both mRNA and protein levels, an effect abolished after treatment with emodin. Moreover, the enhanced adhesion of monocytes to HUVECs (2.1-2.2 fold over control) and elevated chemotaxis activities (2.3-2.4 fold over control) in HUVECs cultured in high glucose medium were completely reversed by emodin. Emodin also suppressed activation of p38 MAPK and ERK1/2 due to high glucose. Our data demonstrated that endothelial cytotoxicity occurred clearly when HUVECs were exposed to high glucose milieu and emodin was able to alleviate the impairments. The protective effects of emodin might be related to the inhibition of CCL5 expression and subsequent cell stress/inflammatory events possibly mediated by activation of MAPK signaling pathways.

Squamosamide Derivative FLZ Protects Pancreatic β-Cells from Glucotoxicity by Stimulating Akt-FOXO1 Pathway

Chronic hyperglycemia increases apoptosis and reduces glucose-stimulated insulin secretion. Although protective agents have been searched extensively, none has been found so far. Here we tested FLZ, a synthetic derivative of squamosamide from a Chinese herb, as a potential candidate for antiglucotoxicity in INS-1E cells and mouse islets. Chronic culture of β-cells in 30 mM glucose caused progressive reduction of cell viability, accompanied with increased apoptosis and reduced insulin secretion. These effects on apoptosis and insulin were reversed by FLZ in a dose-dependent manner. FLZ treatment also increased forkhead box O1 protein phosphorylation and reduced its nuclear location. On the contrary, FLZ increased pancreatic and duodenal homeobox-1 expression and its nuclear localization, an effect mediated by increased p-Akt. Consistently, Akt selective inhibitor MK-2206 completely abolished antiglucotoxicity effect of FLZ. Furthermore, FLZ treatment increased cytosolic ATP/ADP ratio. Taken together, our results suggest that FLZ could be a potential therapeutic agent to treat the hyperglycemia-induced β-cell failure.

Jak2/Stat1 pathway mediated tetrahydrobiopterin up-regulation contributes to nitric oxide overproduction in high-glucose cultured rat mesangial cells

Nitric oxide (NO) is crucial for the progression of early diabetic nephropathy (DN). It is important to clarify the mechanism for the production of NO in mesangial cells (MCs). In this study, the amounts/activities of related factors such as reactive oxygen species (ROS), NO, 3 isoforms of nitric oxide synthase (NOS), tetrahydrobiopterin (BH4), GTP cyclohydrolase I (GTPCH I), Jak2, and Stat1 were determined using high-glucose cultured rat MCs. The results showed that the production of BH4 under oxidative stress was strongly stimulated by its rate-limiting enzyme GTP cyclohydrolase, which increased the expression and activity of inducible NOS to facilitate NO synthesis. Furthermore, the relative quantities of activated-Jak2 and activated-Stat1 were increased. Therefore, Jak2/Stat1 pathway mediated BH4 up-regulation can contribute to excessive NO in high-glucose cultured MCs. Our results will be helpful for screening new targets to improve the therapy for early DN.

Glucagon-like peptide 1 stimulates insulin secretion via inhibiting RhoA/ROCK signaling and disassembling glucotoxicity-induced stress fibers

Chronic hyperglycemia leads to pancreatic β-cell dysfunction characterized by diminished glucose-stimulated insulin secretion (GSIS), but the precise cellular processes involved are largely unknown. Here we show that pancreatic β-cells chronically exposed to a high glucose level displayed substantially increased amounts of stress fibers compared with β-cells cultured at a low glucose level. β-Cells at high glucose were refractory to glucose-induced actin cytoskeleton remodeling and insulin secretion. Importantly, F-actin depolymerization by either cytochalasin B or latrunculin B restored glucotoxicity-diminished GSIS. The effects of glucotoxicity on increasing stress fibers and reducing GSIS were reversed by Y-27632, a Rho-associated kinase (ROCK)-specific inhibitor, which caused actin depolymerization and enhanced GSIS. Notably, glucagon-like peptide-1-(7-36) amide (GLP-1), a peptide hormone that stimulates GSIS at both normal and hyperglycemic conditions, also reversed glucotoxicity-induced increase of stress fibers and reduction of GSIS. In addition, GLP-1 inhibited glucotoxicity-induced activation of RhoA/ROCK and thereby resulted in actin depolymerization and potentiation of GSIS. Furthermore, this effect of GLP-1 was mimicked by cAMP-increasing agents forskolin and 3-isobutyl-1-methylxanthine as well as the protein kinase A agonist 6-Bnz-cAMP-AM whereas it was abolished by the protein kinase A inhibitor Rp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt. To establish a clinical relevance of our findings, we examined the association of genetic variants of RhoA/ROCK with metabolic traits in homeostasis model assessment index of insulin resistance. Several single-nucleotide polymorphisms in and around RHOA were associated with elevated fasting insulin and homeostasis model assessment index of insulin resistance, suggesting a possible role in metabolic dysregulation. Collectively these findings unravel a novel mechanism whereby GLP-1 potentiates glucotoxicity-diminished GSIS by depolymerizing F-actin cytoskeleton via protein kinase A-mediated inhibition of the RhoA-ROCK signaling pathway.

Role of caveolae in high glucose and TGF-β₁ induced fibronectin production in rat mesangial cells

Accumulation of extracellular matrix (ECM) in glomerular mesangium correlates with loss of renal function in diabetic nephropathy. However, the mechanisms underlying are still incompletely known. In the present study, we explored the role of caveolae in ECM production in rat mesangial cells (MCs) stimulated by high glucose or transforming growth factor-β1 (TGF-β1), and investigated the possible mechanisms. High glucose (HG) or TGF-β1 significantly increased collagen-1 and fibronectin expression at both mRNA and protein levels in time- course dependent manners, and simultaneously induced caveolin-1 tyrosine phosphorylation. Disruption of caveolae with Methyl-β-cyclodextrin (β-MCD) prevented HG and TGF-β1 induced caveolin-1 tyrosine phosphorylation, and attenuated fibronectin but not collagen-1 production. This effect of β-MCD on fibronectin production could be abolished by cholesterol, which restored HG and TGF-β1 induced caveolin-1 tyrosine phosphorylation. In addition, HG and TGF-β1 induced fibronectin production was attenuated by a caveolin-1 scaffold domain peptide. These findings indicate that mesangial cell caveolae regulate fibronectin production at least partly through caveolin-1 phosphorylation.

SGLT2 inhibitor lowers serum uric acid through alteration of uric acid transport activity in renal tubule by increased glycosuria

Sodium glucose cotransporter 2 (SGLT2) inhibitors have been reported to lower the serum uric acid (SUA) level. To elucidate the mechanism responsible for this reduction, SUA and the urinary excretion rate of uric acid (UE(UA)) were analysed after the oral administration of luseogliflozin, a SGLT2 inhibitor, to healthy subjects. After dosing, SUA decreased, and a negative correlation was observed between the SUA level and the UE(UA), suggesting that SUA decreased as a result of the increase in the UE(UA). The increase in UE(UA) was correlated with an increase in urinary D-glucose excretion, but not with the plasma luseogliflozin concentration. Additionally, in vitro transport experiments showed that luseogliflozin had no direct effect on the transporters involved in renal UA reabsorption. To explain that the increase in UE(UA) is likely due to glycosuria, the study focused on the facilitative glucose transporter 9 isoform 2 (GLUT9ΔN, SLC2A9b), which is expressed at the apical membrane of the kidney tubular cells and transports both UA and D-glucose. It was observed that the efflux of [(14) C]UA in Xenopus oocytes expressing the GLUT9 isoform 2 was trans-stimulated by 10 mm D-glucose, a high concentration of glucose that existed under SGLT2 inhibition. On the other hand, the uptake of [(14) C]UA by oocytes was cis-inhibited by 100 mm D-glucose, a concentration assumed to exist in collecting ducts. In conclusion, it was demonstrated that the UE(UA) could potentially be increased by luseogliflozin-induced glycosuria, with alterations of UA transport activity because of urinary glucose.

Estrogen prevents high-glucose-induced damage of retinal ganglion cells via mitochondrial pathway

BACKGROUND

Diabetic retinopathy (DR) is a leading cause of acquired blindness in adults. Previous research has shown that the apoptosis of retinal ganglion cells(RGCs) plays an important role in the initiation and development of diabetic retinopathy. The positive effect of estrogen on the nervous system is currently attracting increasing attention. In this study, we investigated whether17β-estradiolum (E2) has protective effects on RGCs in a high-glucose environment.

METHODS

The cell survival rates were measured by Cell Counting Kit-8, the apoptosis was detected by flow cytometry, the intracellular reactive oxygen species (ROS) levels were examined by immunofluorescence method, and the intracellular mitochondrial membrane potential was examined by confocal microscopy. The expression levels of cytochrome C, Bcl-2, and Bax were analyzed by Western blot method. The effect of estrogen receptor blocker tamoxifen on the RGCs was also evaluated.

RESULTS

It was found that E2 stabilizes the mitochondrial membrane potential, reduces intracellular ROS levels, up-regulates Bcl-2 expression, inhibits Bax expression, decreases the generation of cytochrome C, and finally reduces the apoptosis of RGC-5 cells in a high-glucose environment. These protective functions could be attributed to E2 receptors, which make E2 a prospective patent application candidate in the treatment of DR. Furthermore, when cells were pre-cultured with tamoxifen, we found that tamoxifen inhibited the shielding effects of E2.

CONCLUSION

E2 has a broad application prospect in the treatment of DR.

6,6'-bieckol isolated from Ecklonia cava protects oxidative stress through inhibiting expression of ROS and proinflammatory enzymes in high-glucose-induced human umbilical vein endothelial cells

Hyperglycemia-induced oxidative stress accelerates endothelial cell dysfunctions, which cause various complications of diabetes. The protective effects of 6,6'-bieckol (BEK), one of phlorotannin compound purified from Ecklonia cava against high-glucose-induced oxidative stress was investigated using human umbilical vein endothelial cells (HUVECs), which is susceptible to oxidative stress. High glucose (30 mM) treatment induced HUVECs' cell death, but BEK, at concentration 10 or 50 μg/ml, significantly inhibited the high-glucose-induced cytotoxicity. Furthermore, treatment with BEK dose-dependently decreased thiobarbituric acid reactive substances (TBARS), intracellular reactive oxygen species (ROS) generation, and nitric oxide level increased by high glucose. In addition, high glucose levels induced the overexpressions of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and nuclear factor-kappa B (NF-κB) proteins in HUVECs, but BEK treatment reduced the overexpressions of these proteins. These findings indicate that BEK is a potential therapeutic agent that will prevent diabetic endothelial dysfunction and related complications.

The protective effect of glycyrrhizic acid on renal tubular epithelial cell injury induced by high glucose

The aim of this study was to determine the beneficial effect of glycyrrhizic acid (GA) on type 2 diabetic nephropathy using renal tubular epithelial cell line (NRK-52E). The cells are divided into normal group (NG), high glucose group (HG), and treatment group (HG + GA). The methylthiazoletetrazolium (MTT) assay was used to detect the cell proliferation. Cell cycle analysis was performed using flow cytometry. Model driven architecture (MDA), reactive oxygen species (ROS) and superoxide dismutase (SOD) were also measured. Electron microscopy and histological were used to detect the changes in cell ultrastructure. The phosphorylation of AMP-activated protein kinase (AMPK), silent information regulator T1 (SIRT1), manganese-superoxide dismutase (Mn-SOD) and transforming growth factor-β1 (TGF-β1) were assessed by immunohistochemistry, immunofluorescence, and western blotting. Real-time fluorescent quantitative PCR (RT-qPCR) was used to measure Mn-SOD and PPARγ co-activator 1α (PGC-1a) mRNA. We find that high glucose increases NRK-52E cell proliferation and TGF-β1 expression, but decreases expression of AMPK, SIRT1 and Mn-SOD. These effects are significantly attenuated by GA. Our findings suggest that GA has protective effects against high glucose-induced cell proliferation and oxidative stress at least in part by increasing AMPK, SIRT1 and Mn-SOD expression in NRK-52E cells.

Hyperglycemia induces memory impairment linked to increased acetylcholinesterase activity in zebrafish (Danio rerio)

Diabetes mellitus, which causes hyperglycemia, affects the central nervous system and can impairs cognitive functions, such as memory. The aim of this study was to investigate the effects of hyperglycemia on memory as well as on the activity of acethylcholinesterase. Hyperglycemia was induced in adult zebrafish by immersion in glucose 111mM by 14 days. The animals were divided in 4 groups: control, glucose-treated, glucose-washout 7-days and glucose-washout 14-days. We evaluated the performance in inhibitory avoidance task and locomotor activity. We also determined acethylcholinesterase activity and gene expression from whole brain. In order to counteract the effect of hyperglycemia underlined by effects on acethylcholinesterase activity, we treated the animals with galantamine (0.05ng/g), an inhibitor of this enzyme. Also we evaluated the gene expression of insulin receptor and glucose transporter from zebrafish brain. The hyperglycemia promoted memory deficit in adult zebrafish, which can be explained by increased AChE activity. The ache mRNA levels from zebrafish brain were decrease in 111mM glucose group and returned to normal levels after 7 days of glucose withdrawal. Insulin receptors (insra-1, insra-2, insrb-1 and insrb-2) and glut-3 mRNA levels were not significantly changed. Our results also demonstrated that galantamine was able to reverse the memory deficit caused by hyperglycemia, demonstrating that these effects involve modulation of AChE activity. These data suggest that the memory impairment induced by hyperglycemia is underlined by the cholinergic dysfunction caused by the mechanisms involving the control of acetylcholinesterase function and gene expression.

AKAP150 mobilizes cPKC-dependent cardiac glucotoxicity

Activation of conventional PKCs (cPKC) is a key signaling that directs the cardiac toxicity of hyperglycemia. AKAP150, a scaffold protein of the A-kinase anchoring proteins (AKAPs) family, is less defined regarding its capability to anchor and regulate cardiac cPKC signaling. This study was designed to investigate the role of AKAP150 in cPKC-mediated cardiac glucotoxicity. In cardiac tissues from streptozotocin-induced diabetic rats and high-glucose-treated neonatal rat cardiomyocytes, both mRNA and protein levels of AKAP150 increased significantly, and marked elevations were observed in cPKC activity and both expression and phosphorylation levels of p65 NF-κB and p47(phox). AKAP150 knockdown was established via intramyocardial injection in vivo and transfection in vitro of adenovirus carrying AKAP150-targeted shRNA. Downregulation of AKAP150 reversed diabetes-induced diastolic dysfunction as manifested by decreased left ventricular end-diastolic diameter and early/late mitral diastolic wave ratio. AKAP150 inhibition also abrogated high-glucose-induced cardiomyocyte apoptosis (TUNEL staining and annexin V/propidium iodide flow cytometry) and oxidative stress (ROS production, NADPH oxidase activity, and lipid peroxidation). More importantly, reduced AKAP150 expression significantly inhibited high-glucose-induced membrane translocation and activation of cPKC and suppressed the increases in the phosphorylation of p65 NF-κB and p47(phox). Immunofluorescent coexpression and immunoprecipitation indicated enhanced anchoring of AKAP150 with cPKC within the plasma membrane under hyperglycemia, and AKAP150 preferentially colocalized and functionally bound with PKCα and -β isoforms. These results suggest that cardiac AKAP150 positively responds to hyperglycemia and enhances the efficiency of glucotoxicity signaling through a cPKC/p47(phox)/ROS pathway that induces myocardial dysfunction, cardiomyocyte apoptosis, and oxidative stress.

Glucotoxicity targets hepatic glucokinase in Zucker diabetic fatty rats, a model of type 2 diabetes associated with obesity

A loss of glucose effectiveness to suppress hepatic glucose production as well as increase hepatic glucose uptake and storage as glycogen is associated with a defective increase in glucose phosphorylation catalyzed by glucokinase (GK) in Zucker diabetic fatty (ZDF) rats. We extended these observations by investigating the role of persistent hyperglycemia (glucotoxicity) in the development of impaired hepatic GK activity in ZDF rats. We measured expression and localization of GK and GK regulatory protein (GKRP), translocation of GK, and hepatic glucose flux in response to a gastric mixed meal load (MMT) and hyperglycemic hyperinsulinemic clamp after 1 or 6 wk of treatment with the sodium-glucose transporter 2 inhibitor (canaglifrozin) that was used to correct the persistent hyperglycemia of ZDF rats. Defective augmentation of glucose phosphorylation in response to a rise in plasma glucose in ZDF rats was associated with the coresidency of GKRP with GK in the cytoplasm in the midstage of diabetes, which was followed by a decrease in GK protein levels due to impaired posttranscriptional processing in the late stage of diabetes. Correcting hyperglycemia from the middle diabetic stage normalized the rate of glucose phosphorylation by maintaining GK protein levels, restoring normal nuclear residency of GK and GKRP under basal conditions and normalizing translocation of GK from the nucleus to the cytoplasm, with GKRP remaining in the nucleus in response to a rise in plasma glucose. This improved the liver's metabolic ability to respond to hyperglycemic hyperinsulinemia. Glucotoxicity is responsible for loss of glucose effectiveness and is associated with altered GK regulation in the ZDF rat.

Neuroprotective effects of citicoline in in vitro models of retinal neurodegeneration

In recent years, citicoline has been the object of remarkable interest as a possible neuroprotectant. The aim of this study was to investigate if citicoline affected cell survival in primary retinal cultures and if it exerted neuroprotective activity in conditions modeling retinal neurodegeneration. Primary retinal cultures, obtained from rat embryos, were first treated with increasing concentrations of citicoline (up to 1000 μM) and analyzed in terms of apoptosis and caspase activation and characterized by immunocytochemistry to identify neuronal and glial cells. Subsequently, excitotoxic concentration of glutamate or High Glucose-containing cell culture medium (HG) was administered as well-known conditions modeling neurodegeneration. Glutamate or HG treatments were performed in the presence or not of citicoline. Neuronal degeneration was evaluated in terms of apoptosis and loss of synapses. The results showed that citicoline did not cause any damage to the retinal neuroglial population up to 1000 μM. At the concentration of 100 μM, it was able to counteract neuronal cell damage both in glutamate- and HG-treated retinal cultures by decreasing proapoptotic effects and contrasting synapse loss. These data confirm that citicoline can efficiently exert a neuroprotective activity. In addition, the results suggest that primary retinal cultures, under conditions inducing neurodegeneration, may represent a useful system to investigate citicoline neuroprotective mechanisms.

Endothelin-1 mediated high glucose-induced epithelial-mesenchymal transition in renal tubular cells

OBJECTIVE

The pathogenesis of interstitial fibrosis in diabetic nephropathy (DN) is an intractable problem without good therapy. Emerging evidence suggests that epithelial-mesenchymal transition (EMT) is an important mechanism for tubular epithelial cells undergoing profibrotic change in DN. Endothelin-1 (ET-1) is an important cytokine which can cause fibrogenesis and is reportedly involved in DN. However, the role of ET-1 in EMT in DN is unknown. The present study was designed to investigate the role of ET-1 in high glucose-induced EMT and the signaling pathway mediating the effect of ET-1 in renal tubular cells.

METHOD

Tubular epithelial cells (NRK52E) were treated with normal glucose (d-glucose 5.6mmol/L, NG), high glucose (30mmol/L, HG), high osmotic (d-glucose 5.6mmol/L+d-mannitol 24.4mmol/L), HG+ETA antagonist BQ123 (2μg/ml), ET-1, ET-1+ hypoxia inducible factor (HIF)-1α siRNA, CoCl2 (100μmol/L), CoCl2+HIF-1α siRNA or CoCl2+BQ123. The supernatant level of ET-1 was measured by ELISA and the expression of vimentin, E-cadherin and HIF-1α was detected by RT-PCR and western blot.

RESULT

The ET-1 level increased markedly in the supernatant of NRK52E incubated with HG. In NRK52E induced with HG or ET-1, the expression of vimentin was upregulated, whereas the expression of E-cadherin was downregulated. BQ123 attenuated HG- and CoCl2-induced EMT while HIF-1α siRNA did not affect ET-1 induced EMT.

CONCLUSIONS

High glucose induced ET-1 production that mediated the EMT induced by high glucose in renal tubular epithelial cells, and HIF-1α acted as the upstream signal to regulate ET-1.

[Salidroside attenuates high glucose-induced apoptosis in human umbilical vein endothelial cells via activating the Ca(2)+/CaM/CAMKIIδ/eNOS pathway]

OBJECTIVE

Endothelial oxidative stress plays an important role in the pathogenesis of cardiovascular disease. Salidroside, a phenylpropanoid glycoside isolated from Rhodiola rosea L, could exert potent antioxidant properties. In this study, we investigated the protective effects, and related mechanism of salidroside against high glucose (33 mmol/L)-induced cell damage in human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were cultured in normal glucose (5.5 mmol/L), high glucose (33 mmol/L), high salidroside (10 µg/ml+33 mmol/L glucose), moderate salidroside (4 µg/ml+33 mmol/L glucose), low salidroside (1 µg/ml+33 mmol/L glucose) and very low salidroside (0.1 µg/ml+33 mmol/L glucose) for 48 h. Cell viability, the level of malondialdehyde (MDA) , reactive oxygen species (ROS) , nitric oxide (NO) , [Ca(2)+]i, calmodulin (CaM) , calmodulin-dependent kinase (CaMK) IIδ, endothelial nitric oxide synthase (eNOS) , active caspase-3 protein expression and eNOS ser 1177 phosphorylation of HUVECs post various treatments were measured. The cell viability was assessed with MTT assay, and the level of ROS, and [Ca(2)+]i was analyzed using flow cytometry. Nitric oxide and MDA was detected by Nitric Oxide Assay Kit and MDA Assay Kit. Western blot was performed to detect the protein expressions of eNOS, active caspase-3 and eNOS ser 1177 phosphorylation.

RESULTS

Comparing to the normal glucose group, high glucose treatment increased the cell damage, the level of NO and [Ca(2)+]i (P < 0.05) , downregulated CAMKIIδ, eNOS expression and eNOS ser 1177 phosphorylation (P < 0.05), elevated the concentration of MDA and ROS (P < 0.05) in HUVECs. Salidroside treatment significantly attenuated high glucose-induce cell damage on cultured HUVECs in a dose-dependent manner. Comparing to the high glucose group, 10 µg/ml Salidroside significantly increased cell viability (P < 0.05) , inhibited high glucose-induced release of MDA , generation of ROS, active caspase 3 protein expression (P < 0.05) , upregulated the release of nitric oxide and [Ca(2)+]i by HUVECs (P < 0.05) , enhanced CaM, CAMKIIδ, eNOS expression and eNOS ser 1177 phosphorylation in HUVECs (P < 0.05) .

CONCLUSIONS

These findings suggeste that salidroside could attenuate high glucose induced apoptosis in HUVEC, partly through activating the Ca(2)+/CaM/CAMKIIδ/eNOS pathway.

Toxicity generated through inhibition of pyruvate carboxylase and carnitine palmitoyl transferase-1 is similar to high glucose/palmitate-induced glucolipotoxicity in INS-1 beta cells

This work was initiated to determine whether toxicity generated through inhibition of mitochondrial fuel metabolism is similar to high glucose/palmitate (HG/PA)-induced glucolipotoxicity. Influx of glucose and free fatty acids into the tricarboxylic acid (TCA) cycle was inhibited by treatment with the pyruvate carboxylase (PC) inhibitor phenylacetic acid (PAA) and carnitine palmitoyl transferase-1 (CPT-1) inhibitor etomoxir (Eto), or knockdown of PC and CPT-1. Treatment of PAA/Eto or knockdown of PC/CPT-1 induced apoptotic death in INS-1 beta cells. Similar to HG/PA treatment, PAA/Eto increased endoplasmic reticulum stress responses but decreased the Akt signal. JNK inhibitor or chemical chaperone was protective against both PAA/Eto- and HG/PA-induced cell death. All attempts to reduce [Ca²⁺](i), stimulate lipid metabolism, and increase the TCA cycle intermediate pool protected PAA/Eto-induced death as well as HG/PA-induced death. These data suggest that signals induced from impaired mitochondrial fuel metabolism play a critical role in HG/PA-induced glucolipotoxicity.

[Effect of sequoyitol on expression of NOX4 and eNOS induced with glucose in human umbilical vein endothelial cells]

OBJECTIVE

To investigate the protective effect and mechanism of sequoyitol (Sep) on high glucose-induced human umbilical vein endothelial cells (HUVECs) injury.

METHODS

HUVECs were cultured with high glucose (30 mmol/L) in the presence or absence of sequoyitol (0.1, 1 and 10 micromol/L) for 24 h. Cell proliferation was measured by BrdU marking and cell cycle was detected by flow cytometry. 2', 7'-dichlorofluorescein diacetate was used to evaluate intracellular reactive oxygen species (ROS) levels. The NO, malonydialdehyde (MDA) and H2O2 levels were determined by colorimetric method according to the manufacturer's instructions. The expression of endothelial nitric oxide synthase (eNOS) and NADPH oxidase 4 (NOX4) were measured by real-time PCR and Western blot.

RESULTS

In the present study, we found that sequoyitol pretreatment for 1 h significantly decreased cell injury, promoted cell proliferation. Meanwhile sequoyitol significantly down-regulated NOX4 expression and decreased the level of ROS, MDA and H2O2 and obviously increased NO levels and up-regulated eNOS expression.

CONCLUSION

Sequoyitol alleviates high glucose-induced cell injuries in HUVECs via inhibiting oxidative stress and up-regulating eNOS expression.