Effect Of High Glucose Levels Research Articles

English

An extract from the seeds of Trigonella foenum graecum (Fenugreek) was evaluated for its protective effect against hydrogen peroxide (H2O2) induced oxidation in normal sheep erythrocytes (red blood cells (RBCs)). RBCs, treated with increasing concentrations of 30% H2O2 along with fenugreek seed extract (FSE) were analyzed for hemolysis and lipid peroxidation. Sheep RBCs treated with increasing concentrations of glucose, to study effect of high glucose level or hyperglycemia on normal SRBC, were found to be more susceptible to lipid peroxidation than those from normal subjects. However, on treatment with FSE, the oxidative modifications in both the groups (RBCs treated with glucose and not treated with glucose) were found to reduce significantly. The inhibition of lipid peroxidation was concentration-dependent up to 100 μl of extract, which contained 0.75 mM gallic acid equivalent (GAE) of phenolic compounds. The total phenolic content in the extract was determined spectrophotometrically according to the Folin-Ciocalteau procedure and was expressed as mg or mM GAE. The results indicate that the extract of fenugreek seeds contains antioxidants and protects cellular structures from oxidative damage. These findings demonstrate the potent antioxidant properties of the fenugreek seeds.   Key words: Fenugreek seed extract (FSE), type II diabetes, osmofragility test, lipid peroxidation.

Hyperglycemia and xerostomia are key determinants of tooth decay in type 1 diabetic mice

Insulin-dependent type 1 diabetes mellitus (DM) and oral diseases are closely interrelated. Poor metabolic control in diabetics is associated with a high risk of gingivitis, periodontitis and tooth loss. Salivary flow declines in diabetics and patients suffer from xerostomia. Reduced saliva predisposes to enamel hypomineralization and caries formation; however, the mechanisms that initiate and lead to progression of tooth decay and periodontitis in type 1 DM have not been explored. To address this issue, we analyzed tooth morphology in Akita −/− mice that harbor a point mutation in the Ins2 insulin gene, which leads to progressive hyperglycemia. Mandibles from Akita −/− and wild-type littermates were analyzed by microCT, scanning EM and histology; teeth were examined for amelogenin (Amel) and ameloblastin (Ambn) expression. Mice were injected with pilocarpine to assess saliva production. As hyperglycemia may alter pulp repair, the effect of high glucose levels on the proliferation/differentiation of cultured MD10-F2 pulp cells was also analyzed. Results showed that Akita −/− mice at 6 weeks of age showed chalky white incisors that correlated with marked hyperglycemia and impaired saliva production. MicroCT of Akita −/− teeth revealed excessive enamel wearing and hypomineralization; immunostaining for Amel and Ambn was decreased. A striking feature was invasion of dentinal tubules with Streptococcus mitis and microabcesses that originated in the coronal pulp and progressed to pulp necrosis and periapical periodontitis. High levels of glucose also inhibited MD10-F2 cell proliferation and differentiation. Our findings provide the first evidence that hyperglycemia in combination with reduced saliva in a model of type1 DM leads to decreased enamel mineralization/matrix proteins and predisposes to excessive wearing and decay. Importantly, hyperglycemia adversely affects enamel matrix proteins and pulp repair. Early detection and treatment of hyperglycemia and hyposalivation may provide a useful strategy for preventing the dental complications of diabetes and promoting oral health in this population.

High glucose levels increase the expression of neurotrophic factors associated with p-p42/p44 MAPK in Schwann cells in vitro

Diabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes mellitus. One contributing factor to DPN is altered neurotrophism due to changes in the synthesis and expression of neurotrophins. Schwann cells (SCs) are the myelin-forming cells of the peripheral nervous system that promote nerve regeneration through the expression and secretion of neurotrophic factors (NTFs). Therefore, in this study, using SCs cultured in the presence of high levels of glucose for 24 h, with and without the p42/p44 mitogen-activated protein kinase (MAPK) inhibitor, PD98059, we investigated the effect of high glucose levels on SCs over a short period of time. The cultured cells were evaluated using 3(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay, Hoechst staining, immunocytochemistry, reverse transcriptase-polymerase chain reaction and western blot analysis. High glucose levels did not promote morphological abnormalities or decrease the viability of SCs. However, high glucose levels enhanced the expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and induced the activation of p42/p44 MAPK in cultured SCs in a dose-dependent manner. Additionally, the phosphorylation of p42/p44 MAPK may be associated with the expression of NTFs by SCs exposed to high glucose conditions; the excessive activation of p42/p44 MAPK inhibited the expression of NTFs. These observations demonstrate that exposure to high glucose levels lead to acutely elevated levels of NGF and BDNF in SCs over a short period of time, which may be involved in the p42/p44 MAPK pathway.

Glomerular VEGF resistance induced by PKCδ/SHP‐1 activation and contribution to diabetic nephropathy

This study characterizes the effect of glucose-induced activation of protein kinase Cδ (PKCδ) and Src homology-2 domain-containing phosphatase-1 (SHP-1) expression on vascular endothelial growth factor (VEGF) actions in glomerular podocytes in cultures and in glomeruli of diabetic rodents. Elevation of glucose levels induced PKCδ and p38 mitogen-activated protein kinase (p38 MAPK) to increase SHP-1 expression, increased podocyte apoptosis, and inhibited VEGF activation in podocytes and glomerular endothelial cells. The adverse effects of high glucose levels can be negated by molecular inhibitors of PKCδ, p38MAPK, and SHP-1 and only partially reduced by antioxidants and nuclear factor-κB (NF-κB) inhibitor. Increased PKCδ activation and SHP-1 expression correlated with loss of VEGF signaling and podocyte numbers in the glomeruli of diabetic rats and mice. In contrast, diabetic PKCδ-knockout (Prkcd(-/-)) mice did not exhibit activation of p38 MAPK and SHP-1 or inhibition of VEGF signaling in renal glomeruli. Functionally, diabetic Prkcd(-/-) mice had decreased expressions of TGFβ, VEGF, and extracellular matrix and less albuminuria than diabetic Prkcd(+/+) mice. Hyperglycemia and diabetes can cause glomerular podocyte apoptosis and endothelial dysfunction partly due to increased PKCδ/p38 MAPK activation and the expression of SHP-1 to cause VEGF resistance, independent of NF-κB activation.

High Glucose Promotes Pancreatic Cancer Cell Proliferation via the Induction of EGF Expression and Transactivation of EGFR

Multiple lines of evidence suggest that a large portion of pancreatic cancer patients suffer from either hyperglycemia or diabetes, both of which are characterized by high blood glucose level. However, the underlying biological mechanism of this phenomenon is largely unknown. In the present study, we demonstrated that the proliferative ability of two human pancreatic cancer cell lines, BxPC-3 and Panc-1, was upregulated by high glucose in a concentration-dependent manner. Furthermore, the promoting effect of high glucose levels on EGF transcription and secretion but not its receptors in these PC cell lines was detected by using an EGF-neutralizing antibody and RT-PCR. In addition, the EGFR transactivation is induced by high glucose levels in concentration- and time-dependent manners in PC cells in the presence of the EGF-neutralizing antibody. These results suggest that high glucose promotes pancreatic cancer cell proliferation via the induction of EGF expression and transactivation of EGFR. Our findings may provide new insight on the links between high glucose level and PC in terms of the molecular mechanism and reveal a novel therapeutic strategy for PC patients who simultaneously suffer from either diabetes or hyperglycemia.

High glucose concentrations alter the biomineralization process in human osteoblastic cells

Diabetes mellitus (DM) may alter bone remodeling, as osteopenia and osteoporosis are among the complications. Moreover, DM increases the risk and severity of chronic inflammatory periodontal disease, in which bone resorption occurs. Broad evidence suggests that chronic inflammation can contribute to the development of DM and its complications. Hyperglycemia is a hallmark of DM that may contribute to sustained inflammation by increasing proinflammatory cytokines, which are known to cause insulin resistance, via toll-like receptor (TLR)-4-mediated mechanisms. However, the mechanisms by which bone-related complications develop in DM are still unknown. Studies done on the effect of high glucose concentrations on osteoblast functions are contradictory because some suggest increases (although others suggest reductions) in the biomineralization process. Therefore, we evaluated the effect of high glucose levels on biomineralization and inflammation markers in a human osteoblastic cell line. Cells were treated with either physiological 5.5 mM or increasing concentrations of glucose up to 24 mM, and we determined the following: i) the quantity and quality of calcium-deposit crystals in culture and ii) the expression of the following: a) proteins associated with the process of biomineralization, b) the receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG), c) cytokines IL1, IL6, IL8, IL10, MCP-1 and TNF alpha, and d) TLR-2, -3, -4 and -9. Our results show that high glucose concentrations (12 mM and particularly 24 mM) alter the biomineralization process in osteoblastic cells and provoke the following: i) a rise in mineralization, ii) an increase in the mRNA expression of RANKL and a decrease of OPG, iii) an increase in the mRNA expression of osteocalcin, bone sialoprotein and the transcription factor Runx2, iv) a diminished quality of the mineral, and v) an increase in the expression of IL1beta, IL6, IL8, MCP-1 and IL10 mRNAs. In addition we found that both high glucose levels and hyperosmotic conditions provoked TLR-2, -3, -4 and -9 overexpression in osteoblastic cells, suggesting that they are susceptible to osmotic stress.

Impact of the U.S. Food and Drug Administration Cardiovascular Assessment Requirements on the Development of Novel Antidiabetes Drugs

Lingering questions related to cardiovascular (CV) safety of type 2 diabetes treatments resulted in new U.S. Food and Drug Administration (FDA) regulations requiring careful assessment of CV risk. These new requirements will provide the medical community with robust data to estimate CV risk associated with new therapeutic agents. To meet these requirements, phase 2 and 3 development programs will need to be larger and more comprehensive and will include high-risk patients. In addition, it is likely that most (if not all) newly approved drugs will be required to conduct post-approval CV safety outcome studies. The purpose of this article is to review the drivers for the new FDA requirements and how these new requirements will affect the development of novel antidiabetes drugs. The goals of antidiabetes treatment are to forestall the metabolic effects of high glucose levels and to prevent microvascular and macrovascular complications. Compelling data in type 2 diabetic patients support the conclusion that improved long-term glycemic control reduces the risk of microvascular complications (1,2). Based on several large outcome studies (e.g., the Diabetes Control Complications Trial and the UK Prospective Diabetes Study [UKPDS]), glycosylated hemoglobin (HbA1c) was established as a surrogate biomarker of glycemic control and therapeutic goals were set accordingly (3). Cardiovascular disease is the leading cause of death in patients with type 2 diabetes; more than 60% die of CV disease, and an even greater proportion have serious CV-related complications. Diabetes is associated with a two- to fourfold increase in the risk of coronary heart disease and death (4). Patients with type 2 diabetes who have not had a myocardial infarction (MI) have a risk of infarction similar to that of nondiabetic patients who have had a prior MI (5–7). Pooled data from patients with acute coronary syndrome (ACS) in …

Effect of high glucose levels on the calcification of vascular smooth muscle cells by inducing osteoblastic differentiation and intracellular calcium deposition via BMP-2/Cbfα-1 pathway

In this paper, we investigate the effect and the possible mechanism of high glucose levels on the calcification of human aortic smooth muscle cells (HASMCs). HASMCs were divided into four groups: normal glucose group (NG), osmolality control group (OC), high glucose group (HG, HASMCs culture medium containing 30 mmol/L glucose), and high glucose plus recombinant human Noggin protein (bone morphogenetic protein-2 (BMP-2) antagonist) group (HN). The mRNA levels and the protein expressions of BMP-2 and core binding factor alpha-1 (Cbfα-1) were measured by real-time quantitative polymerase chain reaction (PCR) and Western blot. After induced by 10 mmol/L β-glycerol phosphoric acid, cells were harvested for assessments of alkaline phosphatase (ALP) activities at Days 1, 2, and 3, and intracellular calcium contents at Days 7 and 14, respectively. High glucose levels increased the mRNA levels and the protein expressions of BMP-2 and Cbfα-1 (P<0.05). The expression of Cbfα-1 was partially blocked by Noggin protein (P<0.05), while BMP-2 was not (P>0.05). After being induced by β-glycerol phosphoric acid, high glucose levels increased the ALP activity [(48.63±1.03) vs. (41.42±2.28) U/mg protein, Day 3; P<0.05] and the intracellular calcium content [(2.76±0.09) vs. (1.75±0.07) μmol/mg protein, Day 14; P<0.05] in a time-dependent manner when compared with the NG group, while the ALP activity could not be blocked by Noggin protein [(48.63±1.03) vs. (47.37±0.97) U/mg protein, Day 3; P>0.05]. These results show that high glucose levels can evoke the calcification of HASMCs by inducing osteoblastic trans-differentiation and intracellular calcium deposition via the BMP-2/Cbfα-1 pathway, which can be partially blocked by Noggin protein.

Anserine inhibits carnosine degradation but in human serum carnosinase (CN1) is not correlated with histidine dipeptide concentration

Background We reported an association of a particular allele of the carnosinase ( CNDP1 Mannheim) gene with reduced serum carnosinase (CN1) activity and absence of nephropathy in diabetic patients. Carnosine protects against the adverse effects of high glucose levels but serum carnosine concentration was generally low. Methods We measured the concentration of two further histidine dipeptides, anserine and homocarnosine, via HPLC. CN1 activity was measured fluorometically and for concentration we developed a capture ELISA. Results We found an association between the CNDP1 Mannheim allele and reduced serum CN1 activity for all three dipeptides but no correlation to serum concentrations although anserine and homocarnosine inhibited carnosinase activity. Patients with liver cirrhosis have low CN1 activity (0.24 ± 0.17 μmol/ml/h, n = 7 males; normal range: 3.2 ± 1.1, n = 104; p < 0.05) and CN1 concentrations (2.3 ± 1.5 μg/ml; normal range: 24.9 ± 8.9, p < 0.05) but surprisingly, histidine dipeptide concentrations in serum are not increased compared to controls. Conclusions Serum histidine dipeptide concentrations are not correlated to CN1 activity. The protective effect of low CN1 activity might be related either to turnover of CN1 substrates or a protective function of dipeptides might be localized in other tissues.

Identification of the novel protein FAM172A, and its up-regulation by high glucose in human aortic smooth muscle cells

The family with sequence similarity 172, member A (FAM172A) is a hypothetical protein. We recently cloned the FAM172A gene from normal human aortic tissues. In a previous study we also showed that the FAM172A gene was up-regulated by high glucose levels in macrophages. In the present study, we further identified the FAM172A protein at the level of translation and studied the effects of high glucose levels on its expression in human aortic smooth muscle cells. The FAM172A gene was subcloned into the eukaryotic expression vectors, PDC315 and pEGFP-N2. The cloned sequence shows an open reading frame of 1251 nucleotides encoding a protein of 416 amino acids. We further expressed the recombinant FAM172A protein and generated rabbit anti-human FAM172A polyclonal antibodies. The FAM172A protein was identified for the first time at the translation level by Western blot analysis. Western blotting also demonstrated that the FAM172A protein could be detected in human aortic endothelial, human aortic smooth muscle cells and THP-1-derived macrophages, the highest expression being observed in the human aortic smooth muscle cells. By a combination of bioinformatics and confocal laser scanning microscopy, we found that the FAM172A protein in HEK293 cells, was mainly located in the nucleus, and that there was an Arb2 conserved domain in the FAM172A protein sequence. We also presented evidence that the FAM172 protein expression in human aortic smooth muscle cells was up-regulated by high glucose levels in a concentration-dependent and time-course manner. We speculated that as a novel protein, FAM172A could be involved in the pathogenesis of high glucose-induced vascular damage.

Response to Letter by O'Connell et al

Response: We acknowledge the interest of O'Connell et al regarding the GLIAS study1 which allows us to highlight some questions that, due to conciseness, were not completely addressed in the original publication. Hyperglycemia in acute ischemic stroke (IS) could be the reflection of many physiological and pathological mechanisms. But in our opinion, the key question is the deleterious effect of high glucose levels itself, not the possible causes of hyperglycemia, and we sought to look for the clinically significant glucose threshold independent of other factors that could influence those levels. It is true that reinstitution of feeding could influence glucose levels but, to minimize this effect, capillary glucose determinations were done before meals. Although glucose levels may have been influenced by stroke severity, we adjust for it in a multivariate regression analysis. O'Connell et al are also concerned by the exclusion criteria in …

The effect of short-term, high glucose concentration on endothelial cells and leukocytes in a 3D in vitro human vascular tissue model

Efforts to determine a link between diabetes and atherosclerosis have involved examining the effect of high glucose levels on the adhesion and migration of circulating leukocytes, mostly monocytes and T lymphocytes. Leukocyte differentiation and proliferation within the subendothelial space can also be investigated by the use of a 3D in vitro human vascular tissue model. This model was used to study the effect of short-term, high glucose concentration on certain cell behavior associated with the early stages of atherosclerosis. Samples were exposed to either a 30- or 5.6-mM glucose concentration for 9 h to represent either hyperglycemic or normoglycemic conditions, respectively. There was a significant increase in vascular cell adhesion molecule-1 expression on the endothelial cells exposed to a 30-mM compared to a 5.6-mM glucose concentration. There was no significant difference in either intercellular adhesion molecule-1 or E-selectin expression on the endothelial cells exposed to a 30-mM compared to a 5.6-mM glucose concentration. After the endothelium was exposed to 30 mM glucose concentration, there was a 70% increase in the number of monocytes (CD14(+)) migrating across the endothelium and a 28% increase in the number of these monocytes differentiating into macrophages, compared to cell migration and differentiation across the endothelium exposed to 5.6 mM glucose concentration. Also, for the endothelium exposed to 30 mM glucose concentration, there were nearly 2.5 times more T lymphocytes that migrated across the endothelium, along with significant cell proliferation, compared to cell migration across the endothelium exposed to 5.6 mM glucose concentration.

Effect of high glucose levels in human platelet NTPDase and 5′-nucleotidase activities

Objectives The objective of this work was to evaluate the effect of different glucose levels on the ATP, ADP and AMP hydrolysis in the platelets of diabetic, hypertensive and diabetic/hypertensive participants. Methods The activities of the enzymes NTPDase (ATP and ADP hydrolysis) and 5′-nucleotidase (AMP hydrolysis), and CD39 expression were analyzed in human blood platelets of diabetic (DM-2), hypertensive (HT) and diabetic/hypertensive (DM-2/HT) patients. To evaluate the interference of glucose and fructose in NTPDase and 5′-nucleotidase activities, experiments were performed with glucose, fructose and mannitol concentrations ranging from 5 to 30 mM in platelet-rich plasma (PRP). Pre-incubation times of 10, 120 min and 24 h were used. Results NTPDase and 5′-nucleotidase activities increased with increasing glucose and fructose concentrations ( P < 0.001) and the different times of pre-incubation did not interfere in ectonucleotidases activities ( P > 0.5). NTPDase and 5′-nucleotidase activities demonstrated a positive correlation between serum glucose levels and ATP and ADP hydrolysis in DM-2 and DM-2/HT patients. CD39 expression demonstrated that DM-2, HT and DM-2/HT groups presented a significant increase when compared to the control group ( P < 0.004). Conclusion The hydrolysis of adenine nucleotides is enhanced in platelets of patients with diabetes and hypertension. We observed that an increasing glucose concentration had a direct effect on ATP, ADP and AMP hydrolysis. Furthermore, CD39 expression was enhanced in all patients groups, indicating that these enzyme activities are related with diabetes and hypertension.

Lutein prevents the effect of high glucose levels on immune system cells in vivo and in vitro

Diabetic patients present an increased susceptibility to frequent and protracted infections. The recognition of an impaired immune system has implications for the diagnosis, treatment and outcome of infections. Nuclear Factor kappa B (NF-kappaB) is a redox sensitive transcription factor involved in immune response, cell proliferation and apoptosis that has been associated to the development of diabetic complications. Herein we study the effects of high glucose on oxidative stress markers (malondialdeyde and glutathione contents) and NF-kappaB activity in U937 cells (a human promonocytic cell line). Furtheremore effects of lutein treatment in lymphocytes from diabetic rats was studied. The results show that high glucose induces oxidative stress in immune system cells, both in vitro and in vivo, as well as an increase in their NF-kappaB activity. It is also showed that lutein, a natural antioxidant without hypoglycemiant properties, is able to prevent all the alterations observed. Thus, this study confirms the role of oxidative stress in the immune system impairment described in diabetes, and allows the proposal of antioxidants for the clinical management of the diabetes-associated susceptibility to infections.

Differential Analysis of Effect of High Glucose Level in the Development of Neuropathy in a Tissue Culture Model of Diabetes Mellitus: Role of Hyperosmolality

To analyse the contributions of metabolic toxicity of high glucose level and accompanying hyperosmolality to the development of diabetic neuropathy, mouse dorsal root ganglion (DRG) cultures were used. DRGs from postnatal day 7 mice were embedded in collagen gel and incubated in RPMI 1640 culture medium with increasing concentrations of glucose or equimolar amounts of mannitol which would create similar osmolalities. Outgrowth of axons from the peripheral nerve attached to DRG and migration of cells into the gel were quantified. The extent of cell death, apoptosis and mitosis among the migrating cells and apoptosis among DRG neurons following exposure to high glucose or mannitol were also evaluated. The growth of axons was almost equally affected by increasing concentrations of glucose or mannitol up to 395 mOsm/kg H (2)O. Number of migrating cells was close to control values with mannitol between 340-395 mOsm/kg H (2)O while high concentrations of glucose always decreased it. Exposure to high glucose or mannitol led to increased proportions of dead and apoptotic migrating cells and apoptotic DRG neurons. Mitotic activity was also negatively affected by high glucose or mannitol. While glucose proved significantly more detrimental to migrating cells than mannitol in the latter tests, the extent of apoptosis was similar among DRG neurons in both conditions. In conclusion, the contribution of hyperosmolality to the development of neuropathy in high glucose condition appears to be quite significant. The peripheral nerve cells and neurons, however, are differentially affected by hyperosmolality and metabolic toxicity of high glucose.

Increased renal gene transcription of protein kinase C-β in human diabetic nephropathy: relationship to long-term glycaemic control

Activation of protein kinase C (PKC) isoforms has been implicated as a central mediator in the pathogenesis of diabetic nephropathy. Although high glucose levels stimulate catalytic activity of PKC, the effects of high glucose levels on the expression of genes encoding PKC isoforms are unknown. We sought to determine whether in addition to activation, diabetes may lead to increased transcription of two PKC isoforms that have been implicated in the pathogenesis of diabetic nephropathy, PKC-alpha and PKC-beta. Recent advances in molecular biological techniques now permit quantitative analysis of mRNA from archival, formalin-fixed, paraffin-embedded tissue sections. RNA was extracted from scraped 6 microm sections of biopsy tissue, and PRKC-alpha and PRKC-beta (also known as PRKCA and PRKCB) mRNA measured using real-time PCR. Expression of genes encoding PKC isoforms was examined in renal biopsies (n=25) with classical histological features of diabetic nephropathy and compared with that in normal control tissue (n=6). Peptide localisation of PKC-alpha, PKC-beta and the activated forms phosphorylated PKC-alpha and -beta was also performed on matched paraffin-embedded sections of renal biopsies using immunohistochemistry. The effects of high glucose on PRKC-beta expression and peptide production in cultured human proximal tubular epithelial cells were assessed. Quantitative real-time PCR demonstrated a 9.9-fold increase in PRKC-beta mRNA in kidney biopsies of diabetic patients relative to control (p<0.001). No increase in PRKC-alpha expression was seen. In addition, a correlation between renal PRKC-beta mRNA and HbA(1c) was observed in diabetic patients (r=0.63, p<0.05). There was co-localisation of PKC-beta and phospho-PKC-beta predominantly to proximal tubules. A 60% increase in PRKC-beta mRNA and peptide in cultured human proximal tubular epithelial cells exposed to high glucose (p<0.05) was seen in vitro. PKC-beta is upregulated at the gene expression level in human diabetic nephropathy. PRKC-beta mRNA correlates closely with serum HbA(1c), possibly partially explaining the relationship between glycaemic control and progression of diabetic nephropathy. Archival human tissue provides a valuable resource for molecular analyses.

Synergistic effect of high glucose and ANG II on proliferation of mouse embryonic stem cells: Involvement of PKC and MAPKs as well as AT1 receptor

This study examined the synergistic effect of high glucose levels and ANG II on proliferation and its related signal pathways using mouse embryonic stem (ES) cells. The combined use of a high glucose concentration (25 mM) and ANG II increased the level of [3H]thymidine/BrdU incorporation, and the number of cells compared with either treatment alone. Each treatment with high glucose or ANG II increased the cell population in the S phase compared with control, and the combined treatment of a high glucose concentration and ANG II significantly increased the number of cells in the S phase according to FACS analysis. Moreover, the high glucose-induced increase in [3H]thymidine incorporation was blocked by inhibiting the ANG II type 1 (AT1) receptor. The combined high glucose and ANG II significantly increased the STAT3 phosphorylation compared with high glucose or ANG II alone. ANG II stimulated the influx of Ca2+ in 25 mM glucose compared with 5 mM glucose. High glucose levels increase the level of PKC alpha, epsilon, and zeta translocation from the cytosol to the membrane fraction. In an examination of other signal pathways, the combined treatment significantly increased the level of p44/42, p38 MAPKs phosphorylation compared with either treatment alone. Indeed, the combined treatment increased the mRNA expression level of the protooncogenes and cell cycle regulatory proteins. In conclusion, the combined treatment of a high glucose concentration and ANG II had a synergistic effect in stimulating mouse ES cell proliferation through the Ca2+/PKC, MAPKs, and the AT1 receptor.

A novel mechanism of action for statins against diabetes-induced oxidative stress

Atorvastatin exerts beneficial vascular effects in diabetes, but the underlying mechanisms are yet to be elucidated. The aim of the present study was to determine whether Rac-1 is involved in the effect of atorvastatin on oxidative stress and vascular dysfunction. Using human aortic endothelial cells (HAECs) we evaluated the effect of high glucose levels on peroxide production by dihydrodichlorofluorescein and on Rac-1 activity using immunocytochemistry to detect Rac-1 translocation to the membrane. We evaluated vascular function, peroxide production by dihydroethidium and NADPH oxidase activity in vessels from atorvastatin-treated mice. Rac-1 activity was also assessed, both by immunoprecipitation of the Rac-p21-activated kinase complex and by analysis of Rac-1 translocation to the membrane. These experiments were also conducted in vessels infected with an adenoviral vector carrying a constitutively active mutant of Rac-1. In HAECs exposed to high glucose levels, atorvastatin prevented oxidative stress, and this protection was associated with impaired Rac-1 activation. This effect was also observed in a murine model of diabetes mellitus. More importantly, the addition of geranylgeranyl pyrophosphate (GGPP) blocked the effects of atorvastatin in both glucose-exposed HAECs and diabetic vessels. Atorvastatin failed to afford protection against vascular abnormalities in the presence of a constitutively active mutant of Rac-1. The results of this study demonstrate that the vascular antioxidant effect of atorvastatin in diabetes is mediated through inhibition of Rac-1 via a reduction in GGPP. Thus, selective Rac-1 inhibition should be considered in the design of novel pharmacological strategies to reduce the impact of diabetes mellitus on vascular function.

Heterogeneous Nuclear Ribonucleoprotein K Modulates Angiotensinogen Gene Expression in Kidney Cells

The present studies aimed to identify the 70-kDa nuclear protein that binds to an insulin-responsive element in the rat angiotensinogen gene promoter and to define its action on angiotensinogen gene expression. Nuclear proteins were isolated from rat kidney proximal tubular cells and subjected to two-dimensional electrophoresis. The 70-kDa nuclear protein was detected by Southwestern blotting and subsequently identified by mass spectrometry, which revealed that it was identical to 65-kDa heterogeneous nuclear ribonucleoprotein K (hnRNP K). hnRNP K bound to the insulin-responsive element of the rat angiotensinogen gene was revealed by a gel mobility shift assay and chromatin immunoprecipitation assay. hnRNP K inhibited angiotensinogen mRNA expression and promoter activity. In contrast, hnRNP K down-expression by small interference RNA enhanced angiotensinogen mRNA expression. Moreover, hnRNP K interacted with hnRNP F in pulldown and co-immunoprecipitation assays. Co-transfection of hnRNP K and hnRNP F further suppressed angiotensinogen mRNA expression. Finally, in vitro and in vivo studies demonstrated that high glucose increases and insulin inhibits hnRNP K expression in rat kidney proximal tubular cells. In conclusion, our experiments revealed that hnRNP K is a nuclear protein that binds to the insulin-responsive element of the rat angiotensinogen gene promoter and modulates angiotensinogen gene transcription in the kidney.

Carnosine as a Protective Factor in Diabetic Nephropathy

The risk of diabetic nephropathy is partially genetically determined. Diabetic nephropathy is linked to a gene locus on chromosome 18q22.3-q23. We aimed to identify the causative gene on chromosome 18 and to study the mechanism by which the product of this gene could be involved in the development of diabetic nephropathy. DNA polymorphisms were determined in 135 case (diabetic nephropathy) and 107 control (diabetes without nephropathy) subjects. The effect of carnosine on the production of extracellular matrix components and transforming growth factor-beta (TGF-beta) after exposure to 5 and 25 mmol/l d-glucose was studied in cultured human podocytes and mesangial cells, respectively. A trinucleotide repeat in exon 2 of the CNDP1 gene, coding for a leucine repeat in the leader peptide of the carnosinase-1 precursor, was associated with nephropathy. The shortest allelic form (CNDP1 Mannheim) was more common in the absence of nephropathy (P = 0.0028, odds ratio 2.56 [95% CI 1.36-4.84]) and was associated with lower serum carnosinase levels. Carnosine inhibited the increased production of fibronectin and collagen type VI in podocytes and the increased production of TGF-beta in mesangial cells induced by 25 mmol/l glucose. Diabetic patients with the CNDP1 Mannheim variant are less susceptible for nephropathy. Carnosine protects against the adverse effects of high glucose levels on renal cells.