Glucose regulates interleukin-8 production in aortic endothelial cells through activation of the p38 mitogen-activated protein kinase pathway in diabetes

Regulation of blood-retinal barrier cell-junctions in diabetic retinopathy

Loss of the blood-retinal barrier (BRB) integrity and subsequent damage to the neurovascular unit in the retina are the underlying reasons for diabetic retinopathy (DR). Damage to BRB eventually leads to severe visual impairment in the absence of prompt intervention. Diabetic macular edema and proliferative DR are the advanced stages of the disease where BRB integrity is altered. Primary mechanisms contributing to BRB dysfunction include loss of cell-cell barrier junctions, vascular endothelial growth factor, advanced glycation end products-induced damage, and oxidative stress. Although much is known about the involvement of adherens and tight-junction proteins in the regulation of vascular permeability in various diseases, there is a significant gap in our knowledge on the junctional proteins expressed in the BRB and how BRB function is modulated in the diabetic retina. In this review article, we present our current understanding of the molecular composition of BRB, the changes in the BRB junctional protein turnover in DR, and how BRB functional modulation affects vascular permeability and macular edema in the diabetic retina.

Methylglyoxal triggers human aortic endothelial cell dysfunction via modulation of the KATP/MAPK pathway

Endothelial dysfunction is a key risk factor in diabetes-related multiorgan damage. Methylglyoxal (MGO), a highly reactive dicarbonyl generated primarily as a by-product of glycolysis, is increased in both type 1 and type 2 diabetic patients. MGO can rapidly bind with proteins, nucleic acids, and lipids, resulting in structural and functional changes. MGO can also form advanced glycation end products (AGEs). How MGO causes endothelial cell dysfunction, however, is not clear. Human aortic endothelial cells (HAECs) from healthy (H-HAECs) and type 2 diabetic (D-HAECs) donors were cultured in endothelial growth medium (EGM-2). D-HAECs demonstrated impaired network formation (on Matrigel) and proliferation (MTT assay), as well as increased apoptosis (caspase-3/7 activity and TUNEL staining), compared with H-HAECs. High glucose (25 mM) or AGEs (200 ng/ml) did not induce such immediate, detrimental effects as MGO (10 µM). H-HAECs were treated with MGO (10 µM) for 24 h with or without the ATP-sensitive potassium (K_ATP) channel antagonist glibenclamide (1 µM). MGO significantly impaired H-HAEC network formation and proliferation and induced cell apoptosis, which was reversed by glibenclamide. Furthermore, siRNA against the K_ATP channel protein Kir6.1 significantly inhibited endothelial cell function at basal status but rescued impaired endothelial cell function upon MGO exposure. Meanwhile, activation of MAPK pathways p38 kinase, c-Jun NH²-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) (determined by Western blot analyses of their phosphorylated forms, p-JNK, p-p38, and p-ERK) in D-HAECs were significantly enhanced compared with those in H-HAECs. MGO exposure enhanced the activation of all three MAPK pathways in H-HAECs, whereas glibenclamide reversed the activation of p-stress-activated protein kinase/JNK induced by MGO. Glyoxalase-1 (GLO1) is the endogenous MGO-detoxifying enzyme. In healthy mice that received an inhibitor of GLO1, MGO deposition in aortic wall was enhanced and endothelial cell sprouting from isolated aortic segment was significantly inhibited. Our data suggest that MGO triggers endothelial cell dysfunction by activating the JNK/p38 MAPK pathway. This effect arises partly through activation of K_ATP channels. By understanding how MGO induces endothelial dysfunction, our study may provide useful information for developing MGO-targeted interventions to treat vascular disorders in diabetes.

Acute Insulin Resistance in Myocardial Ischemia: Causes and Consequences

Diabetes mellitus is associated with increased risk for cardiovascular mortality because of multiple pathophysiologic mechanisms. Acute stress-induced hyper-glycemia during acute myocardial infarction has gained much attention, as blood glucose levels seem to be an independent risk factor for acute myocardial infarction–related death. Clinical studies that identify stress-induced hyperglycemia as a risk factor are reviewed and its causes are discussed. They can be summarized as the consequence of acute insulin resistance, which in its turn is caused by stress hormones and by proinflammatory cytokines. Hyperglycemia causes the release of proinflammatory cytokines, the induction of reactive radicals, alterations in cardiovascular substrate metabolism, and propagation of coagulation and apoptosis. These all have harmful effects during and after acute myocardial infarction. Recommendations are for strict glycemic control in hyperglycemic patients with acute myocar-dial infarction, although the target glucose level is still a subject of debate.

High glucose-induced oxidative stress increases IL-8 production in human gingival epithelial cells

OBJECTIVE

Diabetes is often associated with increased prevalence and severity of periodontal disease. We hypothesized that gingival epithelial cells modify periodontal disease progression and predicted that hyperglycemia would activate an inflammatory response in human gingival epithelial cells (HGECs).

MATERIALS AND METHODS

We tested our hypothesis in immortalized HGECs (epi 4 cells) isolated from periodontal tissue and transfected with the simian virus 40 T antigen. The epi 4 cells were cultured in high (25 mM, HG) and normal (6 mM, NG) glucose conditions.

RESULTS

The epi 4 cells showed increased interleukin-8 (IL-8) protein secretion and mRNA expression when cultured in HG, compared with in NG. These effects were not associated with increased cell proliferation and were not observed in a hyperosmolar control group (normal glucose with 19 mM mannitol). Increased IL-8 secretion in HG was inhibited by pretreatment with an antioxidant, N-acetylcysteine, or a protein kinase C inhibitor, Ro31-8220. Hyperglycemia did not affect IL-8 secretion by gingival fibroblasts or periodontal ligament cells. In epi 4 cells, hyperglycemia also induced expression of toll-like receptor 2 (TLR2) but not TLR4.

CONCLUSION

These findings suggest a potential participation of epithelial cells in periodontal disease during diabetes by evoking an excessive host inflammatory response.

Advanced Glycation End Products Impair Glucose-Stimulated Insulin Secretion of a Pancreatic β-Cell Line INS-1-3 by Disturbance of Microtubule Cytoskeleton via p38/MAPK Activation

Advanced glycation end products (AGEs) are believed to be involved in diverse complications of diabetes mellitus. Overexposure to AGEs of pancreatic β-cells leads to decreased insulin secretion and cell apoptosis. Here, to understand the cytotoxicity of AGEs to pancreatic β-cells, we used INS-1-3 cells as a β-cell model to address this question, which was a subclone of INS-1 cells and exhibited high level of insulin expression and high sensitivity to glucose stimulation. Exposed to large dose of AGEs, even though more insulin was synthesized, its secretion was significantly reduced from INS-1-3 cells. Further, AGEs treatment led to a time-dependent increase of depolymerized microtubules, which was accompanied by an increase of activated p38/MAPK in INS-1-3 cells. Pharmacological inhibition of p38/MAPK by SB202190 reversed microtubule depolymerization to a stabilized polymerization status but could not rescue the reduction of insulin release caused by AGEs. Taken together, these results suggest a novel role of AGEs-induced impairment of insulin secretion, which is partially due to a disturbance of microtubule dynamics that resulted from an activation of the p38/MAPK pathway.

Serum level of Interleukin-8 in subjects with diabetes, diabetes plus oral lichen planus, and oral lichen planus: A biochemical study

BACKGROUND

Correlation between diabetes mellitus (DM) and oral lichen planus (OLP) seems probable. Since Interleukin-8 (IL-8) is an important inflammatory mediator involved in both conditions, this study aimed to measure and compare the serum level of IL-8 in DM, OLP, and DM + OLP patients in comparison with healthy individuals.

MATERIALS AND METHODS

This cross sectional study was conducted on 75 patients (30 OLP, 5 OLP and type II DM, 20 type II DM, and 20 healthy controls). Serum levels of IL-8, fasting blood sugar (FBS) and 2-h postprandial blood sugar were measured in the four groups. Data were analyzed using SPSS version 20 by one-way ANOVA and post_hocleast significant difference test.

RESULTS

Type II DM patients with OLP had the highest mean serum level of IL-8 followed by OLP, DM and control groups, respectively. Pairwise comparison of groups revealed significant differences in serum IL-8 between the control and OLP and also control and OLP+DM (P < 0.05) groups. No other significant differences were noted. The mean levels of FBS and 2-h postprandial blood sugar were the highest in OLP+DM patients followed by DM, OLP and control groups, respectively.

CONCLUSION

The ascending trend of serum level of IL-8 in the control, DM, OLP, and DM+OLP patients may indicate the role of this factor in the pathogenesis of DM and OLP. Moreover, it may play a synergistic role in patients suffering from both conditions.

Protective effects of genistein in homocysteine-induced endothelial cell inflammatory injury

Hyperhomocysteinemia is a risk factor for cardiovascular disease and the mechanism of homocysteine (HCY)-induced vascular endothelial cell injury has been intensively studied for many years. Recently, a large number of studies have shown inhibitory effects of genistein (GEN), a soy isoflavone, in the process of endothelial cell injury. In the present study, the protective effects of GEN in HCY-induced endothelial cell inflammatory injury were investigated. A model of HCY-induced endothelial cell (ECV-304) inflammatory injury was established in vitro, and the protective effect of GEN in this procession was explored. According to our results, GEN protected HCY-induced endothelial cell from viability decreases, meanwhile prevented the changes of cell morphology and the production of reactive oxygen species (ROS). The expression of NF-kB P-65, IL-6, and ICAM-1 was all down-regulated. During the HCY-induced endothelial cell injury, the endothelial cell apoptosis and proliferation disorder were alleviated. Therefore, we conclude that HCY-induced endothelial cell inflammatory injury could be blocked by GEN. The present findings suggest that GEN protects HCY-induced endothelial cell inflammatory injury may through reducing the release of ROS, inhibiting NF-kB activation, down-regulating the expression of cytokine IL-6 and adhesion molecules ICAM-1, avoiding inflammatory cells and platelet adhesion, accordingly, leading to a balance of endothelial cell proliferation and apoptosis.

Luteolin protects against vascular inflammation in mice and TNF-alpha-induced monocyte adhesion to endothelial cells via suppressing IΚBα/NF-κB signaling pathway

Vascular inflammation plays a significant role in the pathogenesis of atherosclerosis. Luteolin, a naturally occurring flavonoid present in many medicinal plants and some commonly consumed fruits and vegetables, has received wide attention for its potential to improve vascular function in vitro. However, its effect in vivo and the molecular mechanism of luteolin at physiological concentrations remain unclear. Here, we report that luteolin as low as 0.5 μM significantly inhibited tumor necrosis factor (TNF)-α-induced adhesion of monocytes to human EA.hy 926 endothelial cells, a key event in triggering vascular inflammation. Luteolin potently suppressed TNF-α-induced expression of the chemokine monocyte chemotactic protein-1 (MCP-1) and adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), key mediators involved in enhancing endothelial cell-monocyte interaction. Furthermore, luteolin inhibited TNF-α-induced nuclear factor (NF)-κB transcriptional activity, IκBα degradation, expression of IκB kinase β and subsequent NF-κB p65 nuclear translocation in endothelial cells, suggesting that luteolin can inhibit inflammation by suppressing NF-κB signaling. In an animal study, C57BL/6 mice were fed a diet containing 0% or 0.6% luteolin for 3 weeks, and luteolin supplementation greatly suppressed TNF-α-induced increase in circulating levels of MCP-1/JE, CXCL1/KC and sICAM-1 in C57BL/6 mice. Consistently, dietary intake of luteolin significantly reduced TNF-α-stimulated adhesion of monocytes to aortic endothelial cells ex vivo. Histology shows that luteolin treatment prevented the eruption of endothelial lining in the intima layer of the aorta and preserved elastin fibers' delicate organization as shown by Verhoeff-Van Gieson staining. Immunohistochemistry studies further show that luteolin treatment also reduced VCAM-1 and monocyte-derived F4/80-positive macrophages in the aorta of TNF-α-treated mice. In conclusion, luteolin protects against TNF-α-induced vascular inflammation in both in vitro and in vivo models. This anti-inflammatory effect of luteolin may be mediated via inhibition of the NF-κB-mediated pathway.

Sulforaphane reduces vascular inflammation in mice and prevents TNF-α-induced monocyte adhesion to primary endothelial cells through interfering with the NF-κB pathway

Sulforaphane, a naturally occurring isothiocyanate present in cruciferous vegetables, has received wide attention for its potential to improve vascular function in vitro. However, its effect in vivo and the molecular mechanism of sulforaphane at physiological concentrations remain unclear. Here, we report that a sulforaphane concentration as low as 0.5 μM significantly inhibited tumor necrosis factor-α (TNF-α)-induced adhesion of monocytes to human umbilical vein endothelial cells, a key event in the pathogenesis of atherosclerosis both in static and under flow conditions. Such physiological concentrations of sulforaphane also significantly suppressed TNF-α-induced production of monocyte chemotactic protein-1 and adhesion molecules including soluble vascular adhesion molecule-1 and soluble E-selectin, key mediators in the regulation of enhanced endothelial cell-monocyte interaction. Furthermore, sulforaphane inhibited TNF-α-induced nuclear factor (NF)-κB transcriptional activity, Inhibitor of NF-κB alpha (IκBα) degradation and subsequent NF-κB p65 nuclear translocation in endothelial cells, suggesting that sulforaphane can inhibit inflammation by suppressing NF-κB signaling. In an animal study, sulforaphane (300 ppm) in a mouse diet significantly abolished TNF-α-increased ex vivo monocyte adhesion and circulating adhesion molecules and chemokines in C57BL/6 mice. Histology showed that sulforaphane treatment significantly prevented the eruption of endothelial lining in the intima layer of the aorta and preserved elastin fibers' delicate organization, as shown by Verhoeff-van Gieson staining. Immunohistochemistry studies showed that sulforaphane treatment also reduced vascular adhesion molecule-1 and monocyte-derived F4/80-positive macrophages in the aorta of TNF-α-treated mice. In conclusion, sulforaphane at physiological concentrations protects against TNF-α-induced vascular endothelial inflammation, in both in vitro and in vivo models. This anti-inflammatory effect of sulforaphane may be, at least in part, associated with interfering with the NF-κB pathway.

Canna indica L. attenuates high-glucose- and lipopolysaccharide-induced inflammatory mediators in monocyte/macrophage

ETHNOPHARMACOLOGICAL RELEVANCE

Canna indica L. (CI) has been widely used as a folklore medicine in tropical and subtropical areas with beneficial effects in numerous diseases, including infection, rheumatism, hepatitis, and it has also been identified as an antioxidant.

MATERIALS AND METHODS

The present study aimed to investigate the effect of Canna indica CI ethanolic extract (CIE) on productions of nitric oxide (NO), prostaglandin E2 (PGE2), and interleukin-1β (IL-1β) in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. In addition, the effects of CIE in high glucose (HG)-induced U937 monocytes on mRNA expressions of IL-8 and monocyte chemoattractant protein-1 (MCP-1), and regulation of mitogen-activated protein kinase (MAPK) pathways were also identified.

RESULTS

CIE was found to inhibit the production of inflammatory mediators including NO, IL-1β, and PGE2 from LPS-induced RAW 264.7 macrophages. The increases in HG-induced mRNA expressions of IL-8 and MCP-1 were also significantly inhibited by CIE. Stimulation of HG in U937 monocytes resulted in activation of p38 MAPK, ERK1/2, and JNK. However, CIE treatment significantly decreased phosphorylation of p38 MAPK, ERK1/2, and JNK.

CONCLUSION

The present study demonstrated that CIE suppressed the LPS-induced inflammatory mediator production and also inhibited HG-induced inflammatory mediator expression by the regulation of MAPK pathway.

Genistein inhibits TNF-α-induced endothelial inflammation through the protein kinase pathway A and improves vascular inflammation in C57BL/6 mice

Genistein, a soy isoflavone, has received wide attention for its potential to improve vascular function, but the mechanism of this effect is unclear. Here, we report that genistein at physiological concentrations (0.1 μM-5 μM) significantly inhibited TNF-α-induced adhesion of monocytes to human umbilical vein endothelial cells, a key event in the pathogenesis of atherosclerosis. Genistein also significantly suppressed TNF-α-induced production of adhesion molecules and chemokines such as sICAM-1, sVCAM-1, sE-Selectin, MCP-1 and IL-8, which play key role in the firm adhesion of monocytes to activated endothelial cells (ECs). Genistein at physiologically relevant concentrations didn't significantly induce antioxidant enzyme activities or scavenge free radicals. Further, blocking the estrogen receptors (ERs) in ECs didn't alter the preventive effect of genistein on endothelial inflammation. However, inhibition of protein kinase A (PKA) significantly attenuated the inhibitory effects of genistein on TNF-α-induced monocyte adhesion to ECs as well as the production of MCP-1 and IL-8. In animal study, dietary genistein significantly suppressed TNF-α-induced increase in circulating chemokines and adhesion molecules in C57BL/6 mice. Genistein treatment also reduced VCAM-1 and monocytes-derived F4/80-positive macrophages in the aorta of TNF-α-treated mice. In conclusion, genistein protects against TNF-α-induced vascular endothelial inflammation both in vitro and in vivo models. This anti-inflammatory effect of genistein is independent of the ER-mediated signaling machinery or antioxidant activity, but mediated via the PKA signaling pathway.

Ginkgo biloba extract reduces high-glucose-induced endothelial reactive oxygen species generation and cell adhesion molecule expression by enhancing HO-1 expression via Akt/eNOS and p38 MAP kinase pathways

AIM

Hyperglycemia is one of the major risk factors leading to vascular complications in clinical diabetes mellitus. Ginkgo biloba extract (GBE), an antioxidant herbal medicine, possesses anti-inflammatory effects. We examined whether GBE can reduce high glucose-induced endothelial adhesiveness to monocytes, an in vitro sign mimicking in vivo early atherogenesis, through selective regulation of heme oxygenase (HO)-1 expression.

METHODS

Human aortic endothelial cells (HAECs) were cultured with normal glucose or high glucose (25 mM) for 4 days and subsequently combined with GBE (EGb761, Dr. Willmar Schwabe, Karlsruhe, Germany) treatment in the last 18 h of the 4-day period. The endothelial reactive oxygen species (ROS) generation, adhesion molecule expression and the adhesiveness to monocytes were examined. The specific signal pathways such as HO-1 were also examined.

RESULTS

High glucose increased ROS generation, adhesion molecule expression and the adhesiveness to monocytes in HAECs. These high glucose-induced phenomena could be suppressed by GBE (100 μg/ml)-induced HO-1 expression in a dose-dependent and time-dependent manner. In addition, jun N-terminal kinases inhibitor or phosphoinositide 3 kinase inhibitor could reduce GBE-induced HO-1 expression. Furthermore, HO-1 inhibitor, HO-1 siRNA, endothelial nitric oxide synthase (eNOS) siRNA, or nuclear factor erythroid 2-related factor (Nrf) 2 siRNA blocked the cytoprotective effects of GBE. Meanwhile, p38/mitogen-activated protein kinase (MAPK) inhibitor could also reduce the effects of GBE on HO-1 induction.

CONCLUSION

GBE could reduce high glucose-induced endothelial adhesion via enhancing HO-1 expression through the Akt/eNOS and p38/MAPK pathways. Our findings suggest a potential strategy targeting on HO-1 induction by GBE for endothelial protection in the presence of high glucose such as that in diabetes mellitus.

The expression of suppressor of cytokine signaling 1 and 3 in fat and placental tissue from women with gestational diabetes

The suppressor of cytokine signaling (SOCS) proteins are feedback inhibitors of signaling pathways induced by cytokines, hormones and growth factors. In the present study we measured the expression of SOCS1, SOCS3, interleukin-6 (IL-6), IL-6 receptor, IL-8 and leptin mRNA in paired samples of subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT) and placental tissue obtained from 18 pregnant women with normal glucose tolerance (NGT) and 20 subjects with gestational diabetes mellitus (GDM), using quantitative RT-PCR. The patients with GDM had significantly higher IL-8 mRNA expression in VAT than the women with NGT (p = 0.007), whereas the expression of SOCS1, SOCS3 and other genes study did not differ significantly between the two groups. Stepwise regression analysis revealed that SOCS1 mRNA expression in VAT was significantly associated with prepregnancy BMI (β = -0.68, p = 0.03) and IL-8 mRNA expression (β = 0.66, p = 0.03), whereas SOCS3 mRNA expression in VAT was independently predicted by IL-6 mRNA expression (β = 0.94, p = 0.0002, R(2) = 0.88). In conclusion, our results did not show significant differences in SOCS1 and SOCS3 mRNA expression in adipose and placental tissue obtained from pregnant women with and without GDM.

Epigallocatechin gallate reduces vascular inflammation in db/db mice possibly through an NF-κB-mediated mechanism

SCOPE

Hyperglycemia-induced vascular inflammation resulting in the adhesion of monocytes to endothelium is a key event in the pathogenesis of atherosclerosis in diabetes. We investigated whether epigallocatechin gallate (EGCG), a major catechin found in green tea, reduces vascular inflammation in diabetes.

METHODS AND RESULTS

Human aortic endothelial cells (HAEC) were pretreated with green tea catechins before the addition of high glucose (25 mM) for 72 h. EGCG at physiologically achievable concentration (1 μM) significantly inhibited high glucose induced adhesion of monocytes to HAEC both in static and under flow conditions. EGCG also reduced nuclear factor κB (NF-κB) regulated transcriptional activity in ECs. Six-week-old diabetic db/db mice were fed a diet containing 0% or 0.1% EGCG for 8 weeks. ECs were isolated from aortic vessels of db/db, db/db-EGCG, and control db/+ mice. EGCG supplementation greatly suppressed diabetes-increased monocytes adhesion to ECs, which is associated with reduced circulating levels of chemokines, and reduced secretions of chemokines and adhesion molecules by aortic ECs from db/db-EGCG mice. EGCG treatment reduced nuclear translocation of NF-κB p65 in aortic vessels, decreased blood pressure and serum concentrations of cholesterol and triglycerides in db/db-EGCG mice.

CONCLUSION

EGCG may have a direct protective effect against vascular inflammation in diabetes.

Genistein prevents hyperglycemia-induced monocyte adhesion to human aortic endothelial cells through preservation of the cAMP signaling pathway and ameliorates vascular inflammation in obese diabetic mice

Hyperglycemia-induced vascular inflammation resulting in the enhanced monocyte-endothelial cell (EC) interaction is the key event in the pathogenesis of atherosclerosis in diabetes. Here, we investigated the effect of isoflavone genistein on hyperglycemia-stimulated vascular inflammation. Human aortic EC (HAEC) were pretreated with genistein before the addition of high glucose (HG; 25 mmol/L) for 48 h. Genistein at a physiological concentration (0.1 μmol/L) significantly inhibited HG-induced adhesion of monocytes to HAEC and suppressed endothelial production of monocyte chemotactic protein-1 (MCP-1) and IL-8. Inhibition of adenylate cyclase or protein kinase A (PKA) significantly attenuated the antiadhesion effect of genistein. Consistently, genistein improved HG-impaired intracellular cAMP production and PKA activity in HAEC. Six-week-old diabetic db/db mice were untreated (db/db) or treated with a diet containing 1 g genistein/kg diet (db/db+G) for 8 wk. Their nondiabetic db/+ mice were used as normal controls. Circulating concentrations of MCP-1/JE and KC were significantly greater, whereas IL-10 concentrations were lower in db/db mice than those in normal mice. Dietary supplementation of genistein did not normalize but significantly suppressed the elevated serum concentrations of MCP-1/JE from 286 ± 30 ng/L to 181 ± 35 ng/L and KC from 321 ± 21 ng/L to 232 ± 20 ng/L while increasing that of IL-10 from 35 ± 4 ng/L to 346 ± 35 ng/L in db/db+G mice. Further, genistein treatment suppressed diabetes-induced adhesion of monocytes to EC by 87% and endothelial secretion of adhesion molecules. We conclude that genistein improves diabetes-caused vascular inflammation, which may be mediated through promoting the cAMP/PKA pathway.

p38 mitogen-activated protein kinase (MAPK) promotes cholesterol ester accumulation in macrophages through inhibition of macroautophagy

p38 MAPK has been strongly implicated in the development of atherosclerosis, but its role in cholesterol ester accumulation in macrophages and formation of foam cells, an early step in the development of atherosclerosis, has not been investigated. We addressed this issue and made some brand new observations. First, elevated intracellular cholesterol level induced by the exposure to LDL-activated p38 MAPK and activation of p38 MAPK with anisomycin increased the ratio of cholesterol esters over free cholesterol, whereas inhibition of p38 MAPK with SB203580 or siRNA reduced the LDL loading-induced intracellular accumulation of free cholesterol and cholesterol esters in macrophages. Second, exposure to LDL cholesterol inhibited autophagy in macrophages, and inhibition of autophagy with 3-methyladenine increased intracellular accumulation of cholesterol (free cholesterol and cholesterol esters), whereas activation of autophagy with rapamycin decreased intracellular accumulation of free cholesterol and cholesterol esters induced by the exposure to LDL cholesterol. Third, LDL cholesterol loading-induced inhibition of autophagy was prevented by blockade of p38 MAPK with SB203580 or siRNA. Neutral cholesterol ester hydrolase was co-localized with autophagosomes. Finally, LDL cholesterol loading and p38 activation suppressed expression of the key autophagy gene, ulk1, in macrophages. Together, our results provide brand new insight about cholesterol ester accumulation in macrophages and foam cell formation.

Terminal arteriolar network structure/function and plasma cytokine levels in db/db and ob/ob mouse skeletal muscle

OBJECTIVE

To investigate the terminal arteriolar network structure and function in relation to circulating plasma cytokine levels in db/db, ob/ob, and their genetic background control, C57/bl6, mice.

METHODS

Arteriolar network size and erythrocyte distribution were observed in the resting cremaster muscle (n = 45, pentobarbital 50 mg/kg i.p.). Structural remodeling and inflammatory state were related to 21 plasma cytokine levels.

RESULTS

db/db networks were shorter, had fewer branches, and smaller diameters than C57/bl6 controls. ob/ob networks were longer, with similar branch numbers, however with non-uniform diameters. Shunting of erythrocytes to the specific terminal arteriolar branches of the network (functional rarefaction) was prominent in db/db and ob/ob, with further evidence of shunting between networks seen as no flow to 50% of ob/ob arteriolar networks.

CONCLUSIONS

Altered levels of plasma cytokines are consistent with structural remodeling seen in db/db, and a pro-inflammatory state for both db/db and ob/ob. Differences in network structure alone predict overall reduced uniform oxygen delivery in db/db or ob/ob. Shunting probably increases heterogeneous oxygen delivery and is strain-dependent.

High glucose condition upregulated Txnip expression level in rat mesangial cells through ROS/MEK/MAPK pathway

Thioredoxin interacting protein (Txnip) is one of the most abundantly up-regulated genes in response to hyperglycemia. The increased renal expression of Txnip was associated with type IV collagen accumulation in streptozotocin-induced diabetic mice. As the mechanism of action of high glucose is unknown, we undertook the investigation of the signaling pathway on the upregulation of Txnip expression induced by high glucose in rat mesangial cells. Rat mesangial cells were exposed to normal (5.5 mM) or high (25 mM) glucose at different time points. Txnip expression was determined using real-time RT-PCR and western-blotting at transcription and translation level, respectively. Intracellular reactive oxygen species (ROS) was detected by FACS Calibur flow cytometer using fluorescent probe (DCFH-DA).The treatment with high glucose resulted in an increase of Txnip mRNA from 4 h to 12 h and Txnip protein from 12 to 24 h in comparison with normal glucose condition. In addition, N-acetyl-cysteine (NAC) was found to decrease Txnip protein expression under high glucose condition. Furthermore, p38MAPK inhibitor SB203580 suppressed Txnip expression at transcription and protein level significantly to high glucose exposure. These results suggest that high glucose exposure improves Txnip mRNA and protein expression level by ROS/MEK/MAPK signaling pathway.

Antipermeability function of PEDF involves blockade of the MAP kinase/GSK/beta-catenin signaling pathway and uPAR expression

PURPOSE

Pigment epithelium-derived factor (PEDF) is a potent inhibitor of vascular endothelial growth factor (VEGF)-induced endothelial permeability. The goal of this study was to understand the mechanism by which PEDF blocks VEGF-induced increases in vascular permeability.

METHODS

The paracellular permeability of bovine retinal endothelial (BRE) cells was measured by assaying transendothelial cell electrical resistance and tracer flux. Western blot analysis was used to show phosphorylation of VEGFR2, MAP kinases, and glycogen synthase kinase 3 (GSK3)-beta. Confocal imaging and Western blot analysis were used to determine subcellular distribution of beta-catenin. Real-time RT-PCR and Western blot analysis were used to quantify urokinase plasminogen activator receptor (uPAR) expression.

RESULTS

PEDF blocked VEGF-induced phosphorylation of extracellular signal-regulated kinase (ERK), p38 MAP kinase, the p38 substrate MAP kinase-activated protein kinase-2 (MAPKAPK-2), and GSK3-beta, but it had no effect on the phosphorylation of VEGFR2. In addition, the VEGF-induced transcriptional activation of beta-catenin and uPAR expression were blocked by PEDF and by inhibitors of p38 and MEK. Finally, the VEGF-induced increase in permeability was blocked by both PEDF and the same kinase inhibitors.

CONCLUSIONS

The data suggest that p38 MAP kinase and ERK act upstream of GSK/beta-catenin in VEGF-induced activation of the uPA/uPAR system and that PEDF-mediated inhibition of the VEGF-induced increase in vascular permeability involves blockade of this pathway. These findings are important for developing precise and potent therapies for treatment of diseases characterized by vascular barrier dysfunction.

Diabetes is a proinflammatory state: a translational perspective

The diabetic state confers an increased propensity to accelerated atherogenesis. Inflammation is pivotal in atherosclerosis; in addition to the established risk factors, inflammation appears to play a pivotal role in diabetes and its complications. Evidence for increased inflammation includes: increased levels of plasma C-reactive protein, the prototypic marker of inflammation; increased levels of plasminogen-activator inhibitor; increased monocyte superoxide and proinflammatory cytokine release (IL-1, IL-6 and TNF-alpha); increased monocyte adhesion to endothelium; increased NF-kappaB activity; and increased Toll-like receptor 2 and 4 expression and activity in diabetes. Thus, it appears that both Type 1 and Type 2 diabetes are proinflammatory states and that these could contribute to increased diabetic vasculopathies.

Murine 12/15-lipoxygenase regulates ATP-binding cassette transporter G1 protein degradation through p38- and JNK2-dependent pathways

12/15-Lipoxygenase (12/15LO) plays a role in the pathogenesis of atherosclerosis and diabetes and has been implicated in low density lipoprotein oxidation. Murine macrophages express high levels of 12/15LO and are key cells involved in the accumulation and efflux of oxidized low density lipoprotein in the arterial wall. During this process, macrophages up-regulate scavenger receptors that regulate lipid uptake, and ATP-binding cassette (ABC) transporters, that regulate lipid efflux. We have previously demonstrated that 12/15LO enhances the turnover and serine phosphorylation of ABCG1. In the current study, we further elucidate the mechanisms by which 12/15LO regulates ABCG1. Proteasomal inhibitors blocked the down-regulation of ABCG1 expression and resulted in accumulation of phosphorylated ABCG1. Macrophages that lack 12/15LO have enhanced transporter expression, reduced ABCG1 phosphorylation, and increased cholesterol efflux. Conversely, macrophages that overexpress 12/15LO have reduced ABCG1 expression, increased transporter phosphorylation, and reduced cholesterol efflux. 12/15LO plays a key role in activating the MAPK pathway. Inhibition of the p38 or JNK pathways with pharmacological inhibitors or dominant negative constructs blocked 12S-hydroxyeicosatetranoic acid-mediated degradation of ABCG1. Moreover, we isolated macrophages from JNK1-, JNK2-, and MKK3-deficient mice to analyze the involvement of specific MAPK pathways. JNK2- and MKK3-, but not JNK1-deficient macrophages were resistant to the down-regulation of ABCG1 protein, reduction in efflux, and increase in serine phosphorylation by 12S-hydroxyeicosatetranoic acid. These findings provide evidence that 12/15LO regulates ABCG1 expression and function through p38- and JNK2-dependent mechanisms, and that targeting these pathways may provide novel approaches for regulating cholesterol homeostasis.

Increased secretion of IP-10 from monocytes under hyperglycemia is via the TLR2 and TLR4 pathway

Among the chemokines, members of the CXC family include IP-10 (interferon-gamma induced protein of 10kDa). Elevated serum IP-10 levels have been shown in diabetes. However, there is a paucity of data examining the sources and regulation of IP-10 under hyperglycemic conditions and this was the overall aim of the study. Type 1 diabetes (T1DM) is a pro-inflammatory state. We previously demonstrated increased toll like receptor (TLR) 2 and 4 activation in monocytes of T1DM patients. Thus, we also examined the role of the TLR pathway in modulating IP-10 release from human monocytes under hyperglycemia. Also, circulating and monocytic levels of IP-10 in patients with T1DM with and without microvascular complications (T1DM-MV and T1DM) and controls (C) was assessed. Under HG, IP-10 mRNA and protein were significantly increased compared to normoglycemia. Incubation of monocytes with dominant negative Ikb but not control vector significantly abrogated HG-induced IP-10 release. Furthermore, both TLR2 siRNA as well as TLR4 siRNA, either alone or in combination significantly abrogated HG-induced IP-10 release. Serum and monocytic levels of IP-10 were significantly increased in T1DM and T1DM-MV compared to matched controls. Thus, we demonstrate increased circulating and monocytic IP-10 in T1DM. Down-regulation of TLR2 and TLR4 abrogates HG-induced IP-10 release via NF-kappaB inhibition.

Signal transduction pathways involved in brain death-induced renal injury

Kidneys derived from brain death organ donors show an inferior survival when compared to kidneys derived from living donors. Brain death is known to induce organ injury by evoking an inflammatory response in the donor. Neuronal injury triggers an inflammatory response in the brain, leading to endothelial dysfunction and the release of cytokines in the circulation. Serum levels of interleukin-6, -8, -10, and monocyte chemoattractant protein-1 (MCP-1) are increased after brain death. Binding with cytokine-receptors in kidneys stimulates activation of nuclear factor-kappa B (NF-kappaB), selectins, adhesion molecules and production of chemokines leading to cellular influx. Mitogen-activated protein kinases (MAP-kinases) mediate inflammatory responses and together with NF-kappaB they seem to play an important role in brain death induced renal injury. Altering the activation state of MAP-kinases could be a promising drug target for early intervention to reduce cerebral injury related donor kidney damage and improve outcome after transplantation.

Up-regulation of thioredoxin interacting protein (Txnip) by p38 MAPK and FOXO1 contributes to the impaired thioredoxin activity and increased ROS in glucose-treated endothelial cells

Oxidative stress induced by hyperglycemia is a key factor in the development of cardiovascular diseases in diabetes. Thioredoxin (Trx) system, a major thiol antioxidant system, regulates the reduction of intracellular reactive oxygen species (ROS). In this study, we demonstrated that high glucose significantly increased intracellular ROS levels in human aortic endothelial cells (HAECs). Additionally, high glucose reduced the antioxidant activity of thioredoxin. To investigate the mechanisms involved, we found that glucose enhanced the expression of thioredoxin interacting protein (Txnip), a Trx inhibitory protein, through p38 mitogen-activated protein kinase (MAPK). We also showed that glucose regulated Txnip at transcription level and p38 MAPK and forkhead box O1 transcriptional factor (FOXO1) were involved in the process. Taken together, upregulation of Txnip and subsequent impairment of thioredoxin antioxidative system through p38 MAPK and FOXO1 may represent a novel mechanism for glucose-induced increase in intracellular ROS.

Sphingosine-1-phosphate inhibits high glucose-mediated ERK1/2 action in endothelium through induction of MAP kinase phosphatase-3

Endothelial activation is a key early event in vascular complications of Type 1 diabetes. The nonobese diabetic (NOD) mouse is a well-characterized model of Type 1 diabetes. We previously reported that Type 1 diabetic NOD mice have increased endothelial activation, with increased production of monocyte chemoattractant protein (MCP)-1 and IL-6, and a 30% increase of surface VCAM-1 expression leading to a fourfold increase in monocyte adhesion to the endothelium. Sphingosine-1-phosphate (S1P) prevents monocyte:endothelial interactions in these diabetic NOD mice. Incubation of diabetic NOD endothelial cells (EC) with S1P (100 nmol/l) reduced ERK1/2 phosphorylation by 90%, with no significant changes in total ERK1/2 protein. In the current study, we investigated the mechanism of S1P action on ERK1/2 to reduce activation of diabetic endothelium. S1P caused a significant threefold increase in mitogen-activated kinase phosphatase-3 (MKP-3) expression in EC. MKP-3 selectively regulates ERK1/2 activity through dephosphorylation. Incubation of diabetic NOD EC with S1P and the S1P(1)-selective agonist SEW2871 significantly increased expression of MKP-3 and reduced ERK1/2 phosphorylation, while incubation with the S1P(1)/S1P(3) antagonist VPC23019 decreased the expression of MKP-3, both results supporting a role for S1P(1) in MKP-3 regulation. To mimic the S1P-mediated induction of MKP-3 diabetic NOD EC, we overexpressed MKP-3 in human aortic endothelial cells (HAEC) cultured in elevated glucose (25 mmol/l). Overexpression of MKP-3 in glucose-cultured HAEC decreased ERK1/2 phosphorylation and resulted in decreased monocyte:endothelial interactions in a static monocyte adhesion assay. Finally, we used small interfering RNA to MKP-3 and observed increased monocyte adhesion. Moreover, S1P was unable to inhibit monocyte adhesion in the absence of MKP-3. Thus, one mechanism for the anti-inflammatory action of S1P in diabetic EC is inhibition of ERK1/2 phosphorylation through induction of MKP-3 expression via the S1P-S1P(1) receptor axis.

15d-PGJ2 upregulates synthesis of IL-8 in endothelial cells through induction of oxidative stress

15-Deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)) is a cyclopentenone prostaglandin regarded as antiinflammatory mediator, which can act through peroxisome proliferator-activated receptor-gamma (PPARgamma) or through G protein-coupled surface receptors. It has been demonstrated that 15d-PGJ(2) potently increases the generation of interleukin-8 (IL-8) in human microvascular endothelial cells (HMEC-1s); however, the mechanism of this induction is not known. The aim of the study was to find the pathway involved in 15d-PGJ(2)-mediated IL-8 stimulation. Our data confirmed that the effect of 15d-PGJ(2) is independent of PPARgamma. For the first time, we excluded the activation of G proteins and the contribution of G protein-coupled surface receptors in endothelial cells treated with 15d-PGJ(2). Instead, we demonstrated that stimulation of IL-8 involved induction of oxidative stress, activation of p38 kinases, and increase in stability of IL-8 mRNA. Upregulation of IL-8 promoter, although measurable, seemed to play a less-pronounced role. Additionally, our results indicate the involvement of cAMP elevation and may suggest a role for ATF2 transcription factor. Concomitant induction of heme oxygenase-1 in HMEC-1s did not influence the synthesis of IL-8. In summary, we showed that 15d-PGJ(2), acting through oxidative stress, may exert proinflammatory effects. The upregulation of IL-8 is mostly associated with p38-mediated stabilization of mRNA.

Defining human diabetic nephropathy on the molecular level: integration of transcriptomic profiles with biological knowledge

Diabetic nephropathy (DN) is the most common cause for end stage renal disease (ESRD). Next to environmental factors, genetic predispositions determine the susceptibility for DN and its rate of progression to ESRD. With the availability of genome wide expression profiling we have the opportunity to define relevant pathways activated in the individual diabetic patient, integrating both environmental exposure and genetic background. In this review we summarize current understanding of how to link comprehensive gene expression data sets with biomedical knowledge and present strategies to build a transcriptional network of DN. Information about the individual disease processes of DN might allow the implementation of a personalized molecular medicine approach with mechanism-based patient management. Web based search engines like Nephromine are essential tools to facilitate access to molecular data of genomics, proteomics and metabolomics of DN.

Selenium inhibits high glucose- and high insulin-induced adhesion molecule expression in vascular endothelial cells

BACKGROUND

Initiation of an atherosclerotic lesion requires endothelial expression of adhesion molecules. Selenium (Se), a biologically essential trace element, can inhibit cytokine (e.g., TNF-alpha)-induced expression of adhesion molecules. Atherosclerosis is accelerated in diabetic patients. This is at least partially caused by hyperglycemia and hyperinsulinemia increasing adhesion molecule expression. These experiments tested whether Se can also alter high glucose- and high insulin-induced expression of adhesion molecules.

METHODS

Human umbilical vein endothelial cells (HUVECs) were pretreated with Se and stimulated by high glucose or high insulin. Expression of adhesion molecules was measured by Western blot.

RESULTS

Se (100 nmol/L) significantly inhibited glucose (25 mmol/L)-induced expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin. Moreover, Se significantly inhibited insulin (100 nmol/L)-induced VCAM-1 and ICAM-1 expression, whereas high insulin had no inducing effect on E-selectin. Se also inhibited high glucose- and high insulin-induced activation of p38 mitogen-activated protein kinase (p38), which indicated that the preventive effects of Se on adhesion molecules may be associated with p38. The important role of p38 in Se effects was further confirmed using p38 inhibitor SB203580.

CONCLUSIONS

These results suggest that Se can inhibit high glucose- and high insulin-induced expression of adhesion molecules. Such antagonism is at least partially mediated through the modulation of p38 pathway. Therefore, Se may be considered as a potential preventive intervention for diabetes-accelerated atherosclerosis.

High glucose stimulates GRO secretion from rat microglia via ROS, PKC, and NF-kappaB pathways

Hyperglycemia causes direct neuronal damage in diabetic encephalopathy. Microglia have been found to be activated in diabetic encephalopathy, presumably mediating and amplifying neuron degeneration. Chemokine IL-8 plays an important role in the pathogenesis of encephalopathy. Therefore, we investigated whether high glucose could activate microglia and stimulate IL-8 secretion and if so, the possible mechanisms that were involved. ELISA results showed that treatment with high glucose (35 mM) compared with treatment with low glucose (10 mM) time-dependently elevated secretion of GRO (the rat ortholog of human IL-8) in primary cultured rat microglia. Real-time PCR results showed GRO mRNA expression also increased in response to high glucose in a time-dependent manner. These effects were specific to high glucose because the osmolality control had no such effect. High-glucose treatment stimulated the formation of ROS, as seen in the DCF fluorescence assay, increased phosphorylation of PKC, as seen in the Western blot analysis, and activated NF-kappaB, as seen in the luciferase reporter assay. In addition, treatment with the ROS scavenger NAC (2 mM) significantly reduced the high glucose-induced phosphorylation of PKC and GRO secretion. Treatment with the PKC activator PMA (10-50 nM) stimulated GRO secretion, and the PKC inhibitors calphostin C (300 nM) or chelerythrine (1 microM) attenuated the high glucose-induced GRO secretion. Furthermore, the NF-kappaB inhibitors MG132 (10 microM) or PDTC (5 microM) completely blocked the high glucose-induced GRO secretion. In conclusion, high glucose induces GRO secretion and mRNA expression in activated rat microglia, which is mediated by the ROS, PKC, and NF-kappaB pathways. High glucose-induced IL-8 production by microglia may contribute to diabetic encephalopathy.

Simvastatin treatment modifies polymorphonuclear leukocyte function in high-risk individuals: a longitudinal study

BACKGROUND

Although extensive experimental evidence supports a primary role of polymorphonuclear leukocytes (PMNs) in atherosclerosis, few data exist concerning the functional properties of these cells and their pharmacological modulation in high-risk individuals.

OBJECTIVE

The production of the proinflammatory chemokine interleukin-8 (IL-8), migration and chemotaxis, and reactive oxygen species (ROS) generation were investigated in a longitudinal study in PMNs obtained from high-risk individuals during statin treatment. As a secondary endpoint we compared PMN function of high-risk patients with that of controls.

METHODS AND RESULTS

PMNs were isolated from 21 high-risk individuals before treatment and 3 and 30 days after the beginning of simvastatin treatment, and from healthy controls. During treatment a significant reduction was observed both in resting (P = 0.009) and N-formyl-Met-Leu-Phe (fMLP)-stimulated (P = 0.008) IL-8 production, and in the chemotactic index (P = 0.038), whereas ROS generation did not significantly change. In comparison with cells from controls, PMNs obtained from patients before starting simvastatin treatment showed higher resting and fMLP-stimulated IL-8 release (P = 0.007 and P = 0.002, respectively) and ROS generation (resting, P = 0.009; and fMLP-stimulated, P = 0.046), whereas migration and the chemotactic index did not significantly differ.

CONCLUSIONS

An activation of neutrophils is present in high-risk individuals, shown by the enhanced production of IL-8, and increased ROS generation. The 4-week statin treatment is able to reduce the cell capability to produce IL-8, and to decrease chemotaxis, thus affecting the proinflammatory properties of PMNs.

Increased number of islet-associated macrophages in type 2 diabetes

Activation of the innate immune system in obesity is a risk factor for the development of type 2 diabetes. The aim of the current study was to investigate the notion that increased numbers of macrophages exist in the islets of type 2 diabetes patients and that this may be explained by a dysregulation of islet-derived inflammatory factors. Increased islet-associated immune cells were observed in human type 2 diabetic patients, high-fat-fed C57BL/6J mice, the GK rat, and the db/db mouse. When cultured islets were exposed to a type 2 diabetic milieu or when islets were isolated from high-fat-fed mice, increased islet-derived inflammatory factors were produced and released, including interleukin (IL)-6, IL-8, chemokine KC, granulocyte colony-stimulating factor, and macrophage inflammatory protein 1alpha. The specificity of this response was investigated by direct comparison to nonislet pancreatic tissue and beta-cell lines and was not mimicked by the induction of islet cell death. Further, this inflammatory response was found to be biologically functional, as conditioned medium from human islets exposed to a type 2 diabetic milieu could induce increased migration of monocytes and neutrophils. This migration was blocked by IL-8 neutralization, and IL-8 was localized to the human pancreatic alpha-cell. Therefore, islet-derived inflammatory factors are regulated by a type 2 diabetic milieu and may contribute to the macrophage infiltration of pancreatic islets that we observe in type 2 diabetes.

High glucose-induced thioredoxin-interacting protein in renal proximal tubule cells is independent of transforming growth factor-beta1

Hyperglycemia is a causative factor in the pathogenesis of diabetic nephropathy. Here, we demonstrate the transcriptional profiles of the human proximal tubule cell line (HK-2 cells) exposed to high glucose using cDNA microarray analysis. Thioredoxin-interacting protein (Txnip) was the gene most significantly increased among 10 strongly up-regulated and 15 down-regulated genes. Txnip, heat shock proteins 70 and 90, chemokine (C-C motif) ligand 20, and matrix metalloproteinase-7 were chosen for verification of gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the mRNA expression levels of these five genes, consistent with microarray analysis. The increased protein expression of Txnip, CCL20, and MMP7 were also verified by Western blotting and enzyme-linked immunosorbent assay. Increased expression of Txnip and of nitrotyrosine, as a marker of oxidative stress, were confirmed in vivo in diabetic Ren-2 rats. Subsequent studies focused on the dependence of Txnip expression on up-regulation of transforming growth factor (TGF)-beta1 under high-glucose conditions. Overexpression of Txnip and up-regulation of Txnip promoter activity were observed in cells in which the TGF-beta1 gene was silenced in HK-2 cells using short interfering RNA technology. High glucose further increased both Txnip expression and its promoter activity in TGF-beta1 silenced cells compared with wild-type cells exposed to high glucose, suggesting that high glucose induced Txnip through a TGF-beta1-indepen-dent pathway.

High glucose induces IL-1beta expression in human monocytes: mechanistic insights

Previously, IL-1beta secretion from Type 2 diabetic patients has been shown to be increased compared with controls. In this study, we aimed to delineate the mechanism of IL-1beta induction under high-glucose (HG) conditions in human monocytes. THP-1 cells cultured in normal glucose were treated with increasing concentrations of d-glucose (10-25 mM) for 6-72 h. IL-1beta and IL-1 receptor antagonist levels were measured by ELISA and Western blots, whereas mRNA was quantitated by RT-PCR. Specific inhibitors and small interfering RNAs of PKC, p38, ERK1/2, NF-kappaB, and NADPH oxidase were used to determine the mediators in parallel experiments under HG conditions. IL-1beta-secreted protein, cellular protein, and mRNA increase under HG conditions is time and dose dependent, with maximum increase at 15 mM (48 h; P < 0.05). IL-1 receptor antagonist release was time and dose dependent, similar to IL-1beta expression pattern; however, the molar ratio of IL-1beta to IL-1RA was increased. Data from inhibitor and small interfering RNA experiments indicate that IL-1beta release under HG is mediated by PKC-alpha, via phosphorylation of p38 MAPK, and ERK1/2 leading to NF-kappaB activation, resulting in increased mRNA and protein for IL-1beta. At the same time, it appears that NADPH oxidase via p47phox activates NF-kappaB, resulting in increased IL-1beta secretion. Data suggest that, under HG conditions, monocytes release significantly higher amounts of IL-1beta through multiple mechanisms, further compounding the disease progression. Targeting signaling pathways mediating IL-1beta release could result in the amelioration of inflammation and possibly diabetic vasculopathies.

Do glucose and lipids exert independent effects on atherosclerotic lesion initiation or progression to advanced plaques?

It is becoming increasingly clear that suboptimal blood glucose control results in adverse effects on large blood vessels, thereby accelerating atherosclerosis and cardiovascular disease, manifested as myocardial infarction, stroke, and peripheral vascular disease. Cardiovascular disease is accelerated by both type 1 and type 2 diabetes. In type 1 diabetes, hyperglycemia generally occurs in the absence of elevated blood lipid levels, whereas type 2 diabetes is frequently associated with dyslipidemia. In this review article, we discuss hyperglycemia versus hyperlipidemia as culprits in diabetes-accelerated atherosclerosis and cardiovascular disease, with emphasis on studies in mouse models and isolated vascular cells. Recent studies on LDL receptor-deficient mice that are hyperglycemic, but exhibit no marked dyslipidemia compared with nondiabetic controls, show that diabetes in the absence of diabetes-induced hyperlipidemia is associated with an accelerated formation of atherosclerotic lesions, similar to what is seen in fat-fed nondiabetic mice. These effects of diabetes are masked in severely dyslipidemic mice, suggesting that the effects of glucose and lipids on lesion initiation might be mediated by similar mechanisms. Recent evidence from isolated endothelial cells demonstrates that glucose and lipids can induce endothelial dysfunction through similar intracellular mechanisms. Analogous effects of glucose and lipids are also seen in macrophages. Furthermore, glucose exerts many of its cellular effects through lipid mediators. We propose that diabetes without associated dyslipidemia accelerates atherosclerosis by mechanisms that can also be activated by hyperlipidemia.

Aberrant activation profile of cytokines and mitogen-activated protein kinases in type 2 diabetic patients with nephropathy

Cytokine-induced inflammation is involved in the pathogenesis of type 2 diabetes mellitus (DM). We investigated plasma concentrations and ex vivo production of cytokines and chemokines, and intracellular signalling molecules, mitogen-activated protein kinases (MAPK) in T helper (Th) cells and monocytes in 94 type 2 diabetic patients with or without nephropathy and 20 healthy controls. Plasma concentrations of inflammatory cytokines tumour necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-18 and chemokine CCL2 in patients with diabetic nephropathy (DN) were significantly higher than control subjects, while IL-10, CXCL8, CXCL9, CXCL10 and adiponectin concentrations of DN were significantly higher than patients without diabetic nephropathy (NDN) and control subjects (all P < 0.05). Plasma concentrations of TNF-alpha, IL-6, IL-10, IL-18, CCL2, CXCL8, CXCL9, CXCL10 and adiponectin exhibited significant positive correlation with urine albumin : creatinine ratio in DN patients. The percentage increases of ex vivo production of IL-6, CXCL8, CXCL10, CCL2 and CCL5 upon TNF-alpha activation were significantly higher in both NDN and DN patients than controls (all P < 0.05). The percentage increases in IL-18-induced phosphorylation of extracellular signal-regulated kinase (ERK) in Th cells of NDN and DN were significantly higher than controls (P < 0.05), while the percentage increase in TNF-alpha-induced phosphorylation of p38 MAPK in monocytes and IL-18-induced phosphorylation of p38 MAPK in Th cells and monocytes were significantly higher in NDN patients than controls. These results confirmed that the aberrant production of inflammatory cytokines and chemokines and differential activation of MAPK in different leucocytes are the underlying immunopathological mechanisms of type 2 DM patients with DN.

CCAAT/enhancer-binding protein alpha mediates induction of hepatic phosphoenolpyruvate carboxykinase by p38 mitogen-activated protein kinase

Excessive hepatic gluconeogenesis and glucose production are important contributors to hyperglycemia in both type 1 and type 2 diabetes. In diabetic humans and animal models, elevated levels of p38 mitogen-activated protein kinase (p38) are observed in several tissues. Our study shows that activity of p38 is significantly elevated in livers of db/db or streptozocin-induced type 1 diabetic mice. Using cultured hepatoma cells, we find that activation of p38 enhances expression of hepatic gluconeogenic gene phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, our studies demonstrate that activation of p38 stimulates phosphorylation of CCAAT/enhancer-binding protein alpha (C/EBPalpha) at serine 21 and increases its transactivation activity in the context of PEPCK gene transcription. Our results indicate that C/EBPalpha mediates p38-stimulated PEPCK transcription in liver cells.

Fludarabine induces pro-inflammatory activation of human monocytic cells through a MAPK/ERK pathway

Fludarabine is a nucleoside analogue that has been successfully employed for the treatment of low-grade lymphoid malignancies and, more recently, in nonmyeloablative preparative regimens for stem cell transplantation, due to its strong cytotoxic activity on lymphocytes. In this paper, we show that fludarabine can also induce pro-inflammatory stimulation of monocytic cells, as evaluated by increased expression of ICAM-1 and IL-8 release. To study the mechanisms involved, we employed selective inhibitors of MAPK and NF-kappaB pathways, both of which have been implicated in the modulation of ICAM-1 and IL-8. Our results showed that fludarabine effects were mediated through the activation of ERK and were independent on p38, JNK or NF-kappaB pathways. By Western blotting analysis we corroborated that fludarabine induced a rapid activation of ERK that was sustained for at least 30 min. Moreover, pro-inflammatory activation of monocytic cells by fludarabine was largely attenuated by coadministration of the free radical scavenger N-acetylcysteine suggesting the involvement of reactive oxygen species in fludarabine effects. Finally, we showed that fludarabine induced the activation of the transcription factor AP-1 not only in monocytic cells but also in non-proliferating lymphocytes from chronic lymphocytic leukemia. It is possible that some of fludarabine side effects in vivo may be attributed to cell activation/differentiation rather than induction of apoptosis.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

Increased monocytic activity and biomarkers of inflammation in patients with type 1 diabetes

Type 1 diabetes is associated with increased vascular complications, and monocytes are pivotal cells in atherogenesis. However, there are few data on monocyte function and inflammation in type 1 diabetes. The aim of this study was to compare monocyte function and biomarkers of inflammation in type 1 diabetic subjects without macrovascular disease with that in matched control subjects (n = 52 per group). Fasting blood was obtained for biomarkers of inflammation (C-reactive protein [CRP], plasma-soluble cell adhesion molecules [CAMs], monocyte chemoattractant protein 1, nitrotyrosine, CD40 ligand [CD40L], and monocyte function). High-sensitive CRP, soluble intracellular adhesion molecule (sICAM), sCD40L, and nitrotyrosine levels were significantly elevated in type 1 diabetic subjects compared with in control subjects (P < 0.05). Monocyte superoxide anion release was significantly increased in the resting (37%; P < 0.05) and activated state (26%; P < 0.005) in type 1 diabetic compared with in control subjects. Monocyte interleukin (IL)-6 levels were significantly elevated in type 1 diabetic subjects compared with in control subjects in the resting state (51%; P < 0.05) and after lipopolysaccharide activation (31%; P < 0.01). Monocyte IL-1beta levels were increased in the activated monocytes in type 1 diabetic compared with in control subjects. There were no significant differences in monocyte tumor necrosis factor levels or adhesion between the two groups. Thus type 1 diabetes is a proinflammatory state, as evidenced by increased levels of monocyte IL-6, superoxide anion, and plasma CRP, sICAM, sCD40L, and nitrotyrosine levels. These results have a major implication on our understanding of the role of inflammation in vasculopathies in type 1 diabetes.

Macrophage-secreted factors induce adipocyte inflammation and insulin resistance

Macrophage infiltration into adipose tissue increases with obesity, a condition associated with low-grade inflammation and insulin resistance. We investigated the direct effects of macrophage-secreted factors on adipocyte inflammation and insulin resistance. 3T3-L1 adipocytes incubated with media conditioned by RAW264.7 macrophages (RAW-CM) showed dramatically increased transcription of several inflammation-related genes, greater nuclear factor kappa B (NF-kappaB) activity, and enhanced binding of U937 monocytes. All of these effects were prevented by co-incubation with pyrrolidinedithiocarbamate, an NF-kappaB inhibitor. Adipocytes incubated with RAW-CM also released more non-esterified fatty acids and this increased lipolysis was not suppressed by insulin. In addition, RAW-CM treatment decreased insulin-stimulated glucose uptake in adipocytes. Taken together, these results indicate that macrophage-secreted factors induce inflammatory responses and reduce insulin responsiveness in adipocytes. These effects of macrophage-secreted factors on adipocytes may contribute significantly to the systemic inflammation and insulin resistance associated with obesity.

Biological determinants of and reference values for plasma interleukin-8, monocyte chemoattractant protein-1, epidermal growth factor, and vascular endothelial growth factor: Results from the STANISLAS cohort

BACKGROUND

Interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF) are known to be involved in various diseases related to inflammation, vascular remodeling, or growth deregulation. In addition, increases in plasma concentrations of these cytokines appear to provide useful diagnostic and prognostic information. We therefore investigated which factors most strongly influence the biological variations of plasma IL-8, MCP-1, EGF, and VEGF concentrations.

METHODS

We used the Evidence biochip array analyzer to quantify plasma IL-8, MCP-1, EGF, and VEGF concentrations in a subsample of 304 children (age range, 4-17 years) and 540 adults (age range, 18-55 years) from the STANISLAS family study. We also calculated reference intervals for the 4 cytokines.

RESULTS

We found the following associations with plasma marker concentrations: Age, neutrophil count, and glucose concentration were positively associated with IL-8 concentrations in children and adults, as were smoking and platelet count in adults. MCP-1 concentrations were associated with age and smoking in both children and adults, monocyte count in children, and sex and hematocrit in adults. EGF concentrations were associated with platelet count in children and monocyte count and glucose in adults. VEGF concentrations were associated with age in children and adults and platelet count and alanine aminotransferase activity in adults.

CONCLUSION

Our results for IL-8, MCP-1, EGF, and VEGF may be useful for interpretation of patients' laboratory results and for understanding the regulation of concentrations of these cytokines in physiologic conditions.

Correction of nitrergic neurovascular dysfunction in diabetic mouse corpus cavernosum by p38 mitogen-activated protein kinase inhibition

Increased p38 mitogen-activated protein kinase (MAPK) in response to stress stimuli, including hyperglycemia, contributes to diabetic somatic neuropathy. However, effects on autonomic nerve and vascular function have not been determined. The aim of this study was to investigate the effects of the p38 MAPK inhibitor, LY2161793, on penile neurovascular function in streptozotocin-induced diabetic mice. Diabetes duration was 6 weeks and intervention LY2161793 treatment was given for the final 2 weeks. In vitro measurements on phenylephrine-precontracted corpus cavernosum revealed a 32% reduction in maximum nitrergic nerve-mediated relaxation with diabetes that was 74% corrected by LY2161793 treatment. Maximum nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was 42% attenuated by diabetes and 88% restored by LY2161793. Moreover, treatment partially corrected a diabetic deficit in endothelium-independent relaxation to a nitric oxide donor. Thus, p38 MAPK inhibition corrects nitric oxide-dependent indices of diabetic erectile autonomic neuropathy and vasculopathy, a therapeutic approach potentially worthy of consideration for clinical trials.

p38 mitogen-activated protein kinase downregulates endothelial progenitor cells

BACKGROUND

Transplantation of endothelial progenitor cells (EPCs) improves neovascularization after ischemia, but patients with coronary artery disease (CAD) or diabetes mellitus show a reduced number of EPCs and impaired functional activity. Therefore, we investigated the effects of risk factors, such as glucose and TNF-alpha, on the number of EPCs in vitro to elucidate the underlying mechanisms.

METHODS AND RESULTS

EPCs of patients or healthy subjects were isolated from peripheral blood. Incubation with glucose or TNF-alpha dose-dependently reduced the number of EPCs (79.9+/-1.3% and 74.3+/-8.1% of control; P<0.05, respectively). This reduction was not caused by apoptosis. TNF-alpha and glucose induced a dose- and time-dependent activation of the p38 MAP kinase, the downstream kinase mitogen- and stress-activated kinase 1, and the transcription factor cAMP-responsive element-binding protein (CREB), in EPCs. Moreover, EPCs from CAD patients had significantly higher basal p38-phosphorylation levels (1.83+/-0.2-fold increase; P<0.05) compared with healthy subjects. The inhibition of the p38-kinase by SB203580 or infection with a dominant negative p38 kinase adenovirus significantly increased basal number of EPCs (136.7+/-6.3% and 142.9+/-18% versus control, respectively). Likewise, ex vivo cultivation of EPCs from patients with CAD with SB203580 significantly increased the number of EPCs and partially reversed the impaired capacity for neovascularization of EPCs in vivo (relative blood flow: 0.40+/-0.03 versus 0.64+/-0.08, P<0.05). The increased numbers of EPCs by SB203580 were associated with an augmentation of EPC proliferation and a reduction of cells expressing the monocytic marker proteins CD14 and CD64, suggesting that p38 regulates proliferation and differentiation events.

CONCLUSIONS

These results demonstrate that p38 MAP kinase plays a pivotal role in the signal transduction pathways regulating the number of EPCs ex vivo. SB203580 can prevent the negative effects of TNF-alpha and glucose on the number of EPCs and may be useful to improve the number of EPCs for potential cell therapy.

An immune origin of type 2 diabetes?

Subclinical, low-grade systemic inflammation has been observed in patients with type 2 diabetes and in those at increased risk of the disease. This may be more than an epiphenomenon. Alleles of genes encoding immune/inflammatory mediators are associated with the disease, and the two major environmental factors the contribute to the risk of type 2 diabetes-diet and physical activity-have a direct impact on levels of systemic immune mediators. In animal models, targeting of immune genes enhanced or suppressed the development of obesity or diabetes. Obesity is associated with the infiltration and proinflammatory activity of macrophages in adipose tissue, and immune mediators may be important regulators of insulin resistance, mitochondrial function, ectopic lipid storage and beta cell dysfunction or death. Intervention studies targeting these pathways would help to determine the contribution of an activated innate immune system to the development of type 2 diabetes.

Sphingosine-1-Phosphate Prevents Tumor Necrosis Factor-α–Mediated Monocyte Adhesion to Aortic Endothelium in Mice

OBJECTIVE

Endothelial activation and monocyte adhesion to endothelium are key events in inflammation. Sphingosine-1-phosphate (S1P) is a sphingolipid that binds to G protein-coupled receptors on endothelial cells (ECs). We examined the role of S1P in modulating endothelial activation and monocyte-EC interactions in vivo.

METHODS AND RESULTS

We injected C57BL/6J mice intravenously with tumor necrosis factor (TNF)-alpha in the presence and absence of the S1P1 receptor agonist SEW2871 and examined monocyte adhesion. Aortas from TNF-alpha-injected mice had a 4-fold increase in the number of monocytes bound, whereas aortas from TNF-alpha plus SEW2871-treated mice had few monocytes bound (P<0.0001). Using siRNA, we found that inhibiting the S1P1 receptor in vascular ECs blocked the ability of S1P to prevent monocyte-EC interactions in response to TNF-alpha. We examined signaling pathways downstream of S1P1 and found that 100 nM S1P increased phosphorylation of Akt and decreased activation of c-jun.

CONCLUSIONS

Thus, we provide the first evidence that S1P signaling through the endothelial S1P1 receptor protects the vasculature against TNF-alpha-mediated monocyte-EC interactions in vivo.

TRAIL counteracts the proadhesive activity of inflammatory cytokines in endothelial cells by down-modulating CCL8 and CXCL10 chemokine expression and release

Exposure of endothelial cells to recombinant tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induced a modest (2-fold) increase of HL-60 cell adhesion as compared to TNF-α (40-fold) or interleukin 1β (IL-1β; 20-fold). However, pretreatment of endothelial cultures with TRAIL determined a significant reduction of the proadhesive activity induced by both TNF-α and IL-1β. Unexpectedly, the antiadhesive activity of TRAIL was not due to interference with the nuclear factor κB (NF-κB)-mediated up-regulation of surface intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and E-selectin adhesion molecules in response to inflammatory cytokines. In searching for the molecular mechanism underlying this biologic activity of TRAIL, a cDNA microarray analysis was performed. TRAIL pretreatment variably down-modulated the mRNA steady-state levels of several TNF-α-induced chemokines, and, in particular, it abrogated the TNF-α-mediated up-regulation of CCL8 and CXCL10. Of note, the addition of optimal concentrations of recombinant CCL8 plus CXCL10 to endothelial cultures completely restored the proadhesive activity of TNF-α. Moreover, experiments performed with agonistic anti-TRAIL receptor antibodies demonstrated that both TRAIL-R1 and TRAIL-R2 contributed, although at different levels, to TRAIL-induced chemokine modulation. Taken together, our data suggest that TRAIL might play an important role in modulating leukocyte/endothelial cell adhesion by selectively down-regulating CCL8 and CXCL10 chemokines.