The Prominent Role of P38 Mitogen-Activated Protein Kinase in Insulin-Mediated Enhancement of VCAM-1 Expression in Endothelial Cells

Vitexin Suppresses High-Glucose-upregulated Adhesion Molecule Expression in Endothelial Cells through Inhibiting NF-κB Signaling Pathway

Vascular damage is one of the significant complications of diabetes mellitus (DM). Central to this damage is endothelial damage, especially under high-glucose conditions, which promotes inflammation via the NF-κB signaling pathway. Inflammatory processes in endothelial cells directly contribute to endothelial dysfunction, such as promoting inflammatory cytokine release and activation of adhesion molecules. Vitexin, a compound found in many medicinal plants, shows promise in countering oxidative stress in diabetic contexts and modulating blood glucose. However, its effect on high-glucose-induced endothelial cell activation has not yet been studied. This research explores vitexin's potential role in this process, focusing on its influence on the NF-κB pathway in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were stimulated with 30 mM glucose (high glucose, HG) with or without vitexin treatment for 24 h. Western blotting assay was conducted for the NF-κB pathway and p-p38. Adhesion molecules (ICAM-1, VCAM-1, E-selectin, and MCP-1) were studied using flow cytometry, while pro-inflammatory cytokines were investigated using ELISA. Monocyte adhesion and vascular permeability tests were conducted to confirm the protective effect of vitexin under HG exposure. This study confirms vitexin's capacity to suppress p38 MAPK and NF-κB activation under HG conditions, reducing HG-elevated adhesion molecules and pro-inflammatory cytokine secretion. Additionally, vitexin mitigates HG-stimulated vascular permeability and monocyte adhesion. In conclusion, this study shows the therapeutic potential of vitexin against hyperglycemia-related vascular complications via p38 MAPK/NF-κB inhibition.

Endothelial Insulin Resistance Exacerbates Experimental Periodontitis

Epidemiological studies suggest that the severity of periodontitis is higher in people with diabetes than in healthy individuals. Insulin resistance might play a crucial role in the pathogenesis of multiple diabetic complications and is reportedly induced in the gingiva of rodents with type 2 diabetes; however, the molecular mechanisms underlying the pathogenesis of diabetes-related periodontitis remain unclear. Therefore, we aimed to investigate whether endothelial insulin resistance in the gingiva may contribute to the pathogenesis of periodontitis as well as elucidate its underlying molecular mechanisms. We demonstrated that insulin treatment downregulated lipopolysaccharide (LPS)-induced or tumor necrosis factor α (TNFα)-induced VCAM1 expression in endothelial cells (ECs) via the PI3K/Akt activating pathway, resulting in reduced cellular adhesion between ECs and leukocytes. Hyperglycemia-induced selective insulin resistance in ECs diminished the effect of insulin on LPS- or TNFα-stimulated VCAM1 expression. Vascular endothelial cell-specific insulin receptor knockout (VEIRKO) mice exhibited selective inhibition of the PI3K/Akt pathway in the gingiva and advanced experimental periodontitis-induced alveolar bone loss via upregulation of Vcam1, Tnfα, Mcp-1, Rankl, and neutrophil migration into the gingiva compared with that in the wild-type (WT) mice despite being free from diabetes. We also observed that insulin-mediated activation of FoxO1, a downstream target of Akt, was suppressed in the gingiva of VEIRKO and high-fat diet (HFD)-fed mice, hyperglycemia-treated ECs, and primary ECs from VEIRKO. Further analysis using ECs transfected with intact and mutated FoxO1, with mutations at 3 insulin-mediated phosphorylation sites (T24A, S256D, S316A), suggested that insulin-mediated regulation of VCAM1 expression and cellular adhesion of ECs with leukocytes was attenuated by mutated FoxO1 overexpression. These results suggest that insulin resistance in ECs may contribute to the progression of periodontitis via dysregulated VCAM1 expression and cellular adhesion with leukocytes, resulting from reduced activation of the PI3K/Akt/FoxO1 axis.

Diabetic cardiomyopathy and inflammation: development of hostile microenvironment resulting in cardiac damage

Diabetes mellitus is emerging as a major risk factor for heart failure. Diabetic cardiomyopathy is defined as a myocardial dysfunction that is not caused by underlying hypertension or coronary artery disease. Studies about clinical features, natural history and outcomes of the disease are few and often conflicting, because a universally accepted operative definition of diabetic cardiomyopathy is still lacking. Hyperglycemia and related metabolic and endocrine disorders are the triggering factors of myocardial damage in diabetic cardiomyopathy through multiple mechanisms. Among these mechanisms, inflammation has a relevant role, similar to other chronic myocardial disease, such as hypertensive or ischemic heart disease. A balance between inflammatory damage and healing processes is fundamental for homeostasis of myocardial tissue, whereas diabetes mellitus produces an imbalance, promoting inflammation and delaying healing. Therefore, diabetes-related chronic inflammatory state can produce a progressive qualitative deterioration of myocardial tissue, which reflects on progressive left ventricular functional impairment, which can be either diastolic, with prevalent myocardial hypertrophy, or systolic, with prevalent myocardial fibrosis. The aim of this narrative review is to summarize the existing evidence about the role of inflammation in diabetic cardiomyopathy onset and development. Ultimately, potential pharmacological strategies targeting inflammatory response will be reviewed and discussed.

Effects of coal-fired PM2.5 on the expression levels of atherosclerosis-related proteins and the phosphorylation level of MAPK in ApoE-/- mice

Background

Air pollution increases the morbidity and mortality of cardiovascular disease (CVD). Atherosclerosis (AS) is the pathological basis of most CVD, and the progression of atherosclerosis and the increase of fragile plaque rupture are the mechanism basis of the relationship between atmospheric particulate pollution and CVD. The aim of the present study was to investigate the effects of coal-fired fine particulate matter (PM_2.5) on the expression levels of atherosclerosis-related proteins (von Willebrand factor (vWF), Endothelin-1 (ET-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin, and to explore the role and mechanism of the progression of atherosclerosis induced by coal-fired PM_2.5 via the mitogen-activated protein kinase (MAPK) signaling pathways.

Methods

Different concentrations of PM_2.5 were given to apolipoprotein-E knockout (ApoE^−/−) mice via intratracheal instillation for 8 weeks. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of vWF, ET-1 in serum of mice. Immunohistochemistry was used to observe the expression and distribution of ICAM-1 and E-selectin in the aorta of mice. Western blot was used to investigate the phosphoylation of proteins relevant to MAPK signaling pathways.

Results

Coal-fired PM_2.5 exacerbated atherosclerosis induced by a high-fat diet. Fibrous cap formation, foam cells accumulation, and atherosclerotic lesions were observed in the aortas of PM_2.5-treated mice. Coal-fired PM_2.5 increased the protein levels of ET-1, ICAM-1, and E-selectin, but there was no significant difference in the vWF levels between the PM_2.5-treatment mice and the HFD control mice. Coal-fired PM_2.5 promoted the phosphorylation of p38, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) in aortic tissues of mice.

Conclusion

Coal-derived PM_2.5 exacerbated the formation of atherosclerosis in mice, increased the expression levels of atherosclerosis-related proteins in mice serum, and promoted the phosphorylation of proteins relevant to MAPK signaling pathway. Thus, MAPK signaling pathway may play a role in the atherosclerosis pathogenesis induced by Coal-derived PM_2.5.

Cynandione A inhibits lipopolysaccharide-induced cell adhesion via suppression of the protein expression of VCAM‑1 in human endothelial cells

Cynandione A (CA) is one of the most active compounds in the roots of Cynanchum wilfordii, the extracts of which have been used extensively in East Asia to treat various diseases including anti‑ischemic stroke. In the present study, the anti‑adherent activity of CA in lipopolysaccharide (LPS)‑stimulated human umbilical vascular endothelial cells (HUVECs) was investigated. CA markedly reduced the expression of vascular adhesion molecule‑1 (VCAM‑1) by LPS in HUVECs. The results also demonstrated that CA significantly reduced the expression of pro‑inflammatory and chemoattractant cytokines, including interleukin (IL)‑1β, IL‑6, IL‑8, monocyte chemoattractant protein‑1 and tumor necrosis factor‑α, in LPS‑activated human endothelial cells. CA inhibited the phosphorylation of mitogen‑activated protein kinases, including the extracellular signal‑regulated kinase 1/2 and p38 kinases. It was found that CA decreased the IKK/IκB‑α phosphorylation of inhibitor of nuclear factor (NF)‑κB kinase/inhibitor of NF‑κB‑α, suppressed translocation of the NF‑κB p65 subunit into the nucleus and inhibited the transcriptional activity of NF‑κB. CA also decreased human monocyte cell adhesion to endothelial cells in LPS‑stimulated conditions. These results demonstrated that CA inhibited the protein expression of VCAM‑1 and pro‑inflammatory cytokines by suppressing the transcriptional activity of NF‑κB. The results also suggested that CA may be important in the development of anti‑inflammatory drugs by inhibiting the expression of cell adhesion molecules.

Omega-3 fatty acids attenuate constitutive and insulin-induced CD36 expression through a suppression of PPARα/γ activity in microvascular endothelial cells

Microvascular dysfunction occurs in insulin resistance and/or hyperinsulinaemia. Enhanced uptake of free fatty acids (FFA) and oxidised low-density lipoproteins (oxLDL) may lead to oxidative stress and microvascular dysfunction interacting with CD36, a PPARα/γ-regulated scavenger receptor and long-chain FFA transporter. We investigated CD36 expression and CD36-mediated oxLDL uptake before and after insulin treatment in human dermal microvascular endothelial cells (HMVECs), ± different types of fatty acids (FA), including palmitic, oleic, linoleic, arachidonic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids. Insulin (10−8 and 10−7 M) time-dependently increased DiI-oxLDL uptake and CD36 surface expression (by 30 ± 13%, p<0.05 vs. untreated control after 24 hours incubation), as assessed by ELISA and flow cytometry, an effect that was potentiated by the PI3-kinase inhibitor wortmannin and reverted by the ERK1/2 inhibitor PD98059 and the PPARα/γ antagonist GW9662. A ≥24 hour exposure to 50 μM DHA or EPA, but not other FA, blunted both the constitutive (by 23 ± 3% and 29 ± 2%, respectively, p<0.05 for both) and insulin-induced CD36 expressions (by 45 ± 27 % and 12 ± 3 %, respectively, p<0.05 for both), along with insulin-induced uptake of DiI-oxLDL and the downregulation of phosphorylated endothelial nitric oxide synthase (P-eNOS). At gel shift assays, DHA reverted insulin-induced basal and oxLDL-stimulated transactivation of PPRE and DNA binding of PPARα/γ and NF-κB. In conclusion, omega-3 fatty acids blunt the increased CD36 expression and activity promoted by high concentrations of insulin. Such mechanisms may be the basis for the use of omega-3 fatty acids in diabetic microvasculopathy.

Mechanism of the effect of saikosaponin on atherosclerosis in vitro is based on the MAPK signaling pathway

The present study aimed to investigate the effects of saikosaponin on oxidized low‑density lipoprotein (ox‑LDL)‑induced human umbilical vein endothelial cell (HUVEC) injury and apoptosis, and examine the involvement of the mitogen‑activated protein kinase (MAPK) signaling pathway. The viability and apoptosis of HUVECs were detected using an MTT assay and flow cytometry. ELISA analysis was applied to measure the levels of tumor necrosis factor (TNF)‑α and interleukin (IL)‑6 cytokines. Nuclear factor (NF)‑κB p65 nuclear translocation was observed using immunofluorescence staining. The levels of intercellular adhesion molecule 1 and vascular cell adhesion molecule‑1 were detected using reverse transcription‑polymerase chain reaction analysis. The phosphorylation of B‑cell lymphoma 2 (Bcl‑2), Bcl‑2‑associated X protein (Bax), caspase‑3 p38, c‑Jun N‑terminal kinase (JNK) and extracellular signal‑regulated kinase (ERK)1/2 were detected using western blot analysis. The results revealed that saikosaponin increased the viability of the HUVECs and decreased the early‑stage apoptotic rate of the HUVECs induced by ox‑LDL. The expression levels of inflammatory cytokines in the injured vascular endothelial cells were decreased, the expression levels of adhesion molecules were reduced, the activity of superoxide dismutase was increased, and malondialdehyde content was decreased. Therefore, the inflammatory response and oxidative stress were inhibited. Simultaneously, the levels of Bcl‑2 increased, the levels of Bax and caspase‑3 decreased, and the nuclear translocation of NF‑κB p65 was significantly inhibited. The protein levels of phosphorylated p38 and JNK were reduced, whereas that of ERK1/2 remained unaffected. It was concluded that the MAPK signaling pathway mediated HUVEC injury induced by ox‑LDL. However, saikosaponin inhibited the HUVEC injury induced by ox‑LDL through inhibiting the ERK1/2 and p38 MAPK signaling pathways, and possibly also through the JNK and p38 MAPK signaling pathway.

Short-term high glucose exposure impairs insulin signaling in endothelial cells

Background

Hyperglycemia is the hallmark of diabetes and its cardiovascular complications. Insulin plays an important role in the regulation of vascular homeostasis and maintenance of endothelial function. Insulin signaling occurs after binding to the insulin receptor, causing activation of two separate and parallel pathways: PI3K/AKT/eNOS and Ras/Raf/MAPK pathways. AKT phosphorylates eNOS at Ser1177, resulting in increased nitric oxide production and vasodilation. The MAPK pathway results in endothelin-1 production and vasoconstriction and mitogenic effects.

Methods

We studied the effects of physiological insulin treatment in human umbilical vein endothelial cells (HUVECs) on the two pathways under high glucose conditions, which mimic the in vivo condition of hyperglycemia. HUVECs were incubated with insulin at different physiological concentrations (from 10⁻¹⁰ to 10⁻⁸ M) for 30 min after 24 h of exposition to normal (5 mmol/L, NG) or high glucose (25 mmol/L, HG). Phosphorylated forms of AKT, eNOS, ERK1/2, p38, JNK and insulin receptor-β subunit (IRβ) were evaluated.

Results

In normal glucose, the active phosphorylated forms of AKT, eNOS, ERK1/2, p38 and JNK were increased in insulin treated cells, in a dose-dependent manner. In high glucose, insulin was not able to activate the PI3K/AKT/eNOS pathway, with the phosphorylated form of eNOS reduced with respect to the control. However, insulin was able to induce the up-regulation of phospho-ERK1/2, -p38 and -JNK. Moreover, we found reduced levels of IRβ phosphorylated form in high glucose as compared to the control. Insulin was able to increase phospho-IRβ in normal glucose but not in high glucose, in which the total protein levels remained reduced.

Conclusions

Exposure to short-term high glucose negatively affects insulin signaling even when physiological insulin concentrations are added. The impairment of the PI3K/AKT/eNOS pathway after physiological insulin treatment could contribute to detrimental effects on cardiovascular homeostasis under high glucose conditions, and might shift toward the activation of certain mitogenic effectors, such as ERK1/2, p38 and JNK, the only ones that respond to physiological insulin treatment in high glucose.

Irradiated U937 cells trigger inflammatory bystander responses in human umbilical vein endothelial cells through the p38 pathway

Radiation-induced bystander effects are a well-known phenomenon that are observed when treating cancer and other diseases after radiotherapy, and even after occupational exposure to radiation. However, little is known about the crosstalk between irradiated macrophages and endothelial cells that line the circulatory system, which may play a role in the development of atherosclerosis. In the current study, we found that the expression of inducible nitric oxide synthase (iNOS) and the intracellular level of nitric oxide (NO) in gamma-irradiated U937 macrophage cells were significantly increased. When human umbilical vein endothelial cells (HUVECs) were co-cultured with gamma-irradiated U937 cells, additional micronuclei (MN) and apoptosis were induced so that the plating efficiency of the bystander HUVECs decreased and P38 was overexpressed in the bystander HUVECs cells. In addition, the contents of vascular cell adhesion molecule 1 (VCAM-1) and the activities of matrix metalloproteinase-9 (MMP-9) in the culture medium of bystander HUVECs were increased. Furthermore, during cell co-culture the adhesive ability of irradiated U937 cells to the bystander HUVECs increased. When U937 cells were treated with 500 μM S-methylisothiourea sulfate (SMT) (iNOS inhibitor) before irradiation, and HUVECs were treated with 10 μM SB203580 (p38 inhibitor) before cell co-culture or treated with 20 μM c-PTIO (NO scavenger) in the co-culture medium, the bystander micronuclei and the amounts of VCAM-1 and MMP-9 in the medium of bystander HUVECs were diminished, and the ability of irradiated U937 cells adhering to HUVECs was also reduced, while the plating efficiency of bystander HUVECs partially recovered. These results demonstrated that irradiated U937 cells appear to release nitric oxide and thereby further trigger apoptosis and inflammatory responses in the bystander HUVECs through a p38-dependent pathway.

Co-activation of nuclear factor-κB and myocardin/serum response factor conveys the hypertrophy signal of high insulin levels in cardiac myoblasts

Hyperinsulinemia contributes to cardiac hypertrophy and heart failure in patients with the metabolic syndrome and type 2 diabetes. Here, high circulating levels of tumor necrosis factor (TNF)-α may synergize with insulin in signaling inflammation and cardiac hypertrophy. We tested whether high insulin affects activation of TNF-α-induced NF-κB and myocardin/serum response factor (SRF) to convey hypertrophy signaling in cardiac myoblasts. In canine cardiac myoblasts, treatment with high insulin (10(-8) to 10(-7) m) for 0-24 h increased insulin receptor substrate (IRS)-1 phosphorylation at Ser-307, decreased protein levels of chaperone-associated ubiquitin (Ub) E3 ligase C terminus of heat shock protein 70-interacting protein (CHIP), increased SRF activity, as well as β-myosin heavy chain (MHC) and myocardin expressions. Here siRNAs to myocardin or NF-κB, as well as CHIP overexpression prevented (while siRNA-mediated CHIP disruption potentiated) high insulin-induced SR element (SRE) activation and β-MHC expression. Insulin markedly potentiated TNF-α-induced NF-κB activation. Compared with insulin alone, insulin+TNF-α increased SRF/SRE binding and β-MHC expression, which was reversed by the NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) and by NF-κB silencing. In the hearts of db/db diabetic mice, in which Akt phosphorylation was decreased, p38MAPK, Akt1, and IRS-1 phosphorylation at Ser-307 were increased, together with myocardin expression as well as SRE and NF-κB activities. In response to high insulin, cardiac myoblasts increase the expression or the promyogenic transcription factors myocardin/SRF in a CHIP-dependent manner. Insulin potentiates TNF-α in inducing NF-κB and SRF/SRE activities. In hyperinsulinemic states, myocardin may act as a nuclear effector of insulin, promoting cardiac hypertrophy.

Muscle inflammatory signaling in response to 9 days of physical inactivity in young men with low compared with normal birth weight

OBJECTIVE

The molecular mechanisms linking physical inactivity and muscle insulin resistance in humans have been suggested to include increased muscle inflammation, possibly associated with impaired oxidative metabolism. We employed a human bed rest study including 20 young males with normal birth weight (NBW) and 20 with low birth weight (LBW) and increased risk of diabetes.

METHODOLOGY

The subjects were studied before and after 9 days of bed rest using the euglycemic-hyperinsulinemic clamp and muscle biopsy excision. Muscle inflammatory status was assessed as nuclear factor-κB (NF-κB) activity and mRNA expression of the pro-inflammatory MCP1 (CCL2) and IL6 and the macrophage marker CD68. Furthermore, mRNA expression of genes central to oxidative phosphorylation (OXPHOS) was measured including ATP5O, COX7A1, NDUFB6, and UQCRB.

RESULTS

At baseline, muscle inflammatory status was similar in NBW and LBW individuals. After bed rest, CD68 expression was increased in LBW (P=0.03) but not in NBW individuals. Furthermore, expression levels of all OXPHOS genes were reduced after bed rest in LBW (P ≤ 0.05) but not in NBW subjects and were negatively correlated with CD68 expression in LBW subjects (P ≤ 0.03 for all correlations). MCP1 expression and NF-κB activity were unaffected by bed rest, and IL6 expression was too low for accurate measurements. None of the inflammatory markers correlated with insulin sensitivity.

CONCLUSIONS

Although LBW subjects exhibit disproportionately elevated CD68 mRNA expression suggesting macrophage infiltration and reduced OXPHOS gene expression when exposed to bed rest, our data altogether do not support the notion that bed rest-induced (9 days) insulin resistance is caused by increased muscle inflammation.

Relevance of new drug discovery to reduce NF-κB activation in cardiovascular disease

The transcription factor nuclear factor-κB (NF-κB) is a main regulator of the expression of several genes involved in the activation of inflammation, cell proliferation, cell immunity and apoptosis. Excess or inappropriate activation of NF-κB has been observed in human inflammatory diseases, including atherosclerosis. Because of the extensive involvement of NF-κB signaling in human diseases, efforts have been made in developing inhibitors of this pathway. Here we will provide an overview of the biology of NF-κB activation pathways. We will here especially focus on current knowledge of the role of the classical ("canonical") NF-κB activation pathway as a potential therapeutic target for anti-atherosclerotic therapies in clinical applications, and discuss classical and novel therapeutic strategies to reduce its prolonged activation.

Reducing cardiovascular disease risk in patients with type 2 diabetes and concomitant macrovascular disease: can insulin be too much of a good thing?

Despite improvement of microvascular outcomes as a consequence of optimal glucose control in patients with type 2 diabetes, prevention of macrovascular complications is still a major challenge. Of interest, large-scale intervention studies (Action to Control Cardiovascular Risk in Diabetes, Action in Diabetes and Vascular Disease-Preterax and Diamicron Modified Release Controlled Evaluation and Veterans Affairs Diabetes Trial) comparing standard therapy versus more intensive glucose-lowering therapy failed to report beneficial impacts on macrovascular outcomes. Consequently, it is currently under debate whether the high doses of exogenous insulin that were administered in these trials to achieve strict target glucose levels could be responsible for these unexpected outcomes. Additionally, a potential role for plasma insulin levels in predicting macrovascular outcomes has emerged in patients with or without type 2 diabetes. These observations, combined with evidence from in vitro and animal experiments, suggest that insulin might have intrinsic atherogenic effects. In this review, we summarize clinical trials, population-based studies as well as data emerging from basic science experiments that point towards the hypothesis that the administration of high insulin doses might not be beneficial in patients with type 2 diabetes and established macrovascular disease.

Bacteroides fragilis enterotoxin upregulates intercellular adhesion molecule-1 in endothelial cells via an aldose reductase-, MAPK-, and NF-κB-dependent pathway, leading to monocyte adhesion to endothelial cells

Enterotoxigenic Bacteroides fragilis (ETBF) produces a ∼ 20-kDa heat-labile enterotoxin (BFT) that plays an essential role in mucosal inflammation. Although a variety of inflammatory cells is found at ETBF-infected sites, little is known about leukocyte adhesion in response to BFT stimulation. We investigated whether BFT affected the expression of ICAM-1 and monocytic adhesion to endothelial cells (ECs). Stimulation of HUVECs and rat aortic ECs with BFT resulted in the induction of ICAM-1 expression. Upregulation of ICAM-1 was dependent on the activation of IκB kinase (IKK) and NF-κB signaling. In contrast, suppression of AP-1 did not affect ICAM-1 expression in BFT-stimulated cells. Suppression of NF-κB activity in HUVECs significantly reduced monocytic adhesion, indicating that ICAM-1 expression is indispensable for BFT-induced adhesion of monocytes to the endothelium. Inhibition of JNK resulted in a significant attenuation of BFT-induced ICAM-1 expression in ECs. Moreover, inhibition of aldose reductase significantly reduced JNK-dependent IKK/NF-κB activation, ICAM-1 expression, and adhesion of monocytes to HUVECs. These results suggest that a signaling pathway involving aldose reductase, JNK, IKK, and NF-κB is required for ICAM-1 induction in ECs exposed to BFT, and may be involved in the leukocyte-adhesion cascade following infection with ETBF.

Major contribution of the P2Y₁receptor in purinergic regulation of TNFα-induced vascular inflammation

BACKGROUND

Atherosclerosis is an inflammatory disease, and extracellular nucleotides are one of the factors possibly involved in vascular inflammation. The P2Y(1) receptor for adenosine 5'-diphosphate has been shown to be involved in the development of atherosclerosis in apolipoprotein E--deficient mice. Our aim is to determine whether the endothelial P2Y(1) receptor plays a role in leukocyte recruitment during vascular inflammation and characterize underlying mechanisms.

METHODS AND RESULTS

We show here that the P2Y(1) receptor plays a role in leukocyte recruitment in inflamed mouse femoral arteries. Moreover, in wild-type bone marrow--transplanted chimeric P2Y(1)-deficient mice with an apolipoprotein E--deficient background, a strong reduction of adhesion molecule--dependent leukocyte recruitment was observed after local injection of tumor necrosis factor and interleukin 1β, excluding a role for the platelet or other hematopoietic cell type P2Y(1) in these events. Similarly, the in vitro adhesion of isolated mouse monocytes to tumor necrosis factor α--stimulated murine endothelial cell monolayers and their migration across the cell layers were strongly reduced in P2Y(1)-deficient compared with wild-type endothelial cells, as was the expression of the adhesion molecules P-selectin, Vascular cell adhesion molecule 1, and intercellular adhesion molecule 1. Pharmacological inhibition using the selective antagonist MRS2500 also resulted in decreased expression of adhesion molecules. These events are related to the p38 mitogen-activated protein kinase and activating transcription factor 2 pathway. Finally, in vivo administration of MRS2500 resulted in strong reduction of leukocyte recruitment in inflamed femoral arteries of apolipoprotein E--deficient mice.

CONCLUSIONS

The data highlight a key role of the endothelial P2Y(1) receptor in acute vascular inflammation. Pharmacological targeting the P2Y(1) receptor could represent a promising approach for the treatment of vascular inflammation.

NHE-1 and β1 integrin dependent monocyte adhesion and migration after glucose, insulin or PPARγ stimulation

In the present study the effect of high glucose concentrations, insulin, PPARγ activators (rosiglitazone) and NHE-1 inhibitors (cariporide) in atherosclerosis-related functions of human monocytes was investigated. Monocyte adhesion to laminin-1, collagen type IV and endothelial cells, as well as monocyte migration through the same substrates were studied. Incubation of the monocyte suspension with high glucose concentrations, insulin and rosiglitazone induced all the studied atherosclerosis-related functions of the monocytes. In all these functions the addition of cariporide counteracted the activity of glucose, insulin and rosiglitazone. The use of antigen for β1 integrin also counteracted the activity of the above in monocyte adhesion in all three substrates. The data of the present study suggests that PPARγ activation in monocytes induces atherosclerosis, and that NHE-1 and β1 integrin play an important role in the beginning of atherosclerosis.

Cellular and molecular mechanisms of vascular injury in diabetes--part I: pathways of vascular disease in diabetes

Diabetes-induced micro- and macrovascular complications are the major causes of morbidity and mortality in diabetic patients. While hyperglycemia is a key factor for the pathogenesis of diabetic microvascular complications, it is only one of the multiple factors capable of increasing the risk of macrovascular complications. Hyperglycemia induces vascular damage probably through a single common pathway - increased intracellular oxidative stress - linking four major mechanisms, namely the polyol pathway, advanced glycation end-products (AGEs) formation, the protein kinase C (PKC)-diacylglycerol (DAG) and the hexosamine pathways. In addition, in conditions of insulin resistance, i.e., preceding the onset of type 2 diabetes, the phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway is selectively inhibited, while the mitogen activated protein (MAP)-kinase pathway remains largely unaffected, thus allowing compensatory hyperinsulinemia to elicit pro-atherogenic events in vascular smooth muscle and endothelial cells, including increased cell proliferation, and the expression of plasminogen activator inhibitor-1, as well as of proinflammatory cytokines and endothelial adhesion molecules.

Cellular and molecular mechanisms of vascular injury in diabetes--part II: cellular mechanisms and therapeutic targets

Although the mechanisms by which insulin-resistance and hyperglycemia lead to cardiovascular disease are still incompletely understood, all mechanisms apparently converge on the vessel wall and the endothelium as a common disease target. Endothelial cells play a crucial role in vascular homeostasis, providing a functional barrier and modulating several signals involved in vasomotion, as well as antiplatelet, anti-inflammatory, anti-proliferative, and anti-oxidant properties of the vessel wall. Endothelial cell dysfunction occurs early in diabetes and insulin resistance states. Since atherosclerosis may result from an imbalance between the magnitude of vascular injury and the capacity of repair, a role has been recently postulated for a defective mobilization of vascular progenitors, including endothelial progenitor cells, in the pathogenesis of vascular disease. Here we summarize the evidence for such an occurrence. We also here highlight how new insights into pathways of vascular damage in diabetes may indicate new targets for preventive and treatment strategies.

Insulin suppresses HDL-mediated cholesterol efflux from macrophages through inhibition of neutral cholesteryl ester hydrolase and ATP-binding cassette transporter G1 expressions

AIMS

We studied the effect of insulin on HDL-mediated cholesterol efflux from macrophages. The potential involvement of cholesteryl ester hydrolysis and membrane cholesterol transport was also addressed.

METHODS

Human monocyte-derived THP-1 cells were developed into macrophages. Cholesterol efflux was measured by incubating macrophages, labeled with [³H]-cholesterol, with HDL for 24 h. The cells were treated with insulin (0-500 nM) for 30 min prior to the addition of HDL. To investigate the molecular mechanisms of the effect of insulin, the expressions of neutral cholesteryl ester hydrolase (nCEH) and ATP-binding cassette transporter (ABC) G1 were analyzed.

RESULTS

Insulin inhibited, in a concentration-dependent manner, HDL-mediated cholesterol efflux from macrophages. Insulin also inhibited the enzyme activity of nCEH and its mRNA and protein expression in cells. Insulin also suppressed the expressions of mRNA and protein for ABCG1.

CONCLUSIONS

Insulin inhibits HDL-mediated cholesterol efflux from macrophages, which may result from the suppression of nCEH and ABCG1 expressions. Our findings show part of the potential molecular mechanism of atherogenesis in type 2 diabetes with hyperinsulinemia.

Radiation-induced interleukin-6 expression through MAPK/p38/NF-kappaB signaling pathway and the resultant antiapoptotic effect on endothelial cells through Mcl-1 expression with sIL6-Ralpha

PURPOSE

To investigate the mechanism of interleukin-6 (IL-6) activity induced by ionizing radiation.

METHODS AND MATERIALS

Human umbilical vascular endothelial cells (HUVECs) were irradiated with different doses to induce IL-6. The IL-6 promoter assay and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to examine transcriptional regulation. Specific chemical inhibitors, decoy double-stranded oligodeoxynucleotides, and Western blotting were conducted to investigate the signal transduction pathway. Recombinant soluble human IL-6 receptor alpha-chain (sIL6-Ralpha) and specific small interfering RNA were used to evaluate the biologic function of radiation-induced IL-6.

RESULTS

Four grays of radiation induced the highest level of IL-6 protein. The promoter assay and RT-PCR data revealed that the induction of IL-6 was mediated through transcriptional regulation. The p38 inhibitor SB203580, by blocking nuclear factor-kappaB (NF-kappaB) activation, prevented both the transcriptional and translational regulation of radiation-induced IL-6 expression. The addition of sIL6-Ralpha rescued HUVECs from radiation-induced death in an IL-6 concentratio-dependent manner. The antiapoptotic effect of combined sIL6-Ralpha and radiation-induced IL-6 was inhibited by mcl-1-specific small interfering RNA.

CONCLUSION

Radiation transcriptionally induces IL-6 expression in endothelial cells through mitogen-activated protein kinase/p38-mediated NF-kappaB/IkappaB (inhibitor of NF-kappaB) complex activation. In the presence of sIL6-Ralpha, radiation-induced IL-6 expression acts through Mcl-1 expression to rescue endothelial cells from radiation-induced death.

Extracellular PBEF/NAMPT/visfatin activates pro-inflammatory signalling in human vascular smooth muscle cells through nicotinamide phosphoribosyltransferase activity

AIMS/HYPOTHESIS

Extracellular pre-B cell colony-enhancing factor/nicotinamide phosphoribosyltransferase/visfatin (ePBEF/NAMPT/visfatin) is an adipocytokine, whose circulating levels are enhanced in metabolic disorders, such as diabetes mellitus and obesity. Here, we explored the ability of ePBEF/NAMPT/visfatin to promote vascular inflammation, as a condition closely related to atherothrombotic diseases. We specifically studied the ability of PBEF/NAMPT/visfatin to directly activate pathways leading to inducible nitric oxide synthase (iNOS) induction in cultured human aortic smooth muscle cells, as well as the mechanisms involved.

METHODS

iNOS levels and extracellular signal-regulated kinase (ERK) 1/2 activity were determined by western blotting. Nuclear factor (NF)-kappaB activity was assessed by electrophoretic mobility shift assay.

RESULTS

ePBEF/NAMPT/visfatin (10-250 ng/ml) induced iNOS in a concentration-dependent manner. At a submaximal concentration (100 ng/ml), ePBEF/NAMPT/visfatin time-dependently enhanced iNOS levels up to 18 h after stimulation. Over this time period, ePBEF/NAMPT/visfatin elicited a sustained activation of NF-kappaB and triggered a biphasic ERK 1/2 activation. By using the respective ERK 1/2 and NF-kappaB inhibitors, PD98059 and pyrrolidine dithiocarbamate, we established that iNOS induction by ePBEF/NAMPT/visfatin required the consecutive upstream activation of ERK 1/2 and NF-kappaB. The pro-inflammatory action of ePBEF/NAMPT/visfatin was not prevented by insulin receptor blockade. However, exogenous nicotinamide mononucleotide, the product of NAMPT activity, mimicked NF-kappaB activation and iNOS induction by ePBEF/NAMPT/visfatin, while the NAMPT inhibitor APO866 prevented the effects of ePBEF/NAMPT/visfatin on iNOS and NF-kappaB.

CONCLUSIONS/INTERPRETATION

Through its intrinsic NAMPT activity, ePBEF/NAMPT/visfatin appears to be a direct contributor to vascular inflammation, a key feature of atherothrombotic diseases linked to metabolic disorders.

Contribution of insulin resistance to vascular dysfunction

Insulin is a vascular hormone, able to influence vascular cell responses. In this review, we consider the insulin actions on vascular endothelium and on vascular smooth muscle cells (VSMC) both in physiological conditions and in the presence of insulin resistance. In particular, we focus the relationships between activation of insulin signalling pathways of phosphatidylinositol-3 kinase (PI3-K) and mitogen-activated protein kinase (MAPK) and the different vascular actions of insulin, with a particular attention to the insulin ability to activate the pathway nitric oxide (NO)/cyclic GMP/PKG via PI3-K, owing to the peculiar relevance of NO in vascular biology. We also discuss the insulin actions mediated by the MAPK pathway (such as endothelin-1 synthesis and secretion and VSMC proliferation and migration) and by the interactions between the two pathways, both in insulin-sensitive and in insulin-resistant states. Finally, we consider the influence of free fatty acids, cytokines and endothelin on vascular insulin resistance.

Vascular actions of insulin with implications for endothelial dysfunction

Hemodynamic actions of insulin depend largely on the hormone's ability to stimulate synthesis and release of endothelial mediators, whose balanced activity ensures dynamic control of vascular function. Nitric oxide (NO), endothelin-1 (ET-1), and reactive oxygen species (ROS) are important examples of endothelial mediators with opposing properties on vascular tone, hemostatic processes, and vascular permeability. Reduced NO bioavailability, resulting from either insufficient production or increased degradation of NO, characterizes endothelial dysfunction. In turn, endothelial dysfunction predicts vascular complications of metabolic and hemodynamic disorders. In the cardiovascular system, insulin stimulates the production and release of NO, ET-1, and ROS via activation of distinct intracellular signaling pathways. Under insulin-resistant conditions, increased insulin concentrations and/or impaired insulin-signaling pathways in the vasculature may contribute to imbalance in secretion of endothelial mediators that promote pathogenesis of vascular abnormalities. This short review describes signaling pathways involved in insulin-stimulated release of NO, ROS, and ET-1 and suggests possible molecular mechanisms by which abnormal insulin signaling may contribute to endothelial dysfunction.

Biology of neurotensin: revisited study

The tridecapeptide neurotensin (NT) acts in the mammalian brain as a primary neurotransmitter or neuromodulator of classical neurotransmitters. Morphological and functional in vitro and in vivo studies have demonstrated the existence of close interactions between NT and dopamine both in limbic and in striatal brain regions. Additionally, biochemical and neurochemical evidence indicates that in these brain regions NT also plays a crucial role in the regulation of the aminoacidergic signalling. Immune cells, such as lymphocytes, macrophages and mast cells are reported to be activated by neuropeptides, such as neurotensin; this activation leads to cytokine and immunoglobulin production. In addition, neurotensin increases calcium level and the production of nitric oxide. Therefore neurotensin is deeply involved in immunity and inflammation but its real function still remains to be elucidated.

Insulin potentiates cytokine-induced VCAM-1 expression in human endothelial cells

Hyperinsulinemia is an independent risk factor for cardiovascular events and may contribute to cardiovascular disease. Low-grade chronic inflammation has been implicated in the pathogenesis of atherosclerosis. We aimed at determining the impact of pathophysiologically high insulin concentrations on cytokine-induced endothelial activation in human umbilical vein endothelial cells (HUVEC). HUVEC were incubated with insulin (0-24 h)+/-tumor necrosis factor (TNF)-alpha or lipopolysaccharide (LPS). At pathophysiological/pharmacological concentrations (10(-9)-10(-7) mol/L), insulin selectively induced VCAM-1 expression and potentiated the effects of TNF-alpha andLPS, effects reverted by the proteasome inhibitor lactacystin. Compared with TNF-alpha alone, insulin+TNF-alpha doubled U937 cell adhesion. Insulin markedly increased TNF-alpha-induced NF-kappaB activation and induced phosphorylated IkappaB-alpha accumulation. Therefore, hyperinsulinemia enhances cytokine-induced VCAM-1 expression in endothelial cells, thus potentially contributing to detrimental effects of other inflammatory stimuli on atherogenesis.

Substance P: An Inflammatory Peptide

Substance P (SP) is involved in neurogenic inflammation and in the pathogenesis of several inflammatory diseases, demonstrating that there is a narrow interrelationship between the nervous system and immunity. Macrophage functions are altered in stress, therefore, since SP is a macrophage activator, its biological effect has been intimately linked to stress. In fact, SP enhances LPS-induced macrophage TNFα production from stressed animals and stimulates the production of IL-8 CXC chemokine response in a mast cell line in vitro. The stress-induced cytokines from macrophage also alter and contribute to inflammation. Understanding the pathophysiology of inflammation and the role of the chemical mediator SP may improve inflammation management.