High insulin exacerbates neutrophil-endothelial cell adhesion through endothelial surface expression of intercellular adhesion molecule-1 via activation of protein kinase C and mitogen-activated protein kinase

Type 1 diabetes mellitus: Roles of neutrophils in the pathogenesis

Circulating neutrophil counts are reduced both in healthy autoantibody-positive individuals and in patients with type 1 diabetes, which may be related on cell-specific autoimmunity. This paper was written to give an update on roles of neutrophils in the pathogenesis of type 1 diabetes mellitus. Different research search engines like PubMed Central, Scopus, Web of Science, Researchgate, Google Scholar etc were utilised for writing this paper. A drop in blood neutrophil counts in type 1 diabetes may be caused by decreased neutrophil generation and maturation, tissue maintenance, consumption, or peripheral damage. Neutrophil count variations between studies may be explained by results from various stages of diabetes or by ethnic groups. Neutrophils can induce type 1 diabetes by colonizing pancreatic islets and interacting with other immune cells, according to exciting findings that shed new light on their role in the pathogenesis of the disease. Knowing more about the function of neutrophils in the pathogenesis of type 1 diabetes will help in early diagnosis, treatment, and even prevention of the disease.

Executable models of immune signaling pathways in HIV-associated atherosclerosis

Atherosclerosis (AS)-associated cardiovascular disease is an important cause of mortality in an aging population of people living with HIV (PLWH). This elevated risk has been attributed to viral infection, anti-retroviral therapy, chronic inflammation, and lifestyle factors. However, the rates at which PLWH develop AS vary even after controlling for length of infection, treatment duration, and for lifestyle factors. To investigate the molecular signaling underlying this variation, we sequenced 9368 peripheral blood mononuclear cells (PBMCs) from eight PLWH, four of whom have atherosclerosis (AS+). Additionally, a publicly available dataset of PBMCs from persons before and after HIV infection was used to investigate the effect of acute HIV infection. To characterize dysregulation of pathways rather than just measuring enrichment, we developed the single-cell Boolean Omics Network Invariant Time Analysis (scBONITA) algorithm. scBONITA infers executable dynamic pathway models and performs a perturbation analysis to identify high impact genes. These dynamic models are used for pathway analysis and to map sequenced cells to characteristic signaling states (attractor analysis). scBONITA revealed that lipid signaling regulates cell migration into the vascular endothelium in AS+ PLWH. Pathways implicated included AGE-RAGE and PI3K-AKT signaling in CD8+ T cells, and glucagon and cAMP signaling pathways in monocytes. Attractor analysis with scBONITA facilitated the pathway-based characterization of cellular states in CD8+ T cells and monocytes. In this manner, we identify critical cell-type specific molecular mechanisms underlying HIV-associated atherosclerosis using a novel computational method.

Nutrient regulation of inflammatory signalling in obesity and vascular disease

Despite obesity and diabetes markedly increasing the risk of developing cardiovascular diseases, the molecular and cellular mechanisms that underlie this association remain poorly characterised. In the last 20 years it has become apparent that chronic, low-grade inflammation in obese adipose tissue may contribute to the risk of developing insulin resistance and type 2 diabetes. Furthermore, increased vascular pro-inflammatory signalling is a key event in the development of cardiovascular diseases. Overnutrition exacerbates pro-inflammatory signalling in vascular and adipose tissues, with several mechanisms proposed to mediate this. In this article, we review the molecular and cellular mechanisms by which nutrients are proposed to regulate pro-inflammatory signalling in adipose and vascular tissues. In addition, we examine the potential therapeutic opportunities that these mechanisms provide for suppression of inappropriate inflammation in obesity and vascular disease.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

Endoglin Mediates Vascular Endothelial Growth Factor-A-Induced Endothelial Cell Activation by Regulating Akt Signaling

In diabetic nephropathy, differential expression of growth factors leads to vascular changes, including endothelial cell activation, monocyte infiltration, and inflammation. Endoglin plays an important role in endothelial function and is also associated with inflammation. In the kidney, vascular endoglin expression is increased in animal models of renal injury, where it contributes to disease severity, possibly by promoting endothelial cell activation and inflammation. Herein, we investigated whether endoglin expression is associated with diabetic nephropathy. In addition, we examined whether reducing endothelial endoglin expression in vitro affects endothelial cell activation and monocyte adhesion and, if so, which intracellular pathways are involved. Finally, we analyzed whether glomerular endoglin expression is correlated with endothelial cell activation in patients with diabetic nephropathy. Endoglin levels were significantly increased in mice with type 1 diabetes compared with control mice. Reducing endoglin expression in cultured endothelial cells significantly impaired the vascular endothelial growth factor-A-induced up-regulation of activation markers and monocyte adhesion. This was mediated by increased phosphorylation of Akt, thereby inhibiting activating transcription factor 2 phosphorylation, which regulates vascular cell adhesion molecule-1 (VCAM1) gene transcription in these cells. Last, endoglin colocalized with VCAM-1 in the glomeruli of diabetic patients, glomerular VCAM-1 expression was significantly increased in these patients, and this increase in VCAM-1 expression was correlated with increased glomerular endoglin expression. Thus, targeting endoglin function may have therapeutic value in patients at risk for diabetic nephropathy.

Higher serum levels of uric acid are associated with a reduced insulin clearance in non-diabetic individuals

AIMS

Decreased insulin clearance has been reported to be associated with insulin resistance-related disorders and incident type 2 diabetes. The aim of this study was to evaluate whether higher levels of uric acid (UA), a known risk factor of type 2 diabetes, are associated with a reduced insulin clearance.

METHODS

440 non-diabetic individuals were stratified in tertiles according to serum UA levels. Insulin clearance and skeletal muscle insulin sensitivity were assessed by euglycemic hyperinsulinemic clamp. Hepatic insulin resistance was estimated by the liver IR index.

RESULTS

Subjects with higher levels of UA displayed an unfavorable metabolic phenotype with a worse lipid profile, increased levels of 2-h post-load glucose levels, fasting, and 2-h post-load insulin levels, hsCRP, liver IR index, and lower levels of eGFR and skeletal muscle insulin sensitivity, in comparison to individuals with lower UA levels. Moreover, subjects with higher UA concentrations exhibited decreased levels of insulin clearance even after adjustment for age, gender, BMI, eGFR, and skeletal muscle insulin sensitivity. In a multivariate regression analysis model including several confounding factors, UA concentration was an independent predictor of insulin clearance (β = - 0.145; P = 0.03). However, when liver IR index was included in the model, the independent association between UA levels and insulin clearance was not retained. Accordingly, in a mediation analysis, liver IR index was a mediator of the negative effects of UA levels on insulin clearance (t = - 2.55, P = 0.01).

CONCLUSIONS

Higher serum levels of UA may affect insulin clearance by impairing hepatic insulin sensitivity.

Probing of peripheral blood mononuclear cells anchoring on TNF-alpha challenged-vascular endothelia in an in vitro model of the retinal microvascular

Retinopathy is a complication of diabetes that affects the eyes; it stems from damage to the microvasculature of the retina and eventually compromises vision. The diagnosis of retinopathy is difficult to make because there are no early symptoms or warning signs. Dysfunction of the retina's microvascular networks is believed to be associated with inflammatory cytokines and tumor necrosis factor alpha (TNF-α). To investigate the effect of these cytokines, such as TNF-α, a polydimethylsiloxane (PDMS)/glass hydride microfluidic device reflecting the physiological structure of the retina's microvasculature was developed. In this model, the bifurcations and tortuosity of branch vessels were based on photographs of the fundus and an endothelial cell layer (EA.hy926 cells) were reconstructed within the microfluidic network. The adhesion, spreading, and growth of cells was ensured by optimizing the conditions for cell seeding and perfusion. Fluorescent staining was used to visualize the cytoskeleton and measurement of the nitric oxide (NO) level proved that the endothelial EA.hy926 cells had spread in the direction of flow perfusion system, forming artificial vascular networks. The endothelial layer was further challenged by TNF-α perfusion. Cytokine treatment increased the anchoring of peripheral blood mononuclear cells (PBMCs) on the endothelial layer. The microfluidic device developed in this study provides a low-cost platform reflecting the physiological structures of the retina's microvasculature. It is anticipated that this device will be useful in evaluating the diseased retina as well as in drug screening.

ERK2 and Akt are negative regulators of insulin and Tumor Necrosis Factor-α stimulated VCAM-1 expression in rat aorta endothelial cells

Background

Diabetes is quickly becoming the most widespread disorder in the Western world. Among the most prevalent effects of diabetes is atherosclerosis, which in turn is driven in part by inflammation. Both insulin and Tumor Necrosis Factor-alpha (TNFα) increase the presence of Vascular Cellular Adhesion Molecule-1 (VCAM-1) expression. The aim of this study is to determine the effects of downregulating Extracellular signal-Regulated Kinase-2 (ERK2) and Akt on insulin and TNFa-stimulated VCAM-1 expression.

Methods

Here we begin to define the relationships between ERK2 and Akt regulation of insulin and TNFα-stimulated VCAM-1 expression in Rat Arterial Endothelial Cells (RAEC) by transfecting RAEC with ERK2 and Akt RNA interference (RNAi) and then treating these cells with insulin (10 nM) or TNFα (10 ng/mL) alone or in combination.

Results

Western blot analyses, flow cytometry and confocal microscopy were used to determine changes in VCAM-1 expression within the above-stated parameters. Cells transfected with ERK2 or Akt RNAi plasmids increased insulin and TNFα-stimulated VCAM-1 total protein expression significantly (P < 0.05) greater than that seen in mock transfected cells and expressed cell surface VCAM-1 greater than that seen in mock transfected cells as indicated by flow cytometry and confocal microscopy. Nevertheless, the decrease of both kinases did not increase insulin or TNFα-stimulated VCAM-1 expression above that seen when one or the other RNAi was present.

Conclusions

Taken together, our results demonstrate that ERK2 and Akt may be negative regulators of insulin and TNF-α stimulated VCAM-1 and that their loss or down regulation might upregulate VCAM-1 expression and contribute to vascular disease.

Effect of Nitric Oxide on the Expression of Matrix Metalloproteinase and Its Association with Migration of Cultured Trabecular Meshwork Cells

Purpose

To determine the effect of exogenous nitric oxide (NO) on the migration of trabecular meshwork (TM) cells and its association with expression of matrix metalloproteinases (MMPs).

Methods

Primary human TM cells treated with 1 or 10 µM S-nitroso-N-acetyl-penicillamine (SNAP) and examined for changes in adherence. TM cells were seeded onto transwell culture inserts, and changes in their migratory activity were quantified. Reverse transcription polymerase chain reaction was performed to determine the relative changes in mRNA expression of MMPs and tissue inhibitor of metalloproteinases (TIMPs).

Results

Treatment with SNAP did not significantly suppress TM cell adhesion or migration (p > 0.05). Treatment of TM cells with 10 µM SNAP decreased expression of MMP-2 and increased expression of membrane type MMP-1 and TIMP-2. Treatment with interleukin-1α triggered MMP-3 expression but did not exert significant effects on MMP-3 activation in response to SNAP.

Conclusions

These data suggest that NO revealed no significant effect on the migration of TM cells because NO decreased MMP-2 and increased TIMP-2 expression. Although expression of certain MMPs and TIMPs change in response to NO donors, NO may modulate trabecular outflow by changing the cellular production of extracellular matrix without having a significant effect on the migration of TM cells.

New molecular insights in diabetic nephropathy

Diabetes mellitus represents one of the major causes of functional kidney impairment. The review highlights the most significant steps made over the last decades in understanding the molecular basis of diabetic nephropathy (DN), which may provide reliable biomarkers for early diagnosis and prognosis, along with new molecular targets for personalized medicine. There is an increased interest in developing new therapeutic strategies to slow DN progression for improving patients' quality of life and reducing all-cause morbidity and disease-associated mortality. It is highly important to have a science-based medical attitude when facing diabetic patients with associated comorbidities and risk of rapid evolution toward end-stage renal disease. The data discussed herein were mainly from MEDLINE and PubMed articles published in English from 1990 to 2015 and from up-to-date. The search term was "diabetic nephropathy and oxidative stress".

Extracellular signal-regulated kinase-5: Novel mediator of insulin and tumor necrosis factor α-stimulated vascular cell adhesion molecule-1 expression in vascular cells

BACKGROUND

Atherosclerosis may be stimulated by the increased presence of insulin and tumor necrosis-factor-α (TNFα) with subsequent expression of vascular cell adhesion molecule-1 (VCAM-1). We hypothesized that extracellular signal-regulated kinase-5 (ERK5) plays an important role in insulin and TNFα-stimulated total and cell surface VCAM-1 expression.

METHODS

Rat aorta vascular endothelial cells were first transfected with either no inhibitory RNA, inactive (scrambled) inhibitory ERK5 RNA (scERK5) or active inhibitory ERK5 RNA (siERK5) and then treated with either (i) no analog; (ii) insulin (1 nM), or TNFα (1 ng/mL) alone, or (iii) insulin plus TNFα for 6 h. Thereafter either total VCAM-1 protein or surface VCAM-1 protein was determined.

RESULTS

Genetic inhibition of ERK5 decreased TNFα-stimulated total VCAM-1 expression by 57% and surface expression by 27%. In contrast, genetic inhibition of ERK5 did not significantly decrease insulin-stimulated total or surface VCAM-1 expression. Interestingly, genetic inhibition of ERK5 did not significantly decrease insulin plus TNFα-stimulated total VCAM-1 expression, but significantly (P < 0.05) decreased insulin plus TNFα-stimulated surface VCAM-1 expression 41%.

CONCLUSIONS

We report here that ERK5 plays a minor role in insulin-stimulation of VCAM-1, but plays a significant role in TNFα-stimulation of both total and cell surface VCAM-1 protein expression. Taken together, these results demonstrate that not only does ERK5 have differential mediation of insulin and TNFα-stimulated VCAM-1 expression, but also has differential regulation of insulin plus TNFα-stimulated total and surface VCAM-1 expression, suggesting that other intermediates of the insulin and TNFα intracellular pathways are contributing to atherogenesis.

Diabetes alters the expression of partial vasoactivators in cerebral vascular disease susceptible regions of the diabetic rat

BACKGROUND

The pathogenesis between cerebral vascular disease (CVD) and the endothelial dysfunction (ETD) remains elusive in diabetes. Therefore, we investigated the expression of partial vasoactivators which be closely relative to ETD in CVD susceptible brain regions in the diabetic rat. The aim was to search some possible pathogenesis.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin and a high lipid/sugar diet. The expression of vasoactivators ET-1, CGRP, VCAM-1, ICAM-1 and P-selectin were assessed by immunohistochemical staining and measurement of optic density of positive cells in the frontal and temporal lobe, basal ganglia and thalamus at 4 weeks after establishment of the diabetic model.

RESULTS

The expression of ET-1, VCAM-1, ICAM-1 and P-selectin significantly increased and CGRP significantly decreased in the diabetic group, and the expression of these vasoactivators was significantly different among the frontal, temporal lobe, basal ganglia and thalamus, and among the emotion, splanchno-motor and neuroendocrine center in the diabetic group.

CONCLUSIONS

Diabetes alters the expression of partial vasoactivators in cerebral vascular disease susceptible regions of the diabetic rat. Therefore, we suggested that CVD complications in diabetes are partly caused by ETD via an imbalance expression of endothelial vasoactivators, which might be associated with dysfunction of emotion, autonomic nerve and endocrine center. However, further studies are warranted.

Soluble platelet/endothelial cell adhesion molecule (sPECAM)-1 is increased in polycystic ovary syndrome and related to endothelial dysfunction

Striking evidence indicates endothelial impairment in polycystic ovary syndrome (PCOS) but the mechanisms linking PCOS status to cardiovascular risk remain elusive. Platelet/endothelial cell adhesion molecule (PECAM)-1 is a soluble (s) signaling molecule involved in inflammation and angiogenesis with predictive value for endothelial dysfunction in patients at risk. In a prospective, controlled study, sPECAM-1 levels and the relationships to metabolic, inflammatory and vascular PCOS traits were evaluated in 26 patients and 29-age- and body mass index-matched controls. To assess endothelial injury, carotid artery intimae-media thickness (CIMT) and brachial artery flow-mediated vasodilatation (FMD) were employed. Of the 26 women with PCOS, 25 completed a six-month metformin combined with ethinylestradiol 0.3 mg/drospirenone 3 mg therapy. Soluble PECAM-1 levels were increased in PCOS (p = 0.018 vs. Controls) and significantly decreased at follow-up (p = 0.0002). Smoking and weight had no effect on sPECAM-1 dynamics. In both univariate and multivariate analysis, basal sPECAM-1 was inversely related to FMD (r = -0.311, p = 0.021) but not CIMT. To conclude, sPECAM-1 is increased in PCOS, an effect reversed by combined metformin and anti-androgenic contraceptive therapy. Elevated sPECAM-1 contributes to endothelial dysfunction however further studies are inquired to assess its relevance as biomarker and potential therapeutic target in PCOS.

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.

Neutrophil and cytokine dysregulation in hyperinsulinemic obese horses

Equine metabolic syndrome is characterized by obesity and regional adiposity coupled with evidence of recurrent laminitis. Although inflammation has been well characterized in several experimental models of acute laminitis, the inflammatory events associated with endocrinopathic laminitis are not well documented. The aim of this study was to characterize selected markers of inflammation in horses with clinical evidence of equine metabolic syndrome (EMS). Neutrophil phagocytosis and oxidative burst, as well as endogenous and stimulated cytokine expression were evaluated. A marked increase in neutrophil reactive oxygen species production upon phagocytosis was observed in horses with EMS that was strongly correlated to the blood insulin concentration. Increased oxidative burst activity of neutrophils in hyperinsulinemic horses may predispose horses with metabolic syndrome to laminitis. In contrast, peripheral blood cells of obese hyperinsulinemic horses showed decreased endogenous proinflammatory cytokine gene expression (IL-1 and IL-6) and similar cytokine response following immune stimulation compared to that of control horses. This may suggest that, unlike in people, cytokine-mediated inflammation does not increase in direct response to obesity or insulin resistance in horses. This species-specific disparity may explain the difference in clinical outcomes observed in obese horses compared to obese people.

Flavonoids inhibit high glucose-induced up-regulation of ICAM-1 via the p38 MAPK pathway in human vein endothelial cells

Recently, several flavonoids have been shown to have cardioprotective, cancer preventive, or anti-inflammatory properties. However, the specific mechanisms underlying their protective effects remain unclear. We aimed to investigate the different effects of three representative flavonoids-hesperidin, naringin, and resveratrol-on intracellular adhesion molecule-1 (ICAM-1) induction in human umbilical vein endothelial cells (HUVECs) by using high-glucose (HG) concentrations and the possible underlying molecular mechanisms. In HG-induced HUVEC cultures, the effects of three different flavonoids on ICAM-1 production and p38 phosphorylation were examined in the presence or absence of inhibitors targeting the mitogen-activated protein kinase (MAPK) signal transduction pathway. HG stimulation of HUVECs increased the levels of the adhesion molecules ICAM-1 and endothelial selectin (E-selectin). Pretreatment with all the three flavonoids drastically inhibited ICAM-1 expression in a time-dependent manner, but did not alter VCAM-1 and E-selectin expressions. Moreover, we investigated the effects of flavonoids on the MAPK signal transduction pathway, because MAPK families are associated with vascular inflammation under stress. These flavonoids did not block HG-induced phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), but completely inhibited the HG-induced phosphorylation of p38 MAPK. SB202190, an inhibitor of p38 MAPK, also inhibited the HG-induced enrichment of ICAM-1. This study demonstrated that hesperidin, naringin, and resveratrol reduced the HG-induced ICAM-1 expression via the p38 MAPK signaling pathway, contributing to the inhibition of monocyte adhesion to endothelial cells.

Loss of insulin signaling in vascular endothelial cells accelerates atherosclerosis in apolipoprotein E null mice

To determine whether insulin action on endothelial cells promotes or protects against atherosclerosis, we generated apolipoprotein E null mice in which the insulin receptor gene was intact or conditionally deleted in vascular endothelial cells. Insulin sensitivity, glucose tolerance, plasma lipids, and blood pressure were not different between the two groups, but atherosclerotic lesion size was more than 2-fold higher in mice lacking endothelial insulin signaling. Endothelium-dependent vasodilation was impaired and endothelial cell VCAM-1 expression was increased in these animals. Adhesion of mononuclear cells to endothelium in vivo was increased 4-fold compared with controls but reduced to below control values by a VCAM-1-blocking antibody. These results provide definitive evidence that loss of insulin signaling in endothelium, in the absence of competing systemic risk factors, accelerates atherosclerosis. Therefore, improving insulin sensitivity in the endothelium of patients with insulin resistance or type 2 diabetes may prevent cardiovascular complications.

Changes in cytokine levels during acute hyperinsulinemia in offspring of type 2 diabetic subjects

OBJECTIVE

To investigate the changes in the levels of cytokines and adhesion molecules in response to acute hyperinsulinemia in the offspring of type 2 diabetic subjects.

METHODS

Forty healthy offspring of type 2 diabetic subjects and 19 control offspring of healthy parents were included in the study. Twenty offspring had normal glucose tolerance (NGT) and twenty offspring impaired glucose tolerance (IGT). Insulin sensitivity was determined by the hyperinsulinemic euglycemic clamp and insulin secretion with the intravenous glucose tolerance test. The levels of cytokines and adhesion molecules were measured before and at the end of the clamp.

RESULTS

Acute hyperinsulinemia induced by the euglycemic hyperinsulinemic clamp reduced the levels of TNF-alpha, IL-8, IL-10 and IL-18 in healthy controls but not in the offspring of type 2 diabetic subjects having NGT or IGT. In response to insulin, levels of hs-CRP decreased and levels of IL-6 increased significantly in all study groups. The levels of adhesion molecules (ICAM-1, VCAM-1, E-Selectin) remained unchanged in response to hyperinsulinemia.

CONCLUSIONS

The suppression of cytokine levels (particularly proinflammatory cytokines) during acute hyperinsulinemia observed in healthy controls was not present in offspring of type 2 diabetic patients. This emphasizes the crucial role of low-grade inflammation in insulin resistance in subjects with high risk of developing diabetes.

Insulin may cause deterioration of proliferative diabetic retinopathy

Diabetes mellitus (DM) can cause many systemic complications, including proliferative diabetic retinopathy (PDR). Retinal neovascularization (RNV) is the typical symptom of PDR, representing an important risk factor for severe vision loss in patients with DM. Diabetic hyperglycemia plays a major role in the destruction of retinal capillary walls, resulting in retinal ischemia and up-regulation of vascular endothelial growth factor (VEGF), leading to neovascularization. The transcriptional regulation of VEGF is mediated by transcription factor hypoxia-inducible factor 1 (HIF-1). Insulin is the mainstay of treatment for DM, but some studies have demonstrated that insulin had the ability to stimulate VEGF and HIF-1 expression in retinal pigment epithelial cells, retinal epithelial cells and vascular smooth muscle cells. In addition to the mitogenic effect of insulin makes it as an assistant agent has long been used in vitro cell culture. Other studies confirmed that insulin increased leukostasis in retinal microcirculation. Based on these experimental results, we hypothesize that long-term insulin therapy maybe improves the expression of VEGF and increase the risk of RNV, eventually deteriorates PDR in patients with DM.

Endothelial dysfunction and diabetes: roles of hyperglycemia, impaired insulin signaling and obesity

Endothelial dysfunction comprises a number of functional alterations in the vascular endothelium that are associated with diabetes and cardiovascular disease, including changes in vasoregulation, enhanced generation of reactive oxygen intermediates, inflammatory activation, and altered barrier function. Hyperglycemia is a characteristic feature of type 1 and type 2 diabetes and plays a pivotal role in diabetes-associated microvascular complications. Although hyperglycemia also contributes to the occurrence and progression of macrovascular disease (the major cause of death in type 2 diabetes), other factors such as dyslipidemia, hyperinsulinemia, and adipose-tissue-derived factors play a more dominant role. A mutual interaction between these factors and endothelial dysfunction occurs during the progression of the disease. We pay special attention to the possible involvement of endoplasmic reticulum stress (ER stress) and the role of obesity and adipose-derived adipokines as contributors to endothelial dysfunction in type 2 diabetes. The close interaction of adipocytes of perivascular adipose tissue with arteries and arterioles facilitates the exposure of their endothelial cells to adipokines, particularly if inflammation activates the adipose tissue and thus affects vasoregulation and capillary recruitment in skeletal muscle. Hence, an initial dysfunction of endothelial cells underlies metabolic and vascular alterations that contribute to the development of type 2 diabetes.

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.

Diabetes and vessel wall remodelling: from mechanistic insights to regenerative therapies

Over the past two decades, extensive research has focused on arterial remodelling in both physiological and pathological ageing. The concept now describes the growth as well as the rearrangement of cellular components and extracellular matrix, resulting in either reduction or increase in vessel lumen. In diabetes, remodelling extends to capillaries, microvascular beds, and arteries of different calibre. This process is paralleled by accelerated atherosclerosis and accounts for an increased incidence of ischaemic complications. The incapacity of pre-existing and de novo formed collaterals to bypass atherosclerotic occlusions, combined with a decline in tissue capillary density, is responsible for the delayed recovery from ischaemia and ultimately leads to organ failure. The mechanisms of vascular remodelling are incompletely understood, but metabolic and mechanical factors seem to play an important role. Hyperglycaemia represents the main factor responsible for the fast progression of atherosclerosis as well as microangiopathy. However, intensive blood glucose control alone is insufficient to reduce the risk of macrovascular complications. Pharmacological control of oxidative stress and stimulation of nitric oxide release have proved to exert beneficial effects on vascular remodelling in experimental diabetic models. New approaches of regenerative medicine using vascular progenitor cells for the treatment of ischaemic disease have been shown to be safe and are now being tested for efficacy in pre-clinical and clinical trials.

Inflammatory mechanisms of diabetic complications

Activation of inflammatory processes may contribute to the development of type 2 diabetes mellitus. In addition, inflammation appears to be a major mechanism responsible for vascular damage leading to the clinically well-recognized complications of diabetes. Inflammatory cytokine and chemokine mediators released from visceral fat contribute to atherosclerotic plaque formation and increased risk for myocardial infarction and stroke. Activation of growth factors and adhesion molecules may promote the movement of inflammatory cells into the renal microvasculature, predisposing to the development of diabetic nephropathy. Emerging evidence also indicates that markers of inflammation are associated with the more severe forms of diabetic retinopathy. Future approaches to the treatment of diabetic complications may involve regulation of inflammatory processes, specifically targeting factors that contribute to vascular damage.

Treatment of spontaneously hypertensive rats with rosiglitazone and/or enalapril restores balance between vasodilator and vasoconstrictor actions of insulin with simultaneous improvement in hypertension and insulin resistance

Spontaneously hypertensive rats (SHRs) exhibit endothelial dysfunction and insulin resistance. Reciprocal relationships between endothelial dysfunction and insulin resistance may contribute to hypertension by causing imbalanced regulation of endothelial-derived vasodilators (e.g., nitric oxide) and vasoconstrictors (e.g., endothelin-1 [ET-1]). Treatment of SHRs with rosiglitazone (insulin sensitizer) and/or enalapril (ACE inhibitor) may simultaneously improve hypertension, insulin resistance, and endothelial dysfunction by rebalancing insulin-stimulated production of vasoactive mediators. When compared with WKY control rats, 12-week-old vehicle-treated SHRs were hypertensive, overweight, and insulin resistant, with elevated fasting levels of insulin and ET-1 and reduced serum adiponectin levels. In mesenteric vascular beds (MVBs) isolated from vehicle-treated SHRs and preconstricted with norepinephrine (NE) ex vivo, vasodilator responses to insulin were significantly impaired, whereas the ability of insulin to oppose vasoconstrictor actions of NE was absent (versus WKY controls). Three-week treatment of SHRs with rosiglitazone and/or enalapril significantly reduced blood pressure, insulin resistance, fasting insulin, and ET-1 levels and increased adiponectin levels to values comparable with those observed in vehicle-treated WKY controls. By restoring phosphatidylinositol 3-kinase-dependent effects, rosiglitazone and/or enalapril therapy of SHRs also significantly improved vasodilator responses to insulin in MVB preconstricted with NE ex vivo. Taken together, our data provide strong support for the existence of reciprocal relationships between endothelial dysfunction and insulin resistance that may be relevant for developing novel therapeutic strategies for the metabolic syndrome.

Insulin differentially regulates monocyte and polymorphonuclear neutrophil functions in healthy young and elderly humans

CONTEXT

Insulin can regulate immune cell function. Aging is associated with various degrees of insulin resistance together with reduced immune cell activity.

OBJECTIVE

We investigated the hypothesis that blood monocytes and polymorphonuclear neutrophils (PMNs) are less responsive to the action of insulin in elderly subjects. DESIGN-INTERVENTION: We evaluated the effect of hyperinsulinemia (0.7 mU/kg(-1) fat-free mass per minute(-1)) on monocyte and PMN activity using a 4-h euglycemic clamp technique.

PARTICIPANTS

Eight young (24 +/- 6 yr old) and nine elderly (69 +/- 4 yr old) healthy volunteers participated in the study.

MAIN OUTCOME MEASURES

Monocyte and PMN receptor expression and density were measured using flow cytometric detection. PMN chemotaxis toward formyl-Met-Leu-Phe (fMLP) was evaluated using a two-compartment chamber. PMN and monocyte phagocytosis was determined by measuring the engulfment of opsonized particles. Microbicidal functions were determined based on the production of reactive oxygen species (ROS) and bactericidal protein by stimulated cells.

RESULTS

The density of PMN and monocyte insulin receptors was not affected by age or insulin clamp treatment regardless of the age. Insulin was able to regulate the expression of receptors involved in PMN action in the young-adult group only. PMN chemotaxis was up-regulated by insulin in both groups. In contrast, although insulin stimulated phagocytosis and bactericidal activity in young-adult subjects, the ability of PMN to adapt to physiological hyperinsulinemia was blunted in the older group. The effect of insulin on monocyte bactericidal properties seemed to be limited, although a suppressive action on fMLP-induced ROS production was detected in young adults.

CONCLUSIONS

We confirmed the presence of the insulin receptor on monocyte and PMN membranes. We revealed that insulin has a limited action on monocyte function. Insulin has a priming effect on the main PMN functions. Immune cell function adapted poorly to insulin infusion in the elderly subjects.

Leukocyte recruitment and vascular injury in diabetic nephropathy

Different types of activated leukocytes play a crucial role in the pathogenesis of most kidney diseases from acute to chronic stages; however, diabetic nephropathy was not considered an inflammatory disease in the past. This view is changing now because there is a growing body of evidence implicating inflammatory cells at every stage of diabetic nephropathy. Renal tissue macrophages, T cells, and neutrophils produce various reactive oxygen species, proinflammatory cytokines, metalloproteinases, and growth factors, which modulate the local response and increase inflammation within the diabetic kidney. Although the precise mechanisms that direct leukocyte homing into renal tissues are not fully identified, it has been reported that intercellular adhesion molecule-1 and the chemokines CCL2 and CX3CL1 probably are involved in leukocyte migration in diabetic nephropathy. This review focuses on the molecular mechanisms of leukocyte recruitment into the diabetic kidney and the involvement of immigrated immune cells in the damage to renal tissues.

Insulin enhances leukocyte-endothelial cell adhesion in the retinal microcirculation through surface expression of intercellular adhesion molecule-1

The purpose of this study was to evaluate the effects of insulin on leukocyte-endothelial cell adhesion in the retinal microcirculation in vitro and in vivo. Human retinal endothelial cells (HRECs) were cultured in medium with or without insulin, and neutrophils allowed to adhere. Adherent neutrophils were quantified by measuring myeloperoxidase activity. Surface expression of endothelial adhesion molecules were studied with the use of an enzyme immunoassay. Insulin at concentrations of 50 and 100 microU/ml significantly increased neutrophil adhesion to HRECs compared with the control cells (P < 0.01, respectively). Surface expression of intercellular adhesion molecule-1 (ICAM-1) significantly increased when HRECs were exposed to 100 microU/ml insulin, as compared with the control cells (P < 0.05). Anti-ICAM-1 antibody significantly inhibited neutrophils adhesion to HRECs (P < 0.0001). Brown-Norway rats received subcutaneous injection of 0.2 U per 100 g body weight insulin three times. Control rats received the same amount of phosphate-buffered saline. Leukocyte entrapment in the retina was evaluated using acridine orange leukocyte fluorography. The number of leukocytes trapped in the retina of insulin-treated rats was significantly elevated compared with that in the control animals (P < 0.0001). These results suggested that insulin enhances leukostasis in retinal microcirculation. Hyperinsulinemia may be a risk factor of retinal microcirculatory disturbances.

Intercellular adhesion molecule-1 deficiency is protective against nephropathy in type 2 diabetic db/db mice

Diabetic nephropathy is a leading cause of end-stage renal failure and is a growing concern given the increasing incidence of type 2 diabetes. Diabetic nephropathy is associated with progressive kidney macrophage accumulation and experimental studies suggest that intercellular adhesion molecule (ICAM)-1 facilitates kidney macrophage recruitment during type 1 diabetes. To ascertain the importance of ICAM-1 in promoting type 2 diabetic nephropathy, the development of renal injury in ICAM-1 intact and deficient db/db mice with equivalent hyperglycemia and obesity between ages 2 and 8 mo was examined and compared with results with normal db/+ mice. Increases in albuminuria (11-fold), glomerular leukocytes (10-fold), and interstitial leukocytes (three-fold) consisting of predominantly CD68+ macrophages were identified at 8 mo in diabetic db/db mice compared with nondiabetic db/+ mice. In comparison to db/db mice, ICAM-1-deficient db/db mice had marked reductions in albuminuria at 6 mo (77% downward arrow) and 8 mo (85% downward arrow). There was also a significant decrease in glomerular (63% downward arrow) and interstitial (83% downward arrow) leukocytes in ICAM-1-deficient db/db mice, which were associated with reduced glomerular hypertrophy and hypercellularity and tubular damage. The development of renal fibrosis (expression of TGF-beta1, collagen IV, and interstitial alpha-smooth muscle actin) was also strikingly attenuated in the ICAM-1-deficient db/db mice. Additional in vitro studies showed that macrophage activation by high glucose or advanced glycation end products could promote ICAM-1 expression on tubular cells and macrophage production of active TGF-beta1. Thus, ICAM-1 appears to be a critical promoter of nephropathy in mouse type 2 diabetes by facilitating kidney macrophage recruitment.

Differences in platelet endothelial cell adhesion molecule-1 expression between peripheral circulation and pancreatic microcirculation in cerulein-induced acute edematous pancreatitis

AIM: To investigate the changes of platelet endothelial cell adhesion molecule-1 (PECAM-1) expression on polymorphonuclear leukocytes (PMNs) in peripheral circulation and pancreatic microcirculation in cerulein-induced acute edematous pancreatitis (AEP).

METHODS: Fifty Wistar rats were randomly divided into control group (n = 10) and AEP group (n = 40). A model of AEP was established by subcutaneous injection of cerulein 5.5 and 7.5 μg/kg at 0 and 1 h after the beginning of experiment respectively. PECAM-1 expression on PMNs from splenic vein and inferior vena cava was determined by RT-PCR at mRNA level and determined by flow cytometry at protein level.

RESULTS: In experimental rats, an increased PECAM-1 mRNA expression was seen from 4 to 8 h of AEP in peripheral circulation (0.77±0.25%, 0.76±0.28%, 0.89±0.30%, 1.00±0.21%), while in pancreatic microcirculation, expression decreased from 2 h and reached the lowest level at 6 h of AEP (0.78±0.29%, 0.75±0.26%, 0.62±0.28%, 0.66±0.20%). There were significant differences at 8-h time point of AEP between peripheral circulation and pancreatic microcirculation (1.00±0.21% vs 0.66±0.20%, P<0.05). Meanwhile, the difference at protein level was also found.

CONCLUSION: A reverse expression of PECAM-1 on PMNs was found between peripheral circulation and pancreatic microcirculation, suggesting that inhibition of PECAM-1 expression may improve the pathological change of AEP.

In vivo evidences that insulin regulates human polymorphonuclear neutrophil functions

Polymorphonuclear neutrophils (PMN) are able to destroy invasive mircoorganisms by a wide variety of functions. Whereas insulin does not stimulate hexose transport in PMN, previous reports have clearly shown that this hormone regulates glucose metabolism inside this cell, raising the question of insulin action on PMN functions in humans. It is interesting that in vitro studies established a strong relationship between specific binding of insulin to its PMN membrane receptor and the activation of the main PMN functions. Therefore, investigation in healthy subjects under strict euglycemia and physiological insulinemia was performed to understand the in vivo-specific action of insulin on PMN functions without hyperglycemia interferences. We determined numerous PMN functions before and after hyperinsulinemia (0.5 mU/kg/min) and euglycemia (0.9 g/l) clamp for 4 h in eight adult healthy volunteers (24+/-6 years). The total number of PMN and the number of PMN expressing CD11b, CD15, CD62L, and CD89 were significantly increased over baseline (P<0.001), whereas the density of these receptors was down-regulated (P<0.01) by insulin. PMN chemotaxis (+117%, P<0.05), phagocytosis (+29%, P<0.001), and bactericidal (+17-25%, P<0.001) capacities were increased during the insulin clamp (P<0.05). Therefore, insulin treatment may modulate PMN functions not only by attainment of a better metabolic control, as suggested by in vivo studies in diabetic patients, but also through a direct effect of insulin.

Cell signalling-mediating insulin increase of mRNA expression for cationic amino acid transporters-1 and -2 and membrane hyperpolarization in human umbilical vein endothelial cells

Insulin induces vasodilatation in human subjects and increases L-arginine transport and NO synthesis in human umbilical vein endothelial cells (HUVEC). Cell signalling events associated with insulin effects on activity and mRNA expression of the human cationic amino acid transporters 1 (hCAT-1) and 2B (hCAT-2B) are unknown. L-arginine transport and eNOS activity were determined in HUVEC exposed to insulin. mRNA levels for hCAT-1, hCAT-2B and eNOS were quantitated by real time RT-PCR and endothelial NO synthase (eNOS) protein was identified by Western blot analysis. Intracellular Ca2+, L-arginine and L-citrulline levels, L-[3H]citrulline formation from L-[(3)H]arginine, cGMP formation, nitrite level, ATP release and membrane potential were determined. Insulin increased L-arginine transport and the mRNA levels for hCAT-1 and hCAT-2B and eNOS expression and activity. Insulin also induced membrane hyperpolarization and increased intracellular Ca2+, L-[3H]citrulline, cGMP and nitrite formation. Insulin-mediated stimulation of the L-arginine/NO pathway is thus associated with increased hCAT-1 and hCAT-2B mRNA, and eNOS expression, via mechanisms involving membrane hyperpolarization, mitogen-activated protein kinases p42 and p44, phosphatidylinositol 3-kinase, NO and protein kinase C. We have characterized a cell signalling pathway by which hyperinsulinaemia could lead to vasodilatation in human subjects, and which could have implications in patients in whom plasma insulin levels are altered, such as in diabetes mellitus.

Neurotransmitters regulate the migration and cytotoxicity in natural killer cells

Natural killer (NK) cells and cytotoxic T lymphocytes (CTL), the functional coordination of which are governed by various signal substances, are crucial in the body's defense of tumor and virus-infected cells. We investigated the role of various neurotransmitters and hormones on the regulation of functional parameters, including NK cell cytotoxicity, and the migration of NK cells and CTL within a three-dimensional collagen lattice. Using peripheral blood CTL and NK cells, we show that the neurotransmitters endorphin, histamine and substance P increase NK cell cytotoxicity, while norepinephrine inhibits cytotoxicity. Moreover, substance P reduces migratory activity, while norepinephrine increases NK cell and CTL migration. Furthermore, all three steroid hormones which were investigated, namely cortisone, testosterone, and estradiol, had regulatory influence on both cytotoxicity and migration of NK cells. These results further specify the functional basis of the complex interconnection between the immune and neuro-endocrine systems.

Hypertension in diabetes: The role of the vasculature

This review is focused on the interplay between two major factors affecting the vascular tree in diabetes, insulin resistance, and hyperglycemia. The implications for vascular function, structure, and the interaction between vascular cells and other tissues by which they are affected under these conditions are reviewed.

Cerivastatin ameliorates high insulin-enhanced neutrophil-endothelial cell adhesion and endothelial intercellular adhesion molecule-1 expression by inhibiting mitogen-activated protein kinase activation

BACKGROUND AND AIMS

There is growing evidence that hyperinsulinemia is linked to the development of atherosclerosis in patients with diabetes. We demonstrated previously that high insulin exacerbates neutrophil-endothelial cell adhesion and endothelial intercellular adhesion molecule (ICAM)-1 expression through activation of protein kinase C (PKC) and mitogen-activated protein (MAP) kinase. Though 3-hydroxymethyl-3-glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have been employed as therapeutic agents in the treatment of dyslipidemia, which is frequently accompanied by diabetes mellitus; it is not known whether statins protect against leukocyte-endothelial interactions, especially in hyperinsulinemia. In this study, we determined which statin(s) could protect against endothelial reactions to high insulin.

METHODS

Studies of adhesion between neutrophils from healthy volunteers and human umbilical vein endothelial cells incubated in regular insulin-rich medium with or without statins were performed. Adhered neutrophils were quantified by measuring their myeloperoxidase (MPO) activities, and endothelial expression of ICAM-1 was examined using an enzyme immunoassay.

RESULTS

Both the increased neutrophil-endothelial cell adhesion and ICAM-1 expression caused by high insulin (100 microU/ml) for 48 h were significantly attenuated by pretreatment with cerivastatin (0.01 microM), but not by fluvastatin (0.5 microM) or pravastatin (0.05 microM). These protective actions of cerivastatin were attenuated by a key intermediate in the cholesterol biosynthesis pathway, mevalonate (400 microM). In addition, cerivastatin attenuated both neutrophil-endothelial cell adhesion and endothelial ICAM-1 expression enhanced by a MAP kinase activator, anisomycin (1 microM) but not by a PKC activator, PMA (10 nM).

CONCLUSIONS

These results suggest that through inhibiting MAP kinase but not PKC activation therapy with cerivastatin would be promising strategy for inhibiting neutrophil-endothelial cell adhesion and endothelial ICAM-1 expression enhanced by high insulin, which is closely correlated with atherosclerosis.

E-selectin-inducing activity in plasma from type 2 diabetic patients with maculopathy

Diabetic maculopathy (DMa) is a leading cause of visual loss in the western world. We examined whether plasma from type 2 diabetic patients with DMa contains factor(s) capable of inducing expression of the adhesion molecules E-selectin and VCAM-1 or cellular proliferation in cultured endothelial cells. Four gender-, age-, and duration (diabetes groups)-matched groups of 20 subjects each participated: 1) subjects with normal glucose tolerance (NGT), 2) subjects with impaired glucose tolerance (IGT), 3) type 2 diabetic patients without retinopathy, and 4) type 2 diabetic patients with DMa. Fasting plasma was added to in vitro-grown human umbilical vein endothelial cells for 6 h, after which E-selectin and VCAM-1 expression was measured. Proliferation was evaluated by thymidine incorporation. The individuals were characterized by measurement of 24-h ambulatory blood pressure, urinary albumin excretion rate, Hb A(1c), and blood lipids. Plasma from type 2 diabetic patients with DMa induced a significantly higher expression of E-selectin in endothelial cells than did plasma from subjects with NGT (259 +/- 23 x 10(3) vs. 198 +/- 19 x 10(3); arbitrary absorbance units; P < 0.05). There were no significant differences in plasma stimulatory effects on VCAM-1 expression or on thymidine incorporation between groups. These findings suggest that plasma from type 2 diabetic patients with DMa contains factor(s) capable of inducing the expression of E-selectin in endothelial cells. Enhanced expression of E-selectin may contribute to the development of DMa in type 2 diabetes.