Similar effects of resistin and high glucose on P-selectin and fractalkine expression and monocyte adhesion in human endothelial cells

Adipokines and Bacterial Metabolites: A Pivotal Molecular Bridge Linking Obesity and Gut Microbiota Dysbiosis to Target

Adipokines are essential mediators produced by adipose tissue and exert multiple biological functions. In particular, adiponectin, leptin, resistin, IL-6, MCP-1 and PAI-1 play specific roles in the crosstalk between adipose tissue and other organs involved in metabolic, immune and vascular health. During obesity, adipokine imbalance occurs and leads to a low-grade pro-inflammatory status, promoting insulin resistance-related diabetes and its vascular complications. A causal link between obesity and gut microbiota dysbiosis has been demonstrated. The deregulation of gut bacteria communities characterizing this dysbiosis influences the synthesis of bacterial substances including lipopolysaccharides and specific metabolites, generated via the degradation of dietary components, such as short-chain fatty acids, trimethylamine metabolized into trimethylamine-oxide in the liver and indole derivatives. Emerging evidence suggests that these bacterial metabolites modulate signaling pathways involved in adipokine production and action. This review summarizes the current knowledge about the molecular links between gut bacteria-derived metabolites and adipokine imbalance in obesity, and emphasizes their roles in key pathological mechanisms related to oxidative stress, inflammation, insulin resistance and vascular disorder. Given this interaction between adipokines and bacterial metabolites, the review highlights their relevance (i) as complementary clinical biomarkers to better explore the metabolic, inflammatory and vascular complications during obesity and gut microbiota dysbiosis, and (ii) as targets for new antioxidant, anti-inflammatory and prebiotic triple action strategies.

The role of oxidative stress in diabetes mellitus-induced vascular endothelial dysfunction

Diabetes mellitus is a metabolic disease characterized by long-term hyperglycaemia, which leads to microangiopathy and macroangiopathy and ultimately increases the mortality of diabetic patients. Endothelial dysfunction, which has been recognized as a key factor in the pathogenesis of diabetic microangiopathy and macroangiopathy, is characterized by a reduction in NO bioavailability. Oxidative stress, which is the main pathogenic factor in diabetes, is one of the major triggers of endothelial dysfunction through the reduction in NO. In this review, we summarize the four sources of ROS in the diabetic vasculature and the underlying molecular mechanisms by which the pathogenic factors hyperglycaemia, hyperlipidaemia, adipokines and insulin resistance induce oxidative stress in endothelial cells in the context of diabetes. In addition, we discuss oxidative stress-targeted interventions, including hypoglycaemic drugs, antioxidants and lifestyle interventions, and their effects on diabetes-induced endothelial dysfunction. In summary, our review provides comprehensive insight into the roles of oxidative stress in diabetes-induced endothelial dysfunction.

High Serum Levels of Resistin is Associated With Acute Cerebral Infarction

BACKGROUND

The inflammatory process is involved in the pathogenesis of atherosclerosis and brain tissue injury following cerebral ischemia. Human resistin is a member of small cysteine-rich secreted proteins and has been implicated in inflammatory responses. This study investigated the association of serum resistin level with acute cerebral infarction (ACI). We also investigated its association with the short-term functional outcome.

METHODS

This study included 106 patients with ACI and 106 age-matched and sex-matched healthy control subjects. Serum resistin level was assessed by using enzyme-linked immunosorbent sandwich assay. The association of serum resistin levels with ACI was analyzed by logistic regression analysis.

RESULTS

The serum resistin level was significantly higher in patients with ACI than the control group [median (interquartile range), 35.7 ng/mL (13.0 to 70.5) ng/mL vs. 10.5 ng/ml (15.4 to 16.6), P<0.001]. Logistic regression analysis showed that serum resistin level was associated with an ACI (odds ratio=1.055, 95% confidence interval: 1.035-1.074, P<0.001). Among stroke subtypes, the serum resistin level was higher in the patients with large artery atherosclerosis than those with other subtypes (P=0.013). High resistin levels were also significantly associated with unfavorable functional outcome at discharge (odds ratio=1.043, 95% confidence interval: 1.024-1.063, P<0.001).

CONCLUSIONS

This study suggests the potential association of resistin with stroke and cerebral atherosclerosis. Increased serum resistin levels were also associated with early unfavorable neurological outcome.

Resistin levels and inflammatory and endothelial dysfunction markers in obese postmenopausal women with type 2 diabetes mellitus

BACKGROUND

Obesity-associated coronary heart disease (CHD) risk is higher in women than in men with type 2 diabetes (T2DM). Resistin, an adipokine secreted by adispose tissue, may contribute to this higher risk.

AIMS

To explore the relationships among resistin levels and common inflammatory and endothelial dysfunction markers and CHD risk in obese post-menopausal T2DM women.

METHODS

Serum levels of resistin, hsCRP, IL-6, Soluble vascular cell adhesion molecule (sVCAM), homocysteine (tHcy), HOMA-IR and metabolic parameters were determined in a group of 132 T2DM women with and without documented CHD and in 55 non-diabetic women.

RESULTS

Resistin, sVCAM, IL-6 and tHcy levels were comparable in T2DM and controls. CHD women showed higher resistin, sVCAM and tHcy levels than those without CHD, and for resistin this difference remained significant after age-adjustment (P = 0.013); conversely hsCRP were ~ 2X higher in T2DM women than in controls (P = 0.0132) without any difference according to CHD history. At univariate analysis resistin levels were significantly associated with age, waist circumference, hypertension, tHcy, hsPCR, sVCAM, IL-6, HDL-cholesterol, triglycerides and creatinine levels, but only creatinine, triglycerides, hsCRP, IL-6 and sVCAM were independently associated to resistin levels at stepwise regression analysis. Resistin levels were independently associated to CHD, increasing the risk by 1.15 times (0.986-1.344 95% CI), together with age, tHcy, LDL-C and hypertension.

CONCLUSIONS

Circulating resistin levels were comparable in obese/overweight T2DM and control women. In T2DM women, resistin levels correlated with markers of renal function, systemic inflammation and endothelial dysfunction and were independently associated with a higher CHD risk.

The possible role of endocrine dysfunction of adipose tissue in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is diabetes that is first diagnosed in the second or third trimester of pregnancy in patients who did not have a history of diabetes before pregnancy. Consequences of GDM include increased risk of macrosomia and birth complications in the infant and an increased risk of maternal type 2 diabetes mellitus (T2DM) after pregnancy. There is also a longer-term risk of obesity, T2DM, and cardiovascular diseases in the child. GDM is the result of impaired glucose tolerance due to pancreatic β-cell dysfunction on a background of insulin resistance that physiologically increases during pregnancy. The strongest clinical predictors of GDM are overweight and obesity. The fact that women with GDM are more likely to be overweight or obese suggests that adipose tissue dysfunction may be involved in the pathogenesis of GDM, similarly to T2DM. Adipose tissue is not only involved in energy storage but also functions as an active endocrine organ secreting adipokines (specific hormones and cytokines) with the ability to alter insulin sensitivity. Recent evidence points to a crucial role of numerous adipokines produced by fat in the development of GDM. The following text summarizes the current knowledge about a possible role of selected adipokines in the development of GDM.

Coordinated Contribution of NADPH Oxidase- and Mitochondria-Derived Reactive Oxygen Species in Metabolic Syndrome and Its Implication in Renal Dysfunction

Metabolic syndrome (MetS), a complex of interrelated risk factors for cardiovascular disease and diabetes, is comprised of central obesity (increased waist circumference), hyperglycemia, dyslipidemia (high triglyceride blood levels, low high-density lipoprotein blood levels), and increased blood pressure. Oxidative stress, caused by the imbalance between pro-oxidant and endogenous antioxidant systems, is the primary pathological basis of MetS. The major sources of reactive oxygen species (ROS) associated with MetS are nicotinamide-adenine dinucleotide phosphate (NADPH) oxidases and mitochondria. In this review, we summarize the current knowledge regarding the generation of ROS from NADPH oxidases and mitochondria, discuss the NADPH oxidase- and mitochondria-derived ROS signaling and pathophysiological effects, and the interplay between these two major sources of ROS, which leads to chronic inflammation, adipocyte proliferation, insulin resistance, and other metabolic abnormalities. The mechanisms linking MetS and chronic kidney disease are not well known. The role of NADPH oxidases and mitochondria in renal injury in the setting of MetS, particularly the influence of the pyruvate dehydrogenase complex in oxidative stress, inflammation, and subsequent renal injury, is highlighted. Understanding the molecular mechanism(s) underlying MetS may lead to novel therapeutic approaches by targeting the pyruvate dehydrogenase complex in MetS and prevent its sequelae of chronic cardiovascular and renal diseases.

Adipokines: New Potential Therapeutic Target for Obesity and Metabolic, Rheumatic, and Cardiovascular Diseases

Besides its role as an energy storage organ, adipose tissue can be viewed as a dynamic and complex endocrine organ, which produces and secretes several adipokines, including hormones, cytokines, extracellular matrix (ECM) proteins, and growth and vasoactive factors. A wide body of evidence showed that adipokines play a critical role in various biological and physiological functions, among which feeding modulation, inflammatory and immune function, glucose and lipid metabolism, and blood pressure control. The aim of this review is to summarize the effects of several adipokines, including leptin, diponectin, resistin, chemerin, lipocalin-2 (LCN2), vaspin, omentin, follistatin-like 1 (FSTL1), secreted protein acidic and rich in cysteine (SPARC), secreted frizzled-related protein 5 (SFRP5), C1q/TNF-related proteins (CTRPs), family with sequence similarity to 19 member A5 (FAM19A5), wingless-type inducible signaling pathway protein-1 (WISP1), progranulin (PGRN), nesfatin-1 (nesfatin), visfatin/PBEF/NAMPT, apelin, retinol binding protein 4 (RPB4), and plasminogen activator inhibitor-1 (PAI-1) in the regulation of insulin resistance and vascular function, as well as many aspects of inflammation and immunity and their potential role in managing obesity-associated diseases, including metabolic, osteoarticular, and cardiovascular diseases.

The role of adipokines in the modulation of lymphoid lineage cell development and activity: An overview

Adipokines are predominantly known to play a vital role in the control of food intake, energy homeostasis and regulation of glucose and lipid metabolism. However, evidence supporting the concept of their extensive involvement in immune system defence mechanisms and inflammatory processes continues to grow. Some of the adipokines, that is, leptin and resistin, have been recognized to exhibit mainly pro-inflammatory properties, whereas others such as visfatin, chemerin, apelin and vaspin have been found to exert regulatory effects. In contrast, adiponectin or omentin are known for their anti-inflammatory activities. Hence, adipokines influence the activity of various cells engaged in innate immune response and inflammatory processes mainly by affecting adhesion molecule expression, chemotaxis, apoptosis and phagocytosis, as well as mediators production and release. However, much less is known about the role of adipokines in processes involving lymphoid lineage cells. This review summarizes the current knowledge regarding the importance of different adipokines in the lymphopoiesis, recirculation, differentiation and polarization of lymphoid lineage cells. It also provides insight into the influence of selected adipokines on the activity of those cells in tissues.

Increased fractalkine and vascular dysfunction in obesity and in type 2 diabetes. Effects of oral antidiabetic treatment

Activation of fractalkine and other chemokines plays an important role in atherogenesis and, in conjunction with endothelial dysfunction, promotes premature vascular damage in obesity and diabetes. We hypothesized that increased circulating fractalkine coexists with impaired vasomotor function in metabolically healthy or unhealthy obesity, and that treatment with antidiabetic drugs may impact these abnormalities in type 2 diabetes. Compared to lean subjects, in both obese groups the vasodilator responses to acetylcholine and sodium nitroprusside were impaired (both P < .001); ET_A-receptor blockade resulted in greater vasodilation (both P < .001); and plasma levels of fractalkine, E-selectin and monocyte chemoattractant protein (MCP)-1 were increased (all P < .05). In diabetic patients, oral antidiabetic drugs (glyburide, metformin or pioglitazone) reduced circulating levels fractalkine and E-selectin (both P < .05), without affecting vascular responses (all P > .05). Our findings indicate that insulin resistant states are associated with elevated atherogenic chemokines and impaired vascular reactivity. Antidiabetic treatment results in lower circulating fractalkine, which may provide cardiovascular benefits.

The GEF Cytohesin-2/ARNO Mediates Resistin induced Phenotypic Switching in Vascular Smooth Muscle Cells

The pro-inflammatory adipokine resistin induces a phenotypic switch of vascular smooth muscle cells (VSMC), a process decisive for atherosclerosis, including morphological changes, increased synthetic activity, proliferation and migration. The guanine-exchange factor ARNO (Cytohesin-2) has been shown to be important for morphological changes and migration of other cell types. In this study we dissected the role of ARNO in resistin induced VSMC phenotypic switching and signalling. Firstly, treatment with the cytohesin inhibitor Secin H3 prevented the resistin mediated induction of morphological changes in VSMC. Secondly, Secin H3 treatment as well as expression of an inactive ARNO (EK) reduced resistin induced VSMC synthetic activity, as assessed by matrix metalloproteinase 2 (MMP-2) expression, as well as the migration into a wound in vitro compared to ARNO WT expression. Thirdly, we found ARNO to influence MMP-2 expression and migration via activation of p38 MAPK and the JNK/AP-1 pathway. Interestingly, these processes were shown to be dependent on the binding of PIP₃, as mutation of the ARNO PH-domain inhibited VSMC migration, MMP-2 expression as well as p38 MAPK and JNK signalling. Thus, we demonstrate that ARNO is an important link in resistin dependent cell signalling leading to morphological changes, MMP-2 production and migration of VSMC.

Ghrelin combined with sodium tanshinone IIA sulfonate pretreatment reduces apoptosis and fractalkine expression induced by high-dose glucose in human umbilical vein endothelial cells

BACKGROUND

To explore the regulatory role of ghrelin combined with sodium tanshinone IIA sulfonate (STS) pretreatment in cell apoptosis and fractalkine (FKN) expression of human umbilical vein endothelial cells (HUVECs) induced with high-dose glucose.

METHODS

HUVECs were assigned into control group, high-dose glucose group (HG group), high-dose glucose with ghrelin group (Gr+HG group), and high-dose glucose companied with ghrelin and STS group (Gr+STS+HG group). The apoptosis of HUVECs was determined by Hoechst 33258 straining and flow cytometry (FCM). Nitric oxide (NO) level was measured by total NO assay kit. The mRNA and protein levels of β-catenin, p-GSK-3β and FKN were accessed by Western blot and real-time quantitative polymerase chain reaction (RT-qPCR), respectively.

RESULTS

High-dose glucose significantly accelerated apoptosis in HUVECs. The apoptotic rate was lower in Gr+HG group and much lower in Gr+STS+HG group than control group. NO level was significantly reduced in the HG group, which was partly inhibited in Gr+HG group and obviously increased in Gr+STS+HG group than controls. In addition, mRNA levels of GSK-3β and FKN in HUVECs decreased in Gr+HG group, which was more obviously decreased in Gr+STS+HG group. However, ghrelin treatment upregulated β-catenin and p-GSK-3β (Ser9), but downregulated FKN during high-dose glucose treatment, which was more obvious in Gr+STS+HG group.

CONCLUSIONS

Pretreatment of ghrelin combined with STS reduces the apoptosis rate of HUVECs induced by high glucose environment and inhibits the expression of FKN via β-catenin/Wnt signaling pathway.

Targeted Transfection Using PEGylated Cationic Liposomes Directed Towards P-Selectin Increases siRNA Delivery into Activated Endothelial Cells

: The progress in small-interfering RNA (siRNA) therapeutics depends on the development of suitable nanocarriers to perform specific and effective delivery to dysfunctional cells. In this paper, we questioned whether P-selectin, a cell adhesion molecule specifically expressed on the surface of activated endothelial cells (EC) could be employed as a target for nanotherapeutic intervention. To this purpose, we developed and characterized P-selectin targeted PEGylated cationic liposomes able to efficiently pack siRNA and to function as efficient vectors for siRNA delivery to tumour necrosis factor-α (TNF-α) activated EC. Targeted cationic liposomes were obtained by coupling a peptide with high affinity for P-selectin to a functionalized PEGylated phospholipid inserted in the liposomes' bilayer (Psel-lipo). As control, scrambled peptide coupled cationic liposomes (Scr-lipo) were used. The lipoplexes obtained by complexation of Psel-lipo with siRNA (Psel-lipo/siRNA) were taken up specifically and at a higher extent by TNF-α activated b.End3 endothelial cells as compared to non-targeted Scr-lipo/siRNA. The Psel-lipo/siRNA delivered with high efficiency siRNA into the cells. The lipoplexes were functional as demonstrated by the down-regulation of the selected gene (GAPDH). The results demonstrate an effective targeted delivery of siRNA into cultured activated endothelial cells using P-selectin directed PEGylated cationic liposomes, which subsequently knock-down the desired gene.

Adipocytokine Involvement in Innate Immune Mechanisms

The innate immune response is defined as an immensely complex and sophisticated process aimed at defending the organism against any disturbance in the body homeostasis, including invading pathogens. It requires a close cooperation of a vast amount of different cell types, recognized as inflammatory migrating cells, as well as stationary cells that form tissues. Moreover, innate immune mechanisms require an efficient functioning of various humoral components that exert a significant impact on physiological and pathological processes. Apart from commonly mentioned humoral factors, this group also includes a family of proteins known as adipocytokines that may act as pro- or anti-inflammatory agents or act both ways. Leptin, predominantly characterized as a proinflammatory adipokine, plays a crucial role in endothelium remodeling and regulation, as well as in cell survival and production of numerous cytokines. Adiponectin, similar to leptin, acts on the endothelial cells and the phagocytic properties of immune cells; however, it exerts an anti-inflammatory impact. Resistin has a documented role in the control of angiogenesis and stimulation of proinflammatory mediator generation and release. Furthermore, there are adipokines, ie, visfatin and chemerin, whose participation in the inflammatory processes is ambiguous. This review focuses on the current knowledge on the extensive role of selected adipokines in innate immune response.

The role of obesity and adipose tissue dysfunction in gestational diabetes mellitus

Gestational diabetes mellitus is defined as diabetes diagnosed in the second or third trimester of pregnancy in patients with no history of diabetes prior to gestation. It is the most common complication of pregnancy. The underlying pathophysiology shares some common features with type 2 diabetes mellitus (T2DM) combining relatively insufficient insulin secretion with increased peripheral insulin resistance. While a certain degree of insulin resistance is the physiological characteristics of the second half of pregnancy, it is significantly more pronounced in patients with gestational diabetes. Adipose tissue dysfunction and subclinical inflammation in obesity are well-described causes of increased insulin resistance in non-pregnant subjects and are often observed in individuals with T2DM. Emerging evidence of altered adipokine expression and local inflammation in adipose tissue in patients with gestational diabetes suggests an important involvement of adipose tissue in its etiopathogenesis. This review aims to summarize current knowledge of adipose tissue dysfunction and its role in the development of gestational diabetes. We specifically focus on the significance of alterations of adipokines and immunocompetent cells number and phenotype in fat. Detailed understanding of the role of adipose tissue in gestational diabetes may provide new insights into its pathophysiology and open new possibilities of its prevention and treatment.

Lymphocytes and macrophages in adipose tissue in obesity: markers or makers of subclinical inflammation?

Obesity is accompanied by the development of chronic low-grade inflammation in adipose tissue. The presence of chronic inflammatory response along with metabolically harmful factors released by adipose tissue into the circulation is associated with several metabolic complications of obesity such as type 2 diabetes mellitus or accelerated atherosclerosis. The present review is focused on macrophages and lymphocytes and their possible role in low-grade inflammation in fat. Both macrophages and lymphocytes respond to obesity-induced adipocyte hypertrophy by their migration into adipose tissue. After activation and differentiation, they contribute to the development of local inflammatory response and modulation of endocrine function of adipose tissue. Despite intensive research, the exact role of lymphocytes and macrophages within adipose tissue is only partially clarified and various data obtained by different approaches bring ambiguous information with respect to their polarization and cytokine production. Compared to immunocompetent cells, the role of adipocytes in the obesity-related adipose tissue inflammation is often underestimated despite their abundant production of factors with immunomodulatory actions such as cytokines or adipokines such as leptin, adiponektin, and others. In summary, conflicting evidence together with only partial correlation of in vitro findings with true in vivo situation due to great heterogeneity and molecular complexity of tissue environment calls for intensive research in this rapidly evolving and important area.

Linking resistin, inflammation, and cardiometabolic diseases

Adipose tissue secretes a variety of bioactive substances that are associated with chronic inflammation, insulin resistance, and an increased risk of type 2 diabetes mellitus. While resistin was first known as an adipocyte-secreted hormone (adipokine) linked to obesity and insulin resistance in rodents, it is predominantly expressed and secreted by macrophages in humans. Epidemiological and genetic studies indicate that increased resistin levels are associated with the development of insulin resistance, diabetes, and cardiovascular disease. Resistin also appears to mediate the pathogenesis of atherosclerosis by promoting endothelial dysfunction, vascular smooth muscle cell proliferation, arterial inflammation, and the formation of foam cells. Thus, resistin is predictive of atherosclerosis and poor clinical outcomes in patients with cardiovascular disease and heart failure. Furthermore, recent evidence suggests that resistin is associated with atherogenic dyslipidemia and hypertension. The present review will focus on the role of human resistin in the pathogeneses of inflammation and obesity-related diseases.

Resistin's, obesity and insulin resistance: the continuing disconnect between rodents and humans

PURPOSE

This review aimed to discuss the conflicting findings from resistin research in rodents and humans as well as recent advances in our understanding of resistin's role in obesity and insulin resistance.

METHODS

A comprehensive review and synthesis of resistin's role in obesity and insulin resistance as well as conflicting findings from resistin research in rodents and humans.

RESULTS

In rodents, resistin is increased in high-fat/high-carbohydrate-fed, obese states characterized by impaired glucose uptake and insulin sensitivity. Resistin plays a causative role in the development of insulin resistance in rodents via 5' AMP-activated protein kinase (AMPK)-dependent and AMPK-independent suppressor of cytokine signaling-3 (SOCS-3) signaling. In contrast to rodents, human resistin is primarily secreted by peripheral-blood mononuclear cells (PBMCs) as opposed to white adipocytes. Circulating resistin levels have been positively associated with central/visceral obesity (but not BMI) as well as insulin resistance, while other studies show no such association. Human resistin has a role in pro-inflammatory processes that have been conclusively associated with obesity and insulin resistance. PBMCs, as well as vascular cells, have been identified as the primary targets of resistin's pro-inflammatory activity via nuclear factor-κB (NF-κB, p50/p65) and other signaling pathways.

CONCLUSION

Mounting evidence reveals a continuing disconnect between resistin's role in rodents and humans due to significant differences between these two species with respect to resistin's gene and protein structure, differential gene regulation, tissue-specific distribution, and insulin resistance induction as well as a paucity of evidence regarding the resistin receptor and downstream signaling mechanisms of action.

Association between resistin levels and cardiovascular disease events in older adults: The health, aging and body composition study

OBJECTIVE

Prospective data on the association between resistin levels and cardiovascular disease (CVD) events are sparse with conflicting results.

METHODS

We studied 3044 aged 70-79 years from the Health, Aging, and Body Composition Study. CVD events were defined as coronary heart disease (CHD) or stroke events. «Hard » CHD events were defined as CHD death or myocardial infarction. We estimated hazard ratio (HR) and 95% confidence intervals (CI) according to the quartiles of serum resistin concentrations and adjusted for clinical variables, and then further adjusted for metabolic disease (body mass index, fasting plasma glucose, abdominal visceral and subcutaneous adipose tissue, leptin, adiponectin, insulin) and inflammation (C-reactive protein, interleukin-6, tumor necrosis factors-α).

RESULTS

During a median follow-up of 10.1 years, 559 patients had « hard » CHD events, 884 CHD events and 1106 CVD Events. Unadjusted incidence rate for CVD events was 36.6 (95% CI 32.1-41.1) per 1000 persons-year in the lowest quartile and 54.0 per 1000 persons-year in the highest quartile (95% CI 48.2-59.8, P for trend < 0.001). In the multivariate models adjusted for clinical variables, HRs for the highest vs. lowest quartile of resistin was 1.52 (95% CI 1.20-1.93, P < 0.001) for « Hard » CHD events, 1.41 (95% CI 1.16-1.70, P = 0.001) for CHD events and 1.35 (95% CI 1.14-1.59, P = 0.002) for CVD events. Further adjustment for metabolic disease slightly reduced the associations while adjustment for inflammation markedly reduced the associations.

CONCLUSIONS

In older adults, higher resistin levels are associated with CVD events independently of clinical risk factors and metabolic disease markers, but markedly attenuated by inflammation.

Research advances in the relationship between nonalcoholic fatty liver disease and atherosclerosis

Nonalcoholic fatty liver disease (NAFLD) is a metabolic stress-induced liver disease that is closely related not only to genetic susceptibility but also to insulin resistance and highly linked with metabolic syndrome. In recent years, the prevalence of NAFLD has increased rapidly, paralleling the epidemic of type 2 diabetes mellitus and obesity leading to cardiovascular disease. It has been demonstrated that NAFLD is highly associated with atherosclerosis. With recently gained knowledge, it appears that NAFLD may induce insulin resistance, dyslipidemia, oxidative stress, inflammation, and fluctuation of adipokines associated with atherosclerosis. In this review, we aimed to summarize recent discoveries related to both NAFLD and atherosclerosis, and to identify possible mechanisms linking them.

Endothelin-1 activation of the endothelin B receptor modulates pulmonary endothelial CX3CL1 and contributes to pulmonary angiogenesis in experimental hepatopulmonary syndrome

Hepatic production and release of endothelin-1 (ET-1) binding to endothelin B (ETB) receptors, overexpressed in the lung microvasculature, is associated with accumulation of pro-angiogenic monocytes and vascular remodeling in experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL). We have recently found that lung vascular monocyte adhesion and angiogenesis in HPS involve interaction of endothelial C-X3-C motif ligand 1 (CX3CL1) with monocyte CX3C chemokine receptor 1 (CX3CR1), although whether ET-1/ETB receptor activation influences these events is unknown. Our aim was to define if ET-1/ETB receptor activation modulates CX3CL1/CX3CR1 signaling and lung angiogenesis in experimental HPS. A selective ETB receptor antagonist, BQ788, was given for 2 weeks to 1-week CBDL rats. ET-1 (±BQ788) was given to cultured rat pulmonary microvascular endothelial cells overexpressing ETB receptors. BQ788 treatment significantly decreased lung angiogenesis, monocyte accumulation, and CX3CL1 levels after CBDL. ET-1 treatment significantly induced CX3CL1 production in lung microvascular endothelial cells, which was blocked by inhibitors of Ca(2+) and mitogen-activated protein kinase (MEK)/ERK pathways. ET-1-induced ERK activation was Ca(2+) independent. ET-1 administration also increased endothelial tube formation in vitro, which was inhibited by BQ788 or by blocking Ca(2+) and MEK/ERK activation. CX3CR1 neutralizing antibody partially inhibited ET-1 effects on tube formation. These findings identify a novel mechanistic interaction between the ET-1/ETB receptor axis and CX3CL1/CX3CR1 in mediating pulmonary angiogenesis and vascular monocyte accumulation in experimental HPS.

Subendothelial resistin enhances monocyte transmigration in a co-culture of human endothelial and smooth muscle cells by mechanisms involving fractalkine, MCP-1 and activation of TLR4 and Gi/o proteins signaling

The cytokine resistin and the chemokine fractalkine (FKN) were found at increased levels in human atherosclerotic plaque, in the subendothelium, but their role in this location still needs to be characterized. Recently, high local resistin in the arterial vessel wall was shown to contribute to an enhanced accumulation of macrophages by mechanisms that need to be clarified. Our recent data showed that resistin activated smooth muscle cells (SMC) by up-regulating FKN and MCP-1 expression and monocyte chemotaxis by activating toll-like receptor 4 (TLR4) and Gi/o proteins. Since in the vessel wall both endothelial cells (EC) and SMC respond to cytokines and promote atherosclerosis, we questioned whether subendothelial resistin (sR) has a role in vascular cells cross-talk leading to enhanced monocyte transmigration and we investigated the mechanisms involved. To this purpose we used an in vitro system of co-cultured SMC and EC activated by sR and we analyzed monocyte transmigration. Our results indicated that: (1) sR enhanced monocyte transmigration in EC/SMC system compared to EC cultured alone; (2) sR activated TLR4 and Gi/o signaling in EC/SMC system and induced the secretion of more FKN and MCP-1 compared to EC cultured alone and used both chemokines to specifically recruit monocytes by CX3CR1 and CCR2 receptors. Moreover, FKN produced by resistin in EC/SMC system, by acting on CX3CR1 on EC/SMC specifically contributes to MCP-1 secretion in the system and to the enhanced monocyte transmigration. Our study indicates new possible targets for therapy to reduce resistin-dependent enhanced macrophage infiltration in the atherosclerotic arterial wall.

Resistin in rodents and humans

Obesity is characterized by excess accumulation of lipids in adipose tissue and other organs, and chronic inflammation associated with insulin resistance and an increased risk of type 2 diabetes. Obesity, type 2 diabetes, and cardiovascular diseases are major health concerns. Resistin was first discovered as an adipose-secreted hormone (adipokine) linked to obesity and insulin resistance in rodents. Adipocyte-derived resistin is increased in obese rodents and strongly related to insulin resistance. However, in contrast to rodents, resistin is expressed and secreted from macrophages in humans and is increased in inflammatory conditions. Some studies have also suggested an association between increased resistin levels and insulin resistance, diabetes and cardiovascular disease. Genetic studies have provided additional evidence for a role of resistin in insulin resistance and inflammation. Resistin appears to mediate the pathogenesis of atherosclerosis by promoting endothelial dysfunction, vascular smooth muscle cell proliferation, arterial inflammation, and formation of foam cells. Indeed, resistin is predictive of atherosclerosis and poor clinical outcomes in patients with coronary artery disease and ischemic stroke. There is also growing evidence that elevated resistin is associated with the development of heart failure. This review will focus on the biology of resistin in rodents and humans, and evidence linking resistin with type 2 diabetes, atherosclerosis, and cardiovascular disease.

Davallialactone from mushroom reduced premature senescence and inflammation on glucose oxidative stress in human diploid fibroblast cells

Mushrooms are both food and a source of natural compounds of biopharmaceutical interest. The purpose of this study was to clarify whether davallialactone from mushroom extract affected the pathogenesis of hyperglycemia oxidative stress and the aging process in human diploid fibroblast (HDF) cells. The high-glucose state with glucose oxidase resulted in glucose oxidative stress, induction of inflammatory molecules, dysfunction of antioxidant molecules, and activation of mitogen-activated protein kinase (MAPKs) and its downstream signaling in old HDF cells. The exposure of glucose oxidative stress in middle-stage cells led to stress-induced premature senescence (SIPS) via senescence-associated β-galactosidase (SA β-gal) activity and displayed replicative senescence phenomena. However, davallialactone reduces the pathogenesis of glucose oxidative stress and the aging process through down-regulation of SA β-gal activity. These results strongly suggest that natural compounds, especially mushroom extract davallialactone, improve the pathogenesis of glucose oxidative stress and the aging process. Hence, davallialactone has potential in the treatment of diabetes mellitus or age-related disease complications.

The involvement of the monocytes/macrophages in chronic inflammation associated with atherosclerosis

Atherosclerosis is a progressive chronic disease of large and medium arteries, characterized by the formation of atherosclerotic plaques. Monocytes and macrophages are key factors in lesion development, participating to the processes that mediate the progression of the atherosclerotic plaque (lipid accumulation, secretion of pro-inflammatory and cytotoxic factors, extracellular matrix remodeling). The recruitment of the monocytes in the vascular wall represents a hallmark in the pathology of the atherosclerotic lesion. Monocyte adhesion and transmigration are dependent on the complementary adhesion molecules expressed on the endothelial surface, whose expression is modulated by chemical mediators. The atherosclerotic plaque is characterized by a heterogeneous population of macrophages reflecting the complexity and diversity of the micro-environment to which cells are exposed after entering the arterial wall. Within the atherosclerotic lesions, macrophages differentiate, proliferate and undergo apoptosis. Taking into account that their behavior has a direct and critical influence on all lesional stages, the development of therapeutic approaches to target monocytes/macrophages in the atherosclerotic plaque became a focal interest point for researchers in the field.

Diabetes alters activation and repression of pro- and anti-inflammatory signaling pathways in the vasculature

A central mechanism driving vascular disease in diabetes is immune cell-mediated inflammation. In diabetes, enhanced oxidation and glycation of macromolecules, such as lipoproteins, insults the endothelium, and activates both innate and adaptive arms of the immune system by generating new antigens for presentation to adaptive immune cells. Chronic inflammation of the endothelium in diabetes leads to continuous infiltration and accumulation of leukocytes at sites of endothelial cell injury. We will describe the central role of the macrophage as a source of signaling molecules and damaging by-products which activate infiltrating lymphocytes in the tissue and contribute to the pro-oxidant and pro-inflammatory microenvironment. An important aspect to be considered is the diabetes-associated defects in the immune system, such as fewer or dysfunctional athero-protective leukocyte subsets in the diabetic lesion compared to non-diabetic lesions. This review will discuss the key pro-inflammatory signaling pathways responsible for leukocyte recruitment and activation in the injured vessel, with particular focus on pro- and anti-inflammatory pathways aberrantly activated or repressed in diabetes. We aim to describe the interaction between advanced glycation end products and their principle receptor RAGE, angiotensin II, and the Ang II type 1 receptor, in addition to reactive oxygen species (ROS) production by NADPH-oxidase enzymes that are relevant to vascular and immune cell function in the context of diabetic vasculopathy. Furthermore, we will touch on recent advances in epigenetic medicine that have revealed high glucose-mediated changes in the transcription of genes with known pro-inflammatory downstream targets. Finally, novel anti-atherosclerosis strategies that target the vascular immune interface will be explored; such as vaccination against modified low-density lipoprotein and pharmacological inhibition of ROS-producing enzymes.

Inflammatory effects of resistin on human smooth muscle cells: up-regulation of fractalkine and its receptor, CX3CR1 expression by TLR4 and Gi-protein pathways

In the atherosclerotic plaque, smooth muscle cells (SMC) acquire an inflammatory phenotype. Resistin and fractalkine (CX3CL1) are found in human atheroma and not in normal arteries. CX3CL1 and CX3CR1 are predominately associated with SMC. We have questioned whether resistin has a role in the expression of CX3CL1 and CX3CR1 in SMC thus contributing to the pro-inflammatory status of these cells. Cultured human aortic SMC were stimulated with 100 ng/ml resistin for 4, 6, 12, and 24 h, and then CX3CL1 and CX3CR1 expression was assessed by quantitative reverse transcription with the polymerase chain reaction and Western blot. We found that resistin up-regulated CX3CL1 and CX3CR1 in SMC and induced the phosphorylation of p38MAPK and STAT3. Inhibitors of p38MAPK, JAK-STAT, NF-kB, and AP-1 significantly reduced CX3CL1 and CX3CR1 expression. Knockdown of STAT1 and STAT3 with decoy oligodeoxinucleotides and the silencing of p65 and cjun with short interfering RNA decreased CX3CL1 and CX3CR1 expression. Anti-TLR4 antibody and pertussis toxin also reduced CX3CL1 and CX3CR1 protein expression. xCELLigence experiments revealed that resistin probably uses Gi-proteins for its effect on SMC. The CX3CL1 induced by resistin exhibited a chemotactic effect on monocyte transmigration. Thus, (1) resistin contributes to the pro-inflammatory state of SMC by the up-regulation of CX3CL1 and CX3CR1 expression via a mechanism involving NF-kB, AP-1, and STAT1/3 transcription factors, (2) resistin employs TLR4 and Gi-protein signaling for its effect on SMC, (3) CX3CL1 induced by resistin is functional in monocyte chemotaxis. The data reveal new mechanisms by which resistin promotes the inflammatory phenotype of SMC.

Fractalkine and its receptor (CX3CR1) in patients with stable coronary artery disease and diabetes mellitus

BACKGROUND

Fractalkine and its receptor CX3CR1 are associated with atherosclerosis. In vitro studies have shown increased expression of fractalkine in endothelial and vascular smooth muscle cells when stimulated with a high concentration of glucose. Increased serum levels of fractalkine have been shown in patients with type 2 diabetes mellitus (T2DM) and also in unstable coronary artery disease (CAD) patients. We investigated whether CAD patients with T2DM or metabolic syndrome have increased circulating and gene expression levels of fractalkine compared to CAD patients without these conditions.

METHODS

Serum levels of fractalkine were analyzed by the enzyme-linked immunosorbent assay (ELISA) method in 1001 patients with angiographically verified CAD, of which 200 had T2DM and 244 had metabolic syndrome. All patients were taking aspirin as an antithrombotic treatment. Gene expression of fractalkine and CX3CR1 in circulating leukocytes was explored in a subset of patients (n=168).

RESULTS

We found no significant difference in circulating levels of fractalkine in patients with T2DM [653 (556, 775) pg/mL] compared to patients without T2DM [646 (553, 761) pg/mL], p=0.50. There was also no difference between patients with and without metabolic syndrome (p=0.60). Fractalkine was not expressed in circulating leukocytes, and CX3CR1 was not expressed differently between any of the groups (p=0.13 and p=0.32, respectively). Smokers had lower fractalkine levels (p<0.001), and patients on angiotensin II receptor blockers had higher levels (p=0.047) compared to nonaffected patients.

CONCLUSIONS

In the present CAD population, no differences in circulating levels of fractalkine or expression levels of CX3CR1 were observed between patients with and without T2DM, or with and without metabolic syndrome, which may be related to their underlying disease.

Adipokines and the cardiovascular system: mechanisms mediating health and disease

This review focuses on the role of adipokines in the maintenance of a healthy cardiovascular system, and the mechanisms by which these factors mediate the development of cardiovascular disease in obesity. Adipocytes are the major cell type comprising the adipose tissue. These cells secrete numerous factors, termed adipokines, into the blood, including adiponectin, leptin, resistin, chemerin, omentin, vaspin, and visfatin. Adipose tissue is a highly vascularised endocrine organ, and different adipose depots have distinct adipokine secretion profiles, which are altered with obesity. The ability of many adipokines to stimulate angiogenesis is crucial for adipose tissue expansion; however, excessive blood vessel growth is deleterious. As well, some adipokines induce inflammation, which promotes cardiovascular disease progression. We discuss how these 7 aforementioned adipokines act upon the various cardiovascular cell types (endothelial progenitor cells, endothelial cells, vascular smooth muscle cells, pericytes, cardiomyocytes, and cardiac fibroblasts), the direct effects of these actions, and their overall impact on the cardiovascular system. These were chosen, as these adipokines are secreted predominantly from adipocytes and have known effects on cardiovascular cells.

A novel pro-inflammatory mechanism of action of resistin in human endothelial cells: up-regulation of SOCS3 expression through STAT3 activation

Resistin is a significant local and systemic regulatory cytokine involved in inflammation. Suppressors of cytokine signaling (SOCS) proteins are intracellular regulators of receptor signal transduction induced by several cytokines in a cytokine and cell specific manner. Resistin up-regulates SOCS3 expression in mice adipocytes but it is not known whether this is a common occurrence in other cells. We questioned whether resistin-induces SOCS3 in human endothelial cells and if signal transducer and activator of transcription (STAT) proteins are involved in the process. The Real-Time PCR and Western blot analysis showed that in resistin-activated HEC the gene and protein expression of SOCS3 were significantly increased. Furthermore, resistin induced activation of STAT3 as characterized by increased tyrosine phosphorylation. Resistin-induced SOCS3 expression was blocked by specific inhibitors of STAT3 signaling and by the transfection of siRNA specific for STAT3. Silencing of SOCS3 gene expression by transfection with SOCS3 siRNA reduced the expression of resistin induced-P-selectin and fractalkine in HEC. Together, our results demonstrate that in HEC (1) resistin up-regulates SOCS3 expression and activates STAT3 transcription factor; (2) the increase in SOCS3 mRNA and protein expression as well as STAT3 activation have a long-lasting effect (up to 18h); (3) inhibition of SOCS3 function prevents resistin-induced expression of cell adhesion molecules P-selectin and fractalkine and thus activation of endothelial cells. The data uncover a new resistin-mediated mechanism in human endothelial cells and designate SOCS3 as a novel therapeutic target to modulate resistin-dependent inflammation in vessel wall diseases.

Inflammation and metabolic dysfunction: links to cardiovascular diseases

Abdominal obesity is a major risk factor for cardiovascular disease, and recent studies highlight a key role of adipose tissue dysfunction, inflammation, and aberrant adipokine release in this process. An increased demand for lipid storage results in both hyperplasia and hypertrophy, finally leading to chronic inflammation, hypoxia, and a phenotypic change of the cellular components of adipose tissue, collectively leading to a substantially altered secretory output of adipose tissue. In this review we have assessed the adipo-vascular axis, and an overview of adipokines associated with cardiovascular disease is provided. This resulted in a first list of more than 30 adipokines. A deeper analysis only considered adipokines that have been reported to impact on inflammation and NF-κB activation in the vasculature. Out of these, the most prominent link to cardiovascular disease was found for leptin, TNF-α, adipocyte fatty acid-binding protein, interleukins, and several novel adipokines such as lipocalin-2 and pigment epithelium-derived factor. Future work will need to address the potential role of these molecules as biomarkers and/or drug targets.

Caffeic acid disturbs monocyte adhesion onto cultured endothelial cells stimulated by adipokine resistin

Adipokines have been implicated in the pathogenesis of atherosclerosis via pro-inflammatory mechanisms contributing to insulin resistance. The adipokine resistin causes endothelium dysfunction, which plays an important role in sustaining atherogenesis. This study investigated whether resistin induced expression of cell adhesion molecules and integrins in endothelial cells and THP-1 monocytes and whether such induction was attenuated by 1-20 μM caffeic acid. Resistin enhanced endothelial expression of vascular cell adhesion molecule 1 (VCAM-1), intercellular cell adhesion molecule 1 (ICAM-1), and E-selectin and monocyte expression of β1, β2, and α4 integrins. The enhancement of these proteins was diminished by caffeic acid with reduced THP-1 cell adhesion on activated endothelium. Caffeic acid at ≤20 μM demoted resistin-stimulated interleukin 8 (IL-8) production responsible for ICAM-1 and β2 integrin induction. The endothelial up-regulation of IL-8 secretion by resistin entailed toll-like receptor 4 (TLR4) activation, but caffeic acid diminished IL-8 production and TLR4 induction. Furthermore, caffeic acid encumbered resistin-activated nuclear factor κB (NF-κB) signaling. These results demonstrate that caffeic acid blocked monocyte trafficking to resistin-activated endothelium via disturbing NF-κB signaling responsive to IL-8. Therefore, caffeic acid may have therapeutic potential in preventing obesity-associated atherosclerosis.

Effect of hyperglycemia on human monocyte activation

Our recent study defined the chemokine-induced human monocyte signaling under normoglycemic condition. To explore the hyperglycemia-induced monocyte signaling, we performed adhesion, migration, and transmigration assays on human monocytes obtained from THP-1 cell line in the presence of normal (5 mM) and high (10 and 20 mM) glucose concentrations without chemokines. We observed augmented (P < 0.01) monocyte adhesion to human umbilical vein endothelial cell monolayer at 10 than 5 mM glucose with no further increase at 20-mM glucose concentration (P < 0.07 vs 10 mM; P < 0.01 vs 5 mM). But incremental increases in monocyte migration (P < 0.01), transmigration (P < 0.01), and stress fiber response (P < 0.01) were observed at 10- and 20-mM glucose concentrations in comparison to 5-mM glucose concentrations. We found gradational increase (P < 0.01) in phosphorylation of Akt(S473) and glycogen synthase kinase (GSK3β(S9)) in hyperglycemia (10 and 20 mM) when compared with 5 mM glucose. Furthermore, hyperglycemia (both 10 and 20 mM)-treated monocyte showed up-regulated phosphorylation of p101 and p110γ subunits of PI-3 kinase in comparison to 5 mM glucose. Hyperglycemia-induced monocyte migration was restored to basal levels in the presence of PI-3 kinase inhibitor, LY. These observations imply that modest hyperglycemia per se, as is commonly observed in diabetic individuals, is a potent stimulator of monocyte activity even without chemokines.

Association of resistin with heart failure and mortality in patients with stable coronary heart disease: data from the heart and soul study

BACKGROUND

Resistin is a pro-inflammatory signaling molecule that is thought to contribute to atherosclerosis. We sought to evaluate whether resistin is predictive of worse cardiovascular outcomes among ambulatory patients with stable coronary heart disease (CHD).

METHODS AND RESULTS

We measured baseline serum resistin in 980 participants with documented CHD. After a mean follow-up of 6.1 (range, 0.1 to 9.0) years, 358 (36.5%) were hospitalized for myocardial infarction or heart failure or had died. As compared with participants who had resistin levels in the lowest quartile, those with resistin levels in the highest quartile were at an increased risk of heart failure (hazard ratio [HR], 2.06; 95% confidence interval [CI], 1.26-3.39) and death (HR, 1.56; 95% CI, 1.11-2.18), adjusted for age, sex, and race. Further adjustments for obesity, hypertension, insulin resistance, dyslipidemia, and renal dysfunction eliminated these associations. Resistin levels were not associated with an increased risk of non-fatal myocardial infarction (unadjusted HR, 1.18; 95% CI, 0.68-2.05).

CONCLUSIONS

Elevated serum resistin is associated with higher rates of mortality and hospitalization for heart failure. However, this appears to be explained by the association of resistin with traditional measures of cardiovascular risk. Thus, serum resistin does not add prognostic information among high-risk persons with established CHD.

Fractalkine/CX3CR1 and atherosclerosis

Fractalkine is a unique chemokine which has both adhesive and chemoattractant functions. With the increasing emphasis on the importance of inflammation in atherosclerosis, more attention has been focused on the role of chemokines in atherosclerosis. It has been shown that fractalkine/CX3CR1 participates in the atherosclerotic pathological process through mediating the recruitment of leukocytes and the interaction of vascular cells and leukocytes. Some signal pathways are simultaneously activated through fractalkine/CX3CR1 coupling to promote the inflammatory response in atherosclerotic vessels. Additionally, fractalkine has cytotoxic effects on endothelium as well as anti-apoptosis and proliferative effects on vascular cells which consequently changes plaque components and stability in plaque. Several studies have showed that fractalkine or CX3CR1 deficiency in atherosclerotic mice would ameliorate the severity of plaque. Population studies on CX3CR1 polymorphism have confirmed that 280M-containing haplotype is associated with reduced risk of atherosclerotic disease. Despite the apparent association with atherosclerosis, further studies on fractalkine/CX3CR1 chemokine pair are clearly warranted to more fully elucidate this relationship.

Inflammation, a link between obesity and cardiovascular disease

Obesity, the most common nutritional disorder in industrialized countries, is associated with an increased mortality and morbidity of cardiovascular disease (CVD). Obesity is primarily considered to be a disorder of energy balance, and it has recently been suggested that some forms of obesity are associated with chronic low-grade inflammation. The present paper focuses on the current status of our knowledge regarding chronic inflammation, a link between obesity and CVDs, including heart diseases, vascular disease and atherosclerosis. The paper discusses the methods of body fat evaluation in humans, the endocrinology and distribution of adipose tissue in the genders, the pathophysiology of obesity, the relationship among obesity, inflammation, and CVD, and the adipose tissue-derived cytokines known to affect inflammation. Due to space limitations, this paper focuses on C-reactive protein, serum amyloid A, leptin, adiponectin, resistin, visfatin, chemerin, omentin, vaspin, apelin, and retinol binding protein 4 as adipokines.