TNF-α levels are associated with skin capillary recruitment in humans: a potential explanation for the relationship between TNF-α and insulin resistance

Obesity-Related Inflammation and Endothelial Dysfunction in COVID-19: Impact on Disease Severity

The coronavirus disease 2019 (COVID-19) pandemic has put into evidence another pandemic – obesity. Currently, several studies have documented the association between obesity and COVID-19 severity. The mechanisms underlying the increased risk of complications and mortality in obese patients with COVID-19 are of diverse nature. Inflammation plays a central role in obesity. Metabolic alterations seen in obese patients are related to an inflammatory response, and several studies report elevated levels of circulating inflammatory cytokines in obese patients. Also, deregulated expression of adipokines, such as leptin and resistin, increase the expression of vascular adhesion molecule 1 and intercellular adhesion molecule 1 that contribute to increased vascular leukocyte adhesiveness and additional oxidative stress. Additionally, it is now recognized that the chronic impairment of systemic vascular endothelial function in patients with cardiovascular and metabolic disorders, including obesity, when intensified by the detrimental effects of SARS-CoV-2 over the endothelium, may explain their worse outcomes in COVID-19. In fact, vascular endothelial dysfunction may contribute to a unfavorable response of the endothelium to the infection by SARS-CoV-2, whereas alterations in cardiac structure and function and the prothrombotic environment in obesity may also provide a link to the increased cardiovascular events in these patients.

Capillary Rarefaction in Obesity and Metabolic Diseases-Organ-Specificity and Possible Mechanisms

Obesity and its comorbidities like diabetes, hypertension and other cardiovascular disorders are the leading causes of death and disability worldwide. Metabolic diseases cause vascular dysfunction and loss of capillaries termed capillary rarefaction. Interestingly, obesity seems to affect capillary beds in an organ-specific manner, causing morphological and functional changes in some tissues but not in others. Accordingly, treatment strategies targeting capillary rarefaction result in distinct outcomes depending on the organ. In recent years, organ-specific vasculature and endothelial heterogeneity have been in the spotlight in the field of vascular biology since specialized vascular systems have been shown to contribute to organ function by secreting varying autocrine and paracrine factors and by providing niches for stem cells. This review summarizes the recent literature covering studies on organ-specific capillary rarefaction observed in obesity and metabolic diseases and explores the underlying mechanisms, with multiple modes of action proposed. It also provides a glimpse of the reported therapeutic perspectives targeting capillary rarefaction. Further studies should address the reasons for such organ-specificity of capillary rarefaction, investigate strategies for its prevention and reversibility and examine potential signaling pathways that can be exploited to target it.

Organ dysfunction in cirrhosis: a mechanism involving the microcirculation

INTRODUCTION

Microcirculation is essential for adequate tissue perfusion and organ function. Microcirculatory changes may occur in cirrhosis, inducing loss of multiorgan function. The aim was to evaluate preliver transplantation and postliver transplantation aspects of multiorgan function, microcirculation, inflammatory, and endothelial biomarkers and survival in a controlled study including cirrhotic outpatients.

PATIENTS AND METHODS

We accessed functional capillary density (FCD) and red blood cell acceleration (RBCA) by nailfold videocapillaroscopy. Inflammatory and endothelial biomarkers [interleukin-6 (IL-6), soluble intercellular adhesion molecule-1, endothelin-1, and tumor necrosis factor-α] were analyzed. Cerebral and renal functions were assessed to represent organ dysfunction and regression analyses were carried out. Receiver operating characteristic curves were constructed and survival Kaplan-Meier analysis was carried out.

RESULTS

Fifty-four patients and 18 controls were included. Inflammatory and endothelial markers increased in advanced disease. FCD was reduced and RBCA was progressively lower according to disease severity. RBCA correlated inversely with inflammatory and endothelial biomarkers, and directly with renal function. The presence of hepatic encephalopathy correlated inversely with RBCA and directly with IL-6 and endothelin-1. In multivariate analysis, RBCA was an independent factor for organ dysfunction. The area under the receiver operating chartacteristic curve for IL-6 for survival was 0.74 (0.59-0.89), P=0.05. Transplant-free survival was 97.5% for values under 5.78 ng/ml (IL-6 best cutoff) and 83.9% above 5.78 ng/ml, log-rank=0.018. Eleven patients underwent transplantation, with an overall improvement in microcirculatory function.

CONCLUSION

Our results suggest a mechanism of organ damage in cirrhosis, where microcirculatory dysfunction could be correlated to inflammatory and endothelial biomarkers, and loss of multiorgan function. IL-6 seems to be an important survival marker of inflammation. Liver transplantation improved microcirculatory dysfunction, corroborating this hypothesis.

Obesity and diabetes: An update

The twin epidemic of obesity and diabetes is a major crisis globally. Several epidemiologic studies reveal the parallel escalation of obesity and diabetes. The term 'diabesity' expresses their close relationship to each other, wherein both these metabolic disorders are characterized by defects of insulin action. The pathophysiology connecting obesity and diabetes is chiefly attributed to two factors: insulin resistance and insulin deficiency. Recent years have seen an increasing body of work on the following metabolic defects common to both obesity and diabetes such as, impaired tissue perfusion, sleep disturbances, androgen dysfunction, altered Vitamin D levels and GI stress. The scope of this review is to present the most widely accepted theories that link the two diseases, provide an update on some proposed unifying metabolic defects and highlight current and future prevention and management strategies.

At the crossroad between obesity and gastric cancer

Obesity has reached epidemic proportions worldwide with disproportionate prevalence in different communities and ethnic groups. Recently, the American Medical Association recognized obesity as a disease, which is a significant milestone that opens the possibilities of treating obesity under standardized health plans. Obesity is an inflammatory disease characterized by elevated levels of biomarkers associated with abnormal lipid profiles, glucose levels, and blood pressure that lead to the onset of metabolic syndrome. Interestingly, inflammatory biomarkers, in particular, have been implicated in the risk of developing several types of cancer. Likewise, obesity has been linked to esophageal, breast, gallbladder, kidney, pancreatic, and colorectal cancers. Thus, there exists a link between obesity status and tumor appearance, which may be associated to the differential levels and the circulating profiles of several inflammatory molecules. For example, mediators of the inflammatory responses in both obesity and gastric cancer risk are the same: pro-inflammatory molecules produced by the activated cells infiltrating the inflamed tissues. These molecules trigger pathways of activation shared by obesity and cancer. Therefore, understanding how these different pathways are modulated would help reduce the impact that both diseases, and their concomitant existence, have on society.

Metabolic syndrome in overweight and obese adolescents: a comparison of two different diagnostic criteria

BACKGROUND

Due to the lack of consensus on its definition, the metabolic syndrome (MS) in children and adolescents is not formally recognized. However, several researchers have changed the adult criteria for pediatric standards in order to assess the prevalence.

OBJECTIVE

The aim of this study was to evaluate the frequency of MS and its components according to two of the currently used definitions in overweight and obese adolescents.

METHODS

A cross-sectional study with 232 adolescents with excess weight from a public school of the city of Rio de Janeiro. Anthropometric, blood pressure, and biochemical variables were assessed. MS was defined using two different diagnostic criteria: the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATPIII) and International Diabetes Federation (IDF).

RESULTS

MS was diagnosed in 40.4 and 24.6% of obese adolescents and 9.4 and 1.9% of overweight adolescents according to the NCEP-ATPIII and IDF criteria, respectively. The degree of agreement, assessed by the κ index, from the definitions adopted in this study was 0.48.

CONCLUSION

The results show a significant difference between the two diagnostic criteria. A higher frequency was found when the NCEP-ATPIII was used, which is of concern given the association of MS with diabetes and cardiovascular disease.

Cytokine networking of innate immunity cells: a potential target of therapy

Innate immune cells, particularly macrophages and epithelial cells, play a key role in multiple layers of immune responses. Alarmins and pro-inflammatory cytokines from the IL (interleukin)-1 and TNF (tumour necrosis factor) families initiate the cascade of events by inducing chemokine release from bystander cells and by the up-regulation of adhesion molecules required for transendothelial trafficking of immune cells. Furthermore, innate cytokines produced by dendritic cells, macrophages, epithelial cells and innate lymphoid cells seem to play a critical role in polarization of helper T-cell cytokine profiles into specific subsets of Th1/Th2/Th17 effector cells or regulatory T-cells. Lastly, the innate immune system down-regulates effector mechanisms and restores homoeostasis in injured tissue via cytokines from the IL-10 and TGF (transforming growth factor) families mainly released from macrophages, preferentially the M2 subset, which have a capacity to induce regulatory T-cells, inhibit the production of pro-inflammatory cytokines and induce healing of the tissue by regulating extracellular matrix protein deposition and angiogenesis. Cytokines produced by innate immune cells represent an attractive target for therapeutic intervention, and multiple molecules are currently being tested clinically in patients with inflammatory bowel disease, rheumatoid arthritis, systemic diseases, autoinflammatory syndromes, fibrosing processes or malignancies. In addition to the already widely used blockers of TNFα and the tested inhibitors of IL-1 and IL-6, multiple therapeutic molecules are currently in clinical trials targeting TNF-related molecules [APRIL (a proliferation-inducing ligand) and BAFF (B-cell-activating factor belonging to the TNF family)], chemokine receptors, IL-17, TGFβ and other cytokines.

Inverse correlation of serum inflammatory markers with metabolic parameters in healthy, Black and White prepubertal youth

OBJECTIVE

To examine for the first time the associations between pro-inflammatory cytokines and obesity-related metabolic biomarkers in, exclusively prepubertal, otherwise healthy obese and non-obese Black and White children, 7-9 years of age.

DESIGN AND METHODS

Body mass index (BMI), homeostasis model assessment-estimated insulin resistance, visceral adipose tissue and subcutaneous adipose tissue (SAT (magnetic resonance imaging)); total body fat (dual-energy X-ray absorptiometry), ectopic, intrahepatic lipid (IHL) and intramyocellular lipid (IMCL) fat (proton magnetic resonance spectroscopy) and serum levels of interleukin (IL)-1, IL-6, IL-8, tumor necrosis factor alpha (TNF-α) and monocyte chemoattractant protein-1 were measured in 40 obese and non-obese children. Relationships between inflammatory cytokines and obesity were assessed by analysis of variance and Spearman's rank correlation.

RESULTS

Significant inverse correlations were found between BMI z-score, SAT, total BF, and IHL and levels of TNF-α (Spearman's ρ=-0.36, -0.39, -0.43 and -0.39, respectively; P<0.05). Levels of IL-8 were significantly and inversely correlated with IMCL (-0.39; P=0.03) and remained significant after adjusting for race. IMCL was inversely associated with TNF-α only after adjusting for race (-0.37; P=0.04).

CONCLUSIONS

Relationships between pro-inflammatory and metabolic markers commonly observed in adults are reversed in healthy, Black and White children before puberty. Prospective studies are warranted to determine how these inverse relationships modify chronic disease risk later in life.

Microvascular dysfunction: a potential mechanism in the pathogenesis of obesity-associated insulin resistance and hypertension

The intertwined epidemics of obesity and related disorders such as hypertension, insulin resistance, type 2 diabetes, and subsequent cardiovascular disease pose a major public health challenge. To meet this challenge, we must understand the interplay between adipose tissue and the vasculature. Microvascular dysfunction is important not only in the development of obesity-related target-organ damage but also in the development of cardiovascular risk factors such as hypertension and insulin resistance. The present review examines the role of microvascular dysfunction as an explanation for the associations among obesity, hypertension, and impaired insulin-mediated glucose disposal. We also discuss communicative pathways from adipose tissue to the microcirculation.

Metabolic disturbances linked to obesity: the role of impaired tissue perfusion

Associated with elevated risk of cardiovascular events and cancer, obesity is a worldwide problem affecting developed and developing countries. Microcirculatory vessels, represented by arterioles, capillaries and venules (mean internal diameter < 100 microm), are the place where blood/tissue nutrition and exchange effectively take place. Microvascular dysfunction is an early event in obesity probably secondary to endothelial dysfunction and capillaries rarefaction. New research techniques allow the investigation of the microcirculation in different vascular beds in humans. Studies suggest a link between endothelial dysfunction and visceral obesity. Oxidative stress, inflammation and renin-angiotensin system are among factors considered to be involved on microvascular dysfunction in obesity. Microcirculatory impairment present in obesity suggests that it could be an important causal factor in obesity-related disorders such as insulin resistance and hypertension.

Contribution of insulin resistance to vascular dysfunction

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

Microvascular function is impaired in ankylosing spondylitis and improves after tumour necrosis factor alpha blockade

OBJECTIVES

Ankylosing spondylitis (AS) is associated with increased cardiovascular morbidity and mortality. Microvascular function has been linked to several risk factors for cardiovascular disease. Inflammation in AS may cause microvascular dysfunction. To test this, we assessed microvascular function in (a) patients with AS compared to healthy controls and (b) patients with AS before and after 1 month of anti-tumour necrosis factor (TNF)alpha treatment with etanercept.

METHODS

A total of 15 consecutive patients with AS, who were scheduled for etanercept treatment according to the Assessment in Ankylosing Spondylitis (ASAS) group guidelines, and 12 healthy controls matched for age and sex, were recruited. Endothelium-dependent and independent vasodilatation in skin were evaluated with laser Doppler fluxmetry after iontophoresis of acetylcholine and sodium nitroprusside, respectively. Videomicroscopy was used to measure recruitment of skin capillaries after arterial occlusion.

RESULTS

Compared to healthy controls, patients with AS had impaired endothelium-dependent vasodilatation and capillary recruitment. Following anti-TNFalpha treatment, microvascular function improved significantly for endothelium-dependent vasodilatation (p = 0.03) and capillary recruitment (p = 0.006). A significant correlation was observed between changes in endothelium-dependent vasodilatation and changes in erythrocyte sedimentation rate (ESR) (r = -0.56; p = 0.03).

CONCLUSION

Microvascular dysfunction is present in patients with AS with active disease, but improves as inflammation regresses after TNFalpha blockade.

Incorporation of the fasting free fatty acid concentration into quantitative insulin sensitivity check index improves its association with insulin sensitivity in adults, but not in children

OBJECTIVE

Based on fasting insulin and glucose, several indices of insulin sensitivity have been developed in adults. Recently, it has been demonstrated that incorporation of the fasting free fatty acid (FFA) concentration improves the association with insulin sensitivity in adults. We investigated the association of clamp-derived insulin sensitivity with indices of insulin sensitivity derived from fasting blood in prepubertal children and adults, with and without incorporation of FFAs.

DESIGN AND METHODS

We studied 59 healthy adults and 29 of them are prepubertal children. We measured insulin sensitivity with the euglycemic-hyperinsulinemic clamp. Based on fasting insulin and glucose, we estimated insulin sensitivity with the homeostasis model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI), and the revised QUICKI after the incorporation of FFAs.

RESULTS

The associations of HOMA and QUICKI with clamp-derived insulin sensitivity in children (r=-0.55 and 0.54 respectively; P<0.01) were similar to those in adults (r=-0.54 and 0.53 respectively; P<0.01). However, incorporation of FFAs into the QUICKI model resulted in an increase in the association in adults, but not in children (r=0.68 and 0.48 respectively; P<0.01). Adding FFA levels to a regression model with glucose and insulin as independent variables resulted in an increase in the explained variance in clamp-derived insulin sensitivity in adults, but not in children (P value 0.004 in adults and 0.3 in children).

CONCLUSIONS

HOMA and QUICKI are associated with clamp-derived insulin sensitivity in both children and adults. Incorporating fasting levels of FFAs into the QUICKI model improves the association with clamp-derived insulin sensitivity in adults, but not in children.

The association between insulin resistance and cytokines in adolescents: the role of weight status and exercise

Increased adiposity is associated with insulin resistance (IR) and an inflammatory response in adults. We tested the hypotheses that cytokines associated with adiposity are also correlated with IR in early adolescents and that these relationships are moderated by weight status, levels of vigorous physical activity (VPA), or maximal aerobic power (pVO2max). Body mass, stature, and a fasting blood sample were obtained from 120 midpubertal adolescents (60 girls and 60 boys). Habitual VPA was obtained by a survey. Predicted VO2max was determined using a cycle ergometer test. Weight status was based on body mass index (BMI) percentiles (normal weight=BMI<75th percentile, overweight=BMI>95th percentile). Glucose, insulin, adiponectin, resistin, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 were measured; and IR index was based on the Homeostatic Model Assessment. Adiponectin, resistin, and TNF-alpha were associated with IR in all adolescents (R2=0.329, P<.001; R2=0.152, P=.001; and R2=0.141, P=.002; respectively); but interleukin-6 was not (R2=0.148, P=.114). The degree of association between adiponectin and IR was stronger in overweight than in normal-weight adolescents (P<.050). When regression models included weight status, neither TNF-alpha nor resistin was significantly related to IR (P>.050). Exercise did not moderate the association between these cytokines and IR. However, higher levels of VPA and/or pVO2max were associated with higher adiponectin, lower resistin, and lower TNF-alpha in at least one of the sexes. Our results indicate that the pathophysiology of obesity is already established in early adolescents. Increased adiposity, resulting in reduced adiponectin and increased resistin and TNF-alpha, may link these cytokines with IR in adolescents.

Microcirculation in obesity: an unexplored domain

Obesity is traditionally linked to diabetes and cardiovascular diseases. Very recent experimental, clinical and epidemiological, sometimes provocative, data challenge this automaticity by showing that not the amount but the distribution of fat is the important determinant. Moderate abdominal fat accumulation may thus be more harmful than even consequent overweight. In view of the worldwide burden of obesity, factors leading to it in children and young adults must urgently be identified. Since obesity is a very complex cardiometabolic situation, this will require to focus investigations on uncomplicated obese subjects and adequate animal models. The recent discovery of intergenerational transmissions of obesity risk factors and also the key role played by gestational and perinatal events (epigenetic factors) give rise to completely new concepts and research avenues. Considering the potential close relationship between microcirculation and tissue metabolism, demonstrations of structural and/or functional abnormalities in microvascular physiology very early in life of subjects at risk for obesity might provide a solid basis for further investigations of such links. Microcirculation(arterioles, capillaries and venules) is conceivably a key compartment determining over one or several decades the translation of genetic and epigenetic factors into fat accumulation. Available animal models should serve to answer this cardinal question.

Urinary cortisol is inversely associated with capillary recruitment in women: a potential explanation for the cortisol–blood pressure relationship

The relationships of cortisol with elevated blood pressure and insulin resistance are likely to be the result of a complex interplay of different mechanisms. We hypothesize that cortisol is associated with impaired microvascular function and that this contributes to cortisol-associated high blood pressure and insulin resistance. We examined 24 h urinary free cortisol excretion in 56 healthy adults (26 women). Blood pressure was assessed by 24 h ambulatory measurements. Insulin sensitivity was determined using the hyperinsulinaemic euglycaemic clamp technique. Skin capillary recruitment after arterial occlusion was visualized with videomicroscopy and endothelium-(in)dependent vasodilation was evaluated with iontophoresis of acetylcholine and sodium nitroprusside combined with laser Doppler fluxmetry. Men were characterized by higher urinary cortisol excretion [median (interquartile range), 162 (130–194) compared with 118 (99–156) nmol/24 h, P<0.05]. In women, but not in men, urinary cortisol excretion was associated with impaired capillary recruitment (r=−0.66, P<0.001), higher systolic blood pressure (r=0.64, P<0.001) and lower insulin sensitivity (r=−0.43, P<0.05). Urinary cortisol excretion was not associated with endothelium-(in)dependent vasodilation in men or women. Regression analysis demonstrated that capillary recruitment statistically explained 37% of the association between urinary cortisol and blood pressure in women. Capillary recruitment did not explain part of the association between urinary cortisol and insulin sensitivity. In conclusion, urinary cortisol excretion is inversely associated with capillary recruitment in women, but not in men, and capillary recruitment explains part of the cortisol–blood pressure relationship. These data suggest that, in women, impairment of capillary function mediates some of the adverse effects of cortisol and thus may provide a target to prevent such adverse effects.

Microvascular dysfunction: causative role in the association between hypertension, insulin resistance and the metabolic syndrome?

The metabolic syndrome defines a clustering of metabolic risk factors that confers an increased risk for type 2 diabetes and cardiovascular disease. The metabolic syndrome seems to have multiple etiological factors and microvascular dysfunction may be one potential factor explaining the clustering of multiple metabolic risk factors including hypertension, obesity, insulin resistance and glucose intolerance. Microvascular dysfunction may increase not only peripheral vascular resistance and blood pressure, but may also decrease insulin-mediated glucose uptake in muscle. The present article summarizes some of the data concerning the role of microvascular dysfunction in the metabolic syndrome.

Meeting report: ISN forefronts in nephrology on endothelial biology and renal disease: from bench to prevention

This ISN-sponsored Forefront in Nephrology meeting, which has brought together 120 scientists from 21 countries, has been concerned with various aspects of endothelial function and dysfunction and their contribution to progression of chronic kidney disease and/or its cardiovascular complications. The following themes were discussed in great depth: (1) phenotypical changes in the vascular endothelium - permeability, senescence, and apoptosis; (2) regulation of endothelial nitric oxide (NO) synthase function - caveolar and shear stress mechanisms, epigenetic regulation, S-nitrosylation, and Rho-kinase regulation; (3) oxidative stress and hypoxia-induced changes; (4) organellar dysfunction - lysosomes, mitochondria, and endoplasmic reticulum; (5) NO-independent mechanisms of vasomotion - epoxides, heme oxygenase-1 and carbon monoxide, thromboxane, tumor necrosis factor-alpha, and uric acid; (6) endothelial crosstalk with podocytes, monocytes, smooth muscle cells, and platelets; (7) candidate clinical biomarkers of endothelial dysfunction - functional testing of macro- and micro-vascular functions, surrogate markers, circulating detached endothelial cells, and endothelial precursor cells; and culminated in Round Table discussion on the diagnosis of endothelial dysfunction and its treatment options. In conclusion, this meeting has focused on several key problems of endothelial cell pathobiology relevant to chronic kidney disease.