Adipose Tissue Has Anti-Inflammatory Properties: Focus on IL-1 Receptor Antagonist (IL-1Ra)

Patients with Severe Obesity during the COVID-19 Pandemic: How to Maintain an Adequate Multidisciplinary Nutritional Rehabilitation Program?

BACKGROUND

The COVID-19 pandemic is spreading all over the world, particularly in developed countries where obesity is also widespread. There is a high frequency of increased BMI in patients admitted to intensive care for SARS-CoV-2 infection with a major severity in patients with an excess of visceral adiposity. Patients at risk of severe SARS-CoV-2 acute respiratory syndrome are characterised by the high prevalence of pre-existing diseases (high blood pressure and cardiovascular disease, diabetes, chronic respiratory disease, or cancer), most of them typically present in severely obese patients. Indeed, the biological role of adipose tissue in sustaining SARS-CoV-2 infection is not completely elucidated.

SUMMARY

The forced isolation due to pandemic containment measures abruptly interrupted the rehabilitation programs to which many patients with severe obesity were enrolled. People affected by obesity, and especially those with severe obesity, should continue clinical rehabilitation programs, taking extra measures to avoid COVID-19 infection and reinforcing the adoption of preventive procedures. In this review, the available data on obesity and COVID-19 are discussed along with evidence-based strategies for maintaining the necessary continuous rehabilitation programs. Key Messages: Greater attention is needed for obese and severely obese patients in the face of the current COVID-19 pandemic, which represents a huge challenge for both patients and healthcare professionals. The adoption of new strategies to guarantee adequate and continuous multidisciplinary nutritional rehabilitation programs will be crucial to control the severity of SARS-CoV-2 infection in high-risk populations as well as the worsening of obesity-linked complications. Health authorities should be urged to equip hospitals with tools for the diffusion of telemedicine to maintain physician-patient communication, which is fundamental in chronic and complicated obese patients.

Overweight/obesity affects histological features and inflammatory gene signature of synovial membrane of Rheumatoid Arthritis

Overweight/obesity influence disease burden and clinical outcome of Rheumatoid Arthritis (RA). The impact of overweight/obesity on synovial tissue (ST) inflammation is largely unknown. Here, we investigated the histological and transcriptional signature of ST obtained from RA in different disease phases (disease onset, failure to first-line conventional DMARDs and in sustained clinical and ultrasound remission) finding that overweight/obese DMARDs naive RA showed higher likelihood of follicular synovitis, higher IHC scores for sublining inflammatory cells (CD68⁺, CD21⁺ and CD20⁺) and higher IL-1RA plasma levels than normal weight RA. Regardless to the synovitis pattern, overweight/obese DMARDs naive RA showed a worse clinical response to “Treat-to-target” (T2T) than normal weight RA at 6 and 12 months follow-up. Conversely, MTX-IR RA did not show significant differences in synovial inflammation based on BMI category. Overweight/obese RA in stable clinical and US remission showed higher degree of residual synovitis in terms of sublining CD68⁺, CD20⁺ cells and lining and sublining CD3⁺ compared to normal weight RA. Finally, gene expression profile analysis revealed that ST of overweight/obese DMARDs naive RA is enriched by CCL3 and MyD88 compared to normal weight RA in sustained disease remission, the latter correlating with BMI and IHC scores for synovial CD68⁺ cells. These findings suggest that indeed overweight/obese RA show higher degree of synovitis at disease onset and after remission achievement that influences the response rate to T2T and should be considered within the management of patients with RA.

Computational deconvolution of synovial tissue cellular composition: presence of adipocytes in synovial tissue decreased during arthritis pathogenesis and progression

Osteoarthritis (OA) and rheumatoid arthritis (RA) are the most common forms of arthritis. The synovial tissue is the major site of inflammation of OA and RA and consists of diverse cells. Synovial tissue cell composition changes during arthritis pathogenesis and progression have not been systematically characterized and may provide critical insights into disease processes. In this study we aimed at systematically examining cellular changes in synovial tissue. Publicly available synovial tissue transcriptomic data sets were used. We computationally estimated cell compositions in synovial tissue based on transcriptomic data and compared cell compositions in different diseases or at different disease stages. Synovial fibroblasts, macrophages, adipocytes, and immune cells were the major cell types in all synovial tissue. Both OA and RA patients had a significantly lower adipocyte fraction compared with healthy controls. The decrease trend was also observed during OA and RA progression. The fraction of monocytes was also increased in both OA and RA arthritis patients, consistent with the observations that inflammation involved in both OA and RA. But the monocyte fraction in RAs was much higher than the ones in healthy controls and OAs. The M2 macrophage fraction was reduced in RA compared with OA, the reduction trend continued during RA progression from the early- to the late-stage. There were consistent cell composition differences between different types or stages of arthritis. Both in RA and OA, the new discovery of changes in the adipocyte and M2 macrophage fractions has potential leading to novel therapeutic development.

Neuraxial TNF and IFN-beta co-modulate persistent allodynia in arthritic mice

In rheumatoid arthritis, joint pain can persist despite resolution of swelling. Similarly, in the murine K/BxN serum transfer model, a persistent tactile allodynia is observed after the resolution of joint inflammation (post-inflammatory pain) in male mice. Here, we found female wild type (WT) mice show inflammatory, but reduced post-inflammatory tactile allodynia. The transition to the post-inflammatory phenotype is dependent on TLR4 signaling. At the spinal level, we found differences in TNF and IFNβ mRNA expression in WT and TLR4 deficient males. In wild type male and female mice, there is differential temporal spinal expression of TNF and IFNβ. In WT males, blockade of TNF or administration of IFNβ was insufficient to affect the persistent allodynia. However, co-administration of intrathecal (IT) IFNβ and anti-TNF antibodies in male WT mice permanently reversed tactile allodynia. IT IFNβ treatment induces expression of anti-inflammatory proteins, contributing to the beneficial effect. Together, these experiments illustrated differences in the transition to chronic tactile allodynia in male and female animals and the complexities of effective pharmacologic interventions.

Interleukin-1β signaling in osteoarthritis - chondrocytes in focus

Osteoarthritis (OA) can be regarded as a chronic, painful and degenerative disease that affects all tissues of a joint and one of the major endpoints being loss of articular cartilage. In most cases, OA is associated with a variable degree of synovial inflammation. A variety of different cell types including chondrocytes, synovial fibroblasts, adipocytes, osteoblasts and osteoclasts as well as stem and immune cells are involved in catabolic and inflammatory processes but also in attempts to counteract the cartilage loss. At the molecular level, these changes are regulated by a complex network of proteolytic enzymes, chemokines and cytokines (for review: [1]). Here, interleukin-1 signaling (IL-1) plays a central role and its effects on the different cell types involved in OA are discussed in this review with a special focus on the chondrocyte.

Vulvar lichen sclerosus: A new regenerative approach through fat grafting

OBJECTIVE. The aim of this study was to evaluate the efficacy of fat grafting in the treatment of severe vulvar lichen sclerosus (LS). Our primary outcome was to assess the improvement of mucocutaneous trophism, the resolution/reduction of symptoms, and the histological features of the vulvar skin after treatment. The secondary outcome was to evaluate the improvement in life quality, and in resumption and quality of sexual life. METHODS. Between 2011 and 2014, 36 patients were offered fat grafting to treat LS. Inclusion criteria were age between 25 and 80 years, histopathologic diagnosis of LS, good health, failure of previous first line treatments. RESULTS. 34 out of 36 patients (94%) showed a better vulvar trophismof the skin and mucosae; 27 (75%) had an improvement in caliber and elasticity of the vaginal introitus; clitoris burying degree was reduced in 18 patients (50%), 30 (83%) reported an increased volume of labia major a and minor a, 34 (94%) had a complete disappearance of scratching lesions, and 28 (78%) showed a remission of white lesions. Eventually 34 patients (95%) stopped using topical corticosteroids routinely. The improvement in life quality was significant for both DLQI (p b 0001) and FSFI (p b 0001). CONCLUSIONS. Fat grafting may have a role as a support and completion treatment in selected cases of women with vulvar LS who do not respond to first line therapy or in severe cases where the anatomical impairment does not allow a regular sexual function and a good quality of life.

Minireview: Emerging Concepts in Islet Macrophage Biology in Type 2 Diabetes

Chronic systemic inflammation is a hallmark feature of obesity and type 2 diabetes. Both resident and recruited islet macrophages contribute to the proinflammatory milieu of the diabetic islet. However, macrophages also appear to be critical for β-cell formation during development and support β-cell replication in experimental models of pancreas regeneration. In light of these findings, perhaps macrophages in the islet need to be viewed more as a fulcrum where deleterious inflammatory activation is balanced with beneficial tissue repair processes. Undoubtedly, defining the factors that contribute to the ontogeny, heterogeneity, and functionality of macrophages in normal, diseased, and regenerating islets will be necessary to determine whether that fulcrum can be moved to preserve functional β-cell mass in persons with diabetes. The intent of this review is to introduce the reader to emerging concepts of islet macrophage biology that may challenge the perception that macrophage accumulation in islets is merely a pathological feature of type 2 diabetes.

Molecular pathways linking metabolic inflammation and thermogenesis

Obesity is caused by chronic positive energy balance because of higher energy intake relative to energy expenditure. Thermogenesis, the capacity of an organism to produce heat, is an important component of energy expenditure. Thus targeting the molecular mechanisms controlling thermogenesis could be an effective strategy for the prevention or treatment of obesity. Thermogenesis is modulated by three major factors: environmental temperature, nutrient quantity and quality, and by systemic inflammation. Obesity is now recognized to be a state of chronic low-grade systemic inflammation, which has been proposed to play a major role in the pathogenesis of obesity and obesity-associated diseases. This review discussed the molecular pathways that are recruited during metabolic inflammation and that are also implicated in the control of thermogenesis and energy balance. It emerges that the complex signalling network recruited during metabolic inflammation exerts a balanced action on the modulation of thermogenesis and energy balance, with some pathways promoting weight gain whereas other pathways have opposite actions. It is thus concluded that immunomodulation of metabolic inflammation, rather than an anti-inflammatory intervention aiming at its suppression, may be a more promising strategy to increase thermogenesis for the treatment or prevention of obesity and its associated diseases.

The Relation between Inflammation and Neuropsychological Test Performance

Background. Considerable research documents an association between pro- and anti-inflammatory markers and Alzheimer's disease (AD), yet the differential relation between these markers and neuropsychological functioning in AD and nondemented controls has received less attention. The current study sought to evaluate the relationship between peripheral markers of inflammation (both pro- and anti-inflammatory) and neuropsychological functioning through the Texas Alzheimer's Research and Care Consortium (TARCC) cohort. Methods. There were 320 participants (Probable AD n = 124, Controls n = 196) in the TARCC Longitudinal Research Cohort available for analysis. Regression analyses were utilized to examine the relation between proinflammatory and anti-inflammatory markers and neuropsychological functioning. Follow-up analyses were conducted separately by case versus control status. Results. Proinflammatory and anti-inflammatory markers were found to be associated with neuropsychological testing. Third tertile proinflammatory markers were negatively associated with measures of attention and language, and anti-inflammatory markers were positively associated with measures of immediate verbal memory and delayed verbal and visual memory. Conclusions. These findings support the link between peripheral inflammatory markers and neuropsychological functioning and suggest the utility of examining profiles of inflammatory markers in the future.

Comparison of rheumatoid articular adipose and synovial tissue reactivity to proinflammatory stimuli: contribution to adipocytokine network

OBJECTIVES

(1) To compare spontaneous and stimuli-induced adipocytokine secretion by articular adipose tissue (AAT) and synovial membrane (SM) explants obtained from patients with rheumatoid arthritis (RA). (2) To investigate the biological activity of AAT and SM released factors.

METHODS

Tissues were obtained from patients undergoing joint replacement surgery. Tissue explants were treated with proinflammatory cytokines relevant to RA pathogenesis (interleukin 1β (IL-1β), tumour necrosis factor (TNF), interferon γ, IL-15, IL-17, IL-23). Selected adipocytokine (TNF, IL-6, IL-8, IL-1β, IL-1Ra, adiponectin, leptin) concentrations were measured in culture supernatants using ELISA. The biological activity of tissue-conditioned media was evaluated by measuring production of selected factors (IL-6, IL-8, Dickkopf-1, osteoprotegerin) by fibroblast-like synoviocytes (FLS).

RESULTS

Spontaneous cytokine release from AAT was ≤12% of that produced by SM, while leptin was secreted in similar amounts. AAT was highly reactive to proinflammatory cytokines (IL-1β>TNF). AAT treated with IL-1β released four times more leptin, similar amounts of IL-6 and IL-8 and about 20% of TNF, as compared with SM. Upon activation, the IL-1 receptor antagonist (IL-1Ra)/IL-1β ratio was higher in AAT than in SM cultures. Irrespective of activation status, SM produced twice as much adiponectin as AAT. Conditioned media from AAT and SM cultures similarly upregulated IL-6, IL-8, Dickkopf-1 and osteoprotegerin production by rheumatoid FLS.

CONCLUSION

Rheumatoid AAT is highly reactive tissue which upon stimulation secretes considerable amounts of proinflammatory (IL-6, IL-8, TNF) and anti-inflammatory (IL-1Ra) cytokines and classical adipokines. This tissue releases biologically active factors that intensify pathogenic activities of rheumatoid FLS. Thus, AAT should be considered an important contributor to the pathological processes taking place in the RA joint.

Correlative studies on the effects of obesity, diabetes and hypertension on gene expression in omental adipose tissue of obese women

OBJECTIVE

A major consequence of obesity is the enormous expansion of and enhanced inflammatory response seen in visceral adipose tissue. I hypothesized that the expression of inflammatory markers in visceral omental fat would correlate with the extent of visceral adiposity as measured by waist circumference or body mass index and that diabetes and hypertension, defined as subjects taking anti-hypertensive drugs, would be associated with changes in mRNA expression in visceral fat.

DESIGN AND METHODS

The expression of 106 mRNAs by RT-PCR was examined in observational studies using extracts of omental fat of obese women undergoing bariatric surgery as well as the circulating levels of some adipokines. We also compared the mRNA levels of 65 proteins in omental fat removed during gastric bypass surgery of women with and without hypertension and those with type 2 diabetes.

RESULTS

Out of 106 mRNAs the expression of 10 mRNAs in omental fat of women not taking anti-hypertensive drugs correlated with waist circumference while 7 different mRNAs had significant correlations with circulating glucose. The correlations of waist circumference with mRNA expression were abolished, except for interleukin (IL)-1 receptor antagonist (IL-1RA), in women taking anti-hypertensive drugs. The correlations of blood glucose with omental fat mRNA expression were abolished, except for that of Akt1 and Akt2, in women taking anti-hypertensive drugs. However, the expression of 4 different mRNAs in omental fat was affected by circulating glucose in subjects taking anti-hypertensive drugs. The circulating levels of IL-1 RA, but not fatty acid binding protein 4, adipsin and phospholipase A2, correlated with both waist circumference and mRNA expression in omental fat.

CONCLUSION

In female bariatric surgery patients, the mRNA expression of some proteins in omental fat was affected by the degree of obesity, whereas hypertension and diabetes affected a separate set of mRNAs.Nutrition and Diabetes (2011) 1, e17; doi:10.1038/nutd.2011.14; published online 26 September 2011.

Interleukin 1 receptor antagonist mediates the beneficial effects of systemic interferon beta in mice: implications for rheumatoid arthritis

OBJECTIVES

Interferon beta (IFNβ) therapy is effective in multiple sclerosis and murine models of arthritis. Surprisingly, systemic IFNβ treatment induces only minimal improvement in rheumatoid arthritis (RA). To explain this paradox, the authors evaluated the mechanism of IFNβ benefit in passive K/BxN arthritis and the effect of IFNβ treatment on RA synovium.

METHODS

Interleukin 10 (IL-10) null, IL-1 receptor antagonist (IL-1Ra) null, IL-1Ra transgenic and wild-type mice were administered K/BxN serum and in some cases treated with IFNβ or normal saline. Clinical response and histological scores were assessed. Gene expression was measured by quantitative PCR. Serum IL-1Ra and IL-6 were measured by ELISA. Paired synovial biopsy specimens from RA patients pre-IFNβ and post-IFNβ treatment (purified natural fibroblast IFNβ (Frone) subcutaneously three times weekly 6 million IU, 12 million IU or 18 million IU) were immunostained for IL-1Ra and IL-10.

RESULTS

Il1rn transgenic mice had an attenuated course of arthritis, whereas Il1rn(-/-) and Il10(-/-) mice had more severe serum transfer arthritis than wild-type mice. Daily IFNβ treatment significantly decreased arthritis severity in Il10(-/-) but not Il1rn(-/-) mice. IFNβ treatment did not reduce the histological scores in Il1rn(-/-) mice or gene expression of articular cytokines and chemokines. Paired synovial biopsy specimens from RA patients treated with IFNβ demonstrated a trend towards increased IL-1Ra and reduced IL-10 expression on day 85 levels compared with pretreatment specimens.

CONCLUSIONS

The anti-inflammatory effects of IFNβ in passive K/BxN arthritis are dependent on IL-1Ra, but not IL-10. Systemic IFNβ treatment in RA increases synovial IL-1Ra production, but also decreases IL-10 production.

Is the incidence of rheumatoid arthritis rising?: results from Olmsted County, Minnesota, 1955-2007

OBJECTIVE

To examine trends in the incidence and prevalence of rheumatoid arthritis (RA) from 1995 to 2007.

METHODS

To augment our preexisting inception cohort of patients with RA (1955-1994), we assembled a population-based incidence cohort of individuals >or=18 years of age who first fulfilled the American College of Rheumatology 1987 criteria for the classification of RA between January 1, 1995 and December 31, 2007 and a cohort of patients with prevalent RA on January 1, 2005. Incidence and prevalence rates were estimated and were age-and sex-adjusted to the white population in the US in 2000. Trends in incidence rates were examined using Poisson regression methods.

RESULTS

The 1995-2007 incidence cohort comprised 466 patients (mean age 55.6 years), 69% of whom were female and 66% of whom were rheumatoid factor positive. The overall age- and sex-adjusted annual RA incidence was 40.9/100,000 population. The age-adjusted incidence in women was 53.1/100,000 population (versus 27.7/100,000 population in men). During the period of time from 1995 to 2007, the incidence of RA increased moderately in women (P = 0.02) but not in men (P = 0.74). The increase was similar among all age groups. The overall age- and sex-adjusted prevalence on January 1, 2005 was 0.72% (95% confidence interval [95% CI] 0.66, 0.77), which is an increase when compared with a prevalence of 0.62% (95% CI 0.55, 0.69) in 1995 (P < 0.001). Applying the prevalence on January 1, 2005 to the US population in 2005 showed that an estimated 1.5 million US adults were affected by RA. This is an increase from the previously reported 1.3 million adults with RA in the US.

CONCLUSION

The incidence of RA in women appears to have increased during the period of time from 1995 to 2007. The reasons for this recent increase are unknown, but environmental factors may play a role. A corresponding increase in the prevalence of RA was also observed.

Kitasato symposium 2009: new prospects for cytokine inhibition

The Kitasato Symposium 2009: New Prospects for Cytokine Inhibition was held in Berlin, Germany from 7 to 9 May 2009. The key aims of this meeting were to bring together a group of front-line researchers and rheumatologists to evaluate the use of cytokine blockade and to examine the role of certain cytokines in the pathogenesis of rheumatoid arthritis and other autoimmune diseases. A keynote lecture delivered by Professor Jean-Michel Dayer provided an up-to-date overview of the interactions occurring between the immune system and acute phase proteins. Other speakers discussed the role of cytokines in rheumatoid arthritis, including their role in joint destruction, as well as their regulatory role upon T cells and B cells. The involvement of cytokines in other autoimmune diseases was also addressed.

Cytokines in chronic rheumatic diseases: is everything lack of homeostatic balance?

Biological systems have powerful inbuilt mechanisms of control intended to maintain homeostasis. Cytokines are no exception to this rule, and imbalance in cytokine activities may lead to inflammation with subsequent tissue and organ damage, altered function, and death. Balance is achieved through multiple, not mutually exclusive, mechanisms including the simultaneous production of agonist and antagonistic cytokines, expression of soluble receptors or membrane-bound nonsignaling receptors, priming and/or reprogramming of signaling, and uncoupling of ligand/receptor pairing from signal transduction. Insight into cytokine balance is leading to novel therapeutic approaches particularly in autoimmune conditions, which are intimately linked to a dysregulated cytokine production.

Cartilage homeostasis in health and rheumatic diseases

As the cellular component of articular cartilage, chondrocytes are responsible for maintaining in a low-turnover state the unique composition and organization of the matrix that was determined during embryonic and postnatal development. In joint diseases, cartilage homeostasis is disrupted by mechanisms that are driven by combinations of biological mediators that vary according to the disease process, including contributions from other joint tissues. In osteoarthritis (OA), biomechanical stimuli predominate with up-regulation of both catabolic and anabolic cytokines and recapitulation of developmental phenotypes, whereas in rheumatoid arthritis (RA), inflammation and catabolism drive cartilage loss. In vitro studies in chondrocytes have elucidated signaling pathways and transcription factors that orchestrate specific functions that promote cartilage damage in both OA and RA. Thus, understanding how the adult articular chondrocyte functions within its unique environment will aid in the development of rational strategies to protect cartilage from damage resulting from joint disease. This review will cover current knowledge about the specific cellular and biochemical mechanisms that regulate cartilage homeostasis and pathology.

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.

Adipokines as emerging mediators of immune response and inflammation

The scientific interest in the biology of white adipose tissue (WAT) has increased since the discovery of leptin in 1994. The description of the product of the gene obese (ob) demonstrated the role of adipose tissue in the physiopathology of obesity-related diseases, and helped to increase the identification of numerous other adipokines, many of a pro-inflammatory nature. It has become increasingly evident that WAT-derived adipokines can be considered as a hub between obesity-related exogenous factors, such as nutrition and lifestyle, and the molecular events that lead to metabolic syndrome, inflammatory and/or autoimmune conditions, and rheumatic diseases. In this Review, we will discuss the progress in adipokine research, focusing particular attention to the roles of leptin, adiponectin, resistin, visfatin, and other recently identified adipokines in inflammatory, autoimmune and rheumatic diseases.

Low physical activity and obesity: causes of chronic disease or simply predictors?

BACKGROUND AND PURPOSE

Many studies have shown associations between risk of morbidity and mortality with both obesity and low physical activity (PA), but association does not imply causality. Moreover, there is an inverse relationship between PA and obesity; therefore, controlling for one of these factors when investigating the risk associated with the other is essential. The purpose of this review is to determine whether low PA and obesity actually cause metabolic dysfunction and chronic disease, especially type 2 diabetes (T2D), rather than simply operating as predictors or markers.

METHODS

The case for causality is strengthened if the following two conditions are satisfied: first, that significant associations between obesity or low PA and risk persist after controlling appropriately; and second, that the physiological mechanisms by which obesity or low PA may exert a causal effect are clearly established. The studies examined include those that have used cardiorespiratory (CR) fitness as a surrogate measure for PA, thus also providing evidence for low CR fitness as an independent risk factor in its own right.

RESULTS AND CONCLUSIONS

Low PA and poor CR fitness are independent predictors of mortality related to type 2 diabetes and chronic disease in general. Together with well-demonstrated mechanisms, there is strong evidence that low PA and low CR fitness are direct, independent causes of metabolic dysfunction and type 2 diabetes. Despite some reports to the contrary, there is evidence that both general and visceral obesity are predictors of mortality and morbidity after controlling for PA. However, in the absence of established mechanisms, evidence is insufficient to conclude that either general or visceral obesity is a direct, independent cause of metabolic dysfunction or type 2 diabetes.

Adipose tissue macrophages

It is now broadly accepted that low-grade chronic inflammation associated with obesity leads to the onset of insulin resistance and type 2 diabetes mellitus. Obesity-associated inflammation is characterized by an increased abundance of macrophages in adipose tissue along with production of inflammatory cytokines. Adipose tissue macrophages (ATMs) are suspected to be the major source of inflammatory mediators such as TNF-alpha and IL-6 that interfere with adipocyte function by inhibiting insulin action. However, ATMs phenotypically resemble alternatively activated (M2) macrophages and are capable of anti-inflammatory mediator production challenging the concept that ATMs are simply the "bad guys" in obese adipose tissue. Triggers promoting ATM recruitment, ATM functions and dysfunctions, and stimuli and molecular mechanisms that drive them into becoming detrimental to their environment are subject to current research. Strategies to interfere with ATM recruitment and adverse activation could give rise to novel options for treatment and prevention of insulin resistance and type 2 diabetes mellitus.

Human adipose tissue macrophages are of an anti-inflammatory phenotype but capable of excessive pro-inflammatory mediator production

OBJECTIVE

Obesity is associated with a chronic low-grade inflammation and an increased abundance of macrophages in adipose tissue. Adipose tissue macrophages (ATMs) are assumed to interfere with adipocyte function leading to insulin resistance, thereby contributing to the pathogenesis of type 2 diabetes mellitus. Macrophages exist in separate types of differentiation, but the nature of ATMs is largely unknown.

DESIGN AND MEASUREMENTS

Stromal vascular cells (SVCs) and ATMs were isolated from human adipose tissues from different locations. We characterized ATMs phenotypically and functionally by flow cytometry, endocytosis assay and determination of secreted cytokines. For comparison, we used macrophages of the 'classical' (M1) and the 'alternative', anti-inflammatory (M2) type differentiated in vitro from peripheral blood monocytes.

RESULTS

Like prototypic M2 macrophages, ATMs expressed considerable amounts of mannose receptor, haemoglobin scavenger receptor CD163 and integrin alphavbeta5. The number of cells expressing these molecules correlated significantly with the donors' body mass indices (BMIs). Notably, SVCs positive for the common monocyte/macrophage marker CD14 contained a considerable fraction of blood monocytes, the abundance of which did not correlate with the BMIs, pointing to the requirement of the surface markers identified here for the identification of ATMs. ATMs showed endocytic activities similar to M2 macrophages and accordingly secreted high amounts of IL-10 and IL-1 receptor antagonist. However, basal and induced secretion of pro-inflammatory mediators TNF-alpha, IL-6, IL-1, MCP-1 and MIP-1alpha was even higher in ATMs than in pro-inflammatory M1 macrophages.

CONCLUSION

ATMs comprise a particular macrophage type that is M2-like by surface marker expression, but they are competent to produce extensive amounts of inflammatory cytokines, which could considerably contribute to the development of insulin resistance.

Attenuated fever in rats during late pregnancy is linked to suppressed interleukin-6 production after localized inflammation with turpentine

An attenuated fever response to pathogens during late pregnancy is a phenomenon that has been described in several mammalian species, and although mechanisms are not completely understood, decreased prostaglandin E2 (PGE2) synthesis has been implicated. Upstream of PGE2, there is evidence to suggest that anti-inflammatory cytokines such as interleukin-1 receptor antagonist (IL-1ra) could play a significant role. In the present study we addressed the role of pro-inflammatory cytokines during late pregnancy, specifically interleukin-6 (IL-6), an important circulating mediator in fever. Turpentine oil (TURP), a very potent pyrogen and activator of IL-6, was injected into the hind-limb muscle of rats at the 18th day of pregnancy (GD 18) or in non-pregnant (NP) age-matched female controls. As expected, TURP injection induced a highly significant fever in the NP animals, which peaked 11 h post-injection and lasted for over 24 h. This was accompanied by a significant rise in circulating IL-6 levels, which correlated with changes in PGE2 synthesizing enzymes expression in the hypothalamus. In complete contrast, TURP-induced fever was totally absent in GD 18 animals whose body temperature did not deviate from basal values. The lack of response was additionally reflected by the absence of change in IL-6 concentration and by the significant attenuation of PGE2 synthesizing enzymes expression, which correlated with the suppressed expression of SOCS3, a hypothalamic marker of IL-6 activity. Contrary to the changes in circulating IL-6 levels at GD 18, IL-1ra was induced to levels comparable to those of NP females, suggesting that the influence of this anti-inflammatory cytokine on the fever response to TURP is at best minimal. These data further confirm the importance of IL-6 in fever generation and provide evidence that it may be a key component of the attenuated fever response in late pregnancy.