Nathalie Esser

Inflammation as a link between obesity, metabolic syndrome and type 2 diabetes

It is recognized that a chronic low-grade inflammation and an activation of the immune system are involved in the pathogenesis of obesity-related insulin resistance and type 2 diabetes. Systemic inflammatory markers are risk factors for the development of type 2 diabetes and its macrovascular complications. Adipose tissue, liver, muscle and pancreas are themselves sites of inflammation in presence of obesity. An infiltration of macrophages and other immune cells is observed in these tissues associated with a cell population shift from an anti-inflammatory to a pro-inflammatory profile. These cells are crucial for the production of pro-inflammatory cytokines, which act in an autocrine and paracrine manner to interfere with insulin signaling in peripheral tissues or induce β-cell dysfunction and subsequent insulin deficiency. Particularly, the pro-inflammatory interleukin-1β is implicated in the pathogenesis of type 2 diabetes through the activation of the NLRP3 inflammasome. The objectives of this review are to expose recent data supporting the role of the immune system in the pathogenesis of insulin resistance and type 2 diabetes and to examine various mechanisms underlying this relationship. If type 2 diabetes is an inflammatory disease, anti-inflammatory therapies could have a place in prevention and treatment of type 2 diabetes.

Anti-inflammatory agents to treat or prevent type 2 diabetes, metabolic syndrome and cardiovascular disease

Introduction: There is a growing body of evidence to suggest that chronic silent inflammation is a key feature in abdominal obesity, metabolic syndrome, type 2 diabetes (T2DM) and cardiovascular disease (CVD). These observations suggest that pharmacological strategies, which reduce inflammation, may be therapeutically useful in treating obesity, type 2 diabetes and associated CVD. Area covered: The article covers novel strategies, using either small molecules or monoclonal antibodies. These strategies include: approaches targeting IKK-b-NF-kB (salicylates, salsalate), TNF-α (etanercept, infliximab, adalimumab), IL-1β (anakinra, canakinumab) and IL-6 (tocilizumab), AMP-activated protein kinase activators, sirtuin-1 activators, mammalian target of rapamycin inhibitors and C-C motif chemokine receptor 2 antagonists. Expert opinion: The available data supports the concept that targeting inflammation improves insulin sensitivity and β-cell function; it also ameliorates glucose control in insulin-resistant patients with inflammatory rheumatoid diseases as well in patients with metabolic syndrome or T2DM. Although promising, the observed metabolic effects remain rather modest in most clinical trials. The potential use of combined anti-inflammatory agents targeting both insulin resistance and insulin secretion appears appealing but remains unexplored. Large-scale prospective clinical trials are underway to investigate the safety and efficacy of different anti-inflammatory drugs. Further evidence is needed to support the concept that targeting inflammation pathways may represent a valuable option to tackle the cardiometabolic complications of obesity.

Obesity phenotype is related to NLRP3 inflammasome activity and immunological profile of visceral adipose tissue.

Aims/hypothesisObesity is a heterogeneous condition comprising both individuals who remain metabolically healthy (MHO) and those who develop metabolic disorders (metabolically unhealthy, MUO). Adipose tissue is also heterogeneous in that its visceral component is more frequently associated with metabolic dysfunction than its subcutaneous component. The development of metabolic disorders is partly mediated by the NLR family pyrin domain containing-3 (NLRP3) inflammasome, which increases the secretion of inflammatory cytokines via activation of caspase-1. We compared the immunological profile and NLRP3 activity in adipose tissue between MUO and MHO individuals.MethodsMHO and MUO phenotypes were defined, respectively, as the absence and the presence of the metabolic syndrome. Cellular composition and intrinsic inflammasome activity were investigated by flow cytometry, quantitative RT-PCR and tissue culture studies in subcutaneous and visceral adipose tissue from 23 MUO, 21 MHO and nine lean individuals.ResultsWe found significant differences between the three study groups, including an increased secretion of IL-1β, increased expression of IL1B and NLRP3, increased number of adipose tissue macrophages and decreased number of regulatory T cells in the visceral adipose tissue of MUO patients compared with MHO and lean participants. In macrophages derived from visceral adipose tissue, both caspase-1 activity and IL-1β levels were higher in MUO patients than in MHO patients. Furthermore, caspase-1 activity was higher in CD11c+CD206+ adipose tissue macrophages than in CD11c−CD206+ cells.Conclusions/interpretationThe MUO phenotype seems to be associated with an increased activation of the NLPR3 inflammasome in macrophages infiltrating visceral adipose tissue, and a less favourable inflammatory profile compared with the MHO phenotype.

Unsaturated fatty acids prevent activation of NLRP3 inflammasome in human monocytes/macrophages

The NLRP3 inflammasome is involved in many obesity-associated diseases, such as type 2 diabetes, atherosclerosis, and gouty arthritis, through its ability to induce interleukin (IL)-1β release. The molecular link between obesity and inflammasome activation is still unclear, but free fatty acids have been proposed as one triggering event. Here we reported opposite effects of saturated fatty acids (SFAs) compared with unsaturated fatty acids (UFAs) on NLRP3 inflammasome in human monocytes/macrophages. Palmitate and stearate, both SFAs, triggered IL-1β secretion in a caspase-1/ASC/NLRP3-dependent pathway. Unlike SFAs, the UFAs oleate and linoleate did not lead to IL-1β secretion. In addition, they totally prevented the IL-1β release induced by SFAs and, with less efficiency, by a broad range of NLRP3 inducers, including nigericin, alum, and monosodium urate. UFAs did not affect the transcriptional effect of SFAs, suggesting a specific effect on the NLRP3 activation. These results provide a new anti-inflammatory mechanism of UFAs by preventing the activation of the NLRP3 inflammasome and, therefore, IL-1β processing. By this way, UFAs might play a protective role in NLRP3-associated diseases.

Antidiabetic agents: Potential anti-inflammatory activity beyond glucose control

A growing body of evidence is emerging to show that abdominal obesity, the metabolic syndrome, type 2 diabetes, cardiovascular disease and microvascular diabetic complications are intimately related to chronic inflammation. These observations pave the way to the development of new pharmacological strategies that aim to reduce silent inflammation. However, besides specific anti-inflammatory agents, glucose-lowering medications may also exert anti-inflammatory effects that could contribute to improved outcomes in diabetic patients. Most studies have used metformin, an AMP-activated protein kinase (AMPK) activator, and thiazolidinediones (TZDs), which act as peroxisome proliferator-activated receptor-gamma (PPARγ) agonists. Both pharmacological classes (considered insulin-sparing agents or insulin sensitizers) appear to have greater anti-inflammatory activity than insulin-secreting agents such as sulphonylureas or glinides. In particular, TZDs have shown the widest range of evidence of lowered tissue (visceral fat and liver) and serum inflammation. In contrast, despite reducing postprandial hyperglycaemia, the effect of α-glucosidase inhibitors on inflammatory markers appears rather modest, whereas dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) and glucagon-like peptide-1 (GLP-1) receptor agonists appear more promising in this respect. These incretin-based therapies exert pleiotropic effects, including reports of anti-inflammatory activity. No human data are available so far regarding sodium-glucose cotransporter type 2 (SGLT2) inhibitors. Although they may have indirect effects due to reduced glucotoxicity, their specific mode of action in the kidneys does not suggest systemic anti-inflammatory activity. Also, in spite of the complex relationship between insulin and atherosclerosis, exogenous insulin may also exert anti-inflammatory effects. Nevertheless, for all these glucose-lowering agents, it is essential to distinguish between anti-inflammatory effects resulting from better glucose control and potential anti-inflammatory effects related to intrinsic actions of the pharmacological class. Finally, it would also be of major clinical interest to define what role the anti-inflammatory effects of these glucose-lowering agents may play in the prevention of macrovascular and microvascular diabetic complications.

Free fatty acids as modulators of the NLRP3 inflammasome in obesity/type 2 diabetes

Free fatty acids (FFAs) are metabolic intermediates that may be obtained through the diet or synthesized endogenously. In addition to serving as an important source of energy, they produce a variety of both beneficial and detrimental effects. They play essential roles as structural components of all cell membranes and as signaling molecules regulating metabolic pathways through binding to nuclear or membrane receptors. However, under conditions of FFAs overload, they become toxic, inducing ROS production, ER stress, apoptosis and inflammation. SFAs (saturated fatty acids), unlike UFAs (unsaturated fatty acids), have recently been proposed as triggers of the NLRP3 inflammasome, a molecular platform mediating the processing of IL-1β in response to infection and stress conditions. Interestingly, UFAs, especially ω-3 FAs, inhibit NLRP3 inflammasome activation in various settings. We focus on emerging models of NLRP3 inflammasome activation with a special emphasis on the molecular mechanisms by which FFAs modulate the activation of this complex. Taking into consideration the current literature and FFA properties, we discuss the putative involvement of mitochondria and the role of cardiolipin, a mitochondrial phospholipid, proposed to be sensed by NLRP3 after release, exposure and/or oxidation. Finally, we review how this SFA-mediated NLRP3 inflammasome activation contributes to the development of both insulin resistance and deficiency associated with obesity/type 2 diabetes. In this context, we highlight the potential clinical use of ω-3 FAs as anti-inflammatory compounds.

Acute-phase serum amyloid a in osteoarthritis: regulatory mechanism and proinflammatory properties.

Objective To determine if serum amyloid A (A-SAA) could be detected in human osteoarthritic (OA) joints and further clarify if high A-SAA level in joints result from a local production or from a diffusion process from abnormally elevated plasma concentration. Regulatory mechanism of A-SAA expression and its pro-inflammatory properties were also investigated. Methods A-SAA levels in serum and synovial fluid of OA (n = 29) and rheumatoid arthritis (RA) (n = 27) patients were measured and compared to matched-healthy volunteers (HV) (n = 35). In vitro cell cultures were performed on primary joint cells provided from osteoarthritis patients. Regulatory mechanisms were studied using Western-blotting, ELISA and lentiviral transfections. Results A-SAA was statistically increased in OA plasma patients compared to HV. Moreover, A-SAA level in OA plasma and synovial fluid increased with the Kellgren & Lauwrence grade. For all OA and RA patients, A-SAA plasma level was higher and highly correlated with its corresponding level in the synovial fluid, therefore supporting that A-SAA was mainly due to the passive diffusion process from blood into the joint cavity. However, A-SAA expression was also observed in vitro under corticosteroid treatment and/or under IL-1beta stimuli. A-SAA expression was down-regulated by PPAR-γ agonists (genistein and rosiglitazone) and up-regulated by TGF-β1 through Alk1 (Smad1/5) pathway. RhSAA induced proinflammatory cytokines (IL-6, IL-8, GRO-α and MCP-1) and metalloproteinases (MMP-1, MMP-3 and MMP-13) expression in FLS and chondrocytes, which expression was downregulated by TAK242, a specific TLR4 inhibitor. Conclusion Systemic or local A-SAA expression inside OA joint cavity may play a key role in inflammatory process seen in osteoarthritis, which could be counteracted by TLR4 inhibition.

Inflammatory markers and cardiometabolic diseases.

Abstract Objectives: A growing body of evidence emerges that obesity, metabolic syndrome, type 2 diabetes and cardiovascular disease are intimately related to chronic inflammation. Methods: A narrative review summarizing the most recent data of the literature describing the pathological implications of inflammation in obese patients with cardiometabolic disorders. Results: Besides high-sensitive C-reactive protein, various circulating or in situ inflammatory markers have been identified, presumably reflecting the presence of inflammation in various key-organs (visceral adipose tissue, skeletal muscle, pancreatic islets, liver, intestine, arterial wall). Available data support the concept that targeting inflammation, not only reduces systemic inflammatory markers, but also improves insulin sensitivity and ameliorates glucose control in insulin-resistant patients, thus potentially reducing the risk of cardiovascular complications. Conclusion: These observations confirm the role of inflammation in cardiometabolic diseases and support the development of pharmacological strategies that aim at reducing inflammation, especially in patients with type 2 diabetes.

Aptitude physique versus adiposité : aspects physiopathologiques et impacts cardio-métaboliques chez le sujet adulte non diabétique

Summary Excessive fat depots, especially abdominal adiposity, exert deleterious cardiometabolic effects whereas physical exercise and good cardiorespiratory fitness globally exert a favourable influence. Therefore, the negative effects of excessive fat mass (“fatness”) might be counterbalanced by the positive effects of regular physical activity leading to high “fitness”. The present article first analyzes the various pathophysiological mechanisms explaining why muscular exercise exerts beneficial effects in overweight people and attempts to separate the effects of physical activity from those due to fitness. Finally, it describes most important studies focusing on the relationships between “fitness” and “fatness” in non-diabetic overweight or obese adults and their respective influences on metabolic disturbances (metabolic syndrome) and on death rate, especially cardiovascular mortality.

P2149 Différences d’activité de l’inflammasome NLRP3 entre sujets obèses avec et sans anomalies métaboliques

Objectif L’interleukine-1 beta (IL-1β), cytokine pro-inflammatoire, est impliquee dans la pathogenie de l’insulinoresistance associee a l’obesite via l’activation de l’inflammasome NLRP3. L’obesite est une maladie heterogene ; certains patients sont obeses mais « metaboliquement sains » (MHO pour Metabolically Healthy Obese), tandis que d’autres (MUO pour Metabolically Unhealthy Obese) developpent des anomalies metaboliques liees a l’insulinoresistance. Le tissu adipeux visceral, present en quantite plus abondante chez les sujets MUO, pourrait jouer a ce niveau un role pathogenique important. Le but de cette etude est de determiner si les anomalies metaboliques observees chez les sujets MUO peuvent s’expliquer par des differences d’activation de l’inflammasome et de composition cellulaire dans leur tissu adipeux visceral. Materiels et methodes Des biopsies de tissu adipeux visceral et sous-cutane ont ete realisees chez 23 sujets MUO (avec criteres de syndrome metabolique et une glycemie a jeun pathologique), 21 sujets MHO (definis par l’absence de syndrome metabolique) apparies pour l’âge et l’indice de masse corporel, ainsi que chez 9 sujets controles de poids normal. Resultats Compares aux sujets controles et MHO, le tissu adipeux visceral des sujets MUO est caracterise par une expression accrue des genes de l’IL-1β et de NLRP3, une secretion plus elevee d’IL-1β, une infiltration de macrophages pro-inflammatoires (avec une activite de caspase-1 et production d’IL-1β accrues) et un moindre pourcentage de lymphocytes T regulateurs, et ce de facon statistiquement significative. Des differences similaires ont egalement ete trouvees entre le tissu adipeux visceral et le tissu adipeux sous-cutane des sujets MUO. Conclusion La presence d’anomalies metaboliques chez les sujets MUO est associee a une activation de l’inflammasome NLRP3 dans les macrophages infiltrant leur tissu adipeux visceral. La graisse viscerale des sujets MHO est caracterisee par un profil inflammatoire plus favorable.