Caroline Maria Oliveira Volpe

HMGB1, TLR and RAGE: a functional tripod that leads to diabetic inflammation.

Introduction: Despite advances in treatment of diabetes mellitus, its prevalence continues to rise globally. Medications available are unable to control the vascular complications. Proposals for new therapeutic targets must take into account the hyperglycemia-induced signaling pathways that give rise to the inflammatory profile of the disease. Areas covered: How high-mobility-group box-1 (HMGB1) protein, acting as an activator of Toll-like receptors (TLR) and receptors for advanced glycation end products (RAGE), creates a functional tripod that contributes to increased production of pro-inflammatory mediators, and sustains the chronic inflammatory state associated with diabetes. The interaction of TLR2 and TRL4 with host-derived ligands, which links diabetic complications with the innate immune response, and the activation of RAGE, which induces a cascade of metabolic responses, leading to the production and secretion of pro-inflammatory cytokines. Expert opinion: Considering the involvement of the innate immune system, in association with the role of HMGB1 as an activator of TLR and RAGE, diabetes should be considered and treated as a metabolic and immunological disease, triggered by hyperglycemia. HMGB1 plays a central role in mediating injury and inflammation, and interactions involving HMGB1–TLR–RAGE constitute a tripod that trigger NF-κB activation. Blockade or downregulation of HMGB1, and/or control of the inflammatory tripod, represent a promising therapeutic approach for the treatment of diabetes.

The Production of Nitric Oxide, IL-6, and TNF-Alpha in Palmitate-Stimulated PBMNCs Is Enhanced through Hyperglycemia in Diabetes

We examined nitric oxide (NO), IL-6, and TNF-α secretion from cultured palmitate-stimulated PBMNCs or in the plasma from type 2 diabetes mellitus (T2MD) patients or nondiabetic (ND) controls. Free fatty acids (FFA) have been suggested to induce chronic low-grade inflammation, activate the innate immune system, and cause deleterious effects on vascular cells and other tissues through inflammatory processes. The levels of NO, IL-6, TNF-α, and MDA were higher in supernatant of palmitate stimulated blood cells (PBMNC) or from plasma from patients. The results obtained in the present study demonstrated that hyperglycemia in diabetes exacerbates in vitro inflammatory responses in PBMNCs stimulated with high levels of SFA (palmitate). These results suggest that hyperglycemia primes PBMNCs for NO, IL-6, and TNF-alpha secretion under in vitro FFA stimulation are associated with the secretion of inflammatory biomarkers in diabetes. A combined therapy targeting signaling pathways activated by hyperglycemia in conjunction with simultaneous control of hyperglycemia and hypertriglyceridemia would be suggested for controlling the progress of diabetic complications.

Cellular death, reactive oxygen species (ROS) and diabetic complications

Chronic or intermittent hyperglycemia is associated with the development of diabetic complications. Several signaling pathways can be altered by having hyperglycemia in different tissues, producing oxidative stress, the formation of advanced glycation end products (AGEs), as well as the secretion of the pro-inflammatory cytokines and cellular death (pathological autophagy and/or apoptosis). However, the signaling pathways that are directly triggered by hyperglycemia appear to have a pivotal role in diabetic complications due to the production of reactive oxygen species (ROS), oxidative stress, and cellular death. The present review will discuss the role of cellular death in diabetic complications, and it will suggest the cause and the consequences between the hyperglycemia-induced signaling pathways and cell death. The signaling pathways discussed in this review are to be described step-by-step, together with their respective inhibitors. They involve diacylglycerol, the activation of protein kinase C (PKC) and NADPH-oxidase system, and the consequent production of ROS. This was initially entitled the “dangerous metabolic route in diabetes”. The historical usages and the recent advancement of new drugs in controlling possible therapeutical targets have been highlighted, in order to evaluate the evolution of knowledge in this sensitive area. It has recently been shown that the metabolic responses to stimuli (i.e., hyperglycemia) involve an integrated network of signaling pathways, in order to define the exact responses. Certain new drugs have been experimentally tested—or suggested and proposed—for their ability to modulate the possible biochemical therapeutical targets for the downregulation of retinopathy, nephropathy, neuropathy, heart disease, angiogenesis, oxidative stress, and cellular death. The aim of this study was to critically and didactically evaluate the exact steps of these signaling pathways and hence mark the indicated sites for the actions of such drugs and their possible consequences. This review will emphasize, besides others, the therapeutical targets for controlling the signaling pathways, when aimed at the downregulation of ROS generation, oxidative stress, and, consequently, cellular death—with all of these conditions being a problem in diabetes.

The dual role of free fatty acid signaling in inflammation and therapeutics.

Obesity, type 2 diabetes, insulin resistance, dyslipidemia, cardiovascular diseases and atherosclerosis have all been associated with high levels of free fatty acid (FFA). In the present review, we suggest that FFA may act as either pro- or anti-inflammatory agents depending on the chemical structure. Saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA) significantly differ in their contributions to inflammation. While SFAs have been shown to induce inflammation, PUFAs have anti-inflammatory effects by downregulating NF-kappaB, IL-1β, TNF-α and IL-6 despite upregulating of IL-10. It is suggested that FFA may activate Toll Like Receptor-4 (TLR4) and G protein-coupled receptors (GPCR) activating signaling pathways that promote production and release of inflammatory cytokines (IL-6 and TFN-α). Fatty acid action on TLR4, peroxisome proliferator-activated receptors (PPARs) and GPCRs are potential therapeutic targets for controlling FFA-induced inflammation. Approaches that downregulate the inflammatory properties of free fatty acid are discussed in this manuscript. In this review, some patents associated with controlling FFA effects are also reported.

Inflammasome as a New Therapeutic Target for Diabetic Complications.

BACKGROUND Inflammation is an innate immune response which is considered a common basis for several diseases such as ageing, diabetes, obesity, gout, neurodegenerative diseases and others. Among other platforms, inflammasomes are part of a superfamily of Pattern Recognition Receptors (PRR) and act as cytoplasmatic sensors for stimulation with Pathogen Associated Molecular Pattern (PAMPs) and/or Danger/Damage-Associated Molecular Patterns (DAMPs) leading to an infectious/ pathogenic or sterile inflammation. Inflammasomes constitute a complex platform with high molecular weight and functionality, divided into two families: NOD-like or NLR and PYHIN (pyrin and HIN200 - hematopoietic interferoninducible nuclear antigens). After activation by PAMPs or DAMPs, NLRP3 inflammasome promotes conversion of procaspase 1 in caspase-1 to form the active complex which is able to cleave pro-IL-1β and pro-IL-18 in respective active inflammatory cytokines IL-1β and IL-18 inducing cellular death by pyroptosis. Diabetes has a very intricate pathology with metabolic adaptation and inflammatory components apparently responsible for diabetic complications. OBJECTIVE The present review evaluates the role of inflammasome, emphasizing NRLP3 on diabetes. An overview on several inflammatory diseases in which inflammasomes appear to play a role is included. Patents on inflammasomes associated with diabetes are evaluated and discussed. CONCLUSION There are a significant number of patents on inflammation but few of them are specifically on inflammasome and diabetes. The patents WO2015003246; US20130273588; WO2012016145; and CN104258398 are shown and their mechanisms are discussed. In conclusion, deeply studies on inflammasomes mechanisms will help the proposition of new therapeutic targets for controlling inflammatory process in diabetic complications.

Suppressive effect of aqueous humor from person with Type 2 diabetes with or without retinopathy on reactive oxygen species generation

AIM To evaluate the antioxidant capacity and concentrations of vascular endothelial growth factor (VEGF) and interleukin 6 (IL-6) in aqueous humor from patients with type 2 diabetes mellitus (T2DM) with or without retinopathy. METHODS Aqueous humor was obtained during elective cataract surgery from T2DM patients with or without retinopathy and from healthy subjects. Reducing response was evaluated by MTT dye reduction and the generation of reactive oxygen species (ROS) was determined by chemiluminescence assay. Granulocytes were treated with phorbol dibutyrate (PDB)-stimulated. Cytokines were quantified by ELISA. RESULTS Antioxidant capacity of aqueous humor from patients with retinopathy was greater (P<0.05) than that of healthy controls or persons with diabetes without retinopathy. ROS production in PDB (protein kinase C activator)-stimulated granulocytes from T2DM patients with or without retinopathy was inhibited by autologous aqueous humor. Concentrations of VEGF and IL-6 were similar in aqueous humor from healthy controls and from patients without retinopathy, but lower (P<0.05) than those from T2DM patients with retinopathy. Plasma levels of VEGF and IL-6 were similar (P>0.05) in healthy controls and in T2DM patients with and without retinopathy. CONCLUSION Aqueous humor from T2DM patients with retinopathy exhibits elevated antioxidant activity with significant suppressive effect on ROS production and enhanced levels of locally secreted VEGF and IL-6 in comparison with T2DM patients without retinopathy. These results suggest an inflammatory profile in the absence of typical oxidative stress for T2DM patients with retinopathy, possibly resulting from the compensatory antioxidant response detected in the aqueous humor improving the ocular redox state.

Vitamin complex (ascorbic acid, alpha-tocopherol and beta-carotene) induces micronucleus formation in PBMNC unrelated to ROS production.

Abstract Objectives To evaluate the correlation between reactive oxygen species (ROS) production and micronucleus formation induced by a vitamin complex in peripheral blood mononuclear cells from healthy people aged between 40 and 85 years old. Methods Peripheral blood mononuclear cells (PBMNCs) were purified utilizing ficoll-hypaque gradient. ROS production by PBMNCs was quantified by luminol-dependent chemiluminescence in the presence or in the absence of the vitamin complex. DNA damage in PBMNC by the vitamin complex was detected by the micronucleus technique. Statistical analyses were made with the Students ‘t’ test and the Pearson correlation. P < 0.05 was considered significant. Results The vitamin complex induced MN formation in PBMNC but did not augment ROS production. There was no correlation between ROS production and MN formation either in the presence or in the absence of the vitamin complex. Discussion There was no increase in the ROS production in the presence of the vitamin complex. The vitamin complex induced an augmentation in the MN formation. There was no correlation between ROS production and the induction of MN formation. Since no association could be detected between ROS production and MN formation, additional studies are required in order to investigate the possible mechanism of vitamin-induced MN formation.

Quantification of NGAL in Urine of Endurance Cycling Athletes

BACKGROUND Neutrophil gelatinase-associated lipocalin (NGAL) is a glycoprotein released during early phases of a postischemic kidney in response to kidney injury, inflammation, and oxidative stress. It can be detected in urine after 2 hours of an ischemic event. The aim was to measure and to correlate the level of urine NGAL (uNGAL) with urea, creatinine, and glomerular filtration rate (GFR) of endurance cycling athletes (n = 19) and physically active individuals (control, n = 17). METHODS Quantification of urea and creatinine were performed by dry chemical method, and GFR was calculated using the modification of diet in renal disease formula, according to Brazilian Society of Nephrology. uNGAL analyses were performed by enzyme linked immunoabsorbent assay. Analyses were performed 48 hours after exercises. RESULTS uNGAL (in ng/mL) levels, expressed as median, minimum, and maximum, in cyclist group, 387.7 (109.7-1691.0), was significantly higher than that observed in control (physically active) group, 141.5 (4.8-657.0), (P < .05). No significant correlations were observed between uNGAL and creatinine, urea, or GFR (P > .05). CONCLUSIONS Results have pointed to increased uNGAL levels in endurance cycling athletes. Increase of uNGAL in absence of clinical signs or alterations in creatinine, urea, or GFR might suggest that there is metabolic adaptation to endurance exercise, or possibly predisposition to acute kidney injury over time.

Impaired Clearance of Neutrophils Extracellular Trap (NET) May Induce Detrimental Tissular Effect

Neutrophils Extracellular Trap (NET) is composed of nuclear chromatin with hyper segmentation of nuclear lobes, citrullination of histone-associated DNA and mixing with cytoplasmic proteins including the enzyme myeloperoxidase. It is believed that neutrophils trap can kill microorganisms and constitutes a new form of innate defense. However, in some conditions, NET formation may be detrimental to the organism due to its association with autoantibody formation. Thus, NETs can be beneficial or detrimental depending of the DNA clearance recent registered patents describing the processes, products, methods and therapeutic indications of the neutrophil extracellular trap (NET) phenomenon have been reported. The patents US8710039; EP2465536; EP2651440; US20130302345; US20140099648; US20130183662; WO2012166611; and RU2463349C2, related to NETosis, suggest an association between NET formation and autoimmunity. However, its function is still not fully understood. Some parasites have learned to escape from NET using nucleases. NET persistence could be due to a possible enzymatic inhibition as suggested in Grabar´s theory for explaining the induction of physiologic or pathologic autoantibodies. In the present mini-review NET persistence due to impairment in the homeostasis clearance of DNA is discussed.

Therapeutic Approach on AGE-RAGE Interaction and Its Function in Diabetic Inflammation Process

Advanced glycation end products (AGEs) are important biochemical compounds found in diabetes mellitus and are likely to be associated with an inflammatory process. Within the vessel wall, AGEs may interact with specific receptors to modulate a large number of cellular properties by activating several signaling pathways. One of these receptors is called “receptor for AGE” (RAGE). The AGE-RAGE interactions enhance transcription genes encoding for cytokines, growth factors, adhesive molecules and increased classical acute phase proteins. Potential preventive and therapeutic approaches toward diabetes and its complications include inhibition of AGE formation, breakage of preformed AGE-proteins crosslink, blockade of AGE-RAGE interactions with RAGE competitors, antibody antagonists and RAGE specific metabolic inhibition. Blockade of AGE-RAGE complex formation suppresses the levels of pro-inflammatory cytokines and growth factors and it may be considered as a target for overcoming diabetic complications. This concise review about AGE-RAGE interaction and diabetes complications discusses pathophysiological mechanisms at a glance. Patents on inhibition of AGE formation, RAGE expression and AGE-RAGE interaction are shown and discussed here.