Circulating soluble RAGE isoforms are attenuated in obese, impaired-glucose-tolerant individuals and are associated with the development of type 2 diabetes

Assessment of EN-RAGE, sRAGE, and its isoforms: cRAGE, esRAGE in obese patients treated by moderate caloric restriction combined with physical activity conducted in hospital condition

BACKGROUND

AGEs, their receptor (RAGE), and the extracellular newly identified receptor for AGEs product-binding protein (EN-RAGE) are implicated in the pathogenesis of inflammation.

AIM

We analyzed serum EN-RAGE, soluble RAGE (sRAGE), and their isoforms: endogenous secretory - esRAGE and cleaved - cRAGE concentrations in lean controls (n = 74) and in patients with obesity (n = 71) treated for three weeks with moderate calorie restriction (CR) combined with physical activity in a hospital condition.

METHODS

Using the ELISA method, serum sRAGE, esRAGE, and EN-RAGE were measured before and after CR.

RESULTS

The serum level of sRAGE and esRAGE in patients with obesity was lower than that in non-obese individuals, contrary to cRAGE. EN-RAGE concentration was about three times higher in obese patients. Gradually, a rise in BMI resulted in sRAGE, esRAGE reduction, and EN-RAGE increase. The sRAGE concentration was sex-dependent, indicating a higher value in lean men. A moderate negative correlation was observed between BMI and all RAGE isoforms, whereas EN-RAGE displays a positive correlation. CR resulted in an expected decrease in anthropometric, metabolic, and proinflammatory parameters and EN-RAGE, but no RAGE isoforms. The ratio EN-RAGE/sRAGE was higher in obese humans than in control and was not modified by CR.

CONCLUSION

Obesity decreases sRAGE and esRAGE and increases EN-RAGE concentration. Moderate CR and physical activity by decreasing inflammation reduces EN-RAGE but is insufficient to increase sRAGE and esRAGE to the extent observed in lean patients. EN-RAGE instead of sRAGE could be helpful to indicate a better outcome of moderate dietary intervention in obese subjects.

Dietary and serum advanced glycation end-products and clinical outcomes in breast cancer

One in five women with breast cancer will relapse despite ideal treatment. Body weight and physical activity are strongly associated with recurrence risk, thus lifestyle modification is an attractive strategy to improve prognosis. Trials of dietary modification in breast cancer are promising but the role of specific diets is unclear, as is whether high-quality diet without weight loss can impact prognosis. Advanced glycation end-products (AGEs) are compounds produced in the body during sugar metabolism. Exogenous AGEs, such as those found in food, combined with endogenous AGEs, make up the total body AGE load. AGEs deposit in tissues over time impacting cell signaling pathways and altering protein functions. AGEs can be measured or estimated in the diet and measured in blood through their metabolites. Studies demonstrate an association between AGEs and breast cancer risk and prognosis. Here, we review the clinical data on dietary and serum AGEs in breast cancer.

Effects of acute aerobic exercise on circulating sTLR and sRAGE profiles in normal- and abnormal-glucose-tolerant individuals

BMI-matched normal- (NGT, n = 10, 41 ± 4y, 35.6 ± 3.0 kg/m2 ) and abnormal-glucose-tolerant (AGT, n = 16, 51 ± 3y, 34.3 ± 1.5 kg/m2 ) participants were evaluated for body composition, metabolic health (oral glucose tolerance test [OGTT]), and VO2 max. Participants also completed a treadmill walking test at 65% VO2 max for 30 min. Total sRAGE, esRAGE, sTLR2, and sTLR4 were assessed via ELISA, and cRAGE was calculated. AGT exhibited greater (p < 0.05) body fat % (+24%), fasting plasma glucose (+37%), OGTT AUC (+59%), and HOMA-IR (+55%) and lower (p < 0.05) VO2 max (-24%). sTLR2 was 33% lower in AGT than NGT (main effect, p = 0.034). However, sTLR2 did not change (p > 0.05) following AE. sTLR4 tended to be 36% lower in AGT than NGT (main effect, p = 0.096) and did not change following AE (p > 0.05). Total sRAGE and isoforms were similar (p > 0.05) between groups and did not change following AE (p > 0.05). sTLR2 was correlated with (p < 0.05) basal BG (r = -0.505) and OGTT AUC (r = -0.687). sTLR4 was correlated with basal BG (p < 0.10, r = -0.374) and OGTT AUC (p < 0.05, r = -0.402). Linear regressions were predictive of sTLRs in the basal state (sTLR2: R2  = 0.641, p = 0.01; sTLR4: R2  = 0.566, p = 0.037) and after acute exercise state (sTLR2: R2  = 0.681, p = 0.004, sTLR4: R2  = 0.568, p = 0.036).These findings show circulating sTLR profiles are disrupted in AGT and acute AE minimally modulates their levels.

Effects of different doses of exercise in adjunct to diet-induced weight loss on the AGE-RAGE axis in patients with short standing type 2 diabetes: Secondary analysis of the DOSE-EX multi-arm, parallel-group, randomised trial

AIMS/HYPOTHESIS

These secondary analyses aimed to investigate the effects of different volumes of exercise in adjunct to diet-induced weight loss and standard care on advanced glycation end-products (AGEs) and receptor for AGE (RAGE). We hypothesized that exercise in adjunct to a diet-induced weight loss would dose-dependently increase the soluble decoy receptor for AGE (sRAGE) more than diet-induced weight loss and standard care alone. Secondarily, we expected changes in sRAGE to be associated with improved glycaemic control and inversely associated with low-grade inflammation.

METHODS

The DOSE-EX study was a 16-week parallel-group, 4-arm, single-centre, assessor-blinded, randomised, controlled trial (NCT03769883). We included persons living with T2D, duration ≤7 years, BMI >27 kg/m2 and <40 kg/m2, without severe diabetic complications. Participants were randomised (1:1:1:1) to either 1) standard care as control (CON), 2) standard care + diet (DCON), 3) standard care + diet + moderate exercise dose (MED) or 4) standard care + diet + high exercise dose (HED). Standard care included algorithm-guided pharmacological treatment. The diet intervention aimed at 25% reduced energy intake. The supervised exercise sessions included two aerobic sessions + one combined (aerobic and resistance training) session per week for the MED group, and four aerobic sessions + two combined sessions per week for the HED group. Primary outcome was the change in sRAGE from baseline to 16-week follow-up. Secondary outcomes encompassed changes in advanced glycation endproducts (AGE), glycaemic control and markers of low-grade inflammation.

RESULTS

A total of 80 participants (CON: n = 20, DCON: n = 19, MED: n = 20, HED: n = 21) were included in this secondary analysis. The mean age was 58.3 years (SD 9.9), 53% males, and median T2D duration was 4.1 years (IQR 2.0-5.5). No change in sRAGE was observed in any of the groups from baseline to follow-up (p > 0.05).

CONCLUSION/INTERPRETATION

A 16-week intervention with either three or six exercise sessions per week in adjunct to diet-induced weight loss did not change the levels of sRAGE in persons living with well-regulated, short standing T2D.

Soluble receptor for advanced glycation end-products (sRAGE) in childhood obesity: association with gene expression of RAGE and cardiometabolic markers

Introduction

Introduction: advanced glycation end-products (AGEs) interact with the receptor for AGEs (RAGE). Full-length RAGE is associated with intracellular signal transduction, and soluble-RAGE (sRAGE) lacks the transmembrane and cytoplasmic domains, acting as a competitive inhibitor of AGEs-RAGE binding. sRAGE levels in healthy children are associated with cell surface expression of RAGE. However, the expression of RAGE has not been explored in childhood obesity. Objective: the study aim was to evaluate the sRAGE levels and the gene expression of RAGE in children and its association with cardiometabolic markers. Methods: this is a cross-sectional study with 6-11-year children, 20 with overweight and 20 with obesity. Anthropometric measurements included waist circumference (cm) (WC), neck circumference (NC), weight (kg), fat mass (%), trunk fat (kg), muscular mass (kg), height (cm), and body mass index (BMI) (kg/m2). Blood samples following an overnight fast were collected to measure glucose (mg/dl) and lipid profile with colorimetric methods. sRAGE was determined in serum using the enzyme-linked immunosorbent assay (ELISA). Quantitative reverse transcription (RT-qPCR) was performed to analyze RAGE transcripts in peripheral blood mononuclear cells isolated by Ficoll®-Hypaque. Results: we found higher RAGE (p = 0.0315) and lower sRAGE (p = 0.0305) levels in the obesity group. sRAGE level showed a negative correlation with RAGE (r = -0.35) and BMI (r = -0.24), and positive with HDL-cholesterol (r = 0.29). Regression analysis suggests that HDL-C and RAGE levels are predictors of sRAGE levels. Conclusions: expression of RAGE is associated with lower sRAGE levels in childhood obesity. Moreover, obese children show higher cardiometabolic risk markers, and a positively associated with sRAGE.

Soluble RAGE and skeletal muscle tissue RAGE expression profiles in lean and obese young adults across differential aerobic exercise intensities

Nearly 40% of Americans have obesity and are at increased risk for developing type 2 diabetes. Skeletal muscle is responsible for >80% of insulin-stimulated glucose uptake that is attenuated by the inflammatory milieu of obesity and augmented by aerobic exercise. The receptor for advanced glycation endproducts (RAGE) is an inflammatory receptor directly linking metabolic dysfunction with inflammation. Circulating soluble isoforms of RAGE (sRAGE) formed either by proteolytic cleavage (cRAGE) or alternative splicing (esRAGE) act as decoys for RAGE ligands, thereby counteracting RAGE-mediated inflammation. We aimed to determine if RAGE expression or alternative splicing of RAGE is altered by obesity in muscle, and whether acute aerobic exercise (AE) modifies RAGE and sRAGE. Young (20-34 yr) participants without [n = 17; body mass index (BMI): 22.6 ± 2.6 kg/m2] and with obesity (n = 7; BMI: 32.8 ± 2.9 kg/m2) performed acute aerobic exercise (AE) at 40%, 65%, or 80% of maximal aerobic capacity (V̇o2max; mL/kg/min) on separate visits. Blood was taken before and 30 min after each AE bout. Muscle biopsy samples were taken before, 30 min, and 3 h after the 80% V̇o2max AE bout. Individuals with obesity had higher total RAGE and esRAGE mRNA and RAGE protein (P < 0.0001). In addition, RAGE and esRAGE transcripts correlated to transcripts of the NF-κB subunit P65 (P < 0.05). There was no effect of AE on total RAGE or esRAGE transcripts, or RAGE protein (P > 0.05), and AE tended to decrease circulating sRAGE in particular at lower intensities of exercise. RAGE expression is exacerbated in skeletal muscle with obesity, which may contribute to muscle inflammation via NF-κB. Future work should investigate the consequences of increased skeletal muscle RAGE on the development of obesity-related metabolic dysfunction and potential mitigating strategies.NEW & NOTEWORTHY This study is the first to investigate the effects of aerobic exercise intensity on circulating sRAGE isoforms, muscle RAGE protein, and muscle RAGE splicing. sRAGE isoforms tended to diminish with exercise, although this effect was attenuated with increasing exercise intensity. Muscle RAGE protein and gene expression were unaffected by exercise. However, individuals with obesity displayed nearly twofold higher muscle RAGE protein and gene expression, which positively correlated with expression of the P65 subunit of NF-κB.

Correlation between serum advanced glycation end products and dietary intake of advanced glycation end products estimated from home cooking and food frequency questionnaires

BACKGROUND & AIMS

To our knowledge the association between dietary advanced glycation end-products (dAGEs) and cardiometabolic disease is limited. Our aim was to examine the association between dAGEs and serum concentration of carboxymethyl-lysine (CML) or soluble receptor advanced glycation end-products (sRAGEs), and to assess the difference on dAGEs and circulating AGEs according to lifestyle and biochemical measures.

METHODS AND RESULTS

52 overweight or obese adults diagnosed with type 2 diabetes were included in this cross-sectional analysis. dAGEs were estimated from a Food Frequency Questionnaire (FFQ) or from a FFQ + Home Cooking Frequency Questionnaire (HCFQ). Serum concentrations of CML and sRAGEs were measured by ELISA. Correlation tests were used to analyze the association between dAGEs derived from the FFQ or FFQ + HCFQ and concentrations of CML or sRAGEs. Demographic characteristics, lifestyle factors and biochemical measures were analyzed according to sRAGEs and dAGEs using student t-test and ANCOVA. A significant inverse association was found between serum sRAGEs and dAGEs estimated using the FFQ + HCFQ (r = -0.36, p = 0.010), whereas no association was found for dAGEs derived from the FFQ alone. No association was observed between CML and dAGEs. dAGEs intake estimated from the FFQ + HCFQ was significantly higher among younger and male participants, and in those with higher BMI, higher Hb1Ac levels, longer time with type 2 diabetes, lower adherence to Mediterranean diet, and higher use of culinary techniques that generate more AGEs (all p values p < 0.05).

CONCLUSIONS

These results show knowledge on culinary techniques is relevant to derive the association between dAGEs intake and cardiometabolic risk factors.

Advanced glycation end product signaling and metabolic complications: Dietary approach

Advanced glycation end products (AGEs) are a heterogeneous collection of compounds formed during industrial processing and home cooking through a sequence of nonenzymatic glycation reactions. The modern western diet is full of heat-treated foods that contribute to AGE intake. Foods high in AGEs in the contemporary diet include processed cereal products. Due to industrialization and marketing strategies, restaurant meals are modified rather than being traditionally or conventionally cooked. Fried, grilled, baked, and boiled foods have the greatest AGE levels. Higher AGE-content foods include dry nuts, roasted walnuts, sunflower seeds, fried chicken, bacon, and beef. Animal proteins and processed plant foods contain furosine, acrylamide, heterocyclic amines, and 5-hydroxymethylfurfural. Furosine (2-furoil-methyl-lysine) is an amino acid found in cooked meat products and other processed foods. High concentrations of carboxymethyl-lysine, carboxyethyl-lysine, and methylglyoxal-O are found in heat-treated nonvegetarian foods, peanut butter, and cereal items. Increased plasma levels of AGEs, which are harmful chemicals that lead to age-related diseases and physiological aging, diabetes, and autoimmune/inflammatory rheumatic diseases such as systemic lupus erythematosus and rheumatoid arthritis. AGEs in the pathophysiology of metabolic diseases have been linked to individuals with diabetes mellitus who have peripheral nerves with high amounts of AGEs and diabetes has been linked to increased myelin glycation. Insulin resistance and hyperglycemia can impact numerous human tissues and organs, leading to long-term difficulties in a number of systems and organs, including the cardiovascular system. Plasma AGE levels are linked to all-cause mortality in individuals with diabetes who have fatal or nonfatal coronary artery disease, such as ventricular dysfunction. High levels of tissue AGEs are independently associated with cardiac systolic dysfunction in diabetic patients with heart failure compared with diabetic patients without heart failure. It is widely recognized that AGEs and oxidative stress play a key role in the cardiovascular complications of diabetes because they both influence and are impacted by oxidative stress. All chronic illnesses involve protein, lipid, or nucleic acid modifications including crosslinked and nondegradable aggregates known as AGEs. Endogenous AGE formation or dietary AGE uptake can result in additional protein modifications and stimulation of several inflammatory signaling pathways. Many of these systems, however, require additional explanation because they are not entirely obvious. This review summarizes the current evidence regarding dietary sources of AGEs and metabolism-related complications associated with AGEs.

Implications of receptor for advanced glycation end products for progression from obesity to diabetes and from diabetes to cancer

Obesity and type 2 diabetes mellitus (T2DM) are chronic pathologies with a high incidence worldwide. They share some pathological mechanisms, including hyperinsulinemia, the production and release of hormones, and hyperglycemia. The above, over time, affects other systems of the human body by causing tissue hypoxia, low-grade inflammation, and oxidative stress, which lay the pathophysiological groundwork for cancer. The leading causes of death globally are T2DM and cancer. Other main alterations of this pathological triad include the accumulation of advanced glycation end products and the release of endogenous alarmins due to cell death (i.e., damage-associated molecular patterns) such as the intracellular proteins high-mobility group box protein 1 and protein S100 that bind to the receptor for advanced glycation products (RAGE) - a multiligand receptor involved in inflammatory and metabolic and neoplastic processes. This review analyzes the latest advanced reports on the role of RAGE in the development of obesity, T2DM, and cancer, with an aim to understand the intracellular signaling mechanisms linked with cancer initiation. This review also explores inflammation, oxidative stress, hypoxia, cellular senescence, RAGE ligands, tumor microenvironment changes, and the “cancer hallmarks” of the leading tumors associated with T2DM. The assimilation of this information could aid in the development of diagnostic and therapeutic approaches to lower the morbidity and mortality associated with these diseases.

Receptor for the Advanced Glycation End Products (RAGE) Pathway in Adipose Tissue Metabolism

Advanced glycation end products (AGEs) are mediators in the process of cellular dysfunction in response to hyperglycemia. Numerous data indicate that the accumulation of AGEs in the extracellular matrix plays a key role in the development of obesity-related adipose tissue dysfunction. Through binding of their membrane receptor (RAGE), AGEs affect numerous intracellular pathways and impair adipocyte differentiation, metabolism, and secretory activity. Therefore, inhibiting the production and accumulation of AGEs, as well as interfering with the metabolic pathways they activate, may be a promising therapeutic strategy for restoring normal adipose tissue function and, thus, combating obesity-related comorbidities. This narrative review summarizes data on the involvement of the RAGE pathway in adipose tissue dysfunction in obesity and the development of its metabolic complications. The paper begins with a brief review of AGE synthesis and the RAGE signaling pathway. The effect of the RAGE pathway on adipose tissue development and activity is then presented. Next, data from animal and human studies on the involvement of the RAGE pathway in obesity, diabetes, and cardiovascular diseases are summarized. Finally, therapeutic perspectives based on interference with the RAGE pathway are discussed.

RAGE pathways play an important role in regulation of organ fibrosis

Organ fibrosis is a pathological process of fibroblast activation and excessive deposition of extracellular matrix after persistent tissue injury and therefore is a common endpoint of many organ pathologies. Multiple cellular types and soluble mediators, including chemokines, cytokines and non-peptidic factors, are implicated in fibrogenesis and the remodeling of tissue architecture. The molecular basis of the fibrotic process is complex and consists of closely intertwined signaling networks. Research has strived for a better understanding of these pathological mechanisms to potentially reveal novel therapeutic targets for fibrotic diseases. In light of new knowledge, the receptor for advanced glycation end products (RAGE) emerged as an important candidate for the regulation of a wide variety of cellular functions related to fibrosis, including inflammation, cell proliferation, apoptosis, and angiogenesis. RAGE is a pattern recognition receptor that binds a broad range of ligands such as advanced glycation end products, high mobility group box-1, S-100 calcium-binding protein and amyloid beta protein. Although the link between RAGE and fibrosis has been established, the exact mechanisms need be investigated in further studies. The aim of this review is to collect all available information about the intricate function of RAGE and its signaling cascades in the pathogenesis of fibrotic diseases within different organs. In addition, to the major ligands and signaling pathways, we discuss potential strategies for targeting RAGE in fibrosis. We emphasize the functional links between RAGE, inflammation and fibrosis that may guide further studies and the development of improved therapeutic drugs.

Blood and Tissue Advanced Glycation End Products as Determinants of Cardiometabolic Disorders Focusing on Human Studies

Cardiometabolic disorders are characterised by a cluster of interactive risk determinants such as increases in blood glucose, lipids and body weight, as well as elevated inflammation and oxidative stress and gut microbiome changes. These disorders are associated with onset of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). T2DM is strongly associated with CVD. Dietary advanced glycation end products (dAGEs) attributable from modern diets high in sugar and/or fat, highly processed foods and high heat-treated foods can contribute to metabolic etiologies of cardiometabolic disorders. This mini review aims to determine whether blood dAGEs levels and tissue dAGEs levels are determinants of the prevalence of cardiometabolic disorders through recent human studies. ELISA (enzyme-linked immunosorbent assay), high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) for blood dAGEs measurement and skin auto fluorescence (SAF) for skin AGEs measurement can be used. Recent human studies support that a diet high in AGEs can negatively influence glucose control, body weight, blood lipid levels and vascular health through the elevated oxidative stress, inflammation, blood pressure and endothelial dysfunction compared with a diet low in AGEs. Limited human studies suggested a diet high in AGEs could negatively alter gut microbiota. SAF could be considered as one of the predictors affecting risks for cardiometabolic disorders. More intervention studies are needed to determine how dAGEs are associated with the prevalence of cardiometabolic disorders through gut microbiota changes. Further human studies are conducted to find the association between CVD events, CVD mortality and total mortality through SAF measurement, and a consensus on whether tissue dAGEs act as a predictor of CVD is required.

Advanced Glycation End Products and Inflammatory Cytokine Profiles in Maintenance Hemodialysis Patients After the Ingestion of a Protein-Dense Meal

OBJECTIVE

The goal of this investigation was to evaluate circulating and skeletal muscle inflammatory biomarkers between maintenance hemodialysis (MHD) and demographic-matched control subjects (CON) before and after ingestion of a protein-rich meal.

DESIGN AND METHODS

CON (n = 8; 50 ± 2 years; 31 ± 1 kg/m2) and MHD patients (n = 8; 56 ± 5 years; 32 ± 2 kg/m2) underwent a basal blood draw and muscle biopsy and serial blood draws after the ingestion of a mixed meal on a nondialysis day. Plasma advanced glycation end products (AGEs) and markers of oxidation were assessed via liquid chromatography-tandem mass spectrometry before and after the meal (+240 min). Circulating inflammatory cytokines and soluble receptors for AGE (sRAGE) isoforms (endogenous secretory RAGEs and cleaved RAGEs) were determined before and after the meal (+240 min). Basal muscle was probed for inflammatory cytokines and protein expression of related signaling components (RAGE, Toll-like receptor 4, oligosaccharyltransferase subunit 48, TIR-domain-containing adapter-inducing interferon-β, total IκBα, and pIκBα).

RESULTS

Basal circulating AGEs were 7- to 343-fold higher (P < .001) in MHD than those in CON, but only MG-H1 increased in CON after the meal (P < .001). There was a group effect (MHD > CON) for total sRAGEs (P = .02) and endogenous secretory RAGEs (P < .001) and a trend for cleaved RAGEs (P=.09), with no meal effect. In addition, there was a group effect (MHD < CON; P < .05) for circulating fractalkine, interleukin (IL)10, IL17A, and IL1β and a trend (P < .10) for IL6 and macrophage inflammatory protein 1 alpha, whereas tumor necrosis factor alpha was higher in MHD (P < .001). In muscle, Toll-like receptor 4 (P = .03), TIR-domain-containing adapter-inducing interferon-β (P = .002), and oligosaccharyltransferase subunit 48 (P = .02) expression was lower in MHD than that in CON, whereas IL6 was higher (P = .01) and IL8 (P = .08) tended to be higher in MHD.

CONCLUSION

Overall, MHD exhibited an exaggerated, circulating, and skeletal muscle inflammatory biomarker environment, and the meal did not appreciably affect the inflammatory status.

Association of α-Dicarbonyls and Advanced Glycation End Products with Insulin Resistance in Non-Diabetic Young Subjects: A Case-Control Study

α-Dicarbonyls and advanced glycation end products (AGEs) may contribute to the pathogenesis of insulin resistance by a variety of mechanisms. To investigate whether young insulin-resistant subjects present markers of increased dicarbonyl stress, we determined serum α-dicarbonyls-methylglyoxal, glyoxal, 3-deoxyglucosone; their derived free- and protein-bound, and urinary AGEs using the UPLC/MS-MS method; soluble receptors for AGEs (sRAGE), and cardiometabolic risk markers in 142 (49% females) insulin resistant (Quantitative Insulin Sensitivity Check Index (QUICKI) ≤ 0.319) and 167 (47% females) age-, and waist-to-height ratio-matched insulin-sensitive controls aged 16-to-22 years. The between-group comparison was performed using the two-factor (sex, presence/absence of insulin resistance) analysis of variance; multiple regression via the orthogonal projection to latent structures model. In comparison with their insulin-sensitive peers, young healthy insulin-resistant individuals without diabetes manifest alterations throughout the α-dicarbonyls-AGEs-sRAGE axis, dominated by higher 3-deoxyglucosone levels. Variables of α-dicarbonyls-AGEs-sRAGE axis were associated with insulin sensitivity independently from cardiometabolic risk markers, and sex-specifically. Cleaved RAGE associates with QUICKI only in males; while multiple α-dicarbonyls and AGEs independently associate with QUICKI particularly in females, who displayed a more advantageous cardiometabolic profile compared with males. Further studies are needed to elucidate whether interventions alleviating dicarbonyl stress ameliorate insulin resistance.

Effects of an exercise-based lifestyle intervention on systemic markers of oxidative stress and advanced glycation endproducts in persons with type 2 diabetes: Secondary analysis of a randomised clinical trial

AIMS/HYPOTHESIS

This secondary analysis aimed to investigate the effects of a 12 months intensive exercise-based lifestyle intervention on systemic markers of oxidative stress in persons with type 2 diabetes. We hypothesized lifestyle intervention to be superior to standard care in decreasing levels of oxidative stress.

METHODS

The study was based on the single-centre, assessor-blinded, randomised, controlled U-turn trial (ClinicalTrial.gov NCT02417012). Persons with type 2 diabetes ˂ 10 years, ˂ 3 glucose lowering medications, no use of insulin, BMI 25-40 kg/m² and no severe diabetic complications were included. Participants were randomised (2:1) to either intensive exercise-based lifestyle intervention and standard (n = 64) or standard care alone (n = 34). Standard care included individual education in diabetes management, advice on a healthy lifestyle and regulation of medication by a blinded endocrinologist. The lifestyle intervention included five to six aerobic exercise sessions per week, combined with resistance training two to three times per week and an adjunct dietary intervention aiming at reduction of ∼500 kcal/day (month 0-4). The diet was isocaloric from months 5-12. The primary outcome of this secondary analysis was change in oxidative stress measured by 8-oxo-7,8-dihydroguanosine (8-oxoGuo) and secondarily in 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), as markers of RNA and DNA oxidation, respectively, from baseline to 12-months follow-up.

RESULTS

A total of 77 participants, 21 participants receiving standard care and 56 participants receiving the lifestyle intervention, were included in the analysis. Mean age at baseline was 54.1 years (SD 9.1), 41% were women and mean duration of type 2 diabetes was 5.0 years (SD 2.8). From baseline to follow-up the lifestyle group experienced a 7% decrease in 8-oxoGuo (-0.15 nmol/mmol creatinine [95% CI -0.27, -0.03]), whereas standard care conversely was associated with a 8.5% increase in 8-oxoGuo (0.19 nmol/mmol creatinine [95% CI 0.00, 0.40]). The between group difference in 8-oxoGuo was -0.35 nmol/mmol creatinine [95% CI -0.58, -0.12,], p = 0.003. No between group difference was observed in 8-oxodG.

CONCLUSION/INTERPRETATION

A 12 months intensive exercise-based lifestyle intervention was associated with a decrease in RNA, but not DNA, oxidation in persons with type 2 diabetes.

Circulating levels of AGEs and soluble RAGE isoforms are associated with all-cause mortality and development of cardiovascular complications in type 2 diabetes: a retrospective cohort study

BACKGROUND

Advanced glycation end-products (AGEs) and their interaction with the receptor for advanced glycation end-products (RAGE) play a pivotal role in the development and progression of type 2 diabetes. In this retrospective cohort study, we explored the association of circulating levels of soluble RAGE (sRAGE) isoforms, i.e., endogenous secretory esRAGE and cleaved cRAGE, AGEs and their respective ratios with 15-year all-cause mortality in type 2 diabetes.

METHODS

Baseline AGEs and sRAGE isoforms concentration were measured by ELISA in 362 patients with type 2 diabetes and in 125 age- and gender-matched healthy control subjects (CTR). Independent predictors of mortality were determined using Cox proportional-hazards models and used to build and validate a nomogram for all-cause mortality prediction in type 2 diabetes.

RESULTS

AGEs, total sRAGE, cRAGE and the AGEs/sRAGE and AGEs/esRAGE ratios were significantly increased in patients with type 2 diabetes compared to CTR (p < 0.001). In CTR subjects, but not in type 2 diabetes patients, a significant negative correlation between cRAGE and age was confirmed (p = 0.003), whereas the AGEs/sRAGE (p = 0.032) and AGEs/cRAGE (p = 0.006) ratios were positively associated with age. At an average follow-up of 15 years (4,982 person-years), 130 deaths were observed. The increase in the AGEs/cRAGE ratio was accompanied by a higher risk of all-cause mortality in patients with type 2 diabetes (HR per each SD increment = 1.30, 95% CI 1.15-1.47; p < 0.001). Moreover, sRAGE was associated with the development of major adverse cardiovascular events (MACE) in type 2 diabetes patients without previous MACE (OR for each SD increase: 1.48, 95% CI 1.11-1.89). A nomogram based on age, sex, HbA1c, systolic blood pressure, and the AGEs/cRAGE ratio was built to predict 5-, 10- and 15-year survival in type 2 diabetes. Patients were categorized into quartiles of the monogram scores and Kaplan-Meier survival curves confirmed the prognostic accuracy of the model (log-rank p = 6.5 × 10- 13).

CONCLUSIONS

The ratio between AGEs and the cRAGE isoform is predictive of 15-year survival in patients with type 2 diabetes. Our data support the assessment of circulating AGEs and soluble RAGE isoforms in patients with type 2 diabetes as predictors of MACE and all-cause mortality.

Soluble Receptor for Advanced Glycation End Products (sRAGE) Isoforms Predict Changes in Resting Energy Expenditure in Adults with Obesity during Weight Loss

Background

Accruing evidence indicates that accumulation of advanced glycation end products (AGEs) and activation of the receptor for AGEs (RAGE) play a significant role in obesity and type 2 diabetes. The concentrations of circulating RAGE isoforms, such as soluble RAGE (sRAGE), cleaved RAGE (cRAGE), and endogenous secretory RAGE (esRAGE), collectively sRAGE isoforms, may be implicit in weight loss and energy compensation resulting from caloric restriction.

Objectives

We aimed to evaluate whether baseline concentrations of sRAGE isoforms predicted changes (∆) in body composition [fat mass (FM), fat-free mass (FFM)], resting energy expenditure (REE), and adaptive thermogenesis (AT) during weight loss.

Methods

Data were collected during a behavioral weight loss intervention in adults with obesity. At baseline and 3 mo, participants were assessed for body composition (bioelectrical impedance analysis) and REE (indirect calorimetry), and plasma was assayed for concentrations of sRAGE isoforms (sRAGE, esRAGE, cRAGE). AT was calculated using various mathematical models that included measured and predicted REE. A linear regression model that adjusted for age, sex, glycated hemoglobin (HbA1c), and randomization arm was used to test the associations between sRAGE isoforms and metabolic outcomes.

Results

Participants (n = 41; 70% female; mean ± SD age: 57 ± 11 y; BMI: 38.7 ± 3.4 kg/m2) experienced modest and variable weight loss over 3 mo. Although baseline sRAGE isoforms did not predict changes in ∆FM or ∆FFM, all baseline sRAGE isoforms were positively associated with ∆REE at 3 mo. Baseline esRAGE was positively associated with AT in some, but not all, AT models. The association between sRAGE isoforms and energy expenditure was independent of HbA1c, suggesting that the relation was unrelated to glycemia.

Conclusions

This study demonstrates a novel link between RAGE and energy expenditure in human participants undergoing weight loss.This trial was registered at clinicaltrials.gov as NCT03336411.

Does AGE-RAGE Stress Play a Role in the Development of Coronary Artery Disease in Obesity?

This article deals with the role of AGE (advanced glycation end products)-RAGE (receptor for AGE) stress (AGE/sRAGE) in the development of coronary artery disease (CAD) in obesity. CAD is due to atherosclerosis in coronary artery. The serum/plasma levels of AGE and sRAGE are reduced, while AGE-RAGE stress and expression of RAGE are elevated in obese individuals. However, the levels of AGE are elevated in obese individuals with more than one metabolic syndrome. The increases in the AGE-RAGE stress would elevate the expression and production of atherogenic factors, including reactive oxygen species, nuclear factor-kappa B, cytokines, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, endothelial leukocyte adhesion molecules, monocyte chemoattractant protein-1, granulocyte-macrophage colony-stimulating factor, and growth factors. Low levels of sRAGE would also increase the atherogenic factors. The increases in the AGE-RAGE stress and decreases in the levels of sRAGE would induce development of atherosclerosis, leading to CAD. The therapeutic regimen for AGE-RAGE stress-induced CAD in obesity would include lowering of AGE intake, prevention of AGE formation, degradation of AGE in vivo, suppression of RAGE expression, blockade of AGE-RAGE interaction, downregulation of sRAGE expression, and use of antioxidants. In conclusion, the data suggest that AGE-RAGE stress is involved in the development of CAD in obesity, and the therapeutic interventions to reduce AGE-RAGE would be helpful in preventing, regressing, and slowing the progression of CAD in obesity.

Nutrient regulation of inflammatory signalling in obesity and vascular disease

Despite obesity and diabetes markedly increasing the risk of developing cardiovascular diseases, the molecular and cellular mechanisms that underlie this association remain poorly characterised. In the last 20 years it has become apparent that chronic, low-grade inflammation in obese adipose tissue may contribute to the risk of developing insulin resistance and type 2 diabetes. Furthermore, increased vascular pro-inflammatory signalling is a key event in the development of cardiovascular diseases. Overnutrition exacerbates pro-inflammatory signalling in vascular and adipose tissues, with several mechanisms proposed to mediate this. In this article, we review the molecular and cellular mechanisms by which nutrients are proposed to regulate pro-inflammatory signalling in adipose and vascular tissues. In addition, we examine the potential therapeutic opportunities that these mechanisms provide for suppression of inappropriate inflammation in obesity and vascular disease.

Modulation of soluble receptor for advanced glycation end products isoforms and advanced glycation end products in long-living individuals

Background: Circulating levels of soluble receptor for advanced glycation end products (sRAGE) and advanced glycation end products (AGEs) correlate with aging/cardiovascular risk, which is delayed in long-living individuals (LLIs). AGEs/sRAGE isoforms (cleaved RAGE [cRAGE] and secretory RAGE [esRAGE]) ratio is a valuable marker for disease risk. Results: We evaluated circulating sRAGE isoforms, and AGEs in LLIs (n = 95; 90-105 years) and controls (n = 94; 11-89 years). cRAGE decreased with age in controls and further declined in LLIs. esRAGE increased in LLIs. AGEs rose with age in controls and decreased in LLIs that were characterized by a lower AGEs/sRAGE ratio. Notably, cRAGE and AGE/esRAGE ratio better discriminated controls from LLIs. Conclusion: circulating cRAGE could be considered a reliable marker of chronological age while esRAGE a protective factor for longevity.

Soluble Receptor for Advanced Glycation End-products regulates age-associated Cardiac Fibrosis

Myocardial aging increases the cardiovascular risk in the elderly. The Receptor for Advanced Glycation End-products (RAGE) is involved in age-related disorders. The soluble isoform (sRAGE) acts as a scavenger blocking the membrane-bound receptor activation. This study aims at investigating RAGE contribution to age-related cardiac remodeling.

We analyzed the cardiac function of three different age groups of female Rage-/- and C57BL/6N (WT) mice: 2.5- (Young), 12- (Middle-age, MA) and 21-months (Old) old. While aging, Rage-/- mice displayed an increase in left ventricle (LV) dimensions compared to age-matched WT animals, with the main differences observed in the MA groups. Rage-/- mice showed higher fibrosis and a larger number of α-Smooth Muscle Actin (SMA)+ cells with age, along with increased expression of pro-fibrotic Transforming Growth Factor (TGF)-β1 pathway components. RAGE isoforms were undetectable in LV of WT mice, nevertheless, circulating sRAGE declined with aging and inversely associated with LV diastolic dimensions. Human cardiac fibroblasts stimulated with sRAGE exhibited a reduction in proliferation, pro-fibrotic proteins and TGF-beta Receptor 1 (TGFbR1) expression and Smad2-3 activation. Finally, sRAGE administration to MA WT animals reduced cardiac fibrosis.

Hence, our work shows that RAGE associates with age-dependent myocardial changes and indicates sRAGE as an inhibitor of cardiac fibroblasts differentiation and age-dependent cardiac fibrosis.

Metabolic syndrome and the plasma proteome: from association to causation

Background

The metabolic syndrome (MetS), defined by the simultaneous clustering of cardio-metabolic risk factors, is a significant worldwide public health burden with an estimated 25% prevalence worldwide. The pathogenesis of MetS is not entirely clear and the use of molecular level data could help uncover common pathogenic pathways behind the observed clustering.

Methods

Using a highly multiplexed aptamer-based affinity proteomics platform, we examined associations between plasma proteins and prevalent and incident MetS in the KORA cohort (n = 998) and replicated our results for prevalent MetS in the HUNT3 study (n = 923). We applied logistic regression models adjusted for age, sex, smoking status, and physical activity.

We used the bootstrap ranking algorithm of least absolute shrinkage and selection operator (LASSO) to select a predictive model from the incident MetS associated proteins and used area under the curve (AUC) to assess its performance. Finally, we investigated the causal effect of the replicated proteins on MetS using two-sample Mendelian randomization.

Results

Prevalent MetS was associated with 116 proteins, of which 53 replicated in HUNT. These included previously reported proteins like leptin, and new proteins like NTR domain-containing protein 2 and endoplasmic reticulum protein 29. Incident MetS was associated with 14 proteins in KORA, of which 13 overlap the prevalent MetS associated proteins with soluble advanced glycosylation end product-specific receptor (sRAGE) being unique to incident MetS. The LASSO selected an eight-protein predictive model with an (AUC = 0.75; 95% CI = 0.71–0.79) in KORA.

Mendelian randomization suggested causal effects of three proteins on MetS, namely apolipoprotein E2 (APOE2) (Wald-Ratio = − 0.12, Wald-p = 3.63e−13), apolipoprotein B (APOB) (Wald-Ratio = − 0.09, Wald-p = 2.54e−04) and proto-oncogene tyrosine-protein kinase receptor (RET) (Wald-Ratio = 0.10, Wald-p = 5.40e−04).

Conclusions

Our findings offer new insights into the plasma proteome underlying MetS and identify new protein associations. We reveal possible casual effects of APOE2, APOB and RET on MetS. Our results highlight protein candidates that could potentially serve as targets for prevention and therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01299-2.

Circulating Ligands of the Receptor for Advanced Glycation End Products and the Soluble Form of the Receptor Modulate Cardiovascular Cell Apoptosis in Diabetes

We determined whether plasma concentrations of the receptor for advanced glycation end products (RAGE) and the soluble (s) form of RAGE (sRAGE) in healthy individuals and patients with type 2 diabetes (T2D) modulate vascular remodeling. Healthy individuals and patients with T2D were divided into two age groups: young = <35 years old or middle-aged (36-64 years old) and stratified based on normal glucose tolerance (NGT), impaired (IGT), and T2D. Plasma titers of sRAGE, the RAGE ligands, AGEs, S100B, S100A1, S100A6, and the apoptotic marker Fas ligand Fas(L) were measured by enzyme-linked immunosorbent assay (ELISA). The apoptotic potential of the above RAGE ligands and sRAGE were assessed in cultured adult rat aortic smooth muscle cells (ASMC). In NGT individuals, aging increased the circulating levels of AGEs and S100B and decreased sRAGE, S100A1 and S100A6. Middle-aged patients with T2D presented higher levels of circulating S100B, AGEs and FasL, but lower levels of sRAGE, S100A1 and S100A6 than individuals with NGT or IGT. Treatment of ASMC with either AGEs or S100B at concentrations detected in T2D patients increased markers of inflammation and apoptosis. Responses attenuated by concomitant administration of sRAGE. In middle-aged patients with T2D, lower circulating plasma levels of sRAGE may limit decoy and exogenous trapping of deleterious pro-apoptotic/pro-inflammatory RAGE ligands AGEs and S100B, increasing the risk for diabetic complications.

Effects of the age/rage axis in the platelet activation

Platelet activity is essential in cardiovascular diseases. Therefore our objective was to evaluate the main effects of activating RAGE in platelets which are still unknown. A search for RAGE expression in different databases showed poor or a nonexistent presence in platelets. We confirmed the expression in platelets and secreted variable of RAGE (sRAGE). Platelets from elderly adults expressed in resting showed 3.2 fold more RAGE from young individuals (p < 0.01) and 3.3 fold with TRAP-6 (p < 0.001). These results could indicate that the expression of RAGE is more inducible in older adults. Then we found that activating RAGE with AGE-BSA-derived from methylglyoxal and subthreshold TRAP-6, showed a considerable increase with respect to the control in platelet aggregation and expression of P-selectin (respectively, p < 0.01). This effect was almost completely blocked by using a specific RAGE inhibitor (FSP-ZM1), confirming that RAGE is important for the function and activation platelet. Finally, we predict the region stimulated by AGE-BSA is located in region V of RAGE and 13 amino acids are critical for its binding. In conclusion, the activation of RAGE affects platelet activation and 13 amino acids are critical for its stimulation, this information is crucial for future possible treatments for CVD.

The role of soluble receptor for advanced glycation end-products (sRAGE) in the general population and patients with diabetes mellitus with a focus on renal function and overall outcome

Isoforms of the receptor for advanced glycation end-product (RAGE) protein, which lack the transmembrane and the signaling (soluble RAGE or sRAGE) domains are hypothesized to counteract the detrimental action of the full-length receptor by acting as a decoy, and they provide a potential tool to treat RAGE-associated diseases. Multiple studies have explored the relationship between sRAGE and endogenous secretory RAGE and its polymorphism and obesity, metabolic syndrome, atherosclerosis, kidney function, and increased mortality in the general population. In addition, sRAGE may be a key player in the pathogenesis of diabetes mellitus and its microvascular (e.g. kidney disease) as well as macrovascular (e.g. cardiovascular disease) complications. In this review, we focus on the role of sRAGE as a biomarker in these specific areas. As there is a lack of an underlying unifying hypothesis about how sRAGE changes according to the disease condition or risk factor, there is a call to incorporate all three players of the AGE-RAGE axis into a new universal biomarker/risk marker: (AGE + RAGE)/sRAGE. However, the measurement of RAGE in humans is not practical as it is a cell-bound receptor for which tissue is required for analysis. A high AGE/sRAGE ratio may be a valuable alternative and practical universal biomarker/risk marker for diseases associated with the AGE-RAGE axis, irrespective of low or high serum sRAGE concentrations.

Accumulation of advanced glycation end products (AGEs) is associated with the severity of aortic stenosis in patients with concomitant type 2 diabetes

BACKGROUND

Accumulation of advanced glycation end products (AGEs) leads to chronic glycation of proteins and tissue damage, particularly in patients with diabetes mellitus (DM). We aimed to evaluate whether increased accumulation of AGEs in patients with aortic stenosis (AS) and concomitant type 2 diabetes (DM) is associated with AS severity.

METHODS

We prospectively enrolled 76 patients with severe AS (47.1% males; nonDM), aged 68 [66-72] years, and 50 age-matched DM patients with a median blood glucose level of 7.5 [5.9-9.1] mM and glycated hemoglobin (HbA1c) of 6.8 [6.3-7.8]%, scheduled for aortic valve replacement. Valvular expression of AGEs, AGEs receptor (RAGE), interleukin-6 (IL-6), and reactive oxygen species (ROS) induction were evaluated ex vivo by immunostaining and calculated as the extent of positive immunoreactive areas/total sample area. Plasma levels of AGEs and soluble RAGE (sRAGE) were assessed by ELISAs.

RESULTS

Subjects with DM had increased valvular expression of both AGEs (6.6-fold higher, 15.53 [9.96-23.28]%) and RAGE (1.8-fold higher, 6.8 [4.9-8.45]%) compared to nonDM patients (2.05 [1.21-2.58]% and 2.4 [1.56-3.02]%, respectively; both p < 0.001). Plasma levels of AGEs (12-fold higher) and sRAGE (1.3-fold higher) were elevated in DM patients, compared to nonDM (both p < 0.0001). The percentage of valvular ROS-positive (2.28 [1.6-3.09] vs. 1.15 [0.94-1.4]%, p < 0.0001) but not IL-6-positive areas was higher within DM, compared to nonDM valves. In DM patients, the percentage of valvular AGEs- and RAGE-positive areas correlated with HbA1c (r = 0.77, p < 0.0001 and r = 0.30, p = 0.034). Similarly, plasma AGEs and sRAGE levels were associated with HbA1c in the DM group (r = 0.32, p = 0.024 and r = 0.33, p = 0.014, respectively). In all DM patients, we found an association between the amount of valvular AGEs and the disease severity measured as aortic valve area (AVA; r = 0.68, p < 0.0001). Additionally, in DM patients with HbA1c > 7% (n = 24, 48%) we found that valvular expression of AGEs correlated with mean transvalvular pressure gradient (PG_mean; r = 0.45, p = 0.027). Plasma AGEs levels in the whole DM group correlated with AVA (r = - 0.32, p = 0.02), PG_mean (r = 0.31, p = 0.023), and PG_max (r = 0.30, p = 0.03).

CONCLUSIONS

Our study suggests that poorly-controlled diabetes leads to increased AGEs and RAGE valvular accumulation, which at least partially, might result in AS progression in DM patients.

Can advanced glycation end-products and their receptors be affected by weight loss? A systematic review

Advanced glycation end products (AGEs) have been implicated in the pathogenesis of most chronic diseases. Therefore, identification of treatments that can attenuate the effects of these compounds and prevent cardiometabolic complications is of extreme public health interest. Recently, body weight management interventions showed positive results on reducing serum AGE concentrations. Moreover, the soluble receptor for advanced glycation end products (sRAGE) is considered to be a novel biomarker to identify patients with obesity most likely to benefit from weight management interventions. This systematic review aimed to critically analyze papers evaluating the effects of weight loss on serum AGEs and its receptors in adults with excess body weight. MEDLINE, Cochrane, Scopus, and Lilacs databases were searched. Three studies evaluating the response of AGEs to energy-restricted diets and six assessing sRAGE as the primary outcome were included. Energy-restricted diets and bariatric surgery reduced serum AGE concentrations, but effects on endogenous secretory RAGE (esRAGE) and sRAGE concentrations are conflicting. These results may be associated with mechanisms related to changes in dietary intake and limiting endogenous AGE formation. Therefore, the role of energy-restricted diets and bariatric surgery on lowering serum AGE concentrations, as well as its effects on AGEs receptors, deserves further investigation.

Modulation of soluble receptor for advanced glycation end-products (RAGE) isoforms and their ligands in healthy aging

The receptor for advanced glycation end-products (RAGE) recognizes several ligands involved in inflammatory diseases. Two circulating soluble isoforms exist: esRAGE derived from alternative splicing and cRAGE generated by the membrane-bound RAGE (FL-RAGE) proteolysis. Together, esRAGE and cRAGE constitute sRAGE and function as decoy receptors preventing FL-RAGE/ligands binding.

We determined serum concentration of both, esRAGE and cRAGE, and their ligands AGEs, HMGB1 and S100A8/A9 in a healthy population of 169 subjects aged 20-90 years. cRAGE showed a negative (r=-0.375, P<0.0001) while AGEs (r=0.160, P=0.0384) and S100A8/A9 (r=0.207, P=0.0091) a positive correlation with age. esRAGE did not change during aging and inversely correlated with Hemoglobin, ALT, insulin, HOMA index, Waist-Hip ratio (W/H), Waist Circumference (WC) and positively with AGEs. cRAGE exhibited also an inverse correlation with WC, W/H, PAI-1, HMGB1, AGEs and S100A8/A9. Age, W/H, HMGB1, S100A8/A9 and AGEs are independent predictors of cRAGE, whereas W/H and AGEs associate with esRAGE. Treatment of cells with glycated albumin reduced cRAGE production and upregulated FL-RAGE.

These results indicate that in a healthy population cRAGE is a biomarker of aging while esRAGE represents a more reliable marker of obesity and insulin resistance. Hence, sRAGE isoforms levels could be differentially associated with age-related diseases risk factors.

Advanced Glycation End Products: Building on the Concept of the "Common Soil" in Metabolic Disease

The role of advanced glycation end products (AGEs) in promoting and/or exacerbating metabolic dysregulation is being increasingly recognized. AGEs are formed when reducing sugars nonenzymatically bind to proteins or lipids, a process that is enhanced by hyperglycemic and hyperlipidemic environments characteristic of numerous metabolic disorders including obesity, diabetes, and its complications. In this mini-review, we put forth the notion that AGEs span the spectrum from cause to consequence of insulin resistance and diabetes, and represent a "common soil" underlying the pathophysiology of these metabolic disorders. Collectively, the surveyed literature suggests that AGEs, both those that form endogenously as well as exogenous AGEs derived from environmental factors such as pollution, smoking, and "Western"-style diets, contribute to the pathogenesis of obesity and diabetes. Specifically, AGE accumulation in key metabolically relevant organs induces insulin resistance, inflammation, and oxidative stress, which in turn provide substrates for excess AGE formation, thus creating a feed-forward-fueled pathological loop mediating metabolic dysfunction.

Advanced glycation end-products regulate extracellular matrix-adipocyte metabolic crosstalk in diabetes

The adipose tissue extracellular matrix (ECM) regulates adipocyte cellular metabolism and is altered in obesity and type 2 diabetes, but mechanisms underlying ECM-adipocyte metabolic crosstalk are poorly defined. Advanced glycation end-product (AGE) formation is increased in diabetes. AGE alter tissue function via direct effects on ECM and by binding scavenger receptors on multiple cell types and signaling through Rho GTPases. Our goal was to determine the role and underlying mechanisms of AGE in regulating human ECM-adipocyte metabolic crosstalk. Visceral adipocytes from diabetic and non-diabetic humans with obesity were studied in 2D and 3D-ECM culture systems. AGE is increased in adipose tissue from diabetic compared to non-diabetic subjects. Glycated collagen 1 and AGE-modified ECM regulate adipocyte glucose uptake and expression of AGE scavenger receptors and Rho signaling mediators, including the DIAPH1 gene, which encodes the human Diaphanous 1 protein (hDia1). Notably, inhibition of hDia1, but not scavenger receptors RAGE or CD36, attenuated AGE-ECM inhibition of adipocyte glucose uptake. These data demonstrate that AGE-modification of ECM contributes to adipocyte insulin resistance in human diabetes, and implicate hDia1 as a potential mediator of AGE-ECM-adipocyte metabolic crosstalk.

Crucial players in Alzheimer's disease and diabetes mellitus: Friends or foes?

Alzheimer's disease (AD) and diabetes mellitus, especially type 2 (T2DM), are very common and widespread diseases in contemporary societies, and their incidence is steadily on the increase. T2DM is a multiple metabolic disorder, with several mechanisms including hyperglycaemia, insulin resistance, insulin receptor and insulin growth factor disturbances, glucose toxicity, formation of advanced glycation end products (AGEs) and the activity of their receptors. AD is the most common form of dementia, characterized by the accumulation of extracellular beta amyloid peptide aggregates and intracellular hyper-phosphorylated tau proteins, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. The aim of this paper is to provide a comprehensive review of the evidence linking T2DM to the onset and development of AD and highlight the unknown or poorly studied "nooks and crannies" of this interesting relationship, hence providing an opportunity to stimulate new ideas for the analysis of comorbidities between AD and DM. Despite, indication of possible biomarkers of early diagnosis of T2DM and AD, this review is also an attempt to answer the question as to whether the crucial factors in the development of both conditions support the link between DM and AD.

Experimental Hyperglycemia Alters Circulating Concentrations and Renal Clearance of Oxidative and Advanced Glycation End Products in Healthy Obese Humans

The purpose of this investigation was to evaluate the effects of experimental hyperglycemia on oxidative damage (OX), advanced glycation end products (AGEs), and the receptor for AGEs (RAGE) through an in vivo approach. Obese subjects (n = 10; 31.2 ± 1.2 kg·m⁻²; 56 ± 3 years) underwent 24 h of hyperglycemic clamp (+5.4 mM above basal), where plasma at basal and after 2 h and 24 h of hyperglycemic challenge were assayed for OX (methionine sulfoxide, MetSO, and aminoadipic acid, AAA) and AGE-free adducts (N^e-carboxymethyllysine, CML; N^e-carboxyethyllysine, CEL; glyoxal hydroimidazolone-1, GH-1; methylglyoxal hydroimidazolone-1, MG-H1; and 3-deoxyglucosone hydroimidazolone, 3DG-H) via liquid chromatography–tandem mass spectrometry (LC–MS/MS). Urine was also analyzed at basal and after 24 h for OX and AGE-free adducts and plasma soluble RAGE (sRAGE) isoforms (endogenous secretory RAGE, esRAGE, and cleaved RAGE, cRAGE), and inflammatory markers were determined via enzyme-linked immunosorbent assay (ELISA). Skeletal muscle tissue collected via biopsy was probed at basal, 2 h, and 24 h for RAGE and OST48 protein expression. Plasma MetSO, AAA, CEL, MG-H1, and G-H1 decreased (−18% to −47%; p < 0.05), while CML increased (72% at 24 h; p < 0.05) and 3DG-H remained unchanged (p > 0.05) with the hyperglycemic challenge. Renal clearance of MetSO, AAA, and G-H1 increased (599% to 1077%; p < 0.05), CML decreased (−30%; p < 0.05), and 3DG-H, CEL, and MG-H1 remained unchanged (p > 0.05). Fractional excretion of MetSO, AAA, CEL, G-H1, and MG-H1 increased (5.8% to 532%; p < 0.05) and CML and 3DG-H remained unchanged (p > 0.05). Muscle RAGE and OST48 expression, plasma sRAGE, IL-1β, IL-1Ra, and TNFα remained unchanged (p > 0.05), while IL-6 increased (159% vs. basal; p > 0.05). These findings suggest that individuals who are obese but otherwise healthy have the capacity to prevent accumulation of OX and AGEs during metabolic stress by increasing fractional excretion and renal clearance.

Cytokine, Chemokine, and Cytokine Receptor Changes Are Associated With Metabolic Improvements After Bariatric Surgery

CONTEXT

Altered cytokine levels and chronic low-grade inflammation contribute to metabolic dysfunction in obesity. The extent of cytokine changes and their impact on metabolic improvements after bariatric surgery have not been fully explored.

OBJECTIVE

To compare 76 circulating cytokines, chemokines, and secreted cytokine receptors in subjects with obesity and lean subjects and determine how these cytokines are altered by bariatric surgery.

DESIGN, SETTING, AND PARTICIPANTS

A total of 37 patients with obesity and 37 lean patients in a cross-sectional study at an academic medical center. We also investigated cytokine changes in 25 patients with obesity after bariatric surgery.

INTERVENTION

Bariatric surgery (Roux-en-Y gastric bypass and vertical sleeve gastrectomy).

MAIN OUTCOME MEASURES

Quantification of 76 circulating cytokines, chemokines, and secreted cytokine receptors.

RESULTS

A total of 13 cytokines were significantly higher, and 4 lower, in patients with obesity relative to lean controls. Soluble vascular endothelial growth factor receptor 2 (sVEGFR2), soluble TNF receptor (sTNFR) 1, and sTNFR2 were positively correlated, and soluble receptor for advanced glycation end-products was inversely correlated, with weight and body mass index. sTNFR2 was positively correlated with fasting glucose, homeostatic model assessment of insulin resistance, and hemoglobin A1c. After bariatric surgery, adiponectin increased, and leptin decreased. Elevated sVEGFR2 levels in patients with obesity were decreased (P = 0.01), whereas reduced chemokine (C-X-C motif) ligand (CXCL) 12 levels in patients with obesity increased (P = 0.03) after surgery. Patients with higher soluble interleukin receptor (sIL) 1R2 and sIL-6R levels before surgery had greater weight loss after surgery (P < 0.05).

CONCLUSIONS

We demonstrate that chemokine (C-C motif) ligand (CCL) 14, sVEGFR2, and platelet-derived growth factor BB are elevated in obesity, and CXCL12, CCL11, and CCL27 are lower in obesity. We found clinically concordant directionality between lean and patients with obesity and before vs after surgery for six cytokines, suggesting that bariatric surgery shifted the cytokine profiles of patients with obesity toward that of lean controls.

Divergent Changes in Plasma AGEs and sRAGE Isoforms Following an Overnight Fast in T1DM

Advanced glycation end products (AGEs) promote the development of diabetic complications through activation of their receptor (RAGE). Isoforms of soluble RAGE (sRAGE) sequester AGEs and protect against RAGE-mediated diabetic complications. We investigated the effect of an overnight fast on circulating metabolic substrates, hormones, AGEs, and sRAGE isoforms in 26 individuals with type 1 diabetes (T1DM). Blood was collected from 26 young (18–30 years) T1DM patients on insulin pumps before and after an overnight fast. Circulating AGEs were measured via LC-MS/MS and sRAGE isoforms were analyzed via ELISA. Glucose, insulin, glucagon, and eGFR_cystatin-c decreased while cortisol increased following the overnight fast (p < 0.05). AGEs (CML, CEL, 3DG-H, MG-H1, and G-H1) decreased (21–58%, p < 0.0001) while total sRAGE, cleaved RAGE (cRAGE), and endogenous secretory RAGE (esRAGE) increased (22–24%, p < 0.0001) following the overnight fast. The changes in sRAGE isoforms were inversely related to MG-H1 (rho = −0.493 to −0.589, p < 0.05) and the change in esRAGE was inversely related to the change in G-H1 (rho = −0.474, p < 0.05). Multiple regression analyses revealed a 1 pg/mL increase in total sRAGE, cRAGE, or esRAGE independently predicted a 0.42–0.52 nmol/L decrease in MG-H1. Short-term energy restriction via an overnight fast resulted in increased sRAGE isoforms and may be protective against AGE accumulation.

Corrigendum: Obesity and Comorbidity: Could Simultaneous Targeting of esRAGE and sRAGE Be the Panacea?

[This corrects the article DOI: 10.3389/fphys.2019.00787.].

Obesity and Comorbidity: Could Simultaneous Targeting of esRAGE and sRAGE Be the Panacea?

Obesity, a chronic multifaceted disease, predisposes its patients to increased risk of metabolic disorders such as: diabetes mellitus, cardiovascular diseases, dyslipidemia, etc. Recent studies reported it to be amongst the leading causes of deaths in the world. Although several treatment options for obesity abound, many of them have not been able to successfully reverse the existing obesity and metabolic dysregulation. This has therefore warranted the need for either alternative therapies or diversification of the treatment approach for obesity and its comorbidity. When the receptor for advanced glycation end products (RAGE) interacts with its ligand, RAGE-ligand activates an inflammatory signaling cascade, that leads to the activation of nuclear factor kappa B (NF-κB) and transcription of inflammatory cytokines. This action has been associated with the development of obesity and its mediated metabolic dysregulation. In view of the increasing prevalence of obesity globally and the potential threat it places on life expectancy, this article reviewed the promising potentials of targeting endogenous secretory receptor for advanced glycation end products/soluble receptors for advanced glycation end products signaling as a treatment approach for obesity. We carried out a literature search in several electronic data bases such as: Pubmed, Pubmed Central, Google, Google Scholar, Scopus, and Medline from 1980 to 2019 to acquire the status of information concerning this. The article suggests the need for the development of an esRAGE/sRAGE targeted pharmacotherapy as a treatment approach for obesity and its comorbidity.

Endogenous secretory RAGE increases with improvements in body composition and is associated with markers of adipocyte health

BACKGROUND AND AIMS

The receptor for advanced glycation end products (RAGE) is implicated in obesogenesis. Conversely, soluble RAGE (sRAGE) competitively inhibits RAGE. Our aim was to determine the effects of weight-loss via alternate day fasting (ADF) on sRAGE isoforms and evaluate potential relationships with body composition.

METHODS AND RESULTS

42 obese participants were randomized to control (CON) or ADF. For 24 weeks, the ADF group consumed 25% or 125% of their caloric requirements on alternating days while the CON group did not change their diet. Body fat was measured via DXA, visceral fat (VAT) via MRI and subcutaneous fat (SAT) was derived by subtracting VAT from total fat. sRAGE isoforms were measured via ELISAs. After 24 weeks, ADF -6.8 (-9.5, -3.5)kg (Median, IQR) lost more weight than CON -0.3 (-1.9, 1.0)kg (p < 0.05). The change in endogenous secretory RAGE (esRAGE) was different between ADF 15 (-30, 78)pg/mL and CON -21 (-72, 16)pg/mL after 24 weeks (p < 0.05). To examine the effect of changes in body composition, the cohort was stratified by median weight-, fat-, SAT-, and VAT-loss. The changes in all sRAGE isoforms were different between those above and below median weight-loss (p < 0.05) with sRAGE isoforms tending to decrease in individuals below the median. Changes in total sRAGE and esRAGE were different between individuals above compared to below median fat- and SAT-loss (p < 0.05). Those above median fat-loss increased esRAGE by 29 (-5, 66)pg/mL (p < 0.05).

CONCLUSION

Improvements in body composition are related to increased sRAGE isoforms, implicating sRAGE as a potential target for the treatment of obesity.

CLINICAL TRIAL REGISTRATION

NCT00960505.

Development of type 2 diabetes mellitus in people with intermediate hyperglycaemia

BACKGROUND

Intermediate hyperglycaemia (IH) is characterised by one or more measurements of elevated blood glucose concentrations, such as impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and elevated glycosylated haemoglobin A1c (HbA1c). These levels are higher than normal but below the diagnostic threshold for type 2 diabetes mellitus (T2DM). The reduced threshold of 5.6 mmol/L (100 mg/dL) fasting plasma glucose (FPG) for defining IFG, introduced by the American Diabetes Association (ADA) in 2003, substantially increased the prevalence of IFG. Likewise, the lowering of the HbA1c threshold from 6.0% to 5.7% by the ADA in 2010 could potentially have significant medical, public health and socioeconomic impacts.

OBJECTIVES

To assess the overall prognosis of people with IH for developing T2DM, regression from IH to normoglycaemia and the difference in T2DM incidence in people with IH versus people with normoglycaemia.

SEARCH METHODS

We searched MEDLINE, Embase, ClincialTrials.gov and the International Clinical Trials Registry Platform (ICTRP) Search Portal up to December 2016 and updated the MEDLINE search in February 2018. We used several complementary search methods in addition to a Boolean search based on analytical text mining.

SELECTION CRITERIA

We included prospective cohort studies investigating the development of T2DM in people with IH. We used standard definitions of IH as described by the ADA or World Health Organization (WHO). We excluded intervention trials and studies on cohorts with additional comorbidities at baseline, studies with missing data on the transition from IH to T2DM, and studies where T2DM incidence was evaluated by documents or self-report only.

DATA COLLECTION AND ANALYSIS

One review author extracted study characteristics, and a second author checked the extracted data. We used a tailored version of the Quality In Prognosis Studies (QUIPS) tool for assessing risk of bias. We pooled incidence and incidence rate ratios (IRR) using a random-effects model to account for between-study heterogeneity. To meta-analyse incidence data, we used a method for pooling proportions. For hazard ratios (HR) and odds ratios (OR) of IH versus normoglycaemia, reported with 95% confidence intervals (CI), we obtained standard errors from these CIs and performed random-effects meta-analyses using the generic inverse-variance method. We used multivariable HRs and the model with the greatest number of covariates. We evaluated the certainty of the evidence with an adapted version of the GRADE framework.

MAIN RESULTS

We included 103 prospective cohort studies. The studies mainly defined IH by IFG5.6 (FPG mmol/L 5.6 to 6.9 mmol/L or 100 mg/dL to 125 mg/dL), IFG6.1 (FPG 6.1 mmol/L to 6.9 mmol/L or 110 mg/dL to 125 mg/dL), IGT (plasma glucose 7.8 mmol/L to 11.1 mmol/L or 140 mg/dL to 199 mg/dL two hours after a 75 g glucose load on the oral glucose tolerance test, combined IFG and IGT (IFG/IGT), and elevated HbA1c (HbA1c5.7: HbA1c 5.7% to 6.4% or 39 mmol/mol to 46 mmol/mol; HbA1c6.0: HbA1c 6.0% to 6.4% or 42 mmol/mol to 46 mmol/mol). The follow-up period ranged from 1 to 24 years. Ninety-three studies evaluated the overall prognosis of people with IH measured by cumulative T2DM incidence, and 52 studies evaluated glycaemic status as a prognostic factor for T2DM by comparing a cohort with IH to a cohort with normoglycaemia. Participants were of Australian, European or North American origin in 41 studies; Latin American in 7; Asian or Middle Eastern in 50; and Islanders or American Indians in 5. Six studies included children and/or adolescents.Cumulative incidence of T2DM associated with IFG5.6, IFG6.1, IGT and the combination of IFG/IGT increased with length of follow-up. Cumulative incidence was highest with IFG/IGT, followed by IGT, IFG6.1 and IFG5.6. Limited data showed a higher T2DM incidence associated with HbA1c6.0 compared to HbA1c5.7. We rated the evidence for overall prognosis as of moderate certainty because of imprecision (wide CIs in most studies). In the 47 studies reporting restitution of normoglycaemia, regression ranged from 33% to 59% within one to five years follow-up, and from 17% to 42% for 6 to 11 years of follow-up (moderate-certainty evidence).Studies evaluating the prognostic effect of IH versus normoglycaemia reported different effect measures (HRs, IRRs and ORs). Overall, the effect measures all indicated an elevated risk of T2DM at 1 to 24 years of follow-up. Taking into account the long-term follow-up of cohort studies, estimation of HRs for time-dependent events like T2DM incidence appeared most reliable. The pooled HR and the number of studies and participants for different IH definitions as compared to normoglycaemia were: IFG5.6: HR 4.32 (95% CI 2.61 to 7.12), 8 studies, 9017 participants; IFG6.1: HR 5.47 (95% CI 3.50 to 8.54), 9 studies, 2818 participants; IGT: HR 3.61 (95% CI 2.31 to 5.64), 5 studies, 4010 participants; IFG and IGT: HR 6.90 (95% CI 4.15 to 11.45), 5 studies, 1038 participants; HbA1c5.7: HR 5.55 (95% CI 2.77 to 11.12), 4 studies, 5223 participants; HbA1c6.0: HR 10.10 (95% CI 3.59 to 28.43), 6 studies, 4532 participants. In subgroup analyses, there was no clear pattern of differences between geographic regions. We downgraded the evidence for the prognostic effect of IH versus normoglycaemia to low-certainty evidence due to study limitations because many studies did not adequately adjust for confounders. Imprecision and inconsistency required further downgrading due to wide 95% CIs and wide 95% prediction intervals (sometimes ranging from negative to positive prognostic factor to outcome associations), respectively.This evidence is up to date as of 26 February 2018.

AUTHORS' CONCLUSIONS

Overall prognosis of people with IH worsened over time. T2DM cumulative incidence generally increased over the course of follow-up but varied with IH definition. Regression from IH to normoglycaemia decreased over time but was observed even after 11 years of follow-up. The risk of developing T2DM when comparing IH with normoglycaemia at baseline varied by IH definition. Taking into consideration the uncertainty of the available evidence, as well as the fluctuating stages of normoglycaemia, IH and T2DM, which may transition from one stage to another in both directions even after years of follow-up, practitioners should be careful about the potential implications of any active intervention for people 'diagnosed' with IH.

A single high-fat meal alters human soluble RAGE profiles and PBMC RAGE expression with no effect of prior aerobic exercise

A high-fat diet can induce inflammation and metabolic diseases such as diabetes and atherosclerosis. The receptor for advanced glycation endproducts (RAGE) plays a critical role in metabolic disease pathophysiology and the soluble form of the receptor (sRAGE) can mitigate these effects. However, little is known about RAGE in the postprandial condition and the effect of exercise in this context. Thus, we aimed to determine the effects of a single high-fat meal (HFM) with and without prior exercise on peripheral blood mononuclear cell (PBMC) RAGE biology. Healthy males (n = 12) consumed a HFM on two occasions, one without prior exercise and one 16-18 hours following acute aerobic exercise. Total soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) were determined via ELISA and cleaved RAGE (cRAGE) was calculated as the difference between the two. Isolated PBMCs were analyzed for RAGE, ADAM10, TLR4, and MyD88 protein expression and ADAM10 activity. The HFM significantly (P < 0.01) attenuated sRAGE, esRAGE, and cRAGE by 9.7%, 6.9%, and 10.5%, respectively. Whereas, the HFM increased PBMC RAGE protein expression by 10.3% (P < 0.01), there was no meal effect on PBMC TLR4, MYD88, or ADAM10 protein expression, nor ADAM10 activity. There was also no exercise effect on any experimental outcomes. These findings suggest that PBMC RAGE and soluble RAGE may be important in the postprandial response to a HFM, and that prior aerobic exercise does not alter these processes in young healthy adult males. The mechanisms by which a HFM induces RAGE expression and reduces circulating soluble RAGE isoforms requires further study.

Metabolic Derangements Contribute to Reduced sRAGE Isoforms in Subjects with Alzheimer's Disease

Although there is evidence for metabolic dysfunction and chronic inflammation in Alzheimer's disease (AD), circulating levels of soluble receptor for advanced glycation end products (sRAGE) and the receptor for advanced glycation end products (RAGE) ligand S100B have not been characterized. sRAGE is an important mediator in disease as it can act as a ligand decoy for RAGE and attenuate downstream inflammatory signaling. Cognitively healthy elderly and AD participants with and without type 2 diabetes (n = 135) were stratified according to the clinical dementia rating (CDR; 0 = normal cognition (NC); ≥0.5 = AD). Total serum sRAGE, endogenous secretory RAGE (esRAGE), and S100B were assayed via ELISAs, and cleaved RAGE (cRAGE) and the cRAGE : esRAGE ratio were calculated. cRAGE : esRAGE was lower in AD compared to NC (p < 0.05). Metabolic substratifications were used to investigate the factors that influence sRAGE pathology in AD. Stratification by BMI classification, median fat mass, median HOMA-IR, median insulin, and median amylin were all metabolic or anthropometric factors which significantly interacted with sRAGE profiles within AD subjects. There were no significant differences in serum S100B between groups. These characterizations of sRAGE contribute evidence to the link between impaired metabolism and cognitive decline due to AD.