Receptor for advanced glycation end products (RAGE) in a dash to the rescue: inflammatory signals gone awry in the primal response to stress

Aldosterone, Methylglyoxal, and Glycated Albumin Interaction with Macrophage Cells Affects Their Viability, Activation, and Differentiation

BACKGROUND

The inflammatory response in diabetes is strongly correlated with increasing amounts of advanced glycation end products (AGEs), methylglyoxal (MGO), aldosterone (Aldo), and activation of macrophages. Aldo is known to be associated with increased pro-inflammatory responses in general, but its significance in inflammatory responses under glycated circumstances has yet to be understood. In the current work, the aim of our study was to study the macrophage immune response in the presence of AGEs, MGO, and Aldo to comprehend their combined impact on diabetes-associated complications.

METHODS AND RESULTS

The viability of macrophages upon treatment with glycated HSA (Gly-HSA) promoted cell growth as the concentration increased from 100 to 500 μg/mL, whereas MGO at a high concentration (≥300 μM) significantly hampered cell growth. At lower concentrations (0.5-5 nM), Aldo strongly promoted cell growth, whereas at higher concentrations (50 nM), it was seen to inhibit growth when used for cell treatment for 24 h. Aldo had no effect on MGO-induced cell growth inhibition after 24 h of treatment. However, compared to MGO or Aldo treatment alone, an additional decrease in viability could be seen after 48 h of treatment with a combination of MGO and Aldo. Treatment with Aldo and MGO induced expression of TNF-α independently and when combined. However, when combined, Aldo and MGO significantly suppressed the expression of TGF-β. Aldo, Gly-HSA, and MGO strongly induced the transcription of NF-κB and RAGE mRNA and, as expected, also promoted the formation of reactive oxygen species. Also, by inducing iNOS and MHC-II and suppressing CD206 transcript expression, Gly-HSA strongly favored the differentiation of macrophages into M1 type (pro-inflammatory). On the other hand, the combination of Aldo and MGO strongly induced the expression of MHC-II, CD206, and ARG1 (M2 macrophage marker). These findings suggest that Gly-HSA, MGO, and Aldo differently influence macrophage survival, activation, and differentiation.

CONCLUSIONS

Overall, this study gives an insight into the effects of glycated protein and MGO in the presence of Aldo on macrophage survival, activation, differentiation, and inflammatory response.

Recombinant soluble form of receptor for advanced glycation end products ameliorates microcirculation impairment and neuroinflammation after subarachnoid hemorrhage

Impaired cerebral microcirculation after subarachnoid hemorrhage (SAH) has been shown to be related to delayed ischemic neurological deficits (DIND). We previously demonstrated the involvement of the receptor for advanced glycation end products (RAGE) in the pathogenesis of SAH related neuronal death. In the present study, we aimed to investigate the therapeutic effects of a recombinant soluble form of RAGE (sRAGE) on microcirculation impairment following SAH. Intrathecal injection of autologous blood in rats, mixed primary astrocyte and microglia cultures exposed to hemolysates and endothelial cells ​(ECs) from human brain microvascular exposed to glia-conditioned medium or SAH patient's CSF were used as experimental SAH models in vivo and in vitro. The results indicated that intrathecal administration of recombinant sRAGE significantly ameliorated the vasoconstriction of cortical arterioles and associated perfusion impairment, brain edema, reduced cell death, endothelial dysfunction, and improved motor performance at 24 and 48 ​h after SAH induction in rats. The in vitro results further showed that recombinant sRAGE significantly reduced astrocyte swelling and microglia activation, in parallel with decreased mRNA expression levels of pro-inflammatory cytokines including interleukin-6 (IL-6) and interleukin-1β (IL-1β) in vitro. Moreover, the in vitro model of SAH-induced p-eNOS and eNOS suppression, along with stress fiber formation in brain microvascular ECs, was effectively reversed by sRAGE treatment and led to a decrease in cleaved-caspase 3 expression. In summary, recombinant sRAGE effectively lessened microcirculation impairment and vascular injury after SAH via the mechanism of anti-inflammation, which may provide a potential therapeutic strategy for SAH.

The role of sRAGE in cardiovascular diseases

Advanced glycation end products (AGEs), by-products of glucose metabolism, have been linked to the emergence of cardiovascular disorders (CVD). AGEs can cause tissue damage in four different ways: (1) by altering protein function, (2) by crosslinking proteins, which makes tissue stiffer, (3) by causing the generation of free radicals, and (4) by activating an inflammatory response after binding particular AGE receptors, such as the receptor for advanced glycation end products (RAGE). It is suggested that the soluble form of RAGE (sRAGE) blocks ligand-mediated pro-inflammatory and oxidant activities by serving as a decoy. Therefore, several studies have investigated the possible anti-inflammatory and anti-oxidant characteristics of sRAGE, which may help lower the risk of CVD. According to the results of various studies, the relationship between circulating sRAGE, cRAGE, and esRAGE and CVD is inconsistent. To establish the potential function of sRAGE as a therapeutic target in the treatment of cardiovascular illnesses, additional studies are required to better understand the relationship between sRAGE and CVD. In this review, we explored the potential function of sRAGE in different CVD, highlighting unanswered concerns and outlining the possibilities for further investigation.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Integrating bulk and single-cell sequencing reveals the phenotype-associated cell subpopulations in sepsis-induced acute lung injury

The dysfunctional immune response and multiple organ injury in sepsis is a recurrent theme impacting prognosis and mortality, while the lung is the first organ invaded by sepsis. To systematically elucidate the transcriptomic changes in the main constituent cells of sepsis-injured lung tissue, we applied single-cell RNA sequencing to the lung tissue samples from septic and control mice and created a comprehensive cellular landscape with 25044 cells, including 11317 immune and 13727 non-immune cells. Sepsis alters the composition of all cellular compartments, particularly neutrophils, monocytes, T cells, endothelial, and fibroblasts populations. Our study firstly provides a single-cell view of cellular changes in septic lung injury. Furthermore, by integrating bulk sequencing data and single-cell data with the Scissors-method, we identified the cell subpopulations that are most associated with septic lung injury phenotype. The phenotypic-related cell subpopulations identified by Scissors-method were consistent with the cell subpopulations with significant composition changes. The function analysis of the differentially expressed genes (DEGs) and the cell-cell interaction analysis further reveal the important role of these phenotype-related subpopulations in septic lung injury. Our research provides a rich resource for understanding cellular changes and provides insights into the contributions of specific cell types to the biological processes that take place during sepsis-induced lung injury.

Glucose and MMP-9 dual-responsive hydrogel with temperature sensitive self-adaptive shape and controlled drug release accelerates diabetic wound healing

Chronic diabetic wounds are an important healthcare challenge. High concentration glucose, high level of matrix metalloproteinase-9 (MMP-9), and long-term inflammation constitute the special wound environment of diabetic wounds. Tissue necrosis aggravates the formation of irregular wounds. All the above factors hinder the healing of chronic diabetic wounds. To solve these issues, a glucose and MMP-9 dual-response temperature-sensitive shape self-adaptive hydrogel (CBP/GMs@Cel&INS) was designed and constructed with polyvinyl alcohol (PVA) and chitosan grafted with phenylboric acid (CS-BA) by encapsulating insulin (INS) and gelatin microspheres containing celecoxib (GMs@Cel). Temperature-sensitive self-adaptive CBP/GMs@Cel&INS provides a new way to balance the fluid-like mobility (self-adapt to deep wounds quickly, approximately 37 °C) and solid-like elasticity (protect wounds against external forces, approximately 25 °C) of self-adaptive hydrogels, while simultaneously releasing insulin and celecoxib on-demand in the environment of high-level glucose and MMP-9. Moreover, CBP/GMs@Cel&INS exhibits remodeling and self-healing properties, enhanced adhesion strength (39.65 ± 6.58 kPa), down-regulates MMP-9, and promotes cell proliferation, migration, and glucose consumption. In diabetic full-thickness skin defect models, CBP/GMs@Cel&INS significantly alleviates inflammation and regulates the local high-level glucose and MMP-9 in the wounds, and promotes wound healing effectively through the synergistic effect of temperature-sensitive shape-adaptive character and the dual-responsive system.

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The hydrogel with temperature-sensitive adaptive shape can fill irregular wounds.

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The hydrogel on-demand releases drugs responding to diabetic wound environment.

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The hydrogel significantly accelerated diabetic wound healing.

Receptor for Advanced Glycation End-Products Promotes Activation of Alveolar Macrophages through the NLRP3 Inflammasome/TXNIP Axis in Acute Lung Injury

The roles of thioredoxin-interacting protein (TXNIP) and receptor for advanced glycation end-products (RAGE)-dependent mechanisms of NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-driven macrophage activation during acute lung injury are underinvestigated. Cultured THP-1 macrophages were treated with a RAGE agonist (S100A12), with or without a RAGE antagonist; cytokine release and intracytoplasmic production of reactive oxygen species (ROS) were assessed in response to small interfering RNA knockdowns of TXNIP and NLRP3. Lung expressions of TXNIP and NLRP3 and alveolar levels of IL-1β and S100A12 were measured in mice after acid-induced lung injury, with or without administration of RAGE inhibitors. Alveolar macrophages from patients with acute respiratory distress syndrome and from mechanically ventilated controls were analyzed using fluorescence-activated cell sorting. In vitro, RAGE promoted cytokine release and ROS production in macrophages and upregulated NLRP3 and TXNIP mRNA expression in response to S100A12. TXNIP inhibition downregulated NLRP3 gene expression and RAGE-mediated release of IL-1β by macrophages in vitro. In vivo, RAGE, NLRP3 and TXNIP lung expressions were upregulated during experimental acute lung injury, a phenomenon being reversed by RAGE inhibition. The numbers of cells expressing RAGE, NLRP3 and TXNIP among a specific subpopulation of CD16+CD14+CD206- (“pro-inflammatory”) alveolar macrophages were higher in patients with lung injury. This study provides a novel proof-of-concept of complex RAGE–TXNIP–NLRP3 interactions during macrophage activation in acute lung injury.

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.

The effects of metformin monotherapy and combination of metformin and glibenclamide therapy on the expression of RAGE, Sirt1, and Nrf2 genes in peripheral blood mononuclear cells of type 2 diabetic patients

Purpose

Although metformin is the first-line treatment of type 2 diabetes mellitus (T2DM), a few studies have evaluated the benefits of monotherapies (metformin) versus combination therapy (metformin and glibenclamide) for treatment of T2DM patients. The present study aimed to evaluate the effect of monotherapy with metformin compared to combination therapy with metformin and glibenclamide on the expression of RAGE, Nrf 2, and Sirt1genes.

Methods

EightyT2DM patients and 40 healthy individuals participated in this case-control study. The patients in the treatment group were divided into two groups who received either metformin alone (n = 40) or metformin in combination with glibenclamide (n = 40). FBS, HbA1c, and fructosamine were measured. The expression of RAGE, Nrf 2, and Sirt 1 genes in PBMC of all subjects were assessed using real-time PCR.

Results

RAGE gene expression in both treatment groups was significantly lower than the control (P < 0.05). RAGE gene expression was significantly reduced in the combination of metformin and glibenclamide treated group compared to metformin group (P < 0.05). Additionally, the expression of Sirt 1 and Nrf 2 genes in both treatment groups was higher than that of the control group (P < 0.05). The expression of Sirt 1 and Nrf 2 genes in metformin and glibenclamide treated group were higher than the metformin group (P < 0.05).

Conclusion

Combination therapy (metformin and glibenclamide) showed stronger effect on repression of the RAGE gene and activation of Nrf 2 and Sirt 1 genes compared to monotherapy (metformin); therefore, it can be concluded that combination therapy may have more protective effects on the T2DM patients. No significant correlation was observed between HbA1c and RAGE, Sirt 1, and Nrf 2 genes expression.

Generation, biochemical characterizations and validation of potent nanobodies derived from alpaca specific for human receptor of advanced glycation end product

A detrimental role of the receptor for the advanced glycation end product (RAGE) has been identified in the immune response, and various pathological conditions and its V and C1 domains in the extracellular region of RAGE are believed to be the main ligand-binding domains. Consequently, specific inhibitors targeting those domains could be of clinical value in fighting against the pathological condition associated with RAGE over-activation. Single-domain antibodies, also called nanobodies (Nbs), are antibody fragments engineered from the heavy-chain only antibodies found in camelids, which offer a range of advantages in therapy. In this study, we report the development and characterization of the V-C1 domain-specific Nbs. Three Nbs (3CNB, 4BNB, and 5ENB) targeting V-C1 domain of human RAGE were isolated from an immunized alpaca using a phage display. All of these Nbs revealed high thermostability. 3CNB, 4BNB, and 5ENB bind to V-C1 domain with a dissociation constant (K_D) of 27.25, 39.37, and 47.85 nM, respectively, using Isothermal Titration Calorimetry (ITC). After homodimerization using human IgG1-Fc fusion, their binding affinity improved to 0.55, 0.62, and 0.41 nM, respectively, using Surface Plasmon Resonance (SPR). Flow cytometry showed all the Fc fusions Nbs can bind to human RAGE expressed on the cell surface. Competitive ELISA further confirmed their V-C1-hS100B blocking ability in solution, providing insights into the applicability of Nbs in treating RAGE-associated diseases.

Hemodialysis Patients with Higher Serum Levels of Soluble Receptor for Advanced Glycation End Products Have an Increased Risk for Arteriovenous Fistula Failure

BACKGROUND

Arteriovenous fistula (AVF) failure due to thrombosis is a major cause of morbidity in patients undergoing regular hemodialysis (HD). Advanced glycation end products (AGEs) and their receptor (RAGE) might contribute to inflammation, neointimal hyperplasia, and thrombosis. RAGE has a C-truncated secretory receptor form, called soluble RAGE (sRAGE). In this study, we aimed to evaluate the association of serum sRAGE with AVF failure due to thrombosis in HD patients.

METHODS

Eighty-eight prevalent HD patients with functional AVF were included in the study. The presence of stenosis, clinical and laboratory data, and serum sRAGE was evaluated at inclusion. sRAGE concentration was measured by a competitive enzyme-linked immunosorbent assay, and stenosis was detected by ultrasound. Patients were prospectively followed up for 36 months. During this period, AVF failure (defined as the absence of blast or palpable thrill and impossible cannulation with 2 needles because of complete thrombosis) was noted and thrombosis was certified by ultrasound examination.

RESULTS

During follow-up, 16 (18.18%) patients lost their vascular access due to thrombosis. In multivariate Cox regression analysis, sRAGE was a significant predictor of vascular access thrombosis (hazard ratio = 1.15, 95% confidence interval: 1.03-1.25, p = 0.012). Kaplan-Meier analysis showed a significantly lower AVF patency time in patients with sRAGE >16.78 ng/mL than those with sRAGE <16.78 ng/mL (p = 0.02). In the subgroup of patients with stenosis at baseline, sRAGE, serum albumin, obesity, and ischemic heart disease were associated with thrombosis.

CONCLUSION

In our study, baseline, systemic sRAGE is associated with the occurrence of thrombosis of AVF, and this marker has a significant impact on AVF survival.

Central Nervous System Tissue Regeneration after Intracerebral Hemorrhage: The Next Frontier

Despite marked advances in surgical techniques and understanding of secondary brain injury mechanisms, the prognosis of intracerebral hemorrhage (ICH) remains devastating. Harnessing and promoting the regenerative potential of the central nervous system may improve the outcomes of patients with hemorrhagic stroke, but approaches are still in their infancy. In this review, we discuss the regenerative phenomena occurring in animal models and human ICH, provide results related to cellular and molecular mechanisms of the repair process including by microglia, and review potential methods to promote tissue regeneration in ICH. We aim to stimulate research involving tissue restoration after ICH.

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.

Effect of the consumption of yacon flour and energy-restricted diet on glycation markers, and association between these markers and factors linked to obesity in adults with excess body weight: A randomized, double-blind, placebo-controlled clinical trial

OBJECTIVES

Regardless of the positive effect of yacon on metabolic markers, this food contains fructose molecules, which can originate advanced glycation end products (AGEs). High AGEs serum concentrations can contribute to excess body weight. We evaluated the effect of consuming an energy-restricted diet and yacon flour on glycation markers concentrations, and the associations between these markers and factors linked to obesity in adults with excess body weight.

METHODS

Twenty-six adults with excess body weight were included in this randomized, parallel, double-blind, placebo-controlled, 6-week clinical trial. Subjects were randomly allocated to the control group (n = 13) or the yacon-flour group (n = 13), and daily consumed a breakfast drink either not containing or containing 25 g of yacon flour (8.7 g of fructooligosaccharides). Energy-restricted diets were prescribed for both groups. Biochemical markers, anthropometric variables, and body composition were evaluated at baseline and the end of the study.

RESULTS

AGEs and early glycation products did not increase in the yacon flour group. Soluble receptor for AGEs (sRAGE) decreased regardless of group. Besides, changes in AGEs were positively associated with changes in body fat (β = 0.04, P = 0.038) and in sRAGE, with insulin (β = 0.02, P = 0.035) and homeostasis model assessment index of insulin resistance (β = 0.01, P = 0.049).

CONCLUSIONS

The consumption of 25 g of yacon flour associated with an energy-restricted diet did not increase concentrations of glycation markers. Changes in glycation markers were positively associated with changes in consolidated anthropometric and biochemical markers related to being overweight. Assessing glycation markers may be a useful strategy for monitoring responses to dietary interventions in subjects with excess body weight.

Role of the Receptor for Advanced Glycation End Products in Heat Stress-Induced Endothelial Hyperpermeability in Acute Lung Injury

Objective

To study the role of the receptor for advanced glycation end products (RAGE) in endothelial barrier dysfunction induced by heat stress, to further explore the signal pathway by which RAGE contributes to heat-induced endothelia response, and thereby find a novel target for the clinical treatment of ALI (acute lung injury) induced by heatstroke.

Methods

This study established the animal model of heatstroke using RAGE knockout mice. We observed the role of RAGE in acute lung injury induced by heatstroke in mice by evaluating the leukocytes, neutrophils, and protein concentration in BALF (Bronchoalveolar lavage fluids), lung wet/dry ratio, histopathological changes, and the morphological ultrastructure of lung tissue and arterial blood gas analysis. To further study the mechanism, we established a heat stress model of HUVEC and concentrated on the role of RAGE and its signal pathway in the endothelial barrier dysfunction induced by heat stress, measuring Transendothelial electrical resistance (TEER) and western blot.

Results

RAGE played a key role in acute lung injury induced by heatstroke in mice. The mechanism C-Jun is located in the promoter region of the RAGE gene. C-Jun increased the RAGE protein expression while HSF1 suppressed RAGE protein expression. The overexpressed RAGE protein then increased HUVEC monolayer permeability by activating ERK and P38 MAPK under heat stress.

Conclusion

This study indicates the critical role of RAGE in heat stress-induced endothelial hyperpermeability in acute lung injury and suggests that RAGE could be a potential therapeutic target in protecting patients against acute lung injury induced by heatstroke.

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.

MD2 activation by direct AGE interaction drives inflammatory diabetic cardiomyopathy

Hyperglycemia activates toll-like receptor 4 (TLR4) to induce inflammation in diabetic cardiomyopathy (DCM). However, the mechanisms of TLR4 activation remain unclear. Here we examine the role of myeloid differentiation 2 (MD2), a co-receptor of TLR4, in high glucose (HG)- and diabetes-induced inflammatory cardiomyopathy. We show increased MD2 in heart tissues of diabetic mice and serum of human diabetic subjects. MD2 deficiency in mice inhibits TLR4 pathway activation, which correlates with reduced myocardial remodeling and improved cardiac function. Mechanistically, we show that HG induces extracellular advanced glycation end products (AGEs), which bind directly to MD2, leading to formation of AGEs-MD2-TLR4 complex and initiation of pro-inflammatory pathways. We further detect elevated AGE-MD2 complexes in heart tissues and serum of diabetic mice and human subjects with DCM. In summary, we uncover a new mechanism of HG-induced inflammatory responses and myocardial injury, in which AGE products directly bind MD2 to drive inflammatory DCM.

The mechanisms underlying cardiac inflammation in diabetic cardiomyopathy are incompletely understood. Here the authors show that advanced glycation end products bind to the TLR4 co-receptor MD2 initiating pro-inflammatory pathways.

Liver Transplantation

The field of liver transplantation has changed since the MELD scoring system became the most widely used donor allocation tool. Due to the MELD-based allocation system, sicker patients with higher MELD scores are being transplanted. Persistent organ donor shortages remain a challenging issue, and as a result, the wait-list mortality is a persistent problem for most of the regions. This chapter focuses on deceased donor and live donor liver transplantation in patients with complications of portal hypertension. Special attention will also be placed on donor-recipient matching, perioperative management of transplant patients, and the impact of hepatic hemodynamics on transplantation.

Dynamic oligomerization of hRAGE's transmembrane and cytoplasmic domains within SDS micelles

The human Receptor for Advanced Glycation End Products (hRAGE) is a pattern recognition receptor implicated in inflammation and adhesion. It is involved in both innate and adaptive immunity. Its aberrant signaling is tied to the pathogenesis of diabetic complications, neurodegenerative disorders, and chronic inflammatory responses. Previous structural studies have focused on its extracellular domains with their canonical constant and variable Ig folds, and to a much lesser extent, the intrinsically disorder cytoplasmic domain. No experimental data are reported on the transmembrane domain, which is integral to signaling. We have constructed, expressed and purified the transmembrane domain attached to the cytoplasmic domain of hRAGE in E. coli. Multiple self-associated forms of these domains were observed in vitro. This pattern of mixed oligomers resembled previously reported in vivo forms of the complete receptor. The self-association of these two domains was further characterized using: SDS-PAGE, intrinsic tryptophan fluorescence and heteronuclear NMR spectroscopy. NMR conditions were assessed across time and temperature within micelles. Our data show that the transmembrane and cytoplasmic domains of hRAGE undergo dynamic oligomerizations that can occur in the absence of its extracellular domains or ligand binding. And, such associations are only partially disrupted even with prolonged incubation in strong detergents.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Advanced glycation end products and their receptors did not show any association with body mass parameters in metabolically healthy adolescents

AIM

We determined the relationship between circulating advanced glycation end products (AGEs), AGE receptors and homeostatic model assessment for insulin resistance (HOMA-IR) in metabolically healthy obese and normal weight adolescents.

METHODS

In 2015, we recruited 80 normal weight adolescents and 80 with obesity from schools Leon city, Mexico, and put them into metabolically healthy (HOMA-IR <3.0) and unhealthy (HOMA-IR >3.0) groups. We measured their body mass index (BMI) and carried out detailed blood analyses.

RESULTS

We found a higher triglycerides, triglycerides/high-density lipoproteins cholesterol (TG/HDL-C) index, HOMA-IR, tumour necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) in the metabolically healthy group and found correlations between HOMA-IR with BMI, the TG/HDL-C index and IL-6 and the TG/HDL-C index and BMI and (TNF-α). There was no correlation between markers of obesity and circulating N-carboxymethyl-lysine (CML) or soluble receptor for advanced glycation end products (sRAGE). Some unhealthy adolescents had higher CML (15.5 ± 2.7 U/mL, p < 0.028) and sRAGE (3123 ± 1364 pg/mL, p < 0.001) than the healthy group.

CONCLUSION

HOMA-IR and the TG/HDL-C index were associated with BMI and inflammation markers. CML and sRAGE were not associated with obesity or inflammation. These parameters were higher in unhealthy obese adolescents.

HMGB1-induced autophagy facilitates hepatic stellate cells activation: a new pathway in liver fibrosis

High-mobility group box-1 (HMGB1) plays a context-dependent role in autophagy, which is required for hepatic stellate cells (HSCs) activation. However, the significance of HMGB1-induced HSCs autophagy in liver fibrosis has not been elucidated. Here, we first documented an enrichment of peripheral and intrahepatic HMGB1 signal in hepatitis B virus (HBV)-related liver fibrosis progression, and presented a direct evidence of anatomic proximity of HMGB1 with a-SMA (a marker for HSCs activation) in cirrhotic liver specimens. Then, we demonstrated the autophagy-inducing effects by serum-sourced HMGB1 in both primary murine HSCs and human HSCs cell line (LX-2), reflected by increased number of autophagic vacuoles (AVs) under the transmission electron microscope (TEM) and up-regulated protein expression of lipidated microtubule-associated light chain 3 (LC3-II) (a marker for autophagosome) in Western blot analysis. Intriguingly, there is a possible translocation of endogenous HMGB1 from the nucleus to cytoplasm to extracellular space, during exogenous HMGB1-induced HSCs autophagy. Meanwhile, the dose- and time-dependent effects by recombinant HMGB1 (rHMGB1) in enhancing LX-2 autophagy and fibrogenesis have been revealed with activated extracellular regulated protein kinase (ERK)/c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) and restrained mammalian target of rapamycin (mTOR)/STAT3 signaling pathways. Additionally, the ERK or JNK inhibitor could not only inhibit rHMGB1-induced autophagy and fibrogenesis in LX-2 cells, but also restore the suppressed mTOR and STAT3 pathways. Furthermore, using LC3-siRNA transfected LX-2, we found HMGB1-induced fibrogenesis is dependent on its autophagy-inducing effects. Finally, we elucidated the involvement of extracellular HMGB1-receptor for advenced glycation end product (RAGE) axis and endogenous HMGB1 in exogenous HMGB1-induced effects. Our findings could open new perspectives in developing an antifibrotic therapy by targetting the HSCs autophagy.

Neuroarthropathy in diabetes: pathogenesis of Charcot arthropathy

Charcot neuroarthropathy is a rare but serious complication of diabetes, causing progressive destruction of the bones and joints of the foot leading to deformity, altered biomechanics and an increased risk of ulceration.

Management is complicated by a lack of consensus on diagnostic criteria and an incomplete understanding of the pathogenesis. In this review, we consider recent insights into the development of Charcot neuroarthropathy.

It is likely to be dependent on several interrelated factors which may include a genetic pre-disposition in combination with diabetic neuropathy. This leads to decreased neuropeptides (nitric oxide and calcitonin gene-related peptide), which may affect the normal coupling of bone formation and resorption, and increased levels of Receptor activator of nuclear factor kappa-B ligand, potentiating osteoclastogenesis.

Repetitive unrecognized trauma due to neuropathy increases levels of pro-inflammatory cytokines (interleukin-1β, interleukin-6, tumour necrosis factor α) which could also contribute to increased bone resorption, in combination with a pre-inflammatory state, with increased autoimmune reactivity and a profile of monocytes primed to transform into osteoclasts - cluster of differentiation 14 (CD14).

Increased blood glucose and loss of circulating Receptor for Advanced Glycation End-Products (AGLEPs), leading to increased non-enzymatic glycation of collagen and accumulation of AGLEPs in the tissues of the foot, may also contribute to the pathological process.

An understanding of the relative contributions of each of these mechanisms and a final common pathway for the development of Charcot neuroarthropathy are still lacking.

Cite this article: S. E. Johnson-Lynn, A. W. McCaskie, A. P. Coll, A. H. N. Robinson. Neuroarthropathy in diabetes: pathogenesis of Charcot arthropathy. Bone Joint Res 2018;7:373–378. DOI: 10.1302/2046-3758.75.BJR-2017-0334.R1.

High expression of the HMGB1-TLR4 axis and its downstream signaling factors in patients with Parkinson's disease and the relationship of pathological staging

Objective

To detect the expression of high-mobility group box protein 1 (HMGB1) and toll-like receptor 4 (TLR4) and their downstream signaling factors-myeloid differentiation factor 88 (MyD88), nuclear factor kappa B (NF-κB), and tumor necrosis factor alpha (TNF-α)-in the sera of patients with Parkinson's disease (PD) in order to evaluate the relationship of the HMGB1-TLR4 axis with PD development and progression.

Methods

The serum HMGB1 and TLR4 protein levels of 120 patients with PD and 100 healthy volunteers were measured using double-antibody sandwich ELISA, and their correlations with PD staging, disease duration, drug treatment effectiveness, and clinical classification were analyzed. In addition, their correlations with the key downstream factors of the HMGB1-TLR4 axis (MyD88, NF-κB, and TNF-α) were analyzed.

Results

HMGB1 and TLR4 expressions were higher in the peripheral blood of patients with PD than in healthy volunteers. PD patients with poor drug treatment outcomes had significantly higher HMGB1 and TLR4 expressions than PD patients with stable drug treatment outcomes. Higher HMGB1 and TLR4 expressions were found in patients at higher PD stages, and patients with >4-year disease duration had significantly higher HMGB1 and TLR4 expressions than patients with <4-year disease duration. No significant difference in HMGB1 and TLR4 expressions was found among patients with tremor-dominant, akinetic-rigid, and mixed subtypes of PD. NF-κB and TNF-α expressions were positively correlated with high expression of the HMGB1-TLR4 axis.

Conclusion

High expression of the HMGB1-TLR4 axis is closely associated with PD development, progression, drug treatment effectiveness, staging, and disease duration and has great significance for PD diagnosis and treatment.

Inhibition of GLO1 in Glioblastoma Multiforme Increases DNA-AGEs, Stimulates RAGE Expression, and Inhibits Brain Tumor Growth in Orthotopic Mouse Models

Cancers that exhibit the Warburg effect may elevate expression of glyoxylase 1 (GLO1) to detoxify the toxic glycolytic byproduct methylglyoxal (MG) and inhibit the formation of pro-apoptotic advanced glycation endproducts (AGEs). Inhibition of GLO1 in cancers that up-regulate glycolysis has been proposed as a therapeutic targeting strategy, but this approach has not been evaluated for glioblastoma multiforme (GBM), the most aggressive and difficult to treat malignancy of the brain. Elevated GLO1 expression in GBM was established in patient tumors and cell lines using bioinformatics tools and biochemical approaches. GLO1 inhibition in GBM cell lines and in an orthotopic xenograft GBM mouse model was examined using both small molecule and short hairpin RNA (shRNA) approaches. Inhibition of GLO1 with S-(p-bromobenzyl) glutathione dicyclopentyl ester (p-BrBzGSH(Cp)₂) increased levels of the DNA-AGE N²-1-(carboxyethyl)-2′-deoxyguanosine (CEdG), a surrogate biomarker for nuclear MG exposure; substantially elevated expression of the immunoglobulin-like receptor for AGEs (RAGE); and induced apoptosis in GBM cell lines. Targeting GLO1 with shRNA similarly increased CEdG levels and RAGE expression, and was cytotoxic to glioma cells. Mice bearing orthotopic GBM xenografts treated systemically with p-BrBzGSH(Cp)₂ exhibited tumor regression without significant off-target effects suggesting that GLO1 inhibition may have value in the therapeutic management of these drug-resistant tumors.

AGE-induced neuronal cell death is enhanced in G2019S LRRK2 mutation with increased RAGE expression

Background

Leucine-rich repeat kinase 2 (LRRK2) mutations represent the most common genetic cause of sporadic and familial Parkinson’s disease (PD). Especially, LRRK2 G2019S missense mutation has been identified as the most prevalent genetic cause in the late-onset PD. Advanced glycation end products (AGEs) are produced in high amounts in diabetes and diverse aging-related disorders, such as cardiovascular disease, renal disease, and neurological disease. AGEs trigger intracellular signaling pathway associated with oxidative stress and inflammation as well as cell death. RAGE, receptor of AGEs, is activated by interaction with AGEs and mediates AGE-induced cytotoxicity. Whether AGE and RAGE are involved in the pathogenesis of mutant LRRK2 is unknown.

Methods

Using cell lines transfected with mutant LRRK2 as well as primary neuronal cultures derived from LRRK2 wild-type (WT) and G2019S transgenic mice, we compared the impact of AGE treatment on the survival of control and mutant cells by immunostaining. We also examined the levels of RAGE proteins in the brains of transgenic mice and PD patients by western blots.

Results

We show that LRRK2 G2019S mutant-expressing neurons were more sensitive to AGE-induced cell death compared to controls. Furthermore, we found that the levels of RAGE proteins were upregulated in LRRK2 G2019S mutant cells.

Conclusions

These data suggest that enhanced AGE-RAGE interaction contributes to LRRK2 G2019S mutation-mediated progressive neuronal loss in PD.

The AGE-RAGE Axis: Implications for Age-Associated Arterial Diseases

The process of advanced glycation leads to the generation and accumulation of an heterogeneous class of molecules called advanced glycation endproducts, or AGEs. AGEs are produced to accelerated degrees in disorders such as diabetes, renal failure, inflammation, neurodegeneration, and in aging. Further, AGEs are present in foods and in tobacco products. Hence, through both endogenous production and exogenous consumption, AGEs perturb vascular homeostasis by a number of means; in the first case, AGEs can cause cross-linking of long-lived molecules in the basement membranes such as collagens, thereby leading to “vascular stiffening” and processes that lead to hyperpermeability and loss of structural integrity. Second, AGEs interaction with their major cell surface signal transduction receptor for AGE or RAGE sets off a cascade of events leading to modulation of gene expression and loss of vascular and tissue homeostasis, processes that contribute to cardiovascular disease. In addition, it has been shown that an enzyme, which plays key roles in the detoxification of pre-AGE species, glyoxalase 1 (GLO1), is reduced in aged and diabetic tissues. In the diabetic kidney devoid of Ager (gene encoding RAGE), higher levels of Glo1 mRNA and GLO1 protein and activity were observed, suggesting that in conditions of high AGE accumulation, natural defenses may be mitigated, at least in part through RAGE. AGEs are a marker of arterial aging and may be detected by both biochemical means, as well as measurement of “skin autofluorescence.” In this review, we will detail the pathobiology of the AGE-RAGE axis and the consequences of its activation in the vasculature and conclude with potential avenues for therapeutic interruption of the AGE-RAGE ligand-RAGE pathways as means to forestall the deleterious consequences of AGE accumulation and signaling via RAGE.

S100A8/A9 and sRAGE kinetic after polytrauma; an explorative observational study

Background

Following tissue injury after trauma, the activation of innate immune pathways results in systemic inflammation, organ failure and an increased risk of infections. The objective of this study was to characterize the kinetics of the S100A8/S100A9 complex, a new-recognized alarmin, as well as its soluble receptor sRAGE, over time after trauma as potential early biomarkers of the risk of organ damage.

Methods

We collected comprehensive data from consenting patients admitted to an ICU following severe trauma. The blood samples were taken at Day 0 (admission), Day1, 3 and 5 S100A8/A9 and sRAGE were measured by ELISA. Biomarkers levels were reported as median (IQR).

Results

Thirty-eight patients sustaining in majority a blunt trauma (89%) with a median ISS of 39 were included. In this cohort, the S100A8/A9 complex increased significantly over time (p = 0.001), but its levels increment over time (D0 to D5) was significantly smaller in patients developing infection (7.6 vs 40.1 mcg/mL, p = 0.011). The circulating level of sRAGE circulating levels decreased over time (p < 0.0001) and was higher in patients who remained in shock on day 3 (550 vs 918 pg/mL; p = 0.02) or 5 (498 vs 644 pg/mL; p = 0.045). Admission sRAGE levels were significantly higher in non-survivors (1694 vs 745 pg/mL; p = 0.015) and was higher in patients developing renal failure (1143 vs 696 pg/mL, p = 0.011).

Discussion

Our findings reveal an interesting association between the biomarker S100A8/9 least increase over time and the presence of infectious complication after trauma. We describe that the sRAGE decline over time is in relation with shock and markers of ischemic injury. We also confirm the association of sRAGE levels measured at admission with mortality and the development of renal failure.

Conclusions

This work illustrates the importance of following the circulating level of biomarker overtime. The utilization of S1008/9 as a tool to stratify infection risk and trigger early interventions need to be validated prospectively.

Evaluation of the Antioxidant and Antiglycation Effects of Lactarius deterrimus and Castanea sativa Extracts on Hepatorenal Injury in Streptozotocin-Induced Diabetic Rats

The present study aimed to investigate the beneficial effects of the treatment with extracts from the edible mushroom Lactarius deterrimus (Ld) and the chestnut Castanea sativa (Cs), separately and in combination (MIX Ld/Cs), on oxidative stress and advanced glycation end-product (AGE)-mediated hepatorenal injury in a rat model of streptozotocin (STZ)-induced diabetes by examining pathways responsible for maintenance of redox homeostasis. An experimental model of diabetes was induced in rats by the administration of 40 mg/kg STZ intraperitoneally (i.p.) for 5 consecutive days. The examined extracts were applied separately at a dose of 60 mg/kg i.p. and in combination (60 mg/kg each extract; i.p.) for 4 weeks, starting from the last day of STZ administration. The improvement of hepatorenal function in diabetic rats treated with the extracts was associated with an improved glycemic and lipid status and suppression of oxidative stress and thereby oxidative damage of lipids and DNA. Besides the fact that both extracts inhibited protein glycation and AGE formation in vitro, they also reduced non-enzymatic glycosylation in diabetic rats in vivo. The observed antiglycation activity of the examined extracts (separately and in combination) was accompanied with the inhibition of CML-mediated RAGE/NF-κB activation and reduction of enzymatic O-GlcNAcylation in liver and kidney tissues of diabetic rats. Taken together, these results reveal that the administration of chestnut and mushroom extracts, either individually or together, activates a coordinated cytoprotective response against diabetes-induced hepatorenal injury not only through recovery of the antioxidant defense system of the cell, but also through a marked antiglycation activity.

The effects of physical exercise on nonmotor symptoms and on neuroimmune RAGE network in experimental parkinsonism

Parkinson's disease (PD) prodromal stages comprise neuropsychiatric perturbations that critically compromise a patient's quality of life. These nonmotor symptoms (NMS) are associated with exacerbated innate immunity, a hallmark of overt PD. Physical exercise (PE) has the potential to improve neuropsychiatric deficits and to modulate immune network including receptor for advanced glycation end products (RAGE) and Toll-like receptors (TLRs) in distinct pathological settings. Accordingly, the present study aimed to test the hypothesis that PE 1) alleviates PD NMS and 2) modulates neuroimmune RAGE network in experimental PD. Adult Wistar rats subjected to long-term mild treadmill were administered intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and probed for PD NMS before the onset of motor abnormalities. Twelve days after MPTP, neuroimmune RAGE network transcriptomics (real-time quantitative PCR) was analyzed in frontal cortex, hippocampus, and striatum. Untrained MPTP animals displayed habit-learning and motivational deficits without gross motor impairments (cued version of water-maze, splash, and open-field tests, respectively). A suppression of RAGE and neuroimmune-related genes was observed in frontal cortex on chemical and physical stressors (untrained MPTP: RAGE, TLR5 and -7, and p22 NADPH oxidase; saline-trained animals: RAGE, TLR1 and -5 to -11, TNF-α, IL-1β, and p22 NADPH oxidase), suggesting the recruitment of compensatory mechanisms to restrain innate inflammation. Notably, trained MPTP animals displayed normal cognitive/motivational performances. Additionally, these animals showed normal RAGE expression and neuroprotective PD-related DJ-1 gene upregulation in frontal cortex when compared with untrained MPTP animals. These findings corroborate PE efficacy in improving PD NMS and newly identify RAGE network as a neural substrate for exercise intervention. Additional research is warranted to unveil functional consequences of PE-induced modulation of RAGE/DJ-1 transcriptomics in PD premotor stages.NEW & NOTEWORTHY This study newly shows that physical exercise (PE) corrects nonmotor symptoms of the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of experimental parkinsonism. Additionally, we show that suppression of neuroimmune receptor for advanced glycation end products (RAGE) network occurs in frontal cortex on chemical (MPTP) and physical (PE) interventions. Finally, PE normalizes frontal cortical RAGE transcriptomics and upregulates the neuroprotective DJ-1 gene in the intranasal MPTP model of experimental parkinsonism.

Lung adenocarcinoma expressing receptor for advanced glycation end-products with primary systemic AL amyloidosis: a case report and literature review

Background

Receptor for advanced glycation end-products (RAGE), a receptor for amyloids, is constitutively expressed in lungs and generally observed to be downregulated in lung cancer tissues. However, increasing levels of RAGE or serum amyloids is associated with poor outcome in lung cancer patients. We report a rare case of primary systemic amyloid light-chain (AL) amyloidosis in biopsy-proven multiple organs with early-stage non-small cell lung cancer (NSCLC) that displayed strong staining for RAGE in the tumour tissue. Interestingly, compared with randomly selected lung cancer biopsy samples, including all representative histological subtypes of NSCLC and small-cell lung cancer, only the NSCLC in the present case showed strong expression for RAGE that can bind amyloids.

Case presentation

A 71-year-old woman was admitted to our hospital for comprehensive investigation of nephrotic syndrome. Computed tomography showed a small nodule in the right upper lung lobe with hilar mediastinal lymph node enlargement. Pathological examination of transbronchial biopsy samples of the nodule yielded a diagnosis of lung adenocarcinoma. Furthermore, the pathological detection of amyloid deposition in biopsy samples of a subcarinal lymph node, gastric and duodenal mucosa, cardiac muscle, and bone marrow led to a diagnosis of primary systemic AL amyloidosis with nephrotic syndrome and cardiomyopathy. In addition, RAGE was detected in lung tumour tissues surrounded by normal lung tissues with amyloid deposition.

Conclusion

The RAGE positivity of the lung cancer cells in this case suggests an interaction between amyloid-containing tissues and RAGE-expressing cancer cells. Lung adenocarcinoma with RAGE expression may be a complication of underlying amyloidosis.

Regulation of striatal astrocytic receptor for advanced glycation end-products variants in an early stage of experimental Parkinson's disease

Convincing evidence indicates that advanced glycation end-products and danger-associated protein S100B play a role in Parkinson's disease (PD). These agents operate through the receptor for advanced glycation end-products (RAGE), which displays distinct isoforms playing protective/deleterious effects. However, the nature of RAGE variants has been overlooked in PD studies. Hence, we attempted to characterize RAGE regulation in early stages of PD striatal pathology. A neurotoxin-based rodent model of PD was used in this study, through administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to C57BL/6 mice. Animals were killed 6 h post-MPTP to assess S100B/RAGE contents (RT-qPCR, ELISA) and RAGE isoform density (WB) and cellular distribution (immunohistochemistry). Dopaminergic and gliotic status were also mapped (HPLC-ED, WB, immunohistochemistry). At this preliminary stage of MPTP-induced PD in mice, RAGE inhibitory isoforms were increased whereas full-length RAGE was not affected. This putative cytoprotective RAGE phenotype paired an inflammatory and pro-oxidant setting fueling DAergic denervation. Increased RAGE inhibitory variants occur in astrocytes showing higher S100B density but no overt signs of hypertrophy or NF-κB activation, a canonical effector of RAGE. These findings expand our understanding of the toxic effect of MPTP on striatum and offer first in vivo evidence of RAGE being a responder in early stages of astrogliosis dynamics, supporting a protective rather tissue-destructive phenotype of RAGE in the initial phase of PD degeneration. These data lay the groundwork for future studies on the relevance of astrocytic RAGE in DAergic neuroprotection strategies. We report increased antagonistic RAGE variants paralleling S100B up-regulation in early stages of MPTP-induced astrogliosis dynamics . We propose that selective RAGE regulation reflects a self-protective mechanism to maintain low levels of RAGE ligands , preventing long-term inflammation and oxidative stress arising from sustained ligands/flRAGE activation . Understanding loss of RAGE protective response to stress may provide new therapeutic options to halt or slow down dopaminergic axonopathy and, ultimately, neuronal death .

Enzymatically Modified Low-Density Lipoprotein Promotes Foam Cell Formation in Smooth Muscle Cells via Macropinocytosis and Enhances Receptor-Mediated Uptake of Oxidized Low-Density Lipoprotein

OBJECTIVE

Enzyme-modified nonoxidized low-density lipoprotein (ELDL) is present in human atherosclerotic lesions. Our objective is to understand the mechanisms of ELDL uptake and its effects on vascular smooth muscle cells (SMC).

APPROACH AND RESULTS

Transformation of murine aortic SMCs into foam cells in response to ELDL was analyzed. ELDL, but not acetylated or oxidized LDL, was potent in inducing SMC foam cell formation. Inhibitors of macropinocytosis (LY294002, wortmannin, amiloride) attenuated ELDL uptake. In contrast, inhibitors of receptor-mediated endocytosis (dynasore, sucrose) and inhibitor of caveolae-/lipid raft-mediated endocytosis (filipin) had no effect on ELDL uptake in SMC, suggesting that macropinocytosis is the main mechanism of ELDL uptake by SMC. Receptor for advanced glycation end products (RAGE) is not obligatory for ELDL-induced SMC foam cell formation, but primes SMC for the uptake of oxidized LDL in a RAGE-dependent manner. ELDL increased intracellular reactive oxygen species, cytosolic calcium, and expression of lectin-like oxidized LDL receptor-1 in wild-type SMC but not in RAGE(-/-) SMC. The macropinocytotic uptake of ELDL is regulated predominantly by intracellular calcium because ELDL uptake was completely inhibited by pretreatment with the calcium channel inhibitor lacidipine in wild-type and RAGE(-/-) SMC. This is in contrast to pretreatment with PI3 kinase inhibitors which completely prevented ELDL uptake in RAGE(-/-) SMC, but only partially in wild-type SMC.

CONCLUSIONS

ELDL is highly potent in inducing foam cells in murine SMC. ELDL endocytosis is mediated by calcium-dependent macropinocytosis. Priming SMC with ELDL enhances the uptake of oxidized LDL.

A Snapshot of the Plant Glycated Proteome: STRUCTURAL, FUNCTIONAL, AND MECHANISTIC ASPECTS

Glycation is the reaction of carbonyl compounds (reducing sugars and α-dicarbonyls) with amino acids, lipids, and proteins, yielding early and advanced glycation end products (AGEs). The AGEs can be formed via degradation of early glycation intermediates (glycoxidation) and by interaction with the products of monosaccharide autoxidation (autoxidative glycosylation). Although formation of these potentially deleterious compounds is well characterized in animal systems and thermally treated foods, only a little information about advanced glycation in plants is available. Thus, the knowledge of the plant AGE patterns and the underlying pathways of their formation are completely missing. To fill this gap, we describe the AGE-modified proteome ofBrassica napusand characterize individual sites of advanced glycation by the methods of liquid chromatography-based bottom-up proteomics. The modification patterns were complex but reproducible: 789 AGE-modified peptides in 772 proteins were detected in two independent experiments. In contrast, only 168 polypeptides contained early glycated lysines, which did not resemble the sites of advanced glycation. Similar observations were made withArabidopsis thaliana The absence of the early glycated precursors of the AGE-modified protein residues indicated autoxidative glycosylation, but not glycoxidation, as the major pathway of AGE formation. To prove this assumption and to identify the potential modifying agents, we estimated the reactivity and glycative potential of plant-derived sugars using a model peptide approach and liquid chromatography-mass spectrometry-based techniques. Evaluation of these data sets together with the assessed tissue carbohydrate contents revealed dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, ribulose, erythrose, and sucrose as potential precursors of plant AGEs.

Hormetic and regulatory effects of lipid peroxidation mediators in pancreatic beta cells

Nutrient sensing mechanisms of carbohydrates, amino acids and lipids operate distinct pathways that are essential for the adaptation to varying metabolic conditions. The role of nutrient-induced biosynthesis of hormones is paramount for attaining metabolic homeostasis in the organism. Nutrient overload attenuate key metabolic cellular functions and interfere with hormonal-regulated inter- and intra-organ communication, which may ultimately lead to metabolic derangements. Hyperglycemia and high levels of saturated free fatty acids induce excessive production of oxygen free radicals in tissues and cells. This phenomenon, which is accentuated in both type-1 and type-2 diabetic patients, has been associated with the development of impaired glucose tolerance and the etiology of peripheral complications. However, low levels of the same free radicals also induce hormetic responses that protect cells against deleterious effects of the same radicals. Of interest is the role of hydroxyl radicals in initiating peroxidation of polyunsaturated fatty acids (PUFA) and generation of α,β-unsaturated reactive 4-hydroxyalkenals that avidly form covalent adducts with nucleophilic moieties in proteins, phospholipids and nucleic acids. Numerous studies have linked the lipid peroxidation product 4-hydroxy-2E-nonenal (4-HNE) to different pathological and cytotoxic processes. Similarly, two other members of the family, 4-hydroxyl-2E-hexenal (4-HHE) and 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), have also been identified as potential cytotoxic agents. It has been suggested that 4-HNE-induced modifications in macromolecules in cells may alter their cellular functions and modify signaling properties. Yet, it has also been acknowledged that these bioactive aldehydes also function as signaling molecules that directly modify cell functions in a hormetic fashion to enable cells adapt to various stressful stimuli. Recent studies have shown that 4-HNE and 4-HDDE, which activate peroxisome proliferator-activated receptor δ (PPARδ) in vascular endothelial cells and insulin secreting beta cells, promote such adaptive responses to ameliorate detrimental effects of high glucose and diabetes-like conditions. In addition, due to the electrophilic nature of these reactive aldehydes they form covalent adducts with electronegative moieties in proteins, phosphatidylethanolamine and nucleotides. Normally these non-enzymatic modifications are maintained below the cytotoxic range due to efficient cellular neutralization processes of 4-hydroxyalkenals. The major neutralizing enzymes include fatty aldehyde dehydrogenase (FALDH), aldose reductase (AR) and alcohol dehydrogenase (ADH), which transform the aldehyde to the corresponding carboxylic acid or alcohols, respectively, or by biding to the thiol group in glutathione (GSH) by the action of glutathione-S-transferase (GST). This review describes the hormetic and cytotoxic roles of oxygen free radicals and 4-hydroxyalkenals in beta cells exposed to nutritional challenges and the cellular mechanisms they employ to maintain their level at functional range below the cytotoxic threshold.

The Toll of Vascular Insufficiency: Implications for the Management of Peripheral Arterial Disease

Peripheral artery disease (PAD) can result in limb loss within six months of diagnosis in a subset of patients who cannot undergo endovascular or surgical revascularization yet continues to maintain a marginal position in cardiovascular research. While a body of literature continues to grow describing the role of danger signaling and innate immunity in cardiac biology, the role of these pathways in the ischemic myopathy associated with PAD has not been extensively studied. The following report will review the current literature on the role of Toll-like receptor (TLR) signaling in cardiovascular biology as well as in nonischemic myopathy. While attenuation of TLR signaling has not been shown to be clinically useful in the treatment of infectious inflammation, it may show promise in the management of severe arterial insufficiency.

Presymptomatic MPTP Mice Show Neurotrophic S100B/mRAGE Striatal Levels

AIMS

Astrocytic S100B and receptor for advanced glycation endproducts (RAGE) have been implicated in Parkinson׳s disease (PD) pathogenesis through yet unclear mechanisms. This study attempted to characterize S100B/mRAGE (signaling isoform) axis in a dying-back dopaminergic (DAergic) axonopathy setting, which mimics an early event of PD pathology.

METHODS

C57BL/6 mice were submitted to a chronic MPTP paradigm (20 mg/kg i.p., 2 i.d-12 h apart, 5 days/week for 2 weeks) and euthanized 7 days posttreatment to assess mRAGE cellular distribution and S100B/mRAGE density in striatum, after probing their locomotor activity (pole test and rotarod). Dopaminergic status, oxidative stress, and gliosis were also measured (HPLC-ED, WB, IHC).

RESULTS

This MPTP regimen triggered increased oxidative stress (augmented HNE levels), gliosis (GS/Iba1-reactive morphology), loss of DAergic fibers (decreased tyrosine hydroxylase levels), and severe hypodopaminergia. Biochemical deficits were not translated into motor abnormalities, mimicking a presymptomatic PD period. Remarkably, striatal neurotrophic S100B/mRAGE levels and major neuronal mRAGE localization coexist with compensatory responses (3-fold increase in DA turnover), which are important to maintain normal motor function.

CONCLUSION

Our findings rule out the involvement of S100B/mRAGE axis in striatal reactive gliosis, DAergic axonopathy and warrant further exploration of its neurotrophic effects in a presymptomatic compensatory PD stage, which is a fundamental period for successful implementation of therapeutic strategies.

The Association of -429T>C and -374T>A Polymorphisms in the RAGE Gene with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a complex disorder characterized by hyperandrogenism and insulin resistance. In addition, a number of females with PCOS have ovaries with multiple cysts, an irregular or no menstrual cycle, and an imbalance of female hormones compared to those of normal controls. A variety of genetic factors have been involved in the pathogenesis of PCOS. Among these genetic factors, the receptor for advanced glycation end products (RAGE) that is associated with diabetes and involved in the complications of PCOS, was selected. We aimed to assess the relationship between -429T>C and -374T>A single nucleotide polymorphisms (SNPs) of RAGE gene with the susceptibility to PCOS.128 controls and 265 PCOS patients were used for -374T>A polymorphism and 141 controls and 290 PCOS patients were used for -429T>C polymorphism, respectively. Genotyping of two polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay and statistical analysis was performed. P values for both alleles were higher than 0.05. Frequencies of genotype and allele of two polymorphisms in RAGE gene showed no significant differences between controls and PCOS patients. The initial study on the correlation between RAGE gene and PCOS indicates that the two polymorphisms of RAGE are not associated with the pathogenesis of PCOS. However, further studies regarding the association between RAGE gene and PCOS patients in different ethnic groups are required.

The Receptor for Advanced Glycation Endproducts Does Not Contribute to Pathology in a Mouse Mesenteric Ischemia/Reperfusion-Induced Injury Model

The receptor for advanced glycation endproducts (RAGE) can engage a diverse class of ligands and contribute to the immune and inflammatory response to infection and injury. It is known to be a pathogenic receptor in many inflammatory diseases, including ischemia/reperfusion (IR) injuries in several tissues; however, its role has not been investigated in IR injuries of the intestine to date. Mesenteric (or intestinal) IR leads to recruitment of inflammatory cells into intestinal interstitial spaces, which markedly disrupts intestinal mucosa. IR-induced mucosal injury is accompanied by the development of a local and systemic inflammatory response and remote organ injury, and results in high mortality in the clinic. We hypothesized that elimination of RAGE signaling using RAGE^−/− mice would result in decreased local and remote organ injury and reduced inflammation in a mesenteric IR model, and thus be a target for therapeutic intervention. We found that RAGE ligands including HMGB-1 and C3a were elevated after mesenteric IR indicating the potential for enhanced RAGE activation in this model. However despite this, wild-type and RAGE^−/− mice both displayed similar degrees of mesenteric injury, neutrophil infiltration, intestinal edema, cytokine generation, neutrophil mobilization, and remote organ injury after mesenteric IR. We, therefore, conclude that despite its role in other organ IR injuries, and the robust production of RAGE ligands after intestinal ischemia, RAGE itself does not directly influence tissue injury and the inflammatory response in mesenteric IR.

Expression of the receptor for advanced glycation end-products and frequency of polymorphism in lung cancer

Receptor for advanced glycation end products (RAGE) is associated with the pathogenesis of cancer progression. The pathological effects mediated through RAGE are physiologically inhibited by soluble RAGE (sRAGE). The aim of the present study was to identify the expression of the sRAGE, RAGE and RAGE ligands in serum samples and lung cancer tissue obtained from lung cancer patients. Using ELISA and immunohistochemistry, it was observed that the sRAGE levels were downregulated in the serum, the expression of RAGE was decreased in the lung cancer tissue and the RAGE ligands HMGB1 and S100 were upregulated in cancer tissue. Furthermore, the presence of several selected types of RAGE polymorphism that occur in lung cancers were measured in the tissue samples. An association between the -429T/C and 2184A/G polymorphisms of RAGE and the genesis and progression of lung cancer was identified. The comparison between various histological subtypes and stages of lung cancer was performed with the aim to clarify the biological role of the RAGE gene, and identify a biomarker to aid diagnosis and predict the prognosis for lung cancer patients.

Advanced glycation end products and schizophrenia: A systematic review

Oxidative stress has become an exciting area of research on schizophrenia, which is a highly prevalent condition that affects approximately 1% of the worldwide population. Advanced glycation end products (AGEs), which are considered metabolic biomarkers of increased oxidative stress, have a pathogenic role in the development and progression of different oxidative stress-based diseases including atherosclerosis, diabetes, neurodegenerative disorders and schizophrenia. AGE formation and accumulation as well as the activation of its receptor (RAGE) can lead to signaling through several inflammatory signaling pathways and further damaging effects. This systematic review is based on a search conducted in July 2014 in which 6 studies were identified that met our criteria. In this work, we describe how recent methodological advances regarding the role of AGEs may contribute to a better understanding of the pathophysiology of schizophrenia and provide a different approach in the comprehension of the relationship between cardiovascular disease and schizophrenia. These latest findings may lead to new directions for future research on novel diagnostic and treatment strategies.

Synergistic effect of HMGB1 knockdown and cordycepin in the K562 human chronic myeloid leukemia cell line

The high-mobility group box 1 (HMGB1) protein is a DNA-binding nuclear protein, which is overexpressed in leukemia cells. Cordycepin is characterized by strong antileukemic properties and is regarded as an effective natural compound for leukemia therapy. The aim of the present study was to investigate the impact of HMGB1 knockdown and cordycepin treatment on proliferation, apoptosis, reactive oxygen species (ROS) levels and adhesion of K562 human chronic myeloid leukemia cells. The Cell Counting kit‑8 assay was used to determine the proliferation of K562 cells. The cell cycle and apoptosis of K562 cells was determined using flow cytometric analysis. In addition, a cell adhesion assay was performed. Western blotting was used to determine the protein expression of cyclooxygenase 2, Bax, receptor for advanced glycation end-products and Bcl‑2. The data collected demonstrated that HMGB1 knockdown combined with cordycepin treatment had significant anti‑proliferative and pro‑apoptotic effects. In addition, it increased the ROS levels and reduced the adhesion of K562 cells. It was also identified that HMGB1 knockdown had synergistic effects with cordycepin, which aided in accelerating apoptosis, and inhibiting proliferation and adhesion in chronic myeloid leukemia cells. These results indicated that HMGB1 may be used as a potential therapeutic target, with cordycepin having potential as an auxiliary drug. Therefore, it is suggested that HMGB1 knockdown and corycepin treatement may present a promising therapeutic strategy for leukemia.

Receptor for advanced glycation end-products regulates lung fluid balance via protein kinase C-gp91(phox) signaling to epithelial sodium channels

The receptor for advanced glycation end-products (RAGE), a multiligand member of the Ig family, may play a crucial role in the regulation of lung fluid balance. We quantified soluble RAGE (sRAGE), a decoy isoform, and advanced glycation end-products (AGEs) from the bronchoalveolar lavage fluid of smokers and nonsmokers, and tested the hypothesis that AGEs regulate lung fluid balance through protein kinase C (PKC)-gp91(phox) signaling to the epithelial sodium channel (ENaC). Human bronchoalveolar lavage samples from smokers showed increased AGEs (9.02 ± 3.03 μg versus 2.48 ± 0.53 μg), lower sRAGE (1,205 ± 292 pg/ml versus 1,910 ± 263 pg/ml), and lower volume(s) of epithelial lining fluid (97 ± 14 ml versus 133 ± 17 ml). sRAGE levels did not predict ELF volumes in nonsmokers; however, in smokers, higher volumes of ELF were predicted with higher levels of sRAGE. Single-channel patch clamp analysis of rat alveolar epithelial type 1 cells showed that AGEs increased ENaC activity measured as the product of the number of channels (N) and the open probability (Po) (NPo) from 0.19 ± 0.08 to 0.83 ± 0.22 (P = 0.017) and the subsequent addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.15 ± 0.07 (P = 0.01). In type 2 cells, human AGEs increased ENaC NPo from 0.12 ± 0.05 to 0.53 ± 0.16 (P = 0.025) and the addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.10 ± 0.03 (P = 0.013). Using molecular and biochemical techniques, we observed that inhibition of RAGE and PKC activity attenuated AGE-induced activation of ENaC. AGEs induced phosphorylation of p47(phox) and increased gp91(phox)-dependent reactive oxygen species production, a response that was abrogated with RAGE or PKC inhibition. Finally, tracheal instillation of AGEs promoted clearance of lung fluid, whereas concomitant inhibition of RAGE, PKC, and gp91(phox) abrogated the response.

Activation of the High-Mobility Group Box 1 Protein-Receptor for Advanced Glycation End-Products Signaling Pathway in Rats During Neurogenesis After Intracerebral Hemorrhage

Background and Purpose—

Following intracerebral hemorrhage (ICH), high-mobility group box 1 protein (HMGB1) may promote neurogenesis that supports functional recovery. How HMGB1 regulates or participates in this process is unclear, as are the pattern recognition receptors and signaling pathways involved.

Methods—

ICH was induced by injection of collagenase in Sprague–Dawley rats, which were treated 3 days later with saline, with the HMGB1 inhibitor ethyl pyruvate or with FPS-ZM1, an antagonist of the receptor for advanced glycation end-products. A Sham group was treated with saline solution instead of collagenase and then treated 3 days later with saline again or with ethyl pyruvate or N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1). Expression of the following proteins was measured by Western blot, immunohistochemistry, or immunofluorescence: HMGB1, receptor for advanced glycation end-products, toll-like receptor (TLR)-2, TLR4, brain-derived neurotrophic factor, and matrix metalloproteinase-9. The number of cells positive for 5-bromo-2-deoxyuridine or doublecortin was determined by immunohistochemistry and immunofluorescence.

Results—

Levels of HMGB1, receptor for advanced glycation end-products, TLR4, TLR2, brain-derived neurotrophic factor, and matrix metalloproteinase-9 were significantly higher 14 days after ICH than at baseline, as were the numbers of 5-bromo-2-deoxyuridine- or doublecortin-positive cells. At the same time, HMGB1 moved from the nucleus into the cytoplasm. Administering ethyl pyruvate significantly reduced all these ICH-induced increases, except the increase in TLR4 and TLR2. Administering FPS-ZM1 reduced the ICH-induced increases in the expression of brain-derived neurotrophic factor and matrix metalloproteinase-9 and in the numbers of 5-bromo-2-deoxyuridine- or doublecortin-positive cells.

Conclusions—

These findings suggest that HMGB1 acts via the receptor for advanced glycation end-products signaling pathway to promote neurogenesis in later phases of ICH.

Characterization of IL-22 and antimicrobial peptide production in mice protected against pulmonary Cryptococcus neoformans infection

Cryptococcus neoformans is a significant cause of fungal meningitis in patients with impaired T cell-mediated immunity (CMI). Experimental pulmonary infection with a C. neoformans strain engineered to produce IFN-γ, H99γ, results in the induction of Th1-type CMI, resolution of the acute infection, and protection against challenge with WT Cryptococcus. Given that individuals with suppressed CMI are highly susceptible to pulmonary C. neoformans infection, we sought to determine whether antimicrobial peptides were produced in mice inoculated with H99γ. Thus, we measured levels of antimicrobial peptides lipocalin-2, S100A8, S100A9, calprotectin (S100A8/A9 heterodimer), serum amyloid A-3 (SAA3), and their putative receptors Toll-like receptor 4 (TLR4) and the receptor for advanced glycation end products (RAGE) in mice during primary and recall responses against C. neoformans infection. Results showed increased levels of IL-17A and IL-22, cytokines known to modulate antimicrobial peptide production. We also observed increased levels of lipocalin-2, S100A8, S100A9 and SAA3 as well as TLR4(+) and RAGE(+) macrophages and dendritic cells in mice inoculated with H99γ compared with WT H99. Similar results were observed in the lungs of H99γ-immunized, compared with heat-killed C. neoformans-immunized, mice following challenge with WT yeast. However, IL-22-deficient mice inoculated with H99γ demonstrated antimicrobial peptide production and no change in survival rates compared with WT mice. These studies demonstrate that protection against cryptococcosis is associated with increased production of antimicrobial peptides in the lungs of protected mice that are not solely in response to IL-17A and IL-22 production and may be coincidental rather than functional.