Receptor for advanced glycation end-products signals through Ras during tobacco smoke-induced pulmonary inflammation

Breath of fresh air: Investigating the link between AGEs, sRAGE, and lung diseases

Advanced glycation end products (AGEs) are compounds formed via non-enzymatic reactions between reducing sugars and amino acids or proteins. AGEs can accumulate in various tissues and organs and have been implicated in the development and progression of various diseases, including lung diseases. The receptor of advanced glycation end products (RAGE) is a receptor that can bind to advanced AGEs and induce several cellular processes such as inflammation and oxidative stress. Several studies have shown that both AGEs and RAGE play a role in the pathogenesis of lung diseases, such as chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, cystic fibrosis, and acute lung injury. Moreover, the soluble form of the receptor for advanced glycation end products (sRAGE) has demonstrated its ability to function as a decoy receptor, possessing beneficial characteristics such as anti-inflammatory, antioxidant, and anti-fibrotic properties. These qualities make it an encouraging focus for therapeutic intervention in managing pulmonary disorders. This review highlights the current understanding of the roles of AGEs and (s)RAGE in pulmonary diseases and their potential as biomarkers and therapeutic targets for preventing and treating these pathologies.

Inflammatory Cytokine Elaboration Following Secondhand Smoke (SHS) Exposure Is Mediated in Part by RAGE Signaling

The receptor for advanced glycation end products (RAGE) is a key contributor to immune and inflammatory responses in myriad diseases. RAGE is a transmembrane pattern recognition receptor with a special interest in pulmonary anomalies due to its naturally abundant pulmonary expression. Our previous studies demonstrated an inflammatory role for RAGE following acute 30-day exposure to secondhand smoke (SHS), wherein immune cell diapedesis and cytokine/chemokine secretion were accentuated in part via RAGE signaling. However, the chronic inflammatory mechanisms associated with RAGE have yet to be fully elucidated. In this study, we address the impact of long-term SHS exposure on RAGE signaling. RAGE knockout (RKO) and wild-type (WT) mice were exposed to SHS using a nose-only delivery system (Scireq Scientific, Montreal, Canada) for six months. SHS-exposed animals were compared to mice exposed to room air (RA) only. Immunoblotting was used to assess the phospho-AKT and phospho-ERK activation data, and colorimetric high-throughput assays were used to measure NF-kB. Ras activation was measured via ELISAs. Bronchoalveolar lavage fluid (BALF) cellularity was quantified, and a mouse cytokine antibody array was used to screen the secreted cytokines. The phospho-AKT level was decreased, while those of phospho-ERK, NF-kB, and Ras were elevated in both groups of SHS-exposed mice, with the RKO + SHS-exposed mice demonstrating significantly decreased levels of each intermediate compared to those of the WT + SHS-exposed mice. The BALF contained increased levels of diverse pro-inflammatory cytokines in the SHS-exposed WT mice, and diminished secretion was detected in the SHS-exposed RKO mice. These results validate the role for RAGE in the mediation of chronic pulmonary inflammatory responses and suggest ERK signaling as a likely pathway that perpetuates RAGE-dependent inflammation. Additional characterization of RAGE-mediated pulmonary responses to prolonged exposure will provide a valuable insight into the cellular mechanisms of lung diseases such as chronic obstructive pulmonary disease.

Oxidative Stress in Diabetic Peripheral Neuropathy: Pathway and Mechanism-Based Treatment

Diabetic peripheral neuropathy (DPN) is a major complication of diabetes mellitus with a high incidence. Oxidative stress, which is a crucial pathophysiological pathway of DPN, has attracted much attention. The distortion in the redox balance due to the overproduction of reactive oxygen species (ROS) and the deregulation of antioxidant defense systems promotes oxidative damage in DPN. Therefore, we have focused on the role of oxidative stress in the pathogenesis of DPN and elucidated its interaction with other physiological pathways, such as the glycolytic pathway, polyol pathway, advanced glycosylation end products, protein kinase C pathway, inflammation, and non-coding RNAs. These interactions provide novel therapeutic options targeting oxidative stress for DPN. Furthermore, our review addresses the latest therapeutic strategies targeting oxidative stress for the rehabilitation of DPN. Antioxidant supplements and exercise have been proposed as fundamental therapeutic strategies for diabetic patients through ROS-mediated mechanisms. In addition, several novel drug delivery systems can improve the bioavailability of antioxidants and the efficacy of DPN.

Paracrine Signals in Calcified Conditioned Media Elicited Differential Responses in Primary Aortic Vascular Smooth Muscle Cells and in Adventitial Fibroblasts

Our goal was to determine if paracrine signals from different aortic layers can impact other cell types in the diabetic microenvironment, specifically medial vascular smooth muscle cells (VSMCs) and adventitial fibroblasts (AFBs). The diabetic hyperglycemic aorta undergoes mineral dysregulation, causing cells to be more responsive to chemical messengers eliciting vascular calcification. Advanced glycation end-products (AGEs)/AGE receptors (RAGEs) signaling has been implicated in diabetes-mediated vascular calcification. To elucidate responses shared between cell types, pre-conditioned calcified media from diabetic and non-diabetic VSMCs and AFBs were collected to treat cultured murine diabetic, non-diabetic, diabetic RAGE knockout (RKO), and non-diabetic RKO VSMCs and AFBs. Calcium assays, western blots, and semi-quantitative cytokine/chemokine profile kits were used to determine signaling responses. VSMCs responded to non-diabetic more than diabetic AFB calcified pre-conditioned media. AFB calcification was not significantly altered when VSMC pre-conditioned media was used. No significant changes in VSMCs signaling markers due to treatments were reported; however, genotypic differences existed. Losses in AFB α-smooth muscle actin were observed with diabetic pre-conditioned VSMC media treatment. Superoxide dismutase-2 (SOD-2) increased with non-diabetic calcified + AGE pre-conditioned VSMC media, while same treatment decreased diabetic AFBs levels. Overall, non-diabetic and diabetic pre-conditioned media elicited different responses from VSMCs and AFBs.

The receptor for advanced glycation end products (RAGE) is involved in mitochondrial function and cigarette smoke-induced oxidative stress

The mechanisms underlying muscle dysfunction with Chronic Obstructive Pulmonary Disease (COPD) are poorly understood. Indirect evidence has recently suggested a role of Advanced Glycation End Products (AGEs) and their receptor (RAGE) in the pathophysiology of COPD. Accordingly, this study aimed to examine the redox balance and mitochondrial alterations in the skeletal muscle of a mouse model deficient in the receptor for AGE (RAGE-KO) and wild-type C57BL/6 exposed to cigarette smoke for 8-months using immunoblotting, spectrophotometry, and high-resolution respirometry. Cigarette smoke exposure increased by two-fold 4-HNE levels (P < 0.001), a marker of oxidative stress, and markedly downregulated contractile proteins, mitochondrial respiratory complexes, and uncoupling proteins levels (P < 0.001). Functional alterations with cigarette smoke exposure included a greater reliance on complex-I supported respiration (P < 0.01) and lower relative respiratory capacity for fatty acid (P < 0.05). RAGE knockout resulted in 47% lower 4-HNE protein levels than the corresponding WT control mice exposed to cigarette smoke (P < 0.05), which was partly attributed to increased Complex III protein levels. Independent of cigarette smoke exposure, RAGE KO decreased mitochondrial specific maximal respiration (P < 0.05), resulting in a compensatory increase in mitochondrial content measured by citrate synthase activity (P < 0.001) such that muscle respiratory capacity remained unaltered. Together, these findings suggest that knockout of RAGE protected the skeletal muscle against oxidative damage induced by 8 months of cigarette smoke exposure. In addition, this study supports a role for RAGE in regulating mitochondrial content and function and can thus serve as a potential therapeutic target.

The role of HMGB1/RAGE/TLR4 signaling pathways in cigarette smoke-induced inflammation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common chronic respiratory disease with irreversible and continuous progression. It has become the fifth most burdensome disease and the third most deadly disease globally. Therefore, the prevention and treatment of COPD are urgent, and it is also important to clarify the pathogenesis of it. Smoking is the main and most common risk factor for COPD. Cigarette smoke (CS) can cause lung inflammation and other pathological mechanisms in the airways and lung tissue. Airway inflammation is one of the important mechanisms leading to the pathogenesis of COPD. Recent studies have shown that high mobility group box 1 (HMGB1) is involved in the occurrence and development of respiratory diseases, including COPD. HMGB1 is a typical damage-associated molecular pattern (DAMP) protein, which mainly exerts its activity by binding to the receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4) and further participate in the process of airway inflammation. Studies have shown that the abnormal expression of HMGB1, RAGE, and TLR4 are related to inflammation in COPD. Herein, we discuss the roles of HMGB1, RAGE, and TLR4 in CS/cigarette smoke extract-induced inflammation in COPD, providing a new target for the diagnosis, treatment and prevention of COPD.

RAGE signaling during tobacco smoke-induced lung inflammation and potential therapeutic utility of SAGEs

BACKGROUND

Smoke exposure culminates as a progressive lung complication involving airway inflammation and remodeling. While primary smoke poses the greatest risk, nearly half of the US population is also at risk due to exposure to secondhand smoke (SHS).

METHODS

We used WT, RAGE-/- (KO), and Tet-inducible lung-specific RAGE overexpressing transgenic (TG) mice to study the role of RAGE during short-term responses to SHS. We evaluated SHS effects in mice with and without semi-synthetic glycosaminoglycan ethers (SAGEs), which are anionic, partially lipophilic sulfated polysaccharide derivatives known to inhibit RAGE signaling. TG Mice were weaned and fed doxycycline to induce RAGE at postnatal day (PN) 30. At PN40, mice from each line were exposed to room air (RA) or SHS from three Kentucky 3R4F research cigarettes via a nose-only delivery system (Scireq Scientific, Montreal, Canada) five days a week and i.p. injections of PBS or SAGE (30 mg/kg body weight) occurred three times per week from PN40-70 before mice were sacrificed on PN70.

RESULTS

RAGE mRNA and protein expression was elevated following SHS exposure of control and TG mice and not detected in RAGE KO mice. Bronchoalveolar lavage fluid (BALF) analysis revealed RAGE-mediated influence on inflammatory cell diapedesis, total protein, and pro-inflammatory mediators following exposure. Lung histological assessment revealed indistinguishable morphology following exposure, yet parenchymal apoptosis was increased. Inflammatory signaling intermediates such as Ras and NF-κB, as well as downstream responses were influenced by the availability of RAGE, as evidenced by RAGE KO and SAGE treatment.

CONCLUSIONS

These data provide fascinating insight suggesting therapeutic potential for the use of RAGE inhibitors in lungs exposed to SHS smoke.

Increased Production of Interleukin-10 and Tumor Necrosis Factor-Alpha in Stimulated Peripheral Blood Mononuclear Cells after Inhibition of S100A12

Sepsis may induce immunosuppression and result in death. S100A12 can bind to the receptor for advanced glycation end-products (RAGE) and Toll-like receptor (TLR)4 following induction of various inflammatory responses. It is unclear whether S100A12 significantly influences the immune system, which may be associated with sepsis-related mortality. We measured plasma S100A12 levels and cytokine responses (mean ± standard error mean) of lipopolysaccharide (LPS)-stimulated peripheral blood mononuclear cells (PBMCs) after S100A12 inhibition in healthy controls and patients with sepsis on days one and seven. Day one plasma soluble RAGE (sRAGE) and S100A12 levels in patients with sepsis were significantly higher than those in controls (2481.3 ± 295.0 vs. 1273.0 ± 108.2 pg/mL, p < 0.001; 530.3 ± 18.2 vs. 310.1 ± 28.1 pg/mL, p < 0.001, respectively). Day seven plasma S100A12 levels in non-survivors were significantly higher than those in survivors (593.1 ± 12.7 vs. 499.3 ± 23.8 pg/mL, p = 0.002, respectively). In survivors, plasma sRAGE levels were significantly decreased after 6 days (2297.3 ± 320.3 vs. 1530.1 ± 219.1 pg/mL, p = 0.009, respectively), but not in non-survivors. Inhibiting S100A12 increased the production of tumor necrosis factor (TNF)-α and interleukin (IL)-10 in stimulated PBMCs for both controls and patients. Therefore, S100A12 plays an important role in sepsis pathogenesis. S100A12 may competitively bind to TLR4 and RAGE, resulting in decreased IL-10 and TNF-α production.

The axis of the receptor for advanced glycation endproducts in asthma and allergic airway disease

Asthma is a generalized term that describes a scope of distinct pathologic phenotypes of variable severity, which share a common complication of reversible airflow obstruction. Asthma is estimated to affect almost 400 million people worldwide, and nearly ten percent of asthmatics have what is considered "severe" disease. The majority of moderate to severe asthmatics present with a "type 2-high" (T2-hi) phenotypic signature, which pathologically is driven by the type 2 cytokines Interleukin-(IL)-4, IL-5, and IL-13. However, "type 2-low" (T2-lo) phenotypic signatures are often associated with more severe, steroid-refractory neutrophilic asthma. A wide range of clinical and experimental studies have found that the receptor for advanced glycation endproducts (RAGE) plays a significant role in the pathogenesis of asthma and allergic airway disease (AAD). Current experimental data indicates that RAGE is a critical mediator of the type 2 inflammatory reactions which drive the development of T2-hi AAD. However, clinical studies demonstrate that increased RAGE ligands and signaling strongly correlate with asthma severity, especially in severe neutrophilic asthma. This review presents an overview of the current understandings of RAGE in asthma pathogenesis, its role as a biomarker of disease, and future implications for mechanistic studies, and potential therapeutic intervention strategies.

Exposure to second-hand cigarette smoke exacerbates the progression of osteoarthritis in a surgical induced murine model

Osteoarthritis (OA), formerly understood to be a result of passive wear, is now known to be associated with chronic inflammation. Cigarette smoking promotes systemic inflammation and has been implicated in increased joint OA incidence in some studies, though the recent observational data on the association are contradictory. We hypothesize that second-hand smoke (SHS) treatment will increase the incidence of OA in a mouse model that has been subjected to a surgical destabilization of the medial meniscus (DMM). To test this hypothesis, we applied either SHS treatment or room air (RA) to mice for 28 days post-DMM surgery. Histopathology findings indicated that the knees of SHS mice exhibited more severe OA than their control counterparts. Increased expression of matrix metalloprotease-13 (MMP-13), an important extracellular protease known to degrade articular cartilage, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), an intracellular effector of inflammatory pathways, were observed in the SHS group. These findings provide greater understanding and evidence for a detrimental role of cigarette smoke on OA progression and systemic inflammation.

Immune Resistance in Lung Adenocarcinoma

Lung cancer is the leading cancer killer worldwide, imposing grievous challenges for patients and clinicians. The incidence of lung adenocarcinoma (LUAD), the main histologic subtype of lung cancer, is still increasing in current-, ex-, and even non-smokers, whereas its five-year survival rate is approximately 15% as the vast majority of patients usually present with advanced disease at the time of diagnosis. The generation of novel drugs targeting key disease driver mutations has created optimism for the treatment of LUAD, but, as these mutations are not universal, this therapeutic line benefits only a subset of patients. More recently, the advent of targeted immunotherapies and their documented clinical efficacy in many different cancers, including LUAD, have started to change cancer management. Immunotherapies have been developed in order to overcome the cancer's ability to develop mechanisms of immune resistance, i.e., to adapt to and evade the host inflammatory and immune responses. Identifying a cancer's immune resistance mechanisms will likely advance the development of personalized immunotherapies. This review examines the key pathways of immune resistance at play in LUAD and explores therapeutic strategies which can unleash potent antitumor immune responses and significantly improve therapeutic efficacy, quality of life, and survival in LUAD.

Effects of Inhaled Tobacco Smoke on the Pulmonary Tumor Microenvironment

Tobacco smoke is a multicomponent mixture of chemical, organic, and inorganic compounds, as well as additive substances and radioactive materials. Many studies have proved the carcinogenicity of various of these compounds through the induction of DNA adducts, mutational potential, epigenetic changes, gene fusions, and chromosomal events. The tumor microenvironment plays an important role in malignant tumor formation and progression through the regulation of expression of key molecules which mediate the recruitment of immune cells to the tumor site and subsequently regulate tumor growth and metastasis. In this chapter, we discuss the effects of inhaled tobacco smoke in the tumor microenvironment of the respiratory tract. The mechanisms underlying these effects as well as their link with tumor progression are analyzed.

RAGE and AXL expression following secondhand smoke (SHS) exposure in mice

Aim and Purpose: Tobacco exposure is one of the top three global health risks leading to the development of chronic obstructive pulmonary disease (COPD). Although there is extensive research into the effects of cigarette smoke, the effect of secondhand smoke (SHS) in the lung remains limited. SHS induces receptors for advanced glycation end-products (RAGE) and an inflammatory response that leads to COPD characteristics. Semi-synthetic glycosaminoglycan ethers (SAGEs) are sulfated polysaccharides derived from hyaluronic acid that inhibit RAGE signaling. The growth arrest-specific 6 (Gas6) protein is known to induce dynamic cellular responses and is correlated with cell function. Gas6 binds to the AXL tyrosine kinase receptor and AXL-mediated signaling is implicated in proliferation and inflammation. This project's purpose was to study the correlation between RAGE, AXL, and Gas6 during SHS exposure in the lung. Methods: C57Bl/6 mice were exposed to SHS alone or SHS + SAGEs for 4 weeks and compared to control animals exposed to room air (RA). Results: Compared to controls we observed: 1) increased RAGE mRNA and protein expression in SHS-exposed lungs which was decreased by SAGEs; 2) decreased expression of total AXL, but highly elevated pAXL expression following exposure; 3) highly elevated Gas6 expression when RAGE was targeted by SAGEs during SHS exposure; 4) SHS-mediated BALF cellularity and inflammatory molecule elaboration; and 5) the induction of both RAGE and AXL by Gas6 in cell culture models. Conclusions: Our results suggest that there is a possible correlation between RAGE and AXL during SHS exposure. Additional research is critically needed that dissects the molecular interplay between these two important signaling cascades. At this point, the current studies provide insight into tobacco-mediated effects in the lung and clarify possible avenues for alleviating complications that could arise during SHS exposure such as those observed during COPD exacerbations.

Novel insights into the role of LRRC8A in ameliorating alveolar fluid clearance in LPS induced acute lung injury

Leucine-rich repeat-containing 8A (LRRC8A) protein was recently identified as an essential component of volume-regulated anion channel which plays a central role in maintaining cell volume. The aim of this study was to elucidate the role of LRRC8A in alveolar fluid clearance (AFC) and the effect of inflammatory cytokines on LRRC8A and the underlying mechanism. Lipopolysaccharide (LPS) was used to generate a rat acute lung injury model. The results showed that the concentrations of IL-1β, TNF-α and IL-6 in bronchoalveolar lavage fluid increased significantly, but the expression of LRRC8A in the lung tissue decreased dramatically in the acute lung injury group followed by a decline in the AFC rate. Additionally, LRRC8A knockdown reduced AFC in normal rats. However, specific overexpression of LRRC8A in the lung could increase AFC. Furthermore, we observed the effects of LPS, IL-1β, TNF-α and IL-6 on the LRRC8A current in alveolar type II (ATII) cells, and IL-1β showed the greatest inhibition among them, which was involved in phospho-p38 activation. Overall, LRRC8A plays an essential role in the progression of AFC in LPS-induced acute lung injury, and chronic treatment with IL-1β or TNF-α could inhibit the function of LRRC8A in ATII cells by targeting phospho-p38. All of the findings suggested that LRRC8A could be a new partner in AFC and a potential target for the treatment of acute lung injury.

Single-photon emission computed tomography/computed tomography imaging of RAGE in smoking-induced lung injury

Background

Expression of the Receptor for Advanced Glycation Endproducts (RAGE) initiates pro-inflammatory pathways resulting in lung destruction. We hypothesized that RAGE directed imaging demonstrates increased lung uptake in smoke-exposure.

Methods

After exposure to room air or to cigarette smoke for 4-weeks or 16-weeks, rabbits were injected with ^99mTc-anti-RAGE F(ab’)₂ and underwent Single-Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) imaging. Lung radiotracer uptake was calculated as percent injected dose (%ID). Lungs were dissected for gamma well counting and histological analysis.

Results

^99mTc-anti-RAGE F(ab’)₂ SPECT/CT imaging demonstrated increased lung expression of RAGE with smoke exposure compared to room air control at 4-weeks: Room air right (R) 0.75 ± 0.38%ID, left (L) 0.62 ± 0.32%ID vs. Smoke exposed R 0.17 ± 0.03, L 0.17 ± 0.02%ID (p = 0.02 and 0.028, respectively). By 16-weeks of smoke exposure, the uptake decreased to 0.19 ± 0.05%ID R and 0.17 ± 0.05%ID L, significantly lower than 4-week imaging (p = 0.0076 and 0.0129 respectively). Staining for RAGE confirmed SPECT results, with the RAGE ligand HMGB1 upregulated in the macrophages of 4-week smoke-exposed rabbits.

Conclusions

RAGE-directed imaging identified pulmonary RAGE expression acutely in vivo in an animal model of emphysema early after smoke exposure, with diminution over time. These studies document the extent and time course of RAGE expression under smoke exposure conditions and could be utilized for disease monitoring and examining response to future RAGE-targeted therapies.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1064-4) contains supplementary material, which is available to authorized users.

Receptor for advanced glycation end-products modulates lung development and lung sensitivity to hyperoxic injury in newborn mice

The receptor for advanced glycation end-products is mainly expressed in type I alveolar epithelial cells but its importance in lung development and response to neonatal hyperoxia is unclear. Therefore, our study aimed at the analysis of young wildtype and RAGE knockout mice which grew up under normoxic or hyperoxic air conditions for the first 14 days followed by a longer period of normoxic conditions. Lung histology, expression of lung-specific proteins, and respiratory mechanics were analyzed when the mice reached an age of 2 or 4 months. These analyses indicated less but larger and thicker alveoli in RAGE knockout mice, reverse differences in the mRNA and protein amount of pro-surfactant proteins (pro-SP-B, pro-SP-C) and aquaporin-5, and differences in the amount of elastin and CREB, a pro-survival transcription factor, as well as higher lung compliance. Despite this potential disadvantages, RAGE knockout lungs showed less long-term damages mediated by neonatal hyperoxia. In detail, the hyperoxia-mediated reduction in alveoli, enlargement of airspaces, fragmentation of elastic fibers, and increased lung compliance combined with reduced peak airflows was less pronounced in RAGE knockout mice. In conclusion, RAGE supports the alveolarization but makes the lung more susceptible to hyperoxic injury shortly after birth. Blocking RAGE function could still be a helpful tool in reducing hyperoxia-mediated lung pathologies during alveolarization.

RAGE is a Critical Mediator of Pulmonary Oxidative Stress, Alveolar Macrophage Activation and Emphysema in Response to Cigarette Smoke

The receptor for advanced glycation end products (RAGE), a cell membrane receptor, recognizes ligands produced by cigarette smoke (CS) and has been implicated in the pathogenesis of COPD. We demonstrate that deletion or pharmacologic inhibition of RAGE prevents development of CS-induced emphysema. To identify molecular pathways by which RAGE mediates smoking related lung injury we performed unbiased gene expression profiling of alveolar macrophages (AM) obtained from RAGE null and C57BL/6 WT mice exposed to CS for one week or four months. Pathway analysis of RNA expression identified a number of genes integral to the pathogenesis of COPD impacted by the absence of RAGE. Altered expression of antioxidant response genes and lung protein 4-HNE immunostaining suggest attenuated oxidative stress in the RAGE null mice despite comparable CS exposure and lung leukocyte burden as the WT mice. Reduced endoplasmic reticulum stress in response to CS exposure also was observed in the AM from RAGE null mice. These findings provide novel insight into the sources of oxidative stress, macrophage activation, and the pathogenesis of lung disease due to CS exposure.

The usefulness of soluble receptor for advanced glycation end-products in the identification of COPD frequent exacerbator phenotype

Introduction

Exacerbations of COPD (ECOPDs) are important events in the course of COPD, accelerating the rate of decline in lung function and increasing the mortality risk. A growing body of evidence suggests the significance of the “frequent exacerbator” phenotype. This phenotype seems to be associated with a more severe airflow limitation, symptoms, health-related quality of life impairment, and higher mortality. However, there is no described biomarker that would help to identify this group of patients.

Patients and methods

Patients with COPD in “D” GOLD category were monitored for 3 years according to events of ECOPD. Serum samples were collected from the patients. Circulating level of plasma soluble receptor for advanced glycation end-products (sRAGE) was measured using commercially available high sensitivity kits. The receiver operating characteristic (ROC) curve analysis was used to assess the usefulness of sRAGE to identify frequent exacerbator phenotype. Log-rank test was used in the analysis of time to the subsequent exacerbation. Pearson (R) or Spearman’s rank (R_S) correlation coefficients were used for correlation analysis.

Results

Nineteen patients were enrolled. The area under the ROC curve (AUROC) for sRAGE for the identification of frequent exacerbator phenotype was 0.81. Analysis identified the cutoff point as 850.407 pg/mL, characterized by a sensitivity of 0.80 (95% CI: 0.28–1.0) and specificity of 0.93 (95% CI: 0.66–1.0). Additionally, in the group with sRAGE ≤850.407 pg/mL, we observed significantly shorter time to the subsequent exacerbation: median of 32 vs 105.5 days (P=0.03). Correlation analysis revealed significant negative correlation between sRAGE and the number of exacerbations requiring hospitalization during the whole time of follow-up (R_S=−0.53; P=0.02) and significant positive correlation with FEV₁ expressed as the percentage of reference value (R=0.6; P=0.006).

Conclusion

sRAGE seems to be useful in the identification of frequent exacerbator phenotype. This parameter may also be used in the prediction of time to ECOPD. Our findings should be confirmed in a sufficiently powered larger sample.

The Interplay Between Immune Response and Bacterial Infection in COPD: Focus Upon Non-typeable Haemophilus influenzae

Chronic obstructive pulmonary disease (COPD) is a debilitating respiratory disease and one of the leading causes of morbidity and mortality worldwide. It is characterized by persistent respiratory symptoms and airflow limitation due to abnormalities in the lower airway following consistent exposure to noxious particles or gases. Acute exacerbations of COPD (AECOPD) are characterized by increased cough, purulent sputum production, and dyspnea. The AECOPD is mostly associated with infection caused by common cold viruses or bacteria, or co-infections. Chronic and persistent infection by non-typeable Haemophilus influenzae (NTHi), a Gram-negative coccobacillus, contributes to almost half of the infective exacerbations caused by bacteria. This is supported by reports that NTHi is commonly isolated in the sputum from COPD patients during exacerbations. Persistent colonization of NTHi in the lower airway requires a plethora of phenotypic adaptation and virulent mechanisms that are developed over time to cope with changing environmental pressures in the airway such as host immuno-inflammatory response. Chronic inhalation of noxious irritants in COPD causes a changed balance in the lung microbiome, abnormal inflammatory response, and an impaired airway immune system. These conditions significantly provide an opportunistic platform for NTHi colonization and infection resulting in a "vicious circle." Episodes of large inflammation as the consequences of multiple interactions between airway immune cells and NTHi, accumulatively contribute to COPD exacerbations and may result in worsening of the clinical status. In this review, we discuss in detail the interplay and crosstalk between airway immune residents and NTHi, and their effect in AECOPD for better understanding of NTHi pathogenesis in COPD patients.

Long-term endurance running activity causes pulmonary changes depending on the receptor for advanced glycation end-products

The receptor for advanced glycation end-products (RAGE) is an immunoglobulin superfamily cell adhesion molecule predominantly expressed in the lung, but its pulmonary importance is incompletely understood. Since RAGE alters the respiratory mechanics, which is also challenged by endurance running activity, we studied the RAGE-dependent effect of higher running activity on selected lung parameters in a long-term animal model using wild-type (WT) and RAGE knockout (RAGE-KO) mice. Higher long-term running activity of mice was ensured by providing a running wheel for 8 months. Recording the running activity revealed that RAGE-KO mice are more active than WT mice. RAGE-KO caused an increased lung compliance which additionally increased after long-term running activity with minor limitation of the expiratory flow, whereas the respiratory mechanics of WT mice remained constant. Although RAGE-KO mice had a less dense alveolar-capillary barrier for immune cells, higher long-term running activity led only in WT mice to more leukocyte infiltrations in the lung tissue and aggregations of lymphoid cells in the airways. In this regard, WT mice of the activity group were also more sensitive to ventilation-mediated airway damages. In contrast to RAGE-KO mice of the activity group, lungs of WT mice did not show an increase in the cAMP response element-binding protein, a transcription factor regulating many pro-survival genes. Our findings suggest an important role of RAGE in the physical capability due to its effect on the lung compliance as well as RAGE as a mediator of airway damages caused by higher long-term running activity.

Inhibition of RAGE Attenuates Cigarette Smoke-Induced Lung Epithelial Cell Damage via RAGE-Mediated Nrf2/DAMP Signaling

The oxidative stress and cellular apoptosis by environmental factor including cigarette smoke induces alveolar airway remodeling leading to chronic obstructive pulmonary disease (COPD). Recently, the receptor for advanced glycan end products (RAGE) which is highly expressed in alveolar epithelium is emerging as a biomarker for COPD susceptibility or progression. However, it still remains unknown how RAGE plays a role in cigarette smoke extract (CSE)-exposed human alveolar type II epithelial cell line. Therefore, we determined the efficacy of RAGE-specific antagonist FPS-ZM1 in response to CSE-induced lung epithelial cells. CSE induced the elevated generation of RONS and release of pro-inflammatory cytokines, and impaired the cellular antioxidant defense system. Further, CSE induced the alteration of RAGE distribution via the activation of redox-sensitive DAMP (Damage-associated molecular patterns) signaling through Nrf2 in cells. Although pre-treatment with SB202190 (p38 inhibitor) or SP600125 (JNK inhibitor) failed to recover the alteration of RAGE distribution, treatment of FPS-ZM1 significantly exhibited anti-inflammatory and anti-oxidative/nitrosative effects, also inhibited the activation of redox-sensitive DAMP signaling through Nrf2 (nuclear factor erythroid 2-related factor 2) migration in the presence of CSE. Taken together, our data demonstrate that RAGE and Nrf2 play a pivotal role in maintenance of alveolar epithelial integrity.

Tobacco Smoke Induces and Alters Immune Responses in the Lung Triggering Inflammation, Allergy, Asthma and Other Lung Diseases: A Mechanistic Review

Many studies have been undertaken to reveal how tobacco smoke skews immune responses contributing to the development of chronic obstructive pulmonary disease (COPD) and other lung diseases. Recently, environmental tobacco smoke (ETS) has been linked with asthma and allergic diseases in children. This review presents the most actual knowledge on exact molecular mechanisms responsible for the skewed inflammatory profile that aggravates inflammation, promotes infections, induces tissue damage, and may promote the development of allergy in individuals exposed to ETS. We demonstrate how the imbalance between oxidants and antioxidants resulting from exposure to tobacco smoke leads to oxidative stress, increased mucosal inflammation, and increased expression of inflammatory cytokines (such as interleukin (IL)-8, IL-6 and tumor necrosis factor α ([TNF]-α). Direct cellular effects of ETS on epithelial cells results in increased permeability, mucus overproduction, impaired mucociliary clearance, increased release of proinflammatory cytokines and chemokines, enhanced recruitment of macrophages and neutrophils and disturbed lymphocyte balance towards Th2. The plethora of presented phenomena fully justifies a restrictive policy aiming at limiting the domestic and public exposure to ETS.

COPD as an endothelial disorder: endothelial injury linking lesions in the lungs and other organs? (2017 Grover Conference Series)

Chronic obstructive pulmonary disease (COPD) is characterized by chronic expiratory airflow obstruction that is not fully reversible. COPD patients develop varying degrees of emphysema, small and large airway disease, and various co-morbidities. It has not been clear whether these co-morbidities share common underlying pathogenic processes with the pulmonary lesions. Early research into the pathogenesis of COPD focused on the contributions of injury to the extracellular matrix and pulmonary epithelial cells. More recently, cigarette smoke-induced endothelial dysfunction/injury have been linked to the pulmonary lesions in COPD (especially emphysema) and systemic co-morbidities including atherosclerosis, pulmonary hypertension, and chronic renal injury. Herein, we review the evidence linking endothelial injury to COPD, and the pathways underlying endothelial injury and the "vascular COPD phenotype" including: (1) direct toxic effects of cigarette smoke on endothelial cells; (2) generation of auto-antibodies directed against endothelial cells; (3) vascular inflammation; (4) increased oxidative stress levels in vessels inducing increases in lipid peroxidation and increased activation of the receptor for advanced glycation end-products (RAGE); (5) reduced activation of the anti-oxidant pathways in endothelial cells; (6) increased endothelial cell release of mediators with vasoconstrictor, pro-inflammatory, and remodeling activities (endothelin-1) and reduced endothelial cell expression of mediators that promote vasodilation and homeostasis of endothelial cells (nitric oxide synthase and prostacyclin); and (7) increased endoplasmic reticular stress and the unfolded protein response in endothelial cells. We also review the literature on studies of drugs that inhibit RAGE signaling in other diseases (angiotensin-converting enzyme inhibitors and angiotensin receptor blockers), or vasodilators developed for idiopathic pulmonary arterial hypertension that have been tested on cell culture systems, animal models of COPD, and/or smokers and COPD patients.

Inhibition of the receptor for advanced glycation end-products (RAGE) protects from secondhand smoke (SHS)-induced intrauterine growth restriction IUGR in mice

Intrauterine growth restriction (IUGR) is a disease affecting 10% of all pregnancies. IUGR is associated with maternal, fetal, or placental abnormalities. Studies investigating the effects of secondhand smoke (SHS) exposure and IUGR are limited. The receptor for advanced glycation end-products (RAGE) is a pro-inflammatory transmembrane receptor increased by SHS in the placenta. We tested the hypothesis that inhibition of RAGE during SHS exposure protects from smoke-induced IUGR. C57BL/6 mice were exposed to SHS or SHS + semi-synthetic glycosaminoglycan ethers (SAGEs) known to inhibit RAGE signaling. Trophoblast cells were treated with cigarette smoke extract (CSE) with or without SAGEs in order to address the effects of RAGE inhibition during trophoblast invasion in vitro. SHS-treated mice demonstrated a significant reduction in fetal weight (7.35-fold, P ≤ 0.0001) and placental weight (1.13-fold, P ≤ 0.0001) compared with controls. Mice co-treated with SHS and SAGEs were protected from SHS-induced fetal weights decreases. SHS treatment of C57BL/6 mice activated placental extracellular signal-regulated kinase (ERK) (3.0-fold, P ≤ 0.05), JNK (2.4-fold, P ≤ 0.05) and p38 (2.1-fold, P ≤ 0.05) and the expression of inflammatory mediators including TNF-α (1.34-fold, P ≤ 0.05) and IL-1β (1.03-fold, P ≤ 0.05). SHS-mediated activation of these molecules was reduced to basal levels when SAGE was co-administered. Invasion of trophoblast cells decreased 92% (P < 0.002) when treated with CSE and CSE-mediated invasion was completely reversed by SAGEs. We conclude that RAGE inhibition protects against fetal weight loss during SHS-induced IUGR. These studies provide insight into tobacco-mediated IUGR development and clarify avenues that may be helpful in the alleviation of placental complications.

Receptor for advanced glycation end-products and World Trade Center particulate induced lung function loss: A case-cohort study and murine model of acute particulate exposure

World Trade Center-particulate matter(WTC-PM) exposure and metabolic-risk are associated with WTC-Lung Injury(WTC-LI). The receptor for advanced glycation end-products (RAGE) is most highly expressed in the lung, mediates metabolic risk, and single-nucleotide polymorphisms at the AGER-locus predict forced expiratory volume(FEV). Our objectives were to test the hypotheses that RAGE is a biomarker of WTC-LI in the FDNY-cohort and that loss of RAGE in a murine model would protect against acute PM-induced lung disease. We know from previous work that early intense exposure at the time of the WTC collapse was most predictive of WTC-LI therefore we utilized a murine model of intense acute PM-exposure to determine if loss of RAGE is protective and to identify signaling/cytokine intermediates. This study builds on a continuing effort to identify serum biomarkers that predict the development of WTC-LI. A case-cohort design was used to analyze a focused cohort of male never-smokers with normal pre-9/11 lung function. Odds of developing WTC-LI increased by 1.2, 1.8 and 1.0 in firefighters with soluble RAGE (sRAGE)≥97pg/mL, CRP≥2.4mg/L, and MMP-9≤397ng/mL, respectively, assessed in a multivariate logistic regression model (ROCAUC of 0.72). Wild type(WT) and RAGE-deficient(Ager-/-) mice were exposed to PM or PBS-control by oropharyngeal aspiration. Lung function, airway hyperreactivity, bronchoalveolar lavage, histology, transcription factors and plasma/BAL cytokines were quantified. WT-PM mice had decreased FEV and compliance, and increased airway resistance and methacholine reactivity after 24-hours. Decreased IFN-γ and increased LPA were observed in WT-PM mice; similar findings have been reported for firefighters who eventually develop WTC-LI. In the murine model, lack of RAGE was protective from loss of lung function and airway hyperreactivity and was associated with modulation of MAP kinases. We conclude that in a multivariate adjusted model increased sRAGE is associated with WTC-LI. In our murine model, absence of RAGE mitigated acute deleterious effects of PM and may be a biologically plausible mediator of PM-related lung disease.

Effect of long-term maternal smoking on the offspring's lung health

Maternal smoking during pregnancy contributes to long-term health problems in offspring, especially respiratory disorders that can manifest in either childhood or adulthood. Receptors for advanced glycation end products (RAGE) are multiligand receptors abundantly localized in the lung, capable of responding to by-products of reactive oxygen species and proinflammatory responses. RAGE signaling is a key regulator of inflammation in cigarette smoking-related pulmonary diseases. However, the impact of maternal cigarette smoke exposure on lung RAGE signaling in the offspring is unclear. This study aims to investigate the effect of maternal cigarette smoke exposure (SE), as well as mitochondria-targeted antioxidant [mitoquinone mesylate (MitoQ)] treatment, during pregnancy on the RAGE-mediated signaling pathway in the lung of male offspring. Female Balb/c mice (8 wk) were divided into a sham group (exposed to air), an SE group (exposed to cigarette smoke), and an SE + MQ group (exposed to cigarette smoke with MitoQ supplement from mating). The lungs from male offspring were collected at 13 wk. RAGE and its downstream signaling, including nuclear factor-κB and mitogen-activated protein kinase family consisting of extracellular signal-regulated kinase 1, ERK2, c-JUN NH2-terminal kinase (JNK), and phosphorylated JNK, in the lung were significantly increased in the SE offspring. Mitochondrial antioxidant manganese superoxide dismutase was reduced, whereas IL-1β and oxidative stress response nuclear factor (erythroid-derived 2)-like 2 were significantly increased in the SE offspring. Maternal MitoQ treatment normalized RAGE, IL-1β, and Nrf-2 levels in the SE + MQ offspring. Maternal SE increased RAGE and its signaling elements associated with increased oxidative stress and inflammatory cytokines in offspring lungs, whereas maternal MitoQ treatment can partially normalize these changes.

Cigarette smoke extract (CSE) induces RAGE-mediated inflammation in the Ca9-22 gingival carcinoma epithelial cell line

OBJECTIVE

The oral environment is anatomically positioned as a significant gateway for exposure to environmental toxicants. Cigarette smoke exposure compromises oral health by orchestrating inflammation. The receptor for advanced glycation end-products (RAGE) has been implicated in smoke-induced inflammatory effects; however, its role in the oral cavity is unknown. The purpose of this study was to determine RAGE expression by immortalized gingival carcinoma cells and the degree to which RAGE-mediated signaling influences inflammation.

DESIGN

Gingival epithelia cells (Ca9-22) were exposed to 10% cigarette smoke extract (CSE) for six hours and screened for RAGE expression and inflammatory mediators.

RESULTS

Quantitative PCR and immunoblotting revealed increased RAGE expression following exposure. Furthermore, exposure activated RAGE signaling intermediates including Ras and NF-κB. IL-6 and IL-1β were also elevated in cell culture medium from CSE-exposed cells when compared to controls. A family of anionic, partially lipophilic sulfated polysaccharide derivatives known as semi-synthetic glycosaminoglycan ethers (SAGEs) were used in an effort to block RAGE signaling. Co-treatment of CSE and SAGEs ameliorated inflammatory responses.

CONCLUSIONS

These results provide a new perspective on a mechanism of cigarette smoke induced oral inflammation. Further work may show RAGE signaling as a potential target in the treatment of diseases of the oral cavity exacerbated by tobacco smoke exposure.

All the "RAGE" in lung disease: The receptor for advanced glycation endproducts (RAGE) is a major mediator of pulmonary inflammatory responses

The receptor for advanced glycation endproducts (RAGE) is a pro-inflammatory pattern recognition receptor (PRR) that has been implicated in the pathogenesis of numerous inflammatory diseases. It was discovered in 1992 on endothelial cells and was named for its ability to bind advanced glycation endproducts and promote vascular inflammation in the vessels of patients with diabetes. Further studies revealed that RAGE is most highly expressed in lung tissue and spurred numerous explorations into RAGE's role in the lung. These studies have found that RAGE is an important mediator in allergic airway inflammation (AAI) and asthma, pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), acute lung injury, pneumonia, cystic fibrosis, and bronchopulmonary dysplasia. RAGE has not yet been targeted in the lungs of paediatric or adult clinical populations, but the development of new ways to inhibit RAGE is setting the stage for the emergence of novel therapeutic agents for patients suffering from these pulmonary conditions.

Plausible Roles for RAGE in Conditions Exacerbated by Direct and Indirect (Secondhand) Smoke Exposure

Approximately 1 billion people smoke worldwide, and the burden placed on society by primary and secondhand smokers is expected to increase. Smoking is the leading risk factor for myriad health complications stemming from diverse pathogenic programs. First- and second-hand cigarette smoke contains thousands of constituents, including several carcinogens and cytotoxic chemicals that orchestrate chronic inflammatory responses and destructive remodeling events. In the current review, we outline details related to compromised pulmonary and systemic conditions related to smoke exposure. Specifically, data are discussed relative to impaired lung physiology, cancer mechanisms, maternal-fetal complications, cardiometabolic, and joint disorders in the context of smoke exposure exacerbations. As a general unifying mechanism, the receptor for advanced glycation end-products (RAGE) and its signaling axis is increasingly considered central to smoke-related pathogenesis. RAGE is a multi-ligand cell surface receptor whose expression increases following cigarette smoke exposure. RAGE signaling participates in the underpinning of inflammatory mechanisms mediated by requisite cytokines, chemokines, and remodeling enzymes. Understanding the biological contributions of RAGE during cigarette smoke-induced inflammation may provide critically important insight into the pathology of lung disease and systemic complications that combine during the demise of those exposed.

Blockade of RAGE ameliorates elastase-induced emphysema development and progression via RAGE-DAMP signaling

The receptor for advanced glycan end products (RAGE) has been identified as a susceptibility gene for chronic obstructive pulmonary disease (COPD) in genome-wide association studies (GWASs). However, less is known about how RAGE is involved in the pathogenesis of COPD. To determine the molecular mechanism by which RAGE influences COPD in experimental COPD models, we investigated the efficacy of the RAGE-specific antagonist FPS-ZM1 administration in in vivo and in vitro COPD models. We injected elastase intratracheally and the RAGE antagonist FPS-ZM1 in mice, and the infiltrated inflammatory cells and cytokines were assessed by ELISA. Cellular expression of RAGE was determined in protein, serum, and bronchoalveolar lavage fluid of mice and lungs and serum of human donors and patients with COPD. Downstream damage-associated molecular pattern (DAMP) pathway activation in vivo and in vitro and in patients with COPD was assessed by immunofluorescence staining, Western blot analysis, and ELISA. The expression of membrane RAGE in initiating the inflammatory response and of soluble RAGE acting as a decoy were associated with up-regulation of the DAMP-related signaling pathway via Nrf2. FPS-ZM1 administration significantly reversed emphysema in the lung of mice. Moreover, FPS-ZM1 treatment significantly reduced lung inflammation in Nrf2^+/+ , but not in Nrf2^-/- mice. Thus, our data indicate for the first time that RAGE inhibition has an essential protective role in COPD. Our observation of RAGE inhibition provided novel insight into its potential as a therapeutic target in emphysema/COPD.-Lee, H., Park, J.-R., Kim, W. J., Sundar, I. K., Rahman, I., Park, S.-M., Yang. S.-R. Blockade of RAGE ameliorates elastase-induced emphysema development and progression via RAGE-DAMP signaling.

Impacts of cigarette smoking on immune responsiveness: Up and down or upside down?

Cigarette smoking is associated with numerous diseases and poses a serious challenge to the current healthcare system worldwide. Smoking impacts both innate and adaptive immunity and plays dual roles in regulating immunity by either exacerbation of pathogenic immune responses or attenuation of defensive immunity. Adaptive immune cells affected by smoking mainly include T helper cells (Th1/Th2/Th17), CD4+CD25+ regulatory T cells, CD8+ T cells, B cells and memory T/B lymphocytes while innate immune cells impacted by smoking are mostly DCs, macrophages and NK cells. Complex roles of cigarette smoke have resulted in numerous diseases, including cardiovascular, respiratory and autoimmune diseases, allergies, cancers and transplant rejection etc. Although previous reviews have described the effects of smoking on various diseases and regional immunity associated with specific diseases, a comprehensive and updated review is rarely seen to demonstrate impacts of smoking on general immunity and, especially on major components of immune cells. Here, we aim to systematically and objectively review the influence of smoking on major components of both innate and adaptive immune cells, and summarize cellular and molecular mechanisms underlying effects of cigarette smoking on the immune system. The molecular pathways impacted by cigarette smoking involve NFκB, MAP kinases and histone modification. Further investigations are warranted to understand the exact mechanisms responsible for smoking-mediated immunopathology and to answer lingering questions over why cigarette smoking is always harmful rather than beneficial even though it exerts dual effects on immune responses.

Cigarette smoke and decreased oxygen tension inhibit pulmonary claudin-6 expression

PURPOSE

Chronic obstructive pulmonary disease is a condition involving perturbed barrier integrity coincident with both emphysema and inflammation of the airways, and smoking is considered a major risk factor. Claudins (Cldns) stabilize barriers and contribute to tight junctions by preventing paracellular transport of extracellular fluid constituents.

METHODS

To determine Cldn6 was differentially influenced by tobacco smoke, Cldn6 was evaluated in cells and tissues by q-PCR, immunoblotting, and immunohistochemistry following exposure. Cldn6 transcriptional regulation was also assessed using luciferase reporter constructs.

RESULTS

Q-PCR and immunoblotting revealed that Cldn6 was decreased in alveolar type II-like epithelial cells (A549) and primary small airway epithelial cells when exposed to cigarette smoke extract (CSE). Cldn6 was also markedly decreased in the lungs of mice exposed to acute tobacco smoke delivered by a nose-only automated smoke machine compared to controls. Luciferase reporter assays incorporating 0.5-kb, 1.0-kb, or 2.0-kb of the Cldn6 promoter revealed decreased transcription of Cldn6 following exposure to CSE. Cldn6 transcriptional regulation was also assessed in hypoxic conditions due to low oxygen tension observed during smoking. Hypoxia and hypoxia inducible factor-1 alpha caused decreased transcription of the Cldn6 gene via interactions with putative response elements in the proximal promoter sequence.

CONCLUSIONS

These data reveal that tight junctional proteins such as Cldn6 are differentially regulated by tobacco-smoke exposure and that Cldns are potentially targeted when epithelial cells respond to tobacco smoke. Further research may show that Cldns expressed in tight junctions between parenchymal cells contribute to impaired structural integrity of the lung coincident with smoking.

Targeting Inflammation in Cancer Prevention and Therapy

Inflammation is associated with the development and malignant progression of most cancers. As most of the cell types involved in cancer-associated inflammation are genetically stable and thus are not subjected to rapid emergence of drug resistance, the targeting of inflammation represents an attractive strategy both for cancer prevention and for cancer therapy. Tumor-extrinsic inflammation is caused by many factors, including bacterial and viral infections, autoimmune diseases, obesity, tobacco smoking, asbestos exposure, and excessive alcohol consumption, all of which increase cancer risk and stimulate malignant progression. In contrast, cancer-intrinsic or cancer-elicited inflammation can be triggered by cancer-initiating mutations and can contribute to malignant progression through the recruitment and activation of inflammatory cells. Both extrinsic and intrinsic inflammation can result in immunosuppression, thereby providing a preferred background for tumor development. In clinical trials, lifestyle modifications including healthy diet, exercise, alcohol, and smoking cessation have proven effective in ameliorating inflammation and reducing the risk of cancer-related deaths. In addition, consumption of certain anti-inflammatory drugs, including aspirin, can significantly reduce cancer risk, suggesting that common nonsteroidal anti-inflammatory drugs (NSAID) and more specific COX2 inhibitors can be used in cancer prevention. In addition to being examined for their preventative potential, both NSAIDs and more potent anti-inflammatory antibody-based drugs need to be tested for their ability to augment the efficacy of more conventional therapeutic approaches on the basis of tumor resection, radiation, and cytotoxic chemicals. Cancer Prev Res; 9(12); 895-905. ©2016 AACR.

Iridoids are natural glycation inhibitors

Glycation of amino acid residues in proteins leads to the eventual formation of advanced glycation end products (AGEs). AGE formation significantly influences human health and the aging process. AGE accumulation rates may be slowed by modifications to lifestyle or by pharmacological strategies. But the use of therapeutic drugs is not an appropriate means of controlling AGEs within the general population. However, phytochemical constituents in plant-based foods exhibit anti-glycation activities and may be more appropriate for general consumption. Among these phytochemicals are iridoids. The anti-AGE potential of iridoids has been demonstrated in vitro and in vivo, while also revealing possible mechanisms of action. Inclusion of iridoid food sources in the diet may be a useful component of strategies intended to mitigate AGE accumulation within the body.

Emphysema requires the receptor for advanced glycation end-products triggering on structural cells

Pulmonary emphysema is characterized by persistent inflammation and progressive alveolar destruction. The receptor for advanced glycation end-products (RAGE) is a multiligand cell surface receptor reported to be involved in the process of acute alveolar epithelial cell injury. However, studies that address the role of RAGE in pulmonary emphysema are inconclusive. We investigated the role of RAGE in the development of elastase-induced pulmonary inflammation and emphysema in mice. RAGE-sufficient (RAGE(+/+)) mice and RAGE-deficient (RAGE(-/-)) mice were treated with intratracheal elastase on Day 0. Airway inflammation, static lung compliance, lung histology, and the levels of neutrophil-related chemokine and proinflammatory cytokines in bronchoalveolar lavage fluid were determined on Days 4 and 21. Neutrophilia in bronchoalveolar lavage fluid, seen in elastase-treated RAGE(+/+) mice, was reduced in elastase-treated RAGE(-/-) mice on Day 4, and was associated with decreased levels of keratinocyte chemoattractant, macrophage inflammatory protein-2, and IL-1β. Static lung compliance values and emphysematous changes in the lung tissue were decreased in RAGE(-/-) mice compared with RAGE(+/+) mice on Day 21 after elastase treatment. Experiments using irradiated, bone marrow-chimeric mice showed that the mice expressing RAGE on radioresistant structural cells, but not hematopoietic cells, developed elastase-induced neutrophilia and emphysematous change in the lung. In contrast, mice expressing RAGE on hematopoietic cells, but not radioresistant structural cells, showed reduced neutrophilia and emphysematous change in the lung. These data identify the importance of RAGE expressed on lung structural cells in the development of elastase-induced pulmonary inflammation and emphysema. Thus, RAGE represents a novel therapeutic target for preventing pulmonary emphysema.

Circulating soluble receptor for advanced glycation end products (sRAGE) as a biomarker of emphysema and the RAGE axis in the lung

Chronic obstructive pulmonary disease (COPD) is a complex and heterogeneous disease that has been traditionally characterized by incompletely reversible airflow limitation. Yet, the latter is poorly correlated with many other clinically relevant characteristics of the disease. Thus, the identification of biomarkers to more accurately assess this heterogeneity and disease severity may facilitate the discovery and development of new treatments and better management of patients with COPD. One molecule that has attracted attention as a potentially useful biomarker specifically for the emphysema subpopulation is the soluble receptor for advanced glycation end products (sRAGE). As the soluble isoform of a key proinflammatory signaling receptor, sRAGE acts as a "decoy" for RAGE ligands and prevents their interaction with the receptor. Multiple reports have now linked sRAGE to COPD, and more specifically to emphysema, and evidence is accumulating that this link is likely mechanistic in nature. Here we review the current state of knowledge about sRAGE biology, the mechanistic links to COPD, and the evidence for using it as a biomarker for emphysema. We also discuss sRAGE as a potential target for therapeutic intervention in COPD.

Cardiomyocyte mitochondrial respiration is reduced by receptor for advanced glycation end-product signaling in a ceramide-dependent manner

Cigarette smoke exposure is associated with an increased risk of cardiovascular complications. The role of advanced glycation end products (AGEs) is already well established in numerous comorbidities, including cardiomyopathy. Given the role of AGEs and their receptor, RAGE, in activating inflammatory pathways, we sought to determine whether ceramides could be a mediator of RAGE-induced altered heart mitochondrial function. Using an in vitro model, we treated H9C2 cardiomyocytes with the AGE carboxy-methyllysine before mitochondrial respiration assessment. We discovered that mitochondrial respiration was significantly impaired in AGE-treated cells, but not when cotreated with myriocin, an inhibitor of de novo ceramide biosynthesis. Moreover, we exposed wild-type and RAGE knockout mice to secondhand cigarette smoke and found reduced mitochondrial respiration in the left ventricular myocardium from wild-type mice, but RAGE knockout mice were protected from this effect. Finally, conditional overexpression of RAGE in the lungs of transgenic mice elicited a robust increase in left ventricular ceramides in the absence of smoke exposure. Taken together, these findings suggest a RAGE-ceramide axis as an important contributor to AGE-mediated disrupted cardiomyocyte mitochondrial function.

RAGE-ligands axis: A new 'driving force' for cigarette smoke-induced airway inflammation in COPD?

Receptor for advanced glycation end products (RAGE) was recently shown to contribute to cigarette smoke (CS)-induced airway inflammation in chronic obstructive pulmonary disease (COPD). In this study, RAGE small interfering ribonucleic acid (RNA) transfection attenuated increased messenger RNA levels of common RAGE ligands HMGB1, S100A8, S100A9 and S100A12, but not S100B following exposure to CS extract. Our findings and those from recent studies suggest a positive feedback involving RAGE and its ligands as a new 'driving force' for CS-induced airway inflammation in COPD.

Update on Head and Neck Cancer: Current Knowledge on Epidemiology, Risk Factors, Molecular Features and Novel Therapies

Tobacco use and alcohol consumption are the main risk factors associated with head and neck squamous cell carcinoma (SCC) development due to their cytotoxic and mutagenic effects on the exposed epithelia of the upper aerodigestive tract. Epstein-Barr virus (EBV) and high-risk human papillomaviruses (HPVs), both encoding viral oncoproteins able to interfere with cell cycle control, have been recognized as the etiological agents of nasopharynx carcinoma and a fraction of oropharyngeal carcinoma, respectively. Head and neck SCC is a deadly disease and despite innovative treatments represents a major challenge for patients. Recently, a number of genomic studies have highlighted the molecular heterogeneity of head and neck SCC based on methylation profiles, microRNA expression, mutated genes and new druggable pathways which may represent new targets for cancer-tailored therapies. To date, cetuximab is the only FDA-approved anti-epidermal growth factor receptor therapy for the treatment of head and neck SCC. In addition, a number of monoclonal antibodies targeting AKT, mTOR and PI3K pathways are under evaluation. Several therapeutic vaccines against HPV16 and EBV proteins are also under study. The purpose of this article is to review the epidemiology, pathogenesis and molecular features of head and neck SCC, with an emphasis on new therapies.

The receptor for advanced glycation end products (RAGE) contributes to the progression of emphysema in mice

Several recent clinical studies have implied a role for the receptor for advanced glycation end products (RAGE) and its variants in chronic obstructive pulmonary disease (COPD). In this study we have defined a role for RAGE in the pathogenesis of emphysema in mice. RAGE deficient mice (RAGE-/-) exposed to chronic cigarette smoke were significantly protected from smoke induced emphysema as determined by airspace enlargement and had no significant reduction in lung tissue elastance when compared to their air exposed controls contrary to their wild type littermates. The progression of emphysema has been largely attributed to an increased inflammatory cell-mediated elastolysis. Acute cigarette smoke exposure in RAGE-/- mice revealed an impaired early recruitment of neutrophils, approximately a 6-fold decrease compared to wild type mice. Hence, impaired neutrophil recruitment with continued cigarette smoke exposure reduces elastolysis and consequent emphysema.

Effect of chronic hypoxia on RAGE and its soluble forms in lungs and plasma of mice

The receptor for advanced glycation end products (RAGE) is a multi-ligand receptor. Alternative splicing and enzymatic shedding produce soluble forms that protect against damage by ligands including Advanced Glycation End products (AGEs). A link between RAGE and oxygen levels is evident from studies showing RAGE-mediated injury following hyperoxia. The effect of hypoxia on pulmonary RAGE expression and circulating sRAGE levels is however unknown. Therefore mice were exposed to chronic hypoxia for 21 d and expression of RAGE, sheddases in lungs and circulating sRAGE were determined. In addition, accumulation of AGEs in lungs and expression of the AGE detoxifying enzyme GLO1 and receptors were evaluated. In lung tissue gene expression of total RAGE, variants 1 and 3 were elevated in mice exposed to hypoxia, whereas mRAGE and sRAGE protein levels were decreased. In the hypoxic group plasma sRAGE levels were enhanced. Although the levels of pro-ADAM10 were elevated in lungs of hypoxia exposed mice, the relative amount of the active form was decreased and gelatinase activity unaffected. In the lungs, the RAGE ligand HMGB1 was decreased and of the AGEs, only LW-1 was increased by chronic hypoxia. Gene expression of AGE receptors 2 and 3 was significantly upregulated. Chronic hypoxia is associated with downregulation of pulmonary RAGE protein levels, but a relative increase in sRAGE. These alterations might be part of the adaptive and protective response mechanism to chronic hypoxia and are not associated with AGE formation except for the fluorophore LW-1 which emerges as a novel marker of tissue hypoxia.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

Antiglycation Activity of Iridoids and Their Food Sources

Iridoids are dietary phytochemicals that may have the ability to inhibit the formation of advanced glycation end products (AGEs). Three studies were conducted to investigate this anti-AGE potential. First, the inhibition of fluorescence intensity by food-derived iridoids, after 4 days of incubation with bovine serum albumin, glucose, and fructose, was used to evaluate in vitro antiglycation activity. Next, an 8-week open-label pilot study used the AGE Reader to measure changes in the skin autofluorescence of 34 overweight adults who consumed daily a beverage containing food sources of iridoids. Finally, a cross-sectional population study with 3913 people analyzed the relationship between daily iridoid intake and AGE accumulation, as measured by skin autofluorescence with the TruAge scanner. In the in vitro test, deacetylasperulosidic acid and loganic acid both inhibited glycation in a concentration-dependent manner, with respective IC₅₀ values of 3.55 and 2.69 mM. In the pilot study, average skin autofluorescence measurements decreased by 0.12 units (P < 0.05). The cross-sectional population survey revealed that, for every mg of iridoids consumed, there is a corresponding decline in AGE associated age of 0.017 years (P < 0.0001). These results suggest that consumption of dietary sources of iridoids may be a useful antiaging strategy.

Conditionally induced RAGE expression by proximal airway epithelial cells in transgenic mice causes lung inflammation

Background

Receptors for advanced glycation end-products (RAGE) are multiligand cell-surface receptors expressed abundantly by distal pulmonary epithelium. Our lab has discovered RAGE-mediated effects in the orchestration of lung inflammation induced by tobacco smoke and environmental pollutants; however, the specific contribution of RAGE to the progression of proximal airway inflammation is still inadequately characterized.

Methods and results

We generated a Tet-inducible transgenic mouse that conditionally overexpressed RAGE using the club cell (Clara) secretory protein (CCSP) promoter expressed by club (Clara) cells localized to the proximal airway. RAGE was induced for 40 days from weaning (20 days of age) until sacrifice date at 60 days. Immunohistochemistry, immunoblotting, and qPCR revealed significant RAGE up-regulation when compared to non-transgenic controls; however, H&E staining revealed no detectible morphological abnormalities and apoptosis was not enhanced during the 40 days of augmentation. Freshly procured bronchoalveolar lavage fluid (BALF) from CCSP-RAGE TG mice had significantly more total leukocytes and PMNs compared to age-matched control littermates. Furthermore, CCSP-RAGE TG mice expressed significantly more tumor necrosis factor alpha (TNF-α), interleukin 7 (IL-7), and interleukin 14 (IL-14) in whole lung homogenates compared to controls.

Conclusions

These data support the concept that RAGE up-regulation specifically in lung airways may function in the progression of proximal airway inflammation.

Antenatal exposure of maternal secondhand smoke (SHS) increases fetal lung expression of RAGE and induces RAGE-mediated pulmonary inflammation

Background

Receptors for advanced glycation end-products (RAGE) are immunoglobulin-like pattern recognition receptors abundantly localized to lung epithelium. Our research demonstrated that primary tobacco smoke exposure increases RAGE expression and that RAGE partly mediates pro-inflammatory signaling during exposure. However, the degree to which RAGE influences developing lungs when gestating mice are exposed to secondhand smoke (SHS) has not been determined to date.

Methods

Timed pregnant RAGE null and wild type control mice were exposed to 4 consecutive days of SHS from embryonic day (E) 14.5 through E18.5 using a state of the art nose-only smoke exposure system (Scireq, Montreal, Canada). RAGE expression was assessed using immunofluorescence, immunoblotting, and quantitative RT-PCR. TUNEL immunostaining and blotting for caspase-3 were performed to evaluate effects on cell turnover. Matrix abnormalities were discerned by quantifying collagen IV and MMP-9, a matrix metalloprotease capable of degrading basement membranes. Lastly, TNF-α and IL-1β levels were assessed in order to determine inflammatory status in the developing lung.

Results

Pulmonary RAGE expression was elevated in both dams exposed to SHS and in fetuses gestating within mothers exposed to SHS. Fetal weight, a measure of organismal health, was decreased in SHS-exposed pups, but unchanged in SHS-exposed RAGE null mice. TUNEL assessments suggested a shift toward pulmonary cell apoptosis and matrix in SHS-exposed pups was diminished as revealed by decreased collagen IV and increased MMP-9 expression. Furthermore, SHS-exposed RAGE null mice expressed less TNF-α and IL-1β when compared to SHS-exposed controls.

Conclusions

RAGE augmentation in developing pups exposed to maternal SHS weakens matrix deposition and influences lung inflammation.

Acute secondhand smoke-induced pulmonary inflammation is diminished in RAGE knockout mice

The receptor for advanced glycation end-products (RAGE) has increasingly been demonstrated to be an important modulator of inflammation in cases of pulmonary disease. Published reports involving tobacco smoke exposure have demonstrated increased expression of RAGE, its participation in proinflammatory signaling, and its role in irreversible pulmonary remodeling. The current research evaluated the in vivo effects of short-term secondhand smoke (SHS) exposure in RAGE knockout and control mice compared with identical animals exposed to room air only. Quantitative PCR, immunoblotting, and immunohistochemistry revealed elevated RAGE expression in controls after 4 wk of SHS exposure and an anticipated absence of RAGE expression in RAGE knockout mice regardless of smoke exposure. Ras activation, NF-κB activity, and cytokine elaboration were assessed to characterize the molecular basis of SHS-induced inflammation in the mouse lung. Furthermore, bronchoalveolar lavage fluid was procured from RAGE knockout and control animals for the assessment of inflammatory cells and molecules. As a general theme, inflammation coincident with leukocyte recruitment was induced by SHS exposure and significantly influenced by the availability of RAGE. These data reveal captivating information suggesting a role for RAGE signaling in lungs exposed to SHS. However, ongoing research is still warranted to fully explain roles for RAGE and other receptors in cells coping with involuntary smoke exposure for prolonged periods of time.

The role of 8-oxoguanine DNA glycosylase-1 in inflammation

Many, if not all, environmental pollutants/chemicals and infectious agents increase intracellular levels of reactive oxygen species (ROS) at the site of exposure. ROS not only function as intracellular signaling entities, but also induce damage to cellular molecules including DNA. Among the several dozen ROS-induced DNA base lesions generated in the genome, 8-oxo-7,8-dihydroguanine (8-oxoG) is one of the most abundant because of guanine’s lowest redox potential among DNA bases. In mammalian cells, 8-oxoG is repaired by the 8-oxoguanine DNA glycosylase-1 (OGG1)-initiated DNA base excision repair pathway (OGG1–BER). Accumulation of 8-oxoG in DNA has traditionally been associated with mutagenesis, as well as various human diseases and aging processes, while the free 8-oxoG base in body fluids is one of the best biomarkers of ongoing pathophysiological processes. In this review, we discuss the biological significance of the 8-oxoG base and particularly the role of OGG1–BER in the activation of small GTPases and changes in gene expression, including those that regulate pro-inflammatory chemokines/cytokines and cause inflammation.

Primary alveolar macrophages exposed to diesel particulate matter increase RAGE expression and activate RAGE signaling

Receptors for advanced glycation end-products (RAGE) are members of the immunoglobulin superfamily of cell-surface receptors implicated in mechanisms of pulmonary inflammation. In the current study, we test the hypothesis that RAGE mediates inflammation in primary alveolar macrophages (AMs) exposed to diesel particulate matter (DPM). Quantitative RT-PCR and immunoblotting revealed that RAGE was up-regulated in Raw264.7 cells, an immortalized murine macrophage cell line and primary AMs exposed to DPM for 2 h. Because DPM increased RAGE expression, we exposed Raw264.7 cells and primary AMs isolated from RAGE null and wild-type (WT) mice to DPM prior to the assessment of inflammatory signaling intermediates. DPM led to the activation of Rat sarcoma GTPase (Ras), p38 MAPK and NF-κB in WT AMs and, when compared to WT AMs, these intermediates were diminished in DPM-exposed AMs isolated from RAGE null mice. Furthermore, cytokines implicated in inflammation, including IL-4, IL-12, IL-13 and TNFα, were all significantly decreased in DPM-exposed RAGE null AMs compared to similarly exposed WT AMs. These results demonstrate that diesel-induced inflammatory responses by primary AMs are mediated, at least in part, via RAGE signaling mechanisms. Further work may show that RAGE signaling in both alveolar epithelial cells and resident macrophages is a potential target in the treatment of inflammatory lung diseases exacerbated by environmental pollution.