Relationship of Soluble RAGE with Insulin Resistance and Beta Cell Function during Development of Type 2 Diabetes Mellitus

Exploring the underlying mechanisms of fisetin in the treatment of hepatic insulin resistance via network pharmacology and in vitro validation

OBJECTIVE

To characterize potential mechanisms of fisetin on hepatic insulin resistance (IR) using network pharmacology and in vitro validation.

METHODS

Putative targets of fisetin were retrieved from the Traditional Chinese Medicine Systems Pharmacology database, whereas the potential genes of hepatic IR were obtained from GeneCards database. A protein-protein interaction (PPI) network was constructed according to the intersection targets of fisetin and hepatic IR using the Venn diagram. The biological functions and potential pathways related to genes were determined using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Cell experiments were also conducted to further verify the mechanism of fisetin on hepatic IR.

RESULTS

A total of 118 potential targets from fisetin were associated with hepatic IR. The areas of nodes and corresponding degree values of TP53, AKT1, TNF, IL6, CASP3, CTNNB1, JUN, SRC, epidermal growth factor receptor (EGFR), and HSP90AA1 were larger and could be easily found in the PPI network. Furthermore, GO analysis revealed that these key targets were significantly involved in multiple biological processes that participated in oxidative stress and serine/threonine kinase activity. KEGG enrichment analysis showed that the PI3K/AKT signaling pathway was a significant pathway involved in hepatic IR. Our in vitro results demonstrated that fisetin treatment increased the expressions of EGFR and IRS in HepG2 and L02 cells under normal or IR conditions. Western blot results revealed that p-AKT/AKT levels were significantly up-regulated, suggesting that fisetin was involved in the PI3K/AKT signaling pathway to regulate insulin signaling.

CONCLUSION

We explored the pharmacological actions and the potential molecular mechanism of fisetin in treating hepatic IR from a holistic perspective. Our study lays a theoretical foundation for the development of fisetin for type 2 diabetes.

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

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

Crosstalk Between Senescent Bone Cells and the Bone Tissue Microenvironment Influences Bone Fragility During Chronological Age and in Diabetes

Bone is a complex organ serving roles in skeletal support and movement, and is a source of blood cells including adaptive and innate immune cells. Structural and functional integrity is maintained through a balance between bone synthesis and bone degradation, dependent in part on mechanical loading but also on signaling and influences of the tissue microenvironment. Bone structure and the extracellular bone milieu change with age, predisposing to osteoporosis and increased fracture risk, and this is exacerbated in patients with diabetes. Such changes can include loss of bone mineral density, deterioration in micro-architecture, as well as decreased bone flexibility, through alteration of proteinaceous bone support structures, and accumulation of senescent cells. Senescence is a state of proliferation arrest accompanied by marked morphological and metabolic changes. It is driven by cellular stress and serves an important acute tumor suppressive mechanism when followed by immune-mediated senescent cell clearance. However, aging and pathological conditions including diabetes are associated with accumulation of senescent cells that generate a pro-inflammatory and tissue-destructive secretome (the SASP). The SASP impinges on the tissue microenvironment with detrimental local and systemic consequences; senescent cells are thought to contribute to the multimorbidity associated with advanced chronological age. Here, we assess factors that promote bone fragility, in the context both of chronological aging and accelerated aging in progeroid syndromes and in diabetes, including senescence-dependent alterations in the bone tissue microenvironment, and glycation changes to the tissue microenvironment that stimulate RAGE signaling, a process that is accelerated in diabetic patients. Finally, we discuss therapeutic interventions targeting RAGE signaling and cell senescence that show promise in improving bone health in older people and those living with diabetes.

The CDKAL1 rs7747752-Bile Acids Interaction Increased Risk of Gestational Diabetes Mellitus: A Nested Case-Control Study

AIMS

The study aimed to explore additive interactions of CDKAL1 rs7747752 and GUDCA/DCA for GDM risk and whether the interactive effects on the risk of GDM was mediated via increasing lysophosphatidylcholines (LPC) 18:0 and/or saturated fatty acid (SFA) 16:0.

METHODS

A 1:1 age-matched study nested in a prospective cohort of pregnant women (207 pairs) was organized in Tianjin, China. Additive interactions were used to test interaction effects while mediation analyses and Sobel tests were used to test mediation effects of LPC18:0 and SFA16:0 between copresence of rs7747752 and low GUDCA/DCA, and GDM risk.

RESULTS

The CDKAL1 rs7747752 was associated with GDM (P<0.05). The rs7747752 C polymorphism markedly enhanced ORs of low GUDCA from 4.04 (0.72-22.8) to 9.02 (1.63-49.7) and low DCA from 1.67 (0.68-4.11) to 4.24 (1.84-9.76), both with significant additive interactions. Further adjustment for LPC18:0 attenuated the interactive effects of rs7747752 and low DCA, with a significant mediation effect (P=0.003). High SFA16:0 did not mediate the interactive effects of rs7747752 and low DCA/GUDCA on GDM risk.

CONCLUSIONS

The CDKAL1 rs7747752 C carrier status and low GUDCA/DCA had significant additive interactions on the risk of GDM with the effect from interaction with DCA being partially mediated via increasing LPC18:0.

The relationship between endogenous secretory RAGE and cardiac autonomic function in prediabetes

AIMS

The putative protective role of esRAGE for cardiac autonomic function (CAF) remains unclear. To address this question, the present study has assessed the relationship of serum AGEs, sRAGE and esRAGE, and tissue AGEs with CAF in a high-risk population without diabetes.

MATERIAL AND METHODS

This study enrolled 48 subjects of mean age 52.7 ± 11.2 years and mean BMI 28.4 ± 6.3 kg/m² , divided into two groups according to glucose tolerance: 16 with normal glucose tolerance (NGT) and 24 with prediabetes. A standard oral glucose tolerance test (OGTT) was performed. The glucose tolerance was defined according to 2006 WHO criteria. Fasting, 120-minutes glucose, lipids, creatinine, and HbA1c were measured. eGFR was calculated (CKD-EPI). Fasting, 120-minutes insulin (ECLIA method), advanced glycation end products (AGEs), plasma-soluble receptor for AGE (sRAGE), and endogenous secreted isoform of the receptor for AGE (esRAGE), (ELISA method) were assessed. HOMA-IR was calculated. Tissue AGEs were assessed by skin autofluorescence (AGE-Reader, DiagnOpticsTM). CAF was evaluated with ANX 3.0 autonomic nervous-monitoring system (ANSAR), applying deep breathing, Valsalva, and standing.

RESULTS

There was a significant decline in CAF in prediabetes in comparison with NGT. Serum and tissue AGEs, sRAGE, and esRAGE levels were similar between groups. On the matrix analysis, both sympathetic and parasympathetic activities at baseline and after standing and sympathetic tone during Valsalva were positively related to esRAGE in prediabetes. Multivariate regression analysis showed that esRAGE is an independent contributor to sympathetic, parasympathetic, and total autonomic tone in prediabetes accounting for about 28%, 34%, and 35% of their variances, respectively.

CONCLUSION

Our results have demonstrated that CAF is decreased in prediabetes. esRAGE, but not sRAGE, is reciprocally related to CAF, probably opposing the negative effects of glycation.

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

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

Methylglyoxal and soluble RAGE in type 2 diabetes mellitus: Association with oxidative stress

Purpose

Methylglyoxal (MGO) and MGO related advance end product (AGE) are thought to contribute to the development of diabetes and its complications. The present study was intended to determine plasma MGO and sRAGE levels in T2DM patients and to assess the relationship between MGO and other parameters, such as sRAGE and oxidative markers.

Methods

The study was carried out in 100 control and T2DM subjects. Methylglyoxal, sRAGE, HbA1c, and other markers were measured by using a standard protocol and the relationship between variables was analyzed using Spearman's correlation analysis.

Results

Plasma MGO levels in patients with T2DM (221.1 ± 9.50 ng/mL) were significantly higher than in control subjects (121.1 ± 6.52 ng/mL, P < 0.001). The plasma level of MGO was positively correlated with glycosylated hemoglobin (HbA1c, r = 0.50, P < 0.001). Plasma soluble form of RAGE (sRAGE) was significantly decreased in T2DM subjects (5.3 ± 0.64 ng/mL) as compared to the control group (7.7 ± 0.86 ng/mL, p < 0.05). However, at increased level of glycation (HbA1c > 10%), the sRAGE level was 6.2 ± 0.42 ng/mL and was not statistically significant as compared to control healthy group (> 0.05). Moreover, we have not found any correlation between MGO and other markers (p > 0.05).

Conclusions

The findings of the present study showed that increased plasma MGO level is significantly associated with the HbA1c levels in T2DM patients. Moreover, the study shows that plasma sRAGE level is significantly augmented at increased level of glycation (HbA1c > 10%) in T2DM patients.

RAGE is a Potential Cause of Onset and Progression of Nonalcoholic Fatty Liver Disease

OBJECTIVE

Fatty liver is a rising global health concern, significantly increasing the burden of health care cost. Nonalcoholic fatty liver disease (NAFLD) has a correlation with metabolic syndrome and its complications.

METHOD

We reviewed the literature regarding the mechanisms of developing NAFLD through AGE-RAGE signaling.

RESULTS

NAFLD, metabolic syndrome, and production of advanced glycation end-products (AGEs) share many common risk factors and appear to be connected. AGE induces production of the receptor for AGE (RAGE). AGE-RAGE interaction contributes to fat accumulation in the liver leading to inflammation, fibrosis, insulin resistance, and other complications of the fatty liver disease. The immune system, especially macrophages, has an important defense mechanism against RAGE pathway activities.

CONCLUSION

Soluble form of RAGE (sRAGE) has the capability to reduce inflammation by blocking the interaction of AGE with RAGE. However, sRAGE has some limitations, and the best method of usage is probably autotransplantation of transfected stem cells or monocytes, as a precursor of macrophages and Kupffer cells, with a virus that carries sRAGE to alleviate the harmful effects of AGE-RAGE signaling in the settings of fatty liver disease.

Serum levels of advanced glycation end-products (AGEs) and the decoy soluble receptor for AGEs (sRAGE) can identify non-alcoholic fatty liver disease in age-, sex- and BMI-matched normo-glycemic adults

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a serious health problem affecting ~25% of the global population. While NAFLD pathogenesis is still unclear, multiple NAFLD parameters, including reduced insulin sensitivity, impaired glucose metabolism and increased oxidative stress are hypothesised to foster the formation of advanced glycation end-products (AGEs). Given the link of AGEs with end organ damage, there is scope to examine the role of the AGE/RAGE axis activation in liver injury and NAFLD.

METHODS

Age, sex and body mass index matched normo-glycemic NAFLD adults (n = 58) and healthy controls (n = 58) were enrolled in the study. AGEs were analysed by liquid chromatography-mass spectrometry (CML, CEL), fluorescence (pentosidine, AGE fluorescence), colorimetry (fructosamine) and ELISA (sRAGE). Their association with liver function, inflammation, fibrosis and stage of NAFLD was examined.

RESULTS

Early and advanced glycation end-products, except N^ε-carboxymethyl-L-lysine (CML), were 10-30% higher, sRAGE levels 1.7-fold lower, and glycation/sRAGE ratios 4-fold higher in the NAFLD cases compared to controls. While AGEs presented weak to moderate correlations with indices of liver function and damage (AST/ALT, HOMA-IR, TNF-α and TGF-β1), including sRAGE to characterize the AGEs/sRAGE axis strengthened the associations observed. High glycation/sRAGE ratios were associated with 1.3 to 14-fold likelihood of lower AST/ALT ratios. The sum of AGEs/sRAGE ratios accurately distinguished between healthy controls and NAFLD patients (area under the curve of 0.85). Elevated AGEs/sRAGE (>7.8 mmol/pmol) was associated with a 12-fold likelihood of the presence of NAFLD.

CONCLUSION

These findings strengthen the involvement of AGEs-RAGE axis in liver injury and the pathogenesis of NAFLD.

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

The soluble receptor for advanced glycation end products (sRAGE) may be protective against inflammation associated with obesity and type 2 diabetes (T2DM). The aim of this study was to determine the distribution of sRAGE isoforms and whether sRAGE isoforms are associated with risk of T2DM development in subjects spanning the glucose tolerance continuum. In this retrospective analysis, circulating total sRAGE and endogenous secretory RAGE (esRAGE) were quantified via ELISA, and cleaved RAGE (cRAGE) was calculated in 274 individuals stratified by glucose tolerance status (GTS) and obesity. Group differences were probed by ANOVA, and multivariate ordinal logistic regression was used to test the association between sRAGE isoform concentrations and the proportional odds of developing diabetes, vs. normal glucose tolerance (NGT) or impaired glucose tolerance (IGT). When stratified by GTS, total sRAGE, cRAGE, and esRAGE were all lower with IGT and T2DM, while the ratio of cRAGE to esRAGE (cRAGE:esRAGE) was only lower (P < 0.01) with T2DM compared with NGT. When stratified by GTS and obesity, cRAGE:esRAGE was higher with obesity and lower with IGT (P < 0.0001) compared with lean, NGT. In ordinal logistic regression models, greater total sRAGE (odds ratio, 0.91; P < 0.01) and cRAGE (odds ratio, 0.84; P < 0.01) were associated with lower proportional odds of developing T2DM. Reduced values of sRAGE isoforms observed with both obesity and IGT are independently associated with greater proportional odds of developing T2DM. The mechanisms by which each respective isoform contributes to obesity and insulin resistance may reveal novel treatment strategies for diabetes.

An insight on the association of glycation with hepatocellular carcinoma

Hepato-cellular carcinoma (HCC) is one of the frequent cause of cancer-related death worldwide and dominant form of primary liver cancer. However, the reason behind a steady increase in the incidence of this form of cancer remains elusive. Glycation has been reported to play a significant role in the induction of several chronic diseases including cancer. Several risk factors that could induce HCC have been reported in the literature. Deciphering the complex patho-physiology associated with HCC is expected to provide new targets for the early detection, prevention, progression and recurrence. Even-though, some of the causative aspects of HCC is known, the advanced glycation end products (AGEs) related mechanism still needs further research. In the current manuscript, we have tried to uncover the possible role of glycation in the induction of HCC. In the light of the available scientific literature, we advocate in-depth comprehensive studies which will shed light towards mechanistic association of glycation with HCC.

The AGE-RAGE Axis and Its Relationship to Markers of Cardiovascular Disease in Newly Diagnosed Diabetic Patients

AIM

The purpose of the study was the simultaneous measurement of all the different components of the AGE-RAGE axis as well as several non-invasive markers of cardiovascular disease (CVD) in a cohort of newly diagnosed diabetic patients.

MATERIALS AND METHODS

In 80 newly diagnosed diabetic patients we measured serum carboxymethyllysine (CML), soluble RAGE (sRAGE) and peripheral mononuclear (PMNC) RAGE and AGER1 mRNA together with ICAM-1, VCAM-1, and malondialdehyde (MDA). We also assessed cardiovascular function by measurement of flow-mediated vasodilation (FMD), intima-media thickness (IMT) and arterial stiffness. Univariant correlation analysis was used to determine correlation between the variables in the study and multiple regression analysis was used to examine the association between the AGE-RAGE axis components and FMD, IMT and arterial stiffness.

RESULTS

Serum CML correlated positively with sRAGE, PMNC RAGE, HOMA-IR, ICAM-1, VCAM-1 and MDA, but inversely with PMNC AGER1. sRAGE and RAGE was positively correlated with AGER; IMT was positively correlated with HOMA-IR, ICAM-1, VCAM-1, MDA, and sRAGE and arterial stiffness had correlation with HOMA-IR, ICAM-1, VCAM-1, MDA, CML, sRAGE, AGER1 and RAGE. In multivariate analysis we found a significant relationship between CML with PMNC RAGE, HOMA-IR; sRAGE with VCAM-1 and MDA; PMNC RAGE with PMNC AGER1and CML; PMNC AGER1 with PMNC RAGE; FMD with sRAGE, CML and HbA1c; IMT with sRAGE, and arterial stiffness with sRAGE, sCML and AGER1.

CONCLUSIONS

We found significant and strong associations between the different components of the AGE-RAGE axis and also found significant association between AGE-RAGE axis markers, especially sRAGE with several noninvasive markers of cardiovascular disease risk. sRAGE, an easily measured parameter in blood, may potentially be used as a surrogate marker of AGEs-RAGE in patients with diabetes.

Hepatic insulin resistance both in prediabetic and diabetic patients determines postprandial lipoprotein metabolism: from the CORDIOPREV study

Background/aims

Previous evidences have shown the presence of a prolonged and exaggerated postprandial response in type 2 diabetes mellitus (T2DM) and its relation with an increase of cardiovascular risk. However, the response in prediabetes population has not been established. The objective was to analyze the degree of postprandial lipemia response in the CORDIOPREV clinical trial (NCT00924937) according to the diabetic status.

Methods

1002 patients were submitted to an oral fat load test meal (OFTT) with 0.7 g fat/kg body weight [12 % saturated fatty acids (SFA), 10 % polyunsaturated fatty acids (PUFA), 43 % monounsaturated fatty acids (MUFA), 10 % protein and 25 % carbohydrates]. Serial blood test analyzing lipid fractions were drawn at 0, 1, 2, 3 and 4 h during postprandial state. Postprandial triglycerides (TG) concentration at any point >2.5 mmol/L (220 mg/dL) has been established as undesirable response. We explored the dynamic response in 57 non-diabetic, 364 prediabetic and 581 type 2 diabetic patients. Additionally, the postprandial response was evaluated according to basal insulin resistance subgroups in patients non-diabetic and diabetic without pharmacological treatment (N = 642).

Results

Prevalence of undesirable postprandial TG was 35 % in non-diabetic, 48 % in prediabetic and 59 % in diabetic subgroup, respectively (p < 0.001). Interestingly, prediabetic patients displayed higher plasma TG and large triacylglycerol-rich lipoproteins (TRLs-TG) postprandial response compared with those non-diabetic patients (p < 0.001 and p = 0.003 respectively). Moreover, the area under the curve (AUC) of TG and AUC of TRLs-TG was greater in the prediabetic group compared with non-diabetic patients (p < 0.001 and p < 0.005 respectively). Patients with liver insulin resistance (liver-IR) showed higher postprandial response of TG compared with those patients with muscle-IR or without any insulin-resistance respectively (p < 0.001).

Conclusions

Our findings demonstrate that prediabetic patients show a lower phenotypic flexibility after external aggression, such as OFTT compared with nondiabetic patients. The postprandial response increases progressively according to non-diabetic, prediabetic and type 2 diabetic state and it is higher in patients with liver insulin-resistance. To identify this subgroup of patients is important to treat more intensively in order to avoid future cardiometabolic complications.

The Time Is Right for a New Classification System for Diabetes: Rationale and Implications of the β-Cell-Centric Classification Schema

The current classification system presents challenges to the diagnosis and treatment of patients with diabetes mellitus (DM), in part due to its conflicting and confounding definitions of type 1 DM, type 2 DM, and latent autoimmune diabetes of adults (LADA). The current schema also lacks a foundation that readily incorporates advances in our understanding of the disease and its treatment. For appropriate and coherent therapy, we propose an alternate classification system. The β-cell-centric classification of DM is a new approach that obviates the inherent and unintended confusions of the current system. The β-cell-centric model presupposes that all DM originates from a final common denominator-the abnormal pancreatic β-cell. It recognizes that interactions between genetically predisposed β-cells with a number of factors, including insulin resistance (IR), susceptibility to environmental influences, and immune dysregulation/inflammation, lead to the range of hyperglycemic phenotypes within the spectrum of DM. Individually or in concert, and often self-perpetuating, these factors contribute to β-cell stress, dysfunction, or loss through at least 11 distinct pathways. Available, yet underutilized, treatments provide rational choices for personalized therapies that target the individual mediating pathways of hyperglycemia at work in any given patient, without the risk of drug-related hypoglycemia or weight gain or imposing further burden on the β-cells. This article issues an urgent call for the review of the current DM classification system toward the consensus on a new, more useful system.