Glycation and insulin resistance: novel mechanisms and unique targets?

Advanced glycation end products and insulin resistance in diabetic nephropathy

Insulin resistance is a central hallmark that connects the metabolic syndrome and diabetes to the resultant formation of advanced glycation end products (AGEs), which further results in the complications of diabetes, including diabetic nephropathy. Several factors play an important role as an inducer to diabetic nephropathy, and AGEs elicit their harmful effects via interacting with the receptor for AGEs Receptor for AGEs, by induction of pro-inflammatory cytokines, oxidative stress, endoplasmic reticulum stress and fibrosis in the kidney tissues leading to the loss of renal function. Insulin resistance results in the activation of other alternate pathways governed by insulin, which results in the hypertrophy of the renal cells and tissue remodeling. Apart from the glucose uptake and disposal, insulin dependent PI3K and Akt also upregulate the expression of endothelial nitric oxide synthase, that results in increasing the bioavailability of nitric oxide in the vascular endothelium, which further results in tissue fibrosis. Considering the global prevalence of diabetic nephropathy, and the impact of protein glycation, various inhibitors and treatment avenues are being developed, to prevent the progression of diabetic complications. In this chapter, we discuss the role of glycation in insulin resistance and further its impact on the kidney.

Isorhamnetin as a potential therapeutic agent for diabetes mellitus through PGK1/AKT activation

CONTEXT

Type 2 Diabetes Mellitus (T2D) is a significant health concern worldwide, necessitating novel therapeutic approaches beyond conventional treatments.

OBJECTIVE

To assess isorhamnetin's potential in improving insulin sensitivity and mitigating T2D characteristics through oxidative and glycative stress modulation.

MATERIALS AND METHODS

T2D was induced in mice with a high-fat diet and streptozotocin injections. Isorhamnetin was administered at 10 mg/kg for 12 weeks. HepG2 cells were used to examine in vitro effects on stress markers and insulin sensitivity. Molecular effects on the PGK1 and AKT signalling pathway were also analyzed.

RESULTS

The administration of isorhamnetin significantly impacted both in vivo and in vitro models. In HepG2 cells, oxidative and glycative stresses were markedly reduced, indicating a direct effect of isorhamnetin on cellular stress pathways, which are implicated in the deterioration of insulin sensitivity. Specifically, treated cells showed a notable decrease in markers of oxidative stress, such as malondialdehyde, and advanced glycation end products, highlighting isorhamnetin's antioxidant and antiglycative properties. In vivo, isorhamnetin-treated mice exhibited substantially lower fasting glucose levels compared to untreated T2D mice, suggesting a strong hypoglycemic effect. Moreover, these mice showed improved insulin responsiveness, evidenced by enhanced glucose tolerance and insulin tolerance tests. The molecular investigation revealed that isorhamnetin activated PGK1, leading to the activation of the AKT signalling pathway, crucial for promoting glucose uptake and reducing insulin resistance. This molecular action underscores the potential mechanism through which isorhamnetin exerts its beneficial effects in T2D management.

DISCUSSION

The study underscores isorhamnetin's multifaceted role in T2D management, emphasizing its impact on oxidative and glycative stress reduction and molecular pathways critical for insulin sensitivity.

CONCLUSION

Isorhamnetin presents a promising avenue for T2D treatment, offering a novel approach to enhancing insulin sensitivity and managing glucose levels through the modulation of key molecular pathways. Further research is needed to translate these findings into clinical practice.

Crocetin ameliorative effect on diabetic nephropathy in rats through a decrease in transforming growth factor-β and an increase in glyoxalase-I activity

BACKGROUND & AIMS

Glycation, oxidative stress, and inflammation due to the elevation of transforming growth factor-β1 (TGF-β1) participate in diabetic nephropathy (DN). Thus, we investigated for the first time the effect of crocetin (Crt) on the renal histopathological parameters, TGF-β1 and glycation, oxidative stress, as well as inflammatory markers in the DN rat model.

METHODS

Forty male Wistar rats were randomly divided into 4 equal groups: normal (N), N + Crt, DN, and DN + Crt. DN was induced in rats with a combination of nephrectomy and streptozotocin. Treated groups received 100 mg/kg of Crt via intraperitoneal injection monthly for 3 months. Different glycation (glycated albumin, glycated LDL, Methylglyoxal, and pentosidine), oxidative stress (advanced oxidation protein products, malondialdehyde, glutathione, and paraoxonase-I (PON-1)), and inflammatory markers (tumor necrosis factor-α, myeloperoxidase, and TGF-β1), blood glucose, insulin, lipid profile, creatinine in the serum, and proteinuria, as well as the glyoxalase-1 (GLO-1) activity, was determined.

RESULTS

Crt decreased renal biochemical (Cre and PU) and histopathological (glomerulosclerosis) renal dysfunction parameters, diverse glycation, oxidative stress, and inflammatory markers in the DN rats. Furthermore, the treatment corrected glycemia, insulin resistance, and dyslipidemia as well as induced the activities of GLO-1 and PON-1. Over and above, the treatment decreased TGF-β1 in their serum (p > 0.001).

CONCLUSIONS

Crocetin improved DN owing to an advantageous effect on metabolic profile. Further, the treatment with a reducing effect on TGF-β1, oxidative stress, glycation, and inflammation markers along with an increase in Glo-1 activity showed multiple protective effects on kidney tissue.

NAFLD: An Emerging Causal Factor for Cardiovascular Disease

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease worldwide that poses a significant threat to human health. Cardiovascular disease (CVD) is the leading cause of mortality in NAFLD patients. NAFLD and CVD share risk factors such as obesity, insulin resistance, and type 2 diabetes. However, whether NAFLD is a causal risk factor for CVD remains a matter of debate. This review summarizes the evidence from prospective clinical and Mendelian randomization studies that underscore the potential causal relationship between NAFLD and CVD. The mechanisms of NAFLD contributing to the development of CVD and the necessity of addressing CVD risk while managing NAFLD in clinical practice are also discussed.

Effect of Phenolics from Aeonium arboreum on Alpha Glucosidase, Pancreatic Lipase, and Oxidative Stress; a Bio-Guided Approach

Metabolic syndrome (MetS) is a global issue affecting over a billion people, raising the risk of diabetes, cardiovascular disorders, and other ailments. It is often characterized by hypertension, dyslipidemia and/or obesity, and hyperglycemia. Chemical investigation of Aeonium arboreum (L.) Webb & Berthel led to the isolation of six compounds, viz. β-sitosterol, β-sitosterol glucoside, myricetin galactoside, quercetin rhamnoside, kaempferol rhamnoside, and myricetin glucoside. Interestingly, A. arboreum's dichloromethane (DCM), 100 and 50% MeOH Diaion fractions and the isolated compound (quercetin-3-rhamnoside) revealed potent α-glucosidase inhibitory activity, especially 50% Diaion fraction. In addition, they also showed very potent antioxidant potential, especially the polar fractions, using DPPH, ABTS, FRAP, ORAC, and metal chelation assays. Notably, the 50% Diaion fraction had the highest antioxidant potential using DPPH and ORAC assays, while the 100% Diaion fraction and quercetin-3-rhamnoside showed the highest activity using ABTS, FRAP, and metal chelation assays. Also, quercetin-3-rhamnoside showed a good docking score of -5.82 kcal/mol in comparison to acarbose. In addition, molecular dynamic stimulation studies illustrated high stability of compound binding to pocket of protein. Such potent activities present A. arboreum as a complementary safe approach for the management of diabetes mellitus as well as MetS.

Alfuzosin ameliorates diabetes by boosting PGK1 activity in diabetic mice

AIMS

Diabetes mellitus (DM) has become a global problem, causing a huge economic burden. The purpose of this study is to find a new potential method and mechanism for the treatment of DM.

MAIN METHODS

The oxidation, glycation and insulin resistance cell models were built to screen the potential anti-diabetic chemicals. Then the DM mice were induced by the combination of high-fat diet (HFD) and intraperitoneal injection of streptozotocin (50 mg/kg) for five days. The alfuzosin (1.2 mg/kg) was administered by intraperitoneal injection once daily for sequential 12 weeks. Fasting blood glucose, blood lipid, oxidative stress and key markers of glucose metabolism were detected. PGK1/AKT/GLUT4 pathway related proteins were analyzed by Western blot.

KEY FINDINGS

Alfuzosin ameliorated oxidative stress, glycative stress and insulin resistance in HepG2 cells. Further, in a high-fat diet/streptozotocin (HFD/STZ)-induced diabetic mouse model, alfuzosin reduced fasting blood glucose, improved insulin sensitivity. Mechanically, alfuzosin activated PGK1 directly to stimulate the protein kinase B (AKT) signaling pathway, thus facilitating glucose uptake as well as improving insulin resistance.

SIGNIFICANCE

The present finding has shed a new light on the treatment of DM and provides validation for PGK1 as a therapeutic target for DM.

High hemoglobin glycation index is associated with increased risk of diabetes: A population-based cohort study in China

PURPOSE

The hemoglobin glycation index (HGI) quantifies the mismatch between glycated hemoglobin A1c and average glycemia among individuals. Currently, it is unknown the potential role of HGI in exhaustively evaluating the progression of glucose metabolism/the risk of developing diabetes mellitus. Therefore, this study aimed to investigate the association between HGI and the risk of incident diabetes.

METHODS

A total of 7,345 participants aged at least 40 years and without diabetes were divided into three groups according to the tertile of their baseline HGI level and followed for a median of 3.24 years to track new-onset diabetes. Using multivariate Cox regression analyses, we explored the association between the HGI, both categorized and continuous, and incident diabetes.

RESULTS

During follow-up, 742 subjects (263 males and 479 females) developed diabetes mellitus. Higher HGI was associated with an increased risk of diabetes, even when adjusted for confounding factors, and every standard deviation increase in HGI was associated with a significant risk increase of 30.6% for diabetes (hazard ratio 1.306, 95% confidence interval 1.232-1.384).

CONCLUSIONS

Participants with a higher HGI were at a higher risk of future diabetes, irrespective of their glycemic conditions. Consequently, HGI may be employed to identify individuals at high risk for diabetes.

Nutrition Alters the Stiffness of Adipose Tissue and Cell Signaling

Adipose tissue is a complex organ composed of various cell types and an extracellular matrix (ECM). The visceral adipose tissue (VAT) is dynamically altered in response to nutritional regimens that lead to local cues affecting the cells and ECM. The adipocytes are in conjunction with the surrounding ECM that maintains the tissue's niche, provides a scaffold for cells and modulates their signaling. In this study, we provide a better understanding of the crosstalk between nutritional regimens and the ECM's stiffness. Histological analyses showed that the adipocytes in mice fed a high-fat diet (HFD) were increased in size, while the ECM was also altered with changes in mass and composition. HFD-fed mice exhibited a decrease in elastin and an increase in collagenous proteins. Rheometer measurements revealed a stiffer ECM in whole tissue (nECM) and decellularized (deECM) in HFD-fed animals. These alterations in the ECM regulate cellular activity and influence their metabolic function. HFD-fed mice expressed high levels of the receptor for advanced-glycation-end-products (RAGE), indicating that AGEs might play a role in these processes. The cells also exhibited an increase in phosphoserine³³² of IRS-1, a decrease in the GLUT4 transporter levels at the cells' membrane, and a consequent reduction in insulin sensitivity. These results show how alterations in the stiffness of ECM proteins can affect the mechanical cues transferred to adipocytes and, thereby, influence the adipocytes' functionality, leading to metabolic disorders.

1,8 cineole protects type 2 diabetic rats against diabetic nephropathy via inducing the activity of glyoxalase-I and lowering the level of transforming growth factor-1β

Purpose

Diabetes leading to the production and circulation of glycation products along with the reduction of the activity of glyoxalase-I (GLO-I) contribute to diabetic nephropathy. Therefore, we studied the effect of 1,8 cineole (Cin) on the formation of diverse glycation products and the activity of GLO-I as well as renal histopathological alterations in the type-2 diabetic rat.

Methods

Type 2 diabetes was induced in rats with a combination of streptozotocin and nicotinamide (55 + 200 mg/kg). Two groups of rats, normal and diabetic, were treated intragastrically with Cin (200 mg/kg) once daily for 2 months. Fasting blood sugar, insulin resistance index, lipid profile, the activity of GLO-I, glycation products (Glycated albumin, Glycated LDL, Methylglyoxal, and advanced glycation end products), and oxidative stress (Advanced oxidation protein products, malondialdehyde, oxidized LDL, and reduced glutathione), inflammatory markers (Tumor necrosis factor-α and Transforming growth factor-1β), creatinine in the serum (Cre), and proteinuria (PU) in the urine of all rats was determined as well as renal histopathological alterations were investigated.

Results

Cin reduced biochemical (Cre and PU) and histopathological (glomerulosclerosis) indicators of renal dysfunction in the diabetic rat compared to untreated diabetic rats. Moreover, the treatment decreased different glycation, oxidative stress, and pro-inflammatory markers (p < 0.001). Further, Cin had an advantageous effect on glucose and lipid metabolism.

Conclusions

Cin ameliorated diabetic nephropathy via reduction of TGF-1β following to decrease the formation of different glycation products, oxidative stress, and inflammatory process with the induction of the activity of glyoxalase-I in type 2 diabetic rats.

Phenolics from Chrozophora oblongifolia Aerial Parts as Inhibitors of α-Glucosidases and Advanced Glycation End Products: In-Vitro Assessment, Molecular Docking and Dynamics Studies

Simple Summary

The chemical investigation of Chrozophora oblongifolia aerial parts resulted in the isolation of five phenolic compounds. The isolated metabolites were tested for their antioxidant and advanced glycation end-products (AGEs) formation, α-glucosidase, and lipase inhibitory activities. 1,3,6-Trigalloyl glucose exhibited the highest activity as an antioxidant and AGEs inhibitor as well as an α-glucosidase inhibitor. It showed promising binding affinity and stability towards the human intestinal maltase-glucoamylase α-glucosidases, as revealed through coupled molecular docking and dynamics studies that could encourage the utilization of this compound in the management of diabetes and its complications.

Abstract

Modern life is associated with low physical activity that leads to the accumulation of fats, gaining more weight, and obesity. Accumulation of fat in the abdomen region contributes to diabetes via insulin resistance and hyperglycemia. Polyphenols are major plant constituents that exert antidiabetic activity through different mechanisms, including radicle scavenging activity, regulation of glucose uptake, and inhibition of fat and polysaccharide hydrolysis in addition to their inhibitory role regarding the formation of advanced glycation end products (AGEs). Chemical investigation of C. oblongifolia aerial parts resulted in the isolation of five major compounds: apeginin-7-O-β-D-glucoside (1), quercetin-3-O-β-D-glucuronic acid (2), quercetin-3-O-β-D-galacturonic acid (3), rutin (4), and 1,3,6-trigalloyl glucose (5). The isolated compounds were tested for their antioxidant and AGEs formation, α-glucosidase, and lipase inhibitory activities. Compound 5 revealed the highest antioxidant and AGEs inhibitory activity in bovine serum albumin (BSA)-methylglyoxal, BSA-fructose, and arginine-methylglyoxal models. Moreover, it exhibited a potent inhibitory profile on Saccharomyces cerevisiae α-glucosidases compared to the positive control, acarbose. Compound (5) further depicted promising binding affinity and stability towards the human intestinal maltase-glucoamylase α-glucosidases, which is a diabetes-related therapeutic target, through coupled molecular docking and dynamics studies. The obtained results encourage the usage of 1,3,6-trigalloyl glucose in the management of diabetes and its complications. However, detailed in-vivo studies for this compound should be performed.

Food-Related Carbonyl Stress in Cardiometabolic and Cancer Risk Linked to Unhealthy Modern Diet

Carbonyl stress is a condition characterized by an increase in the steady-state levels of reactive carbonyl species (RCS) that leads to accumulation of their irreversible covalent adducts with biological molecules. RCS are generated by the oxidative cleavage and cellular metabolism of lipids and sugars. In addition to causing damage directly, the RCS adducts, advanced glycation end-products (AGEs) and advanced lipoxidation end-products (ALEs), cause additional harm by eliciting chronic inflammation through receptor-mediated mechanisms. Hyperglycemia- and dyslipidemia-induced carbonyl stress plays a role in diabetic cardiovascular complications and diabetes-related cancer risk. Moreover, the increased dietary exposure to AGEs/ALEs could mediate the impact of the modern, highly processed diet on cardiometabolic and cancer risk. Finally, the transient carbonyl stress resulting from supraphysiological postprandial spikes in blood glucose and lipid levels may play a role in acute proinflammatory and proatherogenic changes occurring after a calorie dense meal. These findings underline the potential importance of carbonyl stress as a mediator of the cardiometabolic and cancer risk linked to today’s unhealthy diet. In this review, current knowledge in this field is discussed along with future research courses to offer new insights and open new avenues for therapeutic interventions to prevent diet-associated cardiometabolic disorders and cancer.

Phloroglucinol prevents albumin glycation as well as diminishes ROS production, glycooxidative damage, nitrosative stress and inflammation in hepatocytes treated with high glucose

The treatment of diabetes mellitus aftermaths became one of medicine's most significant therapeutical and financial issues in the XXI century. Most of which are related to protein glycation and oxidative stress caused by long lasting periods of hyperglycemia. Thus, even within a venerable one, searching for new drugs, displaying anti-glycation and anti-oxidative properties seem useful as an additive therapy of diabetes. In this paper, we assessed the anti-glycating properties of phloroglucinol, a drug discovered in the XIX century and still used in many countries for its antispasmodic action. Herewith, we present its effect on protein glycation, glycoxidation, and oxidative damage in an albumin glycation/oxidation model and HepG2 cells treated with high glucose concentrations. The phloroglucinol showed the strongest and the widest protective effect within all analyzed antiglycating (aminoguanidine, pioglitazone) and anti-oxidative (vitamin C, GSH) agents. To the very best of our knowledge, this is the first study showing the properties of phloroglucinol in vitro what once is proven in other models might deepen its clinical applications.

Role of Long Non-Coding RNAs and the Molecular Mechanisms Involved in Insulin Resistance

Long non-coding RNAs (lncRNAs) are single-stranded RNA biomolecules with a length of >200 nt, and they are currently considered to be master regulators of many pathological processes. Recent publications have shown that lncRNAs play important roles in the pathogenesis and progression of insulin resistance (IR) and glucose homeostasis by regulating inflammatory and lipogenic processes. lncRNAs regulate gene expression by binding to other non-coding RNAs, mRNAs, proteins, and DNA. In recent years, several mechanisms have been reported to explain the key roles of lncRNAs in the development of IR, including metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), imprinted maternal-ly expressed transcript (H19), maternally expressed gene 3 (MEG3), myocardial infarction-associated transcript (MIAT), and steroid receptor RNA activator (SRA), HOX transcript antisense RNA (HOTAIR), and downregulated Expression-Related Hexose/Glucose Transport Enhancer (DREH). LncRNAs participate in the regulation of lipid and carbohydrate metabolism, the inflammatory process, and oxidative stress through different pathways, such as cyclic adenosine monophosphate/protein kinase A (cAMP/PKA), phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT), polypyrimidine tract-binding protein 1/element-binding transcription factor 1c (PTBP1/SREBP-1c), AKT/nitric oxide synthase (eNOS), AKT/forkhead box O1 (FoxO1), and tumor necrosis factor-alpha (TNF-α)/c-Jun-N-terminal kinases (JNK). On the other hand, the mechanisms linked to the molecular, cellular, and biochemical actions of lncRNAs vary according to the tissue, biological species, and the severity of IR. Therefore, it is essential to elucidate the role of lncRNAs in the insulin signaling pathway and glucose and lipid metabolism. This review analyzes the function and molecular mechanisms of lncRNAs involved in the development of IR.

Preventive Effect of Eucalyptol on the Formation of Aorta Lesions in the Diabetic-Atherosclerotic Rat

Background:

Glycation, inflammation, and oxidative stress are the cardinal motivators of diabetes vascular complications. Here, we studied the effect of eucalyptol (EUC) on the formation of atheromatous lesions, glycation, oxidative stress, and inflammatory markers as well as insulin resistance, lipid profile, and activity of glyoxalase-1 (GLO-I) in the atherosclerotic rat model.

Methods:

Diabetic-atherosclerosis induced in rats with a combination of streptozotocin and atherogenic diet. Two groups of rats, normal and diabetic-atherosclerotic, were treated intragastrically with EUC (200 mg/kg) once daily for 3 months. Fasting blood sugar (FBS), insulin, insulin resistance index, lipid profile, the activity of GLO-I, low-density lipoprotein (LDL) glycation and oxidation markers, inflammatory markers, creatinine in the serum, and proteinuria in the urine of all rats were determined.

Results:

EUC inhibited the formation of any atheromatous lesions in atherosclerotic rats. Further, EUC displayed the lowering effect on glycemia, insulin resistance, LDL glycation, and oxidation products, and tumor necrosis factor (TNF)-α as well as it exhibited the improving effect on lipid profile, the activity of GLO-I, and renal function in the diabetic rat (P < 0.001).

Conclusions:

EUC prevented the formation of the atheromatous lesions and improved renal function in the atherosclerotic rat model due to a reduction of glycation, oxidative stress, and inflammatory mediators.

In vitro chronic glycation induces AGEs accumulation reducing insulin-stimulated glucose uptake and increasing GLP1R in adipocytes

Intracellular AGEs accumulation increases RAGE and GLP1R and reduces glucose uptake in adipocytes.

Associations of dietary patterns and nutrients with coronary artery calcification and pericardial adiposity in a longitudinal study of adults with and without type 1 diabetes

PURPOSE

To examine the associations of dietary patterns and nutrients with coronary artery calcification (CAC) and pericardial adiposity (PAT) in adults with and without type 1 diabetes.

METHODS

We conducted a six-year longitudinal analysis of data from Coronary Artery Calcification in Type 1 Diabetes study [n = 1255; T1D: n = 563; non-DM: n = 692] collected at baseline, year 3 and year 6. Participants completed a validated food frequency questionnaire, a physical examination, and fasting (12 h overnight fast) biochemical analyses. CAC and PAT were measured using electron beam computed tomography. Dietary patterns were identified using factor analysis. Generalized estimating equations were used to examine associations of dietary patterns and nutrients with CAC and PAT in models adjusted for traditional cardiovascular risks.

RESULTS

The 'starchy veggies, meats and alcohol pattern' was associated with significantly increased risk of CAC presence in all adjusted models; an increasing trend was observed with CAC progression. Increasing intake of dietary proteins and total fats were also associated with higher risk of the presence and/or progression of CAC in adjusted models (all p < 0.05). PAT was positively associated with dietary total fats, and inversely associated with dietary intakes of saturated fats, omega-3 fats and fiber in models adjusted for age, sex, total calories, time, diabetes status, systolic blood pressure, serum lipids and physical activity.

CONCLUSION

Diets high in total fats and proteins, and in meats (processed and red) and alcohol may increase risks of CAC, while saturated fats, omega-3-fats and fiber may be protective against pericardial adiposity as a risk factor for coronary artery disease. ClinicalTrials.gov Identifier: NCT00005754.

Methylglyoxal-Scavenging Enzyme Activities Trigger Erythroascorbate Peroxidase and Cytochrome c Peroxidase in Glutathione-Depleted Candida albicans

γ-Glutamylcysteine synthetase (Gcs1) and glutathione reductase (Glr1) activity maintains minimal levels of cellular methylglyoxal in Candida albicans. In glutathione-depleted Δgcs1, we previously saw that NAD(H)-linked methylglyoxal oxidoreductase (Mgd1) and alcohol dehydrogenase (Adh1) are the most active methylglyoxal scavengers. With methylglyoxal accumulation, disruptants lacking MGD1 or ADH1 exhibit a poor redox state. However, there is little convincing evidence for a reciprocal relationship between methylglyoxal scavenger genes-disrupted mutants and changes in glutathione-(in)dependent redox regulation. Herein, we attempt to demonstrate a functional role for methylglyoxal scavengers, modeled on a triple disruptant (Δmgd1/Δadh1/Δgcs1), to link between antioxidative enzyme activities and their metabolites in glutathione-depleted conditions. Despite seeing elevated methylglyoxal in all of the disruptants, the result saw a decrease in pyruvate content in Δmgd1/Δadh1/Δgcs1 which was not observed in double gene-disrupted strains such as Δmgd1/Δgcs1 and Δadh1/Δgcs1. Interestingly, Δmgd1/Δadh1/Δgcs1 exhibited a significantly decrease in H₂O₂ and superoxide which was also unobserved in Δmgd1/Δgcs1 and Δadh1/Δgcs1. The activities of the antioxidative enzymes erythroascorbate peroxidase and cytochrome c peroxidase were noticeably higher in Δmgd1/Δadh1/Δgcs1 than in the other disruptants. Meanwhile, Glr1 activity severely diminished in Δmgd1/Δadh1/Δgcs1. Monitoring complementary gene transcripts between double gene-disrupted Δmgd1/Δgcs1 and Δadh1/Δgcs1 supported the concept of an unbalanced redox state independent of the Glr1 activity for Δmgd1/Δadh1/Δgcs1. Our data demonstrate the reciprocal use of Eapx1 and Ccp1 in the absence of both methylglyoxal scavengers; that being pivotal for viability in non-filamentous budding yeast.

Molecular investigation of glycated insulin-induced insulin resistance via insulin signaling and AGE-RAGE axis

Hyperglycemic condition in diabetes promotes glycation of various plasma proteins including insulin. Glycation of insulin has been reported to reduce its biological activity. Reduced biological activity of glycated insulin could be either due to reduced affinity for the insulin receptor and impaired insulin signaling, or it can act as a ligand for the receptor for advanced glycation end products (RAGE) and activates oxidative stress and pro-inflammatory pathways leading to insulin resistance. This study investigates the effect of glycated insulin on both insulin and RAGE signaling. Glycated insulin treatment to Chinese hamster ovary (CHO-IR-GLUT4) cells stably expressing insulin receptor (IR) and glucose transporter fused with a green fluorescent protein (GLUT4-GFP) resulted in the impairment of insulin signaling, as the phosphorylation of IR and AKT significantly reduced, which affected GLUT4 translocation and glucose uptake. Moreover, it also activated RAGE signaling as observed by increased expression of NADPH oxidase accompanied by an increase in reactive oxygen species (ROS). Immunofluorescence study indicated the translocation of NF-κB to the nucleus upon treatment of glycated insulin. This was associated with increased RAGE expression, Caspase 3, and cell death. Downregulation of RAGE with the losartan treatment restored the impaired insulin signaling and glucose uptake. Additionally, in silico study demonstrated that glycated insulin has reduced binding affinity to insulin receptor and increased binding affinity to RAGE. Overall, this study demonstrates the role of glycated insulin in exacerbating insulin resistance by impairing insulin signaling as well as stimulating AGE-RAGE signaling.

Lipid Profile Modulates Cardiometabolic Risk Biomarkers Including Hypertension in People with Type-2 Diabetes: A Focus on Unbalanced Ratio of Plasma Polyunsaturated/Saturated Fatty Acids

Type 2 diabetes mellitus (T2DM) is associated with lipid metabolism disorder, particularly elevated plasma levels of non-esterified free fatty acids (NEFFA) and an increased cardiovascular disease risk, such as essential hypertension (H). The plasma unbalance of saturated fatty acid (SFA)/polyunsaturated fatty acid (PUFA) ratio is a likely contributor, but the mechanisms involved are not clearly elucidated. The aim of this study is to explore the association between plasma SFA/PUFA ratio and the clusters of cardiometabolic syndrome (CMS), including the atherogenic biomarkers, inflammatory status, feeding patterns, and physical activity in people with T2DM with or without essential hypertension. The study was conducted on 784 adult male and female participants, aged between 30 and 50 years, and divided into 3 groups: 100 T2DM without hypertension (D); 368 T2DM with hypertension (DM); and 316 hypertensive participants without T2DM (H). All Participants were phenotyped regarding CMS clusters according to the NCEP/ATPIII criteria. Insulin resistance was assessed by Homeostasis model assessment (HOMA model). Metabolic, atherogenic, and inflammatory parameters were analyzed by biochemical methods; NEFFA by microfluorimetry; SFA, PUFA-n6 and PUFA-n3 by gas phase chromatography. Dietary lipids and physical activity were analyzed through the use of validated questionnaires. The clusters of CMS were found in all groups. Dyslipidemia was correlated with accretion NEFFA levels in all groups, but more accentuated in the DH group (r = +0.77; p < 0.001). Similarly, plasma PUFA/SFA ratio and PUFA-3 level was lower, concomitantly with a higher plasma ApoB100/ApoA1 (p < 0.001), lipoprotein (a), homocysteine (p < 0.001), and pro-inflammatory cytokines (TNFα, IL-6, IL1-β) in the DH group. Likewise, the depletion of PUFA-n3/PUFA-n6 ratio is associated with the decrease of omega 3-DHA (docosahexaenoic acid) and omega 3-EPA (eicosapentaenoic acid) (p < 0.001). It appears that the PUFAs-n3 ratio modulates cardiometabolic risk, inflammatory state and atherogenic biomarkers. The plasma unbalanced ratio of SFA/PUFA reflects dietary fatty acids intake. The contribution of dietary lipids is undisputed. Nutritional recommendations are required to determine the fatty acids ratio (saturated and unsaturated) provided in the diet.

Free advanced glycation end product distribution in blood components and the effect of genetic polymorphisms

One hypothesis regarding the cause of diabetic complications is that advanced glycation end products (AGEs) bind to the AGE receptor and induce changes in gene expression. However, what AGEs exist in vivo and how individual AGEs are produced and impact body metabolic process to cause diabetes complications are not understood. We developed a new precise method to measure AGEs using LC-MS/MS with a new column and measured 7 free AGEs, including N(6)-carboxymethyllysine (CML), N(6)-(1-carboxyethyl)-l-lysine (CEL) and N5-(5-hydro-5-methyl-4-imidazolon-2-yl)L-ornithine (MG-H1), in human blood components. Blood was obtained from 9 people, and free AGEs were measured in individual blood components with LC-MS/MS before and after a meal. Free CML and CEL were abundant in erythrocytes, with 92% of free CML and 85% of free CEL localized in erythrocytes. In contrast, 60% of free MG-H1 was distributed in the serum. After the meal, free serum MG-H1 increased, but CML and CEL did not. CML and CEL are mainly distributed in erythrocytes and were not affected by the meal, indicating that they are produced in vivo. However, the main source of MG-H1 is the meal. The effect of genetic polymorphisms on AGEs was also investigated. Low activity type aldehyde dehydrogenase 2 (ALDH2) increased the CML concentration in the blood. This is the first observation that shows that the metabolic process of CML and CEL is different from that of MG-H1 and the effect of ALDH2 SNPs on CML.

Albumin as a drug: its biological effects beyond volume expansion

Albumin is the most abundant and perhaps most important protein in human blood. Research has identified many of albumin's possible roles in modulating acid-base balance, modifying inflammation, maintaining vascular endothelial integrity, and binding endogenous and exogenous compounds. Albumin plays a key role in the homeostasis of vascular endothelium, offering protection from inflammation and damage to the glycocalyx. Albumin binds a diverse range of compounds. It transports, delivers and clears drugs, plus it helps with uptake, storage and disposal of potentially harmful biological products. The biological effects of albumin in critical illness are incompletely understood, but may enhance its clinical role beyond use as an intravenous fluid. In this article, we summarise the evidence surrounding albumin's biological and physiological effects beyond its use for plasma volume expansion, and explore potential mechanistic effects of albumin as a disease modifier in patients with critical illness.

Albumin as a drug: its biological effects beyond volume expansion

Albumin is the most abundant and perhaps most important protein in human blood. Research has identified many of albumin's possible roles in modulating acid-base balance, modifying inflammation, maintaining vascular endothelial integrity, and binding endogenous and exogenous compounds. Albumin plays a key role in the homeostasis of vascular endothelium, offering protection from inflammation and damage to the glycocalyx. Albumin binds a diverse range of compounds. It transports, delivers and clears drugs, plus it helps with uptake, storage and disposal of potentially harmful biological products. The biological effects of albumin in critical illness are incompletely understood, but may enhance its clinical role beyond use as an intravenous fluid. In this article, we summarise the evidence surrounding albumin's biological and physiological effects beyond its use for plasma volume expansion, and explore potential mechanistic effects of albumin as a disease modifier in patients with critical illness.

Effects of the Lysulin™ supplementation on pre-diabetes: A randomized double-blind, placebo-controlled clinical trial

BACKGROUND AND AIMS

Diabetes is a leading cause of morbidity and mortality worldwide. Recent studies have demonstrated that nutraceutical products have beneficial effects in diabetes. Present study aims to investigate whether a product (Lysulin™) containing amino acid lysine, micronutrient zinc and vitamin C will have beneficial effects in pre-diabetes.

METHODS

A randomized, double-blind, placebo-controlled trial was conducted for a period of 6 months. The two parallel groups (1:1) were Lysulin™ (Interventional group-IG) and placebo (control group-CG). Evaluations were done at baseline, 1, 3 and 6 months. Primary outcome was defined as change in glycaemic control measured by HbA1c from baseline. Other outcomes included change in; fasting plasma glucose (FPG), 2-h OGTT plasma glucose and lipid profile from baseline. Three multiple regression analyses were performed, where change in FPG, 2-h OGTT, and HbA1c post intervention from baseline respectively were the continuous dependent variable with other independent variables.

RESULTS

One hundred and ten participants were recruited, 50% (n = 55) were males and mean age (±SD) was 46.7 ± 9.9 years. A significantly higher percentage of participants in CG (25.4%, n = 14) developed diabetes in comparison to IG (7.3%, n = 4) (p = 0.018). FPG, 2-h OGTT and HbA1c significantly reduced in the IG only. Both total cholesterol and LDL cholesterol decreased significantly from baseline only in the IG. In all three regression models the best predictor of respective dependent variable was Lysulin™ treatment.

CONCLUSIONS

Lysulin™ improved glycaemic control, with reduced progression to diabetes, in those with pre-diabetes. Treatment also showed a beneficial reduction in total and LDL cholesterol levels.

TRIAL REGISTRATION

Sri Lanka Clinical Trials Registry, identifier: SLCTR/2018/022 (http://slctr.lk/trials/1290). Registered on 13th July 2018; Study protocol version 2.0 (23rd March 2018).

The Herbal Combination CPA4-1 Inhibits Changes in Retinal Capillaries and Reduction of Retinal Occludin in db/db Mice

Increased formation of advanced glycation end products (AGEs) plays an important role in the development of diabetic retinopathy (DR) via blood-retinal barrier (BRB) dysfunction, and reduction of AGEs has been suggested as a therapeutic target for DR. In this study, we examined whether CPA4-1, a herbal combination of Cinnamomi Ramulus and Paeoniae Radix, inhibits AGE formation. CPA4-1 and fenofibrate were tested to ameliorate changes in retinal capillaries and retinal occludin expression in db/db mice, a mouse model of obesity-induced type 2 diabetes. CPA4-1 (100 mg/kg) or fenofibrate (100 mg/kg) were orally administered once a day for 12 weeks. CPA4-1 (the half maximal inhibitory concentration, IC₅₀ = 6.84 ± 0.08 μg/mL) showed approximately 11.44-fold higher inhibitory effect on AGE formation than that of aminoguanidine (AG, the inhibitor of AGEs, IC₅₀ = 78.28 ± 4.24 μg/mL), as well as breaking effect on AGE-bovine serum albumin crosslinking with collagen (IC₅₀ = 1.30 ± 0.37 μg/mL). CPA4-1 treatment ameliorated BRB leakage and tended to increase retinal occludin expression in db/db mice. CPA4-1 or fenofibrate treatment significantly reduced retinal acellular capillary formation in db/db mice. These findings suggested the potential of CPA4-1 as a therapeutic supplement for protection against retinal vascular permeability diseases.

Glycation of glucose sensitive lysine residues K36, K438 and K549 of albumin is associated with prediabetes

Prediabetes is a risk factor for the development of diabetes. Early diagnosis of prediabetes may prevent the onset and progression of diabetes and its associated complications. Therefore, this study aimed at the identification of novel markers for efficient prediction of prediabetes. In this pursuit, we have evaluated the ability of glycated peptides of albumin in predicting prediabetes. Glycated peptides of in vitro glycated albumin were characterized by data dependent acquisition and parallel reaction monitoring using LC-HRMS. Amongst 14 glycated peptides characterized in vitro, four peptides, particularly, FK(CML)DLGEENFK, K(AML)VPQVSTPTLVEVSR, K(CML)VPQVSTPTLVEVSR, and K(AML)QTALVELVK, corresponding to 3 glucose sensitive lysine residues K36, K438, and K549, respectively showed significantly higher abundance in prediabetes than control. Additionally, the abundance of three of these peptides, namely K(AML)QTALVELVK, K(CML)VPQVSTPTLVEVSR and FK(CML)DLGEENFK was >1.8-fold in prediabetes, which was significantly higher than the differences observed for FBG, PPG, and HbA1c. Further, the four glycated peptides showed a significant correlation with FBG, PPG, HbA1c, triglycerides, VLDL, and HDL. This study supports that glycated peptides of glucose sensitive lysine residues K36, K438 and K549 of albumin could be potentially useful markers for prediction of prediabetes. SIGNIFICANCE: Undiagnosed prediabetes may lead to diabetes and associated complications. This study reports targeted quantification of four glycated peptides particulary FK(CML)DLGEENFK, K(AML)VPQVSTPTLVEVSR, K(CML)VPQVSTPTLVEVSR, and K(AML)QTALVELVK, corresponding to 3 glucose sensitive lysine residues K36, K438 and K549 respectively by parallel reaction monitoring in healthy and prediabetic subjects. These peptides showed significantly higher abundance in prediabetes than healthy subjects, and showed significant correlation with various clinical parameters including FBG, PPG, HbA1c, and altered lipid profile. Therefore, together these four peptides constitute a panel of markers that can be useful for prediction of prediabetes.

Intra-Abdominal Fat Adipocyte Hypertrophy through a Progressive Alteration of Lipolysis and Lipogenesis in Metabolic Syndrome Rats

This study evaluates the progressive participation of enzymes involved in lipolysis and lipogenesis, leading to adipocyte hypertrophy in a metabolic syndrome (MS) rat model caused by chronic consumption of 30% sucrose in drinking water. A total of 70 male Wistar rats were divided into two groups: C and MS. Each of these groups were then subdivided into five groups which were sacrificed as paired groups every month from the beginning of the treatment until 5 months. The intra-abdominal fat was dissected, and the adipocytes were extracted. Lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), protein kinases A (PKA), and perilipin A expressions were determined. The LPL and HSL activities were evaluated by spectrophotometry. Histological staining was performed in adipose tissue. Significant increases were observed in blood pressure, HOMA-IR, leptin, triglycerides, insulin, intra-abdominal fat, and number of fat cells per field (p = 0.001) and in advanced glycosylation products, adipocyte area, LPL, HSL activities and/or expression (p ≤ 0.01) in the MS groups progressively from the third month onward. Lipogenesis and lipolysis were increased by LPL activity and HSL activity and/or expression. This was associated with hyperinsulinemia and release of non-esterified fatty acids causing a positive feedback loop that contributes to the development of adipocyte hypertrophy.

Fructose-induced AGEs-RAGE signaling in skeletal muscle contributes to impairment of glucose homeostasis

Increased fructose intake has been linked to the development of dyslipidemia, obesity and impaired glucose tolerance. Due to its specific metabolic fate, fructose impairs normal lipid and carbohydrate metabolism and facilitates the non-enzymatic glycation reaction leading to enhanced accumulation of advanced glycation end products (AGEs). However, the formation of fructose-AGEs under in vivo setup and its tissue specific accumulation is less explored. Here, we investigated the impact of high fructose on AGEs accumulation in skeletal muscle and its causal role in impaired glucose homeostasis. In L6 rat skeletal muscle cells, chronic exposure to fructose induced AGEs accumulation and the cellular level of the receptor for AGEs (RAGE) and the effect was prevented by pharmacological inhibition of glycation. Under in vivo settings, Sprague Dawley rats exposed to 20% fructose in drinking water for 16 weeks, displayed increased fasting glycemia, impaired glucose tolerance, decreased skeletal muscle Akt (Ser-473) phosphorylation, and enhanced triglyceride levels in serum, liver and gastrocnemius muscle. We also observed a high level of AGEs in serum and gastrocnemius muscle of fructose-supplemented animals, associated with methylglyoxal accumulation and up regulated expression of RAGE in gastrocnemius muscle. Treatment with aminoguanidine inhibited fructose-induced AGEs accumulation and normalized the expression of RAGE and Dolichyl-Diphosphooligosaccharide-Protein Glycosyltransferase (DDOST) in gastrocnemius muscle. Inhibition of AGEs-RAGE axis counteracted fructose-mediated glucose intolerance without affecting energy metabolism. These data reveal diet-derived AGEs accumulation in skeletal muscle and the implication of tissue specific AGEs in metabolic derangement, that may open new perspectives in pathogenic mechanisms and management of metabolic diseases.

Metabolic Syndrome in Heart Failure: Friend or Foe?

The interplay between metabolic syndrome (MetS) and heart failure (HF) is intricate. Population studies show that MetS confers an increased risk to develop HF and this effect is mediated by insulin resistance (IR). However, obesity, a key component in MetS and common partner of IR, is protective in patients with established HF, although IR confers an increased risk of dying by HF. Such phenomenon, known as "obesity paradox," accounts for the complexity of the HF-MetS relationship. Because IR impacts more on outcomes than MetS itself, the former may be considered the actual target for MetS in HF patients.

Glycation Damage: A Possible Hub for Major Pathophysiological Disorders and Aging

Glycation is both a physiological and pathological process which mainly affects proteins, nucleic acids and lipids. Exogenous and endogenous glycation produces deleterious reactions that take place principally in the extracellular matrix environment or within the cell cytosol and organelles. Advanced glycation end product (AGE) formation begins by the non-enzymatic glycation of free amino groups by sugars and aldehydes which leads to a succession of rearrangements of intermediate compounds and ultimately to irreversibly bound products known as AGEs. Epigenetic factors, oxidative stress, UV and nutrition are important causes of the accumulation of chemically and structurally different AGEs with various biological reactivities. Cross-linked proteins, deriving from the glycation process, present both an altered structure and function. Nucleotides and lipids are particularly vulnerable targets which can in turn favor DNA mutation or a decrease in cell membrane integrity and associated biological pathways respectively. In mitochondria, the consequences of glycation can alter bioenergy production. Under physiological conditions, anti-glycation defenses are sufficient, with proteasomes preventing accumulation of glycated proteins, while lipid turnover clears glycated products and nucleotide excision repair removes glycated nucleotides. If this does not occur, glycation damage accumulates, and pathologies may develop. Glycation-induced biological products are known to be mainly associated with aging, neurodegenerative disorders, diabetes and its complications, atherosclerosis, renal failure, immunological changes, retinopathy, skin photoaging, osteoporosis, and progression of some tumors.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

Rapid Non-Enzymatic Glycation of the Insulin Receptor under Hyperglycemic Conditions Inhibits Insulin Binding In Vitro: Implications for Insulin Resistance

The causes of insulin resistance are not well-understood in either type 1 or type 2 diabetes. Insulin (INS) is known to undergo rapid non-enzymatic covalent conjugation to glucose or other sugars (glycation). Because the insulin receptor (IR) has INS-like regions associated with both glucose and INS binding, we hypothesize that hyperglycemic conditions may rapidly glycate the IR, chronically interfering with INS binding. IR peptides were synthesized spanning IR- associated INS-binding regions. Glycation rates of peptides under hyperglycemic conditions were followed over six days using matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. INS conjugated to horse-radish peroxidase was used to determine INS binding to IR peptides in glycated and non-glycated forms. Several IR peptides were glycated up to 14% within days of exposure to 20-60 mM glucose. Rates of IR-peptide glycation were comparable to those of insulin. Glycation of four IR peptides significantly inhibits INS binding to them. Glycation of intact IR also decreases INS binding by about a third, although it was not possible to confirm the glycation sites on the intact IR. Glycation of the IR may therefore provide a mechanism by which INS resistance develops in diabetes. Demonstration of glycation of intact IR in vivo is needed.

Glycated albumin (GA) and inflammation: role of GA as a potential marker of inflammation

AIMS

Abnormal levels of glycated albumin (GA) are associated with the onset of both diabetes and inflammation. Although inflammation has long been associated with diabetes, this article aims to explore the underlying mechanisms of this relationship as it pertains to the role of GA.

METHODS

We have reviewed 52 research articles since the year 2000. Common search terms used were "(inflammatory mediator) and GA" or "inflammation and GA". The findings have been organized according to diabetic complications with respect to the interactions of GA and inflammatory mediators. Glycated albumin and specific inflammatory mediators have been reported to play various roles in the pathogenesis of insulin resistance, atherosclerosis, coronary artery disease, retinopathy, and nephropathy. In the case of nephropathy and recently retinopathy, there is considerable evidence for GA in concert with inflammation playing a direct role in organ pathology. There is copious literature detailing GA's involvement in stimulating inflammatory markers and certain pro-inflammatory cytokines. A recent clinical study has shown GA to be a marker for inflammation in non-diabetic rheumatoid arthritis patients with the significance of standard inflammatory markers.

CONCLUSIONS

The clinical utility of GA measurement may likely reside in its versatility as both a mediator of inflammation as well as a marker to track hyperglycemia and other diabetes complications. Further understanding of the role GA plays in glycemic and inflammatory diseases could lead to its acceptance as an independent bio-inflammatory marker.

The endothelial border to health: Mechanistic evidence of the hyperglycemic culprit of inflammatory disease acceleration

The endothelial cell (EC) layer constitutes a barrier that controls movements of fluid, solutes and cells between blood and tissue. Further, the endothelial layer regulates vascular tone and directs local humoral and cellular inflammatory processes. The strategic position makes it an important player for maintenance of health and for development of a number of diseases. Endothelial dysfunction is known to be an important component of type 2 diabetes, but is also assumed to be involved in many other diseases, for example, rheumatoid arthritis, inflammatory bowel disease, asthma, and cardiovascular diseases. We here suggest that the EC plays a pivotal role in disease pathophysiology through initiation, potentiation, and maintenance of several inflammatory mechanisms. Our contention is based on the observation that hyperglycemia-intermittent or sustained, local or systemic-is a major culprit for several endothelial dysfunctions. There is also mounting epidemiological evidence that dietary intake of refined sugars is important for the development of a number of diseases beyond obesity and type 2 diabetes. Various diseases involving inflammatory and immunological components are accelerated by hyperglycemic events because the endothelium transduces "high glucose" signaling into significant pathophysiological phenomena leading to reduced endothelial barrier function, compromised vascular tone regulation and inflammation (e.g., cytokine secretion and RAGE activation). In addition, endothelial extracellular proteins form epitopes for potential specific antibody formation upon interactions with reducing sugars. This paper reviews the endothelial metabolism, biology, inflammatory processes, physical barrier functions, and summarizes evidence that although stochastic in nature, endothelial responses to hyperglycemia are major contributors to disease pathophysiology. We present molecular and mechanistic evidence that both biological and physical barriers, protein function, specific immunity, and inflammatory processes are compromised by hyperglycemic events and thus, hyperglycemic events alone should be considered risk factors for numerous human diseases. © 2017 IUBMB Life, 69(3):148-161, 2017.

Carbonyl stress phenomena during chronic infection with Opisthorchis felineus

Infection with the fish borne liver fluke Opisthorchis felineus is common in the Eastern Europe (Ukraine, European part of Russia), Northern Asia (Siberia) and Central Asia (Northern Kazakhstan). Better understanding of the molecular pathogenesis of the biliary tract and liver during chronic opisthorchiasis can be expected to improve protection against and management of complications of this disease. We hypothesize that infection with O. felineus associates with formation of methylglyoxal and carbonyl stress in the liver and hence here we investigated the glyoxalase system and the receptor for advanced glycated end products (RAGE) in the liver of hamsters infected with this liver fluke. Expression of mRNA encoding glyoxalase 1 decreased at 8weeks of the infection and catalytic activity as well decreased at 8 and 12weeks after infection, and the expression of the glyoxalase 2 decreased until 36week post-infection, which associated with the decreasing activity of the enzyme at 8 and 12weeks post-infection. Glutathione levels in infected livers had decreased at week 8, whereas up-regulation of RAGE at mRNA levels was seen for the extended duration of the experimental infection of the hamsters. This outcome supported the notion of hepatic dicarbonyl stress during chronic opisthorchiasis. The inhibition of the glyoxalase system and accumulation of methylglyoxal at the early stages of the infection may underpin development of insulin resistance during opisthorchiasis.

Cross-sectional Analysis of AGE-CML, sRAGE, and esRAGE with Diabetes and Cardiometabolic Risk Factors in a Community-Based Cohort

BACKGROUND

Advanced glycation end products (AGEs) and their receptors are regarded as central to the development of diabetic complications, but associations with diabetes and cardiometabolic outcomes in previous studies are mixed.

METHODS

Using ELISA assays, we measured N(6)-carboxymethyllysine (AGE-CML), soluble receptor for AGEs (sRAGE), and endogenous secreted receptor for AGEs (esRAGE) in 1874 participants from the Atherosclerosis Risk in Communities study. We conducted a cross-sectional analysis to evaluate associations of these biomarkers with demographics, diabetes, hyperglycemia, cardiometabolic measures, and genetic variants in the gene encoding RAGE, AGER (advanced glycosylation end-product specific receptor).

RESULTS

After adjustment for demographics and body mass index (BMI), there were no significant differences in AGE-CML, sRAGE, or esRAGE by diabetes or hemoglobin A_1c. Black race and AGER genetic variants were strongly associated with lower sRAGE and esRAGE even after adjustment [percent difference (95% CI) in black vs whites in sRAGE: -29.17 (-34.86 to -23.48), esRAGE: -26.97 (-33.11 to -20.84); with rs2070600 in sRAGE: -30.13 (-40.98 to -19.29), and esRAGE: -30.32 (-42.42 to -18.21); with rs2071288 in sRAGE: -20.03 (-34.87 to -5.18), and esRAGE: -37.70 (-55.75 to -19.65)]. Estimated glomerular filtration rate and albuminuria significantly correlated with sRAGE and esRAGE. BMI and C-reactive protein significantly negatively correlated with AGE-CML, sRAGE, and esRAGE. AGE-CML was modestly correlated with fructosamine and glycated albumin.

CONCLUSIONS

AGE-CML, sRAGE, and esRAGE were more related to genetic, kidney, and inflammatory measures than to diabetes in this community-based population. Our results suggest that, when measured by ELISA, these biomarkers lack specificity and are of limited value in evaluating the role of these compounds in diabetes.

The role of miR-190a in methylglyoxal-induced insulin resistance in endothelial cells

Methylglyoxal (MGO) is a reactive dicarbonyl produced as by-product of glycolysis, and its formation is heightened in hyperglycaemia. MGO plasma levels are two-fold to five-fold increased in diabetics and its accumulation promotes the progression of vascular complications. Impairment of endothelium-derived nitric oxide represents a common feature of endothelial dysfunction in diabetics. We previously demonstrated that MGO induces endothelial insulin resistance. Increasing evidence shows that high glucose and MGO modify vascular expression of several microRNAs (miRNAs), suggesting their potential role in the impairment of endothelial insulin sensitivity. The aim of the study is to investigate whether miRNAs may be involved in MGO-induced endothelial insulin resistance in endothelial cells. MGO reduces the expression of miR-190a both in mouse aortic endothelial cells (MAECs) and in aortae from mice knocked-down for glyoxalase-1. miR-190a inhibition impairs insulin sensitivity, whereas its overexpression prevents the MGO-induced insulin resistance in MAECs. miR-190a levels are not affected by the inhibition of ERK1/2 phosphorylation. Conversely, ERK1/2 activation is sustained by miR-190a inhibitor and the MGO-induced ERK1/2 hyper-activation is reduced by miR-190a mimic transfection. Similarly, protein levels of the upstream KRAS are increased by both MGO and miR-190a inhibitor, and these levels are reduced by miR-190a mimic transfection. Interestingly, silencing of KRAS is able to rescue the MGO-impaired activation of IRS1/Akt/eNOS pathway in response to insulin. In conclusion, miR-190a down-regulation plays a role in MGO-induced endothelial insulin resistance by increasing KRAS. This study highlights miR-190a as new candidate for the identification of strategies aiming at ameliorating vascular function in diabetes.

Processed Meat, but Not Unprocessed Red Meat, Is Inversely Associated with Leukocyte Telomere Length in the Strong Heart Family Study

BACKGROUND

Telomeres are repetitive nucleotide sequences (TTAGGG) and their associated proteins at the end of eukaryote chromosomes. Telomere length shortens throughout the lifespan with each cell division, and leukocyte telomere length (LTL) is often used as a biomarker of cellular aging. LTL is related to many chronic diseases, including cardiovascular disease and diabetes. However, to our knowledge, the relation between LTL and risk factors for cardiovascular disease and diabetes, such as dietary intake of processed meat and unprocessed red meat, is largely unknown.

OBJECTIVE

We examined the associations of processed meat intake and unprocessed red meat intake with LTL.

METHODS

This cross-sectional study comprised 2846 American Indians from the Strong Heart Family Study who participated in the 2001-2003 examination. Dietary factors, including past-year consumption of processed meat and unprocessed red meat, were assessed with the use of a 119-item Block Food-Frequency Questionnaire. LTL was measured with the use of quantitative polymerase chain reaction. Generalized estimating equations were used to examine the associations of intake of processed meat and unprocessed red meat with LTL.

RESULTS

Consumption of processed meat was negatively associated with LTL after adjustment for age, sex, site, education, smoking, alcohol use, physical activity, and other dietary factors. For every additional daily serving of processed meat, LTL was 0.021 units (telomeric product-to-single-copy gene ratio) shorter (β ± SE = -0.021 ± 0.008, P = 0.009). No association was observed between the intake of unprocessed red meat and LTL (β ± SE = 0.008 ± 0.011, P = 0.46).

CONCLUSIONS

In the Strong Heart Family Study, consumption of processed meat, but not unprocessed red meat, was associated with shorter LTL, a potential mediator for several age-related diseases. Further studies are needed to better understand the biological mechanism by which processed meat intake influences cellular aging.

Role of Galectin-3 in Obesity and Impaired Glucose Homeostasis

Galectin-3 is an important modulator of several biological functions. It has been implicated in numerous disease conditions, particularly in the long-term complications of diabetes because of its ability to bind the advanced glycation/lipoxidation end products that accumulate in target organs and exert their toxic effects by triggering proinflammatory and prooxidant pathways. Recent evidence suggests that galectin-3 may also participate in the development of obesity and type 2 diabetes. It has been shown that galectin-3 levels are higher in obese and diabetic individuals and parallel deterioration of glucose homeostasis. Two studies in galectin-3 knockout mice fed a high-fat diet (HFD) have shown increased adiposity and adipose tissue and systemic inflammation associated with altered glucose homeostasis, suggesting that galectin-3 negatively modulates the responsiveness of innate and adaptive immunity to overnutrition. However, these studies have also shown that impaired glucose homeostasis occurs in galectin-3 knockout animals independently of obesity. Moreover, another study reported decreased weight and fat mass in HFD-fed galectin-3 knockout mice. In vitro, galectin-3 was found to stimulate differentiation of preadipocytes into mature adipocytes. Altogether, these data indicate that galectin-3 deserves further attention in order to clarify its role as a potential player and therapeutic target in obesity and type 2 diabetes.

Accumulation of advanced glycation end-products and activation of the SCAP/SREBP Lipogenetic pathway occur in diet-induced obese mouse skeletal muscle

Aim of this study was to investigate whether advanced glycation end-products (AGEs) accumulate in skeletal myofibers of two different animal models of diabesity and whether this accumulation could be associated to myosteatosis. Male C57Bl/6j mice and leptin-deficient ob/ob mice were divided into three groups and underwent 15 weeks of dietary manipulation: standard diet-fed C57 group (C57, n = 10), high-fat high-sugar diet-fed C57 group (HFHS, n = 10), and standard diet-fed ob/ob group (OB/OB, n = 8). HFHS mice and OB/OB mice developed glycometabolic abnormalities in association with decreased mass of the gastrocnemius muscle, fast-to-slow transition of muscle fibers, and lipid accumulation (that occurred preferentially in slow compared to fast fibers). Moreover, we found in muscle fibers of HFHS and OB/OB mice accumulation of AGEs that was preferential for the lipid-accumulating cells, increased expression of the lipogenic pathway SCAP/SREBP, and co-localisation between AGEs and SCAP-(hyper)expressing cells (suggestive for SCAP glycosylation). The increased expression of the SCAP/SREBP lipogenic pathway in muscle fibers is a possible mechanism underlying lipid accumulation and linking myosteatosis to muscle fiber atrophy and fast-to-slow transition that occur in response to diabesity.

Fructosamine 3-kinase and glyoxalase I polymorphisms and their association with soluble RAGE and adhesion molecules in diabetes

Advanced glycation end-products (AGEs) are key players in pathogenesis of long-term vascular diabetes complications. Several enzymes such as fructosamine 3-kinase (FN3K) and glyoxalase I (GLO I) are crucial in preventing glycation processes. The aim of our study was to evaluate an association of FN3K (rs1056534, rs3848403) and GLO1 rs4746 polymorphisms with parameters of endothelial dysfunction and soluble receptor for AGEs (sRAGE) in 595 diabetic and non-diabetic subjects. Genotypic and allelic frequencies of mentioned polymorphisms did not differ between subgroups. In diabetic patients significant differences were observed in sRAGE concentrations according to their rs1056534 and rs3848403 genotype. While GG and CG genotypes of rs1056534 with mutated G allele were associated with significant decrease of sRAGE (GG: 1055+/-458 and CG: 983+/-363 vs. CC: 1796+/-987 ng/l, p<0.0001), in rs3848403 polymorphism TT genotype with mutated T allele was related with significant sRAGE increase (TT: 1365+/-852 vs. CT: 1016+/-401 and CC: 1087+/-508 ng/l, p=0.05). Significant differences in adhesion molecules were observed in genotype subgroups of GLO1 rs4746 polymorphism. In conclusion, this is the first study describing significant relationship of FN3K (rs1056534) and (rs3848403) polymorphisms with concentration of sRAGE in patients with diabetes.

Dietary consumption of advanced glycation end products and pancreatic cancer in the prospective NIH-AARP Diet and Health Study

BACKGROUND

Advanced glycation end products (AGEs) are a heterogeneous group of compounds present in uncooked foods as well as in foods cooked at high temperatures. AGEs have been associated with insulin resistance, oxidative stress, and chronic inflammation in patients with diabetes. Dietary AGEs are an important contributor to the AGE pool in the body. N(ϵ)-(carboxymethyl)lysine (CML) AGE is one of the major biologically and chemically well-characterized AGE markers. The consumption of red meat, which is CML-AGE rich, has been positively associated with pancreatic cancer in men.

OBJECTIVES

With the use of a published food CML-AGE database, we estimated the consumption of CML AGE in the prospective NIH-AARP Diet and Health Study and evaluated the association between CML-AGE consumption and pancreatic cancer and the mediating effect of CML AGE on the association between red meat consumption and pancreatic cancer.

DESIGN

Multivariate Cox proportional hazard regression models were used to estimate HRs and 95% CIs for pancreatic cancer.

RESULTS

During an average of 10.5 y of follow-up, we identified 2193 pancreatic cancer cases (1407 men and 786 women) from 528,251 subjects. With the comparison of subjects in the fifth and the first quintiles of CML-AGE consumption, we observed increased pancreatic cancer risk in men (HR: 1.43; 95% CI: 1.06, 1.93, P-trend = 0.003) but not women (HR: 1.14; 95% CI: 0.76, 1.72, P-trend = 0.42). Men in the highest quintile of red meat consumption had higher risk of pancreatic cancer (HR: 1.35; 95% CI: 1.07, 1.70), which attenuated after adjustment for CML-AGE consumption (HR: 1.20; 95% CI: 0.95, 1.53).

CONCLUSION

Dietary CML-AGE consumption was associated with modestly increased risk of pancreatic cancer in men and may partially explain the positive association between red meat and pancreatic cancer.

The clinical burden of type 2 diabetes in patients with acute coronary syndromes: prognosis and implications for short- and long-term management

Type 2 diabetes mellitus (T2DM) is associated with increased morbidity and mortality in patients with acute coronary syndromes (ACS). Cardiometabolic risk factors, including hyperglycaemia, insulin resistance, atherogenic dyslipidaemia, increased visceral fat and inflammation, are associated with increased risk in this population and represent potential targets for treatment. In this review, management strategies for patients with T2DM post-ACS, both in the acute-care setting and in the long-term, are discussed. Although the benefits of long-term, aggressive, multifactorial risk factor modification are well established, a significant burden of recurrent events remains and the search for novel strategies continues. Several studies are assessing the potential cardiovascular (CV) benefits and safety of various classes of newer agents. Of these, AleCardio (aleglitazar), Examination of Cardiovascular Outcomes With Alogliptin versus Standard of Care in Patients With Type 2 Diabetes Mellitus and Acute Coronary Syndrome (EXAMINE; alogliptin) and Evaluation of LIXisenatide in Acute Coronary Syndrome (ELIXA; lixisenatide) specifically address patients with type 2 diabetes post-ACS. The mechanisms of action of these new therapies and aims of the CV outcome studies are briefly reviewed. The prevalence of type 2 diabetes continues to increase worldwide highlighting the need for new strategies that address the complex underlying processes that drive atherosclerosis and CV events in this high-risk patient population.

Is Alzheimer's disease related to metabolic syndrome? A Wnt signaling conundrum

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. AD is characterized by a progressive loss of cognitive functions. For years, it has been thought that age is the main risk factor for AD. Recent studies suggest that life style factors, including nutritional behaviors, play a critical role in the onset of dementia. Evidence about the relationship between nutritional behavior and AD includes the role of conditions such as obesity, hypertension, dyslipidemia and elevated glucose levels. The coexistence of some of these cardio-metabolic risk factors is generally known as metabolic syndrome (MS). Some clinical studies support the role of MS in the onset of AD. However, the cross-talk between the molecular signaling implicated in these disorders is unknown. In the present review, we focus on the molecular correlates that support the relationship between MS and the onset of AD. We also discuss relevant issues such as the role of leptin, insulin and renin-angiotensin signaling in the brain and the possible role of Wnt signaling in both MS and AD. We discuss the evidence supporting the use of ob/ob mice, high-fructose diets, aortic coarctation-induced hypertension and Octodon degus, which spontaneously develops β-amyloid deposits and metabolic derangements, as suitable animal models to address the relationships between MS and AD. Finally, we examine emergent data supporting the role of Wnt signaling in the modulation of AD and MS, implicating this pathway as a therapeutic target in both conditions.