A 4-week high-AGE diet does not impair glucose metabolism and vascular function in obese individuals

Comparative Study of the Effects of Dietary-Free and -Bound Nε-Carboxymethyllysine on Gut Microbiota and Intestinal Barrier

Nε-carboxymethyllysine (CML) is produced by a nonenzymatic reaction between reducing sugar and ε-amino group of lysine in food and exists as free and bound forms with varying digestibility and absorption properties in vivo, causing diverse interactions with gut microbiota. The effects of different forms of dietary CML on the gut microbiota and intestinal barrier of mice were explored. Mice were exposed to free and bound CML for 12 weeks, and colonic morphology, gut microbiota, fecal short-chain fatty acids (SCFAs), intestinal barrier, and receptor for AGE (RAGE) signaling cascades were measured. The results indicated that dietary-free CML increased the relative abundance of SCFA-producing genera including Blautia, Faecalibacterium, Agathobacter, and Roseburia. In contrast, dietary-bound CML mainly increased the relative abundance of Akkermansia. Moreover, dietary-free and -bound CML promoted the gene and protein expression of zonula occludens-1 and claudin-1. Additionally, the intake of free and bound CML caused an upregulation of RAGE expression but did not activate downstream inflammatory pathways due to the upregulation of oligosaccharyl transferase complex protein 48 (AGER1) expression, indicating a delicate balance between protective and proinflammatory effects in vivo. Dietary-free and -bound CML could modulate the gut microbiota community and increase tight-junction expression, and dietary-free CML might exert a higher potential benefit on gut microbiota and SCFAs than dietary-bound CML.

Dietary Nε-(carboxymethyl)lysine is a trigger of non-alcoholic fatty liver disease under high-fat consumption

The irreversible glycation of proteins produces advanced glycation end products (AGEs) which are triggered to bind the receptor for AGE (RAGE), thereby activating mitogen-activated protein kinase/nuclear factor-κB signaling pathway and stimulating proinflammatory cytokines, ultimately leading to chronic disorders. In this study, we focus the promoting effect of Nε-carboxymethyl-lysine (CML), one of the most dietary AGEs, on non-alcoholic fatty liver disease (NAFLD) and evaluated NAFLD-related biomarkers. Oxidative stress and hepatic steatosis were assessed in oleic acid (OA)-induced HepG2 cells. Using OA-induced HepG2 cells, we show that CML results in oxidative stress and steatosis and drives major changes in hepatic lipid metabolism. Administration of CML exacerbated NAFLD-related symptoms by increasing body and liver weight gain, serum alanine aminotransferase and lipid levels, and insulin resistance in mild high-fat diet-induced mice. Moreover, hepatic histological analysis data, such as staining, western blotting, and RNA-seq, indicate that CML aggravates NAFLD in association with activation of the de novo lipogenesis pathway, consistent with the in vitro assays. Our findings could contribute to model studies related to the prevention and treatment of NAFLD progression due to excessive consumption of dietary AGEs.

Dietary Advanced Glycation End Products: Their Role in the Insulin Resistance of Aging

Insulin resistance (IR) is commonly observed during aging and is at the root of many of the chronic nontransmissible diseases experienced as people grow older. Many factors may play a role in causing IR, but diet is undoubtedly an important one. Whether it is total caloric intake or specific components of the diet, the factors responsible remain to be confirmed. Of the many dietary influences that may play a role in aging-related decreased insulin sensitivity, advanced glycation end products (AGEs) appear particularly important. Herein, we have reviewed in detail in vitro, animal, and human evidence linking dietary AGEs contributing to the bodily burden of AGEs with the development of IR. We conclude that numerous small clinical trials assessing the effect of dietary AGE intake in combination with strong evidence in many animal studies strongly suggest that reducing dietary AGE intake is associated with improved IR in a variety of disease conditions. Reducing AGE content of common foods by simple changes in culinary techniques is a feasible, safe, and easily applicable intervention in both health and disease. Large-scale clinical trials are still needed to provide broader evidence for the deleterious role of dietary AGEs in chronic disease.

Habitual intake of advanced glycation endproducts is not associated with worse insulin sensitivity, worse beta cell function, or presence of prediabetes or type 2 diabetes: The Maastricht Study

BACKGROUND & AIMS

A diet high in advanced glycation endproducts (AGEs) is a potential risk factor for insulin resistance, beta cell dysfunction, and ultimately type 2 diabetes. We investigated associations between habitual intake of dietary AGEs and glucose metabolism in a population-based setting.

METHODS

In 6275 participants of The Maastricht Study (mean ± SD age: 60 ± 9, 15.1% prediabetes and 23.2% type 2 diabetes), we estimated habitual intake of dietary AGEs N^ε-(carboxymethyl)lysine (CML), N^ε-(1-carboxyethyl)lysine (CEL), and N^δ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) by combining a validated food frequency questionnaire (FFQ) with our mass-spectrometry dietary AGE database. We determined insulin sensitivity (Matsuda- and HOMA-IR index), beta cell function (C-peptidogenic index, glucose sensitivity, potentiation factor, and rate sensitivity), glucose metabolism status, fasting glucose, HbA1c, post-OGTT glucose, and OGTT glucose incremental area under the curve. Cross-sectional associations between habitual AGE intake and these outcomes were investigated using a combination of multiple linear regression and multinomial logistic regression adjusting for several potential confounders (demographic, cardiovascular, and lifestyle factors).

RESULTS

Generally, higher habitual intake of AGEs was not associated with worse indices of glucose metabolism, nor with increased presence of prediabetes or type 2 diabetes. Higher dietary MG-H1 was associated with better beta cell glucose sensitivity.

CONCLUSIONS

The present study does not support an association of dietary AGEs with impaired glucose metabolism. Whether higher intake of dietary AGEs translates to increased incidence of prediabetes or type 2 diabetes on the long term should be investigated in large prospective cohort studies.

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

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

Dietary Nε-(carboxymethyl) lysine affects cardiac glucose metabolism and myocardial remodeling in mice

BACKGROUND

Myocardial remodeling is a key factor in the progression of cardiovascular disease to the end stage. In addition to myocardial infarction or stress overload, dietary factors have recently been considered associated with myocardial remodeling. N^ε-(carboxymethyl)lysine (CML) is a representative foodborne toxic product, which can be ingested via daily diet. Therefore, there is a marked need to explore the effects of dietary CML on the myocardium.

AIM

To explore the effects of dietary CML (dCML) on the heart.

METHODS

C57 BL/6 mice were divided into a control group and a dCML group. The control group and the dCML group were respectively fed a normal diet or diet supplemented with CML for 20 wk. Body weight and blood glucose were recorded every 4 wk. ¹⁸F-fluorodeoxyglucose (FDG) was used to trace the glucose uptake in mouse myocardium, followed by visualizing with micro-positron emission tomography (PET). Myocardial remodeling and glucose metabolism were also detected. In vitro, H9C2 cardiomyocytes were added to exogenous CML and cultured for 24 h. The effects of exogenous CML on glucose metabolism, collagen I expression, hypertrophy, and apoptosis of cardiomyocytes were analyzed.

RESULTS

Our results suggest that the levels of fasting blood glucose, fasting insulin, and serum CML were significantly increased after 20 wk of dCML. Micro-PET showed that ¹⁸F-FDG accumulated more in the myocardium of the dCML group than in the control group. Histological staining revealed that dCML could lead to myocardial fibrosis and hypertrophy. The indexes of myocardial fibrosis, apoptosis, and hypertrophy were also increased in the dCML group, whereas the activities of glucose metabolism-related pathways and citrate synthase (CS) were significantly inhibited. In cardiomyocytes, collagen I expression and cellular size were significantly increased after the addition of exogenous CML. CML significantly promoted cellular hypertrophy and apoptosis, while pathways involved in glucose metabolism and level of Cs mRNA were significantly inhibited.

CONCLUSION

This study reveals that dCML alters myocardial glucose metabolism and promotes myocardial remodeling.

Advanced Glycation End Products and Their Effect on Vascular Complications in Type 2 Diabetes Mellitus

Diabetes is well established as a chronic disease with a high health burden due to mortality or morbidity from the final outcomes of vascular complications. An increased duration of hyperglycemia is associated with abnormal metabolism. Advanced glycation end products (AGEs) are nonenzymatic glycated forms of free amino acids that lead to abnormal crosslinking of extra-cellular and intracellular proteins by disrupting the normal structure. Furthermore, the interaction of AGEs and their receptors induces several pathways by promoting oxidative stress and inflammation. In this review, we discuss the role of AGEs in diabetic vascular complications, especially type 2 DM, based on recent clinical studies.

Advanced Glycation End Products (AGEs) and Chronic Kidney Disease: Does the Modern Diet AGE the Kidney?

Since the 1980s, chronic kidney disease (CKD) affecting all ages has increased by almost 25%. This increase may be partially attributable to lifestyle changes and increased global consumption of a “western” diet, which is typically energy dense, low in fruits and vegetables, and high in animal protein and ultra-processed foods. These modern food trends have led to an increase in the consumption of advanced glycation end products (AGEs) in conjunction with increased metabolic dysfunction, obesity and diabetes, which facilitates production of endogenous AGEs within the body. When in excess, AGEs can be pathological via both receptor-mediated and non-receptor-mediated pathways. The kidney, as a major site for AGE clearance, is particularly vulnerable to AGE-mediated damage and increases in circulating AGEs align with risk of CKD and all-cause mortality. Furthermore, individuals with significant loss of renal function show increased AGE burden, particularly with uraemia, and there is some evidence that AGE lowering via diet or pharmacological inhibition may be beneficial for CKD. This review discusses the pathways that drive AGE formation and regulation within the body. This includes AGE receptor interactions and pathways of AGE-mediated pathology with a focus on the contribution of diet on endogenous AGE production and dietary AGE consumption to these processes. We then analyse the contribution of AGEs to kidney disease, the evidence for dietary AGEs and endogenously produced AGEs in driving pathogenesis in diabetic and non-diabetic kidney disease and the potential for AGE targeted therapies in kidney disease.

A 4-Week Diet Low or High in Advanced Glycation Endproducts Has Limited Impact on Gut Microbial Composition in Abdominally Obese Individuals: The deAGEing Trial

Dietary advanced glycation endproducts (AGEs), abundantly present in Westernized diets, are linked to negative health outcomes, but their impact on the gut microbiota has not yet been well investigated in humans. We investigated the effects of a 4-week isocaloric and macronutrient-matched diet low or high in AGEs on the gut microbial composition of 70 abdominally obese individuals in a double-blind parallel-design randomized controlled trial (NCT03866343). Additionally, we investigated the cross-sectional associations between the habitual intake of dietary dicarbonyls, reactive precursors to AGEs, and the gut microbial composition, as assessed by 16S rRNA amplicon-based sequencing. Despite a marked percentage difference in AGE intake, we observed no differences in microbial richness and the general community structure. Only the Anaerostipes spp. had a relative abundance >0.5% and showed differential abundance (0.5 versus 1.11%; p = 0.028, after low- or high-AGE diet, respectively). While the habitual intake of dicarbonyls was not associated with microbial richness or a general community structure, the intake of 3-deoxyglucosone was especially associated with an abundance of several genera. Thus, a 4-week diet low or high in AGEs has a limited impact on the gut microbial composition of abdominally obese humans, paralleling its previously observed limited biological consequences. The effects of dietary dicarbonyls on the gut microbiota composition deserve further investigation.

The RAGE/DIAPH1 Signaling Axis & Implications for the Pathogenesis of Diabetic Complications

Increasing evidence links the RAGE (receptor for advanced glycation end products)/DIAPH1 (Diaphanous 1) signaling axis to the pathogenesis of diabetic complications. RAGE is a multi-ligand receptor and through these ligand-receptor interactions, extensive maladaptive effects are exerted on cell types and tissues targeted for dysfunction in hyperglycemia observed in both type 1 and type 2 diabetes. Recent evidence indicates that RAGE ligands, acting as damage-associated molecular patterns molecules, or DAMPs, through RAGE may impact interferon signaling pathways, specifically through upregulation of IRF7 (interferon regulatory factor 7), thereby heralding and evoking pro-inflammatory effects on vulnerable tissues. Although successful targeting of RAGE in the clinical milieu has, to date, not been met with success, recent approaches to target RAGE intracellular signaling may hold promise to fill this critical gap. This review focuses on recent examples of highlights and updates to the pathobiology of RAGE and DIAPH1 in diabetic complications.