Fructose-derived advanced glycation end-products drive lipogenesis and skeletal muscle reprogramming via SREBP-1c dysregulation in mice

Exploring the glycation association with dyslipidaemia: Novel approach for diabetic nephropathy

The transcription factor known as sterol regulatory element-binding protein (SREBP) and the glycation pathways, specifically the formation of Advanced Glycation End Products (AGEs), have a significant and deleterious impact on the kidney. They alter renal lipid metabolism and promote glomerulosclerosis, mesangial cell expansion, tubulointerstitial fibrosis, and inflammation, leading to diabetic nephropathy (DN) progression. Although several pieces of scientific evidence are reported for potential causes of glycation and lipotoxicity in DN, the underlying mechanism of renal lipid accumulation still needs to be fully understood. We provide a rationalized view on how AGEs exert multiple effects that cause SREBP activation and inflammation, contributing to DN through Receptor for AGEs (RAGE) signaling, AGE-R1-dependent downregulation of Sirtuin 1 (SIRT-1), and increased SREBP Cleavage Activating Protein (SCAP) glycosylation. This review emphasizes the association between glycation and the SREBP pathway and how it affects the onset of DN associated with obesity. Finally, we discuss the correlation of glycation and the SREBP pathway with insulin resistance (IR), oxidative stress, endoplasmic reticulum stress, inflammation, and existing and emerging therapeutic approaches toward better controlling obesity-related DN.

Vitamin D3 mitigates myopathy and metabolic dysfunction in rats with metabolic syndrome: the potential role of dipeptidyl peptidase-4

Metabolic syndrome is associated with vitamin D3 deficiency. This work aims to examine the efficacy of vitamin D3 in inhibiting MetS-induced myopathy and to determine whether the beneficial effects of vitamin D3 are mediated by the inhibition of dipeptidyl peptidase-4 (DPP-4). An in silico study investigated the potential effectiveness of vitamin D3 on the inhibition of the DPP-4 enzyme. An in vitro assay of the DPP-4 inhibitory effect of vitamin D3 was performed. In vivo and over 12 weeks, both diet (with 3% salt) and drinking water (with 10% fructose) were utilized to induce MetS. In the seventh week, rats received either vitamin D3, vildagliptin, a combination of both, or vehicles. Serum lipids, adipokines, glycemic indices, and glucagon-like peptide-1 (GLP-1), muscular glucose transporter type-4 (GLUT-4) content, DPP-4, adenosine monophosphate kinase (AMPK) activities, and Sudan Black B-stained lipids were assessed. Muscular reactive oxygen species (ROS), caspase-3, and desmin immunostaining were used to determine myopathy. MetS-induced metabolic dysfunction was ameliorated by vitamin D3, which also reduced intramuscular glycogen and lipid accumulation. This is demonstrated by the attenuation of MetS-induced myopathy by vitamin D3, decreased oxidative stress, increased desmin immuno-expression, and caspase-3 activity. Our in silico data demonstrated that vitamin D3 is capable of inhibiting DPP-4, which is further supported by biochemical findings. Vitamin D3 increased serum GLP-1, muscular AMPK activity, and GLUT-4 content, whereas the levels of muscular ROS were decreased in MetS. Vildagliptin and its combination with vitamin D3 yielded comparable results. It is suggested that the DPP-4 inhibitory potential of vitamin D3 is responsible for the amelioration of MetS-induced metabolic changes and myopathy.

Slot Blot- and Electrospray Ionization-Mass Spectrometry/Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry-Based Novel Analysis Methods for the Identification and Quantification of Advanced Glycation End-Products in the Urine

Proteins, saccharides, and low molecular organic compounds in the blood, urine, and saliva could potentially serve as biomarkers for diseases related to diet, lifestyle, and the use of illegal drugs. Lifestyle-related diseases (LSRDs) such as diabetes mellitus (DM), non-alcoholic steatohepatitis, cardiovascular disease, hypertension, kidney disease, and osteoporosis could develop into life-threatening conditions. Therefore, there is an urgent need to develop biomarkers for their early diagnosis. Advanced glycation end-products (AGEs) are associated with LSRDs and may induce/promote LSRDs. The presence of AGEs in body fluids could represent a biomarker of LSRDs. Urine samples could potentially be used for detecting AGEs, as urine collection is convenient and non-invasive. However, the detection and identification of AGE-modified proteins in the urine could be challenging, as their concentrations in the urine might be extremely low. To address this issue, we propose a new analytical approach. This strategy employs a method previously introduced by us, which combines slot blotting, our unique lysis buffer named Takata's lysis buffer, and a polyvinylidene difluoride membrane, in conjunction with electrospray ionization-mass spectrometry (ESI)/matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). This novel strategy could be used to detect AGE-modified proteins, AGE-modified peptides, and free-type AGEs in urine samples.

Sirtuin 1 as a potential biomarker of undernutrition in the elderly: a narrative review

Undernutrition and inflammatory processes are predictors of early mortality in the elderly and require a rapid and accurate diagnosis. Currently, there are laboratory markers for assessing nutritional status, but new markers are still being sought. Recent studies suggest that sirtuin 1 (SIRT1) has the potential to be a marker for undernutrition. This article summarizes available studies on the association of SIRT1 and undernutrition in older people. Possible associations between SIRT1 and the aging process, inflammation, and undernutrition in the elderly have been described. The literature suggests that low SIRT1 levels in the blood of older people may not be associated with physiological aging processes, but with an increased risk of severe undernutrition associated with inflammation and systemic metabolic changes.

FPS-ZM1 attenuates the deposition of lipid in the liver of diabetic mice by sterol regulatory element binding protein-1c

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) shares common pathogenic mechanisms of type 2 diabetes mellitus (T2DM) with upregulated advanced glycation end products (AGEs). Here, we aim to investigate the effect of FPS-ZM1, an inhibitor for receptor for AGEs (RAGE), on lipid deposition in the liver of mice.

METHODS

KK-Ay mice were used as models of T2DM with NAFLD, while C57BL/6j mice were controls. Additionally, KK-Ay mice were treated with DMSO (with a concentration of 1%), with or without FPS-ZM1 (3 mg/kg/day, i.p). Lipid deposition in hepatocytes was observed using oil red O stain. Levels of AGEs and RAGE were measured. Sterol regulatory element-binding protein-1c (SREBP-1c), as well as nuclear factor κB p65 (p65 nfκb) and mitogen-activated protein kinase p38 (p38 MAPK), were also detected.

RESULTS

Lipid deposition is increased in the hepatocytes of KK-Ay mice compared to C57BL/6j mice. In addition, not only were the levels of AGEs elevated in plasma, but also the levels of RAGE in liver tissue. Although total SREBP-1c levels did not change in the liver of diabetic mice, mature SREBP-1c increased in KK-Ay mice with diabetes mellitus. Moreover, diabetic mice showed increased levels of phosphorylated-p65 nfκb (p-p65 nfκb) and phosphorylated-p38 MAPK (p-p38 MAPK). On the contrary, FPS-ZM1 decreased lipid deposition in liver cells, as well as mature SREBP-1c, p-p65 nfκb and p-p38 MAPK levels in liver tissue.

CONCLUSION

Generally, FPS-ZM1 may attenuate lipid deposition in hepatocytes of diabetic mice via SREBP-1c down-regulation. This may depend on the downregulation of p65 nfκb and p38 MAPK phosphorylation.

Advanced Glycation End-Products Acting as Immunomodulators for Chronic Inflammation, Inflammaging and Carcinogenesis in Patients with Diabetes and Immune-Related Diseases

Increased production of advanced glycation end products (AGEs) among reducing sugars (glucose, fructose, galactose, or ribose) and amino acids/proteins via non-enzymatic Maillard reaction can be found in lifestyle-related disease (LSRD), metabolic syndrome (MetS), and obesity and immune-related diseases. Increased serum levels of AGEs may induce aging, diabetic complications, cardiovascular diseases (CVD), neurodegenerative diseases (NDD), cancer, and inflamm-aging (inflammation with immunosenescence). The Maillard reaction can also occur among reducing sugars and lipoproteins or DNAs to alter their structure and induce immunogenicity/genotoxicity for carcinogenesis. AGEs, as danger-associated molecular pattern molecules (DAMPs), operate via binding to receptor for AGE (RAGE) or other scavenger receptors on cell surface to activate PI3K-Akt-, P38-MAPK-, ERK1/2-JNK-, and MyD88-induced NF-κB signaling pathways to mediate various pathological effects. Recently, the concept of "inflamm-aging" became more defined, and we have unveiled some interesting findings in relation to it. The purpose of the present review is to dissect the potential molecular basis of inflamm-aging in patients with diabetes and immune-mediated diseases caused by different AGEs.

Pomegranate supplementation alleviates dyslipidemia and the onset of non-alcoholic fatty liver disease in Wistar rats by shifting microbiota and producing urolithin-like microbial metabolites

Non-alcoholic fatty liver disease (NAFLD), obesity and related chronic diseases are major non-communicable diseases with high mortality rates worldwide. While dietary sugars are known to be responsible for insulin resistance and metabolic syndrome (MetS), the underlying pathophysiological effects of sustained fructose consumption require further elucidation. We hypothesize that certain bioactive compounds (i.e. punicalagin and ellagic acid) from dietary pomegranate could counteract the harmful effects of sustained fructose consumption in terms of obesity and liver damage. The present study aimed to elucidate both the molecular mechanisms involved in the pathophysiology associated with fructose intake and the effect of a punicalagin-rich commercial pomegranate dietary supplement (P) used as a nutritional strategy to alleviate fructose-induced metabolic impairments. Thus, nineteen Wistar rats fed on a basal commercial feed were supplemented with either 30% (w/v) fructose in drinking water (F; n = 7) or 30% (w/v) fructose solution plus 0.2% (w/v) P (F + P; n = 6) for 10 weeks. The results were compared to those from a control group fed on the basal diet and provided with drinking water (C; n = 6). Body weight and energy intake were registered weekly. P supplementation decreased fat depots, counteracted the dyslipidemia caused by F and improved markers of liver injury including steatosis. The study of the microbiota by metagenomics and urine by untargeted MS-based metabolomics revealed microbial metabolites from P that may be responsible for these health benefits.

Generation and Accumulation of Various Advanced Glycation End-Products in Cardiomyocytes May Induce Cardiovascular Disease

Cardiomyocyte dysfunction and cardiovascular diseases (CVDs) can be classified as ischemic or non-ischemic. We consider the induction of cardiac tissue dysfunction by intracellular advanced glycation end-products (AGEs) in cardiomyocytes as a novel type of non-ischemic CVD. Various types of AGEs can be generated from saccharides (glucose and fructose) and their intermediate/non-enzymatic reaction byproducts. Recently, certain types of AGEs (Nε-carboxymethyl-lycine [CML], 2-ammnonio-6-[4-(hydroxymetyl)-3-oxidopyridinium-1-yl]-hexanoate-lysine [4-hydroxymethyl-OP-lysine, hydroxymethyl-OP-lysine], and Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine [MG-H1]) were identified and quantified in the ryanodine receptor 2 (RyR2) and F-actin-tropomyosin filament in the cardiomyocytes of mice or patients with diabetes and/or heart failure. Under these conditions, the excessive leakage of Ca2+ from glycated RyR2 and reduced contractile force from glycated F-actin-tropomyosin filaments induce cardiomyocyte dysfunction. CVDs are included in lifestyle-related diseases (LSRDs), which ancient people recognized and prevented using traditional medicines (e.g., Kampo medicines). Various natural compounds, such as quercetin, curcumin, and epigallocatechin-3-gallate, in these drugs can inhibit the generation of intracellular AGEs through mechanisms such as the carbonyl trap effect and glyoxalase 1 activation, potentially preventing CVDs caused by intracellular AGEs, such as CML, hydroxymethyl-OP, and MG-H1. These investigations showed that bioactive herbal extracts obtained from traditional medicine treatments may contain compounds that prevent CVDs.

Anti-Glycation Properties of Zinc-Enriched Arthrospira platensis (Spirulina) Contribute to Prevention of Metaflammation in a Diet-Induced Obese Mouse Model

Advanced glycation end products (AGEs) exert a key pathogenic role in the development of obesity and insulin resistance. Thanks to its abundance in bioactive compounds, the microalga Arthrospira platensis (spirulina, SP) is proposed as a nutritional supplement. Here, we investigated the potential anti-glycating properties of SP enriched with zinc (Zn-SP) and the following impact on diet-induced metabolic derangements. Thirty male C57Bl6 mice were fed a standard diet (SD) or a high-fat high-sugar diet (HFHS) for 12 weeks, and a subgroup of HFHS mice received 350 mg/kg Zn-SP three times a week. A HFHS diet induced obesity and glucose intolerance and increased plasma levels of pro-inflammatory cytokines and transaminases. Zn-SP administration restored glucose homeostasis and reduced hepatic dysfunction and systemic inflammation. In the liver of HFHS mice, a robust accumulation of AGEs was detected, paralleled by increased expression of the main AGE receptor (RAGE) and depletion of glyoxalase-1, whereas Zn-SP administration efficiently prevented these alterations reducing local pro-inflammatory responses. 16S rRNA gene profiling of feces and ileum content revealed altered bacterial community structure in HFHS mice compared to both SD and HFHS + Zn-SP groups. Overall, our study demonstrates relevant anti-glycation properties of Zn-SP which contribute to preventing AGE production and/or stimulate AGE detoxification, leading to the improvement of diet-related dysbiosis and metabolic derangements.

Dietary Intake of Fructooligosaccharides Protects against Metabolic Derangements Evoked by Chronic Exposure to Fructose or Galactose in Rats

SCOPE

Diets rich in fat and sugars evoke chronic low-grade inflammation, leading to metabolic derangements. This study investigates the impact of fructose and galactose, two commonly consumed simple sugars, on exacerbation of the harmful effects caused by high fat intake. Additionally, the potential efficacy of fructooligosaccharides (FOS), a fermentable dietary fiber, in counteracting these effects is examined.

METHODS AND RESULTS

Male Sprague-Dawley rats (six/group) are fed 8 weeks as follows: control 5% fat diet (CNT), 20% fat diet (FAT), FAT+10% FOS diet (FAT+FOS), FAT+25% galactose diet (FAT+GAL), FAT+GAL+10% FOS diet (FAT+GAL+FOS), FAT+25% fructose diet (FAT+FRU), FAT+FRU+10% FOS diet (FAT+FRU+FOS). The dietary manipulations tested do not affect body weight gain, blood glucose, or markers of systemic inflammation whereas significant increases in plasma concentrations of triacylglycerols, cholesterol, aspartate aminotransferase, and alanine aminotrasferase are detected in both FAT+FRU and FAT+GAL compared to CNT. In the liver and skeletal muscle, both sugars induce significant accumulation of lipids and advanced glycation end-products (AGEs). FOS supplementation prevents these impairments.

CONCLUSION

This study extends the understanding of the deleterious effects of a chronic intake of simple sugars and demonstrates the beneficial role of the prebiotic FOS in dampening the sugar-induced metabolic impairments by prevention of lipid and AGEs accumulation.

Multiphoton imaging of the monosachharide induced formation of fluorescent advanced glycation end products in tissues

We studied the in vitro rate of fluorescent advanced glycation end products (fAGEs) formation with multiphoton microscopy in different porcine tissues (aorta, cornea, kidney, dermis, and tendon). These tissues were treated with d-glucose, d-galactose, and d-fructose, three primary monosaccharides found in human diets. We found that the use of d-fructose resulted in the highest glycation rate, followed by d-galactose and then d-glucose. Moreover, compared to non-collagen tissue constituents such as elastic fibers and cells, the rate of tissue glycation was consistently higher in collagen, suggesting that collagen is a more sensitive target for fAGE formation. However, we also found that collagen in different tissues exhibits different rates of fAGE formation, with slower rates observed in tightly packed tissues such as cornea and tendon. Our study suggests that for fAGE to be developed into a long-term glycemic biomarker, loosely organized collagen tissues located in the proximity of vasculature may be the best targets.

SIRT1/SREBPs-mediated regulation of lipid metabolism

Sirtuins, also called silent information regulator 2, are enzymes that rely on nicotinamide adenine dinucleotide (NAD+) to function as histone deacetylases. Further investigation is warranted to explore the advantageous impacts of Sirtuin 1 (SIRT1), a constituent of the sirtuin group, on lipid metabolism, in addition to its well-researched involvement in extending lifespan. The regulation of gene expression has been extensively linked to SIRT1. Sterol regulatory element-binding protein (SREBP) is a substrate of SIRT1 that has attracted significant interest due to its role in multiple cellular processes including cell cycle regulation, DNA damage repair, and metabolic functions. Hence, the objective of this analysis was to investigate and elucidate the correlation between SIRT1 and SREBPs, as well as assess the contribution of SIRT1/SREBPs in mitigating lipid metabolism dysfunction. The objective of this research was to investigate whether SIRT1 and SREBPs could be utilized as viable targets for therapeutic intervention in managing complications associated with diabetes.

Analysis of Crude, Diverse, and Multiple Advanced Glycation End-Product Patterns May Be Important and Beneficial

Lifestyle-related diseases (LSRDs), such as diabetes mellitus, cardiovascular disease, and nonalcoholic steatohepatitis, are a global crisis. Advanced glycation end-products (AGEs) have been extensively researched because they trigger or promote LSRDs. Recently, techniques such as fluorimetry, immunostaining, Western blotting, slot blotting, enzyme-linked immunosorbent assay, gas chromatography-mass spectrometry, matrix-assisted laser desorption-mass spectrometry (MALDI-MS), and electrospray ionization-mass spectrometry (ESI-MS) have helped prove the existence of intra/extracellular AGEs and revealed novel AGE structures and their modifications against peptide sequences. Therefore, we propose modifications to the existing categorization of AGEs, which was based on the original compounds identified by researchers in the 20th century. In this investigation, we introduce the (i) crude, (ii) diverse, and (iii) multiple AGE patterns. The crude AGE pattern is based on the fact that one type of saccharide or its metabolites or derivatives can generate various AGEs. Diverse and multiple AGE patterns were introduced based on the possibility of combining various AGE structures and proteins and were proven through mass analysis technologies such as MALDI-MS and ESI-MS. Kampo medicines are typically used to treat LSRDs. Because various compounds are contained in Kampo medicines and metabolized to exert effects on various organs or tissues, they may be suitable against various AGEs.

Is the Novel Slot Blot a Useful Method for Quantification of Intracellular Advanced Glycation End-Products?

Various types of advanced glycation end-products (AGEs) have been identified and studied. I have reported a novel slot blot analysis to quantify two types of AGEs, glyceraldehyde-derived AGEs, also called toxic AGEs (TAGE), and 1,5-anhydro-D-fructose AGEs. The traditional slot blot method has been used for the detection and quantification of RNA, DNA, and proteins since around 1980 and is one of the more commonly used analog technologies to date. However, the novel slot blot analysis has been used to quantify AGEs from 2017 to 2022. Its characteristics include (i) use of a lysis buffer containing tris-(hydroxymethyl)-aminomethane, urea, thiourea, and 3-[3-(cholamidopropyl)-dimetyl-ammonio]-1-propane sulfonate (a lysis buffer with a composition similar to that used in two-dimensional gel electrophoresis-based proteomics analysis); (ii) probing of AGE-modified bovine serum albumin (e.g., standard AGE aliquots); and (iii) use of polyvinylidene difluoride membranes. In this review, the previously used quantification methods of slot blot, western blot, immunostaining, enzyme-linked immunosorbent assay, gas chromatography-mass spectrometry (MS), matrix-associated laser desorption/ionization-MS, and liquid chromatography-electrospray ionization-MS are described. Lastly, the advantages and disadvantages of the novel slot blot compared to the above methods are discussed.

Accelerated AGEing: The Impact of Advanced Glycation End Products on the Prognosis of Chronic Kidney Disease

Advanced glycation end products (AGEs) are aging products. In chronic kidney disease (CKD), AGEs accumulate due to the increased production, reduced excretion, and the imbalance between oxidant/antioxidant capacities. CKD is therefore a model of aging. The aim of this review is to summarize the present knowledge of AGEs in CKD onset and progression, also focusing on CKD-related disorders (cardiovascular diseases, sarcopenia, and nutritional imbalance) and CKD mortality. The role of AGEs as etiopathogenetic molecules, as well as potential markers of disease progression and/or therapeutic targets, will be discussed.

Why Is Longevity Still a Scientific Mystery? Sirtuins-Past, Present and Future

The sirtuin system consists of seven highly conserved regulatory enzymes responsible for metabolism, antioxidant protection, and cell cycle regulation. The great interest in sirtuins is associated with the potential impact on life extension. This article summarizes the latest research on the activity of sirtuins and their role in the aging process. The effects of compounds that modulate the activity of sirtuins were discussed, and in numerous studies, their effectiveness was demonstrated. Attention was paid to the role of a caloric restriction and the risks associated with the influence of careless sirtuin modulation on the organism. It has been shown that low modulators' bioavailability/retention time is a crucial problem for optimal regulation of the studied pathways. Therefore, a detailed understanding of the modulator structure and potential reactivity with sirtuins in silico studies should precede in vitro and in vivo experiments. The latest achievements in nanobiotechnology make it possible to create promising molecules, but many of them remain in the sphere of plans and concepts. It seems that solving the mystery of longevity will have to wait for new scientific discoveries.

Dietary advanced glycation end-products (dAGEs) intake and its relation to sarcopenia and frailty - The Rotterdam Study

Studies on mice have shown a relationship between dietary intake of advanced glycation end-products (dAGEs) and deterioration of musculoskeletal health, but human studies are absent. We investigated the relationship between dietary intake of carboxymethyllysine (dCML) - an AGE prototype - and risk of sarcopenia at baseline and after 5 years of follow-up and a single evaluation of physical frailty in participants from the population-based Rotterdam Study. Appendicular lean mass (ALM) was obtained using insight dual-energy X-ray absorptiometry and hand grip strength (HGS) using a hydraulic hand dynamometer. Subjects with both low ALM and weak HGS were classified as having sarcopenia. Frailty (yes/no) was defined by presence of ≥3 and pre-frailty by presence of 1 or 2 components namely, exhaustion, weakness, slowness, weight loss or low physical activity. dCML was calculated using a food frequency questionnaire and dAGE databases. Logistic regression analysis was used to evaluate the odds of physical frailty and prevalent sarcopenia at baseline and follow-up and incident sarcopenia. 2782 participants with an age 66.4 ± 9.9 years and dCML intake 3.3 ± 1.3 mg/day, had data on sarcopenia at both time points. Of whom 84 had sarcopenia at baseline and 73 developed sarcopenia at follow-up. We observed an association of one SD increase in dCML intake with prevalent sarcopenia at baseline [odds ratio, OR = 1.27 (1.01-1.59)] and no association of dCML with incident sarcopenia at 5-year follow-up [OR = 1.12 (0.86-1.44)]. For frailty we analyzed 3577 participants, of whom 1972 were pre-frail and 158 were frail. We observed no association of dCML with either pre-frailty [OR = 0.99 (0.91-1.07)] or frailty [OR = 1.01 (0.83-1.22)] when non-frail subjects were used as reference. Our results show an association of dAGEs with sarcopenia cross-sectionally but not longitudinally where inconclusive findings are observed possibly due to a very low incidence of sarcopenia. There was no association with frailty cross-sectionally.

The Correlation between the Level of Skin Advanced Glycation End Products in Type 2 Diabetes Mellitus and the Stages of Diabetic Retinopathy and the Types of Traditional Chinese Medicine Syndrome

Objective

We aimed to analyze the correlation between the level of skin advanced glycation end products (AGEs) in type 2 diabetes mellitus (T2DM) patients and the diabetic retinopathy (DR) staging in different traditional Chinese medicine (TCM) syndromes.

Methods

416 T2DM patients were divided into normal group, nonproliferative diabetic retinopathy (NPDR) group (mild, moderate, and severe), and proliferative diabetic retinopathy (PDR) group according to the DR grade. Patients' height, weight, fasting blood glucose (FBG), hemoglobin A1C (HbA1c), blood lipid, renal function, and skin AGEs were measured. According to TCM syndrome differentiation criteria, 230 patients with T2DM and DR were divided into I. qi and yin deficiency, collateral stasis group; II. liver and kidney deficiency, eye collaterals loss group; and III. yin and yang deficiency, blood stasis, and phlegm coagulation group.

Results

The skin AGEs levels of different DR staging groups were statistically significant (P < 0.05), and the skin AGEs levels in the mild and moderate NPDR groups were significantly higher (P < 0.05) than those of the normal group. It was significantly higher (P < 0.05) in the severe NPDR group than in the normal group, mild and moderate NPDR groups. The skin AGEs levels of the PDR group were significantly higher (P < 0.05) than the normal group, mild and moderate NPDR groups. It was positively correlated with DR stage, HbA1c, total cholesterol (TC), low-density lipoprotein (LDL), and urine metal analysis (UMA) (r = 0.467, 0.411, 0.413, 0.503, 0.424, P < 0.05). The skin AGEs levels of the qi and yin deficiency and collaterals stasis syndrome group were significantly higher (P < 0.05) than in the liver and kidney deficiency and eye collaterals loss groups. It was also significantly higher (P < 0.05) in yin and yang deficiency, blood stasis, and phlegm coagulation syndrome groups than in qi and yin deficiency and collaterals stasis syndrome groups.

Conclusion

There is a positive correlation between skin AGEs and DR staging in T2DM patients. Skin AGEs level is predictive for the risk of DR complications in T2DM patients and is vital in assessing DR degree per TCM syndrome type.

Studies about the Dietary Impact on "Free" Glycation Compounds in Human Saliva

Glycation reactions play a key role in post-translational modifications of amino acids in food proteins. Questions have arisen about a possible pathophysiological role of dietary glycation compounds. Several studies assessed the metabolic fate of dietary glycation compounds into blood and urine, but studies about saliva are rare. We investigated here the dietary impact on salivary concentrations of the individual Maillard reaction products (MRPs) N-ε-fructosyllysine, N-ε-carboxymethyllysine (CML), N-ε-carboxyethyllysine (CEL), pyrraline (Pyr), and methylglyoxal-derived hydroimidazolone 1 (MG-H1). Quantitation was performed using stable isotope dilution analysis (LC-MS/MS). We describe here, that a low MRP diet causes a significant lowering of salivary levels of Pyr from 1.9 ± 0.4 ng/mL to below the LOD and MG-H1 from 2.5 ± 1.5 ng/mL to 0.7 ± 1.8 ng/mL. An impact on the salivary protein fraction was not observed. Furthermore, salivary Pyr and MG-H1 levels are modified in a time-dependent manner after a dietary intervention containing 1.2 mg Pyr and 4.7 mg MG-H1. An increase in mean salivary concentrations to 1.4 ng/mL Pyr and 4.2 ng/mL MG-H1 was observed within 30–210 min. In conclusion, saliva may be a useful tool for monitoring glycation compound levels by using Pyr and MG-H1 as biomarkers for intake of heated food.

Fructose-mediated NLRP3 activation induces inflammation and lipogenesis in adipose tissue

Adipose tissue plays a crucial role in energy intake and regulation of metabolic homeostasis. Fructose consumption implicates in development and progression of metabolic dysfunctions. Fructose is a lipogenic sugar known to induce inflammatory response. However, the role of specific inflammatory signal such as nucleotide-binding and oligomerization domain-like receptor, leucine-rich repeat and pyrin domain containing protein 3 (NLRP3) in fructose-induced inflammatory response and its relevance to lipogenesis in adipose tissue are elusive. We assessed NLRP3 activation and its significance in inflammatory response and lipogenesis in epididymal adipose tissue of 60% fructose diet (HFrD)-fed rats. The long term consumption of HFrD led to impairment of glucose metabolism, development of visceral adiposity, insulin resistance, and elevation of serum triglycerides level, accompanied by activation of NLRP3 in adipose tissue. NLRP3 inflammasome activation in adipose tissue was associated with up-regulated expression of Nlrp3, Asc, and Caspase-1, and raised caspase-1 activity, which resulted in increased expression of IL-1β and IL-18 and secretion of IL-1β. Moreover, lipid accumulation and expression of transcription factors exacerbating accumulation of lipids were augmented in adipose tissue of HFrD-fed rats. Treatment with glyburide, quercetin or allopurinol corrected HFrD-induced dyslipidemia or hyperuricemia, and blocked NLRP3 activation, leading to mitigated inflammatory signalling and lipid accumulation in adipose tissue, improved glucose tolerance and insulin sensitivity in HFrD-fed rats. These data suggest the role of NLRP3 inflammasome to establish linkage among inflammation, lipid accumulation and insulin resistance in adipose tissue, and targeting NLRP3 inflammasome may be a plausible approach for prevention and management for fructose-induced metabolic impairments.

Maternal high-fat diet aggravates fructose-induced mitochondrial damage in skeletal muscles and causes differentiated adaptive responses on lipid metabolism in adult male offspring

Maternal high-fat diet (HFD) is associated with metabolic disturbances in the offspring. Fructose is a highly consumed lipogenic sugar; however, it is unknown whether skeletal muscle of maternal HFD offspring respond differentially to a fructose overload. Female Wistar rats received standard diet (STD: 9% fat) or isocaloric high-fat diet (HFD: 29% fat) during 8 weeks before mating until weaning. After weaning, male offspring received STD and, from 120 to 150 days-old, they drank water or 15% fructose in water (STD-F and HFD-F). At 150th day, we collected the oxidative soleus and glycolytic extensor digitorum longus (EDL) muscles. Fructose-treated groups exhibited hypertriglyceridemia, regardless of maternal diet. Soleus of maternal HFD offspring showed increased triglycerides and monounsaturated fatty acid content, independent of fructose, with increased fatty acid transporters and lipogenesis markers. The EDL exhibited unaltered triglycerides content, with an apparent equilibrium between lipogenesis and lipid oxidation markers in HFD, and higher lipid uptake (fatty acid-binding protein 4) accompanied by enhanced monounsaturated fatty acid in fructose-treated groups. Mitochondrial complexes proteins and Tfam mRNA were increased in the soleus of HFD, while uncoupling protein 3 was decreased markedly in HFD-F. In EDL, maternal HFD increased ATP synthase, while fructose decreased Tfam predominantly in STD offspring. Maternal HFD and fructose induced mitochondria ultrastructural damage, intensified in HFD-F in both muscles. Thus, alterations in molecular markers of lipid metabolism and mitochondrial function in response to fructose are modified by an isocaloric and moderate maternal HFD and are fiber-type specific, representing adaptation/maladaptation mechanisms associated with higher skeletal muscle fructose-induced mitochondria injury in adult offspring.

Curcumin Prevents the Glycation of Tricarboxylic Acid Cycle and Cell Respiration Proteins in the Heart of Mice Fed with a High-Fructose Diet

BACKGROUND

A high fructose diet (HFD) induces protein glycation. The latter is related to a higher risk of cardiovascular disease. Curcumin is a natural pleiotropic compound that may possess antiglycant properties.

OBJECTIVE

To analyze the effect of curcumin on the content of glycated proteins in the hearts of 6-week-old mice fed with a HFD for 15 weeks.

METHODS

Mice were allocated in four groups (n = 6/group): a control group that received a standard diet (CT); a group that received 30% w/v fructose in water (F); a group that received 0.75% w/w curcumin supplemented in food (C); a group that received 30% w/v fructose in water and 0.75% w/w curcumin supplemented in food (F+C). The content of glycated proteins in the heart was determined by Western Blot (whereas the spots were detected by 2D-PAGE) using anti-AGE and anti-CML antibodies. A densitometric analysis was performed using the ImageLab software. Glycated proteins were identified by MALDI-TOF-MS, and an ontological analysis was performed in terms of biological processes and molecular function based on the STRING and DAVID databases.

RESULTS

Fourteen glycated protein spots were detected, two of them with anti-AGE and the other 12 with anti-CML. In total, eleven glycated proteins were identified, out of which three had decreased glycation levels due to curcumin exposure. The identified proteins participate in processes such as cellular respiration, oxidative phosphorylation, lipid metabolism, carbohydrate metabolism, the tricarboxylic acid cycle (TAC), and the organization of intermediate filaments.

CONCLUSIONS

Curcumin decreased the fructose-induced glycation level of the ACO2, NDUFS7, and DLAT proteins.

AGEs-Induced and Endoplasmic Reticulum Stress/Inflammation-Mediated Regulation of GLUT4 Expression and Atherogenesis in Diabetes Mellitus

In recent decades, complex and exquisite pathways involved in the endoplasmic reticulum (ER) and inflammatory stress responses have been demonstrated to participate in the development and progression of numerous diseases, among them diabetes mellitus (DM). In those pathways, several players participate in both, reflecting a complicated interplay between ER and inflammatory stress. In DM, ER and inflammatory stress are involved in both the pathogenesis of the loss of glycemic control and the development of degenerative complications. Furthermore, hyperglycemia increases the generation of advanced glycation end products (AGEs), which in turn refeed ER and inflammatory stress, contributing to worsening glycemic homeostasis and to accelerating the development of DM complications. In this review, we present the current knowledge regarding AGEs-induced and ER/inflammation-mediated regulation of the expression of GLUT4 (solute carrier family 2, facilitated glucose transporter member 4), as a marker of glycemic homeostasis and of cardiovascular disease (CVD) development/progression, as a leading cause of morbidity and mortality in DM.

Deletion of RAGE fails to prevent hepatosteatosis in obese mice due to impairment of other AGEs receptors and detoxifying systems

Advanced glycation endproducts (AGEs) are involved in several diseases, including NAFLD and NASH. RAGE is the main receptor mediating the pro-inflammatory signalling induced by AGEs. Therefore, targeting of RAGE has been proposed for prevention of chronic inflammatory diseases. However, the role of RAGE in the development of NAFLD and NASH remains poorly understood. We thus aimed to analyse the effect of obesity on AGEs accumulation, AGE-receptors and AGE-detoxification, and whether the absence of RAGE might improve hepatosteatosis and inflammation, by comparing the liver of lean control, obese (LeptrDb-/-) and obese RAGE-deficient (RAGE-/- LeptrDb-/-) mice. Obesity induced AGEs accumulation and RAGE expression with hepatosteatosis and inflammation in LeptrDb-/-, compared to lean controls. Despite the genetic deletion of RAGE in the LeptrDb-/- mice, high levels of intrahepatic AGEs were maintained accompanied by decreased expression of the protective AGE-receptor-1, impaired AGE-detoxifying system glyoxalase-1, and increased expression of the alternative AGE-receptor galectin-3. We also found sustained hepatosteatosis and inflammation as determined by persistent activation of the lipogenic SREBP1c and proinflammatory NLRP3 signalling pathways. Thus, RAGE targeting is not effective in the prevention of NAFLD in conditions of obesity, likely due to the direct liver specific crosstalk of RAGE with other AGE-receptors and AGE-detoxifying systems.

Altered hepatic sphingolipid metabolism in insulin resistant mice: Role of advanced glycation endproducts

High plasma levels of the sphingolipid intermediates ceramide (Cer) and sphingosine-1-phosphate (S1P) are suggested to be involved in the development of insulin resistance (IR). Recent evidence indicates that advanced glycation endproducts (AGEs) can alter the sphingolipids metabolism equilibrium. Since enzymes responsible for sphingolipid rheostat maintenance are highly expressed in liver, we thus investigated whether AGEs accumulation can affect hepatic sphingolipids metabolism in insulin resistant mice. Two different models of IR were examined: genetically diabetic LeptrDb-/- (DbDb) and diet-induced insulin resistant C57Bl/6J mice fed a 60% trans-fat diet (HFD). In addition, a group of HFD mice was supplemented with the anti-AGEs compound pyridoxamine. AGEs were evaluated in the liver by western blotting. Cer and S1P were measured by UHPLC-MS/MS. The expression of RAGE and of enzymes involved in sphingolipid metabolism were assessed by RT-PCR and western blotting. HepG2 cells were used to study the effect of the major AGE Nε-(carboxymethyl)lysine (CML)-albumin on sphingolipid metabolism and the role of the receptor of AGEs (RAGE). High levels of AGEs and RAGE were detected in the liver of both DbDb and HFD mice in comparison to controls. The expression of enzymes of sphingolipid metabolism was altered in both models, accompanied by increased levels of Cer and S1P. Specifically, ceramide synthase 5 and sphingosine kinase 1 were increased, while neutral ceramidase was reduced. Pyridoxamine supplementation to HFD mice diminished hepatic AGEs and prevented alterations of sphingolipid metabolism and the development of IR. CML administration to HepG2 cells evoked alterations similar to those observed in vivo, that were in part mediated by the binding to RAGE. The present study shows a direct involvement of AGEs in alterations of sphingolipid metabolism associated to the development of IR. The modulation of sphingolipids metabolism through the prevention of AGEs accumulation by pyridoxamine may reduce the development of IR.

Attenuation of glycation and biochemical aberrations in fructose‐loaded rats by polyphenol‐rich ethyl acetate fraction of Parkia biglobosa (jacq.) Benth. (Mimosaceae) leaves

Background

Different parts of the Parkia biglobosa plant are employed in traditional medicine in different African communities. However, information ratifying its use and biochemical influence on health is still scanty in literature. Thus, the present study assessed the influence of the ethyl acetate fraction of Parkia biglobosa leaves (EAFPB) on some biochemical parameters of sub-chronic fructose-loaded rats.

Methodology

Twenty-five Wistar rats were randomized into five groups (n = 5). The normal control group was maintained on normal diet only while the high fructose solution (HFS) control (placebo), reference and treatment groups received high fructose solution (3 g/kg/d b.w of fructose) for 30 days before treatment. Based on pilot study, two doses (100 and 200 mg/kg/d b.w) of EAFPB were selected and were administered to two groups of test animals while the reference group received 300 mg/kg/d b.w. of metformin for 14 days. Thereafter, blood was collected from fasted animals for biochemical analyses for the examination of level of glycated hemoglobin (HbA1c), liver status (alanine and aspartate aminotransferases (ALT and AST) and alkaline phosphatase (ALP) activities, and bilirubin level), lipid profile (total cholesterol, triglyceride, and low- and high-density lipoproteins levels) and lipid peroxidation (malondialdehyde – MDA level).

Results

EAFPB was shown to have a good DPPH radical scavenging activity (EC50 = 0.395 mg/ml). Chromatographic analysis of EAFPB revealed 28 known flavonoids (mainly kaempferol (21.31 mg/100 g), quercetin (12.84 mg/100 g), and luteolin (6.75 mg/100 g)), four hydrocinnamic acids derivatives (mainly P-coumaric acid (6.73 mg/100 g)), and 11 phenolic acids derivatives (mainly chlorogenic acid (48.18 mg/100 g) and protocatechuic acid (21.58 mg/100 g)). Relative to normal control, it was observed that fructose overload significantly increased serum activities of ALP, ALT, and AST, and levels of MDA, total cholesterol, low density lipoprotein and triglyceride in placebo. However, EAFPB significantly tapered the elevated serum activities of ALP, ALT, and AST. In addition, relative to placebo, the increased levels of HbA1c, MDA, and lipid health markers were also rebated by EAFPB.

Conclusions

Ethyl acetate fraction of Parkia biglobosa leaves attenuates biochemical aberrations in fructose-loaded rats, an effect attributable to the rich store of polyphenolic compounds in the fraction.

Graphical abstract

Sarcopenia in Chronic Kidney Disease: Focus on Advanced Glycation End Products as Mediators and Markers of Oxidative Stress

Sarcopenia is common in chronic kidney disease (CKD), and it is independently associated with morbidity and mortality. Advanced glycation end products (AGE) are mainly known as aging products. In CKD, AGE accumulate due to increased production and reduced kidney excretion. The imbalance between oxidant/antioxidant capacities in CKD patients is one of the main factors leading to AGE synthesis. AGE can, in turn, promote CKD progression and CKD-related complications by increasing reactive oxygen species generation, inducing inflammation, and promoting fibrosis. All these derangements can further increase AGE and uremic toxin accumulation and promote loss of muscle mass and function. Since the link between AGE and sarcopenia in CKD is far from being fully understood, we revised hereby the data supporting the potential contribution of AGE as mediators of oxidative stress in the pathogenesis of sarcopenia. Understanding how AGE and oxidative stress impact the onset of sarcopenia in CKD may help to identify new potential markers of disease progression and/or therapeutic targets.

Effects of High Intakes of Fructose and Galactose, with or without Added Fructooligosaccharides, on Metabolic Factors, Inflammation, and Gut Integrity in a Rat Model

SCOPE

A high fructose and galactose intake show adverse metabolic effects in animal models and in humans, but it is yet unknown if addition of fermentable dietary fiber can mitigate such effects. This study investigate the effects of high intakes of fructose and galactose, with/without added fructooligosaccharides (FOS), on metabolic factors, inflammation, and gut integrity markers in rats.

METHODS AND RESULTS

Rats (n = 6/group) receive different carbohydrates at isocaloric conditions for 12 weeks as follows: 1) starch (control), 2) fructose, 3) galactose, 4) starch + FOS (FOS control), 5) fructose + FOS, and 6) galactose + FOS, together with a high amount of n-6 polyunsaturated fatty acids (n-6 PUFA) in all diets except for in 7) starch + olive oil (negative control). The rats fed the galactose and galactose + FOS diets exhibit lower body weight than other groups. High-galactose diets has more pronounced effects on metabolic factors and gut permeability than high-fructose diets. High-fructose diets show less pronounced effect on these selected markers. No differences in inflammatory markers are detected for any of the diets.

CONCLUSIONS

The results suggest potential adverse effects of high galactose and fructose on metabolic factors and gut integrity markers, but not on inflammation. However, several mechanisms are at play, and general net effects are difficult to determine conclusively for the conditions tested.

Effects of Exogenous Dietary Advanced Glycation End Products on the Cross-Talk Mechanisms Linking Microbiota to Metabolic Inflammation

Heat-processed diets contain high amounts of advanced glycation end products (AGEs). Here we explore the impact of an AGE-enriched diet on markers of metabolic and inflammatory disorders as well as on gut microbiota composition and plasma proteins glycosylation pattern. C57BL/6 mice were allocated into control diet (CD, n = 15) and AGE-enriched diet (AGE-D, n = 15) for 22 weeks. AGE-D was prepared replacing casein by methylglyoxal hydroimidazolone-modified casein. AGE-D evoked increased insulin and a significant reduction of GIP/GLP-1 incretins and ghrelin plasma levels, altered glucose tolerance, and impaired insulin signaling transduction in the skeletal muscle. Moreover, AGE-D modified the systemic glycosylation profile, as analyzed by lectin microarray, and increased Nε-carboxymethyllysine immunoreactivity and AGEs receptor levels in ileum and submandibular glands. These effects were associated to increased systemic levels of cytokines and impaired gut microbial composition and homeostasis. Significant correlations were recorded between changes in bacterial population and in incretins and inflammatory markers levels. Overall, our data indicates that chronic exposure to dietary AGEs lead to a significant unbalance in incretins axis, markers of metabolic inflammation, and a reshape of both the intestinal microbiota and plasma protein glycosylation profile, suggesting intriguing pathological mechanisms underlying AGEs-induced metabolic derangements.

Receptor for advanced glycation end products modulates oxidative stress and mitochondrial function in the soleus muscle of mice fed a high-fat diet

Accumulation of advanced glycation end products (AGEs) and activation of the receptor for AGEs (RAGE) are implicated in the progression of pathologies associated with aging, chronic inflammation, diabetes, and cellular stress. RAGE activation is also implicated in cardiovascular complications of type 2 diabetes, such as nephropathy, retinopathy, accelerated vascular diseases, and cardiomyopathy. Studies investigating the effects of AGE/RAGE axis activation on skeletal muscle oxidative stress and metabolism are more limited. We tested whether a high-fat diet (HFD) would alter circulating AGE concentration, skeletal muscle AGE accumulation, and oxidative stress in wild-type and RAGE-deficient mice. The physiological significance of AGE/RAGE axis activation in HFD-fed mice was evaluated in terms of exercise tolerance and mitochondrial respiratory chain complex activity. HFD elicited adiposity, abnormal fat distribution, and oral glucose intolerance. HFD also induced accumulation of N^ε-carboxymethyl-l-lysine, increased protein carbonyl levels, and impaired respiratory chain complex activity in soleus muscle. Ablation of RAGE had no effects on weight gain and oral glucose tolerance in HFD-fed mice. Peak aerobic capacity and mitochondrial cytochrome-c oxidase activity were restored in HFD-fed RAGE^-/- mice. We concluded that RAGE signaling plays an important role in skeletal muscle homeostasis of mice under metabolic stress. Novelty HFD in mice induces accumulation of AGEs, oxidative stress, and mitochondrial dysfunction in the soleus muscle. RAGE, the multi-ligand receptor for AGEs, modulates oxidative stress and mitochondrial electron transport chain function in the soleus muscle of HFD-fed mice.

Advanced glycation end products and chronic inflammation in adult survivors of childhood leukemia treated with hematopoietic stem cell transplantation

BACKGROUND

Among survivors of pediatric acute lymphoblastic leukemia (ALL), those who received hematopoietic stem cell transplantation (HSCT) conditioned with total-body irradiation (TBI) show the highest risk of late complications, including cardiovascular (CV) disease. Advanced glycation end products (AGEs) have been associated with CV disease in diabetes mellitus and other clinical conditions. This study explores AGEs plasma levels, inflammatory status, and lipid profile in survivors of pediatric ALL who received HSCT conditioned with TBI.

PROCEDURE

Inclusion criteria were (a) previous diagnosis of ALL at age < 18 years, treated with HSCT conditioned with TBI; (b) age > 18 at the time of the study enrollment; (c) off-therapy for at least five years. Radiotherapy other than TBI, preexisting heart disease, glucose metabolism impairment, body mass index > 25, active graft versus host disease (GvHD), smoking, or treatment with cholesterol lowering medications were exclusion criteria. Eighteen survivors and 30 age-matched healthy controls were enrolled.

RESULTS

AGEs plasma levels were markedly higher in ALL survivors than in healthy subjects (2.15 ± 2.21 vs 0.29 ± 0.15 pg/mL, P < 0.01). Survivors also showed higher levels of high-sensitivity C-reactive protein (2.32 ± 1.70 vs 0.88 ± 1.09 mg/dL, P < 0.05), IL-1β (7.04 ± 1.52 vs 4.64 ± 2.02 pg/mL, P < 0.001), IL17 (37.44 ± 3.51 vs 25.19 ± 6.34 pg/mL, P < 0.001), an increased glutathione/reduced glutathione ratio (0.085 ± 0.07 vs 0.041 ± 0.036, P < 0.05) and slight alterations in their lipid profile.

CONCLUSIONS

Our data show AGEs accumulation and chronic inflammation in ALL survivors who received HSCT conditioned with TBI. These alterations may contribute to the increased risk of CV disease reported in these subjects.

Impact of intracellular toxic advanced glycation end-products (TAGE) on murine myoblast cell death

BACKGROUND

Sarcopenia is a progressive condition that is characterized by decreases in skeletal muscle mass and function. Although sarcopenia is associated with lifestyle-related diseases (LSRD), the mechanisms underlying cell death in myoblasts, which differentiate to myotubes, remain unclear. We previously designated glyceraldehyde (an intermediate of glucose/fructose metabolism)-derived advanced glycation end-products (AGEs) as toxic AGEs (TAGE) because of their cytotoxicity and involvement in LSRD, and hypothesized that TAGE contribute to cell death in myoblasts.

METHODS

C2C12 cells, which are murine myoblasts, were treated with 0, 0.5, 1, 1.5, and 2 mM glyceraldehyde for 24 h. Cell viability and intracellular TAGE were then assessed using 5-[2,4,-bis(sodioxysulfonyl)phenyl]-3-(2-methoxy-4-nitrophenyl)-2-(4-nitrophenyl)-2H-tetrazole-3-ium (WST-8) and slot blot assays. Cells were pretreated with 8 mM aminoguanidine, an inhibitor of AGE production, for 2 h, followed by 0, 1.5, and 2 mM glyceraldehyde for 24 h. Cell viability and intracellular TAGE levels were then assessed. Serum TAGE levels in STAM mice, in which there were four stages (no steatosis, simple steatosis, steatohepatitis, and fibrosis), were measured using a competitive enzyme-linked immunosorbent assay. Results were expressed as TAGE units (U) per milliliter of serum, with 1 U corresponding to 1.0 μg of glyceraldehyde-derived AGE-bovine serum albumin (BSA) (TAGE-BSA). The viability of cells treated with 20, 50, and 100 μg/mL non-glycated BSA and TAGE-BSA for 24 h was assessed using the WST-8 assay.

RESULTS

In C2C12 cells treated with 1.5 and 2 mM glyceraldehyde, cell viability decreased to 47.7% (p = 0.0021) and 5.0% (p = 0.0001) and intracellular TAGE levels increased to 6.0 and 15.9 μg/mg protein, respectively. Changes in cell viability and TAGE production were completely inhibited by 8 mM aminoguanidine. Serum TAGE levels at the steatohepatitis and fibrosis stages were 10.51 ± 1.16 and 10.44 ± 0.95 U/mL, respectively, and were higher than those at the no steatosis stage (7.27 ± 0.18 U/mL). Cell death was not induced by 20 or 50 μg/mL TAGE-BSA. The viabilities of C2C12 cells treated with 100 μg/mL non-glycated BSA and TAGE-BSA were 105.0% (p = 0.2890) and 85.3% (p = 0.0217), respectively.

CONCLUSION

Intracellular TAGE strongly induced cell death in C2C12 cells and may also induce myoblast cell death in LSRD model mice.

High fructose-containing drinking water-induced steatohepatitis in rats is prevented by the nicotinamide-mediated modulation of redox homeostasis and NADPH-producing enzymes

An imbalance in the redox state, increased levels of lipid precursors and overactivation of de novo lipogenesis determine the development of fibrosis during nonalcoholic steatohepatitis (NASH). We evaluated the modulation of NADPH-producing enzymes associated with the antifibrotic, antioxidant and antilipemic effects of nicotinamide (NAM) in a model of NASH induced by excess fructose consumption. Male rats were provided drinking water containing 40% fructose for 16 weeks. During the last 12 weeks of fructose administration, water containing NAM was provided to some of the rats for 5 h/day. The biochemical profiles and the ghrelin, leptin, lipoperoxidation and TNF-α levels in serum and the glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME) and NADP⁺-dependent isocitric dehydrogenase (IDP) levels, the reduced/oxidized glutathione (GSH/GSSG) and reduced/oxidized nicotinamide adenine dinucleotide (phosphate) (NAD(P)H/NAD(P)⁺) ratios, and the levels of various lipogenic and fibrotic markers in the liver were evaluated. The results showed that hepatic fibrosis induced by fructose consumption was associated with weight gain, hunger-satiety system dysregulation, hyperinsulinemia, dyslipidemia, lipoperoxidation and inflammation. Moreover, increased levels of hepatic G6PD and ME activity and expression, the NAD(P)H/NAD(P)⁺ ratios, and GSSG concentration and increased expression of lipogenic and fibrotic markers were detected, and these alterations were attenuated by NAM administration. Specifically, NAM diminished the activity and expression of G6PD and ME, and this effect was associated with a decrease in the NADPH/NADP⁺ ratios, increased GSH levels and decreased lipoperoxidation and inflammation, ameliorating fibrosis and NASH development. NAM reduces liver steatosis and fibrosis by regulating redox homeostasis through a G6PD- and ME-dependent mechanism.

KRIT1 Deficiency Promotes Aortic Endothelial Dysfunction

Loss-of-function mutations of the gene encoding Krev interaction trapped protein 1 (KRIT1) are associated with the pathogenesis of Cerebral Cavernous Malformation (CCM), a major cerebrovascular disease characterized by abnormally enlarged and leaky capillaries and affecting 0.5% of the human population. However, growing evidence demonstrates that KRIT1 is implicated in the modulation of major redox-sensitive signaling pathways and mechanisms involved in adaptive responses to oxidative stress and inflammation, suggesting that its loss-of-function mutations may have pathological effects not limited to CCM disease. The aim of this study was to address whether KRIT1 loss-of-function predisposes to the development of pathological conditions associated with enhanced endothelial cell susceptibility to oxidative stress and inflammation, such as arterial endothelial dysfunction (ED) and atherosclerosis. Silencing of KRIT1 in human aortic endothelial cells (HAECs), coronary artery endothelial cells (HCAECs), and umbilical vein endothelial cells (HUVECs) resulted in increased expression of endothelial proinflammatory adhesion molecules vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) and in enhanced susceptibility to tumor necrosis factor alpha (TNF-α)-induced apoptosis. These effects were associated with a downregulation of Notch1 activation that could be rescued by antioxidant treatment, suggesting that they are consequent to altered intracellular redox homeostasis induced by KRIT1 loss-of-function. Furthermore, analysis of the aorta of heterozygous KRIT1^+/- mice fed a high-fructose diet to induce systemic oxidative stress and inflammation demonstrated a 1.6-fold increased expression of VCAM-1 and an approximately 2-fold enhanced fat accumulation (7.5% vs 3.6%) in atherosclerosis-prone regions, including the aortic arch and aortic root, as compared to corresponding wild-type littermates. In conclusion, we found that KRIT1 deficiency promotes ED, suggesting that, besides CCM, KRIT1 may be implicated in genetic susceptibility to the development of atherosclerotic lesions.

Dietary Glycotoxins Impair Hepatic Lipidemic Profile in Diet-Induced Obese Rats Causing Hepatic Oxidative Stress and Insulin Resistance

Nonalcoholic fatty liver disease (NAFLD) is caused by excessive liver lipid accumulation, but insulin resistance is specifically associated with impaired lipid saturation, oxidation, and storage (esterification), besides increased de novo lipogenesis. We hypothesized that dietary glycotoxins could impair hepatic lipid metabolism in obesity contributing to lipotoxicity-driven insulin resistance and thus to the onset of nonalcoholic steatohepatitis (NASH). In diet-induced obese rats with methylglyoxal-induced glycation, magnetic resonance spectroscopy, mass spectrometry, and gas chromatography were used to assess liver composition in fatty acyl chains and phospholipids. High-fat diet-induced obesity increased liver lipid fraction and suppressed de novo lipogenesis but did not change fatty acid esterification and saturation or insulin sensitivity. Despite a similar increase in total lipid fraction when supplementing the high-fat diet with dietary glycotoxins, impairment in the suppression of de novo lipogenesis and decreased fatty acid unsaturation and esterification were observed. Moreover, glycotoxins also decreased polyunsaturated cardiolipins and caused oxidative stress, portal inflammation, and insulin resistance in high-fat diet-induced obese rats. Dietary glycated products do not change total lipid levels in the liver of obese rats but dramatically modify the lipidemic profile, leading to oxidative stress, hepatic lipotoxicity, and insulin resistance in obesity and thus contribute to the onset of NASH.

A study on hepatopathic, dyslipidemic and immunogenic properties of fructosylated-HSA-AGE and binding of autoantibodies in sera of obese and overweight patients with fructosylated-HSA-AGE

Over consumption of fructose may lead to obesity and dyslipidemia and cause fructosylation-induced alterations in the structure and function of proteins. The aim of this study was to investigate the role of fructosylated-HSA-AGE in the pathogenesis of fatty liver (NAFLD and NASH) by biochemical, immunological and histological studies. Immunogenicity of fructosylated-HSA-AGE was probed by inducing antibodies in rabbits. Fructosylated-HSA-AGE was found to be highly immunogenic. Furthermore, fructosylated-HSA-AGE caused mild fibrosis with steatosis and portal inflammation of hepatocytes in experimental animals. Liver function test and dyslipidemic parameters in immunized animals were also found to be raised. Ultrasonography, which should form part of the assessment of chronically raised transaminases, shows fatty infiltration. Interestingly, alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin, total cholesterol (TC) and triglyceride (TG) profiles confirms USG images of overweight, obese patients. Thus, present study demonstrates that fructosylated-HSA-AGE is hepatotoxic, immunologically active and may cause dyslipidemia.

Reduced Susceptibility to Sugar-Induced Metabolic Derangements and Impairments of Myocardial Redox Signaling in Mice Chronically Fed with D-Tagatose when Compared to Fructose

Background

D-tagatose is an isomer of fructose and is ~90% as sweet as sucrose with less caloric value. Nowadays, D-tagatose is used as a nutritive or low-calorie sweetener. Despite clinical findings suggesting that D-tagatose could be beneficial in subjects with type 2 diabetes, there are no experimental data comparing D-tagatose with fructose, in terms of metabolic derangements and related molecular mechanisms evoked by chronic exposure to these two monosaccharides.

Materials and methods

C57Bl/6j mice were fed with a control diet plus water (CD), a control diet plus 30% fructose syrup (L-Fr), a 30% fructose solid diet plus water (S-Fr), a control diet plus 30% D-tagatose syrup (L-Tg), or a 30% D-tagatose solid diet plus water (S-Tg), during 24 weeks.

Results

Both solid and liquid fructose feeding led to increased body weight, abnormal systemic glucose homeostasis, and an altered lipid profile. These effects were associated with vigorous increase in oxidative markers. None of these metabolic abnormalities were detected when mice were fed with both the solid and liquid D-tagatose diets, either at the systemic or at the local level. Interestingly, both fructose formulations led to significant Advanced Glycation End Products (AGEs) accumulation in mouse hearts, as well as a robust increase in both myocardial AGE receptor (RAGE) expression and NF-κB activation. In contrast, no toxicological effects were shown in hearts of mice chronically exposed to liquid or solid D-tagatose.

Conclusion

Our results clearly suggest that chronic overconsumption of D-tagatose in both formulations, liquid or solid, does not exert the same deleterious metabolic derangements evoked by fructose administration, due to differences in carbohydrate interference with selective proinflammatory and oxidative stress cascades.

Fructose liquid and solid formulations differently affect gut integrity, microbiota composition and related liver toxicity: a comparative in vivo study

Despite clinical findings suggesting that the form (liquid versus solid) of the sugars may significantly affect the development of metabolic diseases, no experimental data are available on the impact of their formulations on gut microbiota, integrity and hepatic outcomes. In the present sudy, C57Bl/6j mice were fed a standard diet plus water (SD), a standard diet plus 60% fructose syrup (L-Fr) or a 60% fructose solid diet plus water (S-Fr) for 12 weeks. Gut microbiota was characterized through 16S rRNA phylogenetic profiling and shotgun sequencing of microbial genes in ileum content and related volatilome profiling. Fructose feeding led to alterations of the gut microbiota depending on the fructose formulation, with increased colonization by Clostridium, Oscillospira and Clostridiales phyla in the S-Fr group and Bacteroides, Lactobacillus, Lachnospiraceae and Dorea in the L-Fr. S-Fr evoked the highest accumulation of advanced glycation end products and barrier injury in the ileum intestinal mucosa. These effects were associated to a stronger activation of the lipopolysaccharide-dependent proinflammatory TLR4/NLRP3 inflammasome pathway in the liver of S-Fr mice than of L-Fr mice. In contrast, L-Fr intake induced higher levels of hepatosteatosis and markers of fibrosis than S-Fr. Fructose-induced ex novo lipogenesis with production of SCFA and MCFA was confirmed by metagenomic analysis. These results suggest that consumption of fructose under different forms, liquid or solid, may differently affect gut microbiota, thus leading to impairment in intestinal mucosa integrity and liver homeostasis.

Effects of vitamin D on insulin resistance and myosteatosis in diet-induced obese mice

Epidemiological studies pointed out to a strong association between vitamin D deficiency and type 2 diabetes prevalence. However, the role of vitamin D supplementation in the skeletal muscle, a tissue that play a crucial role in the maintenance of glucose homeostasis, has been scarcely investigated so far. On this basis, this study aimed to evaluate the effect of vitamin D supplementation in a murine model of diet-induced insulin resistance with particular attention to the effects evoked on the skeletal muscle. Male C57BL/6J mice (n = 40) were fed with a control or a High Fat-High Sugar (HFHS) diet for 4 months. Subsets of animals were treated for 2 months with vitamin D (7 μg·kg-1, i.p. three times/week). HFHS diet induced body weight increase, hyperglycemia and impaired glucose tolerance. HFHS animals showed an impaired insulin signaling and a marked fat accumulation in the skeletal muscle. Vitamin D reduced body weight and improved systemic glucose tolerance. In addition, vitamin D restored the impaired muscle insulin signaling and reverted myosteatosis evoked by the diet. These effects were associated to decreased activation of NF-κB and lower levels of TNF-alpha. Consistently, a significantly decreased activation of the SCAP/SREBP lipogenic pathway and lower levels of CML protein adducts and RAGE expression were observed in skeletal muscle of animals treated with vitamin D.

Collectively, these data indicate that vitamin D-induced selective inhibition of signaling pathways (including NF-κB, SCAP/SREBP and CML/RAGE cascades) within the skeletal muscle significantly contributed to the beneficial effects of vitamin D supplementation against diet-induced metabolic derangements.

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.

Protective Effects of Pyridoxamine Supplementation in the Early Stages of Diet-Induced Kidney Dysfunction

Pyridoxamine, a structural analog of vitamin B6 that exerts antiglycative effects, has been proposed as supplementary approach in patients with initial diabetic nephropathy. However, the molecular mechanism(s) underlying its protective role has been so far slightly examined. C57Bl/6J mice were fed with a standard diet (SD) or a diet enriched in fat and fructose (HD) for 12 weeks. After 3 weeks, two subgroups of SD and HD mice started pyridoxamine supplementation (150 mg/kg/day) in the drinking water. HD fed mice showed increased body weight and impaired glucose tolerance, whereas pyridoxamine administration significantly improved insulin sensitivity, but not body weight, and reduced diet-induced increase in serum creatinine and urine albumin. Kidney morphology of HD fed mice showed strong vacuolar degeneration and loss of tubule brush border, associated with a drastic increase in both advanced glycation end products (AGEs) and AGEs receptor (RAGE). These effects were significantly counteracted by pyridoxamine, with consequent reduction of the diet-induced overactivation of NF-kB and Rho/ROCK pathways. Overall, the present study demonstrates for the first time that the administration of the antiglycative compound pyridoxamine can reduce the early stages of diet-dependent kidney injury and dysfunction by interfering at many levels with the profibrotic signaling and inflammatory cascades.

Similarities and interactions between the ageing process and high chronic intake of added sugars

In our societies, the proportions of elderly people and of obese individuals are increasing. Both factors are associated with high health-related costs. During obesity, many authors suggest that it is a high chronic intake of added sugars (HCIAS) that triggers the shift towards pathology. However, the majority of studies were performed in young subjects and only a few were interested in the interaction with the ageing process. Our purpose was to discuss the metabolic effects of HCIAS, compare with the effects of ageing, and evaluate how deleterious the combined action of HCIAS and ageing could be. This effect of HCIAS seems mediated by fructose, targeting the liver first, which may lead to all subsequent metabolic alterations. The first basic alterations induced by fructose are increased oxidative stress, protein glycation, inflammation, dyslipidaemia and insulin resistance. These alterations are also present during the ageing process, and are closely related to each other, one leading to the other. These basic alterations are also involved in more complex syndromes, which are also favoured by HCIAS, and present during ageing. These include non-alcoholic fatty liver disease, hypertension, neurodegenerative diseases, sarcopenia and osteoporosis. Cumulative effects of ageing and HCIAS have been seldom tested and may not always be strictly additive. Data also suggest that some of the metabolic alterations that are more prevalent during ageing could be related more with nutritional habits than to intrinsic ageing. In conclusion, it is clear that HCIAS interacts with the ageing process, accelerates the accumulation of metabolic alterations, and that it should be avoided.

Fructose, Glucocorticoids and Adipose Tissue: Implications for the Metabolic Syndrome

The modern Western society lifestyle is characterized by a hyperenergetic, high sugar containing food intake. Sugar intake increased dramatically during the last few decades, due to the excessive consumption of high-sugar drinks and high-fructose corn syrup. Current evidence suggests that high fructose intake when combined with overeating and adiposity promotes adverse metabolic health effects including dyslipidemia, insulin resistance, type II diabetes, and inflammation. Similarly, elevated glucocorticoid levels, especially the enhanced generation of active glucocorticoids in the adipose tissue due to increased 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity, have been associated with metabolic diseases. Moreover, recent evidence suggests that fructose stimulates the 11β-HSD1-mediated glucocorticoid activation by enhancing the availability of its cofactor NADPH. In adipocytes, fructose was found to stimulate 11β-HSD1 expression and activity, thereby promoting the adipogenic effects of glucocorticoids. This article aims to highlight the interconnections between overwhelmed fructose metabolism, intracellular glucocorticoid activation in adipose tissue, and their metabolic effects on the progression of the metabolic syndrome.

Dietary Sugars and Endogenous Formation of Advanced Glycation Endproducts: Emerging Mechanisms of Disease

The rapid increase in metabolic diseases, which occurred in the last three decades in both industrialized and developing countries, has been related to the rise in sugar-added foods and sweetened beverages consumption. An emerging topic in the pathogenesis of metabolic diseases related to modern nutrition is the role of Advanced Glycation Endproducts (AGEs). AGEs can be ingested with high temperature processed foods, but also endogenously formed as a consequence of a high dietary sugar intake. Animal models of high sugar consumption, in particular fructose, have reported AGE accumulation in different tissues in association with peripheral insulin resistance and lipid metabolism alterations. The in vitro observation that fructose is one of the most rapid and effective glycating agents when compared to other sugars has prompted the investigation of the in vivo fructose-induced glycation. In particular, the widespread employment of fructose as sweetener has been ascribed by many experimental and observational studies for the enhancement of lipogenesis and intracellular lipid deposition. Indeed, diet-derived AGEs have been demonstrated to interfere with many cell functions such as lipid synthesis, inflammation, antioxidant defences, and mitochondrial metabolism. Moreover, emerging evidence also in humans suggest that this impact of dietary AGEs on different signalling pathways can contribute to the onset of organ damage in liver, skeletal and cardiac muscle, and the brain, affecting not only metabolic control, but global health. Indeed, the most recent reports on the effects of high sugar consumption and diet-derived AGEs on human health reviewed here suggest the need to limit the dietary sources of AGEs, including added sugars, to prevent the development of metabolic diseases and related comorbidities.

Reactive Carbonyl Species Scavengers-Novel Therapeutic Approaches for Chronic Diseases

PURPOSE OF THE REVIEW

To summarize recent evidence supporting the use of reactive carbonyl species scavengers in the prevention and treatment of disease.

RECENT FINDINGS

The newly developed 2-aminomethylphenol class of scavengers shows great promise in preclinical trials for a number of diverse conditions including neurodegenerative diseases and cardiovascular disease. In addition, new studies with the thiol-based and imidazole-based scavengers have found new applications outside of adjunctive therapy for chemotherapeutics.

SUMMARY

Reactive oxygen species (ROS) generated by cells and tissues act as signaling molecules and as cytotoxic agents to defend against pathogens, but ROS also cause collateral damage to vital cellular components. The polyunsaturated fatty acyl chains of phospholipids in the cell membranes are particularly vulnerable to damaging peroxidation by ROS. Evidence suggests that the breakdown of these peroxidized lipids to reactive carbonyls species plays a critical role in many chronic diseases. Antioxidants that abrogate ROS-induced formation of reactive carbonyl species also abrogate normal ROS signaling and thus exert both beneficial and adverse functional effects. The use of scavengers of reactive dicarbonyl species represent an alternative therapeutic strategy to potentially mitigate the adverse effects of ROS without abrogating normal signaling by ROS. In this review, we focus on three classes of reactive carbonyl species scavengers: thiol-based scavengers (2-mercaptoethanesulfonate and amifostine), imidazole-based scavengers (carnosine and its analogs), and 2-aminomethylphenols-based scavengers (pyridoxamine, 2-hydroxybenzylamine, and 5'-O-pentyl-pyridoxamine) that are either undergoing pre-clinical studies, advancing to clinical trials, or are already in clinical use.

Potential involvement of dietary advanced glycation end products in impairment of skeletal muscle growth and muscle contractile function in mice

Diets enriched with advanced glycation end products (AGE) have recently been related to muscle dysfunction processes. However, it remains unclear whether long-term exposure to an AGE-enriched diet impacts physiological characteristics of skeletal muscles. Therefore, we explored the differences in skeletal muscle mass, contractile function and molecular responses between mice receiving a diet high in AGE (H-AGE) and low in AGE (L-AGE) for 16 weeks. There were no significant differences between L-AGE and H-AGE mice with regard to body weight, food intake or epididymal fat pad weight. However, extensor digitorum longus (EDL) and plantaris (PLA) muscle weights in H-AGE mice were lower compared with L-AGE mice. Higher levels of N ε -(carboxymethyl)-l-lysine, a marker for AGE, in EDL muscles of H-AGE mice were observed compared with L-AGE mice. H-AGE mice showed lower muscle strength and endurance in vivo and lower muscle force production of PLA muscle in vitro. mRNA expression levels of myogenic factors including myogenic factor 5 and myogenic differentiation in EDL muscle were lower in H-AGE mice compared with L-AGE mice. The phosphorylation status of 70-kDa ribosomal protein S6 kinase Thr389, an indicator of protein synthesis signalling, was lower in EDL muscle of H-AGE mice than that of L-AGE mice. These findings suggest that long-term exposure to an AGE-enriched diet impairs skeletal muscle growth and muscle contractile function, and that these muscle dysfunctions may be attributed to the inhibition of myogenic potential and protein synthesis.

Formation of Fructose-Mediated Advanced Glycation End Products and Their Roles in Metabolic and Inflammatory Diseases

Fructose is associated with the biochemical alterations that promote the development of metabolic syndrome (MetS), nonalcoholic fatty liver disease, and type 2 diabetes. Its consumption has increased in parallel with MetS. It is metabolized by the liver, where it stimulates de novo lipogenesis. The triglycerides synthesized lead to hepatic insulin resistance and dyslipidemia. Fructose-derived advanced glycation end products (AGEs) may be involved via the Maillard reaction. Fructose has not been a main focus of glycation research because of the difficulty in measuring its adducts, and, more importantly, because although it is 10 times more reactive than glucose, its plasma concentration is only 1% of that of glucose. In this focused review, I summarize exogenous and endogenous fructose metabolism, fructose glycation, and in vitro, animal, and human data. Fructose is elevated in several tissues of diabetic patients where the polyol pathway is active, reaching the same order of magnitude as glucose. It is plausible that the high reactivity of fructose, directly or via its metabolites, may contribute to the formation of intracellular AGEs and to vascular complications. The evidence, however, is still unconvincing. Two areas that have been overlooked so far and should be actively explored include the following: 1) enteral formation of fructose AGEs, generating an inflammatory response to the receptor for AGEs (which may explain the strong association between fructose consumption and asthma, chronic bronchitis, and arthritis); and 2) inactivation of hepatic AMP-activated protein kinase by a fructose-mediated increase in methylglyoxal flux (perpetuating lipogenesis, fatty liver, and insulin resistance). If proven correct, these mechanisms would put the fructose-mediated Maillard reaction in the limelight again as a contributing factor in chronic inflammatory diseases and MetS.

How Can Diet Affect the Accumulation of Advanced Glycation End-Products in the Human Body?

The accumulation of advanced glycation end products (AGEs) is associated with the complications of diabetes, kidney disease, metabolic disorders and degenerative diseases. It is recognized that the pool of glycation products found in the human body comes not only from an endogenous formation, but also from a dietary exposure to exogenous AGEs. In recent years, the development of pharmacologically-active ingredients aimed at inhibiting endogenous glycation has not been successful. Since the accumulation of AGEs in the human body appears to be progressive throughout life, an early preventive action against glycation could be effective through dietary adjustments or supplementation with purified micronutrients. The present article provides an overview of current dietary strategies tested either in vitro, in vivo or both to reduce the endogenous formation of AGEs and to limit exposure to food AGEs.