Endogenous formation of Nε-(carboxymethyl)lysine is increased in fatty livers and induces inflammatory markers in an in vitro model of hepatic steatosis

Comprehensive characterization of differential glycation in hepatocellular carcinoma using tissue proteomics with stable isotopic labeling

Glycation is a non-enzymatic posttranslational modification coming from the reaction between reducing sugars and free amino groups in proteins, where early glycation products (fructosyl-lysine, FL) and advanced glycation end products (AGEs) are formed. The occurrence of glycation and accumulation of AGEs have been closely associated with hepatocellular carcinoma (HCC). Here, we reported the characterization of differential glycation in HCC using tissue proteomics with stable isotopic labeling; early glycation-modified peptides were enriched with boronate affinity chromatography (BAC), and AGEs-modified peptides were fractionated with basic reversed-phase separation. By this integrated approach, 3717 and 1137 early and advanced glycated peptides corresponding to 4007 sites on 1484 proteins were identified with a false discovery rate (FDR) of no more than 1%. One hundred fifty-five sites were modified with both early and advanced end glycation products. Five early and 7 advanced glycated peptides were quantified to be differentially expressed in HCC tissues relative to paired adjacent tissues. Most (8 out of 10) of the proteins corresponding to the differential glycated peptides have previously been reported with dysregulation in HCC. The results together may deepen our knowledge of glycation as well as provide insights for therapeutics.

Lindera obtusiloba Blume Alleviates Non-Alcoholic Fatty Liver Disease Promoted by Nε-(carboxymethyl)lysine

Non-alcoholic fatty liver disease (NAFLD) is a major issue because it is closely associated with metabolic diseases. Advanced glycation end products (AGEs) are implicated as risk factors for steatosis during NAFLD progression. AGEs influence NAFLD progression through a receptor-independent pathway involving AGE cross-link formation and a receptor-dependent pathway that binds to receptors like receptors for advanced glycation end products (RAGE). The objectives of this study are to examine the effect of Lindera obtusiloba Blume (LO) on NAFLD promoted by Nε-(carboxymethyl)lysine (CML), one of the most common dietary AGEs. The anti-glycation effects of LO were evaluated by inhibiting the AGEs formation and AGEs-collagen cross-links breaking. The efficacy of LO against NAFLD promoted by CML was assessed using both in vitro and in vivo models. NAFLD was induced in mice by feeding a high-fat diet and orally administering CML over a period of 12 weeks, and the effects of LO on lipid metabolism and its regulatory mechanisms were investigated. LO showed the effect of inhibited AGEs formation and breakage, and collagen cross-linking. Fed a high-fat diet with administered CML by gavage, LO administration resulted in a reduction in body weight, fat mass, serum triglycerides, total cholesterol, and low-density lipoprotein cholesterol levels. LO reduced hepatic CML accumulation and RAGE expression in mice fed a high-fat diet and orally administered CML. LO alleviated hepatic steatosis accompanied by lipid accumulation and histological damage by suppressing the expression of sterol regulatory element-binding protein 1c, carbohydrate response element binding protein, fatty acid synthase, stearoyl-CoA desaturase1, tumor necrosis factor-α, and interleukin-1β. LO alleviated the MAPK/NF-κB expression by attenuating CML and RAGE expression. Taken together, our results demonstrate that LO alleviates the progression of NAFLD by lowering the levels of AGEs by downregulating CML/RAGE expression.

Accumulation of Non-Pathological Liver Fat Is Associated with the Loss of Glyoxalase I Activity in Humans

The underlying molecular mechanisms for the development of non-alcoholic fatty liver (NAFL) and its progression to advanced liver diseases remain elusive. Glyoxalase 1 (Glo1) loss, leading to elevated methylglyoxal (MG) and dicarbonyl stress, has been implicated in various diseases, including obesity-related conditions. This study aimed to investigate changes in the glyoxalase system in individuals with non-pathological liver fat. Liver biopsies were obtained from 30 individuals with a narrow range of BMI (24.6-29.8 kg/m2). Whole-body insulin sensitivity was assessed using HOMA-IR. Liver biopsies were analyzed for total triglyceride content, Glo1 and Glo2 mRNA, protein expression, and activity. Liquid chromatography-tandem mass spectrometry determined liver dicarbonyl content and oxidation and glycation biomarkers. Liver Glo1 activity showed an inverse correlation with HOMA-IR and liver triglyceride content, but not BMI. Despite reduced Glo1 activity, no associations were found with elevated liver dicarbonyls or glycation markers. A sex dimorphism was observed in Glo1, with females exhibiting significantly lower liver Glo1 protein expression and activity, and higher liver MG-H1 content compared to males. This study demonstrates that increasing liver fat, even within a non-pathological range, is associated with reduced Glo1 activity.

Molecular mechanism and therapeutic significance of essential amino acids in metabolically associated fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), also known as metabolically associated fatty liver disease (MAFLD), is a systemic metabolic disease characterized by lipid accumulation in the liver, lipid toxicity, insulin resistance, intestinal dysbiosis, and inflammation that can progress from simple steatosis to nonalcoholic steatohepatitis (NASH) and even cirrhosis or cancer. It is the most prevalent illness threatening world health. Currently, there are almost no approved drug interventions for MAFLD, mainly dietary changes and exercise to control weight and regulate metabolic disorders. Meanwhile, the metabolic pathway involved in amino acid metabolism also influences the onset and development of MAFLD in the body, and most amino acid metabolism takes place in the liver. Essential amino acids are those amino acids that must be supplemented from outside the diet and that cannot be synthesized in the body or cannot be synthesized at a rate sufficient to meet the body's needs, including leucine, isoleucine, valine (collectively known as branched-chain amino acids), tryptophan, phenylalanine (which are aromatic amino acids), histidine, methionine, threonine and lysine. The metabolic balance of the body is closely linked to these essential amino acids, and essential amino acids are closely linked to the pathophysiological process of MAFLD. In this paper, we will focus on the metabolism of essential amino acids in the body and further explore the therapeutic strategies for MAFLD based on the studies conducted in recent years.

What is the influence of policosanol supplementation on liver enzymes? A systematic review and dose-response meta-analysis of randomized controlled trials

OBJECTIVE

Policosanol is a mixture of long chain alcohols refined from sugar cane. Significant reductions in liver enzymes have been observed in some studies. However, the impact of policosanol on liver enzymes remained controversial. The current meta-analysis aims to evaluate the effect of policosanol supplementation on the levels of alanine transaminase (ALT) and aspartate transaminase (AST).

METHODS

The literature was systematically searched for studies published up to November 2023 in PubMed/Medline, Google Scholar, EMBASE, and Scopus. Randomized controlled trial (RCT) studies were included to evaluate the intervention effect of policosanol compared to placebo on ALT and AST. DerSimonian and Laird models were used to calculate effect sizes.

RESULTS

Twenty-three trials including 2535 participants were included in the study. The combination of effect sizes, regarding the random-effects model, demonstrated significant changes in ALT serum levels after intervention (WMD: -1.48 U/L; 95% CI: -2.33 to -0.64; P = 0.001), and AST (WMD: -1.10 U/L; 95% CI: -1.70 to -0.51; P < 0.001). Subgroup analysis of AST and ALT showed that this reduction effect was most often observed at the dose of 20 mg/d. The dose-response analysis represented a non-significant non-linear connection between the dosage and duration of policosanol intervention in ALT and AST serum reduction.

CONCLUSION

Policosanol supplementation exerts a beneficial effect on liver enzymes as well as ALT and AST concentrations in adults. However, further long-term and well-designed RCTs with better quality are needed to further assess and confirm these results.

Associations of dietary advanced glycation end products with liver steatosis via vibration controlled transient elastography in the United States: a nationwide cross-sectional study

PURPOSE

Large population-based studies for the associations between dietary advanced glycation end products (dAGEs) intake and liver steatosis remain lacking. It is necessary to clarify the relationship of dAGEsintake with liver steatosis through the National Health and Nutrition Survey (NHANES).

METHODS

A total of 5856 participants in the NHANES 2017-2018 were included. The dietary AGEs intake, including ε-(carboxymethyl)lysine(CML), Nε-(1-carboxyethyl)lysine (CEL), and Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) were estimated using the combination of ultra-performance LC-tandem MS dietary AGEs database and two 24-h dietary recall interviews. Liver steatosis was assessed by controlled attenuation parameter via transient elastography. Logistic regression model was adopted to explore the relationships between dAGEs intake and hepatic steatosis.

RESULTS

Compared with individuals of total dAGEs, CML, MG-H1 in the lowest tertile, those in the highest tertile had highest risk of hepatic steatosis, and the corresponding odds radios(ORs) (95% confidence interval(CI)) were 1.37 (1.01, 1.84), 1.36 (1.04,1.78) and 1.40 (1.06, 1.85), respectively. Subgroups analysis found that the positive association between dAGEs, CML, CEL and MG-H1 and hepatic steatosis appeared stronger in subjects with obesity and those with abnormal waist circumference (WC).

CONCLUSION

There was a positive correlation between dAGEs, CML, MG-H1, and hepatic steatosis, and this association mainly existed in subjects with obesity and those with abnormal WC. Dietary AGEs restriction might be of high priority for subjects with obesity for the prevention of fatty liver disease. Further longitudinal studies are required to confirm the causal associations and explore the potential mechanisms.

Comparative analysis of Nε-carboxymethyl-lysine and inflammatory markers in diabetic and non-diabetic coronary artery disease patients

BACKGROUND

Coronary artery disease (CAD) is a major cause of death worldwide, and India contributes to about one-fifth of total CAD deaths. The development of CAD has been linked to the accumulation of Nε-carboxymethyl-lysine (CML) in heart muscle, which correlates with fibrosis.

AIM

To assess the impact of CML and inflammatory markers on the biochemical and cardiovascular characteristics of CAD patients with and without diabetes.

METHODS

We enrolled 200 consecutive CAD patients who were undergoing coronary angiography and categorized them into two groups based on their serum glycosylated hemoglobin (HbA1c) levels (group I: HbA1c ≥ 6.5; group II: HbA1c < 6.5). We analyzed the levels of lipoproteins, plasma HbA1c levels, CML, interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and nitric oxide.

RESULTS

Group I (81 males and 19 females) patients had a mean age of 54.2 ± 10.2 years, with a mean diabetes duration of 4.9 ± 2.2 years. Group II (89 males and 11 females) patients had a mean age of 53.2 ± 10.3 years. Group I had more severe CAD, with a higher percentage of patients with single vessel disease and greater stenosis severity in the left anterior descending coronary artery compared to group II. Group I also exhibited a larger left atrium diameter. Group I patients exhibited significantly higher levels of CML, TNF-α, and IL-6 and lower levels of nitric oxide as compared with group II patients. Additionally, CML showed a significant positive correlation with IL-6 (r = 0.596, P = 0.001) and TNF-α (r = 0.337, P = 0.001) and a negative correlation with nitric oxide (r=-4.16, P = 0.001). Odds ratio analysis revealed that patients with CML in the third quartile (264.43-364.31 ng/mL) were significantly associated with diabetic CAD at unadjusted and adjusted levels with covariates.

CONCLUSION

CML and inflammatory markers may play a significant role in the development of CAD, particularly in diabetic individuals, and may serve as potential biomarkers for the prediction of CAD in both diabetic and non-diabetic patients.

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

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

Digestibility of Malondialdehyde-Induced Dietary Advanced Lipoxidation End Products and Their Effects on Hepatic Lipid Accumulation in Mice

Advanced lipoxidation end products (ALEs) are formed by modifying proteins with lipid oxidation products. The health effects of ALEs formed in vivo have been extensively studied. However, the digestibility, safety, and health risk of ALEs in heat-processed foods remain unclear. This investigation was performed to determine the structure, digestibility, and effect on the mice liver of dietary ALEs. The results showed that malondialdehyde (MDA) was able to alter the structure of myofibrillar proteins (MPs) to form linear, loop, and cross-linked types of Schiff bases and dihydropyridine derivatives under simulated heat processing, leading to the intra- and intermolecular aggregation of MPs and, thus, reducing the digestibility of MPs. In addition, dietary ALE intake resulted in abnormal liver function and lipid accumulation in mice. The core reason for these adverse effects was the destructive effect of ALEs on the intestinal barrier. Because the damage to the intestinal barrier leads to an increase in lipopolysaccharide levels in the liver, it induces liver damage by modulating hepatic lipid metabolism.

Dietary advanced glycation end products are associated with an increased risk of non-alcoholic fatty liver disease in Iranian adults

BACKGROUND

Dietary advanced glycation end products(AGEs) may contribute to increased inflammation and oxidative stress as risk factors for chronic diseases such as liver disease. In the current study, we aimed to examine the possible association of dietary AGEs with the odds of non-alcoholic fatty liver disease (NAFLD) in Iranian adults.

METHODS

A total of 675 participants (225 newly diagnosed NAFLD cases and 450 controls), aged  20-60 years, were recruited for this case-control study. Nutritional data were measured using a validated food frequency questionnaire, and dietary AGEs were determined for all participants. An ultrasound scan of the liver performed the detection of NAFLD in participants of the case group without alcohol consumption and other causes of hepatic disorders. We used logistic regression models, adjusted for potential confounders, to estimate the odds ratios(ORs) and 95% confidence interval(CI) of NAFLD across tertiles of dietary AGEs.

RESULTS

Mean ± SD age and body mass index of the participants were 38.13 ± 8.85 years and 26.85 ± 4.31 kg/m², respectively. The median(IQR) of dietary AGEs in participants was 3262(2472-4301). In the sex and age-adjusted model, the odds of NAFLD were increased across tertiles of dietary AGEs intake(OR:16.48;95%CI:9.57-28.40, P_trend<0.001). Also, in the final model, after controlling for confounding effects of BMI, smoking, physical activity, marital status, socio-economic status, and energy intake, the odds of NAFLD were increased across tertiles of dietary AGEs intake(OR:12.16; 95%CI:6.06-24.39, P_trend<0.001).

CONCLUSION

Our results showed that greater adherence to dietary pattern with high dietary AGEs intake was significantly related to increased odds of NAFLD.

Development of thiazole-appended novel hydrazones as a new class of α-amylase inhibitors with anticancer assets: an in silico and in vitro approach

Hyperamylasemia is reported to be associated with numerous chronic diseases, including diabetes and cancer. Considering this fact, we developed a series of thiazole-clubbed hydrazones. The derivatives were explored for their in vitro α-amylase inhibitory activity, which was further corroborated with their anticancer assets using a panel of cancer cells, including colon cancer (HCT-116), lung cancer (A549), and breast cancer (MDA-MB-231). To better understand pharmacokinetics, the synthetic derivatives were subjected to in silico ADMET prediction. The in vitro based biological investigation revealed that compared to the reference drug acarbose (IC50 = 0.21 ± 0.008 μM), all the synthesized compounds (5a-5aa) exhibited in vitro α-amylase inhibitory response in the range of IC50 values from 0.23 ± 0.003 to 0.5 ± 0.0 μM. Along with this, the proliferations of the HCT-116, A549 and MDA-MB-231 cells were inhibited when treated with the synthesized compounds. Notable cancer cell growth inhibition was observed for compounds 5e, 5f and 5y, which correlated with their α-amylase inhibition. Additionally, the kinetics investigation revealed that 5b, 5e, 5f and 5y exhibit uncompetitive inhibition. 5b was found to be the least cytotoxic and most potent α-amylase inhibitor and was further validated by absorption and fluorescence quenching technique.

Beneficial Effect of Cuban Policosanol on Blood Pressure and Serum Lipoproteins Accompanied with Lowered Glycated Hemoglobin and Enhanced High-Density Lipoprotein Functionalities in a Randomized, Placebo-Controlled, and Double-Blinded Trial with Healthy Japanese

This study evaluated the efficacy and safety of 20 mg of Cuban policosanol in blood pressure (BP) and lipid/lipoprotein parameters of healthy Japanese subjects via a placebo-controlled, randomized, and double-blinded human trial. After 12 weeks of consumption, the policosanol group showed significantly lower BP, glycated hemoglobin (HbA1c), and blood urea nitrogen (BUN) levels. The policosanol group also showed lower aspartate aminotransferase (AST), alanine aminotransferase (ALT), and γ-glutamyl transferase (γ-GTP) levels at week 12 than those at week 0: A decrease of up to 9% (p < 0.05), 17% (p < 0.05), and 15% (p < 0.05) was observed, respectively. The policosanol group showed significantly higher HDL-C level and HDL-C/TC (%), approximately 9.5% (p < 0.001) and 7.2% (p = 0.003), respectively, than the placebo group and a difference in the point of time and group interaction (p < 0.001). In lipoprotein analysis, the policosanol group showed a decrease in oxidation and glycation extent in VLDL and LDL with an improvement of particle shape and morphology after 12 weeks. HDL from the policosanol group showed in vitro stronger antioxidant and in vivo anti-inflammatory abilities. In conclusion, 12 weeks of Cuban policosanolconsumption in Japanese subjects showed significant improvement in blood pressure, lipid profiles, hepatic functions, and HbA1c with enhancement of HDL functionalities.

Glycation and a Spark of ALEs (Advanced Lipoxidation End Products) - Igniting RAGE/Diaphanous-1 and Cardiometabolic Disease

Obesity and non-alcoholic fatty liver disease (NAFLD) are on the rise world-wide; despite fervent advocacy for healthier diets and enhanced physical activity, these disorders persist unabated and, long-term, are major causes of morbidity and mortality. Numerous fundamental biochemical and molecular pathways participate in these events at incipient, mid- and advanced stages during atherogenesis and impaired regression of established atherosclerosis. It is proposed that upon the consumption of high fat/high sugar diets, the production of receptor for advanced glycation end products (RAGE) ligands, advanced glycation end products (AGEs) and advanced lipoxidation end products (ALEs), contribute to the development of foam cells, endothelial injury, vascular inflammation, and, ultimately, atherosclerosis and its consequences. RAGE/Diaphanous-1 (DIAPH1) increases macrophage foam cell formation; decreases cholesterol efflux and causes foam cells to produce and release damage associated molecular patterns (DAMPs) molecules, which are also ligands of RAGE. DAMPs stimulate upregulation of Interferon Regulatory Factor 7 (IRF7) in macrophages, which exacerbates vascular inflammation and further perturbs cholesterol metabolism. Obesity and NAFLD, characterized by the upregulation of AGEs, ALEs and DAMPs in the target tissues, contribute to insulin resistance, hyperglycemia and type two diabetes. Once in motion, a vicious cycle of RAGE ligand production and exacerbation of RAGE/DIAPH1 signaling ensues, which, if left unchecked, augments cardiometabolic disease and its consequences. This Review focuses on RAGE/DIAPH1 and its role in perturbation of metabolism and processes that converge to augur cardiovascular disease.

From Inflammation to Fibrosis: Novel Insights into the Roles of High Mobility Group Protein Box 1 in Schistosome-Induced Liver Damage

Schistosomiasis is a chronic helminthic disease of both humans and animals and the second most prevalent parasitic disease after malaria. Through a complex migration process, schistosome eggs trapped in the liver can lead to the formation of granulomas and subsequent schistosome-induced liver damage, which results in high mortality and morbidity. Although praziquantel can eliminate mature worms and prevent egg deposition, effective drugs to reverse schistosome-induced liver damage are scarce. High mobility group box 1 (HMGB1) is a multifunctional cytokine contributing to liver injury, inflammation, and immune responses in schistosomiasis by binding to cell-surface Toll-like receptors and receptors for advanced glycation end products. HMGB1 is increased in the serum of patients with schistosomiasis and enables hepatic stellate cells to adopt a proliferative myofibroblast-like phenotype, which is crucial to schistosome-induced granuloma formation. Inhibition of HMGB1 was found to generate protective responses against fibrotic diseases in animal models. Clinically, HMGB1 presents a potential target for treatment of the chronic sequelae of schistosomiasis. Here, the pivotal role of HMGB1 in granuloma formation and schistosome-induced liver damage, as well the potential of HMGB1 as a therapeutic target, are discussed.

Does AGE-RAGE Stress Play a Role in the Development of Coronary Artery Disease in Obesity?

This article deals with the role of AGE (advanced glycation end products)-RAGE (receptor for AGE) stress (AGE/sRAGE) in the development of coronary artery disease (CAD) in obesity. CAD is due to atherosclerosis in coronary artery. The serum/plasma levels of AGE and sRAGE are reduced, while AGE-RAGE stress and expression of RAGE are elevated in obese individuals. However, the levels of AGE are elevated in obese individuals with more than one metabolic syndrome. The increases in the AGE-RAGE stress would elevate the expression and production of atherogenic factors, including reactive oxygen species, nuclear factor-kappa B, cytokines, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, endothelial leukocyte adhesion molecules, monocyte chemoattractant protein-1, granulocyte-macrophage colony-stimulating factor, and growth factors. Low levels of sRAGE would also increase the atherogenic factors. The increases in the AGE-RAGE stress and decreases in the levels of sRAGE would induce development of atherosclerosis, leading to CAD. The therapeutic regimen for AGE-RAGE stress-induced CAD in obesity would include lowering of AGE intake, prevention of AGE formation, degradation of AGE in vivo, suppression of RAGE expression, blockade of AGE-RAGE interaction, downregulation of sRAGE expression, and use of antioxidants. In conclusion, the data suggest that AGE-RAGE stress is involved in the development of CAD in obesity, and the therapeutic interventions to reduce AGE-RAGE would be helpful in preventing, regressing, and slowing the progression of CAD in obesity.

Simvastatin Improves Microcirculatory Function in Nonalcoholic Fatty Liver Disease and Downregulates Oxidative and ALE-RAGE Stress

Increased reactive oxidative stress, lipid peroxidation, inflammation, and fibrosis, which contribute to tissue damage and development and progression of nonalcoholic liver disease (NAFLD), play important roles in microcirculatory disorders. We investigated the effect of the modulatory properties of simvastatin (SV) on the liver and adipose tissue microcirculation as well as metabolic and oxidative stress parameters, including the advanced lipoxidation end product–receptors of advanced glycation end products (ALE-RAGE) pathway. SV was administered to an NAFLD model constructed using a high-fat–high-carbohydrate diet (HFHC). HFHC caused metabolic changes indicative of nonalcoholic steatohepatitis; treatment with SV protected the mice from developing NAFLD. SV prevented microcirculatory dysfunction in HFHC-fed mice, as evidenced by decreased leukocyte recruitment to hepatic and fat microcirculation, decreased hepatic stellate cell activation, and improved hepatic capillary network architecture and density. SV restored basal microvascular blood flow in the liver and adipose tissue and restored the endothelium-dependent vasodilatory response of adipose tissue to acetylcholine. SV treatment restored antioxidant enzyme activity and decreased lipid peroxidation, ALE-RAGE pathway activation, steatosis, fibrosis, and inflammatory parameters. Thus, SV may improve microcirculatory function in NAFLD by downregulating oxidative and ALE-RAGE stress and improving steatosis, fibrosis, and inflammatory parameters.

Early postnatal exposure of rat pups to methylglyoxal induces oxidative stress, inflammation and dysmetabolism at adulthood

This work aimed to investigate the effects of early progeny exposure to methylglyoxal (MG), programming for metabolic dysfunction and diabetes-like complications later in life. At delivery (PN1), the animals were separated into two groups: control group (CO), treated with saline, and MG group, treated with MG (20 mg/kg of BW; i.p.) during the first 2 weeks of the lactation period. In vivo experiments and tissue collection were done at PN90. Early MG exposure decreased body weight, adipose tissue, liver and kidney weight at adulthood. On the other hand, MG group showed increased relative food intake, blood fructosamine, blood insulin and HOMA-IR, which is correlated with insulin resistance. Besides, MG-treated animals presented dyslipidaemia, increased oxidative stress and inflammation. Likewise, MG group showed steatosis and perivascular fibrosis in the liver, pancreatic islet hypertrophy, increased glomerular area and pericapsular fibrosis, but reduced capsular space. This study shows that early postnatal exposure to MG induces oxidative stress, inflammation and fibrosis markers in pancreas, liver and kidney, which are related to metabolic dysfunction features. Thus, nutritional disruptors during lactation period may be an important risk factor for metabolic alterations at adulthood.

Elevated serum levels of methylglyoxal are associated with impaired liver function in patients with liver cirrhosis

Methylglyoxal (MGO) is a highly reactive dicarbonyl species that forms advanced glycation end products (AGEs). The binding of these AGEs to their receptor (RAGE) causes and sustains severe inflammation. Systemic inflammation is postulated to be a major driver in the progression of liver cirrhosis. However, the role of circulating MGO levels in liver cirrhosis remains unknown. In this study, we investigated the serum levels of two dicarbonyl species, MGO and glyoxal (GO) using tandem mass spectrometry (HPLC-MS/MS) and evaluated their association with disease severity. A total of 51 inpatients and outpatients with liver cirrhosis of mixed etiology and different disease stages were included. Elevated MGO levels were seen in an advanced stage of liver cirrhosis (p < 0.001). High MGO levels remained independently associated with impaired liver function, as assessed by the model for end-stage liver disease (MELD) (β = 0.448, p = 0.002) and acute decompensation (AD) (β = 0.345, p = 0.005) scores. Furthermore, MGO was positively correlated with markers of systemic inflammation (IL-6, p = 0.004) and the development of ascites (p = 0.013). In contrast, no changes were seen in GO serum levels. Circulating levels of MGO are elevated in advanced stages of liver cirrhosis and are associated with impaired liver function and liver-related parameters.

Advanced Glycation End-Products in Common Non-Infectious Liver Diseases: Systematic Review and Meta-Analysis

BACKGROUND

Excessive intake of fructose, glucose and alcohol is associated with the development of non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD). At the same time, these dietetic factors create an environment favorable for the generation of advanced glycation end-products. For this reason, advanced glycation end-products (AGEs) are hypothesized to play role in the development of NAFLD and ALD. In this systematic review and meta-analysis, we explore the relationship between NAFLD and ALD with AGE levels, including their diagnostic accuracy.

METHODS

The systematic review and meta-analysis has been pre-registered with PROSPERO (CRD42021240954) and was performed in accordance with the PRISMA guidelines. Meta-analyses were performed using the meta R package.

RESULTS

We have obtained 11 studies meeting our inclusion criteria, reporting data on 1844 participants (909 with NAFLD, 169 with ALD and 766 healthy controls). NAFLD was associated with significantly higher AGE fluorescence and serum N-(carboxyethyl)lysine (CEL) levels. Patients with alcoholic cirrhosis had significantly higher levels of N-(carboxymethyl)lysine (CML). Only individual studies examined AGEs in the context of their diagnostic accuracy. AGE fluorescence distinguished low and moderate steatosis with an AUC of 0.76. The ratio of CML, CEL and pentosidine to a soluble variant of the AGE receptor differentiated patients with NAFLD from healthy controls with high AUC (0.83-0.85). Glyceraldehyde-derived AGE separated non-alcoholic fatty liver (NAFL) from non-alcoholic steatohepatitis (NASH) with acceptable performance (AUC 0.78).

CONCLUSIONS

In conclusion, NAFLD and ALD are associated with significantly higher levels of several AGEs. More research is needed to examine the diagnostic accuracy of AGEs, however individual studies show that AGEs perform well in distinguishing NAFL from NASH.

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.

Advanced glycation end product: A potential biomarker for risk stratification of non-alcoholic fatty liver disease in ELSA-Brasil study

BACKGROUND

Liver diseases are associated with the excess formation of advanced glycation end products (AGEs), which induce tissue inflammation and oxidative damage. However, the trend of oxidative marker levels according to the steatosis grade in non-alcoholic fatty liver disease (NAFLD) is unclear.

AIM

To compare serum AGE levels between participants with NAFLD accordingly to steatosis severity in the baseline ELSA-Brasil population.

METHODS

In 305 individuals at baseline ELSA-Brasil, NAFLD-associated steatosis was classified by ultrasound hepatic attenuation. The participants were grouped according to the severity of steatosis: mild and moderate/severe pooled. The measurement of serum fluorescent AGE concentrations was based on spectrofluorimetric detection. Serum AGE content and clinical and laboratory characteristics of the participants were compared between groups. The correlation between serum AGE levels and the grade of steatosis was analyzed. Logistic regression analysis was used to investigate the relationship between serum AGE levels and steatosis severity. A P value < 0.05 was considered statistically significant.

RESULTS

According to the steatosis severity spectrum in NAFLD, from mild to moderate/severe, individuals with the most severe steatosis grade had a higher incidence of metabolic syndrome (63% vs 34%, P ≤ 0.001), diabetes mellitus (37% vs 14%, P ≤ 0.001), and high cholesterol levels (51% vs 33%, P < 0.001). Moreover, individuals with increasing severity of steatosis presented increasing waist circumference, body mass index, systolic and diastolic blood pressure, fasting blood glucose, glycated hemoglobin, insulin, triglycerides, alanine aminotransferase, gamma-glutamyl transferase, C-reactive protein, and uric acid levels and lower high-density lipoprotein. Higher serum AGE content was present in the moderate/severe group of individuals than in the mild group (P = 0.008). In addition, the serum AGE levels were correlated with the steatosis grade in the overall sample (rho = 0.146, P = 0.010). Logistic regression analysis, after adjusting for confounding variables, showed that subjects with higher serum AGE content had a 4.6-fold increased chance of having moderate or severe steatosis when compared to low levels of serum AGEs. According to the results of the receiver operator characteristic curves analyses (areas under the curve, AUC = 0.83), AGEs could be a good marker of steatosis severity in patients with NAFLD and might be a potential biomarker in predicting NAFLD progression, strengthening the involvement of AGE in NAFLD pathogenesis.

CONCLUSION

NAFLD-associated steatosis was associated with serum AGE levels; therefore, plasmatic fluorescent AGE quantification by spectroscopy could be a promising alternative method to monitor progression from mild to severe NAFLD accordingly to steatosis grade.

Hepatocyte and immune cell crosstalk in non-alcoholic fatty liver disease

Introduction: Nonalcoholic fatty liver disease (NAFLD) is the most widespread chronic liver disease in the world. It can evolve into nonalcoholic steatohepatitis (NASH) where inflammation and hepatocyte ballooning are key participants in the determination of this steatotic state.Areas covered: To provide a systematic overview and current understanding of the role of inflammation in NAFLD and its progression to NASH, the function of the cells involved, and the activation pathways of the innate immunity and cell death; resulting in inflammation and chronic liver disease. A PubMed search was made with relevant articles together with relevant references were included for the writing of this review.Expert opinion: Innate and adaptive immunity are the key players in the NAFLD progression; some of the markers presented during NAFLD are also known to be immunity biomarkers. All cells involved in NAFLD and NASH are known to have immunoregulatory properties and their imbalance will completely change the cytokine profile and form a pro-inflammatory microenvironment. It is necessary to fully answer the question of what initiators and metabolic imbalances are particularly important, considering sterile inflammation as the architect of the disease. Due to the shortage of elucidation of NASH progression, we discuss in this review, how inflammation is a key part of this development and we presume the targets should lead to inflammation and oxidative stress treatment.

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.

Early AGEing and metabolic diseases: is perinatal exposure to glycotoxins programming for adult-life metabolic syndrome?

Perinatal early nutritional disorders are critical for the developmental origins of health and disease. Glycotoxins, or advanced glycation end-products, and their precursors such as the methylglyoxal, which are formed endogenously and commonly found in processed foods and infant formulas, may be associated with acute and long-term metabolic disorders. Besides general aspects of glycotoxins, such as their endogenous production, exogenous sources, and their role in the development of metabolic syndrome, we discuss in this review the sources of perinatal exposure to glycotoxins and their involvement in metabolic programming mechanisms. The role of perinatal glycotoxin exposure in the onset of insulin resistance, central nervous system development, cardiovascular diseases, and early aging also are discussed, as are possible interventions that may prevent or reduce such effects.

Non-alcoholic fatty liver and lipid profile status in patients with melasma: A case-control study

BACKGROUND

There are pieces of evidence regarding the association between melasma and metabolic syndrome. To assess the prevalence and grade of nonalcoholic fatty liver and lipid profile status in patients with melasma, we designed this case-control study.

METHODS

This study was performed on 30 consecutive women with melasma who referred to the dermatology clinic of the hospital as the case group and 34 healthy women. For all participants, serum lipid profiles and liver enzymes were checked. Also, the existence of fatty liver was assessed by ultrasonography.

RESULTS

Except for serum level of LDL (low-density lipoprotein) that was significantly higher in the melasma group than in the healthy group (104.23 ± 25.00 mg/dl versus 89.85 ± 23.00 mg/dl, p = 0.020), the level of other parameters including other lipid profiles, blood sugar, or liver enzymes was similar in both groups. In ultrasonography, the overall prevalence of fatty liver was 23.3% in the melasma group and 20.6% in the control group, and no difference was found between the two groups in grade of fatty liver (p = 0.791).

CONCLUSION

The study showed a higher serum LDL level in patients with melasma compared to women without melasma, but there was no difference between the groups in prevalence or grade of fatty liver.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

Journey to a Receptor for Advanced Glycation End Products Connection in Severe Acute Respiratory Syndrome Coronavirus 2 Infection: With Stops Along the Way in the Lung, Heart, Blood Vessels, and Adipose Tissue

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people worldwide and the pandemic has yet to wane. Despite its associated significant morbidity and mortality, there are no definitive cures and no fully preventative measures to combat SARS-CoV-2. Hence, the urgency to identify the pathobiological mechanisms underlying increased risk for and the severity of SARS-CoV-2 infection is mounting. One contributing factor, the accumulation of damage-associated molecular pattern molecules, is a leading trigger for the activation of nuclear factor-kB and the IRF (interferon regulatory factors), such as IRF7. Activation of these pathways, particularly in the lung and other organs, such as the heart, contributes to a burst of cytokine release, which predisposes to significant tissue damage, loss of function, and mortality. The receptor for advanced glycation end products (RAGE) binds damage-associated molecular patterns is expressed in the lung and heart, and in priming organs, such as the blood vessels (in diabetes) and adipose tissue (in obesity), and transduces the pathological signals emitted by damage-associated molecular patterns. It is proposed that damage-associated molecular pattern-RAGE enrichment in these priming tissues, and in the lungs and heart during active infection, contributes to the widespread tissue damage induced by SARS-CoV-2. Accordingly, the RAGE axis might play seminal roles in and be a target for therapeutic intervention in SARS-CoV-2 infection.

Novel Organic Mineral Complex Prevents High-Fat Diet-Induced Changes in the Gut and Liver of Male Sprague-Dawley Rats

Diet-induced obesity and metabolic syndrome are associated with the onset of gastrointestinal diseases, such as hepatic steatosis and gut inflammation. Prior research shows that a proprietary soil-derived organic mineral complex (OMC) prevents hyperglycemia, endotoxemia, and liver injury in rats fed a high-fat diet (HFD) for 10 weeks. The aim of this study was to further examine the effects of OMC on the liver and gastrointestinal health of these rats. Six-week-old male Sprague-Dawley rats (n = 36) were divided into two dietary groups: Chow or HFD fed for 10 weeks. Animals were further divided (n = 6/group) and administered 0, 0.6, or 3.0 mg/mL OMC in their drinking water. The 10-week HFD resulted in significant liver fat accumulation. Both OMC doses prevented hepatic increases in the glycation end product Nε-(carboxymethyl)lysine (CML) induced by HFD (p < 0.05). Low-dose OMC was associated with higher expression of occludin in the small intestine of rats fed either diet (two-way ANOVA, p < 0.042). Linear discriminant analysis (LDA) effect size (LEfSe) indicated significant differences in fecal microbial composition of untreated HFD-fed rats in comparison to untreated Chow rats at 10 weeks (LDA score > 2.0 : 18). After 10 weeks, untreated HFD-fed rats were also more abundant in bacteria associated with obesity and metabolic disease in comparison to corresponding week 0 samples (LDA score > 2.0 : 31), 10-week untreated Chow (LDA > 2.0 : 18), or 10-week OMC-treated HFD-fed rats (0.6 mg/mL; LDA > 2.0 : 80, 3.0 mg/mL; LDA > 2.0 : 8). Low-dose OMC prevented the HFD-induced increase in the Firmicutes-to-Bacteroidetes (F/B) ratio (p < 0.0416). Study animals treated with OMC exhibited no significant changes in the gut microbiota at week 10, although gut inflammatory biomarkers were not significantly altered by diet or OMC treatment. These results indicate that OMC supplementation ameliorates glycosylation reactions and modifies HFD-induced alterations in the intestinal microbiota.

Binding of CML-Modified as Well as Heat-Glycated β-lactoglobulin to Receptors for AGEs Is Determined by Charge and Hydrophobicity

Intake of dietary advanced glycation end products (AGEs) is associated with inflammation-related health problems. Nε-carboxymethyl lysine (CML) is one of the best characterised AGEs in processed food. AGEs have been described as ligands for receptors present on antigen presenting cells. However, changes in protein secondary and tertiary structure also induce binding to AGE receptors. We aimed to discriminate the role of different protein modifications in binding to AGE receptors. Therefore, β-lactoglobulin was chemically modified with glyoxylic acid to produce CML and compared to β-lactoglobulin glycated with lactose. Secondary structure was monitored with circular dichroism, while hydrophobicity and formation of β-sheet structures was measured with ANS-assay and ThT-assay, respectively. Aggregation was monitored using native-PAGE. Binding to sRAGE, CD36, and galectin-3 was measured using inhibition ELISA. Even though no changes in secondary structure were observed in all tested samples, binding to AGE receptors increased with CML concentration of CML-modified β-lactoglobulin. The negative charge of CML was a crucial determinant for the binding of protein bound CML, while binding of glycated BLG was determined by increasing hydrophobicity. This shows that sRAGE, galectin-3, and CD36 bind to protein bound CML and points out the role of negatively charged AGEs in binding to AGE receptors.

Pyridoxamine improves metabolic and microcirculatory complications associated with nonalcoholic fatty liver disease

OBJECTIVE

We investigated the protective effects of pyridoxamine against metabolic and microcirculatory complications in nonalcoholic fatty liver disease.

METHODS

Nonalcoholic fatty liver disease was established by a high-fat diet administration over 28 weeks. Pyridoxamine was administered between weeks 20 and 28. The recruitment of leukocytes and the number of vitamin A-positive hepatic stellate cells were examined by in vivo microscopy. Laser speckle contrast imaging was used to evaluate microcirculatory hepatic perfusion. Thiobarbituric acid reactive substances measurement and RT-PCR were used for oxidative stress and inflammatory parameters. advanced glycation end products were evaluated by fluorescence spectroscopy.

RESULTS

The increase in body, liver, and fat weights, together with steatosis and impairment in glucose metabolism observed in the nonalcoholic fatty liver disease group were attenuated by pyridoxamine treatment. Regarding the hepatic microcirculatory parameters, rats with high-fat diet-induced nonalcoholic fatty liver disease showed increased rolling and adhesion of leukocytes, increased hepatic stellate cells activation, and decreased tissue perfusion, which were reverted by pyridoxamine. Pyridoxamine protected against the increased hepatic lipid peroxidation observed in the nonalcoholic fatty liver disease group. Pyridoxamine treatment was associated with increased levels of tumor necrosis factor alpha (TNF-α) mRNA transcripts in the liver.

CONCLUSION

Pyridoxamine modulates oxidative stress, advanced glycation end products, TNF-α transcripts levels, and metabolic disturbances, being a potential treatment for nonalcoholic fatty liver disease-associated microcirculatory and metabolic complications.

Beneficial Effects of Low-Calorie-Carbohydrate/High-Agar Diet on Cardiometabolic Disorders Associated with Non-Alcoholic Fatty Liver Disease in Obese Rats

Energy restriction and low carbohydrate diets are recommended as nutrition therapies to prevent becoming overweight or obese. However, their beneficial effects in non-alcoholic fatty liver disease (NAFLD) are less well investigated. In addition, the effects of the type of polysaccharides incorporated into these diets and their contents have been scarcely studied. Therefore, this study aimed to elucidate whether low-calorie-carbohydrate high-agar diets could improve liver metabolic dysfunction, membrane fluidity, oxidative damage, and endothelial dysfunction in obese rats. Obesity was induced by feeding rats a high-fat diet (HFD) for 10 weeks. The obese rats were then divided into two homogenous groups: the first group was fed low-calorie-carbohydrate/high-agar diet (LCC/HA) and the second continued to consume the HFD for 4 weeks [obese control (Ob-C)]. Normo-ponderal rats were fed a normal diet during the entire study, and were used as the control (N-C). Compared with the Ob-C group, body weight, hepatic lipids, low density lipoproteins cholesterol (C), the non esterified cholesterol/phospholipids ratio, serum transaminases activities, and lipid peroxidation markers (thiobarbituric acid reactive substances and lipid hydroperoxides) were reduced in LCC/HA group (P<0.05). However, the serum concentration of high density lipoproteins-C was enhanced (P<0.05). In addition, we observed improved antioxidant defence and endothelial dysfunction associated with antioxidant enzymes, such as superoxide dismutase, glutathione peroxidase, and catalase (P<0.05), and nitric oxide level (P<0.05). These findings suggest that hypocaloric diets low in energy and carbohydrates and rich in agar may be beneficial against HFD-induced hepatic steatosis damage, and may be a promising therapeutic strategy to counteract NAFLD development associated with obesity.

Middle- and high-molecular weight adiponectin levels in relation to nonalcoholic fatty liver disease

Objective

Adiponectin (APN) circulates as high‐molecular weight (HMW), medium‐molecular weight (MMW), and low‐molecular weight (LMW) forms. Nonalcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease. Currently, the role of LMW, MMW, and HMW APN remains largely unclear in NAFLD.

Methods

We examined the variation of these forms and analyzed the related clinical characteristics in NAFLD. A total of 63 male NAFLD patients (mean age: 43.00 ± 6.10 years) and 70 healthy male subjects (mean age: 42.53 ± 7.98 years) were included in the study. Total APN and other clinical characteristics were measured. The changes in HMW, MMW, and LMW APN were determined in NAFLD patients and NAFLD patients on a high‐fat diet, and the association between the groups was further analyzed.

Results

Decreased levels of total APN and three APN isoforms were found in NAFLD. Significantly decreased levels of HMW (P < .01) and MMW (P < .001) were observed in NAFLD of high‐fat diet patients. In NAFLD patients, height (R = −.270, P = .032) and N‐epsilon‐(carboxymethyl) lysine (R = −.259, P = .040) significantly correlated with total APN. HMW APN was significantly associated with fasting plasma glucose (R = .350, P = .016), alanine aminotransferase (R = −.321, P = .029), and aspartate aminotransferase (R = −.295, P = .045). Additionally, MMW APN was significantly associated with total cholesterol (R = .357, P = .014) and high‐density lipoprotein (R = .556, P < .0001). Low‐density lipoprotein (R = −.283, P = .054) was also clearly associated with LMW APN in NAFLD patients.

Conclusion

These results suggest that HMW and MMW APN may be involved in the pathogenesis and progression of NAFLD.

Advanced glycation end-products regulate extracellular matrix-adipocyte metabolic crosstalk in diabetes

The adipose tissue extracellular matrix (ECM) regulates adipocyte cellular metabolism and is altered in obesity and type 2 diabetes, but mechanisms underlying ECM-adipocyte metabolic crosstalk are poorly defined. Advanced glycation end-product (AGE) formation is increased in diabetes. AGE alter tissue function via direct effects on ECM and by binding scavenger receptors on multiple cell types and signaling through Rho GTPases. Our goal was to determine the role and underlying mechanisms of AGE in regulating human ECM-adipocyte metabolic crosstalk. Visceral adipocytes from diabetic and non-diabetic humans with obesity were studied in 2D and 3D-ECM culture systems. AGE is increased in adipose tissue from diabetic compared to non-diabetic subjects. Glycated collagen 1 and AGE-modified ECM regulate adipocyte glucose uptake and expression of AGE scavenger receptors and Rho signaling mediators, including the DIAPH1 gene, which encodes the human Diaphanous 1 protein (hDia1). Notably, inhibition of hDia1, but not scavenger receptors RAGE or CD36, attenuated AGE-ECM inhibition of adipocyte glucose uptake. These data demonstrate that AGE-modification of ECM contributes to adipocyte insulin resistance in human diabetes, and implicate hDia1 as a potential mediator of AGE-ECM-adipocyte metabolic crosstalk.

Neutrophil-derived advanced glycation end products-Nε-(carboxymethyl) lysine promotes RIP3-mediated myocardial necroptosis via RAGE and exacerbates myocardial ischemia/reperfusion injury

Nε-(carboxymethyl) lysine (CML), the major member of advanced glycation end products, was widely studied in diabetic complications and aging-associated diseases. However, the impact of CML on myocardial ischemia/reperfusion injury (MI/RI) was rarely reported. In the present study, CML was increased in both patients with acute myocardial infarction (53.4 ± 7.8 vs. 28.1 ± 4.4 ng; P = 0.017), and mice underwent MI/RI (16.4 ± 1.4 vs. 10.8 ± 0.9 ng; P = 0.006). Depletion of neutrophils reduced CML (17.8 ± 1.0 vs. 9.9 ± 0.3 ng; P < 0.001), indicating neutrophils were the major cells contributing to CML formation during MI/RI. CML treatment exacerbated MI/RI by elevating myocardial injury marker (274.3 ± 18.0 vs. 477.2 ± 34.3 pg; P < 0.001), enlarging myocardial infarct size (32.9 ± 3.6 vs. 45.2 ± 3.8%; P = 0.03), increasing myocardial fibrosis (17.5 ± 1.6 vs. 29.7 ± 2.2%; P < 0.001) and impairing cardiac function (59.4 ± 2.4% vs. 46.0 ± 1.3%; P = 0.001). Further study revealed that CML increased the phosphorylation of receptor interacting protein (RIP) 3, an important initiator of necroptosis, and its downstream proteins. Receptor for advanced glycation end product (RAGE) deficiency effectively blocked RIP3 phosphorylation induced by CML and rescued CML-mediated MI/RI, indicating CML promoted RIP3-mediated necroptosis through RAGE. In addition, glyoxalase-1 overexpression could effectively attenuate MI/RI by reducing CML formation, providing a potential therapeutic target for MI/RI.-Yang, J., Zhang, F., Shi, H., Gao, Y., Dong, Z., Ma, L., Sun, X., Li, X., Chang, S., Wang, Z., Qu, Y., Li, H., Hu, K., Sun, A., Ge, J. Neutrophil-derived advanced glycation end products-Nε-(carboxymethyl) lysine promotes RIP3-mediated myocardial necroptosis via RAGE and exacerbates myocardial ischemia/reperfusion injury.

Development and Progression of Non-Alcoholic Fatty Liver Disease: The Role of Advanced Glycation End Products

Non-alcoholic fatty liver disease (NAFLD) affects up to 30% of the adult population and is now a major cause of liver disease-related premature illness and deaths in the world. Treatment is largely based on lifestyle modification, which is difficult to achieve in most patients. Progression of simple fatty liver or steatosis to its severe form non-alcoholic steatohepatitis (NASH) and liver fibrosis has been explained by a 'two-hit hypothesis'. Whilst simple steatosis is considered the first hit, its transformation to NASH may be driven by a second hit. Of several factors that constitute the second hit, advanced glycation end products (AGEs), which are formed when reducing-sugars react with proteins or lipids, have been implicated as major candidates that drive steatosis to NASH via the receptor for AGEs (RAGE). Both endogenous and processed food-derived (exogenous) AGEs can activate RAGE, mainly present on Kupffer cells and hepatic stellate cells, thus propagating NAFLD progression. This review focuses on the pathophysiology of NAFLD with special emphasis on the role of food-derived AGEs in NAFLD progression to NASH and liver fibrosis. Moreover, the effect of dietary manipulation to reduce AGE content in food or the therapies targeting AGE/RAGE pathway on disease progression is also discussed.

Indole-4-carboxaldehyde Isolated from Seaweed, Sargassum thunbergii, Attenuates Methylglyoxal-Induced Hepatic Inflammation

Glucose degradation is aberrantly increased in hyperglycemia, which causes various harmful effects on the liver. Glyoxalase-1 (Glo-1) is a ubiquitous cellular enzyme that participates in the detoxification of methylglyoxal (MGO), a cytotoxic byproduct of glycolysis that induces protein modification (advanced glycation end-products, AGEs) and inflammation. Here, we investigated the anti-inflammatory effect of indole-4-carboxaldehyde (ST-I4C), which was isolated from the edible seaweed Sargassum thunbergii, on MGO-induced inflammation in HepG2 cells, a human hepatocyte cell line. ST-I4C attenuated the MGO-induced expression of inflammatory-related genes, such as tumor necrosis factor (TNF)-α and IFN-γ by activating nuclear factor-kappa B (NF-κB) without toxicity in HepG2 cells. In addition, ST-I4C reduced the MGO-induced AGE formation and the expression of the receptor for AGE (RAGE). Interestingly, both the mRNA and protein expression levels of Glo-1 increased following ST-I4C treatment, and the decrease in Glo-1 mRNA expression caused by MGO exposure was rescued by ST-I4C pretreatment. These results suggest that ST-I4C shows anti-inflammatory activity against MGO-induced inflammation in human hepatocytes by preventing an increase in the pro-inflammatory gene expression and AGE formation. Therefore, it represents a potential therapeutic agent for the prevention of hepatic steatosis.

Advanced glycation endproducts produced by in vitro glycation of type I collagen modulate the functional and secretory behavior of dorsal root ganglion cells cultivated in two-dimensional system

Advanced glycation end-products (AGEs) are proteins/lipids that are glycated upon sugar exposure and are often increased during inflammatory diseases such as osteoarthritis and neurodegenerative disorders. Here, we developed an extracellular matrix (ECM) using glycated type I collagen (ECM-GC), which produced similar levels of AGEs to those detected in the sera of arthritic mice. In order to determine whether AGEs were sufficient to stimulate sensory neurons, dorsal root ganglia (DRGs) cells were cultured on ECM-GC or ECM-NC-coated plates. ECM-GC or ECM-NC were favorable for DRG cells expansion. However, ECM-GC cultivated neurons displayed thinner F-actin filaments, rounded morphology, and reduced neuron interconnection compared to ECM-NC. In addition, ECM-GC did not affect RAGE expression levels in the neurons, although induced rapid p38, MAPK and ERK activation. Finally, ECM-GC stimulated the secretion of nitrite and TNF-α by DRG cells. Taken together, our in vitro glycated ECM model suitably mimics the in vivo microenvironment of inflammatory disorders and provides new insights into the role of ECM impairment as a nociceptive stimulus.

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.

Advanced glycation end products as biomarkers in systemic diseases: premises and perspectives of salivary advanced glycation end products

Advanced glycation end products (AGEs) are glycated proteins associated with high dry temperature food processing, coloring and flavor modification of food products. Previous studies on diet-related disease support the role of the glycation products as biomarkers in local and general proinflammatory response. Exogenous and endogenous AGEs are involved in chronic low-level inflammation, which underlies the onset of metabolic syndrome influenced by food intake, there by demonstrating their implication in diet-related pathologies. Although studies have revealed a strong association between the accumulation of AGEs and the occurrence/worsening of metabolic diseases, their routine use for the diagnosis or monitoring of local and general disease has not yet been reported.

Crosstalk between nonalcoholic fatty liver disease and cardiometabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is a chronic condition characterized by fat accumulation combined with low-grade inflammation in the liver. A large body of clinical and experimental data shows that increased flux of free fatty acids from increased visceral adipose tissue and de novo lipogenesis can lead to NAFLD and insulin resistance. Thus, individuals with obesity, insulin resistance, and dyslipidaemia are at the greatest risk of developing NAFLD. Conversely, NAFLD is a phenotype of cardiometabolic syndrome. Notably, researchers have discovered a close association between NAFLD and impaired glucose metabolism and focused on the role of NAFLD in the development of type 2 diabetes. Moreover, recent studies provide substantial evidence for an association between NAFLD and atherosclerosis and cardiometabolic disorders. Even if NAFLD can progress into severe liver disorders including nonalcoholic steatohepatitis (NASH) and cirrhosis, the majority of subjects with NAFLD die from cardiovascular disease eventually. In this review, we propose a potential pathological link between NAFLD/NASH and cardiometabolic syndrome. The potential factors that can play a pivotal role in this link, such as inflammation, insulin resistance, alteration in lipid metabolism, oxidative stress, genetic predisposition, and gut microbiota are discussed.

Glyoxalase 1 Modulation in Obesity and Diabetes

Significance: Obesity and type 2 diabetes mellitus are increasing globally. There is also increasing associated complications, such as non-alcoholic fatty liver disease (NAFLD) and vascular complications of diabetes. There is currently no licensed treatment for NAFLD and no recent treatments for diabetic complications. New approaches are required, particularly those addressing mechanism-based risk factors for health decline and disease progression. Recent Advances: Dicarbonyl stress is the abnormal accumulation of reactive dicarbonyl metabolites such as methylglyoxal (MG) leading to cell and tissue dysfunction. It is a potential driver of obesity, diabetes, and related complications that are unaddressed by current treatments. Increased formation of MG is linked to increased glyceroneogenesis and hyperglycemia in obesity and diabetes and also down-regulation of glyoxalase 1 (Glo1)-which provides the main enzymatic detoxification of MG. Glo1 functional genomics studies suggest that increasing Glo1 expression and activity alleviates dicarbonyl stress; slows development of obesity, related insulin resistance; and prevents development of diabetic nephropathy and other microvascular complications of diabetes. A new therapeutic approach constitutes small-molecule inducers of Glo1 expression-Glo1 inducers-exploiting a regulatory antioxidant response element in the GLO1 gene. A prototype Glo1 inducer, trans-resveratrol (tRES)-hesperetin (HESP) combination, in corrected insulin resistance, improved glycemic control and vascular inflammation in healthy overweight and obese subjects in clinical trial. Critical Issues: tRES and HESP synergize pharmacologically, and HESP likely overcomes the low bioavailability of tRES by inhibition of intestinal glucuronosyltransferases. Future Directions: Glo1 inducers may now be evaluated in Phase 2 clinical trials for treatment of NAFLD and vascular complications of diabetes.

Hepatic Fat Content and Liver Enzymes Are Associated with Circulating Free and Protein-Bound Advanced Glycation End Products, Which Are Associated with Low-Grade Inflammation: The CODAM Study

Advanced glycation end products (AGEs) accumulate in fatty livers and may contribute to low-grade inflammation (LGI), potentially via their receptor, RAGE. It is unknown if the AGE accumulation in fatty livers results in elevated circulating AGEs. In a cohort study, we investigated the association of liver fat and hepatocellular damage with circulating AGEs and soluble RAGE (sRAGE) and subsequently the association of circulating AGEs and sRAGE with LGI. Cross-sectional associations of liver fat percentage (eLF%; ln-transformed) and liver enzymes (LE score; standardized) with circulating AGEs (free CML, CEL, and MG-H1 in nM and protein-bound CML, CEL, and pentosidine in nmol/mmol lysine; ln-transformed) and sRAGE (pg/ml, ln-transformed) and additionally of AGEs and sRAGE with LGI (standardized) were determined by multiple linear regression. eLF% was positively associated with circulating free CEL (β = 0.090; 95% CI 0.041; 0.139) but inversely with protein-bound CML (β = -0.071; 95% CI -0.108; -0.034). Similarly, the LE score was positively associated with free CML (β = 0.044; 95% CI 0.012; 0.076) and CEL (β = 0.040; 95% CI 0.009; 0.072) but inversely with protein-bound CML (β = -0.037; 95% CI -0.060; -0.013). Free CML (β = 0.297; 95% CI 0.049; 0.545) was positively associated with LGI, while protein-bound CML (β = -0.547; 95% CI -0.888; -0.207) was inversely associated, although this association was absent after adjustment for BMI. eLF% and LE score were not associated with sRAGE and sRAGE not with LGI after adjustment for BMI. Liver fat and enzymes were positively associated with circulating free AGEs, which were associated with LGI. In contrast, inverse relations were observed of liver fat and enzymes with circulating protein-bound AGEs and of protein-bound AGEs with LGI. These data suggest that hepatic steatosis and inflammation affect the formation and degradation of hepatic protein-bound AGEs resulting in elevated circulating free AGE levels. These alterations in AGE levels might influence LGI, but this is likely independent of RAGE.

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

OBJECTIVE

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

METHOD

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

RESULTS

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

CONCLUSION

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

RAGE deficiency does not affect non-alcoholic steatohepatitis and atherosclerosis in Western type diet-fed Ldlr-/- mice

Non-alcoholic fatty liver disease is a spectrum of liver diseases ranging from steatosis only to non-alcoholic steatohepatitis (NASH). The latter is characterized by hepatic inflammation, which increases the risk of cardiovascular disease. It is poorly understood which factors contribute to the onset of hepatic inflammation characterizing the progression from steatosis to NASH. Previously, we demonstrated increased advanced glycation endproducts (AGEs) in the livers of NASH patients. We hypothesise that AGEs play a key role in NASH development by activating their proinflammatory receptor, RAGE. RAGE-deficient mice and wildtype littermates, both on Ldlr^−/− background, were fed a Western type diet (WTD) for 3 or 12 weeks. Flow cytometry, histology, gene expression and AGE measurements were performed to evaluate the effects of RAGE deficiency. RAGE-deficient mice displayed reduced weight gain and visceral fat expansion compared to control mice. No difference in adipose tissue inflammation was observed between groups. RAGE deficiency did not affect WTD-induced monocytosis, circulating lipids or hepatic steatosis. WTD-induced hepatic neutrophil and macrophage accumulation and atherosclerotic plaque development was comparable between control and RAGE-deficient mice. No difference in AGE levels was observed. RAGE does not seem to play a major role in the development of NASH or atherosclerosis in a hyperlipidemic mouse model.

Impact of obesity and overweight on DNA stability: Few facts and many hypotheses

Health authorities are alarmed worldwide about the increase of obesity and overweight in the last decades which lead to adverse health effects including inflammation, cancer, accelerated aging and infertility. We evaluated the state of knowledge concerning the impact of elevated body mass on genomic instability. Results of investigations with humans (39 studies) in which DNA damage was monitored in lymphocytes and sperm cells, are conflicting and probably as a consequence of heterogeneous study designs and confounding factors (e.g. uncontrolled intake of vitamins and minerals and consumption of different food types). Results of animal studies with defined diets (23 studies) are more consistent and show that excess body fat causes DNA damage in multiple organs including brain, liver, colon and testes. Different molecular mechanisms may cause genetic instability in overweight/obese individuals. ROS formation and lipid peroxidation were found in several investigations and may be caused by increased insulin, fatty acid and glucose levels or indirectly via inflammation. Also reduced DNA repair and formation of advanced glycation end products may play a role but more data are required to draw firm conclusions. Reduction of telomere lengths and hormonal imbalances are characteristic for overweight/obesity but the former effects are delayed and moderate and hormonal effects were not investigated in regard to genomic instability in obese individuals. Increased BMI values affect also the activities of drug metabolizing enzymes which activate/detoxify genotoxic carcinogens, but no studies concerning the impact of these alterations of DNA damage in obese individuals are available. Overall, the knowledge concerning the impact of increased body weight and DNA damage is poor and further research is warranted to shed light on this important issue.

Adipose tissue macrophages induce hepatic neutrophil recruitment and macrophage accumulation in mice

OBJECTIVE

Obesity is a risk factor for non-alcoholic steatohepatitis (NASH). This risk has been attributed to visceral adipose tissue (vAT) expansion associated with increased proinflammatory mediators. Accumulation of CD11c⁺ proinflammatory adipose tissue macrophages (ATM) is an important driver of vAT inflammation. We investigated the role of ATMs in hepatic inflammation during NASH development.

DESIGN

vAT isolated from lean, obese or ATM-depleted (using clodronate liposomes) obese mice was transplanted to lean ldlr^-/- acceptor mice. Systemic and hepatic inflammation was assessed either after 2 weeks on standard chow or after 8 weeks on high cholesterol diet (HCD) to induce NASH.

RESULTS

Transplanting donor vAT from obese mice increased HCD-induced hepatic macrophage content compared with lean-transplanted mice, worsening liver damage. ATM depletion prior to vAT transplantation reduced this increased hepatic macrophage accumulation. On chow, vAT transplantation induced a more pronounced increase in circulating and hepatic neutrophil numbers in obese-transplanted than lean-transplanted mice, while ATM depletion prior to vAT transplantation reversed this effect. Microarray analysis of fluorescence-activated cell sorting of CD11c⁺ and CD11c^- macrophages isolated from donor adipose tissue showed that obesity resulted in enhanced expression of neutrophil chemotaxis genes specifically in CD11c⁺ ATMs. Involvement of the neutrophil chemotaxis proteins, CXCL14 and CXCL16, was confirmed by culturing vAT. In humans, CD11c expression in vAT of obese individuals correlated with vAT expression of neutrophil chemotactic genes and with hepatic expression of neutrophil and macrophage marker genes.

CONCLUSION

ATMs from obese vAT induce hepatic macrophage accumulation during NASH development, possibly by enhancing neutrophil recruitment.