Elevation of Nepsilon-(carboxymethyl)lysine-modified advanced glycation end products in chronic liver disease is an indicator of liver cirrhosis

Skin advanced glycation end-products as indicators of the metabolic profile in diabetes mellitus: correlations with glycemic control, liver phenotypes and metabolic biomarkers

INTRODUCTION

The production of advanced glycation end-products (AGEs) is a key pathomechanism related to the complications of diabetes mellitus. The measurement of HbA1c as one of the AGEs is widely used in the clinic, but also other proteins undergo glycation in the course of diabetes. Here, we measure skin AGEs (SAGEs) in patients with diabetes type 1 (DM1) and type 2 (DM2) and correlate them with metabolic markers as well as non-invasively measured liver fibrosis and steatosis.

PATIENTS AND METHODS

In this cross-sectional study, a total of 64 patients with either DM1 or DM2 and 28 healthy controls were recruited. SAGEs were measured using autofluorescence (AGE Reader). Liver fibrosis and steatosis were quantified using transient elastography, which determines liver stiffness measurement (LSM) and controlled attenuation parameter (CAP). FGF19, FGF21 and GDF-15 were measured in blood samples using ELISA.

RESULTS

SAGEs were elevated in both groups of patients with diabetes as compared to healthy controls (both p < 0.001) and were higher in patients with DM2 in comparison to DM1 (p = 0.006). SAGEs correlated positively with HbA1c (r = 0.404, p < 0.001), CAP (r = 0.260, p = 0.016) and LSM (r = 0.356, p < 0.001), and negatively with insulin growth factor binding protein 3 (p < 0.001). We also detected a positive correlation between GDF15 and SAGEs (r = 0.469, p < 0.001).

CONCLUSIONS

SAGEs are significantly elevated in patients with both DM types 1 and 2 and correlate with metabolic markers, including HbA1c and GDF15. They might also help to detect patients with advanced liver injury in the setting of diabetes.

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.

Plasma pentosidine as a useful biomarker of sarcopenia, low gait speed, and mortality in patients with cirrhosis

Purpose

The accumulation of advanced glycation end products (AGEs) is associated with various diseases and age-related impairments, including loss of muscle mass and function. We investigated the association between plasma pentosidine, which is one of the AGEs, and sarcopenia, low gait speed, and mortality in patients with cirrhosis.

Methods

This retrospective study divided 128 patients with cirrhosis into three groups by 25th and 75th quartiles of baseline plasma pentosidine levels: low (L)-, intermediate (I)-, and high (H)-pentosidine (Pen) groups. Sarcopenia was diagnosed following the Japan Society of Hepatology criteria. Low gait speed was defined as <0.8 m/s. The cumulative survival rates were compared between the three groups. Cox proportional hazards regression analysis was performed to identify independent factors associated with mortality.

Results

Of the 128 patients, 40 (31.3%) and 34 (26.6%) had sarcopenia and low gait speed, respectively. The prevalence of sarcopenia and low gait speed significantly increased stepwise with increasing plasma pentosidine levels, with the highest in the H-Pen group (59.4% [19/32] and 56.3% [18/32], respectively) and lowest in the L-Pen group (18.8% [6/32] and 6.3% [2/32], respectively). Multivariate analysis identified plasma pentosidine levels as a significant and independent factor associated with sarcopenia (odds ratio [OR], 1.07; p = 0.036) and low gait speed (OR, 1.06; p = 0.036), with the cutoff levels of 0.0792 μg/mL (sensitivity/specificity, 0.600/0.773) and 0.0745 μg/mL (sensitivity/specificity, 0.735/0.691), respectively. The cumulative survival rates were significantly lower in the H-Pen group than in the L-Pen (hazard ratio [HR], 11.7; p = 0.001) and I-Pen (HR, 4.03; p < 0.001) groups. Plasma pentosidine levels were identified as a significant and independent prognostic factor (HR, 1.07; p < 0.001).

Conclusion

Plasma pentosidine levels are associated with sarcopenia, low gait speed, and mortality and may serve as a useful surrogate biomarker for these clinical events in patients with cirrhosis.

Efficiency of Bone Marrow-Derived Mesenchymal Stem Cells and Hesperetin in the Treatment of Streptozotocin-Induced Type 1 Diabetes in Wistar Rats

Type 1 diabetes mellitus (T1DM) was established to be ameliorated by islet transplantation, but the shortage of the transplanted human islet tissue and the use of immunosuppressive drugs to inhibit the rejection of allogeneic grafts make this type of therapy is limited. Nowadays, therapy with stem cells is one of the most promising future treatments. This kind of therapy could have a profound impact on both replacement, as well as regenerative therapies, to improve or even cure various disorders, including diabetes mellitus. Flavonoids have also been shown to possess anti-diabetic effects. Thus, this study aims to evaluate the effectiveness of the bone marrow-derived mesenchymal stem cells (BM-MSCs) and hesperetin in the treatment of a T1DM rat model. T1DM was induced in male Wistar rats that had been starved for 16 h via intraperitoneal injection of STZ at a dose of 40 mg/kg body weight (b.wt.). After 10 days of STZ injection, the diabetic rats were allocated into four groups. The first diabetic animal group was considered a diabetic control, while the other three diabetic animal groups were treated for six weeks, respectively, with hesperetin (given orally at a dose of 20 mg/kg b.wt.), BM-MSCs (injected intravenously at a dose of 1 × 10⁶ cells/rat/week), and their combination (hesperetin and BM-MSCs). The use of hesperetin and BM-MSCs in the treatment of STZ-induced diabetic animals significantly improved the glycemic state, serum fructosamine, insulin and C-peptide levels, liver glycogen content, glycogen phosphorylase, glucose-6-phosphatase activities, hepatic oxidative stress, and mRNA expressions of NF-κB, IL-1β, IL-10, P53, and Bcl-2 in pancreatic tissue. The study suggested the therapy with both hesperetin and BM-MSCs produced marked antihyperglycemic effects, which may be mediated via their potencies to ameliorate pancreatic islet architecture and insulin secretory response, as well as to decrease hepatic glucose output in diabetic animals. The improvement effects of hesperetin and BM-MSCs on the pancreatic islets of diabetic rats may be mediated via their antioxidant, anti-inflammatory, and antiapoptotic actions.

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.

Association between Fasting and Postprandial Levels of Liver Enzymes with Metabolic Syndrome and Suspected Prediabetes in Prepubertal Children

Elevated liver enzyme activity may be associated with metabolic syndrome (MetS); however, it is not included in the MetS definition for children. Postprandial changes in the levels of biochemistry tests are related to manifestations of metabolic abnormalities. We assessed the association between fasting and postprandial liver enzymes levels with MetS and elevated hemoglobin A1c (HbA1c) in children aged 9-11. The study included 51 girls and 48 boys, all presumably healthy. In all participants' anthropometric indices, fasting glucose, insulin, lipid profile and HbA1c were measured. Enzymes, including alanine aminotransferase (ALT) and gamma-glutamyl transferase (GGT), were assayed in fasting and postprandial states. Individuals were divided into subgroups: with (MetS(+): n = 26); without MetS (MetS(-): n = 73); with HbA1c levels ≤ 5.3% (n = 39); and ≥5.7% (n = 11). Elevated fasting GGT levels were found in 23% of MetS(+) children and rarely in MetS(-) children; increased postprandial GGT was noted in 35% of MetS(+) individuals. Postprandial GGT changes tend to predict MetS (OR = 1.16; p = 0.092). Increased fasting ALT was found rarely in MetS(+) children, but did not occur in MetS(-) children. HbA1c ≥ 5.7% occurred rarely and neither fasting ALT nor GGT were related to elevated HbA1c. However, postprandial change of ALT was a good positive predictor of increased HbA1c (OR = 1.33; p = 0.021). Postprandial GGT performs better as an indicator of metabolic syndrome occurrence, and instead postprandial ALT may predict prediabetes in prepubertal children.

Allicin Alleviates Diabetes Mellitus by Inhibiting the Formation of Advanced Glycation End Products

Advanced glycation end products (AGEs) cause damage to pancreatic β-cells and trigger oxidative stress and inflammation, which promotes the development and progression of diabetes and its complications. Therefore, it is important to inhibit the formation of AGEs as part of the treatment of diabetes. Allicin is a natural antimicrobial agent with abundant pharmacological activities, and recent studies have reported its therapeutic effects in diabetes; however, the mechanism of these therapeutic effects is still unclear. Thus, the purpose of this study was to further investigate the association between allicin treatment of diabetes and AGEs. First, we established a streptozocin (STZ)-induced diabetic rat model and treated the rats with allicin for six weeks. We measured glycolipid metabolism, AGE levels, receptor of advanced glycation end products (RAGE) levels, oxidative stress, and other related indicators. The results showed that allicin improved blood glucose and body weight, reduced lipid accumulation, and inhibited AGE formation in rats. Treatment with allicin also inhibited RAGEs and thereby prevented AGE activity, which, in turn, alleviated oxidative stress and promoted insulin secretion. To further verify the effect of allicin on AGEs, we also performed in vitro nonenzymatic glycation simulation experiments. These results showed that allicin inhibited the production of AGEs by suppressing the production of AGEs intermediates. Thus, our research suggests that allicin may alleviate diabetes by inhibiting the formation of AGEs and reducing RAGE levels to relieve oxidative stress and promote insulin secretion.

Alcoholic Liver Disease Is Associated with Elevated Plasma Levels of Novel Advanced Glycation End-Products: A Preliminary Study

Elucidating the biochemical mechanisms associated with the progression of alcoholic liver disease (ALD) to more advanced stages such as alcoholic hepatitis (AH) remains an important clinical and scientific challenge. Several hypotheses point to the involvement of advanced glycation end-products (AGEs) in alcohol-associated liver injuries. Recently, we determined the structure of a synthetic, melibiose-derived AGE (MAGE), which was an analog of the novel AGE subgroup AGE10. The primary objective of our study was to determine whether AGE10 was associated with alcoholic hepatitis. The secondary objective was to provide a diagnostic accuracy of AGE10 in AH. To achieve this objective, we examined the plasma levels of AGE10 in 65 healthy individuals and 65 patients with AH. The AGE10 level was measured using a competitive ELISA. Our study confirmed that patients with AH had significantly higher plasma concentrations of AGE10 compared with healthy controls (184.5 ± 71.1 μg/mL and 123.5 ± 44.9 μg/mL, respectively; p < 0.001). In addition, AGE10 showed an acceptable performance as a diagnostic marker of AH, with an AUC of 0.78. In conclusion, AH was associated with elevated levels of novel advanced glycation end-product AGE10.

Skin Autofluorescence Measurement as Initial Assessment of Hepatic Parenchyma Quality in Patients Undergoing Liver Resection

Skin autofluorescence (SAF) can detect advanced glycation end products (AGEs) that accumulate in tissues over time. AGEs reflect patients’ general health, and their pathological accumulation has been associated with various diseases. This study aimed to determine whether its measurements can correlate with the liver parenchyma quality. This prospective study included 186 patients who underwent liver resections. Liver fibrosis and/or steatosis > 10% were found in almost 30% of the patients. ROC analysis for SAF revealed the optimal cutoff point of 2.4 AU as an independent predictor for macrovesicular steatosis ≥ 10% with an AUC of 0.629 (95% CI 0.538−0.721, p = 0.006), 59.9% sensitivity, 62.4% specificity, and positive (PPV) and negative (NPV) predictive values of 45.7% and 74.1%, respectively. The optimal cutoff point for liver fibrosis was 2.3 AU with an AUC of 0.613 (95% CI 0.519−0.708, p = 0.018), 67.3% sensitivity, 55.2% specificity, and PPV and NPV of 37.1% and 81.2%, respectively. In the multivariable logistic regression model, SAF ≥ 2.4 AU (OR 2.16; 95% CI 1.05−4.43; p = 0.036) and BMI (OR 1.21; 95% CI 1.10−1.33, p < 0.001) were independent predictors of macrovesicular steatosis ≥ 10%. SAF may enhance the available non-invasive methods of detecting hepatic steatosis and fibrosis in patients prior to liver resection.

Metabolic perturbations and health impact from exposure to a combination of multiple harmful Maillard reaction products on Sprague-Dawley rats

The present study aimed to investigate the metabolic perturbations and health impact of the co-accumulation of Maillard reaction products (MRPs), including acrylamide, harmane, and N^ε-(carboxymethyl)lysine (CML), via serum biochemical and histopathological examinations as well as metabolomic analysis. Sprague-Dawley rats were treated with acrylamide (2 mg per kg body weight [bw]), harmane (1 mg per kg bw), CML (2 mg per kg bw), and combinations of these MRPs. Harmane did not cause adverse effects on the health of rats, whereas acrylamide and CML resulted in significantly (P < 0.05) decreased insulin sensitivity (HOMA-IR > 1), increased oxidative stress levels, and pathological injuries to the pancreas, liver, and gastrocnemius. Owing to the antioxidant and anti-diabetic activities of harmane, the effects of the combination of the MRPs on oxidative stress levels, blood glucose metabolism, and pathological injuries to the pancreas and gastrocnemius were relieved. However, new health problems, including pathological injury of the kidneys and increased cancer risk, were observed. Metabolomic analysis revealed that this may be related to the effects of MRPs on the arginine biosynthesis pathway, which resulted in the abnormal metabolism of fumaric acid and the tricarboxylic acid cycle. These results indicated that the mechanisms of the combined effect of MRPs and their effects on health cannot be predicted from the effects of individual MRPs.

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.

[Chronic kidney injury in patients with liver diseases - Reappraising pathophysiology and treatment options]

Acute and chronic kidney disease concurs commonly with liver disease and is associated with a wide array of complications including dialysis dependency and increased mortality. Patients with liver disease or liver cirrhosis show a higher prevalence of chronic kidney disease. This is attributed to concomitant comorbidities, such as metabolic syndrome, chronic inflammation, hypercoagulability, hyperfibrinolysis, diabetes mellitus and dyslipidaemias. But chronic progressive kidney disease is not always due to hepatorenal syndrome. Beyond that, other diseases or disease entities should be considered. Among them are diabetic nephropathy, secondary IgA nephropathy, hepatitis C -associated membranoproliferative Glomerulonephritis (MPGN) and hepatitis B-associated membranous nephropathy.Coexisting diseases, similar underlying pathophysiologic mechanisms, or simultaneously concurring pathophysiological processes and overlapping clinical manifestations, impede the etiologic diagnosis and corresponding treatment of chronic kidney disease in the setting of chronic liver disease. In this review, we focus on common and rare pathologies, which can lead to chronic kidney disease in this particular patient group and try to summarize the most recent therapeutic modalities.

Advanced glycation end products and their adverse effects: The role of autophagy

The critical roles played by advanced glycation endproducts (AGEs) accumulation in diabetes and diabetic complications have gained intense recognition. AGEs interfere with the normal functioning of almost every organ with multiple actions like apoptosis, inflammation, protein dysfunction, mitochondrial dysfunction, and oxidative stress. However, the development of a potential treatment strategy is yet to be established. Autophagy is an evolutionarily conserved cellular process that maintains cellular homeostasis with the degradation and recycling systems. AGEs can activate autophagy signaling, which could be targeted as a therapeutic strategy against AGEs induced problems. In this review, we have provided an overview of the adverse effects of AGEs, and we put forth the notion that autophagy could be a promising targetable strategy against AGEs.

Tissue-specific Fixation Methods Are Required for Optimal In Situ Visualization of Hyaluronan in the Ovary, Kidney, and Liver

Hyaluronan (HA) is a ubiquitous component of the extracellular matrix. The spatial-temporal localization of HA can be visualized in situ using biotinylated HA binding proteins (HABPs). This assay is sensitive to fixation conditions, and there are currently no best practices for HA detection. Thus, the goal of this study was to optimize fixation conditions for visualizing HA in the ovary, kidney, and liver through analysis of six commonly used fixatives for HA detection: Bouin's Solution, Carnoy's Solution, Ethanol-Formalin-Glacial Acetic Acid (EFG), Histochoice, Modified Davidson's Solution, and 10% Neutral Buffered Formalin. Organs were harvested from CB6F1 mice and fixed with one of the identified fixatives. Fixed organs were sectioned, and the HABP assay was performed on sections in parallel. Hematoxylin and eosin staining was also performed to visualize tissue architecture. HABP signal localization and intensity varied between fixatives. EFG and Carnoy's Solution best preserved the HA signal intensity in the ovary and liver, showing HA localization in various sub-organ structures. In the kidney, only Modified Davidson's Solution was less than optimal. Our findings demonstrate that fixation can alter the ability to detect HA in tissue macro- and microstructures, as well as localization in a tissue-specific manner, in situ.

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.

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.

Hepatogenous Diabetes: An Underestimated Problem of Liver Cirrhosis

The prevalence of diabetes mellitus in cirrhotic patients is much higher than that in the general population. Two types of diabetes are usually seen in patients with cirrhosis: type 2 diabetes mellitus and hepatogenous diabetes (HD). The HD is an acquired condition which is believed to be caused by impaired insulin clearance and pancreatic β-cell dysfunction in cirrhotic patients. Increased levels of advanced glycation end products and hypoxia-inducible factors have been implicated in the pathogenesis of HD. Patients with HD typically present with normal fasting glucose, but abnormal response to an oral glucose tolerance test, which is required for the diagnosis. Because the level of glycated hemoglobin is often falsely low in patients with cirrhosis, it does not help in the early diagnosis of HD. HD is associated with an increased rate of complications of cirrhosis, decreased 5-year survival rate, and increased risk of hepatocellular carcinoma. The major complications of cirrhosis associated with HD include hepatic encephalopathy (HE), spontaneous bacterial peritonitis, sepsis, variceal hemorrhage, and renal dysfunction. Treatment of HD may be difficult as many antihyperglycemic therapies are associated with increased risk of complications in cirrhosis, particularly hypoglycemia. Biguanides, alpha-glucosidase inhibitors, and new medications such as dipeptidyl peptidase-4 inhibitors and sodium-glucose co-transporter 2 inhibitors appear to be safe in patients with cirrhosis. Though insulin therapy is currently advocated, requirement of insulin is variable and is difficult to predict. The liver transplantation usually results in reversal of HD. This review article provides an overview of magnitude, patients' characteristics, clinical implications, pathophysiological mechanisms, diagnosis, and management of HD.

The Role of Glyoxalase-I (Glo-I), Advanced Glycation Endproducts (AGEs), and Their Receptor (RAGE) in Chronic Liver Disease and Hepatocellular Carcinoma (HCC)

Glyoxalase-I (Glo-I) and glyoxalase-II (Glo-II) comprise the glyoxalase system and are responsible for the detoxification of methylglyoxal (MGO). MGO is formed non-enzymatically as a by-product, mainly in glycolysis, and leads to the formation of advanced glycation endproducts (AGEs). AGEs bind to their receptor, RAGE, and activate intracellular transcription factors, resulting in the production of pro-inflammatory cytokines, oxidative stress, and inflammation. This review will focus on the implication of the Glo-I/AGE/RAGE system in liver injury and hepatocellular carcinoma (HCC). AGEs and RAGE are upregulated in liver fibrosis, and the silencing of RAGE reduced collagen deposition and the tumor growth of HCC. Nevertheless, data relating to Glo-I in fibrosis and cirrhosis are preliminary. Glo-I expression was found to be reduced in early and advanced cirrhosis with a subsequent increase of MGO-levels. On the other hand, pharmacological modulation of Glo-I resulted in the reduced activation of hepatic stellate cells and therefore reduced fibrosis in the CCl₄-model of cirrhosis. Thus, current research highlighted the Glo-I/AGE/RAGE system as an interesting therapeutic target in chronic liver diseases. These findings need further elucidation in preclinical and clinical studies.

Fructose-human serum albumin interaction undergoes numerous biophysical and biochemical changes before forming AGEs and aggregates

Fructose is a reducing and highly lipogenic sugar that has unique metabolic effects in the liver. Non-enzymatic fructosylation of proteins generates advanced glycation end products (AGEs). Human serum albumin (HSA) may undergo fructosylation vis-à-vis AGEs formation. High fructose consumption may lead to structurally altered and functionally compromised fructosylated-HSA-AGEs, which can cause damage to hepatocytes resulting in hepatic macro- and microvesicular steatosis. In this study, HSA was incubated with varying concentrations of fructose for 10days and the induced changes were studied. Fructosylated-HSA exhibited hyperchromicity, increased AGE-specific fluorescence, quenching of tryptophan fluorescence and increased melting temperature. Nε-[carboxymethyl]-lysine (CML), was detected by liquid chromatography mass spectrometry (LC-MS). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed decreased mobility in fructosylated-HSA. Perturbations in secondary and tertiary structure were revealed by fourier transform-infrared spectroscopy (FT-IR), supported by far- and near-UV circular dichroism (CD). Dynamic light scattering (DLS) and Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) mass spectrometry studies suggested increase in molecular mass of fructosylated-HSA. Amyloidogenic aggregates were confirmed from Congo red, Thioflavin T assay and Scanning electron microscope (SEM). These investigations confirmed the structural alterations in fructosylated-HSA and warrants further study to probe the role of fructosylated-HSA-AGEs in hepatopathy vis-à-vis fatty liver diseases.

Hepatic microvascular dysfunction and increased advanced glycation end products are components of non-alcoholic fatty liver disease

BACKGROUND

This study aimed to investigate the pathophysiology of hepatic microcirculatory dysfunction in non-alcoholic fatty liver disease (NAFLD).

METHODS

In Wistar rats, NAFLD model was induced by 20 weeks of high-fat diet (HFD) feeding. Rolling and adhesion of leukocytes and tissue perfusion in hepatic microcirculation were examined using in vivo microscopic and laser speckle contrast imaging (LSCI), respectively. Oxidative stress and inflamatory parameters were analysed by TBARs, catalase enzyme activity, RT-PCR and ELISA. The participation of advanced glycation end-products (AGE) and its receptor RAGE was evaluated by the measurement of gene and protein expression of RAGE by RT-PCR and Western-blot, respectively and by liver and serum quantification of fluorescent AGEs.

RESULTS

Wistar rats fed high-fat diet (HFD) showed increase in epididymal and abdominal fat content, systolic arterial blood pressure, fasting blood glucose levels, hepatic triglycerides and cholesterol, and impairment of glucose and insulin metabolisms. Liver histology confirmed the presence of steatosis and ultrasound analysis revealed increased liver size and parenchymal echogenicity in HFD-fed rats. HFD causes significant increases in leukocyte rolling and adhesion on hepatic microcirculation and decrease in liver microvascular blood flow. Liver tissue presented increase in oxidative stress and inflammtion. At 20 weeks, there was a significantly increase in AGE content in the liver and serum of HFD-fed rats and an increase in RAGE gene expression in the liver.

CONCLUSION

The increase in liver AGE levels and microcirculatory disturbances could play a role in the pathogenesis of liver injury and are key components of NAFLD.

Effects of ferric citrate supplementation on advanced glycation end products in a rat model of streptozotocin/nicotinamide-induced diabetes

SCOPE

Diabetes is associated with the increased risks of anemia and activation of advanced glycation end products (AGEs) and the receptor for AGEs (RAGE). However, the effects of pharmacological doses of iron supplementation on AGE metabolism are less clear. The aim was to investigate the effect of ferric citrate supplementation on AGE metabolism.

METHODS AND RESULTS

Diabetes was induced in overnight starved rats by intraperitoneal injections of 40 mg/kg streptozotocin and 120 mg/kg nicotinamide. Diabetic rats were fed a standard diet or pharmacological doses of ferric citrate (0.5, 1, 2, and 3 g of ferric iron/kg diet) for 10 weeks. Ferric citrate supplementation showed a dose-related effect on the hepatic steatosis score, malondialdehyde, cathepsin D, and glyoxalase I. A Western blot analysis revealed that >1 g of ferric iron suppressed hepatic AGE receptor 1 and high-mobility group-box 1 expressions but increased heme oxygenase-1 and RAGE expressions. Further analysis showed that high doses of ferric iron triggered sterol regulatory element-binding protein 1c, p38-mitogen-activated protein kinase, and nuclear factor-κB protein expressions.

CONCLUSION

Overall, the present results suggest a dose-related effect of ferric citrate supplementation on AGE metabolism, and this effect was more evident at high iron doses (>1 g of ferric iron/kg diet).

Fructosylation induced structural changes in mammalian DNA examined by biophysical techniques

Glycosylation of DNA, proteins, lipids, etc. by reducing sugars, can lead to the formation of advanced glycation end products (AGEs). These products may accumulate and involve in the pathogenesis of a number of diseases, contributing to tissue injury via several mechanisms. In this study, fructosylation of calf thymus dsDNA was carried out with varying concentrations of fructose. The neo-structure of fructosylated-DNA was studied by various biophysical techniques and morphological characterization. Fructosylated-DNA showed hyperchromicity, increase in fluorescence intensity and decrease in melting temperature. The CD signal of modified-DNA shifted in the direction of higher wavelength indicative of structural changes in DNA. FTIR results indicated shift in specific band positions in fructosylated-DNA. Morphological characterization of fructosylated-DNA exhibited strand breakage and aggregation. The results suggest that the structure and conformation of DNA may be altered under high concentrations of fructose.

Dietary glycotoxins and infant formulas

Advanced glycation end products constitute a complex group of compounds derived from the nonenzymatic glycation of proteins, lipids, and nucleic acids formed endogenously, but also from exogenous supplies such as tobacco smoking (glycotoxins). Accumulating evidence underlies the beneficial effect of the dietary restriction of glycotoxins in animal studies and also in patients with diabetic complications and metabolic diseases. Composition of infant formulas and their processing methods render an extraordinary favorable milieu for the formation of glycotoxins, and the content of glycotoxins in infant formula exceeds that of breast milk by hundred folds. Data from a limited number of short-term small studies in healthy infants do not provide direct evidence of acute negative health effects of glycotoxins in early infancy. However, the effects in sensitive groups on the state of future health in adulthood remain unclear.

Diabetes mellitus in patients with cirrhosis: clinical implications and management

Disorders of glucose metabolism, namely glucose intolerance and diabetes, are frequent in patients with chronic liver diseases. In patients with cirrhosis, diabetes can be either a classical type 2 diabetes mellitus or the so-called hepatogenous diabetes, i.e. a consequence of liver insufficiency and portal hypertension. This review article provides an overview of the possible pathophysiological mechanisms explaining diabetes in patients with cirrhosis. Cirrhosis is associated with portosystemic shunts as well as reduced hepatic mass, which can both impair insulin clearance by the liver, contributing to peripheral insulin resistance through insulin receptors down-regulation. Moreover, cirrhosis is associated with increased levels of advanced-glycation-end products and hypoxia-inducible-factors, which may play a role in the development of diabetes. This review also focuses on the clinical implications of diabetes in patients with cirrhosis. First, diabetes is an independent factor for poor prognosis in patients with cirrhosis. Specifically, diabetes is associated with the occurrence of major complications of cirrhosis, including ascites and renal dysfunction, hepatic encephalopathy and bacterial infections. Diabetes is also associated with an increased risk of hepatocellular carcinoma in patients with chronic liver diseases. Last, the management of patients with concurrent diabetes and liver disease is also addressed. Recent findings suggest a beneficial impact of metformin in patients with chronic liver diseases. Insulin is often required in patients with advanced cirrhosis. However, the favourable impact of controlling diabetes in patients with cirrhosis has not been demonstrated yet.

Mechanisms of Diabetes-Induced Liver Damage: The role of oxidative stress and inflammation

Diabetes mellitus is a non-communicable disease that occurs in both developed and developing countries. This metabolic disease affects all systems in the body, including the liver. Hyperglycaemia, mainly caused by insulin resistance, affects the metabolism of lipids, carbohydrates and proteins and can lead to non-alcoholic fatty liver disease, which can further progress to non-alcoholic steatohepatitis, cirrhosis and, finally, hepatocellular carcinomas. The underlying mechanism of diabetes that contributes to liver damage is the combination of increased oxidative stress and an aberrant inflammatory response; this activates the transcription of pro-apoptotic genes and damages hepatocytes. Significant involvement of pro-inflammatory cytokines-including interleukin (IL)-1β, IL-6 and tumour necrosis factor-α-exacerbates the accumulation of oxidative damage products in the liver, such as malondialdehyde, fluorescent pigments and conjugated dienes. This review summarises the biochemical, histological and macromolecular changes that contribute to oxidative liver damage among diabetic individuals.

Advanced Glycation End-Products and Their Receptors: Related Pathologies, Recent Therapeutic Strategies, and a Potential Model for Future Neurodegeneration Studies

Advanced glycation end products (AGEs) are the result of a nonenzymatic reaction between sugars and proteins, lipids, or nucleic acids. AGEs are both consumed and endogenously formed; their accumulation is accelerated under hyperglycemic and oxidative stress conditions, and they are associated with the onset and complication of many diseases, such as cardiovascular diseases, diabetes, and Alzheimer's disease. AGEs exert their deleterious effects by either accumulating in the circulation and tissues or by receptor-mediated signal transduction. Several receptors bind AGEs: some are specific and contribute to clearance of AGEs, whereas others, like the RAGE receptor, are nonspecific, associated with inflammation and oxidative stress, and considered to be mediators of the aforementioned AGE-related diseases. Although several anti-AGE compounds have been studied, understanding the underlying mechanisms of RAGE and targeting it as a therapeutic strategy is becoming increasingly desirable. For achieving these goals efficiently and expeditiously, the C. elegans model has been suggested. This model is already used for studying several human diseases and, by expressing RAGE, could also be used to study RAGE-related pathways and pathologies to facilitate the development of novel therapeutic strategies.

Toxicological evaluation of advanced glycation end product Nε-(carboxymethyl)lysine: Acute and subacute oral toxicity studies

Nε-(carboxymethyl)lysine (CML) as a novel potential noxious compound in various food products has aroused extensive concern in recent years. This study aimed to investigate the oral acute and subacute toxicity of CML in mice as per OECD 420 and 407 guidelines. Acute administration of 2000 and 5000 mg/kg CML did not induce any mortality within 14 days, nevertheless some toxicological symptoms and histopathological changes were observed. The estimated LD50 of CML was >5000 mg/kg. In subacute toxicity test, CML was dosed at 200, 500 and 1000 mg/kg in both genders for 28 days. The body weights reduced which was accompanied with the decrease of food consumptions. Hematology parameters viz. RBC, HGB and MCH showed minor alteration but these were still within normal range. Biochemical analysis of hepatic and renal function markers showed significant elevating in AST, ALT, Cr and BUN etc. Histopathological alterations were observed in lung, liver, kidney and spleen. Subacute toxicity of CML involved oxidative stress caused by reducing antioxidant enzyme (SOD and GSH-Px) activities, and significantly increasing lipid peroxide (MDA) level. In conclusion, CML was unlikely to present an acute hazard, but repeated administration could produce deleterious effects on mice especially inducing liver and kidney damage through oxidative stress.

Advanced Glycation End Products Induce Obesity and Hepatosteatosis in CD-1 Wild-Type Mice

AGEs are a heterogeneous group of molecules formed from the nonenzymatic reaction of reducing sugars with free amino groups of proteins, lipids, and/or nucleic acids. AGEs have been shown to play a role in various conditions including cardiovascular disease and diabetes. In this study, we hypothesized that AGEs play a role in the “multiple hit hypothesis” of nonalcoholic fatty liver disease (NAFLD) and contribute to the pathogenesis of hepatosteatosis. We measured the effects of various mouse chows containing high or low AGE in the presence of high or low fat content on mouse weight and epididymal fat pads. We also measured the effects of these chows on the inflammatory response by measuring cytokine levels and myeloperoxidase activity levels on liver supernatants. We observed significant differences in weight gain and epididymal fat pad weights in the high AGE-high fat (HAGE-HF) versus the other groups. Leptin, TNF-α, IL-6, and myeloperoxidase (MPO) levels were significantly higher in the HAGE-HF group. We conclude that a diet containing high AGEs in the presence of high fat induces weight gain and hepatosteatosis in CD-1 mice. This may represent a model to study the role of AGEs in the pathogenesis of hepatosteatosis and steatohepatitis.

RAGE-mediated inflammation in patients with septic shock

BACKGROUND

The receptor for advanced glycation end-products (RAGE)-pathway is described to be a crucial component of the innate immune response in sepsis. The aims of the present study were, therefore, to delineate the kinetics of membrane-bound RAGE expression, to quantify its soluble isoforms, and to determine the extent of metabolic (e.g., AGE-CML) as well as immunologic (e.g., S100A8/A9) ligands in different inflammatory settings in humans.

MATERIALS AND METHODS

The presented data result from secondary analyses of an observational clinical pilot study, including patients with septic shock (n = 60), postoperative controls (n = 30), and healthy volunteers (n = 30). Surface-bound expression of RAGE by peripheral blood leukocytes was determined by flow cytometry. In addition, plasma levels of sRAGE, esRAGE, AGE-CML, S100A8/A9, S100A8/A9-CML, RBP, RBP-CML, HSA-CML, HMBG-1, and ß-Amyloid were measured using ELISA.

RESULTS

In patients with septic shock, RAGE expression was significantly increased in comparison to both control groups, which was paralleled by a significant increase in sRAGE plasma levels. Formation of AGE-CML was shown to be dependent on the availability of the unmodified protein. However, the total amount of AGE-CML did not differ significantly between septic patients and healthy volunteers at early stages or was even lower in patients with sepsis at later stages. In contrast, immunologic ligands (e.g., S100A8/A9) were shown to be significantly elevated in septic patients within the entire study period.

CONCLUSIONS

Activation of the RAGE-pathway was shown to be of relevance in patients with septic shock, mainly driven by an increase in immunologic (e.g., S100A8/A9) rather than metabolic ligands (e.g., CML-derived AGE-formation).

Contribution of the toxic advanced glycation end-products-receptor axis in nonalcoholic steatohepatitis-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. The main etiologies of HCC are hepatitis B virus and hepatitis C virus (HCV), and non-hepatitis B/non-hepatitis C HCC (NBNC-HCC) has also been identified as an etiological factor. Although the incidence of HCV-related HCC in Japan has decreased slightly in recent years, that of NBNC-HCC has increased. The onset mechanism of NBNC-HCC, which has various etiologies, remains unclear; however, nonalcoholic steatohepatitis (NASH), a severe form of nonalcoholic fatty liver disease, is known to be an important risk factor for NBNC-HCC. Among the different advanced glycation end-products (AGEs) formed by the Maillard reaction, glyceraldehyde-derived AGEs, the predominant components of toxic AGEs (TAGE), have been associated with NASH and NBNC-HCC, including NASH-related HCC. Furthermore, the expression of the receptor for AGEs (RAGE) has been correlated with the malignant progression of HCC. Therefore, TAGE induce oxidative stress by binding with RAGE may, in turn, lead to adverse effects, such as fibrosis and malignant transformation, in hepatic stellate cells and tumor cells during NASH or NASH-related HCC progression. The aim of this review was to examine the contribution of the TAGE-RAGE axis in NASH-related HCC.

Inhibitory effect of receptor for advanced glycation end product‑specific small interfering RNAs on the development of hepatic fibrosis in primary rat hepatic stellate cells

Specific small interfering RNAs (siRNAs) targeting receptor for advanced glycation end products (RAGE) inhibit the expression of RAGE, α-smooth muscle actin and type I collagen in the T6 hepatic stellate cells (HSCs), indicating that RAGE is important for the activation of HSCs and the expression of collagen. The present study aimed to investigate the effect of specific siRNAs targeting RAGE on the development of hepatic fibrosis (HF), using primary rat HSCs, which were isolated and cultured in vitro. The expression vectors for specific siRNAs targeting RAGE were constructed and transfected into primary rat HSCs. Untreated and nonspecific siRNA-transfected primary rat HSCs served as controls. The expression levels of RAGE, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), laminin (LN), hyaluronic acid (HA) and N-terminal procollagen III propeptide (PIIINP) in primary HSCs were detected by reverse transcription quantitative polymerase chain reaction and western blotting. The mRNA and 42 kD protein expression of RAGE in the pAKD-GR126-transfected primary HSCs were significantly downregulated compared with those in the untreated and the pAKD-negative control (NC)-transfected controls. The mRNA and protein expression levels of IL-6, TNF-α, TGF-β1, CTGF, LN, HA and PIIINP in the pAKD-GR126-transfected primary HSCs were also markedly downregulated compared with those in the untreated and pAKD-NC-transfected controls. Therefore, RAGE-specific siRNAs inhibited the expression of RAGE in primary rat HSCs and inhibited the development of HF.

Current perspectives on the health risks associated with the consumption of advanced glycation end products: recommendations for dietary management

Advanced glycation end products (AGEs) constitute a complex group of compounds produced endogenously during the aging process and under conditions of hyperglycemia and oxidative stress. AGEs also have an emerging exogenous origin. Cigarette smoke and diet are the two main exogenous sources of AGEs (glycotoxins). Modern Western diets are rich in AGEs which have been implicated in the pathogenesis of several metabolic and degenerative disorders. Accumulating evidence underlies the beneficial effect of the dietary restriction of AGEs not only in animal studies but also in patients with diabetic complications and metabolic diseases. This article reviews the evidence linking dietary glycotoxins to several disorders from diabetic complications and renal failure to liver dysfunction, female reproduction, eye and cognitive disorders as well as cancer. Furthermore, strategies for AGE reduction are discussed with a focus on dietary modification.

Influence of nonenzymatic posttranslational modifications on constitution, oligomerization and receptor binding of S100A12

This study examined the effect of methylglyoxal (MGO)-derived nonenzymatic posttranslational modifications (nePTMs) on the binding affinity of S100A12 to its natural receptor for advanced glycation end-products (RAGE). Binding of MGO-modified S100A12 to RAGE decreased significantly with increasing MGO concentration and incubation time. Ca²⁺-induced S100A12 hexamerization was impaired only at higher MGO concentrations indicating that the loss of affinity is not predominantly caused by disturbance of ligand oligomerization. nePTM mapping showed carboxyethylation of lysine (CEL) and the N-terminus without preferential modification sites. Besides, hydroimidazolone, hemiaminals, argpyrimidine, and tetrahydropyrimidine rapidly formed at R21. Even at the highest modification rate, hexamerization of synthesized CEL-S100A12 was unaffected and RAGE-binding only slightly impaired. Thus, nePTMs at R21 seem to be the major cause of MGO-induced impairment of S100A12 oligomerization and RAGE binding.

Suppression of dimerumic acid on hepatic fibrosis caused from carboxymethyl-lysine (CML) by attenuating oxidative stress depends on Nrf2 activation in hepatic stellate cells (HSCs)

Hyperglycemia facilitates the formation of advanced glycation end-products (AGEs) in type-2 diabetes. Evidence indicates that carboxymethyl-lysine (CML) is highly prevalent in diabetes, resulting in hepatic fibrosis. The current study was designed to evaluate the effects of dimerumic acid (DMA) identified from Monascus-fermented products on receptor for AGEs (RAGE) signal and hepatic stellate cells (HSCs) activation by CML treatment. We found that DMA (50 μM) eliminated collagen generation, mRNA expressions of α-smooth muscle actin (α-SMA), platelet-derived growth factor-β receptor (PDGF-βR), and procollagen 1a1 (proCol-1a1) in CML (100 μg/ml)-treated HSCs, and these effects were similar to allyl isothiocyanate (AITC; 50 μM). In addition, the suppression of α-SMA, PDGF-βR, proCol-1a1 by DMA were abolished while nuclear factor-erythroid 2-related factor 2 (Nrf2) silence in CML-treated HSCs. These findings suggested that DMA and AITC increased Nrf2 and glutamate-cysteine ligase (GCL) activities thereby inhibiting oxidative stress caused by CML and showing anti-fibrogentic effect in HSCs.

Soluble receptor for advanced glycation end products and risk of liver cancer

Binding of advanced glycation end products (AGEs) to their receptor (RAGE) increases oxidative stress and inflammation and may be involved in liver injury and subsequent carcinogenesis. Soluble RAGE (sRAGE) may neutralize the effects mediated by the AGE/RAGE complex. Epidemiologic studies examining sRAGE or AGEs in association with liver cancer are lacking. We examined the associations between prediagnostic serum concentrations of sRAGE or Nϵ-(carboxymethyl)-lysine (CML)-AGE and hepatocellular carcinoma in a case-cohort study within a cohort of 29,133 Finnish male smokers who completed questionnaires and provided a fasting blood sample between 1985 and 1988. During follow-up beginning 5 years after enrollment through April 2006, 145 liver cancers occurred. Serum concentrations of sRAGE, CML-AGE, glucose, and insulin were measured in case subjects and 485 randomly sampled cohort participants. Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) were available in most cases and in a subset of the study population. Weighted Cox proportional hazards regression was used to calculate relative risks (RR) and 95% confidence intervals (CI) adjusted for age, years of smoking, and body mass index. sRAGE and CML-AGE concentrations were inversely associated with liver cancer. Further adjustment for glucose and insulin or exclusion of case subjects with chronic HBV or HCV did not change the associations.

CONCLUSION

Our results support the hypothesis that sRAGE is inversely associated with liver cancer. The findings need confirmation, particularly in populations that include women and nonsmokers. (HEPATOLOGY 2013 ).

Reactive metabolites and AGE-RAGE-mediated inflammation in patients following liver transplantation

Recent investigations have indicated that reactive metabolites and AGE-RAGE-mediated inflammation might play an important role in the pathogenesis of ischemia-reperfusion injury in liver transplantation. In this observational clinical study, 150 patients were enrolled following liver transplantation from deceased donors. The occurrence of short-term complications within 10 days of transplantation was documented. Blood samples were collected prior to transplantation, immediately after transplantation, and at consecutive time points, for a total of seven days after transplantation. Plasma levels of methylglyoxal were determined using HPLC, whereas plasma levels of L-arginine, asymmetric dimethylarginine, advanced glycation endproducts-carboxylmethyllysine, soluble receptor for advanced glycation endproducts, and total antioxidant capacity were measured by ELISA. Patients following liver transplantation were shown to suffer from increased RAGE-associated inflammation with an AGE load mainly dependent upon reactive carbonyl species-derived AGEs. In contrast, carboxylmethyllysine-derived AGEs were of a minor importance. As assessed by the ratio of L-arginine/asymmetric dimethylarginine, the bioavailability of nitric oxide was shown to be reduced in hepatic IRI, especially in those patients suffering from perfusion disorders following liver transplantation. For the early identification of patients at high risk of perfusion disorders, the implementation of asymmetric dimethylarginine measurements in routine diagnostics following liver transplantation from deceased donors should be taken into consideration.

Development and application of a stable isotope dilution analysis for the quantitation of advanced glycation end products of creatinine in biofluids of type 2 diabetic patients and healthy volunteers

N-(1-Methyl-4-oxoimidazolidin-2-ylidene) α-amino acids were recently identified in roasted meat as so far unknown advanced glycation end products (AGEs) of creatinine. For the first time, this paper reports on the preparation of (13)C-labeled twin molecules of six N-(1-methyl-4-oxoimidazolidin-2-ylidene) α-amino acids and the development of a stable isotope dilution analysis (SIDA) for their simultaneous quantitation in meat, plasma, and urine samples by means of HPLC-MS/MS. Method validation demonstrated good precision (<14% RSD) and accuracy (97-118%) for all analytes and a lower limit of quantitation of 1 pg injected onto the column. The SIDA was applied to monitor plasma appearance and urinary excretion of these AGEs in type 2 diabetes mellitus patients (DM, n = 7) and healthy controls (n = 10) prior to and after ingestion of a bolus of processed beef meat. Interestingly, the basal concentration of N-(1-methyl-4-oxoimidazolidin-2-ylidene) aminopropionic acid was elevated in plasma and urine of DM patients compared to healthy individuals. Further, ingestion of processed meat led to a significantly higher concentration of this AGE in biofluids from DM patients when compared to healthy controls. These findings suggest a favored in vivo formation, as demonstrated by physiological model incubations of creatinine and carbohydrates (37 °C, pH 7.4), or a more efficient dietary up-take of N-(1-methyl-4-oxoimidazolidin-2-ylidene) α-amino acids in hyperglycemic diabetes patients.

Serum autofluorescence, a potential serum marker for the diagnosis of liver fibrosis in rats

Fluctuations in serum autofluorescence (AF) intensity have recently been widely used as markers of certain diseases such as cancer. To determine the diagnostic value of serum AF intensity for liver fibrosis in rats, we induced liver fibrosis by subcutaneous injection of carbon tetrachloride into rats. The rat serum AF intensities were detected at the excitation wavelength of 337 nm and the emission wavelength of 512 nm. The degree of liver fibrosis was evaluated by Van Gieson’s staining. The relationship between serum AF intensity and the degree of liver fibrosis was analyzed by Spearman and Pearson Correlation. The diagnostic sensitivity and specificity of the serum AF was determined by analyzing the receiver operating characteristic (ROC) curves. Our results show that the serum AF intensity in the rat liver fibrosis model increased when compared with control rats eight weeks and twelve weeks post induction of liver fibrosis. However, there was no significant difference in serum AF intensity between fibrotic and control rats at four week post induction. Furthermore, serum AF intensity correlated positively with the severity of the degree of hepatic fibrosis. ROC analysis further suggested that serum AF intensity is a valid marker for staging fibrosis. Therefore, it may potentially be developed as a novel diagnostic tool for hepatic fibrosis.

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

BACKGROUND & AIMS

Increased lipid peroxidation and inflammation are major factors in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A lipoxidation product that could play a role in the induction of hepatic inflammation is N(ε)-(carboxymethyl)lysine (CML). The aim of the present study was to investigate the relationship between steatosis and CML and to study the role of CML in hepatic inflammation.

METHODS

We included 74 obese individuals, which were categorized into 3 groups according to the grade of hepatic steatosis. CML accumulation in liver biopsies was assessed by immunohistochemistry and plasma CML levels were measured by mass spectrometry. Plasma CML levels were also determined in the hepatic artery, portal, and hepatic vein of 22 individuals, and CML fluxes across the liver were calculated. Hepatocyte cell lines were used to study CML formation during intracellular lipid accumulation and the effect of CML on pro-inflammatory cytokine expression. Gene expression levels of the inflammatory markers were determined in liver biopsies of the obese individuals.

RESULTS

CML accumulation was significantly associated with the grade of hepatic steatosis, the grade of hepatic inflammation, and gene expression levels of inflammatory markers PAI-1, IL-8, and CRP. Analysis of CML fluxes showed no release/uptake of CML by the liver. Lipid accumulation in hepatocytes, induced by incubation with fatty acids, was associated with increased CML formation and expression of the receptor for advanced glycation endproducts (RAGE), PAI-1, IL-8, IL-6, and CRP. Pyridoxamine and aminoguanidine inhibited the endogenous CML formation and the increased RAGE, PAI-1, IL-8, IL-6, and CRP expression. Incubation of hepatocytes with CML-albumin increased the expression of RAGE, PAI-1, and IL-6, which was inhibited by an antibody against RAGE.

CONCLUSIONS

Accumulation of CML and a CML-upregulated RAGE-dependent inflammatory response in steatotic livers may play an important role in hepatic steatosis and in the pathogenesis of NAFLD.

Increased liver stiffness denotes hepatic dysfunction and mortality risk in critically ill non-cirrhotic patients at a medical ICU

INTRODUCTION

Hepatic dysfunction is a common finding in critically ill patients on the ICU and directly influences survival. Liver stiffness can be measured by the novel method of transient elastography (fibroscan) and is closely associated with hepatic fibrosis in patients with chronic liver disease, but also is increased in patients with acute hepatitis, acute liver failure and cholestasis. We investigated liver stiffness as a potentially useful tool for early detection of patients with hepatic deterioration and risk stratification with respect to short- and long-term mortality.

METHODS

We prospectively evaluated 108 consecutive critically ill patients at our medical intensive care unit (ICU) with subsequent longitudinal liver stiffness measurements (admission, Day 3, Day 7 and weekly thereafter) during the course of ICU treatment. Outcome was followed after discharge (median observation time 237 days).

RESULTS

Liver stiffness could be reliably measured in 71% of ICU patients at admission (65% at Day 3, 63% at Day 7). Critically ill patients (n = 108) had significantly increased liver stiffness compared to sex- and age-matched standard care patients (n = 25). ICU patients with decompensated cirrhosis showed highest liver stiffness, whereas other critical diseases (for example, sepsis) and comorbidities (for example, diabetes, obesity) did not impact stiffness values. At admission to the ICU, liver stiffness is closely related to hepatic damage (liver synthesis, cholestasis, fibrosis markers). During the course of ICU treatment, fluid overload (renal failure, volume therapy) and increased central venous pressure (mechanical ventilation, heart failure) were major factors determining liver stiffness. Liver stiffness values > 18 kilopascal (kPa) at ICU admission were associated with increased ICU and long-term mortality, even in non-cirrhotic patients.

CONCLUSIONS

Considering that liver stiffness cannot be validly measured in about 30% of ICU patients, transient elastography performed at ICU admission might be a useful tool to early identify liver dysfunction and predict mortality in critically ill patients at a medical ICU.

Hepato-/reno-protective activity of Chinese prescription Kangen-karyu through inhibition of AGE formation and fibrosis-related protein expression in type 2 diabetes

OBJECTIVES

This study was conducted to examine whether Kangen-karyu, a Chinese prescription, has an ameliorative effect on diabetes-induced alterations such as advanced glycation endproduct (AGE) formation or the fibrotic response in liver and kidney of type 2 diabetic db/db mice.

METHODS

Kangen-karyu (100 or 200 mg/kg body weight/day, p.o.) was administered every day for 18 weeks to db/db mice, and its effect was compared with vehicle-treated db/db and m/m mice.

KEY FINDINGS

The administration of Kangen-karyu decreased the elevated serum glucose concentration in db/db mice. The increased serum creatinine and urea nitrogen levels, which reflect renal dysfunction in db/db mice, were significantly lowered by Kangen-karyu administration. The db/db mice exhibited the up-regulation of AGEs and its receptor expression in liver and kidney; however, Kangen-karyu treatment significantly reduced expression except for the receptor. Moreover, the augmented expressions of fibrosis-related proteins, transforming growth factor (TGF)-β1, fibronectin and collagen IV were down-regulated by Kangen-karyu administration.

CONCLUSIONS

These results provide important evidence that Kangen-karyu exhibits a pleiotropic effect on AGE formation and fibrosis-related parameters, representing hepatoprotective and renoprotective effects against the development of diabetic complications in type 2 diabetic db/db mice.

What is the role of the receptor for advanced glycation end products-ligand axis in liver injury?

Multiligand receptor for advanced glycation end products (RAGE) is expressed in a wide variety of tissues, including the liver. Interactions with its ligands lead to cellular activation and thus prolonged inflammation and apoptosis. RAGE also exists in a soluble, truncated isoform called soluble RAGE, which has the same ligand-binding specificity as membrane-RAGE; acting as decoy, it can contribute to the removal/neutralization of circulating ligands and the resultant reduction of signaling pathway activation. Experimental and clinical studies have highlighted the idea that the RAGE-ligand axis is involved in the development of liver fibrosis, inflammation, and regeneration after a massive injury and in the setting of liver transplantation. The involvement of the RAGE-ligand axis in vascular disease, diabetes, cancer, and neurodegeneration is well established, but it still needs to be clarified in the setting of liver diseases. We present a review of the recent literature on this receptor in surgical and clinical settings involving the liver, and we highlight the open issues and possible directions of future research.

Oxidative damage in the liver of rats treated with glycolaldehyde

Liver diseases are often associated with hyperglycemia, inflammation, and oxidative stress. These conditions, commonly associated with diabetes mellitus and obesity, facilitate the formation of advanced glycation end products (AGEs). These products are known to impair protein function and promote inflammation. Accumulation of AGEs such as N(ε)-(carboxymethyl)lysine (CML) is related to chronic liver diseases and their severity. Although several reports suggest a crucial role of AGEs in liver failure, there is little investigation on the direct effects of reducing sugars, precursors of AGEs, and on the onset and progression of liver failure. In this work, we investigate the effects of intravenously administrated glycolaldehyde (GA), a short-chain aldehyde, on oxidative parameters in the liver of Wistar rats. Animals received a single injection of GA (10, 50, or 100 mg/kg) and were sacrificed after 6, 12, or 24 hours. Levels of protein carbonyl, lipid peroxidation, and reduced thiol were quantified. The activities of catalase, superoxide dismutase, and glyoxalase I were also assessed. The amount of CML was quantified with specific antibody. There was an increase in oxidative stress markers in the liver of GA-treated rats. Glycolaldehyde induced a decrease in the activities of all enzymes assayed. Also, all tested doses led to an increase in CML content. Our data suggest that GA might play an important role in liver diseases through the impairment of antioxidant defenses and generation of AGEs.

Glycolaldehyde induces oxidative stress in the heart: a clue to diabetic cardiomyopathy?

Cardiovascular complications account for 80% of the mortality related to diabetes mellitus. Hyperglycemia is believed to be the major culprit of angiopathy and cardiomyopathy. High glucose levels and oxidative stress cause elevation of Advanced Glycation End-products that are known to contribute to diabetic complications and correlate with many diseases. However, there are few reports describing the effects of glycating agents other than glucose. Here, we aimed to evaluate the effects of glycolaldehyde (GA) on oxidative stress parameters in the heart of Wistar rats. Male Wistar rats received a single injection of GA (10, 50 or 100 mg/Kg) and were sacrificed 6, 12 or 24 h after injection. As indexes of oxidative stress, we quantified protein carbonylation, lipid peroxidation and total reduced thiols. The activities of superoxide dismutase, catalase and glyoxalase I were assayed. Also, the content of N (ɛ)-(carboxymethyl)lysine (CML) was quantified. Glycolaldehyde induced an imbalance in the redox status, with increased protein carbonylation and lipoperoxidation. Catalase and glyoxalase I had a decrease in their activities. Despite the oxidative stress, we observed no increase in CML content. These results suggest that short-chain aldehydes such as GA might have a significant role in the development of diabetic cardiomyopathy.