Methylglyoxal in Metabolic Disorders: Facts, Myths, and Promises

Methylglyoxal: A Key Factor for Diabetic Retinopathy and Its Effects on Retinal Damage

Background: Diabetic retinopathy is the most common retinal vascular disease, affecting the retina's blood vessels and causing chronic inflammation, oxidative stress, and, ultimately, vision loss. Diabetes-induced elevated glucose levels increase glycolysis, the main methylglyoxal (MGO) formation pathway. MGO is a highly reactive dicarbonyl and the most rapid glycation compound to form endogenous advanced glycation end products (AGEs). MGO can act both intra- and extracellularly by glycating molecules and activating the receptor for AGEs (RAGE) pathway. Conclusions: This review summarizes the sources of MGO formation and its actions on various cell pathways in retinal cells such as oxidative stress, glycation, autophagy, ER stress, and mitochondrial dysfunction. Finally, the detoxification of MGO by glyoxalases is discussed.

Early Methylglyoxal Exposure Leads to Worsened Cardiovascular Function in Young Rats

BACKGROUND

Though maternal diabetes effects are well described in the literature, the effects of maternal diabetes in postnatal phases are often overlooked. Diabetic individuals have higher levels of circulating glycotoxins, and there is a positive correlation between maternal-derived glycotoxins and circulating glycotoxins in their progeny. Previous studies evaluated the metabolic effects of high glycotoxin exposure during lactation in adult animals. However, here we focus on the cardiovascular system of juvenile rats.

METHODS

For this, we used two experimental models: 1. High Methylglyoxal (MG) environment: pregnant Wistar rats were injected with PBS (VEH group) or Methylglyoxal (MG group; 60 mg/kg/day; orally, postnatal day (PND) 3 to PND14). 2. GLO-1 inhibition: pregnant Wistar rats were injected with dimethyl sulfoxide (VEH group) or a GLO-1 inhibitor (BBGC group; 5 mg/kg/day; subcutaneously, PND1-PND5). The offspring were evaluated at PND45.

RESULTS

MG offspring presented cardiac dysfunction and subtly worsened vasomotor responses in the presence of perivascular adipose tissue, without morphological alterations. In addition, an endogenous increase in maternal glycotoxins impacts offspring vasomotricity due to impaired redox status.

CONCLUSIONS

Our data suggest that early glycotoxin exposure led to cardiac and vascular impairments, which may increase the risk for developing cardiovascular diseases later in life.

Exploring Maternal Diet-Epigenetic-Gut Microbiome Crosstalk as an Intervention Strategy to Counter Early Obesity Programming

Alterations in a mother's metabolism and endocrine system, due to unbalanced nutrition, may increase the risk of both metabolic and non-metabolic disorders in the offspring's childhood and adulthood. The risk of obesity in the offspring can be determined by the interplay between maternal nutrition and lifestyle, intrauterine environment, epigenetic modifications, and early postnatal factors. Several studies have indicated that the fetal bowel begins to colonize before birth and that, during birth and nursing, the gut microbiota continues to change. The mother's gut microbiota is primarily transferred to the fetus through maternal nutrition and the environment. In this way, it is able to impact the establishment of the early fetal and neonatal microbiome, resulting in epigenetic signatures that can possibly predispose the offspring to the development of obesity in later life. However, antioxidants and exercise in the mother have been shown to improve the offspring's metabolism, with improvements in leptin, triglycerides, adiponectin, and insulin resistance, as well as in the fetal birth weight through epigenetic mechanisms. Therefore, in this extensive literature review, we aimed to investigate the relationship between maternal diet, epigenetics, and gut microbiota in order to expand on current knowledge and identify novel potential preventative strategies for lowering the risk of obesity in children and adults.

(+)-Catechin mitigates impairment in insulin secretion and beta cell damage in methylglyoxal-induced pancreatic beta cells

BACKGROUND

The formation of advanced glycation end products (AGEs) is the central process contributing to diabetic complications in diabetic individuals with sustained and inconsistent hyperglycemia. Methylglyoxal, a reactive carbonyl species, is found to be a major precursor of AGEs, and its levels are elevated in diabetic conditions. Dysfunction of pancreatic beta cells and impairment in insulin secretion are the hallmarks of diabetic progression. Exposure to methylglyoxal-induced AGEs alters the function and maintenance of pancreatic beta cells. Hence, trapping methylglyoxal could be an ideal approach to alleviate AGE formation and its influence on beta cell proliferation and insulin secretion, thereby curbing the progression of diabetes to its complications.

METHODS AND RESULTS

In the present study, we have explored the mechanism of action of (+)-Catechin against methylglyoxal-induced disruption in pancreatic beta cells via molecular biology techniques, mainly western blot. Methylglyoxal treatment decreased insulin synthesis (41.5%) via downregulating the glucose-stimulated insulin secretion pathway (GSIS). This was restored upon co-treatment with (+)-Catechin (29.9%) in methylglyoxal-induced Beta-TC-6 cells. Also, methylglyoxal treatment affected the autocrine function of insulin by disrupting the IRS1/PI3k/Akt pathway. Methylglyoxal treatment suppresses Pdx-1 and Maf A levels, which are responsible for beta cell maintenance and cell proliferation. (+)-Catechin could significantly augment the levels of these transcription factors.

CONCLUSION

This is the first study to examine the impact of a natural compound on methylglyoxal with the insulin-mediated autocrine and paracrine activities of pancreatic beta cells. The results indicate that (+)-Catechin exerts a protective effect against methylglyoxal exposure in pancreatic beta cells and can be considered a potential anti-glycation agent in further investigations on ameliorating diabetic complications.

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

Evidence that methylglyoxal and receptor for advanced glycation end products are implicated in bladder dysfunction of obese diabetic ob/ob mice

Glycolytic overload in diabetes causes large accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO) and overproduction of advanced glycation end products (AGEs), which interact with their receptors (RAGE), leading to diabetes-associated macrovascular complications. The bladder is an organ that stays most in contact with dicarbonyl species, but little is known about the importance of the MGO-AGEs-RAGE pathway to diabetes-associated bladder dysfunction. Here, we aimed to investigate the role of the MGO-AGEs-RAGE pathway in bladder dysfunction of diabetic male and female ob/ob mice compared with wild-type (WT) lean mice. Diabetic ob/ob mice were treated with the AGE breaker alagebrium (ALT-711, 1 mg/kg) for 8 wk in drinking water. Compared with WT animals, male and female ob/ob mice showed marked hyperglycemia and insulin resistance, whereas fluid intake remained unaltered. Levels of total AGEs, MGO-derived hydroimidazolone 1, and RAGE in bladder tissues, as well as fluorescent AGEs in serum, were significantly elevated in ob/ob mice of either sex. Collagen content was also markedly elevated in the bladders of ob/ob mice. Void spot assays in filter paper in conscious mice revealed significant increases in total void volume and volume per void in ob/ob mice with no alterations of spot number. Treatment with ALT-711 significantly reduced the levels of MGO, AGEs, RAGE, and collagen content in ob/ob mice. In addition, ALT-711 treatment normalized the volume per void and increased the number of spots in ob/ob mice. Activation of AGEs-RAGE pathways by MGO in the bladder wall may contribute to the pathogenesis of diabetes-associated bladder dysfunction.NEW & NOTEWORTHY The involvement of methylglyoxal (MGO) and advanced glycation end products (AGEs) in bladder dysfunction of diabetic ob/ob mice treated with the AGE breaker ALT-711 was investigated here. Diabetic mice exhibited high levels of MGO, AGEs, receptor for AGEs (RAGE), and collagen in serum and/or bladder tissues along with increased volume per void, all of which were reduced by ALT-711. Activation of the MGO-AGEs-RAGE pathway in the bladder wall contributes to the pathogenesis of diabetes-associated bladder dysfunction.

The insulin receptor regulates the persistence of mechanical nociceptive sensitization in flies and mice

Early phase diabetes is often accompanied by pain sensitization. In Drosophila, the insulin receptor (InR) regulates the persistence of injury-induced thermal nociceptive sensitization. Whether Drosophila InR also regulates the persistence of mechanical nociceptive sensitization remains unclear. Mice with a sensory neuron deletion of the insulin receptor (Insr) show normal nociceptive baselines; however, it is uncertain whether deletion of Insr in nociceptive sensory neurons leads to persistent nociceptive hypersensitivity. In this study, we used fly and mouse nociceptive sensitization models to address these questions. In flies, InR mutants and larvae with sensory neuron-specific expression of RNAi transgenes targeting InR exhibited persistent mechanical hypersensitivity. Mice with a specific deletion of the Insr gene in Nav1.8+ nociceptive sensory neurons showed nociceptive thermal and mechanical baselines similar to controls. In an inflammatory paradigm, however, these mutant mice showed persistent mechanical (but not thermal) hypersensitivity, particularly in female mice. Mice with the Nav1.8+ sensory neuron-specific deletion of Insr did not show metabolic abnormalities typical of a defect in systemic insulin signaling. Our results show that some aspects of the regulation of nociceptive hypersensitivity by the insulin receptor are shared between flies and mice and that this regulation is likely independent of metabolic effects.

Sex-specificities in offspring neurodevelopment and behaviour upon maternal glycation: Putative underlying neurometabolic and synaptic changes

AIM

Lactation is an important programming window for metabolic disease and neuronal alterations later in life. We aimed to study the effect of maternal glycation during lactation on offspring neurodevelopment and behaviour, assessing possible sex differences and underpinning molecular players.

METHODS

Female Wistar rats were treated with the Glyoxalase-1 inhibitor S-p-Bromobenzylguthione cyclopentyl diester (BBGC 5 mg/kg). A control and vehicle group treated with dimethyl sulfoxide were considered. Male and female offspring were tested at infancy for neurodevelopment hallmarks. After weaning, triglycerides and total antioxidant capacity were measured in breast milk. At adolescence, offspring were tested for locomotor ability, anxious-like behaviour, and recognition memory. Metabolic parameters were assessed, and the hippocampus and prefrontal cortex were collected for molecular analysis.

KEY FINDINGS

Maternal glycation reduced triglycerides and total antioxidant capacity levels in breast milk. At infancy, both male and female offspring presented an anticipation on the achievement of neurodevelopmental milestones. At adolescence, male offspring exposed to maternal glycation presented hyperlocomotion, whereas offspring of both sexes presented a risk-taking phenotype, accompanied by GABA_A receptor upregulation in the hippocampus. Females also demonstrated GABA_A and PSD-95 changes in prefrontal cortex. Furthermore, lower levels of GLO1 and consequently higher accumulation of AGES were also observed in both male and female offspring hippocampus.

SIGNIFICANCE

Early exposure to maternal glycation induces changes in milk composition leading to neurodevelopment changes at infancy, and sex-specific behavioural and neurometabolic changes at adolescence, further evidencing that lactation period is a critical metabolic programming window and in sculpting behaviour.

Exposure to Obesogenic Environments during Perinatal Development Modulates Offspring Energy Balance Pathways in Adipose Tissue and Liver of Rodent Models

Obesogenic environments such as Westernized diets, overnutrition, and exposure to glycation during gestation and lactation can alter peripheral neuroendocrine factors in offspring, predisposing for metabolic diseases in adulthood. Thus, we hypothesized that exposure to obesogenic environments during the perinatal period reprograms offspring energy balance mechanisms. Four rat obesogenic models were studied: maternal diet-induced obesity (DIO); early-life obesity induced by postnatal overfeeding; maternal glycation; and postnatal overfeeding combined with maternal glycation. Metabolic parameters, energy expenditure, and storage pathways in visceral adipose tissue (VAT) and the liver were analyzed. Maternal DIO increased VAT lipogenic [NPY receptor-1 (NPY1R), NPY receptor-2 (NPY2R), and ghrelin receptor], but also lipolytic/catabolic mechanisms [dopamine-1 receptor (D1R) and p-AMP-activated protein kinase (AMPK)] in male offspring, while reducing NPY1R in females. Postnatally overfed male animals only exhibited higher NPY2R levels in VAT, while females also presented NPY1R and NPY2R downregulation. Maternal glycation reduces VAT expandability by decreasing NPY2R in overfed animals. Regarding the liver, D1R was decreased in all obesogenic models, while overfeeding induced fat accumulation in both sexes and glycation the inflammatory infiltration. The VAT response to maternal DIO and overfeeding showed a sexual dysmorphism, and exposure to glycotoxins led to a thin-outside-fat-inside phenotype in overfeeding conditions and impaired energy balance, increasing the metabolic risk in adulthood.

The immune-stress/endocrine-redox-metabolic nature of psychosis' etiopathology; focus on the intersystemic pathways interactions

The evidence supporting the involvement of a number of systems in the neurobiological etiopathology of psychosis has recently grown exponentially. Indeed, the focus of research has changed from measuring solely neurotransmitters to estimating parameters from fields like immunity, stress/endocrine, redox, and metabolism. Yet, little is known regarding the exact role of each one of these fields on the formation of not only the brain neuropathological substrate in psychosis but also the associated general systemic pathology, in terms of causality directions. Research has shown deviations in the levels and/or function of basic effector molecules of the aforementioned fields namely cytokines, pro-/anti- oxidants, glucocorticoids, catecholamines, glucose, and lipids metabolites as well as kynurenines, in psychosis. Yet the evidence regarding their impact on neurotransmitters is minimal and the findings concerning these systems' interactions in the psychotic context are even more dispersed. The present review aims to draw holistically the frame of the hitherto known "players" in the field of psychosis' cellular pathobiology, with a particular focus on their in-between interactions.

Can grape polyphenols affect glycation markers? A systematic review

Advanced glycation end-products (AGEs) favor inflammation and oxidative stress, playing a role in chronic diseases pathogenesis. Grape polyphenols exert antiglycative and antioxidant effects which may contribute to prevent chronic diseases. However, clinical evidence of grape polyphenols on chronic disease prevention and treatment by glycation markers modulation are limited. Therefore, we aimed to critically analyze studies about that topic to investigate the antiglycative power of dietary grape polyphenol, and to explore the molecular mechanism involved. This systematic review was conducted and reported according to PRISMA guidelines. The following search terms were used: "grape", "extract", "grape seed extract", "grape skin extract", "polyphenol extract", "grape polyphenol(s)", "grape juice", "resveratrol", "quercetin", "catechin", "epicatechin", "procyanidin(s)", and "anthocyanin(s)". Seven studies were included. Glycated hemoglobin was not affected. The interventions duration may not have been enough to detect changes. Grape polyphenols reduced fructosamine and methylglyoxal (MGO) concentrations, and increased endogenous secretory RAGE (esRAGE) gene expression but did not affect the serum concentration. Resveratrol antiglycative effects are mainly due its ability to trap MGO and downregulate RAGE. In conclusion, grape polyphenols may have a positive impact on early glycation products, AGEs and esRAGE. Future studies are needed to explore how they modulate AGEs and receptors in chronic diseases.

Depot-specific adipose tissue modulation by SGLT2 inhibitors and GLP1 agonists mediates their cardioprotective effects in metabolic disease

Sodium-glucose transporter-2 inhibitors (SGLT-2i) and glucagon-like peptide 1 (GLP-1) receptor agonists are newer antidiabetic drug classes, which were recently shown to decrease cardiovascular (CV) morbidity and mortality in diabetic patients. CV benefits of these drugs could not be directly attributed to their blood glucose lowering capacity possibly implicating a pleotropic effect as a mediator of their impact on cardiovascular disease (CVD). Particularly, preclinical and clinical studies indicate that SGLT-2i(s) and GLP-1 receptor agonists are capable of differentially modulating distinct adipose pools reducing the accumulation of fat in some depots, promoting the healthy expansion of others, and/or enhancing their browning, leading to the suppression of the metabolically induced inflammatory processes. These changes are accompanied with improvements in markers of cardiac structure and injury, coronary and vascular endothelial healing and function, vascular remodeling, as well as reduction of atherogenesis. Here, through a summary of the available evidence, we bring forth our view that the observed CV benefit in response to SGLT-2i or GLP-1 agonists therapy might be driven by their ameliorative impact on adipose tissue inflammation.

Methylglyoxal - an advanced glycation end products (AGEs) precursor - Inhibits differentiation of human MSC-derived osteoblasts in vitro independently of receptor for AGEs (RAGE)

A major precursor of advanced glycation end-products (AGEs) - methylglyoxal (MG) - is a reactive carbonyl metabolite that originates from glycolytic pathways. MG formation and accumulation has been implicated in the pathogenesis of diabetes and age-related chronic musculoskeletal disorders. Human bone marrow-derived stromal cells (BMSCs) are multipotent cells that have the potential to differentiate into cells of mesenchymal origin including osteoblasts, but the role of MG on their differentiation is unclear. We therefore evaluated the effect of MG on proliferation and differentiation of BMSC-derived osteoblasts. Cells were treated with different concentrations of MG (600, 800 and 1000 μM). Cell viability was assessed using a Cell Counting Kit-8 assay. Alkaline phosphatase (ALP) activity and calcium deposition assays were performed to evaluate osteoblast differentiation and mineralization. Gene expression was measured using qRT-PCR, whereas AGE specific receptor (RAGE) and collagen 1 were examined by immunocytochemistry and Western blotting. RAGE knockdown was performed by transducing RAGE specific short hairpin RNAs (shRNAs) using lentivirus. During osteogenic differentiation, MG treatment resulted in reduction of cell viability (27.7 %), ALP activity (45.5 %) and mineralization (82.3 %) compared to untreated cells. MG significantly decreased expression of genes involved in osteogenic differentiation - RUNX2 (2.8 fold), ALPL (3.2 fold), MG detoxification through glyoxalase - GLO1 (3 fold) and collagen metabolism - COL1A1 (4.9 fold), COL1A2 (6.8 fold), LOX (5.4 fold) and PLOD1 (1.7 fold). MG significantly reduced expression of collagen 1 (53.3 %) and RAGE (43.1 %) at protein levels. Co-treatment with a MG scavenger - aminoguanidine - prevented all negative effects of MG. RAGE-specific knockdown during MG treatment did not reverse the effects on cell viability, osteogenic differentiation or collagen metabolism. In conclusion, MG treatment can negatively influence the collagen metabolism and differentiation of BMSCs-derived osteoblasts through a RAGE independent mechanism.

Liraglutide reduces oxidative stress and improves energy metabolism in methylglyoxal-induced SH-SY5Y cells

Diabetes mellitus can result in severe complications, such as neurodegenerative diseases including cognitive impairment and dementia. The glucagon-like peptide-1 (GLP-1) receptor agonist, liraglutide, is a novel antidiabetic drug with neuroprotective effects against neurodegenerative diseases. In this study, we explored the protective effect of liraglutide on SH-SY5Y cells exposed to methylglyoxal (MG), a byproduct of glucose metabolism that plays a key role in the development of diabetic encephalopathy. We found that liraglutide reduced the MG-induced oxidative stress, increased the activity of superoxide dismutase (SOD) and expression levels of P22phox, Gp91phox, and Xdh genes, and reduced reactive oxygen species (ROS) content. Metabolomics analysis based on ¹H nuclear magnetic resonance showed that liraglutide induced alterations in metabolites involved in energy metabolism，including promotion of gluconeogenesis. Moreover, we found that liraglutide promoted oxidative phosphorylation and inhibited glycolysis in SH-SY5Y cells. This study revealed that liraglutide improved diabetes-related neuropathy damage by reducing the level of oxidative stress and maintaining the balance of energy metabolism, thus offering new insights into the potential mechanism of liraglutide in neuronal protection.

Quantitative Chemoproteomic Profiling of Protein Cross-Links Induced by Methylglyoxal

Methylglyoxal (MGO) is a highly reactive metabolite mainly formed as a byproduct of glycolysis. Elevated MGO has been considered as a risk factor for several diseases including diabetes and neurodegeneration. While MGO modifications on proteins were globally profiled, the cross-links between proteins induced by MGO in proteomes are unexplored to date. Here, we reported a quantitative chemoproteomic platform based on mass shifts that enables identification of events of protein cross-links induced by MGO in proteomes. A total of 66 cross-linked targets were identified from the profiling experiments when cells were treated with MGO, among which the components of functional complexes such as spliceosomes and ribosomes were enriched. We found that inosine-5'-monophosphate dehydrogenase 2 (IMPDH2) was homocross-linked by MGO and the active-site Cys331 was critical for mediating the cross-link, which in turn affected IMPDH2's activity. Our study has provided new clues for the functional impact in proteomes by MGO, and the methodology can be, in principle, applied to profile protein cross-links induced by other reactive metabolites.

Moxifloxacin Induced Liver Injury by Causing Lachnospiraceae Deficiency and Interfering with Butyric Acid Production through Gut–Liver Axis

Cases of unpredictable, idiosyncratic liver damage of moxifloxacin (MXF) have been occasionally reported. However, the health effects of MXF exposure remain controversial. The current study examined the metabolic phenotypes and intestinal flora characteristics of hepatotoxicity induced by MXF. Rats were administered moxifloxacin hydrochloride tablets at doses of 36, 72, and 108 mg/kg body weight/day for 21 days. The levels of tricarboxylic acid cycle intermediates were decreased, whereas those of lipids (arachidonic acid, hexadecanoic acid, and linoleic acid) were increased, reflecting disorders of energy–related and lipid metabolism. Enrichment analysis of the differential metabolites suggested that butanoate metabolism was associated with MXF–induced liver injury. 16S rRNA sequencing uncovered that the diversity of gut intestinal was decreased in MXF–treated rats. Specifically, the abundance of Muribaculaceae was increased, whereas that of Lachnospiraceae, a family of butyrate–producing bacteria, was decreased. The combined serum metabonomics and gut microbiome datasets illustrated the involvement of butanoic acid and energy metabolism in the regulatory changes of the gut–liver axis associated with MXF–induced liver injury. The regulation of endogenous small molecules and intestinal flora during drug–induced liver injury was first described from the perspective of the gut–liver axis, providing a research basis for the mechanism of clinical drug–induced liver injury.

Methylglyoxal impairs β-adrenergic signalling in primary rat adipocytes

Methylglyoxal (MG) is dicarbonyl aldehyde generated intracellularly from glucose and from some other compounds. Its increased formation is associated with several harmful consequences. In the present study, short-term effects of MG on metabolism of isolated rat adipocytes were determined. Insulin-induced lipogenesis was unchanged by MG. However, epinephrine-stimulated lipolysis was shown to be significantly reduced in adipocytes exposed to 200 µM MG. This inhibitory effect was similar in the presence of low and high concentrations of glucose, and also in the presence of alanine. However, MG failed to affect lipolysis induced by forskolin (activator of adenylate cyclase), dibutyryl-cAMP (activator of PKA) and DPCPX (adenosine A₁ receptor antagonist). It was also revealed that lipolysis was unchanged by MG in fat cells pre-incubated with this compound, and then stimulated with epinephrine alone. Our results suggest that MG may impair β-adrenergic signalling in rat adipocytes due to interaction with epinephrine, and thereby disturbs lipolysis.

Intestinal AMPK modulation of microbiota mediates crosstalk with brown fat to control thermogenesis

The energy-dissipating capacity of brown adipose tissue through thermogenesis can be targeted to improve energy balance. Mammalian 5'-AMP-activated protein kinase, a key nutrient sensor for maintaining cellular energy status, is a known therapeutic target in Type II diabetes. Despite its well-established roles in regulating glucose metabolism in various tissues, the functions of AMPK in the intestine remain largely unexplored. Here we show that AMPKα1 deficiency in the intestine results in weight gain and impaired glucose tolerance under high fat diet feeding, while metformin administration fails to ameliorate these metabolic disorders in intestinal AMPKα1 knockout mice. Further, AMPKα1 in the intestine communicates with brown adipose tissue to promote thermogenesis. Mechanistically, we uncover a link between intestinal AMPKα1 activation and BAT thermogenic regulation through modulating anti-microbial peptide-controlled gut microbiota and the metabolites. Our findings identify AMPKα1-mediated mechanisms of intestine-BAT communication that may partially underlie the therapeutic effects of metformin.

Natural and Synthetic Agents Targeting Reactive Carbonyl Species against Metabolic Syndrome

Reactive carbonyl species (RCS) may originate from the oxidation of unsaturated fatty acids and sugar in conditions of pathology. They are known to have high reactivity towards DNA as well as nucleophilic sites of proteins, resulting in cellular dysfunction. It has been considered that various pathological conditions are associated with an increased level of RCS and their reaction products. Thus, regulating the levels of RCS may be associated with the mitigation of various metabolic and neurodegenerative disorders. In order to perform a comprehensive review, various literature databases, including MEDLINE, EMBASE, along with Google Scholar, were utilized to obtain relevant articles. The voluminous review concluded that various synthetic and natural agents are available or in pipeline research that hold tremendous potential to be used as a drug of choice in the therapeutic management of metabolic syndrome, including obesity, dyslipidemia, diabetes, and diabetes-associated complications of atherosclerosis, neuropathy, and nephropathy. From the available data, it may be emphasized that various synthetic agents, such as carnosine and simvastatin, and natural agents, such as polyphenols and terpenoids, can become a drug of choice in the therapeutic management for combating metabolic syndromes that involve RCS in their pathophysiology. Since the RCS are known to regulate the biological processes, future research warrants detailed investigations to decipher the precise mechanism.

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.

Methylglyoxal Scavengers Attenuate Angiogenesis Dysfunction Induced by Methylglyoxal and Oxygen-Glucose Deprivation

Cerebral endothelial cells play an essential role in brain angiogenesis, and their function has been found to be impaired in diabetes. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite of glucose formed mainly during glycolysis, and its levels can be elevated in hyperglycemic conditions. MG is a potent precursor of AGEs (advanced glycation end-products). In this study, we investigated if MG can induce angiogenesis dysfunction and whether MG scavengers can ameliorate angiogenesis dysfunction induced by MG. Here, we used cultured human brain microvascular endothelial cells (HBMECs) treated with MG and oxygen-glucose deprivation (OGD) to mimic diabetic stroke in vitro. We also used the MG challenged chicken embryo chorioallantoic membrane (CAM) to study angiogenesis in vivo. Interestingly, administration of MG significantly impaired cell proliferation, cell migration, and tube formation and decreased protein expression of angiogenesis-related factors, which was rescued by three different MG scavengers, glyoxalase 1 (GLO1), aminoguanidine (AG), and N-acetyl cysteine (NAC). In cultured CAM, MG exposure significantly reduced angiogenesis and the angiogenesis-related dysfunction could be attenuated by pretreatment with AG or NAC. Treatment of cultured HBMECs with MG plus OGD increased cellular apoptosis significantly, which could be prevented by exposure to GLO1, AG, or NAC. We also noted that administration of MG increased cellular oxidative stress as measured by reactive oxygen species (ROS) generation, enhanced AGE accumulation, and receptor for advanced glycation end-product (RAGE) expression in the cultured HBMECs, which were partially reversed by GLO1, AG, or NAC. Taken together, our findings demonstrated that GLO1, AG, or NAC administration can ameliorate MG-induced angiogenesis dysfunction, and this can be mainly attributed to attenuated ROS production, reduced cellular apoptosis, and increased levels of angiogenic factors. Overall, this study suggested that GLO1, AG, or NAC may be promising candidate compounds for the treatment of angiogenesis dysfunction caused by hyperglycemia in diabetic ischemic stroke.

Methylglyoxal Exacerbates Lipopolysaccharide-Induced Acute Lung Injury via RAGE-Induced ROS Generation: Protective Effects of Metformin

Purpose

Methylglyoxal (MGO) is a highly reactive dicarbonyl species implicated in diabetic-associated diseases. Acute lung injury (ALI) symptoms and prognosis are worsened by diabetes and obesity. Here, we hypothesized that elevated MGO levels aggravate ALI, which can be prevented by metformin. Therefore, this study evaluated the lung inflammation in lipopolysaccharide (LPS)-exposed mice pretreated with MGO.

Methods

C57Bl/6 male mice treated or not with MGO for 12 weeks were intranasally instilled with LPS (30 µg) to induce ALI, and metformin (300 mg/kg) was given as gavage in the last two weeks of treatment. After 6 h, bronchoalveolar lavage fluid (BALF) and lung tissues were collected to quantify the cell infiltration, cytokine levels, reactive-oxygen species (ROS) production, and RAGE expression.

Results

LPS exposure markedly increased the neutrophil infiltration in BALF and lung tissue, which was accompanied by higher levels of IFN-γ, TNF-α and IL-1β compared with untreated group. MGO treatment significantly increased the airways neutrophil infiltration and mRNA expressions of TNF-α and IL-1β, whereas COX-2 expression remained unchanged. In lung tissues of LPS-exposed mice, MGO treatment significantly increased the immunostaining and mRNA expression of RAGE, and the ROS levels. Serum MGO concentration achieved after 12-week intake was 9.2-fold higher than control mice, which was normalized by metformin treatment. Metformin also reduced the inflammatory markers in response to MGO.

Conclusion

MGO intake potentiates the LPS-induced ALI, increases RAGE expression and ROS generation, which is normalized by metformin. MGO scavengers may be a good adjuvant therapy to reduce ALI in patients with cardiometabolic diseases.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Advanced Glycation End Products Associated With Cardiometabolic Biomarkers in Treated Human Immunodeficiency Virus Infection

Background

Despite advances in antiretroviral therapy (ART), people living with human immunodeficiency virus (HIV) continue to be at increased risk of cardiometabolic complications compared to HIV-uninfected individuals. Advanced glycation end products (AGEs) are implicated in the development and progression of cardiometabolic complications in the general population. Their role in HIV remains unclear.

Methods

ACTG A5260s is a prospective open-label randomized trial in which ART-naive people living with HIV were randomized to tenofovir disoproxil fumarate /emtricitabine plus atazanavir/ritonavir, darunavir/ritonavir, or raltegravir over 96 weeks. Changes in circulating AGEs with ART initiation were assessed, and linear regression was used to examine the associations between serum AGEs with carotid intima-media thickness (cIMT), visceral and subcutaneous adipose tissue, total fat, lean mass, body mass index, insulin resistance, leptin, and adiponectin.

Results

Overall, 214 participants were included. Ninety percent were male, 48% were White, the median age was 36 years, median HIV-1 RNA was 4.58 log₁₀ copies/mL, and median CD4 count was 338 cells/µL. Most AGEs remained relatively unchanged following 96 weeks of ART initiation, except for methylglyoxal-derived hydroimidazolone 1 (MG-H1), which increased following 96 weeks of ART (mean fold change, 1.15 [95% confidence interval, 1.02–1.30]). No differences were detected across ART regimens. Increases in AGE levels over time were associated with worsening body fat composition measures, insulin resistance, and cIMT, even after adjusting for clinically relevant factors.

Conclusions

AGE levels did not decrease following ART initiation. Most AGE levels remained stable, except for MG-H1, which increased. In people with HIV on ART, the accumulation of circulating AGEs over time appears to be independently associated with worsening cardiometabolic biomarkers.

Summary: Antiretroviral therapy (ART) does not appear to be effective in reducing advanced glycation end product (AGE) levels. On the contrary, AGE levels seem to increase following ART initiation. Accumulation of AGEs was found to be independently associated with cardiometabolic complications in treated people living with HIV.

Metabolic Disease Programming: From Mitochondria to Epigenetics, Glucocorticoid Signalling and Beyond

Embryonic and foetal development are critical periods of development in which several environmental cues determine health and disease in adulthood. Maternal conditions and an unfavourable intrauterine environment impact foetal development and may programme the offspring for increased predisposition to metabolic diseases and other chronic pathologic conditions throughout adult life. Previously, non-communicable chronic diseases were only associated with genetics and lifestyle. Now the origins of non-communicable chronic diseases are associated with early-life adaptations that produce long-term dysfunction. Early-life environment sets the long-term health and disease risk and can span through multiple generations. Recent research in developmental programming aims at identifying the molecular mechanisms responsible for developmental programming outcomes that impact cellular physiology and trigger adulthood disease. The identification of new therapeutic targets can improve offspring's health management and prevent or overcome adverse consequences of foetal programming. This review summarizes recent biomedical discoveries in the Developmental Origins of Health and Disease (DOHaD) hypothesis and highlight possible developmental programming mechanisms, including prenatal structural defects, metabolic (mitochondrial dysfunction, oxidative stress, protein modification), epigenetic and glucocorticoid signalling-related mechanisms suggesting molecular clues for the causes and consequences of programming of increased susceptibility of offspring to metabolic disease after birth. Identifying mechanisms involved in DOHaD can contribute to early interventions in pregnancy or early childhood, to re-set the metabolic homeostasis and break the chain of subsequent events that could lead to the development of disease.

Unripe Carica papaya Protects Methylglyoxal-Invoked Endothelial Cell Inflammation and Apoptosis via the Suppression of Oxidative Stress and Akt/MAPK/NF-κB Signals

Methylglyoxal (MGO), a highly reactive dicarbonyl compound, causes endothelial oxidative stress and vascular complications in diabetes. Excessive MGO-induced ROS production triggers eNOS uncoupling, inflammatory responses, and cell death signaling cascades. Our previous study reported that unripe Carica papaya (UCP) had antioxidant activities that prevented H₂O₂-induced endothelial cell death. Therefore, this study investigated the preventive effect of UCP on MGO-induced endothelial cell damage, inflammation, and apoptosis. The human endothelial cell line (EA.hy926) was pretreated with UCP for 24 h, followed by MGO-induced dicarbonyl stress. Treated cells were evaluated for intracellular ROS/O₂^•− formation, cell viability, apoptosis, NO releases, and cell signaling through eNOS, iNOS, COX-2, NF-κB, Akt, MAPK (JNK and p38), and AMPK/SIRT1 autophagy pathways. UCP reduced oxidative stress and diminished phosphorylation of Akt, stress-activated MAPK, leading to the decreases in NF-kB-activated iNOS and COX-2 expression. However, UCP had no impact on the autophagy pathway (AMPK and SIRT1). Although UCP pretreatment decreased eNOS phosphorylation, the amount of NO production was not altered. The signaling of eNOS and NO production were decreased after MGO incubation, but these effects were unaffected by UCP pretreatment. In summary, UCP protected endothelial cells against carbonyl stress by the mechanisms related to ROS/O₂^•− scavenging activities, suppression of inflammatory signaling, and inhibition of JNK/p38/apoptosis pathway. Thus, UCP shows considerable promise for developing novel functional food and nutraceutical products to reduce risks of endothelial inflammation and vascular complications in diabetes.

Mechanisms underlying electro-mechanical dysfunction in the Zucker diabetic fatty rat heart: a model of obesity and type 2 diabetes

Diabetes mellitus (DM) is a major and worsening global health problem, currently affecting over 450 million people and reducing their quality of life. Type 2 diabetes mellitus (T2DM) accounts for more than 90% of DM and the global epidemic of obesity, which largely explains the dramatic increase in the incidence and prevalence of T2DM in the past 20 years. Obesity is a major risk factor for DM which is a major cause of morbidity and mortality in diabetic patients. The electro-mechanical function of the heart is frequently compromised in diabetic patients. The aim of this review is to discuss the pathophysiology of electro-mechanical dysfunction in the diabetic heart and in particular, the Zucker diabetic fatty (ZDF) rat heart, a well-studied model of T2DM and obesity.

Effect of the consumption of yacon flour and energy-restricted diet on glycation markers, and association between these markers and factors linked to obesity in adults with excess body weight: A randomized, double-blind, placebo-controlled clinical trial

OBJECTIVES

Regardless of the positive effect of yacon on metabolic markers, this food contains fructose molecules, which can originate advanced glycation end products (AGEs). High AGEs serum concentrations can contribute to excess body weight. We evaluated the effect of consuming an energy-restricted diet and yacon flour on glycation markers concentrations, and the associations between these markers and factors linked to obesity in adults with excess body weight.

METHODS

Twenty-six adults with excess body weight were included in this randomized, parallel, double-blind, placebo-controlled, 6-week clinical trial. Subjects were randomly allocated to the control group (n = 13) or the yacon-flour group (n = 13), and daily consumed a breakfast drink either not containing or containing 25 g of yacon flour (8.7 g of fructooligosaccharides). Energy-restricted diets were prescribed for both groups. Biochemical markers, anthropometric variables, and body composition were evaluated at baseline and the end of the study.

RESULTS

AGEs and early glycation products did not increase in the yacon flour group. Soluble receptor for AGEs (sRAGE) decreased regardless of group. Besides, changes in AGEs were positively associated with changes in body fat (β = 0.04, P = 0.038) and in sRAGE, with insulin (β = 0.02, P = 0.035) and homeostasis model assessment index of insulin resistance (β = 0.01, P = 0.049).

CONCLUSIONS

The consumption of 25 g of yacon flour associated with an energy-restricted diet did not increase concentrations of glycation markers. Changes in glycation markers were positively associated with changes in consolidated anthropometric and biochemical markers related to being overweight. Assessing glycation markers may be a useful strategy for monitoring responses to dietary interventions in subjects with excess body weight.

Impairment of the angiogenic process may contribute to lower success rate of root canal treatments in diabetes mellitus

AIM

To investigate the association between root canal treatment outcome, diabetes mellitus, and alterations of the angiogenic process.

METHODOLOGY

A retrospective observational study was conducted in healthy (control group, CG) and diabetic (type II diabetes mellitus group, DG) patients after root canal treatment. The follow-up appointments were performed to clinically and radiographically observe symptoms, the healing of periapical lesions and the quality of root fillings. In the animal model study, diabetic Goto-Kakizaki (GK) rats and control Wistar rats were used. After 21 days of pulp exposure and the development of apical periodontitis (AP), the mandibles were removed for scintigraphic, radiographic, histopathological and molecular analyses. Chi-square tests were performed to examine the variables related to endodontic outcome and differences between animal groups were assessed using the Student's t-test.

RESULTS

The group of patients with diabetes had a significantly lower rate of success following root canal treatment than the CG (p < .001). Logistic regression suggested that diabetes is a risk factor for success of root canal treatment. In the animal study, GK rats had significantly higher fasting glycaemia at t0 and t21 (p < .001) and triglycerides levels (p < .05) and area under the curve (AUC) during the insulin tolerance test at t21 (p < .001). AP area was significantly greater in GK rats (p < .05). Histologically, diabetic rats had increased signs of periodontal ligament inflammation 21 days after the induction of apical periodontitis, with fibro-hyaline matrix filling and vessel with undefined walls. Wistar rats had significantly increased vascular endothelial growth factor (VEGF) levels and VEGF/Ang-2 ratio 21 days after AP induction (p < .08; p < .07). GK rats had intrinsically lower levels of VEGF than control rats (p < .05), which did not change after AP.

CONCLUSION

Diabetes mellitus should be considered as an important factor in the prognosis of root canal treatment and its outcomes over time. Future strategies to improve angiogenesis and tissue repair should be pursued to achieve better root canal treatment outcomes in diabetic patients.

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.

Methylglyoxal Drives a Distinct, Nonclassical Macrophage Activation Status

Metabolic complications in diabetic patients are driven by a combination of increased levels of nutrients and the presence of a proinflammatory environment. Methylglyoxal (MG) is a toxic byproduct of catabolism and has been strongly associated with the development of such complications. Macrophages are key mediators of inflammatory processes and their contribution to the development of metabolic complications has been demonstrated. However, a direct link between reactive metabolites and macrophage activation has not been demonstrated yet. Here, we show that acute MG treatment activated components of the p38 MAPK pathway and enhanced glycolysis in primary murine macrophages. MG induced a distinct gene expression profile sharing similarities with classically activated proinflammatory macrophages as well as metabolically activated macrophages usually found in obese patients. Transcriptomic analysis revealed a set of 15 surface markers specifically upregulated in MG-treated macrophages, thereby establishing a new set of targets for diagnostic or therapeutic purposes under high MG conditions, including diabetes. Overall, our study defines a new polarization state of macrophages that may specifically link aberrant macrophage activation to reactive metabolites in diabetes.

Methylglyoxal influences development of Caenorhabditis elegans via lin-41-dependent pathway

Methylglyoxal is a highly reactive dicarbonyl compound. It can be obtained either endogenously through biological enzymatic/non-enzymatic pathways or exogenously via the uptake of certain foods and beverages, such as Manuka honey. Studies about its biological properties are quite controversial, though the majority reported a positive association between methylglyoxal and certain pathologies. In this report, we tested if methylglyoxal can alter the development of animals using Caenorhabditis elegans as the in vivo model. Treatment of methylglyoxal at 0.1 and 1 mmol/L for 2 days significantly inhibited the development of Caenorhabditis elegans, particularly targeting the transition from L3 stage. Pharyngeal pumping rate, the food intake marker was also significantly reduced by methylglyoxal at both 0.1 and 1 mmol/L. Additionally, treatment of 0.1 mmol/L methylglyoxal increased, while 1 mmol/L methylglyoxal decreased the nematodes' average moving speed. The effect of methylglyoxal on development was in part due to the modulation of lin-41, which encodes a homolog of human TRIM71. The mutation of lin-41 could alleviate or abolish the effects of methylglyoxal on growth rate, body size, pumping rate and locomotive activity. In summary, these results suggested that methylglyoxal influenced the development of Caenorhabditis elegans, which is in part via the lin-41-dependent pathway.

Identifying insomnia-related chemicals through integrative analysis of genome-wide association studies and chemical-genes interaction information

STUDY OBJECTIVES

Insomnia is a common sleep disorder and constitutes a major issue in modern society. We provide new clues for revealing the association between environmental chemicals and insomnia.

METHODS

Three genome-wide association studies (GWAS) summary datasets of insomnia (n = 113,006, n = 1,331,010, and n = 453,379, respectively) were driven from the UK Biobank, 23andMe, and deCODE. The chemical-gene interaction dataset was downloaded from the Comparative Toxicogenomics Database. First, we conducted a meta-analysis of the three datasets of insomnia using the METAL software. Using the result of meta-analysis, transcriptome-wide association studies were performed to calculate the expression association testing statistics of insomnia. Then chemical-related gene set enrichment analysis (GSEA) was used to explore the association between chemicals and insomnia.

RESULTS

For GWAS meta-analysis dataset of insomnia, we identified 42 chemicals associated with insomnia in brain tissue (p < 0.05) by GSEA. We detected five important chemicals such as pinosylvin (p = 0.0128), bromobenzene (p = 0.0134), clonidine (p = 0.0372), gabapentin (p = 0.0372), and melatonin (p = 0.0404) which are directly associated with insomnia.

CONCLUSION

Our study results provide new clues for revealing the roles of environmental chemicals in the development of insomnia.

Methylglyoxal mediated glycation leads to neo-epitopes generation in fibrinogen: Role in the induction of adaptive immune response

In diabetes mellitus, hyperglycemia mediated non-enzymatic glycosylation of proteins results in the pathogenesis of diabetes-associated secondary complications via the generation of advanced glycation end products (AGEs). The focus of this study is to reveal the immunological aspects of methylglyoxal (MG) mediated glycation of fibrinogen protein. The induced immunogenicity of modified fibrinogen is analyzed by direct binding and inhibition ELISA. Direct binding ELISA confirmed that MG glycated fibrinogen (MG-Fib) is highly immunogenic and induces a high titer of antibodies in comparison to its native analog. Cross-reactivity and antigen-binding specificity of induced antibodies were confirmed by inhibition ELISA. The enhanced affinity of immunoglobulin G (IgG) from immunized rabbits' sera and MG glycated fibrinogen is probably the aftermath of neo-epitopes generation in the native structure of protein upon modification. Thus, we deduce that under the glycative stress, MG-mediated structural alterations in fibrinogen could induce the generation of antibodies which might serve as a potential biomarker in diabetes mellitus and its associated secondary disorders.

Gastrointestinal manifestations after Roux-en-Y gastric bypass surgery in individuals with and without type 2 diabetes

BACKGROUND

Roux-en-Y gastric bypass (RYGB) surgery is an effective treatment for obesity, which improves cardiovascular health and reduces the risk of premature mortality. However, some reports have suggested that RYGB may predispose patients to adverse health outcomes, such as inflammatory bowel disease (IBD) and colorectal cancer.

OBJECTIVES

The present prospective study aimed to evaluate the impact of RYGB surgery on cardiovascular risk factors and gastrointestinal inflammation in individuals with and without type 2 diabetes (T2D).

SETTING

University hospital setting in Finland.

METHODS

Blood and fecal samples were collected at baseline and 6 months after surgery from 30 individuals, of which 16 had T2D and 14 were nondiabetics. There were also single study visits for 6 healthy reference patients. Changes in cardiovascular risk factors, serum cholesterol, and triglycerides were investigated before and after surgery. Fecal samples were analyzed for calprotectin, anti-Saccharomyces cerevisiae immunoglobulin A antibodies (ASCA), active lipopolysaccharide (LPS) concentration, short-chain fatty acids (SCFAs), intestinal alkaline phosphatase activity, and methylglyoxal-hydro-imidazolone (MG-H1) protein adducts formation.

RESULTS

After RYGB, weight decreased on average -21.6% (-27.2 ± 7.8 kg), excess weight loss averaged 51%, and there were improvements in cardiovascular risk factors. Fecal calprotectin levels (P < .001), active LPS concentration (P < .002), ASCA (P < .02), and MG-H1 (P < .02) values increased significantly, whereas fecal SCFAs, especially acetate (P < .002) and butyrate (P < .03) levels, were significantly lowered.

CONCLUSION

The intestinal homeostasis is altered after RYGB, with several fecal markers suggesting increased inflammation; however, clinical significance of the detected changes is currently uncertain. As chronic inflammation may predispose patients to adverse health effects, our findings may have relevance for the suggested association between RYGB and increased risks of incident IBD and colorectal cancer.

Medical honey for canine nasal intertrigo: A randomized, blinded, placebo-controlled, adaptive clinical trial to support antimicrobial stewardship in veterinary dermatology

Intertrigo is a skin fold dermatitis often requiring recurrent treatment with topical antiseptics or antibiotics, which can select antimicrobial resistance. To minimize this risk, we tested the effectiveness of medical-grade Manuka honey at treating intertrigo as compared to a placebo hydrogel. We additionally characterized the culturable microbial flora of intertrigo and recorded any adverse effect with either treatment. During this randomized, placebo-controlled, double-blinded, adaptive group-sequential trial, the owners washed the affected sites on their dog with water, dried and applied a thin film of either the honey or the placebo product once daily for 21 days. Cytological and lesional composite scores, owner-assessed pruritus, and microbial cultures were assessed prior to treatment and on Day-22. The fixed effects of time, treatment, and animal-related variables on the pruritus and on each composite score, accounting for random dog effect, were estimated separately with generalized linear mixed models for repeated count outcomes (α = 0.05). The null hypothesis of equal treatment effects was rejected at the first interim analysis. The placebo (n = 16 dogs) outperformed the medical honey (n = 13 dogs) at improving both the cytological score (Treatment×Time = -0.35±0.17; P = 0.04) and clinical score (Treatment×Time = -0.28±0.13; P = 0.04). A microbial burden score higher than 4 increased the severity of the cytological score (dichotomous score: 0.29±0.11; P = 0.01), which in turn increased the severity of the clinical score and pruritus score. For every unit increase in cytological score, the linear predictor of clinical score increased by 0.042±0.019 (P = 0.03), and the one of pruritus score increased by 0.12±0.05 (P = 0.01). However, medical honey outperformed the placebo at alleviating the dog's owner-assessed pruritus after statistically controlling for masking effects (Time = -0.94±0.24; P = 0.002; and Treatment×Time = 0.80±0.36; P = 0.04). Unilateral tests of the least-square mean estimates revealed that honey only significantly improved the pruritus (Hommel-adjusted P = 0.003), while the placebo only improved the cytological and clinical scores (Hommel-adjusted P = 0.01 and 0.002, respectively). Taken together, these results question the value of Manuka honey at treating nasal intertrigo in dogs.

Deamidated Human Triosephosphate Isomerase is a Promising Druggable Target

Therapeutic strategies for the treatment of any severe disease are based on the discovery and validation of druggable targets. The human genome encodes only 600-1500 targets for small-molecule drugs, but posttranslational modifications lead to a considerably larger druggable proteome. The spontaneous conversion of asparagine (Asn) residues to aspartic acid or isoaspartic acid is a frequent modification in proteins as part of the process called deamidation. Triosephosphate isomerase (TIM) is a glycolytic enzyme whose deamidation has been thoroughly studied, but the prospects of exploiting this phenomenon for drug design remain poorly understood. The purpose of this study is to demonstrate the properties of deamidated human TIM (HsTIM) as a selective molecular target. Using in silico prediction, in vitro analyses, and a bacterial model lacking the tim gene, this study analyzed the structural and functional differences between deamidated and nondeamidated HsTIM, which account for the efficacy of this protein as a druggable target. The highly increased permeability and loss of noncovalent interactions of deamidated TIM were found to play a central role in the process of selective enzyme inactivation and methylglyoxal production. This study elucidates the properties of deamidated HsTIM regarding its selective inhibition by thiol-reactive drugs and how these drugs can contribute to the development of cell-specific therapeutic strategies for a variety of diseases, such as COVID-19 and cancer.

Dietary Genistein Reduces Methylglyoxal and Advanced Glycation End Product Accumulation in Obese Mice Treated with High-Fat Diet

Our previous study has found that dietary genistein could ameliorate high-fat diet (HFD)-induced obesity and especially lower methylglyoxal (MGO) and advanced glycation end product (AGE) accumulation in healthy mice exposed to genistein and HFD. However, it is still unclear whether dietary genistein intervention has a similar beneficial effect in obese mice. In this study, the mice were induced with obesity after being fed a HFD for nine weeks before being administered with two doses of genistein, 0.1% (G 0.1) and 0.2% (G 0.2), in the HFD for additional 19 weeks. After 19 week treatment, genistein supplementation reduced body and liver weights, plasma and liver MGO levels, and kidney AGE levels in mice. Mechanistically, genistein upregulated the expressions of glyoxalase I and II and aldose reductase to detoxify MGO, and genistein and its microbial metabolites, dihydrogenistein and 6'-hydroxy-O-demethylangolensin, were able to trap endogenous MGO via formation of MGO conjugates. Taken together, our results provide novel insights into the antiobesity and antiglycation roles of dietary genistein in obese subjects.

Glycation of fibronectin inhibits VEGF-induced angiogenesis by uncoupling VEGF receptor-2-c-Src crosstalk

Glycation of extracellular matrix proteins has been demonstrated to contribute to the pathogenesis of vascular complications. However, no previous report has shown the role of glycated fibronectin (FN) in vascular endothelial growth factor (VEGF)‐induced angiogenesis. Thus, this study aimed to investigate the effects of glycated FN on VEGF signalling and to clarify the molecular mechanisms involved. FN was incubated with methylglyoxal (MGO) in vitro to synthesize glycated FN, and human umbilical vein endothelial cells (HUVECs) were seeded onto unmodified and MGO‐glycated FN. Then, VEGF‐induced angiogenesis and VEGF‐induced VEGF receptor‐2 (VEGFR‐2) signalling activation were measured. The results demonstrated that normal FN‐positive bands (260 kD) vanished and advanced glycation end products (AGEs) appeared in MGO‐glycated FN and glycated FN clearly changed to a higher molecular mass. The glycation of FN inhibited VEGF‐induced VEGF receptor‐2 (VEGFR‐2), Akt and ERK1/2 activation and VEGF‐induced cell migration, proliferation and tube formation. The glycation of FN also inhibited the recruitment of c‐Src to VEGFR‐2 by sequestering c‐Src through receptor for AGEs (RAGE) and the anti‐RAGE antibody restored VEGF‐induced VEGFR‐2, Akt and ERK1/2 phosphorylation, endothelial cell migration, proliferation and tube formation. Furthermore, the glycation of FN significantly inhibited VEGF‐induced neovascularization in the Matrigel plugs implanted into subcutaneous tissue of mice. Taken together, these data suggest that the glycation of FN may inhibit VEGF signalling and VEGF‐induced angiogenesis by uncoupling VEGFR‐2‐c‐Src interaction. This may provide a novel mechanism for the impaired angiogenesis in diabetic ischaemic diseases.

Curcumin derivatives for Type 2 Diabetes management and prevention of complications

Type 2 diabetes Mellitus (T2DM) is characterized by chronically increased blood glucose levels, which is associated with impairment of the inflammatory and oxidative state and dyslipidaemia. Although it is considered a world heath concern and one of the most studied diseases, we are still pursuing an effective therapy for both the pathophysiological mechanisms and the complications. Curcumin, a natural compound found in the rhizome of Curcuma longa, is well known for its numerous biological activities, as demonstrated by several studies supporting that curcumin possesses hypoglycaemic, hypolipidemic, anti-inflammatory and antioxidant properties, among others. These effects have been explored to the attenuation of hyperglycaemia and progression of DM complications, being appointed as a potential therapeutic approach. Besides its strong intrinsic activity, the polyphenol has low bioavailability, compromising its therapeutic efficacy. In order to overcome this limitation, several chemical strategies have been applied to curcumin, such as drug delivery systems, chemical manipulation and the use of adjuvant therapies. Given the promising results obtained with curcumin derivative, in this review we discuss not only the therapeutic targets of curcumin, but also its most recently developed analogues and their efficacy in the management of T2DM pathophysiology and complications.

Carbenium ion-mediated oligomerization of methylglyoxal for secondary organic aerosol formation

Secondary organic aerosol (SOA) from photochemical oxidation of volatile organic compounds represents one of the most dominant constituents of fine particulate matter in the troposphere, with profound implications for air quality and climate. However, the fundamental chemical mechanisms leading to SOA formation remain highly uncertain. Here, we show oligomer formation from methylglyoxal with the carbenium ions as the key intermediate using quantum chemical calculations. This cationic oligomerization is demonstrated to proceed via barrierless pathways and occurs at fast rates on weakly acidic aqueous aerosols and/or cloud droplets under typical tropospheric conditions. In contrast to a previously proposed hydration mechanism, out results reveal that the carbenium ion-mediated oligomerization of methylglyoxal provides a major SOA source from anthropogenic and biogenic emissions.

Secondary organic aerosol (SOA) represents a major constituent of tropospheric fine particulate matter, with profound implications for human health and climate. However, the chemical mechanisms leading to SOA formation remain uncertain, and atmospheric models consistently underpredict the global SOA budget. Small α-dicarbonyls, such as methylglyoxal, are ubiquitous in the atmosphere because of their significant production from photooxidation of aromatic hydrocarbons from traffic and industrial sources as well as from biogenic isoprene. Current experimental and theoretical results on the roles of methylglyoxal in SOA formation are conflicting. Using quantum chemical calculations, we show cationic oligomerization of methylglyoxal in aqueous media. Initial protonation and hydration of methylglyoxal lead to formation of diols/tetrol, and subsequent protonation and dehydration of diols/tetrol yield carbenium ions, which represent the key intermediates for formation and propagation of oligomerization. On the other hand, our results reveal that the previously proposed oligomerization via hydration for methylglyoxal is kinetically and thermodynamically implausible. The carbenium ion-mediated mechanism occurs barrierlessly on weakly acidic aerosols and cloud/fog droplets and likely provides a key pathway for SOA formation from biogenic and anthropogenic emissions.

Cyanidin Attenuates Methylglyoxal-Induced Oxidative Stress and Apoptosis in INS-1 Pancreatic β-Cells by Increasing Glyoxalase-1 Activity

Recently, the mechanisms responsible for anti-glycation activity of cyanidin and its derivatives on the inhibition of methylglyoxal (MG)-induced protein glycation and advanced glycation-end products (AGEs) as well as oxidative DNA damage were reported. In this study, we investigated the protective effect of cyanidin against MG-induced oxidative stress and apoptosis in rat INS-1 pancreatic β-cells. Exposure of cells to cytotoxic levels of MG (500 µM) for 12 h caused a significant reduction in cell viability. However, the pretreatment of cells with cyanidin alone (6.25–100 μM) for 12 h, or cotreatment of cells with cyanidin (3.13–100 μM) and MG, protected against cell cytotoxicity. In the cotreatment condition, cyanidin (33.3 and 100 μM) also decreased MG-induced apoptosis as determined by caspase-3 activity. Furthermore, INS-1 cells treated with MG increased the generation of reactive oxygen species (ROS) during a 6 h exposure. The MG-induced increase in ROS production was inhibited by cyanidin (33.3 and 100 μM) after 3 h stimulation. Furthermore, MG diminished the activity of glyoxalase 1 (Glo-1) and its gene expression as well as the level of total glutathione. In contrast, cyanidin reversed the inhibitory effect of MG on Glo-1 activity and glutathione levels. Interestingly, cyanidin alone was capable of increasing Glo-1 activity and glutathione levels without affecting Glo-1 mRNA expression. These findings suggest that cyanidin exerts a protective effect against MG-induced oxidative stress and apoptosis in pancreatic β-cells by increasing the activity of Glo-1.

miR-450a-5p Eliminates MGO-Induced Insulin Resistance via Targeting CREB

Background and Objectives

miR-450a-5p was involved in fat formation, however, its role in insulin resistance remains unclear. This study investigated the effects of miR-450a-5p on endothelial cells, with the aim of finding a potential target for diabetes mellitus.

Methods and Results

Human umbilical vein endothelial cells (HUVECs) were treated with low-glucose, high-glucose, methylglyoxal (MGO), and insulin alone or in combination with MGO. The expression of miR-450a-5p in treated cells was measured by quantitative real-time polymerase chain reaction (qRT-PCR) assays. The cell activity, migration and fat formation were determined by MTT experiments, Transwell assay and oil red O staining. The expressions of eNOS/AKT pathway-related proteins in cells were assessed by Western blot (WB) analysis. Furthermore, the target gene of miR-450a-5p was analyzed by double-luciferase reporter analysis, and its effects on eNOS/AKT pathway were estimated. We found that the expression of miR-450a-5p was decreased obviously in endothelial cells treated with high-glucose and MGO. In vitro cell experiments showed that MGO could not only promote the activity of endothelial cells, but also accelerate cell migration and fat accumulation, which, however, could be reversed by up-regulation of miR-450a-5p. Moreover, MGO inhibited eNOS/AKT pathway activation and NO release mediated by insulin, and such effects were reversed by up-regulation of miR-450a-5p. Furthermore, CREB was the target gene for miR-450a-5p, had an activation effect on the eNOS/AKT pathway.

Conclusions

Up-regulated miR-450a-5p eliminates MGO-induced insulin resistance via targeting CREB, and therefore could be used as a potential target to improve insulin resistance and treat patients with diabetes-related diseases.

Multitarget and promising role of dihydromyricetin in the treatment of metabolic diseases

Dihydromyricetin (DMY or DHM), also known as ampelopsin, is the main natural flavonol compound extracted from the plant Ampelopsis grossedentata (Hand. -Mazz) W.T. Wang. In recent years, accumulating studies have been conducted to explore the extensive biological functions of DMY, including antitumor, anti-inflammation, organ-protective, and metabolic regulation effects. DMY acts as a potential preventive or therapeutic agent in treating multiple diseases, such as diabetes mellitus, atherosclerosis, nonalcoholic fatty liver disease and osteoporosis. This review article summarizes the preventive and therapeutic potential of DMY in multiple metabolic diseases and the main signaling pathways in which DMY participates to offer a comprehensive understanding and guidance for future studies.

Brain Senescence Caused by Elevated Levels of Reactive Metabolite Methylglyoxal on D-Galactose-Induced Aging Mice

Aging is a complex natural phenomenon that is manifested by degenerative changes in the structure and function of cells and tissues. D-Galactose-induced aging mice are an artificial accelerated aging model that causes memory and learning impairment, oxidative stress, and neuroinflammation. In this study, we examined the underlying mechanism of an aging mouse model induced by D-galactose. Our behavioral Morris water maze results revealed that D-galactose administration for 2 months significantly induced memory and learning impairment in C57BL/6J mice. High performance liquid chromatography (HPLC) results showed elevated levels of the metabolite methylglyoxal (MG) in D-galactose-induced aging mice. Whether and how D-galactose induces senescence by elevated levels of reactive metabolite MG remain unclear. In our study, MG mainly accumulated through the following two aspects: to increase its source, namely, the triose phosphate produced by the glycolysis pathway, and to reduce its detoxification system, namely, the glyoxalase system. Therefore, elevated MG levels may be one of the causes of brain senescence in D-galactose-induced mice. However, the molecular mechanism of the increased level of the reaction metabolite methylglyoxal requires further exploration.