Methylglyoxal and glyoxalase 1-a metabolic stress pathway-linking hyperglycemia to the unfolded protein response and vascular complications of diabetes

Mitochondria regulate MR1 protein expression and produce self-metabolites that activate MR1-restricted T cells

Mitochondria coordinate several metabolic pathways, producing metabolites that influence the immune response in various ways. It remains unclear whether mitochondria impact antigen presentation by the MHC-class-I-related antigen-presenting molecule, MR1, which presents small molecules to MR1-restricted T-lymphocytes. Here, we demonstrate that mitochondrial complex III and the enzyme dihydroorotate dehydrogenase are essential for the cell-surface expression of MR1 and for generating uridine- and thymidine-related compounds that bind to MR1 and are produced upon oxidation by reactive oxygen species. One mitochondria-derived immunogenic formylated metabolite we identified is 5-formyl-deoxyuridine (5-FdU). Structural studies indicate that 5-FdU binds in the A'-antigen-binding pocket of MR1, positioning the deoxyribose toward the surface of MR1 for TCR interaction. 5-FdU stimulates specific T cells and detects circulating T cells when loaded onto MR1-tetramers. 5-FdU-reactive cells resemble adaptive T cells and express the phenotypes of naïve, memory, and effector cells, indicating prior in vivo stimulation. These findings suggest that mitochondria may play a role in MR1-mediated immune surveillance.

Skin autofluorescence of advanced glycation end-products, glycemic memory, and diabetes complications

Since the pionneer work of Meerwaldt and the Groningen team, who related skin autofluorescence (SAF) to the dermal concentrations of advanced glycation end-products (AGEs), hundreds of articles have been devoted to its application in diabetes. Due to the slow turnover of the AGEs formed on collagen of the skin, the SAF can reflect the progressive accumulation of AGEs and hence be a marker of long-term glucose exposure. Accordingly, relations with HbA1c from the previous 3-10 years have been established in both type 1 and type 2 diabetes, and even in gestational diabetes mellitus. Other important determinants of SAF exist however, notably age, renal function, diet, and genetics. SAF is also related to current and future micro- and macrovascular complications of diabetes, as expected for a marker of glycemic memory. It is also related to some important emerging diabetes complications and comorbidities such as cancer, cognitive decline and liver disease. Quantitative information on glucose exposure during the previous years may be pertinent to personnalize care for patients with diabetes: priority for glucose control when SAF is low, and for screening for complications once SAF is high.

Molecular mechanism of ectopic lipid accumulation induced by methylglyoxal via activation of the NRF2/PI3K/AKT pathway implicates renal lipotoxicity caused by diabetes mellitus

Patients with chronic kidney disease (CKD) have a high incidence of dyslipidemia comprising high triglyceride (TG) and low high-density lipoprotein (HDL)-cholesterol levels. An abnormal increase of TGs within cells can lead to intracellular lipid accumulation. In addition to dyslipidemia, hyperglycemia in diabetes may elicit ectopic lipid deposition in non-adipose tissues. Hyperglycemia increases intracellular levels of methylglyoxal (MG) leading to cellular dysfunction. A deficit of glyoxalase I (GLO1) contributes to dicarbonyl stress. Whether dicarbonyl stress induced by MG causes renal lipotoxicity through alteration of lipid metabolism signaling is still unknown. In this study, mice with high fat diet-induced diabetes were used to investigate the renal pathology induced by MG. NRK52E cells treated with MG were further used in vitro to delineate the involvement of lipogenic signaling. After treatment with MG for 12 weeks, plasma TG levels, renal fatty changes, and tubular injuries were aggravated in diabetic mice. In NRK52E cells, MG activated the nuclear factor erythroid 2-related factor 2 (Nrf2)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and sterol regulatory element-binding protein 1 (SREBP1), resulting in stimulation of fatty acid synthase. The intracellular accumulation of lipid droplets was mainly contributed by TGs, which increased the oxidative stress accompanied by high Nrf2 expression. In addition, MG time-dependently activated cyclin D, cyclin-dependent kinase 4 (CDK4), and cleaved caspase-3, evidencing that G0/G1 arrest was associated with apoptosis of NRK52E cells. In conclusion, our studies revealed the mechanism of lipotoxicity caused by MG. The target of such dicarbonyl stress may become a promising therapy for diabetic CKD.

Maladaptive response following glucose overload in GLUT4-overexpressing H9C2 cardiomyoblasts

BACKGROUND

Glucose overload drives diabetic cardiomyopathy by affecting the tricarboxylic acid pathway. However, it is still unknown how cells could overcome massive chronic glucose influx on cellular and structural level.

METHODS/MATERIALS

Expression profiles of hyperglycemic, glucose transporter-4 (GLUT4) overexpressing H9C2 (KE2) cardiomyoblasts loaded with 30 mM glucose (KE230L) and wild type (WT) cardiomyoblasts loaded with 30 mM glucose (WT30L) were compared using proteomics, real-time polymerase quantitative chain reaction analysis, or Western blotting, and immunocytochemistry.

RESULTS

The findings suggest that hyperglycemic insulin-sensitive cells at the onset of diabetic cardiomyopathy present complex changes in levels of structural cell-related proteins like tissue inhibitor of metalloproteases-1 (1.3 fold), intercellular adhesion molecule 1 (1.8 fold), type-IV-collagen (3.2 fold), chaperones (Glucose-Regulated Protein 78: 1.8 fold), autophagy (Autophagosome Proteins LC3A, LC3B: 1.3 fold), and in unfolded protein response (UPR; activating transcription factor 6α expression: 2.3 fold and processing: 2.4 fold). Increased f-actin levels were detectable with glucose overload by immnocytochemistry. Effects on energy balance (1.6 fold), sirtuin expression profile (Sirtuin 1: 0.7 fold, sirtuin 3: 1.9 fold, and sirtuin 6: 4.2 fold), and antioxidant enzymes (Catalase: 0.8 fold and Superoxide dismutase 2: 1.5 fold) were detected.

CONCLUSION

In conclusion, these findings implicate induction of chronic cell distress by sustained glucose accumulation with a non-compensatory repair reaction not preventing final cell death. This might explain the chronic long lasting pathogenesis observed in developing heart failure in diabetes mellitus.

Modulatory effects of rutin and vitamin A on hyperglycemia induced glycation, oxidative stress and inflammation in high-fat-fructose diet animal model

In the current study we investigated the impact of combination of rutin and vitamin A on glycated products, the glyoxalase system, oxidative markers, and inflammation in animals fed a high-fat high-fructose (HFFD) diet. Thirty rats were randomly divided into six groups (n = 5). The treatments, metformin (120 mg/kg), rutin (100 mg/kg), vitamin A (43 IU/kg), and a combination of rutin (100 mg/kg) and vitamin A (43 IU/kg) were given to relevant groups of rats along with high-fructose high-fat diet for 42 days. HbA1c, D-lactate, Glyoxylase-1, Hexokinase 2, malondialdehyde (MDA), glutathione peroxidase (GPx), catalase (CAT), nuclear transcription factor-B (NF-κB), interleukin-6 (IL-6), interleukin-8 (IL-8) and histological examinations were performed after 42 days. The docking simulations were conducted using Auto Dock package. The combined effects of rutin and vitamin A in treated rats significantly (p < 0.001) reduced HbA1c, hexokinase 2, and D-lactate levels while preventing cellular damage. The combination dramatically (p < 0.001) decreased MDA, CAT, and GPx in treated rats and decreased the expression of inflammatory cytokines such as IL-6 andIL-8, as well as the transcription factor NF-κB. The molecular docking investigations revealed that rutin had a strong affinity for several important biomolecules, including as NF-κB, Catalase, MDA, IL-6, hexokinase 2, and GPx. The results propose beneficial impact of rutin and vitamin A as a convincing treatment strategy to treat AGE-related disorders, such as diabetes, autism, alzheimer's, atherosclerosis.

Molecular Assessment of Methylglyoxal-Induced Toxicity and Therapeutic Approaches in Various Diseases: Exploring the Interplay with the Glyoxalase System

This comprehensive exploration delves into the intricate interplay of methylglyoxal (MG) and glyoxalase 1 (GLO I) in various physiological and pathological contexts. The linchpin of the narrative revolves around the role of these small molecules in age-related issues, diabetes, obesity, cardiovascular diseases, and neurodegenerative disorders. Methylglyoxal, a reactive dicarbonyl metabolite, takes center stage, becoming a principal player in the development of AGEs and contributing to cell and tissue dysfunction. The dual facets of GLO I-activation and inhibition-unfold as potential therapeutic avenues. Activators, spanning synthetic drugs like candesartan to natural compounds like polyphenols and isothiocyanates, aim to restore GLO I function. These molecular enhancers showcase promising outcomes in conditions such as diabetic retinopathy, kidney disease, and beyond. On the contrary, GLO I inhibitors emerge as crucial players in cancer treatment, offering new possibilities in diseases associated with inflammation and multidrug resistance. The symphony of small molecules, from GLO I activators to inhibitors, presents a nuanced understanding of MG regulation. From natural compounds to synthetic drugs, each element contributes to a molecular orchestra, promising novel interventions and personalized approaches in the pursuit of health and wellbeing. The abstract concludes with an emphasis on the necessity of rigorous clinical trials to validate these findings and acknowledges the importance of individual variability in the complex landscape of health.

Melanoxetin: A Hydroxylated Flavonoid Attenuates Oxidative Stress and Modulates Insulin Resistance and Glycation Pathways in an Animal Model of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (DM) continues to escalate, necessitating innovative therapeutic approaches that target distinct pathways and address DM complications. Flavonoids have been shown to possess several pharmacological activities that are important for DM. This study aimed to evaluate the in vivo effects of the flavonoid melanoxetin using Goto-Kakizaki rats. Over a period of 14 days, melanoxetin was administered subcutaneously to investigate its antioxidant, anti-inflammatory, and antidiabetic properties. The results show that melanoxetin reduced insulin resistance in adipose tissue by targeting protein tyrosine phosphatase 1B. Additionally, melanoxetin counteracted oxidative stress by reducing nitrotyrosine levels and modulating superoxide dismutase 1 and hemeoxygenase in adipose tissue and decreasing methylglyoxal-derived hydroimidazolone (MG-H1), a key advanced glycation end product (AGE) implicated in DM-related complications. Moreover, the glyoxalase 1 expression decreased in both the liver and the heart, correlating with reduced AGE levels, particularly MG-H1 in the heart. Melanoxetin also demonstrated anti-inflammatory effects by reducing serum prostaglandin E2 levels, and increasing the antioxidant status of the aorta wall through enhanced acetylcholine-dependent relaxation in the presence of ascorbic acid. These findings provide valuable insights into melanoxetin's therapeutic potential in targeting multiple pathways involved in type 2 DM, particularly in mitigating oxidative stress and glycation.

Synthesis, Characterization, Antiglycation Evaluation, Molecular Docking, and ADMET Studies of 4-Thiazolidinone Derivatives

The design and development of new small-molecule glycation inhibitors are essential for preventing various chronic diseases, including diabetes mellitus, immunoinflammation, cardiovascular, and neurodegenerative diseases. 4-Thiazolidinone or thiazolidine-4-one is a well-known heterocyclic compound with the potential to inhibit the formation of advanced glycation end products. In the present work, we report the synthesis and characterization of four new 5-arylidene 3-cyclopropyl-2-(phenylimino)thiazolidin-4-one (1-4) compounds and their human serum albumin glycation inhibitory activity. One of the compounds 5-(2H-1,3-benzodioxol-5-ylmethylidene)-3-cyclopropyl-2-(phenylimino)-1,3-thiazolidin-4-one (3) showed potent inhibition in the synthesis of initial, intermediary, and final products of glycation reactions. Besides, conformational changes in the α-helix and β-sheet (due to hyperglycemia) were also found to be reversed upon the addition of (3). Experimental findings were complemented by computational [molecular docking, ADME/Tox, and density functional theory (DFT)] studies. The docking scores of the compounds were in order 1 > 3 > 2 > 4, indicating the importance of the polar group at the 5-arylidene moiety. The results of ADME/Tox and DFT calculations revealed the safe nature of the compounds with high drug-likeness and stability. Overall, we speculate that the results of this study could provide valuable insights into the biological activity of 4-thiazolidinones.

Communal interaction of glycation and gut microbes in diabetes mellitus, Alzheimer's disease, and Parkinson's disease pathogenesis

Diabetes and its complications, Alzheimer's disease (AD), and Parkinson's disease (PD) are increasing gradually, reflecting a global threat vis-à-vis expressing the essentiality of a substantial paradigm shift in research and remedial actions. Protein glycation is influenced by several factors, like time, temperature, pH, metal ions, and the half-life of the protein. Surprisingly, most proteins associated with metabolic and neurodegenerative disorders are generally long-lived and hence susceptible to glycation. Remarkably, proteins linked with diabetes, AD, and PD share this characteristic. This modulates protein's structure, aggregation tendency, and toxicity, highlighting renovated attention. Gut microbes and microbial metabolites marked their importance in human health and diseases. Though many scientific shreds of evidence are proposed for possible change and dysbiosis in gut flora in these diseases, very little is known about the mechanisms. Screening and unfolding their functionality in metabolic and neurodegenerative disorders is essential in hunting the gut treasure. Therefore, it is imperative to evaluate the role of glycation as a common link in diabetes and neurodegenerative diseases, which helps to clarify if modulation of nonenzymatic glycation may act as a beneficial therapeutic strategy and gut microbes/metabolites may answer some of the crucial questions. This review briefly emphasizes the common functional attributes of glycation and gut microbes, the possible linkages, and discusses current treatment options and therapeutic challenges.

Methylglyoxal-induced neurotoxic effects in primary neuronal-like cells transdifferentiated from human mesenchymal stem cells: Impact of low concentrations

In the last decades, advanced glycation end-products (AGEs) have aroused the interest of the scientific community due to the increasing evidence of their involvement in many pathophysiological processes including various neurological disorders and cognitive decline age related. Methylglyoxal (MG) is one of the reactive dicarbonyl precursors of AGEs, mainly generated as a by-product of glycolysis, whose accumulation induces neurotoxicity. In our study, MG cytotoxicity was evaluated employing a human stem cell-derived model, namely, neuron-like cells (hNLCs) transdifferentiated from mesenchymal stem/stromal cells, which served as a source of human based species-specific "healthy" cells. MG increased ROS production and induced the first characteristic apoptotic hallmarks already at low concentrations (≥10 μM), decreased the cell growth (≥5-10 μM) and viability (≥25 μM), altered Glo-1 and Glo-2 enzymes (≥25 μM), and markedly affected the neuronal markers MAP-2 and NSE causing their loss at low MG concentrations (≥10 μM). Morphological alterations started at 100 μM, followed by even more marked effects and cell death after few hours (5 h) from 200 μM MG addition. Substantially, most effects occurred as low as 10 μM, concentration much lower than that reported from previous observations using different in vitro cell-based models (e.g., human neuroblastoma cell lines, primary animal cells, and human iPSCs). Remarkably, this low effective concentration approaches the level range measured in biological samples of pathological subjects. The use of a suitable cellular model, that is, human primary neurons, can provide an additional valuable tool, mimicking better the physiological and biochemical properties of brain cells, in order to evaluate the mechanistic basis of molecular and cellular alterations in CNS.

The genetic polymorphisms and activity of glyoxalase 1 as a risk factor for acute coronary syndrome in South Indians with type 2 diabetes mellitus

OBJECTIVE

The individuals' genetic traits predispose them to a higher or lower risk of Type 2 diabetes mellitus (T2DM) and its complications, for example, acute coronary syndrome (ACS). As carbonyl stress is responsible for the pathogenesis and complications of T2DM, and glyoxalase 1 (GLO1) is the most crucial determinant of carbonyl stress, the study aimed to explore the association between GLO1 gene polymorphism, GLO1 activity in red blood cell (RBC), plasma methylglyoxal (MG) levels, and ACS risk in South Indian T2DM patients.

METHODS

A total of 150 T2DM patients with ACS as cases and 150 T2DM patients without ACS as controls were recruited in a case-control study. The rs4746, rs1049346 and rs1130534 of the GLO1 gene were analysed using TaqMan allele discrimination assay. The RBC GLO1 activity and plasma MG levels were measured.

RESULTS

Significantly lower RBC GLO1 activity and higher plasma MG levels were found in cases compared to controls (p < 0.001 and p = 0.008, respectively). The genotype and allele frequencies of rs1049346 significantly differed between cases and controls (p < 0.001). For rs1130534 and rs1049346, no significant difference was found. For rs1049346, the TT and CC genotypes were associated with higher (p = 0.002) and lower (p = 0.001) ACS risk, respectively, in various genetic models. The TT genotype of rs1049346 was associated with lower RBC GLO1 activity (p = 0.004) and higher MG level (p = 0.010). In haplotype analysis, higher ACS susceptibility with the TAT haplotype (p < 0.001) and lower ACS susceptibility with the TAC haplotype (p < 0.001) were observed. Also, lower RBC GLO1 activity was associated with the TAT haplotype (p = 0.002).

CONCLUSIONS

The rs1049346 of the GLO1 gene may be associated with ACS risk in South Indian T2DM patients, and the T and C allele might be essential precipitating and protective factors, respectively.

Elevated methylglyoxal levels inhibit tomato fruit ripening by preventing ethylene biosynthesis

Methylglyoxal (MG), a toxic compound produced as a by-product of several cellular processes, such as respiration and photosynthesis, is well known for its deleterious effects, mainly through glycation of proteins during plant stress responses. However, very little is known about its impact on fruit ripening. Here, we found that MG levels are maintained at high levels in green tomato (Solanum lycopersicum L.) fruits and decline during fruit ripening despite a respiratory burst during this transition. We demonstrate that this decline is mainly mediated through a glutathione-dependent MG detoxification pathway and primarily catalyzed by a Glyoxalase I enzyme encoded by the SlGLYI4 gene. SlGLYI4 is a direct target of the MADS-box transcription factor RIPENING INHIBITOR (RIN), and its expression is induced during fruit ripening. Silencing of SlGLYI4 leads to drastic MG overaccumulation at ripening stages of transgenic fruits and interferes with the ripening process. MG most likely glycates and inhibits key enzymes such as methionine synthase and S-adenosyl methionine synthase in the ethylene biosynthesis pathway, thereby indirectly affecting fruit pigmentation and cell wall metabolism. MG overaccumulation in fruits of several nonripening or ripening-inhibited tomato mutants suggests that the tightly regulated MG detoxification process is crucial for normal ripening progression. Our results underpin a SlGLYI4-mediated regulatory mechanism by which MG detoxification controls fruit ripening in tomato.

Type 2 Diabetes (T2DM) and Parkinson's Disease (PD): a Mechanistic Approach

Growing evidence suggest that there is a connection between Parkinson's disease (PD) and insulin dysregulation in the brain, whilst the connection between PD and type 2 diabetes mellitus (T2DM) is still up for debate. Insulin is widely recognised to play a crucial role in neuronal survival and brain function; any changes in insulin metabolism and signalling in the central nervous system (CNS) can lead to the development of various brain disorders. There is accumulating evidence linking T2DM to PD and other neurodegenerative diseases. In fact, they have a lot in common patho-physiologically, including insulin dysregulation, oxidative stress resulting in mitochondrial dysfunction, microglial activation, and inflammation. As a result, initial research should focus on the role of insulin and its molecular mechanism in order to develop therapeutic outcomes. In this current review, we will look into the link between T2DM and PD, the function of insulin in the brain, and studies related to impact of insulin in causing T2DM and PD. Further, we have also highlighted the role of various insulin signalling pathway in both T2DM and PD. We have also suggested that T2DM-targeting pharmacological strategies as potential therapeutic approach for individuals with cognitive impairment, and we have demonstrated the effectiveness of T2DM-prescribed drugs through current PD treatment trials. In conclusion, this investigation would fill a research gap in T2DM-associated Parkinson's disease (PD) with a potential therapy option.