Methylglyoxal induces advanced glycation end product (AGEs) formation and dysfunction of PDGF receptor‐β: implications for diabetic atherosclerosis

Protein Oxidation in Aging and Alzheimer's Disease Brain

Proteins are essential molecules that play crucial roles in maintaining cellular homeostasis and carrying out biological functions such as catalyzing biochemical reactions, structural proteins, immune response, etc. However, proteins also are highly susceptible to damage by reactive oxygen species (ROS) and reactive nitrogen species (RNS). In this review, we summarize the role of protein oxidation in normal aging and Alzheimer's disease (AD). The major emphasis of this review article is on the carbonylation and nitration of proteins in AD and mild cognitive impairment (MCI). The oxidatively modified proteins showed a strong correlation with the reported changes in brain structure, carbohydrate metabolism, synaptic transmission, cellular energetics, etc., of both MCI and AD brains compared to the controls. Some proteins were found to be common targets of oxidation and were observed during the early stages of AD, suggesting that those changes might be critical in the onset of symptoms and/or formation of the pathological hallmarks of AD. Further studies are required to fully elucidate the role of protein oxidation and nitration in the progression and pathogenesis of AD.

Reactive Carbonyl Species and Protein Lipoxidation in Atherogenesis

Atherosclerosis is a multifactorial disease of medium and large arteries, characterized by the presence of lipid-rich plaques lining the intima over time. It is the main cause of cardiovascular diseases and death worldwide. Redox imbalance and lipid peroxidation could play key roles in atherosclerosis by promoting a bundle of responses, including endothelial activation, inflammation, and foam cell formation. The oxidation of polyunsaturated fatty acids generates various lipid oxidation products such as reactive carbonyl species (RCS), including 4-hydroxy alkenals, malondialdehyde, and acrolein. RCS covalently bind to nucleophilic groups of nucleic acids, phospholipids, and proteins, modifying their structure and activity and leading to their progressive dysfunction. Protein lipoxidation is the non-enzymatic post-translational modification of proteins by RCS. Low-density lipoprotein (LDL) oxidation and apolipoprotein B (apoB) modification by RCS play a major role in foam cell formation. Moreover, oxidized LDLs are a source of RCS, which form adducts on a huge number of proteins, depending on oxidative stress intensity, the nature of targets, and the availability of detoxifying systems. Many systems are affected by lipoxidation, including extracellular matrix components, membranes, cytoplasmic and cytoskeletal proteins, transcription factors, and other components. The mechanisms involved in lipoxidation-induced vascular dysfunction are not fully elucidated. In this review, we focus on protein lipoxidation during atherogenesis.

Methylglyoxal, a highly reactive dicarbonyl compound, as a threat for blood brain barrier integrity

The brain is a highly metabolically active organ requiring a large amount of glucose. Methylglyoxal (MGO), a by-product of glucose metabolism, is known to be involved in microvascular dysfunction and is associated with reduced cognitive function. Maintenance of the blood-brain barrier (BBB) is essential to maintain optimal brain function and a large amount of evidence indicates negative effects of MGO on BBB integrity. In this review, we summarized the current literature on the effect of MGO on the different cell types forming the BBB. BBB damage by MGO most likely occurs in brain endothelial cells and mural cells, while astrocytes are most resistant to MGO. Microglia on the other hand appear to be not directly influenced by MGO but rather produce MGO upon activation. Although there is clear evidence that MGO affects components of the BBB, the impact of MGO on the BBB as a multicellular system warrants further investigation. Diminishing MGO stress can potentially form the basis for new treatment strategies for maintaining optimal brain function.

The process of methylglyoxal-induced retinal capillary endothelial cell degeneration in rats

Methylglyoxal, a highly reactive dicarbonyl compound, is increased and accumulated in patients with diabetic mellitus. Methylglyoxal forms advanced glycation end products (AGE), contributing to the pathogenesis of diabetic complications, including diabetic retinopathy. Recent studies have shown that methylglyoxal induces diabetic retinopathy-like abnormalities in retinal vasculature. In this study, we investigated the processes and mechanisms of methylglyoxal-induced retinal capillary endothelial cell degeneration in rats. Morphological changes in vascular components (endothelial cells, pericytes, and basement membranes) were assessed in the retinas 2, 7, and 14 days after intravitreal injection of methylglyoxal. Intravitreal methylglyoxal injection induced retinal capillary endothelial cell degeneration in a dose- and time-dependent manner. Changes in the shape and distribution of pericytes occurred before the initiation of capillary regression in the retinas of methylglyoxal-injected eyes. The receptor for AGEs (RAGEs) antagonist FPS-ZM1, and the matrix metalloproteinase (MMP) inhibitor GM6001 significantly attenuated methylglyoxal-induced capillary endothelial cell degeneration. FPS-ZM1 failed to prevent pathological changes in pericytes in methylglyoxal-injected eyes. In situ zymography revealed that MMP activity was enhanced at sites of blood vessels with reduced pericyte coverage in methylglyoxal-injected eyes. These results suggest that intravitreal methylglyoxal injection induces pathological changes in pericytes before the initiation of capillary endothelial cell degeneration via an AGE-RAGE-independent pathway. The capillary endothelial cell degeneration is mediated by activating the AGE-RAGE pathway and increasing MMP activity in endothelial cells by impairing pericyte function in the retina.

Glycolaldehyde induces synergistic effects on vascular inflammation in TNF-α-stimulated vascular smooth muscle cells

Atherosclerosis is a chronic inflammatory disease that contributes to disease progression is associated with the expression of adhesion molecules in vascular smooth muscle cells (VSMCs). Glycolaldehyde (GA) has been shown to impair cellular function in various disorders, including diabetes, and renal diseases. This study investigated the effect of GA on the expression of adhesion molecules in the mouse VSMC line, MOVAS-1. Co-incubation of VSMCs with GA (25–50 μM) dose-dependently increased the protein and mRNA level of Vcam-1 and ICAM-1. Additionally, GA upregulated intracellular ROS production and phosphorylation of MAPK and NK-κB. GA also elevated TNF-α-induced PI3K-AKT activation. Furthermore, GA enhanced TNF-α-activated IκBα kinase activation, subsequent IκBα degradation, and nuclear translocation of NF-κB. These findings suggest that GA stumulated VSMC adhesive capacity and the induction of VCAM-1 and ICAM-1 in VSMCs through inhibition of MAPK and NF-κB signaling pathways, providing insights into the effect of GA to induce inflammation within atherosclerotic lesions.

Methylglyoxal and high glucose inhibit VEGFR2 phosphorylation at specific tyrosine residues

Diabetes is characterized by hyperglycemia and a significant risk of vascular complications. Vascular endothelial growth factor (VEGF) and its main receptor VEGFR2 (KDR), which is highly expressed in vascular endothelial cells, are essential mediators of vascular maintenance and angiogenesis. During glycolysis after high calorie food intake, methylglyoxal (MGO) is formed and MGO blood levels are elevated in diabetes. MGO reacts with arginine residues to generate MG-H1 or with lysine residues to carboxyethyl lysine which are common components of advanced glycation end-products. Therefore, the question arises whether hyperglycemic conditions affect VEGF signaling via a ligand-independent direct modification of signaling components. As a first step, the effect of MGO on VEGFR2 activation was investigated in cultured endothelial cells from human umbilical vein by determination of VEGFR2 phosphorylation at selected tyrosine residues by ELISA and immunoblotting using phospho-specific antibodies. Phosphorylation of VEGFR2-Y996, VEGFR2-Y1054, or VEGFR2-Y1175 reached a maximum 5 min after stimulation of endothelial cells with VEGF. Phosphorylation was significantly inhibited by 100 µM MGO and to a lesser extent by high glucose treatment. 2,3-Pentanedione and glyoxal were investigated for comparison. In summary, VEGFR2 phosphorylation is sensitive to MGO or high glucose concentrations which may be relevant in the pathophysiology of microvascular disease in diabetes.

Glycation of Tie-2 Inhibits Angiopoietin-1 Signaling Activation and Angiopoietin-1-Induced Angiogenesis

The impairment of the angiopoietin-1 (Ang-1)/Tie-2 signaling pathway has been thought to play a critical role in diabetic complications. However, the underlying mechanisms remain unclear. The present study aims to investigate the effects of Tie-2 glycation on Ang-1 signaling activation and Ang-1-induced angiogenesis. We identified that Tie-2 was modified by advanced glycation end products (AGEs) in aortae derived from high fat diet (HFD)-fed mice and in methylglyoxal (MGO)-treated human umbilical vein endothelial cells (HUVECs). MGO-induced Tie-2 glycation significantly inhibited Ang-1-evoked Tie-2 and Akt phosphorylation and Ang-1-regulated endothelial cell migration and tube formation, whereas the blockade of AGE formation by aminoguanidine remarkably rescued Ang-1 signaling activation and Ang-1-induced angiogenesis in vitro. Furthermore, MGO treatment markedly increased AGE cross-linking of Tie-2 in cultured aortae ex vivo and MGO-induced Tie-2 glycation also significantly decreased Ang-1-induced vessel outgrow from aortic rings. Collectively, these data suggest that Tie-2 may be modified by AGEs in diabetes mellitus and that Tie-2 glycation inhibits Ang-1 signaling activation and Ang-1-induced angiogenesis. This may provide a novel mechanism for Ang-1/Tie-2 signal dysfunction and angiogenesis failure in diabetic ischaemic diseases.

Modification of Fibronectin by Non-Enzymatic Glycation Impairs K+ Channel Function in Rat Cerebral Artery Smooth Muscle Cells

Fibronectin (FN) enhances K+ channel activity by integrin-mediated mechanisms. As vascular smooth muscle (VSM) K+ channels mediate vasodilation, we hypothesized that modification of fibronectin, via advanced non-enzymatic glycation, would alter signaling of this extracellular matrix protein through these channels. Bovine FN (1 mg/ml) was glycated (gFN) for 5 days using methylglyoxal (50 mM), and albumin was similarly glycated as a non-matrix protein control. VSM cells were isolated from rat cerebral arteries for measurement of macroscopic K+ channel activity using whole cell patch clamp methodology. Pharmacological inhibitors, iberiotoxin (0.1 μM) and 4-aminopyridine (0.1 mM), were used to identify contributions of large-conductance, Ca2+-activated, K+ channels and voltage-gated K+ channels, respectively. Compared with baseline, native FN enhanced whole cell K+ current in a concentration-dependent manner, whereas gFN inhibited basal current. Furthermore, native albumin did not enhance basal K+ current, but the glycated form (gAlb) caused inhibition. gFN was shown to impair both the Kv and BKCa components of total macroscopic K+ current. Anti-integrin α5 and β1 antibodies attenuated the effects of both FN and gFN on macroscopic K+ current at +70 mV. Consistent with an action on BKCa activity, FN increased, whereas gFN decreased the frequency of spontaneous transient outward current (STOCs). In contrast, gAlb inhibited whole cell K+ current predominantly through Kv, showing little effect on STOCs. A function-blocking, anti-RAGE antibody partially reversed the inhibitory effects of gFN, suggesting involvement of this receptor. Further, gFN caused production of reactive oxygen species (ROS) by isolated VSMCs as revealed by the fluorescent indicator, DHE. Evoked ROS production was attenuated by the RAGE blocking antibody. Collectively, these studies identify ion channel-related mechanisms (integrin and ROS-mediated) by which protein glycation may modify VSMC function.

Acyclovir alleviates insulin resistance via activating PKM1 in diabetic mice

AIMS

Diabetes mellitus (DM) is a major global health threat characterized by insulin resistance. A new tactic to ameliorate insulin resistance, thereby reversing the exacerbation of DM, is urgently needed. The work is aiming to provide a new strategy for DM treatment as well as to identify new targets.

MAIN METHODS

C57BL/6 N mice were raised with high-fat diet (HFD) and infused with streptozotocin (STZ) to induce diabetes. The blood glucose, serum insulin, blood lipid and oxidative stress were detected. In vitro insulin resistance model experiment has been made to examine the molecular mechanisms underlying anti-diabetic effect of potential active chemicals in human hepatocellular carcinoma cells (HepG2).

KEY FINDINGS

Acyclovir, an antiviral nucleotide analog, alleviates insulin resistance by reducing blood lipids as well as oxidative stress and elevating insulin sensitivity on diabetic mice, which is in accord with results in the insulin resistance model of HepG2 cells. Mechanically, acyclovir stimulates pyruvate kinase M1 (PKM1) directly to activate adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)/Sirtuin1 (SIRT1) signaling pathway, thus improving insulin resistance.

SIGNIFICANCE

The present study supports that acyclovir should be translated to remedy DM, and PKM1 might be a valuable target to develop new medicines.

Methylglyoxal reduces molecular responsiveness to 4 weeks of endurance exercise in mouse plantaris muscle

Endurance exercise triggers skeletal muscle adaptations, including enhanced insulin signaling, glucose metabolism, and mitochondrial biogenesis. However, exercise-induced skeletal muscle adaptations may not occur in some cases, a condition known as exercise-resistance. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite and has detrimental effects on the body such as causing diabetic complications, mitochondrial dysfunction, and inflammation. This study aimed to clarify the effect of methylglyoxal on skeletal muscle molecular adaptations following endurance exercise. Mice were randomly divided into 4 groups (n = 12 per group): sedentary control group, voluntary exercise group, MG-treated group, and MG-treated with voluntary exercise group. Mice in the voluntary exercise group were housed in a cage with a running wheel, while mice in the MG-treated groups received drinking water containing 1% MG. Four weeks of voluntary exercise induced several molecular adaptations in the plantaris muscle, including increased expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α), mitochondria complex proteins, toll-like receptor 4 (TLR4), 72-kDa heat shock protein (HSP72), hexokinase II, and glyoxalase 1; this also enhanced insulin-stimulated Akt Ser⁴⁷³ phosphorylation and citrate synthase activity. However, these adaptations were suppressed with MG treatment. In the soleus muscle, the exercise-induced increases in the expression of TLR4, HSP72, and advanced glycation end products receptor 1 were inhibited with MG treatment. These findings suggest that MG is a factor that inhibits endurance exercise-induced molecular responses including mitochondrial adaptations, insulin signaling activation, and the upregulation of several proteins related to mitochondrial biogenesis, glucose handling, and glycation in primarily fast-twitch skeletal muscle.

Diabetes Impaired Ischemia-Induced PDGF (Platelet-Derived Growth Factor) Signaling Actions and Vessel Formation Through the Activation of Scr Homology 2-Containing Phosphatase-1

Objective

Critical limb ischemia is a major complication of diabetes characterized by insufficient collateral vessel development and proper growth factor signaling unresponsiveness. Although mainly deactivated by hypoxia, phosphatases are important players in the deregulation of proangiogenetic pathways. Previously, SHP-1 (Scr homology 2-containing phosphatase-1) was found to be associated with the downregulation of growth factor actions in the diabetic muscle. Thus, we aimed to gain further understanding of the impact of SHP-1 on smooth muscle cell (SMC) function under hypoxic and diabetic conditions.

Approach and Results

Despite being inactivated under hypoxic conditions, high glucose level exposure sustained SHP-1 phosphatase activity in SMC and increased its interaction with PDGFR (platelet-derived growth factor receptor)-β, thus reducing PDGF proangiogenic actions. Overexpression of an inactive form of SHP-1 fully restored PDGF-induced proliferation, migration, and signaling pathways in SMC exposed to high glucose and hypoxia. Nondiabetic and diabetic mice with deletion of SHP-1 specifically in SMC were generated. Ligation of the femoral artery was performed, and blood flow was measured for 4 weeks. Blood flow reperfusion, vascular density and maturation, and limb survival were all improved while vascular apoptosis was attenuated in diabetic SMC-specific SHP-1 null mice as compared to diabetic mice.

Conclusions

Diabetes and high glucose level exposure maintained SHP-1 activity preventing hypoxia-induced PDGF actions in SMC. Specific deletion of SHP-1 in SMC partially restored blood flow reperfusion in the diabetic ischemic limb. Therefore, local modulation of SHP-1 activity in SMC could represent a potential therapeutic avenue to improve the proangiogenic properties of SMC under ischemia and diabetes.

Growth Factor Deregulation and Emerging Role of Phosphatases in Diabetic Peripheral Artery Disease

Peripheral artery disease is caused by atherosclerosis of lower extremity arteries leading to the loss of blood perfusion and subsequent critical ischemia. The presence of diabetes mellitus is an important risk factor that greatly increases the incidence, the progression and the severity of the disease. In addition to accelerated disease progression, diabetic patients are also more susceptible to develop serious impairment of their walking abilities through an increased risk of lower limb amputation. Hyperglycemia is known to alter the physiological development of collateral arteries in response to ischemia. Deregulation in the production of several critical pro-angiogenic factors has been reported in diabetes along with vascular cell unresponsiveness in initiating angiogenic processes. Among the multiple molecular mechanisms involved in the angiogenic response, protein tyrosine phosphatases are potent regulators by dephosphorylating pro-angiogenic tyrosine kinase receptors. However, evidence has indicated that diabetes-induced deregulation of phosphatases contributes to the progression of several micro and macrovascular complications. This review provides an overview of growth factor alterations in the context of diabetes and peripheral artery disease, as well as a description of the role of phosphatases in the regulation of angiogenic pathways followed by an analysis of the effects of hyperglycemia on the modulation of protein tyrosine phosphatase expression and activity. Knowledge of the role of phosphatases in diabetic peripheral artery disease will help the development of future therapeutics to locally regulate phosphatases and improve angiogenesis.

Antiglycative and anti-inflammatory effects of lipophilized tyrosol derivatives

Abstract

To expand the application of tyrosol, a series of lipophilized tyrosol derivatives were synthesized via esterification of tyrosol with fatty acids of different chain lengths. The antiglycative activity of tyrosol esters so prepared was subsequently examined in the bovine serum albumin/glucose system. A quasi-parabolic shape was observed when the activity was plotted against alkyl chain length. Additionally, the anti-inflammatory effects of these derivatives were evaluated against methylglyoxal-induced inflammation in RAW264.7 cells. The same trend on anti-inflammatory activity was found as in the antiglycation study. The results showed that tyrosol esters with C12:0 and C14:0 were two most efficient ones among all the tested derivatives. Thus, some lipophilized tyrosol derivatives were stronger antiglycative and anti-inflammatory agents compared to the parent compound, tyrosol.

Graphical abstract

CD44, a Predominant Protein in Methylglyoxal-Induced Secretome of Muscle Cells, is Elevated in Diabetic Plasma

Methylglyoxal (MG), a glycolytic intermediate and reactive dicarbonyl, is responsible for exacerbation of insulin resistance and diabetic complication. In this study, MG-induced secretome of rat muscle cells was identified and relatively quantified by SWATH-MS. A total of 643 proteins were identified in MG-induced secretome, of which 82 proteins were upregulated and 99 proteins were downregulated by more than 1.3-fold in SWATH analysis. Further, secretory proteins from the classical secretory pathway and nonclassical secretory pathway were identified using SignalP and SecretomeP, respectively. A total of 180 proteins were identified with SignalP, and 113 proteins were identified with SecretomeP. The differentially expressed proteins were functionally annotated by KEGG pathway analysis using Cytoscape software with plugin clusterMaker. The differentially expressed proteins were found to be involved in various pathways like extracellular matrix (ECM)-receptor interaction, leukocyte transendothelial migration, fluid shear stress and atherosclerosis, complement and coagulation cascades, and lysosomal pathway. Since the MG levels are high in diabetic conditions, the presence of MG-induced secreted proteins was inspected by profiling human plasma of healthy and diabetic subjects (n = 10 each). CD44, a predominant MG-induced secreted protein, was found to be elevated in the diabetic plasma and to have a role in the development of insulin resistance.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Almond-supplemented diet improves sexual functions beyond Phosphodiesterase-5 inhibition in diabetic male rats

Hyperglycemia, an important feature of diabetes, can cause oxidative stress, which is associated with varieties of diabetic complications including erectile dysfunction. Therefore, this study sought to investigate the effect of almond-supplemented diet on some biochemical indices relevant to erection in diabetic male rats. Forty-two male rats were divided into two groups: A (n = 6) and B (n = 36). Diabetes was induced in Group B via injection of a single dose of STZ (50 mg/kg) intraperitoneally and confirmed 72 h after induction. Diabetic rats (blood glucose ≥250 mg/dL) were subsequently divided into six groups (n = 6). Fourteen days after confirmation of diabetes, rats were fed with diets containing almond drupe and seeds (10 and 20% inclusion) for fourteen days. The effects of the diets on blood glucose, sexual behavior, sexual hormones, phosphodiesterase-5 activity, nitric oxide, H₂S, and AGEs levels were evaluated. Significant increase in blood glucose level, phosphodiesterase-5 activity, and glycated hemoglobin was observed in diabetic rats. Furthermore, diabetes caused a significant decrease in nitric oxide, H₂S, sexual hormones (testosterone, follicle-stimulating hormone and luteinizing hormone) levels, and sexual behavioral indices. However, treatment with diets supplemented with almond drupe and seeds significantly reversed these effects in diabetic rats. Findings in this study revealed that almond-supplemented diets enhance some important biomarkers relevant to erection in diabetic rats. Thus, dietary inclusion of almond (drupe and seeds) could serve as a cheap and readily available nutraceutical in the management of erectile dysfunction associated with diabetes.

Alr2321, a multiple stress inducible glyoxalase I of Anabaena sp. PCC7120 detoxifies methylglyoxal and reactive species oxygen

Abiotic stresses enhance the cellular level of reactive oxygen species (ROS) which consequently leads to toxic methylglyoxal (MG) production. Glyoxalases (GlyI & GlyII) catalyze the conversion of toxic MG into non-toxic lactic acid but their properties and functions have been overlooked in cyanobacteria. This is the first attempt to conduct a genome-wide analysis of GlyI protein (PF00903) from Anabaena sp. PCC7120. Out of total nine GlyI domain possessing proteins, only three (Alr2321, Alr4469, All1022) harbour conserve His/Glu/His/Glu metal binding site at their homologous position and are deficient in conserved region specific for Zn²⁺ dependent members. Their biochemical, structural and functional characterization revealed that only Alr2321 is a homodimeric Ni²⁺ dependent active GlyI with catalytic efficiency 11.7 × 10⁶ M^-1 s^-1. It has also been found that Alr2321 is activated by various divalent metal ions and has maximum GlyI activity with Ni²⁺ followed by Co²⁺ > Mn²⁺ > Cu²⁺ and no activity with Zn^2+. Moreover, the expression of alr2321 was found to be maximally up-regulated under heat (19 fold) followed by cadmium, desiccation, arsenic, salinity and UV-B stresses. BL21/pGEX-5X2-alr2321 showed improved growth under various abiotic stresses as compared to BL21/pGEX-5X2 by increased scavenging of intracellular MG and ROS levels. Taken together, these results suggest noteworthy links between intracellular MG and ROS, its detoxification by Alr2321, a member of GlyI family of Anabaena sp. PCC7120, in relation to abiotic stress.

Inhibition of Glyoxalase-I Leads to Reduced Proliferation, Migration and Colony Formation, and Enhanced Susceptibility to Sorafenib in Hepatocellular Carcinoma

Background: Glyoxalase-I (Glo-I) is essential for detoxification of methylglyoxal (MGO), a byproduct of glycolysis. Overexpression of Glo-I has been linked to multi-drug resistance in cancer therapy. The aim of this study was to analyze Glo-I in hepatocellular carcinoma (HCC) and the effect of the multi-tyrosine kinase inhibitor sorafenib on Glo-I. Methods: Expression and specific activity of Glo-I was measured in human HCC samples, HCC-cell lines (HepG2, Huh7) and a hepatocyte cell line (AML 12). Cells were either treated with Glo-I inhibitors, ethyl pyruvate (EP, 1-20 mM) and BrBzGSHCp2 (1-10 μM), or sorafenib (2.5-10 μM) and protein expression (Western Blot), proliferation (WST-assay), migration (scratch assay), and colony formation (clonogenic assay) were assessed. Results: High expression of Glo-I was detected in human HCC tissue samples. Huh7 showed highest expression and activity of Glo-I and revealed highest proliferation compared to AML 12 and HepG2. Targeting Glo-I by EP or BrBzGSHCp₂ led to significantly reduced proliferation (20 mM EP 24 h: 57 ± 12%), migration and colony formation. Glo-I inhibition by 20 mM EP resulted in reduced expression of PDGFR-β (18 ± 10%), VEGFR2 (46 ± 11%), VEGF (61 ± 10%), pERK/ERK (62 ± 6%), NF-κB (44 ± 12%) as well as stimulation of Nrf2 (243 ± 36%). Similar results were seen with BrBzGSHCp2. Sorafenib treatment revealed elevation of Glo-I (10 μM: 209 ± 25%) and MGO. Co-treatment of EP and sorafenib led to an additional reduction of proliferation compared to sorafenib alone. Conclusion: Glo-I is positively correlated with HCC proliferation. Inhibition of Glo-I reduced proliferation, migration, and colony formation. In turn, sorafenib increases Glo-I. Co-treatment using Glo-I inhibitors could enhance susceptibility of HCC to sorafenib.

Methylglyoxal, a potent inducer of AGEs, connects between diabetes and cancer

Diabetes is one of the most frequent diseases throughout the world and its incidence is predicted to exponentially progress in the future. This metabolic disorder is associated with major complications such as neuropathy, retinopathy, atherosclerosis, and diabetic nephropathy, the severity of which correlates with hyperglycemia, suggesting that they are triggered by high glucose condition. Reducing sugars and reactive carbonyl species such as methylglyoxal (MGO) lead to glycation of proteins, lipids and DNA and the gradual accumulation of advanced glycation end products (AGEs) in cells and tissues. While AGEs are clearly implicated in the pathogenesis of diabetes complications, their potential involvement during malignant tumor development, progression and resistance to therapy is an emerging concept. Meta-analysis studies established that patients with diabetes are at higher risk of developing cancer and show a higher mortality rate than cancer patients free of diabetes. In this review, we highlight the potential connection between hyperglycemia-associated AGEs formation on the one hand and the recent evidence of pro-tumoral effects of MGO stress on the other hand. We also discuss the marked interest in anti-glycation compounds in view of their strategic use to treat diabetic complications but also to protect against augmented cancer risk in patients with diabetes.

Expert curation for building network-based dynamical models: a case study on atherosclerotic plaque formation

Knowledgebases play an increasingly important role in scientific research, where the expert curation of biological knowledge in forms that are amenable to computational analysis (using ontologies for example)–provides a significant added value and enables new types of computational analyses for high throughput datasets. In this work, we demonstrate how expert curation can also play a more direct role in research, by supporting the use of network-based dynamical models to study a specific biological process. This curation effort is focused on the regulatory interactions between biological entities, such as genes or proteins and compounds, which may interact with each other in a complex manner, including regulatory complexes and conditional dependencies between co-regulators. This critical information has to be captured and encoded in a computable manner, which is currently far beyond the current capabilities of automatically constructed network. As a case study, we report here the prior knowledge network constructed by the sysVASC consortium to model the biological events leading to the formation of atherosclerotic plaques, during the onset of cardiovascular disease and discuss some specific examples to illustrate the main pitfalls and added value provided by the expert curation during this endeavor.

Database URL: http://biomodels.caltech.edu

Investigating the Glycating Effects of Glucose, Glyoxal and Methylglyoxal on Human Sperm

Glycation is the non-enzymatic reaction between reducing sugars, such as glucose, and proteins, lipids or nucleic acids, producing Advanced Glycation End (AGE) products. AGEs, produced during natural senescence as well as through lifestyle factors such as diet and smoking, are key pathogenic compounds in the initiation and progression of diabetes. Importantly, many of these factors and conditions also have influence on male fertility, affecting sperm count and semen quality, contributing to the decreasing trend in male fertility. This study investigated the impact of AGEs on sperm damage. In vitro sperm glycation assays were used to determine the levels and localization of the potent AGE compound, carboxymethyl-lysine (CML) in response to treatment with the glycating compounds glucose, glyoxal and methylglyoxal. Sperm function assays were then used to assess the effects of glycation on motility and hyaluronan binding, and levels of oxidative DNA damage were analyzed through measurement of the marker, 8-oxoguanine. Results showed that glyoxal, but not glucose or methylglyoxal, induced significant increases in CML levels on sperm and this correlated with an increase in 8-oxoguanine. Immunocytochemistry revealed that AGEs were located on all parts of the sperm cell and most prominently on the head region. Sperm motility and hyaluronidase activity were not adversely affected by glycation. Together, the observed detrimental effects of the increased levels of AGE on DNA integrity, without an effect on motility and hyaluronidase activity, suggest that sperm may retain some fertilizing capacity under these adverse conditions.

Manipulation of glyoxalase pathway confers tolerance to multiple stresses in rice

Crop plants face a multitude of diverse abiotic and biotic stresses in the farmers' fields. Although there now exists a considerable knowledge of the underlying mechanisms of response to individual stresses, the crosstalk between response pathways to various abiotic and biotic stresses remains enigmatic. Here, we investigated if the cytotoxic metabolite methylglyoxal (MG), excess of which is generated as a common consequence of many abiotic and biotic stresses, may serve as a key molecule linking responses to diverse stresses. For this, we generated transgenic rice plants overexpressing the entire two-step glyoxalase pathway for MG detoxification. Through assessment of various morphological, physiological and agronomic parameters, we found that glyoxalase-overexpression imparts tolerance towards abiotic stresses like salinity, drought and heat and also provides resistance towards damage caused by the sheath blight fungus (Rhizoctonia solani) toxin phenylacetic acid. We show that the mechanism of observed tolerance of the glyoxalase-overexpressing plants towards these diverse abiotic and biotic stresses involves improved MG detoxification and reduced oxidative damage leading to better protection of chloroplast and mitochondrial ultrastructure and maintained photosynthetic efficiency under stress conditions. Together, our findings indicate that MG may serve as a key link between abiotic and biotic stress response in plants.

Advanced glycation end (AGE) product modification of laminin downregulates Kir4.1 in retinal Müller cells

Diabetic retinopathy (DR) is a major cause of adult blindness. Retinal Müller cells maintain water homeostasis and potassium concentration via inwardly rectifying Kir4.1 channels. Accumulation of advanced glycation end products (AGEs) is a major pathologic event in DR. While diabetes leads to a decrease in the Kir4.1 channels, it remains unknown whether AGEs-linked to the basement membrane (BM) affect normal Kir4.1 channels. For this study, we hypothesized that AGE-modification of laminin is detrimental to Kir4.1 channels, therefore, disrupting Müller cell function. The AGE-modified laminin-coated substrates were prepared by incubating Petri-dishes with laminin and methylglyoxal for seven days. The rat Müller cells (rMC-1) were propagated on AGE-modified laminin, and Kir4.1 expression and function were evaluated. Quantification of AGEs using ELISA revealed a dose-dependent increase in methylglyoxal-hydro-imidazolone adducts. The rMC-1 propagated on AGE-modified laminin demonstrated a decrease in Kir4.1 levels in immunofluorescence and western blot studies and a decrease in the Kir4.1 channel function. Kir4.1 decrease on AGE-modified laminin resulted in a disorganization of an actin cytoskeleton and disruption of α-dystroglycan-syntrophin-dystrophin complexes. Our studies suggest that AGE-modification of laminin is detrimental to Kir4.1 channels. By studying the role of AGEs in Kir4.1 channels we have identified a novel mechanism of Müller cell dysfunction and its subsequent involvement in DR.

Glycation of human serum albumin impairs binding to the glucagon-like peptide-1 analogue liraglutide

The long-acting glucagon-like peptide-1 analogue liraglutide has proven efficiency in the management of type 2 diabetes and also has beneficial effects on cardiovascular diseases. Liraglutide's protracted action highly depends on its capacity to bind to albumin via its palmitic acid part. However, in diabetes, albumin can undergo glycation, resulting in impaired drug binding. Our objective in this study was to assess the impact of human serum albumin (HSA) glycation on liraglutide affinity. Using fluorine labeling of the drug and ¹⁹F NMR, we determined HSA affinity for liraglutide in two glycated albumin models. We either glycated HSA in vitro by incubation with glucose (G25- or G100-HSA) or methylglyoxal (MGO-HSA) or purified in vivo glycated HSA from the plasma of diabetic patients with poor glycemic control. Nonglycated commercial HSA (G0-HSA) and HSA purified from plasma of healthy individuals served as controls. We found that glycation decreases affinity for liraglutide by 7-fold for G100-HSA and by 5-fold for MGO-HSA compared with G0-HSA. A similarly reduced affinity was observed for HSA purified from diabetic individuals compared with HSA from healthy individuals. Our results reveal that glycation significantly impairs HSA affinity to liraglutide and confirm that glycation contributes to liraglutide's variable therapeutic efficiency, depending on diabetes stage. Because diabetes is a progressive disease, the effect of glycated albumin on liraglutide affinity found here is important to consider when diabetes is managed with this drug.

Pioglitazone Attenuates Atherosclerosis in Diabetic Mice by Inhibition of Receptor for Advanced Glycation End-Product (RAGE) Signaling

Background

Peroxisome proliferator-activated receptor-γ (PPAR-γ) exhibits anti-inflammatory and anti-diabetic properties, and is protective against cardiovascular diseases. This study aimed to determine the effects of a PPAR-γ agonist pioglitazone on atherogenesis in an ApoE knockout mouse (ApoE^−/−) diabetic mouse model and in a cultured vascular smooth muscle cells (VSMCs) model.

Material/Methods

Male ApoE^−/− mice were rendered diabetic by 5 daily intraperitoneal injections of streptozotocin. Pioglitazone (20 mg/kg/d) or PPAR-γ inhibitor GW9662 (1 mg/kg/d) were administered for 12 weeks. At the end of treatment, mice were killed and the aortae were isolated. Oil Red O staining was used to evaluate atherosclerotic plaque area. H&E staining was used to evaluate the number of complicated plaques. Western blotting and immunohistochemistry were used to determine the expression of advanced glycation end-products (RAGE) and PPAR-γ. The effects of pioglitazone and GW9662 on RAGE and PPAR-γ expression were examined in cultured primary mouse VSMCs in hyperglycemic conditions.

Results

Administration of pioglitazone in diabetic ApoE^−/− mice successfully reduced atherosclerotic plaque area and the number of complicated plaques. Moreover, pioglitazone inhibited RAGE and stimulated PPAR-γ protein expression in atherosclerotic plaques of diabetic ApoE^−/− mice. In cultured VSMCs upon high-glucose challenge, pioglitazone downregulated RAGE mRNA and protein expression. Blockade of PPAR-γ activity by GW9662 remarkably attenuated the inhibitory actions of pioglitazone on atherogenesis, both in diabetic ApoE^−/− mice and in cultured VSMCs, upon high-glucose challenge.

Conclusions

Pioglitazone has a therapeutic effect on atherosclerosis in diabetes, and inhibition of RAGE signaling plays a critical role in mediating the beneficial effects of pioglitazone.

Proatherogenic effects of 4-hydroxynonenal

4-hydroxy-2-nonenal (HNE) is a α,β-unsaturated hydroxyalkenal generated by peroxidation of n-6 polyunsaturated fatty acid. This reactive carbonyl compound exhibits a huge number of biological properties that result mainly from the formation of HNE-adducts on free amino groups and thiol groups in proteins. In the vascular system, HNE adduct accumulation progressively leads to cellular dysfunction and tissue damages that are involved in the progression of atherosclerosis and related diseases. HNE contributes to the atherogenicity of oxidized LDL, by forming HNE-apoB adducts that deviate the LDL metabolism to the scavenger receptor pathway of macrophagic cells, and lead to the formation of foam cells. HNE activates transcription factors (Nrf2, NF-kappaB) that (dys)regulate various cellular responses ranging from hormetic and survival signaling at very low concentrations, to inflammatory and apoptotic effects at higher concentrations. Among a variety of cellular targets, HNE can modify signaling proteins involved in atherosclerotic plaque remodeling, particularly growth factor receptors (PDGFR, EGFR), cell cycle proteins, mitochondrial and endoplasmic reticulum components or extracellular matrix proteins, which progressively alters smooth muscle cell proliferation, angiogenesis and induces apoptosis. HNE adducts accumulate in the lipidic necrotic core of advanced atherosclerotic lesions, and may locally contribute to macrophage and smooth muscle cell apoptosis, which may induce plaque destabilization and rupture, thereby increasing the risk of athero-thrombotic events.

Dual signaling evoked by oxidized LDLs in vascular cells

The oxidative theory of atherosclerosis relies on the modification of low density lipoproteins (LDLs) in the vascular wall by reactive oxygen species. Modified LDLs, such as oxidized LDLs, are thought to participate in the formation of early atherosclerotic lesions (accumulation of foam cells and fatty streaks), whereas their role in advanced lesions and atherothrombotic events is more debated, because antioxidant supplementation failed to prevent coronary disease events and mortality in intervention randomized trials. As oxidized LDLs and oxidized lipids are present in atherosclerotic lesions and are able to trigger cell signaling on cultured vascular cells and macrophages, it has been proposed that they could play a role in atherogenesis and atherosclerotic vascular remodeling. Oxidized LDLs exhibit dual biological effects, which are dependent on extent of lipid peroxidation, nature of oxidized lipids (oxidized phospholipids, oxysterols, malondialdehyde, α,β-unsaturated hydroxyalkenals), concentration of oxidized LDLs and uptake by scavenger receptors (e.g. CD36, LOX-1, SRA) that signal through different transduction pathways. Moderate concentrations of mildly oxidized LDLs are proinflammatory and trigger cell migration and proliferation, whereas higher concentrations induce cell growth arrest and apoptosis. The balance between survival and apoptotic responses evoked by oxidized LDLs depends on cellular systems that regulate the cell fate, such as ceramide/sphingosine-1-phosphate rheostat, endoplasmic reticulum stress, autophagy and expression of pro/antiapoptotic proteins. In vivo, the intimal concentration of oxidized LDLs depends on the influx (hypercholesterolemia, endothelial permeability), residence time and lipid composition of LDLs, oxidative stress intensity, induction of defense mechanisms (antioxidant systems, heat shock proteins). As a consequence, the local cellular responses to oxidized LDLs may stimulate inflammatory or anti-inflammatory pathways, angiogenic or antiangiogenic responses, survival or apoptosis, thereby contributing to plaque growth, instability, complication (intraplaque hemorrhage, proteolysis, calcification, apoptosis) and rupture. Finally, these dual properties suggest that oxLDLs could be implicated at each step of atherosclerosis development, from early fatty streaks to advanced lesions, depending on the nature and concentration of their oxidized lipid content.

A, Kazi RS, Banarjee R, Rathore R, MV V, HV T, Kumar Bhat M, MJ K. Methylglyoxal attenuates insulin signaling and downregulates the enzymes involved in cholesterol biosynthesis

Methylglyoxal (MG) is a highly reactive dicarbonyl known to be elevated under the hyperglycemic conditions of diabetes and is implicated in the development of diabetic complications.

Overexpression of a glyoxalase gene, OsGly I, improves abiotic stress tolerance and grain yield in rice (Oryza sativa L.)

Glyoxalase I (Gly I) is a component of the glyoxalase system which is involved in the detoxification of methylglyoxal, a byproduct of glycolysis. In the present study, a gene of rice (Oryza sativa L., cv. Nipponbare) encoding Gly I was cloned and characterized. The quantitative real-time PCR analysis indicated that rice Gly I (OsGly I) was ubiquitously expressed in root, stem, leaf, leaf sheath and spikelet with varying abundance. OsGly I was markedly upregulated in response to NaCl, ZnCl₂ and mannitol in rice seedlings. For further functional investigation, OsGly I was overexpressed in rice using Agrobacterium-mediated transformation. Transgenic rice lines exhibited increased glyoxalase enzyme activity, decreased methylglyoxal level and improved tolerance to NaCl, ZnCl₂ and mannitol compared to wild-type plants. Enhancement of stress tolerance in transgenic lines was associated with reduction of malondialdehyde content which was derived from cellular lipid peroxidation. In addition, the OsGly I-overexpression transgenic plants performed higher seed setting rate and yield. Collectively, these results indicate the potential of bioengineering the Gly I gene in crops.

Trapping Methylglyoxal by Genistein and Its Metabolites in Mice

Increasing evidence supports dicarbonyl stress such as methylglyoxal (MGO) as one of the major pathogenic links between hyperglycemia and diabetic complications. In vitro studies have shown that dietary flavonoids can inhibit the formation of advanced glycation end products (AGEs) by trapping MGO. However, whether flavonoids can trap MGO in vivo and whether biotransformation limits the trapping capacity of flavonoids remain virtually unknown. In this study, we investigated whether genistein (GEN), the major soy isoflavone, could trap MGO in mice by promoting the formation of MGO adducts of GEN and its metabolites. Two different mouse studies were conducted. In the acute study, a single dose of MGO and GEN were administered to mice via oral gavage. In the chronic study, MGO was given to mice in drinking water for 1 month and then GEN was given to mice for 4 consecutive days via oral gavage. Two mono-MGO adducts of GEN and six mono-MGO adducts of GEN phase I and microbial metabolites were identified in mouse urine samples from these studies using liquid chromatography/electrospray ionization tandem mass spectrometry. The structures of these MGO adducts were confirmed by analyzing their MS(n) (n = 1-4) spectra as well as by comparing them with the tandem mass spectra of authentic standards. All of the MGO adducts presented in their phase II conjugated forms in mouse urine samples in the acute and chronic studies. To our knowledge, this is the first in vivo evidence to demonstrate the trapping efficacy of GEN in mice and to show that the metabolites of GEN remain bioactive.

RAGE axis in neuroinflammation, neurodegeneration and its emerging role in the pathogenesis of amyotrophic lateral sclerosis

RAGE, the receptor of advanced glycation end-products, is thought to be one of the potential contributors to the neurodegeneration. It has been shown that RAGE activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines. RAGE involvement has been documented in the pathogenesis of a number of neurodegenerative diseases such amyotrophic lateral sclerosis (ALS), Alzheimer's, Parkinson's, Huntington's, Creutzfeld-Jakob' diseases and various neurodegenerative conditions such as diabetic neuropathy, familial amyloid polyneuropathy, Charcot neuroarthropathy and vasculitic neuropathy. Although the detailed mechanisms of RAGE contribution to the neurodegeneration remains unclear, studies indicate that RAGE detrimental actions are exerted via its binding to the pro-inflammatory ligands such as advanced glycation end-products, S100/calgranulin and amphoterin and subsequent activation of downstream regulatory pathways such as NF-κB, STAT and JKN pathways. Here, in this review we attempt to shed light onto molecular events and pathological pathways involved in neuroinflammation, neurodegeneration and its emerging role in the pathogenesis of amyotrophic lateral sclerosis (ALS)--a progressive and fatal neurodegenerative disorder, summarizing current knowledge and the prospect of RAGE in the pathogenesis of this disastrous disease.

Mechanisms of distal axonal degeneration in peripheral neuropathies

Peripheral neuropathy is a common complication of a variety of diseases and treatments, including diabetes, cancer chemotherapy, and infectious causes (HIV, hepatitis C, and Campylobacter jejuni). Despite the fundamental difference between these insults, peripheral neuropathy develops as a combination of just six primary mechanisms: altered metabolism, covalent modification, altered organelle function and reactive oxygen species formation, altered intracellular and inflammatory signaling, slowed axonal transport, and altered ion channel dynamics and expression. All of these pathways converge to lead to axon dysfunction and symptoms of neuropathy. The detailed mechanisms of axon degeneration itself have begun to be elucidated with studies of animal models with altered degeneration kinetics, including the slowed Wallerian degeneration (Wld(S)) and Sarm knockout animal models. These studies have shown axonal degeneration to occur through a programmed pathway of injury signaling and cytoskeletal degradation. Insights into the common disease insults that converge on the axonal degeneration pathway promise to facilitate the development of therapeutics that may be effective against other mechanisms of neurodegeneration.

Methylglyoxal, a reactive glucose metabolite, enhances autophagy flux and suppresses proliferation of human retinal pigment epithelial ARPE-19 cells

Methylglyoxal (MGO), a glycolytic metabolite, induces oxidative injury and apoptotic cell death that play a pathogenetic role in age-related macular degeneration (AMD). This study examined the impact of MGO on cell proliferation and autophagy flux in retinal pigment epithelium (RPE) ARPE-19 cells and elucidated the underlying mechanism. Short-term MGO exposure suppressed cell proliferation without induction of apoptotic cell death, increased production of reactive oxygen species, and potentiated H2O2-exhibited cytotoxicity in ARPE-19 cells. Conversely, pretreatment with N-acetylcysteine, a ROS scavenger, and aminoguanidine, an MGO blocker, prevented MGO-induced growth retardation. MGO significantly enhanced autophagy flux and increased intracellular accumulation of autophagosomes, which was functionally confirmed by addition of autophagy enhancer or inhibitors. Signaling kinetic observation indicated that MGO remarkably triggered phosphorylation of Akt, ERK1/2, p38 MAPK, and JNK1/2. Blockade of kinase activity demonstrated that the hyperphosphorylation of Akt, ERK1/2, JNK, and p38 MAPK were all involved in the MGO-enhanced autophagy and growth-arresting effect in ARPE-19 cells. Moreover, pretreatment with autophagic flux inhibitors including 3-methyladenine, bafilomycin A, and chloroquine effectively ameliorated MGO- but not H2O2-mediated ARPE-19 cytotoxicity. In conclusion, modulation of autophagy flux activity by using autophagic or kinase inhibitors may be an applicable modality to treat AMD.

The role of methylglyoxal and the glyoxalase system in diabetes and other age-related diseases

The formation and accumulation of advanced glycation endproducts (AGEs) are related to diabetes and other age-related diseases. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is the major precursor in the formation of AGEs. MGO is mainly formed as a byproduct of glycolysis. Under physiological circumstances, MGO is detoxified by the glyoxalase system into D-lactate, with glyoxalase I (GLO1) as the key enzyme in the anti-glycation defence. New insights indicate that increased levels of MGO and the major MGO-derived AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1), and dysfunctioning of the glyoxalase system are linked to several age-related health problems, such as diabetes, cardiovascular disease, cancer and disorders of the central nervous system. The present review summarizes the mechanisms through which MGO is formed, its detoxification by the glyoxalase system and its effect on biochemical pathways in relation to the development of age-related diseases. Although several scavengers of MGO have been developed over the years, therapies to treat MGO-associated complications are not yet available for application in clinical practice. Small bioactive inducers of GLO1 can potentially form the basis for new treatment strategies for age-related disorders in which MGO plays a pivotal role.

Fatty acid synthase cooperates with glyoxalase 1 to protect against sugar toxicity

Fatty acid (FA) metabolism is deregulated in several human diseases including metabolic syndrome, type 2 diabetes and cancers. Therefore, FA-metabolic enzymes are potential targets for drug therapy, although the consequence of these treatments must be precisely evaluated at the organismal and cellular levels. In healthy organism, synthesis of triacylglycerols (TAGs)—composed of three FA units esterified to a glycerol backbone—is increased in response to dietary sugar. Saturation in the storage and synthesis capacity of TAGs is associated with type 2 diabetes progression. Sugar toxicity likely depends on advanced-glycation-end-products (AGEs) that form through covalent bounding between amine groups and carbonyl groups of sugar or their derivatives α-oxoaldehydes. Methylglyoxal (MG) is a highly reactive α-oxoaldehyde that is derived from glycolysis through a non-enzymatic reaction. Glyoxalase 1 (Glo1) works to neutralize MG, reducing its deleterious effects. Here, we have used the power of Drosophila genetics to generate Fatty acid synthase (FASN) mutants, allowing us to investigate the consequence of this deficiency upon sugar-supplemented diets. We found that FASN mutants are lethal but can be rescued by an appropriate lipid diet. Rescued animals do not exhibit insulin resistance, are dramatically sensitive to dietary sugar and accumulate AGEs. We show that FASN and Glo1 cooperate at systemic and cell-autonomous levels to protect against sugar toxicity. We observed that the size of FASN mutant cells decreases as dietary sucrose increases. Genetic interactions at the cell-autonomous level, where glycolytic enzymes or Glo1 were manipulated in FASN mutant cells, revealed that this sugar-dependent size reduction is a direct consequence of MG-derived-AGE accumulation. In summary, our findings indicate that FASN is dispensable for cell growth if extracellular lipids are available. In contrast, FA-synthesis appears to be required to limit a cell-autonomous accumulation of MG-derived-AGEs, supporting the notion that MG is the most deleterious α-oxoaldehyde at the intracellular level.

Consumption of sugar and lipid (fat) enriched food increases the risk of developing metabolic diseases and cancers. However, lipids are essential molecules for life, as they are the major components of cell membranes. Metabolism refers to biochemical reactions that transform nutrients into molecules required by an organism, although toxic by-products can also formed. Sugars or their derivatives are likely to induce toxic effects by forming stable conjugates with proteins. To neutralize their toxic potential, sugars are metabolized and stored as fat. Here, we have used the fruitfly model to investigate the consequences of lipogenesis deficiency upon ingestion of sugar-enriched diets. We show that lipogenesis deficient animals are dramatically sensitive to dietary sugar. Further, we have identified the sugar by-product responsible for intracellular toxicity, in the context of lipogenesis inhibition. Our study reveals that inhibiting lipogenesis does not disrupt cellular growth if extracellular lipids are available. In contrast lipogenesis inhibition may have deleterious consequences due to accumulation of toxic by-products. The efficacy of lipogenic inhibitors in fighting cancers and metabolic diseases is currently under investigation. Therefore, to evaluate the clinical benefit of these inhibitors, accumulation of the toxic molecules should be monitored in both sick and healthy cells.

Beneficial effects of platelet-derived growth factor on hemorrhagic shock in rats and the underlying mechanisms

Studies have shown that local application of platelet-derived growth factor (PDGF) can be used for the treatment of acute and chronic wounds. We investigated if systemic application of PDGF has a protective effect on acute hemorrhagic shock in rats in the present study. Using hemorrhagic shock rats and isolated superior mesenteric arteries, the effects of PDGF-BB on hemodynamics, animal survival, and vascular reactivity as well as the roles of the gap junction proteins connexin (Cx)40 and Cx43, PKC, and Rho kinase were observed. PDGF-BB (1–15 μg/kg iv) significantly improved the hemodynamics and blood perfusion to vital organs (liver and kidney) as well as vascular reactivity and improved the animal survival in hemorrhagic shock rats. PDGF recovering shock-induced vascular hyporeactivity depended on the integrity of the endothelium and myoendothelial gap junction. Cx43 antisense oligodeoxynucleotide abolished these improving effects of PDGF, whereas Cx40 oligodeoxynucleotide did not. Further study indicated that PDGF increased the activity of Rho kinase and PKC as well as vascular Ca2+ sensitivity, whereas it did not interfere with the intracellular Ca2+ concentration in hypoxia-treated vascular smooth muscle cells. In conclusion, systemic application of PDGF-BB may exert beneficial effects on hemorrhagic shock, which are closely related to the improvement of vascular reactivity and hemodynamics. The improvement of PDGF-BB in vascular reactivity is vascular endothelium and myoendothelial gap junction dependent. Cx43, Rho kinase, and PKC play very important role in this process. These findings suggest that PDGF may be a potential measure to treat acute clinical critical diseases such as severe trauma, shock, and sepsis.

PDGF-BB does not accelerate healing in diabetic mice with splinted skin wounds

Topical application of platelet-derived growth factor-BB (PDGF-BB) is considered to accelerate tissue repair of impaired chronic wounds. However, the vast literature is plagued with conflicting reports of its efficacy in animal models and this is often influenced by a wide array of experimental variables making it difficult to compare the results across the studies. To mitigate the confounding variables that influence the efficacy of topically applied PDGF-BB, we used a controlled full thickness splinted excisional wound model in db/db mice (type 2 diabetic mouse model) for our investigations. A carefully-defined silicone-splinted wound model, with reduced wound contraction, controlled splint and bandage maintenance, allowing for healing primarily by reepithelialization was employed. Two splinted 8 mm dorsal full thickness wounds were made in db/db mice. Wounds were topically treated once daily with either 3 µg PDGF-BB in 30 µl of 5% PEG-PBS vehicle or an equal volume of vehicle for 10 days. Body weights, wound contraction, wound closure, reepithelialization, collagen content, and wound bed inflammation were evaluated clinically and histopathologically. The bioactivity of PDGF-BB was confirmed by in vitro proliferation assay. PDGF-BB, although bioactive in vitro, failed to accelerate wound healing in vivo in the db/db mice using the splinted wound model. Considering that the predominant mechanism of wound healing in humans is by re-epeithelialization, the most appropriate model for evaluating therapeutics is one that uses splints to prevent excessive wound contraction. Here, we report that PDGF-BB does not promote wound closure by re-epithelialization in a murine splinted wound model. Our results highlight that the effects of cytoactive factors reported in vivo ought to be carefully interpreted with critical consideration of the wound model used.

Impairment of aldehyde dehydrogenase-2 by 4-hydroxy-2-nonenal adduct formation and cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin

Reactive aldehydes such as 4-hydroxy-2-nonenal (4HNE) are generated in the myocardium in cardiac disease. 4HNE and other toxic aldehydes form adducts with proteins, leading to cell damage and organ dysfunction. Aldehyde dehydrogenases (ALDHs) metabolize toxic aldehydes such as 4HNE into nontoxic metabolites. Both ALDH levels and activity are reduced in cardiac disease. We examined whether reduced ALDH2 activity contributes to cardiomyocyte hypertrophy in mice fed a high-fat diet and injected with low-dose streptozotocin (STZ). These mice exhibited most of the characteristics of metabolic syndrome/type-2 diabetes mellitus (DM): increased blood glucose levels depicting hyperglycemia (415.2 ± 18.7 mg/dL vs. 265.2 ± 7.6 mg/dL; P < 0.05), glucose intolerance with normal plasma insulin levels, suggesting insulin resistance and obesity as evident from increased weight (44 ± 3.1 vs. 34.50 ± 1.32 g; P < 0.05) and body fat. Myocardial ALDH2 activity was 60% lower in these mice (0.1 ± 0.012 vs. 0.04 ± 0.015 µmol/min/mg protein; P < 0.05). Myocardial 4HNE levels were also elevated in the hyperglycemic hearts. Co-immunoprecipitation study showed that 4HNE formed adducts on myocardial ALDH2 protein in the mice exhibiting metabolic syndrome/type-2 DM, and they had obvious cardiac hypertrophy compared with controls as evident from increased heart weight (HW), HW to tibial length ratio, left ventricular (LV) mass and cardiomyocyte hypertrophy. Cardiomyocyte hypertrophy was correlated inversely with ALDH2 activity (R (2 )= 0.7; P < 0.05). Finally, cardiac dysfunction was observed in mice with metabolic syndrome/type-2 DM. Therefore, we conclude that reduced ALDH2 activity may contribute to cardiac hypertrophy and dysfunction in mice presenting with some of the characteristics of metabolic syndrome/type-2 DM when on a high-fat diet and low-dose STZ injection.

A vascular piece in the puzzle of adipose tissue dysfunction: mechanisms and consequences

In the last years, several studies unravelled many aspects of adipose tissue pathophysiology in metabolic diseases. Some studies suggested hypoxia as one of such aspects, despite the exact mechanisms and pathophysiological significance is still partially unknown. Adipose tissue was shown to be hypoxic in obesity, mainly resulting from adipocyte hypertrophy, leading to increased activation of inflammatory pathways. In animal and cell models, hypoxia-induced inflammation was shown to lead to endocrine alterations and dysmetabolism. However, recent evidences suggest that instead of a simple low oxygenation theory, adipose tissue microvasculature may be regulated by a series of factors, including vasoactive factors like angiotensin II, angiogenesis and glycation, among others. This review summarizes the current knowledge about the role of these factors in the regulation of adipose tissue irrigation and the functional consequences of adipose tissue microvascular dysfunction.