Pyridinium-carbaldehyde: active Maillard reaction product from the reaction of hexoses with lysine residues

Besides the formation of the aminotriazine N6-[4-(3-amino-1,2,4-triazin-5-yl)-2,3-dihydroxybutyl]-L-lysine, the reaction of [1-13C]D-glucose with lysine and aminoguanidine leads to the generation of 6-[2-([[amino(imino)methyl]hydrazono]methyl)pyridinium-1-yl]-L-norleucine (14-13C1). The dideoxyosone N6-(2,3-dihydroxy-5,6-dioxohexyl)-L-lysine was shown to be a precursor in the formation of 14-13C1, which proceeds via the reactive carbonyl intermediate 6-(2-formylpyridinium-1-yl)-L-norleucine (13-13C1). In order to study the reactivity of 13-13C1, the model compound 1-butyl-2-formylpyridinium (18) was prepared in a two-step procedure starting from 2-pyridinemethanol. The reaction of the pyridinium-carbaldehyde 18 with L-lysine yielded the Strecker analogous degradation product 2-(aminomethyl)-1-butylpyridinium and another compound, which was shown to be as 1-butyl-2-[(2-oxopiperidin-3-ylidene)methyl]pyridinium. Reaction of 18 with the C-H acidic 4-hydroxy-5-methylfuran-3(2H)-one leads to the formation of the condensation product 1-butyl-2-[hydroxy-(4-hydroxy-5-methyl-3-oxofuran-2(3H)-ylidene)methyl]-pyridinium.     

Synthesis and biological evaluation of stilbene derivatives coupled to NO donors as potential antidiabetic agents

The work is focused on the design of drugs that prevent and treat diabetes and its complications. A novel class of stilbene derivatives were prepared by coupling NO donors of alkyl nitrate and were fully characterised by NMR and other techniques. These compounds were tested in vitro activity, including α-glucosidase inhibitory activity, aldose reductase (AR) inhibitory activity and advanced glycation end products (AGEs) formation inhibitory activity. A class of modified compounds could play a significant effect for treatment of diabetic complications. Target compounds 3e and 7c offered a potential drug design concept for the development of therapeutic or preventive agents for diabetes and its complications.     

Inhibition by active site directed covalent modification of human glyoxalase I

The glyoxalase pathway is responsible for conversion of cytotoxic methylglyoxal (MG) to d-lactate. MG toxicity arises from its ability to form advanced glycation end products (AGEs) on proteins, lipids and DNA. Studies have shown that inhibitors of glyoxalase I (GLO1), the first enzyme of this pathway, have chemotherapeutic effects both in vitro and in vivo, presumably by increasing intracellular MG concentrations leading to apoptosis and cell death. Here, we present the first molecular inhibitor, 4-bromoacetoxy-1-(S-glutathionyl)-acetoxy butane (4BAB), able to covalently bind to the free sulfhydryl group of Cys60 in the hydrophobic binding pocket adjacent to the enzyme active site and partially inactivate the enzyme. Our data suggests that partial inactivation of homodimeric GLO1 is due to the modification at only one of the enzymatic active sites. Although this molecule may have limited use pharmacologically, it may serve as an important template for the development of new GLO1 inhibitors that may combine this strategy with ones already reported for high affinity GLO1 inhibitors, potentially improving potency and specificity.     

miR-375 在AGEs介导糖尿病血管损伤细胞中的生物学功能

目的：探讨miR-375 在血管损伤细胞中的表达及生物学功能。方法：利用基因克隆技术构建miR-375表达载体;然后将 miR-375 表达质粒转染至血管损伤细胞中,同时分别设立Huvec12对照组,血管损伤细胞组,血管损伤抑制组,Huvec12 转染 miR-375 组。24h 后收集细胞,在mRNA 和蛋白水平检测Mtpn、NFγB、profilin1、sICAM1 的表达,经荧光染色观察细胞F-actin 的 变化,再用流式细胞仪检测细胞凋亡。结果：血管损伤细胞中过表达miR-375后,在mRNA和蛋白水平靶基因Mtpn 下降,NFγB 的表达活性下降,使糖尿病血管病变的标志profilin1 下调;F-actin 表达恢复;细胞粘附因子（sICAM1）表达下降,细胞凋亡减少。 结论：初步证明miR-375 可以抑制AGEs 介导的糖尿病血管细胞损伤的发生,可能成为糖尿病血管损伤并发症基因治疗的靶点。     

Reaction of pyridoxamine with malondialdehyde: Mechanism of inhibition of formation of advanced lipoxidation end-products

Summary. Advanced glycation end products (AGEs) and advanced lipoxidation end products (ALEs) are implicated in many age-related chronic diseases and in protein aging. Recent studies suggest that pyridoxamine (PM) is an efficient AGEs/ALEs inhibitor in various biological systems. Because malondialdehyde (MDA) is an important intermediate in the formation of ALEs during lipid peroxidation, the purpose of this study is to determine whether PM can trap MDA directly and thereby prevent ALEs formation. PM reacted readily with MDA under physiological conditions. Within 6 h, a 1-pyridoxamino-propenal adduct derived from reaction of equimolar PM + MDA was detected. A 1-amino-3-iminopropene complex and a dihydropyridine-pyridinium complex were also identified after 7 d incubation. PM also greatly inhibited the lipofuscin-like fluorescence formation induced by MDA reaction with bovine serum albumin (BSA). Our results showed clearly that PM inhibited the formation of ALEs by trapping MDA directly under physiological condition, and provide insight into the mechanism of action of PM in protecting proteins against carbonyl stress.     

Modulation of advanced glycation endproduct synthesis by kynurenines in human lens proteins

Human lens proteins (HLP) become chemically modified by kynurenines and advanced glycation end products (AGEs) during aging and cataractogenesis. We investigated the effects of kynurenines on AGE synthesis in HLP. We found that incubation with 5 mM ribose or 5 mM ascorbate produced significant quantities of pentosidine, and this was further enhanced in the presence of two different kynurenines (200–500 µM): N-formylkynurenine (Nfk) and kynurenine (Kyn). Another related compound, 3-hydroxykynurenine (3OH-Kyn), had disparate effects; low concentrations (10–200 µM) promoted pentosidine synthesis, but high concentrations (200–500 µM) inhibited it. 3OH-Kyn showed similar effects on pentosidine synthesis from Amadori-enriched HLP or ribated lysine. Chelex-100 treatment of phosphate buffer reduced pentosidine synthesis from Amadori-enriched HLP by ∼ 90%, but it did not inhibit the stimulating effect of 3OH-Kyn and EDTA. 3OH-Kyn (100–500 μM) spontaneously produced copious amounts of H₂O₂ (10–25 μM), but externally added H₂O₂ had only a mild stimulating effect on pentosidine but had no effect on N^ε-carboxymethyl lysine (CML) synthesis in HLP from ribose and ascorbate. Further, human lens epithelial cells incubated with ribose and 3OH-Kyn showed higher intracellular pentosidine than cells incubated with ribose alone. CML synthesis from glycating agents was inhibited 30 to 50% by 3OH-Kyn at concentrations of 100–500 μM. Argpyrimidine synthesis from 5 mM methylglyoxal was slightly inhibited by all kynurenines at concentrations of 100–500 μM. These results suggest that AGE synthesis in HLP is modulated by kynurenines, and such effects indicate a mode of interplay between kynurenines and carbohydrates important for AGE formation during lens aging and cataract formation.     

Substituted benzenediol Schiff bases as promising new anti-glycation agents

A feature of diabetes is that the rate of protein glycation and the formation of advanced glycation endproducts (AGEs) increases spontaneously due to the abnormally elevated levels of sugar in the blood. The glycation of proteins is associated with a large number of late diabetic complications (retinopathy, neuropathy, atherosclerosis, end stage renal diseases, rheumatoid arthritis and neurodegenerative diseases). The increase in diabetic complications is a major cause of morbidity and mortality, which has increased significantly in the last two decades. Therefore, there is a considerable recent interest in the identification of lead molecules, which can inhibit the glycation process or slow it down considerably. A new class of anti-glycation agents has been identified, based on the spectrofluorimetric analysis of fluorescent advanced glycation endproducts (AGEs), benzenediol Schiff bases, and their structure-activity relationships have been studied. Some of these compounds have shown a promising anti-glycation potential in vitro.     

Cell signaling and receptors in toxicity of advanced glycation end products (AGEs): α-dicarbonyls,radicals, oxidative stress and antioxidants

Considerable attention has been paid to the toxicity of advanced glycation end products (AGEs), including relation to various illnesses. AGEs, generated nonenzymatically from carbohydrates and proteins, comprises large numbers of simple and more complicated compounds. Many reports deal with a role for receptors (RAGE) and cell signaling, including illnesses and aging. Reactive oxygen species appear to participate in signaling. RAGE include angiotensin II type 1 receptors. Many signaling pathways are involved, such as kinases, p38, p21, TGF-β, NF-κβ, TNF-α, JNK and STAT. A recent review puts focus on α-dicarbonyl metabolites, formed by carbohydrate oxidation, and imine derivatives from protein condensation, as a source via electron transfer (ET) of ROS and oxidative stress (OS). The toxic species have been related to illnesses and aging. Antioxidants alleviate the adverse effects.     

Advanced glycoxidation and lipoxidation end products (AGEs and ALEs): an overview of their mechanisms of formation

Abstract

Advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs) have a pathogenetic role in the development and progression of different oxidative-based diseases including diabetes, atherosclerosis, and neurological disorders. AGEs and ALEs represent a quite complex class of compounds that are formed by different mechanisms, by heterogeneous precursors and that can be formed either exogenously or endogenously. There is a wide interest in AGEs and ALEs involving different aspects of research which are essentially focused on set-up and application of analytical strategies (1) to identify, characterize, and quantify AGEs and ALEs in different pathophysiological conditions; (2) to elucidate the molecular basis of their biological effects; and (3) to discover compounds able to inhibit AGEs/ALEs damaging effects not only as biological tools aimed at validating AGEs/ALEs as drug target, but also as promising drugs. All the above-mentioned research stages require a clear picture of the chemical formation of AGEs/ALEs but this is not simple, due to the complex and heterogeneous pathways, involving different precursors and mechanisms. In view of this intricate scenario, the aim of the present review is to group the main AGEs and ALEs and to describe, for each of them, the precursors and mechanisms of formation.     

Glycated Proteins Can Enhance Photooxidative Stress in Aged and Diabetic Lenses

This study intends to clarify the ability of different carbonyl-containing lens metabolites to form advanced glycation end products, which possess photosensitizer activity and to investigate whether these modified proteins could be implicated in lens photodamage. Calf lens protein was experimentally glycated with either methylglyoxal, glyoxal, ascorbic acid, or fructose to obtain models of aged and diabetic cataractous lenses. Being exposed to 200 J/cm 2 UVA radiation the model glycated proteins produced 2-3-fold more singlet oxygen compared to the unmodified protein and the superoxide radical formation was 30-80% higher than by the native protein. Ascorbylated proteins demonstrated the highest photosensitizer activity. Biological responses of glycation-related photosensitizers were studied on cultured lens epithelial cells irradiated with 40 J/cm 2 UVA. Tissue culture studies revealed a significant increase in thiobarbituric acid reactive substances in the culture medium of lens epithelial cells after irradiation and treatment with glycated proteins. Lens proteins had a protective effect against UVA induced cytotoxicity, however, this protective effect decreased with the increasing photosensitizer activity of experimentally glycated proteins. The documented glycation-related photosensitization could explain the accelerated pathogenic changes in human lens at advanced age and under diabetic conditions.