Intervention against the Maillard reaction in vivo

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives

Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.

Competent antioxidant and antiglycation properties of zinc oxide nanoparticles (ZnO-NPs) phyto-fabricated from aqueous leaf extract of Boerhaavia erecta L

During the present century, plant-based zinc oxide nanoparticles (ZnO-NPs) are exploited extensively for their vast biological properties due to their unique characteristic features and eco-friendly nature. Diabetes is one of the fast-growing human diseases/abnormalities worldwide, and the need for new/ novel antiglycation products is the need of the hour. The study deals with the phyto-fabrication of ZnO-NPs from Boerhaavia erecta, a medicinally important plant, and to evaluate their antioxidant and antiglycation ability in vitro. UV-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the phyto-fabricated ZnO-NPs. The characterization of nanoparticles revealed that the particles showed an absorption peak at 362 nm and band gap energy of 3.2 eV, approximately 20.55 nm in size, with a ZnO elemental purity of 96.61%. The synthesized particles were found agglomerated when observed under SEM, and the FT-IR studies proved that the phyto-constituents of the extract involved during the different stages (reduction, capping, and stabilization) of nanoparticles synthesis. The antioxidant and metal chelating activities confirmed that ZnO-NPs could inhibit the free radicals generated, which was dose-dependent with an IC₅₀ value between 1.81 and 1.94 mg mL^-1, respectively. In addition, the phyto-fabricated nanoparticles blocked the formation of advanced glycation end products (AGEs) as noticed through inhibition of Amadori products, trapping of reactive dicarbonyl intermediate and breaking the cross-link of glycated protein. It was also noted that the phyto-fabricated ZnO-NPs significantly prevented the damage of red blood corpuscles (RBCs) induced by MGO. The present study's findings will provide an experimental basis for exploring ZnO-NPs in diabetes-related complications.

Oxidative stress, inflammation and hormesis: The role of dietary and lifestyle modifications on aging

Oxidative stress (OS) is primarily caused by the formation of free radicals and reactive oxygen species; it is considered as one of the prominent factors in slowing down and degrading cellular machinery of an individual, and it eventually leads to aging and age-related diseases by its continuous higher state. The relation between molecular damage and OS should be particularized to understand the beginning of destruction at the cellular levels, extending outwards to affect tissues, organs, and ultimately to the organism. Several OS biomarkers, which are established at the biomolecular level, are useful in investigating the disease susceptibility during aging. Slowing down the aging process is a matter of reducing the rate of oxidative damage to the cellular machinery over time. The breakdown of homeostasis, the mild overcompensation, the reestablishment of homeostasis, and the adaptive nature of the process are the essential features of hormesis, which incorporates several factors, including calorie restriction, nutrition and lifestyle modifications that play an important role in reducing the OS. In the current review, along with the concept and theories of aging (with emphasis on free radical theory), various manifestations of OS with special attention on mitochondrial dysfunction and age-related diseases have been discussed. To alleviate the OS, hormetic approaches including caloric restriction, exercise, and nutrition have also been discussed.

Glycolaldehyde, an Advanced Glycation End Products Precursor, Induces Apoptosis via ROS-Mediated Mitochondrial Dysfunction in Renal Mesangial Cells

Glycolaldehyde (GA) is a reducing sugar and a precursor of advanced glycation end products (AGEs). The role of precursor and precursor-derived AGEs in diabetes and its complications have been actively discussed in the literature. This study aimed to elucidate the mechanism of GA-induced apoptosis in renal cells. Immunoblotting results showed that GA (100 μM) caused cytotoxicity in murine renal glomerular mesangial cells (SV40 MES 13) and induced apoptosis via major modulators, decreasing Bcl-2 and increasing Bax, cytochrome c, and cleaved caspase-3/-9 expression. GA-derived AGE accumulation and receptor for AGE (RAGE) expression increased in mesangial cells; however, cells that were cotreated with aminoguanidine (AG) showed no increase in GA-derived AGE concentration. Furthermore, reactive oxygen species (ROS) production was increased by GA, while AG inhibited AGE formation, leading to a decrease in ROS levels in mesangial cells. We evaluated apoptosis through fluorescence-activated cell sorting, and used TUNEL staining to study DNA fragmentation. Additionally, we measured ATP generation and used MitoTracker staining to access changes in mitochondrial membrane potential. This study showed that GA increased AGE concentration, RAGE expression, and excessive ROS generation, leading to renal mesangial cell damage via GA-induced apoptosis pathway caused by mitochondrial dysfunction.

Differences in advanced glycation endproducts (AGEs) in plasma from birds and mammals of different body sizes and ages

Birds and mammals provide a physiological paradox: similar-sized mammals live shorter lives than birds; yet, birds have higher blood glucose concentrations than mammals, and higher basal metabolic rates. We have previously shown that oxidative stress patterns between mammals and birds differ, so that birds, generally, have lower blood antioxidant capacity, and lower lipid peroxidation concentration. There is a close association between oxidative stress and the production of carbohydrate-based damaged biomolecules, Advanced Glycation End-products (AGEs). In mammals, AGEs can bind to their receptor (RAGE), which can lead to increases in reactive oxygen species (ROS) production, and can decrease antioxidant capacity. Here, we used plasma from birds and mammals to address whether blood plasma AGE-BSA concentration is associated with body mass and age in these two groups. We found a statistically significantly higher average concentrations of AGE-BSA in birds compared with mammals, and we found a significantly positive correlation between AGE-BSA and age in mammals, though, this correlation disappeared after phylogenetic correction. We propose that the higher AGE concentration in birds is mainly attributable to greater AGE-production due to elevated basal glucose concentrations and decreased AGE-clearance given differences in glomerular filtration rates in birds compared with mammals. Additionally, due to the potential lack of an AGE receptor in birds, AGE accumulation may not be closely linked to oxidative stress and therefore pose a lesser physiological challenge in birds compared to mammals.

Natural Products as a Source of Inspiration for Novel Inhibitors of Advanced Glycation Endproducts (AGEs) Formation

Protein glycation, a post-translational modification found in biological systems, is often associated with a core defect in glucose metabolism. In particular, advanced glycation endproducts are complex heterogeneous sugar-derived protein modifications implicated in the progression of pathological conditions such as atherosclerosis, diabetic complications, skin diseases, rheumatism, hypertension, and neurodegenerative diseases. Undoubtedly, there is the need to expand the knowledge about antiglycation agents that can offer a therapeutic approach in preventing and treating health issues of high social and economic importance. Although various compounds have been under consideration, little data from clinical trials are available, and there is a lack of approved and registered antiglycation agents. Next to the search for novel synthetic advanced glycation endproduct inhibitors, more and more the efforts of scientists are focusing on researching antiglycation compounds from natural origin. The main purpose of this review is to provide a thorough overview of the state of scientific knowledge in the field of natural products from plant origin (e.g., extracts and pure compounds) as inhibitors of advanced glycation endproduct formation in the period between 1990 and 2019. Moreover, the objectives of the summary also include basic chemistry of AGEs formation and classification, pathophysiological significance of AGEs, mechanisms for inhibiting AGEs formation, and examples of several synthetic anti-AGEs drugs.

Pleiotropic Actions of Aldehyde Reductase (AKR1A)

We provide an overview of the physiological roles of aldehyde reductase (AKR1A) and also discuss the functions of aldose reductase (AKR1B) and other family members when necessary. Many types of aldehyde compounds are cytotoxic and some are even carcinogenic. Such toxic aldehydes are detoxified via the action of AKR in an NADPH-dependent manner and the resulting products may exert anti-diabetic and anti-tumorigenic activity. AKR1A is capable of reducing 3-deoxyglucosone and methylglyoxal, which are reactive intermediates that are involved in glycation, a non-enzymatic glycosylation reaction. Accordingly, AKR1A is thought to suppress the formation of advanced glycation end products (AGEs) and prevent diabetic complications. AKR1A and, in part, AKR1B are responsible for the conversion of d-glucuronate to l-gulonate which constitutes a process for ascorbate (vitamin C) synthesis in competent animals. AKR1A is also involved in the reduction of S-nitrosylated glutathione and coenzyme A and thereby suppresses the protein S-nitrosylation that occurs under conditions in which the production of nitric oxide is stimulated. As the physiological functions of AKR1A are currently not completely understood, the genetic modification of Akr1a could reveal the latent functions of AKR1A and differentiate it from other family members.

Glycation changes molecular organization and charge distribution in type I collagen fibrils

Collagen fibrils are central to the molecular organization of the extracellular matrix (ECM) and to defining the cellular microenvironment. Glycation of collagen fibrils is known to impact on cell adhesion and migration in the context of cancer and in model studies, glycation of collagen molecules has been shown to affect the binding of other ECM components to collagen. Here we use TEM to show that ribose-5-phosphate (R5P) glycation of collagen fibrils - potentially important in the microenvironment of actively dividing cells, such as cancer cells - disrupts the longitudinal ordering of the molecules in collagen fibrils and, using KFM and FLiM, that R5P-glycated collagen fibrils have a more negative surface charge than unglycated fibrils. Altered molecular arrangement can be expected to impact on the accessibility of cell adhesion sites and altered fibril surface charge on the integrity of the extracellular matrix structure surrounding glycated collagen fibrils. Both effects are highly relevant for cell adhesion and migration within the tumour microenvironment.

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.

How Does Pyridoxamine Inhibit the Formation of Advanced Glycation End Products? The Role of Its Primary Antioxidant Activity

Pyridoxamine, one of the natural forms of vitamin B6, is known to be an effective inhibitor of the formation of advanced glycation end products (AGEs), which are closely related to various human diseases. Pyridoxamine forms stable complexes with metal ions that catalyze the oxidative reactions taking place in the advanced stages of the protein glycation cascade. It also reacts with reactive carbonyl compounds generated as byproducts of protein glycation, thereby preventing further protein damage. We applied Density Functional Theory to study the primary antioxidant activity of pyridoxamine towards three oxygen-centered radicals (•OOH, •OOCH3 and •OCH3) to find out whether this activity may also play a crucial role in the context of protein glycation inhibition. Our results show that, at physiological pH, pyridoxamine can trap the •OCH3 radical, in both aqueous and lipidic media, with rate constants in the diffusion limit (>1.0 × 108 M - 1 s - 1 ). The quickest pathways involve the transfer of the hydrogen atoms from the protonated pyridine nitrogen, the protonated amino group or the phenolic group. Its reactivity towards •OOH and •OOCH3 is smaller, but pyridoxamine can still scavenge them with moderate rate constants in aqueous media. Since reactive oxygen species are also involved in the formation of AGEs, these results highlight that the antioxidant capacity of pyridoxamine is also relevant to explain its inhibitory role on the glycation process.

Studies on the Formation of 3-Deoxyglucosone- and Methylglyoxal-Derived Hydroimidazolones of Creatine during Heat Treatment of Meat

Dicarbonyl compounds such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG) are formed via caramelization and the Maillard reaction in food during heating or in vivo as byproducts of glycolysis. Recently, it was shown that creatine, an amino compound linked to the energy metabolism in vertebrate muscle, reacts rapidly with methylglyoxal under physiological conditions to form N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine (MG-HCr), a methylglyoxal-derived hydroimidazolone of creatine. Based on the observation that heated meat contains only small amounts of MGO and 3-DG when compared to many other foodstuffs, the aim of this study was to investigate a possible reaction of creatine with 3-DG and MGO in meat. From incubation mixtures consisting of 3-DG and creatine, a new hydroimidazolone of creatine, namely N-(4-butyl-1,2,3-triol-5-oxo-1-imidazolin-2-yl)sarcosine (3-DG-HCr), was isolated and characterized via spectroscopic means. To quantitate 3-DG-HCr and MG-HCr, meat and fish products were analyzed via HPLC-MS/MS using isotopically labeled standard material. Whereas samples of raw fish and meat contained only trace amounts of the hydroimidazolones (below 5 μg/kg), up to 28.3 mg/kg MG-HCr and up to 15.3 mg/kg 3-DG-HCr were found in meat and fish products. The concentrations were dependent on the heat treatment and presumably on the smoking process. In comparison to the lysine and arginine derivatives CEL, pyrraline, and MG-H1, the derivatization rate of creatine as MG-HCr and 3-DG-HCr was higher than of lysine and arginine, which clearly demonstrates the 1,2-dicarbonyl scavenging properties of creatine in meat.

Neurons and Microglia; A Sickly-Sweet Duo in Diabetic Pain Neuropathy

Diabetes is a common condition characterized by persistent hyperglycemia. High blood sugar primarily affects cells that have a limited capacity to regulate their glucose intake. These cells include capillary endothelial cells in the retina, mesangial cells in the renal glomerulus, Schwann cells, and neurons of the peripheral and central nervous systems. As a result, hyperglycemia leads to largely intractable complications such as retinopathy, nephropathy, hypertension, and neuropathy. Diabetic pain neuropathy is a complex and multifactorial disease that has been associated with poor glycemic control, longer diabetes duration, hypertension, advanced age, smoking status, hypoinsulinemia, and dyslipidemia. While many of the driving factors involved in diabetic pain are still being investigated, they can be broadly classified as either neuron -intrinsic or -extrinsic. In neurons, hyperglycemia impairs the polyol pathway, leading to an overproduction of reactive oxygen species and reactive nitrogen species, an enhanced formation of advanced glycation end products, and a disruption in Na⁺/K⁺ ATPase pump function. In terms of the extrinsic pathway, hyperglycemia leads to the generation of both overactive microglia and microangiopathy. The former incites a feed-forward inflammatory loop that hypersensitizes nociceptor neurons, as observed at the onset of diabetic pain neuropathy. The latter reduces neurons' access to oxygen, glucose and nutrients, prompting reductions in nociceptor terminal expression and losses in sensation, as observed in the later stages of diabetic pain neuropathy. Overall, microglia can be seen as potent and long-lasting amplifiers of nociceptor neuron activity, and may therefore constitute a potential therapeutic target in the treatment of diabetic pain neuropathy.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Advanced glycation end products induce brain-derived neurotrophic factor release from human platelets through the Src-family kinase activation

Background

Brain-derived neurotrophic factor (BDNF) exerts beneficial effects not only on diabetic neuropathies but also on cardiovascular injury. There is argument regarding the levels of serum BDNF in patients with diabetes mellitus (DM). Because BDNF in peripheral blood is rich in platelets, this may represent dysregulation of BDNF release from platelets. Here we focused on advanced glycation end products (AGEs), which are elevated in patients with DM and have adverse effects on cardiovascular functions. The aim of this study is to elucidate the role of AGEs in the regulation of BDNF release from human platelets.

Methods

Platelets collected from peripheral blood of healthy volunteers were incubated with various concentrations of AGE (glycated-BSA) at 37 °C for 5 min with or without BAPTA-AM, a cell permeable Ca²⁺ chelator, or PP2, a potent inhibitor of Src family kinases (SFKs). Released and cellular BDNF were measured by ELISA and calculated. Phosphorylation of Src and Syk, a downstream kinase of SFKs, in stimulated platelets was examined by Western blotting and immunoprecipitation.

Results

AGE induced BDNF release from human platelets in a dose-dependent manner, which was dependent on intracellular Ca²⁺ and SFKs. We found that AGE induced phosphorylation of Src and Syk.

Conclusions

AGE induces BDNF release from human platelets through the activation of the Src-Syk-(possibly phospholipase C)-Ca²⁺ pathway. Considering the toxic action of AGEs and the protective roles of BDNF, it can be hypothesized that AGE-induced BDNF release is a biological defense system in the early phase of diabetes. Chronic elevation of AGEs may induce depletion or downregulation of BDNF in platelets during the progression of DM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0505-y) contains supplementary material, which is available to authorized users.

Effect of glycation inhibitors on aging and age-related diseases

Vast evidence supports the view that glycation of proteins is one of the main factors contributing to aging and is an important element of etiopathology of age-related diseases, especially type 2 diabetes mellitus, cataract and neurodegenerative diseases. Counteracting glycation can therefore be a means of increasing both the lifespan and healthspan. In this review, accumulation of glycation products during aging is presented, pathophysiological effects of glycation are discussed and ways of attenuation of the effects of glycation are described, concentrating on prevention of glycation. The effects of glycation and glycation inhibitors on the course of selected age-related diseases, such as Alzheimer's disease, Parkinson's disease and cataract are also reviewed.

Targeting advanced glycation with pharmaceutical agents: where are we now?

Advanced glycation end products (AGEs) are the final products of the Maillard reaction, a complex process that has been studied by food chemists for a century. Over the past 30 years, the biological significance of advanced glycation has also been discovered. There is mounting evidence that advanced glycation plays a homeostatic role within the body and that food-related Maillard products, intermediates such as reactive α-dicarbonyl compounds and AGEs, may influence this process. It remains to be understood, at what point AGEs and their intermediates become pathogenic and contribute to the pathogenesis of chronic diseases that inflict current society. Diabetes and its complications have been a major focus of AGE biology due to the abundance of excess sugar and α-dicarbonyls in this family of diseases. While further temporal information is required, a number of pharmacological agents that inhibit components of the advanced glycation pathway have already showed promising results in preclinical models. These therapies appear to have a wide range of mechanistic actions to reduce AGE load. Some of these agents including Alagebrium, have translated successfully to clinical trials, while others such as aminoguanidine, have had undesirable side-effect profiles. This review will discuss different pharmacological agents that have been used to reduce AGE burden in preclinical models of disease with a focus on diabetes and its complications, compare outcomes of those therapies that have reached clinical trials, and provide further rationale for the use of inhibitors of the glycation pathway in chronic diseases.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Redox Signaling in Diabetic Nephropathy: Hypertrophy versus Death Choices in Mesangial Cells and Podocytes

This review emphasizes the role of oxidative stress in diabetic nephropathy, acting as trigger, modulator, and linker within the complex network of pathologic events. It highlights key molecular pathways and new hypothesis in diabetic nephropathy, related to the interferences of metabolic, oxidative, and inflammatory stresses. Main topics this review is addressing are biomarkers of oxidative stress in diabetic nephropathy, the sources of reactive oxygen species (mitochondria, NADPH-oxidases, hyperglycemia, and inflammation), and the redox-sensitive signaling networks (protein kinases, transcription factors, and epigenetic regulators). Molecular switches deciding on the renal cells fate in diabetic nephropathy are presented, such as hypertrophy versus death choices in mesangial cells and podocytes. Finally, the antioxidant response of renal cells in diabetic nephropathy is tackled, with emphasis on targeted therapy. An integrative approach is needed for identifying key molecular networks which control cellular responses triggered by the array of stressors in diabetic nephropathy. This will foster the discovery of reliable biomarkers for early diagnosis and prognosis, and will guide the discovery of new therapeutic approaches for personalized medicine in diabetic nephropathy.

Consequences of metabolic and oxidative modifications of cartilage tissue

A hallmark of chronic metabolic diseases, such as diabetes and metabolic syndrome, and oxidative stress, as occurs in chronic inflammatory and degenerative conditions, is the presence of extensive protein post-translational modifications, including glycation, glycoxidation, carbonylation and nitrosylation. These modifications have been detected on structural cartilage proteins in joints and intervertebral discs, where they are known to affect protein folding, induce protein aggregation and, ultimately, generate microanatomical changes in the proteoglycan-collagen network that surrounds chondrocytes. Many of these modifications have also been shown to promote oxidative cleavage as well as enzymatically-mediated matrix degradation. Overall, a general picture starts to emerge indicating that biochemical changes in proteins constitute an early event that compromises the anatomical organization and viscoelasticity of cartilage, thereby affecting its ability to sustain pressure and, ultimately, impeding its overall bio-performance.

Nonenzymatic Reactions above Phospholipid Surfaces of Biological Membranes: Reactivity of Phospholipids and Their Oxidation Derivatives

Phospholipids play multiple and essential roles in cells, as components of biological membranes. Although phospholipid bilayers provide the supporting matrix and surface for many enzymatic reactions, their inherent reactivity and possible catalytic role have not been highlighted. As other biomolecules, phospholipids are frequent targets of nonenzymatic modifications by reactive substances including oxidants and glycating agents which conduct to the formation of advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs). There are some theoretical studies about the mechanisms of reactions related to these processes on phosphatidylethanolamine surfaces, which hypothesize that cell membrane phospholipids surface environment could enhance some reactions through a catalyst effect. On the other hand, the phospholipid bilayers are susceptible to oxidative damage by oxidant agents as reactive oxygen species (ROS). Molecular dynamics simulations performed on phospholipid bilayers models, which include modified phospholipids by these reactions and subsequent reactions that conduct to formation of ALEs and AGEs, have revealed changes in the molecular interactions and biophysical properties of these bilayers as consequence of these reactions. Then, more studies are desirable which could correlate the biophysics of modified phospholipids with metabolism in processes such as aging and diseases such as diabetes, atherosclerosis, and Alzheimer's disease.

Hyperglycemia / hypoglycemia-induced mitochondrial dysfunction and cerebral ischemic damage in diabetics

Enhancement of ischemic brain damage is one of the most serious complications of diabetes. Studies from various in vivo and in vitro models of cerebral ischemia have led to an understanding of the role of mitochondria and complex interrelated mitochondrial biochemical pathways leading to the aggravation of ischemic neuronal damage. Advancements in the elucidation of the mechanisms of ischemic brain damage in diabetic subjects have revealed a number of key mitochondrial targets that have been hypothesized to participate in enhancement of brain damage. The present review initially discusses the neurobiology of ischemic neuronal injury, with special emphasis on the central role of mitochondria in mediating its pathogenesis and therapeutic targets. Later it further details the potential role of various biochemical mediators and second messengers causing widespread ischemic brain damage among diabetics via mitochondrial pathways. The present review discusses preclinical data which validates the significance of mitochondrial mechanisms in mediating the aggravation of ischemic cerebral injury in diabetes. Exploitation of these targets may provide effective therapeutic agents for the management of diabetes-related aggravation of ischemic neuronal damage.

Prevention of protein glycation by natural compounds

Non-enzymatic protein glycosylation (glycation) contributes to many diseases and aging of organisms. It can be expected that inhibition of glycation may prolong the lifespan. The search for inhibitors of glycation, mainly using in vitro models, has identified natural compounds able to prevent glycation, especially polyphenols and other natural antioxidants. Extrapolation of results of in vitro studies on the in vivo situation is not straightforward due to differences in the conditions and mechanism of glycation, and bioavailability problems. Nevertheless, available data allow to postulate that enrichment of diet in natural anti-glycating agents may attenuate glycation and, in consequence, ageing.

Neurochemical, structural and neurobehavioral evidence of neuronal protection by whey proteins in diabetic albino mice

Background

Diabetes Mellitus (DM) is associated with pathological changes in the central nervous system (CNS) and alterations in oxidative stress. The aim of this study was to determine whether dietary supplement with whey protein (WP) could improve neurobehavior, oxidative stress and neuronal structure in the CNS.

Methods

Animals were distributed in three groups, a control group (N), a diabetic mellitus group (DM) and a DM group orally supplemented with WP (WP).

Results

The DM group of animals receiving WP had reduced blood glucose, significantly decreased free radical Diphenyl-picrylhydrazyl (DPPH) and lower lipid peroxidation in brain tissue. The WP group of animals showed improvement in balancing, coordination and fore-limb strength, oxidative stress and neuronal structure.

Conclusion

The results of this study show that dietary supplementation with WP reduced oxidative stress, protected CNS neurons and improved the neurobehavior of diabetic mice.

Oxidative Stress in Alzheimer's Disease: Should We Keep Trying Antioxidant Therapies?

The risk of chronic diseases such as Alzheimer's disease is growing as a result of the continuous increasing average life span of the world population, a syndrome characterized by the presence of intraneural neurofibrillary tangles and senile plaques composed mainly by beta-amyloid protein, changes that may cause a number of progressive disorders in the elderly, causing, in its most advanced stage, difficulty in performing normal daily activities, among other manifestations. Therefore, it is important to understand the underlying pathogenic mechanisms of this syndrome. Nevertheless, despite intensive effort to access the physiopathological pathways of the disease, it remains poorly understood. In that context, some hypotheses have arisen, including the recent oxidative stress hypothesis, theory supported by the involvement of oxidative stress in aging, and the vulnerability of neurons to oxidative attack. In the present revision, oxidative changes and redox mechanisms in Alzheimer's disease will be further stressed, as well as the grounds for antioxidant supplementation as adjuvant therapy for the disease will be addressed.

A DFT study of the carboxymethyl-phosphatidylethanolamine formation from glyoxal and phosphatidylethanolamine surface. Comparison with the formation of N(ε)-(carboxymethyl)lysine from glyoxal and l-lysine

Mechanisms of the generation of CML and CM-PE from the reactions between glyoxal and l-lysine, and glyoxal and phosphatidylethanolamine (PE) were studied using the DFT method.

Pyridoxamine dihydrochloride in diabetic nephropathy (PIONEER-CSG-17): lessons learned from a pilot study

BACKGROUND/AIMS

Pyridoxamine dihydrochloride (Pyridorin™) blocks pathogenic oxidative pathways in the progression of diabetic nephropathy. The pyridoxamine pilot study was designed to test entry criteria and outcomes. Subjects had SCr 1.3-3.5 mg/dl, protein-to-creatinine ≥1,200 mg/g and used a surrogate outcome of ΔSCr over 52 weeks. Subjects had to be on a maximally tolerated dose of ACE/ARB for 3 months; stable other antihypertensive doses for 2 months; stable diuretic dose for 2 weeks, and BP ≤160/90 mm Hg; or enter a Pharmaco-Stabilization Phase (PSP). This pilot failed to detect an effect on ΔSCr in intent-to-treat analysis.

METHODS

We queried the locked clinical trial database for subgroups in which there was a treatment effect.

RESULTS

Subjects not requiring PSP and those with entry SCr <2.0 mg/dl had a treatment effect. Subjects entering PSP required more changes in antihypertensive medications and experienced larger ΔSCr over 52 weeks. PSP subjects with BP >140/90 mm Hg had no treatment effect, but those ≤140/90 mm Hg did.

CONCLUSION

Time required for acute effects of ACE/ARB to stabilize is unknown, but these data suggest >3 months. Thus, subjects in the pivotal trial must be on ACE/ARB for 6 months. Frequent antihypertensive adjustment could engender SCr changes unrelated to CKD progression. Thus, we will require subjects to have BP ≤150/90 mm Hg and on stable antihypertensives for 26 weeks, or ≤140/90 mm Hg and on stable antihypertensives for 13 weeks. Since ΔSCr over 52 weeks is limited as a surrogate outcome, the pivotal trial uses a time-to-event analysis of baseline SCr to at least a 50% increase in SCr or ESRD as the primary outcome. This substantial ΔSCr is protected from noise and is clinically relevant. The pyridoxamine pilot provided critical information to inform the design of PIONEER-CSG-17, which we conducted under the SPA agreement with FDA.

Beneficial effect of Azadirachta indica on advanced glycation end-product in streptozotocin-diabetic rat

CONTEXT

Both oxidation and hyperglycemia cause increased glycation and the formation of advanced glycation end-products (AGEs) which underlie the complications of diabetes.

OBJECTIVE

The goal of this article is to determine the effect of the chloroform extract from leaves of Azadirachta indica A. Juss; (Meliaceae) (AI) on the formation of glycated protein.

MATERIALS AND METHODS

Chloroform extract was subjected to in vitro bioassays to evaluate advanced glycation end-products formation. Bovine serum albumin (BSA)-glucose, BSA-methylglyoxal, Amadori-rich protein, glycated hemoglobin, oxidation, and glycation of LDL were determined. Doses of AI of 200 mg/kg/d by oral gavage were administered once daily for 30 d, at streptozotocin-induced diabetic rats. After this period, renal damage (TBARS), glucose, methylglyoxal, glycolaldehyde, and tail tendon collagen were investigated.

RESULTS AND DISCUSSION

AI exhibits protective action in BSA against glycation formation, GHb, protein levels, and LDL against glycation and oxidation. The renal glucose level decreases a 3.9 mg/g wet tissue. TBA-reactive substance showed a significant decrease to 1.82 mmol/mg protein. In addition, AI showed inhibitory activity against AGEs formation, methylglyoxal, and glycolaldehyde levels in kidney. Treatment with AI in rat tail tendon produced a reduction in cross-linking of collagen proteins. The antiglycation activities of A. indica were attributed in part to their antioxidant activity. AI alleviated oxidative stress under diabetic conditions through the inhibition of lipid peroxidation prevents the onset renal damage.

CONCLUSION

We found that A. indica is an inhibitor AGE formation, and oxidative stress with a renoprotective effect, which are considered to play important roles in diabetic kidney disease.

Genotoxic Maillard byproducts in current phytopharmaceutical preparations of Echinodorus grandiflorus

Extracts of Echinodorus grandiflorus obtained from dried leaves by three different techniques were evaluated by bacterial lysogenic induction assay (Inductest) in relation to their genotoxic properties. Before being added to test cultures, extracts were sterilized either by steam sterilization or ultraviolet light. Only the extracts prepared by infusion and steam sterilized have shown genotoxic activity. The phytochemical analysis revealed the presence of the flavonoids isovitexin, isoorientin, swertisin and swertiajaponin, isolated from a genotoxic fraction. They were assayed separately and tested negative in the Inductest protocol. The development of browning color and sweet smell in extracts submitted to heat, prompted further chemical analysis in search for Maillard's reaction precursors. Several aminoacids and reducing sugars were cast in the extract. The presence of characteristic Maillard's melanoidins products was determined by spectrophotometry in the visible region and the inhibition of this reaction was observed when its characteristic inhibitor, sodium bisulfite, was added prior to heating. Remarkably, this is the first paper reporting on the appearance of such compounds in a phytomedicine preparation under a current phytopharmaceutical procedure. The genotoxic activity of such heat-prepared infusions imply in some risk of developing degenerative diseases for patients in long-term, uncontrolled use of such phytomedicines.

Baking, ageing, diabetes: a short history of the Maillard reaction

The reaction of reducing carbohydrates with amino compounds described in 1912 by Louis-Camille Maillard is responsible for the aroma, taste, and appearance of thermally processed food. The discovery that non-enzymatic conversions also occur in organisms led to intensive investigation of the pathophysiological significance of the Maillard reaction in diabetes and ageing processes. Dietary Maillard products are discussed as "glycotoxins" and thus as a nutritional risk, but also increasingly with regard to positive effects in the human body. In this Review we give an overview of the most important discoveries in Maillard research since it was first described and show that the complex reaction, even after over one hundred years, has lost none of its interdisciplinary actuality.

Differential effects of glyoxalase 1 overexpression on diabetic atherosclerosis and renal dysfunction in streptozotocin-treated, apolipoprotein E-deficient mice

The reactive dicarbonyls, glyoxal and methylglyoxal (MG), increase in diabetes and may participate in the development of diabetic complications. Glyoxal and MG are detoxified by the sequential activities of glyoxalase 1 (GLO1) and glyoxalase 2. To determine the contribution of these dicarbonyls to the etiology of complications, we have genetically manipulated GLO1 levels in apolipoprotein E‐null (Apoe^−/−) mice. Male Apoe^−/− mice, hemizygous for a human GLO1 transgene (GLO1TGApoe^−/− mice) or male nontransgenic Apoe^−/− litter mates were injected with streptozotocin or vehicle and 6 or 20 weeks later, aortic atherosclerosis was quantified. The GLO1 transgene lessened streptozotocin (STZ)‐induced increases in immunoreactive hydroimidazolone (MG‐H1). Compared to nondiabetic mice, STZ‐treated GLO1TGApoe^−/− and Apoe^−/− mice had increased serum cholesterol and triglycerides and increased atherosclerosis at both times after diabetes induction. While the increased GLO1 activity in the GLO1TGApoe^−/− mice failed to protect against diabetic atherosclerosis, it lessened glomerular mesangial expansion, prevented albuminuria and lowered renal levels of dicarbonyls and protein glycation adducts. Aortic atherosclerosis was also quantified in 22‐week‐old, male normoglycemic Glo1 knockdown mice on an Apoe^−/− background (Glo1KDApoe^−/− mice), an age at which Glo1KD mice exhibit albuminuria and renal pathology similar to that of diabetic mice. In spite of ~75% decrease in GLO1 activity and increased aortic MG‐H1, the Glo1KDApoe^−/− mice did not show increased atherosclerosis compared to age‐matched Apoe^−/− mice. Thus, manipulation of GLO1 activity does not affect the development of early aortic atherosclerosis in Apoe^−/− mice but can dictate the onset of kidney disease independently of blood glucose levels.

Increased levels of methylglyoxal and methylglyoxal‐derived advanced glycation end products may contribute to the development of diabetic complications. We show that overexpression of an enzyme that participates in the pathway of methylglyoxal detoxification, glyoxalase 1, protects streptozotocin‐treated, apolipoprotein E‐deficient mice from diabetic kidney disease but not from diabetes‐induced accelerated aortic atherosclerosis.

DFT study of the mechanism of the reaction of aminoguanidine with methylglyoxal

We have studied the mechanism of the reaction between aminoguanidine (AG) and methylglyoxal (MG) by carrying out Dmol3/DFT calculations, obtaining intermediates, transition-state structures, and free-energy profiles for all of the elementary steps of the reaction. Designed models included explicit water solvent, which forms hydrogen-bond networks around the reactants and intermediate molecules, facilitating intramolecular proton transfer in some steps of the reaction mechanism. The reaction take place in four steps, namely: (1) formation of a guanylhydrazone-acetylcarbinol adduct by condensation of AG and MG; (2) dehydration of the adduct; (3) formation of an 1,2,4-triazine derivative by ring closure; and (4) dehydration with the formation of 5-methyl 3-amino-1,2,4-triazine as the final product. From a microkinetic point of view, the first dehydration step was found to be the rate-determining step for the reaction, with the reaction having an apparent activation energy of 12.65 kcal mol⁻¹. Additionally, some analogous structures of intermediates and transition states for the reaction between AG and 2,3-dicarbonyl-phosphatidylethanolamine, a possible intermediate in Amadori-glycated phosphatidylethanolamine (Amadori-PE) autooxidation, were obtained to evaluate the reaction above a phosphatidylethanolamine (PE) surface. Our results are in agreement with experimental results obtaining by other authors, showing that AG is efficient at trapping dicarbonyl compounds such as methylglyoxal, and by extension these compounds joined to biomolecules such as PE in environments such as surfaces and their aqueous surroundings.

Synthesis of 4-methoxybenzoylhydrazones and evaluation of their antiglycation activity

A series of 4-methoxybenzoylhydrazones 1-30 was synthesized and the structures of the synthetic derivatives elucidated by spectroscopic methods. The compounds showed a varying degree of antiglycation activity, with IC50 values ranging between 216.52 and 748.71 µM, when compared to a rutin standard (IC50=294.46±1.50 µM). Compounds 1 (IC50=216.52±4.2 µM), 3 (IC50=289.58±2.64 µM), 6 (IC50=227.75±0.53 µM), 7 (IC50=242.53±6.1) and 11 (IC50=287.79±1.59) all showed more activity that the standard, and these compounds have the potential to serve as possible leads for drugs to inhibit protein glycation in diabetic patients. A preliminary SAR study was performed.

The efficiency of compounds with α-amino-β-mercapto-ethane group in protection of human serum albumin carbonylation and cross-linking with methylglyoxal

Substances containing an α-amino-β-mercapto-ethane pharmacophore may be used as effective methylglyoxal scavengers and inhibitors of protein carbonylation and cross-linking.

Markers of Oxidative Stress during Diabetes Mellitus

The prevalence of diabetes mellitus is rising all over the world. Uncontrolled state of hyperglycemia due to defects in insulin secretion/action leads to a variety of complications including peripheral vascular diseases, nephropathy, neuropathy, retinopathy, morbidity, and/or mortality. Large body of evidence suggests major role of reactive oxygen species/oxidative stress in development and progression of diabetic complications. In the present paper, we have discussed the recent researches on the biomarkers of oxidative stress during type 2 diabetes mellitus.

Vascular effects of advanced glycation endproducts: Clinical effects and molecular mechanisms

The enhanced generation and accumulation of advanced glycation endproducts (AGEs) have been linked to increased risk for macrovascular and microvascular complications associated with diabetes mellitus. AGEs result from the nonenzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids, potentially altering their function by disrupting molecular conformation, promoting cross-linking, altering enzyme activity, reducing their clearance, and impairing receptor recognition. AGEs may also activate specific receptors, like the receptor for AGEs (RAGE), which is present on the surface of all cells relevant to atherosclerotic processes, triggering oxidative stress, inflammation and apoptosis. Understanding the pathogenic mechanisms of AGEs is paramount to develop strategies against diabetic and cardiovascular complications.

Tuning a 96-well microtiter plate fluorescence-based assay to identify AGE inhibitors in crude plant extracts

Advanced glycation end-products (AGEs) are involved in the pathogenesis of numerous diseases. Among them, cellular accumulation of AGEs contributes to vascular complications in diabetes. Besides using drugs to lower blood sugar, a balanced diet and the intake of herbal products potentially limiting AGE formation could be considered beneficial for patients’ health. The current paper presents a simple and cheap high-throughput screening (HTS) assay based on AGE fluorescence and suitable for plant extract screening. We have already implemented an HTS assay based on vesperlysines-like fluorescing AGEs quickly (24 h) formed from BSA and ribose under physiological conditions. However, interference was noted when fluorescent compounds and/or complex mixtures were tested. To overcome these problems and apply this HTS assay to plant extracts, we developed a technique for systematic quantification of both vesperlysines (λ_exc 370 nm; λ_em 440 nm) and pentosidine-like (λ_exc 335 nm; λ_em 385 nm) AGEs. In a batch of medicinal and food plant extracts, hits were selected as soon as fluorescence decreased under a fixed threshold for at least one wavelength. Hits revealed during this study appeared to contain well-known and powerful anti-AGE substances, thus demonstrating the suitability of this assay for screening crude extracts (0.1 mg/mL). Finally, quercetin was found to be a more powerful reference compound than aminoguanidine in such assay.

The unique reactivity of N-phenacyl-derived thiazolium salts toward α-dicarbonyl compounds

Advanced glycation end products (AGEs), a heterogeneous mixture of compounds formed by non-enzymatic chemical reactions between sugars and the nucleophilic residues of proteins, have been implicated in the pathogenesis of a number of diseases. ALT-711 is an N-phenacyl-derived thiazolium carbene developed as a therapeutic agent for cardiovascular diseases that is proposed to function through cleaving preformed AGE-protein crosslinks. However, despite promising results in animal models and clinical trials, its mechanism of action still remains controversial. Herein, we report the first systematic investigations into dicarbonyl cleavage by ALT-711. We demonstrate that it is capable of cleaving α-diketones more efficiently and likely via a distinct mechanism compared with other N-heterocyclic carbene precursors. We also show that ALT-711 reacts rapidly with α-keto aldehydes to form cyclic diol products, and it can efficiently scavenge methylglyoxal under physiological conditions to protect Escherichia coli from lethal concentrations of this reactive α-keto aldehyde. This work suggests ALT-711 may be especially suited for α-dicarbonyl clearance in vivo and supports a mode of action similar to that originally proposed. To this end, our findings may provide insights into the development of next-generation crosslink breakers.

Current therapeutic interventions in the glycation pathway: evidence from clinical studies

The increased formation of advanced glycation endproducts (AGEs) constitutes a potential mechanism of hyperglycaemia-induced micro- and macrovascular disease in diabetes. In vitro and animal experiments have shown that various interventions can inhibit formation and/or actions of AGEs, in particular the specific AGE inhibitor aminoguanidine and the AGEs crosslink breaker alagebrium, and the B vitamins pyridoxamine and thiamine, and the latter's synthetic derivative, benfotiamine. The potential clinical value of these interventions, however, remains to be established. The present review provides, from the clinical point of view, an overview of current evidence on interventions in the glycation pathway relating to (i) the clinical benefits of specific AGE inhibitors and AGE breakers and (ii) the potential AGE-inhibiting effects of therapies developed for purposes unrelated to the glycation pathway. We found that safety and/or efficacy in clinical studies with the specific AGE inhibitor, aminoguanidine and the AGE breaker, alagebrium, appeared to be a concern. The clinical evidence on the potential AGE-inhibiting effects of B vitamins is still limited. Finally, current evidence for AGE inhibition by therapies developed for purposes unrelated to glycation is limited due to a large heterogeneity in study designs and/or measurement techniques, which have often been sub-optimal. We conclude that, clinical evidence on interventions to inhibit formation and/or action of AGEs is currently weak and unconvincing.

[Analysis of the mRNA expression of the S100β protein in adipocytes of patients with diabetes mellitus, type 2]

OBJECTIVE

This study aims to explore the possible relationship between the expression level of S100β protein mRNA with diabetes mellitus type 2 in adipocytes from patients with this disease in comparison with normoglycemic individuals.

MATERIALS AND METHODS

Samples of adipose tissue of eight patients from the coronary section of the Institute Dante Pazzanese of Cardiology (IDPC), four in Group Diabetes and four of Normoglycemic group, were evaluated by RT-PCR real time.

RESULTS

An increase around 15 times values, between the threshold cycle (ΔCt), of mRNA expression of S100β protein in adipocytes of the diabetes group was observed in comparison to the control group (p = 0.015).

CONCLUSION

Our results indicate, for the first time, that there is coexistence of increased expression of the S100β and the type 2 diabetes mellitus gene.

Molecular strategies to prevent, inhibit, and degrade advanced glycoxidation and advanced lipoxidation end products

The advanced glycoxidation end products (AGEs) and lipoxidation end products (ALEs) contribute to the development of diabetic complications and of other pathologies. The review discusses the possibilities of counteracting the formation and stimulating the degradation of these species by pharmaceuticals and natural compounds. The review discusses inhibitors of ALE and AGE formation, cross-link breakers, ALE/AGE elimination by enzymes and proteolytic systems, receptors for advanced glycation end products (RAGEs) and blockade of the ligand-RAGE axis.

Vitamin D reduces deposition of advanced glycation end-products in the aortic wall and systemic oxidative stress in diabetic rats

AIMS

Vitamin D may have an important role in reducing the risk of cardiovascular disease. Advanced glycation end-products (AGEs) such as Nε-(carboxymethyl)lysine (CML), have been implicated in diabetic vascular complications via oxidative stress-mediated pathways. We investigated the potential protective effect of vitamin D on CML accumulation in the diabetic aortic wall. To test the effects of vitamin D on systemic oxidative stress we also assessed liver oxidative stress index (OSI) and serum total antioxidant capacity (TAC).

METHODS

Male Wistar rats were assigned to three groups: control, untreated diabetes, and diabetes+cholecalciferol. Diabetes was induced by streptozotocin, followed by oral administration of cholecalciferol (500 IU/kg) for 10 weeks in the treatment group. Aortic CML accumulation was determined by ELISA and immunohistochemical assays. OSI was assessed by measuring TAC and the level of total peroxides in the liver and serum using colorimetric assays.

RESULTS

Untreated diabetes was associated with significantly elevated CML levels in the aortic wall (19.5 ± 3.3 vs 10.2 ± 4.7 ng/mL), increased liver OSI (6.8 ± 1.9 vs 3.1 ± 0.7), and reduced serum TAC (0.4 ± 0.1 vs 0.8 ± 0.3 mmol Trolox/L), in comparison with the control group. Cholecalciferol significantly blocked the accumulation of CML in the aortic wall (10.4 ± 8.4 vs 19.5 ± 3.3 ng/mL), decreased liver OSI (4.2 ± 1.4 vs 6.8 ± 1.9), and improved serum TAC (1.0 ± 0.2 vs 0.4 ± 0.1 mmol Trolox/L), compared with the untreated diabetic group.

CONCLUSIONS

Streptozotocin-diabetes resulted in increased deposition of AGEs and increased oxidative stress in the serum and liver. Vitamin D supplementation may provide significant protection against oxidative stress-mediated vascular complications in diabetes.

Oxidative stress as an underlying contributor in the development of chronic complications in diabetes mellitus

The high prevalence of diabetes mellitus and its increasing incidence worldwide, coupled with several complications observed in its carriers, have become a public health issue of great relevance. Chronic hyperglycemia is the main feature of such a disease, being considered the responsible for the establishment of micro and macrovascular complications observed in diabetes. Several efforts have been directed in order to better comprehend the pathophysiological mechanisms involved in the course of this endocrine disease. Recently, numerous authors have suggested that excess generation of highly reactive oxygen and nitrogen species is a key component in the development of complications invoked by hyperglycemia. Overproduction and/or insufficient removal of these reactive species result in vascular dysfunction, damage to cellular proteins, membrane lipids and nucleic acids, leading different research groups to search for biomarkers which would be capable of a proper and accurate measurement of the oxidative stress (OS) in diabetic patients, especially in the presence of chronic complications. In the face of this scenario, the present review briefly addresses the role of hyperglycemia in OS, considering basic mechanisms and their effects in diabetes mellitus, describes some of the more commonly used biomarkers of oxidative/nitrosative damage and includes selected examples of studies which evaluated OS biomarkers in patients with diabetes, pointing to the relevance of such biological components in general oxidative stress status of diabetes mellitus carriers.

Synthesis and evaluation of naphthoic acid derivatives as fluorescent probes to screen advanced glycation end-products breakers

Advanced glycation end-products, namely AGEs, are involved in the pathogenesis of numerous diseases. If AGEs inhibitors are well-known, only few products are described as compounds able to destroy those deleterious products. In this work, we describe naphthoic acid derivatives, particularly 1-(naphthalen-1-yl)propane-1,2-dione 9, allowing the simple and rapid detection of AGEs breakers using a 96-well microplate fluorescence assay. Since the inaugurate publication about AGEs breakers whose activity was demonstrated using HPLC analysis, this work proposes the first assay suitable for automated and high throughput screening of AGEs breakers.

Evaluation of the antioxidant and anti-glication effects of the hexane extract from Piper auritum leaves in vitro and beneficial activity on oxidative stress and advanced glycation end-product-mediated renal injury in streptozotocin-treated diabetic rats

The aim of this study was to investigate the antioxidant activity of hexane extracts from leaves of Piper auritum (HS). Eight complementary in vitro test methods were used, including inhibition of DPPH· radicals, nitric oxide, superoxide anion, ion-chelating, ABTS, oxygen radical absorbance capacity, β-carotene bleaching and peroxy radical scavenging. The results indicated that HS possesses high antioxidant activity. To add to these finding we tested the effect against oxidative stress in liver, pancreas and kidney in diabetic rats. Low levels of SOD, CAT, GPx and GSH in diabetic rats were reverted to near normal values after treatment with HS. These results suggest that P. auritum prevents oxidative stress, acting as a suppressor of liver cell damage. Given the link between glycation and oxidation, we proposed that HS might possess significant in vitro antiglycation activity. Our data confirmed the inhibitory effect of HS on bovine serum albumin, serum glycosylated protein, glycation of LDL, and glycation hemoglobin. The effect of HS on diabetic renal damage was investigated using streptozotocin-induced diabetic rats. The oral administration of HS at a dose of 200 and 400 mg/kg body weight/day for 28 days significantly reduced advanced glycation endproduct (AGE) formation, elevated renal glucose and thiobarbituric acid-reactive substance levels in the kidneys of diabetic rats. This implies that HS would alleviate the oxidative stress under diabetes through the inhibition of lipid peroxidation. These findings indicate that oxidative stress is increased in the diabetic rat kidney and that HS can prevent renal damage associated with diabetes by attenuating the oxidative stress.