Kinetics of glycoxidation of bovine serum albumin by methylglyoxal and glyoxal and its prevention by various compounds

Strategies to make human skin models based on cellular senescence for ageing research

Human skin ageing is closely related to the ageing of the whole organism, and it's a continuous multisided process that is influenced not only by genetic and physiological factors but also by the cumulative impact of environmental factors. Currently, there is a scientific community need for developing skin models representing ageing processes to (i) enhance understanding on the mechanisms of ageing, (ii) discover new drugs for the treatment of age-related diseases, and (iii) develop effective dermo-cosmetics. Bioengineers worldwide are trying to reproduce skin ageing in the laboratory aiming to better comprehend and mitigate the senescence process. This review provides details on the main ageing molecular mechanisms and procedures to obtain in vitro aged skin models.

Anti-diabetes and neuroprotection potential and primary safety studies of Isatis tinctoria L. hydroalcoholic leaf extract

PURPOSE

Natural plant raw materials, previously underestimated in therapeutics, are becoming the subject of research for new applications in medicine. In our research, the hydroalcoholic extract of Isatis tinctoria leaf, rich in flavonoid compounds such as vicenin-2 and quercetin, was examined as a potential antidiabetic and neuroprotective agent.

METHODS

The effect of the extract and its main flavonoid compounds on protein glycation, alpha-glucosidase activity, and acetylcholinesterase activity was tested. In vitro, in the mouse hippocampal neuronal cell line and in vivo, using a mouse model, the safety of the extract was screened for.

RESULTS

Our experiments demonstrated significant inhibition of protein glycation, alpha-glucosidase activity, acetylcholinesterase activity, and β-amyloid aggregation by the extract, in a concentration-dependent manner. The extract had a strong reducing effect and did not exhibit cytotoxicity up to a concentration of 25 mg/mL. Intraperitoneal administration of the extract to mice did not have negative effects on body mass, locomotor activity, coordination, and liver cell integrity.

CONCLUSIONS

Our research sheds new light on this raw material and deepens knowledge of its activity. This may result in the recognition of its therapeutic effects and even in its introduction in the modern treatment of diseases characterized by pathological changes associated with hyperglycemia, oxidation, and inflammation.

Label-free visualization of unfolding and crosslinking mediated protein aggregation in nonenzymatically glycated proteins

Nonenzymatic glycation (NEG) unfolds and crosslinks proteins, resulting in aggregation. Label-free evaluation of such structural changes, without disturbing molecular integrity, would be beneficial for understanding the fundamental mechanisms of protein aggregation. The current study demonstrates the assessment of NEG-induced protein aggregation by combining autofluorescence (AF) spectroscopy and imaging. The methylglyoxal (MG) induced protein unfolding and the formation of cross-linking advanced glycation end-products (AGEs) leading to aggregation were evaluated using deep-UV-induced-autofluorescence (dUV-AF) spectroscopy in proteins with distinct structural characteristics. Since the AGEs formed on proteins are fluorescent, the study demonstrated the possibility of autofluorescence imaging of NEG-induced protein aggregates. Autofluorescence spectroscopy can potentially reveal molecular alterations such as protein unfolding and cross-linking. In contrast, AGE-based autofluorescence imaging offers a means to visually explore the structural arrangement of aggregates, regardless of whether they are amyloid or non-amyloid in nature.

Novel Properties of Old Propranolol-Assessment of Antiglycation Activity through In Vitro and In Silico Approaches

Hypertension has earned the "silent killer" nickname since it may lead to a number of comorbidities, including diabetes and cardiovascular diseases. Oxidative stress and protein glycation play vital roles in the pathogenesis of hypertension. Several studies have shown that they profoundly account for vascular dysfunction, endothelial damage, and disruption of blood pressure regulatory mechanisms. Of particular note are advanced glycation end products (AGEs). AGEs alter vascular tissues' functional and mechanical properties by binding to receptors for advanced glycation end products (RAGE), stimulating inflammation and free radical-mediated pathways. Propranolol, a nonselective beta-adrenergic receptor antagonist, is one of the most commonly used drugs to treat hypertension and cardiovascular diseases. Our study is the first to analyze propranolol's effects on protein glycoxidation through in vitro and in silico approaches. Bovine serum albumin (BSA) was utilized to evaluate glycoxidation inhibition by propranolol. Propranolol (1 mM) and BSA (0.09 mM) were incubated with different glycating (0.5 M glucose, fructose, and galactose for 6 days and 2.5 mM glyoxal and methylglyoxal for 12 h) or oxidizing agents (chloramine T for 1 h). Biomarkers of protein glycation (Amadori products (APs), β-amyloid (βA), and advanced glycation end products (AGEs)), protein glycoxidation (dityrosine (DT), kynurenine (KYN), and N-formylkynurenine (NFK)), protein oxidation (protein carbonyls (PCs), and advanced oxidation protein products (AOPPs)) were measured by means of colorimetric and fluorimetric methods. The scavenging of reactive oxygen species (hydrogen peroxide, hydroxyl radical, and nitric oxide) and the antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl radical and ferrous ion chelating (FIC) assays)) of propranolol were also evaluated. Additionally, in silico docking was performed to showcase propranolol's interaction with BSA, glycosides, and AGE/RAGE pathway proteins. The products of protein glycation (↓APs, ↓βA, ↓AGEs), glycoxidation (↓DT, ↓KYN, ↓NFK), and oxidation (↓PCs, ↓AOPPs) prominently decreased in the BSA samples with both glycating/oxidizing factors and propranolol. The antiglycoxidant properties of propranolol were similar to those of aminoguanidine, a known protein oxidation inhibitor, and captopril, which is an established antioxidant. Propranolol showed a potent antioxidant activity in the FIC and H2O2 scavenging assays, comparable to aminoguanidine and captopril. In silico analysis indicated propranolol's antiglycative properties during its interaction with BSA, glycosidases, and AGE/RAGE pathway proteins. Our results confirm that propranolol may decrease protein oxidation and glycoxidation in vitro. Additional studies on human and animal models are vital for in vivo verification of propranolol's antiglycation activity, as this discovery might hold the key to the prevention of diabetic complications among cardiology-burdened patients.

The antiglycation potential of H1 receptor antagonists - in vitro studies in bovine serum albumin model and in silico molecular docking analyses

The H1 receptor belongs to the family of rhodopsin-like G-protein-coupled receptors activated by the biogenic amine histamine. H1 receptor antagonists are widely used in the treatment of allergies. However, these drugs could have a much broader spectrum of activity, including hypoglycemic effects, which can broaden the spectrum of their use. The aim of the study was to evaluate the antiglycation potential of twelve H1 receptor antagonists (diphenhydramine, antazoline, promethazine, ketotifen, clemastine, pheniramine, cetirizine, levocetirizine, bilastine, fexofenadine, desloratadine, and loratadine). Bovine serum albumin (BSA) was glycated with sugars (glucose, fructose, galactose, and ribose) and aldehydes (glyoxal and methylglyoxal) in the presence of H1 blockers. The tested substances did not induce a significant decrease in the content of albumin glycation end-products, and the inhibition rate of glycoxidation was not influenced by the chemical structure or generation of H1 blockers. None of the tested H1 receptor antagonists exhibited strong antiglycation activity. Antiglycemic potential of H1 blockers could be attributed to their antioxidant and anti-inflammatory activity, as well as their effects on carbohydrate metabolism/metabolic balance at the systemic level.

Scavenging Glyoxal and Methylglyoxal by Synephrine Alone or in Combination with Neohesperidin at High Temperatures

α-Dicarbonyl compounds, such as glyoxal (GO) and methylglyoxal (MGO), are a series of chemical hazards that exist in vivo and in vitro, posing a threat to human health. We aimed to explore the scavenging effects on GO/MGO by synephrine (SYN) alone or in combination with neohesperidin (NEO). First, through LC-MS/MS, we confirmed that both SYN and NEO could effectively remove GO and form GO adducts, while NEO could also clear MGO by forming MGO adducts, and its ability to clear MGO was stronger than that of GO. Second, a synergistic inhibitory effect on GO was found when SYN and NEO were used in combination by using the Chou-Talalay method; on the other hand, SYN could promote NEO to clear more MGO, although SYN could not capture MGO. Third, after synthesizing four GO/MGO-adducts (SYN-GO-1, SYN-GO-3, NEO-GO-7, and NEO-MGO-2) and identifying their structure through NMR, strict correlations between the GO/MGO-adducts and the GO/MGO-clearance rate were found when using SYN and NEO alone or in combination. Furthermore, it was inferred that the synergistic effect between SYN and NEO stems from their mutual promotion in capturing more GO by the quantitative analysis of the adducts in the combined model. Finally, a study was conducted on flowers of Citrus aurantium L. var. amara Engl. (FCAVA, an edible tea) rich in SYN and NEO, which could serve as an effective GO and MGO scavenger in the presence of both GO and MGO. Therefore, our study provided well-defined evidence that SYN and NEO, alone or in combination, could efficiently scavenge GO/MGO at high temperatures, whether in the pure form or located in FCAVA.

Impact of using whole chestnut flour as a substitute for cake flour on digestion, functional and storage properties of chiffon cake: A potential application study

Developing fresh cake product with rich nutrition and high quality has become a hot spot in food industry. In this study, whole chestnut flour as a high-quality dietary source was successfully substituted for cake flour in the production of chestnut chiffon cake with 40-55% substitution rate, and its application prospects were further evaluated through studying nutritional and storage properties. The results showed that chestnut chiffon cake with 45% and 50% substitution rate could significantly increase the resistant component, scavenging activity and ferric reducing antioxidant power, surprisingly decrease predicted glycemic index to 54.05-57.28, and reduce the acetate/propionate ratio and Firmicutes/Bacteroidetes value for human gut microbiota as well. Comparatively, chestnut chiffon cake with 45% substitution rate had more application potential due to its higher free water retention at day 7 and higher resilience throughout the storage time. Overall, this study could provide valuable information for the development of modern nutritional cake industry.

Protein Advanced Glycation End Products and Their Implications in Pancreatic Cancer

Protein advanced glycation end products (AGE) formed by nonenzymatic glycation can disrupt the normal structure and function of proteins, and stimulate the receptor for AGEs (RAGE), triggering intricate mechanisms that are etiologically related to various chronic diseases, including pancreatic cancer. Many common risk factors of pancreatic cancer are the major sources for the formation of protein AGEs and glycative stress in the human body. Abnormal accumulation of protein AGEs can impair the cellular proteome and promote AGE-RAGE driven pro-inflammatory signaling cascades, leading to increased oxidative stress, protease resistance, protein dysregulation, transcription activity of STAT, NF-κB, and AP-1, aberrant status in ubiquitin-proteasome system and autophagy, as well as other molecular events that are susceptible for the carcinogenic transformation towards the development of neoplasms. Here, we review studies to highlight our understanding in the orchestrated molecular events in bridging the impaired proteome, dysregulated functional networks, and cancer hallmarks initiated upon protein AGE formation and accumulation in pancreatic cancer.

Antioxidant and Anti-Glycation Potential of H2 Receptor Antagonists-In Vitro Studies and a Systematic Literature Review

Background: Histamine H2 receptor antagonists are a group of drugs that inhibit gastric juice secretion in gastrointestinal diseases. However, there is evidence to suggest that H2 blockers have a broader spectrum of activity. The antioxidant properties of H2 blockers have not been fully elucidated, and their anti-glycation potential has not been studied to date. Therefore, this is the first study to compare the antioxidant and antiglycation potentials of the most popular H2 antagonists (ranitidine, cimetidine, and famotidine) on protein glycoxidation in vitro. Methods: Bovine serum albumin (BSA) was glycated using sugars (glucose, fructose, galactose, and ribose) as well as aldehydes (glyoxal and methylglyoxal). Results: In the analyzed group of drugs, ranitidine was the only H2 blocker that significantly inhibited BSA glycation in all tested models. The contents of protein carbonyls, protein glycoxidation products (↓dityrosine, ↓N-formylkynurenine), and early (↓Amadori products) and late-stage (↓AGEs) protein glycation products decreased in samples of glycated BSA with the addition of ranitidine relative to BSA with the addition of the glycating agents. The anti-glycation potential of ranitidine was comparable to those of aminoguanidine and Trolox. In the molecular docking analysis, ranitidine was characterized by the lowest binding energy for BSA sites and could compete with protein amino groups for the addition of carbonyl groups. H2 blockers also scavenge free radicals. The strongest antioxidant properties are found in ranitidine, which additionally has the ability to bind transition metal ions. The systematic literature review also revealed that the anti-glycation effects of ranitidine could be attributed to its antioxidant properties. Conclusions: Ranitidine showed anti-glycation and antioxidant properties. Further research is needed, particularly in patients with diseases that promote protein glycation.

Black Pepper (Piper nigrum) Alleviates Oxidative Stress, Exerts Potential Anti-Glycation and Anti-AChE Activity: A Multitargeting Neuroprotective Agent against Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a family of disorders that cause progressive structural and functional degeneration of neurons. Among all the organs in the body, the brain is the one that is the most affected by the production and accumulation of ROS. Various studies have shown that an increase in oxidative stress is a common pathophysiology for almost all NDs, which further affects various other pathways. The available drugs lack the wide spectrum necessary to confront these complexities altogether. Hence, a safe therapeutic approach to target multiple pathways is highly desirable. In the present study, the hexane and ethyl acetate extracts of Piper nigrum (black pepper), an important spice, were evaluated for their neuroprotective potential in hydrogen peroxide-induced oxidative stress in human neuroblastoma cells (SH-SY5Y). The extracts were also subjected to GC/MS to identify the important bioactives present. The extracts exhibited neuroprotection by significantly decreasing the oxidative stress and restoring the mitochondrial membrane potential in the cells. Additionally, the extracts displayed potent anti-glycation and significant anti-Aβ fibrilization activities. The extracts were competitive inhibitors of AChE. The multitarget neuroprotective mechanism displayed by Piper nigrum indicates it as a potential candidate in the treatment of NDs.

Agomelatine's antiglycoxidative action-In vitro and in silico research and systematic literature review

Introduction

Agomelatine is an atypical antidepressant drug enhancing norepinephrine and dopamine liberation; nevertheless, additional mechanisms are considered for the drug's pharmacological action. Since protein glycoxidation plays a crucial role in depression pathogenesis, agomelatine's impact on carbonyl/oxidative stress was the research purpose.

Methods

Reactive oxygen species scavenging (hydroxyl radical, hydrogen peroxide, and nitrogen oxide) and antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl radical and ferrous ion chelating assays) of agomelatine were marked. Agomelatine's antiglycoxidation properties were assayed in sugars (glucose, fructose, and galactose) and aldehydes- (glyoxal and methylglyoxal) glycated bovine serum albumin (BSA). Aminoguanidine and α-lipoic acid were used as standard glycation/oxidation inhibitors.

Results

Agomelatine did not show meaningful scavenging/antioxidant capacity vs. standards. Sugars/aldehydes increased glycation (↑kynurenine, ↑N-formylkynurenine, ↑dityrosine, ↑advanced glycation end products, and ↑β-amyloid) and oxidation (↑protein carbonyls and ↑advanced oxidation protein products) parameters in addition to BSA. Standards restored BSA baselines of glycation and oxidation markers, unlike agomelatine which sometimes even intensifies glycation above BSA + glycators levels. Molecular docking analysis of agomelatine in BSA demonstrated its very weak binding affinity.

Discussion

Agomelatine's very low affinity to the BSA could proclaim non-specific bonding and simplify attachment of glycation factors. Thereby, the drug may stimulate brain adaptation to carbonyl/oxidative stress as the systematic review indicates. Moreover, the drug's active metabolites could exert an antiglycoxidative effect.

Interaction of Hyaluronan Acid with Some Proteins in Aqueous Solution as Studied by NMR

According to actual literature data, hyaluronic acid (HA) that is presented in the extracellular matrix can interact with proteins and thereby affect several important functions of the cell membrane. The purpose of this work was to reveal the features of the interaction of HA with proteins using the PFG NMR method by sampling two systems: aqueous solutions of HA with bovine serum albumin (BSA) and aqueous solutions of HA with hen egg-white lysozyme (HEWL). It was found that the presence of BSA in the HA aqueous solution initiates a certain additional mechanism; as a result, the population of HA molecules in the gel structure increases to almost 100%. At the same time, for an aqueous solution of HA/HEWL, even in the range of low (0.01-0.2%) HEWL contents, strong signs of degradation (depolymerization) of some HA macromolecules were observed such that they lost the ability to form a gel. Moreover, lysozyme molecules form a strong complex with degraded HA molecules and lose their enzymatic function. Thus, the presence of HA molecules in the intercellular matrix, as well as in the state associated with the surface of the cell membrane, can, in addition to the known ones, perform one more important function: the function of protecting the cell membrane from the destructive action of lysozymes. The obtained results are important for understanding the mechanism and features of the interaction of extracellular matrix glycosaminoglycan with cell membrane proteins.

In Vitro Antiglycation Potential of Erva-Baleeira (Varronia curassavica Jacq.)

BACKGROUND

Varronia curassavica Jacq. (Boraginaceae) is traditionally used in the treatment of inflammatory processes. The ethanolic extract of its leaves (EEVc) showed anti-inflammatory properties and low toxicity. Medicinal plants have aroused interest for their antiglycation activities. The formation and accumulation of advanced glycation end products (AGEs) are associated with several chronic diseases. The objective of this study was to evaluate the antiglycation potential of EEVc and two isolated compounds.

METHODS

The compounds brickellin and cordialin A were obtained by chromatographic methods and identified by spectrometric techniques. Analysis of fluorescent AGEs, biomarkers of amino acid residue oxidation, protein carbonyl groups and crosslink formation were performed in samples obtained from an in vitro model system of protein glycation with methylglyoxal.

RESULTS

EEVc, brickellin and cordialin A significantly reduced the in vitro formation of AGEs, and reduced the damage caused by oxidative damage to the protein.

CONCLUSIONS

According to the results, EEVc, brickellin and cordialin A are potential candidates against AGEs formation, which opens the way to expand the therapeutic arsenal for many pathologies resulting from glycoxidative stress.

Two faces of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) - An antioxidant or a toxin?

2,2,6,6-Tetramethylpiperidine-1-oxyl, commonly known as TEMPO, is one of the compounds called nitroxides that are used in the chemical industry for synthesis of many organic compounds as well as for electrodes in all-organic radical batteries. Additionally, TEMPO is a widely used antioxidant in scientific studies. Technological progress and simultaneous care for the environment leads to resorting to new industrial methods which require the use of compounds that have not been fully tested for their impact on living organisms. Therefore, TEMPO may be an environmental pollutant and its effect on living organisms is not fully understood. The aim of our study was to determine the influence of TEMPO on the physiology, chronological lifespan and wide transcription changes of a eukaryotic model organism, namely the Saccharomyces cerevisiae yeast. For this purpose, we used the BY4741 wild-type and isogenic mutants with a disorder in the response to oxidative stress (sod1Δ, sod2Δ, yap1Δ) and repair of DNA damage (rad52Δ). We showed that supplementation with TEMPO inhibited the cell growth rate of all analyzed strains while simultaneously slowing down the aging of post-mitotic cells in the yeast population. In addition, TEMPO-treated yeast cells manifested a significantly increased level of metabolism in the wild-type and sod2Δ strains. TEMPO also displayed genoprotective effect by reducing the number of DNA double-strand breaks in cells. Here, we are the first to show the widespread effect of TEMPO on yeast. In conclusion, we have shown that, contrary to the commonly accepted notion, TEMPO has also a toxic effect, especially on active mitotic cells. We hypothesize that translation impairment or ribosome biogenesis disorder is likely to be considered secondary effects of TEMPO toxicity related to cell cycle arrest. Therefore, despite the growing interest in the use of this compound in the chemical industry, its toxic effect on the environment, especially biosphere, should be taken into account.

Antiglycoxidative properties of amantadine – a systematic review and comprehensive in vitro study

An important drug used in the treatment of Parkinson’s disease is amantadine. We are the first to perform a comprehensive study based on various glycation and oxidation factors, determining the impact of amantadine on protein glycoxidation. Sugars (glucose, fructose, galactose) and aldehydes (glyoxal, methylglyoxal) were used as glycation agents, and chloramine T was used as an oxidant. Glycoxidation biomarkers in albumin treated with amantadine were generally not different from the control group (glycation/oxidation factors), indicating that the drug did not affect oxidation and glycation processes. Molecular docking analysis did not reveal strong binding sites of amantadine on the bovine serum albumin structure. Although amantadine poorly scavenged hydroxyl radical and hydrogen peroxide, it had significantly lower antioxidant and antiglycation effect than all protein oxidation and glycation inhibitors. In some cases, amantadine even demonstrated glycoxidant, proglycation, and prooxidant properties. In summary, amantadine exhibited weak antioxidant properties and a lack of antiglycation activity.

Phytochemicals as Potential Inhibitors of Advanced Glycation End Products: Health Aspects and Patent Survey

BACKGROUND

The glycation of proteins and lipids synthesizes the advanced glycation end products (AGEs), i.e., substances that irreversibly damage macromolecules present in tissues and organs, which contribute to the impairment of biological functions. For instance, the accumulation of AGEs induces oxidative stress, the inflammatory responses, and consequently the on set/worsening of diseases, including obesity, asthma, cognitive impairment, and cancer. There is a current demand on natural and low-cost sources of anti-AGE agents. As a result, food phytochemicals presented promising results to inhibit glycation and consequently, the formation of AGEs.

OBJECTIVE

Here we describe how the AGEs are present in food via Maillard reaction and in organs via natural aging, as well as the effects of AGEs on the worsening of diseases. Also we described the methods used to detect AGEs in samples, and the current findings on the use of phytochemicals (phenolic compounds, phytosterols, carotenoids, terpenes and vitamins) as natural therapeuticals to inhibit health damages via inhibition of AGEs in vitro and in vivo.

METHODS

This manuscript reviewed publications available in the PubMed and Science Direct databases dated from the last 20 years on the uses of phytochemicals for the inhibition of AGEs. Recent patents on the use of anti-AGEs drugs were reviewed with the use of Google Advanced Patents database.

RESULTS AND DISCUSSION

There is no consensus about which concentration of AGEs in blood serum should not be hazardous to the health of individuals. Food phytochemicals derived from agroindustry wastes, including peanut skins, and the bagasses derived from citrus and grapes are promising anti-AGEs agents via scavenging of free radicals, metal ions, the suppression of metabolic pathways that induces inflammation, the activation of pathways that promote antioxidant defense, and the blocking of AGE connection with the receptor for advanced glycation endproducts (RAGE).

CONCLUSION

Phytochemicals derived from agroindustry are promising anti-AGEs, which can be included to replace synthetic drugs to inhibit AGE formation, and consequently to act as therapeutical strategy to prevent and treat diseases caused by AGEs, including diabetes, ovarian cancer, osteoporosis, and Alzheimer's disease.

Neutrophil Activation by Mineral Microparticles Coated with Methylglyoxal-Glycated Albumin

Hyperglycemia-induced protein glycation and formation of advanced glycation end-products (AGEs) plays an important role in the pathogenesis of diabetic complications and pathological biomineralization. Receptors for AGEs (RAGEs) mediate the generation of reactive oxygen species (ROS) via activation of NADPH-oxidase. It is conceivable that binding of glycated proteins with biomineral particles composed mainly of calcium carbonate and/or phosphate enhances their neutrophil-activating capacity and hence their proinflammatory properties. Our research managed to confirm this hypothesis. Human serum albumin (HSA) was glycated with methylglyoxal (MG), and HSA-MG was adsorbed onto mineral microparticles composed of calcium carbonate nanocrystals (vaterite polymorph, CC) or hydroxyapatite nanowires (CP). As scopoletin fluorescence has shown, H₂O₂ generation by neutrophils stimulated with HSA-MG was inhibited with diphenyleneiodonium chloride, wortmannin, genistein and EDTA, indicating a key role for NADPH-oxidase, protein tyrosine kinase, phosphatidylinositol 3-kinase and divalent ions (presumably Ca²⁺) in HSA-MG-induced neutrophil respiratory burst. Superoxide anion generation assessed by lucigenin-enhanced chemiluminescence (Luc-CL) was significantly enhanced by free HSA-MG and by both CC-HSA-MG and CP-HSA-MG microparticles. Comparing the concentrations of CC-bound and free HSA-MG, one could see that adsorption enhanced the neutrophil-activating capacity of HSA-MG.

Oleuropein-Enriched Extract From Olive Mill Leaves by Homogenizer-Assisted Extraction and Its Antioxidant and Antiglycating Activities

Olive oil consumption has increased in the last two decades and consequently, its wastes have increased, which generates a tremendous environmental impact. Among the by-products are the olive mill leaves, which are easier and inexpensive to treat than other olive by-products. However, little research has been done on their chemical composition and potential bioactivity. Hence, in this study, olive mill leaves were used to obtain Oleuropein-Enriched Extracts (OLEU-EE) using Conventional Extraction, Ultrasound-Assisted Extraction, and Homogenization-Assisted Extraction. These three techniques were evaluated using a Factorial Design to determine the parameters to obtain an OLEU-EE with high contents of Total Phenolic Compounds (TPC), Antioxidant Activity (AA), and Oleuropein concentration (OLEU). From the results, the Homogenizer-Assisted Extraction (HAE) technique was selected at 18,000 rpm, solid:liquid ratio 1:10, and 30 s of homogenization with 70% ethanol, due to its high TPC (5,196 mg GA/100 g), AA (57,867 μmol of TE/100 g), and OLEU (4,345 mg of OLEU/100 g). In addition, the antiglycating effect of OLEU-EE on the levels of (1) fluorescent Advanced Glycation End Products (AGEs) were IC50 of 0.1899 and 0.1697 mg/mL for 1λEXC 325/λEM 440 and 2λEXC 389/λEM 443, respectively; (2) protein oxidative damage markers such as dityrosine (DiTyr), N-formylkynurenine (N-formyl Kyn), and kynurenine (Kyn) were IC50 of 0.1852, 0.2044, and 0.1720 mg/mL, respectively. In conclusion, OLEU-EE from olive mill leaves has different capacities to inhibit AGEs evidenced by the IC50 of fluorescent AGEs and protein oxidation products, together with the scavenging free radical evidenced by the concentration of Trolox Equivalent. Therefore, OLEU-EE could be potential functional ingredients that prevent oxidative damage caused by free radicals and AGEs accumulation.

Anti-Glycation and Anti-Aging Properties of Resveratrol Derivatives in the in-vitro 3D Models of Human Skin

Purpose

Human skin undergoes modifications affecting its structural properties and barrier functions involved in protection against age-related damage. Glycation is a non-enzymatic reaction between macromolecules and sugars causing alterations to the elastic fibers and premature aging of the skin. Glycation can be prevented by a range of bioactive molecules; however, at present only a few of them are validated for inclusion in cosmetic products. There is also a demand for reproducible in-vitro assays demonstrating the anti-aging effect of compounds on the skin. This study aimed to define the potential targets for screening and validation of anti-glycation activity of novel cosmetic candidates from natural products and to provide a plausible mechanism for their anti-aging potential based on 3D skin models.

Methods

Dermal fibroblasts and 3D skin models were treated with glycation agent and topical applications of Resveratrol derivatives. The samples were analyzed for advanced glycation end products (AGEs) alongside an organization of elastic fibers and expression of proliferative, senescence, and oxidative stress markers by autofluorescence, immunocytochemistry and quantitative assays.

Results

Accumulation of AGEs in the 3D skin model is associated with reduced stratification of the epidermis and re-organization of the collagen in the upper, cell-dense layer of the dermis. Treatment of dermal fibroblasts with Resveratrol, OxyResveratrol, Piceatannol, and Triacetyl Resveratrol ameliorates the effects of glycation consistent with cellular aging. Subsequent topical application of the compounds in skin models results in a reduction in glycation-induced AGEs, an increase in collagen expression and a stratification of the epidermis.

Conclusion

Glycation could result in age-related alterations in the structural and cellular organizations of the superficial layers of the skin, which can be restored by Resveratrol derivatives, pointing to their promising capacities as bioactive ingredients in cosmetic products. Insight into the potential parameters affected by skin glycation could also serve as a reference for screening the bioactive molecules for cosmetic purposes.

Fructose and methylglyoxal-induced glycation alters structural and functional properties of salivary proteins, albumin and lysozyme

Glycation process refers to reactions between reduction sugars and amino acids that can lead to formation of advanced glycation end products (AGEs) which are related to changes in chemical and functional properties of biological structures that accumulate during aging and diseases. The aim of this study was to perform and analyze in vitro glycation by fructose and methylglyoxal (MGO) using salivary fluid, albumin, lysozyme, and salivary α-amylase (sAA). Glycation effect was analyzed by biochemical and spectroscopic methods. The results were obtained by fluorescence analysis, infrared spectroscopy (total attenuated reflection-Fourier transform, ATR-FTIR) followed by multivariate analysis of principal components (PCA), protein profile, immunodetection, enzymatic activity and oxidative damage to proteins. Fluorescence increased in all glycated samples, except in saliva with fructose. The ATR-FTIR spectra and PCA analysis showed structural changes related to the vibrational mode of glycation of albumin, lysozyme, and salivary proteins. Glycation increased the relative molecular mass (Mr) in protein profile of albumin and lysozyme. Saliva showed a decrease in band intensity when glycated. The analysis of sAA immunoblotting indicated a relative reduction in intensity of its correspondent Mr after sAA glycation; and a decrease in its enzymatic activity was observed. Carbonylation levels increased in all glycated samples, except for saliva with fructose. Thiol content decreased only for glycated lysozyme and saliva with MGO. Therefore, glycation of salivary fluid and sAA may have the potential to identify products derived by glycation process. This opens perspectives for further studies on the use of saliva, an easy and non-invasive collection fluid, to monitor glycated proteins in the aging process and evolution of diseases.

Inhibition on α-Glucosidase Activity and Non-Enzymatic Glycation by an Anti-Oxidative Proteoglycan from Ganoderma lucidum

The prevention of postprandial hyperglycemia and diabetic complications is crucial for diabetes management. Inhibition of α-glucosidase to slow carbohydrate metabolism is a strategy to alleviate postprandial hyperglycemia. In addition, suppression of non-enzymatic glycation can diminish the advanced glycation end products and reduce the oxidative stress and inflammation, thereby preventing the diabetic complications. In this study, an anti-oxidative proteoglycan (named FYGL) extracted from Ganoderma lucidum was investigated in vitro for its inhibitory effect on α-glucosidase and non-enzymatic glycation using molecular kinetics, intrinsic fluorescence assay, and bovine serum albumin glycation models. The molecular kinetics and fluorescence assay revealed that FYGL decreases α-glucosidase activity by forming a FYGL-α-glucosidase complex. To evaluate the anti-glycation effect, fructose-glycated and methylglyoxal-glycated BSA models were analyzed by spectroscopic and SDS-PAGE methods. Results showed that FYGL inhibited the glycation at every stage and suppressed glycoxidation, possibly due to its anti-oxidative capacity and FYGL-BSA complex formation. Furthermore, we demonstrated in vivo that FYGL could alleviate postprandial hyperglycemia in db/db mice as well as AGE accumulation and vascular injury in diabetic rats. Overall, FYGL possesses anti-postprandial hyperglycemia and anti-glycation functions and would be potentially used in clinic for diabetes and related complication management.

Evidence from a Systematic Review and Meta-Analysis Pointing to the Antidiabetic Effect of Polyphenol-Rich Plant Extracts from Gymnema montanum, Momordica charantia and Moringa oleifera

In vitro and animal model studies are of great interest for selecting new phytochemicals, including polyphenols with antioxidative properties, as candidates for antidiabetic drugs. This review provides evidence from a critical literature data analysis on the effects of plant extract supplementation in diabetes mellitus management. We considered and meta-analyzed the efficacy of oral supplementation of plant extracts in animal model studies and examined physiological and oxidative stress parameters. Finally, 23 articles were included in the meta-analysis, revealing three plants with experimentally confirmed in vivo and in vitro antidiabetic properties: Gymnema montanum, Momordica charantia and Moringa oleifera. The following parameter changes resulted from an investigation of the supplementation: reduced oxidative stress, decreased insulin resistance, increased insulin release, reduced adiposity, and a modulatory effect on glycolysis and gluconeogenesis, as well as attenuation of diabetes-associated weight loss, reduced fasting blood glucose and lowered oxidative status. A comparison of Gymnema montanum versus Glybenclamide revealed the superiority of extracts over drug administration in some aspects. Although the analyzed extracts are promising candidates for antidiabetic treatment, there is much inconsistent data in the literature. Therefore, ultimate references for using these compounds in the prevention of diabetes are currently not applicable.

Role of saturated and unsaturated fatty acids on dicarbonyl-albumin derived advanced glycation end products in vitro

Glycation is a non-enzymatic reaction that occurs between the free amino group of proteins and reducing sugars and/or lipids, leading to the formation of advanced glycation end products (AGEs). The reaction also produces reactive oxygen species that have detrimental effects on cellular and extracellular proteins. Aminoguanidine is a known inhibitor of AGEs, and some fatty acids are known to have a beneficial role in vivo by reducing inflammation and oxidative stress. However, the role of fatty acids on AGE formation has not been thoroughly reported. We investigated the role of a range of fatty acids in the formation of AGEs and their reactive intermediates using an in vitro BSA-dicarbonyl model. The model assessed a time-dependent (0-72 h) and dicarbonyl concentration (0-2 mM) -dependent studies for the optimal formation of AGEs. A 72 h time point was found to be optimal for the reaction of BSA with either methylglyoxal (MGO) or glyoxal (GO) to generate AGE-BSA complexes. When arachidonic, eicosapentaenoic or docosahexaenoic acids were included in the reaction, a significant decrease in protein-bound fluorescent AGEs was seen compared to the respective controls. In contrast, saturated and 18 carbon polyunsaturated fatty acids showed no significant activity. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis showed saturated fatty acids significantly decreased the production of N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) from GO and MGO models, respectively, whilst increasing methylglyoxal-derived hydroimidazolone (MG-H1). In contrast, arachidonic, eicosapentaenoic and docosahexaenoic acids did not significantly change either CEL or MG-H1 compared to no treatment controls whilst significantly reducing CML levels.

Dual-Retarder Mueller Polarimetry System for Extraction of Optical Properties of Serum Albumin Protein Media

A dual liquid-crystal variable retarder Mueller polarimetry system incorporating a gold-based surface plasmon resonance prism coupler was proposed for extracting the optical properties of serum albumin protein media in the reflectance configuration. The feasibility of the proposed system was demonstrated by measuring the circular dichroism and circular birefringence properties of glucose tissue phantom solutions with different albumin concentrations. The results showed that the circular dichroism increased with albumin concentration, while the optical rotation angle increased with glucose concentration. Both properties reduced over time as a result of the protein glycation effect, which led to a gradual reduction in the glucose content of the sample.

Pleiotropic Properties of Valsartan: Do They Result from the Antiglycooxidant Activity? Literature Review and In Vitro Study

Valsartan belongs to angiotensin II type 1 (AT1) receptor blockers (ARB) used in cardiovascular diseases like heart failure and hypertension. Except for its AT1-antagonism, another mechanism of drug action has been suggested in recent research. One of the supposed actions refers to the positive impact on redox balance and reducing protein glycation. Our study is aimed at assessing the antiglycooxidant properties of valsartan in an in vitro model of oxidized bovine serum albumin (BSA). Glucose, fructose, ribose, glyoxal (GO), methylglyoxal (MGO), and chloramine T were used as glycation or oxidation agents. Protein oxidation products (total thiols, protein carbonyls (PC), and advanced oxidation protein products (AOPP)), glycooxidation products (tryptophan, kynurenine, N-formylkynurenine, and dityrosine), glycation products (amyloid-β structure, fructosamine, and advanced glycation end products (AGE)), and albumin antioxidant activity (total antioxidant capacity (TAC), DPPH assay, and ferric reducing antioxidant power (FRAP)) were measured in each sample. In the presence of valsartan, concentrations of protein oxidation and glycation products were significantly lower comparing to control. Moreover, albumin antioxidant activity was significantly higher in those samples. The drug's action was comparable to renowned antiglycation agents and antioxidants, e.g., aminoguanidine, metformin, Trolox, N-acetylcysteine, or alpha-lipoic acid. The conducted experiment proves that valsartan can ameliorate protein glycation and oxidation in vitro in various conditions. Available animal and clinical studies uphold this statement, but further research is needed to confirm it, as reduction of protein oxidation and glycation may prevent cardiovascular disease development.

Polyphenol-rich Indian ginger cultivars ameliorate GLUT4 activity in C2C12 cells, inhibit diabetes-related enzymes and LPS-induced inflammation: An in vitro study

Diabetes is a chronic metabolic disorder that results in distorted insulin signaling and microvascular complications. Current antidiabetic drugs possess harmful long term side effects, necessitating the need for alternate or compliment therapy with lesser issues. Medicinal plants such as ginger have been reported to possess several beneficial activities including antidiabetic activity. The antidiabetic efficacy of microwave-assisted polyphenolic extracts of Indian ginger cultivars from Odisha (MPO) and Tamil Nadu (MPT) is reported here. MPT and MPO showed insulin stimulated glucose uptake of 1.74 ± 0.25 and 1.47 ± 0.15 fold at 6.25 µg/ml of concentrations in C2C12 cells respectively when compared to control. MPT possessed α-amylase, α-glucosidase inhibitory and anti-glycation properties. It also showed DPPH radical scavenging activity (7.69 ± 0.001%), inhibited LPS-induced nitric oxide production (1.06 ± 0.004 fold) than the latter and increased the GLUT4 protein expression by 1.4 fold. Major active compounds such as shogaol and gingerol derivatives, curcumene, zingiberone were identified through GC-ESI/MS analysis and D-pinitol (cyclitol) was identified through HPLC analysis in this variety. This is the first paper to report the presence of an antidiabetic compound, D-pinitol, in the ginger variety. Polyphenol rich, biologically potent ginger extracts can be a good food and nutraceutical supplement to address diabetes and related complications. PRACTICAL APPLICATIONS: Ginger is a native spice of South Asian Countries including India. Ginger extracts possess several medicinal properties such as anti-inflammatory, antidiabetic and antioxidant activities. It is used to treat nausea, vomiting and commonly used as a food flavouring agent and dietary food supplement. Our study shows the antidiabetic, anti-glycation and antioxidant efficacy of polyphenol rich Indian ginger cultivars grown in different geographical regions. Variations in the biological activities between the MPT and MPO ginger variety was observed. Different environmental conditions and their corresponding metabolite accumulation can be correlated with the better activity shown by MPT variety. It showed an increased GLUT4 expression even at a lower dose of 6.25 µg/ml. Ginger cultivar, especially MPT variety can be used as an adjuvant therapy for treating diabetes. Therefore, our study indicates that polyphenols rich ginger cultivar has major application in functional food product development.

Protective actions of bioactive flavonoids chrysin and luteolin on the glyoxal induced formation of advanced glycation end products and aggregation of human serum albumin: In vitro and molecular docking analysis

The post-translational modification of proteins by nonenzymatic glycation (NEG) and the accumulation of AGEs are the two underlying factors associated with the long-term pathogenesis in diabetes. Glyoxal (GO) is a reactive intermediate which has the ability to modify proteins and generate AGEs at a faster rate. Human serum albumin (HSA) being the most abundant serum protein has a higher chance to be modified by NEG. The key objective of the present study is to investigate the potency of chrysin and luteolin as antiglycating and antifibrillating agents in the GO-mediated glycation and fibril formation of HSA. AGEs formation were confirmed from the absorption and fluorescence spectral measurements. Both the flavonoids were able to quench the AGEs fluorescence intensity in vitro indicating the antiglycating nature of the molecules. The formation of fibrils in the GO-modified HSA was confirmed by the Thioflavin T (ThT) fluorescence assay and the flavonoids were found to exihibit the antifibrillation properties in vitro. Docking results suggested that both the flavonoids interact with various amino acid residues of subdomain IIA including glycation prone lysines and arginines via non-covalent forces and further stabilized the structure of HSA, which further explains their mechanisms of action as antiglycating and antifibrillating agents.

A New Insight into Meloxicam: Assessment of Antioxidant and Anti-Glycating Activity in In Vitro Studies

Meloxicam is a non-steroidal anti-inflammatory drug, which has a preferential inhibitory effect to cyclooxyganase-2 (COX-2). Although the drug inhibits prostaglandin synthesis, the exact mechanism of meloxicam is still unknown. This is the first study to assess the effect of meloxicam on protein glyco-oxidation as well as antioxidant activity. For this purpose, we used an in vitro model of oxidized bovine serum albumin (BSA). Glucose, fructose, ribose, glyoxal and methylglyoxal were used as glycating agents, while chloramine T was used as an oxidant. We evaluated the antioxidant properties of albumin (2,2-di-phenyl-1-picrylhydrazyl radical scavenging capacity, total antioxidant capacity and ferric reducing antioxidant power), the intensity of protein glycation (Amadori products, advanced glycation end products) and glyco-oxidation (dityrosine, kynurenine, N-formylkynurenine, tryptophan and amyloid-β) as well as the content of protein oxidation products (advanced oxidation protein products, carbonyl groups and thiol groups). We have demonstrated that meloxicam enhances the antioxidant properties of albumin and prevents the protein oxidation and glycation under the influence of various factors such as sugars, aldehydes and oxidants. Importantly, the antioxidant and anti-glycating activity is similar to that of routinely used antioxidants such as captopril, Trolox, reduced glutathione and lipoic acid as well as protein glycation inhibitors (aminoguanidine). Pleiotropic action of meloxicam may increase the effectiveness of anti-inflammatory treatment in diseases with oxidative stress etiology.

Antiglycation Activities and Common Mechanisms Mediating Vasculoprotective Effect of Quercetin and Chrysin in Metabolic Syndrome

Multiple risk factors combine to increase the risk of vascular dysfunction in patients suffering from metabolic syndrome (MetS). The current study investigates the extent to which quercetin (Q) and chrysin (CH) protect against vascular dysfunction in MetS rats. MetS was induced by feeding rats a high-salt diet (3%) and fructose-enriched water (10%) for 12 weeks. Thoracic aorta was isolated from MetS rats and from control rats, with the latter being injured by methylglyoxal (MG). Aortae were incubated with CH and Q, and vascular reactivity was evaluated through the analysis of aortic contraction and relaxation in response to PE and ACh, respectively. The formation of advanced glycation end products (AGEs) and the free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) were also evaluated following the introduction of CH and Q. The increased vasoconstriction and impaired vasodilation in MetS aortae were significantly ameliorated by Q and CH. Similarly, they ameliorated glycation-associated exaggerated vasoconstriction and impaired vasodilation produced by MG in control aortae. In addition, both Q and CH were effective in reducing the formation of AGEs and inhibition of glycosylation in response to MG or fructose treatment. Finally, Q successfully scavenged DPPH free radicals while CH showed significant vasodilation of precontracted aorta that was inhibited by L-NAME. In conclusion, Q and CH provide protection against vascular dysfunction in MetS by interfering with AGEs formations and AGEs-associated vascular deterioration, with CH being largely dependent on NO-mediated mechanisms of vasodilation.

Effect of advanced glycation end products on platelet activation and aggregation: a comparative study of the role of glyoxal and methylglyoxal

Advanced glycation end products (AGEs) arising from dietary intake have been associated with numerous chronic diseases including cardiovascular diseases. The interaction between platelets and AGEs has been proposed to play a role in the etiology of cardiovascular diseases. However, the effects of the interaction between platelets and Maillard reaction products generated from glyoxal (Gly) or methylglyoxal (MG) are poorly understood. In this work, the effects of AGEs generated by the reaction between Gly or MG with Lys or bovine serum albumin (BSA) on platelet activation and aggregation were assessed. AGEs were generated incubating Gly or MG with Lys or BSA during 5 hours or 14 days, respectively. AGEs generation were characterized by kinetic studies and by amino acid analysis. Human platelet-rich plasma (PRP) was incubated with different concentrations of AGEs from Lys-MG or Lys-Gly and BSA-MG or BSA-Gly. Platelet activation was determined quantifying the expression of CD62 (P-selectin) in PRP exposed to different AGEs concentrations. It was found that Lys-MG and Lys-Gly induced an increase in P-selectin expression (p < .05), being 33.9% higher for Lys-MG when compared to Lys-Gly. Platelets incubated in the presence of BSA-MG and BSA-Gly did not show an increase in the P-selectin expression. Platelet aggregation was significantly higher for the mixture Lys-MG (in all the range of concentrations evaluated), whereas for Lys-Gly it was only significant the highest concentration (Lys 168 µM/Gly 168 µM). It was observed a significant increase in platelet aggregation induced by ADP for samples BSA-Gly. AGEs formed with MG-Lys induce a higher activation and aggregation of platelets when compared to those formed from Gly-Lys.

Interference with AGEs formation and AGEs-induced vascular injury mediates curcumin vascular protection in metabolic syndrome

Vascular dysfunction predisposes to cardiovascular complications of metabolic syndrome (MetS). The current study investigated the mechanism(s) of curcumin's (CUR) protective effect against vascular reactivity irregularities in MetS. MetS was induced by feeding rats on high fructose high salt diet. Tension studies were undertaken in aortic rings to assess the influence of CUR on vasoconstrictor or vasorelaxant responses. The effect on advanced glycation endproducts (AGEs) was studied by incubating aortic tissues with methylglyoxal, the AGEs precursor, in the absence and presence of CUR. In addition, CUR effects on in-vitro generation of AGEs and diphenyl-2-picrylhydrazyl (DPPH) free radicals were studied. The incubation with CUR for 1 hr produced significant and concentration-dependent alleviation of the exaggerated vasoconstriction observed in aortas isolated from MetS, however failed to improve the concomitant attenuation of vasodilatory responses to ACh in PE-precontracted aortas. By contrast, CUR caused direct concentration-dependent vasodilations of precontracted aortas, effects that were blunted after nitric oxide synthase inhibition by L-NAME. Similar to its effects in MetS aortas, CUR alleviated exaggerated PE vasoconstriction but did not affect impaired ACh vasodilations in AGEs-exposed aortas. In addition, CUR showed significant dose-dependent DPPH free radicals scavenging activity and inhibited both MG and fructose induced AGEs formation at the level of protein oxidation step as evident from the effect on dityrosine and N-formylkyramine. CUR alleviates exaggerated vasoconstriction in MetS through interfering with AGEs formation and AGEs-induced vascular injury. Free radical scavenging and direct vasodilatory activities could also participate in the advantageous vascular actions of CUR.

Effects of Moringa oleifera on Glycaemia and Insulin Levels: A Review of Animal and Human Studies

Diabetes and related neurological complications are serious worldwide public health problems. The increasing number of affected individuals make it necessary to implement novel nutritional and therapeutic interventions. The tree Moringa oleifera (MO) has been used as a food source and for traditional medicine purposes due to possible antihyperglycemic, antioxidant, anti-inflammatory, and lipid regulating properties. These properties may be explained by the presence of numerous phytochemicals in the leaves, fruits, roots and, oil of the tree. The evidence for acute antihyperglycemic effects of MO extract on diabetic animal models seems to be robust, but more chronic and long-term studies are needed. In contrast, the hypoglycemic effects of MO on humans are not as clear. The scarce number of human studies, together with a diverse range of methodologies and MO doses, may explain this. In addition, evidence regarding changes in insulin levels due to MO intervention is ambiguous, both in animal and human studies. Therefore, more structured studies are needed to clarify if MO has an effect on insulin levels or activity.

Psiadia punctulata major flavonoids alleviate exaggerated vasoconstriction produced by advanced glycation end products

Exaggerated vasoconstriction plays important roles in vascular complication in aging and many diseases like diabetes. Here, we investigated the protective effect of Psiadia punctulata (PP) on advanced glycation end products (AGEs)-induced aggravated vasoconstriction. The effect of total methanol extract of PP leaves (PPT) on AGE-induced vascular injury was studied through bioassay-guided fractionation procedures in order to find the bioactive fraction and isolate the bioactive compounds. Vascular reactivity was studied using the isolated artery technique by adding cumulative concentrations of phenylephrine (PE) or acetyl choline (ACh). In addition, the antiglycating effect, as well as the effect on AGEs intermediates dityrosine and N`-formylkynurenine and their radical scavenging activity were measured. The results showed that PPT alleviated the AGEs-induced aggravated vasoconstriction in a concentration-dependent manner. The bioassay guided fractionation procedures suggested the chloroform fraction (Fr I) to be responsible for the activity. Chemical investigation of this fraction resulted in isolation of four major bioactive compounds that were identified as: umuhengerin (1), gardenin (2), luteolin-3`,4`-dimethyl ether (3), and 5,3`-dihydroxy-6,7,4`,5`-tetramethoxyflavone (4). The four compounds alleviated the exaggerated vasoconstriction in a dose dependent manner. In search for their mechanism of action, we observed that PPT, Fr. I and the isolated compounds did not improve the impaired vasodilation associated with AGEs exposure. PPT, Fr. I and the isolated compounds 1–4 inhibited AGEs formation and their protein oxidation intermediates. Furthermore, PPT, Fr. I and the isolated compounds 1–4 showed weak radical scavenging activity with compound 4 as the most potent. In conclusion, PPT appears to protect against AGEs-induced exaggerated vasoconstriction through antiglycation and radical scavenging activities.

Cinnamaldehyde protects from methylglyoxal-induced vascular damage: Effect on nitric oxide and advanced glycation end products

The protective effect and mechanism(s) of action of cinnamaldehyde on the highly reactive secondary sugar derivative, methylglyoxal, induced vascular damage were investigated using isolated rat thoracic aorta. Aorta was incubated with methylglyoxal and cinnamaldehyde where vascular reactivity was assessed through phenylephrine- and acetylcholine-induced contraction and relaxation, respectively. Cinnamaldehyde's antioxidant activity, ability to induce aortic nitric oxide release, and effect on advanced glycation end products formation (AGEs) was also studied. Results showed that cinnamaldehyde significantly alleviated the exaggerated contraction and improved the attenuated dilation of the aorta secondary to incubation with methylglyoxal. Furthermore, cinnamaldehyde stimulated aortic nitric oxide production from isolated aorta giving levels similar to acetylcholine and significantly reduced both methylglyoxal-induced AGEs and protein oxidation products formation. In conclusion, cinnamaldehyde protects from methyglyoxal-induced vascular damage mainly by improving the vasodilation in addition to endothelial nitric oxide production and reducing the detrimental AGE-inflicted vascular damage. PRACTICAL APPLICATIONS: The use of naturally occurring products to alleviate various disease-related complications is highly attractive due to their easy availability, relatively affordable prices compared to pharmaceutical products, and their favorable safety profile. In the case of cinnamaldehyde, its excessive and highly reputable consumption in the food industry facilitates promoting a daily intake of the natural compound with the purpose of counteracting the destructive effect that elevated blood glucose has on vascular function. According to findings obtained from this study, frequent cinnamaldehyde intake will improve vascular reactivity by acting on vasodilatory mechanisms and inhibiting glycation reactions, hence improving the hyperglycemia associated hypertensive state. The study also paves the way for future research to determine the clinical efficacy of cinnamaldehyde having established its competence in protecting vascular function in a lab setting.

Phloretin and its methylglyoxal adduct: Implications against advanced glycation end products-induced inflammation in endothelial cells

Methylglyoxal (MGO), a cytotoxic factor, reacts irreversibly with the side chains of lysine, cysteine, and arginine residues in proteins to form advanced glycation end products (AGEs) which might be a major pathological factor associated with diabetic complications. Thus, it is necessary to prevent or alleviate such diseases through inhibiting the formation of AGEs or lowering these AGEs-induced cellular damages. Based on our previous work, it was known that phloretin, an apple polyphenol, can inhibit the formation of AGEs under simulated physiological conditions. In this study, we found that phloretin prevented the formation of AGEs through trapping MGO in human umbilical endothelial cells (HUVECs). The phloretin-MGO adducts were analyzed in PBS and HUVECs. Surprisingly, only 1 MGO-phloretin adduct was detected in HUVECs, which was formed within 0.5 h and metabolized eventually within 24 h. The specific phloretin-MGO adduct was synthesized and identified by MS and NMR analysis. Its anti-inflammatory effect against AGEs was further investigated together with the parent compound, phloretin, which was proved to be through RAGE/p38 MAPK/NF-κB signaling pathway. Taken together, our data indicated the positive role of phloretin-MGO adduct on phloretin's protective effects, which might offer a new insight into the action mechanism of polyphenols against AGEs-induced damages.

Inhibition of Advanced Glycation End-Product Formation by High Antioxidant-Leveled Spices Commonly Used in European Cuisine

Spices and herbs, as good sources of polyphenols, could be strong inhibitors of advanced glycation end-product (AGE) formation. The aim of this research was to measure the ability of various spices to inhibit AGEs and to study the correlation of AGE inhibition with total phenolic (TP) content and antioxidant capacity. Fourteen spices commonly used in European cuisine were extracted with a 50% ethanol solution, and their water and total phenolic contents and antioxidant capacities were examined. Antioxidant capacity was evaluated using three methods: (1) Measurement of the radical scavenging ability of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and (2) 2,2-diphenyl-1-picrylhydrazyl (DPPH●); and (3) photochemiluminescence (PCL) assay. Antiglycation properties were studied in vivo using two model systems: Bovine serum albumin-glucose (BSA-glucose) and bovine serum albumin-methylglyoxal (BSA-MGO). The most potent glycation inhibitors, according to the BSA-MGO assay, were star anise (88%), cinnamon (85%), allspice (81%), and cloves (79%), whereas in the BSA-glucose measurement, oregano was noted to be a very effective inhibitor of the glycation process. The ability to inhibit glycation was highly correlated with TP values in the BSA-MGO and BSA-glucose assay (r = 0.84 and 0.76, respectively). Our research showed the high antiglycation ability of cinnamon, cloves, and allspice, and we suggest, for the first time, that anise could also be considered a good glycation inhibitor.

Glycation interferes with natural killer cell function

One hallmark of molecular aging is glycation, better known as formation of so-called advanced glycation end products (AGEs), where reactive carbonyls react with amino-groups of proteins. AGEs accumulate over time and are responsible for various age-dependent diseases and impairments. Two very potent dicarbonyls to generate AGEs are glyoxal (GO) and methylglyoxal (MGO). The plasma level of such dicarbonyls is higher in aging and age-related diseases. Natural killer (NK) cells are cells of the innate immune system and provide a major defense against tumor cells and virus infected cells. They are able to kill modified or infected cells and produce different cytokines to modulate the function of other immune cells. Here we investigated the effect of GO- and MGO-induced glycation on the function of NK cells. Using the human NK cell line NK-92, we could demonstrate that both GO and MGO lead to glycation of cellular proteins, but that MGO interferes much stronger with NK cell function (cytotoxicity) than GO. In addition, glycation of NK cell targets, such as K562 tumor cells, also interferes with their lysis by NK cells. From this data we conclude that glycation acts negatively on NK cells function and reduces their cytotoxic potential towards tumor cells.

New compounds of Siolmatra brasiliensis and inhibition of in vitro protein glycation damage

Twenty compounds were isolated from the hydroethanolic extract of the stems of Siolmatra brasiliensis, five flavonoids, two lignans, one glucosyl phytosterol, seven nor-cucurbitacins, one new phenolic derivative named siolmatrin (1) and four new dammarane-type saponins named siolmatrosides II-V (2-5), the structures of the compounds were assigned by means of 1D and 2D NMR experiments and HRESIMS of the natural compounds and some acetyl derivatives. The effects of the crude hydroethanolic extract (SbExt) and the ethyl acetate fraction (SbEtAc) of Siolmatra brasiliensis stems on the formation of advanced glycation end-products (AGEs) were also investigated. In the in vitro model system of protein glycation using bovine serum albumin (BSA) and glucose, addition of SbExt or SbEtAc inhibited the formation of fluorescent AGEs, in parallel to minor levels of fructosamine (SbEtAc) and markers of tyrosine and tryptophan oxidation (SbExt and SbEtAc). Protein crosslinking, which represents changes of late stages of protein glycation, was reduced in the presence of SbExt and SbEtAc. Siolmatra brasiliensis stems seem to be a promising source of compounds having ability to prevent glycoxidation changes, arising as an interesting option to be studied as a complementary therapy for complications of diabetes.

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.

Fructose liquid and solid formulations differently affect gut integrity, microbiota composition and related liver toxicity: a comparative in vivo study

Despite clinical findings suggesting that the form (liquid versus solid) of the sugars may significantly affect the development of metabolic diseases, no experimental data are available on the impact of their formulations on gut microbiota, integrity and hepatic outcomes. In the present sudy, C57Bl/6j mice were fed a standard diet plus water (SD), a standard diet plus 60% fructose syrup (L-Fr) or a 60% fructose solid diet plus water (S-Fr) for 12 weeks. Gut microbiota was characterized through 16S rRNA phylogenetic profiling and shotgun sequencing of microbial genes in ileum content and related volatilome profiling. Fructose feeding led to alterations of the gut microbiota depending on the fructose formulation, with increased colonization by Clostridium, Oscillospira and Clostridiales phyla in the S-Fr group and Bacteroides, Lactobacillus, Lachnospiraceae and Dorea in the L-Fr. S-Fr evoked the highest accumulation of advanced glycation end products and barrier injury in the ileum intestinal mucosa. These effects were associated to a stronger activation of the lipopolysaccharide-dependent proinflammatory TLR4/NLRP3 inflammasome pathway in the liver of S-Fr mice than of L-Fr mice. In contrast, L-Fr intake induced higher levels of hepatosteatosis and markers of fibrosis than S-Fr. Fructose-induced ex novo lipogenesis with production of SCFA and MCFA was confirmed by metagenomic analysis. These results suggest that consumption of fructose under different forms, liquid or solid, may differently affect gut microbiota, thus leading to impairment in intestinal mucosa integrity and liver homeostasis.

Generation of Advanced Glycation End-Products (AGEs) by glycoxidation mediated by copper and ROS in a human serum albumin (HSA) model peptide: reaction mechanism and damage in motor neuron cells

Glucose, in the presence of reactive oxygen species (ROS), acts as an as an oxidative agent and drives deleterious processes in Diabetes Mellitus. We have studied the mechanism and the toxicological effects of glucose-dependent glycoxidation reactions driven by copper and ROS, using a model peptide based on the exposed sequence of Human Serum Albumin (HSA) and containing a lysine residue susceptible to copper complexation. The main products of these reactions are Advanced Glycation End-products (AGEs). Carboxymethyl lysine and pyrraline condensed on the model peptide, generating a Modified Peptide (MP). These products were isolated, purified, and tested on cultured motor neuron cells. We observed DNA damage, enhancement of membrane roughness, and formation of domes. We evaluated nuclear abnormalities by the cytokinesis-blocked micronucleus assay and we measured cytostatic and cytotoxic effects, chromosomal breakage, nuclear abnormalities, and cell death. AGEs formed by glycoxidation caused large micronucleus aberrations, apoptosis, and large-scale nuclear abnormalities, even at low concentrations.

The role of glycation in the pathogenesis of aging and its prevention through herbal products and physical exercise

[Purpose]

Advanced glycation end products (AGEs) are non-enzymatic modifications of proteins or lipids after exposure to sugars. In this review, the glycation process and AGEs are introduced, and the harmful effects of AGEs in the aging process are discussed.

[Methods]

Results from human and animal studies examining the mechanisms and effects of AGEs are considered. In addition, publications addressing means to attenuate glycation stress through AGE inhibitors or physical exercise are reviewed.

[Results]

AGEs form in hyperglycemic conditions and/or the natural process of aging. Numerous publications have demonstrated acceleration of the aging process by AGEs. Exogenous AGEs in dietary foods also trigger organ dysfunction and tissue aging. Various herbal supplements or regular physical exercise have beneficial effects on glycemic control and oxidative stress with a consequent reduction of AGE accumulation during aging.

[Conclusion]

The inhibition of AGE formation and accumulation in tissues can lead to an increase in lifespan.