Protein glycation and oxidative stress in diabetes mellitus and ageing

The biochemistry of melanogenesis: an insight into the function and mechanism of melanogenesis-related proteins

Melanin is an amino acid derivative produced by melanocyte through a series of enzymatic reactions using tyrosinase as substrate. Human skin and hair color is also closely related to melanin, so understanding the mechanisms and proteins that produce melanin is very important. There are many proteins involved in the process of melanin expression, For example, proteins involved in melanin formation such as p53, HNF-1α (Hepatocyte nuclear factor 1α), SOX10 (Sry-related HMg-Box gene 10) and pax3 (paired box gene 3), MC1R(Melanocortin 1 Receptor), MITF (Microphthalmia-associated transcription factor), TYR (tyrosinase), TYRP1 (tyrosinase-related protein-1), TYRP2 (tyrosinase-related protein-2), and can be regulated by changing their content to control the production rate of melanin. Others, such as OA1 (ocular albinism type 1), Par-2 (protease-activated receptor 2) and Mlph (Melanophilin), have been found to control the transfer rate of melanosomes from melanocytes to keratinocytes, and regulate the amount of human epidermal melanin to control the depth of human skin color. In addition to the above proteins, there are other protein families also involved in the process of melanin expression, such as BLOC, Rab and Rho. This article reviews the origin of melanocytes, the related proteins affecting melanin and the basic causes of related gene mutations. In addition, we also summarized the active ingredients of 5 popular whitening cosmetics and their mechanisms of action.

Top weapons in skin aging and actives to target the consequences of skin cell senescence

Skin aging has long been considered a purely cosmetic problem. However, as life expectancy increases, skin aging is taking on a functional dimension that goes beyond cosmetics and appearance. Preventive or therapeutic strategies are needed to target cellular senescence, a key process underlying the alterations in skin function and appearance that occur with aging, as well as to address the age-related skin changes associated with 'dermatoporosis' and chronic skin insufficiency/fragility syndrome. Thus, given the need for effective anti-aging products that improve both the appearance and function of the skin, it is essential to distinguish active ingredients that have been proven to be effective, among the large number of available over-the-counter cosmeceuticals. This brief review focuses on a core group of topical actives, describing their clinical effects on senescence and aging, and their molecular mechanisms of action. These actives include hyaluronic acid, which has hydrating and viscoelastic properties and has been shown to reduce skin atrophy; retinaldehyde, which activates retinoid receptors and increases cutaneous elasticity; vitamins C and E, which provide stable oxidative protection; and niacinamide, which reduces inflammation and mitigates the effects of senescence.

Effects of qigong Training on Muscle Strengths, Flexibility, Cardiopulmonary Fitness, and Antioxidant/Oxidant Responses in Sedentary Middle-Aged and Elderly Type 2 Diabetes Mellitus Women: A Quasi-Experimental Design, Placebo-Controlled Study

Background: Qigong exercise training has been suggested to elicit beneficial effects on physical functioning, reduction of oxidative stress, and improved antioxidant capacity in women. However, regular exercise training may support the development of antioxidant defense mechanisms and beneficially modulate oxidant/antioxidant responses. Objective: To evaluate the effects of an 8-week qigong exercise training on exercise performance and oxidative stress responses in sedentary middle-aged and elderly women suffering from type 2 diabetic mellitus (T2DM). Method/design: Quasi-experimental design, placebo-controlled study. Setting: The Department of Physical Therapy, Faculty of Allied Health Science, Burapha University, Thailand. Participants: Thirty-six sedentary middle-aged and elderly women with T2DM. Intervention: Participants were allocated to qigong exercise (n = 20) or to the control group (CG, n = 20). Primary outcome measures: Muscle strengths, flexibility, VO2 max predicted, and walking intensity derived from the 6-minute walk test. Secondary outcome measures: Fasting plasma glucose, antioxidant/oxidant stress parameters, and body composition. Results: Leg strength and trunk flexibility were improved after qigong training and changes were significantly different compared with the CG (all p < 0.05). VO2 max predicted, 6-min walking distance, and walking intensity were all increased (p < 0.05), and oxidative stress markers were diminished after qigong training (p < 0.05). The antioxidant/oxidant balance was improved after qigong training (p < 0.05). Conclusion: The presented findings indicate that 8 weeks of qigong training significantly improved leg strength and trunk flexibility in middle-aged and elderly women with T2DM, partly associated with a more favorable antioxidant/oxidant balance. These effects may beneficially impact on health in this specific population. Clinical Trial Number: TCTR20221003001.

Effect of edible oil type on the formation of protein-bound Nε-(carboxymethyl)lysine in roasted pork patties

Protein-bound Nε-(carboxymethyl)lysine (CML), an advanced glycation end product within meat products, poses a potential health risk to humans. The objective of this study was to explore the impact of various edible oils on the formation of protein-bound CML in roasted pork patties. Eleven commercially edible oils including lard oil, corn oil, palm oil, olive oil, flaxseed oil, blended oil, camellia oil, walnut oil, soybean oil, peanut oil, and colza oil were added to pork tenderloin mince, respectively, at a proportion of 4 % to prepare raw pork patties. The protein-bound CML contents in the pork patties were determined by HPLC-MS/MS before and after roasting at 200 °C for 20 min. The results indicated that walnut oil, flaxseed oil, colza oil, olive oil, lard oil, corn oil, blended oil, and palm oil significantly reduced the accumulation of protein-bound CML in pork patties, of which the inhibition rate was in the 24.43 %-37.96 % range. Moreover, the addition of edible oil contributed to a marginal reduction in the loss of lysine. Meanwhile, glyoxal contents in pork patties were reduced by 16.72 %-43.21 % after roasting. Other than blend oil, all the other edible oils restrained protein oxidation in pork patties to varying degrees (between 20.16 % and 61.26 %). In addition, camellia oil, walnut oil, and flaxseed oil increased TBARS values of pork patties by 2.2-8.6 times when compared to the CON group. After analyzing the fatty acid compositions of eleven edible oils, five main fatty acids (palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid) were selected to establish Myofibrillar protein-Glucose-fatty acids systems to simulate the roasting process. The results showed that palmitic acid, oleic acid, linoleic acid, and linolenic acid obviously mitigated the formation of myofibrillar protein-bound CML, exhibiting suppression rates ranging from 10.38 % to 40.32 %. In conclusion, the addition of specific edible oil may curb protein-bound CML production in roasted pork patty by restraining protein or lipid oxidation, reducing lysine loss, and suppressing glyoxal production, which may be attributed to the fatty acid compositions of edible oils. This finding provides valuable guidance for the selection of healthy roasting oils in the thermal processing of meat products.

Antidiabetic Effect of Fermented Mesembryanthemum crystallinum L. in db/db Mice Involves Regulation of PI3K-Akt Pathway

Type 2 diabetes (T2D) is a serious health issue with increasing incidences worldwide. However, current medications have limitations due to side effects such as decreased appetite, stomach pain, diarrhea, and extreme tiredness. Here, we report the effect of fermented ice plant (FMC) in the T2M mouse model of db/db mice. FMC showed a greater inhibition of lipid accumulation compared to unfermented ice plant extract. Two-week oral administration with FMC inhibited body weight gain, lowered fasting blood glucose, and improved glucose tolerance. Serum parameters related to T2D including insulin, glycosylated hemoglobin, adiponectin, and cholesterols were improved as well. Histological analysis confirmed the protective effect of FMC on pancreas and liver destruction. FMC treatment significantly increased the expression and phosphorylation of IRS-1, PI3K, and AKT. Additionally, AMP-activated protein kinase phosphorylation and nuclear factor erythroid 2-related factor 2 were also increased in the liver tissues of db/db mice treated with FMC. Overall, our results indicate the anti-diabetic effect of FMC; therefore, we suggest that FMC may be useful as a therapeutic agent for T2D.

Revealing a Third Dissolved-Phase Xenon-129 Resonance in Blood Caused by Hemoglobin Glycation

Hyperpolarized (HP) xenon-129 (¹²⁹Xe), when dissolved in blood, has two NMR resonances: one in red blood cells (RBC) and one in plasma. The impact of numerous blood components on these resonances, however, has not yet been investigated. This study evaluates the effects of elevated glucose levels on the chemical shift (CS) and T2* relaxation times of HP ¹²⁹Xe dissolved in sterile citrated sheep blood for the first time. HP ¹²⁹Xe was mixed with sheep blood samples premixed with a stock glucose solution using a liquid-gas exchange module. Magnetic resonance spectroscopy was performed on a 3T clinical MRI scanner using a custom-built quadrature dual-tuned ¹²⁹Xe/¹H coil. We observed an additional resonance for the RBCs (¹²⁹Xe-RBC1) for the increased glucose levels. The CS of ¹²⁹Xe-RBC1 and ¹²⁹Xe-plasma peaks did not change with glucose levels, while the CS of ¹²⁹Xe-RBC2 (original RBC resonance) increased linearly at a rate of 0.015 ± 0.002 ppm/mM with glucose level. ¹²⁹Xe-RBC1 T2* values increased nonlinearly from 1.58 ± 0.24 ms to 2.67 ± 0.40 ms. As a result of the increased glucose levels in blood samples, the novel additional HP ¹²⁹Xe dissolved phase resonance was observed in blood and attributed to the ¹²⁹Xe bound to glycated hemoglobin (HbA_1c).

Photoaging and Topical Rejuvenation

Photoaging is a complex process of skin changes associated with chronic ultraviolet exposure. Prevention with photoprotection and treatment with topical retinoids are the core components of a topical antiaging regimen. Other topicals such as hydroquinone, vitamin C, niacinamide, and alpha hydroxyl acid can be added based on specific concerns. However, caution must be used with some of these products as the stability and absorption are major considerations. A simple topical regimen will reduce irritability and enhance compliance.

Formation of advanced glycation end products of chicken breast meat induced by freeze-thaw cycles and subsequent cooking

The impacts of freeze-thaw (F-T) cycles and cooking on the basic composition, protein and lipid oxidation, and advanced glycation end products (AGEs) of chicken breasts were studied. During F-T cycles, the moisture and protein contents of raw and cooked chicken breasts decreased, and protein and lipid oxidation occurred, increasing carbonyl and TBARS contents. Meanwhile, the contents of methylglyoxal, glyoxal, and hydroxymethylfurfural in raw meat increased by 2.27, 2.27, and 5 times, respectively, whereas glyoxal and hydroxymethylfurfural contents increased by 2.73 and 3 times, respectively, after cooking as F-T cycles increased. The formation of carboxymethyl lysine, pentosidine, and fluorescent AGEs in cooked samples was confirmed using an ELISA kit and fluorescent intensity. The study also revealed that AGEs contents of chicken meat were negatively correlated with moisture contents and positively correlated with carbonyl and TBARS levels. Therefore, F-T cycles and subsequent cooking promoted AGEs formation in cooked meat.

Aging - what it is and how to measure it

The current understanding of the biology of aging is largely based on research aimed at identifying factors that influence lifespan. However, lifespan as a sole proxy measure of aging has limitations because it can be influenced by specific pathologies (not generalized physiological deterioration in old age). Hence, there is a great need to discuss and design experimental approaches that are well-suited for studies targeting the biology of aging, rather than the biology of specific pathologies that restrict the lifespan of a given species. For this purpose, we here review various perspectives on aging, discuss agreement and disagreement among researchers on the definition of aging, and show that while slightly different aspects are emphasized, a widely accepted feature, shared across many definitions, is that aging is accompanied by phenotypic changes that occur in a population over the course of an average lifespan. We then discuss experimental approaches that are in line with these considerations, including multidimensional analytical frameworks as well as designs that facilitate the proper assessment of intervention effects on aging rate. The proposed framework can guide discovery approaches to aging mechanisms in all key model organisms (e.g., mouse, fish models, D. melanogaster, C. elegans) as well as in humans.

Mesenchymal Stem Cell Derived Exosomes Therapy in Diabetic Wound Repair

Nowadays, refractory diabetic wounds cause a worldwide medical burden. Mesenchymal stem cells derived exosomes (MSC-Exos) show promise as a solid alternative to existing therapeutics in the latest researches, since MSC-Exos share similar biologic activity but less immunogenicity when compared with MSCs. To facilitate further understanding and application, it is essential to summarize the current progress and limitations of MSC-Exos in the treatment of diabetic wounds. In this review, we introduce the effects of different MSC-Exos on diabetic wounds according to their origins and contents and discuss the specific experimental conditions, target wound cells/pathways, and specific mechanisms. In addition, this paper focuses on the combination of MSC-Exos and biomaterials, which improves the efficacy and utilization of MSC-Exos therapy. Together, exosome therapy has high clinical value and application prospects, both in its role and in combination with biomaterials, while novel drugs or molecules loaded into exosomes as carriers targeting wound cells will be development trends.

Effect of aging on the biaxial mechanical behavior of human descending thoracic aorta: Experiments and constitutive modeling considering collagen crosslinking

Collagen crosslinking, an important contributor to the stiffness of soft tissues, was found to increase with aging in the aortic wall. Here we investigated the mechanical properties of human descending thoracic aorta with aging and the role of collagen crosslinking through a combined experimental and modeling approach. A total of 32 samples from 17 donors were collected and divided into three age groups: <40, 40-60 and > 60 years. Planar biaxial tensile tests were performed to characterize the anisotropic mechanical behavior of the aortic samples. A recently developed constitutive model incorporating collagen crosslinking into the two-fiber family model (Holzapfel and Ogden, 2020) was modified to accommodate biaxial deformation of the aorta, in which the extension and rotation kinematics of bonded fibers and crosslinks were decoupled. The mechanical testing results show that the aorta stiffens with aging with a more drastic change in the longitudinal direction, which results in altered aortic anisotropy. Our results demonstrate a good fitting capability of the constitutive model considering crosslinking for the biaxial aortic mechanics of all age groups. Furthermore, constitutive modeling results suggest an increased contribution of crosslinking and strain energy density to the biaxial stress-stretch behaviors with aging and point to excessive crosslinking as a prominent contributor to aortic stiffening.

Exosomes Derived from Adipose Mesenchymal Stem Cells Promote Diabetic Chronic Wound Healing through SIRT3/SOD2

Chronic wounds resulting from diabetes are a major health concern in both industrialized and developing countries, representing one of the leading causes of disability and death. This study aimed to investigate the effect of adipose mesenchymal stem cell-derived exosomes (ADSC-exos) on diabetic wounds and the mechanism underlying this effect. The results showed that ADSC-exos could improve oxidative stress and secretion of inflammatory cytokines in diabetic wounds, thereby increasing periwound vascularization and accelerating wound healing. At the cellular level, ADSC-exos reduced reactive oxygen species (ROS) generation in human umbilical vein endothelial cells (HUVECs) and improved mitochondrial function in a high-glucose environment. Moreover, the Western blot analysis showed that the high-glucose environment decreased Sirtuin 3 (SIRT3) expression, while exosome treatment increased SIRT3 expression. The activity of superoxide dismutase 2 (SOD2) was enhanced, and the level of inflammatory cytokines was decreased. Further, SIRT3 interference experiments indicated that the effects of ADSC-exos on oxidative stress and angiogenesis were partly dependent on SIRT3. After SIRT3 was inhibited, ROS production increased, while mitochondrial membrane potential and SOD2 activity decreased. These findings confirmed that ADSC-exos could improve the level of high-glucose-induced oxidative stress, promote angiogenesis, and reduce mitochondrial functional impairment and the inflammatory response by regulating SIRT3/SOD2, thus promoting diabetic wound healing.

Polyol pathway and redox balance in diabetes

Diabetes is a major public health disease that is globally approaching epidemic proportions. One of the major causes of type 2 diabetes is either a defect in insulin secretion or insulin action which is usually caused by a combination of genetic and environmental factors. Not only these factors but others such as deregulation of various pathways, and oxidative stress are also known to trigger the redox imbalance in diabetics. Increasing evidences suggest that there are tight interactions between the development of diabetes and redox imbalance. An alternate pathway of glucose metabolism, the polyol pathway, becomes active in patients with diabetes that disturbs the balance between NADH and NAD+ . The occurrence of such redox imbalance supports other pathways that lead to oxidative damage to DNA, lipids, and proteins and consequently to oxidative stress which further ascend diabetes and its complications. However, the precise mechanism through which oxidative stress regulates diabetes progression remains to be elucidated. The understanding of how antioxidants and oxidants are controlled and impact the generation of oxidative stress and progression of diabetes is essential. The main focus of this review is to provide an overview of redox imbalance caused by oxidative stress through the polyol pathway. Understanding the pathological role of oxidative stress in diabetes will help to design potential therapeutic strategies against diabetes.

The multifaceted role of cytochrome P450-Derived arachidonic acid metabolites in diabetes and diabetic cardiomyopathy

Understanding lipid metabolism is a critical key to understanding the pathogenesis of Diabetes Mellitus (DM). It is known that 60-90% of DM patients are obese or used to be obese. The incidence of obesity is rising owing to the modern sedentary lifestyle that leads to insulin resistance and increased levels of free fatty acids, predisposing tissues to utilize more lipids with less glucose uptake. However, the exact mechanism is not yet fully elucidated. Diabetic cardiomyopathy seems to be associated with these alterations in lipid metabolism. Arachidonic acid (AA) is an important fatty acid that is metabolized to several bioactive compounds by cyclooxygenases, lipoxygenases, and the more recently discovered, cytochrome P450 (P450) enzymes. P450 metabolizes AA to either epoxy-AA (EETs) or hydroxy-AA (HETEs). Studies showed that EETs could have cardioprotective effects and beneficial effects in reversing abnormalities in glucose and insulin homeostasis. Conversely, HETEs, most importantly 12-HETE and 20-HETE, were found to interfere with normal glucose and insulin homeostasis and thus, might be involved in diabetic cardiomyopathy. In this review, we highlight the role of P450-derived AA metabolites in the context of DM and diabetic cardiomyopathy and their potential use as a target for developing new treatments for DM and diabetic cardiomyopathy.

Oxidative stress in obesity and insulin resistance

Since obesity is one of the main factors in the development of insulin resistance (IR) and is also associated with increased oxidative stress (OxS) rate, this study aims to review the published literature to collate and provide a comprehensive summary of the studies related to the status of the OxS in the pathogenesis of obesity and related IR. OxS represents an imbalance between the production of reactive oxygen and nitrogen species (RONS) and the capacity of the antioxidant defense system (AOS) to neutralize RONS. A steady-state of RONS level is maintained through endogenous enzymatic and non-enzymatic AOS components. Three crucial enzymes, which suppress the formation of free radicals, are superoxide dismutases, catalases, and glutathione peroxidases. The second line of AOS includes non-enzymatic components such as vitamins C and E, coenzyme Q, and glutathione which neutralizes free radicals by donating electrons to RONS. Emerging evidence suggests that high RONS levels contribute to the progression of OxS in obesity by activating inflammatory pathways and thus leading to the development of pathological states, including IR. In addition, decreased level of AOS components in obesity increases the susceptibility to oxidative tissue damage and further progression of its comorbidities. Increased OxS in accumulated adipose tissue should be an imperative target for developing new therapies in obesity-related IR.

Liposome-encapsulated glycyrrhizin alleviates hyperglycemia and glycation-induced iron-catalyzed oxidative reactions in streptozotocin-induced diabetic rats

Glycyrrhizin, a bioactive constituent of Glycyrrhiza glabra has been reported to ameliorate diabetes. Here, the effects of liposome-encapsulated glycyrrhizin on STZ-induced diabetes and associated oxidative stress were investigated. Wistar rats were grouped as control (NC, received placebo), diabetic (DC, STZ-induced), diabetic treated with free glycyrrhizin (DTG, 3 i.v. doses, 1.6 mg/0.5 ml), empty liposomes (DTl, 3 i.v. doses), and liposome-encapsulated glycyrrhizin (DTbd, 3 i.v. doses, 1.6 mg/0.5 ml). Serum glucose, insulin, intraperitoneal glucose tolerance test and glycohemoglobin were estimated. Free iron and iron-mediated oxidative stress were examined. Histological examinations of the kidney and liver were performed. Liposomal-glycyrrhizin treatment caused significant improvement of hyperglycemia (DC vs. DTbd p < .05), glucose intolerance (DC vs. DTG p < .01 and DC vs. DTbd p < .05), insulin (DC vs. DTG p < .1, DTbd vs. DC p < .05 and DTbd vs. DTG p < .1) and glycohemoglobin (DC vs. DTG p < .1 and DC vs. DTbd p < .05) levels in the DTbd group. Alleviation of free iron release (DC vs. DTbd p < .05), lipid peroxidation (DC + H₂O₂ vs. DTbd + H₂O₂ p < .05), deoxyribose (DC + H₂O₂ vs. DTbd + H₂O₂, p < .05), and DNA degradation occurred in the DTbd group. The abnormalities of the kidney and liver were abolished in the DTbd group. The inhibitory effects were more pronounced compared to free glycyrrhizin. Liposome-encapsulated glycyrrhizin treatment caused inhibition of diabetic complications through its antioxidant effects and can be exploited for effective treatment of diabetes.

The association of oxidative stress biomarkers with type 2 diabetes mellitus: A systematic review and meta-analysis

BACKGROUND AND AIMS

Oxidative stress plays a major role in the development of type 2 diabetes mellitus (T2DM). However, there were controversial outcomes in the literature between the association of oxidative stress biomarkers and T2DM. The purpose of this systematic review and meta-analysis was to critically examine the association of oxidative stress biomarkers with T2DM.

METHODS

We systematically searched different electronic databases including PubMed/Medline, EMBASE, ScienceDirect, Web of Science, and Cochrane Library to find the relevant studies up to May 2021. The pooled standard mean difference (SMD) with a 95% confidence interval (CI) was used to define the variation between the study groups.

RESULTS

A total of 22 case-control studies with 2853 subjects (1667 diabetic patients and 1186 healthy controls) were found to be eligible for this meta-analysis. The pooled results of meta-analysis showed a significant difference in the levels malondialdehyde (SMD [95% CI]: 2.27 [1.62, 2.91]), nitric oxide (SMD [95% CI]: 1.40 [0.00, 2.81]), glutathione (SMD [95% CI]: -1.76 [-2.94, -0.59]), and total antioxidant status (SMD [95% CI]: -1.40 [-2.28, -0.51]) between the patient group and healthy subjects, whereas no significant difference was observed in the superoxide dismutase levels (SMD [95% CI]: -1.20 [-2.55, 0.15]) and glutathione peroxidase levels (SMD [95% CI]: 0.07 [-2.80, 2.94]).

CONCLUSION

The present analysis suggests that oxidative stress might have a potential role in the pathogenesis of T2DM in humans. However, further studies should be needed to elucidate the possible mechanism and strengthen this evidence.

Rosmarinic acid inhibits DNA glycation and modulates the expression of Akt1 and Akt3 partially in the hippocampus of diabetic rats

Non-enzymatic glycation of DNA and the associated effects are among pathogenic factors in diabetes mellitus. Natural polyphenols have anti-diabetic activity. Herein, the protective role of one of the phytochemicals, rosmarinic acid (RA), was evaluated in glycation (with fructose) of human DNA and expression of Akt genes in the hippocampus of diabetic rats. In-vitro studies using fluorescence, agarose gel electrophoresis, fluorescence microscopy, and thermal denaturation analyses revealed that glycation causes DNA damage and that RA inhibits it. In-vivo studies were performed by induction of diabetes in rats using streptozotocin. The diabetic rats were given RA daily through gavage feeding. The expression of Akt genes (inhibitors of apoptosis) in the hippocampus was evaluated using RT-qPCR. In diabetic rats, Akt1 and Akt3 were significantly down-regulated compared to the control group. Treating the diabetic rats with RA returned the expression of Akt1 and Akt3 relatively to the normal condition. Past studies have shown that diabetes induces apoptosis in the hippocampal neurons. Given that glycation changes the genes expression and causes cell death, apoptosis of the hippocampal neurons can be due to the glycation of DNA. The results also suggest that RA has reliable potency against the gross modification of DNA under hyperglycemic conditions.

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.

Effects of chromium supplementation on oxidative Stress biomarkers

Aim: This systematic review and meta-analysis aimed to evaluate the effects of chromium supplementation on oxidative stress biomarkers such as superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GPX), malondialdehyde (MDA), total antioxidant status (TAS), thiobarbituric acid reactive substances (TBARS), catalase (CAT), nitric oxide (NO), total antioxidant capacity (TAC) and protein carbonyl. Methods: Relevant studies, published from inception until July 2019, were searched through PubMed/Medline, Scopus, ISI Web of Science, Embase, and Google Scholar. All randomized clinical trials investigating the effect of chromium supplementation on oxidative stress were included. Results: Out of 252 citations, 10 trials that enrolled 595 subjects were included. Chromium supplementation resulted in a significant increase in GSH (WMD: 64.79 mg/dl, 95% CI: 22.43 to 107.15; P=0.003) but no significant change in MDA, TAS, TBARS levels, SOD, CAT levels and GPX. Chromium picolinate supplementation resulted in a significant increase in TAC while failing to have a significant effect on NO. Moreover, both chromium picolinate and chromium dinicocysteinate supplementation reduced protein carbonyl levels. Conclusion: Overall, this meta-analysis demonstrated that chromium supplementation increased GSH without any significant changes in the mean of GPX, MDA, TAS, TBARS, CAT and SOD.

Effect of Glycation on Interlamellar Bonding of Arterial Elastin

BACKGROUND

Interlamellar bonding in the arterial wall is often compromised by cardiovascular diseases. However, several recent nationwide and hospital-based studies have uniformly reported reduced risk of thoracic aortic dissection in patients with diabetes. As one of the primary structural constituents in the arterial wall, elastin plays an important role in providing its interlamellar structural integrity.

OBJECTIVE

The purpose of this study is to examine the effects of glycation on the interlamellar bonding properties of arterial elastin.

METHODS

Purified elastin network was isolated from porcine descending thoracic aorta and incubated in 2 M glucose solution for 7, 14 or 21 days at 37 °C. Peeling and direct tension tests were performed to provide complimentary information on understanding the interlamellar layer separation properties of elastin network with glycation effect. Peeling tests were simulated using a cohesive zone model (CZM). Multiphoton imaging was used to visualize the interlamellar elastin fibers in samples subjected to peeling and direct tension.

RESULTS

Peeling and direct tension tests show that interlamellar energy release rate and strength both increases with the duration of glucose treatment. The traction at damage initiation estimated for the CZM agrees well with the interlamellar strength measurements from direct tension tests. Glycation was also found to increase the interlamellar failure strain of arterial elastin. Multiphoton imaging confirmed the contribution of radially running elastin fibers to resisting dissection.

CONCLUSIONS

Nonenzymatic glycation reduces the propensity of arterial elastin to dissection. This study also suggests that the CZM effectively describes the interlamellar bonding properties of arterial elastin.

Acetoacetate enhancement of glucose mediated DNA glycation

Acetoacetate (AA) is a ketone body, which generates reactive oxygen species (ROS). ROS production is impacted by the formation of covalent bonds between amino groups of biomacromolecules and reducing sugars (glycation). Glycation can damage DNA by causing strand breaks, mutations, and changes in gene expression. DNA damage could contribute to the pathogenesis of various diseases, including neurological disorders, complications of diabetes, and aging. Here we studied the enhancement of glucose-mediated DNA glycation by AA for the first time. The effect of AA on the structural changes, Amadori and advanced glycation end products (AGEs) formation of DNA incubated with glucose for 4 weeks were investigated using various techniques. These included UV-Vis, circular dichroism (CD) and fluorescence spectroscopy, and agarose gel electrophoresis. The results of UV-Vis and fluorescence spectroscopy confirmed that AA increased the DNA-AGE formation. The NBT test showed that AA also increased Amadori product formation of glycated DNA. Based on the CD and agarose gel electrophoresis results, the structural changes of glycated DNA was increased in the presence of AA. The chemiluminescence results indicated that AA increased ROS formation. Thus AA has an activator role in DNA glycation, which could enhance the adverse effects of glycation under high glucose conditions.

Neopterin and biopterin levels and tryptophan degradation in patients with diabetes

This study aimed to evaluate the possible changes of neopterin, biopterin levels and tryptophan degradation in diabetes and to compare the results within diabetes groups and with healthy subjects. Diabetes mellitus patients and healthy controls were recruited the study. Patients were further subgrouped according to their drug therapy. Serum neopterin concentrations were detected by ELISA. Urinary neopterin, biopterin, serum tryptophan (Trp) and kynurenine (Kyn) levels were detected by HPLC. There was no difference between controls and diabetes patients in serum neopterin, urinary neopterin and biopterin levels (p > 0.05, all). Serum Trp and Kyn levels were significantly different in type 1 diabetes (T1DM) patients compared to controls (p < 0.05, both). Serum neopterin levels were significantly higher in type 2 diabetes patients (T2DM) compared to T1DM (p < 0.05). Urinary biopterin levels of T2DM patients using both metformin and vildagliptin were significantly higher than T1DM patients (p < 0.05). The correlations between serum neopterin and urinary neopterin, Kyn and Kyn/Trp were statistically significant in control and patient groups (p < 0.05, all). The study showed that Kyn/Trp was altered in diabetes patients due to immune modulation. On the other hand, although xenobiotic exposure may change pteridine levels, metformin and/or vildagliptin use in T2DM patients did not have any effect on the measured parameters.

Phytochemical investigation, in vitro and in vivo antioxidant properties of aqueous and organic extracts of toxic plant: Atractylis gummifera L

ETHNOPHARMACOLOGICAL RELEVANCE

Atractylis gummifera is a toxic plant widely used in Mediterranean traditional medicine against colds, dizziness, and headaches, as an antisyphilitic, against boils, as a purgative, emetic and deworming. All studies reported on this plant have been carried out either on the plant and its traditional uses, or on cases of poisoning by this plant. However, few pharmacological studies have readjusted the traditional uses of this plant.

AIM OF THE STUDY

The purpose of this article is to carry out a preliminary phytochemical study of Atractylis gummifera and to evaluate in vitro and in vivo antioxidant activity of its aqueous and organic extracts and to provide a complementary analysis of the mechanisms of action of the different antioxidant activity tests studied.

METHODS

The phytochemical study consisted of the hot and cold preparation of aqueous extracts: (decocted, infused, macerated), organic extracts: (methanolic, methanolic macerated, chloroformic, ethyl acetate, petroleum ether) and the determination of the secondary metabolites of these extracts. In addition, the biological study consisted of evaluating antioxidant activity in vitro by five different methods (H₂O₂ radical reduction, DPPH, ABTS, FRAP and RP) and in vivo by SOD and MDA assays.

RESULTS

The methanolic macerated is the richest in total polyphenols (102 ± 1.38 mg EAG/gE), tannins (144.09 ± 3.96 mg EC/gE) and flavonoids (17.25 ± 0.06 mg ER/gE). The same extract has the highest percentage to inhibit hydrogen peroxide (19.24 ± 1.10%) and the most potent reducing power of the ABTS radical (122.6 ± 0.63 mg ET/gE). We also noted that aqueous macerated has the most potent anti-radical activity of DPPH with an IC50 of 2.78 ± 1.03 μg/mL, the strongest reducing power of iron 96.15 ± 1.12 mg EAA/gE and which was confirmed by the FRAP test (102.5 ± 1.66 mg ET/gE). These results are in agreement with the in vivo study which showed an increase in SOD secretion in diabetic mice treated with aqueous macerated extract (904.26 ± 29.10 units/g liver and 714.16 ± 24.83 units/g kidney) and methanol macerated extract (813.61 ± 24.03 units/g liver and 719.46 ± 42.10 units/g kidney) with a statistically insignificant difference between these two extracts. Furthermore, we observed a return to normal MDA levels in mice treated with aqueous macerated extract (128.61 ± 15.76 nM/g liver and 103.18 ± 12.67 nM/g kidney) and methanol macerated extract (130.73 ± 10.73 nM/g liver and 34.28 ± 5.73 nM/g kidney).

CONCLUSION

The aqueous and organic extracts more particularly those prepared by aqueous and methanolic macerations are rich in polyphenols, flavonoids and tannins, and they represent a rich source of natural antioxidants, also they prevent lipid peroxidation and stimulate the secretion of the enzymatic antioxidant SOD.

Beneficial effects of (-)-epigallocatechin-3-O-gallate on diabetic peripheral neuropathy in the rat model

Diabetic neuropathic pain is characterized by spontaneous pain with hyperalgesia and allodynia. We investigated whether (-)-epigallocatechin-3-O-gallate could improve diabetic neuropathic pain development through hypoglycemic, hypolipidemic, antioxidant, and anti-inflammatory effects. Diabetes was induced in rats by streptozotocin (55 mg/kg/once) and treated with (-)-epigallocatechin-3-O-gallate (25 mg/kg/orally/once/daily/5 weeks). Diabetic rats showed an increase in serum levels of glucose, nitric oxide, triglyceride, total cholesterol, and low-density lipoprotein-cholesterol with a decrease in high-density lipoprotein-cholesterol and body weight. Also, there was an elevation in brain malondialdehyde with a marked reduction in brain levels of glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase. Furthermore, diabetic rats showed a clear reduction in plasma levels of insulin and an increase in plasma cytokines (interleukin-6 and tumor necrosis factor-α). Moreover, diabetic rats exhibited hyperalgesia as indicated by a hot plate, tail immersion, formalin, and carrageenan-induced edema tests as well as brain histopathological changes (neuron degeneration, gliosis, astrocytosis, congestion and hemorrhage). (-)-Epigallocatechin-3-O-gallate treatment ameliorated alterations in body weight, biochemical parameters, pain sensation, and histopathological changes in brain tissue. (-)-Epigallocatechin-3-O-gallate offers promising hypoglycemic, hypolipidemic, antioxidant and anti-inflammatory effects, which can prevent the development and progression of diabetic neuropathic pain.

Fatty acid synthase and adenosine monophosphate-activated protein kinase regulate cell survival and drug sensitivity in diffuse large B-cell lymphoma

Fatty acid synthesis is crucial in supporting the survival and proliferation of multiple forms of cancer. The high metabolic demands of fatty acid synthesis are regulated by the AMP-activated kinase and activity of the fatty acid synthase enzyme. In this study, the roles of these enzymes in diffuse large B-cell lymphoma (DLBCL) were investigated by genetic knock-down and pharmacological activation of AMP-activated kinase by metformin, and selective inhibition of fatty acid synthase using the novel drug Fasnall. We observed distinct heterogeneity and adaptive plasticity of lipid metabolism in a panel of DLBCL cell lines and demonstrate the therapeutic potential of inhibiting fatty acid synthesis in a subset of DLBCL cells. The translational relevance of these in vitro data is supported by the strong correlation between AMP-activated protein kinase expression in primary DLBCL samples and disease relapse. Inhibition of fatty acid synthase with Fasnall may represent a therapeutic option for DLBCL that preferentially subverts to de novo fatty acid synthesis.

Polyphenols and AGEs/RAGE axis. Trends and challenges

The formation of advanced glycation end-products (AGEs) is a key pathophysiological event linked not only to the onset and progression of diabetic complications, but also to neurodegeneration, cardiovascular diseases, cancer, and others important human diseases. AGEs contributions to pathophysiology are mainly through the formation of cross-links and by engaging the receptor for advanced glycation end-products (RAGE). Polyphenols are secondary metabolites found largely in fruits, vegetables, cereals, and beverages, and during many years, important efforts have been made to elucidate their beneficial effects on human health, mainly ascribed to their antioxidant activities. In the present review, we highlighted the beneficial actions of polyphenols aimed to diminish the harmful consequences of advanced glycation, mainly by the inhibition of ROS formation during glycation, the inhibition of Schiff base, Amadori products, and subsequent dicarbonyls group formation, the activation of the glyoxalase system, as well as by blocking either AGEs-RAGE interaction or cell signaling.

Glycation and Advanced Glycation End-Product Formation with Icodextrin and Dextrose

Objective

To review protein glycation and advanced glycation end-product formation with particular reference to its occurrence in the peritoneum following exposure to peritoneal dialysis fluid.

Data sources

Articles identified through searches on MEDLINE and BIDS and references cited therein.

Study selection

Studies on the interaction of amino groups with glucose, maltose and glucose polymers. Studies containing evidence of peritoneal advanced glycation end-product formation.

Data extraction

Studies evaluated as to whether they are in vivo, ex vivo or in vitro under non-physiological or physiological conditions.

Results

Protein glycation is slower with maltose and glucose polymers than with equimolar glucose. Advanced glycation end-product formation occurs with all three sugars, but to a greater extent after standard heat sterilization of dialysis fluid and to a lesser extent in heat sterilized fluids containing icodextrin rather than glucose. Glucose degradation products significantly contribute to protein-linked advanced glycation end-productlike fluorescence. Histology and immunohistochemistry demonstrate diabetiform changes and advanced glycation end-products in the peritoneal membrane following exposure to glucose-containing peritoneal dialysis fluids. Their presence is likely to be detrimental to peritoneal function and may contribute to loss of ultrafiltration.

Conclusions

Advanced glycation end-product formation is lower but still significant with heat sterilized peritoneal dialysis fluid containing icodextrin than with glucose. More research is needed to investigate the interaction of glucose degradation products and glucose polymers with proteins and the possible consequences of advanced glycation end-product formation on peritoneal function.

Protein-Bound Anthocyanin Compounds of Purple Sweet Potato Ameliorate Hyperglycemia by Regulating Hepatic Glucose Metabolism in High-Fat Diet/Streptozotocin-Induced Diabetic Mice

Purple sweet potato is known as a rich source of protein and anthocyanins. Anthocyanins can form complexes with protein present in food products through non-covalent forces or covalent bonds during processing, transportation, and storage as their protein affinity. We evaluated the hypoglycemic effects of protein-bound anthocyanin compounds of purple sweet potato (p-BAC-PSP) and free anthocyanin compounds of purple sweet potato (FAC-PSP) in high-fat diet/streptozotocin-induced diabetic mice. The results showed that administration of both p-BAC-PSP and FAC-PSP improved diabetic condition, as evidenced by the improvement of glucose tolerance and lipid metabolism, and the decrease of oxidative stress and liver damage. For the mechanism study, we have found that p-BAC-PSP and FAC-PSP induced the expression of AMP-activated protein kinase in liver. With p-BAC-PSP or FAC-PSP treatment, glucose transporter type 2, the protein levels of glucokinase, and insulin receptor α were found to be improved significantly (p < 0.05). Glycolysis key genes, phosphofructokinase and pyruvate kinase, were upregulated in two treatment groups, while gluconeogenic genes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were downregulated. Our findings suggested that p-BAC-PSP has great potential as a dietary supplement with hypoglycemic activity for general, pre-diabetic, and diabetic population.

Urinary angiotensinogen increases in the absence of overt renal injury in high fat diet-induced type 2 diabetic mice

AIM OF THE STUDY

During type 2 diabetes (T2D) and hypertension there is stimulation of renal proximal tubule angiotensinogen (AGT), but whether urinary excretion of AGT (uAGT) is an indicator of glomerular damage or intrarenal RAS activation is unclear. We tested the hypothesis that elevations in uAGT can be detected in the absence of albuminuria in a mouse model of T2D.

METHODS

Male C57BL/6 mice (N = 10) were fed a high fat (HFD; 45% Kcal from fat) for 28 weeks, and the metabolic phenotype including body weight, blood pressures, glucose, insulin, ippGTT, HOMA-IR, and cholesterol was examined. In addition, kidney Ang II content and reactive oxygen species (ROS) was measured along with urinary albumin, creatinine, Ang II, and AGT.

RESULTS

All parameters consistent with T2D were present in mice after 12-14 weeks on the HFD. Systolic BP increased after 18 weeks in HFD but not NFD mice. Intrarenal ROS and Ang II concentrations were also increased in HFD mice. Remarkably, these changes paralleled the augmentation uAGT excretion (3.66 ± 0.50 vs. 0.92 ± 0.13 ng/mg by week 29; P < 0.01), which occurred in the absence of overt albuminuria.

CONCLUSIONS

In HFD-induced T2D mice, increases in uAGT occur in the absence of overt renal injury, indicating that this biomarker accurately detects early intrarenal RAS activation.

The Role of Bone Morphogenetic Protein 7 (BMP-7) in Inflammation in Heart Diseases

Bone morphogenetic protein-7 is (BMP-7) is a potent anti-inflammatory growth factor belonging to the Transforming Growth Factor Beta (TGF-β) superfamily. It plays an important role in various biological processes, including embryogenesis, hematopoiesis, neurogenesis and skeletal morphogenesis. BMP-7 stimulates the target cells by binding to specific membrane-bound receptor BMPR 2 and transduces signals through mothers against decapentaplegic (Smads) and mitogen activated protein kinase (MAPK) pathways. To date, rhBMP-7 has been used clinically to induce the differentiation of mesenchymal stem cells bordering the bone fracture site into chondrocytes, osteoclasts, the formation of new bone via calcium deposition and to stimulate the repair of bone fracture. However, its use in cardiovascular diseases, such as atherosclerosis, myocardial infarction, and diabetic cardiomyopathy is currently being explored. More importantly, these cardiovascular diseases are associated with inflammation and infiltrated monocytes where BMP-7 has been demonstrated to be a key player in the differentiation of pro-inflammatory monocytes, or M1 macrophages, into anti-inflammatory M2 macrophages, which reduces developed cardiac dysfunction. Therefore, this review focuses on the molecular mechanisms of BMP-7 treatment in cardiovascular disease and its role as an anti-fibrotic, anti-apoptotic and anti-inflammatory growth factor, which emphasizes its potential therapeutic significance in heart diseases.

Mitoprotective Clinical Strategies in Type 2 Diabetes and Fanconi Anemia Patients: Suggestions for Clinical Management of Mitochondrial Dysfunction

Oxidative stress (OS) and mitochondrial dysfunction (MDF) occur in a number of disorders, and several clinical studies have attempted to counteract OS and MDF by providing adjuvant treatments against disease progression. The present review is aimed at focusing on two apparently distant diseases, namely type 2 diabetes (T2D) and a rare genetic disease, Fanconi anemia (FA). The pathogenetic links between T2D and FA include the high T2D prevalence among FA patients and the recognized evidence for OS and MDF in both disorders. This latter phenotypic/pathogenetic feature-namely MDF-may be regarded as a mechanistic ground both accounting for the clinical outcomes in both diseases, and as a premise to clinical studies aimed at counteracting MDF. In the case for T2D, the working hypothesis is raised of evaluating any in vivo decrease of mitochondrial cofactors, or mitochondrial nutrients (MNs) such as α-lipoic acid, coenzyme Q10, and l-carnitine, with possibly combined MN-based treatments. As for FA, the established knowledge of MDF, as yet only obtained from in vitro or molecular studies, prompts the requirement to ascertain in vivo MDF, and to design clinical studies aimed at utilizing MNs toward mitigating or delaying FA's clinical progression. Altogether, this paper may contribute to building hypotheses for clinical studies in a number of OS/MDF-related diseases.

[Correlation of cardiovascular risk factors with brain iron deposition: A magnetic resonance imaging study]

OBJECTIVE

To study the correlation of common cardiovascular risk factors with brain iron deposition.

METHODS

Eighty-four elderly subjects without neurological diseases or brain trauma were included in the study. The cardiovascular risk factors were comprehensively assessed. MRI examination was performed to obtain high-resolution T1-weighted images and enhanced susceptibility weighted angiography (ESWAN) images, and R2^* figure was obtained by post-processing the ESWAN sequence. High definition T1 images were segmented using computer segmentation technique. After registration to the ESWAN image, R2^* values of each region of interest were extracted. Multiple linear regression analysis was used to analyze the relationship of R2^* values in each area of interest with gender, age and vascular risk factors.

RESULTS

Smoking was associated with increased R2^* values in the hippocampus, white matter and cortex (β=0.244, 0.317, 0.277, P<0.05 or P<0.01). Hypertension was correlated with the increase of R2^* in the putamen (β=0.241, P=0.027). Hyperglycemia was associated with the increase of R2^* in the thalamus (β=0.234, P<0.05). In the thalamus, the R2^* value of males was higher than that of females (β=0.320, P<0.05). Age was correlated with the R2^* values of thalamus, caudate nucleus, pallidus, white matter and cortex (β=-0.218、-0.254、0.216、-0.280 and -0.238, P<0.05 or P<0.01).

CONCLUSIONS

Common cardiovascular risk factors may lead to iron deposition in the brain, and the deposition patterns vary with the gender, age and different risk factors.

Effect of High Glucose-Induced Oxidative Stress on Paraoxonase 2 Expression and Activity in Caco-2 Cells

(1) Background: Hyperglycemia leads to several biochemical and physiological consequences, such as the generation of advanced glycation end products (AGEs) and reactive oxygen species (ROS), which are involved in the development of several human diseases. Intestinal cells are continuously exposed to pro-oxidants and lipid peroxidation products from ingested foods, and also to glyco-oxidative damage. It has been reported that free radical generation may be linked to the development of inflammation-related gastrointestinal diseases. (2) Methods: The effects of high glucose (HG) treatment (50 mM) were assessed in terms of free radical production, lipid peroxidation, and AGEs formation. Furthermore, the expression and the antiapoptotic and antioxidant activity of the paraoxonase-2 (PON2) enzyme in intestinal cells has been investigated. (3) Results: Caco-2 cells treated with media supplied with high glucose (HG) (50 mM) showed, with respect to physiological glucose concentration (25 mM), an increase in ROS production, lipid peroxidation, and AGEs formation. Moreover, a lower PON2 expression and activity in HG-treated cells was related to activation of the apoptotic pathways. (4) Conclusions: Our results demonstrated that high glucose concentrations triggered glyco-oxidative stress in intestinal cells; the downregulation of PON2 could result in a higher oxidative stress and might contribute to intestinal dysfunction.

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.

In vitro and in vivo inhibition of maillard reaction products using amino acids, modified proteins, vitamins, and genistein: A review

Maillard reaction is known to result in loss of nutrients, particularly that of essential amino acids; decrease in digestibility and safety issues due to the development of toxic compounds. Maillard reaction products are also known to cause oxidation of tissues and inflammation, thus increasing the risk of cardiovascular diseases and diabetes. The aim of this review is to present a detailed information about the role of foodborne constituents as antibrowning agents to significantly reduce the harmful compounds like advanced glycation end products (AGEs) during food processing. This review includes strategies involving addition of amino acids, aromatic compounds, vitamins, modification of amino acids, and reducing sugars as antibrowning agents to reduce the AGEs. The role of Food borne functional ingredients such as catechin, epicathechin, luteolin, and ferulic acids as inhibitors of AGEs is also discussed. Among the naturally occurring inhibitors, genistein could be a crucial and safe agent to reduce reactive intermediates. PRACTICAL APPLICATIONS: Maillard reaction leads to changes in food color, protein functionality, protein digestibility, and loss of nutrient from foods. Maillard reaction products (MRPs) is also reported to be associated with various inflammatory conditions and may contribute to the progress of chronic diseases, including diabetes. It is hence necessary to reduce the MRPs, in both food and biological products, to offset this phenomenon. Among the strategies adopted till date, chemical agents could inhibit reactive carbonyl species and reactive oxygen species, but also are known to elicit serious side effects. Dietary flavonoids could be a very good inhibitor of MRPs both in biological and in food systems. It could be suggested that dietary flavonoids and isoflavones can be used as antibrowning agents in food and pharmaceutical industries particularly for targeted and sustained release of hypoglycemic drug in the intestines.

Glycation of Plant Proteins: Regulatory Roles and Interplay with Sugar Signalling?

Glycation can be defined as an array of non-enzymatic post-translational modifications of proteins formed by their interaction with reducing carbohydrates and carbonyl products of their degradation. Initial steps of this process rely on reducing sugars and result in the formation of early glycation products-Amadori and Heyns compounds via Schiff base intermediates, whereas their oxidative degradation or reactions of proteins with α-dicarbonyl compounds yield a heterogeneous group of advanced glycation end products (AGEs). These compounds accompany thermal processing of protein-containing foods and are known to impact on ageing, pathogenesis of diabetes mellitus and Alzheimer's disease in mammals. Surprisingly, despite high tissue carbohydrate contents, glycation of plant proteins was addressed only recently and its physiological role in plants is still not understood. Therefore, here we summarize and critically discuss the first steps done in the field of plant protein glycation during the last decade. We consider the main features of plant glycated proteome and discuss them in the context of characteristic metabolic background. Further, we address the possible role of protein glycation in plants and consider its probable contribution to protein degradation, methylglyoxal and sugar signalling, as well as interplay with antioxidant defense.