Age-dependent accumulation of N epsilon-(carboxymethyl)lysine and N epsilon-(carboxymethyl)hydroxylysine in human skin collagen

Early- and life-long intake of dietary advanced glycation end-products (dAGEs) leads to transient tissue accumulation, increased gut sensitivity to inflammation, and slight changes in gut microbial diversity, without causing overt disease

Dietary advanced glycation end-products (dAGEs) accumulate in organs and are thought to initiate chronic low-grade inflammation (CLGI), induce glycoxidative stress, drive immunosenescence, and influence gut microbiota. Part of the toxicological interest in glycation products such as dietary carboxymethyl-lysine (dCML) relies on their interaction with receptor for advanced glycation end-products (RAGE). It remains uncertain whether early or lifelong exposure to dAGEs contributes physiological changes and whether such effects are reversible or permanent. Our objective was to examine the physiological changes in Wild-Type (WT) and RAGE KO mice that were fed either a standard diet (STD - 20.8 ± 5.1 µg dCML/g) or a diet enriched with dCML (255.2 ± 44.5 µg dCML/g) from the perinatal period for up to 70 weeks. Additionally, an early age (6 weeks) diet switch (dCML→STD) was explored to determine whether potential harmful effects of dCML could be reversed. Previous dCML accumulation patterns described by our group were confirmed here, with significant RAGE-independent accumulation of dCML in kidneys, ileum and colon over the 70-week dietary intervention (respectively 3-fold, 17-fold and 20-fold increases compared with controls). Diet switching returned tissue dCML concentrations to their baseline levels. The dCML-enriched diet had no significative effect on endogenous glycation, inflammation, oxidative stress or senescence parameters. The relative expression of TNFα, VCAM1, IL6, and P16 genes were all upregulated (∼2-fold) in an age-dependent manner, most notably in the kidneys of WT animals. RAGE knockout seemed protective in this regard, diminishing age-related renal expression of TNFα. Significant increases in TNFα expression were detectable in the intestinal tract of the Switch group (∼2-fold), suggesting a higher sensitivity to inflammation perhaps related to the timing of the diet change. Minor fluctuations were observed at family level within the caecal microbiota, including Eggerthellaceae, Anaerovoracaceae and Marinifilaceae communities, indicating slight changes in composition. Despite chronic dCML consumption resulting in higher free CML levels in tissues, there were no substantial increases in parameters related to inflammageing. Age was a more important factor in inflammation status, notably in the kidneys, while the early-life dietary switch may have influenced intestinal susceptibility to inflammation. This study affirms the therapeutic potential of RAGE modulation and corroborates evidence for the disruptive effect of dietary changes occurring too early in life. Future research should prioritize the potential influence of dAGEs on disease aetiology and development, notably any exacerbating effects they may have upon existing health conditions.

Rapid formation of N ε-(carboxymethyl)lysine (CML) from ribose depends on glyoxal production by oxidation

N ε-(Carboxymethyl)lysine (CML) is a major advanced glycation end-product (AGE) involved in protein dysfunction and inflammation in vivo. Its accumulation increases with age and is enhanced with the pathogenesis of diabetic complications. Therefore, the pathways involved in CML formation should be elucidated to understand the pathological conditions involved in CML. Ribose is widely used in glycation research because it shows a high reactivity with proteins to form AGEs. We previously demonstrated that ribose generates CML more rapidly than other reducing sugars, such as glucose; however, the underlying mechanism remains unclear. In this study, we focused on the pathway of CML formation from ribose. As a result, glyoxal (GO) was the most abundant product generated from ribose among the tested reducing sugars and was significantly correlated with CML formation from ribose-modified protein. The coefficient of determination (R 2) for CML formation between the ribose-modified protein and Amadori products or the ribose degradation product (RDP)-modified protein was higher for the RDP-modified protein. CML formation from ribose degradation products (RDP) incubated with protein significantly correlated with CML formation from GO-modified protein (r s = 0.95, p = 0.0000000869). GO and CML formation were inhibited by diethylenetriaminepentaacetic acid (DTPA) and enhanced by iron chloride. Additionally, flavonoid compounds such as isoquercetin, which are known to inhibit CML, also inhibited GO formation from ribose and CML formation. In conclusion, ribose undergoes auto-oxidation and oxidative cleavage between C-2 and C-3 to generate GO and enhance CML accumulation.

N-acetyl-L-hydroxyproline - A potent skin anti-ageing active preventing advanced glycation end-product formation in vitro and ex vivo

OBJECTIVE

Advanced glycation end-products (AGEs) represent a large group of compounds generated by a non-enzymatic reaction between reducing sugars and amino groups. The formation and accumulation of AGEs in the skin lead to protein crosslinking, dermal stiffening and yellowing, which ultimately contribute to cutaneous ageing. Amino acids have been described to exhibit anti-glycation effects. The objective of this study was to understand the inhibitory role of the amino acid derivative N-acetyl-L-hydroxyproline (NAHP) as an anti-glycation active for human skin.

METHODS

A cell-free assay investigating the inhibition of glycation of serum albumin by NAHP was used to determine the capability of NAHP to decrease AGE formation. Also, by assessing the amount of the AGE N-(carboxymethyl)lysine (CML) the anti-glycation abilities of NAHP were investigated utilizing dot blot analysis. The improvement of cell-matrix interaction by NAHP was determined in vitro using a glycated fibroblast-populated collagen lattice (FPCL) dermis model. In skin biopsies, AGE autofluorescence was determined after treatment with NAHP and/or glucose ex vivo.

RESULTS

NAHP significantly and dose-dependently inhibited levels of AGEs, which were induced by the glycation of a protein solution. This decrease could be visualized by showing that the brownish appearance as well as the AGE-specific fluorescence of glucose-treated samples were reduced after the application of increasing amounts of NAHP. Also, CML formation was dose-dependently inhibited by NAHP. In FPCLs, the contractile capacity of fibroblasts was significantly disturbed after glycation. This could be prevented by the addition of NAHP. Compared to glyoxal-treated samples, the co-application of NAHP significantly decreased the diameter as well as the weight of glycated FPCLs. Ex vivo application of glucose to skin explants showed a higher AGE fluorescence signal compared to control explants. Co-treatment with NAHP and glucose decreased the level of AGE fluorescence in comparison to glucose-treated explants.

CONCLUSION

These data provide clear evidence that under glycation stress conditions treatment with NAHP inhibited AGE formation in vitro and ex vivo and prevented the loss of cellular contractile forces in a glycated dermis model. Thus, NAHP obviously provides a beneficial treatment option to counteract AGE-related changes in human skin such as dermal stiffening and yellowish skin appearance.

Increased Diabetes Complications in a Mouse Model of Oxidative Stress Due to 'Mismatched' Mitochondrial DNA

Associations between chronic diabetes complications and mitochondrial dysfunction represent a subject of major importance, given the diabetes pandemic and high personal and socioeconomic costs of diabetes and its complications. Modelling diabetes complications in inbred laboratory animals is challenging due to incomplete recapitulation of human features, but offer mechanistic insights and preclinical testing. As mitochondrial-based oxidative stress is implicated in human diabetic complications, herein we evaluate diabetes in a unique mouse model that harbors a mitochondrial DNA from a divergent mouse species (the 'xenomitochondrial mouse'), which has mild mitochondrial dysfunction and increased oxidative stress. We use the streptozotocin-induced diabetes model with insulin supplementation, with 20-weeks diabetes. We compare C57BL/6 mice and the 'xenomitochondrial' mouse, with measures of heart and kidney function, histology, and skin oxidative stress markers. Compared to C57BL/6 mice, the xenomitochondrial mouse has increased diabetic heart and kidney damage, with cardiac dysfunction, and increased cardiac and renal fibrosis. Our results show that mitochondrial oxidative stress consequent to divergent mtDNA can worsen diabetes complications. This has implications for novel therapeutics to counter diabetes complications, and for genetic studies of risk, as mtDNA genotypes may contribute to clinical outcomes.

Soluble RAGE and skeletal muscle tissue RAGE expression profiles in lean and obese young adults across differential aerobic exercise intensities

Nearly 40% of Americans have obesity and are at increased risk for developing type 2 diabetes. Skeletal muscle is responsible for >80% of insulin-stimulated glucose uptake that is attenuated by the inflammatory milieu of obesity and augmented by aerobic exercise. The receptor for advanced glycation endproducts (RAGE) is an inflammatory receptor directly linking metabolic dysfunction with inflammation. Circulating soluble isoforms of RAGE (sRAGE) formed either by proteolytic cleavage (cRAGE) or alternative splicing (esRAGE) act as decoys for RAGE ligands, thereby counteracting RAGE-mediated inflammation. We aimed to determine if RAGE expression or alternative splicing of RAGE is altered by obesity in muscle, and whether acute aerobic exercise (AE) modifies RAGE and sRAGE. Young (20-34 yr) participants without [n = 17; body mass index (BMI): 22.6 ± 2.6 kg/m2] and with obesity (n = 7; BMI: 32.8 ± 2.9 kg/m2) performed acute aerobic exercise (AE) at 40%, 65%, or 80% of maximal aerobic capacity (V̇o2max; mL/kg/min) on separate visits. Blood was taken before and 30 min after each AE bout. Muscle biopsy samples were taken before, 30 min, and 3 h after the 80% V̇o2max AE bout. Individuals with obesity had higher total RAGE and esRAGE mRNA and RAGE protein (P < 0.0001). In addition, RAGE and esRAGE transcripts correlated to transcripts of the NF-κB subunit P65 (P < 0.05). There was no effect of AE on total RAGE or esRAGE transcripts, or RAGE protein (P > 0.05), and AE tended to decrease circulating sRAGE in particular at lower intensities of exercise. RAGE expression is exacerbated in skeletal muscle with obesity, which may contribute to muscle inflammation via NF-κB. Future work should investigate the consequences of increased skeletal muscle RAGE on the development of obesity-related metabolic dysfunction and potential mitigating strategies.NEW & NOTEWORTHY This study is the first to investigate the effects of aerobic exercise intensity on circulating sRAGE isoforms, muscle RAGE protein, and muscle RAGE splicing. sRAGE isoforms tended to diminish with exercise, although this effect was attenuated with increasing exercise intensity. Muscle RAGE protein and gene expression were unaffected by exercise. However, individuals with obesity displayed nearly twofold higher muscle RAGE protein and gene expression, which positively correlated with expression of the P65 subunit of NF-κB.

Extracellular vesicle-matrix interactions

The extracellular matrix in microenvironments harbors a variety of signals to control cellular functions and the materiality of tissues. Most efforts to synthetically reconstitute the matrix by biomaterial design have focused on decoupling cell-secreted and polymer-based cues. Cells package molecules into nanoscale lipid membrane-bound extracellular vesicles and secrete them. Thus, extracellular vesicles inherently interact with the meshwork of the extracellular matrix. In this Review, we discuss various aspects of extracellular vesicle-matrix interactions. Cells receive feedback from the extracellular matrix and leverage intracellular processes to control the biogenesis of extracellular vesicles. Once secreted, various biomolecular and biophysical factors determine whether extracellular vesicles are locally incorporated into the matrix or transported out of the matrix to be taken up by other cells or deposited into tissues at a distal location. These insights can be utilized to develop engineered biomaterials where EV release and retention can be precisely controlled in host tissue to elicit various biological and therapeutic outcomes.

Inhibitory Effects of Parachlorella Beijerinckii Extracts on the Formation of Advanced Glycation End Products and Glycative Stress-Induced Inflammation in an In Vitro Skin Dermis-Like Model

Advanced glycation end products (AGEs) are formed via a nonenzymatic glycosylation reaction called glycation. The formation and accumulation of AGEs increases in skin with age, contributing to the appearance of facial wrinkles and loss of skin elasticity. Therefore, inhibition of AGEs may delay skin aging. The microalgae Parachlorella beijerinckii has been used as a health food supplement for many years and contains carotenoids and vitamins that have antioxidant and anti-inflammatory effects. The aim of this study was to investigate whether Chlorella extract also has antiglycation activity. Antiglycation activity was measured using fluorescent AGEs, Nε-(carboxymethyl) lysine (CML), and Nε-(carboxymethyl) arginine (CMA) from glycated bovine serum albumin and type I collagen in vitro. A gel with a dermis-like structure consisting of collagen and a live fibroblast cell line was glycated with glyoxal. The content of fluorescent AGE, CML, and CMA, and the gel contraction activity were measured. In addition, to investigate the level of inflammation induced by the glycation of the collagen gel, the expression level of the receptor for AGEs and interleukin-8 were examined. Fat-solubleChlorella extract suppressed the formation of fluorescent AGEs, CML, and CMA in both models. These results indicated that Chlorella extract directly inhibited AGE formation. The collagen gel contracted over time during culturing, whereas contraction was inhibited in the glyoxal-treated collagen gel. Chlorella extract remarkably attenuated the glyoxal-induced gel contraction. Moreover, Chlorella extract substantially decreased the fluorescent AGEs, CML, and CMA in the collagen gels with glyoxal. Glyoxal exposure increased the expression levels of interleukin-8 and receptor for AGE proteins in collagen gels, while Chlorella extract inhibited this increase. This study showed that fat-solubleChlorella extract has a direct inhibitory effect on AGEs and decreases receptor expression for AGE-mediated inflammation by reducing AGEs. Chlorella may delay skin aging by inhibiting the formation and accumulation of AGEs.

Exceptionally versatile take II: post-translational modifications of lysine and their impact on bacterial physiology

Among the 22 proteinogenic amino acids, lysine sticks out due to its unparalleled chemical diversity of post-translational modifications. This results in a wide range of possibilities to influence protein function and hence modulate cellular physiology. Concomitantly, lysine derivatives form a metabolic reservoir that can confer selective advantages to those organisms that can utilize it. In this review, we provide examples of selected lysine modifications and describe their role in bacterial physiology.

Controlled Formation of Carboxymethyllysine in Bone Matrix through Designed Glycation Reaction

It has been a challenge to establish a link between specific advanced glycation end products (AGEs) as causal agents of different pathologies and age‐related diseases, primarily because of the lack of suitable in vitro experimental strategies facilitating increased formation of a specific AGE, here carboxymethyllysine (CML), over other AGEs under controlled conditions. CML is of considerable importance to various oxidative stress–related diseases, because in vivo formation of this AGE is connected with cellular oxidative/carbonyl metabolism. The mechanistic implications of CML accumulation in bone remain to be elucidated. To facilitate such studies, we developed a new in vitro strategy that allows preferential generation of CML in bone matrix over other AGEs. Using bone samples from human donors of different age (young, middle‐age, and elderly), we show successful in vitro generation of the desired levels of CML and show that they mimic those observed in vivo in several bone disorders. Formation of such physiologically relevant CML levels was achieved by selecting two oxidative/carbonyl stress compounds naturally produced in the human body, glyoxal and glyoxylic acid. Kinetic studies using the two compounds revealed differences not only between their reaction rates but also in the progression and enhanced formation of CML over other AGEs (measured by their collective fluorescence as fluorescent AGEs [fAGEs]) Consequently, through the regulation of reaction time, the levels of CML and fAGEs could be controlled and separated. Given that the developed approach does not fully eliminate the formation of other uncharacterized glycation products, this could be considered as the study limitation. We expect that the concepts of our experimental approach can be used to develop diverse strategies facilitating production of the desired levels of selected AGEs in bone and other tissues, and thus, opens new avenues for investigating the role and mechanistic aspects of specific AGEs, here CML, in bone. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Full incorporation of the noncanonical amino acid hydroxylysine as a surrogate for lysine in green fluorescent protein

The canonical set of amino acids leads to an exceptionally wide range of protein functionality, nevertheless, this set still exhibits limitations. The incorporation of noncanonical amino acids into proteins can enlarge its functional scope. Although proofreading will counteract the charging of tRNAs with other amino acids than the canonical ones, the translation machinery may still accept noncanonical amino acids as surrogates and incorporate them at the canonically prescribed locations within the protein sequence. Here, we use a cell-free expression system to demonstrate the full replacement of l-lysine by l-hydroxylysine at all lysine sites of recombinantly produced GFP. In vivo, as a main component of collagen, post-translational l-hydroxylysine generation enables the formation of cross-links. Our work represents a first step towards in vitro production of (modified) collagens, more generally of proteins that can easily be crosslinked.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

Is skin autofluorescence (SAF) representative of dermal advanced glycation endproducts (AGEs) in dark skin? A pilot study

Aims

Non-invasively assessed skin autofluorescence (SAF) measures advanced glycation endproducts (AGEs) in the dermis. SAF correlates with dermal AGEs in Caucasians and Asians, but studies in dark-skinned subjects are lacking. In this pilot we aimed to assess whether SAF signal is representative of intrinsic fluorescence (IF) and AGE accumulation in dark skin.

Methods

Skin biopsies were obtained in 12 dark-skinned subjects (6 healthy subjects, median age 22 years; 6 diabetes mellitus (DM) subjects, 65 years). SAF was measured with the AGE Reader, IF using confocal microscopy, and AGE distribution with specific antibodies. CML and MG-H1 were quantified with UPLC-MS/MS and pentosidine with HPLC and fluorescent detection.

Results

SAF correlated with IF from the dermis (405nm, r = 0.58, p < 0.05), but not with CML (r = 0.54, p = 0.07). CML correlated with IF from the dermis (405nm, r = 0.90, p < 0.01). UV reflectance and the coefficient of variation of SAF were negatively correlated (r = -0.80, p < 0.01). CML and MG-H1 were predominantly present around blood vessels, in collagen and fibroblasts in the dermis.

Conclusion

This proof of concept study is the first to compare non-invasive SAF with AGE levels measured in skin biopsies in dark-skinned subjects. SAF did not correlate with individual AGEs from biopsies, but was associated with IF. However, the intra-individual variance was high, limiting its application in dark-skinned subjects on an individual basis.

Circulating and Extracellular Vesicles Levels of N-(1-Carboxymethyl)-L-Lysine (CML) Differentiate Early to Moderate Alzheimer's Disease

BACKGROUND

Both advanced glycation end products (AGEs) N-(1-carboxymethyl)-L-lysine (CML) and pentosidine were found in the brain from Alzheimer's disease (AD) patients and were associated with the neuropathological hallmarks of AD. In AD patients, the circulating level of both AGEs remains unknown. Moreover, their levels in peripheral extracellular vesicles (EVs) and their association with AD remain to be determined. Finally, it is not known if neuronal cells can release AGEs via EVs and propagate AGEs.

OBJECTIVE

To determine the levels of circulating CML and pentosidine during the progression of AD. Moreover, their levels in circulating EVs were determined and their association with the clinical cognitive scores were analyzed. Finally, we have studied the possibility that neuronal cells eliminate and transfer these AGEs through EVs.

METHODS

CML and pentosidine levels were measured in serum and in circulating EVs. Released-EVs from SK-N-SH neuronal cells were isolated and CML levels were also determined.

RESULTS

The levels of CML in albumin-free serum proteins were higher in the early stage of AD while the levels of pentosidine remained unchanged. In contrast, the levels of CML in the EVs were lower in the moderate stage of AD. Interestingly, the levels of CML in serum were negatively correlated with the clinical cognitive scores MMSE and MoCA. For the first time, we were able to demonstrate that CML was present in EVs released from neuronal cells in culture.

CONCLUSION

Peripheral and circulating EVs levels of CML can differentiate early to moderate AD. In the brain, neuronal CML can propagate from cells-to-cells via EVs.

Advanced Glycation End-Products Can Activate or Block Bitter Taste Receptors

Bitter taste receptors (T2Rs) are expressed in several tissues of the body and are involved in a variety of roles apart from bitter taste perception. Advanced glycation end-products (AGEs) are produced by glycation of amino acids in proteins. There are varying sources of AGEs, including dietary food products, as well as endogenous reactions within our body. Whether these AGEs are T2R ligands remains to be characterized. In this study, we selected two AGEs, namely, glyoxal-derived lysine dimer (GOLD) and carboxymethyllysine (CML), based on their predicted interaction with the well-studied T2R4, and its physiochemical properties. Results showed predicted binding affinities (K_d) for GOLD and CML towards T2R4 in the nM and μM range, respectively. Calcium mobilization assays showed that GOLD inhibited quinine activation of T2R4 with IC₅₀ 10.52 ± 4.7 μM, whilst CML was less effective with IC₅₀ 32.62 ± 9.5 μM. To characterize whether this antagonism was specific to quinine activated T2R4 or applicable to other T2Rs, we selected T2R14 and T2R20, which are expressed at significant levels in different human tissues. A similar effect of GOLD was observed with T2R14; and in contrast, GOLD and CML activated T2R20 with an EC₅₀ of 79.35 ± 29.16 μM and 65.31 ± 17.79 μM, respectively. In this study, we identified AGEs as novel T2R ligands that caused either activation or inhibition of different T2Rs.

Food advanced glycation end products as potential endocrine disruptors: An emerging threat to contemporary and future generation

Mankind exposure to chemicals in the past century has increased dramatically throughout environment. There is no question that chemicals interfere with the physiology of biological system. Abundance of chemicals is documented to be detrimental to human and wildlife. The mammalian endocrine system is comprised of many interacting tissues mediate themselves through hormones that are essential for metabolism, growth and development. Humans secrete over fifty different hormones to orchestrate major physiological functions however; these vital functions can be intervened by huge number of internal and external chemical stressors that are identified as endocrine disruptors. Advanced glycation end products (AGEs), familiarly known as Maillard products, formed through non-enzymatic glycation whose production is augmented on aging as well as environmental stressors. Processed foods have become very popular today due to their taste, convenience, and inexpensiveness. Manufacture of these day-to-day foods involves extreme temperatures on processing results in the formation of AGEs could independently promote oxidative stress, aging, diabetes, cancer, degenerative diseases, more fascinatingly hormonal disruption is the subject of interest of this review. Based on some substantial observations documented till time, we discuss the emergence of dietary AGEs as potential endocrine disruptors by emphasizing their occurrence, mechanisms and participation in endocrine interruption. Both economically and in terms of human life, AGEs may represent an enormous cost for the future society. Therefore, by explicating their novel role in endocrine diseases, the review strives to make an impact on AGEs and their exposure among public as well as scientific communities.

Impact of Non-Enzymatic Glycation in Neurodegenerative Diseases: Role of Natural Products in Prevention

Non-enzymatic protein glycosylation is the addition of free carbonyls to the free amino groups of proteins, amino acids, lipoproteins and nucleic acids resulting in the formation of early glycation products. The early glycation products are also known as Maillard reaction which undergoes dehydration, cyclization and rearrangement to form advanced glycation end-products (AGEs). By and large the researchers in the past have also established that glycation and the AGEs are responsible for most type of metabolic disorders, including diabetes mellitus, cancer, neurological disorders and aging. The amassing of AGEs in the tissues of neurodegenerative diseases shows its involvement in diseases. Therefore, it is likely that inhibition of glycation reaction may extend the lifespan of an individual. The hunt for inhibitors of glycation, mainly using in vitro models, has identified natural compounds able to prevent glycation, especially polyphenols and other natural antioxidants. Extrapolation of results of in vitro studies on the in vivo situation is not straightforward due to differences in the conditions and mechanism of glycation, and bioavailability problems. Nevertheless, existing data allow postulating that enrichment of diet in natural anti-glycating agents may attenuate glycation and, in consequence may halt the aging and neurological problems.

Fighting against Skin Aging: The Way from Bench to Bedside

As the most voluminous organ of the body that is exposed to the outer environment, the skin suffers from both intrinsic and extrinsic aging factors. Skin aging is characterized by features such as wrinkling, loss of elasticity, laxity, and rough-textured appearance. This aging process is accompanied with phenotypic changes in cutaneous cells as well as structural and functional changes in extracellular matrix components such as collagens and elastin. In this review, we summarize these changes in skin aging, research advances of the molecular mechanisms leading to these changes, and the treatment strategies aimed at preventing or reversing skin aging.

An advanced glycation endproduct (AGE)-rich diet promotes accumulation of AGEs in Achilles tendon

Advanced Glycation Endproducts (AGEs) accumulate in long‐lived tissue proteins like collagen in bone and tendon causing modification of the biomechanical properties. This has been hypothesized to raise the risk of orthopedic injury such as bone fractures and tendon ruptures. We evaluated the relationship between AGE content in the diet and accumulation of AGEs in weight‐bearing animal Achilles tendon. Two groups of mice (C57BL/6Ntac) were fed with either high‐fat diet low in AGEs high‐fat diet (HFD) (n = 14) or normal diet high in AGEs (ND) (n = 11). AGE content in ND was six to 50‐fold higher than HFD. The mice were sacrificed at week 40 and Achilles and tail tendons were carefully excised to compare weight and nonweight‐bearing tendons. The amount of the AGEs carboxymethyllysine (CML), methylglyoxal‐derived hydroimidazolone (MG‐H1) and carboxyethyllysine (CEL) in Achilles and tail tendon was measured using ultraperformance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) and pentosidine with high‐pressure liquid chromatography (HPLC) with fluorescent detection. AGEs in Achilles tendon were higher than in tail tendon for CML (P < 0.0001), CEL (P < 0.0001), MG‐H1 and pentosidine (for both ND and HFD) (P < 0.0001). The AGE‐rich diet (ND) resulted in an increase in CML (P < 0.0001), MG‐H1 (P < 0.001) and pentosidine (P < 0.0001) but not CEL, in Achilles and tail tendon. This is the first study to provide evidence for AGE accumulation in injury‐prone, weight‐bearing Achilles tendon associated with intake of an AGE‐rich diet. This indicates that food‐derived AGEs may alter tendon properties and the development of tendon injuries.

Probing Protein Glycation by Chromatography and Mass Spectrometry: Analysis of Glycation Adducts

Glycation is a non-enzymatic post-translational modification of proteins, formed by the reaction of reducing sugars and α-dicarbonyl products of their degradation with amino and guanidino groups of proteins. Resulted early glycation products are readily involved in further transformation, yielding a heterogeneous group of advanced glycation end products (AGEs). Their formation is associated with ageing, metabolic diseases, and thermal processing of foods. Therefore, individual glycation adducts are often considered as the markers of related pathologies and food quality. In this context, their quantification in biological and food matrices is required for diagnostics and establishment of food preparation technologies. For this, exhaustive protein hydrolysis with subsequent amino acid analysis is the strategy of choice. Thereby, multi-step enzymatic digestion procedures ensure good recoveries for the most of AGEs, whereas tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode with stable isotope dilution or standard addition represents “a gold standard” for their quantification. Although the spectrum of quantitatively assessed AGE structures is continuously increases, application of untargeted profiling techniques for identification of new products is desired, especially for in vivo characterization of anti-glycative systems. Thereby, due to a high glycative potential of plant metabolites, more attention needs to be paid on plant-derived AGEs.

Advanced glycation end products among patients maintained on antipsychotics

The aim of this study was to measure advanced glycation end products (AGEs) among participants maintained on antipsychotics using the AGE Reader and to compare them with controls from the general population. Participants maintained on antipsychotics for at least 6 months were recruited from the Psychiatry Department at Rumailah Hospital, Doha, Qatar. Healthy controls were recruited from the primary healthcare centers in Doha, Qatar. AGEs of a total of 86 participants (48 patients and 38 controls) were recorded. Among the group maintained on antipsychotics, women, smokers, and Arabs had significantly higher AGEs levels compared with men, nonsmokers, and non-Arabs, respectively (P<0.05). The levels of AGEs were higher among the group of patients maintained on antipsychotics in comparison to controls; however, the difference did not reach statistical significance. This is the first study to examine AGEs in patients maintained on antipsychotics. Our findings showed that such patients do not differ significantly from controls comparing AGEs levels. Future investigations might need to consider recruiting a larger sample size using a prospective design.

The association between various smoking behaviors, cotinine biomarkers and skin autofluorescence, a marker for advanced glycation end product accumulation

BACKGROUND

Skin autofluorescence, a biomarker for advanced glycation end products (AGEs) accumulation, has been shown to predict diabetes-related cardiovascular complications and is associated with several environmental and lifestyle factors. In the present study, we examined the association between various smoking behaviors and skin autofluorescence, as well as the association between several cotinine biomarkers and skin autofluorescence, using both epidemiological and metabolomics data.

METHODS

In a cross-sectional study, we evaluated participants from the LifeLines Cohort Study and the Qatar Metabolomics Study on Diabetes (QMDiab). In the LifeLines Cohort Study smoking behavior and secondhand smoking were assessed in 8,905 individuals including 309 individuals (3.5%) with type 2 diabetes. In QMDiab, cotinine biomarkers were measured in saliva, plasma and urine in 364 individuals of whom 188 (51%) had type 2 diabetes. Skin autofluorescence was measured non-invasively in all participants using the AGE Reader.

RESULTS

Skin autofluorescence levels increased with a higher number of hours being exposed to secondhand smoking. Skin autofluorescence levels of former smokers approached levels of never smokers after around 15 years of smoking cessation. Urinary cotinine N-oxide, a biomarker of nicotine exposure, was found to be positively associated with skin autofluorescence in the QMDiab study (p = 0.03).

CONCLUSIONS

In the present study, we have demonstrated that secondhand smoking is associated with higher skin autofluorescence levels whereas smoking cessation has a beneficial effect on skin autofluorescence. Finally, urinary cotinine N-oxide might be used as an alternative way for questionnaires to examine the effect of (environmental) tobacco smoking on skin autofluorescence.

Dicarbonyls and Advanced Glycation End-Products in the Development of Diabetic Complications and Targets for Intervention

Advanced glycation end-products (AGEs) are non-enzymatic protein and amino acid adducts as well as DNA adducts which form from dicarbonyls and glucose. AGE formation is enhanced in diabetes and is associated with the development of diabetic complications. In the current review, we discuss mechanisms that lead to enhanced AGE levels in the context of diabetes and diabetic complications. The methylglyoxal-detoxifying glyoxalase system as well as alternative pathways of AGE detoxification are summarized. Therapeutic approaches to interfere with different pathways of AGE formation are presented.

A new dermocosmetic containing retinaldehyde, delta-tocopherol glucoside and glycylglycine oleamide for managing naturally aged skin: results from in vitro to clinical studies

INTRODUCTION

Natural aging of skin tissues, the addition of the cumulative action of the time and radiation exposure result in skin atrophy, wrinkles and degeneration of the extracellular matrix (ECM). The aim of the study was to investigate the beneficial effect of a combination containing retinaldehyde (RAL), delta-tocopherol glucoside (delta-TC) and glycylglycine ole-amide (GGO) and of a dermocosmetic containing the combination.

MATERIALS AND METHODS

The protective effect of the combination was assessed through in vitro gene expression of ultraviolet (UV)-irradiated fibroblasts. A skin aging assay using UV light on ex vivo skin samples and a clinical study conducted in 36 women aged from 35 to 55 years with a minimum of level 4 to a maximum of level 6 on the crow's feet photoscale assessed the antiaging effect of the dermocosmetic.

RESULTS

When added to UV-irradiated fibroblasts, the combination substantially improved the ECM in activating the elastin fiber production (fibrillin 2, fibulin 1 and 5 and lysyl oxidase-like 2) as well as that of proteins involved in the cellular ECM interactions (integrin b1, paxillin and actin a2). An ex vivo photodamaged human skin model showed that the dermocosmetic formulation containing the combination of the active ingredients protected the elastic network against UV-induced alterations including both elastin and fibrillin-rich fibers in the dermis. A daily application of the dermocosmetic for 2 months on naturally aged skin resulted in a statistically significant improvement (p<0.05) of visible signs of aging comprising crow's feet, wrinkles and periocular fine lines. Finally, the formulation was well tolerated.

CONCLUSION

The dermocosmetic containing RAL, delta-TC and GGO provides a substantial benefit in the daily care of naturally aged skin in women aged 35-55 years.

Skin autofluorescence, a non-invasive biomarker for advanced glycation end products, is associated with the metabolic syndrome and its individual components

BACKGROUND

The metabolic syndrome (MetS) comprises several cardiometabolic risk factors associated with increased risk for both type 2 diabetes and cardiovascular disease. Skin autofluorescence (SAF), a non-invasive biomarker of advanced glycation end products accumulation, is associated with cardiovascular complications in subjects with diabetes. The aim of the present study was to examine the association between SAF and the presence of MetS as well as its individual components in a general population.

METHODS

For this cross-sectional analysis, we included 78,671 non-diabetic subjects between 18 and 80 years of age who participated in the LifeLines Cohort Study and had SAF measurement obtained non-invasively using the AGE Reader. MetS was defined according to the revised NCEP ATP III criteria. Students unpaired t test was used to test differences between groups. Both logistic and linear regression analyses were performed in order to test associations between the individual MetS components and SAF.

RESULTS

Subjects with MetS had higher SAF (2.07 ± 0.45 arbitrary units, AU) compared to individuals without MetS (1.89 ± 0.42 AU) (p < 0.001). There was a positive association between the number of MetS components and higher SAF Z-scores (p < 0.001). Individuals in the highest SAF tertile had a higher presence of MetS (OR 2.61; 95% CI 2.48-2.75) and some of the individual components compared to subjects in the lowest SAF tertile. After correction for age, gender, creatinine clearance, HbA1c and smoking status, only elevated blood pressure and low HDL cholesterol remained significantly associated with higher SAF (p = 0.002 and p = 0.001 respectively).

CONCLUSION

Skin autofluorescence was associated with the presence of MetS and some of its individual components. In addition, increasing SAF Z-scores were observed with a higher number of MetS components. Prospective studies are needed to establish whether SAF can be used as an (additional) screening tool to predict both cardiovascular disease and type 2 diabetes in high-risk populations.

The effects of advanced glycation end products (AGEs) on dermal wound healing and scar formation: a systematic review

Introduction:

With ageing, the skin gradually loses its youthful appearance and functions like wound healing and scar formation. The pathophysiological theory of Advanced Glycation End products (AGEs) has gained traction during the last decade. This review aims to document the influence of AGEs on the mechanical and physiologic properties of the skin, how they affect dermal wound healing and scar formation in high-AGE populations like elderly patients and diabetics, and potential therapeutic strategies.

Methods:

This systematic literature study involved a structured search in Pubmed and Web of Science with qualitative analysis of 14 articles after a three-staged selection process with the use of in- and exclusion criteria.

Results:

Overall, AGEs cause shortened, thinned, and disorganized collagen fibrils, consequently reducing elasticity and skin/scar thickness with increased contraction and delayed wound closure. Documented therapeutic strategies include dietary AGE restriction, sRAGE decoy receptors, aminoguanidine, RAGE-blocking antibodies, targeted therapy, thymosin β4, anti-oxidant agents and gold nanoparticles, ethyl pyruvate, Gal-3 manipulation and metformin.

Discussion:

With lack of evidence concerning scars, no definitive conclusions can yet be made about the role of AGEs on possible appearance or function of scar tissue. However, all results suggest that scars tend to be more rigid and contractile with persistent redness and reduced tendency towards hypertrophy as AGEs accumulate.

Conclusion:

Abundant evidence supports the pathologic role of AGEs in ageing and dermal wound healing and the effectiveness of possible therapeutic agents. More research is required to conclude its role in scar formation and scar therapy.

Our skin is the body’s first line of defense. It is the barrier that protects us from chemical and biological threats such as viruses, bacteria or corrosive liquids. It is the sensor that allows us to detect physical threats like extreme temperatures, pressure and pain. And when these preventative measures fail, the skin has yet another property: the ability to heal.

Skin changes visibly with age, most notably with the appearance of wrinkles. However, there is more to ageing than meets the eye; invisible alterations cause the decline of various functions of the skin, such as wound healing and scar formation. An array of non-conclusive research has been done in this field. One theory that has gained traction during the last decade is the Advanced Glycation End products (AGEs) theory. The theory states that AGEs play an important role in skin aging, wound healing and the effectiveness of different therapeutic options. Their presence supposedly indicates a diminished ability for wound healing and scar formation.

AGEs are proteins to which sugar molecule is bound. The sugar molecule inhibits the original protein from functioning properly. As skin contains many proteins like collagen, the formation of these AGEs could be a viable explanation for the diminished functioning with ageing. In this review, we investigated whether the accumulation of AGEs affects wound healing and scar formation.

Normal scar formation results in a thin scar. However, it may happen that scarring results in thick, large, painful and itchy scars. We investigated whether people with a high AGE content in their skin, like diabetics and elderly, have difficulties forming aesthetically pleasing scars. Secondly, we investigated which therapies reduce the AGE content and, if so, whether these therapies can improve wound healing and scarring. This literature study involved research in scientific databases with qualitative analysis of 14 articles after a three-staged selection process with the use of set criteria.

We found the different ways in which AGEs affect skin properties and wound healing. Collagen, one of the most important proteins in the skin, is affected by these AGEs. Once a sugar binds to it, the collagen strings becomes thinner and shorter, and the different collagen proteins cross-link with each other in an unstructured way. The result of these alterations is a reduced elasticity, i.e. the skin becomes stiffer. The scar will be thinner and the time for wounds to close is longer. We also found strategies to diminish the AGE content, including dietary AGE restriction and Metformin, a drug used in diabetes.

We can conclude that there is proof of AGEs playing an important role in skin ageing, wound healing and the effectiveness of different therapeutic options. However, more research is required to conclude the exact role of AGEs in scar formation and scar therapy.

Carboxymethyl-lysine: thirty years of investigation in the field of AGE formation

In 1985 carboxymethyl-lysine (CML), the first glycoxidation product, was discovered by Dr Ahmed while trying to identify the major products formed in reactions of glucose with lysine under physiological conditions. From that moment, a significant number of researchers have joined efforts to study its formation routes both in foods and in living beings, and the possibility of the existence of an additive action between food-occurring and in vivo produced CML and to explore all the implications associated with its appearance in the biological systems, regardless of its origin. This review presents interesting information on the latest advances in the research on CML sources, mitigation strategies, intake, metabolism and body fluid and tissue delivery, its possible in vivo synergy with highly modified advanced glycation end products-protein, and the physio-pathological implications derived from the presence of this compound in body fluids and tissues.

Glyco-redox, a link between oxidative stress and changes of glycans: Lessons from research on glutathione, reactive oxygen and nitrogen species to glycobiology

Reduction-oxidation (redox) response is one of the most important biological phenomena. The concept introduced by Helmut Sies encouraged many researchers to examine oxidative stress under pathophysiological conditions. Our group has been interested in redox regulation under oxidative stress as well as glycobiology in relation to disease. Current studies by our group and other groups indicate that functional and structural changes of glycans are regulated by redox responses resulting from the generation of reactive oxygen species (ROS) or reactive nitrogen species (RNS) in various diseases including cancer, diabetes, neurodegenerative disease such as Parkinson disease, Alzheimer's disease and amyotrophic lateral sclerosis (ALS), and chronic obstructive pulmonary disease (COPD), even though very few investigators appear to be aware of these facts. Here we propose that the field "glyco-redox" will open the door to a more comprehensive understanding of the mechanism associated with diseases in relation to glycan changes under oxidative stress. A tight link between structural and functional changes of glycans and redox system under oxidative stress will lead to the recognition and interest of these aspects by many scientists. Helmut's contribution in this field facilitated our future perspectives in glycobiology.

The pecking order of skin Advanced Glycation Endproducts (AGEs) as long-term markers of glycemic damage and risk factors for micro- and subclinical macrovascular disease progression in Type 1 diabetes

To date more than 20 glycation products were identified, of which ~15 in the insoluble human skin collagen fraction. The goal of this review is to streamline 30 years of research and ask a set of important questions: in Type 1 diabetes which glycation products correlate best with 1) past mean glycemia 2) reversibility with improved glycemic control, 2) cross-sectional severity of retinopathy, nephropathy and neuropathy and 3) the future long-term risk of progression of micro- and subclinical macrovascular disease. The trio of glycemia related glycation markers furosine (FUR)/fructose-lysine (FL), glucosepane and methylglyoxal hydroimidazolone (MG-H1) emerges as extraordinarily strong predictors of existing and future microvascular disease progression risk despite adjustment for both past and prospective A1c levels. X(2) values are up to 25.1, p values generally less than 0.0001, and significance remains after adjustment for various factors such as A1c, former treatment group, log albumin excretion rate, abnormal autonomic nerve function and LDL levels at baseline. In contrast, subclinical cardiovascular progression is more weakly correlated with AGEs/glycemia with X(2) values < 5.0 and p values generally < 0.05 after all adjustments. Except for future carotid intima-media thickness, which correlates with total AGE burden (MG-H1, pentosidine, fluorophore LW-1 and decreased collagen solubility), adjusted FUR and Collagen Fluorescence (CLF) are the strongest markers for future coronary artery calcium deposition, while cardiac hypertrophy is associated with LW-1 and CLF adjusted for A1c. We conclude that a robust clinical skin biopsy AGE risk panel for microvascular disease should include at least FUR/FL, glucosepane and MG-H1, while a macrovascular disease risk panel should include at least FL/FUR, MG-H1, LW-1 and CLF.

Glycation vs. glycosylation: a tale of two different chemistries and biology in Alzheimer's disease

In our previous studies, we reported that the activity of an anti-oxidant enzyme, Cu,Zn-superoxide dismutase (Cu,Zn-SOD) became decreased as the result of glycation in vitro and in vivo. Glycated Cu,Zn-SOD produces hydroxyl radicals in the presence of transition metals due to the formation of a Schiff base adduct and a subsequent Amadori product. This results in the site-specific cleavage of the molecule, followed by random fragmentation. The glycation of other anti-oxidant enzymes such as glutathione peroxidase and thioredoxin reductase results in a loss or decrease in enzyme activity under pathological conditions, resulting in oxidative stress. The inactivation of anti-oxidant enzymes induces oxidative stress in aging, diabetes and neurodegenerative disorders. It is well known that the levels of Amadori products and N(e)-(carboxylmethyl)lysine (CML) and other carbonyl compounds are increased in diabetes, a situation that will be discussed by the other authors in this special issue. We and others, reported that the glycation products accumulate in the brains of patients with Alzheimer's disease (AD) patients as well as in cerebrospinal fluid (CSF), suggesting that glycation plays a pivotal role in the development of AD. We also showed that enzymatic glycosylation is implicated in the pathogenesis of AD and that oxidative stress is also important in this process. Specific types of glycosylation reactions were found to be up- or downregulated in AD patients, and key AD-related molecules including the amyloid-precursor protein (APP), tau, and APP-cleaving enzymes were shown to be functionally modified as the result of glycosylation. These results suggest that glycation as well as glycosylation are involved in oxidative stress that is associated with aging, diabetes and neurodegenerative diseases such as AD.

Salacia chinensis L. extract ameliorates abnormal glucose metabolism and improves the bone strength and accumulation of AGEs in type 1 diabetic rats

Although extracts of the roots and stems of Salacia chinensis have been used in folk medicines for chronic diseases such as rheumatism, irregular menstruation, asthma and diabetes mellitus, little is known about the mechanism by which Salacia chinensis extract (SCE) ameliorates these diseases. To clarify whether SCE ameliorates the progression of lifestyle-related diseases, the inhibitory effect of SCE on the formation of advanced glycation end products (AGEs) was analyzed in a rat model of streptozotocin-induced diabetes. Although the oral administration of SCE did not ameliorate the diabetes-induced decrease in body weight, it ameliorated the increase in glycoalbumin levels in diabetic rats. An analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) demonstrated that the levels of N(ε)-(carboxymethyl)lysine (CML) were highest in the femurs and that they increased by the induction of diabetes. The administration of SCE also ameliorated the decreased femur strength and the accumulation of CML. Furthermore, when all of the carbohydrates in the chow of diabetic rats were replaced with free glucose, the administration of SCE significantly ameliorated a diabetes-induced increase in glycoalbumin and decrease in serum creatinine level and body weight. This study provides evidence to support that SCE ameliorates diabetes-induced abnormalities by improving the uptake of glucose by various organs.

The Receptor for Advanced Glycation End Products (Rage) and Its Ligands in Plasma and Infrainguinal Bypass Vein

OBJECTIVE

The aim was to investigate whether RAGE and its ligands are associated with infrainguinal bypass outcome in patients with and without diabetes.

METHODS

This was a prospective observational cohort. Patients (n = 68) with (n = 38) and without (n = 30) diabetes undergoing infrainguinal vein bypass for peripheral arterial disease were followed for 3 years. Endosecretory RAGE (esRAGE), S100A12, advanced glycation end products, and carboxymethyl-lysine (CML) were determined in plasma using ELISA. The influence of plasma levels on the main outcome (amputation free survival) was evaluated using Cox proportional hazard analysis. Plasma esRAGE, CML, and S100A12 in healthy controls (n = 30) without cardiovascular disease matched for sex and age were compared with patients, using the Mann-Whitney U test. Veins from bypass surgery procedures were stained and S100A12, RAGE, AGE, and CML were determined using immunohistochemistry.

RESULTS

Forty-six patients survived with an intact leg during follow up. Seventeen died (median survival time 702 days, IQR 188-899 day), and six had amputations. High plasma S100A12 was associated with reduced amputation free survival (hazard ratio [HR] 2.99; 95% CI 1.24-7.24) when comparing levels above the 75th percentile with levels below. The increased risk was unchanged adjusting for age, sex, and diabetes. Diabetic patients had higher plasma S100A12 (11.75 ng/mL; 95% CI 8.12-15.38 ng/mL) than non-diabetic patients (5.0141 ng/mL; 95% CI 3.62-6.41 ng/mL), whereas plasma CML, esRAGE, and AGE were similar. Plasma CML and S100A12 were higher in patients than in controls (1.25 μg/mL, 95% CI 1.18-1.32 μg/mL vs. 0.8925 μg/mL, 95% CI 0.82-0.96 μg/mL; and 8.7 μg/mL, 95% CI 6.52-10.95 μg/mL vs. 3.47 μg/mL, 95% CI 2.95-3.99 μg/mL, respectively). The proportion of vein tissue stained for AGE (21%), RAGE (5%), CML (9%) and S100A12 (3%), were similar in patients with and without diabetes.

CONCLUSIONS

Plasma S100A12 and CML are elevated in peripheral arterial disease and markers of RAGE and its ligands are found in vein used for bypass. This indicates a role for S100A12, CML, and RAGE in peripheral arterial disease complications by activation of the RAGE system.

Soft-shelled turtle eggs inhibit the formation of AGEs in the serum and skin of diabetic rats

Although soft-shelled turtle eggs (STE) have been used as a folk medicine for revitalization and the prevention of lifestyle-related diseases, the scientific evidence to support the use of STE in this manner is scarce. To clarify the physiological evidence, STE was administered to diabetic rats and the inhibitory effects on the formation of advanced glycation end-products (AGEs), which are known to increase with the progression of lifestyle-related diseases, were examined. STE and citric acid were administered to diabetic rats for 3 months, and serum N^ε-(carboxymethyl)lysine (CML) contents were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Although the administration of STE did not affect the body weight, glycoalbumin or ketone body levels, it significantly reduced the serum level of CML. The accumulation of AGEs, which was measured by fluorescence intensity in the auricle skin and the lower gums, was also reduced by the administration of STE to a similar extent to that observed with citric acid. This report provides the first evidence that the oral administration of STE reduces the formation of AGEs, suggesting that one of the health effects of STE may be the inhibition of AGEs formation.

Human Achilles tendon glycation and function in diabetes

Diabetic patients have an increased risk of foot ulcers, and glycation of collagen may increase tissue stiffness. We hypothesized that the level of glycemic control (glycation) may affect Achilles tendon stiffness, which can influence gait pattern. We therefore investigated the relationship between collagen glycation, Achilles tendon stiffness parameters, and plantar pressure in poorly (n = 22) and well (n = 22) controlled diabetic patients, including healthy age-matched (45-70 yr) controls (n = 11). There were no differences in any of the outcome parameters (collagen cross-linking or tendon stiffness) between patients with well-controlled and poorly controlled diabetes. The overall effect of diabetes was explored by collapsing the diabetes groups (DB) compared with the controls. Skin collagen cross-linking lysylpyridinoline, hydroxylysylpyridinoline (136%, 80%, P < 0.01) and pentosidine concentrations (55%, P < 0.05) were markedly greater in DB. Furthermore, Achilles tendon material stiffness was higher in DB (54%, P < 0.01). Notably, DB also demonstrated higher forefoot/rearfoot peak-plantar-pressure ratio (33%, P < 0.01). Overall, Achilles tendon material stiffness and skin connective tissue cross-linking were greater in diabetic patients compared with controls. The higher foot pressure indicates that material stiffness of tendon and other tissue (e.g., skin and joint capsule) may influence foot gait. The difference in foot pressure distribution may contribute to the development of foot ulcers in diabetic patients.

Prevention of dicarbonyl-mediated advanced glycation by glyoxalases: implication in skin aging

Skin aging is the result of intrinsic chronological aging and photoaging, due to UV exposure, that both share important histological modifications and molecular features, including alterations of proteins. One of the main damage is glycation that occurs when reducing sugars react non-enzymatically with proteins. This reaction also happens when the dicarbonyl compounds GO (glyoxal) and MG (methylglyoxal), which are glucose derivatives, react with proteins. These compounds can be detoxified by the glyoxalase system composed of two enzymes, Glo1 (glyoxalase I) and Glo2 (glyoxalase II). The aims of the present mini-review are to briefly summarize our current knowledge of the biological roles of these enzymes in aging and then discuss the relevance of studying the role of glycation and of detoxifying systems in human skin aging.

Mangosteen pericarp extract inhibits the formation of pentosidine and ameliorates skin elasticity

The inhibition of advanced glycation end-products (AGEs) by daily meals is believed to become an effective prevention for lifestyle-related diseases. In the present study, the inhibitory effect of hot water extracts of mangosteen (Garcinia mangostana L.) pericarp (WEM) on the formation of pentosidine, one of AGEs, in vitro and in vivo and the remedial effect on skin conditions were measured. WEM significantly inhibited pentosidine formation during gelatin incubation with ribose. Several compounds purified from WEM, such as garcimangosone D and rhodanthenone B, were identified as inhibitors of pentosidine formation. Oral administration of WEM at 100 mg/day to volunteer subjects for 3 months reduced the serum pentosidine contents. Because obtaining skin biopsies from healthy volunteers is ethically difficult, AGE accumulation in the skin was estimated by a fluorescence detector. The oral administration of WEM significantly reduced the skin autofluorescence intensity, demonstrating that WEM also reduced AGE accumulation in the skin. Furthermore, the elasticity and moisture content of the skin was also improved by WEM. These results demonstrate that intakes of WEM reduces the glycation stress and results in the improvement of skin conditions.

A high-fat diet increases oxidative renal injury and protein glycation in D-galactose-induced aging rats and its prevention by Korea red ginseng

Declining renal function is commonly observed with age. Obesity induced by a high-fat diet (HFD) may reduce renal function. Korean red ginseng (KRG) has been reported to ameliorate oxidative tissue injury and have an anti-aging effect. This study was designed to investigate whether HFD would accelerate the D-galactose-induced aging process in the rat kidney and to examine the preventive effect of KRG on HFD and D-galactose-induced aging-related renal injury. When rats with D-galactose-induced aging were fed an HFD for 9 wk, enhanced oxidative DNA damage, renal cell apoptosis, protein glycation, and extracellular high mobility group box 1 protein (HMGB1), a signal of tissue damage, were observed in renal glomerular cells and tubular epithelial cells. However, treatment of rats with HFD- plus D-galactose-induced aging with KRG restored all of these renal changes. Our data suggested that a long-term HFD may enhance D-galactose-induced oxidative renal injury in rats and that this age-related renal injury could be suppressed by KRG through the repression of oxidative injury.

Specific tandem mass spectrometric detection of AGE-modified arginine residues in peptides

Glycation is a non-enzymatic reaction of protein amino and guanidino groups with reducing sugars or dicarbonyl products of their oxidative degradation. Modification of arginine residues by dicarbonyls such as glyoxal and methylglyoxal results in formation of advanced glycation end-products (AGEs). In mammals, these modifications impact in diabetes mellitus, uremia, atherosclerosis and ageing. However, due to the low abundance of individual AGE-peptides in enzymatic digests, these species cannot be efficiently detected by LC-ESI-MS-based data-dependent acquisition (DDA) experiments. Here we report an analytical workflow that overcomes this limitation. We describe fragmentation patterns of synthetic AGE-peptides and assignment of modification-specific signals required for unambiguous structure retrieval. Most intense signals were those corresponding to unique fragment ions with m/z 152.1 and 166.1, observed in the tandem mass spectra of peptides, containing glyoxal- and methylglyoxal-derived hydroimidazolone AGEs, respectively. To detect such peptides, specific and sensitive precursor ion scanning methods were established for these signals. Further, these precursor ion scans were incorporated in conventional bottom-up proteomic approach based on data-dependent acquisition (DDA) LC-MS/MS experiments. The method was successfully applied for the analysis of human serum albumin (HSA) and human plasma protein tryptic digest with subsequent structure confirmation by targeted LC-MS/MS (DDA). Altogether 44 hydroimidazolone- and dihydroxyimidazolidine-derived peptides representing 42 AGE-modified proteins were identified in plasma digests obtained from type 2 diabetes mellitus (T2DM) patients.

Biological Effects Induced by Specific Advanced Glycation End Products in the Reconstructed Skin Model of Aging

Advanced glycation end products (AGEs) accumulate in the aging skin. To understand the biological effects of individual AGEs, skin reconstructed with collagen selectively enriched with N^ɛ-(carboxymethyl)-lysine (CML), N^ɛ-(carboxyethyl)-lysine (CEL), methylglyoxal hydroimidazolone (MG-H1), or pentosidine was studied. Immunohistochemistry revealed increased expression of α6 integrin at the dermal epidermal junction by CEL and CML (p<0.01). Laminin 5 was diminished by CEL and MG-H1 (p<0.05). Both CML and CEL induced a robust increase (p<0.01) in procollagen I. In the culture medium, IL-6, VEGF, and MMP1 secretion were significantly decreased (p<0.05) by MG-H1. While both CEL and CML decreased MMP3, only CEL decreased IL-6 and TIMP1, while CML stimulated TIMP1 synthesis significantly (p<0.05). mRNA expression studies using qPCR in the epidermis layer showed that CEL increased type 7 collagen (COL7A1), β1, and α6 integrin, while CML increased only COL7A1 (p<0.05). MG-H1-modified collagen had no effect. Importantly, in the dermis layer, MMP3 mRNA expression was increased by both CML and MG-H1. CML also significantly increased the mRNAs of MMP1, TIMP1, keratinocyte growth factor (KGF), IL-6, and monocyte chemoattractant protein 1 (MCP1) (p<0.05). Mixed effects were present in CEL-rich matrix. Minimally glycoxidized pentosidine-rich collagen suppressed most mRNAs of the genes studied (p<0.05) and decreased VEGF and increased MCP1 protein expression. Taken together, this model of the aging skin suggests that a combination of AGEs tends to counterbalance and thus minimizes the detrimental biological effects of individual AGEs.

Systemic stiffening of mouse tail tendon is related to dietary advanced glycation end products but not high-fat diet or cholesterol

Tendon pathology is related to metabolic disease and mechanical overloading, but the effect of metabolic disease on tendon mechanics is unknown. This study investigated the effect of diet and apolipoprotein E deficiency (ApoE(-/-)) on mechanical properties and advanced glycation end product (AGE) cross-linking of non-weight-bearing mouse tail tendons. Twenty ApoE(-/-) male mice were used as a model for hypercholesterolemia along with 26 wild-type (WT) mice. One-half of the mice from each group was fed a normal diet (ND) and the other half was fed a high-fat diet (HFD) to induce obesity. All were killed at 40 wk, and tail tendon fascicles were mechanically tested to failure and analyzed for AGEs. Diets were also analyzed for AGEs. ApoE(-/-) mice displayed a 14% increase in plateau modulus compared with WT mice (P < 0.05), whereas HFD mice displayed a 13% decrease in plateau modulus (P < 0.05) and a 12% decrease in total modulus (P < 0.05) compared with ND mice. Tail tendons of HFD mice had significantly lower concentrations of AGEs [carboxymethyllysine (CML): 26%, P < 0.0001; methylglyoxal-derived hydroimidazolone 1 (MG-H1): 15%, P < 0.005; pentosidine: 13%, P < 0.0005]. The HFD had ∼44-fold lower content of CML (P < 0.01), ∼29-fold lower content of carboxyethyllysine (P < 0.005), and ∼16-fold lower content of MG-H1 (P < 0.05) compared with ND. ApoE(-/-) increased, whereas HFD decreased mouse tail tendon stiffness. Dietary AGE content may be a crucial determinant for accumulation of AGE cross-links in tendons and for tissue compliance. The results demonstrate how systemic metabolic factors may influence tendon health.

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

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

Advanced glycation end products play adverse proinflammatory activities in osteoporosis

Osteoporosis is a major public health burden that is expected to further increase as the global population ages. In the last twenty years, advanced glycation end products (AGEs) have been shown to be critical mediators both in the pathogenesis and development of osteoporosis and other chronic degenerative diseases related to aging. The accumulation of AGEs within the bone induces the formation of covalent cross-links with collagen and other bone proteins which affects the mechanical properties of tissue and disturbs bone remodelling and deterioration, underlying osteoporosis. On the other hand, the gradual deterioration of the immune system during aging (defined as immunosenescence) is also characterized by the generation of a high level of oxidants and AGEs. The synthesis and accumulation of AGEs (both localized within the bone or in the systemic circulation) might trigger a vicious circle (in which inflammation and aging merged in the word "Inflammaging") which can establish and sustain the development of osteoporosis. This narrative review will update the molecular mechanisms/pathways by which AGEs induce the functional and structural bone impairment typical of osteoporosis.