Two fluorescent wavelengths, 440(ex)/520(em) nm and 370(ex)/440(em) nm, reflect advanced glycation and oxidation end products in human skin without diabetes

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.

Synchronous Front-Face Fluorescence Spectra: A Review of Milk Fluorophores

Milk is subjected to different industrial processes, provoking significant physicochemical modifications that impact milk's functional properties. As a rapid and in-line method, front-face fluorescence can be used to characterize milk instead of conventional analytical tests. However, when applying fluorescence spectroscopy for any application, it is not always necessary to determine which compound is responsible for each fluorescent response. In complex matrixes such as milk where several variables are interdependent, the unique identification of compounds can be challenging. Thus, few efforts have been made on the chemical characterization of milk' fluorescent spectrum and the current information is dispersed. This review aims to organize research findings by dividing the milk spectra into areas and concatenating each area with at least one fluorophore. Designations are discussed by providing specific information on the fluorescent properties of each compound. In addition, a summary table of all fluorophores and references cited in this work by area is provided. This review provides a solid foundation for further research and could serve as a central reference.

Resolving fluorescence spectra of Maillard reaction products formed on bovine serum albumin using parallel factor analysis

Formation of Maillard reaction products (MRPs) is increasingly studied by the use of fluorescence spectroscopy, and most often, by measuring single excitation/emission pairs or use of unresolved spectra. However, due to the matrix complexity and potential co-formation of fluorescent oxidation products on tryptophan and tyrosine residues, this practice will often introduce errors in both identification and quantification. The present study investigates the combination of fluorescence excitation emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) to resolve the EEMs into its underlying fluorescent signals, allowing for better identification and quantification of MRPs. EEMs were recorded on a sample system of bovine serum albumin incubated at 40 °C for up to one week with either glucose, methylglyoxal or glyoxal added. Ten unique PARAFAC components were resolved, and assignment was attempted based on similarity with fluorescence of pure standards of MRPs and oxidation products and reported data from literature. Of the ten fluorescent PARAFAC components, tyrosine and buried and exposed tryptophan were resolved and identified, as well as the formation of specific MRPs (argpyrimidine and Nα-acetyl-Nδ-(5-methyl-4-imidazolon-2-yl)ornithine) and tryptophan oxidation products (kynurenine and dioxindolylalanine). The formation of the PARAFAC resolved protein modifications were qualitatively validated by liquid chromatography-mass spectrometry.

Autofluorescence spectroscopy in photodynamic therapy for skin rejuvenation: A theranostic approach in aesthetic medicine

BACKGROUND

The method of photodynamic therapy for skin rejuvenation (PDT-SR) provides an improvement in appearance with a safe and painless effect. The quality of treatment is most often assessed subjectively. The most informative morphological control methods are rarely used due to the invasiveness of the sampling procedure.

AIM

This study aimed to find out the possibility of using skin autofluorescence spectroscopy (SAF) for an objective assessment of changes occurring in the skin during PDT-SR.

METHODS

This study included 12 volunteers (10 women, 2 men) aged 32 to 79 years. Two (n = 6) or three (n = 6) PDT sessions were performed at intervals of 13-30 days. Photosensitizer chlorin e6, exposure 20 min, energy density 18-24 J/cm2 were used. SAF spectra were recorded using a two-wavelength fiber optic spectrometer under excitation at wavelengths (λex) of 365 nm and 440 nm. Measurements were made both before and after each PDT session and up to 25-238 days from the start of treatment. For the evaluation, we used the spectra AF365(λ) and AF440(λ) averaged over 40 points corrected for diffuse reflection at λex=440 nm in the range λem= 460-700 nm, as well as the spectra of the ratios AFN365(λ) and AFN440(λ), which were obtained by dividing the intensities of the current spectra by the intensities collected before PDT-SR.

RESULTS

PDT-SR led to changes in both the intensity and shape of the spectra. Analysis of the spectra using numerical fitting of the spectra showed that the main changes can be explained by changes in the content of advanced glycation end products (AGEs), as well as lipofuscin-like lipopigments (LPs) and porphyrins (PPs). The spectra of AGEs upon excitation at wavelengths of 365 and 440 nm differ, which may be due to the formation of two types of bonds, with collagen and elastin. By the end of the study, the vast majority of the examined volunteers showed a significant decrease of the parameters characterizing both of these types of AGEs, AGE365 (0.56-1.2) and AGE440 (0.58-1.01), relative to the beginning of the study. In most cases, a decrease was also noted for LPs and PPs. AGE365 and AGE440 were positively correlated with the age of the volunteers (r2 = 0.26-0.46 %). A steady decrease in the content of AGEs occurred approximately on the 40th day.

CONCLUSION

SAF spectroscopy makes it possible to assess changes in the content of AGEs, LPs, and PPs in the skin during PDT-SR. The method has great potential for non-invasive monitoring of the treatment process, as well as its improvement, including through its personalization. In addition, the method can be used to study the mechanisms of age-related skin changes at the molecular level and to study the processes of rejuvenation.

Skin autofluorescence, a non-invasive biomarker of advanced glycation end products, and its relation to radiographic and MRI based osteoarthritis

OBJECTIVES

Accumulation of advanced glycation end products (AGEs) in articular cartilage during aging has been proposed as a mechanism involved in the development of osteoarthritis (OA). Therefore, we investigated a cross-sectional relationship between skin AGEs, a biomarker for systemic AGEs accumulation, and OA.

METHODS

Skin AGEs were estimated with the AGE Reader™ as skin autofluorescence (SAF). Knee and hip X-rays were scored according to Kellgren and Lawrence (KL) system. KL-sum score of all four joints was calculated per participant to assess severity of overall radiographic OA (ROA) including or excluding those with prosthesis. Knee MRI of tibiofemoral joint (TF_MRI) was assessed for cartilage loss. Sex-stratified regression models were performed after testing interaction with SAF.

RESULTS

2,153 participants were included for this cross-sectional analysis. In women (n = 1,206) for one unit increase in SAF, the KL-sum score increased by 1.15 (95% confidence interval = 1.00-1.33) but excluding women with prosthesis, there was no KL-sum score increase [0.96 (0.83-1.11)]. SAF was associated with higher prevalence of prosthesis [Odds ratio, OR = 1.67 (1.10-2.54)] but not with ROA [OR = 0.83 (0.61-1.14)] when compared to women with no ROA. In men (n = 947), there was inconclusive association between SAF and KL sum score or prosthesis. For TF_MRI (n = 103 women), SAF was associated with higher prevalence of cartilage loss, full-thickness [OR = 5.44 (1.27-23.38)] and partial-thickness [OR = 1.45 (0.38-5.54)], when compared to participants with no cartilage loss.

CONCLUSION

Higher SAF in women was associated with higher prosthesis prevalence and a trend towards higher cartilage loss on MRI. Our data presents inconclusive results between SAF and ROA in both sexes.

Maillard reaction between oligopeptides and reducing sugar at body temperature: The putative anti-glycation agents

Type 2 Diabetes mellitus (T2DM) is one of the most common chronic multifactorial diseases, which is associated with the increased concentration of glucose in the blood. Therefore, the utilization of blood lowering agents is clearly a promising approach which can lead to a suppression of the evaluated blood glucose, and thus curing T2DM and other complication. In this study, we evaluated the glucose lowering effect of a varieties of amino acids (alanine and histidine), dipeptides (carnosine and α-alanine-L-histidine), and tripeptide (glutathione) by reacting with glucose, fructose, and sucrose under 37°C and pH 7.4 to mimic their reaction in physiological condition. By measuring the reduction of reactants and the formation of Maillard reaction products over the course of 21 days’ storage, we found that the glucose lowering effect of carnosine was better than the counterparts. The histidine residue in carnosine may contribute to its glucose lowing effect while β-amino acid β-alanine residue could facilitate the glucose lowering effect of carnosine by maintaining its chemical stability during the storage. These results may open up new avenues for the applications of bioactive peptide carnosine as a natural blood sugar lowering agent to control T2DM.

On the Potential Role of the Antioxidant Couple Vitamin E/Selenium Taken by the Oral Route in Skin and Hair Health

The relationship between oxidative stress and skin aging/disorders is well established. Many topical and oral antioxidants (vitamins C and E, carotenoids, polyphenols) have been proposed to protect the skin against the deleterious effect induced by increased reactive oxygen species production, particularly in the context of sun exposure. In this review, we focused on the combination of vitamin E and selenium taken in supplements since both molecules act in synergy either by non-enzymatic and enzymatic pathways to eliminate skin lipids peroxides, which are strongly implicated in skin and hair disorders.

Hibiscus, Rooibos, and Yerba Mate for Healthy Aging: A Review on the Attenuation of In Vitro and In Vivo Markers Related to Oxidative Stress, Glycoxidation, and Neurodegeneration

The world is currently undergoing a demographic change towards an increasing number of elderly citizens. Aging is characterized by a temporal decline in physiological capacity, and oxidative stress is a hallmark of aging and age-related disorders. Such an oxidative state is linked to a decrease in the effective mechanisms of cellular repair, the incidence of post-translational protein glycation, mitochondrial dysfunction, and neurodegeneration, just to name some of the markers contributing to the establishment of age-related reduction-oxidation, or redox, imbalance. Currently, there are no prescribed therapies to control oxidative stress; however, there are strategies to elevate antioxidant defenses and overcome related health challenges based on the adoption of nutritional therapies. It is well known that herbal teas such, as hibiscus, rooibos, and yerba mate, are important sources of antioxidants, able to prevent some oxidation-related stresses. These plants produce several bioactive metabolites, have a pleasant taste, and a long-lasting history as safe foods. This paper reviews the literature on hibiscus, rooibos, and yerba mate teas in the context of nutritional strategies for the attenuation of oxidative stress-related glycoxidation and neurodegeneration, and, here, Alzheimer’s Disease is approached as an example. The focus is given to mechanisms of glycation inhibition, as well as neuroprotective in vitro effects, and, in animal studies, to frame interest in these plants as nutraceutical agents related to current health concerns.

Protein oxidation - Formation mechanisms, detection and relevance as biomarkers in human diseases

Generation of reactive oxygen species and related oxidants is an inevitable consequence of life. Proteins are major targets for oxidation reactions, because of their rapid reaction rates with oxidants and their high abundance in cells, extracellular tissues, and body fluids. Additionally, oxidative stress is able to degrade lipids and carbohydrates to highly reactive intermediates, which eventually attack proteins at various functional sites. Consequently, a wide variety of distinct posttranslational protein modifications is formed by protein oxidation, glycoxidation, and lipoxidation. Reversible modifications are relevant in physiological processes and constitute signaling mechanisms ("redox signaling"), while non-reversible modifications may contribute to pathological situations and several diseases. A rising number of publications provide evidence for their involvement in the onset and progression of diseases as well as aging processes. Certain protein oxidation products are chemically stable and formed in large quantity, which makes them promising candidates to become biomarkers of oxidative damage. Moreover, progress in the development of detection and quantification methods facilitates analysis time and effort and contributes to their future applicability in clinical routine. The present review outlines the most important classes and selected examples of oxidative protein modifications, elucidates the chemistry beyond their formation and discusses available methods for detection and analysis. Furthermore, the relevance and potential of protein modifications as biomarkers in the context of disease and aging is summarized.

The AGE Reader: A non-invasive method to assess long-term tissue damage

AIMS

Advanced glycation endproducts (AGEs) are sugar-modified adducts which arise during non-enzymatic glycoxidative stress. These compounds may become systemically elevated in disease states, and accumulate in tissue, especially on long-lived proteins. AGEs have been implicated in various acute, and chronic diseases, stressing the need for reliable and comprehensive measuring techniques. Measurement of AGEs in tissue such as skin requires invasive skin biopsies. The AGE Reader has been developed to assess skin autofluorescence (SAF) non-invasively using the fluorescent properties of several AGEs.

RESULTS/CONCLUSION

Various studies have shown that SAF is a useful marker of disease processes associated with oxidative stress. It is prospectively associated with the development of cardiovascular events in patients with diabetes, renal or cardiovascular disease, and it predicts diabetes, cardiovascular disease, and mortality in the general population. However, when measuring SAF in individual subjects, several factors may limit the reliability of the measurement. These include endogenous factors present in the skin that absorb emission light such as melanin in dark-skinned subjects, but also factors that lead to temporal changes in SAF such as acute diseases and strenuous physical exercise associated with glycoxidative stress. Also, exogenous factors could potentially influence SAF levels inadvertently such as nutrition, and for example the application of skin care products. This review will address the AGE Reader functionality and the endogenous, and exogenous factors which potentially influence the SAF assessment in individual subjects.

Development of the facial glycation imaging system for in situ human face skin glycation index measurement

Background

The accumulation of advanced glycation end products has been proposed as a causative agent of skin aging, but there are no conventional devices for quantifying advanced glycation end‐product accumulation in facial skin.

Aims

This study aimed to develop a convenient and accurate in situ advanced glycation end‐product measurement system for the human face.

Methods

We developed a facial glycation imaging system, which consisted of illumination (white light‐emitting diode, ultraviolet light‐emitting diode) and image acquisition modules to capture face images. Advanced glycation end product–related autofluorescence and total skin reflectance were calculated to obtain the skin glycation index using an image analysis algorithm. Correlations between the skin glycation index and facial skin elasticity and age were examined in 36 healthy Korean women.

Results

The facial glycation imaging system was validated against a volar forearm skin autofluorescence measurement device, that is, the AGE Reader mu, with forearm skin glycation index (R = 0.64, P < .01). Cheek elasticity was negatively correlated with cheek skin glycation index (R = −0.56, R = −0.57, and R = −0.61, P < .01 for R2, R5, and R7, respectively). Age was significantly correlated with forearm skin glycation index (R = 0.44, P < .01) and cheek skin glycation index (R = 0.48, P < .01).

Conclusion

We successfully developed a novel in situ facial skin glycation index measurement device. Our convenient and accurate system enables in situ skin glycation index monitoring for skin aging studies such as those on anti‐glycation cosmetics.

The Role of Glycation on the Aggregation Properties of IAPP

Epidemiological evidence shows an increased risk for developing Alzheimer's disease in people affected by diabetes, a pathology associated with increased hyperglycemia. A potential factor that could explain this link could be the role that sugars may play in both diseases under the form of glycation. Contrary to glycosylation, glycation is an enzyme-free reaction that leads to formation of toxic advanced glycation end-products (AGEs). In diabetes, the islet amyloid polypeptide (IAPP or amylin) is found to be heavily glycated and to form toxic amyloid-like aggregates, similar to those observed for the Aβ peptides, often also heavily glycated, observed in Alzheimer patients. Here, we studied the effects of glycation on the structure and aggregation properties of IAPP with several biophysical techniques ranging from fluorescence to circular dichroism, mass spectrometry and atomic force microscopy. We demonstrate that glycation occurs exclusively on the N-terminal lysine leaving the only arginine (Arg11) unmodified. At variance with recent studies, we show that the dynamical interplay between glycation and aggregation affects the structure of the peptide, slows down the aggregation process and influences the aggregate morphology.

Characteristics and bioactive properties of mannooligosaccharides derived from agro-waste mannans

Mannooligosaccharides (MOS) were derived using Aspergillus oryzae β-mannanase (ManAo) from different mannan-rich agro-wastes, palm kernel cake (PKC), guar gum and copra meal (CM). Guar gum (GG) released higher amount of MOS (56.31% w/w) from which purification of mannobiose (0.68 mg) and mannotriose (1.26 mg) was demonstrated using size-exclusion chromatography. FTIR analysis of mannan hydrolysates showed characteristic peaks in 1200-900 cm^-1 region indicating the presence of MOS. ¹H &¹³C NMR spectra showed presence of anomeric sugar forms of MOS in different mannan hydrolysates. MOS from locust bean gum and guar gum had both α- and β-anomers while PKC and CM had only α-anomer. Growth promotional activities of different MOS were demonstrated using two probiotic Lactobacilli. Besides, enzymatically derived MOS also showed metal (Fe²⁺) chelating and anti-oxidant activities, wherein best anti-glycating agent was evaluated as MOS from PKC. PKC derived MOS showed highest cytotoxicity (74.19%) against human colon adenocarcinoma cell line (Caco-2). This study demonstrated the prebiotic potential of agro-waste derived MOS and possibility of their utilization as a functional food ingredient.

Development of a novel Maillard reaction-based time–temperature indicator for monitoring the fluorescent AGE content in reheated foods

Dietary advanced glycation end products (AGEs) are formed via the Maillard reaction in foods, especially in reheated foods, and can cause chronic diseases. In this study, a series of Maillard reaction-based time–temperature indicators (TTIs: TTI-1, TTI-2, and TTI-3) were developed with lysine and xylose for monitoring the dynamic formation of fluorescent AGEs in reheated foods. The discoloration kinetics of Maillard reaction-based TTIs and the dynamics of fluorescent AGE formation were explored. Formulas were derived to illustrate the relationship of the color change in the TTIs with time and temperature. The activation energies (E_a values) for generating the TTIs were 96.17, 87.98, and 83.55 kJ mol⁻¹, respectively. TTI-1 was the optimal indicator for instant soy milk powder because it showed the lowest activation energy difference in this study. The results show that this series of Maillard reaction-based TTIs can be used to monitor the AGE contents in various reheated foods.

Dietary advanced glycation end products (AGEs) are formed via the Maillard reaction in foods, especially in reheated foods, and can cause chronic diseases.

Factors associated with obesity alter matrix remodeling in breast cancer tissues

Obesity is associated with a higher risk of developing breast cancer and with worse disease outcomes for women of all ages. The composition, density, and organization of the breast tissue stroma are also known to play an important role in the development and progression of the disease. However, the connections between obesity and stromal remodeling are not well understood. We sought to characterize detailed organization features of the collagen matrix within healthy and cancerous breast tissues acquired from mice exposed to either a normal or high fat (obesity inducing) diet. We performed second-harmonic generation and spectral two-photon excited fluorescence imaging, and we extracted the level of collagen-associated fluorescence (CAF) along with metrics of collagen content, three-dimensional, and two-dimensional organization. There were significant differences in the CAF intensity and overall collagen organization between normal and tumor tissues; however, obesity-enhanced changes in these metrics, especially when three-dimensional organization metrics were considered. Thus, our studies indicate that obesity impacts significantly collagen organization and structure and the related pathways of communication may be important future therapeutic targets.

A variety of processes that affect the perception of skin aging

The purpose of this paper is to discuss the most important factors affecting perceived age. Aging is an unavoidable and irreversible process, but perceived age is a modifiable psychosocial factor. Our exterior has become one of the determinants of our social position, the key to success in our professional and personal lives. Today, we see people through their appearance, we judge after the first impression. With the help of aesthetic medicine, we can change the perceived age, but we cannot stop aging. This article discusses factors affecting the perceived age, such as hair color, skin color, general appearance and environmental factors. Many cannot be avoided, but we can make changes in life to look younger and more well-groomed. Indeed, we can change our habits for the benefit of the whole body, not only for the skin.

Hydrophobicity and aggregation, but not glycation, are key determinants for uptake of thermally processed β-lactoglobulin by THP-1 macrophages

The aim of this study is to investigate the immunological relevance of modifications of food protein structure due to thermal processing. We investigated the uptake of β-lactoglobulin, treated with 3 different processing methods, by THP-1 macrophages: wet heating (60 °C in solution) and high- or low-temperature (130 °C or 50 °C, respectively) dry heating, combined with either of 8 types of saccharides or without saccharide. The processing method that was applied significantly affected the uptake of BLG by THP-1 macrophages, while the type of saccharide only had an influence in high-temperature dry heated samples. A set of physicochemical parameters of processed samples was determined, to determine the samples' molecular weight, hydrophobicity, amyloid-like structure, surface charge and secondary structure. Analysis of protein structure alterations indicated the uptake to be linked to the wet heating processing method and percentage of α-helix structure, amyloid-like structures, polymers, and hydrophobicity. We hypothesize that both amyloid-like structures and molecular weight were related to the increased hydrophobicity and therefore postulate that the exposure of hydrophobic regions is the leading physicochemical characteristic for the observed uptake of wet heated BLG samples by THP-1 macrophages. This work demonstrates how differential thermal processing of foods, through protein modification, can have an impact on its interaction with the immune system.

Repurposing blue laser autofluorescence to measure ocular sun exposure

IMPORTANCE

Excessive ocular sun exposure is linked to various eye pathologies. Conjunctival ultraviolet autofluorescence (CUVAF) is a method of detecting sun-related conjunctival damage; however, the custom-built camera system required is not readily available.

BACKGROUND

We investigated whether blue laser autofluorescence (BAF) on a commonly used confocal scanning laser ophthalmoscope (cSLO) can be utilized to measure CUVAF area.

DESIGN

Cross-sectional evaluation of a diagnostic technology at a medical research institute.

PARTICIPANTS

Sixty-four participants recruited from three on-going observational eye studies in Western Australia.

METHODS

All participants had four images, two of each eye, captured using the CUVAF camera and BAF on the same day. Participants with pterygium or poor quality images were excluded from the analysis. Two graders measured CUVAF area in each image twice. CUVAF area measured by BAF was then compared to measurements determined with the conventional camera system.

MAIN OUTCOME MEASURES

CUVAF area.

RESULTS

After exclusions, 50 participants' images were analysed. Intra- and inter-observer repeatability were similar between the two systems. When comparing CUVAF area measured by BAF to the camera measurement, grader 1 had a mean difference of +1.00 mm² , with 95% limits of agreement -5.75 to 7.77 mm² . Grader 2 had a mean difference of +0.21mm² , with 95% limits of agreement -7.22 to 7.64 mm² .

CONCLUSIONS AND RELEVANCE

BAF on a commercially available cSLO is a valid method for measuring CUVAF area. This finding provides broader opportunity for identifying, monitoring and educating patients with sun-exposure-related ocular conditions and for researching the ocular impacts of sun exposure.

The in vivo and in vitro approaches for establishing a link between advanced glycation end products and lung cancer

Advanced glycation end products (AGEs) are directly related to third aging-associated diseases, such as cardiovascular diseases, arteriosclerosis, and neurodegeneration. Likewise, these irreversible and nonenzymatic products have been reported to be involved in the progression of malignant cancers. In general, aging-associated diseases and the initiation of cancer have been subjects of interest for several years. Few studies on the role of AGEs in cancer have been performed on cell lines. Moreover, past investigations in the field of glycation biology still lack the knowledge of in vivo and in vitro approaches for cancer cells. Accordingly, we aimed to focus on and establish a link between cancer and glycation with respect to all the possible AGEs. In our study, the levels of carboxymethyllysine (CML) increased by 50.94% in an animal model of glycation, whereas in an animal model of cancer, the contents of CML increased by 45.94% compared with their negative controls. Similarly, fluorescent AGEs were also examined and were found to be increased by 65.3% and 58.63% in the animal models of glycation and cancer, respectively, compared with the control subjects. The protein carbonyl contents were also found to be enhanced in the animal models of glycation and cancer. In our study, the levels of reactive oxygen species were also found to be significantly increased in the in vitro model of cancer cells as compared with the controls. Such an initial breakthrough indicated that AGEs were present in the serum of the animal models of cancer and glycation.

Glycation affects fibril formation of Aβ peptides

Increasing evidence shows that β-amyloid (Aβ) peptides, which are associated with Alzheimer disease (AD), are heavily glycated in patients, suggesting a role of this irreversible nonenzymatic post-translational modification in pathology. Previous reports have shown that glycation increases the toxicity of the Aβ peptides, although little is known about the mechanism. Here, we used the natural metabolic by-product methylglyoxal as a glycating agent and exploited various spectroscopic methods and atomic force microscopy to study how glycation affects the structures of the Aβ40 and Aβ42 peptides, the aggregation pathway, and the morphologies of the resulting aggregates. We found that glycation significantly slows down but does not prevent β-conversion to mature fibers. We propose that the previously reported higher toxicity of the glycated Aβ peptides could be explained by a longer persistence in an oligomeric form, usually believed to be the toxic species.

Cathepsin D contributes to the accumulation of advanced glycation end products during photoaging

BACKGROUND

The deposition of advanced glycation end products (AGEs) is accelerated in photoaged skin, but the underlying mechanisms remain elusive. Intracellular degradation has been recently considered to play an important role in AGEs removal. Although lysosomal cathepsin D (CatD), B (CatB), L(CatL) and proteasomes are found to degrade internalized AGEs, it remains unknown which protease degrades internalized AGEs in human dermal fibroblasts (HDFs), and whether a decrease in intracellular degradation contributes to enhanced AGEs deposition in photoaged skin.

OBJECTIVE

This study aims to investigate the specific proteases that contribute to intracellular AGEs degradation in HDFs and regulate AGEs accumulation in photoaged skin.

METHODS

Repetitive UVA irradiation was used to induce primary HDF photoaging in vitro. Uptake and degradation of AGE-BSA were verified and compared between photoaged and non-photoaged fibroblasts with flow cytometry, ELISA and confocal microscopy. Proteasomal and lysosomal activity, expression of CatD, CatB and CatL were also investigated between photoaged and non-photoaged fibroblasts. Further, the effect of protease inhibitors and CatD overexpression via lentiviral transduction on AGE-BSA degradation was analyzed. Finally, the correlation between CatD expression and AGEs accumulation in sun-exposed and sun-protected skin of people from different age was studied with immunohistochemistry.

RESULTS

Fibroblasts underwent photoaging in vitro after repetitive UVA irradiation. AGE-BSA was taken up by both photoaged and non-photoaged fibroblasts, but its degradation was significantly decreased in photoaged cells than that of non-photoaged cells. Although the activity of proteasome, CatB, Cat L and Cat D was significantly reduced in photoaged fibroblasts compared to that of non-photoaged cells, and the expression of CatB, CatL and CatD was profoundly attenuated in photoaged fibroblasts, inhibiting proteasome, CatB and CatL did not affect AGE-BSA degradation in HDFs. In contrast, inhibiting CatD activity dose-dependently decreased AGE-BSA degradation; whereas CatD overexpression significantly increased AGE-BSA degradation. Importantly, AGEs accumulation in photo-damaged skin in vivo was inversely correlated with CatD expression.

CONCLUSION

CatD plays a major role in intracellular AGEs degradation. Decreased CatD expression and activity impairs intracellular AGEs degradation in photoaged fibroblasts, which may contribute to accelerated AGEs deposition in photoaged skin. The present study provides a potentially novel molecular basis for antiphotoaging therapy.

Skin Intrinsic Fluorescence and Age-Related Macular Degeneration: The Beaver Dam Eye Study

Purpose

To determine if skin intrinsic fluorescence (SIF), a noninvasive measure of advanced glycation endproducts and oxidative stress in skin is associated with AMD.

Methods

SIF was measured with the SCOUT DS skin fluorescence spectrometer in a cross-sectional cohort study of 969 persons aged 68 to 102 years from the 1181 who participated in the 25-year follow-up examination in the Beaver Dam Eye Study (BDES) in 2014 to 2016. The SCOUT DS skin fluorescence spectrometer uses five light-emitting diodes, centered at 375 nm to 456 nm. AMD was assessed by grading of digital color 45° stereoscopic fundus photographs of the macula using the Wisconsin Age-Related Maculopathy grading scheme. Analyses included logistic regression with generalized estimating equations to account for correlation between the eyes of a person.

Results

There were data for 1827 eyes for analyses. Early AMD was present in 22% and late AMD in 4% of the eyes. While adjusting for age, sex, smoking status, and history of cardiovascular disease, there were no significant associations of any SIF measure with any AMD or exudative AMD. SIF01 (odds ratio per 1 SD difference on the log scale, 95% confidence interval) (1.66, 1.00-2.74, P = 0.05) and SIF03 (1.81, 1.16-2.81, P = 0.008) were associated with geographic atrophy.

Conclusions

There was a suggestive relationship of two SIF measures, SIF01 and SIF03, using different correction factors from the excitation centered at 375 nm, with the prevalence of geographic atrophy in the BDES. Longitudinal follow-up is indicated to assess a temporal relationship.

Association of Skin Intrinsic Fluorescence with Retinal Microvascular Complications of Long Term Type 1 Diabetes in the Wisconsin Epidemiologic Study of Diabetic Retinopathy

OBJECTIVE

To determine the association between skin intrinsic fluorescence (SIF), a noninvasive measure of advanced glycation endproducts and oxidative stress in skin, and retinal microvascular complications of long duration type 1 diabetes, proliferative diabetic retinopathy (PDR) and macular edema.

METHODS

A cross-sectional cohort study of persons with type 1 diabetes in the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) who participated in a 32-year follow-up examination in 2012-2014. Subjects underwent a physical examination, answered a health questionnaire, and had fundus photographs taken. SIF was measured on the underside of the left forearm near the elbow with the SCOUT DS^® skin fluorescence spectrometer. Two representative SIF measures were used for these analyses: SIF01 excited by an LED centered at 375 nm with correction factors K_x = 0.6 and K_m = 0.2 and SIF15 excited by an LED centered at 456 nm with correction factors K_x = 0.4 and K_m = 0.9.

RESULTS

The 414 participants had mean diabetes duration of 42.2 years (standard deviation 6.8 years, range 32.9-67.9 years). PDR was statistically significantly associated (p < 0.05) with both SIF measures in multivariate models including other relevant factors (odds ratio [OR] = 1.17 for SIF01 and 1.20 for SIF15).

CONCLUSION

Skin intrinsic fluorescence measures are independently associated with PDR in the WESDR. Incidence information is needed to evaluate whether there is a causal relationship.

Sex differences in the association of skin advanced glycation endproducts with knee osteoarthritis progression

Background

The accumulation of advanced glycation endproducts in articular cartilage has been suggested as an etiologic factor in the development and progression of knee osteoarthritis (KOA).

Methods

We conducted a prospective cohort study of skin advanced glycation endproducts (sAGEs) measured non-invasively by skin intrinsic fluorescence and the relationship between sAGE KOA progression in 160 men and 287 women in a sub-cohort of the Osteoarthritis Initiative at a single site. KOA progression was measured by yearly changes in Osteoarthritis Research Society International (OARSI)-defined joint space narrowing (JSN) and by yearly changes in joint space width (JSW) from baseline to 48 months. Sex-stratified repeated measures, mixed models to account for correlation between the knees within persons and adjusted for age, body mass index (BMI), Kellgren-Lawrence (KL) grade, beam angle and rim-to-rim distance were utilized.

Results

Increasing tertiles of sAGE measured at 36 months were associated with greater JSN over 4 years in men but not in women. The percentage of knees with JSN at 48 months, by tertiles of sAGE, were 7.0%, 16.0% and 17.7% in men (p for linear trend = 0.03) and 11.4%, 14.4% and 8.4% in women (p for linear trend = 0.33). Using change in JSW as the outcome, a similar trend was found in men but it was not statistically significant in fully adjusted models and no association was found in women.

Conclusion

This study provides preliminary evidence that sAGEs independent of age and BMI, are associated with knee JSN in men but not in women.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1226-z) contains supplementary material, which is available to authorized users.

Carbonylated proteins exposed to UVA and to blue light generate reactive oxygen species through a type I photosensitizing reaction

BACKGROUND

Carbonylated proteins (CPs) are generated by the reaction of basic amino acid residues in proteins with aldehyde compounds produced during lipid peroxidation. CPs in the stratum corneum (SC) impact skin conditions such as skin moisture functions including water content and transepidermal water loss (TEWL). In addition, CPs can be frequently seen in the SC from sun-exposed sites compared with sun-protected sites.

OBJECTIVE

The aim of this study was to reveal whether CPs could be a generation source of reactive oxygen species (ROS) in the SC following exposure to ultraviolet (UV) radiation and to identify the type of ROS and its generation mechanism.

METHODS

ROS generation was detected using a methyl cypridina luciferin analog (MCLA) chemiluminescence system and an ESR spin-trapping method. CPs in porcine SC, in a keratin film and in bovine serum albumin (BSA) were prepared by reaction with acrolein. Levels of protein carbonylation were quantified by detecting aldehyde residues.

RESULTS

CP levels in the SC were increased in a UVA energy-dependent manner. That result suggested that a source of ROS generation existed in the SC initiated and produced the carbonylation of SC proteins. Carbonylated BSA and carbonylated porcine SC sheets exhibited fluorescence spectra at an excitation wavelength of 430nm and an emission wavelength of 520nm. Irradiation of the SC with UVA increased protein carbonylation and the amount of autofluorescence in the SC. ROS generation in the SC caused by UVA and by short-wavelength visible light (blue light, 400-470nm) was detected by the MCLA chemiluminescence system. Artificially carbonylated porcine SCs and keratin films had increases of chemiluminescence intensity after exposure to both light sources as well. The addition of superoxide dismutase to the MCLA system completely abolished the incremental chemiluminescence intensity after both UVA and blue light exposure of the SC. In addition, acrolein-treated BSA gave ESR signals like hydroxyl radicals (OH) converted from superoxide anion radicals (O₂^-) during irradiation with a xenon arc lamp containing UVA and visible light. From the sum of these results, we consider that CPs are produced from O₂^- initially generated from exposure to UVA and blue light.

CONCLUSION

CPs are excited by absorbing sunlight, particularly UVA and blue light, and result in the generation of O₂^- through a CPs progress new protein carbonylation in stratum corneum through ROS generation. photosensitizing reaction. Further, the results suggest that the O₂^- produces CPs in the SC through lipid peroxidation in the sebum, and finally affects skin conditions including color and moisture functions.

Effects of Collagen Crosslinking on Bone Material Properties in Health and Disease

Data have accumulated to show that various types of collagen crosslinking are implicated in the health of individuals, as well as in a number of disease states, such as osteoporosis, diabetes mellitus, chronic kidney disease, inflammatory bowel disease, or in conditions of mild hyperhomocysteinemia, or when glucocorticoid use is indicated. Collagen crosslinking is a posttranslational modification of collagen molecules and plays important roles in tissue differentiation and in the mechanical properties of collagenous tissue. The crosslinking of collagen in the body can form via two mechanisms: one is enzymatic crosslinking and the other is nonenzymatic crosslinking. Lysyl hydroxylases and lysyl oxidases regulate tissue-specific crosslinking patterns and quantities. Enzymatic crosslinks initially form via immature divalent crosslinking, and a portion of them convert into mature trivalent forms such as pyridinoline and pyrrole crosslinks. Nonenzymatic crosslinks form as a result of reactions which create advanced glycation end products (AGEs), such as pentosidine and glucosepane. These types of crosslinks differ in terms of their mechanisms of formation and function. Impaired enzymatic crosslinking and/or an increase of AGEs have been proposed as a major cause of bone fragility associated with aging and numerous disease states. This review focuses on the effects of collagen crosslinking on bone material properties in health and disease.

Methylglyoxal in diabetes: link to treatment, glycaemic control and biomarkers of complications

Diabetic complications are major health problems worldwide, with the cost of caring for diabetes rising to US$245 billion in 2012 in the U.S.A. alone. It is widely recognized that non-enzymatic glycation in diabetes is a major cause of damage and dysfunction of key vascular cells. MG (methylglyoxal) is directly toxic to tissues, and is a major precursor of AGEs (advanced glycation end-products). Various propensities to diabetic complications are seen among individuals with diabetes, with accelerated rates occurring in some individuals with modest hyperglycaemia, while others never progress in spite of poor glycaemic control over many years. Since production and detoxification of MG is ultimately controlled by enzymatic mechanisms, both genetic and environmental factors could regulate tissue glycation and potentially account for these variable complication rates. Activation of pathways that determine MG levels occurs in susceptible patients, indicting an important role in pathogenesis. MG leads to formation of specific AGEs, which are likely to predict propensity to diabetic complications. We have shown recently that three specific plasma AGE biomarkers [MG-H1 (MG-derived hydroimidazolones), CEL (Nε-carboxyethyl-lysine) and CML (Nε-carboxymethyl-lysine)] predict biopsy-documented fast DN (diabetic nephropathy) progression. Since two of the predictive biomarkers are MG end-products, these outcomes support a role for MG in the development of DN. Our studies on MG and its end-products have also shown anti-complication effects of the drug metformin, which binds and inactivates MG, thus reducing MG-related AGEs. We have also shown that reducing post-meal glucose decreases MG levels, as well as levels of MG-related AGEs. Our clinical outcome studies have been based on the novel concept that the unique glycation products that we can measure reflect the activity of specific chemical pathways that are selectively activated by hyperglycaemia in patients that are inherently more susceptible to diabetic complications, and can be used to solve other diabetes-related medical questions.

Oxidative stress in aging human skin

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

GWAS identifies an NAT2 acetylator status tag single nucleotide polymorphism to be a major locus for skin fluorescence

AIMS/HYPOTHESIS

Skin fluorescence (SF) is a non-invasive marker of AGEs and is associated with the long-term complications of diabetes. SF increases with age and is also greater among individuals with diabetes. A familial correlation of SF suggests that genetics may play a role. We therefore performed parallel genome-wide association studies of SF in two cohorts.

METHODS

Cohort 1 included 1,082 participants, 35-67 years of age with type 1 diabetes. Cohort 2 included 8,721 participants without diabetes, aged 18-90 years.

RESULTS

rs1495741 was significantly associated with SF in Cohort 1 (p < 6 × 10(-10)), which is known to tag the NAT2 acetylator phenotype. The fast acetylator genotype was associated with lower SF, explaining up to 15% of the variance. In Cohort 2, the top signal associated with SF (p = 8.3 × 10(-42)) was rs4921914, also in NAT2, 440 bases upstream of rs1495741 (linkage disequilibrium r (2) = 1.0 for rs4921914 with rs1495741). We replicated these results in two additional cohorts, one with and one without type 1 diabetes. Finally, to understand which compounds are contributing to the NAT2-SF signal, we examined 11 compounds assayed from skin biopsies (n = 198): the fast acetylator genotype was associated with lower levels of the AGEs hydroimidazolones of glyoxal (p = 0.017).

CONCLUSIONS/INTERPRETATION

We identified a robust association between NAT2 and SF in people with and without diabetes. Our findings provide proof of principle that genetic variation contributes to interindividual SF and that NAT2 acetylation status plays a major role.

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

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

The association of skin intrinsic fluorescence with type 1 diabetes complications in the DCCT/EDIC study

OBJECTIVE

To determine whether skin intrinsic fluorescence (SIF) is associated with long-term complications of type 1 diabetes (T1D) and, if so, whether it is independent of chronic glycemic exposure and previous intensive therapy.

RESEARCH DESIGN AND METHODS

We studied 1,185 (92%) of 1,289 active Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) participants from 2010 to 2011. SIF was determined using a fluorescence spectrometer and related cross-sectionally to recently determined measures of retinopathy (stereo fundus photography), cardiac autonomic neuropathy (CAN; R-R interval), confirmed clinical neuropathy, nephropathy (albumin excretion rate [AER]), and coronary artery calcification (CAC).

RESULTS

Overall, moderately strong associations were seen with all complications, before adjustment for mean HbA1c over time, which rendered these associations nonsignificant with the exception of sustained AER>30 mg/24 h and CAC, which were largely unaffected by adjustment. However, when examined within the former DCCT treatment group, associations were generally weaker in the intensive group and nonsignificant after adjustment, while in the conventional group, associations remained significant for CAN, sustained AER>30 mg/24 h, and CAC even after mean HbA1c adjustment.

CONCLUSIONS

SIF is associated with T1D complications in DCCT\EDIC. Much of this association appears to be related to historical glycemic exposure, particularly in the previously intensively treated participants, in whom adjustment for HbA1c eliminates statistical significance.

Clinical and technical factors associated with skin intrinsic fluorescence in subjects with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study

BACKGROUND

The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications(EDIC) studies have established multiyear mean hemoglobin A1c (HbA1c) as predictive of microvascular complications in persons with type 1 diabetes. However, multiyear mean HbA1c is not always available in the clinical setting. Skin advanced glycation end products (AGEs) are thought to partially reflect effects of hyperglycemia over time, and measurement of skin AGEs might be a surrogate for multiyear mean HbA1c. As certain AGEs fluoresce and skin fluorescence has been demonstrated to correlate with the concentration of skin AGEs, noninvasive measurement by skin intrinsic fluorescence(SIF) facilitates the exploration of the association of mean HbA1c and other clinical/technical factors with SIF using the detailed phenotypic database available in DCCT/EDIC.

SUBJECTS AND METHODS

Of the subjects, 1,185 (53% male) had measurements of SIF during years 16/17 of EDIC with mean age and diabetes duration of 51.5 and 29.8 years, respectively. SIF measurements were obtained on the underside of the forearm near the elbow using a skin fluorescence spectrometer. Demographic data and health history were self-reported, and an annual standardized examination measured clinical status. Linear regression models were constructed to identify significant clinical and technical factors associated with SIF, and the final models only used factors that were significant.

RESULTS

SIF ranged from 8.7 to 54.0 arbitrary units and was log-normally distributed. Log(SIF) correlated more with mean HbA1c as the time period increased. In multivariate analyses log(SIF) was significantly associated with mean HbA1c, age,estimated glomerular filtration rate < 60mL/min/m2, smoking status, skin tone, and clinic latitude <37 N.

CONCLUSIONS

SIF reflects age, mean HbA1c over time, smoking, and renal damage, which are known risk factors for diabetes complications.

Advanced glycation end products: Key players in skin aging?

Aging is the progressive accumulation of damage to an organism over time leading to disease and death. Aging research has been very intensive in the last years aiming at characterizing the pathophysiology of aging and finding possibilities to fight age-related diseases. Various theories of aging have been proposed. In the last years advanced glycation end products (AGEs) have received particular attention in this context. AGEs are formed in high amounts in diabetes but also in the physiological organism during aging. They have been etiologically implicated in numerous diabetes- and age-related diseases. Strategies inhibiting AGE accumulation and signaling seem to possess a therapeutic potential in these pathologies. However, still little is known on the precise role of AGEs during skin aging. In this review the existing literature on AGEs and skin aging will be reviewed. In addition, existing and potential anti-AGE strategies that may be beneficial on skin aging will be discussed.

Noninvasive Measurement of Skin Autofluorescence Is Increased in Patients with Systemic Sclerosis: An Indicator of Increased Advanced Glycation Endproducts?

Objective.

Skin autofluorescence noninvasively assesses expression of advanced glycation endproducts and therefore potentially the presence of oxidative stress that is implicated in the pathogenesis of systemic sclerosis (SSc). We investigated whether autofluorescence was increased in patients with SSc, primary Raynaud’s phenomenon (RP), and morphea as compared to healthy controls.

Methods.

Measurements of autofluorescence were made at 5 upper limb sites in 16 healthy controls, 16 patients with diffuse cutaneous SSc (dcSSc), 15 with limited cutaneous SSc (lcSSc), 15 with primary RP, and 13 with morphea. For patients with morphea, additional measurements were made at the affected and an adjacent unaffected site.

Results.

Autofluorescence was significantly increased in patients with dcSSc but not lcSSc as compared to controls at the proximal phalanx [dcSSc median 0.15, interquartile range (IQR) 0.10–0.24, vs control 0.10, IQR 0.07–0.13; p = 0.014], dorsum of the hand (dcSSc 0.17, IQR 0.11–0.36, vs control 0.12, IQR 0.09–0.17; p = 0.031), the wrist (dcSSc 0.22, IQR 0.13–0.33, vs control 0.13, IQR 0.09–0.18; p = 0.005), and forearm (dcSSc 0.19, IQR 0.12–0.47, vs control 0.14, IQR 0.10–0.16; p = 0.022). There was a trend for autofluorescence to be increased in patients with lcSSc and at morphea sites, compared to noninvolved skin.

Conclusion.

Autofluorescence is increased in patients with dcSSc compared to primary RP and to healthy controls. This suggests increased oxidative stress and the potential for autofluorescence as a biomarker.