Advanced glycation end products in skin ageing and photoageing: what are the implications for epidermal function?

The Potential of Exercise on Lifestyle and Skin Function: Narrative Review

BACKGROUND

The skin is an important organ of the human body and has moisturizing and barrier functions. Factors such as sunlight and lifestyle significantly affect these skin functions, with sunlight being extremely damaging. The effects of lifestyle habits such as smoking, diet, and sleep have been studied extensively. It has been found that smoking increases the risk of wrinkles, while excessive fat and sugar intake leads to skin aging. Lack of sleep and stress are also dangerous for the skin's barrier function. In recent years, the impact of exercise habits on skin function has been a focus of study. Regular exercise is associated with increased blood flow to the skin, elevated skin temperature, and improved skin moisture. Furthermore, it has been shown to improve skin structure and rejuvenate its appearance, possibly through promoting mitochondrial biosynthesis and affecting hormone secretion. Further research is needed to understand the effects of different amounts and content of exercise on the skin.

OBJECTIVE

This study aims to briefly summarize the relationship between lifestyle and skin function and the mechanisms that have been elucidated so far and introduce the expected effects of exercise on skin function.

METHODS

We conducted a review of the literature using PubMed and Google Scholar repositories for relevant literature published between 2000 and 2022 with the following keywords: exercise, skin, and life habits.

RESULTS

Exercise augments the total spectrum power density of cutaneous blood perfusion by a factor of approximately 8, and vasodilation demonstrates an enhancement of approximately 1.5-fold. Regular exercise can also mitigate age-related skin changes by promoting mitochondrial biosynthesis. However, not all exercise impacts are positive; for instance, swimming in chlorinated pools may harm the skin barrier function. Hence, the exercise environment should be considered for its potential effects on the skin.

CONCLUSIONS

This review demonstrates that exercise can potentially enhance skin function retention.

Approaches in line with human physiology to prevent skin aging

Skin aging is a complex process that is influenced by intrinsic and extrinsic factors that impact the skin's protective functions and overall health. As the body's outermost layer, the skin plays a critical role in defending it against external threats, regulating body temperature, providing tactile sensation, and synthesizing vitamin D for bone health, immune function, and body homeostasis. However, as individuals age, the skin undergoes structural and functional changes, leading to impairments in these essential functions. In contemporary society, there is an increasing recognition of skin health as a significant indicator of overall wellbeing, resulting in a growing demand for anti-aging products and treatments. However, these products often have limitations in terms of safety, effective skin penetration, and potential systemic complications. To address these concerns, researchers are now focusing on approaches that are safer and better aligned with physiology of the skin. These approaches include adopting a proper diet and maintaining healthy lifestyle habits, the development of topical treatments that synchronize with the skin's circadian rhythm, utilizing endogenous antioxidant molecules, such as melatonin and natural products like polyphenols. Moreover, exploring alternative compounds for sun protection, such as natural ultraviolet (UV)-absorbing compounds, can offer safer options for shielding the skin from harmful radiation. Researchers are currently exploring the potential of adipose-derived stem cells, cell-free blood cell secretome (BCS) and other endogenous compounds for maintaining skin health. These approaches are more secure and more effective alternatives which are in line with human physiology to tackle skin aging. By emphasizing these innovative strategies, it is possible to develop effective treatments that not only slow down the skin aging process but also align better with the natural physiology of the skin. This review will focus on recent research in this field, highlighting the potential of these treatments as being safer and more in line with the skin's physiology in order to combat the signs of aging.

CircRNA-406918 enhances the degradation of advanced glycation end products in photoaged human dermal fibroblasts via targeting cathepsin D

BACKGROUND

Lysosomal cathepsin D (CTSD) can degrade internalized advanced glycation end products (AGEs) in dermal fibroblasts. CTSD expression is decreased in photoaged fibroblasts, which contributes to intracellular AGEs deposition and further plays a role in AGEs accumulation of photoaged skin. The mechanism under downregulated CTSD expression is unclear.

OBJECTIVE

To explore possible mechanism of regulating CTSD expression in photoaged fibroblasts.

METHODS

Dermal fibroblasts were induced into photoaging with repetitive ultraviolet A (UVA) irradiation. The competing endogenous RNA (ceRNA) networks were constructed to predict candidate circRNAs or miRNAs related with CTSD expression. AGEs-BSA degradation by fibroblasts was studied with flow cytometry, ELISA, and confocal microscopy. Effects of overexpressing circRNA-406918 via lentiviral transduction on CTSD expression, autophagy, AGE-BSA degradation were analyzed in photoaged fibroblasts. The correlation between circRNA-406918 and CTSD expression or AGEs accumulation in sun-exposed and sun-protected skin was studied.

RESULTS

CTSD expression, autophagy, and AGEs-BSA degradation were significantly decreased in photoaged fibroblasts. CircRNA-406918 was identified to regulate CTSD expression, autophagy, and senescence in photoaged fibroblasts. Overexpressing circRNA-406918 potently decreased senescence and increased CTSD expression, autophagic flux, and AGEs-BSA degradation in photoaged fibroblasts. Moreover, circRNA-406918 level was positively correlated with CTSD mRNA expression and negatively associated with AGEs accumulation in photodamaged skin. Further, circRNA-406918 was predicted to mediate CTSD expression through sponging eight miRNAs.

CONCLUSION

These findings suggest that circRNA-406918 regulates CTSD expression and AGEs degradation in UVA-induced photoaged fibroblasts and might exert a role in AGEs accumulation in photoaged skin.

In Vitro Determination of the Skin Anti-Aging Potential of Four-Component Plant-Based Ingredient

The beauty industry is actively searching for solutions to prevent skin aging. Some of the crucial elements protecting cells from the aging process are telomere shortening, telomerase expression, cell senescence, and homeostasis of the redox system. Modification of these factors using natural antioxidants is an appealing way to support healthy skin aging. Therefore, in this study, we sought to investigate the antiaging efficacy of a specific combination of four botanical extracts (pomegranate, sweet orange, Cistanche and Centella asiatica) with proven antioxidant properties. To this end, normal human dermal fibroblasts were used as a cell model and the following studies were performed: cell proliferation was established by means of the MTT assay and the intracellular ROS levels in stress-induced premature senescence fibroblasts; telomere length measurement was performed under standard cell culture conditions using qPCR and under oxidative stress conditions using a variation of the Q-FISH technique; telomerase activity was examined by means of Q-TRAP; and AGE quantification was completed by means of ELISA assay in UV-irradiated fibroblasts. As a result, the botanical blend significantly reversed the H2O2-induced decrease in cell viability and reduced H2O2-induced ROS. Additionally, the presence of the botanical ingredient reduced the telomere shortening rate in both stressed and non-stressed replicating fibroblasts, and under oxidative stress conditions, the fibroblasts presented a higher median and 20th percentile telomere length, as well as a lower percentage of short telomeres (<3 Kbp) compared with untreated fibroblasts. Furthermore, the ingredient transiently increased relative telomerase activity after 24 h and prevented the accumulation of UVR-induced glycated species. The results support the potential use of this four-component plant-based ingredient as an antiaging agent.

Research Advances on the Damage Mechanism of Skin Glycation and Related Inhibitors

Our skin is an organ with the largest contact area between the human body and the external environment. Skin aging is affected directly by both endogenous factors and exogenous factors (e.g., UV exposure). Skin saccharification, a non-enzymatic reaction between proteins, e.g., dermal collagen and naturally occurring reducing sugars, is one of the basic root causes of endogenous skin aging. During the reaction, a series of complicated glycation products produced at different reaction stages and pathways are usually collectively referred to as advanced glycation end products (AGEs). AGEs cause cellular dysfunction through the modification of intracellular molecules and accumulate in tissues with aging. AGEs are also associated with a variety of age-related diseases, such as diabetes, cardiovascular disease, renal failure (uremia), and Alzheimer's disease. AGEs accumulate in the skin with age and are amplified through exogenous factors, e.g., ultraviolet radiation, resulting in wrinkles, loss of elasticity, dull yellowing, and other skin problems. This article focuses on the damage mechanism of glucose and its glycation products on the skin by summarizing the biochemical characteristics, compositions, as well as processes of the production and elimination of AGEs. One of the important parts of this article would be to summarize the current AGEs inhibitors to gain insight into the anti-glycation mechanism of the skin and the development of promising natural products with anti-glycation effects.

Advanced glycation end products promote melanogenesis via activating NLRP3 inflammasome in human dermal fibroblasts

Advanced glycation end products (AGEs) accumulation is significantly increased in the dermis of photoaged skin and plays crucial roles in photoaging. Although AGEs have been found to contribute to the yellowish discoloration of photoaged skin, their roles in photoaging-associated hyperpigmentation disorders have not been extensively studied. In this study, we observed that AGEs, NLRP3 and IL-18 were increased in the dermis of sun-exposed skin and lesions of melasma and solar lentigo and that dermal deposition of AGEs was positively correlated with epidermal melanin levels. Additionally, we found AGEs-BSA potently activated NLRP3 inflammasome and promoted IL-18 production and secretion in cultured fibroblasts, which was mediated by RAGE/NF-κB pathway. Moreover, AGEs-BSA significantly promoted melanogenesis through increasing tyrosinase activity and expression of microphthalmia-associated transcription factor and tyrosinase, which was dependent on NLRP3 inflammasome activation and IL-18 secretion in fibroblasts. Notably, AGEs-collagen could activate NLRP3 inflammasome in fibroblasts and enhance melanogenesis. Further, we found IL-18 enhanced melanogenesis through binding to its receptor and activating p38 MAPK and ERK1/2 signaling pathways in melanocytes. Importantly, the pro-melanogenesis of AGEs-BSA was verified in ex vivo cultured skin and mice models. These findings suggest that dermal AGEs stimulate melanogenesis and contribute to the development of photoaging-associated hyperpigmentation disorders.

Up-to-Date Overview of the Use of Natural Ingredients in Sunscreens

The photoprotective skincare segment is in high demand to meet consumer concerns on UV-induced skin damage, with a recent trend towards sunscreen alternatives with a natural origin. In this study, the use of natural ingredients, either from terrestrial or marine origin, in a panel of 444 sunscreen commercial formulations (2021) was analyzed. Ingredients from terrestrial organisms represent the large majority found in the analyzed sunscreen formulations (48%), whereas marine ingredients are present only in 13% of the analyzed products. A deeper analysis regarding the most prevalent families of ingredients from terrestrial and marine organisms used as top ingredients is also presented, as well as their mechanisms of action. This study provides an up-to-date overview of the sunscreen market regarding the use of natural ingredients, which is of relevance for scientists involved in the development of new sunscreens to identify opportunities for innovation.

The role of local retinoids in eliminating signs of skin aging

Skin aging is a complex process involving both internal (chronological aging) and external (biological aging) factors. Slowing down the proliferative and immune processes in the epidermis, reducing the activity of fibroblasts and vascularization of the dermis during chronological aging lead to thinning, dryness, hypersensitivity, vulnerability and superficial wrinkles. Exposure to ultraviolet rays, pollutants, climate, and thermal factors cause keratinocyte disorganization, enhanced melanogenesis, collagen dystrophy, solar elastosis, and disorder of microcirculation. The main signs of external skin aging are deep wrinkles, sagging, pigmentation, telangiectasia, skin neoplasms. Among the local anti-aging agents, retinoids occupy a leading place, as they eliminate the main signs of skin aging. Of the entire group of retinoids, retinoic acids are the most active. However, the possibility of skin irritation limits their use. Therapeutic and cosmetic products with retinol esters (retinol palmitate) have a minimal irritating effect and can be used both for the prevention of skin aging and the elimination of its signs. Oral use of isotretinoin as an anti-aging agent is undesirable due to the many side effects and contraindications.

Boosting the Photoaged Skin: The Potential Role of Dietary Components

Skin photoaging is mainly induced by ultraviolet (UV) irradiation and its manifestations include dry skin, coarse wrinkle, irregular pigmentation, and loss of skin elasticity. Dietary supplementation of nutraceuticals with therapeutic and preventive effects against skin photoaging has recently received increasing attention. This article aims to review the research progress in the cellular and molecular mechanisms of UV-induced skin photoaging. Subsequently, the beneficial effects of dietary components on skin photoaging are discussed. The photoaging process and the underlying mechanisms are complex. Matrix metalloproteinases, transforming growth factors, skin adipose tissue, inflammation, oxidative stress, nuclear and mitochondrial DNA, telomeres, microRNA, advanced glycation end products, the hypothalamic-pituitary-adrenal axis, and transient receptor potential cation channel V are key regulators that drive the photoaging-associated changes in skin. Meanwhile, mounting evidence from animal models and clinical trials suggests that various food-derived components attenuate the development and symptoms of skin photoaging. The major mechanisms of these dietary components to alleviate skin photoaging include the maintenance of skin moisture and extracellular matrix content, regulation of specific signaling pathways involved in the synthesis and degradation of the extracellular matrix, and antioxidant capacity. Taken together, the ingestion of food-derived functional components could be an attractive strategy to prevent skin photoaging damage.

Polygoni Multiflori Radix Preparat Delays Skin Aging by Inducing Mitophagy

Background

As the skin is the largest organ of the human body, it is aging inevitably and produces cosmetic and psychological problems, and even disease. Therefore, the molecular mechanisms related to the prevention of skin aging need to be further explored.

Methods

Aging models were constructed by D-galactose. Mice were administrated with polygoni multiflori radix preparat (PMRP), PMRP and 3-methyladenine, or PMRP and rapamycin intragastrically. The apparent and viscera index of aged rats was measured. Then, the physicochemical property, antioxidant ability, histological structure, mitochondrial membrane potential, ATP and ROS levels, and mitophagy of aged skins were determined. Finally, the expression of PINK1, Parkin, P62, and LC3II/I; apoptosis-related proteins; and the percentage of apoptotic cells were measured.

Results

PMRP relieved skin aging with reducing of thymus index, improvement of pathological damage and histological structure, increase of the expression area of fibrous tissue, the ratio of type I to type III collagen, and antioxidant ability of aged skins. Importantly, PMRP also improved mitochondrial dysfunction with an increase in the content of mitochondrial membrane potential and ATP and a decrease of ROS levels. Moreover, mitophagy was enhanced with the treatment of PMRP when observed using electron microscopy, and the expression of PINK1, Parkin, and LC3I/II was increased with PMRP treatment but P62 expression was decreased. Meanwhile, PMRP alleviated apoptosis with a decrease of apoptotic cell and the expression of Cleaved-cas3, Bax, Cyt-c, AIF, and Smac as well as an increase of Bcl-2 expression.

Conclusion

The results demonstrated that the polygoni multiflori radix preparata may delay skin aging by inducing mitophagy.

Involvement of RAGE and Oxidative Stress in Inflammatory and Infectious Skin Diseases

The surface receptor for advanced glycosylation end-products (RAGE) and its soluble (sRAGE) and endogenous secretory (EN-RAGE) forms belong to the superfamily of toll-like receptors and play important roles in inflammation and autoimmunity, directly or through binding with advanced glycosylation end-products (AGE) and advanced oxidation protein products (AOPP). We reviewed the literature on the role of RAGE in skin diseases. Research in this field is still rather limited (28 articles) but suggests the involvement of RAGE and RAGE-related pathways in chronic inflammatory diseases (lupus, psoriasis, atopic dermatitis, and lichen planus), infectious diseases (leprosy, Staphylococcus aureus-induced skin lesions), alterations of the repairing processes in diabetic skin, systemic sclerosis, and ulcers. These data prompt further research in this field, which not only will be useful to better understand the pathogenetic mechanisms of diseases, but is also likely to have intriguing clinical implications. Indeed, when their role in the complex and multifactorial inflammatory balance will be adequately defined, RAGE and related molecules could be used as markers of disease severity and/or response to treatment. Moreover, future promising therapeutic perspectives could be topical administration of some of these molecules (e.g., sRAGE) to modulate local inflammatory response and/or the development of anti-RAGE antibodies for systemic treatment.

Circular RNA expression profiles significantly altered in UVA-irradiated human dermal fibroblasts

Circular RNAs (circRNAs) have been previously implicated in number of diseases. However, the roles of circRNAs in photoaging remain elusive. In the present study, to understand if photoaging influences the levels of circRNA expression, the expression of circRNAs in ultraviolet A (UVA)-irradiated human dermal fibroblasts were profiled. A total of 128 circRNAs were identified to be differentially expressed (fold change >1.5; P<0.05) after UVA exposure, including 39 upregulated and 89 downregulated circRNAs. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes biological pathway analyses indicated that the differentially expressed circRNAs were associated with extracellular matrix organization and metabolism. The present study revealed an altered circRNA expression pattern in human dermal fibroblasts following UVA-irradiation. These results provide not only a basis for in-depth study of the mechanism of skin photoaging but also a new possibility for the prevention and treatment of photoaging and associated skin diseases.

Diet and Skin Aging-From the Perspective of Food Nutrition

We regularly face primary challenges in deciding what to eat to maintain young and healthy skin, defining a healthy diet and the role of diet in aging. The topic that currently attracts maximum attention is ways to maintain healthy skin and delay skin aging. Skin is the primary barrier that protects the body from external aggressions. Skin aging is a complex biological process, categorized as chronological aging and photo-aging, and is affected by internal factors and external factors. With the rapid breakthrough of medicine in prolonging human life and the rapid deterioration of environmental conditions, it has become urgent to find safe and effective methods to treat skin aging. For diet, as the main way for the body to obtain energy and nutrients, people have gradually realized its importance to the skin. Therefore, in this review, we discuss the skin structure, aging manifestations, and possible mechanisms, summarize the research progress, challenges, possible directions of diet management, and effects of foodborne antioxidants on skin aging from the perspective of food and nutrition.

Expression of elastolytic cathepsins in human skin and their involvement in age-dependent elastin degradation

BACKGROUND

Skin ageing is associated with structure-functional changes in the extracellular matrix, which is in part caused by proteolytic degradation. Since cysteine cathepsins are major matrix protein-degrading proteases, we investigated the age-dependent expression of elastolytic cathepsins K, S, and V in human skin, their in vitro impact on the integrity of the elastic fibre network, their cleavage specificities, and the release of bioactive peptides.

METHODS

Cathepsin-mediated degradation of human skin elastin samples was assessed from young to very old human donors using immunohistochemical and biochemical assays, scanning electron microscopy, and mass spectrometry.

RESULTS

Elastin samples derived from patients between 10 and 86 years of age were analysed and showed an age-dependent deterioration of the fibre structure from a dense network of thinner fibrils into a beaded and porous mesh. Reduced levels of cathepsins K, S, and V were observed in aged skin with a predominant epidermal expression. Cathepsin V was the most potent elastase followed by cathepsin K and S. Biomechanical analysis of degraded elastin fibres corroborated the destructive activity of cathepsins. Mass spectrometric determination of the cleavage sites in elastin revealed that all three cathepsins predominantly cleaved in hydrophobic domains. The degradation of elastin was efficiently inhibited by an ectosteric inhibitor. Furthermore, the degradation of elastin fibres resulted in the release of bioactive peptides, which have previously been associated with various pathologies.

CONCLUSION

Cathepsins are powerful elastin-degrading enzymes and capable of generating a multitude of elastokines. They may represent a viable target for intervention strategies to reduce skin ageing.

The inhibitory effect of the catechin structure on advanced glycation end product formation in alcoholic media

Catechin has a good inhibitory effect on advanced glycation end product (AGE) formation in alcoholic media, which is generated by Maillard reaction is closely related to diabetes.

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.

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.