Reactive carbonyl species (RCS) derived from glycoxidation, mainly α-dicarbonyl compounds (α-DCs), can induce covalent modifications in biological macromolecules, particularly proteins and DNA, leading to formation of advanced glycation end products (AGEs). The excessive accumulation of RCS and AGEs contributes to a pathophysiological condition known as carbonyl stress. Carbonyl stress varies with age, diet, and environmental factors. It is further aggravated by oxidative stress and health conditions like hyperglycemia and renal dysfunction. Increasing evidence indicates that RCS/AGEs-mediated carbonyl stress is involved in disruption of cellular homeostasis and damage of physiological functions of the skin, clinically presenting as chronic inflammation, yellowish discoloration, accelerated aging, and other dermatological abnormalities. Consequently, targeted modulation of the RCS/AGEs axis represents a promising therapeutic strategy for cutaneous health preservation. This review provides a first systematic discussion on the role of RCS/AGEs-induced carbonyl stress in skin ageing and damage. Furthermore, the key intervention strategies against carbonyl stress are summarized, including (i) inhibition of RCS/AGE formation and exogenous intake; (ii) scavenging of preformed RCS/AGEs; (iii) blockade of AGE-receptor interactions. Notably, interventions based on dietary bioactives hold promise for designing personalized diets and developing functional foods to mitigate carbonyl stress-associated skin ageing and damage.

Tea represents an abundant source of naturally occurring polyphenols. Tea polyphenols (TPs) have received growing attentions for its wide consumption in the world, and more importantly its pleiotropic bioeffects for human health. After ingestion, TPs may undergo absorption and phase II reaction in the small intestine, and most undigested proportion would be submitted to the colon to interact with gut microbiota. Interactions between gut microbiota and TPs are bidirectional, including not only bacteria-mediated TPs metabolism, e.g., removal of gallic acid moiety and ring fission to release phenolic acid catabolites, but also TPs-based modification of bacterial profiles. Crosstalk between TPs and gut microbes may benefit for gut barrier function, for example, improvement of the intestinal permeability to alleviate inflammation. Moreover, by reshaping microbial composition and associated metabolites, TPs may exert a systemic protection on host metabolism, which contributes to improve certain chronic metabolic disorders. Given that, further understanding of the metabolic fate of TPs and interplay with gut microbiota as well as potential health-promoting effects are of great significance to development and application of tea and their polyphenolic components in the future as dietary supplements and/or functional ingredients in medical foods.

Tea polysaccharides (TPSs), one of the major bioactive ingredients in tea, have been widely studied due to their variety of biological activities, including antioxidant, cancer prevention, hypoglycemia, anti-fatigue, anti-coagulant, anti-obesity and immunomodulatory effect. The biological effectiveness of TPSs has direct relation with their structures such as monosaccharide composition, molecular weight, glycosidic linkages, conformation and others, which can be influenced by tea materials, processing methods, extraction and purification procedures among others. Comparing to the study of tea polyphenols, the exploration of TPSs in structural elucidation and biofunctionality is very preliminary. Yet several factors affecting the structural change of TPSs have been studied and identified. Consequently, the variation of some TPS biological activity brought by the change of TPS structures has been evaluated and preliminary correlation of structure activity relationship of TPSs has been performed. Therefore, this review aims to serve as a summary research report regarding the influencing factors on TPSs structures and consequential effects on the biological activities of TPSs. We hope to provide updated information and systematic references for future study and functional food development of TPSs.