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The interaction of light with natural matter leads to a plethora of photosensitized reactions. These reactions cause the degradation of biomolecules, such as DNA, lipids, proteins, being therefore detrimental to the living organisms, or they can also be beneficial by allowing the treatment of several diseases by photomedicine. Based on the molecular mechanistic understanding of the photosensitization reactions, we propose to classify them in four processes: oxygen‐dependent (type I and type II processes) and oxygen‐independent [triplet‐triplet energy transfer (TTET) and photoadduct formation]. In here, these processes are discussed by considering a wide variety of approaches including time‐resolved and steady‐state techniques, together with solvent, quencher, and scavenger effects. The main aim of this survey is to provide a description of general techniques and approaches that can be used to investigate photosensitization reactions of biomolecules together with basic recommendations on good practices. Illustration of the suitability of these approaches is provided by the measurement of key biomarkers of singlet oxygen and one‐electron oxidation reactions in both isolated and cellular DNA. Our work is an educational review that is mostly addressed to students and beginners. [ABSTRACT FROM AUTHOR]

The interaction of light with natural matter leads to a plethora of photosensitized reactions. These reactions cause the degradation of biomolecules, such as DNA, lipids, proteins, being therefore detrimental to the living organisms, or they can also be beneficial by allowing the treatment of several diseases by photomedicine. Based on the molecular mechanistic understanding of the photosensitization reactions, we propose to classify them in four processes: oxygen‐dependent (type I and type II processes) and oxygen‐independent [triplet‐triplet energy transfer (TTET) and photoadduct formation]. In here, these processes are discussed by considering a wide variety of approaches including time‐resolved and steady‐state techniques, together with solvent, quencher, and scavenger effects. The main aim of this survey is to provide a description of general techniques and approaches that can be used to investigate photosensitization reactions of biomolecules together with basic recommendations on good practices. Illustration of the suitability of these approaches is provided by the measurement of key biomarkers of singlet oxygen and one‐electron oxidation reactions in both isolated and cellular DNA. Our work is an educational review that is mostly addressed to students and beginners. [ABSTRACT FROM AUTHOR]

Cellular oxidative stress contributes to solar ultraviolet (UV) radiation‐induced skin photoaging and photocarcinogenesis. Light‐driven electron and energy transfer reactions involving non‐DNA chromophores are a major source of reactive oxygen species (ROS) in skin, and the molecular identity of numerous endogenous chromophores acting as UV‐photosensitizers has been explored. Methylglyoxal (MG), a glycolytic byproduct bearing a UV‐active α‐dicarbonyl‐chromophore, is generated under metabolic conditions of increased glycolytic flux, associated with posttranslational protein adduction in human tissue. Here, we undertook a photophysical and photochemical characterization of MG substantiating its fluorescence properties (Stokes shift), phosphorescence lifetime, and quantum yield of singlet oxygen (1O2) formation. Strikingly, upon UV‐excitation (290 nm), a clear emission (around 490 nm) was observed (phosphorescence‐lifetime: 224.2 milliseconds). At micromolar concentrations, MG acts as a UVA‐photosensitizer targeting human HaCaT‐keratinocytes inducing photooxidative stress and caspase‐dependent cell death substantiated by zVADfmk‐rescue and Alexa‐488 caspase‐3 flow cytometry. Transcriptomic analysis indicated that MG (photoexcited by noncytotoxic doses of UVA) elicits expression changes not observable upon isolated MG‐ or UVA‐treatment, with upregulation of the proteotoxic (CRYAB, HSPA6) and oxidative (HMOX1) stress response. Given the metabolic origin of MG and its role in human pathology, future investigations should address the potential involvement of MG‐photosensitizer activity in human skin photodamage. [ABSTRACT FROM AUTHOR]

The unbridled dissemination of multidrug‐resistant pathogens is a major threat to global health and urgently demands novel therapeutic alternatives. Antimicrobial photodynamic therapy (aPDT) has been developed as a promising approach to treat localized infections regardless of drug resistance profile or taxonomy. Even though this technique has been known for more than a century, discussions and speculations regarding the biochemical mechanisms of microbial inactivation have never reached a consensus on what is the primary cause of cell death. Since photochemically generated oxidants promote ubiquitous reactions with various biomolecules, researchers simply assumed that all cellular structures are equally damaged. In this study, biochemical, molecular, biological and advanced microscopy techniques were employed to investigate whether protein, membrane or DNA damage correlates better with dose‐dependent microbial inactivation kinetics. We showed that although mild membrane permeabilization and late DNA damage occur, no correlation with inactivation kinetics was found. On the other hand, protein degradation was analyzed by three different methods and showed a dose‐dependent trend that matches microbial inactivation kinetics. Our results provide a deeper mechanistic understanding of aPDT that can guide the scientific community toward the development of optimized photosensitizing drugs and also rationally propose synergistic combinations with antimicrobial chemotherapy. [ABSTRACT FROM AUTHOR]