Generation and suppression of singlet oxygen in hair by photosensitization of melanin

Antioxidant Properties of Platycladus orientalis Flavonoids for Treating UV-Induced Damage in Androgenetic Alopecia Hair

BACKGROUND

Androgenetic alopecia (AGA) causes thinning hair, but poor hair quality in balding areas and damage from UV radiation have been overlooked. Plant extracts like Platycladus orientalis flavonoids (POFs) may improve hair quality in AGA. This study examines POFs' effectiveness in treating AGA-affected hair and repairing UV-induced damage.

METHODS

Hair samples were analyzed using scanning electron microscopy (SEM) to examine surface characteristics, electron paramagnetic resonance (EPR) spectroscopy to measure free radicals in the hair, and spectrophotometry to assess changes in hair properties.

RESULTS

POFs effectively removed hydroxyl radicals from keratinocytes and had antioxidant properties. They also reduced UV-induced damage to AGA hair by mitigating the production of melanin free radicals. Following POF treatment, the reduction in peroxidized lipid loss in AGA hair was notable at 59.72%, thereby effectively delaying the progression of hair color change. Moreover, protein loss decreased by 191.1 μ/g and tryptophan loss by 15.03%, ultimately enhancing hair's tensile strength.

CONCLUSION

compared to healthy hair, hair damaged by AGA shows more pronounced signs of damage when exposed to UV radiation. POFs help protect balding hair by reducing oxidative damage and slowing down melanin degradation.

The effect of oxidative degradation of Dopa-melanin on its basic physicochemical properties and photoreactivity

Melanin, particularly eumelanin, is commonly viewed as an efficient antioxidant and photoprotective pigment. Nonetheless, the ability of melanin to photogenerate reactive oxygen species and sensitize the formation of cyclobutane pyrimidine dimers may contribute to melanin-dependent phototoxicity. The phototoxic potential of melanin depends on a variety of factors, including molecular composition, redox state, and degree of aggregation. Using complementary spectroscopic and analytical methods we analyzed the physicochemical properties of Dopa-melanin, a synthetic model of eumelanin, subjected to oxidative degradation induced by aerobic photolysis or exposure to 0.1 M hydrogen peroxide. Both modes of oxidative degradation were accompanied by dose-dependent bleaching of melanin and irreversible modifications of its paramagnetic, ion- and electron-exchange and antioxidant properties. Bleached melanin exhibited enhanced efficiency to photogenerate singlet oxygen in both UVA and short-wavelength visible light. Although chemical changes of melanin subunits, including a relative increase of DHICA content and disruption of melanin polymer induced by oxidative degradation were considered, these two mechanisms may not be sufficient for a satisfactory explanation of the elevated photosensitizing ability of the bleached eumelanin. This study points out possible adverse changes in the photoprotective and antioxidant properties of eumelanin that could occur in pigmented tissues after exposure to high doses of intense solar radiation.

Endogenous Photosensitizers in Human Skin

Endogenous photosensitizers play a critical role in both beneficial and harmful light-induced transformations in biological systems. Understanding their mode of action is essential for advancing fields such as photomedicine, photoredox catalysis, environmental science, and the development of sun care products. This review offers a comprehensive analysis of endogenous photosensitizers in human skin, investigating the connections between their electronic excitation and the subsequent activation or damage of organic biomolecules. We gather the physicochemical and photochemical properties of key endogenous photosensitizers and examine the relationships between their chemical reactivity, location within the skin, and the primary biochemical events following solar radiation exposure, along with their influence on skin physiology and pathology. An important take-home message of this review is that photosensitization allows visible light and UV-A radiation to have large effects on skin. The analysis presented here unveils potential causes for the continuous increase in global skin cancer cases and emphasizes the limitations of current sun protection approaches.

How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification

This review critically appraises the reported differences in human hair fibre within three related domains of research: hair classification approaches, fibre characteristics and properties. The most common hair classification approach is based on geo-racial origin, defining three main groups: African, Asian and Caucasian hair. This classification does not account sufficiently for the worldwide hair diversity and intergroups variability in curl, shape, size and colour. A global classification into eight curl types has been proposed but may be too complex for reproducibility. Beyond that, hair cross-sectional shape and area have been found to have an inverse relation to curl: straighter fibres are circular with larger cross-sectional area, whilst the curlier fibres are elliptical with smaller cross-sectional area. These geometrical differences have been associated with bilateral vs homogenous distribution of cortical cell in curly vs straight hair respectively. However, there is no sufficient data demonstrating significant differences in hair amino composition, but proteomic studies are reporting associations of some proteins with curly hair. Eumelanin's relative abundance has been reported in all hair colours except for red hair which has a high pheomelanin content. Higher tensile and fatigue strength of straight hair are reported, however, curly hair fragility is attributed to knotting, and crack and flow formations rather than the structural variations. African hair has been found to have the highest level of lipids, whilst the water sorption of Caucasian hair is the highest, and that of Asian hair the lowest. Not all comparative studies clearly report their hair sampling approaches. Therefore, to strengthen the robustness of comparative studies and to facilitate cross-study data comparisons, it is recommended that the following hair defining characteristics are reported in studies: hair cross sectional diameter/area, curl type, hair assembly colour, as well as where possible donor data (age/gender) and sample pooling approach.

Practical Aspects in the Study of Biological Photosensitization Including Reaction Mechanisms and Product Analyses: A Do's and Don'ts Guide†

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.

Photodynamics of Melanin Radicals: Contribution to Photoprotection by Melanin†

The mechanism of very efficient relaxation of the melanin-photoexcited states, responsible for the photoprotective action of the pigment, remains a subject for intense investigation. The most recent study by C. Grieco, F. Kohl, and B. Kohler, entitled "Ultrafast radical photogeneration pathways in eumelanin," addresses key issues of melanin photophysics and photochemistry. By using femtosecond broad-band pump probe-transient absorption measurements, the researchers were able to identify the absorption spectrum of DOPA melanin radicals for the first time and proposed two distinct mechanisms of radical formation-photoionization and photoinduced charge separation. The observed photodynamic of melanin radicals suggests a new paradigm in which the ultrafast excited state deactivation is due to the efficient recombination of melanin radicals created promptly by photoexcitation.

VDAC1 negatively regulates melanogenesis through the Ca2+-calcineurin-CRTC1-MITF pathway

This study revealed an important and novel role of mitochondrial VDAC1 in regulating melanogenesis in resting melanocytes through a Ca²⁺-regulated pathway that is independent of the alpha-MSH/UVB pathway.

Melanocytes produce melanin for protecting DNA from ultraviolet exposure to maintain genomic stability. However, the precise regulation of melanogenesis is not fully understood. VDAC1, which is mainly localized in the outer mitochondrial membrane, functions as a gatekeeper for the entry or exit of Ca²⁺ between mitochondria and the cytosol and participates in multiple physiological processes. Here, we showed a novel role of VDAC1 in melanogenesis. Depletion of VDAC1 increased pigment content and up-regulated melanogenic genes, TYR, TYRP1, and TYRP2. Knockdown of VDAC1 increased free cytosolic Ca²⁺ in cultured melanocytes at the resting state, which activated calcineurin through the Ca²⁺-calmodulin-CaN pathway. The activated CaN dephosphorylated CRTC1 to facilitate its nuclear translocation and ultimately up-regulated the transcription of the master regulator of melanogenesis MITF. Consistently, depletion of Vdac1 in mice led to up-regulation of the transcription of MITF and thereafter its targeted melanogenic genes. These findings suggest that VDAC1 is an important negative regulator of melanogenesis, which expands our knowledge about pigment production and implies its potential role in melanoma.

Genetic Characteristics and Metabolic Interactions between Pseudocercospora fijiensis and Banana: Progress toward Controlling Black Sigatoka

The international importance of banana and severity of black Sigatoka disease have led to extensive investigations into the genetic characteristics and metabolic interactions between the Dothideomycete Pseudocercospora fijiensis and its banana host. P. fijiensis was shown to have a greatly expanded genome compared to other Dothideomycetes, due to the proliferation of retrotransposons. Genome analysis suggests the presence of dispensable chromosomes that may aid in fungal adaptation as well as pathogenicity. Genomic research has led to the characterization of genes and metabolic pathways involved in pathogenicity, including: secondary metabolism genes such as PKS10-2, genes for mitogen-activated protein kinases such as Fus3 and Slt2, and genes for cell wall proteins such as glucosyl phosphatidylinositol (GPI) and glycophospholipid surface (Gas) proteins. Studies conducted on resistance mechanisms in banana have documented the role of jasmonic acid and ethylene pathways. With the development of banana transformation protocols, strategies for engineering resistance include transgenes expressing antimicrobial peptides or hydrolytic enzymes as well as host-induced gene silencing (HIGS) targeting pathogenicity genes. Pseudocercospora fijiensis has been identified as having high evolutionary potential, given its large genome size, ability to reproduce both sexually and asexually, and long-distance spore dispersal. Thus, multiple control measures are needed for the sustainable control of black Sigatoka disease.

Photosensitization Reactions of Biomolecules: Definition, Targets and Mechanisms

Photosensitization reactions have been demonstrated to be largely responsible for the deleterious biological effects of UV and visible radiation, as well as for the curative actions of photomedicine. A large number of endogenous and exogenous photosensitizers, biological targets and mechanisms have been reported in the past few decades. Evolving from the original definitions of the type I and type II photosensitized oxidations, we now provide physicochemical frameworks, classifications and key examples of these mechanisms in order to organize, interpret and understand the vast information available in the literature and the new reports, which are in vigorous growth. This review surveys in an extended manner all identified photosensitization mechanisms of the major biomolecule groups such as nucleic acids, proteins, lipids bridging the gap with the subsequent biological processes. Also described are the effects of photosensitization in cells in which UVA and UVB irradiation triggers enzyme activation with the subsequent delayed generation of superoxide anion radical and nitric oxide. Definitions of photosensitized reactions are identified in biomolecules with key insights into cells and tissues.

Co-Encapsulation of Methylene Blue and PARP-Inhibitor into Poly(Lactic-Co-Glycolic Acid) Nanoparticles for Enhanced PDT of Cancer

The development of resistance against photodamage triggered by photodynamic therapy (PDT) is ascribed mainly to the cellular redox defenses and repair. If the tumor tissue is not promptly eliminated by the first few PDT sessions, PDT-resistance can be favored, challenging the efficacy of the treatment. Although the mechanism of PDT resistance is still unclear, in vitro assays have evidenced that it can be developed through the PARP damage-repair signaling pathway. Therefore, inhibition of poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) has the potential to increase PDT efficacy. This work reports on the synthesis of a controlled release system of a photosensitizer, methylene blue (MB) and a PARP-inhibitor, the veliparib. MB and veliparib were co-encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (VMB-NPs). A colloidal stable aqueous suspension of nanoparticles was obtained. The average hydrodynamic diameter was 90 nm and a narrow size distribution was obtained, with a polydispersity index (PDI) of 0.08. The release kinetics of MB and veliparib from VMB-NPs showed an initial burst of 8.7% and 58.3% release of the total amounts of MB and veliparib respectively, in the first 6 h, and a delayed release of up to 11.3% and 70%, in 19 days, for MB and veliparib, respectively. The VMB-NPs showed no cytotoxicity in the dark but the viability of B16F10-Nex2 cells decreased by 36% when the cells were irradiated (102 J/cm², 660 nm) and treated with VMB-NPs containing 1.0 µM of MB and 8.3 µM of veliparib. Considering the increased photoactivity even at low MB and veliparib concentrations and the absence of cytotoxicity in dark, the co-encapsulation of MB and veliparib was shown to be a promising strategy to improve the PDT efficacy.

New insight into melanin for food packaging and biotechnology applications

Melanin is a dark brown to black biomacromolecule with biologically active multifunctional properties that do not have a precise chemical structure, but its structure mainly depends on the polymerization conditions during the synthesis process. Natural melanin can be isolated from various animal, plant, and microbial sources, while synthetic melanin-like compounds can be synthesized by simple polymerization of dopamine. Melanin is widely used in various areas due to its functional properties such as photosensitivity, light barrier property, free radical scavenging ability, antioxidant activity, etc. It also has an excellent ability to act as a reducing agent and capping agent to synthesize various metal nanoparticles. Melanin nanoparticles (MNP) or melanin-like nanoparticles (MLNP) have the unique potential to act as functional materials to improve nanocomposite films' physical and functional properties. Various food packaging and biomedical applications have been made alone or by mixing melanin or MLNP. In this review, the general aspects of melanin that highlight biological activity, along with a description of MNP and the use as nanofillers in packaging films as well as reducing and capping agents and biomedical applications, were comprehensively reviewed.

Self-assembled guanosine-hydrogels for drug-delivery application: Structural and mechanical characterization, methylene blue loading and controlled release

It is known that guanosine derivatives (G) self-assemble in water forming long, flexible, and interacting aggregates (the so-called G-quadruplexes): by modulating the quadruplex charges, e.g. simply using a mixture of guanosine 5'-monophosphate (GMP) and guanosine (Gua), multi-responsive, self-healing hydrogels can be obtained. In this paper, the potential application of G-hydrogels as drug delivery systems has been assessed. Hydrogels were prepared at different Gua:GMP molar ratios. The photosensitizer Methylene Blue and the pro-apoptotic protein cytochrome C were used as cargo molecules. Small angle x-ray scattering and atomic force microscopy experiments confirmed the presence of G-quadruplexes disposed in swollen matrices with different mesh-sizes. Rheology measurements showed that the Gua:GMP molar ratio leads to specific drug release mechanisms, as the gel strength is finely tuned by electrostatic repulsion and van der Waals attraction between G-quadruplexes. Noteworthy, the gel cohesion and the drug release were pH responsive. Swelling, self-healing and cell viability features were also investigated: the results qualify the Gua:GMP hydrogel as an excellent biomaterial that can entrap and deliver key biomolecules in a sustained and responsive release manner.

Lipofuscin in keratinocytes: Production, properties, and consequences of the photosensitization with visible light

A dysfunction in the mitochondrial-lysosomal axis of cellular homeostasis is proposed to cause cells to age quicker and to accumulate lipofuscin. Typical protocols to mediate lipofuscinogenesis are based on the induction of the senescent phenotype either by allowing many consecutive cycles of cell division or by treating cells with physical/chemical agents such as ultraviolet (UV) light or hydrogen peroxide. Due to a direct connection with the physiopathology of age-related macular degeneration, lipofuscin that accumulates in retinal pigment epithelium (RPE) cells have been extensively studied, and the photochemical properties of RPE lipofuscin are considered as standard for this pigment. Yet, many other tissues such as the brain and the skin may prompt lipofuscinogenesis, and the properties of lipofuscin granules accumulated in these tissues are not necessarily the same as those of RPE lipofuscin. Here, we present a light-induced protocol that accelerates cell aging as judged by the maximization of lipofuscinogenesis. Photosensitization of cells previously incubated with nanomolar concentrations of 1,9-dimethyl methylene blue (DMMB), severely and specifically damages mitochondria and lysosomes, leading to a lipofuscin-related senescent phenotype. By applying this protocol in human immortalized non-malignant keratinocytes (HaCaT) cells, we observed a 2.5-fold higher level of lipofuscin accumulation compared to the level of lipofuscin accumulation in cells treated with a typical UV protocol. Lipofuscin accumulated in keratinocytes exhibited the typical red light emission, with excitation maximum in the blue wavelength region (~450 nm). Fluorescence lifetime image microscopy data showed that the keratinocyte lipofuscin has an emission lifetime of ~1.7 ns. Lipofuscin-loaded cells (but not control cells) generated a substantial amount of singlet oxygen (¹O₂) when irradiated with blue light (420 nm), but there was no ¹O₂ generation when excitation was performed with a green light (532 nm). These characteristics were compared with those of RPE cells, considering that keratinocyte lipofuscin lacks the bisretinoids derivatives present in RPE lipofuscin. Additionally, we showed that lipofuscin-loaded keratinocytes irradiated with visible light presented critical DNA damages, such as double-strand breaks and Fpg-sensitive sites. We propose that the DMMB protocol is an efficient way to disturb the mitochondrial-lysosomal axis of cellular homeostasis, and consequently, it can be used to accelerate aging and to induce lipofuscinogenesis. We also discuss the consequences of the lipofuscin-induced genotoxicity of visible light in keratinocytes.

The role of hydrogen peroxide and singlet oxygen in the photodegradation of melanin

When aging, melanin in human retinal pigment epithelium (RPE) undergoes oxidative modifications, which increase its photoreactivity and reduce its antioxidant capacity, elevating the risk of chronic phototoxicity to the retina. The aim of this research was to examine the effect of iron on the degradation of melanin induced by hydrogen peroxide and light, and to elucidate the role of hydrogen peroxide and singlet oxygen in the photodegradation of melanin. A water-soluble synthetic model of eumelanin with and without iron ions was treated either with exogenous hydrogen peroxide or with intense violet light. Oxidative modifications of melanin were analyzed by electron paramagnetic resonance (EPR) spectroscopy, absorption spectrophotometry, dynamic light scattering (DLS) and by chemical analysis of melanin subunits. The results showed that although iron strongly accelerated melanin degradation induced by hydrogen peroxide, it had very little influence on the rate of photodegradation of melanin. On the other hand, the photodegradation of melanin was partly inhibited by NaN₃. The determination of hydrogen peroxide together with oxygen uptake indicates that irradiated melanin generates similar amounts of singlet oxygen and hydrogen peroxide. Analysis of melanin samples exhibiting comparable reduction of their EPR signal revealed that the loss of the representative melanin subunits was much higher in irradiated samples than in those treated with hydrogen peroxide in the dark. In conclusion, hydrogen peroxide, formed during the aerobic photolysis of melanin, is not responsible for the accompanying oxidative modifications of melanin. On the other hand, singlet oxygen can be considered as a key oxidizing agent involved in the photodegradation of melanin.

JNK suppresses melanogenesis by interfering with CREB-regulated transcription coactivator 3-dependent MITF expression

Melanogenesis is a critical self-defense mechanism against ultraviolet radiation (UVR)-induced skin damage and carcinogenesis; however, dysregulation of melanin production and distribution causes skin-disfiguring pigmentary disorders. Melanogenesis is initiated by UVR-induced cAMP generation and ensuing activation of transcription factor CREB, which induces expression of the master melanogenic regulator MITF. Recent studies have demonstrated that recruitment of CRTCs to the CREB transcription complex is also required for UVR-stimulated melanogenesis. Therefore, modulation of cAMP-CRTC/CREB-MITF signaling may be a useful therapeutic strategy for UVR-associated skin pigmentary disorders. Methods: We identified the small-molecule Ro31-8220 from CREB/CRTC activity screening and examined its melanogenic activity in cultured mouse and human melanocytes as well as in human skin. Molecular mechanisms were deciphered by immunoblotting, RT-PCR, promoter assays, tyrosinase activity assays, immunofluorescent examination of CRTC3 subcellular localization, and shRNA-based knockdown. Results: Ro31-8220 suppressed basal and cAMP-stimulated melanin production in melanocytes and human melanocyte co-culture as well as UVR-stimulated melanin accumulation in human skin through downregulation of MITF and tyrosinase expression. Mechanistically, down regulation of MITF expression by Ro31-8220 was due to inhibition of transcriptional activity of CREB, which was resulted from phosphorylation-dependent blockade of nuclear translocation of CRTC3 via JNK activation. The selective JNK activator anisomycin also inhibited melanin production through phosphoinhibition of CRTC3, while JNK inhibition enhanced melanogenesis by stimulating CRTC3 dephosphorylation and nuclear migration. Conclusions: Melanogenesis can be enhanced or suppressed via pharmacological modulation of a previously unidentified JNK-CRTC/CREB-MITF signaling axis. As Ro31-8220 potently inhibits UVR-stimulated melanin accumulation in human skin, suggesting that small-molecule JNK-CRTC signaling modulators may provide therapeutic benefit for pigmentation disorders.

Mechanisms of Photosensitized Lipid Oxidation and Membrane Permeabilization

Lipid oxidation encompasses chemical transformations affecting animals and plants in many ways, and light is one of the most common triggers of lipid oxidation in our habitat. Still, the molecular mechanisms and biological consequences of photoinduced lipid oxidation were only recently understood at the molecular level. In this review, we focus on the main mechanisms of photosensitized lipid oxidation and membrane permeabilization, dissecting the consequences of both singlet oxygen and contact-dependent pathways and discussing how these reactions contribute to chemical and biophysical changes in lipid membranes. We aim to enable scientists to develop novel and more efficient photosensitizers in photomedicine, as well as better strategies for sun protection.

Photoprotection against visible light-induced pigmentation

OBJECTIVE

This paper presents in vivo an in vitro studies demonstrating the induction of pigmentation in human skin by visible light which can be blocked by using formulation containing the correct amount of yellow iron oxide (YIO).

METHODS

An in vitro absorption method was developed to determine the protection provided by a test formulation containing 4.5% YIO using an IPD UVA-VIS action spectrum. Following the development of the in vitro method and in vivo study with 10 normal healthy volunteers with Fitzpatrick skin phototypes IV to VI was conducted to verify if the predictive model.

RESULTS

The in vitro model for visible light protection provided a protection factor of 2.5 using the in vitro absorption spectrum of 4.5% of YIO with a very similar result from the in vivo study with a protection factor of 3.0. Multiple daily exposures of visible light have shown increase in skin pigmentation and the application of YIO provide less development of pigmentation when compared to unprotected skin.

CONCLUSION

In vitro testing of the absorbance of the pigmented formulation using a proposed action spectrum for immediate pigment darkening (IPD) response in the visible light range supports the in vivo protection observations for persistent pigment darkening (PPD) and can be used as predictor for skin pigmentation induced by visible light.

Melanosomes: Biogenesis, Properties, and Evolution of an Ancient Organelle

Melanosomes are organelles that produce and store melanin, a widespread biological pigment with a unique suite of properties including high refractive index, semiconducting capabilities, material stiffness, and high fossilization potential. They are involved in numerous critical biological functions in organisms across the tree of life. Individual components such as melanin chemistry and melanosome development have recently been addressed, but a broad synthesis is needed. Here, we review the hierarchical structure, development, functions, and evolution of melanosomes. We highlight variation in melanin chemistry and melanosome morphology and how these may relate to function. For example, we review what is known of the chemical differences between different melanin types (eumelanin, pheomelanin, allomelanin) and whether/how melanosome morphology relates to chemistry and color. We integrate the distribution of melanin across living organisms with what is known from the fossil record and produce hypotheses on its evolution. We suggest that melanin was present in life forms early in evolutionary history and that melanosomes evolved at the origin of organelles. Throughout, we discuss the (sometimes gaping) holes in our knowledge and suggest areas that need particular attention as we move forward in our understanding of these still-mysterious organelles and the materials that they contain.

Antioxidant role on the protection of melanocytes against visible light-induced photodamage

Visible light can induce the generation of singlet oxygen and can cause oxidative stress, especially in melanocytes due to melanin photosensitization. Currently, there is no organic UV-filter that provide visible light protection. Previous studies showed that some antioxidants, such as apigenin (API), chrysin (CRI) and beta-carotene (BTC) besides neutralizing radical chain reactions can also quench singlet oxygen via physical or chemical quenching and exhibit potential for use in photoprotection. Therefore, the aim of this study is to evaluate the efficacy of API, CRI and BTC on the protection against cell death induced by melanin photosensitization and understand the underlying mechanisms that are involved in the protection. Precise protocols of melanogenesis and quantification of singlet oxygen generation were developed. Viability of B16-F10 cells with melanin basal levels and after melanogenesis induction was evaluated after visible light exposure in the presence and absence of API, CRI and BTC. Results showed that API and BTC protected cells from photoinduced cell death API exhibiting superior photoprotective effect. We noticed that the efficiency of cell protection and the rate of singlet oxygen suppression are not well correlated, at least for the studied series of antioxidants, indicating that the anti-radical capacity should be playing a major role in protecting cells against the damage induced by melanin photosensitization. In terms of sun care strategies, both API and BTC offer protection against visible light-induced damages and may be effective topical antioxidants to be added to sunscreens.

Formation of UV-induced DNA damage contributing to skin cancer development

UV-induced DNA damage plays a key role in the initiation phase of skin cancer. When left unrepaired or when damaged cells are not eliminated by apoptosis, DNA lesions express their mutagneic properties, leading to the activation of proto-oncogene or the inactivation of tumor suppression genes. The chemical nature and the amount of DNA damage strongly depend on the wavelength of the incident photons. The most energetic part of the solar spectrum at the Earth's surface (UVB, 280-320 nm) leads to the formation of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (64PPs). Less energetic but 20-times more intense UVA (320-400 nm) also induces the formation of CPDs together with a wide variety of oxidatively generated lesions such as single strand breaks and oxidized bases. Among those, 8-oxo-7,8-dihydroguanine (8-oxoGua) is the most frequent since it can be produced by several mechanisms. Data available on the respective yield of DNA photoproducts in cells and skin show that exposure to sunlight mostly induces pyrimidine dimers, which explains the mutational signature found in skin tumors, with lower amounts of 8-oxoGua and strand breaks. The present review aims at describing the basic photochemistry of DNA and discussing the quantitative formation of the different UV-induced DNA lesions reported in the literature. Additional information on mutagenesis, repair and photoprotection is briefly provided.

Spectroscopy as a tool to evaluate hair damage and protection

OBJECTIVE

Methods that can be used to analyse hair damage and to support a claim of hair protection are important for the cosmetic industry. There are many approaches available, but they are usually laborious and expensive. The researchers propose a simple fluorescence method that is based upon the emissive properties of damaged hair.

METHODS

Hair fluorescence was observed when using both fluorimetry and microscopic procedures. The method was developed by comparing native hair with hair that was damaged by UVA and visible light.

RESULTS

Spectroscopic properties (absorption and emission) of hair in the visible range are presented. The changes in the emissive properties of hair during irradiation were characterized and they were correlated with photobleaching, which is due to the generation of singlet oxygen. Emissions were also obtained in the hair shafts that had been previously treated with chamomile extract and this treatment was able to avoid hair bleaching.

CONCLUSION

The emissive properties of hair in the visible range can be used as a tool for the evaluation of hair damage and protection. This method can be useful as a tool in order to claim substantiation.

Combination of Natural Extracts and Photobiomodulation in Keratinocytes Subjected to UVA Radiation

Natural extracts (NE) with antioxidant properties can minimize the effects of photoaging. Photobiomodulation (PBM) has proven to be a useful tool for the modulation of cell metabolism. Here, we investigate the associations of antioxidants with PBM with the aim of promoting skin rejuvenation. We began with standardization of the experimental protocol. Extracts of chamomile, rosemary, blueberry, green tea, figs, pomegranate and nutwood were tested. A custom irradiation system (366 ± 10 nm) was used to simulate sun exposure. A light emitting diode system (640 ± 12.5 nm) was used for PBM. Viability assessments were performed by the (3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) MTT assay method. Based on the results, radiant exposure to UVA was defined as 9 and 1 J cm^-2 for PBM. Extract concentrations were established on the basis of dark toxicities, which ranged from 0.01% to 0.3%. The data show that PBM is a promising therapy to restore keratinocytes after UVA damage; however, the detailed mechanism and effects require further exploration. Moreover, although the combination of PBM with NE may be a useful strategy, the choice of a NE is challenging, since the working concentration and other properties, such as photosensitivity, may bring about unwanted results.

Photodegradation of Eumelanin and Pheomelanin and Its Pathophysiological Implications

Eumelanin is photoprotective for pigmented tissues while pheomelanin is phototoxic. In this review, we summarize current understanding of how eumelanin and pheomelanin structures are modified by ultraviolet A (UVA) and also by visible light and how reactive oxygen species participate in those processes. Alkaline hydrogen peroxide oxidation was employed to characterize eumelanin and benzothiazole-type pheomelanin, giving pyrrole-2,3,5-tricarboxylic acid (PTCA) and thiazole-2,4,5-tricarboxylic acid (TTCA), respectively. Reductive hydrolysis with hydroiodic acid gives 4-amino-3-hydroxyphenylalanine (4-AHP) from the benzothiazine moiety of pheomelanin. The results show that the photoaging of eumelanin gives rise to free PTCA (produced by peroxidation in situ) and pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA, produced by cross-linking). The TTCA/4-AHP ratio increases with photoaging, indicating the conversion of benzothiazine to the benzothiazole moiety. Analysis of those markers and their ratios show that both eumelanin and pheomelanin in human retinal pigment epithelium melanosomes undergo extensive structural modifications due to their lifelong exposure to blue light. Using synthetic melanins, we also found that singlet oxygen, in addition to superoxide anions, is photogenerated and quenched upon UVA irradiation. The (patho)physiological significance of those findings is discussed in relation to the tanning process, to melanomagenesis in the skin and to age-related macular degeneration in the eyes.

Roles of reactive oxygen species in UVA-induced oxidation of 5,6-dihydroxyindole-2-carboxylic acid-melanin as studied by differential spectrophotometric method

Eumelanin photoprotects pigmented tissues from ultraviolet (UV) damage. However, UVA-induced tanning seems to result from the photooxidation of preexisting melanin and does not contribute to photoprotection. We investigated the mechanism of UVA-induced degradation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-melanin taking advantage of its solubility in a neutral buffer and using a differential spectrophotometric method to detect subtle changes in its structure. Our methodology is suitable for examining the effects of various agents that interact with reactive oxygen species (ROS) to determine how ROS is involved in the UVA-induced oxidative modifications. The results show that UVA radiation induces the oxidation of DHICA to indole-5,6-quinone-2-carboxylic acid in eumelanin, which is then cleaved to form a photodegraded, pyrrolic moiety and finally to form free pyrrole-2,3,5-tricarboxylic acid. The possible involvement of superoxide radical and singlet oxygen in the oxidation was suggested. The generation and quenching of singlet oxygen by DHICA-melanin was confirmed by direct measurements of singlet oxygen phosphorescence.

Aerobic photoreactivity of synthetic eumelanins and pheomelanins: generation of singlet oxygen and superoxide anion

In this work, we examined photoreactivity of synthetic eumelanins, formed by autooxidation of DOPA, or enzymatic oxidation of 5,6-dihydroxyindole-2-carboxylic acid and synthetic pheomelanins obtained by enzymatic oxidation of 5-S-cysteinyldopa or 1:1 mixture of DOPA and cysteine. Electron paramagnetic resonance oximetry and spin trapping were used to measure oxygen consumption and formation of superoxide anion induced by irradiation of melanin with blue light, and time-resolved near-infrared luminescence was employed to determine the photoformation of singlet oxygen between 300 and 600 nm. Both superoxide anion and singlet oxygen were photogenerated by the synthetic melanins albeit with different efficiency. At 450-nm, quantum yield of singlet oxygen was very low (~10^-4 ) but it strongly increased in the UV region. The melanins quenched singlet oxygen efficiently, indicating that photogeneration and quenching of singlet oxygen may play an important role in aerobic photochemistry of melanin pigments and could contribute to their photodegradation and photoaging.

Photodynamic Efficiency: From Molecular Photochemistry to Cell Death

Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.

Effective protection of biological membranes against photo-oxidative damage: Polymeric antioxidant forming a protecting shield over the membrane

We have prepared a chitosan polymer modified with gallic acid in order to develop an efficient protection strategy biological membranes against photodamage. Lipid bilayers were challenged with photoinduced damage by photosensitization with methylene blue, which usually causes formation of hydroperoxides, increasing area per lipid, and afterwards allowing leakage of internal materials. The damage was delayed by a solution of gallic acid in a concentration dependent manner, but further suppressed by the polymer at very low concentrations. The membrane of giant unilamellar vesicles was covered with this modified macromolecule leading to a powerful shield against singlet oxygen and thus effectively protecting the lipid membrane from oxidative stress. The results have proven the discovery of a promising strategy for photo protection of biological membranes.

Melanin photosensitization and the effect of visible light on epithelial cells

Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (¹O₂) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize ¹O₂ with similar yields, and pheomelanin is more efficient than eumelanin at generating ¹O₂ and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer.

Singlet molecular oxygen generation by light-activated DHN-melanin of the fungal pathogen Mycosphaerella fijiensis in black Sigatoka disease of bananas

In pathogenic fungi, melanin contributes to virulence, allowing tissue invasion and inactivation of the plant defence system, but has never been implicated as a factor for host cell death, or as a light-activated phytotoxin. Our research shows that melanin synthesized by the fungal banana pathogen Mycosphaerella fijiensis acts as a virulence factor through the photogeneration of singlet molecular oxygen O2 (1Δg). Using analytical tools, including elemental analysis, ultraviolet/infrared absorption spectrophometry and MALDI-TOF mass spectrometry analysis, we characterized both pigment content in mycelia and secreted to the culture media as 1,8-dihydroxynaphthalene (DHN)-melanin type compound. This is sole melanin-type in M. fijiensis. Isolated melanins irradiated with a Nd:YAG laser at 532 nm produced monomol light emission at 1270 nm, confirming generation of O2 (1Δg), a highly reactive oxygen specie (ROS) that causes cellular death by reacting with all cellular macromolecules. Intermediary polyketides accumulated in culture media by using tricyclazole and pyroquilon (two inhibitors of DHN-melanin synthesis) were identified by ESI-HPLC-MS/MS. Additionally, irradiation at 532 nm of that mixture of compounds and whole melanized mycelium also generated O2 (1Δg). A pigmented-strain generated more O2 (1Δg) than a strain with low melanin content. Banana leaves of cultivar Cavendish, naturally infected with different stages of black Sigatoka disease, were collected from field. Direct staining of the naturally infected leaf tissues showed the presence of melanin that was positively correlated to the disease stage. We also found hydrogen peroxide (H2O2) but we cannot distinguish the source. Our results suggest that O2 (1Δg) photogenerated by DHN-melanin may be involved in the destructive effects of Mycosphaerella fijiensis on banana leaf tissues. Further studies are needed to fully evaluate contributions of melanin-mediated ROS to microbial pathogenesis.

Membrane changes under oxidative stress: the impact of oxidized lipids

Studying photosensitized oxidation of unsaturated phospholipids is of importance for understanding the basic processes underlying photodynamic therapy, photoaging and many other biological dysfunctions. In this review we show that the giant unilamellar vesicle, when used as a simplified model of biological membranes, is a powerful tool to investigate how in situ photogenerated oxidative species impact the phospholipid bilayer. The extent of membrane damage can be modulated by choosing a specific photosensitizer (PS) which is activated by light irradiation and can react by either type I and or type II mechanism. We will show that type II PS generates only singlet oxygen which reacts to the phospholipid acyl double bond. The byproduct thus formed is a lipid hydroperoxide which accumulates in the membrane as a function of singlet oxygen production and induces an increase in its area without significantly affecting membrane permeability. The presence of a lipid hydroperoxide can also play an important role in the formation of the lipid domain for mimetic plasma membranes. Lipid hydroperoxides can be also transformed in shortened chain compounds, such as aldehydes and carboxylic acids, in the presence of a PS that reacts via the type I mechanism. The presence of such byproducts may form hydrophilic pores in the membrane for moderate oxidative stress or promote membrane disruption for massive oxidation. Our results provide a new tool to explore membrane response to an oxidative stress and may have implications in biological signaling of redox misbalance.

EPR Studies of DOPA-Melanin Complexes with Netilmicin and Cu(II) at Temperatures in the Range of 105-300 K

The application of electron paramagnetic resonance (EPR) spectroscopy in pharmacy of melanin complexes with netilmicin and Cu(II) was presented. The continuous microwave saturation of EPR spectra of DOPA-melanin and the complexes was performed. EPR spectra were measured on an X-band (9.3 GHz) spectrometer at temperatures in the range of 105-300 K. Paramagnetic copper ions decrease the intensity of the EPR lines of melanin's free radicals. It was found that fast spin-lattice relaxation characterizes DOPA-melanin-Cu(II) complexes. Slow spin-lattice relaxation processes exist in melanin's paramagnetic centers of DOPA-melanin and DOPA-melanin-netilmicin, [DOPA-melanin-netilmicin]-Cu(II), [DOPA-melanin-Cu(II)]-netilmicin complexes. Spin-lattice relaxation processes are faster at higher temperatures. The homogeneous broadening of EPR lines for melanin complexes was observed. The practical consequences of differences between paramagnetic properties of melanin complexes with netilmicin and the complexes with Cu(II) were discussed.

Novel properties of melanins include promotion of DNA strand breaks, impairment of repair, and reduced ability to damage DNA after quenching of singlet oxygen

Melanins have been associated with the development of melanoma and its resistance to photodynamic therapy (PDT). Singlet molecular oxygen ((1)O(2)), which is produced by ultraviolet A solar radiation and the PDT system, is also involved. Here, we investigated the effects that these factors have on DNA damage and repair. Our results show that both types of melanin (eumelanin and pheomelanin) lead to DNA breakage in the absence of light irradiation and that eumelanin is more harmful than pheomelanin. Interestingly, melanins were found to bind to the minor grooves of DNA, guaranteeing close proximity to DNA and potentially causing the observed high levels of strand breaks. We also show that the interaction of melanins with DNA can impair the access of repair enzymes to lesions, contributing to the perpetuation of DNA damage. Moreover, we found that after melanins interact with (1)O(2), they exhibit a lower ability to induce DNA breakage; we propose that these effects are due to modifications of their structure. Together, our data highlight the different modes of action of the two types of melanin. Our results may have profound implications for cellular redox homeostasis, under conditions of induced melanin synthesis and irradiation with solar light. These results may also be applied to the development of protocols to sensitize melanoma cells to PDT.