Spin-Restricted Descriptions of Singlet Oxygen Reactions from XMS-CASPT2 Benchmarks

Reactions of singlet oxygen are numerous, some of which are desired but many are unwanted. Therefore, the ability to correctly predict and interpret this reactivity for complex molecular systems is essential to our understanding of singlet oxygen reactions. DFT is widely used for predicting many reactions but is not suited to degenerate electronic structures; application to isolated singlet oxygen often uses the spin-unrestricted formalism, which results in severe spin contamination. In this work, we demonstrate that spin-restricted DFT can correctly describe the reaction pathway for four prototypical singlet oxygen reactions. By careful benchmarking with XMS-CASPT2, we show that, from the first transition state onward, the degeneracy of the 1Δg state is broken due to differing interactions of the (degenerate) π* orbitals with the organic substrate; this result is well replicated with DFT. These findings demonstrate the utility of using spin-restricted DFT to explore reactions, opening the way to confidently use this computationally efficient method for molecular systems of medium to large organic molecules.

Photoinactivation of the bacteriophage PhiX174 by UVA radiation and visible light in SM buffer and DMEM-F12

OBJECTIVE

It has been observed that viruses can be inactivated by UVA radiation and visible light. The aim of this study is to investigate whether a medium that contains a photosensitizer might have an influence on viral reduction under irradiation by UVA, violet or blue light. Test virus is the bacteriophage PhiX174 in the photosensitizer-free SM buffer and DMEM-F12, which contains the known photosensitizer riboflavin.

RESULTS

The determined PhiX174 D90 doses in SM buffer and DMEM were 36.8 J/cm² and 13.6 J/cm² at 366 nm, 153.6 J/cm² and 129.1 J/cm² at 408 nm and 4988 J/cm² and 2477.1 J/cm² at 455 nm, respectively. It can be concluded that the medium has a large influence on the results. This might be caused by the photosensitizer riboflavin in DMEM-F12. As riboflavin is a key component in many cell culture media, irradiation experiments with viruses in cell culture media should be avoided if the investigation of intrinsical photoinactivation properties of viruses is aimed for.

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.

Phototherapy: Theory and practice

Despite the development of highly effective biologics for skin diseases such as psoriasis or atopic dermatitis, UVA and UVB therapy, alone or in combination, are still essential components of various guidelines. Phototherapy is not only a first-line treatment and highly effective for a number of skin diseases, but is also economical and has few side effects. The targeted use of UVA and UVB, if necessary, in combination with the photosensitizer psoralen in the context of PUVA therapy, enables the dermatologist to effectively treat a wide variety of skin diseases. Indications for phototherapy include epidermal diseases such as atopic dermatitis, psoriasis and vitiligo, as well as photodermatoses, mycosis fungoides, graft-versus-host disease and deep dermal diseases such as scleroderma. This article reviews the physical principles, molecular mechanisms, current treatment regimens, and individual indications for phototherapy and photochemotherapy.

Phototherapie in Theorie und Praxis

Die Therapie oder Kombinationstherapie mit UV‐A‐ oder UV‐B‐Strahlen ist trotz der Entwicklung hochwirksamer Biologika bei Hauterkrankungen wie Psoriasis oder atopischer Dermatitis nach wie vor unverzichtbarer Bestandteil verschiedener Leitlinienempfehlungen. Die Phototherapie ist nicht nur eine sehr effektive Erstlinientherapie bei verschiedenen Hauterkrankungen, sondern auch kostengünstig und nebenwirkungsarm. Der gezielte Einsatz von UV‐A und UV‐B, gegebenenfalls auch in Kombination mit dem Photosensibilisator Psoralen im Rahmen einer PUVA‐Therapie, ermöglicht dem Dermatologen eine effektive Behandlung verschiedener Hautkrankheiten. Indikationen für die Phototherapie sind epidermale Erkrankungen wie die atopische Dermatitis, die Psoriasis und die Vitiligo, ferner Photodermatosen, die Mycosis fungoides, die Graft‐versus‐Host‐Erkrankung sowie tiefe dermale Erkrankungen wie die Sklerodermie. Dieser Artikel gibt einen Überblick über die physikalischen Grundlagen, die molekularen Mechanismen, die derzeitigen Behandlungsmethoden und die einzelnen Indikationen für die Phototherapie und die Photochemotherapie.

The Glycolysis-derived α-Dicarbonyl Metabolite Methylglyoxal is a UVA-photosensitizer Causing the Photooxidative Elimination of HaCaT Keratinocytes with Induction of Oxidative and Proteotoxic Stress Response Gene Expression†

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 (1 O2 ) 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.

Highly Efficient Antibacterial Polymer Composites Based on Hydrophobic Riboflavin Carbon Polymerized Dots

Development of new types of antimicrobial coatings is of utmost importance due to increasing problems with pathogen transmission from various infectious surfaces to human beings. In this study, new types of highly potent antimicrobial polyurethane composite films encapsulated by hydrophobic riboflavin-based carbon polymer dots are presented. Detailed structural, optical, antimicrobial, and cytotoxic investigations of these composites were conducted. Low-power blue light triggered the composites to eradicate Escherichia coli in 30 min, whereas the same effect toward Staphylococcus aureus was reached after 60 min. These composites also show low toxicity against MRC-5 cells. In this way, RF-CPD composites can be used for sterilization of highly touched objects in the healthcare industry.

Role of ROS‑mediated autophagy in melanoma (Review)

Melanoma is the most aggressive form of skin cancer with the poorest prognosis and its pathogenesis has yet to be fully elucidated. As key factors that regulate cellular homeostasis, both reactive oxygen species (ROS) and autophagy are involved in the development of melanoma, from melanomagenesis to progression and drug resistance. However, the interaction between ROS and autophagy in the etiology and treatment of melanoma is not well characterized. The present review examined the production of ROS and the role of oxidative stress in melanoma, and summarized the role of ROS‑mediated autophagy in melanomagenesis and melanoma cell fate decision following treatment with various anticancer drugs. The present findings may lead to a better understanding of the pathogenesis and progression of melanoma, and suggest promising treatment options for this disease.

Photodegradation of Riboflavin under Alkaline Conditions: What Can Gas-Phase Photolysis Tell Us about What Happens in Solution?

The application of electrospray ionisation mass spectrometry (ESI-MS) as a direct method for detecting reactive intermediates is a technique of developing importance in the routine monitoring of solution-phase reaction pathways. Here, we utilise a novel on-line photolysis ESI-MS approach to detect the photoproducts of riboflavin in aqueous solution under mildly alkaline conditions. Riboflavin is a constituent of many food products, so its breakdown processes are of wide interest. Our on-line photolysis setup allows for solution-phase photolysis to occur within a syringe using UVA LEDs, immediately prior to being introduced into the mass spectrometer via ESI. Gas-phase photofragmentation studies via laser-interfaced mass spectrometry of deprotonated riboflavin, [RF - H]-, the dominant solution-phase species under the conditions of our study, are presented alongside the solution-phase photolysis. The results obtained illustrate the extent to which gas-phase photolysis methods can inform our understanding of the corresponding solution-phase photochemistry. We determine that the solution-phase photofragmentation observed for [RF - H]- closely mirrors the gas-phase photochemistry, with the dominant m/z 241 condensed-phase photoproduct also being observed in gas-phase photodissociation. Further gas-phase photoproducts are observed at m/z 255, 212, and 145. The value of exploring both the gas- and solution-phase photochemistry to characterise photochemical reactions is discussed.

Quenching effects of (-)-Epigallocatechin gallate for singlet oxygen production and its protection against oxidative damage induced by Ce6-mediated photodynamic therapy in vitro

BACKGROUND

Singlet oxygen (¹O₂) is highly reactive to biological components such as lipids, proteins and DNA, which induces oxidative damage to cells and tissues. Natural antioxidants may function as ¹O₂ quencher to prevent ¹O₂ involved photosensitized oxidation in biological system.

METHODS

Time-resolved measurement of ¹O₂ luminescence was employed to evaluate the ¹O₂ quenching abilities of natural antioxidants in air-statured phosphate buffered saline (PBS), including (-)-Epigallocatechin gallate (EGCG), Proanthocyanidins, L-carnosine and Vitamin C. The ¹O₂ quenching effects and rate constant of EGCG were investigated by detecting the absorption, fluorescence and ¹H-NMR spectroscopy and ¹O₂ luminescence decay curves, respectively. In addition, the protective activity of EGCG against ¹O₂ oxidative damage caused by Ce6-mediated photodynamic therapy (PDT) was verified in cells.

RESULTS

EGCG, proanthocyanidins, L-carnosine and Vitamin C efficiently quenched ¹O₂ luminescence at 1270 nm. The triplet-state quenching rate constants of EGCG for Rose Bengal (RB), Chlorin e6, AlPcS and HiPorfin are 2.21 × 10⁹, 4.90 × 10⁸, 3.30 × 10⁸, 1.78 × 10⁹ M^-1s^-1, while the ¹O₂ quenching rate constants are 2.80 × 10⁸, 1.50 × 10⁸, 1.30 × 10⁸, 1.70 × 10⁸ M^-1s^-1, respectively. Furthermore, EGCG could effectively quench ¹O₂ production to prevent NIH/3T3 cells oxidative damage induced by Ce6-mediated PDT.

CONCLUSIONS

EGCG is an efficient quencher for both triplet-state photosensitizers and ¹O₂. The quenching ability of EGCG during photosensitization for selected photosensitizers is: RB > HiPorfin > Ce6 > AlPcS. EGCG could be used to protect normal cells and tissue against oxidative damage.

Soil Acidobacteria Strain AB23 Resistance to Oxidative Stress Through Production of Carotenoids

Metagenomic studies revealed the prevalence of Acidobacteria in soils, but the physiological and ecological reasons for their success are not well understood. Many Acidobacteria exhibit carotenoid-related pigments, which may be involved in their tolerance of environmental stress. The aim of this work was to investigate the role of the orange pigments produced by Acidobacteria strain AB23 isolated from a savannah-like soil and to identify putative carotenoid genes in Acidobacteria genomes. Phylogenetic analysis revealed that strain AB23 belongs to the Occallatibacter genus from the class Acidobacteriia (subdivision 1). Strain AB23 produced carotenoids in the presence of light and vitamins; however, the growth rate and biomass decreased when cells were exposed to light. The presence of carotenoids resulted in tolerance to hydrogen peroxide. Comparative genomics revealed that all members of Acidobacteriia with available genomes possess the complete gene cluster for phytoene production. Some Acidobacteriia members have an additional gene cluster that may be involved in the production of colored carotenoids. Both colored and colorless carotenoids are involved in tolerance to oxidative stress. These results show that the presence of carotenoid genes is widespread among Acidobacteriia. Light and atmospheric oxygen stimulate carotenoid synthesis, but there are other natural sources of oxidative stress in soils. Tolerance to environmental oxidative stress provided by carotenoids may offer a competitive advantage for Acidobacteria in soils.

Bioengineered Skin Intended as In Vitro Model for Pharmacosmetics, Skin Disease Study and Environmental Skin Impact Analysis

This review aims to be an update of Bioengineered Artificial Skin Substitutes (BASS) applications. At the first moment, they were created as an attempt to replace native skin grafts transplantation. Nowadays, these in vitro models have been increasing and widening their application areas, becoming important tools for research. This study is focus on the ability to design in vitro BASS which have been demonstrated to be appropriate to develop new products in the cosmetic and pharmacology industry. Allowing to go deeper into the skin disease research, and to analyze the effects provoked by environmental stressful agents. The importance of BASS to replace animal experimentation is also highlighted. Furthermore, the BASS validation parameters approved by the OECD (Organisation for Economic Co-operation and Development) are also analyzed. This report presents an overview of the skin models applicable to skin research along with their design methods. Finally, the potential and limitations of the currently available BASS to supply the demands for disease modeling and pharmaceutical screening are discussed.

Biological effects of a new ultraviolet A1 prototype based on light-emitting diodes on the treatment of localized scleroderma

Ultraviolet A₁ (UVA₁ ) phototherapy (spectral range 340-400 nm) is a well-established treatment option for various skin diseases such as localized scleroderma. Recent improvements of conventional UVA₁ light sources (metal-halide or fluorescent lamps) have brought attention to a new light-emitting diode (LED) technology with remarkable advantages in handling and clinical routine. This study provides a preclinical histological and molecular evaluation of an LED-based UVA₁ prototype with a narrower spectral range (360-400 nm) for treating localized scleroderma. Scleroderma mouse models and fibroblasts in vitro were exposed to LED-based UVA₁ phototherapy or to irradiation with a commercially available metal-halide lamp emitting low-dose (20, 40 J/cm² ), medium-dose (60 J/cm² ) and high-dose (80, 100 J/cm² ) UVA₁ light. Both UVA₁ light sources affected inflammatory genes (IL-1α and IL-6) and growth factors (TGFß-1 and TGFß-2). Increased collagen type 1 was reduced after UVA₁ phototherapy. Matrix metalloproteinase-1 was more enhanced after a medium dose of LED-based UVA₁ phototherapy than after conventional treatment. In vivo, dermal thickness and the amount of collagen were reduced after both treatment methods. Remarkably, myofibroblasts were more effectively reduced by a medium dose of LED-based UVA₁ phototherapy. The study indicates that LED-based UVA₁ phototherapy yields similar or even better results than conventional treatment. In terms of biosafety and patient comfort, LED-based UVA₁ phototherapy offers clear advantages over conventional treatment because of the use of a narrower and less harmful UVA₁ spectrum, less heat generation and shorter treatment times at the same irradiation intensity. Clinical studies are required to confirm these results in patients with localized scleroderma.

From sunscreens to medicines: Can a dissipation hypothesis explain the beneficial aspects of many plant compounds?

Medicine has utilised plant‐based treatments for millennia, but precisely how they work is unclear. One approach is to use a thermodynamic viewpoint that life arose by dissipating geothermal and/or solar potential. Hence, the ability to dissipate energy to maintain homeostasis is a fundamental principle in all life, which can be viewed as an accretion system where layers of complexity have built upon core abiotic molecules. Many of these compounds are chromophoric and are now involved in multiple pathways. Plants have further evolved a plethora of chromophoric compounds that can not only act as sunscreens and redox modifiers, but also have now become integrated into a generalised stress adaptive system. This could be an extension of the dissipative process. In animals, many of these compounds are hormetic, modulating mitochondria and calcium signalling. They can also display anti‐pathogen effects. They could therefore modulate bioenergetics across all life due to the conserved electron transport chain and proton gradient. In this review paper, we focus on well‐described medicinal compounds, such as salicylic acid and cannabidiol and suggest, at least in animals, their activity reflects their evolved function in plants in relation to stress adaptation, which itself evolved to maintain dissipative homeostasis.

Nectandra cuspidata fraction and the isolated polyphenols protect fibroblasts and hairless mice skin from UVB-induced inflammation and oxidative stress

Excessive exposure to UVB radiation can lead to oxidative and inflammatory damage that compromises the cutaneous integrity. The application on the skin of photochemoprotective products is considered a relevant approach for the prevention of oxidative damage. In this study the in vitro and in vivo photochemoprotective effects of antioxidant plant materials obtained from the leaves of Nectandra cuspidata Nees following UVB irradiation were evaluated. The cytoprotective effect, reactive oxygen species (ROS) production and lipid peroxidation (LPO) were assessed in L-929 fibroblasts treated with the ethyl acetate fraction (EAF) or isolated compounds (epicatechin, isovitexin and vitexin) before or after irradiation with UVB (500 mJ/cm²). EAF substantially reduced the dead of cells and inhibited the UVB-induced ROS production and LPO in both treatments, compared with the irradiated untreated fibroblasts, presenting effects similar or better than pure compounds. The in vivo photochemoprotective effects of a topical emulsion containing 1% EAF (F2) were evaluated in hairless mice exposed to UVB. F2 improved all evaluated parameters in the skin of animals, inhibited ROS production, increased antioxidant defenses by decreasing reduced glutathione (GSH) and catalase depletion, reduced the activities of metalloproteinases (MMP-2 and MMP-9) and myeloperoxidase, decreased epidermal thickness and skin edema, and inhibited the appearance of sunburn cells as well as the recruitment of neutrophils and mast cell inflammatory infiltrates. These findings show that EAF presents high photochemoprotective effects, and that a topical formulation containing it may have potential for skin care.

Benzofuran hydrazones as potential scaffold in the development of multifunctional drugs: Synthesis and evaluation of antioxidant, photoprotective and antiproliferative activity

New benzofuranhydrazones 3-12 were easily prepared and assayed for their radical-scavenging ability. Hydrazones 3-12 showed different extent antioxidant activity in DPPH, FRAP and ORAC assays. Good antioxidant activity is related to the number and position of hydroxyl groups on the arylidene moiety. High antioxidant activity is showed by the 2-hydroxy-4-(diethylamino)benzylidene derivative 11. Furthermore, hydrazones 3-12 showed photoprotective capacities with satisfactory in vitro SPF as compared to the commercial PBSA sunscreen filter. The antiproliferative effects of the hydrazones 3-12 was tested on erythroleukemia K562 and Colo-38 melanoma human cells. All the compounds showed growth inhibition in the micromolar to sub micromolar concentration range. If taken together these results points to benzofuran hydrazones as potential multifunctional molecules especially in the treatment of neoplastic diseases being the good antioxidant properties of 5, 7 and 11 correlated to their high antiproliferative activity.

UVA, metabolism and melanoma: UVA makes melanoma hungry for metastasis

Ultraviolet (UV) radiation has a plethora of effects on human tissues. In the UV spectrum, wavelengths above 320 nm fall into the UVA range, and for these, it has been shown that they induce reactive oxygen species (ROS), DNA mutations and are capable to induce melanoma in mice. In addition to this, it was recently shown that UVA irradiation and UVA-induced ROS also increase glucose metabolism of melanoma cells. UVA irradiation causes a persistent increase in glucose consumption, accompanied by increased glycolysis, increased lactic acid production and activation of the pentose phosphate pathway. Furthermore, it was shown that the enhanced secretion of lactic acid is important for invasion of melanoma in vitro. The current knowledge of this link between UVA, metabolism and melanoma, possible mechanisms of UVA-induced glucose metabolism and their starting points are discussed in this review with focus on ROS- and UVA-induced cellular stress signalling, DNA damage signalling and DNA repair systems. When looking at the benefits of UVA-induced glucose metabolism, it becomes apparent that there are more advantages of these metabolic changes than one would expect. Besides the role of lactic acid as initiator of protease expression and invasion, its role for immune escape of melanoma cells and the pentose phosphate pathway-derived nicotinamide adenine dinucleotide phosphate (NADPH) as part of a ROS detoxification strategy are discussed.

Design, synthesis and biological evaluation of novel hydroxy-phenyl-1H-benzimidazoles as radical scavengers and UV-protective agents

An ever-increasing incidence of skin neoplastic diseases is registered. Therefore, it is important to protect the skin from the UV radiation that reaches the epidermis and dermis but also to block ROS generated by them. Our attention was attracted in developing new compounds provided with both UV filtering and antioxidant capacities. To this end, 2-phenyl-1H-benzimidazole-5-sulfonic acid (PBSA), a known UV filter, was selected as lead compound for its lack of antioxidant activity, high water solubility and good safety profile. PBSA was sequentially modified introducing hydroxyls on the phenyl ring and also substituting the functional group in position 5 of the benzimidazole ring. At the end of the synthetic study, a new, very potent class of antioxidants has been obtained. Surprisingly some of the developed molecules, while devoid of significant UV-filtering activity was endowed with potent UV-filtering booster capability if associated with known commercial UVB and UVA filters.

Endogenous Generation of Singlet Oxygen and Ozone in Human and Animal Tissues: Mechanisms, Biological Significance, and Influence of Dietary Components

Recent studies have shown that exposing antibodies or amino acids to singlet oxygen results in the formation of ozone (or an ozone-like oxidant) and hydrogen peroxide and that human neutrophils produce both singlet oxygen and ozone during bacterial killing. There is also mounting evidence that endogenous singlet oxygen production may be a common occurrence in cells through various mechanisms. Thus, the ozone-producing combination of singlet oxygen and amino acids might be a common cellular occurrence. This paper reviews the potential pathways of formation of singlet oxygen and ozone in vivo and also proposes some new pathways for singlet oxygen formation. Physiological consequences of the endogenous formation of these oxidants in human tissues are discussed, as well as examples of how dietary factors may promote or inhibit their generation and activity.

A quantitative structure–property relationship (QSPR) study of singlet oxygen generation by pteridines

Singlet oxygen production quantum yields of pteridine photosensitizers were analyzed with the QSPR method. The ability of pterins and flavins to generate¹O₂in D₂O correlated withE_HOMOand electronegativity, as well as with the dipole moment and some other parameters.

Singlet Oxygen-Mediated Oxidation during UVA Radiation Alters the Dynamic of Genomic DNA Replication

UVA radiation (320–400 nm) is a major environmental agent that can exert its deleterious action on living organisms through absorption of the UVA photons by endogenous or exogenous photosensitizers. This leads to the production of reactive oxygen species (ROS), such as singlet oxygen (¹O₂) and hydrogen peroxide (H₂O₂), which in turn can modify reversibly or irreversibly biomolecules, such as lipids, proteins and nucleic acids. We have previously reported that UVA-induced ROS strongly inhibit DNA replication in a dose-dependent manner, but independently of the cell cycle checkpoints activation. Here, we report that the production of ¹O₂ by UVA radiation leads to a transient inhibition of replication fork velocity, a transient decrease in the dNTP pool, a quickly reversible GSH-dependent oxidation of the RRM1 subunit of ribonucleotide reductase and sustained inhibition of origin firing. The time of recovery post irradiation for each of these events can last from few minutes (reduction of oxidized RRM1) to several hours (replication fork velocity and origin firing). The quenching of ¹O₂ by sodium azide prevents the delay of DNA replication, the decrease in the dNTP pool and the oxidation of RRM1, while inhibition of Chk1 does not prevent the inhibition of origin firing. Although the molecular mechanism remains elusive, our data demonstrate that the dynamic of replication is altered by UVA photosensitization of vitamins via the production of singlet oxygen.

Fast and effective inactivation of Bacillus atrophaeus endospores using light-activated derivatives of vitamin B2

Highly resistant endospores may cause severe problems in medicine as well as in the food and packaging industries. We found that bacterial endospores can be inactivated quickly with reactive oxygen species (ROS) that were generated by a new generation of flavin photosensitizers. Flavins like the natural compound vitamin B2 are already known to produce ROS but they show a poor antimicrobial photodynamic killing efficacy due to the lack of positive charges. Therefore we synthesized new flavin photosensitizers that have one (FLASH-01a) or eight (FLASH-07a) positive charges and can hence attach to the negatively charged surface of endospores. In this study we used standardized Bacillus atrophaeus endospores (ATCC 9372) as a biological surrogate model for a proof-of-concept study of photodynamic inactivation experiments using FLASH-01a and FLASH-07a. After incubation of spores with different flavin concentrations, the flavin derivatives were excited with blue light at a light dose of 70 J cm(-2). The inactivation of spores was investigated either in suspension or after attachment to polyethylene terephthalate (PET) surfaces. Incubation of spores suspended in Millipore water with 4 mM FLASH-01a for 10 seconds and irradiation with blue light for 10 seconds caused a biologically relevant decrease of spore survival of 3.5 log10 orders. Using FLASH-07a under the same conditions we achieved a decrease of 4.4 log10 orders. Immobilized spores on PET surfaces were efficiently killed with 7.0 log10 orders using 8 mM FLASH-07a. The total treatment time (incubation + irradiation) was as short as 20 seconds. The results of this study show evidence that endospores can be fastly and effectively inactivated with new generations of flavin photosensitizers that may be useful for industrial or medical applications in the future.

An essential role of NAD(P)H oxidase 2 in UVA-induced calcium oscillations in mast cells

Solar UVA radiation (320-400 nm) is known to have immunomodulatory effects, but the detailed mechanisms involved are not fully elucidated. UVA irradiation has been shown to induce calcium oscillations in rat peritoneal mast cells due to NAD(P)H oxidase (NOX) activation, but the specific NOX isoforms have not been identified. In the present work effects of UVA irradiation were investigated in isolated rat peritoneal mast cells, in cultured rat mast cell line RBL-2H3, and in mouse bone marrow-derived mast cells (BMMC). It was found that UVA irradiation by alternate 340/380 nm (3.2-5.6 μW cm(-2)) or by LED (380 nm, 80 μW cm(-2)) induced calcium oscillations in isolated rat peritoneal mast cells, in RBL-2H3, and in BMMC. Such UVA-induced calcium oscillations resembled closely those induced by surface IgE receptor (FcεRI) activation. It was found that RBL-2H3 expressed high levels of gp91(phox) (NOX2), p22(phox), p67(phox), p47(phox), p40(phox), Rac1, Rac2, moderate levels of DUOX2, but did not express NOX1, NOX3, NOX4, or DUOX1. The specific cellular localizations of gp91(phox) (NOX2), p22(phox), p47(phox), p67(phox), p40(phox) and Rac1/2 were confirmed by immunocytochemistry. UVA-induced reactive oxygen species (ROS) production in RBL-2H3 was completely suppressed by the NOX inhibitor diphenyleneiodonium chloride (DPI) or by the antioxidant N-acetyl-l-cysteine (NAC). siRNA suppression of gp91(phox) (NOX2), p22(phox) and p47(phox) expression inhibited markedly UVA-induced calcium oscillations, ROS and IL-6/LTC4 production in RBL-2H3. Taken together these data indicate that NOX2 plays an essential role in UVA irradiation-induced calcium oscillations, ROS and mediator production in mast cells.