Time-Resolved Investigations of Singlet Oxygen Luminescence in Water, in Phosphatidylcholine, and in Aqueous Suspensions of Phosphatidylcholine or HT29 Cells

Singlet oxygen-induced alteration of bacteria associated with phytodetritus: Effect of irradiance

Contrasting irradiation of senescent cells of the diatom Thalassiosira sp. in association with the bacterium Pseudomonas stutzeri showed the effect of intensity of irradiance on the transfer of singlet oxygen (1 O2 ) to bacteria attached to phytoplanktonic cells. Under low irradiances, 1 O2 is produced slowly, favors the oxidation of algal unsaturated lipids (photodynamic effect), and limits 1 O2 transfer to attached bacteria. However, high irradiances induce a rapid and intense production of 1 O2 , which diffuses out of the chloroplasts and easily reaches the attached bacteria, where it efficiently oxidizes their unsaturated membrane components. Analysis of numerous sinking particle samples collected in different regions of the Canadian Arctic showed that the photooxidation state of attached bacteria increased from ice-covered areas to open water, in agreement with in vitro results. Photooxidation of bacteria appeared to be particularly intense in sea ice, where the sympagic algae-bacteria association is maintained at relatively high irradiances for long periods of time.

Flexible Modulation of Cellular Activities with Cationic Photosensitizers: Insights of Alkyl Chain Length on Reactive Oxygen Species Antimicrobial Mechanisms

Cationic photosensitizers have good binding ability with negatively charged bacteria and fungi, exhibiting broad applications potential in antimicrobial photodynamic therapy (aPDT). However, cationic photosensitizers often display unsatisfactory transkingdom selectivity between mammalian cells and pathogens, especially for eukaryotic fungi. It is unclear which biomolecular sites are more efficient for photodynamic damage, owing to the lack of systematic research with the same photosensitizer system. Herein, a series of cationic aggregation-induced emission (AIE) derivatives (CABs) (using berberine (BBR) as the photosensitizers core) with different length alkyl chains are successfully designed and synthesized for flexible modulation of cellular activities. The BBR core can efficiently produce reactive oxygen species (ROS) and achieve high-performance aPDT . Through the precise regulation of alkyl chain length, different bindings, localizations, and photodynamic killing effects of CABs are achieved and investigated systematically among bacteria, fungi, and mammalian cells. It is found that intracellular active substances, not membranes, are more efficient damage sites of aPDT. Moderate length alkyl chains enable CABs to effectively kill Gram-negative bacteria and fungi with light, while still maintaining excellent mammalian cell and blood compatibility. This study is expected to provide systematic theoretical and strategic research guidance for the construction of high-performance cationic photosensitizers with good transkingdom selectivity.

Dynamic photodamage of red blood cell induced by CisDiMPyP porphyrin

It is well-known that oxidative damage in red blood cell (RBC) usually causes morphological changes and increased membrane rigidity. Although many studies have focused on investigating how RBC responds to a photodynamic stimulus, the intermediate steps between membrane damage and hemolysis are not reported. To give a comprehensive insight into changes of RBC membrane property under different oxidative damage levels, we employed the photoactivation of CisDiMPyP porphyrin that primarily generates singlet oxygen ¹O₂ as oxidant species. We found that there were distinguishable characteristic damages depending on the ¹O₂ flux over the membrane, in a way that each impact of photooxidative damage was categorized under three damage levels: mild (maintaining the membrane morphology and elasticity), moderate (membrane elongation and increased membrane elasticity) and severe (wrinkle-like deformation and hemolysis). When sodium azide (NaN₃) was used as a singlet oxygen quencher, delayed cell membrane alterations and hemolysis were detected. The delay times showed that ¹O₂ indeed plays a key role that causes RBC photooxidation by CisDiMPyP. We suggest that the sequence of morphological changes (RBC discoid area expansion, wrinkle-like patterns, and hemolysis) under photooxidative damage occurs due to damage to the lipid membrane and cytoskeletal network proteins.

Curcumin-loaded multifunctional chitosan gold nanoparticles: An enhanced PDT/PTT dual-modal phototherapeutic and pH-responsive antimicrobial agent

Overuse of antibiotics has led to the emergence of multidrug resistant (MDR) bacteria.. Photothermal (PTT) and photodynamic therapy (PDT) have may be effective alternatives for antibiotics in the treatment of bacterial infections. In this study, based on chitosan (CS)-coated gold nanoparticles, a pH stimulus-responsive drug delivery system was developed, which can anchor to the cell membrane for photodynamic therapy and photothermal therapy, and enhance the therapeutic potential of curcumin (Cur). Release experiments showed that AuNPs/CS-Cur nanocomposites released curcumin in a pH-dependent manner, which may facilitate the drug to be delivered to the acidic bacterial infection environment. CS as the outer layer covered on gold nanoparticles could improve the dispersibility of Cur in aqueous solution, gold nanoparticles prevent rapid photobleaching of curcumin, thus ensuring the yield of singlet oxygen under irradiation, and enhance the electrostatic binding with bacteria cell membrane. Under light conditions, AuNPs/CS-Cur can produce a large amount of reactive oxygen species and heat to kill S. aureus and E. coli. Compared with free Cur-mediated PDT, the complex significantly improved the synergistic PTT/PDT photoinactivation ability against S. aureus and E. coli. In addition, AuNPs/CS-Cur had good biocompatibility. Therefore, AuNPs/CS-Cur possessed the characteristics of electrostatic targeting, photodynamic and photothermal antibacterial therapy, which would become an efficient and safe antibacterial nano-platform and provide new ideas for the treatment of bacterial infection.

Photodynamic Methylene Blue-Embedded Intragastric Satiety-Inducing Device to Treat Obesity

Bariatric surgery is the most effective treatment for weight recidivism, and endoscopic bariatric treatment has been developed for a similar effect without anatomical modification. An intragastric satiety-inducing device (ISD) is a minimally invasive approach to induce satiety by continuously pressing the stomach and stimulating ghrelin-producing cells. To enhance the therapeutic effects of ISD, photodynamic therapy (PDT) can be combined by generating singlet oxygen under laser irradiation. Methylene blue (MB), as a photosensitizer (PS), was coated on the ISD surface for singlet oxygen production to stimulate or destroy cells. Ghrelin-producing cells effectively inhibited ghrelin secretion and induced gastrointestinal satiety signals compared with the MB-uncoated device via PDT. Herein, MB-embedded ISDs were developed, and their photoresponsive abilities were demonstrated in the device itself and in vitro. PDT with an MB-embedded ISD was successfully performed in a porcine model, which had 2-fold reduced body weight gain (12% in PDT vs 24% in control) and 2-fold reduced ghrelin levels (21.2 pg/mL in PDT vs 45.1 pg/mL in control) at the first week postprocedure. The simple and unique operation extends the point of view in PDT and is expected to be a novel endoscopic bariatric therapy.

Mn2O3 as an Electron Shuttle between Peroxymonosulfate and Organic Pollutants: The Dominant Role of Surface Reactive Mn(IV) Species

The environmentally benign Mn oxides play a crucial role in the transformation of organic contaminants, either through catalytically decomposing oxidants, e.g., peroxymonosulfate (PMS), or through directly oxidizing the target pollutants. Because of their dual roles and the complex surface chemical reactions, the mechanism involved in Mn oxide-catalyzed PMS activation processes remains obscure. Here, we clearly elucidate the mechanism involved in the Mn₂O₃ catalyzed PMS activation process by means of separating the PMS activation and the pollutant oxidation process. Mn₂O₃ acts as a shuttle that mediates the electron transfer from organic substrates to PMS, accompanied by the redox cycle of surface Mn(IV)/Mn(III). Multiple experimental results indicate that PMS is bound to the surface of Mn₂O₃ to form an inner-sphere complex, which then decomposes to form long-lived surface reactive Mn(IV) species, without the generation of sulfate radicals (SO₄^•-) and hydroxyl radicals (HO^•). The surface reactive Mn(IV) species are proposed to be responsible for the degradation of organic contaminants (e.g., phenol) and the formation of singlet oxygen (¹O₂), followed by the regeneration of the surface Mn(III) sites on Mn₂O₃. This study advances the fundamental understanding of the underlying mechanism involved in transition metal oxide-catalyzed PMS activation processes.

Photo-Oxidation of Therapeutic Protein Formulations: From Radical Formation to Analytical Techniques

UV and ambient light-induced modifications and related degradation of therapeutic proteins are observed during manufacturing and storage. Therefore, to ensure product quality, protein formulations need to be analyzed with respect to photo-degradation processes and eventually protected from light exposure. This task usually demands the application and combination of various analytical methods. This review addresses analytical aspects of investigating photo-oxidation products and related mediators such as reactive oxygen species generated via UV and ambient light with well-established and novel techniques.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

Photosensitizers Mediated Photodynamic Inactivation against Fungi

Superficial and systemic fungal infections are essential problems for the modern health care system. One of the challenges is the growing resistance of fungi to classic antifungals and the constantly increasing cost of therapy. These factors force the scientific world to intensify the search for alternative and more effective methods of treatment. This paper presents an overview of new fungal inactivation methods using Photodynamic Antimicrobial Chemotherapy (PACT). The results of research on compounds from the groups of phenothiazines, xanthanes, porphyrins, chlorins, porphyrazines, and phthalocyanines are presented. An intensive search for a photosensitizer with excellent properties is currently underway. The formulation based on the existing ones is also developed by combining them with nanoparticles and common antifungal therapy. Numerous studies indicate that fungi do not form any specific defense mechanism against PACT, which deems it a promising therapeutic alternative.

Stimuli-Responsive Nanoplatform-Assisted Photodynamic Therapy Against Bacterial Infections

Bacterial infections are common diseases causing tremendous deaths in clinical settings. It has been a big challenge to human beings because of the antibiotics abuse and the newly emerging microbes. Photodynamic therapy (PDT) is a reactive oxygen species-based therapeutic technique through light-activated photosensitizer (PS). Recent studies have highlighted the potential of PDT as an alternative method of antibacterial treatment for its broad applicability and high efficiency. However, there are some shortcomings due to the low selectivity and specificity of PS. Growing evidence has shown that drug delivery nanoplatforms have unique advantages in enhancing therapeutic efficacy of drugs. Particularly, stimuli-responsive nanoplatforms, as a promising delivery system, provide great opportunities for the effective delivery of PS. In the present mini-review, we briefly introduced the unique microenvironment in bacterial infection tissues and the application of PDT on bacterial infections. Then we review the stimuli-responsive nanoplatforms (including pH-, enzymes-, redox-, magnetic-, and electric-) used in PDT against bacterial infections. Lastly, some perspectives have also been proposed to further promote the future developments of antibacterial PDT.

Antimicrobial photodynamic therapy (aPDT) for biofilm treatments. Possible synergy between aPDT and pulsed electric fields

Currently, microbial biofilms have been the cause of a wide variety of infections in the human body, reaching 80% of all bacterial and fungal infections. The biofilms present specific properties that increase the resistance to antimicrobial treatments. Thus, the development of new approaches is urgent, and antimicrobial photodynamic therapy (aPDT) has been shown as a promising candidate. aPDT involves a synergic association of a photosensitizer (PS), molecular oxygen and visible light, producing highly reactive oxygen species (ROS) that cause the oxidation of several cellular components. This therapy attacks many components of the biofilm, including proteins, lipids, and nucleic acids present within the biofilm matrix; causing inhibition even in the cells that are inside the extracellular polymeric substance (EPS). Recent advances in designing new PSs to increase the production of ROS and the combination of aPDT with other therapies, especially pulsed electric fields (PEF), have contributed to enhanced biofilm inhibition. The PEF has proven to have antimicrobial effect once it is known that extensive chemical reactions occur when electric fields are applied. This type of treatment kills microorganisms not only due to membrane rupture but also due to the formation of reactive compounds including free oxygen, hydrogen, hydroxyl and hydroperoxyl radicals. So, this review aims to show the progress of aPDT and PEF against the biofilms, suggesting that the association of both methods can potentiate their effects and overcome biofilm infections.

An insight into the bioelectrochemical photoreduction of CO2 to value-added chemicals

Goal of sustainable carbon neutral economy can be achieved by designing an efficient CO₂ reduction system to generate biofuels, in particular, by mimicking the mechanism of natural photosynthesis using semiconducting nanomaterials interfaced with electroactive bacteria (EAB) in a photosynthetic microbial electrosynthesis (PMES) system. This review paper presents an overview of the recent advancements in the biohybrid photoanode and photocathode materials. We discuss the reaction mechanism observed at photoanode and photocathode to enhance our understanding on the solar driven MES. We extend the discussion by showcasing the potential activity of EABs toward high selectivity and production rates for desirable products by manipulating their genomic sequence. Additionally, the critical challenges associated in scaling up the PMES system including the strategies for diminution of reactive oxygen species, low solubility of CO₂ in the typical electrolytes, low selectivity of product species are presented along with the suggestions of alternative strategies to achieve economically viable generation of (bio)commodities.

Singlet Oxygen in Plants: Generation, Detection, and Signaling Roles

Singlet oxygen (1O2) refers to the lowest excited electronic state of molecular oxygen. It easily oxidizes biological molecules and, therefore, is cytotoxic. In plant cells, 1O2 is formed mostly in the light in thylakoid membranes by reaction centers of photosystem II. In high concentrations, 1O2 destroys membranes, proteins and DNA, inhibits protein synthesis in chloroplasts leading to photoinhibition of photosynthesis, and can result in cell death. However, 1O2 also acts as a signal relaying information from chloroplasts to the nucleus, regulating expression of nuclear genes. In spite of its extremely short lifetime, 1O2 can diffuse from the chloroplasts into the cytoplasm and the apoplast. As shown by recent studies, 1O2-activated signaling pathways depend not only on the levels but also on the sites of 1O2 production in chloroplasts, and can activate two types of responses, either acclimation to high light or programmed cell death. 1O2 can be produced in high amounts also in root cells during drought stress. This review summarizes recent advances in research on mechanisms and sites of 1O2 generation in plants, on 1O2-activated pathways of retrograde- and cellular signaling, and on the methods to study 1O2 production in plants.

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.

Excitation of Fluorescent Lipid Probes Accelerates Supported Lipid Bilayer Formation via Photosensitized Lipid Oxidation

Fluorescent lipid probes are commonly used to label membranes of cells and model membranes like giant vesicles, liposomes, and supported lipid bilayers (SLB). Here, we show that excitation of fluorescent lipid probes with BODIPY-like conjugates results in a significant acceleration of the rupture and SLB formation process for unsaturated phospholipid vesicles on SiO₂ surfaces. The resulting SLBs also have smaller measured masses, which is indicative of a reduction in membrane thickness and/or membrane density. The excitation of fluorescent probes with NBD and Texas Red conjugates does not accelerate the SLB formation process. In the absence of fluorescent probes or light, the inclusion of oxidized phospholipids also accelerates SLB formation. The excitation-induced acceleration caused by BODIPY-like probes is eliminated when the probes are present with saturated phospholipids not susceptible to oxidation, and it is attenuated when a lipophilic antioxidant (α-tocopherol) is present. These results suggest that BODIPY-phospholipid conjugates are photosensitizers, and their excitation causes oxidation of lipid membranes, which significantly alters membrane properties.

Oxygen distribution in the fluid/gel phases of lipid membranes

The interactions between oxygen and lipid membranes play fundamental roles in basic biological processes (e.g., cellular respiration). Obviously, membrane oxidation is expected to be critically dependent on the distribution and concentration of oxygen in the membrane. Here, we combined theoretical and experimental methods to investigate oxygen partition and distribution in lipid membranes of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a temperature range between 298 and 323 K, specifically focusing on the changes caused by the lipid phase and phase transition. Even though oxygen is known to be more concentrated in the center of fluid phase membranes than on the headgroup regions, the distribution profile of oxygen inside gel-phase bilayers remained to be determined. Molecular dynamics simulations now show that the distribution of oxygen inside DPPC bilayers dramatically changes upon crossing the main transition temperature, with oxygen being nearly depleted halfway from the headgroups to the membrane center below the transition temperature. In a parallel approach, singlet oxygen luminescence emission measurements employing the photosensitizer Pheophorbide-a (Pheo) confirmed the differences in oxygen distribution and concentration profiles between gel- and fluid-phase membranes, revealing changes in the microenvironment of the embedded photosensitizer. Our results also reveal that excited triplet state lifetime, as it can be determined from the singlet oxygen luminescence kinetics, is a useful probe to assess oxygen distribution in lipid membranes with distinct lipid compositions.

Singlet oxygen phosphorescence detection in vivo identifies PDT-induced anoxia in solid tumors

Extracorporeal measurements through the skin achieve sufficient SNR to analyze ¹O₂ kinetics and evaluate PDT efficiency.

Singlet oxygen partition between the outer-, inner- and membrane-phases of photo/chemotherapeutic liposomes

Herein, we developed a strategy to quantify the fraction of singlet oxygen lifetime spent in the three distinct local liposomal environments through the combination of direct and indirect singlet oxygen detection approaches.

Cell Death Mechanisms Induced by Photo-Oxidation Studied at the Cell Scale in the Yeast Saccharomyces cerevisiae

Blue light (400–430 nm) is known to induce lethal effects in some species of fungi by photo-oxidation caused by the excitation of porphyrins but the mechanisms involved remain poorly understood. In this work, we exposed the yeast Saccharomyces cerevisiae to a high density light flux with two-photon excitation (830 nm equivalent to a one-photon excitation around 415 nm) and used quasi real-time visualization with confocal microscopy to study the initiation and dynamics of photo-oxidation in subcellular structures. Our results show that the oxidation generated by light treatments led to the permeabilization of the plasma membrane accompanied by the sudden expulsion of the cellular content, corresponding to cell death by necrosis. Moreover, excitation in the plasma membrane led to very fast oxidation and membrane permeabilization (<60 s) while excitation at the center of the cell did not induce permeabilization even after a period exceeding 600 s. Finally, our study shows that the relationship between the laser power used for two-photon excitation and the time required to permeabilize the plasma membrane was not linear. Thus, the higher the power used, the lower the energy required to permeabilize the plasma membrane. We conclude that fungal destruction can be generated very quickly using a high density light flux. Better knowledge of the intracellular processes and the conditions necessary to induce necrosis should make it possible in the future to improve the efficiency of antimicrobial strategies photo-oxidation-based.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Multifunctional Electrospun Nanofibers for Enhancing Localized Cancer Treatment

Localized cancer treatment is one of the most effective strategies in clinical destruction of solid tumors at early stages as it can minimize the side effects of cancer therapeutics. Electrospun nanofibers have been demonstrated as a promising implantable platform in localized cancer treatment, enabling the on-site delivery of therapeutic components and minimizing side effects to normal tissues. This Review discusses the recent cutting-edge research with regard to electrospun nanofibers used for various therapeutic approaches, including gene therapy, chemotherapy, photodynamic therapy, thermal therapy, and combination therapy, in enhancing localized cancer treatment. Furthermore, it extensively analyzes the current challenges and potential breakthroughs in utilizing this novel platform for clinical transition in localized cancer treatment.

Antimicrobial photodynamic therapy - what we know and what we don't

Considering increasing number of pathogens resistant towards commonly used antibiotics as well as antiseptics, there is a pressing need for antimicrobial approaches that are capable of inactivating pathogens efficiently without the risk of inducing resistances. In this regard, an alternative approach is the antimicrobial photodynamic therapy (aPDT). The antimicrobial effect of aPDT is based on the principle that visible light activates a per se non-toxic molecule, the so-called photosensitizer (PS), resulting in generation of reactive oxygen species that kill bacteria unselectively via an oxidative burst. During the last 10-20 years, there has been extensive in vitro research on novel PS as well as light sources, which is now to be translated into clinics. In this review, we aim to provide an overview about the history of aPDT, its fundamental photochemical and photophysical mechanisms as well as photosensitizers and light sources that are currently applied for aPDT in vitro. Furthermore, the potential of resistances towards aPDT is extensively discussed and implications for proper comparison of in vitro studies regarding aPDT as well as for potential application fields in clinical practice are given. Overall, this review shall provide an outlook on future research directions needed for successful translation of promising in vitro results in aPDT towards clinical practice.

Electropermeabilization by uni- or bipolar nanosecond electric pulses: The impact of extracellular conductivity

Cellular effects caused by nanosecond electric pulses (nsEP) can be reduced by an electric field reversal, a phenomenon known as bipolar cancellation. The reason for this cancellation effect remains unknown. We hypothesized that assisted membrane discharge is the mechanism for bipolar cancellation. CHO-K1 cells bathed in high (16.1mS/cm; HCS) or low (1.8mS/cm; LCS) conductivity solutions were exposed to either one unipolar (300-ns) or two opposite polarity (300+300-ns; bipolar) nsEP (4-40kV/cm) with increasing interpulse intervals (0.1-50μs). Time-lapse YO-PRO-1 (YP) uptake revealed enhanced membrane permeabilization in LCS compared to HCS at all tested voltages. The time-dependence of bipolar cancellation was similar in both solutions, using either identical (22kV/cm) or isoeffective nsEP treatments (12 and 32kV/cm for LCS and HCS, respectively). However, cancellation was significantly stronger in LCS when the bipolar nsEP had no, or very short (<1μs), interpulse intervals. Finally, bipolar cancellation was still present with interpulse intervals as long as 50μs, beyond the time expected for membrane discharge. Our findings do not support assisted membrane discharge as the mechanism for bipolar cancellation. Instead they exemplify the sustained action of nsEP that can be reversed long after the initial stimulus.

Singlet oxygen feedback delayed fluorescence of protoporphyrin IX in organic solutions

The PpIX DF show the significant role of SOFDF mechanism at high concentrations and at atmospheric partial pressure of oxygen and should be considered when developing diagnostic tools for clinical applications.

HER2-HER3 dimer quantification by FLIM-FRET predicts breast cancer metastatic relapse independently of HER2 IHC status

Overexpression of HER2 is an important prognostic marker, and the only predictive biomarker of response to HER2-targeted therapies in invasive breast cancer. HER2-HER3 dimer has been shown to drive proliferation and tumor progression, and targeting of this dimer with pertuzumab alongside chemotherapy and trastuzumab, has shown significant clinical utility. The purpose of this study was to accurately quantify HER2-HER3 dimerisation in formalin fixed paraffin embedded (FFPE) breast cancer tissue as a novel prognostic biomarker.FFPE tissues were obtained from patients included in the METABRIC (Molecular Taxonomy of Breast Cancer International Consortium) study. HER2-HER3 dimerisation was quantified using an improved fluorescence lifetime imaging microscopy (FLIM) histology-based analysis. Analysis of 131 tissue microarray cores demonstrated that the extent of HER2-HER3 dimer formation as measured by Förster Resonance Energy Transfer (FRET) determined through FLIM predicts the likelihood of metastatic relapse up to 10 years after surgery (hazard ratio 3.91 (1.61-9.5), p = 0.003) independently of HER2 expression, in a multivariate model. Interestingly there was no correlation between the level of HER2 protein expressed and HER2-HER3 heterodimer formation. We used a mathematical model that takes into account the complex interactions in a network of all four HER proteins to explain this counterintuitive finding.Future utility of this technique may highlight a group of patients who do not overexpress HER2 protein but are nevertheless dependent on the HER2-HER3 heterodimer as driver of proliferation. This assay could, if validated in a group of patients treated with, for instance pertuzumab, be used as a predictive biomarker to predict for response to such targeted therapies.

Synthesis and characterization of photodynamic activity of an iodinated Chlorin p6copper complex

A novel iodinated copper complex of Chlorinp₆that acts as type I photosensitizer and capable of inducing phototoxicity in cancer cells under hypoxia.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.

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.

Singlet oxygen luminescence kinetics in a heterogeneous environment – identification of the photosensitizer localization in small unilamellar vesicles

Singlet oxygen luminescence kinetics in microheterogeneous environment reflect the localization of the photosensitizer.

Spectroscopic investigation on sonodynamic and sonocatalytic damage of BSA molecules by Thymol Blue (TB) derivants under ultrasonic irradiation

In this paper, the Thymol Blue derivants including Thymol Blue (thymolsulfonphthalein), Thymol Blue-DA (3,3'-Bis [N,N-bis (carboxymethyl) aminomethyl] thymolsulfonphthalein) and Thymol Blue-DA-Fe(III) (3,3'-Bis [N,N-bis (carboxymethyl) aminomethyl] thymolsulfonphthalein-Ferrous(III)) were adopted as sonosensitizers to study the sonodynamic and sonocatalytic activities under ultrasonic irradiation. At first, the interaction of Thymol Blue derivants with bovine serum albumin (BSA) was studied by fluorescence spectroscopy. On that basis, the sonodynamic and sonocatalytic damages of Thymol Blue derivants to BSA under ultrasonic irradiation were investigated by the combination of UV-vis, circular dichroism (CD) and fluorescence spectroscopy. Meanwhile, some influenced factors (ultrasonic irradiation time, Thymol Blue derivants concentration and ionic strength) on the damaging degree of BSA molecules were also reviewed. In addition, synchronous fluorescence spectra were used to estimate the binding and damage sites of Thymol Blue derivants to BSA. Finally, the generation of ROS during sonodynamic and sonocatalytic processes was confirmed by the method of Oxidation-Extraction Spectrometry (OEP). Perhaps, this paper may offer some important subjects for the study of Thymol Blue derivants in sonodynamic therapy (SDT) and sonocatalytic therapy (SCT) technologies for tumor treatment and the effect of the amino acid and central metal.

Reactive oxygen species: re-evaluation of generation, monitoring and role in stress-signaling in phototrophic organisms

This review provides an overview about recent developments and current knowledge about monitoring, generation and the functional role of reactive oxygen species (ROS) - H2O2, HO2, HO, OH(-), (1)O2 and O2(-) - in both oxidative degradation and signal transduction in photosynthetic organisms including microscopic techniques for ROS detection and controlled generation. Reaction schemes elucidating formation, decay and signaling of ROS in cyanobacteria as well as from chloroplasts to the nuclear genome in eukaryotes during exposure of oxygen-evolving photosynthetic organisms to oxidative stress are discussed that target the rapidly growing field of regulatory effects of ROS on nuclear gene expression.

Functional roles of flavonoids in photoprotection: new evidence, lessons from the past

We discuss on the relative significance of different functional roles potentially served by flavonoids in photoprotection, with special emphasis to their ability to scavenge reactive oxygen species (ROS) and control the development of individual organs and whole plant. We propose a model in which chloroplast-located flavonoids scavenge H2O2 and singlet oxygen generated under excess light-stress, thus avoiding programmed cell death. We also draw a picture in which vacuolar flavonoids in conjunction with peroxidases and ascorbic acid constitute a secondary antioxidant system aimed at detoxifying H2O2, which may diffuse out of the chloroplast at considerable rates and enter the vacuole following excess light stress-induced depletion of ascorbate peroxidase. We hypothesize for flavonols key roles as developmental regulators in early and current-day land-plants, based on their ability to modulate auxin movement and auxin catabolism. We show that antioxidant flavonoids display the greatest capacity to regulate key steps of cell growth and differentiation in eukaryotes. These regulatory functions of flavonoids, which are shared by plants and animals, are fully accomplished in the nM concentration range, as likely occurred in early land plants. We therefore conclude that functions of flavonoids as antioxidants and/or developmental regulators flavonoids are of great value in photoprotection. We also suggest that UV-B screening was just one of the multiple functions served by flavonoids when early land-plants faced an abrupt increase in sunlight irradiance.

On the mechanism of Candida spp. photoinactivation by hypericin

The photoprocesses involved in hypericin photoinactivation of three different Candida species (C. albicans, C. parapsilosis and C. krusei) have been examined. Production of singlet oxygen from the triplet state and of superoxide from both the triplet state and the semiquinone radical anion are demonstrated. Hydrogen peroxide is formed downstream of these early events. The outcome of the photodynamic treatments is dictated by the intracellular distribution of hypericin, which is different in the three species and affects the ability of hypericin to produce the different reactive oxygen species and trigger cell-death pathways. The results are in line with the previously-observed different susceptibilities of the three Candida species to hypericin photodynamic treatments.

Temporal profile of the singlet oxygen emission endogenously produced by photosystem II reaction centre in an aqueous buffer

The temporal profile of the phosphorescence of singlet oxygen endogenously photosensitized by photosystem II (PSII) reaction centre (RC) in an aqueous buffer has been recorded using laser excitation and a near infrared photomultiplier tube. A weak emission signal was discernible, and could be fitted to the functional form a[exp(-t/τ(2) - exp(-t/τ(1)], with a > 0 and τ(2) > τ(1). The value of τ(2) decreased from 11.6 ± 0.5 μs under aerobic conditions to 4.1 ± 0.2 μs in oxygen-saturated samples, due to enhanced bimolecular quenching of the donor triplet by oxygen, whereas that of τ(1), identifiable with the lifetime of singlet oxygen, was close to 3 μs in both cases. Extrapolations based on the low amplitude of the emission signal of singlet oxygen formed by PSII RC in the aqueous buffer and the expected values of τ(1) and τ(2) in chloroplasts indicate that attempts to analyse the temporal profile of singlet oxygen in chloroplasts are unlikely to be rewarded with success without a significant advance in the sensitivity of the detection equipment.

Light-induced TPP photoproduct formation in chloroform and protective role of lipids

In this contribution, the influence of lipids on excitation energy transfer from lipophilic photosensitizer tetraphenylporphyrin to oxygen was investigated in chloroform solutions of phosphatidylcholine as well as in bulk lipid. The excited states kinetics were examined in a wide range of lipid concentrations (from zero to the saturated concentration) by direct time- and spectral-resolved detection of weak near infrared phosphorescence of the photosensitizer (around 840 nm) and singlet oxygen (about 1278 nm). While photosensitizer triplet kinetics follows single-exponential decay with lifetime of 0.52 μs in pure chloroform, two distinct components with lifetimes of approximately 0.4 and 1 μs appear after phosphatidylcholine addition. Both the lifetimes exhibit shortening tendency with increasing lipid concentration. Relative weights of the two components depend on the lipid concentration. Singlet oxygen kinetics exhibit single-exponential rise with lifetimes roughly corresponding to the shorter components of photosensitizer decays while their decays require two exponentials. The lifetime of the longer component decreases with increasing concentration of lipid from (77.6 ± 1.3) μ s at pure chloroform to (14.3 ± 1.1) μ s at the saturated lipid concentration. The time-constants obtained in bulk lipid sample follow the above-mentioned trends. Tetraphenylporphyrin photoproduct formation under pulsed excitation in chloroform solutions was demonstrated. The quantum yield of singlet oxygen production of the photoproduct is lower than that of the tetraphenylporphyrin. It was shown that lipids prevent the singlet-oxygen mediated formation of TPP photoproduct, probably by efficient quenching of singlet oxygen. This quenching is justified by shortening of the longer component of singlet oxygen luminescence decays with increasing concentration of the lipid. Moreover, the lipids also quench triplet states of the photosensitizer.

Irradiation- and sensitizer-dependent changes in the lifetime of intracellular singlet oxygen produced in a photosensitized process

Singlet oxygen, O(2)(a(1)Δ(g)), was produced upon pulsed-laser irradiation of an intracellular photosensitizer and detected by its 1275 nm O(2)(a(1)Δ(g)) → O(2)(X(3)Σ(g)(-)) phosphorescence in time-resolved experiments using (1) individual mammalian cells on the stage of a microscope and (2) suspensions of mammalian cells in a 1 cm cuvette. Data were recorded using hydrophilic and, independently, hydrophobic sensitizers. The microscope-based single cell results are consistent with a model in which the behavior of singlet oxygen reflects the environment in which it is produced; nevertheless, the data also indicate that a significant fraction of a given singlet oxygen population readily crosses barriers between phase-separated intracellular domains. The singlet oxygen phosphorescence signals reflect the effects of singlet-oxygen-mediated damage on cell components which, at the limit, mean that data were collected from dead cells and, in some cases, reflect contributions from both intracellular and extracellular populations of singlet oxygen. Despite the irradiation-induced changes in the environment to which singlet oxygen is exposed, the "inherent" intracellular lifetime of singlet oxygen does not appear to change appreciably as the cell progresses toward death. The results obtained from cell suspensions reflect key features that differentiate cell ensemble from single cell experiments (e.g., the ensemble experiment is more susceptible to the effects of sensitizer that has leaked out of the cell). Overall, the data clearly indicate that measuring the intracellular lifetime of singlet oxygen in a O(2)(a(1)Δ(g)) → O(2)(X(3)Σ(g)(-)) phosphorescence experiment is a challenging endeavor that involves working with a dynamic system that is perturbed during the measurement. The most important aspect of this study is that it establishes a useful framework through which future singlet oxygen data from cells can be interpreted.

Spectroscopic investigation on protein damage by ciprofloxacin under ultrasonic irradiation

In recent years, sonodynamic activities of many drugs have attracted more and more attention of researchers. The correlative study will promote the development of sonodynamic therapy (SDT) in anti-tumor treatment. In this work, bovine serum albumin (BSA) was used as a protein model to investigate the intensifying effects of ciprofloxacin (CPFX) ultrasonically induced protein damage by UV-vis and fluorescence spectra. Meanwhile, the conformation of BSA is changed upon the addition of CPFX and metal ions under ultrasound (US) so that the damaging site of BSA is considered. Various influencing factors, such as US irradiation time, metal ions, solution temperature and ionic strength, on the ultrasonically induced BSA damage are discussed. It was showed that CPFX could enhance ultrasonically induced BSA damage. The damage degree of BSA was aggravated with the increasing of US irradiation time, solution temperature, ionic strength as well as the addition of metal ions. Furthermore, the reactive oxygen species (ROS) in reaction system were detected by oxidation-extraction photometry (OEP). Experimental results also showed that US could activate CPFX to produce ROS, which were mainly determined as superoxide radical anion (.O2-) and hydroxyl radical (.OH).

Singlet oxygen: there is indeed something new under the sun

Singlet oxygen, O(2)(a(1)Delta(g)), the lowest excited electronic state of molecular oxygen, has been known to the scientific community for approximately 80 years. It has a characteristic chemistry that sets it apart from the triplet ground state of molecular oxygen, O(2)(X(3)Sigma), and is important in fields that range from atmospheric chemistry and materials science to biology and medicine. For such a "mature citizen", singlet oxygen nevertheless remains at the cutting-edge of modern science. In this critical review, recent work on singlet oxygen is summarized, focusing primarily on systems that involve light. It is clear that there is indeed still something new under the sun (243 references).

A helpful technology--the luminescence detection of singlet oxygen to investigate photodynamic inactivation of bacteria (PDIB)

Photodynamic inactivation of bacteria (PDIB) is considered a new approach for the struggle against multiresistant bacteria. To achieve a sufficient level of bacteria killing, the photosensitizer must attach to and/or penetrate the bacteria and generate a sufficiently high amount of singlet oxygen. To optimize PDIB, the direct detection and quantification of singlet oxygen in bacteria is a helpful tool. Singlet-oxygen luminescence is a very weak signal, in particular in living bacteria. We first performed experiments in aqueous photosensitizer solution to optimize the luminescence system. We eliminated non-singlet-oxygen photons, which is important for the quantification of singlet oxygen and its rise and decay rates. This procedure is even more important when the laser excitation beam is scattered by bacteria (diameter 1 microm). In suspensions with both Gram-positive and Gram-negative bacteria we then clearly detected singlet oxygen by its luminescence and determined the respective rise and decay times. The decay times should provide an indication of localization of singlet oxygen and hence of the photosensitizer even in small bacteria.