A test of the singlet oxygen mechanism of cationic dye photosensitization of mitochondrial damage

Development of a method for assessing the depth of penetration of ethosomes with methylene blue into the skin during application and photodynamic exposure

A wide range of literature sources report on the potential benefits of transdermal drug delivery. Among these advantages, the following are distinguished – minimal injury, reduction of side effects, and prevention of degradation or metabolism in the gastrointestinal tract or liver. However, transdermal delivery of most molecules often excludes due to the barrier function of the skin, which prevents the penetration of exogenous substances. To overcome this barrier and increase skin absorption, ethosomal complexes use, by means penetration into the deep layers of the skin and/or systemic circulation is possible. This work devotes to the development of a non-invasive method for assessing the depth of penetration by ethosomes with methylene blue (MB) into the skin during application and photodynamic exposure. MB as photosensitizer (PS) was chosen, since there are a sufficient number of publications on its positive effect on the restoration of the cell’s respiratory chain of various organs and therefore the restoration of their metabolism. Besides MB has proven to be an effective PS, destructed pathogenic microbes and viruses, including SARS-CoV-2. However, for more effective Covid-19 therapy and antibiotic-resistant microbial diseases, the penetration of MB into the vascular system of the epidermis or mucous tissue is required. Nowadays, the existing methods for assessing the penetration depth of PS are time consuming and require the use of animal skin or model samples. The LESA-01 BIOSPEC system with specially designed optical adapters that allow assessing the drug fluorescence intensity on skin surface and at a depth of up to 2 mm in the investigation was used.

Bisretinoids of the Retina: Photo-Oxidation, Iron-Catalyzed Oxidation, and Disease Consequences

The retina and, in particular, retinal pigment epithelial cells are unusual for being encumbered by exposure to visible light, while being oxygen-rich, and also amassing photoreactive molecules. These fluorophores (bisretinoids) are generated as a byproduct of the activity of vitamin A aldehyde-the chromophore necessary for vision. Bisretinoids form in photoreceptor cells due to random reactions of two molecules of vitamin A aldehyde with phosphatidylethanolamine; bisretinoids are subsequently transferred to retinal pigment epithelial (RPE) cells, where they accumulate in the lysosomal compartment with age. Bisretinoids can generate reactive oxygen species by both energy and electron transfer, and they become photo-oxidized and photolyzed in the process. While these fluorescent molecules are accrued by RPE cells of all healthy eyes, they are also implicated in retinal disease.

Function-adaptive clustered nanoparticles reverse Streptococcus mutans dental biofilm and maintain microbiota balance

Dental plaques are biofilms that cause dental caries by demineralization with acidogenic bacteria. These bacteria reside inside a protective sheath which makes any curative treatment challenging. We propose an antibiotic-free strategy to disrupt the biofilm by engineered clustered carbon dot nanoparticles that function in the acidic environment of the biofilms. In vitro and ex vivo studies on the mature biofilms of Streptococcus mutans revealed >90% biofilm inhibition associated with the contact-mediated interaction of nanoparticles with the bacterial membrane, excessive reactive oxygen species generation, and DNA fragmentation. An in vivo examination showed that these nanoparticles could effectively suppress the growth of S. mutans. Importantly, 16S rRNA analysis of the dental microbiota showed that the diversity and richness of bacterial species did not substantially change with nanoparticle treatment. Overall, this study presents a safe and effective approach to decrease the dental biofilm formation without disrupting the ecological balance of the oral cavity.

Effective photo-enhancement of cellular activity of fluorophore-octaarginine antisense PNA conjugates correlates with singlet oxygen formation, endosomal escape and chromophore lipophilicity

Photochemical internalization (PCI) is a cellular drug delivery method based on the generation of light-induced reactive oxygen species (ROS) causing damage to the endosomal membrane and thereby resulting in drug release to the cytoplasm. In our study a series of antisense fluorophore octaarginine peptide nucleic acid (PNA) conjugates were investigated in terms of PCI assisted cellular activity. It is found that tetramethylrhodamine and Alexa Fluor 555 conjugated octaarginine PNA upon irradiation exhibit more than ten-fold increase in antisense activity in the HeLa pLuc705 luciferase splice correction assay. An analogous fluorescein conjugate did not show any significant enhancement due to photobleaching, and neither did an Alexa Fluor 488 conjugate. Using fluorescence microscopy a correlation between endosomal escape and antisense activity was demonstrated, and in parallel a correlation to localized formation of ROS assigned primarily to singlet oxygen was also observed. The results show that tetramethylrhodamine (and to lesser extent Alexa Fluor 555) conjugated octaarginine PNAs are as effectively delivered to the cytosol compartment by PCI as by chloroquine assisted delivery and also indicate that efficient photodynamic endosomal escape is strongly dependent on the quantum yield for photochemical singlet oxygen formation, photostability as well as the lipophilicity of the chromophore.

Analysis of mitochondrial dynamics and functions using imaging approaches

Mitochondria are organelles that have been primarily known as the powerhouse of the cell. However, recent advances in the field have revealed that mitochondria are also involved in many other cellular activities like lipid modifications, redox balance, calcium balance, and even controlled cell death. These multifunctional organelles are motile and highly dynamic in shapes and forms; the dynamism is brought about by the mitochondria's ability to undergo fission and fusion with each other. Therefore, it is very important to be able to image mitochondrial shape changes to relate to the variety of cellular functions these organelles have to accomplish. The protocols described here will enable researchers to perform steady-state and time-lapse imaging of mitochondria in live cells by using confocal microscopy. High-resolution three-dimensional imaging of mitochondria will not only be helpful in understanding mitochondrial structure in detail but it also could be used to analyze their structural relationships with other organelles in the cell. FRAP (fluorescence recovery after photobleaching) studies can be performed to understand mitochondrial dynamics or dynamics of any mitochondrial molecule within the organelle. The microirradiation assay can be performed to study functional continuity between mitochondria. A protocol for measuring mitochondrial potential has also been included in this unit. In conclusion, the protocols described here will aid the understanding of mitochondrial structure-function relationship.

Modifications of nucleosides by endogenous mutagens-DNA adducts arising from cellular processes

DNA damage plays a significant role in mutagenesis, carcinogenesis and ageing. Chemical transformations leading to DNA damage include reactions of the base units with agents of endogenous and exogenous origin. The vast majority of damage arising from cellular processes such as metabolism and lipid peroxidation are identical or very similar to those induced by exposure to environmental agents. A detailed knowledge of the types and prevalence of endogenous DNA damage provides insight into the chemical nature of species involved in these modifications and may be of help in understanding their influence on the induction of cancer or other diseases. This knowledge may also be essential to the development of rational chemopreventive strategies directed against the initiation of oxidative stress- and lipid peroxidation-associated pathology. The present work reviews findings regarding the interaction between DNA bases and various reactive species arising from lipid peroxidation and other cellular processes, drawing attention to the mechanism responsible for the formation of the resulted modifications. The biological consequences of these interactions are also briefly discussed.

Mechanisms involved in A2E oxidation

A2E is one of the bis-retinoid pyridinium compounds that accumulate as lipofuscin pigments in retinal pigment epithelial (RPE) cells in association with aging and in some inherited forms of retinal degeneration. Here we observed that 430nm irradiation of A2E in the presence of the spin trap DMPO, led to the appearance of a superoxide dismutase-inhibitable electron paramagnetic resonance (EPR) spectrum characteristic of DMPO-OH; this finding was indicative of hydroxyl radical (OH) formation following initial spin trapping of superoxide anion by DMPO. We also observed an increase in dihydroethidium (HEt) fluorescence and luminol-based chemiluminescence that on the basis of inhibition by superoxide dismutase, was indicative of superoxide anion generation when A2E was irradiated at 430nm in cell-free systems. Nevertheless, while A2E was readily oxidized in the presence of a singlet oxygen generator, superoxide anion did not serve to oxidize A2E. Specifically, by HPLC quantitation and FAB-mass spectroscopy, there was no evidence of A2E oxidation when A2E was incubated with a superoxide anion generator (xanthine/xanthine oxidase) in a variety of solvents (100% PBS, 30% DMSO in PBS, 100% MeOH and CHCl3) or in the presence of detergent. On the other hand, however, peroxy-A2E, an oxidized form of A2E with an endoperoxide moiety on the short-arm of the molecule, readily underwent further oxygen addition when incubated with xanthine/xanthine oxidase. Superoxide anion may be generated by irradiation of A2E but is not involved in the early events that oxidize A2E. Superoxide can contribute to the further oxidation of already-oxidized A2E.

Calcium microdomains and oxidative stress

The phenomenon of calcium microdomains is firmly established in the field of subcellular physiology. These regions of localized, transient calcium increase are exemplified by the spontaneous 'sparks' released through the ryanodine receptor in myocytes, but include subplasmalemmal microdomains, focal calcium oscillations and microdomains enclosed within organelles, such as the endoplasmic reticulum, golgi and mitochondria. Increasing evidence suggests that oxidative stress regulates both the formation and disappearance of microdomains. Calcium release channels and transporters are all modulated by redox state, while several mechanisms that generate oxidative or nitrosative stress are regulated by calcium. Here, we discuss the evidence for the regulation of calcium microdomains by redox state, and, by way of example, demonstrate that the frequency of calcium sparks in cardiomyocytes is increased in response to oxidative stress. We consider the evidence for the existence of analogous microdomains of reactive oxygen and nitrogen species and suggest that the refinement of imaging techniques for these species might lead to similar concepts. The interaction between Ca(2+) microdomains and proteins that modulate their formation results in a complex and dynamic, spatial signaling mechanism, which is likely to be broadly applicable to different cell types, adding new dimensions to the calcium signaling 'toolkit'.

Methylene blue in photodynamic therapy: From basic mechanisms to clinical applications

Methylene blue (MB) is a molecule that has been playing important roles in microbiology and pharmacology for some time. It has been widely used to stain living organisms, to treat methemoglobinemia, and lately it has been considered as a drug for photodynamic therapy (PDT). In this review, we start from the fundamental photophysical, photochemical and photobiological characteristics of this molecule and evolved to show in vitro and in vivo applications related to PDT. The clinical cases shown include treatments of basal cell carcinoma, Kaposi's Sarcoma, melanoma, virus and fungal infections. We concluded that used together with a recently developed continuous light source (RL50(®)), MB has the potential to treat a variety of cancerous and non-cancerous diseases, with low toxicity and no side effects.

RPE lipofuscin and its role in retinal pathobiology

Emerging evidence indicates that the autofluorescent pigments that accumulate as lipofuscin in retinal pigment epithelial (RPE) cells may reach levels that contribute to a decline in cell function. Since recent findings with respect to the origin, composition and adverse effects of RPE lipofuscin have informed our view of this material, the goal of this article is to review our current understanding of these issues.

Mitochondria in health and disease: perspectives on a new mitochondrial biology

The integrity of mitochondrial function is fundamental to cell life. It follows that disturbances of mitochondrial function will lead to disruption of cell function, expressed as disease or even death. In this review, I consider recent developments in our knowledge of basic aspects of mitochondrial biology as an essential step in developing our understanding of the contributions of mitochondria to disease. The identification of novel mechanisms that govern mitochondrial biogenesis and replication, and the delicately poised signalling pathways that coordinate the mitochondrial and nuclear genomes are discussed. As fluorescence imaging has made the study of mitochondrial function within cells accessible, the application of that technology to the exploration of mitochondrial bioenergetics is reviewed. Mitochondrial calcium uptake plays a major role in influencing cell signalling and in the regulation of mitochondrial function, while excessive mitochondrial calcium accumulation has been extensively implicated in disease. Mitochondria are major producers of free radical species, possibly also of nitric oxide, and are also major targets of oxidative damage. Mechanisms of mitochondrial radical generation, targets of oxidative injury and the potential role of uncoupling proteins as regulators of radical generation are discussed. The role of mitochondria in apoptotic and necrotic cell death is seminal and is briefly reviewed. This background leads to a discussion of ways in which these processes combine to cause illness in the neurodegenerative diseases and in cardiac reperfusion injury. The demands of mitochondria and their complex integration into cell biology extends far beyond the provision of ATP, prompting a radical change in our perception of mitochondria and placing these organelles centre stage in many aspects of cell biology and medicine.

Interplay between mitochondria and cellular calcium signalling

Mitochondria are increasingly ascribed central roles in vital cell signalling cascades. These organelles are now recognised as initiators and transducers of a range of cell signals, including those central to activation and amplification of apoptotic cell death. Moreover, as the main source of cellular ATP, mitochondria must be responsive to fluctuating energy demands of the cell. As local and global fluctuations in calcium concentration are ubiquitous in eukaryotic cells and are the common factor in a dizzying array of intra- and inter-cellular signalling cascades, the relationships between mitochondrial function and calcium transients is currently a subject of intense scrutiny. It is clear that mitochondria not only act as local calcium buffers, thus shaping spatiotemporal aspects of cytosolic calcium signals, but that they also respond to calcium uptake by upregulating the tricarboxylic acid cycle, thus reacting metabolically to local signalling. In this chapter we review current knowledge of mechanisms of mitochondrial calcium uptake and release and discuss the consequences of mitochondrial calcium handling for cell function, particularly in conjunction with mitochondrial oxidative stress.

Spontaneous changes in mitochondrial membrane potential in single isolated brain mitochondria

In this study we measured DeltaPsim in single isolated brain mitochondria using rhodamine 123. Mitochondria were attached to coverslips and superfused with K(+)-based HEPES-buffer medium supplemented with malate and glutamate. In approximately 70% of energized mitochondria we observed large amplitude spontaneous fluctuations in DeltaPsim with a time course comparable to that observed previously in mitochondria of intact cells. The other 30% of mitochondria maintained a stable DeltaPsim. Some of the "stable" mitochondria began to fluctuate spontaneously during the recording period. However, none of the initially fluctuating mitochondria became stable. Upon the removal of substrates from the medium or application of small amounts of Ca(2+), rhodamine 123 fluorescence rapidly dropped to background values in fluctuating mitochondria, while nonfluctuating mitochondria depolarized with a delay and often began to fluctuate before complete depolarization. The changes in DeltaPsim were not connected to oxidant production since reducing illumination or the addition of antioxidants had no effect on DeltaPsim. Fluctuating mitochondria did not lose calcein, nor was there any effect of cyclosporin A on DeltaPsim, which ruled out a contribution of permeability transition. We conclude that the fluctuations in DeltaPsim reflect an intermediate, unstable state of mitochondria that may lead to or reflect mitochondrial dysfunction.

Binding, Aggregation and Photochemical Properties of Methylene Blue in Mitochondrial Suspensions

Methylene Blue (MB) has well-established photochemical properties and has been used in a variety of photochemical applications including photodynamic therapy. Despite the fact that most of MB's cytotoxic effects in cells are attributed to mitochondrial damage, the interactions of this dye with mitochondria and the consequent effects on photochemical properties have not yet been fully determined. We monitored MB binding, aggregation and its ability to release singlet oxygen (1O2) on irradiation when interacting with mitochondrial suspensions. MB actively binds to mitochondria and enters the matrix in a manner stimulated by the mitochondrial proton potential and by the increase in mitochondrial concentrations. The greater accumulation of MB in mitochondria with elevated proton potentials or those treated with high concentrations of MB results in the formation of MB dimers, previously shown to be less effective generators of 1O2. Accumulation of MB within mitochondria with high membrane potentials also results in the reduction of MB to the photochemically inactive leuco-MB. Indeed, irradiation of mitochondria with high proton potentials in the presence of MB results in the generation of approximately half the quantity of 1O2 compared with 1O2 generated in mitochondria with low proton potentials. These differences in photochemical properties should influence the cytotoxic effects of photodynamic treatment in the presence of MB.

A2E, a byproduct of the visual cycle

A substantial portion of the lipofuscin that accumulates with age and in some retinal disorders in retinal pigment epithelial (RPE) cells, forms as a consequence of light-related vitamin A recycling. Major constituents of RPE lipofuscin are the di-retinal conjugate A2E and its photoisomers. That the accretion of A2E has consequences for the cell, with the adverse effects of A2E being attributable to its amphiphilic structure and its photoreactivity, is consistent with evidence of an association between atrophic age-related macular degeneration (AMD) and excessive lipofuscin accumulation.

A2E-epoxides damage DNA in retinal pigment epithelial cells. Vitamin E and other antioxidants inhibit A2E-epoxide formation

The autofluorescent pigments that accumulate in retinal pigment epithelial cells with aging and in some retinal disorders have been implicated in the etiology of macular degeneration. The major constituent is the fluorophore A2E, a pyridinium bisretinoid. Light-exposed A2E-laden retinal pigment epithelium exhibits a propensity for apoptosis with light in the blue region of the spectrum being most damaging. Efforts to understand the events precipitating the death of the cells have revealed that during irradiation (430 nm), A2E self-generates singlet oxygen with the singlet oxygen in turn reacting with A2E to generate epoxides at carbon-carbon double bonds. Here we demonstrate that A2E-epoxides, independent of singlet oxygen, exhibit reactivity toward DNA with oxidative base changes being at least one of these lesions. Mass spectrometry revealed that the antioxidants vitamins E and C, butylated hydroxytoluene, resveratrol, a trolox analogue (PNU-83836-E), and bilberry extract reduce A2E-epoxidation, whereas single cell gel electrophoresis and cell viability studies revealed a corresponding reduction in the incidence of DNA damage and cell death. Vitamin E, a lipophilic antioxidant, produced a more pronounced decrease in A2E-epoxidation than vitamin C, and treatment with both vitamins simultaneously did not confer additional benefit. Studies in which singlet oxygen was generated by endoperoxide in the presence of A2E revealed that vitamin E, butylated hydroxytoluene, resveratrol, the trolox analogue, and bilberry reduced A2E-epoxidation by quenching singlet oxygen. Conversely, vitamin C and ginkgolide B were not efficient quenchers of singlet oxygen under these conditions.

Photophysical and photosensitizing properties of selected cyanines

The present work has been carried out to obtain detailed information about the photophysical and photobiological properties of selected cyanines, in view of their possible use as photosensitizing agents. All the cyanines studied by us except CY-IV (3,3'-diethyl-4,4'-oxacarbocyanine), expressed an accelerated photobleaching in aqueous medium, a poor generation of singlet oxygen, and a relative weak photosensitizing activity towards albumin. On the cellular level, all cyanines exhibited a significant phototoxicity towards Balb/c 3T3 cells, upon irradiation with a total fluence of 30 J/cm(2). CY-III (3,3'-diethylcarbothiocayanine iodide) and CY-II (1,1'-diethyl-4,4'-carbocyanine iodide) appear to be promising photosensitizers, in spite of previous reports on the inefficiency of the former cyanine, and the rapid photobleaching of the latter compound.

Intracellular distribution of the fluorescent dye nonyl acridine orange responds to the mitochondrial membrane potential: implications for assays of cardiolipin and mitochondrial mass

Cardiolipin, a polyunsaturated acidic phospholipid, is found exclusively in bacterial and mitochondrial membranes where it is intimately associated with the enzyme complexes of the respiratory chain. Cardiolipin structure and concentration are central to the function of these enzyme complexes and damage to the phospholipid may have consequences for mitochondrial function. The fluorescent dye, 10 nonyl acridine orange (NAO), has been shown to bind cardiolipin in vitro and is frequently used as a stain in living cells to assay cardiolipin content. Additionally, NAO staining has been used to measure the mitochondrial content of cells as dye binding to mitochondria is reportedly independent of the membrane potential. We used confocal microscopy to examine the properties of NAO in cortical astrocytes, neonatal cardiomyocytes and in isolated brain mitochondria. We show that NAO, a lipophilic cation, stained mitochondria selectively. However, the accumulation of the dye was clearly dependent upon the mitochondrial membrane potential and depolarisation of mitochondria induced a redistribution of dye. Moreover, depolarisation of mitochondria prior to NAO staining also resulted in a reduced NAO signal. These observations demonstrate that loading and retention of NAO is dependant upon membrane potential, and that the dye cannot be used as an assay of either cardiolipin or mitochondrial mass in living cells.

Mitochondrial oxidative stress and cell death in astrocytes —requirement for stored Ca2+ and sustained opening of the permeability transition pore

The role of oxidative stress is established in a range of pathologies. As mitochondria are a major source of reactive oxygen species (ROS), we have developed a model in which an intramitochondrial photosensitising agent is used to explore the consequences of mitochondrial ROS generation for mitochondrial function and cell fate in primary cells. We have found that, in astrocytes, the interplay between mitochondrial ROS and ER sequestered Ca2+ increased the frequency of transient mitochondrial depolarisations and caused mitochondrial Ca2+ loading from ER stores. The depolarisations were attributable to opening of the mitochondrial permeability transition pore (mPTP). Initially, transient events were seen in individual mitochondria, but ultimately, the mitochondrial potential(Δψm) collapsed completely and irreversibly in the whole population. Both ROS and ER Ca2+ were required to initiate these events, but neither alone was sufficient. Remarkably, the transient events alone appeared innocuous, and caused no increase in either apoptotic or necrotic cell death. By contrast, progression to complete collapse ofΔψ m caused necrotic cell death. Thus increased mitochondrial ROS generation initiates a destructive cycle involving Ca2+ release from stores and mitochondrial Ca2+-loading,which further increases ROS production. The amplification of oxidative stress and Ca2+ loading culminates in opening of the mPTP and necrotic cell death in primary brain cells.

Spontaneous changes in mitochondrial membrane potential in cultured neurons

Using the mitochondrial membrane potential (DeltaPsi(m))-sensitive fluorescent dyes 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide (JC-1) and tetramethylrhodamine methyl ester (TMRM), we have observed spontaneous changes in the DeltaPsi(m) of cultured forebrain neurons. These fluctuations in DeltaPsi(m) appear to represent partial, transient depolarizations of individual mitochondria. The frequency of these DeltaPsi(m) fluctuations can be significantly lowered by exposure to a photo-induced oxidant burden, an ATP synthase inhibitor, or a glutamate-induced sodium load, without changing overall JC-1 fluorescence intensity. These spontaneous fluctuations in JC-1 signal were not inhibited by altering plasma membrane activity with tetrodotoxin or MK-801 or by blocking the mitochondrial permeability transition pore (PTP) with cyclosporin A. Neurons loaded with TMRM showed similar, low-amplitude, spontaneous fluctuations in DeltaPsi(m). We hypothesize that these DeltaPsi(m) fluctuations are dependent on the proper functioning of the mitochondria and reflect mitochondria alternating between the active and inactive states of oxidative phosphorylation.

A comparative study of the photosensitizing characteristics of some cyanine dyes

The present work has been carried out to explore the potential application of cyanines in photodynamic therapy. After photosensitization, the in vitro cytotoxic and antiproliferative activity on HeLa cells of a total of 35 cyanines belonging to several chemical subgroups is explored. Most of these cyanines have never been used before in similar experimental work. From a first set of experiments, it is found that none of the krypto-, oxa- and imidacyanines is photobiologically active on HeLa cells. Conversely, five thiacyanines (Thiacl-5), one rhodacyanine (Rhodac) and four indocyanines (Indoc2, Indoc4, Indoc5, Indoc7) show photodependent cytotoxicity or antiproliferative effects. A more detailed study shows that out of the ten selected compounds, eight cyanines feature significant photodependent cytotoxic and antiproliferative effects. All possess maximum absorption ranges between 545 and 824 nm. In particular, Rhodac, a tetramethinemeromonomethine rhodacyanine dye with an absorption maximum of 655 nm (ethanol) and a molar absorption coefficient epsilon = 108000 shows very promising photo-dependent biological activity. In general, the measured singlet oxygen quantum yield of the selected cyanines is low (< 0.08) and does not correlate with the degree of photosensitization. Furthermore, the present study shows that cyanines with a partition coefficient close to 1.5 accumulate to the highest extent in HeLa cells, while the more hydrophobic compounds (e.g., indocyanines) concentrate less intracellularly.

Slow fluorescent indicators of membrane potential: a survey of different approaches to probe response analysis

Basic tenets related to the use of three main classes of potentiometric redistribution fluorescent dyes (carbocyanines, oxonols, and rhodamines) are discussed in detail. They include the structure/function relationship, formation of nonfluorescent (H-type) and fluorescent (J-type) dimers and higher aggregates, probe partitioning between membranes and medium and binding to membranes and intracellular components (with attendant changes in absorption and emission spectra, fluorescence quantum yield and lifetime). The crucial importance of suitable probe-to-cell concentration ratio and selection of optimum monitored fluorescence wavelength is illustrated in schematic diagrams and possible artifacts or puzzling results stemming from faulty experimental protocol are pointed out. Special attention is paid to procedures used for probe-response calibration (potential clamping by potassium in the presence of valinomycin, use of gramicidin D in combination with N-methylglucamine, activation of Ca-dependent K-channels by A23187, the null-point technique). Among other problems treated are dye toxicity, interaction with mitochondria and other organelles, and possible effects of intracellular pH and the quantity of cytosolic proteins and/or RNA on probe response. Individual techniques using redistribution dyes (fluorescence measurements in cuvettes, flow cytometry and microfluorimetry of individual cells including fluorescence confocal microscopy) are discussed in terms of reliability, limitations and drawbacks, and selection of suitable probes. Up-to-date examples of application of slow dyes illustrate the broad range of problems in which these probes can be used.

Phototherapeutic potential of alternative photosensitizers to porphyrins

Because of promising clinical results obtained with photodynamic therapy, more and more photosensitizers continue to be isolated (from natural sources), synthesized and evaluated, the development of which is considered to be a key factor for the successful clinical application of photodynamic therapy. Porphyrins and their analogs (as classical types of phototherapeutic agents) have been extensively reviewed. In this review, we have attempted to summarize the phototherapeutic potential (in particular, anticancer and antiviral aspects) of nonporphyrin photosensitizers (as a new generation of phototherapeutic agents) in more detail, which have been relatively much less reviewed hitherto. They include anthraquinones, anthrapyrazoles, perylenequinones, xanthenes, cyanines, acridines, phenoxazines and phenothiazines. They have shown certain phototherapeutic advantages over the presently used porphyrins. Some anthraquinones, perylenequinones, cyanines, phenoxazines and phenothiazines exhibit strong light absorption in the 'phototherapeutic window' (600-1000 nm), high photosensitizing efficacy and low delayed skin photosensitivity. Some of the nonporphyrin photosensitizers (such as rhodamine 123, merocyanine 540 and some cyanine cationic dyes) demonstrate higher selectivity for tumor cells. They can also be explored in connection with selective carcinoma photolysis strategy based on mitochondrion-, lysosome- or DNA-directed localization mode.

Photochemical interactions of methylene blue and analogues with DNA and other biological substrates

The light-induced reactions of methylene blue and related phenothiazinium dyes with biological substrates are described. The properties of the excited states of the dyes, their reactions with nucleic acids and their photosensitised chemical modifications of nucleic acid bases are examined. Reports on phenothiazinium dye-induced damage to proteins, lipids, biological membranes, organelles, viruses, bacteria, mammalian cells and carcinomas are reviewed.

Photophysical properties of 3,3'-dialkylthiacarbocyanine dyes in organized media: unilamellar liposomes and thin polymer films

All symmetrical dialkylthiacarbocyanine dyes, with the exception of the diethyl derivatives, are incorporated into liposomes. Absorption and fluorescence data indicate a solubilization site close to the bilayer surface with the alkyl chains penetrating into the lipid bilayer. Incorporation into organized assemblies affects the photophysical parameters of these dyes. Photoisomerization occurring from the first excited state becomes more difficult as the restrictive effect of the solubilization site increases. As a consequence, competing deactivation processes, such as fluorescence and triplet formation, become more efficient with the result that fluorescence quantum yields, triplet yields and singlet oxygen quantum yields are larger in liposomes than in homogeneous solution. Dihexylthiacarbocyanine iodide has a fluorescence quantum yield of 0.27 and 0.10 (25 degrees C) in dimyristoylphosphatidyl-choline liposomes and ethanol, respectively, and the singlet oxygen yield increases by a factor three to 0.006 on going from ethanol to liposomes. The effect of a highly organized environment is even more pronounced in thin polymer films. In these systems, photoisomerization is completely inhibited and only triplet formation is observed in the transient absorption spectrum.

Iminium salt of copper benzochlorin (CDS1), a novel photosensitizer for photodynamic therapy: mechanism of cell killing

The mechanism of cell killing by CDS1, an iminium salt of octaethylbenzochlorin with copper in the aromatic ring, in combination with light from a noncoherent light source was investigated. Using a standard clonogenic assay and the AY-27 FANFT tumor line, photoactivation of CDS1 was shown to be cytotoxic. The photodynamic cell killing ability of CDS1 required the presence of molecular oxygen. The reactive species generated by light activation of CDS1 were effectively quenched by N,N'-diphenyl-p-phenylenediamine. Additionally, the photodynamic effect of CDS1 was not enhanced by deuterium oxide. To characterize the reactive oxygen species generated by the photoactivation of CDS1 the well-characterized erythrocyte ghost model was used. Superoxide dismutase and catalase were potent inhibitors of CDS1-induced lipid peroxidation of erythrocyte membranes. Sodium azide only partially inhibited lipid peroxidation. These findings differed from the known singlet oxygen generator, tin (II) etiopurpurin dichloride (SnET2). Sodium azide was a potent inhibitor of SnET2-induced lipid peroxidation, whereas superoxide dismutase and catalase were totally ineffective. Based on these results, we conclude that CDS1 requires the presence of molecular oxygen for cell killing to occur but appears to act primarily through a non-singlet oxygen mechanism.