Distribution and retention of rose bengal and disulphonated aluminium phthalocyanine: a comparative study in unicellular eukaryote

Generation of singlet oxygen inside living cells: correlation between phosphorescence decay lifetime, localization and outcome of photodynamic action

Photodynamic therapy (PDT) is a promising alternative treatment for localized lesions and infections, utilizing reactive oxygen species (ROS) generated by photosensitizers (PS) upon light activation. Singlet oxygen (1O2) is a key ROS responsible for photodynamic damage. However, the effectiveness of PS in biological systems may not correlate with the efficiency of singlet oxygen generation in homogeneous solutions. This study investigated singlet oxygen generation and its decay in various cellular microenvironments using liposome and ARPE-19 cell models. Rose Bengal (RB), methylene blue (MB), and protoporphyrin IX (PpIX) were employed as selected PS. Lifetimes of singlet oxygen generated by the selected photosensitizers in different cellular compartments varied, indicating different quenching rates with singlet oxygen. RB, located near cell membranes, exhibited the highest phototoxicity and lipid/protein peroxidation, followed by PpIX, while MB showed minimal cytotoxicity in similar conditions. Singlet oxygen decay lifetimes provide insights into PS localization and potential phototoxicity, highlighting the importance of the lipid microenvironment in PDT efficacy, providing useful screening method prior to in vivo applications.

Effects of polyallylamine-coated nanoparticles on the optical and photochemical properties of rose bengal

BACKGROUND

Inasmuch as optical and photochemical properties of a photosensitizer can be modified upon association with the nanoparticle (NP), we wondered whether the effectiveness of phototherapeutic rose bengal (RB) was affected upon tethering to the sodium lanthanide fluoride NP with an outer polyallylamine (PAH) coat.

METHODS

RB molecules were electrostatically bound to the NaYF 4 :Gd 3+ :Nd 3+ NPs with inner silica and outer PAH coats. The products were analyzed for their size, shape and zeta potential using transmission electron microscopy and dynamic light scattering instrument. Ultraviolet-visible absorption spectrometry and fluorescence spectrometry were used to examine the spectral properties. Photodynamic effect in terms of singlet oxygen generation was quantitatively determined using the indicator 1,3-diphenylisobenzofuran (DPBF). Photocytotoxicity mediated by NP-bound RB was tested using A549 cells (Student's t test was used for statistical evaluation).

RESULTS

NP-bound RB had the major absorbance peak at 561 nm, in comparison with 549 nm for free RB, accompanied with a significant decrease in absorptivity. The molar extinction coefficient becomes 36 000 M -1 cm -1 , only ~35% of that for free RB. Fluorescence spectral analyses showed a paradoxical decrease in the emission with higher NP concentrations even at very low dilutions. Most importantly, the association of RB with these NPs drastically increased its singlet oxygen production upon irradiation. The interaction of RB with PAH coat could partly account for this enhancement, given our finding that PAH in solution also caused a drastic rise in DPBF reactivity by free RB. These NPs exhibited strong photocytotoxic effects, and their promise in photodynamic therapy was addressed.

CONCLUSION

Our findings provide evidence that the PAH coat plays a key role in enhanced biological activities of RB delivered via NPs, including the increase in singlet oxygen production and photocytotoxic effects.

Non-Polymeric Nanogels as Versatile Nanocarriers: Intracellular Transport of the Photosensitizers Rose Bengal and Hypericin for Photodynamic Therapy

The use of nanocarriers for intracellular transport of actives has been extensively studied in recent years and represents a central area of nanomedicine. The main novelty of this paper lies on the use of nanogels formed by a low-molecular-weight gelator (1). Here, non-polymeric, molecular nanogels are successfully used for intracellular transport of two photodynamic therapy (PDT) agents, Rose Bengal (RB) and hypericin (HYP). The two photosensitizers (PSs) exhibit different drawbacks for their use in clinical applications. HYP is poorly water-soluble, while the cellular uptake of RB is hindered due to its dianionic character at physiological pH values. Additionally, both PSs tend to aggregate precluding an effective PDT. Despite the different nature of these PSs, nanogels from gelator 1 provide, in both cases, an efficient intracellular transport into human colon adenocarcinoma cells (HT-29) and a notably improved PDT efficiency, as assessed by confocal laser scanning microscopy and flow cytometry. Furthermore, no significant dark toxicity of the nanogels is observed, supporting the biocompatibility of the delivery system. The developed nanogels are highly reproducible due to their non-polymeric nature, and their synthesis is easily scaled up. The results presented here thus confirm the potential of molecular nanogels as valuable nanocarriers, capable of entrapping both hydrophobic and hydrophilic actives, for PDT of cancer.

The Dimerisation of Phthalocyanines

In this review, we have shown that the dimerisation of phthalocyanine compounds, notably here the sulphonated aluminium phthalocyanines, is dependent upon concentration, on the medium in which the dye is dissolved, and upon pH. Complex equilibria between various monomer and dimer species are observed as a function of pH, and the probable structures of the dimers elucidated by semi-empirical and ab initio calculations. The formation of a red-shifted dimer leads to the quenching of monomer singlet state in concentrated solution, in reverse micelles, and in lipid vesicles, and this behaviour can account for the fluorescence intensity distributions and decay characteristics of phthalocyanine dyes in living cells as a function of irradiation time.

Cationic Phosphorus Dendrimer Enhances Photodynamic Activity of Rose Bengal against Basal Cell Carcinoma Cell Lines

In the last couple of decades, photodynamic therapy emerged as a useful tool in the treatment of basal cell carcinoma. However, it still meets limitations due to unfavorable properties of photosensitizers such as poor solubility or lack of selectivity. Dendrimers, polymers widely studied in biomedical field, may play a role as photosensitizer carriers and improve the efficacy of photodynamic treatment. Here, we describe the evaluation of an electrostatic complex of cationic phosphorus dendrimer and rose bengal in such aspects as singlet oxygen production, cellular uptake, and phototoxicity against three basal cell carcinoma cell lines. Rose bengal-cationic dendrimer complex in molar ratio 5:1 was compared to free rose bengal. Obtained results showed that the singlet oxygen production in aqueous medium was significantly higher for the complex than for free rose bengal. The cellular uptake of the complex was 2-7-fold higher compared to a free photosensitizer. Importantly, rose bengal, rose bengal-dendrimer complex, and dendrimer itself showed no dark toxicity against all three cell lines. Moreover, we observed that phototoxicity of the complex was remarkably enhanced presumably due to high cellular uptake. On the basis of the obtained results, we conclude that rose bengal-cationic dendrimer complex has a potential in photodynamic treatment of basal cell carcinoma.

Inhibition of phagocytic activity of ARPE-19 cells by free radical mediated oxidative stress

Oxidative stress is a main factor responsible for key changes leading to the onset of age-related macular degeneration (ARMD) that occur in the retinal pigment epithelium (RPE), which is involved in phagocytosis of photoreceptor outer segments (POS). In this study, hydrogen peroxide (H2O2), H2O2 and iron ions (Fe) or rose Bengal (RB) in the presence of NADH and Fe were used to model free radical mediated oxidative stress to test if free radicals and singlet oxygen have different efficiency to inhibit phagocytosis of ARPE-19 cells. Free radical mediated oxidative stress was confirmed by HPLC-EC(Hg) measurements of cholesterol hydroperoxides in treated cells. Electron paramagnetic resonance (EPR) spin trapping was employed to detect superoxide anion. Cell survival was analyzed by the MTT assay. Specific phagocytosis of fluorescein-5-isothiocyanate-labeled POS and non-specific phagocytosis of fluorescent beads were measured by flow cytometry. HPLC analysis of cells photosensitized with RB in the presence of NADH and Fe indicated substantial increase in formation of free radical-dependent 7α/7β-hydroperoxides. EPR spin trapping confirmed the photogeneration of superoxide anion in samples enriched with RB, NADH and Fe. For all three protocols sub-lethal oxidative stress induced significant inhibition of the specific phagocytosis of POS. In contrast, non-specific phagocytosis was inhibited only by H2O2 or H2O2 and Fe treatment. Inhibition of phagocytosis was transient and recoverable by 24 h. These results suggest that free radicals may exert similar to singlet oxygen efficiency in inhibiting phagocytosis of RPE cells, and that the effect depends on the location where initial reactive species are formed.

Photosensitized oxidative stress to ARPE-19 cells decreases protein receptors that mediate photoreceptor outer segment phagocytosis

PURPOSE

To determine whether previously shown photodynamic (PD)-induced inhibition of specific photoreceptor outer segment (POS) phagocytosis by ARPE-19 cells is associated with reductions in receptor proteins mediating POS phagocytosis, and if PD treatment with merocyanine-540 (MC-540) produces additional effects leading to its inhibition of nonspecific phagocytosis.

METHODS

ARPE-19 cells preloaded with MC-540 or rose bengal (RB) were sublethally irradiated with green light. Phagocytosis of POS was measured by flow cytometry and POS receptor proteins (Mer tyrosine kinase receptor [MerTK] and integrin subunits αv and β5) and β-actin were quantified by Western blotting at 0.5 and 24 hours after irradiation, with comparison to samples from nonsensitized control cultures. The intact integrin heterodimer αvβ5 was quantified by immunoprecipitation followed by blotting. The distribution of N-cadherin, ZO-1, and F-actin was visualized by fluorescence microscopy.

RESULTS

Mild PD stress mediated by both photosensitizers that elicits no significant morphologic changes produces transient and recoverable reductions in MerTK. The individual αv and β5 integrin subunits are also reduced but only partially recover. However, there is sufficient recovery to support full recovery of the functional heterodimer. Light stress mediated by MC-540 also reduced levels of actin, which is known to participate in the internalization of particles regardless of type.

CONCLUSIONS

After PD treatment POS receptor protein abundance and phagocytosis show a coincident in time reduction then recovery suggesting that diminution in receptor proteins contributes to the phagocytic defect. The additional inhibition of nonspecific phagocytosis by MC-540-mediated stress may result from more widespread effects on cytosolic proteins. The data imply that phagocytosis receptors in RPE cells are sensitive to oxidative modification, raising the possibility that chronic oxidative stress in situ may reduce the efficiency of the RPE's role in photoreceptor turnover, thereby contributing to retinal degenerations.

Sub-lethal photodynamic damage to ARPE-19 cells transiently inhibits their phagocytic activity

Efficient phagocytosis of photoreceptor outer segments (POS) membranes by retinal pigment epithelium (RPE) plays a key role in biological renewal of these highly peroxidizable structures. Here, we tested whether photodynamic treatment, mediated by merocyanine 540 (MC 540), rose Bengal or a zinc-substituted chlorophyllide inhibited phagocytic activity of ARPE-19 cells in vitro. Specific phagocytosis of fluorescein-5-isothiocyanate-labeled POS isolated from cow retinas and nonspecific phagocytosis of fluorescent polystyrene beads were measured by flow cytometry. Photodynamic treatment, mediated by all three photosensitizers with sub-threshold doses, induced significant inhibition of the cell-specific phagocytosis. The nonspecific phagocytosis was inhibited by photodynamic treatment mediated only by MC 540. The inhibition of phagocytosis was a reversible phenomenon and after 24 h, the photodynamically treated cells exhibited phagocytic activity that was comparable with that of untreated cells. This study provides proof of principle that sub-threshold photodynamic treatment of ARPE-19 cells with appropriate photosensitizers is a convenient experimental approach for in vitro study of the effects of oxidative stress on specific phagocytic activity of RPE cells. We postulate that oxidative damage to key components of the cell phagocytic machinery may be responsible for severe impairment of its activity, which can lead to retinal degeneration.

Apoptosis in tumour cells photosensitized with Rose Bengal acetate is induced by multiple organelle photodamage

Rose Bengal (RB) is a very efficient photosensitizer which undergoes inactivation of its photophysical and photochemical properties upon addition of a quencher group-i.e. acetate-to the xanthene rings. The resulting RB acetate (RB-Ac) derivative behaves as a fluorogenic substrate: it easily enters the cells where the native photoactive molecule is restored by esterase activities. It is known that the viability of RB-Ac-loaded cells is strongly reduced by light irradiation, attesting to the formation of intracellular RB. The aim of this study was to identify the organelles photodamaged by the intracellularly formed RB. RB-Ac preloaded rat C6 glioma cells and human HeLa cells were irradiated at 530 nm. Fluorescence confocal imaging and colocalization with specific dyes showed that the restored RB molecules redistribute dynamically through the cytoplasm, with the achievement of a dynamic equilibrium at 30 min after the administration, in the cell systems used; this accounted for a generalized damage to several organelles and cell structures (i.e. the endoplasmic reticulum, the Golgi apparatus, the mitochondria, and the cytoskeleton). The multiple organelle damage, furthermore, led preferentially to apoptosis as demonstrated by light and electron microscopy and by dual-fluorescence staining with FITC-labelled annexin V and propidium iodide.

Apoptosis induction and mitochondria alteration in human HeLa tumour cells by photoproducts of Rose Bengal acetate

The aim of this work was to investigate the apoptosis induction and mitochondria alteration after photodamage exerted by incubation of HeLa cells with Rose Bengal acetate-derivative (RBAc) followed by irradiation for a total dose of 1.6 J/cm2. This treatment was previously demonstrated to reduce cell viability under mild treatment conditions, suggesting the restoration of the photoactive molecule in particularly sensitive cell sites. Indeed, Rose Bengal (RB) is a very efficient photosensitizer, whose photophysical properties are inactivated by addition of the quencher group acetate. The RBAc behaves as a fluorogenic substrate by entering easily the cells where the original, photoactive molecule is restored by specific esterases. Different intracellular sites of photodamage of RB are present. In particular, fluorescence imaging of Rodamine 123 and JC-1 labelled cells showed altered morphology and loss of potential membrane of mitochondria. MTT and NR assays gave indications of alteration of mitochondrial and lysosomal enzyme activities. These damaged sites were likely responsible for triggering apoptosis. Significant amount of apoptotic cell death (about 40%) was induced after light irradiation followed RBAc incubation as revealed by morphological (modification of cell shape and blebs formation), cytochemical (FITC-Annexin-V positive cells) and nuclear fragmentation assays.

Rose Bengal adsorbed on microgranular cellulose: evidence on fluorescent dimers

Rose Bengal adsorbed on microgranular cellulose was studied in the solid phase by total and diffuse reflectance and steady-state emission spectroscopy. A simple monomer-dimer equilibrium fitted reflectance data up to dye loadings of 4 x 10(-7) mol (g cellulose)(-1) and allowed calculation of monomer and dimer spectra. Further increase of dye loading resulted in the formation of higher aggregates. Observed emission and excitation spectra and quantum yields were corrected for reabsorption and reemission of luminescence, using a previously developed model, within the assumption that only monomers are luminescent [M. G. Lagorio, L. E. Dicelio, M. I. Litter and E. San Roman, J. Chem. Soc., Faraday Trans., 1998, 94, 419]. An apparent increase of fluorescence quantum yield with dye loading was found, which was attributed to the occurrence of dimer fluorescence. Extension of the model to two luminescent species (i.e. monomer and dimer) yielded constant fluorescence quantum yields for the monomer, phiM= 0.120 +/- 0.004, and for the dimer, phiD= 0.070 +/- 0.006. The monomer quantum yield is close to the value found for the same dye in basic ethanol. The presence of fluorescent dimers and calculated quantum yields are supported by analysis of the excitation spectra and other experimental evidence. The possible occurrence of non-radiative energy transfer and the effect of surface charge on the properties of the dimer are analyzed.

Enzyme-assisted cell photosensitization: a proposal for an efficient approach to tumor therapy and diagnosis. The rose bengal fluorogenic substrate

Rose bengal, a xanthene derivative among the most efficient producer of singlet oxygen, was submitted to a chemical modification consisting in the introduction of an acetate group into the aromatic ring fluorophore structure. The acetate group acts as a quencher, thus inactivating both fluorescence and photosensitization properties of the molecule. In the modified structure, rose bengal acts as a fluorogenic substrate giving rise to the cellular reaction termed fluorochromasia. The acetate group is recognized by a carboxylic esterase activity that splits it. Removal of the quencher group results in restoring the native structure of photosensitizer inside the cells. The intracellular turnover of rose bengal acetate was studied in rat glioma-derived cultures cells, in terms of the balance of the processes of influx and enzyme hydrolysis of the fluorogenic substrate, and of the efflux of the fluorescent product. A large intracellular accumulation of photosensitizer is obtained when treatments are performed with the fluorogenic substrate, even at the drug concentration at which rose bengal does not enter the cells. The intracellular localization allows rose bengal to exert a more effective photosensitization effect. Provided that the quencher group is selected according to the metabolic properties of the tumor cells, the use of fluorogenic substrates as photosensitizer precursors could improve fluorescence diagnosis and the photodynamic therapy of tumors, exploiting the biological properties that distinguish pathological from normal conditions.