Effects of NaCl upon TPPS4 triplet state characteristics and singlet oxygen formation

Use of photosensitive molecules in the crosslinking of biopolymers: applications and considerations in biomaterials development

The development of diverse types of biomaterials has significantly contributed to bringing new biomedical strategies to treat clinical conditions. Applications of these biomaterials can range from mechanical support and protection of injured tissues to joint replacement, tissue implants, and drug delivery systems. Among the strategies commonly used to prepare biomaterials, the use of electromagnetic radiation to initiate crosslinking stands out. The predominance of photo-induced polymerization methods relies on a fast, efficient, and straightforward process that can be easily adjusted to clinical needs. This strategy consists of irradiating the components that form the material with photons in the near ultraviolet-visible wavelength range (i.e., ∼310 to 750 nm) in the presence of a photoactive molecule. Upon photon absorption, photosensitive molecules can generate excited species that initiate photopolymerization through different reaction mechanisms. However, this process could promote undesired side reactions depending on the target zone or treatment type (e.g., oxidative stress and modification of biomolecules such as proteins and lipids). This review explores the basic concepts behind the photopolymerization process of ex situ and in situ biomaterials. Particular emphasis was put on the photosensitization initiated by the most employed photosensitizers and the photoreactions that they mediate in aqueous media. Finally, the undesired oxidation reactions at the bio-interface and potential solutions are presented.

Effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) aggregation on its spectral and kinetic characteristics and singlet oxygen production

The present work reports the effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS₄) aggregation on its excited states absorption spectra, triplet states quenching by molecular oxygen and singlet oxygen production. Experimental techniques such as optical absorption, Z-scan with a white light continuum source and the Laser Flash Photolysis were used to fulfil the study. J-aggregates possess reverse saturable absorption in the 505-660 nm spectral range with a peak centered close to 540 nm. These facts together with their fast relaxation time suggest that they can be employed as material for ultrafast optical limiting and switching. Even though aggregation reduces the porphyrin excited-state lifetimes and quantum yields, it does not reduce the probability of the contact between the quencher and the excited aggregate. Aggregation does not change the contribution of energy transfer mechanisms to triplet state quenching by molecular oxygen. The production of singlet oxygen, the intense absorption in the phototherapeutic window and the high efficiency of conversion of light energy into heat, allow consider J-aggregates as a theranostic agent for photomedicine. It is proposed to use J-aggregates for diagnostics by photoacoustic images and in combination with a near-infrared photodynamic/photothermal dual mode therapy, thus improving synergistically the therapeutic response.

Delocalized triplet state in porphyrin J-aggregates revealed by EPR spectroscopy

In this work, the electronic structure of the triplet state of self-assembled J-aggregates of tetrakis(4-sulfonatophenyl)porphyrin (TPPS) has been characterized by means of time-resolved electron paramagnetic resonance spectroscopy. Several insights into the triplet properties of the aggregate have been gained through comparison with the corresponding monomeric unit in both free base and acidified forms. Molecular distortions in the monomeric acidified TPPS cause variation in its zero-field splitting parameters and a redirection of triplet spin sublevel activity. The aggregation process does not alter the mechanism of triplet state population compared to the acidified monomer but it is accompanied by a further reduction in the zero-field splitting parameter D, which is possibly indicative of the formation of a delocalized triplet state species. The detection of a long-lived spin-polarized radical species also proves polaron generation and movement to a trap site in the J-aggregates.

Cationic dendritic starch as a vehicle for photodynamic therapy and siRNA co-delivery

Cationic enzymatically synthesized glycogen (cESG) is a naturally-derived, nano-scale carbohydrate dendrite that has shown promise as a cellular delivery vehicle owing to its flexibility in chemical modifications, biocompatibility and relative low cost. In the present work, cESG was modified and evaluated as a vehicle for tetraphenylporphinesulfonate (TPPS) in order to improve cellular delivery of this photosensitizer and investigate the feasibility of co-delivery with short interfering ribonucleic acid (siRNA). TPPS was electrostatically condensed with cESG, resulting in a sub-50nm particle with a positive zeta potential of approximately 5mV. When tested in normal ovarian surface epithelial and ovarian clear cell carcinoma cell culture models, encapsulation of TPPS in cESG significantly improved cell death in response to light treatment compared to free drug alone. Dosages as low as 0.16μM TPPS resulted in cellular death upon illumination with a 4.8J/cm² light dosage, decreasing viability by 96%. cESG-TPPS was then further evaluated as a co-delivery system with siRNA for potential combination therapy, by charge-based condensation of an siRNA directed at reducing expression of manganese superoxide dismutase (Sod2) as a proof of principle target. Simultaneous delivery of TPPS and siRNA was achieved, reducing Sod2 protein expression to 48%, while maintaining the photodynamic properties of TPPS under light exposure and maintaining low dark toxicity. This study demonstrates the versatility of cESG as a platform for dual delivery of small molecules and oligonucleotides, and the potential for further development of this system in combination therapy applications.

Combined use of optical spectroscopy and computational methods to study the binding and the photoinduced conformational modification of proteins when NMR and X-ray structural determinations are not an option

The functions of proteins depend on their interactions with various ligands and these interactions are controlled by the structure of the polypeptides. If one can manipulate the structure of proteins, their functions can in principle be modulated. The issue of protein structure-function relationship is not only a central problem in biophysics, but is becoming clear that the ability to "artificially" modify the structure of proteins could be relevant in fields beyond the biomedical area to provide, for instance, light responses in proteins which would not possess such properties in their native state. This chapter presents an overview of the combination of optical electronic and vibrational spectroscopy with various computational methods to investigate the binding between photoactive ligands and proteins.

Enhancing Photodynamic Therapy Efficacy by Using Fluorinated Nanoplatform

Photodynamic therapy (PDT) is a noninvasive therapeutic modality with fast healing process and little or no scarring. The production of reactive oxygen species is highly dependent on oxygen concentration, and thus, the therapeutic efficacy of PDT would be retarded by inefficient oxygen supply in hypoxic tumor cell and the oxygen self-consuming mechanism of PDT. It is well-known that perfluorocarbons are endowed with properties of enhanced oxygen solubility and transfer capacity. Herein, we prepared a series of nanoplatforms of spherical micelles with different ratios of pentafluorophenyl to porphyrin in the core and utilized these micelles as models to examine the influence of content of fluorinated segments on the PDT effect of porphyrins. It was found for the first time, as far as we are aware, that the production efficacy of singlet oxygen increased with the rising in the ratio of pentafluorophenyl to porphyrin. Thus, this work presents a new avenue to improve PDT efficacy by enhancing oxygen solubility and diffusivity of nanoplatforms with the incorporation of perfluorocarbon segments.

Photocytotoxicity of a cyanine dye with two chromophores toward melanoma and normal cells

BACKGROUND

Due to high optical absorption, triplet quantum yield and affinity to biological structures bichromophoric cyanine dyes (BCDs) can be considered promising sensitizers for application in photodynamic therapy (PDT). In this work, we report on the study of the BCD photocytotoxicity toward melanoma and normal cells in comparison with that of commercial photosensitizer Photogem®.

METHODS

The cytotoxic and phototoxic effects were measured by standard tests of cell viability. The drug uptake was obtained by the flow cytometry and optical absorption techniques. The BCD intracellular distribution was obtained by the fluorescence image microscopy using specific organelle markers.

RESULTS

Both drugs demonstrated increased cytotoxicity under irradiation, while in darkness their cytotoxic effect at concentrations lower than 20 μM after 24 h of incubation did not exceed 20%. For 5 h of incubation, BCD photocytotoxicity in relation to melanoma cells reached 100% already at concentrations below 5 μM, while for normal cells the effect did not exceed 70% even for the 20 μM concentration. It is shown that BCD penetrates into the cells and is located predominantly in perinuclear cytoplasmic structures.

CONCLUSIONS

The BCD photosensitizing characteristics appear more adequate for application in PDT than that of the actually applied commercial photosensitizer Photogem®. Higher light absorption by BCD in the near IR region and its preferential localization in mitochondria can explain its high photocytotoxicity.

GENERAL SIGNIFICANCE

BCD can be considered as a new promising photosensitizer class for cancer PDT.

Photoinduced partial unfolding of tubulin bound to meso-tetrakis(sulfonatophenyl) porphyrin leads to inhibition of microtubule formation in vitro

The irradiation of the complex formed by meso-tetrakis (sulfonatophenyl) porphyrin (TSPP) and tubulin was investigated as well as its effects on the structure and function of the protein. We have used tubulin as a model target to investigate whether photoactive ligands docked to the protein can affect the structure and function of the protein upon exposure to visible light. We observed that laser irradiation prompts bleaching of the porphyrin which is accompanied by a sharp decrease (∼2 ns) in the average fluorescence lifetime of the protein and a change in the dichroic spectrum consistent with a decrease of helical structure. The result indicated the photoinduced partial unfolding of tubulin. We also observed that such partial conformational change inhibits the formation of microtubules in vitro. We investigated whether photosensitization of reactive oxygen species was responsible for these effects. Even upon removal of O2 the protein still undergoes conformational changes indicating that irradiation of the bound porphyrin does not require the presence of O2 to prompt conformational and functional effects opening the possibility that other mechanisms (e.g., charge transfer) are responsible for the photoinduced mechanism.

Temperature and oxygen-concentration dependence of singlet oxygen production by RuPhen as induced by quasi-continuous excitation

Assessment of partial pressure of oxygen (pO2) by luminescence lifetime measurements of ruthenium coordination complexes has been studied intensively during the last few decades. RuPhen (dichlorotris(1,10-phenanthroline) ruthenium(ii) hydrate) is a water soluble molecule that has been tested previously for in vivo pO2 detection. In this work we intended to shed light on the production of singlet oxygen by RuPhen. The quantum yield of singlet oxygen production by RuPhen dissolved in 0.9% aqueous NaCl solution (pH = 6) was measured at physiological temperatures (285-310 K) and various concentrations of molecular oxygen. In order to minimize the bleaching of RuPhen, the samples were excited with low power (<2 mW) laser pulses (20 μs long), created by pulsing a cw laser beam with an acousto-optical modulator. We show that, whereas the RuPhen phosphorescence lifetime decreases rapidly with an increase of temperature (keeping the oxygenation level constant), the quantum yield of singlet oxygen production by RuPhen is almost identical in the temperature range of 285-310 K. For air-saturated conditions at 310 K the measured quantum yield is about 0.25. The depopulation rate constants of the RuPhen (3)MLCT (metal-to-ligand charge-transfer) state are determined in the absence and in the presence of oxygen. We determined that the excitation energy for the RuPhen (3)MLCT→d-d transition is 49 kJ mol(-1) in the 0.9% NaCl solution (pH = 6).

Electron cryo-microscopy of TPPS4⋅2HCl tubes reveals a helical organisation explaining the origin of their chirality

A widely studied achiral porphyrin, which is highly soluble in aqueous solutions (TPPS4), is shown to self-assemble into helical nanotubes. These were imaged by electron cryo-microscopy and a state-of-the-art image analysis allows building a map at ∼5 Å resolution, one of the highest obtained so far for molecular materials. The authors were able to trace the apparent symmetry breaking to existing nuclei in the "as received samples", while carefully purified samples show that both handnesses occur in equal amounts.

Hypericin encapsulated in solid lipid nanoparticles: phototoxicity and photodynamic efficiency

The hydrophobicity of some photosensitizers can induce aggregation in biological systems, which consequently reduces photodynamic activity. The conjugation of photosensitizers with nanocarrier systems can potentially be used to overcome this problem. The objective of this study was to prepare and characterise hypericin-loaded solid lipid nanoparticles (Hy-SLN) for use in photodynamic therapy (PDT). SLN were prepared using the ultrasonication technique, and their physicochemical properties were characterised. The mean particle size was found to be 153 nm, with a low polydispersity index of 0.28. One of the major advantages of the SLN formulation is its high entrapment efficiency (EE%). Hy-SLN showed greater than 80% EE and a drug loading capacity of 5.22% (w/w). To determine the photodynamic efficiency of Hy before and after encapsulation in SLN, the rate constants for the photodecomposition of two (1)O2 trapping reagents, DPBF and AU, were determined. These rate constants exhibited an increase of 60% and 50% for each method, respectively, which is most likely due to an increase in the lifetime of the triplet state caused by the increase in solubility. Hy-SLN presented a 30% increase in cell uptake and a correlated improvement of 26% in cytotoxicity. Thus, all these advantages suggest that Hy-loaded SLN has potential for use in PDT.

Enhanced Photodynamic Selectivity of Nano-Silica-Attached Porphyrins Against Breast Cancer Cells

The synthesis and characterization of bare silica (4 nm in diameter) nanoparticle-attached meso-tetra(N-methyl-4-pyridyl)porphine (SiO(2)-TMPyP, 6 nm in diameter) are described for pH-controllable photosensitization. Distinguished from organosilanes, SiO(2) nanoparticles were functionalized as a potential quencher of triplet TMPyP and/or singlet oxygen ((1)O(2)) at alkaline pH, thereby turning off sensitizer photoactivity. In weak acidic solutions, TMPyP was released from SiO(2) surface for efficient production of (1)O(2). By monitoring (1)O(2) luminescence at 1270 nm, quantum yields of (1)O(2) production were found to be pH-dependent, dropping from ~ 0.45 in a pH range of 3-6 to 0.08 at pH 8-9, which is consistent with pH-dependent adsorption behavior of TMPyP on SiO(2) surface. These features make bare SiO(2)-attached cationic porphyrin a promising candidate for use in PDT for cancer treatment in which efficient (1)O(2) production at acidic pH and sensitizer deactivation at physiological pH are desirable. The enhanced therapeutic selectivity was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests and trypan blue exclusion tests of cell viability in breast cancer cell lines. Bimolecular quenching rate constants of (1)O(2) by free TMPyP, SiO(2) and SiO(2)-TMPyP nanoparticles were also determined.

Spectroscopic studies of aggregation behavior of meso-tetra(4-hydroxyphenyl)porphyrin in aqueous AOT solution

The interactions of two amphiphilic porphyrins with anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in aqueous solutions were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, resonance light scattering technique, fluorescence anisotropy and surface tension measurements. The two porphyrins, meso-tetra(4-hydroxyphenyl)porphyrin (THPP) and meso-tetra(3,5-dibromo-4-hydroxylphenyl)porphyrin (T(DBHP)P), exist as irregular aggregates in aqueous solutions with a broad and low absorption peak near the maximum of monomer peak. The interaction of THPP with AOT leads to the formation of a fluorescent aggregate of porphyrin which was assigned as J-type aggregate according to exciton theory. A long red-shifted Soret band together with a new strong Q-band, a broad emission peak and a sharply peaked resonance light scattering signal are observed for this J-aggregate. The formation of J-aggregate is independent of the initial THPP concentration and can be influenced greatly by ionic strength. The aggregation kinetics has been investigated by UV-vis absorption spectroscopy and fluorescence anisotropy. Conversion of the porphyrin monomers to J-aggregate is observed. The addition of THPP increases the surface tension of solution and changes the critical micelle concentration of AOT. J-aggregate was not observed for T(DBHP)P in AOT solutions which only shows solubilization. The mechanism of aggregation was discussed.

Effects of environment on the photophysical characteristics of mesotetrakis methylpyridiniumyl porphyrin (TMPyP)

Porphyrins are an important class of organic molecules, with interesting linear and nonlinear optical properties given mainly by their extended π-conjugation structure. Their photophysical properties can be greatly affected by the surrounding environment, which can be used to tune its final properties. Here we report on an experimental study of the photophysical properties of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) in aqueous and in several organic solvents and its interaction with micelles formed from negatively charged sodium dodecylsulphate (SDS), positively charged cetyl trimethyl ammonium bromide (CTAB) and neutral TRITON X-100. By using the Z-scan technique, flash-photolysis and time-resolved fluorescence techniques, we were able to evaluate the excited state dynamics of the TMPyP, and observed that the tetrapyrrole ring plays important role due to hydrogen bonds formation between nitrogen atom and water, while the side groups determine the porphyrin localization in non-aqueous micelle part.

Imidazole-modified porphyrin as a pH-responsive sensitizer for cancer photodynamic therapy

5,10,15,20-Tetrakis(N-(2-(1H-imidazol-4-yl)ethyl)benzamide)porphyrin produced twice as many singlet oxygen ((1)O(2)) molecules at pH 5.0 (quantum yield 0.53 ± 0.01) than at pH 7.4, whereas the (1)O(2) quenching rate was reduced by a factor of 2.5 for a pH change from 7.4 to 5.0.

Cyclodextrin carriers of positively charged porphyrin sensitizers

The cationic sensitizer 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) forms supramolecular complexes with native, per-methylated, sulfonated and dimethyl-sulfonated cyclodextrins (CDs). Binding interactions were proved by NMR, mass spectra, capillary zone electrophoresis, UV-Vis and fluorescence spectroscopy. The 2D-NMR experiments on native CDs indicate that the interaction of TMPyP with the external CD surface is the dominant binding mode. The high binding affinity of TMPyP towards sulfonated CDs is due to electrostatic interactions. Binding is accompanied by an increase of the TMPyP basicity. Whereas betaCD does not affect the lifetime of the TMPyP triplet states, binding with sulfonated CDs causes the protonation of the TMPyP triplet states even in neutral solution. The diprotonated anionic sensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPSH(2)(2+)) forms host-guest complexes with native betaCD and gammaCD, similarly as in its non-protonated state. The positive charge of pyrrole nitrogen atoms does not significantly influence the mode of the interaction. In contrast to TMPyP, the lifetimes of the triplet states of bound TPPSH(2)(2+) to native CDs increase.

Spectroscopic studies on the interaction of a water-soluble cationic porphyrin with proteins

The interaction of a water-soluble cationic porphyrin, meso-tetrakis (4-N,N,N-trimethylanilinium) porphyrin (TMAP), with two proteins, bovine serum albumin (BSA) and human serum albumin (HSA), was studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence anisotropy and synchronous fluorescence spectroscopy at neutral aqueous solutions. Free base TMAP bound to proteins as monomers and no aggregation was observed. The binding of TMAP quenched the fluorescence of the protein. On the contrary, the fluorescence of TMAP was enhanced and the fluorescence anisotropy increased due to the binding. The direct static binding mechanism could account for the quenching by TMAP and the binding constants were calculated. TMAP showed a higher quenching efficiency and binding constant of HSA than BSA. The binding of TMAP had no obvious effect on the molecular conformation of the protein. There was only one binding site for TMAP and it was located on the surface of the protein molecule. Electrostatic force played an important role in the binding due to the opposite charges on porphyrin and the proteins.

Protoporphyrin IX nanoparticle carrier: preparation, optical properties, and singlet oxygen generation

The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 micros, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (eta Delta) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.