Picosecond fluorescence spectroscopy on incorporation processes of hematoporphyrin derivative into malignant tumor cells in vitro

Strong enhancement of the two-photon absorption of tetrakis(4-sulfonatophenyl)porphyrin diacid in water upon aggregation

A strong enhancement of the two-photon absorption (TPA) cross section of tetrakis(4-sulfonatophenyl)porphyrin diacid (H(4)TPPS(2-)) at various wavelengths when a J-type aggregate is formed in water with respect to the one observed for the H(4)TPPS(2-) monomer in a mixture of water, dimethyl sulfoxide (DMSO), and urea is presented. The TPA properties are characterized by the open aperture Z-scan technique and the ultrafast two-photon absorption spectroscopy with white light continuum probe (TPA-WLCP) technique. The observed enhancement is discussed in terms of possible electronic cooperative effects in the aggregate.

Theoretical Investigation of One-Photon and Two-Photon Absorption Properties for Multiply N-Confused Porphyrins

We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G*) and ZINDO/SOS methods. The electronic structure, one-photon absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths lambda(max) are blue-shifted and the TPA cross sections delta(max) are increased 22.7-112.1 GM when the N atoms one by one are inverted from core to beta position to form multiply N-confused porphyrins. Especially delta(max) of N3CP get to 164.7 GM. The electron donors -C6F5s at meso-position can make the TPA cross section delta(max) increase. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N3CP, N4CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation.

Internalization of aggregated photosensitizers by tumor cells: subcellular time-resolved fluorescence spectroscopy on derivatives of pyropheophorbide-a ethers and chlorin e6 under femtosecond one- and two-photon excitations

Amphiphilic sensitizers self-associate in aqueous environments and form aggregated species that exhibit no or only negligible photodynamic activity. However, amphiphilic photosensitizers number among the most potent agents of photodynamic therapy. The processes by which these sensitizers are internalized into tumor cells have yet to be fully elucidated and thus remain the subject of debate. In this study the uptake of photosensitizer aggregates into tumor cells was examined directly using subcellular time-resolved fluorescence spectroscopy with a high temporal resolution (20-30 ps) and high sensitivity (time-correlated single-photon counting). The investigations were performed on selected sensitizers that exhibit short fluorescence decay times (< 50 ps) in aggregated form. Derivatives of pyropheophorbide-a ether and chlorin e6 with varying lipophilicity were used for the study. The characteristic fluorescence decay times and spectroscopic features of the sensitizer aggregates measured in aqueous solution also could be observed in A431 human endothelial carcinoma cells administered with these photosensitizers. This shows that tumor cells can internalize sensitizers in aggregated form. Uptake of aggregates and their monomerization inside cells were demonstrated directly for the first time by means of fluorescence lifetime imaging with a high temporal resolution. Internalization of the aggregates seems to be endocytosis mediated. The degree of their monomerization in tumor cells is strongly influenced by the lipophilicity of the compounds.

Photophysical properties of porphyrins in biological membranes

This review illustrates the photophysical properties of some porphyrins, especially those used for biomedical applications, in relation to their photosensitizing efficiency in biological membranes. Porphyrin absorption and luminescence properties are mainly examined. The factors influencing the affinity of porphyrins for biological membranes, including the dye hydrophobicity, the charge and aggregation state, the pH of the medium and the physicochemical properties of the dye environment, are discussed. These factors determine the differences in the photophysical properties of porphyrins in biological membranes. Particular attention is paid to the porphyrin aggregation state: only monomeric species and possibly planar end-to-end aggregates are endowed with significant photosensitizing ability. Many conclusions presented are based on data obtained on membrane model systems such as micelles or liposomes which can mimic specific situations occurring in cells.

Femtosecond studies of hematoporphyrin derivative in solution: effect of pH and solvent on the excited state dynamics

We report direct femtosecond measurements of the excited state dynamics of hematoporphyrin derivative (HpD) in solution. The dynamics are found to be very sensitive to the solvent and pH of aqueous solutions. The decay of the excited singlet states is much faster in acidic and pH 7 buffer aqueous solutions (< 230 ps) than in basic aqueous solutions or organic solvents (> 10 ns). The dynamical results show strong correlation with static fluorescence measurements: weaker fluorescence in acidic and pH 7 buffer solutions corresponding to shorter-lived excited states. A new fast decay component with a time constant around 5 ps is identified both in acidic aqueous solutions and in organic solvents such as acetone and attributed to internal conversion from the second to the first excited singlet state of aggregates or certain oligomers in HpD, in accord with the observation that the fast decay component is larger at a higher concentration. Oxygen is found to have no effect on the dynamics on the time scale investigated, 1 ns, indicating that oxygen quenching of the singlet excited states is insignificant on this time scale. The sensitive solvent and pH dependence of the excited state dynamics has important clinical implications in the use of HpD as a photosensitizing agent.

Time-resolved in-vivo fluorescence of photosensitizing porphyrins

Various components of photosensitizing porphyrins (e.g. monomers, aggregates, ionic species) have been recently localized in single cells by time-resolved fluorescence microscopy. Novel time-resolving techniques, based on picosecond laser diodes, a frequency-doubled Nd:YAG laser and time-gated microscopic equipment, were used for in-vivo measurements of the chick chorioallantoic membrane (CAM) exhibiting a pronounced vasculature. Changes of the fluorescence decay kinetics after light exposure were correlated with the formation of a photoproduct (Photosan, aminolaevulinic acid) or changes of the intracellular binding sites (tetraphenyl-porphyrins). Fluorescent components with different decay times were shown to be distributed differently within the tissue.

Laser picosecond microspectrofluorometry of haematoporphyrin in cells and liposomes

The results of a laser picosecond microspectrofluorometric study of the spectral and kinetic characteristics of haematoporphyrin (Hp) fluorescence at various sites in cultured SPEV cells and phosphatidylcholine liposomes are presented. The computer-controlled detection system is based on the single-photon counting method with picosecond time resolution. In aqueous medium, the Hp fluorescence spectrum is characterized by two bands at 615 and 675 nm. In living cells and liposomes, Hp fluorescence is red shifted to 630 and 690 nm. In addition a new band at 665 nm is detected. The dependence of this band on the incubation time and Hp concentration was investigated. The fluorescence decay kinetics of Hp in a culture medium, liposome and a cell nuclear membrane were measured. Possible Hp aggregate formation in the lipid bilayer and its implications are discussed.

Time-resolved luminescence spectroscopy of photosensitizers of biomedical interest

Studying the fluorescence decay of chromophores, either used as fluorescent labels to stain specific biomolecules or as photosensitizers to produce irreversible chemical or physico-chemical modifications on biological substrates, is being demonstrated to be a valuable method of investigating the interactions underlying a variety of phenomena. In fact, all possible primary steps in a photosensitized biological system are phenomena that may occur during the chromophore S1 lifetime and act as quenching mechanisms of the S1 state. Thus they can be identified, and the relative importance of the corresponding transient species quantitatively determined, with suitable techniques of time-resolved fluorescence spectroscopy. The examples discussed in this paper concern both tumor photosensitizing drugs, such as anthracyclines and porphyrins, and skin sensitizers (e.g. furocoumarins).

Time-gated fluorescence spectroscopy of the tumor localizing fraction of HpD in the presence of cationic surfactant

Time-gated fluorescence spectroscopy was performed on the tumor localizing fraction (TLF) of HpD in buffer at different concentrations of cationic surfactant. This technique obtains emission spectra with programmable delay relative to the excitation pulse. According to the measured fluorescence decay-time constants (approximately 0.7, approximately 3 and approximately 15 ns) three gates were considered, delayed by 0, 5 and 18 ns, respectively, to evaluate the contribution of the emitting molecular species to the spectra. Simultaneous to these measurements, fluorescence decay waveforms and time-integrated spectra were also detected. In buffer and in detergent micelles the fluorescence spectra are given by the superposition of the emission of the different molecular species present in the solution, and no appreciable interaction among the chromophores is observed. On the contrary, in the pre-micellar range of the surfactant, evidence for the existence of an energy transfer mechanism was found. This effect seems to be related to the configurational state of the TLF polymeric chains and depends on the relative TLF/surfactant concentration.

Picosecond fluorescence of R3230AC mammary carcinoma mitochondria after treatment with hematoporphyrin derivative and Photofrin II in vivo

Hematoporphyrin derivative (HPD) and other porphyrin samples were excited by 20-ps 532-nm laser pulses. Fluorescence was detected using a low-jitter streak camera. Data were fitted to a sum of exponential decay times on the order of picoseconds. Fluorescence of porphyrins in aqueous solution show various behaviors depending on the hydrophobicity of the porphyrins. The most hydrophilic porphyrins show long decays only (greater than 500 ps). Porphyrins intermediate in hydrophobicity have intensity-dependent fast decays. The most hydrophobic have fast decays (less than 20 ps). Picosecond fluorescences of mitochondria prepared from rat tumors treated in vivo with HPD or Photofrin II show an increase in the ratio of fast to slow decays when compared to the injected porphyrins. These results are consistent with the concentration of the more hydrophobic porphyrins in mitochondria in photosensitization treatment. Thus picosecond fluorescence studies of porphyrins may provide a means to obtain photoproperties which differentiate between effective and ineffective in vivo photosensitizers.

Ocular fluorometry: principles, fluorophores, instrumentation, and clinical applications

Ocular fluorometry is rapidly evolving as a versatile technique for research and diagnosis in ophthalmology. The main reasons for this increasing success are 1) the ideal characteristics of the eye as an optical device for excitation of tissue fluorescence and for the detection of the fluorescent emission; 2) the development of novel fluorometric techniques, including differential and time-resolved fluorescence spectroscopy; and 3) the increasing use of coupling geometries with high-resolution and high spatial selectivity. Both endogenous and exogenous fluorophores are of interest to ocular fluorometry. The most significant among endogenous fluorophores are the fluorescing pigments of the lens and of the retinal pigment epithelium (RPE). The nature, topography, and fluorescence properties of such pigments depend on age and pathology and on the level of light exposure. Exogenous fluorophores of interest are both intentionally induced and unintentionally accumulated drugs (some of which are phototoxic). Laser-based fluorometric techniques play a leading role in ocular fluorometry. The peculiar properties of the laser for the excitation of fluorescence make this source a favorite candidate for ocular fluorometry both in vitro and in vivo.