Variation in the fluorescence decay properties of haematoporphyrin derivative during its conversion to photoproducts

Validation of photodynamic action via photobleaching of a new curcumin-based composite with enhanced water solubility

Motivated by the photochemical and photophysical properties of curcumin-based composites, the characteristics of a new curcumin-based water-soluble salt were investigated via absorption and fluorescence spectroscopy. Photobleaching was investigated using a set of LEDs in three different wavelengths (405 nm, 450 nm and 470 nm) to illuminate an aqueous solution of curcumin, evaluating its degradation for five different exposure times (0, 5, 15, 45 and 105 minutes). The results were compared with equivalent measurements of dark degradation and illumination in the presence of a singlet-oxygen quencher. Three solution concentrations (50, 100 and 150 μg/ml) were studied. To measure the fluorescence, it was used low power 405 nm excitation laser source. Time dependent photodegradation of curcumin was observed, as compared to the natural degradation of samples maintained on a dark environment. Two main absorption peaks were detected and their relation responded to both concentration and wavelength of the illumination source. A spectral correlation between absorption of curcumin and the emission bands of the sources showed an optimal spectral overlap for the 450 nm LED. For this source, photobleaching showed a less intense degradation on the presence of singlet oxygen quencher. This last result confirmed singlet oxygen production in vitro, indicating a strong potential of this composite to be used as a blue-light-activated photosensitizer.

Monitoring photosensitizer uptake using two photon fluorescence lifetime imaging microscopy

Photodynamic Therapy (PDT) provides an opportunity for treatment of various invasive tumors by the use of a cancer targeting photosensitizing agent and light of specific wavelengths. However, real-time monitoring of drug localization is desirable because the induction of the phototoxic effect relies on interplay between the dosage of localized drug and light. Fluorescence emission in PDT may be used to monitor the uptake process but fluorescence intensity is subject to variability due to scattering and absorption; the addition of fluorescence lifetime may be beneficial to probe site-specific drug-molecular interactions and cell damage. We investigated the fluorescence lifetime changes of Photofrin(®) at various intracellular components in the Mat-LyLu (MLL) cell line. The fluorescence decays were analyzed using a bi-exponential model, followed by segmentation analysis of lifetime parameters. When Photofrin(®) was localized at the cell membrane, the slow lifetime component was found to be significantly shorter (4.3 ± 0.5 ns) compared to those at other locations (cytoplasm: 7.3 ± 0.3 ns; mitochondria: 7.0 ± 0.2 ns, p < 0.05).

Characterization of Photofrin photobleaching for singlet oxygen dose estimation during photodynamic therapy of MLL cells in vitro

A singlet oxygen dose model is developed for PDT with Photofrin. The model is based on photosensitizer photobleaching kinetics, and incorporates both singlet oxygen and non-singlet oxygen mediated bleaching mechanisms. To test our model, in vitro experiments were performed in which MatLyLu (MLL) cells were incubated in Photofrin and then irradiated with 532 nm light. Photofrin fluorescence was monitored during treatment and, at selected fluence levels, cell viability was determined using a colony formation assay. Cell survival correlated well to calculated singlet oxygen dose, independent of initial Photofrin concentration or oxygenation. About 2 x 10(8) molecules of singlet oxygen per cell were required to reduce the surviving fraction by 1/e. Analysis of the photobleaching kinetics suggests that the lifetime of singlet oxygen in cells is 0.048 +/- 0.005 micros. The generation of fluorescent photoproducts was not a result of singlet oxygen reactions exclusively, and therefore did not yield additional information to aid in quantifying singlet oxygen dose.

Photobleaching kinetics of Photofrinin vivoand in multicell tumour spheroids indicate two simultaneous bleaching mechanisms

We present a detailed investigation of Photofrin photobleaching and photoproduct accumulation. Fisher rats were sensitized with 10 mg kg(-1) Photofrin and irradiated 24 h later with 514 nm light at 5 or 100 mW cm(-2). Fluorescence spectra were collected from the skin throughout treatment, and sensitizer bleaching and fluorescent photoproduct formation were quantified using spectral analysis. Photofrin bleaching was slightly more rapid at the higher irradiance under these conditions. However, accumulation of photoproduct was significantly enhanced at lower irradiance. To interpret these unexpected findings, we developed a new mathematical model in which reactions between singlet oxygen (1O2) and the photosensitizer and reactions between the sensitizer triplet and biological targets are both allowed to contribute to bleaching. Predictions of this model were tested in experiments performed on EMT6 spheroids sensitized with concentrations of 2.5, 10 and 30 microg mL(-1) Photofrin and subjected to PDT. Photofrin bleaching and photoproduct formation in these spheroids were measured using confocal fluorescence spectroscopy. In qualitative agreement with the mixed-mechanism model predictions, at the highest drug concentration Photofrin bleaching was more efficient via 1O2 reactions, while at the lowest concentration triplet reactions were more efficient. At all concentrations, photoproduct accumulation was greater under conditions of abundant oxygen.

Monitoring photoproduct formation and photobleaching by fluorescence spectroscopy has the potential to improve PDT dosimetry with a verteporfin-like photosensitizer

In current clinical practice, photodynamic therapy (PDT) is carried out with prescribed drug doses and light doses as well as fixed drug-light intervals and illumination fluence rates. This approach can result in undesirable treatment outcomes of either overtreatment or undertreatment because of biological variations between different lesions and patients. In this study, we explore the possibility of improving PDT dosimetry by monitoring drug photobleaching and photoproduct formation. The study involved 60 mice receiving the same drug dose of a novel verteporfin-like photosensitizer, QLT0074, at 0.3 mg/kg body weight, followed by different light doses of 5, 10, 20, 30, 40 or 50 J/cm2 at 686 nm and a fluence rate of 70 mW/cm2. Photobleaching and photoproduct formation were measured simultaneously, using fluorescence spectroscopy. A ratio technique for data processing was introduced to reliably detect the photoproduct formed by PDT on mouse skin in vivo. The study showed that the QLT0074 photoproduct is stable and can be reliably quantified. Three new parameters, photoproduct score (PPS), photobleaching score (PBS) and percentage photobleaching score (PBS%), were introduced and tested together with the conventional dosimetry parameter, light dose, for performance on predicting PDT-induced outcome, skin necrosis. The statistical analysis of experimental results was performed with an ordinal logistic regression model. We demonstrated that both PPS and PBS improved the prediction of skin necrosis dramatically compared to light dose. PPS was identified as the best single parameter for predicting the PDT outcome.

The photobleaching of disulfonated aluminium phthalocyanine in microbial systems

Front-face illumination spectroscopic techniques were used to study photobleaching of disulfonated aluminium phthalocyanine (AlPcS2) in the bacteria and yeast cells Escherichia coil, Porphyromonas gingivalis (Gram-negative bacteria), Streptococcus mutans (a Gram-positive bacterium), and the yeast Candida albicans. The photobleaching of AlPcS2 with the microbes studied is complex, involving reactive species generated by type I and type II processes with the rate dependent on the relative contributions of the different photobleaching mechanisms. The average rate of photobleaching of the AlPcS2 monomer in the presence of both E. coli and C. albicans increases as the fluence of the illumination source decreases. The effects of oxygen and sensitiser concentration on the rate of AlPcS2 photobleaching in these systems are also investigated.

Fluorescence spectroscopy of normal mouse skin exposed to 5-aminolaevulinic acid and red light

Photobleaching and phototransformation of protoporphyrin IX (PpIX) was investigated in normal mouse skin. The PpIX was induced by topical application of 5-aminolaevulinic acid (ALA). Exposure to laser light (635 nm) caused photobleaching of PpIX fluorescence and formation of fluorescent products. Analysis of the fluorescence spectra revealed appearance of new fluorescent photoproducts during light exposure. The main photoproduct, supposedly chlorin-type photoprotoporphyrin (PPp), exhibited fluorescence with an emission maximum at 675 nm. The other products exhibited main fluorescence peaks at around 588 and 623 nm that can presumably be attributed to an endogenous metallo-porphyrin and water-soluble porphyrin(s), respectively. Our results indicate that light exposure causes alterations in the enzymatic pathway of PpIX synthesis from ALA and leads to accumulation of intermediate water-soluble porphyrins. ALA-induced porphyrins are transported away from the treated area and partly deposited in remote skin sites.

Phototransformations of 5-aminolevulinic acid-induced protoporphyrin IX in vitro: a spectroscopic study

Human adenocarcinoma cells of the line WiDr were incubated with 5-aminolevulinic acid to induce protoporphyrin IX (PpIX) and then exposed to laser light of wavelength 635 nm. The PpIX fluorescence decreased with increasing exposure. The decay rate was slightly dependent on the initial PpIX concentration. The PpIX fluorescence was halved by a fluence of about 40 J/cm2. Several fluorescing photoproducts were formed. The main one, supposedly the chlorine-type photoprotoporphyrin (Ppp), had a fluorescence excitation spectrum stretching out to about 680 nm with a maximum at around 668 nm. The formation kinetics of this product was dependent on the initial PpIX concentration. Moreover, it was selectively bleached by exposure to light at 670 nm. A photoproduct with an emission maximum at 652 nm, different from Ppp, remained after this exposure. Traces of a photoproduct(s) with fluorescence emission slightly blue-shifted compared with that of PpIX, supposedly water-soluble porphyrins, were also detected after light exposure.

Mathematical description of photobleaching in vivo describing the influence of tissue optics on measured fluorescence signals

The observed decrease in the fluorescence signal during photodynamic therapy (PDT) may contain dosimetric information as this photobleaching provides direct information on the photodynamic processes occurring in the tissue. A correct interpretation of the photobleaching signal, however, is crucial for its use in dosimetry. In this study the influence of scattering and absorption phenomena in tissue on the emitted fluorescence signal are described mathematically. Analytical solutions of the resulting expression show a difference from the single-decaying-exponential function generally used for describing photobleaching signals. The solutions are a function of the fluence rate at the inner side of tissue boundary psi(0*), the photobleaching dose constant beta, the incident irradiation power I0 and time. The accuracy of the results was investigated by comparison of the analytic solutions with numerical calculations using fluence rate profiles and escape functions obtained by Monte Carlo (MC) simulations. Good resemblance is observed when the value for psi(0*) calculated by the MC simulations is used in the analytical solutions. Experimental results in this study indicate the photobleaching dose constant of ALA-induced PpIX to be 33 +/- 3 J cm-2. Determination of beta for different types of photosensitizer and the development of an accurate method to determine psi(0*) can make monitoring of photobleaching during PDT valuable for dosimetry.

Quantitative optical spectroscopy for tissue diagnosis

The interaction of light within tissue has been used to recognize disease since the mid-1800s. The recent developments of small light sources, detectors, and fiber optic probes provide opportunities to quantitatively measure these interactions, which yield information for diagnosis at the biochemical, structural, or (patho)physiological level within intact tissues. However, because of the strong scattering properties of tissues, the reemitted optical signal is often influenced by changes in biochemistry (as detected by these spectroscopic approaches) and by physiological and pathophysiological changes in tissue scattering. One challenge of biomedical optics is to uncouple the signals influenced by biochemistry, which themselves provide specificity for identifying diseased states, from those influenced by tissue scattering, which are typically unspecific to a pathology. In this review, we describe optical interactions pursued for biomedical applications (fluorescence, fluorescence lifetime, phosphorescence, and Raman from cells, cultures, and tissues) and then provide a descriptive framework for light interaction based upon tissue absorption and scattering properties. Finally, we review important endogenous and exogenous biological chromophores and describe current work to employ these signals for detection and diagnosis of disease.

Spectroscopic studies of photobleaching and photoproduct formation of porphyrins used in tumour therapy

The illumination of haematoporphyrin, meso-tetraphenylporphyrin tetrasulphonate and haematoporphyrin derivative in aqueous solution causes two simultaneously occurring processes: photodegradation and the formation of stable photoproducts absorbing in the red spectral region. In the case of haematoporphyrin and its derivatives, these photoproducts have an absorption maximum around 640 nm (photoproduct 640). The former process, which is detected as the bleaching of the porphyrin absorption spectrum as well as a decrease in the fluorescence intensity, is slightly dependent on the solution pH and becomes dominant when the formation of the photoproduct reaches saturation. For the most part, the photodegradation can be explained as the opening of the porphyrin ring, leading to an increase in light absorbance in the UV region. The formation of photoproduct 640 is closely related to the aggregation state of the porphyrins, and shows a distinct dependence on the medium pH. The effectiveness of photoproduct 640 formation strongly increases in neutral and alkaline solutions, whereas the porphyrins are photostable below pH 5. The spectroscopic features of the photoproducts of haematoporphyrin and haematoporphyrin derivative, with absorption bands in the visible region, are similar to those of chlorin and/or porphyrin-chlorin linked systems. On the basis of these spectroscopic studies, it is suggested that photoproduct 640 is a chlorin-type molecule formed predominantly from the aggregates of porphyrins when photo-oxidation and photoreduction are in competition.

HepG2 human hepatocarcinoma cells: an experimental model for photosensitization by endogenous porphyrins

Endogenous protoporphyrin IX (PpIX) synthesis after delta-aminolaevulinic acid (ALA) administration occurs in cancer cells in vivo; PpIX, which has a short half-life, may thus constitute a good alternative to haematoporphyrin derivative (HPD) (or Photofrin). This study assesses the ability of the human hepatocarcinoma cell line HepG2 to synthesize PpIX in vitro from exogenous ALA, and compares ALA-induced toxicity and phototoxicity with the photodynamic therapy (PDT) effects of HPD on this cell line. ALA induced a dose-dependent dark toxicity, with 79% and 66% cell survival for 50 and 100 micrograms ml-1 ALA respectively after 3 h incubation; the same treatment, followed by laser irradiation (lambda = 632 nm, 25 J cm-2), induced a dose-dependent phototoxicity, with 54% and 19% cell survival 24 h after PDT. Whatever the incubation time with ALA, a 3 h delay before light exposure was found to be optimal to reach a maximum phototoxicity. HPD induced a slight dose-dependent toxicity in HepG2 cells and a dose- and time-dependent phototoxicity ten times greater than that of ALA-PpIX PDT. After 3 h incubation of 2.5 and 5 micrograms ml-1 HPD, followed by laser irradiation (lambda = 632 nm, 25 J cm-2), cell survival was 59% and 24% respectively at 24 h. Photoproducts induced by light irradiation of porphyrins absorb light in the red spectral region at longer wavelengths than the original porphyrins. The possible enhancement of PDT effects after HepG2 cell incubation with ALA or HPD was investigated by irradiating cells successively with red light (lambda = 632 nm) and light (lambda = 650 nm)(ABSTRACT TRUNCATED AT 250 WORDS)

Malignancies and atherosclerotic plaque diagnosis--is laser induced fluorescence spectroscopy the ultimate solution?

A non-invasive diagnostic tool that can identify diseased tissue sites in situ and in real time could have a major impact on the detection and treatment of cancer and atherosclerosis. A review of the research performed on the utilization of laser induced fluorescence spectroscopy (LIFS) as a means of diseased tissue diagnosis is presented. Special emphasis is given to problems which were raised during clinical trials and recent experimental studies. The common origin and possible solution of these problems are shown to be related to, firstly, the identification of the fluorescent chemical species, secondly, the determination of the excitation/collection geometry and its effect to the method and, finally, the further elaboration on the laser-tissue interaction.

Photofrin-induced fluorescence in progressive and regressive murine colonic cancer cells: correlation with cell photosensitivity

Microspectrofluorometry and fluorescence imaging were used to investigate the intracellular fluorescence of two murine colonic cancer cell lines--a progressive cell line (PROb) and a regressive cell line (REGb)--incubated with Photofrin. These two cell lines, which were initially cloned from the same chemically induced colonic murine cancer, differ in their metastatic properties and have been considered as models to mimic the tumoral cell heterogeneity. The fluorescence from cytoplasmic area of cells incubated with Photofrin appeared as a complex emission, with two maxima at 632 and 695 nm assigned to monomer species, and a poorly resolved band around 665 nm assigned to aggregates. The spectral distribution was shown to depend on the incubation time, with an aggregate contribution increasing for extended periods. The amount of Photofrin uptake, as determined from the total fluorescence intensity, was found for PROb to be twice that for REGb. However, the phototoxicities were quite similar for both cell lines, suggesting that drug concentration may not be the only determining factor in photobiological efficiency.

Photodynamic therapy of experimental colonic tumours with 5-aminolevulinic-acid-induced endogenous porphyrins

5-Aminolevulinic acid (5-ALA) is a precursor in the biosynthesis of haem. External application of 5-ALA leads to the formation of protoporphyrin IX, the last intermediate product before haem, which is an effective sensitiser. The 5-ALA-induced endogenous photosensitisation of tumour cells has been exploited for photodynamic therapy (PDT). Experimental human G-3 colonic tumours were transplanted into nude mice, and ten mice were treated by PDT. Ten animals served as controls. We measured a fluorescence intensity of the tumour that was about eight times higher than in the surrounding tissue; a good correlation between the fluorescence intensity and the photodynamic effect was found. Tumour growth was inhibited significantly after PDT, two tumours being destroyed completely after the second PDT treatment. In addition, on-line fluorescence detection during PDT showed a change in the intensity and the fluorescence spectrum of protoporphyrin IX caused by photobleaching and the formation of photoproducts.

Photodynamic therapy in psoriasis: suppression of cytokine production in vitro and recording of fluorescence modification during treatment in vivo

Photodynamic therapy (PDT) consists of the combination of photosensitizers absorbing light mainly in the red spectral region and irradiation with light of corresponding wavelengths. We analysed its effects on the cytokine secretion (IL-1 beta, TNF alpha, IL-6) of freshly isolated peripheral mononuclear cells from six patients with chronic plaque-stage psoriasis in comparison with PUVA. PUVA treatment resulted in a decreased production of all three cytokines, but most pronounced in the case of IL-6. PDT caused a similar change in the cytokine pattern, but its effectiveness was lower. In vivo fluorescence recordings were performed on psoriatic plaque lesions after topical application of the photosensitizer Photosan-3. Under irradiation, progressive photobleaching was noted with increasing radiation dosage. This is the first reported study of photochemical reactions using on-line fluorescence recordings during PDT of psoriatic lesions in vivo. Our results demonstrate the capacity of PDT to cause immunomodulatory effects similar to PUVA, thus indicating its potential application to the treatment of this common disease.

In vivo photoproduct formation during PDT with ALA-induced endogenous porphyrins

The administration of 5-aminolevulinic acid (ALA) in tumor-bearing nude mice leads to the formation of the fluorescent, photounstable photosensitizer protoporphyrin IX in tumor tissue. On-line fluorescence spectroscopy during photodynamic therapy (PDT) shows the in vivo formation of chlorintype photoproducts of protoporphyrin. The fluorescence of protoporphyrin as well as its photoproducts is bleached completely at the end of the PDT (100 J cm-2, 630 nm). These findings were also verified using ultrashort laser pulses and time-correlated single-photon counting. A photinduced shortening of the decay times and decrease in the integral fluorescence intensity were measured in vivo due to the photodestruction of the endogenous photosensitizer protoporphyrin IX in the tumor.

Phototransformations of porphyrins in aqueous and micellar media

Porphyrin photoproducts with absorption maxima at 640 and 660 nm are formed in aqueous and micellar solutions during light exposure. Changes in the dimethoxyhaematoporphyrin (DMHp) Soret band on irradiation suggest that the photoproduct (640 nm) formation is conditioned by the "sandwich"-type self-associates. The formation of the photoproduct (660 nm) in micellar haematoporphyrin (Hp) and photosan-3 (PS) solutions and its formation in small amounts in phosphate-buffered solution (PBS), is related to the presence of covalently linked porphyrin structures and/or interaction with surfactant molecules. PS is the most photostable of the three investigated porphyrins. Its photostability is probably due to the presence of covalently linked "sandwich"-type aggregates.

Quantum yields and kinetics of the photobleaching of hematoporphyrin, Photofrin II, tetra(4-sulfonatophenyl)-porphine and uroporphyrin

Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4-sulfonatophenyl)porphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 x 10(-5), 5.4 x 10(-5), 9.8 x 10(-6), and 2.8 x 10(-5) for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 microM) significantly reduced the photobleaching yields. However, D2O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1 M. Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mM furfuryl alcohol increased the photobleaching yields of HP and URO more than 5-fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10-fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues during PDT may be complex.

[A simple setup for measuring scattering in testing the photodynamic effectiveness of dyes]

An experimental setup for the determination of the photodynamic activity of dyes on the basis of scattering measurements is described. With its aid, photochemically induced morphological changes and the process of cell lysis can be registered, and action spectra measured by varying the irradiation wavelength. Different photoproducts of the photosensitizer hematoporphyrin derivative (HPD) were tested in human erythrocyte suspensions. The photodynamic activity of these products was found to depend on absorption behavior, but is lower than that of HPD.