Adjaci F. Uchoa

Giant vesicles under oxidative stress induced by a membrane-anchored photosensitizer.

We have synthesized the amphiphile photosensitizer PE-porph consisting of a porphyrin bound to a lipid headgroup. We studied by optical microscopy the response to light irradiation of giant unilamellar vesicles of mixtures of unsaturated phosphatidylcholine lipids and PE-porph. In this configuration, singlet oxygen is produced at the bilayer surface by the anchored porphyrin. Under irradiation, the PE-porph decorated giant unilamellar vesicles exhibit a rapid increase in surface area with concomitant morphological changes. We quantify the surface area increase of the bilayers as a function of time and photosensitizer molar fraction. We attribute this expansion to hydroperoxide formation by the reaction of the singlet oxygen with the unsaturated bonds. Considering data from numeric simulations of relative area increase per phospholipid oxidized (15%), we measure the efficiency of the oxidative reactions. We conclude that for every 270 singlet oxygen molecules produced by the layer of anchored porphyrins, one eventually reacts to generate a hydroperoxide species. Remarkably, the integrity of the membrane is preserved in the full experimental range explored here, up to a hydroperoxide content of 60%, inducing an 8% relative area expansion.

Chlorin photosensitizers sterically designed to prevent self-aggregation.

The synthesis and photophysical evaluation of new chlorin derivatives are described. The Diels-Alder reaction between protoporphyrin IX dimethyl ester and substituted maleimides furnishes endo-adducts that completely prevent the self-aggregation of the chlorins. Fluorescence, resonant light scattering (RLS) and (1)H NMR experiments, as well as X-ray crystallographic have demonstrated that the configurational arrangement of the synthesized chlorins prevent π-stacking interactions between macrocycles, thus indicating that it is a nonaggregating photosensitizer with high singlet oxygen (Φ(Δ)) and fluorescence (Φ(f)) quantum yields. Our results show that this type of synthetic strategy may provide the lead to a new generation of PDT photosensitizers.

Photodynamic Therapy Using Methylene Blue to Treat Cutaneous Leishmaniasis

OBJECTIVE The purpose of this study was to show the efficiency and underlying mechanism of action of photodynamic therapy (PDT) using methylene blue (MB) and non-coherent light sources to treat cutaneous leishmaniasis (CL). BACKGROUND DATA Systemic treatment can cause severe side effects, and PDT using porphyrin precursors as sensitizers has been used as an alternative to treat CL. MB has been used under illumination or in the dark to treat a wide range of medical conditions, and it exhibits antimicrobial activity against protozoa and viruses. METHODS In in vitro tests, the cell viability (via a MTT colorimetric assay) of Leishmania amazonensis parasites was evaluated as a function of MB concentration. In in vivo experiments, we analyzed the treatment of two lesions from a patient with leishmaniasis. The patient received a low dose of pentavalent antimony (SbV), and one lesion was treated with PDT. RESULTS We observed IC(50) decreases from 100 to 20 μM in response to PDT when MB was used in different concentrations in in vitro tests. Use of SbV in combination with the PDT protocol produced faster wound recovery when compared with the use of SbV alone. CONCLUSIONS The in vitro experiments and the results from the clinical case suggest that the inexpensive PDT protocol that is based on MB and RL50® may be used to treat CL caused by L. amazonensis.

A new micro/nanoencapsulated porphyrin formulation for PDT treatment

The highly hydrophobic 5,10,15-triphenyl-20-(3-N-methylpyridinium-yl)porphyrin (3MMe) cationic species was synthesized, characterized and encapsulated in marine atelocollagen/xanthane gum microcapsules by the coacervation method. Further reduction in the capsule size, from several microns down to about 300-400 nm, was carried out successfully by ultrasonic processing in the presence of up to 1.6% Tween 20 surfactant, without affecting the distribution of 3MMe in the oily core. The resulting cream-like product exhibited enhanced photodynamic activity but negligible cytotoxicity towards HeLa cells. The polymeric micro/nanocapsule formulation was found to be about 4 times more phototoxic than the respective phosphatidylcholine lipidic emulsion, demonstrating high potentiality for photodynamic therapy applications.

Generation and suppression of singlet oxygen in hair by photosensitization of melanin.

We have studied the spectroscopic properties of hair (white, blond, red, brown, and black) under illumination with visible light, giving special emphasis to the photoinduced generation of singlet oxygen ((1)O(2)). Irradiation of hair shafts (λ(ex)>400 nm) changed their properties by degrading the melanin. Formation of C3 hydroperoxides in the melanin indol groups was proven by (1)H NMR. After 532-nm excitation, all hair shafts presented the characteristic (1)O(2) emission (λ(em)=1270 nm), whose intensity varied inversely with the melanin content. (1)O(2) lifetime was also shown to vary with hair type, being five times shorter in black hair than in blond hair, indicating the role of melanin as a (1)O(2) suppressor. Lifetime ranged from tenths of a nanosecond to a few microseconds, which is much shorter than the lifetime expected for (1)O(2) in the solvents in which the hair shafts were suspended, indicating that (1)O(2) is generated and suppressed inside the hair structure. Both eumelanin and pheomelanin were shown to produce and to suppress (1)O(2), with similar efficiencies. The higher amount of (1)O(2) generated in blond hair and its longer lifetime is compatible with the stronger damage that light exposure causes in blond hair. We propose a model to explain the formation and suppression of (1)O(2) in hair by photosensitization of melanin with visible light and the deleterious effects that an excess of visible light may cause in hair and skin.

Relationship between structure and photoactivity of porphyrins derived from protoporphyrin IX

Protoporphyrin (Pp IX) derivatives were prepared to study the relationship between photosensitizer structure and photoactivity, with an emphasis on understanding the role of membrane interactions in the efficiency of photosensitizers used in photodynamic therapy (PDT). The synthetic strategies described here aimed at changing protoporphyrin periferic groups, varying overall charge and oil/water partition, while maintaining their photochemical properties. Three synthetic routes were used: (1) modification of Pp IX at positions 31 and 81 by addition of alkyl amine groups of different lengths (compounds 2–5), (2) change of Pp IX at positions 133 and 173, generating alkyl amines (compounds 6 and 7, a phosphate amine (compound 8, and quarternary ammonium compounds (compounds 9 and 10), and (3) amine-alkylation of Hematoporphyrin IX (Hp IX) at positions 31, 81, 133 and 173(compound 12). Strategy 1 leads to hydrophobic compounds with low photocytotoxicity. Strategy 2 leads to compounds 6–10 that have high levels of binding/incorporation in vesicles, mitochondria and cells, which are indicative of high bioavailability. Addition of the phosphate group (compound 8), generates an anionic compound that has low liposome and cell incorporation, plus low photocytotoxicity. Compound 12 has intermediate incorporation and photocytotoxic properties. Compound modification is also associated with changes in their sub-cellular localization: 30% of 8 (anionic) is found in mitochondria as compared to 95% of compound 10 (cationic). Photocytotoxicity was shown to be highly correlated with membrane affinity, which depends on the asymmetrical and amphiphilic characters of sens, as well as with sub-cellular localization.

Effects of Oxygen, Heavy Water, and Glycerol on Electron Transfer in the Acceptor Part of Rhodobacter sphaeroides Reaction Centers

The kinetics of electron transfer between primary and secondary quinone acceptors of the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides wild type was studied at the wavelengths 400 and 450 nm. It was shown that removing of molecular oxygen from RC preparations slowed down the fast phase of the process from 4–4.5 µsec to tens of microseconds. Similar effects were observed after the incubation of RC in heavy water for 72 h or glycerol addition (90% v/v) to RC preparations. The observed effects are interpreted in terms of the influence of these agents on the hydrogen bond system of the RC. The state of this system can determine the formation of different RC conformations that are characterized by different rates of electron transfer between quinone acceptors.

Chlorophyllin Derivatives as Photosensitizers: Synthesis and Photodynamic Properties

Two new photosensitizers (PSs) derived from copper-chlorophyllin were designed to have excitation wavelengths appropriate for the use in photodynamic therapy (PDT) and to have amphiphilic character with positive charge, which favors binding to cell membranes and walls and the intracellular localization in mitochondria. Herein we describe the synthesis and characterization of several properties of these two new PS, i.e., photophysical (absorption, fluorescence and singlet oxygen emission quantum yields, Φf and ΦΔ, respectively), physical-chemical (aggregation) and photobiological (binding, incorporation and cell killing). As expected, the aggregation affected not only the absorption spectra but also lowered considerably the values of Φf and ΦΔ, which could be controlled by the interaction of the PS with aqueous micelles. In vitro studies were performed in cells, mitochondria, and vesicles to determine uptake, membrane binding, cytotoxicity, phototoxicity, and intracellular localization. The positively charged derivatives showed to be considerably more efficient for cell killing than methylene blue.

Stabilization of the electron in the quinone acceptor part of the Rhodobacter sphaeroides reaction centers

The evolution of the light-induced absorption difference spectrum (380–500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 μs. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40°C.