Mechanisms of photodynamic effects of furocoumarins

Photoantimicrobials in agriculture

Classical approaches for controlling plant pathogens may be impaired by the development of pathogen resistance to chemical pesticides and by limited availability of effective antimicrobial agents. Recent increases in consumer awareness of and/or legislation regarding environmental and human health, and the urgent need to improve food security, are driving increased demand for safer antimicrobial strategies. Therefore, there is a need for a step change in the approaches used for controlling pre- and post-harvest diseases and foodborne human pathogens. The use of light-activated antimicrobial substances for the so-called antimicrobial photodynamic treatment is known to be effective not only in a clinical context, but also for use in agriculture to control plant-pathogenic fungi and bacteria, and to eliminate foodborne human pathogens from seeds, sprouted seeds, fruits, and vegetables. Here, we take a holistic approach to review and re-evaluate recent findings on: (i) the ecology of naturally-occurring photoantimicrobials, (ii) photodynamic processes including the light-activated antimicrobial activities of some plant metabolites, and (iii) fungus-induced photosensitization of plants. The inhibitory mechanisms of both natural and synthetic light-activated substances, known as photosensitizers, are discussed in the contexts of microbial stress biology and agricultural biotechnology. Their modes-of-antimicrobial action make them neither stressors nor toxins/toxicants (with specific modes of poisonous activity), but a hybrid/combination of both. We highlight the use of photoantimicrobials for the control of plant-pathogenic fungi and quantify their potential contribution to global food security.

Antimicrobial Effect of Phytochemicals from Edible Plants

Current strategies of combating bacterial infections are limited and involve the use of antibiotics and preservatives. Each of these agents has generally inadequate efficacy and a number of serious adverse effects. Thus, there is an urgent need for new antimicrobial drugs and food preservatives with higher efficacy and lower toxicity. Edible plants have been used in medicine since ancient times and are well known for their successful antimicrobial activity. Often photosensitizers are present in many edible plants; they could be a promising source for a new generation of drugs and food preservatives. The use of photodynamic therapy allows enhancement of antimicrobial properties in plant photosensitizers. The purpose of this review is to present the verified data on the antimicrobial activities of photodynamic phytochemicals in edible species of the world’s flora, including the various mechanisms of their actions.

On the mechanism of erythrocyte hemolysis induced by photooxidized psoralen

Contemporary concepts on a possible mechanism of erythrocyte hemolysis induced by photooxidized psoralen - the medicinal photosensitizing furocoumarin - are reviewed. The hypothesis on the mechanochemical mechanism of hemolysis is considered in view of recent data on photoinduced aggregation in photooxidized psoralen solutions. Appropriate chemical structures of photoproduct hemolysins and aggregating photoproducts are discussed.

Spectroscopic properties and singlet oxygen production by the compound ethyl 3,12-dioxopyran[3,2-a]xanthone-2-carboxylate

The steady state and time resolved experiments together with absorption and emission spectroscopies and quantum chemical calculations have been employed to investigate spectroscopic properties of a xanthone-type compound (ethyl 3,12-dioxopyran[3,2-a]xanthone-2-carboxylate). The spectroscopic data show good agreement with results obtained from quantum chemical calculations. Additionally, this compound shows expressive quantum efficiency for triplet population and a quantum efficiency of singlet oxygen generation very close to unity. Correlations between the nature of singlet and triplet excited states and spectroscopic properties were performed in order to understand the high quantum efficiency of singlet oxygen generation by this compound.

Photohemolysis Sensitized by the Furocoumarin Derivative Alloimperatorin and its Hydroperoxide Photooxidation Product

The dark and photosensitized effects of alloimperatorin methyl ether 1 (hereafter simply alloimperatorin) and its photooxygenation product alloimperatorin hydroperoxide 2 were investigated on human erythrocytes. The results reveal that the furocoumarin 1 photosensitizes efficiently the hemolysis of erythrocytes. The rate of photohemolysis increases on raising the temperature of the postirradiated incubation from 4°C to 37°C. Thermal activation of the photohemolysis and inhibition by 2,6-di-tert-butyl-p-cresol (BHT) suggest that the furocoumarin 1 photosensitizes lipid peroxidation, increasing permeability in the erythrocyte membrane. The hydroperoxide 2 induces dark and photosensitized hemolysis more efficiently than the furocoumarin 1. The rate of hemolysis induced by 2 increases with the incubation temperature and decreases in the presence of tert-butanol and BHT. The hydroperoxide 2 photosensitizes the formation of lipid peroxidation products as shown by the reaction with thiobarbituric acid. This process is diminished by BHT. Our data imply that the photohemolysis sensitized by the furocoumarin 1 is caused by the in situ-formed photooxygenation product 2. Such hydroperoxides are potent hemolytic agents in the dark and especially on photosensitization.

The susceptibility of dermatophytes to photodynamic treatment with special focus on Trichophyton rubrum

Owing to the accessibility of skin to light, many applications of photodynamic treatment (PDT) have been developed within dermatology. The recent increase of dermatological antimicrobial PDT investigations is related to the growing problem of bacterial and fungal resistance to antibiotics. This review focuses on the susceptibility of dermatophytic fungi, in particular Trichophyton rubrum, to PDT and shows its potential usefulness in treatment of clinical dermatophytoses. There are no data indicating significant differences in PDT susceptibility between various dermatophytes and it is unlikely that treatment problems of especially T. rubrum with current antimycotics would occur in case of PDT. Red light 5-aminolevulinic acid-mediated PDT is after repeated sessions successful in in vivo treatment of onychomycosis (fungal nail infection) caused by various dermatophytes. Regarding skin dermatophytoses, UVA-1 PDT with cationic porphyrins appears to be safe and efficient. Most effective toward T. rubrum ex vivo is 5,10,15-tris(4-methylpyridinium)-20-phenyl-[21H,23H]-porphine trichloride (Sylsens B) when combined with UVA-1 radiation or red light; this creates the possibility of efficiently treating nail infections and remaining spores in hair follicles. If the promising in vitro and ex vivo results could be transferred to clinical practice, then PDT has a good prospect to become a worthy alternative to established antifungal drugs.

Differentiation and apoptosis in UVA-irradiated cells treated with furocoumarin derivatives

In this review we summarize the structure and biological effects of linear and angular psoralens. These compounds exhibit interesting biological effects on the cell cycle, apoptosis and differentiation. These molecules should be considered promising drugs in the therapy of several diseases, including psoriasis, mycosis fungoides and cancer. Also, preclinical data demonstrate a possible use of these molecules for the treatment of beta-thalassemia and other hematological disorders.

Identification of psoralen loaded PLGA microspheres in rat skin by light microscopy

Drug delivery systems involving the use of polymers are widely studied and discovery of biocompatible polymers has become the focus of research in this area. Psoralen loaded poly(DL-lactide-co-glycolide) (PLGA) microspheres to be used in PUVA therapy (psoralen and UVA irradiation (ultraviolet A, 320-400 nm) of psoriasis were identified in paraffin sections by histological analysis. The psoralen loaded PLGA microspheres were prepared using the solvent evaporation technique. They were spherical and possessed an external smooth surface as observed by scanning electron microscopy (SEM) analysis. This study describes a modification in the routine preparation of microsphere samples for examination by light microscopy. The changes involved fixative agents and/or stains allowing the identification of microspheres containing a non-fluorescent material. The preservation and identification of microspheres in tissues for histological processing in paraffin was greatly improved by these modifications as proven by our results.

The mitochondrial effects of novel apoptogenic molecules generated by psoralen photolysis as a crucial mechanism in PUVA therapy

The generation of photoproducts of psoralen (POPs) might be relevant in cell death induced by psoralen plus UVA, namely PUVA, which is a recognized effective treatment for cutaneous T-cell lymphoma, chronic graft-versus-host disease, and psoriasis. We investigated the occurrence of POP-induced cell death and the underlying mechanisms. POPs were produced by irradiating a psoralen solution with UVA. Jurkat cells treated in the dark with these mixtures died mainly through an apoptotic mechanism. POPs were separated by high-performance liquid chromatography (HPLC), and cells were added with each of these fractions. A total of 2 dimers of psoralen and 6-formyl-7-hydroxycoumarin (FHC) were identified in the apoptogenic fractions. Apoptosis was preceded by mitochondrial dysfunction caused by the opening of the mitochondrial permeability transition pore (PTP). In fact, both mitochondrial depolarization and cell death were prevented by the PTP inhibitor cyclosporin A (CsA). PTP opening was also documented in isolated mitochondria added with POP, suggesting that apoptosis is caused by a direct effect of POP on mitochondria. In fact, FHC alone induced PTP opening and CsA-inhibitable cell death of Jurkat cells, whereas nontransformed T lymphocytes were resistant. Along with identifying novel apoptogenic molecules, the present results indicate that POP generation directs transformed cells to apoptosis.

Photodynamic Action and Antimicrobial Activity of Some Excited Metabolites ofDalbergia Sissoidesand Their Ability to Cleave DNA

The photodynamic properties of two quinones, 4-methoxydalbergione (DS1) and sissoidenone (DS2), and a coumarin, dalbergin {6-hydroxy-7-methoxy-4-phenylcoumarin, (DS3)}, have been studied. Photogeneration of singlet oxygen (1O2) was monitored by both optical and EPR methods. Based on RNO bleaching, relative to Rose Bengal (RB), the singlet oxygen generating efficiencies of DS1, DS2, and DS3 were determined as 0.10, 0.051 and 0.041, respectively. Using the SOD inhibitable cytochrome c reduction assay, the photogeneration of superoxide anion (O2-•) was monitored. The formation of O2-•was enhanced in the presence of electron donors such as EDTA, DETAPAC and NADH. Photolysis of DS1 and DS3 in DMSO in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generated a twelve line EPR spectrum characteristic of an O2-•adduct. In the photosensitization of the DS series, both Type I and Type II paths were involved. The quantum mechanically calculated lowest unoccupied molecular orbital (LUMO) energies of DS1 and DS2 were correlated with the experimental redox potential. Photoinduced DNA scission by DS1, DS2, and DS3 confirms the generation of O2-•from these metabolites.

Photoreaction of skin-sensitizing trimethyl psoralen with lipid membrane models

The concerted photoreaction between trimethyl psoralen (TMP) and isomeric model compounds of oleic acid methyl ester (OAME) and eadilic acid methyl ester (EAME) are explored using density functional theory. The S(1) surfaces all reveal large barriers (25-31 kcal/mol) to reach the decay channels, whereas the S(2) surfaces differ considerably between the furan and pyrone side adducts. For the pyrone side adducts, a small barrier to reach the intersection between the S(1) and S(2) states is found, followed by a small second barrier on the S(1) surface to the low-lying decay channel. For the furan-side adducts, no such intersection between S(1) and S(2) is seen, which thus prevents these products from being formed in high yields. The photoinduced cycloaddition is more favorable between OAME and the pyrone side double bond of TMP than for any of the other systems, which agrees with the experimental findings that this is formed in the highest yield. The computed UV absorption spectra of TMP and the TMP(pyrone)-OAME cycloadduct agree well with the experimental spectra.

Vibronic absorption, fluorescence, and phosphorescence spectra of psoralen: a quantum chemical investigation

Excited state potential energy hypersurfaces of 7H-furo[3,2-g][1]benzopyran-7-one (psoralen) have been explored employing (time-dependent) Kohn-Sham density functional theory. At selected points, we have determined electronic excitation energies and electric dipole (transition) moments utilizing a combined density functional/multireference configuration interaction method. Spin-orbit coupling has been taken into account employing an efficient, non-empirical spin-orbit mean-field Hamiltonian. Franck-Condon factors have been computed for vibrational modes with large displacements in the respective Dushinsky transformations. The simulated band spectra closely resemble experimental band shapes and thus validate the theoretically determined nuclear structures at the S(0), S(1), and T(1) minima. In the S(1) (pi(HOMO)-->pi*(LUMO)) state, the lactone bond of the pyrone ring is significantly elongated. From excited vibrational levels of the S(1) state a conical intersection between a (pi-->sigma*) excited state and the electronic ground state may be energetically accessible. Fast non-radiative decay via this relaxation pathway could explain the low fluorescence quantum yield of psoralen. The T(1) (pi(HOMO-1)-->pi*(LUMO)) exhibits a diradicaloid electronic structure with a broken C(5)-C(6) double bond in the pyrone ring. A variational multireference spin-orbit configuration interaction procedure yields a phosphorescence lifetime of 3 s, in excellent agreement with experimental estimates.

Phototoxicity, distribution and kinetics of association of UVA-activated chlorpromazine, 8-methoxypsoralen, and 4,6,4′-trimethylangelicin in Jurkat cells

Extracorporeal phototherapy (ECP) is a therapeutic approach based on photobiological effects of 8-methoxypsoralen (8-MOP) on white blood cells isolated from the blood, exposed to UVA and then reinfused into the patient. 8-MOP is presently the only drug approved for clinical application of ECP; therefore, identification of other photosensitizers with better photochemical and pharmacokinetic properties might enhance the efficacy of this treatment modality. Among such alternative drugs are 4,6,4'-trimethylangelicin (TMA) and chlorpromazine (CPZ), which have previously been studied in an animal model for ECP. In this current study, cellular bioavailability of 8-MOP, TMA and CPZ was investigated in vitro, using low doses of UVA relevant for the clinical setting of ECP. Our fluorescence microscopy study revealed that 8-MOP and CPZ penetrated readily into the cells, where they accumulated with similar kinetics. No distinct fluorescence was observed in cells incubated with TMA. We found that the phototoxic efficiency of 8-MOP was an order of magnitude greater than that of CPZ, i.e., to obtain a similar reduction in survival of cells subjected to photosensitization by the drugs, the concentration of CPZ needed to be 10 times higher than that of 8-MOP. The photoactivated TMA exhibited the highest pro-apoptotic efficiency. A clear indication of photoinduced formation of reactive oxygen species and peroxidation of lipids was observed only in CPZ-sensitized cells, suggesting different mechanisms for phototoxicity mediated by CPZ and by the two furocoumarins.

Systemic Suppression of the Contact Hypersensitivity by the Products of Protoporphyrin IX Photooxidation

Photodynamic therapy (PDT) is frequently accompanied by induction of systemic immunosuppression. Photochemical mechanisms underlying this effect are not completely understood. Here, we demonstrate the immunosuppressive activity of photooxidation products of protoporphyrin IX dimethyl ester (PPIX) in a murine model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB). Intravenous injection of the preirradiated solution of PPIX to mice resulted in fluence-dependent suppression of the CHS. The samples of photodecomposed PPIX with suppressive effect on the CHS contained chlorin-type products, namely, two isomers of photoprotoporphyrin (pPP1 and pPP2) as main photoproducts. Concentration-dependent suppression of the CHS was also induced when purified pPP1 or pPP2 were injected to mice intravenously. These purified photoproducts exerted equal immunosuppressive activity. The highest suppression of the CHS was induced when pPP1 was injected 20 h before sensitization with DNFB. The lowest suppression was at its injection time 24 h before challenge. The pPP1-induced suppression of the CHS was adoptively transferable and was associated with generation of cells with suppressive functions. These suppressor cells inhibited the efferent phase of the CHS. Our results strongly indicate that induction of systemic immunosuppression by PDT with PPIX may proceed through photobleaching of photosensitizer and generation of photoprotoporphyrins, which can affect T cell immunity.

Effect of psoralens on Fenton-like reaction generating reactive oxygen species

Psoralens (psoralen, 5-methoxypsoralen, 8-methoxypsoralen, khellin, and visnagin) in 1 mM doses were shown to enhance the generation of reactive oxygen species, such as the hydroxyl radical (HO*), the superoxide anion radical (O2(-)), and singlet oxygen ((1)O(2)), from the system generating chemiluminescence (CL), as well as free radicals in the absence of light. The system that generated CL was made up of CoCl(2) and H(2)O(2). Incubation of psoralens in 0.2 mM doses with the generating system showed that only 8-methoxypsoralen and khellin have antioxidative effects. Antioxidative effects were also observed in the case of visnagin but in low concentration (0.05 mM). High doses of psoralens (1 mM) showed prooxidative effects. Measurements were done using a deoxyribose assay, the CL method, and spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide and 2,2,6,6-tetramethylpiperidine combined with electron spin resonance spectroscopy and spectrophotometry methods.

Phototoxicity of Protoporphyrin IX, Diarginine Diprotoporphyrinate and N,N-Diphenylalanyl Protoporphyrin Toward Human Fibroblasts and Keratinocytes In Vitro: Effect of 5-Methoxypsoralen ¶

The phototoxicity of two new porphyrin photosensitizers, diarginine diprotoporphyrinate (PP(Arg)2) and N,N-diphenylalanyl protoporphyrin (PP(Phe)2), and the synergistic effect of 5-methoxyposralen (5-MOP) have been studied in comparison with that of protoporphyrin IX (PPIX). Under ultraviolet-A (UV-A) irradiation (lambda=365 nm), the phototoxicity of the porphyrins toward cultured human fibroblasts and keratinocytes decreases in the order: PPIX > PP(Arg)2 > PP(Phe)2. A synergistic effect of 5-MOP on the phototoxicity of PPIX, PP(Arg)2 and PP(Phe)2 has been observed. The combination of PPIX, PP(Arg)2 and PP(Phe)2 with 0.1-0.5 microM 5-MOP significantly potentiates the phototoxicity of the three porphyrins. The most effective potentiation was observed with the water-soluble PP(Arg)2 and 5-MOP concentrations lower than 0.75 microM. Above this 5-MOP concentration this potentiation is abolished. The intracellular concentration of PPIX and PP(Phe)2 is independent of the presence of 5-MOP. On the other hand, the intracellular content of PP(Arg)2 is decreased in a concentration-dependent manner by the psoralen. Illumination with red light, not absorbed by 5-MOP, leads to a weak potentiation of the PP(Arg)2 phototoxic effect in the presence of 5-MOP, suggesting that dark interaction of 5-MOP with cell membranes aggravated by porphyrin photosensitization is involved in the observed phenomena. The results are tentatively explained by differences in hydrophobicity and molecular structures of the examined photosensitizers. PPIX, which is barely soluble in water, has a significantly higher affinity for cell membranes and simultaneously exerts a stronger phototoxic effect than PP(Arg)2 whose solubility in water is high. On the other hand, the weak phototoxicity of PP(Phe)2 could be explained by the steric hindrance brought by the phenylalanyl substituents on the pyrrole ring. The loss in the PP(Arg)2 cell content probably explains the inhibition of the synergistic effect of 5-MOP on the PP(Arg)2 phototoxicity at high 5-MOP concentration. This study suggests that PP(Arg)2 in combination with 5-MOP might reveal a strong phototoxic effect when applied to skin cancer treatment.

8-Methoxypsoralen and long-wave ultraviolet A inhibit the release of proinflammatory mediators and cytokines from human Fc epsilon RI+ cells: an in vitro study

The in vitro effects of 8-MOP (concentrations of 20, 100 and 500 ng/ml) alone or in combination with UVA on mediator release from human basophils and skin mast cells (HSMC), activated with immunological and non-immunological stimuli, were investigated. With respect to basophils activated with anti-IgE serum, the results of this study show that: (i) 8-MOP alone inhibits histamine, LTC(4), IL-4 and IL-13 release concentration dependently with a maximal effect at 500 ng/ml (a concentration not reached in vivo); and (ii) UVA irradiation (5 J/cm(2)), after 8-MOP incubation, enhances this inhibitory effect on all released mediators, but for IL-4 and IL-13 the percentage inhibition is also significant for the 8-MOP concentrations (20-100 ng/ml) employed in vivo during PUVA treatment. Moreover, histamine release from basophils activated with non-immunological stimuli (FMLP and A23187) is inhibited by 8-MOP, alone or in combination with UVA. With respect to the HSMC activated with anti-IgE serum, the results show that: (i) 8-MOP alone reduces histamine release concentration dependently; and (ii) this inhibitory effect is enhanced by UVA irradiation (5 J/cm(2)). Histamine release from HSMC activated with A23187 is not modified either by 8-MOP alone or by 8-MOP plus UVA.

PUVA-induced apoptosis involves mitochondrial dysfunction caused by the opening of the permeability transition pore

The mechanism of cell death was investigated in Jurkat cells exposed to the combination of psoralen and UVA irradiation (PUVA). Apoptosis was by far prevailing over necrosis and involved mitochondrial dysfunction. The collapse of mitochondrial membrane potential, appears to be caused by the opening of the mitochondrial permeability transition pore since its inhibitor, cyclosporin A, prevented mitochondrial dysfunction and largely attenuated apoptosis. Apoptosis also occurred in cells treated with the photoproducts generated by irradiating psoralen in vitro with an oxygen-dependent process. Thus, the involvement of reactive oxygen species in the onset of PUVA-induced apoptosis appears mostly related to psoralen photooxidation.

Furocoumarin photolysis: chemical and biological aspects

Furocoumarins (psoralens) undergo photolysis when subjected to UVA radiation in solution. Several products are formed, depending on the molecular structure and experimental conditions. Some products are the result of anoxic mechanisms (cyclodimerisation, addition of solvent), others of oxic pathways, leading to oxidised products. The mechanisms thought to underlie photolysis are described and the possible biological relevance of the photoproducts and intermediates is discussed.

Fig leaf tanning lotion and sun-related burns: case reports

A sun tan is considered a symbol of well-being in our society, but incorrect methods of sun exposure can create serious problems. We present two cases of severe sun-related burns caused by fig leaf decoction used as home-made tanning lotion. Twenty four-thirty six hours after application and sun exposure, patients developed a phytophotodermatitis characterised by erythema, and blister formation involving all the photoexposed areas (45-70% BSA). Their general conditions became rapidly critical and they were admitted to our Burn Centre. The patients were discharged after 11 and 26 days, respectively. Haemolytic anaemia and retinal haemorrhages presented as systemic complications due to the furocoumarins present in the fig leaf decoction.

Effects of glutathione peroxidase and catalase on hemolysis and methemoglobin modifications induced by photooxidized psoralen

Psoralen photooxidation products (POP products) were obtained by UVA irradiation (365 nm, 180-640 W/m2) of an aqueous psoralen solution with fluences of 0-800 kJ/m2. Preincubation of POP products with glutathione peroxidase (GSHPer) or catalase, as well as presence of catalase during UVA irradiation of the aqueous psoralen solution did not influence their hemolytic activity. However, both GSHPer and catalase inhibited POP-induced conversion of methemoglobin. This indicates that hydrogen peroxide and psoralen peroxides destructible by GSHPer, which are being produced during psoralen photooxidation, do not possess hemolytic activity. Furthermore, hydrogen peroxide does not appear to serve as an intermediate in the process of hemolysin formation. Hydrogen peroxide generated during psoralen photooxidation is apparently the main POP product responsible for MetHb conversion.

Psoralen-ultraviolet A-induced erythema: sensitivity correlates with the concentrations of psoralen in suction blister fluid

Since the advent of psoralen-ultraviolet A (PUVA) therapy, the value of plasma 8-methoxypsoralen (8-MOP) concentrations to predict PUVA-induced erythema has been widely investigated. Plasma 8-MOP concentrations have not been proportional to, and cannot alone predict, the degree of PUVA-induced erythema. We assumed that PUVA-induced erythema was related more closely to psoralen concentrations in the skin tissue rather than those within blood vessels. This study was designed to investigate the correlations between the 8-MOP concentrations in suction blister fluid (SBF) and in plasma, with the degree of PUVA-induced erythema. 8-MOP concentrations in plasma and SBF were measured in 15 vitiligo patients and 11 volunteers. Blood and SBF samples were collected 2 h after taking 8-MOP, and 8-MOP concentrations in plasma and SBF were quantified using reverse-phase high-performance liquid chromatography. Eleven volunteers were phototested using a series of doses of ultraviolet A at the time of sampling. The erythema responses were estimated visually to determine the minimal phototoxic dose (MPD). SBF 8-MOP concentrations showed a weak positive correlation with plasma 8-MOP concentrations, which means that we could not predict the exact SBF 8-MOP concentrations using the plasma 8-MOP concentrations. The MPD showed a better correlation with the log of the SBF 8-MOP concentration than with that of the plasma 8-MOP concentration. These results show that plasma 8-MOP concentration cannot represent the exact SBF 8-MOP concentration, and that SBF 8-MOP concentrations, which are representative of the skin tissue 8-MOP level, are more closely related to the erythemal sensitivity during PUVA therapy.

PUVA inhibits DNA replication, but not gene transcription at nonlethal dosages

The combination of psoralens and UVA radiation (PUVA photochemotherapy) is an established treatment for many skin disorders. UVA-induced psoralen-DNA interactions are assumed to contribute to the cutaneous anti-inflammatory and anti-proliferative effects of PUVA. PUVA-induced DNA modifications might interfere not only with DNA replication, but also with gene transcription of proinflammatory genes. We therefore studied the effect of PUVA on cell proliferation and on the transcription of the c-jun and intercellular adhesion molecule-1 genes in a promyelocytic (HL60) and a keratinocyte (HaCaT) cell line. PUVA inhibited cell proliferation increasingly with increasing 8-methoxypsoralen concentrations or UVA doses. The inhibition was observed at conditions not affecting cell viability up to 48 h after PUVA. In contrast, PUVA did not inhibit gene transcription at anti-proliferative, yet nonlethal conditions. Baseline and phorbol-ester induced c-jun mRNA expression was not inhibited, nor was baseline and IFN-gamma or phorbol-ester induced intercellular adhesion molecule-1 mRNA expression. In order to assess possible transcriptional effects of PUVA-generated reactive oxygen intermediates, the reactive oxygen intermediates-sensitive transcription factor nuclear factor kappaB was assayed in mobility shift experiments. Nuclear factor kappaB-specific binding activity was not induced 1-24 h after PUVA in extracts from PUVA-treated cells when compared with controls, whereas the pro-oxidant cytokine TNF-alpha caused a marked increase in nuclear factor kappaB binding. The presented data suggest that PUVA inhibits cell proliferation, but not transcription, at nonlethal PUVA conditions. Furthermore, the data do not support a major role for PUVA-generated reactive oxygen intermediates in the regulation of gene transcription.

Narrow band UVB (311 nm) phototherapy and PUVA photochemotherapy: a combination

BACKGROUND

Psoralen-UVA (PUVA) photochemotherapy is widely used for the treatment of psoriasis despite concerns of skin carcinogenesis from high cumulative UVA doses and number of treatments.

OBJECTIVE

We attempted to determine whether combined bath-PUVA with narrow-band (311 nm) phototherapy improves efficacy and reduces long-term toxicity.

METHODS

Twelve psoriatic patients underwent phototesting with 311 nm lamps and, after topical bath-water psoralen sensitization, with 311 nm, UVA, or both radiations. Patients were treated with bath-PUVA on one side of the body and with bath-PUVA plus 311 nm exposures (bath-PUVA-311 nm) on the other side. On both sides, four weekly treatments were delivered and UVA doses were increased once weekly whereas 311 nm doses were adjusted at each exposure.

RESULTS

Psoralen sensitization did not modify the erythematous threshold to 311 nm radiation. However, 311 nm exposures enhanced the phototoxic activity of bath-PUVA. Bath-PUVA-311 nm cleared psoriasis with fewer exposures and lower cumulative UVA doses under the same minimally erythemogenic conditions.

CONCLUSION

Combination with 311 nm exposures enhanced the phototoxic and therapeutic activities of bath-PUVA.

Photoreaction of new psoralen analogs with DNA: sequence and mutation specificity in the Escherichia coli lacZ gene

New thio- and seleno-analogs of psoralen were synthesized and analyzed for their photoreactivity toward DNA. Using oligonucleotides of defined sequence, we first showed that these derivatives predominantly generated interstrand crosslinks at 5'-TpA sites. We also observed a surprisingly high reactivity of 7H-thiopyrano[3,2-f][1]benzofuran-7-one (PSO[O-S]) with the BamHI and PstI oligomers, giving rise to the formation of crosslinks at 5'-ApT sites and of the thymidine-psoralen-cytosine type. Next, the sequence specificity in the photochemical binding of all the compounds was investigated in two DNA fragments encompassing the lacZ gene of Escherichia coli, using the T4 DNA polymerase sequencing methodology. Resulting maps demonstrated that thio- and seleno-analogs of psoralen preferentially photoreacted with thymine and cytosine residues. The AT-rich sequences proved to be particularly reactive sites as did adjacent thymines, especially at C-surrounding residues. Likewise, photoaddition at cytosines in CA/AC context was observed. It was highly significant that all of the derivatives exhibited similar sequence specificities with only minor differences. However, PSO(O-S) differed from the other heteropsoralens. Photoadducts occurred with a higher frequency at AC and CA dinucleotides, and new sites were detected. A comparison with 8-methoxypsoralen photobinding is also reported. Finally, the mutagenic consequences of photoadducts induced in M13mp19 DNA by PSO(O-S) were determined in a forward system that detects all classes of mutagenic events. The high phototoxicity exhibited by PSO(O-S) could be attributed to crosslinks, and the comparison of the observed mutational specificity with the photoadduct distribution within the same gene showed that mutations were targeted at potential monoadduct sites where photolesions were detected in our footprinting experiments.

p53 mutation in squamous cell carcinomas from psoriasis patients treated with psoralen + UVA (PUVA)

Individuals suffering from psoriasis are treated with a combination of psoralen and UVA radiation, commonly referred to as "PUVA" therapy. Epidemiologic studies have shown that PUVA therapy is a risk factor for skin cancer in psoriasis patients. Although PUVA treatment induces skin cancer in laboratory animals, it is unknown whether the increased incidence of skin cancer reported in PUVA-treated psoriasis patients is due to the carcinogenic effects of PUVA or due to other factors such as UVB. Because UV and PUVA induce different types of DNA damage resulting in unique types of p53 mutation, we investigated whether skin cancers from PUVA-treated psoriasis patients have PUVA-type or UV-type p53 mutations. Analysis of 17 squamous cell carcinomas (SCCs) from Austrian PUVA-treated patients revealed a total of 25 p53 mutations in 11 SCCs. A majority of p53 mutations occurred at 5'TpG sites. Although previous studies have shown that 5'TpA sites are the primary targets for PUVA mutagenesis, substitutions at 5'TpG sites are also quite common. Interestingly, a sizable portion of p53 mutations detected were C-->T or CC-->TT transitions, characteristic of UV-induced mutations. Because some psoriasis patients had substantial exposure to UVB before PUVA therapy and because the light sources used in PUVA therapy contained small but significant wavelengths in the UVB region, it is possible that the C-->T and CC-->TT transitions detected in SCCs from PUVA-treated patients were induced by UVB. Nonetheless, our results indicate that both PUVA and UVB may play a role in the development of skin cancer in Austrian psoriasis patients who undergo PUVA therapy.

Photochemical and photobiological studies of a furonaphthopyranone as a benzo-spaced psoralen analog in cell-free and cellular DNA

Photobiological activities of the benzo-spaced psoralen analog furonaphthopyranone 3 have been investigated in cell-free and cellular DNA. The molecular geometry parameters of 3 suggest that it should not form interstrand crosslinks with DNA. With cell-free DNA no evidence for crosslinking but also not for monoadduct formation was obtained; rather, the unnatural furocoumarin 3 induces oxidative DNA modifications under near-UVA irradiation. The enzymatic assay of the photosensitized damage in cell-free PM2 DNA revealed the significant formation of lesions sensitive to formamidopyrimidine DNA glycosylase (Fpg protein). In the photooxidation of calf thymus DNA by the furonaphthopyranone 3, 0.29 +/- 0.02% 8-oxo-7,8-dihydroguanine (8-oxoGua) was observed. With 2'-deoxyguanosine (dGuo), the guanidine-releasing photooxidation products oxazolone and oxoimidazolidine were formed predominately, while 8-oxodGuo and 4-HO-8-oxodGuo were obtained in minor amounts. The lack of a significant D2O effect in the photooxidation of DNA and dGuo reveals that singlet oxygen (type II process) plays a minor role; control experiments with tert-butanol and mannitol confirm the absence of hydroxyl radicals as oxidizing species. The furonaphthopyranone 3 (Ered = -1.93 +/- 0.03V) should act in its singlet-excited state as electron acceptor for the photooxidation of dGuo (delta GET ca -6 kcal/mol), which corroborates photoinduced electron transfer (type I) as a major DNA-oxidizing mechanism. A comet assay in Chinese hamster ovary (CHO) AS52 cells demonstrated that the psoralen analog 3 damages cellular DNA upon near-UVA irradiation; however, no photosensitized mutagenicity was observed in CHO AS52 cell cultures.

Bath-5-methoxypsoralen-UVA therapy for psoriasis

BACKGROUND

After oral intake, 5-methoxypsoralen (5-MOP) is as effective as 8-MOP for PUVA therapy for psoriasis, with a lower incidence of acute cutaneous side effects.

OBJECTIVE

We compared bath-water delivery of 5-MOP and 8-MOP for photochemotherapy of psoriasis.

METHODS

Twenty-two patients underwent phototesting with 0.0003% 5-MOP or 8-MOP aqueous solutions. Twelve patients with palmar psoriasis were studied with a side-to-side comparison, and 10 patients with recurrent plaque-type psoriasis were treated with one therapy or the other.

RESULTS

Minimal phototoxic dose (MPD) values were 2.8 +/- 1.2 J/cm2 with 8-MOP and 2.0 +/- 1.2 J/cm2 with 5-MOP (p < 0.01). Both therapies cleared palmar lesions but 8-MOP required more UVA irradiation (46.3 +/- 21.0 J/cm2 vs 30.2 +/- 21.5 J/cm2; p < 0.01) and more exposures (21.0 +/- 6.0 vs 17.0 +/- 5.0; p = 0.02). Bath-5-MOP-UVA was also more effective in the treatment of plaque-type psoriasis (cumulative UVA doses, 56.8 +/- 39.2 vs 59.1 +/- 27.9 J/cm2; number of exposures, 20.0 +/- 5.7 vs 21.6 +/- 4.7), but these differences were not significant (p = NS). Patients developed an intense tan significantly earlier with 5-MOP than with 8-MOP (3.5 +/- 0.5 weeks vs 4.4 +/- 0.5 weeks; p < 0.01).

CONCLUSION

Bath-5-MOP-UVA was more phototoxic than bath-8-MOP-UVA. It was more effective in the treatment of palmar psoriasis, whereas its greater pigmentogenic activity appeared to have an adverse effect on therapeutic effectiveness in the treatment of plaque-type psoriasis.

Sites of preferred interaction between double-stranded pBR322 DNA and 7-methylpyrido[3,4-c]psoralen

7-Methylpyrido[3,4-c]psoralen has recently been found to photosensitize the crosslinking and cleavage of double-stranded pBR322 DNA (4361 bp) with an unusual degree of site specificity. Following cleavage of the photosensitized pBR322 with the restriction enzymes Pvu II and BamH I, the main fragments were analyzed electrophoretically. Only three possible cleavage areas on the plasmid were suggested by this analysis. They were within the ranges bounded by the positions 801-926, 3172-3303 and 4226-4310. The sensitizer also induced selective cleavage in the related plasmid pUC19 (2686 bp), but the pattern was somewhat more complicated and was not analyzed in detail.

Suppression of delayed-type hypersensitivity and hemolysis induced by previously photooxidized psoralen: effect of fluence rate and psoralen concentration

The kinetics of the formation of biologically active psoralen photooxidation (POP) products were analyzed by the biological effects produced. Effects of the UV light fluence rate and psoralen concentration during the preirradiation were investigated to assess the yield of POP products, which were active in vivo (inducing suppression of delayed-type hypersensitivity [DTH] reaction to sheep red blood cells) and in vitro (altering the human erythrocyte membrane permeability). It was shown that the reciprocity law of the irradiation fluence rate and time was not valid in the case of POP-induced hemolysis and DTH suppression. Immunosuppressive POP products were more efficiently formed at low fluence rate (20.8 W/m2), whereas POP hemolysins were more efficiently produced at a high fluence rate (180 W/m2) of UV light. The yield of immunosuppressive POP products was enhanced in dilute psoralen solutions, while the POP hemolysins yield increased with increasing psoralen concentration. A kinetic scheme for psoralen photoproduct formation was proposed. Kinetic analysis showed that a labile intermediate was produced as the result of excitation of psoralen. This intermediate was either converted to a stable immunosuppressive POP product, or two intermediates combined to form a POP hemolysin. It is proposed that PUVA therapy conditions are more favorable for the formation of immunosuppressive rather than membrane-damaging psoralen photooxidation products.

6,4,4'-Trimethylangelicin photoadduct immunodetection in DNA: induction and repair in Fanconi's anemia and normal human fibroblasts

6,4,4'-Trimethylangelicin (TMA)-photoinduced monoadducts (MAs) were detected and quantified on DNA of normal human and Fanconi's anemia (FA) fibroblasts (complementation groups A and D) by immuno-electron microscopy. TMA-modified DNA was extracted from the cells just after photoreaction, or after a subsequent 24 h repair period, for analysis of the MA processing capabilities of the different cell lines. Unmodified DNA was extracted from the control cells in parallel. The immunoreaction with antibody 7E3 was performed on single-stranded DNA fragments obtained by heat-formamide denaturation. On single-stranded DNA fragments scanned in the electron microscope, IgG-labeled MA sites appeared as isolated or clustered IgG molecules, which were not homogeneously distributed. The isolated IgG and the different clusters (doublets, triplets or near-neighbors (within a distance of 250 nucleotides)) were measured separately for induction frequency and removal. Few interstrand cross-links (CLs) were present on X-shape DNA fragments. At time zero, the distribution patterns of TMA-photoinduced IgG-labeled MA sites and CLs, and their amount per 10(6) nucleotides, were similar in the three cell lines. After the 24 h repair period, FA cells from two different genetic complementation groups demonstrated impaired incision-excision repair capabilities for both MAs (singlets or clusters) and CLs when compared with normal cells. In each cell line, the relative proportions of TMA-induced lesions remaining at time 24 h were similar to those initially induced. This implies analogous processing kinetics towards the TMA-photoinduced clusters of MAs and CLs in a given cell line.

Effects of beta-carotene and alpha-tocopherol on photogenotoxicity induced by 8-methoxypsoralen: the role of oxygen

The protective effect of beta-carotene (beta-C) and alpha-tocopherol (alpha-T), singularly and in equimolar mixtures, toward the photomutagenicity induced by 8-methoxypsoralen (8-MOP), at different oxygen partial pressure (pO2), was evaluated in two different experimental models: Salmonella typhimurium TA102 and Saccharomyces cerevisiae D7. After phototreatment with 8-MOP, the results show a lethal effect under hypoxic conditions in both experimental model systems, an increase in revertants associated to the pO2 increase in S. typhimurium TA102, and a decrease in revertants and convertants associated to the pO2 increase in S. cerevisiae D7. In S. typhimurium TA102, in atmospheric condition, beta-C and alpha-T (1.86 or 18.6 microM) show a protective effect only at the higher dosage. Alpha-T was more protective than beta-C. The equimolar mixtures show an antimutagenic effect at both dosage used with a synergistic effect at lower dosage and an additive antimutagenic activity at higher dosage. An inhibition of the spontaneous mutagenicity by mixtures at higher dosage was also observed. The results obtained in S. typhimurium TA102 show an antimutagenic effects of beta-C, alpha-T and their mixture at 190 mmHg pO2, confirming the data obtained in air condition. At 380 mmHg pO2, alpha-T and the mixture show a significant antimutagenic activity; at 570 mmHg pO2, only alpha-T is protective. At 760 mmHg pO2, no protective effect was observed by the two antioxidants, and beta-C increases the photomutagenicity induced by 8-MOP. In S. cerevisiae D7 a protective effect was only observed at 380 mmHg pO2 with the mixture. No antigenotoxic effect was found in the other experimental conditions, even if the uptake of the two antioxidants was confirmed by HPLC. Our results underline the role of oxygen in the photomutagenicity induced by 8-MOP and in the antimutagenic activity of beta-C and alpha-T. This is the first report confirming in a cellular experimental model the data obtained in some chemical systems: the protective effect of beta-C only at low pO2 and the synergistic effect of mixture of beta-C and alpha-T.

Sensitization of photohemolysis by hypericin and Photofrin

Sensitization of post-irradiation (delayed) photohemolysis (DPH) and "during irradiation" (continuous) photohemolysis (CPH) were investigated for sodium hypericin and Photofrin. The photohemolysis rate and relative steepness of the photohemolysis curves were measured for a range of sensitizer concentrations and DPH irradiation times. The data are analyzed by a multihit model based on the assumption that photohemolysis requires thermal activation of light-activated damage. A key result of the model is the photohemolysis rate has a power dependence of 1 or more on the irradiation time and sensitizer concentration for DPH and a power dependence of less than 1 on sensitizer concentration for CPH. The data for sodium hypericin are consistent with the predictions and indicative of a square dependence of photohemolysis rate on the absorbed light dose. The results for Photofrin led to an approximately square dependence of the photohemolysis rate on DPH irradiation time and an apparently anomalous 1.24 power dependence on sensitizer concentration. The model predicts also that the relative steepness of the photohemolysis curves is independent of the light dose and sensitizer concentration for DPH and almost independent of the sensitizer concentration for CPH. This prediction is confirmed to within +/- 10% for all sets of DPH and CPH curves. The relationship of the multihit kinetics model to detailed photohemolysis mechanisms is discussed.