Studies on the nature of in vitro and in vivo photosensitization reactions by psoralens and porphyrins

What Are Reactive Oxygen Species, Free Radicals, and Oxidative Stress in Skin Diseases?

Oxygen in the atmosphere is a crucial component for life-sustaining aerobic respiration in humans. Approximately 95% of oxygen is consumed as energy and ultimately becomes water; however, the remaining 5% produces metabolites called activated oxygen or reactive oxygen species (ROS), which are extremely reactive. Skin, the largest organ in the human body, is exposed to air pollutants, including diesel exhaust fumes, ultraviolet rays, food, xenobiotics, drugs, and cosmetics, which promote the production of ROS. ROS exacerbate skin aging and inflammation, but also function as regulators of homeostasis in the human body, including epidermal keratinocyte proliferation. Although ROS have been implicated in various skin diseases, the underlying mechanisms have not yet been elucidated. Current knowledge on ROS-related and oxidative stress-related skin diseases from basic research to clinical treatment strategies are discussed herein. This information may be applied to the future treatment of skin diseases through the individual targeting of the ROS generated in each case via their inhibition, capture, or regulation.

Combining Visible Light and Non-Focused Ultrasound Significantly Reduces Propionibacterium acnes Biofilm While Having Limited Effect on Host Cells

Bacterial biofilms are highly resistant to antibiotics and have been implicated in the etiology of 60%–80% of chronic microbial infections. We tested a novel combination of low intensity ultrasound and blue light against biofilm and planktonic bacteria. A laboratory prototype was built which produced both energies uniformly and coincidently from a single treatment head, impinging upon a 4.45 cm² target. To demonstrate proof of concept, Propionibacterium acnes biofilms were cultured on Millicell hanging inserts in 6-well plates. Hanging inserts with biofilms were treated in a custom exposure chamber designed to minimize unwanted ultrasound reflections. Coincident delivery of both energies demonstrated synergy over either alone, killing both stationary planktonic and biofilm cultures of P. acnes. Reduction in biofilm bacteria was dose dependent on exposure time (i.e., energy delivered). P. acnes biofilms were significantly reduced by dual energy treatment (p < 0.0001), with a >1 log₁₀ reduction after a 5 min (9 J/cm²) and >3 log₁₀ reduction after a 30 min (54 J/cm²) treatment (p < 0.05). Mammalian cells were found to be unaffected by the treatment. Both the light and the ultrasound energies are at levels previously cleared by the FDA. Therefore, this combination treatment could be used as a safe, efficacious method to treat biofilm related syndromes.

Lipid monolayer as a simple model membrane for comparative assessment of the photodynamic therapy photosensitizer efficiency via macroscopic measurements

Cellular membrane is one of the main targets of photodynamic therapy. Its high complexity has led to the study of the efficiency of photosensitizers on artificial lipid systems mimicking membranes. However, the preliminary analysis of this efficiency remains limited due to difficulty of the model construction and/or implementation of the required measurement techniques. Hereby, we propose a quite simple way for the rapid comparative assessment of novel photosensitizers in terms of membrane photodegradation, based on simple and fast measurements, such as wetting angle and surface plasmon resonance spectroscopy. As a proof of concept, we applied this methodology to two bacteriopurpurinimide derivatives. We have shown in particular that such complementary techniques can be employed not only for the multiparametric monitoring of the kinetics of the photodegradation, but also for the comparison of the damaging efficiency of the photosensitizers in the lipid structures as well.

Direct observation of key photoinduced dynamics in a potential nano-delivery vehicle of cancer drugs

The crucial photoinduced dynamics in ZnO nanoparticles (NPs) upon complexation with the cancer drug protoporphyrin IX (PP).

Fernblock, a nutriceutical with photoprotective properties and potential preventive agent for skin photoaging and photoinduced skin cancers

Many phytochemicals are endowed with photoprotective properties, i.e., the capability to prevent the harmful effects of excessive exposure to ultraviolet (UV) light. These effects include photoaging and skin cancer, and immunosuppression. Photoprotection is endowed through two major modes of action: UV absorption or reflection/scattering; and tissue repair post-exposure. We and others have uncovered the photoprotective properties of an extract of the fern Polypodium leucotomos (commercial name Fernblock). Fernblock is an all-natural antioxidant extract, administered both topically (on the skin) or orally. It inhibits generation of reactive oxygen species (ROS) production induced by UV including superoxide anion. It also prevents damage to the DNA, inhibits UV-induced AP1 and NF-κB, and protects endogenous skin natural antioxidant systems, i.e., CAT, GSH, and GSSR. Its photoprotective effects at a cellular level include a marked decrease of UV-mediated cellular apoptosis and necrosis and a profound inhibition of extracellular matrix remodeling. These molecular and cellular effects translate into long-term inhibition of photoaging and carcinogenesis that, together with its lack of toxicity, postulate its use as a novel-generation photoprotective nutriceutical of phytochemical origin.

Preliminary clinical and pharmacologic investigation of photodynamic therapy with the silicon phthalocyanine photosensitizer pc 4 for primary or metastatic cutaneous cancers

Photodynamic therapy (PDT) for cutaneous malignancies has been found to be an effective treatment with a range of photosensitizers. The phthalocyanine Pc 4 was developed initially for PDT of primary or metastatic cancers in the skin. A Phase I trial was initiated to evaluate the safety and pharmacokinetic profiles of systemically administered Pc 4 followed by red light (Pc 4-PDT) in cutaneous malignancies. A dose-escalation study of Pc 4 (starting dose 0.135 mg/m(2)) at a fixed light fluence (135 J/cm(2) of 675-nm light) was initiated in patients with primary or metastatic cutaneous malignancies with the aim of establishing the maximum tolerated dose (MTD). Blood samples were taken at intervals over the first 60 h post-PDT for pharmacokinetic analysis, and patients were evaluated for toxicity and tumor response. A total of three patients (two females with breast cancer and one male with cutaneous T-cell lymphoma) were enrolled and treated over the dose range of 0.135 mg/m(2) (first dose level) to 0.54 mg/m(2) (third dose level). Grade 3 erythema within the photoirradiated area was induced in patient 2, and transient tumor regression in patient 3, in spite of the low photosensitizer doses. Pharmacokinetic observations fit a three-compartment exponential elimination model with an initial rapid distribution phase (∼0.2 h) and relatively long terminal elimination phase (∼28 h), Because of restrictive exclusion criteria and resultant poor accrual, the trial was closed before MTD could be reached. While the limited accrual to this initial Phase I study did not establish the MTD nor establish a complete pharmacokinetic and safety profile of intravenous Pc 4-PDT, these preliminary data support further Phase I testing of this new photosensitizer.

Oligo/polynucleotide-based gene modification: strategies and therapeutic potential

Oligonucleotide- and polynucleotide-based gene modification strategies were developed as an alternative to transgene-based and classical gene targeting-based gene therapy approaches for treatment of genetic disorders. Unlike the transgene-based strategies, oligo/polynucleotide gene targeting approaches maintain gene integrity and the relationship between the protein coding and gene-specific regulatory sequences. Oligo/polynucleotide-based gene modification also has several advantages over classical vector-based homologous recombination approaches. These include essentially complete homology to the target sequence and the potential to rapidly engineer patient-specific oligo/polynucleotide gene modification reagents. Several oligo/polynucleotide-based approaches have been shown to successfully mediate sequence-specific modification of genomic DNA in mammalian cells. The strategies involve the use of polynucleotide small DNA fragments, triplex-forming oligonucleotides, and single-stranded oligodeoxynucleotides to mediate homologous exchange. The primary focus of this review will be on the mechanistic aspects of the small fragment homologous replacement, triplex-forming oligonucleotide-mediated, and single-stranded oligodeoxynucleotide-mediated gene modification strategies as it relates to their therapeutic potential.

Light, including ultraviolet

Ultraviolet (UV) light is intricately linked to the functional status of the cutaneous immune system. In susceptible individuals, UV radiation can ignite pathogenic inflammatory pathways leading to allergy or autoimmunity. In others, this same UV radiation can be used as a phototherapy to suppress pathogenic cutaneous immune responses. These vastly different properties are a direct result of UV light's ability to ionize molecules in the skin and thereby chemically alter them. Sometimes these UV-induced chemical reactions are essential, the formation of pre-vitamin D(3) from 7-dehydrocholesterol, for example. In other instances they can be potentially detrimental. UV radiation can ionize a cell's DNA causing adjacent pyrimidine bases to chemically bond to each other. To prevent malignant transformation, a cell may respond to this UV-induced DNA damage by undergoing apoptosis. Although this pathway prevents skin cancer it also has the potential of inducing or exacerbating autoreactive immune responses by exposing the cell's nuclear antigens. Ultraviolet-induced chemical reactions can activate the immune system by a variety of other mechanisms as well. In response to UV irradiation keratinocytes secrete cytokines and chemokines, which activate and recruit leukocytes to the skin. In some individuals UV-induced chemical reactions can synthesize novel antigens resulting in a photoallergy. Alternatively, photosensitizing molecules can damage cells by initiating sunburn-like phototoxic reactions. Herein we review all types of UV-induced skin reactions, especially those involving the immune system.

Suppression of the barley uroporphyrinogen III synthase gene by a Ds activation tagging element generates developmental photosensitivity

Chlorophyll production involves the synthesis of photoreactive intermediates that, when in excess, are toxic due to the production of reactive oxygen species (ROS). A novel, activation-tagged barley (Hordeum vulgare) mutant is described that results from antisense suppression of a uroporphyrinogen III synthase (Uros) gene, the product of which catalyzes the sixth step in the synthesis of chlorophyll and heme. In homozygous mutant plants, uroporphyrin(ogen) I accumulates by spontaneous cyclization of hydroxyl methylbilane, the substrate of Uros. Accumulation of this tetrapyrrole intermediate results in photosensitive cell death due to the production of ROS. The efficiency of Uros gene suppression is developmentally regulated, being most effective in mature seedling leaves compared with newly emergent leaves. Reduced transcript accumulation of a number of nuclear-encoded photosynthesis genes occurs in the mutant, even under 3% light conditions, consistent with a retrograde plastid-nuclear signaling mechanism arising from Uros gene suppression. A similar set of nuclear genes was repressed in wild-type barley following treatment with a singlet oxygen-generating herbicide, but not by a superoxide generating herbicide, suggesting that the retrograde signaling apparent in the mutant is specific to singlet oxygen.

The practicalities of photodynamic therapy in acne vulgaris

A staple clinical skill in a dermatologist's repertoire is the ability to treat acne vulgaris effectively. Light-based therapies such as photodynamic therapy (PDT) widen the therapeutic options available for acne. Numerous review articles have agreed on the answer to core questions such as: 'Does PDT work?' and 'Which acne lesions respond best to PDT?' They conclude that PDT is especially useful in inflammatory acne and may be superior to light therapy alone. This literature review seeks to offer guidance regarding treatment-specific queries about the photosensitizer, route of administration, treatment intervals, light sources and patient selection. Ovid Medline, PubMed and EMBASE database searches were executed between January 2007 and March 2008. Due to the scarcity of data, all five randomized trials, four of which were at least investigator blinded and controlled, 12 open clinical studies, two case reports and two abstracts published in English were considered. Four hundred and nineteen patients were recruited. As the quality of the data was suboptimal in a significant number of articles, the conclusions are drawn in very broad strokes: topical short-contact (90 min or less) 5-aminolaevulinic acid or methyl aminolaevulinate using a noncoherent light source at 2-4-week intervals for a total of two to four treatments produces the greatest clinical effect. Papulopustular acne is more responsive and all Fitzpatrick skin types are eligible. However, patients with skin types I-III have a reduced risk of postinflammatory hyperpigmentation seen in darker skin types. These treatment parameters demonstrate a good side-effect profile resulting in acne remission for at least 3 months to a year in a relatively cost-effective manner. Well-designed nonsplit-face randomized controlled trials would offer further guidance, especially for queries surrounding the light source and illumination schemes.

Photodegradation of 5-methyltetrahydrofolate in the presence of Uroporphyrin

The main form of folate in human plasma is 5-methyltetrahydrofolate (5MTHF). The observation that folate in human serum is photosensitive supports the hypothesis that humans developed dark skin in high ultraviolet fluences areas in order to protect folate in the blood from UV radiation. However, folates alone are quite photostable. Therefore, in this study, we examined for the first time the photodegradation of 5MTHF in the presence of the endogenous photosensitizer uroporphyrin (Uro), which is sometimes present in low concentration in human serum, under UV and near-UV light exposure. We found strong indications that while 5MTHF alone is rather photostable, it is degraded quickly in the presence of Uro. Using deuterium oxide (D(2)O) as an enhancer of the lifetime of singlet oxygen and the singlet oxygen sensor green reagent (SOSG) as a scavenger of singlet oxygen, we have found that the photodegradation most likely proceeds via a type II photosensitization. Our results show that singlet oxygen is likely to be the main intermediate in the photodegradation of 5MTHF mediated by Uro. Our findings may be useful for further studies the evolution of human skin colours.

Formation of 8-hydroxy-2'-deoxyguanosine in the DNA of cultured human keratinocytes by clinically used doses of narrowband and broadband ultraviolet B and psoralen plus ultraviolet A

Psoralen plus ultraviolet A (PUVA) and narrowband ultraviolet B (UVB) are widely used in skin disease phototherapy. Recently, the efficacy of UVB therapy has been greatly improved by narrowband UVB, compared to conventional broadband UVB. The objectives of the current study were to evaluate the influence of UVB-induced and PUVA-induced oxidative stress on cultured keratinocytes. We analyzed 8-hydroxy-2'-deoxyguanosine (8-OH-dG) in human keratinocytes (HaCaT cell line) using a high-performance liquid chromatography system equipped with an electrochemical detector. Non-irradiated human keratinocytes contained a baseline of 1.48 +/- 0.22 (mean +/- SD) 8-OH-dG per 10(6) deoxyguanosine (dG) residues in cellular DNA, which increased linearly with higher doses of UVB. When their abilities to induce 8-OH-dG were compared to each other, based on the minimal erythemal and therapeutically used doses, by irradiating them with broadband UVB at 100 mJ/cm(2), the amount of 8-OH-dG increased to 3.42 +/- 0.46 residues per 10(6) dG, while a narrowband UVB treatment at 1000 mJ/cm(2), with biological effects comparable to those elicited by 100 mJ/cm(2) broadband UVB, increased it to 2.06 +/- 0.31 residues per 10(6) dG. PUVA treatment, with 100 ng/mL 8-methoxypsoralen and 5000 mJ/cm(2) UVA, increased the 8-OH-dG level to 4.52 +/- 0.42 residues per 10(6) dG. When HaCaT cells treated with 2000 mJ/cm(2) narrowband UVB were cultured and the amount of 8-OH-dG was monitored in the living cells, 65.6% of the residues were repaired 24 h after treatment. Our study provides a warning that widely used narrowband UVB and PUVA induce cellular oxidative DNA damage at the therapeutically used doses, although to a lesser degree than broadband UVB with the same clinically effective dose.

Identification of quenchers of photoexcited States as novel agents for skin photoprotection

Photooxidative stress is a key mechanism in UVA-induced skin photodamage. Photoexcited states of endogenous UVA chromophores such as porphyrins, melanin precursors, and cross-link-fluorophores of skin collagen exert skin photodamage by direct reaction with substrate molecules (type I photosensitization) or molecular oxygen (type II), leading to formation of reactive oxygen species. Based on our previous research on the role of photoexcited states of endogenous skin chromophores as sensitizers of photooxidative stress, we describe here the identification of a novel class of chemopreventive agents for topical skin photoprotection: quenchers of photoexcited states (QPES). QPES compounds antagonize the harmful excited state chemistry of endogenous sensitizers by physical quenching, facilitating the harmless return of the sensitizer excited state to the electronic ground state by energy dissipation. To identify QPES compounds suitable for development, we designed a primary screening assay based on QPES suppression of photosensitized plasmid cleavage using conditions that exclude antioxidants. This screen is followed with a screen to test for nonsacrificial quenching of dye-sensitized singlet oxygen ((1)O(2)) formation by electron paramagnetic resonance detection of 2,2,6,6-tetramethyl-piperidine-1-oxyl, a stable free radical indicative of (1)O(2) formation. These initial screens identified a pyrrolidine pharmacophore with pronounced QPES activity, and l-proline and other noncytotoxic proline derivatives containing this pharmacophore were then screened for efficacy in cellular models of sensitized photodamage. These compounds showed QPES protection against dye-sensitized and psoralen-UVA-induced apoptosis and suppression of proliferation in cultured human skin keratinocytes and fibroblasts. Furthermore, QPES photoprotection of reconstructed full thickness human skin exposed to solar simulated light has been demonstrated.

In Vivo Oxygen Radical Generation in the Skin of the Protoporphyria Model Mouse with Visible Light Exposure: An L-Band ESR Study

Although oxygen radicals are thought to play a key role in the skin injury that is caused by protoporphyria, there is no direct evidence of generation of these radicals in vivo. This study measured the generation of oxygen radicals caused by visible light non-invasively in the skin of griseofulvin-induced protoporphyria model mice, using an in vivo electron spin resonance spectrometer equipped with a surface-coil-type resonator that could detect radicals within about 0.5 mm of the skin surface. A durable nitroxyl radical was administered intravenously as a probe. Light irradiation enhanced the decay of the nitroxyl signal in griseofulvin-treated mice, whereas light irradiation did not enhance the signal decay in control mice. The enhanced signal decay was completely suppressed by intravenous administration of hydroxyl radical scavengers, superoxide dismutase or catalase, or the intraperitoneal administration of desferrioxamine. The enhanced signal decay with illumination was reversible, and quickly responded to turning the light on and off. These observations suggest that the hydroxyl radical is generated via an iron-catalyzed reaction in the skin. This paper demonstrates, for the first time, the specific generation of oxygen radicals in response to light irradiation of the skin of protoporphyria model mice.

Orally administered polypodium leucotomos extract decreases psoralen-UVA–induced phototoxicity, pigmentation, and damage of human skin

BACKGROUND

The use of psoralen-UVA (PUVA) in patients of skin phototype I to II is limited by side effects of acute phototoxicity and possible long-term carcinogenesis.

OBJECTIVE

We sought to assess oral Polypodium leucotomos (PL) extract in decreasing PUVA-induced phototoxicity of human skin on a clinical and histologic level.

METHODS

A total of 10 healthy patients with skin phototypes II to III were exposed to PUVA alone (using 0.6 mg/kg oral 8-methoxypsoralen) and to PUVA with 7.5 mg/kg of oral PL.

RESULTS

Clinically, phototoxicity was always lower in PL-treated skin after 48 to 72 hours (P<.005), and pigmentation was also reduced 4 months later. Histologically, PL-treated skin showed a significant numeric reduction of sunburn cells (P=.05), preservation of Langerhans cells (P< or =.01), decrease of tryptase-positive mast cell infiltration (P<.05), and decrease of vasodilation (P< or =.01). No differences were found in Ki-67+ proliferating cells.

CONCLUSIONS

PL is an effective chemophotoprotector against PUVA-induced skin phototoxicity and leads to substantial benefits of skin protection against damaging effects of PUVA as evidenced by histology.

Detection of Enhanced Monohydroxyeicosatetraenoic Acid and F2-Isoprostane Levels in Human Plasma Samples after Extracorporeal Photoimmunotherapy

To investigate the involvement of reactive oxygen species in extracorporeal photoimmunotherapy (photopheresis), we have introduced two highly sensitive and specific techniques for the detection and quantitative measurement of oxygenated nonenzymatically formed arachidonic acid isomers [mono-hydroxyeicosatetraenoic acids (HETEs) and F2-isoprostanes] by gas chromatography-mass spectrometry/negative ion chemical ionization (GC-MS/NICI) in plasma samples of patients suffering from cutaneous T-cell lymphoma and progressive systemic scleroderma II. The analysis of HETEs involved hydrogenation, solid phase extraction on a C18 cartridge, formation of pentafluorobenzyl bromide and trimethylsilyl ether derivatives. In the case of F2-isoprostanes, the analytical procedure was similar to that of HETEs except that the hydrogenation step was omitted. In the plasma of healthy volunteers picomole amounts of 2-, 5-, 8-12-, 15-HETEs, 8-iso-PGF(2alpha) and 9alpha,11alpha-PGF(2alpha) were quantified by using 12-hydroxy-heptadecatrienoic acid and PGF(2alpha)-d4 as internal standards of HETEs and isoprostanes, respectively. Analysis of plasma samples obtained from patients before and after extracorporeal photoimmunotherapy revealed characteristic increases in both, HETE and isoprostane levels. The enhancement of indicators of lipid peroxidation is in correspondence with a moderate loss of alpha-tocopherol, the most important lipid-soluble antioxidant in human plasma. Thus, our data confirm the involvement of lipid peroxidation in extracorporeal photoimmunotherapy.

Effect of UV-B radiation on some common antibiotics

Some of the commonly used antibiotics such as cephaloridine, cephalexin, cephradine, nystatin and nafcillin were tested for generation of singlet oxygen (1O(2)) under UV-B (290-320 nm) exposure and the order for 1O(2) generation was obtained: cephaloridine>cephalexin>nystatin>cephradine>nafcillin. In vitro study with deoxyguanosine (dGuo) showed that 1O(2) was responsible for drug-sensitized photodegradation of the guanine base of DNA and RNA. Sodium azide (NaN(3)) and 1,4-diazabicyclo [2.2.2] octane (DABCO) accorded significant inhibition (76-98%) in the production of (1)O(2) and photo-oxidation of dGuo. The combined effect of drug and UV-B irradiation is of paramount importance in view of cell-damaging reactions by 1O(2). Our findings are important because of increasing UV-B radiation on the earth's surface due to depletion of the stratospheric ozone layer. The selected drugs are used routinely for the treatment of various diseases and their combined action may cause undesirable phototoxic responses. Our study suggests that exposure to sunlight should be avoided after the intake of the photosensitive drugs.

A sensitive gas chromatography-mass spectrometry assay reveals increased levels of monohydroxyeicosatetraenoic acid isomers in human plasma after extracorporeal photoimmunotherapy and under in vitro ultraviolet A exposure

Extracorporeal photoimmunotherapy (photopheresis) is a highly effective therapy in the treatment of various disorders. Although extracorporeal photoimmunotherapy has been successfully used for more than 10 y, its mechanism of action is still unclear. The formation of reactive oxygen species have been implicated in extracorporeal photoimmunotherapy, but malonyl dialdehyde as a marker of systemic lipid peroxidation did not increase significantly during treatment. To investigate further the involvement of reactive oxygen species in extracorporeal photoimmunotherapy, we have introduced a highly sensitive negative ion gas chromatography-mass spectrometry based method for quantitating oxygenated arachidonic acid isomers (hydroxyeicosatetraenoic acids) in plasma samples of patients treated with extracorporeal photoimmunotherapy. In the plasma of healthy volunteers pmole amounts of 2-, 3-, 5-, 8-12-, and 15-hydroxyeicosatetraenoic acid were detected and we observed a dose-dependent augmentation in these metabolites when the blood was irradiated with increasing doses of ultraviolet A in the presence of the photosensitizer 8-methoxypsoralen. Analysis of plasma samples obtained from patients before and after extracorporeal photoimmunotherapy revealed a characteristic increase in total hydroxyeicosatetraenoic acid levels, particularly of 5-hydroxyeicosatetraenoic acid which contributed 80% to the sum of all hydroxyeicosatetraenoic acid isomers. Chiral phase high-performance liquid chromatography indicated almost equal amounts of 5S- and 5R-hydroxyeicosatetraenoic acid suggesting that the majority of lipid peroxidation products are formed via nonenzymatic oxidation reactions.

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.

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.

Photocarcinogenesis: an overview

Photocarcinogenesis represents the sum of a complex of simultaneous and sequential biochemical events that ultimately lead to the occurrence of skin cancer. These events, initiated by UV radiation of appropriate wavelength, include the formation of DNA photoproducts: DNA repair; mutation of proto-oncogenes and tumor suppressor genes; UV-production of radical species with subsequent effects on mutation and extra-nuclear function; and other epigenetic events that influence the course of carcinogenesis. The epigenetic influences may include immunological responses, antioxidant defenses, and dietary factors. This review represents an effort to provide current research results in the aforementioned areas and an attempt to meld these events into a comprehensive overview of photocarcinogenesis. If effective prevention and intervention strategies for skin cancer are to developed, a more thorough understanding of the disease process is imperative.

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.

Topical or oral administration with an extract of Polypodium leucotomos prevents acute sunburn and psoralen-induced phototoxic reactions as well as depletion of Langerhans cells in human skin

Sunburn, immune suppression, photoaging, and skin cancers result from uncontrolled overexposure of human skin to solar ultraviolet radiation (UVR). Preventive measures, including photoprotection, are helpful and can be achieved by topical sunscreening agents. Polypodium leucotomos (PL) has been used for the treatment of inflammatory diseases and has shown some in vitro and in vivo inmunomodulating properties. Its beneficial photoprotective effects in the treatment of vitiligo and its antioxidant properties encouraged us to evaluate in vivo the potentially useful photoprotective property of natural extract of PL after topical application or oral ingestion. Twenty-one healthy volunteers [either untreated or treated with oral psoralens (8-MOP or 5-MOP)] were enrolled in this study and exposed to solar radiation for evaluation of the following clinical parameters: immediate pigment darkening (IPD), minimal erythema dose (MED), minimal melanogenic dose (MMD), and minimal phototoxic dose (MPD) before and after topical or oral administration of PL. Immunohistochemical assessment of CD1a-expressing epidermal cells were also performed. PL was found to be photoprotective after topical application as well as oral administration. PL increased UV dose required for IPD (P < 0.01), MED (P < 0.001) and MPD (P < 0.001). After oral administration of PL, MED increased 2.8 +/- 0.59 times and MPD increased 2.75 +/- 0.5 and 6.8 +/- 1.3 times depending upon the type of psoralen used. Immunohistochemical study revealed photoprotection of Langherhans cells by oral as well as topical PL. The observed photoprotective activities of oral or topical PL reveal a new avenue in examining the potentially useful field of systemic photoprotection and suggests that PL can be used as adjunct treatment and can make photochemotherapy and phototherapy possibly safe and effective when the control of cutaneous phototoxicity to PUVA or UVB is a limiting factor in such phototherapies.

Photosensitization of uroporphyrin augments the ultraviolet A-induced synthesis of matrix metalloproteinases in human dermal fibroblasts

Porphyria cutanea tarda is characterized by severe connective tissue damage in sun-exposed skin. The regulated synthesis and degradation of the extracellular matrix by various matrix metalloproteinases (MMPs) determine its amount and composition within the skin. In this study, we therefore asked whether long-wave ultraviolet irradiation (340-450 nm) in conjunction with uroporphyrin I could modulate the synthesis of MMPs with substrate specificities for dermal (collagens I, III, V; proteoglycans) and basement membrane components (collagens IV, VII; fibronectin; laminin) and whether synthesis of the counteracting tissue inhibitor of metalloproteinases is also affected. After irradiation of uroporphyrin-pretreated fibroblasts, specific mRNAs of MMP-1 and MMP-3 increased concomitantly up to 2.7-fold compared with ultraviolet-irradiated cells and up to 10-fold compared with mock-irradiated or uroporphyrin I-treated controls. In contrast, mRNA levels of tissue inhibitor of metalloproteinases remained unaltered. Similar results were obtained by immunoprecipitation. Gelatin and casein zymography revealed increased proteolytic activity of MMP-2 and MMP-3 in blister fluids of patients with porphyria cutanea tarda, indicating that similar events may occur in vivo. Using deuterium oxide as enhancer and sodium azide as quencher of singlet oxygen, we could increase or reduce MMP synthesis, suggesting that singlet oxygen is the major intermediate in the upregulation of MMPs after irradiation of uroporphyrin-pretreated fibroblasts. Taken together, our results show that ultraviolet irradiation alone, and to a greater extent in conjunction with uroporphyrin I, results in an unbalanced synthesis of MMPs that may contribute to the destruction of the dermis and basement membrane, leading to blistering and accelerated photoaging in porphyria cutanea tarda patients.

Inhibition of ultraviolet-induced formation of reactive oxygen species, lipid peroxidation, erythema and skin photosensitization by polypodium leucotomos

The acute reactions of human skin to solar ultraviolet radiation (290-400 nm) are recognized as a form of inflammation reactions that are mediated by several possible mechanisms including (a) direct action of photons on DNA, (b) generation of reactive free radicals and reactive oxygen species involving the formation of O2.-, 1O2, H2O2, OH, etc., (c) generation of prostaglandins (PGD2, PGE2, etc.), histamine, leucotrienes, and other inflammatory mediators. It is conceivable that UV-induced reactions represent oxidative stress mediated by the formation of free radicals, reactive oxygen, lipid peroxidation, liberation of membrane phospholipids, and subsequent formation of prostaglandins by cyclo-oxygenase pathway. In this study, we examined the role of reactive oxygen species and lipid peroxidation in in vitro reactions as well as in vivo skin inflammation reactions induced by (a) UVB radiation (290-320 nm), and (b) skin photosensitization reaction by PUVA treatment involving 8-methoxypsoralen and UVA (320-400 nm) radiation and presented data for the generation of superoxide anion O2.-) and lipid peroxides. We have also evaluated, both in vitro as well as in vivo systems, the quenching or the inhibition of O2.- by a plant extract known as Polypodium leucotomos. The P. leucotomos extract was found to exhibit interesting antioxidant and anti-inflammatory as well as photoprotective properties against photo-oxidative stress involving the generation of reactive oxygen, lipid peroxidation under in vitro reactions as well as in vivo experimental conditions. Significant inhibition of UVB-induced erythemal response, and 8-methoxypsoralen plus UVA-induced phototoxic reaction after topical application or oral administration of the photosensitizer could be demonstrated in guinea pig skin and human skin following the topical application of P. leucotomos extract. The photoprotective mechanism of P.leucotomos involving interaction with reactive oxygen species or free radicals appears to have potential clinical usefulness in preventing sunburn and inhibiting phototoxic reaction.

Furocoumarin-photosensitized hydroxylation of guanosine in RNA and DNA

Guanosine hydroxylation was used as a marker for assessing photooxidation of DNA and RNA sensitized by monofunctional and bifunctional furocoumarins. DNA or RNA, treated with sensitizer and UVA light, was enzymatically hydrolyzed, dephosphorylated and then analyzed by reversed-phase HPLC with electrochemical detection. Hydroxylated guanosine, i.e. 8-hydroxy-2'-deoxyguanosine (8-OHdG) or 8-hydroxyguanosine (8-OHG), was quantitated. 3-Carbethoxypsoralen (3-CP) was found to be an efficient photosensitizer for oxidation of guanosine in DNA, resulting in conversion of up to 0.4% of guanosine residues to 8-OHdG. In contrast, dramatically lower levels of guanosine hydroxylation were observed in 3-CP-photosensitized RNA. Psoralen was found to be a more efficient photosensitizer than angelicin in both DNA and RNA. Additional studies of oxidation of 3-CP-photosensitized DNA indicated that double-stranded DNA is 10 times more susceptible to photooxidation than single-stranded DNA, implicating 3-CP binding to DNA as an important mechanistic step in photooxidation of guanosine. The effects of D2O and degassing with argon on photooxidation of guanosine in DNA sensitized by 3-CP were inconsistent with a mechanism involving 1O2. In addition, chelation of adventitious metal ions present in preparations of DNA photosensitized by 3-CP had no effect on hydroxylation of guanosine.

8-methoxypsoralen increases daytime plasma melatonin levels in humans through inhibition of metabolism

It is well established that in healthy humans oral intake of 5- or 8-methoxypsoralen (5- and 8-MOP) is followed by a significant increase in plasma melatonin concentrations. The effect of psoralen on rat melatonin has been studied in vitro and in vivo and a stimulation of release or secretion from the pineal gland has been suggested. In this study we examined the time-related changes in plasma concentrations of 8-MOP, melatonin and 6-sulfatoxymelatonin in 15 patients admitted for routine psoralen plus UVA therapy. On the first day of treatment blood samples were collected before, and 30, 60, 66 and 90 min after intake of 8-MOP (0.6 mg/kg). Although the rate of 8-MOP absorption varied greatly, a significant increase (P = 0.0002) in melatonin levels was found 60 min after 8-MOP intake. During UVA exposure a strongly correlated decrease in mean melatonin and mean 8-MOP concentrations was found, indicating an effect of UVA radiation, either direct or 8-MOP mediated, on circulating melatonin levels. Plasma 6-sulfatoxymelatonin concentrations decreased significantly between all time points, suggesting inhibition of melatonin metabolism.

Free radicals in cutaneous biology

During the past 25 years, the field of free radical biology has germinated, sprouted, and flowered. Free radicals derived from molecular oxygen, formerly of interest only to radiation chemists, are now known to play multiple roles in living systems. We will here consider the generalities of this field with some special focus on skin as a site of oxygen radical production and as a target upon which the damaging propensities of these radicals are exerted.

An outbreak of phytophotodermatitis due to celery

BACKGROUND

Celery is known to contain psoralens, a group of substances that cause a toxic dermal reaction on exposure to ultraviolet A rays (UVA). An outbreak of phytophotodermatitis amongst 11 workers in a celery harvest in southern Israel is reported.

METHODS

Analysis of the trigger factors was carried out. The patients were questioned regarding their working conditions. Samples of the celery that the workers had been harvesting were analyzed for levels of total psoralens by means of high performance liquid chromatography (HPLC). Levels of UVA were measured.

RESULTS

It was found that the celery harvested in the south of the country contained 84 micrograms/g fresh weight (f.wt.) total psoralens as compared to 35 micrograms/g f.wt. in celery harvested in the north of the country at the same time. The following year the celery harvested in the south contained only 26 micrograms/g f.wt. total psoralens. Other risk factors noted were that the subjects had fair skin, wore no protective clothing, and worked with moist hands. In addition, the days were clear and sunny thus ensuring maximal UV radiation for that time of the year.

CONCLUSIONS

Multiple factors contributed to the outbreak of phytophotodermatitis. A late harvest in the south of the country is incriminated as the cause of the unusually high levels of psoralens in the celery of that year.

Interest of photochemical methods for induction of lipid peroxidation

Lipid peroxidation, which plays a part in a wide variety of biological processes, is an integral process in the oxidation of unsaturated fatty acids via a radical chain reaction. Among the various species which may induce this reaction in vivo, reactive forms of oxygen such as peroxide anion, the hydroxyl radical and singlet oxygen are of cardinal importance. These species may be generated enzymatically, chemically or by various radiochemical and photochemical reactions. We present here the advantages of photochemical induction of peroxidation, and we describe the principles of the reactions, the photosensitizers that can be employed to generate the various reactive species of oxygen, and the techniques, direct (ESR) or indirect (specific traps), used to detect the reactive species. Photosensitization can induce the formation of a whole gamut of products of lipid peroxidation: conjugated dienes, aldehydes, hydroperoxides, etc. The relative proportions of the various hydroperoxides of fatty acids or cholesterol depend on the nature of the reactive species involved. Utilization of photochemical reactions is an effective and clean way of inducing peroxidation, allowing fine control of both initiation and orientation.

Chemistry and biology of heme. Effect of metal salts, organometals, and metalloporphyrins on heme synthesis and catabolism, with special reference to clinical implications and interactions with cytochrome P-450

Although free porphyrins occur in nature in small quantities, no known function has been assigned to them. In contrast, heme and cobalamin, which are Fe and Co chelates of porphyrins or porphyrin derivatives, respectively, carry out crucial biological functions. Heme is the prosthetic group for a number of hemoproteins. These include myoglobin and hemoglobin, which carry out oxygen binding or transport; mitochondrial cytochromes aa3, b, c, and c3, which are important in transferring electrons; microsomal cytochrome P-450, which catalyzes mixed-function oxidations; catalase, which decomposes H2O2; peroxidase, which activates H2O2; and tryptophan pyrrolase, which catalyzes the oxidation of tryptophan. Recently, heme has also been shown to be the prosthetic group of prostaglandin and peroxide synthetase and indoleamine dioxygenase. The elegant studies of the biochemical pathway for the formation of heme demonstrated the arrangement in the porphyrin macrocycle of the carbon and nitrogen atoms originating from the eight glycine and the succinic acid molecule that are the precursors of porphyrins. There are eight enzymes involved in the synthesis of heme. The first and last three of these enzymes are localized in mitochondria, while the intermediate enzymes are localized in cytosol. The catalytic site of HMOX recognizes metalloporphyrins with central metal atoms other than iron; it favors some of these metalloporphyrins over heme as a potential substrate, sometimes by a large factor, permitting the synthetic heme analogue to serve as a potent competitive inhibitor of HMOX reaction. Since these synthetic metalloporphyrins do not bind molecular oxygen, they are not metabolically degraded by ring rupture and do not add to the body pool of bile pigment. One possible consequence of this competitive inhibition of heme degradation is suppression of bile pigment formation to such a degree that excessive plasma levels of bilirubin may be diminished. The studies of Drummond and Kappas (1981) and later studies in rats, mice, monkeys, and man, and also our studies have proved the latter phenomenon. The compound does not appear to affect the metabolic disposition of preformed bilirubin but inhibits biliary bilirubin excretion derived from the metabolism of endogenous or exogenous heme. Whether some of the effect of Sn-PP on naturally occurring or experimentally induced jaundice in animals reflects diversion of heme to nonheme to oxygenase-dependent pathways of heme metabolism, or whether a pathway which is normally latent becomes activated concurrent with HMOX inhibition is not known.(ABSTRACT TRUNCATED AT 400 WORDS)

Topical vitamin C protects porcine skin from ultraviolet radiation-induced damage

Ultraviolet radiation damage to the skin is due, in part, to the generation of reactive oxygen species. Vitamin C (L-ascorbic acid) functions as a biological co-factor and antioxidant due to its reducing properties. Topical application of vitamin C has been shown to elevate significantly cutaneous levels of this vitamin in pigs, and this correlates with protection of the skin from UVB damage as measured by erythema and sunburn cell formation. This protection is biological and due to the reducing properties of the molecule. Further, we provide evidence that the vitamin C levels of the skin can be severely depleted after UV irradiation, which would lower this organ's innate protective mechanism as well as leaving it at risk of impaired healing after photoinduced damage. In addition, vitamin C protects porcine skin from UVA-mediated phototoxic reactions (PUVA) and therefore shows promise as a broad-spectrum photoprotectant.

Photoinduced cutaneous inflammatory response by psoralens

Our studies describe the inflammatory response in rabbit skin induced by topical application of 8-methoxypsoralen (8-MOP) and UVA-visible irradiation (320-700 nm). Increase in vascular permeability (iVP) and accumulation of polymorphonuclear leucocytes (aPMN) at the test sites were quantitated using 125I-albumin and 51Cr-labelled PMNs respectively. Erythema was graded visually. 8-MOP cream was applied topically and irradiated. The erythemal response, aPMN and iVP at the test sites were quantitated at 6, 24, 48 and 72 h post-irradiation. The iVP and aPMN were maximal at 24 h; the erythemal response was the same at 24-48 h. The responses were dependent on 8-MOP concentration and irradiation dose. Topical application of 200 micrograms 8-MOP cream followed by irradiation for 2 h (9.4 J cm-2) produced 3-7 times iVP, 2-4 times aPMN and intense erythema at the test sites after 24 h. Neither aPMN nor iVP was detected before 6 h and erythemal response was not observable up to 16 h after irradiation. The aPMN and iVP gradually subsided in 72 h, although the erythemal response was still present. The repeated exposure of 8-MOP-treated sites for three consecutive days 24 h apart did not produce appreciable iVP or aPMN at 72 h or 24 h after the last exposure; however, erythema persisted. The 8-MOP-treated sites previously exposed for three consecutive days on reapplication of 8-MOP cream plus irradiation showed significantly less response compared with non-pretreated sites. Our results suggest that the erythemal response is not directly related to either iVP or aPMN.

Photodynamic degradation of vitamin E induced by psoralens

Psoralens and other furocoumarins currently used in PUVA photochemotherapy are shown to have, to a variable extent, the ability to hasten the rate of ultraviolet-induced photooxidation of alpha-tocopherol (alpha-T) in ethanol or ethanol-phosphate buffer (pH 6.8). The sensitizing effect varies significantly with the substrate concentration and the nature of the furocoumarin used, and is dependent on the presence of oxygen. Scavengers of singlet oxygen, e.g., sodium azide, markedly inhibit the psoralen-sensitized photooxidation of alpha-T, whereas superoxide dismutase exerts an opposite, accelerating effect on the reaction rate. Catalase has no significant influence on the kinetics of alpha-T decay. Analysis of the products formed by psoralen-sensitized photooxidation of alpha-T in ethanol-phosphate buffer showed the presence of alpha-tocopherolquinone, its 2,3-epoxide and two related compounds containing the 7-oxaspiro[4.5]dec-1-ene-3,6-dione ring system. The nature of these products, coupled with the results of the kinetic experiments, suggest that psoralens induce a type II, oxygen-dependent photodegradation of alpha-T primarily mediated by singlet oxygen.

Activation of macrophages by Photofrin II during photodynamic therapy

In order to obtain information about the activation of macrophages (M phi s) during photodynamic therapy (PDT), the influence of Photofrin II (Pf II) on the viability of thioglycollate-elicited murine M phi s and the subsequent generation of superoxide anion was studied. Irradiations were performed at an energy density of 5 J cm-2, a power density of 150 mW cm-2 and a wavelength of 405 nm. Viability of M phi s was assessed using the acridine orange-ethidium bromide assay. Superoxide anion generation was determined using ferricytochrome c (cyt c) and nitroblue tetrazolium (NBT) reduction. Our results indicate that the M phi s are highly susceptible to PDT as their viability is decreased to approximately 30% by 1 microgram ml-1 Pf II at the energy density indicated above. Within the first 30 min of addition of the photosensitizer, a reducing agent is generated intracellularly by the stimulation of the M phi s. An extracellular release of superoxide anion does not occur, as measured by the cyt c assay. Preincubation of the cells for 1 or 24 h with Pf II and a second challenge with phorbol myristate acetate (PMA) does not enhance the reduction of NBT. Thus, Pf II exerts an immediate effect on the M phi s which could be interpreted as a first step for subsequent reactions.

Mechanisms of photodynamic effects of furocoumarins

The photosensitizing action of furocoumarins on biological systems occurs by both an oxygen-independent pathway, which involves the photoaddition of the sensitizer to nucleic acids, proteins and lipids, and an oxygen-dependent pathway, which includes furocoumarins in the category of photodynamic sensitizers. The photodynamic action of furocoumarins, as studied using isolated biomolecules, human erythrocytes and human skin, appears to involve both activated oxygen species (singlet oxygen, superoxide anion, and hydroxyl radicals) and radical species formed by electron transfer from or to photoexcited furocoumarins. Another oxygen-dependent process involves the formation of photo-oxidized furocoumarin derivatives, which can react in the dark with several substrates (in particular, membrane components), causing an irreversible damage of cells. The latter type of process is temperature dependent. The relative importance of the different photosensitization mechanisms under various experimental conditions is discussed.

Genotoxicity of singlet oxygen

Singlet oxygen, 1O2 (1 delta g), fulfills essential prerequisites for a genotoxic substance, like hydroxyl radicals and other oxygen radicals: it can react efficiently with DNA and it can be generated inside cells, e.g. by photosensitization and enzymatic oxidation. As might be anticipated from the non-radical character of singlet oxygen, the pattern of DNA modifications it produces is very different from that caused by hydroxyl radicals. While hydroxyl radicals produce DNA strand breaks and sites of base loss (AP sites) in high yield and react with all four bases of DNA, singlet oxygen generates predominantly modified guanine residues and few strand breaks and AP sites. There is now convincing evidence that a major product of base modification caused by singlet oxygen is 8-hydroxyguanine (7,8-dihydro-8-oxoguanine). Indeed, the recently reported miscoding properties of 8-hydroxyguanine can explain the predominant type of mutations observed when DNA modified by singlet oxygen is replicated in cells. There are also strong indications that singlet oxygen generated by photosensitization can act as an ultimate DNA modifying species inside cells. However, indirect genotoxic mechanisms involving other reactive oxygen species produced from singlet oxygen are also possible and appear to predominate in some cases. The cellular defense system against oxidants consists of effective singlet oxygen scavengers such as carotenoids. The observation that carotenoids can inhibit neoplastic cell transformation when administered not only together with but also after the application of chemical or physical carcinogens might indicate a role of singlet oxygen in tumor promotion that could be independent of the direct or indirect DNA damaging properties.