Sister chromatid exchanges in lymphocytes of psoriatics after treatment with 8-methoxypsoralen and long wave ultraviolet radiation

Micronucleus evaluation in mitogen-stimulated lymphocytes of PUVA treated patients

PUVA describes the treatment of patients with psoralens plus an exposure to a source of UV light of 320-400 nm (UVA). Contradictory results have been reported on the chromosomal damage of PUVA when assayed by sister chromatid exchange (SCE) method. Micronucleus (MN) test is used to detect both clastogenic (breaking) and aneugenic (abnormal segregation) effect of physical/chemical agents on the chromosomes. No data have been found on the MN formation in the cells of PUVA treated patients. Frequency of micronuclei in 72 hours cultivated/mitogen-stimulated lymphocytes of patients have been evaluated at zero time and after 20, 40, 60 sessions of PUVA treatment. While the beginning MN frequency was approximately 0.22% (n=23), it raised to approximately 0.32 (n=23), approximately 0.42 (n=14) and approximately 0.53% (n=10) corresponding respectively to 20, 40 and 60 sessions. These sessions correspond reciprocally to 54+/-23, 172+/-48, 300+/-61 joules/cm2 of UVA and 13, 26, 39 mg/kg of 8-metoxypsoralen (8-MOP). While large interindividual variances were apparent, highly significant differences have been observed between initial MN frequency and after that of the 20, 40 and 60 sessions, (p = 0.000, p = 0.004, p = 0.005, reciprocally, Wilcoxon two-related samples test). The coefficient of correlation between MN frequency and UVA doses starting from zero to 60 sessions of treatment has been found as r = 0.61. This indicates a significant relationship between UVA doses and MN frequencies. However, MN inducibility and synergistic property of 8-MOP with UVA should be taken into account. Gradual MN increase during different sessions of PUVA treatment shows that--once appeared--a part of MN at least persist in the cells of patients from a few days to a few weeks. Smoking as a confounding factor seems to increase MN frequency (p = 0.053, Mann-Whitney U-test) in the beginning population, taken as the control population. This is the first report on the kinetics of MN formation during different sessions of PUVA treatment. Based on our results, we concluded that PUVA treatment causes a detectable chromosome damaging effect on the relatively profound cells/tissues of its human users. Therapists should be careful with its use, especially on the patients who may be more susceptible to carcinogenesis (e.g. immunosuppressed and/or elderly subjects).

Oxyradical-mediated clastogenic plasma factors in psoriasis: increase in clastogenic activity after PUVA

Psoriasis is a common skin disorder characterized by hyperproliferation and incomplete differentiation of epidermal keratinocytes. Psoralen plus UVA (PUVA) is one of the treatments proposed for this disease. We had reported previously that exposure of regular blood cultures from healthy donors to PUVA leads to chromosomal breakage via the formation of transferable clastogenic materials, a phenomenon inhibitable by superoxide dismutase. In the present paper we show that these clastogenic factors (CF) are also formed in vivo. The CF were found in about 50% of the psoriasis patients studied (14 out of 31). In PUVA-treated psoriasis patients, the clastogenic activity of the plasma increased significantly between the first and the last (16th) exposure to PUVA. We hypothesize that CF formation in psoriasis is similar to that in other diseases accompanied by oxidative stress, in particular chronic inflammatory diseases with autoimmune reactions such as lupus erythematosus, progressive systemic sclerosis, rheumatoid arthritis and others. Increased superoxide production by phagocytes, formation of lipid peroxidation products and release of cytokines are considered to be responsible for the superoxide-stimulating and chromosome-damaging properties of patients' plasma. During PUVA therapy, superoxide generated via the interaction of psoralen with UVA may contribute to CF formation in addition to superoxide from inflammatory cells. An increased risk of cancer and leukemia is observed in diseases accompanied by CF formation. Therefore CF may contribute to the well-known risk of photocarcinogenesis by PUVA therapy. This additional risk may be preventable by antioxidants and superoxide scavengers.

Chromosome damage in PUVA-treated human lymphocytes is related to active oxygen species and clastogenic factors

Besides the direct interaction of psoralens with DNA and other macromolecules, the role of reactive oxygen species in the PUVA-induced cellular injury has been stressed. The present study shows that treatment of human blood cultures with 5-methoxypsoralen or 8-methoxypsoralen, followed by UVA exposure, results in chromosome damage. The supernatant of these cultures contains secondarily formed chromosome damaging material, called clastogenic factor (CFs). Not only CF formation, but also CF action is inhibited by superoxide dismutase (SOD), suggesting that superoxide is formed on the pathway to chromosome aberration. CF is detectable in the cell culture supernatants after a minimal delay of 18 h, and reaches a plateau at 24 h of cultivation. SOD is no longer protective if added after 24 h, i.e., the enzyme can prevent, but not repair the oxyradical-induced damage.

Mutagenic risk in psoriatic patients before and after 8-methoxypsoralen and long-wave ultraviolet radiation

Sister-chromatid exchange (SCE) analysis was carried out in different age groups prior to and after therapy with 8-Methoxypsoralen (8-MOP) followed by exposure of the patient to long-wave UV-A (PUVA) and compared to control. The SCE frequencies were increased significantly in PUVA-treated patients as compared to their pre-treatment SCE levels and to controls. A significant increase in SCEs was found in smoking PUVA-treated patients as compared to non-smoking PUVA-treated patients. This study indicates a detectable chromosome-damaging effect of PUVA therapy on its human users.

Cytogenetic effects during extracorporeal photopheresis treatment of two patients with cutaneous T-cell lymphoma

The effect of extracorporeal photopheresis (EP) on various cytogenetic parameters has been investigated. During EP the photoactivatable agent 8-methoxypsoralen (8-MOP) was administered orally. After 2 h a leukocyte-enriched blood fraction was collected by haemocentrifugation, irradiated with UVA extracorporeally, and reinfused to the patient. Two patients suffering from cutaneous T-cell lymphoma showed a marked clinical improvement in response to therapy. In order to investigate the cytogenetic effects and mutagenic risk of EP, the mitotic index (MI), the type and number of chromosomal aberrations and the rate of sister chromatid exchanges (SCE) were studied. Following EP treatment the patients' lymphocytes were cultured and stimulated with phytohaemagglutinin (PHA) for 48 or 72 h. The cultured lymphocytes showed a decreased MI after 48 h as an indicator of cytotoxic effects, but not after 72 h. In lymphocyte cultures not stimulated with PHA, the MI was decreased even after 72 h. The number of chromosomal aberrations and SCE were increased upon treatment, but only transiently, returning to basal levels between consecutive treatments. Our data provides no evidence for increased mutagenic risk as a consequence of effective EP treatment.

Sister chromatid exchange frequency in human epidermal cells in culture treated with 8-methoxypsoralen and long-wave UV radiation

The effects of 8-methoxypsoralen with long-wave ultraviolet radiation on the sister chromatid exchange frequency in human epidermal cells in culture was investigated. With a constant amount of radiation the number of exchanges increased in an approximately linear manner with increasing concentrations of 8-methoxypsoralen up to 0.3 micrograms/ml. Above this concentration there were fewer dividing cells and an apparent departure from linearity in the dose-response curve. These results show that 8-methoxypsoralen concentrations equivalent to those found in the serum of patients undergoing photochemotherapy, in conjunction with UVA radiation, cause striking increases in sister chromatid exchange frequency in human epidermal cells in vitro.

Mutagenicity and toxicity of furocoumarins: comparative investigations in 2 test systems

The phototoxicity and the photomutagenicity of the 2 linear furocoumarins 8-methoxypsoralen (8-MOP) and 8-isoamylenoxypsoralen (8-IOP) and of the angular derivative 5'-methylangelicin (5'-MA) were studied in 2 different test systems. In human lymphocytes, sister-chromatid exchange analysis (SCE analysis) was carried out. We found an increase in SCE frequency after treatment with 8-MOP and 5'-MA, but no enhancement was caused by 8-IOP. In the algal system Chlamydomonas reinhardii, 8-MOP and 5'-MA showed a similarly strong influence with regard to phototoxicity; 8-IOP exhibited a weaker effect within the same irradiation time. For photomutagenicity in Chlamydomonas, 8-MOP proved to be the strongest derivative; 8-IOP, however, was capable of inducing about the same numbers of revertants, but only under certain conditions. The angular 5'-MA showed a weak mutagenic activity in contrast to the psoralens. The influence of the structure of the derivatives and of the experimental conditions on the effects obtained are discussed with regard to the therapeutic risk of monofunctional and bifunctional furocoumarins.

Sister chromatid exchange and chromosome aberration rates in a group of psoriatics before and after a course of PUVA treatment

Blood was cultured and chromosome preparations were examined for sister chromatid exchanges and chromosome aberrations in eighteen patients receiving photochemotherapy with 8-MOP and UV-A for the treatment of psoriasis, both before starting treatment and again 6 months later. The UV-A was administered both by means of low output (irradiance: 1.1--2.25 mW/cm2) and high output (irradiance: 6.1--7.6 mW/cm2) UV-A radiation cubicles. Irrespective of the intensity of irradiation or the total dose of UV-A administered there was no evidence of chromosome damage in lymphocytes following treatment.

5-Methoxypsoralen, an ingredient in several suntan preparations, has lethal, mutagenic and clastogenic properties

Many furocoumarins found in several species of plant are potent photosensitizing agents known to cause lethal and mutagenic effects in a wide range of organisms, from viruses to man. Their role in the aetiology of cancer is debatable, but work has focused on the PUVA (psoralen-UVA) treatment of psoriasis with 8-methoxypsoralen (8-MOP) and near UV radiation. Bergaptene (5-methoxypsoralen, 5-MOP) is a major constiutent of oil of bergamot, and might be expected to have qualitatively similar photosensitizing properties to 8-MOP. Although 5-MOP is widely used as a stimulus to melanin deposition in several suntan preparations surprisingly little is known about its basic photobiology. We report here that 5-MOP has the expected properties of other biologically active furocoumarins. These properties include lethal and mutagenic photosensitization of bacteria, 'dark' induced frameshift mutagenesis in bacteria, and lethal and clastogenic effects on mammalian cells in tissue culture.

Photochemotherapy of psoriasis: DNA damage in blood lymphocytes

DNA synthesis assessed by 3H thymidine incorporation was measured in lymphocytes from patients with psoriasis receiving photochemotherapy with 8-methoxypsoralen (8-MOP) and UV-A (PUVA). The emission from the UVA source contained sufficient short wavelengths (UV-B) to impair 3H-thymidine incorporation but could be screened out with clear plastic screens. When lymphocytes were irradiated in vitro in a 1/10 dilution of plasma containing 8-MOP, increasing doses of UV-A produced progressive inhibition of phytohaemagglutinin (PHA)-induced DNA synthesis. Cells from patients given several previous treatments were inhibited significantly more than those from patients receiving their first exposure. This was also true for unirradiated cells sugesting either an accumulation of 8-MOP within cells, persistence of DNA damage or alteration of the lymphocyte population. Lymphocytes removed immediately after patients were irradiated showed less 3H thymidine incorporation than cells taken just prior to irradiation, which confirms that PUVA treatment exerts in vivo effects on circulating lymphocytes.

Unscheduled DNA synthesis in psoriatic skin after ultraviolet irradiation and the effects of a combined treatment with 8-methoxypsoralen and longwave ultraviolet radiation: a clinical study

Biopsies were taken from psoriatic patients undergoing photochemotherapy and then studied by autoradiography to investigate possible unscheduled DNA synthesis (UDS) following 8-MOP photodamage in epidermal cels. No sparse labelling was found in seventy samples taken from twenty-four different patients during PUVA therapy, indicating a lack of UDS. In contrast, UDS was observed in three patients irradiated with an all-spectrum UV lamp, as a test for DNA damage and excision repair activity. The incorporation of 3HTdR in these keratinocytes which were not undergoing S-phase was not affected by the dose of UV-A received during different stages of PUVA treatment. The results are discussed in terms of repair of the induced photodamage at the level of DNA, and in relation to a possible risk of this treatment when it is given over a long period of time.

[DNA-repair of lymphocytes during PUVA-treatment (author's transl)]

In 20 psoriatic patients under PUVA maintenance treatment blood samples had been collected imediately before and after the UVA irradiation. The DNA-repair activity has been determined in the isolated lymphocytes by the incorporation of 3H-thymidine during the first 3 h (inhibition of the semiconservative replication by hydroxyurea). There is evidence for an increased repair activity in the lymphocytes after PUVA treatment whereas the lymphocytes exposed only to 8-MOP (before UVA irradiation) show lower values. The difference is statistically significant 45 and 90 min after irradiation, but not any more after 3 h.

Inhibition of human blood platelet aggregation by photochemotherapy in vitro and in vivo

Irradiation of human blood platelets with UV-A in vitro impairs their ability to aggregate after challenge with collagen. There also appears to be mild and transient inhibition of platelet aggregability in psoriatics during the fourth week of photochemotherapy.

Mutagenicity of 8-methoxypsoralen and long-wave ultraviolet irradiation in diploid human skin fibroblasts: an improved risk estimate in photochemotherapy

Cell killing and the induction of mutation were studied in dividing and non-dividing human skin fibroblasts as a result of treatment by 8-methoxypsoralen (8-MOP) and long-wave UV irradiation (UVA). The cytotoxic effect was highly dependent upon the duration of the UVA exposure. The frequency of mutations increased linearly with the UVA dose at concentrations of 10 and 0.25 microliter 8-MOP/ml, the latter representing the concentration in the skin during PUVA treatment. The number of mutations induced per unit dose (= per microgram 8-MOP/ml per joule UVA/m2) was calculated: for dividing cells this value was 3.3 X 10(-8) per cell and for non-dividing cells 0.6 X 10.8(-8) per cell. On the basis of these values the expected number of induced mutants in the human skin per session of photochemotherapy is 1.2 X 10(-5), and per 30 years of maintenance therapy 1.3 X 10(-2) per cell. A comparison was made between this frequency and the frequency to be expected from spontaneous mutation. In addition the significance of absence in patients of SCE induction by photochemotherapy is discussed.

Psoralen/UVA treatment and chromosomes. II. Analyses of psoriasis patients

Five psoriasis patients treated with 8-methoxypsoralen and UVA (PUVA) were studied by lymphocyte cultures at the 1st, 5th, 10th and 20th treatment and at a maintenance treatment 6 months later. Abnormal amounts of chromosome aberrations were not found, and the frequency of sister chromatid exchange (examined at the last treatment) was not increased. In vitro experiments with nanogram doses of psoralen (similar to plasma levels in patients) showed no increase in chromosome aberration or SCE freqency. The results indicate that therapeutic doses of PUVA have no clastogenic effect.