Photoinactivation of skin fibroblasts by fractionated treatment with 8-methoxypsoralen and UVA

Lectin staining of the endothelial cell membrane is more sensitive to ultraviolet radiation than the epidermal cell staining in guinea-pig skin

Ultraviolet radiation (UVR)-induced alterations in lectin stainings of both endothelial and epidermal cells were histochemically analysed in guinea-pig skin using Bandeiraea simplicifolia agglutinin-I and Ricinus communis agglutinin-I. The endothelial cell staining with both lectins was more sensitive to a single exposure to middle-wave UVR (UVB) and topical psoralen plus long-wave UVR (UVA) (PUVA) than the epidermal cell staining. More remarkable changes were seen following PUVA radiation than UVB radiation. No significant alterations were induced by UVA radiation alone or psoralen alone. The results suggest that the endothelial cell is a susceptible target for UVB and PUVA radiation.

Effect of long-term PUVA treatment of psoriasis on the collagen and elastin gene expression and growth of skin fibroblasts in vitro

The proliferation rate, collagen metabolism and collagen and elastin messenger-RNA levels were studied in fibroblasts derived from patients who had received many courses of either systemic 8-methoxypsoralen or topical trioxsalen PUVA treatment. The proliferation rate of fibroblasts as measured by the incorporation of 3H-thymidine or by cellular division was decreased in those obtained from patients who had PUVA treatment as compared with controls. Collagen synthesis was slightly increased in the cells from PUVA-treated patients, but the relative collagen synthesis and the ratio between types I and III collagen were unchanged. The levels of collagen and elastin mRNAs were increased in fibroblasts derived from the PUVA-treated patients. No significant differences in histology or immunochemistry could be found in the biopsies taken from topical and systemic PUVA-treated patients.

Psoralen photochemotherapy

Psoralens and sunlight have been used by the Egyptians and Indians for hundreds of years for the treatment of vitiligo. The combination of oral psoralens and artificial ultraviolet A (PUVA) therapy was approved for the management of severe psoriasis by the Food and Drug Administration in 1982. Since then PUVA therapy has been found to be an effective modality in the treatment of many cutaneous conditions. When properly administered, the major short-term side effects are minimal. The long-term side effects may include an increased risk of squamous cell carcinoma, atypical cutaneous pigmentation, accelerated skin aging, and ophthalmologic abnormalities. By careful patient selection and limiting the cumulative UVA dosage and frequency by using combinations or alternative therapies, these side effects may be reduced. Continued reporting of carefully carried out long-term prospective studies will provide us with more knowledge of the long-term side effects of PUVA. In the meantime, for each patient on PUVA therapy the risk/benefit ratio should be carefully considered.

Penetration and localization of furocoumarins in single living cells studied by microspectrofluorometry

The microspectrofluorometric technique has been used to study the penetration and the localization of psoralen, 4,5',8-trimethylpsoralen and 4'-aminomethyltrioxsalen in single living L-cells. The concentration of the different compounds inside the cell reached a plateau in 2 min with psoralen and aminomethyltrioxsalen and in 20 min with trioxsalen. Washing of the cells with culture medium produced only a partial removal of the three furocoumarins, distributed apparently in equivalent amount in the nucleus and cytoplasm.

DNA replication and cell-cycle progression of cultured mouse FM3a cells after treatment with 8-methoxypsoralen plus near UV-radiation

To investigate the response of cells to one type of DNA damage--namely DNA crosslinks--cell-cycle progression and macromolecular synthesis were studied with cultured mouse FM3A cells. Treatment of the cells with low doses of 8-methoxypsoralen (8-MOP) plus near-UV radiation (0.1 micrograms/ml plus 5 kJ/m2 or 1.0 micrograms/ml plus 1-2.5 kJ/m2) halted the progression of cells through the cell cycle temporarily for the first several hours. Then the cells resumed progression through the cell cycle, and most of the cells reached, and were finally arrested at, the G2 phase of the cycle. There was a rapid decrease of incorporation of [3H]thymidine into cellular Dna immediately after the treatment. Then, after 8 h of incubation, the incorporation of [3H]thymidine recovered to some extent depending on the dose of 8-MOP plus near-UV radiation. Thus the decrease and recovery of the incorporation of [3H]thymidine were correlated with the halt and resumption in the cell-cycle process. Synthesis of RNA and protein was measured by determination of the amounts in the cells or by the incorporation of radioactive precursors after treatment. RNA and protein synthesis were stimulated by low doses of 8-MOP plus near-UV radiation, but inhibited severely by high doses.

Induction and repair of psoralen cross-links in DNA of normal human and xeroderma pigmentosum fibroblasts

Skin fibroblasts from normal human subjects were exposed in vitro to long-wave ultraviolet radiation (UVA, 320-400 nm) alone, or in combination with 8-methoxypsoralen (8-MOP). DNA damage was analysed with the alkaline elution technique before and after post-treatment incubation of the cells at 37 degrees C for various times. Cells treated with UVA at 1.1 J/cm/ showed an increased DNA elution rate, which returned to the normal level within 30 min of post-treatment incubation. In cells treated with PUVA (8-MOP at 20 microgram/ml plus UVA at 0.04 J/cm2), the alkaline elution rate was not different from untreated control cells, either before or after post-treatment incubation for time up to 7 days. When the PUVA treatment was followed first by a washing, to remove any unbound 8-MOP, and then by UVA (PUVA + UVA) at 1.1 J/cm2, the alkaline elution rate decreased below the control level. During the post-treatment incubation of the PUVA + UVA-treated cells there was a gradual increase of the alkaline elution rate to a level significantly above that in control cells. This increase was observed after 30 min. It reached a maximum after 24 h and remained after 7 days of post-treatment incubation. Cells from a patient with xeroderma pigmentosum of complementation group A, which were given the same PUVA + UVA treatment, did not show any change in the alkaline elution rate during the post-treatment incubation. If, as seems likely, an increased alkaline elution rate indicates as increase of DNA breaks, and a decreased alkaline elution rate indicates the sealing of breaks and/or the formation of cross-links, and results would suggest the following: (1) UVA irradiation in itself is capable of inducing DNA breaks, which are rapidly sealed during post-treatment incubation; (2) PUVA treatment induces mono-adducts, some of which appear to remain in the DNA for at least 7 days of post-treatment incubation and can be activated to form DNA cross-links by a second dose of UVA; (3) DNA cross-links induced by PUVA + UVA can be recognized by a repair process that involves the formation of DNA breaks. This process is not observed in xeroderma pigmentosum cells of group A.

Action spectra for 8-methoxypsoralen and 3-carbethoxypsoralen in skin fibroblasts in vitro

8-methoxypsoralen (8-MOP) and 3-Carbethoxypsoralen (3-CPs) are known photoreagents which have been employed in the treatment of psoriasis. Using skin fibroblasts grown in vitro we have determined the action spectra of both compounds in the long ultraviolet range. Narrow-band interference filters were applied to a Xenon lamp. Reduction in methyl-3H-thymidine (3H-TdR) uptake served as a parameter for photoinhibited cells. The results show a linear increate of 8-MOP-mediated photoinhibition with increasing wavelengths; 3-CPs showed comparatively weak inhibitory rates at the lower wavelength range (349-365 nm). Possibly this is due to the formation of 3-CPs photoproducts which are unreactive with DNA. Compared to 8-MOP, the monofunctional photoreagent 3-CPs is a weak photoinhibitor.

[8-Methoxypsoralen (8-MOP)-a new galenic form and its relation to 8-MOP serum levels (author's transl)]

A bioequivalence study was performed with two different 8-MOP preparations. Thirty-eight patients participated in the investigation. We compared a product already marketed containing a micronized powder in hard gelatine capsules with a new product in soft gelatine capsules containing the 8-MOP in a solution. With the new galenic preparation the serum level obtained was 3.2 (P less than or equal to 0.01) times higher than with the old product. Thus, the improved resorption out of the solution was mainly responsible for these results.

DNA repair responses in human skin cells

Sunlight and some environmental chemical agents produce lesions in the DNA of human skin cells that if unrepaired may interfere with normal functioning of these cells. The most serious outcome of such interactions may be malignancy. It is therefore important to develop an understanding of mechanisms by which the lesions may be repaired or tolerated without deleterious consequences. Our models for the molecular processing of damaged DNA have been derived largely from the study of bacterial systems. Some similarities but significant differences are revealed when human cell responses are tested against these models. It is also of importance to learn DNA repair responses of epidermal keratinocytes for comparison with the more extensive studies that have been carried out with dermal fibroblasts. Our experimental results thus far indicate similarities for the excision-repair of ultraviolet-induced pyrimidine dimers in human keratinocytes and fibroblasts. Both the monoadducts and the interstrand crosslinks produced in DNA by photoactivated 8-methoxypsoralen (PUVA) can be repaired in normal human fibroblasts but not in those from xeroderma pigmentosum patients. The monoadducts, like pyrimidine dimers, are probably the more mutagenic/carcinogenic lesions while the crosslinks are less easily repaired and probably result in more effective blocking of DNA function. It is suggested that a split-dose protocol that maximizes the production of crosslinks while minimizing the yield of monoadducts may be more effective and potentially less carcinogenic than the single ultraviolet exposure regimen in PUVA therapy for psoriasis.

A comparison of the photochemical actions of 5- and 8-methoxypsoralen on CHO cells

Chinese Hamster ovary (CHO) cells were treated with 5- or 8-methoxypsoralen (MOP) in combination with longwave UV light (UVA). The toxicity and the action of these substances on DNA synthesis as well as well as the nature of damage caused by them in combination with UVA light and the ability of the cells to repair this damage was examined. 8-MOP induces interstrand crosslinks within the DNA when applied together with UVA light. It decreases the rate of DNA synthesis at sublethal doses. 5-MOP shows the same effect though it induces virtually no DNA crosslinks. The repair of damage process. It is not quite complete at 24 h. Neither compound has an effect on CHO cells when applied without UVA light.

Inhibitory effect of 8-methoxysporalen plus UVA (PUVA) on the systemic induction of contact sensitivity to dinitrochlorobenzene (DNCB) in guinea pigs

To investigate the influence of 8-MOP and UVA on the induction of cell-mediated immunity, guinea pigs, sensitized with a single injection of dinitrofluorobenzene (DNFB) in Freund's complete adjuvant (FCA) in all footpads and the nuchal skin, were treated with 8-MOP, UVA, or 8-MOP + UVA on days 0, 2, and 5 and tested with dinitrochlorobenzene (DNCB) on day 14 after sensitization. Two control groups, exposed in a covered condition to the PUVA 4000 lamp, to observe the heat effect, showed a slightly enhanced contact sensitivity in comparison to the only sensitized control group. No altered reactivity was observed after irradiation with longwave UV light alone, whereas a statistically significant enhanced resp. reduced contact sensitivity was obtained after the treatment with 8-MOP alone and the combined action of 8-MOP + UVA, respectively.

Photoinactivation and recovery in skin fibroblasts after formation of mono- and bifunctional adducts by furocoumarins-plus-UVA

Cultured skin fibroblasts from young male guinea pigs were irradiated with UVA light in the presence of 8-methoxypsoralen (8-MOP) or angelicin. As compared to 8-MOP 30 times higher concentrations of angelicin were needed to obtain comparative inhibition rates of DNA-synthesis. Complete cellular recovery could be observed when the cell cultures were treated with angelicin-plus-UVA (320-400 nm) or 8-MOP-plus-395 nm. Both treatment schedules are known to cause monofunctional photoreactions. In contrast to this, bifunctional photoreactions caused by 8-MOP-plus-365 nm produced an inhibition of DNA synthesis which lasted more than four days. Also, UVA (320-400 nm) applied to cells treated with 3H-labeled 8-MOP resulted in a dose-dependent binding of 8-MOP molecules again lasting several days. Application of 8-MOP-plus-UVA (320-400 nm) to cells growing in log-phase showed a characteristic change in morphology. An increasing number of polynuclear and hyperchromatic cells appeared with time after treatment. In this subpopulation of cells DNA synthesis continued without division as revealed by DNA measurements and autoradiography. It is concluded that monofunctional adducts caused by angelicin-plus-UVA as well as 8-MOP-plus-395 nm permit cellular recovery whereas bifunctional photoadducts remained without recovery. In the latter case semiconservative DNA synthesis continued leading to hyperchromatic cells which could serve as a parameter for the presence of cross-linked nuclear DNA strands.

The effects of long-term local PUVA treatment on collagen metabolism in human skin

The effect of photochemotherapy on skin collagen metabolism was investigated in 57 patients with psoriasis. Twenty-eight patients were treated with trioxsalen baths and UVA irradiation, nine with ditranol and UVB irradiation, and 20 untreated psoriasis patients served as controls. No significant changes were found between the treated groups and the control group in urinary hydroxyproline excretion, skin hydroxyproline content, or in the activities of two enzymes catalyzing collagen biosynthesis, prolyl hydroxylase, and galactosylhydroxylysyl glucosyltransferase in the skin. When the same parameters were compared with the cumulative doses of UVA irradiation, skin prolyl hydroxylase activity slightly decreased with increasing UVA doses, whereas no changes were found in skin hydroxyproline content or galactosyl-hydroxylysyl glucosyltransferase activity. It was concluded that long-term local PUVA therapy does not significantly alter collagen metabolism in the skin.

Pharmacokinetic and clinical comparison of two 8-methoxypsoralen brands

We compared the Danish 8-MOP brand Meladinine with the Austrial brand Oxsoralen because of our discouraging result with PUVA in treating psoriasis. Nine healthy volunteers participated in the investigation. The plasma level of 8-MOP was measured by a gas chromatogrpahic-mass spectrometric method using isotopic dilution technique. The level obtained with Oxsoralen was on the average 5.8 times higher than that with Meladinine.