An action spectrum for lethal photosensitization of Candida albicans by 8-MOP after low-dose broad-band UV-A irradiation; an action spectrum for 8-MOP 4',5'-monoadducts

Comparison of narrow-band (311 nm) UVB and broad-band UVA after oral or bath-water 8-methoxypsoralen in the treatment of psoriasis

BACKGROUND

There is a disparity between the absorption spectrum of 8-methoxypsoralen and the action spectrum for psoralen-sensitized erythema. In an action spectrum corrected for unsensitized reaction 313 and 365 nm have similar efficacies.

OBJECTIVE

We evaluated the relative erythemogenic and antipsoriatic efficacy of narrow-band (311 nm) UVB with and without prior psoralen exposure. We also compared the effects of narrow-band UVB and broad-band UVA after oral and bath-water psoralen exposure.

METHODS

Patients with psoriasis underwent half-side comparison studies. In one group the therapeutic efficacy of 311 nm UVB with and without oral psoralen was assessed. The second group received UVA and 311 nm UVB after oral psoralen. The third group was exposed to both radiation sources after bath-water exposure.

RESULTS

The erythemogenic, pigmentogenic, and therapeutic efficacy of 311 nm was increased by oral psoralen. With systemic 8-methoxypsoralen, UVA was comparable to 311 nm UVB. After bath-water exposure, 311 nm was clearly superior to broad-band UVA.

CONCLUSION

The efficacy of narrow-band 311 nm UVB can be enhanced by psoralen. Narrow-band 311 nm UVB is also effective after psoralen bath-water delivery.

An action spectrum for the elicitation of erythema in skin persistently sensitized by photobound 8-methoxypsoralen

Human skin can be rendered persistently photosensitive by topical application of aqueous 8-methoxypsoralen (8-MOP) and exposure to a suberythemogenic dose of more than 380 nm radiation. We report an action spectrum for the elicitation of phototoxic erythema induced by a second exposure of skin pretreated in this way. After correction for unsensitized skin erythema this action spectrum resembles the absorption spectrum of the 4',5'-monoadduct of 8-MOP to DNA. This suggests that the monoadduct is the chromophore for erythema elicited by the second irradiation, and supports the DNA crosslink as the crucial photoproduct causing phototoxic erythema due to 8-MOP in human skin.

Effect on topical 5-methoxypsoralen on tumorigenesis induced in albino and pigmented hairless mouse skin by UV irradiation

A new line of the Skh:HRII hairless pigmented mouse (black juvenile coat) is described which has been selectively bred for the capacity to respond consistently to simulated solar UV radiation with a continuous and strong tan. This mouse demonstrates a degree of protection from chronic UV-induced tumorigenesis when compared with the Skh:HRI hairless albino mouse, and has been used here to study the effect of induced melanogenesis on phototumorigenesis. Mice were irradiated for 10 weeks with incremental doses of simulated solar UV radiation (UVA + B) from a fluorescent tube source which induced tumours in 100% of albino mice and 93% of black mice by 200 days (minimally oedemal), or with 60% of this dose (sub-oedemal) which induced tumours in 85% of albino mice and 65% of black mice. Mice were also exposed to the UVA component of these radiation sources, obtained by window glass filtration. The effect of topical 5-methoxypsoralen (5-MOP) was examined, at either 0.003% with minimally oedemal UVA + B or its UVA component alone, or at 0.01% with sub-oedemal UVA + B or its UVA component alone, in both albino and black mice. The 5-MOP concentrations were selected as the maximum concentration which did not increase the erythema and oedema responses after a single exposure to minimally oedemal or sub-oedemal UVA + B. At 200 days, the tumorigenic response to sub-oedemal UVA + B was significantly increased by topical 5-MOP, to 100% in albinos and 93% in black mice. In contrast, tumorigenesis in response to minimally oedemal UVA + B was unaffected by topical 5-MOP. The UVA component alone of either irradiation regime was not tumorigenic under these conditions. When combined with topical 5-MOP, the UVA of minimally oedemal UVA + B became moderately tumorigenic, and resulted in a tumour incidence of 23% in albinos and 14.5% in black mice. However, the UVA component of sub-oedemal UVA + B, when combined with topical 5-MOP, was highly tumorigenic specifically in albino mice, inducing tumours in 93% of albino mice but in only 27% of black mice. Tan intensity resulting from minimally oedemal UVA + B was not enhanced by topical 5-MOP, and its UVA component combined with 5-MOP resulted in only a minimal tan. However, the tan intensity resulting from sub-oedemal UVA + B with topical 5-MOP was strongly increased, although its UVA component combined with 5-MOP did not produce a perceptible tan.(ABSTRACT TRUNCATED AT 400 WORDS)

Action spectra and chromophores for lethal photosensitization of Candida albicans by DNA monoadducts formed by 8-methoxypsoralen and monofunctional furocoumarins

The red-shift of furocoumarin action spectra, compared with their absorption spectra, has been investigated. An action spectrum for 8-methoxypsoralen (8-MOP) monoadduct formation in the yeast Candida albicans has been determined. The yeast cells were initially exposed to sublethal doses of monochromatic UVA at different wavelengths. Monoadduct formation was monitored by growth inhibition induced, after washing out any unbound 8-MOP, by re-irradiation with a constant second (non-lethal) dose of 330 nm radiation. A comparison between this action spectrum and the absorption spectrum of the dark complex of 8-MOP and DNA was made. In addition, the action spectra of monoadduct formation of five monofunctional compounds including a coumarin derivative have been determined. These action spectra were compared with their respective DNA dark complex absorption spectra. In general, the peaks of the furocoumarin DNA dark complexes show a red-shift when compared with the free furocoumarin molecule and the action spectra show peaks which correspond with the peaks of the dark complexes. Such data indicate that the DNA dark complex is the chromophore for growth inhibition in yeast rather than the free furocoumarin. The similarity of the 8-MOP monoadduct formation action spectrum and 8-MOP action spectra suggests that spectral dependence for the photobiological effects (including the red-shift) is dependent on monoadduct formation rather than, as previously suggested by several authors, crosslink formation. The action spectrum for the coumarin derivative 4-methyl N-ethylpyrrolo (3,2-g) coumarin (PCNEt) correlated well with the free molecule absorption spectrum rather than DNA dark complex indicating that the free molecule is the chromophore.(ABSTRACT TRUNCATED AT 250 WORDS)

A first approach to an action spectrum for 8-MOP phototumorigenesis in mice

Groups of hairless albino mice were treated with 8-MOP and exposed to a fixed daily dose of UVR obtained from one of four different emission spectra. Each spectrum was obtained by filtering a xenon arc source with a different WG filter. The resultant spectra showed differences in their proportions of shorter UVA wavelengths. A decreased proportion of the shorter wave bands systematically increased the time to first tumor. These data suggest that the action spectrum for 8-MOP sensitized phototumorigenesis is similar to that of acute 8-MOP action spectra in mammalian skin, which usually show maximal activity in the 320-335 nm region.