Monofunctional psoralens plus UVA radiation are not severely phototoxic and have less mutagenic activity than bifunctional psoralens plus UVA radiation.

The purpose of this study was to evaluate pigment producing effect using various concentrations(0.02%, 0.1%, 0.5%) of monofunctional psoralens such as angelicin, khellin and comparing it's effect with TMP in topical photochemotherapy.

Ninty three C57BL mice were painted with either angelicin, khellin or TMP solution in concentrations of 0.02%, 0.1% and 0.5% each and were UVA irradiated. Skin biopsies were performed at 1,3,5 weeks after UVA irradiation. The pigment producing effects were measured by the number, area and perimeter of the melanocytes after topical PUVA.

The comparison of melanocyte numbers between different psoralens after five weeks of photochemotherapy showed a significant difference in decreasing order of TMP, khellin and angelicin. The area and perimeter of melanocytes were larger in the TMP group after five weeks photochemotherapy than the other group. However in the khellin and angelicin group, the area and perimeter of melanocytes were not increased by increasing the frequency of the UVA irradiation.

The number, area and perimeter of melanocytes after topical PUVA increased in the TMP group compared to angelicin or khellin group. We expect the clinical application of angelicin and khellin in vitiligo is possible considering the result of the study of pigment producing effect with a higher concentration and higher dose of UVA.