Psoralen

Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered as a derivative of umbelliferone. Psoralen occurs naturally in the seeds of Psoralea corylifolia, as well as in the common fig, celery, parsley, West Indian satinwood, and in all citrus fruits. It is widely used in PUVA (psoralen + UVA) treatment for psoriasis, eczema, vitiligo, and cutaneous T-cell lymphoma; these applications are typically through the use of medications such as Methoxsalen. Many furanocoumarins are extremely toxic to fish, and some are deposited in streams in Indonesia to catch fish. Psoralen is a mutagen, and is used for this purpose in molecular biology research. Psoralen intercalates into DNA and on exposure to ultraviolet (UVA) radiation can form monoadducts and covalent interstrand cross-links (ICL) with thymines, preferentially at 5'-TpA sites in the genome, inducing apoptosis. Psoralen plus UVA (PUVA) therapy can be used to treat hyperproliferative skin disorders like psoriasis and certain kinds of skin cancer. Unfortunately, PUVA treatment itself leads to a higher risk of skin cancer. An important use of psoralen is in PUVA treatment for skin problems such as psoriasis and, to a lesser extent, eczema and vitiligo. This takes advantage of the high UV absorbance of psoralen. The psoralen is applied first to sensitise the skin, then UVA light is applied to clean up the skin problem. Psoralens are also used in photopheresis, where they are mixed with the extracted leukocytes before UV radiation is applied. Despite the photocarcinogenic properties of psoralen, it was used as a tanning activator in sunscreens until 1996. Psoralens are used in tanning accelerators, because psoralen increases the skin's sensitivity to light. Some patients have had severe skin loss after sunbathing with psoralen-containing tanning activators.