Psoralen plus UVA

In the presence of UVA the psoralen interacts with DNA, forms thymine dimers, and inhibits DNA synthesis. Psoralen plus UVA (PUVA) treatment is used chiefly in severe psoriasis (a disease characterised by increased epidermal proliferation), and cutaneous T cell lymphoma. 

Nowadays, many human skin diseases, such as psoriasis, T-cell lymphoma (cutaneous T-cell lymphoma, CTCL mycosis fungoides MF), and vitiligo, are commonly treated with a combination of psoralens and UVA radiation commonly referred as PUVA (psoralens plus UVA) therapy. 

Data from animals and humans indicate that at least some photoirritants enhance UV-associated skin carcinogenesis. 8-Methoxypsoralen (8-MOP), used in psoralen plus UVA treatment therapy,12 is considered to be a photococarcinogen in humans, whereas several fluoroquinolones have been demonstrated to be photoirritants and photochemical carcinogens in hairless mice.11 However, data for many other classes of pharmaceuticals are unavailable. 

The therapeutic effect of ECP for GVHD appears to involve induction of apoptosis in psoralen plus UVA-exposed lymphocytes, modulation of monoc3de-derived dendritic cell differentiation, increased production of antiinflammatory cytokines, decreased dendritic cell antigen-presenting function, and induction of regulatory T cells that establish immune tolerance [200,201]. 

Vitiligo No safe and relfable treatment. Methoxsalen or other psoralen. Topically or syscemically, plus daily exposure to UVA (PUVA) is toxic, and ineffective in Caucasians. Sunscreens to protect the depigmented areas and reduce pigmentation of surrounding skin. Probably an autoimmune disease Note dose-dependent risk of squamous cell cancer with PUVA... 

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