ABSTRACT
Phototherapy is commonly prescribed to patients with widespread psoriasis. Analogous to normal skin, irradiation with either UVB (280--320 nm) or psoralens
and UVA (320-390 nm; PUVA therapy) reduces the retinol content of psoriatic skin (176). Moreover, PUV A therapy normalizes the increased 3~dehydroretinol levels in the healing lesions skin without the normal levels in uninvolved
indicating that the reduction of lesional 3-dehydroretinol is closely related to the healing process. In contrast, PUV A therapy reduces the retinol concentrations in both normal and lesional epidermis. The disparate susceptibility of the two retinoids to PUV A (320-360 nm) is not readily explained by different absorption maxima of retinol and 3-dehydroretinol (Amax 326 and 352 nm, respectively; see Section IV.B). 5. Epidermal Epidermal tumors differ widely in their origin, biological behavior, and clinical appearance. The tumors are either benign (e.g., seborrheic keratosis and keratoacanthoma), premalignant (e.g., actinic keratosis), semimalignant (e.g., basal cell
squamous cell carcinoma). Interestingly, whereas retinol levels vary on whether or not the tumors appear on sun-exposed areas (low levels in UV··induced tumors), the 3-dehydroretinollevel appears to be related to the proliferative potential of the tumor (210). Thus, 3-dehydroretinol concentrations are normal in seborrheic keratosis, slightly elevated in actinic keratosis, and markedly elevated in basal cell and squamous cell carcinomas. Another common finding in the two carcinomas is a reduced content of the fatty
esters of vitamin A which corroborates the markedly low retinyl ester content observed UV-induced carcinomas in hairless mice Keratoacanthoma is of interest in this context since it undergoes mucous metaplasia and regression when topically treated with RA (212). Keratoacanthoma occurs spontaneously in humans but may also be induced chemically in animal skin. The tumor is pseudomalignant; it rapidly grows to form a crater filled with horny material, but regresses spontaneously within months. Interestingly, the hyperproliferative circumference of human keratoacanthomas is characterized by a :<dO-fold increase in the 3-dehydroretinol concentration and a 4-fold increase in cellular retinoic acid binding protein level (see below).
