Effects of porphyrins on skin.

Porphyrins and radiation induce activation of the complement system, release of mediators from mast cells, dermal accumulation of neutrophils, and activation of factor XII-dependent pathways. Recent studies have also shown that porphyrins and radiation have profound effects on the eicosanoid metabolism of mast cells, endothelial cells, macrophages and epidermal and dermal homogenates. In vitro, prostaglandin D2 (PGD2) was generated when mast cells were exposed to protoporphyrin and radiation. Exposure of cultured human umbilical vein endothelial cells or human omental microvascular endothelial cells to uroporphyrin or protoporphyrin and radiation resulted in predominant generation of PGF2 alpha, while PGE was generated after the exposure of macrophages to Photofrin II and radiation. Activities of epidermal eicosanoid-metabolizing enzymes in protoporphyric mice were suppressed following in vivo exposure to radiation, whereas activities of the dermal enzymes were enhanced 18 h after radiation. These effects of porphyrins on skin contribute to the development of porphyrin-induced cutaneous phototoxicity, which is seen in patients with porphyrias and as a consequence of photodynamic therapy.