DEVELOPMENT AND CHARACTERIZATION OF A NOVEL SKIN MODEL FOR CUTANEOUS PHOTOTOXICOLOGY

The biological consequences of exposure to ultraviolet radiation (UV) has been receiving increased attention. Most known biological effects (such as sunburn and skin cancer) are attributed to mid-wave UVB (290- 320 nm) exposure. Phototoxicity, a nonimmunological UV-induced respons e, has been studied using in vivo (human and animal) and in vitro mode ls. Ethical considerations and model limitations underscore the need f or a reliable in vitro model to assess cutaneous photoxicity that woul d ideally possess viable cells and have a normal anatomical structure with an intact and functional vasculature. This would allow therapeuti c or preventive drugs to be tested in a system in which their disposit ion (cutaneous concentration-time profile) has been shown to be simila r to the in vivo setting. In addition, morphological, biochemical and physiological changes should be easily monitored within the same syste m. The purpose of this study was to characterize the isolated perfused porcine skin flap (IPPSF) developed in our laboratory as a model for UVB exposure. IPPSFs (n greater than or equal to 4/ treatment) were ir radiated with UVB doses of 1260 mJ/cm(2), 630 mJ/ cm(2), 315 mJ/cm(2) or 0 mJ/cm(2) both in vitro and in situ. Biomarkers used to assess pho totoxicity demonstrated a decrease in glucose utilization, an increase in vascular resistance (pressure/flow) and an increase in the release of PGE(2). Morphologically, intracellular and intercellular epidermal edema and sunburn (pyknotic) cells (SBC) increased with dose. The num ber of SBC (mean SBC+/-SE) along a unit length of epidermis from high dose to low dose were as follows: 1.35+/-0.21, 0.93+/-0.18, 0.83+/-0.1 9 and 0.09+/-0.06 for the in vitro; 6.52+/-1.11, 4.73+/-0.65, 4.16+/-0 .90 and 0.09+/-0.6 for the in situ. Cell proliferation, assessed by im munohistochemical staining for proliferating cell nuclear antigen (PCN A) and expressed as the growth fraction, decreased in vivo and in situ 24 h after UVB exposure. Ultrastructurally, SBC in the IPPSF appeared comparable to those found in human skin. These findings suggest that the IPPSF may be a valuable alternative in vitro model to investigate both the mechanism of UVB-induced phototoxicity and its therapeutic mo dulation.