Miniature swine model of phototoxicity testing

Authors

Leigh, H., Forbes, P.D., Lawson, C., Kim, D.Y., White, D., Brown, L.D., Wehmeier, D.R., Liu, J., Bouchard, G.F.

Abstract

Background/Purpose: This study determined the threshold doses for ‘solar erythema’ and for
phototoxic responses to 8-methoxypsoralen (8-MOP) in white skin Hanford and grey skin
Yucatan miniature swine.

Methods: For threshold erythema determinations, the UVR exposures included both UVA
(315–400 nm) and UVB (290–315 nm) radiation by positioning one fluorescent ‘sunlamp’
among 10 ‘PUVA’ lamps.With this configuration the UVR exposures ranged from 0.5–2.8
times the ‘instrumental MED’ (MEDi) for Hanford and from 1.0–5.6 times the MEDi for
Yucatan. For phototoxicity determinations (i.e., with and without topically-applied graduated
concentrations of 8-MOP), the UVB component was minimized by extinguishing the
sunlamp, thus permitting higher UVA exposures.

Results: The Hanford had the lower UV erythema dose threshold (1.0–1.4 times the MEDi)
and the erythema that developed was readily observable. The exposure doses for the phototoxicity
test were 5 J/cm2 of UVA in 35 minutes or 10 J/cm2 in 70 minutes.The phototoxic
(vascular) response to 8-MOP was observed in the two highest concentrations (0.01% and
0.1%) in Hanford pigs, in a dose-related manner. Microscopic evidence of a dose-related
response was also observed as the concentration of 8-MOP increased.

Conclusion: This verified that the Hanford miniature swine is the preferable strain for
phototoxic effects. In contrast, UVR exposure of the Yucatan pig skin produced tanning
rather than erythema, confirming that the Yucatan is the more appropriate strain for studying
the melanization response. Thus, Hanford and Yucatan miniature swine have cutaneous
photobiological responses that reflect their respective strain differences.

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