Protoporhyrin IX fluoresence kinetics in UV-induced tumours and normal skin hairless mice after topical appliction of 5-aminolevulinic acid methyl ester

摘要

Accumulation of protoporphyrin IX(PpIX)was investigated in normal skin and UV-induced tumours in hairless mice after topical application of a cream containing 2,8 or 16% of 5-aminolevulinic acid methyl ester (ALA-Me).Higher levels of PpIX were mesaured in tumours compared to normal skin.The maximal amount of PpIX was reached at 1.5,3 and 4h after 2,8 and 16% ALA-Me application,respectively.Higher tumour to normal skin PpIX fluorescence ratios were measured after application of 8 and 16% ALA-Me than after applicationof 2%.After irradiation with a broad spectrum of visible light from a silde projector,more than 90% of PpIX was bleached by fluences of 36 and 48 J/cm~2,at fluence rates of 10 and 40mW/cm~2 respectively.At these fluences,the PpIX photobleaching rate was significantly higher (P<0.05)in normal mouse skin that in tumours.In addition,for a given fluence,more PpIX was photobleached at the lower fluence rate (10mW/cm~2)than at the higher fluence rate (40mW/cm~2)in normal skin(P<0.001)as well as in tumours (P<0.05)after exposure to 24J/cm~2 of light.In conclusion,the highest tumour to normal skin PpIX ratio was observed 3h after application of 8% ALA-Me,suggesting that light exposure should be performed at this time in order to achieve an optimal PDT effect in this tumour model.