Effects of pretreatment with calcipotriol on protoporphyrin IX content in the normal epithelium of nude mice after topical application of aminolevulinic acid

Abstract

Objective To evaluate the effect of pretreatment with calcipotriol on protoporphyrin IX (PpIX) content in the normal epithelium of nude mice after topical application of aminolevulinic acid (ALA) . Methods A total of 36 BALB/C nude mice were randomly and equally divided into 2 groups: calcipotriol + ALA group topically pretreated with calcipotriol ointment for 3 days followed by topical application of ALA, and ALA group topically treated with ALA alone. At 2, 3, 4, 5, 6 and 7 hours after ALA application, 3 mice in each group were sacrificed separately, and skin tissues were obtained from the experimental region in the back of mice. A fluorospectrophotometer was used to detect the PpIX content in the normal epithelial tissue of the nude mice, and an inverted fluorescence phase-contrast microscope to observe the fluorescence intensity and distribution of PpIX in the frozen sections of epithelial tissues. Results During 2 - 8 hours after topical application of ALA, the content of PpIX in the skin tissues of nude mice in the two groups gradually increased over time. Correlation analysis revealed no correlations between the PpIX content in the ALA group and the treatment duration (r = 0.451, P = 0.369) , while the PpIX content in the calcipotriol + ALA group was strongly correlated with the treatment duration (r = 0.913, P = 0.011) . The PpIX content in the ALA group reached a peak at 5 hours [ (461.24 ± 43.45) ng/g tissues], while the PpIX content in the calcipotriol + ALA group peaked at 6 hours [ (668.88 ± 42.46) ng/g tissues]. At 2, 3, 4, 5, 6 and 7 hours after ALA application, the PpIX content was significantly higher in the calcipotriol + ALA group than in the ALA group (P < 0.05 or 0.01) . Frozen-section examination showed that PpIX was diffusely distributed in the epidermis and dermis of the nude mice, and the fluorescence intensity of PpIX was higher in the calcipotriol + ALA group than in the ALA group at 5, 6 and 7 hours after ALA application. Conclusion Pretreatment with calcipotriol can increase the content of PpIX in the normal epidermis and dermis of nude mice after topical application of ALA, which provides a theoretical basis for the clinical application of calcipotriol as a local synergist of ALA-PDT. Key words: Photochemotherapy; Cholecalciferol; Aminolevulinic acid; Protoporphyrins; Disease models, animal; Calcipotriol