Fig. 3

Concentration profile of betulinic acid correlative to skin thickness. Thoracic skin of seven horses (two technical replicates each) were used for 24-h Franz-type diffusion cell experiments with “Basiscreme DAC” containing 1% betulinic acid and 20% medium-chain triglycerides. Data represent mean concentration (±SD) of betulinic acid in cryostat skin slices at different skin depths. Detected amounts of BA by far exceeded the determined IC₅₀ values for equine melanoma cells after 24 h, especially in the uppermost skin layers (410 μm). As minor cream residues on the skin surface after cleaning with a cotton swab cannot be excluded, data for 10 μm skin depth were eliminated in this figure. Hematoxylin and eosin staining of equine lateral thoracic skin kindly provided by the Institute for Anatomy, University of Veterinary Medicine Hannover, Foundation, Hannover, Germany