VITAMIN E METABOLISM 93 CH 3 Fe scorc etc. Acid, F AgNO3 CH 3 16H33 ¸ H3 CH 3 3 METASTABLE EPOXIDE IRREVERSIBLY ON STANDING CH 3 O•C16H33 H3C ]' •' •)•CH3 CH3 a-TOCOPHERYL QUINONE 2H Zn CH3-COOIt CH 3 HO ••C16tt33 •H3C •[ •r•CH 3 CH 3 QUINOL Figure 7. Schematic diagram of the formation of o•-tocopherol quinone and quinol from o•-tocopherol (from ref. 13). experimental results shown in Figures 6-8 indicate that vitamin E follows a very complicated metabolic pathway. At this stage of research, however, it can be concluded that the skin is capable of vitamin E metabolism and that vitamin E is metabolized to its more hydrophilic matabolites, which may be more easily excreted from the body.

94 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS O . O ' 8•.o i i ! Figure 8. Stability of vitamin E in receptor solution without contacting skin: Chromatograms of samples in UV and radioanalysis at 24 hours. CONCLUSION Percutaneous absorption of vitamin E has been investigated. The radiolabeled vitamin E promptly penetrated the skin while nonlabeled vitamin E appeared after a long time lag. HPLC analysis in line with UV and a liquid scintillation counter showed that vitamin E was extensively metabolized to ot-tocopherol quinone and more hydrophilic metabolites in the hairless mouse skin. Since vitamin E undergoes significant metabo- lism during skin permeation, the data with radiolabeled vitamin E does not necessarily represent the characteristics of intact vitamin E itself. Total radioactivity has to be identified from the possible metabolites. ACKNOWLEDGMENTS The authors express thanks to Professor Richard Chang and Dr. Allan Cooney in the Chemical Biology Laboratory, College of Pharmacy, Rutgers University, for their valu- able discussions and kindness in providing HPLC in line with LSC for this study. The radiolabeled ot-tocopherol and ot-tocopherol quinone standaMs offered by Dr. L.J. Machlin of Hoffmann-La Roche, Nutley, New Jersey, are greatly appreciated. A grad-