Comparison of the Inhibitory Effects of Monomeric, Dimeric, and Trimeric Procyanidins on the Biochemical Markers of Skin Tumor Promotion in Mouse Epidermisin vivo

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Abstract
Several procyanidin dimers and an epicatechin trimer purified from Douglas fir bark tannins were compared with their monomer components (+)-catechin and (-)-epicatechin for their abilities to inhibit the biochemical effects of the potent tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) in mouse epidermis in vivo. Topical applications of the procyanidins, 15 min before the tumor promoter, inhibit TPA-induced ornithine decarboxylase (ODC) activity and this inhibition increases with the degree of polymerization (trimer > dimer > monomer). At a dose of 10 µmol, all procyanidin dimers inhibit the ODC response to TPA to a greater degree than 20 µmol of epicatechin and 10 µmol of epicatechin and/or catechin. Under similar conditions, catechin and epicatechin fail to inhibit the hydroperoxide (HPx) response to TPA whereas the procyanidin dimers inhibit this response by almost 40%. At a dose of 10 µmol, the epicatechin trimer also inhibits TPA-induced ODC activity and HPx production to a greater degree than 10 - 30 µmol of epicatechin. However, these various treatments with monomeric, dimeric, and trimeric procyanidins do not differ significantly in their abilities to inhibit TPA-stimulated DNA synthesis. These results suggest that some of the antitumor-promoting effects of procyanidins might increase at the biflavanoid and triflavanoid levels.

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