Proanthocyanidins and ellagitannins: new insights into the use for antiadhesive prophylaxis against viral and microbial pathogens and as skin active compounds

The study deals with molecular investigations on potential targets for proanthocyanidins and ellagitannins used as antiadhesive compounds for antiviral, antimicrobial and wound-healing activity. Antibacterial and antiviral effects of defined proanthocyanidins and ellagitannins were investigated against Herpes simplex virus I (HSV-1) and Porphyromonas gingivalis, the major pathogen for periodontitis. Geraniin, procyanidin B2 and 3,3′-digalloylated B2 exhibited strong antiviral activity. Galloylation strongly increased the activity. Activity was due to an inhibition of viral adhesion to host cells; penetration and replication were not influenced. The digalloylated dimer interacts with the major viral surface gD-adhesin, which was oligomerized, forming a rigid structure, not able to initiate further adsorption process. Antiadhesive effects of oligomeric proanthocyanidins against P. gingivalis were due to inhibition of the major bacterial adhesins (Lys- and Arg-gingipaine). Additionally the expression of bacterial virulence factors is inhibited significantly, leading to a diminished pathogenic activity. The role of procyanidin-enriched extracts within clinical development products is discussed. Positive effects of tannins on skin are traditionally described, while the mode of action is unknown. Therefore the influence on geraniin on cell physiology of skin cells was investigated. Geraniin stimulated cell differentiation of keratinocytes (involucrin, cytokreatin 1, 10) and proteins responsible for formation of extracellular matrix (collagen). Potential pathways how tannins act on skin physiology are discussed. Summarizing it is shown that tannins act quite specifically on defined targets. Effects on target proteins are not as unspecific as often claimed. Therefore the medical use of tannins has to be investigated in more detail.