Neuritogenesis of Herbal Geniposide-Related Compounds in PC12h Cells

Previously, we have reported that geniposide, a compound isolated from an extract of Gardenia fructus, has neuritogenic activity in PC12h cells, a subclone of the rat pheochromocytoma cell. In this study, we have examined the effects of seven geniposide-related compounds (S-1, 6α-hydroxygeniposide; S-2, 6β-hydroxygeniposide; S-3, 6α-methoxygeniposide; S-4, 6β-methoxygeniposide; S-5, loganin; S-6, 7-ketologanin; and S-7, syringopicroside) isolated from various medicinal herbs. The geniposide-type iridoids S-1, S-2, S-3, and S-4, and S-7 induced neurite outgrowth that was similar or more potent to that of geniposide. S-2 and S-4, which are optical isomers of S-1 and S-3, respectively, were particularly potent. The 2 loganin-type iridoids, S-5 and S-6, showed less activity than geniposide. The neuritogenic activity of geniposide-type iridoids appears to be not necessarily correlated directly to their hydrophobicity. These results suggest that geniposide-type iridoids have potent neuritogenic activity and that specific configurations for the interactions between iridoid compounds and the target molecule are necessary for neuritogenic function.