Photochemistry and photocytotoxicity of alkaloids from Goldenseal (Hydrastis canadensis L.). 2. Palmatine, hydrastine, canadine, and hydrastinine.

Goldenseal is an herb that is widely used in dietary supplements, eye washes, and skin lotions. The presence of Goldenseal root powder in dietary supplements and the topical application of Goldenseal preparations raise the possibility that an adverse phototoxic reaction may result from an interaction between its constituent alkaloids and light in exposed tissues. We have previously shown that berberine, the major alkaloid in Goldenseal powder, in combination with UVA causes DNA damage and cell death in HaCaT keratinocytes [(2001) Chem. Res. Toxicol. 14, 1529]. We have studied the photochemical and photobiological properties of four minor alkaloids found in Goldenseal, namely, hydrastine, palmatine, canadine, and hydrastinine. UVA radiation of palmatine in aqueous solutions generated no (1)O(2), but in CH(2)Cl(2), copious amounts of (1)O(2) were detected (Phi = 0.2). Palmatine also photogenerated oxygen-centered radicals, (*)OH and O(2)(*)(-) in aerated aqueous buffer and acetonitrile, respectively, as detected by the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). In nitrogen-sparged acetonitrile containing DMPO, we observed the neutral palmatine radical formed by one-electron reduction. UVA irradiation (4 J/cm(2)) of HaCaT keratinocytes in the presence of palmatine (50 microM) resulted in a 50% decrease in cell viability but no DNA damage as measured by the comet assay. UVA irradiation of hydrastine, hydrastinine, or canadine (50 microM) did not cause DNA damage or cell death in keratinocytes. Although palmatine is photoactive, it is present in such small amounts in Goldenseal root powder that the phototoxicity of the herb is most likely due to berberine, the major constituent alkaloid.