ESI-TOF MS analysis and DNA cleavage activity of complexes formed by luteolin and five metal ions in hot water

Luteolin is a common flavonoid in plants and exhibits a variety of biological activities. In this study, luteolin was reacted in hot water with five trace metal elements found in plants, and the products were tested by electrospray-ionization time-of-flight mass spectrometry (ESI-TOF MS). Luteolin formed complexes with Ca2+, Mg2+, and Zn2+ in both 2:1 and 3:1 ratios, in addition to a complex with Cu2+ in a 2:1 ratio. A luteolin-iron (III) complex was also formed in a 2:1 ratio, and a small amount of Fe2+ was produced to form a luteolin-iron (II) complex in a 2:1 ratio. The formed luteolin-Cu2+ complex exhibited significant DNA cleavage activity in a time- and concentration-dependent manner, while no or little such activity was observed for luteolin or Cu2+ alone. Therefore, complexes of luteolin and trace metal elements may exist in cooked foods and medicinal plant decoctions, which could influence associated health and therapeutic effects.