Antioxidative constituents in Heterotheca inuloides.

Sesquiterpenoids, 7-hydroxy-3,4-dihydrocadalin and 7-hydroxycadalin, and flavonoids, quercetin, kaempferol and their glycosides, isolated from Heterotheca inuloides (Asteraceae), a Mexican medicinal plant known as "arnica", were evaluated as antioxidants. These compounds showed potent scavenging activity on diphenyl-p-picrylhydrazyl (DPPH) radical. Microsomal lipid peroxidation induced by Fe(III)-ADP/NADPH was inhibited by both terpenoids and flavonoids, though only flavonoids possessed superoxide anion scavenging activity in microsome. Flavonoids also scavenged enzymatically and non-enzymatically generated superoxide anion. On the other hand, mitochondrial lipid peroxidation induced by Fe(III)-ADP/NADH was inhibited only by sesquiterpenoids. Furthermore, these terpenes protected mitochondrial enzyme activity against oxidative stress. These results showed that two types of antioxidants existed in the dried flower of H. inuloides and would contribute to protection of tissues against various oxidative stresses.