Antioxidant activity of compounds in Euphrasia officinalis L. – revaluation of a traditional medicinal plant

Euphrasia officinalis L. (eyebright) is a valuable plant in traditional medicine as a remarkable remedy for inflamed eye disorders since ancient times. Our knowledge is still lacking exact details in phytochemical composition, and way of mechanism of active compounds of eyebright. Our aim was to contribute to the phytotherapeutical revaluation of Euphrasia officinalis L. by investigating the main chemical groups of the herb and to understand their role in the inflammatory process, in which free radicals are considered to play a significant role via different biochemical pathways. After a successive extraction of Euphrasiae herba with n-hexane, chloroform, ethyl-acetate and methanol, as follows, the main compounds were identified as iridoids and phenolics/flavonoids. The content of Flavonoids, polyphenols, tannins and hydroxycinnamic derivatives were determined, results are: 0.38g/100g, 1.47g/100g, 0.56g/100g, 1.97g/100g, respectively. Then preliminary assays were performed to study the free radical scavenging activity (DPPH, ABTS and TBA assay). The lyophilised decoctum of Euphrasiae herba showed a considerable scavenging activity, so it was reasonable to elucidate the main chemical groups, and find correlation between the active compounds and the free radical scavenging activity. Methanolic extract of eyebright herb was fractionated by polyamid column chromatography using water (7 fractions: iridoids) and methanol (8 fractions: phenolics/flavonoids). For the qualitative analyses of the fractions TLC, HPLC and LC-MS/MS methods were developed and used. We have found that the fraction containing simple caffeoyl-derivatives provided the highest scavenging activity in both DPPH and ABTS assays. Those fractions which were rich in flavonoids were also notable antioxidants. The scavenging effect of Euphrasia officinalis L. is a combination of the iridoids and phenolics/flavonoids, however the phenolic components basically determine the effect.