HPTLC-profiling of eleutherosides, mechanism of antioxidative action of eleutheroside E1, the PAMPA test with LC/MS detection and the structure–activity relationship

Human body is constantly generating free radicals, which causes oxidative stress. Despite naturally occurring antioxidant systems in human body, free radicals cause lipid, proteins and DNA oxidation. New antioxidants are still urgent as well as their mechanisms of action should be explained. In this study, we investigated the mechanism by which eleutherosides B, E and E1 may act as antioxidants, identified eleutherosides in Eleutherococcus lasiogyne and Eleutherococcus giraldii, and explained in vitro the absorption of eleutheroside E1 based on passive transport. The DPPH∗ and DB-HPTLC tests were used to assess the antioxidant activity. Of the three eleutherosides, only eleutheroside E1 exhibited a strong anti-DPPH∗ activity (EC50 37.03 μg/mL; 63 mMol) compared to the raw extracts (EC50 170 and 180 μg/mL for E. lasiogyne and E. giraldii). This activity was also confirmed by the DB-HPTLC autography technique. According to Załuski's hypothesis, the antioxidant mechanism of eleutheroside E1 is based on the complexation of DPPH∗ molecule with its aryl radical. During this reaction, the aryl radical of eleutheroside E1 (E1∗) and DPPHH are created. Next, the aryl radical (E1∗) is complexed with another DPPH∗ molecule. Additionally, the aryl radical can be stabilized by the presence of the methoxy groups in the aromatic ring, which increases its antioxidative action. The HPTLC-identification of extracts showed the presence of eleutherosides B, E and E1 in both species. The PAMPA test coupled with LC/MS detection showed a low permeability of eleutheroside E1 across artificial membrane. Because eleutherosides belong to the polyphenols, the TPC and TFC were quantified. The TPC and TFC varied from 51.4 to 49.3 mg/g dry extract for TPC, and from 5.73 to 4.91 mg/g dry extract for TFC, for E. giraldii and E. lasiogyne, respectively. In conclusion, eleutheroside E1 in its pure form could be a chemopreventive ingredient of new pharmacological or dietary products, stimulating the GALT. These findings can explain partially the adaptogenic activity of eleutheroside E1 on the GALT, which has been still unknown.