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Metabolism of Echinacea alkamides by human recombinant P450 enzymes
Preparations from Echinacea plant parts are commonly used in contemporary alternative medicine for the treatment and prevention of upper respiratory tract infections. The phytochemicals thought to be mainly responsible for the immunomodulatory properties are the alkamides found in ethanolic extracts, with the most abundant ones being the isomers N-isobutyldodeca-2E,4E,8Z,10Z-tetraenamide (compound 8) and N-isobutyldodeca-2E,4E,8Z,10E-tetraenamide (compound 9). The market for this herbal medicine and the research devoted to the study of its therapeutic effects are increasing every year. However, few studies have focused on its metabolism, which can affect its therapeutic outcomes. In this study, we evaluated which human cytochrome P450 enzymes were predominantly involved in the metabolism of Echinacea alkamides. Recombinant human cytochromes P450 and pure compounds 8 and 9 synthesized for this study were used to investigate the relative importance of each isoform in alkamide metabolism. The main metabolites were found to be the expected epoxidation, N-dealkylation and hydroxylation products, with different metabolite profiles seen for each compound. The most abundant metabolite for compound 8 was an epoxide, whereas an N-dealkylated product was dominant for compound 9. For both compounds, the major isoforms involved in the production of epoxides were P450's 1A1, 1A2 and 2A13, whereas for the N-dealkylation only P450's 1A1 and 1A2 were important. Only low concentrations of hydroxylated metabolites were seen. In summary, the relative importance of the main human xenobiotic-metabolising P450's in the metabolism of the most abundant Echinacea alkamides have been established and the metabolites formed have been identified in this study. There are no standardization requirements for the phytochemical composition of Echinacea-based products, and different Echinacea preparations are likely to contain different relative concentrations of individual alkamides. Since P450 forms differ in abundance between individuals and tissues, as well as in their importance in alkamide metabolism, variations in metabolism may have a significant influence on the therapeutic outcome of different Echinacea preparations. Further work is in progress to evaluate how metabolism may affect the bioavailability of individual alkamides for therapeutic purposes.