Modulation of the expression of hepatic and renal genes encoding xenobiotic metabolizing enzymes by an aspalathin-enriched green rooibos (Aspalathus linearis) extract (GRE) was investigated in the liver and kidneys of F344 rats following dietary exposure of 28 d, as well as selected xenobiotic metabolizing genes in rat primary hepatocytes. In the liver, GRE upregulated genes (p < 0.05) encoding aldehyde dehydrogenase, glucose phosphate isomerase, and cytochrome P450 while 17β-hydroxysteroid dehydrogenase 2 (Hsd17β2) was downregulated. In primary hepatocytes, GRE lacked any effect, while aspalathin downregulated Hsd17β2, mimicking the effect of GRE in vivo, and upregulated catechol-O-methyl transferase and marginally (p < 0.1) cytochrome P450 2e1. In the kidneys, GRE upregulated (p < 0.05) genes encoding the phase II xenobiotic metabolism enzymes, glutathione-S-transferase mµ and microsomal glutathione-S-transferase, while downregulating genes encoding the ATP binding cassette transporter, cytochrome P450, gamma glutamyltransferase 1, and N-acetyltransferase 1. Differential modulation of the expression of xenobiotic metabolizing genes in vivo and in vitro by GRE is dose-related, duration of exposure, the tissue type, and interactions between specific polyphenol and/or combinations thereof. Aspalathin is likely to be responsible for the downregulation of estradiol and testosterone catabolism by GRE in the liver. The differential gene expression by GRE in the liver and kidneys could, depending on the duration exposure and dose utilized, determine the safe use of such an extract in humans for specific health and/or disease outcomes.
Georg Thieme Verlag KG Stuttgart · New York.