Production of enterodiol from defatted flaxseeds through biotransformation by human intestinal bacteria

The effects of enterolignans, e.g., enterodiol (END) and particularly its oxidation product, enterolactone (ENL), on prevention of hormone-dependent diseases, such as osteoporosis, cardiovascular diseases, hyperlipemia, breast cancer, colon cancer, prostate cancer and menopausal syndrome, have attracted much attention. To date, the main way to obtain END and ENL is chemical synthesis, which is expensive and inevitably leads to environmental pollution. To explore a more economic and eco-friendly production method, we explored biotransformation of enterolignans from precursors contained in defatted flaxseeds by human intestinal bacteria. We cultured fecal specimens from healthy young adults in media containing defatted flaxseeds and detected END from the culture supernatant. Following selection through successive subcultures of the fecal microbiota with defatted flaxseeds as the only carbon source, we obtained a bacterial consortium, designated as END-49, which contained the smallest number of bacterial types still capable of metabolizing defatted flaxseeds to produce END. Based on analysis with pulsed field gel electrophoresis, END-49 was found to consist of five genomically distinct bacterial lineages, designated Group I-V, with Group I strains dominating the culture. None of the individual Group I-V strains produced END, demonstrating that the biotransformation of substrates in defatted flaxseeds into END is a joint work by different members of the END-49 bacterial consortium. Interestingly, Group I strains produced secoisolariciresinol, an important intermediate of END production; 16S rRNA analysis of one Group I strain established its close relatedness with Klebsiella. Genomic analysis is under way to identify all members in END-49 involved in the biotransformation and the actual pathway leading to END-production. Biotransformation is a very economic, efficient and environmentally friendly way of mass-producing enterodiol from defatted flaxseeds. (Authors abstract)
Epidemiologic and pharmacologic studies have shown that enterodiol (END) and enterolactone (ENL) have preventive effects on osteoporosis, cardiovascular diseases, hyperlipemia, breast cancer, colon cancer, prostate cancer and menopausal syndrome. Previous research assessed 68 common plant foods and found that flaxseed flour and its defatted meal produced the highest yield of END and ENL in vitro, up to 800 times higher than that from others. The precursors of END and ENL synthesis include secoisolariciresinol diglucoside (SDG), secoisolariciresinol (SECO), matairesinol (MAT), lariciresinol (LCS) and pinoresinol (PRS). The biotransformation of precursors in plants to END or ENL could prove valuable. Biotransformation of SDG to END and ENL by human intestinal bacteria has been studied. Bacteria that can produce END and ENL on plant lignans under strictly anaerobic conditions have been isolated from human feces but sufficient yields for marketing scale production has not been achieved. To establish a method for producing enterolignans from defatted flaxseeds by bacterial biotransformation, human fecal samples were screened to obtain cultures that can efficiently produce END. After 49 rounds of selection by successive subcultures of human fecal bacterial microbiota in media containing defatted flaxseeds as the only carbon source, a group of mixed bacteria that could metabolize flaxseeds to produce END under both anaerobic and aerobic culture conditions were produced. This study shows that some bacteria require strict anaerobic conditions to grow and metabolize plant lignans to produce enterolignans, which significantly restricts large scale production. In this study, the highly efficient production of END from defatted flaxseeds through biotransformation by human intestinal bacteria without having to culture the bacteria under anaerobic conditions is described. In the absence of common carbon sources, the biotransformation of flaxseeds into END was found to be enhanced. END-49 was highly efficient in converting flaxseed lignans into END, producing up to 3.9 mg per gram, much higher than previously reported 0.6 mg per gram. The method described in this study has been optimized and could be used to obtain bacterial consortia that can convert plant lignans into END or related products. The authors suggest that biotransformation is a very economic, efficient and environmentally friendly way of mass-producing enterodiol from defatted flaxseeds. (Editors comments)