Biol. Pharm. Bull. 30(11) 2204—2206 (2007)

(SDG), pinoresinol diglucoside (PDG), arctiin, and matairesinol, are converted to the mammalian lignans enterolactone (ENL) and enterodiol (END) by intestinal bacteria. The metabolic processes of the aforementioned intestinal bacteria include deglucosylation, ring cleavage, demethylation, dehydroxylation, and oxidation. We have isolated bacteria that participate in these metabolic processes from human feces. ENL and END have two enantiomeric mirror image forms (Fig. 1). A ( )-form of ENL was formed by anaerobic incubation of PDG derived from Eucommia ulmoides OLIV. with a bacterial mixture from human feces. On the other hand, a ( )-form of ENL was obtained by incubation of SDG isolated from flaxseed. We were interested in whether the same or different bacteria are involved in the biotransformation of the respective enantiomeric forms. Previously, we isolated Eggerthella (Eg.) sp. SDG-2 and strain ARC-1 and demonstrated that these two bacteria participated in enantioselective dehydroxylation when incubated with dihydroxyenterolactone (DHENL) or dihydroxyenterodiol (DHEND), i.e., Eg. sp. SDG-2 converted ( )-DHENL and ( )-DHEND to ( )-ENL and ( )-END, respectively, but not for ( )-DHENL and ( )-DHEND. Conversely, strain ARC-1 had dehydroxylation activity for ( )-DHENL and ( )-DHEND, but not ( )-DHENL and ( )-DHEND. We also reported the isolation and characterization of a human intestinal bacterium, Eubacterium (E.) sp. ARC-2, capable of demethylating ( )-arctigenin to ( )-DHENL. E. sp. ARC2 could convert both ( )-secoisolariciresinol and ( )-secoisolariciresinol 4 -O-methyl ether to ( )-DHEND and ( )DHEND, respectively, without enantioselectivity. In the course of our studies on the enantioselective biotransformation of natural lignans to mammalian lignans, we report here the isolation of bacteria capable of enantioselectively oxidizing ( )and ( )-END from human feces.