Human Intestinal Bacterium, Strain END-2 Is Responsible for Demethylation as Well as Lactonization during Plant Lignan Metabolism

Abstract

Plant lignans and isoflavones that have estrogen-like properties, are classified as phytoestrogens based on their activities and chemical structures.1,2) Experimental and epidemiological studies have shown that phytoestrogens have potential health benefits in treating hormone-dependent diseases such as breast and prostate cancers. 3-7)Because ingested plant lignans undergo metabolic degradation, their transformation and metabolites have been extensively studied. [8][9][10][11][12][13] The mammalian lignans, enterolactone (ENL) and enterodiol (END), are of considerable interest since their isolation from the urine of humans and other animals in 1980.14) Subsequent studies have verified that the origins of mammalian lignans are plant lignans and that intestinal bacteria play a critical role in the formation of ENL and END. [15][16][17][18] Intestinal bacteria metabolize plant lignans by processes such as deglucosylation, demethylenation, ring cleavage, demethylation, dehydroxylation and oxidation. Several human intestinal bacteria that function in these processes have been isolated and characterized. 10,11,[19][20][21][22] However, ENL and END have two enantiomeric, mirror image forms. The ENL that is transformed via the anaerobic incubation of pinoresinol diglucoside (PDG) from Eucommia ulmoides OLIV. with intestinal bacteria, assumes the (Ϫ)-form.10) On the other hand, the ENL that is obtained via incubation with secoisolariciresinol diglucoside (SDG) from flaxseed, assumes the (ϩ)-form.13) We investigated which bacteria are involved in the transformation of the respective enantiomeric forms.The human intestinal bacteria, Eggerthella (Eg.) sp. SDG-2 and strain ARC-1 enantioselectively dehydroxylate dihydroxyenterolactone (DHENL) and dihydroxyenterodiol (DHEND). Moreover, the bacterial strains, strain END-2 and Ruminococcus (R.) sp. END-1, which oxidize END to ENL were isolated from human feces.24) When strain END-2 was incubated with a mixture of (ϩ)-END and (Ϫ)-END, only (ϩ)-END was oxidized to (ϩ)-ENL, and (Ϫ)-END remained unchanged (Fig. 1). Conversely, R. sp. END-1 converted only (Ϫ)-END to (Ϫ)-ENL.Here, we further describe the substrate specificity and cooperative behavior of strain END-2 with strain ARC-1 during the metabolism of plant lignans. MATERIALS AND METHODSGeneral Fecal suspensions and intestinal bacteria were incubated in an anaerobic model EAN-140 incubator (Tabai Co., Osaka, Japan). Optical rotations were measured in MeOH using a DIP-360 automatic polarimeter (Jasco Co., Tokyo, Japan). H-1 H-correlated spectroscopy, heteronuclear multiple-quantum coherence, heteronuclear multiple-bond coherence and nuclear Overhauser effect spectroscopy experiments were performed using a Varian Unity 500 ( 1 H: 500 MHz, 13 C: 125 MHz) and a Varian Gemini 300 ( 1 H: 300 MHz, 13 C: 75 MHz). Samples were separated by TLC on plates precoated with silica gel 60-F 254 (0.25 mm, Merck Co., Darmstadt, Germany), and spots were detected under UV excitation or by exposure to I 2 vapor. Samples were also separated by chrom...

Enterolignan-Producing Phenotypes Are Associated with Increased Gut Microbial Diversity and Altered Composition in Premenopausal Women in the United States

“…We found that microbial diversity was significantly different (Simpson Index, p<0.05) between high and low ENL excreters and was positively associated with fiber intake. The association between ENL excretion and microbial diversity may reflect the complexity of the microbial metabolism involved in ENL metabolism since there are several transformations involved in the production of enterolignans from lignans and different bacteria species can catalyze each step (15–17, 66–68). In a recent study comparing human populations consuming either a western diet or a rural sub-Saharan traditional diet, dietary fiber intake was also associated with gut microbial diversity (69).…”

“…For example, isolated Eggerthella lenta cannot reduce SECO; however, it can dehydroxylate 2, 3-bis-(3, 4-dihydroxy-benzyl) butane-1, 4-diol to END, one of the intermediary steps in ENL production (12, 15). END can then be converted to ENL by different bacteria (16, 17). Several more bacterial groups likely play similarly unique and complex biochemical roles in the transformation of plant lignans to enterolignans (16).…”

Cereal Lignans, Natural Compounds of Interest for Human Health?

“…These compounds are not directly bioavailable and require metabolic steps which involve both mammalian (glucuronidation and to a lesser degree, sulfation) and gut microbial processes [80]. When lignan glycosides are consumed with the diet, they are released from the matrix after mastication, are deglycosylated and are converted in the liver to glucuronidated [81], methylated and sulfated derivatives [82] that can be identified in human urine [83], but also to enterodiol and enterolactone by the intestinal microbiota [20] (Figure 4).…”

Use of antibiotics is associated with lower enterolactone plasma concentration

“…The pathway from plant lignan to enterolignans varies between the different types of plant lignans; however, for the majority of the plant lignans, the final step is likely to include dehydrogenation of enterodiol to enterolactone [12]. Bacterial strains capable in catalyzing enterolactone from enterodiol have been identified in studies with human fecal samples and categorized to be subdominant members of the microbiota [13][14][15][16].Production, circulation, and excretion of enterolignans are subject to a substantial interindividual variation [17,18] even in animal experiments with controlled plant lignan intake [19]. A recent study concluded that high excretion of enterolactone, but not enterodiol, is associated with high diversity of the gut microbial community [11].…”