Microb Cell Fact., 2020., Apr 3;19(1):82. doi: 10.1186/s12934-020-01341-0.

Impact of lignans in oilseed mix on gut microbiome composition and enterolignan production in younger healthy and premenopausal women: an in vitro pilot study.

Corona G Kreimes A Barone M et al.


BACKGROUND: Dietary lignans belong to the group of phytoestrogens together with coumestans, stilbenes and isoflavones, and themselves do not exhibit oestrogen-like properties. Nonetheless, the gut microbiota converts them into enterolignans, which show chemical similarity to the human oestrogen molecule. One of the richest dietary sources of lignans are oilseeds, including flaxseed. The aim of this pilot study was to determine the concentration of the main dietary lignans in an oilseed mix, and explore the gut microbiota-dependent production of enterolignans for oestrogen substitution in young and premenopausal women. The oilseed mix was fermented in a pH-controlled batch culture system inoculated with women’s faecal samples. The lignan content and enterolignan production were measured by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), and the faecal-derived microbial communities were profiled by 16S rRNA gene-based next-generation sequencing. RESULTS:  In vitro batch culture fermentation of faecal samples inoculated with oilseed mix for 24 h resulted in a substantial increase in enterolactone production in younger women and an increase in enterodiol in the premenopausal group. As for the gut microbiota, different baseline profiles were observed as well as different temporal dynamics, mainly related to Clostridiaceae, and Klebsiella and Collinsella spp. CONCLUSIONS:

Despite the small sample size, our pilot study revealed that lignan-rich oilseeds could strongly influence the faecal microbiota of both younger and premenopausal females, leading to a different enterolignan profile being produced. Further studies in larger cohorts are needed to evaluate the long-term effects of lignan-rich diets on the gut microbiota and find out how enterolactone-producing bacterial species could be increased. Diets rich in lignans could potentially serve as a safe supplement of oestrogen analogues to meet the cellular needs of endogenous oestrogen and deliver numerous health benefits, provided that the premenopausal woman microbiota is capable of converting dietary precursors into enterolignans.

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Key Points

Numerous clinical trials and animal model studies have demonstrated the association between high concentrations of ED and EL in blood and urine and various health benefits.  In particular, a number of studies have revealed that the anticancer effect of enterolignans is higher than that of their precursors (i.e. dietary lignans) and that the decreased risk of cancer correlates with blood and urinary levels of enterolignans but not with lignan-rich diets thus emphasizing the relevance of the gut microbiota as a key mediator of their effect. Although the lignan transformation by the gut microbiota is recognized as essential in protecting against menopausal symptoms as well as certain hormone-dependent chronic diseases (e.g. cancer, cardiovascular disease and osteoporosis), to date only a few bacterial species have been identified as enabling such a transformation. This study investigated the lignan profile of a commercially prepared blend of oilseeds as a functional dietary supplement for women, by ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS), and then used this as a substrate for inoculating stool samples from young and premenopausal women in in vitro anaerobic stirred batch culture systems, to simulate the physicochemical characteristics of the distal colon. The aim of these experiments was to determine the production of oilseed mix-derived enterolignans and to explore differences in bacterial taxa that could be involved in lignan transformation. The study investigated the dynamics of individual lignans (Seco, Lari, Pino and Mat) as well as enterolignans (ED and EL), gut microbial profiles and metabolic end products of microbial fermentation.

The study determined the concentration of four main dietary lignans in an oilseed mix commercially prepared from the following ingredients: pumpkin, sunflower seeds, buckwheat and millet flakes, milled flaxseed, hemp and chia. Compared to flaxseed, the oilseed mix had 4 times less free lignans with Seco being 8.2 times less and Mat almost 6 times less than in flaxseed. Comparable volumes of Lari were found in both flaxseed and oilseed mix: 44.2 mg/100 g and 44.9 mg/100 g, respectively. Seco and Mat are the main substrate for enterolignans, with Seco being converted to EL via ED, and Mat being directly converted to EL. Adding 0.5 g of oilseed mix to the stool samples of Yds resulted in a tenfold increase in EL concentration and a decrease in ED in 24 h, as compared to the negative control. Contrary to this, the same amount of supplement in the presence of PD samples resulted in a significant ED boost, whose 24-h concentration increased 110 times compared to the negative control and 80 times compared to the YD group under the same experimental conditions.

However, despite such a high volume of ED, EL levels. Despite the small sample size and obvious limitations of an in vitro study, the findings support that the faecal microbiota of healthy younger women is more efficient in converting dietary lignans into enterolignans, especially EL, than the microbiota of older premenopausal women. Furthermore, the study points to Klebsiella and Collinsella spp. as previously overlooked members of human gut microbiota with a strong potential to be directly involved in EL/ED production. To this end, in vitro gut microbiota models have proved to be useful tools to study the effects of food components, diet, and pharmaceutical molecules on gut microbiota composition. Future in vivo studies in larger cohorts are needed to confirm how diet can modulate the microbiota composition, favouring microbial species capable of producing EL more effectively. If a woman’s microbiota effectively converts dietary lignans to EL, consistent consumption of lignan-rich foods will potentially preserve a woman’s health in the long term, preventing or at least delaying the onset of degenerative conditions typically associated with menopause.