Mammalian lignan formation in rats fed a wheat bran diet

Effect of the form of the sesame-based diet on the absorption of lignans

The effect of different forms of sesame-based diets on the concentration of plasma lignans was assayed by estimating the levels of certain lignans (sesame lignans and enterolignans) in the plasma of experimental animals. In a series of experiments, male Wistar rats were fed either a raw sesame-enriched diet or a tahini-enriched diet. The plasma concentration of the lignans (sesame lignans and enterolignans) was determined at various time intervals over a 24 h period after a single administration. Enterodiol and enterolactone concentration in the tahini-treated group was significantly higher than in the raw sesame-treated group. In another series of experiments, male Wistar rats were fed, for 15 d, diets enriched in raw dehulled sesame, sesame perisperm, sesame oil, tahini and a polyphenolic extract derived from the seed perisperm. Enterodiol and enterolactone plasma concentration was high in the case of the sesame perisperm in spite of its low concentration in the assessed sesame lignans. Overall, the levels of the sesame lignans and enterolignans present in plasma seem to be influenced not only by the amount of lignan intake but also by other factors such as the form of the sesame-based diet.

Hypoglycemic effects of the wood of Taxus yunnanensis on streptozotocin-induced diabetic rats and its active components

Hypoglycemic effects of the H(2)O and MeOH extracts of the wood of Taxus yunnanensis were examined in streptozotocin (STZ)-induced diabetic rats. The H(2)O extract significantly lowered the fasting blood glucose level by 33.7% at a 100mg/kg dose on intraperitoneal administration. From the active H(2)O extract of the wood, three lignans, i.e., isotaxiresinol (1), secoisolariciresinol (2) and taxiresinol (3), were isolated as major components. These lignans were further tested for their hypoglycemic effects on the same experimental model. At a dose of 100mg/kg (i.p.), isotaxiresinol (1) reduced the fasting blood glucose level of diabetic rats by 34.5%, while secoisolariciresinol (2) and taxiresinol (3) reduced by 33.4% and 20.9%, respectively. The blood glucose lowering effects of 1 and 2 were stronger than the mixture of tolbutamide (200mg/kg) and buformin (1mg/kg) used as a positive control, which lowered fasting blood glucose level by 24.0%.

The relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed

Flaxseed is one of the richest sources of lignans and is increasingly used in food products or as a supplement. Plant lignans can be converted by intestinal bacteria into the so-called enterolignans, enterodiol and enterolactone. For a proper evaluation of potential health effects of enterolignans, information on their bioavailability is essential. The aim of this study was to investigate whether crushing and milling of flaxseed enhances the bioavailability of enterolignans in plasma. In a randomized, crossover study, 12 healthy subjects supplemented their diet with 0.3 g whole, crushed, or ground flaxseed/(kg body weight . d). Each subject consumed flaxseed for 10 successive days separated by 11-d run-in/wash-out periods, in which the subjects consumed a diet poor in lignans. Blood samples were collected at the end of each run-in/wash-out period, and at the end of each supplement period. Plasma enterodiol and enterolactone were measured using LC-MS-MS. The mean relative bioavailability of enterolignans from whole compared with ground flaxseed was 28% (P < or = 0.01), whereas that of crushed compared with ground flaxseed was 43% (P < or = 0.01). Crushing and milling of flaxseed substantially improve the bioavailability of the enterolignans.

Suitability of a batch in vitro fermentation model using human faecal microbiota for prediction of conversion of flaxseed lignans to enterolactone with reference to an in vivo rat model

BACKGROUND

In vitro fermentation models have been used widely for studies of shortchain fatty acid (SCFA) formation from carbohydrates, whereas the suitability of these methods for enterolactone (ENL) formation has received less attention.

AIM

The aim was to study the suitability of an in vitro fermentation model for prediction of bioconversion of lignans to ENL, to compare the approach with that of an in vivo rat model and to study the SCFA formation in both models.

METHODS

Predigested samples of rye bran (R), flaxseed meal (F) alone, or in combination with rye bran (R&F) and a faecal control were incubated in an in vitro fermentation model using human faecal microbiota. In the in vivo experiment rats consumed a non-fibre control diet (C) or diets supplemented either with rye bran (R), flaxseed meal (F) alone, or with their combination (R&F) for four weeks. Enterodiol (END), ENL and SCFA concentrations were measured from in vitro faecal fermentation samples and from the intestinal contents of rats. Plasma ENL concentrations from rats were also measured.

RESULTS

The highest ENL production was found in vitro with the F supplement (areas under curve: 740 +/- 4, 7,500 +/- 400, 2,600 +/- 500 and 1,520 +/- 70 nmol x h for the R, F, R&F supplements and faecal control, respectively). In vivo, the concentration of ENL in caecal digesta from flaxseed meal was significantly (P < 0.05) enhanced by the presence of rye bran (medians 261, 407 and 24 nmol/g in the F, R&F and C groups, respectively). No correlation was found between the models regarding ENL production, possibly due to different responses to the presence of rye bran matrix, differences in microbiota or application of a batch in the in vitro fermentation model. Rye bran supplementation enhanced butyrate production both in vitro and in vivo.

CONCLUSION

In vitro fermentation and the in vivo rat models responded differently to the presence of rye bran and no correlation with regard to the ENL formation from flaxseed lignans was observed.

Optimization of a liquid chromatography-tandem mass spectrometry method for quantification of the plant lignans secoisolariciresinol, matairesinol, lariciresinol, and pinoresinol in foods

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of the four major enterolignan precursors [secoisolariciresinol, matairesinol, lariciresinol, and pinoresinol] in foods. The method consists of alkaline methanolic extraction, followed by enzymatic hydrolysis using Helix pomatia (H. pomatia) beta-glucuronidase/sulfatase. H. pomatia was selected from several enzymes based on its ability to hydrolyze isolated lignan glucosides. After ether extraction samples were analyzed and quantified against secoisolariciresinol-d8 and matairesinol-d6. The method was optimized using model products: broccoli, bread, flaxseed, and tea. The yield of methanolic extraction increased up to 81%, when it was combined with alkaline hydrolysis. Detection limits were 4-10 microg/(100 g dry weight) for solid foods and 0.2-0.4 microg/(100 mL) for beverages. Within- and between-run coefficients of variation were 6-21 and 6-33%, respectively. Recovery of lignans added to model products was satisfactory (73-123%), except for matairesinol added to bread (51-55%).

Secoisolariciresinol and isotaxiresinol inhibit tumor necrosis factor-α-dependent hepatic apoptosis in mice

The effects of secoisolariciresinol (1) and isotaxiresinol (2), two major lignans isolated from the wood of Taxus yunnanensis, on tumor necrosis factor-alpha (TNF-alpha)-dependent hepatic apoptosis induced by D-galactosamine (d-GalN)/lipopolysaccharide (LPS) were investigated in mice. Co-administration of d-GalN (700 mg/kg) and LPS (10 microg/kg) resulted in a typical hepatic apoptosis characterized by DNA fragmentation and the formation of apoptotic bodies. Serum glutamic pyruvic transaminase (sGPT) and glutamic oxaloacetic transaminase (sGOT) levels were also raised at 8 h after d-GalN/LPS intoxication due to a severe necrosis of hepatocytes. Pre-administration of 1 or 2 (50, 10 mg/kg, i.p.) 12 and 1 h before d-GalN/LPS significantly reduced DNA fragmentation and prevented chromatin condensation, apoptotic body formation and hepatitis. Pro-inflammatory cytokines such as TNF-alpha and interferon-gamma (IFN-gamma) secreted from LPS-activated macrophages are important mediators of hepatocyte apoptosis in this model. Pre-treatment with 1 or 2 significantly inhibited the elevation of serum TNF-alpha and IFN-gamma levels. In a separate experiment, both lignans had a significant dose-dependent protective effect on d-GalN/TNF-alpha-induced cell death in primary cultured mouse hepatocytes and TNF-alpha-mediated cell death in murine L929 fibrosarcoma cells. These results indicated that 1 and 2 prevent d-GalN/LPS-induced hepatic injury by inhibiting hepatocyte apoptosis through the blocking of TNF-alpha and IFN-gamma production by activated macrophages and direct inhibition of the apoptosis induced by TNF-alpha.

Dietary lignins are precursors of mammalian lignans in rats

The mammalian lignans enterolactone (ENL) and enterodiol, commonly found in human plasma and urine, are phytoestrogens that may contribute to the prevention of breast cancer and coronary heart disease. They are formed by the conversion of dietary precursors such as secoisolariciresinol and matairesinol lignans by the colonic microflora. The identification of lignins, cell-wall polymers structurally related to lignans, as precursors of mammalian lignans is reported here for the first time. In study 1, rats were fed rye or wheat bran (15% diet) for 5 d. Untreated brans and brans extracted with solvents to remove lignans were compared. ENL was estimated in urine samples collected for 24 h by time-resolved fluoroimmunoassay. ENL urinary excretion was reduced from 18.6 to 5.3 nmol/d (n=8; P<0.001) when lignans were removed from rye bran and from 30.5 to 6.2 nmol/d (P<0.001) when they were removed from wheat bran. These results suggest that lignins, embedded in the cell wall and retained in the bran during solvent extraction, account for 26-32% of the ENL formed from cereal brans. In study 2, rats were fed a deuterated synthetic lignin (0.2% diet) together with wheat bran (15%) for 3 d. The detection of deuterated ENL by LC-tandem MS in urine (20 nmol/d) clearly confirms the conversion of lignin into mammalian lignans. More research is warranted to determine the bioavailability of lignins in the human diet.