Role of plasma lipoproteins in the transport of the soyabean isoflavones daidzein and daidzein-7-O-β-d-glucoside

Abstract

Isoflavone intake is associated with various properties beneficial to human health which are related to their antioxidant activity, for example, to their ability to increase LDL oxidation resistance. However, the distribution of isoflavones among plasma lipoproteins has not yet been elucidated in vivo. Therefore, the objective of the present study was to investigate the association between daidzein (DAI) and lipoproteins in human plasma upon administration of the aglycone and glucoside form. Five men aged 22-30 years participated in a randomised, double-blind study in cross-over design. After ingestion of DAI and daidzein-7-O-b-D-glucoside (DG) (1 mg DAI aglycone equivalents/kg body weight) blood samples were drawn before isoflavone administration as well as 1, 2, 3, 4·5, 6, 8, 10, 12, 24 and 48 h post-dose. Concentrations of DAI in the different lipoprotein fractions (chylomicrons, VLDL, LDL, HDL) and in the non-lipoprotein fraction were analysed using isotope dilution capillary GC/MS. The lipoprotein fraction profiles were similar for all subjects and resembled those obtained for plasma in our previously published study. The lipoprotein distribution based on the area under the concentration -time profiles from 0 h to infinity in the different fractions were irrespective of the administered form: non-lipoprotein fraction (53 %) . LDL (20 %) . HDL (14 %) . VLDL (9·5 %) . chylomicrons (2·5 %). Of DAI present in plasma, 47 % was associated to lipoproteins. Concentrations in the different lipoprotein fractions as well as in the non-lipoprotein fraction were always higher after the ingestion of DG than of DAI. Taken together, these results demonstrate an association between isoflavones and plasma lipoproteins in vivo. Dietary isoflavones, a subclass of flavonoids, have been the focus of much of the recent interest in the nutritional benefits of soya foods (1) . The exact role that isoflavones play in the health-related effects of soya foods and their potential for adverse effects have been controversial and difficult to discern (2,3) . This may be in part due to the lack of basic knowledge regarding absorption, distribution, metabolism and excretion.In a recently published study, we investigated the difference in the bioavailability of the isoflavone daidzein (DAI) in the aglycone and glucoside form when administered as pure compounds (4) . In most subjects the plasma appearance and disappearance curves revealed a biphasic pattern with an early peak before the peak plasma concentration which has also been reported by other authors (5,6) . Possible reasons for this behaviour discussed so far are enterohepatic recycling and some small initial absorption in the upper gastrointestinal tract along with predominant absorption in the large intestine.A third explanation might be the absorption of isoflavones via a chylomicron-mediated mechanism and distribution of isoflavones bound to lipoproteins throughout the body. Several observations provide evidence for this hypothesis: It is known that water-insoluble compounds, for...

Isoflavone supplementation in postmenopausal women does not affect leukocyte LDL receptor and scavenger receptor CD36 expression: A double‐blind, randomized, placebo‐controlled trial

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Genistein as a potential inducer of the anti‐atherogenic enzyme paraoxonase‐1: studies in cultured hepatocytes in vitro and in rat liver in vivo

“…Thus, it has been hypothesized that soy isoflavones may exhibit beneficial cardiovascular effects . A number of anti‐atherogenic properties have been attributed to dietary isoflavones, including diminished low‐density lipoprotein (LDL) oxidation . Interestingly around 20% of blood isoflavones are present in the LDL fraction .…”