AbstractThe presence of phytoestrogens (PEs) in soya based baby foods has attracted a lot of attention due to their ability to act as endocrine disruptive compounds (EDCs). Infants and young children have critical windows of sensitivity to EDCs during their development. Positive health effect of PEs are many such as being anti-cancer, antiobesity, promotes bone formation and wound healing. The negative health effects reported include increased incidences of hypospadias, cryptochidism, prepubertal gynecomastia and reduced fertility. Use of soya-based weaning gruels is widespread in Kenya. Estrogenic and androgenic reporter gene assays (using MMV-Luc and TARM-Luc cell lines respectively) were used to characterise the transcription activity of ten PEs (apigenin, daidzein, daidzin, genistein, genistin, enterodiol, equol, formononetin, glycitein and matairesinol) and in the Kenyan based gruel/flour extracts. A modified Hygiene Based Margin of Safety (HBMOS) method was used to estimate the estrogenicity due to daidzein and genistein in the flours.
Standard curves of 17(3-estradiol and testosterone hormones and some PEs in the MMV-Luc and in TARM-Luc cell lines respectively were established. PEs and flour/gruel extracts enhanced testosterone hormone androgenic activity and gave more additive and synergistic bioactive effects in a dose and flour blend dependent manner respectively. The effect of heating and storage on the transcriptional capability of the PEs apigenin, genistein and formononetin and flour extracts was dose and flour type dependent and compound specific in MMV-Luc cell line. Quantification of the estrogenicity of the flour extracts (both uncooked and those cooked and/or stored) on MMV-Luc cell line revealed potent estrogenicity. The exposure level of genistein and daidzein in baby gruel flours was above the acceptable daily intake ADI for phytoestrogens which is I mg/Kgbw/day for each phytoestrogen. The total estrogenicity due to genistein and daidzein in the flour was below the tolerable daily intake (TDI) of 50 ng/kgbw and was of partial agonist proportions as determined by HBMOS.
In conclusion our results indicate that the two cell lines can characterise the estrogenic and androgenic activity of PEs. The results on effect of heat and storage on the bioactivity of PEs underline the need to couple up the RGA method with physico-chemical methods which can elucidate on actual chemical changes in future studies. This is to enable ease of interpretation as the three chemicals varied in their bioactivity and no generalisation was possible. They also show that the PEs and the flour extracts can act as potential endocrine disrupters at the level of nuclear receptor which may have health implications, which could be positive or negative. Caution can be directed to especially mothers of boy infants due to ability of PEs and flour extracts to synergistically interact with testosterone and give significant androgenic activity.
|Date of Award||Dec 2012|
|Supervisor||Lisa Connolly (Supervisor) & Christopher Elliott (Supervisor)|
Estrogenic and androgenic endocrine disrupting activity and risk assessment of phytoestrogens in Kenyan soya-based weaning flours
Ngoda, P. (Author). Dec 2012
Student thesis: Doctoral Thesis › Doctor of Philosophy