Exploring the Potential of ToxCast Data in Supporting Read-Across for Evaluation of Food Chemical Safety.

The intention of this study was to determine the utility of high-throughput screening (HTS) data, as exemplified by ToxCast and Tox21, for application in toxicological read-across in food-relevant chemicals. Key questions were addressed on the extent to which the HTS data could provide information enabling (1) the elucidation of underlying bioactivities associated with apical toxicological outcomes, (2) the closing of existing toxicological data gaps, and (3) the definition of the boundaries of chemical space across which bioactivity could reliably be extrapolated. Results revealed that many biological targets apparently activated within the chemical groupings lack, at this time, validated toxicity pathway associations. Therefore, as means of providing proof-of-principle, a comparatively well-characterized end point-estrogenicity-was selected for evaluation. This was facilitated through the preparation of two exploratory case studies, focusing upon groupings of paraben-gallates and pyranone-type compounds (notably flavonoids). Within both, the HTS data were seen to reflect estrogenic potencies in a manner which broadly corresponded to established structure-activity group relationships, with parabens and flavonoids displaying greater estrogen receptor affinity than benzoate esters and alternative pyranone-containing molecules, respectively. As such, utility in the identification of out-of-domain compounds was demonstrated, indicating potential for application in addressing point (3) as detailed above.

Potential of ToxCast Data in the Safety Assessment of Food Chemicals.

Tox21 and ToxCast are high-throughput in vitro screening programs coordinated by the U.S. National Toxicology Program and the U.S. Environmental Protection Agency, respectively, with the goal of forecasting biological effects in vivo based on bioactivity profiling. The present study investigated whether mechanistic insights in the biological targets of food-relevant chemicals can be obtained from ToxCast results when the chemicals are grouped according to structural similarity. Starting from the 556 direct additives that have been identified in the ToxCast database by Karmaus et al. [Karmaus, A. L., Trautman, T. D., Krishan, M., Filer, D. L., and Fix, L. A. (2017). Curation of food-relevant chemicals in ToxCast. Food Chem. Toxicol. 103, 174-182.], the results showed that, despite the limited number of assays in which the chemical groups have been tested, sufficient results are available within so-called "DNA binding" and "nuclear receptor" target families to profile the biological activities of the defined chemical groups for these targets. The most obvious activity identified was the estrogen receptor-mediated actions of the chemical group containing parabens and structurally related gallates, as well the chemical group containing genistein and daidzein (the latter 2 being particularly active toward estrogen receptor ß as a potential health benefit). These group effects, as well as the biological activities of other chemical groups, were evaluated in a series of case studies. Overall, the results of the present study suggest that high-throughput screening data could add to the evidence considered for regulatory risk assessment of food chemicals and to the evaluation of desirable effects of nutrients and phytonutrients. The data will be particularly useful for providing mechanistic information and to fill data gaps with read-across.

Studies to investigate the absorption and excretion of shea oleine sterols in rat and man.

Shea oleine (SU), an oil fraction derived from the nut of the African tree, Butyrospermum parkii, is used as a frying oil and, after hardening (SH), in margarine and toffee fat. Both SU and SH contain a high level (approximately 8%) of 4,4-dimethylsterols (4,4-DMS), mostly as esters of cinnamic acid. As part of a series of studies evaluating SU, investigations to study rat and human dietary utilization were carried out. These comprised fecal fat analysis of groups of Wistar rats and a small number (four subjects) of human volunteers. Groups of rats were administered SU in a semisynthetic diet over 3 weeks at up to 20% in the diet (approximately 10 g/kg/day). In the human study, four male volunteers consumed a single 25-g portion of SU (approximately 0.4 g/kg) and ate no other vegetable fat during the course of the study. No preferential absorption of any of the 4,4-DMS occurred in the rat or man. Apparent absorption of the most prominent sterol fraction in the unsaponifiable material, 4,4-DMS, as estimated by its disappearance from feces, was similar in both species (27% to 52% in the rat compared with 13% to 49% in human subjects). Both rats and humans showed a similar profile of dietary and fecal 4,4-DMS fraction sterol components.

A 13-week feeding study in the rat with shea oleine and hardened shea oleine.

Shea oleine is an oil fraction derived from the nut of the tree, Butyrospermum parkii, which grows in central and western Africa. There are several uses of shea oleine, including its use as a cooking oil and, after hardening, in margarine and toffee fat. As part of a series of studies, a 13-week rat feeding study was conducted in which groups of Colworth-Wistar rats (15 male and 15 female) were fed 27.5% total fat semipurified diets containing 20% (w/w) shea oleine (SU) or hardened shea oleine (SH). Equivalent groups of rats were fed either 20% (w/w) palm oil (PU), soyabean oil (BU), or the hardened (hydrogenated) equivalents (PH and BH, respectively). Assessments of body weight, food and water intake, clinical pathology, organ weights, and macroscopic histopathology were carried out. Results showed that shea oleine diets produced similar biological effects to palm oil and and soyabean oil diets. A slightly reduced body weight gain was noted in rats fed either of the shea oleine diets in comparison with palm oil and soyabean oil. The process of hardening had no significant impact on the normal growth in rats fed shea oleine, although minor differences compared with unhardened diets comprised some small changes in clinical chemistry parameters, raised liver weight, and less liver lipid. In addition, raised alkaline phosphatase and an increase in food intake were noted in rats fed SH. All diets were well tolerated in the growing rat and none of the findings in the study were considered to be adverse.