Endocrine Abstracts

Introduction: Glucosinolates (GLS) are secondary plant metabolites found in members of families within the order Brassicales (e.g. broccoli, pak choi, cauliflower, kale, mustard or rapeseed), but they are also present in plants of Moringaceae (moringa) and Caricaceae (papaya). Some GLS-derived breakdown products, i.e. sulforaphane, were extensively studied for their beneficial effects on colon-cancer incidence. This preventive nutritional approach might require the prophylactic use of highly dosed, enriched GLS-preparations of Brassica plant extracts. Goitrogenicity is a known consequence of nutrition containing high Brassica content due to the release of thiocyanate and inhibition of thyreoperoxidase (TPO). Detailed and recent studies about this topic are rare, but nevertheless needed for a potential preventive or therapeutic use of GLS. Therefore, we used several in vitro approaches to assess the goitrogenic potential of various GLS-extracts.

Hypothesis: Some GLS exert potential goitrogenic effects via competitive inhibition of the sodium-iodide-symporter (NIS) by thiocyanate ions and/or direct effects of specific GLS breakdown products on type 1 deiodinase or thyreoperoxidase (TPO) activity.

Methods: NIS-inhibition was tested by their interference with non-isotopic iodide uptake into rat thyrocytes (FRTL5). Interference with Dio1 activity was detected via a non-isotopic iodide-release assay. SCN⁻ -release from GLS was tested by a colorimetric reaction. TPO-interference was detected by applying the test compounds to recombinant TPO enzyme.

Results/conclusion: To investigate and exclude possible adverse GLS effects, we established a screening platform for the potential goitrogenic action of GLS and their breakdown products. Several of the GLS extracts inhibited Dio1 or TPO activity within a high supra-physiological μM concentration range. Furthermore, several extracts released significant amounts of SCN – after hydrolysis, thus potentially enhancing to the overall SCN⁻ – load of the organism. It appears mandatory that appropriate in vivo studies address these adverse GLS effects. This work is supported by the Bundesministerium für Bildung und Forschung.