ABSTRACT
Phytochemicals have a profound influence on long-term health. However, their dietary intake does not necessarily reflect their bioavailability, i.e., the dose reaching the target tissue. Understanding the bioavailability of phytochemicals is critical and must always be considered. In comparison with that of macronutrients, the beneficial intake range of micronutrients and phytochemicals is relatively narrow and there is a possibility of both adverse effects at higher doses and no effect at very low doses. Isothiocyanates, derived from glucosinolates, may be cited as an example of a group of phytochemicals exhibiting such a small beneficial dose window. At low concentrations, these compounds activate mitogen-activated protein kinases (MAPK) such as ERK2, JNK1, or p38, leading to expression of survival genes (c-Fos, c-Jun) and defensive genes (phase 2 detoxifying enzymes, such as glutathione-S-transferase and quinone reductase) involved in the “homeostasis response.” Increasing concentrations of isothiocyanates may additionally activate the caspase pathway, leading to apoptosis: finally, pharmacological and suprapharmacological doses may lead to nonspecific necrotic cell death and genotoxicity [1].
