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In the past few decades, there has been a lot of interest in plant constituents for their antioxidant, anti-inflammatory, anti-microbial and anti-proliferative properties. However, concerns have been raised on their potential toxic effects particularly when consumed at high dose. The anti-thyroid effects of some plant constituents have been known for some time. Indeed, epidemiological observations have shown the causal association between staple food based on brassicaceae or soybeans and the development of goiter and/or hypothyroidism. Herein, we review the main plant constituents that interfere with normal thyroid function such as cyanogenic glucosides, polyphenols, phenolic acids, and alkaloids. In detail, we summarize the in vitro and in vivo studies present in the literature, focusing on the compounds that are more abundant in foods or that are available as dietary supplements. We highlight the mechanism of action of these compounds on thyroid cells by giving a particular emphasis to the experimental studies that can be significant for human health. Furthermore, we reveal that the anti-thyroid effects of these plant constituents are clinically evident only when they are consumed in very large amounts or when their ingestion is associated with other conditions that impair thyroid function., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Cruciferous vegetables have the reputation to protect against cancer, an effect attributed to glucosinolates (GLS) and their breakdown products. However, some GLS are mutagenic, an activity associated with cancer initiation rather than chemoprevention. We show that juices from steamed pak choi sprouts are strongly mutagenic in Salmonella typhimurium TA100 upon addition of fresh myrosinase. Growth of the plants in the presence of methyl jasmonate, a hormone eliciting defence factors, led to 20-fold enhanced mutagenic activity. The level of 1-methoxy-3-indolylmethyl (1-MIM)-GLS was similarly increased, whereas those of other GLS were only elevated 0.8- to 3.2-fold. 1-MIM-GLS is a potent mutagen, whose activity is further enhanced by human sulphotransferase 1A1 (hSULT1A1), an activation not observed with other GLS. The mutagenicity of the pak choi juices was increased 20-fold in bacteria expressing hSULT1A1. A tiny level of juice from elicitated sprouts, 0.04% in the mutagenicity assay, was sufficient to double the number of revertants above the spontaneous level. We conclude that pak choi juice is mutagenic, an activity that can be strongly affected by the growth conditions. It is owed essentially to a single component, 1-MIM-GLS. We recommend using cultivars, growth conditions and/or food preparations that keep the level of this GLS congener low., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Glucosinolates are compounds produced by commercial crops which can hydrolyse in a range of natural toxins that may exert detrimental effects on beneficial soil organisms. This study examined the effects of 2-phenylethyl isothiocyanate and 3-phenylpropionitrile on the survival and growth of the woodlouse Porcellio scaber exposed for 28 d. 2-Phenylethyl isothiocyanate dissipated from the soil with half-lives ranging from 19 to 96 h. Exposure through soil showed toxic effects only on survival. The LC50s after 28 d were significantly different at 65.3 mg kg(-1) for 2-phenylethyl isothiocyanate and 155 mg kg(-1) for 3-phenylpropionitrile. A toxicokinetic-toxicodynamic (TKTD) approach, however, revealed that both compounds in fact have very similar effect patterns. The TKTD model was better suited to interpret the survival data than descriptive dose-response analysis (LC(x)), accounting for the fast dissipation of the compounds in the soil. Found effects were within environmentally relevant concentrations. Care should therefore be taken before allowing these natural toxins to enter soil ecosystems in large quantities., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Chemopreventive effects of broccoli, a highly valued vegetable, have been known for a long time. Several studies have demonstrated that broccoli might be beneficial by reducing the risk for the development of certain forms of cancer. These effects are generally attributed to glucosinolate-derived degradation products like isothiocyanates and indoles which are formed by the hydrolytic action of plant myrosinase and/or glucosidases deriving from the human microbial flora. However, recent in vitro and experimental animal studies indicate that broccoli, its extracts and the glucosinolate-derived degradation products might also have undesirable effects, especially genotoxic activities. However, the relevance of the genotoxic activities to human health is not known yet. This paper gives an overview on genotoxic, anti-genotoxic/chemopreventive, nutritive and antinutritive properties of broccoli, its ingredients and their degradation products. A qualitative comparison of the benefit and risk of broccoli consumption benefit-risk assessment shows that the benefit from intake in modest quantities and in processed form outweighs potential risks. For other preparations (fortified broccoli-based dietary supplements, diets with extraordinary high daily intake, consumption as a raw vegetable) further studies both for potential risks and beneficial effects are needed in order to assess the benefit and risk in the future., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The influence of dietary fibre on the biological effects of glucosinolates was investigated in gnotobiotic rats harbouring a human whole faecal flora. Animals were fed for 6 wk with diets containing 12% rapeseed meal (RSM) supplemented or not supplemented with 10% inulin (INL) or oat fibre. Both fibre types enhanced the liver hypertrophy due to RSM to equal extents, but had different effects on the other glucosinolate-related toxic effects. INL partially restored a normal thyroid hormone status whereas kidney weight, goitre and growth deficit were increased on exposure to the diet containing oat fibre. Oat fibre and, to a lesser extent, INL modulated the alterations of digestive xenobiotic-metabolizing enzymes (XME) induced by RSM. They counter-balanced the induction of hepatic cytochrome P-450 and lessened the induction of uridine diphosphate-glucuronosyltransferase in the liver but did not modify depletion of its activity in the small intestine. On the other hand, they enhanced the induction of glutathione S-transferase in the liver and the large intestine but not in the small intestine. These findings give new evidence that the biological effects of naturally occurring non-nutrient compounds are closely dependent on the composition of the diet. Two mechanisms are proposed to explain the different influence of INL and oat fibre on RSM toxicity. Their different fermentative characteristics could lead to a modulation of the bacterial metabolism of glucosinolates in the caecum. Alternatively, their own action on the digestive XME could modify the subsequent metabolism of bacterial glucosinolate derivatives.

Sulfur-containing phytochemicals of two different kinds are present in all Brassica oleracea (Cruciferae) vegetables (cabbage, broccoli, etc.). They are glucosinolates (previously called thioglucosides) and S-methyl cysteine sulfoxide. These compounds, which are derived in plant tissue by amino acid biosynthesis, show quite different toxicological effects and appear to possess anticarcinogenic properties. Glucosinolates have been extensively studied since the mid-nineteenth century. They are present in plant foods besides Brassica vegetables with especially high levels in a number of seed meals fed to livestock. About 100 different kinds of glucosinolates are known to exist in the plant kingdom, but only about 10 are present in Brassica. The first toxic effects of isothiocyanates and other hydrolytic products from glucosinolates that were identified were goitre and a general inhibition of iodine uptake by the thyroid. Numerous studies have indicated that the hydrolytic products of at least three glucosinolates, 4-methyl-sulfinylbutyl (glucoraphanin), 2-phenylethyl (gluconasturtiin) and 3-indolylmethyl (glucobrassicin), have anticarcinogenic activity. Indole-3-carbinol, a metabolite of glucobrassicin, has shown inhibitory effects in studies of human breast and ovarian cancers. Kale poisoning, or a severe haemolytic anaemia, was discovered in cattle in Europe in the 1930s, but its link with the hydrolytic product of S-methyl cysteine sulfoxide was only shown about 35 years later. S-methyl cysteine sulfoxide and its metabolite methyl methane thiosulfinate were shown to inhibit chemically-induced genotoxicity in mice. Thus, the cancer chemopreventive effects of Brassica vegetables that have been shown in human and animal studies may be due to the presence of both types of sulfur-containing phytochemicals (i.e. certain glucosinolates and S-methyl cysteine sulfoxide).

To examine the possible harmful effects of feeding Brussels sprouts to rats, groups of 10 male, weanling rats received the non-dehydrated vegetable in moist diets at levels providing 2.5-30% of the dry matter for 4 wk. A first study comprised test diets with 15 and 30% of the dry matter as uncooked or cooked Brussels sprouts and control diets without and with 0.2% potassium thiocyanate (KSCN) for comparison. The second study comprised diets with 0, 2.5, 5, 10 and 20% of the cooked vegetable and diets with 0 and 20% of the cooked vegetable with extra iodine. Diets with the uncooked vegetable contained considerably less intact glucosinolates than did diets with the cooked product, probably as a result of more extensive enzymatic degradation in the uncooked product. Growth depression and decreased food intake, not accompanied by decreased food efficiency, occurred in rats fed 10% or more dry matter as Brussels sprouts. These findings were less marked with the cooked than with the uncooked vegetable, probably because of unpalatability. Decreased levels of blood haemoglobin and plasma thyroxin were found with 15% or more Brussels sprouts. Prothrombin times were increased if 2.5% or more was fed. Thyroid stimulating hormone was increased by feeding potassium thiocyanate, but not by feeding the vegetable. Increased kidney weights and impaired kidney function not accompanied by microscopic renal changes were observed in rats fed 10% or more Brussels sprouts. Increased liver weights, which occurred from the 5% level, were accompanied by microscopic hepatic changes only at feeding levels from 10% of the cooked vegetable. 'Morphological activation' of the thyroid was increased with 10% or more of the cooked vegetable and with 0.2% KSCN. Iodine supplementation of the diets did not influence the results obtained with the vegetable. These studies indicated that 2.5% Brussels sprouts dry matter in the diet was not without effect, and that the thyroid characteristics were less sensitive to Brussels sprouts than were other criteria examined.