Dimethyl disulphide in the blood of cattle fed on brassicas

Consumption of brown onions (Alliumcepavar.cavalierand var.destiny) moderately modulates blood lipids, haematological and haemostatic variables in healthy pigs

Although garlic and onions have long been associated with putative cardiovascular health benefits, the effects of different commercially available onions and level of intake have not been studied. Therefore, the aim of the present study was to evaluate the potential health benefits of raw onions using the pig as a biomedical model. Twenty-five female (Large White×Landrace) pigs were used in a (2×2)+1 factorial experiment. Pigs were fed a standard grower diet supplemented with 100 g tallow/kg with the addition ofAllium cepavar.cavalieror var.destinyat 0, 10 or 25 g/MJ digestible energy for 6 weeks. Overall, the consumption of onions resulted in significant reductions in plasma triacylglycerol; however, the reductions were most pronounced in pigs feddestinyonions (−26 %,P=0·042). Total plasma cholesterol and LDL:HDL ratios were not significantly different. Onion supplementation, regardless of the variety, resulted in dose-dependent reductions in erythrocyte counts and Hb levels, while the white blood cell concentrations, particularly lymphocytes, were increased in pigs that consumed onions. Furthermore, indices of blood clotting were largely unaffected by onion consumption. In conclusion, dietary supplementation with raw brown onions has moderate lipid-modulating and immunostimulatory properties. However, daily onion intake >25 g/MJ digestible energy could be detrimental to erythrocyte numbers.

The role of plant secondary metabolites in mammalian herbivory: ecological perspectives

Plant secondary metabolites (PSM) have many ecological functions, but have long been considered as defences against pathogens or herbivores (vertebrate or invertebrate), reducing the likelihood and extent of attack. However, mammalian herbivores ingest many foods containing PSM and use both behavioural methods and physiological strategies to limit their negative effects. Most physiological counter-adaptations are inducible in response to ingested PSM, providing efficient protection against toxic effects. Possible positive effects of PSM include antioxidant and anthelminthic properties and complex formation between protein and condensed tannins that protects dietary protein from degradation by the symbiotic microflora of foregut fermenters, increasing its utilisation by the animal. This protein effect is probably only beneficial to animals under a narrow range of nutrient-rich conditions found mainly in agricultural systems. There are many examples of PSM causing food avoidance or reducing food intake, but there is as yet relatively little evidence for positive selection of them by herbivores. Although the feedback mechanisms relating the post-ingestive consequences of PSM to subsequent foraging behaviour are beginning to be understood, knowledge of the integration of behavioural and physiological strategies for regulating the effects of PSM is relatively poor. The opportunities for learned avoidance of PSM may be restricted in animals with complex diets that cannot associate a particular feedback signal with a given food type. A greater emphasis on the study of subclinical effects of PSM rather than acute effects, on pharmaco-kinetic studies in relation to behavioural studies and on the use of realistic experimental models is advocated.

Comparative effects of mono-, di-, tri-, and tetrasulfides derived from plants of the Allium family: redox cycling in vitro and hemolytic activity and Phase 2 enzyme induction in vivo

Epidemiological evidence indicates that a high dietary intake of plants of the Allium family, such as garlic and onions, decreases the risk of cancer in humans. It has been suggested that this effect is due to the ability of the aliphatic mono-, di-, tri-, and tetrasulfides derived from these vegetables to increase tissue activities of Phase 2 detoxification enzymes. In contrast, toxic effects have been recorded in domestic and farm animals after the consumption of garlic or onions, involving oxidative damage to erythrocytes and consequent hemolytic anemia. This effect again has been attributed to the aliphatic sulfides. In the present study, the ability of sulfides derived from garlic and onions to generate "active oxygen" species and cause oxidative damage to erythrocytes in vitro has been compared, together with their ability to cause hemolytic anemia and increase the activity of the Phase 2 enzymes quinone reductase (QR) and glutathione S-transferase (GST) in rats. Monosulfides were without significant effect on any parameter. Di-, tri-, and tetrasulfides generated hydrogen peroxide in the presence of GSH and hemoglobin and caused oxidative damage to erythrocytes in vitro. The activity decreased in the order of tetra- > tri- > disulfide, with the allyl compounds being more potent than the propyl. In vivo, both allyl and propyl tri- and tetrasulfides were powerful hemolytic agents. In contrast, only the allyl sulfides increased the activities of QR and GST; the propyl derivatives were completely without effect. Allyl and propyl tri- and tetrasulfides, thus, may contribute to the toxic effects of Allium vegetables, while only the allyl derivatives are effective in increasing tissue activities of cancer-protective enzymes.

Toxicity of thiols and disulphides: involvement of free-radical species

Sulphur is essential to life, and thiols and disulphides play essential roles in cellular biochemistry. Such compounds are also widely distributed in the food of man and his domestic animals, and they are extensively used in industry. However, many thiols and disulphides have been shown to be toxic. Aliphatic, aromatic, and heterocyclic compounds of this type are haemolytic agents in animals while aminothiols have been shown to induce many cytotoxic effects in vitro and the epidithiodioxopiperazine mycotoxin, sporidesmin, is a potent hepatotoxic agent. Structure-activity relationships among these compounds and factors which modulate their harmful effects are consistent with a toxic mechanism involving redox cycling between the thiol and the corresponding disulphide. Thiyl radicals and "active oxygen" species are formed in this process, and it is suggested that these substances are responsible for initiating the tissue damage provoked by thiols and disulphides.