Glycoalkaloids toxic effects

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Gee, J., Wortley, G., Johnson, I., Price, K., Rutten, A., Houben, G., and Penninks, A. (1996). Effect of saponins and glycoalkaloids on the permeability and viability of mammalian intestinal cells and on the integrity of tissue preparations in vitro. Toxic. In Vitro 10,117-128. Gonzalez, J., Roldan, A., Gallardo, T., and Prado, F. (1989). Quantitative determinations of chemical compounds with nutritional value from INCA crop Chenopodium quinoa. Plant Foods Hum. Nutr. 39, 331-337. 

Conversely, the expression of a yeast derived invertase in potatoes leads to a reduction of these naturally occurring toxicants. The elucidation of the biochemical reason for this reduction (dilution effect due to the increase of the tubers or metabolic interference with the sugar moieties needed for the biosynthesis of the glycoalkaloids) is part of our ongoing research. 

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