Toxicants, natural plant poisons

Detractors of herbal medicine use have legitimate concerns about dosage variability, possible toxicity and adulteration, herb-drug interactions, and above all, lack of FDA regulation. Far from being intrinsically harmless, many pharmacologically active plant alkaloids and other compounds are natural defensive poisons their very effectiveness may be an unanticipated consequence of their adaptive toxicity to grazing animals and... 

Other chemicals may after repeated exposure cause more subtle effects on the skin such as allergic reactions. Skin sensitization can be caused by nickel in jewellery or the constituents of some washing powders. Sensitization of the skin leading to allergic, contact dermatitis can be very serious as well as disfiguring and is the most common industrial disease (see Chapter 7). Some natural toxicants, such as nettle sting (formic acid) and the very potent substances in the plant poison ivy, can be skin irritants. 

Hartwell (1982b) and others cantion that natural plants may possess toxicity, even serious or fatal toxicity, as presented in the disclaimer to Hartwell s book. Neither the author nor the pnbUsher makes any medical claims for any herb. This information is compiled from the published literature. Some plants contain deadly poisons and some mentioned herein are extremely dangerous. Well, for that matter, so are some of the synthetic medical compounds produced en masse in the laboratory. 

Pyrrolizidine alkaloids poison animals grazing on toxic wild plants and those fed contaminated feed, causing economic losses. They poison humans through deliberate consumption of certain foods and herbal medicines and through consumption of food contaminated by wild plants, such as via transport of the toxins by bees into honey. Analytical methods are required for different purposes - to detect the presence of pyrrolizidine alkaloids, to quantify the total level of the toxins, or to measure the quantity of individual compounds. The task is made more challenging by the variety of PAs, their widespread nature and their different forms. Analytical methods are based on color reactions, enzyme linked immunosorbent assays (ELlSAs), spectroscopy, and the full range of chromatographic techniques. A lack of reference standards and... 

Abrin is a natural poison found in the seeds of a plant called the rosary pea or jequirity pea (Abrus precatorius). It is similar to ricin, although it is about 75 times more poisonous. Like ricin it is referred to as a toxalbumin, destroying ribosomes, which are responsible for protein synthesis, leading to cell death and tissue damage. Abrin has some potential medical uses, such as in treatment to kill cancer cells. To date, abrin is not known to have been used as a terrorist weapon although, like ricin, its highly toxic nature lends itself well to this purpose. 

P. R. Cheeke and L. R. Shull, Natural Toxicants in Feeds and Poisonous Plants, AVI, Westport, CT, 1985. 

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. 

---