The earliest humans have used plant extracts and animal venoms for hunting, war, assassination, and political intrigue for millennia. The Ebers Papyrus, which dates to around 1550 BC, describes concoctions using plant substances as primary ingredients. The toxic properties of plants and animals often enhance their ability to survive in their surroundings and against predators. Some toxic compounds are used primarily to aid an animal in obtaining food, whereas plants have developed toxic properties to specifically ward off being used as food. These toxic compounds are invaluable as tools and in the insight that they provide into the systems that they disrupt and poison. One major complication to the study of plant and animal poisons arises from their complexity as mixtures. Studies readily separate and evaluate individual components, but it is very difficult to use purified components to make the original toxin or venom. Nevertheless, extensive study of many toxins has contributed to a greater understanding of their biology and chemistry. Toxins have been utilized as tools to study human biochemistry and physiology in order to pave the way for new pharmaceuticals. Clinical evaluation of human poisoning is complicated by questionable identification of plant or animal species and the inability to quantify the level of exposure. In this chapter, an overview of specific plant and animal toxins and their effects will precede a short discussion of the considerable effort to harness the natural pharmacopeia for clinical use.
INTRODUCTION TO PLANT TOXICITIES
The plant kingdom contains potentially 300,000 species, and the toxic effects of plants serve primarily as defense mechanisms against natural predators. Toxicity in humans can result from simply touching as well as ingesting plants to cause a truly wide array of deleterious effects. Toxic effects on humans can range from simple hay fever caused by exposure to plant pollen all the way to serious systemic reactions caused by ingestion of specific plants. Table 26-1 lists some of the poisoning syndromes that plants can produce (Nelson et al., 2007).
Table 26-1Poisoning Syndromes Caused by Plants ||Download (.pdf) Table 26-1 Poisoning Syndromes Caused by Plants
|SYNDROME ||GENERA ||MECHANISM(S) |
|Antimuscarinic ||Atropa, Datura, Hyoscyanmus, Solanum ||Blockade of muscarinic cholinoceptors |
|Cardiotoxic ||Adenium, Digitalis, Convallaria, Nerium ||Inhibition of cellular Na+, K+-ATPase increases contractility, enhanced vagal effect |
|Convulsants ||Anemone, Conium, Labrunum, Nicotinia, Ranunculus ||Blockade of gamma-aminobutyric acid (GABA) receptor on the neuronal chloride channel, alteration of acetylcholine homeostasis, mimic excitatory amino acids, sodium channel alteration, hypoglycemia |
|Cyanogenic ||Eriobotrya, Hydrangea, Prunus ||Gastric acid hydrolysis of cyanogenic glycosides releases cyanide |
|Dysrhythmia ||Acotinum, Rhododendron, Veratrum ||Sodium channel activation |
|Nicotinic ||Conium, Laburnum, Lobelia, Nicotinia ||Stimulation of nicotinic cholinoceptors |
|Pyrrolizidine ||Crotalaria, Heliotropium, Senecia ||Pyrroles injure endothelium of hepatic or pulmonary vasculature leading to veno-occlusive disease and hepatic necrosis |
|Toxalbumin ||Abrus, Ricinus ||Protein synthesis inhibitors leading to multiple organ system failure |
Many variables can affect ...