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Historical Use of Toxic Plants

Godwin Anywar

Department of Plant Sciences, Microbiology & Biotechnology, College of Natural Sciences, Makerere University, Kampala, Uganda

CONTENTS

1. 1.1 Introduction to Toxic Plants
2. 1.2 Poisonous Plants as Sources of Traditional and Modern Medicines
3. 1.3 Toxic Plants and Justice
   1. 1.3.1 Toxic Plants in Capital Punishment
   2. 1.3.2 Trial by Ordeal
4. 1.4 Toxic Plants in Poisoned Weapons
   1. 1.4.1 Arrow Poisons
5. 1.5 Plant Fishing Poisons/Piscicides/Ichthyotoxins
6. 1.6 Poisonous Plants as Food
7. 1.7 Poisonous Plants as Biopesticides
8. 1.8 Toxic Psychoactive Plants for Recreational and Religious Purposes
9. 1.9 Poisonous Plants in Warfare and Bioterrorism
10. 1.10 Poisonous Plants as Carcinogens and Teratogen
11. 1.11 Conclusion

1.1 Introduction to Toxic Plants

Numerous poisonous plants exist in our environment and have been the subject of great speculation, study, and concern. Poisonous plants have been used as food, medicines, agents for crime, means of dispensing justice, capital punishment, suicide, bioterrorism, fishing poisons, and for recreational and spiritual purposes as hallucinogens or psychoactive agents. Such plants can cause a wide range of adverse effects when ingested by animals or people, depending on the organ system affected [1, 2].

Plant toxicity is due to a wide diversity of chemical toxins [1-3]. Certain plant species have multiple toxins with the ability to affect different systems [2]. Other less studied forms of toxicity of plant compounds, such as those that manifest as subacute and chronic types in the form of carcinogens, teratogens, endocrine disruptors, and genotoxic compounds, are difficult to attribute to specific plants or their compounds [4]. The toxicity of different plant species is dependent on the susceptibility of the organism in question, the growth stage or part of the plant ingested, the amount consumed, and the species [2]. In the same vein, the observed effects of ingestion of toxic plants range from mild forms to those that result in death after ingestion of even very small quantities. Additionally, there are only a few plant toxins with antidotes, with most other poisoning cases managed symptomatically [1]. The good news is that antidotes are rarely necessary when managing poisonings by plant toxins in patients [5].

This chapter looks at some notable examples of widely studied toxic plants but is by no means exhaustive. Even among the widely studied examples, there is incomplete toxicity information [6-8]. The chapter introduces the reader to numerous general aspects of toxic plants. Toxic plants are of great economic importance in the livestock industry but also pose a threat to the health of humans and domestic animals, which are often exposed to the same toxic plants because of a shared environment. Various toxic compounds from plants such as those used in arrow and dart poisons could prove valuable for drug discovery and research [9].

1.2 Poisonous Plants as Sources of Traditional and Modern Medicines

Traditional medicine has been the source of several modern drugs. Many well-known poisonous plants are widely used in traditional medicine and are a source of life-saving drugs [3, 9]. Nature produces a variety of toxic compounds, many of which have found applications as anticancer drugs [10]. The same toxic compounds can serve as therapeutic compounds depending on the dose administered. This fact is well articulated in Paracelsus' dictum, which states that only the dose determines that a thing is not a poison [3]. Table 1.1 shows some common poisonous plants from which modern drugs have been obtained.

Several toxic compounds from plants belong to several classes of compounds, including alkaloids, glycosides, flavonoids, proteins, and saponins [1, 3, 25]. Most saponins can cause hemolysis of erythrocytes at doses of only a few milligrams per milliliter but may also have other toxic properties. Saponin-containing plants are extensively used as fishing poisons. Alkaloids have extraordinary structural diversity and a wide variety of pharmacological activities, such as muscle relaxants and cardiovascular and respiratory agents [2, 3]. They belong to the most powerful plant constituents and are responsible for the activity of a host of poison ingredients. Flavonoids, which have a wide structural variety, show a broad range of activities but are rarely used as a primary source of toxicity for mammals, except for several compounds of special structure such as rotenoids, which are used for fish poisoning [3].

Table 1.1 Some common drugs derived from toxic plants.

Name of plant Toxic principles/drug(s) derived Use of drug Strychnos spp. Strychnine Neuropharmacological science [11] Strophanthus spp. Ouabain Acute cardiac insufficiency [12, 13] Strophanthus spp. k-Strophanthin Acute cardiac insufficiency/cardiotonic research [12, 13] Physostigma venenosum Physostigmine Glaucoma and myasthenia gravis [14, 15] Chondrodendron tomentosum D-Tubocurarine Muscle relaxant in anesthesia [14, 16] Rauwolfia serpentina Reserpine (Serpalan and Serpasil) Antihypertensive and psychotropic [17, 18] Rauwolfia vomitoria Ajmaline Cardiac arrhythmias [19] Catharanthus roseus Ajmaline Cardiac arrhythmias [19] Vincristine Pediatric malignancies, acute lymphocytic leukemia, lymphoid blast crisis of chronic myeloid leukemia, and both Hodgkin's and non-Hodgkin's lymphomas [14] Digitalis purpurea Digitoxin Tachyarrhythmia [14] Taxus brevifolia Taxol (docetaxel/Taxotere) Ovarian, breast, and colon cancers and Kaposi's sarcoma [20] Colchicum autumnale Colchicine Gout [21]; familial Mediterranean fever [22] Melilotus officinalis/Melilotus albus Dicoumarol (warfarin) Thrombotic conditions [23] Camptotheca acuminata Camptothecin Anticancer [20] Podophyllum emodi/Podophyllum peltatum Podophyllotoxin Anticancer [5, 24] Papaver somniferum Morphine Analgesic [14] Erythroxylum coca Cocaine (benzoylmethylecgonine) Local anesthetic [14] Atropa belladonna
Datura stramonium
Hyoscyamus niger
Hyoscyamus muticus Scopolamine Prevention of motion sickness and postoperative nausea and vomiting; parkinsonism; ophthalmic treatment [14]

Almost all the active ingredients of African arrow poison come from plants. At least 80% of the poisons are based on cardioactive components, mostly cardiac glycosides from the genera Acokanthera, Parquetina, and Strophanthus. Other genera with numerous poisonous species are Adenium, Mansonia, Calotropis, Pergularia, Corchorus, Erythrophleum, Euphorbia, Gnidia, and Jatropha [3]. Many other plant toxins used have a variety of activities, but their toxic effects are more long term than acute, e.g. sesquiterpene lactones, iridoids, pyrrolizidine alkaloids, and tannins. Some alkaloid-bearing plants that are used as base poisons include Strychnos spp., Boophone disticha, Crinum spp., Triclisia dictyophylla, Nicotiana spp., Physostigma venenosum, Sarcocephalus latifolius, and Erythrophleum spp. [3, 26].

Some medicinal plant species used in African traditional medicine have potential or well-known toxicities. However, some of the toxic effects of plants are not easy to discern because they are either subacute or chronic. This is compounded by the fact that very few African plants have been tested for toxicity. Tamokou and Kuete [27] evaluated 120 African medicinal plants that had been previously screened for their toxic effects and found that about 40% of them were potentially toxic, with symptoms affecting neurological, hepatic, renal, gastrointestinal, and cardiovascular systems.

1.3 Toxic Plants and Justice

1.3.1 Toxic Plants in Capital Punishment

In 399 BCE, Socrates was sentenced...