Earth And Medicine: Tropical Rainforests

Our Vegetables Our Drugs

Episode 11

The tropics are areas located around the equator defined by warmer climates with an average temperature of about 27°C. These regions receive a substantial amount of solar radiation and rainfall compared to others.  In the tropics, there exists various biomes such as Deserts, Savannahs and Tropical rainforests. Tropical rainforests are forests that consists of dense evergreen and broadleaf trees. They have a high level of rainfall and are always wet for most of the year. They could be very large (>1 million Km²) and are arguably the most important ecosystem on Earth. Examples of rainforests include the Amazon rainforests in South America (Brazil, Columbia, Peru, Bolivia,e.t.c), the Congo rainforests (Gabon, Central African Republic, Congo, Democratic Republic of the Congo (DRC, Zaire), Uganda, e.t.c), Indonesian rainforests (Sumatran, Borneo), Southern Asian rainforests (Thailand, Malaysia, e.t.c), and New Guinea rainforests (Papua New Guinea, Indonesia), e.t.c.

It is worth knowing that tropical rainforests house a vast plant and animal diversity. It is estimated that thousands of species in tropical rainforests have never been encountered or described by scientists. These organisms include insects, mammals, reptiles, birds, fungi, bacteria and several other forms of life and are found in the various strata of rainforests. Forests are also dwellings to native and archaic tribes living in Central Africa, South America and the Indo-Pacific regions. The forest cleanses and purifies our atmosphere by absorbing large volumes of waste gases such as carbon dioxide. 

Indeed the rainforests are crucial for life. Forests are the origins of food crops and many drugs available today. Over a hundred thousand years ago, human ancestors (hominids) with no tools depended on vegetation and animals they could find or capture. Vegetation includes wild fruits, foliage, and other parts of plants (similar to the diet of chimpanzees and gorillas). Since humans originated from Africa, their diets were certainly obtained from the forests in which they inhabited. As civilization progressed, we shifted from gathering food to cultivating plants that we found to be edible. Likewise, early humans discovered that certain plants are capable of curing or alleviating ailments and diseases; for instance, pubescent leaves were found to ameliorate gastrointestinal disturbances such as indigestion and infections with intestinal worms. The knowledge which was passed from generation to generation ushered in the development of native medicine in various tribes. Tropical rainforests are deemed the world's largest medicine chest. It is estimated that a quarter of medicines are sourced from the tropical rainforest. The journey of many important drugs we (antimalarials, anti-inflammatory, anaesthetics,e.t.c) we use in medicine today began from the accidental usage of forest produce.

Medicinal plants manufacture phytochemicals which are responsible for their chemical and therapeutic effects. Phytochemicals which are regarded as secondary metabolites include flavonoids, tannins, alkaloids, volatile oils, glycosides, carotenoids, and many others.

Below are ten examples and botanical descriptions of very common and important vegetable drugs which have their origins in tropical rainforests in several regions of the world. 

1. Curare (extract)

Geographical source: South America, Amazon region

Botanical source: Curare is a poison obtained from plants in the genus Chondrodendron, family Menispermaceae. 

Common usage: It is used in poison arrows by hunters and is very potent in causing paralysis of muscles.

Active constituents: (+)-tubocurarine

Pharmacology and medical importance:- the component is a neuromuscular blocking agent at the endplate, interfering with the actions of acetylcholine. Due to its high toxicity, it is no longer used in clinical settings. It is also an abundant source of alkaloids.

2. Jaborandi (leaves)

Geographical source: Brazil

Botanical source: Pilocarpus jaborandi family Rutaceae

Active constituents: pilocarpine, isopilocarpine, other alkaloids, volatile oils

Pharmacology: it acts as an agonist on cholinergic receptors, induces contraction of smooth muscles. It is also antagonistic to tropane alkaloids. It causes constriction of pupils, impeding the flow of aqueous humour in the eye.

Clinicals: Opthalmology- for treatment of intraocular pressure and glaucoma.

3. African rauwolfia (root)

Geographical source: grows extensively in Africa especially western to eastern regions.

Botanical source: Rauwolfia vomitoria family Apocynaceae

Active principle: reserpine, rescinammine, resepoxidine, ajmaline

Actions: reserpine is a very potent diuretic, increases urine flow through the urinary tubules

Clinicals: treatment of hypertension, oedema and neuropsychiatric disorders

4. Coca (leaves)

Geographical location: South America 

Botanical source: Erythroxylum coca and other species

Common usage: Coca is used by folks for its sedative, numbing and high sensations.

Active principle: cocaine, hygrine, ecgonine, cinnamoylcocaine

Clinicals: cocaine is used as a local anaesthetic and sedative. It is very addictive.

5. Acacia gum (gum arabic)

Geographical source: East Africa, Nigeria, tropical Africa. The tree is available in Northern Nigeria.

Chemistry: This gum is composed of calcium salts of arabic acids. These are hydrolyzable into simple monosaccharides.

Pharmaceutical applications: gums are used in the compounding of tablets as binders and bulking agents. They are also demulcents and are included in some cough medicines. The gum is soluble in water.

6. Senna (leaves)

Geographical source: Sudan, India

Botanical source: Cassia acutifolia, C. augustifolia

Active constituents: The shrub has compound leaves which are rich in anthraquinone glycosides.

Medicinal use: treatment of constipation. It is used as a purgative.

7. Quillaia (bark)

Geographical source: South America

Botanical source: Quillaja saponica

Chemistry: Quillaja bark is rich in saponins, (steroidal glycosides with lathering properties)

Usage: quillaia extract is used in the preparation of beverages giving it foamy features. It is also used in the preparation of adjuvants for vaccines.

8. Cinchona (bark)

Geographical source: South America

Botanical source: several cinchona species are valuable although the total alkaloid content may vary: C. officinalis,  C. succirubia family Rubiaceae

History: Cinchona's antimalarial properties have been observed before modern times. Cinchona bark is one of the oldest drugs. Chloroquine and Hydroxychloroquine are based upon quinine.

Active principles: quinine alkaloids: quinine, quinidine, cinchonine, cinchonidine

Indications: acute malaria infections by Plasmodium falciparum and P. vivax.

9. Cocoa (seeds)

Geographical source: Brazil, Peru, Bolivia, Ghana, Nigeria.

Botanical nomenclature: Theobroma cacao family Sterculiaceae

Common usage: cocoa is used in preparing beverages, chocolates, and cocoa butter

Active constituents: purine alkaloids: caffeine, theophylline, theobromine. Volatile oils are present.

Clinicals: The above compounds are diuretics and central nervous system stimulants. They act on the vascular system and are also used in treating ailments such as headaches. 

10. Coconut (fruit)

Geographical source: Tropics of Africa, Caribbean islands

Botanical source: Cocos nucifera family Palmae

Active constituents: medium-chain triglycerides (lauric, myristic, caproic, capric acids), electrolytes, fats, polyphenols, potassium.

Medicinal use: Coconut is very nutritive and rich in calories and is more absorbable in the gut. It is used as an energy source and for electrolyte replenishment.

Limitations in the sourcing of plant-based medicine

A major challenge endangering the existence of these drugs is deforestation. The indiscriminate logging of wood, destruction, burning and clearing for agricultural and industrial purposes and climate change has led to the destruction of habitats and extinction of these valuable plants. One way to ensure a continuous supply of these drugs is to restrict sourcing from the wild and encourage cultivation instead. Another bottleneck is that many of these plants do not grow outside their natural habitat. Some require special conditions such as sunlight, humidity, soil water and other requirements which may not be available elsewhere. These have limited the supply of these drugs worldwide. Despite these constraints, we still have a lot to benefit from nature, but for us to continue to enjoy mother nature gift of medicine, we must continue to conserve her heritage and put back whatever we take from her.