Plants have directly contributed to the development of important drugs. The antimalarial drug artemisinin, the painkiller morphine, and the cancer chemotherapy taxol are just three examples of plant-derived drugs. Africa is endowed with up to 45,000 plant species, or about 25% of the world’s plant genetic resources. More than 5,000 plant species of this enormous African resource are used in traditional medicines. Medicinal plant specialists, Associate Professor Adeyemi Aremu and Professor Nox Makunga shed light on some of these plants.
Artemisia afra Jacques. ex Willd. (African wormwood)
Artemisia afra is the only species of its genus indigenous to the African continent. It is often considered a potential flagship plant due to its wide popularity and various uses in traditional African medicine. African wormwood has been used for coughs, colds, flu and malaria.
Scientific evidence of its antimicrobial, antidepressant, antioxidant and anti-inflammatory effects has been reported. African wormwood sparked global interest when it was promoted as having the potential to treat COVID-19 and was tested in laboratory studies. The extracts had some degree of inhibitory activity against feline coronavirus and SARS-CoV-2. But this requires further clinical study to reach a valid conclusion.
The traditional uses and growing popularity of African wormwood have given rise to a number of commercial herbal products. But with insufficient clinical data, it is not yet known whether African wormwood is a treasure trove of new medicines.
Catharanthus roseus (L.) G. Don
This plant is also known as Cape periwinkle, graveyard plant, Madagascar periwinkle, old maid or rosy periwinkle. It is native and endemic to Madagascar. The plant is commonly used as a tonic and emetic for the treatment of many health problems, including rheumatism, diabetes, and skin and venereal diseases.
Periwinkle has several phytochemicals associated with antioxidant, antimicrobial, antidiabetic, and anticancer properties. Alkaloids remain one of the signatures. Two of its alkaloids, vincristine and vinblastine, have been widely explored by the pharmaceutical industry. These two alkaloids were the first anti-cancer agents of plant origin deployed for clinical purposes.
Griffonia simplicifolia (DC.) Baill. (Griffonia, Atooto, gbogbotri, kajya, kanya, kwakuo-aboto)
Griffonia simplicifolia is a woody climbing shrub. He is from West and Central African countries including Benin, Cameroon, Ivory Coast, Gabon, Ghana, Liberia, Nigeria and Togo. In traditional African medicine, the seeds are said to exert several medicinal effects and have been explored as an aphrodisiac and remedy for diarrhoea, stomach-ache and dysentery.
The chemical properties of the plant have been widely studied. It was found to contain rich phytochemicals with enormous pharmaceutical value. In particular, the seeds are known as an excellent source of 5-hydroxy-L-tryptophan (commercially called oxitriptan) which the body uses to produce serotonin. Serotonin is a neurotransmitter known to affect sleep, appetite, pain, and mood. It plays an important role in the treatment of depression, insomnia, obesity, and related health conditions, especially those associated with mental health.
The seed of Griffonia simplicifolia remains one of the most reliable and abundant sources. Commercial interest has grown over the years. Recent estimates put the annual bulk seed extract market value for the plant at between US$32 million and US$100 million, and demand is expected to increase by 7% per year.
twisted Sceletium (L.) NEBr. (kanna, kougoed)
Kanna is a succulent endemic to South Africa. It is uncommon in semi-arid areas and used for conditions related to stress, depression, pain and anxiety. The mesembrine-type alkaloids are dominant and generally responsible for kanna’s pharmacological effects as a psychoactive and mood-boosting herb. Zembrin® was developed as a standardized extract of the plant. It is used as a dietary supplement with the potential to improve mood, relieve stress, and improve cognition. The use of this species stems from the traditions of the Khoekhoe and the San.
Many other medicinal uses have been reported for this species as it can be used to treat headaches, abdominal pain, and respiratory ailments. Trimesemine™ (a commercially available extract with a high concentration of mesembrine) has been shown to act as a monoamine releaser, increasing serotonin, a chemical messenger produced by the body that is also known to regulate mood. It is potentially useful for attention deficit and other central nervous system disorders such as Alzheimer’s disease.
Strophanthus gratus (Wall.and hook.) Baill. (Climbing oleander)
Strophanthus gratus, a vigorous evergreen climber, occurs in tropical regions from Senegal to the Democratic Republic of the Congo. In traditional medicine, oleander has been used to treat snakebites, wounds, gonorrhea, constipation and fever. The root is considered an aphrodisiac.
Cardiac glycosides, which are organic compounds that increase the output force of the heart, are the signature compounds of the plant. In particular, ouabain has been identified as the major dominant glycoside in the seed.
Ouabain, a cardio glycoside, was isolated because of the way climbing oleander is used in traditional medicine. It is now used as a treatment for heart failure and arrhythmias or irregular heartbeats. Recent studies have also found a new use that may prove relevant for metastatic prostate cancer.
Pelargonium sidoides DC (African geranium, South African geranium)
This medicinal geranium native to South Africa and the highlands of Lesotho has root tubers that are harvested for medicinal purposes. People use these tubers for diarrhea, colic, gastritis, tuberculosis, cough, liver disorder, menstrual disorder, gonorrhea, and many other medical conditions.
Clinical evidence suggests the efficacy of extracts prepared from this species for the management of acute respiratory tract infections. These data support the use of this medicinal geranium in particular to relieve symptoms of acute inflammation of the nasal cavity and sinuses and the common cold in adults. Umckaloabo® (EPs® 7630), a standardized proprietary extract, is one of the most successful plant-derived pharmaceuticals from this species. A number of clinical studies have shown that it can reduce the symptoms of acute bronchitis.
Over-the-counter medicines (Kaloba and Umcka) made from extracts of this pelargonium are now sold worldwide. Linctagon® is a pelargonium-inspired medicine that is prescribed to help the body fight off colds and flu by boosting the immune system.
Siphonochilus aethiopicus (Schweinf.) BL Burtt (African ginger, wild ginger)
African ginger is native to western and southern tropical Africa, where it is found in about 30 African countries. This wide range of distribution likely explains its use for a variety of health conditions. These include respiratory problems (like cough and flu), pain, inflammation, and malaria.
An analysis of the essential oil from the root and rhizome of African ginger found about 70 compounds in the root and 60 compounds in the rhizomes. The bioactive compounds siphonochilone and eucalyptol found in the roots and rhizomes have shown potential for the treatment of asthma and allergic reactions. In a clinical trial, eucalyptol, present in root and rhizome essential oil, demonstrated anti-inflammatory activity in bronchial asthma.
In South Africa, this species is classified as critically endangered because it has been overexploited for traditional medicine. This species is rapidly heading towards extinction in South Africa in the wild. Cultivation is strongly encouraged for its conservation.