Senna occidentalis, commonly known as coffee senna, is a weed widely used in traditional medicine around the world. For instance, in Hausa medicine — a type of folk medicine still practiced today in Northern Nigeria — coffee senna is used to treat a wide variety of ailments, such as hepatitis, malaria and typhoid fever. The plant’s leaves are also used to make a decoction that reduces fever.
Meanwhile in Ayurvedic medicine, coffee senna is used to improve digestion, cleanse the throat, purify the blood and treat cough, asthma and other respiratory ailments. Coffee senna leaves are also useful for various topical applications. When applied to the skin, they could treat skin diseases like scabies and ringworms, and even poisonous snake bites.
In a recent study, researchers from Nigeria and Malaysia evaluated the ability of hexane, methanol and aqueous leaf extracts of coffee senna to prevent B-hematin formation in vitro. This event — also known as hemazoin formation — is a distinctive feature of malaria and occurs while Plasmodium parasites, the blood-feeding, single-celled organisms that cause malaria, invade red blood cells (erythrocytes). Hemazoin is crucial to the survival of these parasites.
The researchers reported the antimalarial activity of coffee senna leaf extracts in an article published in the International Journal of Herbal Medicine.
Coffee senna leaves can inhibit the growth of malaria-causing parasites
The search for natural antimalarial agents in plants has yielded significant success in terms of drug discovery. In Northern Nigeria, coffee senna is known as a folk medicine that could treat malaria. To investigate how coffee senna works against the disease, the researchers first obtained extracts from the plant’s leaves using various solvents. They then examined whether these extracts can inhibit B-hematin formation and heme polymerization — two events facilitated by malarial parasites for their survival.
Earlier studies suggest that the degradation of hemoglobin, the principal component of erythrocytes, is vital to the growth of malaria parasites inside the human body. This is because these microorganisms have a limited capacity to produce amino acids, and breaking down hemoglobin provides them with what they need.
However, recent studies have found that during the early stages of erythrocyte infection, malaria parasites digest hemoglobin to prevent early cell lysis. The degradation of hemoglobin releases free heme in the form of a-hematin, which is toxic to the parasites. To avoid this toxic compound, malarial parasites transform a-hematin to non-toxic B-hematin crystals. The formation of B-hematin via heme polymerization ensures the survival of malaria parasites; hence, these two events make good targets for antimalarial agents.
The researchers reported that the methanolic and aqueous leaf extracts of coffee senna showed good inhibitory activities (83.08 percent and 83.97 percent, respectively) against B-hematin formation at 500 mcg/mL, while the hexane extract only inhibited B-hematin formation by 54.92 percent. In vitro antimalarial assays also revealed that the extracts suppressed the growth of the malaria parasite in a dose-dependent manner. (Related: Researchers confirm the antiplasmodial effects of bellyache bush on malaria-infected mice.)
At 6.25 mcg/mL, the hexane extract suppressed parasite growth by 73 percent, but this increased to 84.43 percent when the extract’s concentration reached 50 mcg/mL. The half maximal inhibitory concentration (IC50) of the coffee senna hexane extract was 3.47 mcg/mL. The researchers also confirmed the presence of anthraquinones, phenols, tannins, alkaloids and flavonoids in coffee senna.
Based on these findings, the researchers concluded that coffee senna is an excellent natural antimalarial agent.