Medicinal plants are an integral part of African culture, one of the oldest and most diverse in the world.
In South Africa, 21st century drug therapy is used side-by-side with traditional African medicines to heal the sick. While plants have been used in African medicine to treat fever, asthma, constipation, esophageal cancer and hypertension, scientific analyses of the purported benefits of many plants is still scant. A team of researchers has now examined the effectiveness of 16 plants growing in the country's Kwa-Zulu Natal region and concluded that eight plant extracts may hold value for treating high blood pressure (hypertension).
The study, entitled ACE Inhibitor Activity of Nutritive Plants in Kwa-Zulu Natal, was conducted by Irene Mackraj and S. Ramesar, both of the Department of Physiology and Physiological Chemistry; and H. Baijnath, Department of Biological and Conservation Sciences; University of Kwa-Zulu Natal, Durban, South Africa. Dr. Mackraj is presenting the team's findings at the 120th annual meeting of the American Physiological Society (APS; www.The-APS.org), being held as part of the Experimental Biology (EB '07) conference. More than 12,000 scientific researchers will attend the gathering being held April 28-May 2, 2007 at the Washington, DC Convention Center.
Background and Methodology
Hypertension is treated with medication, including drugs such as angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor blockers (ARB). These drugs not only lower blood pressure but offer additional protection to the brain and heart. ACEI, in particular, provide beneficial properties to patients with type 1 diabetes.
In an effort to identify indigenous plants consumed by the local population in Kwa-Zulu Natal that hold potential antihypertensive properties, the researchers examined 16 plants to identify ACE inhibitor activity. The plants were:
- Amaranthus dubius, a flowering plant also known as spleen amaranth
- Amaranthus hybridus, commonly known as smooth pigweed or slim amaranth
- Amaranthus spinosus, also known as spiny amaranth
- Asystasia gangetica, an ornamental, ground cover known as Chinese violet. Also used in Nigerian folk medicine for the management of asthma.
- Centella asiatica, a small herbaceous annual plant commonly referred to as Asiatic pennywort
- Ceratotheca triloba, a tall annual plant that flowers in summer sometimes referred to as poppy sue
- Chenopodium album, also called lamb's quarters, this is a weedy annual plant
- Emex australis, commonly known as southern three corner jack
- Galinsoga parviflora, commonly referred to as gallant soldier
- Justicia flava, also known as yellow justicia and taken for coughs and treatment of fevers
- Momordica balsamina, an African herbal traditional medicine also known as the balsam apple
- Oxygonum sinuatum, an invasive weed with no common name
- Physalis viscosa, known as starhair ground cherry
- Senna occidentalis, a very leafy tropical shrub whose seeds have been used in coffee; called septic weed
- Solanum nodiflorum, also known as white nightshade
- Tulbaghia violacea, a bulbous plant with hairless leaves often referred to as society or wild garlic
Dried leaves from the plants were ground and used to prepare organic and acqueous extracts. Ten grams of ground plant material was suspended in either a methanol or distilled water solution for 48 hours. Each solution was subsequently filtered and the filtrate was left to air dry resulting in the specific test compound. ACE activity was determined using a flourimetric method with Hip-His-Leu as a substrate. The fluorescence of the o-phthaldialdehyde was measured to determine the effect of the plant on ACE activity.
Plasma ACE activity was determined using rat plasma. The IC50 of the conventional ACEI, captopril was determined to test the sensitivity of the assay. At least three separate determinations were conducted for each test compound. A tannin test was only conducted on those plant extracts that exhibited over 50 percent ACE inhibition in the initial analysis. The data was subjected to GraphPad Instat (GraphPad Software Inc, San Diego, CA, USA). All values were expressed as mean, SEM. A probability where p<0.05 was considered significant.
Results: Eight of Sixteen Plants Showed ACEI
Eight of the 16 plants demonstrated ACE inhibition activity. The plants were then subjected to a gelatin salt block test for tannins to eliminate any false positive results. None of the plants tested positive for tannins, hence eliminating any false positive results.
Ultimately, the eight plants that showed significant ACEI activity in both extract forms were: Amaranthus dubius, Amaranthus hybridus, Asystasia gangetica, Galinsoga parviflora, Justicia flava, Oxygonum sinuatum, Physalis viscosa, and Tulbaghia violacea.
The Stand Out "Wild Garlic" (Tulbaghia violacea) Plant
Only one plant -- Tulbaghia violacea -- showed more than 50 percent inhibition in both extract preparations. These findings are in keeping with those of another group (1999). Further testing has revealed that the plant has promising hypotensive affects. The plant is commonly associated with onions and garlic and highly concentrated in Southern Africa. It is best known as "wild garlic."
Researchers have recorded (1962) that the plant was pounded into formulations and used by native South Africans to relieve stomach ailments, rheumatism and high fevers. Other researchers found (1966) that native South Africans rubbed the leaves of the plant on the head for sinus headaches and used plant infusions for colic and restlessness in young children. The most direct discovery is the 1993 finding that large doses of popular garlic preparations significantly decreased the diastolic blood pressure in human patients 5-14 hours after the dose with no significant side effects. In addition, wild and cultivated garlic preparations were shown to decrease systolic blood pressure in rats.
In this study Tulbaghia violacea has shown properties related to lowering blood pressure. Since the number of hypertensive individuals around the world is on the rise, it is worthwhile to pursue further studies involving this extract. Yesterday's folk remedies may one day be just what the 21st century doctor orders.