Nigeria researchers identify, validate more medicinal plants for hypertension treatment
*Bitter leaf, guava, never die plant, red acalypha, mistletoe, banana, garlic, beetroot top list
Some medicinal plants have been shown to reverse or improve deranged cardiovascular parameters particularly raised blood pressure and other complications associated with these diseases.
In Nigeria, several plant species have been employed for treatment of these conditions with appreciable patient response. Some scientific studies have verified the claims made by these traditional healers or patients themselves.
A new study on medicinal plants used for management of hypertension in Nigeria published in the journal Annual Research & Review in Biology noted that herbal antihypertensive recipes are prepared as decoctions, infusions, powders and or juice.
According to the study, plants, which were most frequently prescribed, include: Allium species (garlic and onions), Persea americana (avocado), Acalypha godseffiana, Zingiber officinale (ginger), Sida acuta (broom weed), Hunteria umbellata, Rauwolfia vomitoria (commonly called Chieftaincy leaf, serpent wood or swizzler stick in English, asofeyeje in Yoruba, akanta in Ibo, and wada in Hausa), Viscum album (mistletoe) and Aframomum melegueta (alligator pepper/ grain of paradise).
The researchers include: Kingsley I. Eghianruwa, Olayinka A. Oridupa and Adebowale B. Saba of the Department of Veterinary Physiology, Biochemistry and Pharmacology, University of Ibadan, Ibadan, Oyo State.
The researchers concluded: “In conclusion, this study has highlighted various medicinal and food plants used in Nigeria for management of hypertension. Most of these plants are readily available and affordable at various regions of the countries. However, more research is warranted to identify the most abundant plant in each region of the country and educate individuals on proper use of the medicinal plants with scientific evidence of efficacy. Further to scientific verification of pharmacological effect of the medicinal plants, research to isolate and chemically characterize the bioactive principle responsible for the antihypertensive effect should also be done as a prerequisite for drug development candidature.”
Below are summaries of the findings of researchers on some of the plants employed for management of hypertension in Nigeria?
Bitter leaf (Vernonia amygdalina)
Aqueous extract of Vernonia amygdalina was investigated for its cardiovascular effects in normotensive Sprague-Dawley rats. Administration of the extract intravenously via the femoral vein at doses of 5.0 and 10.0mg/kg caused a bi-phasic alteration of blood pressure, observed as an initial transient rise in mean arterial pressure with a subsequent decline beyond the basal levels. This pattern of response was particularly observed in rats administered with the dose of 10 mg/kg; initial blood pressure of 73.7+3.4 mmHg increased to 101.9+ 4.1 mmHg in the first phase and declined to 60.2 ± 2.5 mmHg in the second phase. However, the prominent biphasic response was not observed with higher doses (50 and 100mg/kg).
Contractility study with cumulative addition of the plant extract to isolated rings of aorta precontracted with noradrenaline produced a dose-dependent relaxation of the aortic smooth muscle. Maximum relaxation of 31.3 ± 3.1 per cent was observed with extract concentration of 2.7 mg/ml.
The authors suggested a direct vaso-relaxant mechanism of action for the antihypertensive effect of V. amygdalina.
Parinari curatellifolia (family Chrysobalanaceae) is used locally in the South Western Part of Nigeria to treat hypertension. It is called nawarre-baa (monkey’s plum) in Fula-Fulfulde; bobwohi in Gwari; fara rura, gwànjáa kúsá in Hausa; odaubi in Idoma; ijakor in Igala; mándo in Kanuri; kóbenci (the fruit) and pútú (the tree) in Nupe; ibyua in Tiv; and abo idofun, idofun and ìdòfún ako in Yoruba.
Investigations on the antihypertensive potential of the seed extract revealed that Parinari curatellifolia exhibited negative inotropic andchronotropic effects on isolated rabbit heart. A dose-dependent reduction in systolic and diastolic blood pressure, and mean arterial blood pressure were observed in normotensive and salt-induced hypertensive rats. Percentage change in mean arterial blood pressure was increased compared to the control rats in the normotensive group. Salt loading increased Nitric Oxide Synthase (NOS) activity and production of thiobarbituric acid reactive substances (TBARS) with decrease in the catalase, superoxide dismutase and glutathione peroxidase activities in the liver. The extract reversed these biochemical anomalies and also decreased elevated serum levels of creatinine, urea, glucose, triglycerides, low density lipoprotein (LDL) and total cholesterol, and increased serum concentration of high-density lipoprotein (HDL)/ good cholesterol.
Guava (Psidium guajava)
The leaf of Psidium guajava (family, Myrtaceae), commonly known as guava is used traditionally for its hypotensive effect. The study by Ojewole investigated the hypotensive effects of P. guajava leaf aqueous extract (50-800 mg/kg) in Dahl salt-induced hypertension model in rats. Acute intravenous administrations of the plant extract (50-800 mg/kg i.v.) produced dose-dependent, significant reductions in systemic arterial blood pressures and heart rates of hypertensive, Dahl salt-sensitive rats.
The numerous tannins, polyphenolic compounds, flavonoids, pentacyclic triterpenoids, guajaverin, quercetin, and other chemical compounds present in the plant are speculated to account for the observed hypoglycemic and hypotensive effects of the plant’s leaf extract.
Never die plant (Bryophyllum pinnatum)
Commonly called Resurrection plant, Never Die plant, Air plant, Miracle leaf, or Life plant; Bryophyllum pinnatum belongs to the plant family Crassulaceae. It is known as odaa opue in Ibo, ewe abamoda or odundun in Yoruba, and da bu si in Chinese. To the Edo, it is danweshin or ekpokpo; afiayo in Efik; umbu in Ijo-Izon.
Aqueous and methanol leaf extracts of the herb were investigated using their effects on arterial blood pressures and heart rates of normotensive and spontaneously hypertensive rats. The effect of the extracts on isolated guinea pig atria was also determined. The extracts at doses of 50-800 mg/kg i.v. or i.p. produced dose-dependent, significant reduction in arterial blood pressures and heart rates of anaesthetized normotensive and hypertensive rats. The extract had more profound hypotensive effects on hypertensive rats compared to the normotensive rats.
The leaf extracts at concentrations of 0.25 – 5.0 mg/ml also produced dose-dependent significant (p<0.001– 0.05) negative inotropic and chronotropic effects on isolated guinea-pig atria, and inhibited contractions stimulated by electrical field stimulation (ES)-provoked. Also, the extract inhibited contractions of isolated thoracic aortic strips induced by potassium and receptor-mediated agonist drugs in a non-specific manner.
The extract showed remarkable hypotensive effect in this study and the authors reported that further studies are on going to elucidate the plausible mechanism/s of hypotensive action of the plant. Cardio-depression and vasodilation were suggested to contribute significantly to the antihypertensive effect of the herb.
Avocado (Persea americana)
The aqueous seed extract (AE) of Persea americana (family Lauraceae) has been investigated for its antihypertensive effect using the mean arterial pressure (MAP) and heart rate (HR) of hypertensive and naive rats.
P. Americana extract at doses of 240, 260, 280 mg/kg were administered to the rats with bolus doses of Ach (1, 2, 4 μg/kg). Pretreatment for 10 consecutive days significantly reduced MAP from 125.7±11.2 to 92.1 ±8.5 mmHg and HR from 274.6 ± 39.3 to 161.6 ±11.6 beats /min.
Also, acute injections of P. americana extract significantly reduced MAP from baseline values in naive rats. The effects of AE on MAP were comparable with those of Ach. Combination of AE with 2 μg/kg of Ach only significantly potentiated the MAP reducing effect of 240mg/kg of AE. It is concluded that the aqueous seed extract of P. americana reduces BP and HR in normotensive rats. This observation lends credence to its use by herbalists for the management of hypertension.
Sansevieria senegambica (Family Agavaceae or Ruscaceae) is an ornamental plant used in traditional health practice in southern Nigeria for treating bronchitis, inflammation, coughs, boils and hypertension. It is also used in arresting the effects of snake bites, as well as in compounding solutions used as hair tonics.
It is called Oja Ikoko in Yoruba.
The study by Ayalogu et al. reported the effects of aqueous extract of the leaves of Sansevieria senegambica on plasma marker enzymes, plasma chemistry and the haematological profile of salt-loaded rats. Salt loading was carried out via incorporation into feed of rats for a period of six weeks. The extract at doses of 150 mg/kg or 200 mg/kg had no significant effects on markers of liver and kidney functions, but it caused leukocytosis and significantly increased (p < 0.05) plasma levels of calcium and potassium. On the contrary, rats administered with the extract had significantly decreased (p<0.05) plasma sodium and chloride levels compared to the control rats. The extract was suggested to act as a potassium-sparing diuretic with the mechanism of antihypertensive action probably via alteration of plasma sodium and potassium balances, or through calcium-mediated changes in vascular muscle tone.
Zobo (Hibiscus sabdariffa)
Calyces of Hibiscus sabdariffa (family: Malvaceae) are brewed up as a local beverage in all parts of Nigeria. It is acclaimed to have several medicinal effects, which include antihypertensive effect. The antihypertensive effect of the aqueous extracts of the calyx of H. sabdariffa was investigated in anaesthetized rats.
A dose-dependent, but relatively vagal-independent decrease in mean arterial pressure was observed in rats administered with the extract. The hypotensive effect of the extract was significantly inhibited by atropine, cimetidine and promethazine. However, the extract did not inhibit the induction of increase in blood pressure by bilateral carotid occlusion (48.05 +/- 6.83 mmHg to 46.53 ±7.49 mmHg). Cumulative doses of the extract in isolated aortic rings precontracted with noradrenaline produced dose-dependent relaxation of the rings.
The authors stated that the mechanism of antihypertensive effect of the H. sadariffa calyces were not mediated via inhibition of the sympathetic nervous system. However, the involvements of acetylcholine-like and histamine-like mechanisms as well as direct vaso-relaxant effects were suggested.
A clinical study has been reported, involving patients with moderate essential hypertension (45 per cent males and 55 per cent females; mean age 52.6±7.9 years), but excluded those with secondary hypertension or using two medications. The observations in the experimental group were compared to a control group of males (30 per cent) and females (70 per cent) with mean age of 51.5±10.1 years. Systolic and diastolic blood pressures were measured on days 0, 12 and 15 of intervention.
In the experimental group, the study reported that systolic and diastolic pressure was significantly lowered by 11.2 per cent and 10.7 per cent respectively by day 12 of treatment compared to day 0. By day 15, systolic and diastolic blood pressure was elevated by 7.9 per cent and 5.6 per cent respectively.
A further study has been reported in which the efficacy of aqueous extract of calyx H. sabdariffa was assessed in salt- and L-NAME-induced hypertension and in normotensive controls. A dose-dependent decrease in the blood pressure and heart rate of hypertensive and normotensive rats was observed post-injection (IV) of H. sabdariffa (1-125 mg/kg). This suggested that H. sabdariffa possesses anti-hypertensive, hypotensive and negative chronotropic effects, with the most significant (p<0.05) lowering of the mean arterial pressure in the hypertensive rats (salt-induced: 94.4+/-8.6mmHg; L-NAME-induced: 136.5+/-10.3 mm Hg) compared to the normotensive controls (50.2+/-5.1 mmHg) .
A similar study evaluated the hypotensive effects of aqueous seed extract of H. sabdariffa in normotensive cat. The effects of the aqueous extract were compared with normal basal rhythm and Acetylcholine. The study showed the extract significantly lowered cat blood pressure, even at a minimum concentration of 500μg/ml. The maximum response shown by the study was at a concentration of 1mg/ml of the extract. However, this concentration of the extract was less potent compared to acetylcholine.
The study by Onyenekwe et al. reported that the LD50 of H. sabdariffa calyx extract was ˃5000 mg/kg. It further corroborated the findings by other researchers on the ability of the extract to significantly (p<0.05) lower systolic and diastolic blood pressure in spontaneously hypertensive and normotensive Wistar-Kyoto rats. The reduction in blood pressure in both groups was positively correlated with weight. In summary, the extract of H. sabdariffa demonstrated it had a vasodilator effect in the isolated aortic rings of hypertensive rats, thereby lowering blood pressure. The effects observed were suggested to be mediated via the endothelium-derived nitric oxide-cGMP-relaxant pathway and inhibition of calcium (Ca2+) influx into vascular smooth muscle cells. Another study attempted to characterize vascular effects of crude extract of dried and powdered calyces of H. sabdariffa on isolated thoracic aorta of male Wistar rats. The plant was extracted by solvent-solvent extraction with cyclohexane, dichloromethane, ethyl acetate, butanol and a final residual marc was obtained. These fractions were purified by several chromatography methods and assessed for their vascular effects. The crude extract induced mainly endothelium-dependent relaxation of aorta, which was associated with NOS activation, and also endothelium – independent relaxation associated with activation of smooth muscle potassium channels. The result of phytochemical analysis carried out in this study revealed the presence of phenolic acids in the ethyl acetate extract and anthocyans in the butanol extract. The potency of the vasorelaxant property of the extracts showed that Butanol extract > Crude extract > Residual marc > Ethyl acetate extract.
The authors suggested that the strong vasorelaxant activity of butanol extract is essentially due to the presence of anthocyans.
Mistletoe (Loranthus micranthus)
Loranthus micranthus (Family: Loranthaceae) is a semi-parasitic shrub, which is also called African mistletoe. In Nigeria, it has been found growing on several tree crops including Kola acuminata, K. nitida, Mangifera indica, Azadirachta indica, Psidium guajava, Jatropha curcas, and Persia sp.
Like all parasitic plants, this plant also obtains its nutrients and support from the host trees on which it grows. A previous study by Obatomi et al. investigated the effect of the aqueous extract of L. micranthus in normotensive and spontaneous hypertensive rats. The rats were orally administered with the extract at a dose of 1.32 g/kg per day for eight days. Mean Arterial Pressure (MAP) was significantly reduced in both normotensive and spontaneous hypertensive rats, with a significant (p<0.05) reduction of the serum total cholesterol on days six, seven, and eight.
Iwalokun et al. reported a study on the mechanism of antihypertensive effect of this plant. The extract was partitioned into n-butanol (BF), chloroform (CF), ethyl acetate (EAF) and water (WF) fractions. The median effective concentrations and maximum relaxation of the fractions were determined in epinephrine or KCl pre-contracted rat aorta ring model. Serum lipid profiles and nitric oxide (NO) levels of mice administered with 250-mg/kg b.w. (p.o.) of each fraction for 21 days were determined using spectrophotometric methods. The fractions elicited a dose-dependent inhibitory effect on rat aorta precontracted with norepinephrine or KCl with the highest relaxant effect by BF< WF > CF > EAF.
A similar order of activity was observed in the ability of these fractions to inhibit elevated artherogenic lipids, raise serum nitric oxide and reduce cardiac arginase in mice. The researchers concluded that the anti-hypertensive activity of L. micranthus involves anti-artherogenic events, vasorelaxation, cardiac arginase reduction and NO elevation.
Commonly called Red acalypha and Popose pupa locally, Acalypha wilkesiana, belongs to the plant family Euphorbiaceae. It is called aworoso in Yoruba (Ijebu). It is popularly used for the treatment of malaria, dermatological and gastrointestinal disorders. The leaf decoction is used for the treatment of gastrointestinal disorders and fungal infection particularly Impetigo contagiosa and Tinea versicolour which affect the back, chest and axillae of many babies in Nigeria.
Nworgu et al. evaluated the cardiovascular effect of Acalypha wilkesiana leaves, a medicinal plant used by traditional healers for treatment of hypertension. Graded doses of the aqueous extract of A. wilkesiana leaves were administered to rabbits through the auricular vein and blood pressure was measured using the carotid artery. Also, the effect of the extract on isolated rabbit cardiac tissue; portal vein and aortic rings of rats were investigated. The extract at a dose of 20 mg/kg produced a significant decrease in systolic, diastolic and mean arterial blood pressure. The extract at a dose of 10 mg/ml also reduced the rate and force of contraction of isolated rabbit heart. Cumulative doses of the extract at concentrations of 10 – 80 mg/ml produced no effect on the adrenaline-induced contraction of the portal vein or aortic rings of rats.
The authors concluded that the extract of Acalypha wilkesiana leaves exerted blood pressure lowering effect mainly via inhibition of the force and rate of contraction of the heart.
Garlic (Allium sativum)
A study was carried out on the cardiovascular effect of Allium sativum (Family: Amaryllidaceae), commonly known as garlic on normotensive and two-kidney one-clip (2K1C)-induced hypertensive rats. Mean arterial blood pressure (MAP) and heart rate (HR) of anesthetized rats were measured via the left common carotid artery connected to a recording device. Nwokocha et al. reported that intravenous injection of A. sativum (5-20 mg/kg) caused a significant (p<0.05), dose-dependent decrease in MAP and HR in both the normotensive and 2K1C rats, with more significant effects observed in normotensive rats. No significant difference was observed on the hypotensive and the negative chronotropic activities of the extract when the rats were pre-treated with atropine sulphate (2 mg/kg, i.v.).
The authors inferred from the study that A. sativum caused hypotension and bradycardia which did not involve the cholinergic pathway in both normotensive and 2K1C rats. From this result, the mechanism of action of A. sativum was suggested to probably involve a peripheral mechanism for hypotension.
Clinical trial involving patients with stage 1 essential hypertension (n=210) reported the effect of A. sativum on blood pressure. Patients were administered with A. sativum tablets at the dose of 300 mg/day, 600 mg/day, 900 mg/day, 1200 mg/day and 1500mg/day in divided doses for 24 weeks, with two additional groups receiving atenolol and placebo tables respectively. Their blood pressure was monitored at weeks 0, 12 and 24. The study reported a dose- and duration-dependent significant (p<0.05) decreases in systolic and diastolic blood pressure of these patients compared to patients that received atenolol or placebo.
The in-silico study has been reported on sweet proteins isolated from six plants: Thaumatococcus danielli (family: Marantaceae/called miraculous fruit; miraculous berry; Yoruba soft cane; Moi Moi leaf plant), Pentadiplandra brazzeana (family: Capparaceae and called gbegbe in Yoruba), Dioscoreophyllum cumminsii (Serendipity berry), Capparis masaikai (known as mabinlang, grows in the subtropical region of the Yunnan province of China and bear fruits of tennis-ball size), Curculigo latifolia (Curculigo is a flowering plant genus in the family Hypoxidaceae) and Richadella dulcifica. The study was informed by the increasing rate of consumption of low-calorie artificial sweeteners by patients with diseases linked to sugar consumption. The potential of replacement of conventional sugar with these sweet proteins derived majorly from under-utilized plants had thus been proposed.
The investigation conducted to verify the ability of sweet proteins to release Angiostensin-Converting Enzyme (ACE)-inhibitory peptides is emphasised in this review article. Elevation of ACE is an important pathogenic mechanism of hypertension because it mediates arterial vasoconstriction. The sweet proteins investigated were Thaumatin from
Thaumatococcus danielli, Brazzein from Pentadiplandra brazzeana,
Monellin from Dioscoreophyllum cumminsii, Madinlin from Capparis masaikai, Curculin from Curculigo latifolia and Miraculin from Richadella dulcifica.
Synsepalum dulcificum is a plant known for its berry that, when eaten, causes sour foods (such as lemons and limes) subsequently consumed to taste sweet. This effect is due to miraculin. Common names for this species and its berry include miracle fruit, miracle berry, miraculous berry, sweet berry, and in West Africa, where the species originates, agbayun, taami, asaa, and ledidi.
These were selected for sequence alignment using Basic Local Alignment Search Tool (BLAST) analysis and biological activity search using BIOPEP. Although BLAST analysis gave no homologous similarity among the proteins, BIOPEP analysis showed that they demonstrated either di- or tri-peptide with a total of 51, 14, 40, 28, 30 and 59 potential ACE inhibitory peptides from Thaumatin, Brazzein, Monellin, Madinlin,
Curculin and Miraculin respectively.
The combined digestion with pepsin, trypsin and chymotrypsin A, a simulation of human gastrointestinal digestion released 8, 2, 9, 2, 5 and 11 ACE inhibitory peptides from Thaumatin, Brazzein, Monellin, Madinlin, Curculin and Miraculin respectively. These results add value to these proteins by demonstrating their innate nutraceutical potential in their ability to reduce hypertension.
Bananas contain plenty of potassium, a mineral that plays a vital role in managing hypertension.
According to the American Heart Association, potassium reduces the effects of sodium and alleviates tension in the walls of the blood vessels.
Adults should aim to consume 4,700 milligrams (mg) of potassium daily. Other potassium-rich foods include: avocado, cantaloupe and honeydew melon, halibut, mushrooms, sweet potatoes, tomatoes, tuna, and beans.
People with kidney disease should speak to their doctors about potassium, as too much can be harmful.
Drinking beet juice can reduce blood pressure in the short and long terms.
In 2015, researchers reported that drinking red beet juice led to lower blood pressure in people with hypertension who drank 250 milliliters, about 1 cup, of the juice every day for four weeks. The researchers noticed some positive effects within 24 hours.
In this study, those who drank 1 cup of the beet juice every day had an average drop in blood pressure of around 8/4 millimeters of mercury (mm Hg). For many, this change brought their blood pressure within the normal range. On average, a single blood pressure medication reduces levels by 9/5 mm Hg.
The researchers suggested that beet’s high levels of inorganic nitrate caused the reduction in blood pressure.
It may help to drink a glass of beet juice each day, add beets to salads, or prepare the vegetables as a healthful side dish.
Watermelon contains an amino acid called citrulline, which may help to manage high blood pressure.
Citrulline helps the body to produce nitric oxide, a gas that relaxes blood vessels and encourages flexibility in arteries. These effects aid the flow of blood, which can lower high blood pressure.
In one study, adults with obesity and prehypertension or mild hypertension that took watermelon extract showed reduced blood pressure in the ankles and brachial arteries. The brachial artery is the main artery in the upper arm.
Researchers have also found that animals given a diet rich in watermelon had better heart health. In one study, mice that drank a solution containing watermelon juice had 50 percent less plaque in their arteries than the control group.
The mice that drank the solution also had 50 percent less low-density lipoprotein cholesterol, which many describe as bad cholesterol, and they showed 30 percent less weight gain than the control animals.
To boost watermelon intake, add the fruit to salads and smoothies, or enjoy it in a chilled watermelon soup.
Leafy green vegetables
Leafy green vegetables are rich in nitrates, which help to manage blood pressure. Some research suggests that eating one–two servings of nitrate-rich vegetables every day can reduce hypertension for up to 24 hours.
Examples of leafy greens include: cabbage, collard greens, fennel, kale, lettuce, mustard greens, spinach, and Swiss chard.
To consume a daily dose of green vegetables, stir spinach into curries and stews, sauté Swiss chard with garlic for a tasty side dish, or bake a batch of kale chips.
Fermented foods are rich in probiotics, which are beneficial bacteria that play an important role in maintaining gut health. Eating probiotics can have a modest effect on high blood pressure, according to a review of nine studies.