Scientists demonstrate how extracts of cocoyam (Colocasia esculenta) leaves and yam (Dioscorea species) products could be used to reduce blood pressure and ‘cure’ cancer.
Hypertension is a chronic and asymptomatic to symptomatic disorder characterised by a persistently elevated blood pressure (BP) exceeding 140/90 mmHg or greater. Cardiovascular disease alone accounts for nearly 30 per cent of all deaths worldwide and 10 per cent of all years of healthy life lost to the disease.
Colocasia esculenta (CE) is traditionally used for the treatment of various ailments such as high blood pressure, rheumatic pain, pulmonary congestion, etc. Hence in the present study, the effect of aqueous extract of CE leaves (AECE) was evaluated for antihypertensive and acute diuretic activity in rats.
A preliminary phytochemical evaluation, published in Iran Journal of Pharmaceutical Research, revealed the presence of carbohydrates, saponins, tannins, and flavonoids in AECE.
The animals did not show any sign of toxicity and mortality after the administration of AECE 2000 mg/Kg in acute oral toxicity study. The administration of AECE (100, 200, and 400 mg/Kg/day, p.o.) for six weeks and AECE (10, 20, and 40 mg/Kg, IV) on the day of the experiment in renal artery-occluded hypertensive rats and AECE (20 and 40 mg/Kg, IV) in noradrenalin-induced hypertension in rats produced significant anti-hypertensive effects.
AECE (400 mg/Kg, p.o.) showed positive diuretic activity at 5 h. AECE (200 and 400 mg/Kg, p.o.) significantly increased sodium and chloride content of urine in five hours and 24-hour and additionally potassium in 24-hour urine.
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“Hence, the results of the present study revealed the antihypertensive and weak diuretic activity of AECE. These effects may be attributed due to the ACE inhibitory, vasodilatory, β-blocking, and/ or Ca2+ channel blocking activities, which were reported for the phyto-constitunts, specifical flavonoids such as vitexin, isovitexin, orientin, and isoorientin present in the leaves of CE.”
According to the study, Taro is the common name for edible aroids, which are important staple foods in many parts of the world, particularly in Asia and the Pacific Islands. Within the family Araceae, there is one ‘‘true taro’’, namely CE. Extract of CE leaves has been traditionally used for the treatment of various ailments in Ayurveda and Unani medicine. CE is traditionally used in various diseases such as high BP, hepatic disorder, rheumatic pain, pulmonary congestion, ulcers etc. The CE has been reported for anti-inflammatory, hypolipidemic, anti-cancer, antioxidant, and antibacterial activities.
The leaves of Colocasia esculenta contain flavonoids such as vitexin, isovitexin, orientin, isoorientin, schaftoside, isoschaftoside, luteolin, apigenin, vitamins A, B, and C, thiamine riboflavin, niacin, oxalic acid, and minerals such as magnesium, calcium, phosphorus, sodium, potassium, iron, zinc, copper, and boron. Some of these phytoconstituents are reported for ACE inhibitor, hypotensive, anti-inflammatory, antispasmodic, vasodilatory, and β-blocking, Ca2+ channel blocking, and diuretic activity.
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Also, powdered-yam-products (PYP) and water extracts of yam tuber (WEY) were found effectively to reduce the blood pressure of Spontaneously Hypertensive Rat (SHR) and should be beneficial in food processing in the development of functional foods for blood pressure regulation.
The study titled “Effects of Different Types of Yam (Dioscorea alata) Products on the Blood Pressure of Spontaneously Hypertensive Rats” was published in the journal Bioscience Biotechnology and Biochemistry.
The researchers are from the Graduate Institute of Biomedical Materials and Tissue Engineering, Taipei medical university, Taiwan, Taipei.
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The aim of the study was to investigate different yam treatments, including PYP and liquid-yam-products (LYP), with respect to spontaneously hypertensive rats (SHRs) blood pressure.
PYP included alcohol-insoluble solids of yam tuber, hot-air-drying (HAD) of yam tuber slices, and steam-cooked once or twice followed by HAD which were subsequently powdered.
LYP included WEY heated at 90 degrees C (WEY90H) or 95 degrees C for 10 minutes (WEY95H) and then stored at 4 degrees C for different numbers of days. PYP, WEY, and WEYH were found effectively to reduce the blood pressure of SHR and should be beneficial in food processing in the development of functional foods for blood pressure regulation.
Another study on the “Potential health benefits of water yam (Dioscorea alata)” published in the journal Food & Function by researchers at Kwame Nkrumah University of Science and Technology and International Institute of Tropical Agriculture concluded the low sodium but high potassium and total dietary fibre (TDF) contents indicate the possible preventive role that (yam) Dioscorea alata could play in managing related chronic diseases.
“This shows the potential use of D. alata as a functional food to supplement the fibre and mineral needs of consumers. Thus, there is a need to exploit its use in food fortifications and formulations,” it noted.
Yam is the third most important root and tuber crop in the tropics but few species are grown as health food and/or for medicinal purposes. To ascertain the potential health benefits and alternate usage of the species, 20 varieties of Dioscorea alata (water yam) were investigated for their TDF, dry matter and amylose contents as well as selected minerals in comparison with Dioscorea rotundata, the preferred species in yam-growing areas.
The results show significant differences among the test varieties in all the parameters determined. Generally, the test varieties had lower dry matter but higher amylose contents. “TDF contents of the varieties were higher than that reported for brown rice, while two varieties had comparable values to whole wheat flour. Identified varieties with higher amylose and TDF contents could be of use to diabetics and other health-conscious individuals due to their slower absorption rates.”
Another study published in the journal Foods and titled “The Dioscorea Genus (Yam)—An Appraisal of Nutritional and Therapeutic Potentials” concluded: “Dioscorea species provide safety nets as foods and conventional and unconventional medicine during famine and endangered periods. Yam constituents such as flavonoid, diosgenin and dioscorin, tannin, saponin and total phenols place them as good food source of bioactive compounds to consumers.
“…Investigation to study the medicinal potential of over 600 wild and domesticated Dioscorea species requires a multidisciplinary dimension involving indigenous natives who have a thorough grasp of these plants while adopting a well thought out strategy that puts into context society, health, conservation and sustainable use of species biodiversity. Numerous synthetic contraceptives and steroid-related hormonal medications are made of dioscin. Unfortunately, the global need for dioscin is around 8000 tons but present production status puts it at 3000 tons.
“Further in vivo study is highly encouraged with respect to oxidative stress and antioxidant activities using purified compounds isolated from yam species. For most developing and poor countries, it is imperative to diversify into functional foods, including from Dioscorea species. These can be consumed on a regular basis thus serving both nutritional and medicinal purposes. These plants, often in the wild, can be targeted for increased production and conservation. The local populace should be enlightened on the consumption values which directly can lead to a reduction in the cost of health care while leading to an improved diet.
“Recently, the poisoning cases are occasionally reported in association with the rising popularity of Dioscorea consumption prescriptions in clinical use. Chronic and excessive exposure to D. bulbifera tuber has caused liver injury in some patients.
Also, in vivo and in vitro experimental studies have demonstrated that D. bulbifera tuber could induce hepatotoxicity, increase relative liver weight and can cause death. It is noteworthy to mention that concentrated herbal preparations of samples of Dioscorea species abound, with most of them having little or no information about the exact composition and required dosage, thereby increasing health risks to potential consumers. It thus becomes imperative to establish estimated toxicity values for Dioscorea species towards efficient utilisation in food-based clinical management.
“Scientific investigations into the clinical use of Dioscorea species with a focus on reducing the risk of ovarian cancer, treatment of menopause complications and female ageing diseases needs to focus on characterising the bioactive compounds and proteins isolated from diverse species. This includes amino acid sequencing, in vivo pharmacokinetic study as well as modulating mechanisms. This will help in the establishment of multi-target-based anti-menopausal drug screening, towards developing more effective drug candidates for future use.
“Furthermore, research to support the use of Dioscorea as a therapeutic agent against asthma, urinary tract infections and bladder-related complications, rheumatism, arthritis, pelvic cramps and so forth, need to be promoted. Most of the studies have been limited to in vitro and animal models.
It is very important to have further insights into the effects of yam on degenerative diseases while putting into consideration the feasibility and long-term effects on humans. Limited or no data on safety, toxicity and efficacy as use as contraceptives on human health, during pregnancy, lactation and childhood suggest an issue of concern.
The paucity of data on the safety of diosgenin and other bioactive compounds suggests that further investigation should focus on development, toxicity, neurotoxicity and allergenicity. While preclinical and mechanistic findings tend to support the use of diosgenin as a novel, multi-target-based chemo-preventive and therapeutic agent against different forms of cancer, research should also focus on developing and evaluating standards of evidence.
“On a commercial scale, the introduction of Dioscorea extracts into the growing international market of natural herbs is highly encouraged. The Mexican experience of biodiversity loss of wild Mexican yams should form the basis for conscious sustainable natural resource management, especially in Africa as mentioned earlier.”
In vitro cytotoxicity screening provides insights and preliminary data that help select plant extracts with potential anticancer properties for future work and in vivo replication. A study by Itharat et al. showed that aqueous and ethanol extracts of the rhizome of D. membranacea and D. birmanica were cytotoxic against three human cancer cell lines while remaining non-cytotoxic to normal cells.
The use of active compounds naphthofuranoxepins (dioscorealide A and B) and dihydrophenanthrene from D. membranacea (locally known as Hua-Khao-yen) rhizome in Thai medicine is highly potent and has exhibited cytotoxic activity against five types of human cancer cells. This was supported by a more recent study, which highlighted the utilisation of dioscorealide B as a possible anticancer agent for liver cancer and cholangiocarcinoma.
The hepatotoxic compound diosbulbin B has also been reported as a major anti-tumour bioactive component of D. bulbifera (air potato) in a dose-dependent manner, with no significant toxicity in vivo at dosage between 2 and 16 mg/kg.
Notwithstanding the availability of numerous anti-diabetic medicines in the pharmaceutical industry and market, diabetes and related complications remain a medical burden.
Plants’ anti-diabetic potential stems from their ability to restore the function of the pancreatic tissues, which leads to three possible outcomes: increasing the insulin output, inhibiting the intestinal absorption of glucose and restoring the facilitation of metabolites in insulin-dependent processes.
There is minimal evidence on specific action pathways in the treatment of diabetes; however, we can infer that most plants that contain bioactive substances such as flavonoids, alkaloids and glycosides offer a buffer to patient management.
D. dumetorum, commonly known as bitter yam, has long been proven to play active role in the treatment of diabetes in traditional medicine due to its hypoglycemic effect. Literature reveals that aqueous extract of D. dumetorum tuber; known for its alkaloid (discretize) content, control hypercholesterolemia, hyperlipidemia and hyperketonemia.
In 2015, a study, which evaluated the anti-diabetic potential and free radical scavenging activity of copper nanoparticles (CuNPs) synthesise with the aid of D. bulbifera tuber extract revealed promising anti-diabetic and antioxidant properties.
In animal studies, extract of D. bulbifera and D. alata tuber showed significant reduction in blood glucose level as well as increased body weight in rats treated with streptozotocin and alloxan, respectively.
Another study showed, however, that consumption of D. bulbifera by female diabetic rats decreased hyperglycemia and bone fragility. A similar trend was observed on dexamethasone-induced diabetic rats treated with D. polystachya extract.
The quest for novel drugs in the clinical treatment of diabetic complications such as peripheral neuropathy has led to the discovery of DA-9801, an ethanol extract of D. japonica, D. rhizoma and D. nipponica, as a potential therapeutic agent.
Peripheral neuropathy is a common disorder among diabetic patients, a result of the malfunctioning of the peripheral nerves. Peripheral neuropathy is characterised by symptoms such as pain, numbness and chronic aberrant sensations, which often disrupt sleep and can lead to depression, thus affecting the quality of life.
An investigation conducted by Song et al. on the inhibitory effects of DA-9801 on transport activities of clinically important transporters showed that inhibitory effects in vitro did not translate into in vivo herb-drug interaction in rats.
Interestingly, Jin et al. and Moon et al. further buttressed the potential therapeutic applications of DA-9801 for the treatment of diabetic peripheral neuropathy. These studies show that DA-9801 reduced blood glucose levels and increased the response latency to noxious thermal stimuli. It is anticipated that DA-9801 can be used as a botanical drug for the treatment of diabetic neuropathy.
Transporters are critical in the absorption, distribution and elimination of drugs, thus modulating efficacy and toxicity. This prediction of interaction is vital in clinical studies and the drug development process. Sato et al. demonstrated that the natural product diosgenin remains a candidate for use in acute improvement of blood glucose level in type I diabetes mellitus. Also, Omoruyi supports the use of D. polygonoides extracts in clinical management of metabolic disorders such as diabetes.
Jeong et al. reported the anti-obesity effect of D. oppositifolia extract on diet-induced obese mice. In their study, a high-fat diet was given to female mice with 100 mg/kg of n-butanol extract of D. oppositifolia for eight weeks.
The authors observed a significant decrease in total body weight and parametrial adipose tissue weight; as well as a decrease in total cholesterol, triglyceride level and low-density lipoprotein (LDL)-cholesterol in blood serum; female mice associated with the ingestion of D. oppositifolia n-butanol extract. The observed effect of D. oppositifolia n-butanol extract is mediated through suppression of feeding efficiency and absorption of dietary fat.
An earlier study, which evaluated the anti-obesity effect of methanol extract of D. nipponica Makino powder, reported the effectiveness of the extract against body and adipose tissue weight gains in rodents induced by a high-fat diet.
The anti-obesity potential of the extract of D. serious tubers extracted using a solvent cold percolation method has been reported. When compared with a commercially available anti-obesity medication (herbex), D. serious tubers extract showed a significantly higher anti-obesity activity.
The author attributed the result to be associated with the bioactive compounds of D. serious tubers, which can act as lipase and α-amylase inhibitors and thus are useful for the development of anti-obesity therapeuticals.
Extracts of Dioscorea species have been used in the clinical management of other metabolic disorders such as abnormal cholesterol level. Several animal studies have shown the antilipemic effects of sapogenin and diosgenin-rich extract of Dioscorea species like D. polygonoides (Jamaican bitter yam) on hypercholesterolemic animals such as mice and rat, thus resulting in the reduction in the concentrations of blood cholesterol.
Another study which investigated the effect of D. alata L. on the mucosal enzyme activities in the small intestine and lipid metabolism of adult Balb/c mice showed constant improvement in the cholesterol profile of the liver and plasma of mice fed with 50 per cent raw lyophilized yam for a duration of 21 days.
The authors also observed an increase in fecal excretions of neutral steroid and bile acids whereas absorption of fat was reduced in mice fed with 50 per cent yam diet. Yeh et al. observed a significant reduction in plasma triglyceride and cholesterol in male Wistar rat as a result of consumption of a 10 per cent high cholesterol diet supplemented with 40 per cent D. alata.
In an animal study using Swiss albino mice with streptozotocin-induced dementia, D. bulbifera tubers were reported as having the potential to preserve memory while serving as a preserving, curing and restorative agent.
The authors further highlighted the possible delay of onset of neurodegenerative diseases as well as mitigation with the ingestion of dietary polyphenols that confer protection against oxidative stress and neurodegeneration.
Also, the neuro-protective effect of D. pseudojaponica Yamamoto using senescent mice induced by D-galactose indicated the useful potential of yam for treatment of cognitive impairment; a process partly mediated via enhancing endogenous antioxidant enzymatic activities.
The steroidal saponin—diosgenin—one of the major bioactive compounds in yam was found to aid the restoration of axonal atrophy and synaptic degeneration, thus improving memory dysfunction in transgenic mouse models of Alzheimer’s disease.
Diosgenin administration prior to surgery in rat test models reduced significantly the death rate while improving impaired neurological functions, thus establishing the potential cerebral protection of diosgenin against transient focal cerebral ischemia-reperfusion (I/R) injury.
Menopause is associated with a decline in estrogen level produced by the ovaries resulting in several side effects including mental changes, hot flashes, skin ageing, osteoporosis and cardiovascular problems.
Hormone replacement therapies (HRT) such as estrogen and progesterone replacement have been deployed to handle these challenges with side effects; however, HRT may predispose users to the development of degenerative diseases such as ovarian cancer.
Rossouw et al. reported an increase in the incidence of coronary heart disease and breast cancer amongst women on estrogen and progestin therapy, hence necessitating alternative treatment options that are as effective and less detrimental.
Many traditional systems have implemented treatment plans with a number of plant species for the management of physiological changes associated with menstruation, conception, pregnancy, birth, lactation and menopause.
There is reported evidence that Dioscorea species while serving as nutritional supplements proffer medicinal properties and relief of menopausal symptoms. A Taiwanese study examined the efficacy of D. alata in the treatment of menopausal symptoms in 50 women.
The authors recorded an evident improvement in the accessed parameters, including feeling tense/nervous or excitable, insomnia, musculoskeletal pain as well as the positive effect of the blood hormone profile among women that received D. alata.
Similarly, Wu et al. found that replacing two-thirds of staple food with yam for 30 days positively influenced antioxidant status, lipids and sex hormones of 22 apparently healthy postmenopausal women.
Chinese anti-menopausal medicine formula containing rhizomes of D. oppositifolia L. have shown the potential to regulate serum levels of estrogen, follicle-stimulating hormone and luteinizing hormone thereby alleviating some side effects in post-menopausal women. This is in line with the study by Lu et al., whose research result supports the use of D. oppositifolia in Chinese medicine for easing menopausal disorders.
Proteins isolated from D. alata, D. zingiberensis and D. oppositifolia showed potential to upregulate the translational levels of estrogen receptor beta, thus possibly reducing the risk of ovarian cancer. D collettii var. hypoglauca have been implicated in the production of herbal formula feng bei bi xie used primarily for the treatment of cervical carcinoma, which is prevalent within female aging period.
In Central America, patients with blood stasis and anemic conditions are treated with a decoction obtained from the rhizomes of D. bartletti; while in Latin American communities, the use of decoctions to ameliorate pains of childbirth, painful menstruation, ovarian pains and vaginal cramping have been reported.
The diosgenin composition of yam has placed Dioscorea species as major constituents for commercial progesterone production used for the treatment of menopausal hot flashes. When administered orally to female Sprague Dawley rats, Higdon et al. reported an increase in uterine weight, vaginal opening, vaginal cell proliferation and reduced bone loss.
This estrogenic influence mechanism is consistent with the findings of Michel et al. who reported mild in vitro biding affinity for estrogen alpha and beta-receptors in their test models.
Although an in vitro bioassay does not necessarily correspond to in vivo efficacy, the data seem to implicate a significant influence of Dioscorea species in the management of issues related to women’s reproductive health.