Can extracts of the tubers and leaves of some species of yam be used to beat cancer, diabetes, pain, arthritis, bone loss, and premenopausal syndrome?
Researchers say the tuber of yam (Dioscorea esculenta) may provide a possible source for the discovery of anti-inflammatory agents (painkillers) without the adverse effects associated with the use of aspirin and other non-steroidal anti- inflammatory drugs.
The study published in African Journal of Biotechnology is titled "Anti-inflammatory studies of yam (Dioscorea esculenta) extract on wistar rats."
The researchers from the Department of Pharmacognosy, University of Ibadan, Ibadan, Oyo State, led by J. O. Olayemi and E. O. Ajaiyeoba, evaluated the defatted methanol extract of Dioscorea esculenta tuber for anti-inflammatory properties in animal model using Wistar rats.
The study was done using the cotton thread method in measuring the right hind paw oedema and granuloma tissue formation in rats. The extract was tested at doses between 100 - 200 mg/kg body weight of rats.
Preliminary phytochemical screening confirmed the presence of saponins, disgenin, -sistosterol, stigmasterol, cardiac glycosides, fat and starch.
The extract exhibited significant inhibition of the carrageenan-induced oedema that was dose-dependent with a good initial effect in one hour and two hour at doses of 100 mg/kg and 150 mg/kg, respectively.
The observed activity was comparable to that of 150 mg/kg acetylsalicylic acid that was used as a reference drug in the study. Dioscorea esculenta tuber methanol extract supports the folkloric use for management of inflammation.
The researchers concluded: "This result indicated that the yam species has anti- inflammatory activity. It seems the anti inflammatory property is short lived and one may suggest this action is quickly metabolized and removed from the system after reaching its peak in two h. This activity is optimally active at doses between 100 mg/kg and 150 mg/kg in the present study.
"A number of adverse effects have been associated with the use of aspirin and other non-steroidal anti- inflammatory drugs. This necessitates the need to source newer compounds from natural products with less or no adverse effects. The tuber of D. esculenta may provide a possible source for the discovery of anti-inflammatory agents."
Commonly called English lesser yam, Chinese yam, Lagos yam and Hausa potato, Dioscorea esculenta belongs to the plant family Dioscoreaceae.
The Yorubas call it igu àlùbọ́sà and odunkun.
Dioscorea esculenta is an edible tuber found in Nigeria, China, Mexico and some other parts of the world. The tuber is a staple food in most parts of West Africa including Nigeria.
Externally, the tuber has been applied to ulcers, boils and abscesses. It contains allantoin, a cell-proliferant that speeds up the healing processes. It has been used traditionally as a contraceptive, in the treatment of menopausal symptoms and various disorders of the genital organs.
It has been suggested for ethno-medicinal uses as an anti-fatigue, anti- inflammatory, anti-stress, anti-spasmodic and immune deficiency remedies in various ethno-medicines. The peel has been reported to possess anticancer and antifungal properties.
The main constituent of Dioscorea species is the well-known saponin, dioscin. The aglycone, diosgenin, is the major starting material used in the industrial production of steroidal hormones. Diosgenin has also been utilized for hundreds of years to treat rheumatism and arthritis-like ailments.
In addition, it is used for spasmodic cough, diarrhea and nausea of pregnant women. Dioscoretine has been shown to be the hypoglycemic agent of Dioscorea dumetorum.
Also, Dioscorea alata has been shown to prevent bone loss in premenopausal women.
Chinese researchers have demonstrated that yam (Dioscorea alata) prevented loss of Bone Mineral Density (BMD) and improved bone calcium status without stimulating uterine hypertrophy in in ovariectomised female BALB/C mice. They concluded that Dioscorea alata might be beneficial for postmenopausal women for preventing bone loss.
The study published in the Journal of the Science of Food and Agriculture is titled "The bone‐protective effect of a Taiwanese yam (Dioscorea alata L. cv. Tainung No. 2) in ovariectomised female BALB/C mice."
Commonly called English winged yam; water yam; white yam; ten-months yam; greater yam; greater asiatic yam; large leaf yam, Dioscorea alata belongs to the plant family Dioscoreaceae.
In Nigeria, it is called ígìorùa and udin in Edo; èbìgè in Efik; baк̉ar dóóya (a wild form) and jikin mutun (man's body) in Hausa; àbìrè in Ibibio; jí àbàlà in Ibo; wùrà in Nupe; agbo in Tiv; akẹnẹdo in Urhobo; ewura in Yoruba.
It is widely grown for consumption after peeling and boiling or baking. It is not mashed nor made into fufu. The uncooked tuber is toxic, and is said to produce narcosis. Saponin is present and cooking renders the tubers safe to eat.
Though it is an exotic plant it has gained and maintains a position of considerable importance in the W African food economy, and it has been pointed out that in the Delta area of Nigeria where traditionally subsistence hinged on fishing, agriculture has been made entirely and only possible on the arrival of exotic food plants amongst them the water-yam.
The other important species are the cocoyam and the plantain. The tuber is high in carbohydrates, 88 per cent. Protein is about seven per cent in Ivorean material.
According to the new study published in the Journal of the Science of Food and Agriculture, yam products have been marketed for treating postmenopausal syndromes.
The study investigated the effects of Dioscorea alata L. cv. Tainung No. 2 (TNG yam) on the bone density of ovariectomised (OVX) female BALB/c mice and the mechanism whereby TNG yam exerted this effect.
Sham and OVX control groups were fed a control diet while remaining OVX mice were randomly allocated into experimental diets, that is yam (630 g TNG powder kg-1), E2 (20 mg 17β‐oestradiol kg-1), or genistein (2 g genistein kg-1) diet. After 12 weeks of feeding, the uterine weight, indices of bone mass and caecal short chain fatty acids were determined.
The results of the study showed neither a yam nor genistein diet restored the OVX‐induced uterine atrophy, as did the E2 diet.
The femoral and lumbar bone mineral density (BMD) of mice fed the yam diet was greater than those of the sham group, respectively (P < 0.05 vs OVX control), while the lumbar BMD of yam and sham groups were similar (P > 0.05 vs sham).
According to the study, the femoral ash and calcium content in the yam group was significantly greater than that in the OVX control group, respectively (P < 0.05 vs OVX control).
The total short chain fatty acid content in the caecum, only enhanced in the yam group, was not correlated with the calcium content of either bone or the plasma calcium level.
Another study has examined the estrogenic effect of yam ingestion in healthy postmenopausal women.
The study published in the Journal of the American College of Nutrition concluded: "Although the exact mechanism is not clear, replacing two thirds of staple food with yam for 30 days improves the status of sex hormones, lipids, and antioxidants. These effects might reduce the risk of breast cancer and cardiovascular diseases in postmenopausal women."
Twenty-four apparently healthy postmenopausal women were recruited to replace their staple food (rice for the most part) with 390 g of yam (Dioscorea alata) in two of three meals per day for 30 days and 22 completed the study.
Fasting blood and first morning urine samples were collected before and after yam intervention for the analyses of blood lipids, sex hormones, urinary estrogen metabolites and oxidant stress biomarker.
The design was a one arm, pre-post study. A similar study of postmenopausal women (n = 19) fed 240 g of sweet potato for 41 days was included as a control study. Serum levels of estrone, estradiol and sex hormone binding globulin (SHBG) were analyzed for this control group.
The results of the study showed that after yam ingestion, there were significant increases in serum concentrations of estrone (26 per cent), sex hormone binding globulin (SHBG) (9.5 per cent), and near significant increase in estradiol (27 per cent).
According to the study, no significant changes were observed in serum concentrations of dehydroepiandrosterone sulfate, androstenedione, testosterone, follicular stimulating hormone, and luteinizing hormone.
Free androgen index estimated from the ratio of serum concentrations of total testosterone to SHBG decreased. Urinary concentrations of the genotoxic metabolite of estrogen, 16α-hydroxyestrone decreased significantly by 37 per cent.
Plasma cholesterol concentration decreased significantly by 5.9 per cent. Lag time of low-density lipoprotein oxidation prolonged significantly by 5.8 per cent and urinary isoprostane levels decreased significantly by 42 per cent.
For the control subjects fed with sweet potato, all three hormone parameters measured were not changed after intervention.
Yet another has examined the effect of combined doxorubicin and Dioscorea esculenta on apoptosis induction in human breast cancer cell.
The study published in AIP Conference Proceedings concluded that the combination of doxorubicin and Dioscorea esculenta is a promising candidate for the treatment of breast cancer cells.
Until now, chemotherapy for breast cancer is largely ineffective, but innovative combinations of chemotherapeutic agents and natural compounds represent a promising strategy.
Nigerian and Indian researchers have also identified a new source of elemol rich essential oil and existence of multicellular oil glands in leaves of the Dioscorea species.
The study was published in Scientific World Journal.
Prof. Olukemi Odukoya and Dr. Joy Odimegwu of the Department of Pharmacognosy University of Lagos; and Dr. Ritesh Yadav and Neelam S. Sangwan of Indian's Central Institute of Medicinal and Aromatic Plants reported for the first time that the leaves of Dioscorea composita and Dioscorea floribunda grown under the field conditions exhibited the presence of multicellular oil glands on the epidermal layers of the plants using stereomicroscopy (SM) and scanning electron microscopy (SEM).
The researchers noted: "Essential oil was also isolated from the otherwise not useful herbage of the plant, and gas chromatographic-mass spectroscopy analysis revealed confirmation of the essential oil constituents. Out of the 76 compounds detected in D. floribunda and 37 from D. composita essential oil, major terpenoids which are detected and reported for Dioscorea leaf essential oil are α -terpinene, nerolidol, citronellyl acetate, farnesol, elemol, α -farnesene, valerenyl acetate, and so forth.
"Elemol was detected as the major constituent of both the Dioscorea species occupying 41 per cent and 22 per cent of D. Floribunda and D. composita essential oils, respectively. In this paper, we report for the first time Dioscorea as a possible novel bio-resource for the essential oil besides its well-known importance for yielding diosgenin."
A study published in the journal Evidence Based Complementary and Alternative Medicine evaluated the effect of an ethanol extract of the rhizomes of Dioscorea alata L. cv. Phyto, Dispo85E, on bone formation and investigated the mechanisms involved.
The study is titled "Anti-osteoporotic Activity of Dioscorea alata L. cv. Phyto through Driving Mesenchymal Stem Cells Differentiation for Bone Formation."
The results showed that Dispo85E increased the activity of alkaline phosphatase (ALP) and bone nodule formation in primary bone marrow cultures. In addition, Dispo85E stimulated pluripotent C3H10T1/2 stem cells to differentiate into osteoblasts rather than adipocytes.
According to the study, the in vivo data indicated that Dispo85E promotes osteoblastogenesis by increasing ALP activity and bone nodule formation in both intact and ovariectomized (OVX) mice. Microcomputed tomography (μCT) analysis also showed that Dispo85E ameliorates the deterioration of trabecular bone mineral density (tBMD), trabecular bone volume/total volume (BV/TV), and trabecular bone number (Tb.N) in OVX mice.
The researchers concluded: "Our results suggested that Dispo85E is a botanical drug with a novel mechanism that drives the lineage-specific differentiation of bone marrow stromal cells and is a candidate drug for osteoporosis therapy."
Osteoporosis is a prevalent bone disease that is defined by a low bone mass and an increased risk of fractures.
Another study published in the Journal Research and www.fasebj.org found that Dioscorea esculenta-induced increase in muscle sex steroid hormones is associated with enhanced insulin sensitivity in a type 2 diabetes rat model.
The Japanese researchers from the Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan; and Graduate School of Human Development and Environment, Kobe University, Kobe, Japan, assessed the effects of chronic Dioscorea esculenta administration and exercise training on muscle sex steroid hormone levels and insulin resistance in type 2 diabetes rats.
Twenty-week-old male Otsuka Long Evans Tokushima Fatty (OLETF) rats were assigned randomly to the control, D. esculenta treatment, D. esculenta with areductase inhibitor treatment, or the exercise training groups (running at 25m /min for one hour, five days/week; n=10 each group).
Eight weeks of D. esculenta treatment or exercise training significantly attenuated the increase in plasma insulin and fasting glucose levels. Plasma and muscle concentrations of dehydroepiandrosterone and 5 a-dihydrotestosterone (DHT) and the expression of 5 a-reductase increased significantly in the
D. esculenta-treated and exercise training groups, and both treatments led to the upregulation of glucose transporter-4 translocation with concomitant increases in PKB and PKC-z/l phosphorylation.
Furthermore, the glucose metabolic clearance rate, which represents insulin sensitivity, increased significantly in both the D. esculenta-treated and exercise training groups. These effects were suppressed by administration of the DHT synthetic inhibitor.
Together, these findings suggest that the D. esculenta-induced increase in muscle sex steroid hormone levels helps decrease insulin resistance in type 2 diabetes.
Another study published in the British Journal of Medicine & Medical Research found that Dioscorea alata reduces body weight by reducing food intake and fasting blood glucose level.
The researchers from the Departments of Physiology, Faculty of Basic Medical Sciences, University of Uyo, Akwa Ibom State, and University of Nigeria,
Nsukka, Enugu State, concluded: "Therefore, we recommend that with further research into the extraction of the active constituent of Dioscorea alata that caused the reduced food intake, this plant could serve as a great therapeutic diet in the management of diabetes."
Until now, Dioscorea alata has been observed to possess flavonoids, which induce anti-diabetic effect, and phenolic compounds which could help in weight management.
It has been postulated that any therapeutic regimes that can limit weight gain while simultaneously controlling blood glucose levels will be effective in managing diabetes. This study was conducted to determine the effect of this rich plant on food intake, blood glucose and body weight in a normal non- diabetic state.