Dioscorea alata Linn

Synonyms

Dioscorea atropurpurea Roxb, Dioscorea globosa Roxb, Dioscorea purpurea Roxb. [1] [3]

Vernacular Names:

Malaysia Ubi Gadong Merah, Ubi Jawa (short tuber with white flesh), Ubi Teropong (long white tubers), Ubi Kenduduk (small red tubers), Ubi Nasi (large red tubers), Ubi Tiang, Ubi Merah, Ubi Kipas, Ubi Keledang, Ubi Paha Kerbau, Ubi Sukun, Ubi Ketoping, Ubi Sekol, Ubi Ular, Ubi Telinga Gajah
Indonesia Uwi (Java); Huwi (Sunda)
Thailand Man
India Kaashthaaluka, Aaluka [Ayurveda]; Perumvalli kizhangu [Siddha/Tamil]
China Mao shu
English Greater Yam, Water Yam, Winged Yam. [1] [2] [4] [5] [6]

General Information

Description

Dioscorea alata Linn is a member of the Dioscoreaceae family. It is essentially a twining plant with the stems possessing four or more rows of wings rendering a stellate appearance in cross-section. The wings are also present on the petioles. The stem is usually green but in some cultivars the wings may be purple or reddish due to anthocyanin pigments. There are not spines on the stem. The leaves are ovate deeply cordate with 5-7 nerves and opposite, large and of light green colour. The male flowers are in slender fascicled spikes. The capsule is obcordate measuring 2.5-4cm long. The tuber shape is extremely variable but generally cylindrical. The tuber flesh is white or purplish and loose in texture. They possess a thin layer of though sclerenchymatous fibres just below the tuber skin. [2] [4]

Plant Part Used

Tuber. [1] [2] [6]

Chemical Constituents

1-feruloylglycerol; 2-deoxyribitol; 6-deoxysorbitol; anthocyanins; coenzyme Q(9); cyanidin; D-fructose; D-glucose; diosgenin; gamma-tocopherol-9; glycerol; hydro-Q(9) chromene; ipomeanol; peonidin-3-gentiobioside acylate; sinapic acid; sucrose; RRR-alpha-tocopherol. [1] [7]

Traditional Used:

In Traditional Chinese Medicine, D. alata is believed to fortify the spleen and check diarrhea, nourish the lungs and enrich the kidneys, resolve toxin and close sores. The Indians on the other hand considered it a cholagogue, antispasmodic and diuretic.

Obstetrics and Gynaecologic Disorders

The tuber has been promoted to relieve dysmenorrhoea and reduce symptoms related to menopause or perimenopausal period. A compound found in the tuber, diosgenin probably is the one responsible for this action. Diosgenin  is involved in the commercial production of steroid including oestrogen, progesterone and systemic corticosteroids and androgens. However, this transformation does not seem to occur in the human body. Probably diosgenin acts indirectly to improved the perimenopausal symptoms as indicated in the two clinical trials cited below. [1] [2] [6] [8] [9]

Other uses

The plant is used in the treatment of diarrhea, frequency of micturition, cough, diabetes mellitus, ulcerating sores, burns and scalds. [6]

Pre-Clinical Data

Pharmacology

Oestrogenic activity

The ethyl acetate extracts of D. alata tubers was found to activate oestrogen receptors alpha and beta. A total of five compounds isolated (hydro-Q(9) chromene, gamma-tocopherol-9, RRR-alpha-tocopherol, coenzyme Q(9) and feruloylglycerol) seem to activate human ER alpha and beta. This could explain the effects of D. alata tuber on menopausal symptoms in the clinical studies below. [7] [8] [9]

Antiosteoporotic activity

The in vitro study of the effects of ethanol extract of tuber of D. alata on primary bone marrow cultures showed that it could increase the activity of alkaline phosphatase and bone marrow nodule formation and at the same time stimulate Pluripotent C310T1/2 stem cells to differentiate into osteoblasts rather than adipocytes,. The in vivo studies showed that it promotes osteoblastogenesis by increasing alkaline phosphatase activity and bone nodule formation in both intact and ovariectomised mice. A microcomputed tomography analysis indicated that the extract could ameliorate the deterioration of trabecular bone mineral density, trabecular bone volume/total volume and trabecular bone number in ovarectomised mine. [10]

Nutritional value

The tuber of seven cultivars of D. alata were found to contain a total of 7.4% crude protein, 75.6-84.3% starch, vitamin C 13.0-24.7mg/100g fresh weight, total oxalates 486-781 mg/100g dry weight with 50-75% in water soluble form. It was also found to have good amounts of minerals. The phytic acid content was low, 58.6 to 198.0mg/100g dry weight. This indicates the overall nutritional superiority of the yam. [11]

Gylcaemic index

The glycaemic index of D. alata was found to be 62 (sem 6). It was found that boiling helps reduce the glycaemic index while roasting or baking causes it to increase. [12] [13]

Antidiabetic activity

The alloxan induced diabetic rats showed positive response towards treatment with 100 and 200mg/kg dose of ethanol extract of tubers of D. alata. After 21 days of treatment the blood glucose level significantly reduced by 47.48% (in 100mg dose) and 52.09% (in 200mg dose). There was also a reversal of serum lipid levels, total protein, albumin and creatinine to near normal levels.

Another extract of D. alata tagged as Dispo85E, was found to enhance the clearance of AGEs (advanced glycation end products) through HGF (hepatocyte growth factor)-induced autophagic-lysosomal pathway. Dispo85E was found to also improve retinal and renal functions in  AGEs-induced diabetic mice.

D. alata shows good potential in not only being developed into an antidiabetic drug but also could also help ally diabetic vascular complications. [14] [15]

Antifibrosis activity

The aqueous extract of D. alata was found to show anti-fibrosis activity by down regulating the TGF-beta/smad signaling pathway and modulating EMT (Epithelial-mesenchymal transition in kidneys) expression. This was evidenced by the fact that it could suppress beta-HB-induced expression of fibronectin in NRK-49F cells (rat fibroblast cells) concomitantly with the inhibition of Smad2/3, pSmad2/3 and Smad4 and increased in Smad7 expression. The extract was also seen to decrease alpha-SMA (alpha-smooth muscle actin) and MMP-2 levels with an increase in E-cadherin expression.  [16]

Immuno-modulating activity

Dioscorin is a glycoprotein that could be isolated from D. alata. This compound was found to have the ability to stimulate phagocytosis of RAW264.7 cells against E.coli while at the same time it was able to stimulate proliferation of splenic cells to the tune of 1.38 to 1.48-fold in a dose dependent manner. This compound was found to be an activator of TLR4 (Toll-like receptor 4)-signaling pathway which is crucial for activating both innate and adaptive immunity. This is evidenced by the fact that dioscorin is able to induce TLR4-downstream cytokine expression in bone marrow cells isolated from TLR4-functional C3H/HeN mice. It was found to also stimulate multiple signaling molecules i.e. NF-kappaB, ERK, JNK and p38 and induced the expression of cytokines (TNF-alpha, IL-1beta, and IL-6) in murine RAW 264.7 macrophages. ERK, p38, JNK, and NF-kappaB-mediated pathways are all involved in dioscorin-mediated TNF-alpha production.

In comparing the dioscorin from two different species (i.e. D. alata and D. japonica), it was found that the dioscorin from D. alata has a higher ability to stimulate phagocytic activity while that from D. japonica has higher ability to enhance the proliferation of lymphoid cells. [17] [18] [19]

Antioxidant activity

Freeze-dried powder of D. alata was proven to have antioxidative effects as evidenced by its ability to reverse the hyperhomocysteinemia induced by methionine in rats. Other biomarkers of oxidative stress seen together with hyperhomocysteinaemia that was reversed by the presence of D. alata included lowered platelet aggregation, malondialdehyde, and hepatic reactive oxygen species. There was observed increase in hepatic catalase and glutathione/glutathione disulphate ratio. However, it did not induce activity of antioxidant enzymes such as hepatic superoxide dismutase, glutathione peroxidase and glutathione reductase. [20]

Antihypertensive activity

The glycoprotein and its hydrolysates showed inhibitory activity against angiotensin converting enzyme (ACE) in a dose dependent manner. Dioscorin showed mixed non-competitive inhibition with an apparent inhibition constant (Ki) of 1.738 microM in a dose of 31.25 microg (0.8microM). It was found that the process of pepsin hydrolysis could increase the ACE inhibitory activity from 51 % to 75% at 32 hours of hydrolysis.

Different processing technique had different impact on the antihypertensive activity of D. alata tuber. Powdered yam products, water extract of yam tuber and heated water extract were found to be the more effective process in reducing blood pressure of spontaneous hypertensive rats. [21] [22]

Toxicities

Toxicity study on D. alata yam water extract did not show any form of toxicity in both kidneys and liver. On the contrary the extract showed protective activity against damage by acetaminophen challenge to the kidneys and liver of rats. [23]

Teratogenic effects

No docementation

Clinical Data

Clinical Trials

Two clinical trials were recorded for the plant whereby the oestrogenic effects were studied. The first study done in China to looked at the oestrogenic effects of consuming D.alata tubers in postmenopausal women. The study proved that by replacing two thirds of staple food with D. alata tubers for 30 days there was significant improvement in the status of sex hormones, lipids, and antioxidant in the women under study. They found a significant increase in serum concentration of estrone (26%), sex hormone binding globulin (SHBG) (9.5%), and estradiol (27%). The urinary concentration of the genotoxic metabolite of oestrogen, 16alpha-hydroxyestrone decreased significantly by 37% and those of isoprostanes decreased by 42%. There was also a significant decrease in cholesterol level by 5.9%.

In the study done on Taiwanese women was to assess the efficacy of D. alata on reducing menopausal symptoms. They found that 12mg D. alata extract given in a dose to 2 sachet daily did improve symptoms related to menopause, especially the psychological parameters. A safety monitoring showed no signs of adverse reaction during the period of administration i.e. 12 months. They found that these women reported general improvement in almost all the clinical symptoms investigated. There was a significant reduction in the total Greene Scores especially for the psychological parameters of anxiety (feeling tense or nervous [p=0.007]; insomnia [p=0.004]; excitable [p=0.047]; musculoskeletal pain [p=0.019]). The extracts also showed positive effects on blood hormone profiles. [8] [9]

Adverse Effects in Human:

No documentation

Used in Certain Conditions

Pregnancy / Breastfeeding

No documentation

Age Limitations

Neonates / Adolescents

No documentation

Geriatrics

No documentation

Chronic Disease Conditions

No documentation

Interactions

Interactions with drugs

There exist possible interactions with anti-diabetic and anti-hypertensive therapeutics. Users of these drugs should be cautious when taking D. alata as food or medicine. [14] [15] [21] [22]

Interactions with Other Herbs / Herbal Constituents

No documentation

Contraindications

Contraindications

No documentation

Case Reports

No documentation

References

1. Khare CP. Indian Medicinal Plants: An Illustrated Dictionary Springer-Verlag, Berlin 2007 pg. 215
2. Hu SY. Food Plants of China China University Press, Hong Kong 2005 pg. 144 – 145
3. Onwueme, IC, Charles WB. Tropical Root and Tuber Crops: Production, Perspectives and Future Prospects Food and Agriculture Organization (FAO), Rome 1994 pg. 52
4. Ridley HN. Flora of the Malay Peninsula Volume 4 L. Reeve & Co. Ltd. London 1924 pg. 319
5. Burkill IH. A Dictionary of the Economic Products of the Malay Peninsula Volume 1, Ministry of Agriculture and Cooperatvies, Malaysia, Kuala Lumpur 1966, pg. 826 – 828
6. Zhou J. Encyclopedia of Traditional Chinese Medicine Volume 5 Springer-Verlag, Berlin pg. 428
7. Cheng WY, Kuo YH, Huang CJ. Isolation and identification of novel estrogenic compounds in yam tuber (Dioscorea alata Cv. Tainung No. 2). J Agric Food Chem. 2007 Sep 5;55(18):7350-8. Epub 2007 Aug 8.
8. Wu WH, Liu LY, Chung CJ, Jou HJ, Wang TA. Estrogenic effect of yam ingestion in healthy postmenopausal women. J Am Coll Nutr. 2005 Aug;24(4):235-43.
9. Hsu CC, Kuo HC, Chang SY, Wu TC, Huang KE. The assessment of efficacy of Diascorea alata for menopausal symptom treatment in Taiwanese women. Climacteric. 2011 Feb;14(1):132-9. doi: 10.3109/13697137.2010.498594. Epub 2010 Jul 23.
10. Peng KY, Horng LY, Sung HC, Huang HC, Wu RT. Antiosteoporotic Activity of Dioscorea alata L. cv. Phyto through Driving Mesenchymal Stem Cells Differentiation for Bone Formation. Evid Based Complement Alternat Med. 2011;2011:712892. doi: 10.1155/2011/712892. Epub 2011 Jun 29.
11. Wanasundera JP, Ravindran G. Nutritional assessment of yam (Dioscorea alata) tubers. Plant Foods Hum Nutr. 1994 Jul;46(1):33-9
12. Ramdath DD, Isaacs RL, Teelucksingh S, Wolever TM. Glycaemic index of selected staples commonly eaten in the Caribbean and the effects of boiling v. crushing. Br J Nutr. 2004 Jun;91(6):971-7.
13.Bahado-Singh PS, Wheatley AO, Ahmad MH, Morrison EY, Asemota HN. Food processing methods influence the glycaemic indices of some commonly eaten West Indian carbohydrate-rich foods. Br J Nutr. 2006 Sep;96(3):476-81.
14. Maithili V, Dhanabal SP, Mahendran S, Vadivelan R. Antidiabetic activity of ethanolic extract of tubers of Dioscorea alata in alloxan induced diabetic rats. Indian J Pharmacol. 2011 Jul;43(4):455-9. doi: 10.4103/0253-7613.83121.
15. Peng KY, Horng LY, Sung HC, Huang HC, Wu RT. Hepatocyte growth factor has a role in the amelioration of diabetic vascular complications via autophagic clearance of advanced glycation end products: Dispo85E, an HGF inducer, as a potential botanical drug. Metabolism. 2011 Jun;60(6):888-92. 
16. Liu SF, Chang SY, Lee TC, Chuang LY, Guh JY, Hung CY, Hung TJ, Hung YJ, Chen PY, Hsieh PF, Yang YL. Dioscorea alata attenuates renal interstitial cellular fibrosis by regulating Smad- and epithelial-mesenchymal transition signaling pathways. PLoS One. 2012;7(11):e47482. 
17. Fu SL, Hsu YH, Lee PY, Hou WC, Hung LC, Lin CH, Chen CM, Huang YJ. Dioscorin isolated from Dioscorea alata activates TLR4-signaling pathways and induces cytokine expression in macrophages. Biochem Biophys Res Commun. 2006 Jan 6;339(1):137-44. Epub 2005 Nov 9.
18. Liu YW, Shang HF, Wang CK, Hsu FL, Hou WC. Immunomodulatory activity of dioscorin, the storage protein of yam (Dioscoreaalata cv. Tainong No. 1) tuber. Food Chem Toxicol. 2007 Nov;45(11):2312-8. Epub 2007 Jun 14.
19. Lin PL, Lin KW, Weng CF, Lin KC. Yam storage protein dioscorins from Dioscorea alata and Dioscorea japonica exhibit distinct immunomodulatory activities in mice. J Agric Food Chem. 2009 Jun 10;57(11):4606-13. 
20. Chang SJ, Lee YC, Liu SY, Chang TW. Chinese yam (Dioscorea alata cv. Tainung No. 2) feeding exhibited antioxidative effects in hyperhomocysteinemia rats. J Agric Food Chem. 2004 Mar 24;52(6):1720-5.
21. Hsu FL, Lin YH, Lee MH, Lin CL, Hou WC. Both dioscorin, the tuber storage protein of yam (Dioscorea alata cv. Tainong No. 1), and its peptic hydrolysates exhibited angiotensin converting enzyme inhibitory activities. J Agric Food Chem. 2002 Oct 9;50(21):6109-13.
22. Liu YH, Lin YS, Liu DZ, Han CH, Chen CT, Fan M, Hou WC. Effects of different types of yam (Dioscorea alata) products on the blood pressure of spontaneously hypertensive rats. Biosci Biotechnol Biochem. 2009 Jun;73(6):1371-6. Epub 2009 Jun 7.
23. Lee SC, Tsai CC, Chen JC, Lin JG, Lin CC, Hu ML, Lu S. Effects of "Chinese yam" on hepato-nephrotoxicity of acetaminophen in rats. Acta Pharmacol Sin. 2002 Jun;23(6):503-8.