Plant Profiler

Wild yam (Dioscorea villosa)


Wild yam (Dioscorea villosa) Image
Synonyms / Common Names / Related Terms
Atlantic yam, barbasco, batata silvestre, black yam, China root, colic root, devil's bones, Dioscorea, Dioscorea barbasco, Dioscorea hypoglauca, Dioscorea macrostachya, Dioscorea opposita, Dioscorea villosa, Dioscoreae (family), diosgenin, Mexican yam, natural DHEA, phytoestrogen, potassium, rheumatism root, shan yao, white yam, wild yam root, yam, yellow yam, yuma.

Note: "Yams" sold in the supermarket are actually members of the sweet potato family and are not true yams.



Mechanism of Action

Pharmacology:

  • Constituents: The species considered to be yams are defined by their constituent, diosgenin. This saponin is present in species originating in North America or in Asia. Medicinal species include Dioscorea villosa, D. opposita, D. hypoglauca, D. composata, D. deltoida, D. parazeri, D. mastrostachya, D. floribunda, and D. barbasco. The principal Mexican wild yam species are D. macrostachya and D. barbasco. Common names include Atlantic yam, China root, colic root, devil's bones, Mexican wild yam, rheumatism root, and yuma. African species may not have the same chemical constituents (although African Dioscorea species possess hypoglycemic effects, hypoglycemia is not observed after administration of Mexican wild yam [D. macrostachya, D. barbasco]).
  • Dioscoreaceae Villosa includes saponins (diosgenin, dioscin) and an alkaloid (dioscorin).3,15 Diosgenin is considered the primary active ingredient in wild yam, and is structurally similar to cholesterol.
  • Diosgenin levels vary markedly between different yam species.4,5 Consumers can expect a considerable range of diosgenin-related effects based on the source species as well as technique of growing, harvesting, processing, and storage conditions. Typical standardization of wild yam products is to 10% diosgenin per dose. In one study, white, yellow, and black yams had a potassium content >200mg (5.1mEq)/100g following leaching in water, normal cooking, and double cooking.18
  • Hormonal properties: Estrogenic and anti-inflammatory effects of diosgenin have been hypothesized as due to structural similarities to estrogen precursors. However, no natural progesterones, estrogens, or other reproductive hormones are found in Dioscorea. Diosgenin is not converted into hormones in the human body, and can only be transformed into progesterone through chemical manipulation.3 Synthetic progesterone has reportedly been added to some wild yam products. In ovariectomized mice, 20-40mg/kg of the wild yam constituent diosgenin, injected subcutaneously each day for 15 days, was found to stimulate mammary gland epithelial growth without observed progestinic effects.19 Furthermore, based on in vitro study, wild yam root may possess antagonistic (blocking) activity, including antiestrogenic activity.6
  • Lipid-lowering properties: Diosgenin has been found in multiple animal studies to decrease intestinal cholesterol absorption and reduce total serum cholesterol levels. In everted rat jejunum, diosgenin has been found to competitively inhibit cholesterol absorption.7 Giving Wistar rats 1% diosgenin in their diets increases biliary cholesterol output 200-400%.8,9 Diosgenin has been found to reduce the total body pool of cholesterol.10 Hypercholestoleremic rats treated with diosgenin have experienced decreased cholesterol absorption, increased hepatic cholesterol synthesis, and increased biliary cholesterol secretion with no alteration in serum cholesterol.11,12,16 Hypercholesterolemic mice fed a 1% diosgenin diet for 15 days have had decreased cholesterol absorption, increased fecal excretion of cholesterol, and decreased plasma cholesterol levels.13 Hypercholesterolemic rats fed both clofibrate and diosgenin have shown a greater decrease in LDL cholesterol than those fed either compound alone; however, the combination partially reversed the elevation in HDL cholesterol seen in the diosgenin-only group.12
  • Administering vitamin C enhanced the cholesterol-lowering effects of clofibrate and diosgenin.14 In hypercholesterolemic monkeys, a synthetic analog of diosgenin decreased absorption of dietary cholesterol, increased biliary secretion of endogenous cholesterol, and reduced hypercholesterolemia.2
  • In rats, oral administration of diosgenin increases cholesterol and phospholipid content in hepatocyte cell membranes while maintaining cholesterol/phospholipid molar ratios. Secretion of surfactant-like cholesterol and lipid vesicles also increases. These changes have been hypothesized to mediate protection against bile salt toxicity.20
  • Other properties: Feeding rats a 0.5% diosgenin diet for seven days almost completely prevents indomethacin-induced ulcers and lowers serum indomethacin levels.17 In rats with cholestasis induced by estradiol-17β, diosgenin increases biliary secretion. However, estrogen-induced morphologic changes appear to be unaffected.20 Diosgenin and dioscin have been shown to inhibit fungal growth in vitro.1

Pharmacodynamics/Kinetics:

  • After oral administration, diosgenin is metabolized in the liver and eliminated via the bile.16

References

  1. Vasiukova, N. I., Paseshnichenko, V. A., Davydova, M. A., and Chalenko, G. I. [Fungiotoxic properties of steroid saponins from the rhizomes of deltoid dioscorea]. Prikl Biokhim Mikrobiol  1977;13(2):172-176. 866299
  2. Malinow, M. R., Elliott, W. H., McLaughlin, P., and Upson, B. Effects of synthetic glycosides on steroid balance in Macaca fascicularis. J Lipid Res 1987;28(1):1-9. 3559397
  3. Araghiniknam M, Chung S, Nelson-White T, and et al. Antioxidant activity of Dioscorea and dehydroepiandrosterone (DHEA) in older humans. Life Sciences 1996;59:L147-L157.
  4. Datta K, Datta SK, and Datta PC. Pharmacognostic evaluation of potential yams Dioscorea. Journal of Economic and Taxonomic Botany 1984;5:181-196.
  5. Huai, Z. P., Ding, Z. Z., He, S. A., and Sheng, C. G. [Research on correlations between climatic factors and diosgenin content in Dioscorea zingiberensis Wright]. Yao Xue Xue Bao  1989;24(9):702-706. 2618721
  6. Rosenberg Zand, R. S., Jenkins, D. J., and Diamandis, E. P. Effects of natural products and nutraceuticals on steroid hormone-regulated gene expression. Clin Chim Acta 2001;312(1-2):213-219. 11580929
  7. Juarez-Oropeza, M. A., Diaz-Zagoya, J. C., and Rabinowitz, J. L. In vivo and in vitro studies of hypocholesterolemic effects of diosgenin in rats. Int J Biochem 1987;19(8):679-683. 3622900
  8. Ulloa, N. and Nervi, F. Mechanism and kinetic characteristics of the uncoupling by plant steroids of biliary cholesterol from bile salt output. Biochim Biophys Acta 11-14-1985;837(2):181-189. 4052446
  9. Nervi, F., Bronfman, M., Allalon, W., Depiereux, E., and Del Pozo, R. Regulation of biliary cholesterol secretion in the rat. Role of hepatic cholesterol esterification. J Clin Invest 1984;74(6):2226-2237. 6511924
  10. Zagoya JCD, Laguna J, and Guzman-Garcia J. Studies on the regulation of cholesterol metabolism by the use of structural analogue, diosgenin. Biochemical Pharmacology 1971;20:3471-3480.
  11. Nervi, F., Marinovic, I., Rigotti, A., and Ulloa, N. Regulation of biliary cholesterol secretion. Functional relationship between the canalicular and sinusoidal cholesterol secretory pathways in the rat. J Clin Invest 1988;82(6):1818-1825. 3198756
  12. Cayen, M. N. and Dvornik, D. Effect of diosgenin on lipid metabolism in rats. J Lipid Res 1979;20(2):162-174. 438658
  13. Uchida, K., Takase, H., Nomura, Y., Takeda, K., Takeuchi, N., and Ishikawa, Y. Changes in biliary and fecal bile acids in mice after treatments with diosgenin and beta-sitosterol. J Lipid Res 1984;25(3):236-245. 6726078
  14. Odumosu, A. How vitamin C, clofibrate and diosgenin control cholesterol metabolism in male guinea-pigs. Int J Vitam Nutr Res Suppl 1982;23:187-195. 6811480
  15. Zakharov, V. N. [Hypolipemic effect of diosponine in ischemic heart disease depending on the type of hyperlipoproteinemia]. Kardiologiia  1977;17(6):136-137. 197285
  16. Cayen, M. N., Ferdinandi, E. S., Greselin, E., and Dvornik, D. Studies on the disposition of diosgenin in rats, dogs, monkeys and man. Atherosclerosis 1979;33(1):71-87. 111685
  17. Yamada, T., Hoshino, M., Hayakawa, T., Ohhara, H., Yamada, H., Nakazawa, T., Inagaki, T., Iida, M., Ogasawara, T., Uchida, A., Hasegawa, C., Murasaki, G., Miyaji, M., Hirata, A., and Takeuchi, T. Dietary diosgenin attenuates subacute intestinal inflammation associated with indomethacin in rats. Am J Physiol 1997;273(2 Pt 1):G355-G364. 9277414
  18. Burrowes, J. D. and Ramer, N. J. Removal of potassium from tuberous root vegetables by leaching. J Ren Nutr 2006;16(4):304-311. 17046614
  19. Aradhana, Rao, A. R., and Kale, R. K. Diosgenin--a growth stimulator of mammary gland of ovariectomized mouse. Indian J Exp Biol 1992;30(5):367-370. 1459613
  20. Accatino, L., Pizarro, M., Solis, N., and Koenig, C. S. Effects of diosgenin, a plant-derived steroid, on bile secretion and hepatocellular cholestasis induced by estrogens in the rat. Hepatology 1998;28(1):129-140. 9657105




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