Astragalus

Scientific Name(s): Astragalus membranaceus (Bunge), and Astragalus membranaceus var. mongholicus (Bunge) P.K. Hsiao, Family: Fabaceae (beans)

Common Name(s): Huang chi , huang qi , astragalus

Uses

Astragalus root may have use in the restoration of immune function after cancer chemotherapy and for the treatment of HIV infection. However, there are no clinical trials to support any of these uses.

Dosing

There is no recent clinical evidence to guide dosage of astragalus products; however, typical recommendations are 2 to 6 g daily of the powdered root.

Contraindications

Contraindications have not yet been identified.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

None well documented.

Adverse Reactions

Astragalus extract was mutagenic in the Ames test for possible carcinogens.

Toxicology

No data.

Botany

The genus Astragalus , commonly known as milk vetches, is comprised of more than 2,000 species distributed worldwide. The Chinese A. membranaceus and the related A. mongholicus are thought to be varieties of the same species. 1 Both are perennial herbs native to the northern provinces of China and are cultivated in China, Korea, and Japan. The dried root is used medicinally. Astragalus roots are sold as 15 to 20 cm long pieces that have a tough, fibrous skin with a lighter interior. It is sold as shredded roots, and in powder, tincture, and encapsulated form. Some products are produced by frying the roots with honey, although the untreated root itself also has a sweet, licorice-like taste.

History

Astragalus root use is very old and well-known in traditional Chinese medicine and is listed in the Pharmacopoeia of China . It is used in China principally as a tonic and for treatment of diabetes and nephritis. It is an important component of Chinese Fu Zheng herbal therapy, in which the goal is to restore immune system function. There is extensive Chinese-language literature on the herb/plant.

Chemistry

A polymerase chain reaction method for measuring astragalus content in a polyherbal preparation has been published. Markers for each component were developed using decamer oligonucleotide primers. 2 Hairy root cultures of astragalus have been established and produced cycloartane saponins. 3 , 4 , 5

Astragalus root contains a series of cycloartane triterpene glycosides denoted astragalosides Ι to VΙΙ, that are based on the genin cycloastragenol and contain 1 to 3 sugars attached at the 3-, 6-, and 25-positions. 6 , 7 , 8 , 9 In the predominant astragalosides Ι to ΙΙΙ, the 3-glucose is acetylated. Several saponins based on the oleanene skeleton also have been reported. 10 The aboveground parts of astragalus contain similar but distinct saponins in the cycloartane series, 11 , 12 and many other species of astragalus contain cycloartane saponins. 13

A variety of immune polysaccharides have been reported from astragalus root. Astragalan Ι is a neutral 36 kD heterosaccharide containing glucose, galactose, and arabinose, while astragalans ΙΙ and ΙΙΙ are 12 kD and 34 kD glucans, respectively. 1 , 14 Three similar polysaccharides and an acidic polysaccharide, AG-2, were isolated. 1 A complex 60 kD acidic polysaccharide, AMem-P, with a high hexuroic acid content from A. membranaceus 15 and a similar but distinct 76 kD acidic polysaccharide, AMon-S from A. mongholicus were reported. 16 Polysaccharides known as astroglucans A-C from A. membranaceus were patented. 17

Isoflavan glycosides based on mucronulatol and isomucronulatol have been found in the roots of A. membranaceus . 9 , 18 Several products appear to use these compounds for standardization despite the lack of reported biological activity. In addition, the free isoflavones afrormosin, calycosin, formononetin, and odoratin have been isolated from the roots. 19 , 20

A unique biphenyl was isolated from A. membranaceus var. mongholicus as an antihepatotoxic agent. 18

Uses and Pharmacology

Immunostimulant

The most common use of astragalus root in herbal medicine in the United States is as an immunostimulant to counteract the immune suppression associated with cancer chemotherapy. This use is based on several observations.

Animal/Clinical data

The cycloartane saponins are capable of stimulating the growth of isolated human lymphocytes. 13 The polysaccharides astragalans Ι and ΙΙ were found to potentiate immunological responses in mice following intraperitoneal administration but not after oral administration. 14 The glycans AMem-P and AMon-S increased phagocytic indices with intraperitoneal injection into mice. 15 , 16

Aqueous extract of astragalus root stimulated phagocytosis of murine macrophages and augmented proliferation of human monocytes in response to phytohemagglutinin, concanavalin A, and pokeweed mitogen. 21 , 22 In cells from cancer patients, which were comparatively resistant to such stimulation, astragalus extract also stimulated mononuclear cells. Using a graft versus host (GVH) model, astragalus extract restored the GVH reaction in vivo for healthy and immunosuppressed patients. 23

These in vitro and in vivo effects justify further human trials of the immunostimulant activity of astragalus root extracts in patients whose immune systems have been suppressed by cancer chemotherapeutic drug regimens.

HIV

Another use of astragalus root in the United States is in the treatment of HIV infection. It may help reduce opportunistic infections, but such use depends on a host-mediated response because the aqueous extract of astragalus has no direct effect on viral infectivity 24 and little effect on viral reverse transcriptase. 25

Animal data

Research reveals no animal data regarding the use of astragalus in HIV.

Clinical data

A pilot trial of a Chinese herbal formulation containing astragalus root was found to improve subjective measures and symptomatology; however, the number of subjects was too small to detect statistically meaningful effects. 26

A series of unverified reports from China claim that treatment with herbal mixtures including astragalus can induce seronegative conversion in a small fraction of HIV patients. 27 , 28

In view of revised opinions on the population dynamics of the HIV virus in infected humans, an attempt to stimulate T-cell proliferation may not be a realistic therapeutic objective because the turnover rate is rapid. Nevertheless, improvement in subjective symptoms in the above study 26 cannot be ignored, and a larger clinical trial might confirm these effects as important.

Other uses

Astragalus often is recommended for the prevention of the common cold; however, there are no published clinical trials that support this use.

The biphenyl compound 4,4′,5,5′,6,6′-hexahydroxy-2,2′-biphenyldicarboxylic acid 5,6:5′,6′-bis (methylene), 4,4′-dimethyl ether, dimethyl ester was isolated as the antihepatotoxic principle of astragalus root. 18 The isoflavones afrormosin, calycosin, and odoratin had antioxidant activity similar to butyl hydroxytoluene or alpha-tocopherol in several experimental models of air oxidation of lipids. 19 , 20

Astragalus root saponins also has diuretic activity presumed to be caused by local irritation of the kidney epithelia. 29 Astragalus saponins showed anti-inflammatory and hypotensive effects in rats. 1

Dosage

There is no recent clinical evidence to guide dosage of astragalus products; however, typical recommendations are 2 to 6 g daily of the powdered root. 30

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

None well documented.

Adverse Reactions

Research reveals little or no information regarding adverse reactions with the use of this product.

Toxicology

An astragalus hot water extract that had been boiled for 90 minutes was mutagenic in the Ames test in S. typhimurium TA98 when activated by S9 rat liver fractions. The activity was dose-dependent. In addition, the mutagenic activity was not removed by XAD-2 resin treatment. The same preparations given by intraperitoneal injection at 1 to 10 g/kg produced chromosomal aberrations in the bone marrow of mice, and increased the incidence of micronucleated cells in bone marrow. No attempt was made to isolate the mutagenic compounds responsible for these effects. 31

The pharmacology and toxicology of the genus Astragalus have been reviewed. 32

Bibliography

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3. Hirotani M, Zhou Y, Rui H, Furuya T. Cycloartane triterpene glycosides from hairy root cultures of Astragalus membranaceus . Phytochemistry . 1994;37:1403-1407.
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11. Zhu YZ, Lu SH, Okada Y, Takata M, Okuyama T. Two new cycloartane-type glucosides, Mongholicoside Ι and ΙΙ, from the aerial part of Astragalus mongholicus . Chem Pharm Bull . 1992;40:2230-2232.
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