Polygonum cuspidatum, commonly called Japanese knotweed, is a member of the buckwheat family (Polygonaceae). It is also known as P. japonicum, Reynoutria japonica, Pleuropteris zuccarinii, and Polygonum zuccarinii, as well as false bamboo (Gleason & Cronquist, 1963; Rhoads & Klein, 1993; Anonymous, 1997). A native of eastern Asia, this species grows in waste areas throughout the northeastern United States and into southern Canada.
Historically, P. cuspidatum was used in folk medicines as laxatives, and occasionally as foods. However, tannins found in members of this genus are known to be carcinogenic (Lewis & Elvin-Lewis, 1977). Large quantities of condensed tannins isolated from several species, including Japanese knotweed, are found to inhibit trypsin, alpha-amylase, and lipase, which are various digestive enzymes, both in vitro and in the digestive tracts of rats (Horigome, et al, 1988; Lehninger, et al, 1993).
P. cuspidatum is therapeutic in several different ways. Extracts from P. cuspidatum appear to have antipyretic and analgesic activities, as studied in intact mice and rats (Lin & Hsu, 1987). The extracts appeared to confer protection of the gastric membrane against stress ulcers, slight inhibition of gastric secretion, and no effect on blood pressure. However, the drug depressed the activity of the central nervous system in mice (Lin & Hsu, 1987).
Roots of P. cuspidatum contain compounds called stilbenes, which are aromatic hydrocarbons having the general formula C14-H12. One stilbene called resveratrol has several physiological activities. First, it inhibits the growth of several bacteria and fungi (Kubo, et al, 1981). That antimicrobial activity is due to not only to resveratrol, but to 2-methoxy-6-acetyl-7-methyljuglone, a naphthoquinone (Kimura, et al, 1983a; Yamaki, et al, 1988). Second, resveratrol exhibits cancer chemopreventive activity by acting as an antioxidant, antimutagen, and anti-inflammatory agent. It also induces human promyelocytic leukemia cell differentiation (antiprogression activity) and inhibits the development of preneoplastic lesions in mouse mammary glands (Jang, et al, 1997). Third, resveratrol inhibits protein-tyrosine kinase, which catalyzes the phosphorylation of tyrosine (Jayatilake, et al, 1993). This kinase is involved in signal transduction in the cytoplasm of a cell involved in the regulation of mitogenesis (Geahlen, 1997). The inhibition of protein-tyrosine kinase by resveratrol is possibly antimutagenic by deterring the kinaseÕs function. Fourth, resveratrol inhibits lipoxygenase products (Kimura, et al, 1995), which are enzymes found in leukocytes, the heart, brain, lung, and spleen (Lehninger, et al, 1993). Fifth, resveratrol, and its glucoside precursor, piceid, inhibit the deposition of triglycerides and cholesterol in the liver of mice (Arichi, et al, 1982). Resveratrol, piceid, and another stilbene compound, 2,3,5,4Õ-tetrahydroxystilbene-2-O-D-glucoside, reduced the elevation of aspartate transaminase and alanine transaminase by inhibiting lipid peroxidation in the livers of rats (Kimura, et al, 1983b). Analysis of these two enzymes in blood serum gives good diagnostic information for heart and liver damage (Lehninger, et al, 1993). Sixth, these same three compounds have shown potential as an antithrombotic, thus preventing the formation of blood clots within blood vessels (Yuchi & Kimura, 1986).
Polydatin, another stilbene compound isolated from P. cuspidatum, protects myocardial cells injured by deprivation of oxygen and glucose, and chlorpromazine, a tranquilizing agent. It also also inhibits platelet aggregation after treatment with clonidine, an antihypertensive drug (Shan, 1988; Luo, et al, 1990).
P. cuspidatum also produces emodin, an anthraquinone, that has several effects. First, it inhibits the motor activity of a parasitic Schistosoma species (Anantaphruti, et al, 1982). Emodin may also be used in conjunction with known antischistosomal drugs. Second, emodin has antineoplastic and antimutagenic activities. One study showed that emodin decreased the mutagenicity of a quinoline product, found in some cooked foods, by direct inhibition of hepatic microsomal activation (Lee & Tsai, 1991). Emodin also inhibits mutagenicity of 1-nitropyrene, a known mutagen, in a dose-dependent fashion by acting as a blocking and/or suppressing agent to reduce the direct-acting mutagenicity of 1-nitropyrene (Su, et al, 1995). Emodin shows cytotoxicity and inhibition precursor incorporation into DNA and RNA activities, which does not allow expression of genetic information in certain cell lines, in which it has been shown to be an antineoplastic agent (Yeh, et al, 1988; Klug & Cummings, 1994). Like resveratrol, emodin is a strong inhibitor of a protein tyrosine kinase (Jayasuriya, et al, 1992; Chang, 1997; Geahlen, 1997). Chang, et al (1996) isolated three classes of protein-tyrosine kinase inhibitors, anthraquinone, stilbene, and flavonoid, from P. cuspidatum, and found that emodin displayed highly selective activities against two different oncogenes, the src-Her-2/neu and ras-oncogenes.
P. cuspidatum also promotes healing of burns by enhancing immune system and cardiac functions. Luo (1993) studied the effects of P. cuspidatum on the restoration of suppressed cell-mediated, humoral, and non-specific immune functions in scald mice. Administration of P. cuspidatum provided immunomodulating effects in a dose-dependent fashion. Lou, et al (1995) showed that P. cuspidatum restored impaired functions, such as response to antigen signal, the proliferative capacity, interleukin II production, and antibody production ability by lymphocytes, in different degrees in severely burned mice. Severely burned animals survived longer while their neutrophil levels and neutrophilic adhesive rates remained near normal due to treatment with P. cuspidatum (Wu, et al, 1994; Wang, et al, 1994). Wu & Huang (1996) administered P. cuspidatum to rats at the early stage of burn shock and found that plasma TNF levels remained normal, adhesive leukocytes remained nearly normal, disturbances in microcirculation were alleviated, and injury to the lung was attenuated.
Another substance isolated from P. cuspidatum is crystal No. 4, which appears to enhance cardiac and microcirculatory functions during burn shock. Administration of crystal No. 4 restored decreased heart functions, such as cardiac output, cardiac index, and stroke volume index; restored pulse pressure to a normal level; decreased the number of adhesive white blood cells; the amount of open capillaries in muscles returned to near normal, allowing for an increased amount and velocity of blood flow; and the degree of tissue damage in the lung was alleviated (Zhu, 1989; Zhao, 1989; Wu, 1992; Luo & Luo, 1994).
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