Biological effects of knotweed
According to the WHO’s recommendation and given the consumer’s negative viewpoint about chemical medications, the demand for herbal medicines, mostly in the developing countries, has increased over the past few years. Among the herbal medicines, those with antioxidant properties that are used for treating diseases like Parkinson’s disease, Alzheimer, cancers, cardiovascular diseases, and so on, have drawn a greater deal of attention. These plants are rich of natural antioxidants that interrupt generation and function of free radicals and hold great promises for treating such diseases (Hsu, 2006; Rathore et al., 2015). Natural antioxidants are polyphenolic compounds (Flavonoid, Tannin, and Anthocyanin) that are found in different parts of the plant like leaf, stem, fruit, root, and even seeds (Ahmadvand et al., 2013). Therefore, extractions of secondary metabolites (such as essence and essential oil) from different parts of herbal plants demonstrate antibacterial, antifungal, antiparasitic, and antioxidant effects (Semnani et al., 2007). Antioxidant properties of herbal medicines depend on polyphenol compounds found in them. These useful chemicals not only used as medication but also as a unique pattern for the development of medicine analogues and a useful model to have a better perception of biological phenomena (Asgari Jahromi et al., 2013).
Knotweed or polygonum avicular from polygonaceae family has semi-erect stem that reaches 50cm in length. The leaves are alternate and narrow with pointy tip and separate with odorless, and small flowers in green with pink edges. Knotweed is highly resistive to external factors like cold, heat, or being trodden and it is found in grasslands, road side, abandoned farms, and rock cracks. This annual plant is found in Australia, Europe, north/south of Africa, Mediterranean, the Middle East, and India (Rathore et al., 2015). In Iran, it can be seen in forests and humid climates like Guilan, Mazandaran, Azerbaijan, and Chahrmahl o Bakhtirai provinces (Ansari et al., 2014).
The chemical composition of knotweed includes, oxalic acid, acetic acid, formic, tannin, nitrate, potassium, glucose, essence, silica, oxy methyl anthraquinone, resins, saccharides, and mucilage (Askari-Jahrom et al., 2013; Rathore et al., 2015). The fruits contain 18% protein, 71% carbohydrate, 64% fat, and 9.1% fiber; along with 0.7mg vitamin b2, 670mg calcium, 420mg phosphor, 12.7mg iron in each 100gr (Srivastava, 2006; Rahore et al., 2015). The herbal plant is astringent and prescribed for diarrhea and bloody diarrhea in particular and to control bleeding. In addition, it is used to treat asthma, bronchitis, pulmonary tuberculosis, eczema, intestine inflammation, edema, stomachache, migraine, infected wounds, sciatica pain, backache, Gout pain, rheumatism, burn and blister. The plant is also used to control fever, stomach secretions, female secretion, blood sugar, constipation, pain, and bile and urinary stones. It is notable that excessive use of the plain results in eczema, hives, skin allergy, and seizure (Liu et al., 2001; Ahmadvand et al., 2013; Hsu, 2006).