What are the benefits of Japanese Knotweed?

Japanese Knotweed, scientifically known as Fallopia japonica, is a plant that is attracting increasing interest for its potential health benefits. Native to Asia, this plant has traditionally been used in alternative medicine, but its effectiveness is now being studied in greater depth. In this article, we take a look at the benefits of Japanese Knotweed, based on solid scientific evidence.

What is Japanese Knotweed?

Japanese Knotweed (Reynoutria japonica) is an invasive alien plant native to East Asia. Imported into England between 1825 and 1848, Japanese knotweed is now found in 40 countries. It is one of the most widespread plants in Europe, disrupting ecosystems and promoting soil erosion.

This fast-growing herbaceous perennial is often found on residential properties as an ornamental plant. It colonises various types of soil and prefers open areas such as riverbanks, roadsides, railway lines, wasteland and gardens. By forming dense colonies, it inhibits the growth of other plant species, reducing species diversity. Japanese knotweed also promotes bank erosion, modifies the chemical composition of the soil and the diversity of micro-organisms, and limits access to banks. Its roots and stems can infiltrate cracks in infrastructures.

Japanese knotweed has a network of fleshy rhizomes containing nutrient reserves. These woody rhizomes, dark brown on the outside and orange on the inside, can grow to a depth of 2-3 metres and extend up to 7 metres from the original plant.

The plant consists of several smooth, hollow, bamboo-like stems, green to reddish, sometimes spotted with purple. The leaves are oval to triangular, 7 to 15 cm long and 5 to 12 cm wide, with a truncated base and pointed tip. They alternate on the stems.

The small, creamy-white flowers appear in clusters in August and September and form white fruits. The plant spreads mainly vegetatively via fragments of rhizomes or stems. Various vectors are involved in dispersal, including water, ice, soiled machinery and excavation work.

What is its chemical composition?

Japanese knotweed is the plant richest in resveratrol. This molecule is also present in red wine. Since the 1990s, it has attracted a great deal of interest from biologists and food supplement retailers. According to Bae and Pyee (2004), rhizomes contain around 197 μg/g DM of resveratrol. The stems contain only 9 μg/g, and the leaves contain no trace. Around thirty constituents have been isolated from the rhizomes. These constituents fall into five main classes: anthraquinones, stilbenes, flavonoids, lignans and phenolic compounds.

At the usual therapeutic doses, anthraquinones act as stimulant laxatives. Emodol, an anthraquinone compound, also has oestrogenic properties. Flavonoids include powerful antioxidants. Stilbenes, including resveratrol and its derivatives, have promising pharmacological properties. Resveratrol is present in sufficient quantities for industrial extraction.

The constituents of Polygonum cuspidatum roots vary according to growing conditions, drying and storage. Zhang et al (2004) report a resveratrol content of 6 to 29 μg/g DM. Zhao et al (2005) found up to 1,810 μg/g DM by HPTLC.

In its country of origin, Japanese knotweed is not invasive and does not cause damage to natural environments. In regions where it is introduced, it becomes invasive and harmful. Research into the constituents of P. cuspidatum focuses mainly on the underground parts. These are widely used in traditional Asian medicines. There are also studies on the phytochemistry of the aerial parts.

What are its properties?

The dried rhizome and young leaves of Japanese knotweed are listed in the Chinese pharmacopoeia (1999). In China, it is known as huzhang (虎杖; pinyin: Hǔzhàng). The rhizome is used as an analgesic, antipyretic, diuretic and expectorant. It treats chronic bronchitis, hepatitis, diarrhoea and cancer. It is also effective against hypertension, atherosclerosis, leucorrhoea, burns and snake bites. Knotweed is renowned for its therapeutic properties, and is included in the pharmacopoeia of traditional Chinese medicine. It is also a major source of resveratrol, an antioxidant with potential effects on slowing cell ageing. Hundreds of clinical studies a year are exploring its other properties.

Anti-inflammatory effects

Research has revealed that Japanese Knotweed has marked anti-inflammatory properties, mainly attributed to specific compounds such as quercetin. Quercetin is a flavonoid naturally present in many plants, including Japanese Knotweed. This bioactive substance has been shown to inhibit inflammatory pathways in the body by reducing the production of pro-inflammatory mediators.

Several in vitro studies and studies on animal models have demonstrated these anti-inflammatory effects. By inhibiting inflammatory pathways, quercetin and other compounds in Japanese Knotweed may help to reduce excessive inflammatory responses that are often associated with chronic diseases such as arthritis, cardiovascular disease and autoimmune disorders.

Recently, BRALLEY et al (4) evaluated an ethanolic extract of P. cuspidatum roots in vivo. They measured its ability to block inflammation of the mouse ear caused by TPA (tetradecanoyl phorbol acetate). This inflammation is characterised by oedema and neutrophil infiltration. The study compared the efficacy of the total extract with purified resveratrol and indomethacin when applied topically.

The results showed that 2.5 mg of P. cuspidatum extract reduced oedema and leucocyte infiltration by 73%, compared with 45% for 0.5 mg of indomethacin. Trans-resveratrol alone also exhibited anti-inflammatory activity, significantly reducing plasma levels of prostaglandin D2 and COX-2 expression. However, P. cuspidatum extract was more effective than resveratrol alone.

BRALLEY et al. suggest a synergistic action between resveratrol, quercetin and emodin to explain this superior efficacy. This study demonstrates the anti-inflammatory activity of P. cuspidatum roots when applied topically, indicating the need for further research to verify possible activity when administered orally or parenterally.

Cardiovascular support

Initial investigations suggest a positive role for Japanese Knotweed in cardiovascular health. Some studies show that its compounds reduce blood cholesterol. They also lower blood pressure. They also improve endothelial function.

Compounds in Japanese Knotweed can inhibit the absorption of cholesterol in the intestine. They also modulate lipid metabolism. Certain compounds promote relaxation of the blood vessels. This helps to lower blood pressure and improve circulation.

Specific compounds stimulate the production of nitric oxide. This molecule dilates the blood vessels and regulates blood pressure. By supporting endothelial function, the plant maintains vascular health. It helps prevent disorders such as atherosclerosis.

The stilbenes extracted from the roots of P. cuspidatum show activity on lipid metabolism. In 1982, ARICHI et al. studied the effects of resveratrol and polydatin on blood lipids and the liver of rats. They observed a reduction in blood lipids and atherogenic risk, with an increase in HDL cholesterol and a decrease in LDL cholesterol.

Resveratrol partially inhibits the accumulation of total cholesterol and triglycerides in the liver. Polydatin, administered orally, reduces lipogenesis and modulates lipid metabolism. It inhibits the absorption of lipids and accelerates their use by the muscles. Polydatin reduces serum LDL cholesterol and triglyceride levels. It also reduces their accumulation in the liver, without altering the weight of the animals.

In 2004, PARK et al. showed that aqueous extract of P. cuspidatum roots reduces cholesterol esterification. This inhibition is achieved by acting on acyl-CoA cholesterol transferase (ACAT). This action reduces cholesterol storage, particularly in the liver. Isolated resveratrol also contributes to this inhibition in a dose-dependent manner.

Liver support

KIMURA et al. studied the hepatoprotective effect of the stilbenes in P. cuspidatum. They demonstrated an inhibition of the rise in transaminases with a diet rich in peroxidised lipids. They measured blood transaminase levels in rats fed this diet for 15 days. Some rats were also given oral polydatin. This significantly reduced transaminase levels.

To understand the mechanism of action, KIMURA et al. measured lipid peroxidation in vitro. They used rat liver microsomes. Induction was by ADP and NADPH, in the presence of polydatin and resveratrol. At 5×10-⁴ M, resveratrol and polydatin completely inhibited lipid peroxidation. Stilbenes could inhibit the production of lipid peroxides in rats fed peroxidised fats. They could also inhibit the inflammatory action of lipid peroxides on liver cells.

These studies show that the lipid-lowering properties of resveratrol and its glucoside have been demonstrated in vitro and in vivo. However, further research into plant extracts, rather than isolated molecules, is required. Clinical trials are also required to confirm these properties. This would enable P. cuspidatum to be used as a cardio-protective agent in Europe.

In addition, synthesised resveratrol has shown anti-diabetic activity in in vitro studies. It increases glucose consumption and insulin sensitivity. To attribute anti-diabetic properties to Japanese knotweed, trials on plant extracts are required.

Potential anti-diabetic effects

Studies conducted on animal models suggest that Japanese Knotweed could have beneficial effects for people with diabetes. Extracts of the plant could positively influence blood sugar levels by improving insulin sensitivity. These effects could be attributed to complex mechanisms involving the regulation of glucose absorption at cellular level.

However, it is important to note that these promising results require further investigation before they can be validated in humans. Rigorous clinical studies are needed to assess the efficacy and safety of Japanese Knotweed as a complementary approach to diabetes management.

Oestrogenic activity

The traditionaluse of P. cuspidatum rhizomes to treat the menopause has attracted the attention of researchers. In 2001, MASTUDA et al. studied this property in vitro. They demonstrated the oestrogenic activity of a methanolic extract of P. cuspidatum roots. They used MCF-7 mammary tumour cells, which proliferate under the influence of oestrogen. With 30 µg/ml of extract, proliferation reached 170%, and 276% with 100 µg/ml. They identified that the oestrogenic activity comes from emodin and emodin-8-O-β-D-glucopyranoside. The free hydroxyl groups in positions 2 and 6 are responsible for this activity.

In 2005, ZHANG et al. tested ethanolic extracts of 32 plants from traditional Chinese medicine, using genetically modified yeast to measure oestrogenic activity. The extract of P. cuspidatum showed the greatest relative oestrogenic potential, although it was 100,000 times lower than that of 17 β-estradiol.

In 2006, ZHANG and his team studied the activity of 7 different fractions of the ethanolic extract of P. cuspidatum roots on the same yeast strains. Fractions 1 and 6 proved to be the most active, confirming thatemodin andemodin-8-O-β-D-glucopyranoside have the strongest oestrogenic activity. The concentration required for 50% efficacy (EC50) for emodin is 10-⁵ g/L, compared with 10-⁷ g/L for 17-β-oestradiol.

These studies show a potential oestrogenic activity of P. cuspidatum, but are not sufficient to demonstrate its efficacy in treating menopausal symptoms. AFSSA and AFSSAPS are calling for in vivo tests to validate the use of this plant as a source of phyto-oestrogens. To date, P. cuspidatum has not been selected as a treatment. Further in vivo studies are needed to complete these results.

Antimicrobial activity

In vitro studies have revealed that Japanese Knotweed may offer antimicrobial activity against certain bacterial and fungal strains. These findings suggest a potential use for the plant in the development of natural treatments for infections. The plant’s bioactive compounds can disrupt the growth of pathogenic micro-organisms. This offers alternatives to conventional antibiotics.

In 2006, SONG et al. studied a methanolic extract of dried rhizomes of P. cuspidatum. They tested 20 bacterial strains, including Streptococcus mutans and Streptococcus sobrinus. They measured the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). MICs varied between 0.5 and 4 mg/ml depending on the strain.Gram- bacteria are more sensitive than Gram- bacteria . The methanolic extract, particularly the fraction containing anthraquinones, terpenes and other phenolic compounds, showed significant antibacterial activity.

In 2007, SHAN et al. studied the antibacterial properties of P. cuspidatum roots against common food bacteria: B. cereus, L. monocytogenes, S. aureus, E. coli, and Salmonella anatum. Methanolic extracts, including polydatin (piceid), resveratrol,emodin and physcione, show variable antibacterial activity depending on the strain. Gram- bacteria are generally more sensitive than Gram- bacteria. The activity seems to be linked to the structure of the compounds, in particular the presence of hydroxyl groups.

In 2005, CHANG et al. tested theantiviral activity of ethanolic and aqueous extracts of P. cuspidatum root on human hepatocytes infected with hepatitis B virus (HBV). The extracts significantly inhibited HBV DNA production in a dose-dependent manner. Ethanolic extracts showed stronger HBV inhibitory properties. P. cuspidatum contains active components that are soluble in water and ethanol, each with distinct effects on the regulation of viral replication.

Antioxidant properties

Japanese Knotweed is rich in antioxidant compounds, particularly flavonoids and polyphenols. These powerful antioxidants act as active defenders against free radicals in the body. Free radicals, produced as a result of natural metabolic processes and environmental factors, can cause cell damage and imbalances in the body. The flavonoids and polyphenols in Japanese Knotweed act by neutralising these free radicals, helping to reduce oxidative stress.

Oxidative stress is linked to numerous health problems, including premature ageing, cardiovascular disease and even certain types of cancer. By consuming antioxidant-rich Japanese Knotweed extracts, it is possible to strengthen the body’s defences against these potential risks. It can also help prevent premature cell ageing by maintaining the integrity of cells and tissues.

In 2007, HSU et al. and PAN et al. studied the antioxidant activity of an ethanolic extract of P. cuspidatum roots in vitro. They measured the IC50 in the presence of DPPH (1,1-Diphenyl-2-picrylhydrazyl). They assessed the extract’s ability to trap the superoxide anion and the hydroxyl radical. The researchers tested its inhibition of lipid peroxidation. They also tested its protection of DNA.

The ethanolic extract of P. cuspidatum showed significant antioxidant capacity, particularly for inhibiting lipid peroxidation. In addition, 500 µg/ml of extract inhibited 80% of lipid peroxidation, compared with 70% for 500 µg/ml of resveratrol alone, indicating that other phenolic components contribute to this activity.

PAN et al. recommend the use of P. cuspidatum as an antioxidant in peanut oil, with an IC50 of 0.03 mg/ml to protect the oil from lipid peroxidation, showing a dose-dependent effect. Resveratrol alone has these properties but with less effectiveness, proving that P. cuspidatum contains other antioxidants.

The stems and leaves of P. cuspidatum also show antioxidant activity, attributed to their content of flavonoids and phenolic compounds (excluding resveratrol).

Effects on the skin

Japanese Knotweed also has skin care applications. Certain topical products containing extracts of this plant are marketed for their soothingand anti-inflammatory propertieson the skin. These properties may be attributed to the presence of compounds that modulate the skin’s inflammatory processes and promote cell regeneration.

Tyrosinase is a key enzyme in the metabolism of melanin by melanocytes. Inhibitors of this enzyme can treathyperpigmentation in dermatology. In 2008, LEU et al. studied theanti-tyrosinase activity of anthraquinones (physcione, emodin, citreorosein, anthraglycoside B) and stilbenes (resveratrol, polydatin) extracted by ethanol from P. cuspidatum, as well as their ability to penetrate the skin.

They assessed the in vitro activity of these compounds on fungal tyrosinases, comparing the inhibitory potential of anthraquinones with that ofkojic acid, the reference whitening agent. The stilbenes showed no activity. Physcione showed the most significant inhibitory activity (70%), comparable to that of kojic acid at the same concentration (10 µM).

For topical use, the researchers measured the ability of the anthraquinones to penetrate pig skin. Physcione, although more lipophilic, showed greater transdermal flux when saturated in ethanol solution, compared with emodin, which is more soluble in ethanol.

These results indicate that physcione has a superior transdermal release potential. Further work is required, in particular to verify the efficacy of anthraquinones on human tyrosinases and to ensure their safety on the skin, given their anti-tumour properties.

Anti-allergic

In 2007, Korean researchers studied theanti-allergic activity of an ethanolic extract of P. cuspidatum roots. They carried out several in vitro tests on two types of mast cell: RBL-2H3 (rat) and BMMCs (mouse). When stimulated by IgE-triggered antigens, P. cuspidatum inhibited mast cell degranulation. This inhibition occurs in a dose-dependent manner, with an IC50 of 62 µg/ml for RBL-2H3 and 46 µg/ml for BMMCs. This inhibition is reversible after washing the cells.

The extract also inhibited antigen-induced expression ofTNF-α and IL-4mRNA. At 100 µg/ml, it has the same inhibitory potential as 20 µg/ml PP2, an inhibitor of Src kinases. LIM et al. have shown that this inhibitory activity results from inhibition of the kinases MAP, Syk, LAT, SLP-76, and Gab2. These kinases are involved in type I hypersensitivity.

LIM et al. also measured the anti-allergic effect of P. cuspidatum in mice in vivo. They induced a local allergic cutaneous reaction. The extract administered orally one hour before intradermal injection of antigen and IgE showed a dose-dependent action. This action is comparable to that of diphenhydramine, a classic antihistamine.

These results suggest that the inhibition of mast cell degranulation by P. cuspidatum is due to its effect on Syk kinase. P. cuspidatum therefore has the potential to treat chronic or acute IgE-induced allergies. However, the active chemical components have yet to be identified.

Neuroprotective properties

In 2006, CHENG et al. studied the effect of polydatin on cerebral infarctions in rats. They induced cerebral ischaemia in vivo, then injected rats with polydatin (7.5 mg, 15 mg, 30 mg/kg). Twenty-four hours after reperfusion, the rats’ brains were analysed. They established a neurological deficit score based on the rats’ mobility and state of consciousness.

The results showed that polydatin reduced the neurological deficit in a dose-dependent manner. At 15 mg/kg, polydatin significantly reduced the neurological deficit and cerebral volume affected by infarction, by inhibiting the adhesion molecules responsible for post-ischaemic tissue damage. In this way, polydatin has a protective effect against cerebral ischaemia-reperfusion damage.

In 2007, WANG et al. studiedemodin-8-O-β-D-glucoside, an anthraquinone extracted from P. cuspidatum. They measured neurological deficit and brain area affected by infarction, as well as superoxide dismutase (SOD) activity, total antioxidant capacity and lipid peroxidation. They found that emodin-8-O-β-D-glucoside increases antioxidant activity and SOD, and decreases lipid peroxidation. This anthraquinone crosses the blood-brain barrier and shows a neuroprotective effect by increasing mitochondrial activity and reducing glutamate-induced neurotoxicity.

These studies reveal the neuroprotective potential of P. cuspidatum. Polydatin and emodin-8-O-β-D-glucoside could be used to prevent brain damage caused by ischaemia-reperfusion. Further studies are needed to elucidate their mechanisms of action and effects in humans.

How can it be used?

Various properties are claimed for P. cuspidatum and uses vary according to region, mainly the plant’s roots and rhizomes.

The Chinese Pharmacopoeia lists P. cuspidatum as “Rhizoma et Radix Polygoni Cuspidati”. After the roots have been cleaned, cut into thin slices and dried, they are used to relieve joint pain, treat jaundice, amenorrhoea and coughs with expectoration. Recommended doses are 9 to 15 g of dried root a day. P. cuspidatum is also applied locally in the form of a decoction or cream to treat burns and wounds, and is used in Asian medical treatises for various inflammations, dermatitis, hyperlipidaemia and liver disorders.

In Japan, known as Itadori-Kon, P. cuspidatum is used to prepare an infusion called “Itadori tea”, recommended as a non-alcoholic source of resveratrol. In Korea, P. cuspidatum rhizomes are commonly used to maintain oral and dental hygiene. Today, P. cuspidatum rhizomes are used in food supplements, creams and cosmetic ointments.

P. cuspidatum is used in oils and creams to treat burns, activating cell renewal and reducing pain. It is also used as a skin whitening agent and in the treatment of atopic dermatitis. For the scalp, it is mixed with other plants to combat grey hair and alopecia.

In Asia, P. cuspidatum is used in potions to treat hepatitis B and detoxify the liver. Food supplements use P. cuspidatum as a source of resveratrol to protect the cardiovascular system. A herbal blend containing 10% P. cuspidatum treats coughs, asthma and chronic bronchitis.

In Korea, P. cuspidatum roots are administered orally or dermally to treat allergies. P. cuspidatum is used to relieve general and arthritic pain, combat infectious fevers and benefit from its antibacterial properties.

What are the precautions for use?

Although Japanese Knotweed offers promising prospects in terms of health benefits, it’s important to note that most research is still preliminary. Safety and possible drug interactions must also be taken into account. Before starting any herbal treatment, consult a health professional.

Although Japanese knotweed is used as a medicinal and food plant in Asia, avoid the same uses in France after picking. It often grows on artificial soils containing pollutants such as herbicides, pesticides and heavy metals. Of these substances, the rhizomes are the most concentrated, followed by the leaves and young shoots. This prevents the tender shoots from being eaten raw or cooked, as they are in Japan, where steaming makes them similar to asparagus spears.

Philipp Franz von Siebold reintroduced Japanese knotweed, an invasive alien plant native to East Asia, to Europe in the 19th century. Initially cultivated as an ornamental, melliferous and fodder plant, this plant stands out for the beauty of its foliage and inflorescences. It first appeared in France in 1939.

Today, Japanese knotweed has become naturalised in many European countries, where it poses serious ecological problems. It colonises reclaimed land, roads, railways and waterways. Human activities, particularly the movement of land contaminated by rhizomes and flooding, encourage its dispersal. In Belgium and the UK, laws are in place to eradicate it and prohibit its planting. In France, a law against invasive species does not yet apply to this plant.

Japanese knotweed has a number of ecological and economic impacts:

• Biodiversity: It destroys biodiversity by rapidly occupying available space, creating shade and releasing toxins that slow the growth of other plants.
• Buildings: Its strong roots can penetrate concrete, damaging house foundations and driveway paving.
• Additional costs: The cost of cutting this plant is high, and its dried stems can block culverts, restricting the flow of water.
• Safety: Along watercourses, it weakens banks, increasing the risk of collapse and ice jams. Along roads, it impedes visibility, hiding signs and limiting access to verges.
• User nuisance: It can block access to watercourses, hindering leisure activities and the maintenance of engineering structures. By creating monospecific environments, it tones down the landscape.

In North America, it has been introduced on the east and west coasts of the United States, reaching the Canadian boreal forest. Wherever it becomes established, it suppresses the growth of other plants, threatening the balance of local ecosystems.