Scientific Name(s): Rheum officinale Baillon, Rheum palmatum L., Rheum rhabarbarum L.
Common Name(s): Bo ye da huang, Chinese rhubarb, Da-huang, Danning Pian, Number Ten, Radix et rhizoma rhei, Rhaptonic, Rheum, Rhubarb, Ta-huang, Turkey rhubarb
Rhubarb is derived from several Rheum species. The perennial herb has a conical rootstock, that is fleshy and yellow inside and produces large, cordate, 7-lobed leaves 30 to 46 cm long. The blade or green leaves of the plant are often considered the most poisonous due to high oxalic acid concentration; however, other chemical constituents of the plant are also toxic. The edible stalks are up to 45 cm long and 2.5 to 5 cm in diameter, and are used in pies, jams, jellies, sauces, and juices.1, 2
Medicinal rhubarb consists of the dried rhizome and root of R. officinale Baillon or R. palmatum, of related species/hybrids grown in China (Chinese rhubarb), or of Rheum emodi or Rheum webbianum native to India, Pakistan, or Nepal (Indian rhubarb).3
Rhubarb was first recorded and rated as one of the inferior remedies in the oldest Chinese herbal books, from 22 to 250 AD.4 In the 1780s, the active constituents responsible for the root's cathartic action and astringency were still unknown. Initially, researchers learned that the medicinal root came from several varieties or species of rhubarb. By the end of the 19th century, it became clear that the particular medicinal characteristics of rhubarb were affected by conditions under which the roots grew, such as soil composition and climate.5
Rhubarb has been used medicinally in Europe since the 13th century. The herb was brought from the eastern Mediterranean by way of the Silk Road, which stretches from China across central Asia. The first reported sighting of the plant in situ was in the mountains of Bulgaria. In 1731, a rhubarb commission was set up at the Mongolian border to import the best possible root at a fixed price. At the same time, the British East India Company secured their positions in Chinese ports. Both companies supplied Europe with rhubarb.5
The Rheum species contains a number of anthraquinone derivatives. The free anthraquinones—rhein, emodin, physcion, and chrysophamol—are present in nearly all species.7 Stilbene glycosides, including rhaponticin and the metabolite rhapontigenin, have been identified in the root.4, 7, 8, 9 Tannins, sennosides, catechins, gallic acid, and cinnaminic acid have been identified.7 Lindleyin, a phytochemical with estrogenic activity, has also been described.10 Rhubarb is also a dietary source of resveratrol.57
Uses and Pharmacology
Rhubarb is widely used in traditional Chinese medicine. Most reported clinical trials have been small and poorly designed, and in some studies, a number of different herbs were coadministered with rhubarb, making it difficult to evaluate which herb contributed to the outcomes.
The actions of emodin and hydroxyanthraquinones in managing cancer have been reviewed.12, 13 Cell cycle inhibition of many human cancer lines has been observed in vitro; however, a mechanism of action is unclear.12, 13, 14, 15, 16 Apoptosis, as well as antitumor action, has been demonstrated, and rhubarb extract has been suggested as an adjunct to chemotherapy.12, 13, 17 Antiangiogenic action has also been shown12, 13; clinical trials are lacking.
Rhubarb extract 20 mg/kg daily administered for 6 weeks to patients undergoing radiation therapy for cancer resulted in a reduction in radiation-induced lung toxicity in a randomized clinical trial. Evaluation of anti-inflammatory markers suggests that an anti-inflammatory action of rhubarb is responsible for the effect.18
In addition to the sennosides present in rhubarb extracts, which have been traditionally used as a laxative, emodin and other anthraquinones exert action on the GI tract. Emodin is metabolized in the large intestine by intestinal bacteria and converted to aglycone, which exerts various effects on absorption, secretion, and motility in the tract, and is also suggested to increase peristalsis without affecting the stomach or duodenum.12 It has been used in cases of GI bleeds to eliminate extravasated blood.12, 19
In a study among patients with septicemia, crude rhubarb extract powder 9 g daily was used to preserve GI function. The investigators suggest that increased perfusion of gastric mucosal blood flow, increased excretion of bacteria and toxins, and decreased permeability of intestinal mucous membranes contributed to the positive effects.20
Rhubarb appears to be a potential source of dietary fiber with a lipid-lowering effect. It has been proposed that rhubarb exerts its effects on cholesterol by inhibition of squalene epoxidase.21 This enzyme is thought to catalyze the rate-limiting step in cholesterol biogenesis. An anti-inflammatory action has also been suggested.22
Experiments in mice and rats receiving a cholesterol-enriched diet or with induced diabetic nephropathy/hyperlipidemia showed an improved lipid profile with rhubarb extract compared with control animals.23, 24, 25 Rabbits with induced atherosclerotic plaques and fed a high-cholesterol diet demonstrated a decrease in plaque rupture with either administration of rhubarb extract or simvastatin compared with control. Lipid profiles were improved in the two experimental arms.22
Treating hypercholesterolemia in men with rhubarb stalk fiber for 4 weeks lowered serum total cholesterol and low-density lipoproteins (LDL), while high-density lipoproteins remained unchanged.26 In 103 patients with atherosclerosis randomized to receive the extract for 6 months, rhubarb extract improved the lipid profile in patients with chronic renal failure (CRF) compared with control.25 Individuals taking rhubarb reported decreased LDL compared with those taking placebo and compared with the pretreatment levels.27
Large, randomized clinical trials are lacking. Acute renal failure has been associated with long-term anthraquinone use.28
A number of studies have observed the effects of rhubarb in rats with CRF. Low molecular weight tannins, purified from rhubarb, produced an increase in glomerular filtration rate, decreased levels of uremic toxins, and increased blood flow to the kidneys.25, 29, 30, 31, 32
Use of rhubarb extract in patients with elevated serum creatinine has been reported to prevent progression of CRF. Trials have been conducted comparing captopril and rhubarb. Allocation to rhubarb or captopril produced a slower progression to CRF when compared with controls, and synergism of rhubarb with captopril was demonstrated.32, 33 Other clinical studies have evaluated rhubarb extracts, either alone or with other herbs, in patients with CRF and report reduced uremic symptoms and reduced blood urea nitrogen.34, 35
Mechanisms of action have been proposed and include inhibition of protein decomposition, accelerated reutilization of certain amino acids, reduction of the formation of free radicals, inhibition of overexpression of plasminogen activator inhibitor-1, and suppression of cytokines.32, 34, 36
Acute ischemic stroke
A systematic review and meta-analysis of randomized clinical trials studied the safety and efficacy of rhubarb root and rhizome-based treatment for acute ischemic stroke as add-on therapy to conventional Western medicine. A total of 12 studies enrolling 968 participants were identified; ages of participants ranged from 57 to 69 years, all were Chinese, disease duration ranged from 6 hours to 14 days, and study duration ranged from 1 week to 30 days. Rhubarb-based interventions included Taohe chengqi, Xinglou chengqi, Dachengqi, modified chengqi, and Sanhua. Significant overall clinical efficacy was demonstrated in the rhubarb intervention group compared with Western medicine controls (n = 788; relative risk [RR] = 1.27; P < 0.01); all trials had a relatively high risk of bias and the funnel plot indicated publication bias. No adverse events were reported in the 6 trials that documented occurrences.55
Traditional Chinese medicine suggests rhubarb improves the memory in senile patients.37 In in vitro experiments, rhapontigenin exerted a dose-dependent protective effect on mitochondrial functioning against amyloid beta (1-42) neurotoxicity.8 Clinical trials are lacking.
The anthraquinone derivatives of rhubarb have been used as antifungal38, 39 and molluscicidal40 agents. Rhein has in vitro antimicrobial activity against a wide spectrum of gram-negative and gram-positive bacteria.13, 39, 41
An extract of rhubarb stalk has been used as a dental desensitizer. Calcium oxalate crystals form and occlude the dentinal tubules responsible for sensitization.42
A Cochrane systematic review and meta-analysis of dietary supplements for dysmenorrhea identified only low or very low quality studies with very small sample sizes. No evidence of any difference in effectiveness was found in 1 randomized clinical trial (N = 45) for the treatment of primary dysmenorrhea with rhubarb (1,260 mg twice daily beginning 2 days before menstruation and continued for the first 3 days of menstruation × 3 cycles [2,520 mg/day]) compared to mefanamic acid (250 mg 3 times daily [750 mg/day]). Mild side effects of bloating and diarrhea were noted in the rhubarb group.56
In vitro studies and in vivo experiments in fish show that rhubarb extract possesses estrogenic activity, which has been suggested to be caused by the chemical lindleyin.10
R. officinale has been used in China to treat neonatal jaundice.43 In rats with induced cholestatic hepatitis, total bilirubin was decreased and the liver enzyme profile was improved with administration of emodin.44 A growth-promoting effect, resulting in liver regeneration, has been demonstrated by emodin.12
Crude rhubarb extract 9 g powder was given daily to patients with sepsis.20 Rhubarb extract 20 mg/kg daily was administered for 6 weeks to patients undergoing radiation therapy.18 Patients with atherosclerosis were given rhubarb extract 50 mg/kg for 6 months.27
In Kampo medicine (the practice and adaptation of traditional Chinese medicine in Japan), long-term (12 months) use of rhubarb extract has been administered to improve Oketsu (blood stagnation), and short-term (2 weeks) use has been administered for lazy bowel syndrome.28, 49
Pregnancy / Lactation
Avoid dosages higher than those found in food because safety and efficacy are not proven. Rhubarb extract has been evaluated in pregnancy-related hypertension at 0.75 g daily50; however, anthraquinones may have uterine-stimulant and genotoxic effects.51, 52
Information is lacking.
With long-term overuse, rhubarb may increase the toxic effects of cardiac glycosides. An effect on antiarrhythmics is possible because of the loss of potassium. Potassium deficiency can be increased by concurrent use of thiazide diuretics, corticosteroids, or licorice root. Additionally, deceased intestinal transit time may reduce the absorption of orally administered drugs.53
Localized oxalosis was noted in a case report. A small amount of rhubarb may have adhered to the wall of the tracheobronchial tree, producing a localized area of oxalosis with accompanying necrosis.54 Consumption of rhubarb in patients with renal stones is not advised because of the oxalate content.13
Emodin was mutagenic in several Salmonella typhimurium strains, and has been demonstrated to be phototoxic in vitro.12
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