Anthraquinone Glycosides

Anthraquinone glycosides are generally orange, red, or brown-red compounds found in fairly limited distribution within the plant kingdom. Their solubility is similar to that of other glycosides with hydrophobic aglycones. Although some aglycones are absorbed within the small intestines, many of the intact glycosides make it to the colon before being hydrolyzed. In traditional Chinese medicine, this fact was exploited, although the rationale was explained differently. Herbs containing anthraquinone glycosides, particularly Rheum palmatum (rhubarb), were administered boiled if noncathartic properties were preferred because this would hydrolyze many of the anthraquinone glycosides. According to one review, boiling reduces the cathartic effects of rhubarb root 50%. Nonboiled forms of the herb were administered when catharsis was the desired outcome.

Anthraquinone glycosides can take 6 to 12 hours or longer to reach the colon, depending on gut motility and transit time of the patient. Once hydrolyzed in the colon, anthraquinones induce water and electrolyte secretion, as well as peristalsis, including catharsis. The contractions caused can be fairly strong and even painful (known as griping); thus, carminatives or antispasmodics are frequently administered simultaneously with anthraquinone glycosides. Use of anthraquinone glycosides for longer than 10 days consecutively can readily lead to induction of atonic constipation as the colon adapts to the cathartic impulses. Persistent use or abuse can also lead to diarrhea with fluid and electrolyte loss and, ultimately, rhabdomyolysis, renal failure, and other severe outcomes.

Some percentage of the anthraquinones are deposited in the colon wall, leaving dark brown or black patches referred to as pseudomelanosis coli. Most clinical research in humans confirms that this does not promote colorec-tal cancer. It is interesting to note that much research in fact shows that anthraquinones are antineoplastic. Emodin, found in rhubarb, is an apopto-sis inducer.

Anthraquinones have other interesting properties. They are antifungal, inhibit excessive renal tubular cell proliferation, delay deterioration of patients in renal failure, modulate inflammation by partially inhibiting cyclooxygenase, and so forth. As far as is known, subcathartic doses or doses of noncathartic forms of herbs containing anthraquinone glycosides do not cause any serious adverse effects and will not cause pseudomelanosis coli. The aglycones can discolor the urine and feces red, brown, or black as they are excreted (Major Anthraquinone Glycoside-Containing Herbs).