The Antibacterial, Antiviral, and Antitumor Effects of Gallic Acid
Gallic acid is an organic acid with broad-spectrum antibacterial, antiviral, and antitumor effects. It is a major component of many Chinese medicinals (such as wubeizi/galla chinensis, moshizi/galla, shanzhuyu/cornus, pomegranate, and dahuang/rhubarb). Chinese medicinals containing gallic acid mostly quench thirst and engender fluids, and cool blood to stop bleeding.
Chinese pharmacologists had mastered the method of extracting gallic acid as early as the Ming dynasty. Li Ting's Yi Xue Ru Men (Introduction to Medicine, 1575) records the process of extracting gallic acid from galla chinensis by fermentation: "Coarse galla chinensis powder, mixed evenly with alum and yeast, like making wine yeast, placed in a porcelain vessel covered from the air; wait until white bloom appears, then take out." Li Ting used galla chinensis to extract gallic acid; what he extracted was gallic acid monohydrate, also called gallnut acid. Li Shizhen also recorded this extraction method in Bencao Gangmu (Compendium of Materia Medica): "When long frost-like blooms grow on the medicine, the medicine is done." In the West, the chemist Scheele first extracted gallic acid only in 1786.
Gallic acid has the chemical formula C6H2(OH)3COOH; it is also known as 3,4,5-trihydroxybenzoic acid, and is widely used in pharmaceuticals, dyes, food, inks, organic synthesis, and other fields.
Gallic acid has promising prospects in biopharmaceuticals. It has anti-inflammatory, anti-mutagenic, antioxidant, and free-radical-scavenging biological activities. In vitro, gallic acid inhibits Staphylococcus aureus, Sarcina, alpha-hemolytic Streptococcus, Neisseria, Pseudomonas aeruginosa, Shigella flexneri, Salmonella typhi Hd, and paratyphi A, with a bacteriostatic concentration of 5 mg/ml; hence gallic acid can treat bacterial dysentery. In vitro, at a 3% concentration it inhibits 17 species of fungi and has some inhibitory effect on influenza virus. Gallic acid also kills trypanosomes, protects the liver, and counteracts the physiological and biochemical changes induced by carbon tetrachloride.
Gallic acid also has marked antitumor effects. Animal experiments show it strongly inhibits lung adenomas in mice induced by morpholine plus sodium nitrite. Gallic acid can inhibit mastocytoma metastasis and prolong patient survival.
We can understand how Chinese ancients regarded gallic acid's effects by looking at the properties of several common Chinese medicinals in which it is a main component.
Galla chinensis was the main Chinese medicinal from which ancients extracted gallic acid. It is not a plant fruit; it is actually the larval gall formed when an insect (the horned-gall aphid or the egg-gall aphid) parasitizes plants of the sumac family such as Rhus chinensis, Rhus potaninii, or Rhus punjabiensis. Each early spring, when Rhus branches sprout buds, the spring migratory aphids produce wingless sexual male and female aphids on the leaf buds; after mating they produce wingless parthenogenetic females called "stem mothers." The stem mothers burrow into the tender tissues, stimulating them to swell into warty galls called "horn galls" (the Chinese medicinal galla chinensis). During gall formation the stem mothers vigorously reproduce parthenogenetically, producing many larvae inside the gall; by September-October these larvae gradually develop into winged adults that fly out of the gall. The galla chinensis sold on the market is mostly horn galls picked in September-October; there are also smaller galls picked in May-June, called "belly galls."
Galla chinensis is rich in gallic acid. TCM holds that it is sour and astringent, cold in nature, and enters the lung, large intestine, and kidney channels. It astringes the lung, stops sweating, astringes the intestines, secures essence, stops bleeding, and detoxifies. It treats chronic cough due to lung deficiency, spontaneous and night sweating, chronic dysentery and diarrhea, rectal prolapse, seminal emission, cloudy urine, nosebleed, hematuria, hemoptysis, vomiting of blood, and welling-abscesses and sores.
Bencao Gangmu summarizes galla chinensis's actions comprehensively: "It astringes the lung and drains fire, resolves phlegm-rheum, stops cough, wasting-thirst, night sweating, vomiting of blood, bleeding, chronic dysentery, jaundice, heart and abdominal pain, and infantile night crying; it treats red, moist, eroded eyes, reduces swelling-toxin and throat impediment, astringes ulcers and metal wounds, and lifts prolapsed rectum and prolapsed uterus." Interestingly, galla chinensis may also be the earliest hair dye; Bencao Bei Yao records its hair-dyeing action: "Its color is black; it can dye hair." Galla chinensis is also a common medicinal for skin diseases, because it acts against many fungi.
From these records we can roughly see that galla chinensis excels at treating respiratory diseases, and also stops bleeding and sweating, while also being antibacterial, antidiarrheal, and detumescent—broadly consistent with our current understanding of gallic acid's medicinal value.
Like galla chinensis, moshizi (Turkish gall) is also a gall: it is formed when the larva of the Cynipidae wasp parasitizes the young twigs of oak-family gall trees. Its main components are Turkish gall tannins, gallic acid, ellagic acid, and resin.
Moshizi was imported into China from the Mediterranean, so ancient TCM texts list it among "sea medicines" (medicines from overseas). Traditional TCM holds that moshizi is bitter, warm, and enters the lung, spleen, and kidney channels; it astringes the intestines, secures essence, astringes the lung, and stops bleeding. It treats chronic diarrhea and dysentery, seminal emission, night sweating, cough, hemoptysis, bloody stool, bleeding from trauma, and chronic ulcers that will not close. Its actions and indications closely resemble those of galla chinensis.
Shanzhuyu (Asiatic cornelian cherry fruit) is another gallic-acid-rich medicinal; it is the flesh of the Cornus officinalis plant. TCM holds that shanzhuyu is sour and slightly warm, entering the liver and kidney channels; it supplements and boosts the liver and kidney, and astringes and stabilizes leakage. It treats dizziness and vertigo, deafness and tinnitus, sore and weak lower back and knees, seminal emission and slippery emission, frequent urination, incessant sweating, and uterine bleeding (vaginal bleeding) in women. Shanzhuyu is a famous yin-enriching, kidney-tonifying medicinal—it is contained in Liuwei Dihuang Wan. The late-Qing/early-Republic physician Zhang Xichun even often used shanzhuyu as an emergency medicinal; for patients with yin-blood depletion from profuse sweating or massive hemorrhage, shanzhuyu has an astringent, rescue-from-collapse effect, but it must be used in large doses to be effective.
Pomegranate is a dual-use fruit, but TCM mainly uses pomegranate peel rather than the seeds. Pomegranate peel is rich in gallic acid. TCM holds it to be sour, astringent, warm, and slightly toxic, entering the large intestine channel; it astringes the intestines, stops bleeding, and expels parasites. It treats diarrhea, dysentery, intestinal wind with bleeding, uterine bleeding, vaginal discharge, parasite accumulation, welling sores, scabies and tinea, and burns.
Besides the peel, pomegranate leaves can also be used medicinally, with actions and indications basically similar to the peel; pomegranate leaves also significantly lower serum total cholesterol and triglycerides in hyperlipidemic rats, raise high-density lipoprotein, and strengthen free-radical scavenging. However, pomegranate peel has some toxicity: it contains too much tannin and irritates the gastrointestinal mucosa, and its total alkaloids cause motor impairment and respiratory paralysis in frogs, mice, guinea pigs, rabbits, and cats.
From TCM literature through the ages we can see that the properties of these four gallic-acid-rich medicinals are very close. Antidiarrheal, thirst-quenching, sweating-astringing, hemostatic, cough-relieving, and detumescent are their main actions—precisely the main medicinal values of gallic acid prepared by modern methods.
Leaf-rhubarb (Rheum palmatum) also contains some gallic acid, though its composition is complex; besides gallic acid it also contains rhein, emodin, and other anthraquinones. TCM holds rhubarb to be bitter and cold, entering the stomach, large intestine, liver, and spleen channels. It purges accumulations, clears damp-heat, drains fire, cools blood, dispels stasis, detoxifies, and stops bleeding. It treats excess-accumulation constipation, heat-binding chest glomus, damp-heat dysentery, jaundice, lin syndrome, edema with abdominal fullness, difficult urination, red eyes, swollen painful throat, mouth and tongue ulcers, stomach-heat vomiting, vomiting of blood, hemoptysis, nosebleed, bloody stool, hematuria, blood amassment, amenorrhea, postpartum stasis abdominal pain, concretions and accumulations, traumatic injury, heat-toxin welling sores, erysipelas, and burns. Thus part of rhubarb's actions closely resemble those of the other gallic-acid-containing medicinals.