The roots and rhizomes of licorice (Glycyrrhiza) species have long been used worldwide as a herbal medicine and natural sweetener. Licorice root is a traditional medicine used mainly for the treatment of peptic ulcer, hepatitis C, and pulmonary and skin diseases, although clinical and experimental studies suggest that it has several other useful pharmacological properties such as antiinflammatory, antiviral, antimicrobial, antioxidative, anticancer activities, immunomodulatory, hepatoprotective and cardioprotective effects. A large number of components have been isolated from licorice, including triterpene saponins, flavonoids, isoflavonoids and chalcones, with glycyrrhizic acid normally being considered to be the main biologically active component. This review summarizes the phytochemical, pharmacological and pharmacokinetics data, together with the clinical and adverse effects of licorice and its bioactive components.

Review of Pharmacological Effects of Glycyrrhiza sp. and its Bioactive Compounds

Pyrrolizidine alkaloid-containing plants are widely distributed in the world and are probably the most common poisonous plants affecting livestock, wildlife, and humans. Because of their abundance and potent toxicities, the mechanisms by which pyrrolizidine alkaloids induce genotoxicities, particularly carcinogenicity, were extensively studied for several decades but not exclusively elucidated until recently. To date, the pyrrolizidine alkaloid-induced genotoxicities were revealed to be elicited by the hepatic metabolism of these naturally occurring toxins. In this review, we present updated information on the metabolism, metabolizing enzymes, and the mechanisms by which pyrrolizidine alkaloids exert genotoxicity and tumorigenicity.

Pyrrolizidine alkaloids--genotoxicity, metabolism enzymes, metabolic activation, and mechanisms.

Hepatic sinusoidal obstruction syndrome associated with consumption of Gynura segetum

Glycyrrhizin is the major active component extracted from licorice (Glycyrrhiza glabra) roots, one of the most widely used herbal preparations for the treatment of liver disorders. This study evaluated the potential beneficial effect of glycyrrhizin in a mouse model of carbon tetrachloride (CCl(4))-induced liver injury. The mice were treated intraperitoneally with CCl(4) (0.5 ml/kg). They received glycyrrhizin (50, 100, 200, 400 mg/kg) 24 h and 0.5 h before and 4 h after administering CCl(4). The serum activities of aminotransferase and the hepatic level of malondialdehyde were significantly higher 24 h after the CCl(4) treatment, while the concentration of reduced glutathione was lower. These changes were attenuated by glycyrrhizin. CCl(4) increased the level of circulating tumor necrosis factor-alpha markedly, which was reduced by glycyrrhizin. The levels of hepatic inducible nitric oxide synthase, cyclooxygenase-2, and heme oxygenase-1 protein expression were markedly higher after the CCl(4) treatment. Glycyrrhizin diminished these alterations for inducible nitric oxide and cyclooxygenase-2 but the protein expression of heme oxygenase-1 was further elevated by the treatment of glycyrrhizin. CCl(4) increased the level of tumor necrosis factor-alpha, inducible nitric oxide synthase, cyclooxygenase-2, and heme oxygenase-1 mRNA expressions. The mRNA expression of heme oxygenase-1 was augmented by the glycyrrhizin treatment, while glycyrrhizin attenuated the increase in tumor necrosis factor-alpha, inducible nitric oxide synthase, and cyclooxygenase-2 mRNA expressions. These results suggest that glycyrrhizin alleviates CCl(4)-induced liver injury, and this protection is likely due to the induction of heme oxygenase-1 and the downregulation of proinflammatory mediators.

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Protective mechanism of glycyrrhizin on acute liver injury induced by carbon tetrachloride in mice.

The traditional Chinese medicines (TCMs) are essential components of alternative medicines. Many TCMs are known to alter the expression of hepatic drug-metabolizing enzymes and transporters. The molecular mechanism by which TCMs and/or their constituents regulate enzyme and transporter expression, however, has remained largely unknown. In this report, we show that two TCMs, Wu Wei Zi (Schisandra chinensis Baill) and Gan Cao (Glycyrrhiza uralensis Fisch), and their selected constituents activate the xenobiotic orphan nuclear receptor pregnane X receptor (PXR). Treatment with TCM extracts and the Schisandrol and Schisandrin constituents of Wu Wei Zi induced the expression of drug-metabolizing enzymes and transporters in reporter gene assays and in primary hepatocyte cultures. The affected enzymes and transporters include CYP3A and 2C isozymes and the multidrug resistance-associated protein 2. In transient transfection and reporter gene assays, the Schisandrin constituents of Wu Wei Zi had an estimated EC50 of 2 and 1.25 microM on hPXR and mPXR, respectively. Interestingly, mutations that were intended to alter the pore of the ligand-binding cavity of PXR had species-specific effects on the activities of the individual Schisandrols and Schisandrins. In rats, the administration of Wu Wei Zi and Gan Cao increased the metabolism of the coadministered warfarin, reinforcing concerns involving the safe use of herbal medicines and other nutraceuticals to avoid PXR-mediated drug-drug interactions. Meanwhile, the activation of PXR and induction of detoxifying enzymes provide a molecular mechanism for the hepatoprotective effects of certain TCMs.

Traditional Chinese Medicines Wu Wei Zi (Schisandra chinensis Baill) and Gan Cao (Glycyrrhiza uralensis Fisch) Activate Pregnane X Receptor and Increase Warfarin Clearance in Rats

Ivo P Nnane

Papers

The effects of pretreatment with glycyrrhizin and glycyrrhetinic acid on the retrorsine-induced hepatotoxicity in rats

High performance liquid chromatographic analysis of a novel aminoalkylpyridine anticonvulsant 2-(4-chlorophenyl)amino-2-(4-pyridyl)ethane.