The Licorice Root Derived Isoflavan Glabridin Inhibits the Activities of Human Cytochrome P450S 3A4, 2B6, and 2C9

Abstract

ABSTRACT:The potent antioxidants licorice root extract and glabridin, an isoflavan purified from licorice root extract, were tested for their ability to modulate the activities of several cytochrome P450 (P450) enzymes. P450 3A4, the major human drug metabolizing P450 enzyme, was inactivated by licorice root extract and by glabridin in a time-and concentration-dependent manner. The inactivation was NADPH-dependent and was not reversible by extensive dialysis. Further analysis showed that the loss in enzymatic activity correlated with a loss in the P450-reduced CO spectrum and with a loss of the intact heme moiety. In contrast, incubations of P450 3A4 with similar concentrations of 2,4-dimethylglabridin and NADPH did not lead to inactivation of P450 3A4. P450 2B6 was also inactivated by glabridin in a time-and concentration-dependent manner. The majority of the glabridin-inactivated P450 2B6 was able to form a reduced CO spectrum suggesting that the heme was not modified with this isoform. High-performance liquid chromatography analysis of the P450 heme confirmed that incubations with glabridin and NADPH did not result in the destruction of the heme moiety. The activity of P450 2C9 was competitively inhibited by glabridin, whereas P450 2D6 and P450 2E1 were virtually unaffected. The data show that glabridin can serve as a substrate for at least three human P450 enzymes and that depending on the isoform, metabolism of glabridin can lead to mechanism-based inactivation or inhibition of the P450. Heme and reduced CO spectral analysis also indicated that glabridin inactivated P450s 2B6 and 3A4 by different mechanisms. Liver microsomal P4501 enzymes are involved in the metabolism of endogenous substrates such as fatty acids, cholesterol, and steroids. These enzymes also carry out an important function in the catalysis and ultimate clearance of many structurally distinct xenobiotics such as drugs, pesticides, carcinogens, and environmental pollutants (Porter and Coon, 1991; Rendic and DiCarlo, 1997). P450 3A4, the major hepatic and intestinal P450 enzyme in humans, metabolizes more than 50% of clinically used drugs such as cyclosporine A, dihydropyridines, ethynylestradiol, midazolam, terfenadine, and triazolam. On average, P450 2B6 comprises approximately 0.2% of human liver P450 and is responsible for the metabolism of roughly 3% of all drugs such as ketamine (Yanagihara et al., 2001), orphenadrine, secobarbital, phenobarbital, dexamethasone, and rifampin (Chang et al., 1997). The P450 2C family comprises approximately 18% of the P450 enzymes found in human liver and are responsible for the metabolism of at least 25% of all drugs including tolbutamide, diclofenac, (S)-warfarin, phenytoin, and hexobarbital.

Identification of Key Licorice Constituents Which Interact with Cytochrome P450: Evaluation by LC/MS/MS Cocktail Assay and Metabolic Profiling

“…Different classes of licorice compounds showed distinct activities on P450 isozymes. Flavonoid glycosides (3-7), saponins (10,15,16,19), and phenolic acids (1,2) showed weak regulatory activities, with inhibition or activation rates of less than 35% at 10 μM. Most of their IC 50 values were higher than 200 μM.…”

“…Previous reports have revealed that glycyrrhetinic acid could inactive CYP 2E1 (14), glabridin (form Glycyrrhiza glabra) could inhibit the activities of 3A4, 2B6, and 2C9 (15), and that glycyrrhizic acid could induce (16) or inhibit (17) human CYP 3A4. Unfortunately, results from single compounds could not represent the action of licorice, which is a multicomponent mixture containing more than 400 compounds (18).…”

Licorice abuse: time to send a warning message

“…One patient exhibited digoxin toxicity due to hypokalemia induced by licorice intake [Harada et al 2002]. Licorice root extracts not including glycyrrhizin causes inhibition of P450 and cytochrome P450 3A4 (CYP3A4) systems [Tsukamoto et al 2005;Kent et al 2002]. A study demonstrated the potentiation of warfarin effects due to the inhibitory effect of licorice on the hepatic microsomal enzyme system [Heck et al 2000].…”

A Comparison Between Lignans from Creosote Bush and Flaxseed and Their Potential to Inhibit Cytochrome P450 Enzyme Activity

“…In particular, bioactivation, or the metabolic activation of a compound to an electrophilic reactive intermediate, which subsequently undergoes covalent binding to critical cellular macromolecules and interferes with their www.intechopen.com function, has long-standing recognition as a biochemical mechanism of organ toxicity (Miller & Miller 1947;Mitchell et al, 1973;Masubuchi et al, 2007). Several examples exist of natural products undergoing P450-mediated bioactivation and irreversible P450 enzyme inhibition and hepatotoxicity (Johnson et al, 2003;Zhou et al, 2004;Surh & Lee 1995;He et al, 1998;Kent et al, 2002). Furthermore, natural products are known to result in significant interactions with coadministered therapeutic agents resulting in adverse effects or therapeutic failures (Dietz & Bolton 2007;Yuan et al, 2004;Kupiec & Raj 2005).…”