Estrogenic activities of extracts of Chinese licorice (Glycyrrhiza uralensis) root in MCF-7 breast cancer cells

Abstract

Despite the wide use of Chinese licorice root (Glycyrrhiza uralensis) for the treatment of menopausal complaints, little is known on its potential estrogenic properties, and available information relative to its effects on cell proliferation is contradictory. In this study, the estrogenic properties of licorice root were evaluated in vitro by use of several assays. The effects of increasing concentrations of a DMSO extract of licorice root on the growth of MCF-7 breast cancer cells were biphasic. The extract showed an ER-dependent growth-promoting effect at low concentrations and an ER-independent anti-proliferative activity at high concentrations. In further experiments, licorice root was sequentially extracted to yield four fractions: hexane, EtOAc, methanol and H₂O. Only the EtOAc extract had effects on cell proliferation similar to the DMSO extract. The hexane extract had no effect on cell growth. In contrast, the methanol and water extracts showed an ER-independent, growth-promoting effect. Similar to its effects on cell proliferation, the EtOAc extract had a biphasic effect on S phase cell cycle distribution and the level of PCNA protein. This extract-induced transactivation of endogenous ERα in MCF-7 cells, supported by inducing down-regulation of ERα protein and mRNA levels, and up-regulation of ERα target genes pS2 and GREB1. These results suggest that the activity of licorice root and the balance between increased risk for cancer and prevention of estrogen-dependent breast cancer may depend on the amount of dietary intake.

Introduction

There is growing interest in the use of herbs to aid in the maintenance of health. Licorice root (Glycyrrhiza) has been employed in traditional Chinese medicine to treat infectious diseases. It is also useful for detoxification, and it possesses anti-ulcer, anti-inflammation, antiviral, anti-atherogenic, and anticarcinogenic activities [1]. Some components of licorice root demonstrate antimicrobial [2], [3] and antioxidant activity in vitro [4], [5]. In Western countries, licorice root is used as flavoring and sweetening agents for tobacco, chewing gum, candy, toothpaste and beverages [1]. In the USA, licorice root is classified as Generally Regarded As Safe (GRAS) [6] and is listed by the Council of Europe as a natural source of food flavoring in category no. 2, indicating that small quantities can be added to foodstuffs to limit the amount of an active compound in the final product [7].

American women are increasingly turning to licorice root as a ‘more natural’ alternative to estrogen replacement therapy in the belief that it has the benefits, without the risks, of estrogen therapy. An important consideration is whether licorice root, as a substitute for hormone replacement therapy, stimulates the progression of estrogen-dependent breast tumors, particularly in hormone-deprived conditions. Previous studies have demonstrated estrogenic effects of individual components or extracts of licorice root [8], [9], [10], [11], [12], [13]. These studies have, however, been limited in scope and have not addressed issues of specificity and mechanism of action.

The type of licorice of primary concern to the western world is Glycyrrhiza glabra, which is indigenous to Turkey, Spain, Iraq, Turkey, Russia and North China. Glycyrrhiza uralensis is indigenous to Northern China, Mongolia and Siberia. As demonstrated by HPLC profiles, the chemical content of G. uralensis is totally different from that of G. glabra [14]. The purpose of the present study was to examine the estrogenic effects and mechanisms of action of G. uralensis extracts with different polarity on estrogen-dependent human breast cancer cells. Included assays of cell growth and cell cycle progression and determination of licorice extracts their capacity to activate ERα and to modulate ERα target genes. A goal of these studies was to evaluate extracts of different polarity and to assess their modes of action and their specific cellular targets. This study was important in order to assess the potential of licorice extracts for clinical use and their possible adverse side effects.