Unequivocal glycyrrhizin isomer determination and comparative in vitro bioactivities of root extracts in four Glycyrrhiza species

Farag, Mohamed A.; Porzel, Andrea; Wessjohann, Ludger A.

Increasing evidence in the literature point toward the marked cytotoxic effect found for licorice flavonoids including isoliquiritigenin [22] . Our objective was also to investigate cytotoxicity potential of licorice extracts with different flavonoid composition as revealed from our chemical analysis [17] . All samples were tested for growth inhibition of (mutated androgen dependent) prostate (PC3) and (androgen independent) colon (HT-29) cancer cell lines at doses of 5, 10 and 20 lg/ ml. All extracts show only weak inhibition in this assay setup, except for G. inflata with an IC 50 value of 13 and 17 lg/ml for HT29 and PC3, respectively. The high content of moderately cytotoxic compounds such as polyphenols and chalcones in G. inflata [17] probably is responsible for the growth inhibition effect. Relevant amounts of licochalcone A, the major isoprenylated retrochalcone in G. inflata, are absent in the other species samples as revealed by 1 H NMR analysis [17] . Thus pure licochalcone A was tested separately and exhibited significant activity at lower IC 50 values (PC3, 9.6 lg/ml; HT29, 8.0 lg/ ml) suggesting that it likely is the main mediator of cytotoxicity in G. inflata extract. Indeed, several laboratories evidenced the marked cytotoxic effect for licochalcone A against various cancer cell lines including lung, colon, prostate and skin cancer cell lines [23] . Several other retrochalcones such as licochalcone C and D were present in G. inflata extract and may act additively or even synergistically with licochalcone A. Our Fig. 3 Anti-inflammatory activity against COX1 and total phenolics (TP) content of Glycyrrhiza sp. extract tested at a dose of 100 lg ml À1 (n = 3). Results are expressed for anti-inflammatory activity as % inhibition to control on the Y 1 axis and for polyphenol content as mg g À1 as displayed on the Y 2 axis. Glycyrrhiza samples include: (GE1, GE2, GE3; G. echinata), (GU1, GU2, GU3; G. uralensis), (GG1, GG2, GG3, GG4; G. glabra) and (GI; G. inflata), for sample codes, see Table 1 .