Characterization Of Antioxidant Constituents From Licorice Roots

Licorice root contains flavonoids with biological activities, several of which were isolated and purified. Licochalcone B and D, isolated from the roots of Glycyrrhiza inflata, were shown to inhibit superoxide anion production in the xantine/xantine oxidase system (79), and to have free-radical-scavenging activity toward the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical. These phenolic compounds were also shown to be effective in protecting biological systems against various oxidative processes. They inhibit mitochondrial lipid peroxidation induced by Fe(III)-ADP/NADH, scavenge superoxide anions in microsomes, and protect red blood cells against oxidative hemolysis (79). Other antioxidant constituents that were isolated from licorice were identified as the isoflavans glabridin, hispaglabridin A, hispaglabridin B, 4-O-methyl glabridin, and two chalcones; isoprenylchalcone and isoquitirigenin (80). Among these compounds, glabridin was the major flavonoid in the licorice root extract (5 g/kg of root).

Possible antiatherogenic effects of licorice are illustrated in Figure 1. Upon LDL incubation with glabridin, the latter was shown to bind to the LDL, and subsequently, to protect it from oxidation (80-82).

Glabridin inhibited AAPH-induced LDL oxidation in a dose-dependent manner, as shown by the inhibition of cholesteryl linoleate hydroperoxide (CL-OOH) formation, as well as by the inhibition of lipid peroxide and aldehyde formation. Addition of glabridin (30 ||M) to LDL that was incubated with AAPH or with copper ions also inhibited the formation of oxy-sterols (7-hydroxycholesterol, 7-ketocholesterol, and 5, 5- epoxycholesterol) by 65%, 70%, and 45%, respectively. Glabridin inhibited the consumption of h-carotene and that of lycopene by 41% and 50%, respectively, after 1 hr of LDL oxidation in the presence of AAPH, but failed to protect vitamin E, the major LDL-associated antioxidant, from oxidation (82) (Fig. 2).

Glabridin was also found to preserve the arylesterase activity of human serum paraoxonase (PON1), including its ability to hydrolyze oxidized LDL (Ox-LDL) cholesteryl linoleate hydroperoxides (72), since PON1 was found to be more potent in reducing the amount of cholesteryl linoleate hydroperoxides when added to Ox-LDL in the presence of glabridin, in comparison to its effects in the absence of glabridin.

Glabridin was also shown to accumulate in macrophages in a dose-and time-dependent process, and in parallel, in glabridin-enriched cells,

FOAM CELL AORTIC LESION

FOAM CELL AORTIC LESION

Licorice

Glabridin (Isoflavan)

Figure 1 Antiatherogenic effects of licorice flavonoids. Dietary consumption of nutrients rich in flavonoids inhibits LDL oxidation, foam cell formation, and the development of aortic atherosclerotic lesions. The major licorice flavonoid, the isoflavan glabridin, is shown, along with its chemical structure. CE, cholesteryl ester; Ox-LDL, oxidized LDL; UC, unesterified cholesterol.

Figure 1 Antiatherogenic effects of licorice flavonoids. Dietary consumption of nutrients rich in flavonoids inhibits LDL oxidation, foam cell formation, and the development of aortic atherosclerotic lesions. The major licorice flavonoid, the isoflavan glabridin, is shown, along with its chemical structure. CE, cholesteryl ester; Ox-LDL, oxidized LDL; UC, unesterified cholesterol.

macrophage-mediated oxidation of LDL was inhibited by up to 80% compared with control cells (Fig. 3a). These effects could be related to glabridin-mediated inhibition of superoxide anion release from macrophages in response to phorbol 12-myristate 13-acetate (PMA) (Fig. 3b), to inhibition of the translocation of P-47 (a cytosolic component of NADPH oxidase) to the plasma membrane, and to a reduction in cellular protein kinase C activity (83) (Fig. 3c), which is required for P-47 phosphorylation and activation. Thus, glabridin-induced inhibition of P-47 phosphorylation may be the primary event responsible for its inhibitory effect on NADPH oxidase-induced macrophage-mediated oxidation of LDL. All the above inhibitory effects of glabridin on the events related to cell-mediated oxidation of LDL required the hydroxyl groups on the isoflavan B ring (81).

The protective capabilities of licorice crude extract, and of its main isolated flavonoid, the isoflavan glabridin, against LDL atherogenic modifications, including LDL oxidation, LDL retention, and LDL aggregation, were also investigated ex vivo in humans, and in the atherosclerotic apolipo-protein E-deficient (E0) mice.

Figure 2 The antioxidative effect of glabridin on LDL endogenous constituents during AAPH-induced LDL oxidation. LDL (100 mg of protein/L) was incubated for 3 hr at 37°C with 5 mM AAPH in the presence of 30 ng/mL of glabridin. The extent of LDL oxidation was measured as formation of thiobarbituric acid reactive substances (TBARS), lipid peroxides, cholesteryl linoleate hydroperoxide (CLOOH), 7-hydroxycholesterol, 7-ketocholesterol, and 5,6-epoxycholesterol. It was also analyzed as the consumption of LDL-associated ß-carotene, lycopene, and vitamin E. Results are expressed as % of control, relative to LDL incubated with AAPH in the absence of glabridin.

Figure 2 The antioxidative effect of glabridin on LDL endogenous constituents during AAPH-induced LDL oxidation. LDL (100 mg of protein/L) was incubated for 3 hr at 37°C with 5 mM AAPH in the presence of 30 ng/mL of glabridin. The extent of LDL oxidation was measured as formation of thiobarbituric acid reactive substances (TBARS), lipid peroxides, cholesteryl linoleate hydroperoxide (CLOOH), 7-hydroxycholesterol, 7-ketocholesterol, and 5,6-epoxycholesterol. It was also analyzed as the consumption of LDL-associated ß-carotene, lycopene, and vitamin E. Results are expressed as % of control, relative to LDL incubated with AAPH in the absence of glabridin.

Weight Loss All Star

Weight Loss All Star

Are you looking to lose weight or even just tone up? What is stopping you from having the body you want and help you feel great at the same time? I created Weight Loss All-Star for all those wanting to lose weight, and keep the weight off. I know how hard it is to do diets and stick with them, and get the motivation to get up and exercise.

Get My Free Ebook


Post a comment