**5.2. Efficacies of hydrophobic extracts from** *G. glabra* **(HPGG)**

The hydrophobic extract from *G. glabra* (HPGG) contains various flavonoids such as glabridin, glabrene, and glabrol (**Figure 3**). HPGG has been known to have antimicrobial and antioxidant activities [15]. In addition, glabridin has the inhibitory effects on melanogenensis and inflammation [16]. In this section, a depigmenting effect of HPGG *in vitro* and *in vivo* studies was examined [17].

(1) Inhibitory effect of tyrosinase activity.

We found that HPGG and its constituents had inhibitory effects on tyrosinase activity by absorbance measurement. Their tyrosinase inhibition doses (IC50: mg/mL) were as follows: glabridin 0.0003, HPGG 0.031, glabrene 0.0046, hydroquinone 0.016, and ascorbic acid 0.21 (**Table 6**) [15]. The latter two compounds are commonly known as depigmenting agents.


**Table 6.** Inhibition against tyrosinase activity.

(2) Melanization assay by 14C‐thiouracil uptake.

**Figure 4.** Melanization assayed by 14C‐thiouracil uptake of B‐16 melanoma cells.

Melanization was assayed by the incorporation of 14C‐thiouracil into B‐16 melanoma cells. Melanization was inhibited by HPGG and glabridin dose‐dependently, although glabridin more strongly inhibited it than HPGG (**Figure 4**) [15].

(3) Application in patients with melasma.

**5.2. Efficacies of hydrophobic extracts from** *G. glabra* **(HPGG)**

20 Biological Activities and Action Mechanisms of Licorice Ingredients

**Sample IC50 (mg/mL)** HPGG 0.0031 Glabridin 0.0003 Glabrene 0.0046 Glabrol >0.1 Ascorbic acid 0.21 Kojic acid 0.058 Hydroquinone 0.016

was examined [17].

(1) Inhibitory effect of tyrosinase activity.

**Table 6.** Inhibition against tyrosinase activity.

(2) Melanization assay by 14C‐thiouracil uptake.

**Figure 4.** Melanization assayed by 14C‐thiouracil uptake of B‐16 melanoma cells.

The hydrophobic extract from *G. glabra* (HPGG) contains various flavonoids such as glabridin, glabrene, and glabrol (**Figure 3**). HPGG has been known to have antimicrobial and antioxidant activities [15]. In addition, glabridin has the inhibitory effects on melanogenensis and inflammation [16]. In this section, a depigmenting effect of HPGG *in vitro* and *in vivo* studies

We found that HPGG and its constituents had inhibitory effects on tyrosinase activity by absorbance measurement. Their tyrosinase inhibition doses (IC50: mg/mL) were as follows: glabridin 0.0003, HPGG 0.031, glabrene 0.0046, hydroquinone 0.016, and ascorbic acid 0.21 (**Table 6**) [15]. The latter two compounds are commonly known as depigmenting agents.

We have first synthesized an HPGG that contains 40% of glabridin and using this HPGG, 0.1 or 0.2% HPGG creams were made. An open study has been carried out with application of 0.1 or 0.2% HPGG cream twice a day in patients with melasma, senile pigment freckle, and postinflammatory pigmented lesions for 4 months. The efficacy was evaluated by measuring skin lightness (*L* value) with colorimeter before and after the application. The *L* value has a theoretical value ranging from of 0 (pure black) to 100 (pure white).

*L* value was significantly improved after the therapy with 0.1% HPGG cream in patients with melasma only (**Table 7**) [15]. However, with 0.2% HPGG cream, not only patients with melasma, but also with the two lesions showed significantly improvement in *L* values (**Table 8**) [15].


**Table 7.** Changes in *L* values by application with 0.1% GPGG cream.


**Table 8.** Changes in *L* values by application with 0.2% GPGG cream.
