Antioxidant Activity of 2% G. glabra L. Hydrogels for Potential Use in Oxidative Stress-Related Skin Conditions ^†

Glycyrrhiza, commonly known as licorice, has been extensively studied for its many pharmacological properties, with recent research also focused on its potential dermatological applications. Its major bioactive constituents, including glycyrrhizin, glabridin, and liquiritin, exhibit potent free radical scavenging activity, inhibit lipid peroxidation, and modulate antioxidant enzymes, contributing to the restoration of redox balance in damaged (but also healthy) skin tissue. Recent formulations incorporating glycyrrhiza extracts have demonstrated important antioxidant performance alongside good biocompatibility and sustained dermal release profiles. These properties have translated into accelerated wound healing, reduced oxidative inflammation, and increased collagen deposition in animal models [1,2,3].

The present study evaluated the antioxidant activity of two hydrogel formulations composed of 2% G. glabra L. methanolic extract (S1 and S2), using two in vitro methods: DPPH (2,2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays. Both hydrogel formulations used xanthan gum as a swelling agent, but different penetration enhancers: S1 had propylene glycol as a penetration enhancer, and S2 had Labrasol as a penetration enhancer. DPPH assay showed S2 hydrogel formulation with the highest antioxidant activity (85.45%) at 1000 µg/mL. However, S1 hydrogel also had a high antioxidant capacity of 82.94%, meaning both formulations are close to ascorbic acid at 50 µg/mL (85.49%) when it comes to antioxidant activity. The FRAP assay further confirmed the antioxidant activity of the two hydrogels, showing the maximum FRAP (%) capacities at 56.42% for S1 and 68.94% for S2 for the 1000 µg/mL concentration.

In comparative studies, other plant-based antioxidants such as Camellia sinensis (green tea), Curcuma longa (turmeric), and Rosa canina have also been explored for topical use. Green tea catechins, for example, offer notable anti-aging and photoprotective benefits, but suffer from instability and limited skin permeation without advanced delivery vehicles [4]. Similarly, curcumin-enriched gels have demonstrated antioxidant activity but are hindered by poor solubility and bioavailability unless formulated with carriers like liposomes or microemulsions [5]. Only the Rosa canina ethanolic hydrogel exhibited similar antioxidant properties with the results obtained in the present study, showing the best DPPH scavenging percent of 85.64% [6].

In conclusion, Glycyrrhiza-based hydrogels offer a unique combination of strong antioxidant potency, high formulation stability, and ease of incorporation into hydrophilic matrices, making them ideal for oxidative stress-related skin conditions such as chronic wounds, dermatitis, and aging.