Synergistic mechanism for the bioactivity fortification of licorice by honey

Honey-processed licorice has been used since ancient times. It was recorded that honey-processing has the effect of improving the immunomodulatory efficacy of licorice, which has been confirmed by modern pharmacological studies. However, it is still unknown why honey-processing can enhance the immunomodulatory activity of licorice. Our previous research demonstrated that honey has natural deep eutectic solvent (NADES) characteristics. In this study, we investigated the synergistic effect of honey on licorice to elucidate the possible potentiation of honey-frying on licorice. Immunological experiments were conducted to investigate whether the honey-processing could enhance the immunomodulatory efficacy of licorice in vivo. Then, the synergistic mechanism of honey and licorice was explored based on cell bioactivity tests, metabolomics analysis, bioavailability test, and Fourier transform-infrared (FT-IR) spectra. Pharmacological experiment verified that honey-processing enhanced the immunomodulatory efficacy of licorice. Moreover, honey increased the total flavonoid and polysaccharide contents in licorice decoction, improved the thermal stability and oral bioavailability of certain pharmacologically active constituents, and augmented their overall immunostimulatory functions. Similar effects of honey were also observed with a honey analogue GFSH, a NADES made of glucose, fructose, and sucrose with certain amount of water. The above effects might be due to multiple molecular interactions between active compounds and sugar molecules of honey. These findings indicate that the biological activities of medicinal plants might be fortified by honey due to the synergism between licorice and honey. At the meantime, these findings provide theoretical and empirical basis for potential novel applications of honey or other NADESs at augmenting the health-promoting effects of medicinal plants.