New strategies for identifying and masking the bitter taste in traditional herbal medicines: The example of Huanglian Jiedu Decoction

Abstract

Suppressing the bitter taste of traditional Chinese medicine (TCM) largely has been a major clinical challenge due to complex and diverse metabolites and high dispersion of bitter metabolites in liquid preparations. In this work, we developed a novel strategy for recognizing bitter substances, hiding their bitter taste, and elucidated the mechanism of flavor masking in TCM. Huanglian Jie-Du Decoction (HLJDD) with an intense bitter taste was studied as a typical case. UHPLC-MS/MS was used to analyze the chemical components in HLJDD, whereas the bitter substances were identified by pharmacophores. Additionally, the screening results of the pharmacophores were further validated by using experimental assays. The mask formula of HLJDD was effectively screened under the condition of clear bitter substances. Subsequently, computational chemistry, molecular docking, and infrared characterization (IR) techniques were then used to explicate the mechanism of flavor masking. Consequently, neotame, γ-CD, and mPEG₂₀₀₀-PLLA₂₀₀₀ significantly reduced the bitterness of HLJDD. Specifically, mPEG₂₀₀₀-PLLA₂₀₀₀ increased the colloid proportion in the decoction system and minimized the distribution of bitter components in the real solution. Sweetener neotame suppressed the perception of bitter taste and inhibited bitter taste receptor activation to eventually reduce the bitter taste. The γ-CD included in the decoction bound the hydrophobic groups of the bitter metabolites in real solution and "packed" all or part of the bitter metabolites into the "cavity". We established a novel approach for screening bitter substances in TCM by integrating virtual screening and experimental assays. Based on this strategy, the bitter taste masking of TCM was performed from three different aspects, namely, changing the drug phase state, component distribution, and interfering with bitter taste signal transduction. Collectively, the methods achieved a significant effect on bitter taste suppression and taste masking. Our findings will provide a novel strategy for masking the taste of TCM liquid preparation/decoction, which will in return help in improving the clinical efficacy of TCM.

Keywords: Huanglian Jie-du Decoction; bitterness; bitterness suppression; mechanism; neotame; γ-CD.

FIGURE 1

Graphic abstract. (A) HLJDD comprises Coptis chinensis Franch, Scutellaria baicalensis Georgi, Phellodendron amurense Rupr., and Gardenia jasminoides J. Ellis. It has a strong bitter taste. (B) UHPLC-MS/MS was used to identify the metabolites in HLJDD, and pharmacophores were used to recognize bitterness metabolites. (C) Multi-angle and multilevel bitter masking strategy with the amphiphilic block polymer, inclusion complex, and sweetener were applied to bitter-taste suppression of HLJDD. This new strategy achieved significant bitterness suppression and revealed the mechanism of bitter taste masking by combining the virtual analysis and experiment assays.

FIGURE 2

TIC detection diagram in the positive ion mode of UHPLC-Q-TOF-MS of HLJDD. (A) Mixed standard; (B) HLJDD.

FIGURE 3

Bitter taste activity of pharmacophore predicted test set compounds and matching results of compounds in the training set and optimal pharmacophore. (A,B,C) show the top 10 pharmacophores of Tas2r10, Tas2r14, and Tas2r46. (D,E,F) show the matching results of compounds in the training set and optimal pharmacophore of Tas2r10, Tas2r14, and Tas2r46. The X-axis represents the pharmacophore (01–10 represents the order of the pharmacophore determined using software), and the Y-axis represents the compounds matching the pharmacophore. Blue indicates that the match is zero, and red shows that the matching activity is good.

FIGURE 4

Taste-masking effect of taste mask formula (n=15, ‾x ± SD). Data shown are the mean± SD. *p<0.05, **p<0.01, and ***p<0.0001 versus HLJJD.

FIGURE 5

Results of IR analysis of the taste masking mechanism of mPEG2000-PLLA2000. (A) IR results of geniposide and geniposide + mPEG2000-PLLA2000, (B) IR results of chlorogenic acid and chlorogenic acid + mPEG2000-PLLA2000, (C) IR results of coptisine and coptisine + mPEG2000-PLLA2000, (D) IR results of epiberberine and epiberberine + mPEG2000-PLLA2000.

FIGURE 6

Interaction diagrams of bitter receptors with limonin, epiberberine, geniposide, and neotame. (A–L) Active pockets of limonin, epiberberine, geniposide, and neotame in Tas2r10, Tas2r14, and Tas2r46, respectively. (a–l) 2D diagram of receptor (Tas2r10, Tas2r14, and Tas2r46)-ligand (limonin, epiberberine, geniposide, and neotame), respectively. (A,a) Tas2r10 with limonin, (B,b) Tas2r10 with epiberberine, (C,c) Tas2r10 with geniposide, (D,d) Tas2r10 with neotame, (E,e) Tas2r14 with limonin, (F,f) Tas2r14 with epiberberine, (G,g) Tas2r14 with geniposide, (H,h) Tas2r14 with neotame, (I,i) Tas2r46 with limonin, (J,j) Tas2r46 with epiberberine, (K,k) Tas2r46 with geniposide, and (L,l) Tas2r46 with neotame. Light green indicates van der Waals interaction. Green indicates hydrogen bond interaction. Rose-red indicates pi–pi interaction. Sulfur yellow indicates pi–sulfur interaction.