Reducing the Bitter Taste of Pharmaceuticals Using Cell-Based Identification of Bitter-Masking Compounds

Identification of 4'-Demethyl-3,9-dihydroeucomin as a Bitter-Masking Compound from the Resin of Daemonorops draco

Masking the bitter taste of foods is one of the key strategies to improve their taste and palatability, particularly in the context of clean labeling, where natural compounds are preferred. Despite the demand, the availability of natural bitter-masking compounds remains limited. Here, we identified the bitter-masking compound 4'-demethyl-3,9-dihydroeucomin (DMDHE) isolated from the resin of Daemonorops draco by means of an activity-guided in vivo (sensory bitterness rating of quinine) and in vitro (cell-based bitter response assays) approach. First, a mean bitter-masking effect of -29.6 ± 6.30% on the bitterness perceived from quinine [10 ppm] was demonstrated for an organic solvent extract of the resin of D. draco (= DD [500 ppm]) in a sensory trial. The results were verified in a cell-based bitter assay in which the bitter taste receptor (TAS2R)-dependent proton secretion serves as an outcome measure of the cellular bitter response in parietal HGT-1 cells. By means of preparative RP-18 high-performance liquid chromatography (HPLC) analysis combined with activity-guided sensory evaluations, the most potent bitter-masking fractions were identified. Subsequent quantitative liquid chromatography/high-resolution mass spectrometry/charged aerosol detection/ultraviolet (LC-HRMS/CAD/UV), NMR analysis, followed by gram-scale synthesis, led to the characterization of DMDHE as bitter-masking homoisoflavanone. DMDHE decreased the sensory bitterness of quinine by 14.8 ± 5.00%. Functional involvement of TAS2R14 was demonstrated by means of a CRISPR-Cas9 approach, which revealed a reduction of the DMDHE-evoked bitter-masking effect by 40.4 ± 9.32% in HGT-1 TAS2R14ko versus HGT-1 wt cells.

Effect of single-administration of D-sorbitol pretreatment on the bitterness and continued willingness to take asenapine: a randomized, single-blind, placebo-controlled, crossover trial

BACKGROUND

Asenapine has unique orally-related side effects, such as a bitter taste induced by sublingual administration, which often results in discontinuation of the medication. While the FDA has approved black-cherry-flavored asenapine, several countries have prescribed only unflavored versions. Specifically, Asians commonly report experiencing the bitterness of asenapine because they are more sensitive to bitter tastes than other ethnic groups. In this study, with the aim of improving adherence by reducing the bitterness of asenapine, we investigated the effects of D-sorbitol, which reduced the bitterness parameters of taste sensors in our previous basic study on the bitterness and continuity of asenapine among patients with schizophrenia.

METHODS

Twenty adult patients with schizophrenia were included in this single-blind, placebo-controlled, crossover trial. Participants rinsed their mouths with single-administration of D-sorbitol or a placebo prior to each administration of asenapine. We then conducted the questionnaires and assessed changes in the bitterness of asenapine (primary end point) and willingness to continue its use (secondary end point).

RESULTS

D-sorbitol significantly improved the bitterness of asenapine (p = 0.038). Although it did not significantly increase the willingness to continue asenapine (p = 0.180), it did show improvement over the placebo in enhancing willingness to continue, especially in patients who were not accustomed to its taste.

CONCLUSION

Our findings indicate that single-administration of D-sorbitol significantly reduces the bitterness of asenapine. In countries where flavored asenapine is not available, this finding could benefit patients who were not accustomed to its bitter taste.

TRIAL REGISTRATION

This study was registered in the Japan Registry of Clinical Trials (jRCTs041210019) on May 14, 2021.

Optimized De Novo Eriodictyol Biosynthesis in Streptomyces albidoflavus Using an Expansion of the Golden Standard Toolkit for Its Use in Actinomycetes

Eriodictyol is a hydroxylated flavonoid displaying multiple pharmaceutical activities, such as antitumoral, antiviral or neuroprotective. However, its industrial production is limited to extraction from plants due to its inherent limitations. Here, we present the generation of a Streptomyces albidoflavus bacterial factory edited at the genome level for an optimized de novo heterologous production of eriodictyol. For this purpose, an expansion of the Golden Standard toolkit (a Type IIS assembly method based on the Standard European Vector Architecture (SEVA)) has been created, encompassing a collection of synthetic biology modular vectors (adapted for their use in actinomycetes). These vectors have been designed for the assembly of transcriptional units and gene circuits in a plug-and-play manner, as well as for genome editing using CRISPR-Cas9-mediated genetic engineering. These vectors have been used for the optimization of the eriodictyol heterologous production levels in S. albidoflavus by enhancing the flavonoid-3'-hydroxylase (F3'H) activity (by means of a chimera design) and by replacing three native biosynthetic gene clusters in the bacterial chromosome with the plant genes matBC (involved in extracellular malonate uptake and its intracellular activation into malonyl-CoA), therefore allowing more malonyl-CoA to be devoted to the heterologous production of plant flavonoids in this bacterial factory. These experiments have allowed an increase in production of 1.8 times in the edited strain (where the three native biosynthetic gene clusters have been deleted) in comparison with the wild-type strain and a 13 times increase in eriodictyol overproduction in comparison with the non-chimaera version of the F3'H enzyme.

Human Gingival Fibroblasts as a Novel Cell Model Describing the Association between Bitter Taste Thresholds and Interleukin-6 Release

Human gingival fibroblast cells (HGF-1 cells) present an important cell model to investigate the gingiva's response to inflammatory stimuli such as lipopolysaccharides from Porphyromonas gingivalis (Pg-LPS). Recently, we demonstrated trans-resveratrol to repress the Pg-LPS evoked release of the pro-inflammatory cytokine interleukin-6 (IL-6) via involvement of bitter taste sensing receptor TAS2R50 in HGF-1 cells. Since HGF-1 cells express most of the known 25 TAS2Rs, we hypothesized an association between a compound's bitter taste threshold and its repressing effect on the Pg-LPS evoked IL-6 release by HGF-1 cells. To verify our hypothesis, 11 compounds were selected from the chemical bitter space and subjected to the HGF-1 cell assay, spanning a concentration range between 0.1 μM and 50 mM. In the first set of experiments, the specific role of TAS2R50 was excluded by results from structurally diverse TAS2R agonists and antagonists and by means of a molecular docking approach. In the second set of experiments, the HGF-1 cell response was used to establish a linear association between a compound's effective concentration to repress the Pg-LPS evoked IL-6 release by 25% and its bitter taste threshold concentration published in the literature. The Pearson correlation coefficient revealed for this linear association was R² = 0.60 (p < 0.01), exceeding respective data for the test compounds from a well-established native cell model, the HGT-1 cells, with R² = 0.153 (p = 0.263). In conclusion, we provide a predictive model for bitter tasting compounds with a potential to act as anti-inflammatory substances.

Sensory evaluation of the bitterness of asenapine using D-sorbitol pretreatment: single-blind, placebo-controlled, crossover trial

BACKGROUND

Antipsychotics are essential in the acute treatment of and maintenance therapy for schizophrenia, but medication adherence and long-term treatment continuity are needed to maximize their effectiveness. Each antipsychotic has various side effects, which may affect adherence. Some patients with schizophrenia are reluctant to take asenapine because of its unique oral-related side effects, such as the bitter taste caused by sublingual administration. Our previous basic research found that D-sorbitol lowered the bitterness parameters of the taste sensors. However, whether D-sorbitol has the same effect in patients remains unclear. Therefore, using a D-sorbitol solution, we aim to evaluate changes in the bitterness of asenapine among patients with schizophrenia.

METHODS

In this single-blind, placebo-controlled, crossover trial, we plan to recruit 20 adult patients with schizophrenia spectrum disorder who take sublingual asenapine tablets. The participants will be divided into two groups (n = 10 each). Each group will be given a D-sorbitol or placebo solution on the first day for rinsing before taking the sublingual asenapine tablets. After a 1-day interval, the participants will rinse their mouths again with a different liquid. Questionnaires regarding changes in taste and the willingness to continue asenapine will be conducted before the start of the study and after each rinse. The primary and secondary end points will be a taste evaluation of bitterness, and the willingness to continue asenapine, respectively. Differences in questionnaire scores between the D-sorbitol and placebo solutions will be calculated and analyzed using a McNemar test.

DISCUSSION

This study aims to determine the efficacy of D-sorbitol in masking the bitter taste of asenapine. To our knowledge, it is the first intervention study using D-sorbitol for bitter taste of asenapine in patients with schizophrenia. Evidence of the efficacy of D-sorbitol could result in D-sorbitol pretreatment being an easy and inexpensive means of improving adherence to asenapine.

TRIAL REGISTRATION

This study was registered in the Japan Registry of Clinical Trials jRCTs041210019, on May 14, 2021. Ethics approval was obtained from the Nagoya University Clinical Research Review Board.

Extracellular Vesicles and Particles Modulate Proton Secretion in a Model of Human Parietal Cells

The secretion of extracellular vesicles and particles (EVPs) is an important mechanism of cellular communication. In this work, we demonstrate a functional role of EVPs in mechanisms regulating gastric acid secretion. HGT-1 cells were used as a model system to assess proton secretion. First, in order to prove EVP secretion by HGT-1 cells, EVPs were isolated by size exclusion chromatography and characterized by nanoparticle tracking analysis, Western blot, and cryo transmission electron microscopy. For examination of the potential role of EVPs in proton secretion, HGT-1 cells were treated with pharmacological EV-inhibitors, resulting in a reduction of histamine-induced proton secretion. To demonstrate the functional role of EVPs in the mechanism of proton secretion, EVP-conditioned supernatant was collected after stimulation of HGT-1 cells with histamine, fractionated, and subjected to an activity screening. The results revealed constituents of the HGT-1-derived secretome with an MW of >100 kDa (including EVPs) to modulate proton secretion, while smaller constituents had no effect. Finally, a dose-dependent modulatory effect on proton secretion of HGT-1 cells was demonstrated by isolated HGT-1-derived EVPs. Hence, this study presents first results on the potential function of EVPs as a previously undiscovered mechanism of regulation of gastric acid secretion by parietal cells.