Oral enzymatic detoxification system: Insights obtained from proteome analysis to understand its potential impact on aroma metabolization

Exploring the Therapeutic Role of Flavonoids Through AMPK Activation in Metabolic Syndrome: A Narrative Review

Metabolic syndrome (MetS) is a cluster of interrelated metabolic abnormalities that significantly elevate the risk of cardiovascular disease, obesity, and diabetes. Flavonoids, a diverse class of bioactive polyphenolic compounds found in plant-derived foods and beverages, have garnered increasing attention as potential therapeutic agents for improving metabolic health. This review provides a comprehensive analysis of the therapeutic effects of flavonoids in the context of the MetS, with a particular focus on their modulation of the AMP-activated protein kinase (AMPK) pathway. AMPK serves as a central regulator of cellular energy balance, glucose metabolism, and lipid homeostasis, making it a critical target for metabolic intervention. Through a systematic review of the literature up to April 2024, preclinical studies across various flavonoid subclasses, including flavonols, and flavan-3-ols, were analysed to elucidate their mechanistic roles in metabolic regulation. Many studies suggests that flavonoids enhance glycolipid metabolism by facilitating glucose transporter 4 (GLUT4) translocation and activating the AMPK pathway, thereby improving glycemic control in diabetes models. In obesity-related studies, flavonoids demonstrated significant inhibitory effects on lipid synthesis, reduced adipogenesis, and attenuated proinflammatory cytokine secretion via AMPK activation. These findings show the broad therapeutic potential of flavonoids in addressing the MetS and its associated disorders. While these preclinical insights highlight flavonoids as promising natural agents for metabolic health improvement, it is important to note that their excessive concentrations may disrupt these pathways, potentially leading to metabolic imbalance and cytotoxicity. Further studies and clinical trials are essential to determine optimal dosing regimens, formulations, and the long-term safety and efficacy of flavonoids. This review highlights the importance of flavonoids for natural interventions targeting MetS and its comorbidities, offering a foundation for future translational research.

Microbial β C-S Lyases: Enzymes with Multifaceted Roles in Flavor Generation

β C-S lyases (β-CSLs; EC 4.4.1.8) are enzymes catalyzing the dissociation of β carbon-sulfur bonds of cysteine S-conjugates to produce odorant metabolites with a free thiol group. These enzymes are increasingly studied for their role in flavor generation in a variety of food products, whether these processes occur directly in plants, by microbial β-CSLs during fermentation, or in the mouth under the action of the oral microbiota. Microbial β-CSLs react with sulfur aroma precursors present in beverages, vegetables, fruits, or aromatic herbs like hop but also potentially with some precursors formed through Maillard reactions in cooked foods such as meat or coffee. β-CSLs from microorganisms like yeasts and lactic acid bacteria have been studied for their role in the release of polyfunctional thiols in wine and beer during fermentation. In addition, β-CSLs from microorganisms of the human oral cavity were shown to metabolize similar precursors and to produce aroma in the mouth with an impact on retro-olfaction. This review summarizes the current knowledge on β-CSLs involved in flavor generation with a focus on enzymes from microbial species present either in the fermentative processes or in the oral cavity. This paper highlights the importance of this enzyme family in the food continuum, from production to consumption, and offers new perspectives concerning the utilization of β-CSLs as a flavor enhancer.

Rattus norvegicus Glutathione Transferase Omega 1 Localization in Oral Tissues and Interactions with Food Phytochemicals

Glutathione transferases are xenobiotic-metabolizing enzymes with both glutathione-conjugation and ligandin roles. GSTs are present in chemosensory tissues and fluids of the nasal/oral cavities where they protect tissues from exogenous compounds, including food molecules. In the present study, we explored the presence of the omega-class glutathione transferase (GSTO1) in the rat oral cavity. Using immunohistochemistry, GSTO1 expression was found in taste bud cells of the tongue epithelium and buccal cells of the oral epithelium. Buccal and lingual extracts exhibited thiol-transferase activity (4.9 ± 0.1 and 1.8 ± 0.1 μM/s/mg, respectively). A slight reduction from 4.9 ± 0.1 to 4.2 ± 0.1 μM/s/mg (p < 0.05; Student's t test) was observed in the buccal extract with 100 μM GSTO1-IN-1, a specific inhibitor of GSTO1. RnGSTO1 exhibited the usual activities of omega GSTs, i.e., thiol-transferase (catalytic efficiency of 8.9 × 104 M-1·s-1), and phenacyl-glutathione reductase (catalytic efficiency of 8.9 × 105 M-1·s-1) activities, similar to human GSTO1. RnGSTO1 interacts with food phytochemicals, including bitter compounds such as luteolin (Ki = 3.3 ± 1.9 μM). Crystal structure analysis suggests that luteolin most probably binds to RnGSTO1 ligandin site. Our results suggest that GSTO1 could interact with food phytochemicals in the oral cavity.

Unlocking Flavor Potential Using Microbial β-Glucosidases in Food Processing

Aroma is among of the most important criteria that indicate the quality of food and beverage products. Aroma compounds can be found as free molecules or glycosides. Notably, a significant portion of aroma precursors accumulates in numerous food products as nonvolatile and flavorless glycoconjugates, termed glycosidic aroma precursors. When subjected to enzymatic hydrolysis, these seemingly inert, nonvolatile glycosides undergo transformation into fragrant volatiles or volatiles that can generate odor-active compounds during food processing. In this context, microbial β-glucosidases play a pivotal role in enhancing or compromising the development of flavors during food and beverage processing. β-glucosidases derived from bacteria and yeast can be utilized to modulate the concentration of particular aroma and taste compounds, such as bitterness, which can be decreased through hydrolysis by glycosidases. Furthermore, oral microbiota can influence flavor perception by releasing volatile compounds that can enhance or alter the perception of food products. In this review, considering the glycosidic flavor precursors present in diverse food and beverage products, we underscore the significance of glycosidases with various origins. Subsequently, we delve into emerging insights regarding the release of aroma within the human oral cavity due to the activity of oral microbial glycosidases.

Nanotechnology-based mucoadhesive and mucus-penetrating drug-delivery systems for transbuccal drug delivery

Buccal drug-delivery systems present a promising approach for the drug delivery to the buccal mucosa, addressing oral cavity-specific problems, enabling systemic delivery and minimizing adverse effects on biological systems. Numerous strategies have been proposed to load drug-containing nanoparticles (NPs) to the buccal mucosa for local and systemic applications. There has been considerable interest in the development of mucoadhesive buccal formulations, particularly hydrogel composites utilizing mucoadhesive films incorporating NPs. Drug permeability and controlled drug release through buccal drug delivery continues to pose a challenge despite the availability of various remedies. This review highlights the need for, mechanisms and latest advances in NP-based transbuccal drug delivery with a focus on various pathological disorders and examples and limitations of the different methods.

Characterization of human oxidoreductases involved in aldehyde odorant metabolism

Oxidoreductases are major enzymes of xenobiotic metabolism. Consequently, they are essential in the chemoprotection of the human body. Many xenobiotic metabolism enzymes have been shown to be involved in chemosensory tissue protection. Among them, some were additionally shown to be involved in chemosensory perception, acting in signal termination as well as in the generation of metabolites that change the activation pattern of chemosensory receptors. Oxidoreductases, especially aldehyde dehydrogenases and aldo-keto reductases, are the first barrier against aldehyde compounds, which include numerous odorants. Using a mass spectrometry approach, we characterized the most highly expressed members of these families in the human nasal mucus sampled in the olfactory vicinity. Their expression was also demonstrated using immunohistochemistry in human epitheliums sampled in the olfactory vicinity. Recombinant enzymes corresponding to three highly expressed human oxidoreductases (ALDH1A1, ALDH3A1, AKR1B10) were used to demonstrate the high enzymatic activity of these enzymes toward aldehyde odorants. The structure‒function relationship set based on the enzymatic parameters characterization of a series of aldehyde odorant compounds was supported by the X-ray structure resolution of human ALDH3A1 in complex with octanal.

Exploring the Impact of α-Amylase Enzyme Activity and pH on Flavor Perception of Alcoholic Drinks

The introduction of a drink in the mouth and the action of saliva and enzymes cause the perception of basic tastes and some aromas perceived in a retro-nasal way. Thus, this study aimed to evaluate the influence of the type of alcoholic beverage (beer, wine, and brandy) on lingual lipase and α-amylase activity and in-mouth pH. It was possible to see that the pH values (drink and saliva) differed significantly from the pH values of the initial drinks. Moreover, the α-amylase activity was significantly higher when the panel members tasted a colorless brandy, namely Grappa. Red wine and wood-aged brandy also induced greater α-amylase activity than white wine and blonde beer. Additionally, tawny port wine induced greater α-amylase activity than red wine. The flavor characteristics of red wines due to skin maceration and the contact of the brandy with the wood can cause a synergistic effect between beverages considered "tastier" and the activity of human α-amylase. We can conclude that saliva-beverage chemical interactions may depend on the saliva composition but also on the chemical composition of the beverage, namely its constitution in acids, alcohol concentration, and tannin content. This work is an important contribution to the e-flavor project, the development of a sensor system capable of mimicking the human perception of flavor. Furthermore, a better understanding of saliva-drink interactions allow us to comprehend which and how salivary parameters can contribute to taste and flavor perception.

Role of Insect and Mammal Glutathione Transferases in Chemoperception

Glutathione transferases (GSTs) are ubiquitous key enzymes with different activities as transferases or isomerases. As key detoxifying enzymes, GSTs are expressed in the chemosensory organs. They fulfill an essential protective role because the chemosensory organs are located in the main entry paths of exogenous compounds within the body. In addition to this protective function, they modulate the perception process by metabolizing exogenous molecules, including tastants and odorants. Chemosensory detection involves the interaction of chemosensory molecules with receptors. GST contributes to signal termination by metabolizing these molecules. By reducing the concentration of chemosensory molecules before receptor binding, GST modulates receptor activation and, therefore, the perception of these molecules. The balance of chemoperception by GSTs has been shown in insects as well as in mammals, although their chemosensory systems are not evolutionarily connected. This review will provide knowledge supporting the involvement of GSTs in chemoperception, describing their localization in these systems as well as their enzymatic capacity toward odorants, sapid molecules, and pheromones in insects and mammals. Their different roles in chemosensory organs will be discussed in light of the evolutionary advantage of the coupling of the detoxification system and chemosensory system through GSTs.

Role of human salivary enzymes in bitter taste perception

The molecules that elicit taste sensation are perceived by interacting with the taste receptors located in the taste buds. Enzymes involved in the detoxification processes are found in saliva as well as in type II cells, where taste receptors, including bitter taste receptors, are located. These enzymes are known to interact with a large panel of molecules. To explore a possible link between these enzymes and bitter taste perception, we demonstrate that salivary glutathione transferases (GSTA1 and GSTP1) can metabolize bitter molecules. To support these abilities, we solve three X-ray structures of these enzymes in complexes with isothiocyanates. Salivary GSTA1 and GSTP1 are expressed in a large panel of subjects. Additionally, GSTA1 levels in the saliva of people suffering from taste disorders are significantly lower than those in the saliva of the control group.

Metabolism of Cysteine Conjugates and Production of Flavor Sulfur Compounds by a Carbon-Sulfur Lyase from the Oral Anaerobe Fusobacterium nucleatum

Flavor perception is a key factor in the acceptance or rejection of food. Aroma precursors such as cysteine conjugates are present in various plant-based foods and are metabolized into odorant thiols in the oral cavity. To date, the involved enzymes are unknown, despite previous studies pointing out the likely involvement of carbon-sulfur lyases (C-S lyases) from the oral microbiota. In this study, we show that saliva metabolizes allyl-cysteine into odorant thiol metabolites, with evidence suggesting that microbial pyridoxal phosphate-dependent C-S lyases are involved in the enzymatic process. A phylogenetic analysis of PatB C-S lyase sequences in four oral subspecies of Fusobacterium nucleatum was carried out and led to the identification of several putative targets. FnaPatB1 from F. nucleatum subspecies animalis, a putative C-S lyase, was characterized and showed high activity with a range of cysteine conjugates. Enzymatic and X-ray crystallographic data showed that FnaPatB1 metabolizes cysteine derivatives within a unique active site environment that enables the formation of flavor sulfur compounds. Using an enzymatic screen with a library of pure compounds, we identified several inhibitors able to reduce the C-S lyase activity of FnaPatB1 in vitro, which paves the way for controlling the release of odorant sulfur compounds from their cysteine precursors in the oral cavity.

Odorant Metabolism in Humans

Odorants are relatively small molecules which are easily taken up and distributed in the human body. Despite their relevance in everyday life, however, only a limited amount of evidence about their metabolism, pathways, and bioactivities in the human body exists. With this Review, we aim to encourage future interdisciplinary research on the function and mechanisms of the biotransformation of odorants, involving different disciplines such as nutrition, medicine, biochemistry, chemistry, and sensory sciences. Starting with a general overview of the different ways of odorant uptake and enzymes involved in the metabolism of odorants, a more precise description of biotransformation processes and their function in the oral cavity, the nose, the lower respiratory tract (LRT), and the gastrointestinal tract (GIT) is given together with an overview of the different routes of odorant excretion. Finally, perspectives for future research are discussed.