Odorant metabolism catalyzed by olfactory mucosal enzymes influences peripheral olfactory responses in rats.

International audienceA large set of xenobiotic-metabolizing enzymes (XMEs), such as the cytochrome P450 monooxygenases (CYPs), esterases and transferases, are highly expressed in mammalian olfactory mucosa (OM). These enzymes are known to catalyze the biotransformation of exogenous compounds to facilitate elimination. However, the functions of these enzymes in the olfactory epithelium are not clearly understood. In addition to protecting against inhaled toxic compounds, these enzymes could also metabolize odorant molecules, and thus modify their stimulating properties or inactivate them. In the present study, we investigated the in vitro biotransformation of odorant molecules in the rat OM and assessed the impact of this metabolism on peripheral olfactory responses. Rat OM was found to efficiently metabolize quinoline, coumarin and isoamyl acetate. Quinoline and coumarin are metabolized by CYPs whereas isoamyl acetate is hydrolyzed by carboxylesterases. Electro-olfactogram (EOG) recordings revealed that the hydroxylated metabolites derived from these odorants elicited lower olfactory response amplitudes than the parent molecules. We also observed that glucurono-conjugated derivatives induced no olfactory signal. Furthermore, we demonstrated that the local application of a CYP inhibitor on rat olfactory epithelium increased EOG responses elicited by quinoline and coumarin. Similarly, the application of a carboxylesterase inhibitor increased the EOG response elicited by isoamyl acetate. This increase in EOG amplitude provoked by XME inhibitors is likely due to enhanced olfactory sensory neuron activation in response to odorant accumulation. Taken together, these findings strongly suggest that biotransformation of odorant molecules by enzymes localized to the olfactory mucosa may change the odorant's stimulating properties and may facilitate the clearance of odorants to avoid receptor saturation

Role of oxidoreductase enzymes in olfactory perireceptor events

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Characterization of rat glutathione transferases in olfactory mucus and epithelium

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Role of human metabolizing enzymes in food perception

International audienceFlavor is the main factor determining food acceptability. Flavor corresponds to the combination of the signals from the gustatory system, the olfactory system and the trigeminal system. Interactions between proteins and flavor molecules in oral/nasal cavities are proposed to modulate flavor perception through a series of events knowns as perireceptor events. Among these proteins involved in this modulation are found enzymes mainly known for their role in the detoxification process. These enzymes are able to recognize a large panel of molecules. We proposed to explore the role of these enzymes in food perception. We demonstrated that enzymatic activities present in the oral epithelium and saliva, and in the olfactory mucus led to odorant molecules metabolization. Enzymes metabolize odorant molecules in order to eliminate them, consequently participating to the termination of the flavor signal. Additionally, the odorant metabolites have their own sensory properties and can also be perceived, contributing to modulate the flavor perception. Using a combination of technics including mass spectroscopy, immunohistochemistry, enzymology and radiocristallography, we identify and characterize different enzymes related to this flavor perception in the oral cavity (at the level of aroma molecules and tastants). This research contributes to clarify the understanding of the metabolization of odorant and tastant molecules in the oral cavity and their consequences on flavor perception

Cytotoxic oxysterols induce caspase-independent myelin figure formation and caspase-dependent polar lipid accumulation.

Oxysterols, mainly those oxidized at the C7 position, induce a complex mode of cell death exhibiting some characteristics of apoptosis associated with a rapid induction of lipid rich multilamellar cytoplasmic structures (myelin figures) observed in various pathologies including atherosclerosis. The aim of this study was to determine the relationships between myelin figure formation, cell death, and lipid accumulation in various cell lines (U937, THP-1, MCF-7 [caspase-3 deficient], A7R5) treated either with oxysterols (7-ketocholesterol [7KC], 7beta-hydroxycholesterol, cholesterol-5alpha,6alpha-epoxide, cholesterol-5beta,6beta-epoxide, 25-hydroxycholesterol) or cytotoxic drugs (etoposide, daunorubicin, tunicamycin, rapamycin). Cell death was assessed by the measurement of cellular permeability with propidium iodide, characterization of the morphological aspect of the nuclei with Hoechst 33342, and identification of myelin figures by transmission electron microscopy. Nile Red staining (distinguishing neutral and polar lipids) was used to identify lipid content by flow cytometry and spectral imaging microscopy. Whatever the cells considered, myelin figures were only observed with cytotoxic oxysterols (7KC, 7beta-hydroxycholesterol, cholesterol-5beta, 6beta-epoxide), and their formation was not inhibited by the broad spectrum caspase inhibitor z-VAD-fmk. When U937 cells were treated with oxysterols or cytotoxic drugs, polar lipid accumulation was mainly observed with 7KC and 7beta-hydroxycholesterol. The highest polar lipid accumulation, which was triggered by 7KC, was counteracted by z-VAD-fmk. These findings demonstrate that myelin figure formation is a caspase-independent event closely linked with the cytotoxicity of oxysterols, and they highlight a relationship between caspase activity and polar lipid accumulation

Perturbateurs endocriniens : effet sur les préférences gustatives et l'obésité

International audiencePlusieurs études relient l’évolution de l’incidence de l’obésité à une évolution sociétale: l’accès des femmes au travail, les facilités de transport et l’essor de l’industrie agroalimentaire ont généré une "transition nutritionnelle" où le repas mijoté à base de produits frais a fait place au repas vite-prêt et fast-foods. La surconsommation de graisses et sucres et la moindre consommation de fruits et légumes sont bien souvent incriminés. Toutefois, l’usage concomitant de produits chimiques dans la production agricole et la confection de produits raffinés et/ou transformés, pourrait être un facteur aggravant, le taux d’obésité pouvant atteindre 50% en régions polluées. Les perturbateurs endocriniens (PE) sont particulièrement suspectés, plusieurs études épidémiologiques reliant l’incidence de l’obésité au degré d’exposition à des contaminants alimentaires ou environnementaux dotés de propriétés oestrogéniques ou anti-androgéniques (bisphénol A, phtalates, pesticides…). Cette hypothèse est soutenue par le fait que les stéroïdes sexuels gouvernent plusieurs déterminants des préférences gustatives: sécrétions salivaires, expression des bourgeons gustatifs, seuils de détections des saveurs, réponses des circuits neuronaux, etc…, mais aussi la formation du tissu adipeux. Expérimentalement, des études menées chez l’animal identifient des effets de PE sur les choix alimentaires tandis que d’autres démontrent l’impact d’une exposition précoce sur la genèse de l’obésité. Cet exposé rapporte des effets de PE sur des organes impliqués dans la régulation des préférences gustatives et de l’adipogenèse, et discute des possibles liens entre “préférence au sucré” et obésité

L'expression protéique dans les glandes salivaires est impactée par un régime maternel de type Western-Diet chez le rat

Methodologie, recherche et revueL'expression protéique dans les glandes salivaires est impactée par un régime maternel de type Western-Diet chez le rat. Journées francophones de nutrition (JFN

Implication des enzymes dans la perception chimio-sensorielle : une piste dans les troubles olfacto-gustatifs induits par des xénobiotiques ?

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Expression and differential localization of xenobiotic transporters in the rat olfactory neuro-epithelium.

International audienceTransporters, such as multidrug resistance P-glycoproteins (MDR), multidrug resistance-related proteins (MRP) and organic anion transporters (OATs), are involved in xenobiotic metabolism, particularly the cellular uptake or efflux of xenobiotics (and endobiotics) or their metabolites. The olfactory epithelium is exposed to both inhaled xenobiotics and those coming from systemic circulation. This tissue has been described as a pathway for xenobiotics to the brain via olfactory perineural space. Thereby, olfactory transporters and xenobiotic metabolizing enzymes, dedicated to the inactivation and the elimination of xenobiotics, have been involved in the toxicological protection of the brain, the olfactory epithelium itself and the whole body. These proteins could also have a role in the preservation of the olfactory sensitivity by inactivation and clearance of the excess of odorant molecules from the perireceptor space. The goal of the present study was to increase our understanding of the expression and the localization of transporters in this tissue. For most of the studied transporters, we observed an opposite mRNA expression pattern (RT-PCR) in the olfactory epithelium compared to the liver, which is considered to be the main metabolic organ. Olfactory epithelium mainly expressed efflux transporters (MRP, MDR). However, a similar pattern was observed between the olfactory epithelium and the olfactory bulb. We also demonstrate distinct cellular immunolocalization of the transporters in the olfactory epithelium. As previously reported, Mrp1 was mainly found in the supranuclear portions of supporting cells. In addition, Mrp3 and Mrp5 proteins, which were detected for the first time in olfactory epithelium, were localized to the olfactory neuron layer, while Mdr1 was localized to the capillary endothelium of lymphatic vessels in the subepithelial region. The pattern of expression and the distinct localization of the olfactory transporters showed in this work may highlight on their specific function in the whole olfactory epithelium

<i>Rattus norvegicus</i> Glutathione Transferase Omega 1 Localization in Oral Tissues and Interactions with Food Phytochemicals

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jafc.4c00483.International audienceGlutathione 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 &lt; 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