Auswahl der wissenschaftlichen Literatur zum Thema „Odorant/xenobiotic metabolism“

Insect antennae have a primary function of detecting odors including sex pheromones and plant volatiles. The assumption that genes uniquely expressed in these antennae have an olfactory role has led to the identification of several genes that are integral components of odorant transduction. In the present study, differential display polymerase chain reaction (ddPCR) was used to isolate 25 antennal-specific mRNAs from the male sphinx moth Manduca sexta. Northern blot analyses revealed that one clone, designated G7-9, was antennal-specific and was highly enriched in male antennae relative to female antennae. In situ hybridization indicated that G7-9 expression was restricted to a spatial domain of the olfactory epithelium occupied exclusively by sex-pheromone-sensitive olfactory sensilla. Amino acid homology and phylogenetic analyses identified G7-9 as a glutathione-S-transferase (GST); we have named the full-length clone GST-msolf1. GSTs are known to function primarily in the detoxification of noxious compounds. Spectrophotometric and chromatographic analyses of total GST activity indicate that the endogenous GSTs of male and female antennae can modify trans-2-hexenal, a plant-derived green leaf aldehyde known to stimulate the olfactory system of M. sexta. The restricted localization of GST-msolf1 to sex-pheromone-sensitive sensilla, the fact that the sex pheromone of M. sexta consists of a complex mixture of aldehyde components, and the observation that antennal GSTs can modify an aldehyde odorant suggest that GST-msolf1 may have a role in signal termination. In the light of the more commonly observed role of GSTs in xenobiotic metabolism, we propose that GST-msolf1 may play a dual role of protecting the olfactory system from harmful xenobiotics and inactivating aldehyde odorants, especially components of the M. sexta sex pheromone.

AbstractOxidoreductases 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.

AbstractOdorants are detected by olfactory sensory neurons, which are covered by olfactory mucus. Despite the existence of studies on olfactory mucus, its constituents, functions, and interindividual variability remain poorly understood. Here, we describe a human study that combined the collection of olfactory mucus and olfactory psychophysical tests. Our analyses revealed that olfactory mucus contains high concentrations of solutes, such as total proteins, inorganic elements, and molecules for xenobiotic metabolism. The high concentrations result in a capacity to capture or metabolize a specific repertoire of odorants. We provide evidence that odorant metabolism modifies our sense of smell. Finally, the amount of olfactory mucus decreases in an age-dependent manner. A follow-up experiment recapitulated the importance of the amount of mucus in the sensitive detection of odorants by their receptors. These findings provide a comprehensive picture of the molecular processes in olfactory mucus and propose a potential cause of olfactory decline.

Aldehyde oxidases (AOXs) are common detoxifying enzymes in several organisms. In insects, AOXs act in xenobiotic metabolism and as odorant-degrading enzymes (ODEs). These last appear as crucial enzymes in the life cycle of insects, helping to reset their olfactory system, particularly in lepidopterans, which fulfill important ecological roles (e.g., pollination or destructive life cycles). A comprehensive understanding of their olfactory system has provided opportunities to study key chemosensory proteins. However, no significant advance has been made around lepidopteran AOXs research, and even less around butterflies, a recently evolved lineage. In this study we have identified novel AOX gene families in moths and butterflies in order to understand their role as ODEs. Eighteen genomes from both moths and butterflies were used for phylogenetics, molecular evolution and sequence analyses. We identified 164 AOXs, from which 91 are new. Their phylogeny showed two main clades that are potentially related to odorant-degrading function, where both moths and butterflies have AOXs. A first ODE-related clade seems to have a non-ditrysian origin, likely related to plant volatiles. A second ODE-related clade could be more pheromone-biased. Molecular evolution analysis suggests a slight purifying selection process, though a number of sites appeared under positive selection. ODE-related AOXs have changed a phenylalanine residue by proline in the active site. Finally, this study could serve as a reference for further evolutionary and functional studies around Lepidopteran AOXs.

The wood-boring beetles, including the majority of Cerambycidae, have developed the ability to metabolize a variety of toxic compounds derived from host plants and the surrounding environment. However, detoxification mechanisms underlying the evolutionary adaptation of a cerambycid beetle Pharsalia antennata to hosts and habitats are largely unexplored. Here, we characterized three key gene families in relation to detoxification (cytochrome P450 monooxygenases: P450s, carboxylesterases: COEs and glutathione-S-transferases: GSTs), by combinations of transcriptomics, gene identification, phylogenetics and expression profiles. Illumina sequencing generated 668,701,566 filtered reads in 12 tissues of P. antennata, summing to 100.28 gigabases data. From the transcriptome, 215 genes encoding 106 P450s, 77 COEs and 32 GSTs were identified, of which 107 relatives were differentially expressed genes. Of the identified 215 genes, a number of relatives showed the orthology to those in Anoplophora glabripennis, revealing 1:1 relationships in 94 phylogenetic clades. In the trees, P. antennata detoxification genes mainly clustered into one or two subfamilies, including 64 P450s in the CYP3 clan, 33 COEs in clade A, and 20 GSTs in Delta and Epsilon subclasses. Combining transcriptomic data and PCR approaches, the numbers of detoxification genes expressed in abdomens, antennae and legs were 188, 148 and 141, respectively. Notably, some genes exhibited significantly sex-biased levels in antennae or legs of both sexes. The findings provide valuable reference resources for further exploring xenobiotics metabolism and odorant detection in P. antennata.

La sensibilité de notre odorat dépend des enzymes du métabolisme des xénobiotiques (EMX). Non seulement les EMX détoxifient la muqueuse nasale mais elles arrêtent aussi le signal olfactif pour en permettre la détection d’un nouveau. Parfois appelées enzymes du métabolisme des odorants (EMO), certaines participent aussi à la genèse de nouveaux métabolites odorants. L’objectif de cette thèse était d’étudier les EMX nasales en utilisant deux modèles innovants respectant au mieux les principes éthiques des 3R (Remplacement, Réduction, Raffinement des expérimentations animales). Alors que les explants olfactifs de rat montrent leurs limites pour étudier la régulation génique des EMX nasales, le modèle tissulaire respiratoire humain est un outil in vitro prometteur pour étudier le métabolisme des odorants. Ces modèles issus de l’ingénierie tissulaire expriment environ 80 isoformes d’EMX et de transporteurs d’efflux. Bien qu’aucune des molécules testées n’ait impacté la régulation génique de certaines EMX exprimées par le modèle tissulaire, les EMX du modèle sont capables de métaboliser des odorants tels que le benzaldéhyde et la 3,4-hexanedione. Pour conclure, la création et l’adaptation de méthodes durant cette thèse permet maintenant d’étudier la contribution de l’épithélium respiratoire humain dans le métabolisme des odorants. Ces travaux montrent l’implication des tissus respiratoires dans le métabolisme des odorants chez l’humain, tout en contribuant à réduire l’expérimentation animale
Our sensitive olfaction relies on Xenobiotic Metabolizing Enzymes (XMEs) that protect the nasal tissue from potentially harmful volatile compounds, but also quickly terminate the olfactory signal to prepare olfactory receptors to detect new odorant stimuli. Some of them also generate metabolites that participate in the odorant signal, hence their other name Odorant Metabolizing Enzymes (OMEs). The objective of this thesis was to study the nasal XMEs using two innovative models that aim to comply as much as possible with the 3R principles (Replacement, Reduction, and Refinement of animal experiments). While rat olfactory explants showed some limitations in investigating XME gene expression, human nasal respiratory mucosa tissue models were promising in vitro tools for the odorant metabolism field. These models express around 80 XME isoforms and efflux transporters. Selected XME genes were not regulated by the compounds chosen for the thesis, however, they were able to metabolize odorants, such as benzaldehyde and 3,4-hexanedione. Overall, protocols were created and adapted to use tissue models to study the implication of the respiratory epithelium in odorant metabolism in humans. This work provides novel knowledge on the involvement of the human respiratory tissue in odorant metabolism and contributes to the reduction of animal experiments