Study of the lipidic fraction of allergenic pollens and its chemical modifications induced by atmospheric pollutants

La fraction lipidique pollinique a un effet adjuvant sur la réaction allergique et elle est impliquée dans les processus de germination. L’altération de cette fraction par les polluants atmosphériques est peu documentée dans la littérature bien que des effets délétères soient possibles sur la santé des sujets allergiques. Notre travail a été effectué sur deux pollens parmi les plus allergisants : la fléole des prés (phleum pratense) et le bouleau (betula pendula). La fraction lipidique des pollens intacts a été identifiée et quantifiée par chromatographie en phase gazeuse équipée d’un détecteur à ionisation de flamme ou couplée à la spectrométrie de masse. Les principales familles chimiques identifiées sont les suivantes : alcanes, alcools, alcènes, acides gras saturés et insaturés, aldéhydes et stérols. Une exposition in vitro des pollens à l’ozone a mis en évidence une réactivité des alcènes et une production d’acides gras saturés et d’aldéhydes. Le dioxyde d’azote a montré quant à lui un rôle protecteur vis-à-vis de la réactivité de l’ozone. La biodisponibilité des lipides des pollens intacts semble faible comme l’ont montré les extractions du pollen en milieu aqueux sans agitation. Par ailleurs, nos résultats semblent donner un nouveau rôle à la rupture des pollens dans l’atmosphère. En effet, nous avons observé une extraction facilitée des lipides pour les pollens broyés et notamment d’espèces immunostimulantes telles que les acides linoléique et α-linolénique. Le rôle d’adjuvants à la réaction allergique de ces lipides extraits du pollen cassé ou pollué devra être précisé dans une étude ultérieure.The pollen lipidic fraction has an adjuvant effect on the allergic reaction and it is involved in germination processes. The alteration of pollen lipids by atmospheric pollutants is poorly documented in the literature although negative health effects are suspected. Our work was carried out on two highly allergenic pollens: timothy grass (phleum pratense) and birch tree (betula pendula). The lipid fraction of intact pollen was identified and quantified by gas chromatography equipped with a flame ionization detector or coupled to mass spectrometry. The main chemical families identified are: alkanes, alcohols, alkenes, saturated and unsaturated fatty acids, aldehydes and sterols. In vitro exposure of pollen to ozone has exhibited the reactivity of alkenes and the production of saturated fatty acids and aldehydes. Nitrogen dioxide has shown a protective role toward the reactivity of ozone. Furthermore, the bioavailability of lipids from intact pollen appears to be low as shown by pollen extractions with aqueous solvent without agitation. Moreover, our results give a new role to the rupture of pollen in the atmosphere. In fact, we observed a facilitated extraction of lipids for crushed pollen and in particular the release of immunostimulatory species such as linoleic and α-linolenic acids. The adjuvancy effects of the lipids extracted from broken or polluted pollen grains to the allergic reaction should be unraveled in a future work

Uptake of ozone on birch pollen grains

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Organic and aqueous extraction of lipids from birch pollen grains exposed to gaseous pollutants

International audienceThe lipid fraction of birch pollen grains (BPGs) is not yet fully described, although pollen lipid molecules may play a role in the allergic immune response. The mechanisms by which atmospheric pollutants modify allergenic pollen grains (PGs) are also far from being elucidated despite high potential effects on allergic sensitization. This work is a contribution to a better description of the lipid profile (both external and cytoplasmic) of BPGs and of alterations induced by gaseous air pollutants. Several lipid extractions were performed using organic and aqueous solvents on BPGs following exposure to ozone and/or nitrogen dioxide and under conditions favoring the release of internal lipids. Ozone reacted with alkenes to produce aldehydes and saturated fatty acids, while nitrogen dioxide was shown to be unreactive with lipids. NO 2 exhibited a protective effect against the reactivity of alkenes with ozone, probably by competition for adsorption sites. The decreased reactivity of ozone during simultaneous exposure to NO 2 /O 3 raised the possibility of a Langmuir-Hinshelwood mechanism. Oxidation reactions induced by exposure of BPGs to ozone did not substantially modify the extraction of lipids by aqueous solvent, suggesting that the bioaccessibility of lipids was not modified by oxidation. On the contrary, the rupture of PGs appeared to be a key factor in enhancing the bioaccessibility of bioactive lipid mediators (linoleic and α-linolenic acids) in an aqueous solution. The internal lipid fraction of BPGs has specific characteristics compared with external lipids, with more abundant hexadecanoic acid, tricosanol, and particularly unsaturated fatty acids (linoleic and α-linolenic acids). Several mechanisms of action of gaseous pollutants on allergenic pollen were identified in this study: gaseous air pollutants can (i) modify the external lipid fraction by reactivity of alkenes, (ii) adsorb on the surface of PGs and be a source of oxidative stress after inhalation of PGs, and (iii) promote the release of cytoplasmic bioactive lipids by facilitating pollen rupture

Modification of the pollen lipid fraction by ozone

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Uptake of ozone and modification of lipids in Betula Pendula pollen

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Chemical modification of coating of Pinus halepensis pollen by ozone exposure

International audiencePollen coating, located on the exine, includes an extractible lipid fraction. The modification of the pollen coating by air pollutants may have implications on the interactions of pollen with plant stigmas and human cells. Pinus halepensis pollen was exposed to ozone in vitro and the pollen coating was extracted with organic solvent and analyzed by GC-MS. Ozone has induced chemical changes in the coating as observed with an increase in dicarboxylic acids, short-chain fatty acids and aldehydes. 4-Hydroxybenzaldehyde was identified as the main reaction product and its formation was shown to occur both on native pollen and on defatted pollen. 4-Hydroxybenzaldehyde is very likely formed via the ozonolysis of acid coumaric-like monomers constitutive of the sporopollenin. Modification of pollen coating by air pollutants should be accounted for in further studies on effect of pollution on germination and on allergenicity

Uptake of ozone and modification of lipids in Betula Pendula pollen.

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Extractable lipids from Phleum pratense pollen grains and their modifications by ozone exposure

International audienceGrass pollen grains are an important source of aeroallergens eliciting respiratory allergic diseases worldwide. In the field of allergology, Phleum pratense pollen is considered as a model for other grass taxa. Upon contact with the aqueous phase of mucosa membranes, lipids are co-delivered from pollen grains with allergens. Lipid molecular species have pro-allergic, pro-inflammatory and immunomodulatory effects on the cells of the allergic immune response. The quantitative analysis of Phleum pratense pollen lipids is missing in the literature. In this work, the total mass of lipids extractable by methylene chloride was determined to be 22 ± 1 µg per mg of Phleum pratense pollen. Eighteen percent of the lipidic mass was quantified and identified by gas chromatographic analysis. Identified lipids included alkanes, alkenes, saturated and unsaturated fatty acids, aldehydes and alcohols. Pollen samples harvested at different times and locations showed a very similar lipidic pattern, both qualitatively and quantitatively. Laboratory ozone exposure of pollen substantially modified its lipidic composition by reactions of ozone with alkenes leading to the production of fatty acids and aldehydes. A deeper knowledge of the lipids released by pollen grains, including pollen from polluted areas, is essential for a better understanding of the chemical environment at the cellular level where allergic reactions take place

Ageing of single pollen grains under controlled environment

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Observations of single pollen grains after ageing under controlled environment

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