Nitration of pollen aeroallergens by nitrate ion in conditions simulating the liquid water phase of atmospheric particles

Alteration of the health effects of bioaerosols by chemical modification in the atmosphere: A review

Bioaerosols are a subset of important airborne particulates that present a substantial human health hazard due to their allergenicity and infectivity. Chemical reactions in atmospheric processes can significantly influence the health hazard presented by bioaerosols; however, few studies have summarized such alterations to bioaerosols and the mechanisms involved. In this paper, we systematically review the chemical modifications of bioaerosols and the impact on their health effects, mainly focusing on the exacerbation of allergic diseases such as asthma, rhinitis, and bronchitis. Oxidation, nitration, and oligomerization induced by hydroxyl radicals, ozone, and nitrogen dioxide are the major chemical modifications affecting bioaerosols, all of which can aggravate allergenicity mainly through immunoglobulin E pathways. Such processes can even interact with climate change including the greenhouse effect, suggesting the importance of bioaerosols in the future implementation of carbon neutralization strategies. In summary, the chemical modification of bioaerosols and the subsequent impact on health hazards indicate that the combined management of both chemical and biological components is required to mitigate the health hazards of particulate air pollution.

Site-specific tyrosine nitration of group 1 allergens of house dust mite Dermatophagoides farinae (der f 1) and Dermatophagoides pteronyssinus (der p 1) in indoor dusts

Nitration can enhance the allergenicity of proteins. The nitration status of house dust mite (HDM) allergens in indoor dusts, however, remains to be elucidated. In the study, site-specific tyrosine nitration degrees of the two important HDM allergens Der f 1 and Der p 1 in indoor dust samples were investigated by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The measured concentrations of native and nitrated allergens in the dusts were in the range of 0.86-29 μg g^-1 for Der f 1 and from below the detection limit to 29 μg g^-1 for Der p 1. Site-specific analysis revealed that all ten tyrosine residues in Der f 1 and Der p 1 were nitrated to different degrees in the investigated samples. The preferred nitration sites were Y₅₆ in Der f 1 and Y₃₇ in Der p 1 with the nitration degrees of 7.6-84% and 17-96% among the detected tyrosine residues, respectively. The measurements reveal high site-specific nitration degrees for tyrosine in Der f 1 and Der p 1 detected in the indoor dust samples. Further investigations are required to find out if the nitration really aggravates the health effects of HDM allergens and if the effects are tyrosine site-dependent.

Indoor heterogeneous photochemistry of molds and their contribution to HONO formation

To better understand the impact of molds on indoor air quality, we studied the photochemistry of microbial films made by Aspergillus niger species, a common indoor mold. Specifically, we investigated their implication in the conversion of adsorbed nitrate anions into gaseous nitrous acid (HONO) and nitrogen oxides (NO_x ), as well as the related VOC emissions under different indoor conditions, using a high-resolution proton transfer reaction-time of flight-mass spectrometer (PTR-TOF-MS) and a long path absorption photometer (LOPAP). The different mold preparations were characterized by the means of direct injection into an Orbitrap high-resolution mass spectrometer with a heated electrospray ionization (ESI-Orbitrap-MS). The formation of a wide range of VOCs, having emission profiles sensitive to the types of films (either doped by potassium nitrate or not), cultivation time, UV-light irradiation, potassium nitrate concentration and relative humidity was observed. The formation of nitrous acid from these films was also determined and found to be dependent on light and relative humidity. Finally, the reaction paths for the NO_x and HONO production are proposed. This work helps to better understand the implication of microbial surfaces as a new indoor source for HONO emission.

Immune Effects of the Nitrated Food Allergen Beta-Lactoglobulin in an Experimental Food Allergy Model

Food proteins may get nitrated by various exogenous or endogenous mechanisms. As individuals might get recurrently exposed to nitrated proteins via daily diet, we aimed to investigate the effect of repeatedly ingested nitrated food proteins on the subsequent immune response in non-allergic and allergic mice using the milk allergen beta-lactoglobulin (BLG) as model food protein in a mouse model. Evaluating the presence of nitrated proteins in food, we could detect 3-nitrotyrosine (3-NT) in extracts of different foods and in stomach content extracts of non-allergic mice under physiological conditions. Chemically nitrated BLG (BLGn) exhibited enhanced susceptibility to degradation in simulated gastric fluid experiments compared to untreated BLG (BLGu). Gavage of BLGn to non-allergic animals increased interferon-γ and interleukin-10 release of stimulated spleen cells and led to the formation of BLG-specific serum IgA. Allergic mice receiving three oral gavages of BLGn had higher levels of mouse mast cell protease-1 (mMCP-1) compared to allergic mice receiving BLGu. Regardless of the preceding immune status, non-allergic or allergic, repeatedly ingested nitrated food proteins seem to considerably influence the subsequent immune response.

Atmospheric protein chemistry influenced by anthropogenic air pollutants: nitration and oligomerization upon exposure to ozone and nitrogen dioxide

The allergenic potential of airborne proteins may be enhanced via post-translational modification induced by air pollutants like ozone (O₃) and nitrogen dioxide (NO₂). The molecular mechanisms and kinetics of the chemical modifications that enhance the allergenicity of proteins, however, are still not fully understood. Here, protein tyrosine nitration and oligomerization upon simultaneous exposure of O₃ and NO₂ were studied in coated-wall flow-tube and bulk solution experiments under varying atmospherically relevant conditions (5-200 ppb O₃, 5-200 ppb NO₂, 45-96% RH), using bovine serum albumin as a model protein. Generally, more tyrosine residues were found to react via the nitration pathway than via the oligomerization pathway. Depending on reaction conditions, oligomer mass fractions and nitration degrees were in the ranges of 2.5-25% and 0.5-7%, respectively. The experimental results were well reproduced by the kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB). The extent of nitration and oligomerization strongly depends on relative humidity (RH) due to moisture-induced phase transition of proteins, highlighting the importance of cloud processing conditions for accelerated protein chemistry. Dimeric and nitrated species were major products in the liquid phase, while protein oligomerization was observed to a greater extent for the solid and semi-solid phase states of proteins. Our results show that the rate of both processes was sensitive towards ambient ozone concentration, but rather insensitive towards different NO₂ levels. An increase of tropospheric ozone concentrations in the Anthropocene may thus promote pro-allergic protein modifications and contribute to the observed increase of allergies over the past decades.

Effect of O3 and NO2 atmospheric pollutants on Platanus x acerifolia pollen: Immunochemical and spectroscopic analysis

In the present study, the effects of two important oxidizing atmospheric pollutants (O₃ and NO₂) on the allergenic properties and chemical composition of Platanus x acerifolia pollen were studied. Pollen samples were subjected to O₃ and/or NO₂ under in vitro conditions for 6h at atmospheric concentration levels (O₃: 0.061ppm; NO₂: 0.025ppm and the mixture of O₃ and NO₂: 0.060 and 0.031ppm respectively). Immunoblotting (using Pla a 1 and Pla a 2 antibodies), infrared and X-ray photoelectron spectroscopy techniques were used. Immunochemical analysis showed that pollen allergenicity changes were different according to the pollutant tested (gas or mixture of gasses) and that the same pollutant gas may interact in a different manner with each specific allergen. The spectroscopy results showed modifications in the FTIR spectral features of bands assigned to proteins, lipids, and polysaccharides of the pollen exposed to the pollutants, as well as in the XPS spectra high-resolution components C 1s, N 1s, and O 1s. This indicates that while airborne, the pollen wall suffers further modifications of its components induced by air pollution, which can compromise the pollen function.

Generation of nitric oxide by olive (Olea europaea L.) pollen during in vitro germination and assessment of the S-nitroso- and nitro-proteomes by computational predictive methods

Nitric oxide is recognized as a signaling molecule involved in a broad range of physiological processes in plants including sexual reproduction. NO has been detected in the pollen grain at high levels and regulates pollen tube growth. Previous studies demonstrated that NO as well as ROS are produced in the olive reproductive tissues in a stage- and tissue-specific manner. The aim of this study was to assess the production of NO throughout the germination of olive (Olea europaea L.) pollen in vitro. The NO fluorescent probe DAF-2DA was used to image NO production in situ, which was correlated to pollen viability. Moreover, by means of a fluorimetric assay we showed that growing pollen tubes release NO. GSNO -a mobile reservoir of NO, formed by the S-nitrosylation of NO with reduced glutathione (GSH) - was for the first time detected and quantified at different stages of pollen tube growth using a LC-ES/MS analysis. Exogenous NO donors inhibited both pollen germination and pollen tube growth and these effects were partially reverted by the specific NO-scavenger c-PTIO. However, little is known about how NO affects the germination process. With the aim of elucidating the putative relevance of protein S-nitrosylation and Tyr-nitration as important post-translational modifications in the development and physiology of the olive pollen, a de novo assembled and annotated reproductive transcriptome from olive was challenged in silico for the putative capability of transcripts to become potentially modified by S-nitrosylation/Tyr-nitration according to well-established criteria. Numerous gene products with these characteristics were identified, and a broad discussion as regards to their potential role in plant reproduction was built after their functional classification. Moreover, the importance of both S-nitrosylation/Tyr-nitrations was experimentally assessed and validated by using Western blotting, immunoprecipitation and proteomic approaches.

Air Pollution and Climate Change Effects on Allergies in the Anthropocene: Abundance, Interaction, and Modification of Allergens and Adjuvants

Air pollution and climate change are potential drivers for the increasing burden of allergic diseases. The molecular mechanisms by which air pollutants and climate parameters may influence allergic diseases, however, are complex and elusive. This article provides an overview of physical, chemical and biological interactions between air pollution, climate change, allergens, adjuvants and the immune system, addressing how these interactions may promote the development of allergies. We reviewed and synthesized key findings from atmospheric, climate, and biomedical research. The current state of knowledge, open questions, and future research perspectives are outlined and discussed. The Anthropocene, as the present era of globally pervasive anthropogenic influence on planet Earth and, thus, on the human environment, is characterized by a strong increase of carbon dioxide, ozone, nitrogen oxides, and combustion- or traffic-related particulate matter in the atmosphere. These environmental factors can enhance the abundance and induce chemical modifications of allergens, increase oxidative stress in the human body, and skew the immune system toward allergic reactions. In particular, air pollutants can act as adjuvants and alter the immunogenicity of allergenic proteins, while climate change affects the atmospheric abundance and human exposure to bioaerosols and aeroallergens. To fully understand and effectively mitigate the adverse effects of air pollution and climate change on allergic diseases, several challenges remain to be resolved. Among these are the identification and quantification of immunochemical reaction pathways involving allergens and adjuvants under relevant environmental and physiological conditions.