A metabolomic, geographic, and seasonal analysis of the contribution of pollen-derived adenosine to allergic sensitization

Abstract

Background Studies on ragweed and birch pollen extracts suggested that the adenosine content is an important factor in allergic sensitization. However, exposure levels from other pollens and considerations of geographic and seasonal factors have not been evaluated. Objective This study compared the metabolite profile of pollen species important for allergic disease, specifically measured the adenosine content, and evaluated exposure to pollen-derived adenosine. Methods An NMR metabolomics approach was used to measure metabolite concentrations in twenty-six pollen extracts. Pollen count data was analyzed from five cities to model exposure. Results A principal component analysis of the various metabolites identified by NMR showed that pollen extracts could be differentiated primarily by sugar content: glucose, fructose, sucrose, and myo-inositol. In extracts of 10 mg of pollen/ml, the adenosine was highest for grasses (45 μM) followed by trees (23 μM) and weeds (19 μM). Pollen count data showed that tree pollen was typically 5–10 times the amount of other pollens. At the daily peaks of tree, grass, and weed season the pollen-derived adenosine exposure per day is likely to only be 1.1, 0.11, and 0.12 μg, respectively. Seasonal models of pollen exposure and respiration suggest that it would be a rare event limited to tree pollen season for concentrations of pollen-derived adenosine to approach physiological levels. Conclusions Sugar content and other metabolites may be useful in classifying pollens. Unless other factors create localized exposures that are very different from these models, pollen-derived adenosine is unlikely to be a major factor in allergic sensitization.

Biochemical composition of Phleum pratense pollen grains: A review

“…Bioaccessibility requires knowledge of the kinetic of release of the biochemical constituents of PG but also of their ability to diffuse into the mucus (Mueller et al, 2016). Such information on bioaccessibility remains scarce for PPPG constituents in particular and for allergenic pollens in general.…”

“…Besides bioavailability, bioactivity requires that compounds extracted from PPPGs reach high enough concentrations for activities in physiological conditions. Mueller et al (2016) have for example calculated concentrations of adenosine in nasal conditions based on assumptions on airborne pollen concentrations and of amount of nasal fluid. They conclude that, most of the time, nasal level of adenosine brought by PGs are too low to reach physiological levels (Mueller et al, 2016).…”

“…Adenosine was identified as a potent immunoregulatory substance in PPPGs and detected to mass fraction between 0.65 and 1.29 µg.mg -1 ; it is controversial whereas such low concentration of bioactive compound may or may not reach significant health-induced effects (Gilles et al, 2011;Mueller et al, 2016).…”

“…A single inflorescence of timothy grass can indeed produce up to 1.2 million PGs (Figure 1) (Albertine et al, 2014). Atmospheric concentrations of grass pollen frequently reach more than a thousand of pollen grains per cubic meter (Mueller et al, 2016). Exposure to allergenic PGs is also effective in indoor air with persistence of allergens observed after the pollen season (Dybendal et al, 1989;Fahlbusch et al, 2001Fahlbusch et al, , 2001Holmquist et al, 1999).…”

Initiating pollen sensitization – complex source, complex mechanisms

“…The latter also instructed activated epithelial cells to secrete IL-8, similarly to the complete pollen extract [138]. However, the significance of adenosine in allergic sensitization has been questioned by Mueller et al who quantified adenosine levels in various pollen extracts and concluded that the measured amounts too low to exert a physiological effect [139]. The discrepancy of these results might be explained by environmental factors influencing the adenosine content in pollen.…”